SIR Analysis and Interference Cancellation in Uplink OFDMA with Large Carrier Frequency/Timing Offsets

In uplink OFDMA, carrier frequency offsets (CFO) and/or timing offsets (TO) of other users with respect to a desired user can cause multiuser interference (MUI). In practical uplink OFDMA systems (e.g., IEEE 802.16e standard), effect of this MUI is made acceptably small by requiring that frequency/timing alignment be achieved at the receiver with high precision (e.g., CFO must be within 1 % of the subcarrier spacing and TO must be within 1/8th of the cyclic prefix duration in IEEE 802.16e), which is realized using complex closed-loop frequency/timing correction between the transmitter and the receiver. An alternate open-loop approach to handle the MUI induced by large CFOs and TOs is to employ interference cancellation techniques at the receiver. In this paper, we first analytically characterize the degradation in the average output signal-to-interference ratio (SIR) due to the combined effect of large CFOs and TOs in uplink OFDMA. We then propose a parallel interference canceller (PIC) for the mitigation of interference due to CFOs and TOs in this system. We show that the proposed PIC effectively mitigates the performance loss due to CFO/TO induced interference in uplink OFDMA.

Micro-treatment options for components of organic fraction of MSW in residential areas

There is a growing interest in management of MSW through micro-treatment of organic fraction of municipal solid wastes (OFMSW) in many cities of India. The OFMSW fraction is high (> 80%) in many pockets within South Indian cities like Bangalore, Chikkamagalur, etc. and is largely represented by vegetable, fruit, packing and garden wastes. Among these, the last three have shown problems for easy decomposition. Fruit wastes are characterized by a large pectin supported fraction that decomposes quickly to organic acids (becomes pulpy) that eventually slow down anaerobic and aerobic decomposition processes. Paper fraction (newsprint and photocopying paper) as well as paddy straw (packing), bagasse (from cane juice stalls) and tree leaf litter (typical garden waste and street sweepings) are found in reasonably large proportions in MSW. These decompose slowly due to poor nutrients or physical state. We have examined the suitability of these substrates for micro-composting in plastic bins by tracking decomposition pattern and physical changes. It was found that fruit wastes decompose rapidly to produce organic acids and large leachate fraction such that it may need to be mixed with leachate absorbing materials (dry wastes) for good composting. Leaf litter, paddy straw and bagasse decompose to the tune of 90, 68 and 60% VS and are suitable for composting micro-treatment. Paper fractions even when augmented with 10% leaf compost failed to show appreciable decomposition in 50 days. All these feedstocks were found to have good biological methane potential (BMP) and showed promise for conversion to biogas under a mixed feed operation. Suitability of this approach was verified by operating a plug-flow type anaerobic digester where only leaf litter gathered nearby (as street sweepings) was used as feedstock. Here only a third of the BMP was realized at this scale (0.18 m(3) biogas/kg VS 0.55 m(3)/kg in BMP). We conclude that anaerobic digestion in plug-flow like digesters appear a more suitable micro-treatment option (2-10 kg VS/day) because in addition to compost it also produces biogas for domestic use nearby.

Mixed saturated-unsaturated alkyl-chain assemblies: Solid solutions of zinc stearate and zinc oleate

The linear saturated stearic acid and the bent mono-unsaturated oleic acid do not mix and form solid solutions. However, the zinc salts of these acids can. From X-ray diffraction and DSC measurements we show that the layered zinc stearate and zinc oleate salts form a homogeneous solid solution at all composition ratios. The solid solutions exhibit a single melting endotherm, with the melting temperature varying linearly with composition but with the enthalpy change showing a minimum. By monitoring features in the infrared spectra that are characteristic of the global conformation of the hydrocarbon chain, and hence can distinguish between stearate and oleate chains, it is shown that solid solution formation is realized by the introduction of gauche defects in a fraction of the stearate chains that are then no longer linear. This fraction increases with oleate concentration. It has also been possible from the spectroscopic measurements to establish a quantitative relation between molecular conformational order and the thermodynamic enthalpy of melting of the solid solutions.

Resource recovery potential from secondary components of segregated municipal solid wastes

Fermentable components of municipal solid wastes (MSW) such as fruit and vegetable wastes (FVW), leaf litter, paddy straw, cane bagasse, cane trash and paper are generated in large quantities at various pockets of the city. These form potential feedstocks for decentralized biogas plants to be operated in the vicinity. We characterized the fermentation potential of six of the above MSW fractions for their suitability to be converted to biogas and anaerobic compost using the solid-state stratified bed (SSB) process in a laboratory study. FVW and leaf litter (papermulberry leaves) decomposed almost completely while paddy straw, sugarcane trash, sugarcane bagasse and photocopying paper decomposed to a lower extent. In the SSB process between 50-60% of the biological methane potential (BMP) could be realized. Observations revealed that the SSB process needs to be adapted differently for each of the feedstocks to obtain a higher gas recovery. Bagasse produced the largest fraction of anaerobic compost (fermentation residue) and has the potential for reuse in many ways.

A unified construction of space-time codes with optimal rate-diversity tradeoff

The problem of constructing space-time (ST) block codes over a fixed, desired signal constellation is considered. In this situation, there is a tradeoff between the transmission rate as measured in constellation symbols per channel use and the transmit diversity gain achieved by the code. The transmit diversity is a measure of the rate of polynomial decay of pairwise error probability of the code with increase in the signal-to-noise ratio (SNR). In the setting of a quasi-static channel model, let n(t) denote the number of transmit antennas and T the block interval. For any n(t) <= T, a unified construction of (n(t) x T) ST codes is provided here, for a class of signal constellations that includes the familiar pulse-amplitude (PAM), quadrature-amplitude (QAM), and 2(K)-ary phase-shift-keying (PSK) modulations as special cases. The construction is optimal as measured by the rate-diversity tradeoff and can achieve any given integer point on the rate-diversity tradeoff curve. An estimate of the coding gain realized is given. Other results presented here include i) an extension of the optimal unified construction to the multiple fading block case, ii) a version of the optimal unified construction in which the underlying binary block codes are replaced by trellis codes, iii) the providing of a linear dispersion form for the underlying binary block codes, iv) a Gray-mapped version of the unified construction, and v) a generalization of construction of the S-ary case corresponding to constellations of size S-K. Items ii) and iii) are aimed at simplifying the decoding of this class of ST codes.

Fermi level depinning at the germanium Schottky interface through sulfur passivation

We demonstrate the depinning of Fermi level on both p- and n-type germanium after sulfur passivation by aqueous (NH4)(2)S treatment. Schottky contacts realized using metals with a wide range of work functions produce nearly ideal behavior confirming that the Fermi level is depinned. Examination of the passivated surface using x-ray photoelectron spectroscopy reveals bonding between Ge and sulfur.It is shown that good Ohmic contacts to n-type Ge and a hole barrier height (phi(Bp)) of 0.6 eV to p-type Ge can be achieved after this passivation treatment, with Zr Schottky contacts. This is the highest phi(Bp) reported so far.

Arginase from Lathyrus sativus

The seeds of Lathyrus sativus contain the unusual amino acid homoarginine. The possible breakdown of homoarginine to lysine and urea has been investigated with enzyme extracts prepared from the seedlings of L. sativus. The results indicate that there is no separate homoarginase enzyme but that the arginase present has about 5 per cent activity towards Image -homoarginine as compared to that obtained with Image -arginine. The enzyme does not show an absolute dependence on Mn2+ for activity and maximal activation of the enzyme has been realized with Fe3+. It is concluded that the breakdown of homoarginine through the urea cycle may only represent a minor pathway for the catabolism of this compound in this plant.

Dynamics and local structure of colossal magnetoresistance manganites

We report Extended X-ray Absorption Fine Structure and anelastic spectroscopy measurements on on hole doped manganese oxides La1-xCaxMnO3 which present the colossal magnetoresistance effect. EXAFS measurements were realized both in the absence and presence of an applied magnetic field of 1.1 Tesla, in a wide temperature range (between 330 and 77 K) and at various dopings (x = 0.25 and x = 0.33). The magnetic field orders the magnetic moments so favouring the electron mobility and the reduction of Mn-O octahedra distortions. We observe the presence of four short and two long Mn-O distances (1.93 and 2.05 Angstrom respectively) above and also below the metal-insulator phase transition. The overall distortion decreases but does not completely disappear in the metallic phase suggesting the possible coexistence of metallic and insulating regions at low temperatures. The magnetic field reduces the lattice distortions showing evidence of a microscopic counterpart of the macroscopic colossal magnetoresistance. We also present preliminary anelastic relaxation spectra in a wide temperature range from 900 K to 1 K on a sample with x = 0.40, in order to study the structural phase transitions and the lattice dynamics. A double peak has been observed at the metal-insulator transition in the imaginary part of Young's modulus. This double peak indicates that the metal-insulator transition could be a more complex phenomenon than a simple second order phase transition. In particular the peak at lower temperatures can be connected with the possible presence of inhomogeneous phase structures. Another intense dissipation peak has been observed corresponding to the structural orthorhombic-trigonal transition around 750 K.

Preparation and characterization of rubidium-beta-alumina by the gel-to-crystallite conversion method

Preparation of Rb-beta -alumina was realized by the gel-to-crystallite conversion method. Reaction of hydrated aluminum hydroxide gel with RbOH in ethanol medium gave rise to the Rb+-inserted pseudoboehmite precursor under wet chemical conditions. The thermal decomposition of the precursor yielded Rb-beta -alumina. The Rb2O:Al2O3 ratio of monophasic Rb-beta -alumina ranged from 1:10 to 1:22. The extended stability in the compositional range is due to the fact that the conduction planes containing Rb+ and O2- ions can have lower occupancy of Rb+ ions for larger sized alkali ions, permitting the steric separation of the adjoining spinel blocks. High-resolution electron microscopy revealed that the decreasing occupancy of alkali ions in the conduction plane is balanced by changing widths of spinel blocks arising from the shift of tetrahedral Al3+ ions to octahedral sites and an accompanying increase in stacking defects. (C) 2000 Elsevier Science Ltd. All rights reserved.

A Simple Five-Level Inverter Topology for Induction Motor Drive Using Conventional Two-Level Inverters and Flying Capacitor Technique

This paper proposes a new five-level inverter topology for open-end winding induction motor (IM) drive. The popular existing circuit configurations for five-level inverter include the NPC inverter and flying capacitor topologies. Compared to the NPC inverter, the proposed topology eliminates eighteen clamping diodes having different voltage ratings in the present circuit. Moreover it requires only one capacitor bank per phase, whereas flying capacitor schemes for five level topologies require six capacitor banks per phase. The proposed topology is realized by feeding the phase winding of an open-end induction motor with two-level inverters in series with flying capacitors. The flying capacitor voltages are balanced using the switching state redundancy for full modulation range. The proposed inverter scheme is capable of producing two-level to five-level pulse width modulated voltage across the phase winding depending on the modulation range. Additionally, in case of any switch failure in the flying capacitor connection, the proposed inverter topology can be operated as a three-level inverter for full modulation range. The proposed scheme is experimentally verified on a four pole, 5hp induction motor drive.

Microstructure related influence on the electrical properties of pulsed laser ablated (Ba, Sr)TiO3 thin films

The microstructural dependence of electrical properties of (Ba, Sr)TiO3(BST) thin films were studied from the viewpoint of dc and ac electrical properties. The films were grown using a pulsed laser deposition technique in a temperature range of 300 to 600 degrees C, inducing changes in grain size, structure, and morphology. Consequently, two different types of films were realized, of which type I, was polycrystalline, multigrained, while type II was [100] oriented possessing a densely packed fibrous microstructure. Leakage current measurements were done at elevated temperatures to provide evidence of the conduction mechanism present in these films. The results revealed a contribution from both electronic and ionic conduction. In the case of type I films, two trapping levels were identified with energies around 0.5 and 2.73 eV, which possibly originate from oxygen vacancies V-O and Ti3+ centers, respectively. These levels act as shallow and deep traps and are reflected in the current-voltage characteristics of the BST thin films. The activation energy associated with oxygen vacancy motion in this case was obtained as 1.28 eV. On the contrary, type II films showed no evidence of deep trap energy levels, while the identified activation energy associated with shallow traps was obtained as 0.38 eV. The activation energy obtained for oxygen vacancy motion in type II films was around 1.02 eV. The dc measurement results were further elucidated through ac impedance analysis, which revealed a grain boundary dominated response in type I in comparison to type II films where grain response is highlighted. A comparison of the mean relaxation time of the two films revealed three orders of magnitude higher relaxation time in the case of type I films. Due to smaller grain size in type I films the grains were considered to be completely depleted giving rise to only grain boundary response for the bulk of the film. The activation energy obtained from conductivity plots agree very well with that of dc measurements giving values 1.3 and 1.07 eV for type I and type II films, respectively. Since oxygen vacancy transport have been identified as the origin of resistance degradation in BST thin films, type I films with their higher value of activation energy for oxygen ion mobility explains the improvement in breakdown characteristics under constant high dc field stress. The role of microstructure in controlling the rate of degradation is found useful in this instance to enhance the film properties under high electric field stresses. (C) 2000 American Institute of Physics. [S0021-8979(00)00418-7].

Investigations of the Nature of Critical Line Very Close to a Double Critical Point

The curvature of the line of critical points in a reentrant ternary mixture is determined by approaching the double critical point (DCP) extremely closely. The results establish the continuous and quadratic nature of this line. Out study encompasses as small a loop size (ΔT) as 663 mK. The DCP is realized when ΔT becomes zero.

A homotopy approach for stabilizing single-input systems with control structure constraints

A linear state feedback gain vector used in the control of a single input dynamical system may be constrained because of the way feedback is realized. Some examples of feedback realizations which impose constraints on the gain vector are: static output feedback, constant gain feedback for several operating points of a system, and two-controller feedback. We consider a general class of problems of stabilization of single input dynamical systems with such structural constraints and give a numerical method to solve them. Each of these problems is cast into a problem of solving a system of equalities and inequalities. In this formulation, the coefficients of the quadratic and linear factors of the closed-loop characteristic polynomial are the variables. To solve the system of equalities and inequalities, a continuous realization of the gradient projection method and a barrier method are used under the homotopy framework. Our method is illustrated with an example for each class of control structure constraint.

Deformational Behavior of Fiber-Reinforced Concrete Beams in Bending

An experimental study aimed at understanding the deformational behavior of conventionally reinforced steel fiber concrete beams in pure bending is reported in this paper. One group of beams has steel fibers dispersed in the entire volume of the beam and the second has fibers dispersed over half the depth of the beam on the tension side. A comparative study of the deformational characteristics of these beams has been made. Half-depth fiber inclusion, requiring only half the quantity of fibers of full-depth inclusion, is found to be equally effective in improving the deformational behavior of beams. Thus, by such modes of inclusion of fibers, an economical and efficient use of expensive steel fibers can be realized.

Optimal explicit terminal guidance for a launch vehicle

It is observed that general explicit guidance schemes exhibit numerical instability close to the injection point. This difficulty is normally attributed to the demand for exact injection which, in turn, calls for finite corrections to be enforced in a relatively short time. The deviations in vehicle state which need corrective maneuvers are caused by the off-nominal operating conditions. Hence, the onset of terminal instability depends on the type of off-nominal conditions encountered. The proposed separate terminal guidance scheme overcomes the above difficulty by minimizing a quadratic penalty on injection errors rather than demanding an exact injection. There is also a special requirement in the terminal phase for the faster guidance computations. The faster guidance computations facilitate a more frequent guidance update enabling an accurate terminal thrust cutoff. The objective of faster computations is realized in the terminal guidance scheme by employing realistic assumptions that are accurate enough for a short terminal trajectory. It is observed from simulations that one of the guidance parameters (P) related to the thrust steering angular rates can indicate the onset of terminal instability due to different off-nominal operating conditions. Therefore, the terminal guidance scheme can be dynamically invoked based on monitoring of deviations in the lone parameter P.