452 research outputs found
Influence of substrate miscut angle on surface morphology and luminescence properties of AlGaN
The influence of substrate miscut on Al0.5Ga0.5 N layers was investigated using cathodoluminescence (CL) hyperspectral imaging and secondary electron imaging in an environmental scanning electron microscope. The samples were also characterized using atomic force microscopy and high resolution X-ray diffraction. It was found that small changes in substrate miscut have a strong influence on the morphology and luminescence properties of the AlGaN layers. Two different types are resolved. For low miscut angle, a crack-free morphology consisting of randomly sized domains is observed, between which there are notable shifts in the AlGaN near band edge emission energy. For high miscut angle, a morphology with step bunches and compositional inhomogeneities along the step bunches, evidenced by an additional CL peak along the step bunches, are observed
HI in four star-forming low-luminosity E/S0 and S0 galaxies
We present HI data cubes of four low-luminosity early-type galaxies which are
currently forming stars. These galaxies have absolute magnitudes in the range
M_B=-17.9 to -19.9 (H_o=50 km/s/Mpc). Their HI masses range between a few times
10^8 and a few times 10^9 M_sun and the corresponding values for M_HI/L_B are
between 0.07 and 0.42, so these systems are HI rich for their morphological
type. In all four galaxies, the HI is strongly centrally concentrated with high
central HI surface densities, in contrast to what is typically observed in more
luminous early-type galaxies. In two galaxies (NGC 802 and ESO 118-G34), the
kinematics of the HI suggests that the gas is in a strongly warped disk, which
we take as evidence for recent accretion of HI. In the other two galaxies (NGC
2328 and ESO 027-G21) the HI must have been part of the systems for a
considerable time. The HI properties of low-luminosity early-type galaxies
appear to be systematically different from those of many more luminous
early-type galaxies, and we suggest that these differences are due to a
different evolution of the two classes. The star formation history of these
galaxies remains unclear. Their UBV colours and Halpha emission-line strengths
are consistent with having formed stars at a slowly-declining rate for most of
the past 10^10 years. However, the current data do not rule out a small burst
of recent star formation overlaid on an older stellar population.Comment: To appear in AJ, LateX, figures in gif format, paper also available
at http://www.nfra.nl/~morganti/LowLu
Assessing the Potential Return on Investment of the Proposed UK NHS Diabetes Prevention Programme in Different Population Subgroups: An Economic Evaluation
Objectives:
To evaluate potential return on investment of the NHS Diabetes Prevention Programme (DPP) in England, and estimate which population subgroups are likely to benefit most in terms of cost-effectiveness, cost-savings and health benefits.
Design:
Economic Analysis using the School for Public Health Research Diabetes Prevention Model
Setting:
England 2015-16
Population:
Adults aged 16 or over with high risk of type 2 diabetes (HbA1c 6-6.4%). Population subgroups defined by age, sex, ethnicity, socioeconomic deprivation, baseline BMI, baseline HbA1c and working status.
Interventions:
The proposed NHS DPP: An intensive lifestyle intervention focussing on dietary advice, physical activity and weight loss. Comparator: No diabetes prevention intervention.
Main outcome measures:
Incremental costs, savings and return on investment, quality adjusted life years (QALYs), diabetes cases, cardiovascular cases and net monetary benefit from an NHS perspective.
Results:
Intervention costs will be recouped through NHS savings within 12 years, with net NHS saving of ÂŁ1.28 over 20 years for each ÂŁ1 invested. Per 100,000 DPP interventions given, 3,552 QALYs are gained. The DPP is most cost-effective and cost-saving in obese individuals, those with baseline HbA1c 6.2-6.4% and those aged 40-74. QALY gains are lower in minority ethnic and low socioeconomic status subgroups. Probabilistic sensitivity analysis suggests that there is 97% probability that the DPP will be cost-effective within 20 years. NHS savings are highly sensitive to intervention cost, effectiveness and duration of effect.
Conclusions:
The DPP is likely to be cost-effective and cost-saving under current assumptions. Prioritising obese individuals could create the most value for money and obtain the greatest health benefits per individual targeted. Low socioeconomic status or ethnic minority groups may gain fewer QALYs per intervention, so targeting strategies should ensure the DPP does not contribute to widening health inequalities. Further evidence is needed around the differential responsiveness of population subgroups to the DPP.
The effect of a varied NH3 flux on growth of AlN interlayers for InAlN/GaN heterostructures
The effects of AlN interlayer growth conditions on InAlN/AlN/GaN heterostructures are investigated, with interlayers imaged as they would appear prior to InAlN barrier layer deposition using surface atomic force microscopy scans undertaken immediately after growth. Surface morphologies and subsequent heterostructure conductivity suggested minimum on-resistance can be achieved by balancing the underlying GaN channel decomposition and interfacial roughening when deciding AlN interlayer growth parameters on a sapphire substrate of a given miscut. (C) 2013 AIP Publishing LLC. (DOI: 10.1063/1.4818645
Synthesis and Characterization of Silicon Nanorod Arrays for Solar Cell Applications
Silicon nanorods have been grown by chemical vapor deposition of silane, using both gold and indium as catalysts for the vapor liquid solid (VLS) process. Conditions for optimal rod morphology for each catalyst were identified by varying silane partial pressure and temperature in the range P = 0.05-1 Torr and T = 300-600 C, respectively. In most cases, catalyst particles were formed by partial de-wetting of evaporated films of the catalytic material to form droplets with diameters of tens to hundreds of nanometers. Also, periodic arrays of catalyst particles with controlled size and spacing were achieved both by the use of porous alumina membranes and also by electron-beam lithography. Using these techniques, silicon nanorods were grown with diameters of 100 nm to microns and lengths of microns to tens of microns. Four-point and gate-bias-dependent resistance measurements were made on single wires, and these indicate that rods we have grown with gold catalysts and phosphine doping have metal-like conductivity
A full free spectral range tuning of p-i-n doped Gallium Nitride microdisk cavity
Effective, permanent tuning of the whispering gallery modes (WGMs) of p-i-n
doped GaN microdisk cavity with embedded InGaN quantum dots over one free
spectral range is successfully demonstrated by irradiating the microdisks with
a ultraviolet laser (380nm) in DI water. For incident laser powers between 150
and 960 nW, the tuning rate varies linearly. Etching of the top surface of the
cavity is proposed as the driving force for the observed shift in WGMs, and is
supported by experiments. The tuning for GaN/InGaN microdisk cavities is an
important step for deterministically realizing novel nanophotonic devices for
studying cavity quantum electrodynamics
Crystal defect topography of Stranski-Krastanow quantum dots by atomic force microscopy
We demonstrate a technique to monitor the defect density in capped quantum dot (QD) structures by performing an atomic force microscopy (AFM) of the final surface. Using this method we are able to correlate their density with the optical properties of the dot structures grown at different temperatures. Parallel transmission electron microscopy analysis shows that the AFM features are directly correlated with the density of stacking faults that originate from abnormally large dots. The technique is rapid and noninvasive making it an ideal diagnostic tool for optimizing the parameters of practical QD-based devices. (C) 2010 American Institute of Physics. (doi:10.1063/1.3514237
Photospheric Abundances of the Hot Stars in NGC1399 and Limits on the Fornax Cluster Cooling Flow
We present far-UV spectroscopy of the giant elliptical galaxy NGC 1399,
obtained with the Far Ultraviolet Spectroscopic Explorer. Of all quiescent
ellipticals, NGC 1399 has the strongest known ``UV upturn'' -- a sharp spectral
rise shortward of 2500 A. It is now well-established that this emission comes
from hot horizontal branch (HB) stars and their progeny; however, the chemical
composition of these stars has been the subject of a long-standing debate. For
the first time in observations of any elliptical galaxy, our spectra clearly
show photospheric metallic absorption lines within the UV upturn. The abundance
of N is at 45% solar, Si is at 13% solar, and C is at 2% solar. Such abundance
anomalies are a natural consequence of gravitational diffusion. These
photospheric abundances fall in the range observed for subdwarf B stars of the
Galactic field.
Although NGC1399 is at the center of the Fornax cluster, we find no evidence
for O VI cooling flow emission. The upper limit to 1032,1038 emission is
3.9E-15 erg/s/cm2, equivalent to 0.14 M_sun/yr, and less than that predicted by
simple cooling flow models of the NGC 1399 X-ray luminosity.Comment: 4 pages, Latex. 2 figures. Uses corrected version of emulateapj.sty
and apjfonts.sty (included). Accepted for publication in ApJ Letters. Revised
figure placemen
Cytoskeletal variations in an asymmetric cell division support diversity in nematode sperm size and sex ratios
Asymmetric partitioning is an essential component of many developmental processes. As spermatogenesis concludes, sperm are streamlined by discarding unnecessary cellular components into cellular wastebags called residual bodies (RBs). During nematode spermatogenesis, this asymmetric partitioning event occurs shortly after anaphase II, and both microtubules and actin partition into a central RB. Here, we use fluorescence and transmission electron microscopy to elucidate and compare the intermediate steps of RB formation in Caenorhabditis elegans, Rhabditis sp. SB347 (recently named Auanema rhodensis) and related nematodes. In all cases, intact microtubules reorganize and move from centrosomal to non-centrosomal sites at the RB-sperm boundary whereas actin reorganizes through cortical ring expansion and clearance from the poles. However, in species with tiny spermatocytes, these cytoskeletal changes are restricted to one pole. Consequently, partitioning yields one functional sperm with the X-bearing chromosome complement and an RB with the other chromosome set. Unipolar partitioning may not require an unpaired X, as it also occurs in XX spermatocytes. Instead, constraints related to spermatocyte downsizing may have contributed to the evolution of a sperm cell equivalent to female polar bodies
Extended HI disks in dust-lane elliptical galaxies
We present the results of HI observations of five dust-lane ellipticals with
the Australia Telescope Compact Array. Two galaxies (NGC 3108 and NGC 1947) are
detected, and sensitive upper limits are obtained for the other three. In the
two detected galaxies, the HI is distributed in a regular, extended and warped
disk-like structure of low surface brightness. Adding data from the literature,
we find that several more dust-lane ellipticals have regular HI structures.
This HI is likely to be a remnant of accretions/mergers which took place a
considerable time ago, and in which a significant fraction of the gas survived
to form a disk. The presence of regular HI structures suggests that some
mergers lead to galaxies with extended low surface brightness density gas
disks. These gas disk will evolve very slowly and these elliptical galaxies
will remain gas rich for a long period of time. (abridged)Comment: 21 pages, 12 separate jpeg figures, at
http://www.nfra.nl/~morganti/Papers/dust.ps.gz the full ps version is
available. Accepted for publication in A
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