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Search Results: 1 - 10 of 19770 matches for " Alexander Stibor "
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Thermal Imaging as a Noninvasive Diagnostic Tool for Anterior Knee Pain Following Implantation of Artificial Knee Joints
Mathias Glehr,Alexander Stibor,Patrick Sadoghi,Christian Schuster
International Journal of Thermodynamics , 2011, DOI: 10.5541/ijot.334
Abstract: The variety of radiographic diagnostic used to diagnose pain localised close to metal implants is still limited. Especially magnetic resonance results can not be analysed because of artefacts. In this article we present for the first time a direct correlation between an increase in skin temperature and existent anterior knee pain after total knee arthroplasty (TKA) measured with thermography. In a standardised way 26 knees were analysed. Thermographic photos were taken from frontal, medial and lateral directions with a computer-assisted infrared thermograph. In medial location (median 0.95 °C, p=0.0043), as well as in lateral location (median 0.5 °C, p=0.032) temperatures in locations with pain were significantly higher compared to the reference field. Median temperature difference between pain localization and localizations without pain was 0.7 °C and ranged from 0.1 °C to 1.7 °C on the side of the pain. In the ROC analysis the sensitivity of this method was 1.0 and specificity was 0.917. The evidence of a significant increase in skin temperature on the painful sites opened up the possibility to localize and assess pain more precisely in patients with total knee prosthesis. We consider this novel, rapid, inexpensive and non-invasive technology to posses the potential to become a useful and objective tool for diagnosis of pain and inflammation and to generate digital data that can be stored and analysed in clinical practice.
Sublimation of the Endohedral Fullerene Er3N@C80
Alexander Stibor,Hannah Schefzyk,József Fortágh
Physics , 2009, DOI: 10.1039/C0CP00325E
Abstract: The heat of sublimation of the endohedral metallofullerene Er3N@C80 was measured via Knudsen effusion mass spectrometry. The large molecule consists of a C80 fullerene cage which is stabilized by comprising a complex of three erbium atoms bounded to a nitrogen atom and has a mass of 1475 amu. The mass spectrum at a temperature of 1045 K and the relative intensities of the thermal fractions of Er3N@C80 are provided. We also discuss possible thermal decomposition processes for these particles. By measuring the quantity of evaporated molecules in thermal equilibrium through a quadrupole mass spectrometer in a temperature range between 782 K and 1128 K, a value for the sublimation enthalpy of Hsub = 237 +-7 kJ/mol is obtained from the second law method.
A scalable optical detection scheme for matter wave interferometry
Alexander Stibor,Andre Stefanov,Fabienne Goldfarb,Elisabeth Reiger,Markus Arndt
Physics , 2006, DOI: 10.1088/1367-2630/7/1/224
Abstract: Imaging of surface adsorbed molecules is investigated as a novel detection method for matter wave interferometry with fluorescent particles. Mechanically magnified fluorescence imaging turns out to be an excellent tool for recording quantum interference patterns. It has a good sensitivity and yields patterns of high visibility. The spatial resolution of this technique is only determined by the Talbot gratings and can exceed the optical resolution limit by an order of magnitude. A unique advantage of this approach is its scalability: for certain classes of nano-sized objects, the detection sensitivity will even increase significantly with increasing size of the particle.
Electron matter wave interferences at high vacuum pressures
Georg Schütz,Alexander Rembold,Andreas Pooch,Wei-Tse Chang,Alexander Stibor
Physics , 2015,
Abstract: The ability to trap and guide coherent electrons is gaining importance in fundamental as well as in applied physics. In this regard novel quantum devices are currently developed that may operate under low vacuum conditions. Here we study the loss of electron coherence with increasing background gas pressure. Thereby, optionally helium, hydrogen or nitrogen is introduced in a biprism interferometer where the interference contrast is a measure for the coherence of the electrons. The results indicate a constant contrast that is not decreasing in the examined pressure range between $10^{-9}$ mbar and $10^{-4}$ mbar. Therefore, no decoherence was observed even under poor vacuum conditions. Due to scattering of the electron beam with background H$_2$-molecules a signal loss of 94 % was determined. The results may lower the vacuum requirements for novel quantum devices with free coherent electrons.
Effective beam separation schemes for the measurement of the electric Aharonov-Bohm effect in an ion interferometer
Georg Schütz,Alexander Rembold,Andreas Pooch,Henrike Prochel,Alexander Stibor
Physics , 2013,
Abstract: We propose an experiment for the first proof of the type I electric Aharonov-Bohm effect in an ion interferometer for hydrogen. The performances of three different beam separation schemes are simulated and compared. The coherent ion beam is generated by a single atom tip (SAT) source and separated by either two biprisms with a quadrupole lens, two biprisms with an einzel-lens or three biprisms. The beam path separation is necessary to introduce two metal tubes that can be pulsed with different electric potentials. The high time resolution of a delay line detector allows to work with a continuous ion beam and circumvents the pulsed beam operation as originally suggested by Aharonov and Bohm. We demonstrate, that the higher mass and therefore lower velocity of ions compared to electrons combined with the high expected SAT ion emission puts the direct proof of this quantum effect for the first time into reach of current technical possibilities. Thereby a high coherent ion detection rate is crucial to avoid long integration times that allow the influence of dephasing noise from the environment. We can determine the period of the expected matter wave interference pattern and the signal on the detector by determining the superposition angle of the coherent partial beams. Our simulations were tested with an electron interferometer setup and agree with the experimental results. We determine the separation scheme with three biprisms to be most efficient and predict a total signal acquisition time of only 80 s to measure a phase shift from 0 to 2$\pi$ due to the electric Aharonov-Bohm effect.
Correction of dephasing oscillations in matter wave interferometry
Alexander Rembold,Georg Schütz,Wei-Tse Chang,André Stefanov,Andreas Pooch,Ing-Shouh Hwang,Andreas Günther,Alexander Stibor
Physics , 2013, DOI: 10.1103/PhysRevA.89.033635
Abstract: Vibrations, electromagnetic oscillations and temperature drifts are among the main reasons for dephasing in matter-wave interferometry. Sophisticated interferometry experiments, e.g. with ions or heavy molecules, often require integration times of several minutes due to the low source intensity or the high velocity selection. Here we present a scheme to suppress the influence of such dephasing mechanisms - especially in the low-frequency regime - by analyzing temporal and spatial particle correlations available in modern detectors. Such correlations can reveal interference properties that would otherwise be washed out due to dephasing by external oscillating signals. The method is shown experimentally in a biprism electron interferometer where a perturbing oscillation is artificially introduced by a periodically varying magnetic field. We provide a full theoretical description of the particle correlations where the perturbing frequency and amplitude can be revealed from the disturbed interferogram. The original spatial fringe pattern without the perturbation can thereby be restored. The technique can be applied to lower the general noise requirements in matter-wave interferometers. It allows for the optimization of electromagnetic shielding and decreases the efforts for vibrational or temperature stabilization.
Biprism Electron Interferometry with a Single Atom Tip Source
Georg Schütz,Alexander Rembold,Andreas Pooch,Simon Meier,Philipp Schneeweiss,Arno Rauschenbeutel,Andreas Günther,Wei-Tse Chang,Ing-Shouh Hwang,Alexander Stibor
Physics , 2013,
Abstract: Experiments with electron or ion matter waves require a coherent, monochromatic and long-term stable source with high brightness. These requirements are best fulfilled by single atom tip (SAT) field emitters. The performance of an iridium covered W(111) SAT is demonstrated and analyzed for electrons in a biprism interferometer. Furthermore we characterize the emission of the SAT in a separate field electron and field ion microscope and compare it with other emitter types. A new method is presented to fabricate the electrostatic charged biprism wire that separates and combines the matter wave. In contrast to other biprism interferometers the source and the biprism size are well defined within a few nanometers. The setup has direct applications in ion interferometry and Aharonov-Bohm physics.
A Kapitza-Dirac-Talbot-Lau interferometer for highly polarizable molecules
Stefan Gerlich,Lucia Hackermueller,Klaus Hornberger,Alexander Stibor,Hendrik Ulbricht,Michael Gring,Fabienne Goldfarb,Tim Savas,Marcel Mueri,Marcel Mayor,Markus Arndt
Physics , 2008, DOI: 10.1038/nphys701
Abstract: Research on matter waves is a thriving field of quantum physics and has recently stimulated many investigations with electrons, neutrons, atoms, Bose-condensed ensembles, cold clusters and hot molecules. Coherence experiments with complex objects are of interest for exploring the transition to classical physics, for measuring molecular properties and they have even been proposed for testing new models of space-time. For matter-wave experiments with complex molecules, the strongly dispersive effect of the interaction between the diffracted molecule and the grating wall is a major challenge because it imposes enormous constraints on the velocity selection of the molecular beam. We here describe the first experimental realization of a new interferometer that solves this problem by combining the advantages of a Talbot-Lau setup with the benefits of an optical phase grating and we show quantum interference with new large molecules.
Initial size structure of natural phytoplankton communities determines the response to Daphnia diel vertical migration
Florian Haupt,Maria Stockenreiter,Maarten Boersma,Herwig Stibor
Journal of Limnology , 2012, DOI: 10.4081/jlimnol.2012.e13
Abstract: Diel vertical migration (DVM) is a common behavior of many pelagic herbivorous zooplankton species in response to predation pressure. It is characterized by a twice daily habitat shift of the zooplankton species: staying in the epilimnion only during night time and migrating down in the crack of dawn in deeper water layers, staying there during the day time. This causes a discontinuous grazing regime and previous studies have shown that the direction and strength of phytoplankton community responses to zooplankton DVM most probably depends on the size of phytoplankton species. To examine the influence of zooplankton DVM on different sized phytoplankton communities, we designed an experiment where we manipulated the size distribution of a natural phytoplankton community a priori in field mesocosms. We investigated the influence of DVM of the cladoceran Daphnia hyalina on two different phytoplankton communities, by the use of deep (10 m) field enclosures. Epilimnetic lake water, containing a summer phytoplankton community, was filtered with two different mesh sizes (11 mm and 64 mm). The 11 mm phytoplankton community (“small”) contained mainly small algal species, while the 64 mm community (“large”) had a wider range of phytoplankton sizes. To simulate zooplankton DVM, D. hyalina were placed in mesh cages that were lowered or raised (“migration”) as dictated by the study design; a “no migration” (representing absence of DVM) treatment was also tested. Phytoplankton abundance was measured using chlorophyll-a and biovolume; size distribution of the algae and nutrient availability was also determined in each treatment. The results indicated that DVM had contrasting effects on the two evaluated phytoplankton communities. Comparison of “migration” and “no migration” zooplankton treatments showed that nutrient availability and total phytoplankton biovolume was higher in (1) “no migration” treatments with phytoplankton communities comprising mainly small algae and (2) “migration” treatments with phytoplankton communities of a broader size spectrum of algae. Hence our study showed two different mechanisms of how zooplankton DVM may influence the phytoplankton community dynamics. Nutrient cycling was an important factor in phytoplankton communities of mainly small algae, whereas the refuge effect was the main driver of phytoplankton dynamics in phytoplankton communities of a large size spectrum of algae.
Talbot-Lau interferometry with fullerenes: Sensitivity to inertial forces and vibrational dephasing
A. Stibor,K. Hornberger,L. Hackermueller,A. Zeilinger,M. Arndt
Physics , 2004,
Abstract: We discuss matter wave experiments in a near-field interferometer and focus on dephasing phenomena due to inertial forces. Their presence may result in a significant reduction of the observed interference contrast, even though they do not lead to genuine decoherence. We provide quantitative estimates for the most important effects and demonstrate experimentally the strong influence of acoustic vibrations. Since the effects of inertial forces get increasingly important for the interferometry with more massive particles they have to be identified and compensated in future experiments.
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