332 research outputs found
Yukawa potentials in systems with partial periodic boundary conditions I : Ewald sums for quasi-two dimensional systems
Yukawa potentials are often used as effective potentials for systems as
colloids, plasmas, etc. When the Debye screening length is large, the Yukawa
potential tends to the non-screened Coulomb potential ; in this small screening
limit, or Coulomb limit, the potential is long ranged. As it is well known in
computer simulation, a simple truncation of the long ranged potential and the
minimum image convention are insufficient to obtain accurate numerical data on
systems. The Ewald method for bulk systems, i.e. with periodic boundary
conditions in all three directions of the space, has already been derived for
Yukawa potential [cf. Y., Rosenfeld, {\it Mol. Phys.}, \bm{88}, 1357, (1996)
and G., Salin and J.-M., Caillol, {\it J. Chem. Phys.}, \bm{113}, 10459,
(2000)], but for systems with partial periodic boundary conditions, the Ewald
sums have only recently been obtained [M., Mazars, {\it J. Chem. Phys.}, {\bf
126}, 056101 (2007)]. In this paper, we provide a closed derivation of the
Ewald sums for Yukawa potentials in systems with periodic boundary conditions
in only two directions and for any value of the Debye length. A special
attention is paid to the Coulomb limit and its relation with the
electroneutrality of systems.Comment: 40 pages, 5 figures and 4 table
A revision of the status of Lepadogaster lepadogaster (Teleostei : Gobiesocidae): sympatric subspecies or a long misunderstood blend of species?
Molecular (partial mitochondrial 12S ribosomal DNA sequences), morphological and meristic analysis of Lepadogaster lepadogaster lepadogaster, L. l. purpurea and L. zebrina were performed to investigate the relationships between these taxa. On the western shore of mainland Portugal, where the two subspecies of L. lepadogaster occur sympatrically, they differ in microhabitat preferences and their breeding seasons are largely out of phase. This information, combined with data on distribution patterns, led to the following conclusions: Lepadogaster l. purpurea is considered to be a valid species, L. purpurea (Bonnaterre, 1788), different from L. l. lepadogaster, now designated L. lepadogaster (Bonnaterre, 1788). L. zebrina was found to be a synonym of L. lepadogaster. The two newly defined species were found to be in sympatry at Madeira and the Canary islands, the Atlantic coast of the Iberian Peninsula, and the Mediterranean at least as far as Genoa (Italy). Diagnostic characters and a list of synonyms are provided. (C) 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 76, 327-338
Quantitative imaging of concentrated suspensions under flow
We review recent advances in imaging the flow of concentrated suspensions,
focussing on the use of confocal microscopy to obtain time-resolved information
on the single-particle level in these systems. After motivating the need for
quantitative (confocal) imaging in suspension rheology, we briefly describe the
particles, sample environments, microscopy tools and analysis algorithms needed
to perform this kind of experiments. The second part of the review focusses on
microscopic aspects of the flow of concentrated model hard-sphere-like
suspensions, and the relation to non-linear rheological phenomena such as
yielding, shear localization, wall slip and shear-induced ordering. Both
Brownian and non-Brownian systems will be described. We show how quantitative
imaging can improve our understanding of the connection between microscopic
dynamics and bulk flow.Comment: Review on imaging hard-sphere suspensions, incl summary of
methodology. Submitted for special volume 'High Solid Dispersions' ed. M.
Cloitre, Vol. xx of 'Advances and Polymer Science' (Springer, Berlin, 2009);
22 pages, 16 fig
Clusters of galaxies : observational properties of the diffuse radio emission
Clusters of galaxies, as the largest virialized systems in the Universe, are
ideal laboratories to study the formation and evolution of cosmic
structures...(abridged)... Most of the detailed knowledge of galaxy clusters
has been obtained in recent years from the study of ICM through X-ray
Astronomy. At the same time, radio observations have proved that the ICM is
mixed with non-thermal components, i.e. highly relativistic particles and
large-scale magnetic fields, detected through their synchrotron emission. The
knowledge of the properties of these non-thermal ICM components has increased
significantly, owing to sensitive radio images and to the development of
theoretical models. Diffuse synchrotron radio emission in the central and
peripheral cluster regions has been found in many clusters. Moreover
large-scale magnetic fields appear to be present in all galaxy clusters, as
derived from Rotation Measure (RM) studies. Non-thermal components are linked
to the cluster X-ray properties, and to the cluster evolutionary stage, and are
crucial for a comprehensive physical description of the intracluster medium.
They play an important role in the cluster formation and evolution. We review
here the observational properties of diffuse non-thermal sources detected in
galaxy clusters: halos, relics and mini-halos. We discuss their classification
and properties. We report published results up to date and obtain and discuss
statistical properties. We present the properties of large-scale magnetic
fields in clusters and in even larger structures: filaments connecting galaxy
clusters. We summarize the current models of the origin of these cluster
components, and outline the improvements that are expected in this area from
future developments thanks to the new generation of radio telescopes.Comment: Accepted for the publication in The Astronomy and Astrophysics
Review. 58 pages, 26 figure
A sensitive flow cytometric methodology for studying the binding of L. chagasi to canine peritoneal macrophages
BACKGROUND: The Leishmania promastigote-macrophage interaction occurs through the association of multiple receptors on the biological membrane surfaces. The success of the parasite infection is dramatically dependent on this early interaction in the vertebrate host, which permits or not the development of the disease. In this study we propose a novel methodology using flow cytometry to study this interaction, and compare it with a previously described "in vitro" binding assay. METHODS: To study parasite-macrophage interaction, peritoneal macrophages were obtained from 4 dogs and adjusted to 3 × 10(6 )cells/mL. Leishmania (Leishmania) chagasi parasites (stationary-phase) were adjusted to 5 × 10(7 )cells/mL. The interaction between CFSE-stained Leishmania chagasi and canine peritoneal macrophages was performed in polypropylene tubes to avoid macrophage adhesion. We carried out assays in the presence or absence of normal serum or in the presence of a final concentration of 5% of C5 deficient (serum from AKR/J mice) mouse serum. Then, the number of infected macrophages was counted in an optical microscope, as well as by flow citometry. Macrophages obtained were stained with anti-CR3 (CD11b/CD18) antibodies and analyzed by flow citometry. RESULTS: Our results have shown that the interaction between Leishmania and macrophages can be measured by flow cytometry using the fluorescent dye CFSE to identify the Leishmania, and measuring simultaneously the expression of an important integrin involved in this interaction: the CD11b/CD18 (CR3 or Mac-1) β2 integrin. CONCLUSION: Flow cytometry offers rapid, reliable and sensitive measurements of single cell interactions with Leishmania in unstained or phenotypically defined cell populations following staining with one or more fluorochromes
Towards a New Paradigm of Non-Captive Research on Cetacean Cognition
Contemporary knowledge of impressive neurophysiology and behavior in cetaceans, combined with increasing opportunities for studying free-ranging cetaceans who initiate sociable interaction with humans, are converging to highlight serious ethical considerations and emerging opportunities for a new era of progressive and less-invasive cetacean research. Most research on cetacean cognition has taken place in controlled captive settings, e.g., research labs, marine parks. While these environments afford a certain amount of experimental rigor and logistical control they are fraught with limitations in external validity, impose tremendous stress on the part of the captive animals, and place burdens on populations from which they are often captured. Alternatively, over the past three decades, some researchers have sought to focus their attention on the presence of free-ranging cetacean individuals and groups who have initiated, or chosen to participate in, sociable interactions with humans in the wild. This new approach, defined as Interspecies Collaborative Research between cetacean and human, involves developing novel ways to address research questions under natural conditions and respecting the individual cetacean's autonomy. It also offers a range of potential direct benefits to the cetaceans studied, as well as allowing for unprecedented cognitive and psychological research on sociable mysticetes. Yet stringent precautions are warranted so as to not increase their vulnerability to human activities or pathogens. When conducted in its best and most responsible form, collaborative research with free-ranging cetaceans can deliver methodological innovation and invaluable new insights while not necessitating the ethical and scientific compromises that characterize research in captivity. Further, it is representative of a new epoch in science in which research is designed so that the participating cetaceans are the direct recipients of the benefits
Involvement of VDAC, Bax and Ceramides in the Efflux of AIF from Mitochondria during Curcumin-Induced Apoptosis
Contains fulltext :
80085.pdf (publisher's version ) (Open Access)BACKGROUND: We previously identified curcumin as a potent inducer of fibroblast apoptosis, which could be used to treat hypertrophic scar formation. Here we investigated the underlying mechanism of this process. PRINCIPAL FINDINGS: Curcumin-induced apoptosis could not be blocked by caspase-inhibitors and we could not detect any caspase-3/7 activity. Curcumin predominantly induced mitochondria-mediated ROS formation and stimulated the expression of the redox-sensitive pro-apoptotic factor p53. Inhibition of the pro-apoptotic signaling enzyme glycogen synthase kinase-3beta (GSK-3beta) blocked curcumin-induced apoptosis. Apoptosis was associated with high molecular weight DNA damage, a possible indicator of apoptosis-inducing factor (AIF) activity. Indeed, curcumin caused nuclear translocation of AIF, which could be blocked by the antioxidant N-acetyl cysteine. We next investigated how AIF is effluxed from mitochondria in more detail. The permeability transition pore complex (PTPC), of which the voltage-dependent anion channel (VDAC) is a component, could be involved since the VDAC-inhibitor DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) efficiently blocked AIF translocation. However, PTPC is not involved in AIF release since cyclosporine A, a specific inhibitor of the complex did not block apoptosis. Alternatively, the pro-apoptotic protein Bax could have formed mitochondrial channels and interacted with VDAC. Curcumin caused mitochondrial translocation of Bax, which was blocked by DIDS, suggesting a Bax-VDAC interaction. Interestingly, ceramide channels can also release apoptogenic factors from mitochondria and we found that addition of ceramide induced caspase-independent apoptosis. Surprisingly, this process could also be blocked by DIDS, suggesting the concerted action of Bax, VDAC and ceramide in the efflux of AIF from the mitochondrion. CONCLUSIONS: Curcumin-induced fibroblast apoptosis is totally caspase-independent and relies on the mitochondrial formation of ROS and the subsequent nuclear translocation of AIF, which is released from a mitochondrial pore that involves VDAC, Bax and possibly ceramides. The composition of the AIF-releasing channel seems to be much more complex than previously thought
Characterization of an Nmr Homolog That Modulates GATA Factor-Mediated Nitrogen Metabolite Repression in Cryptococcus neoformans
Nitrogen source utilization plays a critical role in fungal development, secondary metabolite production and pathogenesis. In both the Ascomycota and Basidiomycota, GATA transcription factors globally activate the expression of catabolic enzyme-encoding genes required to degrade complex nitrogenous compounds. However, in the presence of preferred nitrogen sources such as ammonium, GATA factor activity is inhibited in some species through interaction with co-repressor Nmr proteins. This regulatory phenomenon, nitrogen metabolite repression, enables preferential utilization of readily assimilated nitrogen sources. In the basidiomycete pathogen Cryptococcus neoformans, the GATA factor Gat1/Are1 has been co-opted into regulating multiple key virulence traits in addition to nitrogen catabolism. Here, we further characterize Gat1/Are1 function and investigate the regulatory role of the predicted Nmr homolog Tar1. While GAT1/ARE1 expression is induced during nitrogen limitation, TAR1 transcription is unaffected by nitrogen availability. Deletion of TAR1 leads to inappropriate derepression of non-preferred nitrogen catabolic pathways in the simultaneous presence of favoured sources. In addition to exhibiting its evolutionary conserved role of inhibiting GATA factor activity under repressing conditions, Tar1 also positively regulates GAT1/ARE1 transcription under non-repressing conditions. The molecular mechanism by which Tar1 modulates nitrogen metabolite repression, however, remains open to speculation. Interaction between Tar1 and Gat1/Are1 was undetectable in a yeast two-hybrid assay, consistent with Tar1 and Gat1/Are1 each lacking the conserved C-terminus regions present in ascomycete Nmr proteins and GATA factors that are known to interact with each other. Importantly, both Tar1 and Gat1/Are1 are suppressors of C. neoformans virulence, reiterating and highlighting the paradigm of nitrogen regulation of pathogenesis
Splint: the efficacy of orthotic management in rest to prevent equinus in children with cerebral palsy, a randomised controlled trial
<p>Abstract</p> <p>Background</p> <p>Range of motion deficits of the lower extremity occur in about the half of the children with spastic cerebral palsy (CP). Over time, these impairments can cause joint deformities and deviations in the children's gait pattern, leading to limitations in moblity. Preventing a loss of range of motion is important in order to reduce secondary activity limitations and joint deformities. Sustained muscle stretch, imposed by orthotic management in rest, might be an effective method of preventing a decrease in range of motion. However, no controlled study has been performed.</p> <p>Methods</p> <p>A single blind randomised controlled trial will be performed in 66 children with spastic CP, divided over three groups with each 22 participants. Two groups will be treated for 1 year with orthoses to prevent a decrease in range of motion in the ankle (either with static or dynamic knee-ankle-foot-orthoses) and a third group will be included as a control group and will receive usual care (physical therapy, manual stretching). Measurements will be performed at baseline and at 3, 6, 9 and 12 months after treatment allocation. The primary outcome measure will be ankle dorsiflexion at full knee extension, measured with a custom designed hand held dynamometer. Secondary outcome measures will be i) ankle and knee flexion during gait and ii) gross motor function. Furthermore, to gain more insight in the working mechanism of the orthotic management in rest, morphological parameters like achilles tendon length, muscle belly length, muscle fascicle length, muscle physiological cross sectional area length and fascicle pennation angle will be measured in a subgroup of 18 participants using a 3D imaging technique.</p> <p>Discussion</p> <p>This randomised controlled trial will provide more insight into the efficacy of orthotic management in rest and the working mechanisms behind this treatment. The results of this study could lead to improved treatments.</p> <p>Trial Registration Number</p> <p>Nederlands Trial Register <a href="http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=2091">NTR2091</a></p
Mass Spectrometry Analysis of Hepcidin Peptides in Experimental Mouse Models
The mouse is a valuable model for unravelling the role of hepcidin in iron homeostasis, however, such studies still report hepcidin mRNA levels as a surrogate marker for bioactive hepcidin in its pivotal function to block ferroportin-mediated iron transport. Here, we aimed to assess bioactive mouse Hepcidin-1 (Hep-1) and its paralogue Hepcidin-2 (Hep-2) at the peptide level. To this purpose, fourier transform ion cyclotron resonance (FTICR) and tandem-MS was used for hepcidin identification, after which a time-of-flight (TOF) MS-based methodology was exploited to routinely determine Hep-1 and -2 levels in mouse serum and urine. This method was biologically validated by hepcidin assessment in: i) 3 mouse strains (C57Bl/6; DBA/2 and BABL/c) upon stimulation with intravenous iron and LPS, ii) homozygous Hfe knock out, homozygous transferrin receptor 2 (Y245X) mutated mice and double affected mice, and iii) mice treated with a sublethal hepatotoxic dose of paracetamol. The results showed that detection of Hep-1 was restricted to serum, whereas Hep-2 and its presumed isoforms were predominantly present in urine. Elevations in serum Hep-1 and urine Hep-2 upon intravenous iron or LPS were only moderate and varied considerably between mouse strains. Serum Hep-1 was decreased in all three hemochromatosis models, being lowest in the double affected mice. Serum Hep-1 levels correlated with liver hepcidin-1 gene expression, while acute liver damage by paracetamol depleted Hep-1 from serum. Furthermore, serum Hep-1 appeared to be an excellent indicator of splenic iron accumulation. In conclusion, Hep-1 and Hep-2 peptide responses in experimental mouse agree with the known biology of hepcidin mRNA regulators, and their measurement can now be implemented in experimental mouse models to provide novel insights in post-transcriptional regulation, hepcidin function, and kinetics
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