302 research outputs found
Theory and design of InGaAsBi mid-infrared semiconductor lasers: type-I quantum wells for emission beyond 3 m on InP substrates
We present a theoretical analysis and optimisation of the properties and
performance of mid-infrared semiconductor lasers based on the dilute bismide
alloy InGaAsBi, grown on conventional (001) InP
substrates. The ability to independently vary the epitaxial strain and emission
wavelength in this quaternary alloy provides significant scope for band
structure engineering. Our calculations demonstrate that structures based on
compressively strained InGaAsBi quantum wells (QWs)
can readily achieve emission wavelengths in the 3 -- 5 m range, and that
these QWs have large type-I band offsets. As such, these structures have the
potential to overcome a number of limitations commonly associated with this
application-rich but technologically challenging wavelength range. By
considering structures having (i) fixed QW thickness and variable strain, and
(ii) fixed strain and variable QW thickness, we quantify key trends in the
properties and performance as functions of the alloy composition, structural
properties, and emission wavelength, and on this basis identify routes towards
the realisation of optimised devices for practical applications. Our analysis
suggests that simple laser structures -- incorporating
InGaAsBi QWs and unstrained ternary
InGaAs barriers -- which are compatible with established
epitaxial growth, provide a route to realising InP-based mid-infrared diode
lasers.Comment: Submitted versio
Magnetic field dependence of the exciton energy in a quantum disk
The groundstate energy and binding energy of an exciton, confined in a^M
quantum disk, are calculated as a function of an external magnetic field. The
confinement potential is a hard wall of finite height. The diamagnetic shift is
investigated for magnetic fields up to 40. Our results are applied to
self-assembled quantum dots and very good
agreement with experiments is obtained. Furthermore, we investigated the
influence of the dot size on the diamagnetic shift by changing the disk radius.
The exciton excited states are found as a function of the magnetic field. The
relative angular momentum is not a quantum number and changes with the magnetic
field strength.Comment: 10 pages, 17 figure
Excitons in type-II quantum dots: Finite offsets
Quantum size effects for an exciton attached to a spherical quantum dot are
calculated by a variational approach. The band line-ups are assumed to be
type-II with finite offsets. The dependence of the exciton binding energy upon
the dot radius and the offsets is studied for different sets of electron and
hole effective masses
Understanding uncertainty in temperature effects on vector-borne disease: A Bayesian approach
Extrinsic environmental factors influence the distribution and population
dynamics of many organisms, including insects that are of concern for human
health and agriculture. This is particularly true for vector-borne infectious
diseases, like malaria, which is a major source of morbidity and mortality in
humans. Understanding the mechanistic links between environment and population
processes for these diseases is key to predicting the consequences of climate
change on transmission and for developing effective interventions. An important
measure of the intensity of disease transmission is the reproductive number
. However, understanding the mechanisms linking and temperature, an
environmental factor driving disease risk, can be challenging because the data
available for parameterization are often poor. To address this we show how a
Bayesian approach can help identify critical uncertainties in components of
and how this uncertainty is propagated into the estimate of . Most
notably, we find that different parameters dominate the uncertainty at
different temperature regimes: bite rate from 15-25 C; fecundity across
all temperatures, but especially 25-32 C; mortality from
20-30 C; parasite development rate at 15-16C and again at
33-35C. Focusing empirical studies on these parameters and
corresponding temperature ranges would be the most efficient way to improve
estimates of . While we focus on malaria, our methods apply to improving
process-based models more generally, including epidemiological, physiological
niche, and species distribution models.Comment: 27 pages, including 1 table and 3 figure
From presence to consciousness through virtual reality
Immersive virtual environments can break the deep, everyday connection between where our senses tell us we are and where we are actually located and whom we are with. The concept of 'presence' refers to the phenomenon of behaving and feeling as if we are in the virtual world created by computer displays. In this article, we argue that presence is worthy of study by neuroscientists, and that it might aid the study of perception and consciousness
Risk Factors for Cholangitis After Pancreatoduodenectomy: A Systematic Review
BACKGROUND: Cholangitis is a late complication after pancreatoduodenectomy with considerable clinical impact and is difficult to treat. The aim of this systematic review was to provide an overview of the literature identifying risk factors for postoperative cholangitis. METHODS: A systematic search of the databases PUBMED and EMBASE was performed to identify all studies reporting on possible risk factors for cholangitis following pancreatoduodenectomy. Data on patient, peri- and postoperative characteristics were collected. Risk of bias assessment was done according to the methodological index for non-randomized studies (MINORS) criteria. RESULTS: In total, 464 studies were identified. Eight studies met the inclusion criteria for this analysis. The definition of postoperative cholangitis was inconsistent, with four studies using the Tokyo Guidelines, whereas other studies used different definitions. Data on 26 potential risk factors concerning the patient, peri- and postoperative characteristics were analyzed. Five factors were significantly associated with cholangitis in two or more studies: high body mass index, duration of surgery, benign disease, postoperative pancreatic fistula, and postoperative serum alkaline phosphatase. CONCLUSION: Multiple potential risk factors for postoperative cholangitis were identified, with large discrepancies between studies. Prospective research, with consensus on the definition, is required to determine the true relevance of these risk factors
Virtual Reality and Anxiety Disorders Treatment: Evolution and Future Perspectives
Virtual reality (VR) is a technology that allows the simulation of different real-life situations on a tridimensional computer-generated environment where the user can interact with the environment as if he/she were the real world. VR has potential as an exposure technique for treating anxiety disorders because VR and real objects have similar characteristics, which creates the illusion that the user is immersed and engaged with objects in the real world. Regarding the efficacy of using virtual reality exposure-based therapy (VR-EBT), for more than two decades, there has been sufficient empirical evidence regarding VR-EBT for treating anxiety disorders. Finally, this chapter ends with some directions and perspectives for future VR-EBT developments and treatments protocols
Assessment of Future Remnant Liver Function Using Hepatobiliary Scintigraphy in Patients Undergoing Major Liver Resection
Tc-99m-mebrofenin hepatobiliary scintigraphy (HBS) was used as a quantitative method to evaluate liver function. The aim of this study was to compare future remnant liver function assessed by Tc-99m-mebrofenin hepatobiliary scintigraphy with future remnant liver volume in the prediction of liver failure after major liver resection. Computed tomography (CT) volumetry and Tc-99m-mebrofenin hepatobiliary scintigraphy were performed prior to major resection in 55 high-risk patients, including 30 patients with parenchymal liver disease. Liver volume was expressed as percentage of total liver volume or as standardized future remnant liver volume. Receiver operating characteristic (ROC) curve analysis was performed to identify a cutoff value for future remnant liver function in predicting postoperative liver failure. Postoperative liver failure occurred in nine patients. A liver function cutoff value of 2.69%/min/m(2) was calculated by ROC curve analysis. Tc-99m-mebrofenin hepatobiliary scintigraphy demonstrated better sensitivity, specificity, and positive and negative predictive value compared to future remnant liver volume. Using Tc-99m-mebrofenin hepatobiliary scintigraphy, one cutoff value suffices in both compromised and noncompromised patients. Preoperative Tc-99m-mebrofenin hepatobiliary scintigraphy is a valuable technique to estimate the risk of postoperative liver failure. Especially in patients with uncertain quality of the liver parenchyma, Tc-99m-mebrofenin HBS proved of more value than CT volumetr
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