Energy and energy flux in axisymmetric slow and fast waves

Aims: We aim to calculate the kinetic, magnetic, thermal, and total energy densities and the flux of energy in axisymmetric sausage modes. The resulting equations should contain as few parameters as possible to facilitate applicability for different observations. 

Methods: The background equilibrium is a one-dimensional cylindrical flux tube model with a piecewise constant radial density profile. This enables us to use linearised magnetohydrodynamic equations to calculate the energy densities and the flux of energy for axisymmetric sausage modes. 

Results: The equations used to calculate the energy densities and the flux of energy in axisymmetric sausage modes depend on the radius of the flux tube, the equilibrium sound and Alfvén speeds, the density of the plasma, the period and phase speed of the wave, and the radial or longitudinal components of the Lagrangian displacement at the flux tube boundary. Approximate relations for limiting cases of propagating slow and fast sausage modes are also obtained. We also obtained the dispersive first-order correction term to the phase speed for both the fundamental slow body mode under coronal conditions and the slow surface mode under photospheric conditions.

The potential of electron beam irradiation for simultaneous surface modification and bioresorption control of PLLA for medical device applications

Bioresorbable polymers have been widely investigated as materials exhibiting significant potential for successful application in the medical fields of bone fixation devices and drug delivery. Further to the ability to control degradation, surface engineering of polymers has been highlighted as a key method central to their development. Previous work has demonstrated the ability of electron beam (e-beam) technology to control the degradation profiles and bioresorption of a number of commercially relevant bioresorbable polymers (poly-l-lactic acid (PLLA), L-lactide/ DL-lactide co-polymer (PLDL) and poly(lactic-co-glycolic acid) (PLGA). This work investigates the further potential of e-beam technology to impart added biofunctionality through the manipulation of polymer (PLLA) surface properties. A Dynamatron Continuous DC e-beam unit (Synergy Health, UK), with beam energies of 0.5, 0.75, and 1.5 MeV, was used for the irradiation of PLLA samples with delivered surface doses of 150 or 500 kGy at each energy level. The chosen conditions reflect the need to achieve a specific surface modification for the control of surface degradation as demonstrated in previous work. Surface characterization was then performed using contact angle analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy.
Results demonstrated a significant increase in surface wettability post e-beam treatment. In correlation with this, XPS data showed the introduction of oxygen-containing functional groups to the surface of PLLA. Raman spectroscopy indicated chain scission in the near surface region of PLLA. E-beam irradiation did not seem to affect the surface roughness of PLLA as a direct consequence of the treatment. In conclusion electron beam surface modification has been found to modify both the surface-to-bulk bioresorption profile and the surface hydrophilicity. Both could provide benefits in relation to the performance of implantable medical devices.

Surface modification of LiV3O8 nanosheets via layer-by-layer self-assembly for high-performance rechargeable lithium batteries

In this work, an economical route based on hydrothermal and layer-by-layer (LBL) self-assembly processes has been developed to synthesize unique Al ₂O₃-modified LiV₃O₈ nanosheets, comprising a core of LiV₃O₈ nanosheets and a thin Al ₂O₃ nanolayer. The thickness of the Al₂O ₃ nanolayer can be tuned by altering the LBL cycles. When evaluated for their lithium-storage properties, the 1 LBL Al₂O ₃-modified LiV₃O₈ nanosheets exhibit a high discharge capacity of 191 mA h g^-1 at 300 mA g^-1 (1C) over 200 cycles and excellent rate capability, demonstrating that enhanced physical and/or chemical properties can be achieved through proper surface modification. © 2014 Elsevier B.V. All rights reserved.

Irradiation of bioresorbable biomaterials for controlled surface degradation

Bioresorbable polymers increasingly are the materials of choice for implantable orthopaedic fixation devices. Controlled degradation of these polymers is vital for preservation of mechanical properties during tissue repair and controlled release of incorporated agents such as osteoconductive or anti-microbial additives. The work outlined in this paper investigates the use of low energy electron beam irradiation to surface modify polyhydroxyacid samples incorporating beta tricalcium phosphate (β-TCP). This work uniquely demonstrates that surface modification of bioresorbable polymers through electron beam irradiation allows for the early release of incorporated agents such as bioactive additives. Samples were e-beam irradiated at an energy of 125 keV and doses of either 150 kGy or 500 kGy. Irradiated and non-irradiated samples were degraded in phosphate buffered saline (PBS), to simulate bioresorption, followed by characterisation. The results show that low energy e-beam irradiation enhances surface hydrolytic degradation in comparison to bulk and furthermore allows for earlier release of incorporated calcium via dissolution into the surrounding medium.

Circular polarisation frequency selective surface operating in Ku and Ka band

A double layer circular polarization (CP) frequency selective surface (FSS) for use as a dual-band quasi-optical diplexer suitable for deployment in reflector antenna systems is described. The FSS was designed to reflect Ku band signals (11.7–12.75 GHz) while transmitting Ka band signals (17.3–20.2 GHz) and conserving CP in each of these bands. The simulated/measured reflection loss over the Ku band was less than 0.05/0.1 dB for both TE and TM polarizations, while the simulated/measured axial ratio was less than 0.2/0.75 dB. Over the Ka band, the simulated/measured transmission loss for both polarizations was below 0.25/0.4 dB and the simulated/measured axial ratio was less than 0.25/0.75 dB. To the best of our knowledge, this is the first report of a metallo-dielectric FSS that simultaneously operates in CP for an oblique angle of incidence in both Ku and Ka bands.

Multilayer Dielectric Stack Parameter Modelling for FSS Design

This paper discusses modelling multilayer dielectric stacks for use as substrate support for frequency selective surface. A method of a fast simulation of multilayer dielectric stack as a complementary tool for FSS design is proposed. Using the method analysis of effect of different parts of the multilayer stack has been performed. The tool has also been used for extraction of material parameters from the measured results. Measured transmission and reflection of a sample manufactured material stack show good agreement with the simulated results obtained for extracted material parameters.

Building sandstone surface modification by biofilm and iron precipitation: emerging block-scale heterogeneity and system response

Stone surfaces are sensitive to their environment. This means that they will often respond to exposure conditions by manifesting a change in surface characteristics. Such changes can be more than simply aesthetic, creating surface/subsurface heterogeneity in stone at the block scale, promoting stress gradients to be set up as surface response to, for example, temperature fluctuations, can diverge from subsurface response. This paper reports preliminary experiments investigating the potential of biofilms and iron precipitation as surface-modifiers on stone, exploring the idea of block-scale surface-to-depth heterogeneity, and investigating how physical alteration in the surface and near-surface zone can have implications for subsurface response and potentially for long-term decay patterns. Salt weathering simulations on fresh and surface-modified stone suggest that even subtle surface modification can have significant implications for moisture uptake and retention, salt concentration and distribution from surface to depth, over the period of the experimental run. The accumulation of salt may increase the retention of moisture, by modifying vapour pressure differentials and the rate of evaporation.
Temperature fluctuation experiments suggest that the presence of a biofilm can have an impact on energy transfer processes that occur at the stone surface (for example, buffering against temperature fluctuation), affecting surface-to-depth stress gradients. Ultimately, fresh and surface-modified blocks mask different kinds of system, which respond to inputs differently because of different storage mechanisms, encouraging divergent behaviour between fresh and surface modified stone over time.