Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Results 1 - 17 de 17
Filter
Add more filters










Publication year range
1.
Water Res ; 46(15): 4761-9, 2012 Oct 01.
Article in English | MEDLINE | ID: mdl-22776209

ABSTRACT

We present experimental results of mass transfer of a non reactive tracer gas (neon) measured in aerobic heterotrophic biofilm developed from activated sludge. Biofilms are grown in various hydrodynamic conditions and the effective diffusivity is used to quantify the mass transfer through the biofilm. Beyond some cross-flow conditions, the effective diffusivity through the biofilm seems larger than in the bulk. This can be explained by a dispersion generated by convection inside the biofilm, as supported by an analytical flow model and in accordance to the numerical simulation proposed by Aspa et al. (2011).


Subject(s)
Biofilms , Membranes, Artificial
2.
Adv Colloid Interface Sci ; 164(1-2): 2-11, 2011 May 11.
Article in English | MEDLINE | ID: mdl-21130419

ABSTRACT

In this paper, we examine the contributions of colloidal surface interaction in filtration processes. In a first part, we describe the way surface interactions affect the transport of colloidal particles or macromolecules towards a membrane, and its theoretical description. The concept of critical flux is introduced and linked to particle-membrane wall and particle-particle surface interactions. From this review, it seems important to consider how surface interactions occur at pore scale and control the development of fouling layers. In this context, we report in a second part experiments where the capture of micron-sized particles is observed in a poly-dimethylsiloxane (PDMS) microfluidic filtration device. Direct observations of the filtering part by video-microscopy allow to investigate the way the fouling of the microchannels by the particles is taking place. The experimental results underline the important role played by the particle-wall interactions on the way particles are captured during filtration. A small change in surface properties of the PDMS has important consequences in the way pore clogging occurs: in more hydrophobic conditions the particles first form arches at the microchannels entrance, then leading to the growth of a filtration cake, whereas in more hydrophilic conditions the particles are captured on the walls between the microchannels, then leading to the progressive formation of dendrites. To conclude, both experimental and theoretical approaches show the important role played by surface interactions in filtration processes. The complex interplay between multi-body surface interactions and hydrodynamics at nanometric scale leads to clogging phenomena observed experimentally in microfluidic systems that have not been predicted by numerical simulations. In the future, the two way coupling between simulation and experimental approaches at the pore scale have to progress in order to reach a full understanding of the contribution of colloid science in membrane processes.


Subject(s)
Colloids/chemistry , Dimethylpolysiloxanes/chemistry , Filtration/methods , Hydrophobic and Hydrophilic Interactions , Algorithms , Hydrodynamics , Microfluidic Analytical Techniques , Microscopy, Confocal , Models, Theoretical , Nanoparticles/chemistry , Particle Size , Surface Properties
3.
Neuroscience ; 168(1): 314-22, 2010 Jun 16.
Article in English | MEDLINE | ID: mdl-20226234

ABSTRACT

Shc(s) family of adaptor molecules has been implicated in several physiological functions. In particular, our previous studies have shown major roles in the mechanisms that control the transition from proliferating neural stem cells (NSCs) to postmitotic neurons in the mammalian brain. In the adult brain, ShcA expression is mainly restricted to a subpopulation of cells in the subventricular zone (SVZ) neurogenic area, enlightening a potential role for this molecule in the establishment/maintenance of this adult NSC niche. In order to investigate this matter, here we took advantage of Cre/lox technology with the purpose of interfering with (or delete) ShcA function in nestin-expressing neural progenitors in vivo. Our analyses revealed signs of anatomical disorganization in the adult brain at the boundary between the striatum and the corpus callosum and reduced thickness both at the ventricular level and through the rostral migratory stream. Analysis of cell proliferation and cell death unveiled a prominent reduction of the former and no substantial alterations of the latter. Ultrastructural studies showed SVZ anatomical disarray and manifest variation in the SVZ cell type composition. In conclusion, these results provide evidence for a role of ShcA in the assembly and/or maintenance of the SVZ NSC niche in the adult brain.


Subject(s)
Lateral Ventricles/anatomy & histology , Shc Signaling Adaptor Proteins/physiology , Stem Cells/cytology , Animals , Axons/ultrastructure , Cell Proliferation , Corpus Callosum/cytology , Corpus Callosum/ultrastructure , Intermediate Filament Proteins/genetics , Lateral Ventricles/cytology , Lateral Ventricles/ultrastructure , Mice , Mice, Inbred C57BL , Mice, Knockout , Nerve Tissue Proteins/genetics , Nestin , Neurogenesis , Organ Size , Prosencephalon/cytology , Prosencephalon/ultrastructure , Shc Signaling Adaptor Proteins/genetics , Src Homology 2 Domain-Containing, Transforming Protein 1 , Stem Cells/metabolism
5.
Water Res ; 40(20): 3793-9, 2006 Dec.
Article in English | MEDLINE | ID: mdl-17074381

ABSTRACT

The efficiency with which a nanofiltration membrane (Desal 5 DK) removes bisphenol A (BPA) was investigated, together with the mechanisms involved. Whereas high retention (>90%) was obtained at the beginning of the filtration, the observed retention coefficient (R(obs)) decreased to around 50% when the membrane became saturated, due to adsorption of BPA onto the membrane structure. The presence of ions (Na+, Cl-) affects the R(obs), this effect being attributed to a change in BPA hydrodynamic radius. Moreover, in our operating conditions, the presence of natural organic matter (1mg/L) in the feed solution does not lead to variation in BPA retention at steady state.


Subject(s)
Endocrine Disruptors/isolation & purification , Phenols/isolation & purification , Water Pollutants, Chemical/isolation & purification , Adsorption , Benzhydryl Compounds , Endocrine Disruptors/chemistry , Phenols/chemistry , Ultrafiltration , Water Pollutants, Chemical/chemistry , Water Purification/methods , Water Supply
6.
Water Res ; 39(8): 1594-600, 2005 Apr.
Article in English | MEDLINE | ID: mdl-15878032

ABSTRACT

This study evaluates the performance of two nanofiltration membranes in removing a herbicide: dichloroaniline. The membranes, one polyamide and one cellulose acetate, have a cut-off in the range 150-300 g/mol (manufacturers' data). The experiments were carried out with solutions of dichloroaniline in demineralized water, with concentrations from 1 to 10 ppb. For each membrane, the amount of herbicide retained and adsorbed by the membrane was determined as a function of feed concentration and transmembrane pressure. The two membranes, made of different materials but having the same nominal cut-off, retained dichloroaniline to very different extents and by different mechanisms.


Subject(s)
Aniline Compounds/isolation & purification , Herbicides/isolation & purification , Nanotechnology , Water Purification/methods , Filtration , Membranes, Artificial , Water Pollutants, Chemical/isolation & purification
7.
Proc Natl Acad Sci U S A ; 100(22): 13036-41, 2003 Oct 28.
Article in English | MEDLINE | ID: mdl-14559968

ABSTRACT

In the brains of adult mammals long-distance cell migration of neuronal precursors is known to occur in the rostral migratory stream, involving chains of cells sliding into astrocytic glial tubes. By combining immunocytochemistry for polysialylated neural cell adhesion molecule (PSA-NCAM), neuronal and glial antigens, endogenous and exogenously administered cell-proliferation markers, and light and electron microscopy 3D reconstructions, we show that chains of newly generated neuroblasts exist both inside and outside the subventricular zone of adult rabbits. Two groups of chains were detectable within the mature brain parenchyma: anterior chains, into the anterior forceps of the corpus callosum, and posterior chains, close to the external capsule. Parenchymal chains were not associated with any special glial structures, thus coming widely in contact with the mature nervous tissue, including unmyelinated/myelinated fibers, astrocytes, neurons, and oligodendrocytes. These chains of cells, unlike those in the subventricular zone, do not display cell proliferation, but they contain BrdUrd administered several weeks before. Telencephalic areas, such as the putamen, amygdala, claustrum, and cortex, adjacent to the chains harbor numerous PSA-NCAM-positive cells. The counting of newly generated cells in these areas shows small differences in comparison with others, and a few cells double-labeled for BrdUrd/PSA-NCAM (after 1-month survival) and for BrdUrd/NeuN (after 2 months) were detectable. These results demonstrate the occurrence of glial-independent chains of migrating neuroblasts, which directly contact the mature brain parenchyma of adult mammals. These chains could provide a possible link between the adult germinative layers and a very low-rate/long-term process of cell addition in the telencephalon.


Subject(s)
Brain/cytology , Cerebral Cortex/cytology , Neuroglia/cytology , Neurons/cytology , Animals , Cell Count , Cell Movement/physiology , Cerebral Cortex/ultrastructure , Neural Pathways/ultrastructure , Neuroglia/ultrastructure , Neurons/ultrastructure , Rabbits
8.
J Neurosci ; 18(24): 10375-88, 1998 Dec 15.
Article in English | MEDLINE | ID: mdl-9852575

ABSTRACT

The substantia gelatinosa of the spinal cord (lamina II) is the major site of integration for nociceptive information. Activation of NMDA glutamate receptor, production of nitric oxide (NO), and enhanced release of substance P and calcitonin gene-related peptide (CGRP) from primary afferents are key events in pain perception and central hyperexcitability. By combining reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry for NO-producing neurons with immunogold labeling for substance P, CGRP, and glutamate, we show that (1) NO-producing neurons in lamina IIi are islet cells; (2) these neurons rarely form synapses onto peptide-immunoreactive profiles; and (3) NADPH diaphorase-positive dendrites are often in close spatial relationship with peptide-containing terminals and are observed at the periphery of type II glomeruli showing glutamate-immunoreactive central endings. By means of confocal fluorescent microscopy in acute spinal cord slices loaded with the Ca2+ indicator Indo-1, we also demonstrate that (1) NMDA evokes a substantial [Ca2+]i increase in a subpopulation of neurons in laminae I-II, with morphological features similar to those of islet cells; (2) a different neuronal population in laminae I-IIo, unresponsive to NMDA, displays a significant [Ca2+]i increase after slice perfusion with either substance P and the NO donor 3morpholinosydnonimine (SIN-1); and (3) the responses to both substance P and SIN-1 are either abolished or significantly inhibited by the NK1 receptor antagonist sendide. These results provide compelling evidence that glutamate released at type II glomeruli triggers the production of NO in islet cells within lamina IIi after NMDA receptor activation. The release of substance P from primary afferents triggered by newly synthesized NO may play a crucial role in the cellular mechanism leading to spinal hyperexcitability and increased pain perception.


Subject(s)
Neuropeptides/metabolism , Nitric Oxide/biosynthesis , Substantia Gelatinosa/cytology , Substantia Gelatinosa/metabolism , Animals , Axons/ultrastructure , Calcitonin Gene-Related Peptide/metabolism , Calcium/metabolism , Enzyme Inhibitors/pharmacology , Fluorescent Dyes , Glutamic Acid/metabolism , Immunohistochemistry , In Vitro Techniques , Male , Microscopy, Confocal , Molsidomine/analogs & derivatives , Molsidomine/pharmacology , NADPH Dehydrogenase/metabolism , Neurons/metabolism , Neurons/physiology , Neurons/ultrastructure , Presynaptic Terminals/ultrastructure , Rats , Rats, Wistar , Substance P/metabolism , Substantia Gelatinosa/ultrastructure
9.
Biotechnol Bioeng ; 56(4): 391-7, 1997 Nov 20.
Article in English | MEDLINE | ID: mdl-18642242

ABSTRACT

The selective precipitation of alpha-lactalbumin (alpha-LA) at a pH around its isoelectric point (4.2) under heat treatment is the basis for a fractionation process of whey proteins. In these conditions, beta-lactoglobulin remains soluble, whereas bovine serum albumin and immunoglobulins co-precipitate. Knowledge of the mechanism governing the alpha-LA precipitation influences the choice of operating conditions and enables optimization of the fractionation process. alpha-LA is a calcium metallo-protein and its isoelectric precipitation is governed by the protein-calcium complexation equilibrium. Citrate, a sequestrant of calcium, decreases the free calcium concentration and displaces the precipitation phenomenon to a lower temperature range. A study of the effect of citrate on the precipitation phenomena of whey proteins is presented. Whatever the citrate content, precipitation curves for bovine serum albumin (BSA) and alpha-LA intersect at a temperature around 45 degrees C. For a temperature of heat treatment lower than 40 degrees C, a selective enrichment in alpha-LA of the precipitated phase is observed. As addition of citrate leads to high alpha-LA precipitated fractions at a temperature around 35 degrees C, the precipitation step may be performed at this temperature. It results in a reduced heat denaturation of whey proteins and in a higher alpha-LA purity in the precipitated fraction. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 391-397, 1997.

10.
Biotechnol Bioeng ; 47(2): 121-30, 1995 Jul 20.
Article in English | MEDLINE | ID: mdl-18623384

ABSTRACT

The selective precipitation of alpha-lactalbumin (alpha-LA) at a pH around its isoelectric point (4.2) under heat treatment is the basis for a fractionation process of whey proteins. As precipitation is a phenomenon dependent on the protein hydrophobicity, and as the release of the tightly bound calcium occurring at pH around 4 modifies the alpha-LA hydrophobicity, the specific role of calcium on isoelectric precipitation is investigated. A study of the extent of alpha-LA precipitation in a whey protein concentrate under various operating conditions of pH, temperature, protein concentration, and calcium content is presented. We propose a mechanism for this phenomenon as a combination of a complexation equilibrium and of an irreversible precipitation, to account for the influence of temperature, alpha-LA concentration total ionic content, and calcium concentration, and also to estimate the complexation equilibrium constant. (c) 1995 John Wiley & Sons, Inc.

11.
Ital J Anat Embryol ; 100 Suppl 1: 167-75, 1995.
Article in English | MEDLINE | ID: mdl-11322289

ABSTRACT

In the mammalian central nervous system cell proliferation is generally linked to developmental processes that are ultimated in the perinatal period. Few exceptions to this rule are known in certain regions of the mammalian brain, namely the post-natal cerebellar cortex and the adult subependymal layer. We report here the results of our studies about cell proliferation and related phenomena in these regions. Cell proliferation was visualised after bromodeoxyuridine incorporation and labeling of the proliferating cell nuclear antigen (PCNA), an endogenous protein expressed during the cell cycle. The occurrence of programmed cell death in the post-natal cerebellar cortex and the persistence of the embryonic isoform of neural cell adhesion molecule (NCAM) associated with proliferating cells in the adult subependymal layer were also investigated.


Subject(s)
Cell Division/physiology , Central Nervous System/growth & development , Central Nervous System/ultrastructure , Neurons/ultrastructure , Animals , Animals, Newborn , Apoptosis/physiology , Bromodeoxyuridine , Central Nervous System/metabolism , Cerebellum/growth & development , Cerebellum/metabolism , Cerebellum/ultrastructure , DNA Fragmentation/physiology , Ependyma/growth & development , Ependyma/metabolism , Ependyma/ultrastructure , Immunohistochemistry , Microscopy, Electron , Neural Cell Adhesion Molecules/metabolism , Neurons/metabolism , Olfactory Pathways/growth & development , Olfactory Pathways/metabolism , Olfactory Pathways/ultrastructure , Proliferating Cell Nuclear Antigen/metabolism , Prosencephalon/growth & development , Prosencephalon/metabolism , Prosencephalon/ultrastructure , Rabbits , Rats , Sheep
12.
Exp Brain Res ; 101(2): 241-52, 1994.
Article in English | MEDLINE | ID: mdl-7843311

ABSTRACT

The volume and cytoarchitectonic organization of the sexually dimorphic medial preoptic nucleus (POM) of the quail are sensitive to plasma levels of testosterone (T). We previously showed that, in castrated quail, T or its estrogenic metabolite, estradiol (E2), increases the size of the large neurons located in the lateral part of POM. Embryonic treatments with estrogens are also known to affect permanently the size of these large neurons. Since the lateral POM also contains a dense population of aromatase-immunoreactive (ARO-ir) cells, and these are known to be a target for steroids, we hypothesized that the effects of steroids identified in previous experiments were primarily directed to these ARO-ir cells. This idea was tested in two experiments in which the size of these cells was measured in male quail under various endocrine conditions. In experiment 1, a detailed analysis of ARO-ir and of non-immunoreactive cells in the POM of adult, sexually mature males revealed that the immunoreactive perikarya are larger than the non-immunoreactive cells and that they constitute the vast majority of the large cells (area > 50 microns 2) in the POM. In experiment 2, it was shown that T and E2 actually increase the size of ARO-ir cells in the POM while the androgenic metabolite of T, dihydrotestosterone has no effect at this level. Taken together, these data suggest that the sex differences and the steroid-induced changes in cell size previously described in the study of POM sections stained for Nissl material largely concern aromatase-containing cells. Since aromatization of T plays a limiting role in the activation of male copulatory behavior, these changes may represent the morphological signature of the mechanisms causally involved in the control of this behavior.


Subject(s)
Androgens/physiology , Aromatase/metabolism , Estrogens/physiology , Neurons/physiology , Preoptic Area/physiology , Animals , Cell Count/drug effects , Coturnix , Immunohistochemistry , Male , Neurons/cytology , Neurons/drug effects , Preoptic Area/cytology , Testosterone/metabolism , Testosterone/pharmacology
13.
Biotechnol Bioeng ; 41(11): 1039-47, 1993 May.
Article in English | MEDLINE | ID: mdl-18601289

ABSTRACT

Transmission of polyethylene glycol (PEG) through ultrafiltration membranes has been studied under various operating conditions of pressure, crossflow, and concentration, using different membranes cut-offs and two module designs with the aim of understanding the separation of PEG from BSA. The influence of protein adsorption and fouling of the choice of a membrane has also been considered. Retention depends in general on the molecule to average pore size ratio, as expected, but also on concentration polarization. Accordingly, all operating and design parameters favoring concentration polarization lead to higher transmission. At high fluxes, flexible macromolecules can pass through the membrane, even if the random coil is larger than the apparent average pore. From a process selectivity point of view, the best way to separate PEG from BSA would be to use a membrane totally retaining BSA and to enhance concentration polarization of PEG. Unfortunately, such conditions also increase fouling and concentration polarization by BSA, which limits flux and thus PEG concentration polarization and transmission. Consequences of such conditions on separation efficiency are discussed.

14.
Brain Res Bull ; 31(5): 601-11, 1993.
Article in English | MEDLINE | ID: mdl-8495382

ABSTRACT

In quail, testosterone (T) activates male copulation and affects the volume and cytoarchitectonic organization of the medial preoptic nucleus (POM). T metabolism (especially its aromatization) is critical for the production of these behavioral effects. We wondered whether T metabolism is also playing a role in the induction of the morphological changes in POM. We compared the effects of T and of its metabolites in this nucleus. To obtain an independent evaluation of the role played by aromatase, morphological effects of T associated or not with the aromatase inhibitor R76713 were also assessed. As previously observed, T increased the POM volume and the cross-sectional area of the neurons in the lateral part of the nucleus. The effects of T on the neurons in the lateral POM were mimicked in part by the combined treatment with estradiol and 5 alpha-dihydrotestosterone. They were also blocked by the aromatase inhibitor. This suggests that T aromatization plays a critical role in the mediation of the cytoarchitectonic effects of T. A specific role for androgens alone remains to be established.


Subject(s)
Coturnix/metabolism , Preoptic Area/physiology , Sex Characteristics , Testosterone/metabolism , Animals , Aromatase Inhibitors , Female , Image Processing, Computer-Assisted , Male , Neurons/drug effects , Orchiectomy , Preoptic Area/cytology , Preoptic Area/drug effects , Sexual Behavior, Animal/drug effects , Triazoles/pharmacology
15.
Bioseparation ; 3(4): 205-15, 1992.
Article in English | MEDLINE | ID: mdl-1369244

ABSTRACT

Ultrafiltration of peptide mixtures is studied under various operating conditions (transmembrane pressure, tangential flow-rate) using two ultrafiltration inorganic membranes M5 and M1 with molecular weight cut-offs, MWCO 10 and 70 kD, respectively. It is shown that the separation of peptides is controlled by a dual mechanism: size exclusion and electrostatic repulsion. When the ionic strength is high enough to screen out the electrostatic interactions, experimental data are in good agreement with a sieving model developed to estimate the intrinsic transmission from the molecular weight of a component and from the MWCO of the membranes. Although the transmission so found is altered by concentration polarisation and pore blocking mechanisms, the results explain the apparent low transmission of peptides by ultrafiltration membranes. If the ionic strength of the fluid is low, electrostatic interactions can influence the transport phenomena, provided that the molecules are highly charged (at pHs away from the pI). For attractive interactions, an apparent partition coefficient larger than 1 is observed. Otherwise, the transmission is lower than predicted by the sieving theoretical equation, as if the partition coefficient were smaller than 1.


Subject(s)
Caseins/isolation & purification , Membranes, Artificial , Peptides/isolation & purification , Ultrafiltration , Diffusion , Osmolar Concentration , Peptides/chemistry , Permeability
16.
Biotechnol Bioeng ; 38(5): 528-34, 1991 Aug 20.
Article in English | MEDLINE | ID: mdl-18604811

ABSTRACT

Ultrafiltration of high-purity grade bovine serum albumin has been carried out under various temperature between 5 and 30 degrees C and at various cross-flow velocities, pressures, and concentrations with the aim of studying protein denaturation and its consequences on the process. Three different pump heads have been tested. Denaturation of proteins in solution has been monitored by laser light scattering and size exclusion chromatography. The rate of protein denaturation increases with temperature, cross-flow, and time. It is observed that membrane fouling is different whether denaturation has occurred or not. Under high-concentration polarization, denaturation can occur in the boundary layer if the wall concentration exceeds 400 g/L. It is shown how the residence time, operating temperature, and pressure play an important part in membrane fouling. This can provide guidelines for process design and control.

17.
Biotechnol Bioeng ; 34(2): 171-9, 1989 Jun 20.
Article in English | MEDLINE | ID: mdl-18588090

ABSTRACT

Ultrafiltration through Carbosep M(4) mineral membrane of protein solutions of decreasing complexity (whey before and after centrifugation or clarification, beta-lactoglobulin) was studied. Mathematical models were used to explain variations in flux with time. Taking into account variations in protein retention and hydraulic resistance of the membrane during ultrafiltration, proteins and lipoproteins were found to be involved not only in the polarization layer (reversible fouling leading to a difference in the osmotic pressure), but also in irreversible fouling by adsorption. Morever, the presence of particles (e.g., inorganic precipitates) in whey explains the build-up of a deposit over and within the membrane which contributes to the decline in flux after 1 h ultrafiltration. The relative importance of these phenomena was quantified.

SELECTION OF CITATIONS
SEARCH DETAIL
...