A study in the biosynthesis of stephania alkaloids

Imperial Users onl

Dark-matter bound states from Feynman diagrams

If dark matter couples directly to a light force mediator, then it may form bound states in the early universe and in the non-relativistic environment of haloes today. In this work, we establish a field-theoretic framework for the computation of bound-state formation cross-sections, de-excitation and decay rates, in theories with long-range interactions. Using this formalism, we carry out specific computations for scalar particles interacting either via a light scalar or vector mediator. At low relative velocities of the interacting particles, the formation of bound states is enhanced by the Sommerfeld effect. For particle-antiparticle pairs, we show that bound-state formation can be faster than annihilation into radiation in the regime where the Sommerfeld effect is important. The field-theoretic formalism outlined here can be generalised to compute bound-state formation cross-sections in a variety of theories, including theories featuring non-Abelian (albeit non-confining) interactions, such as the electroweak interactions.Comment: 36 pages + appendices + references, 9 figures, 1 table; v2: published versio

Microclimate Variability of Select Toronto Neighbourhoods Under Hot Summertime Conditions

Micrometeorological variability within cities has important implications for urban air and water quality, building energy consumption, and human health and thermal comfort. However, the monitoring of microscale climate is not routinely conducted. In most instances, primary meteorological observations are made under reproducible standard conditions (typically at an airport); but these open field observations tend to be unrepresentative of the intra-urban meteorological conditions. This thesis used an alternative approach of conducting mobile traverse measurements using vehicle-mounted sensors to characterize the microclimates of Toronto, ON under hot, summertime weather conditions. Sampling occurred along two routes and incorporated sampling 8 intra-urban neighbourhoods with contrasting surface properties. In addition, a rural reference and two areas identified by Toronto Public Health (TPH) as ‘high-risk’ in relation to human health were sampled – the Thorncliffe Park and Moss Park neighbourhoods. These observations were used to address the following: 1) What is the intra-urban meteorological variability observed by vehicle traverses under daytime and nighttime conditions? 2) Compared to the other neighbourhoods, do the Thorncliffe Park and Moss Park neighbourhoods exhibit microclimates associated with higher human thermal discomfort? 3) How does an urban-scale numerical model perform in predicting neighbourhood-scale microclimates? The results presented in this thesis demonstrate significant microscale intra-urban variability from 9 daytime and 3 nighttime traverses. Numerical model outputs show relatively good agreement with vehicle traverse observations, where ΔTair (mod-obs) \u3c -1.1 ºC and ΔTdew (mod-obs) \u3c -1.7 ºC in 8 of 11 evaluated vehicle traverses. The application of these results can provide insight to where in Toronto public health is at highest risk and where heat mitigation strategies are most needed

Multiple tests for the performance of different investment strategies

In the context of modern portfolio theory, we compare the out-of-sample performance of 8 investment strategies which are based on statistical methods with the out-of-sample performance of a family of trivial strategies. A wide range of approaches is considered in this work, including the traditional sample-based approach, several minimum-variance techniques, a shrinkage, and a minimax approach. In contrast to similar studies in the literature, we also consider shortselling constraints and a risk-free asset. We provide a way to extend the concept of minimum-variance strategies in the context of short-selling constraints. A main drawback of most empirical studies on that topic is the use of simple-testing procedures which do not account for the effects of multiple testing. For that reason we conduct several hypothesis tests which are proposed in the multiple-testing literature. We test whether it is possible to beat a trivial strategy by at least one of the non-trivial strategies, whether the trivial strategy is better than every non-trivial strategy, and which of the non-trivial strategies are significantly outperformed by naive diversification. In our empirical study we use monthly US stock returns from the CRSP database, covering the last 4 decades. --Asset allocation,Certainty equivalent,Investment strategy,Markowitz,Multiple tests,Naive diversification,Out-of-sample performance,Portfolio optimization,Sharpe ratio

The emergence of commercial genomics: analysis of the rise of a biotechnology subsector during the Human Genome Project, 1990 to 2004.

BackgroundDevelopment of the commercial genomics sector within the biotechnology industry relied heavily on the scientific commons, public funding, and technology transfer between academic and industrial research. This study tracks financial and intellectual property data on genomics firms from 1990 through 2004, thus following these firms as they emerged in the era of the Human Genome Project and through the 2000 to 2001 market bubble.MethodsA database was created based on an early survey of genomics firms, which was expanded using three web-based biotechnology services, scientific journals, and biotechnology trade and technical publications. Financial data for publicly traded firms was collected through the use of four databases specializing in firm financials. Patent searches were conducted using firm names in the US Patent and Trademark Office website search engine and the DNA Patent Database.ResultsA biotechnology subsector of genomics firms emerged in parallel to the publicly funded Human Genome Project. Trends among top firms show that hiring, capital improvement, and research and development expenditures continued to grow after a 2000 to 2001 bubble. The majority of firms are small businesses with great diversity in type of research and development, products, and services provided. Over half the public firms holding patents have the majority of their intellectual property portfolio in DNA-based patents.ConclusionsThese data allow estimates of investment, research and development expenditures, and jobs that paralleled the rise of genomics as a sector within biotechnology between 1990 and 2004

Maschinenbaukonjunktur 2007: Mit gemächlicherem Tempo weiter auf Rekordjagd

Die Expansion der Weltwirtschaft wird auch 2007 anhalten. Davon und von der anziehenden Binnenkonjunktur wird die deutsche Wirtschaft profitieren. Allerdings werden die Prognosen für 2007 durch die Mehrwertsteuererhöhung erschwert. Die Konjunkturforscher gehen für 2007 von einem Wachstum von annähernd 2% aus, nach 2,5% in diesem Jahr. Wie schätzt die Industrie ihre Aussichten für 2007 ein? --

Triggers at Work:The disruptive nature of triggers in psychological contracts

In the current era of global competition, innovation, digital transformation, and societal disruptions, organizations are constantly undergoing changes. These changes not only reshape organizations but also impact the psychological contracts of employees. The psychological contract refers to the mutual expectations and obligations between the organization and the employee, forming the basis for how employees evaluate their work environment. When organizations fail to fulfill their obligations, either in a direct or indirect way or as a result of procrastination in delivering on promises, it can lead to a breach of the psychological contract. This breach can have negative consequences for employees, including reduced organizational commitment, lower motivation, higher turnover intention, absenteeism, decreased job satisfaction, lower performance, and even counterproductive work behavior. In times of change, the risk of psychological contract breaches is high, making research on psychological contracts more important than ever. While there has been extensive research on the effects of psychological contract breach, little is known about the process through which it develops. In fact, the dynamics leading to contract breach have not been fully established. The studies in this thesis shows that the process of breach is non-linear rather than linear, an iterative process that involves the perceiving, appraising, and coping with triggers over time. Triggers are those selected stimuli that signal a personally relevant situation within the employment relationship that require attention. They prompt a shift from automatic processing to conscious attention and activate the mental model of the psychological contract, initiating higher order reasoning. Moreover, triggers are highly idiosyncratic, making the process of breach highly idiosyncratic too. The level of attention is the guiding principle for identifying triggers, and as a consequence, comparable or related stimuli from previous triggers will be activated faster. This is due to the memory effect, whereby a stimulus that was (repeatedly) attended to in the past will now be more efficiently identified and selected. As a result, these interconnected triggers can steer conscious attention to the psychological contract more quickly. This interconnectedness of triggers drives an accumulation process that strains the employment relationship until a threshold has been surpassed and the psychological contract breach is perceived. There are fourteen clusters of potential disruptions in which positive and negative triggers, respectively, buffer or increase the strain that is placed on the employment relationship. Hybrid triggers’ impact on the psychological contract seems to level out because of the opposing feelings experienced. The negative impact of triggers with respect to the psychological contract heightens awareness of and attention to new triggers for an average eleven days. This means that managers can use this window of opportunity to intervene and to de-escalate the cumulative effect of triggers. In this way, they can minimize the negative consequences of felt disruptions, for the benefit of employees as well as the organization. Overall, triggers fuel psychological contract dynamics, and it is important to note that more in-depth research from a process perspective is needed to gain more insight into these dynamics. Understanding the triggers as well as the interconnectedness of these triggers and their origin can help managers and organizations mitigate and prevent psychological contract breaches. This can ultimately lead to a more positive and productive employment relationship for both the employee and the employer