Synthetic aperture radar: A focus on current problems

Synthetic aperture radar (SAR) is a powerful tool for mapping and remote sensing. The theory and operation of SAR have seen a period of intense activity in recent years. This paper attempts to review some of the more advanced topics studied in connection with modern SAR systems based on digital processing. Following a brief review of the principles involved in the operation of SAR, attention is focussed on special topics such as advanced SAR modelling and focussing techniques, in particular clutterlock and autofocus, Doppler centroid (DC) estimation methods involving seismic migration technique, moving target imaging, bistatic radar imaging, effects of system nonlinearities, etc.

Novel materials, materials design and synthetic strategies: recent advances and new directions

There have been major advances in solid state and materials chemistry in the last two decades and the subject is growing rapidly. In this account, a few of the important aspects of materials chemistry of interest to the author are presented. Accordingly, transition metal oxides, which constitute the most fascinating class of inorganic materials, receive greater attention, Metal-insulator transitions in oxides, high temperature superconductivity in cuprates and colossal magnetoresistance in manganates are discussed at some length and the outstanding problems indicated, We then discuss certain other important classes of materials which include molecular materials, biomolecular materials and porous solids. Recent developments in synthetic strategies for inorganic materials are reviewed. Some results on metal nanoparticles and nanotubes are briefly presented. The overview, which is essentially intended to provide a flavour of the subject and show how it works, lists references to many crucial reviews in the recent literature.

Roughness generated in surface grinding of metals

When a metal is surface ground the roughness generated is the summation of a function of the wheel roughness and the roughness due to wheel attrition and damage to the workpiece. We identify this function here as a maximum em,elope profile, which is fractal within certain cut off wavelengths determined by the dressing conditions of the wheel. Estimating the global displacement of the binder-grit-workpiece system from the maximum envelope power spectra, we determine the plastic indentation of the workpiece at characteristic length scales using simple contact-mechanical calculation. The estimated roughness corresponds well with that recorded experimentally for hard steel, copper; titanium and aluminium.

Synthetic studies directed towards the potent cytotoxic natural product ottelione A: stereoselective construction of the complete framework

A stereoselective strategy for the rapid acquisition of the complete framework (dideoxyottelione A) of the promising cytotoxic agent ottelione A, with four contiguous stereogenic centres on a hydrindane skeleton and a sensitive 4-methylenecyclohex-2-enone functionality, from the readily available Diels-Alder adduct of 1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene and norbornadiene, is delineated.

Synthetic studies towards novel terpenic natural products kelsoene and poduran: Construction of the complete 4-5-5-fused tricarbocyclic core

A common synthetic approach to the recently reported sesquiterpene kelsoene 1 and the tetraterpene poduran 5, bearing a novel tricyclo[6.2.0.0(2,6)]decane framework, from commercially available 1,5-COD and leading to the first construction of the carbocyclic core present in these natural products is delineated.

Assessing formability of sheet metals through advanced tensile and LASER speckle analysis

The ability of a metal to resist strain localisation and hence reduction in local thickness, is a most important forming property upon stretching. The uniform strain represents in this regard a critical factor to describe stretching ability - especially when the material under consideration exhibits negative strain rate sensitivity and dynamic strain ageing (DSA). A newly developed Laser Speckle Technique (LST), e.g. see [1], was used in-situ during tensile testing with two extensometers. The applied technique facilitates quantitative information on the propagating plasticity (i.e. the so-called PLC bands) known to take place during deformation where DSA is active. The band velocity (V-band), and the bandwidth (W-band) were monitored upon increasing accumulated strain. The knowledge obtained with the LST was useful for understanding the underlying mechanisms for the formability limit when DSA and negative strain rate sensitivity operate. The goal was to understand the relationship between PLC/DSA phenomena and the formability limit physically manifested as shear band formation. Two principally different alloys were used to discover alloying effects.

Electrochemical processing of ocean manganese nodules with microbial enhancement to recover valuable metals

In this paper, electroleaching and electrobioleaching of ocean manganese nodules are discussed along with the role of galvanic interactions in bioleaching. Polarization studies using a manganese nodule slurry electrode system indicated that the maximum dissolution of iron and manganese due to electrochemical reduction occurred at negative DC potentials of -600 and -1,400 mV(SCE). Electroleaching and electrobioleaching of ocean manganese nodules in the presence of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans at the above negative applied DC potentials resulted insignificant dissolution of copper, nickel and cobalt in 1 M H2SO4 and in sulfuric acid solution at pH 0.5 and 2.0. Mechanisms involved in electrobioleaching of ocean manganese nodules are discussed. Galvanic leaching of ocean manganese nodules in the presence of externally added pyrite and pyrolusite for enhancement of dissolution was also studied. Various electrochemical and biochemical parameters were optimized, and the electroleaching and galvanic processes thus developed are shown to yield almost complete dissolution of all metal values. This electrobioleaching process developed in the laboratory may be cost effective, energy efficient and environmentally friendly.

Nanotubes of the disulfides of groups 4 and 5 metals

The layered chalcogenides, having structures analogous to graphite, are known to be unstable toward bending and show high propensity to form curved structures, thus eliminating dangling bonds at the edges. Since the discovery of fullerene and nanotube structures of WS2 and MoS2 by Tenne et al. [1-3], there have been attempts to prepare and characterize nanotubes of other layered dichalcogenides with structures analogous to MoS2. Nanotubes of MoS2 and WS2 were prepared by Tenne et al. by reducing the corresponding oxides to the suboxides followed by heating in an atmosphere of forming gas (5 % H-2 + 95 % N-2) and H2S at 700-900 degreesC [1-3]. Alternative methods of synthesis of MoS2 and WS2 nanotubes have since been proposed by employing the decomposition of the ammonium thiometallates or the corresponding trisulfide precursors. This alternative procedure was based on the observation that the trisulfide seems to be formed as an intermediate in the synthesis of the MoS2 and WS2 nanotubes [4]. Accordingly, the decomposition of the trisulfides of MoS2 and W in a reducing atmosphere directly yielded nanotubes of the disulfides MoS2 and WS2 [5]. In this article, we describe the synthesis, structure, and characterization of a few novel nanotubes of the disulfides of groups 4 and 5 metals. These include nanotubes of NbS2, TaS2, ZrS2, and HfS2. The study enlarges the scope of the inorganic nanotubes significantly and promises other interesting possibilities, including the synthesis of the diselenide nanotubes of these metals.

Non-Fermi-liquid theory for disordered metals near two dimensions

We consider the Finkelstein action describing a system of spin-polarized or spinless electrons in 2+2epsilon dimensions, in the presence of disorder as well as the Coulomb interactions. We extend the renormalization-group analysis of our previous work and evaluate the metal-insulator transition of the electron gas to second order in an epsilon expansion. We obtain the complete scaling behavior of physical observables like the conductivity and the specific heat with varying frequency, temperature, and/or electron density. We extend the results for the interacting electron gas in 2+2epsilon dimensions to include the quantum critical behavior of the plateau transitions in the quantum Hall regime. Although these transitions have a very different microscopic origin and are controlled by a topological term in the action (theta term), the quantum critical behavior is in many ways the same in both cases. We show that the two independent critical exponents of the quantum Hall plateau transitions, previously denoted as nu and p, control not only the scaling behavior of the conductances sigma(xx) and sigma(xy) at finite temperatures T, but also the non-Fermi-liquid behavior of the specific heat (c(v)proportional toT(p)). To extract the numerical values of nu and p it is necessary to extend the experiments on transport to include the specific heat of the electron gas.

Crystal and molecular structure of synthetic cholesterol compounds vitamin D3-analogues (I) 24(S)-hydroxy coprastan-3-one & (II) 24(R)-hydroxy coprastan-3-one

The title compound I (24-(S)-Hydroxy Coprastan-3-one) crystallises in orthorhombic space group P2(1)2(1)2(1) with Z = 4. The unit cell dimensions are a = 6.701(2)Angstrom, b = 11.506(8)Angstrom, c = 32.183(4)Angstrom, V = 2481(2)Angstrom (3), D-cal = 1.077 Mg/m(3). The tide compound II (24-(R)-Hydroxy Coprastan-3-one) crystallises in orthorhombic space group P212121 with two molecules per assymetric unit and with Z = 8. The Unit cell dimensions are a = 10.954(2)Angstrom, b = 21.757(6)Angstrom, c = 21.130(7)Angstrom, V = 5035.0(2)Angstrom (3), D-cal = 1.062 Mg/m(3). In compound I and in both the molecules of compound II, the rings A, B & C are in chair conformation and the five membered ring D is in envelope conformation. The priority sequence attached to the chiral carbon C24 has "S" designation in compound I and "R" designation in compound II. The structures are stabilized by C-H . . .O and O-H---O hydrogen bonds.

Wear of metals: a consequence of stable/unstable material response

Wear of metals in dry sliding is dictated by the material response to traction. This is demonstrated by considering the wear of aluminium and titanium alloys. In a regime of stable homogeneous deformation the material approaching the surface from the bulk passes through microprocessing zones of flow, fracture, comminution and compaction to generate a protective tribofilm that retains the interaction in the mild wear regime. If the response leads to microstructural instabilities such as adiabatic shear bands, the near-surface zone consists of stacks of 500 nm layers situated parallel to the sliding direction. Microcracks are generated below the surface to propagate normally away from the surface though microvoids situated in the layers, until it reaches a depth of 10-20 mum. A rectangular laminate debris consisting of a 20-40 layer stack is produced, The wear in this mode is severe.

Wear of metals-influence of some primary material properties

Specific wear rates of a range of metals and alloys upon dry sliding are compiled together to discern the influence of material properties on wear. No systematic influence of bulk hardness was found. Following our previous work on the influence of power dissipative capacity of metals on wear, we explore the influence of thermal diffusivity on wear of these metals.

Novel metal oxides prepared by ingenious synthetic routes

Several novel oxides have been prepared by the decomposition of carbonate precursors of calcite structure of the general formulas Mn1−xMxCO3 (M = Mg,Co,Cd), Ca1−xMx'CO3, and Ca1−x−yMxMy”CO3.

BCS-BEC crossover induced by a synthetic non-Abelian gauge field

We investigate the ground state of interacting spin-1/2 fermions in three dimensions at a finite density (rho similar to k(F)(3)) in the presence of a uniform non-Abelian gauge field. The gauge-field configuration (GFC) described by a vector lambda equivalent to (lambda(x),lambda(y),lambda(z)), whose magnitude lambda determines the gauge coupling strength, generates a generalized Rashba spin-orbit interaction. For a weak attractive interaction in the singlet channel described by a small negative scattering length (k(F)vertical bar a(s)vertical bar less than or similar to 1), the ground state in the absence of the gauge field (lambda = 0) is a BCS (Bardeen-Cooper-Schrieffer) superfluid with large overlapping pairs. With increasing gauge-coupling strength, a non-Abelian gauge field engenders a crossover of this BCS ground state to a BEC (Bose-Einstein condensate) of bosons even with a weak attractive interaction that fails to produce a two-body bound state in free vacuum (lambda = 0). For large gauge couplings (lambda/k(F) >> 1), the BEC attained is a condensate of bosons whose properties are solely determined by the Rashba gauge field (and not by the scattering length so long as it is nonzero)-we call these bosons ``rashbons.'' In the absence of interactions (a(s) = 0(-)), the shape of the Fermi surface of the system undergoes a topological transition at a critical gauge coupling lambda(T). For high-symmetry GFCs we show that the crossover from the BCS superfluid to the rashbon BEC occurs in the regime of lambda near lambda(T). In the context of cold atomic systems, these results make an interesting suggestion of obtaining BCS-BEC crossover through a route other than tuning the interaction between the fermions.