Immirzi Ambiguity in the Kinematics of Quantum General Relativity

The Immirzi ambiguity arises in loop quantum gravity when geometric operators are represented in terms of different connections that are related by means of an extended Wick transform. We analyze the action of this transform in gravity coupled with matter fields and discuss its analogy with the Wick rotation on which the Thiemann transform between Euclidean and Lorentzian gravity is based. In addition, we prove that the effect of this extended Wick transform is equivalent to a constant scale transformation as far as the symplectic structure and kinematical constraints are concerned. This equivalence is broken in the dynamical evolution. Our results are applied to the discussion of the black hole entropy in the limit of large horizon areas. We first argue that, since the entropy calculation is performed for horizons of fixed constant area, one might in principle choose an Immirzi parameter that depends on this quantity. This would spoil the linearity with the area in the entropy formula. We then show that the Immirzi parameter appears as a constant scaling in all the steps where dynamical information plays a relevant role in the entropy calculation. This fact, together with the kinematical equivalence of the Immirzi ambiguity with a change of scale, is used to preclude the potential non-linearity of the entropy on physical grounds.Comment: very minor stylistic changes, version published in Phys. Rev.

Mass Renormalization in the Su-Schrieffer-Heeger Model

This study of the one dimensional Su-Schrieffer-Heeger model in a weak coupling perturbative regime points out the effective mass behavior as a function of the adiabatic parameter $\omega_{\pi}/J$, $\omega_{\pi}$ is the zone boundary phonon energy and $J$ is the electron band hopping integral. Computation of low order diagrams shows that two phonons scattering processes become appreciable in the intermediate regime in which zone boundary phonons energetically compete with band electrons. Consistently, in the intermediate (and also moderately antiadiabatic) range the relevant mass renormalization signals the onset of a polaronic crossover whereas the electrons are essentially undressed in the fully adiabatic and antiadiabatic systems. The effective mass is roughly twice as much the bare band value in the intermediate regime while an abrupt increase (mainly related to the peculiar 1D dispersion relations) is obtained at $\omega_{\pi}\sim \sqrt{2}J$.Comment: To be published in Phys.Rev.B - 3 figure

Low-temperature electrical transport in bilayer manganite La1.2_{1.2}Sr1.8_{1.8}Mn2_{2}O7_{7}

The temperature $T$ and magnetic field $H$ dependence of anisotropic in-plane $\rho_{ab}$ and out-of-plane $\rho_{c}$ resistivities have been investigated in single crystals of the bilayer manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$. Below the Curie transition temperature $T_c=$ 125 K, $\rho_{ab}$ and $\rho_{c}$ display almost the same temperature dependence with an up-turn around 50 K. In the metallic regime (50 K $\leq T \leq$ 110 K), both $\rho_{ab}(T)$ and $\rho_{c}(T)$ follow a $T^{9/2}$ dependence, consistent with the two-magnon scattering. We found that the value of the proportionality coefficient $B_{ab}^{fit}$ and the ratio of the exchange interaction $J_{ab}/J_c$ obtained by fitting the data are in excellent agreement with the calculated $B_{ab}$ based on the two-magnon model and $J_{ab}/J_c$ deduced from neutron scattering, respectively. This provides further support for this scattering mechanism. At even lower $T$, in the non-metallic regime ($T<$ 50 K), {\it both} the in-plane $\sigma_{ab}$ and out-of-plane $\sigma_{c}$ conductivities obey a $T^{1/2}$ dependence, consistent with weak localization effects. Hence, this demonstrates the three-dimensional metallic nature of the bilayer manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ at $T<T_c$.Comment: 7 pages and 5 figures, accepted for publication in Phys. Rev.

Vibration induced memory effects and switching in ac-driven molecular nanojunctions

We investigate bistability and memory effects in a molecular junction weakly coupled to metallic leads with the latter being subject to an adiabatic periodic change of the bias voltage. The system is described by a simple Anderson-Holstein model and its dynamics is calculated via a master equation approach. The controlled electrical switching between the many-body states of the system is achieved due to polaron shift and Franck-Condon blockade in the presence of strong electron-vibron interaction. Particular emphasis is given to the role played by the excited vibronic states in the bistability and hysteretic switching dynamics as a function of the voltage sweeping rates. In general, both the occupation probabilities of the vibronic states and the associated vibron energy show hysteretic behaviour for driving frequencies in a range set by the minimum and maximum lifetimes of the system. The consequences on the transport properties for various driving frequencies and in the limit of DC-bias are also investigated.Comment: 15 pages, 20 figures, published versio

Economic security as a condition for sustainable development of countries, regions and enterprises

The basis of this research consists of conceptual developments of a methodological nature that allow one to diagnose and assess the limitations, threats and challenges of an economic, social, environmental, resource-technical, administrative and legal nature across the vertical of the economic levels of an integral national system. The purpose of the paper is to formulate an original methodological approach to the research of economic security, considering the causal connection between the elements of the totality of individual determinants and conditions characterizing threats and challenges. The peculiarity of the proposed approach lies in the fact that the authors consider the enterprise as the initial level of the economic system. The economic security of an enterprise largely determines the economic security of other levels of this system. They represent the business environment that can be a carrier of external threats that negatively affect the economic security of the enterprise. We believe that without ensuring economic security at all levels of the economic hierarchy, it is impossible to ensure the implementation of the concept of sustainable development. The use of the matrix principle justifiably allows the authors to solve the evaluation problem within a single methodological approach. It allows identifying the determinants that most affect economic security. It is assumed that the diagnostic results will allow developing specific measures to eliminate or reduce the role of negative factors and motivational and stimulating measures that ensure the resolution of contradictions arising from the presence of restrictions, including environmental and social, on entrepreneurial activity

Парапроктиты: особенности этиологии и актуальные возможности периоперационной антибиотикопрофилактики

Paraproctitis is one of the most common nosologies in coloproctologist’s practice. The main treatment of this pathology is surgical, including dissection, debridement and drainage of the suppurative focus. However, in spite of surgical debridement, adequate perioperative antibiotic prophylaxis and, in rare and difficult cases, antibiotic therapy, are very important. Microbial spectrum obtained from the wound can be diverse, and, considering modern increase in the resistance of microorganisms, the decision on the prescription of effective antibiotic prophylaxis and therapy is not an easy task. In our study, that was carried out at the Municipal Clinical Hospital No. 24 of the Moscow Healthcare Department, we study the effectiveness of using the inhibitor-protected cephalosporin Ceftriaxone/Sulbactam as a drug for the perioperative prophylaxis and possible antibiotic therapy based on the results of microbiological culture. The obtained data show us that use of this drug is etiologically justified.Парапроктиты являются одной из наиболее часто встречающихся нозологий в практике колопроктолога. Основное лечение данной патологии - хирургическое, заключается во вскрытии, санации и дренировании гнойного очага. Но наряду с хирургической санацией весьма значительную роль играет проведение адекватной периоперационной антибиотикопрофилактики, а в редких и сложных случаях - антибиотикотерапии. Микробный пейзаж, высеиваемый из раны, при парапроктитах очень разнообразен, и, учитывая современный рост резистентности микроорганизмов, решение вопроса о назначении эффективной антибиотикопрофилактики и терапии представляется нелегкой задачей. В нашем исследовании, проведенном на базе ГБУЗ ГКБ № 24 ДЗМ, мы изучили целесообразность применения ингибитор-защищенного цефалоспорина Цефтриаксон / Сульбактам в качестве периоперационной профилактики и возможной антибактериальной терапии, основанной на результатах микробиологических посевов. Полученные данные показывают, что применение данного препарата этиологически оправдано