1,789 research outputs found
Effective free energy for pinned membranes
We consider membranes adhered through specific receptor-ligand bonds. Thermal
undulations of the membrane induce effective interactions between adhesion
sites. We derive an upper bound to the free energy that is independent of
interaction details. To lowest order in a systematic expansion we obtain
two-body interactions which allow to map the free energy onto a lattice gas
with constant density. The induced interactions alone are not strong enough to
lead to a condensation of individual adhesion sites. A measure of the thermal
roughness is shown to depend on the inverse square root of the density of
adhesion sites, which is in good agreement with previous computer simulations.Comment: to appear as a Rapid Communication in Phys. Rev.
Isomorphic classical molecular dynamics model for an excess electron in a supercritical fluid
Ring polymer molecular dynamics (RPMD) is used to directly simulate the
dynamics of an excess electron in a supercritical fluid over a broad range of
densities. The accuracy of the RPMD model is tested against numerically exact
path integral statistics through the use of analytical continuation techniques.
At low fluid densities, the RPMD model substantially underestimates the
contribution of delocalized states to the dynamics of the excess electron.
However, with increasing solvent density, the RPMD model improves, nearly
satisfying analytical continuation constraints at densities approaching those
of typical liquids. In the high density regime, quantum dispersion
substantially decreases the self-diffusion of the solvated electron.
In this regime where the dynamics of the electron is strongly coupled to the
dynamics of the atoms in the fluid, trajectories that can reveal diffusive
motion of the electron are long in comparison to .Comment: 24 pages, 4 figure
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Measles vaccination and antibody response in autism spectrum disorder
OBJECTIVE: To test the hypothesis that measles vaccination was involved in the pathogenesis of autism spectrum disorders (ASD) as evidenced by signs of a persistent measles infection or abnormally persistent immune response shown by circulating measles virus or raised antibody titres in children with ASD who had been vaccinated against measles, mumps and rubella (MMR) compared with controls. DESIGN: Case-control study, community based. METHODS: A community sample of vaccinated children aged 10-12 years in the UK with ASD (n = 98) and two control groups of similar age, one with special educational needs but no ASD (n = 52) and one typically developing group (n = 90), were tested for measles virus and antibody response to measles in the serum. RESULTS: No difference was found between cases and controls for measles antibody response. There was no dose-response relationship between autism symptoms and antibody concentrations. Measles virus nucleic acid was amplified by reverse transcriptase-PCR in peripheral blood mononuclear cells from one patient with autism and two typically developing children. There was no evidence of a differential response to measles virus or the measles component of the MMR in children with ASD, with or without regression, and controls who had either one or two doses of MMR. Only one child from the control group had clinical symptoms of possible enterocolitis. CONCLUSION: No association between measles vaccination and ASD was shown
Crisis Decision-Making During Hurricane Sandy: An Analysis of Established and Emergent Disaster Response Behaviors in the New York Metro Area
Objective This collective case study examined how and why specific organizational decision-making processes transpired at 2 large suburban county health departments in lower New York State during their response to Hurricane Sandy in 2012. The study also examined the relationships that the agencies developed with other emerging and established organizations within their respective health systems.
Methods In investigating these themes, the authors conducted in-depth, one-on-one interviews with 30 senior-level public health staff and first responders; reviewed documentation; and moderated 2 focus group discussions with 17 participants.
Results Although a natural hazard such as a hurricane was not an unexpected event for these health departments, they nevertheless confronted a number of unforeseen challenges during the response phase: prolonged loss of power and fuel, limited situational awareness of the depth and breadth of the storm’s impact among disaster-exposed populations, and coordination problems with a number of organizations that emerged in response to the disaster.
Conclusions Public health staff had few plans or protocols to guide them and often found themselves improvising and problem-solving with new organizations in the context of an overburdened health care system
Polygenic risk for Alzheimer's disease shapes hippocampal scene-selectivity
Preclinical models of Alzheimer’s disease (AD) suggest APOE modulates brain function in structures vulnerable to AD pathophysiology. However, genome-wide association studies now demonstrate that AD risk is shaped by a broader polygenic architecture, estimated via polygenic risk scoring (AD-PRS). Despite this breakthrough, the effect of AD-PRS on brain function in young individuals remains unknown. In a large sample (N = 608) of young, asymptomatic individuals, we measure the impact of both (i) APOE and (ii) AD-PRS on a vulnerable cortico-limbic scene-processing network heavily implicated in AD pathophysiology. Integrity of this network, which includes the hippocampus (HC), is fundamental for maintaining cognitive function during ageing. We show that AD-PRS, not APOE, selectively influences activity within the HC in response to scenes, while other perceptual nodes remained intact. This work highlights the impact of polygenic contributions to brain function beyond APOE, which could aid potential therapeutic/interventional strategies in the detection and prevention of AD
Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics 1.0: A General Circulation Model for Simulating the Climates of Rocky Planets
Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments
with Dynamics (ROCKE-3D) is a 3-Dimensional General Circulation Model (GCM)
developed at the NASA Goddard Institute for Space Studies for the modeling of
atmospheres of Solar System and exoplanetary terrestrial planets. Its parent
model, known as ModelE2 (Schmidt et al. 2014), is used to simulate modern and
21st Century Earth and near-term paleo-Earth climates. ROCKE-3D is an ongoing
effort to expand the capabilities of ModelE2 to handle a broader range of
atmospheric conditions including higher and lower atmospheric pressures, more
diverse chemistries and compositions, larger and smaller planet radii and
gravity, different rotation rates (slowly rotating to more rapidly rotating
than modern Earth, including synchronous rotation), diverse ocean and land
distributions and topographies, and potential basic biosphere functions. The
first aim of ROCKE-3D is to model planetary atmospheres on terrestrial worlds
within the Solar System such as paleo-Earth, modern and paleo-Mars,
paleo-Venus, and Saturn's moon Titan. By validating the model for a broad range
of temperatures, pressures, and atmospheric constituents we can then expand its
capabilities further to those exoplanetary rocky worlds that have been
discovered in the past and those to be discovered in the future. We discuss the
current and near-future capabilities of ROCKE-3D as a community model for
studying planetary and exoplanetary atmospheres.Comment: Revisions since previous draft. Now submitted to Astrophysical
Journal Supplement Serie
The properties of the inner disk around HL Tau: Multi-wavelength modeling of the dust emission
We conducted a detailed radiative transfer modeling of the dust emission from
the circumstellar disk around HL Tau. The goal of our study is to derive the
surface density profile of the inner disk and its structure. In addition to the
Atacama Large Millimeter/submillimeter Array images at Band 3 (2.9mm), Band 6
(1.3mm), and Band 7 (0.87mm), the most recent Karl G. Jansky Very Large Array
(VLA) observations at 7mm were included in the analysis. A simulated annealing
algorithm was invoked to search for the optimum model. The radiative transfer
analysis demonstrates that most radial components (i.e., >6AU) of the disk
become optically thin at a wavelength of 7mm, which allows us to constrain, for
the first time, the dust density distribution in the inner region of the disk.
We found that a homogeneous grain size distribution is not sufficient to
explain the observed images at different wavelengths simultaneously, while
models with a shallower grain size distribution in the inner disk work well. We
found clear evidence that larger grains are trapped in the first bright ring.
Our results imply that dust evolution has already taken place in the disk at a
relatively young (i.e., ~1Myr) age. We compared the midplane temperature
distribution, optical depth, and properties of various dust rings with those
reported previously. Using the Toomre parameter, we briefly discussed the
gravitational instability as a potential mechanism for the origin of the dust
clump detected in the first bright ring via the VLA observations.Comment: Accepted for publication in A&A (10 pages
High-Resolution Observations in B1-IRS: ammonia, CCS and water masers
We present a study of the structure and dynamics of the star forming region
B1-IRS (IRAS 03301+3057) using the properties of different molecules at high
angular resolution (~4''). We have used VLA observations of NH3, CCS, and H2O
masers at 1 cm. CCS emission shows three clumps around the central source, with
a velocity gradient from red to blueshifted velocities towards the protostar,
probably due to the interaction with outflowing material. Water maser emission
is elongated in the same direction as a reflection nebula detected at 2micron
by 2MASS, with the maser spots located in a structure of some hundreds of AU
from the central source, possibly tracing a jet. We propose a new outflow model
to explain all our observations, consisting of a molecular outflow near the
plane of the sky. Ammonia emission is extended and anticorrelated with CCS. We
have detected for the first time this anticorrelation at small scales (1400 AU)
in a star forming region.Comment: 6 pages, 3 figures. To appear in the Proceedings of the 2004 European
Workshop: "Dense Molecular Gas around Protostars and in Galactic Nuclei",
Eds. Y.Hagiwara, W.A.Baan, H.J.van Langevelde, 2004, a special issue of ApSS,
Kluwe
The Ursinus Weekly, April 17, 1908
Baseball • The Dean\u27s column • The young ladies entertain • Benefit social • Schaff prize debate • Literary societies • Second team game • College world • Personals • Literary Supplement: St. Valentine at Olevia; An adventure; Eugene Field; The present financial crisis; Railway rate regulation; James Russel Lowellhttps://digitalcommons.ursinus.edu/weekly/2904/thumbnail.jp
The Radial Distribution of Dust Particles in the HL Tau Disk from ALMA and VLA Observations
Understanding planet formation requires one to discern how dust grows in protoplanetary disks. An important parameter to measure in disks is the maximum dust grain size present. This is usually estimated through measurements of the dust opacity at different millimeter wavelengths assuming optically thin emission and dust opacity dominated by absorption. However, Atacama Large Millimeter/submillimeter Array (ALMA) observations have shown that these assumptions might not be correct in the case of protoplanetary disks, leading to overestimation of particle sizes and to underestimation of the disk\u27s mass. Here, we present an analysis of high-quality ALMA and Very Large Array images of the HL Tau protoplanetary disk, covering a wide range of wavelengths, from 0.8 mm to 1 cm, and with a physical resolution of ~7.35 au. We describe a procedure to analyze a set of millimeter images without any assumption about the optical depth of the emission, and including the effects of absorption and scattering in the dust opacity. This procedure allows us to obtain the dust temperature, the dust surface density, and the maximum particle size at each radius. In the HL Tau disk, we found that particles have already grown to a few millimeters in size. We detect differences in the dust properties between dark and bright rings, with dark rings containing low dust density and small dust particles. Different features in the HL Tau disk seem to have different origins. Planet–disk interactions can explain substructure in the external half of the disk, but the internal rings seem to be associated with the presence of snow lines of several molecules
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