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1.
Photon correlation spectroscopy and freeze-fracture electron microscopy have been used to determine the ability of a range of micelle-forming, polyoxyethylene (20) sorbitan monoesters (Tweens) to solubilise vesicles prepared from phosphatidylcholines of different acyl chain lengths and degrees of saturation with a view to rationalising (in terms of their membrane toxicity) which of the micelle-forming surfactants to use as drug delivery vehicles. The phosphatidylcholines used were dimyristoyl-, dipalmitoyl-, distearoyl- and dioleoylphosphatidylcholine (DMPC, DPPC, DSPC and DOPC, respectively) while the nonionic polyoxyethylene sorbitan monoesters studied were polyoxyethylene (20) sorbitan monolaurate (Tween 20), a 9:1 weight ratio mixture of polyoxyethylene (20) sorbitan monopalmitate and monostearate (Tween 40), a 1:1 weight ratio mixture of polyoxyethylene (20) sorbitan monopalmitate and monostearate (Tween 60), and polyoxyethylene (20) sorbitan monooleate (Tween 80). The ability of the Tween micelles to solubilise phospholipid vesicles was found to depend both upon the length of the surfactant acyl chain and the length of the acyl chains of the phospholipid comprising the vesicle. Vesicles composed of long saturated diacyl chain phospholipids, namely DSPC and DPPC, were the most resistant to solubilisation, while those prepared from the shorter acyl chained DMPC were more readily solubilised. In terms of their solubilisation behaviour, vesicles made from phospholipids containing long, unsaturated acyl chains, namely DOPC behaved more akin to those vesicles prepared from DMPC. None of the Tween surfactants were effective at solubilising vesicles prepared from DPPC or DSPC. In contrast, there were clear differences in the ability of the various surfactants to solubilise vesicles prepared from DMPC and DOPC, in that micelles formed from Tween 20 were the most effective solubilising agent while those formed by Tween 60 were the least effective. As a consequence of these observations it was considered that Tween 60 was the surfactant least likely to cause membrane damage in vivo and, therefore, is the most suitable surfactant for use as a micellar drug delivery vehicle.  相似文献   
2.
Manganites of the LA1−x Ca x MnO3 family show a variety of new and poorly understood electronic, magnetic and structural effects. Here we outline a new approach recently proposed by us, where we argue that due to strong Jahn-Teller (JT) coupling with phonons the twofold degeneratee g states at the Mn sites dynamically reorganize themselves into localised, JT polaronsl with exponentially small inter-site hopping, and band-like, nonpolaronic statesb, leading to anew 2-band model for manganites which includes strong Coulomb and Hund’s couplings. We also discuss some results from a dynamical mean-field theory treatment of the model which explains quantitatively a wide variety of experimental results, including insulator-metal transitions and CMR, in terms of the influence of physical conditions on the relative energies and occupation of thel andb states. We argue that this microscopic coexistence of the two types of electronic states, and their relative occupation and spatial correlation is the key to manganite physics. Dedicated to Professor C N R Rao on his 70th birthday  相似文献   
3.
An X-band EPR study on a Na_3(CrMo_6O_(24)H_6)·8H_2O single crystal diluted by its isomor-phic compound Na_3(AlMo_6O_(24)H_6)·8H_2O at room temperature is reported. Using the least squares-fitting method to simulate the EPR data for principal planes, the Hamiltonian parameterswere obtained. The principal values of the g tensors are g_(ZZ) = 1.904, g_(XX)= 1.973, g_(YY)=1.933. The zero field splitting tensor parameters are D = 0.275 cm~(-1), E = 0.05 cm~(-1). The fielddependence of Cr~(3+) energy levels with field at different angles from the principal axes whenthe field is along the principal planes is calculated based on these experimental parameters.The isofrequency plots of calculated field vs. angle are also shown. They agree well with theexperimental results.  相似文献   
4.
5.
A substance on which X-rays fall emits photoelectrons and Auger electrons. The energy spectra of the electrons emitted provide information about the electronic structure in the specimen, ranging from the innermost atomic levels and their dependence on the chemical environment to the molecular orbitals of the valence electrons and the band structure in solids. Electron spectra of this nature can now be recorded with high-resolution instruments; their analysis offers new aspects for investigation of chemical composition. The method of electron spectroscopy developed for this purpose, which has now been developed to a high degree of perfection, will be referred to in the following discussion as ESCA (Electron Spectroscopy for Chemical Analysis).  相似文献   
6.
The transmission electron microscope (TEM) visualization of the supermolecular structure of cold-drawn, oriented nylon 6 bulk material (bristles) by stained ultra-thin sections is reported. For evaluating the electron micrographs optical diffraction (OD) has been applied in comparison with small angle X-ray scattering (SAXS). The deformation of the spherulites was followed by polarization microscopy. In addition, investigations were carried out on commercial nylon 6 fibres. As the main result a transverse structure was revealed within the drawn samples at draw ratios between =4 and 4.5, consisting of mosaic crystals which show some lateral alignment. The structure is described by a modified layer lattice model. While the long period may increase slightly during drawing, the crystallite thickness remains almost constant. Fibres with =3.4 show a similarly oriented structure though the lateral alignment of the crystals is not so pronounced.  相似文献   
7.
A finite spread in axial momentum for the electron beam in a free electron laser amplifier is shown to decrease the small-signal gain. For millimeter and sub-millimeter wave amplifiers, where exponential growth dominates the gain, it is shown that the gain is approximately 3 db below that for a cold beam if the relative momentum spread (u/u)1/2 = (Go/248)1/2 (o/L), where Go1 is the gain in db for the cold-beam case, o is the magnetic wiggler period, and L is the amplifier length. Exact numerical examples are given for representative FEL amplifiers at 35 and 550 GHz.This research was sponsored by the U.S. Office of Naval Research, and by the U.S.-Israel Binational Science Foundation.  相似文献   
8.
After eliminating reflections from the walls of the plasma container, we observed polarization of the coherent synchrotron radiation from a relativistic electron beam rotating in a plasma. Several features of the polarization agree well with calculations based on the single particle synchrotron radiation theory. A particular polarization ratio (Fig. 3) does not, however. We deduce from this direct diffraction of the radiation by the beam electrons. This is strong evidence for beam-particle bunches of size cm. Also, there must be some absorption of the extraordinary wave to account for the observations. We suggest a way to apply these results to measure the pitch angle of the beam.Work supported by Army Research Office.  相似文献   
9.
The various factors influencing the nucleation of radiation damage in the HVEM are reviewed. A method for obtaining quantitative information from observations is given. The effect of reirradiation at room temperature on the damage formed at elevated temperatures is shown. This effect may give experimental information concerning the strain fields surrounding large dislocation loops.  相似文献   
10.
《Analytical letters》2012,45(11):1005-1012
Abstract

A procedure for the determination of propoxyphene (α-d-dimethylamino-1, 2 -diphenyl-3 -methyl-2 -propionoxybutane) in plasma is reported. The method is based on the electron capture characteristics of propoxyphene. The plasma is rendered basic to generate the free amine and extracted with ether. The extract is analyzed by gas chromatography using a 4 foot OV-225 column. An internal standard of imipramine hydrochloride is used to quantitate the propoxyphene. This internal standard is carried through the entire procedure. The ratio of the peak heights of propoxyphene to imipramine is compared to ratios obtained from standards placed in plasma and treated in the same manner as the samples. Six subjects were given propoxyphene at different time intervals, and the data are presented concerning these subjects.  相似文献   
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