1,822 research outputs found
Development of Heterogeneous Photosensitized Transition Metal Oxide Water-Splitting Catalysts on Silica Support
The research presented in this manuscript describes the development of photosensitized inexpensive catalysts based on readily available materials. The investigation covers synthesis and characterization of photosensitizers based on porphyrins, mechanical and thermal coating of solid support with semiconducting transition metal oxides, photosensitization of the semiconducting layer, and characterization of the photoelectrochemical properties displayed by the new materials. The process of water oxidation is of primary interest here, with little emphasis put on reduction of protons to gaseous hydrogen. Photoelectrochemically produced protons serve as a probe of effectiveness of the catalysts. Several systems are described, and two catalysts are identified as the most efficient
A Kohn-Sham system at zero temperature
An one-dimensional Kohn-Sham system for spin particles is considered which
effectively describes semiconductor {nano}structures and which is investigated
at zero temperature. We prove the existence of solutions and derive a priori
estimates. For this purpose we find estimates for eigenvalues of the
Schr\"odinger operator with effective Kohn-Sham potential and obtain
-bounds of the associated particle density operator. Afterwards,
compactness and continuity results allow to apply Schauder's fixed point
theorem. In case of vanishing exchange-correlation potential uniqueness is
shown by monotonicity arguments. Finally, we investigate the behavior of the
system if the temperature approaches zero.Comment: 27 page
Longtime behavior of nonlocal Cahn-Hilliard equations
Here we consider the nonlocal Cahn-Hilliard equation with constant mobility
in a bounded domain. We prove that the associated dynamical system has an
exponential attractor, provided that the potential is regular. In order to do
that a crucial step is showing the eventual boundedness of the order parameter
uniformly with respect to the initial datum. This is obtained through an
Alikakos-Moser type argument. We establish a similar result for the viscous
nonlocal Cahn-Hilliard equation with singular (e.g., logarithmic) potential. In
this case the validity of the so-called separation property is crucial. We also
discuss the convergence of a solution to a single stationary state. The
separation property in the nonviscous case is known to hold when the mobility
degenerates at the pure phases in a proper way and the potential is of
logarithmic type. Thus, the existence of an exponential attractor can be proven
in this case as well
Paleoenvironmental Studies in Southwestern Yukon
The St. Elias Mountain region has occupied an important place in the study of the Quaternary because it presents a relatively accessible non-polar icefield and an array of environments from tundra to boreal forest. Paleoenvironmental studies in southwestern Yukon have documented the broad-scale climatic changes of the past 20 000 years, although few studies exist with well-dated sequences at high temporal resolution. Picea glauca arrived across the entire region around 10 000 years ago; however, the details regarding its migration pathways are not well known. Available records indicate few major changes in the composition of the boreal forest vegetation since that time. A slightly more intense fire regime in the early to mid Holocene has been suggested, but this conclusion is based on only a few studies. Variations in the tree line during the Holocene have been examined, but these studies also lack details. There is no evidence for more extensive grasslands in the area during the Holocene. Paleolimnological studies indicate that changes in populations of aquatic organisms have occurred in response to either Holocene climates or watershed variability.La rĂ©gion du mont St. Elias occupe une place importante dans lâĂ©tude du Quaternaire parce quâelle recĂšle un champ de glace non polaire relativement accessible ainsi quâune panoplie dâenvironnements, allant de la toundra Ă la forĂȘt borĂ©ale. Des Ă©tudes palĂ©oĂ©cologiques effectuĂ©es dans le sud-ouest du Yukon ont permis de documenter les changements climatiques Ă grande Ă©chelle des 20 000 derniĂšres annĂ©es, et ce, mĂȘme sâil existe peu dâĂ©tudes dotĂ©es de sĂ©quences bien datĂ©es de grande rĂ©solution temporelle. Picea glauca est arrivĂ©e dans toute la rĂ©gion il y a environ 10 000 ans. Cependant, les dĂ©tails concernant sa voie de migration ne sont pas bien connus. Les donnĂ©es disponibles indiquent peu de changements majeurs dans la composition de la forĂȘt borĂ©ale depuis cette pĂ©riode. Un rĂ©gime des feux un peu plus intense de lâHolocĂšne infĂ©rieure Ă lâHolocĂšne moyen a Ă©tĂ© suggĂ©rĂ©, mais cette conclusion ne repose que sur un petit nombre dâĂ©tudes. Les variations caractĂ©risant la limite des arbres pendant lâHolocĂšne ont Ă©tĂ© examinĂ©es, mais ces Ă©tudes ne sont Ă©galement pas suffisamment dĂ©taillĂ©es. Il nâexiste pas de preuve quâil existait des prairies Ă plus grande Ă©chelle dans la rĂ©gion pendant lâHolocĂšne. Des Ă©tudes palĂ©olimnologiques indiquent que des changements caractĂ©risant les populations dâorganismes se sont produits en raison de la variabilitĂ© des climats ou dans des bassins hydrographiques de lâHolocĂšne
Mathematical modeling and numerical simulation of semiconductor detectors
We report on a system of nonlinear partial differential equations describing signal conversion and amplification in semiconductor detectors. We explain the main ideas governing the numerical treatment of this system as they are implemented in our code WIAS-TeSCA. This software package has been used by the MPI Semiconductor Laboratory for numerical simulation of innovative radiation detectors. We present some simulation results focussing on three-dimensional effects in X-ray detectors for satellite missions
Microwave properties of : Influence of magnetic scattering
We report measurements of the surface impedance of
, . Increasing
concentration leads to some striking results not observed in samples doped
by non-magnetic constituents. The three principal features of the data
- multiple structure in the transition, a high residual resistance and, at high
concentrations, an upturn of the low data, are all characteristic of
the influence of magnetic scattering on superconductivity, and appear to be
common to materials where magnetism and superconductivity coexist. The low
behavior of appears to change from to at large
doping, and provides evidence of the influence of magnetic pairbreaking of the
.Comment: 5 pages, 3 eps figures, Revtex, 2-column format, uses graphicx. To
appear in Physica C. Postscript version also available at
http://sagar.physics.neu.edu/preprints.htm
On four numerical schemes for a unipolar degenerate drift-diffusion model
International audienceWe consider a unipolar degenerate drift-diffusion system where the relation between the concentration of the charged species c and the chemical potential h is . For four different finite volume schemes based on four different formulations of the fluxes of the problem, we discuss stability and existence results. For two of them, we report a convergence proof. Numerical experiments illustrate the behaviour of the different schemes
Engineering fatty acid synthases for directed polyketide production.
In this study, we engineered fatty acid synthases (FAS) for the biosynthesis of short-chain fatty acids and polyketides, guided by a combined in vitro and in silico approach. Along with exploring the synthetic capability of FAS, we aim to build a foundation for efficient protein engineering, with the specific goal of harnessing evolutionarily related megadalton-scale polyketide synthases (PKS) for the tailored production of bioactive natural compounds
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