24,404 research outputs found
Two-photon excitation of nitric oxide fluorescence as a temperature indicator in unsteady gas-dynamic processes
A laser induced fluorescence technique, suitable for measuring fluctuating temperatures in cold turbulent flows containing very low concentrations of nitric oxide is described. Temperatures below 300 K may be resolved with signal to noise ratios greater than 50 to 1 using high peak power, tunable dye lasers. The method relies on the two photon excitation of selected ro-vibronic transitions. The analysis includes the effects of fluorescence quenching and shows the technique to be effective at all densities below ambient. Signal to noise ratio estimates are based on a preliminary measurement of the two photon absorptivity for a selected rotational transition in the NO gamma (0,0) band
The two-photon absorptivity of rotational transitions in the A2 Sigma hyperon + (v prime = O) - X-2 pion (v prime prime = O) gamma band of nitric oxide
A predominantly single-mode pulsed dye laser system giving a well characterized spatial and temporal output suitable for absolute two-photon absorptivity measurements was used to study the NO gamma(0,0) S11 + R21 (J double prime = 7-1/2) transition. Using a calibrated induced-fluorescence technique, an absorptivity parameter of 2.8 + or - 1.4 x 10 to the minus 51st power cm to the 6th power was obtained. Relative strengths of other rotational transitions in the gamma(0,0) band were also measured and shown to compare well with predicted values in all cases except the O12 (J double prime = 10-1/2) transition
Optical measurements of fluctuating temperatures in a supersonic turbulent flow using one- and two-photon, laser-induced fluorescence
A laser-induced fluorescence technique was developed that provides a practical means of nonintrusively measuring the instantaneous temperatures in low-temperature turbulent flows. The capabilities of the method are reviewed, and its application to a simple, two-dimensional, turbulent boundary-layer flow at Mach 2 is reported. Measurements of the average temperature distribution through the boundary layer and the magnitudes of temperature fluctuations about their average values are presented
Some exact results on the matter star-product in the half-string formalism
We show that the D25 sliver wavefunction, just as the D-instanton sliver,
factorizes when expressed in terms of half-string coordinates. We also
calculate analytically the star-product of two zero-momentum eigenstates of
using the vertex in the oscillator basis, thereby showing that the
star-product in the matter sector can indeed be seen as multiplication of
matrices acting on the space of functionals of half strings. We then use the
above results to establish that the matrices , conjectured by
Rastelli, Sen and Zwiebach to be left and right projectors on the sliver, are
indeed so.Comment: 27 pages; footnote adde
Pathway from condensation via fragmentation to fermionization of cold bosonic systems
For small scattering lengths, cold bosonic atoms form a condensate the
density profile of which is smooth. With increasing scattering length, the
density {\it gradually} acquires more and more oscillations. Finally, the
number of oscillations equals the number of bosons and the system becomes {\it
fermionized}. On this pathway from condensation to fermionization intriguing
phenomena occur, depending on the shape of the trap. These include macroscopic
fragmentation and
{\it coexistence} of condensed and fermionized parts that are separated in
space.Comment: 12 pages, 2 figure
Solitary wave complexes in two-component mixture condensates
Axisymmetric three-dimensional solitary waves in uniform two-component
mixture Bose-Einstein condensates are obtained as solutions of the coupled
Gross-Pitaevskii equations with equal intracomponent but varying intercomponent
interaction strengths. Several families of solitary wave complexes are found:
(1) vortex rings of various radii in each of the components, (2) a vortex ring
in one component coupled to a rarefaction solitary wave of the other component,
(3) two coupled rarefaction waves, (4) either a vortex ring or a rarefaction
pulse coupled to a localised disturbance of a very low momentum. The continuous
families of such waves are shown in the momentum-energy plane for various
values of the interaction strengths and the relative differences between the
chemical potentials of two components. Solitary wave formation, their stability
and solitary wave complexes in two-dimensions are discussed.Comment: 4 pages, 2 figures, 2 table
Beyond Mean-Field Theory for Attractive Bosons under Transverse Harmonic Confinement
We study a dilute gas of attractive bosons confined in a harmonic cylinder,
i.e. under cylindric confinement due to a transverse harmonic potential. We
introduce a many-body wave function which extends the Bethe ansatz proposed by
McGuire (J. Math. Phys. {\bf 5}, 622 (1964)) by including a variational
transverse Gaussian shape. We investigate the ground state properties of the
system comparing them with the ones of the one-dimensional (1D) attractive Bose
gas. We find that the gas becomes ultra 1D as a consequence of the attractive
interaction: the transverse width of the Bose gas reduces by increasing the
number of particles up to a critical width below which there is the collapse of
the cloud. In addition, we derive a simple analytical expression for the
simmetry-breaking solitonic density profile of the ground-state, which
generalize the one deduced by Calogero and Degasperis (Phys. Rev. A {\bf 11},
265 (1975)). This bright-soliton analytical solution shows near the collapse
small deviations with respect to the 3D mean-field numerical solution. Finally,
we show that our variational Gauss-McGuire theory is always more accurate than
the McGuire theory. In addition, we prove that for small numbers of particles
the Gauss-McGuire theory is more reliable than the mean-field theory described
by the 3D Gross-Pitaevskii equation.Comment: To be published in J. Phys. B.: At. Mol. Opt. Phy
Front-End electronics configuration system for CMS
The four LHC experiments at CERN have decided to use a commercial SCADA
(Supervisory Control And Data Acquisition) product for the supervision of their
DCS (Detector Control System). The selected SCADA, which is therefore used for
the CMS DCS, is PVSS II from the company ETM. This SCADA has its own database,
which is suitable for storing conventional controls data such as voltages,
temperatures and pressures. In addition, calibration data and FE (Front-End)
electronics configuration need to be stored. The amount of these data is too
large to be stored in the SCADA database [1]. Therefore an external database
will be used for managing such data. However, this database should be
completely integrated into the SCADA framework, it should be accessible from
the SCADA and the SCADA features, e.g. alarming, logging should be benefited
from. For prototyping, Oracle 8i was selected as the external database manager.
The development of the control system for calibration constants and FE
electronics configuration has been done in close collaboration with the CMS
tracker group and JCOP (Joint COntrols Project)(1).
(1)The four LHC experiments and the CERN IT/CO group has merged their efforts
to build the experiments controls systems and set up the JCOP at the end of
December, 1997 for this purpose.Comment: 3 pages, 4 figures, Icaleps'01 conference PSN WEDT00
Microscopic Structure of a Vortex Line in a Superfluid Fermi Gas
The microscopic properties of a single vortex in a dilute superfluid Fermi
gas at zero temperature are examined within the framework of self-consistent
Bogoliubov-de Gennes theory. Using only physical parameters as input, we study
the pair potential, the density, the energy, and the current distribution.
Comparison of the numerical results with analytical expressions clearly
indicates that the energy of the vortex is governed by the zero-temperature BCS
coherence length.Comment: 4 pages, 4 embedded figures. Added references. To be published in
Physical Review Letter
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