301 research outputs found
Dual time scales in simulated annealing of a two-dimensional Ising spin glass
We apply a generalized Kibble-Zurek out-of-equilibrium scaling ansatz to
simulated annealing when approaching the spin-glass transition at temperature
of the two-dimensional Ising model with random couplings.
Analyzing the spin-glass order parameter and the excess energy as functions of
the system size and the annealing velocity in Monte Carlo simulations with
Metropolis dynamics, we find scaling where the energy relaxes slower than the
spin-glass order parameter, i.e., there are two different dynamic exponents.
The values of the exponents relating the relaxation time scales to the system
length, , are for the relaxation of the order
parameter and for the energy relaxation. We argue that the
behavior with dual time scales arises as a consequence of the entropy-driven
ordering mechanism within droplet theory. We point out that the dynamic
exponents found here for simulated annealing are different from the
temperature-dependent equilibrium dynamic exponent , for which
previous studies have found a divergent behavior; . Thus, our study shows that, within Metropolis dynamics, it is easier
to relax the system to one of its degenerate ground states than to migrate at
low temperatures between regions of the configuration space surrounding
different ground states. In a more general context of optimization, our study
provides an example of robust dense-region solutions for which the excess
energy (the conventional cost function) may not be the best measure of success.Comment: 13 pages, 16 figure
Dynamic scaling in the 2D Ising spin glass with Gaussian couplings
We carry out simulated annealing and employ a generalized Kibble-Zurek
scaling hypothesis to study the 2D Ising spin glass with normal-distributed
couplings. The system has an equilibrium glass transition at temperature .
From a scaling analysis when at different annealing
velocities, we extract the dynamic critical exponent , i.e., the exponent
relating the relaxation time to the system length ; .
We find for both the Edwards-Anderson spin-glass order
parameter and the excess energy. This is different from a previous study of the
system with bimodal couplings [S. J. Rubin, N. Xu, and A. W. Sandvik, Phys.
Rev. E {\bf 95}, 052133 (2017)] where the dynamics is faster and the above two
quantities relax with different exponents (and that of the energy is larger).
We here argue that the different behaviors arise as a consequence of the
different low-energy landscapes---for normal-distributed couplings the ground
state is unique (up to a spin reflection) while the system with bimodal
couplings is massively degenerate. Our results reinforce the conclusion of
anomalous entropy-driven relaxation behavior in the bimodal Ising glass. In the
case of a continuous coupling distribution, our results presented here indicate
that, although Kibble-Zurek scaling holds, the perturbative behavior normally
applying in the slow limit breaks down, likely due to quasi-degenerate states,
and the scaling function takes a different form.Comment: 10 pages, 5 figure
Transverse momentum versus multiplicity fluctuations in high-energy nuclear collisions
We discuss recently measured event-by-event fluctuations of transverse
momentum and of multiplicity in relativistic heavy-ion collisions. It is shown
that the non-monotonic behavior of the p_T-fluctuations as a function of
collision centrality can be fully explained by the observed non-monotonic
multiplicity fluctuations. A possible mechanism responsible for the
multiplicity fluctuations is also considered.Comment: 5 pages, 3 figures, revised & extended, to appear in Phys. Rev.
Motor Axon Synapses on Renshaw Cells Contain Higher Levels of Aspartate than Glutamate
Motoneuron synapses on spinal cord interneurons known as Renshaw cells activate nicotinic, AMPA and NMDA receptors consistent with co-release of acetylcholine and excitatory amino acids (EAA). However, whether these synapses express vesicular glutamate transporters (VGLUTs) capable of accumulating glutamate into synaptic vesicles is controversial. An alternative possibility is that these synapses release other EAAs, like aspartate, not dependent on VGLUTs. To clarify the exact EAA concentrated at motor axon synapses we performed a quantitative postembedding colloidal gold immunoelectron analysis for aspartate and glutamate on motor axon synapses (identified by immunoreactivity to the vesicular acetylcholine transporter; VAChT) contacting calbindin-immunoreactive (-IR) Renshaw cell dendrites. The results show that 71% to 80% of motor axon synaptic boutons on Renshaw cells contained aspartate immunolabeling two standard deviations above average neuropil labeling. Moreover, VAChT-IR synapses on Renshaw cells contained, on average, aspartate immunolabeling at 2.5 to 2.8 times above the average neuropil level. In contrast, glutamate enrichment was lower; 21% to 44% of VAChT-IR synapses showed glutamate-IR two standard deviations above average neuropil labeling and average glutamate immunogold density was 1.7 to 2.0 times the neuropil level. The results were not influenced by antibody affinities because glutamate antibodies detected glutamate-enriched brain homogenates more efficiently than aspartate antibodies detecting aspartate-enriched brain homogenates. Furthermore, synaptic boutons with ultrastructural features of Type I excitatory synapses were always labeled by glutamate antibodies at higher density than motor axon synapses. We conclude that motor axon synapses co-express aspartate and glutamate, but aspartate is concentrated at higher levels than glutamate
No gender-related bias in COPD diagnosis and treatment in Sweden: a randomised, controlled, case-based trial.
Introduction:COPD is a major cause of morbidity and mortality. The prevalence, morbidity and mortality of COPD among females have increased. Previous studies indicate a possible gender bias in the diagnosis and management of COPD. The present study aims to determine if there is gender bias in the management of COPD in Sweden.Methods:This was a double-blind, randomised (1:1), controlled, parallel-group, web-based trial using the hypothetical case scenario of a former smoker (40 pack-years and quit smoking 3 years ago) who was male or female. The participants were blind to the randomisation and the purpose of the trial. The case progressively revealed more information with associated questions on how the physician would manage the patient. Study participants chose from a list of tests and treatments at each step of the case scenario.Results:In total, 134 physicians were randomised to a male (n=62) or a female (n=72) case. There was no difference in initial diagnosis (61 (98%) male cases and 70 (97%) female cases diagnosed with COPD) and planned diagnostic procedures between the male and female cases. Spirometry was chosen by all the physicians as one of the requested diagnostic tests. The management of the hypothetical COPD case did not differ by sex of the responding physician.Conclusion:In Sweden, diagnosis and management of a hypothetical patient with COPD did not differ by the gender of the patient or physician
Validation of the Symptom Pattern Method for Analyzing Verbal Autopsy Data
Chris Murray and colleagues propose and, using data from China, validate a new strategy for analyzing verbal autopsy data that combines the advantages of previous methods
Relativistic Klein-Gordon charge effects by information-theoretic measures
The charge spreading of ground and excited states of Klein-Gordon particles
moving in a Coulomb potential is quantitatively analyzed by means of the
ordinary moments and the Heisenberg measure as well as by use of the most
relevant information-theoretic measures of global (Shannon entropic power) and
local (Fisher's information) types. The dependence of these complementary
quantities on the nuclear charge Z and the quantum numbers characterizing the
physical states is carefully discussed. The comparison of the relativistic
Klein-Gordon and non-relativistic Schrodinger values is made. The
non-relativistic limits at large principal quantum number n and for small
values of Z are also reached.Comment: Accepted in New Journal of Physic
Irreversible Performance of a Quantum Harmonic Heat Engine
The unavoidable irreversible losses of power in a heat engine are found to be
of quantum origin. Following thermodynamic tradition a model quantum heat
engine operating by the Otto cycle is analyzed. The working medium of the model
is composed of an ensemble of harmonic oscillators. A link is established
between the quantum observables and thermodynamical variables based on the
concept of canonical invariance. These quantum variables are sufficient to
determine the state of the system and with it all thermodynamical variables.
Conditions for optimal work, power and entropy production show that maximum
power is a compromise between the quasistatic limit of adiabatic following on
the compression and expansion branches and a sudden limit of very short time
allocation to these branches. At high temperatures and quasistatic operating
conditions the efficiency at maximum power coincides with the endoreversible
result. The optimal compression ratio varies from the square root of the
temperature ratio in the quasistatic limit where their reversibility is
dominated by heat conductance to the temperature ratio to the power of 1/4 in
the sudden limit when the irreversibility is dominated by friction. When the
engine deviates from adiabatic conditions the performance is subject to
friction. The origin of this friction can be traced to the noncommutability of
the kinetic and potential energy of the working medium.Comment: 25 pages, 7 figures. Revision added explicit heat-transfer expression
and extended the discussion on the quantum origin of frictio
Rotation Curve Fitting Model
One key piece of evidence for dark matter is the flat rotation curve problem:
the disagreement between measured galactic rotation curves and their luminous
mass. A novel solution to this problem is presented here. A model of
relativistic frame effects on Doppler shifts due to the slightly curved frames
of an emitting galaxy and the Milky Way is derived. This model predicts
observed Doppler shifted spectra (in excess of the luminous mass) based only on
the observed luminous matter profile and one free model parameter. Fits to the
175 galaxies reported in the SPARC database of galactic rotation profiles and
accurate photometry measurements are compared between this novel model and dark
matter and MOND (RAR) models. We find on the SPARC sample of 175 galaxies; that
MOND-RAR has an average reduced chisquare of for 175 galaxies
fitted, the isothermal dark matter model has for 165 galaxies
fitted, and the new model we present has for 172 galaxies
fitted. Implications of this model are discussed.Comment: 27 pages, 9 figure
- …