General relativistic analysis of peculiar velocities

We give a careful general relativistic and (1+3)-covariant analysis of cosmological peculiar velocities induced by matter density perturbations in the presence of a cosmological constant. In our quasi-Newtonian approach, constraint equations arise to maintain zero shear of the non-comoving fundamental worldlines which define a Newtonian-like frame, and these lead to the (1+3)-covariant dynamical equations, including a generalized Poisson-type equation. We investigate the relation between peculiar velocity and peculiar acceleration, finding the conditions under which they are aligned. In this case we find (1+3)-covariant relativistic generalizations of well-known Newtonian results.Comment: 8 pages, LaTeX2e (iopart); minor changes, matches version accepted for publication by Classical and Quantum Gravit

Increased rates of wound complications with locking plates in distal fibular fractures

Introduction: There is a growing use of locking compression plates in fracture surgery. The current study was undertaken to investigate the wound complication rates of locking versus non-locking plates in distal fibular fractures. Patients and methods: During a 6-year study period all consecutive, closed distal fibular fractures treated with either a locking or a non-locking plate were included and retrospectively analysed for complication related to the fibula. Results: A total of 165 patients received a one-third tubular plate and 40 patients were treated with a locking plate. The two groups were comparable with respect to patient characteristics (age, gender, smokers and diabetics), injury characteristics (affected side, fracture dislocations, number of fractured malleoli and classification) and operation characteristics (surgical delay and duration, use of a tourniquet and plate length). The wound complication rate was 5.5% in the conventional plating group, and 17.5% in the locking plate group (p = 0.019). This difference was largely due to an increase in major complications, for which removal of the plate was necessary (p = 0.008). Conclusion: There is a significant increase in wound complications in distal fibular fractures treated with a locking compression plate. In light of the current study, we would caution against the application of the currently used locking compression plates in the treatment of distal fibular fractures

Local freedom in the gravitational field

In a cosmological context, the electric and magnetic parts of the Weyl tensor, E_{ab} and H_{ab}, represent the locally free curvature - i.e. they are not pointwise determined by the matter fields. By performing a complete covariant decomposition of the derivatives of E_{ab} and H_{ab}, we show that the parts of the derivative of the curvature which are locally free (i.e. not pointwise determined by the matter via the Bianchi identities) are exactly the symmetrised trace-free spatial derivatives of E_{ab} and H_{ab} together with their spatial curls. These parts of the derivatives are shown to be crucial for the existence of gravitational waves.Comment: New results on gravitational waves included; new references added; revised version (IOP style) to appear Class. Quantum Gra

Quasi-Newtonian dust cosmologies

Exact dynamical equations for a generic dust matter source field in a cosmological context are formulated with respect to a non-comoving Newtonian-like timelike reference congruence and investigated for internal consistency. On the basis of a lapse function $N$ (the relativistic acceleration scalar potential) which evolves along the reference congruence according to $\dot{N} = \alpha \Theta N$ ($\alpha = {const}$), we find that consistency of the quasi-Newtonian dynamical equations is not attained at the first derivative level. We then proceed to show that a self-consistent set can be obtained by linearising the dynamical equations about a (non-comoving) FLRW background. In this case, on properly accounting for the first-order momentum density relating to the non-relativistic peculiar motion of the matter, additional source terms arise in the evolution and constraint equations describing small-amplitude energy density fluctuations that do not appear in similar gravitational instability scenarios in the standard literature.Comment: 25 pages, LaTeX 2.09 (10pt), to appear in Classical and Quantum Gravity, Vol. 15 (1998

The timing of ankle fracture surgery and the effect on infectious complications; A case series and systematic review of the literature

Purpose: Information about the influence of delayed surgery on infectious wound complications is ambiguous. A clinical audit was performed to test the hypothesis that early surgery lowers the rate of infectious wound complications. Secondly we looked at the influence of surgical delay and complications on patient reported functional outcome. Methods: All consecutive, closed distal fibular fractures treated surgically with a plate were included and retrospectively analysed for the delay in operation and wound complications. In a second cohort of patients with a AO-Weber B-type ankle fracture outcome was measured using the Olerud-Molander ankle score (OMAS), the American Orthopaedic Foot and Ankle Society score (AOFAS) and a visual analog score (VAS) for overall satisfaction. Results: Patients treated within one day experienced no wound complications (zero out of 60), whereas in the delayed group 11 % (16/145) did (p = 0.004). A similar significant difference was found for the patients treated within one week (2/98) versus after one week (14/107). A systematic review of the literature showed a difference in wound complications of 3.6 % (early) versus 12.9 % (late) (p < 0.0001). After 43 months, the median AOFAS was 11.5 points lower in the complication group, the OMAS 10 points, and the VAS 0.5 points, with all differences being statistically significant. Conclusions: Every effort should be made to operate on closed ankle fractures as soon as reasonably possible. A delay in surgery is associated with a significant rise in infectious wound complications, which significantly lowers outcome and patient satisfaction. These fractures should preferably be treated within the first day

Discriminating between simple and perforated appendicitis

Background: Several studies have been performed in order to diagnose an acute appendicitis using history taking and laboratory investigations. The aim of this study was to create a model for the identification of a perforated appendicitis. Methods: All consecutive patients who have undergone an appendectomy in the Reinier de Graaf hospital between January 1, 2007 and July 31, 2009, were included in a retrospective cohort study. Baseline patient characteristics, history and laboratory data were collected. Variables discriminating perforated from non-perforated appendicitis were identified using univariate and multivariable analyses. Results: A total of 498 patients were included in the study. In the univariate analysis leukocyte count, C-Reactive Protein levels, Erythrocyte Sedimentation Rate levels, days of symptoms and temperature were identified as predictors of perforated appendicitis. The predicted probability (P) of a perforated appendicitis can be calculated from the following model: (P) = 1/(1 + e(-(-2.788 + 0.012 CRP+0.207days with complaints))). Conclusions: Perforation of appendicitis can be predicted from the CRP level and the duration of abdominal pain. These findings might influence th

Isotropic singularity in inhomogeneous brane cosmological models

We discuss the asymptotic dynamical evolution of spatially inhomogeneous brane-world cosmological models close to the initial singularity. By introducing suitable scale-invariant dependent variables and a suitable gauge, we write the evolution equations of the spatially inhomogeneous $G_{2}$ brane cosmological models with one spatial degree of freedom as a system of autonomous first-order partial differential equations. We study the system numerically, and we find that there always exists an initial singularity, which is characterized by the fact that spatial derivatives are dynamically negligible. More importantly, from the numerical analysis we conclude that there is an initial isotropic singularity in all of these spatially inhomogeneous brane cosmologies for a range of parameter values which include the physically important cases of radiation and a scalar field source. The numerical results are supported by a qualitative dynamical analysis and a calculation of the past asymptotic decay rates. Although the analysis is local in nature, the numerics indicates that the singularity is isotropic for all relevant initial conditions. Therefore this analysis, and a preliminary investigation of general inhomogeneous ($G_0$) models, indicates that it is plausible that the initial singularity is isotropic in spatially inhomogeneous brane-world cosmological models and consequently that brane cosmology naturally gives rise to a set of initial data that provide the conditions for inflation to subsequently take place.Comment: 32 pages with 8 pictures. submitted to Class. Quant. Gra

Spherically symmetric relativistic stellar structures

We investigate relativistic spherically symmetric static perfect fluid models in the framework of the theory of dynamical systems. The field equations are recast into a regular dynamical system on a 3-dimensional compact state space, thereby avoiding the non-regularity problems associated with the Tolman-Oppenheimer-Volkoff equation. The global picture of the solution space thus obtained is used to derive qualitative features and to prove theorems about mass-radius properties. The perfect fluids we discuss are described by barotropic equations of state that are asymptotically polytropic at low pressures and, for certain applications, asymptotically linear at high pressures. We employ dimensionless variables that are asymptotically homology invariant in the low pressure regime, and thus we generalize standard work on Newtonian polytropes to a relativistic setting and to a much larger class of equations of state. Our dynamical systems framework is particularly suited for numerical computations, as illustrated by several numerical examples, e.g., the ideal neutron gas and examples that involve phase transitions.Comment: 23 pages, 25 figures (compressed), LaTe

Causal propagation of geometrical fields in relativistic cosmology

We employ the extended 1+3 orthonormal frame formalism for fluid spacetime geometries $({\cal M}, {\bf g}, {\bf u})$, which contains the Bianchi field equations for the Weyl curvature, to derive a 44-D evolution system of first-order symmetric hyperbolic form for a set of geometrically defined dynamical field variables. Describing the matter source fields phenomenologically in terms of a barotropic perfect fluid, the propagation velocities $v$ (with respect to matter-comoving observers that Fermi-propagate their spatial reference frames) of disturbances in the matter and the gravitational field, represented as wavefronts by the characteristic 3-surfaces of the system, are obtained. In particular, the Weyl curvature is found to account for two (non-Lorentz-invariant) Coulomb-like characteristic eigenfields propagating with $v = 0$ and four transverse characteristic eigenfields propagating with $|v| = 1$, which are well known, and four (non-Lorentz-invariant) longitudinal characteristic eigenfields propagating with |v| = \sfrac{1}{2}. The implications of this result are discussed in some detail and a parallel is drawn to the propagation of irregularities in the matter distribution. In a worked example, we specialise the equations to cosmological models in locally rotationally symmetric class II and include the constraints into the set of causally propagating dynamical variables.Comment: 25 pages, RevTeX (10pt), accepted for publication by Physical Review

Visual contrast response functions in Parkinson's disease: evidence from electroretinograms, visually evoked potentials and psychophysics

Objectives: Visual contrast detection thresholds and suprathreshold contrast discrimination thresholds were compared to luminance and flash/pattern electroretinograms (ERG) and visually evoked potentials (VEP) in patients with Parkinson's disease (n=31), patients with multiple system atrophy (n=6), patients with progressive supranuclear palsy (n=6) and control patients without central nervous disease (n=33). Methods: The stimuli were luminance modulated full-field (flash) or horizontally oriented sinewave gratings (pattern), the latter having either a low (0.5 cycles/deg) or medium (4.0 cycles/deg) spatial frequency. Stimulus contrast ranged from 10 to 80% so that contrast response functions could be derived. Results: Contrast thresholds were higher in the patients with Parkinson's disease than in the control patients. Contrast discrimination thresholds were also somewhat elevated in patients with Parkinson's disease. Pattern ERG amplitudes were significantly reduced in patients with Parkinson's disease for the medium spatial frequency stimulus, but less for the low spatial frequency and flash stimuli. Conclusions: Our results suggest that Parkinson’s disease impairs contrast processing in the retina. VEP amplitudes did not significantly differ between the groups for the conditions tested. Patients with progressive supranuclear palsy also showed impaired contrast perception and reduced ERG amplitudes, whereas patients with multiple system atrophy were less impaired