The wall effect in cavity flow

A non-linear theory for the calculation of the flow field of an oblique flat plate under blockage condition is given using the techniques of integral equations. Numerical results are obtained with the aid of a high speed digital computer for the plate situated mid-channel at values of the angle of attack from 50 to 90° and the channel width-chord ratio from 3 to 20. Also obtained are results for the plate situated at two different off-center positions for a channel width-chord ratio 5 and angles of attack less than 30°

The relationship between EUV dimming and coronal mass ejections

Aims. There have been many studies of extreme-ultraviolet (EUV) dimming in association with coronal mass ejection (CME) onsets. However, there has never been a thorough statistical study of this association, covering appropriate temperature ranges. Thus, we make use of a large campaign database utilising the Coronal Diagnostic Spectrometer (CDS) and the Large Angle and Spectrometric COronagraph (LASCO) both on the SOlar and Heliospheric Observatory (SOHO) to associate dimming events detected at 1 and 2 million K with CME activity. The aim is to confirm whether the dimming-CME association is real or not. This in turn will confirm whether special attention should be paid to the EUV dimming in the pre-eruption and eruption periods to study the CME onset process itself. Methods. The CDS CME onset campaign data for Mg IX and FE XVI observations on the solar limb are used to compare to LASCO event lists over a period from 1998 to 2005. Dimming events are identified and the physical extent explored, whilst comparing the events to overlying CME activity. Results. For the identified dimming regions we have shown strong associations with CME onsets, with up to 55% of the dimming events being associated with CME activity. This is compared to the random case where up to 47% of the dimming regions are expected to be associated with CMEs. We have also shown that up to 84% of CMEs associated with our data can be tracked back to dimming regions. This compares to a random case of up to 58%. Conclusions. These results confirm the CME-EUV dimming association, using a statistical analysis for the first time. We discuss the repercussions for the study of CME onsets, i.e. analysis of the dimming regions and the periods up to such dimming may be key to understanding the pre-CME onset plasma processes. The results stress that one emission line may not be sufficient for associating dimming regions with CMEs

Impact Ionisation rate calculations in wide banc gap semiconductors

Calculations of band-to-band impact ionisation rates performed in the semi-classical Fermi’s Golden Rule approximation are presented here for the semiconductors GaAs, In(_0.53)Ga(_0.47)As and Si(_0.5)Ge(_0.5) at 300K. The crystal band structure is calculated using the empirical pseudopotential method. To increase the speed with which band structure data at arbitrary k-vectors can be obtained, an interpolation scheme has been developed. Energies are quadratically interpolated on adapted meshes designed to ensure accuracy is uniform throughout the Brillouin zone, and pseudowavefunctions are quadratically interpolated on a regular mesh. Matrix elements are calculated from the pseudowavefunctions, and include the terms commonly neglected in calculations for narrow band gap materials and an isotropic approximation to the full wavevector and frequency dependent dielectric function. The numerical integration of the rate over all distinct energy and wavevector conserving transitions is performed using two different algorithms. Results from each are compared and found to be in good agreement, indicating that the algorithms are reliable. The rates for electrons and holes in each material are calculated as functions of the k-vector of the impacting carriers, and found to be highly anisotropic. Average rates for impacting carriers at a given energy are calculated and fitted to Keldysh-type expressions with higher than quadratic dependence of the rate on energy above threshold being obtained in all cases. The average rates calculated here are compared to results obtained by other workers, with reasonable agreement being obtained for GaAs, and poorer agreement obtained for InGaAs and SiGe. Possible reasons for the disagreement are investigated. The impact ionisation thresholds are examined and k-space and energy distributions of generated carriers are determined. The role of threshold anisotropy, variation in the matrix elements and the shape of the bands in determining characteristics of the rate, particularly the softness of the rate's threshold behaviour are investigated

The Nature of Active Galactic Nuclei with Velocity Offset Emission Lines

We obtained Keck/OSIRIS near-IR adaptive optics-assisted integral-field spectroscopy to probe the morphology and kinematics of the ionized gas in four velocity-offset active galactic nuclei (AGNs) from the Sloan Digital Sky Survey. These objects possess optical emission lines that are offset in velocity from systemic as measured from stellar absorption features. At a resolution of ~0.18", OSIRIS allows us to distinguish which velocity offset emission lines are produced by the motion of an AGN in a dual supermassive black hole system, and which are produced by outflows or other kinematic structures. In three galaxies, J1018+2941, J1055+1520 and J1346+5228, the spectral offset of the emission lines is caused by AGN-driven outflows. In the remaining galaxy, J1117+6140, a counterrotating nuclear disk is observed that contains the peak of Pa$\alpha$ emission 0.2" from the center of the galaxy. The most plausible explanation for the origin of this spatially and kinematically offset peak is that it is a region of enhanced Pa$\alpha$ emission located at the intersection zone between the nuclear disk and the bar of the galaxy. In all four objects, the peak of ionized gas emission is not spatially coincident with the center of the galaxy as traced by the peak of the near-IR continuum emission. The peaks of ionized gas emission are spatially offset from the galaxy centers by 0.1"-0.4" (0.1-0.7 kpc). We find that the velocity offset originates at the location of this peak of emission, and the value of the offset can be directly measured in the velocity maps. The emission-line ratios of these four velocity-offset AGNs can be reproduced only with a mixture of shocks and AGN photoionization. Shocks provide a natural explanation for the origin of the spatially and spectrally offset peaks of ionized gas emission in these galaxies.Comment: 14 pages, 12 figures, accepted for publication in Ap

Exploring the Relationship of Urban Form and Mental Health in the 500 Largest Cities of the United States

Sustainable development efforts frequently focus on understanding and promoting the factors that influence health and wellbeing. Urban environments have received attention in recent years as spaces which can increase psychological distress. Despite hypothesized reports of urban environments being less conducive to good mental health then natural environments, few studies have investigated the effects of urban form characteristics (size, density, nuisances, transportation, and housing characteristics) and mental health measures at the city level. Using 2014 data from the 500 largest cities in the United States, this thesis evaluates the relationship between urban form and aggregate self-report scores of poor mental health. Results suggest that elements of the built environment have a direct influence on mental health status. The aim of this study is to test the association of urban form characteristics and psychological distress using a cross-sectional analysis of individual health survey responses. Mental health data were collected for a study of Center for Disease Control health characteristics in the 500 largest cities in the United States. Urban form data was collected from both United States Census and GIS datasets such as the Center for Neighborhood Technology’s Housing and Transportation Affordability Index (H+T Index). Linear regression analysis and factor analyses were used to estimate the relationship between psychological distress and urban form characteristics. Results suggest that urban density is negatively associated with mental health status at city level. This finding is logical and confirms earlier research. While measures of housing cost and diversity were slightly negatively associated with mental health, measures of transportation cost and employment access were slightly positively associated

Patterns in mission preaching: the representation of the Christian message and Efik response in the Scottish Calabar Mission, Nigeria, 1846-1900

The principal objective of this thesis is to examine the interaction during the period 1846-1900, between the Christian preaching of the United Presbyterian Church of Scotland and the local response of the Efik people in the Cross River basin of present day South-Eastern Nigeria. The historical development of mission preaching in Calabar, as well as its theological background is established. The interpretation of the mission's proclamation by the Efik people in terms of their local religion and culture is treated. The history of Christian proclamation and local response in the region is thus explored through the following categories of cultural interaction: the representation, rejection, reception, and reformulation of the mission message.The work is an attempt to get beyond crude stereotypes in academic literature of mission preaching as merely a destroyer of indigenous culture. The thesis contends that mission preaching and local response were more diverse than previous scholarly work suggests, and that the sources for this study demonstrate how the Efik people were active agents in the transmission of Christianity within the region, rather than passive recipients. It argues that the nature of the mission's evangelism cannot be properly understood without a proper recognition of the local religious and cultural categories used by the Efik people to reject, receive, reformulate, and "re-present" the biblical message in the region. Conversely, we maintain that in order properly to assess the contribution of the Efik people in the interpretation and transmission of emerging Efik Christianity, it is necessary to establish the form, the content, and the extent of mission preaching.In order to test these hypotheses, this work documents the actual patterns of preaching and response "on the ground" through attention to primary sources. The thesis is divided into three sections. The first section, offers a historical treatment of the origins and expansion of the United Presbyterian Mission in Calabar, and how its message was represented. In the second section, the development of United Presbyterian preaching is analysed from a historical and theological perspective. The third section undertakes a historical exploration of Efik response to the mission message, as interpreted through features of local religion and culture.A conclusion is offered in which a number of findings are summarised. The diversity of mission preaching at Calabar is maintained. Sources depict a more complex relationship between preaching for conversion and social change than has been generally thought. The role of ex-patriate missionary preaching in both evangelism and social change was scaled down considerably as the century progressed, particularly after the introduction of the vernacular translation of the Bible and in light of the increasing colonial presence. This prompted Efik Christians to take more initiative in the interpretation and expansion of a distinctively indigenous Christianity throughout the Cross River area