Silica nanoparticles produced by explosive flash vaporization during earthquakes.

Hydrothermal activity in the crust results in the precipitation of large volumes of silica and often involves the formation of ore deposits, the shaping of geothermal systems, and recurring earthquakes. Pore fluid pressures fluctuate between lithostatic and hydrostatic, depending on seismic activity, and some models suggest the possibility of flash vaporization, given that fluid pressures can drop to the level of vapour at fault jogs during seismic slip. The phase changes of water could create extremely high supersaturations of silica, but the mechanisms of quartz vein formation under such extreme conditions remain unclear. Here we describe flash experiments conducted with silica-saturated solutions under conditions ranging from subcritical to supercritical. We found that amorphous silica is produced instantaneously as spherical nano- to micron-scale particles via nucleation and aggregation during the evaporation of water droplets. The nanoparticles are transformed to microcrystalline quartz very rapidly by dissolution and precipitation in hydrothermal solutions, with this process requiring less than one day under supercritical conditions because of the huge surface areas involved. We suggest that such short-lived silica nanoparticles have significant impacts on the dynamic changes in mechanical behaviour and hydrology of hydrothermal systems in volcanic areas.

Drilling to gabbro in intact ocean crust.

Sampling an intact sequence of oceanic crust through lavas, dikes, and gabbros is necessary to advance the understanding of the formation and evolution of crust formed at mid-ocean ridges, but it has been an elusive goal of scientific ocean drilling for decades. Recent drilling in the eastern Pacific Ocean in Hole 1256D reached gabbro within seismic layer 2, 1157 meters into crust formed at a superfast spreading rate. The gabbros are the crystallized melt lenses that formed beneath a mid-ocean ridge. The depth at which gabbro was reached confirms predictions extrapolated from seismic experiments at modern mid-ocean ridges: Melt lenses occur at shallower depths at faster spreading rates. The gabbros intrude metamorphosed sheeted dikes and have compositions similar to the overlying lavas, precluding formation of the cumulate lower oceanic crust from melt lenses so far penetrated by Hole 1256D.

Relationship of hypotension and cerebral vasospasm in patients with aneurysmal subarachnoid hemorrhage.

OBJECTIVES: Changes in systemic arterial blood pressure and the degree of cerebral vasospasm were investigated in 125 patients with aneurysmal subarachnoid hemorrhage. METHODS: Systemic arterial blood pressure was measured every 2 hours in each patient for a period of more than 2 weeks, and a fall in systemic blood pressure (FBP) was defined as a decrease of >40 mmHg of systolic blood pressure between two consecutive measurements. RESULTS: A total of 91 FBPs occurred in 52 (41.6%) of 125 patients despite specific post-operative management to prevent hypovolemia. Five (5.5%) of the 91 FBPs occurred just before the onset of symptomatic vasospasm. Symptomatic vasospasm was observed in 36 (69.2%) of 52 patients with FBP and in 32 (43.8%) of 73 patients without FBP (p<0.01, chi-squared test). A hypodense area on computed tomographic scans in association with cerebral vasospasm was observed in 25 (48.1%) of 52 patients with FBP and in 21 (28.8%) of 73 patients without FBP (p<0.05). DISCUSSION: We conclude that FBP might result from delayed cerebral vasospasm and/or brain dysfunction owing to subarachnoid hemorrhage itself.

Novel approach to calvarial bone transport using a rabbit model.

Calvarial defects sometimes require cranioplasty to protect the brain. Alloplastic materials, such as acrylic resin, hydroxyapatite ceramics, and titanium, involve various problems, such as vulnerability, infection, deformity resulting from growth, and high cost. We devised a new bone transport model in the rabbit based on the distraction osteogenesis theory of Ilizarov. Twelve Japan white rabbits with a mean body weight of 2.5 kg aged 12 weeks were used. Craniectomy (7 x 14 mm) was performed in 12 rabbits. Trapezoid bone osteotomy was performed anterior to the calvarial defect in 10 rabbits. The distraction device (Extension-plates) was fixed between the trapezoid bone island and the skull. Distraction was initiated 5 days postoperatively. The device was activated once every other day, with approximately 0.75 mm or 0.5 mm per activation. Bone distraction was continued until the rod could not be moved. The lengths of distraction were 4 mm in two cases, 5 mm in one case, 6 mm in one case, and 7 mm in two cases, with a mean of 5.5 +/- 0.56 mm. Both radiographic and histological findings showed osteogenesis by intramembranous ossification and trans-chondroid bone formation. Distraction osteogenesis has potential clinical applications in cranioplasty, especially in children because usage of autogenous bone is difficult if not impossible in most cases.

Attenuation of vascularity by preoperative radiosurgery facilitates total removal of a hypervascular hemangioblastoma at the cerebello-pontine angle: case report.

BACKGROUND: The surgical removal of solid, large, and deep-seated hemangioblastomas remains challenging because it is difficult to control bleeding during the procedure. We used preoperative radiosurgery in a solid, highly vascular hemangioblastoma at the left cerebello-pontine angle and present our angiographic, operative, and histologic findings. CASE DESCRIPTION: A 37-year-old paraplegic woman with multiple hemangioblastomas was re-admitted to our clinic with cerebellar ataxia 6 years after resection of a tumor at the fourth ventricle. A vertebral artery angiogram revealed that the 3.5 cm diameter hemangioblastoma at the left cerebello-pontine angle was highly vascular and fed by the left anterior inferior cerebellar artery and posterior inferior cerebellar artery. Nine months before surgical removal it was treated with stereotactic radiosurgery (gamma knife, margin dose 28 Gy) to inhibit tumor progression and to reduce its vascularity. The tumor was totally removed via the left lateral suboccipital approach; bleeding was well controlled and there were no complications. Pathologic examination of the content of the excised tumor revealed coagulation necrosis with hyaline degeneration of the tumor vessels, resulting in a marked decrease in its vascularity. CONCLUSION: Preoperative radiosurgery led to a marked reduction in the vascularity of this hypervascular hemangioblastoma and was useful for controlling bleeding from the tumor during resection. We succeeded to remove the vascular-rich hemangioblastma after the intentional preoperative radiosurgery. The pathologic changes induced by radiotherapy were confirmed by operative finding.