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 $\omega$ 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

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