161,485 research outputs found
On reduced density matrices for disjoint subsystems
We show that spin and fermion representations for solvable quantum chains
lead in general to different reduced density matrices if the subsystem is not
singly connected. We study the effect for two sites in XX and XY chains as well
as for sublattices in XX and transverse Ising chains.Comment: 10 pages, 4 figure
Cyclic and ruled Lagrangian surfaces in complex Euclidean space
We study those Lagrangian surfaces in complex Euclidean space which are
foliated by circles or by straight lines. The former, which we call cyclic,
come in three types, each one being described by means of, respectively, a
planar curve, a Legendrian curve of the 3-sphere or a Legendrian curve of the
anti de Sitter 3-space. We also describe ruled Lagrangian surfaces. Finally we
characterize those cyclic and ruled Lagrangian surfaces which are solutions to
the self-similar equation of the Mean Curvature Flow. Finally, we give a
partial result in the case of Hamiltonian stationary cyclic surfaces
Spectroscopic characterization of the oxo-transfer reaction from a bis(µ-oxo)dicopper(III) complex to triphenylphosphine
The oxygen-atom transfer reaction from the bis(µ-oxo)dicopper(III) complex [CuIII2(µ-O)2(L)2]2+1, where L =N,N,N,N -tetraethylethylenediamine, to PPh3 has been studied by UV-vis, EPR, 1H NMR and Cu K-edge X-ray absorption spectroscopy in parallel at low temperatures (193 K) and above. Under aerobic conditions (excess dioxygen), 1 reacted with PPh3, giving OPPh3 and a diamagnetic species that has been assigned to an oxo-bridged dicopper(II) complex on the basis of EPR and Cu K-edge X-ray absorption spectroscopic data. Isotope-labeling experiments (18O2) established that the oxygen atom incorporated into the triphenylphosphine oxide came from both complex 1 and exogenous dioxygen. Detailed kinetic studies revealed that the process is a third-order reaction; the rate law is first order in both complex 1 and triphenylphosphine, as well as in dioxygen. At temperatures above 233 K, reaction of 1 with PPh3 was accompanied by ligand degradation, leading to oxidative N-dealkylation of one of the ethyl groups. By contrast, when the reaction was performed in the absence of excess dioxygen, negligible substrate (PPh3) oxidation was observed. Instead, highly symmetrical copper complexes with a characteristic isotropic EPR signal at g= 2.11 were formed. These results are discussed in terms of parallel reaction channels that are activated under various conditions of temperature and dioxygen
Determining the strange and antistrange quark distributions of the nucleon
The difference between the strange and antistrange quark distributions,
\delta s(x)=s(x)-\sbar(x), and the combination of light quark sea and strange
quark sea, \Delta (x)=\dbar(x)+\ubar(x)-s(x)-\sbar(x), are originated from
non-perturbative processes, and can be calculated using non-perturbative models
of the nucleon. We report calculations of and using
the meson cloud model. Combining our calculations of with
relatively well known light antiquark distributions obtained from global
analysis of available experimental data, we estimate the total strange sea
distributions of the nucleon.Comment: 4 pages, 3 figures; talk given by F.-G. at QNP0
Estimating the impact of whaling on global whale watching
After the commercial whaling moratorium was enacted in 1986, whale watching became one of the fastest growing tourism industries worldwide. As whaling was regarded as an activity incompatible with whale watching, the possible resumption of commercial whaling caused an urgent need to investigate the potential negative effects of whaling on the whale-watching industry. We examine the potential impacts of whaling on the global whale-watching tourism industry using unbalanced panel data model. The empirical results indicate that the resumption of commercial whaling has the potential for a negative effect on the global whale-watching industry, especially for nations that are engaged in whaling.delay-difference equation model;global whale watching;whaling
Are Giant Planets Forming Around HR 4796A?
We have obtained FUSE and HST STIS spectra of HR 4796A, a nearby 8 Myr old
main sequence star that possesses a dusty circumstellar disk whose inclination
has been constrained from high resolution near-infrared observations to be ~17
deg from edge-on. We searched for circumstellar absorption in the ground states
of C II at 1036.3 A, O I at 1039.2 A, Zn II at 2026.1 A, Lyman series H2, and
CO (A-X) and failed to detect any of these species. We place upper limits on
the column densities and infer upper limits on the gas masses assuming that the
gas is in hydrostatic equilibrium, is well-mixed, and has a temperature, Tgas ~
65 K. Our measurements suggest that this system possesses very little molecular
gas. Therefore, we infer an upper limit for the gas:dust ratio (<4.0) assuming
that the gas is atomic. We measure less gas in this system than is required to
form the envelope of Jupiter.Comment: 10 pages, 3 figures (including 1 color figure), accepted for
publication in Ap
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