Molecular electronic ground-state theories, whether ab initio, or semiempirical are most often formulated as a variational principle, where the electronic ground-state energy, considered a linear or nonlinear functional of a reduced density matrix, obtains a constrained minimum. In this communication, we present a Lagrangian analysis of the self-consistent-field electronic structure problem, which does not resort to the concept of orthogonal molecular orbitals. We also develop a method of constrained minimization efficiently applicable to nonlinear energy functional minimization, as well as to linear models such as tight-binding. The method is able to treat large molecules with an effort that scales linearly with the system size. It has built-in robustness and leads directly to the desired minimal solution. Performance is demonstrated on linear alkane and polyene chains.
Young adult honey bees work inside the beehive ``nursing'' brood around the clock with no circadian rhythms; older bees forage for nectar and pollen outside with strong circadian rhythms. Previous research has shown that the development of an endogenous rhythm of activity is also seen in the laboratory in a constant environment. Newly emerging bees maintained in isolation are typically arrhythmic during the first few days of adult life and develop strong circadian rhythms by about a few days of age. In addition, average daily levels of period (per) mRNA in the brain are higher in foragers or forager-age bees (> 21 days of age) relative to young nest bees (similar to 7 days of age). The authors used social manipulations to uncouple behavioral rhythmicity, age, and task to determine the relationship between these factors and per. There was no obligate link between average daily levels of per brain mRNA and either behavioral rhythmicity or age. There also were no differences in per brain mRNA levels between nurse bees and foragers in social environments that promote precocious or reversed behavioral development. Nurses and other hive-age bees can have high or low levels of per mRNA levels in the brain, depending on the social environment, while foragers and foraging-age bees always have high levels. These findings suggest a link between honey bee foraging behavior and per up-regulation. Results also suggest task-related differences in the amplitude of per mRNA oscillation in the brain, with foragers having larger diurnal fluctuation in per than nurses, regardless of age. Taken together, these results suggest that social factors may exert potent influences on the regulation of clock genes.
2001. “A Brief History of Ekwilism.” In Critical Interfaces: Contributions in Philosophy, Literature and Culture in Honour of Herbert Grabes, Pp. 333-41. Ed. Gordon Collier, Klaus Schwank and Franz Wieselhuber. Trier: Wissenschaflicher Verlag Trier.
The collision energy dependence of cross-section for reactions where the reactants attract is discussed. Examples include charge recombination A(+) + B- –> products, ion-molecule reactions and other curve crossing processes. The common characteristic of such processes is that on physical grounds there is a critical distance d where capture occurs. Special attention is given to the case where the critical separation is independent of energy and/or impact parameter. A modern example where this is the case is laser-induced association of atoms. The capture cross-section has the functional form sigma = pid(2) (1 - Vg(d)/E-T) where for the collisions discussed the potential is attractive, V-g(d) < 0. Such a cross-section is a decreasing function of the collision energy ET. The same functional form is also useful if the potential is repulsive, V-g(d) > 0. For this well-known case, the cross-section is an increasing function of the collision energy. (C) 2001 Elsevier Science B.V. All rights reserved.
Reactive oxygen species (ROS) are mediators of lung injury, and glutathione (GSH) is the major nonprotein antioxidant that protects the cell from oxidative stress. We have recently shown that H(2)O(2) induces ceramide-mediated apoptosis in human lung epithelial cells. We hypothesized that ROS-mediated depletion of GSH plays a regulatory role in ceramide generation, and thus in the induction of apoptosis. Our present studies demonstrate that GSH at physiologic concentrations (1 to 10 mM) inhibits ceramide production in a time- and dose-dependent manner in A549 human alveolar epithelial cells. On the other hand, buthionine-sulfoximine-mediated depletion of intracellular GSH induces elevation of ceramide levels and apoptosis. In addition, GSH blocks H(2)O(2)-mediated induction of intracellular ceramide generation and apoptosis. These effects were not mimicked by oxidized GSH (GSSG) or other thiol antioxidants, such as dithiothreitol and 2-mercaptoethanol. Moreover, increase of intracellular H(2)O(2), mediated by inhibition of catalase by aminotriazole, also induces ceramide generation and apoptosis. These effects were blocked by N-acetylcysteine. Our results suggest that GSH depletion may be the link between oxidative stress and ceramide-mediated apoptosis in the lung.
The transformation of rainfall into runoff at a basin outlet is the combined effect of many hydrological processes, which occur at a wide range of spatial and temporal scales. However, determining the scale of the combined hydrological response of the basin is still problematic and concepts for its definition are yet to be identified. In this paper high-resolution meteorological radar data are used for the determination of a characteristic temporal scale for the hydrological response of the basin - the 'response time scale' (Ts*). Ts* is defined as the time scale at which the pattern of the time-averaged radar rainfall hietograph is most similar to the pattern of the measured outlet runoff hydrograph. The existence of such similarity at a relatively stable time scale for a specific basin indicates that it is an intrinsic property of the basin and is related to its hydrological response. The identification of the response time scale is carried out by analysis of observations only, without assuming a specific rainfall-runoff model. Ts* is examined in four small basins (10-100 km2) in Israel. The spatial scale is assumed as the entire basin. For all analyzed basins a stable response time scale is identified. Relatively short time scales are found for the urban and arid basins (15-30 min), while for the rural basins longer time scale are identified (90-180 min). The issues of relationship between the response time scale and basin properties and modeling at the response time scale have yet to be determined. ?? 2001 Elsevier Science B.V. All rights reserved.
The transformation of rainfall into runoff at a basin outlet is the combined effect of many hydrological processes, which occur at a wide range of spatial and temporal scales. However, determining the scale of the combined hydrological response of the basin is still problematic and concepts for its definition are yet to be identified. In this paper high-resolution meteorological radar data are used for the determination of a characteristic temporal scale for the hydrological response of the basin - the 'response time scale' (Ts*). Ts* is defined as the time scale at which the pattern of the time-averaged radar rainfall hietograph is most similar to the pattern of the measured outlet runoff hydrograph. The existence of such similarity at a relatively stable time scale for a specific basin indicates that it is an intrinsic property of the basin and is related to its hydrological response. The identification of the response time scale is carried out by analysis of observations only, without assuming a specific rainfall-runoff model. Ts* is examined in four small basins (10-100 km2) in Israel. The spatial scale is assumed as the entire basin. For all analyzed basins a stable response time scale is identified. Relatively short time scales are found for the urban and arid basins (15-30 min), while for the rural basins longer time scale are identified (90-180 min). The issues of relationship between the response time scale and basin properties and modeling at the response time scale have yet to be determined. ?? 2001 Elsevier Science B.V. All rights reserved.
Different approaches for increasing the sensitivity, selectivity and stability of a voltammetric probe for mercury ions were probed. These involve the application of adsorbed monolayers of a host mol., i.e., 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (Kryptofix-222) and thin polymeric films. The stability, reproducibility and durability of the sensors in the anal. of Hg2+ from different sources were examd. and compared. A monolayer of the macrocyclic ligand, which is capable of forming a strong and selective complex with the mercury, is superior to polymeric films in terms of sensitivity and ease of regeneration. However, the stability and durability of polymeric films, in which Kryptofix-222 is incorporated, will eventually dictate their use as preferred interfaces for repetitive analyses esp. in flow anal. systems. An application of a polymer-Kryptofix-222 modified electrode for monitoring mercury in a bioremediation pilot was examd. using an automatic sequential-injection stripping anal. (SISA) system. [on SciFinder(R)]
Different approaches for increasing the sensitivity and selectivity of voltammetric probes for heavy metals were examd. These have involved adsorbed monolayers of host mols., functionalized self-assembled monolayers and thin polymeric films. Two systems are presented that focus on the selective anal. of Hg(II) and Fe(II). The electrode for Hg(II) is based on a macrocyclic ligand, i.e., Kryptofix-222, while that for Fe(II) relies on the selective complexation by ferroin ligands, such as 1,10-phenanthroline. The monomeric and polymeric approaches were examd. and compared for both systems. The principal aim of this manuscript is to highlight the ability of fine-tuning the selectivity characteristics of the solid-liq. interface as a result of considering and optimizing analyte-interface interactions. Basically, an interface comprising a monolayer, which is capable of forming a strong and selective complex with the analyte, is likely to exhibit sensitivity that is at least as good as a polymeric film. However, the stability and durability of the latter usually makes it a superior interface for repetitive anal. and will therefore be the preferred choice for flow anal. systems. [on SciFinder(R)]
The paper presents an extended argument for the claim that mental content impacts the computational individuation of a cognitive system (section 2). The argument starts with the observation that a cognitive system may simultaneously implement a variety of different syntactic structures, but that the computational identity of a cognitive system is given by only one of these implemented syntactic structures. It is then asked what are the features that determine which of implemented syntactic structures is the computational structure of the system, and it is contended that these features are certain aspects of mental content. The argument helps (section 3) to reassess the thesis known as computational externalism, namely, the thesis that computational theories of cognition make essential reference to features in the individual's environment. It is suggested that the familiar arguments for computational externalism—which rest on thought experiments and on exegesis of Marr's theories of vision—are unconvincing, but that they can be improved. A reconstruction of the visex/audex thought experiment is offered in section 3.1. An outline of a novel interpretation of Marr's theories of vision is presented in section 3.2. The corrected arguments support the claim that computational theories of cognition are intentional. Computational externalism is still pending, however, upon the thesis that psychological content is extrinsic.
Analytical and numerical results are presented for the intersection of electronic energies of the same space symmetry for electrons in the field of two Coulomb centers in D-dimensions. We discuss why such crossings are allowed and may be less ``exceptional'' than one could think because even for a diatomic molecule there is more than one parameter in the electronic Hamiltonian. For a one electron diatomic molecule at the large-D limit, the electronic energies are shown analytically to diverge quadratically from the point of their intersection. The one electron two Coulomb centers problem allows a separation of variables even when the charges on the two centers are not equal. The case of two electrons, where their Coulombic repulsion precludes an exact symmetry, is therefore treated in the large-D limit. It is then found that, in addition to the quadratic intersection, there is also a curve crossing where the energies diverge linearly. (C) 2001 American Institute of Physics.
A new approach for designing a voltammetric selective electrode is presented. The approach is based on the formation of a disorganised inert self-assembled monolayer (SAM), in which an amphiphilic molecule is incorporated. The latter serves as the selectivity factor, which extracts the analyte. The purpose of these experiments is to study the parameters that affect the capability of a monolayer to host amphiphiles. As model systems we focused on the incorporation of simple amphiphilic molecules (quaternary alkyl ammonium salts), electroactive amphiphiles (dialkylviologens) and a macrocycle ligand (tetramethylcyclam) into octadecyl silane monolayers formed on indium tin oxide (ITO) and purposely made disorganised alkanethiols on gold. We find that basically, the incorporation of amphiphiles into a hydrophobic inert SAM resembles a reversed stationary phase in liquid chromatography and this configuration can be used for designing selective electrodes.[on SciFinder (R)]
A new approach for designing a voltammetric selective electrode is presented. The approach is based on the formation of a disorganized inert self-assembled monolayer (SAM), in which an amphiphilic mol. is incorporated. The latter serves as the selectivity factor, which exts. the analyte. The purpose of these expts. is to study the parameters that affect the capability of a monolayer to host amphiphiles. As model systems the authors focused on the incorporation of simple amphiphilic mols. (quaternary alkyl ammonium salts), electroactive amphiphiles (dialkylviologens) and a macrocycle ligand (tetramethylcyclam) into octadecyl silane monolayers formed on In Sn oxide (ITO) and purposely made disorganized alkanethiols on Au. Basically, the incorporation of amphiphiles into a hydrophobic inert SAM resembles a reversed stationary phase in liq. chromatog. and this configuration can be used for designing selective electrodes. [on SciFinder(R)]
