An atlas of carbon nanotube optical transitions

Electron-electron interactions are significantly enhanced in one-dimensional systems, and single-walled carbon nanotubes provide a unique opportunity for studying such interactions and the related many-body effects in one dimension. However, single-walled nanotubes can have a wide range of diameters and hundreds of different structures, each defined by its chiral index (n,m), where n and m are integers that can have values from zero up to 30 or more. Moreover, one-third of these structures are metals and two-thirds are semiconductors, and they display optical resonances at many different frequencies. Systematic studies of many-body effects in nanotubes would therefore benefit from the availability of a technique for identifying the chiral index of a nanotube based on a measurement of its optical resonances, and vice versa. Here, we report the establishment of a structure-property 'atlas' for nanotube optical transitions based on simultaneous electron diffraction measurements of the chiral index and Rayleigh scattering measurements of the optical resonances of 206 different single-walled nanotube structures. The nanotubes, which were suspended across open slit structures on silicon substrates, had diameters in the range 1.3-4.7?nm. We also use this atlas as a starting point for a systematic study of many-body effects in the excited states of single-walled nanotubes. We find that electron-electron interactions shift the optical resonance energies by the same amount for both metallic and semiconducting nanotubes, and that this shift (which corresponds to an effective Fermi velocity renormalization) increases monotonically with nanotube diameter. This behaviour arises from two sources: an intriguing cancellation of long-range electron-electron interaction effects, and the dependence of short-range electron-electron interactions on diameter.     

Tobacco industry litigation position on addiction: continued dependence on past views

This paper reviews the tobacco industry's litigation strategy for addressing the addiction issue through trial testimony by its experts, and opening and closing statements by its lawyers. Despite the fact that several companies now claim to accept, in varying degrees, the conclusions of the Surgeon General concerning tobacco addiction, the tobacco industry litigation strategy pertaining to addiction is essentially unchanged since that of the early 1980s when the issue emerged as crucial. The industry uses its experts and the process of cross-examination of plaintiff's experts to imply that the addictiveness of tobacco and nicotine are more comparable to substances such as caffeine, chocolate, and even milk, than to heroin, cocaine and alcohol. Furthermore, the tobacco industry contends that the definition of addiction has now become so broadened as to include carrots and caffeine and hence that any concurrence that smoking is addictive, does not imply that cigarettes are addictive to the standards that drugs such as heroin and cocaine are addictive. Finally, the industry has continuously asserted that tobacco users assumed the risks of tobacco since they understood that quitting could be difficult when they began to use, and moreover, that the main barrier to cessation is lack of desire or motivation to quit and not physical addiction. These positions have been maintained through the 2004-2005 US Government litigation that was ongoing as the time of this writing.     

Pilot-scale in situ bioremedation of uranium in a highly contaminated aquifer. 2. Reduction of u(VI) and geochemical control of u(VI) bioavailability

In situ microbial reduction of soluble U(VI) to sparingly soluble U(IV) was evaluated at the site of the former S-3 Ponds in Area 3 of the U.S. Department of Energy Natural and Accelerated Bioremediation Research Field Research Center, Oak Ridge, TN. After establishing conditions favorable for bioremediation (Wu, et al. Environ. Sci. Technol. 2006, 40, 3988-3995), intermittent additions of ethanol were initiated within the conditioned inner loop of a nested well recirculation system. These additions initially stimulated denitrification of matrix-entrapped nitrate, but after 2 months, aqueous U levels fell from 5 to approximately 1 microM and sulfate reduction ensued. Continued additions sustained U(VI) reduction over 13 months. X-ray near-edge absorption spectroscopy (XANES) confirmed U(VI) reduction to U(IV) within the inner loop wells, with up to 51%, 35%, and 28% solid-phase U(IV) in sediment samples from the injection well, a monitoring well, and the extraction well, respectively. Microbial analyses confirmed the presence of denitrifying, sulfate-reducing, and iron-reducing bacteria in groundwater and sediments. System pH was generally maintained at less than 6.2 with low bicarbonate level (0.75-1.5 mM) and residual sulfate to suppress methanogenesis and minimize uranium mobilization. The bioavailability of sorbed U(VI) was manipulated by addition of low-level carbonate (< 5 mM) followed by ethanol (1-1.5 mM). Addition of low levels of carbonate increased the concentration of aqueous U, indicating an increased rate of U desorption due to formation of uranyl carbonate complexes. Upon ethanol addition, aqueous U(VI) levels fell, indicating that the rate of microbial reduction exceeded the rate of desorption. Sulfate levels simultaneously decreased, with a corresponding increase in sulfide. When ethanol addition ended but carbonate addition continued, soluble U levels increased, indicating faster desorption than reduction. When bicarbonate addition stopped, aqueous U levels decreased, indicating adsorption to sediments. Changes in the sequence of carbonate and ethanol addition confirmed that carbonate-controlled desorption increased bioavailability of U(VI) for reduction.     

How do low-energy (0.1-2 eV) electrons cause DNA-strand breaks?

We overview our recent theoretical predictions and the innovative experimental findings that inspired us concerning the mechanisms by which very low-energy (0.1-2 eV) free electrons attach to DNA and cause strong (ca. 4 eV) covalent bonds to break causing so-called single-strand breaks. Our primary conclusions are that (i) attachment of electrons in the above energy range to base pi* orbitals is more likely than attachment elsewhere and (ii) attachment to base pi* orbitals most likely results in cleavage of sugar-phosphate C-O sigma bonds. Later experimental findings that confirmed our predictions about the nature of the electron attachment event and about which bonds break when strand breaks form are also discussed. The proposed mechanism of strand break formation by low-energy electrons involves an interesting through-bond electron-transfer process.     

Unexpected oxidation of a depsipeptide substrate analogue in crystalline isopenicillin N synthase

Isopenicillin N synthase (IPNS) is a non-heme iron(ii)-dependent oxidase that is central to penicillin biosynthesis. Herein, we report mechanistic studies of the IPNS reaction in the crystalline state, using the substrate analogue delta-(L-alpha-aminoadipoyl)-(3R)-methyl-L-cysteine D-alpha-hydroxyisovaleryl ester (AmCOV) to probe the early stages of the catalytic cycle. The X-ray crystal structure of the anaerobic IPNS:Fe(II):AmCOV complex was solved to 1.40 A resolution, and it reveals several subtle differences in the active site relative to the complex of the enzyme with its natural substrate. The crystalline IPNS:Fe(II):AmCOV complex was then exposed to oxygen gas at high pressure; this brought about reaction to give what appears to be a hydroxymethyl/ene-thiol product. A mechanism for this reaction is proposed. These results offer further insight into the delicate interplay of steric and electronic effects in the IPNS active site and the mechanistic intricacies of this remarkable enzyme.     

Portable linear accelerators for X-ray and electron-beam applications in civil engineering

Portable linear accelerator systems are being used to provide high-intensity X-rays for structural engineering studies and non-destructive testing in the USA and Europe. These devices greatly enhance the ability of engineers to examine structural members for hidden defects, as well as to study internal design and construction details of large buildings, bridges, parking garages and other structures, including steel memebers up to 16" thick and concrete over 62" thick. The resulting radiographic images are of excellent quality, enabling quick, reliable analysis of hidden conditions in the field. Three representative case studies are discussed in detail, and new developemnts are highlighted, including use of robotics for positioning and the use of accelerators for curing composite materials in-situ.     

Introduction to the Special Section on Philosophy and Psychotherapy Integration and to the Inaugural Focus on Moral Philosophy.

The present article introduces this special section exploring intersections between philosophy and psychotherapy, particularly vis-à-vis the latter's integrative challenges and potentialities. Philosophy's principal domains of inquiry are summarized, followed by specification of the aims and propositions guiding this section. Representative areas for applying philosophical analysis to psychotherapeutic theory, research, and practice are identified and briefly elaborated. Subsequent overview of the 1st area of conjunction explored in this section, moral philosophy and psychotherapy, includes a sampling of major theoretical propositions on morality and brief discussion of applied ethics. In these overlapping contexts, the author highlights features of Ronald B. Miller's (2005) inaugural article and Michael J. Mahoney's (2005) commentary. Concluding thoughts pose and address the question of the meanings and implications of philosophical analyses of psychotherapy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adolescent smoking trajectories and nicotine dependence.

The present study correlates empirically constructed prospective adolescent smoking trajectories with indicators of nicotine dependence assessed in adolescence and in adulthood. Excluding individuals who reported no smoking during repeat assessment (nonadopters), we identified five smoking trajectory groups: experimenters (n=116, 48.5%), late increasers (n=39, 16.3%), early increasers (n=37, 15.5%), quitters (n=22, 9.2%), and persistent smokers (n=25, 10.5%). Higher frequency of nicotine dependence symptoms in adolescence occurred in the quitters and persistent smokers groups, who smoked at higher levels relative to the experimenters, late increasers, and early increasers groups, who reported a similar frequency of nicotine dependence symptoms and smoked at low levels. Lifetime nicotine dependence was assessed in adulthood in lifetime daily smokers using the Fagerstr?m Test for Nicotine Dependence (FTND) and the Nicotine Dependence Scale (NDS). Lifetime FTND levels were similar across trajectory groups. Relative to experimenters, all remaining smoking trajectory groups had higher NDS levels that were similar to one another. These results suggest that higher levels of adolescent nicotine dependence were associated with heavier smoking trajectory groups, and that regardless of trajectory group membership, smoking more than a few cigarettes per week throughout adolescence resulted in similar levels of lifetime nicotine dependence as measured by the FTND and NDS.