8,320 research outputs found
Ambipolar diffusion in smoothed particle magnetohydrodynamics
In partially ionised plasmas, the magnetic field can become decoupled from
the neutral gas and diffuse through it in a process known as ambipolar
diffusion. Although ambipolar diffusion has been implemented in several grid
codes, we here provide an implementation in smoothed particle
magnetohydrodynamics (SPMHD). We use the strong coupling approximation in which
the ion density is negligible, allowing a single fluid approach. The equations
are derived to conserve energy, and to provide a positive definite contribution
to the entropy. We test the implementation in both a simple 1D SPMHD code and
the fully 3D code PHANTOM. The wave damping test yields agreement within 0.03-2
per cent of the analytical result, depending on the value of the collisional
coupling constant. The oblique C-shocks test yields results that typically
agree within 4 per cent of the semi-analytical result. Our algorithm is
therefore suitable for exploring the effect ambipolar diffusion has on physical
processes, such as the formation of stars from molecular clouds.Comment: Accepted for publication by MNRA
BurstProbe: Debugging Time-Critical Data Delivery in Wireless Sensor Networks
In this paper we present BurstProbe, a new technique to accurately measure link burstiness in a wireless sensor network employed for time-critical data delivery. Measurement relies on shared probing slots that are embedded in the transmission schedule and used by nodes to assess link burstiness over time. The acquired link burstiness information can be stored in the node's flash memory and relied upon to diagnose transmission problems when missed deadlines occur. Thus, accurate diagnosis is achieved in a distributed manner and without the overhead of transmitting rich measurement data to a central collection point. For the purpose of evaluation we have implemented BurstProbe in the GinMAC WSN protocol and we are able to demonstrate it is an accurate tool to debug time-critical data delivery. In addition, we analyze the cost of implementingBurstProbe and investigate its effectiveness
Age- and activity-related differences in the abundance of Myosin essential and regulatory light chains in human muscle
Traditional methods for phenotyping skeletal muscle (e.g., immunohistochemistry) are labor-intensive and ill-suited to multixplex analysis, i.e., assays must be performed in a series. Addressing these concerns represents a largely unmet research need but more comprehensive parallel analysis of myofibrillar proteins could advance knowledge regarding age- and activity-dependent changes in human muscle. We report a label-free, semi-automated and time efficient LC-MS proteomic workflow for phenotyping the myofibrillar proteome. Application of this workflow in old and young as well as trained and untrained human skeletal muscle yielded several novel observations that were subsequently verified by multiple reaction monitoring (MRM).We report novel data demonstrating that human ageing is associated with lesser myosin light chain 1 content and greater myosin light chain 3 content, consistent with an age-related reduction in type II muscle fibers. We also disambiguate conflicting data regarding myosin regulatory light chain, revealing that age-related changes in this protein more closely reflect physical activity status than ageing per se. This finding reinforces the need to control for physical activity levels when investigating the natural process of ageing. Taken together, our data confirm and extend knowledge regarding age- and activity-related phenotypes. In addition, the MRM transitions described here provide a methodological platform that can be fine-tuned to suite multiple research needs and thus advance myofibrillar phenotyping
Remote functionalisation via sodium alkylamidozincate intermediates : access to unusual fluorenone and pyridyl ketone reactivity patterns
Treating fluorenone or 2-benzoylpyridine with the sodium zincate [(TMEDA)center dot Na(mu-Bu-t)(mu-TMP)Zn(Bu-t)] in hexane solution, gives efficient Bu-t addition across the respective organic substrate in a highly unusual 1,6-fashion, producing isolable organometallic intermediates which can be quenched and aerobically oxidised to give 3-tert-butyl-9H-fluoren-9-one and 2-benzoyl-5-tert-butylpyridine respectively
Star formation and ISM morphology in tidally induced spiral structures
Tidal encounters are believed to be one of the key drivers of galactic spiral
structure in the Universe. Such spirals are expected to produce different
morphological and kinematic features compared to density wave and dynamic
spiral arms. In this work we present high resolution simulations of a tidal
encounter of a small mass companion with a disc galaxy. Included are the
effects of gas cooling and heating, star formation and stellar feedback. The
structure of the perturbed disc differs greatly from the isolated galaxy,
showing clear spiral features that act as sites of new star formation, and
displaying interarm spurs. The two arms of the galaxy, the bridge and tail,
appear to behave differently; with different star formation histories and
structure. Specific attention is focused on offsets between gas and stellar
spiral features which can be directly compared to observations. We find some
offsets do exist between different media, with gaseous arms appearing mostly on
the convex side of the stellar arms, though the exact locations appear highly
time dependent. These results further highlight the differences between tidal
spirals and other theories of arm structure.Comment: 17 pages, 19 colour figures, accepted for publication in MNRA
- …