7,190 research outputs found
Improved Two-Dimensional Kinetics (TDK) computer program
Fluid properties, the boundary layer module, and regenerative cooling are discussed. Chemistry, low density flow effects, test cases, input and output for TDK, and documentation are also discussed
Performance predictions for an SSME configuration with an enlarged throat
The Two Dimensional Kinetics (TDK) computer program that was recently developed for NASA was used to predict the performance of a Large Throat Configuration of the Space Shuttle Main Engine (SSME). Calculations indicate that the current design SSME contains a shock wave that is induced by the nozzle wall shape. In the Large Throat design an even stronger shock wave is predicted. Because of the presence of this shock wave, earlier performance predictions that have neglected shock wave effects have been questioned. The JANNAF thrust chamber performance prediction procedures given in a reference were applied. The analysis includes the effects of two dimensional reacting flow with a shock wave. The effects of the boundary layer with a regenatively cooled wall are also included. A Purdue computer program was used to compute axially symmetric supersonic nozzle flows with an induced shock, but is restricted to flows with a constant ratio of specific heats. Thus, the TDK program was also run with ths assumption and the results of the two programs were compared
Self-consistent theory of large amplitude collective motion: Applications to approximate quantization of non-separable systems and to nuclear physics
The goal of the present account is to review our efforts to obtain and apply
a ``collective'' Hamiltonian for a few, approximately decoupled, adiabatic
degrees of freedom, starting from a Hamiltonian system with more or many more
degrees of freedom. The approach is based on an analysis of the classical limit
of quantum-mechanical problems. Initially, we study the classical problem
within the framework of Hamiltonian dynamics and derive a fully self-consistent
theory of large amplitude collective motion with small velocities. We derive a
measure for the quality of decoupling of the collective degree of freedom. We
show for several simple examples, where the classical limit is obvious, that
when decoupling is good, a quantization of the collective Hamiltonian leads to
accurate descriptions of the low energy properties of the systems studied. In
nuclear physics problems we construct the classical Hamiltonian by means of
time-dependent mean-field theory, and we transcribe our formalism to this case.
We report studies of a model for monopole vibrations, of Si with a
realistic interaction, several qualitative models of heavier nuclei, and
preliminary results for a more realistic approach to heavy nuclei. Other topics
included are a nuclear Born-Oppenheimer approximation for an {\em ab initio}
quantum theory and a theory of the transfer of energy between collective and
non-collective degrees of freedom when the decoupling is not exact. The
explicit account is based on the work of the authors, but a thorough survey of
other work is included.Comment: 203 pages, many figure
Engineering and programming manual: Two-dimensional kinetic reference computer program (TDK)
The Two Dimensional Kinetics (TDK) computer program is a primary tool in applying the JANNAF liquid rocket thrust chamber performance prediction methodology. The development of a methodology that includes all aspects of rocket engine performance from analytical calculation to test measurements, that is physically accurate and consistent, and that serves as an industry and government reference is presented. Recent interest in rocket engines that operate at high expansion ratio, such as most Orbit Transfer Vehicle (OTV) engine designs, has required an extension of the analytical methods used by the TDK computer program. Thus, the version of TDK that is described in this manual is in many respects different from the 1973 version of the program. This new material reflects the new capabilities of the TDK computer program, the most important of which are described
Local harmonic approaches with approximate cranking operators
Methods of large amplitude collective motion in the adiabatic limit are examined with a special emphasis on conservation laws. We show that the restriction to point transformations, which is a usual assumption of the adiabatic time-dependent mean-field theory, needs to be lifted. In order to facilitate the application of large amplitude collective motion techniques, we examine the possibility of representing the RPA normal-mode coordinates by linear combinations of a limited number of one-body operators. We study the pairing-plus-quadrupole model of Baranger and Kumar as an example, and find that such representations exist in terms of operators that are state-dependent in a characteristic manner
Magnetic susceptibility of alkali-TCNQ salts and extended Hubbard models with bond order and charge density wave phases
The molar spin susceptibilities of Na-TCNQ, K-TCNQ and Rb-TCNQ(II)
are fit quantitatively to 450 K in terms of half-filled bands of three
one-dimensional Hubbard models with extended interactions using exact results
for finite systems. All three models have bond order wave (BOW) and charge
density wave (CDW) phases with boundary for nearest-neighbor
interaction and on-site repulsion . At high , all three salts have
regular stacks of anion radicals. The fits place Na and
K in the CDW phase and Rb(II) in the BOW phase with . The Na and
K salts have dimerized stacks at while Rb(II) has regular stacks at
100K. The analysis extends to dimerized stacks and to dimerization
fluctuations in Rb(II). The three models yield consistent values of ,
and transfer integrals for closely related stacks. Model
parameters based on are smaller than those from optical data that in
turn are considerably reduced by electronic polarization from quantum chemical
calculation of , and on adjacent ions. The
analysis shows that fully relaxed states have reduced model parameters compared
to optical or vibration spectra of dimerized or regular stacks.Comment: 9 pages and 5 figure
Synchronized and Desynchronized Phases of Exciton-Polariton Condensates in the Presence of Disorder
Condensation of exciton-polaritons in semiconductor microcavities takes place
despite in plane disorder. Below the critical density the inhomogeneity of the
potential seen by the polaritons strongly limits the spatial extension of the
ground state. Above the critical density, in presence of weak disorder, this
limitation is spontaneously overcome by the non linear interaction, resulting
in an extended synchronized phase. This mechanism is clearly evidenced by
spatial and spectral studies, coupled to interferometric measurements. In case
of strong disorder, several non phase-locked (independent) condensates can be
evidenced. The transition from synchronized phase to desynchronized phase is
addressed considering multiple realizations of the disorder.Comment: 11 pages, 4 figures,corrected typos, added figure
Relativistic Coulomb Sum Rules for
A Coulomb sum rule is derived for the response of nuclei to
scattering with large three-momentum transfers. Unlike the nonrelativistic
formulation, the relativistic Coulomb sum is restricted to spacelike
four-momenta for the most direct connection with experiments; an immediate
consequence is that excitations involving antinucleons, e.g., pair
production, are approximately eliminated from the sum rule. Relativistic recoil
and Fermi motion of target nucleons are correctly incorporated. The sum rule
decomposes into one- and two-body parts, with correlation information in the
second. The one-body part requires information on the nucleon momentum
distribution function, which is incorporated by a moment expansion method. The
sum rule given through the second moment (RCSR-II) is tested in the Fermi gas
model, and is shown to be sufficiently accurate for applications to data.Comment: 32 pages (LaTeX), 4 postscript figures available from the author
Dynamics of long-range order in an exciton-polariton condensate
We report on time resolved measurements of the first order spatial coherence
in an exciton polariton Bose-Einstein condensate. Long range spatial coherence
is found to set in right at the onset of stimulated scattering, on a picosecond
time scale. The coherence reaches its maximum value after the population and
decays slower, staying up to a few hundreds of picoseconds. This behavior can
be qualitatively reproduced, using a stochastic classical field model
describing interaction between the polariton condensate and the exciton
reservoir within a disordered potential.Comment: 7 pages, 4 figure
A Bogomol`nyi equation for intersecting domain walls
We argue that the Wess-Zumino model with quartic superpotential admits static
solutions in which three domain walls intersect at a junction. We derive an
energy bound for such junctions and show that configurations saturating it
preserve 1/4 supersymmetry.Comment: 4 pages revtex. No figures. Revised version to appear in Physical
Review Letters includes discussion of the supersymmetry algebr
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