570 research outputs found
Evaluating epidemic forecasts in an interval format
For practical reasons, many forecasts of case, hospitalization and death
counts in the context of the current COVID-19 pandemic are issued in the form
of central predictive intervals at various levels. This is also the case for
the forecasts collected in the COVID-19 Forecast Hub
(https://covid19forecasthub.org/). Forecast evaluation metrics like the
logarithmic score, which has been applied in several infectious disease
forecasting challenges, are then not available as they require full predictive
distributions. This article provides an overview of how established methods for
the evaluation of quantile and interval forecasts can be applied to epidemic
forecasts in this format. Specifically, we discuss the computation and
interpretation of the weighted interval score, which is a proper score that
approximates the continuous ranked probability score. It can be interpreted as
a generalization of the absolute error to probabilistic forecasts and allows
for a decomposition into a measure of sharpness and penalties for over- and
underprediction
Resonant and non-resonant Tunneling through a double barrier
An explicit expression is obtained for the phase-time corresponding to
tunneling of a (non-relativistic) particle through two rectangular barriers,
both in the case of resonant and in the case of non-resonant tunneling. It is
shown that the behavior of the transmission coefficient and of the tunneling
phase-time near a resonance is given by expressions with "Breit-Wigner type"
denominators. By contrast, it is shown that, when the tunneling probability is
low (but not negligible), the non-resonant tunneling time depends on the
barrier width and on the distance between the barriers only in a very weak
(exponentially decreasing) way: This can imply in various cases, as well-known,
the highly Superluminal tunneling associated with the so-called "generalized
Hartman Effect"; but we are now able to improve and modify the mathematical
description of such an effect, and to compare more in detail our results with
the experimental data for non-resonant tunneling of photons. Finally, as a
second example, the tunneling phase-time is calculated, and compared with the
available experimental results, in the case of the quantum-mechanical tunneling
of neutrons through two barrier-filters at the resonance energy of the set-up.Comment: replaced with some improvements in the text and in the references:
pdf (11 pages) produced from a source-file in Word; including one Figur
Electron propagation in crossed magnetic and electric fields
Laser-atom interaction can be an efficient mechanism for the production of
coherent electrons. We analyze the dynamics of monoenergetic electrons in the
presence of uniform, perpendicular magnetic and electric fields. The Green
function technique is used to derive analytic results for the field--induced
quantum mechanical drift motion of i) single electrons and ii) a dilute Fermi
gas of electrons. The method yields the drift current and, at the same time it
allows us to quantitatively establish the broadening of the (magnetic) Landau
levels due to the electric field: Level number k is split into k+1 sublevels
that render the th oscillator eigenstate in energy space. Adjacent Landau
levels will overlap if the electric field exceeds a critical strength. Our
observations are relevant for quantum Hall configurations whenever electric
field effects should be taken into account.Comment: 11 pages, 2 figures, submitte
Direct measurement of plasmon propagation lengths on lithographically defined metallic waveguides on GaAs
We present optical investigations of rectangular surface plasmon polariton
waveguides lithographically defined on GaAs substrates. The plasmon propagation
length is directly determined using a confocal microscope, with independent
polarization control in both excitation and detection channels. Surface plasmon
polaritons are launched along the waveguide using a lithographically defined
defect at one end. At the remote end of the waveguide they scatter into the
far-field, where they are imaged using a CCD camera. By monitoring the length
dependence of the intensity of scattered light from the waveguide end, we
directly extract the propagation length, obtaining values ranging from LSPP =
10-40 {\mu}m depending on the waveguide width (w=2-5 {\mu}m) and excitation
wavelength (760-920 nm). Results are in good accord with theoretical
expectations demonstrating the high quality of the lithographically defined
structures. The results obtained are of strong relevance for the development of
future semiconductor based integrated plasmonic technologies
Malnutrition in community-dwelling older people: lessons learnt using a new procedure
This article reports the implementation of a new procedure for screening and treatment of malnutrition in a community NHS trust in England. The barriers and facilitators to implementation were assessed with staff from Integrated Community and Older People's Mental Health teams. Data from interviews and surveys were collected at baseline, 2 months after initial training and 16 months after initial training as well as following deployment of a nutrition lead to embed new developments for nutritional care. The adoption of the procedure made screening and treatment of malnutrition simpler and more likely to be actioned. The benefit of a nutrition lead and local nutrition champions to support and empower staff (avoiding reliance on training alone) was shown to drive change for nutritional care across the community. Prioritisation and commitment of leadership at the organisational level are needed to embed and sustain malnutrition screening and treatment in routine practice
Aminomethylation/hydrogenolysis as an alternative to direct methylation of metalated isoquinolines - a novel total synthesis of the alkaloid 7-hydroxy-6-methoxy-1-methylisoquinoline
Highly-substituted isoquinolines are important scaffolds in syntheses of natural products and in drug development and hence, effective synthetic approaches are required. Here we present a novel method for the introduction of a methyl group at C1 of isoquinolines. This is exemplified by a new total synthesis of the alkaloid 7-hydroxy-6-methoxy-1-methylisoquinoline. Direct metalation of 7-benzyloxy-6-methoxyisoquinoline with Knochel-Hauser base, followed by cuprate-mediated methylation gives the target alkaloid directly, but separation from the educt is cumbersome. Quenching the metalated intermediate with Eschenmoser's reagent gives an easy to clean tertiary benzylamine, which, after quaternization with iodomethane, is easily converted into the desired 1-methylisoquinoline by hydrogenolysis of both the benzylamine and benzyl ether groups
Ballistic matter waves with angular momentum: Exact solutions and applications
An alternative description of quantum scattering processes rests on
inhomogeneous terms amended to the Schroedinger equation. We detail the
structure of sources that give rise to multipole scattering waves of definite
angular momentum, and introduce pointlike multipole sources as their limiting
case. Partial wave theory is recovered for freely propagating particles. We
obtain novel results for ballistic scattering in an external uniform force
field, where we provide analytical solutions for both the scattering waves and
the integrated particle flux. Our theory directly applies to p-wave
photodetachment in an electric field. Furthermore, illustrating the effects of
extended sources, we predict some properties of vortex-bearing atom laser beams
outcoupled from a rotating Bose-Einstein condensate under the influence of
gravity.Comment: 42 pages, 8 figures, extended version including photodetachment and
semiclassical theor
Transverse fluctuations of grafted polymers
We study the statistical mechanics of grafted polymers of arbitrary stiffness
in a two-dimensional embedding space with Monte Carlo simulations. The
probability distribution function of the free end is found to be highly
anisotropic and non-Gaussian for typical semiflexible polymers. The reduced
distribution in the transverse direction, a Gaussian in the stiff and flexible
limits, shows a double peak structure at intermediate stiffnesses. We also
explore the response to a transverse force applied at the polymer free end. We
identify F-Actin as an ideal benchmark for the effects discussed.Comment: 10 pages, 4 figures, submitted to Physical Review
Yeast immobilization systems for second-generation ethanol production: actual trends and future perspectives
Yeast immobilization with low-cost carrier materials is a suitable strategy to optimize the fermentation of lignocellulosic hydrolysates for the production of second-generation (2G) ethanol. It is defined as the physical confinement of intact cells to a certain region of space (the carrier) with the preservation of their biological activity. This technological approach facilitates promising strategies for second-generation bioethanol production due to the enhancement of the fermentation performance that is expected to be achieved. Using immobilized cells, the resistance to inhibitors contained in the hydrolysates and the co-utilization of sugars are improved, along with facilitating separation operations and the reuse of yeast in new production cycles. Until now, the most common immobilization technology used calcium alginate as a yeast carrier but other supports such as biochar or multispecies biofilm membranes have emerged as interesting alternatives. This review compiles updated information about cell carriers and yeast-cell requirements for immobilization, and the benefits and drawbacks of different immobilization systems for second-generation bioethanol production are investigated and compared. © 2021 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.publishedVersio
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