13,321 research outputs found
Hot-wire anemometry in hypersonic helium flow
Hot-wire anemometry techniques are described that have been developed and used for hypersonic-helium-flow studies. The short run time available dictated certain innovations in applying conventional hot-wire techniques. Some examples are given to show the application of the techniques used. Modifications to conventional equipment are described, including probe modifications and probe heating controls
Sub-Natural-Linewidth Quantum Interference Features Observed in Photoassociation of a Thermal Gas
By driving photoassociation transitions we form electronically excited
molecules (Na) from ultra-cold (50-300 K) Na atoms. Using a second
laser to drive transitions from the excited state to a level in the molecular
ground state, we are able to split the photoassociation line and observe
features with a width smaller than the natural linewidth of the excited
molecular state. The quantum interference which gives rise to this effect is
analogous to that which leads to electromagnetically induced transparency in
three level atomic systems, but here one of the ground states is a
pair of free atoms while the other is a bound molecule. The linewidth is
limited primarily by the finite temperature of the atoms.Comment: 4 pages, 5 figure
All-optical generation and photoassociative probing of sodium Bose-Einstein condensates
We demonsatrate an all optical technique to evaporatively produce sodium
Bose-Einstein condensates (BEC). We use a crossed-dipole trap formed from light
near 1060 nm, and a simple ramp of the intensity to force evaporation. In
addition, we introduce photoassociation as diagnostic of the trap loading
process, and show that it can be used to detect the onset of Bose-Einstein
condensation. Finally, we demonstrate the straightforward production of
multiple traps with condensates using this technique, and that some control
over the spinor state of the BEC is achieved by positioning the trap as well.Comment: 8 pages, 10 figure
Quarks, Gluons and Frustrated Antiferromagnets
The Contractor Renormalization Group method (CORE) is used to establish the
equivalence of various Hamiltonian free fermion theories and a class of
generalized frustrated antiferromagnets. In particular, after a detailed
discussion of a simple example, it is argued that a generalized frustrated
SU(3) antiferromagnet whose single-site states have the quantum numbers of
mesons and baryons is equivalent to a theory of free massless quarks.
Furthermore, it is argued that for slight modification of the couplings which
define the frustrated antiferromagnet Hamiltonian, the theory becomes a theory
of quarks interacting with color gauge-fields.Comment: 21 pages, Late
Dynamic quantum clustering: a method for visual exploration of structures in data
A given set of data-points in some feature space may be associated with a
Schrodinger equation whose potential is determined by the data. This is known
to lead to good clustering solutions. Here we extend this approach into a
full-fledged dynamical scheme using a time-dependent Schrodinger equation.
Moreover, we approximate this Hamiltonian formalism by a truncated calculation
within a set of Gaussian wave functions (coherent states) centered around the
original points. This allows for analytic evaluation of the time evolution of
all such states, opening up the possibility of exploration of relationships
among data-points through observation of varying dynamical-distances among
points and convergence of points into clusters. This formalism may be further
supplemented by preprocessing, such as dimensional reduction through singular
value decomposition or feature filtering.Comment: 15 pages, 9 figure
Family Teamwork and Psychotherapy
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72387/1/j.1545-5300.1966.00049.x.pd
Research on solar pumped liquid lasers
A solar pumped liquid laser that can be scaled up to high power (10Mw CW) for space applications was developed. Liquid lasers have the inherent advantage over gases in that they provide much higher lasant densities and thus high power densities. Liquids also have inherent advantages over solids in that they have much higher damage thresholds and are much cheaper to produce for large scale applications. Among the liquid laser media that are potential candidates for solar pumping, the POC13:Nd(3+):ZrC14 liquid was chosen for its high intrinsic efficiency as well as its relatively good stability against decomposition due to protic contamination. The development and testing of the laser liquid and the development of a large solar concentrator to pump the laser was emphasized. The procedure to manufacture the laser liquid must include diagnostic tests of the solvent purity (from protic contamination) at various stages in the production process
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