MODIFIED CONDUCTION SHAPE FACTORS FOR ISOTHERMAL BODIES EMBEDDED IN A SEMI-INFINITE MEDIUM

Numerical finite-element method calculations were performed for isothermal surfaces embedded in a semi-infinite medium with convection boundary conditions. A modified shape factor was defined that combines the conduction heat transfer in the medium and the convection to the environment, with the geometrical characteristics of the problem. Infinite finite elements are used; these form the last layer of elements in the infinite directions. The modified shape factors for a sphere and for a long horizontal cylinder are presented in graphs and correlations, both using nondimensional parameters. The heat flux distribution on the surface of the body and the temperature and heat transfer on the surface of the medium are also presented.     

Electromagnetic impedance tomography (EMIT): a new method for impedance imaging

We propose a new impedance imaging method, electromagnetic impedance tomography (EMIT), in which the boundary electric potential measurements in electrical impedance tomography (EIT) are augmented by measurements of the exterior magnetic field induced by the currents excited in the object by the standard EIT procedures. These magnetic measurements can be obtained reliably and inexpensively by simple pickup coils located around the imaged cross section. We derive expressions for the forward problem and for the Jacobian of the measurements, and propose an iterative reconstruction algorithm using a squared error cost function. The performance of EMIT and EIT is compared in numerical simulations using a finite-element model for the conductivity distribution of several phantoms. Evaluation of the rank and condition of the Jacobian demonstrates that the additional magnetic measurements provided by a few pickup coils in EMIT turn an underdetermined EIT problem into a well-posed one with reasonable condition, or significantly improve the conditioning of the EIT problem when it is already fully determined. Reconstructions of various phantoms reveal that EMIT provides particularly significant visual and quantitative improvement (threefold to tenfold reduction in the root-mean-squared error) in the sensitivity at the center of the object, which is the area most difficult to image using EIT.     

The Hierarchical Hidden Markov Model: Analysis and Applications

We introduce, analyze and demonstrate a recursive hierarchical generalization of the widely used hidden Markov models, which we name Hierarchical Hidden Markov Models (HHMM). Our model is motivated by the complex multi-scale structure which appears in many natural sequences, particularly in language, handwriting and speech. We seek a systematic unsupervised approach to the modeling of such structures. By extending the standard Baum-Welch (forward-backward) algorithm, we derive an efficient procedure for estimating the model parameters from unlabeled data. We then use the trained model for automatic hierarchical parsing of observation sequences. We describe two applications of our model and its parameter estimation procedure. In the first application we show how to construct hierarchical models of natural English text. In these models different levels of the hierarchy correspond to structures on different length scales in the text. In the second application we demonstrate how HHMMs can be used to automatically identify repeated strokes that represent combination of letters in cursive handwriting.     

Learning Changing Concepts by Exploiting the Structure of Change

This paper examines learning problems in which the target function is allowed to change. The learner sees a sequence of random examples, labelled according to a sequence of functions, and must provide an accurate estimate of the target function sequence. We consider a variety of restrictions on how the target function is allowed to change, including infrequent but arbitrary changes, sequences that correspond to slow walks on a graph whose nodes are functions, and changes that are small on average, as measured by the probability of disagreements between consecutive functions. We first study estimation, in which the learner sees a batch of examples and is then required to give an accurate estimate of the function sequence. Our results provide bounds on the sample complexity and allowable drift rate for these problems. We also study prediction, in which the learner must produce online a hypothesis after each labelled example and the average misclassification probability over this hypothesis sequence should be small. Using a deterministic analysis in a general metric space setting, we provide a technique for constructing a successful prediction algorithm, given a successful estimation algorithm. This leads to sample complexity and drift rate bounds for the prediction of changing concepts.     

Elementary approximation algorithms for prize collecting Steiner tree problems

This paper deals with approximation algorithms for the prize collecting generalized Steiner forest problem, defined as follows. The input is an undirected graph G=(V,E), a collection T={T₁,…,T_k}, each a subset of V of size at least 2, a weight function , and a penalty function . The goal is to find a forest F that minimizes the cost of the edges of F plus the penalties paid for subsets T_i whose vertices are not all connected by F. Our main result is a -approximation for the prize collecting generalized Steiner forest problem, where n2 is the number of vertices in the graph. This obviously implies the same approximation for the special case called the prize collecting Steiner forest problem (all subsets T_i are of size 2). The approximation algorithm is obtained by applying the local ratio method, and is much simpler than the best known combinatorial algorithm for this problem.Our approach gives a -approximation for the prize collecting Steiner tree problem (all subsets T_i are of size 2 and there is some root vertex r that belongs to all of them). This latter algorithm is in fact the local ratio version of the primal-dual algorithm of Goemans and Williamson [M.X. Goemans, D.P. Williamson, A general approximation technique for constrained forest problems, SIAM Journal on Computing 24 (2) (April 1995) 296–317]. Another special case of our main algorithm is Bar-Yehuda's local ratio -approximation for the generalized Steiner forest problem (all the penalties are infinity) [R. Bar-Yehuda, One for the price of two: a unified approach for approximating covering problems, Algorithmica 27 (2) (June 2000) 131–144]. Thus, an important contribution of this paper is in providing a natural generalization of the framework presented by Goemans and Williamson, and later by Bar-Yehuda.     

Novel acrylic pressure-sensitive adhesive (PSA) containing silver particles

Acrylic pressure-sensitive adhesives (PSAs) are generally considered as nonelectrically conductive materials. The electrical conductivity is incorporated into acrylic polymer after blending with electrical conductive additives like silver particles. After the addition of electrically conductive silver filler, the main and typical properties of PSAs such as tack, peel adhesion, and shear strength will decline. This study is the first trial which reveals that the acrylic self-adhesive basis must be synthesized with ameliorated initial performances like high tack and excellent adhesion. Currently, the electrically conductive solvent-borne acrylic PSA containing silver fillers are not commercially available on the market. They are promising materials which can be applied for the manufacturing of diverse technical or medical high performance self-adhesive products, such as broadest line of special electrically conductive sensitive tapes.     

Effects of three cellulose gums on the texture profile and sensory properties of low fat frankfurters

Composition, textural, viscoelastic, hydration, colour, and sensory attributes of regular and low fat pork/beef frankfurters with and without cellulose gums (carboxymethyl cellulose (CMC) and two types of microcrystalline cellulose (MCC-I and II)) were investigated. Fat was replaced with water in the low fat products. Moisture loss during cooking was reduced in low fat products from 10 to 6% because of the addition of CMC; however, both MCC increased moisture loss by 12–15%. CMC addition also increased the amount of free water. The high fat product was lighter (higher 'L') than the reduced fat frankfurters; gums did not appreciably change the colour. The viscoelastic properties (relaxation time, elastic moduli) were unaffected by the changes in fat level. Product hardness, brittleness, gumminess and chewiness increased with the decrease in fat level. MCC-II improved the textural properties of the low fat product to those of the high fat product. Sensory panel results indicated a decrease in tenderness with low fat and this was not improved by MCC-II. Overall, acceptability scores indicated that all the products (high and low fat) were acceptable.     

Binding Energies of Aromatic 1:1 Hetero-Clusters in a Supersonic Jet

Methods used to experimentally estimate the binding energies of van der Waals clusters containing an aromatic molecule are surveyed. These include microwave and infrared absorption spectroscopies, single and two photon ionization, dispersed fluorescence, and stimulated emission pumping. The problems encountered in the application of these methods are briefly discussed, and prospects for the firm establishment of the binding energies are assessed. Although the present database is too small for firm conclusions, methods based on dispersed fluorescence (i.e., probing the excited state surface) tend to yield lower values for argon adducts than those based on ionization, probing the ground state, or ionic surfaces. A mechanism that may account for this tendency is proposed, and further experiments are proposed to test it.     

Microstructure of GaN grown by lateral confined epitaxy 2. GaN on patterned sapphire

Transmission electron microscopy (TEM), atomic force microscopy (AFM), and photoluminescence (PL) spectroscopy were used in order to study the microstructure and optical properties of GaN films grown by metal-organic chemical vapor deposition (MOCVD) on c-plane sapphire by lateral confined epitaxy (LCE). In this method, the substrate is etched prior to growth to form uniform mesas separated by trenches for laterally restricting growth area. As previously observed for LCE GaN on Si(111), the density of threading dislocations was significantly reduced in the areas close to the edge of mesas due to the lateral propagation of the dislocations. Hence, the overall material quality improves with decreasing mesa size, which is consistent with the observed increase in photoluminescence band edge peak intensity. Electron diffraction indicated ∼1° rotation about the [ ] axis between the mesa and trench material, which was also observed in the image contrast of these two regions with g= . Additionally, LCE samples prepared in [ ] and [ ] cross sections were used for comparing the growth rates in these two perpendicular directions. As theoretically expected, growth in the [ ] direction appears to proceed considerably faster than that in the [% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9qqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaGymaiaaig% daceaIYaGbaebacaaIWaaaaa!38D1!\[11\bar 20\]] direction.     

On Shear Rheology of Gel Propellants

Selected fuel, oxidizer and simulant gels were prepared and rheologically characterized using a rotational rheometer. For fuel gelation both organic and inorganic gellants were utilized, whereas oxidizers and simulants were gelled with addition of silica and polysaccharides, respectively. The generalized Herschel‐Bulkley constitutive model was found to most adequately represent the gels studied. Hydrazine‐based fuels, gelled with polysaccharides, were characterized as shear‐thinning pseudoplastic fluids with low shear yield stress, whereas inhibited red‐fuming nitric acid (IRFNA) and hydrogen peroxide oxidizers, gelled with silica, were characterized as yield thixotropic fluids with significant shear yield stress. Creep tests were conducted on two rheological types of gels with different gellant content and the results were fitted by Burgers‐Kelvin viscoelastic constitutive model. The effect of temperature on the rheological properties of gel propellant simulants was also investigated. A general rheological classification of gel propellants and simulants is proposed.