9,508 research outputs found
Effect of volcanic debris on stratospheric ion conductivity
The reduction is reported of stratospheric ion conductivities in the altitude range of 20 to 27 km attributable to the aerosols injected into the stratosphere by the eruption of volcano Nevado Del Ruiz on November 13, 1985. Three balloon experiments were conducted from Hyderabad, India (17.5 N, 78.6 E) carrying a Langmuir probe payload for measuring stratospheric ion conductivities. The first flight took place about 9 months before the volcanic eruption, the second 3 weeks after the eruption and the third about a year later. Lidar observations from Japan, Hawaii and Europe reported detection of aerosol layers in the 18 to 25 km altitude range attributable to the Nevado Del Ruiz volcanic eruption. A comparison of the conductivity profiles shows that the reduction of ion conductivities is: 57.3 percent at 20 km and 31 percent at 25 km. A year after the eruption, conductivities at all heights tended to recover
Spin Tunneling in Magnetic Molecules: Quasisingular Perturbations and Discontinuous SU(2) Instantons
Spin coherent state path integrals with discontinuous semiclassical paths are
investigated with special reference to a realistic model for the magnetic
degrees of freedom in the Fe8 molecular solid. It is shown that such paths are
essential to a proper understanding of the phenomenon of quenched spin
tunneling in these molecules. In the Fe8 problem, such paths are shown to arise
as soon as a fourth order anisotropy term in the energy is turned on, making
this term a singular perturbation from the semiclassical point of view. The
instanton approximation is shown to quantitatively explain the magnetic field
dependence of the tunnel splitting, as well as agree with general rules for the
number of quenching points allowed for a given value of spin. An accurate
approximate formula for the spacing between quenching points is derived
The high-pressure behavior of CaMoO4
We report a high-pressure study of tetragonal scheelite-type CaMoO4 up to 29
GPa. In order to characterize its high-pressure behavior, we have combined
Raman and optical-absorption measurements with density-functional theory
calculations. We have found evidence of a pressure-induced phase transition
near 15 GPa. Experiments and calculations agree in assigning the high-pressure
phase to a monoclinic fergusonite-type structure. The reported results are
consistent with previous powder x-ray-diffraction experiments, but are in
contradiction with the conclusions obtained from earlier Raman measurements,
which support the existence of more than one phase transition in the pressure
range covered by our studies. The observed scheelite-fergusonite transition
induces significant changes in the electronic band gap and phonon spectrum of
CaMoO4. We have determined the pressure evolution of the band gap for the low-
and high-pressure phases as well as the frequencies and pressure dependences of
the Raman-active and infrared-active modes. In addition, based upon
calculations of the phonon dispersion of the scheelite phase, carried out at a
pressure higher than the transition pressure, we propose a possible mechanism
for the reported phase transition. Furthermore, from the calculations we
determined the pressure dependence of the unit-cell parameters and atomic
positions of the different phases and their room-temperature equations of
state. These results are compared with previous experiments showing a very good
agreement. Finally, information on bond compressibility is reported and
correlated with the macroscopic compressibility of CaMoO4. The reported results
are of interest for the many technological applications of this oxide.Comment: 36 pages, 10 figures, 8 table
Effect of Velocity and Temperature Distribution at the Hole Exit on Film Cooling of Turbine Blades
An existing three-dimensional Navier-Stokes code (Arnone et al, 1991), modified Turbine Branch, to include film cooling considerations (Garg and Gaugler, 1994), has been used to study the effect of coolant velocity and temperature distribution at the hole exit on the heat transfer coefficient on three film-cooled turbine blades, namely, the C3X vane, the VKI rotor, and the ACE rotor. Results are also compared with the experimental data for all the blades. Moreover, Mayle's transition criterion (1991), Forest's model for augmentation of leading edge heat transfer due to free-stream turbulence (1977), and Crawford's model for augmentation of eddy viscosity due to film cooling (Crawford et al, 1980) are used. Use of Mayle's and Forest's models is relevant only for the ACE rotor due to the absence of showerhead cooling on this rotor. It is found that, in some cases, the effect of distribution of coolant velocity and temperature at the hole exit can be as much as 60 percent on the heat transfer coefficient at the blade suction surface, and 50 percent at the pressure surface. Also, different effects are observed on the pressure and suction surface depending upon the blade as well as upon the hole shape, conical or cylindrical
Sustainable Rehabilitation of Sodic Soils Through Biolgical Means-A Case Study
Abstract: Growing of efficient genotypes of crops and trees that could endure sodicity were experimented for rehabilitation of once barren sodic landscape in the middle part of the Gangetic alluvial plain at Banthra Research Station of National Botanical Research Institute, Lucknow,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. The results showed the anthropogenic effect on alteration of surface texture in soils of Typic Natrustalfs. The soils of Inceptic Haplustalfs markedly improved. The soils of Aeric Endoaquepts supporting the stands of forest trees are now devoid of sodicity to about 0.5 m depth, whereas the soils of Aeric Halaquepts though under cultivation have mild sodicity. Strategies for sustainable management of sodic wastelands suggested are maintenance of ground water level in safe zone and follow intensive cropping using biological treatments to get desired and long lasting results
Effect of non-symbiotic microbial inoculants on growth, yield and quality of fennel (Foeniculum vulgare Mill.) grown in sodic soil
The response of non-symbiotic microbial inoculants on growth, yield and quality of fennel(Foeniculum vulgare) grown in partially reclaimed sodic soils was studied at Lucknow (UttarPradesh). The results revealed that inoculation of phosphate solubilizing bacteria or incombination with Azotobacter chroococcum was superior resulting in 14%–15% increase in seedyield. Application of fertilizers (80 kg ha-1 N + 25 kg ha-1 P) with inoculants had an additiveeffect on plant growth. An increase in availability of soil P (41%–44%) and essential oilcontent (10%–14%) was also noticed.
 
Sodicity affects growth, yield and cation composition of fennel (Foeniculum vulgare Mill.)
Field trials were conducted at Banthra, Lucknow, (Uttar Pradesh) to study the effect of sodicity on growth, yield and cation composition of fennel (Foeniculum vulgare mill.) grown in a Typic Natrustalf. The treatments included five exchangeable sodium percentage (ESP) levels (10, 20, 30, 40 & 50) and four genotypes viz., HF-107, NDF-9, Local BRS and NDF-7. An adverse effect of sodicity was observed on emergence of secondary branches and seed setting causing decrease in seed yield. The variety HF-107 produced the highest seed yield (1956 kg ha-1) followed by Local BRS (1709 kg ha-1), NDF-9 (1577 kg ha-1) and NDF-7 (1078 kg ha-1). The cation composition of stover revealed Na inclusion mechanism with narrow K/Na and Ca/Na ratios. The study further revealed that the crop can tolerate medium level of sodicity (ESP 30).
 
Response of fenugreek (Trigonella foenum-gracecum L.) to sodicity
Field trials were conducted at Lucknow (Uttar Pradesh) to study the effect of sodicity on growth, yield and cation composition of fenugreek (Trigonella foenum-graecum L.). The treatments included five exchangeable sodium percentage (ESP) levels (10, 20, 30, 40 and 50) and four varieties namely, HM-346, RMt-1, Hissar Sonali and Kalyanpur Selection. The results showed that the crop was able to endure sodicity at germination stage but an adverse effect was noticed on emergence of branches plant-1 rather than plant height. The yield attributes were unaffected up to ESP 30. The variety Kalyanpur Selection produced greater biomass and seed yield than other genotypes up to ESP 30. The cation composition of plant revealed Na inclusion mechanism and showed narrow K/Na and Ca/Na ratio in the foliage indicating the potential of fenugreek crop to withstand medium level of sodicity.
 
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