2,204 research outputs found
How much time does a measurement take?
We consider the problem of measurement using the Lindblad equation, which
allows the introduction of time in the interaction between the measured system
and the measurement apparatus. We use analytic results, valid for weak
system-environment coupling, obtained for a two-level system in contact with a
measurer (Markovian interaction) and a thermal bath (non-Markovian
interaction), where the measured observable may or may not commute with the
system-environment interaction. Analysing the behavior of the coherence, which
tends to a value asymptotically close to zero, we obtain an expression for the
time of measurement which depends only on the system-measurer coupling, and
which does not depend on whether the observable commutes with the system-bath
interaction. The behavior of the coherences in the case of strong
system-environment coupling, found numerically, indicates that an increase in
this coupling decreases the measurement time, thus allowing our expression to
be considered the upper limit for the duration of the process.Comment: REVISED VERSION: 17 pages, 2 figure
Neutron Stars with Hyperons subject to Strong Magnetic Field
Neutron stars are one of the most exotic objects in the universe and a unique
laboratory to study the nuclear matter above the nuclear saturation density. In
this work, we study the equation of state of the nuclear matter within a
relativistic model subjected to a strong magnetic field. We then apply this EoS
to study and describe some of the physical characteristics of neutron star,
especially the mass-radius relation and chemical compositions. To study the
influence of a the magnetic field and the hyperons in the stellar interior, we
consider altogether four solutions: two different values of magnetic field to
obtain a weak and a strong influence, and two configurations: a family of
neutron stars formed only by protons, electrons and neutrons and a family
formed by protons, electrons, neutrons, muons and hyperons. The limit and the
validity of the results found are discussed with some care. In all cases the
particles that constitute the neutron star are in equilibrium and zero
total net charge. Our work indicates that the effect of a strong magnetic field
has to be taken into account in the description of magnetars, mainly if we
believe that there are hyperons in their interior, in which case, the influence
of the magnetic field can increase the mass by more than 10%. We have also seen
that although a magnetar can reach 2.48, a natural explanation of
why we do not know pulsars with masses above 2.0 arises. We also
discuss how the magnetic field affects the strangeness fraction in some
standard neutron star masses and, to conclude our paper, we revisit the direct
URCA process related to the cooling of the neutron stars and show how it is
affected by the hyperons and the magnetic field.Comment: 16 pages, 8 figure
Epitaxial-tau(Mn,Ni)Al/(Al,Ga)As heterostructures: Magnetic and magneto-optic properties
Ferromagnetic Perpendicularly magnetized epitaxial thin films of tau (Mn,Ni)AI have been successfully grown on AlAs/GaAs heterostructures by molecular beam epitaxy. We have investigated the polar Kerr rotation and magnetization of tau MnAl and (Mn,Ni) Al as a function of Mn and Ni concentration. The largest polar Kerr rotation and remnant magnetization were obtained for Mn0.5Al0.5 thin films with values of 0.16-degrees and 224 emu/cm3, respectively. We observed that the Kerr rotation and magnetization remained constant with Ni additions up to about 12 at. % and subsequently decreased with further Ni additions. We discuss these results and one possible method of enhancing the Kerr rotation
Avaliação e manejo do solo com a tecnologia de corte e trituração visando a sustentabilidade do sistema de produção da agricultura familiar, com ênfase em alternativas ao uso do fogo na Amazônia.
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Business ethics: international analysis of codes of ethics and conduct
Codes of ethics and code of conduct formalize an ideal of expected behavior patterns to managers and employees of organizations, providing standards and orientation that states companies interactions with the community, through products /services, sales force, marketing communications, investments, and relationships with other stakeholders, influencing company reputation and overall Marketing performance. The objective of this study is to analyze the differences in codes of ethics of the largest companies based in Brazil and in Portugal, given their cultural and linguistic similarities. Findings show that the use of codes of ethics are more common in Brazil than in Portugal and that codes of ethics are substantially more extensive and cover a larger number of categories in Brazilian companies, reflecting the organizations’ mission and perception of stakeholders concerns and priorities. We conclude that ethical issues severely impact company reputation and, in a comprehensive sense, overall Marketing performance. Marketing professionals should be systematically aware of how company core values are transmitted to different audiences, including the use of code of ethics to communicate both with internal and external publics.info:eu-repo/semantics/publishedVersio
Efeito da adubação mineral na produção de matéria seca de pimenta longa (Piper hispidinervium).
bitstream/item/60320/1/CPATU-PA180.pd
A characterization of quadric constant mean curvature hypersurfaces of spheres
Let be an immersion of a
complete -dimensional oriented manifold. For any , let
us denote by the function given by
and by , the function given by
, where is a Gauss map. We will prove
that if has constant mean curvature, and, for some and some
real number , we have that , then, is
either a totally umbilical sphere or a Clifford hypersurface. As an
application, we will use this result to prove that the weak stability index of
any compact constant mean curvature hypersurface in
which is neither totally umbilical nor a Clifford hypersurface and has constant
scalar curvature is greater than or equal to .Comment: Final version (February 2008). To appear in the Journal of Geometric
Analysi
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