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Spacing
Kinds of Spacing Terms modified by Spacing Selected AbstractsHighly Stable Au Nanoparticles with Tunable Spacing and Their Potential Application in Surface Plasmon Resonance BiosensorsADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Shuyan Gao Abstract Colloidal Au-amplified surface plasmon resonance (SPR), like traditional SPR, is typically used to detect binding events on a thin noble metal film. The two major concerns in developing colloidal Au-amplified SPR lie in 1) the instability, manifested as a change in morphology following immersion in organic solvents and aqueous solutions, and 2) the uncontrollable interparticle distance, determining probe spacing and inducing steric hindrance between neighboring probe molecules. This may introduce uncertainties into such detecting techniques, degrade the sensitivity, and become the barricade hampering colloidal Au-based transducers from applications in sensing. In this paper, colloidal Au-amplified SPR transducers are produced by using ultrathin Au/Al2O3 nanocomposite films via a radio frequency magnetron co-sputtering method. Deposited Au/Al2O3 nanocomposite films exhibit superior stability, and average interparticle distances between Au nanoparticles with similar average sizes can be tuned by changing surface coverage. These characteristics are ascribed to the spacer function and rim confinement of dielectric Al2O3 and highlight their advantages for application in optimal nanoparticle-amplified SPR, especially when the probe size is smaller than the target molecule size. This importance is demonstrated here for the binding of protein (streptavidin) targets to the probe (biotin) surface. In this case, the dielectric matrix Al2O3 is a main contributor, behaving as a spacer, tuning the concentration of Au nanoparticles, and manipulating the average interparticle distance, and thus guaranteeing an appropriate number of biotin molecules and expected near-field coupling to obtain optimal sensing performance. [source] Improved SERS Performance from Au Nanopillar Arrays by Abridging the Pillar Tip Spacing by Ag SputteringADVANCED MATERIALS, Issue 37 2010Zhulin Huang Ag-capped Au nanopillar arrays on a resin supporter (see left upper figure), with a typical adjacent pillar tip gap of 10 nm, show obviously higher surface-enhanced Raman scattering (SERS) sensitivity (right column in red) than that of the bare Au nanopillar array while using 10 nM R6G as probe molecules. The large-area Ag-capped Au nanopillar array has potential in trace detection of special chemicals. [source] Spacing and crowding among African and Caucasian childrenORTHODONTICS & CRANIOFACIAL RESEARCH, Issue 2 2008EA Mugonzibwa Structured Abstract Authors,,, Mugonzibwa EA, Eskeli R, Laine-Alava MT, Kuijpers-Jagtman AM, Katsaros C Objective,,, To determine spacing and crowding according to ethnic group, gender and dental emergence stage among Tanzanian African and Caucasian children. Design,,, Cross-sectional epidemiological clinical study. Setting,,, A total of 869 African (428 boys, 441 girls) and 706 Caucasian (319 boys, 387 girls) school children, aged 3½,16 years. Main Outcome Measures,,, Comparison of spacing and crowding between African and Caucasian children according to gender and dental emergence stage. Results,,, Spacing was more often found in the maxilla, while crowding was more common in the mandible. Only during the transition of the maxillary permanent front teeth was there significantly more spacing in Caucasians. No gender differences were found. In both samples spacing decreased during later emergence stages. Crowding was more often found in Caucasian children than in African children. In Caucasian children the frequency of crowding increased with advanced emergence stages, while for Africans the trend was not consistent. Conclusion,,, When planning resources for orthodontic treatment for different populations as well as planning treatment for individuals, ethnic background and emergence stage of the dentition need to be considered. [source] Optimising learning using flashcards: Spacing is more effective than crammingAPPLIED COGNITIVE PSYCHOLOGY, Issue 9 2009Nate Kornell The spacing effect,that is, the benefit of spacing learning events apart rather than massing them together,has been demonstrated in hundreds of experiments, but is not well known to educators or learners. I investigated the spacing effect in the realistic context of flashcard use. Learners often divide flashcards into relatively small stacks, but compared to a large stack, small stacks decrease the spacing between study trials. In three experiments, participants used a web-based study programme to learn GRE-type word pairs. Studying one large stack of flashcards (i.e. spacing) was more effective than studying four smaller stacks of flashcards separately (i.e. massing). Spacing was also more effective than cramming,that is, massing study on the last day before the test. Across experiments, spacing was more effective than massing for 90% of the participants, yet after the first study session, 72% of the participants believed that massing had been more effective than spacing. Copyright © 2009 John Wiley & Sons, Ltd. [source] Preemptive Spacing With Vertical Differentiation When Input Quality is of Inelastic SupplyAUSTRALIAN ECONOMIC PAPERS, Issue 2 2000Mark R. Frascatore This paper examines a model of vertical differentiation in which an incumbent engages in preemptive spacing to prevent entry. Input quality is of fixed supply, and the incumbent prevents high-end entry by producing a product with all the quality available. It also commits to the production of a minimum-quality product to deter low-end entry. There is no entry in equilibrium, and the incumbent monopolist chooses to sell only its high-quality product. Commitment to the production of the minimum-quality product is used merely as a credible threat to vigorously compete should an entrant also produce a minimum-quality product. [source] Novel Phthalocyaninatobis(alkylcarboxylato)silicon(IV) Compounds: NMR Data and X-ray Structures To Study the Spacing Provided by Long Hydrocarbon Tails That Enhance Their SolubilityCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2005Jose L. Sosa-Sánchez Dr. Abstract The reaction between trans -PcSiCl2 (1) and the potassium salts of six fatty acids (2,a,2,f) led to the trans -PcSi[OOC(CH2)nCH3]2 compounds (3,a,3,f), which were characterised by elemental analysis, IR, UV/Vis and 1H, 13C, and 29Si NMR spectroscopy. From a detailed study of the NMR spectra, the strong anisotropic currents of the Pc macrocycle were found to have an effect on up to the sixth methylenic group. As expected, the length of the hydrocarbon tail does not affect the chemical shift of the 29Si nucleus of any of the compounds, appearing at around ,222.6. The structures of PcSi[OOC(CH2)nCH3]2, where n=7, 10, 12, 13 and 20, were determined by X-ray crystallography. All the compounds were found to be triclinic with a P space group. In all cases the observed crystallographic pseudosymmetry is Ci and the asymmetric unit consists of half a molecule. The silicon atom is at the centre of a distorted octahedron and hence its coordination number is six. The carboxylate fragments are in a trans configuration with respect to the Pc macrocycle. The supramolecular structures are discussed in detail herein. The correlation between the 1H NMR chemical shifts and the position of the corresponding carbon atoms in the hydrocarbon tail reveals that the dicarboxylate substituents exhibit a spacer-like behaviour that enhances the solubility. A detailed study of the tail variable allowed us to evaluate the loss of radial shielding along the Pc2, ligand. [source] Interaction between a dislocation and monovalent anion in various alkali halide crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2010Y. KohzukiArticle first published online: 30 AUG 2010 Abstract It was investigated from (L0/L)2 versus ,0 curve that the Friedel relation between the effective stress and the average length of dislocation segments, L, is appropriate for the interaction between a dislocation and the monovalent anion in various alkali halides single crystals (NaCl: Br - , NaBr: Cl - or I - , KCl: Br - or I - , and RbCl: Br - or I - ). Here, L0 represents the average spacing of monovalent anions on a slip plane and ,0 is the bending angle at which the dislocation breaks away from the anion at the temperature of 0 K. This is because the anions are the weak obstacles such as impede the dislocation at ,0 above about 150 degrees, where the Friedel relation agrees with the Fleischer one (L02 = L2(,,,0)/2). Furthermore, the values of (L /L0) were found to be within 4.05 to 5.87 for the crystals. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Phase transition behavior and structure of the thermotropic liquid crystal 6-{[(4,-{[(undecyl)carbonyl]oxy}biphenyl-4yl)carbonyl]oxy}-1-hexyneCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2006Leijing Liu Abstract The phase transition behaviors and corresponding structures of 6-{[(4,-{[(undecyl)carbonyl]oxy}biphenyl-4yl)carbonyl]oxy}-1-hexyne (A4EE11) were investigated using differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and wide angle X-ray diffraction (WAXD). In comparison with the published homologues, 5-{[(4,-heptoxy-biphenyl-4-yl)carbonyl]oxy}-1-pentyne (A3EO7) which shows a monotropic smectic A (SmA) phase and a metastable monotropic smectic C (SmC) phase; 5-{[(4,-heptoxy-biphenyl-4-yl)oxy]carbonyl}- 1-pentyne (A3E'O7) that exhibits three enantiotropic stable liquid crystalline (LC) phases, SmA phase, SmC phase and smectic X (SmX) phase; 5-{[(4,-heptoxy-biphenyl-4-yl)carbonyl]oxy}-1-undecyne (A9EO7) which has a monotropic SmA phase and a metastable crystal phase, A4EE11 integrates the enantiotropy, monotropy and metastability of the LC phases of those three compounds. Upon cooling from isotropic state to room temperature, in the temperature range of 62.0 to 58.5°C, A4EE11 shows an enantiotropic smectic A (SmA) phase with a layer spacing d=32.69Å. Further lowering the temperature, it enters into a metastable monotropic smectic B (SmB) phase with a longer layer spacing d=34.22Å which has a tendency towards crystallization. The metastability of the liquid crystalline phase may associate to the linkage order of the ester bridge between the mesogenic core and the flexible spacer. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The deaf mouse mutant whirler suggests a role for whirlin in actin filament dynamics and stereocilia developmentCYTOSKELETON, Issue 7 2007Mette M. Mogensen Abstract Stereocilia, finger-like projections forming the hair bundle on the apical surface of sensory hair cells in the cochlea, are responsible for mechanosensation and ultimately the perception of sound. The actin cytoskeleton of the stereocilia contains hundreds of tightly cross-linked parallel actin filaments in a paracrystalline array and it is vital for their function. Although several genes have been identified and associated with stereocilia development, the molecular mechanisms responsible for stereocilia growth, maintenance and organisation of the hair bundle have not been fully resolved. Here we provide further characterisation of the stereocilia of the whirler mouse mutant. We found that a lack of whirlin protein in whirler mutants results in short stereocilia with larger diameters without a corresponding increase in the number of actin filaments in inner hair cells. However, a decrease in the actin filament packing density was evident in the whirler mutant. The electron-density at the tip of each stereocilium was markedly patchy and irregular in the whirler mutants compared with a uniform band in controls. The outer hair cell stereocilia of the whirler homozygote also showed an increase in diameter and variable heights within bundles. The number of outer hair cell stereocilia was significantly reduced and the centre-to-centre spacing between the stereocilia was greater than in the wildtype. Our findings suggest that whirlin plays an important role in actin filament packing and dynamics during postnatal stereocilium elongation. Cell Motil. Cytoskeleton 2007. © 2007 Wiley-Liss, Inc. [source] Ontogenetic scaling of scansorial surface area and setal dimensions of Chondrodactylus bibronii (Gekkota: Gekkonidae): testing predictions derived from cross-species comparisons of gekkotansACTA ZOOLOGICA, Issue 1 2009Nicole B. Webster Abstract Little is known of how the adhesive apparatus of gekkotans scales with growth. Cross-species comparisons of certain characteristics, using size as a comparator to investigate scaling relationships, suggest certain relationships between subdigital pad area and body size. The manner in which the adhesive apparatus grows and scales within any one species, however, remains unknown, and it is unclear whether interspecific and intraspecific patterns are similar. To address this, we examined a post-hatching ontogenetic series of the southern African gecko Chondrodactylus bibronii and demonstrate that setal density, setal basal diameter and setal spacing remain relatively constant in relation to size, indicating conserved subdigital pad assembly rules that are independent of size. Conversely, however, average and maximal setal lengths increase slightly and isometrically with size, an outcome that is probably explained by setal row recruitment, and the surface area of the subdigital pads scales close to, but below, isometry with respect to body mass and snout,vent length, it therefore does not increase sufficiently with size to compensate for the increase in mass. As a result, relative adhesive capacity decreases with growth with a regression slope of ,0.45. [source] Spatial prediction of river channel topography by krigingEARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2008Carl J. Legleiter Abstract Topographic information is fundamental to geomorphic inquiry, and spatial prediction of bed elevation from irregular survey data is an important component of many reach-scale studies. Kriging is a geostatistical technique for obtaining these predictions along with measures of their reliability, and this paper outlines a specialized framework intended for application to river channels. Our modular approach includes an algorithm for transforming the coordinates of data and prediction locations to a channel-centered coordinate system, several different methods of representing the trend component of topographic variation and search strategies that incorporate geomorphic information to determine which survey data are used to make a prediction at a specific location. For example, a relationship between curvature and the lateral position of maximum depth can be used to include cross-sectional asymmetry in a two-dimensional trend surface model, and topographic breaklines can be used to restrict which data are retained in a local neighborhood around each prediction location. Using survey data from a restored gravel-bed river, we demonstrate how transformation to the channel-centered coordinate system facilitates interpretation of the variogram, a statistical model of reach-scale spatial structure used in kriging, and how the choice of a trend model affects the variogram of the residuals from that trend. Similarly, we show how decomposing kriging predictions into their trend and residual components can yield useful information on channel morphology. Cross-validation analyses involving different data configurations and kriging variants indicate that kriging is quite robust and that survey density is the primary control on the accuracy of bed elevation predictions. The root mean-square error of these predictions is directly proportional to the spacing between surveyed cross-sections, even in a reconfigured channel with a relatively simple morphology; sophisticated methods of spatial prediction are no substitute for field data. Copyright © 2007 John Wiley & Sons, Ltd. [source] Characteristics and dynamics of multiple intertidal bars, north Lincolnshire, EnglandEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2006Selma van Houwelingen Abstract Multiple intertidal bars and troughs, often referred to as ,ridges and runnels', are significant features on many macrotidal sandy beaches. Along the coastline of England and Wales, they are particularly prevalent in the vicinity of estuaries, where the nearshore gradient is gentle and a large surplus of sediment is generally present. This paper examines the dynamics of such bar systems along the north Lincolnshire coast. A digital elevation model of the intertidal morphology obtained using LIDAR demonstrates that three to five intertidal bars are consistently present with a spacing of approximately 100 m. The largest and most pronounced bars (height = 0·5,0·8 m) are found around mean sea level, whereas the least developed bars (height = 0·2,0·5 m) occur in the lower intertidal zone. Annual aerial photographs of the intertidal bar morphology were inspected to try to track individual bars from year to year to derive bar migration rates; however, there is little resemblance between concurrent photographs, and ,resetting' of the intertidal profile occurs on an annual basis. Three-dimensional beach surveys were conducted monthly at three locations along the north Lincolnshire coast over a one-year period. The intertidal bar morphology responds strongly to the seasonal variation in the forcing conditions, and bars are least numerous and flattest during the more energetic winter months. Morphological changes over the monthly time scale are strongly affected by longshore sediment transport processes and the intertidal bar morphology can migrate along the beach at rates of up to 30 m per month. The behaviour of intertidal bars is complex and varies over a range of spatial and temporal scales in response to a combination of forcing factors (e.g. incident wave energy, different types of wave processes, longshore and cross-shore sediment transport), relaxation time and morphodynamic feedback. Copyright © 2005 John Wiley & Sons, Ltd. [source] Particle path length distributions in meandering gravel-bed streams: results from physical modelsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2003Richard S. Pyrce Abstract In gravel-bed rivers with well-de,ned pool,bar morphology, the path length of transported bed particles must be, at least during ,channel-forming' ,ows, equal to the length scale of the morphology. This is the basis for some methods for estimating bed material transport rates. However, previous data, especially from ,eld tests, are often strongly positively skewed with mean much shorter than the pool,bar spacing. One possible explanation is that positively skewed distributions occur only in channels lacking distinct pool,bar topography or only at lower discharges in pool,bar channels. A series of ,ume experiments using ,uorescent tracers was used to measure path length distributions in low-sinuosity meandering channels to assess the relation with channel morphology and ,ow conditions. At channel-forming ,ows, 55 to 75 per cent of the tracer grains were deposited on the ,rst point bar downstream of the point of tracer input, with 15 per cent passing beyond the ,rst bar. Path length distributions are symmetrical with mean equal to the pool,bar spacing and can be described with a Cauchy distribution. In some cases there was a secondary mode close to the point of tracer introduction; this bimodal distribution ,ts a combined gamma,Cauchy distribution. Only when discharge was reduced below the channel-forming ,ow were frequency distributions unimodal and positively skewed with no relation to the pool,bar spacing. Thus, path length distributions become more symmetrical, and mean path length increases to coincide with pool,bar spacing, as ,ow approaches channel-forming conditions. This is a substantial modi,cation of existing models of particle transfer in gravel-bed rivers. Copyright © 2003 John Wiley & Sons, Ltd. [source] Random controls on semi-rhythmic spacing of pools and riffles in constriction-dominated riversEARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2001Douglas M. Thompson Abstract Average pool spacing between five and seven bankfull widths has been documented in environments throughout the world, but has limited theoretical justification in coarse-bedded and bedrock environments. Pool formation in coarse-bedded and bedrock channels has been attributed to bedrock and boulder constrictions. Because the spacing of these constrictions may be irregular in nature, it is difficult to reconcile pool-formation processes with the supposedly rhythmic spacing of pools and riffles. To address these issues, a simulation model for pool and riffle formation is used to demonstrate that semi-rhythmic spacing of pools with an approximate spacing of five to seven bankfull widths can be recreated from a random distribution of obstructions and minimum pool- and riffle-length criteria. It is assumed that a pool,riffle couplet will achieve a minimum length based on dominant-discharge conditions. Values for the minimum-length assumption are based on field data collected in New England and California, while the theoretical basis relies on the demonstrated hydraulic response of individual pools to elongation. Results from the simulations show that the location of pools can be primarily random in character, but still assume an average spacing between four and eight bankfull widths for a variety of conditions. Field verification data generally support the model but highlight a highly skewed distribution of pool-forming elements and pool spacing. The relation between pool spacing and bankfull widths is attributed to the common geometric response of these features to dominant-discharge conditions. Copyright © 2001 John Wiley & Sons, Ltd. [source] Optimum multiple tuned mass dampers for structures under the ground acceleration based on the uniform distribution of system parametersEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 5 2003Chunxiang Li Abstract The five MTMD models, with natural frequencies being uniformly distributed around their mean frequency, have been recently presented by the first author. They are shown to have the near-zero optimum average damping ratio (more precisely, for a given mass ratio there is an upper limit on the total number, beyond which the near-zero optimum average damping ratio occurs). In this paper, the eight new MTMD models (i.e. the UM-MTMD1,UM-MTMD3, US-MTMD1,US-MTMD3, UD-MTMD1 and UD-MTMD2), with the system parameters (mass, stiffness and damping coefficient) being, respectively, uniformly distributed around their average values, have been, for the first time here, proposed to seek for the MTMD models without the near-zero optimum average damping ratio. The structure is represented by the mode-generalized system corresponding to the specific vibration mode that needs to be controlled. Through minimization of the minimum values of the maximum dynamic magnification factors (DMF) of the structure with the eight MTMD models (i.e. through the implementation of Min.Min.Max.DMF), the optimum parameters and values of Min.Min.Max.DMF for these eight MTMD models are investigated to evaluate and compare their control performance. The optimum parameters include the optimum mass spacing, stiffness spacing, damping coefficient spacing, frequency spacing, average damping ratio and tuning frequency ratio. The six MTMD models without the near-zero optimum average damping ratio (i.e. the UM-MTMD1,UM-MTMD3, US-MTMD1, US-MTMD2 and UD-MTMD2) are found through extensive numerical analyses. Likewise, the optimum UM-MTMD3 offers the higher effectiveness and robustness and requires the smaller damping with respect to the rest of the MTMD models in reducing the responses of structures subjected to earthquakes. Additionally, it is interesting to note, by comparing the optimum UM-MTMD3 with the optimum MTMD-1 recently investigated by the first author, that the effectiveness and robustness for the optimum UM-MTMD3 is almost identical to that for the optimum MTMD-1 (without inclusion of the optimum MTMD-1 with the near-zero optimum average damping ratio). Recognizing these performance benefits, it is preferable to employ the optimum UM-MTMD3 or the optimum MTMD-1 without the near-zero optimum average damping ratio, when installing the MTMD for the suppression of undesirable oscillations of structures under earthquakes. Copyright © 2003 John Wiley & Sons, Ltd. [source] Characterization of Nanopore Electrode Structures as Basis for Amplified Electrochemical AssaysELECTROANALYSIS, Issue 19-20 2006Sebastian Neugebauer Abstract A nanopore electrode structure was fabricated consisting of ensembles of nanopores with separately addressable electrodes at the pore bottoms and the rims. A metal/insulator/metal layer structure allowed for adjusting the spacing between the bottom and rim electrodes to be in the range of about 200,nm. Pore diameters varied between 200 and 800,nm. The electrochemical properties of this electrode structure and its perspectives for applications in bioelectronics were studied using cyclic voltammetry and chronoamperometry along with high-resolution scanning electrochemical microscopy (SECM) in constant-distance mode. It was possible to visualize the electrochemical activity of a single nanometric electrode using high-resolution SECM in a combination of sample-generation-tip-collection mode and positive feedback mode. The SECM images suggested an influence of the unbiased rim electrode on redox amplification which was used as a basis for evaluating the feasibility of current amplification by means of redox cycling between the bottom and rim electrodes. Amplification factors superior to those obtained with interdigitated array electrodes could be demonstrated. [source] Simulation of nerve bundle activation by simultaneous multipoint extracellular stimulation with surface electrodesELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 6 2009Hirokazu Takahashi Abstract Neural prostheses for restoring lost functions can benefit from selective activation of nerves. We previously proposed a multipoint gating stimulation, which can selectively activate a desired portion of a nerve bundle, regardless of the density of the electrode. In this paper, we discuss the design of an electrode array and effective strategies to determine the stimulus parameters. Large electrodes were less affected by the relative location of the electrodes and the nodes of Ranvier, suggesting that a rectangular electrode, whose long side along a nerve bundle is longer than the internodal distance (i.e., on the order of 1 mm), would be more effective than a disk electrode. We were able to estimate an appropriate current at each electrode on the basis of a blocking threshold, above which no spike propagation was permitted. For lateral gating stimulation, the gate current should be set above the threshold, while for depthwise gating stimulation, the gate current should be set below the threshold. The spatial resolutions of lateral and depthwise gating stimulation were theoretically estimated to be at least 50 ,m when the grid spacing of the array was 1.2 mm. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(6): 31,40, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10064 [source] Optimization of an Iron Intercalated Montmorillonite Preparation for the Removal of Arsenic at Low Concentrations,ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 1 2007D. Masih Abstract A series of iron intercalated montmorillonites (Fe-Monts) were prepared using (i) ion exchange of native sodium and calcium ions with iron ions, (ii) base hydrolysis of inserted iron ions in montmorillonite suspension, and (iii) insertion of pre-hydrolyzed iron colloid in montmorillonite. The materials were characterized by X-ray diffraction and gas adsorption-desorption techniques. The basal d(001)-spacing and BET specific surface area increased after the intercalation of iron species in montmorillonite. Local iron structure studied by X-ray absorption fine structure (XAFS) spectroscopy showed an unsaturation of the Fe···Fe coordination number (N 2.5) of the intercalated iron species as compared to the bulk iron oxyhydroxides (N 6). The Fe-Monts were employed for arsenic removal from aqueous solutions at low concentration (0.2,16 mg/L). Among the Fe-Monts, the one prepared by the hydrolysis of inserted iron ions, was the best in performance. The saturation adsorption amount of the optimized iron-montmorillonite was 4 and 28 times higher for the removal of arsenite and arsenate, respectively, as compared to bulk iron oxyhydroxide (goethite). Compared with bulk iron oxyhydroxide, the Fe-Monts were superior for arsenate uptake and comparable for arsenite. In addition, arsenite adsorbed on the Fe-Monts was found to be oxidized to arsenate based on XAFS spectroscopy. [source] A simulation study comparing different experimental designs for estimating uptake and elimination ratesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2006Bryan R. Bell Abstract The design of ecotoxicological studies requires decisions about the number and spacing of exposure groups tested, the number of replications, the spacing of sampling times, the duration of the study, and other considerations. For example, geometric spacing of sampling times or toxicant concentrations is often used as a default design. Optimal design methods in statistics can suggest alternative spacing of sampling times that yield more precise estimates of regression coefficients. In this study, we use a computer simulation to explore the impact of the spacing of sampling times and other factors on the estimation of uptake and elimination rate constants in an experiment addressing the bioaccumulation of a contaminant. Careful selection of sampling times can result in smaller standard errors for the parameter estimates, thereby allowing the construction of smaller, more precise confidence intervals. Thus, the effort invested in constructing an optimal experimental design may result in more precise inference or in a reduction of replications in an experimental design. [source] Enhanced Ras activity preserves dendritic size and extension as well as synaptic contacts of neurons after functional deprivation in synRas miceEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2008A. Alpár Abstract The monomeric GTP-binding protein p21Ras has been repeatedly implicated in neuronal stability and plastic changes of the adult nervous system. Recently, we have shown that expression of constitutively active Ras protein in transgenic synRas mice results in a significant increase in the dendritic size and complexity of differentiated pyramidal neurons as well as in increased synaptic connectivity. In the present study, we examined the organization of the vibrissae-barrel cortex in synRas mice and the effects of enhanced Ras activity on deprivation-induced dendritic reorganization after vibrissectomy. The results demonstrate a significant increase in vibrissae-barrel sizes and proportional spacing between barrels in synRas mice, suggesting that the neuronal target specificity of thalamocortical terminals is preserved. Accordingly, the arrangement of double bouquet cells at the borders of barrel columns ensuring functional distinctness is unchanged. Partial vibrissectomy is followed by significant dendritic regression of corresponding pyramidal neurons in the barrel cortex of wild-type mice, which, however, could not be observed in synRas mice. The results provide the first evidence for a role of Ras in preserving neuronal structure after functional deprivation in vivo. [source] Strength Effects in Micropillars of a Dispersion Strengthened Superalloy,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Baptiste Girault The present paper investigates the uniaxial compression behavior of highly alloyed, focused ion beam (FIB) manufactured micropillars, ranging from 200 up to 4000,nm in diameter. The material used was the Ni-based oxide-dispersion strengthened (ODS) alloy Inconel MA6000. Stress,strain curves show a change in slip behavior comparable to those observed in pure fcc metals. Contrary to pure Ni pillar experiments, high critical resolved shear stress (CRSS) values were found independent of pillar diameter. This suggests that the deformation behavior is primarily controlled by the internal obstacle spacing, overwhelming any pillar-size-dependent mechanisms such as dislocation source action or starvation. [source] Water-repellent soil and its relationship to granularity, surface roughness and hydrophobicity: a materials science viewEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2005G. McHale Summary Considerable soil water repellency has been observed at a wide range of locations worldwide. The soil exhibiting water repellency is found within the upper part of the soil profile. The reduced rate of water infiltration into these soils leads to severe runoff erosion, and reduction of plant growth. Soil water repellency is promoted by drying of soil, and can be induced by fire or intense heating of soil containing hydrophobic organic matter. Recent studies outside soil science have shown how enhancement of the natural water repellency of materials, both porous and granular, by surface texture (i.e. surface roughness, pattern and morphology) into super-hydrophobicity is possible. The similarities between these super-hydrophobic materials and observed properties of water-repellent soil are discussed from a non-soil scientist, materials-based perspective. A simple model is developed for a hydrophobic granular surface and it is shown that this can provide a mechanism for enhancement of soil water repellency through the relative size and spacing of grains and pores. The model provides a possible explanation for why soil water repellency should be more prevalent under dry conditions than wet. Consequences for water runoff, raindrop splash and soil erosion are discussed. [source] Determination of moisture content in a deformable soil using time-domain reflectometry (TDR)EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2000D. J. Kim Summary Time-domain reflectometry (TDR) is being used increasingly for measuring the moisture content of porous media. However, successful application for measuring water in soil has been limited to non-deformable soils, and it would be a valuable extension of the technique if it could be used for soils that shrink on drying. We have recently investigated its application to soils rich in clay and organic matter and peats. Here we propose a method for determining moisture content in deformable soils based on the relation between the dielectric constant, K, and the volumetric moisture content, ,, measured by TDR. Parallel TDR probes with a length of 15 cm and a spacing of 2 cm were placed horizontally in soil cores with a diameter of 20 cm and height of 10 cm taken from a forest. The soil is very porous with large proportions of both silt and clay. The sample weight and travel time of the electromagnetic wave guided by parallel TDR probes were simultaneously measured as a function of time, from saturation to oven-dryness during which the core samples shrank considerably. Vertical and horizontal components of shrinkage were also measured to take the air-exposed region of TDR probe into account in the determination of K. The effect of deformation on volumetric moisture content was formulated for two different expressions, namely actual volumetric moisture content (AVMC) and fictitious (uncorrected) volumetric moisture content (FVMC). The effects of air-exposure and expressions of volumetric moisture content on the relation between K and, were examined by fitting the observations with a third-order polynomial. Neglecting the travel time in the air-exposed part or use of the FVMC underestimated the , for a given K. The difference was more pronounced between AVMC and FVMC than between two different dielectric constants, i.e. accounting for air-exposure, Kac, and not accounting for air-exposure, Kau. When the existing empirical models were compared with the fitted results, most underestimated the relation based on the AVMC. This indicates that published empirical models do not reflect the effect of deformation on the determination of , in our forest soil. Correct use of the , expression has more impact on determining moisture content of a deformable soil than the accommodation of travel time through the air-exposed region of TDR probe. [source] The role of methylnaphthalene in EHV cable oil as related to oil breakdown and discharge velocityEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 6 2002A. Al-Sulaiman This experimental investigation explores the effect of high voltage lightning surges on the insulating oil used in the oil filled extra high voltage cables that serve electric power networks worldwide. Using non-uniform electrode configuration, the breakdown voltage and corresponding discharge propagation velocities in oil samples that are doped with trace amounts of 1-Methylnaphthalene are investigated under both polarities of applied stresses in gap spacing of up to 10 mm. Two distinct ranges of additive concentrations are observed which effect these characteristics. Generally, the positive discharge growth decreases with increase in gap spacing while the negative ones show opposite behaviour. Anomalous behaviour of discharge growth is observed at an optimum concentration of additive, as it attains supersonic velocity which increases with the increase in gap spacing. A correlation between the positive impulse breakdown voltage and the discharge propagation velocity is also established. [source] New joint frame synchronisation and carrier frequency offset estimation method for OFDM systems,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 4 2009Zhongshan Zhang We propose a new joint frame synchronisation and carrier frequency offset estimation scheme for burst transmission mode OFDM systems. This scheme uses a central-symmetric and comb-like (CSCL) training sequence, which eases the power detection at the receiver without increasing the total training sequence power. Fine frame synchronisation as well as carrier frequency offset acquisition with a maximum acquisition range of times the sub-carrier spacing can also be performed based on the proposed CSCL training sequence, where N is the discrete Fourier transform (DFT) length and SF is an integer-valued spreading factor used to generate CSCL. The post-acquisition residual carrier frequency offset can be further estimated and corrected via a fine adjustment algorithm. In order to reduce performance loss due to the high peak-to-average power ratio (PAPR) of the CSCL training sequence, a time-domain constant-envelope (CE) training sequence is also proposed. The superior estimation accuracy of the proposed algorithm over that of the Moose algorithm and the SS (Shi and Serpedin) algorithm is proved by computer simulation. Copyright © 2008 John Wiley & Sons, Ltd. [source] Genetic variation for dorsal,ventral patterning of the Drosophila melanogaster eggshellEVOLUTION AND DEVELOPMENT, Issue 2 2005Lisa M. Goering Summary Patterning of the insect eggshell is an excellent system for exploring the molecular basis of phenotypic variation. In Drosophila melanogaster, two dorsal,anterior respiratory appendages are produced in response to signaling through the Epidermal growth factor receptor (Egfr). Previous work implicates Egfr pathway function in both intraspecific variation for dorsal appendage spacing (DAS) on the eggshell, as well as interspecific differences in dorsal appendage number and location. To test the hypothesis that genetic variation in Egfr contributes to variation in eggshell patterning, we have made use of naturally occurring intraspecific variation for DAS as a model quantitative trait. We found that there is substantial segregating genetic variation for DAS in D. melanogaster, and have tested for associations with 289 common polymorphisms in the Egfr locus. A marginal association was seen with two polymorphic sites in Egfr; however, we failed to replicate these findings in a second population, or in a modified quantitative complementation test designed to specifically test the effects of the putative polymorphisms. Therefore, we conclude that the polymorphisms we have identified in Egfr do not contribute to variation in DAS, and further work is required to understand the genetic architecture of this trait. [source] Optimization of Mechanical Properties of NiAl-base Alloy by Suction Casting,ADVANCED ENGINEERING MATERIALS, Issue 4 2006W. Huai The suction-cast NiAl-Cr(Mo)/Hf alloy exhibits a refined microstructure and extended solid solubility. Significant improvement in room temperature ductility and strength was achieved by adopting suction casting technique. In addition, their elevated temperature strength also got slightly increase. The optimized mechanical properties can be attributed to the fine interlamellar spacing, the extended solid solubility and the increased cell eutectic zone as well as the refined Heusler phase. [source] Boundary characteristics in Heavily Deformed Metals,ADVANCED ENGINEERING MATERIALS, Issue 5 2003G. Winther Abstract The potential of creating nanostructured metals by plastic deformation to very high strains is currently the subject of intensive research. An important part of this research concerns evolution of the characteristics of deformation induced boundaries, in particular boundary spacing and boundary misorientation. The aim of this paper is to give an overview of the present understanding of the relations between these characteristics, the microscopic deformation mechanisms and the macroscopic deformation mode. [source] High-Nanofiller-Content Graphene Oxide,Polymer Nanocomposites via Vacuum-Assisted Self-AssemblyADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Karl W. Putz Abstract Highly ordered, homogeneous polymer nanocomposites of layered graphene oxide are prepared using a vacuum-assisted self-assembly (VASA) technique. In VASA, all components (nanofiller and polymer) are pre-mixed prior to assembly under a flow, making it compatible with either hydrophilic poly(vinyl alcohol) (PVA) or hydrophobic poly(methyl methacrylate) (PMMA) for the preparation of composites with over 50 wt% filler. This process is complimentary to layer-by-layer assembly, where the assembling components are required to interact strongly (e.g., via Coulombic attraction). The nanosheets within the VASA-assembled composites exhibit a high degree of order with tunable intersheet spacing, depending on the polymer content. Graphene oxide,PVA nanocomposites, prepared from water, exhibit greatly improved modulus values in comparison to films of either pure PVA or pure graphene oxide. Modulus values for graphene oxide,PMMA nanocomposites, prepared from dimethylformamide, are intermediate to those of the pure components. The differences in structure, modulus, and strength can be attributed to the gallery composition, specifically the hydrogen bonding ability of the intercalating species [source] Surface Nanometer-Scale Patterning in Realizing Large-Scale Ordered Arrays of Metallic Nanoshells with Well-Defined Structures and Controllable PropertiesADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Shikuan Yang Abstract Surface patterns of nanoshell arrays play an important role in diverse applications including surface-enhanced Raman scattering (SERS) sensors, lithium-ion batteries, solar cells, and optical devices. This paper describes an innovative surface nanopatterning technique for realizing large-scale ordered arrays of metallic spherical nanoshells with well-defined structures. Ag nanoshell arrays are prepared using polystyrene sphere templates by an electrophoretic process in Ag colloidal solutions. The fabricated Ag nanoshell arrays have a high controllability of the structural parameters, including the diameter, the surface roughness, and the intershell spacing, giving rise to the tunable properties of nanoshell arrays. As an example, tunable SERS and localized surface plasmon resonance of the nanoshell arrays are demonstrated by controlling the structural parameters. The surface nanopatterning technique shown in this paper is a general fabrication process in achieving not only metallic nanoshell arrays, but also nanoshell arrays of semiconductors and metallic oxides. [source] | ||||||||||||||||||||||||||||||||||||||||||||||