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991.
W. O. Soboyejo K. T. Venkateswara Rao S. M. L. Sastry R. O. Ritchie 《Metallurgical and Materials Transactions A》1993,24(3):585-600
The results of recent studies on the fatigue and fracture behavior of extruded Ti-48A1 + 20 vol pct TiNb and hot-isostatically
pressed (“hipped”) MoSi2 + 20 vol pct Nb are presented (compositions in atomic percent unless stated otherwise). The effects of ductile phase reinforcement
of Ti-48A1 and MoSi2 on the micromechanisms of fracture under monotonie and cyclic loading are elucidated. Micromechanics models are applied to
the prediction of crack-tip shielding components, and the effects of temperature on tensile/compressive/flexure strengths
are discussed. Ductile phase toughening under monotonie loading conditions is shown to be associated with lower fatigue crack
growth resistance. The lower fatigue resistance is attributed to the absence of crack-tip shielding, higher crack opening
displacements, and the effects of inelastic strains that are developed in ductile phase-reinforced composites under cyclic
loading conditions.
S.M.L. SASTRY, formerly Program Manager and Fellow, McDonnell Douglas Research Laboratories.
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
992.
S. Gopalakrishnan S. V. Krishna Mohan Rao T. V. S. R. Appa Rao 《Computers & Structures》1993,49(6):923-930
In this second and final part of this series of papers the details of parametric studies conducted to assess the influence of various geometric and material parameters on the load-displacement response of three reinforced concrete hyperboloid cooling towers are presented. The material model adopted for the nonlinear finite element analysis is described in part I of this paper. 相似文献
993.
This article reviews the clinical diagnosis of appendicitis, indications and options for appendiceal imaging, compares appendiceal CT techniques, and describes the imaging findings with appendicitis and alternative conditions that can clinically mimic appendicitis. 相似文献
994.
A. Arjuna Rao B. S. Murty M. Chakraborty 《Metallurgical and Materials Transactions A》1996,27(3):791-800
The grain-refining behavior of high purity aluminum (HPA1) and commercial purity aluminum (CPA1) containing Fe and Si as impurities
(<0.2 wt pct each) has been studied with and without the presence of Cr in small and large quantities (0.2 and 2 wt pct).
The Al-5Ti-lB master alloy ingot (0.2 wt pct) was used as a grain refiner. The emphasis was on the influence of individual
elements and their interactions with the other elements on the grain-refining behavior of Al. Good grain refinement with insignificant
fading in CPA1 was observed in comparison to HPA1. Similar results were obtained with a small concentration of Cr in HPA1
in HPA1-0.2 wt pct Cr alloy. The CPA1 and HPA1-0.2 wt pct Cr alloy have given the best grain-refining results among all the
cases studied. A combination of small quantities of Fe, Si, and Cr (CPA1-0.2 wt pct Cr) has shown early and significant fading.
A large concentration of Cr (2 wt pct) has shown a poisoning effect irrespective of the presence or absence of impurities
such as Fe and Si in Al. Thus, Cr was found to be beneficial for grain refinement at smaller concentrations in the absence
of impurities. But at higher concentrations of Cr, it had an adverse effect,i.e., led to coarser grain sizes both in the presence and absence of impurities. 相似文献
995.
To obtain highly conductive buried layers in InP:Fe, MeV energy Si, S, and Si/ Simplantations are performed at 200°C. The
silicon and sulfer implants gave 85 and 100 percent activation, respectively, for a fluence of 8 × 1014 cm−2. The Si/S co-implantation also gave almost 100 percent donor activation for a fluence of 8 × 1014 cm−2 of each species. An improved silicon donor activation is observed in the Si/S co-implanted material compared to the material
implanted with silicon alone. The peak carrier concentration achieved for the Si/S co-implant is 2 × 1019 cm3. The lattice damage on the surface side of the profile is effectively removed after rapid thermal annealing. Multiple-energy
silicon and sulfur implantations are performed to obtain thick and buried n+ layers needed for microwave devices and also hyper-abrupt profiles needed for varactor diodes. 相似文献
996.
The atypical antipsychotic clozapine is associated with several well-known abnormalities of blood cell count, whereas only rare reports are associated with the neuroleptic risperidone. This report describes lymphocytopenia and thrombocytopenia under treatment with risperidone which continued after changing to clozapine without other clinically significant abnormal hematological parameters. Within one week after discontinuation of both neuroleptics abnormalities of blood cell count reversed to the initial values. Abnormalities of lymphocytes or thrombocytes are rare side-effects under treatment with risperidone or clozapine. 相似文献
997.
998.
Najeev-ud-din Dunga M.V. Kumar A. Vasi J. Ramgopal Rao V. Baohong Cheng Woo J.C.S. 《Electron Device Letters, IEEE》2002,23(4):209-211
Using a novel gate-induced-drain-leakage (GIDL) current technique and two-dimensional (2-D) simulations, single pocket (SP) SOI MOSFETs have been shown to exhibit reduced floating body effects compared to the homogeneously-doped channel (conventional) SOI MOSFETs. The GIDL current technique has been used to characterize the parasitic bipolar transistor gain for both conventional and SP-SOI MOSFETs. From 2-D device simulations, the lower floating body effects in SP-SOI MOSFETs are analyzed and compared with the conventional MOSFETs 相似文献
999.
Rao V.R. Wittmann F. Gossner H. Eisele I. 《Electron Devices, IEEE Transactions on》1996,43(6):973-976
Vertical n-MOSFETs with channel lengths of 85 nm have been grown by MBE. For drain-to-source voltages VDS>3.3 V, these transistors exhibit hysteresis behavior similar to the reported behavior of fully depleted SOI-MOSFETs. Our results also show a gate voltage controlled turn-off of the drain current when the transistor is operating in the hysteresis mode. We have analyzed this behavior in vertical n-MOSFETs using 2-D device simulation and our results show a threshold value for the hole concentration across the source-channel junction which is required for the forward biasing of this junction. For a transistor operating in the hysteresis mode, we show that the potential barrier height for electron injection across the source-channel junction increases for increasing negative gate voltages during retrace. This results in a gate controlled turn-off of the drain current for SOI and vertical n-MOSFETs operating in the regenerative mode 相似文献
1000.
Bifidobacterium longum has been shown to afford protection against colon tumorigenesis. Lactulose, a keto analog of lactose, serves as a substrate for preferential growth of Bifidobacterium. It is not known whether feeding lactulose along with B. longum will have any advantage over feeding of B. longum alone. To test this combination effect, 61 male Fisher 344 weanling rats were divided into four groups of 15 rats each (16 in the control group) and assigned to one of the following four diets for 13 weeks: (i) AIN76A (control, C); (ii) C + 0.5% B. longum (C+Bl, containing 1 x 10(8) viable cells/g feed); (iii) C + 2.5% lactulose (C+L); (iv) C + 0.5% B. longum + 2.5% lactulose (C+Bl+L). All animals received a s.c. injection of azoxymethane at 16 mg/kg body wt at 7 and 8 weeks of age. Colons of 10 rats from each dietary group were analyzed for aberrant crypt foci (ACF), which are preneoplastic markers. Colonic mucosa and livers from five rats were analyzed for glutathione S-transferase (GST, a Phase II enzyme marker). Results indicate that feeding of lactulose and B. longum singly and in combination reduces the number of ACF (P = 0.0001) and the total number of aberrant crypts significantly (P = 0.0005). The total number of ACF in diets C, C+Bl, C+L and C+Bl+L were 187 +/- 9, 143 +/- 9, 145 +/- 11 and 97 +/- 11 respectively. There was no significant difference in weight gain among treatments. Colonic mucosal GST levels were significantly (P = 0.05) higher in the Bl and L groups compared with group C. Initially there was a mild diarrhea in lactulose-fed rats. There was a positive correlation between higher cecal pH and number of ACF. Results of the study indicate that Bifidobacterium and lactulose exert an additive antitumorigenic effect in rat colon. 相似文献