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Search Results: 1 - 10 of 297839 matches for " J. Ebert "
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Sensory Neurons Do Not Induce Motor Neuron Loss in a Human Stem Cell Model of Spinal Muscular Atrophy
Andrew J. Schwab, Allison D. Ebert
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0103112
Abstract: Spinal muscular atrophy (SMA) is an autosomal recessive disorder leading to paralysis and early death due to reduced SMN protein. It is unclear why there is such a profound motor neuron loss, but recent evidence from fly and mouse studies indicate that cells comprising the whole sensory-motor circuit may contribute to motor neuron dysfunction and loss. Here, we used induced pluripotent stem cells derived from SMA patients to test whether sensory neurons directly contribute to motor neuron loss. We generated sensory neurons from SMA induced pluripotent stem cells and found no difference in neuron generation or survival, although there was a reduced calcium response to depolarizing stimuli. Using co-culture of SMA induced pluripotent stem cell derived sensory neurons with control induced pluripotent stem cell derived motor neurons, we found no significant reduction in motor neuron number or glutamate transporter boutons on motor neuron cell bodies or neurites. We conclude that SMA sensory neurons do not overtly contribute to motor neuron loss in this human stem cell system.
Why isolated streamer discharges hardly exist above the breakdown field in atmospheric air
A. B. Sun,J. Teunissen,U. Ebert
Physics , 2013, DOI: 10.1002/grl.50457
Abstract: We investigate streamer formation in the troposphere, in electric fields above the breakdown threshold. With fully three-dimensional particle simulations, we study the combined effect of natural background ionization and of photoionization on the discharge morphology. In previous investigations based on deterministic fluid models without background ionization, so-called double-headed streamers emerged. But in our improved model, many electron avalanches start to grow at different locations. Eventually the avalanches collectively screen the electric field in the interior of the discharge. This happens after what we call the `ionization screening time', for which we give an analytical estimate. As this time is comparable to the streamer formation time, we conclude that isolated streamers are unlikely to exist in fields well above breakdown in atmospheric air.
Ab initio calculation of Spin-Polarized Low-Energy Electron Diffraction Pattern for the systems Fe(001) and Fe(001)-p(1x1)-O
S. Borek,J. Braun,J. Minár,H. Ebert
Physics , 2015, DOI: 10.1103/PhysRevB.92.075126
Abstract: The construction of a multi-channel vector spin polarimeter requires the development of a new detector type, which works as a spin polarizing mirror with high reflectivity and asymmetry properties to guarantee for a high figure of merit. Technical realizations are found by spin polarized electron scattering from a surface at low energies. A very promising candidate for such a detector suitable material consists of an oxygen passivated iron surface, as for example a Fe(001)-p(1x1)-O surface. We investigate in detail the electronic structure of this adsorbate system and calculate the corresponding spin-polarized low-energy electron scattering. Our theoretical study is based on the fully relativistic SPRKKR-method in the framework of density functional theory. Furthermore, we use the local spin-density approximation in combination with dynamical mean field theory to determine the electronic structure of Fe(001)-p(1x1)-O and demonstrate that a significant impact of correlation effects occurs in the calculated figure of merit.
One-step theory of pump-probe photoemission
J. Braun,R. Rausch,M. Potthoff,J. Minar,H. Ebert
Physics , 2014, DOI: 10.1103/PhysRevB.91.035119
Abstract: A theoretical frame for pump-probe photoemission is presented. The approach is based on a general formulation using the Keldysh formalism for the lesser Green's function to describe the real-time evolution of the electronic degrees of freedom in the initial state after a strong pump pulse that drives the system out of equilibrium. The final state is represented by a time-reversed low-energy electron diffraction state. Our one-step description is related to Pendry's original formulation of the photoemission process as close as possible. The formalism allows for a quantitative calculation of time-dependent photocurrent for simple metals where a picture of effectively independent electrons is assumed as reliable. The theory is worked out for valence- and core-electron excitations. It comprises the study of different relativistic effects as a function of the pump-probe delay.
Calculation of angle-resolved photo emission spectra within the one-step model of photo emission - recent developments
J. Minár,J. Braun,S. Mankovsky,H. Ebert
Physics , 2010,
Abstract: Various technical developments enlarged the potential of angle-resolved photo emission (ARPES) tremendously during the last one or two decades. In particular improved momentum and energy resolution as well as the use of photon energies from few eV up to several keV makes ARPES a rather unique tool to investigate the electronic properties of solids and surfaces. Obviously, this rises the need for a corresponding theoretical formalism that allows to accompany experimental ARPES studies in an adequate way. As will be demonstrated by several examples this goal could be achieved by various recent developments on the basis of the one-step model of photo emission: The spin-orbit induced Rashba-splitting of Shockley-type surface states is discussed using a fully relativistic description. The impact of chemical disorder within surface layers can be handled by means of the Coherent Potential Approximation (CPA) alloy theory. Calculating phonon properties together with the corresponding electron-phonon self-energy allows a direct comparison with features in the ARPES spectra caused by electron-phonon interaction. The same holds for the influence of electronic correlation effects. These are accounted for by means of the dynamical mean field theory (DMFT) that removes the most serious short comings of standard calculations based on the standard LDA. The combination of this approach with the CPA allows the investigation of correlated transition metal alloys. Finally, accounting for the photon momentum and going beyond the single scatter approximation for the final state allows to deal quantitatively with ARPES in the HAXPES regime that reduces the influence of the surface on the spectra and probing primarily the bulk electronic structure this way. Corresponding calculations of ARPES spectra, however, have to deal with thermal vibrations in an adequate way.
Ab-initio description of the magnetic shape anisotropy due to the Breit interaction
S. Bornemann,J. Minar,J. Braun,D. Koedderitzsch,H. Ebert
Physics , 2010,
Abstract: A quantum-mechanical description of the magnetic shape anisotropy, that is usually ascribed to the classical magnetic dipole-dipole interaction, has been developed. This is achieved by including the Breit-interaction, that can be seen as an electronic current-current interaction in addition to the conventional Coulomb interaction, within fully relativistic band structure calculations. The major sources of the magnetic anisotropy, spin-orbit coupling and the Breit-interaction, are treated coherently this way. This seems to be especially important for layered systems for which often both sources contribute with opposite sign to the magnetic anisotropy energy. Applications to layered transition metal systems are presented to demonstrate the implications of this new approach in treating the magnetic shape anisotropy.
Converging seasonal prevalence dynamics in experimental epidemics
Sandra Lass, Jürgen W Hottinger, Thomas Fabbro, Dieter Ebert
BMC Ecology , 2011, DOI: 10.1186/1472-6785-11-14
Abstract: In an outdoor experiment, populations were set up to include the extremes of the prevalence spectrum observed in natural populations: 5% initial prevalence mimicking a newly invading parasite, 100% mimicking a rock pool population founded by infected hosts only, and 50% prevalence which is commonly observed in natural populations in spring. The parasite exhibited similar prevalence changes in all treatments, but seasonal patterns in the 100% treatment differed significantly from those in the 5% and 50% treatments. Populations started with 5% and 50% prevalence exhibited strong and regular seasonality already in the first year. In contrast, the amplitude of changes in the 100% treatment was low throughout the experiment demonstrating the long-lasting effect of initial conditions on prevalence dynamics.Our study shows that the time needed to approach the seasonal changes in prevalence depends strongly on the initial prevalence. Because individual D. magna populations in this rock pool metapopulation are mostly short lived, only few populations might ever reach a point where the initial conditions are not visible anymore.Seasonal changes in prevalence are ubiquitous in infectious diseases of plants, invertebrates and vertebrates [1-7]. Some of the more famous ones are influenza and measles, two of the paradigms for regular seasonal epidemics. Understanding the dynamics of such prevalence patterns has been a major challenge in epidemiology for the last decades. Numerous factors are known to cause and influence seasonal prevalence dynamics. Extrinsic factors affecting prevalence dynamics include physical conditions such as weather as well as community context of the host-parasite system, i.e. interactions with other members of the community [6-13]. Transmission of the influenza virus has been shown to depend on temperature and humidity and to be favoured by dry and cold conditions [14]. Intrinsic factors, inherent properties of the host-parasite system itself, include th
Non-invasive genetic approaches for estimation of ungulate population size: a study on roe deer (Capreolus capreolus) based on faeces
Ebert, C.,Sandrini, J.,Spielberger, B.,Thiele, B.
Animal Biodiversity and Conservation , 2012,
Abstract: Estimating population size is particularly difficult for animal species living in concealing habitats with dense vegetation. This is the case for roe deer as for many other ungulates. Our objective was to develop a non–invasive genetic capture–mark–recapture approach based on roe deer faeces collected along transects. In a pilot study, we collected 1,790 roe deer faeces during five sampling days in a forested study area in south western Germany. We extracted DNA from 410 of these samples and carried out microsatellite analysis using seven dinucleotide markers. The analyses resulted in 328 useable consensus genotypes which were assigned to 174 individuals. The population size estimated using a Bayesian approach was 94 (82–111) male and 136 (121–156) female roe deer. Our study shows that non–invasive genetic methods are a valuable management tool for roe deer.
Endometriosezentren verschiedener Stufen zur Verbesserung der medizinischen Versorgungsqualit t, der Forschung sowie der rztlichen Fort- und Weiterbildung
Ebert AD,Jackisch D,Mueller M,Keckstein J
Journal für Gyn?kologische Endokrinologie , 2008,
Abstract: In Europa wird die Idee der Qualit tsverbesserung auf dem Gebiet der Endometriose vertieft. Verschiedene "Task Forces" arbeiten mit zum Teil identischen Methoden am gleichen Ziel. Die Bildung spezialisierter Endometriosezentren verbunden mit einer breiten Qualifikation der rzte und des medizinischen Personals geh ren begleitet von der Unterstützung der Forschung ebenso in dieses Spektrum wie die Schulung und Information der betroffenen Frauen sowie die Sensibilisierung der Gesundheitspolitik, der Kostentr ger und der Industrie. Vor dem Hintergrund knapper Ressourcen ist eine Bündelung des vorhandenen nationalen und internationalen Engagements absehbar und notwendig. Inwieweit dies zur konsequenten Gründung von einheitlichen nationalen Endometriose-Gruppen als Basis einer europ ischen Dachgesellschaft führen k nnte, bleibt abzuwarten. Wünschenswert ist es allemal.
Multiple X-ray bursts from long discharges in air
C. V. Nguyen,A. P. J. van Deursen,U. Ebert
Physics , 2008, DOI: 10.1088/0022-3727/41/23/234012
Abstract: A lightning surge generator generates a high voltage surge with 1.2 microsec. rise time. The generator fed a spark gap of two pointed electrodes at 0.7 to 1.2 m distances. Gap breakdown occurred between 0.1 and 3 microsec. after the maximum generator voltage of approximately 850 kV. Various scintillator detectors with different response time recorded bursts of hard radiation in nearly all surges. The bursts were detected over the time span between approximately half of the maximum surge voltage and full gap breakdown. The consistent timing of the bursts with the high-voltage surge excluded background radiation as source for the high intensity pulses. In spite of the symmetry of the gap, negative surges produced more intense radiation than positive. This has been attributed to additional positive discharges from the measurement cabinet which occurred for negative surges. Some hard radiation signals were equivalent to several MeV. Pile-up occurs of lesser energy X-ray quanta, but still with a large fraction of these with an energy of the order of 100 keV. The bursts occurred within the 4 nanosec. time resolution of the fastest detector. The relation between the energy of the X-ray quanta and the signal from the scintillation detector is quite complicated, as shown by the measurements.
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