2,253 research outputs found
Formation of Low Threshold Voltage Microlasers
Vertical cavity surface emitting lasers (VCSELs) with threshold voltages of 1.7V have been fabricated. The resistance-area product in these new vertical cavity lasers is comparable to that of edge-emitting lasers, and threshold currents as low as 3 mA have been measured. Molecular beam epitaxy was used to grow n-type mirrors, a quantum well active region, and a heavily Be-doped p-contact. After contact definition and alloying, passive high-reflectivity mirrors were deposited by reactive sputter deposition of SiO2/Si3N4 to complete the laser cavity
Application of Monte Carlo Algorithms to the Bayesian Analysis of the Cosmic Microwave Background
Power spectrum estimation and evaluation of associated errors in the presence
of incomplete sky coverage; non-homogeneous, correlated instrumental noise; and
foreground emission is a problem of central importance for the extraction of
cosmological information from the cosmic microwave background. We develop a
Monte Carlo approach for the maximum likelihood estimation of the power
spectrum. The method is based on an identity for the Bayesian posterior as a
marginalization over unknowns. Maximization of the posterior involves the
computation of expectation values as a sample average from maps of the cosmic
microwave background and foregrounds given some current estimate of the power
spectrum or cosmological model, and some assumed statistical characterization
of the foregrounds. Maps of the CMB are sampled by a linear transform of a
Gaussian white noise process, implemented numerically with conjugate gradient
descent. For time series data with N_{t} samples, and N pixels on the sphere,
the method has a computational expense $KO[N^{2} +- N_{t} +AFw-log N_{t}],
where K is a prefactor determined by the convergence rate of conjugate gradient
descent. Preconditioners for conjugate gradient descent are given for scans
close to great circle paths, and the method allows partial sky coverage for
these cases by numerically marginalizing over the unobserved, or removed,
region.Comment: submitted to Ap
Discovery of the Interstellar Chiral Molecule Propylene Oxide (CHCHCHO)
Life on Earth relies on chiral molecules, that is, species not superimposable
on their mirror images. This manifests itself in the selection of a single
molecular handedness, or homochirality, across the biosphere. We present the
astronomical detection of a chiral molecule, propylene oxide (CHCHCHO),
in absorption toward the Galactic Center. Propylene oxide is detected in the
gas phase in a cold, extended molecular shell around the embedded, massive
protostellar clusters in the Sagittarius B2 star-forming region. This material
is representative of the earliest stage of solar system evolution in which a
chiral molecule has been found
Effectiveness of group-based self-management education for individuals with Type 2 diabetes:A systematic review with meta-analyses and meta-regression
Aims:
Patient education for the management of Type 2 diabetes can be delivered in various forms, with the goal of promoting and supporting positive self-management behaviours. This systematic review aimed to determine the effectiveness of group-based interventions compared with individual interventions or usual care for improving clinical, lifestyle and psychosocial outcomes in people with Type 2 diabetes.
Methods:
Six electronic databases were searched. Group-based education programmes for adults with Type 2 diabetes that measured glycated haemoglobin (HbA1c) and followed participants for ≥ 6 months were included. The primary outcome was HbA1c, and secondary outcomes included fasting blood glucose, weight, body mass index, waist circumference, blood pressure, blood lipid profiles, diabetes knowledge and self-efficacy.
Results:
Fifty-three publications describing 47 studies were included (n = 8533 participants). Greater reductions in HbA1c occurred in group-based education compared with controls at 6–10 months [n = 30 studies; mean difference (MD) = 3 mmol/mol (0.3%); 95% confidence interval (CI): −0.48, −0.15; P = 0.0002], 12–14 months [n = 27 studies; MD = 4 mmol/mol (0.3%); 95% CI: −0.49, −0.17; P < 0.0001], 18 months [n = 3 studies; MD = 8 mmol/mol (0.7%); 95% CI: −1.26, −0.18; P = 0.009] and 36–48 months [n = 5 studies; MD = 10 mmol/mol (0.9%); 95% CI: −1.52, −0.34; P = 0.002], but not at 24 months. Outcomes also favoured group-based education for fasting blood glucose, body weight, waist circumference, triglyceride levels and diabetes knowledge, but not at all time points. Interventions facilitated by a single discipline, multidisciplinary teams or health professionals with peer supporters resulted in improved outcomes in HbA1c when compared with peer-led interventions.
Conclusions:
Group-based education interventions are more effective than usual care, waiting list control and individual education at improving clinical, lifestyle and psychosocial outcomes in people with Type 2 diabetes.No Full Tex
Room-Temperature Continuous-Wave Vertical-Cavity Single-Quantum-Well Microlaser Diodes
Room-temperature continuous and pulsed lasing of vertical-cavity, single-quantum-well, surface-emitting microlasers is achieved at ~983nm. The active Ga[sub][0-8]In[sub][0-2]As single quantum well is 100 [angstroms] thick. These microlasers have the smallest gain medium volumes among lasers ever built. The entire laser structure is grown by molecular beam epitaxy and the microlasers are formed by chemically assisted ion-beam etching. The microlasers are 3-50-μm across. The minimum threshold currents are 1.1 mA (pulsed) and 1.5 mA (CW)
The upper critical field of filamentary Nb3Sn conductors
We have examined the upper critical field of a large and representative set
of present multi-filamentary Nb3Sn wires and one bulk sample over a temperature
range from 1.4 K up to the zero field critical temperature. Since all present
wires use a solid-state diffusion reaction to form the A15 layers,
inhomogeneities with respect to Sn content are inevitable, in contrast to some
previously studied homogeneous samples. Our study emphasizes the effects that
these inevitable inhomogeneities have on the field-temperature phase boundary.
The property inhomogeneities are extracted from field-dependent resistive
transitions which we find broaden with increasing inhomogeneity. The upper
90-99 % of the transitions clearly separates alloyed and binary wires but a
pure, Cu-free binary bulk sample also exhibits a zero temperature critical
field that is comparable to the ternary wires. The highest mu0Hc2 detected in
the ternary wires are remarkably constant: The highest zero temperature upper
critical fields and zero field critical temperatures fall within 29.5 +/- 0.3 T
and 17.8 +/- 0.3 K respectively, independent of the wire layout. The complete
field-temperature phase boundary can be described very well with the relatively
simple Maki-DeGennes model using a two parameter fit, independent of
composition, strain state, sample layout or applied critical state criterion.Comment: Accepted Journal of Applied Physics Few changes to shorten document,
replaced eq. 7-
Ground-State SiO Maser Emission Toward Evolved Stars
We have made the first unambiguous detection of vibrational ground-state
maser emission from SiO toward six evolved stars. Using the Very Large Array,
we simultaneously observed the v=0, J=1-0, 43.4-GHz, ground-state and the v=1,
J=1-0, 43.1-GHz, first excited-state transitions of SiO toward the oxygen-rich
evolved stars IRC+10011, o Ceti, W Hya, RX Boo, NML Cyg, and R Cas and the
S-type star chi Cyg. We detected at least one v=0 SiO maser feature from six of
the seven stars observed, with peak maser brightness temperatures ranging from
10,000 K to 108,800 K. In fact, four of the seven v=0 spectra show multiple
maser peaks, a phenomenon which has not been previously observed. Ground-state
thermal emission was detected for one of the stars, RX Boo, with a peak
brightness temperature of 200 K. Comparing the v=0 and the v=1 transitions, we
find that the ground-state masers are much weaker with spectral characteristics
different from those of the first excited-state masers. For four of the seven
stars the velocity dispersion is smaller for the v=0 emission than for the v=1
emission, for one star the dispersions are roughly equivalent, and for two
stars (one of which is RX Boo) the velocity spread of the v=0 emission is
larger. In most cases, the peak flux density in the v=0 emission spectrum does
not coincide with the v=1 maser peak. Although the angular resolution of these
VLA observations were insufficient to completely resolve the spatial structure
of the SiO emission, the SiO spot maps produced from the interferometric image
cubes suggest that the v=0 masers are more extended than their v=1
counterparts
Networks and the epidemiology of infectious disease
The science of networks has revolutionised research into the dynamics of interacting elements. It could be argued that epidemiology in particular has embraced the potential of network theory more than any other discipline. Here we review the growing body of research concerning the spread of infectious diseases on networks, focusing on the interplay between network theory and epidemiology. The review is split into four main sections, which examine: the types of network relevant to epidemiology; the multitude of ways these networks can be characterised; the statistical methods that can be applied to infer the epidemiological parameters on a realised network; and finally simulation and analytical methods to determine epidemic dynamics on a given network. Given the breadth of areas covered and the ever-expanding number of publications, a comprehensive review of all work is impossible. Instead, we provide a personalised overview into the areas of network epidemiology that have seen the greatest progress in recent years or have the greatest potential to provide novel insights. As such, considerable importance is placed on analytical approaches and statistical methods which are both rapidly expanding fields. Throughout this review we restrict our attention to epidemiological issues
Low-Threshold Electrically Pumps Vertical-Cavity Surface-Emitting Microlasers
Vertical-cavity electrically driven lasers with three GaInAs
quantum wells and diameters of several μm exhibit room-temperature pulsed current thresholds as low as 1.3mA with 958 nm output wavelength
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