Apparent Diffusion Research Articles

Evidence for Apoplasmic Phloem Unloading in Pear Fruit

Pear is a tree fruit species with worldwide distribution and belongs to the Rosaceae family. In this study, the phloem unloading pathway in pear (Pyrus bretschneideri ‘Yali’) fruit was investigated using transmission electron microscopy coupled with a symplasmic tracer dye, carboxyfluorescein diacetate (CFDA). Structurally, the sieve element-companion cell (SE-CC) complex in the phloem cells of major and minor sepal bundles is symplasmically isolated to its surrounding parenchyma cells (PCs) throughout fruit development. This was demonstrated by movement of the fluorescent dye which was restricted to phloem cells only without apparent diffusion. Meanwhile, different sugar contents were examined in fruit phloem exudates, with the results indicating that sorbitol comprised about 70 % of total soluble sugars. Gene transcription of a putative plasma membrane sorbitol transporter (PbSOT1) in flesh tissues enclosing the phloem was examined by RT-qPCR, showing that the transcripts were present at all stages of fruit development, but highest in young fruits. These results potentially suggest that the phloem unloading pathway in the pear fruit is mainly via the apoplasm rather than the symplasm.

Intracellular metabolites in the primate brain are primarily localized in long fibers rather than in cell bodies, as shown by diffusion-weighted magnetic resonance spectroscopy

Due to their pure intracellular compartmentation, the translational diffusion of brain metabolites in vivo depends on the intracellular environment, including viscosity, molecular crowding and subcellular structures. However, as the diffusion time is increased, metabolites have enough time to significantly encounter cell boundaries, so that cell size and geometry are expected to strongly determine metabolite diffusion path. In the present work, diffusion-weighted nuclear magnetic resonance spectroscopy was used to investigate brain metabolite diffusion in vivo, at long and ultra-long diffusion times (from ~80ms to more than 1s), in a voxel with equal proportions of white and grey matter in macaque monkeys. No dramatic dependence of the ADC on the diffusion time was observed, suggesting that metabolites' apparent diffusion is largely unrestricted over these time-scales. In an attempt to explain this stability and relate it to plausible cell geometries, data were analyzed with two simple geometrical models describing diffusion either in fibers such as axons, dendrites and astrocytic processes, or in closed cell bodies. Results support the idea that DW-MRS is sensitive to cell shape, and that a vast fraction of brain metabolites is diffusing in long fibers rather than being confined in cell bodies.

Sulfide stress cracking resistance of the welded WDL690D HSLA steel in H2S environment

Sulfide stress cracking resistance of welded high strength low alloy (HSLA) steel for high pressure vessel (called “WDL690D” steel) was evaluated in NACE “A” solution at room temperature. Though the failure time increased with the decreasing applied stress for either WDL690D base steel or its welded joint, the welded joint presented the lower threshold stress of about 53% YS compared with the base steel of about 65% YS, because of its inhomogeneous microstructure distribution. The hydrogen trapping efficiency of the WDL690D base steel and its welded joint was also investigated by measuring the permeability J∞L and the apparent diffusivity (Dapp). The results showed that the welded joint had lower trapping efficiency, but was more susceptible to SSC. In addition, the fractography of both the WDL690D base steel and its welded joint all exhibited a mixed ductile-brittle rupture when exposed in H2S environment under constant loading stress.

Service Life Checking Calculation of Marine Reinforced Concrete Structures Based on Monte Carlo Method

Checking some apparent chloride diffusion coefficient of concrete in the marine environment meets the requirements of design life based on Monte Carlo method. Through the project investigations, laboratory test data, statistical analysis and to determine random distribution model of the critical chloride concentration, the surface chloride concentration ,using computer program simulation 5000 random groups critical chloride concentration, surface chloride concentration into the life value calculation model, And obtain the derived distribution of the concrete structures service life, in order to determine Compliance with the design life of concrete structures. For the concrete durability design and service life checking provide the effective analysis under the marine environment.

Short-time movement of E. coli chromosomal loci depends on coordinate and subcellular localization

In bacteria, chromosomal architecture shows strong spatial and temporal organization, and regulates key cellular functions, such as transcription. Tracking the motion of chromosomal loci at short timescales provides information related to both the physical state of the nucleo-protein complex and its local environment, independent of large-scale motions related to genome segregation. Here we investigate the short-time (0.1-10 s) dynamics of fluorescently labelled chromosomal loci in Escherichia coli at different growth rates. At these timescales, we observe for the first time a dependence of the loci's apparent diffusion on both their subcellular localization and chromosomal coordinate, and we provide evidence that the properties of the chromosome are similar in the tested growth conditions. Our results indicate that either non-equilibrium fluctuations due to enzyme activity or the organization of the genome as a polymer-protein complex vary as a function of the distance from the origin of replication.

Ageing and durability of concrete in lab and in field conditions: investigation of chloride penetration

Long-term studies under various natural exposure conditions are still needed in order to understand and quantify ageing and durability of concrete structures, in particular in the case of mixtures which incorporate supplementary cementitious materials (e.g. fly ash). With this purpose, a large-scale and long-term experimental program was initiated a lot of years ago by the LPC network within the framework of the French national project “BHP 2000.” From then, further researches have been carried out in order to complement the program. The present paper focuses on chloride penetration in concrete samples in lab conditions and in reinforced concrete (RC) structural elements exposed for 10 years to two different natural environments (tidal zone in marine environment, as well as road and cold environment). Numerous mixtures (28 day cylinder compressive strengths ranging from 20 to 130 MPa) were studied in these various conditions, e.g. high-performance materials with or without silica fume (SF), as well as normal-strength fly-ash (FA) concretes. Carbonation and chloride penetration depths, along with total chloride concentration and degree of saturation profiles, have been measured on the RC structural elements and analyzed as a function of the exposure conditions and of the mix-parameters. In addition, the chloride data have been compared to lab results. Apparent chloride diffusion coefficients, as well as chloride binding isotherms and capacities, have also been assessed on these structural elements and compared to lab results. Good consistence between results in field and in lab conditions has been highlighted, except when carbonation has affected the field results. In addition, the good performance of SF-HPCs and mature FA concretes has been pointed out in the tested outdoor conditions, as well as that of the mature ground granulated blast furnace slag concretes tested in lab.

Sensitivity study on durability variables of marine concrete structures

In order to study the influence of parameters on durability of marine concrete structures, the parameter's sensitivity analysis was studied in this paper. With the Fick's 2nd law of diffusion and the deterministic sensitivity analysis method (DSA), the sensitivity factors of apparent surface chloride content, apparent chloride diffusion coefficient and its time dependent attenuation factor were analyzed. The results of the analysis show that the impact of design variables on concrete durability was different. The values of sensitivity factor of chloride diffusion coefficient and its time dependent attenuation factor were higher than others. Relative less error in chloride diffusion coefficient and its time dependent attenuation coefficient induces a bigger error in concrete durability design and life prediction. According to probability sensitivity analysis (PSA), the influence of mean value and variance of concrete durability design variables on the durability failure probability was studied. The results of the study provide quantitative measures of the importance of concrete durability design and life prediction variables. It was concluded that the chloride diffusion coefficient and its time dependent attenuation factor have more influence on the reliability of marine concrete structural durability. In durability design and life prediction of marine concrete structures, it was very important to reduce the

Evaluation of soil thermal diffusivity algorithms at two equatorial sites in West Africa

<p>This study presents comparisons between six algorithms used in the calculation of apparent thermal diffusivity (K<sub>h</sub>) of the topsoil during measurement campaigns conducted at two equatorial sites. It further investigates the effects of transient and seasonal variations in soil moisture content (theta) on the estimation of K<sub>h</sub>. The data used comprise soil temperatures (T) measured at depths of 0.05 m and 0.10 m, and theta within the period of transition from the dry season to the wet season at Ile Ife (7.55˚ N, 4.55˚ E), and for the peak of the wet season at Ibadan (7.44˚ N, 3.90˚ E). The thermal diffusivity, K<sub>h</sub>, was calculated from six algorithms, of: harmonic, arctangent, logarithmic, amplitude, phase, and conduction-convection. The reliability of these algorithms was tested using their values to model T at a depth of 0.10 m, where direct measurements were available. The algorithms were further evaluated with statistical indices, including the empirical probability distribution function of the differences between the measured and modeled temperatures ([delta capitalized]T). The maximum absolute values of [delta capitalized]T for the six algorithms investigated were: 0.5˚C, 0.5˚C, 0.5˚C, 1˚C, 1˚C and 1˚C, respectively. K<sub>h</sub> showed an increasing trend as theta increased from the dry season to the peak of the wet season, with R<sup>2</sup> = 0.70 for the harmonic algorithm. The accuracy of all of the algorithms in modeling T reduced with transient variations of theta. The harmonic, arctangent and logarithmic algorithms were the most appropriate for calculating K<sub>h</sub> for the region of study. The empirical relation between theta and K<sub>h</sub> and the values of K<sub>h</sub> obtained in this study can be used to improve the accuracy of meteorological and hydrological models.</p>

Diffusion transport of nanoparticles at nanochannel boundaries

The manipulation of matter at the nanoscale has unleashed a great potential for engineering biomedical drug carriers, but the transport of nanoparticles (NPs) under nanoscale confinement is still poorly understood. Using colloidal physics to describe NP interactions, we have computationally studied the passive transport of NPs using experimentally relevant conditions from bulk into a nanochannel of 60–90 nm height. NP size, channel height, and the Debye length are comparable so that changes in nanoscale dimensions may induce substantial changes in NP transport kinetics. We show that subtle changes in nanochannel dimensions may alter the energy barrier by about six orders of magnitude resulting in different NP penetration depths and diffusion mechanisms: ballistic, first-order and quasi zero-order transport regimes. The analysis of NP diffusion by continuum methods reveals that apparent diffusivity is reduced by decreasing channel size. The continuum finite element (FE) numerical method reproduced the colloidal model results only when surface interactions were accounted for. These results give a new insight into NP passive transport at the boundaries of nanoconfined domains, and have implications on the design of nanoscale fluidics and NP systems for biomedical and engineering applications.

Simulation of the Hydrogen Permeation Behavior of X80 Pipeline Steels in H<sub>2</sub>S Saturated Environment by Cathodic-Charging Method

Hydrogen-charging with various current densities was used to introduce hydrogen into X80 pipeline steel. The permeability (J∞L), the apparent diffusivity (Dapp) and the solubility of hydrogen (Capp)in X80 pipeline steels which were calculated by electrochemical hydrogen permeation curves were compared with those obtained from that of X80 pipeline steels in H2S saturated environment. Results show that in 0.5 mol/L H2SO4+ 3.1×10-3mol/L Na4P2O7(hydrogen evolution poison) solution, when hydrogen-charging current density is 30 mA/cm2, the kinetic parameters of hydrogen permeation of X80 pipeline steels agree with that of H2S saturated environment well. Another two heat-treatment specimens of X80 pipeline steel furthermore verified the reliability of the simulating results.

Chemical–physical and in vivo evaluations of a self-assembling amphiphilic peptide as an injectable hydrogel scaffold for biomedical applications

The self-aggregation and gelation of an amphiphilic peptide (C17H35CONH–A4G3ERGD, peptide amphiphile) were studied by light scattering, viscometry, nuclear magnetic resonance diffusometry, and atomic force microscopy. The peptide amphiphile critical aggregation concentration was evaluated to be 16 and 60 µM by light scattering and viscometry, respectively. The observed difference was attributed to the larger sensitivity of the latter technique to the presence of long fibrils. The addition of one equivalent or more of divalent cations (Ca2+ and Mg2+) to peptide amphiphile formed dense incoherent hydrogels. Based on the atomic force microscopy and nanoindentation data, both the hydrogel morphology and stiffness were independent of the cation type and peptide amphiphile concentration. However, gel stiffness increased on increasing Ca2+/peptide amphiphile molar ratio while a parallel decrease in the apparent water diffusion rate was observed by nuclear magnetic resonance diffusometry. The dispersions of endothelial progenitor cells in the peptide amphiphile hydrogels were evaluated in vivo on a rat tissue hypoxia model. Significant capillary formation at the injection site was observed by tissue appearance and histological examination, which indicated endothelial progenitor cell/peptide amphiphile hydrogel-enhanced angiogenesis in ischemic tissue.

The Durability Failure of Pre-Damaged Concrete Induced by Mechanical Load

Chloride ion penetration and freezing and thawing damage are the two main factors that affect the durability of concrete structures. Through the chloride ion penetration test and freezing and thawing test of concrete specimens after tensile and compressive loading, the influence of load-induced damage on the long-term durability of concrete was studied. The results showed that the apparent chloride diffusion coefficient of concrete increased by 6.4% and 34%, and the surface chloride concentration increased 10% and 40%, respectively, both of which showed the "negative effect" when the uniaxial tensile load level reached the 65% and 75% of the ultimate capacity. However, with the increasing uniaxial compressive load level, the impact on the frost resistance of concrete experienced a transformation from the "positive effect" to the "negative effect".

The Effect of Surface Hydrophobation Silane Treatment on Chloride Ion Penetration Resistance for Concrete Structures in Marine Environments

Effect of concrete surface hydropobation treatment against chloride penetration have been studied by in-site exposure test. The results show that the silane impregnated layer can prevent the chlorides penetration into the concrete substrate effectively, reduce the apparent chloride ion diffusion coefficient and surface chloride concentration, and improve the service life of concrete structure; and the depth of concrete convection zone can reduce due to silane impregnated layer for concrete in the marine environment of wetting and drying area.

Water sorption in hybrid silica gels containing colloidal nontronite

Hybrid silica gels (HSGs) were prepared according to an acid-catalyzed sol–gel method using tetraethoxysilane (TEOS) as silica precursors and colloidal suspension of nontronite clay mineral. The silica surfaces were hydrophilic in relation to silanol groups and it was of interest to increase hydrophobicity by substituting silanol by methylated groups through addition of methyltrimethoxysilane (MTMS) in a molar ratio TEOS: MTMS equaled to 1:0.4. The aim of the present paper was to predict effects of water content in soil on HSG hydration by characterizing HSG water desorption and sorption with dynamic vapor sorption device. From desorption kinetics, TEOS HSGs showed higher ability to water surface evaporation and diffusion compared to the TEOS–MTMS HSGs. After complete dehydration, water sorption isotherms Type II were obtained for HSGs. Isotherms were fitted with Brunauer-Emmett-Tellet (BET) and Guggenheim, Andersen, de Boer (GAB) models. The higher monolayer values of water adsorbed for HSGs containing nontronite suggested a major influence of clay minerals on overall hydration. However, the water binding energy depended upon the nature of silica matrix indicating weaker bonds with methylated groups at solid surface in MTMS–TEOS HSGs. Apparent water sorption diffusivities, Dapp were calculated according to Fick’s diffusion model. Maximal Dapp values were obtained in the range 0.2–0.3 aw after which the Dapp decreased in relation with capillary condensation.

A Probabilistic-Based Durability Analysis of Concrete Structures Exposed to Chloride Containing Environment

Time dependency of chloride transport has been studied and an improving model for predicting the apparent chloride diffusion coefficient has been proposed. A probabilistic-based durability analysis to estimate failure probability on the chloride ingress into concrete has been carried out. Results of the analysis demonstrate that the improving model in this paper is appropriate for long term service life prediction of concrete structures exposed to chloride containing environment.

Redox Reactivity of Methylene Blue Bound in Pores of UMCM-1 Metal-Organic Frameworks

Redox processes were studied in the pores of a crystalline UMCM-1 metal organic framework (MOF) material. Methylene blue was employed as an absorbed redox active dye component. From the change in coloration during dye adsorption, it was concluded that an essentially irreversible adsorption process with high pore loading of the resulting MOF structure occurred. The adsorbed methylene blue remained redox active in the MOF pores and there was no evidence of significant losses during extended redox cycling. Due to the size of the pores, the reactivity of the pore-bound methylene blue is closely related to that expected for methylene blue in an aqueous solution. A study of the effect of solution pH on the voltammetric responses revealed an interesting gradual change in electrical pore conductivity form conducting poorly under acidic conditions to conducting very well under alkaline conditions. This is interpreted in terms of charge transport via single-electron hopping conduction in pores. An estimate of the apparent charge diffusion coefficient at pH 7, Dapp = 1.4 × 10−15 m2s−2, is obtained. Potential applications of the new family of redox active hybrid MOF materials are indicated.

Difusividade térmica aparente de sementes de cajá em temperaturas acima do congelamento até ultrabaixas temperaturas

O objetivo do trabalho foi determinar a difusividade térmica aparente de sementes de cajá avaliando o efeito da variação do teor de água e da temperatura e ajustar diferentes modelos matemáticos aos valores experimentais. Sementes com a faixa de teor de água de 6,05 a 61,84% (b.u.) foram submetidas a secagem e à temperatura de 40 ºC. A redução do teor de água ao longo da secagem foi acompanhada pelo método gravimétrico (perda de massa) enquanto a difusividade térmica aparente da semente de cajá foi determinada pelo método de Dickerson. Concluiu-se que a difusividade térmica aparente, em temperatura acima do congelamento e em ultrabaixas temperaturas em função do teor de água (b.u), podem ser representados satisfatoriamente por um modelo de regressão linear e que o valor da difusividade térmica aparente aumenta exponencialmente com o aumento da temperatura.

Computational Modeling of Protein Dynamics in Eukaryotic Cells

Proteins have important functions inside the cell, traveling diffusively or being actively transported to various cellular sites where their activity is needed. Protein motion in the cellular environment is therefore an important topic to understand. However, the cell provides a very complex environment for that motion, which poses problems especially for any modeling effort designed to interpret experimentally observed features. So as to gain a realistic picture of protein dynamics inside the cell, we have recently introduced advanced numerical methods for describing that dynamics [1]. The starting point is an accurate numerical duplicate of the cell determined by LSCM, which can be used as a simulation geometry. Interpreting the internal cellular structures that obstruct the protein motion as the solid component of a porous structure, and treating the motion in the same way as in the case of a porous medium (distinction between effective and apparent diffusion), we can rather accurately take into account the cellular environment in which the motion takes place. The numerical simulations of protein motion in the model cell are based on the lattice-Boltzmann method. Here we use these methods to exactly reproduce photobleaching experiments on the diffusion of Enhanced Yellow Fluorescent Protein (EYFP) in HeLa cells. Comparison of simulated and real experiments can be used to characterize protein motion and the related diffusion coefficients. We pay particular attention to the nuclear translocation of EYFP in these cells.[1] Kuhn T., Ihalainen T. O., Hyvaluoma J., Dross N., Willman S. F., Langovski J., Vihinen-Ranta M. and Timonen J. 2011 Protein Diffusion in Mammalian Cell Cytoplasm. PLoS ONE 6(8): e22962.

Targeting the amyloid-β antibody in the brain tissue of a mouse model of Alzheimer's disease

Alzheimer's disease is a neurodegenerative disease characterized pathologically by amyloid-β (Aβ) aggregates in the brain. Notwithstanding many promising therapeutics that are under development, early diagnosis of Alzheimer's disease is limited. By targeting the Aβ aggregates, diagnosis can be improved and disease progression reduced. Molecular imaging using monoclonal antibodies to target specific isoforms of Aβ aggregates offer increased specificity in comparison to conventional imaging tracers; however, antibodies that are widely used in histology do not necessarily show similar binding in a dynamic in vivo environment. In this study, the diffusion and binding were studied of a classical monoclonal antibody, 6E10, in the brain of the TgCRND8 mouse model of AD. After intracranial injection of fluorescent 6E10, we observed broad and rapid labelling of Aβ deposits in the cortex and corpus callosum within 4h. Aβ plaques were detected up to 2.5mm away from the injection site in TgCRND8 mice and not in wild type mice at all, demonstrating specificity of binding. The apparent diffusivity and elimination constant of the anti-Aβ antibody were found to be independent of both the age of the animal and the accumulation of Aβ in the extracellular space, suggesting broad applicability of this targeting molecule. Mathematical modelling of the diffusion profiles of the anti-Aβ antibody in the brain parenchyma provides insights into the utility of antibodies as molecular imaging tools and targeted therapeutics.

Electroreduction of 6-amino-5-nitroso-1,3-dimethyluracil on polycrystalline platinum and nickel cathodes in acid aqueous solution

The reduction of 6-amino-5-nitroso-1,3-dimethyluracil (ANDMU) is a key step in caffeine synthesis. Electroreduction technology is a promising green chemical process. The voltammetric behavior of ANDMU at polycrystalline platinum and nickel cathodes was studied. The Nicholson theory was used to resolve the reduction process semi-quantitatively. The results show that ANDMU mainly undergoes an ECE (electron transfer, chemical reaction, electron transfer) process involving four electrons on the platinum and nickel cathodes in which the two electron-transfer steps occur at almost the same potential and the rate of the coupling chemical reaction between two electron-transfer steps is very fast. Apparent kinetic data and diffusion coefficient were determined for the platinum rotating-disk electrode.