Microstructural studies on lattice imperfections in irradiated titanium and Ti-5 Pct Ta-2 Pct Nb by X-ray diffraction line-profile analysis

Microstructural parameters such as the average domain size, effective domain size at a particular crystallographic direction, and microstrain within the domains of titanium and Ti-5 pct Ta-2 pct Nb, irradiated with 116 MeV O⁵⁺ ion, have been characterized as a function of dose by X-ray diffraction line-profile analysis (XRDLPA) using different model-based approaches. The dislocation density and stacking-fault probabilities have also been estimated from the analysis. The analysis revealed that there was a significant decrease of the average domain size with dose as compared to the unirradiated sample. The estimated values of dislocation density increased significantly for the irradiated samples and were found to be an order of magnitude more as compared to the unirradiated one. However, the dislocation density became saturated with an increase in dose. The deformation (stacking-fault) probabilities were found to be negligible even with the increase in dose of irradiation.     

NMR structure of neuromedin C, a neurotransmitter with an amino terminal CuII-, NiII-binding (ATCUN) motif

The structure of neuromedin C, a 10-residue bombesin-like neuropeptide with the sequence Gly-Asn-His-Trp-Ala-Val-Gly-His-Leu-Met-NH2, has been investigated. Like human serum albumin, neuromedin C contains the amino-terminal CuII-, NiII-binding (ATCUN) motif which has high affinity for CuII and NiII. The solution structure of the NiII-peptide complex has been calculated based on 2D ROESY data obtained at 25 degrees C, using a hybrid distance geometry-simulated annealing approach. Comparison of 1H, 13C and 15N chemical shifts and ROESY data in the presence and absence of NiII demonstrates that the metal binds at the N-terminus of the peptide, leading to a conformational change. The metal complex adopts a conformation comprising two connected turns including residues 1Gly to 3His and 5Ala to 8His. The first turn corresponds to the NiII coordination ligands in a square planar conformation, and the second reflects the interaction between 4Trp and 8His. The results may have important physiological implications in the phenomenon of neurotransmission.     

Extraction of assam coal through reductive acylation

Assam coal was reductively acylated by using zinc dust, acetic acid and phenol. This reaction resulted in enhanced extractability of coal in quinoline. The residue extracted after the first step was further reductively acylated which rendered it further extractable in quinoline. Three successive steps could solubilize the coal to the extent of 58 per cent on ash balance basis.     

Small-signal model for the single-electron transistor: part I

A simple small-signal model of the single-electron transistor is presented. The terminal voltage variations are considered to be sufficiently small to result in small current variations that can be expressed using linearized relations. The derivation of such relations and the development of an equivalent circuit to represent them are presented. Two-port analysis of the small-signal circuit of the single-electron transistor is proposed and explained using various parameters such as impedance parameters, admittance parameters, and hybrid parameters. The variation of the magnitude of these parameters is plotted with respect to frequency. The transconductance and drain resistances and their frequency variation are also discussed. The effect of parasitic capacitance on the proposed small-signal model is also analyzed.     

Tensile Behavior of Single-Crystal Tin Whiskers

The growth of metallic (predominantly Sn) whiskers from pure metallic platings has been studied for over 50 years. While the phenomenon of Sn whiskering has been studied for decades, very little is known about the mechanical properties of these materials. This can be attributed to the difficulty in handling, gripping, and testing such fine-diameter and high-aspect-ratio whiskers. We report on the stress–strain behavior of Sn whiskers inside a dual-beam focused ion beam (FIB) with a scanning electron microscope (SEM). Lift-out of the whiskers was conducted in situ in the FIB, and the whiskers were tested using a microelectromechanical system tensile testing stage. Using this technique, the whiskers had minimum exposure to ambient air and were not handled by hand. SEM images after fracture enabled reliable calculation of the whisker cross-sectional area. Tests on two different whiskers revealed relatively high tensile strengths of 720 MPa and 880 MPa, respectively, and a limited strain to failure of ～2% to 3%. For both whiskers, the Young’s modulus was between 42 GPa and 45 GPa. It is interesting to note that the whiskers were quite strong and had limited ductility. These findings are intriguing and provide a basis for further work to understand the effect of Sn whisker mechanical properties on short circuits in electronics.     

Prioritized Medium Access Control in Cognitive Radio Ad Hoc Networks: Protocol and Analysis

Cognitive radio (CR) technology enables opportunistic exploration of unused licensed channels. By giving secondary users (SUs) the capability to utilize the licensed channels (LCs) when there are no primary users (PUs) present, the CR increases spectrum utilization and ameliorates the problem of spectrum shortage. However, the absence of a central controller in CR ad hoc network (CRAHN) introduces many challenges in the efficient selection of appropriate data and backup channels. Maintenance of the backup channels as well as managing the sudden appearance of PUs are critical issues for effective operation of CR. In this paper, a prioritized medium access control protocol for CRAHN, PCR-MAC, is developed which opportunistically selects the optimal data and backup channels from a list of available channels. We also design a scheme for reliable switching of a SU from the data channel to the backup channel and vice-versa. Thus, PCR-MAC increases network throughput and decreases SUs’ blocking rate. We also develop a Markov chain-based performance analysis model for the proposed PCR-MAC protocol. Our simulations, carried out in \(NS-3\) , show that the proposed PCR-MAC outperforms other state-of-the-art opportunistic medium access control protocols for CRAHNs.