1,721,433 research outputs found
Cadmium telluride as a potential conversion surface
No full textIn instruments for low energetic neutral atom imaging of space plasmas, a charge state conversion surface (CS) is used to convert neutral atoms into ions for detection. We investigated a cadmium telluride (CdTe) coated sample as a novel material candidate regarding its suit- ability to be used as a CS. We measured the efficiency of converting H and O atoms into negative ions by surface scattering, as well as their angular scattering distribution, for energies from 195 eV to 1 keV at 8 incidence angle. Also, the energy distribution of scattered particles was recorded for incident Oþ2 ions, which confirms that molecules are mainly scattered as single atoms. The mean energy loss per atom was about 45%. The negative ion yield from scattering off CdTe was up to 13% for O and about 2% for H, which is comparable to other CS coat- ings in use. CdTe shows a nearly circular angular scattering cone of width comparable to established CS materials. We conclude that CdTe is a viable CS coating material for ENA instruments in space applications
Detection of Energetic Neutral Particles
No full textThe techniques for the detection of energetic neutral atoms (ENAs) currently in use and those developed for future application in space research are reviewed. Various sources of ENA are currently the target of intense investigations. Typically, ENAs are produced from plasma ions by charge-exchange with a neutral background gas.In addition, the neutral interstellar gas penetrating the heliosphere is also an important source of ENAs. Since ENAs travel virtually unperturbed for very long distances they can be used for remote sensing of space plasma populations, for objects ranging from planetary magnetospheres at all scales to the quite distant heliospheric termination shock. The ENA sources and their respective energy ranges and fluxes are discussed briefly. The energy range of ENAs accessible to direct observation spans from about 10 eV to more than 1 MeV. On the high-energy side, the energy limit for ENAs is given by experimental limitations, but there are also good scientific reasons why ENA fluxes should be negligible at these energies. At the low-energy side, the limit is given by the available instrumentation. Several fundamentally different experimental techniques are necessary to cover such a large energy range. Moreover, not just the mere detection of the ENAs is desired but also the measurement of their arrival direction, possibly in two dimensions, is needed for many applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Development and performance evaluation of a high mass resolution time of flight laser ablation ionisation mass spectrometer
No full textThis thesis contributes to the field of analytical chemistry of solid samples by introducing a new instrument with unprecedented performance characteristics and analytical capabilities. The instrument is based on the laser ablation and ionisation time-of-flight (LI-TOF-MS) technique. This technique has the potential to provide standard free quantitative analysis with sensitivities in the ppm range and below over a wide mass range of several hundred amu and more. LI-TOF-MS was initially developed and commercialised in the 1980ies and 1990ies by a series of companies. However, the interest in the technique faded soon because the laser and computer technology at the time was not sufficient to meet the requirements of reliable quantitative analysis and alternative techniques were preferred. In this thesis, a new instrument, called LMS- GT, is presented. By using modern computer and laser- technology, this instrument achieves mass resolutions of m/Dm = 10000 and sensitivities in the ppm range and below. These performance characteristics open new perspectives for the LIMS technique to rival the dominant analytical techniques.
At the beginning of this project was a miniature LIMS prototype, from which plenty of know-how on laser ablation/ionisation mass spectrometry was collected, an empty laboratory space and the vision that is possible to build a high performance LIMS instrument for element and isotope analysis of solid samples at the micrometre scale.
This thesis documents the technology transfer from the miniature prototype to a reliable full-scale laboratory instrument that was designed from scratch. A series of pre-developments on the miniature prototype allowed to test the potential of a UHV compatible microscope, the application of a high speed switch to blank highly abundant species in the mass spectra and advanced data processing. All of these pre-developments were published in three first author papers and are included in the thesis. Also, a thorough literature research was conducted to find the best instrument layout for the new system and initial parameters for the subsequent modelling of the ion system. The extensive simulation was concurrently carried out in SIMION, ZEMAX and CATIA for ion optics, light optics and mechanical design respectively. After successful completion of the design phase, over 4000 parts and several hundreds of metres of cables were manufactured and assembled. The complete development phase is documented in this thesis.
Now, the initially empty laboratory space hosts an instrument setup of more than 2x2x2.5 m3 size. The commissioning phase showed that the design and assembly was performed correctly: Mass spectra were recorded since the first laser shot.
The thesis concludes with the presentation of the first mass spectra recorded with the new instrument and a detailed discussion of the performance parameters. It was also possible to show good agreement between the simulation and the measurement.LMT
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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