23,855 research outputs found
On a Classical, Geometric Origin of Magnetic Moments, Spin-Angular Momentum and the Dirac Gyromagnetic Ratio
By treating the real Maxwell Field and real linearized Einstein equations as
being imbedded in complex Minkowski space, one can interpret magnetic moments
and spin-angular momentum as arising from a charge and mass monopole source
moving along a complex world line in the complex Minkowski space. In the
circumstances where the complex center of mass world-line coincides with the
complex center of charge world-line, the gyromagnetic ratio is that of the
Dirac electron.Comment: 17 page
The Universal Cut Function and Type II Metrics
In analogy with classical electromagnetic theory, where one determines the
total charge and both electric and magnetic multipole moments of a source from
certain surface integrals of the asymptotic (or far) fields, it has been known
for many years - from the work of Hermann Bondi - that energy and momentum of
gravitational sources could be determined by similar integrals of the
asymptotic Weyl tensor. Recently we observed that there were certain overlooked
structures, {defined at future null infinity,} that allowed one to determine
(or define) further properties of both electromagnetic and gravitating sources.
These structures, families of {complex} `slices' or `cuts' of Penrose's null
infinity, are referred to as Universal Cut Functions, (UCF). In particular, one
can define from these structures a (complex) center of mass (and center of
charge) and its equations of motion - with rather surprising consequences. It
appears as if these asymptotic structures contain in their imaginary part, a
well defined total spin-angular momentum of the source. We apply these ideas to
the type II algebraically special metrics, both twisting and twist-free.Comment: 32 page
An explanation of the Newman-Janis Algorithm
After the original discovery of the Kerr metric, Newman and Janis showed that
this solution could be ``derived'' by making an elementary complex
transformation to the Schwarzschild solution. The same method was then used to
obtain a new stationary axisymmetric solution to Einstein's field equations now
known as the Kerr-newman metric, representing a rotating massive charged black
hole. However no clear reason has ever been given as to why the Newman-Janis
algorithm works, many physicist considering it to be an ad hoc procedure or
``fluke'' and not worthy of further investigation. Contrary to this belief this
paper shows why the Newman-Janis algorithm is successful in obtaining the
Kerr-Newman metric by removing some of the ambiguities present in the original
derivation. Finally we show that the only perfect fluid generated by the
Newman-Janis algorithm is the (vacuum) Kerr metric and that the only Petrov
typed D solution to the Einstein-Maxwell equations is the Kerr-Newman metric.Comment: 14 pages, no figures, submitted to Class. Quantum Gra
Generalized Gross--Perry--Sorkin--Like Solitons
In this paper, we present a new solution for the effective theory of
Maxwell--Einstein--Dilaton, Low energy string and Kaluza--Klein theories, which
contains among other solutions the well known Kaluza--Klein monopole solution
of Gross--Perry--Sorkin as special case. We show also the magnetic and electric
dipole solutions contained in the general one.Comment: 10 latex pages, no figures. To appear in Class. Quant. Gravity
A head-up display for mid-air drone recovery
During mid-air retrieval of parachute packages, the absence of a natural horizon creates serious difficulties for the pilot of the recovery helicopter. A head-up display (HUD) was tested in an attempt to solve this problem. Both a roll-stabilized HUD and a no-roll (pitch only) HUD were tested. The results show that fewer missed passes occurred with the roll-stabilized HUD when the horizon was obscured. The pilots also reported that the workload was greatly reduced. Roll-stabilization was required to prevent vertigo when flying in the absence of a natural horizon. Any HUD intended for mid-air retrieval should display pitch, roll, sideslip, airspeed, and vertical velocity
Radiation Reaction fields for an accelerated dipole for scalar and electromagnetic radiation
The radiation reaction fields are calculated for an accelerated changing
dipole in scalar and electromagnetic radiation fields. The acceleration
reaction is shown to alter the damping of a time varying dipole in the EM case,
but not the scalar case. In the EM case, the dipole radiation reaction field
can exert a force on an accelerated monopole charge associated with the
accelerated dipole. The radiation reaction of an accelerated charge does not
exert a torque on an accelerated magnetic dipole, but an accelerated dipole
does exert a force on the charge. The technique used is that originally
developed by Penrose for non-singular fields and extended by the author for an
accelerated monopole charge.Comment: 11 page
Spinning BTZ Black Hole versus Kerr Black Hole : A Closer Look
By applying Newman's algorithm, the AdS_3 rotating black hole solution is
``derived'' from the nonrotating black hole solution of Banados, Teitelboim,
and Zanelli (BTZ). The rotating BTZ solution derived in this fashion is given
in ``Boyer-Lindquist-type'' coordinates whereas the form of the solution
originally given by BTZ is given in a kind of an ``unfamiliar'' coordinates
which are related to each other by a transformation of time coordinate alone.
The relative physical meaning between these two time coordinates is carefully
studied. Since the Kerr-type and Boyer-Lindquist-type coordinates for rotating
BTZ solution are newly found via Newman's algorithm, next, the transformation
to Kerr-Schild-type coordinates is looked for. Indeed, such transformation is
found to exist. And in this Kerr-Schild-type coordinates, truely maximal
extension of its global structure by analytically continuing to ``antigravity
universe'' region is carried out.Comment: 17 pages, 1 figure, Revtex, Accepted for publication in Phys. Rev.
Random pinning limits the size of membrane adhesion domains
Theoretical models describing specific adhesion of membranes predict (for
certain parameters) a macroscopic phase separation of bonds into adhesion
domains. We show that this behavior is fundamentally altered if the membrane is
pinned randomly due to, e.g., proteins that anchor the membrane to the
cytoskeleton. Perturbations which locally restrict membrane height fluctuations
induce quenched disorder of the random-field type. This rigorously prevents the
formation of macroscopic adhesion domains following the Imry-Ma argument [Y.
Imry and S. K. Ma, Phys. Rev. Lett. 35, 1399 (1975)]. Our prediction of
random-field disorder follows from analytical calculations, and is strikingly
confirmed in large-scale Monte Carlo simulations. These simulations are based
on an efficient composite Monte Carlo move, whereby membrane height and bond
degrees of freedom are updated simultaneously in a single move. The application
of this move should prove rewarding for other systems also.Comment: revised and extended versio
Sign-time distribution for a random walker with a drifting boundary
We present a derivation of the exact sign-time distribution for a random
walker in the presence of a boundary moving with constant velocity.Comment: 5 page
Boundary Conditions for the Einstein Evolution System
New boundary conditions are constructed and tested numerically for a general
first-order form of the Einstein evolution system. These conditions prevent
constraint violations from entering the computational domain through timelike
boundaries, allow the simulation of isolated systems by preventing physical
gravitational waves from entering the computational domain, and are designed to
be compatible with the fixed-gauge evolutions used here. These new boundary
conditions are shown to be effective in limiting the growth of constraints in
3D non-linear numerical evolutions of dynamical black-hole spacetimes.Comment: 21 pages, 12 figures, submitted to PR
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