189 research outputs found
Isolation of endophytic bacteria from arboreal species of the Amazon and identification by sequencing of the 16S rRNA encoding gene
Endophytic bacteria from three arboreal species native to the Amazon (Carapa guianenses, Ceiba pentandra, and Swietenia macrophylla), were isolated and identified, through partial sequencing of the 16S rRNA encoding gene. From these, 16 isolates were obtained, although, when compared to sequences deposited in GenBank, only seven had produced identifiable fragments. Bacillus, Pantoea and two non-culturable samples were identified. Results obtained through sequence analysis revealed low genetic diversity across the isolates, even when analyzing different species and plant structures. This is the first report concerning the isolation and identification of endophytic bacteria in these plant species
Vertical Confinement and Evolution of Reentrant Insulating Transition in the Fractional Quantum Hall Regime
We have observed an anomalous shift of the high field reentrant insulating
phases in a two-dimensional electron system (2DES) tightly confined within a
narrow GaAs/AlGaAs quantum well. Instead of the well-known transitions into the
high field insulating states centered around , the 2DES confined
within an 80\AA-wide quantum well exhibits the transition at .
Comparably large quantum lifetime of the 2DES in narrow well discounts the
effect of disorder and points to confinement as the primary driving force
behind the evolution of the reentrant transition.Comment: 5 pages, 4 figure
Pulsed Magnetic Field Measurements of the Composite Fermion Effective Mass
Magnetotransport measurements of Composite Fermions (CF) are reported in 50 T
pulsed magnetic fields. The CF effective mass is found to increase
approximately linearly with the effective field , in agreement with our
earlier work at lower fields. For a of 14 T it reaches , over 20
times the band edge electron mass. Data from all fractions are unified by the
single parameter for all the samples studied over a wide range of
electron densities. The energy gap is found to increase like at
high fields.Comment: Has final table, will LaTeX without error
Electromagnetic-field quantization and spontaneous decay in left-handed media
We present a quantization scheme for the electromagnetic field interacting
with atomic systems in the presence of dispersing and absorbing
magnetodielectric media, including left-handed material having negative real
part of the refractive index. The theory is applied to the spontaneous decay of
a two-level atom at the center of a spherical free-space cavity surrounded by
magnetodielectric matter of overlapping band-gap zones. Results for both big
and small cavities are presented, and the problem of local-field corrections
within the real-cavity model is addressed.Comment: 15 pages, 5 figures, RevTe
Constraining the mass of dark photons and axion-like particles through black-hole superradiance
Ultralight bosons and axion-like particles appear naturally in different
scenarios and could solve some long-standing puzzles. Their detection is
challenging, and all direct methods hinge on unknown couplings to the Standard
Model of particle physics. However, the universal coupling to gravity provides
model-independent signatures for these fields. We explore here the superradiant
instability of spinning black holes triggered in the presence of such fields.
The instability taps angular momentum from and limits the maximum spin of
astrophysical black holes. We compute, for the first time, the spectrum of the
most unstable modes of a massive vector (Proca) field for generic black-hole
spin and Proca mass. The observed stability of the inner disk of stellar-mass
black holes can be used to derive \emph{direct} constraints on the mass of dark
photons in the mass range . By including also higher azimuthal modes, similar
constraints apply to axion-like particles in the mass range
.
Likewise, mass and spin distributions of supermassive BHs --~as measured
through continuum fitting, K iron line, or with the future space-based
gravitational-wave detector LISA~-- imply indirect bounds in the mass range
approximately , for both axion-like particles and dark photons. Overall,
superradiance allows to explore a region of approximately orders of
magnitude in the mass of ultralight bosons
Search for a Higgs Boson Decaying to Weak Boson Pairs at LEP
A Higgs particle produced in association with a Z boson and decaying into
weak boson pairs is searched for in 336.4 1/pb of data collected by the L3
experiment at LEP at centre-of-mass energies from 200 to 209 GeV. Limits on the
branching fraction of the Higgs boson decay into two weak bosons as a function
of the Higgs mass are derived. These results are combined with the L3 search
for a Higgs boson decaying to photon pairs. A Higgs produced with a Standard
Model e+e- --> Zh cross section and decaying only into electroweak boson pairs
is excluded at 95% CL for a mass below 107 GeV
Passage kinetics of digesta in horses fed with coastcross hay ground to different degrees
Low-frequency dilatational wave propagation through unsaturated porous media containing two immiscible fluids
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