Retrial Queuing Models of Multi-Wavelength FDL Feedback Optical Buffers

Cataloged from PDF version of article.Optical buffers based on Fiber Delay Lines (FDL) have been proposed for contention resolution in optical packet/burst switching systems. In this article, we propose a retrial queuing model for FDL optical buffers in asynchronous optical switching nodes. In the considered system, the reservation model employed is of post-reservation type and optical packets are allowed to re-circulate over the FDLs in a probabilistic manner. We combine the MMPP-based overflow traffic models of the classical circuit switching literature and fixed-point iterations to devise an algorithmic procedure to accurately estimate blocking probabilities as a function of various buffer parameters in the system when packet arrivals are Poisson and packet lengths are exponentially distributed. The proposed algorithm is both accurate and fast, allowing one to use the procedure to dimension optical buffers in next-generation optical packet switching systems

System-theoretical algorithmic solution to waiting times in semi-Markov queues

Cataloged from PDF version of article.Markov renewal processes with matrix-exponential semi-Markov kernels provide a generic tool for modeling auto-correlated interarrival and service times in queueing systems. In this paper, we study the steady-state actual waiting time distribution in an infinite capacity single-server semi-Markov queue with the auto-correlation in interarrival and service times modeled by Markov renewal processes with matrix-exponential kernels. Our approach is based on the equivalence between the waiting time distribution of this semi-Markov queue and the output of a linear feedback interconnection system. The unknown parameters of the latter system need to be determined through the solution of a SDC (Spectral-Divide-and-Conquer) problem for which we propose to use the ordered Schur decomposition. This approach leads us to a completely matrix-analytical algorithm to calculate the steady-state waiting time which has a matrix-exponential distribution. Besides its unifying structure, the proposed algorithm is easy to implement and is computationally efficient and stable. We validate the effectiveness and the generality of the proposed approach through numerical examples. © 2009 Elsevier B.V. All rights reserve

Guanine nucleotide-dependent carboxymethylation: A pathway for aldosterone modulation of apical Na+ permeability in epithelia

A number of recent reviews have dealt extensively with the characteristics of epithelial Na+ channels and their classification according to level of conductance, selectivity for sodium, and sensitivity to amiloride and hormones [1 to 6, this issue]. In the present review, we will focus on Na+ transport regulation by aldosterone in terms of the biochemical pathways involved in the hormone's action on apical Na+ permeability in epithelia.Active transport of Na+ across epithelial tissues is the primary physiological process responsible for maintenance of salt balance in vertebrates. Entry of Na+ into cells at the apical membrane occurs passively by electrodiffusion through amiloride-blockable channels. Intracellular Na+ concentration remains low due to active extrusion across the basolateral membrane in exchange for K+. Aldosterone is the key hormone for long-term regulation of this process in the distal tubule of the kidney and other responsive “high resistance” model epithelia such as toad urinary bladder, frog skin, and A6 cultured cells derived from toad kidney [7, 8]. Its mode of action is complex involving a number of biochemical pathways, and some or possibly all of them ultimately increase the transepithelial Na+ transport rate. Aldosterone increases both the apical Na+ permeability and the number of basolateral pump sites albeit with different time courses and through distinct pathways [9–12].The increase of apical Na+ permeability in response to aldosterone is due to an increase in the number of open Na+ channels in this membrane with virtually no change in channel selectivity or conductance [10, 13]. Stimulation of transport begins after a lag time of 20 to 40 minutes and is maximal within four to six hours of exposure to the hormone. Aldosterone, a steroid hormone, enters cells by diffusion, is bound by an intracellular receptor, migrates to the nucleus, and gives rise to a variety of gene products commonly termed AIPs (aldosterone-induced proteins; cf. Fig. 1), which in turn lead to the various physiological responses. This scheme is supported by observations that increased Na+ transport after aldosterone is abolished by inhibitors of protein or RNA synthesis [14]. It is currently unknown whether any of the AIPs represent apical Na+ channels per se or subunits of these channels. This seems unlikely however in view of overwhelming electrical and biochemical data consistent with the idea that aldosterone stimulates channels pre-existing in the membrane [13, 15–18]. In addition, membrane targeting, channel assembly from subunits, and insertion of these complex molecules into the membrane, would likely take several hours as observed for the basolateral response where it has been demonstrated that pumps are synthesized and inserted over many hours or days [11, 12]. This would seem less plausible at the apical membrane where the more rapid initial increase in permeability occurs within 30 minutes. However, a polypeptide of Mr 70 kD, identified as a component of the Na+ channel, was shown to be induced by aldosterone [19]. Whether this polypeptide represents part of the channel or a regulatory protein is presently unknown.The sequence of events leading to increased channel density following synthesis of AIPs is not understood. However, a number of mechanisms modulate or mediate aldosterone's stimulation of apical Na+ permeability. (1) Activation of phospholipase A increases phospholipid fatty acid metabolism. (2) Methylation of apical proteins and lipids increases amiloride-sensitive Na+ transport. (3) Guanine nucleotides regulate the aldosterone-induced carboxymethylation.These pathways are not mutually exclusive and indeed may represent only a small portion of the complete picture of aldosterone's influence at the apical membrane. Each of these is considered separately below

Prediction of new chromene-based inhibitors of tubulin using structure-based virtual screening and molecular dynamics simulation methods

Multidrug resistance (MDR) is one of the serious problems in cancer research that causes failure in chemotherapy. Chromene-based compounds have been proven to be the novel anti-MDR agents for inhibiting proliferation of tumor cells through tubulin polymerization inhibition of by binding at the colchicine binding site. In this study, we screened a chromene-based database of small molecules using physicochemical, ADMET properties and molecular docking to identify potential hit compounds. In order to validate our hit compounds, molecular dynamics simulations and related analysis were carried out and the results suggest that our hit compounds (PubChem CIDs: 16814409, 17594471, 57367244 and 69899719) can prove to be potential inhibitors of tubulin. The in silico results show that the present hits, like colchicine, effectively suppressed the dynamic instability of microtubules and induced microtubuledepolymerization and cell cycle arrest

Summer Savory: From the Selection of Traditional Applications to the Novel Effect in Relief, Prevention, and Treatment of a Number of Serious Illnesses such as Diabetes, Cardiovascular Disease, Alzheimer’s Disease, and Cancer

ABSTRACTSavory (Satureja L.) plant species have been used for centuries as culinary herbs and spices, as well as traditional remedies for the treatment or relief of various common health symptoms in many parts of the world. Recent studies suggest that the use of some Satureja species is effective in protecting the body against oxidative stress, free radical damage, inflammation, microbial infections, etc., A review of many studies suggests that savory species, in addition to treating minor ordinary ailments, can potentially provide a novel natural prevention or treatment for some chronic and serious illnesses such as diabetes, cardiovascular diseases, cancer, and Alzheimer’s

effectiveness of their teaching skills to reduce stress job psychological empowerment of nursing staff in intensive care units in the center of Shiraz Shahid Rajaee 1392 .

Background and aims: Nurses of critical care wards are faced with a number of stressors that could also threaten the ability of those affected various aspects of health and undermine the quality of their performance. The role of psychological empowerment skills training to reduce stress among working nurses in intensive care wards is unknown. This research was aimed to determine the efficacy of psychological empowerment skills training to reduce stress among working nurses in intensive care wards in medical center of Shahid Rajaee in Shiraz was conducted in 2013. Methods: In this quasi-experimental study, 120 working nurses in intensive care wards randomly divided into interventional and control groups. Then, the workshop of self-empowerment skills training was performed for experimental group and a month after their training psychological empowerment, data were collectd using Osipow questionnaire in both groups. Data was analyzed using SPSS software and t-test, ANOVA, paired t-test, Chi-square and Mann-Whitney tests. Results: The mean score of job stress before training in the control group was 256.68±14.81 in intense level and after training) without training was 265.8±5.16 in severe level. Mean stress scores before training in the intervention group was 269.26±6.18 in intense level and after training was 251.70±17.97 in moderate level. There were significant differences between stress score mean before and after intervention (P=0.002). Conclusion: According to existing stress in the nursing profession; psychological empowerment can be effective to reduce stress and increase the quality of their nurses

TELPACK: An Advanced teletraffic analysis package

Performance evaluation of computer and communication networks gives rise to teletraffic problems of potentially large dimensionality. We briefly summarize a unifying system theoretic approach to efficient solution of a diversity of such problems, and introduce TELPACK, a publicly available software that implements this approach

Matrix-geometric solutions of M/G/1-type Markov chains: A unifying generalized state-space approach

In this paper, we present an algorithmic approach to find the stationary probability distribution of M/G/1-type Markov chains which arise frequently in performance analysis of computer and communication networ ks. The approach unifies finite- and infinite-level Markov chains of this type through a generalized state-space representation for the probability generating function of the stationary solution. When the underlying probability generating matrices are rational, the solution vector for level k, x k, is shown to be in the matrix-geometric form x k+1 = gF k H, k ≥ 0, for the infinite-level case, whereas it takes the modified form x k+1 = g 1F 1 kH 1 + g 2F 2 K-k-1 H 2, 0 ≤ k < K, for the finite-level case. The matrix parameters in the above two expressions can be obtained by decomposing the generalized system into forward and backward subsystems, or, equivalently, by finding bases for certain generalized invariant subspaces of a regular pencil λE - A. We note that the computation of such bases can efficiently be carried out using advanced numerical linear algebra techniques including matrix-sign function iterations with quadratic convergence rates or ordered generalized Schur decomposition. The simplicity of the matrix-geometric form of the solution allows one to obtain various performance measures of interest easily, e.g., overflow probabilities and the moments of the level distribution, which is a significant advantage over conventional recursive methods