1,421 research outputs found
Optical alignment and polarization conversion of neutral exciton spin in individual InAs/GaAs quantum dots
We investigate exciton spin memory in individual InAs/GaAs self-assembled
quantum dots via optical alignment and conversion of exciton polarization in a
magnetic field. Quasiresonant phonon-assisted excitation is successfully
employed to define the initial spin polarization of neutral excitons. The
conservation of the linear polarization generated along the bright exciton
eigenaxes of up to 90% and the conversion from circular- to linear polarization
of up to 47% both demonstrate a very long spin relaxation time with respect to
the radiative lifetime. Results are quantitatively compared with a model of
pseudo-spin 1/2 including heavy-to-light hole mixing.Comment: 5 pages, 3 figure
How schlieren affects beam transmissometers and LISST-Deep: an example from the stratified Danube River delta, NW Black Sea
The term ‘schlieren’ describes angular deflection of a light ray when it passes through a fluid region characterized by refractive index inhomogeneities. These inhomogeneities in the marine environment are generally caused by density variations, i.e. salinity and temperature anomalies. The influence of schlieren on transmissometers and the in situ particle sizer LISST-Deep of Sequoia Scientific are examined in the Danube delta during October 2007. A seasonal pycnocline driven mainly by an intense temperature gradient was identified as a major hydrological feature. It was associated with high buoyancy frequency values and minor changes of the refractive index of seawater. Measurements of two 25-cm path-length transmissometers (660 nm and 470 nm) showed distinguishable peaks at the pycnocline. LISST also uses a 5-cm transmissometer (670 nm), which proved to be very sensitive in both cases. This is mainly due to its very small acceptance angle, which enables enhanced light scattering outside the lens, thus increasing beam attenuation. Subsequently, LISST falsely predicts abundance of large particles within the pycnoclines. A buoyancy frequency N of 0.01 s-1 is the new proposed threshold for schlieren occurrence
SleepTransformer: Automatic Sleep Staging with Interpretability and Uncertainty Quantification.
BACKGROUND: Black-box skepticism is one of the main hindrances impeding deep-learning-based automatic sleep scoring from being used in clinical environments. METHODS: Towards interpretability, this work proposes a sequence-to-sequence sleep staging model, namely SleepTransformer. It is based on the transformer backbone and offers interpretability of the models decisions at both the epoch and sequence level. We further propose a simple yet efficient method to quantify uncertainty in the models decisions. The method, which is based on entropy, can serve as a metric for deferring low-confidence epochs to a human expert for further inspection. RESULTS: Making sense of the transformers self-attention scores for interpretability, at the epoch level, the attention scores are encoded as a heat map to highlight sleep-relevant features captured from the input EEG signal. At the sequence level, the attention scores are visualized as the influence of different neighboring epochs in an input sequence (i.e. the context) to recognition of a target epoch, mimicking the way manual scoring is done by human experts. CONCLUSION: Additionally, we demonstrate that SleepTransformer performs on par with existing methods on two databases of different sizes. SIGNIFICANCE: Equipped with interpretability and the ability of uncertainty quantification, SleepTransformer holds promise for being integrated into clinical settings
Testing of Frozen Turbulence Hypothesis for Wind Turbine Applications with a Scanning LIDAR System
Formation and Structure of Graphene Waves on Fe(110)
A very rich Fe-C phase diagram makes the formation of graphene on iron surfaces a challenging task. Here we demonstrate that the growth of graphene on epitaxial iron films can be realized by chemical vapor deposition at relatively low temperatures, and that the formation of carbides can be avoided in excess of the carbon-containing precursors. The resulting graphene monolayer creates a novel periodically corrugated pattern on Fe(110). Using low-energy electron microscopy and scanning tunneling microscopy, we show that it is modulated in one dimension forming long waves with a period of similar to 4 nm parallel to the [001] direction of the substrate, with an additional height modulation along the wave crests. The observed topography of the graphene/Fe superstructure is well reproduced by density functional theory calculations, and found to result from a unique combination of the lattice mismatch and strong interfacial interaction, as probed by core-level photoemission and x-ray absorption spectroscopy
Channeling of Positrons through Periodically Bent Crystals: on Feasibility of Crystalline Undulator and Gamma-Laser
The electromagnetic radiation generated by ultra-relativistic positrons
channelling in a crystalline undulator is discussed. The crystalline undulator
is a crystal whose planes are bent periodically with the amplitude much larger
than the interplanar spacing. Various conditions and criteria to be fulfilled
for the crystalline undulator operation are established. Different methods of
the crystal bending are described. We present the results of numeric
calculations of spectral distributions of the spontaneous radiation emitted in
the crystalline undulator and discuss the possibility to create the stimulated
emission in such a system in analogy with the free electron laser. A careful
literature survey covering the formulation of all essential ideas in this field
is given. Our investigation shows that the proposed mechanism provides an
efficient source for high energy photons, which is worth to study
experimentally.Comment: 52 pages, MikTeX, 14 figure
What are the career implications of “seeing eye to eye”? Examining the role of leader–member exchange (LMX) agreement on employability and career outcomes
National critical incident reporting systems relevant to anaesthesia: a European survey
Background Critical incident reporting is a key tool in the promotion of patient safety in anaesthesia. Methods We surveyed representatives of national incident reporting systems in six European countries, inviting information on scope and organization, and intelligence on factors determining success and failure. Results Some systems are government-run and nationally conceived; others started out as small, specialty-focused initiatives, which have since acquired a national reach. However, both national co-ordination and specialty enthusiasts seem to be necessary for an optimally functioning system. The role of reporting culture, definitional issues, and dissemination is discussed. Conclusions We make recommendations for others intending to start new systems and speculate on the prospects for sharing patient safety lessons relevant to anaesthesia at European leve
VLT/X-shooter spectroscopy of the afterglow of the Swift GRB 130606A: Chemical abundances and reionisation at
The reionisation of the Universe is thought to have ended around z~6, as
inferred from spectroscopy of distant bright background sources, such as
quasars (QSO) and gamma-ray burst (GRB) afterglows. Furthermore, spectroscopy
of a GRB afterglow provides insight in its host galaxy, which is often too dim
and distant to study otherwise. We present the high S/N VLT/X-shooter spectrum
of GRB130606A at z=5.913. We aim to measure the degree of ionisation of the IGM
between 5.02<z<5.84 and to study the chemical abundance pattern and dust
content of its host galaxy. We measured the flux decrement due to absorption at
Ly, and wavelength regions. The hydrogen and metal
absorption lines formed in the host galaxy were fitted with Voigt profiles to
obtain column densities. Our measurements of the Ly-forest optical
depth are consistent with previous measurements of QSOs, but have a much
smaller uncertainty. The analysis of the red damping wing yields a neutral
fraction (3). We obtain column density measurements of
several elements. The ionisation corrections due to the GRB is estimated to be
negligible (<0.03 dex), but larger corrections may apply due to the
pre-existing radiation field (up to 0.4 dex based on sub-DLA studies). Our
measurements confirm that the Universe is already predominantly ionised over
the redshift range probed in this work, but was slightly more neutral at z>5.6.
GRBs are useful probes of the ionisation state of the IGM in the early
Universe, but because of internal scatter we need a larger statistical sample
to draw robust conclusions. The high [Si/Fe] in the host can be due to dust
depletion, alpha-element enhancement, or a combination of both. The very high
value of [Al/Fe]=2.40+/-0.78 might connected to the stellar population history.
We estimate the host metallicity to be -1.7<[M/H]<-0.9 (2%-13% of solar).
(trunc.)Comment: 15 pages, 12 figure
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