1,955 research outputs found
Effect of multilayer barriers on the optical properties of GaInNAs single quantum-well structures grown by metalorganic vapor phase epitaxy
We report on the effects of combined strain-compensating and strain-mediating layers of various widths on the optical properties of 1.3 ÎŒm GaInNAsâGaAs single quantum well structures grown by metalorganic vapor phase epitaxy (MOVPE). While the emission wavelength of GaInNAsâGaAs quantum wells can be redshifted by the adoption of strain-compensated GaNAs layers, the material quality is degraded by the increased stress at the wellâbarrier interface. This detrimental effect can be cured by inserting a strain-mediating InGaAs layer between them. Contrary to what is expected, however, the emission wavelength is blueshifted by the insertion of the InGaAs layer, which is attributed to the reduced N incorporation due to the improved interface quality. Our results indicate that the optical properties of MOVPE-grown GaInNAsâGaAs quantum wells can be optimized in quantum efficiency and emission wavelength by combination of strain-compensating and strain-mediating layers with suitable characteristics
Impact of pressure drop oscillations on surface temperature and critical heat flux during flow boiling in a microchannel
Flow boiling in microchannel heat sinks is capable of providing the high-heat-flux dissipation required for thermal management of next-generation wide bandgap power electronics at low pumping power and uniform surface temperatures. One of the primary issues preventing implementation of these technologies is the presence of flow boiling instabilities, which may reduce the heat transfer performance. However, the effect of individual instabilities, such as the parallel channel instability or pressure drop oscillations, on the overall heat transfer coefficient and critical heat flux in microchannel heat sinks has not been fully quantified. The primary cause of these dynamic flow boiling instabilities is the interaction between the inertia of a two-phase mixture in a heated channel and sources of compressibility located upstream of the inlet. In order to isolate the effect of pressure drop oscillations on flow boiling heat transfer performance, experiments are performed in a single square microchannel cut into a copper heat sink, with a controlled level of upstream compressibility. The impact of pressure drop oscillations on the heat transfer coefficient and critical heat flux is characterized through analysis of both time-averaged steady-state data as well as high-frequency pressure signals synchronized with high-speed visualization. The dielectric working fluid HFE-7100 is used in all experiments with a saturation temperature of 60°C at the channel outlet pressure. The occurrence and effect of pressure drop oscillations in 20 mm long microchannels of three different channel widths (0.5, 0.75, and 1 mm) are related to mass flux, the degree of two-phase flow confinement, and the severity of pressure drop oscillations
Spectroscopic characterization of 1.3”m GaInNAs quantum-well structures grown by metal-organic vapor phase epitaxy
We report optical studies of high-quality 1.3âÎŒm strain-compensated GaInNAs/GaAs single-quantum-well structures grown by metalorganic vapor phase epitaxy. Photoluminescence excitation (PLE) spectroscopy shows clearly the electronic structure of the two-dimensional quantum well. The transition energies between quantized states of the electrons and holes are in agreement with theoretical calculations based on the band anti-crossing model in which the localized N states interact with the extended states in the conduction band. We also investigated the polarization properties of the luminescence by polarized edge-emission measurements. Luminescence bands with different polarization characters arising from the electron to heavy-hole and light-hole transitions, respectively, have been identified and verify the transition assignment observed in the PLE spectrum
A new dromaeosaurid (Dinosauria: Theropoda) from the Upper Cretaceous Wulansuhai Formation of Inner Mongolia, China
We describe a new dromaeosaurid theropod from the Upper Cretaceous Wulansuhai Formation of Bayan Mandahu, Inner
Mongolia. The new taxon, Linheraptor exquisitus gen. et sp. nov., is based on an exceptionally well-preserved, nearly
complete skeleton. This specimen represents the fifth dromaeosaurid taxon recovered from the Upper Cretaceous
Djadokhta Formation and its laterally equivalent strata, which include the Wulansuhai Formation, and adds to the known
diversity of Late Cretaceous dromaeosaurids. Linheraptor exquisitus closely resembles the recently reported Tsaagan
mangas. Uniquely among dromaeosaurids, the two taxa share a large, anteriorly located maxillary fenestra and a contact
between the jugal and the squamosal that excludes the postorbital from the infratemporal fenestra. These features suggest
a sister-taxon relationship between L. exquisitus and T. mangas, which indicates the presence of a unique dromaeosaurid
lineage in the Late Cretaceous of Asia. A number of cranial and dental features seen in L. exquisitus and T. mangas, and
particularly some postcranial features of L. exquisitus, suggest that these two taxa are probably intermediate in
systematic position between known basal and derived dromaeosaurids. The discovery of Linheraptor exquisitus is thus
important for understanding the evolution of some salient features seen in the derived dromaeosaurids
Inequalities in the dental health needs and access to dental services among looked after children in Scotland: a population data linkage study
Background: There is limited evidence on the health needs and service access among children and young people who are looked after by the state. The aim of this study was to compare dental treatment needs and access to dental services (as an exemplar of wider health and well-being concerns) among children and young people who are looked after with the general child population.
Methods: Population data linkage study utilising national datasets of social work referrals for âlooked afterâ placements, the Scottish census of children in local authority schools, and national health serviceâs dental health and service datasets.
Results: 633â204 children in publicly funded schools in Scotland during the academic year 2011/2012, of whom 10â927 (1.7%) were known to be looked after during that or a previous year (from 2007â2008). The children in the looked after children (LAC) group were more likely to have urgent dental treatment need at 5âyears of age: 23%vs10% (n=209/16533), adjusted (for age, sex and area socioeconomic deprivation) OR 2.65 (95% CI 2.30 to 3.05); were less likely to attend a dentist regularly: 51%vs63% (n=5519/388934), 0.55 (0.53 to 0.58) and more likely to have teeth extracted under general anaesthesia: 9%vs5% (n=967/30253), 1.91 (1.78 to 2.04).
Conclusions: LAC are more likely to have dental treatment needs and less likely to access dental services even when accounting for sociodemographic factors. Greater efforts are required to integrate child social and healthcare for LAC and to develop preventive care pathways on entering and throughout their time in the care system
Search for exotic baryons in double radiative capture on pionic hydrogen
We report a search for low-lying exotic baryons via double radiative capture
on pionic hydrogen. The data were collected at the TRIUMF cyclotron using the
RMC spectrometer by detecting gamma-ray pairs from pion stops in liquid
hydrogen. No evidence was found to support an earlier claim for exotic baryons
of masses 1004 and 1044 MeV/. We obtain upper limits on the branching
ratios for double radiative capture via these exotic states of and respectively.Comment: 13 pages, 4 figure
Devising quality assurance procedures for assessment of legacy geochronological data relating to deglaciation of the last British-Irish Ice Sheet
This contribution documents the process of assessing the quality of data within a compilation of legacy geochronological data relating to the last British-Irish Ice Sheet, a task undertaken as part of a larger community-based project (BRITICE-CHRONO) that aims to improve understanding of the ice sheet's deglacial evolution. As accurate reconstructions depend on the quality of the available data, some form of assessment is needed of the reliability and suitability of each given age(s) in our dataset. We outline the background considerations that informed the quality assurance procedures devised given our specific research question. We describe criteria that have been used to make an objective assessment of the likelihood that an age is influenced by the technique specific sources of geological uncertainty. When these criteria were applied to an existing database of all geochronological data relating to the last British-Irish Ice Sheet they resulted in a significant reduction in data considered suitable for synthesis. The assessed data set was used to test a Bayesian approach to age modelling ice stream retreat and we outline our procedure that allows us to minimise the influence of potentially erroneous data and maximise the accuracy of the resultant age models
Identification of a new p53/MDM2 inhibitor motif inspired by studies of chlorofusin
Previous studies on the natural product chlorofusin have shown that the full peptide and azaphilone structure are required for inhibition of the interaction between MDM2 and p53. In the current work, we utilized the cyclic peptide as a template and introduced an azidonorvaline amino acid in place of the ornithine/azaphilone of the natural product and carried out click chemistry with the resulting peptide. From this small library the first ever non-azaphilone containing chlorofusin analogue with MDM2/p53 activity was identified. Further studies then suggested that the simple structure of the Fmoc-norvaline amino acid that had undergone a click reaction was also able to inhibit MDM2/p53 interaction. This is an example where studies of a natural product have led to the serendipitous identification of a new small molecule inhibitor of a protein-protein interaction
High Magnetic Field NMR Studies of LiVGeO, a quasi 1-D Spin System
We report Li pulsed NMR measurements in polycrystalline and single
crystal samples of the quasi one-dimensional S=1 antiferromagnet
LiVGeO, whose AF transition temperature is K.
The field () and temperature () ranges covered were 9-44.5 T and
1.7-300 K respectively. The measurements included NMR spectra, the spin-lattice
relaxation rate (), and the spin-phase relaxation rate (),
often as a function of the orientation of the field relative to the crystal
axes. The spectra indicate an AF magnetic structure consistent with that
obtained from neutron diffraction measurements, but with the moments aligned
parallel to the c-axis. The spectra also provide the -dependence of the AF
order parameter and show that the transition is either second order or weakly
first order. Both the spectra and the data show that has at
most a small effect on the alignment of the AF moment. There is no spin-flop
transition up to 44.5 T. These features indicate a very large magnetic
anisotropy energy in LiVGeO with orbital degrees of freedom playing an
important role. Below 8 K, varies substantially with the orientation
of in the plane perpendicular to the c-axis, suggesting a small energy
gap for magnetic fluctuations that is very anisotropic.Comment: submitted to Phys. Rev.
Cooperation and Self-Regulation in a Model of Agents Playing Different Games
A simple model for cooperation between "selfish" agents, which play an
extended version of the Prisoner's Dilemma(PD) game, in which they use
arbitrary payoffs, is presented and studied. A continuous variable,
representing the probability of cooperation, [0,1], is assigned to
each agent at time . At each time step a pair of agents, chosen at
random, interact by playing the game. The players update their using a
criteria based on the comparison of their utilities with the simplest estimate
for expected income. The agents have no memory and use strategies not based on
direct reciprocity nor 'tags'. Depending on the payoff matrix, the systems
self-organizes - after a transient - into stationary states characterized by
their average probability of cooperation and average equilibrium
per-capita-income . It turns out that the model
exhibit some results that contradict the intuition. In particular, some games
which - {\it a priory}- seems to favor defection most, may produce a relatively
high degree of cooperation. Conversely, other games, which one would bet that
lead to maximum cooperation, indeed are not the optimal for producing
cooperation.Comment: 11 pages, 3 figures, keybords: Complex adaptive systems, Agent-based
models, Social system
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