4,513 research outputs found
Studies on the mechanism for the isoproterenol-induced stimulation of cardiac glucose-6-phosphate dehydrogenase
Observability of an induced electric dipole moment of the neutron from nonlinear QED
It has been shown recently that a neutron placed in an external quasistatic
electric field develops an induced electric dipole moment
due to quantum fluctuations in the QED vacuum. A
feasible experiment which could detect such an effect is proposed and described
here. It is shown that the peculiar angular dependence of
on the orientation of the neutron spin leads to a
characteristic asymmetry in polarized neutron scattering by heavy nuclei. This
asymmetry can be of the order of for neutrons with epithermal
energies. For thermalized neutrons from a hot moderator one still expects
experimentally accessible values of the order of . The contribution of
the induced effect to the neutron scattering length is expected to be only one
order of magnitude smaller than that due to the neutron polarizability from its
quark substructure. The experimental observation of this scattering asymmetry
would be the first ever signal of nonlinearity in electrodynamics due to
quantum fluctuations in the QED vacuum
Jahn-Teller effect versus Hund's rule coupling in C60N-
We propose variational states for the ground state and the low-energy
collective rotator excitations in negatively charged C60N- ions (N=1...5). The
approach includes the linear electron-phonon coupling and the Coulomb
interaction on the same level. The electron-phonon coupling is treated within
the effective mode approximation (EMA) which yields the linear t_{1u} x H_g
Jahn-Teller problem whereas the Coulomb interaction gives rise to Hund's rule
coupling for N=2,3,4. The Hamiltonian has accidental SO(3) symmetry which
allows an elegant formulation in terms of angular momenta. Trial states are
constructed from coherent states and using projection operators onto angular
momentum subspaces which results in good variational states for the complete
parameter range. The evaluation of the corresponding energies is to a large
extent analytical. We use the approach for a detailed analysis of the
competition between Jahn-Teller effect and Hund's rule coupling, which
determines the spin state for N=2,3,4. We calculate the low-spin/high-spin gap
for N=2,3,4 as a function of the Hund's rule coupling constant J. We find that
the experimentally measured gaps suggest a coupling constant in the range
J=60-80meV. Using a finite value for J, we recalculate the ground state
energies of the C60N- ions and find that the Jahn-Teller energy gain is partly
counterbalanced by the Hund's rule coupling. In particular, the ground state
energies for N=2,3,4 are almost equal
Cost benefit analysis of space communications technology. Volume 2: Final report
For abstract, see preceding accession
Cost benefit analysis of space communications technology: Volume 1: Executive summary
The questions of (1) whether or not NASA should support the further development of space communications technology, and, if so, (2) which technology's support should be given the highest priority are addressed. Insofar as the issues deal principally with resource allocation, an economics perspective is adopted. The resultant cost benefit methodology utilizes the net present value concept in three distinct analysis stages to evaluate and rank those technologies which pass a qualification test based upon probable (private sector) market failure. User-preference and technology state-of-the-art surveys were conducted (in 1975) to form a data base for the technology evaluation. The program encompassed near-future technologies in space communications earth stations and satellites, including the noncommunication subsystems of the satellite (station keeping, electrical power system, etc.). Results of the research program include confirmation of the applicability of the methodology as well as a list of space communications technologies ranked according to the estimated net present value of their support (development) by NASA
Arbitrarily large families of spaces of the same volume
In any connected non-compact semi-simple Lie group without factors locally
isomorphic to SL_2(R), there can be only finitely many lattices (up to
isomorphism) of a given covolume. We show that there exist arbitrarily large
families of pairwise non-isomorphic arithmetic lattices of the same covolume.
We construct these lattices with the help of Bruhat-Tits theory, using Prasad's
volume formula to control their covolumes.Comment: 9 pages. Syntax corrected; one reference adde
Is the Unitarity of the quark-mixing-CKM-matrix violated in neutron -decay?
We report on a new measurement of neutron -decay asymmetry. From the
result \linebreak = -0.1189(7), we derive the ratio of the axial vector
to the vector coupling constant = = -1.2739(19). When
included in the world average for the neutron lifetime = 885.7(7)s, this
gives the first element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix . With this value and the Particle Data Group values for and
, we find a deviation from the unitarity condition for the first row of
the CKM matrix of = 0.0083(28), which is 3.0 times the stated error
Measuring the proton spectrum in neutron decay - latest results with aSPECT
The retardation spectrometer aSPECT was built to measure the shape of the
proton spectrum in free neutron decay with high precision. This allows us to
determine the antineutrino electron angular correlation coefficient a. We aim
for a precision more than one order of magnitude better than the present best
value, which is Delta_a /a = 5%.
In a recent beam time performed at the Institut Laue-Langevin during April /
May 2008 we reached a statistical accuracy of about 2% per 24 hours measurement
time. Several systematic effects were investigated experimentally. We expect
the total relative uncertainty to be well below 5%.Comment: Accepted for publication in the Conference Proceedings of the
International Workshop on Particle Physics with Slow Neutrons 2008 held at
the ILL, France. To be published in Nuclear Instruments and Methods in
Physics Research, Section
Interrelationship between salvage pathway and synthesis de novo of adenine nucleotides in kidney slices
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