630 research outputs found
Mass Density of Individual Cobalt Nanowires
The mass density of nanowires is determined using in-situ resonance frequency
experiments combined with quasi-static nanotensile tests. Our results reveal a
mass density of 7.36 g/cm3 on average which is below the theoretical density of
bulk cobalt. Also the density of electrodeposited cobalt nanowires is found to
decrease with the aspect ratio. The results are discussed in terms of the
measurement accuracy and the microstructure of the nanowires.Comment: 3 Figure
Strength and fracture of Si micropillars: A new scanning electron microscopy-based micro-compression test
A novel method for in situ scanning electron microscope (SEM) micro-compression tests is presented. The direct SEM observation during the instrumented compression testing allows for very efficient positioning and assessment of the failure mechanism. Compression tests on micromachined Si pillars with volumes down to 2 μm3 are performed inside the SEM, and the results demonstrate the potential of the method. In situ observation shows that small diameter pillars tend to buckle while larger ones tend to crack before failure. Compressive strength increases with decreasing pillar diameter and reaches almost 9 GPa for submicrometer diameter pillars. This result is in agreement with earlier bending experiments on Si. Difficulties associated with precise strain measurements are discusse
A comparison of microtensile and microcompression methods for studying plastic properties of nanocrystalline electrodeposited nickel at different length scales
A comparison of microcompression and microtensile methods to study mechanical properties of electrodeposited nanocrystalline (nc) nickel has been performed. Microtensile tests that probe a volume of more than 2 × 106 μm3 show reasonable agreement with results from microcompression tests that probe much smaller volumes down to a few μm3. Differences between the two uniaxial techniques are discussed in terms of measurements errors, probed volume and surface effects, strain rate, and influence of stress state. Uniaxial solicitation in compression mode revealed several advantages for studying stress-strain propertie
Indistinguishable photons from the resonance fluorescence of a single quantum dot in a microcavity
We demonstrate purely resonant continuous-wave optical laser excitation to
coherently prepare an excitonic state of a single semiconductor quantum dot
(QDs) inside a high quality pillar microcavity. As a direct proof of QD
resonance fluorescence, the evolution from a single emission line to the
characteristic Mollow triplet10 is observed under increasing pump power. By
controlled utilization of weak coupling between the emitter and the fundamental
cavity mode through Purcell-enhancement of the radiative decay, a strong
suppression of pure dephasing is achieved, which reflects in close to Fourier
transform-limited and highly indistinguishable photons with a visibility
contrast of 90%. Our experiments reveal the model-like character of the coupled
QD-microcavity system as a promising source for the generation of ideal photons
at the quantum limit. From a technological perspective, the vertical cavity
symmetry -- with optional dynamic tunability -- provides strongly directed
light emission which appears very desirable for future integrated emitter
devices.Comment: 24 pages, 6 figure
A comparison of microtensile and microcompression methods for studying plastic properties of nanocrystalline electrodeposited nickel at different length scales
A comparison of microcompression and microtensile methods to study mechanical properties of electrodeposited nanocrystalline (nc) nickel has been performed. Microtensile tests that probe a volume of more than 2 × 106 μm3 show reasonable agreement with results from microcompression tests that probe much smaller volumes down to a few μm3. Differences between the two uniaxial techniques are discussed in terms of measurements errors, probed volume and surface effects, strain rate, and influence of stress state. Uniaxial solicitation in compression mode revealed several advantages for studying stress–strain properties
On the Move – Do Domestic and Wild Ungulate Species Distributions Overlap in the Mongolian Gobi?
In the Great Gobi B Strictly Protected Area (Great Gobi B), wild and domestic ungulates seasonally share the forage of the semi-desert and desert habitat. Around 130 herder families are grazing their livestock, mainly goats and sheep, in the protected area in winter. Wild ungulates of global significance in Great Gobi B include the reintroduced Przewalski’s horse (Equus ferus przewalskii),which had previously been extinct in the wild. To determine potential habitat overlaps between Przewalski’s horses and livestock, we mapped the movements of 19 livestock herds monitored via GPS collars and ranger observations of Przewalski’s horse herds over a one year period from September 2018 to August 2019. We additionally conducted focus group interviews with nomadic herders about their rangeland management. We found that pasture use in and around the Great Gobi B is still following the nomadic tradition, with herders moving camp locations on average eleven times per year, depending on forage availability. Our results show that the range of Przewalski’s horses and livestock mostly overlap around permanent and ephemeral water points. However, the same resources are used in different seasons. The protected area was recently expanded to twice its size, now also including additional herder households and traditional pastures. For the ongoing discussion about concerning the new zonation of the enlarged protected area it is important to consider both, herder and wildlife movements patterns, to meet the conservation goals of the protected area but also meet the needs of the traditional pastoral herding community
Memory effects in radiative jet energy loss
In heavy-ion collisions the created quark-gluon plasma forms a quickly
evolving background, leading to a time dependent radiative behavior of high
momentum partons traversing the medium. We use the Schwinger Keldysh formalism
to describe the jet evolution as a non-equilibrium process including the
Landau-Pomeranschuk-Migdal effect. Concentrating on photon emission, a
comparison of our results to a quasistatic calculation shows good agreement,
leading to the conclusion that the radiative behavior follows the changes in
the medium almost instantaneously
Electron beam induced softening of fused silica
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Single-particle nonlocality and entanglement with the vacuum
We propose a single-particle experiment that is equivalent to the
conventional two-particle experiment used to demonstrate a violation of Bell's
inequalities. Hence, we argue that quantum mechanical nonlocality can be
demonstrated by single-particle states. The validity of such a claim has been
discussed in the literature, but without reaching a clear consensus. We show
that the disagreement can be traced to what part of the total state of the
experiment one assigns to the (macroscopic) measurement apparatus. However,
with a conventional and legitimate interpretation of the measurement process
one is led to the conclusion that even a single particle can show nonlocal
properties.Comment: 6 pages, 5 figure
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