493 research outputs found
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The Binding of Benzoarylsulfonamide Ligands to Human Carbonic Anhydrase is Insensitive to Formal Fluorination of the Ligand
Auf das Wasser kommt es an: Konservierte Bindungsgeometrie, enthalpiegetriebene Bindungsweise und nichtunterscheidbare Bindungsaffinitäten für fluorierte und nichtfluorierte Liganden von humaner Carbonsäureanhydrase (siehe Bild) stützen die Theorie, dass das Schlüssel-Schloss-Modell einen wichtigen Bestandteil des Bindungsvorgangs unbeachtet lässt: das Wasser, das die Bindungstasche des Proteins füllt und den Liganden umgibt.Chemistry and Chemical Biolog
X-boson cumulant approach to the periodic Anderson model
The Periodic Anderson Model (PAM) can be studied in the infinite U limit by
employing the Hubbard X operators to project out the unwanted states. We have
already studied this problem employing the cumulant expansion with the
hybridization as perturbation, but the probability conservation of the local
states (completeness) is not usually satisfied when partial expansions like the
Chain Approximation (CHA) are employed. Here we treat the problem by a
technique inspired in the mean field approximation of Coleman's slave-bosons
method, and we obtain a description that avoids the unwanted phase transition
that appears in the mean-field slave-boson method both when the chemical
potential is greater than the localized level Ef at low temperatures (T) and
for all parameters at intermediate T.Comment: Submited to Physical Review B 14 pages, 17 eps figures inserted in
the tex
Evidence for Quark-Hadron Duality in the Proton Spin Asymmetry
Spin-dependent lepton-nucleon scattering data have been used to investigate
the validity of the concept of quark-hadron duality for the spin asymmetry
. Longitudinally polarised positrons were scattered off a longitudinally
polarised hydrogen target for values of between 1.2 and 12 GeV and
values of between 1 and 4 GeV. The average double-spin asymmetry in
the nucleon resonance region is found to agree with that measured in
deep-inelastic scattering at the same values of the Bjorken scaling variable
. This finding implies that the description of in terms of quark
degrees of freedom is valid also in the nucleon resonance region for values of
above 1.6 GeV.Comment: 5 pages, 1 eps figure, table added, new references added, in print in
Phys. Rev. Let
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Rational speculative bubbles: an empirical investigation of the London Stock Exchange
In recent years, a sharp divergence of London Stock Exchange equity prices from dividends has been noted. In this paper, we examine whether this divergence can be explained by reference to the existence of a speculative bubble. Three different empirical methodologies are used: variance bounds tests, bubble specification tests, and cointegration tests based on both ex post and ex ante data. We find that, stock prices diverged significantly from their fundamental values during the late 1990's, and that this divergence has all the characteristics of a bubble
Single-spin Azimuthal Asymmetries in Electroproduction of Neutral Pions in Semi-inclusive Deep-inelastic Scattering
A single-spin asymmetry in the azimuthal distribution of neutral pions
relative to the lepton scattering plane has been measured for the first time in
deep-inelastic scattering of positrons off longitudinally polarized protons.
The analysing power in the sin(phi) moment of the cross section is 0.019 +/-
0.007(stat.) +/- 0.003(syst.). This result is compared to single-spin
asymmetries for charged pion production measured in the same kinematic range.
The pi^0 asymmetry is of the same size as the pi^+ asymmetry and shows a
similar dependence on the relevant kinematic variables. The asymmetry is
described by a phenomenological calculation based on a fragmentation function
that represents sensitivity to the transverse polarization of the struck quark.Comment: 4 pages, 1 figure, replaced to correct eprint author field, 2nd
replacement to correct figure; upper limit of model predictions are
corrected. No correction to data or conclusion
Quantum Impurity Entanglement
Entanglement in J_1-J_2, S=1/2 quantum spin chains with an impurity is
studied using analytic methods as well as large scale numerical density matrix
renormalization group methods. The entanglement is investigated in terms of the
von Neumann entropy, S=-Tr rho_A log rho_A, for a sub-system A of size r of the
chain. The impurity contribution to the uniform part of the entanglement
entropy, S_{imp}, is defined and analyzed in detail in both the gapless, J_2 <=
J_2^c, as well as the dimerized phase, J_2>J_2^c, of the model. This quantum
impurity model is in the universality class of the single channel Kondo model
and it is shown that in a quite universal way the presence of the impurity in
the gapless phase, J_2 <= J_2^c, gives rise to a large length scale, xi_K,
associated with the screening of the impurity, the size of the Kondo screening
cloud. The universality of Kondo physics then implies scaling of the form
S_{imp}(r/xi_K,r/R) for a system of size R. Numerical results are presented
clearly demonstrating this scaling. At the critical point, J_2^c, an analytic
Fermi liquid picture is developed and analytic results are obtained both at T=0
and T>0. In the dimerized phase an appealing picure of the entanglement is
developed in terms of a thin soliton (TS) ansatz and the notions of impurity
valence bonds (IVB) and single particle entanglement (SPE) are introduced. The
TS-ansatz permits a variational calculation of the complete entanglement in the
dimerized phase that appears to be exact in the thermodynamic limit at the
Majumdar-Ghosh point, J_2=J_1/2, and surprisingly precise even close to the
critical point J_2^c. In appendices the relation between the finite temperature
entanglement entropy, S(T), and the thermal entropy, S_{th}(T), is discussed
and and calculated at the MG-point using the TS-ansatz.Comment: 62 pages, 27 figures, JSTAT macro
Double-Spin Asymmetry in the Cross Section for Exclusive rho^0 Production in Lepton-Proton Scattering
Evidence for a positive longitudinal double-spin asymmetry = 0.24
+-0.11 (stat) +-0.02 (syst) in the cross section for exclusive diffractive
rho^0(770) vector meson production in polarised lepton-proton scattering was
observed by the HERMES experiment. The longitudinally polarised 27.56 GeV HERA
positron beam was scattered off a longitudinally polarised pure hydrogen gas
target. The average invariant mass of the photon-proton system has a value of
= 4.9 GeV, while the average negative squared four-momentum of the virtual
photon is = 1.7 GeV^2. The ratio of the present result to the
corresponding spin asymmetry in inclusive deep-inelastic scattering is in
agreement with an early theoretical prediction based on the generalised vector
meson dominance model.Comment: 10 pages, 4 embedded figures, LaTe
In-depth exploration of the photophysics of a trinuclear palladium complex
Contains fulltext :
128388.pdf (publisher's version ) (Open Access
Increase of SERS Signal Upon Heating or Exposure to a High-Intensity Laser Field: Benzenethiol on an AgFON Substrate
The surface-enhanced Raman scattering (SERS) signal from an AgFON plasmonic
substrate, recoated with benzenethiol, was observed to increase by about 100%
upon heating for 3.5 min at 100C and 1.5 min at 125C. The signal intensity was
found to increase further by about 80% upon a 10 sec exposure to a
high-intensity (3.2 kW/cm^2) 785-nm cw laser, corresponding to 40 mW in a
40+/-5-um diameter spot. The observed increase in the SERS signal may be
understood by considering the presence of benzenethiol molecules in an
intermediate or 'precursor' state in addition to conventionally ordered
molecules forming a self-assembled monolayer. The increase in the SERS signal
arises from the conversion of the molecules in the precursor state to the
chemisorbed state due to thermal and photo-thermal effects.Comment: 9 pages, 4 figures; J. Phys. Chem. C, accepte
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