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391.
Della Lunga G Pezzato M Baratto MC Pogni R Basosi R 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,164(1):71-77
In the slow-motion region, ESR spectra cannot be expressed as a sum of simple Lorentzian lines. Studies of Freed and co-workers, on nitroxides in liquids gained information on the microscopic models of rotational dynamics, relying much on computer programs for simulation of ESR spectra based on the stochastic Liouville equation (SLE). However, application of Freed's method to copper system of biological interest has been for a long time precluded by lack of a full program able to simulate ESR spectra containing more than one hyperfine interaction. Direct extension of the Freed's approach in order to include superhyperfine interaction is not difficult from a theoretical point of view but the resulting algorithm is problematical because it leads to substantial increase in the dimensions of the matrix related to the spin-hamiltonian operator. In this paper preliminary results of a new program, written in C, which includes the superhyperfine interactions are presented. This preliminary version of the program does not take into account a restoring potential, so it can be used only in isotropic diffusion conditions. A comparison with an approximate method previously developed in our laboratory, based on a post-convolution approach, is discussed. 相似文献
392.
Marek A. Abramowicz Antonio Lanza John C. Miller Sebastiano Sonego 《General Relativity and Gravitation》1997,29(12):1585-1596
We show that the advance of the perihelion of Mercury (and other planets), as well as the deflection of light by the Sun, can be accurately calculated in Newtonian gravity, if one takes into account the fact of the curvature of space. 相似文献
393.
394.
A. Bartolotta G. Di Marco M. Lanza G. Carini 《Journal of Polymer Science.Polymer Physics》1995,33(1):93-104
A study of the thermal and mechanical characteristics of polyethylene oxide-Fe(SCN)3 complexes shows the existence of structures which can be described by considering a crystalline phase of pure polyethelene oxide (PEO) and an amorphous phase of PEO with dissolved salt. Increasing salt contents decrease the content of crystals, favoring the formation of complexes with a high degree of noncrystallinity as a result of strong polymersalt interactions which tend to enhance the distortion degree of the polymeric skeleton. The microscopic homogeneity of the complexes is also confirmed by the presence in the thermal and mechanical spectra of single glass transitions, which shift to higher temperatures with increasing salt content. Two molecular relaxations are present in the mechanical behavior of these systems, the γ-and the αa-processes at low and high temperatures, respectively, and show a relaxation strength which increases with decreasing degree of crystallinity of the polymer up to a X ~ 0.10 molar fraction. Both relaxations exhibit a marked nonexponentiality which has been well accounted for in terms of a gaussian distribution of relaxation times for the γ-process and of the Kolrausch-Williams-Watt exponential function for the αa-process. In the glassy region, the elastic modulus E' reveals a linear temperature dependence which has been interpreted as arising from the anharmonicity of vibrational modes. Increasing noncrystallinity of the system gives rise to an increase of the anharmonicity parameter, which has been ascribed to the influence of the “free volume” in determining the thermal expansivity. ©1995 John Wiley & Sons, Inc. 相似文献
395.
Hall CS Marsh JN Scott MJ Gaffney PJ Wickline SA Lanza GM 《The Journal of the Acoustical Society of America》2000,108(6):3049-3057
Complex molecular signaling heralds the early stages of pathologies such as angiogenesis, inflammation, unstable atherosclerotic plaques, and areas of remote thrombi. In previous studies, acoustic enhancement of blood clot morphology was demonstrated with the use of a nongaseous, fibrin-targeted acoustic nanoparticle emulsion delivered to areas of thrombosis both in vitro and in vivo. In this study, a system was designed and constructed that allows visualization of the evolution of acoustic contrast enhancement. To evaluate the system, two targets were examined: avidin-complexed nitrocellulose membrane and human plasma clots. The time evolution of enhancement was visualized in 10-min increments for 1 h. A monotonic increase was observed in ultrasonic reflection enhancement from specially treated nitrocellulose membranes for targeted emulsions containing perfluorooctylbromide (1.30+/-0.3 dB) and for perfluorooctane (2.64+/-0.5 dB) within the first 60 min of imaging. In comparison, the inherently nonechogenic plasma clots showed a substantial increase of 12.0+/-0.9 dB when targeted with a perfluoro-octane emulsion. This study demonstrates the concept of molecular imaging and provides the first quantifiable time-evolution report of the binding of a site-targeted ultrasonic contrast agent. Moreover, with the incorporation of specific drug treatments into the nanoparticulate contrast agent, ultrasonic molecular imaging may yield reliable detection and quantification of nascent pathologies and facilitate targeted drug therapy. 相似文献
396.
Ian Jones Matthew Inglis Camilla Gilmore Rhys Evans 《Research in Mathematics Education》2013,15(1):34-49
A cumulative body of research has shown that children typically shift from an operational to a relational conception of the equals sign as they move through schooling. Jones (2008) argued that a truly relational conception of the equals sign comprises a substitutive component and a sameness component. Here we present two studies that build on this argument. The first investigated how the equals sign is typically presented to primary children in England, and we report that in the main an operational conception seems to be promoted. The second study measured the impact of a specially designed intervention on early secondary children's conceptions of the equals sign. Pre- and post-test data revealed that the intervention promoted substitutive and sameness components of symbolic equivalence. We consider the theoretical and pedagogical implications of the results. 相似文献
397.
Mirela Kohr Massimo Lanza de Cristoforis Wolfgang L. Wendland 《Potential Analysis》2013,38(4):1123-1171
The purpose of this paper is to use a layer potential analysis and the Leray–Schauder degree theory to show an existence result for a nonlinear Neumann–transmission problem corresponding to the Stokes and Brinkman operators on Euclidean Lipschitz domains with boundary data in L p spaces, Sobolev spaces, and also in Besov spaces. 相似文献
398.
Ricci C Eliasson C Macleod NA Newton PN Matousek P Kazarian SG 《Analytical and bioanalytical chemistry》2007,389(5):1525-1532
In support of the efforts to combat the illegal sale and distribution of counterfeit anti-malarial drugs, we evaluated a new
analytical approach for the characterization and fast screening of fake and genuine artesunate tablets using a combination
of Raman spectroscopy, Spatially Offset Raman Spectroscopy (SORS) and Attenuated Total Reflection-Fourier Transform Infrared
(ATR-FTIR) imaging. Vibrational spectroscopy provided chemically specific information on the composition of the tablets; the
complementary nature of Raman scattering and FTIR imaging allowed the characterization of both the overall and surface composition
of the tablets. The depth-resolving power of the SORS approach provided chemically specific information on the overall composition
of the tablets, non-invasively, through a variety of packaging types. Spatial imaging of the tablet surface (using ATR-FTIR)
identified the location of domains of excipients and active ingredients with high sensitivity and enhanced spatial resolution.
The advantages provided by a combination of SORS and ATR-FTIR imaging in this context confirm its potential for inclusion
in the analytical protocol for forensic investigation of counterfeit medicines. 相似文献
399.
Ricci C Nyadong L Fernandez FM Newton PN Kazarian SG 《Analytical and bioanalytical chemistry》2007,387(2):551-559
This paper reports use of a combination of Fourier-transform infrared (FTIR) spectroscopic imaging and desorption electrospray
ionization linear ion-trap mass spectrometry (DESI MS) for characterization of counterfeit pharmaceutical tablets. The counterfeit
artesunate antimalarial tablets were analyzed by both techniques. The results obtained revealed the ability of FTIR imaging
in non-destructive micro-attenuated total reflection (ATR) mode to detect the distribution of all components in the tablet,
the identities of which were confirmed by DESI MS. Chemical images of the tablets were obtained with high spatial resolution.
The FTIR spectroscopic imaging method affords inherent chemical specificity with rapid acquisition of data. DESI MS enables
high-sensitivity detection of trace organic compounds. Combination of these two orthogonal surface-characterization methods
has great potential for detection and analysis of counterfeit tablets in the open air and without sample preparation. 相似文献
400.
The segmental relaxation in poly(ethylene terephthalate), crystallized from either an isotropic or a cold-drawn glass, is investigated by means of dielectric spectroscopy. It is shown that there exist two distinct alpha relaxation modes: a slow one, characterized by a rather wide frequency interval, and a faster, much narrower one. A simple phenomenological model is developed in order to analyze the polarization autocorrelation functions phi(t)'s associated with these relaxation modes. The model is based on the idea that the growth of crystalline domains causes a progressive confinement of the amorphous regions where, eventually, the observed alpha processes take place. The mechanism of confinement is accounted for by applying to the case of constrained density fluctuations, well known concepts introduced by Adam and Gibbs [J. Chem. Phys. 43, 139 (1965)] concerning the relaxation dynamics in liquids close to the glass transition. Randomness on confining conditions is then introduced, leading to the derivation of analytical expressions which are used afterwards to fit the asymptotic behavior of the phi's for long-time tails. It is found that the slow, broad alpha process takes place in regions where the confining effect of crystals is strong, whereas the amorphous domains relaxing via the fast mode are those where the confinement effect of crystals is weak. The analysis of the phi's by means of this model allows us to relate the fitting exponents to the dispersion in the free energy associated with structural rearrangement. 相似文献