Electron irradiation induced vitrification at dislocations in quartz
Recent observations using the ‘weak beam’ electron microscopy technique of split images of dislocations in quartz have been interpreted as arising either from dissociation of the dislocations into partials1, or from a glassy (metamict) phase at the core2, resulting from irradiation damage. In this letter we describe observations of lattice images of near end-on dislocations in quartz, which enable us to distinguish between these two models.
Lattice Defects and Mechanical Behaviour of Quartz SiO2
Quartz has the chemical composition SiO 2 . It is an abundant mineral in the Earth crust and its mechanical properties govern the rheological behaviour of a number of crustal rocks. Quartz is also a material widely used in industry (resonators, filters...) owing to its remarkable piezoelectric properties. Very small amounts of water in the quartz lattice dramatically affect its mechanical properties. The mechanical strength of wet quartz is at least 10 times lower than that of dry quartz. This effect of water on quartz has been called hydrolytic weakening. The piezoelectric performances of resonators are also dramatically reduced by the presence of amounts of water as small as [H]/[Si] 300 at. ppm. In order to get better performances, crystal growers have investigated the grown-in lattice defects (dislocations, twins, occurrence of water and other chemical impurities) and their influence on piezoelectric performances. The community of mineral physicists have also investigated the lattice defects in quartz, especially dislocations, and the physical factors influencing their mobility. They have also investigated the behaviour of quartz under extreme dynamic pressure ; this situation corresponds to shock waves generated by the impact of meteorites on the Earth's surface. The aim of this article is to review the mechanical behaviour of quartz under various thermomechanical conditions and the role of the impurity water on the relevant physical properties of quartz.
Direct orbital manometry in patients with thyroid-associated orbitopathy.
PURPOSE
To determine orbital tissue tension and orbital compartment compliance in patients with and without thyroid-associated orbitopathy (TAO).


DESIGN
Prospective case series.


PARTICIPANTS
Orbits of patients with TAO (18 orbits) and control patients without TAO (35 orbits) were studied.


METHODS
An orbital manometer was designed to directly measure orbital tissue tension in patients undergoing ocular or orbital surgery.


MAIN OUTCOME MEASURES
Tissue tension was recorded before, during, and for 5 minutes after a 5-ml retrobulbar injection of anesthetic. Orbital compliance was calculated as change in volume divided by change in tissue tension.


RESULTS
Resting orbital tissue tension was 4.4 +/- 2.2 mmHg (mean +/- SD) in normal orbits and 9.7 +/- 4.8 mmHg in orbits of TAO patients (P = 0.0005) Following retrobulbar injection, orbital tissue tension rose to 12.0 +/- 3.6 mmHg (P = 0.0000000000000006 compared with baseline) in the control group and to 36.3 +/- 15.2 mmHg in the TAO group (P = 0.0000007 compared with baseline, and P = 0.000008 TAO group versus control group). Orbital compartment compliance was 0.80 +/- 0.50 ml/mmHg in the control group and 0.27 +/- 0.21 ml/mmHg in the TAO group (P = 0.00001). Resting orbital tissue tension in 8 TAO orbits with compressive optic neuropathy was 12.4 +/- 4.9 mmHg, and was 7.8 +/- 3.5 mmHg in 10 orbits of TAO patients without compressive optic neuropathy (P < 0.05). No adverse events occurred.


CONCLUSIONS
Retrobulbar injection causes consistent measurable changes in orbital tissue tension. Orbital manometry safely demonstrated higher orbital tissue tension and lower orbital compartment compliance in the orbits of TAO patients versus those of normal subjects. Resting orbital tissue tension was higher in the orbits of TAO patients with compressive optic neuropathy than in those orbits without. Compressive optic neuropathy may partially result from an orbital compartment syndrome in some patients with TAO. Directly assessing orbital dynamics in vivo may prove useful as an adjunct in the clinical evaluation of patients with TAO and other orbital disorders.