排序方式: 共有17条查询结果,搜索用时 921 毫秒
1.
Y. Luo M. Piantek J. Miguel M. Bernien W. Kuch R. Haag 《Applied Physics A: Materials Science & Processing》2008,93(2):293-301
We present the synthesis of 4′-amino-4-mercaptobiphenyl (AMB) and its deposition from solution onto Au(111) substrates. The
resulting organic thin films were characterized by contact angle, infrared reflection absorption spectroscopy (IRRAS), X-ray
photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure (NEXAFS) measurements. It is demonstrated
that the majority of AMB molecules are coupled to the gold surface via S–Au covalent bonds, although only little orientational
order of the AMB layer could be detected by NEXAFS. Furthermore, aromatic imine bonds between AMB and 4-hydroxybenzaldehyde
(HB), 4-carboxybenzaldehyde (CB), 4-methylbenzaldehyde (MB), or 4-(trifluoromethyl) benzaldehyde (TMB) have been successfully
formed. As a result of the limited order, this coupling reaction was incomplete. Nevertheless, the experimental results confirmed
the formation of conjugated aromatic imine bonds. 相似文献
2.
We report on viscosity of a Ge17As18Se65 glass over the temperature range of 280-420 °C and the successful co-extrusion and fiber-drawing of two chalcogenide glass boules to form a core/clad. pair. The co-extrusion produces a preform with optimum diameter stability and core/clad. glass ratio, and minimum defects at the core/clad. interface in the middle 120-200 mm region of a 270 mm long preform. Core/clad. fiber is drawn successfully from the extruded preform. An optical loss of 1.7 dB m−1 at 1666 cm−1 (6.0 μm) and 6.7 dB m−1 at 6649 cm−1 (1.55 μm) is reported. 相似文献
3.
Betweenness measures provide quantitative tools to pick out fine details from the massive amount of interaction data that is available from large complex networks. They allow us to study the extent to which a node takes part when information is passed around the network. Nodes with high betweenness may be regarded as key players that have a highly active role. At one extreme, betweenness has been defined by considering information passing only through the shortest paths between pairs of nodes. At the other extreme, an alternative type of betweenness has been defined by considering all possible walks of any length. In this work, we propose a betweenness measure that lies between these two opposing viewpoints. We allow information to pass through all possible routes, but introduce a scaling so that longer walks carry less importance. This new definition shares a similar philosophy to that of communicability for pairs of nodes in a network, which was introduced by Estrada and Hatano [E. Estrada, N. Hatano, Phys. Rev. E 77 (2008) 036111]. Having defined this new communicability betweenness measure, we show that it can be characterized neatly in terms of the exponential of the adjacency matrix. We also show that this measure is closely related to a Fréchet derivative of the matrix exponential. This allows us to conclude that it also describes network sensitivity when the edges of a given node are subject to infinitesimally small perturbations. Using illustrative synthetic and real life networks, we show that the new betweenness measure behaves differently to existing versions, and in particular we show that it recovers meaningful biological information from a protein-protein interaction network. 相似文献
4.
B. Spagnolo S. Spezia L. Curcio N. Pizzolato A. Fiasconaro D. Valenti P. Lo Bue E. Peri S. Colazza 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(1):133-146
We investigate the role of the colored noise in two
biological systems: (i) adults of Nezara viridula (L.)
(Heteroptera: Pentatomidae), and (ii) polymer translocation. In the
first system we analyze, by directionality tests, the response of
N. viridula individuals to subthreshold signals plus noise
in their mating behaviour. The percentage of insects that react to
the subthreshold signal shows a nonmonotonic behaviour,
characterized by the presence of a maximum, as a function of the
noise intensity. This is the signature of the non-dynamical
stochastic resonance phenomenon. By using a “soft” threshold model
we find that the maximum of the input-output cross correlation
occurs in the same range of noise intensity values for which the
behavioural activation of the insects has a maximum. Moreover this
maximum value is lowered and shifted towards higher noise
intensities, compared to the case of white noise. In the second
biological system the noise driven translocation of short polymers
in crowded solutions is analyzed. An improved version of the Rouse
model for a flexible polymer is adopted to mimic the molecular
dynamics by taking into account both the interactions between
adjacent monomers and the effects of a Lennard-Jones potential
between all beads. The polymer dynamics is simulated in a
two-dimensional domain by numerically solving the Langevin equations
of motion in the presence of thermal fluctuations and a colored
noise source. At low temperatures or for strong colored noise
intensities the translocation process of the polymer chain is
delayed. At low noise intensity, as the polymer length increases, we
find a nonmonotonic behaviour for the mean first translocation time
of the polymer centre of inertia. We show how colored noise
influences the motion of short polymers, by inducing two different
regimes of translocation in the dynamics of molecule transport. 相似文献
5.
The presented investigations aimed to enhance surface sensitive infrared spectroscopy for chemical analysis by ultrasonic particle manipulation. The combination of these techniques has the potential for new measurement concepts for use in the chemical analysis of suspensions. Local increases of particle concentration brought about by ultrasound could facilitate measurements of molecular-specific infrared spectra of the suspending phase and particles independently. By changing the frequency of an ultrasonic standing wave around 2 MHz it was possible to control the position of particles in respect to the optically sensitive region of the infrared spectroscope.Results obtained with a set-up that enabled us to explore the application of an ultrasonic standing wave to push suspended particles at or into μm distances of the sensing element of an in-line fiber optic probe and subsequently retract them from there are presented. Light micrographs suggested, that the task was successfully accomplished with polystyrene beads suspended in methanol, aggregates were manipulated to and from the cut surface of the truncated, cone-shaped fibre probe tip by changes of the ultrasonic frequency between 1.85 and 1.87 MHz. Feasibility was confirmed by infrared absorption spectra recorded when PTFE particles suspended in tetrahydrofuran were used. 相似文献
6.
Polymer films have been known to change their physical properties when film thickness is decreased below a certain value.
The cause of this phenomenon is still unclear but it has been suggested that interactions and/or chain free-volume changes
at the surface of the films are largely responsible for this behavior. In this paper, the effect of substrate interactions
on the behavior of polymer thin films is evaluated quantitatively. The infrared spectra of nanothin polyethylene (PE) films
were recorded as a function of temperature and amount of substrate covering the surface of the film. The evolution of specific
bands in the CH2 rocking region of the spectra was used to determine the melting temperature (T
m
) of the material. Results show different variations in T
m
depending on the nature of the substrate, indicating that interactions dominate free-volume considerations in PE thin films.
By varying the amount of surface coverage, a quantitative estimate of the heat of interaction was determined, which confirmed
the importance of surface interactions. 相似文献
7.
M. Hema S. Selvasekerapandian A. Sakunthala H. Nithya 《Physica B: Condensed Matter》2008,403(17):2740-2747
Polymer electrolyte based on PVA doped with different concentrations of NH4Br has been prepared by solution casting technique. The complexation of the prepared polymer electrolytes has been studied using X-ray diffraction (XRD) and Fourier transform infra red (FTIR) spectroscopy. The maximum ionic conductivity (5.7×10−4 S cm−1) has been obtained for 25 mol% NH4Br-doped PVA polymer electrolyte. The temperature dependence of ionic conductivity of the prepared polymer electrolytes obeys Arrhenius law. The ionic transference number of mobile ions has been estimated by dc polarization method and the results reveal that the conducting species are predominantly ions. The dielectric behavior of the polymer electrolytes has been analyzed using dielectric permittivity and electric modulus spectra. 相似文献
8.
L. Andreozzi M. Faetti M. Salmerón Sanchez J. L. Gómez Ribelles 《The European physical journal. E, Soft matter》2008,27(1):87-97
The aim of this work is to explore the consequences on the kinetics of structural relaxation of considering a glass-forming
system to consist of a series of small but macroscopic relaxing regions that evolve independently from each other towards
equilibrium in the glassy state. The result of this assumption is a thermorheologically complex model. In this approach each
relaxing zone has been assumed to follow the Scherer-Hodge model for structural relaxation (with the small modification of
taking a linear dependence of configurational heat capacity with temperature). The model thus developed contains four fitting
parameters. A least-squares search routine has been used to find the set of model parameters that fit simultaneously four
DSC thermograms in PVAc after different thermal histories. The computersimulated curves are compared with those obtained with
Scherer-Hodge model and the model proposed by Gómez and Monleón. The evolution of the relaxation times during cooling or heating
scans and also during isothermal annealing below the glass transition has been analysed. It has been shown that the relaxation
times distribution narrows in the glassy state with respect to equilibrium. Isothermal annealing causes this distribution
to broaden during the process to finally attain in equilibrium the shape defined at temperatures above T
g
. 相似文献
9.
R. M. Garipov 《Algebra and Logic》2003,42(6):365-381
We are engaged in classifying up to isomorphism of discrete subgroups of an affine transformation group on a plane (a two-dimensional space) preserving the Minkowski metric. It is proved that, for subgroups that do not coincide with Euclidean ones, the orbit of almost every point is everywhere dense. 相似文献
10.
Theory of weakly damped free-surface flows: A new formulation based on potential flow solutions 总被引:1,自引:0,他引:1
Several theories for weakly damped free-surface flows have been formulated. In this Letter we use the linear approximation to the Navier-Stokes equations to derive a new set of equations for potential flow which include dissipation due to viscosity. A viscous correction is added not only to the irrotational pressure (Bernoulli's equation), but also to the kinematic boundary condition. The nonlinear Schrödinger (NLS) equation that one can derive from the new set of equations to describe the modulations of weakly nonlinear, weakly damped deep-water gravity waves turns out to be the classical damped version of the NLS equation that has been used by many authors without rigorous justification. 相似文献