Dust cloud evolution in sub-stellar atmospheres via plasma deposition and plasma sputtering

Context. In contemporary sub-stellar model atmospheres, dust growth occurs through neutral gas-phase surface chemistry. Recently, there has been a growing body of theoretical and observational evidence suggesting that ionisation processes can also occur. As a result, atmospheres are populated by regions composed of plasma, gas and dust, and the consequent influence of plasma processes on dust evolution is enhanced.Aim. This paper aims to introduce a new model of dust growth and destruction in sub-stellar atmospheres via plasma deposition and plasma sputtering.Methods. Using example sub-stellar atmospheres from DRIFT-PHOENIX, we have compared plasma deposition and sputtering timescales to those from neutral gas-phase surface chemistry to ascertain their regimes of influence. We calculated the plasma sputtering yield and discuss the circumstances where plasma sputtering dominates over deposition.Results. Within the highest dust density cloud regions, plasma deposition and sputtering dominates over neutral gas-phase surface chemistry if the degree of ionisation is ≳10−4. Loosely bound grains with surface binding energies of the order of 0.1–1 eV are susceptible to destruction through plasma sputtering for feasible degrees of ionisation and electron temperatures; whereas, strong crystalline grains with binding energies of the order 10 eV are resistant to sputtering.Conclusions. The mathematical framework outlined sets the foundation for the inclusion of plasma deposition and plasma sputtering in global dust cloud formation models of sub-stellar atmospheres

Physiology of the visual control system

Neurophysiological aspects of eye movement in visual control system with differentiation of version and vergenc

Visual and control aspects of saccadic eye movements

Physiological, behavioral, and control investigation of rapid saccadic jump eye movement in human

Neural tube-ectoderm interactions are required for trigeminal placode formation

Cranial sensory ganglia in vertebrates develop from the ectodermal placodes, the neural crest, or both. Although much is known about the neural crest contribution to cranial ganglia, relatively little is known about how placode cells form, invaginate and migrate to their targets. Here, we identify Pax-3 as a molecular marker for placode cells that contribute to the ophthalmic branch of the trigeminal ganglion and use it, in conjunction with DiI labeling of the surface ectoderm, to analyze some of the mechanisms underlying placode development. Pax-3 expression in the ophthalmic placode is observed as early as the 4-somite stage in a narrow band of ectoderm contiguous to the midbrain neural folds. Its expression broadens to a patch of ectoderm adjacent to the midbrain and the rostral hindbrain at the 8- to 10-somite stage. Invagination of the first Pax-3-positive cells begins at the 13-somite stage. Placodal invagination continues through the 35-somite stage, by which time condensation of the trigeminal ganglion has begun. To challenge the normal tissue interactions leading to placode formation, we ablated the cranial neural crest cells or implanted barriers between the neural tube and the ectoderm. Our results demonstrate that, although the presence of neural crest cells is not mandatory for Pax-3 expression in the forming placode, a diffusible signal from the neuroectoderm is required for induction and/or maintenance of the ophthalmic placode

Collisionless distribution function for the relativistic force-free Harris sheet

A self-consistent collisionless distribution function for the relativistic analogue of the force-free Harris sheet is presented. This distribution function is the relativistic generalization of the distribution function for the non-relativistic collisionless force-free Harris sheet recently found by Harrison and Neukirch [Phys. Rev. Lett. 102, 135003 (2009)], as it has the same dependence on the particle energy and canonical momenta. We present a detailed calculation which shows that the proposed distribution function generates the required current density profile (and thus magnetic field profile) in a frame of reference in which the electric potential vanishes identically. The connection between the parameters of the distribution function and the macroscopic parameters such as the current sheet thickness is discussed. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3677268]PostprintPeer reviewe

Study of zero-gravity, vapor/liquid separators

Heat exchange, mechanical separation, surface tension, and dielectrophoretic methods of separating vapor from liquid at zero gravity for vapor ventin

Nulling interferometry: impact of exozodiacal clouds on the performance of future life-finding space missions

Earth-sized planets around nearby stars are being detected for the first time by ground-based radial velocity and space-based transit surveys. This milestone is opening the path towards the definition of missions able to directly detect the light from these planets, with the identification of bio-signatures as one of the main objectives. In that respect, both ESA and NASA have identified nulling interferometry as one of the most promising techniques. The ability to study distant planets will however depend on exozodiacal dust clouds surrounding the target stars. In this paper, we assess the impact of exozodiacal dust clouds on the performance of an infrared nulling interferometer in the Emma X-array configuration. For the nominal mission architecture with 2-m aperture telescopes, we found that point-symmetric exozodiacal dust discs about 100 times denser than the solar zodiacal cloud can be tolerated in order to survey at least 150 targets during the mission lifetime. Considering modeled resonant structures created by an Earth-like planet orbiting at 1 AU around a Sun-like star, we show that the tolerable dust density for planet detection goes down to about 15 times the solar zodiacal density for face-on systems and decreases with the disc inclination. The upper limits on the tolerable exozodiacal dust density derived in this study must be considered as rather pessimistic, but still give a realistic estimation of the typical sensitivity that we will need to reach on exozodiacal discs in order to prepare the scientific programme of future Earth-like planet characterisation missions.Comment: 17 pages, accepted for publication in A&

Steam storage systems for flexible biomass CHP plants - Evaluation and initial model based calculation

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Within the present study a novel concept for the demand-oriented power generation of a solid-biomass fueled combined heat and power (CHP) plant is investigated. The integration of a steam storage system into the plants process enables a decoupling of the steam (boiler) and the power generation (steam turbine). By buffering the steam, the power output of the turbine can be adjusted without changing the rated thermal capacity of the plant. Various available storage systems are selected and comparatively evaluated applying the adapted analytic hierarchy process (AHP). The technology assessment revealed that the combination of a steam accumulator and solid concrete storage represents the best suiting option. An initial model based simulation study is performed to identify the fundamental behaviour of this system, integrated in a biomass CHP plant. The operation principle is has proved their technical feasibility and seems to be applicable at a commercial scale. According to the modelling results flexible short term power generation in a time range of up to fifteen minutes is applicable. A load-range of almost the plants rated capacity can be achieved