1,833 research outputs found
Ethylene line emission from the North Pole of Jupiter
A significant enhancement in infrared emission from hydrocarbon constituents of Jupiter's stratosphere was observed at a north polar hot spot (60 degrees latitude, 180 degrees longitude). A unique probe of this phenomena is ethylene (C2H4), which has not been observed previously from the ground. The profile of the emission line from ethylene at 951.742 cm-1, measured near the north pole of Jupiter, was analyzed to determine the morphology of the enhancement, the increase in C2H4 abundance and local temperature, as well as possible information on the altitude (pressure regions) where the increased emission is formed. Measurements were made using infrared heterodyne spectroscopy at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii in December 1989. At 181 degrees longitude a very strong emission line was seen, which corresponds to a 13-fold increase in C2H4 abundance or a 115K increase in temperature in the upper stratosphere, compared to values outside the hot spot. The hot spot was found to be localized to approx. 10 degrees in longitude; the line shape (width) implied that the enhanced emission originated very high in the stratosphere
Scattering into the fifth dimension of N=4 super Yang-Mills
We study an alternative to dimensional regularisation of planar scattering
amplitudes in N=4 super Yang-Mills theory by going to the Coulomb phase of the
theory. The infrared divergences are regulated by masses obtained from a Higgs
mechanism, allowing us to work in four dimensions. The corresponding string
theory set-up suggests that the amplitudes have an exact dual conformal
symmetry. The latter acts on the kinematical variables of the amplitudes as
well as on the Higgs masses in an effectively five dimensional space. We
confirm this expectation by an explicit calculation in the gauge theory. A
consequence of this exact dual conformal symmetry is a significantly reduced
set of scalar basis integrals that are allowed to appear in an amplitude. For
example, triangle sub-graphs are ruled out. We argue that the study of
exponentiation of amplitudes is simpler in the Higgsed theory because
evanescent terms in the mass regulator can be consistently dropped. We
illustrate this by showing the exponentiation of a four-point amplitude to two
loops. Finally, we also analytically compute the small mass expansion of a
two-loop master integral with an internal mass.Comment: 35 pages, many figures. v2: typos and references fixed. v3: minor
changes, version to be published in JHE
Photothermal effects in ultra-precisely stabilized tunable microcavities
We study the mechanical stability of a tunable high-finesse microcavity under
ambient conditions and investigate light-induced effects that can both suppress
and excite mechanical fluctuations. As an enabling step, we demonstrate the
ultra-precise electronic stabilization of a microcavity. We then show that
photothermal mirror expansion can provide high-bandwidth feedback and improve
cavity stability by almost two orders of magnitude. At high intracavity power,
we observe self-oscillations of mechanical resonances of the cavity. We explain
the observations by a dynamic photothermal instability, leading to parametric
driving of mechanical motion. For an optimized combination of electronic and
photothermal stabilization, we achieve a feedback bandwidth of kHz and a
noise level of m rms
Imaging of microwave fields using ultracold atoms
We report a technique that uses clouds of ultracold atoms as sensitive,
tunable, and non-invasive probes for microwave field imaging with micrometer
spatial resolution. The microwave magnetic field components drive Rabi
oscillations on atomic hyperfine transitions whose frequency can be tuned with
a static magnetic field. Readout is accomplished using state-selective
absorption imaging. Quantitative data extraction is simple and it is possible
to reconstruct the distribution of microwave magnetic field amplitudes and
phases. While we demonstrate 2d imaging, an extension to 3d imaging is
straightforward. We use the method to determine the microwave near-field
distribution around a coplanar waveguide integrated on an atom chip.Comment: 11 pages, 4 figure
Characterization of a 450-km Baseline GPS Carrier-Phase Link using an Optical Fiber Link
A GPS carrier-phase frequency transfer link along a baseline of 450 km has
been established and is characterized by comparing it to a phase-stabilized
optical fiber link of 920 km length, established between the two endpoints, the
Max-Planck-Institut f\"ur Quantenoptik in Garching and the
Physikalisch-Technische Bundesanstalt in Braunschweig. The characterization is
accomplished by comparing two active hydrogen masers operated at both
institutes. The masers serve as local oscillators and cancel out when the
double differences are calculated, such that they do not constitute a
limitation for the GPS link characterization. We achieve a frequency
instability of 3 x 10^(-13) in 30 s and 5 x 10^(-16) for long averaging times.
Frequency comparison results obtained via both links show no deviation larger
than the statistical uncertainty of 6 x 10^(-16). These results can be
interpreted as a successful cross-check of the measurement uncertainty of a
truly remote end fiber link.Comment: 14 pages, 6 figure
Construction of the New Prototype of Main Quadrupole Cold Masses for the Arc Short Straight Sections of LHC
Each cold mass of the short straight sections in the eight LHC arcs will contain a 3.25 m long twin aperture quadrupole of a nominal gradient of 223 T/m. This magnet will be aligned in a 5.3 m long inertia tube together with auxiliary magnets on each end. On the quadrupole connection end either a pair of 38 cm long octupole or trim quadrupole magnets will be mounted, on the other end there will be combined sextupole-dipole correctors with a yoke length of 1.26 m. The powering of the main quadrupoles will be assured by two pairs of copper stabilized superconducting bus-bars placed inside the cold mass next to the bus-bars for the main dipole magnets. Each of the two quadrupole apertures will be connected to its quench protection diode. The construction of three prototypes has been entrusted to the CEA/Saclay laboratory, in the frame of the special French contribution to the LHC project. The first cold mass prototype has been completed and warm-measured for its multipole content at CEA. The second cold mass is presently under completion. The paper will review the experience with the development of the quadrupole coils and cold mass construction and gives the results of the first warm magnetic measurements. An outlook for the series manufacture of the 400 arc quadrupole magnets and their cold masses for the LHC machine will complete the report
Down in Jungle Town / music by Theodor Morse; words by Eduard Madden
Cover: colorful drawing of thatched beach houses, surrounded by palm trees, two monkeys sit on the steps of the central hut; an internal description reads a monkey ditty; Publisher: F. B. Haviland Pub. Co. (New York)https://egrove.olemiss.edu/sharris_b/1086/thumbnail.jp
Ground based infrared measurements of the global distribution of ozone in the atmosphere of Mars
The global distribution of ozone in the atmosphere of Mars was determined from Doppler-limited infrared heterodyne spectroscopy measurements at the NASA Infrared Telescope Facility (IRTF) facility during June 3-7, 1988. Mars spectra near two O3 lines arising from the v sub 3 band near 1031.45 cm (-1) were used. The lines were Doppler shifted out of the strong terrestrial ozone absorption spectrum and its effect was removed. Ozone measurements were obtained at eight beam positions over a range of latitudes and local solar zenith angles. The beam size of the planet was 1.4 arcsec. A Martian CO2 line appeared in the spectra and was inverted to retrieve local temperature profiles. Using these temperature profiles, the total ozone column abundance at each position was retrieved by fitting the measured line with synthetic spectra generated by a radiative transfer program. The only previous measurement of ozone at this season was made above the South polar cap by Mariner 7 and revealed an abundance of 10 micron-atm. However, the retrieved O3 column abundances from this investigation are less than 2.2 micron-atm at all positions sampled. These results are consistent with mid-spring abundances predicted by photochemical models of Liu and Donahue, and Shimazaki and Shimizu
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