Excitonic effects in a time-dependent density functional theory.

Excited state properties of one-dimensional molecular materials are dominated by many-body interactions resulting in strongly bound confined excitons. These effects cannot be neglected or treated as a small perturbation and should be appropriately accounted for by electronic structure methodologies. We use adiabatic time-dependent density functional theory to investigate the electronic structure of one-dimensional organic semiconductors, conjugated polymers.

Statistics of entropy production in linearized stochastic systems.

We consider a wide class of linear stochastic problems driven off the equilibrium by a multiplicative asymmetric force. The force breaks detailed balance, maintained otherwise, thus producing entropy. The large deviation function of the entropy production in the system is calculated explicitly.

Small bowel faeces sign in patients without small bowel obstruction.

Aim: To evaluate frequency and clinical relevance of the 'small bowel faeces' sign (SBFS) on computed tomography (CT) in patients with and without small bowel obstruction (SBO) presenting with acute abdominal or acute abdominal and flank pain.

Methods: Abdominal CTs of consecutive patients presenting to the emergency department with abdominal or flank pain over a 6 month period were retrospectively reviewed by six radiologists, independently, for the presence of the SBFS. Examinations with positive SBFS were further evaluated in consensus by three radiologists, blinded to the final diagnosis.

Loop calculus in statistical physics and information science.

Considering a discrete and finite statistical model of a general position we introduce an exact expression for the partition function in terms of a finite series. The leading term in the series is the Bethe-Peierls (belief propagation) (BP) contribution; the rest are expressed as loop contributions on the factor graph and calculated directly using the BP solution. The series unveils a small parameter that often makes the BP approximation so successful.

Type II endoleak after endoaortic graft implantation: diagnosis with helical CT arteriography.

Purpose: To retrospectively assess endoleak shapes and locations within aneurysms to differentiate type II from type I and type III endoleaks.

Materials And Methods: The institutional review board granted an exemption for this HIPAA-compliant study; patient informed consent was not required. A retrospective review of arterial phase helical computed tomographic (CT) studies and medical records was performed for 39 patients (29 men, 10 women; age range, 60-89 years; mean, 78.

Coherence and correlations in multitime quantum measurements of stochastic quantum trajectories.

Quantum effects on multitime distributions and correlation functions of single objects, stemming from both the dynamics and repeated measurements, are calculated for a driven harmonic system using a superoperator generating functional formalism. Marked differences between multipoint observables associated with classical and quantum measurements are identified. The effects of quantum collapse and measurement resolution are discussed.

Diagnosis of weaknesses in modern error correction codes: a physics approach.

One of the main obstacles to the wider use of the modern error-correction codes is that, due to the complex behavior of their decoding algorithms, no systematic method which would allow characterization of the bit-error-rate (BER) is known. This is especially true at the weak noise where many systems operate and where coding performance is difficult to estimate because of the diminishingly small number of errors. We show how the instanton method of physics allows one to solve the problem of BER analysis in the weak noise range by recasting it as a computationally tractable minimization problem.

Semiclassical scattering on conical intersections.

We apply a semiclassical approach to the scattering problem of a vibrational wave packet in the vicinity of a conical intersection of electronic energy surfaces and derive analytical expressions for the scattering matrix. The latter are valid when the scattering length that scales as square root(h) is small and a wave packet passes through the scattering region with a constant velocity. The analytical results are in excellent agreement with numerical simulations for a realistic set of parameters.

Dynamical generalization of nonequilibrium work relation.

The evolution of systems in contact with thermal, chaotic, or turbulent surroundings-often modeled with stochastic equations of motion-can be particularly complex when these equations of motion are nonautonomous, that is, when external parameters of the surroundings are varied with time. In this paper we establish a rigorous equality relating the nonautonomous behavior of such a system, to solutions of the corresponding autonomous equations of motion, for arbitrary initial conditions. If the system is initially in thermal equilibrium, we recover previously known results relating nonequilibrium work values to equilibrium probability distributions.

Error correction on a tree: an instanton approach.

We introduce a method that allows analytical or semianalytical estimating of the post-error correction bit error rate (BER) when a forward-error correction is utilized for transmitting information through a noisy channel. The generic method that applies to a variety of error-correction schemes in the regimes where the BER is low is illustrated using the example of a finite-size code approximated by a treelike structure. Exploring the statistical physics formulation of the problem we find that the BER decreases with the signal-to-noise ratio nonuniformly, i.

Effect of quantum collapse on the distribution of work in driven single molecules.

Two sources of quantum deviations from Jarzynski's celebrated classical relation between the free energy change and the distribution of work are analyzed using an exactly solvable harmonic model: Quantum dynamics retains the Gaussian profile of the distribution and merely gives rise to analytic corrections in variant Planck's over 2pi, whereas quantum measurements (wave function collapse) induce extended power-law tails which fundamentally alter the distribution. These results may be observed in quantum information processing and in experiments involving mechanically or optically driven single quantum objects.

Probability of anomalously large bit-error rate in long haul optical transmission.

We consider a linear model of optical transmission through a fiber with birefringent disorder in the presence of amplifier noise. Both disorder and noise are assumed to be weak, i.e.

Photophoresis of a fine particle in a selectively excited gas.

Motion in a binary gas mixture of a fine particle affected by resonant optical radiation is considered. The Doppler effect leads to the velocity-selective absorption of the traveling light wave by molecules of one of the gas components. Radiation transfers the absorbing molecules from the ground state to excited ones.

Extreme outages caused by polarization mode dispersion.

We study the dependence on fiber birefringence of the bit-error rate (BER) caused by amplifier noise in a linear optical fiber telecommunication system. We show that the probability-distribution function of the BER obtained by averaging over many realizations of birefringent disorder has an extended tail that corresponds to anomalously large values of BER. We specifically discuss the dependence of the tail on such details of pulse detection at the fiber output as setting the clock and filtering procedures.

Compensation for extreme outages caused by polarization mode dispersion and amplifier noise.

Fluctuations of Bit-Error-Rate (BER) stimulated by birefringent disorder in an optical fiber system are found to be strong. The effect may not be analyzed in terms of the average BER but rather requires analyzing the Probability Distribution Function (PDF) of BER. We report the emergence of the extremely extended algebraic-like tail of the PDF, corresponding to anomalously large values of BER.

Light-induced evaporation and condensation growth of aerosol particles.

The nonisothermal evaporation and condensation of a particle suspended in a vapor-gas mixture under the effect of resonant optical radiation is studied. A traveling light wave is absorbed by the aerosol particle and velocity selectively by vapor molecules. The dependence of the evaporation or condensation rate on optical and thermophysical properties of the particle and gaseous molecules is studied.

Exciton coherence and electron energy loss spectroscopy of conjugated molecules.

Signatures of the exciton coherence size, which controls the nonlinear optical response and luminescence of conjugated systems, in the electronic dynamic structure factor S(q,omega) are calculated. We find that for small molecules the momentum dependence of the lowest exciton resonance is purely geometric, reflecting the molecular size rather than a universal exciton size, as suggested recently. For long chains the q dependence is determined by the interplay of the exciton size and the bond-alternation length scales.

Excitonic funneling in extended dendrimers with nonlinear and random potentials.

The mean first passage time (MFPT) for photoexcitations diffusion in a funneling potential of artificial treelike light-harvesting antennas (phenylacetylene dendrimers with generation-dependent segment lengths) is computed. Effects of the nonlinearity of the realistic funneling potential and slow random solvent fluctuations considerably slow down the center-bound diffusion beyond a temperature-dependent optimal size. Diffusion on a disordered Cayley tree with a linear potential is investigated analytically.

Excitonic couplings and electronic coherence in bridged naphthalene dimers.

The electronic excitations of naphthalene and a family of bridged naphthalene dimers are calculated and analyzed by using the Collective Electronic Oscillator method combined with the oblique Lanczos algorithm. All experimentally observed trends in absorption profiles and radiative lifetimes are reproduced. Each electronic excitation is linked to the corresponding real-space transition density matrix, which represents the motions of electrons and holes created in the molecule by photon absorption.

Induction of nonselective permeability of the inner membrane in deenergized mitochondria.

Induction of the nonselective cyclosporin-sensitive pore in the inner mitochondrial membrane under conditions of complete dissipation of ion gradients and transmembrane potential was studied. This approach allows the kinetics of Ca2+-dependent pore opening and the preceding processes of induction to be studied separately. The effects of mitochondrial heterogeneity were also minimized.

Structural and functional consequences of substitutions at the tyrosine 55-lysine 104 hydrogen bond in Escherichia coli inorganic pyrophosphatase.

Tyrosine 55 and lysine 104 are evolutionarily conserved residues that form a hydrogen bond in the active site of Escherichia coli inorganic pyrophosphatase (E-PPase). Here we used site-directed mutagenesis to examine their roles in structure stabilization and catalysis. Though these residues are not part of the subunit interface, Y55F and K104R (but not K104I) substitutions markedly destabilize the hexameric structure, allowing dissociation into active trimers on dilution.