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Network Density (network + density)
Selected AbstractsDextran Microgels for Time-Controlled Delivery of siRNA,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2008Koen Raemdonck Abstract To apply siRNA as a therapeutic agent, appropriate attention should be paid to the optimization of the siRNA gene silencing effect, both in terms of magnitude and duration. Intracellular time-controlled siRNA delivery could aid in tailoring the kinetics of siRNA gene knockdown. However, materials with easily tunable siRNA release properties have not been subjected to thorough investigation thus far. This report describes cationic biodegradable dextran microgels which can be loaded with siRNA posterior to gel formation. Even though the siRNAs are incorporated in the hydrogel network based on electrostatic interaction, still a time-controlled release can be achieved by varying the initial network density of the microgels. To demonstrate the biological functionality of the siRNA loaded gels, we studied their cellular internalization and enhanced green fluorescent protein (EGFP) gene silencing potential in HUH7 human hepatoma cells. [source] Assessing damaged road verges as a suspended sediment source in the Hampshire Avon catchment, southern United KingdomHYDROLOGICAL PROCESSES, Issue 9 2010A. L. Collins Abstract Diffuse sediment pollution impairs water quality, exerts a key control on the transfer and fate of nutrients and contaminants and causes deleterious impacts on freshwater ecology. A variety of catchment sediment sources can contribute to such problems. Sediment control strategies and effective targeting of mitigation options therefore require robust quantitative information on the key sources of the sediment problem at catchment scale. Recent observations by Catchment Sensitive Farming Officers (CSFO's) in England have highlighted road verges damaged and eroded by passing vehicles, particularly large farm machinery, and livestock herd movement as visually important potential sources of local sediment problems. A study was therefore undertaken to assess the relative importance of damaged road verges as a suspended sediment source in three sub-catchments of the Hampshire Avon drainage basin, southern UK. Road verge sediment contributions were apportioned in conjunction with those from agricultural topsoils and channel banks/subsurface sources. Time-integrating isokinetic samplers were deployed to sample suspended sediment fluxes at the outlets of two control sub-catchments drained by the Rivers Chitterne and Till selected to characterize areas with a low road network density and limited visual evidence of verge damage, as well as the River Sem sub-catchment used to represent areas where road verge damage is more prevalent. The findings of a sediment source fingerprinting investigation based on a combination of intermittent sampling campaigns spanning the period 22/5/02,27/4/08 suggested that the respective overall mean relative sediment contributions from damaged road verges were 5 ± 3%, 4 ± 2% and 20 ± 2%. Relative inputs from damaged road verges for any specific sampling period in the River Sem sub-catchment were as high as 33 ± 2%. Reconstruction of historical sources in the same sub-catchment, based on the geochemical record stored in a floodplain depth profile, suggested that the significance of damaged road verges as a sediment source has increased over the past 15,20 years. The findings provide important information on damaged road verges as a primary source of suspended sediment and imply that catchment sediment control strategies and mitigation plans should consider such verges in addition to those agricultural and channel sources traditionally taken into account when attempting to reduce sediment pressures on aquatic resources. Copyright © 2010 John Wiley & Sons, Ltd. [source] Potential of low cost close-range photogrammetry system in soil microtopography quantificationHYDROLOGICAL PROCESSES, Issue 10 2009Mohamed A. M. Abd Elbasit Abstract Soil microtopography is a dynamic soil property which affects most soil-surface and water interaction processes. The importance of soil microtopography has been recognized for a long time, but only limited reports are available in the literature. In this study, the potential of using consumer-grade cameras and close-range photogrammetry procedures to quantify soil microtopography at plot-scale level (,1 m2) were assessed. Five fabricated gypsum surfaces with different degrees of roughness were used to simulate the soil surface conditions with different soil aggregates. The surfaces' digital elevation model (DEM) was generated using the photogrammetry system (PHM) involving a consumer-grade camera, and pin-microrelief meter (PM). The DEM generated using the PHM was assessed for accuracy, roughness indices (RI), depression area percentage (DA%), depression storage capacity (DSC), and micro-rills delineation in comparison with the PM. The accuracy was evaluated using the root mean square error (RMSE) in the x-, y-, and z-directions. Visual comparison between the 3D-visions of the DEM showed strong agreement between the DEM generated by the PHM and the PM, and between the PHM and the 2D images for the different gypsum surfaces. The average RMSE in the x-. y-, and z-direction were 2·08, 1·52, and 0·82 mm for the rough surface, and 4·42, 1·65, and 3·22 mm for the smooth surface. The RIs calculated from the two methods were highly correlated. The small discrepancy between the two methods was discussed. The micro-rills delineation was also similar for the two methods regarding the network density. The grid size did not effect the RI calculation, and has a strong influence on the DA%, DSC, and the delineated micro-rills orders. Results suggest that a consumer-grade camera and close-range photogrammetry have the potential to quantify the soil microtopography. Copyright © 2009 John Wiley & Sons, Ltd. [source] Runoff generation and routing on artificial slopes in a Mediterranean,continental environment: the Teruel coalfield, SpainHYDROLOGICAL PROCESSES, Issue 3 2002José-Manuel Nicolau Abstract The aim of this study was to identify the mechanisms of runoff generation and routing and their controlling factors at the hillslope scale, on artificial slopes derived from surface coal mining reclamation in a Mediterranean,continental area. Rainfall and runoff at interrill and microcatchment scales were recorded for a year on two slopes with different substrata: topsoil cover and overburden cover. Runoff coefficient and runoff routing from interrill areas to microcatchment outlets were higher in the overburden substratum than in topsoil, and greater in the most developed rill network. Rainfall volume is the major parameter responsible for runoff response on overburden, suggesting that this substratum is very impermeable,at least during the main rainfall periods of the year (late spring and autumn) when the soil surface is sealed. In such conditions, most rainfall input is converted into runoff, regardless of its intensity. Results from artificial rainfall experiments, conducted 3 and 7 years after seeding, confirm the low infiltration capacity of overburden when sealed. The hydrological response shows great seasonal variability on the overburden slope in accordance with soil surface changes over the year. Rainfall volume and intensities (I30, I60) explain runoff at the interrill scale on the topsoil slope, where rainfall experiments demonstrated a typical Hortonian infiltration curve. However, no correlation was found at the microcatchment level, probably because of the loss of functionality of the only rill as ecological succession proceeded. The runoff generation mechanism on the topsoil slope is more homogeneous throughout the year. Runoff connectivity, defined as the ratio between runoff rates recorded at the rill network scale and those recorded at the interrill area scale in every rainfall event, was also greater on the rilled overburden slope, and in the most developed rill network. The dense rill networks of the overburden slope guarantee very effective runoff drainage, regardless of rainfall magnitude. Rills drain overland flow from interrill-sealed areas, reducing the opportunity of reinfiltration in areas not affected by siltation. Runoff generation and routing on topsoil slopes are controlled by grass cover and soil moisture content, whereas on overburden slopes rill network density and soil moisture content are the main controlling factors. Copyright © 2002 John Wiley & Sons, Ltd. [source] Investigation of the postcure reaction and surface energy of epoxy resins using time-of-flight secondary ion mass spectrometry and contact-angle measurementsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2009Firas Awaja Abstract Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to investigate correlations between the molecular changes and postcuring reaction on the surface of a diglycidyl ether of bisphenol A and diglycidyl ether of bisphenol F based epoxy resin cured with two different amine-based hardeners. The aim of this work was to present a proof of concept that ToF-SIMS has the ability to provide information regarding the reaction steps, path, and mechanism for organic reactions in general and for epoxy resin curing and postcuring reactions in particular. Contact-angle measurements were taken for the cured and postcured epoxy resins to correlate changes in the surface energy with the molecular structure of the surface. Principal components analysis (PCA) of the ToF-SIMS positive spectra explained the variance in the molecular information, which was related to the resin curing and postcuring reactions with different hardeners and to the surface energy values. The first principal component captured information related to the chemical phenomena of the curing reaction path, branching, and network density based on changes in the relative ion density of the aliphatic hydrocarbon and the C7H7O+ positive ions. The second principal component captured information related to the difference in the surface energy, which was correlated to the difference in the relative intensity of the CxHyNz+ ions of the samples. PCA of the negative spectra provided insight into the extent of consumption of the hardener molecules in the curing and postcuring reactions of both systems based on the relative ion intensity of the nitrogen-containing negative ions and showed molecular correlations with the sample surface energy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Compatibility and viscoelastic properties of brominated isobutylene- co - p -methylstyrene rubber/tackifier blendsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008K. Dinesh Kumar Abstract Brominated isobutylene- co-p -methylstyrene (BIMS) rubber has been blended with hydrocarbon resin tackifier and alkyl phenol formaldehyde resin tackifier, and the compatibility between the blend components has been systematically evaluated. Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) studies show that BIMS rubber and hydrocarbon resin tackifier blends are compatible at all blend proportions studied. However, BIMS rubber and phenol formaldehyde resin blends exhibit very limited compatibility with each other and phase separation even at very low phenolic tackifier concentration. Morphological studies of the rubber,resin blends by scanning electron microscopy (SEM) corroborate well with the DMA and DSC results. From the DMA frequency sweep and temperature sweep studies, it is shown that the hydrocarbon resin tackifier acts as a diluent and causes a decrease in the storage modulus values (by reducing the entanglement and network density) in the rubbery plateau region. On the other hand, phenol formaldehyde resin behaves in the way similar to that of the reinforcing filler by increasing the storage modulus values (by increasing the entanglement and network density) in the rubbery plateau zone. The relaxation time estimated from the different zones of frequency sweep master curves provides information about the influence of the two tackifiers on the viscoelastic properties of the BIMS rubber in the respective zones. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Network structural influences on the adoption of evidence-based prevention in communities,,JOURNAL OF COMMUNITY PSYCHOLOGY, Issue 7 2009Kayo Fujimoto This study examined the impact of key variables in coalition communication networks, centralization and density, on the adoption of evidence-based substance abuse prevention. Data were drawn from a network survey and a corresponding community leader survey that measured leader attitudes and practices toward substance abuse prevention programs. Two types of coalition networks were measured: advice-seeking and discussion relations. For each community, we computed network-level measurements (n=20), and then used multiple linear regression. Results showed that adoption outcomes were associated with a decrease in centralization for the advice network and an increase in centralization for the discussion network, controlling for density. This suggests that community coalitions might consider decreasing their network density in such a manner that distributes power and influence among a broader base of coalition members to seek advice about programs while simultaneously discussing these programs in a more concentrated group to facilitate decisions about which programs to adopt. © 2009 Wiley Periodicals, Inc. [source] Petroleum product scarcity: a review of the supply and distribution of petroleum products in NigeriaOPEC ENERGY REVIEW, Issue 1 2006Osi S. Akpoghomeh Nigeria ranks high among the comity of oil producers both at the world level and among the OPEC eleven. It is, therefore, paradoxical that the supply of all petroleum products is erratic and has declined sharply in the recent past. This paper thus reviews the petroleum product supply and distribution systems in the country to ascertain the extent to which the system may have contributed to the present product scarcity in Nigeria and, by extension, identify the causes of the present regime of petroleum product scarcity. The paper observes that the network density and connectivity of petroleum product distribution pipelines are low and both indicators consequently show the inadequacy/deficiency of the network in ensuring an efficient distribution system. The supply mode, on the other hand, has, over the years, demonstrated its inability to guarantee adequate supply due to factors including sabotage, vandalism, banditry and poorly maintained infrastructure. Further, the federal government and the major and independent marketers could not sustain the importation of petroleum products because of the shortfall between the landed cost of imported products and their selling prices in Nigeria, which made the business unprofitable. Finally, the paper examines the withdrawal by the federal government of subsidies on the price of petroleum products consumed locally. All the above factors together occasioned increases in the cost of products. In conclusion, this paper supports the call for the privatization of refineries and the depot/pipeline system as a viable option to end the supply problems. [source] Self-Assembled Monolayers of Alkoxy-Substituted Octadehydrodibenzo[12]annulenes on a Graphite Surface: Attempts at peri -Benzopolyacene Formation by On-Surface PolymerizationCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2010Kazukuni Tahara Dr. Abstract Self-assembled monolayers of a series of tetraalkoxy-substituted octadehydrodibenzo[12]annulene (DBA) derivatives 1,c,g possessing butadiyne linkages were studied at the 1,2,4-trichlorobenzene (TCB) or 1-phenyloctane/graphite interface by scanning tunneling microscopy (STM). The purpose of this research is not only to investigate the structural variation of two-dimensional (2D) monolayers, but also to assess a possibility for peri -benzopolyacene formation by two-dimensionally controlled polymerization on a surface. As a result, the formation of three structures, porous, linear, and lamella structures, were observed by changing the alkyl chain length and the solute concentration. The formation of multilayers of the lamella structure was often observed for all compounds. The selection of molecular networks is basically ascribed to intermolecular and molecule,substrate interactions per unit area and network density. The selective appearance of the linear structure of 1,d is attributed to favorable epitaxial registry matching between the substrate lattice and the overlayer lattice. Even though the closest interatomic distance between the diacetylenic units of the DBAs in the lamella structure (,0.6,nm) is slightly larger compared to the typical distances necessary for topochemical polymerization, the reactivity toward external stimuli (electronic-pulse irradiation from an STM tip and UV irradiation) was investigated. Unfortunately, no evidence for polymerization of the DBAs on the surface was observed. The present results indicate the necessity for further designing a suitable system for the on-surface construction of structurally novel conjugated polymers, which are otherwise difficult to prepare. [source] | ||||||||||