3,590 research outputs found

    Microfabrication of Laser-Driven Accelerator Structures

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    We discuss the potential for using microfabrication techniques for laser-driven accelerator construction. We introduce microfabrication processes in general, and then describe our investigation of a particular trial process. We conclude by considering the issues microfabrication raises for possible future structures.Comment: 7 pages, 3 figures; Submitted to Tenth Advanced Accelerator Concepts Workshop (AAC 2002), June 23--28, 2002, Mandalay Beach, California (AIP Conference Proceedings

    Photonic Crystal Laser Accelerator Structures

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    Photonic crystals have great potential for use as laser-driven accelerator structures. A photonic crystal is a dielectric structure arranged in a periodic geometry. Like a crystalline solid with its electronic band structure, the modes of a photonic crystal lie in a set of allowed photonic bands. Similarly, it is possible for a photonic crystal to exhibit one or more photonic band gaps, with frequencies in the gap unable to propagate in the crystal. Thus photonic crystals can confine an optical mode in an all-dielectric structure, eliminating the need for metals and their characteristic losses at optical frequencies. We discuss several geometries of photonic crystal accelerator structures. Photonic crystal fibers (PCFs) are optical fibers which can confine a speed-of-light optical mode in vacuum. Planar structures, both two- and three-dimensional, can also confine such a mode, and have the additional advantage that they can be manufactured using common microfabrication techniques such as those used for integrated circuits. This allows for a variety of possible materials, so that dielectrics with desirable optical and radiation-hardness properties can be chosen. We discuss examples of simulated photonic crystal structures to demonstrate the scaling laws and trade-offs involved, and touch on potential fabrication processes.Comment: 3 pages, 3 figures; Submitted to Particale Accelerator Conference (PAC 2003), May 12-16, 2003, Portland, Oregon (IEEE

    Photonic crystal laser-driven accelerator structures

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    Laser-driven acceleration holds great promise for significantly improving accelerating gradient. However, scaling the conventional process of structure-based acceleration in vacuum down to optical wavelengths requires a substantially different kind of structure. We require an optical waveguide that (1) is constructed out of dielectric materials, (2) has transverse size on the order of a wavelength, and (3) supports a mode with speed-of-light phase velocity in vacuum. Photonic crystals--structures whose electromagnetic properties are spatially periodic--can meet these requirements. We discuss simulated photonic crystal accelerator structures and describe their properties. We begin with a class of two-dimensional structures which serves to illustrate the design considerations and trade-offs involved. We then present a three-dimensional structure, and describe its performance in terms of accelerating gradient and efficiency. We discuss particle beam dynamics in this structure, demonstrating a method for keeping a beam confined to the waveguide. We also discuss material and fabrication considerations. Since accelerating gradient is limited by optical damage to the structure, the damage threshold of the dielectric is a critical parameter. We experimentally measure the damage threshold of silicon for picosecond pulses in the infrared, and determine that our structure is capable of sustaining an accelerating gradient of 300 MV/m at 1550 nm. Finally, we discuss possibilities for manufacturing these structures using common microfabrication techniques.Comment: Ph.D. Thesis, Stanford Universit

    Venue for Offshore Environmental Crimes: The Seaward Limits of the Federal Judicial Districts

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    Consider the following scenario: USA Oil, an American company incorporated in Delaware with its principal place of business in California, has been conducting ongoing oil drilling operations in the Gulf of Mexico. The company operates three oil platforms off the Texas coast. One is located two miles offshore, another six miles offshore, and the third ten miles offshore. Federal authorities receive notice that on several occasions since the company began operating these rigs, it deliberately allowed large quantities of oil to leak into the Gulf from each of them. The government seeks to indict USA Oil on three counts of violating the Clean Water Act, as amended by the Oil Pollution Act of 1990. The U.S. Attorney\u27s office in the Southern District of Texas coordinates the investigation as all relevant documents, witnesses, and evidence are located in that district. All of USA Oil\u27s executive officers reside near the company\u27s principal place of business in San Diego, in the Southern District of California. The rig foreman in charge of USA Oil\u27s Gulf of Mexico operations at the time the violations occurred has since left the company and now lives and works for another company near Prudhoe Bay, in the District of Alaska. Where should the government file the indictments? The United States Constitution requires that the trial be held in the district in which the crime was committed, and the government must prove that venue is proper by a preponderance of the evidence. Failure to prove venue in a criminal trial precludes a conviction, and if a verdict of acquittal results from that failure, such failure leads to a double jeopardy bar to reindictment in the appropriate district. Therefore, the government must make an airtight determination at the outset of the prosecution as to where proper venue lies. There are three separate venue provisions for the trial of federal crimes. 18 U.S.C. § 3237 stipulates that venue for offenses begun in one district and completed in another, or for offenses committed in more than one district, lies in any of the districts in which the crime occurred. However, it is the other two provisions which are relevant to the problem of venue for crimes committed offshore but within the territorial sea of the United States. Federal Rule of Criminal Procedure 18 ( Rule 18 ) sets venue for crimes committed within a single judicial district, while 18 U.S.C. § 3238 ( Section 3238 ) applies to crimes committed outside of any judicial district. In the face of the current ambiguity as to the limits between state and domestic federal sovereignty in the marginal seas, there is presently no point at which a definitive geographic line can be drawn dictating where Rule 18 ends and Section 3238 begins. Though in the past there have been few federal criminal prosecutions of environmental crimes committed in the territorial sea, several U.S. Attorney\u27s Offices have become more active in this area, and the Environmental Crimes Section of the United States Department of Justice recently formed a Vessel and International Pollution Unit specifically to address these crimes. Thus, the frequency of prosecutions of this type will probably increase in the near future, placing an even greater premium on the need for a clear resolution of this issue. This Note explores the question of venue for crimes committed offshore but within the twelve-mile seaward limit of federal territorial jurisdictions for the purpose of determining where the seaward limit of the federal judicial district lies and thus where Rule 18 ends and Section 3328 begins. Part II discusses Rule 18 and Section 3238 and illustrates the importance of fixing the location of state boundaries in order to make the proper choice between the two provisions. Because there is no definite answer to the seaward extent of state territory, the possibilities must be extracted from the historical development of legal doctrines regarding offshore boundaries. Therefore, Part III examines the history of the territorial sea and the development of offshore federalism. Part IV discusses the various possible limits of state territory and analyzes the implications of each in the context of the USA Oil hypothetical. Part V proposes a new paradigm for offshore criminal venue that unravels the web of uncertainty currently plaguing the issue

    Quantitative Endothelial Cell Monolayer Impedance Sensing and Analysis

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    The electrical analysis of the biological material has been in existence since the turn of last century. A novel application of this technology to cellular monolayers was implemented by Giaever and Keese 20 years ago with their Electrical Cell-Substrate Impedance Sensing (ECIS) system. The capabilities of a real-time system for endothelial impedance measurement are of immense importance. The endothelium is typically the body’s first contact with stimuli and its reaction to medical conditions of inflammation, disease, and body response are of great significance to understanding the physiology of numerous conditions ranging from heart, lung, and renal disease, to intestinal diseases. It is the purpose of this Master’s thesis to analyze and optimize the ECIS system for making quantitative measurements of endothelial monolayer impedance, and accurately applying the results to a thoroughly reviewed analysis package in order to produce accurate cellular resistance parameters. The optimization of data acquisition (DAQ) is accomplished by systematic noise recognition, examination, and minimization; a task that has previously been unexplored in any studies using the ECIS system. Harmonic, 60 Hz, and Gaussian noise sources were well documented in unfiltered data and successfully minimized in the DAQ. Analog to digital (A/D) noise was found to be the lower limit of reducible noise and was properly documented and considered in analysis. Contamination of the electrode arrays from manufacturing processes and proper electrical connection were also found to be of concern to the proper functioning of the system. Analysis of the optimized acquired data was performed in the LabVIEW programming environment, as it offered a more flexible software package than that provided by the current commercially available ECIS system. The optimized system was applied to a further look into hand arm-vibration syndrome (HAVS) and it was concluded that the acceleration exposure dose, incorrectly calculated from the international standards, did not elicit an acute endothelial inflammation response by our measurements. The cumulative result of this study is that the ECIS system has been optimized and various unresolved sources of error were corrected for a more accurate real-time measurement of the endothelial monolayer barrier function in response to stimuli

    William Arbuthnot Lane (1856-1943): Surgical Innovator and His Theory of Autointoxication.

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    William Arbuthnot Lane contributed to the advancement of many fields of orthopedics, otolaryngology, and general surgery. He is credited for his no-touch technique and the invention of long-handled instruments, some of which are still in use today, to minimize tissue handling. He is most well known for his hypothesis that slowing of gastric contents could cause a variety of ailments and this became known as Lane\u27s disease. Although his surgical treatment of Lane\u27s disease is now defunct, it advanced the surgical technique in colorectal surgery. It seems likely that some of Lane\u27s autointoxication patients would be classified today as patients with colonic inertia, diverticulitis, colonic volvulus, and megacolon or, which are all treated with colectomy. Lane was a pioneer in multiple fields and a true general surgeon. He advanced colorectal surgery immensely and propelled the field of surgery into a new era

    Finally a Case for Collaborative VR?: The Need to Design for Remote Multi-Party Conversations

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    Amid current social distancing measures requiring people to work from home, there has been renewed interest on how to effectively converse and collaborate remotely utilizing currently available technologies. On the surface, VR provides a perfect platform for effective remote communication. It can transfer contextual and environmental cues and facilitate a shared perspective while also allowing people to be virtually co-located. Yet we argue that currently VR is not adequately designed for such a communicative purpose. In this paper, we outline three key barriers to using VR for conversational activity : (1) variability of social immersion, (2) unclear user roles, and (3) the need for effective shared visual reference. Based on this outline, key design topics are discussed through a user experience design perspective for considerations in a future collaborative design framework

    Active progress bars : aiding the switch to temporary activities

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    International audienceCan we design an interface to help people make use of the idle time spent looking at progress bars? We propose to augment progress bars with user-controlled functionalities facilitating the switch to temporary activities. We propose a taxonomy of waiting period contexts and possible temporary tasks, then report on participatory design sessions, and a follow-up survey. Finally we describe an early prototype of active progress bar and report a small controlled experiment used to identify the impact of the tool on primary task satisfaction. The findings suggest that Active Progress Bars lead to significantly higher satisfaction when compared to a control condition

    Influence of internal climate variability on Indian Ocean Dipole properties

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    The Indian Ocean Dipole (IOD) is the dominant mode of interannual variability over the tropical Indian Ocean (IO) and its future changes are projected to impact the climate and weather of Australia, East Africa, and Indonesia. Understanding the response of the IOD to a warmer climate has been largely limited to studies of individual coupled general circulation models or multi-model ensembles. This has provided valuable insight into the IOD’s projected response to increasing greenhouse gases but has limitations in accounting for the role of internal climate variability. Using the Community Earth System Model Large Ensemble (CESM-LE), the IOD is examined in thirty-five present-day and future simulations to determine how internal variability influences properties of the IOD and their response to a warmer climate. Despite small perturbations in the initial conditions as the only difference between ensemble members, significant relationships between the mean state of the IO and the IOD arise, leading to a spread in the projected IOD responses to increasing greenhouse gases. This is driven by the positive Bjerknes feedback, where small differences in mean thermocline depth, which are caused by internal climate variability, generate significant variations in IOD amplitude, skewness, and the climatological zonal sea surface temperature gradient

    Causal effects of wiki site design on anxiety and usability

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    Within society Information Technology (IT) is becoming pervasive. This is no more pronounced than in Higher Education where IT is almost ubiquitously used. Current developments have also seen Web 2.0 tools such as wikis being used in pedagogical contexts. Research in computer anxiety has identified that quality of initial experience may be important in the onset of anxiety towards IT. However the concept of computer anxiety is too vague to reflect likely reactions to specific IT scenarios especially in interactions with social technology such as wikis. Although wikis are growing in popularity little is known about users‟ emotional reaction towards contributing to them, how their experiences shape these emotions as well as the users‟ view of usability above that mentioned in qualitative research. Due to the interface, social and flexible nature of wikis users may be anxious towards editing. This research aims to offer causal insight into the influence of wiki site design characteristics on anxiety towards wiki editing and users usability evaluation of wiki editing experiences. Three experiment-based studies are presented addressing the effects of site characteristics such as in-built training spaces (i.e. tutorials and sandboxes commonly used on wikis), user editing identity as well as aspects inherent to wiki sites such as content flexibility, on anxiety felt by users in editing scenarios and users usability rating of their editing experiences. The research also aimed to identify whether initial experiences affected anxiety about further editing, as suggested by computer anxiety research, or whether emotions are only affected during editing experience. The findings of the initial study on in-built training spaces suggest that the concept of wiki anxiety measured in this research more accurately reflects anxiety experienced during interaction than computer anxiety. Additionally the in-built training spaces using tutorials were seen to lead to better first experiences for novice users in using the wiki markup interface than those without (such as when experiencing sandbox training spaces and no training). Similarly the presence of a tutorial reduced wiki anxiety during interaction but did not affect anxiety towards future editing. From these findings the work advanced to study the effect of identity salience on wiki anxiety during editing and wiki usability focusing on contributing content using a user group with experience editing wikis. This was so as to explore the effect of wiki characteristics on user experience variables above that from first exposure anxiety likely in novice users. The research found that participants were less anxious when editing the wiki anonymously than when editing using a pseudonym and full name identity. There was however no effect of identity salience on usability rating. Additionally the type of edit conducted by participants, in terms of addition or deletion and replacement of content, did not have a significant effect on either anxiety during editing or usability evaluation. Further research exploring the effect of flexibility and other user behaviour on user anxiety and usability evaluation when contributing subsequently found that there was no significant effect of flexibility on the wiki user experience variables. The work demonstrates successful empirical evaluation of the wiki user editing experience can be achieved and can lead to important causal insight into the effects of wiki site design on the users‟ experience. It also identifies aspects of the site that can lead to the reduction of anxiety towards editing during interaction and influence usability rating towards the system
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