597 research outputs found
Direct measurement of the fine-structure interval in alkali atoms using diode lasers
We demonstrate a technique for directly measuring the fine-structure interval
in alkali atoms using two frequency-stabilized diode lasers. Each laser has a
linewidth of order 1 MHz and precise tunability: one laser is tuned to a
hyperfine transition in the D_1 line, and the other laser to a hyperfine
transition in the D_2 line. The outputs of the lasers are fed into a scanning
Michelson interferometer that measures the ratio of their wavelengths
accurately. To illustrate the technique, we measure the fine-structure interval
in Rb, and obtain a value of 237.6000(3)(5) cm^-1 for the hyperfine-free
5P_{3/2} - 5P_{1/2} interval.Comment: 3 pages, 2 figures, to be published in Applied Physics Letters, 20
May 2002 editio
Holographic perfect fluidity, Cotton energy-momentum duality and transport properties
We investigate background metrics for 2+1-dimensional holographic theories
where the equilibrium solution behaves as a perfect fluid, and admits thus a
thermodynamic description. We introduce stationary perfect-Cotton geometries,
where the Cotton--York tensor takes the form of the energy--momentum tensor of
a perfect fluid, i.e. they are of Petrov type D_t. Fluids in equilibrium in
such boundary geometries have non-trivial vorticity. The corresponding bulk can
be exactly reconstructed to obtain 3+1-dimensional stationary black-hole
solutions with no naked singularities for appropriate values of the black-hole
mass. It follows that an infinite number of transport coefficients vanish for
holographic fluids. Our results imply an intimate relationship between
black-hole uniqueness and holographic perfect equilibrium. They also point
towards a Cotton/energy--momentum tensor duality constraining the fluid
vorticity, as an intriguing boundary manifestation of the bulk mass/nut
duality.Comment: V3: 1+39 pages, JHEP versio
High-accuracy wavemeter based on a stabilized diode laser
We have built a high-accuracy wavelength meter for tunable lasers using a
scanning Michelson interferometer and a reference laser of known wavelength.
The reference laser is a frequency stabilized diode laser locked to an atomic
transition in Rb. The wavemeter has a statistical error per measurement of 5
parts in which can be reduced considerably by averaging. Using a second
stabilized diode laser, we have verified that systematic errors are below 4
parts in .Comment: 3 pages, 2 figure
Homogeneous Relaxation at Strong Coupling from Gravity
Homogeneous relaxation is a ubiquitous phenomenon in semiclassical kinetic
theories where the quasiparticles are distributed uniformly in space, and the
equilibration involves only their velocity distribution. For such solutions,
the hydrodynamic variables remain constant. We construct asymptotically AdS
solutions of Einstein's gravity dual to such processes at strong coupling,
perturbatively in the amplitude expansion, where the expansion parameter is the
ratio of the amplitude of the non-hydrodynamic shear-stress tensor to the
pressure. At each order, we sum over all time derivatives through exact
recursion relations. We argue that the metric has a regular future horizon,
order by order in the amplitude expansion, provided the shear-stress tensor
follows an equation of motion. At the linear order, this equation of motion
implies that the metric perturbations are composed of zero wavelength
quasinormal modes. Our method allows us to calculate the non-linear corrections
to this equation perturbatively in the amplitude expansion. We thus derive a
special case of our previous conjecture on the regularity condition on the
boundary stress tensor that endows the bulk metric with a regular future
horizon, and also refine it further. We also propose a new outlook for
heavy-ion phenomenology at RHIC and ALICE.Comment: 60 pages, a section titled "Outlook for RHIC and ALICE" has been
added, accepted for publication in Physical Review
Non-linear electrical conduction and broadband noise in charge-ordered rare earth manganate Nd_0.5Ca_0.5MnO_3
Measurements of the dc transport properties and the low-frequency
conductivity noise in films of charge ordered Nd_0.5Ca_0.5MnO_3 grown on Si
subtrate reveal the existence of a threshold field in the charge ordered regime
beyond which strong non linear conduction sets in along with a large broad band
conductivity noise. Threshold-dependent conduction disappears as T -> T_{CO},
the charge ordering temperature. This observation suggests that the charge
ordered state gets depinned at the onset of the non-linear conduction.Comment: 3 pages of two-column text and 4 eps figure
Magnetic Field resulting from non-linear electrical transport in single crystals of charge-ordered Pr Ca MnO}
In this letter we report that the current induced destabilization of the
charge ordered (CO) state in a rare-earth manganite gives rise to regions with
ferromagnetic correlation. We did this experiment by measurement of the I-V
curves in single crystal of the CO system
PrCaMnO and simultanously measuring the magnetization
of the current carrying conductor using a high T SQUID working at T = 77K.
We have found that the current induced destabilization of the CO state leads to
a regime of negative differential resistance which leads to a small enhancement
of the magnetization of the sample, indicating ferromagnetically aligned
moments.Comment: 4 pages LateX, 4 eps figure
Recrystallization of epitaxial GaN under indentation
We report recrystallization of epitaxial (epi-) GaN(0001) film under
indentation.Hardness value is measured close to 10 GPa, using a Berkovich
indenter. Pop-in burst in the loading line indicates nucleation of dislocations
setting in plastic motion of lattice atoms under stress field for the
recrystallization process. Micro-Raman studies are used to identify the
recrystallization process. Raman area mapping indicates the crystallized
region. Phonon mode corresponding to E2(high) close to 570 cm-1 in the as-grown
epi-GaN is redshifted to stress free value close to 567 cm-1 in the indented
region. Evolution of A1(TO) and E1(TO) phonon modes are also reported to
signify the recrystallization process.Comment: 10 pages, 3 figures
Traversable wormholes in Rastall-Rainbow Gravity
In this paper, we investigate the existence of asymptotically flat wormhole
geometries within the framework of Rastall-Rainbow modified gravity, a
synthesis of two distinct theoretical models: Rastall theory and the Rainbow
description. Our study uncovers that, when considering specific combinations of
free parameters and equations of state, the emergence of static and spherically
symmetric wormholes is not feasible within a zero-tidal-force context. By
considering the subset of viable solutions, we conduct a rigorous assessment of
their stability through adiabatic sound velocity analysis and scrutinize their
compliance with the Weak Energy Condition (WEC). In summary, our inquiry
provides insights into how the interplay between Rastall parameters and Rainbow
functions may alleviate violations of energy conditions in these modified
gravity scenarios.Comment: 12 pages, 6 figure
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