Evaluation of collective transport properties of ionic melts from molecular dynamics simulations

Molecular dynamics simulations of beryllium fluoride (BeF2) have been carried out in the canonical (NVT) ensemble using a rigid-ion potential model. The Green-Kubo formalism has been applied to compute viscosities and ionic conductivities of BeF2 melt. The computational parameters critical for reliably estimating these collective transport properties are shown to differ significantly for viscosity and ionic conductivity. In addition to the equilibrium values of these transport properties, structural relaxation times as well as high-frequency IR-active modes are computed from the pressure and charge-flux auto correlation functions (ACFs) respectively. It is shown that a network-forming ionic melt, such as BeF2, will display persistent oscillatory behaviour of the integral of the charge-flux ACF. By suitable Fourier transformation, one can show that these persistent oscillations correspond to high-frequency, infra-red active vibrations associated with local modes of the network

Limited-Rate Channel State Feedback for Multicarrier Block Fading Channels

The capacity of a fading channel can be substantially increased by feeding back channel state information from the receiver to the transmitter. With limited-rate feedback what state information to feed back and how to encode it are important open questions. This paper studies power loading in a multicarrier system using no more than one bit of feedback per sub-channel. The sub-channels can be correlated and full channel state information is assumed at the receiver.Comment: Submitted to IEEE Transactions on Information Theor

Some Excursions Into Saturn's Faint Rings

Errata inserted at request of author, 21 April 2014.Saturn's E ring: Saturn's tenuous E ring has a double-banded vertical structure, with the density of particles depleted in the equatorial plane of the rings near Enceladus' orbit. We have conducted numerical simulations, supported by orderof-magnitude analytical calculations, to investigate how particles behave in the vicinity of Enceladus' orbit to form the observed vertical structure. We also show that the the radial double-layered Gaussian core of the E-ring [Hedman et al., 2012] is formed entirely due to gravity. Saturn's gravity, including its J2 , J4 and J6 , and effects of Enceladus are considered. The other nearby moons of Saturn are included, though our results show that they have negligible effect over the ~ 200-yr integration. We follow the orbits of particles ejected near Enceladus' southern pole with speeds ranging between ~ 0.8 to 2 times the nominal escape speed at the moon's surface (for an isolated spherical moon). We find that the combination of gravitational deceleration on launch plus the first few subsequent encounters with the moon causes many particles starting with 'escapable' velocities (just enough to escape gravitational influence) to assume an orbital inclination corresponding to a maximum height of 4rE (rE = radius of Enceladus), which gives rise to the double-layered structure. We present the short-term (1-2 days) and longer-term (~ 200-yr) dynamics of particles in Enceladus' vicinity. We argue that non-gravitational forces have little influence in the initial dynamics and formation of radial Gaussian core. Ultrafaint rings: Recent Cassini images identified three tenuous rings [Hedman et al., 2009a] along the orbits of Methone, Anthe and Pallene, three small moons whose orbits nest between those of Mimas and Enceladus. A continuous inclined ring lies along Pallene's orbit, whereas the other two satellites are constrained within arcs of limited longitudinal extents. Two of the moons, Anthe and Methone, are in strong resonances with Mimas, whereas Pallene is in a weak near-resonance with Enceladus. We investigate the longitudinal confinement of material along the orbits of the three small satellites. Anthe, Methone and Pallene along with six nearby major moons of Saturn were included in numerical simulations of particles ejected from the surfaces of these three small moons. 1000 particles were integrated with a range of initial velocities from 1 - 2 m/s from the surface of the moon in all directions with respect to the moons. The particles' trajectories were integrated for 22 years. Our simulations show that differences between the first-order resonances of Anthe and Methone, and the third-order near-resonance of Pallene, may explain the confinement of material in formal cases and the lack of confinement in the Pallene ring. We confirm and identify the resonances

Capnography as an aid in localizing the phrenic nerve in brachial plexus surgery. Technical note

<p>Abstract</p> <p>Background</p> <p>To determine whether monitoring end- tidal Carbon Dioxide (capnography) can be used to reliably identify the phrenic nerve during the supraclavicular exploration for brachial plexus injury.</p> <p>Methods</p> <p>Three consecutive patients with traction pan-brachial plexus injuries scheduled for neurotization were evaluated under an anesthetic protocol to allow intraoperative electrophysiology. Muscle relaxants were avoided, anaesthesia was induced with propofol and fentanyl and the airway was secured with an appropriate sized laryngeal mask airway. Routine monitoring included heart rate, noninvasive blood pressure, pulse oximetry and time capnography. The phrenic nerve was identified after blind bipolar electrical stimulation using a handheld bipolar nerve stimulator set at 2–4 mA. The capnographic wave form was observed by the neuroanesthetist and simultaneous diaphragmatic contraction was assessed by the surgical assistant. Both observers were blinded as to when the bipolar stimulating electrode was actually in use.</p> <p>Results</p> <p>In all patients, the capnographic wave form revealed a notch at a stimulating amplitude of about 2–4 mA. This became progressively jagged with increasing current till diaphragmatic contraction could be palpated by the blinded surgical assistant at about 6–7 mA.</p> <p>Conclusion</p> <p>Capnography is a sensitive intraoperative test for localizing the phrenic nerve during the supraclavicular approach to the brachial plexus.</p

Effect of L- Arginine On Electrocardiographic Changes Induced By Hypercholesterolemia And Isoproterenol In Rabbits

Hypercholesterolemia, a well-known cardiovascular risk factor, is associated with prolonged action potential duration, longer QTc intervals (rate controlled QT interval), suggested that Hypercholesterolemia may have a direct effect on ventricular repolarization. Hypercholesterolemia was induced in rabbits and L-arginine was given orally to animals for sixteen weeks. The isoproterenol was injected in all the animals to produce electrocardiographic changes. ECG was recorded in lead II at start of study, after hypercholesterolemic diet and/ or L-arginine supplementation