Multigrid Waveform Relaxation on Spatial Finite Element Meshes: The Discrete-Time Case

The efficiency of numerically solving time-dependent partial differential equations on parallel computers can be greatly improved by computing the solution on many time levels simultaneously. The theoretical properties of one such method, namely the discrete-time multigrid waveform relaxation method, are investigated for systems of ordinary differential equations obtained by spatial finite-element discretisation of linear parabolic initial-boundary value problems. The results are compared to the corresponding continuous-time results. The theory is illustrated for a one-dimensional and a two-dimensional model problem and checked against results obtained by numerical experiments

Per capita interactions and stress tolerance drive stress-induced changes in biodiversity effects on ecosystem functions

Environmental stress changes the relationship between biodiversity and ecosystem functions, but the underlying mechanisms are poorly understood. Because species interactions shape biodiversity-ecosystem functioning relationships, changes in per capita interactions under stress (as predicted by the stress gradient hypothesis) can be an important driver of stress-induced changes in these relationships. To test this hypothesis, we measure productivity in microalgae communities along a diversity and herbicide gradient. On the basis of additive partitioning and a mechanistic community model, we demonstrate that changes in per capita interactions do not explain effects of herbicide stress on the biodiversity-productivity relationship. Instead, assuming that the per capita interactions remain unaffected by stress, causing species densities to only change through differences in stress tolerance, suffices to predict the stress-induced changes in the biodiversity-productivity relationship and community composition. We discuss how our findings set the stage for developing theory on how environmental stress changes biodiversity effects on ecosystem functions

Evaluation der Effektivität der Knochenmetastasen-Detektion mit der 68Ga-PSMA-PET/CT bei Patienten mit metastasiertem Prostatakarzinom

Zielsetzung: Ziel dieser Studie war es, die unterschiedliche Sensitivität und Spezifität bei der Erkennung von Knochenmetastasen in der 68Ga-PSMA-PET/CT und in der 99mTc-DPD-SPECT/CT bei Prostatakarzinom (PK) Patienten zu evaluieren. Des Weiteren wurde untersucht, inwiefern die verschiedenen Bildmodalitäten von einer zusätzlichen low-dose CT Untersuchung profitieren. Methodik: In dieser retrospektive Studie wurden 54 PK Patienten, die eine 68Ga-PSMA-PET/CT und eine 99mTc-DPD-SPECT/CT innerhalb von 80 Tagen erhalten haben, eingeschlossen. Alle Patienten wurden unabhängig in der 68Ga-PSMA-PET und in der 99mTc-DPD-SPECT von zwei Untersuchern auf Knochenmetastasen untersucht. Es wurden maximal fünf Metastasen in neun Körperregionen (Kopf, Schultergürtel, Rippen/Sternum, Halswirbelsäule, Brustwirbelsäule, Lendenwirbelsäule, Becken, Obere Extremität, Untere Extremität) evaluiert. In einer zweiten Analyse wurde der PET bzw. SPECT Datensatz mit dem low-dose CT Datensatz fusioniert und die o.g. Prozedur wurde mit dem PET/CT und SPECT/CT Datensatz durchgeführt. Die Metastasen wurden als benigne, maligne oder mehrdeutig gewertet. Für die statistische Analyse wurden die mehrdeutigen Läsionen entweder als benigne (optimistische Sichtweise) oder als maligne (pessimistische Sichtweise) gewertet. Für die Validierung der Metastasen wurde ein „Best-Valuable-Comparator“ (BVC) als Referenzdatenbank für alle Knochenmetastasen in dem Studienkollektiv erstellt. Es wurde eine patientenbasierte, eine regionsbasierte und eine läsionsbasierte Analyse mit und ohne CT-Fusion durchgeführt. Die Sensitivität, Spezifität und die Genauigkeit als Area-under-the-curve (AUC) wurden mittels einer Receiver-operating-characteristics (ROC) Analyse errechnet. Ergebnisse: Patientenbasierte Analyse: In 29 von 54 Patienten wurden Knochenmetastasen durch den BVC validiert. Die Genauigkeit gemessen als AUC betrug für die 68Ga-PSMA-PET, 68Ga-PSMA-PET/CT, 99mTc-DPD-SPECT, 99mTc-DPD-SPECT/CT 0,97-0,96; 1,00; 0,86-0,83; 0,83. Der jeweils erste Wert entspricht der optimistischen Sicht, der jeweils zweite Wert entspricht der pessimistischen Sicht. Die Genauigkeit war signifikant höher in der PET und PET/CT als in der SPECT und SPECT/CT. Regionsbasierte Analyse: Die Sensitivität der PET betrug 91,8-97,7 % und die Spezifität 100-99,5 %. Die fusionierte PET/CT hatte eine Sensitivität von 97,7 % und eine Spezifität von 100 %. Die SPECT erreichte eine Sensitivität von 61,2-70,6 % und eine Spezifität von 99,8%-98,3 %. Die fusionierte SPECT/CT hatte eine Sensitivität von 69,4 % und eine Spezifität von 98,3 %. Die Sensitivität und Spezifität der PET und PET/CT war signifikant höher als die der SPECT und SPECT/CT. Der Anteil der korrekt klassifizieren unklaren Läsionen durch die CT-Fusion war signifikant größer bei der PET (100%) als bei der SPECT (52,4%). Fazit: Die 68Ga-PSMA-PET hat eine höhere Genauigkeit im Erkennen von Knochenmetastasen bei Prostatakarzinom-Patienten als die 99mTc-DPD-SPECT. Des Weiteren profitiert die 68Ga-PSMA-PET mehr von einer Fusion mit dem low-dose CT Datensatz als die 99mTc-DPD-SPECT.Purpose: The aim of this study was to compare sensitivity and specificity of 68Ga-PSMA-PET and 99mTc-DPD-SPECT in detecting bone metastases in prostate cancer (PC) patients. Additionally, it was evaluated to what extent each modality profits from a fusion with a low-dose CT scan. Methods: For this retrospective study, 54 PC patients who received 68Ga-PSMA-PET/CT and 99mTc-DPD-SPECT/CT within 80 days were included. All patients were independently analysed by two observers focused on bone lesions. The first look analysis was performed on the 68Ga-PSMA-PET and 99mTc-DPD-SPECT images. Up to five lesions in nine body regions (Skull, Clavicle/Scapula, Ribs/Sternum, Cervical Spine, Thoracic Spine, Lumbar Spine, Hip, Upper Extremities, Lower Extremities) were counted. In a second look analysis the SPECT and PET images were fused with the low-dose CT images. Again, every patient was reviewed. Osseous lesions were classified as benign, malignant or equivocal. Regarding the statistical analysis, equivocal lesions were regarded as positive in a pessimistic view and as negative in an optimistic view. The reference standard was generated by defining a best valuable comparator (BVC) as a reference database for bone lesions in all patients. Lesion, region and patient based analysis was performed with and without CT fusion. Sensitivities, specificities and accuracies (as “area-under-the-curve”=AUC) were calculated using receiver-operating-characteristics (ROC) analysis. Results: Patient based analysis: In 29 out of 54 Patients bone metastases were validated by BVC. Accuracies measured as AUC for 68Ga-PSMA-PET, 99mTc-SPECT, 68Ga-PSMA-PET/CT and 99mTc-SPECT/CT were 0.97-0.96; 1,00; 0.86-0.83; und 0.83, respectively with ranges representing optimistic vs. pessimistic view. The accuracies were significantly higher in PET and PET/CT than in SPECT and SPECT/CT. Region based analysis: Sensitivities of PET were 91.8-97.7% and specificities were 100-99.5%. The merged PET/CT had a sensitivity of 97.7% and a specificity of 100%. The SPECT had a sensitivity of 61.2-70.6% and a specificity of 99.8-98.3%. The merged SPECT/CT had a sensitivity of 69.4% and a specificity of 98.3%. Sensitivity and specificity were significant higher in PET and PET/CT than in SPECT and SPECT/CT. The amount of correct classifications of equivocal lesions by CT was significantly higher in PET (100%) compared to SPECT (52.4%). Conclusion: 68Ga-PSMA-PET performs better than 99mTc-DPD-SPECT in detecting bone metastases in PC patients. Additionally, 68Ga-PSMA-PET benefits more from a fusion with a low-dose CT than 99mTc-DPD-SPECT

Degradation of Toluene and Trichloroethylene by Burkholderia cepacia G4 in Growth-Limited Fed-Batch Culture

Burkholderia (Pseudomonas) cepacia G4 was cultivated in a fed-batch bioreactor on either toluene or toluene plus trichloroethylene (TCE). The culture was allowed to reach a constant cell density under conditions in which the amount of toluene supplied equals the maintenance energy demand of the culture. Compared with toluene only, the presence of TCE at a toluene/TCE ratio of 2.3 caused a fourfold increase in the specific maintenance requirement for toluene from 22 to 94 nmol mg of cells (dry weight)-1 h-1. During a period of 3 weeks, approximately 65% of the incoming TCE was stably converted to unidentified products from which all three chlorine atoms were liberated. When toluene was subsequently omitted from the culture feed while TCE addition continued, mutants which were no longer able to grow on toluene or to degrade TCE appeared. These mutants were also unable to grow on phenol or m- or o-cresol but were still able to grow on catechol and benzoate. Plasmid analysis showed that the mutants had lost the plasmid involved in toluene monooxygenase formation (pTOM). Thus, although strain G4 is much less sensitive to TCE toxicity than methanotrophs, deleterious effects may still occur, namely, an increased maintenance energy demand in the presence of toluene and plasmid loss when no toluene is added.

Adaptive integration of element matrices in finite element moisture transfer simulations

While serving different purposes, numerical simulations of moisture and heat transfer in soils and in building components are very similar in methodology: in both cases, spatially and temporally discretised equations for transfer of moisture and heat in porous materials are solved subject to (atmospheric) boundary conditions. The strongly non-linear transfer equations and boundary conditions however render such hygrothermal simulations computationally very expensive, and an efficient numerical solution algorithm is required. Such increasingly efficient numerical solution schemes allow for more, larger, longer or more precise simulations, widening the application capabilities of hygrothermal simulations. The computational cost of hygrothermal simulations revolves around the serial iterative com-position and decomposition of the coefficient matrix of the system of algebraic equations de-scribing the discretised moisture and heat transfer, and is thus determined by the cost of one (de)composition, and the number of required (de)compositions. This article presents two op-timisation measures for simulations of moisture and heat transfer in building components un-der atmospherical excitation: adaptive integration and variations on the Newton-Raphson iterative scheme. Adaptive integration targets the cost of one (de)composition, while the varia-tions on Newton-Raphson aims at the number of required (de)compositions. While exempli-fied by building physical simulations, the presented optimisation measures are equally valid for simulations of moisture and heat transfer in soils. It will be demonstrated that the common preference for low-order numerical integration of the finite element matrices has an adverse effect on the required spatial discretisation: a fine dis-cretisation throughout is needed for accurate simulation of the moving moisture fronts typical of infiltration problems. Adaptive integration allows to merge low-order numerical integration with rougher spatial discretisations, reducing the number of required integration points and of discretisation nodes. A second section of the article investigates the efficiency of (variations on) the Newton-Raphson scheme. It will be demonstrated that appropriate application of Newton-Raphson on the boundary conditions, of modified iteration and of separate convergence criteria can drastically diminish the number of required (de) compositions.Presenters: name: Janssen, Hans affiliation: Laboratory for Building Physics, Faculty of Engineering, Katholieke Universiteit Leuve

Assessing Customers\u27 Value of Mobile Financial Information Services: Empirical-Based Measures

In this paper, we assess customers’ value which can be provided by mobile financial information services enabling private investors to react promptly to critical market events and to exploit the subsequent abnormal intraday stock price movements. We present two frameworks for evaluating customers’ benefits of a corresponding investment. First, we empirically analyze the impact of timelier information supply on market returns. Our findings indicate that any reduction of the reaction time significantly increases revenues that can be realized by customers. Second, we propose a novel approach to measure customers’ benefits by simulating realizable yields considering trading volumes, transaction costs, and reaction delays on the basis of historical market events and empirical intraday stock price series. The results provide evidence as to how the trading behavior of customers and different product implementation alternatives can affect customers’ benefits and, therefore, the evaluation of the IT investment