951 research outputs found
Erbium dopants in silicon nanophotonic waveguides
The combination of established nanofabrication with attractive material
properties makes silicon a promising material for quantum technologies, where
implanted dopants serve as qubits with high density and excellent coherence
even at elevated temperatures. In order to connect and control these qubits,
interfacing them with light in nanophotonic waveguides offers unique promise.
Here, we present resonant spectroscopy of implanted erbium dopants in such
waveguides. We overcome the requirement of high doping and above-bandgap
excitation that limited earlier studies. We thus observe erbium incorporation
at well-defined lattice sites with a thousandfold reduced inhomogeneous
broadening of about 1 GHz and a spectral diffusion linewidth down to 45 MHz.
Our study thus introduces a novel materials platform for the implementation of
on-chip quantum memories, microwave-to-optical conversion, and distributed
quantum information processing, with the unique feature of operation in the
main wavelength band of fiber-optic communication.Comment: 7 pages, 4 figure
Narrow optical transitions in erbium-implanted silicon waveguides
The realization of a scalable architecture for quantum information processing
is a major challenge for quantum science. A promising approach is based on
emitters in nanostructures that are coupled by light. Here, we show that erbium
dopants can be reproducibly integrated at well-defined lattice sites by
implantation into pure silicon. We thus achieve a narrow inhomogeneous
broadening, less than 1 GHz, strong optical transitions, and an outstanding
optical coherence even at temperatures of 8 K, with an upper bound to the
homogeneous linewidth of around 10 kHz. Our study thus introduces a promising
materials platform for the implementation of on-chip quantum memories,
microwave-to-optical conversion, and distributed quantum information
processing
Chaos in a low-order model of magnetoconvection
In the limit of tall, thin rolls, weakly nonlinear convection in a vertical magnetic field is described by an asymptotically exact third-order set of ordinary differential equations. These equations are shown here to have three codimension-two bifurcation points: a Takens-Bogdanov bifurcation, at which a gluing bifurcation is created; a point at which the gluing bifurcation is replaced by a pair of homoclinic explosions between which there are Lorenz-like chaotic trajectories; and a new type of bifurcation point at which the first of a cascade of period-doubling bifurcation lines originates. The last two bifurcation points are analysed in terms of a one-dimensional map. The equations also have a T-point, at which there is a heteroclinic connection between a saddle and a pair of saddle-foci; emerging from this point is a line of Shil'nikov bifurcations, involving homoclinic connections to a saddle-focus
Fluctuation Properties of Steady-State Langevin Systems
Motivated by stochastic models of climate phenomena, the steady-state of a
linear stochastic model with additive Gaussian white noise is studied.
Fluctuation theorems for nonequilibrium steady-states provide a constraint on
the character of these fluctuations. The properties of the fluctuations which
are unconstrained by the fluctuation theorem are investigated and related to
the model parameters. The irreversibility of trajectory segments, which
satisfies a fluctuation theorem, is used as a measure of nonequilibrium
fluctuations. The moments of the irreversibility probability density function
(pdf) are found and the pdf is seen to be non-Gaussian. The average
irreversibility goes to zero for short and long trajectory segments and has a
maximum for some finite segment length, which defines a characteristic
timescale of the fluctuations. The initial average irreversibility growth rate
is equal to the average entropy production and is related to
noise-amplification. For systems with a separation of deterministic timescales,
modes with timescales much shorter than the trajectory timespan and whose noise
amplitudes are not asymptotically large, do not, to first order, contribute to
the irreversibility statistics, providing a potential basis for dimensional
reduction.Comment: 8 pages, to be published in Physical Review
Laplace Invariants for General Hyperbolic Systems
We consider the generalization of Laplace invariants to linear differential
systems of arbitrary rank and dimension. We discuss completeness of certain
subsets of invariants
How Does Ionizing Irradiation Contribute to the Induction of Anti-Tumor Immunity?
Radiotherapy (RT) with ionizing irradiation is commonly used to locally attack tumors. It induces a stop of cancer cell proliferation and finally leads to tumor cell death. During the last years it has become more and more evident that besides a timely and locally restricted radiation-induced immune suppression, a specific immune activation against the tumor and its metastases is achievable by rendering the tumor cells visible for immune attack. The immune system is involved in tumor control and we here outline how RT induces anti-inflammation when applied in low doses and contributes in higher doses to the induction of anti-tumor immunity. We especially focus on how local irradiation induces abscopal effects. The latter are partly mediated by a systemic activation of the immune system against the individual tumor cells. Dendritic cells are the key players in the initiation and regulation of adaptive anti-tumor immune responses. They have to take up tumor antigens and consecutively present tumor peptides in the presence of appropriate co-stimulation. We review how combinations of RT with further immune stimulators such as AnnexinA5 and hyperthermia foster the dendritic cell-mediated induction of anti-tumor immune responses and present reasonable combination schemes of standard tumor therapies with immune therapies. It can be concluded that RT leads to targeted killing of the tumor cells and additionally induces non-targeted systemic immune effects. Multimodal tumor treatments should therefore tend to induce immunogenic tumor cell death forms within a tumor microenvironment that stimulates immune cells
New optical and near-infrared Surface Brightness Fluctuations models. A primary distance indicator ranging from Globular Clusters to distant galaxies?
We present new theoretical models for Surface Brightness Fluctuations (SBF)
both for optical and near-infrared bands in standard ground-based and Hubble
Space Telescope filter systems. Simple Stellar Population simulations are
adopted. Models cover the age and metallicity ranges from to and
from to 0.04 respectively. Effects due to the variation of the
Initial Mass Function and the stellar color-temperature relations are explored.
Particular attention is devoted to very bright stars in the color-magnitude
diagram and to investigate the effects of mass loss along the Red Giant Branch
(RGB) and the Asymptotic Giant Branch (AGB). It is found that and bands
SBF amplitudes are powerful diagnostics for the morphology of the Horizontal
Branch and the Post-AGB stars population. We point out that a careful treatment
of mass loss process along the RGB and AGB is fundamental in determining
reliable SBF evaluations. The SBF measurements are used to give robust
constraints on the evolution of AGB stars, suggesting that mass loss activity
on AGB stars should be twice more efficient than on the RGB stars. Our models
are able to reproduce the absolute SBF magnitudes of the Galactic Globular
Clusters and of galaxies, and their integrated colors. New calibrations of
absolute SBF magnitude in , , , and photometric filters are
provided, which appear reliable enough to directly gauge distances bypassing
other distance indicators. The SBF technique is also used as stellar population
tracer to derive age and metallicity of a selected sample of galaxies of known
distances. Finally, {\it SBF color} versus {\it integrated color} diagrams are
proposed as particularly useful in removing the well known {\it age-metallicity
degeneracy} affecting our knowledge of remote stellar systems.Comment: AJ accepted, 46 pages, 21 figures, 10 tables, uses aastex.cl
Definition und Klassifikation von Histaminfreisetzung nach Gabe von Arzneimitteln in Anästhesie und Chirurgie: Studien am wachen Menschen
The Functional Trajectory in Frail Compared With Non-frail Critically Ill Patients During the Hospital Stay
Background: Long-term outcome is determined not only by the acute critical illness but increasingly by the reduced functional reserve of pre-existing frailty. The patients with frailty currently account for one-third of the critically ill, resulting in higher mortality. There is evidence of how frailty affects the intrahospital functional trajectory of critically ill patients since prehospital status is often missing.
Methods: In this prospective single-center cohort study at two interdisciplinary intensive care units (ICUs) at a university hospital in Germany, the frailty was assessed using the Clinical Frailty Scale (CFS) in the adult patients with critical illness with an ICU stay >24 h. The functional status was assessed using the sum of the subdomains "Mobility" and "Transfer" of the Barthel Index (MTB) at three time points (pre-hospital, ICU discharge, and hospital discharge).
Results: We included 1,172 patients with a median age of 75 years, of which 290 patients (25%) were frail. In a propensity score-matched cohort, the probability of MTB deterioration till hospital discharge did not differ in the patients with frailty (odds ratio (OR) 1.3 [95% CI 0.8-1.9], p = 0.301), confirmed in several sensitivity analyses in all the patients and survivors only.
Conclusion: The patients with frailty have a reduced functional status. Their intrahospital functional trajectory, however, was not worse than those in non-frail patients, suggesting a rehabilitation potential of function in critically ill patients with frailty
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