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This paper describes a model of electron energization and cyclotron-maser emission applicable to astrophysical magnetized collisionless shocks. It is motivated by the work of Begelman, Ergun and Rees [Astrophys. J. 625, 51 (2005)] who argued that the cyclotron-maser instability occurs in localized magnetized collisionless shocks such as those expected in blazar jets. We report on recent research carried out to investigate electron acceleration at collisionless shocks and maser radiation associated with the accelerated electrons. We describe how electrons accelerated by lower-hybrid waves at collisionless shocks generate cyclotron-maser radiation when the accelerated electrons move into regions of stronger magnetic fields. The electrons are accelerated along the magnetic field and magnetically compressed leading to the formation of an electron velocity distribution having a horseshoe shape due to conservation of the electron magnetic moment. Under certain conditions the horseshoe electron velocity distribution function is unstable to the cyclotron-maser instability [Bingham and Cairns, Phys. Plasmas 7, 3089 (2000); Melrose, Rev. Mod. Plasma Phys. 1, 5 (2017)].
Socio-behavioural factors and pathogens associated with childhood diarrhoea are of global public health concern. Our survey in 696 children aged ⩽2 years in rural West Bengal detected rotavirus as sole pathogen in 8% (17/199) of diarrhoeic stool specimens. Other organisms were detected along with rotavirus in 11% of faecal specimens. A third of the children with rotavirus diarrhoea, according to Vesikari score, had severe illness. The top four rotavirus genotypes were G9P (28%), G1P (19%), G2P (14%) and G8P (8%). In the multivariate model, the practice of ‘drawing drinking water by dipping a pot in the storage vessel’ [adjusted odds ratio (aOR) 2·21, 95% confidence interval (CI) 1·03–4·74, P = 0·041], and ‘children aged ⩽6 months with non-exclusive breastfeeding’ (aOR 2·07, 95% CI 1·1–3·82, P = 0·024) had twice the odds of having diarrhoea. Incidence of rotavirus diarrhoea was 24/100 child-years in children aged >6–18 months, 19/100 child-years in children aged >18–24 months and 5/100 child-years in those aged ⩽6 months. Results have translational implications for future interventions including vaccine development.
Investigation of optical absorption in ∼25μm thick, monocrystalline silicon (Si) substrates obtained from a novel exfoliation technique is done by fabricating solar cells with single heterojunction architecture (without using intrinsic amorphous silicon layer) with diffused back junction and local back contact. The ease of process flow and the rugged and flexible nature of the substrates due to thick metal backing enables use of various light-trapping and optical absorption enhancement schemes traditionally practiced in the industry for thicker (>120μm) substrates. Optical measurement of solar cells using antireflective coating, texturing on both surfaces, and back surface dielectric/metal stack as mirror to reflect the long wavelength light from the back surface show a very low front surface reflectance of 4.6% in the broadband spectrum (300nm-1200nm). The illuminated current voltage (IV) and external quantum efficiency (EQE) measurement of such solar cell shows a high integrated current density of 34.4mA/cm2, which implies significant internal photon reflection. Our best cell with intrinsic amorphous silicon (i-a-Si) layer with only rear surface textured shows an efficiency of 14.9%. EQE data shows improved blue response and current density due to better front surface passivation. Simulations suggest that with optimized light trapping and surface passivation, such thin c-Si cells can reach efficiencies >20%.
Analyses of sulphur isotope compositions in sedimentary pyrites from the Vindhyan, Chattisgarh and Cuddapah basins show heavy δ34S (> +25 ‰) values during the Mesoproterozoic. The data provide evidence in support of a hypothesized global Proterozoic sulphidic anoxic ocean where very low concentrations of marine sulphate, bacterially reduced in closed systems, produced δ34S values in pyrites similar to or even heavier than marine sulphate. The extreme environmental conditions induced by these anoxic oceans could have been responsible for the delayed oxygenation of the biosphere and retarded evolution of multicellular life.
A study of indigenous Bangladesh chickens under village conditions showed that these birds typically lay 3 clutches of eggs and produce on an average 46 eggs per year, and hens need 105-140 days to complete a production cycle. Mortality of scavenging chicks averaged 57% up to three months of age. A rural household earns only 3310 BDT (1USD=70 BDT) in a year from a flock of 18 chickens with an average of 3.9 layers, although cash income is currently estimated to be only 558 BDT. Changes to traditional management practices can be used to increase in laying performance, e.g. early weaning and creep feeding of chicks increase egg production of hens and reduces chick mortality. Early weaning contributes to an increase in annual egg production by shortening the length of the production cycle from 124 to 66 days. Egg production can hence be increased from an average of 46 to 99 eggs per hen per year. Creep feeding reduced chick mortality from 57% to 12%. Improved management practices not only increase egg production, but also contribute to higher household income, up to 23964 BDT per year. Early weaning, creep feeding of chicks and supplemental feeding of hens during the incubation period, were observed to be effective management tools in achieving a transition from subsistence to economically viable semi-commercial production.
In this paper the genetic fitness of the two heterozygotes Hb A/E and β-thalassaemia trait, in Calcutta, is examined in terms of their reproductive performance. It is found from fertility that the heterozygote Hb A/E enjoys some selective advantage over the normal homozygote Hb A/A, but the other heterozygote (β-thalassaemia trait) does not. But from overall reproductive performance (fertility and infant mortality together) it is postulated that the heterozygotes will eventually suffer from a selective disadvantage in a place like Calcutta, where malaria was eradicated about three decades ago.
The relationship between ponderal, linear and lower leg growth in children recovering from severe malnutrition remains unclear. We report on the early growth of 141 severely malnourished Bangladeshi children aged 6 to 36 months of age who were followed for 90 d. Mean (SD) weight for height (WHZ) and height for age (HAZ) catch-up growth Z scores over the 90 d were 1.6 (0.85) and 0.47 (0.325) respectively. mean (SD) lower leg length growth was 10.35 (4.5) mm. Change in HAZ was significantly associated with initial WHZ, but linear growth occurred in the presence of severe wasting and no threshold WHZ score was identified. Lower leg length gain correlated throughout with ponderal indices but with change in HAZ score only after day 45. Only initial WHZ score and maternal height predicted for linear growth and only accounted for 20 % of total variance. We conclude that linear growth occurs early in severely malnourished children but that knemometry behaves as a ponderal index acutely.
The structural transformation of anatase TiO2 by high-energy vibrational ball milling was studied in detail by different analytical methods of x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). This structural transformation involves both phase transition and nanoparticle formation, and no amorphization was observed. The crystallite size was found to decrease with milling time down to nanometer size ∼13 nm and approaching saturation, accompanied by phase transformation to metastable phases, i.e., TiO2(II), which is a high-pressure phase and TiO2(B), which was identified in ball-milled powder reported for the first time in this paper. These phases eventually started transforming to rutile by further milling.
The discovery that C60 Buckminsterfullerene may be created spontaneously in high yield when carbon vapor condenses indicates that graphene sheet curvature and closure is a common occurrence during carbon nucleation to form extended networks. As a consequence, a net microscopic perspective on graphitelike carbonaceous materials has evolved. This perspective is summarized here because the net observations relate to various types of nonplanar graphitic structures that promise to be useful as viable nanoscale engineering materials.
C60 Buckminsterfullerene was discovered in 1985 among the products of chemical nucleation of carbon in the gas phase. The faint whisper, embedded in the helium wind that blew a laser-initiated carbon plasma into a mass spectrometer, was interpreted as the possible signature of the elegant soccer-ball-shaped molecule. That noticed signal, which indicated that a pure 60-carbon-atom molecule might be very stable, was quite unexpected and thus a truly serendipitous discovery. The original aim of the experiments was to simulate the conditions in a red giant carbon star and particularly to probe an earlier proposal that long carbon-chain molecules might have originated in such celestial objects and might have been subsequently ejected into interstellar space. The carbon chains themselves had been discovered to be abundant in certain regions of the interstellar medium by a radioastronomy search program in the late 1970s. The molecular rotational frequencies, which formed the basis for the radio search, resulted from a spectroscopic study of cyanopolyynes that had been synthesized in the laboratory.
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