The Effects of Hypoxia on Sensory Cells of the Cochlea in Chinchilla

The effects of hypoxia on the sensory epithelium of the cochlea were investigated in the chinchilla. Systemic hypoxia was produced by increasing the dead space of the respiratory tidal volume. A disarrangement of hair-cell stereocilia, and cytoplasmic protrusions from sensory cells are the main findings in cochleas from hypoxic animals; these changes take place firstly at the inner hair-cells then, with the increase in degree of hypoxia, at the outer hair-cells. These degenerative changes of sensory cells correlate well with both respiratory suppression and with the elevation of auditory threshold to click stimulation as monitored using the compound action potential recording from the cochlear nerve. The latter measure appears to be a useful indicator of cochlear hypoxia. Our morphological findings are similar to other studies including those which have reported on post-mortem cochlear hair-cell degeneration. Our studies indicate the deleterious effects of long term hypoxia on cochlear mechanisms and point to the need for careful monitoring of cardiovascular and respiratory functions in animals under anaesthesia for physiological studies of the auditory system

Spin Correlations in the Two-Dimensional Spin-5/2 Heisenberg Antiferromagnet Rb2MnF4

We report a neutron scattering study of the instantaneous spin correlations in the two-dimensional spin S=5/2 square-lattice Heisenberg antiferromagnet Rb_2MnF_4. The measured correlation lengths are quantitatively described, with no adjustable parameters, by high-temperature series expansion results and by a theory based on the quantum self-consistent harmonic approximation. Conversely, we find that the data, which cover the range from about 1 to 50 lattice constants, are outside of the regime corresponding to renormalized classical behavior of the quantum non-linear sigma model. In addition, we observe a crossover from Heisenberg to Ising critical behavior near the Neel temperature; this crossover is well described by a mean-field model with no adjustable parameters.Comment: 8 pages, LaTeX, with 6 included EPS figures, submitted to EPJ

rCBFand the rCMRglucose in experimental hydrocephalus measured by the double tracer method of autoradiography

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Characterization of low-energy magnetic excitations in chromium

The low-energy excitations of Cr, i.e. the Fincher-Burke (FB) modes, have been investigated in the transversely polarized spin-density-wave phase by inelastic neutron scattering using a single-(Q+-) crystal with a propagation vector (Q+-) parallel to [0,0,1]. The constant-momentum-transfer scans show that the energy spectra consist of two components, namely dispersive FB modes and an almost energy-independent cross section. Most remarkably, we find that the spectrum of the FB modes exhibits one peak at 140 K near Q = (0,0,0.98) and two peaks near Q = (0,0,1.02), respectively. This is surprising because Cr crystallizes in a centro-symmetric bcc structure. The asymmetry of those energy spectra decreases with increasing temperature. In addition, the observed magnetic peak intensity is independent of Q suggesting a transfer of spectral-weight between the upper and lower FB modes. The energy-independent cross section is localized only between the incommensurate peaks and develops rapidly with increasing temperature.Comment: 6 pages, 8 figure

The monoclinic phase in PZT: new light on morphotropic phase boundaries

A summary of the work recently carried out on the morphotropic phase boundary (MPB) of PZT is presented. By means of x-ray powder diffraction on ceramic samples of excellent quality, the MPB has been successfully characterized by changing temperature in a series of closely spaced compositions. As a result, an unexpected monoclinic phase has been found to exist in between the well-known tetragonal and rhombohedral PZT phases. A detailed structural analysis, together with the investigation of the field effect in this region of compositions, have led to an important advance in understanding the mechanisms responsible for the physical properties of PZT as well as other piezoelectric materials with similar morphotropic phase boundaries.Comment: 5 pages REVTeX file, 6 figures embedded. Presented at the Workshop on "Fundamental Physics of Ferroelectrics" held in Aspen, February 00. To appear in the proceeding

The Uptake of ACNU in the Experimental Brain Tumor and the Effect of Induced Hypertension - Part II -

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Neutron and x-ray diffuse scattering study of tetrathiofulvalene tetracyanoquinodimethane (TTF--TCNQ)

Results of extensive x-ray and neutron scattering experiments are: (1) Below the Peierls transition taking place at 54/sup 0/K, two additional structural phase transitions are observed at 49/sup 0/K and 38/sup 0/K. (2) Above the Peierls transition two different precursor 1-d fluctuations have been observed. Suggestions for future studies are given. (LK

The Persistence and Memory of Polar Nano-Regions in a Ferroelectric Relaxor Under an Electric Field

The response of polar nanoregions (PNR) in the relaxor compound Pb[(Zn$_{1/3}$Nb$_{2/3}$)$_{0.92}$Ti$_{0.08}$]O$_3$ subject to a [111]-oriented electric field has been studied by neutron diffuse scattering. Contrary to classical expectations, the diffuse scattering associated with the PNR persists, and is even partially enhanced by field cooling. The effect of the external electric field is retained by the PNR after the field is removed. The ``memory'' of the applied field reappears even after heating the system above $T_C$, and cooling in zero field