Home About us Contact
|
Home About us Contact | ||
|
|
||
Values Similar (value + similar)
Selected AbstractsPIPD, a new high-modulus and high-strength polymer fibre with exceptional fire protection propertiesFIRE AND MATERIALS, Issue 4-5 2002M.G. Northolt The development of the new high-modulus and high-strength fibre M5, made of poly{2,6-diimidazo[4,5-b:4,,5, -e]-pyridinylene-1,4(2,5-dihydroxy)phenylene} or PIPD, has resulted in an organic polymer fibre with exceptional fire protection properties when compared with PBO, Twaron, Kevlar and Nomex fibres. The PIPD as-spun fibre with a modulus of 150 GPa and a tensile strength of 2.5 GPa is a crystal hydrate containing 21 wt% water. Cone calorimeter measurements yielded a fire performance index (FPI) 20 times higher than Nomex, with extremely low value for the specific extinction area (SEA) characterizing the smoke formation. The PIPD-HT fibre (recrystallized in an after treatment into the anhydrous crystalline structure) with a modulus >300 GPa and a strength >5 GPa has a FPI value similar to PBO but shows much less smoke formation than this fibre. Copyright © 2002 John Wiley & Sons, Ltd. [source] Novel UV-induced photografting process for preparing poly(tetrafluoroethylene)-based proton-conducting membranesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2007Masaharu Asano Abstract A novel process comprising the UV-induced photografting of styrene into poly(tetrafluoroethylene) (PTFE) films and subsequent sulfonation has been developed for preparing proton-conducting membranes. Although under UV irradiation the initial radicals were mainly generated on the surface of the PTFE films by the action of photosensitizers such as xanthone and benzoyl peroxide, the graft chains were readily propagated into the PTFE films. The sulfonation of the grafted films was performed in a chlorosulfonic acid solution. Fourier transform infrared and scanning electron microscopy were used to characterize the grafted and sulfonated membranes. With a view to use in fuel cells, the proton conductivity, water uptake, and mechanical properties of the prepared membranes were measured. Even through the degree of grafting was lower than 10%, the proton conductivity in the thickness direction of the newly prepared membranes could reach a value similar to that of a Nafion membrane. In comparison with ,-ray radiation grafting, UV-induced photografting is very simple and safe and is less damaging to the membranes because significant degradation of the PTFE main chains can be avoided. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2624,2637, 2007 [source] Image contrast in X-ray reflection interface microscopy: comparison of data with model calculations and simulationsJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2008P. Fenter The contrast mechanism for imaging molecular-scale features on solid surfaces is described for X-ray reflection interface microscopy (XRIM) through comparison of experimental images with model calculations and simulated measurements. Images of elementary steps show that image contrast is controlled by changes in the incident angle of the X-ray beam with respect to the sample surface. Systematic changes in the magnitude and sign of image contrast are asymmetric for angular deviations of the sample from the specular reflection condition. No changes in image contrast are observed when defocusing the condenser or objective lenses. These data are explained with model structure-factor calculations that reproduce all of the qualitative features observed in the experimental data. These results provide new insights into the image contrast mechanism, including contrast reversal as a function of incident angle, the sensitivity of image contrast to step direction (i.e. up versus down), and the ability to maximize image contrast at almost any scattering condition defined by the vertical momentum transfer, Qz. The full surface topography can then, in principle, be recovered by a series of images as a function of incident angle at fixed momentum transfer. Inclusion of relevant experimental details shows that the image contrast magnitude is controlled by the intersection of the reciprocal-space resolution function (i.e. controlled by numerical aperture of the condenser and objective lenses) and the spatially resolved interfacial structure factor of the object being imaged. Together these factors reduce the nominal contrast for a step near the specular reflection condition to a value similar to that observed experimentally. This formalism demonstrates that the XRIM images derive from limited aperture contrast, and explains how non-zero image contrast can be obtained when imaging a pure phase object corresponding to the interfacial topography. [source] Electron spin resonance characterization of phosphorus-doped CVD diamond filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2004M. Katagiri Abstract Electron spin resonance technique has been applied to characterize defects and to determine local structure of phosphorus in phosphorus-doped (111)-homoepitaxially grown CVD diamond films. Dominant defects have g -value similar to that of the H1 center in polycrystalline CVD diamond, however, are not accompanied with a unique nearby hydrogen atom. These defects are likely to be located near substrate/ epilayer interface. New phosphorus related center with a tetragonal symmetry has been found. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mechanical and Tribological Properties of Cr-DLC Coatings Deposited by ARC-MAG-RF PACVD Hybrid MethodPLASMA PROCESSES AND POLYMERS, Issue S1 2007Andrzej Czyzniewski Abstract The procedure of Cr-DLC coating deposition using a hybrid ARC-MAG-RF PACVD method is presented in this paper. ARC and MAG techniques were used to deposit a Cr/Cr-C:H interlayer with increasing hardness, but a nearly constant elastic modulus of the value similar to a steel substrate and DLC layer deposited then by RF PACVD technique. As a result of such coating formation the lower level of stresses in the coating-substrate system, both intrinsic and induced by the load applied, was obtained. The resultant Cr-DLC coating is marked by high crack resistance and high adhesion. The Cr-DLC coating shows high wear resistance, but the wear geometry and the friction coefficient depend on a type of the counterpart material. [source] Specific reactions of S -nitrosothiols with cysteine hydrolases: A comparative study between dimethylargininase-1 and CTP synthetasePROTEIN SCIENCE, Issue 8 2007Oliver Braun Abstract S-Transnitrosation is an important bioregulatory process whereby NO+ equivalents are transferred between S -nitrosothiols and Cys of target proteins. This reaction proceeds through a common intermediate R,S,N(O,),S,R, and it has been proposed that products different from S -nitrosothiols may be formed in protein cavities. Recently, we have reported on the formation of such a product, an N -thiosulfoximide, at the active site of the Cys hydrolase dimethylargininase-1 (DDAH-1) upon reaction with S -nitroso- l -homocysteine (HcyNO). Here we have addressed the question of whether this novel product can also be formed with the endogenously occurring S -nitrosothiols S -nitroso- l -cysteine (CysNO) and S -nitrosoglutathione (GSNO). Further, to explore the reason responsible for the unique formation of an N -thiosulfoximide in DDAH-1 we have expanded these studies to cytidine triphosphate synthetase (CTPS), which shows a similar active site architecture. ESI-MS and activity measurements showed that the bulky GSNO does not react with both enzymes. In contrast, S-nitrosylation of the active site Cys occurred in DDAH-1 with CysNO and in CTPS with CysNO and HcyNO. Although kinetic analysis indicated that these compounds act as specific irreversible inhibitors, no N -thiosulfoximide was formed. The reasons likely responsible for the absence of the N -thiosulfoximide formation are discussed using molecular models of DDAH-1 and CTPS. In tissue extracts DDAH was inhibited only by HcyNO, with an IC50 value similar to that of the isolated protein. Biological implications of these studies for the function of both enzymes are discussed. [source] Modular Synthesis and Dynamics of a Variety of Donor,Acceptor Interlocked Compounds Prepared by Click ChemistryCHEMISTRY - AN ASIAN JOURNAL, Issue 5 2007Abstract A series of donor,acceptor [2]-, [3]-, and [4]rotaxanes and self-complexes ([1]rotaxanes) have been synthesized by a threading-followed-by-stoppering approach, in which the precursor pseudorotaxanes are fixed by using CuI -catalyzed Huisgen 1,3-dipolar cycloaddition to attach the required stoppers. This alternative approach to forming rotaxanes of the donor,acceptor type, in which the donor is a 1,5-dioxynaphthalene unit and the acceptor is the tetracationic cyclophane cyclobis(paraquat- p -phenylene), proceeds with enhanced yields relative to the tried and tested synthetic strategies, which involve the clipping of the cyclophane around a preformed dumbbell containing ,-electron-donating recognition sites. The new synthetic approach is amenable to application to highly convergent sequences. To extend the scope of this reaction, we constructed [2]rotaxanes in which one of the phenylene rings of the tetracationic cyclophane is perfluorinated, a feature which significantly weakens its association with ,-electron-rich guests. The activation barrier for the shuttling of the cyclophane over a spacer containing two triazole rings was determined to be (15.5±0.1),kcal,mol,1 for a degenerate two-station [2]rotaxane, a value similar to that previously measured for analogous degenerate compounds containing aromatic or ethylene glycol spacers. The triazole rings do not seem to perturb the shuttling process significantly; this property bodes well for their future incorporation into bistable molecular switches. [source] Syntectonic infiltration by meteoric waters along the Sevier thrust front, southwest MontanaGEOFLUIDS (ELECTRONIC), Issue 4 2006A. C. RYGEL Abstract Structural, petrographic, and isotopic data for calcite veins and carbonate host-rocks from the Sevier thrust front of SW Montana record syntectonic infiltration by H2O-rich fluids with meteoric oxygen isotope compositions. Multiple generations of calcite veins record protracted fluid flow associated with regional Cretaceous contraction and subsequent Eocene extension. Vein mineralization occurred during single and multiple mineralization events, at times under elevated fluid pressures. Low salinity (Tm = ,0.6°C to +3.6°C, as NaCl equivalent salinities) and low temperature (estimated 50,80°C for Cretaceous veins, 60,80°C for Eocene veins) fluids interacted with wall-rock carbonates at shallow depths (3,4 km in the Cretaceous, 2,3 km in the Eocene) during deformation. Shear and extensional veins of all ages show significant intra- and inter-vein variation in ,18O and ,13C. Carbonate host-rocks have a mean ,18OV-SMOW value of +22.2 ± 3, (1,), and both the Cretaceous veins and Eocene veins have ,18O ranging from values similar to those of the host-rocks to as low as +5 to +6,. The variation in vein ,13CV-PDB of ,1 to approximately +6, is attributed to original stratigraphic variation and C isotope exchange with hydrocarbons. Using the estimated temperature ranges for vein formation, fluid (as H2O) ,18O calculated from Cretaceous vein compositions for the Tendoy and Four Eyes Canyon thrust sheets are ,18.5 to ,12.5,. For the Eocene veins within the Four Eyes Canyon thrust sheet, calculated H2O ,18O values are ,16.3 to ,13.5,. Fluid,rock exchange was localized along fractures and was likely coincident with hydrocarbon migration. Paleotemperature determinations and stable isotope data for veins are consistent with the infiltration of the foreland thrust sheets by meteoric waters, throughout both Sevier orogenesis and subsequent orogenic collapse. The cessation of the Sevier orogeny was coincident with an evolving paleogeographic landscape associated with the retreat of the Western Interior Seaway and the emergence of the thrust front and foreland basin. Meteoric waters penetrated the foreland carbonate thrust sheets of the Sevier orogeny utilizing an evolving mesoscopic fracture network, which was kinematically related to regional thrust structures. The uncertainty in the temperature estimates for the Cretaceous and Eocene vein formation prevents a more detailed assessment of the temporal evolution in meteoric water ,18O related to changing paleogeography. Meteoric water-influenced ,18O values calculated here for Cretaceous to Eocene vein-forming fluids are similar to those previously proposed for surface waters in the Eocene, and those observed for modern-day precipitation, in this part of the Idaho-Montana thrust belt. [source] Comparison of hematologic or biochemical parameters among elderly hospital patients, institution-dwelling residents, and health check-up examineesGERIATRICS & GERONTOLOGY INTERNATIONAL, Issue 3 2003Ryuichi Yamamoto Background: The purpose of the present paper was to examine the differences in the levels of hematological or biochemical parameters among elderly hospital patients, nursing home residents, and mass health check-up recipients. Methods: One hundred and 44 geriatric inpatients (aged , 65 years), 237 outpatients, 146 nursing home residents, 120 aged examinees from mass health check-ups, and 512 younger health check-up examinees (controls) were included in the present study. They were divided into five male and five female subgroups, respectively. The levels of hemoglobin (Hb), white blood cells (WBC), serum albumin (Alb), Ca, albumin-corrected Ca, Na, creatinine (Cr), and total cholesterol (TC) were determined and compared. Results: There were significantly lower levels of Hb, Alb, Ca, Na, and TC in inpatients than in other groups in both sexes. In contrast, higher levels of WBC and Cr were found in inpatients. Among women there was no difference in the level of any parameter between nursing home residents, health check-up examinees, and controls. Conclusion: The data indicate that the levels of these parameters are affected to a greater extent in inpatients, and that female nursing home residents and health check-up examinees show values similar to those of controls. [source] ,-Hydroxybutyrate binds to the synaptic site recognizing succinate monocarboxylate: A new hypothesis on astrocyte,neuron interaction via the protonation of succinateJOURNAL OF NEUROSCIENCE RESEARCH, Issue 7 2008Tünde Molnár Abstract Succinate (SUC), a citrate (CIT) cycle intermediate, and carbenoxolone (CBX), a gap junction inhibitor, were shown to displace [3H],-hydroxybutyrate ([3H]GHB), which is specifically bound to sites present in synaptic membrane subcellular fractions of the rat forebrain and the human nucleus accumbens. Elaboration on previous work revealed that acidic pH-induced specific binding of [3H]SUC occurs, and it has been shown to have a biphasic displacement profile distinguishing high-affinity (Ki,SUC = 9.1 ± 1.7 ,M) and low-affinity (Ki,SUC = 15 ± 7 mM) binding. Both high- and low- affinity sites were characterized by the binding of GHB (Ki,GHB = 3.9 ± 0.5 ,M and Ki,GHB = 5.0 ± 2.0 mM) and lactate (LAC; Ki,LAC = 3.9 ± 0.5 ,M and Ki,LAC = 7.7 ± 0.9 mM). Ligands, including the hemiester ethyl-hemi-SUC, and the gap junction inhibitors flufenamate, CBX, and the GHB binding site-selective NCS-382 interacted with the high-affinity site (in ,M: Ki,EHS = 17 ± 5, Ki,FFA = 24 ± 13, Ki,CBX = 28 ± 9, Ki,NCS-382 = 0.8 ± 0.1 ,M). Binding of the Na+,K+ -ATPase inhibitor ouabain, the proton-coupled monocarboxylate transporter (MCT)-specific ,-cyano-hydroxycinnamic acid (CHC), and CIT characterized the low-affinity SUC binding site (in mM: Ki,ouabain = 0.13 ± 0.05, Ki,CHC = 0.32 ± 0.07, Ki,CIT = 0.79 ± 0.20). All tested compounds inhibited [3H]SUC binding in the human nucleus accumbens and had Ki values similar to those observed in the rat forebrain. The binding process can clearly be recognized as different from synaptic and mitochondrial uptake or astrocytic release of SUC, GHB, and/or CIT by its unique GHB selectivity. The transient decrease of extracellular SUC observed during epileptiform activity suggested that the function of the synaptic target recognizing protonated succinate monocarboxylate may vary under different (patho)physiological conditions. Furthermore, we put forward a hypothesis on the synaptic activity-regulated signaling between astrocytes and neurons via SUC protonation. © 2008 Wiley-Liss, Inc. [source] Effect of Light-Curing Method and Cement Activation Mode on Resin Cement Knoop HardnessJOURNAL OF PROSTHODONTICS, Issue 6 2007Rubens Nisie Tango Purpose: To evaluate the Knoop hardness (KHN) of the resin cement Enforce activated by chemical/physical mode or physical mode solely; light-cured directly or through a 1.5 mm thick ceramic disc (HeraCeram) on shade DD2. Materials and Methods: Light-curing was carried out using a conventional quartz tungsten halogen light (QTH) (XL2500) for 40 seconds at 700 mW/cm2; light-emitting diodes (LED) (Ultrablue Is) for 40 seconds at 440 mW/cm2; and Xenon plasma arc (PAC) (Apollo 95E) for 3 seconds at 1600 mW/cm2. Bovine incisors had their buccal faces flattened and hybridized. A mold was seated on these surfaces and filled with cement. A disc of the acid-etched and silanized veneering material was seated over this set for light-curing. After dry storage (24 hours at 37°C), specimens (n= 10) were sectioned for KHN measurements performed in a microhardness tester (50 gf load for 15 seconds). Data were submitted to ANOVA and Tukey's test (,= 0.05). Results: The highest KHN values were obtained with LED, for both dual-cured and light-cured cement. The lowest KHN value was obtained with light-cured PAC. Light-curing with QTH resulted in hardness values similar to PAC in dual-cured groups. Conclusions: Light-curing through HeraCeram can influence resin cement hardness. [source] Incorporation of Chlorella vulgaris and Spirulina maxima biomass in pasta products.JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 10 2010Part 1: Preparation, evaluation Abstract BACKGROUND: Microalgae are able to enhance the nutritional content of conventional foods and hence to positively affect human health, due to their original chemical composition. The aim of the present study was to prepare fresh spaghetti enriched with different amounts of microalgae biomass (Chlorella vulgaris and Spirulina maxima) and to compare the quality parameters (optimal cooking time, cooking losses, swelling index and water absorption), chemical composition, instrumental texture and colour of the raw and cooked pasta enriched with microalgae biomass with standard semolina spaghetti. RESULTS: The incorporation of microalgae results in an increase of quality parameters when compared to the control sample. The colour of microalgae pastas remained relatively stable after cooking. The addition of microalgae resulted in an increase in the raw pasta firmness when compared to the control sample. Of all the microalgae studied, an increase in the biomass concentration (0.5,2.0%) resulted in a general tendency of an increase in the pasta firmness. Sensory analysis revealed that microalgae pastas had higher acceptance scores by the panellists than the control pasta. CONCLUSION: Microalgae pastas presented very appellative colours, such as orange and green, similar to pastas produced with vegetables, with nutritional advantages, showing energetic values similar to commercial pastas. The use of microalgae biomass can enhance the nutritional and sensorial quality of pasta, without affecting its cooking and textural properties. Copyright © 2010 Society of Chemical Industry [source] The drought tolerance limit of Fagus sylvatica forest on limestone in southwestern GermanyJOURNAL OF VEGETATION SCIENCE, Issue 6 2008Stefanie Gärtner Abstract Question: What components of drought influence the drought limit of Fagus sylvatica forests? This study contributes to the ongoing discussion regarding the future of Fagus as a major component of central European forests. Location: The drought limit of F. sylvatica at its ecotone with forest dominated by Quercus pubescens, Q. petraea and their hybrids in two limestone regions (Klettgau, Schwäbische Alb) in southwestern Germany was compared. Methods: Vegetation relevés were classified and a gradient analysis was performed. The vegetation pattern was analysed with several drought relevant variables. Classification trees were used to determine the drought limits of the Fagus forest. Results: The Fagus, Quercus and the ecotone forests were floristically characterized. The lower humidity in the submontane Klettgau, compared to the montane Schwäbische Alb, was compensated for by greater soil moisture (ASWSC). Therefore, Fagus forest in the Schwäbische Alb grew on sites with ASWSC values similar to those of ecotone forest in Klettgau. Conclusions: The interaction between climatic and edaphic drought related factors demonstrates that drought is a complex edaphic-climatic factor. Both components contribute to limiting the distribution of Fagus. For the two regions in southwestern Germany, and under the existing climatic conditions, it could be shown that Fagus is able to dominate forests on soils with very low ASWSC (, 68 l.m -2). [source] Antibacterial and Hemolytic Activities of Quaternary Pyridinium Functionalized PolynorbornenesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 5 2008Tarik Eren Abstract In this study, amphiphilic polyoxanorbornene with different quaternary alkyl pyridinium side chains were synthesized. The biological efficiencies of these polymers, with various alkyl substituents, were determined by bacterial growth inhibition assays and hemolytic activity (HC50) against human red blood cells (RBCs) to provide selectivity of these polymers for bacterial over mammalian cells. A series of polymers with different alkyl substituents (ethyl, butyl, hexyl, octyl, decyl and phenylethyl) and two different molecular weights (3 and 10 kDa) were prepared. The impact of alkyl chain length divided the biological activity into two different cases: those with an alkyl substituent containing four or fewer carbons had a minimum inhibitory concentration (MIC) of 200 µg,·,mL,1 and a HC50 greater than 1,650 µg,·,mL,1, while those with six or more carbons had lower MICs,,,12.5 µg,·,mL,1 and HC50,,,250 µg,·,mL,1. Using MSI-78, the potent Magainin derivative which has an MIC,=,12.0 µg,·,mL,1 and HC50,=,120 µg,·,mL,1, as a comparison, the polymers with alkyl substituents ,C4 (four carbons) were not very potent, but did show selectivity values greater than or equal to MSI-78. In contrast, those with alkyl substituents ,C6 were as potent, or more potent, than MSI-78 and in three specific cases demonstrated selectivity values similar to, or better than, MSI-78. To understand if these polymers were membrane active, polymer induced lipid membrane disruption activities were evaluated by dye leakage experiments. Lipid composition and polymer hydrophobicity were found to be important factors for dye release. [source] The correlation of metallicity gradient with galaxy massMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2005Duncan A. Forbes ABSTRACT A number of previous studies have searched for a correlation between radial metallicity gradients and early-type galaxy mass , no convincing trends have been found. Here we re-examine this issue with several key enhancements: using total metallicity from studies that have broken the age,metallicity degeneracy, excluding galaxies with young stellar ages (i.e. those that have experienced a recent central starburst) and using the K band to derive galaxy luminosities. We find that Coma cluster galaxies have metallicity gradients that correlate with galaxy mass. Furthermore, gradients have values similar to those of monolithic collapse models. The combination of dissipative formation and energy injection from supernovae provides a mechanism for the trends with galaxy mass; however, other explanations are possible. Additional high-quality observational data are needed to constrain further the gas physics involved in galaxy formation. [source] Confinement factor, near and far field patterns in InGaN MQW laser diodesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2005J. Martín Abstract In this work the influence of the QW number in the active region on spectral characteristics in InGaN multi quamtun well lasers is analyzed. A comparison between the abrupt index step structure (Step) and a graded-index structure (GRIN) is done. The effect of the introduction of a p-AlxGa1,xN electron blocking layer, placed above the last InGaN barrier in the Step structure is also analyzed. Calculations of the confinement factor, near and far field patterns were carried out. We found that with the adequate aluminum content in this layer, the confinement factor, near and far field patterns are improved, and values similar to those obtained with GRIN structure can be reached. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Genetic variation in populations of the cacao wilt pathogen, Ceratocystis cacaofunestaPLANT PATHOLOGY, Issue 6 2007C. J. B. Engelbrecht Ceratocystis cacaofunesta (= Ceratocystis fimbriata) causes a lethal wilt disease of cacao (Theobroma cacao) in Latin America. Polymorphic microsatellite markers, (CAT)5 nuclear DNA fingerprints and Hae III mitochondrial DNA fingerprints were used to compare genetic diversity among isolates of C. cacaofunesta collected from populations in western Ecuador, Costa Rica, Colombia, and Rondônia and Bahia in Brazil. Microsatellite markers and nuclear DNA fingerprints separated Ecuadorian isolates from isolates of the other four populations, and these two major groups correspond to genetic lineages already identified from ITS-rDNA sequences and intersterility groupings. Mitochondrial DNA fingerprints also demonstrated substantial diversity and split the Ecuadorian isolates into two groups. All marker types showed limited variation in the Colombian, Costa Rican and Bahian populations, as might be expected for introduced populations that have gone through recent genetic bottlenecks. In contrast, the Rondonian and western Ecuadorian populations showed gene diversity values similar to natural populations of other Ceratocystis species. The Rondonian population was the only sampled population in the native range of T. cacao (the Upper Amazon), and the putatively introduced populations were more closely related to the Rondonian population than to the western Ecuadorian population. The Ecuadorian population is in an area with other native Theobroma species, which may serve as natural hosts. [source] A modelling study of locomotion-induced hyperpolarization of voltage threshold in cat lumbar motoneuronesTHE JOURNAL OF PHYSIOLOGY, Issue 2 2002Yue Dai During fictive locomotion the excitability of adult cat lumbar motoneurones is increased by a reduction (a mean hyperpolarization of ,6.0 mV) of voltage threshold (Vth) for action potential (AP) initiation that is accompanied by only small changes in AP height and width. Further examination of the experimental data in the present study confirms that Vth lowering is present to a similar degree in both the hyperpolarized and depolarized portions of the locomotor step cycle. This indicates that Vth reduction is a modulation of motoneurone membrane currents throughout the locomotor state rather than being related to the phasic synaptic input within the locomotor cycle. Potential ionic mechanisms of this locomotor-state-dependent increase in excitability were examined using three five-compartment models of the motoneurone innervating slow, fast fatigue resistant and fast fatigable muscle fibres. Passive and active membrane conductances were set to produce input resistance, rheobase, afterhyperpolarization (AHP) and membrane time constant values similar to those measured in adult cat motoneurones in non-locomoting conditions. The parameters of 10 membrane conductances were then individually altered in an attempt to replicate the hyperpolarization of Vth that occurs in decerebrate cats during fictive locomotion. The goal was to find conductance changes that could produce a greater than 3 mV hyperpolarization of Vth with only small changes in AP height (< 3 mV) and width (< 1.2 ms). Vth reduction without large changes in AP shape could be produced either by increasing fast sodium current or by reducing delayed rectifier potassium current. The most effective Vth reductions were achieved by either increasing the conductance of fast sodium channels or by hyperpolarizing the voltage dependency of their activation. These changes were particularly effective when localized to the initial segment. Reducing the conductance of delayed rectifier channels or depolarizing their activation produced similar but smaller changes in Vth. Changes in current underlying the AHP, the persistent Na+ current, three Ca2+ currents, the ,h' mixed cation current, the ,A' potassium current and the leak current were either ineffective in reducing Vth or also produced gross changes in the AP. It is suggested that the increased excitability of motoneurones during locomotion could be readily accomplished by hyperpolarizing the voltage dependency of fast sodium channels in the axon hillock by a hitherto unknown neuromodulatory action. [source] Interactive effects of dietary vitamin C and phospholipid in micro-bound diet for growth, survival, and stress resistance of larval red sea bream, Pagrus majorAQUACULTURE NUTRITION, Issue 5 2010T. REN Abstract This study was conducted to examine the effects of dietary ascorbic acid (AsA) and phospholipid (PL) and their interaction on growth, survival, and stress resistance in red sea bream larvae. Twenty-six days old red sea bream were fed nine micro-bound diets supplemented three levels of AsA (0, 800 and 1600 mg kg,1 diet) and PL (0, 20 and 40 g kg,1 diet) for 15 days. Dietary AsA and PL were both significant factors on survival rates. There was also an interaction between dietary AsA and PL on survival rate (P < 0.05). The larvae fed 800 or 1600 mg kg,1 AsA with 40 g kg,1 PL diets showed the highest survival rate, with values similar to those of the live-food supplemented group. Stress resistance against low salinity exposure significantly increased with increased dietary level of AsA and PL. However, significant interaction of AsA and PL was not detected. The larvae fed 1600 mg kg,1 AsA with 40 g kg,1 PL diet showed the highest stress resistance among all diets, but it was not significantly different than that of larvae fed 800 mg kg,1 AsA with 40 g kg,1 PL diet. This study clearly demonstrated that combined use of AsA and PL can improve survival of 26,40 days posthatching red sea bream larvae. Moreover, the present study suggested that 800 mg kg,1 AsA with 40 g kg,1 PL in diet was needed for producing high quality seedling under the stressful conditions. [source] Biocompatibility and Calcification of Bovine Pericardium Employed for the Construction of Cardiac Bioprostheses Treated With Different Chemical Crosslink MethodsARTIFICIAL ORGANS, Issue 5 2010Eduardo Jorge-Herrero Abstract The use of biological materials in the construction of bioprostheses requires the application of different chemical procedures to improve the durability of the material without producing any undesirable effects. A number of crosslinking methods have been tested in biological tissues composed mainly of collagen. The aim of this study was to evaluate the in vitro biocompatibility, the mechanical properties, and in vivo calcification of chemically modified bovine pericardium using glutaraldehyde acetals (GAAs) in comparison with glutaraldehyde (GA) treatment. Homsy's tests showed that the most cytotoxic treatment is GA whereas GAA treatments showed lower cytotoxicity. Regarding the mechanical properties of the modified materials, no significant differences in stress at rupture were detected among the different treatments. Zeta-Potential showed higher negative values for GA treatment (,4.9 ± 0.6 mV) compared with GAA-0.625% (,2.2 ± 0.5 mV) and GAA-1% (,2.2 ± 0.4 mV), which presented values similar to native tissue. Similar results were obtained for calcium permeability coefficients which showed the highest values for GA treatment (0.12 ± 0.02 mm2/min), being significantly lower for GAA treatments or non-crosslinked pericardium. These results confirmed the higher propensity of the GA-treated tissues for attraction of calcium cations and were in good agreement with the calcification degree obtained after 60 days implantation into young rats, which was significantly higher for the GA group (22.70 ± 20.80 mg/g dry tissue) compared with GAA-0.625% and GAA-1% groups (0.49 ± 0.28 mg/g dry tissue and 3.51 ± 3.27 mg/g dry tissue, respectively; P < 0.001). In conclusion, GAA treatments can be considered a promising alternative to GA treatment. [source] Are Standard Human Coagulation Tests Suitable in Pigs and Calves During Extracorporeal Circulation?ARTIFICIAL ORGANS, Issue 7 2001Xavier M. Mueller Abstract: The thrombogenicity of membrane oxygenators as well as clotting parameters profiles, using standard human clotting tests, was analyzed in calves and pigs during 6 h perfusion. Three calves and 3 pigs were connected to extracorporeal circulation with standard heparinization. Blood samples were taken for coagulation variables throughout perfusion, and oxygenators were examined for clot deposits at the end of the experiment. Two out of 3 oxygenators of the calf group presented clot deposits while none in the pig group did. Baseline coagulation variables of pigs showed values similar to those of humans while neither extrinsic nor intrinsic pathways could be activated in calves with standard human coagulation tests. The calf model, in conclusion, was confirmed to be a difficult model for the testing of extracorporeal circulation device resistance to thrombus formation, which is, however, not reflected by standard human coagulation tests. The pig model is a better model in which both coagulation pathways could be activated with standard human coagulation tests. [source] Impact of feral water buffalo and fire on growth and survival of mature savanna trees: An experimental field study in Kakadu National Park, northern AustraliaAUSTRAL ECOLOGY, Issue 6 2005PATRICIA A. WERNER Abstract The impact of feral Asian water buffalo (Bubalus bubalis) and season of fire on growth and survival of mature trees was monitored over 8 years in the eucalypt savannas of Kakadu National Park. Permanently marked plots were paired on either side of a 25-km-long buffalo-proof fence at three locations on an elevational gradient, from ridge-top to the edge of a floodplain; buffalo were removed from one side of the fence. All 750 trees ,,1.4 m height were permanently marked; survival and diameter of each tree was measured annually; 26 species were grouped into four eco-taxonomic groups. The buffalo experiment was maintained for 7 years; trees were monitored an additional year. Fires were excluded from all sites the first 3 years, allowed to occur opportunistically for 4 years and excluded for the final year. Fires were of two main types: low-intensity early dry season and high-intensity late dry season. Growth rates of trees were size-specific and positively related to diameters as exponential functions; trees grew slowest on the two ends of the gradient. Eucalypt mortality rates were 1.5 and 3 times lower than those of pantropics and of arborescent monocots, respectively, but the relative advantage was lost with fires or buffalo grazing. Without buffalo grazing, ground level biomass was 5,8 t ha,1 compared with 2,3 t ha,1, within 3 years. In buffalo-absent plots, trees grew significantly slower on the dry ridge and slope, and had higher mortality across the entire gradient, compared with trees in buffalo-present plots. At the floodplain margin, mortality of small palms was higher in buffalo-present sites, most likely due to associated heavy infestations of weeds. Low-intensity fires produced tree growth and mortality values similar to no-fire, in general, but, like buffalo, provided a ,fertilization' effect for Eucalyptus miniata and Eucalyptus tetrodonta, increasing growth in all size classes. High-intensity fires reduced growth and increased mortality of all functional groups, especially the smallest and largest (>35 cm d.b.h.) trees. When buffalo and fires were excluded in the final year, there were no differences in growth or mortality between paired sites across the environmental gradient. After 8 years, the total numbers of trees in buffalo-absent plots were only 80% of the number in buffalo-present plots, due to relatively greater recruitment of new trees in buffalo-present plots; fire-sensitive pantropics were particularly disadvantaged. Since the removal of buffalo is disadvantageous, at least over the first years, to savanna tree growth and survival due to a rebound effect of the ground-level vegetation and subsequent changes in fire-vegetation interactions, process-orientated management aimed at reducing fuel loads and competitive pressure may be required in order to return the system to a previous state. The ,footprint' of 30 years of heavy grazing by buffalo has implications for the interpretation of previous studies on fire-vegetation dynamics and for current research on vegetation change in these savannas. [source] Carbon Monoxide Mass Transfer for Syngas Fermentation in a Stirred Tank Reactor with Dual Impeller ConfigurationsBIOTECHNOLOGY PROGRESS, Issue 3 2007Andrew J. Ungerman This study compares the power demand and gas-liquid volumetric mass transfer coefficient, kLa, in a stirred tank reactor (STR) (T = 0.211 m) using different impeller designs and schemes in a carbon monoxide-water system, which is applicable to synthesis gas (syngas) fermentation. Eleven different impeller schemes were tested over a range of operating conditions typically associated with the "after large cavity" region (ALC) of a Rushton-type turbine (D/T = 0.35). It is found that the dual Rushton-type impeller scheme exhibits the highest volumetric mass transfer rates for all operating conditions; however, it also displays the lowest mass transfer performance (defined as the volumetric mass transfer coefficient per unit power input) for all conditions due to its high power consumption. Dual impeller schemes with an axial flow impeller as the top impeller show improved mass transfer rates without dramatic increases in power draw. At high gas flow rates, dual impeller schemes with a lower concave impeller have kLa values similar to those of the Rushton-type dual impeller schemes but show improved mass transfer performance. It is believed that the mass transfer performance can be further enhanced for the bottom concave impeller schemes by operating at conditions beyond the ALC region defined for Rushton-type impellers because the concave impeller can handle higher gas flow rates prior to flooding. [source] | |||||||||||||||||||||||||