Direct time-resolved study of the kinetics of the reaction of silylene with phenylsilane in the gas phase. Does SiH2 react with the aromatic ring?

Laser flash photolysis studies of silylene, SiH2, generated by the 193 nm laser flash photolysis phenylsilane, PhSiH3, have been carried out to obtain rate constants for its bimolecular reaction with PhSiH3 itself, in the gas phase. The reaction was studied in SF6 (mostly at 10 Torr total pressure) over the temperature range 298-595 K. The rate constants (also found to be pressure independent) gave the following Arrhenius equation: log(k/cm(3) molecule(-1) s(-1)) = (-9.92 +/- 0.04) + (3.31 +/- 0.27) kJ mol(-1)/RT ln 10 Similar investigations of the reaction of silylene with benzene, C6H6, (295-410 K) gave data suggestive of the fact that SiH2 might be reacting with photochemical products of C6H6 as well as with C6H6 itself. However, in the latter system, apparent rate constants were sufficiently low to indicate that in the reaction of SiH2 with PhSiH3 addition to the aromatic ring was unlikely to be in excess of 3% of the total. Quantum chemical calculations of the energy surface for SiH2 + C6H6 indicate that 7-silanorcaradiene and 7-silacycloheptatriene are possible products but that PhSiH3 formation is unlikely. RRKM calculations suggest that 7-silanorcaradiene should be the initial product but that it cannot be collisionally stabilized under experimental conditions

Bottom-up, not top-down, modulation of imitation by human and robotic models

Visual observation of human actions provokes more motor activation than observation of robotic actions. We investigated the extent to which this visuomotor priming effect is mediated by bottom-up or top-down processing. The bottom-up hypothesis suggests that robotic movements are less effective in activating the ‘mirror system’ via pathways from visual areas via the superior temporal sulcus to parietal and premotor cortices. The top-down hypothesis postulates that beliefs about the animacy of a movement stimulus modulate mirror system activity via descending pathways from areas such as the temporal pole and prefrontal cortex. In an automatic imitation task, subjects performed a prespecified movement (e.g. hand opening) on presentation of a human or robotic hand making a compatible (opening) or incompatible (closing) movement. The speed of responding on compatible trials, compared with incompatible trials, indexed visuomotor priming. In the first experiment, robotic stimuli were constructed by adding a metal and wire ‘wrist’ to a human hand. Questionnaire data indicated that subjects believed these movements to be less animate than those of the human stimuli but the visuomotor priming effects of the human and robotic stimuli did not differ. In the second experiment, when the robotic stimuli were more angular and symmetrical than the human stimuli, human movements elicited more visuomotor priming than the robotic movements. However, the subjects’ beliefs about the animacy of the stimuli did not affect their performance. These results suggest that bottom-up processing is primarily responsible for the visuomotor priming advantage of human stimuli.

Synthesis of the first-membered ring compound containing three tin atoms and one oxygen. The crystal structure of the species [O{Sn(C6H3Et2-2,6)2}3]

Aerial oxidation of the novel homocyclic tetratin species [{SnAr2}3SnArBr] (1) [1] (Ar  C6H3Et2-2,6) affords the tritin heterocycle [O{Sn(C6H3Et2-2,6)2}3] (2), which has been crystallographically characterised; 2 is the first reported oxatristannacyclobutane, and the first heterocyclic tin species having both tintin and tinheteroatom bonds.

Whose land was it anyway? The Crichel Down Rules and the sale of public land

The guiding principle of compulsory purchase of interests in land in England and Wales is that of fairness, best stated in the words of Lord Justice Scott in Horn v Sunderland Corporation when he said that the owner has “the right to be put, so far as money can do it, in the same position as if his land had not been taken from him”. In many instances, land acquired by compulsion subsequently becomes surplus to the requirements of the acquiring authority. This may be because the intended development scheme was scrapped, or substantially modified, or that after the passage of time the use of the land for which the purchase took place is no longer required. More controversially it may be that for ‘operational reasons’ the acquiring authority knowingly purchased more land than was required for the scheme. Under these circumstances, the Crichel Down Rules (‘the Rules’) require government departments and other statutory bodies to offer back to the former owners or their successors, any land previously so acquired by, or under the threat of, compulsory purchase.

The distribution of the ring current: Cluster observations

Extending previous studies, a full-circle investigation of the ring current has been made using Cluster 4-spacecraft observations near perigee, at times when the Cluster array had relatively small separations and nearly regular tetrahedral configurations, and when the Dst index was greater than −30 nT (non-storm conditions). These observations result in direct estimations of the near equatorial current density at all magnetic local times (MLT) for the first time and with sufficient accuracy, for the following observations. The results confirm that the ring current flows westward and show that the in situ average measured current density (sampled in the radial range accessed by Cluster 4–4.5RE) is asymmetric in MLT, ranging from 9 to 27 nAm−2. The direction of current is shown to be very well ordered for the whole range of MLT. Both of these results are in line with previous studies on partial ring extent. The magnitude of the current density, however, reveals a distinct asymmetry: growing from 10 to 27 nAm−2 as azimuth reduces from about 12:00MLT to 03:00 and falling from 20 to 10 nAm−2 less steadily as azimuth reduces from 24:00 to 12:00MLT. This result has not been reported before and we suggest it could reflect a number of effects. Firstly, we argue it is consistent with the operation of region-2 field aligned-currents (FACs), which are expected to flow upward into the ring current around 09:00MLT and downward out of the ring current around 14:00MLT. Secondly, we note that it is also consistent with a possible asymmetry in the radial distribution profile of current density (resulting in higher peak at 4– 4.5RE). We note that part of the enhanced current could reflect an increase in the mean AE activity (during the periods in which Cluster samples those MLT).