1,736 research outputs found
Form factors of heavy-light systems in point-form relativistic quantum mechanics: the Isgur-Wise function
We investigate electromagnetic and weak form factors of heavy-light mesons in
the context of point-form relativistic quantum mechanics. To this aim we treat
the physical processes from which such electroweak form factors are extracted
by means of a coupled channel approach which accounts for the dynamics of the
intermediate gauge bosons. It is shown that heavy-quark symmetry is respected
by this formulation. A simple analytical expression is obtained for the
Isgur-Wise function in the heavy-quark limit. Breaking of heavy-quark symmetry
due to realistic values of the heavy-quark mass are studied numerically.Comment: Presented at the 21st European Conference on Few-Body Problems in
Physics, Salamanca, Spain, 30 August - 3 September 201
Effects of Different Substrates on the Growth and Nutritional Composition of Pleurotus ostreatus: A Review
Mushrooms are a popular food source as they are highly nutritious and flavorful with a high content of proteins, vitamins, and minerals. Mushrooms could be an alternative solution to the world’s food crisis as they are inexpensive to grow on different types of substrates including waste materials. Pleurotus ostreatus, frequently known as oyster mushrooms, are the second most cultivated mushroom in the world. This species is known for its high protein content and easy cultivation. Oyster mushrooms have the potential to produce protein-rich biomass when grown on various substrates. There is a need to identify substrates that are cost-effective for the commercial production of nutritious oyster mushrooms as the substrates used currently are either costly or inadequate to produce oyster mushrooms in the required quantity or quality. Thus, the effects of 6 different lignocellulosic substrates on the growth and nutritional composition of P. ostreatus were reviewed and analyzed in this article. The substrates included in this review were wheat straw, sugarcane bagasse, corncob, softwood sawdust, hardwood sawdust, and general sawdust. Based on the analyzed data, sugarcane bagasse was concluded as the most suitable substrate to grow P. ostreatus. These substrates contain a high amount of nutrients and are also likely to produce a significantly high yield of oyster mushrooms in addition to enhancing the nutritional quality of the mushroom. However, these findings must be evaluated and confirmed through further research in this field
Environment-Induced Decoherence and the Transition From Quantum to Classical
We study dynamics of quantum open systems, paying special attention to those
aspects of their evolution which are relevant to the transition from quantum to
classical. We begin with a discussion of the conditional dynamics of simple
systems. The resulting models are straightforward but suffice to illustrate
basic physical ideas behind quantum measurements and decoherence. To discuss
decoherence and environment-induced superselection einselection in a more
general setting, we sketch perturbative as well as exact derivations of several
master equations valid for various systems. Using these equations we study
einselection employing the general strategy of the predictability sieve.
Assumptions that are usually made in the discussion of decoherence are
critically reexamined along with the ``standard lore'' to which they lead.
Restoration of quantum-classical correspondence in systems that are classically
chaotic is discussed. The dynamical second law -it is shown- can be traced to
the same phenomena that allow for the restoration of the correspondence
principle in decohering chaotic systems (where it is otherwise lost on a very
short time-scale). Quantum error correction is discussed as an example of an
anti-decoherence strategy. Implications of decoherence and einselection for the
interpretation of quantum theory are briefly pointed out.Comment: 80 pages, 7 figures included, Lectures given by both authors at the
72nd Les Houches Summer School on "Coherent Matter Waves", July-August 199
Vacuum polarization calculations for hydrogenlike and alkalilike ions
Complete vacuum polarization calculations incorporating finite nuclear size
are presented for hydrogenic ions with principal quantum numbers n=1-5.
Lithiumlike, sodiumlike, and copperlike ions are also treated starting with
Kohn-Sham potentials, and including first-order screening corrections. In both
cases dominant Uehling terms are calculated with high accuracy, and smaller
Wichmann- Kroll terms are obtained using numerical electron Green's functions.Comment: 23 pages, 1 figur
The electric dipole form factor of the nucleon
The electric dipole form factor of the nucleon stemming from the QCD
term is calculated in chiral perturbation theory in leading
order. To this order, the form factor originates from the pion cloud. Its
momentum-dependence is proportional to a non-derivative time-reversal-violating
pion-nucleon coupling, and the scale for momentum variation--appearing, in
particular, in the radius of the form factor--is the pion mass.Comment: 8 pages, 2 figure
Form Factors of Few-Body Systems: Point Form Versus Front Form
We present a relativistic point-form approach for the calculation of
electroweak form factors of few-body bound states that leads to results which
resemble those obtained within the covariant light-front formalism of Carbonell
et al. Our starting points are the physical processes in which such form
factors are measured, i.e. electron scattering off the bound state, or the
semileptonic weak decay of the bound state. These processes are treated by
means of a coupled-channel framework for a Bakamjian-Thomas type mass operator.
A current with the correct covariance properties is then derived from the
pertinent leading-order electroweak scattering or decay amplitude. As it turns
out, the electromagnetic current is affected by unphysical contributions which
can be traced back to wrong cluster properties inherent in the Bakamjian-Thomas
construction. These spurious contributions, however, can be separated uniquely,
as in the covariant light-front approach. In this way we end up with form
factors which agree with those obtained from the covariant light-front
approach. As an example we will present results for electroweak form factors of
heavy-light systems and discuss the heavy-quark limit which leads to the famous
Isgur-Wise function.Comment: Presented at LIGHTCONE 2011, Dallas, USA, 23 - 27 May, 201
Simulated-tempering approach to spin-glass simulations
After developing an appropriate iteration procedure for the determination of
the parameters, the method of simulated tempering has been successfully applied
to the 2D Ising spin glass. The reduction of the slowing down is comparable to
that of the multicanonical algorithm. Simulated tempering has, however, the
advantages to allow full vectorization of the programs and to provide the
canonical ensemble directly.Comment: 12 pages (LaTeX), 4 postscript figures, uufiles encoded, submitted to
Physical Review
Superselectors: Efficient Constructions and Applications
We introduce a new combinatorial structure: the superselector. We show that
superselectors subsume several important combinatorial structures used in the
past few years to solve problems in group testing, compressed sensing,
multi-channel conflict resolution and data security. We prove close upper and
lower bounds on the size of superselectors and we provide efficient algorithms
for their constructions. Albeit our bounds are very general, when they are
instantiated on the combinatorial structures that are particular cases of
superselectors (e.g., (p,k,n)-selectors, (d,\ell)-list-disjunct matrices,
MUT_k(r)-families, FUT(k, a)-families, etc.) they match the best known bounds
in terms of size of the structures (the relevant parameter in the
applications). For appropriate values of parameters, our results also provide
the first efficient deterministic algorithms for the construction of such
structures
A Spectral Bernstein Theorem
We study the spectrum of the Laplace operator of a complete minimal properly
immersed hypersurface in . (1) Under a volume growth condition on
extrinsic balls and a condition on the unit normal at infinity, we prove that
has only essential spectrum consisting of the half line .
This is the case when , where
is the extrinsic distance to a point of and are the
principal curvatures. (2) If the satisfy the decay conditions
, and strict inequality is achieved at some point
, then there are no eigenvalues. We apply these results to minimal
graphic and multigraphic hypersurfaces.Comment: 16 pages. v2. Final version: minor revisions, we add Proposition 3.2.
Accepted for publication in the Annali di Matematica Pura ed Applicata, on
the 05/03/201
The Electric Dipole Form Factor of the Nucleon in Chiral Perturbation Theory to Sub-leading Order
The electric dipole form factor (EDFF) of the nucleon stemming from the QCD
theta term and from the quark color-electric dipole moments is calculated in
chiral perturbation theory to sub-leading order. This is the lowest order in
which the isoscalar EDFF receives a calculable, non-analytic contribution from
the pion cloud. In the case of the theta term, the expected lower bound on the
deuteron electric dipole moment is |d_d| > 1.4 10^(-4) \theta e fm. The
momentum dependence of the isovector EDFF is proportional to a non-derivative
time-reversal-violating pion-nucleon coupling, and the scale for momentum
variation ---appearing, in particular, in the radius of the form factor--- is
the pion mass.Comment: 14 pages, 3 figure
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