46,136 research outputs found
Do supernovae of type 1 paly a role in cosmic-ray production?
A model of cosmic-ray origin is suggested which aims to account for some salient features of the composition. Relative to solar abundances, the Galactic cosmic rays (GCR) are deficient in hydrogen and helim (H and He) by an order of magnitude when the two compositions are normalized at iron. Our conjectural model implicates supernovae of Type I (SN-I) as sources of some of the GCR. SN-I occur approximately as often as SN-II, through their genesis is thought to be different. Recent studies of nucleosynthesis in SN-I based on accreting white dwarfs, find that the elements from Si to Fe are produced copiously. On the other hand, SN-I are virtually devoid of hydrogen, and upper limits deduced for He are low. If SN-I contribute significantly to the pool of GCR by injecting energetic particles into the interstellar medium (ISM), then this could explain why the resulting GCR is relatively deficient in H and He. A test of the model is proposed, and difficulties are discussed
First steps towards total reality of meromorphic functions
It was earlier conjectured by the second and the third authors that any
rational curve such that the inverse
images of all its flattening points lie on the real line is real algebraic up to a linear fractional transformation of
the image . (By a flattening point on we mean a point
at which the Frenet -frame is degenerate.) Below we
extend this conjecture to the case of meromorphic functions on real algebraic
curves of higher genera and settle it for meromorphic functions of degrees
and several other cases.Comment: 10 pages, 1 figur
Localization Lifetime of a Many-Body System with Periodic Constructed Disorder
We show that, in a many-body system, all particles can be strongly confined
to the initially occupied sites for a time that scales as a high power of the
ratio of the bandwidth of site energies to the hopping amplitude. Such
time-domain formulation is complementary to the formulation of the many-body
localization of all stationary states with a large localization length. The
long localization lifetime is achieved by constructing a periodic sequence of
site energies with a large period in a one-dimensional chain. The scaling of
the localization lifetime is independent of the number of particles for a broad
range of the coupling strength. The analytical results are confirmed by
numerical calculations
Cluster algebras and Poisson geometry
We introduce a Poisson variety compatible with a cluster algebra structure
and a compatible toric action on this variety. We study Poisson and topological
properties of the union of generic orbits of this toric action. In particular,
we compute the number of connected components of the union of generic toric
orbits for cluster algebras over real numbers. As a corollary we compute the
number of connected components of refined open Bruhat cells in Grassmanians
G(k,n) over real numbers.Comment: minor change
Robust ultrafast currents in molecular wires through Stark shifts
A novel way to induce ultrafast currents in molecular wires using two
incident laser frequencies, and , is demonstrated. The
mechanism relies on Stark shifts, instead of photon absorption, to transfer
population to the excited states and exploits the temporal profile of the field
to generate phase controllable transport. Calculations in a
\emph{trans}-polyacetylene oligomer coupled to metallic leads indicate that the
mechanism is highly efficient and robust to ultrafast electronic dephasing
processes induced by vibronic couplings.Comment: 4 pages, 2 figures, accepted to Physical Review Letter
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