A reversible transition in liquid Bi under pressure.

The electrical resistance of solid and liquid Bi has been measured at high pressures and temperatures using a novel experimental design for high sensitivity measurements utilizing a "Paris-Edinburgh" toroid large volume press. An anomalous sharp decrease in resistivity with increasing temperature at constant pressures was observed in the region beyond melting which implies a possible novel transition in the melt. The proposed transition was observed across a range of pressures both in heating and cooling cycles of the sample demonstrating its reversibility. From the measurements it was possible to determine a "phase-line" of this transition on the Bi pressure-temperature phase diagram terminating at the melting curve.

Liquid structure and temperature invariance of sound velocity in supercooled Bi melt.

Structural rearrangement of liquid Bi in the vicinity of the melting point has been proposed due to the unique temperature invariant sound velocity observed above the melting temperature, the low symmetry of Bi in the solid phase and the necessity of overheating to achieve supercooling. The existence of this structural rearrangement is examined by measurements on supercooled Bi. The sound velocity of liquid Bi was measured into the supercooled region to high accuracy and it was found to be invariant over a temperature range of ∼60°, from 35° above the melting point to ∼25° into the supercooled region. The structural origin of this phenomenon was explored by neutron diffraction structural measurements in the supercooled temperature range. These measurements indicate a continuous modification of the short range order in the melt. The structure of the liquid is analyzed within a quasi-crystalline model and is found to evolve continuously, similar to other known liquid pnictide systems. The results are discussed in the context of two competing hypotheses proposed to explain properties of liquid Bi near the melting: (i) liquid bismuth undergoes a structural rearrangement slightly above melting and (ii) liquid Bi exhibits a broad maximum in the sound velocity located incidentally at the melting temperature.

Shadowing and mask opening effects during selective-area vapor-liquid-solid growth of InP nanowires by metalorganic molecular beam epitaxy.

Indium phosphide nanowires were grown by metalorganic molecular beam epitaxy using the selective-area vapor-liquid-solid method. We show experimentally and theoretically that the size of the annular opening around the nanowire has a major impact on nanowire growth rate. In addition, we observed a considerable reduction of the growth rate in dense two-dimensional arrays, in agreement with a calculation of the shadowing of the scattered precursors. Due to the impact of these effects on growth, they should be considered during selective-area vapor-liquid-solid nanowire epitaxy.

Short range order in liquid pnictides.

Liquid pnictides have anomalous physical properties and complex radial distribution functions. The quasi-crystalline model of liquid structure is applied to interpret the three-dimensional structure of liquid pnictides. It is shown that all the column V elements can be characterized by a short range order lattice symmetry similar to that of the underlying solid, the A7 structure, which originates from a Peierls distorted simple cubic lattice. The evolution of the liquid structure down the column as well as its temperature and pressure dependence is interpreted by means of the effect of thermodynamic parameters on the Peierls distortion. Surprisingly, it is found that the Peierls effect increases with temperature and the nearest neighbour distances exhibit negative thermal expansion.

The novel fragment of tyrosyl tRNA synthetase, mini-TyrRS, is secreted to induce an angiogenic response in endothelial cells.

Aminoacyl tRNA synthetases--enzymes that catalyze the first step of protein synthesis--in mammalian cells are now known to have expanded functions, including activities in signal transduction pathways, such as those for angiogenesis and inflammation. The native synthetases themselves are procytokines, having no signal transduction activities. After alternative splicing or natural proteolysis, specific fragments that are potent cytokines and that interact with specific receptors on cell surfaces are released. In this manner, a natural fragment of human tyrosyl tRNA synthetase (TyrRS), mini-TyrRS, has been shown to act as a proangiogenic cytokine. The mechanistic basis for the action of mini-TyrRS in angiogenesis has yet to be established. Here, we show that mini-TyrRS is exported from endothelial cells when they are treated with tumor necrosis factor-alpha. Mini-TyrRS binds to vascular endothelial cells and activates an array of angiogenic signal transduction pathways. Mini-TyrRS-induced angiogenesis requires the activation of vascular endothelial growth factor receptor-2 (VEGFR2/Flk-1/KDR). Mini-TyrRS stimulates VEGFR2 phosphorylation in a VEGF-independent manner, suggesting VEGFR2 transactivation. Transactivation of VEGFR2 and downstream angiogenesis require an intact Glu-Leu-Arg (ELR) motif in mini-TyrRS, which is important for its cytokine activity. These studies therefore suggest a mechanism by which mini-TyrRS induces angiogenesis in endothelial cells and provide further insight into the role of mini-TyrRS as a link between translation and angiogenesis.

The excitation of NMR transitions by the current in a sample and the proposals for its detection.

A new magnetic resonance technique for investigating conducting samples is described. NMR transitions are excited by the magnetic field of alternating current which flows across the sample. The dissipation of the energy caused by NMR transitions results in a change of the impedance of the sample. The NMR signal is detected as an associated change of the voltage drop across a sample while passing through the resonance region. It is predicted that the resonance can be detected by state-of-the-art low-noise superconducting quantum interference device (SQUID)-based NMR spectrometers. The method is believed to be useful for investigations of small-volume samples which are inaccessible by other NMR techniques.

Lyme myocarditis presenting as fascicular tachycardia with underlying complete heart block.

A case of Lyme myocarditis manifest as a fascicular tachycardia is presented. Subtle findings of heart block in the presence of preserved ventricular function led to the correct diagnosis in this otherwise healthy patient. Treatment with ceftriaxone resolved both abnormalities.

On the mechanism of overdrive suppression in the guinea pig sinoatrial node.

Factors underlying overdrive suppression were studied in guinea pig sinoatrial node perfused in vitro. Overdrive (1) is followed by a short suppression and a transient decrease in maximum diastolic potential (Emax); (2) causes an immediate decrease and then a reincrease in force followed after overdrive by a transient overshoot; (3) may induce a marked suppression in high [Ca]0, which is a function of the rate and duration of overdrive and is not affected by tetrodotoxin or atropine; (4) in the presence of acetylcholine (ACh), decreases Emax and causes a longer suppression, which may be associated to a transient hyperpolarization; (5) can be initiated periodically by spontaneous beats and the cycles are abolished by calcium antagonists but not by atropine; (6) in high [Ca]0 (but not in ACh) is followed by an oscillatory potential, the amplitude of which depends of the characteristics of overdrive; (7) does not cause suppression in zero [Ca]0; (8) may cause suppression that is due to failure of conduction; and (9) may be followed by a prolonged transient hyperpolarization in the presence of ACh and Cs. Thus, the sinoatrial node, intracellular calcium accumulation enhances overdrive suppression and causes periodic suppression of spontaneous cyclic rhythms. These calcium actions are direct and not related to a potentiation of ACh effects. The elimination of diastolic depolarization by ACh and Cs reveals an overdrive-induced hyperpolarization possibly related to an electrogenic Na extrusion.