17,520 research outputs found
GaAsP on GaP top solar cells
GaAsP on GaP top solar cells as an attachment to silicon bottom solar cells are being developed. The GaAsP on GaP system offers several advantages for this top solar cell. The most important is that the gallium phosphide substrate provides a rugged, transparent mechanical substrate which does not have to be removed or thinned during processing. Additional advantages are that: (1) gallium phosphide is more oxidation resistant than the III-V aluminum compounds, (2) a range of energy band gaps higher than 1.75 eV is readily available for system efficiency optimization, (3) reliable ohmic contact technology is available from the light-emitting diode industry, and (4) the system readily lends itself to graded band gap structures for additional increases in efficiency
N/P GaAs concentrator solar cells with an improved grid and bushbar contact design
The major requirements for a solar cell used in space applications are high efficiency at AMO irradiance and resistance to high energy radiation. Gallium arsenide, with a band gap of 1.43 eV, is one of the most efficient sunlight to electricity converters (25%) when the the simple diode model is used to calculate efficiencies at AMO irradiance, GaAs solar cells are more radiation resistant than silicon solar cells and the N/P GaAs device has been reported to be more radiation resistant than similar P/N solar cells. This higher resistance is probably due to the fact that only 37% of the current is generated in the top N layer of the N/P cell compared to 69% in the top layer of a P/N solar cell. This top layer of the cell is most affected by radiation. It has also been theoretically calculated that the optimized N/P device will prove to have a higher efficiency than a similar P/N device. The use of a GaP window layer on a GaAs solar cell will avoid many of the inherent problems normally associated with a GaAlAs window while still proving good passivation of the GaAs surface. An optimized circular grid design for solar cell concentrators has been shown which incorporates a multi-layer metallization scheme. This multi-layer design allows for a greater current carrying capacity for a unit area of shading, which results in a better output efficiency
Visualizing the Quantum Interaction Picture in Phase Space
We illustrate the correspondence between the quantum Interaction
Picture-evolution of the state of a quantum system in Hilbert space and a
combination of local and global transformations of its Wigner function in phase
space. To this aim, we consider the time-evolution of a quantized harmonic
oscillator driven by both a linear and a quadratic (in terms of bosonic
creation and annihilation operators) potentials and employ the Magnus series to
derive the exact form of the time-evolution operator. In this case, the
Interaction Picture corresponds to a local transformation of phase
space-reference frame into the one that is co-moving with the Wigner function.Comment: Submitted to New Journal of Physic
SU(3) Spin-Orbit Coupling in Systems of Ultracold Atoms
Motivated by the recent experimental success in realizing synthetic
spin-orbit coupling in ultracold atomic systems, we consider N-component atoms
coupled to a non-Abelian SU(N) gauge field. More specifically, we focus on the
case, referred to here as "SU(3) spin-orbit-coupling," where the internal
states of three-component atoms are coupled to their momenta via a matrix
structure that involves the Gell-Mann matrices (in contrast to the Pauli
matrices in conventional SU(2) spin-orbit-coupled systems). It is shown that
the SU(3) spin-orbit-coupling gives rise to qualitatively different phenomena
and in particular we find that even a homogeneous SU(3) field on a simple
square lattice enables a topologically non-trivial state to exist, while such
SU(2) systems always have trivial topology. In deriving this result, we first
establish an exact equivalence between the Hofstadter model with a 1/N Abelian
flux per plaquette and a homogeneous SU(N) non-Abelian model. The former is
known to have a topological spectrum for N>2, which is thus inherited by the
latter. It is explicitly verified by an exact calculation for N=3, where we
develop and use a new algebraic method to calculate topological indices in the
SU(3) case. Finally, we consider a strip geometry and establish the existence
of three gapless edge states -- the hallmark feature of such an SU(3)
topological insulator.Comment: 4.2 pages, 1 figur
Decoherence of Quantum-Enhanced Timing Accuracy
Quantum enhancement of optical pulse timing accuracy is investigated in the
Heisenberg picture. Effects of optical loss, group-velocity dispersion, and
Kerr nonlinearity on the position and momentum of an optical pulse are studied
via Heisenberg equations of motion. Using the developed formalism, the impact
of decoherence by optical loss on the use of adiabatic soliton control for
beating the timing standard quantum limit [Tsang, Phys. Rev. Lett. 97, 023902
(2006)] is analyzed theoretically and numerically. The analysis shows that an
appreciable enhancement can be achieved using current technology, despite an
increase in timing jitter mainly due to the Gordon-Haus effect. The decoherence
effect of optical loss on the transmission of quantum-enhanced timing
information is also studied, in order to identify situations in which the
enhancement is able to survive.Comment: 12 pages, 4 figures, submitte
Frictional quantum decoherence
The dynamics associated with a measurement-based master equation for quantum
Brownian motion are investigated. A scheme for obtaining time evolution from
general initial conditions is derived. This is applied to analyze dissipation
and decoherence in the evolution of both a Gaussian and a Schr\"{o}dinger cat
initial state. Dependence on the diffusive terms present in the master equation
is discussed with reference to both the coordinate and momentum
representations.Comment: 18 pages, 7 figure
Relationship of serum adiponectin and resistin to glucose intolerance and fat topography in south-Asians
Objectives
South-Asians have lower adiponectin levels compared to Caucasians. It was not clear however, if this intrinsic feature is related to aspects of glucose metabolism. This study aims to determine the relationship between body fat distribution and adipocytokine in South-Asian subjects by measuring serum adipocytokines, adiposity, insulinemia, and glucose tolerance levels.
Methods
In this cross-sectional study, 150 South-Asians (80 males, 70 females) were included, 60 had NGT (Control group, Age 51.33 ± 11.5, BMI 27 ± 2.3), 60 had IGT (Age 57.7 ± 12.5, BMI 27.2 ± 2.7), 30 had type 2 DM (Age 49.5 ± 10.9, BMI 28 ± 1.7). Measures of adiposity, adipocytokines and other metabolic parameters were determined. Parameters were measured using the following: a) Plasma glucose by glucose oxidase method b) CRP by immunoturbidimetric method (Roche/Hitachi analyser) c) insulin by Medgenix INS-ELISA immunoenzymetric assay by Biosource (Belgium) d) Leptin, Adiponectin by radioimmunoassay kits by Linco Research (St. Charles MO) e) Resistin by immunoassay kits by Phoenix Pharmaceuticals INC (530 Harbor Boulevard, Belmont CA 94002, USA).
Results
Adiponectin concentrations were highest in NGT, decreased in IGT and lowest in DMT2, (both p < 0.01). Leptin was significantly higher in DMT2 than IGT and NGT p = 0.02 and 0.04 respectively. There was a significant positive relationships between log adiponectin and 2-hr insulin values, p = 0.028 and history of hypertensions and a ischemic heart disease p = 0.008 with R = 0.65. There was a significant inverse correlation between log adiponectin and resistin, p < 0.01.
Conclusion
Resistin levels had an inverse correlation with adiponectin levels, indicating an inverse relationship between pro-inflammatory cytokines and adiponectin. Adiponectin levels were related to glucose tolerance
Dydrogesterone and norethisterone regulate expression of lipoprotein lipase and hormones-sensitive lipase in human subcutaneous abdominal adipocytes
Aim: In premenopausal women, hyper-androgenicity is associated with central obesity and an increased cardiovascular risk. We investigated the effects of dydrogesterone (DYD)(a non-androgenic progestogen) and norethisterone (NET)(an androgenic progestogen) on lipoprotein lipase (LPL), hormone-sensitive lipase (HSL) and glycerol release in adipocytes isolated from subcutaneous abdominal adipose tissue. Methods: Adipose tissue was obtained from 12 non-diabetic women, mean age 51 years (range 37-78) and mean BMI 25.4kg/m2 (range 20.3-26.4). Adipocytes were treated with increasing doses of DYD and NET for 48 hours prior to protein extraction. Effects on lipogenesis and lipolysis were assessed using western blotting to determine the expression of key enzymes, LPL (56kDa) and HSL (84kDa) respectively. Measurement of glycerol release into the medium provided an assessment of lipolytic activity. Results: Expression of LPL was increased by DYD and NET (mean protein expression relative to control ± SEM); with greatest effect at 10-8M for DYD: 2.32±0.51(p0.05). Conclusions: DYD and NET significantly increased LPL expression relative to control whilst significantly reducing HSL expression. At the concentrations studied, similar effects were observed with the androgenic NET and the non-androgenic DYD despite differing effects on the lipid profile when taken
in combination with estrogen. Further work in this area may improve knowledge about the effects of different progestogens on body fat distribution and enable progestogen use to be tailored to the individual to achieve maximal benefits
Large structures and tethers working group
The Large Structures and Tethers Working Group sought to clarify the meaning of large structures and tethers as they related to space systems. Large was assumed to mean that the characteristic length of the structure was greater than one of such relevant plasma characteristics as ion gyroradius or debey length. Typically, anything greater than or equal to the Shuttle dimensions was considered large. It was agreed that most large space systems that the tether could be better categorized as extended length, area, or volume structures. The key environmental interactions were then identified in terms of these three categories. In the following Working Group summary, these categories and the related interactions are defined in detail. The emphasis is on how increases in each of the three spatial dimensions uniquely determine the interactions with the near-Earth space environment. Interactions with the environments around the other planets and the solar wind were assumed to be similar or capable of being extrapolated from the near-Earth results. It should be remembered in the following that the effects on large systems do not just affect specific technologies but will quite likely impact whole missions. Finally, the possible effects of large systems on the plasma environment, although only briefly discussed, were felt to be of potentially great concern
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