Dynamic Quantized Fracture Mechanics

A new quantum action-based theory, Dynamic Quantized Fracture Mechanics (DQFM), is presented that modifies continuum-based dynamic fracture mechanics. The crack propagation is assumed as quantized in both space and time. The static limit case corresponds to Quantized Fracture Mechanics (QFM), that we have recently developed to predict the strength of nanostructures

Computer vision

The field of computer vision is surveyed and assessed, key research issues are identified, and possibilities for a future vision system are discussed. The problems of descriptions of two and three dimensional worlds are discussed. The representation of such features as texture, edges, curves, and corners are detailed. Recognition methods are described in which cross correlation coefficients are maximized or numerical values for a set of features are measured. Object tracking is discussed in terms of the robust matching algorithms that must be devised. Stereo vision, camera control and calibration, and the hardware and systems architecture are discussed

Quantum Hall Effect in Bernal Stacked and Twisted Bilayer Graphene Grown on Cu by Chemical Vapor Deposition

We examine the quantum Hall effect in bilayer graphene grown on Cu substrates by chemical vapor deposition. Spatially resolved Raman spectroscopy suggests a mixture of Bernal (A-B) stacked and rotationally faulted (twisted) domains. Magnetotransport measurements performed on bilayer domains with a wide 2D band reveal quantum Hall states (QHSs) at filling factors $\nu=4, 8, 12$ consistent with a Bernal stacked bilayer, while magnetotransport measurements in bilayer domains defined by a narrow 2D band show a superposition of QHSs of two independent monolayers. The analysis of the Shubnikov-de Haas oscillations measured in twisted graphene bilayers provides the carrier density in each layer as a function of the gate bias and the inter-layer capacitance.Comment: 5 pages, 4 figure

Anomalous Strength Characteristics of Tilt Grain Boundaries in Graphene

Using molecular dynamics simulations and first principles calculations, we have studied the structure and mechanical strength of tilt grain boundaries in graphene sheets that arise during CVD growth of graphene on metal substrates. Surprisingly, we find that for tilt boundaries in the vicinity of both the zig-zag and arm-chair orientations, large angle boundaries with a higher density of 5-7 defect pairs are stronger than the low-angle boundaries which are comprised of fewer defects per unit length. Interestingly, the trends in our results cannot be explained by a continuum Griffith-type fracture mechanics criterion, which predicts the opposite trend due to that fact that it does not account for the critical bonds that are responsible for the failure mechanism. We have identified the highly-strained bonds in the 7-member rings that lead to the failure of the sheets, and we have found that large angle boundaries are able to better accommodate the strained 7-rings. Our results provide guidelines for designing growth methods to obtain grain boundary structures that can have strengths close to that of pristine graphene

Studies on silane to 70 GPa

Raman and X-ray diffraction studies were made on silane in the diamond anvil cell using three different gaskets, stainless steel, tungsten and rhenium. The structure existing between 10 and 27 GPa is well characterized by the monoclinic space group P21c (#14). While the Gibbs free energy of formation of silane is positive at one atmosphere, it is calculated from the equation of state of silane and its reactants that this becomes negative near 4 GPa and remains negative until 13 GPa and then becomes positive again. At about 27 GPa, where quasi-quantum mechanical calculations suggest there should be a transformation from 4-fold to 6-fold (or even higher), the sample turns black. The Raman modes seize to exist beyond 30 GPa after showing softening above 25 GPa. At higher pressures it turns silvery. The gaskets play a different role as will be discussed. The sample brought back from 70 GPa contains amorphous Si (with attached hydrogen) as well as crystalline silicon. The lowest free energy system at high pressure is the decomposed reactants as observed

Service Utilization Among Relative Caregivers: An Examination of Ethnic Differences

The purpose of this study was to describe differences between Native American, African American, and White caregivers raising relative children. Specifically, service utilization and well-being variables were examined through mean comparisons and multiple regression analyses. Participants included 274 Oklahomans who were primary caregivers to a relative child or had been within the past six months. Data were collected using surveys consisting of five original scales that assessed demographic, service utilization, barriers to service, needs assessment, and well-being variables. This study determined that ethnicity accounts for some differences found in service utilization patterns of relatives raising relative children. Specifically, African Americans were more likely to utilize formal services than Native Americans or Whites. Further, ethnicity predicted the formal service utilization for Native Americans but did not predict service utilization for African Americans or Whites. Finally, descriptive analyses revealed that the demographics of White and Native American participants were very similar.Department of Human Development and Family Scienc

(NH 4 ) 3 C 60 : A New C 60 Superconductor?

The enthalpy of formation (∆H f ) of the ionic solid (NH 4 + ) 3 C 60 3-is assessed. The solid is found to be stable with respect to the standard state reactants (N 2 (g), H 2 (g), and C 60 (s)), with a ∆H f of -1.82 eV/mol. For comparison, this enthalpy of formation is less than the enthalpy of formation of, e.g., K 3 C 60 (-6.27 eV/mol). There are several attractive features of (NH 4 + ) 3 C 60 3-as a new ionic solid and potential superconductor, if it can be synthesized. It is well-known that the size of the NH 4 + cation is almost exactly the same as that of Rb + . Among the M 3 C 60 superconductors, Rb 3 C 60 has the second highest superconducting transition temperature, with T c ) 28 K, which suggests that the T c of a superconducting (NH 4 ) 3 C 60 could be higher than yet achieved for C 60 superconductors, of which Cs 3 C 60 (s) has the highest T c of 40 K. There is a 28% relative mass change when the NH 4 + countercation is replaced by 15 ND 4 + , which is a much larger relative change than can be achieved with the alkali metal atoms, which is important for study of the isotopic substitution effect on T c . There is also the possibility of unique dynamics in which the ammonium ion rotates in the lattice; the presence of a molecular ion, rather than an atomic ion, could play a role in the mechanism of superconductivity, if the solid is superconducting. Finally, alternative methods to produce such an ammonium salt of C 60 , such as electrosynthesis or direct synthesis in liquid ammonia, would be required in contrast to the method of the production of M 3 C 60 (M ) alkali atom) based on vapor phase transport of M via sublimation in sealed tubes

Pressure-induced insulator-to-metal transition in low-dimensional TiOCl

We studied the transmittance and reflectance of the low-dimensional Mott-Hubbard insulator TiOCl in the infrared and visible frequency range as a function of pressure. The strong suppression of the transmittance and the abrupt increase of the near-infrared reflectance above 12 GPa suggest a pressure-induced insulator-to-metal transition. The pressure-dependent frequency shifts of the orbital excitations, as well as the pressure dependences of the charge gap and the spectral weight of the optical conductivity above the phase transition are presented.Comment: 4 pages, 6 figure

Adsorption/desorption and electrically controlled flipping of ammonia molecules on graphene

In this paper, we evaluate of the adsorption/ desorption of ammonia molecules on a graphene surface by studying the Fermi level shift. Based on a physically plausible model, the adsorption and desorption rates of ammonia molecules on graphene have been extracted from the measured Fermi level shift as a function of exposure time. An electric field-induced flipping behavior of ammonia molecules on graphene is suggested, based on field effect transistor (FET) measurements