49 research outputs found
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Dissecting a complex chemical stress: chemogenomic profiling of plant hydrolysates.
The efficient production of biofuels from cellulosic feedstocks will require the efficient fermentation of the sugars in hydrolyzed plant material. Unfortunately, plant hydrolysates also contain many compounds that inhibit microbial growth and fermentation. We used DNA-barcoded mutant libraries to identify genes that are important for hydrolysate tolerance in both Zymomonas mobilis (44 genes) and Saccharomyces cerevisiae (99 genes). Overexpression of a Z. mobilis tolerance gene of unknown function (ZMO1875) improved its specific ethanol productivity 2.4-fold in the presence of miscanthus hydrolysate. However, a mixture of 37 hydrolysate-derived inhibitors was not sufficient to explain the fitness profile of plant hydrolysate. To deconstruct the fitness profile of hydrolysate, we profiled the 37 inhibitors against a library of Z. mobilis mutants and we modeled fitness in hydrolysate as a mixture of fitness in its components. By examining outliers in this model, we identified methylglyoxal as a previously unknown component of hydrolysate. Our work provides a general strategy to dissect how microbes respond to a complex chemical stress and should enable further engineering of hydrolysate tolerance
Search for Branons at LEP
We search, in the context of extra-dimension scenarios, for the possible
existence of brane fluctuations, called branons. Events with a single photon or
a single Z-boson and missing energy and momentum collected with the L3 detector
in e^+ e^- collisions at centre-of-mass energies sqrt{s}=189-209$ GeV are
analysed. No excess over the Standard Model expectations is found and a lower
limit at 95% confidence level of 103 GeV is derived for the mass of branons,
for a scenario with small brane tensions. Alternatively, under the assumption
of a light branon, brane tensions below 180 GeV are excluded
Measurement of Exclusive rho^0 rho^0 Production in Two-Photon Collisions at High Q^2 at LEP
Exclusive rho rho production in two-photon collisions involving a single
highly virtual photon is studied with data collected at LEP at centre-of-mass
energies 89GeV < \sqrt{s} < 209GeV with a total integrated luminosity of
854.7pb^-1 The cross section of the process gamma gamma^* -> rho rho is
determined as a function of the photon virtuality, Q^2 and the two-photon
centre-of-mass energy, Wgg, in the kinematic region: 1.2GeV^2 < Q^2 < 30GeV^2
and 1.1GeV < Wgg < 3GeV
Search for a Higgs Boson Decaying into Two Photons at LEP
A Higgs particle produced in association with a Z boson and decaying into two
photons is searched for in the data collected by the L3 experiment at LEP. All
possible decay modes of the Z boson are investigated. No signal is observed in
447.5 pb^-1 of data recorded at centre-of-mass energies up to 209 GeV. Limits
on the branching fraction of the Higgs boson decay into two photons as a
function of the Higgs mass are derived. A lower limit on the mass of a
fermiophobic Higgs boson is set at 105.4 GeV at 95% confidence level
Search for Heavy Isosinglet Neutrino in e+e- Annihilation at LEP
We report on a search for the first generation heavy neutrino that is an
isosinglet under the standard SU(2)_L gauge group. The data collected with the
L3 detector at center-of-mass energies between 130 GeV and 208 GeV are used.The
decay channel N_e --> eW is investigated and no evidence is found for a heavy
neutrino, N_e, in a mass range between 80 GeV and 205 GeV. Upper limits on the
mixing parameter between the heavy and light neutrino are derived
Dark matter annihilation and its effect on CMB and Hydrogen 21 cm observations
If dark matter is made up of Weakly Interacting Massive Particles, the
annihilation of these particles in halos results in energy being released, some
of which is absorbed by gas, causing partial ionization and heating. Dark
matter annihilation may result in partial ionization and gas heating at high
redshifts, even before the formation of the first stars. It is shown that early
ionization results in a transfer of power to higher multipoles in the large
angle CMB polarization power spectra. Future CMB experiments may be able to
place constraints on certain light dark matter models. We also investigate the
effect of gas heating on the expected H21 cm power spectrum. Heating by
particle annihilation results in a decrease in the amplitude of the H21 cm
power spectrum as the gas temperature becomes comparable to the CMB
temperature , and then an increase as . The result is a
minimum in the power spectrum at the redshift for which .
Only certain models (low particle masses 10 GeV, or favorable halo
parameters) show this effect. Within these models, observations of the H21 cm
power spectrum at multiple redshifts can help us obtain constraints on dark
matter particle and halo properties.Comment: We correct an error in the calculation of in Eq. 6. This
results in a ~ factor 2 increase in the magnitude of the results. New plots
have been computed. Replaced to reflect the published versio
f(1285) Formation in Two-Photon Collisions at LEP
The final state in two-photon collisions is studied with the L3 detector at LEP, at centre-of-mass energies from 183 to 209~GeV with an integrated luminosity of 664.6~pb. The f(1285) meson is observed and the dependence of its production is compared to different form factor models. The -coupling parameter is found to be ~keV. The branching fraction is also measured.The eta pi^+ pi^- final state in two-photon collisions is studied with the L3 detector at LEP, at centre-of-mass energies from 183 to 209 GeV with an integrated luminosity of 664.6/pb. The f_1(1285) meson is observed and the Q^2 dependence of its production is compared to different form factor models. The gamma-gamma coupling parameter is found to be 3.5 +/- 0.6(stat.) +/- 0.5(sys.) keV. The branching fraction (f_1(1285) -> a_0 pi) / (f_1(1285) -> eta pi pi) is also measured.The Î·Ï + Ï â final state in two-photon collisions is studied with the L3 detector at LEP, at centre-of-mass energies from 183 to 209 GeV with an integrated luminosity of 664.6 pb â1 . The f 1 (1285) meson is observed and the Q 2 dependence of its production is compared to different form factor models. The γγ -coupling parameter Πγγ is found to be 3.5±0.6(stat.)±0.5(sys.) keV. The branching fraction Î (f 1 (1285)âa 0 Ï )/ Î (f 1 (1285)â ηÏÏ ) is also measured
Measurement of the Shadowing of High-Energy Cosmic Rays by the Moon: A Search for TeV-Energy Antiprotons
The shadowing of high-energy cosmic rays by the Moon has been observed with a
significance of 9.4 standard deviations with the L3+C muon spectrometer at
CERN. A significant effect of the Earth magnetic field is observed. Since no
event deficit on the east side of the Moon has been observed, an upper limit at
90% confidence level on the antiproton to proton ratio of 0.11 is obtained for
primary energies around 1 TeV
Study of Multiphoton Final States and Tests of QED in e+e- collisions at \root(s) up to 209 GeV
The process e+ e- -> n gamma with n>=2 is studied at centre-of-mass energies
ranging from \root(s)=192 to 208 GeV. The data sample corresponds to a total
integrated luminosity of 427 1/pb. The total and differential cross sections
are found to be in agreement with the QED expectations. Using all the data
collected with the L3 detector above the Z pole, limits on deviations from QED,
excited electrons, contact interactions, extra space dimensions and excited
spin-3/2 leptons are set