The 2003 November 14 occultation by Titan of TYC 1343-1865-1

We observed a stellar occultation by Titan on 2003 November 14 from La Palma Observatory using ULTRACAM with three Sloan filters: u, g, and i (358, 487, and 758 nm, respectively). The occultation probed latitudes 2°?S and 1°?N during immersion and emersion, respectively. A prominent central flash was present in only the i filter, indicating wavelength-dependent atmospheric extinction. We inverted the light curves to obtain six lower-limit temperature profiles between 335 and 485 km (0.04 and 0.003 mb) altitude. The i profiles agreed with the temperature measured by the Huygens Atmospheric Structure Instrument [Fulchignoni, M., and 43 colleagues, 2005. Nature 438, 785 791] above 415 km (0.01 mb). The profiles obtained from different wavelength filters systematically diverge as altitude decreases, which implies significant extinction in the light curves. Applying an extinction model [Elliot, J.L., Young, L.A., 1992. Astron. J. 103, 991 1015] gave the altitudes of line of sight optical depth equal to unity: 396±7 and 401±20 km (u immersion and emersion); 354±7 and 387±7 km (g immersion and emersion); and 336±5 and 318±4 km (i immersion and emersion). Further analysis showed that the optical depth follows a power law in wavelength with index 1.3±0.2. We present a new method for determining temperature from scintillation spikes in the occulting body's atmosphere. Temperatures derived with this method are equal to or warmer than those measured by the Huygens Atmospheric Structure Instrument. Using the highly structured, three-peaked central flash, we confirmed the shape of Titan's middle atmosphere using a model originally derived for a previous Titan occultation [Hubbard, W.B., and 45 colleagues, 1993. Astron. Astrophys. 269, 541 563].

Calcium currents in interstitial cells from the guinea-pig bladder.

OBJECTIVE: To determine whether there are inward currents in interstitial cells (IC) isolated from the guinea-pig detrusor and if so, to characterise them using the patch-clamp technique and pharmacological agents. MATERIALS AND METHODS: Using the whole-cell patch-clamp technique, inward currents were studied in IC enzymatically isolated from the detrusor of the guinea-pig bladder. Currents were evoked by stepping positively from a holding potential of - 80 mV. RESULTS: Outward K+ currents were blocked by Cs+ internal solution to reveal inward currents, which activated at voltages more positive than - 50 mV, peaked at 0 mV, reversed near + 50 mV and were half-maximally activated at - 27 mV. The inward currents showed voltage-dependent inactivation and were half-maximally inactivated at - 36 mV. Fitting the activation and inactivation data with a Boltzmann function revealed a window current between - 40 mV and + 20 mV. The decay of the current evoked at 0 mV could be fitted with a single exponential with a mean time-constant of 88 ms. Replacing external Ca2+ with Ba2+ significantly increased this to 344 ms. The current amplitude was augmented by Ba2+, and by Bay K 8644. Inward currents were significantly reduced by 1 microm nifedipine, across the voltage range, but the blockade was more effective on the current evoked at 0 mV than that evoked by a step to - 20 mV, perhaps indicating voltage-dependence of the action of nifedipine or another component of inward current. Increasing the concentration of the drug to 10 microm caused no further significant reduction either at 0 mV or at -20 mV. However, in the presence of 1 microm nifedipine the latter current was significantly reduced by 100 microm Ni2+. Both currents were significantly reduced in Ca2+-free solution. CONCLUSIONS: IC from the guinea-pig detrusor possess inward currents with typical characteristics of L-type Ca2+ current. They also have a component of inward Ca2+ current, which was resistant to nifedipine, but sensitive to Ni2+. Further work is needed to characterise the latter conductance. PMID: 16686735 [PubMed - indexed for MEDLINE]

Influence of Different European Cements (CEM) on the Hydration of Cover-Zone Concrete during the Curing and Post Curing Periods

The durability of reinforced concrete structures depends, in the main, on the performance of the cover-zone concrete as it is this which protects the steel from the external environment. This paper focusses on the use of discretised electrical property measurements to study depth-related features during both the curing and post-curing period thereby allowing an integrated assessment of the protective properties of the cover region. In the current work, use is made of a small, multi-electrode array embedded within the surface 75mm of concrete specimens. Concretes were manufactured with different European cements (CEM) and water/binder ratios representing mixes which satisfied the minimum requirements for a range of environmental exposure classes including exposure to chlorides. Electrical resistance measurements were taken over a period in excess of 300 days which showed on-going hydration, pozzolanic reaction and pore-structure refinement; in addition, in the post-curing period, when exposed to a cyclic chloride ponding regime, measurements could be used to study the convective zone and ionic enrichment of the surface layer.

Modelling the control of interceptive actions

In recent years, several phenomenological dynamical models have been formulated that describe how perceptual variables are incorporated in the control of motor variables. We call these short-route models as they do not address how perception-action patterns might be constrained by the dynamical properties of the sensory, neural and musculoskeletal subsystems of the human action system. As an alternative, we advocate a long-route modelling approach in which the dynamics of these subsystems are explicitly addressed and integrated to reproduce interceptive actions. The approach is exemplified through a discussion of a recently developed model for interceptive actions consisting of a neural network architecture for the online generation of motor outflow commands, based on time-to-contact information and information about the relative positions and velocities of hand and ball. This network is shown to be consistent with both behavioural and neurophysiological data. Finally, some problems are discussed with regard to the question of how the motor outflow commands (i.e. the intended movement) might be modulated in view of the musculoskeletal dynamics.

Physical origin of the high reactivity of subsurface hydrogen in catalytic hydrogenation

In the catalytic hydrogenation of hydrocarbons, subsurface hydrogen is known experimentally to be much more reactive than surface hydrogen. We use density functional theory to identify low-energy pathways for the hydrogenation of methyl adsorbed on Ni(111) by surface and subsurface hydrogen. The metastability of subsurface hydrogen with respect to chemisorbed hydrogen is mainly responsible for the low activation barrier for subsurface reactions. (C) 1999 American Institute of Physics.