On Peterson surfaces of constant Gaussian curvature

The surfaces of constant Gaussian curvature bearing conjugate networks of conic lines are found.Translated from Ukrainskií Geometricheskií Sbornik, Issue 29, 1986, pp. 3–5.     

Electron Spin Resonance Imaging Probes and a Sample Holder for Thin and Long One-Dimensional Samples

Most electron spin resonance (ESR) experiments involve the use of samples that can be easily placed in millimeter-size tubes and measured efficiently in conventional resonators. However, in some cases, the samples must remain intact, due to which conventional commercial resonators may not be suitable to measure them. Here, we describe a set of three resonators, which can be combined and incorporated as part of a 1-D continuous wave ESR imaging probe to measure and image very thin (~50–500 μm) and very long (~10–30 mm) objects. The dielectric resonators we employ make it possible to greatly enhance spin sensitivity per unit of length––compared to the use of a rectangular ESR cavity, at ~9.3 GHz. In addition, a special sample holder was developed to facilitate the handling and measurement of such thin and long delicate objects, which in our case are the Arabidopsis roots. A detailed design of the resonators, imaging probe, and the sample holder is provided, along with experimental results for the resonator properties, its spin sensitivity, and imaging capability.     

Structure of hybrid organic–inorganic sols for the preparation of hydrothermally stable membranes

A procedure for the preparation of hybrid sols for the synthesis of organic–inorganic microporous materials and thin film membranes is reported. We describe silane reactivity and sol structure for acid-catalysed colloidal sols from mixtures of either tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES), or bis(triethoxysilyl)ethane (BTESE) and MTES. Early-stage hydrolysis and condensation rates of the individual silane precursors were followed with ²⁹Si liquid NMR and structural characteristics of more developed sols were studied with Dynamic Light Scattering. Condensation was found to proceed at more or less similar rates for the different precursors. Homogeneously mixed hybrid colloids can therefore be formed from precursor mixtures. The conditions of preparation under which clear sols with low viscosity could be formed from BTESE/MTES were determined. These sols were synthesised at moderate water/silane and acid/silane ratios and could be applied for the coating of defect-free microporous membranes for molecular separations under hydrothermal conditions.     

Differentiation of Lippia gracilis Schauer Genotypes by LC Fingerprint and Chemometrics Analyses

A liquid chromatographic method with photodiode-array detection has been developed for differentiation of seven genotypes of Lippia gracilis Schauer, originated from Sergipe state (named 106 to 110) and from Bahia state (201 and 202), cultivated and collected in the rural campus of the Federal University of Sergipe. For a comparative analysis of the fingerprint chromatograms, chemometric tools were applied with exploratory methods. The genotypes were differentiated and their relationship with original place was established (Sergipe and Bahia states) by principal component analysis of the fingerprint chromatograms of both leaves and stem samples.     

Filling factor of a paramagnetic sample in a rectangular cavity: theory and application

A computational method is presented for calculating the filling factor of an electron paramagnetic resonance (EPR) tube in a rectangular TE102 cavity. The algorithm employs the conventional finite element method. In addition to the filling factor, the algorithm allows to calculate the quality factor and the reflection coefficient of the loaded cavity. This method allows calculating very accurately the EPR signal intensities from which the spin concentration of paramagnetic samples can be determined. A comparison between the predicted EPR signal intensities to several experimental results was found to be satisfactory. The method also allows optimizing the EPR tube dimensions and its glass quality to improve measurement sensitivity.     

Non-flammable preparative reversed-phase liquid chromatography of recombinant human insulin-like growth factor-I

Acetonitrile is used as an eluent for reversed-phase chromatography. However, because it is a flammable solvent, using acetonitrile on a large scale requires expensive equipment and facilities specially designed for flammable solvents. Using a non-flammable solvent as an eluent eliminates this expense. A method was developed to purify recombinant human insulin-like growth factor I by reversed-phase high-performance liquid chromatography using gradient elution with hexylene glycol, a non-flammable replacement for acetonitrile. The separation produced equivalent yield, purity and throughput as reversed-phase chromatography using elution with acetonitrile.     

Quantitative high-resolution transmission electron microscopy of single atoms

Single atoms can be considered as the most basic objects for electron microscopy to test the microscope performance and basic concepts for modeling image contrast. In this work high-resolution transmission electron microscopy was applied to image single platinum, molybdenum, and titanium atoms in an aberration-corrected transmission electron microscope. The atoms are deposited on a self-assembled monolayer substrate that induces only negligible contrast. Single-atom contrast simulations were performed on the basis of Weickenmeier-Kohl and Doyle-Turner form factors. Experimental and simulated image intensities are in quantitative agreement on an absolute intensity scale, which is provided by the vacuum image intensity. This demonstrates that direct testing of basic properties such as form factors becomes feasible.     

Development of nanoscale inhomogeneities during drying of sol-gel derived amorphous lead zirconate titanate precursor thin films

The structural evolution of sol-gel derived lead zirconate titanate (PZT) precursor films during and after physical drying was investigated by transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), selected area electron diffraction (SAED), and time-resolved X-ray diffraction (XRD). Films were deposited from initial 0.3 mol/dm(3) precursor sols with varying hydrolysis ratios. Zr-rich grains of 1-10 nm size, embedded in a Pb-, Zr-, and Ti-containing amorphous matrix were found in as-dried films. The Zr-rich regions were crystalline at hydrolysis ratios [H(2)O]/[PZT] < 27.6, and amorphous at ratios > 100. X-ray diffraction analysis of PZT and zirconia sols revealed that the crystalline nanoparticles in both sols are identical and are probably composed of nanosized zirconium oxoacetate-like clusters. This study demonstrates that time-resolved X-ray diffraction combined with electron energy loss spectroscopy mapping is a powerful tool to monitor the nanoscale structural evolution of sol-gel derived thin films.     

The β-delayed one- and two-proton emission of 27S

In an experiment performed at the GANIL LISE3 facility, radioactive ²⁷S isotopes have been produced by projectile fragmentation of a 95 AMeV ³⁶Ar primary beam. After selection by means of the LISE3 separator, the isotope of interest was implanted in a silicon-detector telescope where its half-life ( T _1/2 = 15.5(15) ms) and its main decay branches were measured. Received: 19 October 2001 / Accepted: 5 December 2001