933,301 research outputs found
Biomass-supported catalysts on Desulfovibrio desulfuricans and Rhodobacter sphaeroides
A Rhodobacter sphaeroides-supported dried, ground palladium catalyst (‘‘Rs-Pd(0)’’) was compared with a Desulfovibrio desulfuricans-supported catalyst (‘‘Dd-Pd(0)’’)and with unsupported palladium metal particles made by reduction under H2 (‘‘Chem-Pd(0)’’). Cell surface-located clusters of Pd(0) nanoparticles were detected on both D. desulfuricans and R. sphaeroides but the size and location of deposits differed among comparably loaded preparations.\ud
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These differences may underlie the observation of different activities of Dd-Pd(0) and Rs-Pd(0) when compared with respect to their ability to promote hydrogen release from hypophosphite and to catalyze chloride release from chlorinated aromatic compounds. Dd-Pd(0) was more effective in the reductive dehalogenation of polychlorinated biphenyls (PCBs), whereas Rs-Pd(0) was more effective in the initial dehalogenation of pentachlorophenol (PCP) although the rate of chloride release from PCP was comparable with both preparations after 2 h
EXAFS studies on the reduction of palladium(II) in X zeolites
Palladium tetraammine ion exchange into zeolite, temperature treatments under
different atmospheres, and hydrogen reduction have been studied by EXAFS at
the Pd Κ edge. Complete autoreduction is found to take place between 473 and
623 Κ under vacuum.
Α bidisperse Pd metal phase is formed which agglomerates
at the expense of the small particles upon prolonged heating at 623 Κ. In
contrast, a similar treatment under oxygen suppresses autoreduction , and the
Pd cations remain in zeolite coordination sites. Additional small amounts of
palladium oxide are observed under these conditions. If hydrogen is admitted
to the dehydrated, ionic system at 295 K. the oxygen coordination of the Pd
disappears and evidence is obtained for the formation of Pd(0) dimers that
interact with the framework via a long Pd-0 bond
Dynamics of diproton formation in the and reactions in the GeV region
Mechanisms for the production of diproton pairs, , in the
reaction are studied at proton beam energies 0.5 -- 2 GeV in
kinematics similar to those of backward elastic scattering. This reaction
provides valuable information on the short-range and interactions
that is complementary to that investigated in the well known and
processes. The reaction is related to the
subprocesses and using two different
one--pion--exchange (OPE) diagrams. Within both these models a reasonable
agreement could be obtained with the data below 1GeV. The similar energy
dependence of the and cross sections and the small
ratio of about 1.5% in the production of to deuteron final states
follow naturally within the OPE models.Comment: 10 pages, 7 figures, Late
Phase separation and valence instabilities in cuprate superconductors. Effective one-band model approach
We study the Cu-O valence instability (VI) and the related phase separation
(PS) driven by Cu-O nearest-neighbor repulsion , using an effective
extended one-band Hubbard model () obtained from the extended
three-bandHubbard model, through an appropriate low-energy reduction.
is solved by exact diagonalization of a square cluster with 10 unit cells and
also within a slave-boson mean-field theory. Its parameters depend on doping
for or on-site O repulsion . The results using both
techniques coincide in that there is neither VI nor PS for doping levels
if eV. The PS region begins for eV
at large doping and increases with increasing . The PS also
increases with increasing on-site Cu repulsion .Comment: 16 pages and 10 figures in postscript format, compressed with uufile
Pinning Down versus Density
The pinning down number of a topological space is the smallest
cardinal such that for any neighborhood assignment
there is a set with for all . Clearly, c.
Here we prove that the following statements are equivalent:
(1) for each cardinal ;
(2) for each Hausdorff space ;
(3) for each 0-dimensional Hausdorff space .
This answers two questions of Banakh and Ravsky.
The dispersion character of a space is the smallest
cardinality of a non-empty open subset of . We also show that if
then has an open subspace with and
, moreover the following three statements are equiconsistent:
(i) There is a singular cardinal with , i.e.
Shelah's Strong Hypothesis fails;
(ii) there is a 0-dimensional Hausdorff space such that
is a regular cardinal and ;
(iii) there is a topological space such that is a regular
cardinal and .
We also prove that
for any locally compact Hausdorff space ;
for every Hausdorff space we have and
implies ;
for every regular space we have and moreover implies
Exclusive Measurements of : the Effect Revisited
Exclusive measurements of the reactions and
have been carried out at GeV at the
CELSIUS storage ring using the WASA detector. The channel
evidences a pronounced enhancement at low invariant masses - as
anticipated from previous inclusive measurements of the ABC effect. This
enhancement is seen to be even much larger in the isoscalar
channel. The differential distributions prove this enhancement to be of
scalar-isoscalar nature. calculations give a good description of
the data, if a boundstate condition is imposed for the intermediate
system.Comment: extended version, 8 pages, 7 figures, theoretical model calculations
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