An infrared measurement of chemical desorption from interstellar ice analogues

In molecular clouds at temperatures as low as 10 K, all species except hydrogen and helium should be locked in the heterogeneous ice on dust grain surfaces. Nevertheless, astronomical observations have detected over 150 different species in the gas phase in these clouds. The mechanism by which molecules are released from the dust surface below thermal desorption temperatures to be detectable in the gas phase is crucial for understanding the chemical evolution in such cold clouds. Chemical desorption, caused by the excess energy of an exothermic reaction, was first proposed as a key molecular release mechanism almost 50 years ago. Chemical desorption can, in principle, take place at any temperature, even below the thermal desorption temperature. Therefore, astrochemical net- work models commonly include this process. Although there have been a few previous experimental efforts, no infrared measurement of the surface (which has a strong advantage to quantify chemical desorption) has been performed. Here, we report the first infrared in situ measurement of chemical desorption during the reactions H + H2S -> HS + H2 (reaction 1) and HS + H -> H2S (reaction 2), which are key to interstellar sulphur chemistry. The present study clearly demonstrates that chemical desorption is a more efficient process for releasing H2S into the gas phase than was previously believed. The obtained effective cross-section for chemical desorption indicates that the chemical desorption rate exceeds the photodesorption rate in typical interstellar environments

EFFECTS OF TEMPO AND DRUMMING PATTERN UPON THE ENERGY COST AND GROUND REACTION FORCE OF JAPANESE DRUM PLAYING EXERCISE

INTRODUCTION Several investigators have shown the physiological and biomechanical data in music instrumental playing so far (Bejjani & Halpern, 1989; Bouhuys, 1969). However, little quantitative information exists as to the responses to this unique type of exercise. The purpose of this study was to investigate effects of tempo and drumming pattern upon the energy cost and ground reaction force of Japanese drum playing exercise. METHODS Seven virtuosi players performed playing a huge Japanese drum with a pair of large wooden sticks (0.53 kg) at three tempos by three drumming patterns so as to keep a given sound level of 120 dB. Oxygen uptake was determined with Douglas bag technique and ground reaction force was recorded using a strain-gauge type force plate. RESULTS As for tempo and drumming pattern, no significant difference was observed in any physiological variables involving the energy cost. Maximum vertical ground reaction force showed significant difference among tempos (