58,591 research outputs found
Studying pion effects in the quark propagator
Within the framework of Schwinger-Dyson and Bethe-Salpeter equations we
investigate the importance of pions for the quark-gluon interaction. To this
end we choose a truncation for the quark-gluon vertex that includes
intermediate pion degrees of freedom and adjust the interaction such that
unquenched lattice results for various current quark masses are reproduced. The
corresponding Bethe-Salpeter kernel is constructed from constraints by chiral
symmetry. After extrapolation to the physical point we find a considerable
contribution of the pion back reaction to the quark mass function as well as to
the chiral condensate. The quark wave function is less affected.Comment: Talk given at 11th International Conference on Meson-Nucleon Physics
and the Structure of the Nucleon (MENU 2007), Julich, Germany, 10-14 Sep 200
Neutrino emissivities and bulk viscosity in neutral two-flavor quark matter
We study thermodynamic and transport properties for the isotropic
color-spin-locking (iso-CSL) phase of two-flavor superconducting quark matter
under compact star constraints within a NJL-type chiral quark model. Chiral
symmetry breaking and the phase transition to superconducting quark matter
leads to a density dependent change of quark masses, chemical potentials and
diquark gap. A self-consistent treatment of these physical quantities
influences on the microscopic calculations of transport properties. We present
results for the iso-CSL direct URCA emissivities and bulk viscosities, which
fulfill the constraints on quark matter derived from cooling and rotational
evolution of compact stars. We compare our results with the phenomenologically
successful, but yet heuristic 2SC+X phase. We show that the microscopically
founded iso-CSL phase can replace the purely phenomenological 2SC+X phase in
modern simulations of the cooling evolution for compact stars with color
superconducting quark matter interior.Comment: 15 pages, 6 figures, references added, text improve
What Are Kinship Terminologies, and Why Do We Care? A Computational Approach to Analyzing Symbolic Domains
Kinship is a fundamental feature and basis of human societies. We describe a set of computational tools and services, the Kinship Algebra Modeler, and the logic that underlies these. These were developed to improve how we understand both the fundamental facts of kinship, and how people use kinship as a resource in their lives. Mathematical formalism applied to cultural concepts is more than an exercise in model building, as it provides a way to represent and explore logical consistency and implications. The logic underlying kinship is explored here through the kin term computations made by users of a terminology when computing the kinship relation one person has to another by referring to a third person for whom each has a kin term relationship. Kinship Algebra Modeler provides a set of tools, services and an architecture to explore kinship terminologies and their properties in an accessible manner
Computation of unsteady transonic flows through rotating and stationary cascades. 3: Acoustic far-field analysis
A small perturbation type analysis has been developed for the acoustic far field in an infinite duct extending upstream and downstream of an axial turbomachinery stage. The analysis is designed to interface with a numerical solution of the near field of the blade rows and, thereby, to provide the necessary closure condition to complete the statement of infinite duct boundary conditions for the subject problem. The present analysis differs from conventional inlet duct analyses in that a simple harmonic time dependence was not assumed, since a transient signal is generated by the numerical near-field solution and periodicity is attained only asymptotically. A description of the computer code developed to carry out the necessary convolutions numerically is included, as well as the results of a sample application using an impulsively initiated harmonic signal
A formal definition and a new security mechanism of physical unclonable functions
The characteristic novelty of what is generally meant by a "physical
unclonable function" (PUF) is precisely defined, in order to supply a firm
basis for security evaluations and the proposal of new security mechanisms. A
PUF is defined as a hardware device which implements a physical function with
an output value that changes with its argument. A PUF can be clonable, but a
secure PUF must be unclonable. This proposed meaning of a PUF is cleanly
delineated from the closely related concepts of "conventional unclonable
function", "physically obfuscated key", "random-number generator", "controlled
PUF" and "strong PUF". The structure of a systematic security evaluation of a
PUF enabled by the proposed formal definition is outlined. Practically all
current and novel physical (but not conventional) unclonable physical functions
are PUFs by our definition. Thereby the proposed definition captures the
existing intuition about what is a PUF and remains flexible enough to encompass
further research. In a second part we quantitatively characterize two classes
of PUF security mechanisms, the standard one, based on a minimum secret
read-out time, and a novel one, based on challenge-dependent erasure of stored
information. The new mechanism is shown to allow in principle the construction
of a "quantum-PUF", that is absolutely secure while not requiring the storage
of an exponentially large secret. The construction of a PUF that is
mathematically and physically unclonable in principle does not contradict the
laws of physics.Comment: 13 pages, 1 figure, Conference Proceedings MMB & DFT 2012,
Kaiserslautern, German
An Introduction to Conformal Ricci Flow
We introduce a variation of the classical Ricci flow equation that modifies
the unit volume constraint of that equation to a scalar curvature constraint.
The resulting equations are named the Conformal Ricci Flow Equations because of
the role that conformal geometry plays in constraining the scalar curvature.
These equations are analogous to the incompressible Navier-Stokes equations of
fluid mechanics inasmuch as a conformal pressure arises as a Lagrange
multiplier to conformally deform the metric flow so as to maintain the scalar
curvature constraint. The equilibrium points are Einstein metrics with a
negative Einstein constant and the conformal pressue is shown to be zero at an
equilibrium point and strictly positive otherwise. The geometry of the
conformal Ricci flow is discussed as well as the remarkable analytic fact that
the constraint force does not lose derivatives and thus analytically the
conformal Ricci equation is a bounded perturbation of the classical
unnormalized Ricci equation. That the constraint force does not lose
derivatives is exactly analogous to the fact that the real physical pressure
force that occurs in the Navier-Stokes equations is a bounded function of the
velocity. Using a nonlinear Trotter product formula, existence and uniqueness
of solutions to the conformal Ricci flow equations is proven. Lastly, we
discuss potential applications to Perelman's proposed implementation of
Hamilton's program to prove Thurston's 3-manifold geometrization conjectures.Comment: 52 pages, 1 figur
Ice core records of atmospheric CO2 around the last three glacial terminations
Air trapped in bubbles in polar ice cores constitutes an archive for the reconstruction of the global carbon cycle and the relation between greenhouse gases and climate in the past. High-resolution records from Antarctic ice cores show that carbon dioxide concentrations increased by 80 to 100 parts per million by volume 600 ± 400 years after the warming of the last three deglaciations. Despite strongly decreasing temperatures, high carbon dioxide concentrations can be sustained for thousands of years during glaciations; the size of this phase lag is probably connected to the duration of the preceding warm period, which controls the change in land ice coverage and the buildup of the terrestrial biosphere.</jats:p
When is an alternative possibility robust?
According to some, free will requires alternative possibilities. But not any old alternative possibility will do. Sometimes, being able to bring about an alternative does not bestow any control on an agent. In order to bestow control, and so be directly relevant qua alternative to grounding the agent's moral responsibility, alternatives need to be robust. Here, I investigate the nature of robust alternatives. I argue that Derk Pereboom's latest robustness criterion is too strong, and I suggest a different criterion based on the idea that what agents need to be able to do is keep open the possibility of securing their blamelessness, rather than needing to directly ensure their own blamelessness at the time of decision
Spacelike surfaces with free boundary in the Lorentz-Minkowski space
We investigate a variational problem in the Lorentz-Minkowski space \l^3
whose critical points are spacelike surfaces with constant mean curvature and
making constant contact angle with a given support surface along its common
boundary. We show that if the support surface is a pseudosphere, then the
surface is a planar disc or a hyperbolic cap. We also study the problem of
spacelike hypersurfaces with free boundary in the higher dimensional
Lorentz-Minkowski space \l^{n+1}.Comment: 16 pages. Accepted in Classical and Quantum Gravit
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