14,639 research outputs found
Accuracy of ultrasound-guided intra-articular injections in guinea pig knees.
ObjectiveDunkin Hartley guinea pigs, a commonly used animal model of osteoarthritis, were used to determine if high frequency ultrasound can ensure intra-articular injections are accurately positioned in the knee joint.MethodsA high-resolution small animal ultrasound system with a 40 MHz transducer was used for image-guided injections. A total of 36 guinea pigs were anaesthetised with isoflurane and placed on a heated stage. Sterile needles were inserted directly into the knee joint medially, while the transducer was placed on the lateral surface, allowing the femur, tibia and fat pad to be visualised in the images. B-mode cine loops were acquired during 100 µl. We assessed our ability to visualise 1) important anatomical landmarks, 2) the needle and 3) anatomical changes due to the injection.ResultsFrom the ultrasound images, we were able to visualise clearly the movement of anatomical landmarks in 75% of the injections. The majority of these showed separation of the fat pad (67.1%), suggesting the injections were correctly delivered in the joint space. We also observed dorsal joint expansion (23%) and patellar tendon movement (10%) in a smaller subset of injections.ConclusionThe results demonstrate that this image-guided technique can be used to visualise the location of an intra-articular injection in the joints of guinea pigs. Future studies using an ultrasound-guided approach could help improve the injection accuracy in a variety of anatomical locations and animal models, in the hope of developing anti-arthritic therapies. Cite this article: Bone Joint Res 2015;4:1-5
Flow of magnetic repelling grains in a two-dimensional silo
During a typical silo discharge, the material flow rate is determined by the
contact forces between the grains. Here, we report an original study concerning
the discharge of a two-dimensional silo filled with repelling magnetic grains.
This non-contact interaction leads to a different dynamics from the one
observed with conventional granular materials. We found that, although the flow
rate dependence on the aperture size follows roughly the power-law with an
exponent found in non-repulsive systems, the density and velocity
profiles during the discharge are totally different. New phenomena must be
taken into account. Despite the absence of contacts, clogging and intermittence
were also observed for apertures smaller than a critical size determined by the
effective radius of the repulsive grains.Comment: 6 pages, 8 figure
Multifractal properties of growing networks
We introduce a new family of models for growing networks. In these networks
new edges are attached preferentially to vertices with higher number of
connections, and new vertices are created by already existing ones, inheriting
part of their parent's connections. We show that combination of these two
features produces multifractal degree distributions, where degree is the number
of connections of a vertex. An exact multifractal distribution is found for a
nontrivial model of this class. The distribution tends to a power-law one, , in the infinite network limit.
Nevertheless, for finite networks's sizes, because of multifractality, attempts
to interpret the distribution as a scale-free would result in an ambiguous
value of the exponent .Comment: 7 pages epltex, 1 figur
Dynamical evolution of clustering in complex network of earthquakes
The network approach plays a distinguished role in contemporary science of
complex systems/phenomena. Such an approach has been introduced into seismology
in a recent work [S. Abe and N. Suzuki, Europhys. Lett. 65, 581 (2004)]. Here,
we discuss the dynamical property of the earthquake network constructed in
California and report the discovery that the values of the clustering
coefficient remain stationary before main shocks, suddenly jump up at the main
shocks, and then slowly decay following a power law to become stationary again.
Thus, the network approach is found to characterize main shocks in a peculiar
manner.Comment: 10 pages, 3 figures, 1 tabl
Finite elements numerical solution of a coupled profile–velocity–temperature shallow ice sheet approximation model
AbstractThis work deals with the numerical solution of a complex mathematical model arising in theoretical glaciology. The global moving boundary problem governs thermomechanical processes jointly with ice sheet hydrodynamics. One major novelty is the inclusion of the ice velocity field computation in the framework of the shallow ice model so that it can be coupled with profile and temperature equations. Moreover, the proposed basal velocity and shear stress laws allow the integration of basal sliding effects in the global model. Both features were not taking into account in a previous paper (Math. Model. Methods Appl. Sci. 12 (2) (2002) 229) and provide more realistic convective terms and more complete Signorini boundary conditions for the thermal problem. In the proposed numerical algorithm, one- and two-dimensional piecewise linear Lagrange finite elements in space and a semi-implicit upwinding scheme in time are combined with duality and Newton's methods for nonlinearities. A simulation example involving real data issued from Antarctic shows the temperature, profile and velocity qualitative behaviour as well as the free boundaries and basal effects
Paravortex panopea n. sp. (Platyhelminthes: Rhabdocoela) on clams from the northern Patagonian coast, Argentina: Pathogeny and specificity
During a histopathological survey of the geoduck, Panopeaabbreviata (Hiatellidae), and the razor clam, Ensis macha (Pharidae), in northern Patagonian gulfs (Argentina), turbellarian worms were found in the intestine lumen. In this work, we described a new species of Paravortex (Platyhelminthes, Graffillidae). We collected the hosts by scuba diving and dissected alive for studying the turbellarians. In this new species, the pharynx continues in a short esophagus and the latter in a saccular intestine. Gravid specimens have from 2 to 8 twin embryos in the parenchyma. A short penis papilla arises from the seminal vesicle and the gonopore presents a strong sphincter. This species resembled P. nicolli Szidat, 1965, which was described paraziting Mytilus edulis platensis in Buenos Aires, Argentina. The new species can be differentiated from P. nicolli mainly by the presence of a penis papilla and a sphincter between genital atrium and gonopore. This turbellarian species was significantly more prevalent in geoducks (28 %, n = 210) than in razor clams (6 %, n = 480) (KW, p < 0.0001). For both host species, no evidence of direct physical damage caused by turbellarians was observed.Facultad de Ciencias Naturales y Muse
AdS and Lifshitz Black Holes in Conformal and Einstein-Weyl Gravities
We study black hole solutions in extended gravities with higher-order
curvature terms, including conformal and Einstein-Weyl gravities. In addition
to the usual AdS vacuum, the theories admit Lifshitz and Schr\"odinger vacua.
The AdS black hole in conformal gravity contains an additional parameter over
and above the mass, which may be interpreted as a massive spin-2 hair. By
considering the first law of thermodynamics, we find that it is necessary to
introduce an associated additional intensive/extensive pair of thermodynamic
quantities. We also obtain new Liftshitz black holes in conformal gravity and
study their thermodynamics. We use a numerical approach to demonstrate that AdS
black holes beyond the Schwarzschild-AdS solution exist in Einstein-Weyl
gravity. We also demonstrate the existence of asymptotically Lifshitz black
holes in Einstein-Weyl gravity. The Lifshitz black holes arise at the boundary
of the parameter ranges for the AdS black holes. Outside the range, the
solutions develop naked singularities. The asymptotically AdS and Lifshitz
black holes provide an interesting phase transition, in the corresponding
boundary field theory, from a relativistic Lorentzian system to a
non-relativistic Lifshitz system.Comment: typos corrected, references adde
- …