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At least 325 records · Page 18Linked to original sources
PubMed1994

Krypton fluoride excimer laser ablation of tooth tissues: precision tissue machining.

A variety of lasers using different wavelengths have been used to remove dental hard tissue. The infrared lasers produce their effects photothermally whereas ultraviolet excimer lasers remove tissue in a controlled and precise manner by photoablation. This study investigates the use of 248 nm laser radiation in the precision removal of both enamel and dentine using diffraction limited ultraviolet optics. The data showed that enamel and dentine were machined to a high level of precision (1-2 micron tolerances). The rate of removal was greater in dentine than enamel at a range of energy densities between 1.15 and 2.2 J/cm2. The method of removal of both tissues appears to be by the preferential ablation of the organic phases of each, exposing the anatomical details of their structure. An explanation of the possible method of ablation is proposed for these tissues.

Dental Enamel↗
PubMed2005

Quadrupolar relaxation of hyperpolarized krypton-83 as a probe for surfaces.

This work reports the first systematic study of relaxation experienced by the hyperpolarized (hp) noble gas isotope (83)Kr (I=9/2) in contact with surfaces. The spin-lattice relaxation of (83)Kr is found to depend strongly on the chemical composition of the surfaces in the vicinity of the gas. This effect is caused by quadrupolar interactions during brief periods of surface adsorption that are the dominating source of longitudinal spin relaxation in the (83)Kr atoms. Simple model systems of closest packed glass beads with uniform but variable bead sizes are used for the relaxation measurements. The observed relaxation rates depend strongly on the chemical treatment of the glass surfaces and on the surface to volume ratio. Hp (83)Kr NMR relaxation measurements of porous polymers with pore sizes of 70-250 microm demonstrate the potential use of this new technique for material sciences applications.

Gases↗
PubMed2002

Double-well potential energy curve of cadmium-krypton molecule in the B1(5(3)P1) excited state.

The real shape of a double-well B1(5(3)P1)-state potential in CdKr van der Waals molecule was reconstructed applying both the experimental data, using a Birge-Sponer method-based analysis of the B1 <-- X0+(5(1)S0) transition in excitation spectrum, and theoretical result of recent ab initio calculation. An inverse perturbation approach method was used for defining an accurate B1-state potential energy curve.

Cadmium↗
PubMed2006

The far from equilibrium structure of argon clusters doped with krypton or xenon.

Heterogeneous clusters created by doping Ar host clusters with Kr or Xe are shown to have radically different structures from the mixed clusters of the same type created by co-expansion of Ar-Kr or Ar-Xe gas mixtures. In contrast to the co-expansion case, the doped mixed clusters can be produced with Kr or Xe on the surface and Ar in the bulk. With the doping technique it is thus possible to control the surface composition of a specific cluster. A study of the cluster properties as a function of the doping pressure is also reported for the case of Ar clusters doped with Xe. The clusters have been studied by means of synchrotron radiation based X-ray photoelectron spectroscopy.

Argon↗
PubMed1981

Measurements of regional ventilation using nitrogen-13 and krypton-81m in mechanically ventilated dogs.

13N2 and 81Krm were used to measure changes in upper/lower (U/L) ratios of regional ventilation in supine anaesthetised dogs mechanically ventilated at different tidal volumes and the results compared. Analysis of the slopes of the 13N2 washout curves indicated that U/L specific ventilation was less than unity at low tidal volumes and decreased as tidal volume increased. U/L total ventilation, measured using the specific ventilation results and estimations of relative lung using 13N2, also decreased with increase in tidal volume. Preferential distribution of ventilation to dependent lung regions thus increased with tidal volume despite the opposing hydrostatic forces from the abdomen. Regional count density distributions in 81Krm images of the lungs were analysed. At high specific ventilation rates, correction of 81Krm count density is required in order to obtain correct regional ventilation information. The specific ventilation rates in this series were such that the uncorrected U/L count ratios of 81Krm increased as tidal volume increased in contrast to the decrease in U/L total ventilation recorded by the 13N2 method. When corrections using the 13N2 specific ventilation results were applied, the changes in U/L 81Krm count ratios with tidal volume showed a similar trend to the changes in total ventilation measured with 13N2. Sources of error in the two techniques are briefly discussed.

Animals↗