365 research outputs found
Optimal Occulter Design for Finding Extrasolar Planets
One proposed method for finding terrestrial planets around nearby stars is to
use two spacecraft--a telescope and a specially shaped occulter that is
specifically designed to prevent all but a tiny fraction of the starlight from
diffracting into the telescope. As the cost and observing cadence for such a
mission will be driven largely by the separation between the two spacecraft, it
is critically important to design an occulter that can meet the observing goals
while flying as close to the telescope as possible. In this paper, we explore
this tradeoff between separation and occulter diameter. More specifically, we
present a method for designing the shape of the outer edge of an occulter that
is as small as possible and gives a shadow that is deep enough and large enough
for a 4m telescope to survey the habitable zones of many stars for Earth-like
planets. In particular, we show that in order for a 4m telescope to detect in
broadband visible light a planet 0.06 arcseconds from a star shining
times brighter than the planet requires a specially-shaped occulter 50m in
diameter positioned about km in front of the telescope.Comment: 14 pages, 4 figures, 15 subfigure
The energy partitioning of non-thermal particles in a plasma: or the Coulomb logarithm revisited
The charged particle stopping power in a highly ionized and weakly to
moderately coupled plasma has been calculated to leading and next-to-leading
order by Brown, Preston, and Singleton (BPS). After reviewing the main ideas
behind this calculation, we use a Fokker-Planck equation derived by BPS to
compute the electron-ion energy partitioning of a charged particle traversing a
plasma. The motivation for this application is ignition for inertial
confinement fusion -- more energy delivered to the ions means a better chance
of ignition, and conversely. It is therefore important to calculate the
fractional energy loss to electrons and ions as accurately as possible, as this
could have implications for the Laser Megajoule (LMJ) facility in France and
the National Ignition Facility (NIF) in the United States. The traditional
method by which one calculates the electron-ion energy splitting of a charged
particle traversing a plasma involves integrating the stopping power dE/dx.
However, as the charged particle slows down and becomes thermalized into the
background plasma, this method of calculating the electron-ion energy splitting
breaks down. As a result, the method suffers a systematic error of order T/E0,
where T is the plasma temperature and E0 is the initial energy of the charged
particle. In the case of DT fusion, for example, this can lead to uncertainties
as high as 10% or so. The formalism presented here is designed to account for
the thermalization process, and in contrast, it provides results that are
near-exact.Comment: 10 pages, 3 figures, invited talk at the 35th European Physical
Society meeting on plasma physic
Law Students and Cell Phone Use: Results of a Six-School Survey
The sight of a law student using his or her cell phone now is so common that law professors do not give it a second thought. But what, exactly, is the student doing? Texting with friends? Shopping? Watching a movie? To try to find out, during the Fall 2019 semester we asked our six diverse law schools to take an online survey consisting of eighteen questions. To our knowledge, this is the first phone survey of law students.
This paper presents the results of the survey, exploring applications used (text, social media, email, etc.) and differences by audience (e.g., whether students used text or email with employers as opposed to friends)
Durability of Near-Complete Skin Clearance in Patients with Psoriasis Using Systemic Biologic Therapies: Real-World Evidence from the CorEvitas Psoriasis Registry
INTRODUCTION: Near-complete skin clearance has become a rapidly achievable treatment goal for patients with psoriasis receiving systemic biologic therapies. However, real-world evidence for durability of near-complete skin clearance and risk factors associated with loss of near-complete skin clearance is limited.
METHODS: This study described durability of near-complete skin clearance (≥ 90% improvement in Psoriasis Area and Severity Index from initiation; PASI90) and identified clinical factors or patient characteristics associated with loss of PASI90 among patients with psoriasis from the CorEvitas Psoriasis Registry (April 2015-August 2021). Included patients had PASI \u3e 5 at biologic initiation and achieved PASI90 at approximately 6 months from initiation (index). A Kaplan-Meier estimate described time to loss of treatment response over 24 months follow-up from index. Proportional hazards regression was used to identify independent predictors of loss of treatment response.
RESULTS: This study included 687 patient initiations (instances of patients initiating a biologic). Following achievement of PASI90, treatment response was maintained in more than half of patient initiations (54%). Treatment response was maintained at 6, 12, and 18 months from index in an estimated 73% (95% [confidence interval] CI 70-77%), 60% (95% CI 56-63%), and 50% (95% CI 47-54%) of patient initiations, respectively. Adjusted hazards regression suggested non-White race, full-time employment, greater body weight, concomitant psoriatic arthritis, prior use of biologics, and clinically meaningful skin symptoms were associated with loss of treatment response.
CONCLUSIONS: Among real-world patients with psoriasis who achieved PASI90 with biologic therapy, about one-quarter lost response at 6 months, and half lost response at 18 months. Prior use of a biologic therapy and clinically meaningful skin symptoms at index, including itch and skin pain, were associated with loss of treatment response. Therefore, dermatologists may consider focusing on patient-reported symptoms as part of any intervention designed to reduce the likelihood of loss of response to biologic therapies
Functional and Pharmacological Analysis of Cardiomyocytes Differentiated from Human Peripheral Blood Mononuclear-Derived Pluripotent Stem Cells
SummaryAdvances in induced pluripotent stem cell (iPSC) technology have set the stage for routine derivation of patient- and disease-specific human iPSC-cardiomyocyte (CM) models for preclinical drug screening and personalized medicine approaches. Peripheral blood mononuclear cells (PBMCs) are an advantageous source of somatic cells because they are easily obtained and readily amenable to transduction. Here, we report that the electrophysiological properties and pharmacological responses of PBMC-derived iPSC CM are generally similar to those of iPSC CM derived from other somatic cells, using patch-clamp, calcium transient, and multielectrode array (MEA) analyses. Distinct iPSC lines derived from a single patient display similar electrophysiological features and pharmacological responses. Finally, we demonstrate that human iPSC CMs undergo acute changes in calcium-handling properties and gene expression in response to rapid electrical stimulation, laying the foundation for an in-vitro-tachypacing model system for the study of human tachyarrhythmias
On the and as Bound States and Approximate Nambu-Goldstone Bosons
We reconsider the two different facets of and mesons as
bound states and approximate Nambu-Goldstone bosons. We address several topics,
including masses, mass splittings between and and between and
, meson wavefunctions, charge radii, and the wavefunction overlap.Comment: 15 pages, late
The Origin and Kinematics of Cold Gas in Galactic Winds: Insight from Numerical Simulations
We study the origin of Na I absorbing gas in ultraluminous infrared galaxies
motivated by the recent observations by Martin of extremely superthermal
linewidths in this cool gas. We model the effects of repeated supernova
explosions driving supershells in the central regions of molecular disks with
M_d=10^10 M_\sun, using cylindrically symmetric gas dynamical simulations run
with ZEUS-3D. The shocked swept-up shells quickly cool and fragment by
Rayleigh-Taylor instability as they accelerate out of the dense, stratified
disks. The numerical resolution of the cooling and compression at the shock
fronts determines the peak shell density, and so the speed of Rayleigh-Taylor
fragmentation. We identify cooled shells and shell fragments as Na I absorbing
gas and study its kinematics. We find that simulations with a numerical
resolution of \le 0.2 pc produce multiple Rayleigh-Taylor fragmented shells in
a given line of sight. We suggest that the observed wide Na I absorption lines,
= 320 \pm 120 km s^-1 are produced by these multiple fragmented shells
traveling at different velocities. We also suggest that some shell fragments
can be accelerated above the observed average terminal velocity of 750 km s^-1
by the same energy-driven wind with an instantaneous starburst of \sim 10^9
M_\sun. The bulk of mass is traveling with the observed average shell velocity
330 \pm 100 km s^-1. Our results show that an energy-driven bubble causing
Rayleigh-Taylor instabilities can explain the kinematics of cool gas seen in
the Na I observations without invoking additional physics relying primarily on
momentum conservation, such as entrainment of gas by Kelvin-Helmholtz
instabilities, ram pressure driving of cold clouds by a hot wind, or radiation
pressure acting on dust. (abridged)Comment: 65 pages, 22 figures, accepted by Astrophys. J. Changes during
refereeing focused on context and comparison to observation
Recommended from our members
Multidisciplinary Baseline Assessment of Homosexual Men with and without Human Immunodeficiency Virus Infection. I. Overview of Study Design
Although much is known about the virus believed by most experts to be the cause of the acquired immunodeficiency syndrome and about its pathogenic actions, major areas of ignorance remain. Among these are the reasons for the varying time between infection with human immunodeficiency virus and development of acquired imunodeficiency syndrome, the relationship between neurologic and medical aspects of the disease, the time course of neuropsychological findings, and the prevalence of psychiatric morbidity. We assessed 124 homosexual men who were positive for human immunodeficiency virus and 84 who were negative for the virus. In this article we describe the study design, method of recruitment, and medical and demographic characteristics of the cohort, which will be followed up for 5 years
Non-Equilibrium Statistical Physics of Currents in Queuing Networks
We consider a stable open queuing network as a steady non-equilibrium system
of interacting particles. The network is completely specified by its underlying
graphical structure, type of interaction at each node, and the Markovian
transition rates between nodes. For such systems, we ask the question ``What is
the most likely way for large currents to accumulate over time in a network
?'', where time is large compared to the system correlation time scale. We
identify two interesting regimes. In the first regime, in which the
accumulation of currents over time exceeds the expected value by a small to
moderate amount (moderate large deviation), we find that the large-deviation
distribution of currents is universal (independent of the interaction details),
and there is no long-time and averaged over time accumulation of particles
(condensation) at any nodes. In the second regime, in which the accumulation of
currents over time exceeds the expected value by a large amount (severe large
deviation), we find that the large-deviation current distribution is sensitive
to interaction details, and there is a long-time accumulation of particles
(condensation) at some nodes. The transition between the two regimes can be
described as a dynamical second order phase transition. We illustrate these
ideas using the simple, yet non-trivial, example of a single node with
feedback.Comment: 26 pages, 5 figure
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