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71.
We report measurements of nuclear spin-lattice relaxation and dynamic polarization of protons in ethyleneglycol-alcohol mixtures at 9 kG and 4·2 K and 1·3 K. Comparison of experimental results with a proposed model of spin-lattice relaxation indicates that the role of dipolar and exchange reservoirs of paramagnetic ions in nuclear relaxation is not necessarily negligible, particularly in the presence of high concentration of paramagnetic impurities. The influence of methanol is to enhance the dynamic polarization of protons compared to pure ethyleneglycol, in the most favourable cases by almost 50% in our experimental conditions. 相似文献
72.
Ohne Zusammenfassung 相似文献
73.
Zusammenfassung Es wird eine Darstellungsmethode für das vonBerg undBecker beschriebene Indo-oxin angegeben. Für das Produkt werden die Absorptionsspektren in verschiedenen Lösungsmitteln mitgeteilt. Die Darstellung des bisher unbekannten Hydrochlorids wird beschrieben.Mit 2 Abbildungen.Meinem verehrten Lehrer, Herrn Professor Dr.A. Franke, zum 80. Geburtstag gewidmet.W. P. 相似文献
74.
Cheikh?L? Jean-Jacques?Aaron Václav?Kozmík Ji?í?Svoboda Jean-Claude?Brochon Li?Na 《Journal of fluorescence》2010,20(5):1037-1047
The synthesis, electrochemical and optical properties of three fluorescent substituted thieno[3,2-b][1]benzothiophenes (TBT)
derivatives, including 3-methoxythieno[3,2-b][1]benzothiophene (3-MeO-TBT), 2,3-dimethylthieno[3,2-b][1]benzothiophene (2,3-diMe-TBT),
and 6-methoxythieno[3,2-b][1]benzothiophene-2-carboxylate (6-MeO-TBT-2-COOMe), were investigated. The oxidation potential
values varied between 1.40 and 1.20 V/SCE according to the electronic substituent effect, and electropolymerization attempts,
performed in 0.1 M LiClO4 acetonitrile solution, led to the formation of very thin films of poly(3-MeO-TBT) and poly(2,3-di-Me-TBT). Electronic absorption
spectra, fluorescence excitation and emission spectra, fluorescence quantum yields (ΦF) , lifetimes (τF), and other photophysical parameters of the three new TBT derivatives were measured in DMSO solutions at room temperature.
For the methyl-and methoxy-substituted TBT derivatives, the fluorescence emission peak were slightly red shifted relative
to that of unsubstituted TBT (Δλem = 1–12 nm) whereas, in the case of 6-MeO-TBT-2-COOMe, a rather strong red-shift (Δλem = 73 nm) was attributed to the existence of a “push-pull” electronic interaction of the MeO and COOMe groups. All ΦF values were rather high, varying between 0.11 and 0.35, according to the substituent effect. Fluorescence decays were mono-exponential
and τF values were very short, ranging between 0.11 and 0.30 ns for the substituted TBT derivatives until study. 相似文献
75.
Ramesh-Babu Adusumalli Rejin Raghavan Rudy Ghisleni Tanja Zimmermann Johann Michler 《Applied Physics A: Materials Science & Processing》2010,100(2):447-452
The deformation and failure of the secondary cell wall of Spruce wood was studied by in-situ SEM compression of micropillars
machined by the focused ion beam technique. The cell wall exhibited yield strength values of approximately 160 MPa and large
scale plasticity. High resolution SEM imaging post compression revealed bulging of the pillars followed by shear failure.
With additional aid of cross-sectional analysis of the micropillars post compression, a model for deformation and failure
mechanism of the cell wall has been proposed. The cell wall consists of oriented cellulose microfibrils with high aspect ratio
embedded in a hemicellulose-lignin matrix. The deformation of the secondary wall occurs by asymmetric out of plane bulging
because of buckling of the microfibrils. Failure of the cell wall following the deformation occurs by the formation of a shear
or kink band. 相似文献
76.
77.
The crystallization behaviour of as-prepared and nucleated Ge17Sb23Se60 thin films was studied by means of differential scanning calorimetry, X-ray diffraction analysis and scanning electron microscopy. Detailed analysis of the non-isothermal crystal growth kinetics was performed; the apparent activation energy, kinetic model and value of the pre-exponential factor were determined. The kinetic behaviour was found to be surprisingly close to the ideal Johnson–Mehl–Avrami nucleation-growth process, with the only non-ideality being the prolonged peak end tail (which may be a specificity associated with certain thicknesses of thin layers). This corresponds to the initiation of crystal growth in agreement with the classical nucleation theory, with the amount of mechanical defects and strains being negligible. The value of the kinetic parameter suggests two-dimensional crystal growth, which is consistent with the idea of macroscopic crystallites growing in a sterically restricted thin layer. A similar conclusion can be made on the basis of direct microscopic observation of the crystallites’ morphology. 相似文献
78.
We derive upper bounds on the tail distribution of the transient waiting time in the GI/GI/1 queue, given a truncated sequence of the moments of the service time and that of the interarrival time. Our upper bound is given as the objective value of the optimal solution to a semidefinite program (SDP) and can be calculated numerically by solving the SDP. We also derive the upper bounds in closed form for the case when only the first two moments of the service time and those of the interarrival time are given. The upper bounds in closed form are constructed by formulating the dual problem associated with the SDP. Specifically, we obtain the objective value of a feasible solution of the dual problem in closed from, which turns out to be the upper bound that we derive. In addition, we study bounds on the maximum waiting time in the first busy period. 相似文献
79.
L. Krlín R. Paprok V. Svoboda 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(1):95-109
We model and discuss the possible types of motion that charged particles may
undergo in a stationary and spatially periodic electrostatic potential and a
homogeneous magnetic field. The model is considered to be the simplest
approximation of more complex phenomena of plasma edge turbulence in
tokamaks. Therein, low frequency turbulence appears in the plasma edge,
resulting in a fluctuation of the electron density, and also in the
generation of a turbulent electrostatic field. Typical parameters of this
turbulent electrostatic field are an electrical potential amplitude of
10–100 V and wave numbers k≈103 m-1. In our model, we consider these regimes, together
with a homogeneous magnetic field with a magnitude of 1 T. We investigate the
dynamics of singly-ionized carbon ions – a typical plasma impurity – with
kinetic energies on the order of 10 eV. Besides the obvious
Larmor and drift motions, a motion of random-walk and of Lévy walk
character appear therein.
All of these types of motion can play an important role in the modelling of
the anomalous diffusion of particles from the plasma edge turbulence region.
The dynamics mentioned will cause an inevitable escape of energetic
particles and thus of power loss from the thermonuclear reactor.
Moreover, Lévy walk kinetics represents a very interesting kind of
kinetics, currently of great interest, which was previously not so often
discussed. 相似文献
80.
Electrically Switchable Magnetic Molecules: Inducing a Magnetic Coupling by Means of an External Electric Field in a Mixed‐Valence Polyoxovanadate Cluster 下载免费PDF全文
Dr. Salvador Cardona‐Serra Dr. Juan M. Clemente‐Juan Prof. Eugenio Coronado Dr. Alejandro Gaita‐Ariño Dr. Nicolas Suaud Dr. Ondrej Svoboda Dr. Roland Bastardis Prof. Nathalie Guihéry Dr. Juan J. Palacios 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):763-769
Herein we evaluate the influence of an electric field on the coupling of two delocalized electrons in the mixed‐valence polyoxometalate (POM) [GeV14O40]8? (in short V14) by using both a t‐J model Hamiltonian and DFT calculations. In absence of an electric field the compound is paramagnetic, because the two electrons are localized on different parts of the POM. When an electric field is applied, an abrupt change of the magnetic coupling between the two delocalized electrons can be induced. Indeed, the field forces the two electrons to localize on nearest‐neighbors metal centers, leading to a very strong antiferromagnetic coupling. Both theoretical approaches have led to similar results, emphasizing that the sharp spin transition induced by the electric field in the V14 system is a robust phenomenon, intramolecular in nature, and barely influenced by small changes on the external structure. 相似文献