1,721,036 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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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A digital-electronic video-rate reconstruction system for magnetic resonance imaging
No full textA digital-electronic video-rate reconstruction system for Magnetic Resonance Imaging (MRI) has been designed to first order. The maturation of ultra-fast acquisition techniques in MRI has produced the need for a reconstruction system that will enable dynamic processes to be viewed on-line. Conventional reconstruction hardware is not configured for real-time reconstruction and previous developments are limited in accuracy and flexibility. The real-time reconstruction system presented here consists of three main subsystems. A digitizer interfaces with an MR scanner to digitize data matrices of resolutions up to 256 x 256 at arbitrary rates up to video rates. A Fourier processor performs either 2D Fourier transformation or projection filtering on the digitized data at video-rates. A backprojector performs the backprojection operation on filtered-projection data at video-rates. The complete system would be able to reconstruct data acquired from nearly any acquisition technique. True real-time MRI is then possible
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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Multi-spectral confocal microendoscope for in-vivo imaging
No full textThe concept of in-vivo multi-spectral confocal microscopy is introduced. A slit-scanning multi-spectral confocal microendoscope (MCME) was built to demonstrate the technique. The MCME employs a flexible fiber-optic catheter coupled to a custom built slit-scan confocal microscope fitted with a custom built imaging spectrometer. The catheter consists of a fiber-optic imaging bundle linked to a miniature objective and focus assembly. The design and performance of the miniature objective and focus assembly are discussed. The 3mm diameter catheter may be used on its own or routed though the instrument channel of a commercial endoscope. The confocal nature of the system provides optical sectioning with 3μm lateral resolution and 30mum axial resolution. The prism based multi-spectral detection assembly is typically configured to collect 30 spectral samples over the visible chromatic range. The spectral sampling rate varies from 4nm/pixel at 490nm to 8nm/pixel at 660nm and the minimum resolvable wavelength difference varies from 7nm to 18nm over the same spectral range. Each of these characteristics are primarily dictated by the dispersive power of the prism. The MCME is designed to examine cellular structures during optical biopsy and to exploit the diagnostic information contained within the spectral domain. The primary applications for the system include diagnosis of disease in the gastro-intestinal tract and female reproductive system. Recent data from the grayscale imaging mode are presented. Preliminary multi-spectral results from phantoms, cell cultures, and excised human tissue are presented to demonstrate the potential of in-vivo multi-spectral imaging
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High-resolution diffusion imaging with DIFRAD-FSE (diffusion-weighted radial acquisition with fast spin echo) MRI
No full textA novel MRI method, DIFRAD-FSE (D̲i̲f̲fusion with R̲adial A̲cquisition of D̲ata with F̲ast S̲pin-E̲cho) is presented that enables rapid, high-resolution, multi-shot diffusion-weighted MRI without significant artifacts due to motion. Following a diffusion-weighted spin-echo preparation, multiple radial lines of Fourier data are acquired using spin-echo refocusing. Data can be acquired in either 2D or 3D Fourier space. Motion correction is accomplished via one of four correction techniques: phase correction, shift correction, a combination of the phase and shift correction, or magnitude. Images from a radial data set are reconstructed with filtered back projection reconstruction. Results from human brain imaging will demonstrate the ability of DIFRAD-FSE to acquire high-resolution images without significant artifacts due to motion in both 2D and 3D. Results from liver and heart imaging demonstrate the versatility of the 2D DIFRAD-FSE
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Noise-limited performance of a hybrid detector and high-resolution display monitors.
No full textIn this dissertation I describe the analysis of two types of electronic devices. The first is an image intensifier/photomultiplier combination used in a laser communications receiver. The second type is high resolution display monitors to be used in digital radiology. The analysis of these devices centered on the influence of noise on their performance though I also measured other device characteristics. I present here a method of characterizing noise that can be used for a variety of detector and display devices; however, I concentrated my analysis on an optical communication receiver by ITT and high resolution display monitors by MegaScan, Tektronix and US Pixel. The optical receiver is called a hybrid device because it combines an image intensifier (II) and a photomultiplier tube. The II has a large active area and its specially processed photocathode gives it an extended red response. The photomultiplier tube (PMT) provides a high gain, low noise and low dark current. The hybrid tube had a maximum gain of 8 x 10⁶, a noise factor of 1.64 and an information capacity of 1.3 x 10⁶ bits per second. The high resolution monitors we examined were black and white monitors with a pixel matrix of at least 1024 x 1536 pixels and 256 grey levels. The maximum luminance from the monitors was 88 ft-Lamberts (for the US Pixel monitor) and a maximum information capacity of 8.9 x 10⁶ bits (for the MegaScan monitor). We measured spatial and temporal noise for the monitors. Spatial noise was the dominant noise, except at low grey levels. Veiling glare was evident in all three monitors and dramatically reduced the dynamic ranges of the monitors.This item was digitized from a paper original and/or a microfilm copy. If you need
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Computer-generated holograms for free-space optical interconnects
No full textThis dissertation describes an investigation into the use of computer generated holograms to implement free-space optical interconnects. Computer generated holograms are discussed in terms of their theory of operation, design principles, fabrication techniques, optical performance, and sources of error. To motivate the research, discussion of an optoelectronic computing module is included; the device uses computer generated holograms to implement large-fanout optical interconnects. The emphasis of this dissertation is not on a specific application, rather it is focused on understanding the abilities and limitations of computer generated holograms. New contributions are made in the area of hologram design, both individual and multifaceted elements. These design techniques were built into a computer aided design tool (SPIDER 3.0), which was developed to promote the use of computer generated holograms. Hologram fabrication techniques and optical performance are also carefully characterized. Measurements show that performance is poorer than what is expected. Several significant sources of error are identified in the design and fabrication of computer generated holograms, and these effects are shown to explain most of the measured results. The dissertation concludes that computer generated holograms are currently limited by errors in fabrication and in the approximate diffraction theories employed in the design process. While the optical performance of the holograms is not as good as expected, the results are shown to be adequate for successful use in real applications.This item was digitized from a paper original and/or a microfilm copy. If you need higher-resolution images for any content in this item, please contact us at [email protected] file replaced with corrected file October 2023
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Remote-access slit-scanning confocal microscope for in vivo tumor diagnosis
No full textMicroscopic fluorescence imaging of thick biological tissue has been successfully demonstrated with a fiber-based, slit-scanning, confocal microscope. The system developed under this research consists of an illumination arm, a fiber-optic imaging system, and a detection arm. The illumination arm is an anamorphic optical system that converts a circular, laser beam into a cylindrical beam forming a line image at the proximal face of the fiber-optic relay. This relay system is comprised of a fiber-optic imaging bundle, a miniature objective lens, and a miniature hydraulic positioning mechanism. It delivers illumination to a remote sample and simultaneously collects the fluorescence from the sample. The miniature objective lens and positioning mechanism were specially designed and fabricated for this system, allowing for high resolution imaging and optical sectioning in-vivo. The detection arm relays the fluorescence image at the proximal face of the fiber-optic relay with magnification onto a two-dimensional CCD. Characterization of the system has demonstrated a lateral resolution of three microns. The axial resolution when imaging a point object is 10 microns. When imaging a planar object, the axial resolution is 25 microns. Images are acquired at a rate of 2-4 frames per second and the imaging performance has been evaluated with different biological models including animal peritoneal tissue and human prostate tissue in-vitro. In-vivo images of human skin and rat peritoneum have also been acquired to demonstrate that patient motion does not adversely affect the performance of the system. These in-vitro and in vivo images demonstrate the capability of the system to resolve cell nuclear morphology, to visualize cell density and organization, and to image at selected depths below the tissue surface.This item was digitized from a paper original and/or a microfilm copy. If you need higher-resolution images for any content in this item, please contact us at [email protected] file replaced with corrected file September 2023
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