17,315 research outputs found
Predicting the effects of sand erosion on collector surfaces in CSP plants
This paper presents a methodology to predict the optical performance and physical topography of the glass collector surfaces of any given CSP plant in the presence of sand and dust storms, providing that local climate conditions are known and representative sand and dust particles samples are available. Using existing meteorological data for a defined CSP plant in Egypt, plus sand and dust samples from two desert locations in Libya, we describe how to derive air speed, duration, and sand concentrations to use within the Global CSP Laboratory sand erosion simulation rig at Cranfield University. This then allows us to predict the optical performance of parabolic trough collector glass after an extended period by the use of accelerated ageing. However the behavior of particles in sandstorms is complex and has prompted a theoretical analysis of sand particle dynamics which is also described in this paper
The c axis optical conductivity of layered systems in the superconducting state
In this paper, we discuss the c axis optical conductivity Re [sigma_c(omega)]
in the high T_c superconductors, in the superconducting state. The basic
premise of this work is that electrons travelling along the c axis between
adjacent CuO_2 layers must pass through several intervening layers. In earlier
work we found that, for weak inter-layer coupling, it is preferable for
electrons to travel along the c axis by making a series of interband
transitions rather than to stay within a single (and very narrow) band.
Moreover, we found that many of the properties of the normal state optical
conductivity, including the pseudogap could be explained by interband
transitions. In this work we examine the effect of superconductivity on the
interband conductivity. We find that, while the onset of superconductivity is
clearly evident in the spectrum, there is no clear signature of the symmetry of
the superconducting order parameter.Comment: 6 pages, 4 figure
The effect of uniaxial pressure on the magnetic anisotropy of the Mn_{12}-Ac single-molecule magnet
We study the effect of uniaxial pressure on the magnetic hysteresis loops of
the single-molecule magnet Mn_{12}-Ac. We find that the application of pressure
along the easy axis increases the fields at which quantum tunneling of
magnetization occurs. The observations are attributed to an increase in the
molecule's magnetic anisotropy constant D of 0.142(1)%/kbar. The increase in D
produces a small, but measurable increase in the effective energy barrier for
magnetization reversal. Density-functional theory calculations also predict an
increase in the barrier with applied pressure.Comment: version accepted by EPL; 6 pages, including 7 figures. Small changes
and added reference
A spectral method for elliptic equations: the Dirichlet problem
An elliptic partial differential equation Lu=f with a zero Dirichlet boundary
condition is converted to an equivalent elliptic equation on the unit ball. A
spectral Galerkin method is applied to the reformulated problem, using
multivariate polynomials as the approximants. For a smooth boundary and smooth
problem parameter functions, the method is proven to converge faster than any
power of 1/n with n the degree of the approximate Galerkin solution. Examples
in two and three variables are given as numerical illustrations. Empirically,
the condition number of the associated linear system increases like O(N), with
N the order of the linear system.Comment: This is latex with the standard article style, produced using
Scientific Workplace in a portable format. The paper is 22 pages in length
with 8 figure
Marked expansion of exocrine and endocrine pancreas with incretin therapy in humans with increased exocrine pancreas dysplasia and the potential for glucagon-producing neuroendocrine tumors.
Controversy exists regarding the potential regenerative influences of incretin therapy on pancreatic Ī²-cells versus possible adverse pancreatic proliferative effects. Examination of pancreata from age-matched organ donors with type 2 diabetes mellitus (DM) treated by incretin therapy (n = 8) or other therapy (n = 12) and nondiabetic control subjects (n = 14) reveals an ā¼40% increased pancreatic mass in DM treated with incretin therapy, with both increased exocrine cell proliferation (P < 0.0001) and dysplasia (increased pancreatic intraepithelial neoplasia, P < 0.01). Pancreata in DM treated with incretin therapy were notable for Ī±-cell hyperplasia and glucagon-expressing microadenomas (3 of 8) and a neuroendocrine tumor. Ī²-Cell mass was reduced by ā¼60% in those with DM, yet a sixfold increase was observed in incretin-treated subjects, although DM persisted. Endocrine cells costaining for insulin and glucagon were increased in DM compared with non-DM control subjects (P < 0.05) and markedly further increased by incretin therapy (P < 0.05). In conclusion, incretin therapy in humans resulted in a marked expansion of the exocrine and endocrine pancreatic compartments, the former being accompanied by increased proliferation and dysplasia and the latter by Ī±-cell hyperplasia with the potential for evolution into neuroendocrine tumors
Convergence of expansions in Schr\"odinger and Dirac eigenfunctions, with an application to the R-matrix theory
Expansion of a wave function in a basis of eigenfunctions of a differential
eigenvalue problem lies at the heart of the R-matrix methods for both the
Schr\"odinger and Dirac particles. A central issue that should be carefully
analyzed when functional series are applied is their convergence. In the
present paper, we study the properties of the eigenfunction expansions
appearing in nonrelativistic and relativistic -matrix theories. In
particular, we confirm the findings of Rosenthal [J. Phys. G: Nucl. Phys. 13,
491 (1987)] and Szmytkowski and Hinze [J. Phys. B: At. Mol. Opt. Phys. 29, 761
(1996); J. Phys. A: Math. Gen. 29, 6125 (1996)] that in the most popular
formulation of the R-matrix theory for Dirac particles, the functional series
fails to converge to a claimed limit.Comment: Revised version, accepted for publication in Journal of Mathematical
Physics, 21 pages, 1 figur
The impact of asking intention or self-prediction questions on subsequent behavior: a meta-analysis
The current meta-analysis estimated the magnitude of the impact of asking intention and self-prediction questions on rates of subsequent behavior, and examined mediators and moderators of this questionābehavior effect (QBE). Random-effects meta-analysis on 116 published tests of the effect indicated that intention/prediction questions have a small positive effect on behavior (d+ = 0.24). Little support was observed for attitude accessibility, cognitive dissonance, behavioral simulation, or processing fluency explanations of the QBE. Multivariate analyses indicated significant effects of social desirability of behavior/behavior domain (larger effects for more desirable and less risky behaviors), difficulty of behavior (larger effects for easy-to-perform behaviors), and sample type (larger effects among student samples). Although this review controls for co-occurrence of moderators in multivariate analyses, future primary research should systematically vary moderators in fully factorial designs. Further primary research is also needed to unravel the mechanisms underlying different variants of the QBE
Dark Solitons in Discrete Lattices: Saturable versus Cubic Nonlinearities
In the present work, we study dark solitons in dynamical lattices with the
saturable nonlinearity and compare them with those in lattices with the cubic
nonlinearity. This comparison has become especially relevant in light of recent
experimental developments in the former context. The stability properties of
the fundamental waves, for both on-site and inter-site modes, are examined
analytically and corroborated by numerical results. Furthermore, their
dynamical evolution when they are found to be unstable is obtained through
appropriately crafted numerical experiments.Comment: 15 pages, 5 figure
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