Lateral habits ofn-alkane single crystals

The lateral crystal habits ofn-alkanes (n-C _n H_2n+2) have been observed just below the melting points by optical microscopy forn=18, 19, 20, 22, 24, 34, 44, 50 and 65. The shape of the crystals depends on the crystal phase: circular in the rotator phase, lenticular in phase C, and diamond in the low-temperature phase. The rounding of the lateral shape can be explained in terms of thermal roughening of the lateral faces in the disordered phases at high temperature.     

Effect of starting particle size on hot-pressing of magnesium oxide powder prepared by vapour-phase oxidation process

Effect of starting particle size on hot-pressing of magnesium oxide (MgO) powder was examined using seven kinds of MgO powders prepared by a vapour-phase oxidation process; the average primary particle sizes were 11, 25, 32, 44, 57, 107 and 261 nm. These compressed powders (compacts) were hot-pressed at a temperature between 900 and 1300°C. The densifications of these compacts during the hot-pressing proceeded via (i) the sintering of primary particles within secondary particles and the rearrangement of secondary particles/grains (900°C), (ii) the gradual grain growth controlled by the pore migration (900∼1100°C) and (iii) the rapid grain growth due to the active mass transfer (1300°C); the grain sizes of MgO compacts hot-pressed at and below 1100°C were <1 μm, while those at 1300°C attained 20∼30 μm. The transluscent compact with the relative density of 99.7% could be obtained when the compressed powder with the average primary particle size of 44 nm was hot-pressed at a temperature as low as 1100°C for 1 h. This revised version was published online in November 2006 with corrections to the Cover Date.     

A study of effects of mouthwash on the human oral mucosae: with special references to sites, sex differences and smoking

Nitric oxide has been shown to decrease myocardial contractility and O2 consumption. This study was designed to evaluate the hypothesis that nitric oxide-mediated increases in cyclic GMP require elevated cyclic AMP to produce cardiac depression. Using isolated, Langendorff-perfused rat hearts, we determined the effects of intracoronary nitroprusside (NP, 1 and 10 mM) in the absence and presence of isoproterenol (ISO, 10(-8) M) on cardiac function, O2 consumption, cyclic GMP and cyclic AMP. ISO, with and without NP, increased cyclic AMP (from 287 +/- 21 to 477 +/- 33 pmol/g) without altering cyclic GMP. Left-ventricular pressure increased from 97 +/- 12 to 178 +/- 9 mm Hg and dP/dtmax from 1,786 +/- 275 to 4,049 +/- 354 mm Hg/s. NP increased cyclic GMP (from 4 to 30 pmol/g) in both the absence and presence of ISO, but NP did not alter cyclic AMP. Without ISO, NP insignificantly altered left-ventricular pressure; however, in the presence of ISO, NP significantly decreased left-ventricular pressure by -25 +/- 4 mm Hg and decreased dP/dtmax by -619 +/- 142 mm Hg/s. Isoproterenol increased O2 consumption, but the changes with NP were not significant. When this study was repeated in the presence of LY83583, a guanylate cyclase inhibitor, NP still produced cardiac depression in the presence of ISO. Therefore, cardiodepressant effects of NP were only observed against a background of inotropic stimulation with ISO. However, effects of NP on contractility were unrelated to increases in cyclic GMP or cyclic GMP-induced changes in cyclic AMP.     

The predominant contribution of oligopeptide transporter PepT1 to intestinal absorption of beta-lactam antibiotics in the rat small intestine

Although recent evidence suggests that certain beta-lactam antibiotics are absorbed via a specific transport mechanism, its nature is unclear. To confirm whether peptide transport in the rat can be largely ascribed to the intestinal oligopeptide transporter PepT1, the transporter has been functionally characterized and its significance in the intestinal absorption of beta-lactam antibiotics was evaluated. For evaluation of transport activity complementary RNA (cRNA) of rat PepT1 was synthesized in-vitro and expressed in Xenopus laevis oocytes. cRNA induced uptake of several beta-lactam antibiotics and the dipeptide [14C]glycylsarcosine; this was specifically inhibited by various dipeptides and tripeptides but not by their constituent amino acids or by tetra- or pentapeptides. The transport activity of PepT1 for beta-lactam antibiotics correlated well with their in-vivo intestinal transport and absorption. Furthermore, mutual inhibitory effects on uptake were observed between glyclsarcosine and beta-lactam antibiotics. Hybrid depletion of the functional expression of rat PepT1 in oocytes injected with rat intestinal epithelial total mRNA was studied using an antisense oligonucleotide corresponding to the 5'-coding region of PepT1. In oocytes injected with rat mRNA pre-hybridized with the antisense oligonucleotide against rat PepT1, the uptake of [14C]glycylsarcosine was almost completely abolished, whereas its uptake was not influenced by a sense oligonucleotide for the same region of PepT1. Similarly, the uptake of beta-lactam antibiotics was also reduced by the antisense oligonucleotide against rat PepT1. These results demonstrate that the intestinal proton-coupled oligopeptide transporter PepT1 plays a predominant role in the carrier-mediated intestinal absorption of beta-lactam antibiotics and native oligopeptides in the rat.     

Structuring communication software for quality-of-serviceguarantees

We propose architectural mechanisms for structuring host communication software to provide QoS guarantees. We present and evaluate a QoS sensitive communication subsystem architecture for end hosts that provides real time communication support for generic network hardware. This architecture provides services for managing communication resources for guaranteed QoS (real time) connections, such as admission control, traffic enforcement, buffer management, and CPU and link scheduling. The architecture design is based on three key goals: maintenance of QoS guarantees on a per connection basis, overload protection between established connections, and fairness in delivered performance to best effort traffic. Using this architecture we implement real time channels, a paradigm for real time communication services in packet switched networks. The proposed architecture features a process per channel model that associates a channel handler with each established channel. The model employed for handler execution is one of “cooperative” preemption, where an executing handler yields the CPU to a waiting higher priority handler at well defined preemption points. The architecture provides several configurable policies for protocol processing and overload protection. We present extensions to the admission control procedure for real time channels to account for cooperative preemption and overlap between protocol processing and link transmission at a sending host. We evaluate the implementation to demonstrate the efficacy with which the architecture maintains QoS guarantees on outgoing traffic while adhering to the stated design goals     

Selective employment of chemokine receptors as human immunodeficiency virus type 1 coreceptors determined by individual amino acids within the envelope V3 loop

The chemokine receptor CCR5 acts as an essential cofactor for cell entry by macrophage-tropic human immunodeficiency virus type 1 (HIV-1) strains, whereas CXCR4 acts as an essential cofactor for T-cell-line-adapted strains. We demonstrated that the specific amino acids in the V3 loop of the HIV-1 envelope protein that determine cellular tropism also regulate chemokine coreceptor preference for cell entry by the virus. Further, a strong correlation was found between HIV-1 strains classified as syncytium inducing in standard assays and those using CXCR4 as a coreceptor. These data support the hypothesis that progressive adaptation to additional coreceptors is a key molecular basis for HIV-1 phenotypic evolution in vivo.     

Effect of dynamic strain ageing on the tensile properties of a modified 9Cr–1Mo steel

Tensile testing of a modified 9Cr–1Mo steel in two microstructural conditions (710T– normalized at 1100°C, tempered at 710°C, and 550T – normalized at 1100°C tempered at 550°C) in the temperature range 25–450°C, under strain rates of 2.3×10-5–2.3×10-3s-1, exhibited serrated flow curves, with serrations appearing almost at the onset of deformation and disappearing before ultimate strengths were attained. The serrated flow curves (characteristics of dynamic strain ageing) were accompanied by increased ultimate strengths, loss of ductility and negative strain-rate sensitivity, relative to the ambient temperature properties. However, the increase in ultimate strength and the reduction in ductility were much larger for 710T specimens, as compared to 550T ones. In the dynamic strain ageing regime, the work-hardenability of 710T specimens increased rapidly while that of 550T specimens remained practically unaffected. Based on the microstructural consideration and the observed activation energy of 45 kJ mol-1, it is proposed that serrations are initiated by a nitrogen atmosphere formation on the waiting dislocations by a pipe diffusion mechanism, and they disappear by diffusion to the precipitate sinks during deformation. Because the fine alloy carbide precipitates in 550T specimens are more effective sinks than those of 710T ones, they can cause much faster depletion of the atmosphere, resulting in a much smaller effect of dynamic strain ageing on the tensile properties of 550T specimens.