810 research outputs found
ULF vlny/fluktuace ve forešoku: Statistický přístup
Full text linkTitle: ULF waves/fluctuations in the foreshock: Statistical approach Author: Anna Mita Department: Department of Surface and Plasma Science Supervisor: Prof. RNDr. Jana Šafránková, DrSc., Department of Surface and Plasma Science Abstract: The thesis deals with ultra-low frequency (ULF) wave activity in the terrestrial foreshock, a turbulent region upstream of the bow shock that plays a crucial role in the interaction of the solar wind with the magnetosphere. In the thesis, we analyze some aspects of the behavior of ULF waves/fluctuations of the magnetic field, using a statistical point of view. We focused (i) on the boundary between the pure solar wind and wave activity region represented by enhanced ULF fluctuations, and on the changes of the boundary position with solar wind conditions and interplanetary magnetic field orientation; and (ii) on growth rates of foreshock ULF fluctuations at different distances from the bow shock with a special highlight on a region close to the Moon. In both statistical studies, we use THEMIS/ARTEMIS data and describe the behavior of fluctuations by the standard deviations in the ULF range of 0.0017-0.17 Hz. We present a novel coordinate system, determine so-called "foreshock ULF boundary" and report its realistic shape that is consistent with the theory of the foreshock...Název práce: ULF vlny/fluktuace ve forešoku: Statistický přístup Autor: Anna Mita Katedra: Katedra fyziky povrchů a plazmatu Vedoucí disertační práce: Prof. RNDr. Jana Šafránková, DrSc., Katedra fyziky povrchů a plazmatu Abstrakt: Předložená práce se zabývá ULF (Ultra Low Frequency) fluktuacemi v turbulentní oblasti před rázovou vlnou (forešok), která hraje klíčovou roli v interakci slunečního větru s magnetosférou Země. V práci analyzujeme některé aspekty chování ULF vln/fluktuací magnetického pole s využitím statistického zpracování dat naměřených dvěma družicemi projektu THEMIS/ARTEMIS. Zaměřili jsme se (i) na hranici mezi neporušeným slunečním větrem a oblastí charakterizovanou vysokými ULF fluktuacemi a na změny polohy této hranice v závislosti na podmínkách ve slunečním větru a na orientaci meziplanetárního magnetického pole; a (ii) na rychlost růstu nebo tlumení ULF vln/fluktuací v různých vzdálenostech od rázové vlny se zvláštním zřetelem na oblast blízko Měsíce. Ve statistických studiích popisujeme chování fluktuací pomocí směrodatných odchylek v rozsahu 0,0017-0,17 Hz. V práci představujeme nový souřadnicový systém umožňující určit tzv. "foreshock ULF boundary", diskutujeme nalezený tvar a ukazujeme, že je v souladu s teorií formování forešoku. Ve druhé studii se soustřeďujeme na růst (případně...Katedra fyziky povrchů a plazmatuDepartment of Surface and Plasma ScienceFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult
ULF waves/fluctuations in the foreshock: Statistical approach
No full textTitle: ULF waves/fluctuations in the foreshock: Statistical approach Author: Anna Mita Department: Department of Surface and Plasma Science Supervisor: Prof. RNDr. Jana Šafránková, DrSc., Department of Surface and Plasma Science Abstract: The thesis deals with ultra-low frequency (ULF) wave activity in the terrestrial foreshock, a turbulent region upstream of the bow shock that plays a crucial role in the interaction of the solar wind with the magnetosphere. In the thesis, we analyze some aspects of the behavior of ULF waves/fluctuations of the magnetic field, using a statistical point of view. We focused (i) on the boundary between the pure solar wind and wave activity region represented by enhanced ULF fluctuations, and on the changes of the boundary position with solar wind conditions and interplanetary magnetic field orientation; and (ii) on growth rates of foreshock ULF fluctuations at different distances from the bow shock with a special highlight on a region close to the Moon. In both statistical studies, we use THEMIS/ARTEMIS data and describe the behavior of fluctuations by the standard deviations in the ULF range of 0.0017-0.17 Hz. We present a novel coordinate system, determine so-called "foreshock ULF boundary" and report its realistic shape that is consistent with the theory of the foreshock..
Dream on, but with your eyes open: An obituary for Ulf Kadritzke (1943-2020)
Full text linkUlf Kadritzke war der PROKLA als Autor und Mitglied des Redaktionsbeirats viele Jahre eng verbunden. Mit seinen Ideen und seinem Engagement hat er nicht nur die PROKLA bereichert und geprägt. Am 14. November 2020 verstarb Ulf Kadritzke überraschend.Ulf Kadritzke was closely associated with PROKLA for many years as an author and a member of the editorial advisory board. With his ideas and commitment, he enriched and shaped not only PROKLA. Ulf Kadritzke passed away unexpectedly on November 14, 2020
Ulf eta Cornelia: Berlingo maitasun istorio bat
No full text“Ulf and Cornelia: A Berlin love story” is part of the PhD thesis Berlin fin de millenium: An Experiment in Corporeal Ethnography, carried out between 1998 and 2003. In this article, the author puts into practice his investigative endeavor as a discovery process, narrating his encounters with Ulf and Cornelia, two bodies in transit in a Berlin characterized by its dramatic urban transformation. The focus of the ethnography is Ulf’s enamored experience. Using wonder as a knowledge technique, we will dive in the realm previous to the formation of stable identities, meaning the domain of corporeal stimulus and unconscious impulses. The subjects that appear in the scenes of this article, the author himself and the city where they live are in construction.“Ulf y Cornelia: una historia de amor berlinesa” es un apartado que pertenece a la tesis Berlín fin de milenio: un experimento en la etnografía corporal, realizada entre 1998 y 2003. En este artículo, el autor lleva a cabo una labor de investigación puesta en práctica como un proceso de descubrimientos, relatando sus encuentros con Ulf y Cornelia, dos cuerpos en tránsito en un Berlín sumido en una dramática transformación urbana. La etnografía está enfocada particularmente en la experiencia de enamoramiento de Ulf. Utilizando la capacidad de asombro como técnica para el conocimiento, nos sumergiremos en el ámbito anterior a la formación de identidades estables, es decir, en el dominio de estímulos corporales e impulsos inconscientes. Se trata, pues, de un artículo donde tanto los sujetos en escena como el propio autor y la ciudad en la que viven están en proceso de construcción.“Ulf eta Cornelia: maitasun istorio bat Berlinen”, 1999-2003 urteen artean garatutako Berlin fin de millenium: gorputz etnografíaren gaineko esperimentu bat tesiaren ataletako bat da. Artikulu honetan, autoreak, Ulfekin eta Corneliarekin, Berlin behin behineko bizilekutzat duten bi gorputzekin, bizitako uneak kontatzen dizkigu. Zehazki, Ulfen maitemintzea izango da etengabeko aurkikuntza prozesuan oinarritutako etnografía honen ardatza. Lilurarako gaitasuna ezagutzarako teknika bezala erabiliaz, nortasun egonkorrak eratu aurretiko eremura eramango gaitu, hau da, gorputz-estimulu eta bulkada inkontzienteen mundura. Azpimarratu behar da, artikulu honetan protagonista diren pertsonak, autorea bera eta bizi diren hiria eraikuntza prozesuan daudela
A Toolbox for Designing and Analyzing Phase-Shifting Interferometry Algorithms with Characteristic Polynomials
No full textThe Renovated Aperture Area Measurement Facility at the National Institute of Standards and Technology (NIST)
No full textApertures with precisely known area are used in radiometry and photometry to define the optical phase space into which radiant flux is emitted or received. For example, solid angle, needed for the realization of the Candela, is realized with apertures of known area. Another common application is the measurement of irradiance, the radiant flux received at a surface per unit area (or its photometric analog illuminance), which requires an aperture with known area to be placed in front of an optical radiation sensor.
Beginning in the 1990s the National Institute of Standards and Technology (NIST) has developed improved methods for the measurement of radiometric aperture areas to meet the need for aperture area measurements with combined relative standard uncertainties of about 10^4 or lower. At that time a custom optical coordinate measuring machine was constructed at NIST for absolute aperture area measurements that are directly traceable to the length unit meter of the International System of Units (SI). This aperture area measurement (AAM) system consists of a planar air bearing stage with laser interferometer position feedback on both motion axes that is used to precisely locate the edge of an aperture in the focal plane of a high-magnification optical microscope. Aperture areas are calculated from aperture edge points measured along the full lengths of the aperture edges. NIST has provided aperture area calibrations since the early 2000s using the AAM system.
During a recent renovation of the AAM instrument, several components that had become obsolete were updated, including the optical microscope, the camera, and parts of the illumination system. The operating software for the AAM instrument and the software for data analysis was also replaced to take advantage of improved and more widely available algorithms for image processing. My presentation will describe the renovated AAM instrument, the revised traceability of aperture area measurements to the SI, and I will outline the potential for further improvements of the AAM instrument at NIST in the future
Simulation of Bounce Resonance ULF Wave-Particle Interactions
No full textPoloidal mode ultra-low-frequency (ULF) waves with high azimuthal mode number (high-m) are common throughout Earth's magnetosphere. The electric fields in these waves are on the order of tens of millivolts per meter, and are large enough to energize ions and electrons via drift- and drift-bounce wave-particle resonance. In this article, we present full orbit test-particle simulations of drift-bounce resonance using a numerical model of ULF waves. The model uses a dipole magnetic field and can accommodate a realistic ionosphere with height-resolved Pedersen and Hall conductivity. It is demonstrated that second-harmonic poloidal mode waves can energize ions to tens of keV depending on the wave amplitude. The test-particle simulations also predict ion flux oscillations that have energy dispersion similar to many satellite observations. It will be shown that features in the energy dispersion are in agreement with theoretical considerations.CPCI-S(ISTP)[email protected]; [email protected]
THEMIS observations of ULF wave excitation in the nightside plasma sheet during sudden impulse events
No full textSudden impulses (SIs) are an important source of ultra low frequency (ULF) wave activity throughout the Earth's magnetosphere. Most SI-induced ULF wave events have been reported in the dayside magnetosphere; it is not clear when and how SIs drive ULF wave activity in the nightside plasma sheet. We examined the ULF response of the nightside plasma sheet to SIs using an ensemble of 13 SI events observed by THEMIS (Timed History of Events and Macroscale Interactions during Substorms) satellites (probes). Only three of these events resulted in ULF wave activity. The periods of the waves are found to be 3.3, 6.0, and 7.6 min. East-west magnetic and radial electric field perturbations, which typically indicate the toroidal mode, are found to be stronger and can have phase relationships consistent with standing waves. Our results suggest that the two largest-amplitude ULF responses to SIs in the nightside plasma sheet are tailward-moving vortices, which have previously been reported, and the dynamic response of cross-tail currents in the magnetotail to maintain force balance with the solar wind, which has not previously been reported as a ULF wave driver. Both mechanisms could potentially drive standing Alfven waves (toroidal modes) observed via the field-line resonance mechanism. Furthermore, both involve frequency selection and a preference for certain driving conditions that can explain the small number of ULF wave events associated with SIs in the nightside plasma sheet. Citation: Shi, Q. Q., et al. (2013), THEMIS observations of ULF wave excitation in the nightside plasma sheet during sudden impulse events, J. Geophys. Res. Space Physics, 118, 284-298, doi:10.1029/2012JA017984.Astronomy & AstrophysicsSCI(E)10ARTICLE1284-29811
- …
