Discrete element approach for mine dump stability analysis

Mine overburden dumps have posed significant safety issues in the operations of various unit operations of open pit min-ing especially the external dumps. The external dumps are composed of a mixture of fragmented rocks and loose soil. Their charac-teristic is comparable to heavily discontinuous solid mass. The conventional approach of limit equilibrium methods provide safety factors for the slope but nothing about the stress-strain characteristics of the large dump mass. The designs of dump location and their respective geometry are integrated for the know-how of the stability characteristics of these dumps. The discrete element method uses a circular disk to represent the granular solid mass and their interactions are described by the Newton's third law of motion. The displacement is described by the sliding of the circular disk. This work is focused on the modeling efficiency of the discrete element methods to represent the behaviour of mine dump masses with the specified joint plane for the limit equilibrium method. The advantage of the work lies on the ease of information retrieval at any point at the dump mass concerning the stress and strain histories, displacement, failures etc. which when integrated produces a better understanding of the stability of the dump masses.     

Analysis of optimum matching of a DC series motor driven centrifugal pump to a photovoltaic generator

Direct coupling between a photovoltaic (PV) generator and a monoblock DC series motor connected with ventilator load torque centrifugal pump has been analyzed theoretically as a function of the no flow motor-pump speed (w₀) and the water head of the pump. The value of w₀ is directly related with motor terminal voltage which has been derived. The condition of the maximum motor-pump efficiency has been deduced mathematically in terms of the speed-torque constant K₁ at a given w₀ for different water heads. The variation of w₀ and perfectly matched motor constant (M₀) have been calculated at various solar insolation and different water heads. From these theoretical studies, the optimum matching condition has been suggested according to the requirements. One optimally matched monoblock DC series motor and centrifugal pump, of 125 W, was chosen for study. The calculated coupling efficiencies such as electrical energy, mechanical energy, and hydraulic energy of the pump, have been discussed. Some of these results are also compared to information available in the literature.     

Influence of subchronic exposure to lindane on humoral immunity in mice

Lindane suppressed both primary and secondary antibody responses to sheep red blood cell (SRBC) in albino mice, the effects being more pronounced on the secondary than the primary response. However, a longer duration of pesticide exposure induced similar degrees of immunosuppression on both responses. The sequential study of plaque forming cells (PFC) kinetics revealed that suppression of plaque formation not only occurred at peak days but also on pre and post peak days, and there was no delay in peak antibody formation. Moreover, reduction in the primary PFC was not associated with decrease in the antibody response to SRBC. The results indicate that lindane suppresses both primary and secondary humoral immune responses in a time and dose dependent manner, and suggest a threshold susceptibility to exposure.     

Effect of interface coupling between polarization and magnetization in La0.7Pb0.3MnO3 (LPMO)/P(VDF-TrFE) flexible nanocomposite films

Journal of Materials Science - La0.7Pb0.3MnO3(LPMO) nanoparticles (NPs) were prepared by sol–gel auto-combustion method. These were embedded in P(VDF-TrFE) to form (0–3) nanocomposite...     

Effects of cobalt (III) complexes of schiff bases on root tip mitosis

Cytological effects of two newly synthesized Cobalt (III) complexes, namely, [Co(BSOP)(NH₃)₂] [NO₃], (1) and [Co(BSOP)(PY)₂] [NO₃], (2) (where, BSOP = dianion of N, N‐orthophenylenebis (salicylal‐dimine), Py = pyridine) were studied on Allium Cepa root tip cells. Many interesting abnormalities, including diplochromatic structure, grouping, stickiness, beadedness, erosion, fragmentation and bridge formation of chromosomes and granulation of the interphase nucleus were observed under the influence of these cobalt (III) complexes. The mitotic index had been simulated at threshold concentrations, but affected at higher concentrations and prolonged treatment. The inhibitory action in prolonged treatment may be due to an accumulation effect. Mechanisms of such effects have been discussed qualitatively and are described as a non‐delayed type.     

Lanthanide Carboxylate Frameworks: Efficient Heterogeneous Catalytic System for Epoxidation of Olefins

Abstract  

Two lanthanide-based three dimensional metal–organic frameworks (MOF) viz. [Nd(HCOO)₃]_n (1) and [Pr(HCOO)₃]_n (2) have been synthesized and characterized. Both the compounds have similar structure. In this study we have demonstrated that the compounds are highly efficient in catalyzing epoxidation of various cyclic and linear olefinic substrates. MOF compounds are stable and recyclable under the reaction conditions. Notably, MOF systems are remarkably more active and selective than the corresponding lanthanide oxide in epoxidation reaction of olefins.     

Iridium Complexes as a Roadblock for DNA Polymerase during Amplification

Iridium‐based metal complexes containing polypyridyl‐pyrazine ligands show properties of DNA intercalation. They serve as roadblocks to DNA polymerase activity, thereby inhibiting the polymerization process. Upon the addition of increasing concentrations of these iridium complexes, a rapid polymerase chain reaction (PCR)‐based assay reveals the selective inhibition of the DNA polymerization process. This label‐free approach to study the inhibition of fundamental cellular processes via physical roadblock can offer an alternative route toward cancer therapy.     

Organochlorine pesticide-induced oxidative stress and immune suppression in rats

OBJECTIVE: To investigate the different responses to antiretroviral treatment including zidovudine, of patients harbouring HIV with primary resistance to zidovudine, serum viral load, and CD4+ cell counts, for 24 weeks in a group of antiretroviral-naive patients with the codon 215 mutation of the HIV pol gene and in a control group at the start of treatment. DESIGN: A case-control retrospective study (1989-1996). METHOD: Nineteen out of 210 patients previously studied harboured the codon 215 mutation, had a self-reported compliance with treatment, a minimum follow-up of 24 weeks, and were treated with zidovudine alone or in combination with other nucleoside analogues. These patients were matched with 19 patients with wild-type strains at entry by initial CD4+ cell counts, clinical status, and antiretroviral treatment. RESULTS: During the first 12 weeks, CD4+ cell counts increased (76+/-26 and 64+/-26 x 10(6)/l in wild-type and mutant virus-infected groups, respectively), decreasing slightly until week 24, although no significant differences were found between the two groups studied. Serum viral load decreased in both groups (change in serum viral load of 0.80+/-0.11 log10 and 0.87+/-0.26 log10 copies/ml, wild-type and mutant virus-infected, respectively), although no significant differences were found between groups. CONCLUSION: No significant differences were found between patients with the primary mutation to zidovudine and control patients harbouring wild-type virus in terms of short-term response measured by serum viral load and CD4+ cell counts.     

Mesoporous silica MCM-41 with rod-shaped morphology: Synthesis and characterization

A new synthesis route has been established to prepare highly pure mesoporous silica material (Si-MCM-41) with rod-like morphology. To improve the stability and to bring about the long range ordering in the mesoporous material, a series of tetra-alkylammonium salts has been employed in the new procedure in addition to the surfactant, cetyl-trimethylammonium bromide. The mesoporous silica materials have been characterized by small-angle X-ray diffraction (SAX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ sorption and solid state ²⁹Si NMR measurements. The XRD study revealed that an excellent long range structural ordering of mesoporous material can be achieved using tetra-butylammonium bromide as a promoter. SEM study showed that rod-shaped single crystal like particles were formed in hydrothermal synthesis. TEM study revealed the presence of hexagonal voids on the face of the rod-shaped particles while nitrogen sorption study establishes the mesoporosity of the material. A high degree of cross-linking of -Si-O-Si- networks in the mesoporous silica has been evidenced in ²⁹Si NMR study.     

Quantitative field performance analysis of a photovoltaic array

A quantitative analysis of the long-term field performance of a photovoltaic (PV) array has been made considering such field variables as solar insolation, temperature and long-term degradation of a solar cell. It deals with (i) the numerical analysis of two degradation factors of a single crystal solar cell, namely, increased lumped series resistance R_s and decreased short circuit current I_sc, (ii) the field condition V_m — I_m relation, and (iii) the ratio of I_m and I_sc for a PV array. The value of I_m has been computed from the solution of a transcendental equation using Newton–Raphson approximation technique. This approach has been verified by field data obtained in Delhi, India, over a period of four years for the single crystal silicon PV modules (manufactured by CEL, India). It can be used for the study of the long-term field performance of a polycrystalline and amorphous silicon PV module.