Two-stage photoquenching in semi-insulating GaAs:EL2

The photoquenching of EL2 in semi‐insulating gallium arsenide is seen to be a complex process, where at low temperatures the initial slow quenching is followed by a switch to fast quenching. A possible explanation involving lattice strain mediated cooperative structural relaxation arising out of transition to the metastable state is proposed.

Semi-Supervised Classification Using Sparse Gaussian Process Regression

Gaussian Processes (GPs) are promising Bayesian methods for classification and regression problems. They have also been used for semi-supervised learning tasks. In this paper, we propose a new algorithm for solving semi-supervised binary classification problem using sparse GP regression (GPR) models. It is closely related to semi-supervised learning based on support vector regression (SVR) and maximum margin clustering. The proposed algorithm is simple and easy to implement. It gives a sparse solution directly unlike the SVR based algorithm. Also, the hyperparameters are estimated easily without resorting to expensive cross-validation technique. Use of sparse GPR model helps in making the proposed algorithm scalable. Preliminary results on synthetic and real-world data sets demonstrate the efficacy of the new algorithm.

Steady incompressible flow of cohesionless granular materials through a wedge-shaped hopper: Frictional 14kinetic solution to the smooth wall, radial gravity problem

Hybrid frictional-kinetic equations are used to predict the velocity, grain temperature, and stress fields in hoppers. A suitable choice of dimensionless variables permits the pseudo-thermal energy balance to be decoupled from the momentum balance. These balances contain a small parameter, which is analogous to a reciprocal Reynolds number. Hence an approximate semi-analytical solution is constructed using perturbation methods. The energy balance is solved using the method of matched asymptotic expansions. The effect of heat conduction is confined to a very thin boundary layer near the exit, where it causes a marginal change in the temperature. Outside this layer, the temperature T increases rapidly as the radial coordinate r decreases. In particular, the conduction-free energy balance yields an asymptotic solution, valid for small values of r, of the form T proportional r-4. There is a corresponding increase in the kinetic stresses, which attain their maximum values at the hopper exit. The momentum balance is solved by a regular perturbation method. The contribution of the kinetic stresses is important only in a small region near the exit, where the frictional stresses tend to zero. Therefore, the discharge rate is only about 2.3% lower than the frictional value, for typical parameter values. As in the frictional case, the discharge rate for deep hoppers is found to be independent of the head of material.

The Tourism-Development Nexus in Namibia : A Study on National Tourism Policy and Local Tourism Enterprises' Policy Knowledge

The tourism development nexus in southern Africa involves highly topical issues related to tourism planning, power relations, community participation, and natural resources. Namibia offers a particularly interesting context for the study of these issues due to its colonial legacy, vast tourism potential, recently adopted tourism policy and community-based approaches to tourism and natural resource management. This study is an interdisciplinary endeavour to analyse the role of tourism in Namibia s post-apartheid transformation process by focusing on Namibian tourism policy and local tourism enterprises' policy knowledge. Major attention is paid to how the tourism policy's national development objectives are understood and conceptualised by the representatives of different tourism enterprises and the ways in which they relate to the practical needs of the enterprises. Through such local policy knowledge the study explores various opportunities, challenges and constraints related to the promotion of tourism as a development strategy. The study utilises a political economy approach to tourism and development through three current and interrelated discourses which are relevant in the Namibian context. These are tourism, power and inequality, tourism and sustainable development, and tourism and poverty reduction. The qualitative research material was gathered in Namibia in 2006-2007 and 2008. This material consists of 34 semi-structured interviews in 16 tourism enterprises, including private trophy hunting farms and private lodges, small tour operators and community-based tourism enterprises. In addition, the research material consists of observations in the enterprises, and 37 informal and 23 expert interviews. The findings indicate that in the light of local tourism enterprises the tourism policy objectives appear more complex and ambiguous. Furthermore, they involve multiple meanings and interpretations which reflect the socio-economic stratification of the informants and Namibian society, together with the professional stratification of the tourism enterprises and restrictions on the capacity of tourism to address the development objectives. In the light of such findings it is obvious that aspects of power and inequality affect the tourism development nexus in Namibia. The study concludes that, as in the case of other southern African countries, in order to promote sustainable development and reduce poverty, Namibia should not only target tourism growth but pay attention to who benefits from that growth and how. From a political economy point of view, it is important that prevailing structural challenges are addressed equally in the planning of tourism, development and natural resource management. Such approach would help the Namibian majority to enjoy the benefits of increasing tourism in the country.

The status and use of tree biomass in a semi-arid village ecosystem

The status of the tree biomass resource was investigated in Ungra, a semi-arid village ecosystem in South India. There were 57 tree species with 12 trees capita−1 and 35 trees ha−1. Multiple benefit yielding local tree species dominated the village ecosystem, while fuel only or single end use trees accounted for a small proportion of trees. The standing tree biomass is adequate to meet the requirement of biomass fuels for cooking only for about two years. Village tree biomass is presently being depleted largely for export to urban areas. Tree regeneration is now characterized by transformation from multiple-use local tree species to a few single-use species. A large potential exists for tree biomass production along field boundaries (bunds), stream banks and roadsides. Biomass estimation equations were developed for 10 species.

Properties of Toeplitz operators on analytic function spaces : from function symbols to distributions

Toeplitz operators are among the most important classes of concrete operators with applications to several branches of pure and applied mathematics. This doctoral thesis deals with Toeplitz operators on analytic Bergman, Bloch and Fock spaces. Usually, a Toeplitz operator is a composition of multiplication by a function and a suitable projection. The present work deals with generalizing the notion to the case where the function is replaced by a distributional symbol. Fredholm theory for Toeplitz operators with matrix-valued symbols is also considered. The subject of this thesis belongs to the areas of complex analysis, functional analysis and operator theory. This work contains five research articles. The articles one, three and four deal with finding suitable distributional classes in Bergman, Fock and Bloch spaces, respectively. In each case the symbol class to be considered turns out to be a certain weighted Sobolev-type space of distributions. The Bergman space setting is the most straightforward. When dealing with Fock spaces, some difficulties arise due to unboundedness of the complex plane and the properties of the Gaussian measure in the definition. In the Bloch-type spaces an additional logarithmic weight must be introduced. Sufficient conditions for boundedness and compactness are derived. The article two contains a portion showing that under additional assumptions, the condition for Bergman spaces is also necessary. The fifth article deals with Fredholm theory for Toeplitz operators having matrix-valued symbols. The essential spectra and index theorems are obtained with the help of Hardy space factorization and the Berezin transform, for instance. The article two also has a part dealing with matrix-valued symbols in a non-reflexive Bergman space, in which case a condition on the oscillation of the symbol (a logarithmic VMO-condition) must be added.

Descriptions of operators in quantum mechanics

The problem of expressing a general dynamical variable in quantum mechanics as a function of a primitive set of operators is studied from several points of view. In the context of the Heisenberg commutation relation, the Weyl representation for operators and a new Fourier-Mellin representation are related to the Heisenberg group and the groupSL(2,R) respectively. The description of unitary transformations via generating functions is analysed in detail. The relation between functions and ordered functions of noncommuting operators is discussed, and results closely paralleling classical results are obtained.

Bile acid based semi-rigid molecular tweezers

The easily constructed bile acid-based semi-rigid molecular tweezer 2 binds guest 8 in chloroform with an association constant of 83 dm(3) mol(-1).

A classification of homogeneous operators in the Cowen-Douglas class

An explicit construction of all the homogeneous holomorphic Hermitian vector bundles over the unit disc D is given. It is shown that every such vector bundle is a direct sum of irreducible ones. Among these irreducible homogeneous holomorphic Hermitian vector bundles over D, the ones corresponding to operators in the Cowen-Douglas class B-n(D) are identified. The classification of homogeneous operators in B-n(D) is completed using an explicit realization of these operators. We also show how the homogeneous operators in B-n(D) split into similarity classes. (C) 2011 Elsevier Inc. All rights reserved.

Robust Semi-Blind Estimation for Beamforming Based MIMO Wireless Communication

In this paper, we present robust semi-blind (SB) algorithms for the estimation of beamforming vectors for multiple-input multiple-output wireless communication. The transmitted symbol block is assumed to comprise of a known sequence of training (pilot) symbols followed by information bearing blind (unknown) data symbols. Analytical expressions are derived for the robust SB estimators of the MIMO receive and transmit beamforming vectors. These robust SB estimators employ a preliminary estimate obtained from the pilot symbol sequence and leverage the second-order statistical information from the blind data symbols. We employ the theory of Lagrangian duality to derive the robust estimate of the receive beamforming vector by maximizing an inner product, while constraining the channel estimate to lie in a confidence sphere centered at the initial pilot estimate. Two different schemes are then proposed for computing the robust estimate of the MIMO transmit beamforming vector. Simulation results presented in the end illustrate the superior performance of the robust SB estimators.

Perturbative corrections for staggered four-fermion operators

We present results for one-loop matching coefficients between continuum four-fermion operators, defined in the Naive Dimensional Regularization scheme, and staggered fermion operators of various types. We calculate diagrams involving gluon exchange between quark fines, and ''penguin'' diagrams containing quark loops. For the former we use Landau-gauge operators, with and without O(a) improvement, and including the tadpole improvement suggested by Lepage and Mackenzie. For the latter we use gauge-invariant operators. Combined with existing results for two-loop anomalous dimension matrices and one-loop matching coefficients, our results allow a lattice calculation of the amplitudes for KKBAR mixing and K --> pipi decays with all corrections of O(g2) included. We also discuss the mixing of DELTAS = 1 operators with lower dimension operators, and show that, with staggered fermions, only a single lower dimension operator need be removed by non-perturbative subtraction.

Characterization of aerosol black carbon over a tropical semi-arid region of Anantapur, India

Black carbon (BC) aerosol mass concentrations measured using an aethalometer at Anantapur, a semi-arid tropical station in the southern part of peninsular India, from August 2006 to July 2007 are analyzed. Seasonal and diurnal variations of BC in relation to changes in the regional meteorological conditions have been studied along with the mass fraction of BC to the total aerosol mass concentration (M-t) and fine particle mass (FPM) concentration in different months. The data collected during the study period shows that the annual average BC mass concentration at Anantapur is 1.97 +/- 0.12 mu g m(-3). Seasonal variations of BC aerosol mass concentration showed high during the dry (winter and summer) seasons and low during the post-monsoon followed by the monsoon seasons. Diurnal variations of BC aerosols attain a gradual build up in BC concentration from morning and a sharp peak occurs between 07:00 and 09:00 h almost an hour after local sunrise and a broad nocturnal peak from 19:00 to 21:00 h with a minimum in noon hours. The ratio of BC to the fine particle mass concentration was high during the dry season and low during the monsoon season. The regression analysis between BC mass concentration and wind speed indicates that, with increase in wind speeds the BC mass concentrations would decrease and vice-versa. Aerosol BC mass concentration shows a significant positive correlation with total mass concentration (M-t) and aerosol optical depth (ACID, tau(p)) at 500 nm. (C) 2010 Elsevier B.V. All rights reserved.

Toeplitz Operators with Special Symbols on Segal-Bargmann Spaces

We study the boundedness of Toeplitz operators on Segal-Bargmann spaces in various contexts. Using Gutzmer's formula as the main tool we identify symbols for which the Toeplitz operators correspond to Fourier multipliers on the underlying groups. The spaces considered include Fock spaces, Hermite and twisted Bergman spaces and Segal-Bargmann spaces associated to Riemannian symmetric spaces of compact type.