55,463 research outputs found
Report drawn up on behalf of the Committee on Regional Policy, Regional Planning and Transport on the EEC's relations with the COMECON countries in the field of maritime shipping. EP Working Documents, document 51/79, 11 April 1979
CadC-mediated activation of the cadBA promoter in Escherichia coli
The transcriptional activator CadC in Escherichia coli, a member of the ToxR-like proteins, activates transcription of the cadBA operon encoding the lysine decarboxylase CadA and the lysine-cadaverine antiporter CadB. cadBA is induced under conditions of acidic external pH and exogenous lysine; anoxic conditions raise the expression level up to 10 times. To characterize the binding mechanism of CadC, procedures for the purification of this membrane-integrated protein and its reconstitution into proteoliposomes were established. The binding sites of CadC upstream of the cadBA promoter region were determined by in vitro DNaseI protection analysis. Two regions were protected during DNaseI digestion, one from - 144 to - 112 bp, designated Cad1, and another one from - 89 to - 59 bp, designated Cad2. Binding of purified CadC to Cad1 and Cad2 was further characterized by DNA-binding assays, indicating that CadC was able to bind to both DNA fragments. Genetic analysis with promoter-lacZ fusions confirmed that both sites, Cad1 and Cad2, are essential for activation of cadBA transcription. Moreover, these experiments revealed that binding of H-NS upstream of the CadC-binding sites is necessary for repression of cadBA expression at neutral pH and under aerobic conditions. Based on these results, a model for transcriptional regulation of the cadBA operon is proposed, according to which H-NS is involved in the formation of a repression complex under non-inducing conditions. This complex is dissolved by binding of CadC to Cad1 under inducing conditions. Upon binding of CadC to Cad2 cadBA expression is activated. Copyright (C) 2005 S. Karger AG, Basel
Form Invariance of the Neutrino Mass Matrix
Consider the most general Majorana neutrino mass matrix . Motivated by present neutrino-oscillation data, much theoretical effort is
directed at reducing it to a specific texture in terms of a small number of
parameters. This procedure is often {\it ad hoc}. I propose instead that for
any one may choose, it should satisfy the condition , where is a specific unitary matrix such that
represents a well-defined discrete symmetry in the basis,
being a particular integer not necessarily equal to one. I illustrate this
idea with a number of examples, including the realistic case of an inverted
hierarchy of neutrino masses.Comment: Version to appear in PR
Effects of large-scale environment on the assembly history of central galaxies
We examine whether large-scale environment affects the mass assembly history
of their central galaxies. To facilitate this, we constructed dark matter halo
merger trees from a cosmological N-body simulation and calculated the formation
and evolution of galaxies using a semi-analytic method. We confirm earlier
results that smaller halos show a notable difference in formation time with a
mild dependence on large-scale environment. However, using a semi-analytic
model, we found that on average the growth rate of the stellar mass of central
galaxies is largely insensitive to large-scale environment. Although our
results show that the star formation rate (SFR) and the stellar mass of central
galaxies in smaller halos are slightly affected by the assembly bias of halos,
those galaxies are faint, and the difference in the SFR is minute, and
therefore it is challenging to detect it in real galaxies given the current
observational accuracy. Future galaxy surveys, such as the BigBOSS experiment
and the Large Synoptic Survey Telescope, which are expected to provide
observational data for fainter objects, will provide a chance to test our model
predictions.Comment: 7 pages, 5 figure
The phenomenology of electric dipole moments in models of scalar leptoquarks
We study the phenomenology of electric dipole moments (EDMs) induced in
various scalar leptoquark models. We consider generic leptoquark couplings to
quarks and leptons and match to Standard Model effective field theory. After
evolving the resulting operators to low energies, we connect to EDM experiments
by using up-to-date hadronic, nuclear, and atomic matrix elements. We show that
current experimental limits set strong constraints on the possible CP-violating
phases in leptoquark models. Depending on the quarks and leptons involved in
the interaction, the existing searches for EDMs of leptons, nucleons, atoms,
and molecules all play a role in constraining the CP-violating couplings. We
discuss the impact of hadronic and nuclear uncertainties as well as the
sensitivities that can be achieved with future EDM experiments. Finally, we
study the impact of EDM constraints on a specific leptoquark model that can
explain the recent -physics anomalies.Comment: Published versio
Frequency-dependent ratchet effect in superconducting films with a tilted washboard pinning potential
The influence of an ac current of arbitrary amplitude and frequency on the
mixed-state dc-voltage-ac-drive ratchet response of a superconducting film with
a dc current-tilted uniaxial cosine pinning potential at finite temperature is
theoretically investigated. The results are obtained in the single-vortex
approximation, i.e., for non-interacting vortices, within the frame of an exact
solution of the appropriate Langevin equation in terms of a matrix continued
fraction. Formulas for the dc voltage ratchet response and absorbed power in ac
response are discussed as functions of ac current amplitude and frequency as
well as dc current induced tilt in a wide range of corresponding dimensionless
parameters. Special attention is paid to the physical interpretation of the
obtained results in adiabatic and high-frequency ratchet responses taking into
account both running and localized states of the (ac+dc)-driven vortex motion
in a washboard pinning potential. Our theoretical results are discussed in
comparison with recent experimental work on the high-frequency ratchet response
in nanostructured superconducting films [B. B. Jin et al., Phys. Rev. B 81
(2010) 174505].Comment: 13 pages, 11 figure
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