4,416 research outputs found
Clustering of vacancy defects in high-purity semi-insulating SiC
Positron lifetime spectroscopy was used to study native vacancy defects in
semi-insulating silicon carbide. The material is shown to contain (i) vacancy
clusters consisting of 4--5 missing atoms and (ii) Si vacancy related
negatively charged defects. The total open volume bound to the clusters
anticorrelates with the electrical resistivity both in as-grown and annealed
material. Our results suggest that Si vacancy related complexes compensate
electrically the as-grown material, but migrate to increase the size of the
clusters during annealing, leading to loss of resistivity.Comment: 8 pages, 5 figure
Antagonism of neuromuscular blockade but not muscle relaxation affects depth of anaesthesia
Background. Conflicting effects of neuromuscular blocking drugs and anticholinesterases on depth of anaesthesia have been reported. Therefore we evaluated the effect of atracurium and neostigmine on bispectral index (BIS) and middle-latency auditory evoked potentials (AAI). Methods. We studied 40 patients (ASA I-II) aged 18-69 yr. General anaesthesia consisted of propofol and remifentanil by target-controlled infusion and neuromuscular function was monitored by electromyography. When BIS reached stable values, patients were randomly assigned to one of two groups. Group 1 received atracurium 0.4 mg kg−1 and, 5 min later, the same volume of NaCl 0.9%; group 2 received saline first and then atracurium. When the first twitch of a train of four reached 10% of control intensity, patients were again randomized: one group (N) received neostigmine 0.04 mg kg−1 and glycopyrrolate 0.01 mg kg−1, and the control group (G) received only glycopyrrolate. Results. Injection of atracurium or NaCl 0.9% had no effect on BIS or AAI. After neostigmine-glycopyrrolate, BIS and AAI increased significantly (mean maximal change of BIS 7.1 [sd 7.5], P<0.001; mean maximal change of AAI 9.7 [10.5], P<0.001). When glycopyrrolate was injected alone BIS and AAI also increased (mean maximal change of BIS 2.2 [3.4], P=0.008; mean maximal change of AAI 3.5 [5.7], P=0.012), but this increase was significantly less than in group N (P=0.012 for BIS; P=0.027 for AAI). Conclusion. These data suggest that neostigmine alters the state of propofol-remifentanil anaesthesia and may enhance recover
Collisions of micron-sized, charged water droplets in still air
We investigate the effect of electrical charge on collisions of
hydrodynamically interacting, micron-sized water droplets settling through
quiescent air. The relative dynamics of charged droplets is determined by
hydrodynamic interactions, particle and fluid inertia, and electrostatic
forces. We analyse the resulting relative dynamics of oppositely charged
droplets by determining its fixed points and their stable and unstable
manifolds. The stable manifold of a saddle point forms a separatrix that
separates colliding trajectories from those that do not collide. The
qualitative conclusions from this theory are in excellent agreement with
experiments.Comment: 6 pages, 2 figures, supplemental materia
Memory and superposition in a spin glass
Non-equilibrium dynamics in a Ag(Mn) spin glass are investigated by
measurements of the temperature dependence of the remanent magnetisation. Using
specific cooling protocols before recording the thermo- or isothermal remanent
magnetisations on re-heating, it is found that the measured curves effectively
disclose non-equilibrium spin glass characteristics such as ageing and memory
phenomena as well as an extended validity of the superposition principle for
the relaxation. The usefulness of this "simple" dc-method is discussed, as well
as its applicability to other disordered magnetic systems.Comment: REVTeX style; 8 pages, 4 figure
Memory and chaos in an Ising spin glass
The non-equilibrium dynamics of the model 3d-Ising spin glass
- FeMnTiO - has been investigated from the temperature
and time dependence of the zero field cooled magnetization recorded under
certain thermal protocols. The results manifest chaos, rejuvenation and memory
features of the equilibrating spin configuration that are very similar to those
observed in corresponding studies of the archetypal RKKY spin glass Ag(Mn). The
sample is rapidly cooled in zero magnetic field, and the magnetization recorded
on re-heating. When a stop at constant temperature is made during the
cooling, the system evolves toward its equilibrium state at this temperature.
The equilibrated state established during the stop becomes frozen in on further
cooling and is retrieved on re-heating. The memory of the aging at is not
affected by a second stop at a lower temperature
. Reciprocally, the first equilibration at has no influence on
the relaxation at , as expected within the droplet model for domain
growth in a chaotic landscape.Comment: REVTeX style; 4 pages, 4 figure
Fatal myocardial infarction after lung resection in a patient with prophylactic preoperative coronary stenting†
In this report we present the case of a 77-yr-old man who underwent resection of the upper lobe of the left lung for a carcinoma, six weeks after percutaneous transluminal coronary angioplasty (PTCA) with stenting of the left anterior descending (LAD) and circumflex coronary arteries. Antiplatelet therapy with clopidogrel was interrupted two weeks before surgery to allow for epidural catheter placement and to minimize haemorrhage. The surgical procedure was uneventful. In the immediate postoperative period, however, the patient suffered severe myocardial ischaemia. Emergency coronary angiography showed complete thrombotic occlusion of the LAD stent. In spite of successful recanalization, reinfarction occurred and the patient died in cardiogenic shock. Prophylactic preoperative coronary stenting may put the patient at risk of stent thrombosis if surgery cannot be postponed for three months. In such cases, other strategies such as perioperative β-blockade for preoperative cardiac management should be considered. Br J Anaesth 2004; 92: 743-
Short range ferromagnetism and spin glass state in
Dynamic magnetic properties of are
reported. The system appears to attain local ferromagnetic order at
K. Below this temperature the low field
magnetization becomes history dependent, i.e. the zero field cooled (ZFC) and
field cooled (FC) magnetization deviate from each other and closely logarithmic
relaxation appears at our experimental time scales (0.3- sec). The zero
field cooled magnetization has a maximum at K,
whereas the field cooled magnetization continues to increase, although less
sharply, also below this temperature. Surprisingly, the dynamics of the system
shows non-equilibrium spin glass (SG) features not only below the maximum in
the ZFC magnetization, but also in the temperature region between this maximum
and . The aging and temperature cycling experiments show only
quantitative differences in the dynamic behavior above and below the maximum in
the ZFC-magnetization; similarly, memory effects are observed in both
temperature regions. We attribute the high temperature behavior to the
existence of clusters of short range ferromagnetic order below
; the configuration evolves into a conventional spin glass
state at temperatures below .Comment: REVTeX style; 8 pages, 8 figure
Strong rejuvenation in a chiral-glass superconductor
The glassy paramagnetic Meissner phase of a BiSrCaCuO
superconductor ( = 8.18) is investigated by squid magnetometry, using
``dc-memory'' experiments employed earlier to study spin glasses. The
temperature dependence of the zero-field-cooled and thermo-remanent
magnetization is recorded on re-heating after specific cooling protocols, in
which single or multiple halts are performed at constant temperatures. The
'spin' states equilibrated during the halts are retrieved on re-heating. The
observed memory and rejuvenation effects are similar to those observed in
Heisenberg-like spin glasses.Comment: REVTeX 4 style; 5 pages, 5 figure
Obesity: should there be a law against it? Introduction to a symposium
The rapid rise in rates of overweight and obesity among adults and children in Australia and New Zealand has intensified debate about the most effective policies for obesity prevention. Law has much to contribute to this policy discussion, although its role is often misunderstood. The articles in this symposium follow on from a conference hosted in September 2006 by the Centre for Health Governance, Law & Ethics in the Faculty of Law, University of Sydney, titled: Obesity: should there be a law against it? In different ways, these articles provide a variety of perspectives on regulatory responses to obesity, including theoretical justifications for a legal approach, conceptual models that assist in making sense of law's role, as well as specific legal strategies for obesity prevention in various settings
- …