410 research outputs found
On the effects of using CO2 and F2 lasers to modify the wettability of a polymeric biomaterial.
Enhancement of the surface properties of a material by means of laser radiation has been amply demonstrated previously. In this work a comparative study for the surface modification of nylon 6,6 has been conducted in order to vary the wettability characteristics using CO2 and excimer lasers. This was done by producing 50 μm spaced (with depths between 1 and 10 μm) trench-like patterns using various laser parameters such as varying the laser power for the CO2 laser and number of pulses for the excimer laser. Topographical changes were analysed using optical microscopy and white light interferometry which indicated that both laser systems can be implemented for modifying the topography of nylon 6,6. Variations in the surface chemistry were evaluated using energy-dispersive X-ray spectroscopy and x-ray photoelectron spectroscopy analysis and showed that the O2 increased by up to 1.5% At. and decreased by up to 1.6% At. for the CO2 and F2 laser patterned samples, respectively. Modification of the wettability characteristics was quantified by measuring the advancing contact angle, which was found to increase in all instances for both laser systems. Emery paper roughened samples were also analysed in the same manner to determine that the topographical pattern played a major role in the wettability characteristics of nylon 6,6. From this, it is proposed that the increase in contact angle for the laser processed samples is due to a mixed intermediate state wetting regime owed to the periodic surface roughness brought about by the laser induced trench-like topographical patterns
Observations of the post shock break-out emission of SN 2011dh with XMM-Newton
After the occurrence of the type cIIb SN 2011dh in the nearby spiral galaxy M
51 numerous observations were performed with different telescopes in various
bands ranging from radio to gamma-rays. We analysed the XMM-Newton and Swift
observations taken 3 to 30 days after the SN explosion to study the X-ray
spectrum of SN 2011dh. We extracted spectra from the XMM-Newton observations,
which took place ~7 and 11 days after the SN. In addition, we created
integrated Swift/XRT spectra of 3 to 10 days and 11 to 30 days. The spectra are
well fitted with a power-law spectrum absorbed with Galactic foreground
absorption. In addition, we find a harder spectral component in the first
XMM-Newton spectrum taken at t ~ 7 d. This component is also detected in the
first Swift spectrum of t = 3 - 10 d. While the persistent power-law component
can be explained as inverse Compton emission from radio synchrotron emitting
electrons, the harder component is most likely bremsstrahlung emission from the
shocked stellar wind. Therefore, the harder X-ray emission that fades away
after t ~ 10 d can be interpreted as emission from the shocked circumstellar
wind of SN 2011dh.Comment: Accepted for publication as a Research Note in Astronomy and
Astrophysic
Interaction of CO2 laser-modified nylon with osteoblast cells in relation to wettability
It has been amply demonstrated previously that CO2 lasers hold the ability to surface modify various polymers. In addition, it has been observed that these surface enhancements can augment the biomimetic nature of the laser irradiated materials. This research has employed a CO2 laser marker to produce trench and hatch topographical patterns with peak heights of around 1 μm on the surface of nylon 6,6. The patterns generated have been analysed using white light interferometery, optical microscopy and X-ray photoelectron spectroscopy was employed to determine the surface oxygen content. Contact angle measurements were used to characterize each sample in terms of wettability. Generally, it was seen that as a result of laser processing the contact angle, surface roughness and surface oxygen content increased whilst the apparent polar and total surface energies decreased. The increase in contact angle and reduction in surface energy components was found to be on account of a mixed intermediate state wetting regime owing to the change in roughness due to the induced topographical patterns. To determine the biomimetic nature of the modified and as-received control samples each one was seeded with 2×104 cells/ml normal human osteoblast cells and observed after periods of 24 hours and 4 days using optical microscopy and SEM to determine mean cell cover densities and variations in cell morphology. In addition a haeymocytometer was used to show that the cell count for the laser patterned samples had increased by up to a factor of 1.5 compared to the as-received control sample after 4 days of incubation. Significantly, it was determined that all laser-induced patterns gave rise to better cell response in comparison to the as-received control sample studied due to increased preferential cell growth on those surfaces with increased surface roughness
Asymptotic stability of the Cauchy and Jensen functional equations
The aim of this note is to investigate the asymptotic stability behaviour of
the Cauchy and Jensen functional equations. Our main results show that if these
equations hold for large arguments with small error, then they are also valid
everywhere with a new error term which is a constant multiple of the original
error term. As consequences, we also obtain results of hyperstability character
for these two functional equations
Chaos in the one-dimensional gravitational three-body problem
We have investigated the appearance of chaos in the 1-dimensional Newtonian
gravitational three-body system (three masses on a line with pairwise
potential). We have concentrated in particular on how the behavior changes when
the relative masses of the three bodies change (with negative total energy).
For two mass choices we have calculated 18000 full orbits (with initial states
on a lattice on the Poincar\'e section) and obtained dwell time
distributions. For 105 mass choices we have calculated Poincar\'e maps for
starting points. Our results show that the Poincar\'e section
(and hence the phase space) divides into three well defined regions with orbits
of different characteristics: 1) There is a region of fast scattering, with a
minimum of pairwise collisions and smooth dependence on initial values. 2) In
the chaotic scattering region the interaction times are longer, and both the
interaction time and the final state depend sensitively on the starting point
on the Poincar\'e section. For both 1) and 2) the initial and final states
consists of a binary + single particle. 3) The third region consists of
quasiperiodic orbits where the three masses are bound together forever. At the
center of the quasiperiodic region there is the periodic Schubart orbit, whose
stability turns out to correlate strongly with the global behavior.Comment: 24 pages of text (REVTEX 3.0) + 21 pages of figures. Figures are only
available in paper form, ask for a preprint from the author
A data mining algorithm for automated characterisation of fluctuations in multichannel timeseries
We present a data mining technique for the analysis of multichannel
oscillatory timeseries data and show an application using poloidal arrays of
magnetic sensors installed in the H-1 heliac. The procedure is highly
automated, and scales well to large datasets. The timeseries data is split into
short time segments to provide time resolution, and each segment is represented
by a singular value decomposition (SVD). By comparing power spectra of the
temporal singular vectors, singular values are grouped into subsets which
define fluctuation structures. Thresholds for the normalised energy of the
fluctuation structure and the normalised entropy of the SVD are used to filter
the dataset. We assume that distinct classes of fluctuations are localised in
the space of phase differences between each pair of nearest neighbour channels.
An expectation maximisation clustering algorithm is used to locate the distinct
classes of fluctuations, and a cluster tree mapping is used to visualise the
results.Comment: 14 pages, 8 figure
Reversible magnetization of MgB2 single crystals with a two-gap nature
We present reversible magnetization measurements on MgB2 single crystals in
magnetic fields up to 2.5 T applied parallel to the crystal's c-axis. This
magnetization is analyzed in terms of the Hao-Clem model, and various
superconducting parameters, such as the critical fields [Hc(0) and Hc2(0)], the
characteristic lengths [xi(0) and lambda(0)], and the Ginzburg-Landau
parameter, kappa, are derived. The temperature dependence of the magnetic
penetration depth, lambda(T), obtained from the Hao-Clem analysis could not be
explained by theories assuming a single gap. Our data are well described by
using a two-gap model.Comment: 20 pages, 1 table, 4 figures, will be published in Phys. Rev.
Thermal Resonance in Signal Transmission
We use temperature tuning to control signal propagation in simple
one-dimensional arrays of masses connected by hard anharmonic springs and with
no local potentials. In our numerical model a sustained signal is applied at
one site of a chain immersed in a thermal environment and the signal-to-noise
ratio is measured at each oscillator. We show that raising the temperature can
lead to enhanced signal propagation along the chain, resulting in thermal
resonance effects akin to the resonance observed in arrays of bistable systems.Comment: To appear in Phys. Rev.
On the study of oil paint adhesion on optically transparent glass: Conservation of reverse paintings on glass
Archived with thanks to Applied Surface Science, ElsevierReverse painting on glass is a technique which consists of applying a cold paint layer on the reverse-side of glass. The main challenge facing these artworks is the fragile adhesion of the pictorial layer – a simple movement can modify the appearance of the painting. This paper details a study into the adhesion parameters of pigments on glass and the comparison between different pigments. The relationships between the binder (linseed oil) with pigments and the glass with or without the use of an adhesive are studied. Physical analyses by surface characterisation have been carried out to better understand the influence of the pigment. The use of a sessile drop device, optical microscopy, scanning electron microscopy (SEM), a surface 3D profiler and a pencil hardness scratch tester were necessary to establish a comparison of the pictorial layer adhesion. A comparison of the effect of two adhesives; namely ox gall and gum arabic, has shown that the adhesion is not only linked to the physical parameters but that possible chemical reactions can influence the results. Finally, a treatment based on humidity-extreme storage has shown the weakness of some pictorial layers
A New Solution to the Relative Orientation Problem using only 3 Points and the Vertical Direction
This paper presents a new method to recover the relative pose between two
images, using three points and the vertical direction information. The vertical
direction can be determined in two ways: 1- using direct physical measurement
like IMU (inertial measurement unit), 2- using vertical vanishing point. This
knowledge of the vertical direction solves 2 unknowns among the 3 parameters of
the relative rotation, so that only 3 homologous points are requested to
position a couple of images. Rewriting the coplanarity equations leads to a
simpler solution. The remaining unknowns resolution is performed by an
algebraic method using Grobner bases. The elements necessary to build a
specific algebraic solver are given in this paper, allowing for a real-time
implementation. The results on real and synthetic data show the efficiency of
this method
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