Reduction in transmitter power requirement for earth-to-satellite and satellite-to-earth free space optical links with spatial diversity

In the scenario of first laser communication relay satellite being launched into geostationary earth orbit, we evaluate the reduction in transmitter power requirement for earth-to-satellite and satellite-to-earth free space optical links in presence of turbulence and various weather conditions using spatial diversity technique. In channel modeling, Beer Lambert Law incorporates the weather effects. The log-normal probability density function (pdf) models weak turbulence and gamma–gamma pdf moderate to strong turbulence. Using the combined channel state pdf, bit error rate (BER) expressions are derived for on-off keying (OOK), M-ary pulse position modulation (M-PPM) and M-ary differential PPM (M-DPPM) schemes. From the BER plots, we evaluate the minimum average received power required to achieve a desired BER for all three schemes for different channel conditions. Subsequently, minimum transmitter power requirement is evaluated for both uplink and downlink using the range equation. It is observed that presence of moderate, light and thin fog cause additional power requirement. Also, among the three schemes, M-PPM scheme requires the least transmitter power, followed by M-DPPM and OOK schemes. Further, it is seen that the transmitter diversity or multiple input single output technique reduces the uplink minimum transmitter power requirement, whereas for downlink aperture averaging and receiver diversity or single input multiple output techniques can achieve the same. The power requirement for uplink is 8–10 dB more as compared to downlink in presence of turbulence and various weather conditions.     

Dislocation structure of intermetallic Ti3Al subjected to high-temperature deformation

Transmission electron microscopy was used to examine the dislocation structure of intermetallic Ti₃Al subjected to deformation at tempertures T = 1073–1273 K. The microstructure of samples subjected to high-temperature deformation is established to contain mobile superdislocations of a and 2c + a types, and single dislocations with Burgers vector [0001] are also observed on the prismatic planes. Possible models of destruction of barriers associated with 2c + a superdislocations on the pyramidal planes are discussed using the results of computer simulations of the structure of a superdislocation core in in Ti₃Al.     

Relaxation in the wealth exchange models

We examine the concept of relaxation in the wealth exchange models that are recently proposed in econophysics to interpret wealth distributions. To quantify and characterize the process of relaxation, we define an appropriate quantity and evaluate that numerically for the systems of many agents. Also, heuristic arguments are provided in support of some numerical results.     

Solvent density mode instability in non-polar solutions

We analyse the origin of the multiple long time scales associated with the long time decay observed in non-polar solvation dynamics by linear stability analysis of solvent density modes where the effects of compressibility and solvent structure are systematically incorporated. The coupling of the solute-solvent interactions at both ground and excited states of the solute with the compressibility and solvent structure is found to have important effects on the time scales. The present theory suggests that the relatively longer time constant is controlled by the solvent compressibility, while the solvent structure at the nearest-neighbour length scale dominates the shorter time constant.      

A Hybrid Anion for Ionic Liquid and Battery Electrolyte Applications: Half Triflamide,Half Carbonate

The synthesis of a new imide type anion, methylcarbonate(trifluoromethylsulfonyl)imide (MCTFSI) is described and the physicochemical properties of its sodium and N‐butyl‐N‐methyl pyrrolidinium salts as well as structural information obtained by X‐ray diffraction studies of the sodium salt are discussed in terms of charge delocalisation, coordination chemistry and electrochemical behaviour with respect to the analogous imdides bis(trifluoromethanesulfonyl)imide (TFSI) and bis(fluorosulfonyl)imide (FSI). The insight obtained from studying the new anion informs and reemphasizes the concept of weakly coordinating anions and coordination chemistry in designing electrolyte salts.     

Influence of Alkyl Chains of Modified Polysuccinimide‐Based Polycationic Polymers on Polyplex Formation and Transfection

The development of polymers with low toxicity and efficient gene delivery remains a significant barrier of nonviral gene therapy. Modification and tuning of chemical structures of carriers is an attractive strategy for efficient nucleic acid delivery. Here, polyplexes consisting of plasmid DNA (pDNA) and dodecylated or non‐dodecylated polysuccinimide (PSI)‐based polycations are designed, and their transfection ability into HeLa cells is investigated by green fluorescent protein (GFP) expressing cells quantification. All cationic polymers show lower cytotoxicity than those of branched polyethyleneimine (bPEI). PSI and bPEI‐based polyplexes have comparable physicochemical properties such as size and charge. Interestingly, a strong interaction between dodecylated polycations and pDNA caused by the hydrophobic moiety is observed in dodecylated PSI derivatives. Moreover, the decrease of GFP expression is associated with lower dissociation of pDNA from polyplexes according to the heparin displacement assay. Besides, a hydrophobization of PSI cationic derivatives with dodecyl side chains can modulate the integrity of polyplexes by hydrophobic interactions, increasing the binding between the polymer and the DNA. These results provide useful information for designing polyplexes with lower toxicity and greater stability and transfection performance.     

Studying the growth of cubic boron nitride on amorphous tetrahedral carbon interlayers

The growth of cubic boron nitride (cBN) films on bare silicon and amorphous tetrahedral carbon (ta-C) layers prepared on silicon substrates was studied. The cBN films were prepared by radio frequency magnetron sputter deposition at approximately 870 degrees C. The original ta-C interlayers were graphitized and restructured under high temperature and possibly under ion bombardment during BN deposition. The majority of graphitic basal planes were nearly perpendicular to the surface of silicon substrates. The BN films grown on these restructured carbon layers were deposited with higher content of cubic phase and did not show delamination signs. Turbostratic BN (tBN) basal planes extended carbon basal planes and their edges served as cBN nucleation sites. The cBN films grown on textured ta-C interlayers were insensitive to the ambient environment. The residual sp(3)-bonded carbon phase confined in the interlayers probably acts as a diffusion barrier preventing the oxidation of dangling bonds near BN interface and thus precludes weakening the interface as a result of volume expansion. The carbon interlayers also improve the crystallinity of the oriented tBN because they are continuation of carbon graphitic basal planes so that the volume fraction of nitrogen-void (N-void) defects in the sp(2)-bonded BN intermediate layers is reduced. The strong sp(3)-bonded carbon matrix could thereto withstand large compressive stress and facilitates deposition of thicker cBN films.     

Optical behaviour of VTE treated near stoichiometric LiNbO3 crystals

Near stoichiometric LiNbO₃ crystal wafers of thickness up to 2 mm were prepared by vapour transport equilibration technique (VTE) at various process temperatures. Crystals were characterised by measurement of the UV absorption edge, refractive index, second harmonic generation (SHG) efficiency, and conoscopy pattern analysis. The comparison of VTE treated crystals show that the blue shift in cut off wavelength occurred with the increasing process temperature (i.e. increasing Li/Nb ratio). The refractive indices were found decreasing with increasing process temperature of VTE samples. The SHG efficiency increases in the range of 1.98-2.3 times for the VTE processed samples with respected to congruent crystals. Conoscopy pattern reveals the optical homogeneity of the VTE treated crystal.     

A simple approach to intervalley transfer in electric field

Intervalley population transfer as a function of electric field has been investigated in a simple way assuming a Davydov type distribution. It has been shown that the current-voltage characteristics contain a region of negative differential conductivity and the threshold field is 3·5 kV/cm.The authors would like to thank Prof. P. C. Bhattacharya for his interest in this work. One of the authors (R.K.K) wishes to express his appreciation to the CNET, for his appointment as a Visiting Scientist, and to thank Dr. Palmier for helpful discussions.     

The effect of gamma-ray irradiation on the sorptive properties of hydrous SiO2 and ZrO2

The sorption capacities of hydrous SiO₂ and ZrO₂ for the Zn(ammine) ion have been observed to increase on irradiation with γ-rays, by ca. 4.1 and 3.8%, respectively. The rates of sorption increase differently in the irradiated exchangers, depending upon their characteristic natures; e. g. when the external concentration of the Zn(ammine) solution is 0.2M, the increase in the F value due to irradiation is more striking in the case of SiO₂ than for ZrO₂. On the other hand, at a lower external concentration of the Zn(ammine) solution (0.01M), the increase in the F value, particularly during the first five minutes, is more significant for ZrO₂.