Explaining the Coexistence of Large-scale and Small-scale Magnetic Fields in Fully Convective Stars

Despite the lack of a shear-rich tachocline region, low-mass fully convective (FC) stars are capable of generating strong magnetic fields, indicating that a dynamo mechanism fundamentally different from the solar dynamo is at work in these objects. We present a self-consistent three-dimensional model of magnetic field generation in low-mass FC stars. The model utilizes the anelastic magnetohydrodynamic equations to simulate compressible convection in a rotating sphere. A distributed dynamo working in the model spontaneously produces a dipole-dominated surface magnetic field of the observed strength. The interaction of this field with the turbulent convection in outer layers shreds it, producing small-scale fields that carry most of the magnetic flux. The Zeeman���Doppler-Imaging technique applied to synthetic spectropolarimetric data based on our model recovers most of the large-scale field. Our model simultaneously reproduces the morphology and magnitude of the large-scale field as well as the magnitude of the small-scale field observed on low-mass FC stars.

The generation and amplification of intergalactic magnetic fields in analogue laboratory experiments with high power lasers

The advent of high-power laser facilities has, in the past two decades, opened a new field of research where astrophysical environments can be scaled down to laboratory dimensions, while preserving the essential physics. This is due to the invariance of the equations of magneto-hydrodynamics to a class of similarity transformations. Here we review the relevant scaling relations and their application in laboratory astrophysics experiments with a focus on the generation and amplification of magnetic fields in cosmic environment. The standard model for the origin of magnetic fields is a multi stage process whereby a vanishing magnetic seed is first generated by a rotational electric field and is then amplified by turbulent dynamo action to the characteristic values observed in astronomical bodies. We thus discuss the relevant seed generation mechanisms in cosmic environment including resistive mechanism, collision-less and fluid instabilities, as well as novel laboratory experiments using high power laser systems aimed at investigating the amplification of magnetic energy by magneto-hydrodynamic (MHD) turbulence. Future directions, including efforts to model in the laboratory the process of diffusive shock acceleration are also discussed, with an emphasis on the potential of laboratory experiments to further our understanding of plasma physics on cosmic scales.

Transverse Spreading of Electrons in High-Intensity Laser Fields

We show that for collisions of electrons with a high-intensity laser, discrete photon emissions introduce a transverse beam spread that is distinct from that due to classical (or beam shape) effects. Via numerical simulations, we show that this quantum induced transverse momentum gain of the electron is manifest in collisions with a realistic laser pulse of intensity within reach of current technology, and we propose it as a measurable signature of strong-field quantum electrodynamics.

Characterisation of a two-dimensional liquid-filled ion chamber detector array using flattened and unflattened beams for small fields, small MUs and high dose-rates

In this study, the PTW 1000SRS array with Octavius 4D phantom was characterised for FF and FFF beams. MU linearity, field size, dose rate, dose per pulse (DPP) response and dynamic conformal arc treatment accuracy of the 1000SRS array were assessed for 6MV, 6FFF and 10FFF beams using a Varian TrueBeam STx linac. The measurements were compared with a pinpoint IC, microdiamond IC and EBT3 Gafchromic film. Measured dose profiles and FWHMs were compared with film measurements. Verification of FFF volumetric modulated arc therapy (VMAT) clinical plans were assessed using gamma analysis with 3%/3 mm and 2%/2 mm tolerances (10% threshold). To assess the effect of cross calibration dose rate, clinical plans with different dose rates were delivered and analysed. Output factors agreed with film measurements to within 4.5% for fields between 0.5 and 1 cm and within 2.7% for field sizes between 1.5 and 10 cm and were highly correlated with the microdiamond IC detector. Field sizes measured with the 1000SRS array were within 0.5 mm of film measurements. A drop in response of up to 1.8%, 2.4% and 5.2% for 6MV, 6FFF and 10FFF beams respectively was observed with increasing nominal dose rate. With an increase in DPP, a drop of up to 1.7%, 2.4% and 4.2% was observed in 6MV, 6FFF and 10FFF respectively. The differences in dose following dynamic conformal arc deliveries were less than 1% (all energies) from calculated. Delivered VMAT plans showed an average pass percentage of 99.5(��0.8)% and 98.4(��3.4)% with 2%/2 mm criteria for 6FFF and 10FFF respectively. A drop to 97.7(��2.2)% and 88.4(��9.6)% were observed for 6FFF and 10FFF respectively when plans were delivered at the minimum dose rate and calibrated at the maximum dose rate. Calibration using a beam with the average dose rate of the plan may be an efficient method to overcome the dose rate effects observed by the 1000SRS array.

Wave Fields around Wave Energy Converter Arrays

Wave energy converters, by their nature, extract large amounts of energy<br/>from incident waves. If the industry is to progress such that wave energy<br/>becomes a significant provider of power in the future, large wave farms will<br/>be required. Presently, consenting for these sites is a long and problematic<br/>process, mainly due to a lack of knowledge of the potential environmental<br/>impacts. Accurate numerical modelling of the effect of wave energy extraction<br/>on the wave field and subsequent evaluation of changes to coastal<br/>processes is therefore required. Modelling the wave field impact is also<br/>necessary to allow optimum wave farm configurations to be determined.<br/>This thesis addresses the need for more accurate representation of wave<br/>energy converters in numerical models so that the effect on the wave field,<br/>and subsequently the coastal processes, may be evaluated. Using a hybrid<br/>of physical and numerical modelling (MIKE21 BW and SW models) the<br/>effect of energy extraction and operation of a WEC array on the local wave<br/>climate has been determined.<br/>The main outcomes of the thesis are: an improved wave basin facility, in<br/>terms of wave climate homogeneity, reducing the standard deviation of wave<br/>amplitude by up to 50%; experimental measurement of the wave field around<br/>WEC arrays, showing that radiated waves account for a significant proportion<br/>of the wave disturbance; a new representation method of WECs for use<br/>with standard numerical modelling tools, validated against experimental<br/>results.<br/>The methodology and procedures developed here allow subsequent evaluation<br/>of changes to coastal processes and sediment transport due to WEC<br/>arrays.

Discrete Gaussian Sampling for Low-Power Devices

Thesis (Master's)--University of Washington, 2015

Pulsed extremely low-frequency magnetic fields stimulate microvesicle release from human monocytic leukaemia cells

Microvesicles are released from cell surfaces constitutively during early apoptosis or upon activation with various stimuli including sublytic membrane attack complex (MAC). This study shows that an alternating current, pulsed, extremely low-frequency electromagnetic field (0.3 ��T at 10 Hz, 6 V AC) induced transient plasma membrane damage that allowed calcium influx. This in turn caused a release of stimulated microvesicles (sMV). When extracellular calcium was chelated with EGTA, sMV biogenesis initiated by ELFMF was markedly reduced and the reduction was less than when the stimulation was the deposition of sublytic MAC. This suggested that pulsed ELFMF resulted in transcellular membrane pores causing organelles to leak additional calcium into the cytoplasm (which EGTA would not chelate) which itself can lead to sMV release.

Machine learning Vasicek model calibration with Gaussian processes

In this article, we calibrate the Vasicek interest rate model under the risk neutral measure by learning the model parameters using Gaussian processes for machine learning regression. The calibration is done by maximizing the likelihood of zero coupon bond log prices, using mean and covariance functions computed analytically, as well as likelihood derivatives with respect to the parameters. The maximization method used is the conjugate gradients. The only prices needed for calibration are zero coupon bond prices and the parameters are directly obtained in the arbitrage free risk neutral measure.

Predictivity Strength of the Spatial Variability of Phenanthrene Sorption Across Two Sandy Loam Fields

Sorption is commonly agreed to be the major process underlying the transport and fate of polycyclic aromatic hydrocarbons (PAHs) in soils. However, there is still a scarcity of studies focusing on spatial variability at the field scale in particular. In order to investigate the variation in the field of phenanthrene sorption, bulk topsoil samples were taken in a 15��������15-m grid from the plough layer in two sandy loam fields with different texture and organic carbon (OC) contents (140 samples in total). Batch experiments were performed using the adsorption method. Values for the partition coefficient K d (L kg���1) and the organic carbon partition coefficient K OC (L kg���1) agreed with the most frequently used models for PAH partitioning, as OC revealed a higher affinity for sorption. More complex models using different OC compartments, such as non-complexed organic carbon (NCOC) and complexed organic carbon (COC) separately, performed better than single K OC models, particularly for a subset including samples with Dexter n���<���10 and OC <0.04 kg kg���1. The selected threshold revealed that K OC-based models proved to be applicable for more organic fields, while two-component models proved to be more accurate for the prediction of K d and retardation factor (R) for less organic soils. Moreover, OC did not fully reflect the changes in phenanthrene retardation in the field with lower OC content (Faardrup). Bulk density and available water content influenced the phenanthrene transport mechanism phenomenon.

Influence of abiotic stress factors on VOCs emission from Portuguese rice paddy fields: relation with increased climate change

Disserta����o para obten����o do Grau de Mestre em Engenharia do Ambiente Perfil de Gest��o de Sistemas Ambientais

A tour from the City of New-York, to Detroit, in the Michigan Territory, made between the 2d of May and the 22d of September, 1818 : the tour extends from New-York, by Albany, Schenectady, and Utica to Sacket's Harbor, and thence throught Lake Ontario, to St. Lawrence river, and down that stream to Hamilton village. Thence along both banks of the St. Lawrence, from Hamilton to the Thousand Islands; thence to Sacket's Harbor by water; from that place by the route of great Sodus, Geneva, Cananaigua and Batavia, to Buffalo; and from thence to Black Rock, Fort Erie, the Falls of Niagara, Queenston, Lewiston, and the memorable fields of Bridgewater and Chippewa after viewing the interesting place of Niagara, the author traversed the south shore of Lake Erie to the City of Detroit, and visited in the latter range, Dunkirk, Erie, Cleveland, Sandusky, and other places of less note. The tour is accompanied with a map upon which the route will be designated; a particular map of the Falls andRiver of Niagara, and the environs of the City of Detroit /

Errata slip inserted.

Sketches of the Battle Fields of Ontario from the War of 1812, July 15, 1876.

Accompanying caption from the Canadian Illustrated News, July 15, 1876: ���We publish today a page of sketches consisting of the following battle fields in Ontario :--Lundy���s Lane where, without doubt, the hardest fought battle of 1812-15 took place, and in which more troops were engaged than in any other engagement of that war : the battle field of Stony Creek where the Canadians and Indians made a night attack on the Americans and achieved a victory over a greatly superior force and obliged the Americans to retreat back to the shelter of Old Fort George which was the scene of many engagements during the war. Beaver Dam battle field is just in the suburbs of the thriving village of Thorold, and the monument covers the remains of several soldiers whose bodies were unearthed during the building of the new Welland Canal at that place.���