Percolative shunting on electrified surface

The surface discharge of electrified dielectrics at high humidity is considered. The percolative nature of charge transport in electrets is established. Particular attention is given to the phenomena of adsorption and nucleation of electrically conducting phase in the cause of percolation cluster growth on electrified surface. The critical index of the correlation lenght for percolation cluster is found, and its value is in good agreement with the known theoretical estimations.Comment: 4 pages with 1 figure, revtex, published in Tech. Phys. Lett. 25 (1999) 877-879 with one additional figur

Stability properties of periodically driven overdamped pendula and their implications to physics of semiconductor superlattices and Josephson junctions

We consider the first order differential equation with a sinusoidal nonlinearity and periodic time dependence, that is, the periodically driven overdamped pendulum. The problem is studied in the case that the explicit time-dependence has symmetries common to pure ac-driven systems. The only bifurcation that exists in the system is a degenerate pitchfork bifurcation, which describes an exchange of stability between two symmetric nonlinear modes. Using a type of Prufer transform to a pair of linear differential equations, we derive an approximate condition of the bifurcation. This approximation is in very good agreement with our numerical data. In particular, it works well in the limit of large drive amplitudes and low external frequencies. We demonstrate the usefulness of the theory applying it to the models of pure ac-driven semiconductor superlattices and Josephson junctions. We show how the knowledge of bifurcations in the overdamped pendulum model can be utilized to describe effects of rectification and amplification of electric fields in these microstructures.Comment: 15 pages, 7 figures, Revtex 4.1. Revised and expanded following referee's report. Submitted to journal Chaos

Co dimers on hexagonal carbon rings proposed as subnanometer magnetic storage bits

It is demonstrated by means of density functional and ab-initio quantum chemical calculations, that transition metal - carbon systems have the potential to enhance the presently achievable area density of magnetic recording by three orders of magnitude. As a model system, Co_2-benzene with a diameter of 0.5 nm is investigated. It shows a magnetic anisotropy in the order of 0.1 eV per molecule, large enough to store permanently one bit of information at temperatures considerably larger than 4 K. A similar performance can be expected, if cobalt dimers are deposited on graphene or on graphite. It is suggested that the subnanometer bits can be written by simultaneous application of a moderate magnetic and a strong electric field.Comment: 13 pages, 4 figure

Do the precise measurements of the Casimir force agree with the expectations?

An upper limit on the Casimir force is found using the dielectric functions of perfect crystalline materials which depend only on well defined material constants. The force measured with the atomic force microscope is larger than this limit at small separations between bodies and the discrepancy is significant. The simplest modification of the experiment is proposed allowing to make its results more reliable and answer the question if the discrepancy has any relation with the existence of a new force.Comment: 9 pages, LaTeX, 2 Postscript figure

On the Strength of Spin-Isospin Transitions in A=28 Nuclei

The relations between the strengths of spin-isospin transition operators extracted from direct nuclear reactions, magnetic scattering of electrons and processes of semi-leptonic weak interactions are discussed.Comment: LaTeX, 8 pages, 1Postscript with figur

Термодинамическая устойчивость интерметаллических соединений в техническом алюминии

For the following systems Al-Ti, Al-Ni, Al-Zr, Al-Cr, Al-Fe, Al-V the wide range of intermetallic compounds based on aluminum was considered. Thermodynamic parameters such as Gibbs energy and formation enthalpy characterizing the properties of resulting intermetallic compounds were calculated. The relations of these two characteristics versus temperature were established in a wide range. On the basis of the obtained relations the comparative assessment of the compound stability for each binary system was carried out. The level of each intermetallic compound stability was revealed on the ground of the affinity with aluminum. The possibilities of practical application of obtained data for actual metallurgical tasks were definedРассмотрен широкий ряд интерметаллических соединений систем Al-Ti, Al-Ni, Al-Zr, Al-Cr, Al-Fe, Al-V. Рассчитаны такие термодинамические характеристики, как энергия Гиббса и энтальпия образования, характеризующие свойства образующихся интерметаллических соединений. Установлены зависимости данных характеристик от температуры в широком диапазоне. На основании полученных зависимостей проведена сравнительная оценка устойчивости интерметаллических соединений для каждой системы. Показана степень устойчивости каждого интерметаллида исходя из его сродства к алюмини

Electron Correlations in the Low Carrier Density LaFeAsO0.89F0.11 Superconductor (Tc = 28 K)

The crystal structure and numerous normal and superconducting state properties of layered tetragonal (P4/nmm) LaFeAsO, with F-doping of 11 %, are reported. Resistivity measurements give an onset transition temperature Tc = 28.2 K, and low field magnetic susceptibility data indicate bulk superconductivity. In applied magnetic field, analysis of the resistive transition results in a critical field Hc2 = 30 T and a coherence length 35 A. An upper limit for the electron carrier concentration of 1 x 10^21 cm-3 is inferred from Hall data just above Tc. Strong electron-electron correlations are suggested from temperature-dependent resistivity, Seebeck coefficient, and thermal conductivity data. Anomalies near Tc are observed in both Seebeck coefficient and thermal conductivity data.Comment: 13 pages, 8 figure

Послеоперационный делирий и инфаркт миокарда у пациентов пожилого и старческого возраста с переломами шейки бедренной кости: роль послеоперационной анемии

Objective. To assess the impact of anemia on the incidence of myocardial infarction and delirium in the early postoperative period in patients with hip fractures who underwent total hip replacement. Materials and methods. A retrospective study of 303 patients with hip fractures who underwent total hip replacement was performed. Patients were divided into two groups according to the level of hemoglobin (Hb) on the 2nd postoperative day: Group 1 (n = 116) with Hb levels above 100 g/L and Group 2 (n = 187) with Hb levels below 100 g/L. Results and conclusion. Transfusion in Group 1 was performed more often intraoperatively or in the early postoperative hours (67 vs. 35 patients; p 0.001). Hb levels on the 2nd day were significantly higher in Group 1 (108 [104; 117] vs. 87 [80; 92] g/L; p 0.001). Moderate and severe anemia in the early postoperative period was noted in 53.5% and 4.3% of the patients of Group 2, respectively. The incidence of myocardial infarction and delirium was higher in Group 2 than in Group 1 (6.4% vs. 0%; p = 0,013 and 7.5% vs 0.8%; p = 0.021, respectively). The study has shown that moderate and severe anemia in the early postoperative period is associated with an increase in the incidence of myocardial infarction and delirium.Цель исследования: оценка влияния анемии на частоту инфаркта миокарда и делирия в раннем послеоперационном периоде у пациентов с переломами шейки бедренной кости, которым выполнено тотальное эндопротезирование тазобедренного сустава. Материалы и методы. Проведено ретроспективное исследование 303 пациентов с переломами шейки бедренной кости, которым было выполнено тотальное эндопротезирование тазобедренного сустава. Пациенты были разделены на две группы по уровню гемоглобина на 2-е сутки после операции: 1-я группа (n = 116) с уровнем гемоглобина выше 100 г/л; 2-я группа (n = 187) с уровнем гемоглобина ниже 100 г/л. Результаты и заключение. Трансфузия в первой группе проводилась чаще во время операции и в первые часы после операции (67 против 35 пациентов; p0,001). уровень гемоглобина на вторые сутки был существенно выше в первой группе (108 [104;117] против 87 [80;92] г/л; p0,001). Анемия умеренной и тяжелой степени в раннем послеоперационном периоде отмечена соответственно у 53,5% и 4,3% пациентов второй группы. Во второй группе чаще, чем в первой группе, наблюдался инфаркт миокарда (6,4% против 0% ; p = 0,013) и делирий (7,5% против 0,8%; p = 0,021). Было установлено, что анемия средней и тяжелой степени в раннем послеоперационном периоде сопровождается увеличением частоты развития инфаркта миокарда и делирия

A VLA Search for the Geminga Pulsar: A Bayesian Limit on a Scintillating Source

We derive an upper limit of 3 mJy (95% confidence) for the flux density at 317 MHz of the Geminga pulsar (J0633+1746). Our results are based on 7 hours of fast-sampled VLA data, which we averaged synchronously with the pulse period using a period model based on CGRO/EGRET gamma-ray data. Our limit accounts for the fact that this pulsar is most likely subject to interstellar scintillations on a timescale much shorter than our observing span. Our Bayesian method is quite general and can be applied to calculate the fluxes of other scintillated sources. We also present a Bayesian technique for calculating the flux in a pulsed signal of unknown width and phase. Comparing our upper limit of 3 mJy with the quoted flux density of Geminga at 102 MHz, we calculate a lower limit to its spectral index of 2.7. We discuss some possible reasons for Geminga's weakness at radio wavelengths, and the likelihood that many of the unidentified EGRET sources are also radio-quiet or radio-weak Geminga-like pulsars.Comment: 27 pages, including figures. Published in Ap

A CLEAN-based Method for Deconvolving Interstellar Pulse Broadening from Radio Pulses

Multipath propagation in the interstellar medium distorts radio pulses, an effect predominant for distant pulsars observed at low frequencies. Typically, broadened pulses are analyzed to determine the amount of propagation-induced pulse broadening, but with little interest in determining the undistorted pulse shapes. In this paper we develop and apply a method that recovers both the intrinsic pulse shape and the pulse broadening function that describes the scattering of an impulse. The method resembles the CLEAN algorithm used in synthesis imaging applications, although we search for the best pulse broadening function, and perform a true deconvolution to recover intrinsic pulse structre. As figures of merit to optimize the deconvolution, we use the positivity and symmetry of the deconvolved result along with the mean square residual and the number of points below a given threshold. Our method makes no prior assumptions about the intrinsic pulse shape and can be used for a range of scattering functions for the interstellar medium. It can therefore be applied to a wider variety of measured pulse shapes and degrees of scattering than the previous approaches. We apply the technique to both simulated data and data from Arecibo observations.Comment: 9 pages, 6 figures, Accepted for publication in the Astrophysical Journa