Enhanced coding for exponentially distributed signals using suprathreshold stochastic resonance

Our previous work on stochastic resonance (SR) in threshold based systems proved that the SR effect is dependent on the nature of the input signal distribution; more specifically, for certain types of signal distribution SR is not observed [Das A, Stocks NG, Nikitin A, Hines EL. Quantifying stochastic resonance in a single threshold detector for random aperiodic signals. Fluctuation Noise Lett 2004;4:L247–65]. Here we show that suprathreshold stochastic resonance (SSR) – a novel and distinct form of SR – removes this limitation and hence leads to the conclusion that SSR can probably enhance the transmission of signals of any distribution and amplitude. SSR effects are studied in a parallel array of identical nonlinear threshold based devices. A double exponential signal distribution is chosen because this distribution did not demonstrate conventional SR effects in a single threshold device [Das A, Stocks NG, Nikitin A., Hines EL. Quantifying Stochastic resonance in a single threshold detector for random aperiodic signals. Fluctuation and Noise Letters 2004;4:L247-L265.]. SSR as a possible mechanism for enhancing transmission of speech signals in the human ear is also discussed.     

Hexavalent Chromium-Thioacetamide Redox System Initiated Polymerization of Acrylonitrile

Polymerization of acrylonitrile initiated by the Cr⁶⁺/thioacetamide redox system was studied in nitrogen atmosphere in the temperature range 35–45°C. The rate of polymerization and the rate of Cr⁶⁺ ion disappearance were measured. The effect of certain water-miscible organic solvents, neutral electrolytes, and complexing agents on the rate of polymerization was investigated. Chromic acid alone did not initiate the polymerization under deaerated and undeaerated conditions. Depending on the results obtained, a suitable kinetic scheme was proposed and various rate parameters were evaluated.     

Benzylation and Allylation of Naphthols Using Amberlyst-15

A simple and efficient method has been developed for benzylation and allylation of naphthols by treatment of the compounds with benzylic and allylic alcohols, respectively, in the presence of amberlyst-15. Several heterogeneous catalysts were screened for the reaction, and amberlyst-15 was found to be most effective.     

A Novel Synthetic Route to 1-Aryltetralin Lignan Lactone Via Intermolecular Cycloaddition with O-qu Inodimethane

Deoxyisosikkimotoxin 8 has been synthesized by an inter-molecular Diels-Alder approach.     

Efficient Bromination of Alkenes and Alkynes Using Potassium Bromide and Diacetoxy Iodobenzene

Bromination of alkenes and alkynes has efficiently been carried out at room temperature in short reaction times using KBr and diacetoxy iodobenzene in CH₂Cl₂-H₂O (1:1) to prepare the corresponding trans-dibromo compounds in excellent yields.     

Determination of the k 0-values for 75Se, 110mAg, 115Cd–115mIn, 131Ba, and 153Sm by irradiation in highly thermalized neutron flux

The k ₀-values were determined for five high Q ₀(n,γ) reactions, including ⁷⁴Se(n,γ) ⁷⁵Se, ¹⁰⁹Ag(n,γ) ^110mAg, ¹¹⁴Cd(n,γ) ¹¹⁵Cd–^115mIn, ¹³⁰Ba(n,γ) ¹³¹Ba, and ¹⁵²Sm(n,γ) ¹⁵³Sm. These determinations were carried out under favorable experiment conditions: the irradiations were performed in a highly thermalized neutron flux, the irradiated target samples were counted at a far distance from HPGe detector with an efficiency carefully calibrated, and the k ₀-values were calculated against an internal comparator. When compared to the new values from this work, the 2003 recommended ^110mAg k ₀-values are confirmed. The other confirmed recommended k ₀-value is that of ⁷⁵Se 400.7 keV line. However, for the other ⁷⁵Se γ-lines, the new k ₀-values are 4–10 % higher. It is assumed that an inaccurate efficiency calibration was used when the recommended k ₀-values were measured. For the other three nuclides, the new k ₀-values are higher by 4 % for the ¹¹⁵Cd–^115mIn γ-lines, lower by 6–8 % for the ¹³¹Ba γ-lines, and lower by 8.8 % for the ¹⁵³Sm 103.2 keV γ-line.     

Effect of Hall current and chemical reaction on MHD flow along a fluctuating porous flat plate with internal heat absorption/generation

Effect of Hall current on the unsteady free convection flow of a viscous incompressible and electrically conducting fluid past a fluctuating porous flat plate with internal heat absorption/generation in the presence of foreign gasses (such as H₂, CO₂, H₂O, NH₃) was investigated. The results are discussed with the effect of the parameters m, the Hall current, Mt, the hydromagnetic parameter, G _r the Grashoff number for heat transfer, G _c , the Grashoff number for mass transfer, S, the internal heat absorption/generation parameter, α, the transpiration parameter, S _c , the Schmidt parameter, and K _c the chemical reaction parameter for Prandtl number P _r = 0.71, which represents air. Further, the present study accounts for the 1st order chemical reaction affecting the flow characteristics. The governing equations are solved in closed form applying Hh _n (x) function. The effects of pertinent parameters characterizing the flow field are discussed with the help of graphs and tables. The important observation of the present study is that heat generation/absorption modifies the flow of current simultaneously to a magnetic force and thermal bouncy force. Heat generation combined with blowing leads to a sharp fall of temperature.     

Multiple-pulse coherence enhancement of solid state spin qubits

We describe how the spin coherence time of a localized electron spin in solids, i.e., a solid state spin qubit, can be prolonged by applying designed electron spin resonance pulse sequences. In particular, the spin echo decay due to the spectral diffusion of the electron spin resonance frequency induced by the non-Markovian temporal fluctuations of the nuclear spin flip-flop dynamics can be strongly suppressed using multiple-pulse sequences akin to the Carr-Purcell-Meiboom-Gill pulse sequence in nuclear magnetic resonance. Spin coherence time can be enhanced by factors of 4-10 in GaAs quantum-dot and Si:P quantum computer architectures using composite sequences with an even number of pulses.     

Effect of in-medium parameters of ρ meson in its photoproduction reactions on nuclei

There exist model calculations showing the modification of the hadronic parameters of ρ meson in the nuclear environment. From these parameters, we extract the ρ-meson-nucleus optical potential and show the medium effect due to this potential on the ρ-meson mass distribution spectra in the photonuclear reactions. The calculated results reproduced reasonably the measured e ⁺ e ⁻ invariant mass, i.e., ρ-meson mass, distribution spectra in γ, ρ ⁰ → e ⁺ e ⁻ reactions on nuclei.