32,517 research outputs found
Transmission coefficient and two-fold degenerate discrete spectrum of spin-1 bosons in a double-step potential
The scattering of spin-1 bosons in a nonminimal vector double-step potential
is described in terms of eigenstates of the helicity operator and it is shown
that the transmission coefficient is insensitive to the choice of the
polarization of the incident beam. Poles of the transmission amplitude reveal
the existence of a two-fold degenerate spectrum. The results are interpreted in
terms of solutions of two coupled effective Schr\"{o}dinger equations for a
finite square well with additional -functions situated at the borders.Comment: arXiv admin note: substantial text overlap with arXiv:1203.119
Relativistic quantum dynamics of scalar bosons under a full vector Coulomb interaction
The relativistic quantum dynamics of scalar bosons in the background of a
full vector coupling (minimal plus nonminimal vector couplings) is explored in
the context of the Duffin-Kemmer-Petiau formalism. The Coulomb phase shift is
determined for a general mixing of couplings and it is shown that the space
component of the nonminimal coupling is a {\it sine qua non} condition for the
exact closed-form scattering amplitude. It follows that the Rutherford cross
section vanishes in the absence of the time component of the minimal coupling.
Bound-state solutions obtained from the poles of the partial scattering
amplitude show that the time component of the minimal coupling plays an
essential role. The bound-state solutions depend on the nonminimal coupling and
the spectrum consists of particles or antiparticles depending on the sign of
the time component of the minimal coupling without chance for pair production
even in the presence of strong couplings. It is also shown that an accidental
degeneracy appears for a particular mixing of couplings.Comment: 8 pages, 1 table. arXiv admin note: text overlap with arXiv:1403.603
Resetting a functional G1 nucleus after mitosis
© The Author(s) 2015. The maintenance of the correct cellular information goes beyond the simple transmission of an intact genetic code from one generation to the next. Epigenetic changes, topological cues and correct protein-protein interactions need to be re-established after each cell division to allow the next cell cycle to resume in the correct regulated manner. This process begins with mitotic exit and re-sets all the changes that occurred
during mitosis thus restoring a functional G1 nucleus in preparation for the next cell cycle. Mitotic exit is triggered by inactivation of mitotic kinases and the reversal of their phosphorylation activities on many cellular components, from nuclear lamina to transcription factors and chromatin itself. To reverse all these phosphorylations, phosphatases act during mitotic exit in a timely and spatially controlled manner directing the events that lead to a functional G1 nucleus. In this review, we will summarise the recent developments on the
control of phosphatases and their known substrates during mitotic exit, and the key steps that control the restoration of chromatin status, nuclear envelope reassembly and nuclear body re-organisation. Although pivotal work has been conducted in this area in yeast, due to differences between the mitotic exit network between yeast and vertebrates, we will mainly concentrate on the vertebrate system.BBSRC grant (BB/K017632/1)
New solutions of the D-dimensional Klein-Gordon equation via mapping onto the nonrelativistic one-dimensional Morse potential
New exact analytical bound-state solutions of the D-dimensional Klein-Gordon
equation for a large set of couplings and potential functions are obtained via
mapping onto the nonrelativistic bound-state solutions of the one-dimensional
generalized Morse potential. The eigenfunctions are expressed in terms of
generalized Laguerre polynomials, and the eigenenergies are expressed in terms
of solutions of irrational equations at the worst. Several analytical results
found in the literature, including the so-called Klein-Gordon oscillator, are
obtained as particular cases of this unified approac
The formation of planetary disks and winds: an ultraviolet view
Planetary systems are angular momentum reservoirs generated during star
formation. This accretion process produces very powerful engines able to drive
the optical jets and the molecular outflows. A fraction of the engine energy is
released into heating thus the temperature of the engine ranges from the 3000K
of the inner disk material to the 10MK in the areas where magnetic reconnection
occurs. There are important unsolved problems concerning the nature of the
engine, its evolution and the impact of the engine in the chemical evolution of
the inner disk. Of special relevance is the understanding of the shear layer
between the stellar photosphere and the disk; this layer controls a significant
fraction of the magnetic field building up and the subsequent dissipative
processes ougth to be studied in the UV.
This contribution focus on describing the connections between 1 Myr old suns
and the Sun and the requirements for new UV instrumentation to address their
evolution during this period. Two types of observations are shown to be needed:
monitoring programmes and high resolution imaging down to, at least,
milliarsecond scales.Comment: Accepted for publication in Astrophysics and Space Science 9 figure
Spin and pseudospin symmetries of the Dirac equation with confining central potentials
We derive the node structure of the radial functions which are solutions of
the Dirac equation with scalar and vector confining central potentials,
in the conditions of exact spin or pseudospin symmetry, i.e., when one has
, where is a constant. We show that the node structure for exact
spin symmetry is the same as the one for central potentials which go to zero at
infinity but for exact pseudospin symmetry the structure is reversed. We obtain
the important result that it is possible to have positive energy bound
solutions in exact pseudospin symmetry conditions for confining potentials of
any shape, including naturally those used in hadron physics, from nuclear to
quark models. Since this does not happen for potentials going to zero at large
distances, used in nuclear relativistic mean-field potentials or in the atomic
nucleus, this shows the decisive importance of the asymptotic behavior of the
scalar and vector central potentials on the onset of pseudospin symmetry and on
the node structure of the radial functions. Finally, we show that these results
are still valid for negative energy bound solutions for anti-fermions.Comment: 7 pages, uses revtex macro
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