Endobiliäre Radiofrequenzablation in der palliativen Therapie des extrahepatischen cholangiozellulären Karzinoms : Eine retrospektive Studie

Einleitung: Aktueller Standard in der Palliation des irresektablen extrahepatischen Cholangiokarzinoms (eCCA) ist die systemische Erstlinien-Chemotherapie (CT) mit Gemcitabin und Platinderivat, sowie die Optimierung der biliären Drainage mittels Plastik- oder Metallstentimplantation. Als zusätzliches lokalablatives Verfahren steht neben der photodynamischen Therapie die endobiliäre Radiofrequenzablation (eRFA) zur Verfügung. Ziele: Retrospektive Evaluation von Effektivität und Sicherheit einer gleichzeitigen eRFA in Kombination mit einer systemischen CT in einer Kohorte von Patienten mit fortgeschrittenem eCCA. Methodik: Es wurden alle Patienten eingeschlossen, welche am Uniklinikum Bonn zwischen 2011 und 2018 mit irresektablem eCCA behandelt wurden. Es erfolgte eine Stratifizierung gemäß durchgeführter Therapie in 2 Gruppen (eRFA+CT vs. CT mono). Outcome und Komplikationsrate wurden uni- und multivariat verglichen. Ergebnis: 40 Patienten erhielten eine Kombination aus eRFA und CT und 26 Patienten nur CT (CTmono). Die Kombination von eRFA und CT führte zu einem signifikant längeren Gesamtüberleben (OS) als die alleinige CT (p = 0,004). Das mediane OS und das progressionsfreie Überleben (PFS) betrugen 17,3 bzw. 12,9 Monate in der Kombinationsgruppe und 8,6 bzw. 5,7 Monate für die Kontrollgruppe (CTmono). In der Subgruppe der Patienten mit Fernmetastasen war kein Überlebensvorteil durch eRFA+CT mehr nachweisbar. In der multivariaten Analyse waren die Kombination eRFA+CT (HR: 0,422; 95% KI: 0,218 - 0,816, p = 0.010) und eine initiale Tumorresektion (HR: 0,201, 95% KI 0,068; 0,596, p = 0,004) unabhängige Prädiktoren für das Überleben. Nach eRFA kam es häufiger zu post-ERCP-Cholangitiden als in der CTmono-Kontrollgruppe; weitere Komplikationen (Blutung, Pankreatitis, Hämatotoxizität) unterschieden sich nicht signifikant zwischen den Gruppen. Schlussfolgerung: Die Kombination aus endobiliärer RFA und systemischer CT wurde gut vertragen und konnte das Überleben im Vergleich zur alleinigen Standard-CT deutlich verlängern. Die endobiliäre RFA sollte bei der Therapieentscheidung bei fortgeschrittenem eCCA berücksichtigt werden

Evaluation of methods for measuring tool-chip contact length in wet machining using different approaches (microtextured tool, in-situ visualization and restricted contact tool)

The contact length is one of the most important factors to evaluate the chip formation process and the mechanical loads in metal cutting. Over the years, several methods to identify the contact length were developed. However, especially for wet cutting processes the determination of the contact length is still challenging. In this paper, three methods to identify the contact length for dry and wet processes in cutting of Ti6Al4V and AISI4140 + QT are presented, discussed and analyzed. The first approach uses tools with a microtextured rake face. By evaluating the microstructures on the chip, a new method to identify the contact length is established. The second approach applies high speed recordings to identify the contact length. The challenge is thereby the application of high-speed recordings under wet conditions. In the third approach, tools with restricted contact length are used. It is shown that with all three methods the contact length is reduced using metal working fluid

A novel approach for simulating a sawing process with reduced simulation time

The numerical simulation of machining processes enables the analysis of thermo-mechanical effects and can be used to predict process-specific quantities such as cutting force and chip shape. This involves, however, a great amount of computational effort and time depending on the model design. Basically, a simulation can be carried out two- or three-dimensionally. Due to the lower computational effort, 2D simulations were often used in the past to analyse the machining properties. In orthogonal cutting, this leads to a good approximation to the real processes if a suitable ratio between cutting width and depth of cut is applied. Nevertheless, most industrially relevant machining processes cannot be completely simulated with a 2D simulation. For these purposes, 3D simulations must be created. This requires a much greater computational effort, which increases the simulation time. This paper shows an approach to determine the cutting force and the information about the chip shape during sawing (bound orthogonal cutting) with a shortened calculation time. This was achieved by dividing the entire cut into 2D and 3D areas. The ratio between the cutting width and the depth of cut defines the criterion for the division. When it was greater than 10, the cutting process between the corner radii was assumed to be a plane two-dimensional strain state. The results showed a good agreement of the cutting force calculated from the 2D–3D simulation approach with experimental investigations and a 3D simulation. The computing time could be reduced by more than 50%

Information on MIPLIB's timetab-instances

This report provides information for the timetab-instances of the MIPLIB. This includes data for both, the underlying real-world application and the resulting graph problem

A Case Study in Periodic Timetabling

In the overwhelming majority of public transportation companies, designing a periodic timetable is even nowadays largely performed manually. Software tools only support the planners in evaluating a periodic timetable, or by letting them comfortably shift sets of trips by some minutes, but they rarely use optimization methods. One of the main arguments against optimization is that there is no clear objective in practice, but that many criteria such as amount of rolling stock required, average passenger changing time, average speed of the trains, and the number of cross-wise correspondences have to be considered

Simulation-based evaluation of the 3D fluid dynamics of a coolant lubricant in the narrow-closed cutting gap during circular sawing

A method for simulation-based analysis of the 3D fluid dynamics of a coolant lubricant in the saw tooth space is presented. The examination serves on the one hand to characterize the flow around the bounding surfaces of the narrow-closed cutting gap regarding the local flow conditions. On the other hand, the outflow behaviour of the coolant lubricant out of the narrow-closed cutting gap is analysed to get a deeper understanding of the cooling mechanism. Therefore, the model design is described considering the computational domain and the boundary conditions. Finally, an evaluation method for the local flow behaviour at different surfaces and the coolant lubricant outflow of the tooth space in the narrow-closed cutting gap is illustrated

Modelling the Adoption of Nature-Based Solutions (NBS)

Under the umbrella of the EU-Horizon project "Transformation for sustainable nutrient supply and management - trans4num", an agent-based modelling approach is established for ex-ante impact assessment to evaluate the (net) effects of adopting technological and social innovations based on Nature-Based Solutions (NBS)

Determination of the shear angle in the orthogonal cutting process

Determination of the shear angle by experimental and analytical methods, as well as by numerical simulation, is presented. Experimental determination of the shear angle was performed by analyzing the chip roots obtained by the method of cutting process quick stop through purposeful fracture of the workpiece in the area surrounding the primary cutting zone. The analytical determination of the shear angle was carried out using the chip compression ratio and was based on the principle of a potential energy minimum. Measurement of the shear angle in the numerical simulation of orthogonal cutting was performed using the strain rate pattern of the machined material at the selected simulation moment. It was analyzed how the parameters of the Johnson-Cook constitutive equation and the friction model affect the shear angle value. The parameters with a predominant effect on the shear angle were determined. Then the generalized values of these parameters were established with a software algorithm based on identifying the intersection of the constitutive equation parameter sets. The use of generalized parameters provided the largest deviation between experimental and simulated shear angle values from 9% to 18% and between simulated and analytically calculated shear angle values from 7% to 12%.the German Research Foundation (DFG

Improving machinability of additively manufactured components with selectively weakened material

Part design and the possibilities of production are disrupted by the increased usage of additive manufacturing (AM). Featuring excellent creative freedom due to the layer-by-layer buildup of components, AM leads to profound changes in future part design and enables previously impossible geometries. Laser powder bed fusion (LPBF) technology already allows to manufacture small quantities of parts with high productivity and material efficiency. Due to the specific process characteristics, the resulting surface finish of these parts is insufficient for a wide range of applications, and post-processing is usually unavoidable. Specifically for functional surfaces, this post-processing is often done by machining processes, which can pose challenges for intricate and complex AM parts due to excessive machining forces. In the present paper, the influence and the possibilities of the LPBF process parameters on the subtractive post-processing are shown. A novel weakened structure is developed to selectively reduce the strength of the material and improve the cutting conditions. Chip formation, cutting forces and vibrations during drilling as well as cutting forces during an orthogonal cut are examined. To quantify the differences, a comparison of the machinability between bulk material, standard support structures and the weakened structure is carried out.Bundesministerium für Wirtschaft und EnergieProjekt DEA

Numerical modeling of cutting characteristics during short hole drilling : part 2 - modeling of thermal characteristics

The modeling of machining process characteristics and, in particular, of various cutting processes occupies a significant part of modern research. Determining the thermal characteristics in short hole drilling processes by numerical simulation is the object of the present study. For different contact conditions of the workpiece with the drill cutting inserts, the thermal properties of the machined material were determined. The above-mentioned properties and parameters of the model components were established using a three-dimensional finite element model of orthogonal cutting. Determination of the generalized values of the machined material thermal properties was performed by finding the set intersection of individual properties values using a previously developed software algorithm. A comparison of experimental and simulated values of cutting temperature in the workpiece points located at different distances from the drilled hole surface and on the lateral clearance face of the drill outer cutting insert shows the validity of the developed numerical model for drilling short holes. The difference between simulated and measured temperature values did not exceed 22.4% in the whole range of the studied cutting modes.German Research Foundation (DFG