19,351 research outputs found
Peptide:glycosaminoglycan hybrid hydrogels as an injectable intervention for spinal disc degeneration
Degeneration of the spinal discs is a major cause of back pain. During the degeneration process, there is a loss of glycosaminoglycans (GAGs) from the proteoglycan-rich gel in the disc’s nucleus, which adversely alters biomechanical performance. Current surgical treatments for back pain are highly invasive and have low success rates; there is an urgent need for minimally-invasive approaches that restore the physiological mechanics of the spine. Here we present an injectable peptide:GAG hydrogel that rapidly self-assembles in situ and restores the mechanics of denucleated intervertebral discs. It forms a gel with comparable mechanical properties to the native tissue within seconds to minutes depending on the peptide chosen. Unlike other biomaterials that have been proposed for this purpose, these hybrid hydrogels can be injected through a very narrow 25 G gauge needle, minimising damage to the surrounding soft tissue, and they mimic the ability of the natural tissue to draw in water by incorporating GAGs. Furthermore, the GAGs enhance the gelation kinetics and thermodynamic stability of peptide hydrogels, significantly reducing effusion of injected material from the intervertebral disc (GAG leakage of 8 ± 3% after 24 hrs when peptide present, compared to 39 ± 3% when no peptide present). In an ex vivo model, we demonstrate that the hydrogels can restore the compressive stiffness of denucleated bovine intervertebral discs. Compellingly, this novel biomaterial has the potential to transform the clinical treatment of back pain by resolving current surgical challenges, thus improving patient quality of life
Beamforming based Mitigation of Hovering Inaccuracy in UAV-Aided RFET
Hovering inaccuracy of unmanned aerial vehicle (UAV) degrades the performance of UAV-aided radio frequency energy transfer (RFET). Such inaccuracy arises due to positioning error and rotational motion of UAV, which lead to localization mismatch (LM) and orientation mismatch (OM). In this paper, antenna array beam steering based UAV hovering inaccuracy mitigation strategy is presented. The antenna beam does not accurately point towards the field sensor node due to rotational motion of the UAV along with pitch, roll, and yaw, which leads to deviation in the elevation angle. An analytical framework is developed to model this deviation, and its variation is estimated using the data collected through an experimental setup. Closed-form expressions of received power at the field node are obtained for the four cases arising from LM and OM. An optimization problem to estimate the optimal system parameters (transmit power, UAV hovering altitude, and antenna steering parameter) is formulated. The problem is proven to be nonconvex. Therefore, an algorithm is proposed to solve this problem. Simulation results demonstrate that the proposed framework significantly mitigates the hovering inaccuracy; compared to reported state-of-the-art the same performance can be achieved with substantially less transmit power
Annulus fibrosus functional extrafibrillar and fibrous mechanical behaviour: experimental and computational characterisation
The development of current surgical treatments for intervertebral disc damage could benefit from virtual environment accounting for population variations. For such models to be reliable, a relevant description of the mechanical properties of the different tissues and their role in the functional mechanics of the disc is of major importance. The aims of this work were first to assess the physiological hoop strain in the annulus fibrosus in fresh conditions (n = 5) in order to extract a functional behaviour of the extrafibrillar matrix; then to reverse-engineer the annulus fibrosus fibrillar behaviour (n = 6). This was achieved by performing both direct and global controlled calibration of material parameters, accounting for the whole process of experimental design and in silico model methodology. Direct-controlled models are specimen-specific models representing controlled experimental conditions that can be replicated and directly comparing measurements. Validation was performed on another six specimens and a sensitivity study was performed. Hoop strains were measured as 17 ± 3% after 10 min relaxation and 21 ± 4% after 20–25 min relaxation, with no significant difference between the two measurements. The extrafibrillar matrix functional moduli were measured as 1.5 ± 0.7 MPa. Fibre-related material parameters showed large variability, with a variance above 0.28. Direct-controlled calibration and validation provides confidence that the model development methodology can capture the measurable variation within the population of tested specimens
Maximum-Entropy Weighting of Multi-Component Earth Climate Models
A maximum entropy-based framework is presented for the synthesis of
projections from multiple Earth climate models. This identifies the most
representative (most probable) model from a set of climate models -- as defined
by specified constraints -- eliminating the need to calculate the entire set.
Two approaches are developed, based on individual climate models or ensembles
of models, subject to a single cost (energy) constraint or competing
cost-benefit constraints. A finite-time limit on the minimum cost of modifying
a model synthesis framework, at finite rates of change, is also reported.Comment: Inspired by discussions at the Mathematical and Statistical
Approaches to Climate Modelling and Prediction workshop, Isaac Newton
Institute for Mathematical Sciences, Cambridge, UK, 11 Aug. to 22 Dec. 2010.
Accepted for publication in Climate Dynamics, 8 August 201
Efficiency improvements for the numerical computation of NLO corrections
In this paper we discuss techniques, which lead to a significant improvement
of the efficiency of the Monte Carlo integration, when one-loop QCD amplitudes
are calculated numerically with the help of the subtraction method and contour
deformation. The techniques discussed are: holomorphic and non-holomorphic
division into sub-channels, optimisation of the integration contour,
improvement of the ultraviolet subtraction terms, importance sampling and
antithetic variates in loop momentum space, recurrence relations.Comment: 34 pages, version to be publishe
The dynamics of apparent horizons in Robinson-Trautman spacetimes
We present an alternative scheme of finding apparent horizons based on
spectral methods applied to Robinson-Trautman spacetimes. We have considered
distinct initial data such as representing the spheroids of matter and the
head-on collision of two non-rotating black holes. The evolution of the
apparent horizon is presented. We have obtained in some cases a mass gap
between the final Bondi and apparent horizon masses, whose implications were
briefly commented in the light of the thermodynamics of black holes.Comment: 9 pages, 7 figure
The treatment of the infrared region in perturbative QCD
We discuss the contribution coming from the infrared region to NLO matrix
elements and/or coefficient functions of hard QCD processes. Strictly speaking,
this contribution is not known theoretically, since it is beyond perturbative
QCD. For DGLAP evolution all the infrared contributions are collected in the
phenomenological input parton distribution functions (PDFs), at some relatively
low scale Q_0; functions which are obtained from a fit to the `global' data.
However dimensional regularization sometimes produces a non-zero result coming
from the infrared region. Instead of this conventional regularization
treatment, we argue that the proper procedure is to first subtract from the NLO
matrix element the contribution already generated at the same order in \alpha_s
by the LO DGLAP splitting function convoluted with the LO matrix element. This
prescription eliminates the logarithmic infrared divergence, giving a
well-defined result which is consistent with the original idea that everything
below Q_0 is collected in the PDF input. We quantify the difference between the
proposed treatment and the conventional approach using low-mass Drell-Yan
production and deep inelastic electron-proton scattering as examples; and
discuss the potential impact on the `global' PDF analyses. We present arguments
to show that the difference cannot be regarded as simply the use of an
alternative factorization scheme.Comment: 15 pages, 5 figures, title changed, text considerably modified to
improve presentation, and discussion section enlarge
Contrast in Terahertz Images of Archival Documents—Part I: Influence of the Optical Parameters from the Ink and Support
This study aims to objectively inform curators when terahertz time-domain (TD) imaging set in reflection mode is likely to give well-contrasted images of inscriptions in a complex archival document and is a useful non-invasive alternative to current digitisation processes. To this end, the dispersive refractive indices and absorption coefficients from various archival materials are assessed and their influence on contrast in terahertz images from historical documents is explored. Sepia ink and inks produced with bistre or verdigris mixed with a solution of Arabic gum or rabbit skin glue are unlikely to lead to well-contrasted images. However, dispersions of bone black, ivory black, iron gall ink, malachite, lapis lazuli, minium and vermilion are likely to lead to well-contrasted images. Inscriptions written with lamp black, carbon black and graphite give the best imaging results. The characteristic spectral signatures from iron gall ink, minium and vermilion pellets between 5 and 100 cm−1 relate to a ringing effect at late collection times in TD waveforms transmitted through these pellets. The same ringing effect can be probed in waveforms reflected from iron gall, minium and vermilion ink deposits at the surface of a document. Since TD waveforms collected for each scanning pixel can be Fourier-transformed into spectral information, terahertz TD imaging in reflection mode can serve as a hyperspectral imaging tool. However, chemical recognition and mapping of the ink is currently limited by the fact that the morphology of the document influences more the terahertz spectral response of the document than the resonant behaviour of the ink
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