Magnetic resonance imaging of rigid polymers at elevated temperatures with SPRITE

Magnetic resonance imaging has rarely been applied to rigid polymeric materials, due primarily to the strong dipolar coupling and short signal lifetimes inherent in these materials. SPRITE (single point ramped imaging withT ₁ enhancement) (B. J. Balcom, R. P. MacGregor, S. D. Beyea, D. P. Green, R. L. Armstrong, T. W. Bremner: J. Magn. Reson. A123, 131–134, 1996) is particularly well suited to imaging solid materials. With SPRITE, the only requirement is thatT ₂^* be long enough so that the signal can be phase-encoded. The minimum phase encoding time is limited by the maximum gradient strength available and by the instrument deadtime. At present this is usually tens of microseconds and will only improve with refinements in technology. We have used the SPRITE sequence in conjunction with raising the sample temperature to obtain images of rigid polymers that have largely frustrated conventional imaging methods. This approach provides a straightforward and reliable method for imaging a class of samples that, up until now, have been very difficult to image.     

THE ENERGY ASPECT OF THE RECIPROCAL INTERACTIONS OF PAIRS OF TWO DIFFERENT VIBRATION MODES OF A CLAMPED ANNULAR PLATE

The standardized mutual active and reactive sound power of a clamped plate, representing the energy aspect of the reciprocal interactions of two different in vacuo modes, has been computed. It was assumed that the vibrations are axisymmetric, elastic and time harmonic, the plate's transverse deflection is small as compared with the plate's size, and that the vibration velocity is small as compared with the acoustic wavenumber generated. The Kirchhoff-Love theory of a perfectly elastic plate was used. The integral formulae for the mutual sound power were transformed into their Hankel representations which made possible their subsequent computation. A closed path integral was used to express the integral in its Hankel representation to compute the mutual active sound power. The asymptotic stationary phase method was used to compute the two magnitudes, i.e., the mutual active and reactive sound power. The results obtained are the asymptotic formulae valid for the acoustically fast waves. The oscillating as well as the non-oscillating terms have been identified in the formulae to make possible their further separate analysis. The availability of the asymptotic formulae makes possible some fast numerical computations of the mutual sound power. Moreover, the formulae presented herein, together with those for the individual modes known from the literature, make a complete basis for further computations of the total sound power of the plate's damped and forced vibrations in fluid.     

μSR in oxygen deficient YBa2Cu3O x (6.5⩽x⩽7.0)

A systematic μSR study of the local magnetic field distribution in a series of oxygen deficient YBa₂Cu₃O _x samples with 6.5⩽x⩽7.0 is reported. Special attention was given to perform the experiments under the same conditions, so that the oxygen content of the measured samples was the only parameter varied. The behavior of the depolarization rate σ as a function of the oxygen contentx was found to have strong similarities with the behavior of the critical temperatureT _c as a function ofx. In particular, two step-like increases of σ were observed abovex=6.7 and 6.9. The temperature dependence of the normalized depolarization rate σ(T)/σ(0) is well described by the two-fluid model forx⩾6.781(1) and clearly deviates from this behavior forx⩽6.704(1). Our results are compared to those obtained by other groups.     

Low-lying energy levels of the FeH molecule

Multireference configuration interaction (MRCI) and complete active space second-order perturbation theory (CASPT2) calculations are performed on Fe₂ and Fe^? ₂. Although it is not possible to definitively identify the ground states of Fe₂ and Fe^? ₂, the calculations suggest that the ground state of Fe^? ₂ in ⁸Σ^? _u derived from 3d¹³4σ² _g4σ² _u and that the states observed in photodetachment are the ⁹Σ^? _g and ⁷Σ^? _g states with a 3d¹³4σ² _g4σ¹ _u occupation, but that the ground state of Fe₂ is ⁷Δ_u(3d¹⁴4σ² _g) and is not observed in the photo-detachment spectra.     

Infrared spectral changes with crystallization in poly(vinylchloride): Correlations with X-ray and density data

The influence of crystallinity and stereoregularity on the infrared (IR) spectrum of atactic PVC in the solid state has been studied by many researchers [1-12]. Although the molecules in commercial PVC consist of both syndiotactic and isotactic sequences, the bulk polymer is not highly stereoregular, having approximately 50% syndiotacticity. Its infrared spectrum is different from that of highly syndiotactic PVC [3,5,7,9,10-12], particularly in the carbon-to-chlorine stretching region where there are three bands located at 610(615), 635, and 690 cm^?1. These three bands are known to be of complex origin, since each band consists of more than one absorption frequency and its relative intensity depends on the physical state or history of the specimen [3,5,7,9,10-12]. The spectrum in this region is most rigorously interpreted in terms of chain conformational structure, the spatial arrangement of the atoms around the C-C1 bond. Thus, while changes in absorbance intensities for the bands with history do not necessarily reflect changes in crystallinity, their history dependence renders these bands potentially useful as crystallinity indicators.     

Fluid phase equilibrium studies on model substances for supercritical fluid extraction with CO2 up to 100 MPa

Abstract

Multicomponent fluid phase equilibrium data are of increasing interest for applications in Supercritical Fluid Extraction (SFE) where compressed supercritical gases are used for the extraction of low-volatile substances (e.g. caffeine from coffee and tea, hops etc.). Sometimes so-called moderator substances have to be added in order to increase solvent power and/or selectivity. Systematic measurements on a four-component system of the type CO₂ + fatty alcohol (e.g. 1-do-decanol) + alkane (e.g. hexadecane) as a function of the amount of moderator added were performed at 393 K and at pressures from 10 to 100 MPa in an analytical high-pressure cell. Separation factors calculated from the p,T,w/,w, “data are presented and discussed.     

Das Auflösungsvermögen des Szintiscanners “Szintitest” bei der Nierenszintigraphie

Der vom VEB Vakutronik WIB Dresden hergestellete Szintiscanner “Szintitites” wird auf seine Einsatzmöglichlichkeit für die Nierenszintigraphic geprüft. Dazu werden Szintigramme von Modellen aufgenommen, die in ihren Impulsdichten in der Gröβenordnung liegen, wie sie nach Applikation von 300 500µCi¹³¹ J-Hippuran über den Nieren und dem anderen Gewebe der Patienten gefunden werden. Zum Einsatz kommt dabei der Konuskollimator mit einer Apertur von 12 mm. Die besser auflösenden 9- und 19- Kanal-Kollimatoren scheiden für die Nierenszintigraphie mit dem “Szintitest” aus, da ihre Effektivität zu gering ist. Die Einflüsse der Abtastgeschwindigkeit, einer bestimmten Untergrundzählrate und eines variablen Abstandes zwischen Scanner und Objekt werden untersucht. Dabei zeigt sich, daβ ein Körperoberfläche, nicht erreicht werden kann. Das Auflösungsvermögen als 2 cm auch im günstigsten Fall von etwa 8 cm Abstand von der Nierenoberfläche, d. h. 2 4 cm von der Köperoberfläche, nicht werden kann. Das Auflösungsvermögen verschlechtert sich dagegen noch je nach Abstand und Untergrun von 2 auf 3 cm.     

Zur quantitativen Auswertung von Mikro-Autoradiogrammen mit dem Densitron

Die vorliegende Arbeit beschāftigt sich mit der Answertung von Autoradiogrammen inhomogen markierter mikroskopischer Strukturen am Densitron. Dazu fertigten wir von herkömmlichen Stripping-Filmen (z. B. ORW O K 106) Mikro-Stufengraukeile an und bestimmten die Schwärzung S_ijeder Stufe photometrisch. Graukeile geeigneten Schwärzungsumfangs dienten dann zur Einstellung der Farbtrigger des Densitrons, so daß sich die bei dieser Einstellung gemessenen Farbflächen F_i des jeweiligen Objektes bestimmten Schwärzungswerten zuordnen ließen.

Als Modellobjekte verwendelen wir erstens Autoradiogramme von ³H-Thymidin-markierten Tumorzellen. Vergleichsmessungen an unterschiedlich lange exponierten, sonst aber identischen Präparaten ergaben eine gute Reproduzierbarkeit der Meßergebnisse. Als zweites Testobjekt dienlen Autoradiogramme einer nur schwach markierten Struktur im Gehirn von Fröschen. Die an diesem Grenzfall erhaltenen Ergebnisse werden mit Meßwerten verglichen, die vom gleichen Objekt mittels Scanning-Photometrie an einem. Mikroskop-Photometer SMP 01 (OPTON, Oberkoches, BRD) gewonnen wurden.     

Investigating the mechanisms of diamond polishing using Raman spectroscopy

Recent research has shown that a phase transformation of diamond to a different form of carbon is involved when diamonds are polished in the traditional fashion. The question as to how this phase transformation is activated and maintained to produce high wear rates is of great technological interest since it may radically change the way we view the processing of diamond. This paper describes the use of Raman spectroscopy to examine debris produced on the diamond polishing wheel, both during its preparation and during polishing. In addition, polished diamond surfaces were examined for the possible existence of non-diamond surface layers in an attempt to identify material removal mechanisms. Raman spectroscopy proves ideal for these analyses because its relatively high spatial resolution is well suited to the analysis of small wear features and debris particles, and because of the wealth of information it reveals about chemical structure. This level of structural information has been lacking in previous analyses of diamond polishing debris. In addition to the non-diamond carbon found in the wear debris, significant quantities of two iron oxides, magnetite (Fe₃O₄) and haematite (α-Fe₂O₃), were also found. An interesting observation was that a transformation from magnetite to haematite could be induced either by using high power laser excitation or by frictional heating during polishing. It is suggested that some of the Raman peaks previously attributed to lonsdaleite might better be explained by the presence of these oxides.     

Connection Formulas for Second Order Differential Equations with a Complex Parameter and Having an Arbitrary Number of Turning Points

We consider the differential equation on a finite interval I, where I contains m turning points, that is here, zeros of ?. Using asymptotic estimates proved by R. E. LANGER for solutions of (*) for intervals containing only one turning point we derive asymptotic estimates (for ρ → ) for a special fundamental system of solutions of (*) in I. The results obtained are fundamental for the investigation of eigenvalue problems defined by (*) and suitable boundary conditions.