1,410 research outputs found
Experimental investigation of the excess charge and time constant of minority carriers in the thin diffused layer of 0.1 ohm-cm silicon solar cells
An experimental method is presented that can be used to interpret the relative roles of bandgap narrowing and recombination processes in the diffused layer. This method involves measuring the device time constant by open-circuit voltage decay and the base region diffusion length by X-ray excitation. A unique illuminated diode method is used to obtain the diode saturation current. These data are interpreted using a simple model to determine individually the minority carrier lifetime and the excess charge. These parameters are then used to infer the relative importance of bandgap narrowing and recombination processes in the diffused layer
The impact of COVID-19 on BAME populations: a systematic review of experiences and perspectives
Black, Asian, Minority Ethnic (BAME) populations have been disproportionately affected by COVID-19,
having amongst the highest rates of infection and mortality. Additional risk factors for BAME populations
include older age and living with poverty and deprivation. Information has emerged, but peer reviewed
research and literature examining the experiences and/or perspectives of this most recent of diseases on
BAME populations is fragmented and lacks coalescence. This systematic review will therefore bring together
and integrate existing and emergent evidence around the experiences and/or perspectives of COVID-19 on
BAME populations
On subgroups generated by small classes in finite groups
Let be a finite group and be the subgroup of generated by all
non-central elements of that lie in the conjugacy classes of the smallest
size. Recently several results have been proved regarding the nilpotency class
of and , where denotes the Fitting subgroup of
. We prove some conditional results regarding the nilpotency class of
.Comment: 5 pages, re-written in a new forma
WZW orientifolds and finite group cohomology
The simplest orientifolds of the WZW models are obtained by gauging a Z_2
symmetry group generated by a combined involution of the target Lie group G and
of the worldsheet. The action of the involution on the target is by a twisted
inversion g \mapsto (\zeta g)^{-1}, where \zeta is an element of the center of
G. It reverses the sign of the Kalb-Ramond torsion field H given by a
bi-invariant closed 3-form on G. The action on the worldsheet reverses its
orientation. An unambiguous definition of Feynman amplitudes of the orientifold
theory requires a choice of a gerbe with curvature H on the target group G,
together with a so-called Jandl structure introduced in hep-th/0512283. More
generally, one may gauge orientifold symmetry groups \Gamma = Z_2 \ltimes Z
that combine the Z_2-action described above with the target symmetry induced by
a subgroup Z of the center of G. To define the orientifold theory in such a
situation, one needs a gerbe on G with a Z-equivariant Jandl structure. We
reduce the study of the existence of such structures and of their inequivalent
choices to a problem in group-\Gamma cohomology that we solve for all simple
simply-connected compact Lie groups G and all orientifold groups \Gamma = Z_2
\ltimes Z.Comment: 48+1 pages, 11 figure
The Generation of Fullerenes
We describe an efficient new algorithm for the generation of fullerenes. Our
implementation of this algorithm is more than 3.5 times faster than the
previously fastest generator for fullerenes -- fullgen -- and the first program
since fullgen to be useful for more than 100 vertices. We also note a
programming error in fullgen that caused problems for 136 or more vertices. We
tabulate the numbers of fullerenes and IPR fullerenes up to 400 vertices. We
also check up to 316 vertices a conjecture of Barnette that cubic planar graphs
with maximum face size 6 are hamiltonian and verify that the smallest
counterexample to the spiral conjecture has 380 vertices.Comment: 21 pages; added a not
Optoelectronics with electrically tunable PN diodes in a monolayer dichalcogenide
One of the most fundamental devices for electronics and optoelectronics is
the PN junction, which provides the functional element of diodes, bipolar
transistors, photodetectors, LEDs, and solar cells, among many other devices.
In conventional PN junctions, the adjacent p- and n-type regions of a
semiconductor are formed by chemical doping. Materials with ambipolar
conductance, however, allow for PN junctions to be configured and modified by
electrostatic gating. This electrical control enables a single device to have
multiple functionalities. Here we report ambipolar monolayer WSe2 devices in
which two local gates are used to define a PN junction exclusively within the
sheet of WSe2. With these electrically tunable PN junctions, we demonstrate
both PN and NP diodes with ideality factors better than 2. Under excitation
with light, the diodes show photodetection responsivity of 210 mA/W and
photovoltaic power generation with a peak external quantum efficiency of 0.2%,
promising numbers for a nearly transparent monolayer sheet in a lateral device
geometry. Finally, we demonstrate a light-emitting diode based on monolayer
WSe2. These devices provide a fundamental building block for ubiquitous,
ultra-thin, flexible, and nearly transparent optoelectronic and electronic
applications based on ambipolar dichalcogenide materials.Comment: 14 pages, 4 figure
Gastric cancer surgery: Billroth I or Billroth II for distal gastrectomy?
<p>Abstract</p> <p>Background</p> <p>The selection of an anastomosis method after a distal gastrectomy is a highly debatable topic; however, the available documentation lacks the necessary research based on a comparison of early postoperative complications. This study was conducted to investigate the difference of early postoperative complications between Billroth I and Billroth II types of anastomosis for distal gastrectomies.</p> <p>Methods</p> <p>A total of 809 patients who underwent distal gastrectomies for gastric cancer during four years were included in the study. The only study endpoint was analysis of in-patients' postoperative complications. The risk adjusted complication rate was compared by POSSUM (Physiological and operative severity score for enumeration of morbidity and mortality) and the severity of complications was compared by Rui Jin Hospital classification of complication.</p> <p>Results</p> <p>Complication rate of Billroth II type of anastomosis was almost double of that in Billroth I (P = 0.000). Similarly, the risk adjusted complication rate was also higher in Billroth II group. More severe complications were observed and the postoperative duration was significantly longer in Billroth II type (P = 0.000). Overall expenditure was significantly higher in Billroth II type (P = 0.000).</p> <p>Conclusion</p> <p>Billroth II method of anastomosis was associated with higher rate of early postoperative complications. Therefore, we conclude that the Billroth I method should be the first choice after a distal gastrectomy as long as the anatomic and oncological environment of an individual patient allows us to perform it. However more prospective studies should be designed to compare the overall surgical outcomes of both anastomosis methods.</p
Epidural Catheter Placement in Morbidly Obese Parturients with the Use of an Epidural Depth Equation prior to Ultrasound Visualization
Background. Previously, Balki determined the Pearson correlation coefficient with the use of ultrasound (US) was 0.85 in morbidly obese parturients. We aimed to determine if the use of the epidural depth equation (EDE) in conjunction with US can provide better clinical correlation in estimating the distance from the skin to the epidural space in morbidly obese parturients.
Methods. One hundred sixty morbidly obese (≥40 kg/m2) parturients requesting labor epidural analgesia were enrolled. Before epidural catheter placement, EDE was used to estimate depth to the epidural space. This estimation was used to help visualize the epidural space with the transverse and midline longitudinal US views and to measure depth to epidural space. The measured epidural depth was made available to the resident trainee before needle insertion. Actual needle depth (ND) to the epidural space was recorded. Results. Pearson’s correlation coefficients comparing actual (ND) versus US estimated depth to the epidural space in the longitudinal median and transverse planes were 0.905 (95% CI: 0.873 to 0.929) and 0.899 (95% CI: 0.865 to 0.925), respectively. Conclusion. Use of the epidural depth equation (EDE) in conjunction with the longitudinal and transverse US views results in better clinical correlation than with the use of US alone
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