Use Of Lattice Research Articles

B¯→D*ℓν¯form factor at zero recoil from three-flavor lattice QCD: A model independent determination of|Vcb|

We present the first lattice QCD calculation of the form factor for $\overline{B}\ensuremath{\rightarrow}{D}^{*}\ensuremath{\ell}\overline{\ensuremath{\nu}}$ with three flavors of sea quarks. We use an improved staggered action for the light valence and sea quarks (the MILC configurations), and the Fermilab action for the heavy quarks. The form factor is computed at zero recoil using a new double ratio method that yields the form factor more directly than the previous Fermilab method. Other improvements over the previous calculation include the use of much lighter light-quark masses, and the use of lattice (staggered) chiral perturbation theory in order to control the light-quark discretization errors and chiral extrapolation. We obtain for the form factor, ${\mathcal{F}}_{B\ensuremath{\rightarrow}{D}^{*}}(1)=0.921(13)(20)$, where the first error is statistical and the second is the sum of all systematic errors in quadrature. Applying a 0.7% electromagnetic correction and taking the latest PDG average for ${\mathcal{F}}_{B\ensuremath{\rightarrow}{D}^{*}}(1)|{V}_{cb}|$ leads to $|{V}_{cb}|=(38.7\ifmmode\pm\else\textpm\fi{}{0.9}_{\mathrm{exp}}\ifmmode\pm\else\textpm\fi{}{1.0}_{\mathrm{theo}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$.

A new look at discriminative training for hidden Markov models

Discriminative training for hidden Markov models (HMMs) has been a central theme in speech recognition research for many years. One most popular technique is minimum classification error (MCE) training, with the objective function closely related to the empirical error rate and with the optimization method based traditionally on gradient descent. In this paper, we provide a new look at the MCE technique in two ways. First, we develop a non-trivial framework in which the MCE objective function is re-formulated as a rational function for multiple sentence-level training tokens. Second, using this novel re-formulation, we develop a new optimization method for discriminatively estimating HMM parameters based on growth transformation or extended Baum–Welch algorithm. Technical details are given for the use of lattices as a rich representation of competing candidates for the MCE training.

RESEAU SEMANTIQUE ET APPROCHE COMPONENTIELLE DES BASES DE DONNEES LEXICALES MULTILINGUES

The author posits that a componential approach seems, at the moment, more appropriate in specialized lexicography or in terminography than in general lexicography. Although the use of lattices has its merits, the author observes that trees appear to be more effective to find an equivalent in case of lexical gaps.

Modelling Lexical Databases with Formal Concept Analysis

This paper provides guidelines and examples for visualising lexical rela- tions using Formal Concept Analysis. Relations in lexical databases often form trees, imperfect trees or poly-hierarchies which can be embedded into concept lattices. Many- to-many relations can be represented as concept lattices where the values from one domain are used as the formal objects and the values of the other domain as formal at- tributes. This paper further discusses algorithms for selecting meaningful subsets of lex- ical databases, the representation of complex relational structures in lexical databases and the use of lattices as basemaps for other lexical relations. Key Words: Formal Concept Analysis, lexical databases, semantic relations Category: I2 .4

Design and comparison of lattices of topological relations for spatial representation and reasoning

This paper presents an original approach to qualitative spatial representation and reasoning with topological relations based on the use of lattices of relations. This approach has been developed for spatial reasoning in the domain of agricultural landscape analysis. The paper describes first the motivation of the present research work and the general framework of topological relations. Four different lattices of topological relations, including two Galois lattices, are introduced. The choices made for spatial representation and reasoning with these lattices are discussed, together with a thorough study and comparison of the four lattices. The implementation of one of the Galois lattices within an object-based representation system, as well as spatial lattice-based reasoning with topological relations in this system are then detailed.

Turn-on voltage investigation of GaAs-based bipolar transistors with Ga/sub 1-x/In/sub x/As/sub 1-y/Ny base layers

The fundamental lower limit on the turn on voltage of GaAs-based bipolar transistors is first established, then reduced with the use of a novel low energy-gap base material, Ga/sub 1-x/In/sub x/As/sub 1-y/N/sub y/. InGaP/GaInAsN DHBTs (x/spl sim/3y/spl sim/0.01) with high p-type doping levels (/spl sim/3/spl times/10/sup 19/ cm/sup -3/) and dc current gain (/spl beta//sub max//spl sim/68 at 234 /spl Omega///spl square/) are demonstrated. A reduction in the turn-on voltage over a wide range of practical base sheet resistance values (100 to 400 /spl Omega///spl square/) is established relative to both GaAs BJTs and conventional InGaP/GaAs HBTs with optimized base-emitter interfaces-over 25 mV in heavily doped, high dc current gain samples. The potential to engineer turn-on voltages comparable to Si- or InP-based bipolar devices on a GaAs platform is enabled by the use of lattice matched Ga/sub 1-x/In/sub x/As/sub 1-y/N/sub y/ alloys, which can simultaneously reduce the energy-gap and balance the lattice constant of the base layer when x/spl sim/3y.

Enumeration of lattice points in [formula omitted] norm

The enumeration of lattice points is receiving much attention because the use of lattices as vector quantizers in several applications, as for instance still image and video compression, has grown increasingly in the last few years. In image coding applications there is a trade-off between minimum distortion and bit rate, therefore, lattices have to be truncated so that the chosen lattice points, the codebook size, lie within a finite boundary. The determination of this boundary is source dependent. The geometric properties of a memoryless Laplacian source fit properly to model transform coded image statistics. In this case, the l 1 norm is more suitable than the l 2 norm for enumerating lattice points. In this paper we define the contour points, which count how many lattice points are at l 1 distance m from a given lattice point; i.e., they help to establish the lattice boundary or equivalently the codebook size. Explicit combinatorial expressions for the contour points determining the codebook size are given for some of the most used lattices. These expressions are easily implementable in any standard general-purpose programming language. In addition, they pave the way for developing algorithms for labeling lattice points that achieve full efficiency without any memory requirement at all.

MMIE training of large vocabulary recognition systems

This paper describes a framework for optimising the structure and parameters of a continuous density HMM-based large vocabulary recognition system using the Maximum Mutual Information Estimation (MMIE) criterion. To reduce the computational complexity of the MMIE training algorithm, confusable segments of speech are identified and stored as word lattices of alternative utterance hypotheses. An iterative mixture splitting procedure is also employed to adjust the number of mixture components in each state during training such that the optimal balance between the number of parameters and the available training data is achieved. Experiments are presented on various test sets from the Wall Street Journal database using up to 66 hours of acoustic training data. These demonstrate that the use of lattices makes MMIE training practicable for very complex recognition systems and large training sets. Furthermore, the experimental results show that MMIE optimisation of system structure and parameters can yield useful increases in recognition accuracy.

Processing thin films of KNbO3 for optical waveguides

Abstract Thin film waveguides of ferroelectric materials hold great promise for use in active integrated optics devices because of the high optical confinement possible in a thin film structure. KNbO3 is an attractive material for active devices because it possesses large nonlinear optical susceptibilities and large electro-optic coefficients. KNbO3 films with low optical losses are required to produce efficient devices. Epitaxial films of KNbO3 (110) have previously been deposited on single crystal MgO (100) using ion beam sputtering techniques. However, these films contained microstructural defects due to the large lattice mismatch (>4.0%) between KNbO3 and MgO which resulted in high optical losses. Recent work has focused on determining the relationships between microstructure and optical loss through the use of lattice matched substrates. Film composition, epitaxial quality and optical properties of KNbO3 films deposited on MgO and MgAl2O4 have been investigated and are compared.

Micellization of ionic surfactants: calculations based on a self-consistent field lattice model

The equilibrium structure of micelles formed in aqueous solutions of ionic surfactants is studied by using the self-consistent field lattice approach of Scheutjens, Fleer, and Leermarkers. Equilibrium volume fractions profiles of micelles are obtained, and it appears that the surfactant head groups have a rather wide distribution. The boundary between the hydrocarbon core of the micelle and the solution is rather sharp and does not vary with salt concentration. An electrostatic potential develops, which causes accumulation of indifferent counterions in between the head groups and, consequently, leads to partial neutralization of the charges. The remaining net charge in the head group region is independent of the salt concentration. The calculated effects of chain length, salt concentration, and branching on the cmc and the aggregation numbers show a good agreement with experimental data. By use of lattices of different geometry, transitions from small spherical micelles to large rodlike aggregates can be predicted.

Highly uniform, large‐area HgCdTe layers on CdTe and CdTeSe substrates

We report here on the growth of Hg0.8Cd0.2Te on lattice matched substrates of CdTe0.96Se0.04, by organometallic vapor phase epitaxy. Layer properties are compared with those for comparable layers grown on CdTe substrates. It is shown that the use of lattice matched substrates results in active layers of improved structural quality, as evidenced by the results of double‐crystal x‐ray diffraction measurements. A compositional uniformity of better than ±0.005 (in the Cd composition) was obtained over 1×2 cm area substrates and the thickness uniformity was better than ±0.7 μm for 12‐μm‐thick layers. These layers were deposited by the direct reaction of mercury, dimethylcadmium, and diisopropyltelluride, without the interdiffusion of separate layers of HgTe and CdTe. Both n‐ and p‐type layers have been grown, by suitable adjustment of the growth process. Mobility values in excess of 6×104 cm2/V s were obtained in n‐type material (x=0.23), with an electron concentration below 1×1015 cm−3. With p‐type layers, mobility values of 680 cm2/V s were obtained, with a hole concentration of 5×1016 cm−3.

Improved methods for calculating vectors of short length in a lattice, including a complexity analysis

The standard methods for calculating vectors of short length in a lattice use a reduction procedure followed by enumerating all vectors of Z m {{\mathbf {Z}}^m} in a suitable box. However, it suffices to consider those x ∈ Z m {\mathbf {x}} \in {{\mathbf {Z}}^m} which lie in a suitable ellipsoid having a much smaller volume than the box. We show in this paper that searching through that ellipsoid is in many cases much more efficient. If combined with an appropriate reduction procedure our method allows to do computations in lattices of much higher dimensions. Several randomly constructed numerical examples illustrate the superiority of our new method over the known ones.

GaAs metallization: Some problems and trends

Ohmic and Schottky barrier contacts with desired properties are difficult to form on GaAs devices. This is due mainly to the fact that the position of the Fermi energy is loosely ’’pinned’’ near midgap for GaAs surfaces which are metallized using conventional techniques. Doped alloyed metal ohmic and refractory metal Schottky contacts formed on carefully cleaned surfaces are currently widely used. New contacting techniques including the use of lattice matched heterojunctions, nonalloyed n++ and p++ surfaces, graded band gap structures, and special surface treatment prior to metallization promise to provide both greater flexibility and control for future applications.

Natural language symbol string storage

Natural language applications often require the storage of various symbol strings. Both unidirectional trees and lattices may be used to hold a symbolic data base consisting of lexes, lemes, or other symbol strings. This paper empirically compares placing symbolic information into trees and lattices. (A lattice may be thought of as a unidirec tional network with single, initiating, and terminating nodes.) The use of lattices in this way is an extension of the commonly used tree structure. The empirical study presented is the first on this topic known to the author.

Lattice fuzzy logics

Although the characterizing membership functions of fuzzy sets normally have as their range the interval [0, 1], it is possible for the range to be a partially ordered set. The use of lattices for this set is explored. Various forms of restricted infinite lattice are considered. Rose's logical operator for logics whose truth values form lattices are reviewed. A basis for lattice fuzzy logics, using Rose's operators, is discussed and a particular infinite lattice is proposed for use in characterizing lattice fuzzy sets. Some of the concepts are used to extend edge detection techniques in image processing from grey scale to colour images.