Chromosome aberration analysis in radiotherapy patients and simulated partial body exposures: biological dosimetry for non-uniform exposures

Chromosome aberration analysis was carried out in peripheral blood lymphocytes of cancer patients following radiotherapy of lungs, cervix and spine. Radiotherapy in the pelvic region involving large doses (6 Gy) showed an overdispersed distribution of dicentrics. However, when the doses were fractionated (three fractions of 2 Gy) distribution was found to be near Poisson. Spine irradiation covering almost all the lymphocytes pools, indicated a Poisson distribution. The data show that depending on the sites of exposure, the distribution of dicentrics in cells varies and hence there is a non-uniform distribution of lymphocytes in the body. The average dose to the lymphocytes was found to be one sixth of the partial body dose. Based on the non-Poisson distribution of aberrations, the fraction of lymphocytes irradiated, mean dose to the fraction and part of the body exposed was calculated in a case of acute 6 Gy pelvic irradiation. The fraction of cells irradiated was calculated to be 4.11% and the portion of the body exposed was approximately 16.8%. The dose to the irradiated fraction was found to be 5.4 Gy, which is in agreement with the given dose of 6 Gy. In simulated exposures the u values increased systematically with the decrease in fraction of irradiated cells and the calculated dose to the fraction was also in good agreement with the true dose.     

Nonresonant Microwave Absorption in Bi2212 Single Crystal: Second Peak and Microwave Power Dependence

Nonresonant microwave absorption (NMA) measurements were carried out at liquid-nitrogen temperature on a high quality Bi2212 single crystal, as a function of microwave power in three mutual orientations of crystal ab plane, dc field (H_dc), and microwave magnetic field (H_w). NMA line shapes in Bi2212 crystal are complicated with a narrow peak (P₁ peak) located near zero field, followed by a much broader second peak (P₂ peak) in the particular orientations. More excitingly, we show that the P₂ peak qualitatively evolves as a function of microwave power in the orientation of H_dc ab plane, plane, and H_dc H_w. In this configuration, as the microwave power is progressively increased, the broad P₂ peak first gets smeared off and then a multiple peak structure appears, which develops into another narrower second peak (P_s-peak) at high enough microwave powers. In the orientation of plane, H_w ab plane, and H_dc H_w, we report for the first time the appearance and disappearance of a new second peak (P₂-like peak) as a function of microwave power.     

Buck-boost converter feedback controller design via evolutionary search

Buck-boost converters are switched power converters. The model of the converter system varies from the ON state to the OFF state and hence traditional methods of controller design based on approximate transfer function models do not yield good dynamic response at different operating points of the converter system. This article attempts to design a feedback controller for a buck-boost type dc–dc converter using a genetic algorithm. The feedback controller design is perceived as an optimisation problem and a robust controller is estimated through an evolutionary search. Extensive simulation and experimental results provided in the article show the effectiveness of the new approach.     

Performance evaluation of a novel sampling-based texture synthesis technique using different sized patches

We propose a novel sampling-based texture synthesis algorithm called Multipatch, which improves on the results of previous sampling-based algorithms by using patches of different size, and by minimizing global pasting errors. A key feature of the proposed algorithm is that it always converges to a local minimum. Multipatch, the patchwork algorithm, and Wei and Levoy’s multi-resolution texture synthesis algorithm, which is based on a tree-structured vector quantization method, are statistically analyzed and subjectively evaluated. The results of simulations show that the patchwork algorithm yields a perceptually acceptable texture in a shorter expected running time than the other two algorithms; however, Multipatch is the most efficient in terms of obtaining a good quality texture image.     

Perspectives on SnSe-based thin film solar cells: a comprehensive review

Currently, selenium (Se)-based compound semiconductors (CISe, CIGSe and CZTSe) are considered as the active materials in the photovoltaic world. However, these materials exhibit couple of issues related to stoichiometry maintenance and scarcity of their constituent elements (In, Ga), which limit their massive production for future energy demands. These issues could be rectified by introducing a non-toxic, inexpensive and earth-abundant binary material. One such material is a tin monoselenide (SnSe), which exhibits a high chemical stability along with attractive physical properties namely, suitable band gap (1.3 eV), high absorption coefficient (10⁵ cm^?1) and p-type conductivity. These properties indicate SnSe as a competitive substitute in place of conventional absorbers in thin film solar cells. Despite of its remarkable properties, only a few reports were published on the fabrication of SnSe-based solar cells with poor efficiency (≤1 %). This indicates a need to review on the physical properties of SnSe and its device structures in a deeper sense. In this context, the present review describes the different methods of preparation of SnSe films and their physical properties along with the details of photovoltaic device fabrication. We highlighted the different factors that are limiting the efficiency of SnSe solar cells, and a few suggestions were included to overcome these problems for further improvement of these cells. This review will enrich and stimulate the readers to further investigate the growth of SnSe thin films and their devices, for the development of >20 % efficient SnSe solar cells.     

Phase tuning of zirconia nanocrystals by varying the surfactant and alkaline mineralizer

The influence of cationic (CTAB)/neutral polymeric (PVP) surfactants and strong (NaOH)/weak (NH₄OH) alkaline mineralizers on phase stabilization of zirconia nanocrystals synthesized by chemical precipitation is investigated. X-ray diffraction and micro-Raman analysis of the as-prepared samples show that tetragonal zirconia is predominant as compared to monoclinic using PVP with NH₄OH. The phases are also evident from lattice fringes of TEM images and the corresponding SAED pattern. Photoluminescence spectra of samples reveal oxygen vacancies present in the zirconia nanocrystals. The group H Raman vibration modes identified are attributed to surface defects and quantum size effects of nanocrystals. The phase stabilization of zirconia nanocrystals is explained using the polymerization rate of tetramers during synthesis. The rate can be varied by proper selection of the surfactant and the mineralizer. A slow polymerization rate with PVP and NH₄OH favors the formation of tetragonal zirconia. Thus, a simple method for phase stabilization of zirconia nanocrystals at room temperature using chemical precipitation by varying the surfactant and the mineralizer is demonstrated.     

Kinetic studies of sulfuric acid decomposition over Al–Fe2O3 catalyst in the sulfur-iodine cycle for hydrogen production

The decomposition of H₂SO₄ to produce SO₂ is the reaction with the highest energy demand in the sulfur-iodine cycle and it shows a large kinetic barrier. In the present study, alumina supported iron (III) oxide has been chosen for a detailed kinetic study. Experiments were carried out in the temperature range of 1023 K–1173 K using space hour velocities in the range of 0.146–0.731 kmol/kg-h in a quartz tube double stage continuous flow fixed bed reactor with 98% sulfuric acid feed over alumina supported Fe₂O₃ catalyst, nitrogen as inert carrier gas. From the homogeneous kinetic analysis, the apparent activation energy (E_A) was found to be 138.6 kJ/mol. This high activation energy indicates that the experiments were conducted in a kinetic controlled regime. The catalyst was well characterized by XRD, BET, TPR/TPO, SEM and FT-IR before and after reaction.     

Efficiency as a function of MEQ-CWT for large area germanium detectors using LLNL phantom

The lung counting system at Kalpakkam, India, used for the estimation of transuranics deposited in the lungs of occupational workers, consists of an array of three large area germanium detectors fixed in a single assembly. The efficiency calibration for low energy photons was carried out using 2?1Am and 232Th lung sets of Lawrence Livermore National Laboratory phantom. The muscle equivalent chest wall thickness (MEQ-CWT) was derived for the three energies 59.5, 75.95 (average energy of 232Th) and 238.9 keV for the series of overlay plates made of different adipose mass ratios. Efficiency as a function of MEQ-CWT was calculated for individual detectors for the three energies. Variation of MEQ-CWT from 16 to 40 mm resulted in an efficiency variation of around 40 % for all the three energies. The array efficiency for different MEQ-CWT ranged from 1.4×10?3 to 3.2×10?3, 1.5×10?3 to 3.3×10?3 and 1.1×10?3 to 2.3×10?3 for 59.5, 75.95 and 238.9 keV, respectively. In the energy response, efficiency was observed to be maximum for 75.95 keV compared with 59.5 and 238.9 keV.