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Dimensional Reduction (dimensional + reduction)

Distribution by Scientific Domains
Polymers and Materials Science44%
Physics and Astronomy33%

Selected Abstracts

Solution Processing of Chalcogenide Semiconductors via Dimensional Reduction

ADVANCED MATERIALS, Issue 31 2009
David B. Mitzi
Abstract The quest to develop thin-film solution processing approaches that offer low-cost and preferably low-temperature deposition, while simultaneously providing quality semiconductor characteristics, has become an important thrust within the materials community. While inorganic compounds offer the potential for outstanding electronic properties relative to organic systems, the very nature of these materials rendering them good electronic materials,namely strong covalent bonding,also leads to poor solubility. This review presents a "dimensional reduction" approach to improving the solubility of metal chalcogenide semiconductors, which generally involves breaking the extended framework up into discrete metal chalcogenide anions separated by small and volatile cationic species. The resulting soluble precursor may be solution-processed into thin-film form and thermally decomposed to yield the desired semiconductor. Several applications of this principle to the solution deposition of high-performance active layers for transistors (channel mobility >10,cm2 V,1 s,1), solar cells (power conversion efficiency of as high as 12%), and fundamental materials study will be presented using hydrazine as the deposition solvent. [source]

Fabrication of Patterned Polydiacetylene Composite Films Using a Replica-Molding (REM) Technique

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 3 2010
Oktay Yarimaga
Abstract Functional three-dimensional (3D) micropatterns of diacetylene supramolecules embedded in a host polymer have been successfully fabricated by a replica-molding (REM) technique. Dimensional reduction as a result of liquid evaporation during the curing process does not affect the conformational features of the transferred patterns. Polymerization of the diacetylene vesicles using 254,nm UV-light irradiation from the back-side of the transparent substrate induces blue colored polydiacetylene (PDA) micro-images. Interestingly, the polymerization selectively occurs in the molded areas because of the sub-300,nm light blocking property of SU-8. 3D fluorescence patterns are readily obtained by heat treatment of the blue images on the film. [source]

Moduli stabilization in the heterotic/IIB discretuum

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 4 2006
G. Curio
We consider supersymmetric compactifications of type IIB and the weakly coupled heterotic string with G resp. H -flux and gaugino condensation in a hidden sector included. We point out that proper inclusion of the non-perturbative effects changes the Hodge structure of the allowed fluxes in type IIB significantly. In the heterotic theory it is known that, in contrast to the potential read off from dimensional reduction, the effective four-dimensional description demands for consistency a non-vanishing H2,1 component if a H3,0 component is already present balancing the condensate. The H2,1 component causes a non-Kählerness of the underlying geometry whose moduli space is, however, not well-understood. We show that the occurrence of H2,1 might actually be avoided by using a KKLT-like two-step procedure for moduli stabilization. Independently of the H2,1 issue one-loop corrections to the gauge couplings were argued to cause a not well-controlled strong coupling transition. This problem can be avoided as well when the effects of world-sheet instantons are included. They will also stabilize the Kähler modulus what was accomplished by H2,1 before. [source]

M-theory and gauged supergravities,

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 2 2005
D. Roest
Abstract We present a pedagogical discussion of the emergence of gauged supergravities from M-theory. First, a review of maximal supergravity and its global symmetries and supersymmetric solutions is given. Next, different procedures of dimensional reduction are explained: reductions over a torus, a group manifold and a coset manifold and reductions with a twist. Emphasis is placed on the consistency of the truncations, the resulting gaugings and the possibility to generate field equations without an action. Using these techniques, we construct a number of gauged maximal supergravities in diverse dimensions with a string or M-theory origin. One class consists of the CSO gaugings, which comprise the analytic continuations and group contractions of SO(n) gaugings. We construct the corresponding half-supersymmetric domain walls and discuss their uplift to D- and M-brane distributions. Furthermore, a number of gauged maximal supergravities are constructed that do not have an action. [source]

Controlling Electron and Hole Charge Injection in Ambipolar Organic Field-Effect Transistors by Self-Assembled Monolayers

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2009
Xiaoyang Cheng
Abstract Controlling contact resistance in organic field-effect transistors (OFETs) is one of the major hurdles to achieve transistor scaling and dimensional reduction. In particular in the context of ambipolar and/or light-emitting OFETs it is a difficult challenge to obtain efficient injection of both electrons and holes from one injecting electrode such as gold since organic semiconductors have intrinsically large band gaps resulting in significant injection barrier heights for at least one type of carrier. Here, systematic control of electron and hole contact resistance in poly(9,9-di- n -octylfluorene- alt -benzothiadiazole) ambipolar OFETs using thiol-based self-assembled monolayers (SAMs) is demonstrated. In contrast to common believe, it is found that for a certain SAM the injection of both electrons and holes can be improved. This simultaneous enhancement of electron and hole injection cannot be explained by SAM-induced work-function modifications because the surface dipole induced by the SAM on the metal surface lowers the injection barrier only for one type of carrier, but increases it for the other. These investigations reveal that other key factors also affect contact resistance, including i) interfacial tunneling through the SAM, ii) SAM-induced modifications of interface morphology, and iii) the interface electronic structure. Of particular importance for top-gate OFET geometry is iv) the active polymer layer thickness that dominates the electrode/polymer contact resistance. Therefore, a consistent explanation of how SAM electrode modification is able to improve both electron and hole injection in ambipolar OFETs requires considering all mentioned factors. [source]

Solution Processing of Chalcogenide Semiconductors via Dimensional Reduction

ADVANCED MATERIALS, Issue 31 2009
David B. Mitzi
Abstract The quest to develop thin-film solution processing approaches that offer low-cost and preferably low-temperature deposition, while simultaneously providing quality semiconductor characteristics, has become an important thrust within the materials community. While inorganic compounds offer the potential for outstanding electronic properties relative to organic systems, the very nature of these materials rendering them good electronic materials,namely strong covalent bonding,also leads to poor solubility. This review presents a "dimensional reduction" approach to improving the solubility of metal chalcogenide semiconductors, which generally involves breaking the extended framework up into discrete metal chalcogenide anions separated by small and volatile cationic species. The resulting soluble precursor may be solution-processed into thin-film form and thermally decomposed to yield the desired semiconductor. Several applications of this principle to the solution deposition of high-performance active layers for transistors (channel mobility >10,cm2 V,1 s,1), solar cells (power conversion efficiency of as high as 12%), and fundamental materials study will be presented using hydrazine as the deposition solvent. [source]

Conformational analysis: A new approach by means of chemometrics

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2002
Aline Thaís Bruni
Abstract In conformational analysis, the systematic search method completely maps the space but suffers from the combinatorial explosion problem because the number of conformations increases exponentially with the number of free rotation angles. This study introduces a new methodology of conformational analysis that controls the combinatorial explosion. It is based on a dimensional reduction of the system through the use of principal component analysis. The results are exactly the same as those obtained for the complete search but, in this case, the number of conformations increases only quadratically with the number of free rotation angles. The method is applied to a series of three drugs: omeprazole, pantoprazole, lansoprazole,benzimidazoles that suppress gastric-acid secretion by means of H+, K+ -ATPase enzyme inhibition. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 222,236, 2002 [source]

Elastic,ideally plastic beams and Prandtl,Ishlinskii hysteresis operators

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 18 2007
Pavel Krej
Abstract The one-dimensional equation for transversal vibrations of an elastoplastic beam is derived from a general three-dimensional system with a single-yield tensorial von Mises plasticity model. It leads after dimensional reduction to a multiyield scalar Prandtl,Ishlinskii hysteresis model whose weight function is explicitly given. The use of Prandtl,Ishlinskii operators in elastoplasticity is thus not just a questionable phenomenological approach, but in fact quite natural. The resulting partial differential equation with hysteresis is transformed into an equivalent system for which the existence and uniqueness of a strong solution is proved. The proof employs techniques from the mathematical theory of hysteresis operators. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Nonequilibrium quantum anharmonic oscillator and scalar field: high temperature approximations

ANNALEN DER PHYSIK, Issue 6 2009
R.F. Alvarez-Estrada
Abstract We treat a relativistic quantum boson gas, described by a scalar quantum field, with quartic self-interaction (,4) in three spatial dimensions: we review the known equilibrium case and present new proposals off-equilibrium. For high temperature and large spatial scales, the behaviour of the gas at equilibrium simplifies nonperturbatively (equilibrium dimensional reduction or EDR): its thermodynamics is described by classical statistical mechanics with some quantum field effects. By assumption, the initial state of the gas off-equilibrium includes interactions and inhomogeneities and is not far from thermal equilibrium. We employ real-time generating functionals and obtain the free nonequilibrium correlators at non-zero temperature. The nonequilibrium quantum gas appears to simplify nonperturbatively in the regime of high temperature and large temporal and spatial scales (nonequilibrium dimensional reduction or NEDR), its dynamics being described by classical statistical mechanics with some quantum field effects. We outline the renormalization of the ,4 theory, the nonequilibrium statistical mechanics of a quantum anharmonic oscillator and the high temperature simplifications, all of which provide very useful hints for NEDR in the field case. Our main proposals are NEDR and the associated new (renormalized) real-time nonequilibrium generating functionals for the ,4 theory. [source]