7,059 research outputs found
Beach face dynamics as affected by ground water table elevations
This report presents the results of laboratory studies which were carried out in the Coastal
and Oceanographical Engineering Laboratory to investigate the effects of ground water table
elevations on the beach profile changes over the swash zone. The experiment was conducted at
three different water table levels while the other experimental conditions were fixed to constant
values with regular waves. The water table levels included (1) normal water table level which
is the same as mean sea level, (2) a higher level and (3) a lower level than the mean sea
level. Special attention was given to the higher water level to investigate whether this level
enhances erosion of the beach face and also to methods of interpreting the experimental data.
The experiment described herein was carried out with a fairly fine sand and has demonstrated
the significance of beach water table on profile dynamics. The increased water table level
caused distinct effects in three definite zones. First, erosion occurred at the base of the beach
face and the sand eroded was carried up and deposited on the upper portion of the beach
face. Secondly, the bar trough deepened considerably and rapidly and the eroded sand was
deposited immediately landward. This depositional area changed from mildly erosional to
strongly depositional. Third, the area seaward of the bar eroded with a substantial deepening.
The lowered water table appeared to result in a much more stable beach and the resulting
effects were much less. The only noticeable trend was a limited deposition in the scour area at
the base of the beach face. (Document has 37 pages.
Noncommutative open strings from Dirac quantization
We study Dirac commutators of canonical variables on D-branes with a constant
Neveu-Schwarz 2-form field by using the Dirac constraint quantization method,
and point out some subtleties appearing in previous works in analyzing
constraint structure of the brane system. Overcoming some ad hoc procedures, we
obtain desirable noncommutative coordinates exactly compatible with the result
of the conformal field theory in recent literatures. Furthermore, we find
interesting commutator relations of other canonical variables.Comment: 13 pages, revtex, Expressions are change
Conformally-coupled dark spinor and FRW universe
We study conformal coupling of dark spinor fields to gravity and calculate
the energy density and the pressure of the spinor in FRW spacetime. We consider
the renormalizable potential of the spinor field. In the cases where the field
is proportional to some power of the cosmic scale factor , we determine
the Hubble parameter as a function of the scale factor and find analytic
solutions for when the spinor field matter dilutes as the universe
expands. We discuss the possibility that both matter- and dark energy-dominated
eras of our universe can be described by the dark spinor.Comment: 4 pages, Revised argument in section III, results unchanged. To be
published in PR
Isospin particle on with arbitrary number of supersymmetries
We study the supersymmetric quantum mechanics of an isospin particle in the
background of spherically symmetric Yang-Mills gauge field. We show that on
the number of supersymmetries can be made arbitrarily large for a
specific choice of the spherically symmetric SU(2) gauge field. However, the
symmetry algebra containing the supercharges becomes nonlinear if the number of
fermions is greater than two. We present the exact energy spectra and
eigenfunctions, which can be written as the product of monopole harmonics and a
certain isospin state. We also find that the supersymmetry is spontaneously
broken if the number of supersymmetries is even.Comment: 6 page
Correlation of the transient energy margin to Out-of-step impedance relay operation
This research has developed a procedure in which the transient energy margin, for a multimachine power system obtained by the transient energy function method, is related to the apparent impedance of a line protected by the out-of-step relay;In this procedure, only the multimachine system parameters are used, and the conventional intermediate step of forming a two-machine equivalent is eliminated;Two types of energy-based criteria are derived to relate the apparent impedance to the transient energy margin obtained: (i) with the original multimachine system, and (ii) with the inertial equivalents of two groups of machines separated by the line protected by the out-of-step relay;An approximation of the post-disturbance trajectory is developed for the rotor angle positions between the instance of disturbance removal and the controlling u.e.p. Two such approximations are investigated: (i) a linear trajectory, and (ii) the Fourier series approximation. The energy-based criteria are then applied along this approximated trajectory. A technique for generating the swing impedance locus is also presented;The method is tested for a loss of generation distrubance on a 23-generator, 211-bus equivalent of the Florida Power & Light Company network. The results obtained are compared with time simulation results
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