4,982 research outputs found
Quantum Backflow States from Eigenstates of the Regularized Current Operator
We present an exhaustive class of states with quantum backflow -- the
phenomenon in which a state consisting entirely of positive momenta may have
negative current and the probability flows in the opposite direction to the
momentum. They are characterized by a general function of momenta subject to
very weak conditions. Such a family of states is of interest in the light of a
recent experimental proposal to measure backflow. We find one particularly
simple state which has surprisingly large backflow -- about 41 percent of the
lower bound on flux derived by Bracken and Melloy. We study the eigenstates of
a regularized current operator and we show how some of these states, in a
certain limit, lead to our class of backflow states. This limit also clarifies
the correspondence between the spectrum of the regularized current operator,
which has just two non-zero eigenvalues in our chosen regularization, and the
usual current operator.Comment: 16 pages, 2 figure
Decoherence of Histories and Hydrodynamic Equations for a Linear Oscillator Chain
We investigate the decoherence of histories of local densities for linear
oscillators models. It is shown that histories of local number, momentum and
energy density are approximately decoherent, when coarse-grained over
sufficiently large volumes. Decoherence arises directly from the proximity of
these variables to exactly conserved quantities (which are exactly decoherent),
and not from environmentally-induced decoherence. We discuss the approach to
local equilibrium and the subsequent emergence of hydrodynamic equations for
the local densities.Comment: 37 pages, RevTe
Wavefunctions for Highly Anisotropic Homogeneous Cosmologies
The canonical quantization of homogeneous cosmologies is considered in the
high anisotropic limit. Exact wavefunctions are found in this limit when the
momentum constraints are reduced at the classical level. Lorentzian solutions
that represent tunnelling from classically forbidden regimes are identified.
Solutions to the modified Wheeler-DeWitt equation are also found for the vacuum
Bianchi IX model when a quantum reduction of the momentum constraints is
considered.Comment: 11 pages, late
Oxygen-derived species: their relation to human disease and environmental stress.
Free radicals and other reactive oxygen species (ROS) are constantly formed in the human body, often for useful metabolic purposes. Antioxidant defenses protect against them, but these defenses are not completely adequate, and systems that repair damage by ROS are also necessary. Mild oxidative stress often induces antioxidant defense enzymes, but severe stress can cause oxidative damage to lipids, proteins, and DNA within cells, leading to such events as DNA strand breakage and disruption of calcium ion metabolism. Oxidative stress can result from exposure to toxic agents, and by the process of tissue injury itself. Ozone, oxides of nitrogen, and cigarette smoke can cause oxidative damage; but the molecular targets that they damage may not be the same
Sum-over-histories origin of the composition laws of relativistic quantum mechanics and quantum cosmology
The scope of the paper has been broadened to include a more complete
discussion of the following topics: The derivation of composition laws in
quantum cosmology. The connection between the existence of a composition law in
the sum over histories approach to relativistic quantum mechanics and quantum
cosmology, and the existence of a canonical formulation.Comment: 36 page
The exact cosmological solution to the dynamical equations for the Bianchi IX model
Quantum geometrodynamics in extended phase space describes phenomenologically
the integrated system ``a physical object + observation means (a gravitational
vacuum condensate)''. The central place in this version of QGD belongs to the
Schrodinger equation for a wave function of the Universe. An exact solution to
the ``conditionally-classical'' set of equations in extended phase space for
the Bianchi-IX model and the appropriate solution to the Schrodinger equation
are considered. The physical adequacy of the obtained solutions to existing
concepts about possible cosmological scenarios is demonstrated. The
gravitational vacuum condensate is shown to be a cosmological evolution factor.Comment: LaTeX, 14 pages, to be published in Int. J. Mod. Phys.
Approximate Decoherence of Histories and 't Hooft's Deterministic Quantum Theory
This paper explores the possibility that an exactly decoherent set of
histories may be constructed from an approximately decoherent set by small
distortions of the operators characterizing the histories. In particular, for
the case of histories of positions and momenta, this is achieved by doubling
the set of operators and then finding, amongst this enlarged set, new position
and momentum operators which commute, so decohere exactly, and which are
``close'' to the original operators. The enlarged, exactly decoherent, theory
has the same classical dynamics as the original one, and coincides with the
so-called deterministic quantum theories of the type recently studied by 't
Hooft. These results suggest that the comparison of standard and deterministic
quantum theories may provide an alternative method of characterizing emergent
classicality. A side-product is the surprising result that histories of momenta
in the quantum Brownian motion model (for the free particle in the
high-temperature limit) are exactly decoherent.Comment: 41 pages, plain Te
Social media influence on viewer engagement
Society is being reshaped through Social Media. The case of Social Media integration into the London 2012 Olympics mainstream media coverage is used to demonstrate this. Social Media has modified television viewing from a passive to an active activity. It has also allowed opinions to be shared more quickly and broadly. Analysis of practical examples through the theoretical lens of sociomateriality demonstrates that greater use of the components in the \u27Theoretical Framework of Member Needs\u27 reflect the presence of viewers who are more active. This paper discusses the inability to separate the use of technology from its social context, the power of Social Media and the impact of this on business use of Social Media. It also demonstrates a novel method for evaluating the benefits of emerging technologies in society
Complex lapse, complex action and path integrals
Imaginary time is often used in quantum tunnelling calculations. This article
advocates a conceptually sounder alternative: complex lapse. In the ``3+1''
action for the Einstein gravitational field minimally coupled to a Klein-Gordon
field, allowing the lapse function to be complex yields a complex action which
generates both the usual Lorentzian theory and its Riemannian analogue, and in
particular allows a change of signature between the two. The action and
variational equations are manifestly well defined in the Hamiltonian
representation, with the momentum fields consequently being complex. The
complex action interpolates between the Lorentzian and Riemannian actions as
they appear formally in the respective path integrals. Thus the complex-lapse
theory provides a unified basis for a path-integral quantum theory of gravity
involving both Lorentzian and Riemannian aspects. A major motivation is the
quantum-tunnelling scenario for the origin of the universe. Taken as an
explanation for the observed quantum tunnelling of particles, the complex-lapse
theory determines that the argument of the lapse for the universe now is
extremely small but negative.Comment: 12 pages, Te
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