2,374 research outputs found
Multi-Pulse Laser Wakefield Acceleration: A New Route to Efficient, High-Repetition-Rate Plasma Accelerators and High Flux Radiation Sources
Laser-driven plasma accelerators can generate accelerating gradients three
orders of magnitude larger than radio-frequency accelerators and have achieved
beam energies above 1 GeV in centimetre long stages. However, the pulse
repetition rate and wall-plug efficiency of plasma accelerators is limited by
the driving laser to less than approximately 1 Hz and 0.1% respectively. Here
we investigate the prospects for exciting the plasma wave with trains of
low-energy laser pulses rather than a single high-energy pulse. Resonantly
exciting the wakefield in this way would enable the use of different
technologies, such as fibre or thin-disc lasers, which are able to operate at
multi-kilohertz pulse repetition rates and with wall-plug efficiencies two
orders of magnitude higher than current laser systems. We outline the
parameters of efficient, GeV-scale, 10-kHz plasma accelerators and show that
they could drive compact X-ray sources with average photon fluxes comparable to
those of third-generation light source but with significantly improved temporal
resolution. Likewise FEL operation could be driven with comparable peak power
but with significantly larger repetition rates than extant FELs
Optimisation-based Framework for Resin Selection Strategies in Biopharmaceutical Purification Process Development
This work addresses rapid resin selection for integrated chromatographic separations when conducted as part of a high-throughput screening (HTS) exercise during the early stages of purification process development. An optimisation-based decision support framework is proposed to process the data generated from microscale experiments in order to identify the best resins to maximise key performance metrics for a biopharmaceutical manufacturing process, such as yield and purity. A multiobjective mixed integer nonlinear programming (MINLP) model is developed and solved using the ε-constraint method. Dinkelbach's algorithm is used to solve the resulting mixed integer linear fractional programming (MILFP) model. The proposed framework is successfully applied to an industrial case study of a process to purify recombinant Fc Fusion protein from low molecular weight and high molecular weight product related impurities, involving two chromatographic steps with 8 and 3 candidate resins for each step, respectively. The computational results show the advantage of the proposed framework in terms of computational efficiency and flexibility. This article is protected by copyright. All rights reserved
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Two case studies of the application of solar energy for industrial process heat
Case studies of industrial process heat (IPH) have been performed by the Solar Energy Research Institute (SERI) on selected plants in metal processing, oil production, beverage container manufacturing, commercial laundering, paint (resin manufacturing), and food industries. For each plant, the application of solar energy to processes requiring hot water, hot air, or steam was examined, after energy conservation measures were included. A life-cycle economic analysis was performed for the solar system compared to the conventional energy system. The studies of the oil production facility (oil/water separation process) indicate that it could economically employ a solar hot water system immediately. The studies of solar energy applied to the beverage container process (solar air preheat system with partial recycle of oven exhaust gases) indicate a 7.5-yr payback period, based on a solar system installation in 1985
Predicting performance of constant flow depth filtration using constant pressure filtration data
This paper describes a method of predicting constant flow filtration capacities using constant pressure datasets collected during the purification of several monoclonal antibodies through depth filtration. The method required characterisation of the fouling mechanism occurring in constant pressure filtration processes by evaluating the best fit of each of the classic and combined theoretical fouling models. The optimised coefficients of the various models were correlated with the corresponding capacities achieved during constant flow operation at the specific pressures performed during constant pressure operation for each centrate. Of the classic and combined fouling models investigated, the Cake-Adsorption fouling model was found to best describe the fouling mechanisms observed for each centrate at the various different pressures investigated. A linear regression model was generated with these coefficients and was shown to predict accurately the capacities at constant flow operation at each pressure. This model was subsequently validated using an additional centrate and accurately predicted the constant flow capacities at three different pressures (0.69, 1.03 and 1.38 bar). The model used the optimised Cake-Adsorption model coefficients that best described the flux decline during constant pressure operation. The proposed method of predicting depth filtration performance proved to be faster than the traditional approach whilst requiring significantly less material, making it particularly attractive for early process development activities
Nuclear structure beyond the neutron drip line: the lowest energy states in He via their T=5/2 isobaric analogs in Li
The level structure of the very neutron rich and unbound He nucleus has
been the subject of significant experimental and theoretical study. Many recent
works have claimed that the two lowest energy He states exist with spins
and and widths on the order of hundreds of keV.
These findings cannot be reconciled with our contemporary understanding of
nuclear structure. The present work is the first high-resolution study with low
statistical uncertainty of the relevant excitation energy range in the
He system, performed via a search for the T=5/2 isobaric analog states
in Li populated through He+p elastic scattering. The present data show
no indication of any narrow structures. Instead, we find evidence for a broad
state in He located approximately 3 MeV above the neutron
decay threshold
Average seasonal changes in chlorophyll a in Icelandic waters
The standard algorithms used to derive sea surface chlorophyll a concentration from remotely sensed ocean colour data are based almost entirely on the measurements of surface water samples collected in open sea (case 1) waters which cover ~60% of the worlds oceans, where strong correlations between reflectance and chlorophyll concentration have been found. However, satellite chlorophyll data for waters outside the defined case 1 areas, but derived using standard calibrations, are frequently used without reference to local in situ measurements and despite well-known factors likely to lead to inaccuracy. In Icelandic waters, multiannual averages of 8-d composites of SeaWiFS chlorophyll concentration accounted for just 20% of the variance in a multiannual dataset of in situ chlorophyll a measurements. Nevertheless, applying penalized regression spline methodology to model the spatial and temporal patterns of in situ measurements, using satellite chlorophyll as one of the predictor variables, improved the correlation considerably. Day number, representing seasonal variation, accounted for substantial deviation between SeaWiFS and in situ estimates of surface chlorophyll. The final model, using bottom depth and bearing to the sampling location as well as the two variables mentioned above, explained 49% of the variance in the fitting dataset
Bright X-ray radiation from plasma bubbles in an evolving laser wakefield accelerator
We show that the properties of the electron beam and bright x-rays produced
by a laser wakefield accelerator can be predicted if the distance over which
the laser self-focuses and compresses prior to self-injection is taken into
account. A model based on oscillations of the beam inside a plasma bubble shows
that performance is optimised when the plasma length is matched to the laser
depletion length. With a 200~TW laser pulse this results in an x-ray beam with
median photon energy of \unit[20]{keV}, photons above
\unit[1]{keV} per shot and a peak brightness of \unit[3 \times
10^{22}]{photons~s^{-1}mrad^{-2}mm^{-2} (0.1\% BW)^{-1}}.Comment: 5 pages, 4 figure
New Role, New Country: introducing US physician assistants to Scotland
This paper draws from research commissioned by the Scottish Executive Health Department (SEHD). It provides a case study in the introduction of a new health care worker role into an already well established and "mature" workforce configuration It assesses the role of US style physician assistants (PAs), as a precursor to planned "piloting" of the PA role within the National Health Service (NHS) in Scotland
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