3,043 research outputs found

    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

    Three-dimensional dielectric photonic crystal structures for laser-driven acceleration,” Phys.

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    We present the design and simulation of a three-dimensional photonic crystal waveguide for linear laserdriven acceleration in vacuum. The structure confines a synchronous speed-of-light accelerating mode in both transverse dimensions. We report the properties of this mode, including sustainable gradient and optical-to-beam efficiency. We present a novel method for confining a particle beam using optical fields as focusing elements. This technique, combined with careful structure design, is shown to have a large dynamic aperture and minimal emittance growth, even over millions of optical wavelengths

    Three-dimensional dielectric photonic crystal structures for laser-driven acceleration

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    We present the design and simulation of a three-dimensional photonic crystal waveguide for linear laser-driven acceleration in vacuum. The structure confines a synchronous speed-of-light accelerating mode in both transverse dimensions. We report the properties of this mode, including sustainable gradient and optical-to-beam efficiency. We present a novel method for confining a particle beam using optical fields as focusing elements. This technique, combined with careful structure design, is shown to have a large dynamic aperture and minimal emittance growth, even over millions of optical wavelengths

    Major trends in mobility technology research and development: Overview of the results of the NSF-WTEC European study

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    Mobility technologies, including wheelchairs, prostheses, joint replacements, assistive devices, and therapeutic exercise equipment help millions of people participate in desired life activities. Yet, these technologies are not yet fully transformative because many desired activities cannot be pursued or are difficult to pursue for the millions of individuals with mobility related impairments. This WTEC study, initiated and funded by the National Science Foundation, was designed to gather information on European innovations and trends in technology that might lead to greater mobility for a wider range of people. What might these transformative technologies be and how might they arise? Based on visits to leading mobility technology research labs in western Europe, the WTEC panel identified eight major trends in mobility technology research. This commentary summarizes these trends, which are then described in detail in companion papers appearing in this special issue

    Elective Open Suprarenal Aneurysm Repair in England from 2000 to 2010 an Observational Study of Hospital Episode Statistics

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    Background: Open surgery is widely used as a benchmark for the results of fenestrated endovascular repair of complex abdominal aortic aneurysms (AAA). However, the existing evidence stems from single-centre experiences, and may not be reproducible in wider practice. National outcomes provide valuable information regarding the safety of suprarenal aneurysm repair. Methods: Demographic and clinical data were extracted from English Hospital Episodes Statistics for patients undergoing elective suprarenal aneurysm repair from 1 April 2000 to 31 March 2010. Thirty-day mortality and five-year survival were analysed by logistic regression and Cox proportional hazards modeling. Results: 793 patients underwent surgery with 14% overall 30-day mortality, which did not improve over the study period. Independent predictors of 30-day mortality included age, renal disease and previous myocardial infarction. 5-year survival was independently reduced by age, renal disease, liver disease, chronic pulmonary disease, and known metastatic solid tumour. There was significant regional variation in both 30-day mortality and 5-year survival after risk-adjustment. Regional differences in outcome were eliminated in a sensitivity analysis for perioperative outcome, conducted by restricting analysis to survivors of the first 30 days after surgery. Conclusions: Elective suprarenal aneurysm repair was associated with considerable mortality and significant regional variation across England. These data provide a benchmark to assess the efficacy of complex endovascular repair of supra-renal aneurysms, though cautious interpretation is required due to the lack of information regarding aneurysm morphology. More detailed study is required, ideally through the mandatory submission of data to a national registry of suprarenal aneurysm repair

    Spitzer Secondary Eclipse Observations of Five Cool Gas Giant Planets and Empirical Trends in Cool Planet Emission Spectra

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    In this work we present Spitzer 3.6 and 4.5 micron secondary eclipse observations of five new cool (<1200 K) transiting gas giant planets: HAT-P-19b, WASP-6b, WASP-10b, WASP-39b, and WASP-67b. We compare our measured eclipse depths to the predictions of a suite of atmosphere models and to eclipse depths for planets with previously published observations in order to constrain the temperature- and mass-dependent properties of gas giant planet atmospheres. We find that the dayside emission spectra of planets less massive than Jupiter require models with efficient circulation of energy to the night side and/or increased albedos, while those with masses greater than that of Jupiter are consistently best-matched by models with inefficient circulation and low albedos. At these relatively low temperatures we expect the atmospheric methane to CO ratio to vary as a function of metallicity, and we therefore use our observations of these planets to constrain their atmospheric metallicities. We find that the most massive planets have dayside emission spectra that are best-matched by solar metallicity atmosphere models, but we are not able to place strong constraints on metallicities of the smaller planets in our sample. Interestingly, we find that the ratio of the 3.6 and 4.5 micron brightness temperatures for these cool transiting planets is independent of planet temperature, and instead exhibits a tentative correlation with planet mass. If this trend can be confirmed, it would suggest that the shape of these planets' emission spectra depends primarily on their masses, consistent with the hypothesis that lower-mass planets are more likely to have metal-rich atmospheres.Comment: 16 pages, 14 figures, accepted for publication in Ap