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Notes: This paper reports a detailed investigation of the steady shear and extensional properties of mono-disperse polystyrene solutions for a range of molecular weights from 1.95 to 20 million and a range of concentrations from 69 ppm to 777 ppm. The steady shear and dynamic properties are reasonably well described by the Zimm model. The relaxation time and polymer viscosity evaluated using the Zimm model exhibit the expected scaling with concentration and molecular weight for theta solutions. In an extensional flow, these solutions show strain hardening and need about 5.5 to 6 strain units to reach steady state. The stress growth depends both on strain rate and strain. However, at moderate values of strain and when the Weissenberg number exceeds 6, the extensional stress growth depends only on total strain. The steady state extensional viscosity for each fluid was observed to depend on the magnitude of Weissenberg number (Wi). For Wi〈6, the steady state extensional viscosity was observed to be an increasing function of the strain rate. At a Wi∼10, the steady state extensional viscosity exhibits a maximum and surprisingly, for Wi〉10, the steady state extensional viscosity is a decreasing function of the strain rate. The results indicate that even dilute solutions, with concentrations as low as 0.21 times the critical concentration, do show extension thinning under certain conditions. The transient and steady state extensional viscosities are found to be proportional to molecular weight (Mw) and concentration (c). This result is rather unexpected as the Zimm model would predict a scaling with c and Mw0.5 for the transient viscosity and scaling with c and Mw1.5 for the steady state viscosity. On the other hand, the Rouse model predicts a scaling with c and Mw (for transient extensional viscosity) and with c and Mw2 (for steady state extensional viscosity). Hence the data appear to follow a Rouse-like behavior for the transient viscosity. This implies that the advent of the stretching reduces the hydrodynamic interaction and a free draining behavior is obtained. As a result, predictions using the Zimm model parameters, estimated from shear data, are unable to predict the transient extensional viscosity. The data are analyzed using a constitutive equation that incorporates an anisotropic drag coefficient along with a Rouse spectrum of relaxation time. Such a model captures the extensional behavior of the solutions. © 2000 American Institute of Physics.

Notes: Abstract: High-affinity specific receptors of endothelin (ET-1) were identified on primary cultures of mouse embryo striatal astrocytes by binding experiments performed with 125I-ET-1. Stimulation of production of inositol phosphates, a biphasic increase of the intracellular calcium concentration, and inhibition of cyclic AMP accumulation were observed in the same cells under ET-1 stimulation. Pretreatment of these cells with Bordetella pertussis toxin affected these effects to different extends, an observation suggesting that they are mediated by multiple transduction pathways, possibly involving several guanine nucleotide-binding proteins.

Notes: The gustatory system of channel catfish is widely studied for its sensitivity to amino acids. As a first step in identifying the molecular components that play a role in taste transduction in catfish, we cloned the full-length cDNA for Kv2-catfish, a novel K+ channel that is expressed in taste buds. The deduced amino acid sequence is 816 residues, and shares a 56–59% sequence identity with Kv2.1 and Kv2.2, the other members of the vertebrate Kv2 subfamily of voltage-gated K+ channels. The Kv2-catfish RNA was expressed in taste buds, brain, skeletal muscle, kidney, intestine and gills, and its gene is represented as a single copy in the catfish genome. Recombinant channels expressed in Xenopus oocytes were selective for K+, and were inhibited by tetraethylammonium applied to the extracellular side of the membrane during two-electrode voltage clamp analysis with a 50% inhibitory constant of 6.1 mm. The channels showed voltage-dependent activation, and did not inactivate within 200 ms. Functionally, Kv2-catfish is a voltage-gated, delayed rectifier K+ channel, and its primary structure is the most divergent sequence identified among the vertebrate members of the Kv2 subfamily of K+ channels, being related equally well to Kv2.1 and Kv2.2.

Notes: Cesium telluride (Cs2Te) photocathodes, with quantum efficiencies (QEs) of 15%–18% at 251 nm, were fabricated by vapor deposition of Te and Cs onto a Mo substrate and used as an electron source for the Los Alamos Advanced Free-Electron Laser. In the fabrication chamber, the spectral response from 251 to 578 nm was measured before and after a controlled exposure of several photocathodes to air. The 251-nm QE dropped by about a factor of 20 when exposed to 2×10−4 Torr of air for 1 h. Heating degraded photocathodes to 150–200 °C partially rejuvenated their QEs to about 60% of the value before air exposure. The performance of Cs2Te as a source of electrons for accelerators was evaluated in the photoinjector stage of the Advanced Free-Electron Laser. The response time, saturation level, and dark current of cesium telluride photocathodes and the emittance and energy spread of the resulting electron beam were determined to be sufficient for free electron laser applications. © 1995 American Institute of Physics.

Notes: The enhancement of energy loss of short pulses of electrons in plasma has been experimentally observed. An enhancement of up to 3.5×104 over single-particle losses was observed when a 15 ps electron bunch was injected into a preformed target plasma with an electron density of approximately 1013 cm−3. This matches the theoretical prediction that the energy loss should be enhanced when the temporal duration of the electron bunch is approximately equal to π/ωpe, where ωpe is the plasma frequency of the target plasma. 2D numerical simulations are in good agreement with the observations. © 1997 American Institute of Physics.

Notes: Densities of the negative and positive ions of SF6 in a 110-liter Pyrex container were measured using a Gerdien ion counter. The current-voltage characteristics were obtained for gas flows ranging from 40 to 200 cm3 s−1. A quantitative model of the counter was developed to interpret the measured data. The model includes appropriate representation of the developing gas flow and the electric field distribution near the ends of the accelerating electrode. The best-fit value for the negative-ion mobility was μn =0.38 cm2 V−1 s−1, as derived from a comparison of the calculated and the measured characteristics. The mobility of the positive ions was found to equal that of the negative ions within the limits of dispersion of experimental data. The negative-ion density at a pressure of 760 Torr evaluated at the counter entry plane was 3000 cm−3; the value of the positive-ion density was practically identical.

Notes: Virtually all inelastic helium atom scattering experiments utilize time-of-flight (TOF) analysis to energy analyze the scattered beam. To date, the demands upon the accuracy of these TOF measurements have not been particularly great (typically a few percent), and rather rudimentary calibration techniques have sufficed. For certain experiments, e.g., for time-resolved measurements of specular scattering to determine surface-bound states of helium or to observe surface-step interference, this is no longer the case. We describe an in situ calibration technique based upon a variation of the TOF flight path that allows us to calibrate our path length and time origin to within a few millimeters and microseconds, respectively (〈2×10−3). A comparison with "zero flight time'' laser timing measurements shows that finite drawout/transit times through the beam detector can introduce nonnegligible systematic errors into the laser calibration technique, even in the present favorable instance (light beam mass, drawout along the beam axis). We demonstrate the utility of surface diffraction as either a consistency check or to accurately determine unknown reciprocal lattice vectors.

Notes: This paper is devoted to a numerical investigation of the free convection flow about a horizontal cylinder maintained at 0 °C in a water ambient close to the point of maximum density. Complete numerical solutions covering both the transient as well as steady state have been obtained. Principal results indicate that the proximity of the ambient temperature to the point of maximum density plays an important role in the type of convection pattern that may be obtained. When the ambient temperature is within 4.7 °C〈Tamb〈8 °C, a "dual flow'' appears around the cylinder with both upward and downward flow occurring in proximity to the cylinder in two distinct recirculating zones, generally separated by the 4 °C isotherm when Tamb〈5.7 °C. The dual flow behavior is significantly modified as the ambient temperature is altered, disappearing when the ambient temperature is above 8 °C, or below 4.7 °C. Furthermore, when the ambient temperature is within about 4.8 °C〈Tamb〈5.5 °C, a well-defined steady state is never attained. Within this same range, solutions with an initially quasiperiodic behavior which persist for a long time have been observed. Multiple solutions have been observed when the above range of ambient temperature is approached from either side. The results of the computations have been compared with published experimental and numerical data with satisfactory agreement being obtained.

Notes: [Auszug] A retroviral vector containing the wild–type p53 gene under control of a β–actin promoter was produced to mediate transfer of wild–type p53 into human non–small cell lung cancers by direct injection. Nine patients whose conventional treatments failed were entered into ...