Molecular Insights Revealing Interaction of Tim23 and Channel Subunits of Presequence Translocase

Tim23 is an essential channel-forming subunit of the presequence translocase recruiting multiple components for assembly of the core complex, thereby regulating the protein translocation process. However, understanding of the precise interaction of subunits associating with Tim23 remains largely elusive. Our findings highlight that transmembrane helix 1 (TM1) is required for homodimerization of Tim23, while, together with TM2, it is involved in preprotein binding within the channel. Based on our evidence, we predict that the TM1 and TM2 from each dimer are involved in the formation of the central translocation pore, aided by Tim17. Furthermore, TM2 is also involved in the recruitment of Tim21 and the presequence-associated motor (PAM) subcomplex to the Tim23 channel, while the matrix-exposed loop L1 generates specificity in their association with the core complex. Strikingly, our findings indicate that the C-terminal sequence of Tim23 is dispensable for growth and functions as an inhibitor for binding of Tim21. Our model conceptually explains the cooperative function between Tam41 and Pam17 subunits, while the antagonistic activity of Tim21 predominantly determines the bound and free forms of the PAM subcomplex during import.

Power-Controlled Reverse Channel Training in a Multiuser TDD-MIMO Spatial Multiplexing System With CSIR

This paper considers the design of a power-controlled reverse channel training (RCT) scheme for spatial multiplexing (SM)-based data transmission along the dominant modes of the channel in a time-division duplex (TDD) multiple-input and multiple-output (MIMO) system, when channel knowledge is available at the receiver. A channel-dependent power-controlled RCT scheme is proposed, using which the transmitter estimates the beamforming (BF) vectors required for the forward-link SM data transmission. Tight approximate expressions for 1) the mean square error (MSE) in the estimate of the BF vectors, and 2) a capacity lower bound (CLB) for an SM system, are derived and used to optimize the parameters of the training sequence. Moreover, an extension of the channel-dependent training scheme and the data rate analysis to a multiuser scenario with M user terminals is presented. For the single-mode BF system, a closed-form expression for an upper bound on the average sum data rate is derived, which is shown to scale as ((L-c - L-B,L- tau)/L-c) log logM asymptotically in M, where L-c and L-B,L- tau are the channel coherence time and training duration, respectively. The significant performance gain offered by the proposed training sequence over the conventional constant-power orthogonal RCT sequence is demonstrated using Monte Carlo simulations.

Scheduling for Fading Channels Under Partial Channel Information

We consider a scheduler for the downlink of a wireless channel when only partial channel-state information is available at the scheduler. We characterize the network stability region and provide two throughput-optimal scheduling policies. We also derive a deterministic bound on the mean packet delay in the network. Finally, we provide a throughput-optimal policy for the network under QoS constraints when real-time and rate-guaranteed data traffic may be present.

Channel quantization for physical layer network-coded two-way relaying

The design of modulation schemes for the physical layer network-coded two way relaying scenario is considered with the protocol which employs two phases: Multiple access (MA) Phase and Broadcast (BC) phase. It was observed by Koike-Akino et al. that adaptively changing the network coding map used at the relay according to the channel conditions greatly reduces the impact of multiple access interference which occurs at the relay during the MA phase. In other words, the set of all possible channel realizations (the complex plane) is quantized into a finite number of regions, with a specific network coding map giving the best performance in a particular region. We obtain such a quantization analytically for the case when M-PSK (for M any power of 2) is the signal set used during the MA phase. We show that the complex plane can be classified into two regions: a region in which any network coding map which satisfies the so called exclusive law gives the same best performance and a region in which the choice of the network coding map affects the performance, which is further quantized based on the choice of the network coding map which optimizes the performance. The quantization thus obtained analytically, leads to the same as the one obtained using computer search for 4-PSK signal set by Koike-Akino et al., for the specific value of M = 4.

Thermal Efficiency of LPG and PNG-fired burners: Experimental and numerical studies

In the present work, the thermal efficiency of a conventional domestic burner is studied both experimentally and numerically for liquefied petroleum gas (LPG) and piped natural gas (PNG) fuels. Three-dimensional computational fluid dynamic (CFD) modeling of the steady-state flow, combustion and heat transfer to the vessel is reported for the first time in such burners. Based on the insights from the CFD model concerning the flow and heat transfer, design modifications in the form of a circular insert and a radiant sheet are proposed which are observed to increase thermal efficiency for LPG. For PNG, predictions showed that loading height was a much more important factor affecting efficiency than these design modifications and an optimal loading height could be identified. Experiments confirm these trends by showing an improvement in burner thermal efficiency of 2.5% for LPG with the modified design, and 10% for PNG with the optimal loading height, demonstrating that the CFD modeling approach developed in the present work is a useful tool to study domestic burners. (C) 2013 Elsevier Ltd. All rights reserved.

Glycidyl azide polymer crosslinked through triazoles by click chemistry: curing, mechanical and thermal properties

Glycidyl azide polymer (GAP) was cured through click chemistry by reaction of the azide group with bispropargyl succinate (BPS) through a 1,3-dipolar cycloaddition reaction to form 1,2,3-triazole network. The properties of GAP-based triazole networks are compared with the urethane cured GAP-systems. The glass transition temperature (T-g), tensile strength, and modulus of the system increased with crosslink density, controlled by the azide to propargyl ratio. The triazole incorporation has a higher T-g in comparison to the GAP-urethane system (T-g-20 degrees C) and the networks exhibit biphasic transitions at 61 and 88 degrees C. The triazole curing was studied using Differential Scanning Calorimetry (DSC) and the related kinetic parameters were helpful for predicting the cure profile at a given temperature. Density functional theory (DFT)-based theoretical calculations implied marginal preference for 1,5-addition over 1,4-addition for the cycloaddition between azide and propargyl group. Thermogravimetic analysis (TG) showed better thermal stability for the GAP-triazole and the mechanism of decomposition was elucidated using pyrolysis GC-MS studies. The higher heat of exothermic decomposition of triazole adduct (418kJmol(-1)) against that of azide (317kJmol(-1)) and better mechanical properties of the GAP-triazole renders it a better propellant binder than the GAP-urethane system.

Physiological and subjective thermal response from Indians

A controlled laboratory experiment was carried out on forty Indian male college students for evaluating the effect of indoor thermal environment on occupants' response and thermal comfort. During experiment, indoor temperature varied from 21 degrees C to 33 degrees C, and the variables like relative humidity, airflow, air temperature and radiant temperature were recorded along with skin (T-sk) and oral temperature (T-core) from the subjects. From T-sk and T-c, body temperature (T-b) was evaluated. Subjective Thermal Sensation Vote (TSV) was recorded using ASHRAE 7-point scale. In PMV model, Fanger's T-sk equation was used to accommodate adaptive response. Stepwise regression analysis result showed T-b was better predictor of TSV than T-sk and T-core. Regional skin temperature response, lower sweat threshold temperature with no dipping sweat and higher cutaneous sweating threshold temperature were observed as thermal adaptive responses. Using PMV model, thermal comfort zone was evaluated as (22.46-25.41) degrees C with neutral temperature of 23.91 degrees C, whereas using TSV response, wider comfort zone was estimated as (23.25-2632) degrees C with neutral temperature at 24.83 degrees C. It was observed that PMV-model overestimated the actual thermal response. Interestingly, these subjects were found to be less sensitive to hot but more sensitive to cold. A new TSV-PPD relation (PPDnew) was obtained with an asymmetric distribution of hot-cold thermal sensation response in Indians. (C) 2013 Elsevier Ltd. All rights reserved.

Diversity order vs rate in an AWGN channel

We study the diversity order vs rate of an additive white Gaussian noise (AWGN) channel in the whole capacity region. We show that for discrete input as well as for continuous input, Gallager's upper bounds on error probability have exponential diversity in low and high rate region but only subexponential in the mid-rate region. For the best available lower bounds and for the practical codes one observes exponential diversity throughout the capacity region. However we also show that performance of practical codes is close to Gallager's upper bounds and the mid-rate subexponential diversity has a bearing on the performance of the practical codes. Finally we show that the upper bounds with Gaussian input provide good approximation throughout the capacity region even for finite constellation.

Channel estimation at the transmitter in a reciprocal MIMO spatial multiplexing system

This paper considers the problem of channel estimation at the transmitter in a spatial multiplexing-based Time Division Duplex (TDD) Multiple Input Multiple Output (MIMO) system with perfect CSIR. A novel channel-dependent Reverse Channel Training (RCT) sequence is proposed, using which the transmitter estimates the beamforming vectors for forward link data transmission. This training sequence is designed based on the following two metrics: (i) a capacity lower bound, and (ii) the mean square error in the estimate. The performance of the proposed training scheme is analyzed and is shown to significantly outperform the conventional orthogonal RCT sequence. Also, in the case where the transmitter uses water-filling power allocation for data transmission, a novel RCT sequence is proposed and optimized with respect to the MSE in estimating the transmit covariance matrix.

Achievable rate region of gaussian broadcast channel with finite input alphabet and quantized output

In this paper, we study the achievable rate region of two-user Gaussian broadcast channel (GBC) when the messages to be transmitted to both the users take values from finite signal sets and the received signal is quantized at both the users. We refer to this channel as quantized broadcast channel (QBC). We first observe that the capacity region defined for a GBC does not carry over as such to QBC. Also, we show that the optimal decoding scheme for GBC (i.e., high SNR user doing successive decoding and low SNR user decoding its message alone) is not optimal for QBC. We then propose an achievable rate region for QBC based on two different schemes. We present achievable rate region results for the case of uniform quantization at the receivers. We find that rotation of one of the user's input alphabet with respect to the other user's alphabet marginally enlarges the achievable rate region of QBC when almost equal powers are allotted to both the users.

Delay optimal scheduling of a discrete-time batch service queue for point-to-point channel code rate selection

We consider the problem of characterizing the minimum average delay, or equivalently the minimum average queue length, of message symbols randomly arriving to the transmitter queue of a point-to-point link which dynamically selects a (n, k) block code from a given collection. The system is modeled by a discrete time queue with an IID batch arrival process and batch service. We obtain a lower bound on the minimum average queue length, which is the optimal value for a linear program, using only the mean (λ) and variance (σ2) of the batch arrivals. For a finite collection of (n, k) codes the minimum achievable average queue length is shown to be Θ(1/ε) as ε ↓ 0 where ε is the difference between the maximum code rate and λ. We obtain a sufficient condition for code rate selection policies to achieve this optimal growth rate. A simple family of policies that use only one block code each as well as two other heuristic policies are shown to be weakly optimal in the sense of achieving the 1/ε growth rate. An appropriate selection from the family of policies that use only one block code each is also shown to achieve the optimal coefficient σ2/2 of the 1/ε growth rate. We compare the performance of the heuristic policies with the minimum achievable average queue length and the lower bound numerically. For a countable collection of (n, k) codes, the optimal average queue length is shown to be Ω(1/ε). We illustrate the selectivity among policies of the growth rate optimality criterion for both finite and countable collections of (n, k) block codes.

Molecular Dynamics Perspective on the Protein Thermal Stability: A Case Study Using SAICAR Synthetase

The enzyme SAICAR synthetase ligates aspartate with CAIR (5'-phosphoribosyl-4-carboxy-5-aminoimidazole) forming SAICAR (5-amino-4-imidazole-N-succinocarboxamide ribonucleotide) in the presence of ATP. In continuation with our previous study on the thermostability of this enzyme in hyper-/thermophiles based on the structural aspects, here, we present the dynamic aspects that differentiate the mesophilic (E. coli, E. chaffeensis), thermophilic (G. kaustophilus), and hyperthermophilic (M. jannaschii, P. horikoshii) SAICAR synthetases by carrying out a total of 11 simulations. The five functional dimers from the above organisms were simulated using molecular dynamics for a period of 50 ns each at 300 K, 363 K, and an additional simulation at 333 K for the thermophilic protein. The basic features like root-mean-square deviations, root-mean-square fluctuations, surface accessibility, and radius of gyration revealed the instability of mesophiles at 363 K. Mean square displacements establish the reduced flexibility of hyper-/thermophiles at all temperatures. At the simulations time scale considered here, the long-distance networks are considerably affected in mesophilic structures at 363 K. In mesophiles, a comparatively higher number of short-lived (having less percent existence time) C alpha, hydrogen bonds, hydrophobic interactions are formed, and long-lived (with higher percentage existence time) contacts are lost. The number of time-averaged salt-bridges is at least 2-fold higher in hyperthermophiles at 363 K. The change in surface accessibility of salt-bridges at 363 K from 300 K is nearly doubled in mesophilic protein compared to proteins from other temperature classes.

Thermal and Sonochemical Degradation Kinetics of Poly(n-butyl methacrylate-co-alkyl acrylates): Variation of Chain Strength and Stability with Copolymer Composition

The thermal degradation of poly(n-butyl methacrylate-co-alkyl acrylate) was compared with ultrasonic degradation. For this purpose, different compositions of poly (n-butyl methacrylate-co-methyl acrylate) (PBMAMA) and a particular composition of poly(n-butyl methacrylate-co-ethyl acrylate) (PBMAEA) and poly(n-butyl methacrylate-co-butyl acrylate) (PBMABA) were synthesized and characterized. The thermal degradation of polymers shows that the poly(alkyl acrylates) degrade in a single stage by random chain scission and poly(n-butyl methacrylate) degrades in two stages. The number of stages of thermal degradation of copolymers was same as the majority component of the copolymer. The activation energy corresponding to random chain scission increased and then decreased with an increase of n-butyl methacrylate fraction in copolymer. The effect of methyl acrylate content, alkyl acrylate substituent, and solvents on the ultrasonic degradation of these copolymers was investigated. A continuous distribution kinetics model was used to determine the degradation rate coefficients. The degradation rate coefficient of PBMAMA varied nonlinearly with n-butyl methacrylate content. The degradation of poly (n-butyl methacrylate-co-alkyl acrylate) followed the order: PBMAMA < PBMAEA < PBMABA. The variation in the degradation rate constant with composition of the copolymer was discussed in relation to the competing effects of the stretching of the polymer in solution and the electron displacement in the main chain. (C) 2012 Society of Plastics Engineers

Analytical solutions for movement of cold water thermal front in a heterogeneous geothermal reservoir

In the present study an analytical model has been presented to describe the transient temperature distribution and advancement of the thermal front generated due to the reinjection of heat depleted water in a heterogeneous geothermal reservoir. One dimensional heat transport equation in porous media with advection and longitudinal heat conduction has been solved analytically using Laplace transform technique in a semi infinite medium. The heterogeneity of the porous medium is expressed by the spatial variation of the flow velocity and the longitudinal effective thermal conductivity of the medium. A simpler solution is also derived afterwards neglecting the longitudinal conduction depending on the situation where the contribution to the transient heat transport phenomenon in the porous media is negligible. Solution for a homogeneous aquifer with constant values of the rock and fluid parameters is also derived with an aim to compare the results with that of the heterogeneous one. The effect of some of the parameters involved, on the transient heat transport phenomenon is assessed by observing the variation of the results with different magnitudes of those parameters. Results prove the heterogeneity of the medium, the flow velocity and the longitudinal conductivity to have great influence and porosity to have negligible effect on the transient temperature distribution. (C) 2013 Elsevier Inc. All rights reserved.