3,190 research outputs found
InGaAsP/InP laser development for single-mode, high-data-rate communications
Materials studies as well as general and specific device development were carried out in the InGaAsP system. A comparison was made of three standard methods of evaluating substrate quality by means of dislocation studies. A cause of reduced yield of good wafers, the pullover of melt from one bin to the next, has been analyzed. Difficulties with reproducible zinc acceptor doping have been traced to segregation of zinc in the In/Zn alloy used for the doping source. Using EBIC measurments, the pn junction was shown to drift in location depending on factors not always under control. An analysis of contact structures by SIMS showed that the depth to which the sintered Au/Zn contact penetrates into the structure is typically 0.13 microns, or well within the cap layer and out of the p-type cladding and thus not deleterious to laser prformance. The problem of single-mode laser development was investigated and it was shown to be related to the growth habit over four different possible substrate configurations. The fabrication of constricted double heterojunctions, mesa stripe buried heterostructures, and buried heterostructures was discussed, and measurements were presented on the device properties of single-mode buried heterostructure lasers. Results include single spectral line emission at 3 mW and a threshold current of 60 mA
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The experiences of carers looking after people with Parkinson's disease who exhibit impulsive and compulsive behaviours: an exploratory qualitative study
BACKGROUND: Impulsive and compulsive behaviours (ICBs) are a serious complication in Parkinson disease (PD) strongly associated with dopamine replacement therapy used to treat patients. These behaviours comprise abnormal activities such as pathological gambling, binge eating, compulsive shopping, and hypersexuality. These behaviours place a considerable burden on patients and on their carers and families. The aim of this qualitative study is to understand the experiences of carers who were confronted by the development of these behaviours.
DESIGN: An exploratory qualitative study.
METHODS: Using a convenience sampling approach, 13 carers were recruited to participate in semi-structured interviews. Interviews were conducted over the telephone. Verbatim transcripts were analysed used a thematic analysis approach. COREQ guidelines were adhered to in the reporting of this study.
RESULTS: Five main themes were identified: (1) realisation - developing awareness of ICB symptoms and their causes; (2) reacting - confronting and attempts to manage ICBs; (3) reaching out - help-seeking and selective disclosure; (4) reframing - shifting perspectives on ICBs over time; and (5) resignation - impact on relationships and facing the future.
CONCLUSIONS: The profound impact of ICBs on quality of life, relationships, and economic stability was clear in the carers' accounts. Possible avenues for future clinical research are suggested.
RELEVANCE TO CLINICAL PRACTICE: The potentially devastating effects of ICBs provide a strong imperative for nurses and other health professionals to ensure that close monitoring for symptom development together with patient education are always part of practice
Aerosol physical properties in the stratosphere (APPS) radiometer design
The measurement concepts and radiometer design developed to obtain earth-limb spectral radiance measurements for the Aerosol Physical Properties in the Stratosphere (APPS) measurement program are presented. The measurements made by a radiometer of this design can be inverted to yield vertical profiles of Rayleigh scatterers, ozone, nitrogen dioxide, aerosol extinction, and aerosol physical properties, including a Junge size-distribution parameter, and a real and imaginary index of refraction. The radiometer design provides the capacity for remote sensing of stratospheric constituents from space on platforms such as the space shuttle and satellites, and therefore provides for global measurements on a daily basis
The Lennard-Jones-Devonshire cell model revisited
We reanalyse the cell theory of Lennard-Jones and Devonshire and find that in
addition to the critical point originally reported for the 12-6 potential (and
widely quoted in standard textbooks), the model exhibits a further critical
point. We show that the latter is actually a more appropriate candidate for
liquid-gas criticality than the original critical point.Comment: 5 pages, 3 figures, submitted to Mol. Phy
Identifying gravitationally lensed supernovae within the Zwicky Transient Facility public survey
Strong gravitational lensing of supernovae is exceedingly rare. To date, only
a handful of lensed supernovae are known. Despite their rarity, lensed
supernovae have emerged as one of the most promising methods for measuring the
current expansion rate of the Universe and breaking the Hubble tension. We
present an extensive search for gravitationally lensed supernovae within the
Zwicky Transient Facility (ZTF) public survey, covering 12,524 transients with
good light curves discovered during four years of observations. We crossmatch a
catalogue of known and candidate lens galaxies with our transient sample and
find only one coincident source, which was due to chance alignment. To search
for supernovae magnified by unknown lens galaxies, we test multiple methods
that have been suggested in the literature, for the first time on real data.
This includes selecting objects with extremely red colours and those that
appear inconsistent with the host galaxy redshift. In both cases, we find a few
hundred candidates, most of which are due to contamination from activate
galactic nuclei, bogus detections, or unlensed supernovae. The false positive
rate from these methods presents significant challenges for future surveys. In
total, 65 unique transients were identified across all of our selection methods
that required detailed manual rejection, which would be infeasible for larger
samples. Overall, we do not find any compelling candidates for lensed
supernovae, which is broadly consistent with previous estimates for the rate of
lensed supernovae in the ZTF public survey and the number expected to pass the
selection cuts we apply.Comment: Submitte
Data-driven approach to optimum wavelength selection for diffuse optical imaging
The production of accurate and independent images of the changes in concentration of oxyhemoglobin and deoxyhemoglobin by diffuse optical imaging is heavily dependent on which wavelengths of near-infrared light are chosen to interrogate the target tissue. Although wavelengths can be selected by theoretical methods, in practice the accuracy of reconstructed images will be affected by wavelength-specific and system-specific factors such as laser source power and detector sensitivity. We describe the application of a data-driven approach to optimum wavelength selection for the second generation of University College London's multichannel, time-domain optical tomography system (MONSTIR II). By performing a functional activation experiment using 12 different wavelengths between 690 and 870 nm, we were able to identify the combinations of 2, 3, and 4 wavelengths which most accurately reproduced the results obtained using all 12 wavelengths via an imaging approach. Our results show that the set of 2, 3, and 4 wavelengths which produce the most accurate images of functional activation are [770, 810], [770, 790, 850], and [730, 770, 810, 850] respectively, but also that the system is relatively robust to wavelength selection within certain limits. Although these results are specific to MONSTIR II, the approach we developed can be applied to other multispectral near-infrared spectroscopy and optical imaging systems
Failure of interpolation in the intuitionistic logic of constant domains
This paper shows that the interpolation theorem fails in the intuitionistic
logic of constant domains. This result refutes two previously published claims
that the interpolation property holds.Comment: 13 pages, 0 figures. Overlaps with arXiv 1202.1195 removed, the text
thouroughly reworked in terms of notation and style, historical notes as well
as some other minor details adde
Inductive learning spatial attention
This paper investigates the automatic induction of spatial attention
from the visual observation of objects manipulated
on a table top. In this work, space is represented in terms of
a novel observer-object relative reference system, named Local
Cardinal System, defined upon the local neighbourhood
of objects on the table. We present results of applying the
proposed methodology on five distinct scenarios involving
the construction of spatial patterns of coloured blocks
The Environment of M85 optical transient 2006-1: constraints on the progenitor age and mass
M85 optical transient 2006-1 (M85 OT 2006-1) is the most luminous member of
the small family of V838 Mon-like objects, whose nature is still a mystery.
This event took place in the Virgo cluster of galaxies and peaked at an
absolute magnitude of I~-13. Here we present Hubble Space Telescope images of
M85 OT 2006-1 and its environment, taken before and after the eruption, along
with a spectrum of the host galaxy at the transient location. We find that the
progenitor of M85 OT 2006-1 was not associated with any star forming region.
The g and z-band absolute magnitudes of the progenitor were fainter than about
-4 and -6 mag, respectively. Therefore, we can set a lower limit of ~50 Myr on
the age of the youngest stars at the location of the progenitor that
corresponds to a mass of <7 solar mass. Previously published line indices
suggest that M85 has a mean stellar age of 1.6+/-0.3 Gyr. If this mean age is
representative of the progenitor of M85 OT 2006-1, then we can further
constrain its mass to be less than 2 solar mass. We compare the energetics and
mass limit derived for the M85 OT 2006-1 progenitor with those expected from a
simple model of violent stellar mergers. Combined with further modeling, these
new clues may ultimately reveal the true nature of these puzzling events.Comment: 4 pages, accepted to Ap
Characterization of hedgehog acyltransferase inhibitors identifies a small molecule probe for hedgehog signaling by cancer cells
The Sonic Hedgehog (Shh) signaling pathway plays a critical role during embryonic development and cancer progression. N-terminal palmitoylation of Shh by Hedgehog acyltransferase (Hhat) is essential for efficient signaling, raising interest in Hhat as a novel drug target. A recently identified series of dihydrothienopyridines has been proposed to function via this mode of action; however, the lead compound in this series (RUSKI-43) was subsequently shown to possess cytotoxic activity unrelated to canonical Shh signaling. To identify a selective chemical probe for cellular studies, we profiled three RUSKI compounds in orthogonal cell-based assays. We found that RUSKI-43 exhibits off-target cytotoxicity, masking its effect on Hhat-dependent signaling, hence results obtained with this compound in cells should be treated with caution. In contrast, RUSKI-201 showed no off-target cytotoxicity, and quantitative whole-proteome palmitoylation profiling with a bioorthogonal alkyne-palmitate reporter demonstrated specific inhibition of Hhat in cells. RUSKI-201 is the first selective Hhat chemical probe in cells and should be used in future studies of Hhat catalytic function
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