2,157 research outputs found
Isotopic composition of Murchison organic compounds: Intramolecular carbon isotope fractionation of acetic acid. Simulation studies of cosmochemical organic syntheses
Recently, in our laboratories, samples of Murchison acetic acid were decarboxylated successfully and the carbon isotopic composition was measured for the methane released by this procedure. These analyses showed significant differences in C-13/C-12 ratios for the methyl and carboxyl carbons of the acetic acid molecule, strongly suggesting that more than one carbon source may be involved in the synthesis of the Murchison organic compounds. On the basis of this finding, laboratory model systems simulating cosmochemical synthesis are being studied, especially those processes capable of involving two or more starting carbon sources
Stable hydrogen and carbon isotope ratios of extractable hydrocarbons in the Murchison meteorite
A fairly fool-proof method to ensure that the compounds isolated from meteorites are truly part of the meteorites and not an artifact introduced by exposure to the terrestrial environment, storage, or handling is presented. The stable carbon and hydrogen isotope ratios in several of the chemical compounds extracted from the Murchison meteorite were measured. The results obtained by studying the amino acids in this meteorite gave very unusual hydrogen and carbon isotope ratios. The technique was extended to the different classes of hydrocarbons and the hydrocarbons were isolated using a variety of separation techniques. The results and methods used in this investigation are described in this two page paper
Cosmic Rays at the Highest Energies -- First Data from the Pierre Auger Observatory --
The southern Pierre Auger Observatory, presently under construction in
Malarg"ue, Argentina, is nearing completion. The instrument is designed to
measure extensive air-showers with energies ranging from - eV
and beyond. It combines two complementary observation techniques; the detection
of particles at ground and the coincident observation of associated
fluorescence light generated in the atmosphere above the ground. This is being
realized by employing an array of 1600 water Cherenkov detectors, distributed
over an area of 3000 km, and operating 24 wide-angle Schmidt telescopes,
positioned at four sites at the border of the ground array. The Observatory
will reach its full size only in 2007 but data are routinely recorded already
and have started to provide relevant science results. This talk will focus on
the detector characterizations and presents first results on the arrival
direction of extremely-high energy cosmic rays, their energy spectrum, and on
the upper limit of the photon fraction.Comment: Invited paper presented at the International Symposium on Heavy Ion
Physics 2006 (ISHIP 2006), Heavy Ion Physics - Gateway to the Unknown:
Complex Structures in Elementary Matter, April 3-6, 2006 Frankfurt am Main,
Germany; 13 pages, 7 figure
Reaction Operator Approach to Multiple Elastic Scatterings
We apply the GLV Reaction Operator formalism to compute the effects of
multiple elastic scatterings of jets propagating through dense matter. We
derive the elastic Reaction Operator and demonstrate that the recursion
relations have a closed form solution that reduces to the familiar Glauber
form. We also investigate the accuracy of the Gaussian dipole approximation for
jet transverse momentum broadening.Comment: 9 pages, 4 .ps figures. Uses REVTeX and bbox.st
Glory Oscillations in the Index of Refraction for Matter-Waves
We have measured the index of refraction for sodium de Broglie waves in gases
of Ar, Kr, Xe, and nitrogen over a wide range of sodium velocities. We observe
glory oscillations -- a velocity-dependent oscillation in the forward
scattering amplitude. An atom interferometer was used to observe glory
oscillations in the phase shift caused by the collision, which are larger than
glory oscillations observed in the cross section. The glory oscillations depend
sensitively on the shape of the interatomic potential, allowing us to
discriminate among various predictions for these potentials, none of which
completely agrees with our measurements
Efficient NiII2LnIII2 electrocyclization catalysts for the synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary or secondary amines
A series of heterometallic coordination clusters (CCs) [NiII2LnIII2(L1)4Cl2(CH3CN)2] 2CH3CN [Ln = Y (1Y), Sm (1Sm), Eu (1Eu), Gd (1Gd), or Tb (1Tb)] were synthesized by the reaction of (E)-2-(2-hydroxy-3-methoxybenzylidene-amino)phenol) (H2L1) with NiCl2·6(H2O) and LnCl3·x(H2O) in the presence of Et3N at room temperature. These air-stable CCs can be obtained in very high yields from commercially available materials and are efficient catalysts for the room-temperature domino ring-opening electrocyclization synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary or secondary amines under a non-inert atmosphere. Structural modification of the catalyst to achieve immobilization or photosensitivity is possible without deterioration in catalytic activity
Vesiculation and Quenching During Surtseyan Eruptions at Hunga Tonga-Hunga Ha'apai Volcano, Tonga
Surtseyan eruptions are shallow to emergent subaqueous explosive eruptions that owe much of their characteristic behavior to the interaction of magma with water. The difference in thermal properties between water and air affects the cooling and postfragmentation vesiculation processes in magma erupted into the water column. Here we study the vesiculation and cooling processes during the 2009 and 2014–2015 Surtseyan eruptions of Hunga Tonga‐Hunga Ha'apai volcano by combining 2‐D and 3‐D vesicle‐scale analyses of lapilli and bombs and numerical thermal modeling. Most of the lapilli and bombs show gradual textural variations from rim to core. The vesicle connectivity in the lapilli and bombs increases with vesicularity from fully isolated to completely connected and also increases from rim to core in transitional clasts. We interpret the gradual textural variations and the connectivity‐vesicularity relationships as the result of postfragmentation bubble growth and coalescence interrupted at different stages by quenching in water. The measured vesicle size distributions are bimodal with a population of small and large vesicles. We interpret this bimodality as the result of two nucleation events, one prefragmentation with the nucleation and growth of large bubbles and one postfragmentation with nucleation of small vesicles. We link the thermal model with the textural variations in the clasts—showing a dependence on particle size, Leidenfrost effect, and initial melt temperature. In particular, the cooling profiles in the bombs are consistent with the gradual textural variations from rim to core in the clasts, likely caused by variations in time available for vesiculation before quenching
Magnetars in the Metagalaxy: An Origin for Ultra High Energy Cosmic Rays in the Nearby Universe
I show that the relativistic winds of newly born magnetars with khz initial
spin rates, occurring in all normal galaxies, can accelerate ultrarelativistic
light ions with an E^{-1} injection spectrum, steepening to E^{-2} at higher
energies, with an upper cutoff above 10^{21} eV. Interactions with the CMB
yield a spectrum in good accord with the observed spectrum of Ultra-High Energy
Cosmic Rays (UHECR), if ~ 5-10% of the magnetars are born with voltages
sufficiently high to accelerate the UHECR. The form the spectrum spectrum takes
depends on the gravitational wave losses during the magnetars' early spindown -
pure electromagnetic spindown yields a flattening of the E^3 J(E) spectrum
below 10^{20} eV, while a moderate GZK ``cutoff'' appears if gravitational wave
losses are strong enough. I outline the physics such that the high energy
particles escape with small energy losses from a magnetar's natal supernova,
including Rayleigh-Taylor ``shredding'' of the supernova envelope, expansion of
a relativistic blast wave into the interstellar medium, acceleration of the UHE
ions through surf-riding in the electromgnetic fields of the wind, and escape
of the UHE ions in the rotational equator with negligible radiation loss. The
abundance of interstellar supershells and unusually large supernova remnants
suggests that most of the initial spindown energy is radiated in khz
gravitational waves for several hours after each supernova, with effective
strains from sources at typical distances ~ 3 x 10^{-21}. Such bursts of
gravitational radiation should correlate with bursts of ultra-high energy
particles. The Auger experiment should see such bursts every few years.Comment: 49 pages, 2 Figures, LaTeX (aastex, epsfig, graphicx, float), to be
published June 1, 2003 in the ApJ. Corrected discussion of electromagnetic
surf-riding as the acceleration mechanism and more typos, and reference
Electromagnetic corrections in eta --> 3 pi decays
We re-evaluate the electromagnetic corrections to eta --> 3 pi decays at
next-to-leading order in the chiral expansion, arguing that effects of order
e^2(m_u-m_d) disregarded so far are not negligible compared to other
contributions of order e^2 times a light quark mass. Despite the appearance of
the Coulomb pole in eta --> pi+ pi- pi0 and cusps in eta --> 3 pi0, the overall
corrections remain small.Comment: 21 pages, 11 figures; references updated, version published in EPJ
Updated Measurement of the Strong Phase in D0 --> K+pi- Decay Using Quantum Correlations in e+e- --> D0 D0bar at CLEO
We analyze a sample of 3 million quantum-correlated D0 D0bar pairs from 818
pb^-1 of e+e- collision data collected with the CLEO-c detector at E_cm = 3.77
GeV, to give an updated measurement of \cos\delta and a first determination of
\sin\delta, where \delta is the relative strong phase between doubly
Cabibbo-suppressed D0 --> K+pi- and Cabibbo-favored D0bar --> K+pi- decay
amplitudes. With no inputs from other experiments, we find \cos\delta = 0.81
+0.22+0.07 -0.18-0.05, \sin\delta = -0.01 +- 0.41 +- 0.04, and |\delta| = 10
+28+13 -53-0 degrees. By including external measurements of mixing parameters,
we find alternative values of \cos\delta = 1.15 +0.19+0.00 -0.17-0.08,
\sin\delta = 0.56 +0.32+0.21 -0.31-0.20, and \delta = (18 +11-17) degrees. Our
results can be used to improve the world average uncertainty on the mixing
parameter y by approximately 10%.Comment: Minor revisions, version accepted by PR
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