Probing the gravitational geon

The Brill-Hartle gravitational geon construct as a spherical shell of small amplitude, high frequency gravitational waves is reviewed and critically analyzed. The Regge-Wheeler formalism is used to represent gravitational wave perturbations of the spherical background as a superposition of tensor spherical harmonics and an attempt is made to build a non-singular solution to meet the requirements of a gravitational geon. High-frequency waves are seen to be a necessary condition for the geon and the field equations are decomposed accordingly. It is shown that this leads to the impossibility of forming a spherical gravitational geon. The attempted constructs of gravitational and electromagnetic geons are contrasted. The spherical shell in the proposed Brill-Hartle geon does not meet the regularity conditions required for a non-singular source and hence cannot be regarded as an adequate geon construct. Since it is the high frequency attribute which is the essential cause of the geon non-viability, it is argued that a geon with less symmetry is an unlikely prospect. The broader implications of the result are discussed with particular reference to the problem of gravitational energy.Comment: Replaced with revised version (substantial changes and additions, conclusions unchanged), 36 pages, LaTex, 3 figures available from the author

Impurity and Trace Tritium Transport in Tokamak Edge Turbulence

The turbulent transport of impurity or minority species, as for example Tritium, is investigated in drift-Alfv\'en edge turbulence. The full effects of perpendicular and parallel convection are kept for the impurity species. The impurity density develops a granular structure with steep gradients and locally exceeds its initial values due to the compressibility of the flow. An approximate decomposition of the impurity flux into a diffusive part and an effective convective part (characterized by a pinch velocity) is performed and a net inward pinch effect is recovered. The pinch velocity is explained in terms of Turbulent Equipartition and is found to vary poloidally. The results show that impurity transport modeling needs to be two-dimensional, considering besides the radial direction also the strong poloidal variation in the transport coefficients.Comment: 12 Pages, 5 Figure

Computing matrix inversion with optical networks

With this paper we bring about a discussion on the computing potential of complex optical networks and provide experimental demonstration that an optical fiber network can be used as an analog processor to calculate matrix inversion. A 3x3 matrix is inverted as a proof-of-concept demonstration using a fiber network containing three nodes and operating at telecomm wavelength. For an NxN matrix, the overall solving time (including setting time of the matrix elements and calculation time of inversion) scales as O(N^2), whereas matrix inversion by most advanced computer algorithms requires ~O(N^2.37) computational time. For well-conditioned matrices, the error of the inversion performed optically is found to be less than 3%, limited by the accuracy of measurement equipment.Comment: 5 page

Comparison of analytical and wind-tunnel results for flutter and gust response of a transport wing with active controls

Two flutter suppression control laws wre designed and tested on a low speed aeroelastic model of a DC-10 derivative wing. Both control laws demontrated increases in flutter speed in excess of 25 percent above the passive wing flutter speed. In addition, one of the control laws was effective in reducing loads due to turbulence generated in the wind tunnel. The effect of variations in gain and phase on the closed-loop performance was measured and is compared with predictions. In general, both flutter and gust response predictions agree reasonably well with experimental data

Youth Sports Head Injuries: A Legislative Approach

Head injury in youth sports is increasingly relevant to public health; policy is a viable option to mitigate the negative short- and long-term outcomes of head injury. The CDC estimates that U.S. emergency departments treat 173,285 sports related traumatic brain injuries annually in individuals ages 19 and younger. This may be an underestimate, as many concussions in youth sports often go unreported and untreated, increasing the risk of long-term effects from repetitive head injury. To combat brain trauma in youth sports, all fifty states and the District of Columbia have enacted legislation as of 2014. Previous research from Dr. Hosea A. Harvey, JD, of Temple University, examined these laws and found that much of the legislation is inconsistent and varies by state. The legislation primarily focuses on treatment and action plans after a head injury has already occurred. These laws are generally implemented through state athletic associations. A re-examination of the laws in combination with state athletic association concussion information sheets builds upon previous literature. In order to reduce negative effects of head injury in youth sports, the following improvements are suggested: develop more uniform and comprehensive concussion education for stakeholders (coaches, parents, athletes), create effective enforcement mechanisms for existing legislation, and implement measures such as limiting contact practices to reduce overall head injury incidence. Implementing these key aspects into existing state concussion statutes will greatly improve concussion prevention, education, and management

Stability of Gravitational and Electromagnetic Geons

Recent work on gravitational geons is extended to examine the stability properties of gravitational and electromagnetic geon constructs. All types of geons must possess the property of regularity, self-consistency and quasi-stability on a time-scale much longer than the period of the comprising waves. Standard perturbation theory, modified to accommodate time-averaged fields, is used to test the requirement of quasi-stability. It is found that the modified perturbation theory results in an internal inconsistency. The time-scale of evolution is found to be of the same order in magnitude as the period of the comprising waves. This contradicts the requirement of slow evolution. Thus not all of the requirements for the existence of electromagnetic or gravitational geons are met though perturbation theory. From this result it cannot be concluded that an electromagnetic or a gravitational geon is a viable entity. The broader implications of the result are discussed with particular reference to the problem of gravitational energy.Comment: 40 pages, 5 EPS figures, uses overcite.st

The impact of surgical technique on coronal plane motion in total knee arthroplasty

There are two predominant techniques used by most surgeons to perform total knee arthroplasty: gap balancing and measured resection. The purpose of the current study was to observe if surgical technique has an effect on post-operative coronal plane balance throughout range of motion and to observe if surgical technique has an effect on tibial and femoral component migration. This was a randomized, prospective controlled trial. Twenty-three patients (24 knees) were enrolled: twelve knees in each group. All knees showed migration of their components from the initial RSA to their RSA at 6 months. Migration was similar for both groups, but in the GB group, the tibial component internally rotated whereas the measured resection group externally rotated (p=0.03). There was no difference between the GB group and the MR group in terms of coronal plane balance throughout range of motion exhibited post-TKA implantation (p=0.56). Our data demonstrated that post-operative coronal plane balance throughout range of motion of the knee is most easily predicted by pre-implant operative coronal plane balance

Bleaching impacts on carbonate production in the Chagos Archipelago: influence of functional coral groups on carbonate budget trajectories

This is the final version. Available on open access from Springer Verlag via the DOI in this recordReefs in the remote Chagos Archipelago (central Indian Ocean) were severely affected by sea-surface temperature warming and coral bleaching in 2015-2016. Here we assess the impacts of this event on community composition and reef carbonate production at twelve fore reefs sites across three atolls. Bleaching caused a 69% decline in coral cover, mostly driven by mortality of tabular Acropora spp., and a 77% decline in mean coral carbonate production (2015: 13.1±4.8; 2018: 3.0±1.2 kg CaCO3 m2 yr-1). Changes were accompanied by a major shift from competitive to stress-tolerant coral taxa, with magnitudes of decline comparable to those reported elsewhere in the Indian Ocean, despite inter-site differences in dominant coral species. These trends differ from those on reefs dominated by stress-tolerant taxa, which experienced minor declines in production post-warming. The study highlights the potential for different suites of functional coral groups to drive divergent post-bleaching budget responses.Bertarelli Foundatio