Kinetic simulation of neutral∕ionized gas and electrically charged dust in the coma of comet 67P∕Churyumov-Gerasimenko

The cometary coma is a unique phenomenon in the solar system being a planetary atmosphere influenced by little or no gravity. As a comet approaches the sun, the water vapor with some fraction of other gases sublimate, generating a cloud of gas, ice and other refractory materials (rocky and organic dust) ejected from the surface of the nucleus. Sublimating gas molecules undergo frequent collisions and photochemical processes in the near‐nucleus region. Owing to its negligible gravity, comets produce a large and highly variable extensive dusty coma with a size much larger than the characteristic size of the cometary nucleus. The Rosetta spacecraft is en route to comet 67P/Churyumov‐Gerasimenko for a rendezvous, landing, and extensive orbital phase beginning in 2014. Both, interpretation of measurements and safety consideration of the spacecraft require modeling of the comet’s dusty gas environment. In this work we present results of a numerical study of multispecies gaseous and electrically charged dust environment of comet Chyuryumov‐Gerasimenko. Both, gas and dust phases of the coma are simulated kinetically. Photolytic reactions are taken into account. Parameters of the ambient plasma as well as the distribution of electric/magnetic fields are obtained from an MHD simulation [1] of the coma connected to the solar wind. Trajectories of ions and electrically charged dust grains are simulated by accounting for the Lorentz force and the nucleus gravity.

Bone conduction responses of middle ear structures in Thiel embalmed heads

Thiel-embalmed human whole-head specimens offer a promising alternative model for bone conduction (BC) studies of middle ear structures. In this work we present the Thiel model’s linearity and stability over time as well as its possible use in the study of a fixed ossicle chain. Using laser Doppler vibrometry (LDV), the motion of the retroauricular skull, the promontory, the stapes footplate and the round window (RW) were measured. A bone-anchored hearing aid stimulated the ears with step sinus tones logarithmically spread between 0.1 and 10 kHz. Linearity of the model was verified using input levels in steps of 10 dBV. The stability of the Thiel model over time was examined with measurements repeated after hours and weeks. The influence of a cement-fixed stapes was assessed. The middle ear elements measured responded linearly in amplitude for the applied input levels (100, 32.6, and 10 mV). The variability of measurements for both short- (2 h) and long-term (4-16 weeks) repetitions in the same ear was lower than the interindividual difference. The fixation of the stapes induced a lowered RW displacement for frequencies near 750 Hz (-4 dB) and an increased displacement for frequencies above 1 kHz (max. +3.7 dB at 4 kHz). LDV assessment of BC-induced middle ear motion in Thiel heads can be performed with stable results. The vibratory RW response is affected by the fixation of the stapes, indicating a measurable effect of ossicle chain inertia on BC response in Thiel embalmed heads.

Detection efficiency of microchannel plates for e(-) and pi(-) in the momentum range from 17.5 to 345 MeV/c

High-energy e(-) and pi(-) were measured by the multichannel plate (MCP) detector at the PiM1 beam line of the High Intensity Proton Accelerator Facilities located at the Paul Scherrer Institute, Villigen, Switzerland. The measurements provide the absolute detection efficiencies for these particles: 5.8% +/- 0.5% for electrons in the beam momenta range 17.5-300 MeV/c and 6.0% +/- 1.3% for pions in the beam momenta range 172-345 MeV/c. The pulse height distribution determined from the measurements is close to an exponential function with negative exponent, indicating that the particles penetrated the MCP material before producing the signal somewhere inside the channel. Low charge extraction and nominal gains of the MCP detector observed in this study are consistent with the proposed mechanism of the signal formation by penetrating radiation. A very similar MCP ion detector will be used in the Neutral Ion Mass (NIM) spectrometer designed for the JUICE mission of European Space Agency (ESA) to the Jupiter system, to perform measurements of the chemical composition of the Galilean moon exospheres. The detection efficiency for penetrating radiation determined in the present studies is important for the optimisation of the radiation shielding of the NIM detector against the high-rate and high-energy electrons trapped in Jupiter's magnetic field. Furthermore, the current studies indicate that MCP detectors can be useful to measure high-energy particle beams at high temporal resolution. (C) 2015 AIP Publishing LLC.