Two perishable inventory systems with one-way substitution

Motivated by the ABO issue of the blood banks system, in which the portions stored have constant shelf life, we consider two subsystems of perishable inventory. The two Perishable Inventory Subsystems -- PIS A and PIS B, are correlated to each other through a so-called one-way substitution of demands. Specifically, the input streams and the demand streams applied to each subsystem are four Poisson processes which are independent of one another. However, if the shelf of PIS A (blood of type O) is empty of items an arriving demand of type A is unsatisfied, since demand of type A cannot be satisfied by an item of type B (blood portions of type AB), but if the shelf of PIS B is empty of items an arriving demand of type B is applied to PIS A, since demands of type B can be satisfied by both types. Such a one-way substitution of the issuing policy generates for PIS A a modulated Poisson demand process operating in a two-state non-Markovian environment. The performance analysis of PIS B is known from previous work. Hence, in this study we focus on the marginal performance analysis of PIS A. Based on a fluid formulation and a Markovian approximation for the one-way substitution demands process, we develop a unified approach to efficiently and accurately approximate the performance of PIS A. The effectiveness of the approach is investigated by extensive numerical experiments

Product forms as a solution base for queueing systems

A class of queueing networks has a product-form solution. It is interesting to investigate which queueing systems have solutions in the form of linear combinations of product forms. In this paper it is investigated when the equilibrium distribution of one or two-dimensional Markovian queueing systems can be written as linear combination of products of powers. Also some cases with extra supplementary variables are investigated

Microbial carbon mineralization in tropical lowland and montane forest soils of Peru

Climate change is affecting the amount and complexity of plant inputs to tropical forest soils. This is likely to influence the carbon (C) balance of these ecosystems by altering decomposition processes e.g., "positive priming effects" that accelerate soil organic matter mineralization. However, the mechanisms determining the magnitude of priming effects are poorly understood. We investigated potential mechanisms by adding (13)C labeled substrates, as surrogates of plant inputs, to soils from an elevation gradient of tropical lowland and montane forests. We hypothesized that priming effects would increase with elevation due to increasing microbial nitrogen limitation, and that microbial community composition would strongly influence the magnitude of priming effects. Quantifying the sources of respired C (substrate or soil organic matter) in response to substrate addition revealed no consistent patterns in priming effects with elevation. Instead we found that substrate quality (complexity and nitrogen content) was the dominant factor controlling priming effects. For example a nitrogenous substrate induced a large increase in soil organic matter mineralization whilst a complex C substrate caused negligible change. Differences in the functional capacity of specific microbial groups, rather than microbial community composition per se, were responsible for these substrate-driven differences in priming effects. Our findings suggest that the microbial pathways by which plant inputs and soil organic matter are mineralized are determined primarily by the quality of plant inputs and the functional capacity of microbial taxa, rather than the abiotic properties of the soil. Changes in the complexity and stoichiometry of plant inputs to soil in response to climate change may therefore be important in regulating soil C dynamics in tropical forest soils.This study was financed by the UK Natural Environment Research Council (NERC) grant NE/G018278/1 and is a product of the Andes Biodiversity and Ecosystem Research Group consortium (www.andesconservation.org); Patrick Meir was also supported by ARC FT110100457

Contact Modelling in Isogeometric Analysis: Application to Sheet Metal Forming Processes

Isogeometric Analysis (IGA) has been growing in popularity in the past few years essentially due to the extra exibility it introduces with the use of higher degrees in the basis functions leading to higher convergence rates. IGA also o ers the capability of easily reproducing discontinuous displacement and/or strain elds by just manipulating the multiplicity of the knot parametric coordinates. Another advantage of IGA is that it uses the Non-Uniform Rational B-Splines (NURBS) basis functions, that are very common in CAD solid modelling, and consequently it makes easier the transition from CAD models to numerical analysis. In this work it is explored the contact analysis in IGA for both implicit and explicit time integration schemes. Special focus will be given on contact search and contact detection techniques under NURBS patches for both the rigid tools and the deformed sheet blank

Synthesis and Antibacterial Activity of Thiophenes

2-[Bis(methylthio)methylene]propanedinitrile 1a reacted in one-pot successively with piperidine, sodium sulfide, chloroacetonitrile, and potassium carbonate to afford 3-amino-5-(1-piperidinyl)-2,4-thiophenedicarbonitrile 2a. Similar reaction using the last three reagents with ethyl 2-cyano-3,3-bis(methylthio)acrylate 1b produced ethyl 4-amino-5-cyano-2-(methylthio)thiophene-3-carboxylate 2b. The synthesized compounds were characterized by using FT-IR, 1H-NMR, 13C-NMR, and mass spectral data. Antibacterial activities of the synthesized compounds are also reported

Tuning sperm chemotaxis by calcium burst timing

AbstractMarine invertebrate oocytes establish chemoattractant gradients that guide spermatozoa towards their source. In sea urchin spermatozoa, this relocation requires coordinated motility changes initiated by Ca2+-driven alterations in sperm flagellar curvature. We discovered that Lytechinus pictus spermatozoa undergo chemotaxis in response to speract, an egg-derived decapeptide previously noted to stimulate non-chemotactic motility alterations in Strongylocentrotus purpuratus spermatozoa. Sperm of both species responded to speract gradients with a sequence of turning episodes that correlate with transient flagellar Ca2+ increases, yet only L. pictus spermatozoa accumulated at the gradient source. Detailed analysis of sperm behavior revealed that L. pictus spermatozoa selectively undergo Ca2+ fluctuations while swimming along negative speract gradients while S. purpuratus sperm generate Ca2+ fluctuations in a spatially non-selective manner. This difference is attributed to the selective suppression of Ca2+ fluctuations of L. pictus spermatozoa as they swim towards the source of the chemoattractant gradient. This is the first study to compare and characterize the motility components that differ in chemotactic and non-chemotactic spermatozoa. Tuning of Ca2+ fluctuations and associated turning episodes to the chemoattractant gradient polarity is a central feature of sea urchin sperm chemotaxis and may be a feature of sperm chemotaxis in general

Collective Action by Women’s Groups to Combat Drought and Poverty in Northern Kenya

Collective action can be an effective means of local development and risk reduction among rural people, but few examples have been documented in pastoral areas. We conducted extensive interviews for 16 women’s groups residing in northern Kenya. Our objectives were to understand how groups were formed, governed, and sustained and what activities they have pursued. The groups we interviewed were 10 years old, on average. Charter memberships averaged about 24 women, 20 of whom were illiterate. Half of the groups formed after facilitation by a development partner and half formed spontaneously. Groups are governed under detailed constitutional frameworks with elected leaders. Groups primarily form to improve living standards of the members and undertake a wide variety of activities founded on savings and credit schemes, income diversification, small business development, education, health service delivery, and natural resource management. Groups have evolved means to buffer members from drought and poverty. The greatest threats to the sustainability of the groups come from internal factors such as unfavorable group dynamics and illiteracy, while external challenges include drought, poverty, and political incitement. Principles of good group governance and wisdom in business are reportedly the key ingredients for long-term success

Understanding the hydration process of salts:the impact of a nucleation barrier

The solid-state hydration of salts has gained particular interest within the frame of thermochemical energy storage. In this work, the water vapor pressure–temperature (p–T) phase diagram of the following thermochemical salts was constructed by combining equilibrium and nonequilibrium hydration experiments: CuCl2, K2CO3, MgCl2·4H2O, and LiCl. The hydration of CuCl2 and K2CO3 involves a metastable zone of ca. 10 K, and the induction times preceding hydration are well-described by classical homogeneous nucleation theory. It is further shown for K2CO3 (metastable) and MgCl2·4H2O (not metastable) through solubility calculations that the phase transition is not mediated by bulk dissolution. We conclude that the hydration proceeds as a solid–solid phase transition, mobilized by a wetting layer, where the mobility of the wetting layer increases with increasing vapor pressure. In view of heat storage application, the finding of metastability in thermochemical salts reveals the impact of nucleation and growth processes on the thermochemical performance and demonstrates that practical aspects like the output temperature of a thermochemical salt are defined by its metastable zone width (MZW) rather than its equilibrium phase diagram. Manipulation of the MZW by e.g. prenucleation or heterogeneous nucleation is a potential way to raise the output temperature and power on material level in thermochemical applications