3,546 research outputs found
An Analytical Study of Ozone Feedbacks on Kelvin and Rossby–Gravity Waves: Effects on the QBO
An equatorial beta-plane model of the middle atmosphere is used to analytically examine the effects of radiative cooling and ozone heating on the spatial and temporal evolution of the quasi-biennial oscillation (QBO). Under the assumption that the diabatic heating is weak and the background fields of wind, temperature, and ozone are slowly varying, a perturbation analysis yields expressions describing the vertical spatial modulation of Kelvin and Rossby–gravity waves in the presence of ozone. These expressions show that wave-induced changes in the diabatic heating arising from the advection of basic-state ozone reduce the local radiative damping rate by up to 15% below 35 km. In a one-dimensional model of the QBO, eddy ozone heating increases the amplitude of the zonal wind QBO by 1–2 m s−1 and increases the oscillation period by about two months. The significance of these results to the observed QBO is discussed
Intrinsic Spectral Geometry of the Kerr-Newman Event Horizon
We uniquely and explicitly reconstruct the instantaneous intrinsic metric of
the Kerr-Newman Event Horizon from the spectrum of its Laplacian. In the
process we find that the angular momentum parameter, radius, area; and in the
uncharged case, mass, can be written in terms of these eigenvalues. In the
uncharged case this immediately leads to the unique and explicit determination
of the Kerr metric in terms of the spectrum of the event horizon. Robinson's
``no hair" theorem now yields the corollary: One can ``hear the shape" of
noncharged stationary axially symmetric black hole space-times by listening to
the vibrational frequencies of its event horizon only.Comment: Final version with improved abstract, updated references, corrected
typos, and additional discussio
GABA-B receptor function in healthy volunteers, a pharmacokinetic and pharmacodynamic study of two doses of baclofen compared to placebo
AIMS AND HYPOTHESIS To assess the subjective and objective effects of baclofen on brain function in healthy volunteers. BACKGROUND Recent evidence suggests baclofen, a γ-aminobutyric acid type B (GABA-B) receptor agonist, reduces alcohol consumption and craving and promotes abstinence in alcoholics. However, characterisation of the GABA-B receptor system in clinical addiction is limited, and it is unclear why some patients require, or tolerate, higher doses to treat alcoholism. This study assesses the effects of baclofen on brain function in healthy volunteers to inform future studies investigating the sensitivity of GABA-B receptors in alcohol addiction. METHODS Eight healthy male volunteers completed a double blind randomised 3-way cross over study, receiving oral placebo (vitamin C 100mg), 10mg and 60mg baclofen. Subjective and objective measurements were taken at baseline (before medication) and at +30mins, 1, 2, 3, 4 and 6 hours after dosing. Objective measures included blood plasma samples, heart rate and blood pressure. Subjective measures included; the Subjective High Assessment Questionnaire (SHAS), visual analogue scales for sleepy, relaxed, tense and alert and a motor coordination task (zig-zag task). Pharmacokinetic data was obtained using liquid chromatography mass-spectrometry (LC-MS) to measure plasma baclofen concentrations. RESULTS 60mg Baclofen showed changes in subjective measures peaking at 2 hours post dosing compared with placebo, including a significant increase (p<0.05) in total SHAS scores with individual items, including feeling ‘drunk or intoxicated’, effects of alcohol and ‘muddled or confused’ particular affected.. Systolic blood pressure was significantly increased (p<0.05) at the 2 hours post 60mg dose. For both 10mg and 60mg baclofen, peak plasma concentration was achieved 60 minutes post dose. Pharmacokinetic data will be presented. There were no significant changes in these measures between 10mg Baclofen and placebo. CONCLUSIONS The objective and subjective measures used in this study are able to differentiate between placebo and 60mg baclofen. These findings will inform further research investigating the sensitivity of GABA-B receptors in alcohol addiction
Anelastic spectroscopy study of the spin-glass and cluster spin-glass phases of LaSrCuO
The anelastic spectra of LaSrCuO have been measured at
liquid He temperatures slightly below and above the concentration which is considered to separate the spin-glass phase from the
cluster spin-glass (CSG) phase. For all the elastic energy loss
functions show a step below the temperature of freezing into
the CSG state, similarly to what found in samples well within the CSG phase,
but with a smaller amplitude. The excess dissipation in the CSG state is
attributed to the motion of the domain walls between the clusters of
antiferromagnetically correlated spin. These results are in agreement with the
recent proposal, based on inelastic neutron scattering, of an electronic phase
separation between regions with and , at least for
Comment: 5 pages, 3 figures, submitted to Phys. Rev.
Octahedral tilting, monoclinic phase and the phase diagram of PZT
Anelastic and dielectric spectroscopy measurements on PZT close to the
morphotropic (MPB) and antiferroelectric boundaries provide new insight in some
controversial aspects of its phase diagram. No evidence is found of a border
separating monoclinic (M) from rhombohedral (R) phases, in agreement with
recent structural studies supporting a coexistence of the two phases over a
broad composition range x < 0.5, with the fraction of M increasing toward the
MPB. It is also discussed why the observed maximum of elastic compliance
appears to be due to a rotational instability of the polarisation and therefore
cannot be explained by extrinsic softening from finely twinned R phase alone,
but indicates the presence also of M phase, not necessarily homogeneous.
A new diffuse transition is found within the ferroelectric phase near x ~
0.1, at a temperature T_IT higher than the well established boundary T_T to the
phase with tilted octahedra. It is proposed that around T_IT the octahedra
start rotating in a disordered manner and finally become ordered below T_T. In
this interpretation, the onset temperature for octahedral tilting monotonically
increases up to the antiferroelectric transition of PbZrO3, and the depression
of T_T(x) below x = 0.18 would be a consequence of the partial relieve of the
mismatch between the cation radii with the initial stage of tilting below T_IT.Comment: submitted to J. Phys.: Condens. Matte
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