571 research outputs found
Francis, John Wakefield
No full textA carte-de-visite card of John Wakefield Francis, 1789-1861, an American author and physician.https://digitalcommons.lmunet.edu/allmcdv/1190/thumbnail.jp
Numerical and Experimental Studies of Wakefield Accelerators
No full textThis thesis is based on work done by the author on the development of laser wakefield accelerators.Wakefield acceleration in plasmas is a promising technique to provide the next generation of accelerating structures and particle beams. Plasmas can sustain electric fields that are many orders of magnitude stronger than those possible in conventional accelerators. Other benefits of wakefield accelerators are that electron beams produced inside the plasma can be generated with high peak current and ultra-low emittance.These strongly accelerating structures can reduce the size of particle accelerators, making them more available, for example in hospitals, or to increase the energy in particle colliders.In wakefield acceleration, a driver is used to excite a plasma wave.The acceleration of charged particles takes place in a plasma wave excited by, and co-propagating with, the driver. The driver can be a laser pulse or a bunch of charged particles.However, many technical challenges remain to be solved before a reliable particle source can be realized based on this technology.This thesis describes numerical studies performed using particle-in-cell simulations and experimental work using high-intensity laser pulses, with the aim of improving our knowledge on wakefield accelerators. The work presented here focuses on three different topics: trapping mechanisms, achieving higher electron energies and improvement of the betatron X-rays generated.In particular, trapping in a density down-ramp, ionization induced trapping, and trapping by colliding pulses have been investigated numerically and experimentally.A novel guidance technique for high-intensity laser pulses is suggested, the merging of two laser wakefields is experimentally demonstrated and suggested as a possible means of staging wakefield accelerators, and the possibility of carrying out a beam-driven plasma wakefield experiment is investigated through simulations. An improved X-ray source based on laser wakefield acceleration and enhancement of the betatron oscillations through direct laser acceleration is investigated and two applications are demonstrated
Pension Provision and Retirement Saving: Lessons from the United Kingdom
No full textWe describe the trajectory of pension reform in the United Kingdom, which has focussed on keeping the cost of public pension programmes down during a period of steady population ageing whilst attempting to maintain an adequate minimum level of income security for low income households in retirement. Instruments for achieving these aims have been to target public benefits on low income households, permitting individuals to opt out of the second tier of the public programme into private retirement accounts, and the use of tax incentives to encourage additional private retirement saving. Frequent reforms to the pension programme raise the question of whether households can make reasonable private retirement saving provision in the light of growing complexity and potential shortcomings in individual decision-making. This paper sheds some light on these issues.pensions, social security, retirement saving
L'attualismo e il suo autore. Prospettiva per la ricerca futura su Gentile
No full textThis article describes the recent reception of Giovanni Gentile and his doctrine of actualism, describing the philosopher's rehabilitation as a major Italian thinker and actualism as a provocative account of socially situated consciousness. The discussion then turns to the future of Gentile studies, focusing on ways in which the ahistorical methods of analytic philosophy might help restore actualism and its author to their proper place in the philosophical canon
sj-pdf-2-pmj-10.1177_02692163221074876 – Supplemental material for Risk factors associated with poorer experiences of end-of-life care and challenges in early bereavement: Results of a national online survey of people bereaved during the COVID-19 pandemic
No full textSupplemental material, sj-pdf-2-pmj-10.1177_02692163221074876 for Risk factors associated with poorer experiences of end-of-life care and challenges in early bereavement: Results of a national online survey of people bereaved during the COVID-19 pandemic by Lucy Ellen Selman, DJJ Farnell, M Longo, S Goss, K Seddon, A Torrens-Burton, CR Mayland, D Wakefield, B Johnston, A Byrne and E Harrop in Palliative Medicine</p
sj-pdf-1-pmj-10.1177_02692163221074876 – Supplemental material for Risk factors associated with poorer experiences of end-of-life care and challenges in early bereavement: Results of a national online survey of people bereaved during the COVID-19 pandemic
No full textSupplemental material, sj-pdf-1-pmj-10.1177_02692163221074876 for Risk factors associated with poorer experiences of end-of-life care and challenges in early bereavement: Results of a national online survey of people bereaved during the COVID-19 pandemic by Lucy Ellen Selman, DJJ Farnell, M Longo, S Goss, K Seddon, A Torrens-Burton, CR Mayland, D Wakefield, B Johnston, A Byrne and E Harrop in Palliative Medicine</p
sj-pdf-3-pmj-10.1177_02692163221074876 – Supplemental material for Risk factors associated with poorer experiences of end-of-life care and challenges in early bereavement: Results of a national online survey of people bereaved during the COVID-19 pandemic
No full textSupplemental material, sj-pdf-3-pmj-10.1177_02692163221074876 for Risk factors associated with poorer experiences of end-of-life care and challenges in early bereavement: Results of a national online survey of people bereaved during the COVID-19 pandemic by Lucy Ellen Selman, DJJ Farnell, M Longo, S Goss, K Seddon, A Torrens-Burton, CR Mayland, D Wakefield, B Johnston, A Byrne and E Harrop in Palliative Medicine</p
Mrs. and Mr. Wakefield: intertextualidad y reescritura de "Wakefield" de Nathaniel Hawthorne en la novela <i>La mujer de Wakefield</i> de Eduardo Berti
No full textHacia 1999, el escritor argentino Eduardo Berti, con la publicación de su novela La mujer de Wakefield, traza un arco que anuda, mediante una relación intertextual, casi dos siglos y dos hemisferios continentales. En efecto, el cuento “Wakefield” del escritor norteamericano decimonónico Nathaniel Hawthorne, se presenta como texto fuente del texto meta de Berti. Amén de apoderarse de algunos elementos de la diégesis propias del cuento del autor norteamericano, mediante estrategias de expansión, urde el propio, como un rebote cultural de su antecedente. Donde Hawthorne apela a la síntesis, la condensación y la retórica alegórica (propias del cuento), Berti acudirá a una poética sin moralejas, en tanto desata zonas del texto fuente que se hallaban tan sólo insinuadas, latentes o inexistentes. Queda claro que este texto se inscribe en una tradición poderosa de la literatura argentina reciente (Borges, Puig, Piglia, Kohan), en la cual textos del pasado son reescritos y traducen, mediante nuevas poéticas, lecturas renovadoras de ese pasado cultural.By 1999, the Argentine writer Eduardo Berti, with the publication of his novel The Woman in Wakefield draws an arc, through intertextual relationship, that ties nearly two centuries and two continental hemispheres. Indeed, the short story "Wakefield" by the nineteenth-century American writer Nathaniel Hawthorne is presented as text font of the text scopum by Berti. Amen to take over some elements of the diegesis from the American author´s Tale by expansion strategies, weaves his own, as a cultural rebound of its antecedent. Where Hawthorne appeals to the synthesis, condensation and allegorical rhetoric (own tale), Berti attends a poetry without morals; setting free those areas of the source text which have been only insinuated, dormant or nonexistent. It is clear that this text is part of a tradition Argentina powerful recent literature (Borges, Puig, Piglia, Kohan) in which past texts are rewritten and translated through new poetic, renovating readings of that cultural past.Facultad de Humanidades y Ciencias de la Educació
Metamaterial structures for Wakefield acceleration and high power microwave generation
No full textThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2019Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 209-218).This thesis presents the theoretical and experimental investigation of the interaction of metamaterial structures with electron beams for two applications: wakefield acceleration and high power microwave generation. Under the topic of wakefield acceleration, on the theoretical side, several metamaterial structures have been designed and simulated. The novel phenomenon of reversed Cherenkov radiation has been found to enhance the beam-wave interaction in metamaterials. A metallic wagon wheel metamaterial structure was designed and built for use in an experiment at the Argonne Wakefield Accelerator (AWA) Facility. On the experimental side, this thesis presents the first demonstration of high-power, reversed Cherenkov wakefield radiation by short electron bunches passing through the wagon wheel structure at the AWA. Single 45 nC electron bunches of 65 MeV energy traversing the structure generated up to 25 MW in 2 ns pulses at 11.4 GHz, in excellent agreement with theory.Two bunches of 85 nC with appropriate temporal spacing generated up to 80 MW by coherent wakefield superposition. If this power were applied to a trailing witness bunch in a collinear wakefield accelerator, it would provide an accelerating gradient of 75 MV/m. Under the topic of high power microwave generation, on the theoretical side, an analytical theory has been developed to predict the novel Cherenkov-cyclotron interaction in metamaterial-based microwave devices. An S-band metamaterial-loaded waveguide with reverse symmetry has been designed and built to work with the Cherenkov-cyclotron interaction. On the experimental side, this thesis presents the experimental results of the metamaterial-loaded waveguide built at MIT. Power levels to 2.9 MW at 2.4 GHz in full 1 [mu]s pulses were generated by an electron beam of up to 490 kV of voltage and 84 A of current.Frequency tuning measurements verified that pulses above 1 MW of output power were only seen in the Cherenkov-cyclotron mode. With these results, this thesis demonstrates the unique features of metamaterial structures that are very attractive for high-gradient wakefield accelerators and high power microwave sources. Advantages include the high shunt impedance for intense beam-wave interaction; the simple and rugged structure; and a large parameter space for various optimization goalsby Xueying Lu.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Physic
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