Adaptive deformable mirror : based on electromagnetic actuators

Refractive index variations in the earth's atmosphere cause wavefront aberrations and limit thereby the resolution in ground-based telescopes. With Adaptive Optics (AO) the temporally and spatially varying wavefront distortions can be corrected in real time. Most implementations in a ground based telescope include a WaveFront Sensor, a Deformable Mirror and a real time wavefront control system. The largest optical telescopes built today have a ~ 1 Om primary mirror. Telescopes with more collecting area and higher resolution are desired. ELTs are currently designed with apertures up to 42m. For these telescopes serious challenges for all parts of the AO system exist. This thesis addresses the challenges for the DM. An 8m class telescope on a representative astronomical site is the starting point. The atmosphere is characterized by the spatial and temporal spectra of Kolmogorov turbulence and the frozen flow assumption. The wavefront fitting error, caused by a limited number of actuators and the temporal error, caused by a limited control bandwidth, are the most important for the DM design. It is shown that ~5000 actuators and 200Hz closed loop bandwidth form a balanced choice between the errors and correct an 8m wavefront in the visible to nearly diffraction limited. An actuator stroke of ~5.6J.!m and ~0.36J.!m inter actuator stroke is thereby needed. Together with the nm's resolution, low power dissipation, no hysteresis and drift, these form the main DM requirements. The design, realization and tests of a new DM that meets these requirements and is extendable and scalable in mechanics, electronics and control to suit further Extremely Large Telescopes (ELTs) is presented. In the DM a few layers are distinguished: a continuous mirror facesheet, the actuator grid and the base frame. In the underlying layer - the actuator grid - low voltage electromagnetic push-pull actuators are located. Identical actuator modules, each with 61 actuators, hexagonally arranged on a 6mm pitch can be placed adjacent to form large grids. The base frame provides a stable and stiff reference. A thin facesheet is needed for low actuator forces and power dissipation, whereby its lower limit is set by the facesheets inter actuator deflection determined by gravity or wind pressure. For both scaling laws for force and dissipation are derived. Minimum power dissipation is achieved when beryllium is used for the mirror facesheet. Pyrex facesheets with 100J.!m thickness are chosen as a good practical, alternative in the prototype development. Struts (00.1 x 8mm) connect the facesheet to the actuators and ensure a smooth surface over the imposed heights and allow relative lateral movement of the facesheet and the actuator grid. Measurements show 3nm RMS surface unflattness from the glued attachment. The stiffness of the actuators form the out-of-plane constraints for the mirror facesheet and determine the mirrors first resonance frequency. and is chosen such that the resonance frequency is high enough to allow the high control bandwidth but not higher that needed to avoid excessive power dissipation and fix points in the surface in case of failure. The electromagnetic variable reluctance actuators designed, are efficient, have low moving mass and have suitable stiffness. Other advantages are the low costs, low driving voltages and negligible hysteresis and drift. The actuators consist of a closed magnetic circuit in which a PM provides static magnetic force on a ferromagnetic core that is suspended in a membrane. This attraction force is increased of decreased by a current through a coil. The actuators are free from mechanical hysteresis, friction and play and therefore have a high positioning resolution with high reproducibility. The actuator modules are build in layers to reduces the number of parts and the complexity of assembly and to improve the uniformity in properties. Dedicated communication and driver electronics are designed. FPGA implemented PWM based voltage drivers are chosen because of their high efficiency and capability to be implemented in large numbers with only a few electronic components. A multidrop LVDS based serial communication is chosen for its low power consumption, high bandwidth and consequently low latency, low communication overhead and extensive possibilities for customization. A flat-cable connects up to 32 electronics modules to a custom communications bridge, which translates the ethernet packages from the control PC into LVDS. Two DMs prototypes were successfully assembled: a 050mm DM with 61 actuators and a 0l50mm DM with 427 actuators. In the second prototype modularity is shown by the assembly of seven identical grids on a common base. The dynamic performance of each actuator is measured, including its dedicated driver and communication. All actuators were found to be functional, indicating that the manufacturing and assembly process is reliable. A nonlinear mathematical model of the actuator was derived describing both its static and dynamic behavior based on equations from the magnetic, mechanic and electric domains. The actuator model was linearized, leading to expressions for the actuator transfer function and properties such as motor constant, coil inductance, actuator stiffness and resonance frequency. From frequency response function measurements these properties showed slight deviations from the values derived from the model, but the statistical spread for the properties was small, stressing the reliability of the manufacturing and assembly process. The mean actuator stiffness and resonance frequency were 0.47kN/m and 1.8kHz respectively, which is close to their design values of 500N/m and 1.9kHz. The time domain response of an actuator to a 4Hz sine voltage was used to determine hysteresis and semi-static nonlinear response of the actuator. This showed the first to be negligible and the second to remain below 5% for ±10J.!m stroke. Measurements showed that in the expected operating range, the total power dissipation is dominated by indirect losses in FPGAs. The static DM performance is validated using interferometric measurements. The measured influence matrix is used to shape the mirror facesheet into the first 28 Zernike modes, which includes the piston term that represents the best flat mirror. The total RMS error is ~25nm for all modes. The dynamic behavior of the DM is validated by measurements. A laser vibrometer is used to measure the displacement of the mirror facesheet, while the actuators are driven by zero-mean, bandlimited, white noise voltage sequence. Using the MOESP system identification algorithm, high-order black-box models are identified with VAF values around 95%. The first resonance frequency identified is 725Hz, and lower than the 974Hz expected from the analytical model. This is attributed to the variations in actuator properties, such as actuator stiffness. The power dissipation in each actuator of the 050mm mirror to correct a typical Von Karmann turbulence spectrum is ~ 1.5m W

Flexure-based alignment mechanisms : design, development and application

For high accuracy alignment of optical components in optical instruments TNO TPD has developed dedicated,monolithic, flexure-based alignment mechanisms, which provide accuracies below 0.1 µm and 0.1 µrad as well asstabilities down to subnanometer stabilty per minute.High resolution, high stability alignment mechanisms consist of an adjustment mechanism and a locking device.Complex monolithic flexure-based mechanisms were designed to align specific degrees of freedom. They are realizedby means of spark erosion. The benefits of these mechanisms are no play, no hysteresis, high stiffness, a simplifiedthermal design and easy assemblage. The overall system can remain a passive system, which yields simplicity.An actuator is used for positioning. Locking after alignment is mandatory to guarantee sub-nanometer stability perminute. A proper design of the locking device is important to minimize drift during locking.The dedicated alignment mechanisms presented here are based on: (a) the results of an internal ongoing researchprogram on alignment and locking and (b) experience with mechanisms developed at TNO TPD for high precisionoptical instruments, which are used in e.g. a white light interferometer breadboard (Nulling) and an interferometer withpicometer resolution for ESA’s future cornerstone missions "DARWIN" and "GAIA"

Large adaptive deformable membrane mirror with high actuator density: design and first prototypes

A large adaptive deformable mirror with high actuator density is presented. The DM consists of a thin continuous membrane which acts as the correcting element. A grid of low voltage electro-magnetical push-pull actuators, - located in an actuator plate -, impose out-of-plane displacements in the mirror’s membrane. To provide a stable and stiff reference plane for the actuators, a mechanically stable and thermally decoupled honeycomb support structure is added. The design is suited for mirrors up to several hundred mm with an actuator pitch of a few mm.One of the key elements in the design is the actuator grid. Each actuator consists of a closed magnetic circuit in which a strong permanent magnet (PM) attracts a ferromagnetic core. Movement of this core is provided by a low stiffness elastic guiding. A coil surrounds the PM. Both the coil and the PM are connected to the fixed world. By applying a current through the coil, the magnetic force acting on the core can be influenced. This force variation will lead to translation of the ferromagnetic core. This movement is transferred to the reflective mirror surface in a piston-free manner. The design allows for a long total stroke and a large inter actuator stroke. The actuators are produced in arrays which make the design modular and easily extendable.The first actuators and an actuator grid are produced and tested in a dedicated test set-up. This paper describes how relevant actuator properties, such as stiffness and efficiency, can be influenced by the design. The power dissipation in the actuator grid is optimized to a few milliwatts per actuator, thereby avoiding active cooling

Shared decision-making about treatments for early breast cancer : preferences of older patients and clinicians

This thesis describes the preferences of both older patients with breast cancer and clinicians to optimize the current care of this patient group. The significant increase in the number of breast cancer patients above the age of 65 years necessitates insight into their preferences. Decision-making regarding treatment of early breast cancer is often difficult as decisions need to be made between two surgical options and about the addition of systemic therapy. Like younger patients, older patients are faced with these difficult decisions (together with their clinician). However, treatments for early breast cancer differ substantially between younger and older patients, which possibly can be explained by the preferences of older patients or their clinicians. Currently, little is known about the preferences of older patients, while this knowledge is particularly of great value. To assess how the current care of older patients and the treatment-decision-making process with this patient group can be optimised, we explore the preferences and motivations of older patients with early breast cancer; if and how their preferences for treatment and participation in decision-making differ from those of younger patients; and the treatment preferences of breast cancer specialists with regard to treatment of older patients. LUMC / Geneeskund

Functional surface-initiated polymers: Device applications and polymerization techniques

Self-assembled monolayers and surface-initiated polymer, or polymer brushes, have attracted attention as they form dense layers with much higher structural order than bulk or solution polymers. Another field of research which has emerged over the last two decades is the field of organic and polymer electronics. In this field molecular order and surface modification are of major influence on the device performance, hence that both self-assembled monolayers as polymer brushes have been investigated to find applications in organic electronic devices. After an introduction into the field self-assembled monolayers, polymer brushes and organic electronics, the first part of this thesis focusses on three applications of surface modification techniques for applications in devices. Alignment of the active material is crucial for high mobilities in organic electronics. Chapter 2 discusses the synthesis of a liquid crystalline surface-initiated polymer and its application to induce strong homeotropic alignment. The alignment is homogeneous over large areas and can be patterned by combining the polymerization with soft lithographic techniques. Mobilities of organic electronic materials can also be strongly influenced by dopants in the material. In field-effect transistors the positioning of the dopant is thought to be crucial, as the conductance predominantly takes place in only a small channel near the dielectric interface. In chapter 3 dopant functionalized monolayers and polymer brushes are presented which enable the localized deposition of dopants in the channel of organic transistors. It is shown that the mobility of charges and hence the device performance is affected by the introduction of this dopant layer. Polymer brushes have been suggested for the fabrication of highly ordered semiconducting polymers. In chapter 4 the use of a thiophene functionalized polymer brush is shown, that can be used as a template for the subsequent growth of highly conjugated surface grafted polythiophene layers. Thick polythiophene layers are obtained, that are low in roughness and show photoluminescence and polychromism upon doping. The second part (chapter 5 and 6) of this thesis presents new techniques for surface polymerizations. It is attractive to investigate reduction of reactor volume for polymer brush growth. Chapter 5 discusses a method to achieve volume reduction by back-filling the superfluous volume with beads. It is found that this influences the polymerization kinetics significantly. The combined advantages of less volume and enhanced reaction speeds enable reduction of the total amount of monomer needed by up to 90%. Chapter 6 presents a controlled way to convert initiators for atom transfer radical polymerization into initiators for nitroxide mediated polymerization. In this way mixed polymer brushes and block co-polymer brushes become accessible. This combination makes it an attractive tool to fabricate complex polymer architectures. The technologies used in this thesis show that the synthesis of polymer brushes enable the fabrication of complex architectures without the wastes normally associated with surface-initiated polymers. Combined with several functionalized polymer brushes with properties that enhance order, influence mobility or serve as template for the growth of surface attached conjugated polymers this shows the high potential for the application of surface-initiated polymers in organic electronics.Merck Chemical Ltd Cambridge European Trust Isaac Newton Trus

Breast ultrasound diagnostic performance and outcomes for mass lesions using Breast Imaging Reporting and Data System category 0 mammogram

PURPOSE: To evaluate the outcomes and diagnostic performance of ultrasonography after a Breast Imaging Reporting and Data System (Bi-RADS) category 0 mammogram. MATERIAL AND METHODS: This retrospective study reviewed 4,384 consecutive patients who underwent a screening mammography from January 2005 to July 2006; 391 of the 4,384 exams were classified as Bi-RADS category 0. After exclusions, 241 patients received subsequent sonogram. Ultrasonography was considered diagnostic when the Bi-RADS category was changed to 2, 4, or 5, and it was considered indeterminate (Bi-RADS 3) when the results indicated that the patients should return for a mammographic follow-up. The outcomes of these patients were assessed to evaluate the diagnostic performance of ultrasonography. RESULTS: The mean age of the patients was 53.3 years (ranging from 35 to 81). Of the 241 patients, ultrasonography was considered diagnostic in 146 (60.6%) patients and indeterminate in 95 (39.4%) patients. In the diagnostic group, 111 out of 146 patients (70.2%) had a sonogram result of Bi-RADS category 2 after a 2-year follow-up without evidence of malignancy. Furthermore, 35 out of 146 patients (29.8%) had a suspicious sonogram with a result of Bi-RADS category 4. After a tissue sampling procedure, 10 patients were confirmed to have breast cancer, and 25 had benign histopathological features without any evidence of malignancy after a 2-year follow-up. The sensitivity of ultrasonography was 100%, specificity was 89.1%, and overall accuracy was 89.6%. CONCLUSIONS: Based on the degree of resolution and its diagnostic performance, ultrasonography was determined to be an excellent method for the subsequent evaluation of Bi-RADS 0 mammograms

High pressure pre-treatments promote higher rate and degree of enzymatic hydrolysis of cellulose

The effect of high pressure (HP) pre-treatments on the subsequent enzymatic hydrolysis of cellulose from bleached kraft Eucalyptus globulus pulp by cellulase from Tricoderma viride was evaluated. Pressure pre-treatments of 300 and 400 MPa during 5–45 min, lead to both an increased rate and degree of hydrolysis, reaching values ranging from 1.5- to 1.9-fold, quantified by the formation of reducing sugars. Both the pressure and time under pressure influenced the enzymatic hydrosability of the cellulosic pulps, with the former being more important. The results indicate that the pressure pre-treatments promoted an increased accessibility of cellulose towards cellulase in the cell wall. The results obtained open promising possibilities, to contribute to overcome conventional limitations of enzymatic cellulose hydrolysis for the production of fermentable glucose, for the production of second generation bioethanol and chemicals by enhancement of both rate and yield of hydrolysis. The results are also of interest for the preparation of “pressure engineered” celullose with incremented tailored hydrolysis patterns

Potential for CO2 sequestration and enhanced coalbed methane production in the Netherlands

This study investigated the technical and economic feasibility of using CO2 for the enhanced production of coal bed methane (ECBM) in the Netherlands. This concept could lead to both CO2 storage by adsorbing CO2 in deep coal layers that are not suitable for mining, as well as production of methane. For every two molecules of CO2 injected, roughly one molecule of methane is produced. The work included an investigation of the potential CBM reserves in the Dutch underground and the related CO2 storage potential in deep coal layers. The latter was also supported by laboratory experiments on the adsorption capacity of coal. Furthermore, an economic evaluation of ECBM recovery was made by analysing the costs of capturing CO2 from major stationary sources and CO2 transport, modelling the production of ECBM using CO2 injection with reservoir simulations and system analyses to investigate the costs (and it's sensitivities) of gas production. Furthermore, the costs of on-site hydrogen and power production (including on site CO2 removal and injection) were evaluated. CO2 sources in the Netherlands have been inventoried. Annually 3.4 Mtonne CO2 can be captured from chemical installations and transported to sequestration locations at 15 /tonne. Another 55 Mtonne from power generating facilities can be delivered at 40 to 80 /tonne. The technical potential of CBM in the Dutch underground is significant: a maximum reserve of about 60 EJ is stored in coal layers up to a depth of 2000 m. This figure should be compared to the current annual energy consumption of the Netherlands (about 3 EJ) or the known reserves of natural gas in the Netherlands (about 70 EJ in 1994). These reserves are concentrated in four main areas in the Netherlands: Zuid Limburg, the Peel area, the Achterhoek area and Zeeland. The CO2 storage potential could be about 8 Gtonne. This storage potential should be compared to the annual CO2 emissions of the Netherlands: about 180 Mtonne. This means, theoretically, that the total CO2 emissions of the Netherlands could be stored in coal layers for over 40 years and that CBM could meet the total national energy demand of the Netherlands for 20 years. However, it is still uncertain to what extent these reserves can be accessed. With conservative assumptions regarding the potential completion and recovery rate of CBM from coal layers by means of drilling and CO2 injection, as well as by limiting the ECBM recovery to a depth range of 500 -- 1500 metres, the 'proven' reserves could be limited to 0.3 EJ and the 'possible' reserves up to about 3.9 EJ. The accompanying CO2 that can be sequestrated than lays between 54 Mtonne and 0.6 Gtonne. Although those figures are far more modest than the 'theoretical' potential, they are still significant. In case the 'possible' reserves can be accessed, ECBM could supply 5% of the current national energy use on a more than carbon neutral basis for over 25 years. Given the Kyoto targets for 2010, or the national targets for renewable energy, this is a very significant amount. Without any subsidies or carbon taxes, the cost levels for ECBM recovery ranges from 3.5 to 6.5 /GJ methane produced. These costs levels come close to the projected natural gas prices in Europe in a timeframe of 10 to 20 years, which are projected to be between 2.5 and 3.2 /GJ. Inclusion of a carbon tax (or bonus) of 25 /tonne CO2 sequestrated, lowers the price of ECBM to a competitive 1.5 to 4 ?/GJ. The cost level of CO2 sequestration through ECBM is comparable with projected cost levels for CO2 storage in aquifer traps(Steinberg and Cheng 1989) in case the CBM would be sold for current natural gas prices. If the produced CBM is used for electricity or hydrogen production on top of the CBM field, the resulting CO2 can be injected in the coal directly (thereby eliminating CO2 transport costs). CO2 removal from a gas engine or a combined cycle is currently more expensive when compared to CO2 from industrial processes that must be transported to the CBM field. But a (SOFC) fuel cell produces a pure and therefore much cheaper CO2 stream. Although SOFC fuel cells are not fully commercially available and have high capital costs, they could lead to somewhat lower costs of electricity. Without CO2 bonus, on site power generation is more expensive than grid prices for the systems considered. But when a CO2 bonus of 25 /tonne CO2 is assumed, power generation costs are reduced below 3 cent/kWh, which is lower than the current average 3.2 cent/kWh. On the longer term, when SOFC fuel cells could become cheaper, on site power generation could become a (very) attractive alternative. On site (smaller scale) hydrogen production gives similar results. Capital costs for smaller scale on site hydrogen production are relatively high, but with a CO2 bonus of 25 /tonne, hydrogen costs could be lower than current production costs from coal and comparable to production costs from natural gas. Overall, the results of the economic evaluation indicate that CBM by means of enhanced recovery by CO2 injection in deep coal layers can be performed at competitive cost levels when the right system configurations are chosen. A, relatively modest, carbon tax (or 'bonus') of 25 /tonne could easily tick the balance in favour of ECBM recovery in Dutch conditions on short term already. However, a number of important (geo) technical and geological factors play a key role in whether these cost levels can be obtained or not. The dominating factors in the costs are the drilling costs. In case the costs per wellhead appear to be higher than assumed here, the economic performance of the system deteriorates. On the other hand innovations in drilling techniques, gaining more experience with the required drilling methods over time and obtaining 'economies of scale' by drilling relatively large numbers of wells in a short time to exploit larger CBM fields may bring drilling costs (and thus CBM production costs) down considerably. Regarding to the geology, the CBM potential and the actual accessibility of the, theoretical, coal reserves and the predicted presence of producable CBM gas in the coal layers is subject to broad ranges. More detailed surveys of the Dutch underground are needed to reduce uncertainties about CBM gas reserves. This can be obtained by seismic research and obtaining more and better samples of the Dutch underground. Such research is absolutely essential before ECBM is developed in the Netherlands on a significant scale. In conclusion, this study showed that ECBM is likely to become an economically feasible option for the Netherlands on relatively short term. It could at least play a significant (and potentially very large) role in reducing greenhouse gas emission levels for a time period of about 50 years. Although the estimates of energy reserves in the form of CBM are uncertain, they are potentially very significant (varying from 6 -- 60 EJ). The potential CO2 storage capacity is (very) large as well (1-8 Gtonne of CO2). Given the fact that CO2 binds well to the coal matrix, that deep coal layers are unlikely to be accessed for mining or other activities in the future and that CO2 storage with ECBM delivers a clean fossil fuel as a by-product, coal layers may be a preferable CO2 storage medium when compared to (saline) aquifers, empty gas fields or in deep oceans. Therefore, this option deserves further development and study. A mix of more detailed geological surveys combined with getting good quality samples, laboratory experiments, system studies on implementation scenarios and a pilot project (with a special focus on drilling techniques) is recommended

Direct nitrous oxide emissions from oilseed rape cropping - a meta-analysis

Oilseed rape is one of the leading feedstocks for biofuel production in Europe. The climate change mitigation effect of rape methyl ester (RME) is particularly challenged by the greenhouse gas (GHG) emissions during crop production, mainly as nitrous oxide (N2O) from soils. Oilseed rape requires high nitrogen fertilization and crop residues are rich in nitrogen, both potentially causing enhanced N2O emissions. However, GHG emissions of oilseed rape production are often estimated using emission factors that account for crop-type specifics only with respect to crop residues. This meta-analysis therefore aimed to assess annual N2O emissions from winter oilseed rape, to compare them to those of cereals and to explore the underlying reasons for differences. For the identification of the most important factors, linear mixed effects models were fitted with 43 N2O emission data points deriving from 12 different field sites. N2O emissions increased exponentially with N-fertilization rates, but interyear and site-specific variability were high and climate variables or soil parameters did not improve the prediction model. Annual N2O emissions from winter oilseed rape were 22% higher than those from winter cereals fertilized at the same rate. At a common fertilization rate of 200 kg N ha−1 yr−1, the mean fraction of fertilizer N that was lost as N2O-N was 1.27% for oilseed rape compared to 1.04% for cereals. The risk of high yield-scaled N2O emissions increased after a critical N surplus of about 80 kg N ha−1 yr−1. The difference in N2O emissions between oilseed rape and cereal cultivation was especially high after harvest due to the high N contents in oilseed rape's crop residues. However, annual N2O emissions of winter oilseed rape were still lower than predicted by the Stehfest and Bouwman model. Hence, the assignment of oilseed rape to the crop-type classes of cereals or other crops should be reconsidered