26 research outputs found
The composition of the protosolar disk and the formation conditions for comets
Conditions in the protosolar nebula have left their mark in the composition
of cometary volatiles, thought to be some of the most pristine material in the
solar system. Cometary compositions represent the end point of processing that
began in the parent molecular cloud core and continued through the collapse of
that core to form the protosun and the solar nebula, and finally during the
evolution of the solar nebula itself as the cometary bodies were accreting.
Disentangling the effects of the various epochs on the final composition of a
comet is complicated. But comets are not the only source of information about
the solar nebula. Protostellar disks around young stars similar to the protosun
provide a way of investigating the evolution of disks similar to the solar
nebula while they are in the process of evolving to form their own solar
systems. In this way we can learn about the physical and chemical conditions
under which comets formed, and about the types of dynamical processing that
shaped the solar system we see today.
This paper summarizes some recent contributions to our understanding of both
cometary volatiles and the composition, structure and evolution of protostellar
disks.Comment: To appear in Space Science Reviews. The final publication is
available at Springer via http://dx.doi.org/10.1007/s11214-015-0167-
Current status of turbulent dynamo theory: From large-scale to small-scale dynamos
Several recent advances in turbulent dynamo theory are reviewed. High
resolution simulations of small-scale and large-scale dynamo action in periodic
domains are compared with each other and contrasted with similar results at low
magnetic Prandtl numbers. It is argued that all the different cases show
similarities at intermediate length scales. On the other hand, in the presence
of helicity of the turbulence, power develops on large scales, which is not
present in non-helical small-scale turbulent dynamos. At small length scales,
differences occur in connection with the dissipation cutoff scales associated
with the respective value of the magnetic Prandtl number. These differences are
found to be independent of whether or not there is large-scale dynamo action.
However, large-scale dynamos in homogeneous systems are shown to suffer from
resistive slow-down even at intermediate length scales. The results from
simulations are connected to mean field theory and its applications. Recent
work on helicity fluxes to alleviate large-scale dynamo quenching, shear
dynamos, nonlocal effects and magnetic structures from strong density
stratification are highlighted. Several insights which arise from analytic
considerations of small-scale dynamos are discussed.Comment: 36 pages, 11 figures, Spa. Sci. Rev., submitted to the special issue
"Magnetism in the Universe" (ed. A. Balogh
New Strategies in Sport Nutrition to Increase Exercise Performance.
Despite over 50 years of research, the field of sports nutrition continues to grow at a rapid rate. Whilst the traditional research focus was one that centred on strategies to maximize competition performance, emerging data in the last decade has demonstrated how both macronutrient and micronutrient availability can play a prominent role in regulating those cell signalling pathways that modulate skeletal muscle adaptations to endurance and resistance training. Nonetheless, in the context of exercise performance, it is clear that carbohydrate (but not fat) still remains king and that carefully chosen ergogenic aids (e.g. caffeine, creatine, sodium bicarbonate, beta-alanine, nitrates) can all promote performance in the correct exercise setting. In relation to exercise training, however, it is now thought that strategic periods of reduced carbohydrate and elevated dietary protein intake may enhance training adaptations whereas high carbohydrate availability and antioxidant supplementation may actually attenuate training adaptation. Emerging evidence also suggests that vitamin D may play a regulatory role in muscle regeneration and subsequent hypertrophy following damaging forms of exercise. Finally, novel compounds (albeit largely examined in rodent models) such as epicatechins, nicotinamide riboside, resveratrol, ÎČ-hydroxy ÎČ-methylbutyrate, phosphatidic acid and ursolic acid may also promote or attenuate skeletal muscle adaptations to endurance and strength training. When taken together, it is clear that sports nutrition is very much at the heart of the Olympic motto, Citius, Altius, Fortius (faster, higher, stronger)
Orientation of Galaxies in the Local Supercluster: A Review
The progress of the studies on the orientation of galaxies in the Local
Supercluster (LSC) is reviewed and a summary of recent results is given.
Following a brief introduction of the LSC, we describe the results of early
studies based on two-dimensional analysis, which were mostly not conclusive. We
describe next the three-dimensional analysis, which is used widely today.
Difficulties and systematic effects are explained and the importance of
selection effects is described. Then, results based on the new method and
modern databases are given, which are summarized as follows. When the LSC is
seen as a whole, galaxy planes tend to align perpendicular to the LSC plane
with lenticulars showing the most pronounced tendency. Projections onto the LSC
plane of the spin vectors of Virgo cluster member galaxies, and to some extent,
those of the total LSC galaxies, tend to point to the Virgo cluster center.
This tendency is more pronounced for lenticulars than for spirals. It is
suggested that 'field' galaxies, i.e., those which do not belong to groups with
more than three members, may be better objects than other galaxies to probe the
information at the early epoch of the LSC formation through the analysis of
galaxy orientations. Field lenticulars show a pronounced anisotropic
distribution of spin vectors in the sense that they lay their spin vectors
parallel to the LSC plane while field spirals show an isotropic spin-vector
distribution.Comment: 21 pages, 10 figures; Accepted for publication in Astrophysics and
Space Scienc