First-principles hydrogen adsorption properties of Li-decorated ThMoB4-type graphene

The hydrogen storage (1–10H₂) properties of single- and double-side lithium decorated ThMoB₄-type graphene (Li/ThMoB₄C) are systematically investigated by density functional first-principles calculations within Dmol³ package. After well-converged geometry optimizations, it is found that the binding energy of Li adatom is higher enough, and there is no adatom clustering. The average adsorption energies of 1–6 H₂ deviate in 0.20–0.27 eV/H₂ range, which is providing a convenient physical adsorption-desorption cycle. A detailed examination of the binding mechanism between the constituents of the H₂ adsorbed Li-decorated systems is presented by density of states, Mulliken charge analysis, electron density and density difference calculations. For further decoration and adsorption with 12Li adatom and 72H₂ molecules, the computation yields a high gravimetric density of 14.5 wt % with the acceptable adsorption energy. In this way, it is concluded that Li/ThMoB₄ system can be considered as a promising hydrogen storage medium.     

SIMULTANEOUS ESTIMATION OF FRICTIONAL HEAT FLUX AND TWO THERMAL CONTACT PARAMETERS FOR SLIDING CONTACTS

In the dry friction between two solids in imperfect contact, the determination of temperature distribution within solids needs the knowledge of: (1) heat flux generated by friction, (2) thermal contact conductance, and (3) intrinsic heat partition coefficient. In this article, numerical study is conducted in order to estimate the values of these parameters from simulated temperatures. Numerical investigations and a sensitivity analysis are performed in order to show the feasibility and the needed conditions for an accurate estimation. In order to take into account the measurements noise, statistical investigations using a stochastic approach and Monte Carlo method are also performed.     

Modelling of hydrogen induced pressurization of internal cavities

Internal cavities can constitute a crack initiation site especially if filled with hydrogen at high pressure. A new refined equation of state based on recent NIST database has been introduced in order to model the equilibrium pressure. It is based on a thermodynamic definition of fugacity and uses the NIST data relating hydrogen density and pressure to define a new fugacity pressure quadratic dependence. The resulting Equation Of State (EOS) is compared to the standard Abel–Noble EOS and it is shown that for a given fugacity, imposed by a Sievert's law, the corresponding pressure is significantly higher. This new refined EOS was introduced into a previously developed numerical model of hydrogen diffusion and desorption and applied to evaluate the kinetics of pressure build-up within a cavity and its equilibrium pressure. It has been shown that the kinetics of pressure build-up at room temperature, which reaches values close to equilibrium in some hundreds of hours, is compatible with the industrial quality control procedures. The calculated pressures are in the range 4500–8650 bars depending on hydrogen solubility, which differs between the matrix and the segregation bands, and tend to equilibrium values obtained from mass balance approach.     

Influence of Pre-Heated Al 6061 Substrate Temperature on the Residual Stresses of Multipass Al Coatings Deposited by Cold Spray

In this work, the influence of the substrate temperature on the deposition efficiency, on the coating properties and residual stress was investigated. Pure Al coatings were deposited on Al 6061 alloy substrates using a CGT Kinetics 3000 cold spray system. The substrate temperature was in a range between 20 (room temperature) and 375 °C and was kept nearly constant during a given deposition while all the other deposition parameters were unchanged. The deposited coatings were quenched in water (within 1 min from the deposition) and then characterized. The residual stress was determined by Almen gage method, Modified Layer Removal Method, and XRD in order to identify both the mean coating stress and the stress profile through the coating thickness from the surface to the coating-substrate interface. The residual stress results obtained by these three methods were compared and discussed. The coating morphology and porosity were investigated using optical and scanning electron microscopy.     

Tight Upper Bound on the Outage Probability of QSTBC

Recently, the statistical properties of the equivalent channel representation of a multiple-input-multiple output (MIMO) system employing rate one quasi-orthogonal space-time block codes (QSTBC) for n _T=2ⁿ, nges2 transmit antennas was characterized. It was shown, that these QSTBC were capable of achieving a significant fraction of the outage mutual information of a MIMO system. In this letter, based on the Minkowski's determinant inequality and the Meijer's G-function we derive an upper bound for the fraction of outage probability achieved with QSTBC for the general case of n_T=2 ⁿ, nges2 transmit antennas. Simulations results show that this bound gets tight for all signal-to-noise-ratios (SNR) values by increasing the number of receive antennas     

Distribution of Lattice Points

We discuss the lattice structure of congruential random number generators and examine figures of merit. Distribution properties of lattice measures in various dimensions are demonstrated by using large numerical data. Systematic search methods are introduced to diagnose multiplier areas exhibiting good, bad and worst lattice structures. We present two formulae to express multipliers producing worst and bad laice points. The conventional criterion of normalised lattice rule is also questioned and it is shown that this measure used with a fixed threshold is not suitable for an effective discrimination of lattice structures. Usage of percentiles represents different dimensions in a fair fashion and provides consistency for different figures of merits.     

On the definition of sequential consistency

The definition of sequential consistency is compared with an intuitive notion of correctness. That the definition is not strong enough is illustrated through a hypothetical memory system which is clearly incorrect, yet sequentially consistent. It is claimed that the reason for this is the absence of a relation between what actually happens (temporal order) and what seems to happen (logical order). A stronger version of sequential consistency is proposed.     

Impact of spatial correlation on the performance of orthogonal space-time block codes

We analyze the impact of transmitter and receiver spatial correlation on the performance of a multiple-input multiple-output (MIMO) system which applies an orthogonal space-time block code with no channel state information at the transmitter and perfect channel state information at the receiver. We derive a general formula for the bit error rate of a MIMO system with arbitrary number of transmit and receive antennas as a function of the correlation at the transmitter and the receiver. We prove that the diversity advantage is given by M/spl middot/N if M is the rank of the transmit correlation matrix and N the rank of the receive correlation matrix, respectively.