First-principles study of the Young's modulus of Si <001> nanowires

We report the results of first-principles density functional theory calculations of the Young's modulus and other mechanical properties of hydrogen-passivated Si nanowires. The nanowires are taken to have predominantly {100} surfaces, with small {110} facets. The Young's modulus, the equilibrium length and the residual stress of a series of prismatic wires are found to have a size dependence that scales like the surface area to volume ratio for all but the smallest wires. We analyze the physical origin of the size dependence, and compare the results to two existing models.Comment: 5 pages, 3 figure

First-principles calculation of mechanical properties of Si <001> nanowires and comparison to nanomechanical theory

We report the results of first-principles density functional theory calculations of the Young's modulus and other mechanical properties of hydrogen-passivated Si nanowires. The nanowires are taken to have predominantly {100} surfaces, with small {110} facets according to the Wulff shape. The Young's modulus, the equilibrium length and the constrained residual stress of a series of prismatic beams of differing sizes are found to have size dependences that scale like the surface area to volume ratio for all but the smallest beam. The results are compared with a continuum model and the results of classical atomistic calculations based on an empirical potential. We attribute the size dependence to specific physical structures and interactions. In particular, the hydrogen interactions on the surface and the charge density variations within the beam are quantified and used both to parameterize the continuum model and to account for the discrepancies between the two models and the first-principles results.Comment: 14 pages, 10 figure

Power and control: contracts and the patient–physician relationship

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/88075/1/j.1742-1241.2011.02762.x.pd

Gate Coupling to Nanoscale Electronics

The realization of single-molecule electronic devices, in which a nanometer-scale molecule is connected to macroscopic leads, requires the reproducible production of highly ordered nanoscale gaps in which a molecule of interest is electrostatically coupled to nearby gate electrodes. Understanding how the molecule-gate coupling depends on key parameters is crucial for the development of high-performance devices. Here we directly address this, presenting two- and three-dimensional finite-element electrostatic simulations of the electrode geometries formed using emerging fabrication techniques. We quantify the gate coupling intrinsic to these devices, exploring the roles of parameters believed to be relevant to such devices. These include the thickness and nature of the dielectric used, and the gate screening due to different device geometries. On the single-molecule (~1nm) scale, we find that device geometry plays a greater role in the gate coupling than the dielectric constant or the thickness of the insulator. Compared to the typical uniform nanogap electrode geometry envisioned, we find that non-uniform tapered electrodes yield a significant three orders of magnitude improvement in gate coupling. We also find that in the tapered geometry the polarizability of a molecular channel works to enhance the gate coupling

Ethnic Identity, Acculturation, Parenting Beliefs, and Adolescent Adjustment: A Comparison of Asian Indian and European American Families

Currently, little is known about how child-rearing beliefs change as immigrant families adapt to the host culture and about the extent to which these beliefs begin to approximate the American mainstream. This study examined how parents’ child-rearing beliefs were associated with the psychological well-being of 360 (180 Asian Indian and 180 European American) adolescents. Asian Indian adolescents reported higher family conflict, ethnic identity achievement, and anxiety, and their parents endorsed training and shaming child-rearing beliefs more than did European American families. Asian Indian parents who had an integrated or assimilated acculturation style approximated the European families’ family conflict ratings and their child-rearing beliefs. With exposure to situations that challenge their ways of thinking, immigrant parents develop child-rearing beliefs that allow them to function in both cultures and have positive effects on their adolescent children’s psychological adjustment

Influence of Different Strain Rates on the Flow Curve and the Formability of Thin Aluminium and Tinplate Sheets

Due to this high number of produced units and the very thin sheet metals used for beverage cans, precise production processes with high production volumes are necessary. To save expenses, while optimising these processes, numerical simulation methods are exploited. Considering this, it is indispensable to identify the material behaviour as exactly as possible. In practise, often results of quasi static tensile tests are used, although these are insufficient for the precise modelling of the material behaviour during can production, since strain rates of up to 10³ s-1 can occur, here. Therefore, quasi static and high speed tensile test have been done on specimens featuring the typical materials and thicknesses of semi-finished parts used for beverage can production. The results were compared with similar materials at higher sheet metal thicknesses and authenticated by numerical simulation. It was shown that there is an influence of the strain rate on the material behaviour and it is necessary to determine material characteristics at strain rates, which are close to the process speed. Furthermore, the results were classified in their signification for beverage can production and forming technologies in general

Coulomb Gap and Correlated Vortex Pinning in Superconductors

The positions of columnar pins and magnetic flux lines determined from a decoration experiment on BSCCO were used to calculate the single--particle density of states at low temperatures in the Bose glass phase. A wide Coulomb gap is found, with gap exponent $s \approx 1.2$, as a result of the long--range interaction between the vortices. As a consequence, the variable--range hopping transport of flux lines is considerably reduced with respect to the non--interacting case, the effective Mott exponent being enhanced from $p_0 = 1/3$ to $p_{\rm eff} \approx 0.5$ for this specific experiment.Comment: 10 pages, Revtex, 4 figures appended as uu-encoded postscript files, also available as hardcopies from [email protected]

Impact of DNA ligase IV on the fidelity of end joining in human cells

A DNA ligase IV (LIG4)‐null human pre‐B cell line and human cell lines with hypomorphic mutations in LIG4 are significantly impaired in the frequency and fidelity of end joining using an in vivo plasmid assay. Analysis of the null line demonstrates the existence of an error‐prone DNA ligase IV‐independent rejoining mechanism in mammalian cells. Analysis of lines with hypomorphic mutations demonstrates that residual DNA ligase IV activity, which is sufficient to promote efficient end joining, nevertheless can result in decreased fidelity of rejoining. Thus, DNA ligase IV is an important factor influencing the fidelity of end joining in vivo. The LIG4‐defective cell lines also showed impaired end joining in an in vitro assay using cell‐free extracts. Elevated degradation of the terminal nucleotide was observed in a LIG4‐defective line, and addition of the DNA ligase IV–XRCC4 complex restored end protection. End protection by DNA ligase IV was not dependent upon ligation. Finally, using purified proteins, we demonstrate that DNA ligase IV–XRCC4 is able to protect DNA ends from degradation by T7 exonuclease. Thus, the ability of DNA ligase IV–XRCC4 to protect DNA ends may contribute to the ability of DNA ligase IV to promote accurate rejoining in vivo

Atomic layer deposition of ZnS nanotubes

We report on growth of high-aspect-ratio ($\gtrsim300$) zinc sulfide nanotubes with variable, precisely tunable, wall thicknesses and tube diameters into highly ordered pores of anodic alumina templates by atomic layer deposition (ALD) at temperatures as low as 75 $^{\circ}$C. Various characterization techniques are employed to gain information on the composition, morphology, and crystal structure of the synthesized samples. Besides practical applications, the ALD-grown tubes could be envisaged as model systems for the study of a certain class of size-dependent quantum and classical phenomena.Comment: 1 LaTeX source file, 8 eps figures, and the manuscript in PDF forma