Reduced-Rank STAP Schemes for Airborne Radar Based on Switched Joint Interpolation, Decimation and Filtering Algorithm

In this paper, we propose a reduced-rank space-time adaptive processing (STAP) technique for airborne phased array radar applications. The proposed STAP method performs dimensionality reduction by using a reduced-rank switched joint interpolation, decimation and filtering algorithm (RR-SJIDF). In this scheme, a multiple-processing-branch (MPB) framework, which contains a set of jointly optimized interpolation, decimation and filtering units, is proposed to adaptively process the observations and suppress jammers and clutter. The output is switched to the branch with the best performance according to the minimum variance criterion. In order to design the decimation unit, we present an optimal decimation scheme and a low-complexity decimation scheme. We also develop two adaptive implementations for the proposed scheme, one based on a recursive least squares (RLS) algorithm and the other on a constrained conjugate gradient (CCG) algorithm. The proposed adaptive algorithms are tested with simulated radar data. The simulation results show that the proposed RR-SJIDF STAP schemes with both the RLS and the CCG algorithms converge at a very fast speed and provide a considerable SINR improvement over the state-of-the-art reduced-rank schemes

Rosen-Zener Transition in a Nonlinear Two-Level System

We study Rosen-Zener transition (RZT) in a nonlinear two-level system in which the level energies depend on the occupation of the levels, representing a mean-field type of interaction between the particles. We find that the nonlinearity could affect the quantum transition dramatically. At certain nonlinearity the 100% population transfer between two levels is observed and found to be robust over a very wide range of external parameters. On the other hand, the quantum transition could be completely blocked by a strong nonlinearity. In the sudden and adiabatic limits we have derived analytical expressions for the transition probability. Numerical explorations are made for a wide range of parameters of the general case. Possible applications of our theory to Bose-Einstern Condensates (BECs) are discussed.Comment: 8 pages, 8 figure

Felix Alexandrovich Berezin and his work

This is a survey of Berezin's work focused on three topics: representation theory, general concept of quantization, and supermathematics.Comment: LaTeX, 27 page

Quantum and Classical Spins on the Spatially Distorted Kagome Lattice: Applications to Volborthite

In Volborthite, spin-1/2 moments form a distorted Kagom\'e lattice, of corner sharing isosceles triangles with exchange constants $J$ on two bonds and $J'$ on the third bond. We study the properties of such spin systems, and show that despite the distortion, the lattice retains a great deal of frustration. Although sub-extensive, the classical ground state degeneracy remains very large, growing exponentially with the system perimeter. We consider degeneracy lifting by thermal and quantum fluctuations. To linear (spin wave) order, the degeneracy is found to stay intact. Two complementary approaches are therefore introduced, appropriate to low and high temperatures, which point to the same ordered pattern. In the low temperature limit, an effective chirality Hamiltonian is derived from non-linear spin waves which predicts a transition on increasing $J'/J$, from $\sqrt 3\times \sqrt 3$ type order to a new ferrimagnetic {\em striped chirality} order with a doubled unit cell. This is confirmed by a large-N approximation on the O($n$) model on this lattice. While the saddle point solution produces a line degeneracy, $O(1/n)$ corrections select the non-trivial wavevector of the striped chirality state. The quantum limit of spin 1/2 on this lattice is studied via exact small system diagonalization and compare well with experimental results at intermediate temperatures. We suggest that the very low temperature spin frozen state seen in NMR experiments may be related to the disconnected nature of classical ground states on this lattice, which leads to a prediction for NMR line shapes.Comment: revised, section V about exact diagonalization is extensively rewritten, 17 pages, 11 figures, RevTex 4, accepted by Phys. Rev.

Longitudinal spin excitations and magnetic anisotropy in antiferromagnetically ordered BaFe2As2

We report on a spin-polarized inelastic neutron scattering study of spin waves in the antiferromagnetically ordered state of BaFe2As2. Three distinct excitation components are identified, with spins fluctuating along the c-axis, perpendicular to the ordering direction in the ab-plane, and parallel to the ordering direction. While the first two "transverse" components can be described by a linear spin-wave theory with magnetic anisotropy and inter-layer coupling, the third "longitudinal" component is generically incompatible with the local moment picture. It points towards a contribution of itinerant electrons to the magnetism already in the parent compound of this family of Fe-based superconductors.Comment: 4 pages, 4 figures, plus Supplemental Materia

Numerical simulation of flow surrounding a thermoacoustic stack:single-stack against double-stack plate domain

Over the last few decades, numerical simulation has fast become an effective research tool in analyzing internal and external fluid flow. Much of the unknowns associated with microscopic bounded and unbounded fluid behavior generally not obtainable via experimental approach can now be explained in details with computational fluid dynamics modeling. This has much assist designers and engineers in developing better engineering designs. However, the choice of the computational domain selected plays an important role in exhibiting the correct flow patterns associated with changes in certain parameters. This research looked at the outcomes when two computational domains were chosen to represent a system of parallel stack plates in a thermoacoustic resonator. Since the stack region is considered the “heart” of the system, accurate modeling is crucial in understanding the complex thermoacoustic solid-fluid interactions that occur. Results showed that although the general flow pattern and trends have been produced with the single and double plate stack system, details of a neighboring solid wall do affect the developments of vortices in the stack region. The symmetric assumption in the computational domain may result in the absence of details that could generate an incomplete explanation of the patterns observed such as shown in this study. This is significant in understanding the solid-fluid interactions that is thermoacoustic phenomena

IMPROVING THE BUSINESS TRAJECTORY AMONG SMALL AND MEDIUM SIZE CONSTRUCTION FIRMS IN SOUTH AFRICA

Published ArticleThe Construction Industry Development Board (cidb) register of contractors shows that small and medium sized enterprises (SMEs) outnumber established firms in South Africa. However, the failure rate of SME businesses, which has increased in recent years, constitutes a source of concern in the industry. This situation is reflected in the limited number of successful construction SMEs as a percentage of the total registered firms in the industry. The research design for the study reported on entailed semi-structured and unstructured interviews, which were conducted over an extensive period of time to gather sufficient information from the research participants. However, the preliminary findings that form the nexus of this paper are based on the reviewed literature, and a pilot study that was conducted among a purposive sample of construction SMEs - Grades 1 to 5 on the cidb register. It is notable that the initial findings suggest that construction SMEs often encounter difficulty in securing projects, fail to realise core organisational objectives and goals, and are unable to gain cost advantages over their immediate rivals, which affects their business performance. Thus it appears that more effort is required to improve the business performance of construction SMEs in South Africa

Performing percutaneous transphepatic cholangiography using simple x-ray equipment

Percutaneous transhepatic cholangiography (PTC) is a valuable procedure used for diagnosing diseases of bile duct. It is simple to perform, safe, and inexpensive. The only equipment needed to perform PTC is a simple x-ray machine and puncture needle 14cm long and of 0.1cm core diameter. As long as the puncture point is selected accurately and operation is performed correctly, an excellent image can be achieved. This procedure can therefore be used in developing countries where expensive, modern technology is not available. We report a ca.e of a 50 year old female patient in whom the procedure was successfully used.East African Medical Journal, May 1999, 287-28

On SUSY curves

In this note we give a summary of some elementary results in the theory of super Riemann surfaces (SUSY curves)

Multiple sexual partnerships among Nigerian undergraduates: Students’ perspectives of the underlying factors

Introduction:  This study explored factors influencing multiple sexual partnerships among Nigerian undergraduates.Method:  Students aged 16-30 years took part in four focus group discussions that was followed by a cross-sectional survey involving 819 students in this age group.Result:  Peer pressure and strong moral values were identified as major factors influencing multiple sexual partnerships among students. Knowledge of sexually transmitted infection (STI), living off campus and boredom were ranked less important. Ranking of factors influencing multiple sexual partnerships however varied between male and female students.Conclusion:  The study showed that students had perceptions that various individual and environmental factors influence multiple sexual partnerships. These factors were noted to either encourage or discourage multiple sexual partnerships among students but more factors were identified as encouraging such partnerships than those discouraging it. Similarly, male students tended to rank these factors as having significant influence on multiple sexual partnerships than their female counterparts