8,114 research outputs found
Boolean networks with robust and reliable trajectories
We construct and investigate Boolean networks that follow a given reliable
trajectory in state space, which is insensitive to fluctuations in the updating
schedule, and which is also robust against noise. Robustness is quantified as
the probability that the dynamics return to the reliable trajectory after a
perturbation of the state of a single node. In order to achieve high
robustness, we navigate through the space of possible update functions by using
an evolutionary algorithm. We constrain the networks to having the minimum
number of connections required to obtain the reliable trajectory. Surprisingly,
we find that robustness always reaches values close to 100 percent during the
evolutionary optimization process. The set of update functions can be evolved
such that it differs only slightly from that of networks that were not
optimized with respect to robustness. The state space of the optimized networks
is dominated by the basin of attraction of the reliable trajectory.Comment: 12 pages, 9 figure
Absence of Conventional Spin-Glass Transition in the Ising Dipolar System LiHo_xY_{1-x}F_4
The magnetic properties of single crystals of LiHo_xY_{1-x}F_4 with x=16.5%
and x=4.5% were recorded down to 35 mK using a micro-SQUID magnetometer. While
this system is considered as the archetypal quantum spin glass, the detailed
analysis of our magnetization data indicates the absence of a phase transition,
not only in a transverse applied magnetic field, but also without field. A
zero-Kelvin phase transition is also unlikely, as the magnetization seems to
follow a non-critical exponential dependence on the temperature. Our analysis
thus unmasks the true, short-ranged nature of the magnetic properties of the
LiHo_xY_{1-x}F_4 system, validating recent theoretical investigations
suggesting the lack of phase transition in this system.Comment: 5 pages, 4 figure
Evaluation of the Effect of Induced Endotoxemia on ROTEM S® and Platelet Parameters in Beagle Dogs Anaesthetized with Sevoflurane
Endotoxemia is thought to induce severe changes in coagulation status. In this study, blood samples from six beagle dogs receiving 1 mg/kg E. coli lipopolysaccharide (LPS) intravenously were analyzed to describe the concurrent changes in platelet count, platelet function assessed with impedance thromboaggregometry, thromboelastometry and d-dimers during artificially induced endotoxemia and its therapy with fluids and vasopressors at five timepoints (baseline, after LPS and 30 mL/kg Ringer’s acetate, during noradrenaline ± dexmedetomidine infusion, after a second fluid bolus and a second time after vasopressors). Results were analyzed for changes over time with the Friedman test, and statistical significance was set at p < 0.05. We found decreased platelet count and function and changes in all platelet-associated rotational thromboelastometry (ROTEM) variables indicating hypocoagulability, as well as increases in d-dimers indicating fibrinolysis within one hour of intravenous administration of LPS, with partial recovery of values after treatment and over time. The fast changes in platelet count, platelet function and ROTEM variables reflect the large impact of endotoxemia on the coagulation system and support repeated evaluation during the progress of endotoxemic diseases. The partial recovery of the variables after initiation of fluid and vasopressor therapy may reflect the positive impact of the currently suggested therapeutic interventions during septic shock in dogs
Molecular Model for Prenucleation Water Clusters
A molecular model applicable to prenucleation water clusters is described. As an illustration the model is applied to water clusters having clathrate-like structures composed of five-menibered rings. This work was motivated by the apparent inadequacies of the corrected liquid drop model which (in addition to applying bulk properties to small clusters) predicts nucleation rates which may be as much as 1017 larger than experiment. We present the energy of formation at a temperature of 277°K for our molecular model for clusters ranging in size from 5 to 57 molecules. These results agree qualitatively with experiment and, we believe, provide a motivation for further development of the molecular approach
Molecular Model for Ice Clusters in a Supersaturated Vapor
A molecular model previously applied to prenucleation water clusters is used to examine ice Ih, embryos. The canonical partition function is evaluated for clusters having from 6 to 64 water molecules. The intermolecular vibrational free energies are extrapolated to clusters containing up to 120 molecules and free energies of formation, nucleation rates, and critical supersaturation ratios are calculated and compared with experiment. For the clusters studied, the ice Ih structure appears to be much less stable at all temperatures than the more spherical clathratelike cluster
What is the best way to diagnose polycystic ovarian syndrome?
Polycystic ovarian syndrome (PCOS) is diagnosed for women of childbearing age presenting with 2 of the following: 1)oligo- or anovulatory menstrual irregularities, 2) evidence of hyperandrogenism in the absence of secondary cause; 3) enlarged ovaries with multiple small follicular cysts on transvaginal ultrasound (strength of recommendation [SOR]: C, based on expert opinion). Depending on the clinical presentation, secondary causes should be excluded (SOR: C, expert opinion). While not among the diagnostic criteria, insulin resistance is common, and patients with PCOS should be evaluated for metabolic abnormalities, particularly hyperlipidemia and glucose intolerance or diabetes (SOR: B, based on prospective cohort studies)
Nuclear spin driven quantum relaxation in LiY_0.998Ho_0.002F_4
Staircase hysteresis loops of the magnetization of a LiY_0.998Ho_0.002F_4
single crystal are observed at subkelvin temperatures and low field sweep
rates. This behavior results from quantum dynamics at avoided level crossings
of the energy spectrum of single Ho^{3+} ions in the presence of hyperfine
interactions. Enhanced quantum relaxation in constant transverse fields allows
the study of the relative magnitude of tunnel splittings. At faster sweep
rates, non-equilibrated spin-phonon and spin-spin transitions, mediated by weak
dipolar interactions, lead to magnetization oscillations and additional steps.Comment: 5 pages, 5 eps figures, using RevTe
2-D Radiative Transfer in Protostellar Envelopes: II. An Evolutionary Sequence
We present model spectral energy distributions, colors, polarization, and
images for an evolutionary sequence of a low-mass protostar from the early
collapse stage (Class 0) to the remnant disk stage (Class III). We find a
substantial overlap in colors and SEDs between protostars embedded in envelopes
(Class 0-I) and T Tauri disks (Class II), especially at mid-IR wavelengths.
Edge-on Class I-II sources show double-peaked spectral energy distributions,
with a short-wavelength hump due to scattered light and the long-wavelength
hump due to thermal emission. These are the bluest sources in mid-IR
color-color diagrams.
Since Class 0 and I sources are diffuse, the size of the aperture over which
fluxes are integrated has a substantial effect on the computed colors, with
larger aperture results showing significantly bluer colors. This causes overlap
in color-color diagrams between all evolutionary states, especially in the
mid-IR. However the near-IR polarization of the Class 0 sources is much higher
than the Class I-II sources, providing a means to separate these evolutionary
states.
We varied the grain properties in the circumstellar envelope, allowing for
larger grains in the disk midplane and smaller in the envelope. We find that
grain growth in disks of Class I sources can be detected at wavelengths greater
than 100 m.
Our image calculations predict that the diffuse emission from edge-on Class I
and II sources should be detectable in the mid-IR with the Space Infrared
Telescope Facility (SIRTF) in nearby star forming regions (out to several
hundred parsecs).Comment: A version with high-resolution images is available at
http://www.astro.wisc.edu/glimpse/glimpsepubs.htm
Classification cards applied to team and individual learning.
Thesis (Ed.M.)--Boston Universit
Low-Temperature Quantum Relaxation in a System of Magnetic Nanomolecules
We argue that to explain recent resonant tunneling experiments on crystals of
Mn and Fe, particularly in the low-T limit, one must invoke dynamic
nuclear spin and dipolar interactions. We show the low-, short-time
relaxation will then have a form, where depends on the
nuclear , on the tunneling matrix element between the two
lowest levels, and on the initial distribution of internal fields in the
sample, which depends very strongly on sample shape. The results are directly
applicable to the system. We also give some results for the long-time
relaxation.Comment: 4 pages, 3 PostScript figures, LaTe
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