4,527 research outputs found
Limitations on the superposition principle: superselection rules in non-relativistic quantum mechanics
The superposition principle is a very basic ingredient of quantum theory.
What may come as a surprise to many students, and even to many practitioners of
the quantum craft, is tha superposition has limitations imposed by certain
requirements of the theory. The discussion of such limitations arising from the
so-called superselection rules is the main purpose of this paper. Some of their
principal consequences are also discussed. The univalence, mass and particle
number superselection rules of non-relativistic quantum mechanics are also
derived using rather simple methods.Comment: 22 pages, no figure
Test of nuclear level density inputs for Hauser-Feshbach model calculations
The energy spectra of neutrons, protons, and alpha-particles have been
measured from the d+59Co and 3He+58Fe reactions leading to the same compound
nucleus, 61$Ni. The experimental cross sections have been compared to
Hauser-Feshbach model calculations using different input level density models.
None of them have been found to agree with experiment. It manifests the serious
problem with available level density parameterizations especially those based
on neutron resonance spacings and density of discrete levels. New level
densities and corresponding Fermi-gas parameters have been obtained for
reaction product nuclei such as 60Ni,60Co, and 57Fe
Exact T=0 Partition Functions for Potts Antiferromagnets on Sections of the Simple Cubic Lattice
We present exact solutions for the zero-temperature partition function of the
-state Potts antiferromagnet (equivalently, the chromatic polynomial ) on
tube sections of the simple cubic lattice of fixed transverse size and arbitrarily great length , for sizes and and boundary conditions (a) and (b)
, where () denote free (periodic) boundary
conditions. In the limit of infinite-length, , we calculate the
resultant ground state degeneracy per site (= exponent of the ground-state
entropy). Generalizing from to , we determine
the analytic structure of and the related singular locus which
is the continuous accumulation set of zeros of the chromatic polynomial. For
the limit of a given family of lattice sections, is
analytic for real down to a value . We determine the values of
for the lattice sections considered and address the question of the value of
for a -dimensional Cartesian lattice. Analogous results are presented
for a tube of arbitrarily great length whose transverse cross section is formed
from the complete bipartite graph .Comment: 28 pages, latex, six postscript figures, two Mathematica file
The Power Spectrum in de Sitter Inflation, Revisited
We find that the amplitude of quantum fluctuations of the invariant de Sitter
vacuum coincides exactly with that of the vacuum of a comoving observer for a
massless scalar (inflaton) field. We propose redefining the actual physical
power spectrum as the difference between the amplitudes of the above vacua. An
inertial particle detector continues to observe the Gibbons-Hawking
temperature. However, although the resulting power spectrum is still
scale-free, its amplitude can be drastically reduced since now, instead of the
Hubble's scale at the inflationary period, it is determined by the square of
the mass of the inflaton fluctuation field.Comment: 4 page
New non-unitary representations in a Dirac hydrogen atom
New non-unitary representations of the SU(2) algebra are introduced for the
case of the Dirac equation with a Coulomb potential; an extra phase, needed to
close the algebra, is also introduced. The new representations does not require
integer or half integer labels. The set of operators defined are used to span
the complete space of bound state eigenstates of the problem thus solving it in
an essentially algebraic way
Generation of thermo-sensitive allele of the TPR like protein Nup211by PCR mutagenesis
Motivation: TPR proteins are conserved large coiled-coil proteins that localize at the nucleoplasmic side of the nuclear pore complex and participate in multiple aspects of DNA metabolism. The protein Nup211, fission yeast homolog of Mlp1/Mlp2/Tpr, participate in the mRNA export and is essential for vegetative growth. The aim of this work is to create a collection of thermo-sensitive alleles of nup211.Methods: To create the collection, we have generated a new strain with the nup211 gen tagged with GFP at the amino terminal extreme and confirmed by fluorescent microscopy that the protein Nup211 localized in the nuclear envelop. Then, we have carried out a Taq PCR-based Random Mutagenesis with reduced concentration of dATP. The PCR products were transformed into a wild type strain to generate conditional mutants. The transformants obtained whose growth was impaired at 36ÂșC were preselected as thermo-sensitive mutants. To confirm the growth deficiency of these clones, a drop assay was performed and the best candidates were selected. These thermo-sensitive mutants were cultivated at 25ÂșC as well as 36ÂșC and both cultures were subjected to various experiments in order to study any changes in the localization of Nup211.Results: Up to now, we have demonstrated by fluorescent microscopy that the thermo-sensitive mutants show a modified nuclear distribution of Nup211 and different cellular phenotype, suggesting that the differents clones might represent differents nup211 thermo-sensitive alleles. These alleles are going to be subjected to various experiments to clarify the role of the protein in the mRNA export
A useful form of the recurrence relation between relativistic atomic matrix elements of radial powers
Recently obtained recurrence formulae for relativistic hydrogenic radial
matrix elements are cast in a simpler and perhaps more useful form. This is
achieved with the help of a new relation between the and the
terms ( is a Dirac matrix and are constants) in the
atomic matrix elements.Comment: 7 pages, no figure
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