865 research outputs found
Magnetic Field Structure around Low-Mass Class 0 Protostars: B335, L1527 and IC348-SMM2
We report new 350 micron polarization observations of the thermal dust
emission from the cores surrounding the low-mass, Class 0 YSOs L1527,
IC348-SMM2 and B335. We have inferred magnetic field directions from these
observations, and have used them together with results in the literature to
determine whether magnetically regulated core-collapse and star-formation
models are consistent with the observations. These models predict a pseudo-disk
with its symmetry axis aligned with the core magnetic field. The models also
predict a magnetic field pinch structure on a scale less than or comparable to
the infall radii for these sources. In addition, if the core magnetic field
aligns (or nearly aligns) the core rotation axis with the magnetic field before
core collapse, then the models predict the alignment (or near alignment) of the
overall pinch field structure with the bipolar outflows in these sources. We
show that if one includes the distorting effects of bipolar outflows on
magnetic fields, then in general the observational results for L1527 and
IC348-SMM2 are consistent with these magnetically regulated models. We can say
the same for B335 only if we assume the distorting effects of the bipolar
outflow on the magnetic fields within the B335 core are much greater than for
L1527 and IC348-SMM2. We show that the energy densities of the outflows in all
three sources are large enough to distort the magnetic fields predicted by
magnetically regulated models.Comment: Accepted for publication in The Astrophysical Journa
Genetic control of the operculum and capsule morphology of Eucalyptus globulus
The petaline operculum that covers the inner whorls until anthesis and the woody capsule that develops after fertilization are reproductive structures of eucalypts that protect the flower and seeds. Although they are distinct organs, they both develop from flower buds and this common ontogeny suggests shared genetic control. In Eucalyptus globulus their morphology is variable and we aimed to identify the quantitative trait loci (QTL) underlying this variation and determine whether there is common genetic control of these ecologically and taxonomically important reproductive structures.EEA Bella VistaFil: HernĂĄndez, Mariano AgustĂn. University of Tasmania. School of Natural Sciences; Australia.Fil: HernĂĄndez, Mariano AgustĂn. University of Tasmania. ARC Training Centre for Forest Value; Australia.Fil: HernĂĄndez, Mariano AgustĂn. Instituto Nacional de TecnologĂa Agropecuaria (INTA). EstaciĂłn Experimental Agropecuaria Bella Vista; Argentina.Fil: Butler, Jakob B. University of Tasmania. School of Natural Sciences; Australia.Fil: Ammitzboll, Hans. University of Tasmania. School of Natural Sciences; Australia.Fil: Ammitzboll, Hans. University of Tasmania. ARC Training Centre for Forest Value; Australia.Fil: Weller, James L. University of Tasmania. School of Natural Sciences; Australia.Fil: Weller, James L. Australian Research Council Centre of Excellence for Plant Success in Nature and Agriculture; Australia.Fil: Vaillancourt, RenĂ© E. University of Tasmania. School of Natural Sciences; Australia.Fil: Vaillancourt, RenĂ© E. University of Tasmania. ARC Training Centre for Forest Value; Australia.Fil: Potts, Brad M. University of Tasmania. School of Natural Sciences; Australia.Fil: Potts, Brad M. University of Tasmania. ARC Training Centre for Forest Value; Australia
Analytic Detection Thresholds for Measurements of Linearly Polarized Intensity Using Rotation Measure Synthesis
A fully analytic statistical formalism does not yet exist to describe
radio-wavelength measurements of linearly polarized intensity that are produced
using rotation measure synthesis. In this work we extend the analytic formalism
for standard linear polarization, namely that describing measurements of the
quadrature sum of Stokes Q and U intensities, to the rotation measure synthesis
environment. We derive the probability density function and expectation value
for Faraday-space polarization measurements for both the case where true
underlying polarized emission is present within unresolved Faraday components,
and for the limiting case where no such emission is present. We then derive
relationships to quantify the statistical significance of linear polarization
measurements in terms of standard Gaussian statistics. The formalism developed
in this work will be useful for setting signal-to-noise ratio detection
thresholds for measurements of linear polarization, for the analysis of
polarized sources potentially exhibiting multiple Faraday components, and for
the development of polarization debiasing schemes.Comment: 14 pages, 6 figures, accepted for publication in MNRA
Microwave Kinetic Inductance Detector (MKID) Camera Testing for Submillimeter Astronomy
Developing kilopixel focal planes for incoherent submm- and mm-wave detectors remains challenging due to either the large hardware overhead or the complexity of multiplexing standard detectors. Microwave kinetic inductance detectors (MKIDs) provide a efficient means to produce fully lithographic background-limited kilopixel focal planes. We are constructing an MKID-based camera for the Caltech Submillimeter Observatory with 576 spatial pixels each simultaneously sensitive in 4 bands at 230, 300, 350, and 400 GHz. The novelty of MKIDs has required us to develop new techniques for detector characterization. We have measured quasiparticle lifetimes and resonator Qs for detector bath temperatures between 200 mK and 400 mK. Equivalent lifetime measurements were made by coupling energy into the resonators either optically or by driving the third harmonic of the resonator. To determine optical loading, we use both lifetime and internal Q measurements, which range between 15,000 and 30,000 for our resonators. Spectral bandpass measurements confirm the placement of the 230 and 350 GHz bands. Additionally, beam maps measurements conform to expectations. The same device design has been characterized on both sapphire and silicon substrates, and for different detector geometries. We also report on the incorporation of new shielding to reduce detector sensitivity to local magnetic fields
Genetic variation in fire recovery and other fireârelated traits in a global eucalypt species
To understand the potential of forests to adapt to wildfire, we studied the genetic architecture of fire-related structural, damage and recovery traits in a globally important Australian forest tree species, Eucalyptus globulus. Fourteen traits were evaluated in an outcrossed F2 population in a field trial in Tasmania, Australia, which was burnt by a wildfire 14 years after planting. The trial also included open-pollinated families of the grandparental dwarf and tall ecotypes used to produce the F2 population. We studied the phenotypic correlations within the F2 population and performed quantitative trait loci (QTL) analyses using a linkage map comprised of 472 markers. Ecotype comparisons revealed that almost all traits were under genetic control, with trees of the dwarf ecotype significantly more damaged and mainly recovering from lignotubers, whereas tall ecotype trees mainly recovered from epicormic resprouts extending for a variable height up the stem. Within the F2, tree size was negatively correlated with fire damage and positively correlated with recovery. Genetic control of fire-related traits was confirmed by the detection of 38 QTL in the F2 population. These QTL accounted for 4 to 43% of the phenotypic variation in these traits. Several QTL co-located and likely reflect pleiotropic effects. However, many independent QTL were detected, including QTL for crown consumption and trunk scorch, epicormic resprouting, resprout herbivory, and seedling establishment. The QTL detected argue that many genetically controlled mechanisms are responsible for variation in fire damage and recovery.EEA Bella VistaFil: HernĂĄndez, Mariano AgustĂn. Instituto Nacional de TecnologĂa Agropecuaria (INTA). EstaciĂłn Experimental Agropecuaria Bella Vista; ArgentinaFil: HernĂĄndez, Mariano AgustĂn. University of Tasmania. School of Natural Sciences and ARC Training Centre for Forest Value; AustraliaFil: Butler, Jacob B. University of Tasmania. School of Natural Sciences and ARC Training Centre for Forest Value; AustraliaFil: Ammitzboll, Hans. University of Tasmania. School of Natural Sciences and ARC Training Centre for Forest Value; AustraliaFil: Freeman, Jules S. University of Tasmania. School of Natural Sciences and ARC Training Centre for Forest Value; AustraliaFil: Freeman, Jules S. Forest Genetics; Nueva ZelandaFil: OâReillyâWapstra, Julianne. University of Tasmania. School of Natural Sciences and ARC Training Centre for Forest Value; AustraliaFil: Vaillancourt, RenĂ© E. University of Tasmania. School of Natural Sciences and ARC Training Centre for Forest Value; AustraliaFil: Potts, Brad M. University of Tasmania. School of Natural Sciences and ARC Training Centre for Forest Value; Australi
Cloud microphysical effects of turbulent mixing and entrainment
Turbulent mixing and entrainment at the boundary of a cloud is studied by
means of direct numerical simulations that couple the Eulerian description of
the turbulent velocity and water vapor fields with a Lagrangian ensemble of
cloud water droplets that can grow and shrink by condensation and evaporation,
respectively. The focus is on detailed analysis of the relaxation process of
the droplet ensemble during the entrainment of subsaturated air, in particular
the dependence on turbulence time scales, droplet number density, initial
droplet radius and particle inertia. We find that the droplet evolution during
the entrainment process is captured best by a phase relaxation time that is
based on the droplet number density with respect to the entire simulation
domain and the initial droplet radius. Even under conditions favoring
homogeneous mixing, the probability density function of supersaturation at
droplet locations exhibits initially strong negative skewness, consistent with
droplets near the cloud boundary being suddenly mixed into clear air, but
rapidly approaches a narrower, symmetric shape. The droplet size distribution,
which is initialized as perfectly monodisperse, broadens and also becomes
somewhat negatively skewed. Particle inertia and gravitational settling lead to
a more rapid initial evaporation, but ultimately only to slight depletion of
both tails of the droplet size distribution. The Reynolds number dependence of
the mixing process remained weak over the parameter range studied, most
probably due to the fact that the inhomogeneous mixing regime could not be
fully accessed when phase relaxation times based on global number density are
considered.Comment: 17 pages, 10 Postscript figures (figures 3,4,6,7,8 and 10 are in
reduced quality), to appear in Theoretical Computational Fluid Dynamic
On the collisional disalignment of dust grains in illuminated and shaded regions of IC 63
Interstellar dust grain alignment causes polarization from UV to mm wavelengths, allowing the study of the geometry and strength of the magnetic field. Over the last couple of decades, observations and theory have led to the establishment of the radiative alignment torque mechanism as a leading candidate to explain the effect. With a quantitatively well constrained theory, polarization can be used not only to study the interstellar magnetic field, but also the dust and other environmental parameters. Photodissociation regions, with their intense, anisotropic radiation fields, consequent rapid H2 formation, and high spatial density-contrast provide a rich environment for such studies. Here we discuss an expanded optical, NIR, and mm-wave study of the IC 63 nebula, showing strong H2 formation-enhanced alignment and the first direct empirical evidence for disalignment due to gas-grain collisions using high-resolution HCO+(J = 1-0) observations. We find that a relative amount of polarization is marginally anticorrelated with column density of HCO+. However, separating the lines of sight of optical polarimetry into those behind, or in front of, a dense clump as seen from Îł Cas, the distribution separates into two well defined sets, with data corresponding to "shaded" gas having a shallower slope. This is expected if the decrease in polarization is caused by collisions since collisional disalignment rate is proportional to RCânT" role="presentation">RCânTâââ . Ratios of the best-fit slopes for the "illuminated" and "shaded" samples of lines of sight agrees, within the uncertainties, with the square root of the two-temperature H2 excitation in the nebula seen by Thi et al.Fil: Soam, Archana. Sofia Science Center; Estados UnidosFil: Anderson, B. G. Sofia Science Center; Estados UnidosFil: Acosta Pulido, Jose. Instituto de Astrofisica de Canarias; EspañaFil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. GobernaciĂłn. ComisiĂłn de Investigaciones CientĂficas. Instituto Argentino de RadioastronomĂa. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto Argentino de RadioastronomĂa; ArgentinaFil: Vaillancourt, J. E.. Lincoln Laboratory; Estados UnidosFil: Widicus Weaver, S. L.. Department Of Chemistry; Estados UnidosFil: Piirola, V.. University Of Turku; FinlandiaFil: Gordon, M. S.. Sofia Science Center; Estados Unido
Why I tense up when you watch me: inferior parietal cortex mediates an audienceâs influence on motor performance
The presence of an evaluative audience can alter skilled motor performance through changes in force output. To investigate how this is mediated within the brain, we emulated real-time social monitoring of participantsâ performance of a fine grip task during functional magnetic resonance neuroimaging. We observed an increase in force output during social evaluation that was accompanied by focal reductions in activity within bilateral inferior parietal cortex. Moreover, deactivation of the left inferior parietal cortex predicted both inter- and intra-individual differences in socially-induced change in grip force. Social evaluation also enhanced activation within the posterior superior temporal sulcus, which conveys visual information about othersâ actions to the inferior parietal cortex. Interestingly, functional connectivity between these two regions was attenuated by social evaluation. Our data suggest that social evaluation can vary force output through the altered engagement of inferior parietal cortex; a region implicated in sensorimotor integration necessary for object manipulation, and a component of the action-observation network which integrates and facilitates performance of observed actions. Social-evaluative situations may induce high-level representational incoherence between oneâs own intentioned action and the perceived intention of others which, by uncoupling the dynamics of sensorimotor facilitation, could ultimately perturbe motor output
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