827 research outputs found
Review of Speculative "Disaster Scenarios" at RHIC
We discuss speculative disaster scenarios inspired by hypothetical new
fundamental processes that might occur in high energy relativistic heavy ion
collisions. We estimate the parameters relevant to black hole production; we
find that they are absurdly small. We show that other accelerator and
(especially) cosmic ray environments have already provided far more auspicious
opportunities for transition to a new vacuum state, so that existing
observations provide stringent bounds. We discuss in most detail the
possibility of producing a dangerous strangelet. We argue that four separate
requirements are necessary for this to occur: existence of large stable
strangelets, metastability of intermediate size strangelets, negative charge
for strangelets along the stability line, and production of intermediate size
strangelets in the heavy ion environment. We discuss both theoretical and
experimental reasons why each of these appears unlikely; in particular, we know
of no plausible suggestion for why the third or especially the fourth might be
true. Given minimal physical assumptions the continued existence of the Moon,
in the form we know it, despite billions of years of cosmic ray exposure,
provides powerful empirical evidence against the possibility of dangerous
strangelet production.Comment: 28 pages, REVTeX; minor revisions for publication (Reviews of Modern
Physics, ca. Oct. 2000); email to [email protected]
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A Proposal to Search for Charmed Particle Production Near Threshold
We propose to search for charmed particle production thresholds by looking for anomalies in the ratio of K{sup -}/{pi}{sup -} production at P{sub T} {approx} 1 GeV/c as the incident energy is varied. Any anomalous behavior will be further investigated using a two arm effective mass spectrometer
Detection of Elements at All Three r-process Peaks in the Metal-Poor Star HD 160617
We report the first detection of elements at all three r-process peaks in the
metal-poor halo star HD 160617. These elements include arsenic and selenium,
which have not been detected previously in halo stars, and the elements
tellurium, osmium, iridium, and platinum, which have been detected previously.
Absorption lines of these elements are found in archive observations made with
the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. We
present up-to-date absolute atomic transition probabilities and complete line
component patterns for these elements. Additional archival spectra of this star
from several ground-based instruments allow us to derive abundances or upper
limits of 45 elements in HD 160617, including 27 elements produced by
neutron-capture reactions. The average abundances of the elements at the three
r-process peaks are similar to the predicted solar system r-process residuals
when scaled to the abundances in the rare earth element domain. This result for
arsenic and selenium may be surprising in light of predictions that the
production of the lightest r-process elements generally should be decoupled
from the heavier r-process elements.Comment: Published in the Astrophysical Journal (22 pages, 12 figures
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ĐŠĐ”Đ»Ń ŃĐ°Đ±ĐŸŃŃ Đ·Đ°ĐșĐ»ŃŃĐ°Đ”ŃŃŃ ĐČ ĐżŃĐŸĐČĐ”ĐŽĐ”ĐœĐžĐž Đ°ĐœĐ°Đ»ĐžĐ·Đ° ŃŃŃĐ”ĐșŃĐžĐČĐœĐŸŃŃĐž ĐŽĐ”ŃŃДлŃĐœĐŸŃŃĐž ĐżŃДЎпŃĐžŃŃĐžŃ, ĐŸĐșĐ°Đ·ŃĐČĐ°ŃŃĐ”ĐłĐŸ ŃŃĐ»ŃгО ĐČ ŃŃĐ”ŃĐ” ĐłĐŸŃŃĐžĐœĐžŃĐœĐŸĐłĐŸ Đ±ĐžĐ·ĐœĐ”ŃĐ° Đž ĐŸĐ±ŃĐ”ŃŃĐČĐ”ĐœĐœĐŸĐłĐŸ пОŃĐ°ĐœĐžŃ, ŃĐŸĐłĐ»Đ°ŃĐœĐŸ ŃпДŃĐžŃĐžĐșĐ” ĐżŃĐ°ĐșŃĐžŃĐ”ŃĐșĐžŃ
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Đ ĐżŃĐŸŃĐ”ŃŃĐ” ĐžŃŃĐ»Đ”ĐŽĐŸĐČĐ°ĐœĐžŃ ĐżŃĐŸĐČĐŸĐŽĐžĐ»ŃŃ Đ°ĐœĐ°Đ»ĐžĐ· ŃĐșĐŸĐœĐŸĐŒĐžŃĐ”ŃĐșĐžŃ
ĐżĐŸĐșĐ°Đ·Đ°ŃДлДĐč ŃŃŃĐ”ĐșŃĐžĐČĐœĐŸŃŃĐž ĐŽĐ”ŃŃДлŃĐœĐŸŃŃĐž ĐżŃДЎпŃĐžŃŃĐžŃ.This paper examines the financial performance of the enterprise services.
The purpose of the work is to conduct an analysis of the effectiveness of the company, providing services in the hotel business and catering, according to the specifics of practical data.
In the process of the study, an analysis of the economic performance indicators of the enterprise was carried out
Characterizing the Chemistry of the Milky Way Stellar Halo: Detailed Chemical Analysis of a Metal-Poor Stellar Stream
We present the results of a detailed abundance analysis of one of the
confirmed building blocks of the Milky Way stellar halo, a
kinematically-coherent metal-poor stellar stream. We have obtained high
resolution and high S/N spectra of 12 probable stream members using the MIKE
spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the
2dCoude spectrograph on the Smith Telescope at McDonald Observatory. We have
derived abundances or upper limits for 51 species of 46 elements in each of
these stars. The stream members show a range of metallicity (-3.4 < [Fe/H] <
-1.5) but are otherwise chemically homogeneous, with the same star-to-star
dispersion in [X/Fe] as the rest of the halo. This implies that, in principle,
a significant fraction of the Milky Way stellar halo could have formed from
accreted systems like the stream. The stream stars show minimal evolution in
the alpha or Fe-group elements over the range of metallicity. This stream is
enriched with material produced by the main and weak components of the rapid
neutron-capture process and shows no evidence for enrichment by the slow
neutron-capture process.Comment: v2: Removed references to M15 after learning that the source
kinematic data for M15 were incorrect in an earlier paper. M15 is not related
to this stream. (ApJ, accepted; 31 pages, 18 figures, 11 tables
The exposure of the hybrid detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays.
It consists of a surface array to measure secondary particles at ground level
and a fluorescence detector to measure the development of air showers in the
atmosphere above the array. The "hybrid" detection mode combines the
information from the two subsystems. We describe the determination of the
hybrid exposure for events observed by the fluorescence telescopes in
coincidence with at least one water-Cherenkov detector of the surface array. A
detailed knowledge of the time dependence of the detection operations is
crucial for an accurate evaluation of the exposure. We discuss the relevance of
monitoring data collected during operations, such as the status of the
fluorescence detector, background light and atmospheric conditions, that are
used in both simulation and reconstruction.Comment: Paper accepted by Astroparticle Physic
Measurement of the Depth of Maximum of Extensive Air Showers above 10^18 eV
We describe the measurement of the depth of maximum, Xmax, of the
longitudinal development of air showers induced by cosmic rays. Almost four
thousand events above 10^18 eV observed by the fluorescence detector of the
Pierre Auger Observatory in coincidence with at least one surface detector
station are selected for the analysis. The average shower maximum was found to
evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/-
0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured
shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The
interpretation of these results in terms of the cosmic ray mass composition is
briefly discussed.Comment: Accepted for publication by PR
The Pierre Auger Observatory III: Other Astrophysical Observations
Astrophysical observations of ultra-high-energy cosmic rays with the Pierre
Auger ObservatoryComment: Contributions to the 32nd International Cosmic Ray Conference,
Beijing, China, August 201
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