We present a joint experimental and theoretical study of the electronic structure of the cuprate chain systems A_(1-x)CuO_2 (A=Ca,Sr,Ba), as measured using O-K and Cu-L_3 x-ray absorption ...spectroscopy. The doping-dependent behaviour in these systems is radically different to that in conventional 2D cuprate networks formed from corner sharing CuO_4 plaquettes, and follows from the strongly suppressed inter-plaquette hybridisation resulting from the 90 degree Cu-O-Cu interaction pathway in the chain systems. Spectroscopically, this results in (a) a classical mixed-valent scenario whereby the different final states in the Cu-L_3 spectra can be used directly to 'read-off' the Cu valency and (b) a drastic reduction in the dynamic spectral weight transfer from the upper Hubbard band to the low energy scale in the O-K spectra. The final picture emerges of localisation of the doped holes, with the chain then comprised of a mixture of pure Cu(II)O_4 and Cu(III)O_4 plaquettes.
Band structure calculations have been used to identify the different bands
contributing to the polarisation-dependent photoemission spectra of the undoped
model cuprate Sr$_2$CuO$_2$Cl$_2$ at the ...high-symmetry points of the CuO$_2$
plane $\Gamma$, $(\pi/a,0)$ and $(\pi/a,\pi/a)$ and along the high-symmetry
directions $\Gamma - (\pi/a,\pi/a)$ and $\Gamma - (\pi/a,0)$. Results from
calculations within the local density approximation (LDA) have been compared
with calculations taking into account the strong electron correlations by
LDA+U, with the result that the experimental order of energy levels at the
high-symmetry points is better described by the LDA+U calculation than by the
simple LDA. All the main peaks in the photoemission spectra at the high
symmetry points could be assigned to different Cu 3$d$ and O 2$p$ orbitals
which we have classified according to their point symmetries. The dispersions
along the high-symmetry directions were compared with an 11-band tight-binding
model which was fitted both to the LDA+U band structure calculation and the
angle-resolved photoemission data. The mean field treatment successfully
describes the oxygen derived bands but shows discrepancies for the copper ones.
Individual randomized trials comparing aminoglycosides have usually involved a sample size inadequate for reliable detection of small to moderate differences. In a search for overall effects that ...might not be apparent from any single trial, a quantitative overview of all randomized studies comparing amikacin, gentamicin, netilmicin, sisomicin, and tobramycin was performed. These aminoglycosides appeared equally efficacious, except that tobramycin seemed less effective than sisomicin. Patients given gentamicin or sisomicin seemed to run a higher risk of nephrotoxicity than those given amikacin; the risk for patients receiving tobramycin was lower than that for patients given gentamicin but higher than that for those given netilmicin. The only statistically significant difference with regard to auditory toxicity was a lower risk among patients receiving netilmicin than among those given amikacin or tobramycin. Meaningful differences in toxicity may exist for individual aminoglycosides given in efficacious doses. Future trials must include sample sizes sufficient to detect differences of the magnitudes observed in this overview. In the absence of such data, the overview may guide clinicians in determining the risk-to-benefit ratio for a particular aminoglycoside, especially for patients at high risk of toxicity.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Phys.Lett.B524:26-32,2002 Precise data on the neutron magnetic form factor G_{mn} have been obtained
with measurements of the ratio of cross sections of D(e,e'n) and D(e,e'p) up to
momentum transfers ...of Q^2 = 0.9 (GeV/c)^2. Data with typical uncertainties of
1.5% are presented. These data allow for the first time to extract a precise
value of the magnetic radius of the neutron.
Band structure calculations have been used to identify the different bands contributing to the polarisation-dependent photoemission spectra of the undoped model cuprate Sr\(_2\)CuO\(_2\)Cl\(_2\) at ...the high-symmetry points of the CuO\(_2\) plane \(\Gamma\), \((\pi/a,0)\) and \((\pi/a,\pi/a)\) and along the high-symmetry directions \(\Gamma - (\pi/a,\pi/a)\) and \(\Gamma - (\pi/a,0)\). Results from calculations within the local density approximation (LDA) have been compared with calculations taking into account the strong electron correlations by LDA+U, with the result that the experimental order of energy levels at the high-symmetry points is better described by the LDA+U calculation than by the simple LDA. All the main peaks in the photoemission spectra at the high symmetry points could be assigned to different Cu 3\(d\) and O 2\(p\) orbitals which we have classified according to their point symmetries. The dispersions along the high-symmetry directions were compared with an 11-band tight-binding model which was fitted both to the LDA+U band structure calculation and the angle-resolved photoemission data. The mean field treatment successfully describes the oxygen derived bands but shows discrepancies for the copper ones.
Precise data on the neutron magnetic form factor G_{mn} have been obtained with measurements of the ratio of cross sections of D(e,e'n) and D(e,e'p) up to momentum transfers of Q^2 = 0.9 (GeV/c)^2. ...Data with typical uncertainties of 1.5% are presented. These data allow for the first time to extract a precise value of the magnetic radius of the neutron.
