Littérature scientifique sur le sujet « Macromolecular pool size ratio »
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Articles de revues sur le sujet "Macromolecular pool size ratio"
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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.
Texte intégralRésumé :
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.
Texte intégralRésumé :
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.
Texte intégralRésumé :
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.
Texte intégralRésumé :
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.
Thèses sur le sujet "Macromolecular pool size ratio"
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TURATI, LAURA. « Quantitative Magnetization Transfer imaging for in vivo analysis of myelin content in experimental model of demyelination ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2014. http://hdl.handle.net/10281/55300.
Texte intégralRésumé :
La demielinizzazione è un processo patologico in cui le guaine mieliniche, che rivestono gli assoni, sono danneggiate. La demielinizzazione del sistema nervoso centrale (SNC) è la conseguenza di un insulto diretto o indiretto agli oligodendrociti, cellule del SNC deputate alla produzione ed al mantenimento delle guaine mieliniche. La remielinizzazione è invece l’evento naturale che dovrebbe ripristinare la conduzione dell’impulso elettrico assonale e risolvere i deficit funzionali. Nella sclerosi multipla (SM) la perdita di mielina, in particolare in prossimità delle regioni internodali, è associata al blocco della conduzione nervosa e non è compensata da adeguata remielinizzazione. Lo sviluppo di terapie in grado di controllare il processo di demielinizzazione e la valutazione della loro efficacia è in parte complicato dalla difficoltà di valutare in modo non invasivo lo stato della mielina. Nel presente studio, la tecnica ‘quantitative magnetization transfer-MRI’ (qMT-MRI) è stata utilizzata per valutare il grado di de/remielinizzazione nel modello murino sperimentale indotto da cuprizone, un agente chelante del rame a cui gli oligodendrociti sono particolarmente sensibili. L’ipotesi di base dello studio è che il valore di ‘macromolecular pool size ratio’ (F) sia una stima accurata della densità mielinica in vivo; la correlazione tra analisi in MRI ed istologia è stata finora confermata prevalentemente su campioni di SNC ex vivo. Le corrispondenze tra il parametro F, che risulta dall’interpolazione di differenti misure qMT-MRI, con l’intensità di colorazione per fibre mieliniche (mediante Black Gold II), e con l’intensità di immunofluorescenza per la proteina basica della mielina e per la proteina citoscheletrica neuronale beta-tubulina sono state valutate a differenti time-points, in uno studio sperimentale longitudinale. Topi C57BL/6 e SJL/J sono stati trattati con cuprizone al fine di causare perdita selettiva della mielina, che è seguita da spontanea remielinizzazione dopo la sospensione del trattamento. I risultati hanno confermato una correlazione statisticamente significativa delle misure di F con il contenuto di mielina, e dimostrano l’applicabilità di analisi MRI in vivo nei modelli sperimentali di SM, come strumento per il monitoraggio dello stato della mielina.Demyelination is a pathological process in which myelin sheaths, around axons, are damaged. Demyelination of the central nervous system (CNS) is the consequence of a direct or indirect insult to oligodendrocytes, specific cells in the CNS that produce and sustain the myelin sheaths. Instead, remyelination is a spontaneous event in which myelin sheaths are restored in demyelinated nerve regions, thus recovering saltatory signal conduction and resolving functional deficits. In multiple sclerosis (MS), the loss of myelin particularly in internode regions is associated with block of nerve conduction and it is not compensated by adequate remyelination. The development of therapies able to control the process of demyelination and the evaluation of their effectiveness is partially complicated by the difficulty in assessing myelin status non-invasively. In the present study, 'quantitative magnetization transfer MRI' (qMT-MRI) technique is used to assess the degree of de/remyelination in an experimental murine model induced by cuprizone, a copper chelator to which oligodendrocytes are preferentially susceptible. The basic hypothesis of the study is that the in vivo measurement of ‘macromolecular pool size ratio’ (F) could be an accurate estimation of myelin density; the correlation between MRI and histology analysis has so far been confirmed mainly on ex vivo CNS samples. The correspondences between the parameter F, which is interpolated from qMT-MRI measures, with the intensity of staining for myelinated fibers (using Black Gold II), and with the intensity of myelin basic protein and neuronal cytoscheletric protein beta-tubulin immunofluorescences were evaluated at different time-points, in an experimental longitudinal study. C57BL/6 and SJL/J mice were fed with cuprizone in order to cause selective myelin loss, which is followed by spontaneous remyelination upon treatment suspension. The results confirmed a statistically significant correlation between F measures and myelin content, and demonstrated the in vivo applicability of MRI analysis to experimental models of MS, as a tool for monitoring myelin status.
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Parkes, Anthony Richard. « The impact of size and location of pool fires on compartment fire behaviour ». Thesis, University of Canterbury. Civil and Natural Resources Engineering, 2009. http://hdl.handle.net/10092/3444.
Texte intégralRésumé :
An understanding of compartment fire behaviour is important for fire protection
engineers. For design purposes, whether to use a prescriptive code or performance
based design, life safety and property protection issues are required to be assessed. The
use of design fires in computer modelling is the general method to determine fire safety.
However these computer models are generally limited to the input of one design fire,
with consideration of the complex interaction between fuel packages and the
compartment environment being simplified. Of particular interest is the Heat Release
Rate, HRR, as this is the commonly prescribed design parameter for fire modelling. If
the HRR is not accurate then it can be subsequently argued that the design scenario may
be flawed. Therefore the selection of the most appropriate fire design scenario is
critical, and an increased level of understanding of compartment behaviour is an
invaluable aid to fire engineering assumptions.
This thesis details an experimental study to enhance the understanding of the impact and
interaction that the size and location of pool fires within an enclosure have upon the
compartment fire behaviour. Thirty four experiments were conducted in a reduced scale
compartment (½ height) with dimensions of 3.6m long by 2.4m wide by 1.2m high
using five typical ventilation geometries (fully open, soffit, door, window and small
window). Heptane pool fires were used, located in permutations of three evenly
distributed locations within the compartment (rear, centre and front) as well as larger
equivalent area pans located only in the centre. This thesis describes the experimental
development, setup and results of the experimental study. To assist in the classification
of compartment fire behaviour during the experiments, a ‘phi’ meter was developed to
measure the time dependent equivalence ratio. The phi meter was developed and
configured to measure O₂, CO₂ and CO. The background development, calibration, and
experimental results are reported. A review of compartment fire modelling using Fire
Dynamics Simulator, has also been completed and the results discussed.
The results of this experimental study were found to have significant implications for
Fire Safety Engineering in that the size of the fire is not as significant as the location of
the fire. The effect of a fire near the vent opening was found to have a significant impact
on compartment fire behaviour with the vent located fuel source increasing the total
compartment heat release rate by a factor of 1.7 to that of a centrally placed pool fire of
the same total fuel area. The assumption that a fire located in the centre of the room
provides for the highest heat release rate is not valid for post-flashover compartment
fires. The phi meter was found to provide good agreement with the equivalence ratio
calculated from total compartment mass loss rates, and the results of FDS modelling
indicate that the use of the model in its current form can not be applied to complex pool
fire geometries.
Chapitres de livres sur le sujet "Macromolecular pool size ratio"
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Sharma, Shilpi, Arvind Kumar Kourav et Vimal Tiwari. « Fast Fractal Image Compression by Kicking Out Similar Domain Images ». Dans Advances in Systems Analysis, Software Engineering, and High Performance Computing, 318–31. IGI Global, 2018. http://dx.doi.org/10.4018/978-1-5225-3870-7.ch019.
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Fractal algorithms are used to represent similar parts of images into mathematical transforms that can recreate the original image. This chapter presents a fast fractal image compression technique via domain kick-out method, based on averaging of domain images to discard redundant domain images. It accelerates the encoding process by reducing the size of the domain pool. Results of a simulation on the proposed speedup technique on three standard test images shows that performance of the proposed technique is far superior to the present kick out methods of fractal image compression. It has reported a speedup ratio of 31.07 in average while resulting into compression ratio and retrieved image quality comparable to Jacquin's full search method.
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Mathur, Garima, Anjana Pandey et Sachin Goyal. « A Novel Approach to Compress and Secure Human Genome Sequence ». Dans Artificial Intelligence and Communication Technologies, 305–17. Soft Computing Research Society, 2022. http://dx.doi.org/10.52458/978-81-955020-5-9-31.
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DNA sequences can be considered as a pool of genetic information mostly used for reproduction, classification, and detection of disease. FASTA is the commonly used DNA sequence in a textual format whose size is too large which makes it difficult to store and manage; also securing this data is a big issue. Compression techniques that can reduce the size of these DNA data files are the most appropriate solution, reducing the size also reduces the need for resources for transmission. Therefore, this work proposes a novel ASCII-based compression algorithm, in which DNA characters are first converted into ASCII integers and then delta computed, afterwards the LZW compression technique is applied to the computed result. For ensuring the security of data, the blockchain-based framework is used after the compression module to make data immutable. In this paper, for methods like LZW and Huffman code, compression ratio comparisons were also determined for homosapiens, and from the results, it is clear that the proposed algorithm shows a good compression ratio for some randomly selected data sets. Another aim of this paper is to show the benefits of using a blockchain-based framework in securing healthcare data.
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Kuznetsov, Pavel, Anna Mozhayko, Ivan Shakirov, Vitaliy Bobyr, Mikhail Staritsyn et Anton Zhukov. « Modeling of LPBF Scanning Strategy and its Correlation with the Metallic 316 L, 321, and Alnico Magnets Samples Structure ». Dans Advanced Additive Manufacturing [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.102073.
Texte intégralRésumé :
This chapter presents the influence of powder bed laser scanning strategy on the crystallographic structure of the fused specimens 316 L, 321 stainless steel, and Alnico magnets. The main parameters affecting structure are as follows—laser power, stripe width, number of repeated passes with different power, and type of scanning (circle, bidirectional or interlaced, etc.). Changes in the crystallographic structure are studied with regard to melt pool geometry, surface temperature, and surface heat transfer. The correlation is shown between stripe width and laser beam focal spot diameter. Depending on the ratio between stripe width and laser beam focal spot diameter one can see growth elongated and oriented grains or quasi-equiaxed non-oriented grains. The influence of the energy input on the melt pool size and the microstructure of the sample is studied. The influence of the scanning mode (bidirectional and circular) on the temperature distribution in the sample and the microstructure of the sample made of Alnico alloy is considered. All these experimental and model examples clearly demonstrate that it is possible to produce a controllable structure during LPBF process building for advanced additive manufacturing.
Actes de conférences sur le sujet "Macromolecular pool size ratio"
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Ullah, Aman, Huiqi Wang et Rehan Pradhan. « Lipid Derived Block Copolymers as Amphiphilic Nanocarriers for Targeted Delivery ». Dans 2022 AOCS Annual Meeting & Expo. American Oil Chemists' Society (AOCS), 2022. http://dx.doi.org/10.21748/bfgi9101.
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Amphiphilic thermoresponsive block copolymers and ABA type PEG-Lipid conjugated macromolecules have been synthesized using microwave-assisted reversible addition-fragmentation chain transfer (RAFT) polymerization and the copper-catalyzed azide-alkyne cycloaddition, commonly termed “click chemistry”, respectively. Characterization of the block copolymers and conjugates has been carried out with the help of 1H-NMR, FTIR and GPC. These copolymers and conjugates were evaluated for the encapsulation and release of drugs. Carbamazepine, an anticonvulsant drug with poor water solubility was selected to be a hydrophobic drug model in the study. The micellization, drug encapsulation and release behavior of macromolecules was investigated by dynamic light scattering (DLS), transmission electron microscope (TEM) and fluorescence spectroscopy. From the results, it has been concluded that the nanoparticles had different average sizes due to different ratio of hydrophilic contents in the block or conjugate backbone. The particle size and structure could be altered by changing the ratio of hydrophilic and hydrophobic contents. The in vitro drug encapsulations highlighted that all the drug-loaded micelles had spherical or near-spherical morphology. In vitro drug release study showed the controlled release of hydrophobic drug over a period of ~70 hours. The results indicate that there is great potential of renewable lipid-based micelle nanoparticles to be used as amphiphilic drug carriers for targeted delivery applications.
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Raj, Rishi, Jungho Kim, John McQuillen, William Sheredy, Wendell Booth, James Charpie, Jeffrey Eggers, Gregory Funk, Justin Funk et Russell Valentine. « Heater Size and Orientation Effect on Pool Boiling of FC-72 ». Dans 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22682.
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A recent study on pool boiling for upward facing square heaters reported two pool boiling regimes depending on the relative importance of buoyancy and surface tension forces. At higher gravity levels and/or with larger heaters when the ratio of heater size Lh (length of a side for a square heater) to capillary length Lc was greater than 2.1, boiling was buoyancy dominated and the heat transfer results were heater size independent. Boiling was surface tension dominated and heat transfer results were heater size dependent when Lh/Lc<2.1 (small heaters and/or low gravity conditions). This paper studies the effects of orientation on the balance between buoyancy and surface tension forces. The threshold value of Lh/Lc for transition between pool boiling regimes was found to be 1.8 for heaters oriented at 45°, 90°, and 135°.
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Kim, Ho-Young, Yi Gu Kim et Byung Ha Kang. « Enhancement of Natural Convection and Pool Boiling Heat Transfer via Ultrasonic Vibration ». Dans ASME 2003 Heat Transfer Summer Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/ht2003-47131.
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This work experimentally studies the fundamental mechanism by which the ultrasonic vibration enhances natural convection and pool boiling heat transfer. A thin platinum wire is used as both a heat source and a temperature sensor. A high speed video imaging system is employed to observe the behavior of cavitation and thermal bubbles. Experimental results show that the effects of ultrasonic vibration on flow behavior are vastly different depending on the heat transfer regime and the amount of dissolved gas. In the natural convection and subcooled boiling regimes, behavior of cavitation bubbles strongly affects the degree of heat transfer enhancement. In saturated boiling, no cavitation occurs thus the reduced thermal bubble size at departure and acoustic streaming are major factors enhancing heat transfer rate. The highest enhancement ratio is obtained in natural convection regime where no bubbles are present without ultrasonic vibration.
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Lee, Chi Young, Chang Hwan Shin, Dong Seok Oh, Tae Hyun Chun et Wang Kee In. « Parametric Study on Transient Pool Boiling Heat Transfer Using Metal Rodlet ». Dans ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-40281.
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The transient pool boiling heat transfer of zircaloy and stainless steel rodlets was investigated using a quenching method. The influences of quenchant temperature, test specimen size, and material property were examined. The groove-structured surface was also prepared and tested, which could be a valuable attempt to study the effect of a machined surface structure of a vertical rodlet on the rapid cooling heat transfer performance. A test specimen with a small volume-to-heat transfer surface area and small heat capacity showed a shorter quenching time. In the low quenchant temperature condition, a stable film boiling regime was likely to be hardly observed. The grooved surface appeared to have a shorter quenching duration, which could be due to its small volume-to-area ratio. In addition, the groove-structured portion seemed to help the liquid make contact with the heated wall earlier than the plain portion. Based on this work, it was found that the quenching duration and the position of vapor film rupture can be controlled by the surface structure.
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Chien, Liang-Han, Shu-Che Lee, Hon-Zen Wang et Shao-Wen Chen. « Effects of Fluid Properties and Surface Parameters on Pool Boiling of Porous and Pin-Fin Surfaces ». Dans ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer. ASMEDC, 2008. http://dx.doi.org/10.1115/mnht2008-52187.
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The present experimental study investigated the effect of heater size on pool boiling performance for various fluids. Water, methanol and FC-72 were tested at 50 and 70°C saturation temperature on a smooth surface, a porous surface, a pin-fin surface and a structured surface. The boiling test vessel has a 31 mm by 31 mm internal base area and 100 mm height. The sizes of the heating area are: 31×31, 12×12, 9×9, or 6×6 mm2. The test results of all the three fluids showed that boiling performance is independent on heater size for 31mm × 31mm, 12mm × 12 mm heaters, but the boiling heat transfer coefficients for the smooth surface having 6 mm × 6 mm heating area is approximately 70∼100% higher than those for the 12 mm × 12 mm heating area. The 0.2 mm thick square pin-fins, having 0.2 mm depth and 0.4 mm pitch, yields 2-to-3 folds enhancement of boiling performance in FC-72. For methanol and FC-72, the porous surface yields up to seven folds boiling enhancement as compared with the smooth surface. However, the enhancement ratio of the porous surface, having 0.15 mm average particle diameter, is only 2.3 for water. Boiling phenomena observation by a high speed video system showed that the bubble size depends on surface geometries and fluid properties.
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Ghosh, Suhash, Chittaranjan Sahay et Haider Al-Mamoury. « Modeling and Analysis of Weld Geometries, Size and Gap on Weld-Induced Thermal Stresses in a Solid Round-on-Flat Plate Fillet Weld ». Dans ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-71079.
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In this paper a finite element model is presented which describes the effects of fillet weld geometry on the thermal stresses. In a separate research, development of a finite element model for simulating welding-induced thermal stresses is discussed. This nonlinear FE model employs fully coupled three-dimensional thermo-mechanical formulation, including interfacial element to simulate the weaker solidified molten weld pool. Due to the nature of the welding process, heat generation from moving heat source, rapid heating and cooling gives rise to high stresses in the weld. This research investigates the effect of weld shape & size, weld gap, (l/d ratio) depth of weld to size ratio on the generated thermal stresses. The size of the round and flat stocks has been varied to investigate their effects of the stresses as well as to determine the thick-to-thin geometry limits based on acceptable design limits of thermal stresses.
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Mori, Shoji, Lujie Shen et Kunito Okuyama. « Effect of Cell Size of a Honeycomb Porous Plate Attached to a Heated Surface on CHF in Saturated Pool Boiling ». Dans 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22349.
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The critical heat flux (CHF) in a saturated pool boiling of water was investigated experimentally under the condition in which a honeycomb porous plate is attached to the heated surface. In a previous study, the CHF was shown experimentally to be approximately 2.5 times (approximately 2.51 MW/m2) compared to that of a plain surface for the case of a honeycomb porous plate with a vapor escape channel width of 1.4 mm and a channel height (plate thickness) of 1.0 mm (Mori and Okuyama (2009)). The enhancement is considered to result from the capillary supply of liquid onto the heated surface and the release of generated vapor through the channels. In the present paper, the vapor escape channel width was varied in the range of 1.4 mm to 7.9 mm, which was smaller than the Taylor instability wavelength (approximately 15.6 mm), and the effect of the channel width on the saturated pool boiling CHF of water has been investigated. The CHF values predicted by capillary limit models were compared with measured values. As a result, the main mechanisms for CHF enhancement using a honeycomb porous plate were shown to be due to liquid supply to the heated surface as a result of not only capillary suction but also the inflow of liquid through vapor escape channels from the top surface due to gravity. The ratio of the contribution in the mechanisms of the CHF enhancement was found to depend on the vapor escape channel widths. In particular, in the case of a larger cell width, the CHF was enhanced primarily due to the inflow of liquid through vapor escape channels from the top surface.
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Castillo-Orozco, Eduardo, Ashkan Davanlou, Pretam K. Choudhury et Ranganathan Kumar. « On the Impact of Liquid Drops on Immiscible Liquids ». Dans ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2016 Heat Transfer Summer Conference and the ASME 2016 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/icnmm2016-8059.
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The release of liquid hydrocarbons into the water is one of the environmental issues that have attracted more attention after deepwater horizon oil spill in Gulf of Mexico. The understanding of the interaction between liquid droplets impacting on an immiscible fluid is important for cleaning up oil spills as well as the demulsification process. Here we study the impact of low-viscosity liquid drops on high-viscosity liquid pools, e.g. water and ethanol droplets on a silicone oil 10cSt bath. We use an ultrafast camera and image processing to provide a detailed description of the impact phenomenon. Our observations suggest that viscosity and density ratio of the two media play a major role in the post-impact behavior. When the droplet density is larger than that of the pool, additional cavity is generated inside the pool. However, if the density of the droplet is lower than the pool, droplet momentary penetration may be facilitated by high impact velocities. In crown splash regime, the pool properties as well as drop properties play an important role. In addition, the appearance of the central jet is highly affected by the properties of the impacting droplet. In general, the size of generated daughter droplets as well as the thickness of the jet is reduced compared to the impact of droplets with the pool of an identical fluid.
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Fujiwara, Kota, Wataru Kikuchi, Yuki Nakamura, Shimpei Saito, Tomohisa Yuasa, Akiko Kaneko et Yutaka Abe. « Experimental Study of Aerosol Behavior During Pool Scrubbing : Part 1 — Visualization Measurement of Aerosol Particle in a Single Rising Bubble ». Dans 2018 26th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icone26-81383.
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As pool scrubbing plays an important role in fission product (FP) decontamination, a reliable model is needed. Despite the needs, mechanism of FP transfer from air-water from the swarm is not explained exactly which means that the evaluation of physical model used in pre-existing model couldn’t be done enough. Existing model for pool scrubbing is predicted in the MELCOR code. Inside the code, a simple model of bubbly jet divided in 3 regions is used: 1) Globule region where the gas including FP enter and collapse, 2) Swarm rise region where the bubble rises up stationary after the collapse is done and, 3) Entrainment region where the bubble pop out to the atmosphere. In each region, the decontamination factor (DF), the particle density ratio before and after each region, is calculated. On these region, flow and physical force inside the gas phase is predicted to be one of the driving force which cause the FP transfer. Therefore, our study aims at the particle behavior on the gas phase. As to understand the physical phenomenon individually, the study focuses on flow behavior and inner flow of a single rising bubble. As an approach, comparison of bubble containing aerosol and no aerosol has been done for each parameter of size, aspect ratio, velocity. Compared with existing equations, the rising speed of clean bubble condition and aspect ratio of CSI condition agreed well to the MELCOR code [1]. On the other hand, many difference were also measured in other condition. Application of parameters obtained from experiment were done against the MELCOR model. Calculation of velocity inside the oil droplet using the experimental parameters obtained from visualization measurement was done. The local gravitational sedimentation and centrifugal velocity took a higher value in clean bubble and OX50 condition compared to CSI condition. On the other hand, Brownian diffusion velocity had an opposite trend. PIV measurement were performed by a silicone oil to visualize the inner flow clearly and compared with the calculation. Seen from the results, the local diffusion velocity took a lower value compared to the calculation using the MELCOR model.
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Zhang, Chaofan, Daogang Lu, Yu Liu et Haotian Qiu. « Modal analysis and additional fluid mass of coaxial three-layer thin-wall member in annular flow gap ». Dans 2022 29th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/icone29-92274.
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Abstract The sodium-cold pool-type fast reactor is the preferred reactor type for the fourth generation advanced reactor research. The reactor structure of a pool-type fast reactor has the characteristics of large size, thin wall, and relatively low stiffness. Therefore, the seismic design, analysis, and verification of the pool-type fast reactor are the key concerns of the fast reactor safety evaluation. In the fast reactor, many important reactor structures, such as the main pump support cylinder, are immersed in the ring basin of the reactor body. These devices are equipped with thermal shields and can therefore be regarded as coaxial housing systems with water gaps between the cylinders. Under the seismic condition, the fluid-structure coupling effect between the shell and the water gap will change the natural frequency of the shell itself, and the change of structural vibration characteristics is very important to study the seismic performance of the equipment structure in the fast reactor. However, the calculation method based on the dry/wet modal frequency ratio is not suitable for the calculation of additional mass under non-full water conditions. In this paper, based on ANSYS finite element analysis method, a coaxial three-layer shell model with fluid clearance is established to simulate the main pump supporting cylinder and other equipment, and the modes under different frequencies are studied. The additional mass of fluid clearance under different modes is calculated by the relationship between fluid pressure field and shell areal-displacement during vibration. The results are of reference value to the structural design and test of coaxial multi-layer shells such as the support cylinder of the main pump of the fast reactor.