81,801 research outputs found
XLV. Xosé Maria Alvarez Blazquez
No full textIntroduzione bio-bibliografica alla poesia di X. M. Alvarez Blazquez, con antologia di testi e traduzione
Dataset: Alvarez varifocal X-ray lens
No full textThese are processed datasets used for the publication "Alvarez varifocal X-ray lens". File are in the *.dat and HDF format. .
If you require more information and additional data, please contact the corresponding author of this publication, at [email protected]
Harry Bridges by Harry Alvarez
No full textSculpture20” x 23” x 20”Excellent conditionHarry Bridges (1901-1990) was a prominent 20th Century Labor Leader. He led the pivotal 1934 West Coast waterfront workers strike. After founding the ILWU, he served as its President for 40 years, building it into one of the most powerful unions in the U.S. Bridges was known for militant union organizing, union democracy, social justice, racial integration, and internationalism. Bust designed and created by Henry AlvarezHenry Alvarez started Alvarez Wax Productions in 1976, after working for several years with sculptor Katherine Stubergh for a number of years. Although Alvarez specializes in full-size wax sculptures, he designs bronze works as well. Alvarez’s father was a career longshoreman associated with ILWU Pacific Coast Retirees Association, who commissioned the original bust of Harry Bridges for the ILWU headquarters in San Francisco. They also sponsored the bust in Suzzallo Library to commemorate the establishment of the Harry Bridges Chair in 1994.Email from Henry Alvarez. www.alvarezwax.co
TerraSAR-X Calibration Ground Equipment
No full textThe Microwaves and Radar Institute regularly performs calibration campaigns for spaceborne SAR systems, among which have been X-SAR, SRTM, and ASAR. In 2007, the German SAR satellite TerraSAR-X will be launched. Before it is ready for scientific and commercial use, the instrument has to be calibrated to ensure highly accurate data products. An absolute radiometric accuracy of better than 1 dB is required.
The relative and absolute radiometric calibration of SAR systems depends on reference point targets (i. e. passive corner reflectors and active transponders) with precisely known RCS. For the TerraSAR-X mission, the reference targets will be deployed on ground in the South of Germany during a 6 month lasting field campaign. This paper describes these reference targets (i. e. ground receivers, passive corner reflectors, and active transponders) and their characteri-zation
TerraSAR-X Calibration - First Results
No full textAs TerraSAR-X, due for launch in February 2007, will be an operational scientific mission with commercial potential, product quality is of paramount importance. The success or failure of the mission is essentially dependent on the calibration of the TerraSAR-X system ensuring the product quality and the correct in-orbit operation of the entire SAR system.
The essential task of calibrating TerraSAR-X is to estimate and correct systematic error contributions throughout the complete SAR system and to tie-down image information (magnitude and phase) to reference units in geophysical terms. The quality of this calibration process is dependent on the inherent stability of the radar system and the capability to determine and monitor the radiometric and geometric characteristics. In addition to the geometric calibration the main calibration activities are defined by the radiometric accuracy and the radiometric stability specified for the operational modes.
Due to the high degree of flexibility of the instrument, e.g. the large number of operation modes (StripMap, Spotlight, ScanSAR, left/right looking, etc.) and possible antenna beams, the in-orbit calibration procedure of TerraSAR-X is based on a novel antenna model approach.
In addition to the complexity of TerraSAR-X and the tight performance requirements, the main goal after launch of the satellite is to provide calibrated and verified SAR data products as soon as possible. Thus, a strategy for an efficient but robust in-orbit calibration procedure has been developed.
For this purpose, the novel antenna model developed and validated on ground, is verified in orbit by measuring only a number of selected beams using deployed ground receivers and natural targets (e.g. the rain forest).
Absolute calibration, yielding an absolute calibration factor by measuring the radar system against reference ground targets, requires precise and sophisticated ground equipment.
To account for the restricted time of calibration campaigns the number of passes and places of test sites is optimised versus cost and time effort by calibrating several beams and polarisation modes with the same test site. Therefore, corresponding test site configurations have been developed.
The evaluation of measurements performed during the calibration campaigns yields the different calibration parameters like the antenna pattern or the absolute calibration factor.
The paper describes the in-orbit calibration procedure and the different activities performed during the commissioning phase of TerraSAR-X and discuss first results
Alvarez varifocal X-ray lens
No full textVisible light optical elements such as lenses and mirrors have counterparts for X-rays. In the visible regime, a variable focusing power can be achieved by an Alvarez lens which consists of a pair of inline planar refractors with a cubic thickness profile. When the two refractors are laterally displaced in opposite directions, the parabolic component of the wavefront is changed resulting in a longitudinal displacement of the focus. This paper reports an implementation of this concept for X-rays using two planar microfabricated refractive elements. The Alvarez X-ray lens can vary the focal distance of an elliptical X-ray mirror or a planar compound X-ray lens over several millimetres. The study presents the first demonstration of an Alvarez X-ray lens which adaptively corrects defocus and astigmatism aberrations of X-ray optics. In addition, the Alvarez X-ray lens eliminates coma aberration in an elliptical mirror, to the lowest order, when combining the lens with an adjustment of the pitch angle of the mirror
In-flight Monitoring of TerraSAR-X Radar Instrument Stability
No full textFor calibrating and monitoring the radiometric stability, the radar instrument of TerraSAR-X hosts a passive calibration network coupling into an additional port of the T/R modules. Three different types of calibration pulses are applied, whereby sets of these pulses are needed at the start and end of each data acquisition. Additionally, TerraSAR-X has been equipped with an additional calibration mode based on the so-called "PN Gating method".
The PN Gating mode allows operating the T/R modules under most realistic conditions with the advantage that all modules can be characterised simultaneously. The individual characteristics are found by assigning special calibration pulse sequences with orthogonal codes to the T/R modules. During on-ground characterisation of the TerraSAR-X instrument this technique has established as a crucial diagnostic tool for functional checks as well as T/R module drift and failure monitoring. For the first time ever, this innovative method of PN Gating measurements will be applied for in-flight monitoring of a satellite SAR instrument. Starting with the TerraSAR-X commissioning phase the instrument behaviour can be accurately characterised to guarantee the radiometric stability of the system throughout the mission lifetime.
In this paper, the latest results from the in-orbit calibration of TerraSAR-X are shown and compared to on-ground measurements of pre-launch characterisations. The techniques described above are also applicable for characterisation and calibration of other advanced SAR systems coping with multiple mode radar instruments
Absolute Radiometric Calibration of TerraSAR-X - Approach and Ground Targets
No full textThe German SAR satellite TerraSAR-X was successfully launched in June 2007. During the commissioning phase, the first months after launch, a calibration field campaign was carried out to conduct geometric as well as relative and absolute radiometric calibration. This was necessary to prepare the satellite for scientific and commercial use. This paper addresses results concerning the absolute radiometric accuracy and the reference ground targets involved. The two types of utilized ground targets were trihedral corner reflectors and active transponders. It will be shown that an absolute radiometric accuracy of much better than 1 dB can be achieved using both types of targets
Traces and shards of self-injury: Strange accounting with “Author X”
No full textIn this strange account autoethnography, three or four authors explore their lived experiences with self-injury. Strange accounting is both a post-modern style of text, and a method for keeping identities concealed when risks and secrets are in play. Author X, a post-modern place-keeper for an anonymous author who may or may not have contributed to this manuscript, introduces a new dimension and layer of concealment. With Author X in-play and under erasure, the reader will never be sure if there were three or four authors on this manuscript. Through strange accounting, a post-structuralist/postmodernist frame will be applied to understanding the self-injury experience. We frame self-injury as a social practice and, for some, an everyday norm, while remaining acutely aware of the stigma surrounding the topic of self-injury. Each of us, coupled with Author X, provide the others cover to trace stories of self-injury through the literature, our flesh, and our lives
Individual T/R Module Characterisation of the TerraSAR-X Active Phased Array Antenna by Calibration Pulse Sequences with Orthogonal Codes
No full textThe PN Gating mode allows operating all individual T/R modules under most realistic conditions with the advantage that all modules can be characterised simultaneously. For the first time ever, this innovative method is performed by inflight PN Gating measurements during the TerraSAR-X commissioning phase. In this paper, the latest results from the in-orbit calibration of TerraSAR-X after its launch in February 2007 are shown and compared to on-ground measurements of prelaunch characterisations
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