Model-based optimization of multi-stage nanofiltration using the solution-diffusion–electromigration model

Nanofiltration is well suited to separate monovalent ions from multivalent ions, such as the separation of Li+ and Mg2+ from seawater, a potential lithium source for the production of lithium-ion batteries. To the best of our knowledge, there is no existing work on the optimization of a multi-stage membrane plant that differentiates between different ions and that is based on a validated transport model. This study presents a method for modeling predefined membrane interconnections using discretization along the membrane length and across the membrane thickness. The solution-diffusion–electromigration model was used as the transport model in a fundamental membrane flowsheet, and the model was employed to optimize a given flowsheet with a flexible objective function. The methodology was evaluated for three distinct separation tasks, and optimized operating points were found. These show that permeances and feed concentrations might cause negative rejections and positive rejections (especially for bivalent ions) depending on the ions’ properties and fluxes, thereby allowing for a favorable separation between the ions of different valence at optimized conditions. In an application-based case study for the separation of Li+ and Mg2+ from seawater, the method showed that under optimal conditions, the mol-based ratio of Mg2+/Li+ can be reduced from 2383 to 2.8 in three membrane stages

Writing, Calculating and Peer Feedback in a Mathematically-oriented Course for Process Engineers: Raising Motivation and Initiating Processes of Thinking and Learning

Writing assignments can be seen as an important component of learning processes. Especially in the fields of engineering and sciences, writing assignments have the potential to consolidate subject-specific skills and to enhance motivation for solving technical problems. This paper introduces readers to a revised course structure that aims to strengthen motivation and mathematical understanding through written peer feedback based on mathematical exercises with written elements. The assignment was developed for the course Computational Fluid Dynamics in Process Engineering, a mathematically-oriented course for Master students of theoretical mechanical engineering and process engineering. Since the learning content was perceived as complex, students seemed to lack motivation in preparing for the course with the provided exercises. This paper suggests – based on the collected data, consisting of answers to mathematical problems, feedback texts, evaluation results, teachers’ observation, and examination results – that the introduced assignment enhances students’ understanding and has a positive impact on students’ motivation to solve the mathematical exercises

Heteroatomare Polykationen aus Chloroaluminatschmelzen

Im Rahmen dieser Arbeit gelang es, eine Reihe neuer Verbindungen zu synthetisieren, die als strukturbestimmendes Motiv heteroatomare Polykationen enthalten. Diese Cluster sind aus den schwereren Elementen der beiden Hauptgruppen 5 und 6 aufgebaut. Polykationen dieser Elementzusammensetzung waren bisher nur sehr wenige bekannt, ganz im Gegensatz zu den zahlreich beschriebenen homoatomaren. Die Synthesen gelangen aus Lewis-sauren Salzschmelzen in evakuierten Glasampullen. Die feuchtigkeitsempfindlichen Kristalle mussten für alle Untersuchungen unter Inertgasbedingungen gehandhabt werden. Die Verbindungen wurden durch Einkristallstrukturanalyse identifiziert und charakterisiert. Desweiteren fanden EDX- und schwingungsspektroskopische Untersuchungen statt sowie die temperaturabhängige Untersuchung einer Phasenumwandlung. Rechnungen halfen, die Messergebnisse zu verstehen

Monitoring of a polar plasma convection event with GPS

When L-band radio waves of space based systems such as Global Positioning System (GPS) travel trough the ionosphere and plasmasphere their ray paths are perturbed due to the free electrons. Since the last decade these integrated measurements are used to map the ionosphere for navigational and scientific investigations. In November 2001 a polar plasma convection like ionospheric event has been recognised in vertical TEC maps produced with GPS data. This event on the one hand is shortly compared with the behaviour of the Interplanetary Magnetic Field (IMF) to which it may be related according to former publications. On the other hand the 3-dimensional tomography applying also GPS data is tested on its capability to reconstruct this ionospheric event in the European sector. The different mappings of the two monitoring methods are compared.Wenn L-Band-Radiowellen raumgestützter Navigationssysteme wie das Global Positioning System (GPS) die Ionosphäre oder Plasmasphäre durchlaufen, werden Ihre Strahlwege durch die freien Elektronen verändert. Seit dem letzten Jahrzehnt verwendet man diese integrierten Messungen, um die Ionosphäre im Interesse der Navigation und der Wissenschaft abzubilden. Am Beispiel eines Ereignisses vom November 2001 wurde eine polare Plasmakonvektion in der Ionosphäre durch vertikale TEC –Karten (Total Electron Content), die ebenfalls mit Hilfe von GPS Daten erstellt werden, abgebildet. Einerseits wurde das Ereignis der Plasmakonvektion mit dem Verhalten des Interplanetaren Magnetischen Feldes (IMF) kurz verglichen und auf ihren Zusammenhang hin untersucht. Auf der anderen Seite wurde anhand dieses Ereignisses die Methode einer über den europäischen Raum aufgespannten auf GPS–Daten basierenden 3-dimensionale Tomographie auf ihre Reproduzierbarkeit hin geprüft. Die zwei verschiedenen Methoden des Ionosphärenmonitorings werden verglichen

Comparison of electron density profiles in the ionosphere from ionospheric assimilations of GPS, CHAMP profiling and ionosondes over Europe

GPS integrated Total Electron Content measurements received at the ground or in space are used for tomographic reconstruction of the ionospheric electron density distribution. The IRI/GCPM model is used as initialisation of the tomographic MART algorithm. During the procedure GPS TEC data are iteratively assimilated to the model. To test the potential of the reconstruction, electron density profiles from IRI/GCPM and the assimilation are compared with ionosonde measurements and CHAMP radio occultation profiles for dates during the HIRAC campaign in April 2001. All profiling methods show electron density values of similar magnitude. It is shown that including TEC GPS data corrects the model towards the ionosonde measurements.Integrale Messungen der Elektronendichte aus GPS-Boden- sowie Radio-Okkultations-Messungen bilden die Datenbasis der hier vorgestellten 3-dimensionalen Tomographie der ionosphärischen Elektronendichteverteilung. Zur Initialisierung des verwendeten iterativen MART Algorithmus wird das IRI/GCPM Modell verwendet, wobei das Modell während der Iteration sukzessiv an die Messdaten angepasst wird. Um das Potential des Verfahrens abzuschätzen, werden Elektronendichteprofile des IRI/GCPM Modells und der Rekonstruktion mit Ionosondenmessungen und CHAMP Okkultationsprofilen verglichen. Dafür wurden Messungen während der HIRAC Kampagne im April 2001 genutzt. Alle hier gezeigten Profilableitungen geben Elektronendichtewerte der selben Größe wieder. Eine Annäherung des IRI/GCPM Modells an die Messwerte der Ionosonde durch die Assimilation der TEC GPS Daten wird gezeigt

Reactive Flow Simulation of Micromixers Based On Grid Deformation Techniques

Process intensification of engineering applications in the framework of reacting flows in micromixer devices attracts the attention of engineers and scientists from various fields. With the steadily increasing available computational resources the traditional experimentally supported investigations may be extended by computational ones. For this purpose, a simulation framework based on state of the art numerical techniques extended with special grid deformation techniques has been developed. Its validation in terms of comparison with computational and experimental results in reacting, as well as in non-reacting frameworks has been performed on the basis of the T-mixer, and SuperFocus mixer, respectively. The computational efficiency of the developed tool is shown to be applicable for optimization tasks, such as reverse engineering purposes

Ionospheric tomography and first interpretations of including space-based GPS

When L-band radio waves of space-based radio navigation systems such as Global Positioning System (GPS) travel through the atmosphere and ionosphere, their ray paths are bent and their travel time are increased as a result of refractive-index gradients. As the ionosphere is a dispersive medium the two GPS frequencies are subject to different delays in time and modifications in amplitude, phase and polarisation which is an effect of free electrons. By using these two radio frequencies one can derive information about the Total Electron Content integrated along the ray path. After calibration, these data are included into the tomographic reconstruction. The tomographic methode presented in this paper works on algebraic iterative methodes like SART and MART. Calculations are based on International GPS Service (IGS) ground received data. Space-based GPS is provided by LEO (Low Earth Orbiter) satellites like CHAMP. By means of incorporating such occultation data into tomography an improvement of reconstruction of the vertical structure of the electron density is expected. First confirming interpretations of a selected occulation event are presented in this paper. It is shown, that space-based GPS data can improve tomographic results mainly in middle to lower altitudes of the ionosphere.Wenn sich Radiowellen eines Navigationssystemes, wie das des Global Positioning Systems (GPS), in der Atmosphäre und Ionosphäre ausbreiten, erfahren sie eine Beugung des Strahlweges und eine Erhöhung der Laufzeit aufgrund der Gradienten des atmosphärischen Refraktionsindexes. Da die Ionosphäre ein dispersives Medium darstellt, unterliegen beide GPS-Frequenzen dort unterschiedlichen Störungen in Laufzeit und Veränderungen in Amplitude, Phase und Polarisation, was auf die Effekt der freien Elektronen zurückzuführen ist. Unter der Verwendung der beiden Radiofrequenzen kann man Informationen über die Anzahl der über den Strahlweg integrierten Elektronen erhalten. Nach der Kalibrierung dieser Daten, können sie zur tomographischen Rekonstruktion verwendet werden. Die hier vorgestellte Tomographie verwendet algebraisch iterative Methoden, wie SART und MART. Die tomographischen Berechnungen bauen auf bodengestützte GPS-Daten des International GPS Services (IGS) und satellitengestützten GPS-Daten von LEO (Low earth orbiter) Satelliten wie CHAMP auf. Durch die Intergration von Okkultationsdaten in die Tomographie wird eine Verbesserung der Rekonstruktion der vertikalen Struktur der Elektronendichte erwartet. Erste bestätigende Interpretationen eines ausgewählten Okkultationsereignisses werden in diesem Artikel vorgeführt. Es wird gezeigt, dass satellitengestützte GPS-Daten die tomographischen Ergebnisse vorallem in der mittleren und unteren Ionosphäre verbessern können

Can the Indonesian Collective Action Norm of Gotong-Royong Be Strengthened with Economic Incentives? Comparing the Implementation of an Aquaculture Irrigation Policy Program

The Indonesian multi-level governmental program (PITAP) is a participatory pond irrigation management policy established by the Ministry of Marine Affairs and Fisheries. It aims to catalyze the rehabilitation of irrigation canals to improve water access for small-scale aquaculture farmers. In PITAP, traditional aquaculture farmers are incentivized with government funding to create community-based co-management groups (POKLINA), to maintain the self-governance of their irrigation canals. The logic of PITAP is to encourage POKLINA farmers to rehabilitate their irrigation canals through subsidized labor payments that are coupled with strengthening the strong cultural norm of mutual assistance (i.e., collective action) within Indonesian society called Gotong-Royong. PITAP aims to revitalize Gotong-Royong through subsidized labor compensation with the hope that when the subsidy program is over, Gotong-Royong will be revitalized without external support. In this study, we compare and analyze four villages on Lombok, Indonesia, that participated in PITAP program in 2020 and 2021. The study is supported with empirical data using various qualitative data collection methods, including interviews, participant observations, and the collection of policy documents. We further use the Social-Ecological System Framework (SESF) as a diagnostic tool to structure the data collection process and analysis. Findings indicate that different variables hinder and enable collective action in the four villages, leading to different PITAP program outcomes. The likely reason for this, suggested by our findings, is that each village has different social and ecological conditions that influence intrinsic motivation for collective action. PITAP program either crowds out intrinsic motivation under some conditions or crowds it in under others. This suggests the need to consider contextual adaptations in policy design and implementation to improve outcomes better

Mid-range outcomes in 64 consecutive cases of multilevel fusion for degenerative diseases of the lumbar spine

In the treatment of multilevel degenerative disorders of the lumbar spine, spondylodesis plays a controversial role. Most patients can be treated conservatively with success. Multilevel lumbar fusion with instrumentation is associated with severe complications like failed back surgery syndrome, implant failure, and adjacent segment disease (ASD). This retrospective study examines the records of 70 elderly patients with degenerative changes or instability of the lumbar spine treated between 2002 and 2007 with spondylodesis of more than two segments. Sixty-four patients were included; 5 patients had died and one patient was lost to follow-up. We evaluated complications, clinical/radiological outcomes, and success of fusion. Flexion-extension and standing X-rays in two planes, MRI, and/or CT scans were obtained pre-operatively. Patients were assessed clinically using the Oswestry disability index (ODI) and a Visual Analogue Scale (VAS). Surgery performed was dorsolateral fusion (46.9%) or dorsal fusion with anterior lumbar interbody fusion (ALIF; 53.1%). Additional decompression was carried out in 37.5% of patients. Mean follow-up was 29.4±5.4 months. Average patient age was 64.7±4.3 years. Clinical outcomes were not satisfactory for all patients. VAS scores improved from 8.6±1.3 to 5.6±3.0 pre- to post-operatively, without statistical significance. ODI was also not significantly improved (56.1±22.3 pre- and 45.1±26.4 post-operatively). Successful fusion, defined as adequate bone mass with trabeculation at the facets and transverse processes or in the intervertebral segments, did not correlate with good clinical outcomes. Thirty-five of 64 patients (54%) showed signs of pedicle screw loosening, especially of the screws at S1. However, only 7 of these 35 (20%) complained of corresponding back pain. Revision surgery was required in 24 of 64 patients (38%). Of these, indications were adjacent segment disease (16 cases), pedicle screw loosening (7 cases), and infection (one case). At follow-up of 29.4 months, patients with radiographic ASD had worse ODI scores than patients without (54.7 vs. 36.6; P<0.001). Multilevel fusion for degenerative disease still has a high rate of complications, up to 50%. The problem of adjacent segment disease after fusion surgery has not yet been solved. This study underscores the need for strict indication guidelines to perform lumbar spine fusion of more than two levels