The effect of ambipolar diffusion on low-density molecular ISM filaments

The filamentary structure of the molecular interstellar medium and the potential link of this morphology to star formation have been brought into focus recently by high resolution observational surveys. An especially puzzling matter is that local interstellar filaments appear to have the same thickness, independent of their column density. This requires a theoretical understanding of their formation process and the physics that governs their evolution. In this work we explore a scenario in which filaments are dissipative structures of the large-scale interstellar turbulence cascade and ion-neutral friction (also called ambipolar diffusion) is affecting their sizes by preventing small-scale compressions. We employ high-resolution, 3D MHD simulations, performed with the grid code RAMSES, to investigate non-ideal MHD turbulence as a filament formation mechanism. We focus the analysis on the mass and thickness distributions of the resulting filamentary structures. Simulations of both driven and decaying MHD turbulence show that the morphologies of the density and the magnetic field are different when ambipolar diffusion is included in the models. In particular, the densest structures are broader and more massive as an effect of ion-neutral friction and the power spectra of both the velocity and the density steepen at a smaller wavenumber. The comparison between ideal and non-ideal MHD simulations shows that ambipolar diffusion causes a shift of the filament thickness distribution towards higher values. However, none of the distributions exhibit the pronounced peak found in the observed local filaments. Limitations in dynamical range and the absence of self-gravity in these numerical experiments do not allow us to conclude at this time whether this is due to the different filament selection or due to the physics inherent of the filament formation.Comment: A&A accepte

Ambipolar diffusion in low-mass star formation. I. General comparison with the ideal MHD case

In this paper, we provide a more accurate description of the evolution of the magnetic flux redistribution during prestellar core collapse by including resistive terms in the magnetohydrodynamics (MHD) equations. We focus more particularly on the impact of ambipolar diffusion. We use the adaptive mesh refinement code RAMSES to carry out such calculations. The resistivities required to calculate the ambipolar diffusion terms were computed using a reduced chemical network of charged, neutral and grain species. The inclusion of ambipolar diffusion leads to the formation of a magnetic diffusion barrier in the vicinity of the core, preventing accumulation of magnetic flux in and around the core and amplification of the field above 0.1G. The mass and radius of the first Larson core remain similar between ideal and non-ideal MHD models. This diffusion plateau has crucial consequences on magnetic braking processes, allowing the formation of disk structures. Magnetically supported outflows launched in ideal MHD models are weakened when using non-ideal MHD. Contrary to ideal MHD misalignment between the initial rotation axis and the magnetic field direction does not significantly affect the results for a given mu, showing that the physical dissipation truly dominate over numerical diffusion. We demonstrate severe limits of the ideal MHD formalism, which yield unphysical behaviours in the long-term evolution of the system. This includes counter rotation inside the outflow, interchange instabilities, and flux redistribution triggered by numerical diffusion, none observed in non-ideal MHD. Disks with Keplerian velocity profiles form in all our non-ideal MHD simulations, with final mass and size which depend on the initial magnetisation. This ranges from a few 0.01 solar masses and 20-30 au for the most magnetised case (mu=2) to 0.2 solar masses and 40-80 au for a lower magnetisation (mu=5).Comment: Accepted in A&A section 7 (on Wednesday, september the 16th, year 2015

Study of the peptidasic site of cholinesterase: preliminary results

AbstractThe peptidasic site of highly purified human plasma cholinesterase was investigated using active-site-directed inhibitors. Peptidase activity was assayed taking substance P as substrate. Inhibition by organophosphates indicated that the peptidasic site contained an active serine. The presence of essential histidine residues associated with serine was revealed by histidine modifications. Carboxyl group reagents showed that the active centre contained carboxyl groups in a non-polar environment. The removal of sialic acids did not alter peptidase activity. The peptidasic site of cholinesterase shared many properties with serine proteases sites and esteratic sites of cholinesterases. In addition, with the peptidasic site, as well as the esteratic site, there was always the possibility of ‘aging’ when inhibited by DFP or soman

Dynamics of the Transition corona

Magnetic reconnection between open and closed magnetic field in the corona is believed to play a crucial role in the corona/heliosphere coupling. At large scale, the exchange of open/closed connectivity is expected to occur in pseudo-streamer structures. However, there is neither clear observational evidence of how such coupling occurs in pseudo-streamers, nor evidence for how the magnetic reconnection evolves. Using a newly-developed technique, we enhance the off-limb magnetic fine structures observed with AIA and identify a pseudo-streamer-like feature located close to the northern coronal hole. After extrapolating the magnetic field with the PFSS model, we obtain a pseudo-streamer magnetic topology, null-point related topology bounded by open field. We compare the magnetic configuration with the UV observations and identify the magnetic structures expected to be involved in the event. Using an 3D MHD simulation of interchange reconnection, we showed that the evolution of the UV structures follows the magnetic field dynamics and the UV emitting structures have a pattern very similar to the plasma emission derived from the simulation. Our results highlight that the exchange between open and closed in the pseudo-streamer topology related to an observed event occurs at least partially at the null-point, similarly to the interchange reconnection in a single null-point topology. However, our results also indicate that the interchange reconnection in pseudo-streamers is a gradual physical process which opposes to the impulsive reconnection of the solar-jet model

Observations and modeling of seasonal variability in the Straits of Georgia and Juan de Fuca

The Strait of Georgia is a large semi-enclosed basin on the southern coast of British Columbia. Its main connection to the Pacific is to the south, through Juan de Fuca Strait. Abundant freshwater discharge, mainly from the Fraser River, forces an estuarine exchange with oceanic shelf water. The resulting circulation is modulated by tides and winds. Both the coastal wind stress and the flux of freshwater are subject to strong seasonal modulations, producing a marked seasonal cycle in the water properties and circulation of the region. The seasonal variability of the Strait of Georgia and Juan de Fuca Strait is described using data from a series of recent cruises conducted over a five-year period, in addition to longer term historical data sets. To complement the observations, the data are compared with numerical simulations based on the Princeton Ocean Model (POM). Forced with tides, freshwater discharge and seasonal wind stress, the model is integrated over a few years until the system approaches statistical equilibrium. Results show good agreement with observations from Juan de Fuca Strait, as well as over the upper part of the water column within the Strait of Georgia. However, simulation of the seasonal cycle of the deeper waters of the Strait of Georgia is more problematic. The deep water properties apparently are determined by a delicate balance between dense intrusions from the sill area and local vertical mixing

Fortnightly modulation of the estuarine circulation in Juan de Fuca Strait

Riverine discharge into the Strait of Georgia sets up a well-defined estuarine circulation within Juan de Fuca Strait, the main path for the freshwater outflow to the continental shelf. At the landward end of Juan de Fuca Strait, the water flows through narrow channels in which strong tidal currents are known to induce significant mixing of the water column, and a spring-neap modulation of the estuarine exchange. A three-dimensional prognostic numerical model has been developed to study the circulation around Vancouver Island, British Columbia. In a series of simulations, the estuarine circulation within Juan de Fuca Strait is established by the Fraser River freshwater discharge. A fortnightly modulation is imposed on the mixing over the various sills to simulate the spring-neap tidal mixing regime. The resulting variation in the estuarine circulation is found to be largely limited to the eastern section of Juan de Fuca Strait, in the vicinity of the sills. Data from current meter moorings and surface salinity data from lighthouse stations compare favorably with the model results. The effect of local wind forcing on the estuarine exchange is also examined. The model is capable of simulating those rare events during which a concurrence of river freshet, neap tide and northwest wind allows a stronger pulse of fresh surface water to escape relatively unmixed into the eastern end of Juan de Fuca Strait. The disturbance then propagates along the northern shore of the strait as a first mode internal Kelvin wave. Finally, the effect of the fortnightly modulation on the export of freshwater onto the continental shelf is examined. It is found that small amplitude coastal trapped waves are generated near the mouth of Juan de Fuca. However, this fortnightly signal is weak in comparison to the energetic wind-induced variations typically found over the shelf

High-pressure biotechnology in medicine and pharmaceutical science

High-pressure (HP) biotechnology is an emerging technique initially applied for food processing and more recently in pharmaceutical and medical sciences. Pressure can stabilize enzymes and modulate both their activity and specificity. HP engineering of proteins may be used for enzyme-catalyzed synthesis of fine chemicals, pharmaceuticals, and production of modified proteins of medical or pharmaceutical interest. HP inactivation of biological agents is expected to be applicable to sterilization of fragile biopharmaceuticals, or medical compounds. The enhanced immunogenicity of some pressure-killed bacteria and viruses could be applied for making new vaccines. Finally, storage at subzero temperatures without freezing is another potential application of HP for cells, animal tissues, blood cells, organs for transplant, and so forth

Systèmes de production mixtes agriculture pluviale et élevage en zones humide et sub-humide d'Afrique

Ce travail s'inscrit dans une étude générale sur les interactions entre les systèmes de production d'élevage et l'environnement. L'évolution récente des systèmes pastoraux traditionnels africains, vers des systèmes mixtes agriculture et élevage, a des conséquences nouvelles pour l'environnement qui sont d'autant plus profitables que l'association entre l'élevage et l'agriculture est bien maîtrisée

Why aren't they locked in waiting games? Unlocking rules and the ecology of concepts in the semiconductor industry.

International audienceIn a multi-level perspective, regimes can be clearly described as long as they remain stable. To understand how regimes and niches interact during transition, the article contrasts two models of regimes in transition(s). The classical model of evolutionary niches suggests misalignments between rules and competition between niches. Transition management, technological innovation systems and works on transition pathways suggest a second model based on "unlocking rules", which support collective work on a structured set of emerging technologies. The latter model is illustrated with a case study on the International Technology Roadmap for Semiconductors (ITRS)

Platform emergence in double unknown: Common challenge strategy

International audienceThe proposed paper deals with platform emergence in double unknown situations when technology and markets are highly uncertain. The interest in technological platform development to enable creation of products and processes that support present and future development of multiple options is widely recognized by practitioners and academics The existing literature considers already existing platforms and the development is based on exploiting this common platform core to build future markets and technological derivatives. However, when we are in double unknown situations, markets and technologies are highly uncertain and neither options, nor platform core are known. Thus, how can one ensure platform emergence in double unknown?The history of innovation promotes mostly singular challenge strategy to guide innovative development. But in certain sectors, like semiconductors, telecommunications, pharmaceuticals, the success of common challenge strategy applicable to several markets is more important than singular project success. Thus, which strategy to choose for innovative technological platform emergence? Why common challenge strategy appears to be so challenging and risky? The objective of the paper is to define what are the precise market and technological conditions that in certain situations lead to 1) develop common building block (common core) that facilitate all the others projects but don't provide access directly to the market 2) launch singular project exploration to emerge future platform core consequently. We attempt to address our research questions by formally describing each strategy and fabricating simple economical model to compare them. For simulation the data was created by taking into account specifics of real management situations and parameters were chosen based on the literature review. Then we illustrate the insights of the model through a case study of innovative technology development in semiconductor industry. The in-depth empirical case study was conducted in STMicroelectronics, one of the leaders in the semiconductor industry. The data for case study was gathered from advanced technology platform with several interdependent modules developed by company and introduced to the several markets after all. This paper contributes to existing work on platform emergence by introducing the strategy of platform core construction in double unknown based on future common challenge investigation