926 research outputs found
Novel algorithms for early-universe cosmology
No full textFluctuations in the cosmic microwave background (CMB), the radiation left over from the Big Bang, contain information which has been pivotal in establishing the current cosmological model. CMB data can also be used to test theoretically well-motivated additions to the model, including pre-inflationary relics (signatures of bubble collisions arising in eternal inflation) and topological defects that form after inflation (cosmic strings and textures). These relics typically leave sub-dominant, spatially localised signals, hidden in the “noise” of the primary CMB, the instrumental noise, foreground residuals and other systematics. Standard approaches for searching for such signals involve focusing on statistical anomalies, which carry the danger of extreme a posteriori biases. The self-consistent approach to this problem is Bayesian model comparison; however, the full implementation of this approach is computationally intractable with current CMB datasets, and will only become more difficult with data from the next generation of CMB experiments. I will describe a powerful modular algorithm, capable of coping with the volume of data, which combines a candidate-detection stage (using wavelets or optimal filters) with a full Bayesian parameter-estimation and model-selection stage performed in pixel space within the candidate regions. The algorithm is designed to fully account for the “look-elsewhere” effect, and its use of blind analysis techniques further enhances its robustness to unknown systematics. Finally, I will present the results of applying the algorithm to hunt for the signatures of bubble collisions and cosmic textures in the seven-year data from the Wilkinson Microwave Anisotropy Probe
Testing the isotropy of the Universe with the Cosmic Microwave Background
No full textA fundamental assumption in the standard model of cosmology is that the Universe is isotropic on large scales. Breaking this assumption leads to a set of solutions to Einstein’s field equations known as Bianchi cosmologies, of which only the subset linked to universal rotation have ever been tested against data. For the first time, we consider all the degrees of freedom in these solutions to conduct a general test of isotropy using cosmic microwave background data. We develop a new analysis framework for this study. We first analyse WMAP temperature data to test our method against previous studies searching for universal rotation. We include the effect of Bianchi power at the intermediate and small scales (i.e. up to l = 1000), and show that failure to do so results in inaccurate constraints on a significant fraction of the parameter space. We carefully assess the effects of prior choices and show that evidence for global rotation found in previous studies relies on specific a priori assumptions on some parameters. To carry out the first test of the fully anisotropy freedom, we analyse recent data from the Planck mission including, for the first time, the cosmic microwave background (CMB) polarization in the likelihood in addition to the temperature. For the vector mode (associated with vorticity) we obtain a limit on the anisotropic expansion of (σV/H)0 < 4.7 × 10^−11 (95% CI), which is an order of magnitude tighter than previous Planck results that used CMB temperature only. We also place upper limits on other modes of anisotropic expansion, with the weakest limit arising from the regular tensor mode, (σT,reg/H)0 < 1.0 × 10^−6 (95% CI). Including all degrees of freedom simultaneously for the first time, anisotropic expansion of the Universe is strongly disfavoured, with odds of 121,000:1 against
Cosmology in the Presence of Non-Gaussianity
No full textModern observational cosmology relies on statistical inference, which models measurable quantities (including their systematic and statistical uncertainties) as random variates, examples are model parameters (`cosmological parameters') to be estimated via regression, as well as the observable data itself. In various contexts, these exhibit non-Gaussian distribution properties, e.g., the Bayesian joint posterior distribution of cosmological parameters from different data sets, or the random fields affected by late-time nonlinear structure formation like the convergence of weak gravitational lensing or the galaxy density contrast. Gaussianisation provides us with a powerful toolbox to model this non-Gaussian structure: a non-linear transformation from the original non-Gaussian random variate to an auxiliary random variate with (approximately) Gaussian distribution allows one to capture the full distribution structure in the first and second moments of the auxiliary. We consider parametric families of non-linear transformations, in particular Box-Cox transformations and generalisations thereof. We develop a framework that allows us to choose the optimally-Gaussianising transformation by optimising a loss function, and propose methods to assess the quality of the optimal transform a posteriori. First, we apply our maximum-likelihood framework to the posterior distribution of Planck data, and demonstrate how to reproduce the contours of credible regions without bias - our method significantly outperforms the current gold standard, kernel density estimation. Next, we use Gaussianisation to compute the model evidence for a combination of CFHTLenS and BOSS data, and compare to standard techniques. Third, we find Gaussianising transformations for simulated weak lensing convergence maps. This increases the information content accessible to two-point statistics (e.g., the power spectrum) and potentially allows for rapid production of independent mock maps with non-Gaussian correlation structure. With these examples, we demonstrate how Gaussianisation expands our current inference toolbox, and permits us to accurately extract information from non-Gaussian contexts
Considerations in the Interpretation of Cosmological Anomalies
No full textAnomalies drive scientific discovery – they are associated with the cutting edge of the research frontier, and thus typically exploit data in the low signal-to-noise regime. In astronomy, the prevalence of systematics –- both “known unknowns” and “unknown unknowns” – combined with increasingly large datasets, the widespread use of ad hoc estimators for anomaly detection, and the “look-elsewhere” effect, can lead to spurious false detections. In this informal note, I argue that anomaly detection leading to discoveries of new physics requires a combination of physical understanding, careful experimental design to avoid confirmation bias, and self-consistent statistical methods. These points are illustrated with several concrete examples from cosmology
A Compact Integrated High-Voltage Pulser Insensitive to Supply Transients for 3-D Miniature Ultrasound Probes
No full textIn this letter, a compact high-voltage (HV) transmit circuit for dense 2-D transducer arrays used in 3-D ultrasonic imaging systems is presented. Stringent area requirements are addressed by a unipolar pulser with embedded transmit/receive switch. Combined with a capacitive HV level shifter, it forms the ultrasonic HV transmit circuit with the lowest reported HV transistor count and area without any static power consumption. The balanced latched-based level shifter implementation makes the design insensitive to transients on the HV supply caused by pulsing, facilitating application in probes with limited local supply decoupling, such as imaging catheters. Favorable scaling through resource sharing benefits massively arrayed architectures while preserving full individual functionality. A prototype of 8 × 9 elements was fabricated in the TSMC 0.18 μm HV BCD technology and a 160μm×160μm PZT transducer matrix is manufactured on the chip. The system is designed to drive 65-V peak-to-peak pulses on 2-pF transducer capacitance and hardware sharing of six elements allows for an area of only 0.008 mm2 per element. Electrical characterization as well as acoustic results obtained with the 6-MHz central frequency transducer are demonstrated.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationImPhys/Medical Imagin
A Low-Noise HV Interface Circuit for MEMS Vibratory Gyroscope
No full textThe paper presents a low-noise high voltage (HV) CMOS Interface ASIC designed for MEMS vibratory gyroscopes. A closed-loop control is realized in the driving mode. An in-chip level shifter is designed in the loop to achieve a high DC voltage level of 5V which can excite the gyroscope. A DC biasing method is adopted in the interface circuit to convert the amplitude-modulated capacitive signal into voltage. The chip occupies 2.5 X 2.0mm(2) in a 0.35 mu m 2P3M BCD HV process, which offers buried layer and high voltage N-well isolation to block out the potential coupling noise. Simulation results show that the drive axis can accomplish a closed-loop self-oscillation of the MEMS gyroscope.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000304037500035&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Engineering, Electrical & ElectronicPhysics, AppliedEICPCI-S(ISTP)
Practical application of on-line partial discharge monitoring technique on 500kV shunt reactor
No full textConsidering the damage mechanism of oil-impregnated paper insulation in power transformers, shunt reactors and other high voltage electrical apparatus caused by partial discharge, a concept of “destructive partial discharge” is introduced in this paper. The intensity of this discharge is regarded as several thousands pico-coulomb (pC) and may cause the insulation a fatal damage. An oil-paper insulation is usually able to withstand this type of partial discharge for a period of time prior to failure. This provides engineers a time window to detect it. This paper describes an on-line partial discharge monitoring system for 500kV shunt reactors. The commission results from 3 single-phase shunt reactors either connected or disconnected to the grid showed that the on-line partial discharge detecting system has a high noise immunising ability. Two years later after the installation, a pre-warning signal was received from one shunt reactor indicating the existence of an intermittent discharge. The acoustic emission system located its position at the low end of the high voltage bushing in the oil. Dissolved gasses analysis (DGA) in the oil suggested the presence of partial discharge, as acetylene (C2H2) was as high as 20ppm. PD activity was further confirmed by a physical examination on the reactor
EHV/HV Italian Network Three-Phase Power-Flow by PFPD
No full textIn this paper, the three-phase generalization of a single-phase power flow (named PFPD) developed by the first author is presented. This novel formulation is mainly developed for HV/EHV transmission network applications, but it preserves validity also for distribution power system. The algorithm quantitatively aims at investigating the impact of the asymmetrical transmission structures and unbalanced loads on power systems. This impact is evaluated in terms of voltage sequence components. The algorithm is implemented in Matlab environment and tested by several fictitious networks
The Devil's altar? : crime and the early modern public house
No full textWas the early modern public house really such a dangerous place, as Puritan preachers (and many historians) suggested? This article discusses offences by publicans and patrons. It argues that the evidence for crime needs to be carefully contextualised and that taverns could stabilise as well as threaten the social order
The impacts of short break provision on disabled children and families: an international literature review
No full textFor over 30 years, short breaks have been part of the landscape of support provision for families with a disabled child. Historically, the term ‘respite care’ has been used in much of the research literature concerning short breaks for families with a disabled child. However, ‘short breaks’ has become the preferred term, partly due to the negative connotations of family carers requiring ‘respite’ from their children, and partly because short breaks now encompass a much wider range of supports than out-of-home placement in specialist residential facilities (Cramer and Carlin, 2008). As such, the term ‘short breaks’ will be used throughout this review, with the exception of direct quotes from research studies where the term ‘respite’ is used by study participants or study authors
- …
