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排序方式: 共有221条查询结果,搜索用时 46 毫秒
71.
A. Matilla J. M. Tercero C. Valenzuela C. Moreno M. A. Sanjuan 《Journal of solution chemistry》2001,30(6):549-559
The formation of complexes of Zn(II), Cd(II), Hg(II), and Pb(II) and N-carboxymethyl-D,L-threonine (H2CMT, H2L) in aqueous solutions has been studied by spectrophotometric and potentiometric methods. The complexation model for each system has been established by the HYPERQUAD program from the potentiometric data. Three different behaviors are found: ML2H, MLH, ML, MLOH, and ML2 complexes are formed by Zn(II) and Cd(II) ions, ML2H, ML, MLOH, and ML2 are formed by Hg(II) ion, and only 1/1 complexes MLH, ML, and MLOH are formed by the Pb(II) ion. The formation constants determined for all these complexes allow simulation of experimental titration curves with good agreement. The speciation of multimetal systems with H2CMT shows that this compound is a good and selective ligand at low pH for the Hg(II) ion. 相似文献
72.
73.
S.?Stahl F.?Galve J.?Alonso S.?Djekic W.?Quint T.?Valenzuela J.?Verdú M.?VogelEmail author G.?Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,32(1):139-146
We present a new concept for a Penning trap, which is
planar and allows for the implementation of novel confinement
techniques. The trap provides confinement perpendicular to its plane
by an electric potential minimum while a superimposed magnetic
field provides radial confinement. Both the axial position and the depth of the potential minimum
can be controlled by the applied voltages. The device is scalable in the
sense that an arbitrary number of planar traps can be embedded in
one plane thus representing a multitrap array which can be used
for particle interaction studies. Switches between
different traps in the planar array allow for controlled interactions
between the single stored particles. 相似文献
74.
S.?Djekic J.?Alonso H.-J.?Kluge W.?Quint S.?Stahl T.?Valenzuela J.?Verdú M.?VogelEmail author G.?Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2004,31(3):451-457
The present work is concerned with the association of a temperature to a single ion stored in a Penning ion trap. Several methods are described which allow to determine the temperature by measurements of the ions cyclotron and axial trapping frequencies. Recent results of a measurement on a hydrogen-like carbon ion 12C5 + by use of mode coupling are presented and possible further applications are discussed.Received: 8 July 2004, Published online: 6 December 2004PACS:
07.20.-n. Thermal instruments and apparatus - 07.20.Dt. Thermometers - 42.50.Lc Quantum fluctuations - 42.50.Vk Mechanical effects of light on ions 相似文献
75.
Valenzuela SO Monsma DJ Marcus CM Narayanamurti V Tinkham M 《Physical review letters》2005,94(19):196601
A mesoscopic spin valve is used to determine the dynamic spin polarization of electrons tunneling out of and into ferromagnetic (FM) transition metals at finite voltages. The dynamic polarization of electrons tunneling out of the FM slowly decreases with increasing bias but drops faster and even inverts with voltage when electrons tunnel into it. A free-electron model shows that in the former case electrons originate near the Fermi level of the FM with large polarization whereas in the latter, electrons tunnel into hot electron states for which the polarization is significantly reduced. The change in sign is ascribed to the matching of the electron wave function inside and outside the tunnel barrier. 相似文献
76.
Ultrasound enhances liposome-mediated gene transfection 总被引:5,自引:0,他引:5
Previous studies have shown that some series of liposomes, usually containing cationic lipids, are useful tools for gene introduction into cells. To investigate the effect of ultrasound (US) on liposome-mediated transfection, three types of liposomes (designated L1, L2 and L3, in the order of increasing transfection efficiency) containing O,O′-ditetradecanoyl-N-(-trimethylammonioacetyl) diethanolamine chloride, dioleoylphosphatidylethanolamine, and/or cholesterol at varying ratios, were used in this study. HeLa cells were treated with liposome–DNA complexes containing luciferase genes for 2 h before sonication. Optimal US condition for the enhancement was determined to be 0.5 W/cm2, 1 MHz continuous wave for 1 min and was above threshold for inertial cavitation based on EPR detection of free radicals. Luciferase expressions 24 h after the treatments were significantly increased by sonication to 2.4 fold with L1, and 1.7 fold with L2. However, with L3, which showed the highest level of expression among the liposomes, significant but minimal enhancement was observed when sonication was done 15 min after the DNA-L3 treatment, suggesting that efficiency of the liposome also determines the proper timing for sonication. The 2 h pre-sonication incubation with liposome–DNA complexes for L1 and L2 (30 min for L3) required to attain enhancement, suggests that US works to enhance transfection only after cells had enough DNA uptake. 相似文献
77.
Using a simple lattice model for granular media, we present a scenario of self-organization that we term self-organized structuring where the steady state has several unusual features: (1) large-scale spatial and/or temporal inhomogeneities and (2) the occurrence of a nontrivial peaked distribution of large events which propagate like "bubbles" and have a well-defined frequency of occurrence. We discuss the applicability of such a scenario for other models introduced in the framework of self-organized criticality. 相似文献
78.
Can one construct a thermodynamics for compact, slowly moving powders and grains? A few years ago, Edwards proposed a possible step in this direction, raising the fascinating perspective that such systems have a statistical mechanics of their own, different from that of Maxwell, Boltzmann, and Gibbs, allowing us to have some information while still ignoring dynamic details. Recent developments in the theory of glasses have come to confirm these ideas within mean field. In order to go beyond, we explicitly generate Edwards' measure in a 3D model. Comparison of the results with the irreversible compaction data shows very good agreement. The present framework immediately suggests new experimental checks. 相似文献
79.
We report on the degree of order of the vortex solid in YBa2Cu3O7 single crystals observed in ac susceptibility measurements. We show that when vortices are "shaken" by a temporarily symmetric ac field they are driven into an easy-to-move, ordered structure but, on the contrary, when the ac field is temporarily asymmetric, they are driven into a more pinned disordered state. This is characteristic of tearing of the vortex lattice and shows that ordering due to symmetric ac fields is essentially different from an equilibration process or a dynamical crystallization that is expected to occur at high driving currents. 相似文献
80.
G. Werth H. Häffner H.-J. Kluge W. Quint T. Valenzuela J. Verdu 《Hyperfine Interactions》2001,132(1-4):209-212
The mass of the electron in atomic units (m
e) represents the largest error contribution in an experiment to determine the g-factor of the electron bound in hydrogen-like carbon. Recent progress in the calculation reduces the uncertainty of the theoretical
value to such a low value that m
e can be determined from a comparison of experimental and theoretical g-factors. The present preliminary value of the electron mass agrees with the accepted value but reduces the uncertainty by
about a factor 2.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献