34,334 research outputs found

### Are All Particles Identical?

We consider the possibility that all particles in the world are fundamentally
identical, i.e., belong to the same species. Different masses, charges, spins,
flavors, or colors then merely correspond to different quantum states of the
same particle, just as spin-up and spin-down do. The implications of this
viewpoint can be best appreciated within Bohmian mechanics, a precise
formulation of quantum mechanics with particle trajectories. The implementation
of this viewpoint in such a theory leads to trajectories different from those
of the usual formulation, and thus to a version of Bohmian mechanics that is
inequivalent to, though arguably empirically indistinguishable from, the usual
one. The mathematical core of this viewpoint is however rather independent of
the detailed dynamical scheme Bohmian mechanics provides, and it amounts to the
assertion that the configuration space for N particles, even N
``distinguishable particles,'' is the set of all N-point subsets of physical
3-space.Comment: 12 pages LaTeX, no figure

### Seven Steps Towards the Classical World

Classical physics is about real objects, like apples falling from trees,
whose motion is governed by Newtonian laws. In standard Quantum Mechanics only
the wave function or the results of measurements exist, and to answer the
question of how the classical world can be part of the quantum world is a
rather formidable task. However, this is not the case for Bohmian mechanics,
which, like classical mechanics, is a theory about real objects. In Bohmian
terms, the problem of the classical limit becomes very simple: when do the
Bohmian trajectories look Newtonian?Comment: 16 pages, LaTeX, uses latexsy

### Opposite Arrows of Time Can Reconcile Relativity and Nonlocality

We present a quantum model for the motion of N point particles, implying
nonlocal (i.e., superluminal) influences of external fields on the
trajectories, that is nonetheless fully relativistic. In contrast to other
models that have been proposed, this one involves no additional space-time
structure as would be provided by a (possibly dynamical) foliation of
space-time. This is achieved through the interplay of opposite microcausal and
macrocausal (i.e., thermodynamic) arrows of time.Comment: 12 pages, 4 figures; v5: section headlines adde

### Trajectories and Particle Creation and Annihilation in Quantum Field Theory

We develop a theory based on Bohmian mechanics in which particle world lines
can begin and end. Such a theory provides a realist description of creation and
annihilation events and thus a further step towards a "beable-based"
formulation of quantum field theory, as opposed to the usual "observable-based"
formulation which is plagued by the conceptual difficulties--like the
measurement problem--of quantum mechanics.Comment: 11 pages LaTeX, no figures; v2: references added and update

### Thermodynamic entropy production fluctuation in a two dimensional shear flow model

We investigate fluctuations in the momentum flux across a surface
perpendicular to the velocity gradient in a stationary shear flow maintained by
either thermostated deterministic or by stochastic boundary conditions. In the
deterministic system the Gallavotti-Cohen (GC)relation for the probability of
large deviations, which holds for the phase space volume contraction giving the
Gibbs ensemble entropy production, never seems to hold for the flux which gives
the hydrodynamic entropy production. In the stochastic case the GC relation is
found to hold for the total flux, as predicted by extensions of the GC theorem
but not for the flux across part of the surface. The latter appear to satisfy a
modified GC relation. Similar results are obtained for the heat flux in a
steady state produced by stochastic boundaries at different temperatures.Comment: 9 postscript figure

### Investigation of land use of northern megalopolis using ERTS-1 imagery

Primary objective was to produce a color-coded land use map and digital data base for the northern third of Megalopolis. Secondary objective was to investigate possible applications of ERTS products to land use planning. Many of the materials in this report already have received national, dissemination as a result of unexpected interest in land use surveys from ERTS. Of special historical interest is the first comprehensive urban-type land use map from space imagery, which covered the entire state of Rhode Island and was made from a single image taken on 28 July 1972

### Development of optimum clamp combinations for strap-down inertial measuring units with field replaceable sensors

Optimum clamp combinations for strap down inertial measuring units with field replaceable sensor

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