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

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

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

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 $F$ and temperature $T$. 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

A Pliocene gray whale (Eschrichtius sp.) from the eastern North Atlantic

The gray whale Eschrichtius robustus, the only living member of the eschrichtiid lineage, currently inhabits only the North Pacific. Interestingly, however, the holotypes of both E. robustus and the late Miocene Archaeschrichtius ruggieroi (the oldest known eschrichtiid species) come from the North Atlantic and the Mediterranean, respectively. Here we describe a partial mysticete mandible from the Pliocene (3.71–2.76 Ma) of Belgium (Eastern North Atlantic). This new fossil displays a combination of morphological features that makes it nearly identical to modern E. robustus. Nevertheless, given its incomplete nature, the studied specimen is here identified in open nomenclature as belonging to Eschrichtius sp. The recognition of such an early record of Eschrichtius in the North Atlantic suggests that this genus developed a circum-Northern Hemisphere distribution not later than in Pliocene times, thus complicating our understanding of its origin, evolutionary history, and palaeobiogeographic patterns

Dynamics of coherent and incoherent emission from an artificial atom in a 1D space

We study dynamics of an artificial two-level atom in an open 1D space by measuring evolution of its coherent and incoherent emission. States of the atom -- a superconducting flux qubit coupled to a transmission line -- are fully controlled by resonant excitation microwave pulses. The coherent emission -- a direct measure of superposition in the atom -- exhibits decaying oscillations shifted by $\pi/2$ from oscillations of the incoherent emission, which, in turn, is proportional to the atomic population. The emission dynamics provides information about states and properties of the atom. By measuring the coherent dynamics, we derive two-time correlation function of fluctuations and, using quantum regression formula, reconstruct the incoherent spectrum of the resonance fluorescence triplet, which is in a good agreement with the directly measured one.Comment: 4 pages, 4 figure

Defect formation and diffusion mechanism in ion-assisted molecular-beam epitaxy

A simple moving boundary diffusion model has been used to characterize defect incorporation kinetics during ion-assisted molecular-beam epitaxy. The model permits analysis of the dependence of the final defect concentration on the growth rate, defect diffusivity, defect production range, and the shape of defect depth distribution. The results indicate a linear dependence of the final defect concentration on the ion-to-atom flux ratio which is in the growth-rate-limited regime of the model. Comparison between the model and the film strains measured by x-ray rocking curve analyses has been made and reveals that the thermal spike energy deposited by the bombarding ions during epitaxial growth has a significant effect on the apparent activation energy of the defect migration. A transition temperature above which the defect migration is thermally activated and below which the defect migration is cascade assisted can be defined. The experimentally observed temperature dependence of the defect concentration can be attributed to cascade-assisted diffusion of the defects. Comparison between the model and the multisite multiply activated migration model for low-energy dopant incorporation has also been made. The results show the similarity between the defect incorporation and dopant incorporation which gives a unified view of both processes

Non-Ergodic Dynamics of the 2D Random-phase Sine-Gordon Model: Applications to Vortex-Glass Arrays and Disordered-Substrate Surfaces

The dynamics of the random-phase sine-Gordon model, which describes 2D vortex-glass arrays and crystalline surfaces on disordered substrates, is investigated using the self-consistent Hartree approximation. The fluctuation-dissipation theorem is violated below the critical temperature T_c for large time t>t* where t* diverges in the thermodynamic limit. While above T_c the averaged autocorrelation function diverges as Tln(t), for T<T_c it approaches a finite value q* proportional to 1/(T_c-T) as q(t) = q* - c(t/t*)^{-\nu} (for t --> t*) where \nu is a temperature-dependent exponent. On larger time scales t > t* the dynamics becomes non-ergodic. The static correlations behave as Tln{x} for T>T_c and for T<T_c when x < \xi* with \xi* proportional to exp{A/(T_c-T)}. For scales x > \xi*, they behave as (T/m)ln{x} where m is approximately T/T_c near T_c, in general agreement with the variational replica-symmetry breaking approach and with recent simulations of the disordered-substrate surface. For strong- coupling the transition becomes first-order.Comment: 12 pages in LaTeX, Figures available upon request, NSF-ITP 94-10

Near-Equilibrium Dynamics of Crystalline Interfaces with Long-Range Interactions in 1+1 Dimensional Systems

The dynamics of a one-dimensional crystalline interface model with long-range interactions is investigated. In the absence of randomness, the linear response mobility decreases to zero when the temperature approaches the roughening transition from above, in contrast to a finite jump at the critical point in the Kosterlitz-Thouless (KT) transition. In the presence of substrate disorder, there exists a phase transition into a low-temperature pinning phase with a continuously varying dynamic exponent $z>1$. The expressions for the non-linear response mobility of a crystalline interface in both cases are also derived.Comment: 14 Pages, Revtex3.0, accepted to be published in Phys. Rev. E Rapid Communicatio

Peripheral trauma and risk of dystonia: What are the evidences and potential co-risk factors from a population insurance database?

BACKGROUND: Dystonia is a neurological syndrome typically resulting in abnormal postures. OBJECTIVES: We tested the role of physical injury as potential risk factor for development of dystonia using The National Health Insurance Research Database of Taiwan. METHODS: We identified 65704 people who were coded in the database as having had peripheral traumatic injuries (ICD-9-CM 807-848 and 860-959) in the year 2000. Patients with traumatic brain or spine injuries were excluded from analysis. We matched them using purposive sampling with 65704 people in the database who had not suffered peripheral trauma. We looked then at the incidence of dystonia occurring at least 1 year from the date of the peripheral trauma until 2011. Psychiatric symptoms (depression and anxiety) and sleeps difficulties have been investigated as potential covariates. RESULTS: We found 189 patients with dystonia (0.28%) in the trauma group, and 52 patients with dystonia (0.08%) in the non-trauma group. Trauma was independently associated with dystonia (adjusted HR = 3.12, 95% CI = 2.30-4.24). The incidence density of dystonia in the trauma group was 2.27 per 10000 person-years, while it was 0.71 per 10000 person-years in the non-trauma group Beyond the peripheral trauma, other variables associated to the incidence of dystonia included female sex, aged 40 years and above, depression and sleep disorders. CONCLUSION: These data from a large population dataset support traumatic injury as a risk factor for the development of dystonia