Results of a Search for Sub-GeV Dark Matter Using 2013 LUX Data.

The scattering of dark matter (DM) particles with sub-GeV masses off nuclei is difficult to detect using liquid xenon-based DM search instruments because the energy transfer during nuclear recoils is smaller than the typical detector threshold. However, the tree-level DM-nucleus scattering diagram can be accompanied by simultaneous emission of a bremsstrahlung photon or a so-called "Migdal" electron. These provide an electron recoil component to the experimental signature at higher energies than the corresponding nuclear recoil. The presence of this signature allows liquid xenon detectors to use both the scintillation and the ionization signals in the analysis where the nuclear recoil signal would not be otherwise visible. We report constraints on spin-independent DM-nucleon scattering for DM particles with masses of 0.4-5 GeV/c^{2} using 1.4×10^{4} kg day of search exposure from the 2013 data from the Large Underground Xenon (LUX) experiment for four different classes of mediators. This analysis extends the reach of liquid xenon-based DM search instruments to lower DM masses than has been achieved previously.

Limits on Spin-Dependent WIMP-Nucleon Cross Section Obtained from the Complete LUX Exposure.

We present experimental constraints on the spin-dependent WIMP-nucleon elastic cross sections from the total 129.5 kg yr exposure acquired by the Large Underground Xenon experiment (LUX), operating at the Sanford Underground Research Facility in Lead, South Dakota (USA). A profile likelihood ratio analysis allows 90% C.L. upper limits to be set on the WIMP-neutron (WIMP-proton) cross section of σ_{n}=1.6×10^{-41} cm^{2} (σ_{p}=5×10^{-40} cm^{2}) at 35 GeV c^{-2}, almost a sixfold improvement over the previous LUX spin-dependent results. The spin-dependent WIMP-neutron limit is the most sensitive constraint to date.

First Searches for Axions and Axionlike Particles with the LUX Experiment.

The first searches for axions and axionlike particles with the Large Underground Xenon experiment are presented. Under the assumption of an axioelectric interaction in xenon, the coupling constant between axions and electrons g_{Ae} is tested using data collected in 2013 with an exposure totaling 95 live days ×118 kg. A double-sided, profile likelihood ratio statistic test excludes g_{Ae} larger than 3.5×10^{-12} (90% C.L.) for solar axions. Assuming the Dine-Fischler-Srednicki-Zhitnitsky theoretical description, the upper limit in coupling corresponds to an upper limit on axion mass of 0.12 eV/c^{2}, while for the Kim-Shifman-Vainshtein-Zhakharov description masses above 36.6 eV/c^{2} are excluded. For galactic axionlike particles, values of g_{Ae} larger than 4.2×10^{-13} are excluded for particle masses in the range 1-16 keV/c^{2}. These are the most stringent constraints to date for these interactions.

Results from a Search for Dark Matter in the Complete LUX Exposure.

We report constraints on spin-independent weakly interacting massive particle (WIMP)-nucleon scattering using a 3.35×10^{4} kg day exposure of the Large Underground Xenon (LUX) experiment. A dual-phase xenon time projection chamber with 250 kg of active mass is operated at the Sanford Underground Research Facility under Lead, South Dakota (USA). With roughly fourfold improvement in sensitivity for high WIMP masses relative to our previous results, this search yields no evidence of WIMP nuclear recoils. At a WIMP mass of 50 GeV c^{-2}, WIMP-nucleon spin-independent cross sections above 2.2×10^{-46} cm^{2} are excluded at the 90% confidence level. When combined with the previously reported LUX exposure, this exclusion strengthens to 1.1×10^{-46} cm^{2} at 50 GeV c^{-2}.

Improved Limits on Scattering of Weakly Interacting Massive Particles from Reanalysis of 2013 LUX Data.

We present constraints on weakly interacting massive particles (WIMP)-nucleus scattering from the 2013 data of the Large Underground Xenon dark matter experiment, including 1.4×10^{4} kg day of search exposure. This new analysis incorporates several advances: single-photon calibration at the scintillation wavelength, improved event-reconstruction algorithms, a revised background model including events originating on the detector walls in an enlarged fiducial volume, and new calibrations from decays of an injected tritium ß source and from kinematically constrained nuclear recoils down to 1.1 keV. Sensitivity, especially to low-mass WIMPs, is enhanced compared to our previous results which modeled the signal only above a 3 keV minimum energy. Under standard dark matter halo assumptions and in the mass range above 4 GeV c^{-2}, these new results give the most stringent direct limits on the spin-independent WIMP-nucleon cross section. The 90% C.L. upper limit has a minimum of 0.6 zb at 33 GeV c^{-2} WIMP mass.

Results on the Spin-Dependent Scattering of Weakly Interacting Massive Particles on Nucleons from the Run 3 Data of the LUX Experiment.

We present experimental constraints on the spin-dependent WIMP (weakly interacting massive particle)-nucleon elastic cross sections from LUX data acquired in 2013. LUX is a dual-phase xenon time projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota), which is designed to observe the recoil signature of galactic WIMPs scattering from xenon nuclei. A profile likelihood ratio analysis of 1.4×10^{4} kg day of fiducial exposure allows 90% C.L. upper limits to be set on the WIMP-neutron (WIMP-proton) cross section of σ_{n}=9.4×10^{-41} cm^{2} (σ_{p}=2.9×10^{-39} cm^{2}) at 33 GeV/c^{2}. The spin-dependent WIMP-neutron limit is the most sensitive constraint to date.

High-order harmonic generation from a dual-gas, multi-jet array with individual gas jet control.

We present a gas jet array for use in high-order harmonic generation experiments. Precise control of the pressure in each individual gas jet has allowed a thorough investigation into mechanisms contributing to the selective enhancement observed in the harmonic spectra produced by dual-gas, multi-jet arrays. Our results reveal that in our case, the dominant enhancement mechanism is the result of a compression of the harmonic-producing gas jet due to the presence of other gas jets in the array. The individual control of the gas jets in the array also provides a promising method for enhancing the harmonic yield by precise tailoring of the length and pressure gradient of the interaction region.

Three-dimensional electronic spectroscopy of excitons in asymmetric double quantum wells.

We demonstrate three-dimensional (3D) electronic spectroscopy of excitons in a double quantum well system using a three-dimensional phase retrieval algorithm to obtain the phase information that is lost in the measurement of intensities. By extending the analysis of two-dimensional spectroscopy to three dimensions, contributions from different quantum mechanical pathways can be further separated allowing greater insight into the mechanisms responsible for the observed peaks. By examining different slices of the complete three-dimensional spectrum, not only can the relative amplitudes be determined, but the peak shapes can also be analysed to reveal further details of the interactions with the environment and inhomogeneous broadening. We apply this technique to study the coupling between two coupled quantum wells, 5.7 nm and 8 nm wide, separated by a 4 nm barrier. Coupling between the heavy-hole excitons of each well results in a circular cross-peak indicating no correlation of the inhomogeneous broadening. An additional cross-peak is isolated in the 3D spectrum which is elongated in the diagonal direction indicating correlated inhomogeneous broadening. This is attributed to coupling of the excitons involving the two delocalised light-hole states and the electron state localised on the wide well. The attribution of this peak and the analysis of the peak shapes is supported by numerical simulations of the electron and hole wavefunctions and the three-dimensional spectrum based on a density matrix approach. An additional benefit of extending the phase retrieval algorithm from two to three dimensions is that it becomes substantially more reliable and less susceptible to noise as a result of the more extensive use of a priori information.

Isolation of a human myocardial cytosolic phospholipase A2 isoform. Fast atom bombardment mass spectroscopic and reverse-phase high pressure liquid chromatography identification of choline and ethanolamine glycerophospholipid substrates.

Recent studies have demonstrated the existence of a novel family of calcium-independent plasmalogen-selective phospholipases A2 in canine myocardium that have been implicated as enzymic mediators of ischemic membrane damage. We now report that human myocardium contains two functionally distinct isoforms of cytosolic calcium-independent phospholipase A2. The major cytosolic phospholipase A2 isoform preferentially hydrolyzes plasmalogen substrate, possesses a pH optimum of 7.0, and is chromatographically resolvable from a minor cytosolic calcium-independent phospholipase A2 isoform that hydrolyzes plasmenylcholine and phosphatidylcholine substrates at similar rates and possesses a pH optimum of 8.5. The major cytosolic calcium-independent phospholipase A2 isoform was identified as a 40-kD polypeptide after its 182,000-fold purification by sequential column chromatographies to a final specific activity of 67 mumol/mg.min. The purified 40-kD human myocardial phospholipase A2 preferentially hydrolyzes plasmalogens containing arachidonic acid at the sn-2 position. Both reverse-phase HPLC and fast atom bombardment mass spectroscopic analysis of human myocardial ethanolamine and choline glycerophospholipids demonstrated that plasmenylethanolamine and plasmenylcholine molecular species containing arachidonic acid at the sn-2 position are prominent constituents of human myocardium. Collectively, these results identify and characterize the major human myocardial cytosolic calcium-independent phospholipase A2 activity, demonstrate the presence of functionally distinct human myocardial cytosolic calcium-independent phospholipase A2 isoforms, and document the abundance of arachidonoylated plasmalogen molecular species in human myocardium that serve as substrates.

Mechanisms of nicotinamide and thymidine protection from alloxan and streptozocin toxicity.

A common mechanism has been proposed for the beta-cell toxins alloxan (ALX) and streptozocin (STZ) involving the formation of single-strand breaks in DNA that lead to the overactivation of the enzyme poly(ADP-ribose) synthetase and the critical depletion of its substrate NAD. If the toxins act via this common mechanism, the poly(ADP-ribose) synthetase inhibitors nicotinamide and thymidine would be expected to affect the formation of DNA single-strand breaks in a similar fashion. To test the effects of these inhibitors, the formation of single-strand breaks in the DNA of insulin-secreting RINr cells was monitored by assessing changes in the supercoiling of nucleoids after exposure to STZ, ALX, or methylnitrosourea (MNU). With the inclusion of nicotinamide or thymidine and STZ or MNU, more single-strand breaks in RINr cell DNA were detected. These results would be expected if nicotinamide and thymidine acted through inhibition of poly(ADP-ribose) synthetase. However, when the inhibitors were used in combination with ALX, fewer single-strand breaks were present. This suggests a reduction in ALX-induced hydroxyl radicals available to interact with DNA. Because nicotinamide has been demonstrated to be a hydroxyl-radical scavenger, the ability of thymidine to scavenge hydroxyl radicals was investigated. Thymidine, like nicotinamide, was found to be a potent scavenger of hydroxyl radicals. Thus, the mechanisms by which nicotinamide and thymidine protect against the toxic effects of STZ or ALX appear different. These findings suggest that the actions of beta-cell toxins are more complex than simply the overactivation of a single enzyme.

Identification of a point mutation in the thyrotropin receptor of the hyt/hyt hypothyroid mouse.

The hyt/hyt hypothyroid mouse has an autosomal recessive, fetal-onset, severe hypothyroidism related to TSH hyporesponsiveness and associated with elevated TSH. Our previous work has suggested that the hypothyroidism and TSH hyporesponsiveness may result from a mutation in the hyt/hyt TSH receptor (TSHr) of the thyroid gland. Based on DNA sequencing of the entire coding region of the TSHr gene from the wild-type BALB/cBY +/+ mouse, the +/+ TSHr is 92% and 94% identical at the nucleotide and amino acid residue levels, respectively, compared to the rat TSHr gene. The coding region of the hyt/hyt TSHr, compared to that of the +/+ TSHr, has a single base change, CCG to CTG, at nucleotide position 1666, which leads to the replacement of a highly conserved proline at amino acid position 556 with a leucine in transmembrane domain IV. This mutation was introduced by site-directed mutagenesis into the wild-type human TSHr and transiently expressed in COS-7 cells. Although the size and abundance of the mutant TSHr mRNA suggested that there was no effect on the nature of the mRNA, TSH binding and the response to TSH in transfected cells were abolished. Further studies are necessary to clarify how the Pro to Leu replacement interferes with receptor expression on the cell surface or influences TSH binding. These functional consequences of the mutation appear to account for the observed TSH hyporesponsiveness and hypothyroidism in the hyt/hyt mouse.

Heparan sulfate abnormalities in exostosis growth plates.

Hereditary multiple exostoses (HME), a condition associated with development and growth of bony exostoses at the ends of the long bones, is caused by germline mutations in the EXT genes. EXT1 and EXT2 function as glycosyltransferases that participate in the biosynthesis of heparan sulfate (HS) to modify proteoglycans. HS proteoglycans, synthesized by chondrocytes and secreted to the extracellular matrix of the growth plate, play critical roles in growth plate signaling and remodeling. As part of studies to delineate the mechanism(s) by which an exostosis develops, we have systematically evaluated four growth plates from two HME and two solitary exostoses. Mutational events were correlated with the presence/absence and distribution of HS and the normally abundant proteoglycan, perlecan (PLN). DNA from the HME exostoses demonstrated heterozygous germline EXT1 or EXT2 mutations, and DNA from one solitary exostosis demonstrated a somatic EXT1 mutation. No loss of heterozygosity was observed in any of these samples. The chondrocyte zones of four exostosis growth plates showed absence of HS, as well as diminished and abnormal distribution of PLN. These results indicate that, although multiple mutational events do not occur in the EXT1 or EXT2 genes, a complete loss of HS was found in the exostosis growth plates. This functional knockout of the exostosis chondrocytes' ability to synthesize HS chains further supports the observations of cytoskeletal abnormalities and chondrocyte disorganization associated with abnormal cell signaling.

Prediction of obligatory exercise by exercise-related imagery.

Obligatory exercise is a compulsive behavior pattern in which exercise dominates daily life at the expense of other activities and lack of exercise produces withdrawal symptoms. This study examined the hypothesis that obligatory exercise is motivated similarly to eating disorders (cf. S. P. Coen & B. M. Ogles, 1993) and would be predicted by appearance-related imagery. Obligatory exercise (J. K. Thompson & L. Pasman, 1991) and exercise imagery (H. A. Hausenblas, C. R. Hall, W. M. Rodgers, & K. J. Munroe, 1999) were assessed before and after a 10-week exercise program in 243 adult exercisers. Regression analyses revealed that imagery accounted for 20% of the variance in obligatory exercise. Appearance-related imagery did not predict significantly obligatory exercise. Energy-related imagery was the strongest predictor. Obligatory exercise may not be as associated with appearance-related concerns as eating disorders, suggesting different motivational bases for these 2 behavioral patterns.

Repetition and lag effects in movement recognition.

Whether repetition and lag improve the recognition of movement patterns was investigated. Recognition memory was tested for one repetition, two-repetitions massed, and two-repetitions distributed with movement patterns at lags of 3, 5, 7, and 13. Recognition performance was examined both immediately afterwards and following a 48 hour delay. Both repetition and lag effects failed to be demonstrated, providing some support for the claim that memory is unaffected by repetition at a constant level of processing (Craik & Lockhart, 1972). There was, as expected, a significant decrease in recognition memory following the retention interval, but this appeared unrelated to repetition or lag.

Rehearsal of temporal visual information.

This study compared the short-term retention characteristics of temporal information when subjects experienced time under either subject-defined or experimenter-defined rehearsal. Subjects were presented visual durations of 1 and 4 sec. and then required to reproduce these durations following a 15-sec. retention interval. To help maintain the durations in memory, subjects were asked to use either a conscious cognitive strategy or a mental counting strategy. It was predicted that experimenter-defined rehearsal would show less forgetting, as measured by variable error, but this prediction was not supported. There also was no evidence of any response bias or context effects in the temporal reproductions. These results were compared with two previous studies that utilized similar cognitive strategies.

Evidence for a multidimensional self-efficacy for exercise scale.

This series of three studies considers the multidimensionality of exercise self-efficacy by examining the psychometric characteristics of an instrument designed to assess three behavioral subdomains: task, scheduling, and coping. In Study 1, exploratory factor analysis revealed the expected factor structure in a sample of 395 students. Confirmatory factor analysis (CFA) confirmed these results in a second sample of 282 students. In Study 2, the generalizability of the factor structure was confirmed with CFA in a randomly selected sample of 470 community adults, and discriminant validity was supported by theoretically consistent distinctions among exercisers and nonexercisers. In Study 3, change in self-efficacy in conjunction with adoption of novel exercise was examined in a sample of 58 women over 12 weeks. Observed changes in the three self-efficacy domains appeared to be relatively independent. Together, the three studies support a multidimensional conceptualization of exercise self-efficacy that can be assessed and appears to be sensitive to change in exercise behavior.

Individual differences in the mental practice and imagery of motor skill performance.

The role of mental practice in motor skill learning is briefly reviewed, and the relationship between mental practice and imagery discussed. A case is made for the importance of considering individual differences for imagery in motor studies investigating mental practice. Studies that have examined imagery ability in the motor domain are outlined, and the reasons are addressed why a consistent relationship between imagery ability and motor performance has failed to emerge. Finally, an approach for investigating imagery ability is suggested. This approach concentrates on the inclusion and interaction of three imagery related variables: the measurement of imagery ability, the task to be performed, and the imagery instructions that are given to the subjects.

Sabethes (Peytonulus) luxodens, a new species of Sabethini (Diptera: Culicidae) from Ecuador.

The adult male, larva and pupa of Sabethes (Peytonulus) luxodens, a new species from Ecuador, are described. The species is distinguished from Sabethes aurescens (Lutz), which it closely resembles in all life stages.