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At least 847 records · Page 47Linked to original sources
PubMed1992

[Contact cyclophotocoagulation with the continuous wave Nd:YAG laser with quartz fiber. Optimizing coagulation parameters].

Transscleral cyclo-photocoagulation with a cw-Nd:YAG-laser was studied in enucleated porcine eyes with application times of between 10 ms and 1.5 s. Contact coagulation via a quartz fiber (core 600 microns) required about 32% less power to create visible ciliary body coagulation compared to non-contact coagulation via a focusing handpiece. Application of focusing fiber tips led to a further reduction in the coagulation threshold by a factor of 0.6. The energy per laser application required for ciliary body coagulation increased with application time. During contact coagulation using plane fiber tips a pronounced temperature rise was sometimes observed at the fiber tip due to deposits of carbonized tissue with the subsequent risk of scleral damage. In a pilot study five eyes with secondary glaucoma were treated under coagulation conditions found to be optimal (8 W at 0.2 s).

Anesthesia, Local↗
PubMedDate not supplied

[The possibilities for the objective assessment of the color of dental materials on the Quartz-4-type spectrophotometer].

The authors analyzed the possibility of using the Quartz 4 type acoustic-optic spectrophotometer to identify the shades of stomatologic materials. Analysis of spectral aperture coefficient curves was carried out for 10 shades of plastics used to make permanent dentures Sinma-M. The authors came to the conclusion on the usefulness of such method of identification of the stomatologic material shades and even of the intermediate gradations of these shades. Using this method, it is possible to control the material surface color homogeneity.

Color↗
PubMed2004

Influence of interchannel spacing on the dynamical properties of multichannel quartz crystal microbalance.

For a multichannel quartz crystal microbalance (MQCM) device, the key problem in design is to minimize the frequency interference between adjacent channels. In this paper, the effects of interchannel separation on the resonance frequencies and frequency interference of the device are studied. The results show that, for the channels with the same size, the resonant modes will appear alternatively, and the frequency interference keeps oscillating in a very small scope in the cases of large interchannel separations. Based on the studies, the considerations for MQCM design also are discussed.

Letter↗
PubMedDate not supplied

Salivary films on hydroxyapatite studied by an in vitro system for investigating the effect of metal ions and by a quartz-crystal microbalance system for monitoring layer-by-layer film formation.

The salivary film or the acquired pellicle is a protein film formed initially on the enamel surface of teeth. Such a film plays an important role in enamel protection, but is also an initial substructure for the formation of plaque and the cosmetically undesirable colored stain. The composition and the structure of the film are still essentially unknown because of the difficulty of its isolation for characterization. The purpose of this study was to investigate the effect of some metal cations on the salivary film or the pellicle formation, and also to clarify the mechanism of development. First, using infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS), the in situ-formed film in the mouth was confirmed to contain selectively adsorbed well-known proteins. Then, in vitro studies have demonstrated that Ca2+ ions enhance film formation at the initial stage in virtue of Ca bridging and, interestingly, that Mg2+ ions oppositely inhibit the formation. Furthermore, the quartz-crystal microbalance (QCM), utilized successfully for the first time to study the salivary film, has shown the possibility of an alternate accumulation mechanism by which the surface charges on the film are effectively reversed by the opposite charged proteins.

Durapatite↗
PubMedDate not supplied

The effect of composite type on microhardness when using quartz-tungsten-halogen (QTH) or LED lights.

This study evaluates the Knoop microhardness of resin composites cured with different light-emitting diode (LED) based light curing units (LCU) or with a conventional quartz-tungsten-halogen light (QTH). Ten experimental groups with 10 specimens each were used. The specimens were prepared by placing two light-cured resin composites with similar VITA shade A2-microhybrid Filtek Z250/3M ESPE and microfill Durafil VS/Heraeus Kulzer--in a 2.0 mm-thick disc shaped mold. The specimens were polymerized for 40 seconds with the use of one QTH LCU (Optilux 501/Kerr-Demetron) and four LED LCUs: Elipar FreeLight 1 Cordless LED (3M ESPE), Ultrablue II LED with cord (DMC), Ultrablue III LED cordless (DMC) and LEC 470 I (MM Optics). Knoop microhardness was determined at the top and bottom surfaces of the specimens 24 hours following curing. Microhardness values in the microhybrid resin composite group showed no statistically significant differences when cured with LED FreeLight 1 LCU and QTH LCU (p<0.05). The other LED devices evaluated in the study presented lower microhardness values in both surfaces (p<0.05) when compared to QTH. In the microfill resin composite group, no statistically significant differences were observed among all LCUs evaluated on the bottom surfaces (p<0.05). However, on the top surfaces, QTH presented the highest KHN values, and the LED devices presented similar results when compared with KHN values relative to each other (p<0.05).

Analysis of Variance↗
PubMed2006

A contribution to solve the problem of coating properties extraction in quartz crystal microbalance applications.

The problem of coating properties extraction in quartz crystal resonator (QCR) applications is one of the challenging tasks of QCR applications, not completely solved even in theoretical conditions. The present work demonstrates that the problem is determined only for a set of three parameters of the coating, which concentrate the four coating properties. The following parameters are chosen: the surface mass density m8 = p1h1, the loss tangent tan delta1 = G''1/G'1, and the magnitude of the characteristic impedance /Z1(c)/ = (p1/G1/)(1/2). An algorithm is proposed that permits, in ideal conditions, an unambiguous extraction of these parameters, starting only from the admittance spectrum of a three-layer compound resonator, obtained from the one-dimensional transmission-line model (TLM) around the resonance. The algorithm introduces three additional improvements in relation to other routines: the calculation time is drastically reduced, the problem of erroneous solutions related to relative minima in typical fitting routines is eliminated, and a systematic error analysis in the extraction of the coating properties in real practice can be carried out. The use of the proposed algorithm as a tool for studying the effects of different phenomena such as slipping or surface roughness is introduced.

Journal Article↗
PubMed1989

[In vitro studies of refractive corneal surgery using the excimer laser with quartz fiber].

With the application of different approved drugs, UV absorption of the cornea at 308 nm could be increased by more than three orders of magnitude, which provided effective shielding of intraocular structures against 308 nm excimer laser radiation. The width of the thermal damage zones at the edges of 308 nm excimer laser excisions was reduced to a few micrometers by our treatment. The ablation threshold was reduced by this treatment and the ablation rates were increased by a factor of three to five. In principle, these results offer the possibility of performing refractive corneal surgery with excimer lasers at 308 nm via quartz fibers.

Animals↗