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Strong Enhancement (strong + enhancement)
Selected AbstractsVoltammetric Studies of Parallel Electrode Processes Under Low Ionic Strength Conditions.ELECTROANALYSIS, Issue 7 2006Influence of Convection Abstract It is known that either a very strong enhancement or an almost complete depression of the height of one of two waves can be obtained when two analytes (one appropriately charged and one uncharged) are present in a quiet solution containing no supporting electrolyte. In this paper we examine whether these effects can be extended for solutions with forced convection. Three two-analyte mixtures were examined voltammetrically under conditions of no added supporting electrolyte and added convection. The first mixture (1,1,-ferrocenedimethanol and ferrocenesulfonate anion) changes its total charge from ,1 to +1 after electrooxidation of both components. Under all applied conditions, the introduction of convection caused an increase of both waves without changing the wave height ratio. A similar behavior was observed for the mixture of ferrocene and 1,1,-ferrocenedimethanol. For this system the total charge changes from 0 to +2. A substantial influence of convection on the ratio of two waves was found for the third mixture: ferrocene and ferrocenylmethyltrimethylammonium cation (total charge changes from +1 to +3). For this system the convection strongly depressed the migrational effects. The obtained experimental results were verified with simulations using software MIOTRAS. This software is capable of modeling diffusion, migration, convection and following homogenous reactions. The agreement between experiment and simulations was fairly good. [source] Structure,activity analysis of the potentiation by aminothiols of the chromosome-damaging effect of bleomycin in G0 human lymphocytesENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 2 2001George R. Hoffmann Abstract The radioprotective aminothiols 2-[(aminopropyl)amino] ethanethiol (WR-1065) and cysteamine (CSM) potentiate the induction of chromosomal damage by the radiomimetic compound bleomycin (BLM) in G0 human lymphocytes. To investigate the mechanism of potentiation, we measured the clastogenic activity of BLM in the cytokinesis-block micronucleus assay in the presence and absence of amines, thiols, and aminothiols. The hydroxy analog of WR-1065, 2-(3-aminopropylamino) ethanol (WR-OH), potentiates BLM only slightly, indicating the critical nature of the thiol group. As thiols, WR-1065 and CSM may donate electrons for the activation of Fe+2 -BLM or for the regeneration of Fe+2 -BLM from inactive Fe+3 -BLM. The amines putrescine, spermidine, and spermine all potentiate BLM, but they are weaker potentiators than the aminothiols, and they are effective only at high concentrations. Their activity, like that of WR-OH, is probably a consequence of conformational alteration of DNA. Dithioerythritol (DTE) and 2-mercaptoethanol (2-ME), thiols lacking an amino group, are less effective potentiators of BLM than are the aminothiols. The thiol group of WR-1065 and CSM is therefore essential, but insufficient, for explaining the strong enhancement of BLM activity. The cationic nature of CSM and WR-1065, conferred by the amino groups, evidently concentrates the active thiol function at the site of BLM action on DNA. As expected on this basis, the diamine WR-1065 is a more effective potentiator of BLM than is the monoamine CSM, whereas cysteine and N -acetylcysteine (NAC), which lack a net positive charge, potentiate BLM only weakly. These studies suggest that potentiation of the clastogenic action of BLM by aminothiols can be explained by the combination of a thiol-mediated redox mechanism and an amine-mediated targeting of the thiol function to DNA. Environ. Mol. Mutagen. 37:117,127, 2001 © 2001 Wiley-Liss, Inc. [source] Fluid-induced seismicity: Pressure diffusion and hydraulic fracturingGEOPHYSICAL PROSPECTING, Issue 2 2009S.A. Shapiro ABSTRACT Borehole fluid injections are common for the development of hydrocarbon and geothermic reservoirs. Often they induce numerous microearthquakes. Spatio-temporal dynamics of such induced microseismic clouds can be used to characterize reservoirs. However, a fluid-induced seismicity can be caused by a wide range of processes. Here we show that linear pore pressure relaxation and a hydraulic fracturing are two asymptotic end members of a set of non-linear diffusional phenomena responsible for seismicity triggering. To account for the whole range of processes we propose a rather general non-linear diffusional equation describing the pore pressure evolution. This equation takes into account a possibly strong enhancement of the medium permeability. Both linear pore pressure relaxation and hydraulic fracturing can be obtained as special limiting cases of this equation. From this equation we derive the triggering front of fluid induced seismicity, which is valid in the general case of non-linear pore pressure diffusion. We demonstrate corresponding seismicity signatures on different case studies. [source] Methylseleninic acid enhances the effect of etoposide to inhibit prostate cancer growth in vivoINTERNATIONAL JOURNAL OF CANCER, Issue 6 2007Oscar Gonzalez-Moreno Abstract New therapeutic agents are needed for the treatment of androgen-independent prostate cancer (PrCa). We have investigated the effect of methylseleninic acid (MSA) on tumor stage-specific prostate cells derived from the C3 (1)/Tag model for PrCa: Pr111, a slow-growing and nontumorigenic cell line isolated from a prostate intraepithelial neoplasia lesion; Pr14, a tumorigenic line derived from a primary tumor; and Pr14C1, a sub-clone of Pr14 explanted from a lung metastasis. We demonstrate that MSA strongly inhibits cell growth and induces apoptosis in C3 (1)/Tag tumor cells, in a dose-dependent manner. A decrease in phosphorylated ERK1/2 and AKT was also found in tumor cells, but not in Pr111. Microarray analysis using affymetrix showed that the number of genes with an altered expression in tumor cells is significantly higher (p < 0.01) than in nontumoral cells. Pathways analyses revealed a decrease in the expression of genes involved in metabolism (Fabp5, Cyba), signal transduction (ERK, AKT), angiogenesis (neuropilin-1, Flt-4) and transcription (cAMP response element-binding protein) in tumor cells. The expression of neuropilin-1, a protein involved in VEGF signaling and tumor angiogenesis, was 97-fold repressed in Pr14 cells treated with MSA. Combination treatments using low doses of etoposide or taxotere (docetaxel), plus low doses of MSA revealed a strong enhancement of cell growth inhibition and apoptosis in tumor cells. Our in vivo studies using Pr14 cells xenografted into nude mice demonstrated that MSA significantly enhances the chemotherapeutical effect of etoposide, resulting in 78.3% tumor growth inhibition. These results suggest that MSA could be used against PrCa to enhance the effect of etoposide. © 2007 Wiley-Liss, Inc. [source] Atmospheric large-scale dynamics during the 2004/2005 winter drought in portugalINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2007J. Santos Abstract The unusually dry conditions during the 2004/2005 winter in Portugal led to the development of an extreme/severe drought episode throughout the country with major socioeconomic impacts. In fact, at some locations, this winter was the driest in at least the last 60 years. A K-means classification of days into a set of five weather regimes (WRs), relevant for winter precipitation in Portugal, reveals a large prevalence of the two driest weather regimes during the 2004/2005 winter. These two regimes are basically linked to either anticyclonic circulation or easterly winds over Portugal and their prevalence explains the significant precipitation deficit. Winter precipitation variability in Portugal is indeed skillfully represented by linear models where the predictors are the frequencies of occurrence (FO) of these weather regimes. The dominance of the ,dry phases' of the main coupled modes between winter precipitation in Portugal and the large-scale atmospheric circulation also supports the prevalence of the dry regimes and the corresponding lack of precipitation. The predominance of the dry regimes can be explained by a remarkably strong enhancement of the climate-mean North Atlantic ridge, manifested by dynamically coherent anomalies in the geopotential heights, vorticity and temperature fields over the North Atlantic. The persistence of a warm-core asymmetrical eddy over the North Atlantic, with a nearly barotropic equivalent structure, is a manifestation of this large-scale anomaly. The blocking of the westerlies and the consequent northward shift in the axis of maximum moisture transports over the North Atlantic was one of the most striking changes in the large-scale atmospheric flow. Consequently, the main track of the developing baroclinic disturbances was sufficiently distant from Portugal to hamper the development of rain-generating conditions. As these dynamical conditions are common to other reportedly dry winters, they effectively constitute a key factor for the occurrence of a precipitation deficit in Portugal. Copyright © 2006 Royal Meteorological Society [source] Adsorption of 4,4,-thiobisbenzenethiol on silver surfaces: surface-enhanced Raman scattering studyJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2008Yuling Wang Abstract Adsorption of 4,4,-thiobisbenzenethiol (4,4,-TBBT) on a colloidal silver surface and a roughened silver electrode surface was investigated by means of surface-enhanced Raman scattering (SERS) for the first time, which indicates that 4,4,-TBBT is chemisorbed on the colloidal silver surface as dithiolates by losing two H-atoms of the SH bond, while as monothiolates on the roughened silver electrode. The different orientations of the molecules on both silver surfaces indicate the different adsorption behaviors of 4,4,-TBBT in the two systems. It is inferred from the SERS signal that the two aromatic rings in 4,4,-TBBT molecule are parallel to the colloidal silver surface as seen from the disappearance of ,CH band (3054 cm,1), which is a vibrational mode to be used to determine the orientation of a molecule on metals according to the surface selection rule, while on the roughened silver electrode surface they are tilted to the surface as seen from the enhanced signal of ,CH. The orientation of the C-S bond is tilted with respect to the silver surface in both cases as inferred from the strong enhancement of the ,CS. SERS spectra of 4,4,-TBBT on the roughened silver electrode with different applied potentials reveal that the enhancement of 4,4,-TBBT on the roughened silver electrode surface may be related to the chemical mechanism (CM). More importantly, the adsorption of 4,4,-TBBT on the silver electrode is expected to be useful to covalently adsorb metal nanoparticles through the free SH bond to form two- or three- dimensional nanostructures. Copyright © 2007 John Wiley & Sons, Ltd. [source] A biochemical analysis of the interaction of DNA gyrase with the bacteriophage Mu, pSC101 and pBR322 strong gyrase sites: the role of DNA sequence in modulating gyrase supercoiling and biological activityMOLECULAR MICROBIOLOGY, Issue 1 2003Mark Oram Summary Replication of bacteriophage Mu DNA, a process requiring efficient synapsis of the prophage ends, takes place within the confines of the Escherichia coli nucleoid. Critical to ensuring rapid synapsis is the function of the SGS, a strong gyrase site, located at the centre of the Mu genome. Replacement of the SGS by the strong gyrase sites from pSC101 or pBR322 fails to support efficient prophage replication. To probe the unique SGS properties we undertook a biochemical analysis of the interaction of DNA gyrase with the Mu SGS, pSC101 and pBR322 sites. In binding and cleavage assays the order of efficacy was pSC101 > Mu SGS >> pBR322. However, in supercoiling assays the Mu SGS (cloned into pUC19) exhibited a strong enhancement of gyrase-catalysed supercoiling over pUC19 alone; the pSC101 site showed none and the pBR322 site gave a moderate improvement. Most striking was the Mu SGS-dependent increase in processivity of the gyrase reaction. This highly processive supercoiling coupled with efficient binding may account for the unique biological properties of the SGS. The results emphasize the importance of the DNA substrate as an active component in modulating the gyrase supercoiling reaction, and in determining the biological roles of specialized gyrase sites. [source] Excitonic effects in the nonlinear optical response of a Si(111) surfacePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2010Maria Stamova Abstract We discuss methods to calculate the linear and nonlinear optical spectra for cyclic cluster models of an ideal Si(111) surface. The cluster approach offers the possibility to implement the excitonic effects due to the Coulomb interaction between electron and hole in a relatively straight-forward way. In order to appproximate a situation resembling a surface we use clusters with several hundreds of Si atoms. The electronic structure is obtained from a tight-binding parametrization of the hamiltonian. A time-dependent density operator formalism is used to calculate the response functions and for the optical polarization, which also directly describe the response to ultrashort pulses. Their Fourier transforms are the frequency-dependent optical susceptibilities and for second-harmonic () or sum-frequency generation from surfaces. The excitonic Coulomb interaction is treated in the time-dependent Hartree,Fock approximation, leading to large sets of differential equations that are integrated explicitly. The results on the linear susceptibility are in accord with earlier findings on the excitonic origin of the relative intensities of the E1 and E2 peaks near 3.4 and 4.3,eV. We present new results on excitonic effects in the nonlinear spectra and investigate in particular the surface-related peaks near 2,=,1.3,1.5 and 2.4,eV that govern the strong enhancement observed in SHG of clean silicon surfaces. [source] Low frequency noise in Co/Al2O3,Si,/Py magnetic tunnel junctionsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2008R. Guerrero Abstract Low frequency noise and dynamic tunneling resistance have been studied in Co(80 Å)/Al2O3(12 Å)/Py(100 Å) magnetic tunnel junctions (MTJs) with and without asymmetric Si doping of the insulating barrier (Si , 1.8 Å). Variation of the dynamic resistance and tunneling resistance with Si doping and applied bias in these MTJs indicate a transition from the Si-doped regime to Si cluster formation above a , -layer thickness of about 1.2 Å, close to 1 monolayer coverage. The measurements show anomalously strong enhancements of the low frequency noise for Si thickness above 1.2 Å, mainly due to the appearance of random telegraph noise. A simple model, which considers suppression of Coulomb blockade in the array of Si dots, opening two-step tunnel channels, qualitatively explains the variation of both conductivity and noise with Si content. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||