39,290 research outputs found

    A New Approximate Fracture Mechanics Analysis Methodology for Composites with a Crack or Hole

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    A new approximate theory which links the inherent flaw concept with the theory of crack tip stress singularities at a bi-material interface was developed. Three assumptions were made: (1) the existence of inherent flaw (i.e., damage zone) at the tip of the crack, (2) a fracture of the filamentary composites initiates at a crack lying in the matrix material at the interface of the matrix/filament, and (3) the laminate fails whenever the principal load-carrying laminae fails. This third assumption implies that for a laminate consisting of 0 degree plies, cracks into matrix perpendicular to the 0 degree filaments are the triggering mechanism for the final failure. Based on this theory, a parameter bar K sub Q which is similar to the stress intensity factor for isotropic materials but with a different dimension was defined. Utilizing existing test data, it was found that bar K sub Q can be treated as a material constant. Based on this finding a fracture mechanics analysis methodology was developed. The analytical results are correlated well with test results. This new approximate theory can apply to both brittle and metal matrix composite laminates with crack or hole

    Strain modification in coherent Ge and SixGe1–x epitaxial films by ion-assisted molecular beam epitaxy

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    We have observed large changes in Ge and SixGe1–x layer strain during concurrent molecular beam epitaxial growth and low-energy bombardment. Layers are uniformly strained, coherent with the substrate, and contain no dislocations, suggesting that misfit strain is accommodated by free volume changes associated with injection of ion bombardment induced point defects. The dependence of layer strain on ion energy, ion-atom flux ratio, and temperature is consistent with the presence of a uniform dispersion of point defects at high concentration. Implications for distinguishing ion-surface interactions from ion-bulk interactions are discussed

    Dynamical Properties of a Growing Surface on a Random Substrate

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    The dynamics of the discrete Gaussian model for the surface of a crystal deposited on a disordered substrate is investigated by Monte Carlo simulations. The mobility of the growing surface was studied as a function of a small driving force FF and temperature TT. A continuous transition is found from high-temperature phase characterized by linear response to a low-temperature phase with nonlinear, temperature dependent response. In the simulated regime of driving force the numerical results are in general agreement with recent dynamic renormalization group predictions.Comment: 10 pages, latex, 3 figures, to appear in Phys. Rev. E (RC

    The Effect of Infections on the Mortality of Cirrhotic Patients with Hepatic Encephalopathy

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    [[abstract]]Cirrhotic patients are prone to having infections, which may aggravate hepatic encephalopathy (HE). However, the effect of infections on mortality in HE cirrhotic patients is not well described. The National Health Insurance Database, derived from the Taiwan National Health Insurance Programme, was used to identify 4150 adult HE cirrhotic patients hospitalized between 1 January 2004 and 31 December 2004. Nine hundred and eighty-five patients (23.7%) had one or more co-existing infections during their hospitalization. After Cox proportional hazard regression modelling adjusted by the patients' gender, age, and medical comorbidity disorders, the hazard ratios (HRs) in HE patients with infections for 30-day, 30- to 90-day, and 90-day to 1-year mortalities were 1.66 [95% confidence interval (CI) 1.42-1.94], 1.51 (95% CI 1.23-1.85) and 1.34 (95% CI 1.13-1.58), respectively. Compared to the non-infection group, the HRs of pneumonia, spontaneous bacterial peritonitis, urinary tract infection, sepsis without specific focus (SWSF), cellulitis, and biliary tract infection were 2.11, 1.48, 1.06, 2.21, 1.06, and 0.78, respectively, for 30-day mortality; 1.82, 1.22, 0.93, 2.24, 0.31, and 2.82, respectively, for 30- to 90-day mortality; and 2.03, 0.82, 1.24, 1.64, 1.14, and 0.60, respectively, for 90-day to 1-year mortality for HE cirrhotic patients. We conclude that infections increase the mortality of HE cirrhotic patients, especially pneumonia and SWSF.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子
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