36 research outputs found
On the distribution of brightness on the disk of Mars and its stellar magnitude
Brightness distribution on disk of Mars and its stellar magnitud
On a Zero Curvature Representation for Bosonic Strings and -Branes
It is shown that a zero curvature representation for -- dimensional --
brane equations of motion originates naturally in the geometric (Lund- Regge-
Omnes) approach. To study the possibility to use this zero curvature
representation for investigation of nonlinear equations of -- branes, the
simplest case of -- dimensional string () is considered. The connection
is found between the gauge (world--sheet Lorentz) invariance of the
string theory with a nontrivial dependence on a spectral parameter of the Lax
matrices associated with the nonlinear equations describing the embedding of a
string world sheet into flat -- dimensional space -- time. Namely, the
spectral parameter can be identified with a parameter of constant
gauge transformations, after the deformation of the Lax matrices has been
performed.Comment: 14 pages. LATEX. Revised version. Submitted to Phys. Lett. B. The
arrangement of the material is changed. Some additional references are
include
Generalized action principle and extrinsic geometry for N=1 superparticle
It is proposed the generalized action functional for N=1 superparticle in
D=3,4,6 and 10 space-time dimensions. The superfield geometric approach
equations describing superparticle motion in terms of extrinsic geometry of the
worldline superspace are obtained on the base of the generalized action. The
off-shell superdiffeomorphism invariance (in the rheonomic sense) of the
superparticle generalized action is proved. It was demonstrated that the half
of the fermionic and one bosonic (super)fields disappear from the generalized
action in the analytical basis. Superparticle interaction with Abelian gauge
theory is considered in the framework of this formulation. The geometric
approach equations describing superparticle motion in Abelian background are
obtained.Comment: 31 pages. Late
SUPERSTRINGS AND SUPERMEMBRANES IN THE DOUBLY SUPERSYMMETRIC GEOMETRICAL APPROACH
We perform a generalization of the geometrical approach to describing
extended objects for studying the doubly supersymmetric twistor--like
formulation of super--p--branes. Some basic features of embedding world
supersurface into target superspace specified by a geometrodynamical condition
are considered. It is shown that the main attributes of the geometrical
approach, such as the second fundamental form and extrinsic torsion of the
embedded surface, and the Codazzi, Gauss and Ricci equations, have their doubly
supersymmetric counterparts. At the same time the embedding of supersurface
into target superspace has its particular features. For instance, the embedding
may cause more rigid restrictions on the geometrical properties of the
supersurface. This is demonstrated with the examples of an N=1 twistor--like
supermembrane in D=11 and type II superstrings in D=10, where the
geometrodynamical condition causes the embedded supersurface to be minimal and
puts the theories on the mass shell.Comment: 45 pages, LaTeX, 3 appendicie
Near real-time input to a propagation model for nowcasting of HF communications with aircraft on polar routes
There is a need for improved techniques for nowcasting and forecasting (over several hours) HF propagation at northerly latitudes to support airlines operating over the increasingly popular trans-polar routes. In this paper the assimilation of real-time measurements into a propagation model developed by the authors is described, including ionosonde measurements and Total Electron Content (TEC) measurements to define the main parameters of the ionosphere. The effects of D-region absorption in the polar cap and auroral regions are integrated with the model through satellite measurements of the flux of energetic solar protons (>1 MeV) and the X-ray flux in the 0.1-0.8 nm band, and ground-based magnetometer measurements which form the Kp and Dst indices of geomagnetic activity. The model incorporates various features (e.g. convecting patches of enhanced plasma density) of the polar ionosphere that are, in particular, responsible for off-great circle propagation and lead to propagation at times and frequencies not expected from on-great circle propagation alone. The model development is supported by the collection of HF propagation measurements over several paths within the polar cap, crossing the auroral oval, and along the mid-latitude trough