Experimental investigation of the performance of a Ranque–Hilsch vortex tube with regard to a plug located at the hot outlet

In this study, effects of position, diameter (5, 6, 7, 8 mm) and angle (30°–180°) of a mobile plug, located at the hot outlet side in a Ranque–Hilsch Vortex Tube (RHVT), were determined experimentally for best performance. In addition to plug parameters, effects of supply pressure (200–420 kPa) and number of nozzles (2, 4, 6) were also studied. The internal diameter (D) of the vortex tube used in the experiments was 9 mm; the ratio of the length of the vortex tube to its diameter (L/D) was 15. Four different plug locations were studied. The maximum difference in the temperatures of hot and cold streams was obtained for the plug diameter of 5 mm, tip angles of 30° and 60°, 4 nozzles and by keeping the plug location at the far extreme end.     

A space-time block-coded OFDM scheme for unknownfrequency-selective fading channels

We introduce a space-time block-coded orthogonal frequency-division multiplexing (STBC-OFDM) selective fading channels which does not require channel knowledge either at the transmitter or at the receiver. The decoding algorithm is based on generalized maximum-likelihood sequence estimation. We investigate the performance of the proposed scheme over two-tap Rayleigh fading channels. Simulation results show the performance to be near optimum     

Stability effect of some organic and inorganic additions in the EMITFSI–LiTFSI nanocomposite electrolytes for lithium-air batteries

Since the EMITFSI/LiTFSI electrolyte possess low viscosity, high ionic conductivity and thermal stability properties, in this study, 1M 1-ethyl-3-methyl-imidazoliumbis (trifluoromethanesulfonyl) imide (EMITFSI)/Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) based electrolytes were studied for Li-air battery cells. A series of electrolytes was studied with organic compound additions of Poly(ethylene oxide) (PEO) and polyvinylidene fluoride (PVDF). Nano Al₂O₃ particles with 50 nm in size were also used in 1.0 wt% as inorganic additive to provide stability of the polymer added electrolytes. The nanocomposite electrolytes were prepared in a glove box under dry argon atmosphere. Porous electrode, Gas Diffusion Layer (GDL), was used as cathode, a lithium disk was used as anode while glass fiber was used as the separator in ECC-air test cell. The cells were cyclically tested using 0.1 mA/cm² current density over a voltage range of 1.5–4.5 V. Electrochemical impedance spectroscopy measurements was applied to investigate the effect of the PVDF/Al₂O₃ and PEO/Al₂O₃ nano additives on the resistivity of the electrolyte. After the electrochemical cycling test, the morphologies of the cathodes (GDL) were analyzed using scanning electron microscopy, X-ray diffraction analysis to determine reaction products and lithium compounds during cycling test.     

The effects of different cement dosages, slumps and pumice aggregate ratios on the compressive strength and densities of concrete

Compressive strengths of concretes made up of mixtures of pumice aggregate (PA) and normal aggregate were measured. To determine the effect of PA ratio, different cement dosage and slumps on the compressive strength of concrete, (1) 25%, 50%, 75% and 100% pumice ratios were used instead of normal aggregate by volume, (2) 200, 250, 350, 400 and 500 kg/m³ cement dosages were used and (3) 3±1, 5±1 and 7±1 cm slumps were also used in this study.The analysis of the test results leads to the conclusion that PA decreased the density of concretes up to 41.5% and reductions occurred due to the increase of the PA ratio in the mixes. With the increase of cement dosage in the mixes, both density and compressive strength of concretes increased up to 3.2% and 265%, respectively, when compared to the control sample that contain 200 kg/m³ cement dosage. The effect of the slump on the density and compressive strength was varied. Elasticity moduli were decreased with an increase of PA ratio and increased with an increase of cement dosage. Water absorption improved with an increase of cement content.     

A reversible data hiding scheme based on graph neighbourhood degree

Abstract

The perceptibility and capacity are two vital criteria of data hiding scheme. Concerning these criteria, data hiding algorithm used images as cover object based on the graph theory is proposed in this study. Images are quantised according to determined range and then quantised images are divided into n × n sized blocks. Each block is accepted as a graph and vertexes which have the same quantisation value are accepted as neighbours. Neighbourhood degrees of vertexes are calculated and indices of vertexes that have a neighbourhood degree over the threshold value are stored in the codebook. Pixel values indicated by these indices in the codebook are used for data hiding process. In this algorithm, there is no need for edge extraction because of hiding data to pixels containing vertexes having high neighbourhood degrees. The proposed method is compared with similar methods in literature in terms of the perceptibility and capacity. More successful results are provided than the others.     

Impact of receive diversity on the performance of amplify-and-forward relaying under APS and IPS power constraints

In this letter, we investigate the impact of receive diversity on the error rate performance of a relay-assisted cooperative scheme in which the relay terminal is operating in amplify-and-forward (AF) mode under the so-called average power scaling (APS) and instantaneous power scaling (IPS) constraints. We assume that the source and relay terminals are each equipped with one antenna, while the destination terminal is equipped with N receive antennas. Through the derivation of symbol error rate expressions, we demonstrate that the maximum achievable diversity orders under APS and IPS constraints are N+1 and 2N, respectively.