kPa

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Distribution within Medical Sciences

Terms modified by kPa

  • kpa o2

  • Selected Abstracts


    Photofading of phenylazo-aniline, -pyridone and -quinolone disperse dyes on a nylon 6 substrate

    COLORATION TECHNOLOGY, Issue 2 2009
    Yasuyo Okada
    The photofading of phenylazo-aniline, -pyridone and -quinolone disperse dyes on nylon fabric was analysed using the Kubelka,Munk (K/S) spectra of fabrics exposed to a carbon arc in air. The exposure of dyed fabric through ultraviolet and coloured filters, which do not shield the main absorption band, showed a large decrease in the initial rate (KPA) of fading. Compared with the KPA values without filters, the values using filters were half as large for dyes without the nitro groups and a quarter as large for dyes with the nitro groups. The KPA values may be qualitatively explained by the sum of azo scission (decrease of K/S value at ,max) and the conversion of nitro groups to nitroso groups. These phenomena occur, respectively, via thermal disproportionation reactions between hydrazinyl radicals (from the azo group) and the reaction between hydrazinyl and N-centred nitrosyl hydroxide radicals (from the nitro group). The azo scission is promoted by N-centred nitrosyl hydroxide radicals via the latter reactions. [source]


    Effect of placement of calcium sulphate when used for the repair of furcation perforations on the seal produced by a resin-based material

    INTERNATIONAL ENDODONTIC JOURNAL, Issue 2 2007
    L. Zou
    Abstract Aim, To evaluate the sealing ability of calcium sulphate when used under composite resin for the repair of furcation perforations having different diameters. Methodology, Perforations of different diameter were created in the floors of pulp chambers in 60 extracted human molar teeth with either a number 3 (1 mm diameter) or 5 (1.5 mm diameter) round bur. The specimens of each group were divided into four sub-groups which were repaired with composite resin either alone or in combination with calcium sulphate that created an artificial floor (15 teeth group -1). Eight teeth without furcation perforations served as negative controls. In the leakage detection device, 1 mol L,1 glucose solution was forced under a pressure of 1.5 KPa from the crown towards the pulp chamber floor. The concentration of leaked glucose was measured at 1, 2, 4, 7, 10, 15 and 20 days using a glucose oxidase method and the data evaluated using the rank sum test. Results, The specimens with larger perforations repaired with composite resin alone had significantly more leakage (P < 0.05). Using calcium sulphate as an artificial floor significantly decreased leakage of smaller perforations (P < 0.05). In groups repaired with calcium sulphate under composite resin, leakage in smaller perforations was markedly lower than that in larger ones (P < 0.05). No significant difference was found between the specimens with 1 or 1.5 mm perforations repaired with resin alone (P > 0.05). Conclusions, Calcium sulphate significantly improved the sealing ability of 1 mm perforations repaired with composite resin but not for 1.5 mm perforations. [source]


    Insulin resistance is a major determinant of liver stiffness in nondiabetic patients with HCV genotype 1 chronic hepatitis

    ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 6 2009
    S. PETTA
    Summary Background, In patients with chronic hepatitis C (CHC), liver stiffness measurement (LSM) by transient elastography (TE), is closely related to the stage of fibrosis, but may be affected by necroinflammation. Other factors, such as insulin resistance (IR), might influence the performance of LSM. Aims, To evaluate in a cohort of nondiabetic patients with genotype 1 CHC, whether IR and other anthropometric, biochemical, metabolic and histological factors contribute to LSM and to identify the best cut-off values of LSM for predicting different stages of fibrosis. Methods, Nondiabetic patients with genotype 1 CHC (n = 156) were evaluated by liver biopsy (Metavir score), anthropometric, biochemical and metabolic features including IR. Furthermore, all subjects underwent LSM by TE. Results, Severe fibrosis (F3,F4) was associated with LSM (OR 1.291; 95%CI 1.106,1.508). LSM was also independently correlated with low platelets (P = 0.03), high ,GT (P < 0.001) and high HOMA (P = 0.004) levels. A stiffness value ,8 KPa was identified as the best cut-off for predicting severe fibrosis (AUC 0.870); yet this cut-off still failed to rule out F3,F4 fibrosis in 22.7% of patients (false-negative rate) or rule in F3,F4 in 19.6% (false-positive rate). Platelets <200 × 103/mmc and a HOMA of >2.7 were the major determinants of these diagnostic errors in predicting severe fibrosis. Conclusions, In nondiabetic patients with genotype 1 CHC, insulin resistance, ,GT and platelet levels contribute to LSM independently of liver fibrosis. The identification of these three factors contributes to a more correct interpretation of LSM. [source]


    Neutrophils display biphasic relationship between migration and substrate stiffness

    CYTOSKELETON, Issue 6 2009
    Kimberly M. Stroka
    Abstract Neutrophils are one type of migrating cell in the body's innate immune system and are the first line of defense against inflammation or infection. While extensive work exists on the effect of adhesive proteins on neutrophil motility, little is known about how neutrophil motility is affected by the mechanical properties of their physical environment. This study investigated the effects of substrate stiffness on the morphology, random motility coefficient, track speed (v), spreading area, and distribution of turning angles of neutrophils during chemokinesis. Human neutrophils were plated onto polyacrylamide gels of varying stiffness, ranging from 3 to 13 kPa, and coated with the extracellular matrix protein fibronectin, and timelapse images were taken with phase contrast microscopy. Our results show a biphasic behavior between neutrophil motility and substrate stiffness, with the optimum stiffness for motility depending on the concentration of fibronectin on the surface of the gel. On 100 ,g/mL fibronectin, the optimum stiffness is 4 kPa (v = 6.9 ± 0.6 ,m/min) while on 10 ,g/mL fibronectin, the optimum stiffness increases to 7 kPa (v = 4.5 ± 2.0 ,m/min). This biphasic behavior most likely arises because neutrophils on soft gels are less adherent, preventing production of traction forces, while neutrophils on stiff gels adhere strongly, resulting in decreased migration. At intermediate stiffness, however, neutrophils can attain optimal motility as a function of extracellular matrix coating. Cell Motil. Cytoskeleton 2009. © 2009 Wiley-Liss, Inc. [source]


    Sensitivity of alveolar macrophages to substrate mechanical and adhesive properties

    CYTOSKELETON, Issue 6 2006
    Sophie Féréol
    Abstract In order to understand the sensitivity of alveolar macrophages (AMs) to substrate properties, we have developed a new model of macrophages cultured on substrates of increasing Young's modulus: (i) a monolayer of alveolar epithelial cells representing the supple (,0.1 kPa) physiological substrate, (ii) polyacrylamide gels with two concentrations of bis-acrylamide representing low and high intermediate stiffness (respectively 40 kPa and 160 kPa) and, (iii) a highly rigid surface of plastic or glass (respectively 3 MPa and 70 MPa), the two latter being or not functionalized with type I-collagen. The macrophage response was studied through their shape (characterized by 3D-reconstructions of F-actin structure) and their cytoskeletal stiffness (estimated by transient twisting of magnetic RGD-coated beads and corrected for actual bead immersion). Macrophage shape dramatically changed from rounded to flattened as substrate stiffness increased from soft ((i) and (ii)) to rigid (iii) substrates, indicating a net sensitivity of alveolar macrophages to substrate stiffness but without generating F-actin stress fibers. Macrophage stiffness was also increased by large substrate stiffness increase but this increase was not due to an increase in internal tension assessed by the negligible effect of a F-actin depolymerizing drug (cytochalasine D) on bead twisting. The mechanical sensitivity of AMs could be partly explained by an idealized numerical model describing how low cell height enhances the substrate-stiffness-dependence of the apparent (measured) AM stiffness. Altogether, these results suggest that macrophages are able to probe their physical environment but the mechanosensitive mechanism behind appears quite different from tissue cells, since it occurs at no significant cell-scale prestress, shape changes through minimal actin remodeling and finally an AMs stiffness not affected by the loss in F-actin integrity. Cell Motil. Cytoskeleton 2006. © 2006 Wiley-Liss, Inc. [source]


    Biofeedback for foot offloading in diabetic patients with peripheral neuropathy

    DIABETIC MEDICINE, Issue 1 2010
    Z. Pataky
    Diabet. Med. 27, 61,64 (2010) Abstract Aims, The reduction of high plantar pressure in diabetic patients with peripheral neuropathy is mandatory for prevention of foot ulcers and amputations. We used a new biofeedback-based method to reduce the plantar pressure at an at-risk area of foot in diabetic patients with peripheral neuropathy. Methods, Thirteen diabetic patients (age 60.8 ± 12.3 years, body mass index 29.0 ± 5.0 kg/m2) with peripheral neuropathy of the lower limbs were studied. Patients with memory impairment were excluded. The portable in-shoe foot pressure measurement system (PEDAR®) was used for foot offloading training by biofeedback. The learning procedure consisted in sequences of walking (10 steps), each followed by a subjective estimation of performance and objective feedback. The goal was to achieve three consecutive walking cycles of 10 steps, with a minimum of seven steps inside the range of 40,80% of the baseline peak plantar pressure. The peak plantar pressure was assessed during the learning period and at retention tests. Results, A significant difference in peak plantar pressure was recorded between the beginning and the end of the learning period (when the target for plantar pressure was achieved) (262 ± 70 vs. 191 ± 53 kPa; P = 0.002). The statistically significant difference between the beginning of learning and all retention tests persisted, even at the 10-day follow-up. Conclusions, Terminal augmented feedback training may positively affect motor learning in diabetic patients with peripheral neuropathy and could possibly lead to suitable foot offloading. Additional research is needed to confirm the maintenance of offloading in the long term. [source]


    Plantar pressures in diabetic patients with foot ulcers which have remained healed

    DIABETIC MEDICINE, Issue 11 2009
    T. M. Owings
    Abstract Aims, The recurrence of foot ulcers is a significant problem in people with diabetic neuropathy. The purpose of this study was to measure in-shoe plantar pressures and other characteristics in a group of neuropathic patients with diabetes who had prior foot ulcers which had remained healed. Methods, This was an epidemiological cohort study of patients from diabetes clinics of two Swedish hospitals. From a database of 2625 eligible patients, 190 surviving patients with prior plantar ulcers of the forefoot (hallux or metatarsal heads) caused by repetitive stress were identified and 49 patients agreed to participate. Barefoot and in-shoe plantar pressures were measured during walking. Data on foot deformity, activity profiles and self-reported behaviour were also collected. Results, Mean barefoot plantar peak pressure at the prior ulcer site (556 kPa) was lower than in other published series, although the range was large (107,1192 kPa). Mean in-shoe peak pressure at this location averaged 207 kPa when measured with an insole sensor. Barefoot peak pressure only predicted ,35% of the variance of in-shoe peak pressure, indicating variation in the efficacy of the individual footwear prescriptions (primarily extra-depth shoes with custom insoles). Conclusions, We propose that the mean value for in-shoe pressures reported in these patients be used as a target in footwear prescription for patients with prior ulcers. Although plantar pressure is only one factor in a multifaceted strategy to prevent ulcer recurrence, the quantitative focus on pressure reduction in footwear is likely to have beneficial effects. [source]


    Ethnic differences in plantar pressures in diabetic patients with peripheral neuropathy

    DIABETIC MEDICINE, Issue 4 2008
    M. P. Solano
    Abstract Aims To compare plantar foot pressures between Caucasian and Hispanic diabetic patients with peripheral neuropathy (PN) without a history of foot ulceration and between Caucasian and Hispanic non-diabetic individuals. Methods Forty-four Hispanic diabetic patients with PN (HDPN), 35 Caucasian diabetic patients with PN (CDPN), 41 non-diabetic Hispanic subjects and 33 non-diabetic Caucasian subjects participated. Total and regional peak plantar pressures (PPs) and pressure time integrals (PTIs) were assessed using the EMED-SF-4 plantar pressure system. Results Hispanic diabetic patients with PN had significantly lower peak PP than Caucasian diabetic patients with PN in the entire foot (552.4 ± 227.9 vs. 810.1 ± 274.6 kPa; P < 0.001), forefoot (464.1 ± 222.6 vs. 699.6 ± 323.1 kPa; P < 0.001), hindfoot (296.3.4 + 101.8 vs. 398.1 + 178.3 kPa; P < 0.01) and at the fifth metatarsal head (MTH5; 204.3 ± 143.2 vs. 388.2 ± 273.9 kPa; P < 0.001). The PTI in the entire foot, forefoot and MTH5 were also lower in HDPN than in CDPN. The ethnic differences between the diabetic groups with PN for the entire foot, forefoot and MTH5 remained significant after adjusting for the effect of age, gender, weight and duration of diabetes. There were no significant differences in peak PP and PTI among non-diabetic individuals, except for a lower peak PP at the MTH5 in Hispanic compared with Caucasian subjects. Conclusions Despite a well-known higher incidence of foot complications in diabetic Hispanic subjects, dynamic plantar pressures are lower in Hispanic diabetic patients with PN when compared with their Caucasian counterparts, suggesting that differences in other risk factors exist between these two ethnic groups. [source]


    CEC-ESI ion trap MS of multiple drugs of abuse

    ELECTROPHORESIS, Issue 7 2010
    Zeineb Aturki
    Abstract This article describes a method for the separation and determination of nine drugs of abuse in human urine, including amphetamines, cocaine, codeine, heroin and morphine. This method was based on SPE on a strong cation exchange cartridge followed by CEC-MS. The CEC experiments were performed in fused silica capillaries (100,,m×30,cm) packed with a 3,,m cyano derivatized silica stationary phase. A laboratory-made liquid junction interface was used for CEC-MS coupling. The outlet capillary column was connected with an emitter tip that was positioned in front of the MS orifice. A stable electrospray was produced at nanoliter per minute flow rates applying a hydrostatic pressure (few kPa) to the interface. The coupling of packed CEC columns with mass spectrometer as detector, using a liquid junction interface, provided several advantages such as better sensitivity, low dead volume and independent control of the conditions used for CEC separation and ESI analysis. For this purpose, preliminary experiments were carried out in CEC-UV to optimize the proper mobile phase for CEC analysis. Good separation efficiency was achieved for almost all compounds, using a mixture containing ACN and 25,mM ammonium formate buffer at pH 3 (30:70, v/v), as mobile phase and applying a voltage of 12,kV. ESI ion-trap MS detection was performed in the positive ionization mode. A spray liquid, composed by methanol,water (80:20, v/v) and 1% formic acid, was delivered at a nano-flow rate of ,200,nL/min. Under optimized CEC-ESI-MS conditions, separation of the investigated drugs was performed within 13,min. CEC-MS and CEC-MS2 spectra were obtained by providing the unambiguous confirmation of these drugs in urine samples. Method precision was determined with RSDs values ,3.3% for retention times and ,16.3% for peak areas in both intra-day and day-to-day experiments. LODs were established between 0.78 and 3.12,ng/mL for all compounds. Linearity was satisfactory in the concentration range of interest for all compounds (r2,0.995). The developed CEC-MS method was then applied to the analysis of drugs of abuse in spiked urine samples, obtaining recovery data in the range 80,95%. [source]


    Rapid determination of acyclovir in plasma and cerebrospinal fluid by micellar electrokinetic chromatography with direct sample injection and its clinical application

    ELECTROPHORESIS, Issue 4 2006
    Hsin-Hua Yeh
    Abstract A simple MEKC with UV detection at 254,nm for analysis of acyclovir in plasma and in cerebrospinal fluid (CSF) by direct injection without any sample pretreatment is described. The separation of acyclovir from biological matrix was performed at 25°C using a BGE consisting of Tris buffer with SDS as the electrolyte solution. Several parameters affecting the separation of the drug from biological matrix were studied, including the pH and concentrations of the Tris buffer and SDS. Using dyphylline as an internal standard, the linear ranges of the method for the determination of acyclovir in plasma and in CSF all exceeded the range of 2,50,,g/mL; the detection limit of the drug in plasma and in CSF (S/N = 3; injection 3.45,kPa, 5,s) was 1.0,,g/mL. The applicability of the proposed method for determination of acyclovir in plasma and CSF collected at 8,h after intravenous administration of 500,mg acyclovir (Zovirax®) in two patients with herpes simplex encephalitis was demonstrated. [source]


    Low-voltage electroosmosis pump for stand-alone microfluidics devices

    ELECTROPHORESIS, Issue 1-2 2003
    Yuzuru Takamura
    Abstract Two types of low-voltage electroosmosis pumps were developed using microfabrication technology for usage in handy or stand-alone applications of the micrototal analysis systems (,-TAS) and the lab-on-a-chip. This was done by making a thin (<,1 ,m) region in the flow path and by only applying voltages near this thin region using electrodes inserted into the flow path. The inserted electrodes must be free from bubble formation and be gas-tight in order to avoid pressure leakage. For these electrodes, Ag/AgCl or a gel salt bridge was used. For patterning the gel on the chip, a hydrophilic photopolymerization gel and a photolithographic technique were optimized for producing a gel with higher electric conductivity and higher mechanical strength. For high flow rate application, wide (33.2 mm) and thin (400 nm) pumping channels were compacted into a 1 mm×6 mm area by folding. This pump achieves an 800 Pa static pressure and a flow of 415 nL/min at 10 V. For high-pressure application, a pump was designed with the thin and thick regions in series and positive and negative electrodes were inserted between them alternatively. This pump could increase the pumping pressure without increasing the supply voltage. A pump with 10-stage connections generated a pressure of 25 kPa at 10 V. [source]


    Aqueous films limit bacterial cell motility and colony expansion on partially saturated rough surfaces

    ENVIRONMENTAL MICROBIOLOGY, Issue 5 2010
    Gang Wang
    Summary Bacterial motility is a key mechanism for survival in a patchy environment and is important for ecosystem biodiversity maintenance. Quantitative description of bacterial motility in soils is hindered by inherent heterogeneity, pore-space complexity and dynamics of microhydrological conditions. Unsaturated conditions result in fragmented aquatic habitats often too small to support full bacterial immersion thereby forcing strong interactions with mineral and air interfaces that significantly restrict motility. A new hybrid model was developed to study hydration effects on bacterial motility. Simulation results using literature parameter values illustrate sensitivity of colony expansion rates to hydration conditions and are in general agreement with measured values. Under matric potentials greater than ,0.5 kPa (wet), bacterial colonies grew fast at colony expansion rates exceeding 421 ± 94 µm h,1; rates dropped significantly to 31 ± 10 µm h,1 at ,2 kPa; as expected, no significant colony expansion was observed at ,5 kPa because of the dominance of capillary pinning forces in the submicrometric water film. Quantification of hydration-related constraints on bacterial motion provides insights into optimal conditions for bacterial dispersion and spatial ranges of resource accessibility important for bioremediation and biogeochemical cycles. Results define surprisingly narrow range of hydration conditions where motility confers ecological advantage on natural surfaces. [source]


    Nanostructure and nanomechanics of live Phaeodactylum tricornutum morphotypes

    ENVIRONMENTAL MICROBIOLOGY, Issue 5 2008
    Grégory Francius
    Summary The ultrastructure and mechanical properties of the fusiform, triradiate and ovoid morphotypes of Phaeodactylum tricornutum were investigated using atomic force microscopy. Using topographic imaging, we showed that the surface of the ovoid form is rougher than those of the two other specimens, and coated with an outer layer of extracellular polymers. Using spatially resolved force,indentation curves, we found that the valve of the ovoid form is about five times stiffer (Young modulus of ,500 kPa) than those of the other forms (,100 kPa), a finding fully consistent with the fact that only the ovoid form has a silica valve, whereas the valves in the other two consist mostly of organic material. Notably, the girdle region of both fusiform and ovoid forms was five times softer than the valve, suggesting that this region is poor in silica and enriched in organic material. For the triradiate form, we showed the arms to be softer than the core region, presumably as a result of organelle localization. Last, we observed mucilaginous footprints of moderate stiffness (,100 kPa) in the vicinity of ovoid diatoms, which we believe are secreted extracellular polymers. [source]


    Acute CO2 tolerance during the early developmental stages of four marine teleosts

    ENVIRONMENTAL TOXICOLOGY, Issue 6 2003
    T. Kikkawa
    Abstract Ocean sequestration of CO2 is proposed as a possible measure to mitigate climate changes caused by increasing atmospheric concentrations of the gas, but its impact on the marine ecosystem is unknown. We investigated the acute lethal effect of CO2 during the early developmental stages of four marine teleosts: red sea bream (Pagrus major), Japanese whiting (Sillago japonica), Japanese flounder (Paralichthys olivaceus), and eastern little tuna (Euthynnus affinis). The percentages of larvae that hatched and survived were not affected by exposure to water with a PCO2 of 1.0 kPa (= 7.5 mmHg) within 24 h. Median lethal PCO2 values for a 360-min exposure were 1.4 kPa (cleavage), 5.1 kPa (embryo), 7.3 kPa (preflexion), 4.2 kPa (flexion), 4.6 kPa (postflexion), and 2.5 kPa (juvenile) for red sea bream; 2.4 kPa (cleavage), 4.9 kPa (embryo), 5.9 kPa (preflexion), 6.1 kPa (flexion), 4.1 kPa (postflexion), and 2.7 kPa (juvenile) for Japanese whiting; 2.8 kPa (cleavage) and > 7.0 kPa (young) for Japanese flounder; and 11.8 kPa (cleavage) for eastern little tuna. Red sea bream and Japanese whiting of all ontogenetic stages had similar susceptibilities to CO2: the most susceptible stages were cleavage and juvenile, whereas the most tolerant stages were preflexion and flexion. © 2003 Wiley Periodicals, Inc. Environ Toxicol 18: 375,382, 2003 [source]


    Arterial blood gas parameters of normal foals born at 1500 metres elevation

    EQUINE VETERINARY JOURNAL, Issue 1 2010
    E. S. HACKETT
    Summary Reasons for performing study: Arterial blood gas analysis is widely accepted as a diagnostic tool to assess respiratory function in neonates. To the authors' knowledge, there are no published reports of arterial blood gas parameters in normal neonatal foals at altitude. Objective: To provide information on arterial blood gas parameters of normal foals born at 1500 m elevation (Fort Collins, Colorado) in the first 48 h post partum. Hypothesis: Foals born at 1500 m will have lower PaO2 and PaCO2 than foals born at sea level due to low inspired oxygen and compensatory hyperventilation occurring at altitude. Methods: Sixteen foals were studied. Arterial blood gas analysis was performed within 1 h of foaling and subsequent samples were evaluated at 3, 6, 12, 24 and 48 h post partum. Data were compared to those previously reported in healthy foals born near sea level. Results: Mean PaO2 was 53.0 mmHg (7.06 kPa) within 1 h of foaling, rising to 67.5 mmHg (9.00 kPa) at 48 h post partum. PaCO2 was 44.1 mmHg (5.88 kPa) within one hour of foaling, falling to 38.3 mmHg (5.11 kPa) at 48 h. Both PaO2 and PaCO2 were significantly lower in foals born at 1500 m elevation than those near sea level at several time points during the first 48 h. Conclusions and potential relevance: Foals at 1500 m elevation undergo hypobaric hypoxia and compensatory hyperventilation in the first 48 h. Altitude specific normal arterial blood values are an important reference for veterinarians providing critical care to equine neonates. [source]


    Effect of dentin conditioning on dentin permeability and micro-shear bond strength

    EUROPEAN JOURNAL OF ORAL SCIENCES, Issue 6 2007
    Danuchit Banomyong
    The purpose of this study was to compare fluid flow rates across dentin surfaces treated with four conditioners. The effect of conditioning on the micro-shear bond strengths of glass ionomer cement (Fuji IX GP) and resin-based adhesives (Single Bond 2 or Clearfil SE Bond) were also investigated. Under a simulated pressure of 1.3 kPa, two dentin conditioners, phosphoric acid, and a self-etching primer were applied to the dentin surfaces. Dentinal fluid flows at baseline and after conditioning were recorded for 15 min each. The conditioned surfaces were examined using a scanning electron microscope. The micro-shear bond strengths of the glass ionomer cement and of the resin-based adhesives bonded to conditioned dentin surfaces were evaluated while simulated intrapulpal pressure was maintained at 0 or 1.3 kPa. Only the dentin surface etched with phosphoric acid showed a significant increase in permeability. Micro-shear bond strengths of Fuji IX GP were not affected by conditioning the dentin surfaces or by bonding at different intrapulpal pressures (0 or 1.3 kPa). The effects on bond strengths of resin-based adhesives depended on the system used. The simulated positive intrapulpal pressure during bonding significantly affected the adherence of Single Bond 2, whereas Clearfil SE Bond was unaffected. [source]


    A porous-matrix sensor to measure the matric potential of soil water in the field

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2007
    W. R. Whalley
    Summary The matric potential of soil water is probably the most useful assessment of soil water status. However, the water-filled tensiometer (the benchmark instrument for measuring matric potential) typically only operates in the range 0 to ,85 kPa. In this paper, we report the development of a porous-matrix sensor to measure matric potential in the approximate range ,50 to ,300 kPa. The sensor uses a dielectric probe to measure the water content of a ceramic material with known water retention characteristics. The calculation of matric potential takes into account hysteresis through the application of an appropriate model to measured wetting and drying loops. It is important that this model uses closed, rather than open, scanning loops. The calibrated sensors were tested in the field and the output compared with data from water-filled tensiometers and dielectric measurements of soil water content. These comparisons indicated that conventional tensiometers gave stable but false readings of matric potential when soil dried to matric potentials more negative than ,80 kPa. The porous-matrix sensors appeared to give reliable readings of matric potential in soil down to ,300 kPa and also responded appropriately to repeated wetting and drying. This porous-matrix sensor has considerable potential to help understand plant responses to drying soil. [source]


    Soil structure and pedotransfer functions

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2003
    Y.A. Pachepsky
    Summary Accurate estimates of soil hydraulic properties from other soil characteristics using pedotransfer functions (PTFs) are in demand in many applications, and soil structural characteristics are natural candidates for improving PTFs. Soil survey provides mostly categorical data about soil structure. Many available characteristics such as bulk density, aggregate distribution, and penetration resistance reflect not only structural but also other soil properties. Our objective here is to provoke a discussion of the value of structural information in modelling water transport in soils. Two case studies are presented. Data from the US National Pedon Characterization database are used to estimate soil water retention from categorical field-determined structural and textural classes. Regression-tree estimates have the same accuracy as those from textural class as determined in the laboratory. Grade of structure appears to be a strong predictor of water retention at ,33 kPa and ,1500 kPa. Data from the UNSODA database are used to compare field and laboratory soil water retention. The field-measured retention is significantly less than that measured in the laboratory for soils with a sand content of less than 50%. This could be explained by Rieu and Sposito's theory of scaling in soil structure. Our results suggest a close relationship between structure observed at the soil horizon scale and structure at finer scales affecting water retention of soil clods. Finally we indicate research needs, including (i) quantitative characterization of the field soil structure, (ii) an across-scale modelling of soil structure to use fine-scale data for coarse-scale PTFs, (iii) the need to understand the effects of soil structure on the performance of various methods available to measure soil hydraulic properties, and (iv) further studies of ways to use soil,landscape relationships to estimate variations of soil hydraulic properties across large areas of land. [source]


    Pressure plate studies to determine how moisture affects access of bacterial-feeding nematodes to food in soil

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2002
    G.W. Yeates
    Summary Nematode activity in the soil depends on the presence of free water. We conducted pressure plate experiments to understand better how soil matric potential and structural degradation affect the population growth of three bacterial-feeding nematodes (Cephalobus, Pristionchus, Rhabditis). We took undisturbed cores from six soils (sand, silt loam and silty clay loam with four management regimes), and removed all fauna from them. Ten or 30 nematodes were added, and pressures corresponding to soil matric potentials of ,10, ,33, ,50, ,100 or ,1500 kPa were applied for 35 days. The nematodes were then counted. Significant reproduction of all bacterial-feeding nematodes occurred when the diameters of water-filled pores were approximately 1 ,m. This confirms observations using repacked soils and field manipulations. Only for Pristionchus did declining populations match the reduction in total soil porosity related to intensification of land use on the silty clay loam. We had not expected Cephalobus to have the fastest increase in population of the three nematodes in intact soil cores, and our evidence questions the relative importance given to the three nematode families in soil processes. The differing rates of population increase of the three nematodes in the various soils reflect both habitable pore space and trophic interactions. This suggests that the very diversity of nematode assemblages is crucial in the resilience of biological soil processes. That water-filled pores as small as 1 ,m provide suitable spaces for sizeable populations of bacterial-feeding nematodes accords with the observed migration of infective juveniles of trichostrongylid nematodes and mermithids in water films on herbage. Our results imply that assessment of the role of nematodes in soil processes may be a key to the understanding of biological interactions in water films, and the selection pressures on nematode morphology. [source]


    Effects of Ischaemia on Subsequent Exercise-Induced Oxygen Uptake Kinetics in Healthy Adult Humans

    EXPERIMENTAL PHYSIOLOGY, Issue 2 2002
    Michael L. Walsh
    Leg muscles were occluded (33 kPa) prior to exercise to determine whether the induced metabolic changes, and reactive hyperaemia upon occlusion release just prior to the exercise, would accelerate the subsequent oxygen consumption (V,O2) response. Eight subjects performed double bouts (6 min duration, 6 min rest in-between) of square wave leg cycle ergometry both below and above their lactate threshold (LT). Prior to exercise, large blood pressure cuffs were put around the upper thighs. Occlusion durations were 0 min (control), 5 min and 10 min. Ischaemia was terminated within 5 s prior to exercise onset. Heart rate, V,O2, ventilatory rate (V,E), electromyogram (EMG) and haemoglobin/myoglobin (Hb/Mb) saturation were recorded continuously. Single exponential modelling demonstrated that, compared to control (time constant = 53.9 ± 13.9 s), ischaemia quickened the V,O2 response (P < 0.05) for the first bout of exercise above LT (time constant = 48.3 ± 14.5 s) but not to any other exercise bout below or above LT. The 3-6 min integrated EMG (iEMG) slope was correlated to the 3-6 min V,O2 slope (r = 0.73). Hb/Mb saturation verified the ischaemia but did not show a consistent relation to the V,O2 time course. Reactive hyperaemia induced a faster V,O2 response for work rates above LT. The effect, while significant, was not large considering the expected favourable metabolic and circulatory changes induced by ischaemia. [source]


    Body Position and Cardiac Dynamic and Chronotropic Responses to Steady-State Isocapnic Hypoxaemia in Humans

    EXPERIMENTAL PHYSIOLOGY, Issue 2 2000
    S. Deborah Lucy
    Neural mediation of the human cardiac response to isocapnic (IC) steady-state hypoxaemia was investigated using coarse-graining spectral analysis of heart rate variability (HRV). Six young adults were exposed in random order to a hypoxia or control protocol, in supine and sitting postures, while end-tidal PCO2 (PET,CO2) was clamped at resting eucapnic levels. An initial 11 min period of euoxia (PET,O2 100 mmHg; 13.3 kPa) was followed by a 22 min exposure to hypoxia (PET,O2 55 mmHg; 7.3 kPa), or continued euoxia (control). Harmonic and fractal powers of HRV were determined for the terminal 400 heart beats in each time period. Ventilation was stimulated (P < 0.05) and cardiac dynamics altered only by exposure to hypoxia. The cardiac interpulse interval was shortened (P < 0.001) similarly during hypoxia in both body positions. Vagally mediated high-frequency harmonic power (Ph) of HRV was decreased by hypoxia only in the supine position, while the fractal dimension, also linked to cardiac vagal control, was decreased in the sitting position (P < 0.05). However, low-frequency harmonic power (Pl) and the HRV indicator of sympathetic activity (Pl/Ph) were not altered by hypoxia in either position. These results suggest that, in humans, tachycardia induced by moderate IC hypoxaemia (arterial O2 saturation Sa,O2, 85%) was mediated by vagal withdrawal, irrespective of body position and resting autonomic balance, while associated changes in HRV were positionally dependent. [source]


    Chemotactic response of plant-growth-promoting bacteria towards roots of vesicular-arbuscular mycorrhizal tomato plants

    FEMS MICROBIOLOGY ECOLOGY, Issue 3 2003
    Sushma Gupta Sood
    Abstract The chemotactic responses of the plant-growth-promoting rhizobacteria Azotobacter chroococcum and Pseudomonas fluorescens to roots of vesicular-arbuscular mycorrhizal (Glomus fasciculatum) tomato plants were determined. A significantly (P=0.05) greater number of bacterial cells of wild strains were attracted towards vesicular-arbuscular mycorrhizal tomato roots compared to non-vesicular-arbuscular mycorrhizal tomato roots. Substances exuded by roots served as chemoattractants for these bacteria. P. fluorescens was strongly attracted towards citric and malic acids, which were predominant constituents in root exudates of tomato plants. A. chroococcum showed a stronger response towards sugars than amino acids, but the response was weakest towards organic acids. The effects of temperature, pH, and soil water matric potential on bacterial chemotaxis towards roots were also investigated. In general, significantly (P=0.05) greater chemotactic responses of bacteria were observed at higher water matric potentials (0, ,1, and ,5 kPa), slightly acidic to neutral pH (6, 6.5 and 7), and at 20,30°C (depending on the bacterium) than in other environmental conditions. It is suggested that chemotaxis of P. fluorescens and A. chroococcum towards roots and their exudates is one of the several steps in the interaction process between bacteria and vesicular-arbuscular mycorrhizal roots. [source]


    Last-century changes of alpine grassland water-use efficiency: a reconstruction through carbon isotope analysis of a time-series of Capra ibex horns

    GLOBAL CHANGE BIOLOGY, Issue 4 2010
    INĘS C. R. BARBOSA
    Abstract The ecophysiological response of an alpine grassland to recent climate change and increasing atmospheric CO2 concentration was investigated with a new strategy to go back in time: using a time-series of Capra ibex horns as archives of the alpine grasslands' carbon isotope discrimination (13,). From the collection of the Natural History Museum of Bern, horns of 24 males from the population of the Augstmatthorn,Brienzer Rothorn mountains, Switzerland, were sampled covering the period from 1938 to 2006. Samples were taken from the beginning of each year-ring of the horns, representing the beginning of the horn growth period, the spring. The horns' carbon 13C content (,13C) declined together with that of atmospheric CO2 over the 69-year period, but 13, increased slightly (+0.4,), though significantly (P<0.05), over the observation period. Estimated intercellular CO2 concentration increased (+56 ,mol mol,1) less than the atmospheric CO2 concentration (+81 ,mol mol,1), so that intrinsic water-use efficiency increased by 17.8% during the 69-year period. However, the atmospheric evaporative demand at the site increased by approximately 0.1 kPa between 1955 and 2006, thus counteracting the improvement of intrinsic water-use efficiency. As a result, instantaneous water-use efficiency did not change. The observed changes in intrinsic water-use efficiency were in the same range as those of trees (as reported by others), indicating that leaf-level control of water-use efficiency of grassland and forests followed the same principles. This is the first reconstruction of the water-use efficiency response of a natural grassland ecosystem to last century CO2 and climatic changes. The results indicate that the alpine grassland community has responded to climate change by improving the physiological control of carbon gain to water loss, following the increases in atmospheric CO2 and evaporative demand. But, effective leaf-level water-use efficiency has remained unchanged. [source]


    Increased leaf area dominates carbon flux response to elevated CO2 in stands of Populus deltoides (Bartr.)

    GLOBAL CHANGE BIOLOGY, Issue 5 2005
    Ramesh Murthy
    Abstract We examined the effects of atmospheric vapor pressure deficit (VPD) and soil moisture stress (SMS) on leaf- and stand-level CO2 exchange in model 3-year-old coppiced cottonwood (Populus deltoides Bartr.) plantations using the large-scale, controlled environments of the Biosphere 2 Laboratory. A short-term experiment was imposed on top of continuing, long-term CO2 treatments (43 and 120 Pa), at the end of the growing season. For the experiment, the plantations were exposed for 6,14 days to low and high VPD (0.6 and 2.5 kPa) at low and high volumetric soil moisture contents (25,39%). When system gross CO2 assimilation was corrected for leaf area, system net CO2 exchange (SNCE), integrated daily SNCE, and system respiration increased in response to elevated CO2. The increases were mainly as a result of the larger leaf area developed during growth at high CO2, before the short-term experiment; the observed decline in responses to SMS and high VPD treatments was partly because of leaf area reduction. Elevated CO2 ameliorated the gas exchange consequences of water stress at the stand level, in all treatments. The initial slope of light response curves of stand photosynthesis (efficiency of light use by the stand) increased in response to elevated CO2 under all treatments. Leaf-level net CO2 assimilation rate and apparent quantum efficiency were consistently higher, and stomatal conductance and transpiration were significantly lower, under high CO2 in all soil moisture and VPD combinations (except for conductance and transpiration in high soil moisture, low VPD). Comparisons of leaf- and stand-level gross CO2 exchange indicated that the limitation of assimilation because of canopy light environment (in well-irrigated stands; ratio of leaf : stand=3.2,3.5) switched to a predominantly individual leaf limitation (because of stomatal closure) in response to water stress (leaf : stand=0.8,1.3). These observations enabled a good prediction of whole stand assimilation from leaf-level data under water-stressed conditions; the predictive ability was less under well-watered conditions. The data also demonstrated the need for a better understanding of the relationship between leaf water potential, leaf abscission, and stand LAI. [source]


    Pure-Phase Transport and Dissolution of TCE in Sedimentary Rock Saprolite

    GROUND WATER, Issue 3 2006
    M. Lenczewski
    The objective of this study was to experimentally determine the influence of pore structure on the transport and dissolution of trichloroethylene (TCE) in clay-rich saprolite. In order to simulate a "spill," pure-phase TCE containing a water-insoluble fluorescent dye was injected into two heterogeneous 24-cm-diameter by 37-cm-long undisturbed columns of water-saturated saprolite. TCE entry occurred at capillary pressures of 2.7 and 4.0 kPa. Ten or 28 d after injection, the column was sliced horizontally into three sections and visually examined. The distribution of fluorescent dye indicated that pure-phase TCE migrated mainly through fractures in the shale saprolite and through fine root holes or other macropores in the limestone saprolite residuum. Analysis of saprolite subsamples indicated that TCE was present throughout much of the saprolite column but usually at concentrations less than the solubility of TCE. This spreading was caused by diffusion, which also contributed to the rapid dissolution of TCE in the fractures and macropores. Modeling was carried out using previously published dissolution and diffusion equations. The calculations confirm that rapid disappearance of immiscible TCE can occur in this type of material because of the small size of fracture or macropore openings and the high porosity of the fine-grained material. This study indicates that industrial solvents can readily enter fractures and macropores in otherwise very fine-grained subsoils and then rapidly dissolve and diffuse into the fine-pore structure, fromc which they may be very difficult to remove. [source]


    Kinetics of Calcium Carbonate (CaCO3) Precipitation from a Icel-Yavca Dolomite Leach Solution by a Gas (Carbon Dioxide)/Liquid Reaction

    HELVETICA CHIMICA ACTA, Issue 3 2009
    Mehmet Yildirim
    Abstract The effects of time, CO2 -gas-injection pressure, and bulk temperature on the precipitation of Ca2+ ions as a precipitated calcium carbonate (PCC) from a dolomite leach solution were investigated. Precipitation periods from 1 to 7,min were examined, and experiments were run at CO2 -injection pressures of 200,800,kPa. Effects of bulk temperature were studied in the range from 40 to 70°, and precipitation rates of PCC were determined by measuring the Ca2+ concentrations in the initial and effluent solutions. Influences of these parameters on the subsequent incorporation of Mg2+ ions with the precipitate are discussed in detail. Kinetic analysis of the precipitation was performed by considering the rates as a function of CO -ion concentrations. Results obtained by this process clearly show that Ca2+ ions in the solution can successfully be precipitated as a calcium carbonate product containing 54.70% of CaO and 0.77% MgO, at the rate of 2.01,mM h,1. [source]


    Liver stiffness identifies two different patterns of fibrosis progression in patients with hepatitis C virus recurrence after liver transplantation,

    HEPATOLOGY, Issue 1 2010
    José A. Carrión
    Significant liver fibrosis (F , 2) and portal hypertension (hepatic venous pressure gradient [HVPG] , 6 mmHg) at 1 year after liver transplantation (LT) identify patients with severe hepatitis C recurrence. We evaluated whether repeated liver stiffness measurements (LSM) following LT can discriminate between slow and rapid "fibrosers" (fibrosis stage F2-F4 at 1 year after LT). Eighty-four patients who had undergone LT and who were infected with hepatitis C virus (HCV) and 19 LT controls who were not infected with HCV underwent LSM at 3, 6, 9, and 12 months after LT. All HCV-infected patients underwent liver biopsy 12 months after LT (paired HVPG measurements in 74); 31 (37%) were rapid fibrosers. Median LSM (in kilopascal) at months 6, 9, and 12 were significantly higher in rapid fibrosers (9.9, 9.5, 12.1) than in slow fibrosers (6.9, 7.5, 6.6) (P < 0.01 all time points). The slope of liver stiffness progression (kPa × month) in rapid fibrosers (0.42) was significantly greater than in slow fibrosers (0.05) (P < 0.001), suggesting two different speeds of liver fibrosis progression. Figures were almost identical for patients with HVPG , 6 mmHg or HVPG < 6 mmHg at 1 year after LT. Multivariate analysis identified donor age, bilirubin level, and LSM as independent predictors of fibrosis progression and portal hypertension in the estimation group (n = 50) and were validated in a second group of 34 patients. The areas under the receiver operating characteristic curve that could identify rapid fibrosers and patients with portal hypertension as early as 6 months after LT were 0.83 and 0.87, respectively, in the estimation group and 0.75 and 0.80, respectively, in the validation group. Conclusion: Early and repeated LSM following hepatitis C recurrence in combination with clinical variables discriminates between rapid and slow fibrosers after LT. (HEPATOLOGY 2009.) [source]


    Prospective risk assessment for hepatocellular carcinoma development in patients with chronic hepatitis C by transient elastography,

    HEPATOLOGY, Issue 6 2009
    Ryota Masuzaki
    Liver stiffness, noninvasively measured by transient elastography, correlates well with liver fibrosis stage. The aim of this prospective study was to evaluate the liver stiffness measurement (LSM) as a predictor of hepatocellular carcinoma (HCC) development among patients with chronic hepatitis C. Between December 2004 and June 2005, a total of 984 HCV-RNA positive patients, without HCC or a past history of it, visited the University of Tokyo Hospital. LSM was performed successfully in 866 patients, who gave informed consent. During the follow-up period (mean, 3.0 years), HCC developed in 77 patients (2.9% per 1 person-year). The cumulative incidence rates of HCC at 1, 2, and 3 years were 2.4%, 6.0%, and 8.9%, respectively. Adjusting for other significant factors for HCC development, patients with higher LSM were revealed to be at a significantly higher risk, with a hazard ratio, as compared to LSM ,10 kPa, of 16.7 (95% confidence interval [CI], 3.71-75.2; P < 0.001) when LSM 10.1-15 kPa, 20.9 (95% CI, 4.43-98.8; P < 0.001) when LSM 15.1-20 kPa, 25.6 (95%CI, 5.21-126.1; P < 0.001) when LSM 20.1-25 kPa, and 45.5 (95% CI, 9.75-212.3; P < 0.001) when LSM >25 kPa. Conclusions: This prospective study has shown the association between LSM and the risk of HCC development in patients with hepatitis C. The utility of LSM is not limited to a surrogate for liver biopsy but can be applied as an indicator of the wide range of the risk of HCC development. (HEPATOLOGY 2009.) [source]


    Usefulness of transient elastography for assessment of liver fibrosis in chronic hepatitis B: Regression of liver stiffness during entecavir therapy

    HEPATOLOGY RESEARCH, Issue 9 2010
    Masaru Enomoto
    Aim:, The usefulness of transient elastography remains to be validated in chronic hepatitis B, particularly as a tool for monitoring the degree of liver fibrosis during treatment. Methods:, The subjects were 50 patients with chronic hepatitis B virus infection. Liver biopsy was performed in 38 patients, and in 12 patients with platelet counts of 50 × 109/L or less, cirrhosis was clinically diagnosed on the basis of specific signs of portal hypertension. Liver stiffness was measured by transient elastography at baseline and after 12 months of treatment in 20 nucleos(t)ide-naďve patients who started entecavir within 3 months after study entry. Results:, Twenty (40%) patients were classified as F1, 10 (20%) as F2, 5 (10%) as F3, and 15 (30%) as F4 (cirrhosis). Median liver stiffness (interquartile range) was 7.0 kPa (5.6,9.4), 9.8 kPa (5.6,14.7), 9.8 kPa (7.6,12.9), and 17.3 kPa (8.2,27.6) in fibrosis stages F1 to F4, respectively. Liver stiffness significantly correlated with fibrosis stage (r = 0.46; P = 0.0014). Of the patients who started entecavir, median liver stiffness significantly decreased from 11.2 kPa (7.0,15.2) to 7.8 kPa (5.1,11.9; P = 0.0090) during 12 months of treatment. Median levels of amino-terminal peptide of type III procollagen and type IV collagen 7S domain in serum significantly decreased from 0.9 (0.6,1.3) to 0.6 (0.5,0.7) U/mL (P = 0.0010) and from 5.0 (4.4,6.7) to 3.9 (3.2,4.4) ng/mL (P = 0.015), respectively. Conclusion:, Liver stiffness measurement can be useful for monitoring regression of liver fibrosis during entecavir treatment in patients with chronic hepatitis B virus infection. [source]


    Polar-Molecule-Dominated Electrorheological Fluids Featuring High Yield Stresses

    ADVANCED MATERIALS, Issue 45 2009
    Rong Shen
    Abstract Recent works on the development of various electrorheological (ER) fluids composed of TiO2, SrTiO, and CaTiO particles coated with CO/HO polar groups are summarized, in which an extremely large yield stress up to 200,kPa is measured and the dynamical yield stress reaches 117,kPa at a shear rate of 775,s,1. Moreover, unlike that of traditional dielectric ER fluids, the yield stress displays a linear dependence on electric field strength. Experimental results reveal that it is the polar molecules adsorbed onto the dielectric particles that play the decisive role: the polar-molecule-dominated ER effect arises from the alignment of polar molecules by the enhanced local electric field in the gap between neighboring particles. The pretreatment of electrodes and the contrivance of new measuring procedures, which are desirable for the characterization and practical implementation of this material, are also discussed. The successful synthesis of these fluids has made many of the long since conceived applications of the ER effect available. [source]