Areal-Density Capability Measurement Based on 747 Test in Magnetic Recording Systems
A method is presented for determining the areal density (AD) capability of a magnetic recording system based on a set of 747 tests taken over a range of linear densities. By fitting the measured results with a suitable functional form, we can readily predict off-track capability (OTC) at any combination of linear density and track density. Conversely, for a given OTC requirement, we can immediately find the maximum AD that can be reached and the bit aspect ratio required to achieve it. Our results also reveal the effect of skew angle on AD and match well with previous results for perpendicular magnetic recording.
A Physical Model for Predicting Off-Track Capability in Perpendicular Recording
Off-track capability (OTC) after adjacent track squeeze is a critical and independent parameter for determining the track density in hard disk drives. A semi-elliptical equation is derived based on a physical model for the writer pole with an isosceles trapezoid shape. It explains the different behaviors of OTC versus track pitch from both squeeze directions, as well as the variation of OTC versus track pitch due to the change of skew angle. The calculated data of OTC versus track pitch are in good agreement with the experimental data measured from the drive with perpendicular magnetic recording media.
Human exposure to methylmercury from crayfish (Procambarus clarkii) in China
Methylmercury (MeHg) accumulation in aquatic food raises global concerns about human exposure to MeHg. Crayfish is the world’s third largest farmed crustacean species and a favorite aquatic food in many countries. However, human health hazard due to MeHg exposure via crayfish consumption is unclear, partly because appropriate survey data are lacking. We report on mercury concentrations and speciation in edible tail muscle of crayfish collected from restaurants in 23 Chinese cities. On average, MeHg constituted 99.1 % of mercury in tail muscle, and MeHg concentrations were comparable with those reported for fish in China. Variation in MeHg concentrations was not attributable to broad geographic region (i.e., provinces) or tail length. For different populations, potential health risk (characterized by hazard quotient or HQ) of MeHg exposure through crayfish consumption depended largely on crayfish consumption rates. In particular, a health hazard (HQ > 1) was found for high-rate consumers (i.e., 95 %ile or higher) in some cities in the middle and lower reaches of the Yangtze River (MLYR), during the peak consumption season. Our results suggest that more attention should be paid to dietary MeHg intake via crayfish consumption in China, particularly for communities with high consumption in MLYR.