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Stationary
Terms modified by Stationary Selected AbstractsCover Picture: Electrophoresis 22'2009ELECTROPHORESIS, Issue 22 2009Article first published online: 25 NOV 200 Issue no. 22 is a Special Issue on "CE and CEC Innovations" consisting of 24 important contributions in various areas of CE and CEC that are grouped into five different parts. Part I has 7 articles on novel "Stationary Phases for CEC". Part II is on "CE of Microorganisms and their Components and Interactions", and has 4 research articles. "Enantioseparations" constitute part III and has 3 research articles dealing with different chiral species and chiral CE systems. Part IV has 3 contributions on "Detection Approaches in CE". Part V is on "Capillary Coating, Affinity and Separation Media , Applications" and contains 7 research articles dealing with the separations of proteins, lipoproteins, bioactive inflammatory cytokines, inorganic and small organic anions, non-steroidal anti-inflammatory drugs, cell culture media and ancient DNA samples." [source] Stationary and mobile phases in capillary electrochromatography (CEC)JOURNAL OF SEPARATION SCIENCE, JSS, Issue 15-16 2003Jan Jiskra Abstract This review describes the state of the art of capillary electrochromatography (CEC). Properties of and interactions between stationary and mobile phases applied in CEC are described and discussed; developments in stationary phases, partly also monolithic stationary phases, are reviewed. Special attention is paid to the comparison of the behaviour of stationary and/or mobile phases under CEC versus HPLC conditions with respect to variables such as particle and pore size of the stationary phase, mobile phase composition, and temperature. These issues are discussed throughout the paper. A number of applications in CEC is presented as well. [source] Estimation of the Dominating Frequency for Stationary and Nonstationary Fractional Autoregressive ModelsJOURNAL OF TIME SERIES ANALYSIS, Issue 5 2000Jan Beran This paper was motivated by the investigation of certain physiological series for premature infants. The question was whether the series exhibit periodic fluctuations with a certain dominating period. The observed series are nonstationary and/or have long-range dependence. The assumed model is a Gaussian process Xt whose mth difference Yt = (1 ,B)mXt is stationary with a spectral density f that may have a pole (or a zero) at the origin. the problem addressed in this paper is the estimation of the frequency ,max where f achieves the largest local maximum in the open interval (0, ,). The process Xt is assumed to belong to a class of parametric models, characterized by a parameter vector ,, defined in Beran (1995). An estimator of ,max is proposed and its asymptotic distribution is derived, with , being estimated by maximum likelihood. In particular, m and a fractional differencing parameter that models long memory are estimated from the data. Model choice is also incorporated. Thus, within the proposed framework, a data driven procedure is obtained that can be applied in situations where the primary interest is in estimating a dominating frequency. A simulation study illustrates the finite sample properties of the method. In particular, for short series, estimation of ,max is difficult, if the local maximum occurs close to the origin. The results are illustrated by two of the data examples that motivated this research. [source] Cytokines, matrix metalloproteases, angiogenic and growth factors in tears of normal subjects and vernal keratoconjunctivitis patientsALLERGY, Issue 5 2009A. Leonardi Background:, To detect the presence of multiple mediators and growth factors in tears of vernal keratoconjunctivitis (VKC) patients with active disease using stationary phase antibody arrays. Methods:, Tears were collected from 12 normal subjects (CT) and 24 active VKC patients. Tears were centrifuged and successively probed using three microwell plate arrays specific for: (i) cytokines: interleukin (IL)-2, IL-4, IL-5, IL-8, IL-10, IL-12, IL-13, interferon-, and tumour necrosis factor-,; (ii) growth factors: basic fibroblast growth factor (bFGF), platelet-derived growth factor, thrombopoietin, angiopoietin-2, vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), keratocyte growth factor, tissue inhibitor of metalloprotease (TIMP)-1 and heparin-binding epithelial growth factor (HB-EGF) and (iii) matrix metalloprotease (MMP)-1, MMP-2, MMP-3, MMP-8, MMP-9, MMP-10, MMP-13, TIMP-1 and TIMP-2. Results:, Interleukin-8 signals were detected in all CT and highly detected in all VKC samples. The Th2-type cytokines, IL-4, IL-5 and IL-10 were detected only in tears of VKC patients. Signals for bFGF, HB-EGF, VEGF and HGF were detected in 41,87% of VKC samples and in few CT samples. Only TIMP-1 and TIMP-2 were found in all normal and patient tear samples, whereas MMP-1, MMP-2, MMP-3, MMP-9 and MMP-10 were highly present in all VKC samples. Conclusions:, Stationary phase antibody array methodology was useful for the screening of various cytokines, growth factors and MMPs in tears. These analyses identified in tears of VKC patients previously unreported factors including MMP-3 and MMP-10 and multiple proteases, growth factors and cytokines, which may all play an important role in the pathogenesis of conjunctival inflammation. [source] Coherent resonant scattering and free induction decay of 2D-excitons in GaAs SQWPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2009Sergey V. Poltavtsev Abstract Stationary and transient spectroscopy of excitonic induction is applied for measuring the rates of the processes controlling the efficiency of the coherence transfer under the photon-exciton transformations in GaAs/AlGaAs structures with single quantum wells. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The determinants of Canadian children's personal exposures to magnetic fieldsBIOELECTROMAGNETICS, Issue 3 2001Ben G. Armstrong Abstract Study of the health effects of magnetic fields often depends on identifying determinants and hence indicators of personal exposure. This study identified determinants of children's exposure to magnetic fields and constructed a prediction model for them. For 632 children participating in a case,control study of childhood leukemia, we made direct measures of exposure over 48,h using a portable device, together with observations on candidate determinants. A child's age and sex, the proportion of time spent in the home, and their parents' education or income were very weak predictors of (logged) mean 48,h magnetic field (R2,<,1%). More important were province (R2,=,8.0%) and type of residence (R2,=,11.3%). Low temperatures at the time of measurement were associated with high fields (about 20% increase for each 10°C below 14, R2,=,4.9%). Several visible attributes of wiring around residences predicted exposure, mostly captured in the Wertheimer-Leeper wire code (R2,=,13.5%). Stationary 24,h measurement in the bedroom (R2,=,63.3%) and spot measurements outside the house (R2,=,40.7%) predicted personal exposures best. Adding other minor predictors increased only slightly variance explained by 24,h stationary (R2,=,66.2%) and spot (R2,=,46.8%) measurements. Without spot or stationary measurements, the best model was much less powerful (R2,=,29.0%). We conclude that spot measurements outside the residence provide a moderately effective basis for estimating exposure for children living there, but do not perform as well as 24,h stationary measurements in the child's bedroom. Although several other easily-observed variables were associated with personal exposure, they were weak determinants, either individually or in combination. Bioelectromagnetics 22:161,169, 2001. © 2001 Wiley-Liss, Inc. [source] Dynamic Chemical Devices: Photoinduced Electron Transfer and Its Ion-Triggered Switching in Nanomechanical Butterfly-Type Bis(porphyrin)terpyridines,CHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2006Myriam Linke-Schaetzel Dr. Abstract A series of butterfly-type molecular constructs has been prepared in good yield by using a double Stille coupling synthetic protocol. They are composed of a terpyridine (terpy) scaffold and two wings composed of appended porphyrins that are capable of switching from an extended W geometry to a compact U geometry upon cation coordination of the terpy unit. The porphyrin moieties exist in the constructs either as free bases or they can be sequentially metallated, thus giving rise to wings of different "colours". Stationary and time-resolved emission studies of the HZn, ZnAu and Zn2Au constructs show that the electronic properties are strongly dependent on the geometry. In the extended W conformation an energy-transfer process is seen from the free base to the Zn-metallated porphyrin. In the U conformation in Zn2Au the donor luminescence resulting from the singlet excited state of the Zn wing is strongly, quenched not only due to the heavy atom effect but also due to a fast electron-transfer process to the ground state of the Au wing. Furthermore, the binding of (,,,)-diamine substrates to the ZnII,porphyrin sites can also influence the conformation of the system. For the Zn2Zn construct, single-crystal diffraction experiments with synchrotron radiation allowed the structure to be solved by direct methods and fully refined; it shows the expected U conformation. The central Zn atom is six-coordinate, whereby the zinc atom is coordinated by the ,3 -terpy ligand as well by monodentate and semi-chelating acetate anions. The structure is made rigid by hydrogen bonds involving the aqua ligands on the outer Zn centres and acetate oxygen atoms. The present system thus represents a double-trigger-modulated optomechanical switching device with selective substrate binding for either metal atoms or tailored ligands. Both energy- and electron-transfer processes can be controlled opening a means of improving the on/off ratio in future constructs. Une série d'architectures moléculaires, présentant une forme de papillon, a été préparée avec de bons rendements en utilisant une méthodologie synthétique comprenant comme étape clé un double couplage de Stille. Ces architectures sont composées d'un squelette terpyridine (terpy), qui compose le torse du papillon, sur lequel deux ailes porphyriniques ont été greffées; la géométrie peut varier entre une conformation étendue en forme de W, et une conformation compacte en forme de U, dû à la complexation du torse terpy par un cation de taille et coordination adéquate. Les ailes porphyriniques se présentent soit comme bases libres ou, peuvent être métallées successivement avec différentes métaux, pouvant ainsi avoir différentes "couleurs". Des études de fluorescence non seulement stationnaire mais aussi résolues dans le temps sur les architectures HZn, ZnAu et Zn2Au, montrent que les propriétés électroniques sont très dépendantes de la géométrie adoptée. Dans la conformation W étendue, nous avons mis en évidence un processus de transfert d'énergie de la porphyrine base libre vers la porphyrine metalée avec du Zn. Dans la conformation U de Zn2Au la luminescence de l'aile donneuse, à cause de l'état excité singulet, est fortement éteinte, non seulement à cause de l'effet d'atome lourd, mais aussi à cause d'un processus de transfert d'électron vers l'état fondamental de l'aile metalée avec de l'or. De plus, par compléxation avec des (,,,)-diamines des atomes de ZnIIdans les tetrapyrroles porphyrinques, la conformation induite du système peut être profondément influencée. Pour le composé Zn2Zn, que nous avons pu obtenir en monocristaux, des expériences de diffraction en utilisant comme source lumineuse un synchrotron, ont fourni des données qui ont permis de résoudre la structure par des méthodes directes et de la raffiner pour montrer la conformation en U attendue. L'atome central de Zn a une coordination de six dont trois provenant du ligand ,3 -terpy, et les autres de deux anions acetates, un monodenté et l'autre semi-chelatizé. La structure est ligotée par des multiples liaisons hydrogène entre des ligands aqueux sur les atomes de Zn externes et les atomes d'oxygène des anions acetates. Le système présenté est un double effecteur qui montre une commutation opto-mechanique dirigée soit par des ions métalliques, soit par d'autres ligands de taille adaptée. En même temps, les processus de transfert d'énergie et d'électrons peuvent être commuté en laissant de la place pour améliorer le rapport "on/off" dans de futures architectures. Abstract in Romanian:O serie de arhitecturi moleculare având o form, de fluture au fost preparate cu randamente bune utilizând o metodologie sintetic, cuprinzând ca etap, cheie un dublu cuplaj Stille. Aceste architecturi sunt compuse dintr-un schelet terpiridinic (terpy) alc,tuind trupul fluturelui, la care au fost implementate dou, aripi porfirinice care sunt capabile sa varieze între o conforma,ie extins, în forma de liter, W ,i o conformai,ie compact, în form, de litera U, datorit, complexarii trupului terpy printr-un cation de talie ,i coordina,ie adecvat,. Aripile porfirinice se prezintã fie ca base libere sau, datorita unei metalari succesive cu diferite metale, pot avea diferite "culori". Studii de fluorescen,a atât sta,ionar, cât ,i rezolvat, în timp, asupra arhitecturilor HZn, ZnAu ,i Zn2Au, arat, c, proprit,,ile electronice sunt foarte dependente de geometria adoptat,. In conforma,ia W extins,, am putut pune în eviden,, un proces de transfer de energie dinspre baza liber, c,tre porfirina metalat, cu Zn. In conforma,ia U a Zn2Au luminescen,a aripei donoare, datorate st,rii singulet excitate, este puternic stins, nu numai datorit, efectului de atom greu, cât ,i a unui proces de transfer de electron c,tre starea fundamental, a aripei metalat, cu aur. Pe deasupra, complexând (,,,)-diamine c,tre atomii de ZnIIîntre tetrapirolii porfirinici, sunt induse profunde influen,e asupra conforma,iei sistemului. Pentru compusul Zn2Zn, care a putut fi crescut monocristalin, experimente de difrac,ie folosind ca surs, luminoas, un sincrotron au condus la un set de date care a permis ca structura sa fie elucidat, prin metode directe ,i rafinat,, ar,tând conforma,ia în U a,teptat,. Atomul central de Zn are o coordina,ie de sase unde pe lang, lignadul ,3 -terpy, atomul de Zn este coordinat de c,tre doi anioni acetat, unul monodentat, iar cel,lalt semi-chelatizant. Structura este br,zdat, de leg,turi de hidrogen care implic, liganzii apo,i situa,i pe centrii de Zn exteriori, ,i atomii de oxigen din ionii acetat. Sistemul prezentat este un dutblu efector, ar,tând comutare opto-mecanic,, datorat, fie lig,rii prin ioni metalici, fie prin al,i liganzi perfect croitori,i. In acel,i timp, atât procese de transfer de energie, cât ,i de electroni, pot fi perfect comutate, l,sând loc pentru imbun,t,,irea raportului "on/off" în arhitecturi viitoare. [source] Towards Fast Measurement of the Electron Temperature in the SOL of ASDEX Upgrade Using Swept Langmuir ProbesCONTRIBUTIONS TO PLASMA PHYSICS, Issue 9 2010H.W. Müller Abstract On ASDEX Upgrade first experiments were made using single probes with a voltage sweep frequency up to 100kHz. Possibilities and limitations using fast swept probes with a standard diagnostic and analysis tools are discussed. A good agreement between the data derived from fast swept single probe characteristics and floating as well as saturation current measurements was found. In a stationary (non ELMing) plasma the data of the fast swept probe are compared to standard slow swept probes (kHz range) showing an improvement of the measurement by faster sweeping. While ELM filaments already could be resolved the access of electron temperature fluctuations in small scale turbulence still has to be improved. Further comparisons are done in ELMy H-mode with combined ball-pen probe/floating potential measurements which can deliver electron temperatures with 25 , s time resolution at reduced spatial resolution compared to pin probes. During ELMs the electron temperatures derived from the ball-pen probe and fast swept single probes agreed (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Cell distribution of stress fibres in response to the geometry of the adhesive environmentCYTOSKELETON, Issue 6 2006Manuel Théry Abstract Cells display a large variety of shapes when plated in classical culture conditions despite their belonging to a common cell type. These shapes are transitory, since cells permanently disassemble and reassemble their cytoskeleton while moving. Adhesive micropatterns are commonly used to confine cell shape within a given geometry. In addition the micropattern can be designed so as to impose cells to spread upon adhesive and nonadhesive areas. Modulation of the pattern geometry allows the analysis of the mechanisms governing the determination of cell shape in response to external adhesive conditions. In this study, we show that the acquisition of cell shape follows two stages where initially the cell forms contact with the micropattern. Here, the most distal contacts made by the cell with the micropattern define the apices of the cell shape. Then secondly, the cell borders that link two apices move so as to minimise the distance between the two apices. In these cell borders, the absence of an underlying adhesive substrate is overcome by stress fibres forming between the apices, which in turn are marked by an accumulation of focal adhesions. By inhibiting myosin function, cell borders on nonadhesive zones become more concave, suggesting that the stress fibres work against the membrane tension in the cell border. Moreover, this suggested that traction forces are unevenly distributed in stationary, nonmigrating, cells. By comparing the stress fibres in cells with one, two, or three nonadherent cell borders it was reasoned that stress fibre strength is inversely proportional to number. We conclude that cells of a given area can generate the same total sum of tractional forces but that these tractional forces are differently spaced depending on the spatial distribution of its adherence contacts. Cell Motil. Cytoskeleton 2006. © 2006 Wiley-Liss, Inc. [source] Model updating using noisy response measurements without knowledge of the input spectrumEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2005Ka-Veng Yuen Abstract A new probabilistic model identification methodology is proposed using measured response time histories only. The proposed approach requires that the number of independent measurements is larger than the number of independent excitations. Under this condition, no input measurements or any information regarding the stochastic model of the input is required. Specifically, the method does not require the response to be stationary and does not assume any knowledge of the parametric form of the spectral density of the input. Therefore, the method has very wide applicability. The proposed approach allows one to obtain not only the most probable values of the updated model parameters but also their associated uncertainties using only one set of response data. It is found that the updated probability distribution can be well approximated by a Gaussian distribution centered at the most probable values of the parameters. Examples are presented to illustrate the proposed method. Copyright © 2004 John Wiley & Sons, Ltd. [source] Trade-offs and the evolution of life-histories during range expansionECOLOGY LETTERS, Issue 10 2010Olivia J. Burton Ecology Letters (2010) Abstract During range-advance, individuals on the expanding edge of the population face a unique selective environment. In this study, we use a three-trait trade-off model to explore the evolution of dispersal, reproduction and competitive ability during range expansion. We show that range expansion greatly affects the evolution of life-history traits due to differing selection pressures at the front of the range compared with those found in stationary and core populations. During range expansion, dispersal and reproduction are selected for on the expanding population front, whereas traits associated with fitness at equilibrium density (competitive ability) show dramatic declines. Additionally, we demonstrate that the presence of a competing species can considerably reduce the extent to which dispersal is selected upwards at an expanding front. These findings have important implications for understanding both the rate of spread of invasive species and the range-shifting dynamics of native species in response to climate change. [source] Assessment of residency and movement of the endangered bullhead (Cottus gobio) in two Flemish riversECOLOGY OF FRESHWATER FISH, Issue 4 2004G. Knaepkens Abstract,,, Residency and movement of bullheads (Cottus gobio) were assessed by mark-recapture from November 2001 to June 2002 in two Flemish rivers [Steenputbeek (SPB), Laarse Beek (LB)]. Although the majority of the recaptured bullheads (SPB: 66%; LB: 55%) was found in their initial tagging site before the spawning season, some fish had covered distances between 10,100 m (mean: 17 ± 2 m) and 10,70 m (mean: 18 ± 7 m), respectively. During the spawning season, the proportion of fish that moved (SPB: 58%; LB: 75%) and the distances travelled (SPB: between 10 and 90 m, mean 26 ± 3 m; LB: between 30 and 260 m, mean 133 ± 3 m) were significantly larger. In addition, analysis of individual movement behaviour of multiple recaptured bullheads showed that some fish were either always resident or mobile, while others switched between both behaviours. In general, our results suggest that not all bullheads exhibit sedentary behaviour but that the populations under study consist of both stationary and mobile individuals. Resumen 1. Desde Noviembre del año 2001 hasta Junio del 2002, evaluamos la residencia y los movimientos de Cottus gobio a través de técnicas de marcado-recaptura en dos ríos flamencos: Steenputbeek (SPB) y Laarse Beek (LB). Aunque antes de la estación reproductiva, la mayoría de los individuos re-capturados (66% en SPB y 55% en LB) fueron encontrados en las mismas localidades de marcado, algunos peces habían cubierto distancias entre 10 y 100 metros (media = 17.2 ± 2 m) y entre 10 y 70 m (media = 18.0 ± 7 m) en SPB y LB, respectivamente. Durante la estación reproductiva, tanto la proporción de individuos que se movieron (58% en SPB y 75% en LB), como las distancias recorridas fueron significativamente mayores: en SPB, entre 10 y 90 m, media = 26.0 ± 3 m y en LB entre 30 y 260 m, media = 133.0 ± 3 m. 2. Análisis del comportamiento entre múltiples individuos mostró que algunos individuos fueron o residentes o móviles mientras que otros individuos cambiaron entre ambos comportamientos. En general, nuestros resultados sugieren que no todos los individuos muestran comportamiento sedentario sino que la población incluye individuos estacionarios y móviles. [source] End-of-Sample Instability TestsECONOMETRICA, Issue 6 2003D. W. K. Andrews This paper considers tests for structural instability of short duration, such as at the end of the sample. The key feature of the testing problem is that the number, m, of observations in the period of potential change is relatively small,possibly as small as one. The well-known F test of Chow (1960) for this problem only applies in a linear regression model with normally distributed iid errors and strictly exogenous regressors, even when the total number of observations, n+m, is large. We generalize the F test to cover regression models with much more general error processes, regressors that are not strictly exogenous, and estimation by instrumental variables as well as least squares. In addition, we extend the F test to nonlinear models estimated by generalized method of moments and maximum likelihood. Asymptotic critical values that are valid as n,, with m fixed are provided using a subsampling-like method. The results apply quite generally to processes that are strictly stationary and ergodic under the null hypothesis of no structural instability. [source] TWIN SONS OF DIFFERENT MOTHERS: THE LONG AND THE SHORT OF THE TWIN DEFICITS DEBATEECONOMIC INQUIRY, Issue 4 2009KEVIN GRIER Interest in the twin deficits hypothesis fluctuates in tandem with the U.S. current account deficit. Surprisingly though, a statistically robust relationship between budget and trade deficits has been difficult to pin down. We argue that a big part of this difficulty is due to the failure to allow for structural breaks in the series when (either explicitly or implicitly) modeling their time series properties. We show that both series are break stationary (and conditionally heteroskedastic) and argue that while there is no common pattern in the long run, the short-run dynamics reveal a sizeable and fairly persistent positive relationship between budget deficit shocks and current account deficit shocks. (JEL F41, E6, H6) [source] Anodic Stripping Voltammetry Using a Vibrating ElectrodeELECTROANALYSIS, Issue 13 2007Conrad Abstract This work proposes a vibrating microwire electrode as working electrode in stripping voltammetry. The vibration was found to maintain a constant and thin (1,2,,m) diffusion layer during the deposition step. The electrode vibration eliminated the need for external stirring of the solution, thus facilitating in situ detection in the environment. The vibration was effected by fixing a low-voltage (3,V), asymmetric, electrical rotor to the working electrode (a gold microwire of either 5 or 25,,m). The sensitivity of the vibrated electrode was ca. 22×greater than stationary. Measurements of copper (4,nM) by anodic stripping voltammetry using the vibrating electrode had a low standard deviation (1% for n=6) indicating that the diffusion layer had only minor variability. The agitation mechanism was unaffected by water moving at >2,m s,1 and by water pressure equivalent to a depth of >40,m, indicating its suitability for in situ measurements. The vibrating probe was used for in situ detection of copper by anodic stripping voltammetry to a depth of 6,m. Using a 5,min deposition time, the limit of detection for labile copper was 38,pM. [source] Hierarchical processing of sound location and motion in the human brainstem and planum temporaleEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2005Katrin Krumbholz Abstract Horizontal sound localization relies on the extraction of binaural acoustic cues by integration of the signals from the two ears at the level of the brainstem. The present experiment was aimed at detecting the sites of binaural integration in the human brainstem using functional magnetic resonance imaging and a binaural difference paradigm, in which the responses to binaural sounds were compared with the sum of the responses to the corresponding monaural sounds. The experiment also included a moving sound condition, which was contrasted against a spectrally and energetically matched stationary sound condition to assess which of the structures that are involved in general binaural processing are specifically specialized in motion processing. The binaural difference contrast revealed a substantial binaural response suppression in the inferior colliculus in the midbrain, the medial geniculate body in the thalamus and the primary auditory cortex. The effect appears to reflect an actual reduction of the underlying activity, probably brought about by binaural inhibition or refractoriness at the level of the superior olivary complex. Whereas all structures up to and including the primary auditory cortex were activated as strongly by the stationary as by the moving sounds, non-primary auditory fields in the planum temporale responded selectively to the moving sounds. These results suggest a hierarchical organization of auditory spatial processing in which the general analysis of binaural information begins as early as the brainstem, while the representation of dynamic binaural cues relies on non-primary auditory fields in the planum temporale. [source] Changes of effective connectivity between the lateral and medial parts of the prefrontal cortex during a visual taskEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2003Thierry Chaminade Abstract Structural equation modelling was used to study the change of connectivity during a visual task with continuous variation of the attention load. The model was based on areas defined by the haemodynamic responses described elsewhere [Mazoyer, P., Wicker, B. & Fonlupt, P. (2002) A neural network elicited by parametric manipulation of the attention load. Neuroreport, 13, 2331,2334], including occipitotemporal, parietal, temporal and prefrontal (lateral and medial areas) cortices. We have studied stationary- (which does not depend on the attentional load) and attention-related coupling between areas. This allowed the segregation of two subsystems. The first could reflect a system performing the integration step of the visual signal and the second a system participating in response selection. The major finding is the mutual negative influence between the lateral and medial parts of the prefrontal cortex. This negative influence between these two brain regions increased with the attention load. This is interpreted as a modification of the balance between integration and decision processes that are needed for the task to be efficiently completed. [source] ON THE ORIGIN OF MODULAR VARIATIONEVOLUTION, Issue 8 2002Hod Lipson Abstract We study the dynamics of modularization in a minimal substrate. A module is a functional unit relatively separable from its surrounding structure. Although it is known that modularity is useful both for robustness and for evolvability (Wagner 1996), there is no quantitative model describing how such modularity might originally emerge. Here we suggest, using simple computer simulations, that modularity arises spontaneously in evolutionary systems in response to variation, and that the amount of modular separation is logarithmically proportional to the rate of variation. Consequently, we predict that modular architectures would appear in correlation with high environmental change rates. Because this quantitative model does not require any special substrate to occur, it may also shed light on the origin of modular variation in nature. This observed relationship also indicates that modular design is a generic phenomenon that might be applicable to other fields, such as engineering: Engineering design methods based on evolutionary simulation would benefit from evolving to variable, rather than stationary, fitness criteria, as a weak and problem-independent method for inducing modularity. [source] Endocrine signatures underlying plasticity in postembryonic development of a lower termite, Cryptotermes secundus (Kalotermitidae)EVOLUTION AND DEVELOPMENT, Issue 3 2009Judith Korb SUMMARY Wood-dwelling termites are characterized by an extremely high and unique developmental flexibility that allows workers, which are immatures, to explore all caste options. The endocrine signatures underlying this flexibility are only vaguely understood. We determined juvenile hormone (JH) and ecdysteroid hemolymph titers during postembryonic development and in terminal instars of the drywood termite Cryptotermes secundus using field and laboratory colonies. Postembryonic development is characterized by a drop in JH titers at the transition from larval (individuals without wing buds) to nymphal (individuals with wing buds) instars. JH titers were low in winged sexuals and reproducing primary reproductives (<200 pg/,l) but were by an order of magnitude higher in neotenic replacement reproductives. The unique regressive molts of termites seem to be characterized by elevated JH titers, compared with progressive or stationary molts. Ecdysteroid titers were generally low in nymphal instars and in primary reproductives (<50 pg/,l). It was only during the third and fourth nymphal instars and in winged sexuals where some individuals showed elevated ecdysteroid titers. These results are the most comprehensive endocrinological data set available for any lower termite, with the potential to serve as baseline for understanding the extreme developmental flexibility underlying the evolution of social life in termites. [source] Frequency-based fatigue analysis of non-stationary switching random loadsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2007D. BENASCIUTTI ABSTRACT The service loadings in real systems are not only random, but also non-stationary. The spectral methods based on a frequency-domain characterization of random loads, which have been used in alternative to classical time-domain approaches, cannot be applied to non-stationary loads, because the conventional spectral density spectrum is not able to capture the evolutionary frequency characteristics of non-stationary loads. This clearly restricts the applicability of the existing frequency-based methods only to loads which are stationary. At the same time, it is also very difficult to propose general models valid for all types of load non-stationarity encountered in practice. Therefore, a practical approach is to restrict the analysis to a specific class of non-stationary loads; in this work, we consider particular non-stationary loads (i.e. switching loads), which are piecewise stationary in their variance. A frequency-domain analysis of such loads is proposed, which is based on a combination of the frequency-based analysis of each adjacent stationary segment, which can be either Gaussian or non-Gaussian. Numerically simulated load histories, as well as loads measured on mountain bikes in special tracks, are analysed to validate the proposed methodology. The presented results also show the correlation between load non-stationarity and non-Gaussianity. [source] Enhancement of fracture toughness due to energy screening effectin the early stages of non-elastic failureFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2003M. P. WNUK ABSTRACT A triaxiality-dependent cohesive zone model for a stationary and a quasistatic crack is proposed. The model is rooted in the mesomechanical approach to Fracture Mechanics and is inspired by the quantum law concerning emission of light, which was postulated by Max Planck at the end of the 19th century. The model provides an extension of the early concepts of Barenblatt, Dugdale and the Bilby,Cotrell,Swinden team. It also incorporates the experimental observations of the pre-fracture states due to Panin and his school in Tomsk. Relations between micro- and macroparameters that characterize the deformation and fracture processes in dissipative media are described in detail. The analysis suggests that the ratio of the ,true' work of fracture to the total energy dissipated during the course of the irreversible deformation contained within the end zone can be used as a measure of material resistance to a quasistatically propagating fracture. [source] Initial Public Offerings: CFO PerceptionsFINANCIAL REVIEW, Issue 4 2006James C. Brau G14; G24; G32; G34 Abstract We examine four issues pertaining to initial public offerings (IPOs) using a survey of 438 chief financial officers (CFOs). First, why do firms go public? Second, is CFO sentiment stationary across bear and bull markets? Third, what concerns CFOs about going public? Fourth, do CFO perceptions correlate with returns? Results support funding for growth and liquidity as the primary reasons for IPOs. CFO sentiment is generally stationary in pre- and post-bubble years. Managers are concerned with the direct costs of going public, such as underwriting fees, as well as indirect costs. We find a negative relation between a focus on immediate growth and long-term abnormal returns. [source] Modelling Approach for Planar Self-Breathing PEMFC and Comparison with Experimental Results,FUEL CELLS, Issue 4 2004A. Schmitz Abstract This paper presents a model-based analysis of a proton exchange membrane fuel cell,(PEMFC) with a planar design as the power supply for portable applications. The cell is operated with hydrogen and consists of an open cathode side allowing for passive, self-breathing, operation. This planar fuel cell is fabricated using printed circuit board,(PCB) technology. Long-term stability of this type of fuel cell has been demonstrated. A stationary, two-dimensional, isothermal, mathematical model of the planar fuel cell is developed. Fickian diffusion of the gaseous components,(O2, H2, H2O) in the gas diffusion layers and the catalyst layers is accounted for. The transport of water is considered in the gaseous phase only. The electrochemical reactions are described by the Tafel equation. The potential and current balance equations are solved separately for protons and electrons. The resulting system of partial differential equations is solved by a finite element method using FEMLAB,(COMSOL Inc.) software. Three different cathode opening ratios are realized and the corresponding polarization curves are measured. The measurements are compared to numerical simulation results. The model reproduces the shape of the measured polarization curves and comparable limiting current density values, due to mass transport limitation, are obtained. The simulated distribution of gaseous water shows that an increase of the water concentration under the rib occurs. It is concluded that liquid water may condense under the rib leading to a reduction of the open pore space accessible for gas transport. Thus, a broad rib not only hinders the oxygen supply itself, but may also cause additional mass transport problems due to the condensation of water. [source] Assessment of Fuel-Cell-Based Passenger CarsFUEL CELLS, Issue 3 2004T. Grube Abstract Highly efficient energy conversion systems with fuel cells for vehicles, as well as for stationary and portable applications, are currently being discussed all over the world. Fuel cell technology is expected to help reduce primary energy demand and emissions of limited and climate-relevant pollutants. The high flexibility of fuel cell systems with respect to energy carriers opens up possibilities of modifying the energy sector in the long term. Introducing new fuels based on low-carbon, or in the long term carbon-free, energy carriers can contribute to reducing greenhouse gas emissions as well as locally and regionally active atmospheric pollutants. The use of hydrogen as feed gas for fuel cells on the basis of it being a non-fossil, renewable energy, leads to special benefits with respect to conserving resources and climate protection, but at present still represents a medium- to long-term prospect. A major milestone on the road to market success for all energy conversion systems with fuel cells is the reduction of costs. The definition of the ,appropriate" fuel represents a serious obstacle to the market introduction of fuel-cell-powered vehicles. Presenting data from a well-to-wheel analysis of various vehicle fuel systems at FZJ this article aims to discuss the potential benefits of future vehicle concepts with fuel cells in terms of primary energy use and greenhouse gas emissions. Results from a comparison of international studies on this subject will be used to identify relevant assumptions that lead to different answers in the evaluation process. [source] Growth-enhanced fish can be competitive in the wildFUNCTIONAL ECOLOGY, Issue 5 2001J. I. Johnsson Summary 1,The widespread commercial interest in producing growth-enhanced organisms has raised concerns about ecological consequences, emphasizing the need to understand the costs and benefits associated with accelerated growth in nature. Here, sustained-release growth hormone (GH) implants were used to estimate the competitive ability of growth-enhanced fish in the wild. Growth rate, movements and survival over winter were compared between GH-implanted and control Brown Trout in a natural stream. The study was repeated over two consecutive years. 2,GH treatment had no effect on recapture rates, indicating that mortality rates did not differ between GH-treated and control fish. More GH-treated trout (63%) than control fish (41%) were recaptured within their 10 m section of release. Thus, GH-treated fish were more stationary than control fish over winter. 3,GH-treated fish grew about 20% faster than control fish. This was mainly because of a three-fold growth rate increase in GH-treated fish in late summer, whereas growth rates over winter did not differ significantly between treatment groups. These results were consistent over both replicate years. 4,This first study of growth-enhanced fish in the wild shows that they can survive well and therefore may out-compete normal fish with lower growth rates. Although selection against rapid growth may be more intense at other life-history stages and/or during periods of extreme climate conditions, our findings raise concerns that released or escaped growth-enhanced salmonids may compete successfully with resident fish. It is clear that the potential ecological risks associated with growth-enhanced fish should not be ignored. [source] Cretaceous,Tertiary geodynamics: a North Atlantic exerciseGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001Trond H. Torsvik Summary New reconstructions are presented for the Cretaceous,Early Tertiary North Atlantic using a combination of palaeomagnetic, hotspot and magnetic anomaly data. We utilize these reconstructions in an analysis of previously described misfits between the North Atlantic Plate elements at successive intervals during this time period. We are able to achieve reasonable overlap between the hotspot and palaeomagnetic reconstructions between 40 and 95 Ma and thus are able to support the idea that the Indo,Atlantic hotspots are relatively stationary. Small, but systematic discrepancies for this time interval can readily be modelled with a long-term, octopole non-dipole field contribution (G3 = g30/g10 = 0.08). However, hotspot and palaeomagnetic reconstructions for the Early Cretaceous North Atlantic show substantial differences that cannot be explained by constant, non-dipole fields and we favour an explanation for these discrepancies in terms of true polar wander (TPW) triggered by mantle instabilities between 125 and 95 Ma; this constitutes the only identifiable event of significant TPW since the Early Cretaceous. Taken in the context of available geochronological and geological data and seismic tomography from the region, the 95,40 Ma reconstructions and their time-consequent geological products are interpreted in terms of specific conditions of mantle-crust coupling and global plate motions/tectonic activity. Highlights from these reconstructions show uniform NE movement of the coupled North American, Greenland and Eurasian plates from 95 to 80 Ma; a marked cusp in the paths for all three elements at 80 Ma where the three plates simultaneously change direction and follow a uniform NW-directed motion until c. 20 Ma when Eurasia diverges NE, away from the still-NW-moving Greenland and North American elements. Positioning of the Iceland plume beneath the spreading-ridge at 20 Ma may have increased upwelling below the ridge, increased the ridge-push, and caused a NE shift in the absolute direction of Eurasia. [source] Lagged effects of North Atlantic Oscillation on spittlebug Philaenus spumarius (Homoptera) abundance and survivalGLOBAL CHANGE BIOLOGY, Issue 12 2006ANTTI HALKKA Abstract The North Atlantic Oscillation (NAO) is a large-scale pattern of climate variability that has been shown to have important ecological effects on a wide spectrum of taxa. Studies on terrestrial invertebrates are, however, lacking. We studied climate-connected causes of changes in population sizes in island populations of the spittlebug Philaenus spumarius (L.) (Homoptera). Three populations living in meadows on small Baltic Sea islands were investigated during the years 1970,2005 in Tvärminne archipelago, southern Finland. A separate analysis was done on the effects of NAO and local climate variables on spittlebug survival in 1969,1978, for which survival data existed for two islands. We studied survival at two stages of the life cycle: growth rate from females to next year's instars (probably mostly related to overwintering egg survival), and survival from third instar stage to adult. The latter is connected to mortality caused by desiccation of plants and spittle masses. Higher winter NAO values were consistently associated with smaller population sizes on all three islands. Local climate variables entering the most parsimonious autoregressive models of population abundance were April and May mean temperature, May precipitation, an index of May humidity, and mean temperature of the coldest month of the previous winter. High winter NAO values had a clear negative effect on late instar survival in 1969,1978. Even May,June humidity and mean temperature of the coldest month were associated with late instar survival. The climate variables studied (including NAO) had no effect on the growth rate from females to next year's instars. NAO probably affected the populations primarily in late spring. Cold and snowy winters contribute to later snow melt and greater spring humidity in the meadows. We show that winter NAO has a considerable lagged effect on April and May temperature; even this second lagged effect contributes to differences in humidity. The lagged effect of the winter NAO to spring temperatures covers a large area in northern Europe and has been relatively stationary for 100 years at least in the Baltic area. [source] Monocular visual activation patterns in albinism as revealed by functional magnetic resonance imagingHUMAN BRAIN MAPPING, Issue 1 2004Bernd Schmitz Abstract Human albinism is characterized by a disturbance of the chiasmatic projection system leading to predominant representation of just one eye in the contralateral hemisphere. Patients show congenital nystagmus without perceiving oscillopsia. The purpose of the present study was to demonstrate the consequences of atypical chiasmatic crossing with monocular visual stimulation using functional magnetic resonance imaging (fMRI). Sixteen patients with albinism and fifteen normally pigmented controls were stimulated with a monocular visual activation paradigm using flickering checkerboards. In patients, we observed contralaterally dominated activation of visual cortices correlating to clinical albinism parameters. This confirms albinism as a continuous range of hypopigmentation disorders. Additionally, albinos showed activation of the superior colliculus and of visual motion areas although the stimulus was stationary. Activation of visual motion areas is due probably to congenital nystagmus without a conscious correlate like oscillopsia. Hum. Brain Mapping 23:40,52, 2004. © 2004 Wiley-Liss, Inc. [source] A simple model of hillslope response for overland flow generationHYDROLOGICAL PROCESSES, Issue 17 2001Professor Carmelo Agnese Abstract This paper deals with the derivation of the hydrological response of a hillslope on the assumption of quick runoff by surface runoff generation. By using the simple non-linear storage based model, first proposed by Horton, an analytical solution of the overland flow equations over a plane hillslope was derived. This solution establishes a generalization for different flow regimes of Horton's original solution, which is valid for the transitional flow regime only. The solution proposed was compared successfully with that of Horton and, for the turbulent flow regime, to the one derived from kinematic wave theory. This solution can be applied easily to both stationary and non-stationary rainfall excess events. An analytical solution for the instantaneous response function (IRF) was also derived. Finally, simple expressions to compute peak and time to peak of IRF are proposed. Copyright © 2001 John Wiley & Sons, Ltd. [source] On the Distribution of Money Holdings in a Random-Matching Model*INTERNATIONAL ECONOMIC REVIEW, Issue 3 2002Aleksander BerentsenArticle first published online: 6 AUG 200 This article studies stationary and nonstationary distributions of money holdings in a random-matching model. The first part characterizes the stationary distributions of money holdings and derives the optimum quantity of money. The second part considers nonstationary distributions of the optimum quantity of money to show that if the production costs are not too large, any distribution of the optimum quantity of money converges asymptotically to the uniform distribution. [source] | ||||||||||||||||||||||||||||||||||||||||||||||||||||