Improved linear response for stochastically driven systems

The recently developed short-time linear response algorithm, which predicts the average response of a nonlinear chaotic system with forcing and dissipation to small external perturbation, generally yields high precision of the response prediction, although suffers from numerical instability for long response times due to positive Lyapunov exponents. However, in the case of stochastically driven dynamics, one typically resorts to the classical fluctuation-dissipation formula, which has the drawback of explicitly requiring the probability density of the statistical state together with its derivative for computation, which might not be available with sufficient precision in the case of complex dynamics (usually a Gaussian approximation is used). Here we adapt the short-time linear response formula for stochastically driven dynamics, and observe that, for short and moderate response times before numerical instability develops, it is generally superior to the classical formula with Gaussian approximation for both the additive and multiplicative stochastic forcing. Additionally, a suitable blending with classical formula for longer response times eliminates numerical instability and provides an improved response prediction even for long response times

Large closed queueing networks in semi-Markov environment and its application

The paper studies closed queueing networks containing a server station and $k$ client stations. The server station is an infinite server queueing system, and client stations are single-server queueing systems with autonomous service, i.e. every client station serves customers (units) only at random instants generated by a strictly stationary and ergodic sequence of random variables. The total number of units in the network is $N$. The expected times between departures in client stations are $(N\mu_j)^{-1}$. After a service completion in the server station, a unit is transmitted to the $j$th client station with probability $p_{j}$ $(j=1,2,...,k)$, and being processed in the $j$th client station, the unit returns to the server station. The network is assumed to be in a semi-Markov environment. A semi-Markov environment is defined by a finite or countable infinite Markov chain and by sequences of independent and identically distributed random variables. Then the routing probabilities $p_{j}$ $(j=1,2,...,k)$ and transmission rates (which are expressed via parameters of the network) depend on a Markov state of the environment. The paper studies the queue-length processes in client stations of this network and is aimed to the analysis of performance measures associated with this network. The questions risen in this paper have immediate relation to quality control of complex telecommunication networks, and the obtained results are expected to lead to the solutions to many practical problems of this area of research.Comment: 35 pages, 1 figure, 12pt, accepted: Acta Appl. Mat

Pentaquark baryons in SU(3) quark model

We study the SU(3) group structure of pentaquark baryons which are made of four quarks and one antiquark. The pentaquark baryons form {1}, {8}, {10}, {10}-bar, {27}, and {35} multiplets in SU(3) quark model. First, the flavor wave functions of all the pentaquark baryons are constructed in SU(3) quark model and then the flavor SU(3) symmetry relations for the interactions of the pentaquarks with three-quark baryons and pentaquark baryons are obtained.Comment: REVTeX, 36 pages, 8 figures, references added, section for mass sum rules is added, to appear in Phys. Rev.

Joule Heating and Current-Induced Instabilities in Magnetic Nanocontacts

We consider the electrical current through a magnetic point contact in the limit of a strong inelastic scattering of electrons. In this limit local Joule heating of the contact region plays a decisive role in determining the transport properties of the point contact. We show that if an applied constant bias voltage exceeds a critical value, the stationary state of the system is unstable, and that periodic, non-harmonic oscillations in time of both the electrical current through the contact and the local temperature in the contact region develop spontaneously. Our estimations show that the necessary experimental conditions for observing such oscillations with characteristic frequencies in the range $10^8 \div 10^9$ Hz can easily be met. We also show a possibility to manipulate upon the magnetization direction of a magnetic grain coupled through a point contact to a bulk ferromagnetic by exciting the above-mentioned thermal-electric oscillations.Comment: 9 pages, 6 figures, submitted to Physical Review

On the construction of generalized Grassmann representatives of state vectors

Generalized $Z_k$-graded Grassmann variables are used to label coherent states related to the nilpotent representation of the q-oscillator of Biedenharn and Macfarlane when the deformation parameter is a root of unity. These states are then used to construct generalized Grassmann representatives of state vectors.Comment: 8 page

Entropy of semiclassical measures for nonpositively curved surfaces

We study the asymptotic properties of eigenfunctions of the Laplacian in the case of a compact Riemannian surface of nonpositive sectional curvature. We show that the Kolmogorov-Sinai entropy of a semiclassical measure for the geodesic flow is bounded from below by half of the Ruelle upper bound. We follow the same main strategy as in the Anosov case (arXiv:0809.0230). We focus on the main differences and refer the reader to (arXiv:0809.0230) for the details of analogous lemmas.Comment: 20 pages. This note provides a detailed proof of a result announced in appendix A of a previous work (arXiv:0809.0230, version 2

Вплив тіолових антиоксидантів на прояви ендотеліальної дисфункції в судинах головного мозку щурів з порушенням мозкового кровообігу

Modelling of brain blood circulation violation by means of bilateral occlusion of the common carotid artery caused the development of stable endothelial dysfunction, which is manifested in the increased level of homocysteine and nitrotyrosine. At the same time there was observed an increase of production of stable metabolites of nitric oxide and increased expression of neuronal and inducible NO-synthase. Holding pharmacotherapy thiotriazoline, α-lipoic acid, tiocetam and angiolin showed the ability of medications in varying degrees depress the manifestations of the endothelial dysfunction of cerebral vessels. The positive influence of medications manifested in limiting nitrosative stress, normalize homocysteine levels and the expression of NO-synthase. Revealed pathobiochemical effects, caused by the presence in the structure of these neuroprotectors of the thiol group, what allowing these medicines abridge oxidative damage to molecules and increase the bioavailability of nitric oxide in ischemia.Моделирование нарушения мозгового кровообращения с помощью двусторонней окклюзии общихсонных артерий вызывало развитие стабильной эндотелиальной дисфункции, которая проявлялась ввозрастании уровня гомоцистеина и нитротирозина. В то же время наблюдали увеличение продукциистабильных метаболитов оксида азота и повышение экспрессии нейрональной и индуцибельной NO -синтазы. Проведение фармакотерапии тиотриазолином, α-липоевой кислотой, тиоцетамом и ангио-лином продемонстрировало способность препаратов в той или иной степени подавлять проявленияэндотелиальной дисфункции сосудов головного мозга. Положительное влияние препаратов проявлялосьв ограничении нитрозативного стресса, нормализации уровня гомоцистеина и экспрессии нейрональнойNO -синтазы. Обнаружены патобиохимические эффекты, обусловленные наличием в структуре использо-ванных нейропротекторов тиольный группы, что позволяет этим препаратам снижать окислительноеповреждение молекул и повышать биодоступность оксида азота при ишемии.Моделювання порушення мозкового кровообігу за допомогою двосторонньої оклюзії загальних соннихартерій викликало розвиток стабільної ендотеліальної дисфункції, яка проявлялася зростанням рівнягомоцистеїну і нітротирозину. Водночас спостерігали збільшення продукції стабільних метаболітів ок-сиду азоту і підвищення експресії нейрональної та індуцибельної NO -синтази. Проведення фармакотерапіїтіотриазоліном, α-ліпоєвою кислотою, тіоцетамом і ангіоліном продемонструвало здатність препаратівтією чи іншою мірою пригнічувати прояви ендотеліальної дисфункції судин головного мозку. Позитивнийвплив препаратів полягав в обмеженні нітрозативного стресу, нормалізації рівня гомоцистеїну й експресіїнейрональної NO -синтази. Виявлено патобіохімічні ефекти, зумовлені наявністю в структурі використанихнейропротекторів тіольної групи, що дозволяє цим препаратам знижувати окисне пошкодження молекулта підвищувати біодоступність оксиду азоту за умов ішемії

Fragmentation channels of relativistic 7^7Be nuclei in peripheral interactions

Nuclei of $^7$Li were accelerated at the JINR Nuclotron. After the charge-exchange reaction involving these nuclei at an external target a second $^7$Be beam of energy 1.23A GeV was formed. This beam was used to expose photo-emulsion chambers. The mean free path for inelastic $^7$Be interactions in emulsion $\lambda$=14.0$\pm$0.8 cm coincides within the errors with those for $^6$Li and $^7$Li nuclei. More than 10% of the $^7$Be events are associated with the peripheral interactions in which the total charge of the relativistic fragments is equal to the charge of the $^7$Be and in which charged mesons are not produced. An unusual ratio of the isotopes is revealed in the composition of the doubly charged $^7$Be fragments: the number of $^3$He fragments is twice as large as that of $^4$He fragments. In 50% of peripheral interactions, a $^7$Be nucleus decays to two doubly charged fragments. The present paper gives the channels of the $^7$Be fragmentation to charged fragments. In 50% of events, the $^7$Be fragmentation proceeds only to charged fragments involving no emission of neutrons. Of them, the $^3$He+$^4$He channel dominates, the $^4$He+d+p and $^6$Li+pchannels constitute 10% each. Two events involving no emission of neutrons are registered in the 3-body $^3$He+t+p and $^3$He+d+d channels. The mean free path for the coherent dissociation of relativistic $^7$Be nuclei to $^3$He+$^4$He is 7$\pm$1 m. The particular features of the relativistic $^7$Be fragmentation in such peripheral interactions are explained by the $^3$He+$^4$He 2-cluster structure of the $^7$Be nucleus.Comment: 10 pages, 3 figures, 3 tables, conference: Conference on Physics of Fundamental Interactions, Moscow, Russia, 5-9 Dec 200