Black Box Variational Inference

Variational inference has become a widely used method to approximate posteriors in complex latent variables models. However, deriving a variational inference algorithm generally requires significant model-specific analysis, and these efforts can hinder and deter us from quickly developing and exploring a variety of models for a problem at hand. In this paper, we present a "black box" variational inference algorithm, one that can be quickly applied to many models with little additional derivation. Our method is based on a stochastic optimization of the variational objective where the noisy gradient is computed from Monte Carlo samples from the variational distribution. We develop a number of methods to reduce the variance of the gradient, always maintaining the criterion that we want to avoid difficult model-based derivations. We evaluate our method against the corresponding black box sampling based methods. We find that our method reaches better predictive likelihoods much faster than sampling methods. Finally, we demonstrate that Black Box Variational Inference lets us easily explore a wide space of models by quickly constructing and evaluating several models of longitudinal healthcare data

Influence of several factors on ignition lag in a compression-ignition engine

This investigation was made to determine the influence of fuel quality, injection advance angle, injection valve-opening pressure, inlet-air pressure, compression ratio, and engine speed on the time lag of auto-ignition of a Diesel fuel oil in a single-cylinder compression-ignition engine as obtained from an analysis of indicator diagrams. Three cam-operated fuel-injection pumps, two pumps cams, and an automatic injection valve with two different nozzles were used. Ignition lag was considered to be the interval between the start of injection of the fuel as determined with a Stroborama and the start of effective combustion as determined from the indicator diagram, the latter being the point where 4.0 x 10(exp-6) pound of fuel had been effectively burned. For this particular engine and fuel it was found that: (1) for a constant start and the same rate of fuel injection up the point of cut-off, a variation in fuel quantity from 1.2 x 10(exp-4) to 4.1 x 10(exp-4) pound per cycle has no appreciable effect on the ignition lag; (2) injection advance angle increases or decreases the lag according to whether density, temperature, or turbulence has the controlling influence; (3) increase in valve-opening pressure slightly increases the lag; and (4) increase of inlet-air pressure, compression ratio, and engine speed reduces the lag

Investigation of the Discharge Rate of a Fuel-injection System

In connection with the development of a method for analyzing indicator cards taken from high-speed compression-ignition engines, this investigation was undertaken to determine the average quantity of fuel discharged during each crank degree of injection period

Tackling TB together : a community participatory study of the socio-cultural factors influencing an understanding of TB within the Somali community in Sheffield

This report presents the main findings from a study which sought to gain insight into the sociocultural influences on how TB is perceived within the Somali community and how these perspectives affect the prevention, diagnosis and treatment of the disease. The study also gained an understanding of healthcare practitioners’ perceptions of TB among the Somali community and their experiences of providing TB services to Somalis. A community participatory research approach was used which involved Somali community researchers and healthcare practitioners working in partnership with university researchers to design and conduct the research with the support of a community-based project advisory group. Data were collected by means of interviews and focus groups with Somali community leaders, patients suffering from TB, members of the wider Somali community, healthcare practitioners providing TB services and primary care practitioners. The findings identified a general awareness of TB among the Somali community in terms of the signs and symptoms of pulmonary TB, its treatment and prognosis. There was less understanding of nonpulmonary TB among Somali participants and some healthcare practitioners. Many Somalis lacked detailed understanding of how the disease was spread. Established community beliefs, for example that TB was a hereditary disease, or that it could be acquired by sharing eating utensils proved difficult for healthcare practitioners to challenge. Somali people spoke of how TB was perceived to be stigmatised within the Somali community. Whereas a person suffering from TB would generally share the diagnosis with their immediate family, concerns remained about the possibility of being ostracised by members of the wider community if knowledge of the disease became more widespread. This carried implications for contact tracing. However, attitudes towards TB were changing. Community leaders emphasised that as people became more knowledgeable about TB then the stigma would diminish but it was acknowledged that deeply held beliefs about the causes and consequences of TB would take some time to change. A number of barriers that hinder Somali people accessing TB services were identified. Some, like stigma, are embedded in cultural beliefs or are linked to socio-cultural activities such as chewing khat. A lack of trust and confidence in healthcare providers, especially some GPs arose from the protracted time it often took to diagnose TB. Healthcare practitioners lack of understanding of the Somali community and language barriers also hindered the uptake of primary care services. Several avenues through which culturally appropriate strategies targeted at minimising the spread of the disease, ensuring timely diagnosis and effective management of TB were identified. These are captured in the recommendations arising from the study which identify the need for a more proactive approach to raising awareness of TB within the Somali community and among primary care practitioners. Interpretations of TB are culturally bound and in order for TB services the better to meet the needs of the Somali community there is a need to develop greater awareness among healthcare practitioners of the needs of Somali patients and overcome linguistic barriers through improved access to interpreting services, especially in primary care

A Writer for a Shrinking World: Cultural Identity Formation and Globalization in the Novels of Kopano Matlwa

This paper analyzes the novels of author Kopano Matlwa in relation to issues in cultural identity formation during the current period of rapid globalization within the author\u27s home nation of South Africa

Identifying Critical Marine Foraging Habitat of Marbled Murrelets (Brachyramphus marmoratus) in South Puget Sound

Human impacts are increasingly affecting the conservation status of many of the world’s species, particularly those less capable of adapting to rapidly changing environments. Seabirds are one of the most endangered groups of birds in the world due to the synergistic impacts of climate change, pollution, human disturbance, bycatch, and overfishing. Marbled Murrelets (MAMUs; Brachyramphus marmoratus) are small diving seabirds currently listed as Endangered by Washington State and Threatened by the federal government. As such, their habitat selection and population distribution are two important metrics by which to measure their response to altered environmental conditions, including their habitat-use patterns. Despite their protected status, MAMU populations continue to decline, particularly in the Pacific Northwest. While the marine distribution and habitat use patterns of MAMUs in most of WA have been well studied, there is a significant knowledge gap regarding marine habitat use in the South Puget Sound

Sallust\u27s Histories and Triumviral Historiography

This dissertation explores echoes of the triumviral period in Sallust\u27s Histories and demonstrates how, through analogical historiography, Sallust presents himself as a new type of historian whose exempla are flawed and morally ambiguous, and who rejects the notion of a triumphant, ascendant Rome perpetuated by the triumvirs. Just as Sallust\u27s unusual prose style is calculated to shake his reader out of complacency and force critical engagement with the reading process, his analogical historiography requires the reader to work through multiple layers of interpretation to reach the core arguments. In the De Legibus, Cicero lamented the lack of great Roman historians, and frequently implied that he might take up the task himself. He had a clear sense of what history ought to be : encomiastic and exemplary, reflecting a conception of Roman history as a triumphant story populated by glorious protagonists. In Sallust\u27s view, however, the novel political circumstances of the triumviral period called for a new type of historiography. To create a portrait of moral clarity is, Sallust suggests, ineffective, because Romans have been too corrupted by ambitio and avaritia to follow the good examples of the past. In the Histories, Sallust offers new anti-exempla for the triumviral period : morally ambiguous characters who refuse to show readers a clear portrait of good or bad . Sallust\u27s new historiography also forces readers to look beyond the claims of Roman peace and glory which were perpetuated by Cicero and the triumvirs. By alluding to the triumviral period in his dark narrative of the 70s and 60s, Sallust suggests that the pretext of concordia perpetuated by the triumvirs is specious, and that underneath this flimsy pretext is a Rome as troubled by civil strife as were the years of the late republic