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81.
C Thomsen P G S?rensen H Karle P Christoffersen O Henriksen 《Magnetic resonance imaging》1987,5(4):251-257
In vivo tissue characterization by measurement of T1- and T2-relaxation processes is one of the greatest potentials of magnetic resonance imaging (MRI). This may be especially useful in the evaluation of bone marrow disorders as the MRI-signal from bone marrow is not influenced by the overlying osseous tissue. Nine patients with acute leukaemia, one patient with myelodysplastic syndrome, and ten normal volunteers were included in the study. The T1- and T2-relaxation processes were measured in the lumbar spine bone marrow using a wholebody superconductive MR-scanner operating at 1.5 Tesla. In the patients MRI was done at the time of diagnosis and during follow-up of chemotherapy and related to bone marrow biopsies taken within three days of the MRI. At the time of diagnosis T1-relaxation time was increased two to three times in the patients (range 0.7-3.0 sec.) compared to the controls (range 0.38-0.60 sec.). No significant difference was seen in the T2-relaxation process. In relation to chemotherapy T1 decreased towards the normal range in the patients who obtained complete remission, whereas T1 remained prolonged in the patients who did not respond successfully to the treatment. The results indicate that MRI may be a non-invasive clinically useful tool in the evaluation of acute leukaemia especially as a follow-up control of chemotherapy. 相似文献
82.
Hong Wang Jing Jing R. R. Mallik H. T. Chu P. N. Henriksen 《Journal of Crystal Growth》1993,130(3-4):571-577
Atomic force microscopy is used to image the surface relief of epitaxial Bi films grown on mica substrates. Monatomic terrace steps are readily resolved, which provide detailed information on crystal growth and defect structures. The films grow from the coalescence of isolated three-dimensional islands, however, each island grows layer-by-layer. The islands are triangular in shape and when they coalesce to form a continuous film, their structures are either in-phase, and consequently large crystallites are formed, or they are out-of-phase and defect structures are formed. The most common defects observed are twinning and stacking faults. Images showing the microscopic details of stacking faults, twinning, and grain boundaries are observed as a result of islands coalescing to form a continuous film. 相似文献
83.
Henriksen V 《The Journal of the Acoustical Society of America》2008,124(1):510-522
The impedance of a simple artificial ear occluded with an earplug and bypassed with narrow air leaks was measured along with the attenuation of sound through the air leaks. A lumped element model is suggested for the simple occluded artificial ear with an air leak. The suggested model was adapted to the impedance measurements and the attenuation was predicted from the model. The attenuation predictions were compared to the attenuation measurements and were found to be within [-3.5,+3] dB of the measured attenuation over the frequency range of 50-1000 Hz and an attenuation range of -2-38 dB. The average difference between the measured and predicted attenuation for four different leaks in the frequency range of 50-1000 Hz was -0.7 dB, indicating a very slight underestimation of the attenuation. 相似文献
84.
Nicolai Stuhr‐Hansen Thorstein Finn Gtze Lars Henriksen Theis Ivan Slling Annette Langkilde Henning Osholm Srensen 《Heteroatom Chemistry》2009,20(2):101-108
Upon treatment of o‐ and p‐(phenylseleno)nitrobenzenes with sodium methoxide quantitative exchange reactions took place, affording the corresponding methoxynitrobenzenes. Upon reaction between 2,4‐bis(phenylseleno)nitrobenzene 2 and sodium methoxide, an unusual regiopure formation of 4‐methoxy‐2‐(phenylseleno)nitrobenzene 3 was observed. This product remained unreactive toward an excess of sodium methoxide, thus preventing the formation of 2,4‐dimethoxynitrobenzene 6 . The nature of the reactants and of the intermediate Meisenheimer complexes was examined by synthetic investigations, x‐ray crystallography, and DFT calculations. We found that the observed selectivity can be understood in terms of traditional resonance considerations. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:101–108, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20519 相似文献
85.
A finite element formulation for the steady laminar flow of an incompressible fluid with microstructure has been developed. The particular fluids considered are commonly known as micropolar fluids, in which case suspended particulate microstructures are modelled by an ‘extended’ continuum formulation. The particle microspin is a new kinematic variable which is independent of the classical vorticity vector and thereby allows relative rotation between particles and the surrounding fluid. This formulation also gives rise to couple stresses in addition to classical force or traction stresses. The finite element formulation utilizes a variational approach and imposes conservation of mass through a penalty function. A general boundary condition for microspin has been incorporated whereby microspin at a solid boundary is constrained to be proportional to the fluid vorticity. The proportionality constant in this case can vary from zero to unity. Sample solutions are presented for fully developed flow through a straight tube and compared with an analytical solution. Results are also generated for flow through a constricted tube and compared with a Newtonian fluid solution. 相似文献
86.
K E Jensen D Stenver M Jensen P Grundtvig C Thomsen H Karle O Henriksen B Nielsen 《Magnetic resonance imaging》1990,8(3):237-243
Volume selective magnetic resonance (MR) proton spectroscopy was used to investigate changes in the haemopoietic bone marrow in patients with end-stage renal disease undergoing treatment with recombinant human erythropoietin (rHuEPO). Significant changes could be detected in the spectra 14 days after the beginning of treatment, before any response was seen in the haemoglobin concentration of peripheral blood. The spectral changes indicate an alteration in cellular composition of haemopoietic bone marrow with an increase in the amount of haemopoietic active tissue. One patient showed a major change in the spectrum four days after treatment began, indicating that MR spectroscopy may detect early changes in the cellular composition of the bone marrow. This noninvasive method may be useful in evaluating treatment effects of recombinant human haemopoietic growth factors in the bone marrow, as well as investigating bone marrow response from different modes of rHuEPO administration. 相似文献
87.
In the literature (see [5, 6, 8]) there are two families of spaces called Kondratiev spaces: (c)± and (S
c)± for 0 1. We investigate the relation between the spaces and show that they are topologically isomorphic when (d) L2 (d) (d) is the underlying Gel'fand triple for (c)±. In this case we also give the explicit relation between the S-transform and -transform on (c)-1 and (S
c)-1, respectively. 相似文献
88.
Leif Højslet Cristensen Svend Erik Rasmussen Niels Pind Klaus Henriksen 《Analytica chimica acta》1980,116(1):7-17
Inexpensive research equipment for secondary x-ray fluorescence excitation is described. The primary beam from a high-powered x-ray tube is collimated onto the targets, six of which may be easily and safely interchanged. A collimator system ensures that the detector receives radiation from well defined areas of the sample. The geometry minimizes radiation from Compton scattering, the twice-scattered continuum radiation from the x-ray tube, and the characteristic lines from the secondary target. The unit is designed for use with standard x-ray tubes and generators, and is part of an energy-dispersive spectrometer used for multielement analysis. The performance of the system with a variety of samples is described. 相似文献
89.
The base-induced solvolysis of dibenzyl triselenocarbonate in DMSO/water (4:1) has been studied by UV spectrophotometric measurements under pseudo-first order conditions, using KOH, Me4NOH, Bu4nNOH and Bu4nNHCO3 as bases. The reaction is first order with respect to the substrate as well as to the base. Rate constants and activation parameters for the four bases indicate that the rate determining step is the nucleophilic attack by the base, as an ionic couple, on the substrate. Fast reactions, due to strong nucleophilic selenolate species, may follow this slow step; a tentative mechanism is proposed on the basis of experimental evidence. 相似文献
90.
A structure space is a quadrupleX=(X, d, A, P), where for some setR, X A=2
R
,d:X×X A is defined byd(I, J)=J–I, andP is the family of cofinite subsets ofR. Forr P, I X, N
r
(I)={J X: d(I, J) r},To(X)={Q X: if x Q there is anr P such thatN
r
(x)
Q}. ThenTo(X) is a (not usually Hausdorff) topology onX called the hull-kernel topology. Replacing d byd
*, whered
*
(I, J)=d(J, I), or byd
s, whered
s
(I, J.)=d(I, J) d
*
(I, J), and proceeding in the obvious way yields thedual hull-kernel topology
To(X
*) andsymmetric topology To(X
s
). The latter is always a zero-dimensional Hausdorff space. When R is a commutative ring with identity andX is a collection of proper prime ideals ofR, To(X
s
) is usually called thepatch topology. Our generality enables us to improve on known results in the case of space of prime ideals and to apply this theory to a wide variety of algebraic structures. In particular, we establish criteria for a subspace of a structure space to be closed in the symmetric topology; we establish a duality between families of maximal elements in the hull-kernel topology and families of minimal elements in the dual hull-kernel topology of subspaces that are closed in the symmetric topology; we use topological constructions to generalize certain ring theoretic notions, such as radical ideals an annihilator ideals; we use this theory to obtain new results about subspaces of the space prime ideals of a reduced, commutative ring.Presented by F. E. J. Linton.This author's research was supported by a grant from the CUNY-PSC research award program. 相似文献