Home About us Contact
|
Home About us Contact | ||
|
|
||
Conduits
Kinds of Conduits Selected AbstractsSolute and Colloid Transport in Karst Conduits under Low- and High-Flow ConditionsGROUND WATER, Issue 1 2008Nadine Göppert Solute and colloid transport in karst aquifers under low and high flows was investigated by tracer tests using fluorescent dyes (uranine) and microspheres of the size of pathogenic bacteria (1 ,m) and Cryptosporidium cysts (5 ,m), which were injected into a cave stream and sampled at a spring 2.5 km away. The two types of microspheres were analyzed using an epifluorescence microscope or a novel fluorescence particle counter, respectively. Uranine breakthrough curves (BTCs) were regular shaped and recovery approached 100%. Microsphere recoveries ranged between 27% and 75%. During low flow, the 1-,m spheres displayed an irregular BTC preceding the uranine peak. Only a very few 5-,m spheres were recovered. During high flow, the 1-,m-sphere BTC was regular and more similar to the uranine curve. BTCs were modeled analytically with CXTFIT using a conventional advection dispersion model (ADM) and a two-region nonequilibrium model (2RNE). The results show that (1) colloids travel at higher velocities than solutes during low flow; (2) colloids and solutes travel at similar velocities during high flow; (3) higher maximum concentrations occur during high flow; and (4) the 2RNE achieves a better fit, while the ADM is more robust, as it requires less parameters. [source] Altering Investment Decisions to Manage Financial Reporting Outcomes: Asset-Backed Commercial Paper Conduits and FIN 46JOURNAL OF ACCOUNTING RESEARCH, Issue 5 2008DANIEL A. BENS ABSTRACT We evaluate the manner in which sponsors of highly leveraged asset-backed commercial paper (ABCP) conduits responded to Financial Accounting Standards Board Interpretation No. 46 (FIN 46), Consolidation of Variable Interest Entities an Interpretation of ARB No. 51, and its Canadian counterpart Accounting Standards Board of Accounting Guideline 15 (AcG-15), Consolidation of Variable Interest Entities. By matching commercial paper investors with corporations seeking liquidity, ABCP sponsors facilitate a significant amount of short-term, securitized financing in the United States. FIN 46 and AcG-15 require sponsors to consolidate their ABCP conduits with their financial statements. We demonstrate that the volume of ABCP began to decline when FIN 46 was first proposed, and that this decline is primarily attributable to a reduction in North American banks' sponsorship of ABCP. We also demonstrate that North American banks entered into costly restructuring arrangements to avoid having to consolidate their conduits per the new accounting standards. Our results suggest that, in certain settings, accounting standards appear to have real effects on investment activity and product-market competition. [source] Regeneration of canine peroneal nerve with the use of a polyglycolic acid,collagen tube filled with laminin-soaked collagen sponge: a comparative study of collagen sponge and collagen fibers as filling materials for nerve conduitsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 6 2001Toshinari Toba Abstract A novel artificial nerve conduit was developed and its efficiency was evaluated on the basis of promotion of peripheral nerve regeneration across an 80-mm gap in dogs. The nerve conduit was made of a polyglycolic acid,collagen tube filled with laminin-soaked collagen sponge. Conduits filled with either sponge- or fiber-form collagen were implanted into an 80-mm gap of the peroneal nerve (five dogs for each form). Twelve months postoperatively nerve regeneration was superior in the sponge group both morphometrically (percentage of neural tissue: fiber: 39.7 ± 5.2, sponge: 43.0 ± 4.5, n=3) and electrophysiologically (fiber: CMAP 1.06 ± 0.077, SEP 1.32 ± 0.127 sponge: CMAP 1.04 ± 0.106, SEP 1.24 ± 0.197, n=5), although these differences were not statistically significant. The observed regeneration was complementary to successful results reported previously in the same model, in which collagen fibers exclusively were used. The results indicate a possible superiority of collagen sponge over collagen fibers as filling materials. In addition, the mass-producibility, superior scaffolding potential, and capacity for gradual release of soluble factors of the sponge provide make it an attractive alternative to fine fibers, which are both technologically difficult and costly to produce. This newly developed nerve conduit has the potential to enhance peripheral nerve regeneration across longer gaps commonly encountered in clinical settings. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 622,630, 2001 [source] Highly Permeable Genipin-Cross-linked Gelatin Conduits Enhance Peripheral Nerve RegenerationARTIFICIAL ORGANS, Issue 12 2009Ju-Ying Chang Abstract Here we have evaluated peripheral nerve regeneration with a porous biodegradable nerve conduit (PGGC), which was made from genipin-cross-linked gelatin. To examine the effect of pores, nonporous genipin-cross-linked gelatin conduit (GGC) was considered as the control. Both the PGGC and the GGC were dark blue in appearance with a concentric and round lumina. The PGGC featured an outer surface with pores of variable size homogeneously traversing, and a partially fenestrated inner surface connected by an open trabecular meshwork. The GGC had a rough outer surface whereas its inner lumen was smooth. Both PGGCs and GGCs had similar hydrophilicity on condition of the same material and cross-linking degree. The porosity of PGGCs and GGCs was 90.8 ± 0.9% and 24.3 ± 2.9%, respectively. The maximum tensile force of the GGCs (0.12 ± 0.06 kN) exceeded that of the PGGCs (0.03 ± 0.01 kN), but the PGGCs had a higher swelling ratio than GGCs at 0.5, 1, 3, 6, 12, 24, 48, 60, 72, and 84 h after soaking in deionized water. Cytotoxic testing revealed the soaking solutions of both of the tube composites would not produce cytotoxicity to cocultured Schwann cells. After subcutaneous implantation on the dorsal side of the rat, the PGGC was degraded completely after 12 weeks of implantation whereas a thin tissue capsule was formed encapsulating the partially degraded GGC. Biodegradability of both of the tube groups and their effectiveness as a guidance channel were examined as they were used to repair a 10 mm gap in the rat sciatic nerve. As a result, fragmentation of the GGC was still seen after 12 weeks of implantation, yet the PGGC had been completely degraded. Histological observation showed that numerous myelinated axons had crossed over the gap region in the PGGCs after 8 weeks of implantation despite only few myelinated axons and unmyelinated axons mostly surrounded by Schwann cells seen in the GGCs. In addition, the regenerated nerves in the PGGCs presented a significantly higher nerve conductive velocity than those in the GGCs (P < 0.05). Thus, the PGGCs can not only offer effective aids for regenerating nerves but also accelerate favorable nerve functional recovery compared with the GGCs. [source] A Novel Approach to Align Adult Neural Stem Cells on Micropatterned Conduits for Peripheral Nerve Regeneration: A Feasibility StudyARTIFICIAL ORGANS, Issue 1 2009Shan-hui Hsu Abstract There is a strong need for nerve-tissue engineering using the guide conduit and Schwann cells or neural stem cells (NSCs) with regeneration potential for injured peripheral nerves. In this study, micropatterned poly(d,l -lactide) (PLA) conduits were fabricated by microlithography and solvent-casting. The PLA conduits were seeded with the novel green fluorescent protein (GFP)-positive adult mouse NSCs obtained using the patented method of one of the authors. About 85% of the seeded NSCs were successfully aligned on the micropatterned conduits within 72 h and expressed the genes related to the production of neurotrophic factors. Gene expressions for the neurotrophic factors, such as nerve growth factor and brain-derived neurotrophic factor were upregulated by the micropatterned conduits at 72 h. The micropatterned PLA conduits seeded with the aligned NSCs were used to bridge the 10-mm sciatic nerve gaps in rats and were found to facilitate nerve repair and functional recovery during a period of 6 weeks compared with the nonseeded group. This model can be used to study the role of adult NSCs in peripheral-nerve regeneration in the future. [source] Liquid-Liquid Stratified Flow through Horizontal ConduitsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2005T. Sunder Raj Abstract The stratified configuration is one of the basic and most important distributions during two phase flow through horizontal pipes. A number of studies have been carried out to understand gas-liquid stratified flows. However, not much is known regarding the simultaneous flow of two immiscible liquids. There is no guarantee that the information available for gas-liquid cases can be extended to liquid-liquid flows. Therefore, the present work attempts a detailed investigation of liquid-liquid stratified flow through horizontal conduits. Gas-liquid flow exhibits either smooth or wavy stratified orientations, while liquid-liquid flow exhibits other distinct stratified patterns like three layer flow, oil dispersed in water, and water flow, etc. Due to this, regime maps and transition equations available for predicting the regimes in gas-liquid flow cannot be extended for liquid-liquid cases by merely substituting phase physical properties in the equations. Further efforts have been made to estimate the in-situ liquid holdup from experiments and theory. The analysis considers the pronounced effect of surface tension, and attempts to modify the Taitel-Dukler model to account for the curved interface observed in these cases. The curved interface model of Brauner has been validated with experimental data from the present work and those reported in literature. It gives a better prediction of liquid holdup in oil-water flows and reduces to the Taitel-Dukler model for air-water systems. [source] Long-term results of the antegrade continent enema procedure for constipation in adultsCOLORECTAL DISEASE, Issue 5 2004N. P. Lees Abstract Objective The aim of this study was to evaluate the long-term results of the Antegrade Continent Enema (ACE) procedure for treating severe constipation in adults. Methods Over 10 years 37 ACE conduits were created in 32 patients (median age 35 years, 26 women) with constipation caused by slow transit, obstructed defaecation or both. Conduits were created from the appendix (n = 20, 54%), ileum (n = 10, 27%), neoappendix caecostomy (n = 5, 14%) or colon (n = 2, 5%). Clinical records were retrospectively reviewed to determine outcome. Results After a median follow up of 36 (range 13,140) months, 28 (88%) required at least one further procedure on a primary conduit, including reversal in 19 (59%). Five patients had a second conduit fashioned, two successfully. Conduit type and constipation cause did not significantly influence the rates of ACE reversal or major revision. Ileal conduits were associated with fewer minor revision procedures for stenosis (1 in 7 patients) than appendix conduits (21 in 20 patients). There was one (3%) serious complication. Satisfactory ACE function was ultimately achieved in 47% of patients, at last follow up. After ACE reversal, 9 (28%) patients underwent formation of an end stoma and 3 patients had a colectomy. Conclusions Revision procedures are common, but approximately half of patients can expect satisfactory long-term ACE function. ACE conduit reversal does not preclude subsequent alternative surgical strategies to treat this difficult condition. [source] Development of an electrohydraulic total artificial heart system: Improvement of pump unitELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 9 2010Akihiko Homma Abstract An electrohydraulic total artificial heart (EHTAH) system has been developed. The EHTAH system consists of diaphragm-type blood pumps, and electrohydraulic actuator, an internal control unit, a transcutaneous energy transfer system (TETS), a transcutaneous optical telemetry system (TOTS), and an internal battery. The reciprocating rotation of the impeller generates oil pressure that drives the blood pumps at alternating intervals. The blood pumps and the actuator were successfully integrated into the pump unit without oil conduits. As a result of miniaturizing the blood pumps and the actuator, the displacement volume and weight of the EHTAH system were decreased to 872 ml and 2492 g, respectively. Furthermore, the maximum flow rate and efficiency increased up to 12 L/min and 15.4%. The pump units and the EHTAH systems were successfully implanted in 36 calves weighing from 55 to 87 kg. In the longest case, a calf with the pump unit survived for 87 days and a calf with the EHTAH system survived for 70 days. The EHTAH system was powered by the TETS, and was powered every day by the internal battery for 40 minutes. These results indicate that the EHTAH system has the potential to become a fully implantable cardiac replacement system. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(9): 34,46, 2010; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10220 [source] Fabrication and Evaluation of Chitin-Based Nerve Guidance Conduits Used to Promote Peripheral Nerve Regeneration,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Yumin Yang Chitin product was prepared from the chitosan counterpart and both were found to be equally biocompatible with cultured Schwann cells. Chitin- and chitosan-based nerve guidance conduits (NGCs) were surgically implanted to bridge 10-mm-long neural defects in rat sciatic nerves. The regenerative outcome provided positive evidence that chitin- and chitosan-based NGCs produce the similar beneficial effects on peripheral nerve regeneration. [source] A CdSe Nanowire/Quantum Dot Hybrid Architecture for Improving Solar Cell PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 9 2010Yanghai Yu Abstract Incorporating colloidal CdSe quantum dots (QDs) into CdSe nanowire (NW)-based photoelectrochemical solar cells increases their incident-photon-to-carrier conversion efficiencies (IPCE) from 13% to 25% at 500,nm. While the effect could, in principle, stem from direct absorption and subsequent carrier generation by QDs, the overall IPCE increase occurs across the entire visible spectrum, even at wavelengths where the dots do not absorb light. This beneficial effect originates from an interplay between NWs and QDs where the latter fill voids between interconnected NWs, providing electrically accessible conduits, in turn, enabling better carrier transport to electrodes. The presence of QDs furthermore reduces the residual polarization anisotropy of random NW networks. Introducing QDs therefore addresses an important limiting constraint of NW photoelectrochemical solar cells. The effect appears to be general and may aid the future design and implementation of other NW-based photovoltaics. [source] Fish community characteristics of the lower Gambia River floodplains: a study in the last major undisturbed West African riverFRESHWATER BIOLOGY, Issue 2 2009VASILIS LOUCA Summary 1.,The Gambia River is the last major West African river that has not been impounded. However, a hydroelectric dam is being constructed and substantial changes to the hydrology and ecology of the system are expected. 2.,Little information is available on the impact of water impoundments in semi-arid regions on downstream floodplain fish communities, due to the scarcity of pre-intervention data. Because profound impacts on physical habitat, salinity and nutrient transport can occur downstream of such impoundments, a knowledge of the species-habitat associations of biota such as fishes is necessary for understanding likely changes and how to limit them. 3.,Fish were sampled using cast and hand nets along two transects on the floodplain, and with fyke nets in two ,bolongs' (creeks) from May to November 2005 and 2006 in the lower reaches of the Gambia River, close to the salt water front where ecological changes due to the construction of the dam are likely to be pronounced. 4.,Greatest fish species richness was associated with low conductivity, low pH and deep water. Bolongs held greater species richness compared with other floodplain habitats, probably because they acted as conduits for fish moving on and off the floodplain. Species richness and catch biomass increased rapidly following the first rains and then declined. 5.,Using a multivariate analysis, three main species groups were identified on the floodplain; one associated with deeper water, one with less brackish water and one with shallow, open water. Tilapia guineensis was the commonest species on the floodplains. 6.,The floodplains provide nursery habitats as many fish captured were immature, particularly for species where adults are mainly encountered in the main channel. Several small-sized floodplain specialists were also represented by a high proportion of mature individuals. 7.,Impoundment is expected to reduce seasonal flooding of the floodplain in the lower Gambia River, downstream of the impoundment, resulting in reduced occurrence of aquatic habitats, especially bolongs, together with lower dissolved oxygen and increased salinity, leading to alteration of the floodplain fish communities, benefiting salt-tolerant species, reducing overall species richness and probably reducing floodplain fish production. [source] Interspecific relationships among growth, mortality and xylem traits of woody species from New ZealandFUNCTIONAL ECOLOGY, Issue 2 2010Sabrina E. Russo Summary 1.,Wood density is considered a key functional trait influencing the growth and survival of woody plants and has been shown to be related to a slow,fast rate-of-living continuum. Wood density is, however, an emergent trait arising from several vascular properties of wood, including the diameter and frequency of xylem conduits. 2.,We aimed to test the hypotheses that there is a set of inter-related trade-offs linked to the different functions of wood, that these trade-offs have direct consequences for tree growth and survival and that these trade-offs underlie the observed correlations between wood density and demographic rates. We evaluated the covariation between xylem anatomical traits among woody species of New Zealand and whether that covariation had the potential to constrain variation in wood density and demographic rates. 3.,Several xylem traits were strongly correlated with each other, but wood density was not correlated with any of them. We also found no significant relationships between wood density and growth or mortality rate. Instead, growth was strongly related to xylem traits associated with hydraulic capacity (conduit diameter and a conductivity index) and to maximum height, whereas mortality rate was strongly correlated only with maximum height. The diameter and frequency of conduits exhibited a significant negative relationship, suggesting a trade-off, which restricted variation in wood density and growth rate, but not mortality rate. 4.,Our results suggest, for woody species in New Zealand, that growth rate is more closely linked to xylem traits determining hydraulic conductance, rather than wood density. We also found no evidence that denser woods conferred higher survival, or that risk of cavitation caused by wide conduits increased mortality. 5.,In summary, we found little support for the idea that wood density is a good proxy for position along a fast,slow rate-of-living continuum. Instead, the strong, negative relationship between vessel diameter and frequency may constrain the realized diversity of demographic niches of tree species in New Zealand. Trade-offs in function therefore have the potential to shape functional diversity and ecology of forest communities by linking selection on structure and function to population-level dynamics. [source] Ontogenetically stable hydraulic design in woody plantsFUNCTIONAL ECOLOGY, Issue 2 2006J. S. WEITZ Summary 1An important component of plant water transport is the design of the vascular network, including the size and shape of water-conducting elements or xylem conduits. 2For over 100 years, foresters and plant physiologists have recognized that these conduits are consistently smaller near branch tips compared with major branches and the main stem. Empirical data, however, have rarely been assembled to assess the whole-plant hydraulic architecture of woody plants as they age and grow. 3In this paper, we analyse vessels of Fraxinus americana (White Ash) within a single tree. Vessels are measured from cross-sections that span 12 m in height and 18 years' growth. 4We show that vessel radii are determined by distance from the top of the tree, as well as by stem size, independently of tree height or age. 5The qualitative form for the scaling of vessel radii agrees remarkably well with simple power laws, suggesting the existence of an ontogenetically stable hydraulic design that scales in the same manner as a tree grows in height and diameter. 6We discuss the implications of the present findings for optimal theories of hydraulic design. [source] Murray's law and the hydraulic vs mechanical functioning of woodFUNCTIONAL ECOLOGY, Issue 6 2004K. A. McCULLOH Summary 1Murray's law states that the hydraulic conductance per blood volume of the cardiovascular system is maximized when the sum of the vessel radii cubed (, r3) is conserved. 2We hypothesize that Murray's law will apply to xylem conduits as long as they only transport water and do not also help support the plant. Specifically, the less volume of wood occupied by conduits, the more the conduits should conform to Murray's law. 3We tested the applicability of Murray's law along a continuum of decreasing conduit fraction from coniferous (91% conduits) to diffuse-porous (24% conduits) to ring-porous wood (12% conduits), using anatomical and functional tests. The anatomical test compared the , r3 conservation across branch points by direct measurements of conduit radii. The functional test compared the hydraulic conductivity between branches of different ages. 4As predicted, Murray's law was rejected in conifer wood where hydraulic function is coupled to mechanical support. The angiosperm wood did not deviate as strongly from Murray's law, especially the ring-porous type. For comparison we report previously published results from compound leaves and vines which showed general agreement with Murray's law. 5Deviation from Murray's law was associated with fewer, narrower conduits distally causing a decrease in , r3 distally. Although less efficient hydraulically, this configuration is not top-heavy and is more mechanically stable. With the evolution of vessels and fibres, angiosperm wood can more closely approach Murray's law while still meeting mechanical requirements. [source] Natural-gradient tracer experiments in epikarst: a test study in the Acqua dei Faggi experimental site, southern ItalyGEOFLUIDS (ELECTRONIC), Issue 3 2008E. PETRELLA Abstract Two natural-gradient tracer experiments were carried out using borehole fluorometers in order to characterize the internal structure of epikarstic horizons and analyze subsurface flow within these high-conductivity layers. The experiments were carried out in a test site in southern Italy where the epikarst is made up of an upper part with pervasive karstification and a lower part without pervasive karstification. Injection and observation boreholes were 6.9 m apart. An initial experiment demonstrated that wider (conduits) and narrower (fractures and bedding planes) openings coexist in a well-connected network within the lower epikarst. The adjusted aperture of the opening network (105 ,m) suggests that conduits are subordinately developed. The lower epikarstic horizon is hydraulically similar to granular porous media and Darcy's law can be applied to describe groundwater flow. A small value of longitudinal dispersivity (0.13 m) shows that variations in the velocity field in the direction of flow are less significant than those typical of carbonate systems at the same experiment scale. A second experiment demonstrated that longitudinal dispersivity (2.42 m) in the upper epikarst is in agreement with findings in other carbonates at the same experiment scale. However, despite the higher dispersivity and more pervasive karstification, the mean tracer velocity (3.7 m day,1) in the upper epikarst is slightly lower than the velocity in the lower epikarst (13.6 m day,1). [source] Infiltration of basinal fluids into high-grade basement, South Norway: sources and behaviour of waters and brinesGEOFLUIDS (ELECTRONIC), Issue 1 2003S. A. Gleeson Abstract Quartz veins hosted by the high-grade crystalline rocks of the Modum complex, Southern Norway, formed when basinal fluids from an overlying Palaeozoic foreland basin infiltrated the basement at temperatures of c. 220°C (higher in the southernmost part of the area). This infiltration resulted in the formation of veins containing both two-phase and halite-bearing aqueous fluid inclusions, sometimes with bitumen and hydrocarbon inclusions. Microthermometric results demonstrate a very wide range of salinities of aqueous fluids preserved in these veins, ranging from c. 0 to 40 wt% NaCl equivalent. The range in homogenization temperatures is also very large (99,322°C for the entire dataset) and shows little or no correlation with salinity. A combination of aqueous fluid microthermometry, halogen geochemistry and oxygen isotope studies suggest that fluids from a range of separate aquifers were responsible for the quartz growth, but all have chemistries comparable to sedimentary formation waters. The bulk of the quartz grew from relatively low ,18O fluids derived directly from the basin or equilibrated in the upper part of the basement (T < 200°C). Nevertheless, some fluids acquired higher salinities due to deep wall-rock hydration reactions leading to salt saturation at high temperatures (>300°C). The range in fluid inclusion homogenization temperatures and densities, combined with estimates of the ambient temperature of the basement rocks suggests that at different times veins acted as conduits for influx of both hotter and colder fluids, as well as experiencing fluctuations in fluid pressure. This is interpreted to reflect episodic flow linked to seismicity, with hotter dry basement rocks acting as a sink for cooler fluids from the overlying basin, while detailed flow paths reflected local effects of opening and closing of individual fractures as well as reaction with wall rocks. Thermal considerations suggest that the duration of some flow events was very short, possibly in the order of days. As a result of the complex pattern of fracturing and flow in the Modum basement, it was possible for shallow fluids to penetrate basement rocks at significantly higher temperatures, and this demonstrates the potential for hydrolytic weakening of continental crust by sedimentary fluids. [source] Geodetic imaging: reservoir monitoring using satellite interferometryGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2002D. W. Vasco Summary Fluid fluxes within subsurface reservoirs give rise to surface displacements, particularly over periods of a year or more. Observations of such deformation provide a powerful tool for mapping fluid migration within the Earth, providing new insights into reservoir dynamics. In this paper we use Interferometric Synthetic Aperture Radar (InSAR) range changes to infer subsurface fluid volume strain at the Coso geothermal field. Furthermore, we conduct a complete model assessment, using an iterative approach to compute model parameter resolution and covariance matrices. The method is a generalization of a Lanczos-based technique which allows us to include fairly general regularization, such as roughness penalties. We find that we can resolve quite detailed lateral variations in volume strain both within the reservoir depth range (0.4,2.5 km) and below the geothermal production zone (2.5,5.0 km). The fractional volume change in all three layers of the model exceeds the estimated model parameter uncertainty by a factor of two or more. In the reservoir depth interval (0.4,2.5 km), the predominant volume change is associated with northerly and westerly oriented faults and their intersections. However, below the geothermal production zone proper [the depth range 2.5,5.0 km], there is the suggestion that both north- and northeast-trending faults may act as conduits for fluid flow. [source] Bacteria and PAMPs activate nuclear factor ,B and Gro production in a subset of olfactory ensheathing cells and astrocytes but not in Schwann cellsGLIA, Issue 9 2007Adele J. Vincent Abstract The primary olfactory nerves provide uninterrupted conduits for neurotropic pathogens to access the brain from the nasal cavity, yet infection via this route is uncommon. It is conceivable that olfactory ensheathing cells (OECs), which envelope the olfactory nerves along their entire length, provide a degree of immunological protection against such infections. We hypothesized that cultured OECs would be able to mount a biologically significant response to bacteria and pathogen-associated molecular patterns (PAMPs). The response of OECs to Escherichia coli (E. coli) and various PAMPs was compared to that of Schwann cells (SCs), astrocytes (ACs), and microglia (MG). A subset of OECs displayed nuclear localization of nuclear factor ,B), an inflammatory transcription factor, after treatment with E. coli (20% ± 5%), lipopolysacchride (33% ± 9%), and Poly I:C (25% ± 5%), but not with peptidoglycan or CpG oligonucleotides. ACs displayed a similar level of activation to these treatments, and in addition responded to peptidoglycan. The activation of OECs and ACs was enhanced by coculture with MG (56% ± 16% and 85% ± 13%, respectively). In contrast, SCs did not respond to any treatment or to costimulation by MG. Immunostaining for the chemokine Gro demonstrated a functional response that was consistent with NF,B activation. OECs expressed mRNA for Toll-like receptors (TLRs) 2 and 4, but only TLR4 protein was detected by Western blotting and immunohistochemistry. The results demonstrate that OECs possess the cellular machinery that permits them to respond to certain bacterial ligands, and may have an innate immune function in protecting the CNS against infection. © 2007 Wiley-Liss, Inc. [source] Retroviral labeling of Schwann cells: In vitro characterization and in vivo transplantation to improve peripheral nerve regenerationGLIA, Issue 1 2001Afshin Mosahebi Abstract Transplantation of Schwann cells (SCs) is a promising treatment modality to improve neuronal regeneration. Identification of the transplanted cells is an important step when studying the development of this method. Genetic labeling is the most stable and reliable method of cell identification, but it is still unclear whether it has deleterious effect on SC characteristics. Our aim was to achieve a stable population of SCs transduced with the lacZ gene at a high frequency using a retroviral vector in vitro, and to follow the labeled SC in vitro to assess their viability and phenotypic marker expression. Furthermore, we transplanted lacZ -labeled SCs in a conduit to repair peripheral nerve to investigate their effect on nerve regeneration in vivo. Rat and human SCs were cultured and transduced with an MFG lacZ nls marker gene, achieving a transduction rate of 80% and 70%, respectively. Rat SCs were kept in culture for 27 weeks and examined every 4 weeks for expression of lacZ, viability, and phenotypic marker expression of GFAP, p75, MHC I and II. Throughout this period, transduced rat SCs remained viable and continued to proliferate. The proportion of cells expressing lacZ dropped only by 10% and the expression of phenotypic markers remained stable. Transduced human SCs were followed up for 4 weeks in culture. They proliferated and continued to express the lacZ gene and phenotypic marker expression of GFAP and p75 was preserved. Primary culture of transduced rat SCs were transplanted, syngeneically, in a conduit to bridge a 10 mm gap in sciatic nerve and the grafts were examined after 3 weeks for the presence and participation of labeled SCs and for axonal regeneration distance. Transplanted transduced rat SCs were clearly identified, taking part in the regeneration process and enhancing the axonal regeneration rate by 100% (at the optimal concentration) compared to conduits without SCs. Thus, retroviral introduction of lacZ gene has no deleterious effect on SCs in vitro and these SCs take part and enhance nerve regeneration in vivo. GLIA 34:8,17, 2001. © 2001 Wiley-Liss, Inc. [source] Karst Spring Responses Examined by Process-Based ModelingGROUND WATER, Issue 6 2006Steffen Birk Ground water in karst terrains is highly vulnerable to contamination due to the rapid transport of contaminants through the highly conductive conduit system. For contamination risk assessment purposes, information about hydraulic and geometric characteristics of the conduits and their hydraulic interaction with the fissured porous rock is an important prerequisite. The relationship between aquifer characteristics and short-term responses to recharge events of both spring discharge and physicochemical parameters of the discharged water was examined using a process-based flow and transport model. In the respective software, a pipe-network model, representing fast conduit flow, is coupled to MODFLOW, which simulates flow in the fissured porous rock. This hybrid flow model was extended to include modules simulating heat and reactive solute transport in conduits. The application of this modeling tool demonstrates that variations of physicochemical parameters, such as solute concentration and water temperature, depend to a large extent on the intensity and duration of recharge events and provide information about the structure and geometry of the conduit system as well as about the interaction between conduits and fissured porous rock. Moreover, the responses of solute concentration and temperature of spring discharge appear to reflect different processes, thus complementing each other in the aquifer characterization. [source] Interpretation of Spring Recession CurvesGROUND WATER, Issue 5 2002H. Amit Recession curves contain information on storage properties and different types of media such as porous, fractured, cracked lithologies and karst. Recession curve analysis provides a function that quantitatively describes the temporal discharge decay and expresses the drained volume between specific time limits (Hall 1968). This analysis also allows estimating the hydrological significance of the discharge function parameters and the hydrological properties of the aquifer. In this study, we analyze data from perennial springs in the Judean Mountains and from others in the Galilee Mountains, northern Israel. All the springs drain perched carbonate aquifers. Eight of the studied springs discharge from a karst dolomite sequence, whereas one flows out from a fractured, slumped block of chalk. We show that all the recession curves can be well fitted by a function that consists of two exponential terms with exponential coefficients ,1 and ,2. These coefficients are approximately constant for each spring, reflecting the hydraulic conductivity of different media through which the ground water flows to the spring. The highest coefficient represents the fast flow, probably through cracks, or quickflow, whereas the lower one reflects the slow flow through the porous medium, or baseflow. The comparison of recession curves from different springs and different years leads to the conclusion that the main factors that affect the recession curve exponential coefficients are the aquifer lithology and the geometry of the water conduits therein. In normal years of rainy winter and dry summer, ,1 is constant in time. However, when the dry period is longer than usual because of a dry winter, ,1 slightly decreases with time. [source] Altered aquaporin 9 expression and localization in human hepatocellular carcinomaHPB, Issue 1 2009Srikanth Padma Abstract Background:, In addition to the biochemical components secreted in bile, aquaporin (AQP) water channels exist in hepatocyte membranes to form conduits for water movement between the sinusoid and the bile canaliculus. The aim of the current study was to analyse AQP 9 expression and localization in human hepatocellular carcinoma (HCC) and non-tumourigenic liver (NTL) tissue from patients undergoing hepatic resection. Methods:, Archived tissue from 17 patients was sectioned and analysis performed using an antibody raised against AQP 9. Slides were blind-scored to determine AQP 9 distribution within HCC and NTL tissue. Results:, Aquaporin 9 was predominantly expressed in the membranes of hepatocytes and demonstrated zonal distribution relative to hepatic sinusoid structure in normal liver. In HCC arising in the absence of cirrhosis AQP 9 remained membrane-localized with zonal distribution in the majority of NTL. By contrast, AQP 9 expression was significantly decreased in the HCC mass vs. pair-matched NTL. In HCC in the presence of cirrhosis, NTL was characterized by extensive AQP 9 staining in the membrane in the absence of zonal distribution and AQP 9 staining in NTL was significantly greater than that observed in the tumour mass. Conclusions:, These data demonstrate that human HCC is characterized by altered AQP 9 expression and AQP 9 localization in the NTL mass is dependent on underlying liver pathology. Given the central role of AQPs in normal liver function and the potential role of AQPs during transformation and progression, these data may prove valuable in future diagnostic and/or therapeutic strategies. [source] Nerve Repair: A Conducting-Polymer Platform with Biodegradable Fibers for Stimulation and Guidance of Axonal Growth (Adv. Mater.ADVANCED MATERIALS, Issue 43 200943/2009) Effective functional innervation of medical bionic devices, as well as re-innervation of target tissue in nerve and spinal cord injuries, requires a platform that can stimulate and orientate neural growth. Gordon Wallace and co-workers report on p. 4393 that conducting and nonconducting biodegradable polymers show excellent potential as suitable hybrid substrata for neural regeneration and may form the basis of electrically active conduits designed to accelerate nerve repair. [source] A conceptual model of preferential flow systems in forested hillslopes: evidence of self-organizationHYDROLOGICAL PROCESSES, Issue 10 2001Roy C. Sidle Abstract Preferential flow paths are known to be important conduits of subsurface stormflow in forest hillslopes. Earlier research on preferential flow paths focused on vertical transport; however, lateral transport is also evident in steep forested slopes underlain by bedrock or till. Macropores consisting of decayed and live roots, subsurface erosion, surface bedrock fractures, and animal burrows form the basis of a ,backbone' for lateral preferential flow in such sites. Evidence from field studies in Japan indicates that although individual macropore segments are generally <0·5 m in length, they have a tendency to self-organize into larger preferential flow systems as sites become wetter. Staining tests show clear evidence of interconnected macropore flow segments, including: flow within decayed root channels and subsurface erosion cavities; flow in small depressions of the bedrock substrate; fracture flow in weathered bedrock; exchange between macropores and mesopores; and flow at the organic horizon,mineral soil interface and in buried pockets of organic material and loose soil. Here we develop a three-dimensional model for preferential flow systems based on distributed attributes of macropores and potential connecting nodes (e.g. zones of loose soil and buried organic matter). We postulate that the spatially variable and non-linear preferential flow response observed at our Japan field site, as well as at other sites, is attributed to discrete segments of macropores connecting at various nodes within the regolith. Each node is activated by local soil water conditions and is influenced strongly by soil depth, permeability, pore size, organic matter distribution, surface and substrate topography, and possibly momentum dissipation. This study represents the first attempt to characterize the spatially distributed nature of preferential flow paths at the hillslope scale and presents strong evidence that these networks exhibit complex system behaviour. Copyright © 2001 John Wiley & Sons, Ltd. [source] Late malignant change in an ileal conduitINTERNATIONAL JOURNAL OF UROLOGY, Issue 1 2008Sally Wielding Abstract: Around 3000 bowel segment transpositions are performed in the UK each year and although malignancy is well-recognized following ureterosigmoidostomy, reports of similar changes in ileal conduits are sparse. We report a case of ileal adenocarcinoma in a 67-year-old lady some 49 years after ileal conduit, demonstrating previously unassociated histopathological features similar to those seen in collagenous colitis. [source] In situ hydraulic tests in the active fault survey tunnel, Kamioka Mine, excavated through the active Mozumi-Sukenobu Fault zone and their hydrogeological significanceISLAND ARC, Issue 4 2006Tsuyoshi Nohara Abstract The spatial hydrogeological and structural character of the active Mozumi-Sukenobu Fault (MSF) was investigated along a survey tunnel excavated through the MSF in the Kamioka Mine, central Japan. Major groundwater conduits on both sides of the MSF are recognized. One is considered to be a subvertical conduit between the tunnel and the surface, and the other is estimated to be a major reservoir of old meteoric water alongside the MSF. Our studies indicate that part of the MSF is a sub-vertical continuous barrier that obstructs younger meteoric water observed in the south-eastern part of the Active Fault Survey Tunnel (AFST) and water recharge to the rock mass intersected by the north-western part of the AFST. The MSF might be a continuous barrier resulting in the storage of a large quantity of older groundwater to the northwest. The observations and results of in situ hydraulic tests indicate that the major reservoir is not the fault breccia associated with the northeast,southwest trending faults of the MSF, but the zone in which blocks of fractured rocks occur beside high angle faults corresponding to X shears whose tectonic stress field coincides with the present regional stress field and antithetic Riedel shears of the MSF. The results from borehole investigations in the AFST indicate that secondary porosity is developed in the major reservoir due to the destruction of filling minerals and fracture development beside these shears. The increase in hydraulic conductivity is not directly related to increased density of fractures around the MSF. Development of secondary porosity could cause the increase in hydraulic conductivity around the MSF. Our results suggest that minor conduits of the fracture network are sporadically distributed in the sedimentary rocks around the MSF in the AFST. [source] Altering Investment Decisions to Manage Financial Reporting Outcomes: Asset-Backed Commercial Paper Conduits and FIN 46JOURNAL OF ACCOUNTING RESEARCH, Issue 5 2008DANIEL A. BENS ABSTRACT We evaluate the manner in which sponsors of highly leveraged asset-backed commercial paper (ABCP) conduits responded to Financial Accounting Standards Board Interpretation No. 46 (FIN 46), Consolidation of Variable Interest Entities an Interpretation of ARB No. 51, and its Canadian counterpart Accounting Standards Board of Accounting Guideline 15 (AcG-15), Consolidation of Variable Interest Entities. By matching commercial paper investors with corporations seeking liquidity, ABCP sponsors facilitate a significant amount of short-term, securitized financing in the United States. FIN 46 and AcG-15 require sponsors to consolidate their ABCP conduits with their financial statements. We demonstrate that the volume of ABCP began to decline when FIN 46 was first proposed, and that this decline is primarily attributable to a reduction in North American banks' sponsorship of ABCP. We also demonstrate that North American banks entered into costly restructuring arrangements to avoid having to consolidate their conduits per the new accounting standards. Our results suggest that, in certain settings, accounting standards appear to have real effects on investment activity and product-market competition. [source] A composite poly-hydroxybutyrate,glial growth factor conduit for long nerve gap repairsJOURNAL OF ANATOMY, Issue 6 2003P.-N. Mohanna Abstract There is considerable evidence that peripheral nerves have the potential to regenerate in an appropriate microenvironment. We have developed a novel artificial nerve guide composed of poly 3-hydroxybutyrate (PHB) filled with glial growth factor (GGF) suspended in alginate hydrogel. Gaps of 2,4 cm in rabbit common peroneal nerve were bridged using a PHB conduit containing either GGF in alginate hydrogel (GGF) or alginate alone (Alginate), or with an empty PHB conduit (Empty). Tissues were harvested 21, 42 and 63 days post-operatively. Schwann cell and axonal regeneration were assessed using quantitative immunohistochemistry. At 21 days, addition of GGF increased significantly the distance of axonal and Schwann cells regeneration in comparison with that observed in Alginate and Empty conduits for both gap lengths. The axons bridged the 2-cm GGF conduits gap by 63 days, with a comparable rate of regeneration seen in 4-cm conduits. Schwann cells and axonal regeneration quantity was similar for both gap lengths in each group. However, at all time points the quantity of axonal and Schwann cells regeneration in GGF grafts was significantly greater than in both Alginate and Empty conduits, the latter showing better regeneration than Alginate conduits. The results indicate an inhibitory effect of alginate on regeneration, which is partially reversed by the addition of GGF to the conduits. In conclusion, GGF stimulates a progressive and sustainable regeneration increase in long nerve gap conduits. [source] Structure, function and evolution of the gas exchangers: comparative perspectivesJOURNAL OF ANATOMY, Issue 4 2002J. N. Maina Abstract Over the evolutionary continuum, animals have faced similar fundamental challenges of acquiring molecular oxygen for aerobic metabolism. Under limitations and constraints imposed by factors such as phylogeny, behaviour, body size and environment, they have responded differently in founding optimal respiratory structures. A quintessence of the aphorism that ,necessity is the mother of invention', gas exchangers have been inaugurated through stiff cost,benefit analyses that have evoked transaction of trade-offs and compromises. Cogent structural,functional correlations occur in constructions of gas exchangers: within and between taxa, morphological complexity and respiratory efficiency increase with metabolic capacities and oxygen needs. Highly active, small endotherms have relatively better-refined gas exchangers compared with large, inactive ectotherms. Respiratory structures have developed from the plain cell membrane of the primeval prokaryotic unicells to complex multifunctional ones of the modern Metazoa. Regarding the respiratory medium used to extract oxygen from, animal life has had only two choices , water or air , within the biological range of temperature and pressure the only naturally occurring respirable fluids. In rarer cases, certain animals have adapted to using both media. Gills (evaginated gas exchangers) are the primordial respiratory organs: they are the archetypal water breathing organs. Lungs (invaginated gas exchangers) are the model air breathing organs. Bimodal (transitional) breathers occupy the water,air interface. Presentation and exposure of external (water/air) and internal (haemolymph/blood) respiratory media, features determined by geometric arrangement of the conduits, are important features for gas exchange efficiency: counter-current, cross-current, uniform pool and infinite pool designs have variably developed. [source] Regeneration of canine peroneal nerve with the use of a polyglycolic acid,collagen tube filled with laminin-soaked collagen sponge: a comparative study of collagen sponge and collagen fibers as filling materials for nerve conduitsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 6 2001Toshinari Toba Abstract A novel artificial nerve conduit was developed and its efficiency was evaluated on the basis of promotion of peripheral nerve regeneration across an 80-mm gap in dogs. The nerve conduit was made of a polyglycolic acid,collagen tube filled with laminin-soaked collagen sponge. Conduits filled with either sponge- or fiber-form collagen were implanted into an 80-mm gap of the peroneal nerve (five dogs for each form). Twelve months postoperatively nerve regeneration was superior in the sponge group both morphometrically (percentage of neural tissue: fiber: 39.7 ± 5.2, sponge: 43.0 ± 4.5, n=3) and electrophysiologically (fiber: CMAP 1.06 ± 0.077, SEP 1.32 ± 0.127 sponge: CMAP 1.04 ± 0.106, SEP 1.24 ± 0.197, n=5), although these differences were not statistically significant. The observed regeneration was complementary to successful results reported previously in the same model, in which collagen fibers exclusively were used. The results indicate a possible superiority of collagen sponge over collagen fibers as filling materials. In addition, the mass-producibility, superior scaffolding potential, and capacity for gradual release of soluble factors of the sponge provide make it an attractive alternative to fine fibers, which are both technologically difficult and costly to produce. This newly developed nerve conduit has the potential to enhance peripheral nerve regeneration across longer gaps commonly encountered in clinical settings. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 622,630, 2001 [source] | |||||||||||||||||||||||||||||||||||||||||||