209 research outputs found
Development of a reliable platform for Laser-Plasma Accelerator driven Free-Electron Laser Studies
No full textFree-Electron Lasers (FELs) based on start-of-the-art radio-frequency (RF) accelerator facilities have been established as a reliable source of coherent, high-brightness x-ray beams, advancing and pushing the boundaries of a broad range of scientific applications. Their capabilities would unlock significant improvements to applications in medical imaging and semiconductor manufacturing, among others, but to make this technology available to a larger community, significant steps to reduce the cost and footprint of the accelerator facilities are required.
With the emergence of laser-plasma accelerators (LPAs) as powerful, compact alternatives to RF machines, leveraging these sources to drive FELs immediately arose as a promising application. First results of LPA-driven FEL radiation have been achieved by the community over the last few years, but reliable high-gain FEL operation, required to prove the potential of serving as a capable platform for future light source facilities, has yet to be demonstrated.
This dissertation was carried out at the Hundred TeraWatt Undulator (HTU) system, part of the Berkeley Lab Laser Accelerator (BELLA) group at Lawrence Berkeley National Laboratory (LBNL), and driven by the goal to demonstrate reliable operation of an LPA-driven FEL. The work presented here aims to achieve a more repeatable and stable LPA interaction, to enable a first demonstration of LPA-driven FEL lasing on the HTU system, and to develop an experimental platform for subsequent investigations of the LPA-driven FEL performance.
To achieve this goal, a large part of the work conducted as a part of this thesis project went towards improvements of the diagnostic capabilities of the experiment, to obtain new insights into the key parameters of the LPA interaction. These results were used to inform the need for additional stabilization systems to improve system performance, and their subsequent development, installation, and characterization are discussed as well.
The setup and commissioning of new, as well as the upgrade of existing diagnostics enabled the discovery of systematic instabilities of the laser system. Specifically variations of the laser pulse duration and energy, uncovered as part of this work, were shown to significantly impact the LPA performance. Implementing new stabilization capabilities targeted towards these variations, in combination with extensive efforts to further increase long-term reliability of the LPA interaction, yielded successful demonstration and characterization of LPA-driven FEL lasing at 420 nm. Through subsequent improvements to the laser system and operational procedures, first results exceeding 1000-fold gain from an LPA-driven FEL, with higher than 90% reliability, were achieved. During a dedicated follow-up campaign, continuous operation of the LPA-driven FEL over more than eight hours was demonstrated, while maintaining the performance of more than 90% of all shots exhibiting FEL gain. \newline
These results represent an unprecedented level of both shot-to-shot and long-term stability, as well as overall performance for LPA-driven FELs, and serve as a crucial step towards the demonstration of the technology as a viable platform for future compact FEL facilities
The Double-sidedness of racial discourse in Twains Huckleberry Finn: A Reconsideration in Bakhtins Theory
No full textMark Twains The Adventures of Huckleberry Finn (1884) has a history of having fuled an intense controversy over racial discourse. Some identified the author with his narrator Huck who, despite his personal relationship with the negro slave Jim, revealed a racially prejudiced view of his friend. In addition, the conclusion in which Jim is saved by Huck and his white friend Tom has been standing in the center of the controversy, as some interpreted it as a paradoxical satire of the racial realism of 19th Century America, while others saw it as a minstrel show in which Jim is being degraded as a buffoon. It may be worthwhile to discuss passages of the novel which have led to the controversy surrounding the racial discourse to understand how they can be interpreted by both those who have viewed the novel as racist and anti-slavery. Understanding the racial discourse in Huckleberry Finn could be supported by considering Milkhail Bakhtins theory about the relationship between the author and language, between the author and the narrator. Bakhtin argues that the author distances himself from the language and the narrator for the sake of his true intention, which may give a clue to understanding the relationship or distance between Twain and Huckleberry Finns language and between Twain and Huck.마크 트웨인(Mark Twain)의 (The Adventures of Huckleberry Finn, 1884)은 과거에 인종차별적이라는 비판과 반인종차별적이라는 옹호 사이에서 치열한 논쟁을 이끌어낸 바 있다. 이 작품의 인종문제에 대한 공공연한 논쟁은 1957년 미국 흑인지위향상협회(NAACP)가 흑인 인종의 인간성과 존엄성을 모욕한다는 이유로 ??헉??에서 사용되는 검둥이(Nigger)라는 단어를 비판하면서 시작되었다. 비평가들 사이에서도 의 인종문제에 대한 평가는 양극단으로 나뉘어졌다. 존 월리스(John Wallace)가 을 역사상 어처구니 없을 정도로 가장 인종차별적인 쓰레기라고 격렬하게 혹평한 반면에 데이비드 L. 스미스(David L. Smith)는 이 작품이 (멜빌의 작품을 제외한) 대표적인 미국소설들 중에서 단연 가장 반인종차별적이라고 옹호한다. 이 이와 같은 논란을 야기한 것은 아마도 짐(Jim)에 대한 헉(Huck)의 이중적인 태도와 논란의 핵심인 결말 부분에서 기인한 것이다
Book Review: Rethinking Children’s Spaces and Places, New Childhoods Series
No full textThis is the author accepted manuscript. The final version is available from OUP via the DOI in this record.Book review of: David Blundell. London and New York: Bloomsbury Academic. 2016. 223 pp. £15 paperback, £60 hardback, £12 e-book ISBN: 978147258149
Marilyn Weigold
No full textDr. Marilyn E. Weigold is professor of history at Pace University and serves as the official Pace University Historian. She is the author of the official history book of Pace University entitled Opportunitas: the History of Pace University. David Finn, photographs.https://digitalcommons.pace.edu/pace-women/1031/thumbnail.jp
Lagging Behind: Productivity and the Good Fortune of Canadian Provinces
No full textThe good fortune of bountiful natural resources is not enough to ensure rising incomes for Canadians in the long term. Growing labour productivity is the most important determinant of future economic welfare and on that measure, Canada is falling behind its major trading partners. Increasing labour productivity does not mean workers working harder for less money, a common canard. It means more investment in one of three factors: 1) human capital (education or other learning); 2) physical capital (plants or other infrastructure); or 3) technology. Just as an individual’s income is in the long-run dependent on how productive he or she is, so too is that of the nation as a whole. If Canada fails to improve its productivity, the incomes of both individual Canadians and the nation as a whole will fall behind those of other developed countries.Economic Growth and innovation, Canadian provinces, labour productivity
Teaching about Sampling in a Marketing Research Class
No full textIn the spirit of sharing that is characteristic of ABSEL, this paper describes a classroom exercise that the author uses to convey the meaning of a sampling distribution. Although students enrolled in marketing research courses usually are required to have passed an introductory statistics course, the concept of sampling distributions (so important in understanding sampling) seems to have eluded them. A description of the class exercise, instructions to students, and the source program is included
Lenore Hart, 31st Annual ODU Literary Festival
No full textLenore Hart is the author of the novels Waterwoman (a Barnes and Noble Discover Great New Authors title), Ordinary Springs, and Black River. Her recent novel, Becky: The Life and Loves of Becky Thatcher (2008), follows Twain’s characters Tom Sawyer, Huck Finn and Becky Thatcher — as adults — through Civil War-era Missouri, the Comstock mines of the Sierra Nevada and San Francisco. Her books for children include T. Rex at Swan Lake and The Treasure of Savage Island. She lives on the Eastern Shore of Virginia with her husband, novelist David Poyer
Mode of action and catalytic mechanisms of alginatemodifying enzymes Insights from the mannuronan C-5 epimerases and a bifunctional epimerase/lyase from Azotobacter vinelandii
No full textEnzymes are biological catalysts that work efficiently and specifically to make life possible. Among their countless tasks in living organisms, they are responsible for the diversity of material properties found in nature. If we understand how they function, it would open up immense possibilities for using them to produce materials and products from natural biomass. Alginate is a product derived from seaweed, with numerous applications due to its physical properties of viscosity and gel-formation. The properties are tuned from the composition of the two monomers β-d-mannuronic acid (M) and α-l-guluronic acid (G), found in block structures of M-blocks, G-blocks and alternating MG-blocks. G-residues are created from M-residues in these non-random patterns by the mannuronan C-5 epimerases (alginate epimerases). These enzymes are of interest to alginate producing industries, as they offer a way to tailor the alginate composition to a specific use. The thesis is concerned with understanding the molecular mechanisms behind the mode of action of the bacterial alginate epimerases AlgE from the soil bacterium Azotobacter vinelandii. They produce slightly different epimerization block patterns, and one of them has a dual alginate lyase/epimerase activity where it cleaves alginate chains through a β-elimination mechanism.
Combined experimental and computational methodology was used to elucidate how charged residues are involved in substrate binding and processivity in AlgE4, and the direction of binding and movement was modelled. NMR and ITC experiments found that the balance between processivity and substrate binding is fine-tuned through the interplay between positively and negatively charged residues. Flexible loops surrounding the binding groove might help in attachment to the substrate during processive movement. Through a mutational investigation, residue 307 located in one of these loops was found to be essential for the epimerization pattern. The product pattern of the bifunctional AlgE7 was studied using NMR, unravelling a complex interplay between the two activities and effects on activity from changing concentrations of NaCl and Ca2+. Calcium has a structural role in the enzymes, and a combined computational and experimental study of the active module of AlgE6 implies that it might also have at least an indirect role in catalysis. The catalytic mechanism of AlgE7 was further studied, and roles of active site residues were proposed. H154 is most likely the catalytic base in epimerizations and cleavage of M-residues, and Y149 is most likely the catalytic acid. R148, found in the bifunctional AlgEs in place of G148 found in AlgEs with only epimerase activity, was essential for the lyase activity. Its proposed role is in affecting Y149 to donate a proton either to the opposite face of the sugar ring, in epimerizations, or to the glycosidic bond, in chain cleavage. Finally, time-resolved NMR was used to measure and model kinetics of AlgE4, and product inhibition was affirmed with ITC.
The investigations of the mechanisms behind the AlgEs mode of action presented aid in understanding how they create their distinct product patterns. This is important for rational design of enzymes with new or improved functionalities for various needs. In addition, this work has shone new lights on an unusual system of polymer active enzymes. Although being carbohydrate-active, the epimerases are not classified in the CAZy-database. Their inclusion in the CAZypedia lexicon presented in the thesis might be a first step towards classifying these enzymes in a broader context
Mercantilists and classicals: insights from doctrinal history
No full textMonetary theory ; Economists
Shahryari on Bloor and the Strong Program
No full textIn “A Tension in the Strong Program: The Relation between the Rational and the Social”, Shahram Shahryari (2021) advances the following thesis: In his Strong Program in the sociology of science, David Bloor blames traditional philosophy of science for adopting a dualist strategy in explaining scientific developments, as it employs rational explanation for successful science and social explanation for flawed science. Instead, according to Bloor, all scientific developments should be explained monistically, i.e. in terms of social causes. This is also referred to as the Symmetry Principle, and it is a key tenet in the Strong Program. The author detects a tension here, as Bloor apparently asserts that traditional philosophy of science deploys two kinds of explanation, and simultaneously insists that there is only one kind, i.e. social explanation
- …
