2,324,014 research outputs found
Steve Harvey & Carlos II
Foot patrols through Baghdad were slow. Nothing but time to think about sniper sightlines and IEDs hidden in the trash. We gridded the streets in our AO and sidestepped sewage-puddling ditches. Three months in, one block became our favorite. There were fewer adobe-like farmhouses, and beyond them lay the rural red-sanded expanse of the desert. The stagnant heat reminded me of running the firebreak roads at Camp Mackall during SFAS Team Week. I had twelve months to go, a full year to imagine a violent death on a repeating loop. I wanted to make it to my twenty-first birthday so I could walk into a liquor store back home in Fort Worth and buy my old man a nice bottle of Scotch, thank him for loving me, for sending me letters every week
dependence of the - and -induced production of the from nuclei
Using results of a recent calculation of the in the nuclear
medium, which show that the medium width is about five times the free width, we
study the A dependence of the production cross section in the
reactions and . We find a sizable A dependence in the ratio of the
nuclear cross sections for heavy nuclei with respect to a light one due to the
large value of the width in the medium, showing that devoted
experiments, easily within reach in present facilities, can provide good
information on that magnitude by measuring the cross sections studied here.Comment: 14 pages, 5 figure
Behavior of the giant-dipole resonance in Sn and Pb at high excitation energ
The properties of the giant-dipole resonance (GDR) are calculated as a
function of excitation energy, angular momentum, and the compound nucleus
particle decay width in the nuclei Sn and Pb, and are compared
with recent experimental data. Differences observed in the behavior of the
full-width-at-half-maximum of the GDR for Sn and Pb are
attributed to the fact that shell corrections in Pb are stronger than
in Sn, and favor the spherical shape at low temperatures. The effects
shell corrections have on both the free energy and the moments of inertia are
discussed in detail. At high temperature, the FWHM in Sn exhibits
effects due to the evaporation width of the compound nucleus, while these
effects are predicted for Pb.Comment: 28 pages in RevTeX plus eight postscript figures. Submitted to Nucl.
Phys.
Near-infrared photoluminescence from molecular crystals containing tellurium
We report the observation of near-infrared photoluminescence from
Te4(Ga2Cl7)2 and Te4(Al2Cl7)2 molecular crystals containing Te42+ polycations.
The experimental and theoretical results clearly revealed that Te42+ polycation
is one smart near-infrared emitter with characteristic emission peaks at 1252
and 1258 nm for Te4(Ga2Cl7)2 and Te4(Al2Cl7)2 crystals, respectively, resulting
from the intrinsic electronic transitions of Te42+. Furthermore, it was also
found that the emissions strongly depend on the excitation wavelengths for both
Te4(Ga2Cl7)2 and Te4(Al2Cl7)2 samples, most possibly owing to the co-existence
of other Te-related optically active centers. This research not only enriches
the species of luminescent charged p-block element polyhedra and deepens the
understanding of Te-related photophysical behaviors, but also may stimulate
efforts for designing novel material systems using such active centers. It is
also greatly expected that these sub-nanometer optically active species could
exist in other systems such as glasses, polymers, and bulk optical crystals,
and the stabilization of these centers in widely used hosts will pave the way
for their practical applications
The Solar Twin Planet Search. V. Close-in, low-mass planet candidates and evidence of planet accretion in the solar twin HIP 68468
[Methods]. We obtained high-precision radial velocities with HARPS on the ESO
3.6 m telescope and determined precise stellar elemental abundances (~0.01 dex)
using MIKE spectra on the Magellan 6.5m telescope. [Results]. Our data indicate
the presence of a planet with a minimum mass of 26 Earth masses around the
solar twin HIP 68468. The planet is a super-Neptune, but unlike the distant
Neptune in our solar system (30 AU), HIP 68468c is close-in, with a semi-major
axis of 0.66 AU, similar to that of Venus. The data also suggest the presence
of a super-Earth with a minimum mass of 2.9 Earth masses at 0.03 AU; if the
planet is confirmed, it will be the fifth least massive radial velocity planet
discovery to date and the first super-Earth around a solar twin. Both
isochrones (5.9 Gyr) and the abundance ratio [Y/Mg] (6.4 Gyr) indicate an age
of about 6 billion years. The star is enhanced in refractory elements when
compared to the Sun, and the refractory enrichment is even stronger after
corrections for Galactic chemical evolution. We determined a NLTE Li abundance
of 1.52 dex, which is four times higher than what would be expected for the age
of HIP 68468. The older age is also supported by the low log(R'HK) (-5.05) and
low jitter. Engulfment of a rocky planet of 6 Earth masses can explain the
enhancement in both lithium and the refractory elements. [Conclusions]. The
super-Neptune planet candidate is too massive for in situ formation, and
therefore its current location is most likely the result of planet migration
that could also have driven other planets towards its host star, enhancing thus
the abundance of lithium and refractory elements in HIP 68468. The intriguing
evidence of planet accretion warrants further observations to verify the
existence of the planets that are indicated by our data and to better constrain
the nature of the planetary system around this unique star.Comment: A&A, in pres
Duality Anomaly Cancellation, Minimal String Unification and the Effective Low-Energy Lagrangian of 4-D Strings
We present a systematic study of the constraints coming from target-space
duality and the associated duality anomaly cancellations on orbifold-like 4-D
strings. A prominent role is played by the modular weights of the massless
fields. We present a general classification of all possible modular weights of
massless fields in Abelian orbifolds. We show that the cancellation of modular
anomalies strongly constrains the massless fermion content of the theory, in
close analogy with the standard ABJ anomalies. We emphasize the validity of
this approach not only for (2,2) orbifolds but for (0,2) models with and
without Wilson lines. As an application one can show that one cannot build a
or orbifold whose massless charged sector with respect
to the (level one) gauge group is that of the
minimal supersymmetric standard model, since any such model would necessarily
have duality anomalies. A general study of those constraints for Abelian
orbifolds is presented. Duality anomalies are also related to the computation
of string threshold corrections to gauge coupling constants. We present an
analysis of the possible relevance of those threshold corrections to the
computation of and for all Abelian orbifolds. Some
particular {\it minimal} scenarios, namely those based on all
orbifolds except Comment: 69 page
Unification Scale in String Theory
We study the unification scale and gauge coupling constant in 4D string
theory. We show that the fine structure constant is determined by the dimension
of the hidden gauge group and only and are consistent with
minimal string unification while the unification scale can be of order of
.Comment: 12 pages (LaTeX
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