2,326 research outputs found
Investigation of thermodynamic mechanisms for the production of complex compounds essential for the origin of life Final report, 1 Oct. 1965 - 30 Sep. 1966
Thermodynamic equilibria in planetary atmospheres and in origin of organic matter - determination of amino acid pairing and sequences in protein
Investigation of thermodynamic mechanisms for the production of compounds essential for the origin of life First quarter technical report, Oct. 1 - Dec. 31, 1965
Expected thermodynamic equilibrium composition calculated for atmospheres of Earth, Venus, Mars, and Jupite
Semantic Support for Automated Negotiation with Alliances
Companies can form alliances on the Internet to aggregate buying or selling power and create value. More concretely, together resources are shared or new possibilities are exploited that cannot be exploited individually. Most alliances are formed as a result of a negotiation process between the companies that form an alliance. This paper proposes a software framework that enables automated negotiation between alliances. Our framework allows for the semantic description of negotiation objects and their attributes, and provides a mean for the exchange of negotiation messages unambiguously interpretable by all parties involved. The proposed framework supports ad-hoc alliances by allowing parties with a common interest to negotiate on the proposal they want to make to other market participants first
The temperature and chronology of heavy-element synthesis in low-mass stars
Roughly half of the heavy elements (atomic mass greater than that of iron)
are believed to be synthesized in the late evolutionary stages of stars with
masses between 0.8 and 8 solar masses. Deep inside the star, nuclei (mainly
iron) capture neutrons and progressively build up (through the
slow-neutron-capture process, or s-process) heavier elements that are
subsequently brought to the stellar surface by convection. Two neutron sources,
activated at distinct temperatures, have been proposed: 13C and 22Ne, each
releasing one neutron per alpha-particle (4He) captured. To explain the
measured stellar abundances, stellar evolution models invoking the 13C neutron
source (which operates at temperatures of about one hundred million kelvin) are
favoured. Isotopic ratios in primitive meteorites, however, reflecting
nucleosynthesis in the previous generations of stars that contributed material
to the Solar System, point to higher temperatures (more than three hundred
million kelvin), requiring at least a late activation of 22Ne. Here we report a
determination of the s-process temperature directly in evolved low-mass giant
stars, using zirconium and niobium abundances, independently of stellar
evolution models. The derived temperature supports 13C as the s-process neutron
source. The radioactive pair 93Zr-93Nb used to estimate the s-process
temperature also provides, together with the pair 99Tc-99Ru, chronometric
information on the time elapsed since the start of the s-process, which we
determine to be one million to three million years.Comment: 30 pages, 10 figure
Late-Time Optical and UV Spectra of SN 1979C and SN 1980K
A low-dispersion Keck I spectrum of SN 1980K taken in August 1995 (t = 14.8
yr after explosion) and a November 1997 MDM spectrum (t = 17.0 yr) show broad
5500 km s^{-1} emission lines of H\alpha, [O I] 6300,6364 A, and [O II]
7319,7330 A. Weaker but similarly broad lines detected include [Fe II] 7155 A,
[S II] 4068,4072 A, and a blend of [Fe II] lines at 5050--5400 A. The presence
of strong [S II] 4068,4072 A emission but a lack of [S II] 6716,6731 A emission
suggests electron densities of 10^{5-6} cm^{-3}. From the 1997 spectra, we
estimate an H\alpha flux of 1.3 \pm 0.2 \times 10^{-15} erg cm^{-2} s^{-1}
indicating a 25% decline from 1987--1992 levels during the period 1994 to 1997,
possibly related to a reported decrease in its nonthermal radio emission.Comment: 21 pages, 8 figures, submitted to the Astronomical Journa
Resonances, instabilities, and structure selection of driven Josephson lattice in layered superconductors
We investigate dynamics of Josephson vortex lattice in layered high T
superconductors at high magnetic fields. It is shown that the average electric
current depends on the lattice structure and is resonantly enhanced when the
Josephson frequency matches the frequency of the plasma mode. We find the
stability regions of moving lattice. It is shown that a specific lattice
structure at given velocity is uniquely selected by the boundary conditions: at
small velocities periodic triangular lattice is stable and looses its stability
at some critical velocity. At even higher velocities a structure close to a
rectangular lattice is restored.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
Routine activities and proactive police activity: a macro-scale analysis of police searches in London and New York City
This paper explored how city-level changes in routine activities were associated with changes in frequencies of police searches using six years of police records from the London Metropolitan Police Service and the New York City Police Department. Routine activities were operationalised through selecting events that potentially impacted on (a) the street population, (b) the frequency of crime or (c) the level of police activity. OLS regression results indicated that routine activity variables (e.g. day of the week, periods of high demand for police service) can explain a large proportion of the variance in search frequency throughout the year. A complex set of results emerged, revealing cross-national dissimilarities and the differential impact of certain activities (e.g. public holidays). Importantly, temporal frequencies in searches are not reducible to associations between searches and recorded street crime, nor changes in on-street population. Based on the routine activity approach, a theoretical police-action model is proposed
Mass ratio from Doppler beaming and R{\o}mer delay versus ellipsoidal modulation in the Kepler data of KOI-74
We present a light curve analysis and radial velocity study of KOI-74, an
eclipsing A star + white dwarf binary with a 5.2 day orbit. Aside from new
spectroscopy covering the orbit of the system, we used 212 days of publicly
available Kepler observations and present the first complete light curve
fitting to these data, modelling the eclipses and transits, ellipsoidal
modulation, reflection, and Doppler beaming. Markov Chain Monte Carlo
simulations are used to determine the system parameters and uncertainty
estimates. Our results are in agreement with earlier studies, except that we
find an inclination of 87.0 \pm 0.4\degree, which is significantly lower than
the previously published value. We find that the mass ratio derived from the
radial velocity amplitude (q=0.104 \pm 0.004) disagrees with that derived from
the ellipsoidal modulation (q=0.052 \pm 0.004} assuming corotation). This was
found before, but with our smaller inclination, the discrepancy is even larger
than previously reported. Accounting for the rapid rotation of the A-star is
found to increase the discrepancy even further by lowering the mass ratio to
q=0.047 \pm 0.004. These results indicate that one has to be extremely careful
in using the amplitude of an ellipsoidal modulation signal in a close binary to
determine the mass ratio, when a proof of corotation is not firmly established.
The radial velocities that can be inferred from the detected Doppler beaming in
the light curve are found to be in agreement with our spectroscopic radial
velocity determination. We also report the first measurement of R{\o}mer delay
in a light curve of a compact binary. This delay amounts to -56 \pm 17 s and is
consistent with the mass ratio derived from the radial velocity amplitude. The
firm establishment of this mass ratio at q=0.104 \pm 0.004 leaves little doubt
that the companion of KOI-74 is a low mass white dwarf.Comment: 9 pages, 7 figures, 2 tables; accepted for publication in MNRA
A Critical Examination of Spatial Biases Between MODIS and MISR Aerosol Products - Application for Potential AERONET Deployment
AErosol RObotic NETwork (AERONET) data are the primary benchmark for evaluating satellite-retrieved aerosol properties. However, despite its extensive coverage, the representativeness of the AERONET data is rarely discussed. Indeed, many studies have shown that satellite retrieval biases have a significant degree of spatial correlation that may be problematic for higher-level processes or inverse-emissions-modeling studies. To consider these issues and evaluate relative performance in regions of few surface observations, cross-comparisons between the Aerosol Optical Depth (AOD) products of operational MODIS Collection 5.1 Dark Target (DT) and operational MODIS Collection 5.1 Deep Blue (DB) with MISR version 22 were conducted. Through such comparisons, we can observe coherent spatial features of the AOD bias while side-stepping the full analysis required for determining when or where either retrieval is more correct. We identify regions where MODIS to MISR AOD ratios were found to be above 1.4 and below 0.7. Regions where lower boundary condition uncertainty is likely to be a dominant factor include portions of Western North America, the Andes mountains, Saharan Africa, the Arabian Peninsula, and Central Asia. Similarly, microphysical biases may be an issue in South America, and specific parts of Southern Africa, India Asia, East Asia, and Indonesia. These results help identify high-priority locations for possible future deployments of both in situ and ground based remote sensing measurements. The Supplement includes a km1 file
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