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1
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Antihydrogen Formation in Low Energy Collision of Positron with Antiproton

100%
Bhattacharyya S.
Acta Physica Polonica A
|
1994
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vol. 86
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issue 3
297-308
EN
In the present paper two-body radiative recombination rate for the production of antihydrogen (H̅) in a merged beam of slow positrons (e^{+}) and antiprotons (p¯) is studied in the light of a two-step process, which consists of capture in an excited state of H̅ with subsequent decay to the ground state and emission of a photon. Computation is done using the field theory and the Coulomb gauge. Importance of the two-step radiative recombination process relative to the well-known spontaneous photorecombination process, on the two-body radiative recombination rate for antihydrogen formation, is discussed. The present result predicts higher contribution from the two-step radiative recombination process as compared to the spontaneous photorecombination process to the rate of cold antihydrogen formation with the relative collision energy below 0.01 Rydberg, near which experiments are being conducted. However, above 0.1 Rydberg the spontaneous photorecombination process dominates over the two-step radiative recombination process. The present result is valid, as well, for the formation of hydrogen atom due to collision between slow electron and proton.
2
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Angular Differential Cross-Section for Electron Transfer in ION-ION Collision

71%
Bhattacharyya S., Bhattacharyya S., Mitra S.
Acta Physica Polonica A
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1998
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vol. 93
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issue 4
601-610
EN
Angular differential cross-sections for the formation of He^{0} in collision between fast He^{+} ions are calculated using distorted wave Coulomb-Born approximation. The interaction potentials satisfy necessary Coulomb boundary conditions. In absence of any other theoretical results the present results are compared with the existing experimental data.
3
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Three-Particle Recombination at Low Temperature: a QED Approach

64%
Bhattacharyya S., Roy A.
Acta Physica Polonica A
|
2001
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vol. 100
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issue 1
23-40
EN
A theoretical study of the three-body recombination of proton and electron in presence of a spectator electron with electronic beam at near-zero temperature is presented using field theory and invariant Lorentz gauge. Contributions from the Feynman diagrams of different orders give an insight into the physics of the phenomena. Recombination rate coefficient is obtained for low lying principal quantum number n=1 to 10. At a fixed ion beam temperature (300 K) recombination rate coefficient is found to increase in general with n, having a flat and a sharp peak at quantum states 3 and 5, respectively. In absence of any other theoretical and experimental results for low temperature formation of H-atom by three-body recombination at low lying quantum states, we have presented the theoretical results of Stevefelt and group for three-body recombination of deuteron with electron along with the present results. Three-body recombination of antihydrogen in antiproton-positron plasma is expected to yield similar result as that for three-body recombination of hydrogen formation in proton-electron plasma. The necessity for experimental investigation of low temperature three-body recombination at low quantum states is stressed.
4
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Photoionization of He - a Field Theoretic Approach

64%
Bhattacharyya S., Mitra S.
Acta Physica Polonica A
|
2001
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vol. 100
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issue 4
505-516
EN
The present paper deals with the field theoretic study of single ionization cross-sectionsσ_{ph} and σ_C of helium due to photoelectric effect and the Compton scattering, respectively, by photons of energy lying between 0-12 keV. In this energy range,σ_{ph} gradually decreases with energy whileσ_C gradually increases. There is a crossover point around 6.5 keV where σ_{ph}=σ_C=10^{-24} cm^2. Near about this crossover point σ_{ph} andσ_C curves are like mirror images. The ratio σ_C/σ_{ph} lies between 0.3 to 1.5 in the energy range under consideration. The present results are compared with existing theoretical results.
5
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Electron-ion Recombination at Sub-zero Temperature

64%
Bhattacharyya S., Roy A.
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vol. 95
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issue 6
911-920
EN
In this paper we have considered two-step radiative recombination channel over the existing spontaneous radiative recombination channel to explain the causes of experimentally obtained enhanced recombination rate at sub-zero temperature. The existing recombination rate due to spontaneous radiative recombination is 4 times smaller than the recent experimental data. In the case of Ne^{10+} we obtain good agreement between theory and experiment when contribution from two-step radiative recombination channel is added to the spontaneous radiative recombination channel. Recombination rate for Ar^{18+} is calculated. The radiation spectrum given out by two-step radiative recombination and spontaneous radiative recombination in the recombination rate processes are discrete spectrum and continuous spectrum, respectively. Experimental identification of these two channels through the spectral signatures is suggested.
6
Content available remote

Single Ionization of He by High-Energy Proton and Antiproton. A QED Approach

64%
Bhattacharyya S., Pathak K.
Acta Physica Polonica A
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2000
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vol. 98
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issue 4
335-344
EN
We have investigated single ionization of He by fast proton and antiproton using a QED approach. A field theoretical calculation gives the total cross-section of He in single ionization, from which it is seen that the projectile p^{+} or p^{-} gives almost the same values of cross-section. We have also compared our results with other theoretical and experimental results available in this context yet. Behaviour of the cross-section at a lower spectrum of projectile energy is discussed.
7

Melatonin action on thyroid activity in the soft-shelled turtle, Lissemys punctata punctata

51%
Sarkar S., Sarkar N. K., Bhattacharyya S., Das P.
Folia Biologica
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1997
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vol. 45
109-112
EN
Adult female turtles (Lissemys punctata punctata) were treated with pineal indoleamine melatonin (100 mug/100 g) or the antithyroid agent, methylthiouracil (100 mug/100 g) or melatonin together with methylthiouracil (100 mug of each drug/100 g) for 12 days. Melatonin alone inhibited thyroid activity as evidenced by reductions in the gland weight, follicular epithelial cell height, thyroid peroxidase, and plasma thyroxine levels. Methylthiouracil caused hyperplasia of the gland, although it inhibited thyroid activity and reduced thyroid peroxidase and plasma thyroxine levels. Melatonin together with methylthiouracil produced changes similar to those obtained with melatonin alone. The results indicate that melatonin probably exerts inhibitory effects influences on both thyrotropin release from the pituitary and the activity of the thyroid itself in turtles.
8
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Angular Differential Cross-Sections for Electron Transfer in Collisions between Proton and He^{+}(1s) Ions

51%
Bhattacharyya S., Pathak K., Becker A., Faisal F.
Acta Physica Polonica A
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1996
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vol. 90
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issue 6
1143-1153
EN
Angular differential cross-sections for the formation of H, as a result of electron capture by proton from He^{+}(1s) at the centre-of-mass energies from 4 to 24 keV, are calculated using distorted wave Coulomb-Born approximation. The total interaction potentials in the prior-interaction channel and in the post-interaction channel are considered. Coulomb boundary conditions are taken care of with the proper choice of the perturbation potentials in both the prior and the post channels. A prior-post discrepancy is noted. Existing theoretical results are presented along with the present results.
9
Content available remote

Photoconductivity Study of Sputter-Deposited Cu_2O Films

33%
Bhattacharyya S., Reppin D., Sanguino P., Ayouchi R., Polity A., Schwarz R., Hofmann D., Meyer B.
Acta Physica Polonica A
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2011
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vol. 120
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issue 6A
A-11-A-14
EN
Cuprous oxide (Cu_2O) thin films were deposited by radio frequency sputtering technique on fused silica substrates. The X-ray diffraction study of the Cu_2O samples showed reflections from (111) and (200) planes of cubic Cu_2O. The samples were then annealed at 1008 K in nitrogen (N_2) atmosphere. Annealed samples indicated strain relaxation. The samples were then characterized optically by measuring the transmittance using an ultraviolet-visible-near infrared photospectrometer. The band gap of the as-deposited samples were found to be ≈ 2.1 eV, whereas the annealed samples had a band gap of ≈ 2.6 eV. The transient photocurrent decay measurements of the annealed films indicated slow non-exponential power law decays in several time windows, indicating multiple trapping of the carriers in the deep defects within the band gap. The steady-state photo and dark current measurement and persistent photocurrent (PPC) was carried out on the annealed samples. In general, the photocurrent was found to be much smaller than the dark current. The steady-state and transient photocurrent measurements were utilized to determine the carrier lifetime-mobility product, 〈μτ 〉 of the samples and to determine the carrier mobility, 〈μ 〉.
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