Extremely high absolute internal quantum efficiency of photoluminescence in co-doped GaN:Zn,Si

We report on the fabrication of GaN co-doped with silicon and zinc by metalorganic vapor phase epitaxy and a detailed study of photoluminescence in this material. We observe an exceptionally high absolute internal quantum efficiency of blue photoluminescence in GaN:Zn,Si. The value of0.93±0.04 has been obtained from several approaches based on rate equations

Determination of the absolute internal quantum efficiency of photoluminescence in GaN co-doped with Si and Zn

The optical properties of high-quality GaN co-doped with silicon and zinc are investigated by using temperature-dependent continuous-wave and time-resolved photoluminescence measurements. The blue luminescence band is related to the ZnGa acceptor in GaN:Si,Zn, which exhibits an exceptionally high absolute internal quantum efficiency (IQE). An IQE above 90% was calculated for several samples having different concentrations of Zn. Accurate and reliable values of the IQE were obtained by using several approaches based on rate equations. The concentrations of the ZnGa acceptors and free electrons were also estimated from the photoluminescence measurements

A critical role of tropomyosins in TGF-beta regulation of the actin cytoskeleton and cell motility in epithelial cells

We have investigated transforming growth factor beta (TGF-beta)-mediated induction of actin stress fibers in normal and metastatic epithelial cells. We found that stress fiber formation requires de novo protein synthesis, p38Mapk and Smad signaling. We show that TGF-beta via Smad and p38Mapk up-regulates expression of actin-binding proteins including high-molecular-weight tropomyosins, alpha-actinin and calponin h2. We demonstrate that, among these proteins, tropomyosins are both necessary and sufficient for TGF-beta induction of stress fibers. Silencing of tropomyosins with short interfering RNAs (siRNAs) blocks stress fiber assembly, whereas ectopic expression of tropomyosins results in stress fibers. Ectopic-expression and siRNA experiments show that Smads mediate induction of tropomyosins and stress fibers. Interestingly, TGF-beta induction of stress fibers was not accompanied by changes in the levels of cofilin phosphorylation. TGF-beta induction of tropomyosins and stress fibers are significantly inhibited by Ras-ERK signaling in metastatic breast cancer cells. Inhibition of the Ras-ERK pathway restores TGF-beta induction of tropomyosins and stress fibers and thereby reduces cell motility. These results suggest that induction of tropomyosins and stress fibers play an essential role in TGF-beta control of cell motility, and the loss of this TGF-beta response is a critical step in the acquisition of metastatic phenotype by tumor cells

Functional Expression of the Heteromeric “Olfactory” Cyclic Nucleotide-Gated Channel in the Hippocampus: A Potential Effector of Synaptic Plasticity in Brain Neurons

Cyclic nucleotide-gated (cng) channels are important components of signaling systems mediating sensory transduction. In vertebrate photoreceptors, light activates a signaling cascade that causes a decrease in intracellular cGMP concentrations, closing retinal cng channels. Signal transduction in olfactory receptor neurons is believed to proceed via G-protein-mediated elevation of intracellular cAMP in response to odorant binding by 7-helix receptors. cAMP opens the olfactory cng channel, which is highly permeable to Ca^(2+). Here we demonstrate by in situ hybridization and immunohistochemistry with subunit-specific antibodies that both subunits of the heteromeric rat olfactory cng channel are also widely expressed in the brain. Expression of the retinal rod cng channel, however, can be detected only in the eye. In the adult hippocampus, the olfactory cng channel is expressed on cell bodies and processes of CA1 and CA3 neurons. In cultured embryonic hippocampal neurons, the channel is localized to a subset of growth cones and processes. We recorded conductances with the electrophysiological characteristics of the heteromeric olfactory cng channel in excised inside-out patches from these cultured neurons. We also show that Ca^(2+) influx into hippocampal neurons in response to cyclic nucleotide elevation can be detected using fura-2 imaging. Cyclic nucleotide elevation has been implicated in several mechanisms of synaptic plasticity in the hippocampus, and these mechanisms also require elevation of intracellular Ca^(2+). Our results suggest that the “olfactory” cng channel could regulate synaptic efficacy in brain neurons by modulating Ca^(2+) levels in response to changes in cyclic nucleotide concentrations

Calibration of Local Volatility Model with Stochastic Interest Rates by Efficient Numerical PDE Method

Long maturity options or a wide class of hybrid products are evaluated using a local volatility type modelling for the asset price S(t) with a stochastic interest rate r(t). The calibration of the local volatility function is usually time-consuming because of the multi-dimensional nature of the problem. In this paper, we develop a calibration technique based on a partial differential equation (PDE) approach which allows an efficient implementation. The essential idea is based on solving the derived forward equation satisfied by P(t; S; r)Z(t; S; r), where P(t; S; r) represents the risk neutral probability density of (S(t); r(t)) and Z(t; S; r) the projection of the stochastic discounting factor in the state variables (S(t); r(t)). The solution provides effective and sufficient information for the calibration and pricing. The PDE solver is constructed by using ADI (Alternative Direction Implicit) method based on an extension of the Peaceman-Rachford scheme. Furthermore, an efficient algorithm to compute all the corrective terms in the local volatility function due to the stochastic interest rates is proposed by using the PDE solutions and grid points. Different numerical experiments are examined and compared to demonstrate the results of our theoretical analysis

Parameters of loading equilibration in a tube cold pilger mill drive

On the basis of the variational approach and the Gauss-Seidel method there are proposed a technique and a mathematical model for determining the optimal parameters of dynamic load balancing systems on the crankshaft on the example of the cold rolling mill tube with reciprocating motion of an executive element in the form of a large mass working stand. The most compact scheme with the orthogonal motion of the executive element and the balancing load was chosen as the dynamic balance system. Variable parameters include dezaxial values, misalignment angle of cranks, weight of counterweight and balancing weight, lengths of connecting rods of executive and balancing mechanisms. For the existing series of sizes of cold rolling tube mill as the mass and speed of the rolling stand increase, the proportion of dynamic and technological components of the reduced load and respectively the kinematic scheme of the balancing mechanism changes. In this case, the structure of the loading and a set of variable parameters remain unchanged. Therefore, the proposed mathematical model of dynamic programming retains the universality of finding the minimum of maximum of the resulting load. © Published under licence by IOP Publishing Ltd

Расчёт влияния гармоник тягового тока на рельсовую цепь

[For the English abstract and full text of the article please see the attached PDF-File (English version follows Russian version)].ABSTRACT Track circuits, as well as other elements of railway automation, are in the zone of influence of electric rolling stock and, in particular, of traction current. In terms of electromagnetic compatibility this is an area of risk that requires specific tools of study and control. Mathematical description has been developed to calculate the influence of harmonics of traction current, flowing in the contact wire of adjacent track of double-track sections, and of its harmonic components, on track circuits. Equivalent circuit and system of differential equations are shown, which are designed to solve problems to ensure operational reliability of a railway line. Keywords: railway, electromagnetic compatibility, mathematical description, track circuit, traction current harmonics, contact wire, adjacent track.Рельсовые цепи, как и другие элементы железнодорожной автоматики, находятся в зоне влияния электроподвижного состава и, в частности, тягового тока. С точки зрения электромагнитной совместимости - это зона риска, требующая своих средств изучения и контроля. Разработано математическое описание для расчёта влияния гармоник тягового тока, протекающего в контактном проводе смежного пути двухпутных участков, и его гармонических составляющих на рельсовые цепи. Показаны схема замещения и система дифференциальных уравнений, которые призваны решать задачи обеспечения эксплуатационной надёжности железнодорожной линии