3,017 research outputs found

### Fluctuation Theorem in Rachet System

Fluctuation Theorem(FT) has been studied as far from equilibrium theorem,
which relates the symmetry of entropy production. To investigate the
application of this theorem, especially to biological physics, we consider the
FT for tilted rachet system. Under, natural assumption, FT for steady state is
derived.Comment: 6 pages, 2 figure

### Experimental demonstration of violations of the second law of thermodynamics for small systems and short time scales

We experimentally demonstrate the fluctuation theorem, which predicts appreciable and measurable violations of the second law of thermodynamics for small systems over short time scales, by following the trajectory of a colloidal particle captured in an optical trap that is translated relative to surrounding water molecules. From each particle trajectory, we calculate the entropy production/consumption over the duration of the trajectory and determine the fraction of second law–defying trajectories. Our results show entropy consumption can occur over colloidal length and time scales

### Simultaneous X-ray and optical spectroscopy of the Oef supergiant lambda Cep

Probing the structures of stellar winds is of prime importance for the
understanding of massive stars. Based on their optical spectral morphology and
variability, the stars of the Oef class have been suggested to feature
large-scale structures in their wind. High-resolution X-ray spectroscopy and
time-series of X-ray observations of presumably-single O-type stars can help us
understand the physics of their stellar winds. We have collected XMM-Newton
observations and coordinated optical spectroscopy of the O6Ief star lambda Cep
to study its X-ray and optical variability and to analyse its high-resolution
X-ray spectrum. We investigate the line profile variability of the He II 4686
and H-alpha emission lines in our time series of optical spectra, including a
search for periodicities. We further discuss the variability of the broadband
X-ray flux and analyse the high-resolution spectrum of lambda Cep using
line-by-line fits as well as a code designed to fit the full high-resolution
X-ray spectrum consistently. During our observing campaign, the He II 4686 line
varies on a timescale of ~18 hours. On the contrary, the H-alpha line profile
displays a modulation on a timescale of 4.1 days which is likely the rotation
period of the star. The X-ray flux varies on time-scales of days and could in
fact be modulated by the same 4.1 days period as H-alpha, although both
variations are shifted in phase. The high-resolution X-ray spectrum reveals
broad and skewed emission lines as expected for the X-ray emission from a
distribution of wind-embedded shocks. Most of the X-ray emission arises within
less than 2R* above the photosphere.Comment: Accepted for publication in Astronomy & Astrophysic

### The grand canonical ABC model: a reflection asymmetric mean field Potts model

We investigate the phase diagram of a three-component system of particles on
a one-dimensional filled lattice, or equivalently of a one-dimensional
three-state Potts model, with reflection asymmetric mean field interactions.
The three types of particles are designated as $A$, $B$, and $C$. The system is
described by a grand canonical ensemble with temperature $T$ and chemical
potentials $T\lambda_A$, $T\lambda_B$, and $T\lambda_C$. We find that for
$\lambda_A=\lambda_B=\lambda_C$ the system undergoes a phase transition from a
uniform density to a continuum of phases at a critical temperature $\hat
T_c=(2\pi/\sqrt3)^{-1}$. For other values of the chemical potentials the system
has a unique equilibrium state. As is the case for the canonical ensemble for
this $ABC$ model, the grand canonical ensemble is the stationary measure
satisfying detailed balance for a natural dynamics. We note that $\hat
T_c=3T_c$, where $T_c$ is the critical temperature for a similar transition in
the canonical ensemble at fixed equal densities $r_A=r_B=r_C=1/3$.Comment: 24 pages, 3 figure

### Reaction-diffusion systems and nonlinear waves

The authors investigate the solution of a nonlinear reaction-diffusion
equation connected with nonlinear waves. The equation discussed is more general
than the one discussed recently by Manne, Hurd, and Kenkre (2000). The results
are presented in a compact and elegant form in terms of Mittag-Leffler
functions and generalized Mittag-Leffler functions, which are suitable for
numerical computation. The importance of the derived results lies in the fact
that numerous results on fractional reaction, fractional diffusion, anomalous
diffusion problems, and fractional telegraph equations scattered in the
literature can be derived, as special cases, of the results investigated in
this article.Comment: LaTeX, 16 pages, corrected typo

### Trajectories of depressive symptoms after a major cardiac event

Depression is a common comorbidity in cardiac patients. This study sought to document fluctuations of depressive symptoms in the 12 months after a first major cardiac event. In all, 310 patients completed a battery of psychosocial measures including the depression subscale of the Symptom Check List-90-Revised. A total of 252 of them also completed follow-up measures at 3 and 12 months. Trajectories of depressive symptoms were classified as none, worsening symptoms, sustained remission, and persistent symptoms. Although the prevalence of depressive symptoms was consistent at each assessment, there was considerable fluctuation between symptom classes. Regression analyses were performed to identify predictors of different trajectories.Oskar Mittag, Hanna Kampling, Erik Farin and Phillip J Tull

### Variational method and duality in the 2D square Potts model

The ferromagnetic q-state Potts model on a square lattice is analyzed, for
q>4, through an elaborate version of the operatorial variational method. In the
variational approach proposed in the paper, the duality relations are exactly
satisfied, involving at a more fundamental level, a duality relationship
between variational parameters. Besides some exact predictions, the approach is
very effective in the numerical estimates over the whole range of temperature
and can be systematically improved.Comment: 20 pages, 5 EPS figure

### Boundary and Bulk Phase Transitions in the Two Dimensional Q > 4 State Potts Model

The surface and bulk properties of the two-dimensional Q > 4 state Potts
model in the vicinity of the first order bulk transition point have been
studied by exact calculations and by density matrix renormalization group
techniques. For the surface transition the complete analytical solution of the
problem is presented in the $Q \to \infty$ limit, including the critical and
tricritical exponents, magnetization profiles and scaling functions. According
to the accurate numerical results the universality class of the surface
transition is independent of the value of Q > 4. For the bulk transition we
have numerically calculated the latent heat and the magnetization discontinuity
and we have shown that the correlation lengths in the ordered and in the
disordered phases are identical at the transition point.Comment: 11 pages, RevTeX, 6 PostScript figures included. Manuscript
substantially extended, details on the analytical and numerical calculations
added. To appear in Phys. Rev.

### Insights into the Second Law of Thermodynamics from Anisotropic Gas-Surface Interactions

Thermodynamic implications of anisotropic gas-surface interactions in a
closed molecular flow cavity are examined. Anisotropy at the microscopic scale,
such as might be caused by reduced-dimensionality surfaces, is shown to lead to
reversibility at the macroscopic scale. The possibility of a self-sustaining
nonequilibrium stationary state induced by surface anisotropy is demonstrated
that simultaneously satisfies flux balance, conservation of momentum, and
conservation of energy. Conversely, it is also shown that the second law of
thermodynamics prohibits anisotropic gas-surface interactions in "equilibrium",
even for reduced dimensionality surfaces. This is particularly startling
because reduced dimensionality surfaces are known to exhibit a plethora of
anisotropic properties. That gas-surface interactions would be excluded from
these anisotropic properties is completely counterintuitive from a causality
perspective. These results provide intriguing insights into the second law of
thermodynamics and its relation to gas-surface interaction physics.Comment: 28 pages, 11 figure

- …