Computational optimization of gas compressor stations: MINLP models versus continuous reformulations

When considering cost-optimal operation of gas transport networks, compressor stations play the most important role. Proper modeling of these stations leads to nonconvex mixed-integer nonlinear optimization problems. In this article, we give an isothermal and stationary description of compressor stations, state MINLP and GDP models for operating a single station, and discuss several continuous reformulations of the problem. The applicability and relevance of different model formulations, especially of those without discrete variables, is demonstrated by a computational study on both academic examples and real-world instances. In addition, we provide preliminary computational results for an entire network.German Federal Ministry of Economics and Technolog

Analytical and experimental investigations of dual-plane PIV

In its 'classical' form particle image velocimetry (PIV) extracts two components of the flow velocity vector by measuring the displacement of tracer particles within a double-pulsed laser light sheet. The method described in this paper is based on the additional recording of a third exposure of the tracer particles in a parallel light sheet, which is slightly displaced with respect to the first one. The particle images resulting from these three exposures are stored on separate frames. The locations of the correlation peaks, as obtained by cross-correlation methods, are used to determine the projections of the velocity vectors onto the plane between both light sheets. In the manner described below, the amplitudes of these peaks are used to obtain information about the velocity component perpendicular to the light sheet planes. The mathematical background of this method is described in the paper. Numerical simulations show the influence of the main parameters (e.g. light sheet thickness, light sheet displacement and out-of-plane component) on the resolution and reliability of the new method. Two different recording procedures and their results will be shown to demonstrate the ease of operation when applying this technique to liquid flows

Mathematical modelling of polyamine metabolism in bloodstream-form trypanosoma brucei: An application to drug target identification

© 2013 Gu et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are creditedThis article has been made available through the Brunel Open Access Publishing Fund.We present the first computational kinetic model of polyamine metabolism in bloodstream-form Trypanosoma brucei, the causative agent of human African trypanosomiasis. We systematically extracted the polyamine pathway from the complete metabolic network while still maintaining the predictive capability of the pathway. The kinetic model is constructed on the basis of information gleaned from the experimental biology literature and defined as a set of ordinary differential equations. We applied Michaelis-Menten kinetics featuring regulatory factors to describe enzymatic activities that are well defined. Uncharacterised enzyme kinetics were approximated and justified with available physiological properties of the system. Optimisation-based dynamic simulations were performed to train the model with experimental data and inconsistent predictions prompted an iterative procedure of model refinement. Good agreement between simulation results and measured data reported in various experimental conditions shows that the model has good applicability in spite of there being gaps in the required data. With this kinetic model, the relative importance of the individual pathway enzymes was assessed. We observed that, at low-to-moderate levels of inhibition, enzymes catalysing reactions of de novo AdoMet (MAT) and ornithine production (OrnPt) have more efficient inhibitory effect on total trypanothione content in comparison to other enzymes in the pathway. In our model, prozyme and TSHSyn (the production catalyst of total trypanothione) were also found to exhibit potent control on total trypanothione content but only when they were strongly inhibited. Different chemotherapeutic strategies against T. brucei were investigated using this model and interruption of polyamine synthesis via joint inhibition of MAT or OrnPt together with other polyamine enzymes was identified as an optimal therapeutic strategy.The work was carried out under a PhD programme partly funded by Prof. Ray Welland, School of Computing Science, University of Glasgo

Extensive characterization of a high Reynolds number decelerating boundary layer using advanced optical metrology

An experiment conducted in the framework of the EUHIT project and designed to characterize large scale structures in an adverse pressure gradient boundary layer flow is presented. Up to 16 sCMOS cameras were used in order to perform large scale turbulent boundary layer PIV measurements with a large field of view and appropriate spatial resolution. To access the span-wise / wall-normal signature of the structures as well, stereoscopic PIV measurements in span-wise/wall-normal planes were performed at specific stream-wise locations. To complement these large field of view measurements, long-range micro-PIV, time resolved near wall velocity profiles and film-based measurements were performed in order to determine the wall-shear stress and its fluctuations at some specific locations along the model.Comment: 50 page

Self-assembled nanoscale photomimetic models: structure and related dynamics

Using static and time-resolved measurements, dynamics of non-radiative relaxation processes have been studied in self-assembled porphyrin triads of various geometry, containing the main biomimetic components, Zn–porphyrin dimers, free-base extra-ligands (porphyrin, chlorin or tetrahydroporphyrin), and electron acceptors A (quinone or pyromellitimide). The strong quenching of the dimer fluorescence is due to energy and sequential electron transfer (ET) processes to the extra-ligand (~0.9–1.7 ps), which are faster than a slower ET (34–135 ps) from the dimer to covalently linked A in toluene at 293 K. The extra-ligand S₁-state decay (τₛ = 940–2670 ps) is governed by competing processes: a bridge (dimer) mediated long-range (r_DA = 18–24 Å) superexchange ET to an acceptor, and photoinduced hole transfer from the excited extra-ligand to the dimer followed by possible superexchange ET steps to low-lying charge transfer states of the triads. The subsequent ET steps dimer → monomer → A taking place in the triads, mimic the sequence of primary ET reactions in photosynthetic reaction centers in vivo. © 2002 Elsevier Science B.V. All rights reserved

Electron transfer in porphyrin multimolecular self-organized nanostructures

On the base of of covalent and non-covalent bonds nanoscale self-assembling multiporphyrin arrays with well-defined geometry, the controllable number of interacting components and their spectral and photophysical properties were formed. The deactivation of excited singlet and triplet states was studied using steady-state, time-resolved picosecond fluorescence (∆½≈30 ps) and femtosecond pump-probe (∆½≈280 fs) spectroscopy in solvents of various polarity at 77-300 K. It has been found that the competition between the non-radiative energy transfer (within ≤10 ps) and charge transfer (within 300 fs - 700 ps) processes in the systems depends on the structure, spectral and redox properties of interacting subunits and may be driven by the distance, temperature and solvent polarity. The possible pathways and mechanisms of the electron transfer in the systems of various types are discussed (Marcus theory for the “normal” region and the non-adiabatic case, the “superexchange” mechanism)

Competition between electron transfer and energy migration in self-assembled porphyrin triads

The photoinduced electron transfer (ET) and the energy migration (EM) processes have been studied in liquid solutions and polymeric (PMMA) films for the triads consisting of the Zn-octaethylporphyrin chemical dimer (the energy and electron donor, D) and dipyridyl substituted tetrapyrrole extra-ligands (porphyrins, chlorin, tetrahydroporphyrin) as the acceptors, A. On the basis of the time correlated single photon counting technique and femtosecond pump-probe spectroscopy, it has been shown that D fluorescence quenching with time constant ranging from 1.7 to 10 ps is due to competing EM and ET processes from the dimer to A's. In addition, the fluorescence decay time shortening (by ∼1.3–1.6 times in toluene at 293 K) is observed for electron accepting extra-ligands in the triads. The acceptor fluorescence quenching is hard dependent on the mutual spatial arrangement of the triad subunits, but becomes stronger upon the solvent polarity increase (addition of acetone to toluene solutions) as well as the temperature lowering (from 278 to 221 K). The possible reasons and mechanisms of the non-radiative deactivation of locally excited S₁-states in the triads are discussed taking into account a close lying charge-separated state. The obtained experimental data are analyzed using the reduced density matrix formalism in the frame of Haken–Strobl–Reineker approach. This model includes EM and ET processes as well as the dephasing of coherence between the excited electronic states of the triad. © 2001 Elsevier Science B.V. All rights reserved

Photoinduced electron transfer dynamics for self-assembled porphyrin arrays in solutions and films

Electronic excitation energy deactivation in self-assembled porphyrin triads has been studied by the time correlated single photon counting technique as a function of the solvent polarity (toluene-acetone mixtures), temperature (77-350 K), and mutual spatial arrangement of the donor and acceptor subunits. The donor (Zn-octaethylporphyrin chemical dimer) fluorescence quenching with time constant of 1.7÷10 ps is due to competing energy migration and electron transfer processes to the acceptor (dipyridyl substituted tetrapyrrole extra-ligand). The quenching of the acceptor fluorescence (by ~ 1.3–1.6 times) does not significantly depend on the mutual spatial arrangement of the triad subunits and increases with the solvent polarity rising and the decrease of the temperature. The obtained experimental data are analyzed using the reduced density matrix formalism in the frame of Haken-Strobl-Reineker approach taking into account the energy transfer, charge separation, and the dephasing of coherence between the excited electronic states of the triad

Radiofrequency ablation for Barrett's oesophagus related neoplasia with the 360 Express catheter: initial experience from the United Kingdom and Ireland—preliminary results

BACKGROUND: Radio-frequency ablation (RFA) for Barrett's oesophagus (BE)-related neoplasia is currently used after endoscopic resection of visible neoplasia. The HALO 360 balloon has been used to ablate long segment BE. The Barrx™ 360 Express RFA self-sizing catheter ('RFA Express') may potentially allow quicker ablation times and improved treatment outcomes. The aim of this paper is to present real world data on the use of the 360 Express Device. METHODS: Centres in the UK and Ireland submitted cases where the RFA Express was used. The primary outcome was regression of BE at 3 months. Secondary outcomes were the rate of symptomatic stricture formation and resolution of intestinal metaplasia (CR-IM) and dysplasia (CR-D) at End of Treatment (EoT). RESULTS: 11 centres submitted 123 consecutive patients. 112 had a follow up endoscopy. The median age was 67 years (IQR 62-75). 3 dosimetries were used. The mean reduction in Circumferential (C) length was 78% ± 36 and mean reduction in Maximal length (M) was 55% ± 36. 17 patients (15%) developed strictures requiring dilation. There was a higher rate of stricture formation when the 12 J energy was used (p < 0.05). 47 patients had EoT biopsies, 40 (85%) had CR-D and 34(76%) had CR-IM. CONCLUSIONS: The RFA 360 Express catheter shows reduction in length of baseline BE at 3 months after index treatment, and eradication of intestinal metaplasia and dysplasia at 12 months similar to other studies with earlier devices. It appears that the symptomatic stricture rate is slightly higher than previous series with the HALO 360 catheter. This study was performed as part of the HALO registry and has been approved by the Research Ethics Committee - MREC Number 08/H0714/27 Local project reference 08/0104 Project ID 15,033 IRAS Number 54678 EudraCT 2009-015980-1. Registered on ISRCTN as below: ISRCTN93069556. https://doi.org/10.1186/ISRCTN93069556

Position statement and updated international guideline for safe and effective whole-body electromyostimulation training-the need for common sense in WB-EMS application

Whole-Body Electromyostimulation (WB-EMS) is a training technology that enables simultaneous stimulation of all the main muscle groups with a specific impulse intensity for each electrode. The corresponding time-efficiency and joint-friendliness of WB-EMS may be particularly attractive for people unable or unmotivated to conduct (intense) conventional training protocols. However, due to the enormous metabolic and musculoskeletal impact of WB-EMS, particular attention must be paid to the application of this technology. In the past, several scientific and newspaper articles reported severe adverse effects of WB-EMS. To increase the safety of commercial non-medical WB-EMS application, recommendations "for safe and effective whole-body electromyostimulation" were launched in 2016. However, new developments and trends require an update of these recommendations to incorporate more international expertise with demonstrated experience in the application of WB-EMS. The new version of these consensus-based recommendations has been structured into 1) "general aspects of WB-EMS", 2) "preparation for training", recommendations for the 3) "WB-EMS application" itself and 4) "safety aspects during and after training". Key topics particularly addressed are 1) consistent and close supervision of WB-EMS application, 2) mandatory qualification of WB-EMS trainers, 3) anamnesis and corresponding consideration of contraindications prior to WB-EMS, 4) the participant's proper preparation for the session, 5) careful preparation of the WB-EMS novice, 6) appropriate regeneration periods between WB-EMS sessions and 7) continuous interaction between trainer and participant at a close physical distance. In summary, we are convinced that the present guideline will contribute to greater safety and effectiveness in the area of non-medical commercial WB-EMS application