Optical microcavities formed by semiconductor microtubes using a bottlelike geometry

We report on the realization of optical microtube resonators with a bottlelike geometry. The measured eigenenergies and the measured axial field distributions of the modes can be described by a straight and intuitive model using an adiabatic separation of the circulating and the axial propagation. The dispersion of the axial mode energies follows a photonic quasi-Schr?dinger equation including a quasipotential which can be determined for the actual geometry of the microtube in a precise and simple way. We show that tailoring the geometry of the microtube bottle resonators enables the realization of a wide variety of mode distributions and dispersion relations.     

Advanced techniques for all-electrical spectroscopy on spin caloric phenomena

Spin-dependent properties of nanomagnets and magnetic/nonmagnetic hybrid systems have gained a renewed interest after the discovery of spin caloric transport phenomena. To explore such properties in detail, advanced techniques need to be developed. In this paper we report novel approaches to study both the magneto–thermal and magneto–mechanical characteristics of hybrid systems. These techniques involve in particular broadband spectroscopy of spin dynamics and surface acoustic waves in the GHz frequency regime. By these means we investigate ferromagnet/semiconductor hybrid systems to explore spin pumping and the Seebeck effect as well as ferromagnet/piezoelectric hybrid systems to address magneto–mechanical coupling at high frequencies.     

A host-guest optical sensor for aliphatic amines based on lipophilic cyclodextrin

A host-guest optical sensor for the determination of aliphatic amines as exemplified by octylamine is proposed. It is based on the reversible fluorescence enhancement of heptakis(2,6-di-O-isobutyl)-β-cyclodextrin(DOB-β-CD) hosting tetraphenylporphyrin (TPP) immobilized in poly(vinyl chloride) (PVC) membrane by aliphatic amine extracted from aqueous phase into membrane phase. The optimum membrane contained 1.15 wt % TPP, 6.15 wt % DOB-β-CD as sensing reagent and other membrane materials. The fluorescence enhancement of the membrane resulted from the formation of a stable three-component complex among DOB-β-CD, TPP, and aliphatic amines. With the optimum conditions described, the fluorescence response of the sensor to octylamine shows a good correlation with the theoretically derived equation in the range 1.0 × 10^–6 to 8.0 × 10^–4 mol/L. The response characteristics including reversibility, response time, reproducibility and lifetime and selectivity of this optical device are also discussed in detail. This sensor has also been applied for the determination of octylamine in water samples containing interferents with satisfactory recovery.     

The microcrystalline structure of regenerated cellulose fibers as studied in negatively stained ultrathin sections

Summary The microcrystalline structure of viscose rayon and Fortisan, a highly oriented regenerated cellulose fiber, is studied with a new modification of negative staining, by the electron microscope. With this method, the microcrystalline structure of the viscose rayon can be directly observed.The ultrastructure is found to consist of closely packed oblong particles of uniform size in homogeneous distribution, except for the presence of voids and dense skin structures. The particles can be isolated and be demonstrated by metal shadowing as well as by negative staining in the section. The diameter of the particles is 32–40 Å in viscose and somewhat in Fortisan. These dimensions correspond to those calculated from small-angle X-ray scattering for the size of the microcrystallites.In length sections of Fortisan, the particles are seen to be aligned in longitudinal direction, forming long strings of 300–400 Å length.The particles are concluded to be the cellulose microcrystallites as studied by X-ray methods and the particle strings correspond to the molecular strings suggested byKratky.

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Zusammenfassung Die mikrokristalline Struktur von Viskosefasern und Fortisan einer hochorientierten regenierten Zellulosefaser wird elektronenmikroskopisch mit einer neuen Modifikation von negative staining (Färbemethode) untersucht. Mit dieser Methode wird die kristalline Struktur der Faser unmittelbarer Beobachtung zugänglich.Die Ultrastruktur stimmt überein mit dichtgepackten länglichen Partikeln gleicher Größe in homogener Verteilung, mit Ausnahme des Auftretens von Hohlräumen und von dichten gepackten Hautstrukturen. Die Partikel lassen sich isolieren und können sowohl durch Metallbedampfung wie durch negatives staining hinsichtlich ihres Querschnitts untersucht werden. Der Durchmesser ist 32–40 Å in Viskose und etwas größer in Fortisan. Diese Dimensionen entsprechen denen, die sich für die Größe der Mikrokristallite aus Kleinwinkelstreuung ergeben.In den Längsschnitten von Fortisan findet man die Partikel in longitutinaler Richtung aufgereiht, sie bilden lange Stränge von 300–400 Å. Es ist anzunehmen, daß diese Partikel die vonKratky in Zellulose vermuteten Stränge aus Mikrokristalliten sind.

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Research supported by the National Science Foundation and by I.T.T.-Rayonier Inc.     

A general one-pot synthesis for elusive 2-substituted indenes: does bis[2-(tert-butyl)indenyl]zirconium(IV) dichloride/MAO polymerise ethene?

Among the 2-substituted indenes, 2-trifluoroindene and 2-tert-butylindene are poorly or incompletely described in the open literature. We herein describe an efficient one-pot synthesis of these compounds as a variation of the Perkin reaction which allows us to refute an earlier claim that bis(2-tert-butylindenyl)zirconium(IV) dichloride (2a) will not polymerise ethene. In fact, 2a/MAO polymerises ethene to extremely high molecular weights. Extensive DFT calculations on the polymerisation mechanism revealed an unprecedented suppression of the otherwise predominant chain termination by beta-hydride transfer due to steric congestion of the active site.     

The precipitation of hydrated cobalt 1-nitroso-2-naphtholate from homogeneous solution

A method has been developed for determining cobalt by precipitating cobalt^III 1-nitroso-2-naphtholate from homogeneous solution. The reagent is synthesised within the reaction mixture by treating 2-naphthol with nitrous acid in the presence of cobalt^II ion. Thus nitrous acid serves the dual role as oxidant for the cobalt^II ion and also as a reactant in the synthesis of the reagent. Excess reagent precipitates after the cobalt nitroso-naphtholate has settled. A washing procedure has been developed to eliminate the excess reagent without affecting the cobalt nitroso-naphtholate. After washing to remove excess reagent and filtration, the precipitate is dried at 115° and weighed as Co(C₁₀H₆O₂N)₃·H₂O.

The presence offluoride prevents the interference of iron, tungsten and other elements which form strong fluoride complexes.

The precision and accuracy is within 0-1 mg of cobalt at a 10-mg level and within 0-2 mg of cobalt at a 50-mg level.     

Optical probing of a fractionally charged quasihole in an incompressible liquid

In photoluminescence spectroscopy of a low-mobility two-dimensional electron gas subjected to a quantizing magnetic field, we observe an anomaly around nu=1 / 3 at a very low temperature (0.1 K) and an intermediate electron density (0.9 x 10(11) cm(-2)). The anomaly is explained as due to perturbation of the incompressible liquid at the Laughlin state due to close proximity of a localized charged exciton which creates a fractionally charged quasihole in the liquid. The anomaly of approximately 2 meV can be destroyed by applying a small thermal energy of approximately 0.2 meV that is enough to close the quasihole energy gap.     

Sensitive circular dichroism marker for the chromophore environment of photoactive yellow protein: assignment of the 307 and 318 nm bands to the n --> pi* transition of the carbonyl

The absorption and CD spectra of wild-type PYP, apo-PYP, and the mutants, E46Q and M100A, were measured between 250 and 550 nm. At neutral pH, the two very weak absorption bands of wild-type PYP at 307 and 318 nm (epsilon(max) = 600 +/- 100 M(-1) cm(-1) at 318 nm) are associated with quite strong positive CD bands (Deltaepsilon(max) approximately 6.8 M(-1) cm(-1)). Both sets of bands are absent in the apoprotein. On the basis of this evidence, we assign these optical signals to the n --> pi* transition of the oxygen of the carbonyl group of the 4-hydroxycinnamic acid chromophore, which is expected to be electric dipole forbidden but magnetic dipole allowed. The progression of narrow bands at 307 and 318 nm with a shoulder in the CD around 329 nm is due to vibrational fine structure with a frequency of about 1050 +/- 50 cm(-1). This is the carbonyl stretch frequency in the electronically excited state and is well-known from the vibrational structure in the CD spectra of carbonyl compounds. The positive sign of the CD in the near UV is in accordance with the octant rule and the high-resolution X-ray structure, if we assume that the NH group of cysteine 69 to which the carbonyl is hydrogen bonded is the principle perturbant. Similar absorption and CD spectra were observed in the range of 300-340 nm for the mutants E46Q and M100A at neutral pH. Protonation of the trans chromophore by lowering the pH in the dark (without photoisomerization) broadens the 307 and 318 nm CD bands in the mutant E46Q but does not significantly affect their positions or alter their sign. For the long-lived I(2) photointermediate of the mutant M100A with protonated cis chromophore, we observed that the sign of the rotational strength in the 310-320 nm range is negative (i.e., opposite to that in the dark state with trans chromophore). This suggests that the light-induced isomerization of the chromophore, which leads to breaking of the hydrogen bond with the backbone amide of C69, brings the carbonyl into a new protein environment with different asymmetry than in the unbleached protein. The observed change in sign is mainly due to this effect, but a change in chromophore twist may also contribute. Thus, the 318 nm CD signal is a sensitive marker for the environment of the chromophore carbonyl, which samples various environments and configurations during the photocycle.     

Photochemical precipitation of thorium and cerium and their separation from other ions in aqueous solution

Thorium was precipitated from homogeneous solution by exposing solutions of thorium and periodate in dilute perchloric acid to 253.7 nm radiation from a low-pressure mercury lamp. Periodate is reduced photochemically to iodate which causes the formation of a dense precipitate of the basic iodate of thorium(IV). The precipitate was redissolved, the iodate reduced, the thorium precipitated first as the hydroxide, then as the oxalate and ignited to the dioxide for weighing. Thorium(IV) solutions containing 8-200 mg of ThO(2) gave quantitative results with a standard deviation (s) of 0.2 mg. Separations from 25 mg each of iron, calcium, magnesium, 50 mg of yttrium and up to 500 mg of uranium(VI) were quantitative (s = 0.25 mg). Separations from rare earths, except cerium, were accomplished by using hexamethylenetetramine rather than ammonia for the precipitation of the hydroxide. Cerium(III) was similarly precipitated and converted into CeO(2) for weighing. Quantitative results were obtained for 13-150 mg of CeO(2) with a standard deviation of 0.2 mg. Separations from 200 mg of uranium were quantitative. Other rare earths and yttrium interfered seriously. The precipitates of the basic cerium(IV) and thorium iodates obtained are more compact than those obtained by direct precipitation and can be handled easily. Attempts to duplicate Suzuki's method for separating cerium from neodymium and yttrium were not successful.