Coherent responses of resonance atom layer to short optical pulse excitation

Coherent responses of resonance atom layer to short optical pulse excitation are numerically considered. The inhomogeneous broadening of one-photon transition, the local field effect, and the substrate dispersion are involved into analysis. For a certain intensity of incident pulses a strong coherent interaction in the form of sharp spikes of superradiation is observed in transmitted radiation. The Lorentz field correction and the substrate dispersion weaken the effect, providing additional spectral shifts. Specific features of photon echo in the form of multiple responses to a double or triple pulse excitation is discussed.Comment: only PDF,15 page

Botulinum therapy using in the complex treatment of children with the result of the brachial plexus intranatal injury (literature review)

The incidence of plexus brachial birth injuries consists 0.12 % of births (0.04–0.20 %). Although the possibility of complete recovery is relatively high, 10–30 % patients have secondary deformity and limitation of upper limb function due to muscle imbalance and co-contraction around the shoulder and elbow cause abnormal motor performance, osseous deformities and joint contracture. Botulinum toxin type A injections into targeted muscles in combination with occupation therapy, physiotherapy or operative treatment reduce the abnormal cocontraction of the antagonist muscles and help to restore muscles balance and prevent secondary deformities. The article discuses indications for botulinum injection therapy, target muscles, doses of botulinum toxin A, optimal patient’s age and results of treatment

Conversion of terahertz wave polarization at the boundary of a layered superconductor due to the resonance excitation of oblique surface waves

We predict a complete TM-TE transformation of the polarization of terahertz electromagnetic waves reflected from a strongly anisotropic boundary of a layered superconductor. We consider the case when the wave is incident on the superconductor from a dielectric prism separated from the sample by a thin vacuum gap. The physical origin of the predicted phenomenon is similar to the Wood anomalies known in optics, and is related to the resonance excitation of the oblique surface waves. We also discuss the dispersion relation for these waves, propagating along the boundary of the superconductor at some angle with respect to the anisotropy axis, as well as their excitation by the attenuated-total-reflection method.Comment: 4 pages, 5 figure

Nonmonotonic energy harvesting efficiency in biased exciton chains

We theoretically study the efficiency of energy harvesting in linear exciton chains with an energy bias, where the initial excitation is taking place at the high-energy end of the chain and the energy is harvested (trapped) at the other end. The efficiency is characterized by means of the average time for the exciton to be trapped after the initial excitation. The exciton transport is treated as the intraband energy relaxation over the states obtained by numerically diagonalizing the Frenkel Hamiltonian that corresponds to the biased chain. The relevant intraband scattering rates are obtained from a linear exciton-phonon interaction. Numerical solution of the Pauli master equation that describes the relaxation and trapping processes, reveals a complicated interplay of factors that determine the overall harvesting efficiency. Specifically, if the trapping step is slower than or comparable to the intraband relaxation, this efficiency shows a nonmonotonic dependence on the bias: it first increases when introducing a bias, reaches a maximum at an optimal bias value, and then decreases again because of dynamic (Bloch) localization of the exciton states. Effects of on-site (diagonal) disorder, leading to Anderson localization, are addressed as well.Comment: 9 pages, 6 figures, to appear in Journal of Chemical Physic

Polarizable molecular interactions in condensed phase and their equivalent nonpolarizable models

Earlier, using phenomenological approach, we showed that in some cases polarizable models of condensed phase systems can be reduced to nonpolarizable equivalent models with scaled charges. Examples of such systems include ionic liquids, TIPnP-type models of water, protein force fields, and others, where interactions and dynamics of inherently polarizable species can be accurately described by nonpolarizable models. To describe electrostatic interactions, the effective charges of simple ionic liquids are obtained by scaling the actual charges of ions by a factor of 1/sqrt(eps_el), which is due to electronic polarization screening effect; the scaling factor of neutral species is more complicated. Here, using several theoretical models, we examine how exactly the scaling factors appear in theory, and how, and under what conditions, polarizable Hamiltonians are reduced to nonpolarizable ones. These models allow one to trace the origin of the scaling factors, determine their values, and obtain important insights on the nature of polarizable interactions in condensed matter systems.Comment: 43 pages, 3 figure

Localized boundary-domain singular integral equations based on harmonic parametrix for divergence-form elliptic PDEs with variable matrix coefficients

This is the post-print version of the Article. The official publised version can be accessed from the links below. Copyright @ 2013 Springer BaselEmploying the localized integral potentials associated with the Laplace operator, the Dirichlet, Neumann and Robin boundary value problems for general variable-coefficient divergence-form second-order elliptic partial differential equations are reduced to some systems of localized boundary-domain singular integral equations. Equivalence of the integral equations systems to the original boundary value problems is proved. It is established that the corresponding localized boundary-domain integral operators belong to the Boutet de Monvel algebra of pseudo-differential operators. Applying the Vishik-Eskin theory based on the factorization method, the Fredholm properties and invertibility of the operators are proved in appropriate Sobolev spaces.This research was supported by the grant EP/H020497/1: "Mathematical Analysis of Localized Boundary-Domain Integral Equations for Variable-Coefficient Boundary Value Problems" from the EPSRC, UK

Tunable disorder in a crystal of cold polar molecules

In the present work, we demonstrate the possibility of controlling by an external field the dynamics of collective excitations (excitons) of molecules on an optical lattice. We show that a suitably chosen two-species mixture of ultracold polar molecules loaded on an optical lattice forms a phononless crystal, where exciton-impurity interactions can be controlled by applying an external electric field. This can be used for the controlled creation of many-body entangled states of ultracold molecules and the time-domain quantum simulation of disorder-induced localization and delocalization of quantum particles

Feasibility and challenges of performing magnetoencephalography experiments in children with arthrogryposis multiplex congenita

Arthrogryposis multiplex congenita (AMC) has recently drawn substantial attention from researchers and clinicians. New effective surgical and physiotherapeutic methods have been developed to improve the quality of life of patients with AMC. While it is clear that all these interventions should strongly rely on the plastic reorganization of the central nervous system, almost no studies have investigated this topic. The present study demonstrates the feasibility of using magnetoencephalography (MEG) to investigate brain activity in young AMC patients. We also outlined the general challenges and limitations of electrophysiological investigations on patients with arthrogryposis. We conducted MEG recordings using a 306-channel Elekta Neuromag VectorView system during a cued motor task performance in four patients with arthrogryposis, five normally developed children, and five control adults. Following the voice command of the experimenter, each subject was asked to bring their hand toward their mouth to imitate the self-feeding process. Two patients had latissimus dorsi transferred to the biceps brachii position, one patient had a pectoralis major transferred to the biceps brachii position, and one patient had no elbow flexion restoration surgery before the MEG investigation. Three patients who had undergone autotransplantation prior to the MEG investigation demonstrated activation in the sensorimotor area contralateral to the elbow flexion movement similar to the healthy controls. One patient who was recorded before the surgery demonstrated subjectively weak distributed bilateral activation during both left and right elbow flexion. Visual inspection of MEG data suggested that neural activity associated with motor performance was less pronounced and more widely distributed across the cortical areas of patients than of healthy control subjects. In general, our results could serve as a proof of principle in terms of the application of MEG in studies on cortical activity in patients with AMC. Reported trends might be consistent with the idea that prolonged motor deficits are associated with more difficult neuronal recruitment and the spatial heterogeneity of neuronal sources, most likely reflecting compensatory neuronal mechanisms. On the practical side, MEG could be a valuable technique for investigating the neurodynamics of patients with AMC as a function of postoperative abilitation

Использование ботулинотерапии в комплексном лечении детей с последствием интранатальной травмы плечевого сплетения (обзор литературы)

The incidence of plexus brachial birth injuries consists 0.12 % of births (0.04–0.20 %). Although the possibility of complete recovery is relatively high, 10–30 % patients have secondary deformity and limitation of upper limb function due to muscle imbalance and co-contraction around the shoulder and elbow cause abnormal motor performance, osseous deformities and joint contracture. Botulinum toxin type A injections into targeted muscles in combination with occupation therapy, physiotherapy or operative treatment reduce the abnormal cocontraction of the antagonist muscles and help to restore muscles balance and prevent secondary deformities. The article discuses indications for botulinum injection therapy, target muscles, doses of botulinum toxin A, optimal patient’s age and results of treatment.Частота интранатальной травмы плечевого сплетения составляет 0,12 % (0,04–0,20 %) всех новорожденных. Хотя вероятность полного выздоровления относительно высока, у 10–30 % пациентов наблюдаются вторичная деформация и ограничение функции верхней конечности вследствие дисбаланса мышц плечевого пояса, плеча, коконтракции, что приводит к двигательным нарушениям, возникновению контрактур суставов, а также деформации костей. Инъекции ботулинического токсина типа А в мышцы-мишени в сочетании с лечебной физкультурой, физиотерапией или оперативным лечением помогают восстановить мышечный баланс, устранить коконтракцию мышц-антагонистов, предотвратить вторичные деформации. В статье рассматриваются показания к ботулинотерапии, мышцы-мишени, дозы ботулинического токсина А, оптимальный возраст пациента и результаты лечения

Коконтракция у больных с последствиями интранатальной травмы плечевого сплетения (обзор литературы)

The frequency of obstetric palsy ranges from 0.5 to 3.0 cases per 1000 live births. The functional outcome disorders are determined by the nature of the damage and the number of damaged roots of the brachial plexus. There are 50 % of patients have complete recovery, 15 % have severe functional disorders of the upper limb, and 35 % have some limitation of the shoulder joint function. There are 3 variants of residual phenomena in children with obstetric palsy: paresis, paralysis, and co‑contraction. The article describes the mechanisms of nerve regeneration in children and adults, the pathogenesis of contractions and motor disorders in general in children with obstetric palsy, and modern methods of treatment of co‑contraction. This article will be useful for neurologists, rehabilitation specialists, and orthopedists.Частота интранатального повреждения плечевого сплетения, по данным литературы, варьирует от 0,5 до 3 случаев на 1 тыс. живорожденных. Возникающие при повреждении изменения функции верхней конечности (от временных до пожизненных) определяются характером повреждения и числом поврежденных корешков плечевого сплетения. В отдаленные сроки после травмы у около 50 % пациентов наблюдается полное восстановление, у 15 % отмечаются тяжелые функциональные нарушения руки, и у 35 % сохраняется некоторое ограничение функции плечевого сустава. Различают 3 варианта резидуальных явлений у больных с акушерскими параличами: парез, паралич, коконтракция. В статье рассмотрены механизмы регенерации нервов у детей и у взрослых, патогенез коконтракции и двигательных нарушений у детей с последствиями интранатальной травмы плечевого сплетения в целом, а также современные методы лечения коконтракции