5,883 research outputs found
Reconstruction of semileptonically decaying beauty hadrons produced in high energy pp collisions
It is well known that in hadron decays with a single unreconstructible
final state particle, the decay kinematics can be solved up to a quadratic
ambiguity, without any knowledge of the hadron momentum. We present a
method to infer the momenta of hadrons produced in hadron collider
experiments using information from their reconstructed flight vectors. Our
method is strictly agnostic to the decay itself, which implies that it can be
validated with control samples of topologically similar decays to fully
reconstructible final states. A multivariate regression algorithm based on the
flight information provides a hadron momentum estimate with a resolution of
around 60% which is sufficient to select the correct solution to the quadratic
equation in around 70% of cases. This will improve the ability of hadron
collider experiments to make differential decay rate measurements with
semileptonic hadron decays.Comment: 18 pages, 17 figures. Updated version to be published in JHE
The self-consistent general relativistic solution for a system of degenerate neutrons, protons and electrons in beta-equilibrium
We present the self-consistent treatment of the simplest, nontrivial,
self-gravitating system of degenerate neutrons, protons and electrons in
-equilibrium within relativistic quantum statistics and the
Einstein-Maxwell equations. The impossibility of imposing the condition of
local charge neutrality on such systems is proved, consequently overcoming the
traditional Tolman-Oppenheimer-Volkoff treatment. We emphasize the crucial role
of imposing the constancy of the generalized Fermi energies. A new approach
based on the coupled system of the general relativistic
Thomas-Fermi-Einstein-Maxwell equations is presented and solved. We obtain an
explicit solution fulfilling global and not local charge neutrality by solving
a sophisticated eigenvalue problem of the general relativistic Thomas-Fermi
equation. The value of the Coulomb potential at the center of the configuration
is and the system is intrinsically stable against
Coulomb repulsion in the proton component. This approach is necessary, but not
sufficient, when strong interactions are introduced.Comment: Letter in press, Physics Letters B (2011
A nearly zero-energy microgrid testbed laboratory: Centralized control strategy based on SCADA system
Currently, despite the use of renewable energy sources (RESs), distribution networks are facing problems, such as complexity and low productivity. Emerging microgrids (MGs) with RESs based on supervisory control and data acquisition (SCADA) are an effective solution to control, manage, and finally deal with these challenges. The development and success of MGs is highly dependent on the use of power electronic interfaces. The use of these interfaces is directly related to the progress of SCADA systems and communication infrastructures. The use of SCADA systems for the control and operation of MGs and active distribution networks promotes productivity and efficiency. This paper presents a real MG case study called the LAMBDA MG testbed laboratory, which has been implemented in the electrical department of the Sapienza University of Rome with a centralized energy management system (CEMS). The real-time results of the SCADA system show that a CEMS can create proper energy balance in a LAMBDA MG testbed and, consequently, minimize the exchange power of the LAMBDA MG and main grid
Strong electric fields induced on a sharp stellar boundary
Due to a first order phase transition, a compact star may have a
discontinuous distribution of baryon as well as electric charge densities, as
e.g. at the surface of a strange quark star. The induced separation of positive
and negative charges may lead to generation of supercritical electric fields in
the vicinity of such a discontinuity. We study this effect within a
relativistic Thomas-Fermi approximation and demonstrate that the strength of
the electric field depends strongly on the degree of sharpness of the surface.
The influence of strong electric fields on the stability of compact stars is
discussed. It is demonstrated that stable configurations appear only when the
counter-pressure of degenerate fermions is taken into consideration.Comment: 13 pages, 2 figure
A model for the development of types of atolls and volcanic islands on the Pacific lithospheric plate
"This paper is an expansion of a paper first delivered to the Annual Meeting of the Association of Canadian Geographers at Laval University, Quebec, May 1976."A literature review on atoll origins and volcanic island development on the Pacific lithospheric plate is combined with bathymetric data on the Hawaiian, Marshall, Caroline, Tuamotu and Society island chains to produce a model which helps explain the development of all major Pacific plate island types. This model incorporates the concept that as new lithosphere is formed along the East Pacific Rise older crust moves north-west towards Asia, cools and causes ocean deepening. Some distance from the East Pacific Rise relatively fixed melting anomalies produce volcanic island chains. In warmer waters these islands develop fringing reefs which continue to grow to wave level as the islands are carried on the cooling plate into deeper water. Raised volcanic island forms can develop on arches produced by the isostatic subsidence of new magmatic outpourings close by. As volcanic islands with fringing reefs move into deeper water almost-atolls and finally true atolls develop. Partly raised and raised forms result if atolls rise over minor upwarps on the crust produced by, 1) asthenospheric bumps, 2) arch flexuring resulting from isostatic subsidence of nearby magmatic outpourings, 3) compression within the lithosphere alongside Pacific plate subduction zones. The model also helps explain certain types of drowned atolls and guyots."Financial assistance from the University of Winnipeg is acknowledged.
Cooling of young neutron stars in GRB associated to Supernova
Recent observations of the late (-- s) emission of supernovae
(SNe) associated to GRBs (GRB-SN) show a distinctive emission in the X-ray
regime consistent with temperatures -- K. Similar features have
been also observed in the two Type Ic SNe SN 2002ap and SN 1994I that are not
associated to GRBs. We advance the possibility that the late X-ray emission
observed in GRB-SN and in isolated SN is associated to a hot neutron star (NS)
just formed in the SN event, here defined as a neo-NS. We discuss the thermal
evolution of neo-NS in the age regime that spans from minute (just
after the proto-NS phase) up to ages <10-100 yr. We examine the key factor
governing the neo-NS cooling emphasizing on the neutrino emission. A
phenomenological heating source and new boundary conditions are introduced to
mimic the high-temperature atmosphere of young NSs. We match the neo-NS
luminosity to the late X-ray emission of the GRB-SN events URCA-1 in
GRB980425-SN1998bw, URCA-2 in GRB030329-SN2003dh, and URCA-3 in
GRB031203-SN2003lw. By calibrating our additional heating source at early times
to -- erg/g/s, we find a striking agreement of the
luminosity obtained from the cooling of neo-NSs with the late
(-- s) X-ray emission observed in GRB-SN. It is therefore
appropriate to revise the boundary conditions used in the cooling theory of
NSs, to match the proper conditions of the atmosphere at young ages. Additional
heating processes that are still not studied within this context, such as e+e-
pair creation by overcritical fields and nuclear fusion and fission energy
release, might also take place under such conditions and deserve further
analysis. Observation of GRB-SN has shown the possibility of witnessing the
thermal evolution of neo-NSs. A new campaign of dedicated observations is
recommended both of GRB-SN and of isolated Type Ic SN.Comment: Version to be published by Astronomy & Astrophysics. Abstract reduced
with respect to the one to be published in A&A due to arXiv system constraint
of 300 word
Large deviations of the free energy in the p-spin glass spherical model
We investigate the behavior of the rare fluctuations of the free energy in the p-spin spherical model, evaluating the corresponding rate function via the G\ue4rtner-Ellis theorem. This approach requires the knowledge of the analytic continuation of the disorder-averaged replicated partition function to arbitrary real number of replicas. In zero external magnetic field, we show via a one-step replica symmetry breaking calculation that the rate function is infinite for fluctuations of the free energy above its typical value, corresponding to an anomalous, superextensive suppression of rare fluctuations. We extend this calculation to nonzero magnetic field, showing that in this case this very large deviation disappears and we try to motivate this finding in light of a geometrical interpretation of the scaled cumulant generating function
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