Stock Rats Research Articles

Formation of the physical state and carbon stocks in organic matter of agrochernozem under the influence of resource-saving technologies

In the field experiment in the conditions of the Krasnoyarsk forest-steppe, the influence of resource-saving technologies on the physical state of agrochernozem and the carbon reserves of organic substance is studied. It is shown that the productive moisture reserves are satisfactory, in the subsoil layer there is a tendency to increase the moisture reserves by 2-5 mm on the minimum and zero background compared with plowing. Moldboard plowing and minimal tillage by fluffy consistency determined the greatest degree of differentiation of the humus horizon. Resource-saving technologies of main tillage contributed to an increase in bulk density by 0.05-0.08 g/cc while retaining the optimal parameters. The method of the main tillage determined the stocks of the above-ground mortmass. The stock of plant residues on the soil surface at the minimal background increased 1.4 times, at zero - 2.1 times compared with plowing. Stocks of phytomass, roots and underground mortmass were not identified by crop cultivation. The stock rations of carbon in mobile humus of agrochernozem increased 1.4-1.5 times against the background of resource-saving technologies due to newly formed humic acids and water-soluble organic matter.

Joint production, inventory rationing, and order admission control of a stochastic manufacturing system with setups

In this paper, we examine a single-stage, manufacturing system with setups, which produces a single part type to satisfy demand from two customer classes. We address the problem of coordinating production control, stock rationing, and order admission decisions. The optimal policy, in respect to minimizing holding, backorder, lost sales, and setup costs, is derived by formulating the underlying problem as a Markov Decision Process and solving it by means of Dynamic Programming. The structure of the optimal policy is investigated numerically and, on that basis, a parametric control policy is proposed. The Markov chain model of the single-machine manufacturing system, operating under the proposed policy, is developed. Furthermore, analytical expressions of the steady-state probabilities and of the expected total cost are obtained. The proposed policy is compared to the optimal, as well as to three heuristics, in an extended series of experiments. The numerical results indicate that the proposed policy is a very good approximation of the optimal one, and that it largely outperforms the alternative control policies.

Disaster Relief Inventory Management: Horizontal Cooperation between Humanitarian Organizations

Cooperation among humanitarian organizations has attracted increasing attention to enhance effectiveness and efficiency of relief supply chains. Our research focuses on horizontal cooperation in inventory management which is currently implemented in the United Nations Humanitarian Response Depot (UNHRD) network. The present work follows a two‐step research approach, which involves collection of empirical data and quantitative modeling to examine and overcome the coordination challenges of the network. Our interviews with members of the network identified several managerial issues for sustainable cooperative inventory management that the UNHRD network pursues. Using a newsvendor model in the context of non‐cooperative game theory, our research has explored member humanitarian organizations' incentive of joining the network, a coordination mechanism which achieves system optimality, and impacts of members' decisions about stock rationing. Our results indicate that behaviors of member HOs do not necessarily align with the UNHRD's expectation. Our results suggest that for system optimality, a system coordinator should carefully assess the circumstances, including demand coefficient and stock rationing. Our research also proposes a policy priority for the first‐best system optimal inventory management.

Metabolic endocrine factors involved in spawning recovery and rematuration of iteroparous female rainbow trout (Oncorhynchus mykiss)

To determine how energy balance affects metabolic hormones hypothesized to play a role in the onset of a new reproductive cycle in iteroparous salmonids, food availability after spawning was restricted in female rainbow trout. These fish were compared with a control group that was fed a standard brood stock ration. Bodyweight, length, and muscle lipid content were determined, and blood was collected from fish at regular intervals; a subset of fish from each group was sacrificed at each sampling time for the collection of liver and ovary tissue, and to calculate hepatosomatic index (HSI) and gonadosomatic index (GSI). Plasma hormone levels were quantified by radioimmunoassay, and tissue gene expression levels were analyzed using q-RT-PCR. The experiment was conducted twice, using two-year-old and three-year-old post-spawned fish. Food-restriction arrested ovarian growth and development within 15–20weeks, as evidenced by lower GSI in restricted-ration fish. Food restriction also reduced Fulton’s condition factor, muscle lipid content, and specific growth rate from one month onward, and reduced HSI after 3months. In the liver, insulin-like growth factor (igf1 and igf2) gene expression was reduced in three-year-old food-restricted fish within 2months; however, no effect of ration on igf1 or igf2 expression was detected in two-year-old fish. In both years, IGF binding protein-1 (igfbp1) gene expression decreased over time in both treatment groups. Liver leptin (slepA1) gene expression was lower in two-year-old food-restricted fish at 4months. These results show that this feed restriction regime arrested reproductive development and affected factors associated with energy balance purported to play a role in initiating reproductive development within 2–4months after spawning.

Production control and stock rationing for a make-to-stock system with parallel production channels

This article considers the problem of production control and stock rationing in a make-to-stock production system with lost sales, multiple servers in parallel production channels, and several customer classes. It is assumed that independent stationary Poisson demand streams and exponential service times are in operation. At decision epochs, the control specifies whether or not to increase the number of active servers in conjunction with the stock allocation decision. Previously placed production orders cannot be cancelled. The system is modeled as an M/M/s make-to-stock queue, and properties of the optimal cost function and of the optimal production and rationing policies are characterized. It is shown that the optimal production policy is a state-dependent base-stock policy, and the optimal rationing policy is of threshold type. Furthermore, it is shown that the rationing levels are non-increasing in the number of active channels. It is also shown that the optimal ordering policy transforms into a bang-bang type policy when the model is relaxed by allowing order cancellations. Another model with partial order-cancellation flexibility is provided to fill the gap between the no-flexibility and the full-flexibility models. The additional gain that the optimal policy provides over the suboptimal base-stock policy proposed in the literature is qualified along with the value of the flexibility to cancel production orders.

An embedded Markov chain approach to stock rationing

We propose a new method for the analysis of lot-per-lot inventory systems with backorders under rationing. We introduce an embedded Markov chain that approximates the state-transition probabilities. We provide a recursive procedure for generating these probabilities and obtain the steady-state distribution.

A dynamic rationing policy for continuous-review inventory systems

Stock rationing is an inventory policy that allows differential treatment of customer classes without using separate inventories. In this paper, we propose a dynamic rationing policy for continuous-review inventory systems, which utilizes the information on the status of the outstanding replenishment orders. For both backordering and lost sales environments, we conduct simulation studies to compare the performance of the dynamic policy with the static critical level and the common stock policies and quantify the gain obtained. We propose two new bounds on the optimum dynamic rationing policy that enables us to tell how much of the potential gain the proposed dynamic policy realizes. We discuss the conditions under which stock rationing – both dynamic and static – is beneficial and assess the value of the dynamic policy.

Stock rationing in an M/E r /1 multi-class make-to-stock queue with backorders

A model of a single-item make-to-stock production system is presented. The item is demanded by several classes of customers arriving according to Poisson processes with different backorder costs. Item processing times have an Erlang distribution. It is shown that certain structural properties of optimal stock and capacity allocation policies exist for the case where production may be interrupted and restarted. Also, a complete characterization of the optimal policy in the case of uninterrupted production when excess production can be diverted to a salvage market is presented. A heuristic policy is developed and assessed based on the results obtained in the analysis. Finally the value of production status information and the effects of processing time variability are investigated. [Supplemental materials are available for this article. Go to the publisher's online edition of IIE Transactions for the following free supplemental resource: Appendix]

Technical Note—A Make-to-Stock System with Multiple Customer Classes and Batch Ordering

This paper examines the impact of customer order sizes on a make-to-stock system with multiple demand classes. We first characterize the manufacturer's optimal production and rationing policies when the demand is nonunitary and lost if unsatisfied. We also investigate the optimal policies of a backorder system with two demand classes and fixed order sizes. Through a numerical study, we show the effects of batch orders on the manufacturer's inventory cost as well as on the benefit of optimal stock rationing. It is shown that batch ordering may reduce the manufacturer's overall cost if carefully introduced in a first-come-first-served (FCFS) system. With the same effective demand rates, the customers' order sizes also have a strong impact on the benefit of optimal stock rationing.

INFLUENCE OF OCHRATOXIN A AND ZEARALENONE ON SOME MINERALS, LIPID PROFILES AND TISSUE RESIDUES IN LAYING HENS

A problem of anorexia, loss of weight, decrease in egg production, coloacal haemorrhage with a high mortality rate (up to 30%) in an intensive poultry farm for laying hens was recorded. Serum analysis of 50 severely affected birds revealed significant changes in calcium and phosphorus levels. Lipid profiles were also changed compared to their levels in control healthy hens. Examination of kidney, liver and parts of the muscles for detection of ochratoxin and zearalenone residues showed presence of 43, 24 and 19 μg ochratoxin / kg tissue and 28, 12 and 10 μg zearalenone / kg tissue, respectively. Analysis of diet samples taken from the offered and stock ration indicated their contamination with ochratoxin and zearalenone (20 and 64 ppm, respectively).

A stock rationing policy in a ( s,S)-controlled stochastic production system with 2-phase Coxian processing times and lost sales

This paper analyzes a ( s,S)-controlled stochastic production system with multi-class demands and lost sales. Demands in each class are assumed to arrive according to a Poisson process, and the time required to process an item is assumed to follow a 2-phase Coxian distribution. For each class, a stock rationing level is set. When customers arrive, if the inventory level is lower than the predetermined rationing level, the demands are lost for future demands with higher priorities. A behavior of the production system is modeled as a continuous time Markov chain, and an efficient algorithm to calculate the steady-state probability distribution of the system is proposed. The average operating cost under the stock rationing policy is compared with the one without stock rationing. Numerical experiment shows that the proposed stock rationing policy reduces the average operating cost significantly, depending on the system parameters.

Stock Rationing in a Continuous Review Two-Echelon Inventory Model

In this paper we consider a 1-warehouse, N-retailer inventory system where demand occurs at all locations. We introduce an inventory model which allows us to set different service levels for retailers and direct customer demand at the warehouse. For each retailer a critical level is defined, such that a retailer replenishment order is delivered from warehouse stock if and only if the stock level exceeds this critical level. It is assumed that retailer replenishment orders, which are not satisfied from warehouse stock, are delivered directly from the outside supplier, instead of being backlogged. We present an analytical upper bound on the total cost of the system, and develop a heuristic method to optimize the policy parameters. Numerical experiments indicate that our technique provides a very close approximation of the exact cost. Also, we show that differentiating among the retailers and direct customer demand can yield significant cost reductions.

Supply rationing in multi-echelon divergent systems

In this paper we determine a simple inventory control rule for multi-echelon distribution systems under periodic review without lot sizing. The primary focus is the two-echelon model with a stockless central depot, but several extensions (>2 echelons, central stock allowed) are discussed as well. The, control rule consists of two parameter sets: a set of rationing fractions at the central depot with the purpose to minimize inventory imbalance, and a set of order-up-to levels for the local stockpoints with the purpose to achieve a target service level (fill rate) per local stockpoint. The problem to calculate these control parameters is solved by decomposition in two subproblems. First the rationing fractions are determined such that the (approximate) expected system imbalance is minimized. Next the order-up-to levels are calculated such that the target fill rates are achieved. Numerical results show that this control rule, called Balanced Stock (BS) rationing, is accurate and more robust than the Consistent Appropriate Share (CAS) rationing polocy.

Stock-rationing policy for a make-to-stock production system with two priority classes and backordering

This article considers the problem of production control and stock rationing in a make-to-stock production system with two priority customer classes and backordering. The problem is formulated as a queueing control model. With Poisson arrivals and exponential production times, we show that the optimal production control and stock-rationing policies can be characterized by a single, monotone switching curve. © 1997 John Wiley & Sons, Inc. Naval Research Logistics 44: 457–472, 1997

Selenium protection against thyroid dysfunction and/or hyperlipidemia induced by chronic ascorbic acid deficiency: experimental study in guineapigs

The effect of selenium supplementation at abundant, as well as, deficient doses on serum lipid and protein levels was studied in ascorbate-restricted, male guineapigs in the backdrop of normal ascorbate subjects maintained in parallel. Whereas deficient oral feeding of ascorbic acid and/or parenteral administration of selenium at a very low dose in experimental guineapigs fed a stock ration produces hyperlipidemic changes by increasing the cholesterol/phospholipid (C/P) ratio in serum and a lowering of serum protein level, the stock ration plus an excess of selenium intake results in a lowering of hyperlipidemia, slight increases in serum protein followed by concomitant decrease in C/P ratio. Results also indicate that hyperlipidemia led by vitamin C deficiency is independent of any thyroid influences, while hyperlipidemic response of poor selenium nutriture is in part thyroidal. Little information exists at the present time concerning the mechanism by which dietary selenium does exert its anti-atherogenic, as well as, lipid-lowering effects on blood lipid levels, but it seems likely that more than one mechanism may be involved in this respect. It is highly probable that the chemoprotective action of elemental selenium is very much related to its anti-oxidant property which, in turn, is largely influenced by ascorbic acid, another important anti-oxidant, operating both in blood plasma and on cell membranes.

Stock allocation in general multi-echelon distribution systems with ( R, S) order-up-to-policies

In this paper we analyze stock allocation policies in general N-echelon distribution systems, where it is allowed to hold stock at all levels in the network. The goal is to achieve differentiated target customer service levels (fill rates). Various allocation rules and accompanying numerical methods that have already been developed for smaller networks are extended and compared in an extensive numerical experiment. We conclude that the extension of Balanced Stock rationing (see Van der Heijden (1996)) is the most accurate method, in particular in cases of relatively high imbalance. If the imbalance is not too high, the extension of Consistent Appropriate Share rationing (see De Kok et al., 1994; Verrijdt and De Kok, 1996) performs good as well.

Changes in serum lipid profile in atherosclerotic rats on feeding guava pulp and isabgol ( Plantago ovata Forsk.) powder

The effect of selected dietary fibres (from guava pulp and isabgol powder) on serum lipid and protein was investigated in rats fed either fibre-free or fibre-rich (8% by weight) diest for 6 weeks. A proven model of atherosclerosis promoted by an atherogenic (15% butter fat and 1% cholesterol) diet was used to test the effects of hypolipidemic agents present in fibrous foods in the backdrop of stock ration (SR) control animals maintained in parallel. Supplementatation of guava pulp in atherosclerotic subjects reduced total serum lipid, cholesterol and phospholipid levels, although glyceride level was not much affected. Moreover, lowering of total cholesterol or phospholipid level was not equally reflected in animals fed both types of diet and serum triglyceride concentration weer lowest in isabgol-supplemented rats. Comparison of serum lipids in terms of percentage composition also revealed that glyceride level was significantly increased with a concomitant decrease in total cholesterol in animals receiving guava pulp-rich diet. Isabgol powder was, however, ineffective in producing such changes. Inclusion of guava pulp or isabgol powder did not bring about any remarkable improvement at cellular level, but guava pulp alone lessened the severity of cardiac lesions to some extent. Since the C/P ratio in serum is one of the reliable predictors of subjects' risk to hyperlipidemia, ischemic heart disease and arterial/myocardial damage, a decrease in the C/P ratio as evidenced during guava pulp treatment will indicate that dietary fibres of guava pulp are good hypocholesterolemic and/or phospholipid-lowering agents, whereas isabgol husk-fibres were very effective in lowering serum triglyceride level.

The use of N-Alkanes as indigestible markers in studies on intestinal digestion in sheep

Faecal recoveries of herbage n-alkanes (odd-chains) as well as dosed alkanes (C28, C30, and C32) have been shown to be incomplete (Mayes & Lamb, 1984; Mayes et al. 1986). The purpose of this experiment was to identify both the extent and the site or sites of losses of natural and dosed (C32 and C36) alkanes along the digestive tract of sheep and to assess their use as indigestible markers in studies on intestinal digestion. The recovery of both natural and dosed alkanes was compared with that of the conventional marker Cr2O3 at the duodenum, the ileum and in the faeces.Four mature sheep fitted with re-entrant cannulae placed in the proximal duodenum and ileum (Brown et al, 1968) were used. The sheep were fed twice daily and the diet consisted of 700 g hay and 350 g of a stock ration containing; barley 60%, lucerne 30%, fishmeal 5% and molasses 5% (Table 1). Cr2O3 impregnated paper onto which C32 and C36 alkanes had been absorbed was shredded and introduced into the rumen in form of a 2 g pellet twice daily at feeding time.

Sera Fatty Acid Effects on Cultured Rat Splenocytes

Rats were fed either a stock diet or purified diets containing either 10% by weight corn oil or linseed oil for 8 weeks. Splenocytes from rats on the stock ration were cultured for 48 hours in media containing either serum from the rats fed stock diet, corn oil or linseed oil, or fetal bovine serum (FBS). Populations were cultured without stimulation and with stimulation by leucogglutinin (PHA), and the production of prostaglandin F2α by the cells was determined. The serum from the corn oil-fed rats differed markedly in composition from that of the linseed oil-fed rats notably in the higher level of arachidonic acid (20:4ω6) and lower level of timnodonic acid (20:5ω3). FBS also had a lower level of 20:4ω6. These changes were reflected in the fatty acid composition of the spleen choline glycerophosphatide. PGF2α production was significantly depressed in the medium from linseed oil-fed rats compared to the corn oil group. This effect was due to the competition of 20:5ω3 for the cyclooxygenase. Viability of cells was better in rat serum than in FBS. The study shows that when studying functions in cultured cells obtained from rats fed different dietary fats the dietary effect will be abrogated or modified by use of FBS in the medium.

The influence of dietary branched‐chain fatty acids on the fatty acid composition of tissue lipids of rats

AbstractBranched‐chain fatty acids (BCFA) were prepared as a concentrate from the adiposetissue lipids of barley‐fed lambs. The BCFA was included in a stock Oxoid ration at levels of 2.5–15% by weight and these diets were given to appetite to female weanling rats for up to 14 days. The influence of the diets on inter alia growth‐rate and fatty acid composition of tissue lipids was compared with the effect of the same stock diet with inclusions at a level of 5% by weight of 3‐methylhexadecanoic acid (3‐MHD), 4‐methylhexadecanoic acid (4‐MHD), 3,7,11,15‐tetramethylhexadecanoic (phytanic) acid and n‐hexadecanoic (palmitic) acid which, with the stock ration, served as control. Rats receiving diets containing up to 7.5% BCFA grew almost as well as did those given palmitic acid whereas the animals offered the diets containing 3‐MHD, 4‐MHD or 10% BCFA barely subsisted. Rats given 10% BCFA or phytanic acid became moribund within 3 days. BCFA accumulated to widely varying degrees in the lipids of the main internal organs. The higher proportions of these acids constituted some 40–60% of the total fatty acids of the lipids of kidney, liver and heart and were associated with diets containing 10% and 15% BCFA and 5% 3‐MHD. The lower proportions of the branched acids in the lipids of these organs were in the range 15–25% of the total fatty acids and related to diets that included 2.5% BCFA and 5% 4‐MHD. In contrast to the changes in fatty acid composition of the lipids of the main internal organs, those of the central and peripheral nervous systems were only minor, the proportions of branched acids amounting to some 3% in brain tissue and up to 14% in sciatic nerve. Clearance of branched acids from tissue lipids of the main internal organs was almost complete after the animals were returned to the basal diet for 14 days but the loss of branched acids from nerve tissue was evidently less rapid.