Magnetic Resonance in the Spin-Peierls compound α′−NaV2O5\alpha'-NaV_2O_5

We present results from magnetic resonance measurements for 75-350 GHz in $\alpha$'-NaV$_{2}$O$_{5}$. The temperature dependence of the integrated intensity indicates that we observe transitions in the excited state. A quantitative description gives resonances in the triplet state at high symmetry points of the excitation spectrum of this Spin-Peierls compound. This energy has the same temperature dependence as the Spin-Peierls gap. Similarities and differences with the other inorganic compound CuGeO$_{3}$ are discussed.Comment: 2 pages, REVTEX, 3 figures. to be published in Phys.Rev.

Field-induced structural evolution in the spin-Peierls compound CuGeO3_3: high-field ESR study

The dimerized-incommensurate phase transition in the spin-Peierls compound CuGeO$_3$ is probed using multifrequency high-resolution electron spin resonance (ESR) technique, in magnetic fields up to 17 T. A field-induced development of the soliton-like incommensurate superstructure is clearly indicated as a pronounced increase of the ESR linewidth $\Delta B$ (magnon excitations), with a $\Delta B_{max}$ at $B_{c}\sim$ 13.8 T. The anomaly is explained in terms of the magnon-soliton scattering, and suggests that the soliton-like phase exists close to the boundary of the dimerized-incommensurate phase transition. In addition, magnetic excitation spectra in 0.8% Si-doped CuGeO$_3$ are studied. Suppression of the $\Delta B$ anomaly observed in the doped samples suggests a collapse of the long-range-ordered soliton states upon doping, that is consistent with high-field neutron scattering experiments.Comment: Accepted to Phys. Rev.

Physiological stress and spatio-temporal fluctuations of food abundance and population density in Eurasian red squirrels

In continuously changing environments, variation of different ecological factors could affect the functioning of the hypothalamic-pituitary-adrenal (HPA) axis in wild mammals, increasing the secretion of glucocorticoids (GCs). In different animal species, GC concentrations are often used as a measure of the physiological stress response to environmental pressures, such as fluctuations in food abundance, population density, intra-and interspecific competition, and predation risk. However, previous studies reported contrasting results or did not find clear associations between physiological stress and environmental variables. Here, we used concentrations of faecal glucocorticoid metabolites (FGMs) as an integrated measure of physiological stress in wild Eurasian red squirrels (Sciurus vulgaris) from three study areas in the Italian Alps, to investigate whether variations in conifer-seed crop size and/or population density affected HPA axis activity. Squirrel density was estimated in each trapping session using the minimum number of animals alive, and annual counts of fresh cones from different conifer species were used to estimate annual food abundance (MJ/ha). We expected higher FGMs in response to increasing population density and/or decreasing food abundance, since these two variables could act as environmental stressors. Our results showed a lack of association between population density and FGMs and a significant effect of food abundance on FGMs. When conifer seed-crops were poor to moderate, FGMs increased with food abundance, while in the range of high seed-crops, FGMs remained first constant and then slightly decreased with a further increase in seed abundance. We also found differences in FGMs among seasons, as previously observed in this species. Our study adds further evidence that physiological stress can be influenced in different ways by environmental pressures and that long-term studies using individually marked animals are needed to disentangle the potential adaptive outcome of the physiological stress response in pulsed resource systems

Intraoperative management of macroperforations of Descemet's membrane in deep anterior lamellar keratoplasty.

BackgroundTo describe a surgical approach for the completion of pre-descemetic deep anterior lamellar keratoplasty (pdDALK) in the presence of a macroperforation of Descemet's membrane (DM).MethodsUsing case notes, we recorded the details of the intra- and perioperative course of patients who underwent successful pdDALK in the presence of macroperforation. A literature search of pdDALK techniques available to the corneal surgeon in a similar scenario was undertaken.ResultsIn two very different scenarios with intra- or preoperative perforation of DM, a centripetal layered lamellar dissection was performed and allowed completion of pdDALK with a residual recipient central stromal thickness of 36 and 115 µm and good visual outcome.ConclusionDespite very different scenarios, a centripetal layered lamellar dissection offers an approach for the completion of pdDALK in the presence of a macroperforation

High field magnetic resonant properties of beta'-(ET)2SF5CF2SO3

A systematic electron spin resonance (ESR) investigation of the low temperature regime for the (ET)2SF5CF2SO3 system was performed in the frequency range of ~200-700 GHz, using backward wave oscillator sources, and at fields up to 25 T. Newly acquired access to the high frequency and fields shows experimental ESR results in agreement with the nuclear magnetic resonance (NMR) investigation, revealing evidence that the transition seen at 20 K is not of conventional spin-Peierls order. A significant change of the spin resonance spectrum in beta'-(ET)2SF5CF2SO3 at low temperatures, indicates a transition into a three-dimensional-antiferromagnetic (3D AFM) phase.Comment: 4 pages, 7 figures, minor grammatical change

High Magnetic Field ESR in the Haldane Spin Chains NENP and NINO

We present electron spin resonance experiments in the one-dimensional antiferromagnetic S=1 spin chains NENP and NINO in pulsed magnetic fields up to 50T. The measured field dependence of the quantum energy gap for B||b is analyzed using the exact diagonalization method and the density matrix renormalization group method (DMRG). A staggered anisotropy term (-1)^i d(S_i^x S_i^z + S_i^z S_i^x) was considered for the first time in addition to a staggered field term (-1)^i S_i^x B_st. We show that the spin dynamics in high magnetic fields strongly depends on the orthorhombic anisotropy E.Comment: 4 pages, RevTeX, 4 figure

Modulated Phases in Spin-Peierls Systems

Lattice modulations in the high magnetic field phase and close to impurities in spin-Peierls systems are considered and compared to experiment. Necessary extensions of existing theories are proposed. The influence of zero-point fluctuations on magnetic amplitudes is shown.Comment: 10 pages, 4 figures included, to appear in Advances in Solid State Physics/Festkoerperprobleme Spring Conference 1999 of the DP

Functional Staging of Corneal Neovascularization Using Fluorescein and Indocyanine Green Angiography

Court of Appeals No. 89-0340 CA Argument Priority No. 14(b) District Court No. C-86-8833 Judge: John A. Rokic