Concerted hydrogen atom exchange between three HF molecules

We have investigated the termolecular reaction involving concerted hydrogen exchange between three HF molecules, with particular emphasis on the effects of correlation at the various stationary points along the reaction. Using an extended basis, we have located the geometries of the stable hydrogen-bonded trimer, which is of C(sub 3h) symmetry, and the transition state for hydrogen exchange, which is of D(sub 3h) symmetry. The energies of the exchange reation were then evaluated at the correlated level, using a large atomic natural orbital basis and correlating all valence electrons. Several correlation treatments were used, namely, configration interaction with single and double excitations, coupled-pair functional, and coupled-cluster methods. We are thus able to measure the effect of accounting for size-extensivity. Zero-point corrections to the correlated level energetics were determined using analytic second derivative techniques at the SCF level. Our best calculations, which include the effects of connected triple excitations in the coupled-cluster procedure, indicate that the trimer is bound by 9 +/- 1 kcal/mol relative to three separate monomers, in excellent agreement with previous estimates. The barrier to concerted hydrogen exchange is 15 kcal/mol above the trimer, or only 4.7 kcal/mol above three separated monomers. Thus the barrier to hydrogen exchange between HF molecules via this termolecular process is very low

Phased electromagnetic acoustic transducer array for Rayleigh wave surface defect detection

A phased electromagnetic acoustic transducer (EMAT) array system has been developed for detection and characterisation of surface breaking defects. An array of four linear coils which are individually controlled are used to generate a Rayleigh wave. The high current electronics combined with the coil designs enables the array to generate either narrowband or broadband signals, and controlling the phase delay between the channels makes it possible to change the ultrasound wavelength without requiring the physical separation of the coils to be changed. Experimental results show that the four-coil phased array is able to generate a wavelength range from 3.0 mm to 11.7 mm. Surface breaking defects were characterised using a transmit-receive set-up with a broadband EMAT detector being used to detect the Rayleigh wave. Machined surface slots with different depths were used for technique validation. The results show that the array is sensitive to surface defects and that a wide depth sensitivity range for defect sizing can be easily achieved by applying phasing to tune the wavelength of operation. A large increase in detection flexibility is immediately shown

Finding qualitative research: an evaluation of search strategies

BACKGROUND: Qualitative research makes an important contribution to our understanding of health and healthcare. However, qualitative evidence can be difficult to search for and identify, and the effectiveness of different types of search strategies is unknown. METHODS: Three search strategies for qualitative research in the example area of support for breast-feeding were evaluated using six electronic bibliographic databases. The strategies were based on using thesaurus terms, free-text terms and broad-based terms. These strategies were combined with recognised search terms for support for breast-feeding previously used in a Cochrane review. For each strategy, we evaluated the recall (potentially relevant records found) and precision (actually relevant records found). RESULTS: A total yield of 7420 potentially relevant records was retrieved by the three strategies combined. Of these, 262 were judged relevant. Using one strategy alone would miss relevant records. The broad-based strategy had the highest recall and the thesaurus strategy the highest precision. Precision was generally poor: 96% of records initially identified as potentially relevant were deemed irrelevant. Searching for qualitative research involves trade-offs between recall and precision. CONCLUSIONS: These findings confirm that strategies that attempt to maximise the number of potentially relevant records found are likely to result in a large number of false positives. The findings also suggest that a range of search terms is required to optimise searching for qualitative evidence. This underlines the problems of current methods for indexing qualitative research in bibliographic databases and indicates where improvements need to be made

D1/D5 Moduli in SCFT and Gauge Theory, and Hawking Radiation

We construct marginal operators of the orbifold SCFT corresponding to all twenty near-horizon moduli in supergravity, including operators involving twist fields which correspond to the blowing up modes. We identify the operators with the supergravity moduli in a 1-1 fashion by inventing a global SO(4) algebra in the SCFT. We analyze the gauge dynamics of the D1/D5 system relevant to the splitting $(Q_1,Q_5)\to (Q'_1,Q'_5)+ (Q''_1,Q''_5)$ with the help of a linear sigma model. We show in supergravity as well as in SCFT that the absorption cross-section for minimal scalars is the same all over the near-horizon moduli space.Comment: 34 pages, latex, no figure

Multiple Mirror Manifolds and Topology Change in String Theory

We use mirror symmetry to establish the first concrete arena of spacetime topology change in string theory. In particular, we establish that the {\it quantum theories} based on certain nonlinear sigma models with topologically distinct target spaces can be smoothly connected even though classically a physical singularity would be encountered. We accomplish this by rephrasing the description of these nonlinear sigma models in terms of their mirror manifold partners--a description in which the full quantum theory can be described exactly using lowest order geometrical methods. We establish that, for the known class of mirror manifolds, the moduli space of the corresponding conformal field theory requires not just two but {\it numerous} topologically distinct Calabi-Yau manifolds for its geometric interpretation. A {\it single} family of continuously connected conformal theories thereby probes a host of topologically distinct geometrical spaces giving rise to {\it multiple mirror manifolds}.Comment: 18 pp., (uses harvmac and epsf) (Missing reference added.

Closed String Tachyons on C/Z_N

We analyse the condensation of closed string tachyons on the $C/Z_N$ orbifold. We construct the potential for the tachyons upto the quartic interaction term in the large $N$ limit. In this limit there are near marginal tachyons. The quartic coupling for these tachyons is calculated by subtracting from the string theory amplitude for the tachyons, the contributions from the massless exchanges, computed from the effective field theory. We argue that higher point interaction terms are are also of the same order in 1/N as the quartic term and are necessary for existence of the minimum of the tachyon potential that is consistent with earlier analysis.Comment: 19 pages, 1 figure; comments added about $N$ dependence of contact ter

Predicting the Reactions of CS2 with Group IV and Group VI Transition Metal Oxides

Building onto a recent serious of ab initio studies of various acid-gas reactions with metal oxide sorbents, electronic structure methods are being used to study the addition of CS₂ to Group IV (MO₂)ₙ and Group VI (MO₃)ₙ (n = 1, 2, 3) nanoclusters, beginning with the MO₂ and MO₃ monomers according to a “bottom-up” approach. The preliminary density functional theory (DFT) calculations in this study provide structures and vibrational frequency thermodynamic corrections for later expanding upon by way of single point correlated molecular-orbital theory (MO) calculations, mainly CCSD(T) and MP2 to study the structures and energies which could arise from Lewis acid-base addition (physisorption) and formation of COS₂²⁻ (chemisorption) of CS₂ to these clusters will be predicted. For future work, these CS₂ ligand binding energies (LBE) will be compared to established CO₂ results in the literature and to any known experimental and computational values for the interactions of CS₂ with bulk metal oxides. These LBEs will then be analyzed for any correlation to any known trends in the metal oxide Lewis acidity, metal oxide redox chemistry, and acid gas basicity to establish useful thermodynamic benchmarks for the practicality of Group IV and Group VI transition metal oxides for the sequestration and conversion of CS₂. The results of this work and beyond could also have serious implications for the sequestration of CS₂ from high-sulfur areas of the arctic permafrost and could provide valuable mechanistic insights into the possible reactions and products of metal oxide degradation during the Claus Process.https://scholarworks.moreheadstate.edu/celebration_posters_2023/1062/thumbnail.jp

Effects of experience on voluntary intake of supplements by cattle

Experiments examined the effects of prior experience of young cattle on their voluntary intake of supplements, and variability among animals in intake of supplements. Variability was measured using supplement labelled with lithium salts. Experiment 1 examined the effects of offering a concentrate supplement to calves before and/or after weaning on their subsequent intake of the same supplement and of a loose mineral mix supplement. Experience of the concentrate supplement increased acceptance and reduced variability in intake of the loose mineral mix supplement. However, neither voluntary intake (mean is 105 g DM/head.day) nor variability in intake of loose mineral mix supplement was affected by prior experience. Experiments 2 and 3 examined variability in intake of loose mineral mix supplement by weaners in larger groups or offered molasses–urea supplement, respectively. Experiment 4 examined the effects of provision of supplements and/or exposure to human activity and handling on subsequent intake of loose mineral mix supplement. Supplementing grazing weaners with concentrates had a transient effect by increasing voluntary intake of loose mineral mix supplement, but increased exposure to supplements, and human activity and handling while held in yards after weaning had no effects. Variability among animals in intake of loose mineral mix supplement (CV is 52–103%) tended to be greater than with the concentrate or molasses-based supplements (CV is 23–43%), irrespective of previous experience. There were fewer than 1% non-eaters of concentrate supplement and 0–7% non-eaters of loose mineral mix supplement. In experiment 5, prior experience of loose mineral mix supplements increased intake of such supplements by weaners during weeks 1 and 2 but not from weeks 3 to 9. In experiment 6, intake of loose mineral mix supplement by adult cattle was not affected by their experience as weaners of a similar supplement. In conclusion, although prior experience of supplements by young cattle sometimes increased their initial acceptance and voluntary intake of supplements, longer-term intake of supplements was not affected

Orbifold Resolution by D-Branes

We study topological properties of the D-brane resolution of three-dimensional orbifold singularities, C^3/Gamma, for finite abelian groups Gamma. The D-brane vacuum moduli space is shown to fill out the background spacetime with Fayet--Iliopoulos parameters controlling the size of the blow-ups. This D-brane vacuum moduli space can be classically described by a gauged linear sigma model, which is shown to be non-generic in a manner that projects out non-geometric regions in its phase diagram, as anticipated from a number of perspectives.Comment: 26 pages, 2 figures (TeX, harvmac big, epsf

Identification of candidate genes affecting Delta9-tetrahydrocannabinol biosynthesis in Cannabis sativa.

RNA isolated from the glands of a Delta(9)-tetrahydrocannabinolic acid (THCA)-producing strain of Cannabis sativa was used to generate a cDNA library containing over 100 000 expressed sequence tags (ESTs). Sequencing of over 2000 clones from the library resulted in the identification of over 1000 unigenes. Candidate genes for almost every step in the biochemical pathways leading from primary metabolites to THCA were identified. Quantitative PCR analysis suggested that many of the pathway genes are preferentially expressed in the glands. Hexanoyl-CoA, one of the metabolites required for THCA synthesis, could be made via either de novo fatty acids synthesis or via the breakdown of existing lipids. qPCR analysis supported the de novo pathway. Many of the ESTs encode transcription factors and two putative MYB genes were identified that were preferentially expressed in glands. Given the similarity of the Cannabis MYB genes to those in other species with known functions, these Cannabis MYBs may play roles in regulating gland development and THCA synthesis. Three candidates for the polyketide synthase (PKS) gene responsible for the first committed step in the pathway to THCA were characterized in more detail. One of these was identical to a previously reported chalcone synthase (CHS) and was found to have CHS activity. All three could use malonyl-CoA and hexanoyl-CoA as substrates, including the CHS, but reaction conditions were not identified that allowed for the production of olivetolic acid (the proposed product of the PKS activity needed for THCA synthesis). One of the PKS candidates was highly and specifically expressed in glands (relative to whole leaves) and, on the basis of these expression data, it is proposed to be the most likely PKS responsible for olivetolic acid synthesis in Cannabis glands