45 research outputs found

    Asymptotic analysis of retrial queueing system M/M/1 with non-persistent customers and collisions

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    A queuing system with repeated calls, one server, collisions (conflicts) of calls, H-persistence and rejections is considered. A call that found the device free occupies it, and service begins, which ends successfully if no other requests were received during it. If the server is busy, then a conflict (collision) arises between the call that have come for service and the ones being serviced, and in the general case, both calls instantly go to the orbit and repeat the attempt to successfully serve after a random time. In this article, in the event of a collision, one of the calls, for example, which was in service (on the device), goes into the orbit with probability H1, the other goes into orbit with probability H2, and with probability (1−H1) and (1−H2) respectively refuses service and leaves the system. The problem is to find asymptotic probabilities distribution of the calls number in the orbit

    Elemental speciation of the sediments from cold methane seeps on the Laptev Sea shelf

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    Relevance. The lack of elemental speciation data in the bottom sediments of the Laptev Sea, as well as the absence of its quantitative changes in occurrence forms in response to methane emissions. Aim. To assess changes in the elemental speciation in areas where methane-containing fluids are discharged. Objects. Nine samples of bottom sediments taken from three horizons of one “cold seep” and two background stations of the outer shelf-continental slope of the Laptev Sea during the AMK-82 expedition aboard R/V “Academician M.V. Keldysh” in autumn 2020. Methods. Sequential extraction BCR (the European Community Bureau of Reference) was performed to determine the elemental speciation in surface sediments; the residual fraction was determined by dissolving in nitric acid. The obtained fraction solutions were analyzed by ICP-MS (NexIon 300D, Perkin Elmer, Waltham, MA, USA), Pyrolysis (Rock-Eval 6 Turbo, Vinci Technologies). Results. The trend towards an increase in element mobility has been identified as a result of a shift in geochemical conditions that is presumably caused by the authigenic carbonate and sulfide formation. Moreover, the increase in the recoverable fraction (associated only with Fe oxides/hydroxides) is highlighted. We assume that the process of unloading methane-containing fluids plays a significant role in enrichment of authigenic carbonates U, Ni, Zn Co, oxides Fe – Sn and V, authigenic sulfides – Co, Mn and W. We also assume the potential formation of chalcopyrite as an authigenic sulfide in methane discharge areas

    Indole-3-carbinol-induced modulation of NF-kB signalling is breast cancer cell-specific and does not correlate with cell death

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    Indole-3-carbinol (I3C), a dietary chemopreventive compound, induces cell death in human breast cancer cells by modulating activities of Src and epidermal growth factor receptor (EGFR). The effect of I3C on NF-κB, constitutively activated in breast cancer cells, was investigated. Nuclear extracts of MDA-MB-468, MDA-MB-231 and HBL100 cells contained all of the Rel proteins with similar expression patterns in the latter two. The level of NF-κB-regulated reporter gene expression was in the order HBL100 << MDA-MB-468 << MDA-MB-231. Upstream inhibition, using PI3K, EGFR or IKKβ inhibitors, resulted in cell-specific effects on expression of the NF-κB-regulated reporter gene and endogenous genes Bcl-xL, IκBα and IL-6, as well as on cell viability. The expression patterns of Rel and several NF-κB-regulated genes and the response to LY249002 in MDA-MB-468 cells contrasted with those in other cells. I3C induced NF-κB-regulated reporter gene expression at 12 h in MDA-MB-468 cells. Conversely, it was reduced at 24 h in HBL100 cells. I3C treatment for 6 h alone or in combination with TNFα induced NF-κB-regulated reporter gene expression, detected 5 h later, in MDA-MB-468, but not HBL100 cells. I3C induced NF-κB p65/p50 DNA binding at 6.5 h, preceded by association of IKKβ with the Src/EGFR complex and increased phospho-IκBα in MDA-MB468 cells. TNFα increased I3C-induced apoptosis in MDA-MB-468 and MDA-MB-231 cells. It also induced apoptosis, enhanced by I3C, in HBL100 cells. Hence, regulation of constitutive NF-κB was cell-specific. I3C influenced the NF-κB pathway in a cell-specific manner, which was not related to apoptosis. However, the combination of I3C and TNFα increased apoptosis in all cell lines

    Asymptotic Analysis of Retrial Queueing System M/M/1 with Impatient Customers, Collisions and Unreliable Server

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    The retrial queueing system of M=M=1 type with Poisson flow of arrivals, impatient cus- tomers, collisions and unreliable service device is considered in the paper. The novelty of our contribution is the inclusion of breakdowns and repairs of the service into our previous study to make the problem more realistic and hence more complicated. Retrial time of customers in the orbit, service time, impa- tience time of customers in the orbit, server lifetime (depending on whether it is idle or busy) and server recovery time are supposed to be exponentially distributed. An asymptotic analysis method is used to find the stationary distribution of the number of customers in the orbit. The heavy load of the system and long time patience of customers in the orbit are proposed as asymptotic conditions. Theorem about the Gaussian form of the asymptotic probability distribution of the number of customers in the orbit is formulated and proved. Numerical examples are given to show the accuracy and the area of feasibility of the proposed metho

    Dietary Chemopreventive Phytochemicals: Too Little or Too Much?

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    There is a large body of evidence that the consumption of fruit and vegetables can decrease the risk of cancer. However, the link between diet and health is extremely complex. Some dietary phytochemicals seem to offer protection in an exposure-related manner and many molecular targets and signaling pathways affected by phytochemicals have been discovered. Although in vitro studies have contributed significantly to our understanding, quite a number use concentrations orders of magnitude greater than those achievable in humans or toxic to normal tissues (exemplified by toxic concentrations of indole-3-carbinol, epigallocatechin-3-gallate, curcumin, and genistein for breast cells). Such studies may produce results that are physiologically irrelevant, thus hindering predictions of efficacy. Here, we argue for careful consideration to be given to the in vitro experimental conditions under which dietary phytochemicals are investigated. Design features, such as the use of appropriate nontoxic concentrations, extended treatment times, three-dimensional cultures, primary tumor cultures, and comparison of susceptibility of various cancer subtypes, should improve our understanding of their molecular targets. This in turn would facilitate predictions as to their potential usefulness in the clinic

    Asymptotic diffusion analysis of an retrial queueing system M/M/1 with impatient calls

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    In the paper, the retrial queueing system of M/M/1 type with input Poison flow of events and impatient calls is considered. The service time, delay time of calls in the orbit and the impatience time of calls in the orbit have exponential distribution. Asymptotic diffusion analysis method is proposed for the solving problem of finding distribution of the number of calls in the orbit under a long delay of calls in orbit and long time patience of calls in the orbit condition

    Analysis of retrial queueing system M/G/1 with impatient customers, collisions and unreliable server using simulation

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    In this paper, we consider a retrial queueing system of M/G/1 type with an unreliable server, collisions, and impatient customers. The novelty of our work is to carry out a sensitivity analysis applying different distributions of service time of customers on significant performance measures for example on the probability of abandonment, the mean waiting time of an arbitrary, successfully served, impatient customer, etc. A customer is able to depart from the system in the orbit if it does not get its appropriate service after a definite random waiting time so these will be the so-called impatient customers. In the case of server failure, requests are allowed to enter the system but these will be forwarded immediately towards the orbit. The service, retrial, impatience, operation, and repair times are supposed to be independent of each other. Several graphical illustrations demonstrate the comparisons of the investigated distributions and the interesting phenomena which are obtained by our self-developed simulation program. The achieved results are compared to the results of the [2] to check how the system characteristics changes if we use other distributions of service time and to present the advantages of performing simulations in certain scenarios

    EGFR and Src are involved in indole-3-carbinol-induced death and cell cycle arrest of human breast cancer cells

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    Indole-3-carbinol (I3C), a dietary chemopreventive compound, induced marked reduction in epidermal growth factor receptor (EGFR) prior to cell death in cells representing three breast cancer subtypes. Signalling pathways, linking these events were investigated in detail. I3C modulated tyrosine phosphorylation from 30 min in four cell lines. In MDA-MB-468 and HBL100 cells, it induced Src activation after 5 h. In MDA-MB-468 cells, I3C induced signalling between 4.5 and 7 h, which involved sequential activation of Src, EGFR, STAT-1 and STAT-3, followed by EGFR degradation. It also induced physical association between activated Src and EGFR. In MCF7 and MDA-MB-231 cells, I3C modulated expression of cell cycle-related proteins, p21Cip1, p27Kip1, cyclin E, cyclin D1 and CDK6, with upregulation of p21Cip1 and cyclin E being dependent on Src. Inhibition of EGFR by specific inhibitors PD153035 or ZD1839 increased susceptibility to I3C-induced apoptosis of MCF7, MDA-MB-468 and MDA-MB-231 cells. Inhibition of Src sensitized MDA-MB-468 and MDA-MB-231 cells to I3C, whereas overexpression of c-Src increased resistance to I3C in MDA-MB-468 and HBL100 cells. Modulation of Src in MDA-MB-468 cells influenced the basal level of EGFR expression and cell viability; the latter being positively correlated with EGFR activation levels. Therefore, EGFR and Src activities are essential for I3C-induced cell cycle arrest and death; however, I3C-induced pathways depend on specific features of breast cancer cells. The cancer types, which rely on ‘EGFR addiction’ or Src deregulation, are likely to be susceptible to I3C
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