955 research outputs found
Shape complexity and fractality of fracture surfaces of swelled isotactic polypropylene with supercritical carbon dioxide
We have investigated the fractal characteristics and shape complexity of the
fracture surfaces of swelled isotactic polypropylene Y1600 in supercritical
carbon dioxide fluid through the consideration of the statistics of the islands
in binary SEM images. The distributions of area , perimeter , and shape
complexity follow power laws , , and , with the scaling ranges spanning
over two decades. The perimeter and shape complexity scale respectively as
and in two scaling regions delimited by . The fractal dimension and shape complexity increase when the temperature
decreases. In addition, the relationships among different power-law scaling
exponents , , , , and have been derived analytically,
assuming that , , and follow power-law distributions.Comment: RevTex, 6 pages including 7 eps figure
Nanometer-scale sharpness in corner-overgrown heterostructures
A corner-overgrown GaAs/AlGaAs heterostructure is investigated with
transmission and scanning transmission electron microscopy, demonstrating
self-limiting growth of an extremely sharp corner profile of 3.5 nm width. In
the AlGaAs layers we observe self-ordered diagonal stripes, precipitating
exactly at the corner, which are regions of increased Al content measured by an
XEDS analysis. A quantitative model for self-limited growth is adapted to the
present case of faceted MBE growth, and the corner sharpness is discussed in
relation to quantum confined structures. We note that MBE corner overgrowth
maintains nm-sharpness even after microns of growth, allowing the realization
of corner-shaped nanostructures.Comment: 4 pages, 3 figure
Response of Multi-strip Multi-gap Resistive Plate Chamber
A prototype of Multi-strip Multi-gap Resistive Plate chamber (MMRPC) with
active area 40 cm 20 cm has been developed at SINP, Kolkata. Detailed
response of the developed detector was studied with the pulsed electron beam
from ELBE at Helmholtz-Zentrum Dresden-Rossendorf. In this report the response
of SINP developed MMRPC with different controlling parameters is described in
details. The obtained time resolution () of the detector after slew
correction was 91.53 ps. Position resolution measured along ()
and across () the strip was 2.80.6 cm and 0.58 cm, respectively.
The measured absolute efficiency of the detector for minimum ionizing particle
like electron was 95.81.3 . Better timing resolution of the detector
can be achieved by restricting the events to a single strip. The response of
the detector was mainly in avalanche mode but a few percentage of streamer mode
response was also observed. A comparison of the response of these two modes
with trigger rate was studiedComment: 19 pages, 26 figure
Synthesis of nanostructures in nanowires using sequential catalyst reactions.
Nanowire growth by the vapour-liquid-solid (VLS) process enables a high level of control over nanowire composition, diameter, growth direction, branching and kinking, periodic twinning, and crystal structure. The tremendous impact of VLS-grown nanowires is due to this structural versatility, generating applications ranging from solid-state lighting and single-photon sources to thermoelectric devices. Here, we show that the morphology of these nanostructures can be further tailored by using the liquid droplets that catalyse nanowire growth as a 'mixing bowl', in which growth materials are sequentially supplied to nucleate new phases. Growing within the liquid, these phases adopt the shape of faceted nanocrystals that are then incorporated into the nanowires by further growth. We demonstrate this concept by epitaxially incorporating metal-silicide nanocrystals into Si nanowires with defect-free interfaces, and discuss how this process can be generalized to create complex nanowire-based heterostructures.Supported by the National Science Foundation under Grants No. DMR-0606395 and 0907483 (YCC), ERC Grant 279342: InSituNANO (FP, SH), the National Science Council of Taiwan under Grant No. NSC-101-2112-M-009-021-MY3 (YCC), the Center for Interdisciplinary Science under the MOE-ATU project for NCTU (YCC) and the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract DE-AC02-98CH10886 (DZ and EAS).This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nmat435
Efficiency determination of resistive plate chambers for fast quasi-monoenergetic neutrons
Composite detectors made of stainless steel converters and multigap resistive
plate chambers have been irradiated with quasi-monoenergetic neutrons with a
peak energy of 175MeV. The neutron detection efficiency has been determined
using two different methods. The data are in agreement with the output of Monte
Carlo simulations. The simulations are then extended to study the response of a
hypothetical array made of these detectors to energetic neutrons from a
radioactive ion beam experiment.Comment: Submitted to Eur.Phys.J. A; upgraded version correcting some typos
and updating ref.
Surface Crystallization of Liquid Au-Si and Its Impact on Catalysis.
In situ transmission electron microscopy reveals that an atomically thin crystalline phase at the surface of liquid Au-Si is stable over an unexpectedly wide range of conditions. By measuring the surface structure as a function of liquid temperature and composition, a simple thermodynamic model is developed to explain the stability of the ordered phase. The presence of surface ordering plays a key role in the pathway by which the Au-Si eutectic solidifies and also dramatically affects the catalytic properties of the liquid, explaining the anomalously slow growth kinetics of Si nanowires at low temperature. A strategy to control the presence of the surface phase is discussed, using it as a tool in designing strategies for nanostructure growth
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