1,787 research outputs found
Entanglement of a Single Spin-1 Object: An Example of Ubiquitous Entanglement
Using a single spin-1 object as an example, we discuss a recent approach to
quantum entanglement. The key idea of the approach consists in presetting of
basic observables in the very definition of quantum system. Specification of
basic observables defines the dynamic symmetry of the system. Entangled states
of the system are then interpreted as states with maximal amount of uncertainty
of all basic observables. The approach gives purely physical picture of
entanglement. In particular, it separates principle physical properties of
entanglement from inessential. Within the model example under consideration, we
show relativity of entanglement with respect to dynamic symmetry and argue
existence of single-particle entanglement. A number of physical examples are
considered.Comment: 12 pages, 2 figure : title has been changed, paper is re-organized,
new section "Violation of Bell-type condition by single spin-1" is adde
A real Lorentz-FitzGerald contraction
Many condensed matter systems are such that their collective excitations at
low energies can be described by fields satisfying equations of motion formally
indistinguishable from those of relativistic field theory. The finite speed of
propagation of the disturbances in the effective fields (in the simplest
models, the speed of sound) plays here the role of the speed of light in
fundamental physics. However, these apparently relativistic fields are immersed
in an external Newtonian world (the condensed matter system itself and the
laboratory can be considered Newtonian, since all the velocities involved are
much smaller than the velocity of light) which provides a privileged coordinate
system and therefore seems to destroy the possibility of having a perfectly
defined relativistic emergent world. In this essay we ask ourselves the
following question: In a homogeneous condensed matter medium, is there a way
for internal observers, dealing exclusively with the low-energy collective
phenomena, to detect their state of uniform motion with respect to the medium?
By proposing a thought experiment based on the construction of a
Michelson-Morley interferometer made of quasi-particles, we show that a real
Lorentz-FitzGerald contraction takes place, so that internal observers are
unable to find out anything about their `absolute ' state of motion. Therefore,
we also show that an effective but perfectly defined relativistic world can
emerge in a fishbowl world situated inside a Newtonian (laboratory) system.
This leads us to reflect on the various levels of description in physics, in
particular regarding the quest towards a theory of quantum gravity.Comment: 6 pages, no figures. Minor changes reflect published versio
Nonlinear analysis of a simple model of temperature evolution in a satellite
We analyse a simple model of the heat transfer to and from a small satellite
orbiting round a solar system planet. Our approach considers the satellite
isothermal, with external heat input from the environment and from internal
energy dissipation, and output to the environment as black-body radiation. The
resulting nonlinear ordinary differential equation for the satellite's
temperature is analysed by qualitative, perturbation and numerical methods,
which show that the temperature approaches a periodic pattern (attracting limit
cycle). This approach can occur in two ways, according to the values of the
parameters: (i) a slow decay towards the limit cycle over a time longer than
the period, or (ii) a fast decay towards the limit cycle over a time shorter
than the period. In the first case, an exactly soluble average equation is
valid. We discuss the consequences of our model for the thermal stability of
satellites.Comment: 13 pages, 4 figures (5 EPS files
Vibrational signature of broken chemical order in a GeS2 glass: a molecular dynamics simulation
Using density functional molecular dynamics simulations, we analyze the
broken chemical order in a GeS glass and its impact on the dynamical
properties of the glass through the in-depth study of the vibrational
eigenvectors. We find homopolar bonds and the frequencies of the corresponding
modes are in agreement with experimental data. Localized S-S modes and 3-fold
coordinated sulfur atoms are found to be at the origin of specific Raman peaks
whose origin was not previously clear. Through the ring size statistics we
find, during the glass formation, a conversion of 3-membered rings into larger
units but also into 2-membered rings whose vibrational signature is in
agreement with experiments.Comment: 11 pages, 8 figures; to appear in Phys. Rev.
Hidden variables with nonlocal time
To relax the apparent tension between nonlocal hidden variables and
relativity, we propose that the observable proper time is not the same quantity
as the usual proper-time parameter appearing in local relativistic equations.
Instead, the two proper times are related by a nonlocal rescaling parameter
proportional to |psi|^2, so that they coincide in the classical limit. In this
way particle trajectories may obey local relativistic equations of motion in a
manner consistent with the appearance of nonlocal quantum correlations. To
illustrate the main idea, we first present two simple toy models of local
particle trajectories with nonlocal time, which reproduce some nonlocal quantum
phenomena. After that, we present a realistic theory with a capacity to
reproduce all predictions of quantum theory.Comment: 16 pages, accepted for publication in Found. Phys., misprints
corrected, references update
Long-range forecasts of UK winter hydrology
Seasonal river flow forecasts are beneficial for planning agricultural activities, river navigation, and for management of reservoirs for public water supply and hydropower generation. In the United Kingdom (UK), skilful seasonal river flow predictions have previously been limited to catchments in lowland (southern and eastern) regions. Here we show that skilful long-range forecasts of winter flows can now be achieved across the whole of the UK. This is due to a remarkable geographical complementarity between the regional geological and meteorological sources of predictability for river flows. Forecast skill derives from the hydrogeological memory of antecedent conditions in southern and eastern parts of the UK and from meteorological predictability in northern and western areas. Specifically, it is the predictions of the atmospheric circulation over the North Atlantic that provides the skill at the seasonal timescale. In addition, significant levels of skill in predicting the frequency of winter high flow events is demonstrated, which has the potential to allow flood adaptation measures to be put in place
Structural changes in borosilicate glasses as a function of Fe2O3 content: A multi-technique approach
Three series of borosilicate glasses were prepared, ranging from simple ternary sodium borosilicate glasses (SCFe series), to complex borosilicate glasses (CCFe Series), to high-level radioactive waste analogue glasses (HAFe series). 57Fe Mössbauer and Fe K-edge XANES spectroscopies showed that the iron exists exclusively as Fe3+ in predominantly distorted tetrahedral structures ([4]Fe3+), with evidence for lower abundances of higher-coordinated [5 or 6]Fe3+. Raman, B K-edge XANES, and XPS spectroscopies qualitatively demonstrated that Fe3+ preferentially integrates into the borosilicate network through the silicate sub-network in the simple glasses, whereas in the complex glasses it preferentially integrates through the borate sub-network. The [4]B3+ fraction for the SCFe and CCFe glasses showed minimal changes as a function of Fe content, indicating that Fe concentration has no effect on boron coordination and is- therefore unlikely to be competing with [4]B3+ groups for charge compensation, qualitatively supporting the presence of competing tetrahedral avoidance hierarchies
Parity proofs of the Kochen-Specker theorem based on the 24 rays of Peres
A diagrammatic representation is given of the 24 rays of Peres that makes it
easy to pick out all the 512 parity proofs of the Kochen-Specker theorem
contained in them. The origin of this representation in the four-dimensional
geometry of the rays is pointed out.Comment: 14 pages, 6 figures and 3 tables. Three references have been added.
Minor typos have been correcte
Colliding Plane Waves in String Theory
We construct colliding plane wave solutions in higher dimensional gravity
theory with dilaton and higher form flux, which appears naturally in the low
energy theory of string theory. Especially, the role of the junction condition
in constructing the solutions is emphasized. Our results not only include the
previously known CPW solutions, but also provide a wide class of new solutions
that is not known in the literature before. We find that late time curvature
singularity is always developed for the solutions we obtained in this paper.
This supports the generalized version of Tipler's theorem in higher dimensional
supergravity.Comment: latex, 25 pages, 1 figur
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