Dissociation of CH4 at high pressures and temperatures: diamond formation in giant planet interiors? (1/104)

Experiments using laser-heated diamond anvil cells show that methane (CH4) breaks down to form diamond at pressures between 10 and 50 gigapascals and temperatures of about 2000 to 3000 kelvin. Infrared absorption and Raman spectroscopy, along with x-ray diffraction, indicate the presence of polymeric hydrocarbons in addition to the diamond, which is in agreement with theoretical predictions. Dissociation of CH4 at high pressures and temperatures can influence the energy budgets of planets containing substantial amounts of CH4, water, and ammonia, such as Uranus and Neptune.  (+info)

Occupational asthma with paroxysmal atrial fibrillation in a diamond polisher. (2/104)

We present a case of a diamond polisher who developed occupational asthma as a result of prolonged exposure to various potent and well-recognized asthma-inducing agents, including cobalt dust. Although the patient was seen by various medical professionals during the initial course of his illness and given an early diagnosis of a respiratory condition, there were no attempts to evaluate the nature of his work, and therefore to establish a possible causal relationship with his exposures. This case clearly illustrates the importance of such an assessment. The ultimate fate of this patient (he had to retire from his job with a chronic and permanent illness) could have been avoided by early environmental intervention. In addition, this case illustrates a possible complication of asthma, that is, a severe cardiac arrhythmia. In this case, both the patient's symptoms and the prescribed medications contributed to worsening of the patient's underlying condition. Early diagnosis and intervention of this patient's work practices could have avoided this complication.  (+info)

Determination of elastic modulus of dentin by small spherical diamond indenters. (3/104)

A nano-indentation test was applied to determine elastic modulus (E) and hardness (H) of dentin. Three spherical indenters with nominal radii of 20, 5 and 1 microns were used and load/partial-unload cycles were repeated. Each cycle provided E and contact pressure or Meyer's hardness. The plot of contact pressure versus penetration depth was converted into a normalized indentation stress-strain relationship, which was used to select the optimum maximum indentation force for each indenter. The results were compared with those determined by the conventional triangular pyramidal (Berkovich) indenter technique. The comparable E value, irrespective of radius, was 19.5-20.9 GPa and the 1 micron indenter was able to provide E values of peritubular (28.0 GPa) and intertubular dentin (14.9 GPa). The H values generated with the Berkovich indentation technique were comparable to those determined by the spherical indenter technique at indentation strains of 0.9 and 0.5 for the 1 and 5 microns indenters.  (+info)

Microbial activity at gigapascal pressures. (4/104)

We observed physiological and metabolic activity of Shewanella oneidensis strain MR1 and Escherichia coli strain MG1655 at pressures of 68 to 1680 megapascals (MPa) in diamond anvil cells. We measured biological formate oxidation at high pressures (68 to 1060 MPa). At pressures of 1200 to 1600 MPa, living bacteria resided in fluid inclusions in ice-VI crystals and continued to be viable upon subsequent release to ambient pressures (0.1 MPa). Evidence of microbial viability and activity at these extreme pressures expands by an order of magnitude the range of conditions representing the habitable zone in the solar system.  (+info)

Diamond burr superficial keratectomy for recurrent corneal erosions. (5/104)

AIMS: To evaluate the efficacy and safety of diamond burr superficial keratectomy in the treatment of recurrent corneal erosions. METHODS: A retrospective review of 54 eyes (47 patients) with recurrent corneal erosions treated with diamond burr superficial keratectomy. Preoperative and postoperative visual acuities and refractions, slit lamp examination findings, and the incidence of recurrent erosion after keratectomy were studied. Specular microscopy was also performed in six patients before and after surgery. RESULTS: 30 eyes had underlying map dot fingerprint anterior basement membrane corneal dystrophy, while 24 eyes did not. Postoperative follow up time ranged from 3 to 53 months (mean 12.3 months). Corneal erosion recurred in three eyes (6%) after diamond burr superficial keratectomy. This procedure improved the best corrected visual acuity from 20/26 to 20/22 by logMAR statistical evaluation (p=0.002) and caused very little change in the refractive spherical equivalent. No endothelial cell loss or changes in morphology were noted on specular microscopy. CONCLUSION: Diamond burr superficial keratectomy appears to be an effective and safe method of treating recurrent erosions and is a good alternative therapy to needle stromal micropuncture, Nd:YAG induced epithelial adhesion, and excimer laser surface ablation.  (+info)

Quantitative analysis of dental porcelain surfaces following different treatments: correlation between parameters obtained by a surface profiling instrument. (6/104)

This investigation compared, by quantitative analysis, the surface roughness of dental porcelain submitted to three different treatments (glaze, trimming and polishing), utilizing a surface profiling instrument. The parameters Ra (median roughness), Rz (median of the maximum profile heights of five sample lengths), Rpm (median of the maximum profile heights related to the median line of five sample lengths), Pc (peak count per centimeter) and Rpm/Rz (proportional parameter) were evaluated. In addition, the correlation between Ra and the other parameters was analyzed. Based on the results obtained, it was seen that the Ra parameter did not present any correlation with the other parameters in some of the situations evaluated. This demonstrates that complementation of the measurement with other parameters is always necessary, providing a better evaluation of the functional properties of a surface.  (+info)

Surface roughness of composite resins after finishing and polishing. (7/104)

This study evaluated the effect of surface finishing methods on the average surface roughness of resin composites. Seven composites and two polishing systems were used. One hundred and twenty-six conical specimens of each material were prepared in stainless steel molds against a polyester strip. Forty-two of them remained intact and were used as controls. Each half of the remaining samples was polished with either diamond burs or diamond burs + aluminum oxide discs. The results showed no statistical difference in average surface roughness (Ra, microm) between the polyester strip and aluminum oxide discs (p > 0.05). However, finishing with diamond burs showed a statistically higher average roughness for all composites (p < 0.05). Statistical differences were detected among materials (p < 0.05) in the use of diamond burs.  (+info)

A pilot investigation of enamel reduction procedures. (8/104)

OBJECTIVE: To test and describe the use of various combinations of mechanical and chemical techniques for enamel reduction to obtain a smooth surface. METHODS: Bovine teeth (2 surfaces on each of 32 teeth) were used. The teeth were mounted in blocks of dental plaster, which were then mounted in a vise. The mesiodistal enamel contact areas were reduced by various combinations of mechanical and chemical aids. The mesiodistal width of each tooth was measured with a digital caliper after initial reduction of the enamel surface and again after polishing. The teeth were subsequently prepared and mounted for scanning electron microscopy. RESULTS: All combinations yielded statistically significant enamel reduction (p < 0.05). The use of acid stripping in conjunction with mechanical procedures produced especially smooth enamel surfaces. CONCLUSIONS: Steps must be taken to ensure that a smooth enamel surface remains after enamel reduction and polishing. It is recommended that conventional enamel etchants be added to the polishing procedure. Enamel reduction can increase available space, but the quantity of enamel that can be removed without adverse consequences should be carefully evaluated.  (+info)