Activated carbon + HFC 134a based two stage thermal compression adsorption refrigeration using low grade thermal energy sources

A thermodynamic analysis is presented for the two stage thermal compression process for an adsorption refrigeration cycle with HFC-134a as the working fluid and activated carbon as the adsorbent. Three specimens of varying achievable packing densities were evaluated. The influence of evaporating, condensing/adsorption and desorption temperatures was assessed through three performance indicators, namely,the uptake efficiency, the coefficient of performance and the exergetic efficiency. Conditions under which a two stage thermal compression process performs better than the single stage unit are identified. It is concluded that two stage thermal compression will be a viable proposition when the heat source temperature is low or when adsorption characteristics are weak or when adequate packing densities are difficult to realize. (C) 2008 Elsevier Ltd. All rights reserved.

Link route pricing for enhanced QoS

Pricing is an effective tool to control congestion and achieve quality of service (QoS) provisioning for multiple differentiated levels of service. In this paper, we consider the problem of pricing for congestion control in the case of a network of nodes under multiple service classes. Our work draws upon [1] and [2] in various ways. We use the Tirupati pricing scheme in conjunction with the stochastic approximation based adaptive pricing methodology for queue control (proposed in [1]) for minimizing network congestion. However, unlike the methodology of [1] where pricing for entire routes is directly considered, we consider prices for individual link-service grade tuples. Further, we adapt the methodology proposed in [21 for a single-node scenario to the case of a network of nodes, for evaluating performance in terms of price, revenue rate and disutility. We obtain considerable performance improvements using our approach over that in [1]. In particular, our approach exhibits a throughput improvement in the range of 54 to 80 percent in all cases studied (over all routes) while exhibiting a lower packet delay in the range of 26 to 38 percent over the scheme in [1].

Optimization of the distance between source and substrate for device-grade SnS films grown by the thermal evaporation technique

Tin monosulfide (SnS) films with varying distance between the source and substrate (DSS) were prepared by the thermal evaporation technique at a temperature of 300 degrees C to investigate the effect of the DSS on the physical properties. The physical properties of the as-deposited films are strongly influenced by the variation of DSS. The thickness, Sn to S at.% ratio, grain size, and root mean square (rms) roughness of the films decreased with the increase of DSS. The films grown at DSS = 10 and 15 cm exhibited nearly single-crystalline nature with low electrical resistivity. From Hall-effect measurements, it is observed that the films grown at DSS <= 15 cm have p-type conduction and the films grown at higher distances have n-type conduction due to the variation of the Sn/S ratio. The films grown at DSS = 15 cm showed higher optical band gap of 1.36 eV as compared with the films grown at other distances. The effect of the DSS on the physical properties of SnS films is discussed and reported.

Development and transient performance results of a single stage activated carbon - HFC 134a closed cycle adsorption cooling system

A laboratory model of a thermally driven adsorption refrigeration system with activated carbon as the adsorbent and 1,1,1,2-tetrafluoroethane (HFC 134a) as the refrigerant was developed. The single stage compression system has an ensemble of four adsorbers packed with Maxsorb II specimen of activated carbon that provide a near continuous flow which caters to a cooling load of up to 5W in the 5-18 degrees C region. The objective was to utilise the low grade thermal energy to drive a refrigeration system that can be used to cool some critical electronic components. The laboratory model was tested for it performance at various cooling loads with the heat source temperature from 73 to 93 degrees C. The pressure transients during heating and cooling phases were traced. The cyclic steady state and transient performance data are presented. (C) 2010 Elsevier Ltd. All rights reserved.

Training-Symbol Embedded, High-Rate, Single-Symbol ML-Decodable, Distributed STBCs for Relay Networks

Distributed space-time block codes (DSTBCs) from complex orthogonal designs (CODs) (both square and nonsquare), coordinate interleaved orthogonal designs (CIODs), and Clifford unitary weight designs (CUWDs) are known to lose their single-symbol ML decodable (SSD) property when used in two-hop wireless relay networks using amplify and forward protocol. For such networks, in this paper, three new classes of high rate, training-symbol embedded (TSE) SSD DSTBCs are constructed: TSE-CODs, TSE-CIODs, and TSE-CUWDs. The proposed codes include the training symbols inside the structure of the code which is shown to be the key point to obtain the SSD property along with the channel estimation capability. TSE-CODs are shown to offer full-diversity for arbitrary complex constellations and the constellations for which TSE-CIODs and TSE-CUWDs offer full-diversity are characterized. It is shown that DSTBCs from nonsquare TSE-CODs provide better rates (in symbols per channel use) when compared to the known SSD DSTBCs for relay networks. Important from the practical point of view, the proposed DSTBCs do not contain any zeros in their codewords and as a result, antennas of the relay nodes do not undergo a sequence of switch on/off transitions within every codeword, and, thus, avoid the antenna switching problem.

Catalysis of tRNA Aminoacylation: Single Turnover to Steady-State Kinetics of tRNA Synthetases

Aminoacyl-tRNA synthetases (aaRS) catalyze the bimolecular association reaction between amino acid and tRNA by specifically and unerringly choosing the cognate amino acid and tRNA. There are two classes of such synthetases that perform tRNA-aminoacylation reaction. Interestingly, these two classes of aminoacyl-tRNA synthetases differ not only in their structures but they also exhibit remarkably distinct kinetics under pre-steady-state condition. The class I synthetases show initial burst of product formation followed by a slower steady-state rate. This has been argued to represent the influence of slow product release. In contrast, there is no burst in the case of class H enzymes. The tight binding of product with enzyme for class I enzymes is correlated with the enhancement of rate in presence of elongation factor. EF-TU. In spite of extensive experimental studies, there is no detailed theoretical analysis that can provide a quantitative understanding of this important problem. In this article, we present a theoretical investigation of enzyme kinetics for both classes of aminoacyl-tRNA synthetases. We present an augmented kinetic scheme and then employ the methods of time-dependent probability statistics to obtain expressions for the first passage time distribution that gives both the time-dependent and the steady-state rates. The present study quantitatively explains all the above experimental observations. We propose an alternative path way in the case of class II enzymes showing the tRNA-dependent amino acid activation and the discrepancy between the single-turnover and steady-state rate.

Real-World Extensions To Scheduling Algorithms Based On Lagrangian Relaxation

Recently, efficient scheduling algorithms based on Lagrangian relaxation have been proposed for scheduling parallel machine systems and job shops. In this article, we develop real-world extensions to these scheduling methods. In the first part of the paper, we consider the problem of scheduling single operation jobs on parallel identical machines and extend the methodology to handle multiple classes of jobs, taking into account setup times and setup costs, The proposed methodology uses Lagrangian relaxation and simulated annealing in a hybrid framework, In the second part of the paper, we consider a Lagrangian relaxation based method for scheduling job shops and extend it to obtain a scheduling methodology for a real-world flexible manufacturing system with centralized material handling.

Vortex dynamics at rf frequencies in Bi2Sr2CaCu2O8 single crystals

We have studied the low magnetic field high temperature region of the H-T phase diagram of Bi2Sr2CaCu2O8 single crystals using the technique of non-resonant rf response at a frequency of 20 MHz. With H(rf)parallel to a, H parallel to c, the isothermal magnetic field scans below T-c show that the frequency f(H) of the tank circuit decreases continuously with increase in H before saturating at H similar to H-D(T). Such a decrease in f(H) reflects increasing rf penetration into the weakly screened region between CuO bilayers. The saturation of f(H) at its lowest value for H similar to H-D(T) indicates complete rf penetration land hence the disappearance of field dependence) due to the vanishing of the screening rf currents I-rf(c) in those regions or equivalently when the phase coherence between adjacent superconducting layers vanishes. Therefore H,(T) represents the decoupling of the adjacent superconducting bilayers, and hence also a 3D to 2D decoupling transition of the vortex structure. Simultaneous monitoring of the field dependent rf power dissipation P(H) shows a maximum in dP/dH at H-D(T). The observed H-D(T) line in many crystals is in excellent agreement with the (l/t-1) behavior proposed for decoupling.

Effect of ion nitriding on the microstructure and properties of Maraging steel (250 Grade)

In the present investigation, ion nitriding of Maraging steel (250 grade) has been carried out at three different temperatures i.e., at 435 degrees C, 450 degrees C and 465 degrees C for 10 h duration in order to achieve good wear resistance along with high strength required for the slat track component of aircraft. The microstructure of the base material and the nitrided layer was examined by optical and scanning electron microscope, and various phases present were determined by X-ray diffraction. Various properties, such as, hardness, case depth, tensile, impact, fatigue properties and corrosion resistance were investigated for both un-nitrided and ion-nitrided materials. It is observed that the microstructure of the core material remains unaltered and Fe4N is formed in the hardened surface layer after ion nitriding at all the three temperatures employed. Surface hardness increases substantially after ion nitriding. Surface hardness remains almost the same but case depth increases with the increase in ion nitriding temperature due to greater diffusivity at higher temperatures. Tensile strength, fatigue strength and corrosion resistance are improved but ductility and energy absorbed in impact test decrease on ion nitriding. These results are explained on the basis of microstructural observations. The properties obtained after ion nitriding at 450 degrees C for 10 h are found to be optimum when compared to the other two ion nitriding temperatures.

Fluctuations in protein synthesis from a single RNA template: Stochastic kinetics of ribosomes

Proteins are polymerized by cyclic machines called ribosomes, which use their messenger RNA (mRNA) track also as the corresponding template, and the process is called translation. We explore, in depth and detail, the stochastic nature of the translation. We compute various distributions associated with the translation process; one of them-namely, the dwell time distribution-has been measured in recent single-ribosome experiments. The form of the distribution, which fits best with our simulation data, is consistent with that extracted from the experimental data. For our computations, we use a model that captures both the mechanochemistry of each individual ribosome and their steric interactions. We also demonstrate the effects of the sequence inhomogeneities of real genes on the fluctuations and noise in translation. Finally, inspired by recent advances in the experimental techniques of manipulating single ribosomes, we make theoretical predictions on the force-velocity relation for individual ribosomes. In principle, all our predictions can be tested by carrying out in vitro experiments.

Phase transitions and rare-earth magnetism in hexagonal and orthorhombic $DyMnO_{3}$ single crystals

The floating-zone method with different growth ambiences has been used to selectively obtain hexagonal or orthorhombic DyMnO3 single crystals. The crystals were characterized by x-ray powder diffraction of ground specimens and a structure refinement as well as electron diffraction. We report magnetic susceptibility, magnetization and specific heat studies of this multiferroic compound in both the hexagonal and the orthorhombic structure. The hexagonal DyMnO3 shows magnetic ordering of Mn3+ (S = 2) spins on a triangular Mn lattice at T-N(Mn) = 57 K characterized by a cusp in the specific heat. This transition is not apparent in the magnetic susceptibility due to the frustration on the Mn triangular lattice and the dominating paramagnetic susceptibility of the Dy3+ (S = 9/2) spins. At T-N(Dy) = 3 K, a partial antiferromagnetic order of Dy moments has been observed. In comparison, the magnetic data for orthorhombic DyMnO3 display three transitions. The data broadly agree with results from earlier neutron diffraction experiments, which allows for the following assignment: a transition from an incommensurate antiferromagnetic ordering of Mn3+ spins at T-N(Mn) = 39 K, a lock-in transition at Tlock-in = 16 K and a second antiferromagnetic transition at T-N(Dy) = 5 K due to the ordering of Dy moments. Both the hexagonal and the orthorhombic crystals show magnetic anisotropy and complex magnetic properties due to 4f-4f and 4f-3d couplings.

Growth and characterization of pure and doped single crystals of $CuGeO_{3}$

Good quality single crystals of copper metagermanite, CuGeO3, are grown by flux technique. Growth is carried out at relatively low temperatures by using Bi2O3 along with CuO in an optimal flux ratio. Besides rendering the procedure simple, lower growth temperature reduces growth defect concentration. Single crystals of Cu1 - xCoxGeO3 and CuGe1 - yGayO3 are grown by the same method for different values of x and y to investigate the influence of in-chain and off-chain doping on spin-Peierls (SP) transition. Change in color, morphology and surface features as a result of doping are briefly discussed. Spin-Peierls transition of these crystals is studied by susceptibility measurements on a commercial SQUID magnetometer. Cationic substitution resulted in reduction of spin-Peierls transition temperature (T-SP) of CuGeO3. Substitution of magnetic impurity cobalt in-chain site caused more pronounced effects such as suppression of SP phase.

Orchestration of Haemophilus influenzae RecJ Exonuclease by Interaction with Single-Stranded DNA-Binding Protein

RecJ exonuclease plays crucial roles in several DNA repair and recombination pathways, and its ubiquity in bacterial species points to its ancient origin and vital cellular function. RecJ exonuclease from Haemophilus influenzae is a 575-amino-acid protein that harbors the characteristic motifs conserved among RecJ homologs. The purified protein exhibits a process 5'-3' single-stranded-DNA-specific exonuclease activity. The exonuclease activity of H. influenzae RecJ (HiRecJ) was supported by Mg2+ or Mn2+ and inhibited by Cd2+ suggesting a different mode of metal binding in HiRecJ as compared to Escherichia coli RecJ (EcoRecJ). Site-directed mutagenesis of highly conserved residues in HiRecJ abolished enzymatic activity. Interestingly, substitution of alanine for aspartate 77 resulted in a catalytically inactive enzyme that bound to DNA with a significantly higher affinity as compared to the wild-type enzyme. Noticeably, steady-state kinetic studies showed that H. influenzae single-stranded DNA-binding protein (HiSSB) increased the affinity of HiRecJ for single-stranded DNA and stimulated its exonuclease activity. HiSSB, whose C-terminal tail had been deleted, failed to enhance RecJ exonuclease activity. More importantly, HiRecJ was found to directly associate with its cognate single-stranded DNA-binding protein (SSB), as demonstrated by various in vitro assays, Interaction studies carried out with the truncated variants of HiRecJ and HiSSB revealed that the two proteins interact via the C-terminus of SSB protein and the core-catalytic domain of RecJ. Taken together, these results emphasize direct interactio between RecJ and SSB, which confers functional cooperativity to these two proteins. In addition, these results implicate SSB as being involved in the recruitment of RecJ to DNA and provide insights into the interplay between these proteins in repair and recombination pathways.

Influence of cobalt doping on superconducting transition in as-grown YBCO single crystals

The role of a charge buffer layer in the superconductivity of high-T-c materials is best studied by cationic substitutions. In this work, the chain copper in YBCO single crystals is substituted by Co3+ ion and consequent effect on superconducting transition temperature (T-c) studied. The T-c is measured using non-resonant Microwave Absorption technique, which is a highly sensitive and contactless method. It is seen that T-c of as-grown crystals is considerably enhanced by cobalt doping in low concentration regime. In contrast, higher T-c is achieved in undoped crystals only after extended oxygen anneal. When dopant concentration increases beyond an optimal value, T-c decreases and the system does not show superconductivity when cobalt content is high (x > 0.5 in YBa2Cu3-xCOxO7+/-delta). This behaviour consequent to cobalt substitution is discussed with reference to the apical oxygen model. Optimal cobalt doping can be thought of as an alternative to extended oxygen anneal in as-grown crystals of YBCO.