Characterizing Unmixed Trees and Coronas with Respect to PMU Covers

In this dissertation we study the algebraic properties of ideals constructed from graphs. We use algebraic techniques to study the PMU Placement Problem from electrical engineering which asks for optimal placement of sensors, called PMUs, in an electrical power system. Motivated by algebraic and geometric considerations, we characterize the trees for which all minimal PMU covers have the same size. Additionally, we investigate the power edge ideal of Moore, Rogers, and Sather-Wagstaff which identifies the PMU covers of a power system like the edge ideal of a graph identifies the vertex covers. We characterize the trees for which the power edge ideal is unmixed, and we show that such ideals are complete intersections. We also characterize the coronas for which the power edge ideal is unmixed, and we show that such ideals are Cohen-Macaulay. For non-trees, we exhibit graphs whose power edge ideals distinguish between the complete intersection, Gorenstein, Cohen-Macaulay, and unmixed properties. We also provide Macaulay2 code that computes the minimal PMU covers and the power edge ideal of a graph

A Monte Carlo Model of Uncertainty in a Deterministic Hazardous Waste Transportation Risk Assessment

This thesis is aimed at developing and applying advanced modeling tools in the prediction of risk to the general public from transportation of chemical waste on public highways. The modeling tools developed can then be used to compare alternative waste management scenarios. The application considered is related to the transport of hazardous waste generated by the United States Department of Energy (DOE) to current treatment, storage, and disposal facilities. DOE is currently considering four different scenarios. The application considered can be more specifically defined as an analysis of the risk to the general public from transporting the 63 shipments of DOE generated hazardous waste designated as poison by inhalation hazards (PIH), potentially resulting in fatality, by the United States Department of Transportation (DOT) [Title 49, Code of Federal Regulations (Part 173.132)] in the 1992 fiscal year. The analysis is based on current transportation practices employed by DOE. Once the modeling tools have been developed to perform this analysis, similar analysis can be routinely carried out for other health end-points (carcinogenic effects and other adverse health effects other than cancer and lethality) and other waste management scenarios. Two types of tools have been developed, deterministic and probabilistic. Using the probabilistic modeling tool, a cumulative probability distribution of number of people impacted can be developed (for this application impacted means number of individuals experiencing potentially life-threatening health effects due to inhalation of a DOE generated PIH released as a result of a truck transportation accident). The probabilistic modeling tool developed is based upon a Monte Carlo analysis accounting for the uncertainties in the variables involved in the modeling process. The deterministic tool developed provides a simplified version of the probabilistic model such that the prediction will be one risk value which should approximate the mean of the cumulative probability distribution developed by the probabilistic model. Both the deterministic and probabilistic modeling tools require the modeling of the consequence of a release of hazardous waste. The consequence is the result of source term accident modeling (i.e., resulting from a truck accident spill) along with dispersion modeling. The source term modeling employs the use of (1) distributions of meteorological data supplied by the National Weather Service at over 60 locations uniformly distributed around the continental United States and (2) a detailed study on the US DOT HMIRS (Hazardous Materials Information Reporting System) database which encompasses information on thousands of hazardous material transportation accidents since the 1970\u27s. The study of the HMIRS database led to probability distributions on the release amounts (by transport container), breach fractions and accident time (by hour and month). A health criteria, presented at WM-94 by Hartman et. al. (1994), is used in the dispersion modeling to define human health impacts from the concentration history at each downwind location. Reasonable single values for all modeling parameters were used in the deterministic model, whereas probability distributions for release estimates and accident meteorological conditions were used for release amounts and meteorology in the probabilistic model. Realistic scenarios for the transportation accident itself were developed accounting for mixtures of chemicals released as is likely to occur. It was found that the cumulative probability distribution of the number of individuals with potentially life-threatening health effects, is highly skewed. The probability that no individuals will have potentially life-threatening health effects from these 63 shipments is greater than 99%. Therefore the median (the 50-th percentile) of the distribution is 0, and all of the non-zero potentially life-threatening health effects are contained in the upper tail of the cumulative probability distribution (less than 1% chance of occurrence). Table 1 below presents some summary statistics compiled from the distribution. Only 3 (of the 63) shipments had the potential to affect more than 500 people in a single accident. Furthermore, only 14 shipments had the potential to affect more than 100 people. Eliminating, or at least altering the waste management of these shipments, could dramatically reduce risks by reducing the probabilities for a catastrophic accident in which more than 100 people are affected. An additional observation is that the mean of the cumulative probability distribution, 3.48E-4, is located at the 99.947-th percentile and the result of the deterministic calculations of risk, 1.74E-4 (½ of the mean), is located at the 99.941-th percentile. The Monte Carlo analysis helped to provide a great deal of perspective on the deterministic risk value. The fact that there is such a large probability of zero risk and an extremely small probability of a high risk scenario can be very useful in the decision making process

Some problems of capital and class in Kenya

In this paper the authors raise some critical issues related to income distribution and class formation in Kenya. The first section focusses attention on the notion of a salariat and the phenomenon of straddling between permanent employment and private accumulation within private enterprise, a feature of colonial and post-colonial state formation in Kenya. The second section deals with a category of workers who are supposed to be privileged because of the relatively high wages received in comparison to other groups of workers. It is shown here that historical changes in the relations of production, as well as the application of wage guidelines and Industrial Court wage awards, have affected this category of workers, eliminating the privilege which they were supposed to enjoy. Two case studies are given in this context - that of estate agricultural supervisors and bank workers. In the third section, the authors focus on household production of commodities (coffee, tea and milk) in Nyeri and Murang'a in Central Province. The intention here is to explore the implications of both domestic and international capital in household production as they affect the relations of production and distribution in smallholding agriculture. The intention in focussing on these issues is not to make conclusive statements, but rather to draw the attention of researchers to the need for further research in these areas

Pallet Racking Using Cold-reduced Steel

Codes of practice for the design of cold-formed sections have generally included a requirement for the coil material to possess a specified amount of ductility prior to forming. The scientific basis for such ductility requirements is shrouded in historical mystery but code drafting committees have been reluctant to remove these requirements in the absence of good reason. However, very low ductility steels have been used for the manufacture of cold-formed steel components for many years by the two leading UK manufacturers of storage racks without this lack of ductility giving rise to any problems during either manufacture or service. This relatively hard material is produced by taking conventional coil material and cold-reducing it prior to forming it into beam, column and other components. The advantage gained by this procedure is a significant increase in the yield stress but the penalty is a considerable reduction in the ductility. As, up to the present time, storage racking has not been subject to formal approval procedures, the absence of clauses in UK or European Codes of Practice allowing the use of these hard steels has not caused any problems. However, this situation is now changing and it has become necessary to justify their performance in comparison with material of more usual ductility. It may be noted here that the use of low ductility steel is not unique to storage racking because very hard steels have been also used successfully in Europe for the manufacture of profiled steel cladding. Galvanised coil is available with a guaranteed yield stress of 550 N/mm² and several manufacturers successfully form this material. Indeed, the first author has tested roof sheeting made from material which had a measured yield stress in excess of 700 N/mm² together with zero elongation in a conventional tensile test. The buckling-yielding failure modes observed in both single and two-span tests to failure showed no evidence of the influence of reduced ductility. In this paper, the justification for the use of low-yield stress steel is taken a stage further by describing a series of tests on racking components made from both cold-reduced steel and an equivalent hot-rolled steel of similar yield stress but much greater ductility. It is shown that the use of hard steel has no adverse effect on performance. The paper concludes by describing a test to failure of a full scale rack structure fabricated using components made from cold-reduced steel

Early changes in emotional processing as a marker of clinical response to SSRI treatment in depression

Antidepressant treatment reduces behavioural and neural markers of negative emotional bias early in treatment and has been proposed as a mechanism of antidepressant drug action. Here, we provide a critical test of this hypothesis by assessing whether neural markers of early emotional processing changes predict later clinical response in depression. Thirty-five unmedicated patients with major depression took the serotonin re-uptake inhibitor (SSRI), escitalopram (10 mg), over 6 weeks, and were classified as responders (22 patients) versus non-responders (13 patients), based on at least a 50% reduction in symptoms by the end of treatment. The neural response to fearful and happy emotional facial expressions was assessed before and after 7 days of treatment using functional magnetic resonance imaging. Changes in the neural response to these facial cues after 7 days of escitalopram were compared in patients as a function of later clinical response. A sample of healthy controls was also assessed. At baseline, depressed patients showed greater activation to fear versus happy faces than controls in the insula and dorsal anterior cingulate. Depressed patients who went on to respond to the SSRI had a greater reduction in neural activity to fearful versus happy facial expressions after just 7 days of escitalopram across a network of regions including the anterior cingulate, insula, amygdala and thalamus. Mediation analysis confirmed that the direct effect of neural change on symptom response was not mediated by initial changes in depressive symptoms. These results support the hypothesis that early changes in emotional processing with antidepressant treatment are the basis of later clinical improvement. As such, early correction of negative bias may be a key mechanism of antidepressant drug action and a potentially useful predictor of therapeutic response

Predicting treatment response in depression: the role of anterior cingulate cortex.

Background: Identification of biomarkers predicting therapeutic outcome of antidepressant treatment is one of the most important tasks in current research because it may transform the lengthy process of finding the right treatment for a given individual with depression. In the current study, we explored the potential of pretreatment pregenual anterior cingulate cortex activity as a putative biomarker of treatment response. // Methods: Thirty-two medication-free patients with depression were treated for 6 weeks with a selective serotonin reuptake inhibitor, escitalopram. Before treatment began, patients underwent an fMRI scan testing response to brief, masked, presentations of facial expression depicting sadness and happiness. // Results: After 6 weeks of treatment, there were 20 selective serotonin reuptake inhibitor responders and 12 nonresponders. Increased pretreatment pregenual anterior cingulate cortex activity to sad vs happy faces was observed in responders relative to nonresponders. A leave-one-out analysis suggested that activity in the anterior cingulate cortex was able to predict response status at the level of the individual participant. // Conclusions: The study supports the notion of pregenual anterior cingulate cortex as a promising predictor of antidepressant response

Acute angiotensin II receptor blockade facilitates parahippocampal processing during memory encoding in high-trait-anxious individuals

Background Angiotensin II receptor blockers (ARBs) have been associated with preventing posttraumatic stress disorder symptom development and improving memory. However, the underlying neural mechanisms are poorly understood. This study investigated ARB effects on memory encoding and hippocampal functioning that have previously been implicated in posttraumatic stress disorder development. Methods In a double-blind randomized design, 40 high-trait-anxious participants (33 women) received the ARB losartan (50 mg) or placebo. At drug peak level, participants encoded images of animals and landscapes before undergoing functional magnetic resonance imaging, where they viewed the encoded familiar images and unseen novel images to be memorized and classified as animals/landscapes. Memory recognition was assessed 1 hour after functional magnetic resonance imaging. To analyze neural effects, whole-brain analysis, hippocampus region-of-interest analysis, and exploratory multivariate pattern similarity analysis were employed. Results ARBs facilitated parahippocampal processing. In the whole-brain analysis, losartan enhanced brain activity for familiar images in the parahippocampal gyrus (PHC), anterior cingulate cortex, and caudate. For novel images, losartan enhanced brain activity in the PHC only. Pattern similarity analysis showed that losartan increased neural stability in the PHC when processing novel and familiar images. However, there were no drug effects on memory recognition or hippocampal activation. Conclusions Given that the hippocampus receives major input from the PHC, our findings suggest that ARBs may modulate higher-order visual processing through parahippocampal involvement, potentially preserving intact memory input. Future research needs to directly investigate whether this effect may underlie the preventive effects of ARBs in the development of posttraumatic stress disorder

Direct serotonin release in humans shapes aversive learning and inhibition

The role of serotonin in human behaviour is informed by approaches which allow in vivo modification of synaptic serotonin. However, characterising the effects of increased serotonin signalling in human models of behaviour is challenging given the limitations of available experimental probes, notably selective serotonin reuptake inhibitors. Here we use a now-accessible approach to directly increase synaptic serotonin in humans (a selective serotonin releasing agent) and examine its influence on domains of behaviour historically considered core functions of serotonin. Computational techniques, including reinforcement learning and drift diffusion modelling, explain participant behaviour at baseline and after week-long intervention. Reinforcement learning models reveal that increasing synaptic serotonin reduces sensitivity for outcomes in aversive contexts. Furthermore, increasing synaptic serotonin enhances behavioural inhibition, and shifts bias towards impulse control during exposure to aversive emotional probes. These effects are seen in the context of overall improvements in memory for neutral verbal information. Our findings highlight the direct effects of increasing synaptic serotonin on human behaviour, underlining its role in guiding decision-making within aversive and more neutral contexts, and offering implications for longstanding theories of central serotonin function

Pharmacological targeting of cognitive impairment in depression: recent developments and challenges in human clinical research

Impaired cognition is often overlooked in the clinical management of depression, despite its association with poor psychosocial functioning and reduced clinical engagement. There is an outstanding need for new treatments to address this unmet clinical need, highlighted by our consultations with individuals with lived experience of depression. Here we consider the evidence to support different pharmacological approaches for the treatment of impaired cognition in individuals with depression, including treatments that influence primary neurotransmission directly as well as novel targets such as neurosteroid modulation. We also consider potential methodological challenges in establishing a strong evidence base in this area, including the need to disentangle direct effects of treatment on cognition from more generalised symptomatic improvement and the identification of sensitive, reliable and objective measures of cognition