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1
Sisco, Nicholas J., Ping Wang, Ashley M. Stokes et Richard D. Dortch. « Rapid parameter estimation for selective inversion recovery myelin imaging using an open-source Julia toolkit ». PeerJ 10 (29 mars 2022) : e13043. http://dx.doi.org/10.7717/peerj.13043.
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Background Magnetic resonance imaging (MRI) is used extensively to quantify myelin content, however computational bottlenecks remain challenging for advanced imaging techniques in clinical settings. We present a fast, open-source toolkit for processing quantitative magnetization transfer derived from selective inversion recovery (SIR) acquisitions that allows parameter map estimation, including the myelin-sensitive macromolecular pool size ratio (PSR). Significant progress has been made in reducing SIR acquisition times to improve clinically feasibility. However, parameter map estimation from the resulting data remains computationally expensive. To overcome this computational limitation, we developed a computationally efficient, open-source toolkit implemented in the Julia language. Methods To test the accuracy of this toolkit, we simulated SIR images with varying PSR and spin-lattice relaxation time of the free water pool (R1f) over a physiologically meaningful scale from 5% to 20% and 0.5 to 1.5 s−1, respectively. Rician noise was then added, and the parameter maps were estimated using our Julia toolkit. Probability density histogram plots and Lin’s concordance correlation coefficients (LCCC) were used to assess accuracy and precision of the fits to our known simulation data. To further mimic biological tissue, we generated five cross-linked bovine serum albumin (BSA) phantoms with concentrations that ranged from 1.25% to 20%. The phantoms were imaged at 3T using SIR, and data were fit to estimate PSR and R1f. Similarly, a healthy volunteer was imaged at 3T, and SIR parameter maps were estimated to demonstrate the reduced computational time for a real-world clinical example. Results Estimated SIR parameter maps from our Julia toolkit agreed with simulated values (LCCC > 0.98). This toolkit was further validated using BSA phantoms and a whole brain scan at 3T. In both cases, SIR parameter estimates were consistent with published values using MATLAB. However, compared to earlier work using MATLAB, our Julia toolkit provided an approximate 20-fold reduction in computational time. Conclusions Presented here, we developed a fast, open-source, toolkit for rapid and accurate SIR MRI using Julia. The reduction in computational cost should allow SIR parameters to be accessible in clinical settings.
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Capozza, Martina, Rachele Stefania, Luisa Rosas, Francesca Arena, Lorena Consolino, Annasofia Anemone, James Cimino, Dario Livio Longo et Silvio Aime. « An Improved Biocompatible Probe for Photoacoustic Tumor Imaging Based on the Conjugation of Melanin to Bovine Serum Albumin ». Applied Sciences 10, no 23 (24 novembre 2020) : 8313. http://dx.doi.org/10.3390/app10238313.
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A novel, highly biocompatible, well soluble melanin-based probe obtained from the conjugation of melanin macromolecule to bovine serum albumin (BSA) was tested as a contrast agent for photoacoustic tumor imaging. Five soluble conjugates (PheoBSA A-E) were synthesized by oxidation of dopamine (DA) in the presence of variable amounts of BSA. All systems showed the similar size and absorbance spectra, being PheoBSA D (DA:BSA ratio 1:2) the one showing the highest photoacoustic efficiency. This system was then selected for the investigations as it showed a marked enhancement of the photoacoustic (PA) contrast in the tumor region upon iv injection. Biodistribution studies confirmed the accumulation of PheoBSA D within the tumor region and showed fast renal elimination, lack of cell toxicity, and good hemocompatibility. A higher PA contrast enhancement was observed in the case of PC3 prostate tumor xenograft when compared to the TS/A breast one, likely reflecting different vascularization/extravasation properties between the two tumor murine models. The improved PA properties shown by PheoBSA D allowed to set up a 3D dynamic contrast-enhanced (DCE) approach that demonstrated a persistent increase of the PA signal in the tumor region for a long period. Overall, the herein reported results demonstrate that PheoBSA D is a promising blood pool contrast agent for in vivo PA imaging, particularly useful for the set-up of 3D DCE-PA approaches to monitor tumor vascular properties.
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Sun, Shou Jin, et Milan Brandt. « Investigation of Hastelloy C Laser Clad Melt Pool Size and its Effect on Clad Formation ». Key Engineering Materials 384 (juin 2008) : 213–27. http://dx.doi.org/10.4028/www.scientific.net/kem.384.213.
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The melt pool size of a single-track clad in the laser cladding of Hastelloy C, a Nickel based alloy, on mild steel substrate has been investigated. The effect of laser processing parameters, such as laser power density, scan rate and powder mass flow rate on the melt pool size has been examined. It was found that the melt pool size is strictly controlled by the melt pool temperature which increases with laser power but decreases with increasing scan rate and powder mass flow rate. The melt pool size is critical for the clad formation in terms of clad height and dilution with the substrate. The clad height increases linearly with the ratio of melt pool size to powder stream diameter while the dilution is an exponential function of the ratio of melt pool size to laser spot size.
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Hu, Ping, Terrance Leighton, Galina Ishkhanova et Sydney Kustu. « Sensing of Nitrogen Limitation by Bacillus subtilis : Comparison to Enteric Bacteria ». Journal of Bacteriology 181, no 16 (15 août 1999) : 5042–50. http://dx.doi.org/10.1128/jb.181.16.5042-5050.1999.
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ABSTRACT Previous studies showed that Salmonella typhimuriumapparently senses external nitrogen limitation as a decrease in the concentration of the internal glutamine pool. To determine whether the inverse relationship observed between doubling time and the glutamine pool size in enteric bacteria was also seen in phylogenetically distant organisms, we studied this correlation in Bacillus subtilis, a gram-positive, sporulating bacterium. We measured the sizes of the glutamine and glutamate pools for cells grown in batch culture on different nitrogen sources that yielded a range of doubling times, for cells grown in ammonia-limited continuous culture, and for mutant strains (glnA) in which the catalytic activity of glutamine synthetase was lowered. Although the glutamine pool size ofB. subtilis clearly decreased under certain conditions of nitrogen limitation, particularly in continuous culture, the inverse relationship seen between glutamine pool size and doubling time in enteric bacteria was far less obvious in B. subtilis. To rule out the possibility that differences were due to the fact thatB. subtilis has only a single pathway for ammonia assimilation, we disrupted the gene (gdh) that encodes the biosynthetic glutamate dehydrogenase in Salmonella. Studies of the S. typhimurium gdh strain in ammonia-limited continuous culture and of gdh glnA double-mutant strains indicated that decreases in the glutamine pool remained profound in strains with a single pathway for ammonia assimilation. Simple working hypotheses to account for the results with B. subtilis are that this organism refills an initially low glutamine pool by diminishing the utilization of glutamine for biosynthetic reactions and/or replenishes the pool by means of macromolecular degradation.
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Matkovic, Tanja, Matthias Siebert, Elena Knoche, Harald Depner, Sara Mertel, David Owald, Manuela Schmidt et al. « The Bruchpilot cytomatrix determines the size of the readily releasable pool of synaptic vesicles ». Journal of Cell Biology 202, no 4 (19 août 2013) : 667–83. http://dx.doi.org/10.1083/jcb.201301072.
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Synaptic vesicles (SVs) fuse at a specialized membrane domain called the active zone (AZ), covered by a conserved cytomatrix. How exactly cytomatrix components intersect with SV release remains insufficiently understood. We showed previously that loss of the Drosophila melanogaster ELKS family protein Bruchpilot (BRP) eliminates the cytomatrix (T bar) and declusters Ca2+ channels. In this paper, we explored additional functions of the cytomatrix, starting with the biochemical identification of two BRP isoforms. Both isoforms alternated in a circular array and were important for proper T-bar formation. Basal transmission was decreased in isoform-specific mutants, which we attributed to a reduction in the size of the readily releasable pool (RRP) of SVs. We also found a corresponding reduction in the number of SVs docked close to the remaining cytomatrix. We propose that the macromolecular architecture created by the alternating pattern of the BRP isoforms determines the number of Ca2+ channel-coupled SV release slots available per AZ and thereby sets the size of the RRP.
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Kobayashi, Hisataka, et Martin W. Brechbiel. « Dendrimer-based Macromolecular MRI Contrast Agents : Characteristics and Application ». Molecular Imaging 2, no 1 (1 janvier 2003) : 153535002003031. http://dx.doi.org/10.1162/15353500200303100.
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Numerous macromolecular MRI contrast agents prepared employing relatively simple chemistry may be readily available that can provide sufficient enhancement for multiple applications. These agents operate using a ~100-fold lower concentration of gadolinium ions in comparison to the necessary concentration of iodine employed in CT imaging. Herein, we describe some of the general potential directions of macromolecular MRI contrast agents using our recently reported families of dendrimer-based agents as examples. Changes in molecular size altered the route of excretion. Smaller-sized contrast agents less than 60 kDa molecular weight were excreted through the kidney resulting in these agents being potentially suitable as functional renal contrast agents. Hydrophilic and larger-sized contrast agents were found better suited for use as blood pool contrast agents. Hydrophobic variants formed with polypropylenimine diaminobutane dendrimer cores created liver contrast agents. Larger hydrophilic agents are useful for lymphatic imaging. Finally, contrast agents conjugated with either monoclonal antibodies or with avidin are able to function as tumor-specific contrast agents, which also might be employed as therapeutic drugs for either gadolinium neutron capture therapy or in conjunction with radioimmunotherapy.
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Millane, Rick P., et Romain D. Arnal. « Uniqueness of the macromolecular crystallographic phase problem ». Acta Crystallographica Section A Foundations and Advances 71, no 6 (6 octobre 2015) : 592–98. http://dx.doi.org/10.1107/s2053273315015387.
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Uniqueness of the phase problem in macromolecular crystallography, and its relationship to the case of single particle imaging, is considered. The crystallographic problem is characterized by a constraint ratio that depends only on the size and symmetry of the molecule and the unit cell. The results are used to evaluate the effect of various real-space constraints. The case of an unknown molecular envelope is considered in detail. The results indicate the quite wide circumstances under whichab initiophasing should be possible.
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Terashima, Noritsugu, Chisato Ko, Yasuyuki Matsushita et Ulla Westermark. « Monolignol glucosides as intermediate compounds in lignin biosynthesis. Revisiting the cell wall lignification and new 13C-tracer experiments with Ginkgo biloba and Magnolia liliiflora ». Holzforschung 70, no 9 (1 septembre 2016) : 801–10. http://dx.doi.org/10.1515/hf-2015-0224.
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Abstract A large amount of monolignol glucosides (MLGs: p-glucocoumaryl alcohol, coniferin, syringin) are found in lignifying soft xylem near cambium and they disappear with the progress of lignification. Recently, it became a matter of debate whether those MLGs are real intermediates in lignin biosynthesis or only a storage form of monolignols outside of the main biosynthetic pathway. The latter is partly based on a misinterpretation of 14C-tracer experiments and partly on the simple generalization of the results of gene manipulation experiments concerning the flexible and complex lignification. In the present paper, it could be confirmed by the most reliable 13C-tracer method that MLGs are real intermediates in the pathway from l-phenylalanine to macromolecular lignin-polysaccharides complexes in the cell walls. This pathway via MLGs is essential for transport and programmed delivery of specific monolignols in a stable form from intracellular space to specific lignifying sites within the cell wall. The pool size of MLGs is large in most gymnosperm trees and some angiosperm species that emerged in an early stage of phylogeny, while the pool size is small in most angiosperms. This difference in pool size is reasonably understandable from the viewpoint of plant evolution, in the course of which the role of MLGs changed to meet variation in type of major cells, reaction wood formation, and postmortem lignification.
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Berzins, S. P., R. L. Boyd et J. F. A. P. Miller. « The Role of the Thymus and Recent Thymic Migrants in the Maintenance of the Adult Peripheral Lymphocyte Pool ». Journal of Experimental Medicine 187, no 11 (1 juin 1998) : 1839–48. http://dx.doi.org/10.1084/jem.187.11.1839.
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The thymus is essential for the initial seeding of T cells to the periphery, but its role in maintaining the adult T cell pool remains poorly defined. We investigated whether changes to the rate of T cell export could form part of the mechanism(s) controlling the homeostatic regulation of the size and composition of the peripheral T cell pool. Using neonatal thymi grafted under the kidney capsule, we found that irrespective of whether the pool was oversupplied (by thymic grafts) or undersupplied (due to neonatal thymectomy), the thymic export rate was constant from both the host and graft thymus, and the periphery remained constant in size. Recent thymic emigrants (RTE) were also tracked to determine the extent of their acceptance into the T cell pool of a normal mouse. As a population, RTE are phenotypically mature, but were distinct from resident T cells in the periphery, being released in a CD4/CD8 ratio approximately twice that of established peripheral T cells. This export ratio is similar to that of T cells in the mature thymic compartment, but soon after entry into the periphery, the ratio falls, indicating separate thymic and peripheral regulation of the CD4/CD8 ratio. RTE may also be preferentially incorporated into the periphery, causing displacement of resident T cells, thus maintaining the size of the peripheral pool. Although not vital for the maintenance of a functional T cell pool, the acceptance of RTE in a “full” peripheral pool would ensure that the T cell receptor repertoire is kept diverse and that the T cell population encompasses a broad range of naive as well as memory T cells.
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Lewis, D. S., E. M. Jackson et G. E. Mott. « Triiodothyronine accelerates maturation of bile acid metabolism in infant baboons ». American Journal of Physiology-Endocrinology and Metabolism 268, no 5 (1 mai 1995) : E889—E896. http://dx.doi.org/10.1152/ajpendo.1995.268.5.e889.
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We tested the hypothesis that triiodothyronine (T3) treatment accelerates the early postnatal maturation of bile acid metabolism in the baboon. Infant baboons were implanted with 21-day-release pellets containing T3 (n = 12), a placebo pellet (n = 6), or no pellet (n = 13). T3 treatment increased plasma T3 concentrations from 3.0 to 5.0 nmol/l between birth and 15 wk of age. At 15 wk of age, bile acid pool sizes, fractional turnover rates (FTR), and synthetic rates were determined by an isotope-dilution method with 3H- and 14C-labeled cholic (CA) and chenodeoxycholic acid (CDCA). T3 treatment increased CA pool size by 47% and CA synthetic rate by 37% but did not significantly affect CDCA pool size or synthetic rate. Consequently CA-to-CDCA pool size ratio (0.77 vs. 0.42) and biliary CA-to-CDCA concentration ratio (0.88 vs. 0.46) were higher in the T3-treated infants than in combined placebo-treated and nontreated control infants. T3 treatment did not affect the bile acid glycine-to-taurine conjugate ratio, CA FTR, or CDCA pool size, FTR, and synthetic rate. T3 treatment lowered plasma high-density lipoprotein fraction 2 and 3 cholesterol concentrations by 22 and 40%, respectively. T3 treatment also increased hepatic low-density lipoprotein receptor mRNA levels but did not affect plasma low-density lipoprotein cholesterol concentrations. We conclude that modest elevation of plasma T3 during the preweaning period increases the CA-to-CDCA ratio at the end of the preweaning period to near adult values.
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Abdizadeh, H., Y. Vahidshad, H. R. Baharvandi et M. Akbari Baseri. « EFFECT OF REVERSE MICELLE WATER POOL IN SYNTHESIS OF ZIRCONIA STABILIZED COPPER NANOCOMPOSITE ». International Journal of Modern Physics : Conference Series 05 (janvier 2012) : 559–67. http://dx.doi.org/10.1142/s2010194512002474.
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In the water-in-oil (W/O) microemulsions based on anionic (AOT) surfactants, the ω value (molar ratio of water to surfactant), precursor, and surfactant could remarkably affect the synthesis of CuO - ZrO 2 nanocomposite and the morphologies of the sol-gel products simultaneously. In this study, CuO - ZrO 2 nanoparticles are synthesized using microreactors made of surfactant/water/n-hexane microemulsions and discusses the effect of different microemulsion variables on the particle size and particle size distribution by water-to-surfactant molar ratio. The obtained powders are characterized by DTA, XRD, SEM, EDS, and TEM and their physical properties are compared. For AOT surfactant the particle size increased with increasing the water to surfactant molar ratio. The particles size of CuO - ZrO 2 nanocomposite in sample with anionic surfactant with molar ratio of 6 that calcined at 600°C is between 15-20 nm.
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Setiawan, Edi, Faizal Ridwan Zamzani et Nur Fitri Amelia. « CASH POSITION, DEBT TO EQUITY RATIO, RETURN ON ASSET DAN FIRM SIZE TERHADAP DIVIDENT PAYOUT RATIO ». JURNAL NUSANTARA APLIKASI MANAJEMEN BISNIS 3, no 1 (18 avril 2018) : 78. http://dx.doi.org/10.29407/nusamba.v3i1.11980.
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This research is aimed to knowing and analyzing the effect of the cash position, debt to equity ratio, return on asset and firm size to divident payout ratio. The type of data used in this study is pool data which is a combination time series, and cross section. panel data regression anlaysis test, election panel data reression estimation techniques, heteroscedasticity test, regression model analysis, and regression model testin and regression coefficients. The result showed that the partial debt to equity ratio and firm size no significantly influence the divident payout ratio, while the cash position, return on asset significantly influence the divident payout ratio. Simultaneously, cash position, debt to equity ratio, return on asset and firm size variable have a significant to divident payout ratio.
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Lebreton, Philippe, Bernard Jeangros, Christiane Gallet et Jan Scehovic. « Sur l'organisation phytochimique de formations prairiales permanentes ». Canadian Journal of Botany 79, no 4 (1 avril 2001) : 510–19. http://dx.doi.org/10.1139/b01-020.
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Organic and mineral components have been analysed on 18 dicotyledonous species of permanent grassland communities. Multivariate analysis revealed an opposition between a macromolecular pool (cellulose and lignin) and a nutrient pool (potassium and phosphorus, nitrogen). The first pole is characterized by Tragopogon pratensis L. (Compositae) and Galium mollugo L. (Rubiaceae), the second by Anthriscus sylvestris (L.) Hoffm. (Umbelliferae) and Geranium sylvaticum L. (Geraniaceae). The most thermo-helio-xerophilous species (Knautia arvensis (L.) Coult and Tragopogon pratensis) belong to the first group, whereas the second group includes the cool-environment species (like Alchemilla xanthochlora Roth.), which reveals an ecophysiological determinism. Moreover, correlations between the biochemical and ecological structure, and other interrelated parameters, including sclerophylly, have been shown. Compared to lignous and sempervirent plant communities, the grassland species have lower phenolic and lignin contents but higher glucide and nutrient (potassium and phosphorus) contents, which is in accordance with their food value. For this herbaceous community, the C/N ratio indicates the same general equilibrium between cell-wall macromolecules and nitrogen than for two other plant communities (mainly ligneous) previously studied, with some differences revealing distinct trends from the same general metabolic sheme.Key words: dicotyledonous plant communities, biochemical organization, C/N ratio, ecophysiology.
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Davies, G. R., A. Ramani, C. M. Dalton, D. J. Tozer, C. AM Wheeler-Kingshott, G. J. Barker, A. J. Thompson, D. H. Miller et P. S. Tofts. « Preliminary magnetic resonance study of the macromolecular proton fraction in white matter : a potential marker of myelin ? » Multiple Sclerosis Journal 9, no 3 (juin 2003) : 246–49. http://dx.doi.org/10.1191/1352458503ms911oa.
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We report on a new quantitative magnetization transfer (MT) technique that allows for the in vivo estimation of the macromolecular proton fraction (f) and the bound pool T2 relaxation time (T2b), whilst permitting whole brain coverage. In this pilot study, five subjects with multiple sclerosis (MS) and five healthy controls were studied. Both f and T2b were significantly different between MS lesions and normal control white matter (WM). Relationships between f and T1 relaxation time [Spearman’s rank correlation coefficient (rs) =-0.97, P <0.001] and f and the magnetization transfer ratio (MTR; rs =0.80, P <0.001) were observed. C ompared with MTR, f and T2b have the potential advantage of relative independence from MT acquisition protocol while offering more pathologically specific information. In particular, f may provide a more direct indication of myelin content in WM.
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ZHU, HUI, PENG CHEN, RU XIA, JIASHENG QIAN, JIBIN MIAO, BIN YANG et LIFEN SU. « EFFECT OF MACROMOLECULAR COUPLING AGENT PMMA-b-PVTES ON STABILIZING NANO-Si3N4 ». Nano 09, no 08 (décembre 2014) : 1450095. http://dx.doi.org/10.1142/s1793292014500957.
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Poly(methyl methacrylate)-b-poly(vinyltriethoxysilane) (PMMA-b-PVTES) are synthesized using atom transfer radical polymerization (ATRP) and used as macromolecular coupling agents to modify silicon nitride nanoparticles (nano- Si 3 N 4). The chemical composition of copolymers PMMA-b-PVTES and modified nano- Si 3 N 4 are confirmed by various characterization techniques. The modified nano- Si 3 N 4 shows excellent hydrophobic nature, which make nanoparticles (NPs) stably disperse in organic solvent. Transmission electron microscope (TEM), particle size testing, contact angle measuring and sedimentation experiment are employed to examine the dispersion of modified nano- Si 3 N 4 in chloroform. By comparing the effects of copolymers with varied number-average molecular weight (Mn) and block length ratio on stabilizing nano- Si 3 N 4, we discussed the mechanism of macromolecular coupling agent stabilizing NPs. In our experiments, the copolymer PMMA88-b-PVTES17 is found to be the most effective macromolecular coupling agent for stabilizing nano- Si 3 N 4.
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Li, Chen, et G. P. Peterson. « Parametric Study of Pool Boiling on Horizontal Highly Conductive Microporous Coated Surfaces ». Journal of Heat Transfer 129, no 11 (10 avril 2007) : 1465–75. http://dx.doi.org/10.1115/1.2759969.
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To better understand the mechanisms that govern the behavior of pool boiling on horizontal highly conductive microporous coated surfaces, a series of experimental investigations were designed to systematically examine the effects of the geometric dimensions (i.e., coating thickness, volumetric porosity, and pore size, as well as the surface conditions of the porous coatings) on the pool-boiling performance and characteristics. The study was conducted using saturated distilled water at atmospheric pressure (101kPa) and porous surfaces fabricated from sintered isotropic copper wire screens. For nucleate boiling on the microporous coated surfaces, two vapor ventilation modes were observed to exist: (i) upward and (ii) mainly from sideways leakage to the unsealed sides and partially from the center of porous surfaces. The ratio of the heater size to the coating thickness, the friction factor of the two-phase flow to single-phase flow inside the porous coatings, as well as the input heat flux all govern the vapor ventilation mode that occurs. In this investigation, the ratio of heater size to coating thickness varies from 3.5 to 38 in order to identify the effect of heater size on the boiling characteristics. The experimental results indicate that the boiling performance and characteristics are also strongly dependent on the volumetric porosity and mesh size, as well as the surface conditions when the heater size is given. Descriptions and discussion of the typical boiling characteristics; the progressive boiling process, from pool nucleate boiling to film boiling; and the boiling performance curves on conductive microporous coated surfaces are all systematically presented.
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Pramanik, Sudipta, Frederik Tasche, Kay-Peter Hoyer et Mirko Schaper. « Orientation-Dependent Indentation Behaviour of Additively Manufactured FeCo Sample : A Quasi In-Situ Study ». Magnetism 2, no 2 (25 mars 2022) : 88–104. http://dx.doi.org/10.3390/magnetism2020007.
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The quasi in-situ indentation behaviour of <110>||BD and <111>||BD-oriented grains in a FeCo alloy is studied in this investigation. The effect of build height on melt pool shape and melt pool size is also studied by finite element method simulations. As the building height increases, the aspect ratio of the elliptical melt pool increases. Correspondingly, the effect of the laser scan speed on the melt pool shape and size is studied by the finite element method, because, as the laser scan speed increases, the aspect ratio of the elliptical melt pool increases, too. The microstructural characterisation of the indentation area before and after indentation is performed by electron backscatter diffraction (EBSD). Based on the EBSD data grain reference orientation deviation (GROD), calculations are performed to describe the effect of indentations on the neighbouring grain orientations. High GROD angles are detected in the neighbouring grain region adjoining the indented grain. An in-depth slip trace analysis shows the activation of all three slip systems ({110}<111>, {112}<111> and {123}<111>) which is also confirmed by slip lines on the sample surface that are detected by laser scanning confocal microscopy. A high concentration of geometrically necessary dislocations (GNDs) are observed on the adjoining area to the indentation. Local surface topography measurements by laser scanning confocal microscopy confirmed the formation of pile-ups near the indentation.
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Flynn, Kevin J., Michael J. R. Fasham et Charles R. Hipkin. « Modelling the interactions between ammonium and nitrate uptake in marine phytoplankton ». Philosophical Transactions of the Royal Society of London. Series B : Biological Sciences 352, no 1361 (29 novembre 1997) : 1625–45. http://dx.doi.org/10.1098/rstb.1997.0145.
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An empirically based mathematical model is presented which can simulate the major features of the interactions between ammonium and nitrate transport and assimilation in phytoplankton. The model (ammonium-nitrate interaction model), which is configured to simulate a generic microalga rather than a specified species, is constructed on simplified biochemical bases. A major requirement for parametrization is that the N:C ratio of the algae must be known and that transport and internal pool sizes need to be expressed per unit of cell C. The model uses the size of an internal pool of an early organic product of N assimilation (glutamine) to regulate rapid responses in ammonium-nitrate interactions. The synthesis of enzymes for the reduction of nitrate through to ammonium is induced by the size of the internal nitrate pool and repressed by the size of the glutamine pool. The assimilation of intracellular ammonium (into glutamine) is considered to be a constitutive process subjected to regulation by the size of the glutamine pool. Longer term responses have been linked to the nutrient history of the cell using the N:C cell quota. N assimilation in darkness is made a function of the amount of surplus C present and thus only occurs at low values of N:C. The model can simulate both qualitative and quantitative temporal shifts in the ammonium-nitrate interaction, while inclusion of a derivation of the standard quota model enables a concurrent simulation of cell growth and changes in nutrient status.
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Fourme, Roger, Veijo Honkimäki, Eric Girard, Kadda Medjoubi, Anne-Claire Dhaussy et Richard Kahn. « Reduction of radiation damage and other benefits of short wavelengths for macromolecular crystallography data collection ». Journal of Applied Crystallography 45, no 4 (12 juin 2012) : 652–61. http://dx.doi.org/10.1107/s0021889812019164.
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Circumventing radiation damage remains a major problem for X-ray macromolecular crystallography. Analysis of diffraction data collected from normal-sized cryocooled lysozyme crystals shows that the dose required to collect a data set of prescribed resolution and signal-to-noise ratio, assuming an ideally efficient detector, decreases with increasing photon energy in the investigated 6.5–33 keV range. For example, the data collection efficiency is increased by a factor of ∼8 from 8 to 33 keV. Monte Carlo simulations on lysozyme crystals in the range 5–80 keV, taking into account electron escape from samples of different size, also show a positive effect of high energy (albeit less pronounced than in experiments), especially for micrometre-sized samples, and suggest that the optimum energy range is ∼24–41 keV, depending on crystal size. The importance of counting pixel detectors with a good efficiency at high energy is underlined. Macromolecular crystallography beamlines should be modified, or purposely designed, in order to benefit from higher-energy radiation through reduction of global radiation damage, better data accuracy and extension of phasing by anomalous dispersion.
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Gray, Joshua P., Kambiz N. Alavian, Elizabeth A. Jonas et Emma A. Heart. « NAD kinase regulates the size of the NADPH pool and insulin secretion in pancreatic β-cells ». American Journal of Physiology-Endocrinology and Metabolism 303, no 2 (15 juillet 2012) : E191—E199. http://dx.doi.org/10.1152/ajpendo.00465.2011.
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NADPH is an important component of the antioxidant defense system and a proposed mediator in glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells. An increase in the NADPH/NADP+ ratio has been reported to occur within minutes following the rise in glucose concentration in β-cells. However, 30 min following the increase in glucose, the total NADPH pool also increases through a mechanism not yet characterized. NAD kinase (NADK) catalyzes the de novo formation of NADP+ by phosphorylation of NAD+. NAD kinases have been shown to be essential for redox regulation, oxidative stress defense, and survival in bacteria and yeast. However, studies on NADK in eukaryotic cells are scarce, and the function of this enzyme has not been described in β-cells. We employed INS-1 832/13 cells, an insulin-secreting rat β-cell line, and isolated rodent islets to investigate the role of NADK in β-cell metabolic pathways. Adenoviral-mediated overexpression of NADK resulted in a two- to threefold increase in the total NADPH pool and NADPH/NADP+ ratio, suggesting that NADP+ formed by the NADK-catalyzed reaction is rapidly reduced to NADPH via cytosolic reductases. This increase in the NADPH pool was accompanied by an increase in GSIS in NADK-overexpressing cells. Furthermore, NADK overexpression protected β-cells against oxidative damage by the redox cycling agent menadione and reversed menadione-mediated inhibition of GSIS. Knockdown of NADK via shRNA exerted the opposite effect on all these parameters. These data suggest that NADK kinase regulates intracellular redox and affects insulin secretion and oxidative defense in the β-cell.
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Jiang, Yun-Bao, et Li Lin. « Dual Fluorescence of p-Dimethylaminobenzoic Acid in Cetyltrimethylammonium Bromide (CTAB)/1-Heptanol/Water Reverse Micelle ». Applied Spectroscopy 49, no 7 (juillet 1995) : 1017–21. http://dx.doi.org/10.1366/0003702953964868.
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Dual fluorescence of p-dimethylaminobenzoic acid (DMABOA), typical of excited-state twisted intramolecular charge transfer (TICT), in the cetyltrimethylammonium (CTAB)/1-heptanol/H2O reverse micelle has been monitored as a function of a number of factors such as the water pool size, the bulk concentrations of DMABOA and CTAB, and the pH and [KF]/[KBr] ratio in the water pool. Two fluorescence parameters, i.e., the wavelength of the TICT emission band and the intensity ratio of the TICT band to the LE (locally excited state) band, Ia/ Ib, are employed to measure the effects of these factors. The position of the DMABOA molecule in the reverse micelle is ascertained to be among the hydrocarbon chains close to the water pool with its (CH3) 2N group towards the bulk 1-heptanol while the carboxylic group interacts with the polar head of the surfactant electrostatically. The TICT of DMABOA at this position is shown to be similar to that in an organic solvent, and the reverse micelle exerts a restriction on the TICT of DMABOA. It seems that the water molecules in the water pool do not penetrate into the hydrocarbon region of the reverse micelle.
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Wen, Mao Yu, Ching Yen Ho et Kang Jang Jang. « Characteristics of Pool Boiling Heat Transfer from Sintered Surfaces ». Advanced Materials Research 566 (septembre 2012) : 382–85. http://dx.doi.org/10.4028/www.scientific.net/amr.566.382.
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This study investigated the effect of design parameters on pool boiling heat transfer on the sintered surfaces of a tube. The pool boiling experiments were conducted in saturated, deionized and degassed water. Data were taken at an atmospherical pressure and a fixed heat flux of 41,000 . In the experimentation, the effects of the sintering pressure, sintering time, sintering temperature, heating rate, and particle size on the boiling heat-transfer coefficient of the sintered surface were investigated using the Taguchi method, and an orthogonal array table was selected as an experimental plan for some parameters mentioned above. Based on the results of SN (signal/noise) ratio and ANOVA (Analysis of Variance), the optimal conditions of specifications of parameters will be provided. It was found that all the chosen sintering factors have significant effects on the pool boiling heat transfer coefficient. Optimum pool boiling heat transfer coefficient of 5.29 was achieved with a sintering pressure of 2 atmospheres, a sintering time of 2 hr, a sintering temperature of 900 °C, a heating rate of 5 °C/min and a particle size of 0.35 mm in a nitrogen container.
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JIA, X. M., H. SRIPLUNG, V. CHONGSUVIVATWONG et A. GEATER. « Sensitivity of pooled serum testing for screening antibody of schistosomiasis japonica by IHA in a mountainous area of Yunnan, China ». Parasitology 136, no 3 (21 janvier 2009) : 267–72. http://dx.doi.org/10.1017/s0031182008005489.
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SUMMARYPooled sample testing (PST) as a strategy for avoiding testing the majority of individual negative samples has been proposed for screening of diseases in low prevalence areas. There has been no standard guideline for PST in screening ofSchistosoma japonicuminfection of Yunnan, China. To document the optimum pool size with acceptable sensitivity of PST for screening ofSchistosoma japonicuminfection in this setting, an experimental pooling of each of 31 positive sera by IHA with various numbers of 24 negative sera was done. The results were used to create a statistical model which was subsequently used for simulation to predict sensitivity of the pooled serum tests in the population with varying prevalence and pool size. We found that to keep the sensitivity of PST above 90%, 1:05 should be the maximum dilution, that is, the optimum pool size should not be greater than 6. Antigen will have rather little interference if the prevalence of infection is low e.g. 1% or the antigen:antibody ratio is 1:100 or below. Pooled serum testing by IHA is an acceptable sensitive method for detecting antibody forSchistosoma japonicuminfection in this area.
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Henry, Christopher D., Jungho Kim, Brian Chamberlain et Thomas G. Hartman. « Heater size and heater aspect ratio effects on subcooled pool boiling heat transfer in low-g ». Experimental Thermal and Fluid Science 29, no 7 (août 2005) : 773–82. http://dx.doi.org/10.1016/j.expthermflusci.2005.03.003.
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Ou, Xiawei, Shu-Wei Sun, Hsiao-Fang Liang, Sheng-Kwei Song et Daniel F. Gochberg. « Quantitative magnetization transfer measured pool-size ratio reflects optic nerve myelin content in ex vivo mice ». Magnetic Resonance in Medicine 61, no 2 (février 2009) : 364–71. http://dx.doi.org/10.1002/mrm.21850.
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Katmıs, Aslı, Serap Fide, Seyma Karaismailoglu et Serap Derman. « Synthesis and characterization methods of polymeric nanoparticles ». Characterization and Application of Nanomaterials 2, no 2 (14 août 2019) : 60. http://dx.doi.org/10.24294/can.v2i2.791.
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This review provided a detailed overview of the different synthesis and characterization methods of polymeric nanoparticles. Nanoparticles are defined as solid and colloidal particles of macromolecular substances ranging in size under 100 nm. Different types of nanoparticles are used in many biological fields (bio-sensing, biological separation, molecular imaging, anticancer therapy, etc.). The new features and functions provided by nano dimensions are largely different from their bulk forms. High volume/surface ratio, improved resolution and multifunctional capability make these materials gain many new features.
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Ferrandino, Francis J. « The Explicit Dependence of Quadrat Variance on the Ratio of Clump Size to Quadrat Size ». Phytopathology® 95, no 5 (mai 2005) : 452–62. http://dx.doi.org/10.1094/phyto-95-0452.
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In the past decade, it has become common practice to pool mapped binary epidemic data into quadrats. The resultant “quadrat counts” can then be analyzed by fitting them to a probability distribution (i.e., betabinomial). Often a binary form of Taylor's power law is used to relate the quadrat variance to the quadrat mean. The fact that there is an intrinsic dependence of such analyses on quadrat size and shape is well known. However, a clear-cut exposition of the direct connection between the spatial properties of the two-dimensional pattern of infected plants in terms of the geometry of the quadrat and the results of quadrat-based analyses is lacking. This problem was examined both empirically and analytically. The empirical approach is based on a set of stochastically generated “mock epidemics” using a Neyman-Scott cluster process. The resultant spatial point-patterns of infected plants have a fixed number of disease foci characterized by a known length scale (monodisperse) and saturated to a known disease level. When quadrat samples of these epidemics are fit to a beta-binomial distribution, the resulting measures of aggregation are totally independent of disease incidence and most strongly dependent on the ratio of the length scale of the quadrat to the length scale of spatial aggregation and to a lesser degree on disease saturation within individual foci. For the analytical approach, the mathematical form for the variation in the sum of random variates is coupled to the geometry of a quadrat through an assumed exponential autocorrelation function. The net result is an explicit equation expressing the intraquadrat correlation, quadrat variance, and the index of dispersion in terms of the ratio of the quadrat length scale to the correlative length scale.
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Zhao, Chunfang, et Joanna D. Davies. « A peripheral CD4+ T cell precursor for naive, memory, and regulatory T cells ». Journal of Experimental Medicine 207, no 13 (13 décembre 2010) : 2883–94. http://dx.doi.org/10.1084/jem.20100598.
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Mechanisms that control the size of the T cell pool, the ratio between naive cells and memory cells, the number and frequency of regulatory T cells, and T cell receptor (TCR) diversity are necessary to maintain immune integrity and avoid disease. We have previously shown that a subset of naive CD4+ T cells, defined by the expression on their surface of a very low density of CD44 (CD44v.low cells), can inhibit wasting and wasting-associated lymphopenia in mice with cancer. In this study, we further investigate the properties of CD44v.low cells and show that they are significantly more efficient than the remaining naive (CD44low or CD44int) and memory CD4+ cell subsets in reconstituting the overall size of the CD4+ T cell pool, creating a T cell pool with a diverse TCR repertoire, generating regulatory T cells that express forkhead box P3 (FoxP3), and promoting homeostatic equilibrium between naive, memory, and Foxp3+ regulatory T cell numbers. T cell population reconstitution by CD44v.low cells is thymus independent. Compared with CD44int cells, a higher percentage of CD44v.low cells express B cell leukemia/lymphoma 2, interleukin-7 receptor, and CD5. The data support a key role for CD4+ CD44v.low cells as peripheral precursors that maintain the integrity of the CD4+ T cell pool.
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Lu, Jinjing, Shengping Li, Guopeng Liang, Xueping Wu, Qiang Zhang, Chunhua Gao, Jianhua Li et al. « The Contribution of Microorganisms to Soil Organic Carbon Accumulation under Fertilization Varies among Aggregate Size Classes ». Agronomy 11, no 11 (24 octobre 2021) : 2126. http://dx.doi.org/10.3390/agronomy11112126.
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Long-term fertilization alters soil microbiological properties and then affects the soil organic carbon (SOC) pool. However, the interrelations of SOC with biological drivers and their relative importance are rarely analyzed quantitatively at aggregate scale. We investigated the contribution of soil microbial biomass, diversity, and enzyme activity to C pool in soil aggregate fractions (>5 mm, 2–5 mm, 1–2 mm, 0.25–1 mm, and <0.25 mm) at topsoil (0–15 cm) from a 27-year long-term fertilization regime. Compared to CK (no fertilization management), NP (inorganic fertilization alone) decreased all of the microbial groups’ biomass, while NPS and NPM (inorganic fertilization plus the incorporation of maize straw or composted cow manure) significantly reduced this negative effect of NP on microbial biomass and increased the microbial contribution to C pool. The results show that microbial variables were significantly correlated with SOC content in >0.25 mm aggregates rather than in <0.25 mm aggregates. Fungal variables (fungal, AM biomass, and F/B ratio) and enzyme activities (BXYL and LAP) in >0.25 mm aggregates explained 21% and 2% of C, respectively. Overall, organic matter addition could contribute to higher C storage by boosting fungal community and enzyme activity rather than by changing microbial community diversity in macro-aggregates.
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Santos, Ricardo Serrão, Richard D. M. Nash et Stephen J. Hawkins. « Age, Growth and Sex Ratio of the Azorean Rock-Pool Blenny, Parablennius Sanguinolentus Parvicornis ». Journal of the Marine Biological Association of the United Kingdom 75, no 3 (août 1995) : 751–54. http://dx.doi.org/10.1017/s0025315400039175.
Texte intégralRésumé :
The age and population structure of Parablennius sanguinolentus parvicornis (Valenciennes) (Pisces: Blenniidae) from the Azores have been studied. Total length and weight relationships are given for each sex. Age study was based on otoliths readings. The von Bertalanffy growth function was applied to describe the growth in total length with age. At the end of the first year mean (±SD) total length was significantly different in males (7.1 ±1.5 cm) and females (6.1 ±1.2 cm). One-year-old males participate in reproduction as satellites, whereas females do not. The implications of this in early growth rate of the males is discussed. During the two most important months of the reproductive season (i.e. June and July), the sex ratio was significantly biased towards males, particularly in the larger size classes.
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Abbaas, Douaa Younis. « Fractal Image Compression Based on High Entropy Values Technique ». Al-Mustansiriyah Journal of Science 28, no 2 (11 avril 2018) : 119. http://dx.doi.org/10.23851/mjs.v28i2.507.
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There are many attempts tried to improve the encoding stage of FIC because it consumed time. These attempts worked by reducing size of the search pool for pair range-domain matching but most of them led to get a bad quality, or a lower compression ratio of reconstructed image. This paper aims to present a method to improve performance of the full search algorithm by combining FIC (lossy compression) and another lossless technique (in this case entropy coding is used). The entropy technique will reduce size of the domain pool (i. e., number of domain blocks) based on the entropy value of each range block and domain block and then comparing the results of full search algorithm and proposed algorithm based on entropy technique to see each of which give best results (such as reduced the encoding time with acceptable values in both compression quali-ty parameters which are C. R (Compression Ratio) and PSNR (Image Quality). The experimental results of the proposed algorithm proven that using the proposed entropy technique reduces the encoding time while keeping compression rates and reconstruction image quality good as soon as possible.
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Kim, Sang-Young, Wei Chen, Dost Ongur et Fei Du. « Rapid and simultaneous measurement of phosphorus metabolite pool size ratio and reaction kinetics of enzymes in vivo ». Journal of Magnetic Resonance Imaging 47, no 1 (8 mai 2017) : 210–21. http://dx.doi.org/10.1002/jmri.25744.
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Letenneur, Morgan, Alena Kreitcberg et Vladimir Brailovski. « The Average Grain Size and Grain Aspect Ratio in Metal Laser Powder Bed Fusion : Modeling and Experiment ». Journal of Manufacturing and Materials Processing 4, no 1 (11 mars 2020) : 25. http://dx.doi.org/10.3390/jmmp4010025.
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The additive manufacturing (AM) process induces high uncertainty in the mechanical properties of 3D-printed parts, which represents one of the main barriers for a wider AM processes adoption. To address this problem, a new time-efficient microstructure prediction algorithm was proposed in this study for the laser powder bed fusion (LPBF) process. Based on a combination of the melt pool modeling and the design of experiment approaches, this algorithm was used to predict the microstructure (grain size/aspect ratio) of materials processed by an EOS M280 LPBF system, including Iron and IN625 alloys. This approach was successfully validated using experimental and literature data, thus demonstrating its potential efficiency for the optimization of different LPBF powders and systems.
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Xiang, Cheng, Jia Li, Liaoliao Hu, Jian Huang, Tao Luo, Zhisheng Zhong, Yuehui Zheng et Liping Zheng. « Hippo Signaling Pathway Reveals a Spatio-Temporal Correlation with the Size of Primordial Follicle Pool in Mice ». Cellular Physiology and Biochemistry 35, no 3 (2015) : 957–68. http://dx.doi.org/10.1159/000369752.
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Background: The Hippo signaling pathway, a highly conserved cell signaling system, exists in most multicellular organisms and regulates cell proliferation, differentiation, and apoptosis. It has been reported that the members of Hippo signaling are expressed in mammalian ovaries, but the exact functions of this pathway in primordial follicle development remains unclear. Methods: To analyze the spatio-temporal correlation between the core component of Hippo pathway and the size of primordial follicle pool, Western blot, Real-time PCR and immunohistochemistry were used, and the expression and localization of MST1, LATS2 and YAP1 mRNA and protein were examined in 3 d, 1 m, 5 m, 16 m postnatal mice ovary and the culture model of mice primordial follicle in vitro. Results: Both the protein and mRNA expression of the MST1 and LATS2 were decreased significantly as mouse age increased (p < 0.05), however, the mRNA expression of them increased significantly in 16 m compared with 5 m as well as the protein expression of LATS2.The expression of YAP showed the opposite trend, and the significant protein expression of pYAP was increased before 1 m, after which no significant change was observed. Moreover, the ratio of pYAP/YAP decreased significantly. Culturing ovaries for 8 d in vitro resulted in the activation of primordial follicles in 3 d postnatal mice ovaries, and these developed into primary follicles with the expression of PCNA increasing significantly (p < 0.05). The mRNA and protein expression of MST and LATS decreased significantly (p < 0.05), and the expression of YAP increased significantly (p < 0.05, p < 0.01), whereas the ratio of pYAP/YAP decreased significantly (p < 0.05). Conclusion: The above results reveal that the expression of the core components of Hippo pathway changed during mouse follicular development, especially before and after primordial follicle activation in vitro. The primordial follicle activation may be related to the significant decrease of the ratio of pYAP1/YAP1. In conclusion, Hippo signaling pathway expressed in mice ovaries and have spatio-temporal correlation with the size of primordial follicle pool.
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GARCIA, C. M., M. FERNANDEZ, O. D. LOPEZ, M. CASTIÑEIRA, B. MARTINEZ, A. NOGUEIRA et L. TURIÑO. « MICROENCAPSULATION OF SHARK LIVER OIL POOL BY SPRAY DRYING ». Latin American Applied Research - An international journal 48, no 2 (30 mars 2018) : 89–93. http://dx.doi.org/10.52292/j.laar.2018.264.
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The aim of this paper is to study the spray-dried microencapsulation of shark liver oil using gum arabic and maltodextrin as encapsulating agents. A mix design, was developed where the main factor was the ratio between gum arabic and maltodextrin. Vitamin A content in microencapsulated and non-microencapsulated oil was determined by reversed-phase HPLC analysis, as well as the release of vitamin A from the dried product. The following parameters were also evaluated: encapsulation efficiency, loss on drying, surface morphology and particle size. The encapsulation efficiency of microencapsulated oil increased slightly as the concentration of gum increased. To reach higher encapsulation efficiency and lower moisture content of microencapsulated oil, the combination of gum arabic and maltodextrin should be maintained at 47% and 23%, respectively, according to established manufacturing conditions. The microencapsulation of oil by spray drying has no statistically significant effect on the vitamin A content response, or on its release rate.
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Yuliana, Darma, Muhiddin Sirat, Deny Sapto Chondro Utomo, Muhammad Mirandy Pratama Sirat et Ratna Ermawati. « Business Integration Analysis of Aquaponic Technology on Catfish (Clarias sp.) Cultivation in The Strengthening of The Business MSME Scale in Pandemic Covid-19 ». Jurnal Ekonomi Pembangunan 11, no 1 (3 avril 2022) : 42–51. http://dx.doi.org/10.23960/jep.v11i1.443.
Texte intégralRésumé :
The aim of this study was analyzed the effort to implement the integration of aquaponic technology in conventional fish cultivation. The study was conducted for 6 months (May - October 2021) in the Mandiri Sentosa fish farming unit in Marga Agung Village, Jati Agung District, South Lampung Regency. Experimental research with quantitative methods with descriptive analysis of two treatments is the analysis of the feasibility of catfish cultivation business that has not been integrated with Aquaponik technology (P0) and which has been integrated with Aquaponic technology (P1). Each treatment pool with a 2,000 catfish density with 5-7 cm/fish marked size was maintained for 3 months for harvest. The integration of aquaponic technology in the treatment pool (P1) with the number of vegetable seeds of lettuce was 100 seeds per treatment pool. Quantitative method was doing by business analysis to determine the activities of catfish cultivation business (Clarias sp.) Has benefits and deserves to be developed from the parameters of business cost analysis, depreciation, acceptance analysis, net cash flow (net cash flow), R/C ratio, B/C ratio, Break-Even Point (BEP), Payback Period. The conclusion of this research was the farming business based on aquaponic technology in Catfish (Clarias sp.) cultivation was profitable business or very suitable to be developed.
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Trujillo, Paula, Paul E. Summers, Alex K. Smith, Seth A. Smith, Luca T. Mainardi, Sergio Cerutti, Daniel O. Claassen et Antonella Costa. « Pool size ratio of the substantia nigra in Parkinson’s disease derived from two different quantitative magnetization transfer approaches ». Neuroradiology 59, no 12 (6 octobre 2017) : 1251–63. http://dx.doi.org/10.1007/s00234-017-1911-2.
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Roselli, R. J., et W. R. Riddle. « Analysis of noninvasive macromolecular transport measurements in the lung ». Journal of Applied Physiology 67, no 6 (1 décembre 1989) : 2343–50. http://dx.doi.org/10.1152/jappl.1989.67.6.2343.
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Several groups of investigators are measuring transcapillary protein flux in the lung using noninvasive methods. Results from these studies are reported using several different protein transport indexes, including pulmonary transvascular transfer coefficient, relative extravascular protein, pulmonary transcapillary escape rate, protein leak index, lung transferrin index, slope index, and lung-to-heart count ratios. The purpose of this study is to discover the relationships between these indexes by employing a two-compartment theory of protein transcapillary transport in the lung. We found that all the above indexes can be related to a single index, which we call the normalized slope index. This index is the time rate of change of radioactivity originating from protein in lung interstitium divided by radioactivity arising from protein in lung plasma, normalized by this ratio at time 0, and corrected for blood volume changes. In particular the normalized slope index is shown to be the same as pulmonary transcapillary escape rate under normal sampling conditions and is relatively unaffected by changes in interstitial volume. The response of the normalized slope index to changes in microvascular pressure and microvascular permeability is explored by applying a two-pore model of the microvascular barrier. Results indicate that the normalized slope index is relatively insensitive to changes in microvascular pressure but is greatly affected by changes in microvascular permeability (i.e., changes in large-pore size or number). Since all published leak indexes are related, we would encourage all investigators in the field to adopt a single leak index. We recommend that when a two-compartment model is applied to external detection data, the results be expressed as pulmonary transcapillary escape rate.(ABSTRACT TRUNCATED AT 250 WORDS)
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Yashtulov, N. A., M. V. Lebedeva et S. M. Pestov. « CATALYSTS FOR ANODE OXIDATION OF FORMIC ACID ON CARBON NANOTUBES "TAUNIT" ». Fine Chemical Technologies 11, no 5 (28 octobre 2016) : 51–56. http://dx.doi.org/10.32362/2410-6593-2016-11-5-51-56.
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Platinum-palladium/carbon nanjtubes (CNT) carbon nanocomposites were synthesized by chemical reduction of ions in water-organic solutions of reverse microemulsions. Physico-chemical characteristics of the nanocomposites were studied by atomic force microscopy, transmission electron microscopy, photon-correlation spectroscopy, X-ray phase analysis and chronopotentiometry. It was found that the smallest platinum-palladium nanoparticles size is observed when the metal ratio is 3:1 and the water pool size is minimal (ω = 1.5). Testing of catalytic activity in the oxidation of formic acid showed that the platinum-palladium/CNT nanocomposites showed higher corrosion resistance than nanocomposites with pure palladium.
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Abbruzzese, M., L. Reni et E. Favale. « Changes in central delay of soleus H reflex after facilitatory or inhibitory conditioning in humans ». Journal of Neurophysiology 65, no 6 (1 juin 1991) : 1598–605. http://dx.doi.org/10.1152/jn.1991.65.6.1598.
Texte intégralRésumé :
1. Central delay (CD) changes after facilitatory or inhibitory conditioning of the soleus H reflex have been investigated in a group of normal subjects as a function of the conditioning and test stimulus intensities and also as a function of the Hmax/Mmax ratio. Both facilitation and inhibition of the reflex response have been obtained by conditioning stimulation of the ipsilateral tibial nerve at suitable conditioning-test stimulus intervals. CD changes have been extrapolated from the variations of the time interval between afferent and efferent neural volleys underlying the H reflex, directly recorded from the sciatic nerve. 2. The CD was significantly decreased by facilitatory and increased by inhibitory conditioning. Facilitatory CD changes were positively related to test stimulus strength (at a given conditioning stimulus intensity) and negatively related to conditioning stimulus strength (at a given test stimulus intensity). Both trends were reversed after inhibitory conditioning. The effectiveness of facilitatory conditioning was positively related to the individual Hmax/Mmax ratio whereas a negative relationship could be observed after inhibitory conditioning. 3. Also, the "conditioning threshold" (the minimal conditioning stimulus strength affecting the reflex size) and the "maximal conditioning effect" (the conditioning stimulus intensities leading to either the saturation of the facilitatory effect or the suppression of the reflex response) were significantly related to the Hmax/Mmax ratio. 4. We suggest that temporal changes in the H reflex pathway after facilitatory or inhibitory conditioning stimuli depend both on the size of the motoneuronal pool underlying the reflex response, as determined by the test stimulus intensity, and on the individual excitability of the motoneuronal pool, as defined by the Hmax/Mmax ratio.(ABSTRACT TRUNCATED AT 250 WORDS)
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Li, Xiaowen, Wei-Kuo Tao, Alexander P. Khain, Joanne Simpson et Daniel E. Johnson. « Sensitivity of a Cloud-Resolving Model to Bulk and Explicit Bin Microphysical Schemes. Part II : Cloud Microphysics and Storm Dynamics Interactions ». Journal of the Atmospheric Sciences 66, no 1 (1 janvier 2009) : 22–40. http://dx.doi.org/10.1175/2008jas2647.1.
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Abstract Part I of this paper compares two simulations, one using a bulk and the other a detailed bin microphysical scheme, of a long-lasting, continental mesoscale convective system with leading convection and trailing stratiform region. Diagnostic studies and sensitivity tests are carried out in Part II to explain the simulated contrasts in the spatial and temporal variations by the two microphysical schemes and to understand the interactions between cloud microphysics and storm dynamics. It is found that the fixed raindrop size distribution in the bulk scheme artificially enhances rain evaporation rate and produces a stronger near-surface cool pool compared with the bin simulation. In the bulk simulation, cool pool circulation dominates the near-surface environmental wind shear in contrast to the near-balance between cool pool and wind shear in the bin simulation. This is the main reason for the contrasting quasi-steady states simulated in Part I. Sensitivity tests also show that large amounts of fast-falling hail produced in the original bulk scheme not only result in a narrow trailing stratiform region but also act to further exacerbate the strong cool pool simulated in the bulk parameterization. An empirical formula for a correction factor, r(qr) = 0.11qr−1.27 + 0.98, is developed to correct the overestimation of rain evaporation in the bulk model, where r is the ratio of the rain evaporation rate between the bulk and bin simulations and qr(g kg−1) is the rain mixing ratio. This formula offers a practical fix for the simple bulk scheme in rain evaporation parameterization.
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Grushin, Kirill, Mark Andrew White et Svetla Stoilova-McPhie. « Reversible stacking of lipid nanodiscs for structural studies of clotting factors ». Nanotechnology Reviews 6, no 1 (1 février 2017) : 139–48. http://dx.doi.org/10.1515/ntrev-2016-0073.
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AbstractNanodiscs (ND) are discoidal phospholipid bilayers stabilized by a pair of membrane-scaffolding proteins (MSP). The macromolecular composition and size of ND are ideal for structural and functional studies of membrane and membrane-associated proteins. In this work, we investigate the assembly of ND from a galactosylceramide and dioleoyl phosphatidylserine (PS) lipid mixture with two different MSP and at four MSP-to-lipid ratios. This lipid composition has been optimized for structural and biophysical studies of membrane-bound blood clotting factors that require Ca2+ ions for function. We have demonstrated that CaCl2 induces reversible stacking of the ND that depends on the ND size and Ca2+ concentrations. Our biophysical and electron microscopy (EM) studies show a predominant ND population of ~12 nm in diameter for both the ND assembled from MSP1D1 to lipids ratio of 1:40 and from MSP1E3D1-to-lipids ratio of 1:80. Approximately half of the ND population assembled at MSP1E3D1-to-lipids ratio of 1:150 has a diameter of ~16 nm. These larger ND form ordered stacks at 5-mm Ca2+ concentrations, as shown by cryo-EM. The number and length of the ND stacks increase with the increasing in Ca2+ concentration. Adding millimolar concentrations of EDTA reverses the stacking of the ND.
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Spanò, Barbara, Mara Cercignani, Barbara Basile, Silvia Romano, Rosalba Mannu, Diego Centonze, Carlo Caltagirone, Placido Bramanti, Ugo Nocentini et Marco Bozzali. « Multiparametric MR investigation of the motor pyramidal system in patients with ‘truly benign’ multiple sclerosis ». Multiple Sclerosis Journal 16, no 2 (9 décembre 2009) : 178–88. http://dx.doi.org/10.1177/1352458509356010.
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One possible explanation for the mismatch between tissue damage and preservation of neurological functions in patients with benign multiple sclerosis (BMS) is that the pathophysiology differs from that occurring in other multiple sclerosis (MS) phenotypes. The objective of this study was to identify pathologically specific patterns of tissue integrity/damage characteristics of patients with BMS, and markers of potential prognostic value. The pyramidal system was investigated in 10 BMS patients and 20 controls using voxel-based morphometry to assess grey matter (GM) atrophy, and diffusion tractography and quantitative magnetization transfer to quantify the microstructural damage in the corticospinal tracts (CSTs). Widespread reductions in GM volume were found in patients compared with controls, including the primary motor cortex. A significant decrease was observed in the mean macromolecular pool ratio (F) of both CSTs, with no fractional anisotropy (FA) change. GM volume of the primary motor areas was associated with clinical scores but not with the CST parameters. The mismatch between F and FA suggests the presence of extensive demyelination in the CSTs of patients with BMS, in the absence of axonal damage. The lack of correlation with GM volume indicates a complex interaction between disruptive and reparative mechanisms in BMS.
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Laub, Moritz, Michael Scott Demyan, Yvonne Funkuin Nkwain, Sergey Blagodatsky, Thomas Kätterer, Hans-Peter Piepho et Georg Cadisch. « DRIFTS band areas as measured pool size proxy to reduce parameter uncertainty in soil organic matter models ». Biogeosciences 17, no 6 (20 mars 2020) : 1393–413. http://dx.doi.org/10.5194/bg-17-1393-2020.
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Abstract. Soil organic matter (SOM) turnover models predict changes in SOM due to management and environmental factors. Their initialization remains challenging as partitioning of SOM into different hypothetical pools is intrinsically linked to model assumptions. Diffuse reflectance mid-infrared Fourier transform spectroscopy (DRIFTS) provides information on SOM quality and could yield a measurable pool-partitioning proxy for SOM. This study tested DRIFTS-derived SOM pool partitioning using the Daisy model. The DRIFTS stability index (DSI) of bulk soil samples was defined as the ratio of the area below the aliphatic absorption band (2930 cm−1) to the area below the aromatic–carboxylate absorption band (1620 cm−1). For pool partitioning, the DSI (2930 cm−1 ∕ 1620 cm−1) was set equal to the ratio of fast-cycling ∕ slow-cycling SOM. Performance was tested by simulating long-term bare fallow plots from the Bad Lauchstädt extreme farmyard manure experiment in Germany (Chernozem, 25 years), the Ultuna continuous soil organic matter field experiment in Sweden (Cambisol, 50 years), and 7 year duration bare fallow plots from the Kraichgau and Swabian Jura regions in southwest Germany (Luvisols). All experiments were at sites that were agricultural fields for centuries before fallow establishment, so classical theory would suggest that a steady state can be assumed for initializing SOM pools. Hence, steady-state and DSI initializations were compared, using two published parameter sets that differed in turnover rates and humification efficiency. Initialization using the DSI significantly reduced Daisy model error for total soil organic carbon and microbial carbon in cases where assuming a steady state had poor model performance. This was irrespective of the parameter set, but faster turnover performed better for all sites except for Bad Lauchstädt. These results suggest that soils, although under long-term agricultural use, were not necessarily at a steady state. In a next step, Bayesian-calibration-inferred best-fitting turnover rates for Daisy using the DSI were evaluated for each individual site or for all sites combined. Two approaches significantly reduced parameter uncertainty and equifinality in Bayesian calibrations: (1) adding physicochemical meaning with the DSI (for humification efficiency and slow SOM turnover) and (2) combining all sites (for all parameters). Individual-site-derived turnover rates were strongly site specific. The Bayesian calibration combining all sites suggested a potential for rapid SOM loss with 95 % credibility intervals for the slow SOM pools' half-life being 278 to 1095 years (highest probability density at 426 years). The credibility intervals of this study were consistent with several recently published Bayesian calibrations of similar two-pool SOM models, i.e., with turnover rates being faster than earlier model calibrations suggested; hence they likely underestimated potential SOM losses.
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Ou, Xiawei, Shu-Wei Sun, Hsiao-Fang Liang, Sheng-Kwei Song et Daniel F. Gochberg. « The MT pool size ratio and the DTI radial diffusivity may reflect the myelination in shiverer and control mice ». NMR in Biomedicine 22, no 5 (juin 2009) : 480–87. http://dx.doi.org/10.1002/nbm.1358.
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Demmig-Adams, B., et WW Iii Adams. « Chlorophyll and Carotenoid Composition in Leaves of Euonymus kiautschovicus Acclimated to Different Degrees of Light Stress in the Field ». Functional Plant Biology 23, no 5 (1996) : 649. http://dx.doi.org/10.1071/pp9960649.
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The response of carotenoid and chlorophyll composition to the actual degree of excess light experienced in the natural environment was examined in differently angled leaves of the sclerophyllous shrub Euonymus kiautschovicus. Increasing light stress caused a greater conversion of the xanthophyll cycle to zeaxanthin and antheraxanthin as well as thermal dissipation of a greater fraction of the absorbed light. Increasing light stress was also associated with increasing chlorophyll alb ratios and increases in the pool size of the xanthophyll cycle. The response of all other carotenoids to light stress was less pronounced than that of the xanthophyll cycle pool. While the ratio of β-carotene or lutein to chlorophyll increased with increasing light stress, the ratio of neoxanthin to chlorophyll remained constant. Only the (taxonomically restricted) carotenoids lactucaxanthin and �-carotene decreased relative to chlorophyll with increasing light stress. These findings are consistent with an increased emphasis on energy dissipation over light collection with increasing light stress, afforded presumably by a decreased ratio of major, peripheral (bulk chlorophyll-binding) to minor, proximal (xanthophyll cycle-rich) light-harvesting complexes of photosystem II. These responses to light stress within a single species could not be extrapolated to comparisons among different groups of species.
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Xu, Yanan, et Patricia J. Harvey. « Red Light Control of β-Carotene Isomerisation to 9-cis β-Carotene and Carotenoid Accumulation in Dunaliella salina ». Antioxidants 8, no 5 (27 mai 2019) : 148. http://dx.doi.org/10.3390/antiox8050148.
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Dunaliella salina is a rich source of 9-cis β-carotene, which has been identified as an important biomolecule in the treatment of retinal dystrophies and other diseases. We previously showed that chlorophyll absorption of red light photons in D. salina is coupled with oxygen reduction and phytoene desaturation, and that it increases the pool size of β-carotene. Here, we show for the first time that growth under red light also controls the conversion of extant all-trans β-carotene to 9-cis β-carotene by β-carotene isomerases. Cells illuminated with red light from a light emitting diode (LED) during cultivation contained a higher 9-cis β-carotene content compared to cells illuminated with white or blue LED light. The 9-cis/all-trans β-carotene ratio in red light treated cultures reached >2.5 within 48 h, and was independent of light intensity. Illumination using red light filters that eliminated blue wavelength light also increased the 9-cis/all-trans β-carotene ratio. With norflurazon, a phytoene desaturase inhibitor which blocked downstream biosynthesis of β-carotene, extant all-trans β-carotene was converted to 9-cis β-carotene during growth with red light and the 9-cis/all-trans β-carotene ratio was ~2. With blue light under the same conditions, 9-cis β-carotene was likely destroyed at a greater rate than all-trans β-carotene (9-cis/all-trans ratio 0.5). Red light perception by the red light photoreceptor, phytochrome, may increase the pool size of anti-oxidant, specifically 9-cis β-carotene, both by upregulating phytoene synthase to increase the rate of biosynthesis of β-carotene and to reduce the rate of formation of reactive oxygen species (ROS), and by upregulating β-carotene isomerases to convert extant all-trans β-carotene to 9-cis β-carotene.
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Ma, Cong, Xianshun Wei, Biao Yan et Pengfei Yan. « Numerical Simulation of Moving Heat Flux during Selective Laser Melting of AlSi25 Alloy Powder ». Metals 10, no 7 (1 juillet 2020) : 877. http://dx.doi.org/10.3390/met10070877.
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A single-layer three-dimensional model was created to simulate multi-channel scanning of AlSi25 powder in selective laser melting (SLM) by the finite element method. Thermal behaviors of laser power and scanning speed in the procedure of SLM AlSi25 powder were studied. With the increase of laser power, the maximum temperature, size and cooling rate of the molten pool increase, while the scanning speed decreases. For an expected SLM process, a perfect molten pool can be generated using process parameters of laser power of 180 W and a scanning speed of 200 mm/s. The pool is greater than the width of the scanning interval, the depth of the molten pool is close to scan powder layer thickness, the temperature of the molten pool is higher than the melting point temperature of the powder and the parameters of the width and depth are the highest. To confirm the accuracy of the simulation results of forecasting excellent process parameters, the SLM experiment of forming AlSi25 powder was carried out. The surface morphology of the printed sample is intact without holes and defects, and a satisfactory metallurgical bond between adjacent scanning channels and adjacent scanning layers was achieved. Therefore, the development of numerical simulation in this paper provides an effective method to obtain the best process parameters, which can be used as a choice to further improve SLM process parameters. In the future, metallographic technology can also be implemented to obtain the width-to-depth ratio of the SLM sample molten pool, enhancing the connection between experiment and theory.
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Dominiak, Karolina, et Wieslawa Jarmuszkiewicz. « The Relationship between Mitochondrial Reactive Oxygen Species Production and Mitochondrial Energetics in Rat Tissues with Different Contents of Reduced Coenzyme Q ». Antioxidants 10, no 4 (29 mars 2021) : 533. http://dx.doi.org/10.3390/antiox10040533.
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We investigated the relationship between mitochondrial production of reactive oxygen species (ROS) and mitochondrial energetics in various rat tissues with different contents of the reduced coenzyme Q (Q) pool (Q9 + Q10). Our results indicate that similar to the tissue level, mitochondrial H2O2 release under nonphosphorylating conditions was strongly dependent on the amount of the reduced Q pool. Namely, in brain and lung mitochondria, less H2O2 release corresponded to a less reduced Q pool, while in liver and heart mitochondria, higher H2O2 release corresponded to a more reduced Q pool. We can conclude that the differences observed in rat tissues in the size of the reduced Q pool reflect different levels of ROS production and hence may reflect different demands for reduced Q as an antioxidant. Moreover, differences in mitochondrial H2O2 release were observed in different types of rat mitochondria during the oxidation of succinate (complex II substrate), malate plus glutamate (complex I substrate), and their mixture under phosphorylating and nonphosphorylating conditions. Our results indicate the existence of a tissue-specific maximum respiratory chain capacity in ROS production, possibly related to the membrane potential-mediated control of oxidative phosphorylation. We propose the use of a new parameter for the study of isolated mitochondria, RCRROS, the ratio between the formation of mitochondrial ROS under nonphosphorylating and phosphorylating conditions, which represents the maximum factorial increase in mitochondrial ROS formation that can be achieved after all ADP is phosphorylated.
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Nielsen, Tina S., Helle N. Lærke, Peter K. Theil, Jens F. Sørensen, Markku Saarinen, Sofia Forssten et Knud E. Bach Knudsen. « Diets high in resistant starch and arabinoxylan modulate digestion processes and SCFA pool size in the large intestine and faecal microbial composition in pigs ». British Journal of Nutrition 112, no 11 (20 octobre 2014) : 1837–49. http://dx.doi.org/10.1017/s000711451400302x.
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The effects of a high level of dietary fibre (DF) either as arabinoxylan (AX) or resistant starch (RS) on digestion processes, SCFA concentration and pool size in various intestinal segments and on the microbial composition in the faeces were studied in a model experiment with pigs. A total of thirty female pigs (body weight 63·1 (sem4·4) kg) were fed a low-DF, high-fat Western-style control diet (WSD), an AX-rich diet (AXD) or a RS-rich diet (RSD) for 3 weeks. Diet significantly affected the digestibility of DM, protein, fat, NSP and NSP components, and the arabinose:xylose ratio, as well as the disappearance of NSP and AX in the large intestine. RS was mainly digested in the caecum. AX was digested at a slower rate than RS. The digesta from AXD-fed pigs passed from the ileum to the distal colon more than twice as fast as those from WSD-fed pigs, with those from RSD-fed pigs being intermediate (P< 0·001). AXD feeding resulted in a higher number ofFaecalibacterium prausnitzii,Roseburia intestinalis,Blautia coccoides–Eubacterium rectale,Bifidobacteriumspp. andLactobacillusspp. in the faeces sampled at week 3 of the experimental period (P< 0·05). In the caecum, proximal and mid colon, AXD feeding resulted in a 3- to 5-fold higher pool size of butyrate compared with WSD feeding, with the RSD being intermediate (P <0·001). In conclusion, the RSD and AXD differently affected digestion processes compared with the WSD, and the AXD most efficiently shifted the microbial composition towards butyrogenic species in the faeces and increased the large-intestinal butyrate pool size.