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We study synchronization behavior in networks of coupled chaotic oscillators with heterogeneous connection degrees. Our focus is on regimes away from the complete synchronization state, when the coupling is not strong enough, when the oscillators are under the influence of noise or when the oscillators are nonidentical. We have found a hierarchical organization of the synchronization behavior with respect to the collective dynamics of the network. Oscillators with more connections (hubs) are synchronized more closely by the collective dynamics and constitute the dynamical core of the network. The numerical observation of this hierarchical synchronization is supported with an analysis based on a mean field approximation and the master stability function. (C) 2006 American Institute of Physics
Realistic networks display not only a complex topological structure, but also a heterogeneous distribution of weights in the connection strengths. Here we study synchronization in weighted complex networks and show that the synchronizability of random networks with a large minimum degree is determined by two leading parameters: the mean degree and the heterogeneity of the distribution of node's intensity, where the intensity of a node, defined as the total strength of input connections, is a natural combination of topology and weights. Our results provide a possibility for the control of synchronization in complex networks by the manipulation of a few parameters
Dynamical organization of connection weights is studied in scale-free networks of chaotic oscillators, where the coupling strength of a node from its neighbors develops adaptively according to the local synchronization property between the node and its neighbors. We find that when complete synchronization is achieved, the coupling strength becomes weighted and correlated with the topology due to a hierarchical transition to synchronization in heterogeneous networks. Importantly, such an adaptive process enhances significantly the synchronizability of the networks, which could have meaningful implications in the manipulation of dynamical networks
Recently, two different groups have reported independently that the mobility of field-effect transistors made from regioregular poly(3-hexylthiophene) (P3HT) increases strongly with molecular weight. Two different models were presented: one proposing carrier trapping at grain boundaries and the second putting emphasis on the conformation and packing of the polymer chains in the thin layers for different molecular weights. Here, we present the results of detailed investigations of powders and thin films of deuterated P3HT fractions with different molecular weight. For powder samples, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were used to investigate the structure and crystallization behavior of the polymers. The GPC investigations show that all weight fractions possess a rather broad molecular weight distribution. DSC measurements reveal a strong decrease of the crystallization temperature and, most important, a significant decrease of the degree of crystallinity with decreasing molecular weight. To study the structure of thin layers in lateral and vertical directions, both transmission electron microscopy (TEM) and X-ray grazing incidence diffraction (GID) were utilized. These methods show that thin layers of the low molecular weight fraction consist of well-defined crystalline domains embedded in a disordered matrix. We propose that the transport properties of layers prepared from fractions of poly(3-hexylthiophene) with different molecular weight are largely determined by the crystallinity of the samples and not by the perfection of the packing of the chains in the individual crystallites
We present an approach to generate (multivariate) twin surrogates (TS) based on recurrence properties. This technique generates surrogates which correspond to an independent copy of the underlying system, i.e. they induce a trajectory of the underlying system starting at different initial conditions. We show that these surrogates are well suited to test for complex synchronisation and exemplify this for the paradigmatic system of Rossler oscillators. The proposed test enables to assess the statistical relevance of a synchronisation analysis from passive experiments which are typical in natural systems
The spin probes TEMPO, TEMPOL, and CAT-1 were used to investigate microviscosity and micropolarity of imidazolium based ionic liquids bearing either tetrafluoroborate or hexafluorophosphate as anions and a variation of the substitution at the imidazolium ion. The average rotational correlation times (r) obtained by complete simulation of the X-band ESR spectra of TEMPO, TEMPOL, and CAT-1 increase with increasing viscosity of the ionic liquid although no Stokes Einstein behavior is observed. This is caused by microviscosity effects of the ionic liquids shown by application of the Gierer-Wirtz theory. Interestingly, the jump of the probe molecule into the free volume of the ionic liquids is a nonactivated process. The hyperfine coupling constants (A(iso) (N-14)) of TEMPO and TEMPOL dissolved in the ionic liquids do not depend on the structure of the ionic liquids. The A(iso) (N-14) values show a micropolarity of the ionic liquids that is comparable with methylenchloride in case of TEMPO and with dimethylsulfoxide in case of TEMPOL. Micropolarity monitored by CAT-1 strongly depends on structural variation of the ionic liquid. CAT-1 dissolved in imidazolium salts substituted with shorter alkyl chains at the nitrogen atom exhibits a micropolarity comparable with dimethylsulfoxide. A significant lower micropolarity is found for imidazolium. salts bearing a longer alkyl substituent at the nitrogen atom or a methyl substituent at C-2. Copyright (c) 2006 John Wiley & Sons, Ltd
Context: Placental and circulatory soluble fms-like tyrosine kinase 1 (sFlt1) has proven to be elevated in pregnant women with preeclampsia, a disease characterized by hypertension, proteinuria, and endothelial dysfunction. Recent studies also demonstrated an autoantibody against the angiotensin II type 1 (AT1) receptor (AT1-AA) in that disease. Objective: Both factors are discussed as key players in the etiology of preeclampsia. However, it has not yet been clarified whether these two circulating factors correlate and whether synergy determines the severity of pathology. Design: AT1-AA was retrospectively determined by a bioassay and sFlt1 by an ELISA. Patients: Serum from second-trimester pregnancies with normal or abnormal uterine perfusion and in women at term with or without pregnancy pathology was analyzed. Results: Most of the preeclamptic patients were characterized by high sFlt1 levels and the presence of AT1-AA, although the agonistic effects of the antibody did not correlate with the sFlt1 concentrations (P = 0.85). Although AT1- AA was also detected in second-trimester pregnancies evidencing abnormal uterine perfusion without later pathology, sFlt1 was not significantly elevated in these pregnancies, compared with those with normal uterine perfusion. However, whereas women with abnormal perfusion and later pregnancy pathology did not differ in AT1-AA, compared with those with normal outcome, sFlt1 was significantly increased. Again, the two factors did not correlate (P = 0.15). Conclusions: We conclude that AT1-AA bioactivity and sFlt1 concentrations do not correlate, are not mutually dependent, and are thus probably involved in distinct pathogenetic mechanisms. Both factors in combination may not be causative for the early impaired trophoblast invasion and pathological uterine perfusion
Silicon (Si) is the second-most abundant element in the earth's crust. In the pedosphere, however, huge spans of Si contents occur mainly caused by Si redistribution in soil profiles and landscapes. Here, we summarize the current knowledge on the different pools and fluxes of Si in soils and terrestrial biogeosystems. Weathering and subsequent release of soluble Si may lead to (1) secondarily bound Si in newly formed Al silicates, (2) amorphous silica precipitation on surfaces of other minerals, (3) plant uptake, formation of phytogenic Si, and subsequent retranslocation to soils, (4) translocation within soil profiles and formation of new horizons, or (5) translocation out of soils (desilication). The research carried out hitherto focused on the participation of Si in weathering processes, especially in clay neoformation, buffering mechanisms for acids in soils or chemical denudation of landscapes. There are, however, only few investigations on the characteristics and controls of the low-crystalline, almost pure silica compounds formed during pedogenesis. Further, there is strong demand to improve the knowledge of (micro)biological and rhizosphere processes contributing to Si mobilization, plant uptake, and formation of phytogenic Si in plants, and release due to microbial decomposition. The contribution of the biogenic Si sources to Si redistribution within soil profiles and desilication remains unknown concerning the pools, rates, processes, and driving forces. Comprehensive studies considering soil hydrological, chemical, and biological processes as well as their interactions at the scale of pedons and landscapes are necessary to make up and model the Si balance and to couple terrestrial processes with Si cycle of limnic, fluvial, or marine biogeosystems
The Cenozoic Tian Shan is one of the preeminent examples of an intracontinental orogen. However, there remains a significant controversy over when deformation related to the India-Asia collision commenced and therefore how shortening within the mountains has been partitioned over time. One approach has been to look at the modem shortening rate as measured by geodetic studies, combined with estimates of the total shortening across the range and extrapolate backwards. This approach suggests that the onset of range construction was ca. 10 Ma [K.Y. Abdrakhmatov, S.A. Aldazhanov, B.H. Hager, M.W Hamburger, T.A. Herring, K.B. Kalabaev, K.B. Kalabayev, V.I. Makarov, P. Molnar, S.V Panasyuk, M.T. Prilepin, R.E. Reilinger, I.S. Sadybakasov, B.J. Souter, Y.A. Trapeznikov, V.Y. Tsurkov, A.V. Zubovich, Relatively recent construction of the Tien Shan inferred from GPS measurements of present-day crustal deformation rates, Nature 384 (6608) (1996) 450-453]. An alternate method is to determine the age of the onset of exhumation using thermochronology. We present 19 new apatite fission-track (AFT) results from the southwestern Chinese portion of the belt; this region represents the first area exhumed during the late Tertiary along a transect at ca. 76 degrees E. Exhumation commenced at the Oligocene-Miocene boundary (similar to 24 Ma) along the Maidan and Muziduke thrusts, which bound the southern side of the Kokshaal range. Subsequently, deformation propagated ca. 20 km south to the Kashi basin- bounding thrust (KBT), which was exhumed by no earlier than 18.9 +/- 3.3 Ma. Three detrital AFT samples from Plio- Pleistocene strata deposited ca. 20 km farther south contain fission track grain age peaks that young monotonically upwards from 20.9 + 7.0/- 5.3 Ma to 15.9 + 5.4/- 4.0 Ma with a fairly constant lag time of 16 to 18 Ma. These ages, combined with structural data, suggest that both the hanging wall and the footwall of the KBT experienced a renewed episode of exhumation during the latest Cenozoic. The discrepancy between the Late Oligocene-Miocene initiation of significant exhumation shown herein and the 10 Ma initiation estimate from geodesy suggests that the Tian Shan has undergone a complex Late Cenozoic shortening history. Assuming that the present shortening rate could account for the total amount of Cenozoic shortening in 10 Ma and realizing that shortening initiated at least 15 Myr earlier, we conclude that the shortening rate must have varied over time, possibly in pulsed-southward migrating events, and that the present rate may not reflect the average rate since initiation of range uplift. (c) 2006 Elsevier B.V. All rights reserved
Glucosinolates are a group of secondary metabolites that function as defense substances against herbivores and micro-organisms in the plant order Capparales. Indole glucosinolates (IGS), derivatives of tryptophan, may also influence plant growth and development. In Arabidopsis thaliana, indole-3-acetaldoxime (IAOx) produced from tryptophan by the activity of two cytochrome P450 enzymes, CYP79B2 and CYP79B3, serves as a precursor for IGS biosynthesis but is also an intermediate in the biosynthetic pathway of indole-3-acetic acid (IAA). Another cytochrome P450 enzyme, CYP83B1, funnels IAOx into IGS. Although there is increasing information about the genes involved in this biochemical pathway, their regulation is not fully understood. OBP2 has recently been identified as a member of the DNA-binding-with-one- finger (DOF) transcription factors, but its function has not been studied in detail so far. Here we report that OBP2 is expressed in the vasculature of all Arabidopsis organs, including leaves, roots, flower stalks and petals. OBP2 expression is induced in response to a generalist herbivore, Spodoptera littoralis, and by treatment with the plant signalling molecule methyl jasmonate, both of which also trigger IGS accumulation. Constitutive and inducible over- expression of OBP2 activates expression of CYP83B1. In addition, auxin concentration is increased in leaves and seedlings of OBP2 over-expression lines relative to wild-type, and plant size is diminished due to a reduction in cell size. RNA interference-mediated OBP2 blockade leads to reduced expression of CYP83B1. Collectively, these data provide evidence that OBP2 is part of a regulatory network that regulates glucosinolate biosynthesis in Arabidopsis
Olefin metathesis and isomerization : from undesired side reactions to useful synthetic methodology
(2006)
Conversion of ruthenium carbene complexes to ruthenium hydride complexes by organometallic transformations in situ opens up interesting synthetic perspectives. In this account the use of Grubbs' catalyst to synthesize pent-4- enals selectively from diallyl- and allyl homoallyl ethers and scope and limitations of a Tandem RCM-isomerization sequence for the synthesis of cyclic enol ethers are discussed. (c) 2006 Elsevier B.V. All rights reserved
Population-based methods for the genetic mapping of adaptive traits and the analysis of natural selection require that the population structure and demographic history of a species are taken into account. We characterized geographic patterns of genetic variation in the model plant Arabidopsis thaliana by genotyping 115 genome-wide single nucleotide polymorphism (SNP) markers in 351 accessions from the whole species range using a matrix-assisted laser desorption/ionization time-of-flight assay, and by sequencing of nine unlinked short genomic regions in a subset of 64 accessions. The observed frequency distribution of SNPs is not consistent with a constant-size neutral model of sequence polymorphism due to an excess of rare polymorphisms. There is evidence for a significant population structure as indicated by differences in genetic diversity between geographic regions. Accessions from Central Asia have a low level of polymorphism and an increased level of genome-wide linkage disequilibrium (LD) relative to accessions from the Iberian Peninsula and Central Europe. Cluster analysis with the structure program grouped Eurasian accessions into K=6 clusters. Accessions from the Iberian Peninsula and from Central Asia constitute distinct populations, whereas Central and Eastern European accessions represent admixed populations in which genomes were reshuffled by historical recombination events. These patterns likely result from a rapid postglacial recolonization of Eurasia from glacial refugial populations. Our analyses suggest that mapping populations for association or LD mapping should be chosen from regional rather than a species-wide sample or identified genetically as sets of individuals with similar average genetic distances
Graphical models applying partial coherence to multivariate time series are a powerful tool to distinguish direct and indirect interdependencies in multivariate linear systems. We carry over the concept of graphical models and partialization analysis to phase signals of nonlinear synchronizing systems. This procedure leads to the partial phase synchronization index which generalizes a bivariate phase synchronization index to the multivariate case and reveals the coupling structure in multivariate synchronizing systems by differentiating direct and indirect interactions. This ensures that no false positive conclusions are drawn concerning the interaction structure in multivariate synchronizing systems. By application to the paradigmatic model of a coupled chaotic Roessler system, the power of the partial phase synchronization index is demonstrated
Existing theoretical literature fails to explain satisfactorily the differences between the pay of workers who are covered by collective agreements and others who are not. This study aims at providing a model framework that is amenable to an analysis of this issue. Our general-equilibrium approach integrates a dual labor market and a two-sector product market. The results suggest that the so-called "union wage gap" is largely determined by the degree of centralization of the bargains and, to a somewhat lesser extent, by the expenditure share of the unionized sector's goods
New ferroelectrets were developed on the basis of foams from cyclo-olefin polymers and copolymers. The results obtained on the cyclo-olefin polymer foam demonstrate a significant improvement of the service temperature for ferroelectret transducer materials. Suitable compounding and preparation led to cyclo-olefin ferroelectrets with an electromechanical activity of around 15 pC/N, which is thermally stable at least up to 110 degrees C. The properties in sensor and actuator applications are strongly dependent on the processing parameters related to film-making, sensor and actuator preparation, gas content and electric charging. The processing window for the film stretching was very narrow compared to the earlier developed polypropylene ferroelectrets. The film porosity, softness and thus the electromechanical activity are adjusted by gas-diffusion expansion. The activity of the electromechanically operating sensors and actuators was increased by stacking several layers of cellular cyclo-olefin film. For applications such as flat loudspeakers, the foamed films are tuned by tensioning them on a support frame. Correct tensioning was essential also for reducing the distortion levels.
Homopolymers were prepared from diallylammonium monomers bearing 4-methylcoumarin and 4-cyanobiphenyl as fluorescent and mesogenic side groups, as well as their copolymers with diallyldimethylammonium chloride (DADMAC). Organic-inorganic hybrid films were electrostatically self-assembled via the layer-by-layer technique on silicon wafers and quartz plates from the chromophore-bearing polymers and an exfoliated synthetic hectorite. Photophysical studies performed in solution as well as in the self-assembled films demonstrated only a weak tendency for aggregation of the chromophores in the macromolecules. Moreover, assemblies made from the polymers carrying the cyanobiphenyl mesogen were found to exhibit a pronounced internal order
A new precursor route for the preparation of bulk oxides and thin films of bismuth vanadates is proposed. The method involves the thermal treatment under air and mild conditions of hybrid organic-inorganic precursors, made from a zwitterionic salt-free polymer matrix and selected inorganic species. Monoclinic BiVO4 was obtained in the form of bulk oxide by calcination of the powdered homogeneous hybrid materials at 600 degrees C, from precursors containing Bi and V in stoichiometric amounts. In the same way, thermodiffractometry studies performed on a hybrid material exhibiting a Bi/ V molar ratio of 2 revealed that the ionic conductor gamma-Bi4V2O11 phase can be stabilized under very soft thermal conditions (300 degrees C). Additionally, thin films of yellow monoclinic BiVO4 were for the first time fabricated, by thermal treatment of the same hybrid polymeric precursors deposited on quartz substrates by spin coating, using a layer- by-layer technique. The presence of the target phase at the surface of the plates was confirmed by X-ray diffraction as well as UV-vis measurements