2,441 research outputs found
Measuring kinetic energy changes in the mesoscale with low acquisition rates
We describe a new technique to estimate the mean square velocity of a
Brownian particle from time series of the position of the particle sampled at
frequencies several orders of magnitude smaller than the momentum relaxation
frequency. We apply our technique to determine the mean square velocity of
single optically trapped polystyrene microspheres immersed in water. The
velocity is increased applying a noisy electric field that mimics a higher
kinetic temperature. Therefore, we are able to measure the average kinetic
energy change in isothermal and non-isothermal quasistatic processes. Moreover,
we show that the dependence of the mean square time-averaged velocity on the
sampling frequency can be used to quantify properties of the electrophoretic
mobility of a charged colloid. Our method could be applied to detect
temperature gradients in inhomogeneous media and to characterize the complete
thermodynamics of microscopic heat engines.Comment: 9 pages, 5 figure
Spin-wave amplification and lasing driven by inhomogeneous spin transfer torques
We show that an inhomogeneity in the spin-transfer torques in a metallic
ferromagnet under suitable conditions strongly amplifies incoming spin waves.
Moreover, at nonzero temperatures the incoming thermally occupied spin waves
will be amplified such that the region with inhomogeneous spin transfer torques
emits spin waves spontaneously, thus constituting a spin-wave laser. We
determine the spin-wave scattering amplitudes for a simplified model and
set-up, and show under which conditions the amplification and lasing occurs.
Our results are interpreted in terms of a so-called black-hole laser, and could
facilitate the field of magnonics, that aims to utilize spin waves in logic and
data-processing devices.Comment: 5 pages, 4 figure
Sex and Age-Related Differences in Neuroticism and Allostatic Load Index in Urban Patients with General Anxiety Disorder Treated with Alprazolam
Introduction: Allostatic Load (AL) index proposes indicators for the functioningof the main potentially stress-affected systems. Sex differences instress response and stress-related diseases susceptibility have been describedfor the general population. In this observational study we describe the effectsof sex and age on allostatic load variables, in a cohort of patients with generalanxiety disorders and neuroticism treated with alprazolam during 12 weeks,before and after treatment. Methods: Patients with general (DSM IV) anxietydisorders with >6 in Hamilton scale, Allostatic load (>1 Crimmins and SeemanAL modified criteria) and neuroticism >18 (NEO-FFI inventory), wereincluded. All patients completed psychiatric assessment, allostatic load indexdetermination before (−1 week) and after 12 weeks of treatment with alprazolam(0.25 - 1 mg/t.i.d). Allostatic load parameters comprised cardiovascular,metabolic and inflammatory variables. Univariate analysis (two-wayANOVA), Student?s t-test (related variables) and Pearson correlations weredetermined. Results: Fifty-four patients, 35 females (48.6 ± 11.7 years) and 19males (44.2 ± 12.8 years) with general anxiety disorder were included; 28 patientswith <50 years (60.7% females), and 26 with ≥50 years (69.2% females).Younger patients (<50 years) (two-way ANOVA, p = 0.02) were significantlyassociated with lower allostatic load index after treatment. However, womenshowed higher anxiety levels in both, before (Two-way ANOVA, p = 0.059)and after treatment (two-way ANOVA, p = 0.005), with a significantly betterprofile than men in many individual AL variables, particularly cardiovascular(systolic blood pressure), obesity (body mass index), and lipids (higher HDLlevels). After treatment a higher reduction of fibrinogen levels was found inmen (two-way ANOVA, p = 0.02). Conclusions: In this preliminary analysiswe described sex and age differences in psychiatry aspects and allostatic loadindexes in patients with general anxiety disorders in the short-term treatmentwith alprazolam. These considerations remark the need of pondering sex andage differences during the use of drugs for protracted periods.Fil: D`Alessio, Luciana. Universidad Nacional Arturo Jauretche. Unidad Ejecutora de Estudios en Neurociencias y Sistemas Complejos. Provincia de Buenos Aires. Ministerio de Salud. Hospital Alta Complejidad en Red El Cruce Dr. Néstor Carlos Kirchner Samic. Unidad Ejecutora de Estudios en Neurociencias y Sistemas Complejos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Unidad Ejecutora de Estudios en Neurociencias y Sistemas Complejos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Soria, Carlos A.. Henri Laborit Institute Of Biosciences; ArgentinaFil: Remedi, Carolina. Henri Laborit Institute Of Biosciences; Argentina; ArgentinaFil: Roldán, Emilio J. A.. Instituto de Neurobiología IDNEU; Argentin
Arcsine Laws in Stochastic Thermodynamics
We show that the fraction of time a thermodynamic current spends above its
average value follows the arcsine law, a prominent result obtained by L\'evy
for Brownian motion. Stochastic currents with long streaks above or below their
average are much more likely than those that spend similar fractions of time
above and below their average. Our result is confirmed with experimental data
from a Brownian Carnot engine. We also conjecture that two other random times
associated with currents obey the arcsine law: the time a current reaches its
maximum value and the last time a current crosses its average value. These
results apply to, inter alia, molecular motors, quantum dots and colloidal
systems.Comment: 11 pages, 11 figure
Adiabatic processes realized with a trapped Brownian particle
We experimentally realize quasistatic adiabatic processes using a single
optically-trapped micro- sphere immersed in water whose effective temperature
is controlled by an external random electric field. A full energetic
characterization of adiabatic processes that preserve either the position dis-
tribution or the full phase space volume is presented. We show that only in the
latter case the exchanged heat and the change in the entropy of the particle
vanish when averaging over many repetitions. We provide analytical expressions
for the distributions of the fluctuating heat and en- tropy, which we verify
experimentally. We show that the heat distribution is asymmetric for any
non-isothermal quasistatic process. Moreover, the shape of the distribution of
the system entropy change in the adiabatic processes depends significantly on
the number of degrees of freedom that are considered for the calculation of
system entropy
- …