Search Results - (Author, Cooperation:B. Zipfel)

2013-04-13

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Biomechanical Phenomena ; Bones of Lower Extremity/*anatomy & histology/physiology ; Female ; Foot/anatomy & histology/physiology ; Foot Joints/physiology ; *Fossils ; *Gait ; Hominidae/*anatomy & histology/*physiology ; Leg/anatomy & histology/physiology ; Lower Extremity/*anatomy & histology/*physiology ; Male ; Pronation ; South Africa ; *Walking

2011-09-10

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Ankle/*anatomy & histology/physiology ; Ankle Joint/anatomy & histology/physiology ; Biological Evolution ; Biomechanical Phenomena ; Calcaneus/anatomy & histology ; Female ; Foot/*anatomy & histology/physiology ; Foot Bones/*anatomy & histology ; Foot Joints/anatomy & histology/physiology ; *Fossils ; Hominidae/*anatomy & histology/physiology ; Humans ; Locomotion ; Male ; Metatarsal Bones/anatomy & histology ; South Africa ; Talus/anatomy & histology ; Tarsal Bones/*anatomy & histology ; Tibia/anatomy & histology

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Fundamental questions of electron beam ion sources (EBIS) are studied using three different setups. Cryogenic classical EBIS: The limit of ion–ion cooling in EBIS devices operating near the space-charge neutralization limit has been studied experimentally. To investigate different degrees of compensation of the electron beam by highly charged ions, a hemispherical analyzer has been constructed including a novel deceleration optic for high resolution. Using its energy definition we tested different modes of ion transportation in our multipassage magnetic spectrometer, which can be operated chromatically as well as extremely dispersively: up to 200 passages could be obtained. EBIS without magnetic field: First results on ion production in the short trap at the very dense crossover of an electron beam (XEBIS) confined only inertially without the use of magnetic fields are presented. Normal conducting short EBIS: Using a normal conducting field of 0.8 T of 25-cm length an EBIS is under construction to study extremely short ion extraction of approximately 4 μs for single turn injection into a medical synchrotron for cancer therapy (MEDEBIS).

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

The Frankfurt superconducting electron beam ion source (EBIS) is under reconstruction for higher ion yield by employing an immersed gun with a 2-mm-diam cathode for a 3 A electron beam. The trap electrode construction is as simple as possible to avoid any rf production. The ion extraction will be similar to the one applied in our MEDEBIS, using tapered electrodes to create a high axial extraction gradient. Research was continued on the use of oscillating electrons to reduce the power requirements of the beam, investigating the formation of a virtual cathode by decelerating the beam at full magnetic field strength while operating the gun under immersed flow conditions with adjustable compression. The MEDEBIS has proven its quality and reliability for the application as an injector for a medically dedicated synchrotron. To improve its yield of bare nuclei, better vacuum conditions are provided by drilling out the inner windings of the warm solenoid to allow for the installation of higher vacuum conductance. After the successful presentation of our XEBIST principle that delivers highly charged ions as Ar18+ and Ba46+ we have now shown its application for the production of singly charged ions as an injector of metallic ions. Finally, an EBIS/T with an internal Penning trap has been constructed to prepare selected ion species and charge states inside the ionization region. This new device will allow the study of electron–ion interactions in well-defined initial and final charge states, i.e., to be able to distinguish between single and multiple step ionization. If the homogeneity of the magnetic field in the trap region will reach 10−9, the determination of binding energies of highly charged ions may be better than a 1 eV accuracy. © 1998 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

While a high electron current electron beam ion source (EBIS) with high perveance has been proposed for its application at forthcoming TeV hadron colliders, an economical operation has been studied using oscillating electrons to reduce the collector current for low power consumptions. Results with oscillating electrons in our cryogenic EBIS with a 5 T magnetic focusing field are being discussed in relation to normal EBIS operation data considering the oscillation factor, current density, and ion yield. Our simplified EBIS/EBIT studies without magnetic focusing now span from a versatile source for the production of high current singly charged metallic ions up to the use of relativistic electron beams for the production of bare uranium. The XEBIST now works successfully with beam energies up to 10 keV. Barium ions having a charge state up to 46 have been extracted using evaporative cooling by Ar and residual gas. The extension to relativistic beam energies taking advantage of the self-focusing effect at partial space charge compensation will be presented elsewhere at this conference. © 1996 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

The crossover electron beam ion source (XEBIST) without confining magnetic field has made an important step towards higher electron beam energies. By proper matching using a magnetic lens system, a high compression of the electron beam has been achieved. The importance of reducing the lens aberrations by partial neutralization of the beam space charge in the lens section has been demonstrated. The effective current density in the trap region has been further increased by self-pinching in connection with space-charge neutralization. In our first experiments at an electron energy of 22 keV, the average current density in the trap increased from 10 to 150 A/cm2 at 40 ms neutralization time. Highly charged ions like Ar17+ were produced in this way. The combined Penning ion trap and electron beam source (PITEBIS) was operated successfully by radio-frequency modulating the current of the electron beam. This new kind of modulation could be used not only for cleaning EBIS sources from unwanted ion species but also to enhance the yield of highly charged ions by ion cooling. The effect of selective rf heating is demonstrated. © 2002 American Institute of Physics.

Electronic Resource

1432-2102

Schlüsselwörter Elektronenstrahlcomputertomographie ; TIPS ; Aortenaneurysma ; Pavk ; Key words Electron-beam tomography (EBT) ; Aortic aneurysm ; Peripheral arterial occlusive disease

Springer Online Journal Archives 1860-2000

Medicine

Summary Purpose: To evaluate the potential of electron-beam computed tomography (EBT) in the pre- and postinterventional assessment of vascular abdominal pathologies. Material and methods: Forty patients with implanted transjugular portosystemic shunt (TIPS), 12 patients with peripheral arterial occlusive disease and 8 patients with infrarenal abdominal aortic aneurysm after endovascular implantation of bifurcation stents were prospectively examined with contrast-enhanced EBT during one year. The evaluation included analysis of time-density curves (TDC) and 3D reconstructions. Results were compared with Doppler sonography and/or DSA. Results: In 30 of 40 TIPS patients, identical results were found with EBT, Doppler sonography and/or DSA. Reduced perfusions of the TIPS, which were subsequently confirmed by DSA, could not be shown with EBT in 3 patients. Nine of 12 patients with peripheral arterial occlusive disease and angiographically proven stenosis (〉75%) showed a reduced and delayed peak density of the time-density curves. The quantification of arterial stenosis, however, did not follow the angiographic values. In all patients with the implanted bifurcation stents, EBT could correctly exclude a leakage of the stent. Conclusion: EBT has certain avantages over conventional spiral CT in the evaluation of abdominal vascular pathologies due to the additional assessment of perfusion parameters. Clinical indications for the use of EBT are seen especially in the postinterventional follow-up of patients with implanted stents.

Zusammenfassung Fragestellung: Die vorliegende Studie untersucht die Wertigkeit der Elektronenstrahlcomputertomographie (EBT) bei der prä- und postinterventionellen Abklärung von Pathologien des arteriellen und portalvenösen Gefäßsystems. Methodik: Innerhalb eines Jahres wurden 40 Patienten mit transjugulärem portosystemischem Shunt (TIPS), 12 Patienten mit peripherer arterieller Verschlußkrankheit (pavk) und 8 Patienten mit infarenalen Bauchaortenaneurysmata nach interventioneller Therapie prospektiv im EBT untersucht. Im Anschluß an die Untersuchung wurden Zeit-Dichte-Kurven und 3D-Rekonstruktionen der zu beurteilenden Gefäßabschnitte angefertigt. Die Ergebnisse wurden mit Befunden der Dopplersonographie und/oder DSA korreliert. Ergebnisse: Bei 30/40 TIPS-Patienten stimmte die EBT mit der Dopplersonographie bzw. der DSA überein, bei 3 Patienten konnte eine dopplersonographisch nachgewiesene und interventionell bestätigte Minderperfusion des TIPS im EBT nicht diagnostiziert werden. Bei 9/12 Patienten mit angiographisch nachgewiesenen Gefäßstenosen (〉75%) konnte eine Abflachung und ein verzögerter Anstieg der Zeit-Dichte-Kurven nachgewiesen werden. Die Quantifizierung der Stenose mit den Zeit-Dichte-Kurven zeigte jedoch nur eine eingeschränkte Korrelation mit der i.a.-DSA. Bei den Patienten mit endovaskulär implantierter Aortenprothese konnte in allen Fällen eine komplette Ausschaltung des Aortenaneurysmas nachgewiesen werden. Schlußfolgerung: Die Vorteile der FBT bestehen in der Möglichkeit, zusätzlich zur „konventionellen” kontrastverstärkten Schnittbilddiagnostik aufgrund der methodisch bedingten hohen zeitlichen Auflösung auch dynamische Aspekte zu erfassen. Mögliche klinische Indikationen im Bereich des abdominellen Gefäßsystems bestehen insbesondere in der postinterventionellen Untersuchung zur Überprüfung des Interventionserfolges.

Electronic Resource

1572-9540

Springer Online Journal Archives 1860-2000

Physics

Abstract A special problem in atomic physics research with highly charged ions is to prepare ions with a unique charge state inside of EBIS or EBIT devices. On the other hand, there are great losses resulting from the transport of the ions from the source to an external trap. Therefore we are setting up an EBIS/T with internal Penning trap. This new set-up will be able to study electron–ion interaction with well-defined initial and final charge states, distinguishing between single step successive ionisation and multiple step ionisation of charge states similar to the crossed beams method but for much higher charge states. Another feature of this system is to determine with high precision the ion charge state distribution in the EBIS/T by application of Fourier Transform Ion Cyclotron Resonance (FT-ICR). This method allows the on-line monitoring of the ion distribution and the evolution of the charge state population together with its dependence on the degree of space charge compensation of the electron beam in the EBIS/T. It will be possible to study ion dynamics in compensated space charge potentials. In case of high homogeneity of the magnetic field in the trap region, experiments may be considered to measure directly binding energies of highly-charged ions and other topics of high resolution mass spectroscopy.

Electronic Resource