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We examine the influence of noise on the propagation of harmonic signals with two frequencies through discrete bistable media. We show that random fluctuations enhance propagation of this kind of signals for low coupling strengths, similarly to what happens with purely monochromatic signals. As a more relevant finding, we observe that the frequency being propagated with better efficiency can be selected by tuning the intensity of the noise, in such a way that for large noises the highest frequency is transmitted better than the lower one, whereas for small noises the reverse holds. Such a noise-induced frequency selection can be expected to exist for general multifrequency harmonic signals.
We report on the effect of vibrational resonance in a spatially extended system of coupled noisy oscillators under the action of two periodic forces, a low-frequency one (signal) and a high-frequency one (carrier). Vibrational resonance manifests itself in the fact that for optimally selected values of high-frequency force amplitude, the response of the system to a low-frequency signal is optimal. This phenomenon is a synthesis of two effects, a noise- induced phase transition leading to bistability, and a conventional vibrational resonance, resulting in the optimization of signal processing. Numerical simulations, which demonstrate this effect for an extended system, can be understood by means of a zero-dimensional "effective" model. The behavior of this "effective" model is also confirmed by an experimental realization of an electronic circuit.
We show that external fluctuations are able to induce propagation of harmonic signals through monostable media. This property is based on the phenomenon of doubly stochastic resonance, where the joint action of multiplicative noise and spatial coupling induces bistability in an otherwise monostable extended medium, and additive noise resonantly enhances the response of the system to a harmonic forcing. Under these conditions, propagation of the harmonic signal through the unforced medium i observed for optimal intensities of the two noises. This noise-induced propagation is studied and quantified in a simple model of coupled nonlinear electronic circuits.
From the root bark of Erythrina burttii three new isoflav-3-enes, 7,4'-dihydroxy-2'-methoxy-6- (1'',1''-dimethylallyl)isoflav-3-ene (trivial name, burttinol-A), 4'-hydroxy-2'- methoxy-(2'',2''-dimethylpyrano[5'',6'':8,7]isoflav-3-ene (trivial name, burttinol-B), 7,4'-dihydroxy-2'-methoxy-8-(3'',3''-dimethylallyl)isoflav-3-ene (trivial name, burttinol-C), and a new 2-arylbenzofuran, 6,4'-dihydroxy-2'-methoxy-5- (1'',1''-dimethylallyl)-2-arylbenzofuran (trivial name, burttinol-D) were isolated. In addition, the known compounds, abyssinone V-4'-methyl ether, bidwillol A, calopocarpin, erybraedin A, erythrabyssin II, isobavachalcone, phaseollidin and phaseollin were identified. The structures were determined on the basis of spectroscopic evidence.
We report the discovery of a new gravitationally lensed QSO, at a redshift z = 1.689, with four QSO components in a cross-shaped arrangement around a bright galaxy. The maximum separation between images is 2farcs 6, enabling a reliable decomposition of the system. Three of the QSO components have g =~ 19.6, while component A is about 0.6 mag brighter. The four components have nearly identical colours, suggesting little if any dust extinction in the foreground galaxy. The lensing galaxy is prominent in the i band, weaker in r and not detected in g. Its spatial profile is that of an elliptical galaxy with a scale length of ~ 12 kpc. Combining the measured colours and a mass model for the lens, we estimate a most likely redshift range of 0.3 < z < 0.4. Predicted time delays between the components are la 10 days. The QSO shows evidence for variability, with total g band magnitudes of 17.89 and 17.71 for two epochs separated by ~ 2 months. However, the relative fluxes of the components did not change, indicating that the variations are intrinsic to the QSO rather than induced by microlensing. Based in part on observations obtained with the Baade 6.5-m telescope of the Magellan Consortium. Also based in part on observations collected at the European Southern Observatory, La Silla, Chile.
Chiroptcial properties of poly(p-phenyleneethynylene) copolymers in thin films : large g-values
(2002)
Observational data of natural systems, as measured in medical measurements are typically quite different from those obtained in laboratories. Due to the peculiarities of these data, wellknown characteristics, such as power spectra or fractal dimension, often do not provide a suitable description. To study such data, we present here some measures of complexity, which are basing on symbolic dynamics. Firstly, a motivation for using symbolic dynamics and measures of complexity in data analysis based on the logistic map is given and next, two applications to medical data are shown. We demonstrate that symbolic dynamics is a useful tool for the risk assessment of patients after myocardial infarction as well as for the evaluation of th e architecture of human cancellous bone.
Human Rights
(2002)
A significant seasonal variation in size at settlement has been observed in newly settled larvae of Dreissena polymorpha in Lake Constance. Diet quality, which varies temporally and spatially in freshwater habitats, has been suggested as a significant factor influencing the life history and development of freshwater invertebrates. Accordingly, experiments were conducted with field-collected larvae to test the proposal that diet quality can determine planktonic larval growth rates, size at settlement and subsequent post-metamorphic growth rates. Larvae were fed one of two diets or starved. One diet was composed of cyanobacterial cells, which are de; cient in polyunsaturated fatty acids (PUFAs) and the other was a mixed diet rich in PUFAs. Freshly metamorphosed animals from the starvation treatment had a carbon content per individual 70% lower than that of larvae fed the mixed diet. This apparent exhaustion of larval internal reserves resulted in a 50% reduction of the post-metamorphic growth rates. Growth was also reduced in animals previously fed the cyanobacterial diet. Hence, low food quantity or low food quality during the larval stage of D. polymorpha, lead to irreversible effects for post-metamorphic animals and are related to inferior competitive abilities.
Food quality effects of unsaturated fatty acids on larvae of the zebra mussel Dreissena polymorpha
(2002)
In standardized growth experiments, newly hatched larvae of the zebra mussel Dreissena polymorpha were fed diets representing different biochemical compositions. Algae that were rich in (n-3) polyunsaturated fatty acids (PUFAs), except for long-chained (.C18) PUFAs (Chlorella minutissima and Monoraphidium minutum) were of low food quality. Higher growth than on C. minutissima or M. minutum was supported by a culture of the cyanobacterium Aphanothece sp., which contained traces of a long-chained (n-3) PUFA, docosahexaenoic acid (DHA, 22 : 6n-3). The alga Isochrysis aff. galbana, which contained high amounts of the longchained (n-3) PUFAs DHA and eicosapentaenoic acid (EPA, 20 : 5n- 3), supported the highest growth. The alga Nannochloropsis limnetica, which differed from I. galbana by a defi- ciency in DHA, allowed slightly, but significantly lower, growth. Growth of larvae on N. limnetica was increased by enrichment of N. limnetica cells with a lipid extract of I. galbana, showing that larval growth on N. limnetica was limited by the deficiency of a compound that was present in I. galbana. Growth was also enhanced by feeding N. limnetica cells supplemented with DHA, but not by cells enriched with EPA, indicating that DHA was the limiting factor. We conclude that, on DHA-deficient food, the larvae of D. polymorpha were not able to sufficiently convert C18-PUFAs into long- chained (n-3) PUFAs and that the rates for elongation and desaturation of EPA into DHA limited growth.
A simple synthetic route to a new poly(diallylammonium) salt functionalized by a styrene group is presented. This reactive polymer was employed for polyelectrolyte multilayer films using electrostatical layer-by-layer self- assembly, together with an inorganic polyanion, namely an exfoliated hectorite clay. To enhance their stability, the final hybrid multilayers were cross-linked by exposure to UV light, leading only to a minor shrinkage. Alternatively, the reactive polycation was cross-linked after each adsorption step. X-ray reflectometry revealed that the two types of films dispose of an internal order with a short length scale, that seems insensitive to the photo-cross-linking. Cross- linking after each adsorption step, however, results in more regular film growth, and reduces the films? roughness and the amount of polyanion deposited. Under these conditions, the films seem to grow by deposition of submonolayers with a combined vertical and lateral expansion, resulting in the self-healing of previously deposited, incomplete layers.
Yet another Theta-System
(2002)
Thermal properties of block copolymer, poly(N-isopropyl acrylamide)-block-poly(3-[N-(3-methacrylamido-propyl)- N,N-dimethyl]-ammonio propane sulfonate), PNIPA-b-PSPP have been studied in pure and saline (NaCl) aqueous solutions by dynamic laser light scattering (DLS). The copolymer [Mw(PNIPA) 10800 g/mol and Mw(PSPP) 9700 g/mol] exhibits both an upper (UCST 9 oC) and lower (LCST 32 oC) critical solution temperatures in pure water. The addition of NaCl enhances the solubility of the zwitterionic polymer, PSPP, leading to the disappearance of the UCST. On the other hand, the solubility of PNIPA in water decreases as NaCl is added. At 20 oC the copolymer shows a bimodal size distribution through the NaCl concentration range of 0-0.93 M above a certain limiting polymer concentration. The slow and fast components of the diffusion coefficients of the polymer have been calculated. A gradual addition of salt turns the mutual interactions from zwitterionic attractions between PSPP blocks to hydrophobic attractions between PNIPA blocks. The formation of the aggregates and the aggregate sizes at T < UCST and T > LCST are influenced by polymer and salt concentrations. Below UCST the aggregates in saline polymer solutions are larger than those in pure polymer solutions. Above LCST the aggregate size is determined by the salt concentration.
Chitinase B (ChiB) from Serratia marcescens is a family 18 exochitinase whose catalytic domain has a TIM-barrel fold with a tunnel-shaped active site. We have solved structures of three ChiB complexes that reveal details of substrate binding, substrateassisted catalysis, and product displacement. The structure of an inactive ChiB mutant (E144Q) complexed with a pentameric substrate (binding in subsites 22 to 13) shows closure of the ''roof'' of the active site tunnel. It also shows that the sugar in the 21 position is distorted to a boat conformation, thus providing structural evidence in support of a previously proposed catalytic mechanism. The structures of the active enzyme complexed to Allosamidin (an analogue of a proposed reaction intermediate) and of the active enzyme soaked with pentameric substrate show events after cleavage of the glycosidic bond. The latter structure shows reopening of the roof of the active site tunnel and enzyme-assisted product displacement in the 11 and 12 sites, allowing a water molecule to approach the reaction center. Catalysis is accompanied by correlated structural changes in the core of the TIM barrel that involve conserved polar residues whose functions were hitherto unknown. These changes simultaneously contribute to stabilization of the reaction intermediate and alternation of the pKa of the catalytic acid during the catalytic cycle.
A close comparative analysis of the attrition of inflections in historical English and Welsh reveals that Welsh had already lost its entire NP inflection when it surfaces in writing in the 7c AD, while English was still fully inflected both in the NP and VP. The comparison of the modern English and Welsh morphological categories shows that English overtook Welsh in its rate of analyticising drift. This shows first in writing during the Middle English period. Thus in English, the attrition bothfully affected the NP and the VP, while in modern Welsh the attrition of the verbal inflection in the VP is much less advanced than in English. Both languages, however, share the shift in the VP from the synthetism of verbal tense, mood (and voice) marking towards analytic aspect marking, which continues to gain in importance in both languages today. The question is raised, whether this joint development may have been due to the influence of the 'Late British' speaking shifters to Old English, to prolongued areal contactin the island of Britain ("Sprachbund") and/or to a more general drift from syntheticity to analycity in (Western) IE languages in Europe, which affects some languages more than others. The Appendix prints the earliest Old English and Old Welsh texts (dated by absolute chronology) and marks their loss of inflections, in order to highlight the advanced analycity in the Old Welsh NP as opposed to the Old English NP.
The continued linguistic contact in the islands of Britain and Ireland over the past two millenia has led to linguistic convergence processes between the Insular Celtic and West Germanic languages involved. While the Latin, Old Norse and Norman French contact scenarios were recognised and have been well studied since the 19c, the Celtic component received much less scholarly attention until the 1990s because of the continued linguistic bias, once fostered by 19c Anglo-Saxonisms and the idea of racial purity of the Egnlish population. It is only in the very recent past that the many different contact areas between English and the Insular Celtic languages have received recognition after New Labour's post-1997 introduction of "devolution" politics. The closest and longest interaction took of course place between English and Welsh. The present article looks at three major types of interaction which led to convergence in a number of important linguistic features: (1) mutual retention of shared archaic features, (2) mutual shared innovations, and (3) transfer from one language to another, either by unilateral or by bilateral transfer. The exemplary contact features discussed in this article relate to the retention of interdental fricatives, the shared innovation of analycity and multi-word verb formation, and clefting as feature transfer. Transfer is likely to have taken place under the following conditions: (a) earlier written documentation in the donor language, (b) higher frequency of occurrence in the donor language, (c) conformity with other structures in the donor language, and (d) grammaticalisation in the donor language. The conclusion endorses Salikoko Mufwene's claim that the making of English in the island of Britain was subject to the same contact processes which created the English based creoles from indigenised Englishes during the colonial period.
DO-Periphrasis in Irish
(2002)
Periphrastic DO constructions are very common both in English and in the Neo-Brittonic languages and are used for various functional purposes. These form part of a larger linguistic area in western and northern Europe. The literature does not mention comparable constructions for Irish and Scottish Gaelic. Irish informants, however, confirm orally that they are in common use among present day Gaeltacht speakers. They appear also to have been common in late spoken Manx. This study is based on the "Caint Chonamara" electronic corpus, the field work for which was first untertaken by Hans Hartmann (Hamburg) and Tomás de Bhaldraithe (Dublin) in the early 1960s und brought to a close by Arndt Wigger (Wuppertal) in the 1990s. The file for the Ros Muc dialogues yielded a very low return of potential DO constructions, i.e. 14 tokens of DÉAN + VN out of 494 DÉAN tokens altogether in the file. This shows that the DÉAN + VN construction was grammatically correct and acceptable to the native speakers, but was not grammaticalised and had a very low frequency. This result is interesting, but not surprising, since the informants chosen for this file conformed to the NORMS category (non-mobile old rural males. They were born around the turn of the 19c/20c and acquired their language now more than 100 years ago. This was well before the independence of the Republic. They would have acquired their Irish orally from native speakers and underwent very little formal training in Irish, or none. This small sample confirms that Irish did not belong to the broad linguistic area in Western Europe which makes use of periphrastic DO constructions, at least not until very recently.
A report of Mikhail Gasparov's 1989 book on the 'History of European Versification' is the starting point of the discussion in this article of the types of versification found in the Insular Celtic literatures from their first documenation in the early middle ages to the present day, as Gasparov's survey does not cover these poetries. It is claimed here that their metrical constraints were pre-literate and first and foremost geared at aural reception. The introduction of writing led to an increase in metrical sophistication which, while still basically oral, because of the process of "prelecting" (i.e. reading out aloud to illiterate or semi-literate audiences), required a very careful appreciation of their metrical skills. Contact with English and French syllabic poetry in the later middle ages and particularly in the modern period produced so-called "free verse" poetry. The word "free" in this particular context meant that the rather loose metrical constraints of these majority literatures in no way compared with the extraordinarily high metrical sophistication of the native oral derived or "bardic" poetry.
In this article, the synthesis of analogs of N,N',N''-triacetylchitotriose in which the central sugar residue was replaced by a succinic acid is presented. Mol. modeling calcns. revealed that the pseudotrisaccharides exist in low energy extended conformations which show similar space filling as N,N',N''-triacetylchitotriose. Of the N,N',N''-triacetylchitotriose pseudosugar analogs tested as chitinase inhibitors, none showed any appreciable competition (numerical data not presented). The conformational anal. along with further synthetic efforts will hopefully lead to more efficient pseudosaccharides as chitinase inhibitors.