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851.
Litvinov YA Bosch F Geissel H Kurcewicz J Patyk Z Winckler N Batist L Beckert K Boutin D Brandau C Chen L Dimopoulou C Fabian B Faestermann T Fragner A Grigorenko L Haettner E Hess S Kienle P Knöbel R Kozhuharov C Litvinov SA Maier L Mazzocco M Montes F Münzenberg G Musumarra A Nociforo C Nolden F Pfützner M Plass WR Prochazka A Reda R Reuschl R Scheidenberger C Steck M Stöhlker T Torilov S Trassinelli M Sun B Weick H Winkler M 《Physical review letters》2007,99(26):262501
We report on the first measurement of the beta+ and orbital electron-capture decay rates of 140Pr nuclei with the simplest electron configurations: bare nuclei, hydrogenlike, and heliumlike ions. The measured electron-capture decay constant of hydrogenlike 140Pr58+ ions is about 50% larger than that of heliumlike 140Pr57+ ions. Moreover, 140Pr ions with one bound electron decay faster than neutral 140Pr0+ atoms with 59 electrons. To explain this peculiar observation one has to take into account the conservation of the total angular momentum, since only particular spin orientations of the nucleus and of the captured electron can contribute to the allowed decay. 相似文献
852.
The determination of noble metals in environmental samples is of increasing importance. Palladium is often employed as a catalyst in chemical industry and is also used with platinum and rhodium in motor car catalytic converters which might cause environmental pollution problems. Two different sorbents for palladium preconcentration in different samples were investigated: silica gel functionalized with 1,5-bis(di-2-pyridyl)methylene tbiocarbohydrazide (DPTH-gel) and [1,5-Bis(2-pyridyl)-3-sulphophenyI methylene thiocarbonohydrazide (PSTH) immobilised on an anion-exchange resin (Dowex lx8-200)]. The sorbents were tested in a micro-column, placed in the auto-sampler arm, at the flow rate 2.8 mL min(-1). Elution was performed with 4 M HCl and 4 M HNO3, respectively. Satisfactory results were obtained for two sorbents. 相似文献
853.
Antoni Ferragut Jaume Llibre Marco Antonio Teixeira 《Rendiconti del Circolo Matematico di Palermo》2007,56(1):101-115
We studyC
1 perturbations of a reversible polynomial differential system of degree 4 in. We introduce the concept of strongly reversible vector field. If the perturbation is strongly reversible, the dynamics of
the perturbed system does not change. For non-strongly reversible perturbations we prove the existence of an arbitrary number
of symmetric periodic orbits. Additionally, we provide a polynomial vector field of degree 4 in with infinitely many limit cycles in a bounded domain if a generic assumption is satisfied.
The first two authors are partially supported by a MCYT grant number MTM2005-06098-C02-01, and by a CICYT grant number 2005SGR
00550. The second author is partially supported by a FAPESP-BRAZIL grant 10246-2. All authors are also supported by the joint
project CAPES-MECD grant HBP2003-0017. 相似文献
854.
Monné J Díez Y Puy J Galceran J Nelson A 《Langmuir : the ACS journal of surfaces and colloids》2007,23(21):10581-10588
The exponentially decaying permeability model interprets the chronoamperometric currents arising from Tl+ reduction at a Hg electrode covered with a phospholipid monolayer (DOPC) containing gramicidin monomer by combining three processes: (i) the diffusion of an ion to a membrane surface with an array of channels, (ii) the conformational dynamics of the individual channels, and (iii) the passage of the ion through the channels. The introduction of a variable permeability allows us to uncouple the diffusion from the heterogeneous processes, given that the concentration of a species at the active surface can be obtained by semi-integration of the currents. Consideration of a reverse step for the dehydration process at the mouth of the channel allows the analysis of potential steps away from diffusion-limited conditions where a Nernstian-like behavior of the relevant parameter is observed. The model has been successfully applied to data with all trans retinol or benzo-alpha-pyrene as additive to the phospholipid monolayer and to monolayers without any additive at all. 相似文献
855.
The cyclicity of the period annulus of reversible quadratic Hamiltonian systems under quadratic perturbations was studied by several authors for different cases by using different methods. In this paper, we study this problem in a unified way. 相似文献
856.
Jaume Gin 《Chaos, solitons, and fractals》2005,26(5):1259-1266
In this work it is shown that the intrinsic phenomenon (the quantization of the energy) that appears in the first and simple systems studied initially by the quantum theory as the harmonic oscillator and the movement of a charged particle under the Coulomb force, can be obtained from the study of dissipative systems. In others words, we show that this phenomenon of the quantization of the energy of a particle which moves as an harmonic oscillator and which loses and wins energy can be obtained via a classical system of equations. The same also applies to the phenomena of the quantization of the energy of a charged particle which moves under the Coulomb force and which loses and wins energy. 相似文献
857.
For all non-negative integers n1,n2,n3,j1,j2 and j3 with nk+jk>1 for k=1,2,3, (nk,jk)≠(nl,jl) if k≠l, j3=n3−1 and jk≠nk−1 for k=1,2, we study the center variety of the 6-parameter family of real planar polynomial vector given, in complex notation, by , where z=x+iy and A,B,C∈C\{0}. 相似文献
858.
The synthesis of two new bridged polycyclic systems (I and II), possessing a rigid N-arylethylbenzomorphan structure, by mercuric acetate cyclization of the corresponding seco derivatives (IV and VI, respectively) is described. The relative configuration of these compounds and the preferred indolo[2, 3-a]- or benzo[a]quin-olizidine conformation is assigned. 相似文献
859.
Dissociation constants (pK(a1) and pK(a2) in water-ethanol medium for 3-styryl-2-mercaptopropenoic and 3-(1-naphthyl)-2-mercaptopropenoic acid have been determined potentiometrically, and pK(a2) for both in aqueous medium, spectrophotometrically. Neutralization enthalpies in water-ethanol medium have been determined by thermometric titration. The reactions with metal ions have been studied, and the main reactions are described. The most sensitive reactions are with titanium(IV) (pD = 7.00) and nickel(II) (pD = 6.50). 相似文献
860.
Olivella S Solé A Jiménez O Bosch MP Guerrero A 《Journal of the American Chemical Society》2005,127(8):2620-2627
Experimental results of an unprecedented haloform-type reaction in which 4-alkyl-4-hydroxy-3,3-difluoromethyl trifluoromethyl ketones undergo base-promoted selective cleavage of the CO-CF(3) bond, yielding 3-hydroxy-2,2-difluoroacids and fluoroform, are rationalized using DFT (B3LYP) calculations. The gas-phase addition of hydroxide ion to 1,1,1,3,3-pentafluoro-4-hydroxypentan-2-one (R) is found to be a barrierless process, yielding a tetrahedral intermediate (INT), involving a DeltaG(r)(298 K) of -61.4 kcal/mol. The CO-CF(3) bond cleavage in INT leads to a hydrogen-bonded [CH(3)CHOHCF(2)CO(2)H...CF(3)](-) complex by passage through a transition structure (TS1) with a DeltaG()(298 K) of 20.8 kcal/mol and a DeltaG(r)(298 K) of 9.8 kcal/mol. This complex undergoes a proton transfer between its components, yielding a hydrogen-bonded [CH(3)CHOHCF(2)CO(2)...CHF(3)](-) complex. This process has associated with it a DeltaG()(298 K) of only 3.1 kcal/mol and a DeltaG(r)(298 K) of -43.3 kcal/mol. The CO-CF(2) bond cleavage in INT leads to a hydrogen-bonded [CH(3)CHOHCF(2)...CF(3)CO(2)H](-) complex by passage through a transition structure (TS3) with a DeltaG()(298 K) of 29.2 kcal/mol and a DeltaG(r)(298 K) of 25.1 kcal/mol. The lower energy barrier found for CO-CF(3) bond cleavage in INT is ascribed to the larger number of fluorine atoms stabilizing the negative charge accumulated on the CF(3) moiety of TS1, as compared to the number of fluorine atoms stabilizing the negative charge on the CH(3)CHOHCF(2) moiety of TS3. The solvent-induced effects on the two pathways, introduced within the SCRF formalism through PCM calculations, do not reverse the predicted preference of the CO-CF(3) over the CO-CF(2) bond cleavage of R in the gas phase. 相似文献