5,522 research outputs found
Production and Characterization of Femtosecond-Laser-Induced Air Plasma
The purpose of this research was to produce, characterize, and optimize laser induced air plasma as a preliminary step in using the plasma as a source of terahertz radiation. An 800 nanometer, 50 femtosecond, 0.75 Watt, pulsed Ti:Sapphire laser system was used as the source infrared beam. A beam expander was used to expand the beam to a diameter of approximately 6.5 mm, and the beam was focused through a 25 mm focal length achromatic lens to produce laser-induced plasma in ambient air. A 40 kHz ultrasonic transducer was used to detect the plasma. A second harmonic generation crystal was placed within the beam expander to generate 400 nm blue light, enabling production of THz in the plasma via four wave mixing; a third-order nonlinear process. While plasma-produced THz was not detected, all the preliminary groundwork was accomplished, including full characterization of the plasma, blue light, and alignment of the system to generate and detect THz. The electro-optic detection apparatus was assembled, aligned and used to successfully detect a diagnostic THz signal
Microscopic Enhancement of Heavy-Element Production
Realistic fusion barriers are calculated in a macroscopic-microscopic model
for several soft-fusion heavy-ion reactions leading to heavy and superheavy
elements. The results obtained in such a realistic picture are very different
from those obtained in a purely macroscopic model. For reactions on 208:Pb
targets, shell effects in the entrance channel result in fusion-barrier
energies at the touching point that are only a few MeV higher than the ground
state for compound systems near Z = 110. The entrance-channel fragment-shell
effects remain far inside the touching point, almost to configurations only
slightly more elongated than the ground-state configuration, where the fusion
barrier has risen to about 10 MeV above the ground-state energy. Calculated
single-particle level diagrams show that few level crossings occur until the
peak in the fusion barrier very close to the ground-state shape is reached,
which indicates that dissipation is negligible until very late in the fusion
process. Whereas the fission valley in a macroscopic picture is several tens of
MeV lower in energy than is the fusion valley, we find in the
macroscopic-microscopic picture that the fission valley is only about 5 MeV
lower than the fusion valley for soft-fusion reactions leading to compound
systems near Z = 110. These results show that no significant
``extra-extra-push'' energy is needed to bring the system inside the fission
saddle point and that the typical reaction energies for maximum cross section
in heavy-element synthesis correspond to only a few MeV above the maximum in
the fusion barrier.Comment: 7 pages. LaTeX. Submitted to Zeitschrift fur Physik A. 5 figures not
included here. Complete preprint, including device-independent (dvi),
PostScript, and LaTeX versions of the text, plus PostScript files of the
figures, available at http://t2.lanl.gov/publications/publications.html or at
ftp://t2.lanl.gov/pub/publications/mehe
SN1987A - a Testing Ground for the KARMEN Anomaly
We show, that SN1987A can serve as an astrophysical laboratory for testing
the viability of the assertion that a new massive neutral fermion is implied by
the KARMEN data. We show that a wide range of the parameters characterizing the
proposed particle is ruled out by the above constraints making this
interpretation very unlikely.Comment: 12 pages, 1 eps figure embedded, to appear in Phys. Lett.
Power Transmission Control using Distributed Max-Flow
Existing maximum flow algorithms use one processor for all calculations or one processor per vertex in a graph to calculate the maximum possible flow through a graph\u27s vertices. This is not suitable for practical implementation. We extend the max-flow work of Goldberg and Tarjan to a distributed algorithm to calculate maximum flow where the number of processors is less than the number of vertices in a graph. Our algorithm is applied to maximizing electrical flow within a power network where the power grid is modeled as a graph. Error detection measures are included to detect problems in a simulated power network. We show that our algorithm is successful in executing quickly enough to prevent catastrophic power outages
Tecnología y tipología del torques de Sintra (Lisboa, Portugal). Un adorno de oro del Bronce Atlántico compuesto por los tipos Sagrajas-Berzocana y Villena-Estremoz
Not available[es] El estudio del torques de Sintra (Lisboa) ha revelado detalles tecnológicos y tipológicos que indican una mezcla de dos tipos bien conocidos durante el Bronce Final Atlántico de la Península Ibérica: Sagrajas-Berzocana y Villena-Estremoz. Esta combinación refuerza la tesis según la cual ambas tradiciones orfebres coexistieron durante un tiempo. El torques está formado por distintos elementos fabricados con técnicas avanzadas, como la fusión adicional además de una variante de la cera perdida que requiere la utilización del torno. Se pone de relieve la importancia de la investigación tecnológica en los estudios sobre tipología y cronología de objetos metálicos.
[fr] Sur la technologie et la typologie du collier de Sintra (Lisbonne, Portugal) - Un oeuvre d'orfèvrerie du Bronze Final Atlantique composé des types Sagrajas-Berzocana et Villena-Estremoz.
L'étude du collier de Sintra (Lisbonne) a revélé des détails technologiques et typologiques indiquant une combinaison de deux types bien connus dans le Bronze Final Atlantique de la Péninsule Ibérique : Sagrajas-Berzocana et VilIena-Estremoz. Cette combinaison renforce la thèse selon laquelle les deux traditions d'orfèvrerie ont coexisté partiellement dans le temps. Le collier est constitué de différents éléments fabriqués avec des techniques avançees, comme la fonte additionnelle ainsi qu'une version élaborée de la cire perdue faisant appel au tour. L'importance des recherches technologiques pour la typologie et chronologie des objects métalliques est mise en évidence
Résolution en temps d'un circuit de coïncidences particule gamma
Des détecteurs à barrière de surface ont été utilisés dans un circuit de coïncidences rapides particule-gamma en vue de mesurer des vies moyennes de noyaux dans des états excités. L'influence sur la résolution en temps de différents facteurs (résistivité, tension de polarisation, etc.) a été étudiée
Search for long lived heaviest nuclei beyond the valley of stability
The existence of long lived superheavy nuclei (SHN) is controlled mainly by
spontaneous fission and -decay processes. According to microscopic
nuclear theory, spherical shell effects at Z=114, 120, 126 and N=184 provide
the extra stability to such SHN to have long enough lifetime to be observed. To
investigate whether the so-called "stability island" could really exist around
the above Z, N values, the -decay half lives along with the spontaneous
fission and -decay half lives of such nuclei are studied. The
-decay half lives of SHN with Z=102-120 are calculated in a quantum
tunneling model with DDM3Y effective nuclear interaction using
values from three different mass formulae prescribed by Koura, Uno, Tachibana,
Yamada (KUTY), Myers, Swiatecki (MS) and Muntian, Hofmann, Patyk, Sobiczewski
(MMM). Calculation of spontaneous fission (SF) half lives for the same SHN are
carried out using a phenomenological formula and compared with SF half lives
predicted by Smolanczuk {\it et al}. Possible source of discrepancy between the
calculated -decay half lives of some nuclei and the experimental data
of GSI, JINR-FLNR, RIKEN are discussed. In the region of Z=106-108 with N
160-164, the -stable SHN is predicted to have
highest -decay half life () using
value from MMM. Interestingly, it is much greater than the recently measured
() of deformed doubly magic
nucleus. A few fission-survived long-lived SHN which are either -stable
or having large -decay half lives are predicted to exist near
, , and .
These nuclei might decay predominantly through -particle emission.Comment: 14 pages, 6 figures, 1 tabl
Tecnología y tipología del torques de Sintra (Lisboa, Portugal). Un adorno de oro del Bronce Atlántico compuesto por los tipos Sagrajas-Berzocana y Villena-Estremoz
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