1,608 research outputs found
Obstructive sleep apnoea (OSA) - a silent killer in anaesthesia?
Sleep-disordered breathing (SDB) encompasses a wide range of disorders that afflict both adults and children. These disorders are often unrecognised preoperatively and the pathophysiological consequences may impact severely on the patient in the peri-operative period
Hypertension and Anaesthesia
The difficulty that anaesthetists face is that they often, when seeing a patient pre-operatively, do not have the benefit of seeing the patient’s “normal average” blood pressure taken at different times over a period of weeks. The decision to cancel surgery based on the blood pressure found at the pre-operative visit must, therefore, take into account the urgency of the surgery, as well as the presence of end organ damage from chronic hypertension. A detailed history and examination should be performed looking for evidence of coronary artery disease, cerebrovascular disease and renal dysfunction
Acute subarachnoid haemorrhage and the mysterious electrocardiogram
Subarachnoid haemorrhage (SAH) is a devastating neurological insult, and is increasingly understood as a multi-system condition initiated in the central nervous system. Perioperative investigation of patients presenting for aneurysm surgery often includes a routine electrocardiogram (ECG) which frequently reveals an abnormality. We describe a patient who presented with SAH and who was found to have significant Q waves on the ECG suggestive of a trans-mural myocardial infarction, despite a negative medical history for such an event. We brie y highlight the issues faced by the anaesthesiologist when dealing with the patient with SAH and ECG abnormality, and the implications for cardiovascular dysfunctio
Pressure-Induced Anomalous Phase Transitions and Colossal Enhancement of Piezoelectricity in PbTiO
We find an unexpected tetragonal-to-monoclinic-to-rhombohedral-to-cubic phase
transition sequence induced by pressure, and a morphotropic phase boundary in a
pure compound using first-principles calculations. Huge dielectric and
piezoelectric coupling constants occur in the transition regions, comparable to
those observed in the new complex single-crystal solid-solution piezoelectrics
such as Pb(MgNb)O-PbTiO, which are expected to
revolutionize electromechanical applications. Our results show that
morphotropic phase boundaries and giant piezoelectric effects do not require
intrinsic disorder, and open the possibility of studying this effect in simple
systems.Comment: 4 pages, to appear in Phys. Rev. Let
Microscopic origin of Magnetic Ferroelectrics in Nonlinear Multiferroics
A simple but general microscopic mechanism to understand the interplay
between the electric and magnetic degrees of freedom is developed. Within this
mechanism, the magnetic structure generates an electric current which induce an
counterbalance electric current from the spin orbital coupling. When the
magnetic structure is described by a single order parameter, the electric
polarization is determined by the single spin orbital coupling parameter, and
the material is predicted to be a half insulator. This mechanism provides a
simple estimation of the value of ferroelectricity and sets a physical
limitation as well.Comment: 4 pages, 1 figur
First-principles study of epitaxial strain in perovskites
Using an extension of a first-principles method developed by King-Smith and
Vanderbilt [Phys. Rev. B {\bf 49}, 5828 (1994)], we investigate the effects of
in-plane epitaxial strain on the ground-state structure and polarization of
eight perovskite oxides: BaTiO, SrTiO, CaTiO, KNbO, NaNbO,
PbTiO, PbZrO, and BaZrO. In addition, we investigate the effects of
a nonzero normal stress. The results are shown to be useful in predicting the
structure and polarization of perovskite oxide thin films and superlattices.Comment: 10 page
Elastic effects of vacancies in strontium titanate: Short- and long-range strain fields, elastic dipole tensors, and chemical strain
We present a study of the local strain effects associated with vacancy
defects in strontium titanate and report the first calculations of elastic
dipole tensors and chemical strains for point defects in perovskites. The
combination of local and long-range results will enable determination of x-ray
scattering signatures that can be compared with experiments. We find that the
oxygen vacancy possesses a special property -- a highly anisotropic elastic
dipole tensor which almost vanishes upon averaging over all possible defect
orientations. Moreover, through direct comparison with experimental
measurements of chemical strain, we place constraints on the possible defects
present in oxygen-poor strontium titanate and introduce a conjecture regarding
the nature of the predominant defect in strontium-poor stoichiometries in
samples grown via pulsed laser deposition. Finally, during the review process,
we learned of recent experimental data, from strontium titanate films deposited
via molecular-beam epitaxy, that show good agreement with our calculated value
of the chemical strain associated with strontium vacancies.Comment: 14 pages, 11 figures, 4 table
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