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201.
Summary This paper presents the free vibration of thin doubly-curved shallow shells of rectangular planform. The study covers wide combinations of free, simply supported and clamped boundary conditions. Both positive and negative Gaussian curvatures (spherical and hyperbolic paraboloidal shells resepectively) are considered. Thepb-2 Ritz energy based approach, along with the in-plane and transverse deflections assumed in the form of a product of mathematically complete two-dimensional orthogonal polynomials and a basic function, is employed to model the vibratory characteristic of these shells. Numerical results have been established through convergence study and comparison with published data from the open literature. Extensive sets of new results for various ranges of aspect ratio, curvature ratio andx- andy-shallowness ratios have been presented for future reference.  相似文献   
202.
A model is proposed to explain transgranular-stress corrosion cracking (T-SCC) in face-centered cubic (fcc) materials. Crack propagation is shown to be anisotropic, in that growth near {110} < 001> is discontinuous due to crack arrest by dislocation blunting whereas growth away from this growth orientation is continuous. For the former case, renucleation of arrested cracks involves active dissolution of shear bands at the crack tip, which changes the stress state at Lomer-Cottrell locks, causing them to fail by cleavage. Once the crack is nucleated, its instantaneous macroscopic crack-growth velocity is considered to be comprised of multiple nucleation of microcracks with intervening arrests. This microcracking results from the interaction of the stress fields from neighboring cracks which are forming simultaneously, the crack-opening constraint due to ligaments which act as “bridges” behind the crack front, and the localized dissolution at the microcrack tip which affectsK IC and leads to the “cobblestone” appearance. Experimental evidence and theoretical considerations are presented to support the model. The system studied was Cu-25 at. pct Au in 0.6 M NaCl solution at potentials between 300 and 400 mV (sce), which precludes hydrogen embrittlement. This article is based on a presentation made in the symposium “Quasi-Brittle Fracture” presented during the TMS fall meeting, Cincinnati, OH, October 21–24, 1991, under the auspices of the TMS Mechanical Metallurgy Committee and the ASM/MSD Flow and Fracture Committee.  相似文献   
203.
The telecommunications information networking architecture (TINA), which builds on the current advances in broadband communication and distributed computing technologies, specifying a software-based architecture for future information networks that are required to transport multimedia information and manage multimedia communication, is described. An important aspect of the architecture is that service segment functions are separated from delivery segment functions. Another key aspect is the elimination of the rigid division between network applications and operations applications that exists in current-day networks. In the TINA architecture, both kinds of applications execute on a common distributed processing platform that hides from applications the effects and complexities introduced by distribution. The architecture supports application interoperability enabling flexible construction of services, composed of service components distributed across network domains, allowing network operators and service providers to cooperatively meet the needs of the user  相似文献   
204.
Results for the performance of lithium/Mn02 batteries containing solid polymer electrolytes based on poly(ethylene oxide) blends with some acrylic derivatives are presented. The ionic conductivities of the electrolytes are promising for battery application. It was found, however, that interfacial phenomena impair the battery efficiency. Impedance spectroscopy shows resistive limitations at the anode interface of the batteries, caused either by formation of an electrically distinguishable resistive layer or by chemical interaction between the polymer and lithium, influencing, most probably, the kinetics of the lithium oxidation reaction.  相似文献   
205.
The purpose of this study was to compare the effects of a carbohydrate-electrolyte solution, ingested during exercise, with the effects of a preexercise carbohydrate meal on endurance running performance. Ten endurance-trained males completed two 30-km treadmill runs. In one trial subjects consumed a placebo solution 4 hr before exercise and a carbohydrate-electrolyte solution immediately before exercise and every 5 km (C). In the other trial, subjects consumed a 4-hr preexercise high-carbohydrate meal and water immediately before exercise and every 5 km (M). Performance times were identical for M and C, and there was no difference in the self-selected speeds. Oxygen uptake, heart rates, perceived rate of exertion, and respiratory exchange ratios were also similar. However, blood glucose concentration was higher in C during the first 20 km of the 30-km run. In M, blood glucose concentration was maintained above 4.5 mmol.L-1 throughout exercise. Thus, the two conditions produced the same 30-km treadmill running performance time.  相似文献   
206.
The performance of Bicron BC404, BC408 and BC420 scintillators coupled to a Hamamatsu R3432 proximity mesh dynode photomultiplier tube was studied using pion beams from the TRIUMF cyclotron and the Brookhaven National Laboratory AGS accelerator. A system resolution of better than 100 ps seems feasible. This will satisfy the requirement for charged particle identification in the STAR detector at RHIC.  相似文献   
207.
208.
A series of small angle neutron scattering measurements on blends of normal polystyrene (PSH) and labelled (deuterated) polystyrene (PSD) have been made with concentrations of PSD from 5 to 50 mol %. It is shown that the single chain form factor of the polymer in bulk can be obtained from a single concentration measurement for any concentration of labelled molecules, providing the molecular weights of the parent and labelled molecules are the same and the molecular weight distributions are narrow.  相似文献   
209.
Dynamic mechanical properties have been investigated for interpenetrating-network systems based on polyol-cured polyurethanes (PU) and 2 to 1 n-butyl acrylate-n-butyl methacrylate (Ac) networks. The systems were formed simultaneously (SIN) from all of the precursors and reactants for both networks in the same vessel, and sequentially (SIPN) by swelling a precured PU with the reactants that will form the Ac network. If the Ac network is formed after gelation of the PU, the IPNs are transparent and appear to have single T (tan δmax) between those of the homonetworks; visible-phase separation occurs if the Ac is intentionally polymerized prior to PU gelation. Damping curves were lower and broader and the T (tan δmax) and rubber moduli were higher for the SIN than for the SIPN systems. Up to 65 percent Ac, the T (tan δmax) data for both SIN and SIPN fit the Gordon-Taylor equation if a T (tan δmax) for the Ac homonetwork 7°C higher than observed is used, suggesting a higher crosslink density for the Ac network under these conditions. The differences in properties of the SIN and SIPN are assumed to be dependent on sample homogeneity and upon the presence of a tin catalyst in the SIN preparation. This can result in limited Ac-network formation and consequent phase separation before PU gelation has occurred, and the catalyst may also increase the extent of interaction, such as grafting or hydrogen-bond formation between the networks.  相似文献   
210.
Field surveys of a series of conjugated diunsaturated straight-chain primary alcohols, acetates, and aldehydes (dienes), including the 3,5-dode-cadienyl, 8,10-dodecadienyl, 3,5-tetradecadienyl, 8,10-tetradecadienyl, 9,11-tetradecadienyl, and 10,12-tetradecadienyl primary alcohols, acetates, and most aldehydes, and the related monounsaturated straight-chain primary alcohols, acetates, and aldehydes (monoenes), including the 3-dodecadienyl alcohol and acetates, attracted the following species from the title families. Diene attractants have been demonstrated for at least onePhyllonorycter sp.,Chionodes lugubrella (Fabr.),Leptostales ferruminaria (Zell.),Drepana bilineata (Pack.),Pyrausta fodinalis (Led.),Notocelia purpurissatana Heinr.,Phaneta alterana Heinr. Monoene attractants were demonstrated forHedya separatana (Kft.),Cydia fletcherana (Kft.),Barbara mappana Free.,Ancylis burgessiana (Zell.),Ancylis nubeculana Clem.,Evippe prunifoliella Cham.,Phlyctaenia coronata tertialis (Gn.), aChionodes sp., a Gelechiidae sp., and an unidentifiedPhyllonorycter sp. Replicated field experiments showed attraction-inhibition relationships for most species. Electroantennagram data are presented forLeptostales ferruminaria andDrepana bilineata.  相似文献   
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