Mathematical framework for Traction Force Microscopy

International audienceThis paper deals with the Traction Force Microscopy (TFM) problem. It consists in obtaining stresses by solving an inverse problem in an elastic medium, from known experimentally measured displacements. In this article, the application is the determination of the stresses exerted by a living cell at the surface of an elastic gel. We propose an abstract framework which formulates this inverse problem as a constrained minimization problem. The mathematical constraints express the biomechanical conditions that the cell must satisfy. From this framework, two methods currently used can be derived, the adjoint method (AM) and the Fourier Transform Traction Cytometry (FTTC) method. An improvement of the FTTC method is also derived using this framework. The numerical results are compared and show the advantage of the AM, in particular it can capture details more accurately

Impedance spectroscopy characterization of neutron irradiated thermoelectric modules for space nuclear power

The European Space Agency is currently supporting the research and development of advanced radioisotope power systems utilising thermoelectric modules. The performance of thermoelectric modules following exposure to neutron radiation is of significant interest due to the likely application of radioisotope thermoelectric generators in deep space exploration or planetary landers requiring prolonged periods of operation. This study utilises impedance spectroscopy to characterise the effects of neutron irradiation on the performance of complete thermoelectric modules, as opposed to standalone material. For a 50 We americium-241 radioisotope thermoelectric generator design, it is estimated that the TE modules could be exposed to a total integrated flux of approximately 5 × 1013 neutrons cm-2 (>1 MeV). In this study, an equivalent neutron dose was simulated experimentally via an acute 2-hour exposure in a research pool reactor. Bi2Te3-based thermoelectric modules with different leg aspect ratios and microstructures were investigated. Gamma-ray spectroscopy was initially used to identify activated radionuclides and hence quantify irradiation induced transmutation doping. To evaluate the thermoelectric properties pre- and post-irradiation, impedance spectroscopy characterization was employed. Isochronal thermal annealing of defects imparted by the irradiation process, revealed that polycrystalline based modules required significantly higher temperature than those with a monolithic microstructure. Whilst this may indicate a greater susceptibility to neutron irradiation, all tested modules demonstrated sufficient radiation hardness for use within an americium-241 radioisotope thermoelectric generator. Furthermore, the work reported demonstrates that impedance spectroscopy is a highly capably diagnostic tool for characterising the in-service degradation of complete thermoelectric devices

Responsive glyco-poly(2-oxazoline)s: synthesis, cloud point tuning, and lectin binding

A new sugar-substituted 2-oxazoline monomer was prepared using the copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction. Its copolymerization with 2-ethyl-2-oxazoline as well as 2-(dec-9-enyl)-2-oxazoline, yielding well-defined copolymers with the possibility to tune the properties by thiol-ene "click" reactions, is described. Extensive solubility studies on the corresponding glycocopolymers demonstrated that the lower critical solution temperature behavior and pH-responsiveness of these copolymers can be adjusted in water and phosphate-buffered saline (PBS) depending on the choice of the thiol. By conjugation of 2,3,4,6-tetra-O-acetyl-1-thio-beta-D-glucopyranose and subsequent deprotection of the sugar moieties, the hydrophilicity of the copolymer could be increased significantly, allowing a cloud-point tuning in the physiological range. Furthermore, the binding capability of the glycosylated copoly(2-oxazoline) to concanavalin A was investigated

The international post-graduate Master programme for space exploration, SEEDS: education and training from a System Engineering perspective

The SEEDS (SpacE Exploration Development Systems) initiative was initially conceived and promoted by Politecnico di Torino and Thales Alenia Space-Italy in 2005. It aimed at establishing a post-graduate International Master Program in space exploration to offer an opportunity to young engineers to get prepared for the future of Europe in space and specifically in human space exploration. ISAE-Supaero in France and University of Leicester in UK participate to SEEDS together with Politecnico di Torino (Italy). Turin, Toulouse and Leicester have a long common tradition of space activities at both the industrial and academic level and within the SEEDS initiative they represent three poles of European cooperation in space programs. The Master course comprises two different steps in sequence: an initial learning phase and a Project Work phase. Both phases pursue a multidisciplinary approach, where all specialized disciplines are integrated to make the students able to acquire the system view and then to accomplish the conceptual design of a selected case-study. The distinguishing feature of SEEDS is the Project Work activity, performed by all students together under the supervision of academic and industrial tutors. Main objective of the Project Work is to train the students on the basic principles of the system engineering design, through their application to a well-defined project related to a specific human space exploration mission. The Project Work includes the Preparatory Work, during which the students identify the complete architecture and overall scenario of the mission, and the conceptual design activities, performed in the three European sites to develop a limited number of building blocks. Seven academic years of activities have passed and seven project works have been successfully completed, dealing with various space exploration themes. The eighth edition is currently under way with the aim of designing a “Transit and return habitable Mars orbital port”. The paper focuses on the description of the Master Program, both from the point of view of its contents, structure and multidisciplinary design methodologies, and on the main results achieved in terms of Project Work activities. The positive experience of seven years of SEEDS is brought to evidence and the lessons learned are discussed

Electrochemical sulfidation of WS2 nanoarrays:strong dependence of hydrogen evolution activity on transition metal sulfide surface composition

The activity of transition metal sulfides for the hydrogen evolution reaction (HER) can be increased by sulfur-enrichment of active metal-sulfide sites. In this report, we investigate the electrochemical sulfidation of atmospherically aged WS2 nanoarrays with respect to enhancing HER activity. In contrast to MoS2, it is found that sulfidation diminishes HER activity. Electrochemical and XPS experiments suggest the involvement of insoluble tungsten oxides in the altered HER and electron transfer properties. This demonstrates the strong dependence of the transition metal dichalcogenide (TMD) composition with the successful sulfur incorporation and subsequent HER activity

A high-throughput splinkerette-PCR method for the isolation and sequencing of retroviral insertion sites

Insertional mutagens such as viruses and transposons are a useful tool for performing forward genetic screens in mice to discover cancer genes. These screens are most effective when performed using hundreds of mice, however until recently a major limitation to performing screens on this scale has been the cost effective isolation and sequencing of insertion sites. Here we present a method for the high-throughput isolation of insertion sites using a highly efficient splinkerette-PCR method coupled with capillary or 454 sequencing. This protocol includes a description of the procedure for DNA isolation, DNA digestion, linker or splinkerette ligation, primary and secondary PCR amplification, and sequencing. This method, which takes about 1 week to perform, has allowed us to isolate hundreds of thousands of insertion sites from mouse tumours and, unlike other methods, has been specifically optimised for the isolation of insertion sites generated with the murine leukaemia virus (MuLV), and can easily be performed in 96 well plate format for the efficient multiplex isolation of insertion sites

Radiation damage effects on X-Ray detectors for future planetary and astronomy missions

This thesis describes both theoretical and experimental work conducted to further develop X-ray instrumentation for future planetary and astronomy space missions. Such instruments are used to probe, ever deeper, the high energy Universe; from black holes and active galactic nuclei, to supernovae, galaxy formation and clusters. X-rays can also be used to establish the elemental composition of planetary surfaces from orbit or in situ, furthering our understanding of planetary and moon formation in our solar system. Chapter 1 introduces X-ray instrumentation and uses the International X-ray Observatory as a case study to explore the many new developments in X-ray instrumentation, both in optics and detectors. Chapter 2 further explores the field of X-ray optics, particularly the novel Microchannel Plate Optics used on the BepiColombo Mercury Imaging X-ray Spectrometer, MIXS. The characterisation of an MCP optic is presented, demonstrating the best angular resolution measurement of a flat square-pore square-packed Microchannel Plate Optic to date; <2 arcminutes FWHM resolution. Chapter 3 moves from the X-ray optics used on BepiColombo MIXS to the detectors used in the instrument focal plane; Active Pixel Sensor Depleted Field Effect Transistors (DEPFETs). The solar proton radiation environment around Mercury is one of the most damaging in the solar system due to its proximity to the sun, with ~3x1010 10 MeV equivalent solar protons expected over the mission lifetime. This Chapter presents the proton radiation damage experiments conducted at the Birmingham University Cyclotron, establishing the current related damage rate, α, and dark current increase that can be expected from this radiation damage. The design of the MIXS instrument was changed to include an annealing capability based on the findings of the experiment presented here. A follow-up proton irradiation experiment carried out at the University of Technology in Munich, in collaboration with the Max Planck Institute’s Semiconductor Laboratory (MPE-HLL) is also discussed. Chapters 4 and 5 present the experimental and modelling work carried out in the investigation of X-ray CCDs which, to date, have been the X-ray detectors of choice for many space and terrestrial applications. The aim of this work was to improve the quantum efficiency and spectral resolution of the CCD66, a novel CCD structure initially designed with applications such as the Wide Field Imager of the International X-ray Observatory in mind, by direct manipulation of the device depletion region by applying a negative substrate voltage. Modelling work was also undertaken to investigate the effect of X-ray angle of incidence on spectral resolution and quantum efficiency. The future of X-ray astronomy and planetary science depends heavily on advances in optics and detector technology. The work presented in this thesis show incremental, yet mission-enabling developments for X-ray instruments likely to fly in the future such as BepiColombo’s Mercury Imaging X-ray Spectrometer.EThOS - Electronic Theses Online ServiceGBUnited Kingdo