15,204 research outputs found
Optimal design of composite hip implants using NASA technology
Using an adaptation of NASA software, we have investigated the use of numerical optimization techniques for the shape and material optimization of fiber composite hip implants. The original NASA inhouse codes, were originally developed for the optimization of aerospace structures. The adapted code, which was called OPORIM, couples numerical optimization algorithms with finite element analysis and composite laminate theory to perform design optimization using both shape and material design variables. The external and internal geometry of the implant and the surrounding bone is described with quintic spline curves. This geometric representation is then used to create an equivalent 2-D finite element model of the structure. Using laminate theory and the 3-D geometric information, equivalent stiffnesses are generated for each element of the 2-D finite element model, so that the 3-D stiffness of the structure can be approximated. The geometric information to construct the model of the femur was obtained from a CT scan. A variety of test cases were examined, incorporating several implant constructions and design variable sets. Typically the code was able to produce optimized shape and/or material parameters which substantially reduced stress concentrations in the bone adjacent of the implant. The results indicate that this technology can provide meaningful insight into the design of fiber composite hip implants
Sertraline and Phenytoin Drug Interaction in a Geriatric Patient
This report presents the case of a 78-year-old man residing in a nursing home who presented with a 2-month history of increasing lethargy and confusion. These symptoms coincided with the initiation of sertraline in the patient. Among other medications, he was also taking phenytoin. The medical team concluded that the cause of the patient’s lethargy and confusion was a drug interaction between sertraline and phenytoin. Phenytoin was held, while the sertraline was slowly tapered to discontinuation. The patient’s symptoms resolved soon thereafter. Future research is needed to better guide clinicians in appropriate selection, dosing, and monitoring of selective serotonin reuptake inhibitors with concomitant phenytoin use.Key words: phenytoin, sertraline, SSRIs, drug interactio
Lessons lost in sentencing: Welding individualised justice to indigenous justice
Indigenous offenders are heavily over-represented in the Australian and Canadian criminal justice systems. In the case of R v Gladue, the Supreme Court of Canada held that sentencing judges are to recognise the adverse systemic and background factors that many Aboriginal Canadians face and consider all reasonable alternatives to imprisonment in light of this. In R v Ipeelee, the Court reiterated the need to fully acknowledge the oppressive environment faced by Aboriginal Canadians throughout their lives and the importance of sentencing courts applying appropriate sentencing options. In 2013, the High Court of Australia handed down its decision in Bugmy v The Queen. The Court affirmed that deprivation is a relevant consideration and worthy of mitigation in sentencing. However, the Court refused to accept that judicial notice should be taken of the systemic background of deprivation of many Indigenous offenders. The High Court also fell short of applying the Canadian principle that sentencing should promote restorative sentences for Indigenous offenders, given this oft-present deprivation and their over-representation in prison. In this article, we argue that Bugmy v The Queen represents a missed opportunity by the High Court to grapple with the complex interrelationship between individualised justice and Indigenous circumstances in the sentencing of Indigenous offenders
Apes communicate about absent and displaced objects: methodology matters
Displaced reference is the ability to refer to an item that has been moved (displaced) in space and/or time, and has been called one of the true hallmarks of referential communication. Several studies suggest that nonhuman primates have this capability, but a recent experiment concluded that in a specific situation (absent entities) human infants display displaced reference but chimpanzees do not. Here we show that chimpanzees and bonobos of diverse rearing histories are capable of displaced reference to absent and displaced objects. It is likely that some of the conflicting findings from animal cognition studies are due to relatively minor methodological differences, but are compounded by interpretation errors. Comparative studies are of great importance in elucidating the evolution of human cognition, however, greater care must be taken with methodology and interpretation for these studies to accurately reflect species differences
Spherical codes, maximal local packing density, and the golden ratio
The densest local packing (DLP) problem in d-dimensional Euclidean space Rd
involves the placement of N nonoverlapping spheres of unit diameter near an
additional fixed unit-diameter sphere such that the greatest distance from the
center of the fixed sphere to the centers of any of the N surrounding spheres
is minimized. Solutions to the DLP problem are relevant to the realizability of
pair correlation functions for packings of nonoverlapping spheres and might
prove useful in improving upon the best known upper bounds on the maximum
packing fraction of sphere packings in dimensions greater than three. The
optimal spherical code problem in Rd involves the placement of the centers of N
nonoverlapping spheres of unit diameter onto the surface of a sphere of radius
R such that R is minimized. It is proved that in any dimension, all solutions
between unity and the golden ratio to the optimal spherical code problem for N
spheres are also solutions to the corresponding DLP problem. It follows that
for any packing of nonoverlapping spheres of unit diameter, a spherical region
of radius less than or equal to the golden ratio centered on an arbitrary
sphere center cannot enclose a number of sphere centers greater than one more
than the number that can be placed on the region's surface.Comment: 12 pages, 1 figure. Accepted for publication in the Journal of
Mathematical Physic
Cosmic ray feedback in the FIRE simulations: constraining cosmic ray propagation with GeV gamma ray emission
We present the implementation and the first results of cosmic ray (CR)
feedback in the Feedback In Realistic Environments (FIRE) simulations. We
investigate CR feedback in non-cosmological simulations of dwarf, sub-
starburst, and galaxies with different propagation models, including
advection, isotropic and anisotropic diffusion, and streaming along field lines
with different transport coefficients. We simulate CR diffusion and streaming
simultaneously in galaxies with high resolution, using a two moment method. We
forward-model and compare to observations of -ray emission from nearby
and starburst galaxies. We reproduce the -ray observations of dwarf and
galaxies with constant isotropic diffusion coefficient . Advection-only and streaming-only
models produce order-of-magnitude too large -ray luminosities in dwarf
and galaxies. We show that in models that match the -ray
observations, most CRs escape low-gas-density galaxies (e.g.\ dwarfs) before
significant collisional losses, while starburst galaxies are CR proton
calorimeters. While adiabatic losses can be significant, they occur only after
CRs escape galaxies, so they are only of secondary importance for -ray
emissivities. Models where CRs are ``trapped'' in the star-forming disk have
lower star formation efficiency, but these models are ruled out by -ray
observations. For models with constant that match the -ray
observations, CRs form extended halos with scale heights of several kpc to
several tens of kpc.Comment: 31 pages, 26 figures, accepted for publication in MNRA
The origin of ultra diffuse galaxies: stellar feedback and quenching
We test if the cosmological zoom-in simulations of isolated galaxies from the
FIRE project reproduce the properties of ultra diffuse galaxies. We show that
stellar feedback-generated outflows that dynamically heat galactic stars,
together with a passively aging stellar population after imposed quenching
(from e.g. infall into a galaxy cluster), naturally reproduce the observed
population of red UDGs, without the need for high spin halos or dynamical
influence from their host cluster. We reproduce the range of surface
brightness, radius and absolute magnitude of the observed z=0 red UDGs by
quenching simulated galaxies at a range of different times. They represent a
mostly uniform population of dark matter-dominated galaxies with M_star ~1e8
Msun, low metallicity and a broad range of ages. The most massive simulated
UDGs require earliest quenching and are therefore the oldest. Our simulations
provide a good match to the central enclosed masses and the velocity
dispersions of the observed UDGs (20-50 km/s). The enclosed masses of the
simulated UDGs remain largely fixed across a broad range of quenching times
because the central regions of their dark matter halos complete their growth
early. A typical UDG forms in a dwarf halo mass range of Mh~4e10-1e11 Msun. The
most massive red UDG in our sample requires quenching at z~3 when its halo
reached Mh ~ 1e11 Msun. If it, instead, continues growing in the field, by z=0
its halo mass reaches > 5e11 Msun, comparable to the halo of an L* galaxy. If
our simulated dwarfs are not quenched, they evolve into bluer low-surface
brightness galaxies with mass-to-light ratios similar to observed field dwarfs.
While our simulation sample covers a limited range of formation histories and
halo masses, we predict that UDG is a common, and perhaps even dominant, galaxy
type around Ms~1e8 Msun, both in the field and in clusters.Comment: 20 pages, 13 figures; match the MNRAS accepted versio
Compact continuum source-finding for next generation radio surveys
We present a detailed analysis of four of the most widely used radio source
finding packages in radio astronomy, and a program being developed for the
Australian Square Kilometer Array Pathfinder (ASKAP) telescope. The four
packages; SExtractor, SFind, IMSAD and Selavy are shown to produce source
catalogues with high completeness and reliability. In this paper we analyse the
small fraction (~1%) of cases in which these packages do not perform well. This
small fraction of sources will be of concern for the next generation of radio
surveys which will produce many thousands of sources on a daily basis, in
particular for blind radio transients surveys. From our analysis we identify
the ways in which the underlying source finding algorithms fail. We demonstrate
a new source finding algorithm Aegean, based on the application of a Laplacian
kernel, which can avoid these problems and can produce complete and reliable
source catalogues for the next generation of radio surveys.Comment: 14 pages, 12 figures, accepted for publication in MNRA
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