3,010 research outputs found
Temperature Evolution of Sodium Nitrite Structure in a Restricted Geometry
The NaNO nanocomposite ferroelectric material in porous glass was
studied by neutron diffraction. For the first time the details of the crystal
structure including positions and anisotropic thermal parameters were
determined for the solid material, embedded in a porous matrix, in ferro- and
paraelectric phases. It is demonstrated that in the ferroelectric phase the
structure is consistent with bulk data but above transition temperature the
giant growth of amplitudes of thermal vibrations is observed, resulting in the
formation of a "premelted state". Such a conclusion is in a good agreement with
the results of dielectric measurements published earlier.Comment: 4 pages, 4 figure
Interferometry of Direct Photons in Central 280Pb+208Pb Collisions at 158A GeV
Two-particle correlations of direct photons were measured in central
208Pb+208Pb collisions at 158 AGeV. The invariant interferometric radii were
extracted for 100<K_T<300 MeV/c and compared to radii extracted from charged
pion correlations. The yield of soft direct photons, K_T<300 MeV/c, was
extracted from the correlation strength and compared to theoretical
calculations.Comment: 5 pages, 4 figure
Systematics of Inclusive Photon Production in 158 AGeV Pb Induced Reactions on Ni, Nb, and Pb Targets
The multiplicity of inclusive photons has been measured on an event-by-event
basis for 158 AGeV Pb induced reactions on Ni, Nb, and Pb targets. The
systematics of the pseudorapidity densities at midrapidity (rho_max) and the
width of the pseudorapidity distributions have been studied for varying
centralities for these collisions. A power law fit to the photon yield as a
function of the number of participating nucleons gives a value of 1.13+-0.03
for the exponent. The mean transverse momentum, , of photons determined
from the ratio of the measured electromagnetic transverse energy and photon
multiplicity, remains almost constant with increasing rho_max. Results are
compared with model predictions.Comment: 16 pages including 4 figure
Scaling of Particle and Transverse Energy Production in 208Pb+208Pb collisions at 158 A GeV
Transverse energy, charged particle pseudorapidity distributions and photon
transverse momentum spectra have been studied as a function of the number of
participants (N_{part}) and the number of binary nucleon-nucleon collisions
(N_{coll}) in 158 A GeV Pb+Pb collisions over a wide impact parameter range. A
scaling of the transverse energy pseudorapidity density at midrapidity as
N_{part}^{1.08 \pm 0.06} and N_{coll}^{0.83 \pm 0.05} is observed. For the
charged particle pseudorapidity density at midrapidity we find a scaling as
N_{part}^{1.07 \pm 0.04} and N_{coll}^{0.82 \pm 0.03}. This faster than linear
scaling with N_{part} indicates a violation of the naive Wounded Nucleon Model.Comment: 13 pages, 16 figures, submitted to European Physical Journal C
(revised results for scaling exponents
Synthesis and study of Cu<sup>II</sup> complex with nitroxide, a jumping crystal analog
© 2017, Springer Science+Business Media, LLC. We synthesized 1-ethylimidazolyl-substituted nitronyl nitroxides, i.e., 2-(1-ethylimidazol-4-yl)- (L 4Et ) and 2-(1-ethylimidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide-1-oxyl (L 5Et ). The stable radical L 5Et is an ethyl analog of 2-(1-methylimidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide-1-oxyl (L 5Me ) described earlier, the reaction of which with Cu(hfac) 2 (hfac is 1,1,1,5,5,5-hexafluoropentane-2,4-dionate) leads to the formation of the [Cu(hfac) 2 (L 5Me ) 2 ] jumping crystals. The reaction of Cu(hfac) 2 with L 5Et with reagent ratios 1: 2 and 1: 1 yields heterospin complexes [Cu(hfac) 2 (L 5Et ) 2 ] and [Cu(hfac) 2 L 5Et ] 2 , respectively. X-ray diffraction study of the mononuclear complex [Cu(hfac) 2 (L 5Et ) 2 ] determined that the compound has a packing similar to that of jumping crystals studied earlier, with the only difference being that the O..O contacts between neigh- boring nitroxide groups were found to be 0.3—0.5 Å longer than in [Cu(hfac) 2 (L 5Me ) 2 ]. As a result of the lengthening of these contacts, [Cu(hfac) 2 (L 5Et ) 2 ] crystals lack chemomechanical activi- ty. We found that when cooling crystals of binuclear complex [Cu(hfac) 2 L 5Et ] 2 below 50 K, the antiferromagnetic exchange between unpaired electrons of the > N—•O groups of neighboring molecules leads to the full spin-pairing of the nitroxides, with only the Cu 2+ ions contributing to the residual paramagnetism of the compound
Search for DCC in 158A GeV Pb+Pb Collisions
A detailed analysis of the phase space distributions of charged particles and
photons have been carried out using two independent methods. The results
indicate the presence of nonstatistical fluctuations in localized regions of
phase space.Comment: Talk at the PANIC99 Conference, June 9-16, 199
Centrality Dependence of Neutral Pion Production in 158 A GeV Pb + Pb Collisions
The production of neutral pions in 158AGeV Pb+Pb collisions has been studied
in the WA98 experiment at the CERN SPS. Transverse momentum spectra are studied
for the range 0.3 GeV/c < mT-m0 < 4.0 GeV/c. The results for central collisions
are compared to various models. The centrality dependence of the neutral pion
spectral shape and yield is investigated. An invariance of the spectral shape
and a simple scaling of the yield with the number of participating nucleons is
observed for centralities with greater than about 30 participating nucleons
which is most naturally explained by assuming an equilibrated system.Comment: 5 pages, Latex, including 3 eps figures, submitted to Phys.Rev.Lett;
updated pQCD comparison due to new input from the author, updated references,
corrected plotting error in figure
Suppression of High-p_T Neutral Pion Production in Central Pb+Pb Collisions at sqrt{s_NN} = 17.3 GeV Relative to p+C and p+Pb Collisions
Neutral pion transverse momentum spectra were measured in p+C and p+Pb
collisions at sqrt{s_NN} = 17.4 GeV at mid-rapidity 2.3 < eta_lab < 3.0 over
the range 0.7< p_T < 3.5 GeV/c. The spectra are compared to pi0 spectra
measured in Pb+Pb collisions at sqrt{s_NN} = 17.3 GeV in the same experiment.
For a wide range of Pb+Pb centralities (N_part < 300) the yield of pi0's with
p_T > 2 GeV/c is larger than or consistent with the p+C or p+Pb yields scaled
with the number of nucleon-nucleon collisions (N_coll), while for central Pb+Pb
collisions with N_part > 350 the pi0 yield is suppressed.Comment: 5 pages, 4 figure
New Potentialities for Utilization of Associated Petroleum Gases in Power Generation and Chemicals Production
New possibilities for the utilization of associated petroleum gases (APG) and monetization of small-scale and remote Natural Gas resources by power generation and chemicals production are considered and tested. One possibility is the oxy-cracking of APG. This technology allows selective transformation of heavier hydrocarbons that have low octane (methane) numbers and inclined to soot and tar formation, into lighter compounds with higher octane numbers, thus producing gas suitable to feed different types of power engines. Another possibility is the small-scale conversion of APG to syngas to produce more easily transportable and more valuable chemicals or liquid fuels via well-known Fischer–Tropsch process or catalytic synthesis of methanol. For this purpose we have suggested principally new technology for natural gases conversion into syngas, based on the use of 3D (volumetric) matrixes. It allows the relative simple and very compact non-catalytic reformers to be designed for small-scale gas-to liquid (GTL) technologies. Their main advantages are autothermal character of the process without any need in additional heating or power supply, absence of catalyst that allows processing hydrocarbon gases of practically any composition, including APG, without additional pretreatment, very high specific volume capacity, at any rate 10 times higher than that of steam reforming, and simplicity in construction and operation
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