Maximum Rate of Unitary-Weight, Single-Symbol Decodable STBCs

It is well known that the space-time block codes (STBCs) from complex orthogonal designs (CODs) are single-symbol decodable/symbol-by-symbol decodable (SSD). The weight matrices of the square CODs are all unitary and obtainable from the unitary matrix representations of Clifford Algebras when the number of transmit antennas n is a power of 2. The rate of the square CODs for n = 2(a) has been shown to be a+1/2(a) complex symbols per channel use. However, SSD codes having unitary-weight matrices need not be CODs, an example being the minimum-decoding-complexity STBCs from quasi-orthogonal designs. In this paper, an achievable upper bound on the rate of any unitary-weight SSD code is derived to be a/2(a)-1 complex symbols per channel use for 2(a) antennas, and this upper bound is larger than that of the CODs. By way of code construction, the interrelationship between the weight matrices of unitary-weight SSD codes is studied. Also, the coding gain of all unitary-weight SSD codes is proved to be the same for QAM constellations and conditions that are necessary for unitary-weight SSD codes to achieve full transmit diversity and optimum coding gain are presented.

Dislocation mechanisms for plastic flow of nickel in the temperature range 4.2 – 1200 K

The temperature ranges of thermal and athermal deformation behaviour of nickel are identified by employing the temperature-dependence of flow-stress and strain-rate cycling data. The results are used to present a unified view of dislocation mechanisms of glide encompassing the two thermally activated and the intermediate athermal regimes of plastic flow.In the low-temperature thermally activated region (<250 K) the strain rate is found to be controlled by the repulsive intersection of glide and forest dislocations, in accordance with current ideas. The athermal stress in this region can be attributed mainly to the presence of strong attractive junctions which are overcome by means of Orowan bowing, a small contribution also coming from the elastic interactions between dislocations. The values of activation area and activation energy obtained in the high-temperature region (> 750 K) negate the operation of a diffusion-controlled mechanism. Instead, the data support a thermal activation model involving unzipping of the attractive junctions. The internal (long-range) stress contribution here results solely from the elastic interactions between dislocations. This view concerning the high-temperature plastic flow is further supported by the observation that the Cottrell–Stokes law is obeyed over large strains in the range 750–1200 K.

A comparative study of erbium oxide and gadolinium oxide high-k dielectric thin films grown by low-pressure metalorganic chemical vapour deposition (MOCVD) using beta-Diketonates as precursors

In this paper, a comparative study of thin films of Er2O3 and Gd2O3 grown on n-type Si(100) by low-pressure metalorganic chemical vapour deposition (MOCVD) under the identical conditions has been presented. beta-Diketonate complex of rate earth metals was used as precursor. Description on the evolution of the morphology, structure, optical, and electrical characteristics of films with respect to growth parameters and post-deposition annealing process has been presented. As-gown Gd2O3 films grow with <111> texture, whereas the texture of Er2O3 films strongly depends on the growth temperature (either <100> or <111>). Compositional analysis reveals that the Gd2O3 films grown at or above 500degreesC are carbon free whereas Er2O3 films at upto 525degreesC show the presence of heteroatoms and Er2O3 films grown above 525degreesC are carbon five. The effective dielectric constant is in the range of 7-24, while the fixed charge density is in the range - 10(11) to 10(10) CM-2 as extracted from the C-V characteristics. DC I-V study was carried out to examine the leakage behaviour of films. It reveals that the as-grown Gd2O3 film was very leakey in nature. Annealing of the films in oxidizing ambient for a period of 20 min results in a drastic improvement in the leakage behaviour. The presence of heteroatoms (such as carbon) and their effect on the properties of films are discussed.

A k-epsilon model for turbulent weld pool convection in gas metal arc welding process

In this paper, we present a modified k - epsilon model capable of addressing turbulent weld-pool convection in a GMAW process, taking into account the morphology of the phase change interface during a Gas Metal Arc Welding (GMAW) process. A three-dimensional turbulence mathematical model has been developed to study the heat transfer and fluid flow within the weld pool by considering the combined effect of three driving forces, viz., buoyancy, Lorentz force and surface tension (Marangoni convection). Mass and energy transports by the droplets are considered through the thermal analysis of the electrode. The falling droplet's heat addition to the molten pool is considered to be a volumetric heat source distributed in an imaginary cylindrical cavity ("cavity model") within the weld pool. This nature of heat source distribution takes into account the momentum and the thermal, energy of the falling droplets. The numerically predicted weld pool dimensions both from turbulence and laminar models are then compared with the experimental post-weld results sectioned across the weld axis. The above comparison enables us to analyze the overall effects of turbulent convection on the nature of heat and fluid flow and hence on the weld pool shape/size during the arc welding processes.

Enhanced photoluminescence of Gd2O3:Eu3+ nanophosphors with alkali (M = Li+, Na+, K+) metal ion co-doping

Gd1.95Eu0.4M0.01O3 (M = Li+ Na+ K+) nanophosphors have been synthesized by a low temperature solution combustion (LSC) method. Powder X-ray diffraction pattern (PXRD), scanning electron microscopy (SEM), UV-vis and photoluminescence (PL) measurements were carried out to characterize their structural and luminescent properties. The excitation and emission spectra indicated that the phosphor could be well excited by UV light (243 nm) and emit red light about 612 nm. The effect of alkali co-dopant on PL properties has been examined. The results showed that incorporation of Li+, Na+ and K+ in to Gd2O3:Eu3+ phosphor would lead to a remarkable increase of photoluminescence. The PL intensity of Gd2O3:Eu3+ phosphor was improved evidently by co-doping with Li+ ions whose radius is less than that of Gd3+ and hardly with Na+, K+ whose radius is larger than that of Gd3+. The effect of co-dopants on enhanced luminescence was mainly regarded as the result of a suitable local distortion of crystal field surrounding the Eu3+ activator. These results will play an important role in seeking some more effective co-dopants. (C) 2011 Published by Elsevier B.V.

Low-Delay, High-Rate Nonsquare Complex Orthogonal Designs

The maximal rate of a nonsquare complex orthogonal design for transmit antennas is 1/2 + 1/n if is even and 1/2 + 1/n+1 if is odd and the codes have been constructed for all by Liang (2003) and Lu et al. (2005) to achieve this rate. A lower bound on the decoding delay of maximal-rate complex orthogonal designs has been obtained by Adams et al. (2007) and it is observed that Liang's construction achieves the bound on delay for equal to 1 and 3 modulo 4 while Lu et al.'s construction achieves the bound for n = 0, 1, 3 mod 4. For n = 2 mod 4, Adams et al. (2010) have shown that the minimal decoding delay is twice the lower bound, in which case, both Liang's and Lu et al.'s construction achieve the minimum decoding delay. For large value of, it is observed that the rate is close to half and the decoding delay is very large. A class of rate-1/2 codes with low decoding delay for all has been constructed by Tarokh et al. (1999). In this paper, another class of rate-1/2 codes is constructed for all in which case the decoding delay is half the decoding delay of the rate-1/2 codes given by Tarokh et al. This is achieved by giving first a general construction of square real orthogonal designs which includes as special cases the well-known constructions of Adams, Lax, and Phillips and the construction of Geramita and Pullman, and then making use of it to obtain the desired rate-1/2 codes. For the case of nine transmit antennas, the proposed rate-1/2 code is shown to be of minimal delay. The proposed construction results in designs with zero entries which may have high peak-to-average power ratio and it is shown that by appropriate postmultiplication, a design with no zero entry can be obtained with no change in the code parameters.

The irradiation of 1:1 mixture of ammonia:carbon dioxide ice at 30 K using 1 kev electrons

In this Letter the results of an experimental investigation of 1 keV electron irradiation of a 1:1 ice mixture of NH3:CO2 at 30 K was made under ultrahigh vacuum (10(-9) mbar) conditions. Molecular products formed within the ice were detected and monitored using FTIR spectroscopy. The formation of ammonium ions (NH4+), cyanate ions (OCN-), CO was observed leading to the synthesis of ammonium carbamate (NH4NH2CO2). The consequences of these results for prebiotic chemistry in the interstellar medium and star forming regions are discussed. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.

The Kπ form factors from analyticity and unitarity

Analyticity and unitarity techniques are employed to obtain bounds on the shape parameters of the scalar and vector form factors of semileptonic K l3 decays. For this purpose we use vector and scalar correlators evaluated in pQCD, a low energy theorem for scalar form factor, lattice results for the ratio of kaon and pion decay constants, chiral perturbation theory calculations for the scalar form factor at the Callan-Treiman point and experimental information on the phase and modulus of Kπ form factors up to an energy t in = 1GeV 2. We further derive regions on the real axis and in the complex-energy plane where the form factors cannot have zeros.

The 27-plet contributions to the CP-conserving K -> pi l(+)l(-) decays

We revisit the rare kaon decays K -> pi l(+)l(-) which are of special interest due to the recent measurements of the charged kaon decay spectra. We compute the contribution of the 27-plet to the decay amplitudes in one loop SU(3) chiral perturbation theory. We estimate the resulting impact to be similar to 10% to the branching ratios of the charged kaon decays, and also noticeably influence the shape of the spectra. With current values of the constants G(8) associated with the octet and G(27) associated with the 27-plet, the contribution of the latter pushes the spectrum in the correct direction, towards the charged lepton spectra. We also discuss the impact for neutral decay rates and spectra.

Derating Based Hardware Optimizations in Soft Error Tolerant Designs

Ensuring reliable operation over an extended period of time is one of the biggest challenges facing present day electronic systems. The increased vulnerability of the components to atmospheric particle strikes poses a big threat in attaining the reliability required for various mission critical applications. Various soft error mitigation methodologies exist to address this reliability challenge. A general solution to this problem is to arrive at a soft error mitigation methodology with an acceptable implementation overhead and error tolerance level. This implementation overhead can then be reduced by taking advantage of various derating effects like logical derating, electrical derating and timing window derating, and/or making use of application redundancy, e. g. redundancy in firmware/software executing on the so designed robust hardware. In this paper, we analyze the impact of various derating factors and show how they can be profitably employed to reduce the hardware overhead to implement a given level of soft error robustness. This analysis is performed on a set of benchmark circuits using the delayed capture methodology. Experimental results show upto 23% reduction in the hardware overhead when considering individual and combined derating factors.

Algorithmic aspects of k-tuple total domination in graphs

For a fixed positive integer k, a k-tuple total dominating set of a graph G = (V. E) is a subset T D-k of V such that every vertex in V is adjacent to at least k vertices of T Dk. In minimum k-tuple total dominating set problem (MIN k-TUPLE TOTAL DOM SET), it is required to find a k-tuple total dominating set of minimum cardinality and DECIDE MIN k-TUPLE TOTAL DOM SET is the decision version of MIN k-TUPLE TOTAL DOM SET problem. In this paper, we show that DECIDE MIN k-TUPLE TOTAL DOM SET is NP-complete for split graphs, doubly chordal graphs and bipartite graphs. For chordal bipartite graphs, we show that MIN k-TUPLE TOTAL DOM SET can be solved in polynomial time. We also propose some hardness results and approximation algorithms for MIN k-TUPLE TOTAL DOM SET problem. (c) 2012 Elsevier B.V. All rights reserved.

Development of experimental setup for study of adsorption characteristics of porous materials down to 4.2 K

The knowledge of adsorption characteristics of activated carbon (porous material) in the temperature range from 5 to 20 K is essential when used in cryosorption pumps for nuclear fusion applications. However, such experimental data are very scarce in the literature, especially below 77 K. So, an experimental system is designed and fabricated to measure the adsorption characteristics of porous materials under variable cryogenic temperatures (from 5 K to 100 K). This is based on the commercially available micropore-analyser coupled to a closed helium cycle two-stage Gifford McMahon (GM) Cryocooler, which allows the sample to be cooled to 4.2 K. The sample port is coupled to the Cryocooler through a heat switch, which isolates this port from the cold head of the Cryocooler. By this, the sample temperature can now be varied without affecting the Cryocooler. The setup enables adsorption studies in the pressure range from atmospheric down to 10(-4) Pa. The paper describes the details of the experimental setup and presents the results of adsorption studies at 77 K for activated carbon with nitrogen as adsorbate. The system integration is now completed to enable adsorption studies at 4.2 K.

Hot-pressed TiB2-10 wt.% TiSi2 ceramic with extremely good thermal transport properties at elevated temperatures (up to 1273 K)

This contribution reports and analyses the high thermal transport property of hot-pressed TiB2-10 wt.% TiSi2 ceramics. Depending on the test temperature, the thermal conductivity values of the TiB2 composite (which range from 89 to 122W m(-1) K-1) are determined to be 18-25% higher than that of monolithic TiB2. The thermal transport properties are analyzed in terms of electronic and phonon contributions. The electronic contribution is the major component of the thermal conductivity of TiB2 and comparable contributions from both electronic and phonon components are observed for the TiB2-TiSi2 composite. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.