95 research outputs found
Electron-conformational transformations in nanoscopic RyR channels govern both the heart's contraction and beating
We show that a simple biophysically based electron-conformational model of
RyR channel is able to explain and describe on equal footing the oscillatory
regime of the heart's cell release unit both in sinoatrial node (pacemaker)
cells under normal physiological conditions and in ventricular myocytes under
Ca SR overload.Comment: 6 pages, 3 figure
SEM Investigation of ZnO and CdO–ZnO Layers Grown by Sol-Gel Technology and a Multifractal Analysis of their Surface Depending on Synthesis Conditions
Introduction. Super-thin films of zinc oxide regarded as transparent electrodes can be integrated in effective semiconductor heterostructures for use in modern infrared photo electronics and solar power installations. The most important parameter of zinc oxide thin layers is their surface nanorelief, which can be effectively studied using SEM spectroscopy. SEM images allow for a quantitative description of the surface depending on the synthesis conditions using the method of multifractal analysis. Such an approach reveals quantitative relationships between the fractal parameters of the surface topography of the layers in these systems and the temperature regimes used for their final annealing in conventional sol-gel technology.Aim. To reveal quantitative relationships between the fractal parameters of the surface topography of layers in the Zn–O & Zn–Cd–O systems and the temperature conditions of their final annealing. The MFA method was used for a quantitative description of the surface state depending on the synthesis conditions.Materials and methods. Super-thin films in the ZnO and ZnO–CdO systems were synthesized using a modified sol-gel technology. The temperature-concentration ranges of the parameters of the modified technological process, which allows high-quality layers of the material to be reproducibly obtained on a glass substrate, were determined. The surface morphology was investigated by SEM spectroscopy depending on the temperature of the final annealing of the layers. SEM images of the surface served as a basis for multifractal analysis (MFA) of the surface area and volume of nanoforms, which are formed on the surface of the obtained layers thus determining their surface relief.Results. Renyi’s numbers and the parameters of fractal ordering in MFA were chosen as fractal parameters for describing the nano-geometry of the layer surface. MFA was applied to the description of both the surface areas and volumes of nanoforms. Quantitative correlations between Renyi’s numbers, as well as the parameters of fractal ordering for the areas and volumes of surface nanoforms, and the temperature of the final annealing were found.Conclusion. The numerical values of Renyi’s numbers for the surface and volume characteristics of the surface of layers were used to assess the effect of the fractality of the surface on the molar surface energy of the film. Consideration of the fractal geometry of nanoforms with their characteristic sizes smaller than 5·103μm shows the possibility of both an increase in the surface energy of the resulting film and its decrease when changing the characteristic sizes of nanoforms. The latter effect is due to the formation of a highly porous surface at the nano levelIntroduction. Super-thin films of zinc oxide regarded as transparent electrodes can be integrated in effective semiconductor heterostructures for use in modern infrared photo electronics and solar power installations. The most important parameter of zinc oxide thin layers is their surface nanorelief, which can be effectively studied using SEM spectroscopy. SEM images allow for a quantitative description of the surface depending on the synthesis conditions using the method of multifractal analysis. Such an approach reveals quantitative relationships between the fractal parameters of the surface topography of the layers in these systems and the temperature regimes used for their final annealing in conventional sol-gel technology.Aim. To reveal quantitative relationships between the fractal parameters of the surface topography of layers in the Zn–O & Zn–Cd–O systems and the temperature conditions of their final annealing. The MFA method was used for a quantitative description of the surface state depending on the synthesis conditions.Materials and methods. Super-thin films in the ZnO and ZnO–CdO systems were synthesized using a modified sol-gel technology. The temperature-concentration ranges of the parameters of the modified technological process, which allows high-quality layers of the material to be reproducibly obtained on a glass substrate, were determined. The surface morphology was investigated by SEM spectroscopy depending on the temperature of the final annealing of the layers. SEM images of the surface served as a basis for multifractal analysis (MFA) of the surface area and volume of nanoforms, which are formed on the surface of the obtained layers thus determining their surface relief.Results. Renyi’s numbers and the parameters of fractal ordering in MFA were chosen as fractal parameters for describing the nano-geometry of the layer surface. MFA was applied to the description of both the surface areas and volumes of nanoforms. Quantitative correlations between Renyi’s numbers, as well as the parameters of fractal ordering for the areas and volumes of surface nanoforms, and the temperature of the final annealing were found.Conclusion. The numerical values of Renyi’s numbers for the surface and volume characteristics of the surface of layers were used to assess the effect of the fractality of the surface on the molar surface energy of the film. Consideration of the fractal geometry of nanoforms with their characteristic sizes smaller than 5·103μm shows the possibility of both an increase in the surface energy of the resulting film and its decrease when changing the characteristic sizes of nanoforms. The latter effect is due to the formation of a highly porous surface at the nano leve
A simplified model of the source channel of the Leksell Gamma Knife: testing multisource configurations with PENELOPE
A simplification of the source channel geometry of the Leksell Gamma
Knife, recently proposed by the authors and checked for a single
source configuration (Al-Dweri et al 2004), has been used to calculate the dose
distributions along the , and axes in a water phantom with a
diameter of 160~mm, for different configurations of the Gamma Knife including
201, 150 and 102 unplugged sources. The code PENELOPE (v. 2001) has been used
to perform the Monte Carlo simulations. In addition, the output factors for the
14, 8 and 4~mm helmets have been calculated. The results found for the dose
profiles show a qualitatively good agreement with previous ones obtained with
EGS4 and PENELOPE (v. 2000) codes and with the predictions of
GammaPlan. The output factors obtained with our model agree
within the statistical uncertainties with those calculated with the same Monte
Carlo codes and with those measured with different techniques. Owing to the
accuracy of the results obtained and to the reduction in the computational time
with respect to full geometry simulations (larger than a factor 15), this
simplified model opens the possibility to use Monte Carlo tools for planning
purposes in the Gamma Knife.Comment: 13 pages, 8 figures, 5 table
Electron-Conformational Transformations in Nanoscopic RyR Channels Governing Both the Heart's Contraction and Beating
We show that a simple biophysically based electron-conformational model of RyR channel can explain and describe on equal footing the oscillatory regime of the heart's cell release unit both in sinoatrial node (pacemaker) cells under normal physiological conditions and in ventricular myocytes under Ca2+ sarcoplasmic reticulum overload. © 2011 Pleiades Publishing, Ltd.This work was supported by the Ural Branch, Russian Academy of Sciences, project no. 09 M 14 2001
Frustrated magnet Li2ZrCuO4 - Paramagnetism meets paraelectricity
By measuring 7Li nuclear magnetic resonance, Cu2+ electron spin resonance and a complex dielectric constant in the frustrated spin-1/2 chain compound γ-Li2ZrCuO4 we find that the electric sublattice of mobile Li+ ions orders glass-like at T g ∼ 100 K. This yields the emergence of non-equivalent spin sites in the spin-1/2 CuO2 chains. We suggest that such a remarkable interplay between electrical and spin degrees of freedom may influence the properties of the spiral spin state in Li2ZrCuO4 which develops in this material at low temperatures. © 2010 IOP Publishing Ltd
Nanoscale phase separation in films: evidence for the texture driven optical anisotropy
The IR optical absorption (0.1-1.5 eV) in the films
on LAO substrate exhibits the drastic temperature evolution of the spectral
weight evidencing the insulator to metal transition. Single crystal films were
found to reveal strong linear dichroism with anomalous spectral oscillations
and fairly weak temperature dependence. Starting from the concept of phase
separation, we develop the effective medium model to account for these effects.
The optical anisotropy of the films is attributed to the texturization of the
ellipsoidal inclusions of the quasimetal phase caused by a mismatch of the film
and substrate and the twin texture of the latter.Comment: 6 pages, 5 Encapsulated PostScript figures, uses RevTeX
Nanoscale Phase Separation in La0.7Ca0.3MnO3 Films: Evidence for Texture-driven Optical Anisotropy
The infrared optical absorption (0.1 eV < ℏω < 1.5 eV) in La0.7Ca0.3MnO3 films on LaAlO3 substrates exhibits a drastic temperature evolution of the spectral weight, evidencing an insulator-to-metal transition. Single-crystal films were found to reveal strong linear dichroism with anomalous spectral oscillations and fairly weak temperature dependence. Starting from the concept of phase separation, we develop an effective medium model to account for these effects. The optical anisotropy of the films is attributed to the texturization of the ellipsoidal inclusions of the quasimetal phase caused by a mismatch of the film and substrate and the twin texture of the latter.The work was supported by INTAS 01-0654, Federal programme (contract No 40.012.1.1. 1153-14/02), grants RFBR No 01-02-96404, No 02-02-16429, RFMC No E00-3.4-280, E02-3.4-392, CRDF No REC-005 and UR 01.01.042
Effects of bone- and air-tissue inhomogeneities on the dose distributions of the Leksell Gamma Knife calculated with PENELOPE
Monte Carlo simulation with PENELOPE (v.~2003) is applied to calculate
Leksell Gamma Knife dose distributions for heterogeneous
phantoms. The usual spherical water phantom is modified with a spherical bone
shell simulating the skull and an air-filled cube simulating the frontal or
maxillary sinuses. Different simulations of the 201 source configuration of the
Gamma Knife have been carried out with a simplified model of the geometry of
the source channel of the Gamma Knife recently tested for both single source
and multisource configurations. The dose distributions determined for
heterogeneous phantoms including the bone- and/or air-tissue interfaces show
non negligible differences with respect to those calculated for a homogeneous
one, mainly when the Gamma Knife isocenter approaches the separation surfaces.
Our findings confirm an important underdosage (10%) nearby the air-tissue
interface, in accordance with previous results obtained with PENELOPE code with
a procedure different to ours. On the other hand, the presence of the spherical
shell simulating the skull produces a few percent underdosage at the isocenter
wherever it is situated.Comment: 13 pages, 8 figures, 2 table
Dispersion of the dielectric function of a charge-transfer insulator
We study the problem of dielectric response in the strong coupling regime of
a charge transfer insulator. The frequency and wave number dependence of the
dielectric function and its inverse is the main object of consideration. We show that the
problem, in general, cannot be reduced to a calculation within the Hubbard
model, which takes into account only a restricted number of electronic states
near the Fermi energy. The contribution of the rest of the system to the
longitudinal response (i.e. to ) is essential
for the whole frequency range. With the use of the spectral representation of
the two-particle Green's function we show that the problem may be divided into
two parts: into the contributions of the weakly correlated and the Hubbard
subsystems. For the latter we propose an approach that starts from the
correlated paramagnetic ground state with strong antiferromagnetic
fluctuations. We obtain a set of coupled equations of motion for the
two-particle Green's function that may be solved by means of the projection
technique. The solution is expressed by a two particle basis that includes the
excitonic states with electron and hole separated at various distances. We
apply our method to the multiband Hubbard (Emery) model that describes layered
cuprates. We show that strongly dispersive branches exist in the excitonic
spectrum of the 'minimal' Emery model () and consider the
dependence of the spectrum on finite oxygen hopping and on-site
repulsion . The relationship of our calculations to electron energy loss
spectroscopy is discussed.Comment: 22 pages, 5 figure
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