9,961 research outputs found
A Separate Higgs?
We investigate the possibility of a multi-Higgs doublet model where the
lightest neutral Higgs boson () decouples from the fermion sector. We are
partially motivated by the four events with
\,GeV recently observed by the L3 collaboration,
which could be a signal for .
Collider signatures for the additional physical Higgs bosons present in such
models are discussed.Comment: 8 pages (plus 2 figures, available by request), latex,
ANL-HEP-PR-92-10
Using NMR Chemical Shift Perturbations to Map Interactions Between Acyl-Acyl Carrier Proteins and Acyl Homoserine Lactone Synthases
A pandemic of antibiotic resistance is underway and affecting multiple industries, including veterinary, agricultural, and healthcare. High bacterial population density is a major form of defense for bacterial cells against drugs, contributes to antibiotic resistance, and is one of the requirements for the formation of biofilms. Quorum sensing is a form of cell-to-cell communication that both gram-negative and gram-positive bacteria use to account for density behavior. When the population density of bacteria reaches a certain level (a “quorum”), there is an observed coordinated shift in gene expression that leads to optimized growth or virulence. Acyl carrier proteins (ACP) and the enzyme acyl-homoserine lactones synthase (AHLS), which are the building blocks for the formation of quorum sensing molecules, acyl-homoserine lactone (AHL) molecules signal the regulation of some of these expressed genes. AHLs are chemical autoinducers used in quorum sensing. This project contributes to an effort to map interactions between ACP1 and RhlI from Pseudomonas aeruginosa, using nuclear magnetic resonance (NMR) spectroscopy to better predict drug target sites to inhibit the production of AHL molecules. Here, I present the chemical shift backbone assignments for ACP1 and the optimized expression and purification of ACP1 and RhlI
Thermodynamics of an Evaporating Schwarzschild Black Hole in Noncommutative Space
We investigate the effects of space noncommutativity and the generalized
uncertainty principle on the thermodynamics of a radiating Schwarzschild black
hole. We show that evaporation process is in such a way that black hole reaches
to a maximum temperature before its final stage of evolution and then cools
down to a nonsingular remnant with zero temperature and entropy. We compare our
results with more reliable results of string theory. This comparison Shows that
GUP and space noncommutativity are similar concepts at least from view point of
black hole thermodynamics.Comment: 15 Pages, 2 Figures, revised and refernces adde
Female Employment and Fertility in Rural China
Data on 2,288 married women from the 2006 China Health and Nutrition Survey are deployed to study how off-farm female employment affects fertility. Such employment reduces a married woman's actual number of children by 0.64, her preferred number by 0.48, and her probability of having more than one child by 54.8 percent. Causality flows in both directions; hence, we use well validated instrumental variables to estimate employment status. China has deep concerns with both female employment and population size. Moreover, female employment is growing quickly. Hence, its implications for fertility must be understood. Ramifications for China's one-child policy are discussed.
Single Production in Collisions at the NLC
Single production in collisions at the NLC can be used to
probe the Majorana nature of the heavy neutrinos present in the Left-Right
Symmetric Model below the kinematic threshold for their direct production. For
colliders in the TeV range, typical cross sections of order
are obtained, depending on the specific choice of model parameters.
Backgrounds arising from Standard Model processes are shown to be small. This
analysis greatly extends the kinematic range of previous studies wherein the
production of an on-shell, like-sign pair of 's at the NLC was considered.Comment: 13pp, 3 figures (available on request), LaTex, SLAC-PUB-647
Low Scale Non-universal, Non-anomalous U(1)'_F in a Minimal Supersymmetric Standard Model
We propose a non-universal U(1)'_F symmetry combined with the Minimal
Supersymmetric Standard Model. All anomaly cancellation conditions are
satisfied without exotic fields other than three right-handed neutrinos.
Because our model allows all three generations of chiral superfields to have
different U(1)'_F charges, upon the breaking of the U(1)'_F symmetry at a low
scale, realistic masses and mixing angles in both the quark and lepton sectors
are obtained. In our model, neutrinos are predicted to be Dirac fermions and
their mass ordering is of the inverted hierarchy type. The U(1)'_F charges of
the chiral super-fields also naturally suppress the mu term and automatically
forbid baryon number and lepton number violating operators. While all
flavor-changing neutral current constraints in the down quark and charged
lepton sectors can be satisfied, we find that constraint from D0-D0bar turns
out to be much more stringent than the constraints from the precision
electroweak data.Comment: 21 pages, 2 figures; v2: discussion on sparticle mass spectrum
included, 27 pages, 2 figure
The Dynamical Dipole Mode in Fusion Reactions with Exotic Nuclear Beams
We report the properties of the prompt dipole radiation, produced via a
collective bremsstrahlung mechanism, in fusion reactions with exotic beams. We
show that the gamma yield is sensitive to the density dependence of the
symmetry energy below/around saturation. Moreover we find that the angular
distribution of the emitted photons from such fast collective mode can
represent a sensitive probe of its excitation mechanism and of fusion dynamics
in the entrance channel.Comment: 5 pages, 3 figures, to appear in Phys.Rev.
Preconditioning of low-frequency repetitive transcranial magnetic stimulation with transcranial direct current stimulation: evidence for homeostatic plasticity in the human motor cortex
Recent experimental work in animals has emphasized the importance of homeostatic plasticity as a means of stabilizing the properties of neuronal circuits. Here, we report a phenomenon that indicates a homeostatic pattern of cortical plasticity in healthy human subjects. The experiments combined two techniques that can produce long-term effects on the excitability of corticospinal output neurons: transcranial direct current stimulation (TDCS) and repetitive transcranial magnetic stimulation (rTMS) of the left primary motor cortex. "Facilitatory preconditioning" with anodal TDCS caused a subsequent period of 1 Hz rTMS to reduce corticospinal excitability to below baseline levels for >20 min. Conversely, "inhibitory preconditioning" with cathodal TDCS resulted in 1 Hz rTMS increasing corticospinal excitability for at least 20 min. No changes in excitability occurred when 1 Hz rTMS was preceded by sham TDCS. Thus, changing the initial state of the motor cortex by a period of DC polarization reversed the conditioning effects of 1 Hz rTMS. These preconditioning effects of TDCS suggest the existence of a homeostatic mechanism in the human motor cortex that stabilizes corticospinal excitability within a physiologically useful range
Sneutrino identification in dilepton events at the LHC
Heavy neutral resonances appearing in the clean Drell-Yan channel may be the
first new physics to be observed at the proton-proton CERN LHC. If a new
resonance is discovered at the LHC as a (narrow) peak in the dilepton invariant
mass distribution, the characterization of its spin and couplings will proceed
via the measurement of production rates and angular distributions of the decay
products. We discuss the discrimination of a spin-0 resonance (sneutrino)
predicted by supersymmetric theories with R-parity breaking against the spin-1
of Z^\prime bosons and the Randall-Sundrum graviton resonance (spin-2) with the
same mass and producing the same number of events under the observed peak. To
assess the region of sneutrino parameters (couplings and masses) where the spin
determination can be performed to a given confidence level, we focus on the
event rate and the angular distributions of the Drell-Yan leptons, in
particular using the center-edge asymmetry, A_{\rm CE}. We find that although
the measured event rate permits solving the above problem partially, the
center-edge asymmetry, on the contrary allows to differentiate the various
spins entirely with a minimal number of events around 200.Comment: 20 pages; version to appear in PR
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