Charge plate technique in recoil study: Evidence for collection of recoil charged species from solid targets on metal electrodes

The occurrence of charge on recoil⁵⁶Mn produced by the (n,γ) reaction in polycrystalline potassium permanganate has been examined using the ‘charge plate technique’. From considerations of capture gamma ray decay schemes and internal conversion it appears that, in a condensed medium, the recoil atom develops charge after losing much of its initial kinetic energy which allows collection on charged electrodes. Preliminary findings were presented at the International Symposium on Radiochemistry and Radiation Chemistry, RC-41 BARC, Bombay, Feb. 4–6 (1991).     

Cyclic networks with general blocking and starvation

We introducegeneral starvation and consider cyclic networks withgeneral blocking and starvation (GBS). The mechanism of general blocking allows the server to process a limited number of jobs when the buffer downstream is full, and that of general starvation allows the server to perform a limited number of services in anticipation of jobs that are yet to arrive. The two main goals of this paper are to investigate how the throughput of cyclic GBS networks is affected by varying (1) the total number of jobsJ, and (2) the buffer allocationk=(k₁..., k_m) subject to a fixed total buffer capacityK=k ₁ +... + k_m. In particular, we obtain sufficient conditions for the throughput to be symmetric inJ and to be maximized whenJ=K/2. We also show that the equal buffer allocation is optimal under the two regimes of light or heavy usage. In order to establish these results, we obtain several intermediate structural properties of the throughput, using duality, reversibility, and concavity, which are of independent interest.Research supported in part by NSF Grant No. ECS-8919818.     

DDFSGEN

This paper presents a functional compiler for the automatic design of Direct Digital Frequency Synthesizer (DDFS) integrated circuits (ICs) using a ROM based table look-up architecture. The compiler allows the user to specify high-level specifications such as the acceptable spurious response and it generates the IC architecture, floorplan, and layout. To construct the layout for different specifications, a library of parameterized macrocells has been developed in 1.2 m CMOS technology.A test chip with a quadrature DDFS module has been generated, using the compiler, and fabricated. The chip has two input signals: one is for frequency control while the other is for phase initialization. Input and output word lengths are 16 bits and 6 bits respectively. The chip complexity is approximately 12,000 transistors (DDFS core) and the die size is 4.8×2.9mm ². A maximum sample rate of 80 MHz has been attained implying a maximum sine (cosine) output frequency of 40 MHz and a frequency resolution of 1.22 kHz. The maximum spurious level measured is –46 dB.     

Polarographic reduction of some guanylpyrazoline nitrates and the effect of double layer structure on E1/2 values

Polarographic reduction of 4-arylhydrazono-1-guanylnitrate-3-methyl-2-pyrazoline-5-ones takes place in a single 4-electron transfer, giving a diffusion controlled irreversible wave in B.R. buffers of pH range 2.0–10.0. The reduction in these compounds takes place at the ?NH?N=C-bond. Effect of various cations, anions and solvent percentage on the reduction has been discussed. The effect of substituents and its correlation with the Hammett substituent constant (δ) have also been studied.     

Reverse turn induced pi-facial selectivity during polyaniline-supported cobalt(II) salen catalyzed aerobic epoxidation of N-cinnamoyl L-proline derived peptides

A novel chemo- and diastereoselective aerobic epoxidation of the N-cinnamoyl peptides catalyzed by polyaniline-supported cobalt(II) salen (PASCOS) is described. The N-cinnamoyl proline derived peptides 1 show a high pi-facial selectivity during these epoxidations. The origin of this diastereoselectivity in 1 has been attributed to (i) the propensity of the N-cinnamoyl proline amide to exist predominantly as trans rotamer in CDCl3, DMSO-d6, and CH3CN medium and (ii) existence of these peptides as organized structures (gamma- and beta-turns) due to the presence of intramolecular hydrogen bonds. An extensive solution NMR and MD simulation study on 1d and 1f indicates that the origin of the high pi-facial selectivity is due to the well-defined gamma- and beta-turns which result in the hindrance of one face of the cinnamoyl double bond in the transition state of the epoxidation reaction.     

Maximization of atomic information-entropy sum in configuration and momentum spaces

The maximum entropy procedure (MEP ) of Jaynes has been extended to the case involving constraints in complementary spaces. It has been rigorously shown that the sum of information entropies in position and momentum spaces is invariant to uniform scaling of the electron coordinates. A new MEP procedure requires that this sum of entropies must be maximized subject to the known constraints in both spaces. A specific application of this maximization procedure for synthesizing atomic-electron densities in coordinate and momentum spaces has been outlined.     

Hot atom chemistry in oxyanion targets,part II1: Recoil behaviour of56Mn in permanganates

Fractional precipitation techniques have been utilized to separate the lower valent and parent forms of⁵⁶Mn in permanganate targets and an attempt is made to study a few aspects of chemical stabilization of recoil⁵⁶Mn in permanganates. Ammonium permanganate, recoil behaviour of which has not been studied previously, is chosen as one of the targets along with the potassium permanganate for initial retention and also for isothermal annealing.⁵⁶Mn initial retentions of about 12% and about 4% are obtained for potassium and ammonium permanganate, respectively, by activation from a Ra–Be neutron source. A usual trend for KMnO₄ and the reduction of recoil fragments by ammonium ions in NH₄MnO₄ are seen through the isothermal annealing study.     

Formulation–composition map of a lecithin-based emulsion

Formulation–composition map is an interesting tool to predict the nature of an emulsion, stability, viscosity and nevertheless to decide the mixing protocol of its ingredients. Information based on optimum formulation (environmental conditions at which the affinity of an emulsifier for oil and for aqueous phase is same), which is depicted through hydrophilic–lipophilic deviation (HLD) concept, is necessary to make a formulation–composition map of an emulsion. In order to apply this concept in food emulsions, it is necessary to determine characteristic constants of each component of the system, i.e. the aqueous phase, the oil phase and the emulsifier at equilibrium. In this work formulation–composition map of a sunflower oil–water–lecithin system, based on the knowledge of phase behavior of lecithin at equilibrium and emulsification, was made. The shape of inversion line on formulation–composition map was not the classical stair type rather an almost vertical inversion line at water-fraction (f_w) near 0.20 was observed. It was supposed to be linked to the viscosity of oil phase which was 50 times the viscosity of aqueous phase. Additionally, emulsions were of oil-in-water (O/W) type for f_w higher than 0.20, but their viscosity and the drop size behavior with respect to salt concentration as formulation variable did not show the existence of transitional inversion line on formulation–composition map. Such map in advance can certainly facilitate the guidelines for dynamic emulsification.