Effect of tube pitch on heat transfer in shell-and-tube heat exchangers—new simulation software

A new program for simulation and optimization of the shell-and-tube heat exchangers is prepared to obtain useful results by employment of the computing technology fast and accurately. As an application of this program, the effects of transverse and longitudinal tube pitch in the in-line and staggered tube arrangements on the Nusselt numbers, heat transfer coefficients and thermal performance of the heat exchangers were investigated. The obtained values of the tube pitch were compared with literature values.     

Performance analysis of multiuser diversity with antenna selection in MIMO MRC systems

This paper presents a performance analysis of a user scheduling scheme for multiuser multiple-input–multiple-output (MIMO) systems with maximum ratio combining (MRC) and transmit antenna selection exploiting the multiuser and antenna diversities over independent and non-identically distributed (i.ni.d.) Rayleigh fading channels (heterogeneous case). A normalized SNR-based scheduling scheme that can guarantee user fairness is considered and new closed-form expressions for the outage probability, average channel capacity, and average bit error rate are derived. The system performance in the homogenous case (independent and identically distributed (i.i.d.) users) can be simply obtained from the derived expressions as a special case of the heterogenous case. Using the derived analytical expressions the system performances for both heterogenous and homogeneous cases are evaluated and compared. Finally, the impact of receiver antenna correlation on the system performance is evaluated.     

Thermo physical properties of acetone–zinc bromide for using in a low temperature driven absorption refrigeration machine

Thermal physical properties (vapor pressure, density, viscosity, specific heat capacity, specific electrical resistance and specific enthalpy of mixing) of the solution acetone–zinc bromide, which will be used as a working solution in an absorption refrigeration machine, are measured and analyzed. The experimental data were correlated with high accuracy. The required state diagrams (log p, T and h, T) for this solution as well as the log P, h-diagram for the pure acetone are calculated, represented, correlated and discussed. The results indicate that the solution acetone-zinc bromide might be suitable as a working solution to operate an absorption refrigeration machine at low temperature.     

Analysis of the performance of multiuser MIMO systems with user scheduling over Nakagami-m fading channels

A performance analysis of user scheduling schemes for multiuser MIMO systems exploiting the multiuser and antenna diversities over Nakagami-$m$ fading channels is presented. We consider different scheduling schemes including absolute SNR-based scheduling, and normalized SNR-based scheduling schemes for both heterogeneous and homogeneous wireless networks. We derive closed-form expressions for the average spectral efficiency, average bit error rate (BER), and outage probability of the system under study for each scheduling scheme. Using the results obtained from the closed-form analytical expressions, we compare the presented schemes and show their significant advantages.     

Thermodynamic analysis of an absorption refrigeration machine with new working fluid for solar applications

A theoretical analysis was undertaken to examine the efficiency characteristics of acetone-zinc bromide solutions for an absorption refrigeration machine, using low generator temperatures (47–60°C), which allows the use of flat plate solar collectors. The results of the simulation were confirmed with an experimental investigation. The main results showed that the solution is well suited to operate the machine at low temperatures (higher than 50°C).     

Soft X-ray laser emission from W46+

Using published atomic data, the populations of the excited states 1s²2s²2p⁶3s²3p⁶3d⁹4l (l= s, p, d, and f) – 1s²2s²2p⁶3s²3p⁶3d¹⁰of Ni-like W have been calculated for electron densities in the range 10²⁰–10²³ cm^-3and electron temperatures in the range 0.5–1 keV. For those transitions with positive population inversion factor, the gain coefficients are determined and plotted against the electron density.