558 research outputs found
Unconventional motional narrowing in the optical spectrum of a semiconductor quantum dot
Motional narrowing refers to the striking phenomenon where the resonance line
of a system coupled to a reservoir becomes narrower when increasing the
reservoir fluctuation. A textbook example is found in nuclear magnetic
resonance, where the fluctuating local magnetic fields created by randomly
oriented nuclear spins are averaged when the motion of the nuclei is thermally
activated. The existence of a motional narrowing effect in the optical response
of semiconductor quantum dots remains so far unexplored. This effect may be
important in this instance since the decoherence dynamics is a central issue
for the implementation of quantum information processing based on quantum dots.
Here we report on the experimental evidence of motional narrowing in the
optical spectrum of a semiconductor quantum dot broadened by the spectral
diffusion phenomenon. Surprisingly, motional narrowing is achieved when
decreasing incident power or temperature, in contrast with the standard
phenomenology observed for nuclear magnetic resonance
Time-temperature superposition in viscous liquids
Dielectric relaxation measurements on supercooled triphenyl phosphite show
that at low temperatures time-temperature superposition (TTS) is accurately
obeyed for the primary (alpha) relaxation process. Measurements on 6 other
molecular liquids close to the calorimetric glass transition indicate that TTS
is linked to an high-frequency decay of the alpha loss, while
the loss peak width is nonuniversal.Comment: 4 page
Equilibration times in numerical simulation of structural glasses: Comparing parallel tempering and conventional molecular dynamics
Generation of equilibrium configurations is the major obstacle for numerical
investigation of the slow dynamics in supercooled liquid states. The parallel
tempering (PT) technique, originally proposed for the numerical equilibration
of discrete spin-glass model configurations, has recently been applied in the
study of supercooled structural glasses. We present an investigation of the
ability of parallel tempering to properly sample the liquid configuration space
at different temperatures, by mapping the PT dynamics into the dynamics of the
closest local potential energy minima (inherent structures). Comparing the PT
equilibration process with the standard molecular dynamics equilibration
process we find that the PT does not increase the speed of equilibration of the
(slow) configurational degrees of freedom.Comment: 5 pages, 3 figure
From Teamchef Arminius to Hermann Junior: glocalised discourse about a national foundation myth
If for much of the nineteenth and twentieth centuries, the ‘Battle of the Teutoburg Forest’, fought in 9 CE between Roman armies and Germanic tribes, was predominantly a reference point for nationalist and chauvinist discourses in Germany, the first decade of the twenty-first century has seen attempts to link public remembrance with local/regional identities on the one hand and international/intercultural contact on the other. In the run up to and during the ‘anniversary year’ of 2009, German media, sports institutions and various other official institutions articulating tourist, economic and political interests attempted to create a new ‘glocalised’ version of the public memory of the Teutoburg battle. Combining methods of Cognitive Linguistics and Critical Discourse Analysis, the paper analyses the narrative and argumentative topoi employed in this re-orientation of public memory, with a special emphasis on hybrid, post-national identity-construction. Das zweitausendjährige Gedenkjahr der „Schlacht im Teutoburger Wald“ im Jahr 2009 bot eine günstige Gelegenheit, die bis in die zweite Hälfte des 20. Jahrhunderts dominante Tradition nationalistisch–chauvinistischer Deutungen des Sieges von germanischen Stämmen über drei römische Legionen zu korrigieren und zu überwinden. Der Aufsatz analysiert mit Hilfe diskurslinguistischer Methoden die Anstrengungen regionaler Institutionen und Medien, die nationale Vereinnahmung des historischen Gedenkens kritisch zu thematisieren sowie neue, zum eine lokal situierte, zum andern international orientierte Identifikationsangebote anzubieten. Die Analyse zeigt, dass solche „de-nationalisierten“ Identifikationsangebote zwar teilweise auch früher verwendet wurden, aber heutzutage rekontextualisiert und auf innovative Weise in den Vordergrund gestellt werden
Application of Terahertz Radiation to the Detection of Corrosion under the Shuttle's Thermal Protection System
There is currently no method for detecting corrosion under Shuttle tiles except for the expensive process of tile removal and replacement; hence NASA is investigating new NDE methods for detecting hidden corrosion. Time domain terahertz radiation has been applied to corrosion detection under tiles in samples ranging from small lab samples to a Shuttle with positive results. Terahertz imaging methods have been able to detect corrosion at thicknesses of 5 mils or greater under 1" thick Shuttle tiles and 7-12 mils or greater under 2" thick Shuttle tiles
The Localization Transition of the Two-Dimensional Lorentz Model
We investigate the dynamics of a single tracer particle performing Brownian
motion in a two-dimensional course of randomly distributed hard obstacles. At a
certain critical obstacle density, the motion of the tracer becomes anomalous
over many decades in time, which is rationalized in terms of an underlying
percolation transition of the void space. In the vicinity of this critical
density the dynamics follows the anomalous one up to a crossover time scale
where the motion becomes either diffusive or localized. We analyze the scaling
behavior of the time-dependent diffusion coefficient D(t) including corrections
to scaling. Away from the critical density, D(t) exhibits universal
hydrodynamic long-time tails both in the diffusive as well as in the localized
phase.Comment: 13 pages, 7 figures
Entangling single photons on a beamsplitter
We report on a scheme for the creation of time-bin entangled states out of
two subsequent single photons. Both photons arrive on the same input port of a
beamsplitter and the situation in which the photons leave the beamsplitter on
different output ports is post-selected. We derive a full quantum mechanical
analysis of such time-bin entanglement for emitters subject to uncorrelated
dephasing processes and apply this model to sequential single photons emerging
from a single semiconductor quantum dot. Our results indicate that the
visibility of entanglement is degraded by decoherence effects in the quantum
dot, but can be restored by use of CQED effects, namely the Purcell effect.Comment: Accepted EPJ
Nuclear localization and cytosolic overexpression of LASP-1 correlates with tumor size and nodal-positivity of human breast carcinoma
<p>Abstract</p> <p>Background</p> <p>LIM and SH3 protein 1 (LASP-1), initially identified from human breast cancer, is a specific focal adhesion protein involved in cell proliferation and migration, which was reported to be overexpressed in 8–12 % of human breast cancers and thought to be exclusively located in cytoplasm.</p> <p>Methods</p> <p>In the present work we analyzed the cellular and histological expression pattern of LASP-1 and its involvement in biological behavior of human breast cancer through correlation with standard clinicopathological parameters and expression of c-erbB2 (HER-2/neu), estrogen- (ER) and progesterone-receptors (PR). For this purpose immunohistochemical staining intensity and percentage of stained cells were semi-quantitatively rated to define a LASP-1 immunoreactive score (LASP-1-IRS). LASP-1-IRS was determined in 83 cases of invasive ductal breast carcinomas, 25 ductal carcinomas in situ (DCIS) and 18 fibroadenomas. Cellular LASP-1 distribution and expression pattern was visualized by immunofluorescence and confocal microscopy and assessed through separate Western blots of nuclear and cytosol preparations of BT-20, MCF-7, MDA-MB231, and ZR-75/1 breast cancer cells.</p> <p>Results</p> <p>Statistical analysis revealed that the resulting LASP-1-IRS was significantly higher in invasive carcinomas compared to fibroadenomas (p = 0.0176). Strong cytoplasmatic expression of LASP-1 was detected in 55.4 % of the invasive carcinomas, which correlated significantly with nuclear LASP-1-positivity (p = 0.0014), increased tumor size (p = 0.0159) and rate of nodal-positivity (p = 0.0066). However, levels of LASP-1 expression did not correlate with average age at time point of diagnosis, histological tumor grading, c-erbB2-, ER- or PR-expression.</p> <p>Increased nuclear localization and cytosolic expression of LASP-1 was found in breast cancer with higher tumor stage as well as in rapidly proliferating epidermal basal cells. Confocal microscopy and separate Western blots of cytosolic and nuclear preparations confirmed nuclear localization of LASP-1.</p> <p>Conclusion</p> <p>The current data provide evidence that LASP-1 is not exclusively a cytosolic protein, but is also detectable within the nucleus. Increased expression of LASP-1 in vivo is present in breast carcinomas with higher tumor stage and therefore may be related with worse prognosis concerning patients' overall survival.</p
Mitochondrial Lysyl-tRNA Synthetase Independent Import of tRNA Lysine into Yeast Mitochondria
Aminoacyl tRNA synthetases play a central role in protein synthesis by charging tRNAs with amino acids. Yeast mitochondrial lysyl tRNA synthetase (Msk1), in addition to the aminoacylation of mitochondrial tRNA, also functions as a chaperone to facilitate the import of cytosolic lysyl tRNA. In this report, we show that human mitochondrial Kars (lysyl tRNA synthetase) can complement the growth defect associated with the loss of yeast Msk1 and can additionally facilitate the in vitro import of tRNA into mitochondria. Surprisingly, the import of lysyl tRNA can occur independent of Msk1 in vivo. This suggests that an alternative mechanism is present for the import of lysyl tRNA in yeast
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