Home About us Contact
|
Home About us Contact | ||
|
|
||
Disordered Systems (disordered + system)
Selected AbstractsInfluence of electronic correlations on the frequency-dependent hopping transport in Si:PPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2008Elvira Ritz Abstract At low energy scales charge transport in the insulating Si:P is dominated by activated hopping between the localized donor electron states. Thus, theoretical models for a disordered system with electron-electron interaction are appropriate to interpret the electric conductivity spectra. With a newly developed technique we have measured the complex broadband microwave conductivity of Si:P from 100 MHz to 5 GHz in a broad range of phosphorus concentration n /nc from 0.56 to 0.95 relative to the critical value nc = 3:5 × 1018 cm,3 corresponding to the metal-insulator transition driven by doping. At our base temperature of T = 1.1 K the samples are in the zero-phonon regime where they show a super-linear frequency dependence of the conductivity indicating the influence of the Coulomb gap in the density of the impurity states. At higher doping n , nc, an abrupt drop in the conductivity power law ,1(,) , ,, is observed. The dielectric function ,1 increases upon doping following a power law in (1 , n /nc). Dynamic response at elevated temperatures has also been investigated. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Potential fluctuations in disordered semiconductors measured by transport and optical methodsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2004P. Bozsoki Abstract From the recent analysis of the potential fluctuations in disordered semiconductors on the basis of optical and transport measurements [1] it was concluded that these two different kinds of phenomena evidence extremely different energy scales of the random potential in the same sample. We resolve this puzzle using for the analysis of experimental data the well-known theories of transport and optical absorption in a disordered system with long-range potential fluctuations, caused by charged impurities [2, 3]. The key point in our consideration is the essential difference between the density of states caused by the long-range fluctuations and the shape of the absorption coefficient. The latter is known to depend essentially not only on the fluctuation probability but also on the tunnelling efficiency of the optically excited electrons in the potential relief provided by the fluctuations [2]. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Studying natural structural protein fibers by solid-state nuclear magnetic resonanceCONCEPTS IN MAGNETIC RESONANCE, Issue 1 2009Alexandre A. Arnold Abstract As a consequence of evolutionary pressure, various organisms have developed structural fibers displaying a range of exceptional mechanical properties adapted specifically to their functions. An understanding of these properties at the molecular level requires a detailed description of local structure, orientation with respect to the fiber and size of constitutive units, and dynamics on various timescales. The size and lack of long-range order in these protein systems constitute an important challenge to classical structural techniques such as high-resolution NMR and X-ray diffraction. Solid-state NMR overcomes these constraints and is uniquely suited to the study of these inherently disordered systems. Solid-state NMR experiments developed or applied to determine structure, orientation, and dynamics of these complex proteins will be reviewed and illustrated through examples of their applications to fibers such as spider and silkworm silks, collagen, elastin, and keratin. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part A 34A: 24,27, 2009. [source] Engineering Disorder: Engineering Disorder in Superdiffusive Lévy Glasses (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Mater. Engineering disorder makes it possible to realize materials with advanced optical properties. On page 965, Bertolotti et al. report the recipe for Lévy glasses, strongly inhomogeneous disordered systems displaying superdiffusive light transport. The degree of superdiffusion is fine-tuned by embedding transparent spheres varying in size by orders of magnitude in a scattering medium. [source] EXAFS and molecular dynamics studies of ionic solutionsJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Paola D'Angelo This paper focuses on recent advances in the X-ray absorption spectroscopy (XAS) analysis of ionic solutions. The asymmetry of radial distribution functions associated with the solvent molecules surrounding the ions has to be taken into account to perform a reliable structural analysis. Molecular dynamics (MD) simulations provide reliable 's which can be used as starting models in the XAS data analysis. The combined MD-XAS investigation reduces meaningfully the indetermination of the structural parameters, especially for coordination numbers and Debye,Waller factors. Double-electron excitation channels can be present in the XAS spectra of ionic solutions and they have to be accounted for in the background extraction. The ability of the XAS technique to probe three-body correlation functions in ionic solutions with the aid of MD has been shown. The analysis of the low- k region of the spectra allows the detection of a weak but significant hydrogen structural signal. The XAS technique is especially well suited to determine the detailed shape of the nearest-neighbor peak in the atom,atom pair correlation functions of disordered systems. The information that they contain about the short-range atom,atom pairwise interactions can be very helpful for specifying and properly modifying model potentials used in MD simulations. [source] Accurate long-range distance measurements in a doubly spin-labeled protein by a four-pulse, double electron,electron resonance methodMAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2008Michela G. Finiguerra Abstract Distance determination in disordered systems by a four-pulse double electron,electron resonance method (DEER or PELDOR) is becoming increasingly popular because long distances (several nanometers) and their distributions can be measured. From the distance distributions eventual heterogeneities and dynamics can be deduced. To make full use of the method, typical distance distributions for structurally well-defined systems are needed. Here, the structurally well-characterized protein azurin is investigated by attaching two (1-oxyl-2,2,5,5-tetramethylpyrroline-3-methyl) methanethiosulfonate spin labels (MTSL) by site-directed mutagenesis. Mutations at the surface sites of the protein Q12, K27, and N42 are combined in the double mutants Q12C/K27C and K27C/N42C. A distance of 4.3 nm is found for Q12C/K27C and 4.6 nm for K27C/N42C. For Q12C/K27C the width of the distribution (0.24 nm) is smaller than for the K27C/N42C mutant (0.36 nm). The shapes of the distributions are close to Gaussian. These distance distributions agree well with those derived from a model to determine the maximally accessible conformational space of the spin-label linker. Additionally, the expected distribution for the shorter distance variant Q12C/N42C was modeled. The width is larger than the calculated one for Q12C/K27C by 21%, revealing the effect of the different orientation and shorter distance. The widths and the shapes of the distributions are suited as a reference for two unperturbed MTSL labels at structurally well-defined sites. Copyright © 2008 John Wiley & Sons, Ltd. [source] Local level statistics for optical and transport properties of disordered systems at finite temperaturePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2006A. Malyshev Abstract It is argued that the (traditional) global level statistics which determines localization and coherent transport properties of disordered systems (e.g. the Anderson model) at zero temperature becomes inappropriate when it comes to incoherent transport. We define local level statistics which proves to be relevant for finite temperature incoherent transport and optics of one-dimensional systems (e.g. molecular aggregates, conjugated polymers, etc.). (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||