A dynamic neural model of localization of brief successive stimuli in saltation

Somatosensory saltation is an illusion robustly generated using short tactile stimuli [1,2]. There is a perceived displacement of a first stimulus if followed by a subsequent nearby stimulus with a short stimulus onset asynchrony (SOA). Experimental reports suggest that this illusion results from spatiotemporal integration in early processing stages, but the exact neural mechanism is unknown. The neuronal mechanism involved is probably quite generic as similar phenomena occur in other modalities, audition for example [3]

Rapid meridional transport of tropical airmasses to the Arctic during the major stratospheric warming in January 2003

International audienceWe present observations of unusually high values of ozone and N2O in the middle stratosphere that were observed by the airborne submillimeter radiometer ASUR in the Arctic. The observations took place in the meteorological situation of a major stratospheric warming that occurred in mid-January 2003 and was dominated by a wave 2 event. On 23 January 2003 the observed N2O and O3 mixing ratios around 69° N in the middle stratosphere reached maximum values of ~190 ppb and ~10 ppm, respectively. The similarities of these N2O profiles in a potential temperature range between 800 and 1200 K with N2O observations around 20° N on 1 March 2003 by the same instrument suggest that the observed Arctic airmasses were transported from the tropics quasi-isentropically. This is confirmed by 5-day back trajectory calculations which indicate that the airmasses between about 800 and 1000 K had been located around 20° N 3?5 days prior to the measurement in the Arctic. Calculations with a linearized ozone chemistry model along calculated as well as idealized trajectories, initialized with the low-latitude ASUR ozone measurements, give reasonable agreement with the Arctic ozone measurement by ASUR. PV distributions suggest that these airmasses did not stay confined in the Arctic region which makes it unlikely that this dynamical situation lead to the formation of dynamically caused pockets of low ozone

Psychophysikalische Korrelate von Anpassungsprozessen bei lang andauernden Schmerzreizen bei Gesunden und chronischen Schmerzpatienten

Chronische Schmerzsyndrome machen einen großen Anteil klinischer Erscheinungsbilder von Schmerzen aus, die schwierig zu behandeln sind und deshalb oft in eine lange Patientenkarriere mit vielen erfolglosen Behandlungsversuchen münden. Die Prävalenz chronischer Schmerzen in den Industrienationen wird nach einer aktuellen Angabe der International Association for the Study of Pain (IASP) mit etwa 20% der Erwachsenen angegeben, wobei gelegentlich auftretende Schmerzen bei einem weit größeren Bevölkerungsanteil von etwa 80% zu finden sind. Die häufigsten Schmerzsyndrome sind dabei Schmerzen des Bewegungsapparates, vor allem Rückenschmerzen, gefolgt von verschiedenen Formen des Kopfschmerzes. In der experimentellen und klinischen Schmerzforschung wird derzeit auf einer breiten grundwissenschaftlichen Basis in verschiedenen Fachrichtungen nach den Ursachen, Beschreibungsmerkmalen und Therapiemöglichkeiten chronischer Schmerzen gesucht. Die vorliegende psychologische Studie leistet einen Beitrag zum Problem der klinischen Schmerzmessung und unternimmt den Versuch, innerhalb eines experimentellen Schmerzmodells Beschreibungen von Schmerzwahrnehmung und Schmerzverarbeitung zu erarbeiten, die zur Charakterisierung chronischer Schmerzen geeignet sind. In mehreren experimentellen Studien bei Gesunden und chronisch Schmerzkranken werden mit den Methoden der Psychophysik Kennwerte von Sensibilisierung und Gewöhnung bei anhaltenden Hitzeschmerzreizen untersucht und Messverfahren für die klinische Schmerzdiagnostik ausgearbeitet. Die Bedeutsamkeit dieser Parameter wird in einer klinischen Studie mit chronisch Schmerzkranken gezeigt, bei der erstmals verstärkte Sensibilisierung bei Patienten mit Rückenschmerzen nachgewiesen wird

Experimental investigations for the development of a 2pi fission fragment detector

In der vorliegenden Arbeit wurde die Möglichkeit der Realisierung eines 2-Pi-Spaltfragmentdetektors untersucht. Damit soll es möglich sein eine Information über die Kernladungszahl eines Fragments aus spontaner oder teilcheninduzierter Spaltung zu erhalten. Die Meßmethode ist daraufhin ausgelegt, daß der korrespondierende Partner eines im Detektor nachgewiesenen Spaltfragments in einer dicken Quelle oder einem dicken Target gestoppt wird und der Gamma-Zerfall dieses neutronenreichen, meist hoch angeregten Kerns in Ruhe erfolgt . Die emittierte Gamma-Strahlung ist somit weder Dopplerverschoben noch -verbreitert und kann von Germanium-Detektorarrays spektroskopiert werden. Durch die hohe Selektivität der Spaltfragmentdetektion läßt sich damit die Struktur seltener, besonders neutronenreicher Kerne untersuchen. Die Methode basiert auf der Messung des spezifischen Energieverlusts eines Spaltfragments mit Hilfe einer Gasionisationskammer und der anschließenden Messung der Restenergie des Spaltfragments mit Hilfe eines Silizium-Halbleiterdetektors. Hierzu wurden Messungen von Spaltfragmenten aus spontaner Spaltung von 252-Cf mit Hilfe eines Detektorteleskops [Goh94] in Koinzidenz mit einem hochreinen Germanium Detektor durchgeführt. Das Teleskop bestand aus einer Ionisationskammer, die mit einem elektrischen Feld arbeitete, das senkrecht zur mittleren Spaltfragmenttrajektorie verlief, sowie einem ionenimplantierten Si-Detektor. Damit wurde ein Auflösungsvermögen von Z/Delta-Z ~ ll für Molybdän (Z=42) und Z/Delta-Z ~ 10 für Ruthenium (Z=44) gemessen. Um den ionenimplantierten Si-Detektor durch einen kostengünstigeren Detektortyp ersetzen zu können, wurden PIN-Dioden als Detektoren für die Energie der Spaltfragmente getestet. Hierbei wurden die Testkriterien von Schmitt und Pleasonton [SP 66] zugrunde gelegt. Die PIN-Diode der Serienproduktion erreichte näherungsweise alle von Schmitt und Pleasonton angegebenen Kriterien und übertraf das Kriterium für Energieauflösung deutlich. Der Ansatz zur Entwicklung eines Detektors mit großem Raumwinkel ist eine Ionisationskammer, die ein elektrisches Feld besitzt, das parallel zur mittleren Spaltfragmenttrajektorie gerichtet ist. Eine solche Feldgeometrie läßt sich leichter auf einen großen Raumwinkel erweitern. Dies macht die ausschließliche Verwendung von Gitterelektroden notwendig, damit die Spaltfragmente die Elektroden ohne nennenswerten Energieverlust passieren können. Mit Hilfe der Methode der Finiten Elemente wurden Potentialverläufe in einer solchen Ionisationskammer simuliert und auf dieser Basis ein Prototyp konstruiert und gebaut, der mit einer Feldrichtung parallel zur mittleren Spaltfragmenttrajektorie arbeitet. Zum Test dieses Detektors wurde ein Experiment mit protoninduzierter Spaltung von 238-U am Van-de-Graaf-Beschleuniger des Instituts für Kernphysik der Universität Frankfurt am Main durchgeführt. Unter Hinzunahme eines hochreinen Ge-Detektors wurden Spaltfragment-Gamma-Koinzidenzen aufgenommen. Das Ansprechverhalten des Spaltfragmentdetektors wurde mit Hilfe der Energieverlustdaten von Northcliffe und Schilling [NS70] numerisch berechnet. Damit konnte ein Auflösungsvermögen von Z/Delta-Z ~ 29 für Yttrium (Z=39) erreicht werden. Dieses Auflösungsvermögen stimmt ungefähr mit dem von Sistemich et al. [SAB+76] mit Hilfe von massen- und energieseparierten Spaltfragmenten gemessenen Auflösungsvermögen eines DeltaE-E-Detektors mit einem senkrecht zur mittleren Spaltfragmenttrajektorie ausgerichteten elektrischen Feld überein. Eine Auflösung von Nukliden der schweren Spaltfragmentgruppe war in beiden Experimenten nicht möglich. Abschließend wurde auf der Basis der Geometrie des EUROSiB-Detektors [dAP+96] die Realisierbarkeit eines 2-Pi-Spaltfragmentdetektors studiert. Dabei zeigte sich, daß es möglich sein sollte, einen solchen Detektor zu konstruieren, obwohl dieser aufgrund des näherungsweise radialsymmetrischen elektrischen Feldes an den Grenzen des Ionisationskammerbereiches arbeiten wird. Mit Hilfe einer möglichst punktförmigen Quelle sowie einer Segmentierung der PIN-Dioden um eine bessere Ortsauflösung zu erreichen, sollte es möglich sein, ein Auflösungsvermögen zu erhalten, das der Größenordnung des Auflösungsvermögens des Prototypen entspricht. Mit dem vorgeschlagenen Detektor ließe sich eine absolute Effizienz von rund 74% in 2-Pi erreichen.In the present thesis the possibility of realizing a 2pi fission fragment detector has been investigated. The aim of this is to obtain an information about the atomic number of a fragment of spontaneous or particle-induced fission. The method is based on the principle that the corresponding partner of a fragment in the detector is stopped in a thick source or a thick target. Then the gamma-decay of this neutron-rich, often highly excited nucleus occurs at rest. Therefore the emitted gamma-radiation, which can be spectroscopied by gamma-detector arrays, is neither Doppler-shifted nor Doppler-broadened. Due to the high selectivity of the fission fragment detection it is possible to study the structure of rare, particularly neutron-rich nuclei. The method is based on the measurement of a fragment's energy loss with a gas ionization chamber, succeeded by a measurement of the fragment's residual energy using a silicon semiconductor detector. Measurements of fragments from the spontaneous fission of 252Cf using a detector telescope [1] in coincidence with a high-purity germanium detector were performed. The telescope consisted of an ionization chamber with an electrical field the direction of which was perpendicular orientated to the fission fragments' trajectory as well as an ion-implanted Si-detector. The measured resolving power was Z/Delta Z = 11 for Molybdenum (Z=42) and Z/Delta Z = 10 for Ruthenium (Z=44). PIN-diodes were tested for measuring the fission fragments' energies to replace the ion-implanted Si-detector by a less expensive type of detector. For these tests the criteria of Schmitt and Pleasonton [2] were applied. The PIN-diode of the series production reached approximately all criteria given by Schmitt and Pleasonton. It even surpassed the criterion for energy resolution clearly. The base to develop a detector with a large solid angle is an ionization chamber with an electrical field the direction of which is parallel to the average trajectory of the fission fragments. This kind of field geometry can be more easily expanded to cover a large solid angle. It requires the exclusive application of grid electrodes to allow the fission fragments to pass the electrodes with negligible energy loss. The potential distribution inside such an ionization chamber was simulated applying the finite element method. Based on these simulations a prototype detector that works with an electrical field the direction of which is parallel to the fission fragments' average trajectory has been constructed and built. An experiment with proton-induced fission of 238U was performed at the Van de Graaf accelerator of the Institute for Nuclear Physics of the University of Frankfurt / Main to test the new detector. By adding a high-purity germanium detector fission fragment-gamma coincidences were recorded. The response of the fission fragment detector was calculated numerically by using the energy loss data by Northcliffe and Schilling [3]. A resolving power of Z/Delta Z = 29 for Yttrium (Z=39) could be achieved with that. This resolving power agrees roughly with the value measured by Sistemich et al. [4] which was obtained with mass and energy separated fission fragments using a Delta E-E detector with an electrical field the direction of which was perpendicular to the fission fragments' average trajectory. It was not possible to resolve nuclei of the heavy fission fragments' group. Finally the feasibility of a 2pi fission fragment detector was studied on the geometrical basis of the EUROSiB-detector [5]. A detector of this kind should be feasible though it will operate at the limit of the ionization chamber region due to the electrical field which has approximately a radial symmetry. A segmentation of the PIN-diodes would increase the spatial resolution. With that and by using a point source, preferably, it should be possible to reach a resolving power of the order of magnitude of the prototype's resolving power. An absolute efficiency of 74% in 2pi should be achieved with the suggested detector

Trend in ice moistening the stratosphere – constraints from isotope data of water and methane

Water plays a major role in the chemistry and radiative budget of the stratosphere. Air enters the stratosphere predominantly in the tropics, where the very low temperatures around the tropopause constrain water vapour mixing ratios to a few parts per million. Observations of stratospheric water vapour show a large positive long-term trend, which can not be explained by change in tropopause temperatures. Trends in the partitioning between vapour and ice of water entering the stratosphere have been suggested to resolve this conundrum. We present measurements of stratospheric H_(2)O, HDO, CH_4 and CH_(3)D in the period 1991–2007 to evaluate this hypothesis. Because of fractionation processes during phase changes, the hydrogen isotopic composition of H_(2)O is a sensitive indicator of changes in the partitioning of vapour and ice. We find that the seasonal variations of H_(2)O are mirrored in the variation of the ratio of HDO to H_(2)O with a slope of the correlation consistent with water entering the stratosphere mainly as vapour. The variability in the fractionation over the entire observation period is well explained by variations in H_(2)O. The isotopic data allow concluding that the trend in ice arising from particulate water is no more than (0.01±0.13) ppmv/decade in the observation period. Our observations suggest that between 1991 and 2007 the contribution from changes in particulate water transported through the tropopause plays only a minor role in altering in the amount of water entering the stratosphere

Characterization of middle‐atmosphere polar warming at Mars

We characterize middle‐atmosphere polar warming (PW) using nearly three Martian years of temperature observations by the Mars Climate Sounder. We report the observed structure of PW and share hypotheses as to possible explanations, which have yet to be tested with global dynamical models. In the data, PW manifested between p  = 15 Pa and p  = 4.8×10 –3  Pa. The latitude where PW maximized shifted poleward with decreasing pressure. The nightside magnitude was larger than the dayside magnitude. The maximum nightside magnitudes ranged from 22 to 67 K. As expected, the annual maximum magnitude in the north occurred during late‐local fall to middle‐local winter. In the south it occurred during late‐local winter. Also as expected, the maximum magnitude near MY 28's southern winter solstice was smaller than that at that same year's northern winter solstice, when a global dust storm was occurring. Unexpectedly, the maximum magnitude at southern winter solstice was comparable to that at northern winter solstice for both MY 29 and MY 30, years that did not experience global dust storms but certainly experienced greater dust loading during L s  = 270° than L s  = 90°. Another unexpected result was a hemispheric asymmetry in PW magnitude during most of the observed equinoxes. This paper also provides tables of (1) averaged temperatures as a function of latitude, pressure, and season, and (2) the maximum polar warming features as a function of pressure and season. These tables can be used to validate GCM calculations of middle‐atmosphere temperatures and constrain calculations of unobserved winds. Key Points Polar warming is characterized based on nearly three MYs of MCS temperatures Average temperatures are provided for validation of modeled temperatures Polar warming characteristics are provided for constraint of modeled windsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97505/1/jgre20016.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/97505/2/SPICAM_temperatures_v_latitude.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/97505/3/PolarWarming_CrossSections_Dayside.pd

Infrared measurements of atmospheric CH_3CN

For the first time CH_3CN has been measured in the Earth's atmosphere by means of infrared remote sensing. Vertical profiles of volume mixing ratio were retrieved from 12 solar occultation measurements by the balloon-borne JPL MkIV interferometer between 1993 and 2004. Profile retrieval is possible in an altitude range between 12 and 30 km with a precision of ∼20 ppt in the Arctic and ∼30 ppt at mid-latitudes. The retrieved CH_3CN profiles show mixing ratios of 100–150 ppt a few kilometers above the tropopause that decrease to values below 40 ppt at altitudes between 22 and 30 km. The CH_3CN mixing ratios show a reasonably compact correlation with the stratospheric tracers CH_3Cl and CH_4. The CH_3CN altitude profiles and tracer correlations are well reproduced by a 2-dimensional model, suggesting that CH_3CN is long-lived in the lower stratosphere and that previously-proposed ion-molecule reactions do not play a major role as loss processes of CH_3CN

Constraints for the photolysis rate and the equilibrium constant of ClO-dimer from airborne and balloon-borne measurements of chlorine compounds

We analyze measurements of ClO across the terminator taken by the Airborne Submillimeter Radiometer (ASUR) in the activated vortices of the Arctic winters of 1995/1996, 1996/1997, and 1999/2000 to evaluate the plausibility of various determinations of the ClO-dimer photolysis cross section and the rate constant controlling the thermal equilibrium between ClO-dimer and ClO. We use measured ClO during sunlit conditions to estimate total active chlorine (ClOx). As the measurements suggest nearly full chlorine activation in winter 1999/2000, we compare ClOx estimates based on various photolysis frequencies of ClO-dimer with total available inorganic chlorine (Cly), estimated from an N2O-Cly correlation established by a balloon-borne MkIV interferometer measurement. Only ClO-dimer cross sections leading to the fastest photolysis frequencies in the literature (including the latest evaluation by the Jet Propulsion Laboratory) give ClOx mixing ratios that overlap with the estimated range of available Cly. Slower photolysis rates lead to ClOx values that are higher than available Cly. We use the ClOx calculated from sunlit ClO measurements to estimate ClO in darkness based on different equilibrium constants, and compare it with ASUR ClO measurements before sunrise at high solar zenith angles. Calculations with equilibrium constants published in recent evaluations of the Jet Propulsion Laboratory give good agreement with observed ClO mixing ratios. Equilibrium constants leading to a higher ClO/ClOx ratio in darkness yield ClO values that tend to exceed observed abundances. Perturbing the rates for the ClO + BrO reaction in a manner that increases OClO formation and decreases BrCl formation leads to lower ClO values calculated for twilight conditions after sunset, resulting in better agreement with ASUR measurements

Thermal tides in the Martian middle atmosphere as seen by the Mars Climate Sounder

The first systematic observations of the middle atmosphere of Mars (35–80km) with the Mars Climate Sounder (MCS) show dramatic patterns of diurnal thermal variation, evident in retrievals of temperature and water ice opacity. At the time of writing, the data set of MCS limb retrievals is sufficient for spectral analysis within a limited range of latitudes and seasons. This analysis shows that these thermal variations are almost exclusively associated with a diurnal thermal tide. Using a Martian general circulation model to extend our analysis, we show that the diurnal thermal tide dominates these patterns for all latitudes and all seasons