The dependence of diffusion length,lifetime and emitter Gummel-number on temperature and doping

Contents In this paper systematic study of the temperature and doping dependences of the energy gap, the diffusion length, the lifetime and the emitter-Gummel number is presented. Based on a special transistor structure, the above parameters could be measured. The doping concentration in the base varies from 10¹⁶/cm³ to 4×10¹⁸/cm³ while the temperature changes from 100 K to 340 K. It is found that the band gap narrowing is smaller than that published in some literature while it agrees with that recently published by del Alamo and Swanson [25]. This result is fully discussed and explained in the text. The diffusion length is nearly independent of temperature, which is interesting for device modeling. On the other hand, the diffusion length decreases with the doping concentrationN _A . The measured lifetime is inversely proportional to doping concentration with powerm wherem=0.6–0.2 depending on temperature. The results show an exponential increase of the emitter Gummel-number with temperature and an increase with doping concentration in the base.

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Die Abhängigkeit der Diffusionslänge, der Trägerlebensdauer und der Emitter-Gummelzahl von der Temperatur und der Dotierungskonzentration

Übersicht Die Arbeit gibt eine systematische Studie wieder über die Temperatur- und Dotierungsabhängigkeit des Bandabstandes, der Diffusionslänge, der Trägerlebensdauer sowie der Emitter-Gummelzahl. An einer speziell präparierten Transistor-Struktur konnten diese Parameter gemessen werden. Die Dotierungskonzentration in der Basis variierte von 10¹⁶ cm^–3 bis 4×10¹⁸ cm^–3, während sich die Temeraturänderung über den Bereich von 100 K bis 340 K erstreckte. Es zeigt sich, daß die Verminderung des Bandabstandes kleiner ist als in einem Teil der Literatur publiziert, daß sic aber übereinstimmt mit dem von del Alamo und Swanson [25] kürzlich veröffentlichten Wert. Dieses Ergebnis wird ausführlich diskutiert und erklärt. Die Diffusionslänge ist annähernd unabhängig von der Temperatur, was für die Bauelemente-Modellierung von Interesse ist. Andererseits nimmt die Diffusionslänge mit wachsender DotierungskonzentrationN _A ab. Die gemessene Ladungsträgerlebensdauer ist proportionalN _A ^–m , wobeim=0,6–0,2 beträgt, abhängig vom Temperaturbereich. Die Ergebnisse zeigen einen exponentiellen Anstieg der Emitter-Gummelzahl mit der Temperatur und eine Zunahme mit der Dotierungskonzentration der Basiszone.

     

Fabrication of SnO2 Particle-Layers using the Electrospray Method and Gas Sensing Properties for H2

The particle layers of SnO₂ were prepared using the electrospray pyrolysis method from SnCl₂ ethanol solution on the glass substrates heated at 773 K. Pyrex and quartz glass were used for the substrates. The effects of the concentration and the conductivity of the precursor solutions on the morphology and gas sensitivity of the SnO₂ layers were investigated. The sensitivity measurements were carried out for 0.5% H₂ in synthetic air at the operating temperature of 573 K and that was defined by the resistance ratio of the specimen under synthesized dry-air (R_air) and 0.5% H₂ (R_gas), R_air/R_gas. Among the examined concentrations of 1× 10^–4, 1× 10^–3 and 1× 10^–2 mol dm^–3, the layer prepared at 1× 10^–3 mol dm^–3 exhibited the maximum sensitivity of 20. The particle sizes were 110(30), 160(40), and 150(35) nm in diameter at 1× 10^–4, 1× 10^–3, and 1× 10^–2 mol dm^–3, respectively. The values in the parentheses indicate the standard deviation of the measured data. On the other hand, the conductivity of the solution exerted no significant influence on the sensitivity, which was adjusted by the addition of dilute hydrochloric acid. The particle size decreased with the conductivity and became 134(30), 105(20) and 87(20) nm in diameter at 7.8, 27.0 and 86.6 S cm^–1, respectively. Under all the conditions the layers had the dendrite-like structure, indicating the in-flight particle formation. The crystallite size was evaluated to be 6 nm from XRD using the Scherrers equation. These particles of 87–160 nm was thought to consist of smaller primary particles (crystallites). The Pd doping by 1 wt% to SnO₂ enhanced the gas sensitivity by a factor of 4.     

Das elektromagnetische Feld eines in Seewasser parallel zum Spiegel verlegten,geraden stromdurchflossenen isolierten Drahtes mit blanken Enden,in dem dreifach geschichteten Raum: Luft,Wasser, Erde

Ohne ZusammenfassungVerzeichnis der Abkürzungen und Einheiten P _x ,P _z Komponenten desHertzschen Vektors Vm - l Strom im Dipol oder Kabel A - k _p ² =² _{p 0}–j_{0 p} Wellenzahl (p=0, 1, 2) 1/m² - _p = _p +j _p elektrodynamische Leitfähigkeit (p=0, 1, 2) S/m - Integrationsvariable J/m - Wurzelausdrücke in den Integralen 1/m - l·x'/ _p häufiger Faktor vor den Integralen V · m² - z, h, H; a; x, y, R, Längen m - elektrische Feldstärke V/m - magnetische Feldstärke A/m - p Index gemäß dem Raumteil A/m - S _{0, 1} (),S _1,2() Zwei gleichart. Abk. in Gl. 3 (8, 9) Ohm · m - N() bes. Funktion im Nenner von Gl. 3 (10) Ohm² - D() bes. Funktion im Nenner der Gl. 3 (1) m² ₀=4 ·10^–7 H/m ₀=(1/36)·10^–9 F/m für Luft. Mit 3 Textabbildungen     

Water household of the common carp,Cyprinus carpio, when submitted to an osmotic challenge, as determined by diffusion-weighted magnetic resonance imaging at 7 T

In vivo diffusion-weighted magnetic resonance imaging (MRI) was used to determine the effects of an osmotic challenge (1% NaCl) to a freshwater fish, the common carp (Cyprinus carpio). The imaged region covered organs such as the swimbladder, the liver, the kidney, the intestine, the spinal cord, and muscle tissue. A striking difference between salt-treated and control fish was found in the liver. The apparent diffusion coefficient value of livers from control fish was (0.39±0.16) 10⁻⁹ m²/s and of salt-treated fish was (1.23±0.14) 10⁻⁹ m²/s, which points to an increase in extracellular water content. These results were partially confirmed by a decrease in dry/wet weight ratio of the liver tissue. We also found increased levels of stress proteins in liver tissue. TheQ factor of the applied radiofrequency coil dropped dramatically when we performed experiments with salt-exposed fish, indicating an increased conductivity resulting from the increased ion concentration and osmolarity of the fish. The data on plasma osmolarity of salt-exposed fish confirm a significant osmolarity increase upon salt exposure (from 334 to 430 mOsm/kg) and exceeded the osmolarity of the salt water (324 mOsm/kg), indicating that carp tend to cope with an increased salinity by increasing the internal osmolarity (hyperosmotic regulation). These data demonstrate that diffusion-weighted MRI might be a useful and noninvasive tool in the study of osmotic challenges of aquatic organisms.     

Principles and applications of FLASH NMR imaging

Routine clinical NMR scanners apply low-flip-angle gradient-echo sequences as fast-imaging modalities. Fast low-angle shot (FLASH) NMR imaging is the first version of a large family of fast gradient-echo methods. It is based on the application of reduced flip angles for NMR excitation, the acquisition of magnetic field gradient echoes, and considerably shortened repetition times. Under these conditions, transverse magnetization survives. This magnetization can be destroyed in spoiled FLASH or used for imaging in refocused FLASH. The measuring time of FLASH NMR images is dependent on gradient hardware and is under optimal technical conditions user selectable between less than 100 ms and 1 s. Short imaging times give the possibility to apply magnetization preparation before imaging. This technique allows the acquisition of image contrast with respect to any selected parameter, e.g.T ₁ T ₂, or diffusion constant. This FLASH version has been called snapshot-, turbo-, or magnetization-prepared RAGE.     

Contrast enhancement in atherosclerosis development in a mouse model: in vivo results at 2 Tesla

To develop an MRI method for the evaluation of contrast enhancement in early atherosclerotic plaque development in the abdominal aorta of a mouse model. Male apoE^–/– mice from three groups, respectively 4 (n = 6), 8 (n = 11) and 16 (n = 4) weeks were included. Axial T1 spin echo images of the abdominal aorta were obtained above and below the renal arteries (90 m spatial resolution) before and over 1 h after the injection of a macromolecular contrast agent. Signal enhancement was measured in the vessel wall and compared to histological features. Maximal arterial wall signal enhancement was obtained from 16 to 32 min post injection. During this time, the signal-to-noise ratio increased by a factor up to 1.7 in 16 week mice and 2.7 and 2.4 in 8 and 4 weeks mice, respectively. The enhancement of the arterial wall appeared less pronounced in the oldest mice, 16 weeks old, exhibiting more advanced lesions. Using a macromolecular gadolinium agent, contrast uptake in atherogenesis varies with lesion stage and may be related to vessel-wall permeability. Dynamic contrast-enhanced MRI may be useful to evaluate the atherosclerotic plaque activity in mice.     

Der Typ-I-supraleiter im sprungförmigen, äußeren Magnetfeld

Übersicht Zum besseren technischen Verständnis des elektromagnetischen Verhaltens eines Supraleiters wird für den Fall eines plötzlich eingeschalteten äußeren Magnetfeldes der räumliche und zeitliche Verlauf der elektromagnetischen Feldgrößen im Innern des Supraleiters untersucht.Die mit Hilfe der London-Theorie herzuleitenden Feldgleichungen werden für die Geometrie des supraleitenden Halbraums und unter einigen Vernachlässigungen gelöst.Daraus gehen die Verhältnisse beim Normalleiter für den Grenzfall der unendlich großen Eindringtiefe hervor.Während für technische Anwendungsfälle die Dauer bis zum Erreichen statischer Feldzustände beim Supraleiter vernachlässigbar ist, darf sie beim Normalleiter mitunter nicht außer Acht gelassen werden.

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Contents For a better technical understanding of the electromagnetic behaviour the space/time-distribution of the electromagnetic field values within a superconductor subjected to a suddenly applied external magnetic field is investigated.The field equations resulting from the London theory are solved for a semi-infinite superconductor, making some simplifications.The behaviour of a normal conductor is obtained if the penetration depth is considered as infinite.Whereas in technical applications the period of time in which static field conditions are reached can be neglected in super-conductors, in normal conductors it must be taken into account sometimes.

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Verzeichnis der verwendeten Symbole B Magnetische Kraftflußdichte in T - D dielektrische Verschiebungsdichte in Asm^–2 - E Elektrische Feldstärke in Vm^–1 - e 1,6·10^–19 As Elektronenladung - f Frequenz in s^–1 - H Magnetische Feldstärke in Am^–1 - H _e Feldstärke des äußeren Magnetfeldes in Am^–1 - m 9,1·10^–31kg Elektronenmasse - n _s Dichte supraleitender Ladungsträger in m^–3 - S Gesamt-Stromdichte in Am^–2 - S _n normalleitende Stromdichte in Am^–2 - S _s supraleitende Stromdichte in Am^–2 - S _v Verschiebungsstromdichte in Am^–2 - t Zeit in s - v _s Geschwindigkeit supraleitender Ladungsträger in ms^–1 - ₀ 8,86·10^–12AsV^–1m^–1 Dielektrizitätskonstante des leeren Raumes - 10^–21VsmA^–1 (Londonsche) Materialgröße - 10^–7 m supraleitende Eindringtiefe (Londonwert) - ₀ 4·10^–7VsA^–1m^–1 Permeabilitätskonstante des leeren Raumes - Ladungsdichte in Asm^–3 - Relaxationszeit in s - Kreisfrequenz in s^–1 - elektrische Leitfähigkeit in ^–1 m^–1     

Structural, Thermal and Electrical Properties of Ce-Doped SrMnO3

The Sr_1-xCe_xMnO_1- system (0 x 0.5) was investigated with respect to its structural, thermal and electrical properties. Although un-doped SrMnO₃ has the perovskite structure above 1400°C, the structure is unstable at room temperature. However, partial substitution of Ce for Sr in SrMnO₃ stabilizes the perovskite structure down to room temperature. Single phase perovskite is obtained for 0.1 x 0.3 in Sr_1-xCe_xMnO_1-, and it remains stable even following heat treatment at 800°C for 100 h. The dependence of the electrical conductivity on temperature was measured from room temperature to 1000°C in air. Ce doping dramatically enhanced the electrical conductivity of SrMnO₃. Sr_0.7Ce_0.3MnO_1- exhibits a higher conductivity (290 S · cm^-1 at 1000°C) than that of La_0.8Sr_0.2MnO₃ (LSM, about 175 S · cm^-1) and remains n-type over the whole range of temperature examined. The thermal expansion coefficients in the system were nearly constant with values ranging between 1.24 × 10^-6 and 1.01 × 10^-6 cm/cm · K for temperatures of 50°C to 1000°C.     

Properties of CaTi1 − x Fe x O3 − δ Ceramic Membranes

CaCO₃, TiO₂ and Fe₂O₃ were mixed in the appropriate stoichiometric quantities and calcined at 1100C for 10 h. These powder mixtures were uniaxially pressed and sintered at temperatures ranging from 1350 to 1500_C for 2 h in order to obtain dense disk-shaped samples with nominal CaTi_{1 – x}Fe_xO_3– (x = 0.05, 0.15, 0.20, 0.40 and 0.60) compositions. Dilatometry and in situ high temperature powder X-ray diffraction analysis showed a good agreement on the thermal expansion behaviour of these materials between room temperature and 1000_C. The estimated linear thermal expansion coefficient is close to 13× 10^{– 6} K^{– 1} and is little affected by composition. No evidence for surface carbonation was detected in the infrared spectra collected on samples previously annealed in CO₂ atmospheres. The oxygen permeability measured at temperatures ranging from 750 to 1000_C goes through a sharp maximum for x = 0.20. This result is interpreted by structural differences related to change from disordered to ordered oxygen vacancies. The overall performance of CaTi_0.80Fe_0.20O_3– is compared to other mixed conducting materials.     

Synthesis, Physicochemical Characterization and Ionic Conductivity of LaGa0.4Mg0.2M0.4O3−δ (M = Cr, Mn, Fe, Co)

Partial electronic and ionic conductivities, crystal structure, thermal expansion and infrared absorption spectra of the perovskite-type series, LaGa_0.40Mg_0.20M_0.40O_3– (M = Cr, Mn, Fe, and Co), have been studied. The rhombohedral distortion of the perovskite lattice decreases and the unit cell volume increases in the sequence Co < Cr < Mn < Fe. The p-type electronic conduction increases with atomic number of the transition metal cation; the activation energy varies in air from 15.9 to 32.1 kJ/mol. The oxygen ionic conductivity of the M-doped phases at temperatures below 1200 K is significantly lower than that of LaGa(Mg)O₃. The highest ionic conductivity was found for the Fe- and Co-containing phases. The ion transference numbers of La(Ga,Mg,M)O_3– at 970–1270 K were determined to vary in a wide range, from 2 × 10^–5 to 3 × 10^–2. Thermal expansion coefficients, calculated from the dilatometric data collected in the temperature range 300–1100 K, lie in the range (7.2–15.5) × 10^–6 K^–1.     

Fitting interrelated datasets: metabolite diffusion and general lineshapes

Objective

Simultaneous modeling of true 2-D spectroscopy data, or more generally, interrelated spectral datasets has been described previously and is useful for quantitative magnetic resonance spectroscopy applications. In this study, a combined method of reference-lineshape enhanced model fitting and two-dimensional prior-knowledge fitting for the case of diffusion weighted MR spectroscopy is presented.

Materials and methods

Time-dependent field distortions determined from a water reference are applied to the spectral bases used in linear-combination modeling of interrelated spectra. This was implemented together with a simultaneous spectral and diffusion model fitting in the previously described Fitting Tool for Arrays of Interrelated Datasets (FiTAID), where prior knowledge conditions and restraints can be enforced in two dimensions.

Results

The benefit in terms of increased accuracy and precision of parameters is illustrated with examples from Monte Carlo simulations, in vitro and in vivo human brain scans for one- and two-dimensional datasets from 2-D separation, inversion recovery and diffusion-weighted spectroscopy (DWS). For DWS, it was found that acquisitions could be substantially shortened.

Conclusion

It is shown that inclusion of a measured lineshape into modeling of interrelated MR spectra is beneficial and can be combined also with simultaneous spectral and diffusion modeling.

     

A quasi analytical procedure for determining the optimum commutation angles of PWM converters

Contents A method for calculating the optimum commutation times for PWM converters is proposed. The method is mainly analytical and leads to a simple, fast calculation procedure. The time behaviour of any variable, electrical or non electrical, which is considered to be the most characteristic of the behaviour of the system, can be optimized. The validity of the analytical approach is subject to some hypotheses which are often verified in practice. The computation power required by the method is so limited that, in the majority of cases, a minicomputer can be used.

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Quasi analytische Bestimmung der optimalen Steuerwinkel für pulsbreitenmodulierte Frequenzumrichter

Übersicht Man beschreibt ein meist analytisches Verfahren für die Berechnung der optimalen Steuerwinkel für pulsbreiten-modulierte Frequenzumrichter. Durch dieses Verfahren wird es möglich, den Zeitverlauf der bedeutendsten elektrischen und nichtelektrischen Größen des Systems zu optimieren. Das Rechnungsverfahren beruht auf meistens erfüllten Annahmen; auf Grund seiner einfachen und schnellen Durchführung braucht man in den meisten Fällen nur Minicomputer zum Zweck.

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List of symbols fundamental frequency - x(t) modulated wave (input wave) - y(t) variable to be optimized (output wave) - f ^*() transfer function - f ^*() f ^*() amplitude - ^*() f ^*() phase - f(n) f ^*() evaluated only in correspondence with () _f integer multipliers - a _n x(t) Fourier coefficients relative to the terms cos (n _f t) - b _n x(t) Fourier coefficients relative to the terms sin (n _f t) - a _n ,b _n asa _n ,b _n , but relative toy(t) - y _d (t) required output wave-form - a _d (n), b _d (n) y _d (t) Fourier coefficients - y _s (t) deviation function (defined asy(t)–y _d (t)) - a _s (n), b _s (n) y _s (t) Fourier coefficients - ^* rms value ofy _s - as ^* except for some constants - _i commutation angles - m ₁ commutations number in the first half of the period - m number of independent commutations in the period - _ij , _ij x _ij auxiliary variables dependent on the _i - V _k numerical values relative to the links imposed onx(t)'s,y(t)'s harmonics - peak values ofy(t) andx(t) harmonic of ordern - Y _n ,X _n rms values of ordern harmonics ofy(t) andx(t) - _j Lagrange multipliers - z number of constraints relative tox(t)'s harmonics Research supported by Italian Research Council (C.N.R.)     

Ferroelectric Properties of Bi3.25Nd0.75Ti3O12 Thin Films Prepared by MOD Process

Ferroelectric Bi_{4 – x}Nd_xTi₃O₁₂(BNdT) thin films with the composition (x = 0.75) were prepared on Pt/Ti/SiO₂/Si(100) substrate by metal-organic deposition. The films were annealed by various temperatures from 550 to 650C and then the electrical and structural characteristics were investigated for the application of FRAM. Electrical properties such as dielectric constant, 2Pr and capacitance were quite dependent on the thermal heat treatment. The measured 2Pr value on the BNdT capacitor annealed at 650C was 56 C/cm² at an applied voltage of 5 V. No fatigue was observed up to 8 × 10¹⁰ read/write switching cycles at a frequency of 1 MHz regardless of annealing temperatures.     

Transport flüssiger Metalle mittels zylindrischer elektromagnetischer Pumpen in denen das magnetische Wanderfeld durch Induktoren erzeugt wird

ÜBersicht In der Abhandlung wurde ein allgemeines Berechnungsmodell der zylindrischen elektromagnetischen Pumpen mit den das magnetische Wanderfeld erzeugenden Induktoren dargestellt. Zur Lösung der Gleichungen des elektromagnetischen Feldes wurde die Fourier-Transformation angewandt. Es wurden die Verteilungen der magnetischen Induktion sowie der Dichte der elektrodynamischen Kraft für Pumpen mit Kompensationswicklungen und Induktoren, festgesetzt. — Ein Algorithmus zur Berechnung der Geschwindigkeitsverteilung des flüssigen Metalls für den laminaren Durchfluß wurde angegeben.

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The transport of liquid metal in the cylindrical induction pumps with inductors producing the travelling magnetic field

Contents The general calculation model of the cylindrical induction pump with inductors producing the travelling magnetic field has been presented in the paper. — Fourier transform has been applied to solve equations of the electromagnetic field. The distributions of the magnetic flux density and force density have been determined for several induction pumps with inductors possesing compensating windings. — Algorithm for the calculation of velocity distribution of the liquid metal for laminar flow has been given.

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Liste der Symbole A Vektorpotential, Vs/m - B magnetische Induktion, Vs/m² - Eu Euler-Zahl - F _z Komponente der elektrodynamischen Kraft (Förderungskraft), N - f Volumendichte der elektrodynamischen Kraft, N/m³ - Ha Hartmann-Zahl - I₀(x), I₁(x) modifizierte Bessel-Funktionen ersten Grades (nullte und erste Ordnung) - J Stromliniendichte, A/m - j imaginäre Einheit - K Anzahl der Sektionen - K₀(x), K₁(x) modifizierte Bessel-Funktionen zweiten Grades (nullte und erste Ordnung) - L Länge der Hauptwicklung, m - p _b Polpaarzahl - p ₀ Druck, N/m² - Q Metalldurchflußstärke, m³/s - R Radius, m - Re Reynolds-Zahl - Re _m magnetische Reynolds-Zahl - t Zeit, s - v _s Synchrondrehzahl des Wanderfeldes, m/s - v _z Geschwindigkeit des Metalls, m/s - Dichte des flüssigen Metalls, kg/m³ - Permeabilität, Vs/Am - elektrische Leitfähigkeit, S/m - Polteilung - kinematische Viskosität, m²/s - , , Phasenverschiebungswinkel Indizes q Bezugsgröße - r dimensionslose Größe - u Kompensationswicklung - , ,z Vektorenkomponenten im zylindrischen Koordinatensystem     

Transformation method for electromagnetic wave problems with moving boundary conditions

Contents A method for the solution of initial-boundary-value problems of the wave equation with moving boundary conditions is presented, which transforms the wave equation for the region with moving boundary into a form-invariant wave equation for a region with fixed boundary. Two kinds of transformations are found which refer to regions (1) expanding and (2) contracting with (increasing) time. As an application, the compression of microwaves in a one-dimensional cavity 0xs(t) with fixed liner atx=0 and an inward moving liner atx=s(t) is treated analytically. It is shown that large amounts of microwave energy can be generated in the final compression stages(t)0 with the help of a copper liner driven by explosives ( 10^3 m/s$$ " align="middle" border="0"> ), for times of the order of the electromagnetic diffusion time, _D =d ²10^-2s. Such microwave compressions proceed quasi-statically for non-relativistic liner velocities, .

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Transformations-Methode für elektromagnetische Wellenprobleme mit bewegten Randbedingungen

Übersicht Eine Methode zur Lösung von Anfangs-Randwert-Problemen der Wellengleichung mit bewegten Randbedingungen wird gegeben, welche die Wellengleichung für das Gebiet mit bewegter Grenzfläche in eine form-invariante Wellengleichung für ein Gebiet mit ruhender Grenzfläche umformt. Zwei Arten von Transformationen werden gefunden, welche sich auf zeitlich (1) expandierende und (2) schrumpfende Gebiete beziehen. Als Anwendung wird die Kompression von Mikrowellen in einem eindimensionalen Hohlraum 0xs(t) mit einem festen Liner beix=0 und einem nach Innen bewegten Liner beix=s(t) analytisch behandelt. Es wird gezeigt, daß sich große Mengen von Mikrowellen-Energie in der Endphases(t)0 der Kompression mit Hilfe eines durch Explosivstoffe angetriebenen Kupfer Liners ( 10^3 m/s$$ " align="middle" border="0"> ) erzeugen lassen, für Zeiten von der Größenordnung der elektromagnetischen Diffusionszeit _D =d ²10^-2s. Derartige Mikrowellen-Kompressionen erfolgen quasi-statisch bei nicht-relativistischen Liner Geschwindigkeiten, .

     

Early changes in apparent diffusion coefficient of rat brain following total circulatory arrest

The apparent diffusion coefficient (ADC) of rat brain was determined for the cortex [(771±23)×10^–6 m²/s] and caudate-putamen (CP) [(601±25)×10^–6 m²/s]. Using the ultrafast imaging technique U-FLARE changes in ADC were followed with a 2.4-min temporal resolution after the induction of total circulatory arrest by intravenous KC1 injection. For both tissue types, a biphasic decrease of ADC was observed. The initial fast phase led to an ADC decrease by (27±4)% (cortex) and (29±3)% (CP) within 5 min, whereas the slow continuous decrease of the second phase resulted in (68±3)% (cortex) and (66±3)% (CP) of control after 18 min. The similar relative reduction in ADC for the cortex and the CP meant that an effective distinction between both tissue types persisted after the cessation of systemic and cerebral blood flow.Address for correspondence: Max-Planck Institut für neurologische Forschung, Gleuelerstrasse 50, D-50931 Köln, Germany. Additional reprints of this chapter may be obtained from the Reprints Department, Chapman & Hall, One Venn Plaza, New York, NY 10119.     

Dynamic contrast-enhanced MRI using macromolecular contrast media for monitoring the response to isolated limb perfusion in experimental soft-tissue sarcomas

The objective of this study was to evaluate the potential of dynamic contrast-enhanced MRI for quantitative characterization of tumor microvessels and to assess the microvascular changes in response to isolated limb perfusion with TNF- and melphalan. Dynamic contrast-enhanced MRI was performed in an experimental cancer model, using a macromolecular contrast medium, albumin-(Gd-DTPA)₄₅. Small fragments of BN 175, a soft-tissue sarcoma, were implanted in 11 brown Norway (BN) rats. Animals were assigned randomly to a control (Haemaccel) or drug-treated group (TNF-/melphalan). MRI was performed at baseline and 24 h after ILP. The transendothelial permeability (K^PS) and the fractional plasma volume (fPV) were estimated from the kinetic analysis of MR data using a two-compartment bi-directional model. K^PS and fPV decreased significantly in the drug-treated group compared to baseline (p<0.05). In addition, K^PS post therapy was significantly lower (p<0.05) in the drug-treated group than in the control group. There was no significant difference in fPV between the drug-treated and the control group after therapy. Tumor microvascular changes in response to isolated limb perfusion can be determined after 24 h by dynamic contrast-enhanced MRI. The data obtained in this experimental model suggest possible applications in the clinical setting, using the appropriate MR contrast agents.     

Diffusion-weighted echo planar MR imaging of the neck at 3 T using integrated shimming: comparison of MR sequence techniques for reducing artifacts caused by magnetic-field inhomogeneities

Objective

Our objective was to compare available techniques reducing artifacts in echo planar imaging (EPI)-based diffusion-weighed magnetic resonance imaging MRI (DWI) of the neck at 3 Tesla caused by B0-field inhomogeneities.

Materials and methods

A cylindrical fat–water phantom was equipped with a Maxwell coil allowing for additional linear B0-field variations in z-direction. The effect of increasing strength of this superimposed gradient on image quality was observed using a standard single-shot EPI-based DWI sequence (sEPI), a zoomed single-shot EPI sequence (zEPI), a readout-segmented EPI sequence (rsEPI), and an sEPI sequence with integrated dynamic shimming (intEPI) on a 3-Tesla system. Additionally, ten volunteers were examined over the neck region using these techniques. Image quality was assessed by two radiologists. Scan durations were recorded.

Results

With increasing strength of the external gradient, marked distortions, signal loss, and failure of fat suppression were observed using sEPI, zEPI, and rsEPI. These artifacts were markedly reduced using intEPI. Significantly better in vivo image quality was also observed using intEPI compared with the other techniques. Scan time of intEPI was similar to sEPI and zEPI and shorter than rsEPI.

Conclusion

The use of integrated 2D shim and frequency adjustment for EPI-based DWI results in a significant improvement in image quality of the head/neck region at 3 Tesla. Combining integrated shimming with rsEPI or zEPI can be expected to provide additional improvements.

     

Microwave Dielectric Properties of CuO-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Doped ZnNb<Subscript>2</Subscript>O<Subscript>6</Subscript> Ceramics with Low Sintering Temperature

Microwave dielectric properties of low temperature sintering ZnNb₂O₆ ceramics doped with CuO-V₂O₅-Bi₂O₃ additions were investigated systematically. The co-doping of CuO, V₂O₅ and Bi₂O₃ can significantly lower the sintering temperature of ZnNb₂O₆ ceramics from 1150 to 870C. The secondary phase containing Cu, V, Bi and Zn was observed at grain boundary junctions, and the amount of secondary phase increased with increasing CuO-V₂O₅-Bi₂O₃ content. The dielectric properties at microwave frequencies (7–9 GHz) in this system exhibited a significant dependence on the relative density, content of additives and microstructure of the ceramics. The dielectric constant ( _r) of ZnNb₂O₆ ceramics increased from 21.95 to 24.18 with increasing CuO-V₂O₅-Bi₂O₃ additions from 1.5 to 4.0 wt%. The quality factors (Q× f) of this system decreased with increasing CuO-V₂O₅-Bi₂O₃ content and ranged from 36118 to 67100 GHz for sintered ceramics, furthermore, all Q× f values of samples with CuO-V₂O₅-Bi₂O₃ additions are lower than that of un-doped ZnNb₂O₆ ceramics sintered at 1150C for 2 h. The temperature coefficient of resonant frequency ( _f) changed from –33.16 to –25.96 ppm/C with increasing CuO-V₂O₅-Bi₂O₃ from 1.5 to 4.0 wt%     

Oxygen exchange and transport properties of yttria-stabilized zirconia coated with LaCrO3

The oxygen permeation flux through YSZ (Yttria-Stabilized Zirconia) in reducing Po ₂ is mostly controlled by the surface-exchange kinetics in spite of very high temperature [1]. In order to study the kinetics, the YSZ surface was coated with LaCrO₃ on feed side, permeate side, or two sides, and the oxygen fluxes were measured under controlled Po ₂ gradient generated by different CO/CO₂ mixtures (permeate side: ∼3 × 10⁻¹² atm, feed side: 2 × 10⁻¹⁰∼2 × 10⁻⁸ atm) at 1600^∘C. The oxygen flux was determined by measuring the change in CO₂ content of the permeate-side gas. When both feed and permeate surfaces were coated, the oxygen flux increased by ∼6 times. For either permeate- or feed-side coating, the increases were ∼4 times and ∼1.5 times, respectively. A model was proposed in order to estimate the surface-exchange coefficient ( ) of feed and permeate side with or without coating.