Fundamental limits to imaging resolution for focused ion beams

This article investigates the limitations on the formation of focused ion beam images from secondary electrons. We use the notion of the information content of an image to account for the effects of resolution, contrast, and signal‐to‐noise ratio and show that there is a competition between the rate at which small features are sputtered away by the primary beam and the rate of collection of secondary electrons. We find that for small features, sputtering is the limit to imaging resolution, and that for extended small features (e.g., layered structures), rearrangement, redeposition, and differential sputtering rates may limit the resolution in some cases

Emergency Portacaval Shunt Versus Rescue Portacaval Shunt in a Randomized Controlled Trial of Emergency Treatment of Acutely Bleeding Esophageal Varices in Cirrhosis—Part 3

Emergency treatment of bleeding esophageal varices in cirrhosis is of singular importance because of the high mortality rate. Emergency portacaval shunt is rarely used today because of the belief, unsubstantiated by long-term randomized trials, that it causes frequent portal-systemic encephalopathy and liver failure. Consequently, portacaval shunt has been relegated solely to salvage therapy when endoscopic and pharmacologic therapies have failed. Question: Is the regimen of endoscopic sclerotherapy with rescue portacaval shunt for failure to control bleeding varices superior to emergency portacaval shunt? A unique opportunity to answer this question was provided by a randomized controlled trial of endoscopic sclerotherapy versus emergency portacaval shunt conducted from 1988 to 2005. Unselected consecutive cirrhotic patients with acute bleeding esophageal varices were randomized to endoscopic sclerotherapy (n = 106) or emergency portacaval shunt (n = 105). Diagnostic workup was completed and treatment was initiated within 8 h. Failure of endoscopic sclerotherapy was defined by strict criteria and treated by rescue portacaval shunt (n = 50) whenever possible. Ninety-six percent of patients had more than 10 years of follow-up or until death. Comparison of emergency portacaval shunt and endoscopic sclerotherapy followed by rescue portacaval shunt showed the following differences in measurements of outcomes: (1) survival after 5 years (72% versus 22%), 10 years (46% versus 16%), and 15 years (46% versus 0%); (2) median post-shunt survival (6.18 versus 1.99 years); (3) mean requirements of packed red blood cell units (17.85 versus 27.80); (4) incidence of recurrent portal-systemic encephalopathy (15% versus 43%); (5) 5-year change in Child’s class showing improvement (59% versus 19%) or worsening (8% versus 44%); (6) mean quality of life points in which lower is better (13.89 versus 27.89); and (7) mean cost of care per year ($39,200 versus$216,700). These differences were highly significant in favor of emergency portacaval shunt (all p < 0.001). Emergency portacaval shunt was strikingly superior to endoscopic sclerotherapy as well as to the combination of endoscopic sclerotherapy and rescue portacaval shunt in regard to all outcome measures, specifically bleeding control, survival, incidence of portal-systemic encephalopathy, improvement in liver function, quality of life, and cost of care. These results strongly support the use of emergency portacaval shunt as the first line of emergency treatment of bleeding esophageal varices in cirrhosis

The behavior of solid hydrogen at 342 GPa

Theoretical calculations indicate that the hydrogen molecule should depair at high pressures and eventually form a new alkali metal. The resultant alkali metal sample in the diamond anvil cell would not be transparent in the visible. Experimentally, we find that hydrogen is still transparent at 342 GPa. This represents over a 50% increase in the static pressure at which scientific studies have been made by other groups

Use of focused ion beams for making tiny sample holes in gaskets for diamond anvil cells

To achieve multimegabar pressures in the diamond anvil cell, small diamond tips, 20 μm (or less) in diameter and high strength gasket materials are required. To prevent plastic instability it is therefore necessary to drill sample holes with diameters of 10 μm (or less) in extremely strong and tough materials such as tungsten. The present paper describes a technique for drilling such holes using focused ion beams. The superior roundness and surface finish of these holes is one of the reasons our group was able to reach pressures of 342 GPa on hydrogen, significantly higher than that reached by other researchers

Solid hydrogen at 342 GPa: no evidence for an alkali metal

Solid hydrogen, an electrical insulator, is predicted to become an alkali metal under extreme compression, although controversy surrounds the pressure required to achieve this^1–3. The electrical conductivity of hydrogen as a function of pressure and temperature is of both fundamental and practical interest—metallic hydrogen may be of relevance to planetary interiors⁴ and has been suggested as a potential high-temperature superconductor⁵. Calculations^1,2 suggest that depairing (destruction of the molecular bond) should occur around 340 GPa, accompanied by the formation of an alkali metal at this pressure1 or at substantially higher pressures^2,3. Here we report that solid hydrogen does not become an alkali metal at pressures of up to 342 ± 10 GPa, achieved using a diamond anvil cell. This pressure (which is almost comparable to that at the centre of the Earth) significantly exceeds those reached in earlier experiments—216 GPa (ref. 6) and 191 GPa (ref. 7)—at which hydrogen was found to be non-metallic. The failure of solid hydrogen to become an alkali metal at the extreme pressures reported here has implications for our current theoretical understanding of the solid-state phase