930 research outputs found
Propagation of strangelets in the Earth's atmosphere
A new model for the description of the behaviour of strangelets in the
Earth's atmosphere is presented. Strangelet fission induced by collision with
air nuclei is included. It is shown that strangelets with certain parameters of
initial mass and energy may reach depths near sea level, which can be examined
by ground-based experiments.Comment: 10 pages, 6 figure
Strangelets: Who is Looking, and How?
It has been over 30 years since the first suggestion that the true ground
state of cold hadronic matter might be not nuclear matter but rather strange
quark matter (SQM). Ever since, searches for stable SQM have been proceeding in
various forms and have observed a handful of interesting events but have
neither been able to find compelling evidence for stable strangelets nor to
rule out their existence. I will survey the current status and near future of
such searches with particular emphasis on the idea of SQM from strange star
collisions as part of the cosmic ray flux.Comment: Talk given at International Conference on Strangeness in Quark
Matter, 2006. 8 pages. 1 figur
Nonradiative Electronic Deexcitation Time Scales in Metal Clusters
The life-times due to Auger-electron emission for a hole on a deep electronic
shell of neutral and charged sodium clusters are studied for different sizes.
We consider spherical clusters and calculate the Auger-transition probabilities
using the energy levels and wave functions calculated in the
Local-Density-Approximation (LDA).
We obtain that Auger emission processes are energetically not allowed for
neutral and positively charged sodium clusters. In general, the Auger
probabilities in small Na clusters are remarkably different from the
atomic ones and exhibit a rich size dependence.
The Auger decay times of most of the cluster sizes studied are orders of
magnitude larger than in atoms and might be comparable with typical
fragmentation times.Comment: 11 pages, 4 figures. Accepted for publication in Phys. Rev.
Tidal dwarf galaxies as a test of fundamental physics
Within the cold dark matter (CDM) framework tidal dwarf galaxies (TDGs)
cannot contain dark matter, so the recent results by Bournaud et al. (2007)
that 3 rotating TDGs do show significant evidence for being dark matter
dominated is inconsistent with the current concordance cosmological theory
unless yet another dark matter component is postulated. We confirm that the TDG
rotation curves are consistent with Newtonian dynamics only if either an
additional dark matter component is postulated, or if all 3 TDGs happen to be
viewed nearly edge-on, which is unlikely given the geometry of the tidal
debris. We also find that the observed rotation curves are very naturally
explained without any free parameters within the modified Newtonian dynamics
(MOND) framework if inclinations are adopted as derived by Bournaud et al. We
explore different inclination angles and two different assumptions about the
external field effect. The results do not change significantly, and we conclude
therefore that Newtonian dynamics has severe problems while MOND does
exceedingly well in explaining the observed rotation curves of the 3 TDGs
studied by Bournaud et al.Comment: Accepted for publication in A&A Letters, 5 pages, 3 figure
Electromagnetic absorption mechanisms in metal nanospheres: Bulk and surface effects in radiofrequency-terahertz heating of nanoparticles
The following article appeared in Journal of Applied Physics 109.12 (2011): 124306
and may be found at http://scitation.aip.org/content/aip/journal/jap/109/12/10.1063/1.3600222We report on the absorption of electromagnetic radiation by metallic nanoparticles in the radio and far infrared frequency range, and subsequent heating of nanoparticle solutions. A recent series of papers has measured considerable radio frequency (RF) heating of gold nanoparticle solutions. In this work, we show that claims of RF heating by metallic nanoparticles are not supported by theory. We analyze several mechanisms by which nonmagnetic metallic nanoparticles can absorb low frequency radiation, including both classical and quantum effects. We conclude that none of these absorption mechanisms, nor any combination of them, can increase temperatures at the rates recently reported. A recent experiment supports this finding.Support by the Spanish Ministerio de Ciencia e Innovación Grant No. FIS2008-04209 and the Swedish Foundation for Strategic Research (metamaterial Grant No. SSF RMA08-0109) is acknowledged
Spectrophotometric investigations of Blue Compact Dwarf Galaxies: Markarian 35
We present results from a detailed spectrophotometric analysis of the blue
compact dwarf galaxy Mrk 35 (Haro 3), based on deep optical (B,V,R,I) and
near-IR (J,H,K) imaging, Halpha narrow-band observations and long-slit
spectroscopy. The optical emission of the galaxy is dominated by a central
young starburst, with a bar-like shape, while an underlying component of stars,
with elliptical isophotes and red colors, extends more than 4 kpc from the
galaxy center. High resolution Halpha and color maps allow us to identify the
star-forming regions, to spatially discriminate them from the older stars, and
to recognize several dust patches. We derive colors and Halpha parameters for
all the identified star-forming knots. Observables derived for each knot are
corrected for the contribution of the underlying older stellar population, the
contribution by emission lines, and from interstellar extinction, and compared
with evolutionary synthesis models. We find that the contributions of these
three factors are by no means negligible and that they significantly vary
across the galaxy. Therefore, careful quantification and subtraction of
emission lines, galaxy host contribution, and interstellar reddening at every
galaxy position, are essential to derive the properties of the young stars in
BCDs. We find that we can reproduce the colors of all the knots with an
instantaneous burst of star formation and the Salpeter initial mass function
with an upper mass limit of 100 M_solar. In all cases the knots are just a few
Myr old. The underlying population of stars has colors consistent with being
several Gyr old.Comment: 21 pages, 13 figures. Accepted for publication in ApJ, tentatively
scheduled for the ApJ November 1, 2007 v669n1 issu
Hypoalbuminemia in the outcome of patients with non-variceal upper gastrointestinal bleeding
AbstractIntroduction and aimThe role of serum albumin level in patients with non-variceal upper gastrointestinal bleeding (NVUGB) has not been extensively studied. Our aim was to evaluate the role of serum albumin on admission in terms of in-hospital mortality in patients with NVUGB.Materials and methodsPatients admitted with NVUGB during a 4-year period were prospectively included. Demographic, clinical, and laboratory data were collected. ROC curve analysis was used to determine the cutoff value for serum albumin on admission that made a distinction between deceased patients and survivors with respect to serum albumin on admission, as well as its overall performance compared with the Rockall score.Results185 patients with NVUGB were evaluated. Men predominated (56.7%) and a mean age of 59.1±19.9 years was found. Mean serum albumin on admission was 2.9±0.9g/dl with hypoalbuminemia (< 3.5g/dl) detected on admission in 71.4% of cases. The ROC curve found that the best value for predicting hospital mortality was an albumin level of 3.1g/dl (AUROC 0.738). Mortality in patients with albumin ≥ 3.2g/dl was 1.2% compared with 11.2% in patients with albumin<3.2g/dl (P=.009; OR 9.7, 95%CI 1.2-76.5). There was no difference in overall performance between the albumin level (AUORC 0.738) and the Rockall score (AUROC 0.715) for identifying mortality.ConclusionsPatients with hypoalbuminemia presenting with NVUGB have a greater in-hospital mortality rate. The serum albumin level and the Rockall score perform equally in regard to identifying the mortality rate
Lindane and Endosulfan Sulfate Isomers in Crassostrea virginica (Gmelin, 1791) Oyster Populations in Lagoon Systems from Central Gulf of Mexico
The aim of this study was to determine Lindane and Endosulfan Sulfate isomers in Crassostrea virginica oyster populations (Gmelin, 1791) in the Mandinga and Alvarado lagoon systems located in the central Gulf of Mexico. Samples were taken from the main oyster banks of each lagoon system, during the three representative seasons of the region, wet, dry and north winds. By means of free diving, 30 commercial size oysters (7 ± 3 cm) were collected in four oyster banks or stations of the Mandinga lagoon system, totaling 360 organisms, while in the Alvarado lagoon system there were a total of 90 oysters during the annual cycle. Concentration of lindane and endosulfan sulfate isotopes in C. virginica was performed with a gas chromatograph (Thermo Electron Model Trace GC Ultra 115V, Thermo Fisher Scientific Inc©, Monterrey, Nuevo León, México) with an Electron capture detector. Results showed that in the Alvarado Lagoon system mean concentrations of C. virginica oysters for lindane pesticide were 4.11 ± 3.83 ng⋅g-1, whereas for the Mandinga lagoon system, were 8.69 ± 5.15 ng⋅g-1. Endosulfan sulfate showed the highest average concentration in the Mandinga lagoon system with 24.68 ± 1.20 ng ⋅g-1. In addition, the endosulfan sulfate presents differences in its spatial distribution; high concentration levels in the Mandinga lagoon system whereas the lindane heterogeneity at all sampling points in both lagoons. Values of concentrations and relationships between compounds suggest recent contributions that could correspond to the excessive fluctuations of water discharged into the lagoon caused by the atypical rains of the year of sampling. It was concluded that endosulfan sulfate and lindane show concentration in all the points of sampling in both lagoons
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