At a few AU in a minimum mass nebula, embryos' growth is quenched by dynamical isolation due to the depletion of planetesimals in their feeding zone. Their limiting isolation mass increases with the planetesimals surface density. We use a numerical simulation to show that despite stream line interference, convergent embryos essentially retain the strength of non-interacting embryos' Lindblad and corotation torques by their natal disks.
In disks with modest surface density or equivalently accretion rates , embryos capture each other in their mutual mean motion resonances and form a convoy of super-Earths. In more massive disks, they could overcome these resonant barriers to undergo repeated close encounters, including cohesive collisions that enable the formation of massive cores.
This method relies on the assumption that the processes of particle growth and drift control the radial scale of the disk at late stages of disk evolution such that the lifetime of the disk is equal to both the drift timescale and growth timescale of the maximum particle size at a given dust line. We provide an initial proof of concept of our model through an application to the disk TW Hya and are able to estimate the disk dust -to-gas ratio, CO abundance, and accretion rate in addition to the total disk surface density.
We find that our derived surface density profile and dust -to-gas ratio are consistent with the lower limits found through measurements of HD gas.
The CO ice line also depends on surface density through grain adsorption rates and drift and we find that our theoretical CO ice line estimates have clear observational analogues. We further apply our model to a large parameter space of theoretical disks and find three observational diagnostics that may be used to test its validity. First, we predict that the dust lines of disks other than TW Hya will be consistent with the normalized CO surface density profile shape for those disks.
Second, surface density profiles that we derive from disk ice lines should match those derived from disk dust lines. Finally, we predict that disk dust and ice lines will scale oppositely, as a function of surface density, across a large sample of disks. Collision velocity of dust grains in self-gravitating protoplanetary discs. PubMed Central. We have conducted the first comprehensive numerical investigation of the relative velocity distribution of dust particles in self-gravitating protoplanetary discs with a view to assessing the viability of planetesimal formation via direct collapse in such environments.
We develop a criterion for understanding this result in terms of the stopping distance being of the order of the disc scaleheight. These planetesimals would acquire moderate eccentricities and remain unmodified over the remaining lifetime of the disc. Recent high angular resolution observations of protoplanetary disks at different wavelengths have revealed several kinds of structures, including multiple bright and dark rings.
Embedded planets are the most used explanation for such structures, but there are alternative models capable of shaping the dust in rings as it has been observed. Radiative transfer calculations are done using the resulting dust density distributions in order to compare with current multiwavelength observations. We find that the structures in the dust density profiles and radial intensities at different wavelengths strongly depend on the disk viscosity.
The gaps are expected to be shallower and narrower at millimeter emission than at near-infrared, opposite to model predictions of particle trapping. In our models, the total gas surface density is not expected to show strong variations, in contrast to other gap-forming scenarios such as embedded giant planets or radial variations of the disk viscosity. We use simplified prescriptions of the fragmentation velocity threshold, which is assumed to change radially at the location of one, two, or three ice lines.
A clear gap of emission can be formed between ice lines and be surrounded by ring-like structures, in particular between the H2O and CO2 or CO. Childhood to adolescence: dust and gas clearing in protoplanetary disks. Disks are ubiquitous around young stars. Over time, disks dissipate, revealing planets that formed hidden by their natal dust. Since direct detection of young planets at small orbital radii is currently impossible, other tracers of planet formation must be found.
One sign of disk evolution, potentially linked to planet formation, is the opening of a gap or inner hole in the disk. In this thesis, I have identified and characterized several cold disks with large inner gaps but retaining massive primordial outer disks. These large gaps are equivalent to dust clearing from inside the Earth's orbit to Neptune's orbit or even the inner Kuiper belt.
Unlike more evolved systems like our own, the central star is often still accreting and a large outer disk remains.
Outer gap radii of AU were derived. However, spectrophotometric identification is indirect and model-dependent.
To validate this interpretation, I observed three disks with a submillimeter interferometer and obtained the first direct images of the central holes. The images agree well with the gap sizes derived from the spectrophotometry. The derived rotation temperatures are significantly lower for the cold disks than disks without gaps.
Unresolved sub millimeter photometry shows that cold disks have steeper colors, indicating that they are optically thin at these wavelengths, unlike. We study the dust motion at the surface layer of protoplanetary disks. Dust grains in the surface layer migrate outward owing to angular momentum transport via gas-drag force induced by the stellar radiation pressure.
In this study we calculate the mass flux of the outward motion of compact grains and porous dust aggregates by the radiation pressure. The radiation pressure force for porous dust aggregates is calculated using the T-Matrix Method for the Clusters of Spheres.
In addition, we find that the outward mass flux of porous dust aggregates with monomer size of 0. This implies that large compact grains like calcium-aluminum-rich inclusions are hardly transported to the outer region by stellar radiation pressure, whereas porous dust aggregates like chondritic-porous interplanetary dust particles are efficiently transported to the comet formation region.
Crystalline silicates are possibly transported in porous dust aggregates by stellar radiation pressure from the inner hot region to the outer cold cometary region in the protosolar nebula. The surface density of protoplanetary disks is a fundamental parameter that still remains largely unconstrained due to uncertainties in the dust -to-gas ratio and CO abundance.
I will provide an initial proof of concept of our model through an application to the disk TW Hya where we are able to estimate the disk dust -to-gas ratio, CO abundance, and accretion rate in addition to the total disk surface density. Using this method we derive disks that may be much more massive than previously thought, often approaching the limit of gravitational stability. Cleeves, L.
The spatial distribution of gas and solids in protoplanetary disks determines the composition and formation efficiency of planetary systems. A number of disks show starkly different distributions for the gas and small grains compared to millimeter-centimeter-sized dust.
The 12CO is detected out to a radius of au, while the millimeter continuum emission is truncated at just au. Based upon these data, we have built a comprehensive physical and chemical model for the disk structure, which takes into account the complex, coupled nature of the gas and dust and the interplay between the local and external environment. We constrain the distributions of gas and dust , the gas temperatures, the CO abundances, the CO optical depths, and the incident external radiation field.
The latter is consistent with that expected from the local stellar population. We additionally find tentative evidence for ring-like continuum substructure, suggestions of isotope-selective photodissociation, and a diffuse gas halo. This dissertation is composed of three independent projects in astrophysics concerning phenomena that are concurrent with the birth, life, and death of planets.
In Chapter 3, we identify the dynamical mechanisms that control atmospheric heat redistribution on hot Jupiters. Finally, in Chapter 4, we characterize the death of low-mass, short-period rocky planets by their evaporation into a dusty wind. We find that disk surface layers ionized by stellar X-rays are susceptible to charge neutralization by condensatesranging from mum-sized dust to angstrom-sized polycyclic aromatic hydrocarbons PAHs.
Ion densities in X-ray-irradiated surfaces are so low that ambipolar diffusion weakens the MRI. Far-UV ionization of atomic carbon and sulfur produces a plasma so dense that it is immune to ion recombination on grains and PAHs. At smaller radii, both X-ray- and FUV-ionized surface layers cannot sustain the accretion rates generated at larger distance and an additional means of transport is needed.
In the case of transitional disks, it could be provided by planets. Chapter 3: Infrared light curves of transiting hot Jupiters present a trend in which the atmospheres of the hottest planets are less efficient at redistributing the stellar energy. A number of disks show starkly different distributions for the gas and small grains compared to millimeter—centimeter-sized dust.
Effects of photophoresis on the dust distribution in a 3D protoplanetary disc. Photophoresis is a physical process based on momentum exchange between an illuminated dust particle and its gaseous environment.
Its net effect in protoplanetary discs PPD is the outward transport of solid bodies from hot to cold regions. This process naturally leads to the formation of ring-shaped features where dust piles up.
We find that the conditions of pressure and temperature encountered in the inner regions of PPD result in important photophoretic forces, which dramatically affect the radial motion of solid bodies. Moreover, dust particles have different equilibrium locations in the disc depending on their size and their intrinsic density.
The radial transport towards the outer parts of the disc is more efficient for silicates than for iron particles, which has important implications for meteoritic composition. Our results indicate that photophoresis must be taken into account in the inner regions of PPD to fully understand the dynamics and the evolution of the dust composition.
Miyake, Tomoya; Suzuki, Takeru K. We investigate the dynamics of dust grains of various sizes in protoplanetary disk winds driven by magnetorotational turbulence, by simulating the time evolution of the dust grain distribution in the vertical direction. Small dust grains, which are well-coupled to the gas, are dragged upward with the upflowing gas, while large grains remain near the midplane of a disk.
Intermediate-size grains float near the sonic point of the disk wind located at several scale heights from the midplane, where the grains are loosely coupled to the background gas.
Considering the dependence on the distance from the central star, smaller-size grains remain only in an outer region of the disk, while larger-size grains are distributed in a broader region. We also discuss the implications of our result for observations of dusty material around young stellar objects. We derive expressions for the photophoretic force on opaque spherical particles in a dilute gas in the optically thick regime where the radiation field is in local thermal equilibrium.
Under those conditions, the radiation field has a simple form, leading to well defined analytical approximations for the photophoretic force that also consider both the internal thermal conduction within the particle, and the effects of heat conduction and radiation to the surrounding gas.
We derive these results for homogeneous spherical particles; and for the double layered spheres appropriate for modeling solid grains with porous aggregate mantles. We show that highly porous silicate grains have sufficiently low thermal conductivities that photophoretic effects, such as significant relative velocities between particles with differing porosity or levitation above the midplane, are expected to occur.
Planetesimal formation is one of the most important unsolved problems in planet formation theory. In particular, rocky planetesimal formation is difficult because silicate dust grains are easily broken when they collide.
However, the stability of a layer composed of such porous silicate dust aggregates has not been investigated. Therefore, we investigate the gravitational instability GI of this dust layer.
We calculate the equilibrium random velocity considering gravitational scattering and collisions between dust aggregates, drag by mean flow of gas, stirring by gas turbulence, and gravitational scattering by gas density fluctuation due to turbulence.
We derive the condition of the GI using the disk mass, dust -to-gas ratio, turbulent strength, orbital radius, and dust monomer radius. We also find that the dust layer is more unstable in disks with larger mass, higher dust -to-gas ratio, and weaker turbulent strength, at larger orbital radius, and with a larger monomer radius.
X-ray radiative transfer in protoplanetary disks. The role of dust and X-ray background fields. The X-ray luminosities of T Tauri stars are about two to four orders of magnitude higher than the luminosity of the contemporary Sun. As these stars are born in clusters, their disks are not only irradiated by their parent star but also by an X-ray background field produced by the cluster members. Aims: We aim to quantify the impact of X-ray background fields produced by young embedded clusters on the chemical structure of disks.
Further, we want to investigate the importance of the dust for X-ray radiative transfer in disks. The X-ray dust opacities can be calculated for various dust compositions and dust -size distributions. For the X-ray radiative transfer we consider irradiation by the star and by X-ray background fields. Results: For evolved dust populations e.
Consequently the local disk X-ray radiation field is only affected in dense regions close to the disk midplane. Conclusions: Observable signatures of X-ray background fields in low-mass star-formation regions, like Taurus, are only expected for cluster members experiencing a strong X-ray background field e.
After 25 years of laboratory research on protoplanetary dust agglomeration, a consistent picture of the various processes that involve colliding dust aggregates has emerged.
Besides sticking, bouncing and fragmentation, other effects, like, e. For siliceous materials, other processes have to be responsible for turning the dust aggregates into planetesimals. In this article, these processes are discussed, the physical properties of the emerging dusty or icy planetesimals are presented and compared to empirical evidence from within and without the Solar System.
In conclusion, the formation of planetesimals by a gravitational collapse of dust "pebbles" seems the most likely.
Dent, W. We describe a large-scale far-infrared line and continuum survey of protoplanetary disk through to young debris disk systems carried out using the ACS instrument on the Herschel Space Observatory.
The aim was to study the global gas and dust content in a wide sample of circumstellar disks, combining the results with models in a systematic way. In this overview paper we review the scientific aims, target selection and observing strategy of the program.
We summarise some of the initial results, showing line identifications, listing the detections, and giving a first statistical study of line detectability. This is. Additionally, GASPS included continuum photometry at 70, and micron, around the peak of the dust emission. We summarize some of the initial results, showing line identifications, listing the detections, and giving a first statistical study of line detectability.
The [OI] line at 63 micron was the brightest line seen in almost all objects, by a factor of Hull, Charles L. Ilsedore; Hughes, A. All of these characteristics are consistent with models of self-scattering of submillimeter-wave emission from an optically thin inclined disk. The distribution of the polarization position angles across the disk reveals that, while the average orientation is along the minor axis, the polarization orientations show a significant spread in angles; this can also be explained by models of pure scattering.
A comparison of cuts of the polarization fraction across the major and minor axes of both sources reveals that IM Lup has a substantially higher polarization fraction than HL Tau toward the center of the disk. This enhanced polarization fraction could be due a number of factors, including higher optical depth in HL Tau, or scattering by larger dust grains in the more evolved IM Lup disk. This reveals continued tension between grain-size estimates from scattering models and from models of the dust emission spectrum, which find that the bulk of the unpolarized emission in disks is most likely due to millimeter-sized or even centimeter-sized grains.
Composition of early planetary atmospheres - II. Coupled Dust and chemical evolution in protoplanetary discs. We present the next step in a series of papers devoted to connecting the composition of the atmospheres of forming planets with the chemistry of their natal evolving protoplanetary discs.
The model presented here computes the coupled chemical and dust evolution of the disc and the formation of three planets per disc model. We study the dependence of the final orbital radius, mass, and atmospheric chemistry of planets forming in disc models with initial disc masses that vary by 0. The nitrogen content of atmospheres can vary in planets that grow in different disc models. These differences are related to the formation history of the planet, the time and location that the planet accretes its atmosphere, and are encoded in the bulk abundance of NH3.
The processes that govern the evolution of dust and water in the form of vapor or ice in protoplanetary disks are intimately connected. We employ the model to study how dust growth and dynamics influence the vertical distribution of water vapor and water ice in the region just outside the radial snowline.
Our main finding is that coagulation boosted by the enhanced stickiness of icy grains and the ensuing vertical settling of solids results in water vapor being depleted, but not totally removed, from the region above the snowline on a timescale commensurate with the vertical turbulent mixing timescale. Our findings illustrate the importance of dynamical effects and the need for understanding coevolutionary dynamics of gas and solids in planet-forming environments. The formation scenario of a gapped disk, i.
Emission from all three disk components the gas and the small and large dust grains in images exhibits a deficit in brightness in the central region of the disk, in particular, the dust disk in small and large dust grains has asymmetric brightness. The contrast ratio of the flux density in the dust continuum between the peak position to the opposite side of the disk reaches 1.
We suggest the asymmetries and different gap radii of the disk around PDS 70 are potentially formed by several unseen accreting planets inducing dust filtration. Hashimoto, J. Proposed scenarios such as disk-planet interaction, photoevaporation, grain growth , anticyclonic vortex, eccentricity, and their combinations would result in different radial distributions of the gas and the small sub-micron size and large millimeter size dust grains as well as asymmetric structures in a disk.
Here we report Submillimeter Array observations of the dust continuum at 1. PDS 70, a weak-lined T Tauri star, exhibits a gap in the scattered light from its disk with a radius of approx. However, we found a larger gap in the disk with a radius of approx. Evidence for dust grain growth in young circumstellar disks. Hundreds of circumstellar disks in the Orion nebula are being rapidly destroyed by the intense ultraviolet radiation produced by nearby bright stars. These young, million-year-old disks may not survive long enough to form planetary systems.
Nevertheless, the first stage of planet formation-the growth of dust grains into larger particles-may have begun in these systems.
Observational evidence for these large particles in Orion's disks is presented. A model of grain evolution in externally irradiated protoplanetary disks is developed and predicts rapid particle size evolution and sharp outer disk boundaries.
We discuss implications for the formation rates of planetary systems. Near-infrared morphology of protoplanetary nebulae - The icy dust torus of Minkowski's Footprint M High-resolution near-infrared images and ice-band spectra of the protoplanetary nebula M Minkowski's Footprint are presented.
The direct images of the object display a typical bipolar morphology with the star located in the center of the nebula illuminating two lobes. The overall dimensions are the same in the J, H, and K infrared bands, and they are similar to those in the optical range. The near-infrared color images clearly reveal a dust torus around the central star.
The orientation of the object in the plane of the sky allows the simultaneous view of the illuminating star, the nebular lobes, and the dust torus in a highly favorable perspective, only rarely found in other bipolar nebulae. The ice-band spectra make it possible to locate the H2O-ice grains within the dust torus; in addition, the narrow ice feature indicates that the ices are primarily pure crystalline water.
The retention of dust in protoplanetary disks: Evidence from agglomeratic olivine chondrules from the outer Solar System. Schrader, Devin L. By investigating the in situ chemical and O-isotope compositions of olivine in lightly sintered dust agglomerates from the early Solar System, we constrain their origins and the retention of dust in the protoplanetary disk.
The grain sizes of silicates in these agglomeratic olivine AO chondrules indicate that the grain sizes of chondrule precursors in the Renazzo-like carbonaceous CR chondrites ranged from dust in the early Solar System.
AO chondrules may contain, but are not solely composed of, recycled fragments of earlier formed chondrules. They also contain 16O-rich olivine related to amoeboid olivine aggregates and represent the best record of chondrule-precursor materials. These morphologies are consistent with particle agglomeration by electrostatic charging of grains during collision, a process that may explain solid agglomeration in the protoplanetary disk in the micrometer size regime.
The petrographic, isotopic, and chemical compositions of AO chondrules are consistent with chondrule formation by large-scale shocks, bow shocks, and current sheets. We infer that these AO chondrules likely formed in the inner Solar System and migrated to the comet forming region at least 3 Ma after the formation of the first Solar System solids. The icy satellites around Jupiter are considered to have formed in a circumplanetary disk.
While previous models have focused on the formation of the satellites starting from satellitesimals, the question of how satellitesimals themselves form from smaller dust particles has not yet been addressed. In this work, we study the possibility that satellitesimals form in situ in a circumplanetary disk. We calculate the radial distribution of the surface density and representative size of icy dust particles that grow by colliding with each other and drift toward the central planet in a steady circumplanetary disk with a continuous supply of gas and dust from the parent protoplanetary disk.
Radial contraction of the dust layer in the midplane of a gas- dust protoplanetary disk that consists of large dust aggregates is modeled. Sizes of aggregates vary from centimeters to meters assuming the monodispersion of the layer. The highly nonlinear continuity equation for the solid phase of the dust layer is solved numerically. The purpose of the study is to identify the conditions under which the solid matter is accumulated in the layer, which contributes to the formation of planetesimals as a result of gravitational instability of the dust phase of the layer.
We consider the collective interaction of the layer with the surrounding gas of the protoplanetary disk: shear stresses act on the gas in the dust layer that has a higher orbital velocity than the gas outside the layer, this leads to a loss of angular momentum and a radial drift of the layer. The evaporation of water ice and the continuity of the mass flux of the nonvolatile component on the ice line is also taken into account.
It is shown that the accumulation of solid matter on either side of the ice line and in other regions of the disk is determined primarily by the ratio of the radii of dust aggregates on either side of the ice line. If after the ice evaporation the sizes or density of dust aggregates decrease by an order of magnitude or more, the density of the solid phase of the layer's matter in the annular zone adjacent to the ice line from the inside increases sharply.
If, however, the sizes of the aggregates on the inner side of the ice line are only a few times smaller than behind the ice line, then in the same zone there is a deficit of mass at the place of the. We study dust capture by vortices and its long-term consequences in global two-fluid inviscid disk simulations using a new polar grid code RoSSBi.
How to cite. This is a preview of subscription content, log in to check access. Earth Planet Sci Lett 1 — Elsevier, Oxford, pp — Google Scholar. Luminosities for these stars are well determined, but the effective temperature scale is uncertain and abundance analyses are lacking.
Masses are known for very few, and with large relative errors. Astrometric methods provide at present the only means of detecting very low mass objects in significant numbers.
Completion of the near- star parallax catalogue and measurement of additional low-mass binaries are important observational programs. The potential of photometric selection of red dwarf binaries is explored in Chapter II. Separation of binaries from single stars by color anomalies alone is found impractical. Detection by overluminosity in the HR diagram is hampered by the intrinsic spread of the field star population.
However, we find that application of both kinematic and photometric criteria allows binaries to be detected with only moderate contamination by single stars ; we discuss several binary suspects selected in this way.
We examine the status of the least luminous stars ; there is no conclusive evidence that they are not hydrogen-burning objects.
White dwarf-red dwarf composites are detectable by infared color anomalies down to M ,v TURN 21 for the red dwarf component, and our survey is complete to absolute. Astrometric confirmation of young low-mass binaries and multiple systems in the Chamaeleon star-forming regions. Massive primary components appear to avoid the simultaneous formation of equal-mass secondary components, while extremely low-mass secondary components are hard to find for both high and low mass primaries owing to the much higher dynamic range and the faintness of the secondaries.
C A , C B , First evidence of external disc photoevaporation in a low mass star forming region: the case of IM Lup. We model the radiatively driven flow from IM Lup - a large protoplanetary disc expected to be irradiated by only a weak external radiation field at least times lower than the ultraviolet field irradiating the Orion Nebula Cluster proplyds.
Solutions that are consistent with the extent of the observed CO emission generally imply that IM Lup is still in the process of having its disc outer radius truncated. We conclude that IM Lup is subject to substantial external photoevaporation, which raises the more general possibility that external irradiation of the largest discs can be of significant importance even in low mass star forming regions.
Observations are presented of emission lines from organic molecules at frequencies GHz in the vicinity of Chamaeleon MMS1. This chemically rich dense cloud core harbors an extremely young, very low luminosity protostellar object and is a candidate first hydrostatic core.
Column densities are derived and emission maps are presented for species including polyynes, cyanopolyynes, sulphuretted carbon chains, and methanol. The polyyne emission peak lies about AU from the protostar, whereas methanol peaks about 15, AU away.
The abundances of long carbon chains are very large and are indicative of a nonequilibrium carbon chemistry; C6H and HC7N column densities are 5. Deuterated HC,3 and c-C3H2 were detected. Young low-mass stars are known to be bright in X-ray and UV due to a high level of magnetic activity.
We used the Shane 3-m telescope at Lick Observatory on Mount Hamilton, California to observe some of these 2, stars spectroscopically. We measured the equivalent width of lithium at A absorption and H-alpha emission lines. The high percentage of stars with lithium present is further evidence of the importance of UV emission as a youth indicator for low-mass stars.
In addition, we used high-resolution spectra obtained with the Hamilton echelle spectrograph to determine radial velocities for several UV-bright stars. These radial velocities will be useful for the calculation of Galactic UVW space velocities for determination of possible moving group membership. We report the discovery of a pre-main-sequence PMS , low-mass , double-lined, spectroscopic, eclipsing binary in the Orion star-forming region.
We present our observations, including radial velocities derived from optical high-resolution spectroscopy, and present an orbit solution that permits the determination of precise empirical masses for both components of the system.
We find that Par is composed of two equal-mass 0. There is strong evidence, such as the system exhibiting strong Li lines and a center-of-mass velocity consistent with cluster membership, that this system is a member of the Orion star-forming region and quite possibly the Orion Nebula Cluster, and therefore has an age of only a few million years. As there are currently only a few empirical mass and radius measurements for low-mass , PMS stars , this system presents an interesting test for the predictions of current theoretical models of PMS stellar evolution.
During his too short career, Olivier Chesneau pioneered the study of the circumstellar environments of low mass evolved stars using very high angular resolution techniques. He applied state of the art high angular resolution techniques, such as optical interferometry and adaptive optics imaging, to the the study of a variety of objects, from AGB stars to Planetary Nebulae, via e. I present here an overview of this work and most important results by focusing on the paths he followed and key encounters he made to reach these results.
Olivier liked to work in teams and was very strong at linking people with complementary expertises to whom he would communicate his enthusiasm and sharp ideas. His legacy will live on through the many people he inspired. Young stars of low mass in the Gum nebula. Observations are presented for four recently formed stars in the vicinity of the Gum nebula which are heavily obscured by surrounding dust and are associated with small reflection nebulae.
It is suggested that the observed scenario of low-mass stars in an older massive star environment may be analogous to the circumstances surrounding the birth of the sun. Star formation in low metallicity environments is evidently occurring under different conditions than in our Milky Way. Lower metallicity implies a lower dust to gas ratio, most likely leading to less cooling efficiency at high density molecular cores where low mass stars are expected to form.
We outline a project that aims to identify the low mass pre-main sequence populations within the Large and Small Magellanic Cloud. We developed an automatic detection algorithm that systematically analyses near-infrared colour-magnitude diagrammes constructed from the VMC VISTA Magellanic Clouds public survey data. In this poster we present our first results that show that we are able to detect significant numbers of PMS stars with masses down to 1.
We have detected numerous stars with Evolution of GHz emission in low-mass protostars. Kristensen, L. Water is a key tracer of dynamics and chemistry in low-mass star-forming regions, but spectrally resolved observations have so far been limited in sensitivity and angular resolution, and only data from the brightest low-mass protostars have been published.
Aims: The first systematic survey of spectrally resolved water emission in 29 low-mass L low-mass protostars. H2O intensities are compared to inferred envelope properties, e. The line profiles are complex and consist of several kinematic components tracing different physical regions in each system.
In particular, the profiles are typically dominated by a broad Gaussian emission feature, indicating that the bulk of the water emission arises in outflows, not in the quiescent envelope. Several sources show multiple shock components appearing in either emission or absorption, thus constraining the internal geometry of the system. Furthermore, the components include inverse P-Cygni profiles in seven sources six Class 0, one Class I indicative of infalling envelopes, and regular P-Cygni profiles in four sources three Class I, one Class 0 indicative of expanding envelopes.
Aging jets from low-mass stars. An extended faint optical jet is associated with the compact emission region plus faint star known as HH The HH 55 star is an emission line star of spectral type M3. We suggest that these objects are representative of the late evolutionary stage of the HH jet-outflow phenomenon and point out that such objects may be quite common although difficult to detect.
Low-Mass Stars and Their Companions. In this thesis, I present seven studies aimed towards better understanding the demographics and physical properties of M dwarfs and their companions. These studies focus in turn on planetary, brown dwarf, and stellar companions to M dwarfs.
I begin with an analysis of radial velocity and transit timing analyses of multi-transiting planetary systems, finding that if both signals are measured to sufficiently high precision the stellar and planetary masses can be measured to a high precision, eliminating a need for stellar models which may have systematic errors. I then combine long-term radial velocity monitoring and a direct imaging campaign to measure the occurrence rate of giant planets around M dwarfs.
I find that 6. I then analyze four secondary eclipses of the LHS AC system as observed by Spitzer in order to measure the luminosity of the brown dwarf in both Spitzer bandpasses. This is the first non-inflated brown dwarf with a measured mass, radius, and multi-band photometry, making it an ideal test of evolutionary models of field brown dwarfs. In this talk I will review two recent surveys in low-mass star formation undertaken by the Submillimeter Array SMA : a millimeter continuum survey of disks surrounding variably accreting young stars , and a complete continuum and molecular line survey of all protostars in the nearby Perseus Molecular Cloud.
I will highlight several new insights into the processes by which low-mass stars gain their mass that have resulted from the statistical power of these surveys. Ahmic, Mirza; Jayawardhana, R. Characterizing multiplicity in the very low mass VLM domain is a topic of much current interest and fundamental importance. Thus, we argue that there is no significant evolution of multiplicity with age among brown dwarfs and VLM stars between a few Myr to several Gyr. Instead, the observations to date suggest that VLM objects are either less likely to be born in wide multiple systems than solar mass stars or such systems are disrupted very early within the first couple of Myr.
Our results also imply that systems like 2MASSW J and Oph , with planetary mass companions at wide separations, are rare. We report on a near-infrared adaptive optics imaging survey of 31 young brown dwarfs and very low mass VLM stars , 28 of which are in the Chamaeleon I star-forming region, using the ESO Very Large Telescope.
We resolve the suspected 0. By combining our work with previous surveys, we arrive at the largest sample of young VLM objects 72 with high angular resolution imaging to date. Its multiplicity fraction is in statistical agreement with that for VLM objects in the field.
Thus, we argue that there is no significant evolution of multiplicity with age among brown dwarfs and VLM stars in OB and T associations between a few megayears to several gigayears. Instead, the observations so far suggest that VLM objects are either less likely to be born in fragile multiple systems than solar-mass stars or such systems are disrupted very early.
We dedicate this paper to the memory of our coauthor, Eduardo Delgado-Donate, who died in a hiking accident in Tenerife earlier this year. During the last decades, the study of rotation in young low mass stars has been one of the more active areas in the field of stellar evolution. The mean rotation of most of the cool low mass stars remains roughly constant during the T Tauri stage.
This can be explained by the disc locking scenario. This paradigm suggest that star start out as CTTS with periods of days, perhaps locked to their disc, and that this disc is eventually lost mainly by accretion.
At the current time, it is not clear that this is true for all low mass stars. Some authors have questioned its validity for stars less massive than 0. Although the reality may eventually turn out to be considerably more complex, a simple consideration of the effects of and limits on disc locking of young low mass stars seems necessary.
The lifetime of the accretion disc is a free parameter in our model. The resulting rotation rates are in agreement with observed vsin and photometric periods for young stars belonging to co-moving groups and open young clusters. In our numerical model, hierarchical formation of dark matter minihalos and Milky-Way-sized halos are followed by a high-resolution cosmological simulation.
Assuming a Kroupa initial mass function IMF from 0. The higher latitude fields require lower sample sizes because of the high number density of stars in the galactic disk, the required sample sizes are comparable in the high- and middle-latitude fields by photometrically selecting low-metallicity stars with optimized narrow-band filters, and the required number of dwarf galaxies to find one Pop III survivor is less than 10 at stars. Provided that available observations have not detected any survivors, the formation models of low-mass Pop III stars with more than 10 stars per minihalo are already excluded.
Meeting contribution: Low mass stars , brown dwarfs and hot Jupiters. Dr Viti opened with an apology that hers was not a field which could yet produce nice images; the objects she would be describing were too faint to be meaningfully imaged. Yet she would be arguing that even without images, a tremendous amount had been learnt from such objects in the past decade, and that there were exciting prospects for the future.
The primary subject of this talk would be low mass stars LMSs , defined as those stars of around half the mass of the Sun or less. Are planets orbiting low-mass stars suitable for the development of life? Observations in the near future, including radio, will help to assess whether atmospheres do persist over long timescales for planets orbiting nearby M dwarfs, and clarify the nature of the radiation that penetrates to the surface of these planets.
These are important ingredients for assessing planetary habitability, yet the question of habitability can be answered only with the positive measurement of an unambiguous biosignature. Radio and optical SETI observations capable of detecting technological activities of intelligent inhabitants could provide the most compelling evidence for the habitability of exoplanets orbiting M dwarfs. In this presentation we shall consider what information can be gleaned from our observations so far.
The frequency coverage on each star is about MHz bandwidth per star over a range of selected frequencies from GHz. From these observations we derive quantitative results relating to the probability that M dwarfs are actually inhabited. Ionizing UV radiation and supernova SN flows amidst clustered minihalos at high redshift regulated the rise of the first stellar populations in the universe.
Previous studies have addressed the effects of very massive primordial stars on the collapse of nearby halos into new stars , but the absence of the odd-even nucleosynthetic signature of pair-instability SNe in ancient metal-poor stars suggests that Population III stars may have been less than M sun.
We extend our earlier survey of local UV feedback on star formation to M sun stars and include kinetic feedback by SNe for M sun stars. We find radiative feedback to be relatively uniform over this mass range, primarily because the larger fluxes of more massive stars are offset by their shorter lifetimes. Our models demonstrate that prior to the rise of global UV backgrounds, Lyman-Werner LW photons from nearby stars cannot prevent halos from forming new stars.
These calculations also reveal that violent dynamical instabilities can erupt in the UV radiation front enveloping a primordial halo, but that they ultimately have no effect on the formation of a star. Finally, our simulations suggest that relic H II regions surrounding partially evaporated halos may expel LW backgrounds at lower redshifts, allowing stars to form that were previously suppressed.
We provide fits to radiative and kinetic feedback on star formation for use in both semianalytic models and numerical simulations. Dust discs around low-mass main-sequence stars. The current understanding of the formation of circumstellar disks as a natural accompaniment to the process of low-mass star formation is examined. Models of the thermal emission from the dust disks around the prototype stars Alpha Lyr, Alpha PsA, Beta Pic, and Epsilon Eri are discussed, which indicate that the central regions of three of these disks are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest zone lying between about and K.
One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud which sweeps up grains crossing its orbit. The companion shows the effects of irradiation of its atmosphere by the WD, and the tidal lock and inclination ensures that we view the illuminated and far-side hemispheres during each orbit.
Ground-based, J-band upper limits constrain the companion to be a late-type brown dwarf L5 or later. Thus, SDSS is an ideal system for studying the atmosphere of a sub-stellar object heated by a strong continuum.
Given its importance for the characterization of planetary atmosphere and binary star evolution, we propose to carry out phase-resolved 3. Coupled with the exquisite photometric stability of IRAC and the benign environment of Spitzer, this unique target offers an exceptional opportunity to study the effects of irradiation from host stars on their.
The physical conditions in low-mass protostellar outflows revealed by multi-transition water observations. Mottram, J. Outflows are an important part of the star formation process as both the result of ongoing active accretion and one of the main sources of mechanical feedback on small scales. Water is the ideal tracer of these effects because it is present in high abundance for the conditions expected in various parts of the protostar, particularly the outflow.
Aims: We constrain and quantify the physical conditions probed by water in the outflow-jet system for Class 0 and I sources. The lines are decomposed into different Gaussian components, with each component related to one of three parts of the protostellar system; quiescent envelope, cavity shock and spot shocks in the jet and at the base of the outflow. We then use non-LTE radex models to constrain the excitation conditions present in the two outflow-related components.
Results: Water emission at the source position is optically thick but effectively thin, with line ratios that do not vary with velocity, in contrast to CO. The physical conditions of the cavity and spot shocks are similar, with post-shock H2 densities of order - cm-3 and H2O column densities of order - cm H2O emission originates in compact emitting regions: for the spot shocks these correspond to point sources with radii of order AU, while for the cavity shocks these come from a thin layer along the outflow cavity wall with thickness of order AU.
Conclusions: Water emission at the source position traces two distinct kinematic components in the outflow; J shocks at the base of the outflow or in the jet, and C shocks in a thin layer in the cavity wall.
The similarity of the physical conditions is in contrast to off-source determinations which show similar densities but lower column densities and larger filling factors.
We propose. Although a majority of stars in the solar neighborhood are of mid- to late-M type, the magnetically-induced coronal X-ray and chromospheric UV, H-alpha activity of such stars remain essentially unexplored for the important age range Myr.
Such information on high-energy processes associated with young M stars would provide much-needed constraints on models of the effects of stellar irradiation on the physics and chemistry of planet- forming disks and newborn planets. In addition, X-ray and UV observations of ultra- low-mass young stars can serve to probe the presently ill-defined spectral type boundary that determines which very low-mass objects will eventually become M stars -- as opposed to brown dwarfs BDs -- following their pre-main sequence evolutionary stages.
The proposed ADA program will yield the full reduction and analysis of these as-yet unexplored data. Suppression of accretion on to low-mass Population III stars. Motivated by recent theoretical work suggesting that a substantial fraction of Population Pop III stars may have had masses low enough for them to survive to the present day, we consider the role that the accretion of metal-enriched gas may have had in altering their surface composition, thereby disguising them as Pop II stars.
We demonstrate that if weak, solar-like winds are launched from low-mass Pop III stars formed in the progenitors of the dark matter halo of the Galaxy, then such stars are likely to avoid significant enrichment via accretion of material from the interstellar medium.
We find that at early times accretion is easily prevented if the stars are ejected from the central regions of the haloes in which they form , either by dynamical interactions with more massive Pop III stars or by violent relaxation during halo mergers.
While there is no a priori reason to assume that low-mass Pop III stars do not have solar-like winds, without them surface enrichment via accretion is likely to be inevitable. We briefly discuss the implications that our results hold for stellar archaeology. Atmospheric circulations of terrestrial planets orbiting low-mass stars.
Circulations and habitable zones of planets orbiting low-mass stars are investigated. Many of these planets are expected to rotate synchronously relative to their parent stars , thereby raising questions about their surface temperature distributions and habitability.
We use a global circulation model to study idealized, synchronously rotating tidally locked planets of various rotation periods, with surfaces of all land or all water, but with an Earth-like atmosphere and solar insolation.
This concept has little relevance for either dry or aquaplanets, but might become relevant on a planet with both land area and oceans. The circulations on these tidally locked planets exhibit systematic changes as the rotation period is varied.
However, they also reveal abrupt transitions between two different circulation regimes and multiple equilibria. For the dry planet, the transition occurs between a 4-day and a 5-day period, while for the aquaplanet, it occurs between a 3-day and a 4-day period. For both dry and aqua planets, this transition occurs when the Rossby deformation radius exceeds half the planetary radius.
Further investigation on the dry planet reveals that multiple equilibria exist between and h periods. These multiple equilibria may be relevant for real planets within the habitable zones of late K and M stars , because these planets are expected to have rotation periods between 8 and Earth days. A UV spectroscopic snapshot survey of low-mass stars in the Hyades. Because of its proximity, the Myr-old Hyades open cluster is a unique resource for exploring the relationship between magnetic activity, rotation, and age in low-mass stars.
While the cluster has been largely ignored in UV studies of the dependence of activity on rotation, we now have an extensive and growing set of complementary rotation period, Halpha, and X-ray measurements with which to examine in detail the rotation-activity relation at Myr and to constrain theories of magnetic heating.
These stars form a representative sample of low-mass Hyads with known periods and are a significant addition to, and expansion of, the sample of 20 mainly solar-mass rotators with existing mostly low-resolution IUE NUV spectra. The Mg II measurements will contribute significantly to our goal of mapping out the rotation-activity relation star-by-star in this benchmark open cluster. This, in turn, will move us toward an improved understanding of the radiation environment and habitability of the exoplanets we continue to find around low-mass stars.
Observations of the neutron stars in quiescent low-mass X-ray binaries are important for determining their masses and radii which can lead to powerful constraints on the dense matter nuclear equation of state. The interpretation of these sources is complex and their spectra differ appreciably from blackbodies. Further progress hinges on reducing the uncertainties stemming from models of neutron star atmospheres.
We present a suite of low-temperature neutron star atmospheres of different chemical compositions pure H and He. We generated model atmospheres using zcode - a radiation transfer code developed at Los Alamos National Laboratory.
In order to facilitate analytic studies, we developed three-parameter fits to our models, and also compared them to diluted blackbodies in the energy range of 0. From the latter, we extract color-correction factors fc , which represent the shift of the spectra as compared to a blackbody with the same effective temperature.
These diluted blackbodies are also useful for studies of photspheric expansion X-ray bursts. These results enhance our ability to interpret thermal emission from neutron stars and to constrain the mass-radius relationship of these exotic objects.
This research was supported in part by the U. This research was carried out in part under the auspices of the National Nuclear Security Administration of the U. For each star , the observed spectrum is fitted with a non-accreting stellar template and an accretion spectrum obtained from assuming a plane-parallel hydrogen slab.
Five of the eight stars with an IR disk excess show excess UV emission, indicating ongoing accretion. The mass accretion rates are consistent with those of other young star forming regions. Winds from stripped low-mass helium stars and Wolf-Rayet stars. This is the first report of this pathogen affecting calla plants in Serbia. Laminated Root Rot of Western Conifers. Laminated root rot is caused by the native fungus Phellinus weirii Murr. The disease has also been reported in Japan and Manchuria.
In the United States, the pathogen is most destructive in pure Douglas-fir stands west of the crest of the Cascade Range in Washington Studies on storage rot of cocoyam.
Eze, C. S Studies on storage rot of cocoyam Colocasia esculenta L. Schott at Nsukka. Loyonga, S. N and Nzietchueng S. Cocoyam and African food crisi. Paraphoma crown rot of pyrethrum Tanacetum cinerariifolium. Pyrethrum Tanacetum cinerariifolium is commercially cultivated for the extraction of natural pyrethrin insecticides from the oil glands inside seeds. Yield-decline has caused significant yield losses in Tasmania during the last decade. A new pathogen of pyrethrum causing crown rot and reduced.
Rhizoctonia crown and root rot disease nursery. Full Text Available White rot fungi can be used as a pretreatment of biomass to degrade lignin.
Kenaf chips were first inoculated with each fungus separately using corn steep liquor as a fungal growth promoter. The kenaf chips were inoculated with white rot fungus for a period of 1, 2, 4, 8 and 16 weeks, after which they were observed under the scanning electron microscope SEM. SEM observations showed evidence of fungal colonization. When calculating weight loss, both P.
Amounts by mass of cellulose, hemicelluloses, extractives, and lignin in the treated kenaf chips all were lowered. The results show that O. Shell bone histology indicates terrestrial palaeoecology of basal turtles.
The palaeoecology of basal turtles from the Late Triassic was classically viewed as being semi-aquatic, similar to the lifestyle of modern snapping turtles. Lately, this view was questioned based on limb bone proportions, and a terrestrial palaeoecology was suggested for the turtle stem. Here, we present independent shell bone microstructural evidence for a terrestrial habitat of the oldest and basal most well-known turtles, i.
Soft rot erwiniae: from genes to genomes. We currently understand much about how these bacteria attack plants and protect themselves against plant defences.
However, the processes underlying the establishment of infection, differences in host range and their ability to survive when not causing disease, largely remain a mystery. This review will focus on our current knowledge of pathogenesis in these organisms and discuss how modern genomic approaches, including complete genome sequencing of Eca and Ech, may open the door to a new understanding of the potential subtlety and complexity of soft rot erwiniae and their interactions with plants.
The soft rot erwiniae are members of the Enterobacteriaceae, along with other plant pathogens such as Erwinia amylovora and human pathogens such as Escherichia coli, Salmonella spp.
Although the genus name Erwinia is most often used to describe the group, an alternative genus name Pectobacterium was recently proposed for the soft rot species. Ech mainly affects crops and other plants in tropical and subtropical regions and has a wide host range that includes potato and the important model host African violet Saintpaulia ionantha. Ecc affects crops and other plants in subtropical and temperate regions and has probably the widest host range, which also includes potato.
Eca, on the other hand, has a host range limited almost exclusively to potato in temperate regions only. Disease symptoms: Soft rot erwiniae cause general tissue maceration, termed soft rot disease, through the production of plant cell wall degrading enzymes.
Environmental factors such as temperature, low oxygen concentration and free water play an essential role in disease development. On potato, and possibly other plants, disease symptoms may differ, e.
Isolation of laccase gene-specific sequences from white rot and brown rot fungi by PCR. Degenerate primers corresponding to the consensus sequences of the copper-binding regions in the N-terminal domains of known basidiomycete laccases were used to isolate laccase gene-specific sequences from strains representing nine genera of wood rot fungi.
All except three gave the expected PCR product of about bp. Computer searches of the databases identified the sequences of each of the PCR product of about bp. Computer searches of the databases identified the sequence of each of the PCR products analyzed as a laccase gene sequence, suggesting the specificity of the primers.
Demonstration of laccase activity in G. In Brazil, scientific reports on the effectiveness of control methods are scarce. The application of dolomitic limestone or gypsum alone is not effective to recover plants affected by root rot. The typical symptoms were water-soaked lesions on bottom stem and leaf rot.
The lesion rapidly expanded and the plant was softened totally. The fungus grew vigorously at an optimum temperature 25oC and brownish colony and black sporangia were formed on potato dextrose agar medium. On the basis of mycological characteristics, analyzing sequences of internal transcribed spacer region of ribosomal DNA, and pathogenicity test on host plants, the causal fungus was identified as R.
This is the first report of Rhizopus soft rot on lily caused by R. Full Text Available This study was conducted to control ginger rhizome rot treated with the combined treatment, the hairy vetch, carbonized rice husk and eggshell calcium in organic ginger farm. Early symptoms of leaf yellowing and plant wilt began in the chemical fertilizer treatment on July 1.
Ginger rhizome rot was more progressed on October 2, and stem browning and dead plant showed a high disease incidence with from On the other hand, the combined treatment did not occur at all until July 1 and delayed the disease incidence to October 2. It showed a low disease incidence of 1. In the combined treatment, the content of soil Na, Fe, Cu was decreased and organic matter was increased twice with Population density of Pythium sp. The combined treatment, hairy vetch, carbonized rice husk and the eggshell calcium is able to control the ginger rhizome rot in organically cultivated ginger field.
Stand tending and root rot in Norway spruce stands - economical effects caused by root rot at different thinning regimes. This report is divided into three parts: 1 a literature study describing the most common fungi causing rot in wood and descriptions of various strategies to reduce economic loss from root rot , 2 a check of a model describing the development of butt rot in pure Norway spruce plantations in southern Sweden, and 3 simulated economic effects of root rot in stands with various stand tending.
The rot model was used to estimate future rot frequencies in the economic calculations. In order to avoid overestimations of rot frequencies, the calculations were also executed when assuming slower growth of rot than shown in the model. When analysing the economical effects of rot , the following three thinning programmes were used: Program 1: thinning at the ages of and 45 years.
Final felling at the ages , , , , and 70 years. Program 2: thinning at the ages of and years. Final felling at the ages 65 and 75 years. Program 3: thinning at the ages of , , , and 70 years.
Final felling at the ages 80 and 90 years. This result was valid when presuming butt rot in the stand as well as when presuming no butt rot in the stand. There was a small difference between the value at present in programme 1 final felling at the age of 60 years and in programme 3 final felling at the age of 80 years.
When presuming butt rot in the stand, the value at present in programme 3 decreased somewhat more in comparison to the value at present in programme 1. Compared to no butt rot in the stand, the optimal final felling time appeared five to ten years earlier when assuming butt rot in the stand. The calculated optimal time of final felling appeared at the same stand age whether assuming rot preset or not.
The results in this study. Heterogeneity of limbal basal epithelial progenitor cells. Although corneal epithelial stem cells SCs are located at the limbus between the cornea and the conjunctiva, not all limbal basal epithelial cells are SCs.
Basidiomycota basidiomycetes make up 32percent of the described fungi and include most wood decaying species, as well as pathogens and mutualistic symbionts. Prior genomic comparisons suggested that the two decay modes can be distinguished based on the presence or absence of ligninolytic class II peroxidases PODs , as well as the abundance of enzymes acting directly on crystalline cellulose reduced in brown rot.
The newly sequenced Botryobasidium botryosum and Jaapia argillacea genomes lack PODs, but possess diverse enzymes acting on crystalline cellulose, and they group close to the model white rot species Phanerochaete chrysosporium in the PCA. Furthermore, laboratory assays showed that both B. We also found expansions in reducing polyketide synthase genes specific to the brown rot fungi. Our results suggest a continuum rather than a dichotomy between the white rot and brown rot modes of wood decay.
A more nuanced categorization of rot types is needed, based on an improved understanding of the genomics and biochemistry of wood decay.
Future of newer basal insulin. Basal insulin have been developed over the years. In recent times newer analogues have been added to the armanentarium for diabetes therapy.
This review specifically reviews the current status of different basal insulins. Basal stamcellebiologi og cancer. The finding that tumours, like normal tissues, are endowed with varying degrees of cellular heterogeneity has far-reaching consequences for our understanding of cancer. The cancer stem cell and clonal evolution models have both been proposed to explain tumour-associated cellular heterogeneity.
Finally, we discuss the close association between basic stem cell biology and cancer, focusing on the role of self-renewal The influence of root rot incidence on cassava genotype on In Nigeria cassava root rot causes serious yield losses in cassava tuber production every year. However, the influence of root rot incidence on cassava genotype at harvest on consumers' acceptability of the gari produced from it has not been studied. A sensory evaluation was conducted on gari processed from the tuberous Weevil - red rot associations in eastern white pine.
The presence of red rot Fomes pini in pruned white pine stands has often been attributed to the act of pruning. This assumption may well be true for heavily stocked stands where thinning has been neglected and pruning scars are slow to heal. The question then arises: How do we account for the red rot often found in vigorous unpruned white pine stands? Fungi associated with base rot disease of aloe vera Aloe Dec 17, Key words: Fungi, base rot , Aloe vera. Aloe barbadensis Miller, popularly called Aloe vera is a phanerogame angiosperm which belongs to the family.
The plant is a perennial drought resistant succulent plant Figure 1. Aloe vera is Improvement of resistance to Fusarium root rot through gene Fusarium root rot FRR , caused by Fusarium solani f. Development and deployment of resistant materials is the most feasible approach to managing The storage lifespan of kola nuts is challenged by the problem of decay of nuts in storage as a result of the attack by the rot fungus Fusarium spp.
The effect of the neem leaf Azadirachta indica extracts on the rot fungus was investigated in order to aid extended kola nuts storage. The aqueous and ethanolic leaf extracts of Preliminary Studies on the Occurrence of Stem Borers and the Whereas the percentage of plants with stem borers infestation and those with stem Experience with basal area estimation by prisms in lodgepole pine.
Estimation of basal area by prisms offers intriguing possibilities for reducing time and effort in making stand inventories. Increased inventory efficiency is a particular need in stands that are relatively low in value due to small stems , predominance of low value species or heavy defect. In the Pacific Northwest, lodgepole pine characteristically forms dense low Diagnostic of dry rot in living trees. Heterogeneity of basal cells is recognized in terms of gene expression and differentiation capacity.
In this Issue, Pagano and colleagues isolate a subset of immortalized basal cells that are characterized by high motility, suggesting that they might also be heterogeneous in their biophysical properties.
Motility-selected cells displayed an increased ability to colonize the lung in vivo The possible implications of these findings are discussed in terms of basal cell heterogeneity, epithelial cell migration, and modeling of metastasis that occurs early in cancer evolution.
Cancer Prev Res; 10 9 ; Candidate gene association mapping of Sclerotinia stalk rot resistance in sunflower Helianthus annuus L.
Functional markers for Sclerotinia basal stalk rot resistance in sunflower were obtained using gene-level information from the model species Arabidopsis thaliana.
Sclerotinia stalk rot , caused by Sclerotinia sclerotiorum, is one of the most destructive diseases of sunflower Helianthus annuus L. Markers for genes controlling resistance to S.
We sequenced eight candidate genes homologous to Arabidopsis thaliana defense genes known to be associated with Sclerotinia disease resistance in a sunflower association mapping population evaluated for Sclerotinia stalk rot resistance. The total candidate gene sequence regions covered a concatenated length of 3, bp per individual.
Eight SNPs in the coding regions led to changes in amino acid codons. A general linear model with modification to account for population structure was found the best fitting model for this population and was used for association mapping.
These SNP markers associated with Sclerotinia stalk rot resistance can potentially be applied to the selection of favorable genotypes, which will significantly improve the efficiency of MAS during the development of stalk rot resistant cultivars.
Root rot diseases of sugar beet. However, not all these soil-borne pathogens have been reported in all sugar beet production areas. Losses include reduced harvestable tonnage and reduced white sugar recovery.
Many of these pathogens also cause post harvest losses in storage piles. Control for diseases caused by these pathogens include disease resistant cultivars, avoidance of stresses, cultural practices such as water management and the use of fungicides. Energy balance associated with the degradation of lignocellulosic material by white- rot and brown- rot fungi.
The major precursor for this forest SOC is lignocellulosic material, which is made of polysaccharides and lignin. Lignin has traditionally been considered as a recalcitrant polymer that hinders access to the much more labile structural polysaccharides.
This view appears to be partly incorrect from a microbiology perspective yet, as substrate alteration depends on the metabolic potential of decomposers. In forest ecosystems the wood- rotting Basidiomycota fungi have developed two different strategies to attack the structure of lignin and gain access to structural polysaccharides. White- rot fungi degrade all components of plant cell walls, including lignin, using enzymatic systems.
Brown- rot fungi do not remove lignin. They generate oxygen-derived free radicals, such as the hydroxyl radical produced by the Fenton reaction, that disrupt the lignin polymer and depolymerize polysaccharides which then diffuse out to where the enzymes are located The objective of this study was to develop a model to investigate whether the lignin relative persistence could be related to the energetic advantage of brown- rot degradative pathway in comparison to white- rot degradative pathway.
The model simulates the changes in substrate composition over time, and determines the energy gained from the conversion of the lost substrate into CO2.
The energy cost for the production of enzymes involved in substrate alteration is assessed using information derived from genome and secretome analysis. For brown- rot fungus specifically, the energy cost related to the production of OH radicals is also included. The model was run, using data from the literature on populous wood degradation by Trametes versicolor, a white- rot fungus, and Gloeophyllum trabeum, a brown- rot fungus.
It demonstrates that the brown- rot fungus Gloeophyllum trabeum was more efficient than the white- rot. Report Card on Basal Readers. This report examines the nature of the modern basal reader, its economics, and use. First, the report provides a history showing how the confluence of business principles, positivistic science, and behavioral psychology led to the transformation of reading textbooks into basal readers.
Next, the report examines objectives and subjective factors…. Nov 16, The results of this Due to inefficient harvesting, packaging Where there Production and optimization of ligninolytic enzymes by white rot Production and optimization of ligninolytic enzymes by white rot fungus Schizophyllum Biodegrading effects of some rot fungi on Pinus caribaea wood The wood samples were inoculated separately with two species of white- rot fungi; Corioliopsis polyzona and Pleurotus squarrosulus, and two species of brownrot fungi; Pathological and rhizospherical studies on root- rot disease of Feb 5, Rhizoctonia solani root- rot aggressive pathogens to squash on media containing culture of Trichoderma The bacteriology of root region of cat Erwinia carotovora extracellular proteases : characterization and role in soft rot.
Erwinia carotovora subsp. Maceration of potato tuber tissue is caused by secreted pectolytic enzymes. Other cell-degrading enzymes may also have roles in pathogenesis, including cellulases, phospholipases, and protease s. The objectives of this research were to 1 characterize Ecc extracellular protease Prt and 2 elucidate its role in potato soft rot.
A gene enc Ligninolytic white- rot basidiomycetes can effectively degrade colored effluents and conventional dyes. White- rot fungi produce various isoforms of extracellular oxidases including laccase, Mn peroxidase and lignin peroxidase LiP , which are involved in the degradation of lignin in their natural lignocellulosic substrates. The textile industry, by far the most avid user of synthetic dyes, is in need The distribution frequency of pathogenic fungi associated with root and crown rot of winter wheat Triticum aestivum from fields in the North China Plain was determined during the period from to The four most important species identified were Bipolaris sorokiniana We observed that the recovered species varied with the agronomic zone.
Fusarium pseudograminearum was predominant in regions 1 and 3, whereas F. The incidence of F. A negative correlation between the frequency of occurrence of F. The coexistence of Fusarium spp. Moreover, this is the first report on the association between F. Our results would be useful in the framing guidelines for the management of root and crown rot fungi in wheat in different agronomic zones of the North China Plain.
Comparative studies on thermochemical characterization of corn stover pretreated by white- rot and brown- rot fungi. The effects of white- rot and brown- rot fungal pretreatment on the chemical composition and thermochemical conversion of corn stover were investigated. Fungus-pretreated corn stover was analyzed by Fourier transform infrared spectroscopy and X-ray diffraction analysis to characterize the changes in chemical composition.
Differences in thermochemical conversion of corn stover after fungal pretreatment were investigated using thermogravimetric and pyrolysis analysis. The results indicated that the white- rot fungus Irpex lacteus CD2 has great lignin-degrading ability, whereas the brown- rot fungus Fomitopsis sp. IMER2 preferentially degrades the amorphous regions of the cellulose.
The biopretreatment favors thermal decomposition of corn stover. The weight loss of IMER2-treated acid detergent fiber became greater, and the oil yield increased from Full Text Available Phytophthora is a genus of Oomycota responsible for some of the most serious diseases with great economic impact Judelson and Blanco, While 54 species were found in the 20th century Erwin and Ribeiro, another new species have been identified Brasier, since the year They are spread worldwide and have broad range of host plants — fruit trees, citrus, forest and park species.
Phytophthora can cause serious damages in orchards and nurseries of apples, cherries, etc. In Bulgaria they have been found first on young apples and cherries in Plovdiv region Nakova, Surveys have been done for discovering disease symptoms in Plovdiv and Kjustendil regions. Phytophthora strains were identified based on standard morphology methods — types of colonies on PDA, CMA, V 8, type and size of sporangia, oogonia and antheridia, andoospores.
Amplification products concentrations were estimated by comparison with the standard DNA. Phytophthora root and crown rot symptoms first appear in early spring. Infected trees show bud break delay, have small chlorotic leaves, and branches die all of a sudden.
Later symptoms are found in August-September. Leaves of the infected trees show reddish discoloration and drop down. Both symptoms are connected with lesions wet, necrotic in appearance at stem bases of the trees. Morphologically, the isolates acquired from.
The using of antagonistic fungus of Trichoderma harzianum as a biological control agent of the pathogen is one of the important alternatives in controlling P. The objectives of the research were to study about the ability of T. This research was arranged in a completely randomized design, with five treatments of length time application of T. Each treatment was repeated15 times.
The observed parameterswere disease percentage, the inhibition of antagonistic fungus, disease infection rate, plant height, number of leaves, wet and dry weight of plant, stem and leaves on pepper seed, and P.
The result showed that application time of T. The antagonism test showed that T. This result proves that application time of T. Stem Cells. Stem cells are cells with the potential to develop into many different types of cells in the body. There are two main types of stem cells: embryonic stem cells and adult stem cells. Full Text Available This study aimed to evaluate six cauliflower genotypes regarding their resistance to black rot and their production performance.
It was used a randomized block design, with four replications total of 24 plots. Each plot consisted of three planting lines 2.Http olivier de muizon free fr 1s exos html basal stem rot in young oil palm plantings. The Http olivier de muizon free fr 1s exos html primer reaction was used in conjunction with a palm-sampling programme to investigate the possible infection of young palms through cut frond base surfaces. Ganoderma DNA was detected in frond base material at a greater frequency than would be expected by comparison with current infection levels. Comparisons are made between the height of the frond http olivier de muizon free fr 1s exos html infected, the number of frond bases infected, and subsequent development of basal stem rot. The preliminary results suggest that the development of basal stem rot may be more likely to occur when young lower frond bases are infected. Genetic analysis of partial resistance to basal stem muizkn Sclerotinia sclerotiorum in sunflower. Directory of Open Access Journals Sweden. The study was undertaken in a completely randomized design with three replications under controlled conditions. The RILs and their parental lines were inoculated with a moderately ollivier isolate of S. Resistance to disease was evaluated by measuring the percentage of necrosis area three days after inoculation. The frequency distribution of lines for susceptibility to disease showed a http olivier de muizon free fr 1s exos html pattern. Composite interval mapping analysis revealed 5 QTLs for percentage of necrotic area, localized on linkage groups 1, 3, 8, 10 and The sign of additive effect was positive in 5 QTLs, suggesting that the additive allele fxos partial http olivier de muizon free fr 1s exos html to basal stem rot came from the paternal line RHA The phenotypic variance explained by QTLs R2 ranged from 0. Ganoderma boninense is the dominant fungal pathogen of basal stem rot BSR disease on Elaeis guineensis We sequenced the nuclear genome of mycelia using both Illumina and Pacific Biosciences platforms for assembly of scaffolds. The draft genome comprised Research on basal stem rot BSR of ornamental palms caused by basidiospores from Ganoderma boninense. Basidiospores were isolated from the fruiting bodies of Ganoderma infecting oil palms from an estate in Johor and from ornamental palms including oil palms from Jonas blue rise mp3 free download. The spores were then germinated to obtain homokaryotic mycelia. Based on clamp connection formation in paired hyphal fusions, tester strains were identified from the homokaryons isolated. Compatibility tests were then carried out using these testers to determine the relatedness of the homokaryotic Ganoderma isolates, both from Johor and from Singapore. 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