Priority shaping of traffic streams sharing a policed virtual path in an ATM network

Traffic streams with differing service requirements, sharing a single contract for use of a policed virtual path in an ATM network, may be jointly shaped to make the best use of bandwidth available in the path. The shaper may use the information about the network policer to perform self-policing with a form of priority service to ensure satisfactory levels of cell loss and delay for both real-time and non-real-time traffic. Two such shapers are considered assuming a mean bit-rate contract with the network in which a leaky-bucket mechanism performs the policing function. The performance of the shapers is analysed using Markov-modulated models of bursty traffic sources and stochastic fluid methods, and the analytical results are corroborated by simulations. The choice of the shaper type and optimization of the shaper design parameters are discussed using correlated and non-correlated source models.     

Intermediates in the protein folding process: a computational model

The paper presents a model for simulating the protein folding process in silico. The two-step model (which consists of the early stage-ES and the late stage-LS) is verified using two proteins, one of which is treated (according to experimental observations) as the early stage and the second as an example of the LS step. The early stage is based solely on backbone structural preferences, while the LS model takes into account the water environment, treated as an external hydrophobic force field and represented by a 3D Gauss function. The characteristics of 1ZTR (the ES intermediate, as compared with 1ENH, which is the LS intermediate) confirm the link between the gradual disappearance of ES characteristics in LS structural forms and the simultaneous emergence of LS properties in the 1ENH protein. Positive verification of ES and LS characteristics in these two proteins (1ZTR and 1ENH respectively) suggest potential applicability of the presented model to in silico protein folding simulations.     

Irregularities of crystallographic orientation and residual stresses in the crossed-lamellar shell as a natural functionally graded material

The microstructures of different groups of molluscs are characterized by preferential orientations of crystallites (texture), leading to a significant anisotropy of the physical properties of the shells. A complementary characteristic, usually neglected, is the distribution of the residual stresses existing within the shell wall. By means of X-ray diffraction, we study the distribution of stresses with thickness in the shell wall of the gastropod Conus marmoreus, which has a microstructure of the crossed-lamellar type. The results revealed an extraordinary texture inhomogeneity and the existence of tensional residual stresses along the shell thickness, the origins of which are unknown. Some of the observed changes in textural parameters and stresses coincide with the transitions between shell layers, although other features are of unknown origin. Our results provide insight into the microstructural regularities that govern the mesoscale construction of shells, such as that of C. marmoreus.     

Hybrid deposition of piezoelectric (11\bar 20) MgxZn1−xO (0≤x≤0.3) on (01\bar 12) R-sapphire substrates using RF sputtering and MOCVDR-sapphire substrates using RF sputtering and MOCVD

Mg_xZn_1?xO (0≤x≤0.3) films are deposited on R-plane $(01\bar 12)$ sapphire substrates using a hybrid deposition technique: metalorganic chemical vapor deposition and radiofrequency (RF) sputtering. Thick piezoelectric Mg_xZn_1?xO films are deposited by RF sputtering on MOCVD grown thin ZnO buffers on R-sapphire substrate. Molar ratio of ZnO and MgO powders are mixed to form Mg_xZn_1?xO (0≤x≤0.3) sputtering targets with NiO (2–3 wt.%) added for compensation doping to achieve piezoelectricity. Field emission scanning electron microscopy shows that the deposited films are dense and uniform. X-ray diffraction indicates that the sputter-deposited Mg_xZn_1?xO (0≤x≤0.3) films retain the wurtzite crystal structure. The crystallinity of the deposited films is further improved by postannealing at 700°C in oxygen. Compositional analysis of the films is carried out using Rutherford back-scattering. High-frequency and low-loss surface acoustic wave (SAW) testing devices fabricated on these films are demonstrated. The SAW properties are tailored to changing Mg compositions. In the ZnO/R-Al₂O₃ system, two types of wave modes, the Rayleigh-type and the Love-type wave modes, are investigated.     

Serotonergic–Muscarinic Interaction within the Prefrontal Cortex as a Novel Target to Reverse Schizophrenia-Related Cognitive Symptoms

Recent studies revealed that the activation of serotonergic 5-HT_1A and muscarinic M₁, M₄, or M₅ receptors prevent MK-801-induced cognitive impairments in animal models. In the present study, the effectiveness of the simultaneous activation of 5-HT_1A and muscarinic receptors at preventing MK-801-induced cognitive deficits in novel object recognition (NOR) or Y-maze tests was investigated. Activators of 5-HT_1A ({"type":"entrez-nucleotide","attrs":{"text":"F15599","term_id":"1130739","term_text":"F15599"}}F15599), M₁ (VU0357017), M₄ (VU0152100), or M₅ (VU0238429) receptors administered at top doses for seven days reversed MK-801-induced deficits in the NOR test, similar to the simultaneous administration of subeffective doses of {"type":"entrez-nucleotide","attrs":{"text":"F15599","term_id":"1130739","term_text":"F15599"}}F15599 (0.05 mg/kg) with VU0357017 (0.15 mg/kg), VU0152100 (0.05 mg/kg), or VU0238429 (1 mg/kg). The compounds did not prevent the MK-801-induced impairment when administered acutely. Their activity was less evident in the Y-maze. Pharmacokinetic studies revealed high brain penetration of {"type":"entrez-nucleotide","attrs":{"text":"F15599","term_id":"1130739","term_text":"F15599"}}F15599 (brain/plasma ratio 620%), which was detected in the frontal cortex (FC) up to 2 h after administration. Decreases in the brain penetration properties of the compounds were observed after acute administration of the combinations, which might have influenced behavioral responses. This negative effect on brain penetration was not observed when the compounds were administered repeatedly. Based on our results, prolonged administration of a 5-HT_1A activator with muscarinic receptor ligands may be effective at reversing cognitive decline related to schizophrenia, and the FC may play a critical role in this interaction.     

A Scheme for Batch Verification of Integrity Assertions in a Database System

A database management system can ensure the semantic integrity of a database via an integrity control subsystem. A technique for implementation of such a subsystem is proposed. After a database is updated by transactions, its integrity must be verified by evaluation of a set of semantic integrity assertions. For evaluation of an integrity assertion a number of database pages need to be transferred from the secondary storage to the fast memory. Since certain pages may be required for evaluation of different integrity assertions, the order of the evaluation of the integrity assertions determines the total number of pages fetched from the secondary storage. Hence, the schedule for the evaluation determines the cost of the database verification process. We show that the search for an optimal schedule is an NP-hard problem. Four approximation algorithms that find suboptimal schedules are proposed. They are based on the utilization of intersections among sets of pages required for the evaluation of different integrity assertions. The theoretical worst case behaviors of these algorithms are studied. Finally, the algorithms are compared via a simulation study to a naive, random order verification approach. The methods proposed for minimizing the costs of the batch integrity verification also apply to other problems that can be abstracted to the directed traveling salesman optimization problem. For example, the methods are applicable to multiple to multiple-query optimization and to concurrency control via the predicate locks.     

Synthesis and studies of phosphorus-containing polyurethane foams based on tetrakis(hydroxymethyl) phosphonium chloride derivatives

A phosphorus- and nitrogen-containing polyl is prepared by condensing tetrakis(hydroxymethyl)phosphonium chloride with diethanol amine in aqueous medium. The newly synthesized polyol-bis(hydroxymethyl)-N, N-bis(2-hydroxyethyl)aminomethylphosphine oxide (AMPO) is used in the preparation of rigid polyurethane foams with a various phosphorus content. With the view to comparing their properties, polyurethane foams are also prepared on the basis of the commercially available flame retardant diethyl-N, N-bis(2-hydroxyethyl)aminomethylphosphonate (Fyrol 6). The flammability, thermal stability, and thermoechanical properties of the polyurethane foams obtained are studied. A certain difference in the behavior of the two modified polyurethane foams is observed. The polyurethane foams with AMPO exhibit a slight increase in the resistance to combustion (oxygen index) and a noticeable improvement in the thermal and mechanical properties. These differences probably arise as a result of structural and functional differences between the two types of phosphorus-containing flame retardants.     

Ultra-high modulus polyethylene. 1 Effect of drawing temperature

Drawing behaviour and the properties of ultra-drawn high density polyethylene have been investigated as a function of the drawing temperature. An optimum temperature has been found for each type of polyethylene, at which the best drawing behaviour is found. It appears that the temperature range for effective drawing (leading to a high draw ratio and high Young's modulus) depends on the molecular weight and its distribution. The temperature range of the effective drawing is shifted towards higher temperatures for polyethylene exhibiting broader molecular weight distribution and higher weightaverage molecular weight. Ultra-high modulus and transport samples have been obtained by drawing high density polyethylene with broad molecular weight distribution ($\text{M}\text{?}{}_{\mathrm{w}}\text{M}\text{?}{}_{\mathrm{n}}\text{～ 20}$ and $\text{M}\text{?}{}_{\mathrm{w}}\text{～ 200 000}$) at higher drawing temperatures. It has been found that in the range of drawing temperatures 80–105°C the modulus of this polyethylene is higher for samples drawn at higher temperatures. Transparent samples with draw ratios of 35–40 and with Young's moduli of 600–650 kbar (at room temperature) have been obtained by drawing the polyethylene at 100°–105°C. We conclude that the high molecular fraction in the polyethylene, forming tie molecules in the drawn material, is responsible for the high modulus, while the low molecular weight fraction facilitates alignment of the long chains and retards the internal voiding (whitening) to a very high draw ratio during drawing at the higher temperatures.