Structural determinants of calcium signaling by RGD peptides in rat osteoclasts: integrin-dependent and -independent actions

Extensive characterization of the vitronectin receptor (VNR), a member of the integrin group of cell adhesion molecules, which is abundantly expressed in osteoclasts, has revealed a role for this receptor in osteoclast adhesion as well as bone resorption. Earlier evidence from our laboratory suggests that VNR is also capable of transducing intracellular signals following receptor ligand interaction, although this function is poorly understood. Thus, addition of peptides containing the minimal tripeptide Arg-Gly-Asp (RGD) integrin recognition sequence elicits transient increases in intracellular free calcium ions, with maximal responses seen with a bone sialoprotein peptide, BSP-IIA. In the present study we have attempted to determine some of the structural requirements for calcium signaling in osteoclasts using derivatives of the peptide PRGDN/T sequence found in bone sialoprotein. While some peptides, such as the parent sequence PRGDN, can induce both signaling and retractile events, it was found that minor structural modifications yielded peptides such as PRADN which elicited a transient increase in intracellular free calcium ions without promoting a reduction in osteoclast spread area (retraction). Conversely, certain other modifications resulted in peptides, such as PrGDN and benzoyl-RGDN, which effect osteoclast retraction, while having minimal Ca2+ signaling capabilities. Osteoclast adhesion, and hence retraction, are known to be RGD-dependent and integrin-dependent events. However, intracellular Ca2+ signaling is RGD-independent and, based on lack of inhibition by an anti-beta 3 integrin antibody F11 and echistatin, very likely integrin-independent. These data suggest that signaling is not always via VNR and as yet unknown receptors on the osteoclast membrane play a role in osteoclast signaling and hence function.     

Sorption kinetic studies of water vapour on activated carbon beds

Experimental measurements of the adsorption kinetics of water in activated carbon beds at different values of relative humidity have been made. The development of a simple theoretical model based on inter- and intra-particle mass transfer taking into account the thermal effects of sorption of water in activated carbon beds is described. The comparison of the model results with the experimental data is also presented. It is concluded that a single value of the estimated mass transfer coefficient can be used to reasonably predict the adsorption behaviour of water in activated carbon beds.     

Analysis of a thrust bearing with a viscoelastic lubricant

The characteristics of a thrust bearing with a viscoelastic lubricant have been analysed. The elasticity of the lubricant, the volume rate of flow of lubricant and the ratio of the inner and outer radii of the bearing are characterized by the parameters α, β and σ. The effects of these parameters on the pressure distribution and the load-bearing capacity have been studied.     

Recent Developments in Multiphase Metallic Materials

This paper briefly reviews some recent developments in multiphase metallic materials with a specific emphasis on how fundamental metallurgical understanding has guided the development of materials with tailored micro-structures and useful mechanical properties.     

Type-of-service routing in datagram delivery systems

The Internet is expected to support various services, including best-effort services and guaranteed services. For best-effort services, we propose a new approach to achieving type-of-service (TOS) classes with adaptive next-hop routing. We consider two TOS classes, namely, delay-sensitive and throughput-sensitive. As in routing protocols such as OSPF and integrated IS-IS, each node has a different next-hop for each destination and TOS class. Traditionally, a node has a single FCFS queue for each outgoing link, and the next-hops are computed using link measurements. In our approach, we attempt to isolate the two traffic classes by using for each outgoing link a separate FCFS queue for each TOS class; the link is shared cyclicly between its TOS queues. The next-hops for the delay-sensitive traffic adapts to link delays of that traffic. The next-hops for the throughput-sensitive traffic adapts to overall link utilizations. We compare our approach with the traditional approach using discrete-event simulation and Lyapunov analysis (for stability of routes). Our approach offers lower end-to-end delay to the delay-sensitive traffic. A related property is that the routes for the delay-sensitive traffic are more stable, i.e., less oscillations. An unexpected property is that the overall end-to-end delay is lower, because the throughput-sensitive traffic moves away to under-utilized routes     

Asymptotic analysis of single pore gas-solid reactions

The single-pore model for gas-solid reactions proposed by Ramachandran and Smith[1] is used to develop exact, closed-form solutions for the concentrati pore radius and conversion profiles in a long, narrow pore for both cylindrical and slab geometries. For relatively large values of the Thiele modulus, the solutions portray the asymptotic behavior of the reaction scheme in a finite pore. The cases of incomplete conversion associated with pore closure low initial porosities and complete conversion associated with a moving reaction zone at high initial porosities are analyzed. It is shown that the asy results provide very accurate estimates of the overall conversion in applications involving large pore diffusional resistance or fast reactions. The se of the conversion to various physicochemical parameters is also examined. The asymptotic results show good agreement with experimental data for gas-sol     

Interdiffusion and intrinsic diffusion in the Ni AI (δ) phase of the Al-Ni system

Interdiffusion coefficients at 950 to 1150°C and the ratio of intrinsic diffusion coefficients at 1100°C were measured as functions of composition in the NiAl (δ) phase of the Al-Ni system, using a vapor-solid technique. Diffusivity values were also obtained for the Ni₃Al (∈)and Ni (Al) solid solution (ζ) phases from 950 to 1150°C. The interdiffusion coefficient in NiAl (δ) varies several orders of magnitude over the δ phase field with a deep minimum in the diffusivity-composition curve at 48 to 49 at. pct Al. The ratio of intrinsic diffusion coefficients, D_ni/D_aI, in the δ phase also varies with composition from a value of 3 to 3.5 below 50 at. pct Al to 0.1 or less above 50 at. pct Al. Formerly Research Assistant, Department of Mate-rials Science, SUNY at Stony Brook, New York.     

Analysis of the evolution of microcreep during physical aging and mechanical deformation in poly(methyl methacrylate) using a microstructural model

The evolution of poly(methyl methacrylate) (PMMA) during physical aging at 90°C is followed by torsional microcreep tests. On the aged specimen a longitudinal stress is applied which induces a strain of 5 percent after 30 days of creep. The torsional microcreep tests are performed during the longitudinal creep in order to compare the structure evolution of PMMA caused by straining with its evolution measured during aging. The microcreep, for the first 800s, follows a reversible logarithmic law. In this stage the mobile defects achieve their activated form which is perfectly reversible when unloaded. The physical aging reduces this logarithmic part of microcreep. This is due to the decrease of either the number or the volume of the mobile defects. Beyond a critical elongation ? = 1 percent, the longitudinal straining has just the opposite influence, i.e., the logarithmic part of microcreep increases. This critical elongation ? = 1 percent corresponds to the beginning of the steady state longitudinal creep. The transient that precedes this steady state has no detectable influence on the structure of the specimen.