17,882 research outputs found
Radiation from a Superluminal Source
The sweep speed of an electron beam across the face of an oscilloscope can
exceed the velocity of light, although of course the velocity of the electrons
does not. Associated with this possibility there should be a kind of Cherenkov
radiation, as if the oscilloscope trace were due to a charge moving with
superluminal velocity
Circular Orbits Inside the Sphere of Death
A wheel or sphere rolling without slipping on the inside of a sphere in a
uniform gravitational field can have stable circular orbits that lie wholly
above the "equator", while a particle sliding freely cannot.Comment: Figures revised slightly since publicatio
Hidden Momentum in a Coaxial Cable
As an illustration of the concept of "hidden" mechanical momentum, we
consider a coaxial cable one end of which is connected to a battery and the
other to a load resistor. The nonzero electromagnetic momentum of this
configuration is balanced by the slight difference in the mechanical momenta of
the conduction electrons in the inner and outer conductors.Comment: 4 pages, no figure
Can a "Hidden Variable'' Quantum Theory Evade the "No-Cloning" Theorem?
If YES, then we can look forward to physical realization of superluminal
communication, as the original considerations of the ``no-cloning'' theorem
were motivated in part as an explanation of why certain schemes for
superluminal signaling cannot work.
If NO, then it would seem that some aspects of the ``hidden'' variables must
be ``intrinsically hidden'', i.e., ``unknowable'', such that
``hidden-variable'' theories belong more to the ``idealist'' than to the
``realist'' school of thought.
I pose this question without proposing a definite answer. I am unaware of any
commentary on this topic during these 23 years since the formulation of the
``no-cloning'' theorem, but I would be pleased to be enlightened by more
knowledgeable readers
An Electrostatic Wave
In general, Maxwell's equations require that a wave of electric field be
accompanied by a wave of magnetic field, and vice versa. However, it is
possible to have a plane wave in a dielectric medium with electric field E
parallel to the wave vector k (a longitudinal wave) with no time-dependent
magnetic field provided the electric displacement D is zero. We give an example
from plasma physics: the so-called Bernstein wave.Comment: 8 pages, no figure
A Strategy for Accelerator-Based Neutrino Physics in the USA
We outline a strategy for next-generation neutrino physics experiments based
on beams from accelerators in North America. This strategy is based on the
mounting evidence in favor of the large mixing angle solution to solar neutrino
problem, which implies that in addition to measurement of sin^2 2theta_13 and
of the sign of Delta m^2_23, measurement of CP violation in the neutrino sector
is a realizable goal if sin^2 2theta_13 is not too small.
The strategy is to begin with a new detector, 20-30 kton of liquid argon,
designed to make best use of the NUMI beam currently under construction at
FNAL. Then, after new measurements have made the optimal path clearer, we
anticipate choosing among options for neutrino "superbeam" upgrades at BNL
and/or FNAL as well as for second new detector of 100-200 kton.Comment: v2 has an updated Fig. 3, thanks to Debbie Harris. Thanks also to Bob
Shroc
Gaussian Laser Beams via Oblate Spheroidal Waves
We deduce a set of circularly polarized Gaussian laser beam modes via a
separation-of-variables solution to the Helmholtz wave equation in oblate
spheriodal coordinates. On transforming to cylindrical coordinates these become
the well-known Gaussian-Laguerre modes.Comment: 15 pages, 4 figure
Radial Viscous Flow between Two Parallel Annular Plates
An analytic solution to the linearized Navier-Stokes equation is given that
describes the radial flow of an incompressible, viscous fluid between two
parallel, concentric annular plates
A Conducting Checkerboard
The problem of a conducting checkerboard has recently been solved via an
elliptic function whose argument is another elliptic function. The behavior of
the fields and currents near a vertex of the checkerboard pattern can be
discussed by more elementary methods.Comment: 5 pages, 3 figure
An Off-Axis Neutrino Beam
In this pedagogic note, set as problem for the reader, it is shown how the
existence of a maximum energy of a neutrino that appears at a given angle to
the direction of its parent pion leads to a useful enhancment of neutrino flux
in an off-axis beam
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