2,034 research outputs found
Hysteresis, Avalanches, and Noise: Numerical Methods
In studying the avalanches and noise in a model of hysteresis loops we have
developed two relatively straightforward algorithms which have allowed us to
study large systems efficiently. Our model is the random-field Ising model at
zero temperature, with deterministic albeit random dynamics. The first
algorithm, implemented using sorted lists, scales in computer time as O(N log
N), and asymptotically uses N (sizeof(double)+ sizeof(int)) bits of memory. The
second algorithm, which never generates the random fields, scales in time as
O(N \log N) and asymptotically needs storage of only one bit per spin, about 96
times less memory than the first algorithm. We present results for system sizes
of up to a billion spins, which can be run on a workstation with 128MB of RAM
in a few hours. We also show that important physical questions were resolved
only with the largest of these simulations
Physical Structure and Nature of Supernova Remnants in M101
Supernova remnant (SNR) candidates in the giant spiral galaxy M101 have been
previously identified from ground-based H-alpha and [SII] images. We have used
archival Hubble Space Telescope (HST) H-alpha and broad-band images as well as
stellar photometry of 55 SNR candidates to examine their physical structure,
interstellar environment, and underlying stellar population. We have also
obtained high-dispersion echelle spectra to search for shocked high-velocity
gas in 18 SNR candidates, and identified X-ray counterparts to SNR candidates
using data from archival observations made by the Chandra X-ray Observatory.
Twenty-one of these 55 SNR candidates studied have X-ray counterparts, although
one of them is a known ultra-luminous X-ray source. The multi-wavelength
information has been used to assess the nature of each SNR candidate. We find
that within this limited sample, ~16% are likely remnants of Type Ia SNe and
~45% are remnants of core-collapse SNe. In addition, about ~36% are large
candidates which we suggest are either superbubbles or OB/HII complexes.
Existing radio observations are not sensitive enough to detect the non-thermal
emission from these SNR candidates. Several radio sources are coincident with
X-ray sources, but they are associated with either giant HII regions in M101 or
background galaxies. The archival HST H-alpha images do not cover the entire
galaxy and thus prevents a complete study of M101. Furthermore, the lack of HST
[SII] images precludes searches for small SNR candidates which could not be
identified by ground-based observations. Such high-resolution images are needed
in order to obtain a complete census of SNRs in M101 for a comprehensive
investigation of the distribution, population, and rates of SNe in this galaxy.Comment: 37 pages, 4 Tables, 7 Figures, accepted for publication in the
Astronomical Journa
Cost-Effectiveness of Interferon Beta-1a, Interferon Beta-1b, and Glatiramer Acetate in Newly Diagnosed Non-primary Progressive Multiple Sclerosis
AbstractObjectiveTo perform a cost-effectiveness analysis of three immunomodulatory treatments for newly diagnosed nonprimary progressive MS: interferon beta-1a, interferon beta-1b, and glatiramer acetate.MethodsWe developed a state-transition model to estimate the health effects and costs associated with interferon beta-1a, interferon beta-1b, glatiramer acetate, and no treatment for hypothetical cohorts of men and women with non-primary progressive MS. We used the Expanded Disability Status Scale as the measure of disability and included both relapses and disease progression in the model. We evaluated treatment strategies assuming a 10-year treatment duration using the societal perspective. We elicited preferences for disability and treatment states using standard-gamble questions and modeled the disutility associated with treatment administration and side effects explicitly. Main outcome measures were net gains in quality-adjusted life expectancy and incremental cost-effectiveness ratios in dollars per quality-adjusted life year (QALY) gained.ResultsFor treatment duration of 10 years for newly diagnosed non-primary progressive MS, interferon beta-1a yielded the largest gain in quality-adjusted life expectancy with an incremental cost-effectiveness ratio of 1,800,000/QALY for men, compared with no treatment. For a 5-year treatment duration, a âno treatmentâ strategy yielded more quality-adjusted life years than any of the treatment strategies. Cost-effectiveness ratios were similar for all three immunomodulatory treatments evaluated.ConclusionsCost-effectiveness results for all three immunomodulatory treatments for MS were unfavorable in the simulated study population under a wide range of assumptions. For treatment duration less than or equal to 5 years, expected benefits of treatment may not outweigh disutility associated with side effects and treatment discomfort
Universal Pulse Shape Scaling Function and Exponents: A Critical Test for Avalanche Models applied to Barkhausen Noise
In order to test if the universal aspects of Barkhausen noise in magnetic
materials can be predicted from recent variants of the non-equilibrium zero
temperature Random Field Ising Model (RFIM), we perform a quantitative study of
the universal scaling function derived from the
Barkhausen pulse shape in simulations and experiment. Through data collapses
and scaling relations we determine the critical exponents and
in both simulation and experiment. Although we find agreement
in the critical exponents, we find differences between theoretical and
experimental pulse shape scaling functions as well as between different
experiments.Comment: 19 pages (in preprint format), 5 figures, 1 tabl
Driving Rate Effects on Crackling Noise
Many systems respond to slowly changing external conditions with crackling
noise, created by avalanches or pulses of a broad range of sizes. Examples
range from Barkhausen Noise in magnets to earthquakes. Here we discuss how the
scaling behavior of the avalanche size and duration distribution and the power
spectra of this noise depend on the rate at which the external conditionsare
changed. We derive an exponent inequality as a criteria for the relevance of
adding a small driving rate to the adiabatic model. We use the zero temperature
nonequilibrium random field Ising model to test our results, which are expected
to be applicable to a large class of systems with crackling noise. They also
agree with recent experiments on Barkhausen noise in various materials.Comment: 4 pages, 2 figures, REVTe
Destabilizing effects of visual environment motions simulating eye movements or head movements
In the present paper, we explore effects on the human of exposure to a visual virtual environment which has been enslaved to simulate the human user's head movements or eye movements. Specifically, we have studied the capacity of our experimental subjects to maintain stable spatial orientation in the context of moving their entire visible surroundings by using the parameters of the subjects' natural movements. Our index of the subjects' spatial orientation was the extent of involuntary sways of the body while attempting to stand still, as measured by translations and rotations of the head. We also observed, informally, their symptoms of motion sickness
Discovery of an eclipsing X-ray binary with a 32.69 hour period in M101: an analog of Her X-1 or LMC X-4?
We report the discovery of an eclipsing X-ray binary in M101, the first such
system to be discovered outside the Local Group. Based on a sequence of 25
Chandra observations that sample a wide range of orbital phases, we find a
period of 32.688 0.002 hours, which we interpret as an orbital period.
The folded light curve exhibits an eclipse lasting about 8 hours, suggesting a
compact orbit in an nearly edge-on configuration. The X-ray binary has an
average luminosity of erg/sec,
with only one out of the 25 observations significantly lower in flux than the
average light curve.The presence of the eclipse and the 1.4-day orbital
period suggests that this source is an analog of the well studied eclipsing
X-ray binary pulsars Her X-1 or LMC X-4. Combining the Chandra data and the HST
ACS/WFC images, we have identified several possible optical counterparts,
including an O5-O3 star with V = 25.0. Follow-up optical monitoring
observations should be able to identify the donor and further constrain the
orbital properties.Comment: 24 pages, 9 figures, 2 tables, ApJ in pres
Disrupting the Ethical Imperatives of âJuniorâ Critical Qualitative Scholars in the Era of Conservative Modernization
In this article, we wrestle with the core issue of how early career researchers translate central tenets and core concepts of critical theory and critical methodology into their research practice. By way of creative representation, we draw from bell hooks and Cornel Westâs (1991) written rendition of their verbal dialogue in Breaking Bread: Insurgent Black Intellectual Life. Their hope was to offer the book in a dialogic format in such a way that mirrored the synergy in their verbal discussions as friends and intellectual colleagues. In a similar vein, we hope to share with readers the synergy and depth of the narratives that have transpired during our ongoing discussions on the important topic of critical praxis as part of a collaborative research group called the Disruptive Dialogue Project (Gildersleeve, Kuntz, Pasque & Carducci, 2010; Kuntz, Pasque, Carducci, & Gildersleeve, 2009).Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
A statistical mechanical description of metastable states and hysteresis in the 3D soft-spin random-field model at T=0
We present a formalism for computing the complexity of metastable states and
the zero-temperature magnetic hysteresis loop in the soft-spin random-field
model in finite dimensions. The complexity is obtained as the Legendre
transform of the free-energy associated to a certain action in replica space
and the hysteresis loop above the critical disorder is defined as the curve in
the field-magnetization plane where the complexity vanishes; the nonequilibrium
magnetization is therefore obtained without having to follow the dynamical
evolution. We use approximations borrowed from condensed-matter theory and
based on assumptions on the structure of the direct correlation functions (or
proper vertices), such as a local approximation for the self-energies, to
calculate the hysteresis loop in three dimensions, the correlation functions
along the loop, and the second moment of the avalanche-size distribution.Comment: 28 pages, 12 figure
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Modulating Myeloid Immune Cell Migration Using Multivalently Presented Monosaccharide Ligands for Advanced Immunotherapy
Due to their importance for the outcome of the inflammatory response, the motile myeloid cells are a focus of novel treatment options. The interplay of selectins and their ligands with leukocytes and endothelial cells, which mediate endothelial attachment and transmigration of immune cells, can be modulated by selectinâbinding structures. Here, a library of selectinâtargeting ligands coupled to either gold, silver, iron oxide nanospheres, or quantum dots of 5â10Â nm in size is used to systematically study their impact on immune cell motility. The multivalent presentation of the carbohydrate mimetics results in very low subânanomolar binding to L âselectin. Using human primary monocytes, granulocytes, lymphocytes, and macrophages, it is shown that the ligands exhibit only minor effects on uptake, whereas the motility of leukocytes is critically affected as observed in migration assays evaluated by flow cytometry. The carbohydrate mimetic ring structure, sulfation, in particular, and the degree of ligand presentation, are constituents which cohere in this process. Specific carbohydrate ligands can thus selectively regulate leukocyte subsets. These data form the basis for advanced immunotherapy which inhibits the amplification of inflammation by restricting leukocyte influx to injured tissue sites. Furthermore, the targeting ligands may complement existing treatment options for inflammatory diseases
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