Analysis of controlled multiplexing systems via numericalstochastic control methods

The paper demonstrates the usefulness of numerical methods of stochastic control theory for the design, analysis and control of multiplexing type systems and networks, as well as ATM type systems. The sources are of the Markov-modulated type, although the final results hold for other types (e.g. low-order AR schemes). Control problems arise when we wish to control cell loss due to buffer overflows by regulating the sources. The basic control mechanism is the deletion of selected low-priority cells, according to an appropriate state dependent rule. But the same results hold for many other schemes (e.g. purchasing incremental bandwidth). By exploiting the large size of the system (large number of users), the systems can be efficiently approximated by diffusion type processes, whether there is a control term or not, and for many types of control mechanisms. The basic controls are of the “low-priority cell deletion” type, and various extensions. They might be state dependent, and we can obtain optimal controls for cost functions that weigh buffer overflow, controller cell deletion loss as well as queue length. The limit equations are an effective aggregation of the original system. It is shown that there are substantial savings in losses with the use of optimal control techniques. The numerical methods can be used to balance the losses at the control with those due to buffer overflow, to minimize losses at the controller subject to constraints on buffer overflow, and to explore various approximations, systems aggregations, the interaction of multiple source classes of different priorities     

Cytochrome P450 induction, uroporphyrinogen decarboxylase depression, porphyrin accumulation and excretion, and gender influence in a 3-week rat model of porphyria cutanea tarda

An experimental model of porphyria cutanea tarda, consisting of depressed hepatic uroporphyrinogen decarboxylase (URO-D) activity and accumulation of highly carboxylated porphyrins in the liver, was produced in 3 weeks in Fischer 344 rats. A single administration of a polychlorinated biphenyl mixture (Aroclor 1254) to iron-loaded female rats maintained continuously on delta-aminolevulinic acid supplemented drinking water produced the porphyric state. Without iron loading, URO-D activity appeared slightly less inhibited (33% of normal vs 23% of normal) but porphyrin accumulation was dramatically less (70 vs 605 micrograms porphyrin/g liver). Similar treatment in male rats produced URO-D activities of 54 and 70% of normal with and without iron loading, respectively, and porphyrin concentrations of 76 and 17 micrograms/g. When hexachlorobenzene was substituted for Aroclor 1254 treatment in female rats, URO-D activity was 61 and 69% of normal (with and without iron loading, respectively) and liver porphyrin concentrations were 96 and 25 micrograms/g, respectively. Hexachlorobenzene did not produce significant porphyric effects in male rats. Aroclor 1254 induced CYP1A to a greater extent in females than in males and to a greater extent than hexachlorobenzene, which showed a greater propensity to induce CYP2B. Overall correlation between URO-D activity depression and porphyrin accumulation was highest when fitted to an exponential curve, indicating the importance of the extreme of the depression URO-D activity in evoking experimental porphyria cutanea tarda.     

A comparative study of the nonhistone chromosomal proteins (pp23) from rat and bull kidneys

BACKGROUND: Gastrointestinal myoelectric activity during postoperative ileus has been well characterized. However, the common clinical scenario of ileus occurring during and after episodes of sepsis is not well understood. The aim of our study was to determine the effects of a single, sublethal dose of endotoxin on canine gastrointestinal myoelectric activity. METHODS: Eight dogs underwent placement of serosal electrodes on the stomach and small intestine and insertion of a jejunal cannula. After the animals recovered, electrical activity and jejunal mucosal blood flow were determined during fasting and with feeding. Following completion of these baseline studies dogs were given a single, sublethal dose of Escherichia coli lipopolysaccharide (200 g/kg) intravenously, and the studies were repeated daily for 3 consecutive days. RESULTS: Endotoxin resulted in an absence of the interdigestive migrating myoelectric complex for 2 days, a decrease in duodenal and jejunal action potentials during fasting and with feeding, but no decreases in jejunal mucosal blood flow. The gastrointestinal myoelectrical patterns returned to those found in health on postendotoxin day 3. CONCLUSIONS: A single, sublethal dose of endotoxin results in a temporary disruption of gastrointestinal myoelectric activity similar to that seen during postoperative ileus. The etiology of this "adynamic" ileus is unknown but does not appear to be secondary to intestinal ischemia.     

Stress state of foundation beds from surface loads

Solutions of three-dimensional problems for semi-infinite (existing in the form of extent) uniform and triangular strip loads, a uniform load on one quarter of the boundary plane of a half space, and a uniformly loaded corner of a strip foundation, which define the stress state in the bed near the ends of the strips and the ends and corners of the foundations more precisely, are presented. These solutions make it possible to account more accurately for the influence exerted by these stresses on the settlement of neighboring foundations and structures, and calculate more accurately the settlements of open strip foundations. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 5–9, January–February, 1996.     

The detection of real defects in ferromagnetic objects using a magnetic-field imaging film

Tracer patterns of real defects during magnetic monitoring of ferromagnetic objects using a magnetic-field imaging film are presented. The results of production tests on the monitoring of a real object are demonstrated.     

Experimental study of magnetographic flaw inspection of objects during their magnetization with a movable permanent magnet through a magnetic carrier: I

The results of experimental studies on the magnetographic flaw inspection of ferromagnetic articles during the magnetization of a test object with a movable permanent magnet (MPM technique) through a magnetic carrier placed on a test surface are reported. The conditions of the inspection were determined.     

Effect of machining conditions on specific tangential forces

This paper deals with different hypotheses regarding the resistance of deformable material that is subject to plastic strain. For analysing cutting processes, a new cutting layout with a single shear plane is proposed here to calculate the specific tangential forces. The specific tangential forces in the different shear zones were examined by experiment to verify one of the hypotheses in question. These analyses verified that the forces depend fundamentally on cutting parameters and cutting layouts. Hence, it is necessary to take account of a correlation between yield point and deformation temperature, when determining the mechanical properties of the cutting material during machining. It is suggested here to determine the mechanical properties from the conditions compensating the hardening and the softening of the cutting material.