169,846 research outputs found
Multiple bonds and excited states from the Hartree-Fock-Heitler-London method
No full textThe recently proposed Hartree-Fock-Heitler-London, HF-HL, method (Corongiu, G. J. Phys. Chem. A 2006, 110, 11584) previously tested for single bond molecules is validated by potential energy computations for open and closed shells, single and multiple bonds, in ground and excited states of homopolar diatomic molecules of the first and second period. The simple HF-HL function, including the configurations for 2s/2p near degeneracy and avoiding state crossing, yields correct dissociation products, qualitatively correct binding, and accounts for non-dynamical correlation. Addition of ionic structures improves the ab initio HF-HL function and yields about 95% of the experimental binding energies on average. Computed excitation energies are also in agreement with laboratory values as verified for the (3)Pi(u) and (3)Sigma(-)(g) excited states of the C-2 molecule. Computation of the remaining dynamical correlation using a semiempirical functional yields binding energies with an average deviation of 1.5 kcal/mol from laboratory values, and total energies with an average deviation of 0.7 kcal/mol from exact nonrelativistic dissociation energies
Energy and Density Analysis on the H2 Molecule from the United Atom to Dissociationi: the Sigma, Pi, Delta, Phi and Gamma States.
No full textWe present 140 accurate potential energy curves, PECs, for the Sigma, Pi, Delta, Phi, and Gamma manifolds for the H(2) molecule, mapping all the states with energy below the H(2)(+) ground state. The full configuration interaction, nonrelativistic Born-Oppenheimer computations are performed with large and optimized basis sets of Slater-type and spherical Gaussian functions; these new basis sets are somewhat larger than those used in recent published studies on the 60 Sigma state PECs. The full CI computations are performed twice, with Hartree-Fock and with Heitler-London-type functions, allowing the identification of the ionic component in the total energy. The computed energies are within 10 (5) hartree from the most accurate PECs in literature. We aim ( a) at the evaluation of the PECs starting at very short and unexplored internuclear distances (0.01 bohrs) and ending at full dissociation, (b) at the systematic prediction of high excited state PECs dissociating as 1s + 4l and 1s + 5l, and ( c) at the characterization of the evolution of the 140 PEC electronic densities from united atom to dissociation. With this work we fill a gap in today literature, which has dealt mainly with low excited states, generally excluding short internuclear distances. The electronic configuration at the united atom persists as dominant configuration well beyond the equilibrium separation, and it switches to that at dissociation often with energy patterns seemingly irregular, in particular when the values of the principal quantum number at dissociation and at the united atom differ by one or more unit. The Hund's singlet-triplet splitting, which propagates from the united atom to the molecule, is discussed. The singlet and triplet states are rather close in energy in the Pi manifolds, and approach degeneracy in the Delta and Phi manifolds, to become fully degenerate in the Gamma manifolds. Discussions on the correlation energy correction, adiabatic correction, spectroscopic constants and on general features of the H(2) excited states are presented. The H(2) molecule is a system, which-to be understood-needs consideration of both the very short internuclear distances in approaching the united atom and of the very high excited states below H(2)(+). (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 3517-3540, 201
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Role of genetic background in the effects of adolescent nicotine exposure on mesolimbic dopamine transmission
No full textSmoking during adolescence may increase the likelihood to develop nicotine dependence and to abuse other drugs such as cocaine. Despite great efforts to understand underlying neurobiological mechanisms of this progression, less attention has been paid to the role of genetic factors. Here, we investigated the influence of both genetic background and age at first nicotine exposure in the long-lasting effects on mesolimbic dopamine transmission including the increased cocaine-rewarding effect. Mid-adolescent and adult rats of inbred strains Lewis (addiction prone) and Fischer 344 (addiction resistant) were administered nicotine (0.4 mg/kg) or vehicle once daily for 5 days. Changes in dopamine transmission were investigated by in vivo microdialysis and electrophysiology after 30 days of withdrawal, whereas changes in cocaine-rewarding effect were assessed via conditioned place preference paradigm. Nicotine pre-exposure differentially changed mesolimbic dopamine transmission depending on strain and age of pre-exposure. A potentiation of dopamine response to nicotine was observed in nucleus accumbens (NAc) core of both strains and age groups, whereas dopamine response in NAc shell was enhanced exclusively in Lewis rats exposed to nicotine during adolescence. A similar response was observed following cocaine challenge at adulthood. Changes in VTA dopamine cell population and activity were observed only in adolescent nicotine-pretreated Lewis rats, which also showed an increased cocaine-rewarding effect at adulthood. These results highlight the influence of genetic background in the long-lasting effects of nicotine exposure and suggest that exposure during adolescence might increase nicotine and cocaine-rewarding properties in genetically vulnerable individuals, thereby facilitating progression toward dependence
Influence of Age and Genetic Background on Ethanol Intake and Behavioral Response Following Ethanol Consumption and During Abstinence in a Model of Alcohol Abuse
No full textGenetic background and age at first exposure have been identified as critical variables that contribute to individual vulnerability to drug addiction. Evidence shows that genetic factors may account for 40–70% of the variance in liability to addiction. Alcohol consumption by young people, especially in the form of binge-drinking, is becoming an alarming phenomenon predictive of future problems with drinking. Thus, the literature indicates the need to better understand the influence of age and genetic background on the development of alcohol dependence. To this aim, the inbred rat strains Lewis (LEW, addiction prone) and Fischer 344 (F344, addiction resistant) were used as a model of genetic vulnerability to addiction and compared with the outbred strain Sprague-Dawley (SD) in a two-bottle choice paradigm as a model of alcohol abuse. During a 9-week period, adolescent and adult male rats of the three strains were intermittently exposed to ethanol (20%) and water during three 24-h sessions/week. Adult and adolescent SD and LEW rats escalated their alcohol intake over time reaching at stable levels, while F344 rats did not escalate their intake, regardless of age at drinking onset. Among adolescents, only F344 rats consumed a higher total amount of ethanol than adults, although only SD and LEW rats escalated their intake. Adult LEW rats, albeit having a lower ethanol consumption as compared to SD rats but greater than F344, showed a more compulsive intake, consuming higher amounts of ethanol during the first hour of exposure, reaching a higher degree of ethanol preference when start drinking as adolescents. Behavioral analysis during the first hour of ethanol consumption revealed significant strain differences, among which noticeable the lack of sedative effect in the LEW strain, at variance with F344 and SD strains, and highest indices of withdrawal (most notable jumping) in LEW rats during the first hour of abstinence days. The present results underscore the importance of individual genetic background and early onset of alcohol use in the progression toward abuse and development of alcohol addiction
Infrared observations of the candidate double neutron star system PSR J1811-1736
No full textPSR J1811-1736 (Ps = 104 ms) is an old (~1.89 Gyr) binary pulsar (Porb = 18.8 d) in a highly eccentric orbit (e = 0.828) with an unidentified companion. Interestingly, the pulsar timing solution yields an estimated companion mass of 0.93 M⊙ ≤ MC ≤ 1.5 M⊙, compatible with that of a neutron star. As such, it is possible that PSR J1811-1736 is a double neutron star (DNS) system, one of the very few discovered so far. This scenario can be investigated through deep optical/infrared (IR) observations. We used J- H- and K-band images, obtained as part of the UK Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS), and available in the recent Data Release 9 Plus, to search for the undetected companion of the PSR J1811-1736 binary pulsar. We detected a possible companion star to PSR J1811-1736 within the 3σ radio position uncertainty (1.32 arcsec), with magnitudes J = 18.61 ± 0.07, H = 16.65 ± 0.03 and K = 15.46 ± 0.02. The star colours are consistent with either a main sequence (MS) star close to the turn-off or a lower red giant branch (RGB) star, at a pulsar distance of ~5.5 kpc and with a reddening of E(B - V) ~4.9. The star mass and radius would be compatible with the constraints on the masses and orbital inclination of the binary system inferred from the mass function and with the lack of radio eclipses near superior conjunction. Thus, it is possible that it is the companion to PSR J1811-1736. However, based on the star density in the field, we estimated quite a large chance coincidence probability of ~0.27 between the pulsar and the star, which makes the association unlikely. No other star is detected within the 3σ pulsar radio position down to J ~ 20.5, H ~19.4 and K ~18.6, which allows us to rule out a MS companion star earlier than a mid-to-late M spectral typ
Conjugated dienes detected in tissue lipid extracts by second derivative spectrophotometry.
No full textBy studying lipid peroxidation induced by tetrachloromethane in rat liver microsomal PUFA, it has recently been shown that the primary products formed are conjugated diene hydroperoxides having either cis, trans (c,t) or trans,trans (t,t) stereochemistry. Both c,t and t,t hydroperoxidienes present distinct absorbances at 242 nm and 233 nm, respectively. The reaction is kinetically controlled in relation to the total H-atom donating ability of the cell environment. These results have been confirmed in vivo and in vitro experiments performed under different experimental conditions. The need for a precise and objective method to detect conjugated diene signals, the inherent difficulties with current techniques, and the availability of new spectrophotometric techniques have led us to devise a new method based on the second derivatization of the spectrum
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
NMR spin-lattice relaxation times of intracellular Na-23 on rat livers and related lipid peroxidation following CCl4 intoxication.
No full textLiver tissues were isolated from rats acutely intoxicated with carbon tetrachloride, and Na-23 NMR signals were analyzed to investigate the T1 relaxation times of intracellular sodium ions under pathological conditions in presence of the paramagnetic shift reagent (dysprosium tripolyphosphate). We studied the significant increase of T1 found in CCl4 treated rats with respect to controls, which was elsewhere demonstrated as being independent of cell necrosis. Evidence is given that neither fat accumulation nor proliferative processes affect the observed T1 lengthening. When T1 relaxation times were measured in the liver of vitamin E treated rats subsequently intoxicated with carbon tetrachloride, a significative shortening of T1 with respect to CCl4-intoxicated rats was observed. These results were discussed in terms of the antioxidant action exerted by vitamin E, taking into account that peroxidation of microsomal lipids is the key factor in the process of carbon tetrachloride induced liver injury. Furthermore, the observed T1 changes were discussed in terms of the interactions of Na+ with cell membranes and/or the occurrence of viscosity changes
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