9,280 research outputs found
Nonlinear free fall of one-dimensional rigid bodies in hyperviscous fluids
We consider the free fall of slender rigid bodies in a viscous incompressible
fluid. We show that the dimensional reduction (DR), performed by substituting
the slender bodies with one-dimensional rigid objects, together with a
hyperviscous regularization (HR) of the Navier--Stokes equation for the
three-dimensional fluid lead to a well-posed fluid-structure interaction
problem. In contrast to what can be achieved within a classical framework, the
hyperviscous term permits a sound definition of the viscous force acting on the
one-dimensional immersed body. Those results show that the DR/HR procedure can
be effectively employed for the mathematical modeling of the free fall problem
in the slender-body limit.Comment: arXiv admin note: substantial text overlap with arXiv:1305.070
Prescriptionless light-cone integrals
Perturbative quantum gauge field theory seen within the perspective of
physical gauge choices such as the light-cone entails the emergence of
troublesome poles of the type in the Feynman integrals,
and these come from the boson field propagator, where and
is the external arbitrary four-vector that defines the gauge proper.
This becomes an additional hurdle to overcome in the computation of Feynman
diagrams, since any graph containing internal boson lines will inevitably
produce integrands with denominators bearing the characteristic gauge-fixing
factor. How one deals with them has been the subject of research for over
decades, and several prescriptions have been suggested and tried in the course
of time, with failures and successes.
However, a more recent development in this front which applies the negative
dimensional technique to compute light-cone Feynman integrals shows that we can
altogether dispense with prescriptions to perform the calculations. An
additional bonus comes attached to this new technique in that not only it
renders the light-cone prescriptionless, but by the very nature of it, can also
dispense with decomposition formulas or partial fractioning tricks used in the
standard approach to separate pole products of the type , .
In this work we demonstrate how all this can be done.Comment: 6 pages, no figures, Revtex style, reference [2] correcte
Identification of the long polar fimbriae gene variants in the locus of enterocyte effacement-negative Shiga toxin-producing Escherichia coli strains isolated from humans and cattle in Argentina
The long polar fimbriae (Lpf) is one of few adhesive factors of Shiga toxin-producing Escherichia coli (STEC) and it is associated with colonization of the intestine. Studies have demonstrated the presence of lpf genes in several pathogenic E. coli strains, and classification of variants based on polymorphisms in the lpfA1 and lpfA2 genes has been adopted. Using a collection of Argentinean locus of enterocyte effacement (LEE)-negative STEC strains, we determined that the different lpfA types were present in a wide variety of serotypes with no apparent association between the types of lpfA1 or lpfA2 genes and the severity of human disease. The lpfA2-1 was the most prevalent variant identified, which was present in 95.8% of the isolates, and lpfA1-3 and lpfA2-2, proposed as specific biomarkers of E. coli O157:H7, were not found in any of the serotypes studied. The prevalence of lpf genes in a large number of strains is useful to understand the genetic diversity of LEE-negative STEC and to define the association of some of these isolates carrying specific lpf-variants with disease.Fil: Galli, Lucía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico CONICET- La Plata. Instituto de Genética Veterinaria "Ing. Fernando Noel Dulout". Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Instituto de Genética Veterinaria; Argentina. Dirección Nacional de Instituto de Investigación. Administración Nacional de Laboratorio e Instituto de Salud “Dr. C. G. Malbrán”; ArgentinaFil: Torres, Alfredo G.. University of Texas Medical Branch; Estados UnidosFil: Rivas, Marta. Dirección Nacional de Instituto de Investigación. Administración Nacional de Laboratorio e Instituto de Salud “Dr. C. G. Malbrán”; Argentin
Two-loop self-energy diagrams worked out with NDIM
In this work we calculate two two-loop massless Feynman integrals pertaining
to self-energy diagrams using NDIM (Negative Dimensional Integration Method).
We show that the answer we get is 36-fold degenerate. We then consider special
cases of exponents for propagators and the outcoming results compared with
known ones obtained via traditional methods.Comment: LaTeX, 10 pages, 2 figures, styles include
Supplier-Buyer Proximity and Production to Order Choice
We study the determinants of the firm-level choice to produce following an order placed by a downstream firm (production to order) or to produce in advance. We rationalize this choice through a simple theoretical model and apply it to a firm-level empirical analysis. Relying on a large panel of Italian manufacturing firms, we show that two main variables affect this choice: the distance between the supplier and the buyer and the degree of product differentiation in downstream industries where products are sold. The impact of proximity on the choice of producing to order crucially depends on the degree of product differentiation in downstream markets. We find that, in industries where average product differentiation is high, production to order prevails if the supplier is located close to the buyer. On the contrary, proximity is associated to production in advance in homogeneous sectors. We also find that, if suppliers are located in a different country from that of the buyers, they will tend to produce to order if product differentiation in downstream industries is low, and produce in advance if product differentiation is high. We also narrow the scope of our analysis to analyze the determinants of production to order originating from the same province where the supplier is located.Industrial Districts; Networks; Production to Order; Relationship-Specific Investments
Negative Dimensional Integration: "Lab Testing" at Two Loops
Negative dimensional integration method (NDIM) is a technique to deal with
D-dimensional Feynman loop integrals. Since most of the physical quantities in
perturbative Quantum Field Theory (pQFT) require the ability of solving them,
the quicker and easier the method to evaluate them the better. The NDIM is a
novel and promising technique, ipso facto requiring that we put it to test in
different contexts and situations and compare the results it yields with those
that we already know by other well-established methods. It is in this
perspective that we consider here the calculation of an on-shell two-loop three
point function in a massless theory. Surprisingly this approach provides twelve
non-trivial results in terms of double power series. More astonishing than this
is the fact that we can show these twelve solutions to be different
representations for the same well-known single result obtained via other
methods. It really comes to us as a surprise that the solution for the
particular integral we are dealing with is twelvefold degenerate.Comment: 10 pages, LaTeX2e, uses style jhep.cls (included
- …