288 research outputs found
Demonstration of 40â Gbitâs optical packet synchronisation using fibre Bragg gratings and fast-tunable wavelength converters
Simultaneous 160-Gb/s Demultiplexing and Clock Recovery by Utilizing Microwave Harmonic Frequencies in a Traveling-Wave Electroabsorption Modulator
Fission Hindrance in hot 216Th: Evaporation Residue Measurements
The fusion evaporation-residue cross section for 32S+184W has been measured
at beam energies of E_beam = 165, 174, 185, 196, 205, 215, 225, 236, 246,and
257 MeV using the ATLAS Fragment Mass Analyzer. The data are compared with
Statistical Model calculations and it is found that a nuclear dissipation
strength, which increases with excitation energy, is required to reproduce the
excitation function. A comparison with previously published data show that the
dissipation strength depends strongly on the shell structure of the nuclear
system.Comment: 15 pages 9 figure
Low power penalty 80 to 10â Gbitâs OTDM demultiplexer using standing-wave enhanced electroabsorption modulator with reduced driving voltage
Îł decay from states at low excitation energy in the neutron-deficient isotope, 200Rn, identified by correlated radioactive decay
The low-lying level structure of the neutron-deficient isotope 200Rn has been studied using the 176Hf(28Si,4n) reaction at a beam energy of 142 MeV. Evaporation residues were selected using an in-flight recoil mass separator, the Argonne Fragment Mass Analyzer, and implanted in a double-sided silicon strip detector. Prompt Îł rays in 200Rn were observed at the target position using the AYEBALL array of 19 Compton-suppressed germanium detectors, and were identified by the subsequent radioactive decay of associated recoiling ions in the strip detector. Isotopic assignments of the nuclei produced were made on the basis of the mass-to-charge ratio of the recoiling ion and the energy and half-life of its α decay. Previous results concerning transitions in 202Rn were confirmed. The level scheme deduced for 200Rn, compared with those of heavier radon isotopes, is not consistent with the onset of deformation predicted by theoretical calculations. The estimated production cross section for 200Rn in this reaction was 5 ÎŒb
Relative spins and excitation energies of superdeformed bands in 190Hg: Further evidence for octupole vibration
An experiment using the Eurogam Phase II gamma-ray spectrometer confirms the
existence of an excited superdeformed (SD) band in 190Hg and its very unusual
decay into the lowest SD band over 3-4 transitions. The energies and dipole
character of the transitions linking the two SD bands have been firmly
established. Comparisons with RPA calculations indicate that the excited SD
band can be interpreted as an octupole-vibrational structure.Comment: 12 pages, latex, 4 figures available via WWW at
http://www.phy.anl.gov/bgo/bc/hg190_nucl_ex.htm
Superdeformed band in 155Dy: Where does the "island" of superdeformation end?
A superdeformed band of 15 transitions has been found in the 155Dy nucleus. The measurement was performed with a backed target and the large deformation was inferred from the measured Doppler shifts. The new band displays an intensity pattern much different from typical superdeformed bands in this mass region. The dynamic moment of inertia is essentially identical to that of band 1 in 153Dy and is somewhat larger than those of the yrast superdeformed bands in 152, 154Dy, suggesting that the associated configuration has an additional N = 7, j15/2 intruder orbital occupied with respect to the 154Dy core
Cosmology at the Millennium
One hundred years ago we did not know how stars generate energy, the age of
the Universe was thought to be only millions of years, and our Milky Way galaxy
was the only galaxy known. Today, we know that we live in an evolving and
expanding Universe comprising billions of galaxies, all held together by dark
matter. With the hot big-bang model, we can trace the evolution of the Universe
from the hot soup of quarks and leptons that existed a fraction of a second
after the beginning to the formation of galaxies a few billion years later, and
finally to the Universe we see today 13 billion years after the big bang, with
its clusters of galaxies, superclusters, voids, and great walls. The attractive
force of gravity acting on tiny primeval inhomogeneities in the distribution of
matter gave rise to all the structure seen today. A paradigm based upon deep
connections between cosmology and elementary particle physics -- inflation +
cold dark matter -- holds the promise of extending our understanding to an even
more fundamental level and much earlier times, as well as shedding light on the
unification of the forces and particles of nature. As we enter the 21st
century, a flood of observations is testing this paradigm.Comment: 44 pages LaTeX with 14 eps figures. To be published in the Centennial
Volume of Reviews of Modern Physic
Inflation, cold dark matter, and the central density problem
A problem with high central densities in dark halos has arisen in the context
of LCDM cosmologies with scale-invariant initial power spectra. Although n=1 is
often justified by appealing to the inflation scenario, inflationary models
with mild deviations from scale-invariance are not uncommon and models with
significant running of the spectral index are plausible. Even mild deviations
from scale-invariance can be important because halo collapse times and
densities depend on the relative amount of small-scale power. We choose several
popular models of inflation and work out the ramifications for galaxy central
densities. For each model, we calculate its COBE-normalized power spectrum and
deduce the implied halo densities using a semi-analytic method calibrated
against N-body simulations. We compare our predictions to a sample of dark
matter-dominated galaxies using a non-parametric measure of the density. While
standard n=1, LCDM halos are overdense by a factor of 6, several of our example
inflation+CDM models predict halo densities well within the range preferred by
observations. We also show how the presence of massive (0.5 eV) neutrinos may
help to alleviate the central density problem even with n=1. We conclude that
galaxy central densities may not be as problematic for the CDM paradigm as is
sometimes assumed: rather than telling us something about the nature of the
dark matter, galaxy rotation curves may be telling us something about inflation
and/or neutrinos. An important test of this idea will be an eventual consensus
on the value of sigma_8, the rms overdensity on the scale 8 h^-1 Mpc. Our
successful models have values of sigma_8 approximately 0.75, which is within
the range of recent determinations. Finally, models with n>1 (or sigma_8 > 1)
are highly disfavored.Comment: 13 pages, 6 figures. Minor changes made to reflect referee's
Comments, error in Eq. (18) corrected, references updated and corrected,
conclusions unchanged. Version accepted for publication in Phys. Rev. D,
scheduled for 15 August 200
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