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

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. &nbsp

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). &nbsp

Influence of sodicity on cation composition, growth, yield and quality of chilli (Capsicum annuum L.)

Field trials conducted at Lucknow (Uttar Pradesh) to study the performance of chilli(Capsicum annuum) in sodic soil with four genotypes (Jwala, PC-1, KDCS-810 and LCA-235) and five levels of exchangeable sodium percentage (ESP) (10, 20, 30, 40 and 50) indicatedthe adverse effect of sodicity and hence picking of red ripe fruits may be stopped after thesixth one when there is about 25% reduction in fruit size. Maximum mean yield (fresh) wasobtained in LCA-235 (16.2 t ha-1) followed by KDCS-810 (13.1 t ha-1), PC-1 (12.0 t ha-1) andJwala (10.3 t ha-1). There was less reduction in yield of LCA-235 and KDCS-810 than Jwalaand PC-1 at higher sodicity level (ESP=40) revealing greater sodicity tolerance. Cationcomposition of different plant parts indicated salt (Na) exclusion mechanism and higher K/Na and Ca/Na ratio supporting the potential of chilli crop to endure greater degree of sodicity.Physical fruit quality with respect to length, diameter and pod weight were affected by soilsodicity and decreased with increase in soil sodicity. Oleoresin and capsaicin contents didnot vary with increase in sodicity, whereas, ascorbic acid content was reduced. &nbsp