3,170 research outputs found
Thermal modeling of a metallic thermal protection tile for entry vehicles
The thermal Energy Flow Simulation (TEFS) computer program was developed to simulate transient heat transfer through composite solids and predict interfacial temperatures. The program and its usage are described. A simulation of the thermal response of a new thermal protection tile design for the Space Shuttle Orbiter is presented and graphically compared with actual data. An example is also provided which shows the program's usage as a design tool for theoretical models
Green's Functions from Quantum Cluster Algorithms
We show that cluster algorithms for quantum models have a meaning independent
of the basis chosen to construct them. Using this idea, we propose a new method
for measuring with little effort a whole class of Green's functions, once a
cluster algorithm for the partition function has been constructed. To explain
the idea, we consider the quantum XY model and compute its two point Green's
function in various ways, showing that all of them are equivalent. We also
provide numerical evidence confirming the analytic arguments. Similar
techniques are applicable to other models. In particular, in the recently
constructed quantum link models, the new technique allows us to construct
improved estimators for Wilson loops and may lead to a very precise
determination of the glueball spectrum.Comment: 15 pages, LaTeX, with four figures. Added preprint numbe
The Freezing of Random RNA
We study secondary structures of random RNA molecules by means of a
renormalized field theory based on an expansion in the sequence disorder. We
show that there is a continuous phase transition from a molten phase at higher
temperatures to a low-temperature glass phase. The primary freezing occurs
above the critical temperature, with local islands of stable folds forming
within the molten phase. The size of these islands defines the correlation
length of the transition. Our results include critical exponents at the
transition and in the glass phase.Comment: 4 pages, 8 figures. v2: presentation improve
Public Policy and the Non-Secular: How Non-Profit Organizations Preserve Inner City Historic Sacred Places
Historic sacred places represent a pattern of American culture. The sheer abundance of churches, temples and synagogues across the country demonstrate the presence of religious freedom, and the public statement conveyed by sacred places in their craftsmanship, architectural styles and strategic locations in residential neighborhoods. The many ways a community relates to an historic sacred place are representative of how people value cultural resources and what impact these resources can have on community revitalization. When a strong partnership exists between a congregation and community members (whether congregant or not) the outcome is more beneficial to the preservation of a sacred place. This thesis proposes that a healthy partnership can be achieved by non-profit organizations collaborating with urban congregations, to effectively impact their communities and preserve their historic sacred places. The three case studies present exemplary partnerships between congregations and nonprofit organizations in Chicago, Philadelphia and Detroit, where historic congregations are impacting the surrounding community by the preservation of their urban religious properties
Monte Carlo Study of Correlations in Quantum Spin Chains at Non-Zero Temperature
Antiferromagnetic Heisenberg spin chains with various spin values
() are studied numerically with the quantum Monte Carlo
method. Effective spin chains are realized by ferromagnetically coupling
antiferromagnetic spin chains with . The temperature dependence
of the uniform susceptibility, the staggered susceptibility, and the static
structure factor peak intensity are computed down to very low temperatures,
. The correlation length at each temperature is deduced from
numerical measurements of the instantaneous spin-spin correlation function. At
high temperatures, very good agreement with exact results for the classical
spin chain is obtained independent of the value of . For =2 chains which
have a gap , the correlation length and the uniform susceptibility in
the temperature range are well predicted by a semi-classical
theory due to Damle and Sachdev.Comment: LaTeX EPJ macr
Quantum Link Models with Many Rishon Flavors and with Many Colors
Quantum link models are a novel formulation of gauge theories in terms of
discrete degrees of freedom. These degrees of freedom are described by quantum
operators acting in a finite-dimensional Hilbert space. We show that for
certain representations of the operator algebra, the usual Yang-Mills action is
recovered in the continuum limit. The quantum operators can be expressed as
bilinears of fermionic creation and annihilation operators called rishons.
Using the rishon representation the quantum link Hamiltonian can be expressed
entirely in terms of color-neutral operators. This allows us to study the large
N_c limit of this model. In the 't Hooft limit we find an area law for the
Wilson loop and a mass gap. Furthermore, the strong coupling expansion is a
topological expansion in which graphs with handles and boundaries are
suppressed.Comment: Lattice2001(theorydevelop), poster by O. Baer and talk by B.
Schlittgen, 6 page
Description of an aeronautical geometry conversion package: Wave-drag to Langley Wireframe Geometry Standard (LaWGS) to Supersonic Implicit Marching Potential (SIMP)
Documented is an aeronautical geometry conversion package which translates wave-drag geometry into the Langley Wireframe Geometry Standard (LaWGS) format and then into a format which is used by the Supersonic Implicit Marching Potential (SIMP) program. The programs described were developed by Computer Sciences Corporation for the Advanced Vehicles Division/Advanced Concepts Branch at NASA Langley Research Center. Included also are the input and output from a benchmark test case
Progress on Perfect Lattice Actions for QCD
We describe a number of aspects in our attempt to construct an approximately
perfect lattice action for QCD. Free quarks are made optimally local on the
whole renormalized trajectory and their couplings are then truncated by
imposing 3-periodicity. The spectra of these short ranged fermions are
excellent approximations to continuum spectra. The same is true for free
gluons. We evaluate the corresponding perfect quark-gluon vertex function,
identifying in particular the ``perfect clover term''. First simulations for
heavy quarks show that the mass is strongly renormalized, but again the
renormalized theory agrees very well with continuum physics. Furthermore we
describe the multigrid formulation for the non-perturbative perfect action and
we present the concept of an exactly (quantum) perfect topological charge on
the lattice.Comment: 14 pages, 17 figures, Talk presented at LATTICE96(improvement
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