871 research outputs found

    Light Gluino Constituents of Hadrons and a Global Analysis of Hadron Scattering Data

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    Light strongly interacting supersymmetric particles may be treated as partonic constituents of nucleons in high energy scattering processes. We construct parton distribution functions for protons in which a light gluino is included along with standard model quark, antiquark, and gluon constituents. A global analysis is performed of a large set of data from deep-inelastic lepton scattering, massive lepton pair and vector boson production, and hadron jet production at large values of transverse momentum. Constraints are obtained on the allowed range of gluino mass as a function of the value of the strong coupling strength alpha_s(M_Z) determined at the scale of the Z boson mass. We find that gluino masses as small as 10 GeV are admissible provided that alpha_s(M_Z) \ge 0.12. Current hadron scattering data are insensitive to the presence of gluinos heavier than ~ 100 - 150 GeV.Comment: 31 pages, 12 figures, RevTe

    Photometry of Proxima Centauri and Barnard's Star Using HST Fine Guidance Sensor 3: A Search for Periodic Variations

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    We have observed Proxima Centauri and Barnard's Star with Hubble Space Telescope Fine Guidance Sensor 3. Proxima Centauri exhibits small-amplitude, periodic photometric variations. Once several sources of systematic photometric error are corrected, we obtain 2 milli-magnitude internal photometric precision. We identify two distinct behavior modes over the past four years: higher amplitude, longer period; smaller amplitude, shorter period. Within the errors one period (P ~ 83d) is twice the other. Barnard's Star shows very weak evidence for periodicity on a timescale of approximately 130 days. If we interpret these periodic phenomena as rotational modulation of star spots, we identify three discrete spots on Proxima Cen and possibly one spot on Barnard's Star. We find that the disturbances change significantly on time scales as short as one rotation period.Comment: 39 pages, 17 figure

    Brief of Plaintiffs - Appellants in \u3cem\u3eEnvironmental Defense Fund v. TVA\u3c/em\u3e, No. 73-8174

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    Brief of the plaintiffs/appellants in the case of Environmental Defense Fund, et al. v. TVA, et al. in the United States Court of Appeals for the Sixth Circuit

    Interferometric Astrometry of Proxima Centauri and Barnard's Star Using Hubble Space Telescope Fine Guidance Sensor 3: Detection Limits for sub-Stellar Companions

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    We report on a sub-stellar companion search utilizing interferometric fringe-tracking astrometry acquired with Fine Guidance Sensor 3 (FGS 3) on the Hubble Space Telescope. Our targets were Proxima Centauri and Barnard's Star. We obtain absolute parallax values for Proxima Cen pi_{abs} = 0.7687 arcsecond and for Barnard's Star pi_{abs} = 0.5454 arcsecond. Once low-amplitude instrumental systematic errors are identified and removed, our companion detection sensitivity is less than or equal to one Jupiter mass for periods longer than 60 days for Proxima Cen. Between the astrometry and the radial velocity results we exclude all companions with M > 0.8M_{Jup} for the range of periods 1 < P < 1000 days. For Barnard's Star our companion detection sensitivity is less than or equal to one Jupiter mass for periods long er than 150 days. Our null results for Barnard's Star are consistent with those of Gatewood (1995).Comment: 35 pages, 13 figures, to appear in August 1999 A

    High prevalence of <i>Rickettsia africae</i> variants in <i>Amblyomma variegatum</i> ticks from domestic mammals in rural western Kenya: implications for human health

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    Tick-borne spotted fever group (SFG) rickettsioses are emerging human diseases caused by obligate intracellular Gram-negative bacteria of the genus Rickettsia. Despite being important causes of systemic febrile illnesses in travelers returning from sub-Saharan Africa, little is known about the reservoir hosts of these pathogens. We conducted surveys for rickettsiae in domestic animals and ticks in a rural setting in western Kenya. Of the 100 serum specimens tested from each species of domestic ruminant 43% of goats, 23% of sheep, and 1% of cattle had immunoglobulin G (IgG) antibodies to the SFG rickettsiae. None of these sera were positive for IgG against typhus group rickettsiae. We detected Rickettsia africae–genotype DNA in 92.6% of adult Amblyomma variegatum ticks collected from domestic ruminants, but found no evidence of the pathogen in blood specimens from cattle, goats, or sheep. Sequencing of a subset of 21 rickettsia-positive ticks revealed R. africae variants in 95.2% (20/21) of ticks tested. Our findings show a high prevalence of R. africae variants in A. variegatum ticks in western Kenya, which may represent a low disease risk for humans. This may provide a possible explanation for the lack of African tick-bite fever cases among febrile patients in Kenya

    Placenta-Specific Slc38a2/SNAT2 Knockdown Causes Fetal Growth Restriction in Mice

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    Fetal growth restriction (FGR) is a complication of pregnancy that reduces birth weight, markedly increases infant mortality and morbidity and is associated with later-life cardiometabolic disease. No specific treatment is available for FGR. Placentas of human FGR infants have low abundance of sodium-coupled neutral amino acid transporter 2 (Slc38a2/SNAT2), which supplies the fetus with amino acids required for growth. We determined the mechanistic role of placental Slc38a2/SNAT2 deficiency in the development of restricted fetal growth, hypothesizing that placenta-specific Slc38a2 knockdown causes FGR in mice. Using lentiviral transduction of blastocysts with a small hairpin RNA (shRNA), we achieved 59% knockdown of placental Slc38a2, without altering fetal Slc38a2 expression. Placenta-specific Slc38a2 knockdown reduced near-term fetal and placental weight, fetal viability, trophoblast plasma membrane (TPM) SNAT2 protein abundance, and both absolute and weight-specific placental uptake of the amino acid transport System A tracer, 14C-methylaminoisobutyric acid (MeAIB). We also measured human placental SLC38A2 gene expression in a well-defined term clinical cohort and found that SLC38A2 expression was decreased in late-onset, but not early-onset FGR, compared with appropriate for gestational age (AGA) control placentas. The results demonstrate that low placental Slc38a2/SNAT2 causes FGR and could be a target for clinical therapies for late-onset FGR

    Treatment of Heavy Quarks in Deeply Inelastic Scattering

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    We investigate a simplified version of the ACOT prescription for calculating deeply inelastic scattering from Q^2 values near the squared mass M_H^2 of a heavy quark to Q^2 much larger than M_H^2.Comment: 14 pages, 5 figure
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