Involution and Constrained Dynamics I: The Dirac Approach

We study the theory of systems with constraints from the point of view of the formal theory of partial differential equations. For finite-dimensional systems we show that the Dirac algorithm completes the equations of motion to an involutive system. We discuss the implications of this identification for field theories and argue that the involution analysis is more general and flexible than the Dirac approach. We also derive intrinsic expressions for the number of degrees of freedom.Comment: 28 pages, latex, no figure

Microstructure effects on the phase transition behavior of a prototypical quantum material

Materials with insulator metal transitions promise advanced functionalities for future information technology. Patterning on the microscale is key for miniaturized functional devices, but material properties may vary spatially across microstructures. Characterization of these miniaturized devices requires electronic structure probes with sufficient spatial resolution to understand the influence of structure size and shape on functional properties. The present study demonstrates the use of imaging soft X ray absorption spectroscopy with a spatial resolution better than 2 amp; 956;m to study the insulator metal transition in vanadium dioxide thin film microstructures. This novel technique reveals that the transition temperature for the conversion from insulating to metallic vanadium dioxide is lowered by 1.2 K 0.4 K close to the structure edges compared to the center. Facilitated strain release during the phase transition is discussed as origin of the observed behavior. The experimental approach enables a detailed understanding of how the electronic properties of quantum materials depend on their patterning at the micrometer scal

Ultrafast modification of the electronic structure of a correlated insulator

A nontrivial balance between Coulomb repulsion and kinematic effects determines the electronic structure of correlated electron materials. The use of electromagnetic fields strong enough to rival these native microscopic interactions allows us to study the electronic response as well as the time scales and energies involved in using quantum effects for possible applications. We use element specific transient x ray absorption spectroscopy and high harmonic generation to measure the response to ultrashort off resonant optical fields in the prototypical correlated electron insulator NiO. Surprisingly, fields of up to 0.22 V lead to no detectable changes in the correlated Ni 3d orbitals contrary to previous predictions. A transient directional charge transfer is uncovered, a behavior that is captured by first principles theory. Our results highlight the importance of retardation effects in electronic screening and pinpoints a key challenge in functionalizing correlated materials for ultrafast device operatio

Computing multiple-valued logic programs

The logic of signed formula can be used to reason about a wide variety of multiple-valued logics \cite{hah94,lmr96}. The formal theoretical foundation of multiple-valued logic programming based on signed formulas is set forth in \cite{lu96}. The current paper is an investigation into the operational semantics of such signed logic programming. The connection of signed logic programming to constraint logic programming is presented, search space issues are briefly discussed for both general and special cases, and applications to bilattice logic programming and truth-maintenance are analyzed

Computing multiple-valued logic programs

The logic of signed formula can be used to reason about a wide variety of multiple-valued logics \cite{hah94,lmr96}. The formal theoretical foundation of multiple-valued logic programming based on signed formulas is set forth in \cite{lu96}. The current paper is an investigation into the operational semantics of such signed logic programming. The connection of signed logic programming to constraint logic programming is presented, search space issues are briefly discussed for both general and special cases, and applications to bilattice logic programming and truth-maintenance are analyzed

KOMET - A System for the Integration of Heterogeneous Information Sources

. We present KOMET, an architecture for the intelligent integration of heterogeneous information sources. It is based on the idea of a mediator, which is an independent software layer between an application and various knowledge sources which need to be accessed. We present an especially suitable logic-based language for encoding typical mediation tasks like conditional preference strategies, schema integration or data inconsistency resolution. Using annotated logic, KOMET is able to perform various common types of reasoning, such as probabilistic, fuzzy, paraconsistent and certain types of temporal and spatial reasoning. In combination with an extensible type system and the embedding of external knowledge sources as constraint domains, our mediation language offers a rich framework, which not only facilitates access to structured information, but as well supports unstructured and semi-structured information. A number of examples show the practical application of our approach. Keywords..

Computing multiple-valued logic programs

The logic of signed formula can be used to reason about a wide variety of multiple-valued logics \cite{hah94,lmr96}. The formal theoretical foundation of multiple-valued logic programming based on signed formulas is set forth in \cite{lu96}. The current paper is an investigation into the operational semantics of such signed logic programming. The connection of signed logic programming to constraint logic programming is presented, search space issues are briefly discussed for both general and special cases, and applications to bilattice logic programming and truth-maintenance are analyzed

Using the photoinduced L 3 resonance shift in Fe and Ni as time reference for ultrafast experiments at low flux soft x ray sources

We study the optical-pump induced ultrafast transient change of x-ray absorption at L3 absorption resonances of the transition metals Ni and Fe in the Fe0.5Ni0.5 alloy. We find the effect for both elements to occur simultaneously on a femtosecond timescale. This effect may hence be used as a handy cross correlation scheme, providing a time-zero reference for ultrafast optical-pump soft x-ray-probe measurement. The method benefits from a relatively simple experimental setup as the sample itself acts as time-reference tool. In particular, this technique works with low flux ultrafast soft x-ray sources. The measurements are compared to the cross correlation method introduced in an earlier publication

Carbon nanotube based composite membranes for water desalination by membrane distillation

New technologies are required to improve desalination efficiency and increase water treatment capacities. One promising low energy technique to produce potable water from either sea or sewage water is membrane distillation (MD). However, to be competitive with other desalination processes, membranes need to be designed specifically for the MD process requirements. Here we report on the design of carbon nanotube (CNT) based composite material membranes for direct contact membrane distillation (DCMD). The membranes were characterized and tested in a DCMD setup under different feed temperatures and test conditions. The composite CNT structures showed significantly improved performance compared to their pure self-supporting CNT counterparts. The best composite CNT membranes gave permeabilities as high as 3.3×(10 to the 12th power)kg/m s Pa) with an average salt rejection of 95% and lifespan of up to 39 h of continuous testing, making them highly promising candidates for DCMD