3,726 research outputs found
Enhanced photoluminescence emission from two-dimensional silicon photonic crystal nanocavities
We present a temperature dependent photoluminescence study of silicon optical
nanocavities formed by introducing point defects into two-dimensional photonic
crystals. In addition to the prominent TO phonon assisted transition from
crystalline silicon at ~1.10 eV we observe a broad defect band luminescence
from ~1.05-1.09 eV. Spatially resolved spectroscopy demonstrates that this
defect band is present only in the region where air-holes have been etched
during the fabrication process. Detectable emission from the cavity mode
persists up to room-temperature, in strong contrast the background emission
vanishes for T > 150 K. An Ahrrenius type analysis of the temperature
dependence of the luminescence signal recorded either in-resonance with the
cavity mode, or weakly detuned, suggests that the higher temperature stability
may arise from an enhanced internal quantum efficiency due to the
Purcell-effect
Dephasing of quantum dot exciton polaritons in electrically tunable nanocavities
We experimentally and theoretically investigate dephasing of zero dimensional
microcavity polaritons in electrically tunable single dot photonic crystal
nanocavities. Such devices allow us to alter the dot-cavity detuning in-situ
and to directly probe the influence on the emission spectrum of varying the
incoherent excitation level and the lattice temperature. By comparing our
results with theory we obtain the polariton dephasing rate and clarify its
dependence on optical excitation power and lattice temperature. For low
excitation levels we observe a linear temperature dependence, indicative of
phonon mediated polariton dephasing. At higher excitation levels, excitation
induced dephasing is observed due to coupling to the solid-state environment.
The results provide new information on coherence properties of quantum dot
microcavity polaritons.Comment: Figure 2, panel (b) changed to logarithmic + linear scal
Component selection for livestock farms using linear programming
Also available online.Digitized 2007 AES MoU
A Correlation between the Emission Intensity of Self-Assembled Germanium Islands and the Quality Factor of Silicon Photonic Crystal Nanocavities
We present a comparative micro-photoluminescence study of the emission
intensity of self-assembled germanium islands coupled to the resonator mode of
two-dimensional silicon photonic crystal defect nanocavities. The emission
intensity is investigated for cavity modes of L3 and Hexapole cavities with
different cavity quality factors. For each of these cavities many nominally
identical samples are probed to obtain reliable statistics. As the quality
factor increases we observe a clear decrease in the average mode emission
intensity recorded under comparable optical pumping conditions. This clear
experimentally observed trend is compared with simulations based on a
dissipative master equation approach that describes a cavity weakly coupled to
an ensemble of emitters. We obtain evidence that reabsorption of photons
emitted into the cavity mode is responsible for the observed trend. In
combination with the observation of cavity linewidth broadening in power
dependent measurements, we conclude that free carrier absorption is the
limiting effect for the cavity mediated light enhancement under conditions of
strong pumping.Comment: 8 pages, 5 figure
Mirizzi Syndrome Type I: A Case Presentation.
Mirizzi syndrome (MS) is a rare complication of chronic cholelithiasis. The syndrome describes gallstone obstruction of Hartmann\u27s pouch or the cystic duct that extrinsically compresses the common hepatic duct, causing obstructive jaundice. In advanced cases, the gallstones may erode into the biliary tree creating a fistula, requiring prompt diagnosis and careful surgical management. We present a case of an 82-year-old female who presented with upper abdominal pain and jaundice, later diagnosed with suspected MS type I, and managed surgically. We aim to highlight MS type I because of the potential progression and damage to the bile duct, creating complications that may affect overall patient outcome
Effects of varying management levels of crops and livestock on optimal farm organizations
"Publication authorized July 17, 1964.
Using Asymmetry to Your Advantage: Learning to Acquire and Accept External Assistance During Prolonged Split-belt Walking
People can learn to exploit external assistance during walking to reduce energetic cost. For example, walking on a split-belt treadmill affords the opportunity for people to redistribute the mechanical work performed by the legs to gain assistance from the difference in belts’ speed and reduce energetic cost. Though we know what people should do to acquire this assistance, this strategy is not observed during typical adaptation studies. We hypothesized that extending the time allotted for adaptation would result in participants adopting asymmetric step lengths to increase the assistance they can acquire from the treadmill. Here, participants walked on a split-belt treadmill for 45 min while we measured spatiotemporal gait variables, metabolic cost, and mechanical work. We show that when people are given sufficient time to adapt, they naturally learn to step further forward on the fast belt, acquire positive mechanical work from the treadmill, and reduce the positive work performed by the legs. We also show that spatiotemporal adaptation and energy optimization operate over different timescales: people continue to reduce energetic cost even after spatiotemporal changes have plateaued. Our findings support the idea that walking with symmetric step lengths, which is traditionally thought of as the endpoint of adaptation, is only a point in the process by which people learn to take advantage of the assistance provided by the treadmill. These results provide further evidence that reducing energetic cost is central in shaping adaptive locomotion, but this process occurs over more extended timescales than those used in typical studies
Room temperature spin-orbit torque switching induced by a topological insulator
Recent studies on the magneto-transport properties of topological insulators
(TI) have attracted great attention due to the rich spin-orbit physics and
promising applications in spintronic devices. Particularly the strongly
spin-moment coupled electronic states have been extensively pursued to realize
efficient spin-orbit torque (SOT) switching. However, so far current-induced
magnetic switching with TI has only been observed at cryogenic temperatures. It
remains a controversial issue whether the topologically protected electronic
states in TI could benefit spintronic applications at room temperature. In this
work, we report full SOT switching in a TI/ferromagnet bilayer heterostructure
with perpendicular magnetic anisotropy at room temperature. The low switching
current density provides a definitive proof on the high SOT efficiency from TI.
The effective spin Hall angle of TI is determined to be several times larger
than commonly used heavy metals. Our results demonstrate the robustness of TI
as an SOT switching material and provide a direct avenue towards applicable
TI-based spintronic devices
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