1,519 research outputs found
Frateuria defendens reduces yellows disease symptoms in grapevine under field conditions
Yellows diseases in grapevine, associated with the presence of different phytoplasmas, are a major problem for growers, with no environmentally friendly means of control. Frateuria defendens (Frd), a bacterium with endophytic traits, has been shown to reduce yellows symptoms in grapevine plantlets under laboratory conditions. The objective of this study was to test whether similar effects could be achieved under field conditions. A trial was conducted in a heavily infected vineyard in northern Israel for two consecutive years. A suspension of Frd cells (108·mL-1) was applied bi-weekly by foliar spray on grapevines from bud burst to leaf senescence. Frd penetrated the leaves during the growing period but not during leaf senescence and could be detected in the leaves by PCR analysis up to 14 days post-spraying. The rate of yellows infection was lower in the treated grapevines compared to its increase in untreated grapevines and the yield of symptomatic plants was improved by 10 to 20 %. Taken together, the results suggest Frd acted as a biological control agent in vineyards under the experimental conditions tested
Large mass dileptons from the passage of jets through quark gluon plasma
We calculate the emission of large mass dileptons originating from the
annihilation of quark jets passing through quark gluon plasma. Considering
central collisions of heavy nuclei at SPS, RHIC and LHC energies, we find that
the yield due to the jet-plasma interaction gets progressively larger as the
collision energy increases. We find it to be negligible at SPS energies, of the
order of the Drell-Yan contribution and much larger than the normal thermal
yield at RHIC energies and up to a factor of ten larger than the Drell-Yan
contribution at LHC energies. An observation of this new dilepton source would
confirm the occurrence of jet-plasma interactions and of conditions suitable
for jet-quenching to take place.Comment: 9 pages, 11 figures; references added, improved calculation,
conclusions unchange
Limits on WWgamma and WWZ Couplings from W Boson Pair Production
The results of a search for W boson pair production in pbar-p collisions at
sqrt{s}=1.8 TeV with subsequent decay to emu, ee, and mumu channels are
presented. Five candidate events are observed with an expected background of
3.1+-0.4 events for an integrated luminosity of approximately 97 pb^{-1}.
Limits on the anomalous couplings are obtained from a maximum likelihood fit of
the E_T spectra of the leptons in the candidate events. Assuming identical
WWgamma and WWZ couplings, the 95 % C.L. limits are -0.62<Delta_kappa<0.77
(lambda = 0) and -0.53<lambda<0.56 (Delta_kappa = 0) for a form factor scale
Lambda = 1.5 TeV.Comment: 10 pages, 1 figure, submitted to Physical Review
Diffractive J/psi production as a probe of the gluon component in the Pomeron
Presented here is a study of the large p_T J/psi production in hard
diffractive process by the pomeron exchange at the Fermilab Tevatron. We find
that this process (p\bar p \to p+J/psi+X) can be used to probe the gluon
content of the pomeron and to measure the gluon fraction of the pomeron. And
the diffractive direct J/psi production can also provide another crucial test
for the color-octet fragmentation mechanism. Using the renormalised pomeron
flux factor D\approx 1/9, the single diffractive J/psi production cross section
at large p_T (\geq 8GeV) is found to be of order of 0.01 nb, and the ratio of
the single diffractive to the non-diffractive J/psi production is 0.65\pm 0.15%
for the gluon fraction f_g=0.7\pm 0.2.Comment: 13 pages, 6 Postscript figure
Open Problems on Central Simple Algebras
We provide a survey of past research and a list of open problems regarding
central simple algebras and the Brauer group over a field, intended both for
experts and for beginners.Comment: v2 has some small revisions to the text. Some items are re-numbered,
compared to v
Direct Measurement of the Top Quark Mass at D0
We determine the top quark mass m_t using t-tbar pairs produced in the D0
detector by \sqrt{s} = 1.8 TeV p-pbar collisions in a 125 pb^-1 exposure at the
Fermilab Tevatron. We make a two constraint fit to m_t in t-tbar -> b W^+bbar
W^- final states with one W boson decaying to q-qbar and the other to e-nu or
mu-nu. Likelihood fits to the data yield m_t(l+jets) = 173.3 +- 5.6 (stat) +-
5.5 (syst) GeV/c^2. When this result is combined with an analysis of events in
which both W bosons decay into leptons, we obtain m_t = 172.1 +- 5.2 (stat) +-
4.9 (syst) GeV/c^2. An alternate analysis, using three constraint fits to fixed
top quark masses, gives m_t(l+jets) = 176.0 +- 7.9 (stat) +- 4.8 (syst)
GeV/C^2, consistent with the above result. Studies of kinematic distributions
of the top quark candidates are also presented.Comment: 43 pages, 53 figures, 33 tables. RevTeX. Submitted to Phys. Rev.
Measurement of the Boson Mass
A measurement of the mass of the boson is presented based on a sample of
5982 decays observed in collisions at
= 1.8~TeV with the D\O\ detector during the 1992--1993 run. From a
fit to the transverse mass spectrum, combined with measurements of the
boson mass, the boson mass is measured to be .Comment: 12 pages, LaTex, style Revtex, including 3 postscript figures
(submitted to PRL
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