3,351 research outputs found
Tractrices, Bicycle Tire Tracks, Hatchet Planimeters, and a 100-year-old Conjecture
Geometry of the tracks left by a bicycle is closely related with the
so-called Prytz planimeter and with linear fractional transformations of the
complex plane. We describe these relations, along with the history of the
problem, and give a proof of a conjecture made by Menzin in 1906.Comment: 20 pages, 18 figure
SIMS chemical analysis of extended impacts on the leading and trailing edges of LDEF experiment AO187-2
Numerous 'extended impacts' found in both leading and trailing edge capture cells were successfully analyzed for the chemical composition of projectile residues by secondary ion mass spectrometry (SIMS). Most data were obtained from the trailing edge cells where 45 of 58 impacts were classified as 'probably natural' and the remainder as 'possibly man-made debris.' This is in striking contrast to leading edge cells where 9 of 11 impacts so far measured are definitely classified as orbital debris. Although all the leading edge cells had lost their plastic entrance foils during flight, the rate of foil failure was similar to that of the trailing edge cells, 10 percent of which were recovered intact. Ultraviolet embrittlement is suspected as the major cause of failure on both leading and trailing edges. The major impediment to the accurate determination of projectile chemistry is the fractionation of volatile and refractory elements in the hypervelocity impact and redeposition processes. This effect had been noted in a simulation experiment but is more pronounced in the LDEF capture cells, probably due to the higher average velocities of the space impacts. Surface contamination of the pure Ge surfaces with a substance rich in Si, but also containing Mg and Al, provides an additional problem for the accurate determination of impactor chemistry. The effect is variable, being much larger on surfaces that were exposed to space than in those cells that remained intact. Future work will concentrate on the analyses of more leading edge impacts and the development of new SIMS techniques for the measurement of elemental abundances in extended impacts
Feasibility of Photofrin II as a radiosensitizing agent in solid tumors - Preliminary results
Background: Photofrin II has been demonstrated to serve as a specific and selective radiosensitizing agent in in vitro and in vivo tumor models. We aimed to investigate the feasibility of a clinical application of Photofrin II. Material and Methods: 12 patients were included in the study (7 unresectable solid tumors of the pelvic region, 3 malignant gliomas, 1 recurrent oropharyngeal cancer, 1 recurrent adenocarcinoma of the sphenoid sinus). The dose of ionizing irradiation was 30-50.4 Gy; a boost irradiation of 14 Gy was added for the pelvic region. All patients were intravenously injected with 1 mg/kg Photofrin II 24 h prior to the commencement of radiotherapy. Magnetic resonance imaging (MRI) controls and in some cases positron emission tomography (PET) were performed in short intervals. The mean follow-up was 12.9 months. Results: No major adverse events were noted. Minor adverse events consisted of mild diarrhea, nausea and skin reactions. A complete remission was observed in 4/12 patients. A reduction in local tumor volume of > 45% was achieved in 4/12 patients. Stable disease was observed in 4/12 patients. 1 patient showed local disease progression after 5 months. Conclusion: The early follow-up results are encouraging regarding the feasibility of the application of Photofrin II as a radiosensitizing agent
Fast Simulation of Open Queueing Systems
We describe a technique developed by the authors for fast simulation of open queueing networks. The technique takes advantage of the recursive nature of departure times of customers in various parts of the system. The event calendar is circumvented using these recursive relationships whenever possible. A framework for identifying these recursive aspects of a network is presented. The technique involves identifying the servers in the system at which flows merge or diverge. Knowledge about the merge and diverge points defines the dependency relationships a specific customer has with other customers at each point in the system. The concept of a system level is based on these dependency relationships.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Muddled Boundaries of Digital Shrines
International audienceBased on an online ethnography study of 274 YouTube videos posted during the Virginia Tech or the Newtown massacres, this article discusses how users resort to participatory media during such mediatized events to create a digital spontaneous shrine. The assemblage of this sanctuary on a website hosting billions of user-generated contents is made possible by means of folksonomy and website architecture, and a two-fold social dynamic based on participatory commitment and the institutionalization of a collective entity. Unlike “physical” spontaneous shrines erected in public spaces, these digital shrines connect the bereaved with provocative or outrageous contributions, notably tributes from school shooting fans using participatory media to commemorate the killer’s memory. This side effect, generated by the technical properties of the platform, compromises the tranquility of the memorial and muddles the boundaries and the contents of such sanctuaries
Transport through an impurity tunnel coupled to a Si/SiGe quantum dot
Achieving controllable coupling of dopants in silicon is crucial for
operating donor-based qubit devices, but it is difficult because of the small
size of donor-bound electron wavefunctions. Here we report the characterization
of a quantum dot coupled to a localized electronic state, and we present
evidence of controllable coupling between the quantum dot and the localized
state. A set of measurements of transport through this device enable the
determination of the most likely location of the localized state, consistent
with an electronically active impurity in the quantum well near the edge of the
quantum dot. The experiments we report are consistent with a gate-voltage
controllable tunnel coupling, which is an important building block for hybrid
donor and gate-defined quantum dot devices.Comment: 5 pages, 3 figure
The Exomars Climate Sounder (EMCS) Investigation
The ExoMars Climate Sounder (EMCS) investigation is developed at the Jet Propulsion Laboratory (Principal Investigator J. T. Schofield) in collaboration with an international scientific team from France, the United Kingdom and the USA.
EMCS plans to map daily, global, pole-to-pole profiles of temperature, dust, water and CO2 ices, and water vapor from the proposed 2016 ExoMars Trace Gas Orbiter (EMTGO). These profiles are to be assimilated into Mars General Circulation Models (MGCMs) to generate global, interpolated fields of measured and derived parameters such as wind
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Microfabricated devices for performing chemical and biochemical analysis
There is growing interest in microfabricated devices that perform chemical and biochemical analysis. The general goal is to use microfabrication tools to construct miniature devices that can perform a complete analysis starting with an unprocessed sample. Such devices have been referred to as lab-on-a-chip devices. Initial efforts on microfluidic laboratory-on-a-chip devices focused on chemical separations. There are many potential applications of these fluidic microchip devices. Some applications such as chemical process control or environmental monitoring would require that a chip be used over an extended period of time or for many analyses. Other applications such as forensics, clinical diagnostics, and genetic diagnostics would employ the chip devices as single use disposable devices
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