785 research outputs found
Alterations in the morphology of skeletal myofibres after 90 minutes of ischaemia and '- 3 hours of reperfusion
Morphometric, light and electron microscopic methods were employed to determine whether skeletal myofibres were damaged by 90 minutes of tourniquet-mediated ischaemia. Open biceps muscle biopsies were obtained before 90 minutes of upper limb tourniquet ischaemia in 5 Chacma baboons. Further biopsies were obtained just before tourniquet release in 2 animals and after 3 hours' reperfusion in the remaining 3 animals. Other than a slight reduction in myofibre diameter and the anaerobic depletion of intermyofibrillar glycogen, no pathological changes were noted in skeletal myofibres after ischaemia. However, after reperfusion there was myofibre enlargement, intermyofibrillar oedema, internalisation of nuclei, myofibrillar and mitochondrial disorganisation and dissolution, and Z-band streaming. These results show that reperfusion injury affects skeletal myofibres after 90 minutes of tourniquet-mediated ischaemia
The architecture and fine structure of gill filaments in the brown mussel, Perna perna
For many years, bivalve molluscs have played a useful role in determining the impact of pollution on marine organisms. In the northern hemisphere, ecologists from countries subscribing to the International Mussel Watch have used toxin-mediated changes in the organs of Mytilus edulis, especially in the morphology of gill filaments, to indicate the biotoxicity of marine effluent. M. edulis is not indigenous to South African waters. For us to adopt a similar approach on the South African east coast, it is necessary to catalogue both the normal appearance and toxin-mediated changes in our local brown mussel Perna perna. In this study, the gill filaments from five healthy, adult brown mussels were studied by light and transmission electron microscopy. Special attention was paid to filament architecture, ennervation of filaments, number and type of cells populating filament epithelia and variations in epithelial cell morphology and cilia ultrastructure. Filament shape was maintained by thickened chi-tln and strategically placed smooth myocytes. The epithelium was populated with eight morphologically distinctive non-secretory, mucus secreting or sensory cell types in various stages of differentiation. Unmyelinated nerves were situated beneath six cell types. Significant differences in filament architecture and epithelial cell morphology were found between M. edulis and P. perna. It is hoped that this comprehensive description of normal P. perna gill filaments will provide a morphological baseline for local pollution impact studies
A Jurassic (Bathonian-Callovian) Daghanirhynchia brachiopod fauna from Jordan
A Jurassic (Bathonian-Callovian) brachiopod fauna from Jordan consists of seven rhynchonellid species all belonging to the genus Daghanirhynchia of which two are new: Daghanirhynchia rawyaensis and D. jordanica. Emended diagnoses are given for Daghanirhynchia daghaniensis and D. macfadyeni. Additional taxa described include Daghanirhynchia angulocostata, D. susanae and D. triangulata. Threedimensional reconstructions illustrate the internal morphology of the articulated shells for the first time in this genus. The material studied herein was collected from Wadi Zarqa in northwestern Jordan, almost due north of the Dead Sea, and to the east of the Rift Valley. Most species seem to be geographically restricted within the Jurassic Ethiopian Province, however specimens from Somalia and Ethiopia are larger in size than in other parts of the Province and shell size increases in stratigraphically younger specimens. The occurrence of Daghanirhynchia in India is the only appearance of the genus outside the Ethiopian Province
Superluminality in DGP
We reconsider the issue of superluminal propagation in the DGP model of
infrared modified gravity. Superluminality was argued to exist in certain
otherwise physical backgrounds by using a particular, physically relevant
scaling limit of the theory. In this paper, we exhibit explicit
five-dimensional solutions of the full theory that are stable against small
fluctuations and that indeed support superluminal excitations. The scaling
limit is neither needed nor invoked in deriving the solutions or in the
analysis of its small fluctuations. To be certain that the superluminality
found here is physical, we analyze the retarded Green's function of the scalar
excitations, finding that it is causal and stable, but has support on a widened
light-cone. We propose to use absence of superluminal propagation as a method
to constrain the parameters of the DGP model. As a first application of the
method, we find that whenever the 4D energy density is a pure cosmological
constant and a hierarchy of scales exists between the 4D and 5D Planck masses,
superluminal propagation unavoidably occurs.Comment: 23 pages. Minor corrections. Version to appear in JHE
Brans-Dicke DGP Brane Cosmology
We consider a five dimensional DGP-brane scenario endowed with a
non-minimally coupled scalar field within the context of Brans-Dicke theory.
This theory predicts that the mass appearing in the gravitational potential is
modified by the addition of the mass of the effective intrinsic curvature on
the brane. We also derive the effective four dimensional field equations on a
3+1 dimensional brane where the fifth dimension is assumed to have an orbifold
symmetry. Finally, we discuss the cosmological implications of this setup,
predicting an accelerated expanding universe with a value of the Brans-Dicke
parameter consistent with values resulting from the solar system
observations.Comment: 12 pages, 1 figure, to appear in JCA
Strong coupling in massive gravity by direct calculation
We consider four-dimensional massive gravity with the Fierz-Pauli mass term.
The analysis of the scalar sector has revealed recently that this theory
becomes strongly coupled above the energy scale \Lambda = (M_{Pl}^2 m^4)^{1/5}
where m is the mass of the graviton. We confirm this scale by explicit
calculations of the four-graviton scattering amplitude and of the loop
correction to the interaction between conserved sources.Comment: 9 pages, 3 figures, some clarifications adde
Ghosts in asymmetric brane gravity and the decoupled stealth limit
We study the spectrum of gravitational perturbations around a vacuum de
Sitter brane in a 5D asymmetric braneworld model, with induced curvature on the
brane. This generalises the stealth acceleration model proposed by Charmousis,
Gregory and Padilla (CGP) which realises the Cardassian cosmology in which
power law cosmic acceleration can be driven by ordinary matter. Whenever the
bulk has infinite volume we find that there is always a perturbative ghost
propagating on the de Sitter brane, in contrast to the Minkowski brane case
analysed by CGP. We discuss the implication of this ghost for the stealth
acceleration model, and identify a limiting case where the ghost decouples as
the de Sitter curvature vanishes.Comment: 21 page
On brane-induced gravity in warped backgrounds
We study whether modification of gravity at large distances is possible in
warped backgrounds with two branes and a brane-induced term localized on one of
the branes. We find that there are three large regions in the parameter space
where the theory is weakly coupled up to high energies. In one of these regions
gravity on the brane is four-dimensional at arbitrarily large distances, and
the induced Einstein term results merely in the renormalization of the 4d
Planck mass. In the other two regions the behavior of gravity changes at
ultra-large distances; however, radion becomes a ghost. In parts of these
regions, both branes have positive tensions, so the only reason for the
appearance of the ghost field is the brane-induced term. In between these three
regions, there are domains in the parameter space where gravity is strongly
coupled at phenomenologically unacceptable low energy scale.Comment: 12 pages, 2 fig, JHEP3 style required, typos correcte
Inseminação artificial com sêmen resfriado em eqüinos - efeito da adição de antibióticos ao diluente na fertilidade de éguas susceptíveis e resistentes à endometrite e nas características espermáticas
Evaluation of the potential killing performance of novel percussive and cervical dislocation tools in chicken cadavers
1. Four mechanical poultry killing devices; modified Armadillo (MARM), modified Rabbit Zinger (MZIN), modified pliers (MPLI) and a novel mechanical cervical dislocation gloved device (NMCD), were assessed for their killing potential in the cadavers of euthanised birds of 4 type/age combinations: layer/adult, layer/pullet, broiler/slaughter-age and broiler/chick.
2. A 4x4x4 factorial design (batch x device x bird type + age) was employed. Ten bird cadavers per bird type and age were tested with each of the 4 devices (N = 160 birds). All cadavers were examined post-mortem to establish the anatomical damage caused by each device.
3. Three of the mechanical methods: NMCD, MARM and MZIN demonstrated killing potential, as well as consistency in their anatomical effects, with device success rates of over 50% indicating that the devices performed optimally more than half of the time. NMCD had the highest killing potential, with 100% of birds sustaining the required physical trauma to have caused rapid death.
4. The MPLI was inconsistent, and only performed optimally for 27.5% of birds, despite good killing potential when performing well. Severe crushing injury was seen in >50% of MPLI birds, suggesting that birds would die of asphyxia rather than cerebral ischaemia, a major welfare concern. As a result, the modified pliers are not recommended as a humane on-farm killing device for chickens.
5. This experiment provides important data on the killing potential of untried novel percussive and mechanical cervical dislocation methods, informing future studies
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