3,522 research outputs found
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
Atomic layer deposition of ZnS nanotubes
We report on growth of high-aspect-ratio () 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 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
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Probing Single- to Multi-Cell Level Charge Transport in Geobacter Sulfurreducens DL-1
Microbial fuel cells, in which living microorganisms convert chemical energy into electricity, represent a potentially sustainable energy technology for the future. Here we report the single-bacterium level current measurements of Geobacter sulfurreducens DL-1 to elucidate the fundamental limits and factors determining maximum power output from a microbial fuel cell. Quantized stepwise current outputs of 92(±33) and 196(±20) fA are generated from microelectrode arrays confined in isolated wells. Simultaneous cell imaging/tracking and current recording reveals that the current steps are directly correlated with the contact of one or two cells with the electrodes. This work establishes the amount of current generated by an individual Geobacter cell in the absence of a biofilm and highlights the potential upper limit of microbial fuel cell performance for Geobacter in thin biofilms.Chemistry and Chemical Biolog
A Distinct Class of Inducible Murine Type-C Viruses that Replicates in the Rabbit SIRC Cell Line
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
Imaging a 1-electron InAs quantum dot in an InAs/InP nanowire
Nanowire heterostructures define high-quality few-electron quantum dots for
nanoelectronics, spintronics and quantum information processing. We use a
cooled scanning probe microscope (SPM) to image and control an InAs quantum dot
in an InAs/InP nanowire, using the tip as a movable gate. Images of dot
conductance vs. tip position at T = 4.2 K show concentric rings as electrons
are added, starting with the first electron. The SPM can locate a dot along a
nanowire and individually tune its charge, abilities that will be very useful
for the control of coupled nanowire dots
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
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
Role of Nebulin on Actomyosin Interaction Studied in situ in Demembranated Skeletal Muscle Fibers from Newborn Mice
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