Microscopic simulation of electronic noise in semiconductormaterials and devices

We present a microscopic interpretation of electronic noise in semiconductor materials and two-terminal devices. The theory is based on Monte Carlo simulations of the carrier motion self-consistently coupled with a Poisson solver. Current and voltage noise operations are applied and their respective representations discussed. As application we consider the cases of homogeneous materials, resistors, n⁺nn ⁺ structures, and Schottky-barrier diodes. Phenomena associated with coupling between fluctuations in carrier velocity and self-consistent electric field are quantitatively investigated for the first time. At increasing applied fields hot-carrier effects are found to be of relevant importance in all the cases considered here. As a general result, noise spectroscopy is found to be a source of valuable information to investigate and characterize transport properties of semiconductor materials and devices     

The application of semantic classification trees to naturallanguage understanding

This article describes a new method for building a natural language understanding (NLU) system, in which the system's rules are learnt automatically from training data. The method has been applied to design of a speech understanding (SU) system. Designers of such systems rely increasingly on robust matchers to perform the task of extracting meaning from one or several word sequence hypotheses generated by a speech recognizer. We describe a new data structure, the semantic classification tree (SCT), that learns semantic rules from training data and can be a building block for robust matchers for NLU tasks. By reducing the need for handcoding and debugging a large number of rules, this approach facilitates rapid construction of an NLU system. In the case of an SU system, the rules learned by an SCT are highly resistant to errors by the speaker or by the speech recognizer because they depend on a small number of words in each utterance. Our work shows that semantic rules can be learned automatically from training data, yielding successful NLU for a realistic application     

QUEUE

Ohne Zusammenfassung     

Ultrastructure of a bio-electrolytic methanogenic/methanotrophic granular biofilm for the complete degradation of tetrachloroethylene in contaminated groundwater.

The electrolytical methanogenic/methanotrophic coupling (eMaMoC) process was tested in a laboratory-scale single-stage reactor for the treatment of tetrachloroethene (PCE)-contaminated waters. A water electrolysis cell was placed directly in the effluent recirculation loop for the supply of both O2 and H2 to the system: H2 serving as the electron donor for both carbonate reduction into CH4 and reductive dechlorination. The concurrent presence of O2 and CH4 could be used by the methanotrophs for co-metabolically oxidising the chlorinated intermediates left over by the anaerobic transformation of PCE. At a PCE inlet of 33-52 microM and a hydraulic residence time (HRT) of 5.6 days, PCE reductive dechlorination to dichloroethene (DCE) was over 95% with a maximum DCE mineralisation of 83%. Fluorescence in situ hybridisation with 16S rRNA probes related to type I and type II methanotrophic bacteria were utilised to localise the methanotrophic communities in the anaerobic/aerobic granules. It evidenced that with operational time, along with increasing oxygenation rate, methanotrophic communities were specifically colonising onto the outermost layer of the anaerobic/aerobic granule.     

A 200 MHz CMOS Q-enhanced LC bandpass filter

This paper presents design techniques and performance bounds for implementing Q-enhanced, LC bandpass filters in silicon IC technologies. These filters offer significant advantages over switched capacitor and Gm-C based designs, including higher frequency of operation and lower power consumption for a given dynamic range. A prototype 200 MHz, fourth-order filter implemented in a 2 μm n-well CMOS process is described, and measured performance is compared with theoretical predictions. The prototype filter operates at a selectivity Q of 100 and draws less than 8 mA when operating from 3 to 5 V supplies, making it potentially suitable for use as a first IF filter in modern cellular and PCS receivers     

Probing the substrate alignment at the active site of 15-lipoxygenases by targeted substrate modification and site-directed mutagenesis. Evidence for an inverse substrate orientation

For oxygenation of polyenoic fatty acids by 12- and 15-lipoxygenases the methyl terminus of the substrate constitutes the signal for the initial hydrogen abstraction. In contrast, for 5-lipoxygenases an inverse head to tail substrate orientation has been proposed. However, recent structure-based sequence alignments suggested a conserved uniform substrate orientation for 5S- and 15S-lipoxygenation. Oxygenation of 15S-HETE derivatives by various wild-type and mutant lipoxygenases was investigated, and the evidence proved an inverse substrate orientation: (i) Substrate affinity and Vmax of 15S-HETE oxygenation by arachidonic acid 15-lipoxygenases are >1 order of magnitude lower than the corresponding data for polyenoic fatty acids. 5S,15S- and 14R, 15S-DiH(P)ETE were identified as major reaction products. (ii) Methylation of the carboxylate group of 15S-HETE augmented the reaction rate and shifted the reaction specificity strongly toward 5S-lipoxygenation. In contrast, methyl arachidonate was less effectively oxygenated than the free acid. Methylation of 15S-HETrE(8,11,14), which lacks the C5-C6 double bond, was without major impact on the oxygenation rate and on the product specificity. (iii) Introduction of a bulky glycerol moiety at the carboxylic group of 15S-HETE reversed the kinetic effects of methylation and led to a 14R-oxygenation of the substrate. (iv) When the product pattern of 15S-HETE oxygenation by the recombinant wild-type rabbit 15-lipoxygenase was compared with that formed by the Arg403Leu mutant, 5S- and 8S-lipoxygenations were augmented and 14R, 15S-DiH(P)ETE formation was impaired. (v) Phe353Leu or Ile418Ala mutation of the same enzyme, which favored 12S-HETE formation from arachidonic acid, strongly augmented 8S-lipoxygenation of 15S-HETE methyl ester. These kinetic data and the alterations in the product specificity are consistent with the concept of an inverse head to tail substrate orientation during the oxygenation of 15S-HETE methyl ester and/or of free 15S-HETE by 15-LOXs. For 5S- and 8S-lipoxygenation, 15-HETE may slide into the substrate binding pocket with its carboxy terminus approaching the doubly allylic methylenes C-7 or C-10 to the non-heme iron.     

Practical Interdomain Routing Security

This article reviews risks and vulnerabilities in interdomain routing and best practices that can have near-term benefits for routing security. It includes examples of routing failures and common attacks on routers, and countermeasures to reduce router vulnerabilities.     

Computing presentations for subgroups of polycyclic groups and of context-free groups

Algorithms for solving uniform decision problems for algebraic structures crucially depend on the chosen finite presentations for the structures under consideration. Rewriting techniques have been used very successfully to solve uniform decision problems, when the presentations considered involve finite, noetherian, and ()-confluent rewriting systems. Whenever the class of algebraic structures considered is closed under the operation of taking finitely generated substructures, then the algorithms for solving the uniform decision problems can be applied to the substructures as well. However, since these algorithms depend on the form of the presentations, this involves the task of constructing a presentation of a certain form for a substructure given a presentation of this form for the structure itself and a finite set of generating elements for the substructure.This problem, which has received a lot of attention in algebra, is here investigated from an algorithmic point of view. The structures considered are the following two classes of groups, which have been studied extensively before: the polycyclic groups and the context-free groups.Finitely generated context-free groups can be presented by finite, monadic, and -confluent string-rewriting systems. Due to their nice algorithmic properties these systems provide a way to effectively solve many decision problems for context-free groups. Since finitely generated subgroups of context-free groups are again contextfree, they can be presented in the same way. Here we describe a process that, from a finite, monadic, and -confluent string-rewriting system presenting a context-free groupG and a finite subsetU ofG, determines a presentation of this form for the subgroup U ofG that is generated byU. For finitely presented polycyclic groups we obtain an analogous result, when we use finite confluent PCP2-presentations to describe these groups.This work was performed while this author was visiting at the Fachbereich Informatik, Universität Kaiserslautern, during his sabbatical 1991/92