775 research outputs found
Solar Reector Design
The design of solar panels is investigated. Different aspects of this problem are presented. A formula averaging the solar energy received on a given location is derived rst. The energy received by the collecting solar panel is then calculated using a specially designed algorithm. The geometry of the device collecting the energy may then be optimised using different algorithms. The results show that for a given depth, devices of smaller width are more energy efficient than those of wider dimensions. This leads to a more economically efficient design
The quantum world is not built up from correlations
It is known that the global state of a composite quantum system can be
completely determined by specifying correlations between measurements performed
on subsystems only. Despite the fact that the quantum correlations thus suffice
to reconstruct the quantum state, we show, using a Bell inequality argument,
that they cannot be regarded as objective local properties of the composite
system in question. It is well known since the work of J.S. Bell, that one
cannot have locally preexistent values for all physical quantities, whether
they are deterministic or stochastic. The Bell inequality argument we present
here shows this is also impossible for correlations among subsystems of an
individual isolated composite system. Neither of them can be used to build up a
world consisting of some local realistic structure. As a corrolary to the
result we argue that entanglement cannot be considered ontologically robust.
The argument has an important advantage over others because it does not need
perfect correlations but only statistical correlations. It can therefore easily
be tested in currently feasible experiments using four particle entanglement.Comment: Published version. Title change
A toy model for quantum mechanics
The toy model used by Spekkens [R. Spekkens, Phys. Rev. A 75, 032110 (2007)]
to argue in favor of an epistemic view of quantum mechanics is extended by
generalizing his definition of pure states (i.e. states of maximal knowledge)
and by associating measurements with all pure states. The new toy model does
not allow signaling but, in contrast to the Spekkens model, does violate
Bell-CHSH inequalities. Negative probabilities are found to arise naturally
within the model, and can be used to explain the Bell-CHSH inequality
violations.Comment: in which the author breaks his vow to never use the words "ontic" and
"epistemic" in publi
Odd-intrinsic-parity processes within the Resonance Effective Theory of QCD
We analyse the most general odd-intrinsic-parity effective Lagrangian of QCD
valid for processes involving one pseudoscalar with vector mesons described in
terms of antisymmetric tensor fields. Substantial information on the
odd-intrinsic-parity couplings is obtained by constructing the
vector-vector-pseudoscalar Green's three-point function, at leading order in
1/Nc, and demanding that its short-distance behaviour matches the corresponding
OPE result. The QCD constraints thus enforced allow us to predict the decay
amplitude omega -> pion gamma, and the O(p^6) corrections to pion -> gamma
gamma. Noteworthy consequences concerning the vector meson dominance assumption
in the decay omega -> 3 pions are also extracted from the previous analysis.Comment: 20 pages, 4 figure
Anomalous Commutator Algebra for Conformal Quantum Mechanics
The structure of the commutator algebra for conformal quantum mechanics is
considered. Specifically, it is shown that the emergence of a dimensional scale
by renormalization implies the existence of an anomaly or quantum-mechanical
symmetry breaking, which is explicitly displayed at the level of the generators
of the SO(2,1) conformal group. Correspondingly, the associated breakdown of
the conservation of the dilation and special conformal charges is derived.Comment: 23 pages. A few typos corrected in the final version (which agrees
with the published Phys. Rev. D article
Molecular dynamics simulation of the order-disorder phase transition in solid NaNO
We present molecular dynamics simulations of solid NaNO using pair
potentials with the rigid-ion model. The crystal potential surface is
calculated by using an \emph{a priori} method which integrates the \emph{ab
initio} calculations with the Gordon-Kim electron gas theory. This approach is
carefully examined by using different population analysis methods and comparing
the intermolecular interactions resulting from this approach with those from
the \emph{ab initio} Hartree-Fock calculations. Our numerics shows that the
ferroelectric-paraelectric phase transition in solid NaNO is triggered by
rotation of the nitrite ions around the crystallographical c axis, in agreement
with recent X-ray experiments [Gohda \textit{et al.}, Phys. Rev. B \textbf{63},
14101 (2000)]. The crystal-field effects on the nitrite ion are also addressed.
Remarkable internal charge-transfer effect is found.Comment: RevTeX 4.0, 11 figure
The Strong CP Problem and Axions
I describe how the QCD vacuum structure, necessary to resolve the
problem, predicts the presence of a P, T and CP violating term proportional to
the vacuum angle . To agree with experimental bounds, however,
this parameter must be very small ). After briefly
discussing some possible other solutions to this, so-called, strong CP problem,
I concentrate on the chiral solution proposed by Peccei and Quinn which has
associated with it a light pseudoscalar particle, the axion. I discuss in
detail the properties and dynamics of axions, focusing particularly on
invisible axion models where axions are very light, very weakly coupled and
very long-lived. Astrophysical and cosmological bounds on invisible axions are
also briefly touched upon.Comment: 14 pages, to appear in the Lecture Notes in Physics volume on Axions,
(Springer Verlag
Chiral Magnetic Effect in Hydrodynamic Approximation
We review derivations of the chiral magnetic effect (ChME) in hydrodynamic
approximation. The reader is assumed to be familiar with the basics of the
effect. The main challenge now is to account for the strong interactions
between the constituents of the fluid. The main result is that the ChME is not
renormalized: in the hydrodynamic approximation it remains the same as for
non-interacting chiral fermions moving in an external magnetic field. The key
ingredients in the proof are general laws of thermodynamics and the
Adler-Bardeen theorem for the chiral anomaly in external electromagnetic
fields. The chiral magnetic effect in hydrodynamics represents a macroscopic
manifestation of a quantum phenomenon (chiral anomaly). Moreover, one can argue
that the current induced by the magnetic field is dissipation free and talk
about a kind of "chiral superconductivity". More precise description is a
ballistic transport along magnetic field taking place in equilibrium and in
absence of a driving force. The basic limitation is exact chiral limit while
the temperature--excitingly enough- does not seemingly matter. What is still
lacking, is a detailed quantum microscopic picture for the ChME in
hydrodynamics. Probably, the chiral currents propagate through
lower-dimensional defects, like vortices in superfluid. In case of superfluid,
the prediction for the chiral magnetic effect remains unmodified although the
emerging dynamical picture differs from the standard one.Comment: 35 pages, prepared for a volume of the Springer Lecture Notes in
Physics "Strongly interacting matter in magnetic fields" edited by D.
Kharzeev, K. Landsteiner, A. Schmitt, H.-U. Ye
Differential geometry construction of anomalies and topological invariants in various dimensions
In the model of extended non-Abelian tensor gauge fields we have found new
metric-independent densities: the exact (2n+3)-forms and their secondary
characteristics, the (2n+2)-forms as well as the exact 6n-forms and the
corresponding secondary (6n-1)-forms. These forms are the analogs of the
Pontryagin densities: the exact 2n-forms and Chern-Simons secondary
characteristics, the (2n-1)-forms. The (2n+3)- and 6n-forms are gauge invariant
densities, while the (2n+2)- and (6n-1)-forms transform non-trivially under
gauge transformations, that we compare with the corresponding transformations
of the Chern-Simons secondary characteristics. This construction allows to
identify new potential gauge anomalies in various dimensions.Comment: 27 pages, references added, matches published versio
Coalescence of nanoscale metal clusters: Molecular-dynamics study
We study the coalescence of nanoscale metal clusters in an inert-gas
atmosphere using constant-energy molecular dynamics. The coalescence proceeds
via atomic diffusion with the release of surface energy raising the
temperature. If the temperature exceeds the melting point of the coalesced
cluster, a molten droplet forms. If the temperature falls between the melting
point of the larger cluster and those of the smaller clusters, a metastable
molten droplet forms and freezes.Comment: 5 figure
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