Decreasing Concentration Gradient Research Articles

Dissecting the importance and origin of circulating myokines in gastric cancer cachexia

BackgroundSome experimental data suggest that myokines may play an important role in developing cancer-associated cachexia (CAC), but their relevance in humans remains poorly explored. In our study, we tested the hypothesis that circulating myokines are associated with the pathogenesis of CAC in a model population of gastric cancer.MethodsA group of 171 treatment naïve patients with adenocarcinoma of the stomach were prospectively examined. Cachexia was defined as weight loss >5% or weight loss >2% with either BMI <20 kg/m2 or sarcopenia. A panel of 19 myokines was measured in portal and peripheral blood as well as tumour tissue and surrounding gastric mucosa. Moreover, a serum proteomic signature of cachexia was identified by a label-free quantitative proteomics with a nano LC-MS/MS system and stored in a ProteomeXchange database (PXD049334).ResultsOne hundred (58%) patients were diagnosed with CAC. The concentrations of fatty acid-binding protein 3 (FABP3), follistatin-like 1 protein (FSTL−1), interleukin 6 (IL 6), and interleukin 8 (IL 8) were significantly higher in the peripheral blood of cachectic subjects, while leptin levels were lower. Of all the evaluated myokines, tumour tissues showed higher expression levels only for IL-15 and myostatin. However, the analysis of paired samples failed to demonstrate a decreasing concentration gradient between the portal and peripheral blood for any of the myokines, evidencing against their release by the primary tumour. Proteomic analysis identified 28 proteins upregulated and 24 downregulated in the peripheral blood of patients with cachexia. Differentially expressed proteins and 5 myokines with increased serum levels generated a significant protein-protein interaction network.ConclusionsOur study provides clinical evidence that some myokines are involved in the pathogenesis of cachexia and are well integrated into the regulatory network of circulating blood proteins identified among cachectic patients with gastric cancer.

New approach to predict impurity concentration in high-purity antimony metal prepared by vacuum distillation

Previous studies have shown that there is a significant difference in impurity concentration in the distillate, resulting in an unclear average impurity concentration in the distilled product. To address this issue, a variation model of impurity average concentration in the distillate was developed based on the mass conservation of the solute during the vacuum distillation process. Five continuous distillation experiments of crude antimony (Sb) metal were carried out to obtain the variation regularity of impurity average concentration in the distillate, and two verification experiments of vacuum distillation were conducted to verify the model. The research results showed that, the concentration of As impurity in residue decreases exponentially as the distillation proceeds, whereas the concentration of Bi impurity increases exponentially; there are the increasing and decreasing concentration gradients of As and Bi impurities in the distillate along with the decreasing condensing temperature, respectively; the average concentrations of As and Bi impurities in the distillate present the linearly decreasing and exponentially increasing tendency, respectively; the calculated values of As and Bi impurities average concentrations in the distillate are in good agreement with the values of two verification experiments, confirming the efficacy of the model.

Mobility and lability of phosphorus from highly concentrated fertiliser bands

In order to improve crop nutrition, phosphorus (P) fertiliser is increasingly being applied in concentrated bands. Although information is available regarding the sequence of reactions that occur within the band itself, comparatively little is known regarding the reactions controlling P diffusion and availability further away from fertiliser bands. In particular, no previous experiments have utilised in situ methods to examine P speciation with increasing distance from the band. The present study used two contrasting soils in an incubation experiment to investigate the impact of soil characteristics, form of P fertiliser, and the co-application of potassium (K) on changes in P speciation and availability up to 40 mm away from the fertosphere (i.e., volume of soil which includes the fertiliser band and the fertiliser-enriched soil immediately adjacent band). Precipitation of aluminium-P (Al-P) minerals were important for regulating P availability within the fertosphere itself, with this precipitation of Al-P minerals largely driven by changes in fertosphere pH (soluble Al) and solution P. However, adsorption processes were important for controlling P diffusion from the band, primarily by decreasing concentration gradients between the fertosphere and bulk soil. The choice of P fertiliser form was more important in the soil with a low P sorption capacity, where the pH of the fertiliser saturation solution strongly influenced precipitation reactions and P availability. Co-application of K with P fertilisers had the greatest impact on P availability in the soil with a higher concentration of exchangeable cations – these cations could be displaced by the K and precipitate with P. This study therefore demonstrates that P distribution is influenced by soil characteristics, but that P availability is primarily impacted by fertiliser choice and the composition of the nutrient blend in the fertosphere – these findings have important implications for improving P use efficiency in cropping systems.

CO2 Hydrate dissolution rates in unsaturated water quantified with laboratory experiments

Measuring the dissolution rates of CO2 hydrates in marine environments is urgently needed because CO2 hydrate is a powerful means in CO2 ocean sequestration as well as a product of CO2-CH4 gas replacement in hydrate exploitation. The stability of CO2 hydrates is a significant index to evaluate the feasibility of gas hydrate technologies. It is generally agreed that the dissolution of hydrates is diffusion-controlled rather than reaction-controlled. In this work, the dissolution rates of CO2 hydrates in sediments under a variety of experimental conditions were calculated by the CO2 fluxes and mass balance. The in situ CO2 concentrations in static and flowing water layers were measured by Raman spectroscopy. Firstly, the dissolution rates of CO2 hydrate in sediments in different diffusion stages were 314 to 3.5 cm/year and 194 to 1.2 cm/year in static deionized water and brine layer, respectively. The CO2 hydrate underwent a rapid dissolution stage in the beginning of the experiment. Then the dissolution rate slowed down because of the decreasing concentration gradients. The difference of dissolution rates between deionized water and brine is related to the CO2 solubility in different solutions. CO2 hydrates covered with sediments dissolved much slower than hydrates dissolved in direct contact with water layers due to the increased diffusion boundary layers and the decreased diffusion coefficients. Additionally, the dissolution rates of CO2 hydrate that exposed to a variety of flow rates showed a strong velocity dependency. In this work, the dissolution rates of CO2 hydrate under flowing water layers ranged from 5.6 to 365 cm/year with volume flow rates ranged from 1.01 to 8.57 ml/min.

Spatial distribution and air−water exchange of organophosphate esters in the lower Great Lakes

Organophosphate esters (OPEs) have been detected at elevated concentrations in the Great Lakes region, dwarfing other flame retardants, such as polybrominated diphenylethers (PBDEs), as chemicals of emerging concern (CECs). This prompted us to deploy polyethylene (PE) passive samplers in air and water column of the lower Great Lake region (Lake Erie and Lake Ontario) to detect gaseous and dissolved OPEs, evaluate their occurrence and spatial distribution, and estimate their air-water gas exchange fluxes. The median concentration of the total dissolved and gaseous phase OPEs detected (Σ9OPEs) were 95 ng L−1 and 404 pg m−3, respectively, during April–November 2014. Gaseous and dissolved concentrations were dominated by chlorinated compounds, in particular (tris(2-chloroethyl) phosphate (TCEP) and tris(2-chloroisopropyl) phosphate (TCPP), while tri-n-butyl phosphate (TnBP) was the dominant non-chlorinated OPEs in both media. Decreasing concentration gradients from shoreline/nearshore to offshore sites for both gaseous and aqueous OPEs reflect anthropogenic influence from the adjacent rural and urban regions. The partial dependence of gaseous OPEs on temperature indicate the importance of volatilization from local sources, fresh emissions as well as advection from distant sources to air. Almost all OPEs underwent net gas-phase deposition to the lakes, dominated by TCEP and TCPPs with median fluxes of −3980 ng/m2/day and −1320 ng/m2/day; the exception was TnBP, which underwent volatilization with the median fluxes of 1980 ng/m2/day. For all air-water pairs, the gaseous diffusive fluxes were 2–4 orders of magnitude greater than the estimated particle dry deposition fluxes.

Effects of n-heptane concentration on ignition characteristics and flame propagation of dual fuel combustion under engine-like conditions

Natural gas/diesel dual fuel combustion mode is one of the most attractive strategies to achieve ultra-low emissions and efficient combustion in transportation sector. This paper numerically investigated the effects of n-heptane concentration on dual fuel combustion characteristics in terms of ignition and flame development in low-speed engine environments. The results indicate that with the decrease of fuel equivalence ratio, the ignition of dual fuel mixture is delayed and occurs in the leaner fuel mixture. The evolution of heat release rate (HRR) transfers from double peaks to single peak as the fuel equivalence ratio decreases and only rapid growth stage appears in the evolution process of peak temperature Tpeak for the case of Φfuel=2. With the development of dual fuel flame, Tpeak is maintained at the mixture fraction close to ξst, but the flame front still moves to the premixed methane/air mixtures side in physical space. Moreover, the flame propagation between the onset of ignition and the appearance of maximum Tpeak is shortened with the decreasing n-heptane concentration. It is also shown that the characteristic time τmax firstly decreases and then increases with the decrease of fuel equivalence ratio, and the minimum appears in the case with equivalence ratio of Φfuel=4. Meanwhile, the distribution of chemical explosion mode (CEM) becomes wider as the fuel equivalence ratio decreases. With the decreasing concentration gradient, the flame structure with low-intermediate-high temperature exothermic co-existence is formed in the rich fuel region, and it changes to double flame structure gradually as the combustion reaction proceeds. The low concentration gradient produced by the decreasing fuel equivalence ratio affects rection pathways of fuel molecules, which further influences the origination of ignition, flame structure and flame propagation process.

Gas Component Transport Across the Soil‐Atmosphere Interface for Gases of Different Density: Experiments and Modeling

AbstractWe investigate the influence of near‐surface wind conditions on subsurface gas transport and on soil‐atmosphere gas exchange for gases of different density. Results of a sand tank experiment are supported by a numerical investigation with a fully coupled porous medium‐free flow model, which accounts for wind turbulence. The experiment consists of a two‐dimensional bench‐scale soil tank containing homogeneous sand and an overlying wind tunnel. A point source was installed at the bottom of the tank. Gas concentrations were measured at multiple horizontal and vertical locations. Tested conditions include four wind velocities (0.2/1.0/2.0/2.7 m/s), three different gases (helium: light, nitrogen: neutral, and carbon dioxide: heavy), and two transport cases (1: steady‐state gas supply from the point source; 2: transport under decreasing concentration gradient, subsequent to termination of gas supply). The model was used to assess flow patterns and gas fluxes across the soil surface. Results demonstrate that flow and transport in the vicinity of the surface are strongly coupled to the overlying wind field. An increase in wind velocity accelerates soil‐atmosphere gas exchange. This is due to the effect of the wind profile on soil surface concentrations and due to wind‐induced advection, which causes subsurface horizontal transport. The presence of gases with pronounced density difference to air adds additional complexity to the transport through the wind‐affected soil layers. Wind impact differs between tested gases. Observed transport is multidimensional and shows that heavy as well as light gases cannot be treated as inert tracers, which applies to many gases in environmental studies.

Prediction of Negative Food‐Effect on Drug Bioavailability by Mechanistic Biopharmaceutics Classification System (mBCS)‐guided Physiologically‐based Pharmacokinetic modeling

Food can influence drug bioavailability by altering gut physiology and microenvironment. Conventional approaches such as dissolution testing and biopharmaceutics classification system (BCS) often fail to predict food effect on drug bioavailability. To address this, we proposed a mechanistic BCS (mBCS) (Figure 1) based on analysing literature data. The mBCS first classifies drugs based on if their absorption is solubility‐limited (Class I) or permeability‐limited (Class II), which are sub‐grouped based on if the food effect is predictable (IA and IIA) or not predictable (IB, IC, IIB and IIC) using the dissolution testing (Figure 1A). Finally, mBCS allows identifying the mechanisms that lead to unpredictable food‐effect on drug bioavailability. Particularly, out of 288 drugs where the food‐effect data were reported, 105 drugs exhibited negative food effect. Further evaluation suggested that the primary reason for the unpredictable negative food effect is the interplay of intestinal efflux transport and delayed gastric emptying (Figure 1B). For example, amongst all drugs that showed negative food effect, majority (58%) were substrates of GI efflux transporters (e.g., maraviroc, afatinib, furosemide, ixazomib, asciminib, and omadacycline). We thus hypothesized that since gastric emptying time in fed state is higher (>2 h) as compared to the fasting state (15 min), drug co‐administration with food results in decreased concentration gradient across intestinal wall (lumen to blood), which eventually causes desaturation of GI efflux transporters. To test this hypothesis, we developed an mBCS‐guided physiologically based pharmacokinetic (PBPK) model in MATLAB (MathWorks, Natick, MA) by incorporating the regional protein abundance and saturation kinetics (Km and Vmax) of selected drugs (maraviroc, afatinib, and furosemide). The results from maraviroc PBPK modeling are presented below. The model was successful in predicting non‐linear PK within 2‐fold at varied dose ranges (e.g., 0.5, 0.61, 0.88, 1.17, 1.07 and 1.02 folds for 30, 100, 300, 600, 900 and 1200 mg, respectively for maraviroc) in the fasted state. The model successfully captured ~37% reduction in AUC in fed state at lower clinical doses of 100 and 300 mg of maraviroc. Similarly, consistent with the observed clinical data 1, the predicted magnitude of negative food effect was significantly lower (~22 and 18% reduction in AUC) at higher doses of 900 and 1200 mg, respectively. Parameter sensitivity analysis showed that gastric emptying time and kinetic parameters of P‐gp are important mechanisms that regulate non‐linear PK and food effect for maraviroc. Therefore, the proposed mBCS‐guided PBPK modeling approach can be used for prospective prediction of negative food effect, which can also be used to justify clinical trial waiver for the food effect studies.Support or Funding InformationDepartment of Pharmaceutical Sciences, Washington State University, SpokaneMechanistic biopharmaceutics classification system (mBCS) framework (A) and proposed mechanism of interplay between GI efflux and gastric emptying in fasting and fed states for mBCS class‐IIC drugs (B).Figure 1

Tension enhances cell proliferation and collagen synthesis by upregulating expressions of integrin αvβ3 in human keloid-derived mesenchymal stem cells

AimsKeloids are a dermal fibrotic disease whose etiology remains totally unknown and for which there is no successful treatment. Mechanical tension, in addition, is closely associated with the germination and development of keloids. In this study, we investigated the influence of human keloid-derived mesenchymal stem cells (KD-MSCs) on cell proliferation, collagen synthesis, and expressions of integrin αvβ3 under tension. Main methodsKD-MSCs and human normal skin-derived mesenchymal stem cells (NS-MSCs) were isolated and cultured in stem cell medium with a gradual increase in the serum concentration. Cell proliferation and collagen synthesis were detected by Cell Counting Kit-8 (CCK-8) assay and hydroxyproline content analysis under tension respectively. We investigated the messenger RNA expressions of nine integrin subunits, including integrin units α2, α3, α5, αv, α8, α10, α11, β1, and β3, in KD-MSCs stimulated with tension. Identification of differentially expressed genes was performed by Western blot analysis and immunocytochemistry staining. Key findingsWe obtained high-purity KD-MSCs and NS-MSCs using the culture method of decreasing serum concentration gradient gradually. Furthermore, we found that tension enhances cell proliferation and collagen synthesis and promotes expressions of integrin αvβ3 in KD-MSCs. In addition, blocking experiments showed that increased integrin αvβ3 expression affects cell proliferation and collagen synthesis of KD-MSCs under tension. SignificanceOur results suggest that integrin αvβ3 receptor may be sensitive molecules of mechanical tension and could contribute to the occurrence and development of keloids. It could lead to novel targets for therapeutic intervention, treatment, and prevention of recurrence for keloid disorders.

Hydrocarbon and sewage contamination near fringing reefs along the west coast of Havana, Cuba: A multiple sedimentary molecular marker approach

Organic contamination is a major environmental concern in coastal regions, and it can be evaluated by the determination of aliphatic hydrocarbons (AHs), polycyclic aromatic hydrocarbons (PAHs), faecal sterols and linear alkylbenzenes (LABs). The concentrations of these organic markers were obtained from nine surface sediment samples to evaluate a possible contamination near a fringing reef on the west coast of Havana, Cuba. The AH levels ranged from 1.24 to 135.6 μg g−1, the PAH levels were up to 2133 ng g−1, the faecal sterol levels ranged from 0.03 to 1.54 μg g−1, and the total LAB levels were up to 22.7 ng g−1. The highest concentrations were obtained at sites close to Havana Bay and at the sources of untreated sewage input. A decreasing concentration gradient was observed from Havana Bay to the outer sites. Although only two sites presented high levels of contamination, untreated sewage discharged close to the fringing reef may affect its environment.

Developmental biology of the upper limb

This article aims to provide hand surgeons with current knowledge on the developmental biology of the upper limb. It will review positioning, limb bud emergence and formation of the apical ectodermal ridge. The development of the limb bud is analyzed in its three axes: proximal-distal, anteroposterior and dorsoventral. The signaling center and primary morphogens that initiate and stimulate the development of each axis will be described. For the proximal-distal axis, the apical ectodermal ridge stimulates the production of FGFs in the underlying distal mesoderm. The anteroposterior (or radio-ulnar) differentiation is a function of the zone of polarizing activity via the small Sonic hedgehog protein, which diffuses in a decreasing concentration gradient from the ulnar to the radial side of the bud. This gradient is essential to digit identity and numbers. For the dorsoventral differentiation, the signaling center is the dorsal ectoderm, which secretes WNT7A. Limb segmentation is described in three parts (arm, forearm and hand) along with the formation of the digital rays until finger separation. An example of congenital anomalies is provided for each step. To keep the length of this lecture within reason, the embryogenesis of nerves, blood vessels, muscles and tendons will not be discussed. On the other hand, the singularity of the thumb relative to the other fingers will be described. With a better understanding of developmental biology, surgeons should have better insight into congenital anomalies of the upper limb. This approach is the basis for the new OMT classification used by the IFFSH.

Bone morphogenetic protein signaling: a promising target for white matter protection in perinatal brain injury.

Bone morphogenetic protein signaling: a promising target for white matter protection in perinatal brain injury.

Geometries of vasculature bifurcation can affect the level of trophic damage during formation of a brain ischemic lesion.

Ischemic lesion is a common cause of various diseases in humans. Brain tissue is especially sensitive to this type of damage. A common reason for the appearance of an ischemic area is a stop in blood flow in some branch of the vasculature system. Then, a decreasing concentration gradient results in a low mean level of oxygen in surrounding tissues. After that, the biochemical ischemic cascade spreads. In this review, we examine these well-known events from a new angle. It is stressed that there is essential evidence to predict the formation of an ischemic micro-area at the base of vascular bifurcation geometries. Potential applications to improve neuroprotection are also discussed.

Improved source apportionment of PAHs and Pb by integrating Pb stable isotopes and positive matrix factorization application (PAHs): A historical record case study from the northern South China Sea

To obtain the historical changes of pyrogenic sources, integrated source apportionment methods, which include PAH compositions, diagnostic ratios (DRs), Pb isotopic ratios, and positive matrix factorization (PMF) model, were developed and applied in sediments of the northern South China Sea. These methods provided a gradually clear picture of energy structural change. Spatially, Σ15PAH (11.3 to 95.5ng/g) and Pb (10.2 to 74.6μg/g) generally exhibited decreasing concentration gradient offshore; while the highest levels of PAHs and Pb were observed near the southern Taiwan Strait, which may be induced by accumulation of different fluvial input. Historical records of pollutants followed closely with the economic development of China, with fast growth of Σ15PAH and Pb occurring since the 1980s and 1990s, respectively. The phasing-out of leaded gasoline in China was captured with a sharp decrease of Pb after the mid-1990s. PAHs and Pb correlated well with TOC and clay content for core sediments, which was not observed for surface sediments. There was an up-core increase of high molecular PAH proportions. Coal and biomass burning were then qualitatively identified as the major sources of PAHs with DRs. Furthermore, shift toward less radiogenic signatures of Pb isotopic ratios after 1900 revealed the start and growing importance of industrial sources. Finally, a greater separation and quantification of various input was achieved by a three-factor PMF model, which made it clear that biomass burning, coal combustion, and vehicle emissions accounted for 40±20%, 41±13%, and 19±12% of PAHs through the core. Biomass and coal combustion acted as major sources before 2000, while contributions from vehicle emission soared thereafter. The integrated multi-methodologies here improved the source apportionment by reducing biases with a step-down and cross-validation perspective, which could be similarly applied to other aquatic systems.

Methane Adsorption Rate and Diffusion Characteristics in Marine Shale Samples from Yangtze Platform, South China

Knowledge of the gas adsorption rate and diffusion characteristics in shale are very important to evaluate the gas transport properties. However, research on methane adsorption rate characteristics and diffusion behavior in shale is not well established. In this study, high-pressure methane adsorption isotherms and methane adsorption rate data from four marine shale samples were obtained by recording the pressure changes against time at 1-s intervals for 12 pressure steps. Seven pressure steps were selected for modelling, and three pressure steps of low (~0.4 MPa), medium (~4.0 MPa), and high (~7.0 MPa) were selected for display. According to the results of study, the methane adsorption under low pressure attained equilibrium much more quickly than that under medium and high pressure, and the adsorption rate behavior varied between different pressure steps. By fitting the diffusion models to the methane adsorption rate data, the unipore diffusion model based upon unimodal pore size distribution failed to describe the methane adsorption rate, while the bidisperse diffusion model could reasonably describe most of the experimental adsorption rate data, with the exception of sample YY2-1 at high pressure steps. This phenomenon may be related to the restricted assumption on pore size distribution and linear adsorption isotherm. The diffusion parameters α and β/α obtained from the bidisperse model indicated that both macro- and micropore diffusion controlled the methane adsorption rate in shale samples, as well as the relative importance and influence of micropore diffusion and adsorption to adsorption rate and total adsorption increased with increasing pressure. This made the inflection points, or two-stage process, at higher pressure steps not as evident as at low pressure steps, and the adsorption rate curves became less steep with increasing pressure. This conclusion was also supported by the decreasing difference values with increasing pressures between macro- and micropore diffusivities obtained using the bidisperse model, which is roughly from 10−3 to 100, and 10−3 to 10−1, respectively. Additionally, an evident negative correlation between macropore diffusivities and pressure lower than 3–4 MPa was observed, while the micropore diffusivities only showed a gentle decreasing trend with pressure. A mirror image relationship between the variation in the value of macropore diffusivity and adsorption isotherms was observed, indicating the negative correlation between surface coverage and gas diffusivity. The negative correlation of methane diffusivity with pressure and surface coverage may be related to the increasing degree of pore blockage and the decreasing concentration gradient of methane adsorption. Finally, due to the significant deviation between the unipore model and experimental adsorption rate data, a new estimation method based upon the bidisperse model is proposed here.

Semivolatile Organic Compounds (SVOCs) in the atmosphere of Santiago de Cali, Valle del Cauca, Colombia along north-south transect using polyurethane foam disk as passive air samplers

A preliminary evaluation of Semivolatile Organic Compounds (SVOCs) was performed in the atmosphere of Santiago de Cali, Colombia, using passive air samplers based polyurethane foam (PAS-PUF) disks. PAS-PUF were deployed in four sites, along a north-south transect(∼15 km), during one sampling period of ∼4 months in 2011, form the industrial area of Yumbo (EF site) to the agricultural area of Valle del Cauca (FCNE). Results showed, for PCBs and PAHs, a clear north-south (IN > AG) decreasing concentration gradient (∼3 times) while OCPs exhibited an opposite gradient (UR < AG). Endosulfan I showed the highest concentrations in air (∼0.8–60 ng m−3). The HCHs (α- and γ-) concentrations ranged from BDL to ∼19 ng m−3, with α-HCH showing the highest levels (suggesting recent use of technical HCHs) and for DDTs levels fluctuated from BDL to ∼29 ng m−3 (with p,p’-DDE accounting for 50–80% of total DDTs). PAHs levels (∼25–66 ng m−3) were characterized by the abundance of Phenanthrene (34%), fluoranthene (18%) and pyrene (16%). For PCBs, concentrations in air ranged from ∼0.2 to 0.9 ng m−3 and were characterized by middle to a higher molecular weight PCB composition pattern. The results of OCPs are much higher than those found in other areas of Latin America. These results are likely influenced by the proximity of agricultural cultivations (i.e., sugarcane crops) in the southern part of the city. These results provide preliminary information about the presence of SVOCs in the atmosphere of Santiago de Cali, and constitute the basis for future monitoring programs.

Accumulation and distribution of trace metals within soils and the austral cordgrass Spartina densiflora in a Patagonian salt marsh

Concentrations of Cd, Cu, Fe, Pb, and Zn were determined in soils and in below- and above-ground structures of Spartina densiflora in a Patagonian salt marsh (San Antonio, Río Negro, Argentina). Also, the relationship between trace metal concentrations in soils and plants was investigated to improve our knowledge regarding the ability of this plant species to take up and accumulate trace metals from the soil. Our results indicate that, within the studied salt marsh, soil trace metal concentrations follow a decreasing concentration gradient toward the sea. They show moderate pollution and a potentially negative biological effect in one site of the salt marsh. While below-ground structures reflect the soil metal concentration pattern, this is not so evident in above-ground concentrations. Also, S. densiflora is able to absorb a limited amount of metals present in the soil, the soil bioaccumulation factor being lower in sites where soil metal concentration is higher.

The polarity of myxobacterial gliding is regulated by direct interactions between the gliding motors and the Ras homolog MglA

Gliding motility in Myxococcus xanthus is powered by flagella stator homologs that move in helical trajectories using proton motive force. The Frz chemosensory pathway regulates the cell polarity axis through MglA, a Ras family GTPase; however, little is known about how MglA establishes the polarity of gliding, because the gliding motors move simultaneously in opposite directions. Here we examined the localization and dynamics of MglA and gliding motors in high spatial and time resolution. We determined that MglA localizes not only at the cell poles, but also along the cell bodies, forming a decreasing concentration gradient toward the lagging cell pole. MglA directly interacts with the motor protein AglR, and the spatial distribution of AglR reversals is positively correlated with the MglA gradient. Thus, the motors moving toward lagging cell poles are less likely to reverse, generating stronger forward propulsion. MglB, the GTPase-activating protein of MglA, regulates motor reversal by maintaining the MglA gradient. Our results suggest a mechanism whereby bacteria use Ras family proteins to modulate cellular polarity.

Numerical modelling of multicomponent LNAPL dissolution kinetics at residual saturation in a saturated subsurface system

Characterization of aquifers contaminated by petroleum hydrocarbons is limited by the use of dissolution mass transfer correlations developed for single compounds without considering the effects of the mass transfer limitations in presence of other components. A one-dimensional implicit numerical model is developed for the coupled mass transfer and transport processes and the results are analysed using existing mass transfer correlations for better understanding of the single and multicomponent dissolution processes. The mass transfer coefficient in the multicomponent system is found to be more nonlinear and extending with changing slope, unlike the exponential reduction for single compound system. During the initial phase, the dissolution rate of a soluble compound is very high due to the high concentration gradient, and as dissolution progresses, its effective solubility decreases with change in mole fraction. At higher pore volumes, the mole fractions of lower solubility fractions increase which can result in higher effective solubility. The kinetics of interphase mass transfer by dissolution and sorption is favoured by coupled biodegradation. However, mass transfer limitation for more soluble compounds under the conditions of low residual saturation and low mole fraction is observed to be due to low dissolution rate coefficient rather than decreasing concentration gradient.

Optimization of the concentration field in a suspended photocatalytic reactor

In the present study, the photon absorption in a suspended photocatalytic reactor was simulated by adopting Monte Carlo method and the six-flux radiation absorption-scattering model. Different photocatalyst concentrations, i.e. uniform concentrations, linearly increasing concentration gradients and linearly decreasing concentration gradients, were taken into account. Simulation results indicated that increasing the photocatalyst concentration would cause higher photon absorption in the front layer but faster attenuation along the photon transfer direction. To the dilute solutions, the top layer photon loss was linearly influenced by the photocatalyst concentration. And the increasing concentration gradient resulted in higher photon absorption than the decreasing concentration gradient. The present work is expected to be of effective value for obtaining the optimal operating parameters for industrial photocatalytic applications.