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1.
It is known that under resonance conditions, a group of strongly interacting bosonic atoms, trapped in a double-well potential, mimics a single particle, performing Rabi oscillations between the wells. By implication, all atoms need to tunnel at roughly the same time, even though the Bose–Hubbard Hamiltonian accounts only for one-atom-at-a-time transfers. The mechanism of this collective behavior is analyzed, the Rabi frequencies in the process are evaluated, and the limitation of this simple picture is discussed. In particular, it is shown that the small rapid oscillations superimposed on the slow Rabi cycle result from splitting the transferred cluster at the sudden onset of tunnelling, and disappear if tunnelling is turned on gradually. 相似文献
2.
V. V. Kokorin V. A. Chernenko J. Pons C. Segui E. Cesari 《Physics of the Solid State》1997,39(3):485-487
Anomalies have been detected in the temperature behavior of the physical properties of Ni2MnGa in the temperature interval preceding the martensitic transformation, which is attributed to TA
2 phonon mode condensation at T=T
I>T
m (T
m is the martensitic transition temperature).
Fiz. Tverd. Tela (St. Petersburg) 39, 557–559 (March 1997) 相似文献
3.
Pau Bernadó Renato Barbieri Esteve Padrós Claudio Luchinat Miquel Pons 《Journal of the American Chemical Society》2002,124(3):374-375
Addition of Tb3+ to purple membrane (PM) suspensions changes the orientation of the menbrane normal from parallel to perpendicular with respect to the magnetic field. Residual dipolar couplings measured in protein L in the presence of PM are scaled by a factor of -1/2. NMR line broadening and cross-correlation effects induced by the addition of PM are partially reversed by Tb3+ but not by Tm3+ that has no effect on the orientation of PM. This is interpreted as the result of anisotropically restricted motion of protein L in the transiently PM-bound form. 相似文献
4.
A method based on headspace solid-phase microextraction-gas chromatography-mass spectrometry is proposed for the quality control of multilayer packaging and its manufacturing process. Volatile organic compounds (VOCs) are produced in the manufacturing process of the packaging. They can cause organoleptic problems or modify the properties of the packaging depending on the nature and the amount of the VOCs formed. The quantification using packaging samples with a known VOC concentration for the calibration is proposed in order to reduce the analysis time, and the method is validated using a statistical test. Finally, the method is applied to the determination of odour-responsible compounds in multilayer packaging samples obtained under different extrusion-coating conditions, i.e. type of extruder, type of polymer and extrusion speed. 相似文献
5.
We have developed a method for accurate quantitative analysis and statistical comparison of the relative contents of the dystrophin-glycoprotein complex (DGC) in skeletal muscle. This method was applied to compare DGC contents in slow (soleus) and in fast (extensor digitorum longus, EDL) rat skeletal muscles. The quantitative analysis combines a modified bicinchoninic acid (BCA) assay with Western blotting and enhanced chemiluminescence (ECL). This combination allows the use of high levels of detergents and reducing reagents essential for extracting DGC. In addition, the evaluation of the total amount of proteins in each sample makes it possible to have a reference and to accurately compare relative protein levels without using a specific standard. With a large gradient gel, we could concomitantly compare two groups (n = 9) and quantify all protein contents differing highly in their molecular masses (from 35 kDa to 427 kDa). Each experiment was triplicated and normalized; the two muscles were compared using the Mann-Whitney test (P<0.001) to establish their protein content. The DGC relative levels for the slow muscle soleus and the fast muscle EDL differed significantly: dystrophin, beta-dystroglycan, and gamma-sarcoglycan levels were 130%, 110% and 120% higher in the soleus, respectively. The differences observed in the expression level of cytoskeletal associated protein (dystrophin) and transmembranous anchorage components may correspond to a physiological response of the muscle fibers to duration, magnitude, and frequency of the imposed mechanical loading. 相似文献
6.
The interaction of a nonionic polymeric surfactant with an anionic surfactant at the oil–water interface has been studied
by its effects on the droplet size, stability and rheology of emulsions. Oil-in-water (o/w) emulsions were prepared using
isoparaffinic oil and mixtures of a nonionic polymeric surfactant with an anionic surfactant. The macro-molecular surfactant
was a graft copolymer with a backbone of polymethyl methacrylate and grafted polyethylene oxide (a graft copolymer with PEO
chains of MW=750). The anionic surfactant was sodium dodecyl sulfate (SDS). The stabiliza-tion of the emulsion droplets was
found to be different when using one or the other surfactant. The mechanism of stabilization of emulsion droplets by the macro-molecular
surfactant is of the steric type while the stabilization by anionic surfactant is of the electrostatic repulsion type. Emulsions
stabilized with mixtures present both types of stabilization. Other effects on the preparation and stabilization of emulsions
were found to be dependent on properties associated with the surfactant molecular weight such as the Marangoni effect and
Gibbs elasticity. The initial droplet size of the emulsions showed a synergistic effect of the surfactant combination, showing
a minimum for the mixtures compared to the pure components. Emulsion stability also shows a synergistic interaction of both
surfactants. Rheological measurements allow for the estimation of the interparticle interaction when measured as a function
of volume fraction. Most of the effects observed can be attributed to the differences in interfacial tension and droplet radius
produced by both surfactants and their mixtures. The elastic moduli are well explained on the basis of droplet deformation.
Ionic versus steric stabilization produce little difference in the observed rheology, the only important differences observed
concerned the extent of the linear viscoelasticity region.
Received: 22 November 1996 Accepted: 24 March 1997 相似文献
7.
E. Peter Kündig Chantal Dupr Bernadette Bourdin Allan Cunningham Dominique Pons 《Helvetica chimica acta》1994,77(2):421-428
Two new C2 chiral bidentate phosphorous ligands have been prepared in enantiomerically pure form. The two phosphorous centers bear electron-withdrawing groups ((CF3)2CH? O, C6F5) and are linked by a trans-cyclopentane-1,2-diol-derived bridge. Photolysis of [Cr(η6-C6H6)(CO)3] in the presence of these two new ligands and of two previously reported bidentate phosphites, and fluorophosphinites (L) afforded [Cr(η6-C6H6)(CO)L] complexes. IR Spectral comparison of the complexes shows the new ligands to be intermediate in their bonding properties between alkyl phosphites and CO. 相似文献
8.
9.
A technique for computation of the neutralization curves of acid-base solutions, based on an optimization search method, has been developed. The criterion function is the absolute value of the calculated difference between the numbers of positive and negative charges present in the solutions. This technique is generally applicable for solution chemistry, but because of its speed of resolution and its accuracy, it is particularly useful in the control of a real-time process by a computer. 相似文献
10.
The quantification of volatile organic compounds (VOCs) in flexible multilayer packaging materials using headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) was studied. The analytes imclude 22 compounds such as aldehydes. ketones, carboxylic acids and hydrocarbons formed by thermooxidative degradation of polyethylene during the extrusion coating process in the manufacture of the packaging, and many of them are involved in the unpleasant and undesirable odour of these materials. External standard calibration using a solution of the analytes in an appropriate solvent was the first approach studied. Aqueous solutions of the analytes provided low reproducibility and the reduction of aldehydes to alcohols under the HS-SPME conditions. Hexadecane was chosen as the solvent since its polarity is similar to that of polyethylene and its volatility is lower than that of the analytes. However, hexadecane should be added to the sample before the analysis as it modifies the absorption capacity of the fibre. A 75-microm Carboxen-poly(dimethylsiloxane) fibre was used to extract the VOCs from the headspace above the packaging in a 15-ml sealed vial at 100 degrees C after 5 min of preincubation. The influence of the extraction time on the amount extracted was studied for a standard solution of the analytes in hexadecane, together with the influence of the volume of the standard solution and the amount of the sample placed in the vial. Standard addition and multiple HS-SPME were also studied as calibration methods and the results obtained in the quantitative analysis of a packaging material were compared. 相似文献