Positive Lyapunov exponents for a class of ergodic Schrödinger operators

We present a simple method to estimate the Lyapunov exponent (E) for the system

VUV spectroscopy of magnetically trapped atomic hydrogen

We discuss the experimental and theoretical aspects of absorption spectroscopy of cold atomic hydrogen gas in a magnetostatic trap using a pulsed narrow-band source (bandwidth 100 MHz) at the Lyman- wavelength (121.6 nm). A careful analysis of the measured absorption spectra enables us to determine non-destructively the temperature and the density of the trapped gas. The development of this diagnostic technique is important for future attempts to reach Bose-Einstein condensation in trapped atomic hydrogen.     

Typical Transitivity for Lifts of Rotationless Annulus or Torus Homeomorphisms

We say that a homeomorphism h of the base space X (which maybe either the annulus or n-torus, n2) is rotationless if itis area-preserving and has a lift h to the covering space X([0,1]x R or Rⁿ) with mean translation zero ((h(x)–x)dx=0, where is [0,1] x [0,1]). We prove (Theorem 1) that in the space ofrotationless homeomorphisms of X with the uniform topology,the subspace consisting of homeo-morphisms with transitive liftsto X contains a dense G subset. This extends our earlier result,valid only when the base space is the annulus, that typicalrotationless homeomorphisms have recurrent lifts. Our resultalso extends that of Besicovitch, who in 1937 exhibited thefirst transitive homeomorphism of the plane. In this contextwe establish such a homeomorphism which is additionally spatiallyperiodic.     

Aragonite Formation in the Chiton (Mollusca) Girdle

In the chitons (Polyplacophora, Mollusca), the body is not entirely protected by the shell. Mineralized spicules or scales often, but not always, decorate the exposed part of the girdle. Here, we report a study on the composition and ultrastructural organization of these mineralized skeletal parts in four different chiton species. In all specimens, the mineral component (97–98 wt‐%) is aragonite, and the organic matrix (2–3 wt‐%) consists of highly glycosylated proteins. X‐Ray diffraction and scanning electron microscopy show that the organic matrix fibers are aligned, morphologically and crystallographically, with the prismatic aragonite crystals. Matrix and mineral are thus clearly related. The matrix–mineral composite bundles are, however, assembled in the various skeletal parts examined with widely different degrees of alignment and order. In the same organism, the crystals are aligned within a range of ±15° in one type of spicule, while they are randomly oriented in another type. The wide heterogeneity in shape, density, and ultrastructure suggests that the girdle mineralized tissues do not fulfill a fundamental role necessary for the survival of the organism. This, together with the lack of chitin in the organic matrix, supports the hypothesis that they evolved separately from the other chiton mineralized tissues, namely the shell plates and teeth.     

Configuration and optimization of semiconductor gas sensors as gas chromatographic detectors

A tin oxide, gas-sensitive semiconductor sensor was configured as a gas chromatographic detector and its performance was optimized. Two sensor housings were compared but little difference was found in performance. The flow rate and temperature of the column and the internal heater voltage of the sensor affected both the sensitivity and peak shape. The temperature of the sensor surface was the most critical parameter. Optimal conditions for the gas chromatographic detection of a mixture of alkanes (C₁–C₅) and hydrogen were identified by using the simplex technique. The detection limit for hydrogen was improved by a factor of five to 20 ppb (v/v), illustrating the value of optimization and the excellent sensitivity of the detector. It is concluded that semiconductor gas sensors offer significant advantages as gas chromatographic detectors for the determination of reducing gases.     

Substituent electronegativities

It is shown that theoretical calculations (ab initio 6-31g^* basis) of the charge on the hydrogen in molecules HX and ecperimental values for J_CC (ipso-ortho) in monosubstituted benzenes both provid measures of substituent electronegativity.     

Determination of organometallic compounds by capillar gas chromatography – inductively coupled plasma mass spectrometry

The separation and detection of volatile organometallic compounds containing tin, iron, and nickel has been achieved using capillary GC–inductively coupled plasma–mass spectrometry (capillary GC-ICP-MS). Detection limits range from 3.0 to 7.0 pg/s. The presence of volatile organotin compounds in a harbor sediment has been confirmed. The retention range of the organometallic compounds analyzed by capillary GC-ICP-MS has been extended considerably beyond that possible in earlier studies (retention indices up to 3400).