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  • 1
    Electronic Resource
    Electronic Resource
    A molecular beam/surface spectroscopy apparatus for the study of reactions on complex model catalysts (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 4395-4408 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a newly developed ultrahigh vacuum (UHV) experiment which combines molecular beam techniques and in situ surface spectroscopy. It has been specifically designed to study the reaction kinetics and dynamics on complex model catalysts. The UHV system contains: (a) a preparation compartment providing the experimental techniques which are required to prepare and characterize single-crystal based model catalysts such as ordered oxide surfaces or oxide supported metal particles; and (b) the actual scattering chamber, where up to three molecular beams can be crossed on the sample surface. Two beams are produced by newly developed differentially pumped sources based on multichannel arrays. The latter are capable of providing high intensity and purity beams and can be modulated by means of a vacuum-motor driven and computer-controlled chopper. The third beam is generated in a continuous or pulsed supersonic expansion and is modulated via a variable duty-cycle chopper. Angular and time-resolved measurements of desorbing and scattered molecules are performed with a rotatable doubly differentially pumped quadrupole mass spectrometer with a liquid-nitrogen cooled ionizer housing. Time-resolved but angle-integrated measurements are realized with a second nondifferentially pumped quadrupole mass spectrometer. In situ measurements of adsorbed species under reaction conditions are performed by means of an adapted vacuum Fourier transform infrared spectrometer. The spectrometer provides the possibility of time-resolved measurements and can be synchronized with any of the beam sources. This contribution provides a general overview of the system and a description of all new components and their interplay. We also present test data for all components employing simple adsorption/desorption and reaction systems. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1318919
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  • 2
    Electronic Resource
    Electronic Resource
    Rotational alignment in the photodesorption of CO from Cr2O3(0001): A systematic three-dimensional ab initio study (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 762-773 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In recent experiments, the rotational alignment of the laser induced nonthermal desorption of CO adsorbed on an epitaxially grown film of Cr2O3(0001) has been studied [Beauport, Al-Shamery, and Freund, Chem. Phys. Lett. 256, 641 (1996)]. At low-rotational quantum numbers J, the molecules desorb like helicopters (J-vector perpendicular to the surface) while at high J-values cartwheel motion is preferred (J-vector parallel to the surface). These stereodynamic effects and the experimental state resolved velocity distributions of the desorbing species are simulated by means of an exact time-dependent wave packet method in three dimensions. As a basis for this quantum-mechanical treatment of the CO desorption ab initio potential energy surfaces (PES) were used. The PES for the electronic ground state of the CO–Cr2O3(0001) system has been calculated previously by Pykavy et al. [Surf. Sci. 479, 11 (2001)] in an embedded cluster approach. As the intermediate state, generated by the laser irradiation, an internal CO excited state (5σ→2π*) was considered. The PES of this a 3Π-like state of CO adsorbed on Cr2O3(0001) was calculated at the ab initio CASSCF-level. Our key findings in the subsequent wave packet calculations are (1) a high-dimensional treatment of the photodesorption process is very important in this system, essentially the angular coordinates, very often neglected in similar studies, are responsible for a "successful" desorption event; (2) the change from the strongly tilted equilibrium geometry in the electronic ground state to the preferred upright position in the electronically excited state after laser irradiation is essential for the mechanistic picture of the desorption process; (3) the experimental phenomemon of rotational alignment can only be explained if the topologies of the PES of both the electronically excited and the ground state are accounted for; (4) the lifetime of the CO*-intermediate is in the order of 10 fs; (5) the molecule–surface vibrations in the electronic ground state do not much influence the asymptotic results at the experimental temperature of T=100 K. However, the inclusion of excited levels of the hindered rotation helps to gain insight into the desorption mechanism on a microscopic level. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1425383
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  • 3
    Electronic Resource
    Electronic Resource
    Activation of frontoparietal cortices during memorized triple-step sequences of saccadic eye movements: an fMRI study (2001)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 13 (2001), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: To determine the cortical areas controlling memory-guided sequences of saccadic eye movements, we performed functional magnetic resonance imaging (fMRI) in six healthy adults. Subjects had to perform a memorized sequence of three saccades in darkness, after a triple-step stimulus of successively flashed laser targets. To assess the differential contribution of saccadic subfunctions, we applied several control conditions, such as central fixation with or without triple-step visual stimulation, self-paced saccades in darkness, visually guided saccades and single memory-guided saccades. Triple-step saccades strongly activated the regions of the frontal eye fields, the adjacent ventral premotor cortex, the supplementary eye fields, the anterior cingulate cortex and several posterior parietal foci in the superior parietal lobule, the precuneus, and the middle and posterior portion of the intraparietal sulcus, the probable location of the human parietal eye field. Comparison with the control conditions showed that the right intraparietal sulcus and parts of the frontal and supplementary eye fields are more involved in the execution of triple-step saccades than in the other saccade tasks. In accordance with evidence from clinical lesion studies, we propose that the supplementary eye field essentially controls the triggering of memorized saccadic sequences, whereas activation near the middle portion of the right intraparietal sulcus appears to reflect the necessary spatial computations, including the use of extraretinal information (efference copy) about a saccadic eye displacement for updating the spatial representation of the second or third target of the triple-step sequence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.0953-816x.2001.01472.x
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  • 4
    Electronic Resource
    Electronic Resource
    Action observation activates premotor and parietal areas in a somatotopic manner: an fMRI study (2001)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 13 (2001), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Functional magnetic resonance imaging (fMRI) was used to localize brain areas that were active during the observation of actions made by another individual. Object- and non-object-related actions made with different effectors (mouth, hand and foot) were presented. Observation of both object- and non-object-related actions determined a somatotopically organized activation of premotor cortex. The somatotopic pattern was similar to that of the classical motor cortex homunculus. During the observation of object-related actions, an activation, also somatotopically organized, was additionally found in the posterior parietal lobe. Thus, when individuals observe an action, an internal replica of that action is automatically generated in their premotor cortex. In the case of object-related actions, a further object-related analysis is performed in the parietal lobe, as if the subjects were indeed using those objects. These results bring the previous concept of an action observation/execution matching system (mirror system) into a broader perspective: this system is not restricted to the ventral premotor cortex, but involves several somatotopically organized motor circuits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.2001.01385.x
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  • 5
    Electronic Resource
    Electronic Resource
    The influence of OH groups on the growth of rhodium on alumina: a model study (2000)
    Springer
    Catalysis letters 68 (2000), S. 19-24 
    Details
    ISSN: 1572-879X
    Keywords: aluminum oxide ; hydroxyl groups ; rhodium ; growth ; scanning tunneling microscopy ; infrared spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In order to investigate how the presence of surface hydroxyl groups on oxide surfaces affects the interaction with the supported metal, we have modified a well-ordered alumina film on NiAl(110) by Al deposition and subsequent exposure to water. This procedure yields a hydroxylated alumina surface as revealed by infrared and high-resolution electron energy loss spectroscopy. By means of scanning tunneling microscopy, we have studied the growth of rhodium on the modified film at 300 K. Clear differences in the particle distribution and density are observed in comparison to the clean substrate. While, in the latter case, decoration of domain boundaries as typical defects of the oxide film governs the growth mode, a more isotropic island distribution and a drastically increased particle density is found on the hydroxylated surface. From infrared data, it can be deduced that the growth is connected with the consumption of the hydroxyl groups due to the interaction between the metal deposit and the hydroxylated areas. This finding is in line with photoemission results published earlier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019058714724
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  • 6
    Electronic Resource
    Electronic Resource
    Diffusion- and perfusion-weighted MRI in a patient with a prolonged reversible ischaemic neurological deficit (2000)
    Springer
    Neuroradiology 42 (2000), S. 444-447 
    Details
    ISSN: 1432-1920
    Keywords: Key words Magnetic resonance imaging, diffusion-weighted ; Magnetic resonance imaging, perfusion ; Stroke, acute
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We report acute and follow-up diffusion- and perfusion-weighted MRI (DWI, PWI) findings in a patient with a prolonged reversible ischaemic neurological deficit. PWI 12 h after the patient was last seen to be without symptoms revealed a large perfusion deficit in the left posterior MCA territory with a relatively inconspicuous and much smaller abnormality on DWI. Follow-up showed resolution of abnormalities on both DWI and PWI, and conventional MRI was normal, apart from a very slight abnormality, visible only on FLAIR images, at the centre of the initially DWI-positive region. These findings demonstrate the utility of PWI when be used in combination with DWI to investigate the pathophysiology of transient ischemic syndromes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002340000303
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  • 7
    Electronic Resource
    Electronic Resource
    Eine Methode zur Registrierung arterieller Pulsationen mittels Ultraschall (1966)
    Springer
    Pflügers Archiv 291 (1966), S. 268-276 
    Details
    ISSN: 1432-2013
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Eine Methode zur Registrierung arterieller Pulsationen durch Ultraschall (Echoimpulsschallverfahren) wird beschrieben. Durch Schlauchmodelle, Tierexperimente und Ableitungen vom Menschen wird die Zuordnung der Pulsation zur Gefäßwand und die exakte Wiedergabe der Pulskurvenform dargestellt. Die Methode beruht als erste Pulskurvenregistrierung nicht auf dem Prinzip mechanoelektrischer oder mechano-optischer Transducer. Sie ist deshalb nicht auf Druckwirkung der Pulsation auf den Pulsabnehmer angewiesen und eignet sich für die Registrierung von Pulsationen durch starre Oberflächen oder in tiefen Körperregionen, die konventionellen Pulsabnehmern nicht zugänglich sind.
    Notes: Summary A method of recording arterial pulsations by ultrasound is described. Experiments with artificial pulsating tubes and recordings from human arteries and brain arteries of the cat during progredient occlusion of the common carotic artery show that the echopulsations originate at the artery wall. The form of the pulse-curve is the same as that recorded with other probes. This method is the first one which enables pulse-registrations from arteries and other pulsating walls without transducing the pulsation mechanically to the probe. Thus the method can be used for pulse recordings through rigid surfaces or from deeper regions without mechanical penetration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00380583
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  • 8
    Electronic Resource
    Electronic Resource
    Zur Klinik und Pathophysiologie der Vincristinwirkungen am Nervensystem (1969)
    Springer
    Journal of neurology 196 (1969), S. 319-330 
    Details
    ISSN: 1432-1459
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Es wurden 22 Patienten während einer Vincristin-Behandlung mehrfach neurologisch und elektromyographisch untersucht. Die Ergebnisse zeigen eine charakteristische, dosisabhängige Schädigung des Nervensystems. Im Vordergrund stehen bei relativ niedriger Dosierung (weniger als 15 mg) distale Paraesthesien, ein Erlöschen der Eigenreflexe und elektromyographisch eine zunehmende Schwellenerhöhung des H-Reflexes im Vergleich zur Schwelle des direkten Muskelaktionspotentials. Motorische Störungen treten erst bei Dosierungen über 21 mg auf und äußern sich durch starke Atrophie mit relative geringer Parese und muskulärer Hypotonie. Sensible Ausfälle sind auch nach hohen Dosen selten und betreffen dann isoltiert das Berührungs- und Vibrationsempfinden. Die motorische Nervenleitgeschwindigkeit zeigte keine eindeutige Beeinflussung durch die Vincristinbehandlung, während Muskelaktionspotentiale und Nervenaktionspotentiale bei Dosen über 15 mg eine Amplitudenreduktion zeigten. Der bei Gesamtdosen unter 15 mg Vincristin auftretende Verlust der Eigenreflexe und die Schwellenerhöhung des H-Reflexes ohne motorische oder sensible Ausfälle spricht für eine Erregbarkeitsminderung der Motoneurone. Diese Hypothese wird durch morphologische Befunde von Moress gestützt, der bei 2 Patienten nach Vincristin-Behandlung eine Vorderhornzellschädigung fand. Der günstige Effekt des Vincristins bei vermehrter Erregbarkeit der Motoneurone (Spastik) spricht ebenfalls für diese Annahme. Nach unseren Ergebnissen und den morphologischen Befunden der Literatur kommt es erst bei höheren Dosen (〉15 mg) zu einer zusätzlichen Schädigung von Axon und Markscheide des peripheren Nerven i. S. einer toxischen Polyneuropathie, allerdings atypisch, d. h. ohne Schmerzen und typische Sensibilitätsstörung. Eine Besserung der Spastik bei Patienten nach Vincristin (12–15 mg) wird durch Erregungsminderung der Motoneurone erklärt. Eine zusätzliche motorische Axonschädigung ist erst bei mehr als 15 mg Vincristin zu erwarten.
    Notes: Summary Neurological and electromyographical examinations were performed in 22 patients treated with vincristine sulphate. The results show a characteristic development of neurological symptoms in relation to the drug dosage, however, the symptoms are not consistent with a pure neuropathy. With lower doses (15 mg) paresthesia and loss of tendon reflexes are the prominent features. Electromyography reveals increasingly higher thresholds of the H-reflex only as compared to normal persons. Stimulation of mixed nerves after vincristine medication shows higher thresholds for the afferent fibers of the H-reflex than for efferent fibers of the muscle potential. With higher doses (21 mg) lower motor neuron disturbances appear rather suddenly associated with marked atrophy and relatively slight pareses and hypotonia. Cutaneous and deep sensibility remains normal in most cases. In a few cases responses to touch and vibration are diminished. There was no slowing of motor nerve conduction velocity, but with doses exceeding 15 mg a decrease in amplitude of both the muscle action potential and sensory nerve action potential occurred. The loss of tendon reflexes and the increase in threshold of the H-reflex in patients receiving less than 15 mg indicate a diminished excitability of motoneurons. This is in agreement with Moress' findings on autopsy of motoneuron lesions in 2 patients after vincristine treatment. An improved spasticity following the administration of vincristine in 3 patients is explained by the influence of this drug on the excitability of motoneurons. An additional lesion of the axon develops if doses exceed 15 mg.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242385
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  • 9
    Electronic Resource
    Electronic Resource
    Neurologische Störungen bei angiographisch nachgewiesenem Subclavia-Vertebralis-Anzapfsyndrom (subclavian steal) vor und nach dosierter Armarbeit (1966)
    Springer
    Journal of neurology 189 (1966), S. 136-152 
    Details
    ISSN: 1432-1459
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Neurologische Untersuchungen bei neun Fällen von Subclavia-Vertebralis-Anzapfsyndrom (subclavian steal) vor und nach Belastung des kollateral durchbluteten Armes werden mitgeteilt. Bei acht Patienten wurde die Strömungsumkehr der retrograd gefüllten A. vertebralis nach proximalem Subclaviaverschluß angiographisch nachgewiesen. In einem Fall des typischen Syndroms wurde nur der Subclaviaverschluß ohne Spätaufnahmen der Strömungsumkehr angiographisch dargestellt. 7 der 9 Patienten zeigten neurologisch bereits vor Belastung leichte Hirnstammsymptome: Dissoziierte Empfindungsstörungen (3), einseitige spastische Paresen (3), zentraler Lagenystagmus (1) und deutlicher Blickrichtungsnystagmus (1). 6 Patienten hatten ein abnormes Elektronystagmogramm (ENG): leichte optokinetische Seitendifferenzen (4), sakkadierendes Pendelfolgen (3), nur in 2 Fällen Spontannystagmus; darunter die beiden Kranken mit normalem neurologischen Befund. Das Elektrencephalogramm (EEG) war meistens normal und ergab nur in 2 Fällen leichte Seitendifferenzen des α-Rhythmus. Nach maximaler Belastung des kollateral versorgten Armes kam es nur bei drei Patienten zu einer vorübergehenden Änderung des neurologischen und bei je zwei Patienten auch des EEG- und ENG-Befundes. Die neurologischen Ausfälle, die bereits in Ruhe bestehen, können durch zeitweilig insuffiziente Blutversorgung einzelner Hirnstammgebiete im Frühstadium des subclavian steal oder durch Mikroembolien während des Stenosestadiums erklärt werden. Das geringe Ausmaß belastungsabhängiger Befundänderungen spricht für die große Leistungsfähigkeit der Kollateraldurchblutung des Hirnstamms nach erfolgter Anpassung. Die klinische Diagnose „subclavian steal“ ist schon ohne Angiographie möglich, wenn neben einem einseitig verminderten Radialispuls, Blutdruckdifferenzen an den Armen und supraclaviculären Stenosegeräuschen bei Belastung des betroffenen Armes Nackenkopfschmerzen, Übelkeit, Schwindel oder fokale Hirnstammsymptome auftreten.
    Notes: Summary Neurological disturbances in 9 patients with subclavian steal syndrome are described. Diagnosis was ascertained by angiography in each case and evidence of a reversed blood flow in the affected vertebral artery was obtained in 8 cases. Clinical examination revealed brain stem symptoms even during rest in 7 patients. 6 patients had an abnormal electronystagmogram. When the affected arm was exercised vigorously additional neurological symptoms became apparent in 3 cases, changes of either EEG or ENG in 2. Two main pathogenetic factors of permanent brain stem symptoms are discussed: The clinical manifestations included differences of brachial arterial blood pressure, weak radial pulse of the affected side and in most patients supraclavicular bruits. 1) Transiently failing blood supply during the early state of the subclavian steal. 2) Microemboli during the development of arterial stenosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00245780
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  • 10
    Electronic Resource
    Electronic Resource
    Die Beeinflussung der bioelektrischen und mechanischen Aktivität des Säugetiermyokards bei stufenweisem Ersatz von extracellulärem Na+ durch Li+ (1967)
    Springer
    Pflügers Archiv 296 (1967), S. 234-238 
    Details
    ISSN: 1432-2013
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung An elektrisch gereizten, isolierten Papillarmuskeln des Meerschweinchens wurde der Einfluß des stufenweisen Ersatzes von extracellulärem Na+ durch Li+ bei konstantem Ca++-Gehalt von 1,8 mmol/l auf das Verhalten der Kontraktionskraft sowie des Ruhe- und Aktionspotentials untersucht. Dabei fand sich bei Na+-Verminderung auf unter 75% der Norm eine Steigerung der Kontraktionskraft auf ein Vielfaches des Ausgangswerts bei gleichzeitiger Abnahme von Ruhepotential, Overshoot und Aktionspotential-Dauer. Die Befunde zeigen, (a) daß der von Lüttgau u. Niedergerke (1958) für das Froschherz beschriebene Antagonismus zwischen Ca++ und Na+ — in Übereinstimmung mit anderen Autoren — auch am Warmblüter-Myokard vorhanden ist und (b) daß auch am Warmblüter-Myokard die Kontraktionskraft bei Substitution von Na+ durch Li+ in gleicher Weise beeinflußt wird wie durch einfachen Natrium-Entzug oder durch Zusatz von Extra-Calcium.
    Notes: Summary The influence of stepwise substitution of extracellular Na+ by Li+ (a constant calcium concentration of 1.8 mmol/l being maintained) on contractile force, resting and action potentials of electrically stimulated isolated papillary muscles of guinea pigs was studied. Reduction of Na+ below 75% of normal value markedly accentuated contractile force, but decreased resting potential, overshoot and action potential duration. The results indicate that the antagonism between Na+ and Ca++ as described by Lüttgau and Niedergerke (1958) for the frog heart is also present in the mammalian myocardium. The contractile force of the latter is influenced by substitution of Na+ by Li+ in the same manner as by simple sodium depletion or addition of extra-calcium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00363763
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