A caveat regarding chiroptical measurements of chiral anthracyclinones

The specific rotations of anthracyclinones are shown to exhibit dramatic variation induced by protic solvents. The significance of this finding to the evaluation of optical purity of synthetic anthracyclinones is discussed.     

Constrained interpolation and smoothing

Numerical and theoretical questions related to constrained interpolation and smoothing are treated. The prototype problem is that of finding the smoothest convex interpolant to given univariate data. Recent results have shown that this convex programming problem with infinite constraints can be recast as a finite parametric nonlinear system whose solution is closely related to the second derivative of the desired interpolating function. This paper focuses on the analysis of numerical techniques for solving the nonlinear system and on the theoretical issues that arise when certain extensions of the problem are considered. In particular, we show that two standard iteration techniques, the Jacobi and Gauss-Seidel methods, are globally convergent when applied to this problem. In addition we use the problem structure to develop an efficient implementation of Newton's method and observe consistent quadratic convergence. We also develop a theory for the existence, uniqueness, and representation of solutions to the convex interpolation problem with nonzero lower bounds on the second derivative (strict convexity). Finally, a smoothing spline analogue to the convex interpolation problem is studied with reference to the computation of convex approximations to noisy data.     

The kinetics of parasitic growth in GaAs MOVPE

Gallium arsenide (GaAs) deposition was carried out in a horizontal quartz reactor tube with trimethylgallium (TMGa) and arsine (AsH₃) as precursors, using a hydrogen (H₂) carrier gas. Temperatures were in the range 400–500 °C, where surface reactions limit deposition rate. Nucleation time and deposition rate were monitored using laser interferometry, optimum reflectance was gained by aligning a quartz wafer to back reflect the incident beam. The 980 nm infrared laser beam was sufficiently long in wavelength to be able to penetrate the wall deposit. Results showing the effect of temperature and V/III ratio on the nucleation time and deposition rate are presented, where with temperature the nucleation delay was observed to reduce and the growth rate to increase. The nucleation delay is consistent with a thermally activated surface nucleation for the parasitic GaAs. A theoretical growth rate model, based on a restricted set of reaction steps was used to compare with the experimental growth rates. Without any free parameters, the growth rates from theoretical calculation and experiment agreed within a factor of two and showed the same trends with V/III ratio and temperature. The non-linearity of the theoretical growth rates on an Arrhenius plot indicates that there is more than one dominant reaction step over the temperature range investigated. The range of experimental activation energies, calculated from Arrhenius plots, was 17.56–23.59 kJ mol⁻¹. A comparison of these activation energies and minimum deposition temperature with the literature indicates that the wall temperature measurement on an Aixtron reactor is over 100 °C higher than previously reported.     

Conductivity studies of dense yttrium-doped BaZrO3 sintered at 1325 °C

High-temperature proton conductors have wide applications in the areas of fuel cells, electrolysis and hydrogen separation. Barium zirconate-based materials are of interest due to their good stability and high protonic conductivity. The reported conductivity of these ceramic materials is generally less than 10⁻² S/cm, even at high temperatures. This is not high enough for an electrolyte-supported device to achieve an ASR of less than 0.2 Ω cm² therefore thin film electrolytes are required for successful application. As BaZrO₃-based materials have to be sintered at temperatures as high as 1700 °C, this makes it difficult to find a suitable supporting electrode which will not undergo significant chemical reaction with the BaZrO₃-based electrolyte during fabrication of the required electrode supported electrolyte. In this paper, proton-conducting BaZr_0.8Y_0.2O_2.9 was successfully sintered at 1325 °C with a relative density of 96% via addition of 1 wt% ZnO. Fabrication of electrochemical cells using proton-conducting BaZr_0.8Y_0.2O_2.9 as the electrolyte thus becomes possible. The formula of the 1 wt% ZnO added sample is Ba_0.97Zr_0.77Y_0.19Zn_0.04O_3−δ which exhibits a tetragonal structure with space group P4/mbm (127); a=5.9787(1) Å, c=4.2345(1) Å, V=151.36(1) Å³. It was found that a solid solution was formed for a limited range of Zn doping. Conductivity has been studied as a function of atmosphere (air, dry and wet 5% H₂/Ar) with the changes in bulk and grain boundary on changing atmosphere being monitored as a function of time. The total conductivity of Ba_0.97Zr_0.77Y_0.19Zn_0.04O_3–δ is 1.0×10⁻³ S/cm above 600 °C therefore it may be used as a proton-conducting thin film electrolyte for efficient electrochemical devices at such temperatures. The grain boundary resistance is insignificant at high temperature for the well-sintered sample.     

Mono- and dicationic short PEG and methylene dioxyalkylglycerols for use in synthetic gene delivery systems

A range of monocationic and dicationic dioxyalkylglycerol cytofectins have been synthesised possessing methylene and short n-ethylene glycol spacers. The monocationic compounds were found to be effective in transfections when formulated as lipopolyplexes with peptide and DNA components, in particular with shorter PEG head groups which may have less effect on peptide targeting in the ternary complex.     

Anisotropic magnetoresistance components in (Ga,Mn)As

We explore the basic physical origins of the noncrystalline and crystalline components of the anisotropic magnetoresistance (AMR) in (Ga,Mn)As. The sign of the noncrystalline AMR is found to be determined by the form of spin-orbit coupling in the host band and by the relative strengths of the nonmagnetic and magnetic contributions to the Mn impurity potential. We develop experimental methods yielding directly the noncrystalline and crystalline AMR components which are then analyzed independently. We report the observation of an AMR dominated by a large uniaxial crystalline component and show that AMR can be modified by local strain relaxation. Generic implications of our findings for other dilute moment systems are discussed.     

The falling needle viscometer a new technique for viscosity measurements

A new type of viscometer, the Falling Needle Viscometer (FNV) has been developed. It has several advantages over the better known Falling Ball Viscometer (FBV) including better control over the trajectory and terminal velocity and a wall correction which is an integral part of the analytical solution.A Stokes' type solution for the FNV is presented which is compared with experimental measurements made on Glycerol. Experiments were also conducted with a Falling Ball Viscometer and Weissenberg Rheogoniometer using the same fluid and a comparison made among the three systems.Glycerol viscosities measured with the FNV agreed with those measured by the FBV and Weissenberg Rheogoniometer within approximately one percent. It is concluded that the Falling Needle Viscometer is a useful device that in some situations is superior to the Falling Ball Viscometer.

---

Das Nadelfall-Viskosimeter, eine neue Technik zur Zähigkeitsmessung

Zusammenfassung Es wurde ein neues Gerät zur Zähigkeitsmessung, as Nadelfall-Viskosimeter (FNV) entwickelt. Gegenüber dem bekannteren Kugelfall-Viskosimeter (FBV) besitzt es einige Vorteile wie eine bessere Kontrolle über die Bahnkurve und die Endgeschwindigkeit sowie eine Wandkorrektur, die Bestandteil der analytischen Lösung ist.Für das FNV wird eine Lösung vom Stokes'schen Typ vorgestellt und mit experimentellen Meßergebnissen an Glycerin verglichen. Meßwerte am selben Fluid mit Hilfe eines FBV und eines Weissenberg-Rheogoniometers erlaubten einen Vergleich zwischen den drei Systemen.Die mit dem FNV gemessenen Zähigkeiten stimmten mit den anderen Werten innerhalb etwa 1% überein. Daraus wird geschlossen, daß das FNV ein nützliches Gerät ist, das dem FBV auf einigen Gebieten überlegen ist.

---

Nomenclature

Roman letters a Radius of needle or sphere (cm) - b Radius of container (cm) - b ⁺ Ratio of container to needle diameterb/a - C _w Wall correction factor of sphere - d Diameter of needle or sphere (cm) - ECF End correction factor of a finite needle with hemisphere tips - g Gravitational constant - G ⁺ Dimensionless number - L Total needle length minus one diameter (cm) - L Total length of needle (cm) - L ⁺ Total needle length minus one diameter over diameter-L/d - L⁺ Total length to diameter of needle - p Pressure (N/m²) - p ⁺ Dimensionless number - L ⁺/b ⁺ Total needle length to diameter of system - r Radial coordinate (cm) - r ⁺ Dimensionless radial distance(r/a) - Re Reynolds number or - u Velocity in the system length direction (cm/s) - u ⁺ Dimensionless velocity (u/U ) - U _t Measured terminal velocity of needle or sphere (cm/s) - U Terminal velocity of sphere in an unbounded fluid or terminal velocity of a long enough needle (cm/s) - U ⁺ Dimensionless number - T Temperature (°C) - z Coordinate in container length direction (cm) Greek letters Shear rate (l/s) - p Pressure difference - Dynamic viscosity (Ns/m²) - Kinematic viscosity (m²/s) - _f Density of fluid (kg/m³) - _s Density of needle or sphere (kg/m³) - ⁺ Dimensionless density Dedicated to Professor E. R. G. Eckert on the occasion of his 80th birthday     

Proton radioactivity — spherical and deformed

The proton drip line defines one of the fundamental limits to nuclear stability. Nuclei lying beyond this line are energetically unbound to the emission of a constituent proton from their ground states. For near-spherical nuclei in the region of the drip line between Z=69 (Tm) and Z=81 (T1), proton decay transition rates have been shown to be well reproduced by WKB calculations using spectroscopic factors derived from a low-seniority shell model calculation [2]. Another approach using spectroscopic factors obtained from the independent quasiparticle approximation has also proved successful in this region [3]. These interpretations have allowed the extraction of nuclear structure information from nuclei well beyond the proton drip line.