1,828 research outputs found
Quantum systems as classical systems
A characteristical property of a classical physical theory is that the
observables are real functions taking an exact outcome on every (pure) state;
in a quantum theory, at the contrary, a given observable on a given state can
take several values with only a predictable probability. However, even in the
classical case, when an observer is intrinsically unable to distinguish between
some distinct states he can convince himself that the measure of its
''observables'' can have several values in a random way with a statistical
character. What kind of statistical theory is obtainable in this way? It is
possible, for example, to obtain exactly the statistical previsions of quantum
mechanics? Or, in other words, can a physical system showing a classical
behaviour appear to be a quantum system to a confusing observer? We show that
from a mathematical viewpoint it is not difficult to produce a theory with
hidden variables having this property. We don't even try to justify in physical
terms the artificial construction we propose; what we do is to give a general
and rigorous argument showing how the interplay between the classical and
quantum mechanics we offer is interpretable as the difference between an
imaginary very expert observer and another nonexpert observer. This proves also
that besides the well known theorems concerning the impossibility of hidden
variables (cfr. Von Neumann [Neu] and Jauch-Piron [J-P]) there is also room for
a result in favor of the possibility.Comment: late
Kinetic study of styrene/maleic anhydride copolymers using succine anhydride as the model compound
The reaction of aniline with succinic anhydride, a low molecular weight poly[styrene-co-(maleic anhydride)], and a high molecular weight poly[styreneco-( maleic anhydride)] were used to determine if these polymer reactions are diffusion- or reaction-controlled. Kinetic study protocols were developed to determine the rate constants for the succinic anhydride/aniline model reaction and for the 50/50 and 86/14 copolymers. These protocols were then used to gather kinetic data. The succinic anhydride/aniline reaction was determined to be exothermic and to have an induction period. The succinic anhydride/aniline reaction was also determined to have an experimental rate constant of 13 L/molmin 25% at 67 +/- 1.5 degrees Celsius. For the copolymer/aniline reactions, the experimental rate constants at 67 +/- 1.5 degrees Celsius were determined to be .051 L/molmin 15% for the 50/50 polymer and .008 L/molmin 18% for the 86/14 polymer. The model reaction was found to be 250 times faster than the 50/50 polymer/aniline reaction and 1600 times faster than the 86/14 polymer/aniline reaction. The 50/50 polymer/aniline reaction was determined to be 6 times faster than the 86/14 polymer/aniline reaction. At 20 1.5 degrees Celsius, the theoretical diffusion-controlled rate constant for the succinic anhydride/aniline reaction was determined to be 7.09 x 10^11 L/molmin and the experimental rate of reaction was determined to be 0.72 L/molmin 25%. Thus, these reactions were determined to be reaction-controlled
Electron density distribution in paramagnetic chromium A gamma ray diffraction study
High accuracy single crystal structure factors, complete up to sin amp; 61553; amp; 61548; amp; 61472; amp; 61501; amp; 61472; amp; 61489; amp; 61486; amp; 61495; amp; 61496; amp; 61472; amp; 61485; amp; 61489; amp; 61484; amp; 61472; have been measured from paramagnetic chromium at 333 K using 316.5 keV gamma radiation. A detailed description of the electron density distribution is derived in terms of a multipolar atomic deformation model. There is pronounced charge asphericity in the valence region arising from preferential occupancy of the t2g subshell. The 3d charge distribution is contracted by 12.6 relative to the free atom, in accordance with magnetic synchrotron x ray and neutron measurements. By contrast, the atomic crystal scattering factor deduced from experiment is found to be in contradiction with earlier experimental and theoretical work. Achievement of a reliable Debye Waller factor is of vital importance in this context. There is no evidence for an anharmonic term in the atomic potential. Real space and energetic features of the charge density topology are used to characterize the directed metallic bonds. Special attention is paid to the form factor approximation in diffraction data analysis
Reassessment of the electron density in Cu2O using gamma ray diffraction
The electron density distribution in Cu2O has been critically reexamined to test controversial conclusions from earlier experimental and theoretical studies. The electron density is derived via multipole refinement of high quality single crystal diffraction data, collected at room temperature with 316.5 keV gamma radiation. Four gamma lines in the energy range 200 600 keV have been used to extrapolate extinction free low order structure factors. The remaining extinction corrections refine to a crystal mosaicity identical to the observed one. There is no support for anharmonic contributions to the thermal parameters. Important features of the derived electron density are i a partially filled dz2 orbital, ii an incomplete ionization of Cu and O, iii no interstitial Cu Cu charge pileup, thereby refuting the covalent bonding hypothesi
Electron density distribution in paramagnetic chromium A gamma ray diffraction study
High accuracy single crystal structure factors, complete up to sin amp; 61553; amp; 61548; amp; 61472; amp; 61501; amp; 61472; amp; 61489; amp; 61486; amp; 61495; amp; 61496; amp; 61472; amp; 61485; amp; 61489; amp; 61484; amp; 61472; have been measured from paramagnetic chromium at 333 K using 316.5 keV gamma radiation. A detailed description of the electron density distribution is derived in terms of a multipolar atomic deformation model. There is pronounced charge asphericity in the valence region arising from preferential occupancy of the t2g subshell. The 3d charge distribution is contracted by 12.6 relative to the free atom, in accordance with magnetic synchrotron x ray and neutron measurements. By contrast, the atomic crystal scattering factor deduced from experiment is found to be in contradiction with earlier experimental and theoretical work. Achievement of a reliable Debye Waller factor is of vital importance in this context. There is no evidence for an anharmonic term in the atomic potential. Real space and energetic features of the charge density topology are used to characterize the directed metallic bonds. Special attention is paid to the form factor approximation in diffraction data analysis
Construction of a Complete Set of States in Relativistic Scattering Theory
The space of physical states in relativistic scattering theory is
constructed, using a rigorous version of the Dirac formalism, where the Hilbert
space structure is extended to a Gel'fand triple. This extension enables the
construction of ``a complete set of states'', the basic concept of the original
Dirac formalism, also in the cases of unbounded operators and continuous
spectra. We construct explicitly the Gel'fand triple and a complete set of
``plane waves'' -- momentum eigenstates -- using the group of space-time
symmetries. This construction is used (in a separate article) to prove a
generalization of the Coleman-Mandula theorem to higher dimension.Comment: 30 pages, Late
Comment on `On the Quantum Theory of Molecules' [J. Chem.Phys. {\bf 137}, 22A544 (2012)]
In our previous paper [J. Chem.Phys. {\bf 137}, 22A544 (2012)] we argued that
the Born-Oppenheimer approximation could not be based on an exact
transformation of the molecular Schr\"{o}dinger equation. In this Comment we
suggest that the fundamental reason for the approximate nature of the
Born-Oppenheimer model is the lack of a complete set of functions for the
electronic space, and the need to describe the continuous spectrum using
spectral projection.Comment: 2 page
Probabilities from envariance?
Zurek claims to have derived Born's rule noncircularly in the context of an
ontological no-collapse interpretation of quantum states, without any "deus ex
machina imposition of the symptoms of classicality." After a brief review of
Zurek's derivation it is argued that this claim is exaggerated if not wholly
unjustified. In order to demonstrate that Born's rule arises noncircularly from
deterministically evolving quantum states, it is not sufficient to assume that
quantum states are somehow associated with probabilities and then prove that
these probabilities are given by Born's rule. One has to show how irreducible
probabilities can arise in the context of an ontological no-collapse
interpretation of quantum states. It is argued that the reason why all attempts
to do this have so far failed is that quantum states are fundamentally
algorithms for computing correlations between possible measurement outcomes,
rather than evolving ontological states.Comment: To appear in IJQI; 9 pages, LaTe
Physical qubits from charged particles: IR divergences in quantum information
We consider soft photons effects (IR structure of QED) on the construction of
physical qubits. Soft-photons appear when we build charged qubits from the
asymptotic states of QED. This construction is necessary in order to include
the effect of soft photons on entanglement measures. The nonexistence of free
charged particles (due to the long range of QED interactions) lead us to
question the sense of the very concept of free charged qubit. In this letter,
using the "dressing" formalism, we build physical charged qubits from dressed
fields which have the correct asymptotic behavior, are gauge invariant, their
propagators have a particle pole structure and are free from infrared
divergences. Finally, we discuss the impact of the soft corrections on the
entanglement measures.Comment: 4 pages, 2 figures, RevTeX. Version 2: Some references update
- …