On the basis of previous ground-based and fly-by information, we knew that Titan's atmosphere was mainly nitrogen, with some methane, but its temperature and pressure profiles were poorly constrained because of uncertainties in the detailed composition. The extent of atmospheric electricity ('lightning') was also hitherto unknown. Here we report the temperature and density profiles, as determined by the Huygens Atmospheric Structure Instrument (HASI), from an altitude of 1,400 km down to the surface. In the upper part of the atmosphere, the temperature and density were both higher than expected. There is a lower ionospheric layer between 140 km and 40 km, with electrical conductivity peaking near 60 km. We may also have seen the signature of lightning. At the surface, the temperature was 93.65 +/- 0.25 K, and the pressure was 1,467 +/- 1 hPa.

[1] Huygens Atmospheric Structure Instrument (HASI) for the first time performed an in situ measurement of the thermal structure in Titan's atmosphere with a vertical resolution sufficient to analyze the planetary boundary layer (PBL). The vertical potential temperature profile reveals the presence of a weakly convective PBL, with a surface layer thickness of 10 m and an outer layer with a depth of 300 m. With a mean eddy diffusivity of only $7.4 Â 10 À3 m 2 s À1, the turbulence in the PBL is weak. The turbulent heat flux in the surface layer was upward but tiny ($0.02 W m À2 ), indicating that the ground surface was marginally warmer than the air. The surface heat flux is too small to cause a diurnal variation of the PBL except in the lowest few meters, so the observed profile may be a nearly steady state feature within this season at the landing site. In the surface layer the mean wind speed is likely to be less than 0.1 m s À1 . Given the tiny surface heat flux, the buoyant production of turbulence is very weak. The PBL structure reveals that the weather condition at the time and place of the Huygens landing resembles a calm, overcast day on Earth but is clearly different from the PBL typical for the polar night.

Total serum bile acids measured by enzymatic fluorometry and routine liver function tests were determined in a large population including 97 healthy subjects, 138 patients free of hepatobiliary diseases but affected by other diseases, and 344 patients with mild or severe hepatobiliary diseases. In order to define the diagnostic value and some operational characteristics of serum bile acids, sensitivity, specificity, and several predictive value tables for increasing cutoff levels of serum bile acids were calculated by means of a computer program. Serum bile acids and aspartate aminotransferase were found to be similar in sensitivity, specificity, and predictive value. Serum aspartate aminotransferase was found to be more suitable than serum bile acids in detecting mild hepatobiliary diseases, whereas serum bile acids were more sensitive than routine liver tests in the evaluation of severe hepatobiliary diseases. In view of its ability to detect severe hepatobiliary diseases, serum bile acids test may play a decisive role in clinical practice (eg, decision to perform a liver biopsy).

The SIMBIO-SYS (Spectrometer and Imaging for MPO BepiColombo Integrated Observatory SYStem) is a complex instrument suite part of the scientific payload of the Mercury Planetary Orbiter for the BepiColombo mission, the last of the cornerstone missions of the European Space Agency (ESA) Horizon + science program. The SIMBIO-SYS instrument will provide all the science imaging capability of the Bepi-Colombo MPO spacecraft. It consists of three channels: the STereo imaging Channel (STC), with a broad spectral band in the 400-950 nm range and medium spatial resolution (at best 58 m/px), that will provide Digital Terrain Model of the entire surface of the planet with an accuracy better than 80 m; the High Resolution Imaging Channel (HRIC), with broad spectral bands in the 400-900 nm range and high spatial resolution (at best 6 m/px), that will pro-The BepiColombo mission to Mercury Edited by Johannes Benkhoff, Go Murakami and Ayako Matsuoka B G. Cremonese

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