Passive Ballistic Microbunching of Nonultrarelativistic Electron Bunches Using Electromagnetic Wakefields in Dielectric-Lined Waveguides.

Temporally modulated electron beams have a wide array of applications ranging from the generation of coherently enhanced electromagnetic radiation to the resonant excitation of electromagnetic wakefields in advanced-accelerator concepts. Likewise producing low-energy ultrashort microbunches could be useful for ultrafast electron diffraction and new accelerator-based light-source concepts. In this Letter we propose and experimentally demonstrate a passive microbunching technique capable of forming a picosecond bunch train at ∼6 MeV. The method relies on the excitation of electromagnetic wakefields as the beam propagates through a dielectric-lined waveguide. Owing to the nonultrarelativistic nature of the beam, the induced energy modulation eventually converts into a density modulation as the beam travels in a following free-space drift. The modulated beam is further accelerated to ∼20 MeV while preserving the imparted density modulation.

A new pulse sequence for determining T1 and T2 simultaneously.

Determination of the relaxation times T1 and T2 which are important for tissue characterization generally requires the use of different pulse sequences in magnetic resonance imaging. In this study, a new pulse sequence which facilitates simultaneous determination of the T1 and T2 times is presented. Determination takes place in this case pixel by pixel from the measured images. The measuring time corresponds in this case approximately to that of a normal spin-echo sequence with long repetition time and two data acquisitions. The functional dependence of the accuracy of the T1 and T2 determination upon external errors, e.g., angle of rotation errors, is discussed. The tissue contrast behavior of the individual echoes is shown and its dependence on pulse parameters is explained.

Physical principles of NMR tomography.

Using nuclear magnetic resonance tomography it is possible to produce sectional images of the density and relaxation times of the protons within the human body. After a review of the general principles of nuclear magnetic resonance it is explained how this physical effect can be used for generating tomographic images in medical diagnosis. The major components of an imaging system and the physical and technical potentials and limitations of this new method are described. The different appearance of tissue and body fluids in spin-density, T1 and T2 images, as well as resulting problems of interpretation are discussed with typical examples.

Stomatogenesis in the ditransversal ciliate Homalozoon vermiculare (Ciliophora, Rhabdophora).

H. vermiculare possesses about 10 somatic kineties on the right lateral side, 3 somatic kineties on the left lateral side and a single circumoral kinety. The somatic kineties are composed of monokinetids exc\~ept for the anterior ends of the brush kineties which are composed of dikinetids. The circumoral kinety consists of paired kinetosomes one of which is nonciliated and associated with a microtubular lamella and a nematodesma. Stomatogenesis commences when the anteriormost somatic kinetosomes in the opisthe are transformed into the nonciliated kinetosomes of the future oral dikinetid. They lose the somatic infraciliary fibers and the ciliary shaft and each gives rise to a nematodesma and a microtubular ribbon. Adjacent to each of the transformed somatic kinetosomes, a new kinetosome is assembled, thus producing an oral dikinetid anlage. The new anterior kinetosome bears a cilium and becomes the ciliferous kinetosome of the oral wreath of cilia. In protargol stained specimens, proliferation of kinetosomes can first be observed in the left lateral kineties but, eventually, each of the somatic kineties produces one kinetofragment. Thus, H. vermiculare has a holotelokinetal type of stomatogenesis. The cirumoral kinety arises from a counter-clockwise rotation (as viewed from outside the cell) of all 15 dikinetid kinetofragments and subsequent "head to tail" fusion of the fragments after cell division has been completed. The oral apparatus of the proter seems to be largely conserved during division. Some aspects of the evolution of the oral apparatus and the origin of the oral microtubular ribbons are discussed.

Topology, scaling relations and Leonardo's rule in root systems from African tree species.

Aspects of root architecture, including topology, link length, diameter and scaling relations, were analyzed in excavated coarse root systems of three field-grown fruit tree species (Strychnos cocculoides Bak., Strychnos spinosa Lam. and Vangueria infausta Burch) and the fruit-bearing shrub Grewia flava DC. We investigated the root systems using semi-automatic digitizing and computer-based 3-D reconstruction techniques. Topological analysis was carried out to investigate branching patterns as basic determinants of root architecture. New topological indices were developed and revealed significant differences among the species. The different architectural strategies can be explained in terms of cost-benefit relations and efficiency in soil resource exploration and exploitation. In addition, some well-known hypotheses about geometry and scaling, most of them previously unverified by empirical observations on root systems, were tested. For practical applications, the main emphasis is on the relationship between proximal root diameter, an easily determined parameter, and several parameters describing the size of the whole root system. We also tested the "pipe stem" theory, essentially dating back to Leonardo da Vinci, which underlies many models and which we found conformed to our measurement data with reasonable accuracy. A physiological consequence of the "constant cross-sectional area rule" may be a certain homogeneity of hydraulic architecture throughout root systems.

[Part-body hyperthermia with a radiofrequency multiantenna applicator under online control in a 1.5 T MR-tomograph]. / Teilkörperhyperthermie mit einem Radiofrequenz-Multiantennen-Applikator unter online Kontrolle in einem 1.5 T MR-Tomographen.

Objective of this study is the integration of a multiantenna applicator for part-body hyperthermia (BSD 2000/3D) in a 1.5 T MR-tomograph (Siemens Magnetom Symphony) in order to perform noninvasive MR monitoring in real time to increase safety and effectiveness of heat treatments. The positioning unit is mechanically coupled to the MR gantry from the back side and the body coil is utilised for imaging. For that purpose, the hyperthermia antenna system (100 MHz, 1.500 W) and the MR receiver (63.9 MHs) have to be decoupled in terms of high frequency (filter) and electromagnetically (emc). The processing of MR data sets is performed in a hyperthermia planning system. A simultaneous operation of radiofrequency hyperthermia and MR system is possible at clinically relevant power levels. MR imaging is used for tumor-diagnostics (standard spin echo sequences), for hyperthermia planning (T1-weighted gradient echo sequences in equal- and opposed-phase techniques), and for temperature measurements according to the proton resonance frequency method (PRF method, phase evaluation registration using a gradient echo sequence with long echo time). In 33 patients with advanced pelvic and abdominal tumors we performed 150 heat sessions under MR monitoring. For 70% of these patients a visualisation of temperature sensitive data during treatment was possible. The evaluated difference images represent a superposition of real temperature -increase and a (temperature-induced) perfusion elevation. The -hybrid approach renders development of part body hyperthermia possible as an MR-controlled intervention in radiology.

[ECG-triggered NMR-tomography of the heart. Pathological findings]. / EKG-getriggerte NMR-Tomographie des Herzens. Pathologische Befunde.

Initial systematic examinations of the heart by ECG-triggered NMR are reported. Twenty-three abnormal findings were observed amongst 46 patients examined. Special indications are the search for cardiac aneurysms, intracardiac thrombi and changes from pressure and volume stress.

[Assessment of regional ventilation using the inhalation of a radioactive and an aerosol of a 113mIn-labelled colloid solution]. / Otsenka regionarnoi ventiliatsii pri pomoshchi ingalatsii radioaktivnogo gaza i aérozolia kolloidnogo rastvora, mechennogo 113mIn.

Two methods of assessing regional ventilation distribution-dynamic scintigraphy with 133Xe-labelled gas inhalation, and pulmonary scanning following the inhalation of 113mIn-labelled colloid aerosol-were subjected to critical review. A total of 10 normal controls, 5 cardiac patients and 12 patients with pulmonary diseases were examined using both techniques. The subjective imaged of the lungs converged only in 24% of the cases. A considerable discrepancy in the results of the two investigation procedures was noted in 76%, primarily due to the sedimentation of inhaled colloid along the air passages. It is suggested that radio-aerosol scanning cannot visualize actual distribution of ventilation throughout the lungs; however, the method can be useful in the diagnosis of minor bronchial patency disorders before dynamic investigation using 133Xe can detect any changes, or where gamma-counter and analyzer facility is not available. To provide an accurate assessment of regional ventilation, the gas inhalation method should be combined with the dynamic analysis using a gamma-counter and analyzer facility, and perhaps a computer.

[Lung perfusion distribution study by means of 133Xe]. / Issledovanie raspredeleniia legochnoi perfuzii posredstvom 133Xe.

A method for studying regional lung perfusion employing 133Xe is described. Simple radioisotope apparatus with two catheters was used; every isotopic diagnostic department is equipped with it. The possibility of the clinical use of this method was demonstrated in 28 patients with mitral stenosis and in 11 healthy persons. A statistically significant dependence between regional movement of the perfusion to the upper regions of the lungs and the degree of hemodynamics changes in mitral stenosis was noted. Study of the distribution of persusion may be used as a simple method for appraising the hemodynamic changes in mitral stenosis. This method is simple and not burdensome for the patient. It may be recommended first of all in repeated examinations and long-term observations over patients.