182 research outputs found
Best constants in Rosenthal-type inequalities and the Kruglov operator
Let be a symmetric Banach function space on with the Kruglov
property, and let , be an arbitrary
sequence of independent random variables in . This paper presents sharp
estimates in the deterministic characterization of the quantities
in terms of the sum of disjoint copies of individual terms of
. Our method is novel and based on the important recent advances in
the study of the Kruglov property through an operator approach made earlier by
the authors. In particular, we discover that the sharp constants in the
characterization above are equivalent to the norm of the Kruglov operator in
.Comment: Published in at http://dx.doi.org/10.1214/10-AOP529 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Design, Synthesis, and Structure of Copper Dithione Complexes: Redox‐Dependent Charge Transfer
Redox‐active ligands impart versatility in transition metal complexes, which are attractive for photosensitizers, dye sensitized solar cells, photothermal therapy, etc. Dithiolene (Dt) ligands can transition between fully reduced and fully oxidized states. Herein, we report the syntheses, characterization, crystal structures and electronic properties of four [Cu(R2Dt0)2]+/2+ (R = Me, iPr) complexes, [Cu(iPr2Dt0)2][PF6] (1a), [Cu(iPr2Dt0)2][PF6]2 (1b), and [Cu(Me2Dt0)2][PF6] (2a), [Cu(Me2Dt0)2][PF6]2 (2b), where iPr2Dt0 = N,N′‐diisopropyl‐1,2‐piperazine dithione and Me2Dt0 = N,N′‐dimethyl‐1,2‐piperazine dithione. In addition, the molecular structure of [Cu(iPr2Dt0)2][BF4]2(1c) is also reported. Complexes 1a and 2a crystallized in the triclinic, P1 space group, and 1c crystallized in the monoclinic crystal system, space group C2/c. The single‐crystal X‐ray diffraction measurements show that the Cu(I) complexes have a distorted tetrahedral geometry, whereas the Cu(II) complex exhibits a true square‐planar geometry. Cu(I) complexes exhibit a low energy charge‐transfer band (450–650 nm), which are not observed in Cu(II) complexes. Electrochemical studies of these complexes show both ligand‐ and metal‐based redox couples
Electron spin dynamics in quantum dots and related nanostructures due to hyperfine interaction with nuclei
We review and summarize recent theoretical and experimental work on electron
spin dynamics in quantum dots and related nanostructures due to hyperfine
interaction with surrounding nuclear spins. This topic is of particular
interest with respect to several proposals for quantum information processing
in solid state systems. Specifically, we investigate the hyperfine interaction
of an electron spin confined in a quantum dot in an s-type conduction band with
the nuclear spins in the dot. This interaction is proportional to the square
modulus of the electron wave function at the location of each nucleus leading
to an inhomogeneous coupling, i.e. nuclei in different locations are coupled
with different strength. In the case of an initially fully polarized nuclear
spin system an exact analytical solution for the spin dynamics can be found.
For not completely polarized nuclei, approximation-free results can only be
obtained numerically in sufficiently small systems. We compare these exact
results with findings from several approximation strategies.Comment: 26 pages, 9 figures. Topical Review to appear in J. Phys.: Condens.
Matte
Electron Spin-Relaxation Times of Phosphorus Donors in Silicon
Pulsed electron paramagnetic resonance measurements of donor electron spins
in natural phosphorus-doped silicon (Si:P) and isotopically-purified 28Si:P
show a strongly temperature-dependent longitudinal relaxation time, T1, due to
an Orbach process with DeltaE = 126 K. The 2-pulse echo decay is exponential in
28Si:P, with the transverse relaxation (decoherence) time, T2, controlled by
the Orbach process above ~12 K and by instantaneous diffusion at lower
temperatures. Spin echo experiments with varying pulse turning angles show that
the intrinsic T2 of an isolated spin in 28Si:P is ~60 ms at 7 K.Comment: Submitted to PRL on 02.28.200
The spread of bla OXA-48 and bla OXA-244 carbapenemase genes among Klebsiella pneumoniae, Proteus mirabilis and Enterobacter spp. isolated in Moscow, Russia
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