1,313 research outputs found
Local Quantum Fields for Anyons on the Circle leading to Non-Relativistic Anyons in Two Dimensions
Using the method of implementable one-particle Bogoliubov transformations it
is possible to explicitly define a local covariant net of quantum fields on the
(universal covering of the) circle with braid group statistics. These
Anyon fields transform under a representation of for
arbitrary real-valued spin and their commutation relations depend on the
relative winding number of localization regions. By taking the tensor product
with a local covariant field theory on one can obtain a
non-relativistic cone-localized field net for Anyons in two dimensions
Anti-sunward high-speed jets in the subsolar magnetosheath
Using 2008â2011 data from the five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft in Earth's subsolar
magnetosheath, we study high-speed jets identified as intervals when the
anti-sunward component of the dynamic pressure in the subsolar magnetosheath exceeds half of its
upstream solar wind value. Based on our comprehensive data set of 2859
high-speed jets, we obtain the following statistical results on jet properties
and favorable conditions: high-speed jets occur predominantly downstream of
the quasi-parallel bow shock, i.e., when interplanetary magnetic field cone
angles are low. Apart from that, jet occurrence is only very weakly dependent
(if at all) on other upstream conditions or solar wind variability. Typical
durations and recurrence times of high-speed jets are on the order of tens of
seconds and a few minutes, respectively. Relative to the ambient
magnetosheath, high-speed jets exhibit higher speed, density and magnetic
field intensity, but lower and more isotropic temperatures. They are
almost always super-Alfvénic, often even super-magnetosonic, and
typically feature 6.5 times as much dynamic pressure and twice as much total
pressure in anti-sunward direction as the surrounding plasma does. Consequently,
they are likely to have significant effects on the magnetosphere and
ionosphere if they impinge on the magnetopause
The global structure and time evolution of dayside magnetopause surface eigenmodes
Theoretical work and recent observations suggest that the dayside magnetopause may support its own eigenmode, consisting of propagating surface waves which reflect at the northern and southern ionospheres. These magnetopause surface eigenmodes (MSEs) are a potential source of magnetospheric ultralowâfrequency (ULF) waves with frequencies less than 2âmHz. Here we use the Space Weather Modeling Framework to study the magnetospheric response to impulsive solar wind dynamic pressure increases. Waves with 1.8âmHz frequency are excited whose global properties are largely consistent with theoretical predictions for MSE and cannot be explained by other known ULF wave modes. These simulation results lead to two key findings: (1) MSE can be sustained in realistic magnetic field geometries with nonzero flow shear and finite current layer thickness at the magnetopause and (2) MSE can seed the growth of tailward propagating surface waves via the KelvinâHelmholtz instability.Key PointsDayside ULF response to pulse consistent with magnetopause surface eigenmodeMagnetopause surface eigenmodes are a potential source of ULF waves below 2âmHzMagnetopause surface eigenmodes seed tailward propagating surface wave growthPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111803/1/grl52799.pd
Spin axis offset calibration on THEMIS using mirror modes
A newly developed method for determining spin axis offsets of magnetic field
instruments on spacecraft is applied to THEMIS. The formerly used
determination method, relying on solar wind Alfvénic fluctuations, was
rarely applicable due to the orbital restrictions of the mission. With the
new procedure, based on magnetic field observation of mirror modes in the
magnetosheath, updated spin axis offsets can be estimated approximately once
per year. Retrospective calibration of all THEMIS magnetic field measurements
is thereby made possible. Since, up to this point, spin axis offsets could
hardly ever be calculated due to the mission's orbits, this update represents
a substantial improvement to the data. The approximate offset stability is
estimated to be <â0.75âŻnTâŻyearâ1 for the complete course of the
mission
Untersuchungen zur Stabilisierung und Miniaturisierung kationensensitiver Schichten fĂŒr die Entwicklung von optochemischen Mikrosensoren
Im Rahmen der vorliegenden Arbeit wurden optochemische Sensoren (Optroden) zur Detektion der kationischen Spezies Quecksilber(II), Calcium(II) und zur Bestimmung von pH-Werten entwickelt und miniaturisiert.
Der erste thematische Schwerpunkt der Arbeit widmet sich der Verbesserung der StabilitĂ€t von kationensensitiven Rezeptorschichten. Werden diese durch einfache Einkapselung von Indikatoren hergestellt, so wird die StabilitĂ€t der Schicht bedingt durch das Auswaschen des Farbstoffes auf etwa einen Tag begrenzt. Zur UnterdrĂŒckung dieses Farbstoffaustrages wurde eine neue Immobilisierungsmethode entwickelt und erprobt, die in der kovalenten Anbindung von Fluoreszenzindikatoren an das wasserlösliche Polysaccharid Dextran (70.000 g/mol) und der anschlieĂenden Einkapselung der makromolekular gebundenen IndikatormolekĂŒle in hydrophilen Matrices besteht. Als Matrices wurden anorganische Silikagele, die nach dem Sol-Gel-Verfahren hergestellt wurden, und das organische Hydrogel Polyhydroxyethylmethacrylat (PolyHEMA) eingesetzt. Die vorgestellte Immobilisierungsmethode weist gegenĂŒber der direkten kovalenten Anbindung des Indikators an die Matrix eine deutlich erhöhte FlexibilitĂ€t auf, was beispielhaft an drei Analyt-Rezeptor-Paaren dargestellt wird.
Zur Herstellung von Quecksilber-sensitiven Schichten wurden zunĂ€chst Porphyrin-Dextrane synthetisiert und mittels spektroskopischer Methoden sowie durch Elektrophorese charakterisiert. Porphyrin-Dextran-dotierte, mesoporöse Silikagel- Schichten zeigten nach 40tĂ€giger Lagerung in MeĂpuffer noch 92% der anfĂ€nglichen FluoreszenzintensitĂ€t.
Auf der Basis von Fluorescein-Dextran wurden pH-sensitive Silikagel- und PolyHEMA-Schichten hergestellt. Letztere zeigten einen MeĂbereich von pH 5 bis 8 und Ansprechzeiten von 5 Sekunden/pH. Nach 18tĂ€giger Lagerung in MeĂpuffer zeigten die Sensoren noch ĂŒber 95% der ursprĂŒnglichen FluoreszenzintensitĂ€ten.
Durch Coimmobilisierung von Calcium Green-Dextran und Texas Red-Dextran wurde ein Calcium-sensitiver Sensor mit interner Referenz hergestellt. Der MeĂbereich des Sensors liegt zwischen 5  10-8 und 10-5 mol/l Ca(II) bei Ansprechzeiten von 5 Sekunden bis zum Erreichen des SĂ€ttigungswertes. Der Sensor erwies sich als sehr selektiv gegenĂŒber Interferenzen von Na(I), K(I) und Mg(II). Durch die interne Referenzierung des MeĂsignals lĂ€Ăt sich die Reproduzierbarkeit der Sensorsignale entscheidend verbessern.
Als zweiter Schwerpunkt der Arbeit wurde in mehreren Schritten die Miniaturisierung der Calciumsensoren mit interner Referenz vorgenommen. Unter Verwendung von optischer Fasertechnik wurden Mikrosensoren mit Durchmessern von 600 bzw. 50 ”m entwickelt. Basierend auf verjĂŒngten Faserspitzen (Taper) mit Durchmessern von etwa 300 nm wurden die derzeit kleinsten faseroptischen Calciumsensoren (Nanosensoren) erhalten.
Aufgrund der verbesserten StabilitÀt und der extremen Miniaturisierung der vorgestellten optischen Sensoren lassen sich in Zukunft neue analytische Aufgabenstellungen (z.B. Messung in biologischen Zellen) mit einer Ortsauflösung im Nanometerbereich bearbeiten
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How Accurately Can We Measure the Reconnection Rate E M for the MMS Diffusion Region Event of 11 July 2017?
We investigate the accuracy with which the reconnection electric field E M can be determined from in situ plasma data. We study the magnetotail electron diffusion region observed by National Aeronautics and Space Administration's Magnetospheric Multiscale (MMS) on 11 July 2017 at 22:34 UT and focus on the very large errors in E M that result from errors in an L M N boundary normal coordinate system. We determine several L M N coordinates for this MMS event using several different methods. We use these M axes to estimate E M. We find some consensus that the reconnection rate was roughly E M = 3.2 ± 0.6 mV/m, which corresponds to a normalized reconnection rate of 0.18 ± 0.035. Minimum variance analysis of the electron velocity (MVA-v e), MVA of E, minimization of Faraday residue, and an adjusted version of the maximum directional derivative of the magnetic field (MDD-B) technique all produce reasonably similar coordinate axes. We use virtual MMS data from a particle-in-cell simulation of this event to estimate the errors in the coordinate axes and reconnection rate associated with MVA-v e and MDD-B. The L and M directions are most reliably determined by MVA-v e when the spacecraft observes a clear electron jet reversal. When the magnetic field data have errors as small as 0.5% of the background field strength, the M direction obtained by MDD-B technique may be off by as much as 35°. The normal direction is most accurately obtained by MDD-B. Overall, we find that these techniques were able to identify E M from the virtual data within error bars â„20%
Massless bosonic string-localized quantum fields
Masselose bosonische string-lokalisierte Quantenfelder werden untersucht. Nach einem kurzen Ăberblick ĂŒber massive Felder werden die Intertwiner fĂŒr Vektor- und Tensor-Potentiale und fĂŒr allgemeinere Darstellungen konstruiert. Diese Felder sind eindeutig festgelegt durch die Forderung, dass sie verallgemeinerte Potentiale fĂŒr die FeldstĂ€rken sind. Weiters wird bewiesen, dass sie verallgemeinerte Versionen der Lorentz- und der axialen Eichung erfĂŒllen und gewisse symmetrie Eigenschaften besitzen. Es wird auĂerdem erlĂ€utert, warum sie zusĂ€tzliche Indizes benötigen. Zum Schluss wird noch deren Zwei-Punkt Funktion untersucht und es wird gezeigt, dass ihr Verhalten fĂŒr kleine AbstĂ€nde unabhĂ€ngig von der HelizitĂ€t ist.Massless bosonic string-localized quantum fields are studied. After reviewing some facts about massive fields, the corresponding intertwiners for vector- and tensor potentials and for more general representations are constructed. These fields are fixed by the requirement that they are generalized potentials for the field strengths. Furthermore it is proven that they satisfy generalized versions of the Lorentz- and axial gauge and certain symmetry properties. It is also illustrated why they need additional indices. In the end their two-point function is analyzed and it is shown that their short-distance behavior is independent of the helicity
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