23,498 research outputs found
Development of the activated diffusion brazing process for fabrication of finned shell to strut turbine blades
The activated diffusion brazing process was developed for attaching TD-NiCr and U700 finned airfoil shells to matching Rene 80 struts obstructing the finned cooling passageways. Creep forming the finned shells to struts in combination with precise preplacement of brazing alloy resulted in consistently sound joints, free of cooling passageway clogging. Extensive tensile and stress rupture testing of several joint orientation at several temperatures provided a critical assessment of joint integrity of both material combinations. Trial blades of each material combination were fabricated followed by destructive metallographic examination which verified high joint integrity
Different Facets of Chaos in Quantum Mechanics
Nowadays there is no universally accepted definition of quantum chaos. In
this paper we review and critically discuss different approaches to the
subject, such as Quantum Chaology and the Random Matrix Theory. Then we analyze
the problem of dynamical chaos and the time scales associated with chaos
suppression in quantum mechanics. Summary: 1. Introduction 2. Quantum Chaology
and Spectral Statistics 3. From Poisson to GOE Transition: Comparison with
Experimental Data 3.1 Atomic Nuclei 3.2 The Hydrogen Atom in the Strong
Magnetic Field 4. Quantum Chaos and Field Theory 5. Alternative Approaches to
Quantum Chaos 6. Dynamical Quantum Chaos and Time Scales 6.1 Mean-Field
Approximation and Dynamical Chaos 7. ConclusionsComment: RevTex, 25 pages, 7 postscript figures, to be published in Int. J.
Mod. Phys.
Multiple jet impingement heat transfer characteristic: Experimental investigation of in-line and staggered arrays with crossflow
Heat transfer characteristics were obtained for configurations designed to model the impingement cooled midchord region of air cooled gas turbine airfoils. The configurations tested were inline and staggered two-dimensional arrays of circular jets with ten spanwise rows of holes. The cooling air was constrained to exit in the chordwise direction along the channel formed by the jet orifice plate and the heat transfer surface. Tests were run for chordwise jet hole spacings of five, ten, and fifteen hole diameters; spanwise spacings of four, six, and eight diameters; and channel heights of one, two, three, and six diameters. Mean jet Reynolds numbers ranged from 5000 to 50,000. The thermal boundary condition at the heat transfer test surface was isothermal. Tests were run for sets of geometrically similar configurations of different sizes. Mean and chordwise resolved Nusselt numbers were determined utilizing a specially constructed test surface which was segmented in the chordwise direction
Semi-classical calculations of the two-point correlation form factor for diffractive systems
The computation of the two-point correlation form factor K(t) is performed
for a rectangular billiard with a small size impurity inside for both periodic
or Dirichlet boundary conditions. It is demonstrated that all terms of
perturbation expansion of this form factor in powers of t can be computed
directly by semiclassical trace formula. The main part of the calculation is
the summation of non-diagonal terms in the cross product of classical orbits.
When the diffraction coefficient is a constant our results coincide with
expansion of exact expressions ontained by a different method.Comment: 42 pages, 10 figures, Late
Level spacings and periodic orbits
Starting from a semiclassical quantization condition based on the trace
formula, we derive a periodic-orbit formula for the distribution of spacings of
eigenvalues with k intermediate levels. Numerical tests verify the validity of
this representation for the nearest-neighbor level spacing (k=0). In a second
part, we present an asymptotic evaluation for large spacings, where consistency
with random matrix theory is achieved for large k. We also discuss the relation
with the method of Bogomolny and Keating [Phys. Rev. Lett. 77 (1996) 1472] for
two-point correlations.Comment: 4 pages, 2 figures; major revisions in the second part, range of
validity of asymptotic evaluation clarifie
Theoretical derivation of 1/f noise in quantum chaos
It was recently conjectured that 1/f noise is a fundamental characteristic of
spectral fluctuations in chaotic quantum systems. This conjecture is based on
the behavior of the power spectrum of the excitation energy fluctuations, which
is different for chaotic and integrable systems. Using random matrix theory we
derive theoretical expressions that explain the power spectrum behavior at all
frequencies. These expressions reproduce to a good approximation the power laws
of type 1/f (1/f^2) characteristics of chaotic (integrable) systems, observed
in almost the whole frequency domain. Although we use random matrix theory to
derive these results, they are also valid for semiclassical systems.Comment: 5 pages (Latex), 3 figure
Quasiclassical Random Matrix Theory
We directly combine ideas of the quasiclassical approximation with random
matrix theory and apply them to the study of the spectrum, in particular to the
two-level correlator. Bogomolny's transfer operator T, quasiclassically an NxN
unitary matrix, is considered to be a random matrix. Rather than rejecting all
knowledge of the system, except for its symmetry, [as with Dyson's circular
unitary ensemble], we choose an ensemble which incorporates the knowledge of
the shortest periodic orbits, the prime quasiclassical information bearing on
the spectrum. The results largely agree with expectations but contain novel
features differing from other recent theories.Comment: 4 pages, RevTex, submitted to Phys. Rev. Lett., permanent e-mail
[email protected]
The Problem of Inertia in Friedmann Universes
In this paper we study the origin of inertia in a curved spacetime,
particularly the spatially flat, open and closed Friedmann universes. This is
done using Sciama's law of inertial induction, which is based on Mach's
principle, and expresses the analogy between the retarded far fields of
electrodynamics and those of gravitation. After obtaining covariant expressions
for electromagnetic fields due to an accelerating point charge in Friedmann
models, we adopt Sciama's law to obtain the inertial force on an accelerating
mass by integrating over the contributions from all the matter in the
universe. The resulting inertial force has the form , where
depends on the choice of the cosmological parameters such as ,
, and and is also red-shift dependent.Comment: 10 page
Teaching News Literacy During a Pandemic: Adapting to the Virtual Learning Environment
In the fall of 2020, as the coronavirus pandemic shuttered universities and sent much of higher education online, a team of media and information literacy experts at the University of Maine sought meaningful ways to collaboratively teach news literacy from a distance.
The result of their efforts was a weeklong virtual program, Friend, Enemy, or Frenemy? A News Literacy Challenge, open to anyone with an internet connection and an email address. This approach to remote learning scaffolded multiple literacies (critical media, news, and information) into five days, as participants examined different aspects of news production and consumption. The overall objective of the challenge was to render participants more aware of how the news is constructed and, subsequently, more critical of the news they consume and share
Teaching News Literacy During a Pandemic:: Adapting to the Virtual Learning Environment
This lesson plan is based on a collaborative teaching project between the co-authors that was implemented for an online community, over the course of a week in the fall of 2020, in response to the specific teaching and learning challenges presented by the pandemic. The online news literacy program was adapted and expanded from previous iterations of a one-day, in-person workshop, integrating specific pedagogical and engagement strategies for a much broader and more diverse learning community. The authors detail their approach to news literacy from a critical media and information literacy (CMIL) framework and how the program's content and activities were distributed and scaffolded across five days of online engagement
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