16,259 research outputs found
The effects of organic farming on the soil physical environment
The aim of this research was to investigate the effects of organic farming practices on the development of soil physical properties, and in particular, soil structure in comparison with conventional agricultural management. The soil structure of organically and conventionally managed soils at one site was compared in a quantitative manner at different scales of observations using image analysis. Key soil physical and chemical properties were measured as well as the pore fractal geometry to characterise pore roughness. Organically managed soils had higher organic matter content and provided a more stable soil structure than conventionally managed soils. The higher porosity (%) at the macroscale in soil under conventional management was due to fewer larger pores while mesoand microscale porosity was found to be greater under organic management. Organically managed soils typically provided spatially well distributed pores of all sizes and of greater roughness compared to those under conventional management. These variations in the soil physical environment are likely to impact significantly on the performance of these soils for a number of key processes such as crop establishment and water availabilit
The relationship between induced fluid structure and boundary slip in nanoscale polymer films
The molecular mechanism of slip at the interface between polymer melts and
weakly attractive smooth surfaces is investigated using molecular dynamics
simulations. In agreement with our previous studies on slip flow of
shear-thinning fluids, it is shown that the slip length passes through a local
minimum at low shear rates and then increases rapidly at higher shear rates. We
found that at sufficiently high shear rates, the slip flow over atomically flat
crystalline surfaces is anisotropic. It is demonstrated numerically that the
friction coefficient at the liquid-solid interface (the ratio of viscosity and
slip length) undergoes a transition from a constant value to the power-law
decay as a function of the slip velocity. The characteristic velocity of the
transition correlates well with the diffusion velocity of fluid monomers in the
first fluid layer near the solid wall at equilibrium. We also show that in the
linear regime, the friction coefficient is well described by a function of a
single variable, which is a product of the magnitude of surface-induced peak in
the structure factor and the contact density of the adjacent fluid layer. The
universal relationship between the friction coefficient and induced fluid
structure holds for a number of material parameters of the interface: fluid
density, chain length, wall-fluid interaction energy, wall density, lattice
type and orientation, thermal or solid walls.Comment: 33 pages, 14 figure
The Wakefield District prolific and priority offender needs analysis and business case: final report
Dosage compensation in birds
AbstractThe Z and W sex chromosomes of birds have evolved independently from the mammalian X and Y chromosomes [1]. Unlike mammals, female birds are heterogametic (ZW), while males are homogametic (ZZ). Therefore male birds, like female mammals, carry a double dose of sex-linked genes relative to the other sex. Other animals with nonhomologous sex chromosomes possess “dosage compensation” systems to equalize the expression of sex-linked genes. Dosage compensation occurs in animals as diverse as mammals, insects, and nematodes, although the mechanisms involved differ profoundly [2]. In birds, however, it is widely accepted that dosage compensation does not occur [3–5], and the differential expression of Z-linked genes has been suggested to underlie the avian sex-determination mechanism [6]. Here we show equivalent expression of at least six of nine Z chromosome genes in male and female chick embryos by using real-time quantitative PCR [7]. Only the Z-linked ScII gene, whose ortholog in Caenorhabditis elegans plays a crucial role in dosage compensation [8], escapes compensation by this assay. Our results imply that the majority of Z-linked genes in the chicken are dosage compensated
Electron Dynamics in a Coupled Quantum Point Contact Structure with a Local Magnetic Moment
We develop a theoretical model for the description of electron dynamics in
coupled quantum wires when the local magnetic moment is formed in one of the
wires. We employ a single-particle Hamiltonian that takes account of the
specific geometry of potentials defining the structure as well as electron
scattering on the local magnetic moment. The equations for the wave functions
in both wires are derived and the approach for their solution is discussed. We
determine the transmission coefficient and conductance of the wire having the
local magnetic moment and show that our description reproduces the
experimentally observed features.Comment: Based on work presented at 2004 IEEE NTC Quantum Device Technology
Worksho
IGR J17488-2338: a newly discovered giant radio galaxy
We present the discovery of a large scale radio structure associated with IGR
J17488--2338, a source recently discovered by \emph{INTEGRAL} and optically
identified as a broad line AGN at redshift 0.24. At low frequencies, the source
properties are those of an intermediate-power FR II radio galaxy with a linear
size of 1.4\,Mpc. This new active galaxy is therefore a member of a class of
objects called Giant Radio Galaxies (GRGs), a rare type of radio galaxies with
physical sizes larger than 0.7\,Mpc; they represent the largest and most
energetic single entities in the Universe and are useful laboratories for many
astrophysical studies. Their large scale structures could be due either to
special external conditions or to uncommon internal properties of the source
central engine The AGN at the centre of IGR J17488--2338 has a black hole of
1.310 solar masses, a bolometric luminosity of
710erg\,s and an Eddington ratio of 0.3, suggesting that
it is powerful enough to produce the large structure observed in radio. The
source is remarkable also for other properties, among which its X-ray
absorption, at odds with its type 1 classification, and the presence of a
strong iron line which is a feature not often observed in radio galaxies.Comment: 4 pages, 3 figures, accepted for publication on Astronomy and
Astrophysic
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