85 research outputs found
Low secondary electron yield engineered surface for electron cloud mitigation
Secondary electron yield (SEY or δ) limits the performance of a number of devices. Particularly, in high-energy charged particle accelerators, the beam-induced electron multipacting is one of the main sources of electron cloud (e-cloud) build up on the beam path; in radio frequency wave guides, the electron multipacting limits their lifetime and causes power loss; and in detectors, the secondary electrons define the signal background and reduce the sensitivity. The best solution would be a material with a low SEY coating and for many applications δ < 1 would be sufficient. We report on an alternative surface preparation to the ones that are currently advocated. Three commonly used materials in accelerator vacuum chambers (stainless steel, copper, and aluminium) were laser processed to create a highly regular surface topography. It is shown that this treatment reduces the SEY of the copper, aluminium, and stainless steel from δmax of 1.90, 2.55, and 2.25 to 1.12, 1.45, and 1.12, respectively. The δmax further reduced to 0.76-0.78 for all three treated metals after bombardment with 500 eV electrons to a dose between 3.5 à 10-3 and 2.0 à 10-2 C¡mm-2
Strategic sustainable development in the UK construction industry, through the Framework of Strategic Sustainable Development, using Building Information Modelling
The UK Government has set out ambitious plans for all new domestic and commercial buildings to be zero carbon rated by 2016 and 2020 respectively. These are some of the most progressive environmental targets for the built environment in the western world. There are also sustainability principles (SP) that need to be addressed by the UK construction industry, particularly negative impacts such as waste and pollution. Currently, 100 million tonnes of construction waste, including 13 million tonnes of unused materials, is generated each year, with only 20% currently capable of being recycled. The majority of this waste ends up in landfill, contributing to further pollution of the biosphere. The literature suggests that these negative impacts result from a variety of causes, including ineffective leadership, ingrained cultures, outdated technologies and poor logistics.
There are a number of innovative projects within the UK, particularly at a local level, that pose the question as to whether bottom up approaches may be more successful than top down policies, as set by national and local government. This paper presents a case study demonstrating the former approach within the construction industry. Research and consultancy has been undertaken collaboratively between industry, academia and professional practice in the production of 15 individually designed sustainable dwellings in the North East of England. This project has employed Building Information Modelling (BIM) as a new collaborative working platform, aligned to the Modern Method of Construction (MMC). By situating this inquiry within an authentic case study it has highlighted currently ineffective strategies, policies and leadership which have prevented full exploitation of the potential of BIM and MMC towards sustainable production. This inquiry supports the integration of the Framework of Sustainable Strategic Development (FSSD) into construction procurement, as a method for implementing bottom up leadership in a value driven project
Structural plasticity of the selectivity filter in a nonselective ion channel
The sodium potassium ion channel (NaK) is a nonselective ion channel that conducts both sodium and potassium across the cellular membrane. A new crystallographic structure of NaK reveals conformational differences in the residues that make up the selectivity filter between the four subunits that form the ion channel and the inner helix of the ion channel. The crystallographic structure also identifies a side-entry, ion-conduction pathway for Na+ permeation that is unique to NaK. NMR studies and molecular dynamics simulations confirmed the dynamical nature of the top part of the selectivity filter and the inner helix in NaK as also observed in the crystal structure. Taken together, these results indicate that the structural plasticity of the selectivity filter combined with the dynamics of the inner helix of NaK are vital for the efficient conduction of different ions through the non-selective ion channel of NaK
Structural Characterisation of Printable Noble Metal/Poly(Vinyl-ÂAlcohol) Nanocomposites for Optical Applications
This work was conducted under the aegis of the Engineering and Physical Sciences Research Council (EPSRC) of the United Kingdom (EP/I004173/1). Amin Abdolvand is an EPSRC Career Acceleration Fellow at the University of Dundee.In order to enable exploitation of noble metal/poly(vinyl-alcohol) nanocomposites for device fabrication, solutions of poly(vinyl-alcohol) suitable for piezo-driven inkjet printing techniques are identified and discussed in terms of their material properties. The printable poly(vinyl-alcohol) medium is then exploited as a host material through the formation of silver or gold nanoparticles in order to create nanocomposites that exhibit a surface plasmon resonance behaviour associated with the small metallic inclusions. To mitigate some of the material redistribution effects associated with the drying of printed droplets containing finely divided materials, the metallic nanoparticles are formed after the printing and drying process is completed, by way of an in-situ reduction of an appropriate metal salt by the poly(vinyl-alcohol)-host matrix itself, which takes place at modest temperatures compatible with most substrate materials. An obvious application for such nanocomposites is in optical elements whereby the surface plasmon resonance associated with the metal is the functional aspect of devices such as sensors or active optical elements. High Resolution Transmission Electron Microscopy was used to examine the dimensions, distribution, morphology and crystal structure of the silver and gold nanoparticles in detail allowing discussion of their suitability for these applications and what further optimisation may be necessary to adequately control their formation.Publisher PDFPeer reviewe
LongâTerm Retinal Differentiation of Human Induced Pluripotent Stem Cells in a Continuously Perfused Microfluidic Culture Device
Understanding how microenvironmental cues influence cellular behavior will enable development of efficient and robust pluripotent stem cell differentiation protocols. Unlike traditional cell culture dishes, microfluidic bioreactors can provide stable microenvironmental conditions by continuous medium perfusion at a controlled rate. The aim of this study is to investigate whether a microfluidic culture device could be used as a perfused platform for longâterm cell culture processes such as the retinal differentiation of human induced pluripotent stem cells. The perfusion flow rate is established based on the degradation and consumption of growth factors (DKKâ1, Noggin, IGFâ1, and bFGF) and utilizing the PĂŠclet number. The device's performance analyzed by qRTâPCR show improvements compared to the wellâplate control as characterized by significantly higher expression of the markers Pax6, Chx10, and Crx on Day 5, Nrl on day 10, Crx, and Rhodopsin on day 21. Optimization of perfusion rate is an important operating variable in development of robust processes for differentiation cultures. Result demonstrates convective delivery of nutrients via perfusion has a significant impact upon the expression of key retinal markers. This study is the first continuously perfused longâterm (21 days) retinal differentiation of hiPSCs in a microfluidic device
Property and Shape Modulation of Carbon Fibers Using Lasers
An exciting challenge is to create
unduloid-reinforcing fibers
with tailored dimensions to produce synthetic composites with improved
toughness and increased ductility. Continuous carbon fibers, the state-of-the-art
reinforcement for structural composites, were modified via controlled
laser irradiation to result in expanded outwardly tapered regions,
as well as fibers with Q-tip (cotton-bud) end shapes. A pulsed laser
treatment was used to introduce damage at the single carbon fiber
level, creating expanded regions at predetermined points along the
lengths of continuous carbon fibers, while maintaining much of their
stiffness. The range of produced shapes was quantified and correlated
to single fiber tensile properties. Mapped Raman spectroscopy was
used to elucidate the local compositional and structural changes.
Irradiation conditions were adjusted to create a swollen weakened
region, such that fiber failure occurred in the laser treated region
producing two fiber ends with outwardly tapered ends. Loading the
tapered fibers allows for viscoelastic energy dissipation during fiber
pull-out by enhanced friction as the fibers plough through a matrix.
In these tapered fibers, diameters were locally increased up to 53%,
forming outward taper angles of up to 1.8°. The tensile strength
and strain to failure of the modified fibers were significantly reduced,
by 75% and 55%, respectively, ensuring localization of the break in
the expanded region; however, the fiber stiffness was only reduced
by 17%. Using harsher irradiation conditions, carbon fibers were completely
cut, resulting in cotton-bud fiber end shapes. Single fiber pull-out
tests performed using these fibers revealed a 6.75-fold increase in
work of pull-out compared to pristine carbon fibers. Controlled laser
irradiation is a route to modify the shape of continuous carbon fibers
along their lengths, as well as to cut them into controlled lengths
leaving tapered or cotton-bud shapes
First beam test of Laser Engineered Surface Structures (LESS) at cryogenic temperature in CERN SPS accelerator
Electron cloud mitigation is an essential requirement for accelerators of positive particles with high intensity beams to guarantee beam stability and limited heat load in cryogenic systems. Laser Engineered Surface Structures (LESS) are being considered, within the High Luminosity upgrade of the LHC collider at CERN (HL-LHC), as an option to reduce the Secondary Electron Yield (SEY) of the surfaces facing the beam, thus suppressing the elec-tron cloud phenomenon. As part of this study, a 2.2 m long Beam Screen (BS) with LESS has been tested at cryogenic temperature in the COLD bore EXperiment (COLDEX) facility in the SPS accelerator at CERN. In this paper, we describe the manufacturing procedure of the beam screen, the employed laser treatment technique and discuss our first observations in COLDEX confirming electron cloud suppression.Electron cloud mitigation is an essential requirement for accelerators of positive particles with high intensity beams to guarantee beam stability and limited heat load in cryogenic systems. Laser Engineered Surface Structures (LESS) are being considered, within the High Luminosity upgrade of the LHC collider at CERN (HL-LHC), as an option to reduce the Secondary Electron Yield (SEY) of the surfaces facing the beam, thus suppressing the electron cloud phenomenon. As part of this study, a 2.2 m long Beam Screen (BS) with LESS has been tested at cryogenic temperature in the COLD bore EXperiment (COLDEX) facility in the SPS accelerator at CERN. In this paper, we describe the manufacturing procedure of the beam screen, the employed laser treatment technique and discuss our first observations in COLDEX confirming electron cloud suppression
A new method for quantifying anisotropic martensitic transformation strains accumulated during constrained cooling
Martensitic phase transformations during welding can play a major role in determining the final residual stresses and they can be anisotropic if the transformation occurs under stress. Traditionally, the Satoh test has been used to quantify the response, but it suffers from the fact that the temperature is not uniform along the specimen length, making it difficult to interpret the data. This shortcoming is overcome in our new experimental method using digital image correlation (DIC) to quantify the temperature dependent evolution of the transformation strain locally both parallel and perpendicular to an applied load, in this case for a high-strength low alloy (HSLA) steel and a tough, low transformation temperature weld consumable designed to mitigate tensile weld residual stresses. The method is able to separate the volumetric component of the transformation strain from the deviatoric transformation plasticity component. The volumetric component is shown to be independent of applied load, while the deviatoric component varies approximately linearly with applied load. For the HSLA steel studied here the method also reveals that the transformation start temperature rises under both tensile and compressive loading, confirming previous work. From a weld modelling viewpoint our method provides sufficient information to include the stress dependency of the anisotropic transformation strain in numerical finite element models of the weld process
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