30,182 research outputs found
Cusp-scaling behavior in fractal dimension of chaotic scattering
A topological bifurcation in chaotic scattering is characterized by a sudden
change in the topology of the infinite set of unstable periodic orbits embedded
in the underlying chaotic invariant set. We uncover a scaling law for the
fractal dimension of the chaotic set for such a bifurcation. Our analysis and
numerical computations in both two- and three-degrees-of-freedom systems
suggest a striking feature associated with these subtle bifurcations: the
dimension typically exhibits a sharp, cusplike local minimum at the
bifurcation.Comment: 4 pages, 4 figures, Revte
Two-dimensional viscous flow computations of hypersonic scramjet nozzle flowfields at design and off-design conditions
The PARC2D code has been selected to analyze the flowfields of a representative hypersonic scramjet nozzle over a range of flight conditions from Mach 3 to 20. The flowfields, wall pressures, wall skin friction values, heat transfer values and overall nozzle performance are presented
Sheath ionization model of beam emissions from large spacecraft
An analytical model of the charging of a spacecraft emitting electron and ion beams has been applied to the case of large spacecraft. In this model, ionization occurs in the sheath due to the return current. Charge neutralization of spherical space charge flow is examined by solving analytical equations numerically. Parametric studies of potential large spacecraft are performed. As in the case of small spacecraft, the ions created in the sheath by the returning current play a large role in determining spacecraft potential
The construction and evaluation of a word pronunciation test for grades four, five, and six
Thesis (Ed.M.)--Boston Universit
Innermost Stable Circular Orbit of a Spinning Particle in Kerr Spacetime
We study stability of a circular orbit of a spinning test particle in a Kerr
spacetime. We find that some of the circular orbits become unstable in the
direction perpendicular to the equatorial plane, although the orbits are still
stable in the radial direction. Then for the large spin case ($S < \sim O(1)),
the innermost stable circular orbit (ISCO) appears before the minimum of the
effective potential in the equatorial plane disappears. This changes the radius
of ISCO and then the frequency of the last circular orbit.Comment: 25 pages including 8 figure
Phase diagram of aggregation of oppositely charged colloids in salty water
Aggregation of two oppositely charged colloids in salty water is studied. We
focus on the role of Coulomb interaction in strongly asymmetric systems in
which the charge and size of one colloid is much larger than the other one. In
the solution, each large colloid (macroion) attracts certain number of
oppositely charged small colloids (-ion) to form a complex. If the
concentration ratio of the two colloids is such that complexes are not strongly
charged, they condense in a macroscopic aggregate. As a result, the phase
diagram in a plane of concentrations of two colloids consists of an aggregation
domain sandwiched between two domains of stable solutions of complexes. The
aggregation domain has a central part of total aggregation and two wings
corresponding to partial aggregation. A quantitative theory of the phase
diagram in the presence of monovalent salt is developed. It is shown that as
the Debye-H\"{u}ckel screening radius decreases, the aggregation domain
grows, but the relative size of the partial aggregation domains becomes much
smaller. As an important application of the theory, we consider solutions of
long double-helix DNA with strongly charged positive spheres (artificial
chromatin). We also consider implications of our theory for in vitro
experiments with the natural chromatin. Finally, the effect of different shapes
of macroions on the phase diagram is discussed.Comment: 10 pages, 9 figures. The text is rewritten, but results are not
change
Instantons and the singlet-coupling in the chiral quark model
Chiral quark model with a broken-U(3) flavor symmetry can be interpreted as
the effective theory of the instanton-dominated non-perturbative QCD. This
naturally suggests the possibility of a negative singlet/octet coupling ratio,
which has been found, in a previous publication, to be compatible with the
phenomenological description of the nucleon spin-flavor structure.Comment: 9 page
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