249 research outputs found
Coarse-grained simulations of nicotinic acetylcholine receptors in complex mixed membranes: embedded lipids and domain partitioning
No full textNicotinic acetylcholine receptors (nAChRs) are pentameric Ligand Gated Ion Channels that are critical to signaling across synapses and the neuromuscular junction; such signaling is facilitated by high densities of nAChRs in the post-synaptic membrane. Organization of nAChRs, including partitioning behavior in membranes containing dis- tinct lipid domains, is poorly characterized. Numerous experimental studies have shown nAChR gain-of-function likely caused by direct interactions with cholesterol, but a significant role for lipid domains has been suggested by nAChR gain-of-function upon bulk cholesterol depletion. Furthermore, the opportunity for cholesterol to have a direct interactions will likely have a complex dependence on the extent of domain formation and lipid species in the membrane, which has not been previously addressed. In the present research, we use Molecular Dynamics Simulations with coarse-grained resolution via the MARTINI model to investigate concentrations of cholesterol and other lipids local to nAChRs embedded in complex model membranes with a range of head groups and degrees of unsaturation. Cholesterol and unsaturated lipids are observed binding in deep non-annular sites in the nAChR bundle (based on the 2BG9 cryo-EM structure), consistent with our previous predictions. nAChR partitions, however, into cholesterol-poor phases, resulting in dynamic exchange between cholesterol and unsaturated phospholipids.M.S.Includes bibliographical referencesby Liam M. Shar
Asperger's Syndrome And Fiction - Autistic Worlds And Those Who Build Them
No full textDo tangible, testable links exist between the autistic spectrum and creativity? How would such links work from the perspective of an author with Asperger's Syndrome? To what degree would autism mould the author's work, and how would it affect writing technique and style compared to neurotypical (non autistic spectrum authors)? Do these links provide a tangible advantage? Can an Asperger's author successfully engage a non-Asperger's readership? Has Asperger's become fashionable in fiction and if so what are the benefits/consequences? Can an “extraterrestrial stranded without an orientation manual”1 communicate ideas in a meaningful way to non-autistics?
Asperger's Syndrome is a form of high functioning autism where those affected express a range of social, behavioural and perceptual traits which have no actual bearing on their level of intelligence. As an author with Asperger's my intention is to examine the degree to which my autism affects my writing technique and style compared to neurotypical (non autistic) creatives. Asperger's sufferers lack empathy and social skills, therefore creating situations a reader can empathise with is challenging. To an Asperger's other people are 'aliens'. If the characters and scenarios in my work are coloured by my difference, then it may be the difference itself which provides the hook for the reader.
To what extent do Asperger's authors need to 'pretend to be normal' in order to engage a neurotypical reader, or to make their work generally marketable? Is there an argument that they shouldn't even try? With increasing diagnosis and better understanding of the autistic spectrum, the Asperger's limited but intense range of interests and ability to focus without human distraction might link in to creative excellence that has an appeal far beyond the boundaries of the autistic spectrum.
The purpose of this thesis is to investigate whether claims of autistic links to creativity are more than heresay. I examine alleged positive evidence for these links, and see how this evidence ties in with my experience both as an Asperger's and an author, with particular regard to my decisions in crafting my novel The Ghost Land
Nesterov Accelerated ADMM for Distributed Pose Graph Optimization in SLAM problems
No full textA common problem in robotics is the simultaneous localization and mapping (SLAM) problem. Here, a robot needs to create a map of its surroundings while simultaneously localizing itself in this map. An unknown environment is assumed. Traditionally, it has been approached through filtering solutions. This paradigm has shifted to pose graph optimization (PGO). This method scales well with large maps and is fast and accurate. Furthermore, it is especially suited to the distributed SLAM problem as existing distributed optimization methods can be leveraged. One such method is the alternating direction method of multipliers (ADMM), which has been used in distributed PGO. ADMM has a simple implementation and can achieve high accuracies in distributed PGO. A solution of good quality can be acquired in a few iterations with ADMM. However, ADMM is slow to converge to high accuracies. This thesis introduces an algorithm which implements Nesterov acceleration in the ADMM algorithm for distributed PGO in SLAM problems. Such an implementation will be novel. To create the proposed Nesterov accelerated ADMM (N-ADMM) algorithm, the current literature is adapted and extended based on the choices made in this thesis. The main research question is how to make these choices. The proposed N-ADMM algorithm is implemented in C++ and compared with unaccelerated ADMM and the state of the art. N-ADMM has shown better performance in some scenarios. To further research what these scenarios are characterized by, two models are introduced to create new datasets of which the parameters can be controlled. The effects of graph size and bad initial guesses are investigated.Mechanical Engineering | Systems and Contro
Analysing the Performance of SPLITTER: A Noise Removal Algorithm for DESHIMA 2.0
No full textMore insight has been gathered on the performance of the SPLITTER (Stationary spectrum Plus Low-rank Iterative TransmiTtance EstimatoR) algorithm as developed by Brackenhoff for denoising data gathered from observations of high-redshift galaxies. By using matrix decomposition to split the gathered data into a low-rank atmosphere matrix and a sparse matrix with the signal and photon noise, the algorithm avoids the subtraction of two noisy signals, and therefore the factor of √2 additional noise that comes with it. The algorithm was specifically developed for DESHIMA 2.0 (DEep Spectroscopic HIgh-redshift MApper), a wideband spectrometer that achieves a bandwidth from 220 to 440 GHz, using 347 spectral channels. Previous performance tests of the algorithm included the comparison of the weighted root mean square error between SPLITTER and the usual technique of Direct Subtraction on realistic data simulated using the TiEMPO (Time-dependent End-to-end Model for Post-process Optimization) software package. This resulted in a ~1.7 improvement factor for the whole spectrum and ~1.3 in the emission line area.The performance of SPLITTER on two key components of the spectrum have been analyzed separately. First, the measurement of the continuum has been analyzed by using TiEMPO to create realistic simulations of the observation of custom spectra with a linear continuum. SPLITTER showed to be more precise as the noise level was lower, but less accurate, as there was a systematic offset in the estimated continuum. Using a modified black body model for the continuum and assuming the relative offset is independent of the strength of the continuum, the observed offsets and errors were propagated to offsets in estimations of dust temperature and spectral emissivity of the dust . Because of the offset, SPLITTER also showed a systematic offset in estimated , but as the algorithm is more precise, it performed better at estimating , since determines the shape of the spectrum and has less influence on the strength. Second, to test the detection of emission lines, custom spectra have been created containing the same linear continuum and single spectral line at four different frequencies. Each line was set to have a known signal to noise ratio compared to the photon noise in its frequency bin. The retrieved signal to noise ratio as compared to noise of neighboring bins showed an improvement of ~1.9 for SPLITTER compared to Direct Subtraction for bright lines. Weak lines did not show any improvement in SNR. There seemed to be no correlation between continuum overestimation and emission line measurements.Conclusion is that SPLITTER definitely shows improvement in noise reduction, but comes with an overestimation of the continuum. The consequences of this are that Direct Subtraction is still preferred for estimating dust temperature, but for estimations of spectral emissivity and detection of emission lines, SPLITTER is more robust.Applied Physic
Nature-positive Architecture: A Regenerative Design Approach of a Winery in the Quarry of the St. Pietersberg
No full textSustainability in its development is increasingly focusing on nature. However, this research shows that through positive development, benefits are not only gained in nature, but are actually viewed as a common good. From this emerged regenerative development and design, in which there is a judgement from a whole system perspective. Through the knowledge of place, a strategy is first developed within the design process, in which oak regeneration can respond to the respective site patterns. This knowledge should then be used to design in harmony with the larger patterns of place. This is achieved through a partnership between the place (as a living being) and other various living systems. Herein, such a partnership is presented between place, humans and oak forest regeneration. This partnership brings forth new activities and growth through co-evolution, and is made permanent by bridging with viticulture. The regeneration of wood is passed down over several generations, using it not only as a building material, but also with the manufacture of wine barrels. In doing so, this research shows how this material works and is produced, and what other uses, if any, are available at the time the material depreciates.Architecture, Urbanism and Building Sciences | Architectural Engineerin
Characterization of a turbo-switch SOA wavelength converter using spectrographic pulse measurement
No full textWe use the frequency-resolved optical gating (FROG) technique to determine the pulsewidth and chirp characteristics of wavelength-converted pulses from a turbo-switch and asymmetrical Mach-Zehnder filter combination under a variety of operating conditions. The output pulses were found to be near transform limited and had a high tolerance to line rate and input power variations
Active small-scale space debris removal by a space-based laser
No full textSpace debris objects with sizes between 1 and 10 cm form the greatest risks for creating new collisions with active spacecraft as they are too small to track and too large to be shielded against. This research has simulated the performance of a space-based laser system on the removal of these small-scale debris objects. The selected system is placed in a Sun-synchronous orbit and consists of a high power 20 kW laser that shoots 600 J energy pulses with a repetition frequency of 33.33 Hz. The system detects and tracks the objects in-situ using a 1.5 m telescope from 800 km distance. From a distance of about 500 km, the laser fluence on the targets is sufficiently high to trigger ablation on the material surface. This decelerates the debris object and lowers its lifetime. The laser is tested on a randomly generated debris population of 5 000 objects. The results show that after 10 days of simulation, the lifetime of 334 objects are effectively lowered below 25 years and 614 objects are lowered below one month. At longer simulation time the efficiency decreases since less and less objects are left to target. Extrapolating the results, the laser could on an annual basis lower the lifetime of more than 36 000 objects below 1 month and 18 000 objects below 25 years, which is very promising. The results show that a space-based laser system is highly efficient as an Active Debris Removal (ADR) technique for debris objects between 1 and 10 cm.Aerospace Engineerin
Validation of the SU2 Flow Solver for Classical Non Ideal Compressible Fluid Dynamics
No full textThe validation of SU2 for modelling classical non-ideal compressible fluid dynamics will advance the research into efficient ORC turbomachinery design. This study determines the validity of the two-dimensional flow solver for predicting the isentropic expansion of Siloxane MM through a converging-diverging nozzle using compressible Euler equations, adiabatic flow, and the Peng-Robinson equation of state. Two flows with an inlet stagnation temperature of 525K were considered: an expansion from 18.4 bar to 2.1 bar, and an expansion from 11.1 bar to 1.3 bar. Mach number along the centreline and static pressure along the nozzle surface were used as the direct system response quantities used in the analysis. Experimental data and uncertainty came from the ORCHID, model input uncertainty was quantified using stochastic collocation, and the numerical uncertainty was calculated using the Richardson extrapolation. The conclusions were based on a hybrid of the ASME V&V 20 and Real Space validation metrics, with a novel Engineering Response Quantity analysis based on determining the effects of system uncertainty on performance parameters. The studied SU2 model provide valid predictions for Mach number, and invalid predictions for static pressure. The largest error is in the kernel region, where EMach=0.111 and EPressure = 112 kPa. Mach number has a maximum simulation uncertainty of 2% at the transition to the reflex region. Pressure has a maximum uncertainty of 3% at the throat. In the context of turbomachinery the simulation uncertainties translate to +/-0.001 and +/-0.02 on a loss coefficient calculated across a theoretical normal shock, for Mach and pressure respectively. Considering +/-0.01 as significant for a loss coefficient the Mach uncertainty is negligible. Input uncertainty is the largest component of the pressure uncertainty, while experimental uncertainty is dominant for Mach. The input parameters which provide the highest contribution to the uncertainty are critical pressure and temperature. The developed infrastructure can be used for expanding the validation of SU2 to different flow cases.Aerospace Engineerin
Simulating arbitrary interactions between small-scale space debris and a space-based pulsed laser system
No full textThis research investigates the performance of a space-based laser system to remove debris objects with size smaller than 10 cm. The laser system is placed in a 800 km Sun Synchronous Orbit and consists of a 20 kW laser that shoots 300 J energy pulses with a repetition frequency of 66.66 Hz. The system is able to detect and track debris objects in situ using a 2.0 m mirror from 800 km distance. From a distance of about 500 km, the laser fluence on the targets is sufficiently high to trigger ablation, which decelerates the debris objects and reduces their lifetime. The feasibility of the concept is tested in scenarios where the laser system targets the debris objects from a different orbiting altitude and from varying azimuth angles. For many geometries, the laser is capable of significantly reducing the lifetime of the debris object. Extrapolating to longer periods of operation, the laser can be expected to provide a significant reduction of the population of small debris objects in LEO.Astrodynamics & Space Mission
- …
