Quantitative analysis of WC grain shape in sintered WC-Co cemented carbides

The morphology of WC grains is examined by ab initio calculations, and by transmission electron microscopy in a WC-Co cemented carbide. Two compositions are studied to determine the effect of carbon chemical potential on the shape development. The WC grains are found to be truncated triangles, and the grain morphology is adequately reproduced by the ab initio calculations. The energy difference between the two types of grain facets is shown to be due to the formation of stronger bonds with more covalent character between low coordinated W and Co atoms at one type of facet.     

Object characterization with refractometric digital Fourier holography

We demonstrate a digital holographic method in which two different substances in a blend are discerned. The method requires only one set of exposures and one reconstruction in the plane of focus. The phase is unwrapped by Flynn's discontinuity algorithm to produce an image of the variation of the optical distance of the illuminating wave. Objects with indices of refraction that are higher and lower than the mounting liquid are detected as regions in which the phase is increased and decreased, respectively. We also present a method for calculating the volume distribution of substrates in a sample. The method is experimentally demonstrated with crystals of NaCl and KCl.     

Low-temperature thermal conductivity of superconductors with gap nodes

We report a detailed analytic and numerical study of electronic thermal conductivity in d-wave superconductors. We compare theory of the crossover at low temperatures from T dependence to T(3) dependence for increasing temperature with recent experiments on YBa(2)Cu(3)O(7) in zero magnetic field for T approximately [0.04 K,0.4 K] by Hill et al. [Phys. Rev. Lett. 92, 027001 (2004)]. Transport theory, including impurity scattering and inelastic scattering within strong-coupling superconductivity, can consistently fit the temperature dependence of the data in the lower half of the temperature regime. We discuss the conditions under which we expect power-law dependences over wide temperature intervals.     

Single-optical-element soft-x-ray interferometry with a laser-plasma x-ray source

We report on a compact interferometer for the water-window soft-x-ray range that is suitable for operation with laser-plasma sources. The interferometer consists of a single diffractive optical element that focuses impinging x rays to two focal spots. The light from these two secondary sources forms the interference pattern. The interferometer was operated with a liquid-nitrogen jet laser-plasma source at lambda=2.88 nm. Scalar wave-field propagation was used to simulate the interference pattern, showing good correspondence between theoretical and experimental results. The diffractive optical element can simultaneously be used as an imaging optic, and we demonstrate soft-x-ray microscopy with interferometric contrast enhancement of a phase object.     

Narrowband bulk Bragg grating optical parametric oscillator

A narrowband, pulsed optical parametric oscillator (OPO) whose output coupler is a bulk glass Bragg grating is demonstrated. The OPO is based on periodically poled KTiOPO4 and is pumped by a pulsed, frequency-doubled Nd:YAG laser at 532 nm, generating a signal at 975 nm with a total efficiency of 35%. This novel and compact device shows a spectral bandwidth of 0.16 nm (50 GHz), a decrease by a factor of 20 compared with that when a conventional mirror is used. By using a folded cavity, we demonstrate tunable radiation with a tuning range of 60 nm and maintained spectral bandwidth.     

Synthesis of pentacyclic 13-azadibenzo[a,de]anthracenes via anionic cascade ring closure

Bromine-lithium exchange using tert-butyllithium at -78 degrees C initiates a cascade process whereby either xanthone derivatives or pentacyclic 13-azadibenzo[a,de]anthracenes are produced in high yields. The reaction proceeds via a sequential intramolecular trapping of organolithium intermediates.     

Development of a chiral non-aqueous capillary electrophoretic system using the partial filling technique with UV and mass spectrometric detection

A chiral non-aqueous CE system with UV and mass spectrometric detection has been developed. The enantioseparation was promoted by diastereomeric complex (ion-pair) formation between the amines (e.g. salbutamol, atenolol) and the chiral selector, (-)-2,3:4,6-di-O-isopropylidene-2-keto-L-gulonic acid [(-)-DIKGA]. Different solvent mixtures were studied, as well as different concentrations of (-)-DIKGA and ammonium acetate in the background electrolyte. A partial filling technique was developed with a selector plug composed of (-)-DIKGA and ammonium acetate in a solvent mixture of methanol and 2-propanol. The separated enantiomers of pronethalol were detected by a Q-TOF MS system equipped with a sheath-flow electrospray ionization interface.