2,335,556 research outputs found
Vacuum-Ultraviolet negative photoion spectroscopy of SF5Cl
Using vacuum-UV radiation from a synchrotron, gas-phase negative ions are detected by mass spectrometry following photoexcitation of SFCl. F, Cl and SFare observed, and their ion yields recorded in the range 8-30 eV. F and Cl show a linear dependence of signal with pressure, showing that they arise from unimolecular ion-pair dissociation, generically written AB + h C + D (+ neutral(s)). F is the strongest signal, and absolute cross sections are determined by calibrating the signal intensity with that of F from SF and CF. Resonances are observed, and assigned to transitions to Rydberg states of SFCl. The Cl signal is much weaker, despite the S-Cl bond being significantly weaker than the S-F bond. Appearance energies for F and Cl of 12.7 Β± 0.2 and 10.6 Β± 0.2 eV are determined. The spectra suggest that these ions form indirectly by crossing of Rydberg states of SFCl onto an ion-pair continuum
An approximation theorem for nuclear operator systems
We prove that an operator system is nuclear in the category of
operator systems if and only if there exist nets of unital completely positive
maps \phi_\lambda : \cl S \to M_{n_\lambda} and \psi_\lambda : M_{n_\lambda}
\to \cl S such that converges to {\rm
id}_{\cl S} in the point-norm topology. Our proof is independent of the
Choi-Effros-Kirchberg characterization of nuclear -algebras and yields
this characterization as a corollary. We give an example of a nuclear operator
system that is not completely order isomorphic to a unital -algebra.Comment: 10 pages; to appear in JF
On the determinant bundles of abelian schemes
Let \pi:\CA\ra S be an abelian scheme over a scheme which is
quasi-projective over an affine noetherian scheme and let \CL be a symmetric,
rigidified, relatively ample line bundle on \CA. We show that there is an
isomorphism
\det(\pi_*\CL)^{\o times 24}\simeq\big(\pi_*\omega_{\CA}^{\vee}\big)^{\o
times 12d}
of line bundles on , where is the rank of the (locally free) sheaf
\pi_*\CL. We also show that the numbers 24 and are sharp in the
following sense: if is a common divisor of 12 and 24, then there are data
as above such that
\det(\pi_*\CL)^{\o times
(24/N)}\not\simeq\big(\pi_*\omega_{\CA}^{\vee}\big)^{\o times (12d/N)}.Comment: 8 page
Rate constants and Arrhenius parameters for the reactions of OH radicals and Cl atoms with CF3CH2OCHF2, CF3CHClOCHF2 and CF3CH2OCClF2, using the discharge-flow/resonance fluorescence method
Rate constants have been determined for the reactions of OH radicals and Cl atoms with the three partially halogenated methyl-ethyl ethers, CFCHOCHF, CFCHClOCHF and CFCHOCClF, using discharge-flow techniques to generate the OH radicals and the Cl atoms and resonance fluorescence to observe changes in their relative concentrations in the presence of added ether. For each combination of radical and ether, experiments were carried out at three temperatures between 292 and 410 K, yielding the following Arrhenius expressions for the rate constants within this range of temperature:
OH + CFCHOCHF: = (2.00.8) 10 exp( β 2110 150 K / T) cm molecule s
OH + CFCHClOCHF: = (4.5 1.3) 10 exp( β 940 100 K / T) cm molecule s
OH + CFCHOCClF: = (1.6 0.6) 10 exp( β 1100 125 K / T) cm molecule s
Cl + CFCHOCHF: = (6.1 1.4) 10 exp( β 1830 90 K / T) cm molecule s
Cl + CFCHClOCHF: = (7.8 2.6) 10 exp( β 2980 130 K / T) cm molecule s
Cl + CFCHOCClF: = (2.2 0.2) 10 exp( β 2700 40 K / T) cm molecule s
The results are compared with those obtained previously for the same and related reactions of OH radicals and Cl atoms, and the atmospheric implications of the results are considered briefly
Orbital Configurations and Magnetic Properties of Double-Layered Antiferromagnet CsCuClBr
We report the single-crystal X-ray analysis and magnetic properties of a new
double-layered perovskite antiferromagnet, CsCuClBr. This
structure is composed of CuClBr double layers with elongated
CuClBr octahedra and is closely related to the SrTiO
structure. An as-grown crystal has a singlet ground state with a large
excitation gap of K, due to the strong
antiferromagnetic interaction between the two layers. CsCuClBr
undergoes a structural phase transition at K accompanied
by changes in the orbital configurations of Cu ions. Once a
CsCuClBr crystal is heated above , its magnetic
susceptibility obeys the Curie-Weiss law with decreasing temperature even below
and does not exhibit anomalies at . This implies that in
the heated crystal, the orbital state of the high-temperature phase remains
unchanged below , and thus, this orbital state is the metastable
state. The structural phase transition at is characterized as an
order-disorder transition of Cu orbitals.Comment: 6pages. 6figures, to appear in J. Phys. Soc. Jpn. Vol.76 No.
Solvent drag measurement of transcellular and basolateral membrane NaCl reflection coefficient in kidney proximal tubule.
The NaCl reflection coefficient in proximal tubule has important implications for the mechanisms of near isosmotic volume reabsorption. A new fluorescence method was developed and applied to measure the transepithelial (sigma NaClTE) and basolateral membrane (sigma NaClcl) NaCl reflection coefficients in the isolated proximal straight tubule from rabbit kidney. For sigma NaClTE measurement, tubules were perfused with buffers containing 0 Cl, the Cl-sensitive fluorescent indicator 6-methoxy-N-[3-sulfopropyl] quinolinium and a Cl-insensitive indicator fluorescein sulfonate, and bathed in buffers of differing cryoscopic osmolalities containing NaCl. The transepithelial Cl gradient along the length of the tubule was measured in the steady state by a quantitative ratio imaging technique. A mathematical model based on the Kedem-Katchalsky equations was developed to calculate the axial profile of [Cl] from tubule geometry, lumen flow, water (Pf) and NaCl (PNaCl) permeabilities, and sigma NaClTE. A fit of experimental results to the model gave PNaCl = (2.25 +/- 0.2) x 10(-5) cm/s and sigma NaClTE = 0.98 +/- 0.03 at 23 degrees C. For measurement of sigma NaClbl, tubule cells were loaded with SPQ in the absence of Cl. NaCl solvent drag was measured from the time course of NaCl influx in response to rapid (less than 1 s) Cl addition to the bath solution. With bath-to-cell cryoscopic osmotic gradients of 0, -60, and +30 mosmol, initial Cl influx was 1.23, 1.10, and 1.25 mM/s; a fit to a mathematical model gave sigma NaClbl = 0.97 +/- 0.04. These results indicate absence of NaCl solvent drag in rabbit proximal tubule. The implications of these findings for water and NaCl movement in proximal tubule are evaluated
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