Modeling the voltage distribution in a non-locally but globally electroneutral confined electrolyte medium: applications for nanophysiology.

The distribution of voltage in sub-micron cellular domains remains poorly understood. In neurons, the voltage results from the difference in ionic concentrations which are continuously maintained by pumps and exchangers. However, it not clear how electro-neutrality could be maintained by an excess of fast moving positive ions that should be counter balanced by slow diffusing negatively charged proteins. Using the theory of electro-diffusion, we study here the voltage distribution in a generic domain, which consists of two concentric disks (resp. ball) in two (resp. three) dimensions, where a negative charge is fixed in the inner domain. When global but not local electro-neutrality is maintained, we solve the Poisson-Nernst-Planck equation both analytically and numerically in dimension 1 (flat) and 2 (cylindrical) and found that the voltage changes considerably on a spatial scale which is much larger than the Debye screening length, which assumes electro-neutrality. The present result suggests that long-range voltage drop changes are expected in neuronal microcompartments, probably relevant to explain the activation of far away voltage-gated channels located on the surface membrane.

Intensity of Waves Inside a Strongly Disordered Medium.

Anderson localization does not lead to an exponential decay of intensity of an incident wave with the depth inside a strongly disordered three-dimensional medium. Instead, the average intensity is roughly constant in the first half of a disordered slab, sharply drops in a narrow region in the middle of the sample, and then remains low in the second half of the sample. A universal, scale-free spatial distribution of average intensity is found at mobility edges where the intensity exhibits strong sample-to-sample fluctuations. Our numerical simulations allow us to discriminate between two competing local diffusion theories of Anderson localization and to pinpoint a deficiency of the self-consistent theory.

Random Search with Resetting: A Unified Renewal Approach.

We provide a unified renewal approach to the problem of random search for several targets under resetting. This framework does not rely on specific properties of the search process and resetting procedure, allows for simpler derivation of known results, and leads to new ones. Concentrating on minimizing the mean hitting time, we show that resetting at a constant pace is the best possible option if resetting helps at all, and derive the equation for the optimal resetting pace. No resetting may be a better strategy if without resetting the probability of not finding a target decays with time to zero exponentially or faster. We also calculate splitting probabilities between the targets, and define the limits in which these can be manipulated by changing the resetting procedure. We moreover show that the number of moments of the hitting time distribution under resetting is not less than the sum of the numbers of moments of the resetting time distribution and the hitting time distribution without resetting.

Observation of Single-Photon Superradiance and the Cooperative Lamb Shift in an Extended Sample of Cold Atoms.

We report direct, time-resolved observations of single-photon superradiance in a highly extended, elliptical sample of cold ^{87}Rb atoms. The observed rapid decay rate is accompanied by its counterpart, the cooperative Lamb shift. The rate of the strongly directional decay, and the associated shift, scale linearly with the number of atoms, demonstrating the collective nature of the observed quantities.

Nanophase separation in monomolecularly thin water-ethanol films controlled by graphene.

Control over nanoscale patterning of ultrathin molecular films plays an important role both in natural as well as artificial nanosystems. Here we report on nanophase separated patterns of water and ethanol within monomolecularly thin films confined between the cleavage plane of mica and single or a few layers of graphene. Employing scanning force microscopy of the graphene layers conforming to the molecular films we quantify the patterns using the ethanol-water cross correlation and the autocorrelation of domain wall directions. They reveal that lateral pattern dimensions grow and the domain walls stiffen upon increasing the thickness of the graphene multilayers. We attribute the control of the patterns through the graphene layers to the competition between the mechanical deformation energy of the graphene sheets and the electrostatic repulsion of dipoles normal to the interface. The latter results from charge transfer between graphene and the molecules confined between mica and graphene.

[Clinical Case of Brain Abscess in a Patient With Tetralogy Fallot].

We present here a clinical case of brain abscess in a patient aged 26 years with congenital heart disease (CHD) - tetralogy of Fallot (blue type). Blue type CHD often leads to development of complications involving central nervous system (CNS), most often brain abscesses. The cause of difficulty of detection of such complications is one-sided focus of clinicians on cardiac pathology. Complaints indicative of the presence.

Microscopic lensing by a dense, cold atomic sample.

We demonstrate that a cold, dense sample of Rb87 atoms can exhibit a micron-scale lensing effect, much like that associated with a macroscopically sized lens. The experiment is carried out in the fashion of traditional z-scan measurements but in much weaker fields and where close attention is paid to the detuning dependence of the transmitted light. The results are interpreted using numerical simulations and by modeling the sample as a thin lens with a spherical focal length.

Magnetic-field-driven localization of light in a cold-atom gas.

We discover a transition from extended to localized quasimodes for light in a gas of immobile two-level atoms in a magnetic field. The transition takes place either upon increasing the number density of atoms in a strong field or upon increasing the field at a high enough density. It has many characteristic features of a disorder-driven (Anderson) transition but is strongly influenced by near-field interactions between atoms and the anisotropy of the atomic medium induced by the magnetic field.

[Diagnostic opportunities of noninvasive brain thermomonitoring].

Development of new means and methods of cerebral temperature monitoring is an actual problem due to the fact that severity and outcomes of diseases in patients with brain damages (strokes, a head trauma) in big degree depend on development of neurogenetic fever and a local cerebral hyperthermia. The temperature monitoring, which is carried out by the implanted sensors, is applied in neurosurgical patients and is practically not used in patients with disorders of cerebral bloodflow. In this regard, noninvasive techniques of brain temperature registration are developing: proton nuclear magnetic resonance spectroscopy and registration of own electromagnetic radiation (EMR) at the high range of frequencies (microwave). The main objective of the study was to define of diagnostic opportunities of noninvasive temperature measurement of brain by means of microwave radiothermometry.

Absence of Anderson localization of light in a random ensemble of point scatterers.

As discovered by Philip Anderson in 1958, strong disorder can block propagation of waves and lead to the localization of wavelike excitations in space. Anderson localization of light is particularly exciting in view of its possible applications for random lasing or quantum information processing. We show that, surprisingly, Anderson localization of light cannot be achieved in a random three-dimensional ensemble of point scattering centers that is the simplest and widespread model to study the multiple scattering of waves. Localization is recovered if the vector character of light is neglected. This shows that, at least for point scatterers, the polarization of light plays an important role in the Anderson localization problem.

Dynamics of ethanol and water mixtures observed in a self-adjusting molecularly thin slit pore.

The structure of multicomponent fluids in confined geometries is a key to understanding their properties. However, it remains an experimental challenge to gain molecular-scale resolution information on this structure. Here we show that mono- and multilayers of graphene, conforming to heterogeneous monolayers of molecules in a flexible slit pore between a mica surface and the graphene layers, allow for mapping the phase separation of water and ethanol within such a slit pore. Employing scanning force microscopy, we readily distinguish clusters of ethanol and water molecules due their different sizes, and we show that the phase separated water-ethanol structures become coarser under thicker graphenes. Moreover, we obtain a lower bound for the two-dimensional diffusion coefficient of ethanol in water of D ≥ 2 × 10(-14) m(2) s(-1). Thus, the molecularly thin slit pore provides a powerful tool to control and to investigate mixed fluids in self-adjusting nanopores.

[Clinical case of malignant pericardial mesothelioma].

We present a clinical case of pericardial mesothelioma diagnosed in vivo in a 45 years old patient. Pericardial mesothelioma developed asymptomatically and manifested after viral respiratory infection with a clinical picture of exudative pericarditis and progressive heart failure. Mesothelioma was eventually diagnosed but the patient died. Prevalence of primary pericardial mesothelioma, its risk factors, and criteria for diagnosis are also discussed.

Nonspectral relaxation in one dimensional Ornstein-Uhlenbeck processes.

The relaxation of a dissipative system to its equilibrium state often shows a multiexponential pattern with relaxation rates, which are typically considered to be independent of the initial condition. The rates follow from the spectrum of a Hermitian operator obtained by a similarity transformation of the initial Fokker-Planck operator. However, some initial conditions are mapped by this similarity transformation to functions which grow at infinity. These cannot be expanded in terms of the eigenfunctions of a Hermitian operator, and show different relaxation patterns. Considering the exactly solvable examples of Gaussian and generalized Lévy Ornstein-Uhlenbeck processes (OUPs) we show that the relaxation rates belong to the Hermitian spectrum only if the initial condition belongs to the domain of attraction of the stable distribution defining the noise. While for an ordinary OUP initial conditions leading to nonspectral relaxation can be considered exotic, for generalized OUPs driven by Lévy noise, such initial conditions are the rule.

Communication: impact of inertia on biased Brownian transport in confined geometries.

We consider the impact of inertia on biased Brownian motion of point-size particles in a two-dimensional channel with sinusoidally varying width. If the time scales of the problem separate, the adiabatic elimination of the transverse degrees of freedom leads to an effective description for the motion along the channel given by the potential of mean force. The possibility of such description is intimately connected with equipartition. Numerical simulations show that in the presence of external bias the equipartition may break down leading to non-monotonic dependence of mobility on external force and several other interesting effects.

Relation between generalized diffusion equations and subordination schemes.

Generalized (non-Markovian) diffusion equations with different memory kernels and subordination schemes based on random time change in the Brownian diffusion process are popular mathematical tools for description of a variety of non-Fickian diffusion processes in physics, biology, and earth sciences. Some of such processes (notably, the fluid limits of continuous time random walks) allow for either kind of description, but other ones do not. In the present work we discuss the conditions under which a generalized diffusion equation does correspond to a subordination scheme, and the conditions under which a subordination scheme does possess the corresponding generalized diffusion equation. Moreover, we discuss examples of random processes for which only one, or both kinds of description are applicable.

Quantum interference effects in multi-channel correlated tunneling structures.

In multi-channel tunneling systems quantum interference effects modify tunneling conductance spectra due to Fano effect. We investigated the impact of Hubbard type Coulomb interaction on tunneling conductance spectra for the system formed by several interacting impurity atoms or quantum dots localised between the contact leads. It was shown that the Fano shape of tunneling conductance spectra strongly changes in the presence of on-site Coulomb interaction between localised electrons in the intermediate system. The main effect which determines the shape of the tunneling peaks could be not Fano interference but mostly nonequilibrium dependence of the occupation numbers on bias voltage.

Law of mass action, detailed balance, and the modeling of calcium puffs.

Using deterministic-stochastic simulations we show that for intracellular calcium puffs the mixing assumption for reactants does not hold within clusters of receptor channels. Consequently, the law of mass action does not apply and useful definitions of averaged calcium concentrations in the cluster are not obvious. Effective reaction kinetics can be derived, however, by separating concentrations for self-coupling of channels and coupling to different channels, thus eliminating detailed balance in the reaction scheme. A minimal Markovian model can be inferred, describing well calcium puffs in neuronal cells and allowing insight into the functioning of calcium puffs.

Internal friction and mode relaxation in a simple chain model.

We consider the equilibrium relaxation properties of the end-to-end distance and of the principal components in a one-dimensional polymer chain model with nonlinear interaction between the beads. While for the single-well potentials these properties are similar to the ones of a Rouse chain, for the double-well interaction potentials, modeling internal friction, they differ vastly from the ones of the harmonic chain at intermediate times and intermediate temperatures. This minimal description within a one-dimensional model mimics the relaxation properties found in much more complex polymer systems. Thus, the relaxation time of the end-to-end distance may grow by orders of magnitude at intermediate temperatures. The principal components (whose directions are shown to coincide with the normal modes of the harmonic chain, whatever interaction potential is assumed) not only display larger relaxation times but also subdiffusive scaling.

Scaling of the rupture dynamics of polymer chains pulled at one end at a constant rate.

We consider the rupture dynamics of a homopolymer chain pulled at one end at a constant loading rate r . Compared to single bond breaking, the existence of the chain introduces two aspects into rupture dynamics: The non-Markovian aspect in the barrier crossing and the slow down of the force propagation to the breakable bond. The relative impact of both these processes is investigated, and the second one was found to be the most important at moderate loading rates. The most probable rupture force is found to decrease with the number of bonds as f{max} proportional, variant-[ln(const N/r)]2/3 and finally to approach a saturation value independent on N . All of our analytical findings are confirmed by extensive numerical simulations.

Front propagation in a one-dimensional autocatalytic reaction-subdiffusion system.

We study numerically the autocatalytic irreversible reaction A+B-->2A on a one-dimensional lattice for the case of subdiffusive reactants performing symmetric continuous-time random walks with the power-law waiting time density function psi(t) proportional, t(-1-alpha) with 0