Cutting Polytopes and Flag f-Vectors

We show how the flag f -vector of a polytope changes when cutting off any face, generalizing work of Lee for simple polytopes. The result is in terms of explicit linear operators on cd-polynomials. Also, we obtain the change in the flag f -vector when contracting any face of the polytope. Received July 13, 1998, and in revised form April 14, 1999.     

Molecular Studies on the Nephroprotective Potential of Celastrus paniculatus against Lead-Acetate-Induced Nephrotoxicity in Experimental Rats: Role of the PI3K/AKT Signaling Pathway

Chemicals can induce nephrotoxicity, with damage to different segments of the nephron and deterioration of renal function. Nephrotoxicity due to exposure to a toxin such as carbon tetrachloride, sodium oxalate, or heavy metals is the most common cause of kidney injury. The current study aimed to evaluate the protective effects of Celastrus paniculatus seed extract against lead-acetate-induced nephrotoxicity by evaluating the histopathology, immunohistochemistry, ultrastructure, and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway. Twenty-four rats were divided into four groups (n = 6 per group): group 1 contained normal animals and served as the control; group 2 received lead acetate (30 mg/kg body weight (b.w.)/day, oral); group 3 received lead acetate and the standard drug N-acetylcysteine (NAC, 200 mg/kg b.w./day, oral); and group 4 received lead acetate and the ethanolic extract of C. paniculatus seed (EECP; 800 mg/kg b.w./day, oral). Treatment was given for 28 consecutive days. The data were analyzed using one-way analysis of variance with SIGMA PLOT 13 using SYSTAT software followed by Newman–Keul’s test for comparison between the groups. EECP ameliorated the adverse changes caused by lead acetate. PI3K and AKT messenger RNA (mRNA) levels were diminished in lead-acetate-treated rats. Treatment with EECP inhibited the occurrence of shrunken cells, the atrophy of glomeruli, and degenerative changes in renal tubules caused by lead acetate. Interestingly, the PI3K and AKT mRNA levels were significantly increased in EECP-treated animals. Our results clearly evidence for the first time that C. paniculatus seed extract inhibits lead-acetate-induced detrimental changes in kidneys by regulating PI3K/AKT signaling pathways.     

A chemical amplification method for the sequential estimation of phosphorus, arsenic and silicon at ng/ml levels by d.c. polarography

A method is described for the sequential determination of phosphorus, arsenic and silicon at ng/ml levels by d.c. polarography. These elements are converted into their heteropolymolybdates and separated by selective solvent extraction. Determination of the molybdenum in the extract gives an enhancement factor of 12 for determination of the hetero-atom. A further enhancement by a factor of 40 is achieved by determining the molybdenum by catalytic polarography in nitrate medium. Charging-current compensation is employed to improve precision and the detection limit. The detection limits for phosphorus, arsenic and silicon are 0.5, 4.7 and 3.1 mu/gl., respectively and the relative standard deviation is 2-2.5%.     

Velocity and spanwise vorticity measurements in an excited mixing layer of a plane jet

The mixing layer of a plane jet was subjected to periodic weak excitation at two different frequencies corresponding to shear layer mode (St =0.012) and preferred mode (St _D =0.36). The nozzle exit boundary layer was identical for the unexcited and excited flows. Measurements of mean velocity, longitudinal and lateral velocity fluctuations, Reynolds shear stress and spanwise component of fluctuating vorticity were made over a longitudinal distance x/D of 6 for both the unexcited and the excited flows. Even weak excitation was observed to influence the development of the mixing layer. Under shear layer mode of excitation, the width of the layer and longitudinal turbulence level decrease compared to the naturally developing (unexcited) flow whereas preferred mode of excitation results in increase in the width and turbulence levels. The rms spanwise vorticity showed an increase for shear layer mode of excitation whereas the preferred mode of excitation resulted in a decrease compared to the values in an unexcited flow. Spectra of velocity and vorticity fluctuations exhibited subharmonic peaks, suggesting the possible occurrence of vortex pairing in both unexpected and excited flows. The influence of excitation is found to decrease as x/D increases and is not significant at x/D=6.This study was partly supported by a grant from the Research Grant Council, Hong Kong. The support and hospitality of the Department of Mechanical Engineering, University of Hong Kong are gratefully acknowledged by SR. The authors are grateful the referees for valuable comments.     

A simple method for the determination of benzo[a]pyrene and benzo[k]fluoranthene in a mixture

Atmospheric particulate matter is routinely analysed for the concentration of the carcinogen benzo[a]pyrene (BaP). Benzo[k]fluoranthene (BkF) has identical spectral characteristics and interferes in the fluorimetric estimation. A simple method for the determination of BaP in the presence of BkF is described. Based on quenching of the fluorescence of BaP by the addition of small amounts of nitromethane, the method can be used for accurate estimation for wide concentration ratios of BaP to BkF ranging from 0.1 to 10.0.     

High-throughput virtual screening and preclinical analysis identifies CB-1, a novel potent dual B-Raf/c-Raf inhibitor,effective against wild and mutant variants of B-Raf expression in colorectal carcinoma

Paradoxical Raf activation via Raf dimerization is a major drawback of wild/mutant B-Raf inhibitors. Herein, we report that CB-1 a novel, potent B-Raf/c-Raf dual inhibitor, effective against colon cancer cells, irrespective of their genetic status. High-throughput virtual screening of the ChemBridge library against wild B-Raf (B-Raf^WT), mutant B-Raf (B-Raf^V600E), and c-Raf was performed using an automated protocol with the AutoDock-VINA. Caco-2 and HT-29 cells were used. Of the 23,365 compounds screened computationally, CB-1 showed the highest binding energy towards B-Raf^WT with a ΔG_binding score of ? 13.0 kcal/mol. The compound was also predicted to be effective against B-Raf^V600E and c-Raf molecules with ΔG_binding energies of ? 10.6 and ? 10.1 kcal/mol, respectively. The compound inhibited B-Raf^WT, B-Raf^V600E and c-Raf kinases with IC₅₀ values of 27.13, 51.70, and 40.23 nM, respectively. The GI₅₀ value of CB-1 was 247.9 nM in B-Raf^WT-expressing Caco-2 cells and 352.4 nM in B-RafV600E-expressing HT-29 cells. Dose-dependent increases in total apoptosis and G₁ cell cycle phase arrest was observed in CB-1-treated colon cancer cells. The compound decreased B-Raf expression in both wild and mutant colon cancer cells. CB-1, a novel, potent dual B-Raf/c-Raf inhibitor was effective against colon cancer cells bearing wild-type and mutant variants of B-Raf expression.

     

Theoretical band structure calculation and superconductivity of NbC under pressure

Abstract

We report a theoretical calculation of the band structure and superconductivity of niobium carbide in the NaCl structure under pressure. The effect of pressure on the band structure is obtained by means of the self-consistent linear muffin-tin orbital method. The parameters necessary to calculate the superconducting transition temperature (T_c) are taken from our band structure results. The dependence of total energy on volume is calculated and is in good agreement with other earlier works. The calculated value of the cell parameter is in agreement with the experimental value (8.45 a.u). McMillan formula is used to calculate the value of T_c The calculated values of T_c are compared with the available experimental data.