Comparison of the antibacterial activity of chelating agents using the agar diffusion method
Technology Transfer Automated Retrieval System (TEKTRAN)
The agar diffusion assay was used to examine antibacterial activity of 2 metal chelators. Concentrations of 0 to 40 mM of ethylenediaminetetraacetic acid (EDTA) and ethylenediamine-N,N’-disuccinic acid (EDDS) were prepared in 1.0 M potassium hydroxide (KOH). The pH of the solutions was adjusted to 1...
Skóra, Magdalena; Macura, Anna B
2011-01-01
The genus Scopulariopsis is a common soil saprotroph and has been isolated from air, organic waste and also from plant, animal and human tissues. Scopulariopsis has mainly been associated in humans with superficial mycoses, but it has also been described as the cause of subcutaneous and invasive infections. The most common aetiological agent of infections in humans is Scopulariopsis brevicaulis. This species has been reported to be resistant in vitro to broad-spectrum antifungal agents available today. The aim of the study was to establish in vitro antifungal susceptibility of 35 S. brevicaulis strains against amphotericin B (AMB), flucytosine (FC), caspofungin (CAS), terbinafine (TER), ciclopirox (CIC), voriconazole (VOR), clotrimazole (CTR), miconazole (MCZ), econazole (ECO), ketoconazole (KET), itraconazole (ITR), and fluconazole (FLU). Antifungal susceptibility tests were evaluated by an agar diffusion method (Neo-Sensitabs, Rosco, Denmark). AMB, FC, CAS, ITR and FLU showed no antifungal activity against S. brevicaulis. TER, CIC, CTR, KET, VOR, ECO, and MCZ revealed inhibitory activity for S. brevicaulis, but it varied for each of the drugs. The best antifungal effect was observed for TER and CIC. All isolates had large inhibition zones for TER and CIC. CTR was also inhibitory for all tested S. brevicaulis isolates, but the diameters of inhibition zones were smaller than for TER and CIC. Nearly 89% isolates showed inhibition zones for KET and the mean diameter of the inhibition zone was comparable to CTR. The least antifungal activity exhibited VQR, ECO and MCZ. Because of the multiresistance of S. brevicaulis, infections due to this species may not respond to particular antifungal treatment and other therapeutic approaches should be considered, e.g., combined therapy and/or surgery. PMID:21682097
Disk Agar Diffusion Susceptibility Testing of Yeasts
Saubolle, Michael A.; Hoeprich, Paul D.
1978-01-01
A disk agar diffusion method was developed for testing the susceptibility of rapidly growing yeasts in vitro. A totally defined, completely synthetic agar culture medium (synthetic amino acid medium, fungal) and clinical isolates of Candida spp. and Torulopsis glabrata were used. Turbidimetric adjustment of cell suspensions resulted in standard, reproducible inocula, which gave sharp, clear zones of inhibition when applied by an agar overlay method. Optimal disk loads were determined for amphotericin B, amphotericin B methyl ester, 5-fluorocytosine, clotrimazole, and miconazole. Disk potencies were stable over a 2-month period when stored in a vacuum desiccator at −30°C. Using an error ratebounded classification, the zones of inhibition were correlated with both broth dilution and agar dilution minimum inhibitory concentrations (MICs). With amphotericin B and amphotericin B methyl ester, all isolates were susceptible, yielding zone diameters which clustered within 5 mm. Overall correlations between zone diameters and broth dilution MICs with 5-fluorocytosine, miconazole, and clotrimazole were 97, 96, and 82% (excluding T. glabrata), respectively; correlations of zone diameters with agar dilution MICs were 96, 92, and 88%, respectively. Disk diffusion susceptibility testing of yeasts appears to be generally applicable. However, when results are equivocal, quantitative test methods should be used. PMID:568910
Pusnik, Mascha; Imeri, Minire; Deppierraz, Grégoire; Bruinink, Arie; Zinn, Manfred
2016-01-01
A profound in vitro evaluation not only of the cytotoxic but also of bioactive potential of a given compound or material is crucial for predicting potential effects in the in vivo situation. However, most of the current methods have weaknesses in either the quantitative or qualitative assessment of cytotoxicity and/or bioactivity of the test compound. Here we describe a novel assay combining the ISO 10993-5 agar diffusion test and the scratch also termed wound healing assay. In contrast to these original tests this assay is able to detect and distinguish between cytotoxic, cell migration modifying and cytotoxic plus cell migration modifying compounds, and this at higher sensitivity and in a quantitative way. PMID:26861591
Pusnik, Mascha; Imeri, Minire; Deppierraz, Grégoire; Bruinink, Arie; Zinn, Manfred
2016-01-01
A profound in vitro evaluation not only of the cytotoxic but also of bioactive potential of a given compound or material is crucial for predicting potential effects in the in vivo situation. However, most of the current methods have weaknesses in either the quantitative or qualitative assessment of cytotoxicity and/or bioactivity of the test compound. Here we describe a novel assay combining the ISO 10993-5 agar diffusion test and the scratch also termed wound healing assay. In contrast to these original tests this assay is able to detect and distinguish between cytotoxic, cell migration modifying and cytotoxic plus cell migration modifying compounds, and this at higher sensitivity and in a quantitative way. PMID:26861591
Ambaye, A; Kohner, P C; Wollan, P C; Roberts, K L; Roberts, G D; Cockerill, F R
1997-01-01
An evaluation was undertaken to determine the optimal method for the in vitro susceptibility testing of 26 Nocardia asteroides complex isolates to the following antimicrobial agents: amikacin, ampicillin, amoxicillin-clavulanate, ceftriaxone, ciprofloxacin, erythromycin, imipenem, minocycline, and trimethoprim-sulfamethoxazole. Five testing methods were studied including the agar dilution, broth microdilution, and disk diffusion methods, the epsilometer test (E-test), and the BACTEC radiometric method. Results for each antimicrobial agent and each testing method were interpreted as indicating susceptibility, intermediate susceptibility, or resistance according to current guidelines of the National Committee for Clinical Laboratory Standards (NCCLS) for bacteria that grow aerobically and were then compared to a "gold standard" susceptibility test result. The gold standard result for each Nocardia isolate was established by a consensus of the results of the majority of testing methods used in the study. When the results were combined for all antimicrobial agents tested against all Nocardia isolates by all methods, the BACTEC radiometric method produced the highest level of agreement (97.9%) with the consensus results and had the fewest very major (n = 1), major (n = 2), and minor (n = 2) errors. In contrast, the results of the agar dilution method were in least agreement (93.2%) with the consensus results, and this method also produced the most very major (n = 8), major (n = 4), and, along with the disk diffusion method, minor (n = 6) errors. For all test methods, interpretive errors were most frequent when testing ampicillin or amoxicillin-clavulanate. Moreover, for all Nocardia nova isolates tested, ampicillin susceptibility results by any of the testing methods were not in agreement with the results of testing for beta-lactamase by the nitrocefin (Cefinase) disk method. We conclude that among the methods evaluated, the BACTEC radiometric method appeared to be the best for determining the in vitro susceptibilities of members of the N. asteroides complex to a panel of nine antimicrobial agents. However, none of the test methods, including the BACTEC method, accurately predicted the ampicillin resistance of the N. nova isolates tested, all of which produced beta-lactamase. Presuming that this beta-lactamase hydrolyzes ampicillin, this disparity may relate to the NCCLS breakpoints that were used, which may require modification for this antimicrobial agent when tested against N. nova isolates. PMID:9157140
Barry, A L; Fuchs, P C; Gerlach, E H; Allen, S D; Acar, J F; Aldridge, K E; Bourgault, A M; Grimm, H; Hall, G S; Heizmann, W
1990-01-01
A multilaboratory collaborative study was undertaken to determine whether the anaerobic disk diffusion test of Horn et al. could be performed reproducibly and accurately. Tests with nine different antimicrobial disks were evaluated. Reproducibility of the agar diffusion disk method was similar to that of the reference agar dilution test procedure. The anaerobic disk diffusion procedure was found to be a potentially useful method for testing some antimicrobial agents against rapidly growing anaerobes belonging to the Bacteroides fragilis group. These promising results warrant further investigations and validations. PMID:2406872
Modeling development of inhibition zones in an agar diffusion bioassay
Chandrasekar, Vaishnavi; Knabel, Stephen J; Anantheswaran, Ramaswamy C
2015-01-01
A two-temperature agar diffusion bioassay is commonly used to quantify the concentration of nisin using Micrococcus luteus as the indicator microorganism. A finite element computational model based on Fick's second law of diffusion was used to predict the radius of the inhibition zone in this diffusion bioassay. The model developed was used to calculate nisin concentration profiles as a function of time and position within the agar. The minimum inhibitory concentration (MIC) of nisin against M. luteus was determined experimentally. The critical time (Tc) for growth of M. luteus within the agar diffusion bioassay was experimentally determined using incubation studies with nisin. The radius of the inhibition zone was predicted from the computational model as the location where the predicted nisin concentration at Tc was equal to MIC. The MIC was experimentally determined to be 0.156 μg mL−1, and Tc was determined to be 7 h. Good agreement (R2 = 0.984) was obtained between model-predicted and experimentally determined inhibition zone radii. PMID:26405525
Modeling development of inhibition zones in an agar diffusion bioassay.
Chandrasekar, Vaishnavi; Knabel, Stephen J; Anantheswaran, Ramaswamy C
2015-09-01
A two-temperature agar diffusion bioassay is commonly used to quantify the concentration of nisin using Micrococcus luteus as the indicator microorganism. A finite element computational model based on Fick's second law of diffusion was used to predict the radius of the inhibition zone in this diffusion bioassay. The model developed was used to calculate nisin concentration profiles as a function of time and position within the agar. The minimum inhibitory concentration (MIC) of nisin against M. luteus was determined experimentally. The critical time (T c) for growth of M. luteus within the agar diffusion bioassay was experimentally determined using incubation studies with nisin. The radius of the inhibition zone was predicted from the computational model as the location where the predicted nisin concentration at T c was equal to MIC. The MIC was experimentally determined to be 0.156 μg mL(-1), and T c was determined to be 7 h. Good agreement (R (2) = 0.984) was obtained between model-predicted and experimentally determined inhibition zone radii. PMID:26405525
Mignot, L; Junter, G A
1990-05-01
The diffusivity of potassium chloride in composite agar slab/microporous membrane structures loaded with various amounts of Escherichia coli whole cells was determined using both time-lag and steady-state methods. The diffusion coefficient of KCl decreased linearly with the logarithm of the immobilized-cell content. The effect exerted by bacterial growth inside the immobilization matrices on KCl diffusivity was then investigated. The diffusion coefficient of KCl obtained by time-lag analysis decreased during incubation of the immobilized-cell structures, whereas less consistent results arose from the steady-state method. An apparent doubling time for immobilized E. coli, increasing with the initial cell content of the gel, was obtained from the calibration relationship between KCl diffusivity and the number of organisms in agar. PMID:1366531
Bailey, Tom A.
1983-01-01
The reliability, reproducibility, and usefulness of three screening methods -- the cellophane transfer, the agar plug transfer, and the agar dilution -- to screen aquatic fungicides were evaluated. Achlya flagellata and Saprolegnia hypogyna were exposed to 1, 10, and 100 mg/L of malachite green to test each method. The cellophane transfer and agar plug transfer techniques had similar reliability and reproducibility in rating fungicidal activity, and were both superior to the agar dilution technique. The agar plug transfer and agar dilution techniques adequately projected in vivo activity of malachite green, but the cellophane transfer technique overestimated its activity. Overall, the agar plug transfer technique most accurately rated the activity of malachite green and was the easiest test to perform. It therefore appears to be the method of choice for testing aquatic fungicides.
NASA Astrophysics Data System (ADS)
Bante-Guerra, Jose; Macías, J. D.; Caballero-Aguilar, L.; Vales-Pinzón, C.; Alvarado-Gil, J. J.
2013-02-01
Recently, several treatments for fighting malignant tumors have been designed. However these procedures have well known inconveniences, depending on their applicability, tumor size and side effects, among others. Magnetic hyperthermia is a safe, non-invasive method for cancer therapy. This treatment is applied via elevation of target tissue temperature by dissipation of heat from Magnetic Nanoparticles (MNPs), previously located within the tumor. The induction of heat causes cell death and therefore the removal of the tumor. In this work the thermal diffusion in phantoms of agar loaded with magnetic nanoparticles (MNPs) is studied using the infrared thermography technique, which is widely used in biology/medicine (e.g. skin temperature mapping). Agar is one of the materials used to simulate different types of body tissues, these samples are known as "phantoms". Agar is of natural origin, low cost and high degree of biocompatibility. In this work the agar gel was embedded with MNPs by coprecipitation and placed in an alternating magnetic field radiation. As a consequence, the energy from the radiation source is dissipated as heat and then transferred from the MNP to the gel, increasing its temperature. For the temperature analysis, the samples of agar gel were stimulated by RF magnetic field generated by coils. Heating was measured with infrared thermography using a Thermovision A20M infrared camera. Thermographic images allowed obtaining the dependence of thermal diffusion in the phantom as a function of the magnitude of the applied RF magnetic field and the load of magnetic particles.
Aal-Saraj, Ali Burak; Ariffin, Zaihan; Masudi, Sam'an Malik
2012-08-01
The aim of this study was to evaluate the antimicrobial activity of a new experimental nano-hydroxyapatite epoxy resin-based sealer (Nanoseal) with several other commercially available sealers; AH26, Tubliseal, Sealapex and Roekoseal against Enterococcus faecalis, Pseudomonas aeruginosa, Streptococcus mutans, Streptococcus sobrinus and Escherichia coli for up to 7 days. Agar diffusion was used in this study. Fifty Muller-Hinton agar plates were prepared and divided into five experimental groups (n = 10), for each micro-organism. Another 10 agar plates were used as positive and negative controls. Endodontic sealers were tested against each micro-organism. Inhibition zones produced were recorded. The results of this study showed that all test materials exhibited inhibition zones towards the tested micro-organisms for 7 days except for Roekoseal, which showed no inhibition zones. Nanoseal and AH26 exhibited similar zones of inhibition. Significant difference was found between Nanoseal and the other tested sealers (P < 0.001). PMID:22827817
A rapid agar-diffusion test for quantifying the toxic effects of copper on microorganisms.
Rzycki, H
1992-01-01
The rapid agar diffusion test for quantifying the toxic effects of copper on microorganisms was elaborated. The assay was run in standard Petri dishes containing Czapek Solution Agar (Difco). Immediately after inoculation with the organism tested 3.2 mm diameter wells were punched in the agar. Wells were filled (20 microliters) with distilled water (control) and a range of solutions containing 128 to 4096 ppm Cu2+ (as CuSO4). After incubation (2-5 days, 26 degrees C) the diameters of Cu-inhibition zones were measured. Cu-sensitivity indices (ICu's) were calculated according to the formula: ICu = a2/(3.2-b), where: a--slope of the linear regression equation: log [Cu] (x)--inhibition zone diameter (y), b--intercept of the same equation. Additionally for characterization of Cu-sensitivity of the organism tested the predicted highest non-inhibitory Cu concentration (10c) was calculated, where: c = (3.2-b)/a. Both ICu's and adjusted average diameters of Cu-inhibition zones characterized well the Cu-sensitivity in organisms tested, as indicated by the statistical analyses. ICu's correlated very well (negative correlation) with 50% effective doses (Ed50's) of Cu2+ for mycelial growth of Cylindrocarpon destructans. The applicability of the elaborated assay in ecotoxicological studies was discussed. PMID:1283491
Morioka, Ayako; Shimazaki, Yoko; Uchiyama, Mariko; Suzuki, Shoko
2016-05-01
We observed increasing unserotypable (UT) Actinobacillus pleuropneumoniae isolates using agar gel diffusion (AGD) test. To reanalyze their serovar, we performed rapid slide agglutination (RSA) test and multiplex PCR for 47 UT isolates. Of these, 25 were serovar 1 (UT-serovar 1), 20 were serovar 2 (UT-serovar 2) and 2 were serovar 15 (UT-serovar 15). We examined serotyping antigen extraction temperature to determine heat influence. UT-serovar 1 and 15 were influenced by heat, because their precipitation lines were observed in the case of low antigen extraction temperature. To investigate the relationship between antigenicity and genotype, we performed pulsed-field gel electrophoresis (PFGE) analysis using UT-serovar 2 and 15. The predominant PFGE pattern of UT-serovar 2 was identical to that of serovar 2. PMID:26726101
MORIOKA, Ayako; SHIMAZAKI, Yoko; UCHIYAMA, Mariko; SUZUKI, Shoko
2016-01-01
We observed increasing unserotypable (UT) Actinobacillus pleuropneumoniae isolates using agar gel diffusion (AGD) test. To reanalyze their serovar, we performed rapid slide agglutination (RSA) test and multiplex PCR for 47 UT isolates. Of these, 25 were serovar 1 (UT-serovar 1), 20 were serovar 2 (UT-serovar 2) and 2 were serovar 15 (UT-serovar 15). We examined serotyping antigen extraction temperature to determine heat influence. UT-serovar 1 and 15 were influenced by heat, because their precipitation lines were observed in the case of low antigen extraction temperature. To investigate the relationship between antigenicity and genotype, we performed pulsed-field gel electrophoresis (PFGE) analysis using UT-serovar 2 and 15. The predominant PFGE pattern of UT-serovar 2 was identical to that of serovar 2. PMID:26726101
Lu, Ching-Lan; Liu, Chia-Ying; Huang, Yu-Tsung; Liao, Chun-Hsing; Teng, Lee-Jene; Turnidge, John D.; Hsueh, Po-Ren
2011-01-01
We studied the antimicrobial activity of fosfomycin against 960 strains of commonly encountered bacteria associated with urinary tract infection using standard agar dilution and disk diffusion methods. Species studied included 3 common species of Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia; methicillin-susceptible and -resistant Staphylococcus aureus; and vancomycin-susceptible and resistant Enterococcus faecalis and E. faecium. MICs and inhibition zone diameters were interpreted in accordance with both the currently recommended Clinical and Laboratory Standards Institute (CLSI) criteria for urinary tract isolates of Escherichia coli and Enterococcus faecalis and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria for Enterobacteriaceae. Tentative zone diameter interpretive criteria were developed for species not currently published by CLSI or EUCAST. Escherichia coli was uniformly susceptible to fosfomycin, as were most strains of Klebsiella pneumoniae and Enterobacter cloacae. A. baumannii was resistant to fosfomycin, while the prevalence of resistance in P. aeruginosa and S. maltophilia was greatly affected by the choice of MIC breakpoint. New tentative zone diameter criteria for K. pneumoniae, E. cloacae, S. aureus, and E. faecium were able to be set, providing some interim laboratory guidance for disk diffusion until further breakpoint evaluations are undertaken by CLSI and EUCAST. PMID:21670185
Wiegand, Irith; Hilpert, Kai; Hancock, Robert E W
2008-01-01
The aim of broth and agar dilution methods is to determine the lowest concentration of the assayed antimicrobial agent (minimal inhibitory concentration, MIC) that, under defined test conditions, inhibits the visible growth of the bacterium being investigated. MIC values are used to determine susceptibilities of bacteria to drugs and also to evaluate the activity of new antimicrobial agents. Agar dilution involves the incorporation of different concentrations of the antimicrobial substance into a nutrient agar medium followed by the application of a standardized number of cells to the surface of the agar plate. For broth dilution, often determined in 96-well microtiter plate format, bacteria are inoculated into a liquid growth medium in the presence of different concentrations of an antimicrobial agent. Growth is assessed after incubation for a defined period of time (16-20 h) and the MIC value is read. This protocol applies only to aerobic bacteria and can be completed in 3 d. PMID:18274517
Craven, D E; Frasch, C E; Robbins, J B; Feldman, H A
1978-01-01
A serum agar method for serogrouping Neisseria meningitidis is described and compared with conventional bacterial slide agglutination. There was 93% agreement for 300 strains examined individually by each method. Among strains from serogroups A, B, C, Y, and W135, there was 100% correlation, whereas strains from serogroup 29E (Z') had only 67% correlation. The serum agar method was rapid, as well as easy to perform and interpret. The potential benefits of this method for epidemiological studies and reference laboratories processing large numbers of meningococcal isolates are emphasized. Images PMID:96123
Lambert, Frank W.; Brown, June M.; Georg, Lucille K.
1967-01-01
This study was an attempt to develop a fluorescent-antibody (FA) test to differentiate Actinomyces israelii and A. naeslundii as an aid in their laboratory identification. Two strains of A. israelii (X522 and A601) and two strains of A. naeslundii (X454 and X600), which had received intensive study by several investigators, were used for the immunization of rabbits. Working titers, based on tests with antigens prepared from the homologous strains and from well-established heterologous strains, were determined for each labeled antibody preparation. These conjugates and their normal serum control conjugates were used separately to stain 85 cultures of Actinomyes species and 23 strains of other species that might be confused with them. Acetone-precipitated soluble antigens from these same strains were tested with different antisera in the agar-gel diffusion test. Results showed that A. israelii (X522 and A601) and A. naeslundii (X454 and X600) labeled antiglobulins, when used at their working titers, stained most strains of their homologous species. Agar-gel diffusion results showed general agreement with those of the FA tests. The two tests appear to be equal in sensitivity, but the FA test is more specific, since several cross-reactions were noted with the agar-gel diffusion test whereas no cross-reactions were obtained with the FA reagents. Agar-gel and FA studies suggest that at least two serotypes of A. israelii may be associated with human disease. Although the majority of strains tested in this study appear to belong to a common serotype, “serotype 1,” two strains of an apparent second serotype, “serotype 2,” were encountered. FA staining of tissue impression smears from experimentally infected mice was successful when a counterstain, Evans Blue dye, was used. PMID:4964473
A simple agar plate method, using micro-algae, for herbicide bio-assay or detection.
Wright, S J
1975-07-01
A simple, inexpensive method is described for the bio-assay of herbicides using micro-algae growing on agar plates. A result is obtainable in 2 days and the method is suitable for biodetection of herbicide residues, or toxicity studies on soil or aquatic pollutants. PMID:1148432
Technology Transfer Automated Retrieval System (TEKTRAN)
The agar diffusion assay was used to examine antibacterial activity of alkaline salts of fatty acids (FA). Wells in agar media seeded with bacteria were filled with FA-potassium hydroxide (KOH) solutions, plates were incubated, and zones of inhibition were measured. The relationship between bacteric...
MODIFIED AGAR MEDIUM FOR DETECTING ENVIRONMENTAL SALMONELLAE BY THE MOST-PROBABLE-NUMBER METHOD
Salmonellae in the environment remain a potential source of disease. Low numbers of salmonellae have been detected and enumerated from environmental samples by most probable number methods that require careful colony selection from plated agar medium. A modified xylose lysine bri...
An Agar-Based Method for Plating Marine Protozoan Parasites of the Genus Perkinsus
Cold, Emma R.; Freyria, Nastasia J.; Martínez Martínez, Joaquín; Fernández Robledo, José A.
2016-01-01
The genus Perkinsus includes protozoan parasites of mollusks responsible for losses in the aquaculture industry and hampering the recovery of natural shellfish beds worldwide, and they are a key taxon for understanding intracellular parasitism adaptations. The ability to propagate the parasite in liquid media, in the absence of the host, has been crucial for improving understanding of its biology; however, alternative techniques to grow the parasite are needed to explore other basic aspects of the Perkinsus spp. biology. We optimized a DME: Ham’s F12–5% FBS- containing solid agar medium for plating Perkinsus marinus. This solid medium supported trophozoite propagation both by binary fission and schizogony. Colonies were visible to the naked eye 17 days after plating. We tested the suitability of this method for several applications, including the following: 1) Subcloning P. marinus isolates: single discrete P. marinus colonies were obtained from DME: Ham’s F12–5% FBS– 0.75% agar plates, which could be further propagated in liquid medium; 2) Subcloning engineered Perkinsus mediterraneus MOE[MOE]: GFP by streaking cultures on plates; 3) Chemical susceptibility: Infusing the DME: Ham’s F12–5% FBS– 0.75% agar plates with triclosan resulted in inhibition of the parasite propagation in a dose-dependent manner. Altogether, our plating method has the potential for becoming a key tool for investigating diverse aspects of Perkinsus spp. biology, developing new molecular tools, and for biotechnological applications. PMID:27149378
Agar Plate Method for Detection and Enumeration of Alkylbenzenesulfonate-Degrading Microorganisms
Ohwada, Kouichi
1975-01-01
A simple method for detection and enumeration of alkylbenzenesulfonate (ABS)-degrading microorganisms by using agar plates was developed and used in microbiological studies of coastal marine and polluted river waters. The method depends upon the color responses of neutral red in alkaline medium. Neutral red changes from pink, when it enters into ABS micelles, to yellow, when the ABS is degraded, and does not form micelles. When neutral red-tris(hydroxymethyl)-aminomethane buffer solution and then cationic surfactant solution were sprayed onto the agar surface of ABS-nutrient agar cultures, transparent haloes appeared around the colonies of ABS-degrading microorganisms against a pink background. Viable counts of ABS-degrading bacteria isolated from both seawater and freshwater environments were considerably higher in polluted waters than in less polluted areas. Viable counts of ABS-degrading bacteria averaged 1.5 × 105/ml in samples from the surface water of polluted Tokyo Bay and 3.0 × 104/ml in samples from the surface water of polluted Tamagawa River but were fewer in number in samples from less polluted waters. Images PMID:234155
Rapid fluorescence method for screening Salmonella spp. from enteric differential agars.
Aguirre, P M; Cacho, J B; Folgueira, L; López, M; García, J; Velasco, A C
1990-01-01
Four hundred thirty-two lactose-negative colonies isolated from human feces on stool differential agar media were flooded with one drop of MUCAP Test reagent (Biolife Italiana S.r.I., Milan, Italy) and observed under a Wood lamp for the development of a blue fluorescence over or around the colony. On the basis of manual and automated conventional tests for the screening of Salmonella spp., the MUCAP Test yielded the following results: 79 true-positives, 314 true-negatives, 35 false-positives, and 4 false-negatives (sensitivity, 95%; specificity, 90%; positive predictive value, 69%; negative predictive value, 99%). The specificity of the test performed on colonies isolated on MacConkey agar (95%) was higher than that performed on colonies isolated on SS agar (88%; P less than 0.03). The MUCAP Test is an easy, rapid, and sensitive method for the screening of colonies suspected of being Salmonella spp., reducing the number of biochemical tests needed. PMID:2405010
Stone, M S; Wallace, R J; Swenson, J M; Thornsberry, C; Christensen, L A
1983-01-01
An agar disk elution method using round well plates, supplemented Mueller-Hinton agar, and commercial drug disks is described for susceptibility testing of Mycobacterium marinum and the rapidly growing mycobacteria to antibiotics and sulfonamides. By this method, 14 of 14 strains of M. marinum were susceptible to rifampin, doxycycline, minocycline, and trimethoprim-sulfamethoxazole. Identical results were obtained with Middlebrook 7H10 agar and drugs prepared from standard powders. With 58 isolates of Mycobacterium fortuitum and Mycobacterium chelonei, this method had a 92% correlation with broth minimal inhibitory concentration determinations for cefoxitin and greater than 98% for doxycycline, kanamycin, amikacin, and the sulfonamides. Sixty-nine percent of isolates of M. chelonei susceptible to amikacin on supplemented Mueller-Hinton agar were resistant on 7H10 agar, and 15 of 16 M. chelonei isolates susceptible to erythromycin in broth were resistant by disk elution when an endpoint of no growth was used with either agar. The agar disk elution method offers a practical method for testing of most antibacterial agents against these mycobacterial species. Images PMID:6651277
Oja, Terhi; Blomqvist, Brianna; Buckingham-Meyer, Kelli; Goeres, Darla; Vuorela, Pia; Fallarero, Adyary
2014-12-01
The development of biofilms in static plates was monitored. Glass coupons were placed on agar covered with filter paper, which was inoculated with suspended bacteria. The viable cell density, biofilms matrix and biomass were quantified. The method is excellent for adhesion and material studies, due to its simplicity and flexibility. PMID:25455020
Wu, Guoyan; Yang, Qianru; Long, Mei; Guo, Lijuan; Li, Bei; Meng, Yue; Zhang, Anyun; Wang, Hongning; Liu, Shuliang; Zou, Likou
2015-11-01
A variety of disinfectants have been widely used in veterinary hygiene, food industries and environments, which could induce the development of bacterial resistance to disinfectants. The methods used to investigate antimicrobial effects of disinfectant vary considerably among studies, making comparisons difficult. In this study, agar dilution and broth microdilution methods were used to compare the antimicrobial activities of four quaternary ammonium compounds (QACs) against foodborne and zoonotic pathogens. The potential relationship between the presence of QACs resistance genes and phenotypic resistance to QACs was also investigated. Our results indicated that the minimum inhibitory concentrations (MICs) determined by two methods might be different depended upon different QACs and bacteria applied. Regardless of the testing methods, Klebsiella pneumoniae was more tolerant among Gram-negative strains to four QACs, followed by Salmonella and Escherichia coli. The agreement between MICs obtained by the two methods was good, for benzalkonium chloride (78.15%), didecyldimethylammonium chloride (DDAC) (82.35%), cetylpyridinium chloride (CTPC) (97.48%) and cetyltrimethylammonium bromide (CTAB) (99.16%), respectively. Among all Gram-negative bacteria, 94.55% (n=52) of qacEΔ1-positive strains showed higher MICs (512 mg l(-1)) to CTAB. The qacEΔ1 gene was highly associated (P<0.05) with the high MICs of QACs (⩾512 mg l(-1)). In addition, DDAC remained as the most effective disinfectant against both Gram-positive and Gram-negative bacteria. This is the first study that compared the agar dilution and broth microdilution methods to assess the antimicrobial activity of QACs. The study demonstrated the need to standardize method that would be used in evaluating QACs antimicrobial properties in the future. PMID:25944532
Technology Transfer Automated Retrieval System (TEKTRAN)
The agar diffusion assay was used to examine antibacterial activity of alkaline salts of caproic, caprylic, capric, lauric, and myristic acids. A 0.5M concentration of each fatty acid was dissolved in 1.0 M potassium hydroxide (KOH), and pH of the mixtures was adjusted to 10.5 with citric acid. Solu...
Hoelzer, Karin; Cummings, Kevin J; Warnick, Lorin D; Schukken, Ynte H; Siler, Julie D; Gröhn, Yrjo T; Davis, Margaret A; Besser, Tom E; Wiedmann, Martin
2011-12-01
Data generated using different antimicrobial testing methods often have to be combined, but the equivalence of such results is difficult to assess. Here we compared two commonly used antimicrobial susceptibility testing methods, automated microbroth dilution and agar disk diffusion, for 8 common drugs, using 222 Salmonella isolates of serotypes Newport, Typhimurium, and 4,5,12:i-, which had been isolated from clinical salmonellosis cases among cattle and humans. Isolate classification corresponded well between tests, with 95% overall category agreement. Test results were significantly negatively correlated, and Spearman's correlation coefficients ranged from -0.98 to -0.38. Using Cox's proportional hazards model we determined that for most drugs, a 1 mm increase in zone diameter resulted in an estimated 20%-40% increase in the hazard of growth inhibition. However, additional parameters such as isolation year or serotype often impacted the hazard of growth inhibition as well. Comparison of economical feasibility showed that agar disk diffusion is clearly more cost-effective if the average sample throughput is small but that both methods are comparable at high sample throughput. In conclusion, for the Salmonella serotypes and antimicrobial drugs analyzed here, antimicrobial susceptibility data generated based on either test are qualitatively very comparable, and the current published break points for both methods are in excellent agreement. Economic feasibility clearly depends on the specific laboratory settings, and disk diffusion might be an attractive alternative for certain applications such as surveillance studies. PMID:21877930
Cummings, Kevin J.; Warnick, Lorin D.; Schukken, Ynte H.; Siler, Julie D.; Gröhn, Yrjo T.; Davis, Margaret A.; Besser, Tom E.; Wiedmann, Martin
2011-01-01
Abstract Data generated using different antimicrobial testing methods often have to be combined, but the equivalence of such results is difficult to assess. Here we compared two commonly used antimicrobial susceptibility testing methods, automated microbroth dilution and agar disk diffusion, for 8 common drugs, using 222 Salmonella isolates of serotypes Newport, Typhimurium, and 4,5,12:i-, which had been isolated from clinical salmonellosis cases among cattle and humans. Isolate classification corresponded well between tests, with 95% overall category agreement. Test results were significantly negatively correlated, and Spearman's correlation coefficients ranged from −0.98 to −0.38. Using Cox's proportional hazards model we determined that for most drugs, a 1 mm increase in zone diameter resulted in an estimated 20%–40% increase in the hazard of growth inhibition. However, additional parameters such as isolation year or serotype often impacted the hazard of growth inhibition as well. Comparison of economical feasibility showed that agar disk diffusion is clearly more cost-effective if the average sample throughput is small but that both methods are comparable at high sample throughput. In conclusion, for the Salmonella serotypes and antimicrobial drugs analyzed here, antimicrobial susceptibility data generated based on either test are qualitatively very comparable, and the current published break points for both methods are in excellent agreement. Economic feasibility clearly depends on the specific laboratory settings, and disk diffusion might be an attractive alternative for certain applications such as surveillance studies. PMID:21877930
A Method for Cell Culture and Maintenance of Ammonia-Oxidizing Archaea in Agar Stab.
Chu, Yeon-Jin; Lee, Jin-Young; Shin, So-Ra; Kim, Geun-Joong
2015-12-01
Ammonia oxidizing archaea (AOA) are predominantly found and closely linked with geochemical cycling of nitrogen in non-extreme habitats. However, these strains have mainly been investigated using liquid cultures of enriched cells. Here, we provide an agar stab as a simple and reliable means of cultivating and maintaining AOA. PMID:26543273
Perçin, Duygu; Colakoğlu, Selcan; Durmaz, Süleyman; Ekincioğlu, Pınar
2012-10-01
Detection of rectal colonization with carbapenem-resistant Klebsiella pneumoniae (CRKP) is the most important step in the infection control protocols in order to prevent infections caused by CRKP which has an increasing incidence all over the world. In this study, it was aimed to compare the detection rate of 2 mg/L ertapenem EMB agar medium with the other methods recommended by various international guidelines. These methods include direct plate method using ertapenem disc, enrichment method in tryptic soy broth containing 2 mg/L ertapenem and the investigation of the predominant betalactamases in the colonized patients. The lowest inoculum detected by different methods was determined by using simulative challenge test prepared for this purpose. The ability to detect CRKP from rectal swabs was evaluated by using the clinical specimens of 801 patients. For all bacteria isolated, carbapenem susceptibility was evaluated by using E-test method, the presence of beta-lactamases was determined by using modified Hodge test (MHT), and the carbapenemase genes were investigated by using multiplex polymerase chain reaction (PCR). The lowest inoculum detected by ertapenem-EMB agar was 50 CFU/mL whereas the lowest inocula were 1 x 105 and 1 x 103, respectively by tryptic soy broth with ertapenem and direct plate method. No resistance gene were identified by PCR in 13 (39.4%) of 33 isolates, whereas blaOXA-48 was detected in 19 (95%) and blaIMP in 1 (5%) of 20 positive isolates. All of the positive strains were resistant to imipenem and ertapenem, while 2 (10%) strains were found to be susceptible to doripenem and meropenem. While MHT was negative in all strains which were negative for resistance genes, all resistance gene positive strains except one blaOXA-48 strain that was also sensitive to doripenem and meropenem, were found to be positive with MHT. According to the results of PCR, the sensitivities of the three methods were found to be 80%. The specificities, positive and negative predictive values were found to be 15.4%, 59% and 33.3% for ertapenem-EMB agar, 23%, 61.5% and 42.9% for broth with ertapenem and 61.5%, 76% and 66.6% for direct plate method, respectively. Average labor time of the methods (isolation + identification + sensitivity + MHT) was determined as 48 hours for ertapenem-EMB agar, whereas it was 96 hours for the other methods. In conclusion, since ertapenem- EMB agar method is a sensitive and rapid method, it can be used safely for the preliminary detection of CRKP without increasing the workload of the laboratory. PMID:23188568
Johnson, Ronald; Mills, John; Colón-Reveles, Judith
2009-01-01
A method modification study was conducted for the VIDAS Salmonella (SLM) assay (AOAC Performance Tested Method 020901) using the EasySLM method to validate a matrix extension for peanut butter. The VIDAS EasySLM method is a simple enrichment procedure compared to traditional Salmonella methods, requiring only pre-enrichment and a single selective enrichment media, Salmonella Xpress 2 (SX2) broth. SX2 replaces the two selective broths in traditional methods and eliminates the M broth transfer, incubation, and subsequent pooling of M broths prior to VIDAS assay. The validation study was conducted under the AOAC Research Institute Emergency Response Validation program. VIDAS SLM was compared to the U.S. Food and Drug Administration's Bacteriological Analytical Manual (FDA-BAM) method for detection of S. enterica ser. Typhimurium in peanut butter. All peanut butter samples were prepared, blind-coded, and shipped to the method developers' laboratory by Q Laboratories. In addition, Q Laboratories performed most probable number and reference method analyses on peanut butter samples. The VIDAS EasySLM ChromID Salmonella (SM2) Agar was previously validated in the Performance Tested Methods program for the detection of Salmonella in roast beef, raw ground pork, turkey, pork sausage, raw chicken breast, dry pet food, whole milk, ice cream, bagged spinach, shrimp (raw, peeled), raw cod, spent irrigation water, pecans, peanut butter, dry pasta, cake mix, ground black pepper, nonfat dry milk, liquid eggs, cantaloupe, and orange juice. In the matrix extension study for peanut butter, the VIDAS EasySLM method was shown to be equivalent to the appropriate reference culture procedure using both buffered peptone water pre-enrichment and the FDA-BAM lactose pre-enrichment in the two-step enrichment method with SX2 media. The current study extends the validation to include peanut butter. PMID:20166608
Use of urease-bromothymol blue-agar method for large-scale testing of urine on grain and seeds.
Valdes, P A; Ziobro, G C; Ferrera, R S
1996-01-01
The current AOAC method (963.28) for large-scale (50 g) testing of urine on grain is based on the reaction of sodium in urine with magnesium uranyl acetate. Detection of sodium suggests that urine is present and that a test for urea is appropriate. Urea is detected with urease-bromothymol blue-paper and is confirmed through its reaction with xanthydrol to form dixanthylurea crystals, which are detected microscopically. The initial nonspecific test for sodium can be influenced by the presence of salt or other sodium compounds. Furthermore, the magnesium uranyl acetate spray used in Method 963.28 potentially exposes the analyst to the aerosol of a volatile, toxic uranium compound. Excess reagents and analyzed test portions must be disposed of as radioactive waste. In addition, Method 963.28 requires several steps to determine the presence of urea. The alternative AOAC method (972.41) tests for the presence of urea from urine on individual seeds. Urea is enzymatically decomposed to ammonia and carbon dioxide by urease. Liberated ammonia shifts the pH, changing the color of the indicator in the agar from yellow to blue. This study adapts Method 972.41 to larger test samples. Up to 25 g grains and seeds are sprayed with urease test agar instead of being individually immersed in the urease test agar. The modified method was used to analyze urea on seeds and grains of 24 plants from 4 families. The method has a limit of detection of one seed contaminated with 1 microgram urea. PMID:8757445
Lavalle, Christian; Rouleau, Danielle; Gaudreau, Christiane; Roger, Michel; Tsimiklis, Catherine; Locas, Marie-Claude; Gagnon, Simon; Delorme, Jocelyn; Labb, Annie-Claude
2010-01-01
The D-zone test detects inducible clindamycin resistance in Staphylococcus spp. Two other methods not described by the Clinical and Laboratory Standards Institute (CLSI) are available to test for this resistance mechanism: an agar dilution method and new Vitek 2 cards. This study evaluated the performance of both methods in detecting inducible clindamycin resistance. Nonduplicate clinical strains of Staphylococcus spp. (111 Staphylococcus aureus and 52 coagulase-negative staphylococcus strains), intermediate or resistant to erythromycin but susceptible to clindamycin, were obtained from three hospitals in Montreal, Quebec, Canada. Molecular analysis to detect resistance genes was conducted on all strains. A Mueller-Hinton agar containing 1 mg of erythromycin and 0.5 mg of clindamycin/liter was used for the dilution method, and two inocula were tested: 104 and 105 CFU per spot. Plates were read at 24 and 48 h. The Vitek 2 AST-P580 card was used according to the manufacturer's recommendations. The results were compared to those of the D-zone test. The D-zone test was positive in 134 of 163 (82%) strains. With the 104 CFU inoculum, the sensitivities were 84 and 99% at 24 and 48 h, respectively. The 105 CFU inoculum increased the sensitivities at 24 and 48 h to 91 and 100%, respectively. The specificity was 100% for the 104 CFU inoculum at 24 h and 97% for the other combinations. The sensitivity and specificity for the Vitek 2 card were 93 and 100%, respectively. The performance of both the agar dilution method and the Vitek 2 card was good, but these methods were not as sensitive as the D-zone test at 24 h. PMID:20164285
Wexler, H M; Molitoris, E; Murray, P R; Washington, J; Zabransky, R J; Edelstein, P H; Finegold, S M
1996-01-01
A multilaboratory collaborative study was carried out to assess the utility of the spiral gradient endpoint (SGE) method for the determination of the antimicrobial susceptibilities of anaerobes and to evaluate the equivalence of the MICs obtained by the SGE method with those obtained by the reference agar dilution method of the National Committee for Clinical Laboratory Standards. The standard deviation of the MIC obtained by the SGE method for the five participating laboratories was +/- 0.26 of a twofold dilution, whereas it was +/- 1 twofold dilution by the reference method. The interlaboratory reproducibility of the results for two control strains tested with imipenem, chloramphenicol, and metronidazole indicated that 96% of the measurements fell within +/- 1 twofold dilution of the mode. The equivalence of the SGE method with the agar dilution method was assessed with a wide variety of anaerobic organisms. The MICs by both methods were within 1 doubling dilution in 93% of the measurements (n = 1,074). Discrepancies generally occurred with those organism-drug combinations that resulted in tailing endpoints (Fusobacterium nucleatum, 86% agreement) or in cases of light growth (Peptostreptococcus spp., 86% agreement). PMID:8748295
Jones, R N; Barry, A L; Thornsberry, C
1983-01-01
Ceftazidime is a wide-spectrum, beta-lactamase-stable cephalosporin with remarkable potency against Pseudomonas spp., Enterobacteriaceae, and some gram-positive species. The reevaluation of the 30-micrograms ceftazidime disk diffusion tests with commercially prepared disks confirms the proposed susceptibility breakpoint zone of greater than or equal to 17 mm (minimal inhibitory concentration correlate, less than or equal to 8.0 micrograms/ml) and the resistance breakpoint zone of less than or equal to 13 mm (minimal inhibitory concentration correlate, greater than or equal to 32 micrograms/ml). Major and minor interpretive errors were only 4.4%, and these errors could be further reduced to 1.1% by not testing gram-positive organisms, particularly enterococci and Staphylococcus spp. On the basis of the results from a multilaboratory quality control study, the following zone diameter quality control guidelines are suggested: Escherichia coli ATCC 25922, 27 to 31 mm; Staphylococcus aureus, ATCC 25923, 16 to 20 mm; Pseudomonas aeruginosa ATCC 27853, 24 to 28 mm. PMID:6350348
Butler, N J; Langley, G R; Winwood, J
1993-02-01
Synopsis An established cytotoxicity test for plastic materials in medical devices has been adapted and used to assess the relative potential irritancy of cosmetic ingredients and formulations during product development. Serum-free medium containing a novel protein supplement supported growth in suspension of LS mouse fibroblast cells. Release of the vital dye Neutral Red from pre-loaded cells suspended in agar was the endpoint. Test substances and reference standards were applied to a central well cut into the agar, a sensitive method which allowed accurate dose application and yielded consistent results. Relative irritancy potential was measured quantitatively by comparing the diameters of the clear zones of damaged cells which surround the central well. The test has been used with raw materials such as surfactants, preservatives and herbal extracts, as well as finished products ranging from shampoos and conditioners to creams, lotions and coloured cosmetics. The method is practical, versatile, reproducible and economic to use. Résumé Un test de cytotoxicité utilisé pour la détection de toxines dans les plastiques des appareils médicaux a été adapté pour prévenir le potentiel d'irritation relative. Le point mesuré est la libération de la teinture vitale rouge neutre des cellules chargées au préalable, résultant de l'incubation avec des substances tests. La mesure des diamétres de la zone claire de dilutions sequentielles de substances tests permet de calculer l'irritation potentielle d'un produit testé par rapport à un standard. Parmi les modifications, on a pu constater à l'aide d'une ligne de cellules en suspension dérivées de fibroblastes de souris L-929, la pousse en milieu sans sérum pour éviter les produits d'abattoir. A la place du sérum de veau, on a ajouté au milieu une nouvelle protéine innovatrice supportant la pousse normale en suspension. Durant la procédure de test les cellules se trouvaient en suspension dans une solution agar et les substances tests ont été appliquées sur une cellule centrale bien délimitéc sur la gélose plutôt qu'à l'aide d'un disque de papier filtre. L'application par une cellule centrale était plus sensible qu'avec un disque, permettant l'application d'une dose précise et fournissant des résultats plus fiables. Le test modifié a été utilisé sur une période de 4 ans pour des matiéres premières telles que tensioactifs, conservateurs et extraits de plantes, ainsi que des formules de shampooings, savons, lotions hydratantes et cosmétiques colorés. Ces produits ont étéévalués sur des panels de volontaires, et les produits testés sont commercialisés depuis 2 ans au moins. Le test est un moyen pratique, versatile, reproductible et économique de calculer le potentiel d'irritation relative d'une gamme de produits et ingrédients cosmktiques. PMID:19272118
Mathematical Methods for Diffusion MRI Processing
Lenglet, C.; Campbell, J.S.W.; Descoteaux, M.; Haro, G.; Savadjiev, P.; Wassermann, D.; Anwander, A.; Deriche, R.; Pike, G.B.; Sapiro, G.; Siddiqi, K.; Thompson, P.
2009-01-01
In this article, we review recent mathematical models and computational methods for the processing of diffusion Magnetic Resonance Images, including state-of-the-art reconstruction of diffusion models, cerebral white matter connectivity analysis, and segmentation techniques. We focus on Diffusion Tensor Images (DTI) and Q-Ball Images (QBI). PMID:19063977
Tan, Ping; Zhang, Jie; Li, Qing; Yu, Zhi-jun
2014-12-01
In order to study the histological structure of Oncomelania hupensis soft tissue, the fixed soft tissues of O. hupensis were pre-embedded in the agar and made blocks, then dehydrated, transparentized, immersed in paraffin, sectioned, and stained with haematoxylin-eosin (HE). Permanent slides of O. hupensis soft tissue were obtained. The histological structure of soft tissues was clear under the microscope. PMID:25902672
Modeling of the Bacillus subtilis Bacterial Biofilm Growing on an Agar Substrate
Wang, Xiaoling; Wang, Guoqing; Hao, Mudong
2015-01-01
Bacterial biofilms are organized communities composed of millions of microorganisms that accumulate on almost any kinds of surfaces. In this paper, a biofilm growth model on an agar substrate is developed based on mass conservation principles, Fick's first law, and Monod's kinetic reaction, by considering nutrient diffusion between biofilm and agar substrate. Our results show biofilm growth evolution characteristics such as biofilm thickness, active biomass, and nutrient concentration in the agar substrate. We quantitatively obtain biofilm growth dependence on different parameters. We provide an alternative mathematical method to describe other kinds of biofilm growth such as multiple bacterial species biofilm and also biofilm growth on various complex substrates. PMID:26355542
Sartory, David P; Gu, Haoyi; Chen, Chun-Ming
2008-07-01
This study compared the Quanti-Disc most probable number (MPN) test for heterotrophic bacteria from drinking water with the widely used yeast extract agar (YEA) pour plate method. The Quanti-Disc test module contains 50 reaction wells in which a medium has been pre-deposited. The medium contains a suite of three fluorogenic enzyme substrates selected for the detection of enzymes expressed widely by heterotrophic bacteria. The MPN of heterotrophic bacteria is calculated from the number of fluorescing reaction wells after incubation of a sample. Quanti-Disc and the YEA pour plate method were compared according to guidance on comparing methods given in United Kingdom national guidance and ISO 17994:2004. The two methods were also challenged with reference strains and isolates of heterotrophic bacteria from drinking water. This indicated that heterotrophic bacteria commonly encountered in drinking water are detected by both the YEA pour plate method and Quanti-Disc. Analysis of data from split water samples (723 for 37 degrees C tests and 872 for 22 degrees C tests) from nine geographically diverse laboratories in England and Wales demonstrated that the Quanti-Disc method is equivalent to the YEA pour plate method for the analysis of heterotrophic bacteria from drinking and similar waters at 37 degrees C, and superior to YEA for the analysis at 22 degrees C. The Quanti-Disc method is a simple and efficient alternative method for the enumeration of heterotrophic bacteria from drinking water. PMID:18534656
Arantes, Paula Tamião; Sanitá, Paula Volpato; Santezi, Carolina; Barbeiro, Camila de Oliveira; Reina, Bárbara Donadon; Vergani, Carlos Eduardo; Dovigo, Lívia Nordi
2016-03-01
The aim of this study was to establish a reproducible protocol using the methodology of hyaline zones around the colonies on specific agar plates for phospholipase and proteinase production. This was an in vitro double-blind experiment, in which the dependent variables were the enzymatic activity measurements (Pz) for the production of phospholipase (Pz-ph) and the production of secreted aspartyl proteinases (Pz-sap). Three independent variables give rise to different measurement protocols. All measurements were carried out at two different moments by four examiners (E1, E2, E3, and E4). The minimum sample size was 30 Candida albicans clinical isolates. Specific agar plates for phospholipase and SAPs production were prepared according the literature. The intra-and inter-examiner reproducibility for each protocol was estimated using the Intraclass Correlation Coefficient (ICC) and its confidence interval (95% CI). Based on the results obtained for both phospholipase and SAPs, there appears to be no consensus on the protocol chosen for each particular examiner. Measuring the colonies in triplicate may be the main factor associated with the increase in measurement accuracy and should therefore take precedence over measuring only one colony. When only one examiner is responsible for taking measurements, a standard protocol should be put in place and the statistical calibration of this researcher should be done prior to data collection. However, if two or more researchers are involved in the assessment of agar plates, our results suggest that the protocols using software to undertake plate reading is preferred. PMID:26705836
Wu, Vivian C H; Qiu, Xujian; Peggy Hsieh, Y-H
2008-02-01
Escherichia coli O157:H7 survival in apple juice supplemented with Cornus fruit (Cornus officinalis Sieb. et Zucc.) extract was studied. Inoculated samples with or without Cornus fruit extract were kept at 21 and 7 degrees C. Microbial analysis was conducted on days 0, 1, 3, 5, and 7. MacConkey sorbitol agar (MSA), tryptic soy agar (TSA), and thin agar layer (TAL) medium were used to compare the recovery of bacteria stressed under combination treatment. Influence of temperature, storage time, and Cornus fruit on survival of cells was evaluated. The most dramatic reduction of E. coli O157:H7 was observed in apple juice with Cornus fruit extract at 21 degrees C. At 7 degrees C, E. coli O157:H7 was reduced by 2.3logcfu/ml in the apple juice with Cornus fruit extract compared to the control sample on day 7. TAL and TSA were more efficient than MSA. Cornus fruit extract can be used in combination with temperature and storage time controls to inactivate E. coli O157:H7 in apple juice. This study has shown that TAL is a viable method of recovering and differentiating injured microorganisms and apple juice supplemented with Cornus fruit has potential as a value-added beverage with antimicrobial effects and potential health benefits. PMID:17993394
Aulenbach, Brent T.
2010-01-01
Bacteria holding-time experiments of up to 62 h were performed on five surface-water samples from four urban stream sites in the vicinity of Atlanta, GA, USA that had relatively high densities of coliform bacteria (Escherichia coli densities were all well above the US Environmental Protection Agency criterion of 126 colonies (100 ml) − 1 for recreational waters). Holding-time experiments were done for fecal coliform using the membrane filtration modified fecal coliform (mFC) agar method and for total coliform and E. coli using the Colilert®-18 Quanti-Tray® method. The precisions of these analytical methods were quantified. Precisions determined for fecal coliform indicated that the upper bound of the ideal range of counts could reasonably be extended upward and would improve precision. For the Colilert®-18 method, analytical precisions were similar to the theoretical precisions for this method. Fecal and total coliform densities did not change significantly with holding times up to about 27 h. Limited information indicated that fecal coliform densities might be stable for holding times of up to 62 h, whereas total coliform densities might not be stable for holding times greater than about 27 h. E. coli densities were stable for holding times of up to 18 h—a shorter period than indicated from a previous studies. These results should be applicable to non-regulatory monitoring sampling designs for similar urban surface-water sample types.
Entis, P
1996-01-01
Twenty laboratories participated in a collaborative study to validate a 2-day hydrophobic grid membrane filter method using YM-11 agar for enumeration of yeast and mold in foods. Six naturally contaminated food products were included in the study: garlic powder, raw ground beef, walnuts, flour/meal, orange juice, and yogurt. The test method produced significantly higher results than the 5-day pour plate reference method for orange juice and significantly lower, though numerically similar, results for walnuts and yogurt. Differences between the test and reference methods were not significant for garlic powder, raw ground beef, or flour/meal. Repeatability and reproducibility were similar for both the test and reference methods in all cases. The hydrophobic grid membrane filter method for enumeration of yeast and mold in foods has been adopted by AOAC INTERNATIONAL. PMID:8823916
Sakai, Masao; Hosoda, Akifumi; Ogura, Kenjiro; Ikenaga, Makoto
2014-01-01
An agar-degrading bacterium was isolated from soil collected in a vegetable cropping field. The growth of this isolate was enhanced by supplying culture supernatants of bacteria belonging to the order Rhizobiales. Phylogenetic analysis based on 16S rRNA gene sequences indicated the novel bacterium, strain KA5–BT, belonged to the genus Steroidobacter in Gammaproteobacteria, but differed from its closest relative, Steroidobacter denitrificans FST, at the species level with 96.5% similarity. Strain KA5–BT was strictly aerobic, Gram-negative, non-motile, non-spore forming, and had a straight to slightly curved rod shape. Cytochrome oxidase and catalase activities were positive. The strain grew on media containing culture supernatants in a temperature range of 15–37°C and between pH 4.5 and 9.0, with optimal growth occurring at 30°C and pH 6.0–8.0. No growth occurred at 10 or 42°C or at NaCl concentrations more than 3% (w/v). The main cellular fatty acids were iso–C15:0, C16:1ω7c, and iso–C17:1ω9c. The main quinone was ubiquinone-8 and DNA G+C content was 62.9 mol%. In contrast, strain FST was motile, did not grow on the agar plate, and its dominant cellular fatty acids were C15:0 and C17:1ω8c. Based on its phylogenetic and phenotypic properties, strain KA5–BT (JCM 18477T = KCTC 32107T) represents a novel species in genus Steroidobacter, for which the name Steroidobacter agariperforans sp. nov. is proposed. PMID:24621511
ERIC Educational Resources Information Center
Foy, Barry G.
1977-01-01
Two demonstrations are described. Materials and instructions for demonstrating movement of molecules into cytoplasm using agar blocks, phenolphthalein, and sodium hydroxide are given. A simple method for demonstrating that the rate of diffusion of a gas is inversely proportional to its molecular weight is also presented. (AJ)
Crozier-Dodson, Beth Ann; Fung, Daniel Y C
2002-09-01
Thin agar layer (TAL) medium was developed at Kansas State University to improve the resuscitation of injured cells and has been shown to result in higher recovery than is obtained with selective media alone for cold-, heat-, salt-, and acid-injured cells. The experiment presented here was designed to determine the effectiveness of the TAL method for the recovery of possibly injured organisms from air. Eleven agar media were used for the experiment: tryptic soy agar (TSA), MacConkey sorbitol agar (MSA), TAL-MSA, Baird-Parker (BP) agar, TAL-BP agar, modified Oxford (MOX) agar, TAL-MOX agar, xylose lysine sodium desoxycholate (XLD) agar, TAL-XLD agar, Yersinia-selective (CIN) agar, and TAL-CIN agar. The TAL plates were prepared by pipetting 6 ml of selective agar into a BBL Rodac plate (65 by 15 mm). Selective agar was allowed to solidify, and then each plate was overlaid with 6 ml of TSA. Selective agar plates were prepared by pipetting 12 ml of agar into BBL Rodac plates and allowing the agar to solidify. Samples were taken at an indoor cattle facility at five separate locations with a BioScience SAS air-sampling instrument. For each plate, 60 liters of air was sampled. Three replications of the experiment were performed. The TAL method resulted in higher counts of microorganisms on all media tested. In addition, 175 isolates were selected randomly and identified in order to test the selectivity of TAL and the selective media for target organisms. The data obtained in this study show that the TAL resuscitation method is effective and necessary for the recovery of airborne organisms that may be injured. PMID:12233864
Konopliannikov, A G; Lepekhina, L A; Kolesnikova, A I; Ermakov, V I
1986-01-01
Clonogenic cells forming colonies in agar cultures in diffusion chambers and those isolated from subcutaneously transplanted Lewis lung carcinoma do not differ in their sensitivity to 60Co gamma-rays with respect to tumor growth stages. The dose-survival curves for all studied cells are S-shaped with a small shoulder. A cumulative dose-survival curve for malignant clonogenic cells is characterized by the average value of mean lethal dose D0 = 2.24 Gy and extrapolation number n = 2.0. When exposed to gamma-neutron-radiation (252Cf) malignant clonogenic cells exhibit a nearly exponential dose-survival curve with D0 = 0.56 Gy (with respect to a neutron component). The RBE of gamma-neutron radiation (252Cf) is 2.5. PMID:3749472
Lee, Seung Yeob; Shin, Jong Hee; Lee, Kyungwon; Joo, Min Young; Park, Kyung Hwa; Shin, Myung Geun; Suh, Soon Pal; Ryang, Dong Wook; Kim, Soo Hyun
2013-06-01
We evaluated three commercial colistin susceptibility testing methods using 213 bloodstream Acinetobacter isolates identified by gene sequencing. Compared to the agar dilution reference method, excellent categorical agreements (both 99.1%) were observed using Vitek 2 and Etest, compared to 87.3% (95.7% for Acinetobacter baumannii and 80.7% for non-baumannii Acinetobacter isolates) using MicroScan. PMID:23536402
Hyde, K; Steed, A J; Lenehan, H; Saunders, M J; Richards, J T; Lin Yin, J A; Geary, C G
1989-01-01
A modified, small volume, two phase, disc culture system for CFU-GM (seven and 14 days of incubation) was compared with a standard single layer system. The 1 ml single layer cultures were counted unstained in situ before both sets of cultures were transferred to glass slides for staining. Bone marrows were cultured from forty eight subjects, including normal controls and patients with acute non-lymphoblastic leukaemia, acute lymphoblastic leukaemia, and myelodysplastic syndrome. Observer error was least with the disc cultures, whereas variation between replicate cultures was similar for both methods. A high degree of correlation was found between the two methods for both day 7 (r = 0.90) and day 14 (r = 0.91) cultures. The number of colonies and clusters was higher with the disc system, indicating better cloning efficiency. Analysis of subsets of clinical groups showed similar patterns of abnormality with both systems. The simplicity of the method makes the use of this technology possible in most laboratories, and the superior morphological resolution may increase the clinical usefulness of such studies. Images PMID:2613925
Diffusion method of seperating gaseous mixtures
Pontius, Rex B.
1976-01-01
A method of effecting a relatively large change in the relative concentrations of the components of a gaseous mixture by diffusion which comprises separating the mixture into heavier and lighter portions according to major fraction mass recycle procedure, further separating the heavier portions into still heavier subportions according to a major fraction mass recycle procedure, and further separating the lighter portions into still lighter subportions according to a major fraction equilibrium recycle procedure.
Klancnik, Anja; Piskernik, Sasa; Jersek, Barbara; Mozina, Sonja Smole
2010-05-01
The aim of this study was to evaluate diffusion and dilution methods for determining the antibacterial activity of plant extracts and their mixtures. Several methods for measurement of the minimal inhibitory concentration (MIC) of a plant extract are available, but there is no standard procedure as there is for antibiotics. We tested different plant extracts, their mixtures and phenolic acids on selected gram-positive (Staphylococcus aureus, Bacillus cereus, and Listeria monocytogenes) and gram-negative bacteria (Escherichia coli O157:H7, Salmonella Infantis, Campylobacter jejuni, Campylobacter coli) with the disk diffusion, agar dilution, broth microdilution and macrodilution methods. The disk diffusion method was appropriate only as a preliminary screening test prior to quantitative MIC determination with dilution methods. A comparison of the results for MIC obtained by agar dilution and broth microdilution was possible only for gram-positive bacteria, and indicated the latter as the most accurate way of assessing the antimicrobial effect. The microdilution method with TTC (2,3,5-triphenyl tetrazolium chloride) or INT (2-p-iodophenyl-3-p-nitrophenyl-5-phenyl tetrazolium chloride) to indicate the viability of aerobic bacteria was found to be the best alternative approach, while only ATP determination was appropriate for microaerophilic Campylobacter spp. Using survival curves the kinetics of bacterial inactivation on plant extract exposure was followed for 24h and in this way the MIC values determined by the microdilution method were confirmed as the concentrations of extracts that inhibited bacterial growth. We suggest evaluation of the antibacterial activity of plant extracts using the broth microdilution method as a fast screening method for MIC determination and the macrodilution method at selected MIC values to confirm bacterial inactivation. Campylobacter spp. showed a similar sensitivity to plant extracts as the tested gram-positive bacteria, but S. Infantis and E. coli O157:H7 were more resistant. PMID:20171250
Finite difference methods for anomalous diffusion
NASA Astrophysics Data System (ADS)
Meerschaert, M. M.; Tadjeran, C.
2008-12-01
Fractional diffusion equations extend the classical models by substituting fractional derivatives in place of the usual integer order derivatives. Fractional equations have proven useful in modeling tracers in ground water and surface water, and are finding new applications in diverse areas including geomorphology, heat transfer, sound conduction in human tissue, and finance. Available solution methods include semi-analytical transform inversion, particle tracking, finite element, and finite difference methods. This talk will describe stable and consistent implicit Euler methods in sufficient detail for coding. As in the classical case, correctly formulated implicit Euler methods are unconditionally stable, while explicit Euler methods are stable under a significant step size restriction. Tested FORTRAN codes are freely available, and example runs will be presented, in which numerical solutions are compared to exact analytical solutions. Model extensions and open problems will be outlined.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 3 2014-04-01 2014-04-01 false Agar-agar. 184.1115 Section 184.1115 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) DIRECT FOOD SUBSTANCES AFFIRMED AS GENERALLY RECOGNIZED AS SAFE Listing of Specific Substances Affirmed as GRAS §...
Ingham, Steven C; Becker, Katie L; Fanslau, Melody A
2003-11-01
The recently developed 3M Petrifilm Staph Express Count plate (PFSE) method was compared with the U.S. Food and Drug Administration Bacteriological Analytical Manual's Baird-Parker agar spread plate (B-P) method for enumeration of Staphylococcus aureus in naturally contaminated, mechanically separated poultry (MSP; n = 92) and raw milk (n = 12). In addition, mozzarella and Parmesan cheeses and hot-smoked rainbow trout and chub were surface inoculated with a three-strain mixture of S. aureus, stored at 5 degrees C, and periodically analyzed with both methods for numbers of S. aureus. For naturally contaminated raw milk and MSP samples, the PFSE method yielded counts that were not significantly different (P > 0.05) from counts obtained using the B-P method. From raw milk and MSP samples, 60% (21 of 35) and 55% (124 of 226), respectively, of confirmed (DNAse-positive) isolates from PFSE plates were identified by further testing as S. aureus. Corresponding S. aureus identification rates for isolates forming typical colonies on B-P plates were 53% (19 of 36) and 50% (125 of 248). For both methods, other staphylococci composed the vast majority of tested isolates that were not identified as S. aureus. For inoculated hot-smoked fish, S. aureus counts from the PFSE method were not significantly different from counts from the B-P method. Compared to the B-P method, significantly lower numbers of inoculated S. aureus were recovered using the PFSE method in analyses of mozzarella cheese stored 28 and 42 days at 4 degrees C. The PFSE and B-P methods were not significantly different for inoculated cheeses at all other sampling times. DNAse-positive isolates from PFSE analyses of inoculated cheeses and smoked fish were identified as S. aureus 98% (51 of 52) and 86% (36 of 42) of the time, respectively, as compared with 100% (58 of 58) and 95% (40 of 42) of the time for typical B-P isolates. Overall, the PFSE and B-P methods appeared to perform similarly in enumeration of S. aureus in animal-derived foods. PMID:14627298
Smith, Amanda R; Ellison, Alysha L; Robinson, Amanda L; Drake, Maryanne; McDowell, Susan A; Mitchell, James K; Gerard, Patrick D; Heckler, Rachel A; McKillip, John L
2013-04-01
Quality control procedures during food processing may involve direct inoculation of food samples onto appropriate selective media for subsequent enumeration. However, sublethally injured bacteria often fail to grow, enabling them to evade detection and intervention measures and ultimately threaten the health of consumers. This study compares traditional selective and nonselective agar-based overlays versus two commercial systems (Petrifilm and Easygel) for recovery of injured E. coli B-41560 and O157:H7 strains. Bacteria were propagated in tryptic soy broth (TSB), ground beef slurry, and infant milk formula to a density of 10(6) to 10(8) CFU/ml and then were stressed for 6 min either in lactic acid (pH 4.5) or heat shocked for 3 min at 60°C. Samples were pour plated in basal layers of either tryptic soy agar (TSA), sorbitol MacConkey agar (SMAC), or violet red bile agar (VRB) and were resuscitated for 4 h prior to addition of agar overlays. Other stressed bacteria were plated directly onto Petrifilm and Easygel. Results indicate that selective and nonselective agar overlays recovered significantly higher numbers (greater than 1 log) of acid- and heat-injured E. coli O157:H7 from TSB, ground beef, and infant milk formula compared with direct plating onto selective media, Petrifilm, or Easygel, while no significant differences among these media combinations were observed for stressed E. coli B-41560. Nonstressed bacteria from TSB and ground beef were also recovered at densities significantly higher in nonselective TSA-TSA and in VRB-VRB and SMAC-SMAC compared with Petrifilm and Easygel. These data underscore the need to implement food safety measures that address sublethally injured pathogens such as E. coli O157:H7 in order to avoid underestimation of true densities for target pathogens. PMID:23575132
Technology Transfer Automated Retrieval System (TEKTRAN)
Two sampling techniques, agar extraction (AE) and centrifuge sugar flotation extraction (CSFE) were compared to determine their relative efficacy to recover immature stages of Culicoides spp from salt marsh substrates. Three types of samples (seeded with known numbers of larvae, homogenized field s...
New methods in Diffusion Weighted and Diffusion Tensor Imaging
Bammer, Roland; Holdsworth, Samantha J.; Veldhuis, Wouter B.; Skare, Stefan T.
2009-01-01
Synopsis Considerable strides have been made by countless individual researchers in diffusion-weighted imaging (DWI) to push DWI from an experimental tool – limited to a few institutions with specialized instrumentation – to a powerful tool used routinely for diagnostic imaging. Despite its current success, the field of DWI constantly evolves and progress has been made on several fronts, awaiting adoption by vendors and clinical users to bring in the next generation of DWI. These developments are primarily comprised of improved robustness against patient and physiologic motion, increased spatial resolution, new biophysical and tissue models, and new clinical applications for DWI. This article aims to provide a succinct overview of some of these new developments and a description of some of the major challenges associated with DWI. Trying to understand some of these challenges is helpful not only to the technically savvy MRI user, but also to radiologists who are interested in the potential strengths and weaknesses of these techniques, what is in the “diffusion pipeline”, and in how to interpret artifacts on DWI scans. PMID:19406353
Agar degradation by microorganisms and agar-degrading enzymes.
Chi, Won-Jae; Chang, Yong-Keun; Hong, Soon-Kwang
2012-05-01
Agar is a mixture of heterogeneous galactans, mainly composed of 3,6-anhydro-L-galactoses (or L-galactose-6-sulfates) D-galactoses and L-galactoses (routinely in the forms of 3,6-anhydro-L-galactoses or L-galactose-6-sulfates) alternately linked by β-(1,4) and α-(1,3) linkages. It is a major component of the cell walls of red algae and has been used in a variety of laboratory and industrial applications, owing to its jellifying properties. Many microorganisms that can hydrolyze and metabolize agar as a carbon and energy source have been identified in seawater and marine sediments. Agarolytic microorganisms commonly produce agarases, which catalyze the hydrolysis of agar. Numerous agarases have been identified in microorganisms of various genera. They are classified according to their cleavage pattern into three types-α-agarase, β-agarase, and β-porphyranase. Although, in a broad sense, many other agarases are involved in complete hydrolysis of agar, most of those identified are β-agarases. In this article we review agarolytic microorganisms and their agar-hydrolyzing systems, covering β-agarases as well as α-agarases, α-neoagarobiose hydrolases, and β-porphyranases, with emphasis on the recent discoveries. We also present an overview of the biochemical and structural characteristics of the various types of agarases. Further, we summarize and compare the agar-hydrolyzing systems of two specific microorganisms: Gram-negative Saccharophagus degradans 2-40 and Gram-positive Streptomyces coelicolor A3(2). We conclude with a brief discussion of the importance of agarases and their possible future application in producing oligosaccharides with various nutraceutical activities and in sustainably generating stock chemicals for biorefinement and bioenergy. PMID:22526785
New method to measure liquid diffusivity by analyzing an instantaneous diffusion image.
Sun, Licun; Meng, Weidong; Pu, Xiaoyun
2015-09-01
A novel optical method was applied to measure the binary liquid diffusion coefficient (D) quickly. Equipped with an asymmetric liquid-core cylindrical lens (ALCL), the spatially resolving ability of the ALCL in measuring refractive index of liquid was utilized to obtain the gradient distribution of the liquid concentration along diffusive direction. Based on Fick's second law, the D value was then calculated by analyzing diffusion images. It was worth mentioning that only one instantaneous diffusive image was required to measure D value by the method, reducing the measurement time greatly from several hours in traditional methods to a few seconds. The diffusion coefficients of ethylene glycol diffusing in pure water, at temperatures from 288.15 to 308.15 K, were measured by analyzing instantaneous diffusion images, the results were consistent well with the values measured by using holographic interferometry and Taylor dispersion methods. The method is characterized by faster measurement, direct observation of diffusive process, and easy operation, which provides a new method in measuring diffusion coefficient of liquids rapidly. PMID:26368418
Maheux, Andrée F.; Bérubé, Ève; Boudreau, Dominique K.; Villéger, Romain; Cantin, Philippe; Boissinot, Maurice; Bissonnette, Luc
2013-01-01
We first determined the analytical specificity and ubiquity (i.e., the ability to detect all or most strains) of a Clostridium perfringens-specific real-time PCR (rtPCR) assay based on the cpa gene (cpa rtPCR) by using a bacterial strain panel composed of C. perfringens and non-C. perfringens Clostridium strains. All non-C. perfringens Clostridium strains tested negative, whereas all C. perfringens strains tested positive with the cpa rtPCR, for an analytical specificity and ubiquity of 100%. The cpa rtPCR assay was then used to confirm the identity of 116 putative C. perfringens isolates recovered after filtration of water samples and culture on mCP agar. Colonies presenting discordant results between the phenotype on mCP agar and cpa rtPCR were identified by sequencing the 16S rRNA and cpa genes. Four mCP−/rtPCR+ colonies were identified as C. perfringens, whereas 3 mCP+/rtPCR− colonies were identified as non-C. perfringens. The cpa rtPCR was negative with all 51 non-C. perfringens strains and positive with 64 of 65 C. perfringens strains. Finally, we compared mCP agar and a CRENAME (concentration and recovery of microbial particles, extraction of nucleic acids, and molecular enrichment) procedure plus cpa rtPCR (CRENAME + cpa rtPCR) for their abilities to detect C. perfringens spores in drinking water. CRENAME + cpa rtPCR detected as few as one C. perfringens CFU per 100 ml of drinking water sample in less than 5 h, whereas mCP agar took at least 25 h to deliver results. CRENAME + cpa rtPCR also allows the simultaneous and sensitive detection of Escherichia coli and C. perfringens from the same potable water sample. In itself, it could be used to assess the public health risk posed by drinking water potentially contaminated with pathogens more resistant to disinfection. PMID:24077714
Diffuse-Interface Methods in Fluid Mechanics
NASA Technical Reports Server (NTRS)
Anderson, D. M.; McFadden, G. B.; Wheeler, A. A.
1997-01-01
The authors review the development of diffuse-interface models of hydrodynamics and their application to a wide variety of interfacial phenomena. The authors discuss the issues involved in formulating diffuse-interface models for single-component and binary fluids. Recent applications and computations using these models are discussed in each case. Further, the authors address issues including sharp-interface analyses that relate these models to the classical free-boundary problem, related computational approaches to describe interfacial phenomena, and related approaches describing fully-miscible fluids.
Development of a selective agar plate for the detection of Campylobacter spp. in fresh produce.
Yoo, Jin-Hee; Choi, Na-Young; Bae, Young-Min; Lee, Jung-Su; Lee, Sun-Young
2014-10-17
This study was conducted to develop a selective medium for the detection of Campylobacter spp. in fresh produce. Campylobacter spp. (n=4), non-Campylobacter (showing positive results on Campylobacter selective agar) strains (n=49) isolated from fresh produce, indicator bacteria (n=13), and spoilage bacteria isolated from fresh produce (n=15) were plated on four Campylobacter selective media. Bolton agar and modified charcoal cefoperazone deoxycholate agar (mCCDA) exhibited higher sensitivity for Campylobacter spp. than did Preston agar and Hunt agar, although certain non-Campylobacter strains isolated from fresh produce by using a selective agar isolation method, were still able to grow on Bolton agar and mCCDA. To inhibit the growth of non-Campylobacter strains, Bolton agar and mCCDA were supplemented with 5 antibiotics (rifampicin, polymyxin B, sodium metabisulfite, sodium pyruvate, ferrous sulfate) and the growth of Campylobacter spp. (n=7) and non-Campylobacter strains (n=44) was evaluated. Although Bolton agar supplemented with rifampicin (BR agar) exhibited a higher selectivity for Campylobacter spp. than did mCCDA supplemented with antibiotics, certain non-Campylobacter strains were still able to grow on BR agar (18.8%). When BR agar with various concentrations of sulfamethoxazole-trimethoprim were tested with Campylobacter spp. (n=8) and non-Campylobacter (n=7), sulfamethoxazole-trimethoprim was inhibitory against 3 of 7 non-Campylobacter strains. Finally, we validated the use of BR agar containing 50mg/L sulfamethoxazole (BRS agar) or 0.5mg/L ciprofloxacin (BRCS agar) and other selective agars for the detection of Campylobacter spp. in chicken and fresh produce. All chicken samples were positive for Campylobacter spp. when tested on mCCDA, BR agar, and BRS agar. In fresh produce samples, BRS agar exhibited the highest selectivity for Campylobacter spp., demonstrating its suitability for the detection of Campylobacter spp. in fresh produce. PMID:25126968
A vertical diffusion method for the microbiological assay of isoniazid
Lloyd, Janet; Mitchison, D. A.
1964-01-01
A method is described for the assay of isoniazid in serum and other fluids by diffusion along slopes of Löwenstein-Jensen medium inoculated with tubercle bacilli. The method is convenient, rapid and robust, but is less accurate than diffusion systems for the assay of some other substances. PMID:14227431
Fokas method for a multi-domain linear reaction-diffusion equation with discontinuous diffusivity
NASA Astrophysics Data System (ADS)
Asvestas, M.; Sifalakis, A. G.; Papadopoulou, E. P.; Saridakis, Y. G.
2014-03-01
Motivated by proliferation-diffusion mathematical models for studying highly diffusive brain tumors, that also take into account the heterogeneity of the brain tissue, in the present work we consider a multi-domain linear reaction-diffusion equation with a discontinuous diffusion coefficient. For the solution of the problem at hand we implement Fokas transform method by directly following, and extending in this way, our recent work for a white-gray-white matter brain model pertaining to high grade gliomas. Fokas's novel approach for the solution of linear PDE problems, yields novel integral representations of the solution in the complex plane that, for appropriately chosen integration contours, decay exponentially fast and converge uniformly at the boundaries. Combining these method-inherent advantages with simple numerical quadrature rules, we produce an efficient method, with fast decaying error properties, for the solution of the discontinuous reaction-diffusion problem.
Variational methods in steady state diffusion problems
Lee, C.E.; Fan, W.C.P.; Bratton, R.L.
1983-01-01
Classical variational techniques are used to obtain accurate solutions to the multigroup multiregion one dimensional steady state neutron diffusion equation. Analytic solutions are constructed for benchmark verification. Functionals with cubic trial functions and conservational lagrangian constraints are exhibited and compared with nonconservational functionals with respect to neutron balance and to relative flux and current at interfaces. Excellent agreement of the conservational functionals using cubic trial functions is obtained in comparison with analytic solutions.
Syneresis and delayed detachment in agar plates.
Divoux, Thibaut; Mao, Bosi; Snabre, Patrick
2015-05-14
Biogels made of crosslinked polymers such as proteins or polysaccharides behave as porous soft solids and store large amounts of solvent. These gels undergo spontaneous aging, called syneresis, which consists of the shrinkage of the gel matrix and the progressive expulsion of solvent. As a result, a biogel originally casted in a container often loses contact with the container sidewalls, and the detachment time is difficult to anticipate a priori, since it may occur over variable time spans (from hours to days). Here we report on syneresis phenomena in agar plates, which consist of Petri dishes filled with a gel mainly composed of agar. Direct observations and speckle pattern correlation analysis allow us to rationalize the delayed detachment of the gel from the sidewall of the Petri dish. The detachment time t* is surprisingly not controlled by the mass loss as one would intuitively expect. Instead, t* is strongly correlated to the gel minimum thickness emin measured along the sidewall of the plate, and increases as a robust function of emin, independently of the prior mass-loss history. Time-resolved correlation spectroscopy atypically applied to such weakly diffusive media gives access to the local thinning rate of the gel. This technique also allows us to detect the gel micro-displacements that are triggered by water evaporation prior to the detachment, and even to anticipate the latter from a few hours. Our work provides observables to predict the detachment time of agar gels in dishes, and highlights the relevance of speckle pattern correlation analysis for the quantitative investigation of the syneresis dynamics in biopolymer gels. PMID:25812667
Molecular Diffusion Coefficients: Experimental Determination and Demonstration.
ERIC Educational Resources Information Center
Fate, Gwendolyn; Lynn, David G.
1990-01-01
Presented are laboratory methods which allow the demonstration and determination of the diffusion coefficients of compounds ranging in size from water to small proteins. Included are the procedures involving the use of a spectrometer, UV cell, triterated agar, and oxygen diffusion. Results including quantification are described. (CW)
A Bayesian method with reparameterization for diffusion tensor imaging
NASA Astrophysics Data System (ADS)
Zhou, Diwei; Dryden, Ian L.; Koloydenko, Alexey; Li, Bai
2008-03-01
A multi-tensor model with identifiable parameters is developed for diffusion weighted MR images. A new parameterization method guarantees the symmetric positive-definiteness of the diffusion tensor. We set up a Bayesian method for parameter estimation. To investigate properties of the method, Monte Carlo simulated data from three distinct DTI direction schemes have been analyzed. The multi-tensor model with automatic model selection has also been applied to a healthy human brain dataset. Standard tensor-derived maps are obtained when the single-tensor model is fitted to a region of interest with a single dominant fiber direction. High anisotropy diffusion flows and main diffusion directions can be shown clearly in the FA map and diffusion ellipsoid map. For another region containing crossing fiber bundles, we estimate and display the ellipsoid map under the single tensor and double-tensor regimes of the multi-tensor model, suitably thresholding the Bayes factor for model selection.
Lattice Boltzmann method for the fractional advection-diffusion equation
NASA Astrophysics Data System (ADS)
Zhou, J. G.; Haygarth, P. M.; Withers, P. J. A.; Macleod, C. J. A.; Falloon, P. D.; Beven, K. J.; Ockenden, M. C.; Forber, K. J.; Hollaway, M. J.; Evans, R.; Collins, A. L.; Hiscock, K. M.; Wearing, C.; Kahana, R.; Villamizar Velez, M. L.
2016-04-01
Mass transport, such as movement of phosphorus in soils and solutes in rivers, is a natural phenomenon and its study plays an important role in science and engineering. It is found that there are numerous practical diffusion phenomena that do not obey the classical advection-diffusion equation (ADE). Such diffusion is called abnormal or superdiffusion, and it is well described using a fractional advection-diffusion equation (FADE). The FADE finds a wide range of applications in various areas with great potential for studying complex mass transport in real hydrological systems. However, solution to the FADE is difficult, and the existing numerical methods are complicated and inefficient. In this study, a fresh lattice Boltzmann method is developed for solving the fractional advection-diffusion equation (LabFADE). The FADE is transformed into an equation similar to an advection-diffusion equation and solved using the lattice Boltzmann method. The LabFADE has all the advantages of the conventional lattice Boltzmann method and avoids a complex solution procedure, unlike other existing numerical methods. The method has been validated through simulations of several benchmark tests: a point-source diffusion, a boundary-value problem of steady diffusion, and an initial-boundary-value problem of unsteady diffusion with the coexistence of source and sink terms. In addition, by including the effects of the skewness β , the fractional order α , and the single relaxation time τ , the accuracy and convergence of the method have been assessed. The numerical predictions are compared with the analytical solutions, and they indicate that the method is second-order accurate. The method presented will allow the FADE to be more widely applied to complex mass transport problems in science and engineering.
Nagy, Elisabeth; Justesen, Ulrik Stenz; Eitel, Zsuzsa; Urbán, Edit
2015-02-01
With the emergence of antibiotic resistance among Bacteroides fragilis group isolates the need of susceptibility testing in routine laboratories is increasing. The aims of the present study were to evaluate the disk diffusion method for susceptibility testing in case of different clinical isolates of Bacteroides spp by comparing zone diameter results with MICs obtained earlier during an Europe-wide antibiotic susceptibility surveillance, and to propose zone diameter breakpoints, which correlate for the EUCAST MIC breakpoints. We tested 381 clinical isolates of the B. fragilis group to amoxicillin/clavulanic acid, cefoxitin, clindamycin, imipenem, metronidazole, moxifloxacin, piperacillin/tazobactam, tigecycline by agar dilution method previously. The inhibition zones of the same antibiotics including meropenem disc were determined by the disc diffusion on Brucella blood agar supplemented with haemin and vitamin K1. Plates were incubated at 37 °C in an anaerobic atmosphere for 24 h. The zone diameters were read at 100% inhibition. In case of discrepant results MICs were determined by gradient test and compared with the inhibition zones on the same plate. We found a good agreement between the inhibition zone diameters and the MICs for imipenem, metronidazole, moxifloxacin and tigecyclin. The inhibition zone diameters of meropenem also separated clearly the isolates, which can be considered wild-type isolates. In case of amoxicillin/clavulanic acid and piperacillin/tazobactam intermediate and susceptible isolates according to the MIC determination, overlap during the zone diameter determination. Isolates with an inhibition zone <23 mm for amoxicillin/clavulanic acid and <25 mm for piperacillin/tazobactam should be retested by a MIC determination method. The 10 μg clindamycin disc clearly separated the resistant and the susceptible population of B. fragilis group strains. In the case of cefoxitin only resistant population could be separated with an inhibition zone <17 mm, intermediate and susceptible isolates overlap. In conclusion, we suggest that disk diffusion can be an option for susceptibility testing of B. fragilis group isolates for most relevant antibiotics in routine laboratories. PMID:25464140
Quantifying Biomolecule Diffusivity Using an Optimal Bayesian Method
Voisinne, Guillaume; Alexandrou, Antigoni; Masson, Jean-Baptiste
2010-01-01
Abstract We propose a Bayesian method to extract the diffusivity of biomolecules evolving freely or inside membrane microdomains. This approach assumes a model of motion for the particle considered, namely free Brownian motion or confined diffusion. In each framework, a systematic Bayesian scheme is provided for estimating the diffusivity. We show that this method reaches the best performances theoretically achievable. Its efficiency overcomes that of widely used methods based on the analysis of the mean-square displacement. The approach presented here also gives direct access to the uncertainty on the estimation of the diffusivity and predicts the number of steps of the trajectory necessary to achieve any desired precision. Its robustness with respect to noise on the position of the biomolecule is also investigated. PMID:20159156
Diffusion method in random matrix theory
NASA Astrophysics Data System (ADS)
Grela, Jacek
2016-01-01
We introduce a calculational tool useful in computing ratios and products of characteristic polynomials averaged over Gaussian measures with an external source. The method is based on Dysons Brownian motion and Grassmann/complex integration formulas for determinants. The resulting formulas are exact for finite matrix size N and form integral representations convenient for large N asymptotics. Quantities obtained by the method are interpreted as averages over standard matrix models. We provide several explicit and novel calculations with special emphasis on the ? =2 Girko-Ginibre ensembles.
The method for detecting diffusion ring diameter in Hemagglutinin measuring
NASA Astrophysics Data System (ADS)
Jing, Wenbo; Liu, Xue; Duan, Jin; Wang, Xiao-man
2014-11-01
The diffuser ring diameter measurement is the most critical in hemagglutinin Measuring. The traditional methods, such as a vernier caliper or high-definition scanned images are subjective and low for the measurement data reliability. Propose high-resolution diffusion ring image for drop-resolution processing, adaptive Canny operator and local detection method to extract complete and clear diffusion ring boundaries, and finally make use of polynomial interpolation algorithm to make diffusion ring outer boundary pixel coordinates achieve sub-pixel accuracy and the least-squares fitting circle algorithm to calculate the precise center of the circle and the diameter of the diffuser ring. Experimental results show that the method detection time is only 63.61ms, which is a faster speed; diffuser ring diameter estimation error can achieve 0.55 pixel, high stability in experimental data. This method is adapted to the various types of influenza vaccine hemagglutinin content measurements, and has important value in the influenza vaccine quality detection.
A novel method to evaluate spin diffusion length of Pt
NASA Astrophysics Data System (ADS)
Zhang, Yan-qing; Sun, Niu-yi; Che, Wen-ru; Shan, Rong; Zhu, Zhen-gang
2016-05-01
Spin diffusion length of Pt is evaluated via proximity effect of spin orbit coupling (SOC) and anomalous Hall effect (AHE) in Pt/Co2FeAl bilayers. By varying the thicknesses of Pt and Co2FeAl layer, the thickness dependences of AHE parameters can be obtained, which are theoretically predicted to be proportional to the square of the SOC strength. According to the physical image of the SOC proximity effect, the spin diffusion length of Pt can easily be identified from these thickness dependences. This work provides a novel method to evaluate spin diffusion length in a material with a small value.
Practical method for diffusion welding of steel plate in air.
NASA Technical Reports Server (NTRS)
Moore, T. J.; Holko, K. H.
1972-01-01
Description of a simple and easily applied method of diffusion welding steel plate in air which does not require a vacuum furnace or hot press. The novel feature of the proposed welding method is that diffusion welds are made in air with deadweight loading. In addition, the use of an autogenous (self-generated) surface-cleaning principle (termed 'auto-vac cleaning') to reduce the effects of surface oxides that normally hinder diffusion welding is examined. A series of nine butt joints were diffusion welded in thick sections of AISI 1020 steel plate. Diffusion welds were attempted at three welding temperatures (1200, 1090, and 980 C) using a deadweight pressure of 34,500 N/sq m (5 psi) and a two-hour hold time at temperature. Auto-vac cleaning operations prior to welding were also studied for the same three temperatures. Results indicate that sound welds were produced at the two higher temperatures when the joints were previously fusion seal welded completely around the periphery. Also, auto-vac cleaning at 1200 C for 2-1/2 hours prior to diffusion welding was highly beneficial, particularly when subsequent welding was accomplished at 1090 C.
Diffusion accessibility as a method for visualizing macromolecular surface geometry.
Tsai, Yingssu; Holton, Thomas; Yeates, Todd O
2015-10-01
Important three-dimensional spatial features such as depth and surface concavity can be difficult to convey clearly in the context of two-dimensional images. In the area of macromolecular visualization, the computer graphics technique of ray-tracing can be helpful, but further techniques for emphasizing surface concavity can give clearer perceptions of depth. The notion of diffusion accessibility is well-suited for emphasizing such features of macromolecular surfaces, but a method for calculating diffusion accessibility has not been made widely available. Here we make available a web-based platform that performs the necessary calculation by solving the Laplace equation for steady state diffusion, and produces scripts for visualization that emphasize surface depth by coloring according to diffusion accessibility. The URL is http://services.mbi.ucla.edu/DiffAcc/. PMID:26189444
Diffuse Interface Methods for Modeling Drug-Eluting Stent Coatings.
Saylor, David M; Forrey, Christopher; Kim, Chang-Soo; Warren, James A
2016-02-01
An overview of diffuse interface models specific to drug-eluting stent coatings is presented. Microscale heterogeneities, both in the coating and use environment, dictate the performance of these coatings. Using diffuse interface methods, these heterogeneities can be explicitly incorporated into the model equations with relative ease. This enables one to predict the complex microstructures that evolve during coating fabrication and subsequent impact on drug release. Examples are provided that illustrate the wide range of phenomena that can be addressed with diffuse interface models including: crystallization, constrained phase separation, hydrolytic degradation, and heterogeneous binding. Challenges associated with the lack of material property data and numerical solution of the model equations are also highlighted. Finally, in light of these potential drawbacks, the potential to utilize diffuse interface models to help guide product and process development is discussed. PMID:26183961
Yamane, N; Ichiyama, S; Kawahara, S; Iinuma, Y; Saitoh, H; Shimojima, M; Udagawa, H; Nakasone, I
1999-08-01
A newly developed microdilution antimycobacterial susceptibility test, BrothMIC MTB (Kyokuto Pharmaceutical Industrial Co., Ltd., Tokyo, Japan) to determine minimum inhibitory concentrations (MICs) was evaluated at multisites. The test method utilizes air-dried microplates containing serially diluted antimicrobial agents and the modified Middlebrook 7H9 broth. The eight antimycobacterial agents tested were rifampicin, isoniazid, ethambutol, streptomycin, kanamycin, levofloxacin, sparfloxacin and ciprofloxacin. The test plates were reconstituted by inoculation of 0.2 ml of cell suspensions (6 x 10(5) cells/ml) and were incubated at 36 degrees C in 5% to 10% CO2. The growth endpoints were visually read after 7-day and 10-day incubations. The reproducibility was evaluated with the four reference strains of Mycobacterium tuberculosis, and were compared with the agar proportion method described in the National Committee for Clinical Laboratory Standards (NCCLS) M24-T. Of the 1,022 testings of the reference strains, 1,020 (99.8%) of the MICs read after 7-day incubation fell within 3 log2 dilutions. The growth endpoints read after 7-day and 10-day incubations gave equal MIC ranges for the respective agents. The results obtained by the BrothMIC MTB for 93 clinical isolates of M. tuberculosis compared well with those determined by the NCCLS method with 98% to 99% agreements, except for ethambutol. According to the comparative analysis with the agar proportion method, the interpretive MIC breakpoints to discriminate between the isolates susceptible and resistant against the respective agents were proposed. In conclusion, this newly developed microdilution test for M. tuberculosis is a practical, rapid, quantitative, nonradiometric alternative for the determination of MICs in clinical mycobacteriology laboratories. PMID:10511808
Diffusion-equation method for crystallographic figure of merits.
Markvardsen, Anders J; David, William I F
2010-09-01
Global optimization methods play a significant role in crystallography, particularly in structure solution from powder diffraction data. This paper presents the mathematical foundations for a diffusion-equation-based optimization method. The diffusion equation is best known for describing how heat propagates in matter. However, it has also attracted considerable attention as the basis for global optimization of a multimodal function [Piela et al. (1989). J. Phys. Chem. 93, 3339-3346]. The method relies heavily on available analytical solutions for the diffusion equation. Here it is shown that such solutions can be obtained for two important crystallographic figure-of-merit (FOM) functions that fully account for space-group symmetry and allow the diffusion-equation solution to vary depending on whether atomic coordinates are fixed or not. The resulting expression is computationally efficient, taking the same order of floating-point operations to evaluate as the starting FOM function measured in terms of the number of atoms in the asymmetric unit. This opens the possibility of implementing diffusion-equation methods for crystallographic global optimization algorithms such as structure determination from powder diffraction data. PMID:20720322
A fast semi-implicit method for anisotropic diffusion
NASA Astrophysics Data System (ADS)
Sharma, Prateek; Hammett, Gregory W.
2011-06-01
Simple finite differencing of the anisotropic diffusion equation, where diffusion is only along a given direction, does not ensure that the numerically calculated heat fluxes are in the correct direction. This can lead to negative temperatures for the anisotropic thermal diffusion equation. In a previous paper we proposed a monotonicity-preserving explicit method which uses limiters (analogous to those used in the solution of hyperbolic equations) to interpolate the temperature gradients at cell faces. However, being explicit, this method was limited by a restrictive Courant-Friedrichs-Lewy (CFL) stability timestep. Here we propose a fast, conservative, directionally-split, semi-implicit method which is second order accurate in space, is stable for large timesteps, and is easy to implement in parallel. Although not strictly monotonicity-preserving, our method gives only small amplitude temperature oscillations at large temperature gradients, and the oscillations are damped in time. With numerical experiments we show that our semi-implicit method can achieve large speed-ups compared to the explicit method, without seriously violating the monotonicity constraint. This method can also be applied to isotropic diffusion, both on regular and distorted meshes.
Leapfrog/finite element method for fractional diffusion equation.
Zhao, Zhengang; Zheng, Yunying
2014-01-01
We analyze a fully discrete leapfrog/Galerkin finite element method for the numerical solution of the space fractional order (fractional for simplicity) diffusion equation. The generalized fractional derivative spaces are defined in a bounded interval. And some related properties are further discussed for the following finite element analysis. Then the fractional diffusion equation is discretized in space by the finite element method and in time by the explicit leapfrog scheme. For the resulting fully discrete, conditionally stable scheme, we prove an L (2)-error bound of finite element accuracy and of second order in time. Numerical examples are included to confirm our theoretical analysis. PMID:24955431
Leapfrog/Finite Element Method for Fractional Diffusion Equation
Zhao, Zhengang; Zheng, Yunying
2014-01-01
We analyze a fully discrete leapfrog/Galerkin finite element method for the numerical solution of the space fractional order (fractional for simplicity) diffusion equation. The generalized fractional derivative spaces are defined in a bounded interval. And some related properties are further discussed for the following finite element analysis. Then the fractional diffusion equation is discretized in space by the finite element method and in time by the explicit leapfrog scheme. For the resulting fully discrete, conditionally stable scheme, we prove an L 2-error bound of finite element accuracy and of second order in time. Numerical examples are included to confirm our theoretical analysis. PMID:24955431
A method for thermal diffusivity measurement in fluids
NASA Astrophysics Data System (ADS)
Marín, E.; Hernández-Rosales, E.; Mansanares, A. M.; Ivanov, R.; Rojas-Trigos, J. B.; Calderón, A.
2013-10-01
A technique is proposed for thermal diffusivity measurement in fluids. It is based on the Angstrom method, but with excitation of thermal waves by electromagnetic energy absorption and pyroelectric detection. The good agreement between measured thermal diffusivity of air and some test liquids with literature values shows the validity of the method. It is free of some limitations of conventional photopyroelectric technique with length scanning because it is free of moving parts inside the sample and because it avoids problems associated with the non-parallelism between thermal wave generator surface and sensor. It does not require any data normalization procedure or special sample preparation.
Yeh, Ellen; Pinsky, Benjamin A.; Banaei, Niaz; Baron, Ellen Jo
2009-01-01
Background Blood agar is used for the identification and antibiotic susceptibility testing of many bacterial pathogens. In the developing world, microbiologists use human blood agar because of the high cost and inhospitable conditions for raising wool sheep or horses to supply blood. Many pathogens either fail to grow entirely or exhibit morphologies and hemolytic patterns on human blood agar that confound colony recognition. Furthermore, human blood can be hazardous to handle due to HIV and hepatitis [1], [2]. This study investigated whether blood from hair sheep, a hardy, low-maintenance variety of sheep adapted for hot climates, was suitable for routine clinical microbiology studies. Methods and Findings Hair sheep blood obtained by jugular venipuncture was anticoagulated by either manual defibrination or collection in human blood bank bags containing citrate-phosphate-dextrose. Trypticase soy 5% blood agar was made from both forms of hair sheep blood and commercial defibrinated wool sheep blood. Growth characteristics, colony morphologies, and hemolytic patterns of selected human pathogens, including several streptococcal species, were evaluated. Specialized identification tests, including CAMP test, reverse CAMP test, and satellite colony formation with Haemophilus influenzae and Abiotrophia defectiva were also performed. Mueller-Hinton blood agar plates prepared from the three blood types were compared in antibiotic susceptibility tests by disk diffusion and E-test. Conclusions The results of all studies showed that blood agar prepared from citrated hair sheep blood is suitable for microbiological tests used in routine identification and susceptibility profiling of human pathogens. The validation of citrated hair sheep blood eliminates the labor-intensive and equipment-requiring process of manual defibrination. Use of hair sheep blood, in lieu of human blood currently used by many developing world laboratories and as an alternative to cost-prohibitive commercial sheep blood, offers the opportunity to dramatically improve the safety and accuracy of laboratory diagnosis of pathogenic bacteria in resource-poor countries. PMID:19578541
Kofler, Markus; Lenninger, Margit; Mayer, Gert; Neuwirt, Hannes; Grimm, Michael; Bechtold, Thomas
2016-01-20
Renal replacement therapy options are limited to hemodialysis and peritoneal dialysis (70% of US patients) or renal transplantation. Diffusion processes are the main physico-chemical principle behind hemodialysis. An alternative way to achieve liquid flow through membranes bases on the electroosmotic flow which is observed as electrokinetic phenomenon in porous membranes which bear surface charges. Agar consists of the non-ionic agarose and the negatively charged agaropectine thus an electroosmotic flux is observed in analytical electrophoresis. In this study the potential electroosmosis on textile reinforced agar membranes as separation method was investigated. Using a five-chamber electrolysis cell and an agar membrane/cellulose fabric composite an intensive electroosmotic flow of 1-2 ml cm(2) h(-1) at 100 mA cell current could be observed. The movement of cations in the negatively charged agar structure led to an intensive electroosmotic flux, which also transported uncharged molecules such as urea, glucose through the membrane. Separation of uncharged low molecular weight molecules is determined by the membrane characteristic. The transport of ions (K(+), PO4(3-), creatinine) and uncharged molecules (urea, glucose) in electroosmotic separation experiments was monitored using a pH 5.5 phosphate electrolyte with the aim to assess the overall transport processes in the electrochemical cell. The results demonstrate the potential of the method for filtration of biological fluids in the absence of external pressure or high shear rates. PMID:26572331
Stochastic operator-splitting method for reaction-diffusion systems
NASA Astrophysics Data System (ADS)
Choi, TaiJung; Maurya, Mano Ram; Tartakovsky, Daniel M.; Subramaniam, Shankar
2012-11-01
Many biochemical processes at the sub-cellular level involve a small number of molecules. The local numbers of these molecules vary in space and time, and exhibit random fluctuations that can only be captured with stochastic simulations. We present a novel stochastic operator-splitting algorithm to model such reaction-diffusion phenomena. The reaction and diffusion steps employ stochastic simulation algorithms and Brownian dynamics, respectively. Through theoretical analysis, we have developed an algorithm to identify if the system is reaction-controlled, diffusion-controlled or is in an intermediate regime. The time-step size is chosen accordingly at each step of the simulation. We have used three examples to demonstrate the accuracy and robustness of the proposed algorithm. The first example deals with diffusion of two chemical species undergoing an irreversible bimolecular reaction. It is used to validate our algorithm by comparing its results with the solution obtained from a corresponding deterministic partial differential equation at low and high number of molecules. In this example, we also compare the results from our method to those obtained using a Gillespie multi-particle (GMP) method. The second example, which models simplified RNA synthesis, is used to study the performance of our algorithm in reaction- and diffusion-controlled regimes and to investigate the effects of local inhomogeneity. The third example models reaction-diffusion of CheY molecules through the cytoplasm of Escherichia coli during chemotaxis. It is used to compare the algorithm's performance against the GMP method. Our analysis demonstrates that the proposed algorithm enables accurate simulation of the kinetics of complex and spatially heterogeneous systems. It is also computationally more efficient than commonly used alternatives, such as the GMP method.
The Flux-integral Method for Multidimensional Convection and Diffusion
NASA Technical Reports Server (NTRS)
Leonard, B. P.; Macvean, M. K.; Lock, A. P.
1994-01-01
The flux-integral method is a procedure for constructing an explicit, single-step, forward-in-time, conservative, control volume update of the unsteady, multidimensional convection-diffusion equation. The convective plus diffusive flux at each face of a control-volume cell is estimated by integrating the transported variable and its face-normal derivative over the volume swept out by the convecting velocity field. This yields a unique description of the fluxes, whereas other conservative methods rely on nonunique, arbitrary pseudoflux-difference splitting procedures. The accuracy of the resulting scheme depends on the form of the subcell interpolation assumed, given cell-average data. Cellwise constant behavior results in a (very artificially diffusive) first-order convection scheme. Second-order convection-diffusion schemes correspond to cellwise linear (or bilinear) subcell interpolation. Cellwise quadratic subcell interpolants generate a highly accurate convection-diffusion scheme with excellent phase accuracy. Under constant-coefficient conditions, this is a uniformly third-order polynomial interpolation algorithm (UTOPIA).
Preparation of hydroxypropyl agars and their properties.
Zhang, Xiaodong; Liu, Xin; Cao, Mingzhao; Xia, Kai; Zhang, Yuqiao
2015-09-20
A series of hydroxypropyl agars (HPAs) with different hydroxypropyl molar substitution (MS) were prepared and their physicochemical properties were characterized. After hydroxypropylation, the dissolving temperature, the gelling temperature, the gel melting temperature, the gel strength, and the thermal stability of agar all decreased except that its hygroscopicity increased. The gel skeleton structures of raw agar and HPAs were all of the porous network structures, but the pores of gel skeleton structure of HPAs became smaller and denser. PMID:26050892
Methods for diffusive relaxation in the Pn equation
Hauck, Cory D; Mcclarren, Ryan G; Lowrie, Robert B
2008-01-01
We present recent progress in the development of two substantially different approaches for simulating the so-called of P{sub N} equations. These are linear hyperbolic systems of PDEs that are used to model particle transport in a material medium, that in highly collisional regimes, are accurately approximated by a simple diffusion equation. This limit is based on a balance between function values and gradients of certain variables in the P{sub N} system. Conventional reconstruction methods based on upwinding approximate such gradients with an error that is dependent on the size of the computational mesh. Thus in order to capture the diffusion limit, a given mesh must resolve the dynamics of the continuum equation at the level of the mean-free-path, which tends to zero in the diffusion limit. The two methods analyzed here produce accurate solutions in both collisional and non-collisional regimes; in particular, they do not require resolution of the mean-free-path in order to properly capture the diffusion limit. The first method is a straight-forward application of the discrete Galerkin (DG) methodology, which uses additional variables in each computational cell to capture the balance between function values and gradients, which are computed locally. The second method uses a temporal splitting of the fast and slow dynamics in the P{sub N} system to derive so-called regularized equations for which the diffusion limit is built-in. We focus specifically on the P{sub N} equations for one-dimensional, slab geometries. Preliminary results for several benchmark problems are presented which highlight the advantages and disadvantages of each method. Further improvements and extensions are also discussed.
Modeling the flow in diffuse interface methods of solidification.
Subhedar, A; Steinbach, I; Varnik, F
2015-08-01
Fluid dynamical equations in the presence of a diffuse solid-liquid interface are investigated via a volume averaging approach. The resulting equations exhibit the same structure as the standard Navier-Stokes equation for a Newtonian fluid with a constant viscosity, the effect of the solid phase fraction appearing in the drag force only. This considerably simplifies the use of the lattice Boltzmann method as a fluid dynamics solver in solidification simulations. Galilean invariance is also satisfied within this approach. Further, we investigate deviations between the diffuse and sharp interface flow profiles via both quasiexact numerical integration and lattice Boltzmann simulations. It emerges from these studies that the freedom in choosing the solid-liquid coupling parameter h provides a flexible way of optimizing the diffuse interface-flow simulations. Once h is adapted for a given spatial resolution, the simulated flow profiles reach an accuracy comparable to quasiexact numerical simulations. PMID:26382542
Modeling the flow in diffuse interface methods of solidification
NASA Astrophysics Data System (ADS)
Subhedar, A.; Steinbach, I.; Varnik, F.
2015-08-01
Fluid dynamical equations in the presence of a diffuse solid-liquid interface are investigated via a volume averaging approach. The resulting equations exhibit the same structure as the standard Navier-Stokes equation for a Newtonian fluid with a constant viscosity, the effect of the solid phase fraction appearing in the drag force only. This considerably simplifies the use of the lattice Boltzmann method as a fluid dynamics solver in solidification simulations. Galilean invariance is also satisfied within this approach. Further, we investigate deviations between the diffuse and sharp interface flow profiles via both quasiexact numerical integration and lattice Boltzmann simulations. It emerges from these studies that the freedom in choosing the solid-liquid coupling parameter h provides a flexible way of optimizing the diffuse interface-flow simulations. Once h is adapted for a given spatial resolution, the simulated flow profiles reach an accuracy comparable to quasiexact numerical simulations.
Thermal diffusivity of nonflat plates using the flash method
Salazar, Agustin; Fuente, Raquel; Apinaniz, Estibaliz; Mendioroz, Arantza
2011-01-15
The flash method is the standard technique to measure the thermal diffusivity of solid samples. It consists of heating the front surface of an opaque sample by a brief light pulse and detecting the temperature evolution at its rear surface. The thermal diffusivity is obtained by measuring the time corresponding to the half maximum of the temperature rise, which only depends on the sample thickness and thermal diffusivity through a simple formula. Up to now, the flash method has been restricted to flat samples. In this work, we extend the flash method to measure the thermal diffusivity of nonflat samples. In particular, we focus on plates with cylindrical and spherical shapes. The theoretical model indicates that the same expression for flat samples can also be applied to cylindrical and spherical plates, except for extremely curved samples. Accordingly, a curvature limit for the application of the expression for flat samples is established. Flash measurements on lead foils of cylindrical shape confirm the validity of the model.
Method of making gas diffusion layers for electrochemical cells
Frisk, Joseph William; Boand, Wayne Meredith; Larson, James Michael
2002-01-01
A method is provided for making a gas diffusion layer for an electrochemical cell comprising the steps of: a) combining carbon particles and one or more surfactants in a typically aqueous vehicle to make a preliminary composition, typically by high shear mixing; b) adding one or more highly fluorinated polymers to said preliminary composition by low shear mixing to make a coating composition; and c) applying the coating composition to an electrically conductive porous substrate, typically by a low shear coating method.
NASA Astrophysics Data System (ADS)
Lin, Guoxing
2015-10-01
Pulsed field gradient (PFG) diffusion measurement has a lot of applications in NMR and MRI. Its analysis relies on the ability to obtain the signal attenuation expressions, which can be obtained by averaging over the accumulating phase shift distribution (APSD). However, current theoretical models are not robust or require approximations to get the APSD. Here, a new formalism, an effective phase shift diffusion (EPSD) equation method is presented to calculate the APSD directly. This is based on the idea that the gradient pulse effect on the change of the APSD can be viewed as a diffusion process in the virtual phase space (VPS). The EPSD has a diffusion coefficient, Kβ(t)D radβ/sα, where α is time derivative order and β is a space derivative order, respectively. The EPSD equations of VPS are built based on the diffusion equations of real space by replacing the diffusion coefficients and the coordinate system (from real space coordinate to virtual phase coordinate). Two different models, the fractal derivative model and the fractional derivative model from the literature were used to build the EPSD fractional diffusion equations. The APSD obtained from solving these EPSD equations were used to calculate the PFG signal attenuation. From the fractal derivative model the attenuation is exp(-γβgβδβDf1 tα), a stretched exponential function (SEF) attenuation, while from the fractional derivative model the attenuation is Eα,1(-γβgβδβDf2 tα), a Mittag-Leffler function (MLF) attenuation. The MLF attenuation can be reduced to SEF attenuation when α = 1, and can be approximated as a SEF attenuation when the attenuation is small. Additionally, the effect of finite gradient pulse widths (FGPW) is calculated. From the fractal derivative model, the signal attenuation including FGPW effect is exp[ -Df1 ∫0τ Kβ (t)dtα ] . The results obtained in this study are in good agreement with the results in literature. Several expressions that describe signal attenuation have not been reported and that can be of great importance for the PFG experiments. This EPSD equation method provides a new, simple path to calculate signal attenuation of PFG NMR experiments.
Lin, Guoxing
2015-10-01
Pulsed field gradient (PFG) diffusion measurement has a lot of applications in NMR and MRI. Its analysis relies on the ability to obtain the signal attenuation expressions, which can be obtained by averaging over the accumulating phase shift distribution (APSD). However, current theoretical models are not robust or require approximations to get the APSD. Here, a new formalism, an effective phase shift diffusion (EPSD) equation method is presented to calculate the APSD directly. This is based on the idea that the gradient pulse effect on the change of the APSD can be viewed as a diffusion process in the virtual phase space (VPS). The EPSD has a diffusion coefficient, K(β)(t)D rad(β)/s(α), where α is time derivative order and β is a space derivative order, respectively. The EPSD equations of VPS are built based on the diffusion equations of real space by replacing the diffusion coefficients and the coordinate system (from real space coordinate to virtual phase coordinate). Two different models, the fractal derivative model and the fractional derivative model from the literature were used to build the EPSD fractional diffusion equations. The APSD obtained from solving these EPSD equations were used to calculate the PFG signal attenuation. From the fractal derivative model the attenuation is exp(-γ(β)g(β)δ(β)Df1t(α)), a stretched exponential function (SEF) attenuation, while from the fractional derivative model the attenuation is Eα,1(-γ(β)g(β)δ(β)Df2t(α)), a Mittag-Leffler function (MLF) attenuation. The MLF attenuation can be reduced to SEF attenuation when α=1, and can be approximated as a SEF attenuation when the attenuation is small. Additionally, the effect of finite gradient pulse widths (FGPW) is calculated. From the fractal derivative model, the signal attenuation including FGPW effect is exp[ -Df1∫0(τ) K(β)(t)dt(α)]. The results obtained in this study are in good agreement with the results in literature. Several expressions that describe signal attenuation have not been reported and that can be of great importance for the PFG experiments. This EPSD equation method provides a new, simple path to calculate signal attenuation of PFG NMR experiments. PMID:26384777
Adsorptive removal of methylene blue by agar: effects of NaCl and ethanol
2012-01-01
Adsorption of methylene blue (MB) on agar was investigated as a function of temperature (308-328 K), different concentrations of NaCl and HCl and various weight percentages of binary mixtures of ethanol with water. It was observed that the maximum experimental adsorption capacity, qm, exp, in water is up to 50 mg g-1 and decreases with increase in weight percentage of ethanol and NaCl and HCl concentration compared to that of water. Analysis of data using ARIAN model showed that MB adsorbs as monomer and dimer on the surface of agar. Binding constants of MB to agar were calculated using the Temkin isotherm. The process is exothermic in water and other solutions. The mean adsorption energy (E) value indicated binding of MB to agar is chemical adsorption. Kinetics of this interaction obeys from the pseudo-second-order model and diffusion of the MB molecules into the agar is the main rate-controlling step. PMID:22339759
48 CFR 401.371 - AGAR Advisories.
Code of Federal Regulations, 2011 CFR
2011-10-01
... 48 Federal Acquisition Regulations System 4 2011-10-01 2011-10-01 false AGAR Advisories. 401.371 Section 401.371 Federal Acquisition Regulations System DEPARTMENT OF AGRICULTURE GENERAL AGRICULTURE ACQUISITION REGULATION SYSTEM Agency Acquisition Regulations 401.371 AGAR Advisories. The SPE may issue...
48 CFR 401.371 - AGAR Advisories.
Code of Federal Regulations, 2010 CFR
2010-10-01
... 48 Federal Acquisition Regulations System 4 2010-10-01 2010-10-01 false AGAR Advisories. 401.371 Section 401.371 Federal Acquisition Regulations System DEPARTMENT OF AGRICULTURE GENERAL AGRICULTURE ACQUISITION REGULATION SYSTEM Agency Acquisition Regulations 401.371 AGAR Advisories. The SPE may issue...
48 CFR 401.371 - AGAR Advisories.
Code of Federal Regulations, 2013 CFR
2013-10-01
... 48 Federal Acquisition Regulations System 4 2013-10-01 2013-10-01 false AGAR Advisories. 401.371 Section 401.371 Federal Acquisition Regulations System DEPARTMENT OF AGRICULTURE GENERAL AGRICULTURE ACQUISITION REGULATION SYSTEM Agency Acquisition Regulations 401.371 AGAR Advisories. The SPE may issue...
48 CFR 401.371 - AGAR Advisories.
Code of Federal Regulations, 2014 CFR
2014-10-01
... 48 Federal Acquisition Regulations System 4 2014-10-01 2014-10-01 false AGAR Advisories. 401.371 Section 401.371 Federal Acquisition Regulations System DEPARTMENT OF AGRICULTURE GENERAL AGRICULTURE ACQUISITION REGULATION SYSTEM Agency Acquisition Regulations 401.371 AGAR Advisories. The SPE may issue...
48 CFR 401.371 - AGAR Advisories.
Code of Federal Regulations, 2012 CFR
2012-10-01
... 48 Federal Acquisition Regulations System 4 2012-10-01 2012-10-01 false AGAR Advisories. 401.371 Section 401.371 Federal Acquisition Regulations System DEPARTMENT OF AGRICULTURE GENERAL AGRICULTURE ACQUISITION REGULATION SYSTEM Agency Acquisition Regulations 401.371 AGAR Advisories. The SPE may issue...
Agar polysaccharides from Gracilaria species (Rhodophyta, Gracilariaceae).
Marinho-Soriano, E
2001-07-26
Yield, physical and chemical properties of agar from three agarophytes species (Gracilaria gracilis, G. dura and G. bursa-pastoris) were determined. The agar yield from the three species varied significantly (P<0.01). The highest yields of agar (34.8%) and the lowest (30%) were obtained from G. bursa-pastoris and G. gracilis, respectively. Highest gel strength (630+/-15 g cm(-2)) was obtained from agar extracted from G. gracilis and lowest from G. bursa-pastoris (26+/-3.6 g cm(-2)). The values of 3,6-anhydrogalactose were similar for G. gracilis and G. dura and there were no significant differences among the species. The sulfate contents varied significantly (P<0.01) and the higher value was obtained from G. bursa-pastoris. Among the three species, G. gracilis showed superior agar quality than the other two species, hence it can be considered a good potential source for industrial use. PMID:11472802
High-order accurate, low numerical diffusion methods for aerodynamics
NASA Astrophysics Data System (ADS)
Ekaterinaris, John A.
2005-04-01
In recent years numerical methods have been widely used to effectively resolve complex flow features of aerodynamics flows with meshes that are reasonable for today's computers. High-order numerical methods were used mainly in direct numerical simulations and aeroacoustics. For many aeronautical applications, accurate computation of vortex-dominated flows is important because the vorticity in the flow field and the wake of swept wings at an incidence and rotor blades largely determines the distribution of loading. The main deficiency of widely available, second-order accurate methods for the accurate computation of these flows is the numerical diffusion of vorticity to unacceptable levels. Application of high-order accurate, low-diffusion numerical methods can significantly alleviate this deficiency of traditional second order methods. Furthermore, higher-order space discretizations have the potential to improve detached eddy simulation predictions of separated flows with significant unsteadiness. Recently developed high-order accurate finite-difference, finite-volume, and finite-element methods are reviewed. These methods can be used as an attractive alternative of traditional low-order central and upwind computational fluid dynamics methods for improved predictions of vortical and other complex, separated, unsteady flows. The main features of these methods are summarized, from a practical user's point of view, their applicability and relative strength is indicated, and examples from recent applications are presented to illustrate their performance on selected problems.
Measurement of gas diffusion through soils: comparison of laboratory methods.
Allaire, Suzanne E; Lafond, Jonathan A; Cabral, Alexandre R; Lange, Sébastien F
2008-11-01
Gas movement through soils is important for ecosystems and engineering in many ways such as for microbial and plant respiration, passive methane oxidation in landfill covers and oxidation of mine residues. Diffusion is one of the most important gas movement processes and the determination of the diffusion coefficient is a crucial step in any study. Five laboratory methods used for measuring the relative gas diffusion coefficient (D(s)/D(o)) were compared using a loamy sand, a porous media commonly found in agricultural fields and in several engineered structures, such as in landfill final covers. In the absence of macropores, all methods gave rather similar values of D(s)/D(o). Methods allowing the study of microscale variability indicated that the presence of macropores highly influenced gas movement, thus the value of D(s)/D(o), which, near a macropore may be one order of magnitude higher than in regions without macropores. Repacked columns do not allow the study of heterogeneity in D(s)/D(o). Natural spatial variability in D(s)/D(o) due to water distribution and preferential pathways can only be studied in large systems, but these systems are difficult to handle. Advantages and disadvantages of each method are discussed. PMID:18974902
A Numerical Method for Determining Diffusivity from Annealing Experiments
NASA Astrophysics Data System (ADS)
Harris-Kuhlman, K. R.; Kulcinski, G. L.
1998-12-01
Terrestrial analogs of lunar ilmenite (FeTiO3) have been implanted with solar-wind energy 4He at 4 keV and 3He at 3 keV using Plasma Source Ion Implantation (PSII). Isochronal annealing of the samples revealed thermally induced 4He evolution similar to the helium release of the Apollo 11 regoliths reported by Pepin, et. al., [1970]. These annealing experiments are analyzed with a three dimensional numerical method based on Fick's law for diffusion. An iterative method is used to calculate the diffusivity. The code uses an assumed diffusivity to calculate the amount of gas released during a temperature step. The initial depth profile of the implanted species is generated using the TRIM electronic stopping code [Ziegler, 1996]. The calculated value is compared to the measured value and a linear regression is used to calculate a new diffusivity until there is convergence within a specified tolerance level. The diffusivity as a function of temperature is then fitted to an Arrhenius equation. Analysis of results for 4 keV 4He on ilmenite shows two distinct regions of Arrehnius behavior with activation energies of 0.5 +/- 0.1 eV at emperatures below 800 deg C and 1.5 +/- 0.2 eV at temperatures from 800 deg C to 1100 deg C. Pepin, R. O., L. E. Nyquist, D. Phinney, and D. C. Black (1970) "Rare Gases in Apollo 11 Lunar Material," Proceedings of the Apollo 11 Lunar Science Conference, 2, pp. 1435-1454. Ziegler, J. P. (1996) SRIM Instruction Manual: The Stopping and Range of Ions in Matter, (Yorktown, New York: IBM - Research); based on Ziegler, J. P., J. P. Biersack and U. Littmark, The Stopping and Range of Ions in Solids, (New York: Pergamon Press, 1985).
Some basic mathematical methods of diffusion theory. [emphasis on atmospheric applications
NASA Technical Reports Server (NTRS)
Giere, A. C.
1977-01-01
An introductory treatment of the fundamentals of diffusion theory is presented, starting with molecular diffusion and leading up to the statistical methods of turbulent diffusion. A multilayer diffusion model, designed to permit concentration and dosage calculations downwind of toxic clouds from rocket vehicles, is described. The concepts and equations of diffusion are developed on an elementary level, with emphasis on atmospheric applications.
A radial basis function Galerkin method for inhomogeneous nonlocal diffusion
Lehoucq, Richard B.; Rowe, Stephen T.
2016-02-01
We introduce a discretization for a nonlocal diffusion problem using a localized basis of radial basis functions. The stiffness matrix entries are assembled by a special quadrature routine unique to the localized basis. Combining the quadrature method with the localized basis produces a well-conditioned, sparse, symmetric positive definite stiffness matrix. We demonstrate that both the continuum and discrete problems are well-posed and present numerical results for the convergence behavior of the radial basis function method. As a result, we explore approximating the solution to anisotropic differential equations by solving anisotropic nonlocal integral equations using the radial basis function method.
A localized meshless method for diffusion on folded surfaces
NASA Astrophysics Data System (ADS)
Cheung, Ka Chun; Ling, Leevan; Ruuth, Steven J.
2015-09-01
Partial differential equations (PDEs) on surfaces arise in a variety of application areas including biological systems, medical imaging, fluid dynamics, mathematical physics, image processing and computer graphics. In this paper, we propose a radial basis function (RBF) discretization of the closest point method. The corresponding localized meshless method may be used to approximate diffusion on smooth or folded surfaces. Our method has the benefit of having an a priori error bound in terms of percentage of the norm of the solution. A stable solver is used to avoid the ill-conditioning that arises when the radial basis functions (RBFs) become flat.
Support Operators Method for the Diffusion Equation in Multiple Materials
Winters, Andrew R.; Shashkov, Mikhail J.
2012-08-14
A second-order finite difference scheme for the solution of the diffusion equation on non-uniform meshes is implemented. The method allows the heat conductivity to be discontinuous. The algorithm is formulated on a one dimensional mesh and is derived using the support operators method. A key component of the derivation is that the discrete analog of the flux operator is constructed to be the negative adjoint of the discrete divergence, in an inner product that is a discrete analog of the continuum inner product. The resultant discrete operators in the fully discretized diffusion equation are symmetric and positive definite. The algorithm is generalized to operate on meshes with cells which have mixed material properties. A mechanism to recover intermediate temperature values in mixed cells using a limited linear reconstruction is introduced. The implementation of the algorithm is verified and the linear reconstruction mechanism is compared to previous results for obtaining new material temperatures.
Residual Agar Determination in Bacterial Spores by Electrospray Ionization Mass Spectrometry
Wahl, Karen L.; Colburn, Heather A.; Wunschel, David S.; Petersen, Catherine E.; Jarman, Kristin H.; Valentine, Nancy B.
2010-02-15
Presented here is an analytical method to detect residual agar from a bacterial spore sample as an indication of culturing on an agar plate. This method is based on the resolubilization of agar polysaccharide from a bacterial spore sample, enzymatic digestion, followed by electrospray ionization tandem mass spectrometry (ESI-MSn) analysis for detection of a specific agar fragment ion. A range of Bacillus species and strains were selected to demonstrate the effectiveness of this approach. The characteristic agar fragment ion was detected in the spores grown on agar that were washed from 1 to 5 times, irradiated or non-irradiated and not in the spores grown in broth. A sample containing approximately 108 spores is currently needed for confident detection of residual agar from culture on agar plates in the presence of bacterial spores with a limit of detection of approximately 1 ppm agar spiked into a broth-grown spore sample. The results of a proficiency test with 42 blinded samples are presented demonstrating the utility of this method with no false positives and only 3 false negatives for samples that were below the detection level of the method as documented.
Minutes to Millennia: Diffusion Methods in Subduction-Related Volcanism
NASA Astrophysics Data System (ADS)
Morgan, D. J.; Allan, A.; Wilson, C. J. N.; Charlier, B. L.; Davidson, J.
2014-12-01
Diffusion methods have several advantages as relative geochronometers in volcano-related magmatic processes: diffusion stops on eruption, locking in short timescale information; methods are relatively easy to implement; and suitable material is generally abundant. Such methods also pose significant, accompanying challenges: the need for accurate melt palaeothermometry, uncertainties in diffusion parameters, and sometimes even a cryptic connection between mineral zonation and timescale. As all timescales are relative to an event, timing is not absolute, and care must be taken in interpretation. Yet for all the difficulties, diffusion tools are seeing more widespread usage. This has come about because of the potential of diffusion methods to interrogate certain pre-eruptive processes operating over timescales of relevance to human timescales and responses, having direct bearing on hazard mitigation procedures. In studying subduction zone systems we have a wide range of minerals to choose from but will, in subduction-related, andesitic-to-rhyolitic systems, usually be operating away from the relatively well-constrained system of olivine, and instead be dealing with mineral phases that offer different challenges, such as plagioclase, quartz, sanidine, amphibole, orthopyroxene, Fe-Ti oxides and mica. Timescales here span a wide range across different mineral-element combinations, from minutes for Li in plagioclase and quartz to days by Fe-Ti oxides, years by orthopyroxene Fe-Mg and decades to millennia with plagioclase, sanidine and quartz. This contribution will focus on the interpretation of diffusion signals in minerals found in subduction-related volcanic systems. To understand what any modelled timescale means, the process which formed the relevant zonation pattern is absolutely key, yet often elusive. Variations in P, T, X conditions really drive the crystallisation process yet certain zonation patterns are non-unique. This ambiguity necessitates painstaking petrological and geochemical detective work to understand where the zoning came from to begin with, and which parameter or parameters were truly driving the zonation. The rewards are insights into short-lived processes occurring in the build up to, or process of, eruption, which are not accessible via other mechanisms.
Diffusely reflecting paints including polytetrafluoroethylene and method of manufacture
NASA Technical Reports Server (NTRS)
Schutt, J. B.; Shai, M. C. (Inventor)
1985-01-01
The invention pertains to a high diffuse, reflective paint comprising an alcohol soluble binder, polytetrafluoroethylene (TFE) and an alcohol for coating a substrate and forming an optical reference with a superior Lambertian characteristic. A method for making the paint by first mixing the biner and alcohol, and thereafter by mixing in outgassed TFE is described. A wetting agent may be employed to aid the mixing process.
New methods for sedimentation and diffusion analysis of macromolecular structure
Demeler, B.
1992-01-01
Methods are presented to acquire data from analytical ultracentrifugation experiments by computer using the absorption optical scanning system of the Beckman Model-E ultracentrifuge. A computer program was written which analyzes sedimentation velocity experiments by the van Holde-Weischet method and the second moment method. The van Holde-Weischet method allows a high resolution analysis of sedimentation velocity data by eliminating the effects of diffusion on the shape of the moving boundary to provide sedimentation coefficients for a heterogeneous composition of a sample. The second moment method obtains the sedimentation coefficient by calculating the second moment point, by which the sedimentation coefficient is defined. A program was written for the acquisition of data to measure diffusion coefficients from quasi elastic light scattering experiments with a Langely Ford correlator. The analysis of autocorrelation spectra from light scattering experiments is performed by the Levenberg-Marquardt method, which allows fitting of data to nonlinear models. The development of the PPOL-1 208-n series of plasmids and of the miniplasmid pMX is described. These plasmids were designed to allow studies of in vitro transcription and chromatin structure after reconstitution with histones. Sedimentation data are presented which suggests a new method for rapid estimation of the sedimentation coefficient at zero concentration for molecules which show a concentration dependency of the sedimentation coefficient. This is accomplished by linearly extrapolating van Holde-Weischet distributions to zero concentration. Diffusion data for this plasmid DNA is used to demonstrate the feasibility of the multicomponent analysis. Sedimentation measurements were carried out on reconstituted chromatin. The programs were used to demonstrate significant changes in chromatin structure upon ethidium bromide binding.
Hybrid finite element and Brownian dynamics method for diffusion-controlled reactions
Bauler, Patricia; Huber, Gary A.; McCammon, J. Andrew
2012-01-01
Diffusion is often the rate determining step in many biological processes. Currently, the two main computational methods for studying diffusion are stochastic methods, such as Brownian dynamics, and continuum methods, such as the finite element method. This paper proposes a new hybrid diffusion method that couples the strengths of each of these two methods. The method is derived for a general multidimensional system, and is presented using a basic test case for 1D linear and radially symmetric diffusion systems. PMID:22559470
Recovery of Sublethally Injured Bacteria Using Selective Agar Overlays.
ERIC Educational Resources Information Center
McKillip, John L.
2001-01-01
This experiment subjects bacteria in a food sample and an environmental sample to conditions of sublethal stress in order to assess the effectiveness of the agar overlay method to recover sublethally injured cells compared to direct plating onto the appropriate selective medium. (SAH)
Effective Thermal Diffusivity Study of Powder Biocomposites via Photoacoustic Method
NASA Astrophysics Data System (ADS)
Mariucci, V. V. G.; da Cruz, J. A.; Bonadio, T. G. M.; Picolloto, A. M.; Weinand, W. R.; Lima, W. M.; Medina, A. N.; Bento, A. C.
2015-10-01
The effective thermal diffusivity for biocomposites of hydroxyapatite (HAp), and niobium pentoxide (Nb2O5) on powder form was studied via photoacoustic method adapted for porous materials. The concentration of each element was accompanied with the results of X-ray diffractometer (XRD) and scanning electron microscopy (SEM). A theoretical model for the thermal coupling of a three layered sample, designed to contain the powder material is proposed. The method for mixtures obeyed the formula [(1 - x) H A p + ( x) N b 2O5] for 0.0 ≤ x ≤ 1.0. Experimental results for effective thermal diffusivity ranged between (6.4 ± 0.3) × 10-6 m2 s-1 and (9.8 ± 0.4) × 10-6 m2 s-1 for x ≤ 0.7. Values of the effective thermal diffusivity have decreased sharply to (0.7 ± 0.03) ×10-6 m2 s-1 for x > 0.7. SEM micrographs showed a coating of HAp over the particles of Nb2O5 for some mixtures.
Growth kinetics of three species of Tetrahymena on solid agar
Dobra, K.W.; McArdle, E.W.; Ehret, C.F.
1980-01-01
A nutrient-agar method without liquid overlay has been developed for cultivation of ciliates. Three species of Tetrahymena-T. pyriformis strain W, T. rostrata strain UNI, and T. vorax strain V/sub 2/S, representing the 3 main groups of Tetrahymena species, were used; however the method should apply to other ciliates. Growth on the surface of the agar was facilitated by an optimal surface-to-volume ratio yielding a high density of ciliates and short generation times. At the highest density achieved, the cells became irregularly hexagonal and formed a monolayer tissue on the agar. Ciliates grown on agar were like those in liquid culture, typical oral ciliature, food-vacuole formation, and typical cortical patterns being retained. Advantages of this method include high cell density, easy recovery, and optimal O/sub 2/ supply. The organisms can also be cultivated on the surface of sterile cellulose-nitrate filters, facilitating in situ fixation and staining as well as transfer into different media by transfer of filters with cells, without prior centrifugation and resuspension.
A diffusive information preservation method for small Knudsen number flows
NASA Astrophysics Data System (ADS)
Fei, Fei; Fan, Jing
2013-06-01
The direct simulation Monte Carlo (DSMC) method is a powerful particle-based method for modeling gas flows. It works well for relatively large Knudsen (Kn) numbers, typically larger than 0.01, but quickly becomes computationally intensive as Kn decreases due to its time step and cell size limitations. An alternative approach was proposed to relax or remove these limitations, based on replacing pairwise collisions with a stochastic model corresponding to the Fokker-Planck equation [J. Comput. Phys., 229, 1077 (2010); J. Fluid Mech., 680, 574 (2011)]. Similar to the DSMC method, the downside of that approach suffers from computationally statistical noise. To solve the problem, a diffusion-based information preservation (D-IP) method has been developed. The main idea is to track the motion of a simulated molecule from the diffusive standpoint, and obtain the flow velocity and temperature through sampling and averaging the IP quantities. To validate the idea and the corresponding model, several benchmark problems with Kn ˜ 10-3-10-4 have been investigated. It is shown that the IP calculations are not only accurate, but also efficient because they make possible using a time step and cell size over an order of magnitude larger than the mean collision time and mean free path, respectively.
A diffusive information preservation method for small Knudsen number flows
Fei, Fei; Fan, Jing
2013-06-15
The direct simulation Monte Carlo (DSMC) method is a powerful particle-based method for modeling gas flows. It works well for relatively large Knudsen (Kn) numbers, typically larger than 0.01, but quickly becomes computationally intensive as Kn decreases due to its time step and cell size limitations. An alternative approach was proposed to relax or remove these limitations, based on replacing pairwise collisions with a stochastic model corresponding to the Fokker–Planck equation [J. Comput. Phys., 229, 1077 (2010); J. Fluid Mech., 680, 574 (2011)]. Similar to the DSMC method, the downside of that approach suffers from computationally statistical noise. To solve the problem, a diffusion-based information preservation (D-IP) method has been developed. The main idea is to track the motion of a simulated molecule from the diffusive standpoint, and obtain the flow velocity and temperature through sampling and averaging the IP quantities. To validate the idea and the corresponding model, several benchmark problems with Kn ∼ 10{sup −3}–10{sup −4} have been investigated. It is shown that the IP calculations are not only accurate, but also efficient because they make possible using a time step and cell size over an order of magnitude larger than the mean collision time and mean free path, respectively.
Newton-Krylov methods applied to nonequilibrium radiation diffusion
Knoll, D.A.; Rider, W.J.; Olsen, G.L.
1998-03-10
The authors present results of applying a matrix-free Newton-Krylov method to a nonequilibrium radiation diffusion problem. Here, there is no use of operator splitting, and Newton`s method is used to convert the nonlinearities within a time step. Since the nonlinear residual is formed, it is used to monitor convergence. It is demonstrated that a simple Picard-based linearization produces a sufficient preconditioning matrix for the Krylov method, thus elevating the need to form or store a Jacobian matrix for Newton`s method. They discuss the possibility that the Newton-Krylov approach may allow larger time steps, without loss of accuracy, as compared to an operator split approach where nonlinearities are not converged within a time step.
Some Experiments With Agar-Grown Seedlings
ERIC Educational Resources Information Center
Freeland, P. W.
1973-01-01
Two percent agar gel is reported as a better medium for germination and growth studies. Students can be encouraged to undertake many simple experiments and make precise observations by using this medium. (PS)
Characterization of physicochemical properties of carboxymethyl agar.
Cao, Mingzhao; Liu, Xin; Luan, Jimei; Zhang, Xiaodong
2014-10-13
A series of carboxymethyl agars (CMAs) with different degree of substitution (DS) were prepared, and their properties were determined and analyzed. The results showed that with the increase of DS, the dissolving temperature, the gelling temperature, the gel melting temperature, the gel strength, the gel hardness, the gel fracturability, and the solution apparent viscosity of CMA all decreased, except that its gel cohesiveness and gel springiness increased. The variation process of agar molecules in solution from coil to helix could be observed by measuring the optical rotation of the solution at such a low concentration, at which even the solution could not form a gel. The gel skeleton microstructures of both agar and CMA were of porous network structure, and the pore size of CMA became smaller and denser with the increase of its DS. After carboxymethylation, the agar hygroscopicity was improved, but its thermal stability was lowered. PMID:25037374
Diffusion barriers in skin--a new method of comparison.
Foreman, M I; Clanachan, I; Kelly, I P
1983-05-01
Using a method which allows the net barrier potential of skin to be expressed in terms of a 'penetration half-life', skin barriers to nandrolone and allyl oestrenol penetration were compared in human, rat and hamster skin. The ranking order in terms of the net barrier was: human = haired rat greater than or equal to hairless rat greater than hairless hamster. Using the same principles, the net barrier effects of the various layers in whole human skin were also compared. The dermis was only slightly less effective than the stratum corneum as a barrier to diffusion. PMID:6849823
On matrix diffusion: formulations, solution methods and qualitative effects
NASA Astrophysics Data System (ADS)
Carrera, Jesús; Sánchez-Vila, Xavier; Benet, Inmaculada; Medina, Agustín; Galarza, Germán; Guimerà, Jordi
Matrix diffusion has become widely recognized as an important transport mechanism. Unfortunately, accounting for matrix diffusion complicates solute-transport simulations. This problem has led to simplified formulations, partly motivated by the solution method. As a result, some confusion has been generated about how to properly pose the problem. One of the objectives of this work is to find some unity among existing formulations and solution methods. In doing so, some asymptotic properties of matrix diffusion are derived. Specifically, early-time behavior (short tests) depends only on φm2RmDm / Lm2, whereas late-time behavior (long tracer tests) depends only on φmRm, and not on matrix diffusion coefficient or block size and shape. The latter is always true for mean arrival time. These properties help in: (a) analyzing the qualitative behavior of matrix diffusion; (b) explaining one paradox of solute transport through fractured rocks (the apparent dependence of porosity on travel time); (c) discriminating between matrix diffusion and other problems (such as kinetic sorption or heterogeneity); and (d) describing identifiability problems and ways to overcome them. RésuméLa diffusion matricielle est un phénomène reconnu maintenant comme un mécanisme de transport important. Malheureusement, la prise en compte de la diffusion matricielle complique la simulation du transport de soluté. Ce problème a conduit à des formulations simplifiées, en partie à cause de la méthode de résolution. Il s'en est suivi une certaine confusion sur la façon de poser correctement le problème. L'un des objectifs de ce travail est de trouver une certaine unité parmi les formulations et les méthodes de résolution. C'est ainsi que certaines propriétés asymptotiques de la diffusion matricielle ont été dérivées. En particulier, le comportement à l'origine (expériences de traçage courtes) dépend uniquement du terme φm2RmDm / Lm2, alors que le comportement à long terme (traçages de longue durée) ne dépend que de φmRm, et non pas du coefficient de diffusion matricielle ou de la forme et de la taille des blocs. Ceci est toujours vrai pour le temps moyen d'arrivée. Ces propriétés permettent: (a) d'analyser le comportement de la diffusion matricielle; (b) d'expliquer un paradoxe du transport de soluté dans les roches fracturées (la dépendance apparente entre la porosité et le temps de transit); (c) de faire la distinction entre la diffusion matricielle et d'autres problèmes, tels que la sorption cinétique ou l'hétérogénéité et (d) de décrire les problèmes d'identification et les façons de les résoudre. Resumen La difusión en la matriz está reconocida en la actualidad como un importante mecanismo de transporte de solutos. Desgraciadamente, tener en cuenta este proceso complica las simulaciones de transporte. Esto ha llevado a una serie de formulaciones simplificadas, motivadas en parte por el propio método de solución. Como resultado, se ha producido cierta confusión respecto a cuál es la manera adecuada de formular el problema. Uno de los objetivos de este trabajo es encontrar una cierta unidad entre las formulaciones existentes y los métodos de solución, lo que conduce a algunas propiedades asintóticas de la difusión en la matriz; específicamente, se comprueba que el comportamiento para tiempos cortos depende únicamente del parámetro φm2RmDm / Lm2, mientras que el de tiempos largos depende sólo de φmRm, y no del coeficiente de difusión en la matriz o del tamaño o forma del bloque. Esto último también es cierto, en todos los casos, respecto al tiempo medio de llegada (definido como el valor esperado de la distribución de tiempos de llegada). Estas propiedades son útiles para: (a) analizar el comportamiento cualitativo de la difusión en la matriz; (b) explicar una de las paradojas del transporte de solutos en medios fracturados, la aparente dependencia entre porosidad y tiempo de llegada; (c) discriminar entre difusión en la matriz y otros problemas, como las reacciones con cinética química o la heterogeneidad; y (d) describir problemas de identificabilidad y posibles modos de resolverlos.
Diffuse optical methods for assessing breast cancer chemotherapy
NASA Astrophysics Data System (ADS)
Tromberg, Bruce J.
2014-03-01
In his talk, "Diffuse Optical Methods for Assessing Breast Cancer Chemotherapy," SPIE Fellow Bruce Tromberg (Beckman Laser Institute and Medical Clinic) describes a method combining frequency domain photon migration, essentially a method of tracking photon motion in tissue, with a NIR spectroscopy technique using 850nm LEDs. The result is a scatter corrected absorption spectra. The technique takes advantage of elevated blood and water levels and decreased lipid levels in the presence of tumors to provide a more accurate mapping of the breast, allowing more effective treatment. Tromberg's team recently completed their first full mapping of the breast and have taken the instrument from a standalone unit to a portable one suitable for travel. In addition to providing feedback to enhance breast cancer treatment, Tromberg expects that this technique will be applicable in treating other forms of cancer as well.
Agar-Gel Precipitin-Inhibition Test for Coccidioidomycosis
Ray, John G.; Converse, John L.
1967-01-01
In this study of saprophytic and parasitic growth-phase extracts of Coccidioides immitis, an antigen from the spherule culture supernatant fluid detected a specific antibody in heretofore serologically negative suspect coccidioidomycosis human sera when diffused in agar-gel. This antigen-antibody reaction occurred also in some of the serologically positive human coccidioidomycosis sera. This study indicates that this antigen-antibody reaction should be utilized as a possible routine serological test for complete serodiagnosis. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 PMID:4964065
Audicana, A; Perales, I; Borrego, J J
1995-01-01
Kanamycin-esculin-azide agar was modified by increasing the concentration of sodium azide to 0.4 g liter-1 and replacing kanamycin sulfate with 5 mg of oxolinic acid liter-1. The modification, named oxolinic acid-esculin-azide (OAA) agar, was compared with Slanetz-Bartley and KF agars by using drinking water and seawater samples. The OAA agar showed higher specificity, selectivity, and recovery efficiencies than those obtained by using the other media. In addition, no confirmation of typical colonies was needed when OAA agar was used, which significantly shortens the time of sample processing and increases the accuracy of the method. PMID:8534085
Compact finite volume methods for the diffusion equation
NASA Technical Reports Server (NTRS)
Rose, Milton E.
1989-01-01
The paper describes an approach to treating initial-boundary-value problems by finite volume methods in which the parallel between differential and difference arguments is closely maintained. By using intrinsic geometrical properties of the volume elements, it is possible to describe discrete versions of the div, curl, and grad operators which lead, using summation-by-parts techniques, to familiar energy equations as well as the div curl = 0 and curl grad = 0 identities. For the diffusion equation, these operators describe compact schemes whose convergence is assured by the energy equations and which yield both the potential and the flux vector with second-order accuracy. A simplified potential form is especially useful for obtaining numerical results by multigrid and ADI methods.
Compact finite volume methods for the diffusion equation
NASA Technical Reports Server (NTRS)
Rose, Milton E.
1989-01-01
An approach to treating initial-boundary value problems by finite volume methods is described, in which the parallel between differential and difference arguments is closely maintained. By using intrinsic geometrical properties of the volume elements, it is possible to describe discrete versions of the div, curl, and grad operators which lead, using summation-by-parts techniques, to familiar energy equations as well as the div curl = 0 and curl grad = 0 identities. For the diffusion equation, these operators describe compact schemes whose convergence is assured by the energy equations and which yield both the potential and the flux vector with second order accuracy. A simplified potential form is especially useful for obtaining numerical results by multigrid and alternating direction implicit (ADI) methods. The treatment of general curvilinear coordinates is shown to result from a specialization of these general results.
Domain decomposition multigrid methods for nonlinear reaction-diffusion problems
NASA Astrophysics Data System (ADS)
Arrarás, A.; Gaspar, F. J.; Portero, L.; Rodrigo, C.
2015-03-01
In this work, we propose efficient discretizations for nonlinear evolutionary reaction-diffusion problems on general two-dimensional domains. The spatial domain is discretized through an unstructured coarse triangulation, which is subsequently refined via regular triangular grids. Following the method of lines approach, we first consider a finite element spatial discretization, and then use a linearly implicit splitting time integrator related to a suitable decomposition of the triangulation nodes. Such a procedure provides a linear system per internal stage. The equations corresponding to those nodes lying strictly inside the elements of the coarse triangulation can be decoupled and solved in parallel using geometric multigrid techniques. The method is unconditionally stable and computationally efficient, since it avoids the need for Schwarz-type iteration procedures. In addition, it is formulated for triangular elements, thus yielding much flexibility in the discretization of complex geometries. To illustrate its practical utility, the algorithm is shown to reproduce the pattern-forming dynamics of the Schnakenberg model.
Extrapolation techniques applied to matrix methods in neutron diffusion problems
NASA Technical Reports Server (NTRS)
Mccready, Robert R
1956-01-01
A general matrix method is developed for the solution of characteristic-value problems of the type arising in many physical applications. The scheme employed is essentially that of Gauss and Seidel with appropriate modifications needed to make it applicable to characteristic-value problems. An iterative procedure produces a sequence of estimates to the answer; and extrapolation techniques, based upon previous behavior of iterants, are utilized in speeding convergence. Theoretically sound limits are placed on the magnitude of the extrapolation that may be tolerated. This matrix method is applied to the problem of finding criticality and neutron fluxes in a nuclear reactor with control rods. The two-dimensional finite-difference approximation to the two-group neutron fluxes in a nuclear reactor with control rods. The two-dimensional finite-difference approximation to the two-group neutron-diffusion equations is treated. Results for this example are indicated.
Multigrid methods for numerical simulation of laminar diffusion flames
NASA Technical Reports Server (NTRS)
Liu, C.; Liu, Z.; Mccormick, S.
1993-01-01
This paper documents the result of a computational study of multigrid methods for numerical simulation of 2D diffusion flames. The focus is on a simplified combustion model, which is assumed to be a single step, infinitely fast and irreversible chemical reaction with five species (C3H8, O2, N2, CO2 and H2O). A fully-implicit second-order hybrid scheme is developed on a staggered grid, which is stretched in the streamwise coordinate direction. A full approximation multigrid scheme (FAS) based on line distributive relaxation is developed as a fast solver for the algebraic equations arising at each time step. Convergence of the process for the simplified model problem is more than two-orders of magnitude faster than other iterative methods, and the computational results show good grid convergence, with second-order accuracy, as well as qualitatively agreement with the results of other researchers.
Berghaus, Londa J; Gigure, Steeve; Guldbech, Kristen; Warner, Eleanor; Ugorji, Ukachi; Berghaus, Roy D
2015-01-01
MICs of erythromycin, clarithromycin, azithromycin, rifampin, gentamicin, and doxycycline against 101 isolates of Rhodococcus equi were determined by broth macrodilution, disk diffusion, and Etest. Categorical agreement ranged between 85.1 and 100%. Overall, the agreement between Etest and disk diffusion was better than the agreement between broth macrodilution and the agar-based methods. PMID:25378571
The Simulation-Tabulation Method for Classical Diffusion Monte Carlo
NASA Astrophysics Data System (ADS)
Hwang, Chi-Ok; Given, James A.; Mascagni, Michael
2001-12-01
Many important classes of problems in materials science and biotechnology require the solution of the Laplace or Poisson equation in disordered two-phase domains in which the phase interface is extensive and convoluted. Green's function first-passage (GFFP) methods solve such problems efficiently by generalizing the “walk on spheres” (WOS) method to allow first-passage (FP) domains to be not just spheres but a wide variety of geometrical shapes. (In particular, this solves the difficulty of slow convergence with WOS by allowing FP domains that contain patches of the phase interface.) Previous studies accomplished this by using geometries for which the Green's function was available in quasi-analytic form. Here, we extend these studies by using the simulation-tabulation (ST) method. We simulate and then tabulate surface Green's functions that cannot be obtained analytically. The ST method is applied to the Solc-Stockmayer model with zero potential, to the mean trapping rate of a diffusing particle in a domain of nonoverlapping spherical traps, and to the effective conductivity for perfectly insulating, nonoverlapping spherical inclusions in a matrix of finite conductivity. In all cases, this class of algorithms provides the most efficient methods known to solve these problems to high accuracy.
Pigments of fly agaric (Amanita muscaria).
Stintzing, Florian; Schliemann, Willibald
2007-01-01
The complex pigment pattern of fly agaric (Amanita muscaria) cap skins has been studied by LC-DAD and mass spectrometry. Among the betaxanthins the corresponding derivatives of serine, threonine, ethanolamine, alanine, Dopa, phenylalanine and tryptophan are reported for the first time to contribute to the pigment pattern of fly agarics. Betalamic acid, the chromophoric precursor of betaxanthins and betacyanins, muscaflavin and seco-dopas were also detected. Furthermore, the red-purple muscapurpurin and the red muscarubrin were tentatively assigned while further six betacyanin-like components could not be structurally allocated. Stability studies indicated a high susceptibility of pigment extracts to degradation which led to rapid colour loss thus rendering a complete characterization of betacyanin-like compounds impossible at present. Taking into account these difficulties the presented results may be a starting point for a comprehensive characterization of the pigment composition of fly agarics. PMID:18274277
Le Page, S; van Belkum, A; Fulchiron, C; Huguet, R; Raoult, D; Rolain, J-M
2015-09-01
The disk diffusion (DD) method remains the most popular manual technique for antibiotic susceptibility testing (AST) in clinical microbiology laboratories. This is because of its simplicity, reproducibility, and limited cost compared to (automated) microdilution systems, which are usually less sensitive at detecting certain important mechanisms of resistance. Here, we evaluate the PREVI Isola automated seeder system using a new protocol for spreading bacterial suspensions (eight deposits of calibrated inocula of bacteria, followed by two rounds of rotation) in comparison with manual DD reference testing on a large series of clinical and reference strains. The average time required for seeding one agar plate for DD with this new protocol was 51 s per plate, i.e., 70 agar plates/h. Reproducibility and repeatability was assessed on three reference and three randomly chosen clinical strains, as usually requested by the European Committee on Antimicrobial Susceptibility Testing (EUCAST), and was excellent compared to the manual method. The standard deviations of zones of growth inhibition showed no statistical discrimination. The correlation between the two methods, assessed using 294 clinical isolates and a panel of six antibiotics (n?=?3,528 zones of growth inhibition measured), was excellent, with a correlation coefficient of 0.977. The new PREVI Isola protocol adapted for DD had a sensitivity of 99 % and a specificity of 100 % compared to the manual technique for interpreting DD as recommended by the EUCAST. PMID:26092031
Madera-Santana, T J; Freile-Pelegrín, Y; Azamar-Barrios, J A
2014-08-01
The effects of the addition of glycerol (GLY) on the physicochemical and morphological properties of poly(vinyl alcohol) (PVA)-agar films were reported. PVA-agar films were prepared by solution cast method, and the addition of GLY in PVA-agar films altered the optical properties, resulting in a decrease in opacity values and in the color difference (ΔE) of the films. Structural characterization using Fourier transformation infrared (FTIR) spectroscopy and X-ray diffraction (XRD) indicated that the presence of GLY altered the intensity of the bands (from 1200 to 800cm(-1)) and crystallinity. The characterization of the thermal properties indicated that an increase in the agar content produces a decrease in the melting temperature and augments the heat of fusion. Similar tendencies were observed in plasticized films, but at different magnification. The formulation that demonstrated the lowest mechanical properties contained 25wt.% agar, whereas the formulation that contained 75wt.% agar demonstrated a significant improvement. The water vapor transmission rate (WVTR) and surface morphology analysis demonstrated that the structure of PVA-agar films is reorganized upon GLY addition. The physicochemical properties of PVA-agar films using GLY as a plasticizer provide information for the application of this formulation as packaging material for specific food applications. PMID:24875313
Olsson, S; Bergman, B; Bergman, M
1987-01-01
The influence of seven dissimilar disinfectants on the dimensional stability and the surface detail sharpness of two agar impression materials was studied. Two methods for treatment with disinfectant solutions were tested--immersion for 1 hour and spraying. In contrast to immersion the spraying method had no obvious influence on the agar material. It is concluded that if the disinfection method necessitates immersion of the impression in a solution for 1 hour or more the use of agar impression materials should be avoided. PMID:3480616
Wuthiekanun, Vanaporn; Amornchai, Premjit; Langla, Sayan; White, Nicholas J.; Day, Nicholas P. J.; Limmathurotsakul, Direk; Peacock, Sharon J.
2015-01-01
Leptospira Vanaporn Wuthiekanun (LVW) agar was used to develop a disk diffusion assay for Leptospira spp. Ten pathogenic Leptospira isolates were tested, all of which were susceptible to 17 antimicrobial agents (amoxicillin/clavulanic acid, amoxicillin, azithromycin, cefoxitin, ceftazidime, ceftriaxone, chloramphenicol, ciprofloxacin, clindamycin, doripenem, doxycycline, gentamicin, linezolid, nitrofurantoin, penicillin, piperacillin/tazobactam, and tetracycline). All 10 isolates had no zone of growth inhibition for four antimicrobials (fosfomycin, nalidixic acid, rifampicin, and trimethoprim/sulfamethoxazole). Of the ten Leptospira, seven had a growth inhibition zone of ≤ 21 mm for aztreonam, the zone diameter susceptibility break point for Enterobacteriaceae. This assay could find utility as a simple screening method during the epidemiological surveillance of antimicrobial resistance in Leptospira spp. PMID:26055750
Wuthiekanun, Vanaporn; Amornchai, Premjit; Langla, Sayan; White, Nicholas J; Day, Nicholas P J; Limmathurotsakul, Direk; Peacock, Sharon J
2015-08-01
Leptospira Vanaporn Wuthiekanun (LVW) agar was used to develop a disk diffusion assay for Leptospira spp. Ten pathogenic Leptospira isolates were tested, all of which were susceptible to 17 antimicrobial agents (amoxicillin/clavulanic acid, amoxicillin, azithromycin, cefoxitin, ceftazidime, ceftriaxone, chloramphenicol, ciprofloxacin, clindamycin, doripenem, doxycycline, gentamicin, linezolid, nitrofurantoin, penicillin, piperacillin/tazobactam, and tetracycline). All 10 isolates had no zone of growth inhibition for four antimicrobials (fosfomycin, nalidixic acid, rifampicin, and trimethoprim/sulfamethoxazole). Of the ten Leptospira, seven had a growth inhibition zone of ≤ 21 mm for aztreonam, the zone diameter susceptibility break point for Enterobacteriaceae. This assay could find utility as a simple screening method during the epidemiological surveillance of antimicrobial resistance in Leptospira spp. PMID:26055750
A Critical Study of Agglomerated Multigrid Methods for Diffusion
NASA Technical Reports Server (NTRS)
Nishikawa, Hiroaki; Diskin, Boris; Thomas, James L.
2011-01-01
Agglomerated multigrid techniques used in unstructured-grid methods are studied critically for a model problem representative of laminar diffusion in the incompressible limit. The studied target-grid discretizations and discretizations used on agglomerated grids are typical of current node-centered formulations. Agglomerated multigrid convergence rates are presented using a range of two- and three-dimensional randomly perturbed unstructured grids for simple geometries with isotropic and stretched grids. Two agglomeration techniques are used within an overall topology-preserving agglomeration framework. The results show that multigrid with an inconsistent coarse-grid scheme using only the edge terms (also referred to in the literature as a thin-layer formulation) provides considerable speedup over single-grid methods but its convergence deteriorates on finer grids. Multigrid with a Galerkin coarse-grid discretization using piecewise-constant prolongation and a heuristic correction factor is slower and also grid-dependent. In contrast, grid-independent convergence rates are demonstrated for multigrid with consistent coarse-grid discretizations. Convergence rates of multigrid cycles are verified with quantitative analysis methods in which parts of the two-grid cycle are replaced by their idealized counterparts.
A Critical Study of Agglomerated Multigrid Methods for Diffusion
NASA Technical Reports Server (NTRS)
Thomas, James L.; Nishikawa, Hiroaki; Diskin, Boris
2009-01-01
Agglomerated multigrid techniques used in unstructured-grid methods are studied critically for a model problem representative of laminar diffusion in the incompressible limit. The studied target-grid discretizations and discretizations used on agglomerated grids are typical of current node-centered formulations. Agglomerated multigrid convergence rates are presented using a range of two- and three-dimensional randomly perturbed unstructured grids for simple geometries with isotropic and highly stretched grids. Two agglomeration techniques are used within an overall topology-preserving agglomeration framework. The results show that multigrid with an inconsistent coarse-grid scheme using only the edge terms (also referred to in the literature as a thin-layer formulation) provides considerable speedup over single-grid methods but its convergence deteriorates on finer grids. Multigrid with a Galerkin coarse-grid discretization using piecewise-constant prolongation and a heuristic correction factor is slower and also grid-dependent. In contrast, grid-independent convergence rates are demonstrated for multigrid with consistent coarse-grid discretizations. Actual cycle results are verified using quantitative analysis methods in which parts of the cycle are replaced by their idealized counterparts.
NASA Astrophysics Data System (ADS)
Yolcu, Cem; Memiç, Muhammet; Şimşek, Kadir; Westin, Carl-Fredrik; Özarslan, Evren
2016-05-01
We study the influence of diffusion on NMR experiments when the molecules undergo random motion under the influence of a force field and place special emphasis on parabolic (Hookean) potentials. To this end, the problem is studied using path integral methods. Explicit relationships are derived for commonly employed gradient waveforms involving pulsed and oscillating gradients. The Bloch-Torrey equation, describing the temporal evolution of magnetization, is modified by incorporating potentials. A general solution to this equation is obtained for the case of parabolic potential by adopting the multiple correlation function (MCF) formalism, which has been used in the past to quantify the effects of restricted diffusion. Both analytical and MCF results were found to be in agreement with random walk simulations. A multidimensional formulation of the problem is introduced that leads to a new characterization of diffusion anisotropy. Unlike the case of traditional methods that employ a diffusion tensor, anisotropy originates from the tensorial force constant, and bulk diffusivity is retained in the formulation. Our findings suggest that some features of the NMR signal that have traditionally been attributed to restricted diffusion are accommodated by the Hookean model. Under certain conditions, the formalism can be envisioned to provide a viable approximation to the mathematically more challenging restricted diffusion problems.
Stokkou, Sofia; Geginat, Gernot; Schlüter, Dirk
2015-01-01
Sepsis represents a life-threatening infection requiring the immediate start of antibacterial treatment to reduce morbidity. Thus, laboratories use direct antimicrobial susceptibility testing (AST) to rapidly generate preliminary results from positive blood cultures. As the direct AST has not yet been published to be evaluated with EUCAST breakpoints, the purpose of the study was to investigate the reliability of the direct agar diffusion test to correctly produce AST results from positive monobacterial blood cultures compared with the VITEK2-based definitive AST, when current EUCAST breakpoints were used. A total of 428 isolates from unselected monobacterial routine blood cultures and 110 challenge strains were included. Direct agar diffusion-based and standard VITEK2-based AST of 2803 bacterium–drug combinations yielded a total clinical category agreement of 95.47% with 1.28% very major errors and 3.42% combined major and minor errors. On the species level, very major errors were observed in the species–drug combinations Enterococcus spp.–high-level gentamicin (10.87%) and Staphylococcus spp.–rifampicin (5%), only. No very major errors occurred with Enterobacteriaceae and Pseudomonas aeruginosa. In most species–drug combinations, the direct agar diffusion test using EUCAST breakpoints precisely predicted the result of the definitive antibiotic susceptibility test and, thus, it can be used to optimize empiric antibiotic therapy until definitive results are available. PMID:25883798
Luminescent DNA- and agar-based membranes.
Leones, R; Fernandes, M; Ferreira, R A S; Cesarino, I; Lima, J F; Carlos, L D; Bermudez, V de Zea; Magon, C J; Donoso, J P; Silva, M M; Pawlicka, A
2014-09-01
Luminescent materials containing europium ions are investigated for different optical applications. They can be obtained using bio-macromolecules, which are promising alternatives to synthetic polymers based on the decreasing oil resources. This paper describes studies of the DNA- and Agar-europium triflate luminescent membranes and its potential technological applications are expanded to electroluminescent devices. Polarized optical microscopy demonstrated that the samples are birefringent with submicrometer anisotropy. The X-ray diffraction analysis revealed predominantly amorphous nature of the samples and the atomic force microscopy images showed a roughness of the membranes of 409.0 and 136.1 nm for the samples of DNA10Eu and Agar1.11Eu, respectively. The electron paramagnetic resonance spectra of the DNA(n)Eu membranes with the principal lines at g ? 2.0 and g ? 4.8 confirmed uniform distribution of rare earth ions in a disordered matrix. Moreover, these strong and narrow resonance lines for the samples of DNA(n)Eu when compared to the Agar(n)Eu suggested a presence of paramagnetic radicals arising from the DNA matrix. The emission spectra suggested that the Eu3+ ions occupy a single local environment in both matrices and the excitation spectra monitored around the Eu emission lines pointed out that the Eu3+ ions in the Agar host were mainly excited via the broad band component rather than by direct intra-4f(6) excitation, whereas the opposite case occurred for the DNA-based sample. PMID:25924317
Use of agar agar stabilized milled zero-valent iron particles for in situ groundwater remediation
NASA Astrophysics Data System (ADS)
Schmid, Doris; Velimirović, Milica; Wagner, Stephan; Micić Batka, Vesna; von der Kammer, Frank; Hofmann, Thilo
2015-04-01
A major obstacle for use of nanoscale zero-valent iron (nZVI) particles as a nontoxic material for effective in situ degradation of chlorinated aliphatic hydrocarbons (CAHs) is the high production cost. For that reason, submicro-scale milled zero-valent iron particles were recently developed (milled ZVI, UVR-FIA, Germany) by grinding macroscopic raw materials of elementary iron as a cheaper alternative to products produced by solid-state reduction. However, milled ZVI particles tend to aggregate and due to the rather large particle size (d50= 11.9 µm) also rapidly sediment. To prevent aggregation and consequently sedimentation of milled ZVI particles and therefore improve the mobility after in situ application, the use of a stabilizer is considered in literature as a most promising option. In this study, milled ZVI particles (1 g L-1 of particle concentration) were stabilized by environmentally friendly polymer agar agar (>0.5 g L-1), which had a positive impact on the milled ZVI stability. Sedimentation rate was significantly decreased by increasing the suspension viscosity. Column transport experiments were performed for bare and agar agar stabilized milled ZVI particles in commercially available fine grained quartz sand (DORSILIT® Nr.8, Gebrüder Dorfner GmbH Co, Germany) and different porous media collected from brownfields. The experiments were carried out under field relevant injection conditions of 100 m d-1. The maximal travel distance (LT) of less than 10 cm was determined for non-stabilized suspension in fine grained quartz sand, while agar agar (1 g L-1) stabilized milled ZVI suspension revealed LT of 12 m. Similar results were observed for porous media from brownfields showing that mobility of agar agar stabilized particle suspensions was significantly improved compared to bare particles. Based on the mobility data, agar agar stabilized milled zero-valent iron particles could be used for in situ application. Finally, lab-scale batch degradation experiments were performed to determine the impact of agar agar on the reactivity of milled ZVI and investigate the apparent corrosion rate of particles by quantifying the hydrogen gas generated by anaerobic corrosion of milled ZVI. The results indicate that agar agar had a positive impact on the milled ZVI stability and mobility, however adverse impact on the reactivity towards trichloroethene (TCE) was observed compared to the non-stabilized material. On the other hand, this study shows that the apparent corrosion rate of non-stabilized and agar agar stabilized milled ZVI particles is in the same order of magnitude. These data indicate that the dechlorination pathway of TCE by agar agar stabilized milled ZVI particles is possibly impacted by blocking of the reactive sites and not hydrogen revealed during particles corrosion. Finally, calculated longevity of the particles based on the apparent corrosion rate is significantly prolonged compared to the longevity of the nZVI particles reported in previous studies. This research receives funding from the European Union's Seventh Framework Programme FP7/2007-2013 under grant agreement n°309517.
Díez-Aguilar, María; del Campo, Rosa; García-Castillo, María; Zamora, Javier; Cantón, Rafael
2013-01-01
The broth microdilution method for fosfomycin and Pseudomonas aeruginosa was assessed and compared with the approved agar dilution method in 206 genetically unrelated P. aeruginosa clinical isolates. Essential agreement between the two methods was 84%, and categorical agreement was 89.3%. Additionally, Etest and disk diffusion assays were performed. Results validate broth microdilution as a reliable susceptibility testing method for fosfomycin against P. aeruginosa. Conversely, unacceptable concordance was established between Etest and disk diffusion results with agar dilution results. PMID:23939889
NASA Astrophysics Data System (ADS)
Wang, Fei; Kobayashi, Yasukazu; Muhammad, Usman; Wang, Dezheng; Wang, Yao
2016-03-01
The use of numerical analysis to solve the diffusion equation in the uptake method allowed the measurement of molecular diffusivity in a zeolite with a variable pressure around it. The diffusivity was obtained from the data in the measurement of the adsorption isotherm, which means that the diffusivity measurement now needs neither a special instrument nor procedure. The diffusivities of all the gases are readily available from the measurement of their adsorption isotherms and these data include how the diffusivity changes versus adsorbed concentration. The modeling introduced can also be used for a zeolite with a surface barrier.
Method for applying a diffusion barrier interlayer for high temperature components
Wei, Ronghua; Cheruvu, Narayana S.
2016-03-08
A coated substrate and a method of forming a diffusion barrier coating system between a substrate and a MCrAl coating, including a diffusion barrier coating deposited onto at least a portion of a substrate surface, wherein the diffusion barrier coating comprises a nitride, oxide or carbide of one or more transition metals and/or metalloids and a MCrAl coating, wherein M includes a transition metal or a metalloid, deposited on at least a portion of the diffusion barrier coating, wherein the diffusion barrier coating restricts the inward diffusion of aluminum of the MCrAl coating into the substrate.
Migration of chemotactic bacteria in soft agar: role of gel concentration.
Croze, Ottavio A; Ferguson, Gail P; Cates, Michael E; Poon, Wilson C K
2011-08-01
We study the migration of chemotactic wild-type Escherichia coli populations in semisolid (soft) agar in the concentration range C = 0.15-0.5% (w/v). For C≲0.35%, expanding bacterial colonies display characteristic chemotactic rings. At C = 0.35%, however, bacteria migrate as broad circular bands rather than sharp rings. These are growth/diffusion waves arising because of suppression of chemotaxis by the agar and have not been previously reported experimentally to our knowledge. For C = 0.4-0.5%, expanding colonies do not span the depth of the agar and develop pronounced front instabilities. The migration front speed is weakly dependent on agar concentration at C < 0.25%, but decreases sharply above this value. We discuss these observations in terms of an extended Keller-Segel model for which we derived novel transport parameter expressions accounting for perturbations of the chemotactic response by collisions with the agar. The model makes it possible to fit the observed front speed decay in the range C = 0.15-0.35%, and its solutions qualitatively reproduce the observed transition from chemotactic to growth/diffusion bands. We discuss the implications of our results for the study of bacteria in porous media and for the design of improved bacteriological chemotaxis assays. PMID:21806920
Migration of Chemotactic Bacteria in Soft Agar: Role of Gel Concentration
Croze, Ottavio A.; Ferguson, Gail P.; Cates, Michael E.; Poon, Wilson C.K.
2011-01-01
We study the migration of chemotactic wild-type Escherichia coli populations in semisolid (soft) agar in the concentration range C = 0.15–0.5% (w/v). For C≲0.35%, expanding bacterial colonies display characteristic chemotactic rings. At C = 0.35%, however, bacteria migrate as broad circular bands rather than sharp rings. These are growth/diffusion waves arising because of suppression of chemotaxis by the agar and have not been previously reported experimentally to our knowledge. For C = 0.4–0.5%, expanding colonies do not span the depth of the agar and develop pronounced front instabilities. The migration front speed is weakly dependent on agar concentration at C < 0.25%, but decreases sharply above this value. We discuss these observations in terms of an extended Keller-Segel model for which we derived novel transport parameter expressions accounting for perturbations of the chemotactic response by collisions with the agar. The model makes it possible to fit the observed front speed decay in the range C = 0.15–0.35%, and its solutions qualitatively reproduce the observed transition from chemotactic to growth/diffusion bands. We discuss the implications of our results for the study of bacteria in porous media and for the design of improved bacteriological chemotaxis assays. PMID:21806920
NASA Astrophysics Data System (ADS)
Ringermacher, Harry I.
2013-04-01
We describe an analysis of a flash thermographic method to measure thermal diffusivity that is particularly insensitive to heat loss mechanisms near thermal boundaries. This approach is an alternative to the "Parker method" which requires that a plate-like region subject to a uniform energy flux must reach a maximum constant temperature in order to obtain an accurate measurement of thermal diffusivity at the half-temperature point in time. The present approach relies on evaluating another unique point, the inflection point, of the same back-side thermal response curve as Parker's or, from the front side, using a contrast versus time curve in the sample region of interest. This inflection point occurs so early in the response history that little heat loss, for example, near heat-sink boundaries or surface convection, is expressed. Since the method is insensitive to the achieved temperature, it is also insensitive to surface emissivity variations.
Wunschel, David S.; Colburn, Heather A.; Fox, Alvin; Fox, Karen F.; Harley, William M.; Wahl, Jon H.; Wahl, Karen L.
2008-08-01
Detection of small quantities of agar associated with spores of Bacillus anthracis could provide key information regarding its source or growth characteristics. Agar, widely used in growth of bacteria on solid surfaces, consists primarily of repeating polysaccharide units of 3,6-anhydro-L-galactose (AGal) and galactose (Gal) with sulfated and O-methylated galactoses present as minor constituents. Two variants of the alditol acetate procedure were evaluated for detection of potential agar markers associated with spores. The first method employed a reductive hydrolysis step, to stabilize labile anhydrogalactose, by converting to anhydrogalactitol. The second eliminated the reductive hydrolysis step simplifying the procedure. Anhydrogalactitol, derived from agar, was detected using both derivatization methods followed by gas chromatography-mass spectrometry (GC-MS) analysis. However, challenges with artefactual background (reductive hydrolysis) or marker destruction (hydrolysis) lead to the search for alternative sugar markers. A minor agar component, 6-O-methyl galactose (6-O-M gal), was readily detected in agar-grown but not broth-grown bacteria. Detection was optimized by the use of gas chromatography-tandem mass spectrometry (GC-MS-MS). With appropriate choice of sugar marker and analytical procedure, detection of sugar markers for agar has considerable potential in microbial forensics.
Lessing, Paul A.
2008-07-22
An electrochemically active hydrogen diffusion barrier which comprises an anode layer, a cathode layer, and an intermediate electrolyte layer, which is conductive to protons and substantially impermeable to hydrogen. A catalytic metal present in or adjacent to the anode layer catalyzes an electrochemical reaction that converts any hydrogen that diffuses through the electrolyte layer to protons and electrons. The protons and electrons are transported to the cathode layer and reacted to form hydrogen. The hydrogen diffusion barrier is applied to a polymeric substrate used in a storage tank to store hydrogen under high pressure. A storage tank equipped with the electrochemically active hydrogen diffusion barrier, a method of fabricating the storage tank, and a method of preventing hydrogen from diffusing out of a storage tank are also disclosed.
Lessing, Paul A.
2004-09-07
An electrochemically active hydrogen diffusion barrier which comprises an anode layer, a cathode layer, and an intermediate electrolyte layer, which is conductive to protons and substantially impermeable to hydrogen. A catalytic metal present in or adjacent to the anode layer catalyzes an electrochemical reaction that converts any hydrogen that diffuses through the electrolyte layer to protons and electrons. The protons and electrons are transported to the cathode layer and reacted to form hydrogen. The hydrogen diffusion barrier is applied to a polymeric substrate used in a storage tank to store hydrogen under high pressure. A storage tank equipped with the electrochemically active hydrogen diffusion barrier, a method of fabricating the storage tank, and a method of preventing hydrogen from diffusing out of a storage tank are also disclosed.
Sy, Cheng Len; Huang, Tsi-Shu; Chen, Chii Shiang; Chen, Yao-Shen; Tsai, Hung-Chin; Wann, Shue-Renn; Wu, Kuan-Sheng; Chen, Jui-Kuang; Lee, Susan Shin-Jung; Liu, Yung-Ching
2016-03-01
Modified disk diffusion (MDD) and checkerboard tests were employed to assess the synergy of combinations of vancomycin and β-lactam antibiotics for 59 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and Mu50 (ATCC 700699). Bacterial inocula equivalent to 0.5 and 2.0 McFarland standard were inoculated on agar plates containing 0, 0.5, 1, and 2 μg/ml of vancomycin. Oxacillin-, cefazolin-, and cefoxitin-impregnated disks were applied to the surface, and the zones of inhibition were measured at 24 h. The CLSI-recommended checkerboard method was used as a reference to detect synergy. The MICs for vancomycin were determined using the Etest method, broth microdilution, and the Vitek 2 automated system. Synergy was observed with the checkerboard method in 51% to 60% of the isolates when vancomycin was combined with any β-lactam. The fractional inhibitory concentration indices were significantly lower in MRSA isolates with higher vancomycin MIC combinations (P < 0.05). The overall agreement between the MDD and checkerboard methods to detect synergy in MRSA isolates with bacterial inocula equivalent to McFarland standard 0.5 were 33.0% and 62.5% for oxacillin, 45.1% and 52.4% for cefazolin, and 43.1% and 52.4% for cefoxitin when combined with 0.5 and 2 μg/ml of vancomycin, respectively. Based on our study, the simple MDD method is not recommended as a replacement for the checkerboard method to detect synergy. However, it may serve as an initial screening method for the detection of potential synergy when it is not feasible to perform other labor-intensive synergy tests. PMID:26677253
An integration factor method for stochastic and stiff reaction–diffusion systems
Ta, Catherine; Wang, Dongyong; Nie, Qing
2015-08-15
Stochastic effects are often present in the biochemical systems involving reactions and diffusions. When the reactions are stiff, existing numerical methods for stochastic reaction diffusion equations require either very small time steps for any explicit schemes or solving large nonlinear systems at each time step for the implicit schemes. Here we present a class of semi-implicit integration factor methods that treat the diffusion term exactly and reaction implicitly for a system of stochastic reaction–diffusion equations. Our linear stability analysis shows the advantage of such methods for both small and large amplitudes of noise. Direct use of the method to solving several linear and nonlinear stochastic reaction–diffusion equations demonstrates good accuracy, efficiency, and stability properties. This new class of methods, which are easy to implement, will have broader applications in solving stochastic reaction–diffusion equations arising from models in biology and physical sciences.
An integration factor method for stochastic and stiff reaction-diffusion systems
NASA Astrophysics Data System (ADS)
Ta, Catherine; Wang, Dongyong; Nie, Qing
2015-08-01
Stochastic effects are often present in the biochemical systems involving reactions and diffusions. When the reactions are stiff, existing numerical methods for stochastic reaction diffusion equations require either very small time steps for any explicit schemes or solving large nonlinear systems at each time step for the implicit schemes. Here we present a class of semi-implicit integration factor methods that treat the diffusion term exactly and reaction implicitly for a system of stochastic reaction-diffusion equations. Our linear stability analysis shows the advantage of such methods for both small and large amplitudes of noise. Direct use of the method to solving several linear and nonlinear stochastic reaction-diffusion equations demonstrates good accuracy, efficiency, and stability properties. This new class of methods, which are easy to implement, will have broader applications in solving stochastic reaction-diffusion equations arising from models in biology and physical sciences.
A Hidden Pitfall in the Preparation of Agar Media Undermines Microorganism Cultivability
Tanaka, Tomohiro; Kawasaki, Kosei; Daimon, Serina; Kitagawa, Wataru; Yamamoto, Kyosuke; Tamaki, Hideyuki; Tanaka, Michiko; Nakatsu, Cindy H.
2014-01-01
Microbiologists have been using agar growth medium for over 120 years. It revolutionized microbiology in the 1890s when microbiologists were seeking effective methods to isolate microorganisms, which led to the successful cultivation of microorganisms as single clones. But there has been a disparity between total cell counts and cultivable cell counts on plates, often referred to as the “great plate count anomaly,” that has long been a phenomenon that still remains unsolved. Here, we report that a common practice microbiologists have employed to prepare agar medium has a hidden pitfall: when phosphate was autoclaved together with agar to prepare solid growth media (PT medium), total colony counts were remarkably lower than those grown on agar plates in which phosphate and agar were separately autoclaved and mixed right before solidification (PS medium). We used a pure culture of Gemmatimonas aurantiaca T-27T and three representative sources of environmental samples, soil, sediment, and water, as inocula and compared colony counts between PT and PS agar plates. There were higher numbers of CFU on PS medium than on PT medium using G. aurantiaca or any of the environmental samples. Chemical analysis of PT agar plates suggested that hydrogen peroxide was contributing to growth inhibition. Comparison of 454 pyrosequences of the environmental samples to the isolates revealed that taxa grown on PS medium were more reflective of the original community structure than those grown on PT medium. Moreover, more hitherto-uncultivated microbes grew on PS than on PT medium. PMID:25281372
Hombach, Michael; Maurer, Florian P; Pfiffner, Tamara; Böttger, Erik C; Furrer, Reinhard
2015-12-01
Parameters like zone reading, inoculum density, and plate streaking influence the precision and accuracy of disk diffusion antibiotic susceptibility testing (AST). While improved reading precision has been demonstrated using automated imaging systems, standardization of the inoculum and of plate streaking have not been systematically investigated yet. This study analyzed whether photometrically controlled inoculum preparation and/or automated inoculation could further improve the standardization of disk diffusion. Suspensions of Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213 of 0.5 McFarland standard were prepared by 10 operators using both visual comparison to turbidity standards and a Densichek photometer (bioMérieux), and the resulting CFU counts were determined. Furthermore, eight experienced operators each inoculated 10 Mueller-Hinton agar plates using a single 0.5 McFarland standard bacterial suspension of E. coli ATCC 25922 using regular cotton swabs, dry flocked swabs (Copan, Brescia, Italy), or an automated streaking device (BD-Kiestra, Drachten, Netherlands). The mean CFU counts obtained from 0.5 McFarland standard E. coli ATCC 25922 suspensions were significantly different for suspensions prepared by eye and by Densichek (P < 0.001). Preparation by eye resulted in counts that were closer to the CLSI/EUCAST target of 10(8) CFU/ml than those resulting from Densichek preparation. No significant differences in the standard deviations of the CFU counts were observed. The interoperator differences in standard deviations when dry flocked swabs were used decreased significantly compared to the differences when regular cotton swabs were used, whereas the mean of the standard deviations of all operators together was not significantly altered. In contrast, automated streaking significantly reduced both interoperator differences, i.e., the individual standard deviations, compared to the standard deviations for the manual method, and the mean of the standard deviations of all operators together, i.e., total methodological variation. PMID:26468500
A Multiresolution Method for Parameter Estimation of Diffusion Processes
Kou, S. C.; Olding, Benjamin P.; Lysy, Martin; Liu, Jun S.
2014-01-01
Diffusion process models are widely used in science, engineering and finance. Most diffusion processes are described by stochastic differential equations in continuous time. In practice, however, data is typically only observed at discrete time points. Except for a few very special cases, no analytic form exists for the likelihood of such discretely observed data. For this reason, parametric inference is often achieved by using discrete-time approximations, with accuracy controlled through the introduction of missing data. We present a new multiresolution Bayesian framework to address the inference difficulty. The methodology relies on the use of multiple approximations and extrapolation, and is significantly faster and more accurate than known strategies based on Gibbs sampling. We apply the multiresolution approach to three data-driven inference problems – one in biophysics and two in finance – one of which features a multivariate diffusion model with an entirely unobserved component. PMID:25328259
A Multiresolution Method for Parameter Estimation of Diffusion Processes.
Kou, S C; Olding, Benjamin P; Lysy, Martin; Liu, Jun S
2012-12-01
Diffusion process models are widely used in science, engineering and finance. Most diffusion processes are described by stochastic differential equations in continuous time. In practice, however, data is typically only observed at discrete time points. Except for a few very special cases, no analytic form exists for the likelihood of such discretely observed data. For this reason, parametric inference is often achieved by using discrete-time approximations, with accuracy controlled through the introduction of missing data. We present a new multiresolution Bayesian framework to address the inference difficulty. The methodology relies on the use of multiple approximations and extrapolation, and is significantly faster and more accurate than known strategies based on Gibbs sampling. We apply the multiresolution approach to three data-driven inference problems - one in biophysics and two in finance - one of which features a multivariate diffusion model with an entirely unobserved component. PMID:25328259
Thermal diffusivity measurement by lock-in photothermal shadowgraph method
NASA Astrophysics Data System (ADS)
Cifuentes, A.; Alvarado, S.; Cabrera, H.; Calderón, A.; Marín, E.
2016-04-01
Here, we present a novel application of the shadowgraph technique for obtaining the thermal diffusivity of an opaque solid sample, inspired by the orthogonal skimming photothermal beam deflection technique. This new variant utilizes the shadow projected by the sample when put against a collimated light source. The sample is then heated periodically by another light beam, giving rise to thermal waves, which propagate across it and through its surroundings. Changes in the refractive index of the surrounding media due to the heating distort the shadow. This phenomenon is recorded and lock-in amplified in order to determine the sample's thermal diffusivity.
Low density, microcellular, dopable, agar/gelatin foams for pulsed power experiments
McNamara, W.F.; Aubert, J.H.
1997-04-01
Low-density, microcellular foams prepared from the natural polymers agar and gelatin have been developed for pulsed-power physics experiments. Numerous experiments were supported with foams having densities at or below 10 mg/cm{sup 3}. For some of the experiments, the agar/gelatin foam was uniformly doped with metallic elements using soluble salts. Depending on the method of preparation, cell sizes were typically below 10 microns and for one process were below 1.0 micron.
Atomic diffusion theory challenging the Cahn-Hilliard method
NASA Astrophysics Data System (ADS)
Nastar, M.
2014-10-01
Our development of the self-consistent mean-field (SCMF) kinetic theory for nonuniform alloys leads to the statement that kinetic correlations induced by the vacancy diffusion mechanism have a dramatic effect on nanoscale diffusion phenomena, leading to nonlinear features of the interdiffusion coefficients. Lattice rate equations of alloys including nonuniform gradients of chemical potential are derived within the Bragg-Williams statistical approximation and the third shell kinetic approximation of the SCMF theory. General driving forces including deviations of the free energy from a local equilibrium thermodynamic formulation are introduced. These deviations are related to the variation of vacancy motion due to the spatial variation of the alloy composition. During the characteristic time of atomic diffusion, multiple exchanges of the vacancy with the same atoms may happen, inducing atomic kinetic correlations that depend as well on the spatial variation of the alloy composition. As long as the diffusion driving forces are uniform, the rate equations are shown to obey in this form the Onsager formalism of thermodynamics of irreversible processes (TIP) and the TIP-based Cahn-Hilliard diffusion equation. If now the chemical potential gradients are not uniform, the continuous limit of the present SCMF kinetic equations does not coincide with the Cahn-Hilliard (CH) equation. In particular, the composition gradient and higher derivative terms depending on kinetic parameters add to the CH thermodynamic-based composition gradient term. Indeed, a diffusion equation written as a mobility multiplied by a thermodynamic formulation of the driving forces is shown to be inadequate. In the reciprocal space, the thermodynamic driving force has to be multiplied by a nonlinear function of the wave vector accounting for the variation of kinetic correlations with composition inhomogeneities. Analytical expressions of the effective interdiffusion coefficient are given for two limit behaviors of the vacancy, the latter treated as either a conservative species (fixed concentration) or a nonconservative species (time-dependent equilibrium concentration). Relying on the same vacancy diffusion model, we perform kinetic Monte Carlo simulations starting from a sinusoidal composition modulation in binary model alloys, with no interaction or nearest-neighbor interactions leading to clustering or ordering tendencies, along the [100] crystallographic direction of a body centered cubic (bcc) lattice. The resulting temporal variation of the modulation amplitude is compared to the corresponding SCMF equations. Qualitative and satisfying quantitative agreements systematically strengthen our theoretical conclusions. The model alloys are shown to be representative enough of some real alloys, so that one may expect these new heterogeneous correlation effects to be non-negligible in these alloys.
Diffusion NMR methods applied to xenon gas for materials study
NASA Technical Reports Server (NTRS)
Mair, R. W.; Rosen, M. S.; Wang, R.; Cory, D. G.; Walsworth, R. L.
2002-01-01
We report initial NMR studies of (i) xenon gas diffusion in model heterogeneous porous media and (ii) continuous flow laser-polarized xenon gas. Both areas utilize the pulsed gradient spin-echo (PGSE) techniques in the gas phase, with the aim of obtaining more sophisticated information than just translational self-diffusion coefficients--a brief overview of this area is provided in the Introduction. The heterogeneous or multiple-length scale model porous media consisted of random packs of mixed glass beads of two different sizes. We focus on observing the approach of the time-dependent gas diffusion coefficient, D(t) (an indicator of mean squared displacement), to the long-time asymptote, with the aim of understanding the long-length scale structural information that may be derived from a heterogeneous porous system. We find that D(t) of imbibed xenon gas at short diffusion times is similar for the mixed bead pack and a pack of the smaller sized beads alone, hence reflecting the pore surface area to volume ratio of the smaller bead sample. The approach of D(t) to the long-time limit follows that of a pack of the larger sized beads alone, although the limiting D(t) for the mixed bead pack is lower, reflecting the lower porosity of the sample compared to that of a pack of mono-sized glass beads. The Pade approximation is used to interpolate D(t) data between the short- and long-time limits. Initial studies of continuous flow laser-polarized xenon gas demonstrate velocity-sensitive imaging of much higher flows than can generally be obtained with liquids (20-200 mm s-1). Gas velocity imaging is, however, found to be limited to a resolution of about 1 mm s-1 owing to the high diffusivity of gases compared with liquids. We also present the first gas-phase NMR scattering, or diffusive-diffraction, data, namely flow-enhanced structural features in the echo attenuation data from laser-polarized xenon flowing through a 2 mm glass bead pack. c2002 John Wiley & Sons, Ltd.
Bilal, Muhammad; Asgher, Muhammad; Shahid, Muhammad; Bhatti, Haq Nawaz
2016-05-01
Immobilization of enzymes has been regarded as an efficient approach to develop biocatalyst with improved activity and stability characteristics under reaction conditions. In the present study, purified manganese peroxidase (MnP) from Ganoderma lucidum IBL-05 was immobilized in agar-agar support using entrapment technique. Maximum immobilization yield was accomplished at 4.0% agar-agar gel. The immobilized MnP exhibited better resistance to changes in pH and temperature than the free enzyme, with optimal conditions being pH 6.0 and 50°C. The kinetic parameters Km and Kcat/Km for free and entrapped MnP were calculated to be 65.6mM and 6.99M(-1)s(-1), and 82mM and 8.15M(-1)s(-1), respectively. Thermo-stability was significantly improved after immobilization. After 120h, the insolubilized MnP retained its activity up to 71.9% and 60.3% at 30°C and 40°C, respectively. It showed activity until 10th cycle and retained 74.3% residual activity after 3th cycle. The effects of H2O2, ionic strength and potential inhibitors on activity of free and immobilized enzyme were investigated. Moreover, the decolorization of three structurally different dyes was monitored in order to assess the degrading capability of the entrapped MnP. The decolorization efficiencies for all the tested dyes were 78.6-84.7% after 12h. The studies concluded that the toxicity of dyes aqueous solutions was significantly reduced after treatment. The remarkable catalytic, thermo-stability and re-cycling features of the agar-agar immobilized MnP display a high potential for biotechnological applications. PMID:26854887
Reproducibility of the Structural Connectome Reconstruction across Diffusion Methods.
Prčkovska, Vesna; Rodrigues, Paulo; Puigdellivol Sanchez, Ana; Ramos, Marc; Andorra, Magi; Martinez-Heras, Eloy; Falcon, Carles; Prats-Galino, Albert; Villoslada, Pablo
2016-01-01
Analysis of the structural connectomes can lead to powerful insights about the brain's organization and damage. However, the accuracy and reproducibility of constructing the structural connectome done with different acquisition and reconstruction techniques is not well defined. In this work, we evaluated the reproducibility of the structural connectome techniques by performing test-retest (same day) and longitudinal studies (after 1 month) as well as analyzing graph-based measures on the data acquired from 22 healthy volunteers (6 subjects were used for the longitudinal study). We compared connectivity matrices and tract reconstructions obtained with the most typical acquisition schemes used in clinical application: diffusion tensor imaging (DTI), high angular resolution diffusion imaging (HARDI), and diffusion spectrum imaging (DSI). We observed that all techniques showed high reproducibility in the test-retest analysis (correlation >.9). However, HARDI was the only technique with low variability (2%) in the longitudinal assessment (1-month interval). The intraclass coefficient analysis showed the highest reproducibility for the DTI connectome, however, with more sparse connections than HARDI and DSI. Qualitative (neuroanatomical) assessment of selected tracts confirmed the quantitative results showing that HARDI managed to detect most of the analyzed fiber groups and fanning fibers. In conclusion, we found that HARDI acquisition showed the most balanced trade-off between high reproducibility of the connectome, higher rate of path detection and of fanning fibers, and intermediate acquisition times (10-15 minutes), although at the cost of higher appearance of aberrant fibers. PMID:26464179
Method of independently operating a group of stages within a diffusion cascade
Benedict, Manson; Fruit, Allen J.; Levey, Horace B.
1976-06-08
1. A method of operating a group of the diffusion stages of a productive diffusion cascade with countercurrent flow, said group comprising a top and a bottom stage, which comprises isolating said group from said cascade, circulating the diffused gas produced in said top stage to the feed of said bottom stage while at the same time circulating the undiffused gas from said bottom stage to the feed of said top stage whereby major changes in
Kernel weights optimization for error diffusion halftoning method
NASA Astrophysics Data System (ADS)
Fedoseev, Victor
2015-02-01
This paper describes a study to find the best error diffusion kernel for digital halftoning under various restrictions on the number of non-zero kernel coefficients and their set of values. As an objective measure of quality, WSNR was used. The problem of multidimensional optimization was solved numerically using several well-known algorithms: Nelder- Mead, BFGS, and others. The study found a kernel function that provides a quality gain of about 5% in comparison with the best of the commonly used kernel introduced by Floyd and Steinberg. Other kernels obtained allow to significantly reduce the computational complexity of the halftoning process without reducing its quality.
Volume imaging with diffuse light: method, device, and clinical application
NASA Astrophysics Data System (ADS)
Hampel, Uwe; Schleicher, Eckhard; Freyer, Richard
2000-11-01
Diffuse optical imaging and tomography is of some interest in the diagnosis of testicular pathologies. For a clinical evaluation of 3D optical tomography a special laser scanning device as well as dedicated tomography algorithms have been developed. With the device we are able to obtain continuous- wave tomographic scans from an object under investigation using different laser wavelengths. Tomographic image reconstruction is based on the solution of the linearized inverse problem of optical absorption imaging for a three- dimensional volume. Priority is given to a spatial resolution adapted volume discretization and an efficient matrix solution algorithm based on singular value decomposition.
Biological treatment of textile dyes by agar-agar immobilized consortium in a packed bed reactor.
Patel, Yogesh; Gupte, Akshaya
2015-03-01
The decolorization of Acid Maroon V was investigated using bacterial consortium EDPA containing Enterobacter dissolvens AGYP1 and Pseudomonas aeruginosa AGYP2 immobilized in different entrapment matrices. The consortium displayed 96% removal of dye (100 mg/l) within 6 h when immobilized in agar-agar. Under optimum concentrations of agar-agar (3.0% w/v) and cell biomass (0.9 g% w/v), the consortium displayed decolorization for 18 successive batches of Acid Maroon V and also decolorized 14 other different textile dyes. A packed bed reactor under batch mode showed 89% decolorization of dye after 56 repetitive cycles. Under continuous flow mode, maximum color removal was achieved with bed length of 36 cm, hydraulic retention time of 2.66 h, and dye concentration of 100 mg/l. Additionally, the reactor decolorized relatively higher concentrations (100-2000 mg/l) of dye. The synthetic dye wastewater containing five textile dyes was decolorized 92% with 62% COD reduction using an immobilized consortium. PMID:25842535
Bretscher, M.M.
1984-01-01
Simple diffusion theory cannot be used to evaluate control rod worths in thermal neutron reactors because of the strongly absorbing character of the control material. However, reliable control rod worths can be obtained within the framework of diffusion theory if the control material is characterized by a set of mesh-dependent effective diffusion parameters. For thin slab absorbers the effective diffusion parameters can be expressed as functions of a suitably-defined pair of blackness coefficients. Methods for calculating these blackness coefficients in the P/sub 1/, P/sub 3/, and P/sub 5/ approximations, with and without scattering, are presented. For control elements whose geometry does not permit a thin slab treatment, other methods are needed for determining the effective diffusion parameters. One such method, based on reaction rate ratios, is discussed.
Multiclass Data Segmentation Using Diffuse Interface Methods on Graphs.
Garcia-Cardona, Cristina; Merkurjev, Ekaterina; Bertozzi, Andrea L; Flenner, Arjuna; Percus, Allon G
2014-08-01
We present two graph-based algorithms for multiclass segmentation of high-dimensional data on graphs. The algorithms use a diffuse interface model based on the Ginzburg-Landau functional, related to total variation and graph cuts. A multiclass extension is introduced using the Gibbs simplex, with the functional's double-well potential modified to handle the multiclass case. The first algorithm minimizes the functional using a convex splitting numerical scheme. The second algorithm uses a graph adaptation of the classical numerical Merriman-Bence-Osher (MBO) scheme, which alternates between diffusion and thresholding. We demonstrate the performance of both algorithms experimentally on synthetic data, image labeling, and several benchmark data sets such as MNIST, COIL and WebKB. We also make use of fast numerical solvers for finding the eigenvectors and eigenvalues of the graph Laplacian, and take advantage of the sparsity of the matrix. Experiments indicate that the results are competitive with or better than the current state-of-the-art in multiclass graph-based segmentation algorithms for high-dimensional data. PMID:26353341
Validation of the diffusion-barrier charcoal canister method
Martz, D.E.; George, J.L.; Mamich, S.T.; Langner, G.H. Jr.
1989-05-01
A six-month study was conducted by the Technical Measurements Center, US Department of Energy Grand Junction Projects Office, to evaluate the accuracy and reliability of indoor radon measurements using an intermittent diffusion-barrier charcoal canister sampling protocol. Diffusion-barrier charcoal canisters (DBCC) were exposed for seven days in sixteen occupied residences each week during the 26-week study. The radon concentrations measured by the DBCCs were compared to radon concentrations measured by triplicate sets of four different types of alpha-track monitors and integrated hourly radon concentrations measured by a Pylon Model AB-5 continuous radon monitor. The results were also compared with radon-daughter concentrations measured in these same residences by an Eberline WLM-1 working level monitor. Excellent agreement was observed between the integrated mean radon concentrations measured by the DBCCs compared with the six-month alpha-track results, and between the weekly DBCC readings and average weekly radon concentrations measured by the Pylon radon monitors. An intermittent sampling protocol employing six weekly DBCC measurements spaced approximately every two months throughout the year should provide estimates of the average annual indoor radon concentrations that meet the criteria established for the Grand Junction Remedial Action Program. 9 refs., 17 figs., 9 tabs.
Leclercq, A.; Wanegue, C.; Baylac, P.
2002-01-01
A 24-h direct plating method for fecal coliform enumeration with a resuscitation step (preincubation for 2 h at 37 ± 1°C and transfer to 44 ± 1°C for 22 h) using fecal coliform agar (FCA) was compared with the 24-h standardized violet red bile lactose agar (VRBL) method. FCA and VRBL have equivalent specificities and sensitivities, except for lactose-positive non-fecal coliforms such as Hafnia alvei, which could form typical colonies on FCA and VRBL. Recovery of cold-stressed Escherichia coli in mashed potatoes on FCA was about 1 log unit lower than that with VRBL. When the FCA method was compared with standard VRBL for enumeration of fecal coliforms, based on counting carried out on 170 different food samples, results were not significantly different (P > 0.05). Based on 203 typical identified colonies selected as found on VRBL and FCA, the latter medium appears to allow the enumeration of more true fecal coliforms and has higher performance in certain ways (specificity, sensitivity, and negative and positive predictive values) than VRBL. Most colonies clearly identified on both media were E. coli and H. alvei, a non-fecal coliform. Therefore, the replacement of fecal coliform enumeration by E. coli enumeration to estimate food sanitary quality should be recommended. PMID:11916678
A multigrid Newton-Krylov method for flux-limited radiation diffusion
Rider, W.J.; Knoll, D.A.; Olson, G.L.
1998-09-01
The authors focus on the integration of radiation diffusion including flux-limited diffusion coefficients. The nonlinear integration is accomplished with a Newton-Krylov method preconditioned with a multigrid Picard linearization of the governing equations. They investigate the efficiency of the linear and nonlinear iterative techniques.
A fully implicit method for 3D quasi-steady state magnetic advection-diffusion.
Siefert, Christopher; Robinson, Allen Conrad
2009-09-01
We describe the implementation of a prototype fully implicit method for solving three-dimensional quasi-steady state magnetic advection-diffusion problems. This method allows us to solve the magnetic advection diffusion equations in an Eulerian frame with a fixed, user-prescribed velocity field. We have verified the correctness of method and implementation on two standard verification problems, the Solberg-White magnetic shear problem and the Perry-Jones-White rotating cylinder problem.
Experimental Verification to Obtain Intrinsic Thermal Diffusivity by Laser-Flash Method
NASA Astrophysics Data System (ADS)
Akoshima, M.; Hay, B.; Neda, M.; Grelard, M.
2013-05-01
There is a need to obtain highly reliable values of thermophysical properties. The thermal conductivity of solids is often calculated from the thermal diffusivity, specific heat, and density, respectively, measured by the laser-flash method, differential scanning calorimetry, and Archimedes' method. The laser-flash method is one of the most well-known methods for measuring the thermal diffusivity of solids above room temperature. This method is very convenient to measure the thermal diffusivity without contact in a short time. On the other hand, it is considered as an absolute reference measurement method, in particular, because only measurements of basic quantities such as time, temperature, length, and electrical quantities are required, and because the uncertainty of measurement can be analytically evaluated. However, it could be difficult in some cases to obtain reliable thermal-diffusivity values. The measurement results can indeed depend on experimental conditions; in particular, the pulse heating energy. A procedure to obtain the intrinsic thermal-diffusivity value was proposed by National Metrology Institute of Japan (NMIJ). Here, "intrinsic" means unique for the material, independent of measurement conditions. In this method, apparent thermal-diffusivity values are first measured by changing the pulse heating energy at the same test temperature. Then, the intrinsic thermal diffusivity is determined by extrapolating these apparent thermal diffusivities to a zero energy pulse. In order to verify and examine the applicability of the procedure for intrinsic thermal-diffusivity measurements, we have measured the thermal diffusivity of some materials (metals, ceramics) using the laser-flash method with this extrapolation procedure. NMIJ and Laboratoire National de Metrologie et d'essais (LNE) have laser-flash thermal-diffusivity measurement systems that are traceable to SI units. The thermal diffusivity measured by NMIJ and LNE on four materials shows good agreement, although they used different measurement systems and different analysis methods of the temperature-rise curve. Experimental verification on the procedure was carried out using the measured results. Some problems and considered solutions for laser-flash thermal-diffusivity measurements are discussed.
Poisoning with brown fly agaric, Amanita regalis.
Elonen, E; Tarssanen, L; Härkönen, M
1979-01-01
Three patients ate different amounts of a common northern mushroom, brown fly agaric, Amanita regalis. All of them believed they had eaten delicious parasol mushrooms, Macrolepiota procera. The symptoms of poisoning began 1--2 hours after ingestion of the mushrooms. All the patients had marked gastrointestinal symptoms: nausea and heavy vomiting. Two had central nervous system manifestations and cholinergic symptoms: hallucinations, confusion, or loss of consciousness as well as copious salivation, or sweating. All patients recovered within 4--24 hours without any damage to liver, kidneys or central nervous system. It seems that cooking the mushrooms does not completely neutralize the toxic agents of Amanita regalis. The analysis of fried mushrooms shows that it may be possible to identify mushrooms reliably from the remains of a meal. PMID:760400
NASA Technical Reports Server (NTRS)
Miller, Teresa Y.; He, Xiao-Min; Carter, Daniel C.
1992-01-01
Crystals of human serum albumin have been successfully grown in a variety of gels using crystallization conditions otherwise equivalent to those utilized in the popular hanging-drop vapor-equilibrium method. Preliminary comparisons of gel grown crystals with crystals grown by the vapor diffusion method via both ground-based and microgravity methods indicate that crystals superior in size and quality may be grown by limiting solutal convection. Preliminary X-ray diffraction statistics are presented.
Improving agar electrospinnability with choline-based deep eutectic solvents.
Sousa, Ana M M; Souza, Hiléia K S; Uknalis, Joseph; Liu, Shih-Chuan; Gonçalves, Maria P; Liu, LinShu
2015-09-01
Very recently our group has produced novel agar-based fibers by an electrospinning technique using water as solvent and polyvinyl alcohol (PVA) as co-blending polymer. Here, we tested the deep eutectic solvent (DES), (2-hydroxyethyl)trimethylammonium chloride/urea prepared at 1:2 molar ratio, as an alternative solvent medium for agar electrospinning. The electrospun materials were collected with an ethanol bath adapted to a previous electrospinning set-up. One weight percent agar-in-DES showed improved viscoelasticity and hence, spinnability, when compared to 1 wt% agar-in-water and pure agar nanofibers were successfully electrospun if working above the temperature of sol-gel transition (∼80 °C). By changing the solvent medium we decreased the PVA concentration (5 wt% starting solution) and successfully produced composite fibers with high agar contents (50/50 agar/PVA). Best composite fibers were formed with the 50/50 and 30/70 agar/PVA solutions. These fibers were mechanically resistant, showed tailorable surface roughness and diverse size distributions, with most of the diameters falling in the sub-micron range. Both nano and micro forms of agar fibers (used separately or combined) may have potential for the design of new and highly functional agar-based materials. PMID:26116384
Diffusion limitations of the lung - comparison of different measurement methods.
Preisser, A M; Seeber, M; Harth, V
2015-01-01
Pulmonary fibrosis leads to a decrease of oxygen diffusion, in particular during exercise. Bronchial obstruction also could decrease the partial pressure of oxygen (P(a)O(2)). In this study we investigated the validity of blood gas content, especially P(a)O(2) and P(a)O(2) affected by hyperventilation (P(a)O(2corr)) and alveolo-arterial oxygen gradient (P(A-a)O(2)) in comparison with the CO diffusion capacity (DLCO) in different lung diseases. A total of 250 subjects were studied (52.3 ± 12.5 year; F/M 40/210), among which there were 162 subjects with different lung disorders and 88 healthy controls. Pearson's correlation coefficients (r) of DLCO with P(a)O(2), P(a)O(2corr), and PA-aO(2) were analyzed in each group. The results show that the diagnostic power of P(A-a)O(2) against P(a)O(2corr) was equivalent, especially during exercise (r = -0.89 and -0.92, respectively). DLCO showed only weak correlations with P(a)O(2corr) and P(A-a)O(2) (r = 0.17 and -0.19, respectively). In conclusion, DLCO shows a better match with blood gas content during exercise than at rest during which it is routinely tested. Thus, the exercise test is advisable. The P(A-a)O(2) takes into account the level of ventilation, which makes it correlate better with DLCO rather than with blood gas content. The most significant problems in clinical evaluation of blood gas parameters during exercise are the insufficiently defined limits of normal-to-pathological range. PMID:25381558
Dingkang Zhang; Farzad Rahnema; Abderrafi M. Ougouag
2013-09-01
A local incident flux response expansion transport method is developed to generate transport solutions for coupling to diffusion theory codes regardless of their solution method (e.g., fine mesh, nodal, response based, finite element, etc.) for reactor core calculations in both two-dimensional (2-D) and three-dimensional (3-D) cylindrical geometries. In this approach, a Monte Carlo method is first used to precompute the local transport solution (i.e., response function library) for each unique transport coarse node, in which diffusion theory is not valid due to strong transport effects. The response function library is then used to iteratively determine the albedo coefficients on the diffusion-transport interfaces, which are then used as the coupling parameters within the diffusion code. This interface coupling technique allows a seamless integration of the transport and diffusion methods. The new method retains the detailed heterogeneity of the transport nodes and naturally constructs any local solution within them by a simple superposition of local responses to all incoming fluxes from the contiguous coarse nodes. A new technique is also developed for coupling to fine-mesh diffusion methods/codes. The local transport method/module is tested in 2-D and 3-D pebble-bed reactor benchmark problems consisting of an inner reflector, an annular fuel region, and a controlled outer reflector. It is found that the results predicted by the transport module agree very well with the reference fluxes calculated directly by MCNP in both benchmark problems.
Comparative study of methods used to estimate ionic diffusion coefficients using migration tests
Narsilio, G.A. Li, R. Pivonka, P. Smith, D.W.
2007-08-15
Ionic diffusion coefficients are estimated rapidly using electromigration tests. In this paper, electromigration tests are accurately simulated by numerically solving the Nernst-Planck (NP) equation (coupled with the electroneutrality condition (EN)) using the finite element method. Numerical simulations are validated against experimental data obtained elsewhere [E. Samson, J. Marchand, K.A. Snyder, Calculation of ionic diffusion coefficients on the basis of migration test results, Materials and Structures/Materiaux et Constructions 36 (257) (2003) 156-165., H. Friedmann, O. Amiri, A. Ait-Mokhtar, A direct method for determining chloride diffusion coefficient by using migration test, Cement and Concrete Research 34 (11) (2004) 1967-1973.]. It is shown that migration due to the non-linear electric potential completely overwhelms diffusion due to concentration gradients. The effects of different applied voltage differences and chloride source concentrations on estimations of chloride diffusion coefficients are explored. We show that the pore fluid within concrete and mortar specimens generally differs from the curing solution, lowering the apparent diffusion coefficient, primarily due to interactions of chloride ions with other ions in the pore fluid. We show that the variation of source chloride concentration strongly affects the estimation of diffusion coefficients in non-steady-state tests; however this effect vanishes under steady-state conditions. Most importantly, a comparison of diffusion coefficients obtained from sophisticated analyses (i.e., NP-EN) and a variety of commonly used simplifying methods to estimate chloride diffusion coefficients allows us to identify those methods and experimental conditions where both approaches deliver good estimates for chloride diffusion coefficients. Finally, we demonstrate why simultaneous use and monitoring of current density and fluxes are recommended for both the non-steady and steady-state migration tests.
A fast finite volume method for conservative space-fractional diffusion equations in convex domains
NASA Astrophysics Data System (ADS)
Jia, Jinhong; Wang, Hong
2016-04-01
We develop a fast finite volume method for variable-coefficient, conservative space-fractional diffusion equations in convex domains via a volume-penalization approach. The method has an optimal storage and an almost linear computational complexity. The method retains second-order accuracy without requiring a Richardson extrapolation. Numerical results are presented to show the utility of the method.
Laarhoven, Bob; Elissen, H J H; Temmink, H; Buisman, C J N
2016-01-01
An agar sediment test was developed to evaluate the suitability of organic waste streams from the food industry for recovering nutrients by the aquatic worm Lumbriculus variegatus (Lv). The effects of agar gel, sand, and food quantities in the sediment test on worm growth, reproduction, and water quality were studied. Agar gel addition ameliorated growth conditions by reducing food hydrolysis and altering sediment structure. Best results for combined reproduction and growth were obtained with 0.6% agar-gel (20 ml), 10 g. fine sand, 40 g. coarse sand, and 105 mg fish food (Tetramin). With agar gel, ingestion and growth is more the result of addition of food in its original quality. Final tests with secondary potato starch sludge and wheat bran demonstrated that this test is appropriate for the comparison of solid feedstuffs and suspended organic waste streams. This test method is expected to be suitable for organic waste studies using other sediment dwelling invertebrates. PMID:26937632
Laarhoven, Bob; Elissen, H. J. H.; Temmink, H.; Buisman, C. J. N.
2016-01-01
An agar sediment test was developed to evaluate the suitability of organic waste streams from the food industry for recovering nutrients by the aquatic worm Lumbriculus variegatus (Lv). The effects of agar gel, sand, and food quantities in the sediment test on worm growth, reproduction, and water quality were studied. Agar gel addition ameliorated growth conditions by reducing food hydrolysis and altering sediment structure. Best results for combined reproduction and growth were obtained with 0.6% agar-gel (20 ml), 10 g. fine sand, 40 g. coarse sand, and 105 mg fish food (Tetramin). With agar gel, ingestion and growth is more the result of addition of food in its original quality. Final tests with secondary potato starch sludge and wheat bran demonstrated that this test is appropriate for the comparison of solid feedstuffs and suspended organic waste streams. This test method is expected to be suitable for organic waste studies using other sediment dwelling invertebrates. PMID:26937632
Evaluation of CP Chromo Select Agar for the enumeration of Clostridium perfringens from water.
Manafi, Mammad; Waldherr, Kerstin; Kundi, Michael
2013-10-01
The European Directive on drinking water quality has included mCP agar as the reference method for recovering Clostridium perfringens from drinking waters. In the present study, three media (mCP, TSCF and CP Chromo Select Agar) were evaluated for recovery of C. perfringens in different surface water samples. Out of 139 water samples, using a membrane filtration technique, 131 samples (94.2%) were found to be presumptively positive for C. perfringens in at least one of the culture media. Green colored colonies on CP Chromo Select Agar (CCP agar) were counted as presumptive C. perfringens isolates. Out of 483 green colonies on CCP agar, 96.3% (465 strains, indole negative) were identified as C. perfringens, and 15 strains (3.1%) were indole positive and were identified as Clostridium sordellii, Clostridium bifermentans or Clostridium tetani. Only 3 strains (0.6%) gave false positive results and were identified as Clostridium fallax, Clostridium botulinum, and Clostridium tertium. Variance analysis of the data obtained shows statistically no significant differences in the counts obtained between media employed in this work. The mCP method is very onerous for routine screening and bacterial colonies could not be used for further biochemical testing. The colonies on CCP and TSCF were easy to count and subculture for confirmation tests. TSCF detects sulfite-reducing clostridia, including species other than C. perfringens, and in some cases excessive blackening of the agar frustrated counting of the colonies. If the contamination was too high, TSCF did not consistently produce black colonies and as a consequence, the colonies were white and gave false negative results. On the other hand, the identification of typical and atypical colonies isolated from all media demonstrated that CCP agar was the most useful medium for C. perfringens recovery in water samples. PMID:23816139
Method for measurement of diffusivity: Calorimetric studies of Fe/Ni multilayer thin films
Liu, JX; Barmak, K
2015-07-15
A calorimetric method for the measurement of diffusivity in thin film multilayers is introduced and applied to the Fe Ni system. Using this method, the diffusivity in [Fe (25 nm)/Ni (25 nm)](20) multilayer thin films is measured as 4 x 10(-3)exp(-1.6 +/- 0.1 eV/ k(B)T) cm(2)/s, respectively. The diffusion mechanism in the multilayers and its relevance to laboratory synthesis of L1(0) ordered FeNi are discussed. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Diffuse interface method for a compressible binary fluid
NASA Astrophysics Data System (ADS)
Liu, Jiewei; Amberg, Gustav; Do-Quang, Minh
2016-01-01
Multicomponent, multiphase, compressible flows are very important in real life, as well as in scientific research, while their modeling is in an early stage. In this paper, we propose a diffuse interface model for compressible binary mixtures, based on the balance of mass, momentum, energy, and the second law of thermodynamics. We show both analytically and numerically that this model is able to describe the phase equilibrium for a real binary mixture (CO2 + ethanol is considered in this paper) very well by adjusting the parameter which measures the attraction force between molecules of the two components in the model. We also show that the calculated surface tension of the CO2 + ethanol mixture at different concentrations match measurements in the literature when the mixing capillary coefficient is taken to be the geometric mean of the capillary coefficient of each component. Three different cases of two droplets in a shear flow, with the same or different concentration, are simulated, showing that the higher concentration of CO2 the smaller the surface tension and the easier the drop deforms.
Diffuse interface method for a compressible binary fluid.
Liu, Jiewei; Amberg, Gustav; Do-Quang, Minh
2016-01-01
Multicomponent, multiphase, compressible flows are very important in real life, as well as in scientific research, while their modeling is in an early stage. In this paper, we propose a diffuse interface model for compressible binary mixtures, based on the balance of mass, momentum, energy, and the second law of thermodynamics. We show both analytically and numerically that this model is able to describe the phase equilibrium for a real binary mixture (CO_{2} + ethanol is considered in this paper) very well by adjusting the parameter which measures the attraction force between molecules of the two components in the model. We also show that the calculated surface tension of the CO_{2} + ethanol mixture at different concentrations match measurements in the literature when the mixing capillary coefficient is taken to be the geometric mean of the capillary coefficient of each component. Three different cases of two droplets in a shear flow, with the same or different concentration, are simulated, showing that the higher concentration of CO_{2} the smaller the surface tension and the easier the drop deforms. PMID:26871168
Schmidt, Cleber A; Agarrayua, Danielle A; Laporta, Luciane V; Machado, Jaison C; Manfio, Maria L; Bittencourt, Celso F
2009-06-01
Cefuroxime (CFU) is a semi-synthetic cephalosporin with a relatively broad-spectrum antimicrobial activity, and belongs to the second generation of cephalosporins. Regarding the quality control of medicines, a validated microbiological assay for determination of cefuroxime sodium in pharmaceutical formulations has not been reported yet. With this purpose, this paper reports the development and validation of a simple, sensitive, accurate and reproducible agar diffusion method to quantify CFU sodium in injectable formulations. The assay is based on the inhibitory effect of CFU upon the strain of Staphylococcus aureus ATCC 6538P used as test microorganism. The results were treated statistically by analysis of variance and were found to be linear (r=0.9998) in the selected range of 8.0-32.0 microg/ml; precise [repeatability: relative standard deviation (RSD)=1.56%; intermediate precision: between-day RSD=1.27%; between analyst RSD=1.13%] and accurate (101.58%). The bioassay specificity was studied by evaluation of degraded sample at 50 degrees C with analysis at 0, 24 and 48 h in parallel with the pharmacopeial liquid chromatography method for CFU. The results demonstrated the validity of the proposed bioassay, which allows reliable quantitation of CFU sodium in pharmaceutical samples and therefore can be used as a useful alternative methodology for the routine quality control of this medicine. PMID:19344741
Martínez-Mier, E. Angeles; Soto-Rojas, Armando E.; Buckley, Christine M.; Margineda, Jorge; Zero, Domenick T.
2010-01-01
Objective The aim of this study was to assess methods currently used for analyzing fluoridated salt in order to identify the most useful method for this type of analysis. Basic research design Seventy-five fluoridated salt samples were obtained. Samples were analyzed for fluoride content, with and without pretreatment, using direct and diffusion methods. Element analysis was also conducted in selected samples. Fluoride was added to ultra pure NaCl and non-fluoridated commercial salt samples and Ca and Mg were added to fluoride samples in order to assess fluoride recoveries using modifications to the methods. Results Larger amounts of fluoride were found and recovered using diffusion than direct methods (96%–100% for diffusion vs. 67%–90% for direct). Statistically significant differences were obtained between direct and diffusion methods using different ion strength adjusters. Pretreatment methods reduced the amount of recovered fluoride. Determination of fluoride content was influenced both by the presence of NaCl and other ions in the salt. Conclusion Direct and diffusion techniques for analysis of fluoridated salt are suitable methods for fluoride analysis. The choice of method should depend on the purpose of the analysis. PMID:20088217
Determination of thermal diffusivity of opaque materials using the photothermal mirror method
NASA Astrophysics Data System (ADS)
Marcano, Aristides; Gwanmesia, Gabriel; King, Mark; Caballero, Daniel
2014-12-01
A pump-probe photothermal mirror (PTM) method has been developed to determine the thermal diffusivity of opaque solid samples. The method involves the detection of the distortion of a probe beam whose reflection profile is affected by the photoelastic deformation of a polished material surface induced by the absorption of a focused pump field. We have measured the time dependence of the PTM signal of Ti, Al, Cu, Sn, Ag, and Ni samples. We show theoretically and experimentally that the time derivative of the signal in the first microseconds is proportional to the square root of the thermal diffusivity coefficient. The method affords a simple calibration and efficient interpretation of experimental data for a sensitive determination of the thermal diffusivity coefficient for materials. We demonstrate the applicability of the technique by measuring the thermal diffusivities of wadsleyite (?-Mg2SiO4) and diopside (MgCaSi2O6), two important minerals relevant to geophysical studies.
Characterization of bionanocomposite films prepared with agar and paper-mulberry pulp nanocellulose.
Reddy, Jeevan Prasad; Rhim, Jong-Whan
2014-09-22
Crystallized nanocellulose (CNC) was separated from paper-mulberry (Broussonetia kazinoki Siebold) bast pulp by sulfuric acid hydrolysis method and they were blended with agar to prepare bionanocomposite films. The effect of CNC content (1, 3, 5 and 10 wt% based on agar) on the mechanical, water vapor permeability (WVP), and thermal properties of the nanocomposites were studied. Changes of the cellulose fibers in structure, morphology, crystallinity, and thermal properties of the films were evaluated using FT-IR, TEM, SEM, XRD, and TGA analysis methods. The CNC was composed of fibrous and spherical or elliptic granules of nano-cellulose with sizes of 50-60 nm. Properties of agar film such as mechanical and water vapor barrier properties were improved significantly (p<0.05) by blending with the CNC. The tensile modulus and tensile strength of agar film increased by 40% and 25%, respectively, in the composite film with 5 wt% of CNC, and the WVP of agar film decreased by 25% after formation of nanocomposite with 3 wt% of CNC. The CNC obtained from the paper-mulberry bast pulp can be used as a reinforcing agent for the preparation of bio-nanocomposites, and they have a high potential for the development of completely biodegradable food packaging materials. PMID:24906782
Zhao, Su; Ovadia, Jeremy; Liu, Xinfeng; Zhang, Yong-Tao; Nie, Qing
2011-01-01
For reaction-diffusion-advection equations, the stiffness from the reaction and diffusion terms often requires very restricted time step size, while the nonlinear advection term may lead to a sharp gradient in localized spatial regions. It is challenging to design numerical methods that can efficiently handle both difficulties. For reaction-diffusion systems with both stiff reaction and diffusion terms, implicit integration factor (IIF) method and its higher dimensional analog compact IIF (cIIF) serve as an efficient class of time-stepping methods, and their second order version is linearly unconditionally stable. For nonlinear hyperbolic equations, weighted essentially non-oscillatory (WENO) methods are a class of schemes with a uniformly high-order of accuracy in smooth regions of the solution, which can also resolve the sharp gradient in an accurate and essentially non-oscillatory fashion. In this paper, we couple IIF/cIIF with WENO methods using the operator splitting approach to solve reaction-diffusion-advection equations. In particular, we apply the IIF/cIIF method to the stiff reaction and diffusion terms and the WENO method to the advection term in two different splitting sequences. Calculation of local truncation error and direct numerical simulations for both splitting approaches show the second order accuracy of the splitting method, and linear stability analysis and direct comparison with other approaches reveals excellent efficiency and stability properties. Applications of the splitting approach to two biological systems demonstrate that the overall method is accurate and efficient, and the splitting sequence consisting of two reaction-diffusion steps is more desirable than the one consisting of two advection steps, because CWC exhibits better accuracy and stability. PMID:21666863
Thermal Diffusivity of Sintered Steels with Flash Method at Ambient Temperature
NASA Astrophysics Data System (ADS)
Bocchini, G. F.; Bovesecchi, G.; Coppa, P.; Corasaniti, S.; Montanari, R.; Varone, A.
2016-04-01
Due to lack of reliable thermal diffusivity data of sintered steels in literature, experimental investigations were conducted on samples made of different powder types (based on prealloyed, or diffusion-bonded, or admixed powders) and under different process conditions. So the influence of pressing pressure and sintering temperature on thermal diffusivity was established. Thermal diffusivity was measured using the "flash method": a sample in the shape of a slab is irradiated with a light pulse on one of the two surfaces, and temperature of the other surface is detected by an ambient temperature pyrometer. The value of the thermal diffusivity is obtained by a least squares regression on the entire trend of the temperature vs. time using the analytical solution of the heat conduction as regression model. Results show the increase of the thermal diffusivity with increasing density. This outcome can be explained from the mutual effect of thermal conductivity and density on thermal diffusivity in porous media. The experimental results have also permitted to verify the influence of the composition of the sintered materials and carbon contents on thermal diffusivity.
NASA Astrophysics Data System (ADS)
Wang, Hong; Du, Ning
2014-02-01
Fractional diffusion equations model phenomena exhibiting anomalous diffusion that cannot be modeled accurately by second-order diffusion equations. Because of the nonlocal property of fractional differential operators, numerical methods for space-fractional diffusion equations generate dense or even full coefficient matrices with complicated structures. Traditionally, these methods were solved via Gaussian elimination, which requires computational work of O(N3) per time step and O(N2) of memory to store where N is the number of spatial grid points in the discretization. The significant computational work and memory requirement of these methods makes a numerical simulation of three-dimensional space-fractional diffusion equations computationally prohibitively expensive. We present an alternating-direction implicit (ADI) finite difference formulation for space-fractional diffusion equations in three space dimensions and prove its unconditional stability and convergence rate provided that the fractional partial difference operators along x-, y-, z-directions commute. We base on the ADI formulation to develop a fast iterative ADI finite difference method, which has a computational work count of O(Nlog N) per iteration at each time step and a memory requirement of O(N). We also develop a fast multistep ADI finite difference method, which has a computational work count of O(Nlog2 N) per time step and a memory requirement of O(Nlog N). Numerical experiments of a three-dimensional space-fractional diffusion equation show that these both fast methods retain the same accuracy as the regular three-dimensional implicit finite difference method, but have significantly improved computational cost and memory requirement. These numerical experiments show the utility of the fast method.
Tsuboyama-Tanaka, Shoko; Kodama, Yutaka
2015-03-01
The dioecious liverwort, Marchantia polymorpha L., is an emerging model plant. Various molecular biological techniques have been optimized for M. polymorpha for the past several years, and recently we reported a simplified Agrobacterium-mediated transformation method using sporelings (immature thalli from spores) of M. polymorpha. This method, termed AgarTrap (Agar-utilized Transformation with Pouring Solutions), completed by exchanging appropriate solutions on a single Petri dish to produce a sufficient number of independent transgenic sporelings. However, because spores are produced by crosses between males and females, the genetic backgrounds of resulting transgenic sporelings are not uniform. To easily produce transgenic liverworts with a uniform genetic background using AgarTrap, we developed an AgarTrap-mediated transformation method using intact gemmae/gemmalings produced by asexual reproduction. Using AgarTrap with male and female gemmae/gemmalings produced a sufficient number of independent transgenic gemmalings with uniform genetic backgrounds. The optimized transformation efficiencies were approximately 30 and 50 % in males and females, respectively. As with AgarTrap using sporelings, AgarTrap using intact gemmae/gemmalings will be useful in promoting studies of the molecular biology of M. polymorpha. PMID:25663453
Study of acid diffusion behaves form PAG by using top coat method
NASA Astrophysics Data System (ADS)
Sekiguchi, Atsushi; Matsumoto, Yoko
2014-03-01
Our past research on measurements of simulation parameters for ArF resists focused on establishing methods for measuring the following parameters:[1]-[4] • Development parameters[1] • PEB parameters[2] • Dill's ABC parameters[3] • Quencher parameter[4] We entered these parameters into a lithography simulator and performed ArF resist simulations.We then explored ways to optimize the ArF resist material and process. This paper reports on our study of methods for measuring the diffusion length of acid generated from PAG during exposures. In our experiment, we applied a PAG-containing top coat (TC) material (second layer) to a PAG-free ArF resist (first layer), then performed the exposure and PEB processes. The acid generated in the TC during the exposure diffused into the ArF resist in the lower layer (first layer) when PEB was performed. The process of developing this sample removed the TC in the second layer and the parts of the first layer into which the acid had diffused.We obtained the acid diffusion length based on the quantity of film removed by the development. We calculated the acid diffusion coefficient after varying the exposure value and repeating the measurement. For this report, we also performed measurements to determine how differences in PAG anion size, amount of quencher additive, and PEB temperature affected the acid diffusion coefficient.We entered the measurements obtained into the PROLITH simulator and explored the effects of acid diffusion on pattern profile.
A coarse-mesh nodal method-diffusive-mesh finite difference method
Joo, H.; Nichols, W.R.
1994-05-01
Modern nodal methods have been successfully used for conventional light water reactor core analyses where the homogenized, node average cross sections (XSs) and the flux discontinuity factors (DFs) based on equivalence theory can reliably predict core behavior. For other types of cores and other geometries characterized by tightly-coupled, heterogeneous core configurations, the intranodal flux shapes obtained from a homogenized nodal problem may not accurately portray steep flux gradients near fuel assembly interfaces or various reactivity control elements. This may require extreme values of DFs (either very large, very small, or even negative) to achieve a desired solution accuracy. Extreme values of DFs, however, can disrupt the convergence of the iterative methods used to solve for the node average fluxes, and can lead to a difficulty in interpolating adjacent DF values. Several attempts to remedy the problem have been made, but nothing has been satisfactory. A new coarse-mesh nodal scheme called the Diffusive-Mesh Finite Difference (DMFD) technique, as contrasted with the coarse-mesh finite difference (CMFD) technique, has been developed to resolve this problem. This new technique and the development of a few-group, multidimensional kinetics computer program are described in this paper.
The Diffusion of Evaluation Methods among Public Relations Practitioners.
ERIC Educational Resources Information Center
Dozier, David M.
A study explored the relationships between public relations practitioners' organizational roles and the type of evaluation methods they used on the job. Based on factor analysis of role data obtained from an earlier study, four organizational roles were defined and ranked: communication manager, media relations specialist, communication liaison,…
Practical method of diffusion-welding steel plate in air
NASA Technical Reports Server (NTRS)
Holko, K. H.; Moore, T. J.
1971-01-01
Method is ideal for critical service requirements where parent metal properties are equaled in notch toughness, stress rupture and other characteristics. Welding technique variations may be used on a variety of materials, such as carbon steels, alloy steels, stainless steels, ceramics, and reactive and refractory materials.
Method of applying a cerium diffusion coating to a metallic alloy
Jablonski, Paul D.; Alman, David E.
2009-06-30
A method of applying a cerium diffusion coating to a preferred nickel base alloy substrate has been discovered. A cerium oxide paste containing a halide activator is applied to the polished substrate and then dried. The workpiece is heated in a non-oxidizing atmosphere to diffuse cerium into the substrate. After cooling, any remaining cerium oxide is removed. The resulting cerium diffusion coating on the nickel base substrate demonstrates improved resistance to oxidation. Cerium coated alloys are particularly useful as components in a solid oxide fuel cell (SOFC).
Microscopic derivation of causal diffusion equation using the projection operator method.
Koide, T
2005-08-01
We derive a coarse-grained equation of motion of a number density by applying the projection operator method to a non-relativistic model. The derived equation is an integrodifferential equation and contains the memory effect. The equation is consistent with causality and the sum rule associated with the number conservation in the low momentum limit, in contrast to usual acausal diffusion equations given by using the Fick's law. After employing the Markov approximation, we find that the equation has the similar form to the causal diffusion equation. Our result suggests that current-current correlations are not necessarily adequate as the definition of diffusion constants. PMID:16196672
Novel and Simple Screening Methods for Protein Crystallization by Vapor Diffusion Rate Control
NASA Astrophysics Data System (ADS)
Adachi, Hiroaki; Niino, Ai; Matsumura, Hiroyoshi; Takano, Kazufumi; Inoue, Tsuyoshi; Mori, Yusuke; Sasaki, Takatomo
2004-09-01
We investigated the effect of the vapor diffusion rate on the refinement of protein crystals. The reservoir volume, drop-to-reservoir distance, and air space were altered to change the vapor diffusion rate using a very dense insoluble liquid and specific crystallization plates. The experimental results reveal that the drop-to-reservoir distance and air space have a more significant effect on crystal growth than the reservoir volume. We propose new simple and useful methods for screening protein crystal growth conditions based on vapor diffusion rate control.
A test, using atmospheric data, of a method for estimating oceanic eddy diffusivity
NASA Astrophysics Data System (ADS)
Kushner, Paul J.; Held, Isaac M.
G. Holloway has proposed a simple method to estimate the effective horizontal eddy diffusivity for oceanic tracers using satellite measurements of sea-surface height variability. In this method, the diffusivity is assumed to scale as the r.m.s. eddy geostrophic streamfunction. This method should apply analogously in an atmospheric context, in which the energetic eddies are well resolved in data sets and models, and in which both the effective diffusivity and tracer fluxes can be directly calculated. We evaluate Holloway's method using lower-tropospheric daily atmospheric reanalysis data, and find that at a given height the method succesfully yields estimates of the divergent part of the atmospheric sensible heat flux, to within a fairly uniform scaling factor.
A new method of optimal design for a two-dimensional diffuser by using dynamic programming
NASA Technical Reports Server (NTRS)
Gu, Chuangang; Zhang, Moujin; Chen, XI; Miao, Yongmiao
1991-01-01
A new method for predicting the optimal velocity distribution on the wall of a two dimensional diffuser is presented. The method uses dynamic programming to solve the optimal control problem with inequality constraints of state variables. The physical model of optimization is designed to prevent the separation of the boundary layer while approaching the maximum pressure ratio in a diffuser of a specified length. The computational results are in fair agreement with the experimental ones. Optimal velocity distribution on a diffuser wall is said to occur when the flow decelerates quickly at first and then smoothly, while the flow is near separation, but always protected from it. The optimal velocity distribution can be used to design the contour of the diffuser.
First-Order Hyperbolic System Method for Time-Dependent Advection-Diffusion Problems
NASA Technical Reports Server (NTRS)
Mazaheri, Alireza; Nishikawa, Hiroaki
2014-01-01
A time-dependent extension of the first-order hyperbolic system method for advection-diffusion problems is introduced. Diffusive/viscous terms are written and discretized as a hyperbolic system, which recovers the original equation in the steady state. The resulting scheme offers advantages over traditional schemes: a dramatic simplification in the discretization, high-order accuracy in the solution gradients, and orders-of-magnitude convergence acceleration. The hyperbolic advection-diffusion system is discretized by the second-order upwind residual-distribution scheme in a unified manner, and the system of implicit-residual-equations is solved by Newton's method over every physical time step. The numerical results are presented for linear and nonlinear advection-diffusion problems, demonstrating solutions and gradients produced to the same order of accuracy, with rapid convergence over each physical time step, typically less than five Newton iterations.
Kruk, D; Meier, R; Rössler, E A
2012-02-01
By application of the field-cycling technique, we measure the dispersion of the (1)H nuclear magnetic resonance (NMR) spin-lattice relaxation time T(1)(ω) for a series of molecular liquids. We demonstrate that such NMR relaxometry studies can be used for determining diffusion coefficients. A broad frequency range of 10 kHz-20 MHz is covered. By scanning T(1)(ω) one directly probes the spectral density of the diffusion processes. The value of the diffusion coefficient D can be determined from a linear dependence of the (1)H spin-lattice relaxation rate on the square root of the frequency at which it is measured. The power of this method lies in its simplicity, which allows one to determine D(T) independently of the diffusive model. The results obtained are in very good agreement with those of field gradient NMR methods. PMID:22463139
NASA Astrophysics Data System (ADS)
Ziemys, A.; Kojic, M.; Milosevic, M.; Kojic, N.; Hussain, F.; Ferrari, M.; Grattoni, A.
2011-06-01
We present a successful hierarchical modeling approach which accounts for interface effects on diffusivity, ignored in classical continuum theories. A molecular dynamics derived diffusivity scaling scheme is incorporated into a finite element method to model transport through a nanochannel. In a 5 nm nanochannel, the approach predicts 2.2 times slower mass release than predicted by Fick's law by comparing time spent to release 90% of mass. The scheme was validated by predicting experimental glucose diffusion through a nanofluidic membrane with a correlation coefficient of 0.999. Comparison with experiments through a nanofluidic membrane showed interface effects to be crucial. We show robustness of our discrete continuum model in addressing complex diffusion phenomena in biomedical and engineering applications by providing flexible hierarchical coupling of molecular scale effects and preserving computational finite element method speed.
Diffusion-based method for producing density-equalizing maps
Gastner, Michael T.; Newman, M. E. J.
2004-01-01
Map makers have for many years searched for a way to construct cartograms, maps in which the sizes of geographic regions such as countries or provinces appear in proportion to their population or some other analogous property. Such maps are invaluable for the representation of census results, election returns, disease incidence, and many other kinds of human data. Unfortunately, to scale regions and still have them fit together, one is normally forced to distort the regions' shapes, potentially resulting in maps that are difficult to read. Many methods for making cartograms have been proposed, some of them are extremely complex, but all suffer either from this lack of readability or from other pathologies, like overlapping regions or strong dependence on the choice of coordinate axes. Here, we present a technique based on ideas borrowed from elementary physics that suffers none of these drawbacks. Our method is conceptually simple and produces useful, elegant, and easily readable maps. We illustrate the method with applications to the results of the 2000 U.S. presidential election, lung cancer cases in the State of New York, and the geographical distribution of stories appearing in the news. PMID:15136719
Method of fluxless brazing and diffusion bonding of aluminum containing components
NASA Technical Reports Server (NTRS)
Featherston, A. B.; Okelly, K. P. (Inventor)
1976-01-01
A method of diffusion bonding and fluxless brazing of aluminum containing components is reported. The aluminum surfaces are freed of any aluminum oxide coating and are coated with a polymeric sealer which can be thermally removed leaving essentially no residue. The polymeric sealer is being removed in a substantially oxygen free environment, and the aluminum components are then being brazed or diffusion bonded without the use of a flux to remove oxide coating.
Kanmani, Paulraj; Rhim, Jong-Whan
2014-02-15
The use of synthetic petroleum based packaging films caused serious environmental problems due to their difficulty in recycling and poor biodegradability. Therefore, present study was aimed to develop natural biopolymer-based antimicrobial packaging films as an alternative for the synthetic packaging films. As a natural antimicrobial agent, grapefruit seed extract (GSE) has been incorporated into agar to prepare antimicrobial packaging film. The films with different concentrations of GSE were prepared by a solvent casting method and the resulting composite films were examined physically and mechanically. In addition, the films were characterized by FE-SEM, XRD, FT-IR and TGA. The incorporation of GSE caused increase in color, UV barrier, moisture content, water solubility and water vapor permeability, while decrease in surface hydrophobicity, tensile strength and elastic modulus of the films. As the concentration of GSE increased from 0.6 to 13.3 μg/mL, the physical and mechanical properties of the films were affected significantly. The addition of GSE changed film microstructure of the film, but did not influence the crystallinity of agar and thermal stability of the agar-based films. The agar/GSE films exhibited distinctive antimicrobial activity against three test food pathogens, such as Listeria monocytogenes, Bacillus cereus and Escherichia coli. These results suggest that agar/GSE films have potential to be used in an active food packaging systems for maintaining food safety and extending the shelf-life of the packaged food. PMID:24507339
An adaptive pseudo-spectral method for reaction diffusion problems
NASA Technical Reports Server (NTRS)
Bayliss, A.; Matkowsky, B. J.; Gottlieb, D.; Minkoff, M.
1989-01-01
The spectral interpolation error was considered for both the Chebyshev pseudo-spectral and Galerkin approximations. A family of functionals I sub r (u), with the property that the maximum norm of the error is bounded by I sub r (u)/J sub r, where r is an integer and J is the degree of the polynomial approximation, was developed. These functionals are used in the adaptive procedure whereby the problem is dynamically transformed to minimize I sub r (u). The number of collocation points is then chosen to maintain a prescribed error bound. The method is illustrated by various examples from combustion problems in one and two dimensions.
A novel chromogenic ester agar medium for detection of Salmonellae.
Cooke, V M; Miles, R J; Price, R G; Richardson, A C
1999-02-01
A novel agar medium, chromogenic Salmonella esterase (CSE) agar, for the differentiation of salmonellae is described. The agar contains peptones and nutrient extracts together with the following (grams per liter unless otherwise specified): 4-[2-(4-octanoyloxy-3, 5-dimethoxyphenyl)-vinyl]-quinolinium-1-(propan-3-yl carboxylic acid) bromide (SLPA-octanoate; bromide form), 0.3223; lactose, 14. 65; trisodium citrate dihydrate, 0.5; Tween 20, 3.0; ethyl 4-dimethylaminobenzoate, 0.035% (wt/vol), novobiocin, 70 mg liter-1. The key component of the medium is SLPA-octanoate, a newly synthesized ester formed from a C8 fatty acid and a phenolic chromophore. In CSE agar, the ester is hydrolyzed by Salmonella spp. to yield a brightly colored phenol which remains tightly bound within colonies. After 24 h of incubation at 37 or 42 degreesC, colonies of typical Salmonella spp. were burgundy colored on a transparent yellow background, whereas non-Salmonella spp. were white, cream, yellow or transparent. CSE agar was evaluated by using a panel of strains including a high proportion of Salmonella and non-Salmonella strains giving atypical reactions on other differential agars. The sensitivity (93.1%) of CSE agar for non-typhi salmonellae compared favorably with those of Rambach (82. 8%), xylose-lysine-deoxycholate (XLD; 91.4%), Hektoen-enteric (89.7%), and SM ID (91.4%) agars. The specificity (93.9%) was also comparable to those of other Salmonella media (SM ID agar, 95.9%; Rambach agar, 91.8%; XLD agar, 91.8%; Hektoen-enteric agar, 87.8%). Strains of Citrobacter freundii and Proteus spp. giving false-positive reactions with other media gave a negative color reaction on CSE agar. CSE agar enabled the detection of >30 Salmonella serotypes, including agona, anatum, enteritidis, hadar, heidelberg, infantis, montevideo, thompson, typhimurium, and virchow, which accounted for 91.8% of the salmonella isolates recorded by the Public Health Laboratory Service (Colindale, London, England) for 1997. PMID:9925620
A Novel Chromogenic Ester Agar Medium for Detection of Salmonellae
Cooke, Venitia M.; Miles, R. J.; Price, R. G.; Richardson, A. C.
1999-01-01
A novel agar medium, chromogenic Salmonella esterase (CSE) agar, for the differentiation of salmonellae is described. The agar contains peptones and nutrient extracts together with the following (grams per liter unless otherwise specified): 4-[2-(4-octanoyloxy-3,5-dimethoxyphenyl)-vinyl]-quinolinium-1-(propan-3-yl carboxylic acid) bromide (SLPA-octanoate; bromide form), 0.3223; lactose, 14.65; trisodium citrate dihydrate, 0.5; Tween 20, 3.0; ethyl 4-dimethylaminobenzoate, 0.035% (wt/vol), novobiocin, 70 mg liter?1. The key component of the medium is SLPA-octanoate, a newly synthesized ester formed from a C8 fatty acid and a phenolic chromophore. In CSE agar, the ester is hydrolyzed by Salmonella spp. to yield a brightly colored phenol which remains tightly bound within colonies. After 24 h of incubation at 37 or 42C, colonies of typical Salmonella spp. were burgundy colored on a transparent yellow background, whereas non-Salmonella spp. were white, cream, yellow or transparent. CSE agar was evaluated by using a panel of strains including a high proportion of Salmonella and non-Salmonella strains giving atypical reactions on other differential agars. The sensitivity (93.1%) of CSE agar for non-typhi salmonellae compared favorably with those of Rambach (82.8%), xylose-lysine-deoxycholate (XLD; 91.4%), Hektoen-enteric (89.7%), and SM ID (91.4%) agars. The specificity (93.9%) was also comparable to those of other Salmonella media (SM ID agar, 95.9%; Rambach agar, 91.8%; XLD agar, 91.8%; Hektoen-enteric agar, 87.8%). Strains of Citrobacter freundii and Proteus spp. giving false-positive reactions with other media gave a negative color reaction on CSE agar. CSE agar enabled the detection of >30 Salmonella serotypes, including agona, anatum, enteritidis, hadar, heidelberg, infantis, montevideo, thompson, typhimurium, and virchow, which accounted for 91.8% of the salmonella isolates recorded by the Public Health Laboratory Service (Colindale, London, England) for 1997. PMID:9925620
Selected elements in fly agaric Amanita muscaria.
Falandysz, J; Kunito, T; Kubota, R; Lipka, K; Mazur, A; Falandysz, Justyna J; Tanabe, S
2007-09-01
Concentrations of Ag, Al, Ba, Ca, Cd, Co, Cu, Cr, Cs, Fe, Ga, Hg, K, Mg, Mn, Mo, Na, Pb, Rb, Se, Sb, Sr, V, Tl and Zn have been determined in the whole fruiting bodies, as well as separately in caps and stalks, of fly agaric collected from three geographically distant sites in northern part of Poland. The elements were determined using ICP-MS, ICP-OES, HG-AAS and CV-AAS, respectively. For elements such as Al, Ba, Cr, Fe, Ga, Mo, Mn, Pb, Sb, Sr, Tl, and V concentrations were similar in the caps and stalks, respectively, and for K, Zn, Ag, Ca, Cd, Cu, Hg, Mg, Rb and Se were greater in the caps, while for Co, Cs and Na in the stalks. For Ag, Al, Ba, Ca, Cd, Co, Cr, Cs, Fe, Ga, Hg, Mn, Mo, Pb, Rb, Sb, Sr, Tl and V concentration in the caps showed spatial variations (P<0.05), while for Cu, K, Mg, Na, Se and Zn was independent of the site. The elements such as K with median or mean in the caps between 37,000 and 43,000 microg/g.dm and Mg with 920 and 1,100 microg/g dm were most abundant. Next, within median values range from approximately 100 to 500 microg/g dm were such as Ca, Fe and Al, and in descending order they followed by Rb (100-400 microg/g dm); V, Na, Zn (50-200 microg/g dm); Cu, Mn (10-50 microg/g dm); Cd (10-20 microg/g dm); Se (5 microg/g dm); Ba (<1-3); Cr, Ag, Pb, Sr (<1-2 microg/g dm); Cs, Co, Hg (<1-1 microg/g dm); Ga (<0.5), Sb, Mo and Tl (<0.1 microg/g dm). PMID:17849303
Accelerated molecular dynamics and equation-free methods for simulating diffusion in solids.
Deng, Jie; Zimmerman, Jonathan A.; Thompson, Aidan Patrick; Brown, William Michael; Plimpton, Steven James; Zhou, Xiao Wang; Wagner, Gregory John; Erickson, Lindsay Crowl
2011-09-01
Many of the most important and hardest-to-solve problems related to the synthesis, performance, and aging of materials involve diffusion through the material or along surfaces and interfaces. These diffusion processes are driven by motions at the atomic scale, but traditional atomistic simulation methods such as molecular dynamics are limited to very short timescales on the order of the atomic vibration period (less than a picosecond), while macroscale diffusion takes place over timescales many orders of magnitude larger. We have completed an LDRD project with the goal of developing and implementing new simulation tools to overcome this timescale problem. In particular, we have focused on two main classes of methods: accelerated molecular dynamics methods that seek to extend the timescale attainable in atomistic simulations, and so-called 'equation-free' methods that combine a fine scale atomistic description of a system with a slower, coarse scale description in order to project the system forward over long times.
Method of fabricating reflection-mode EUV diffusers
Anderson, Erik; Naulleau, Patrick P.
2005-03-01
Techniques for fabricating well-controlled, random relief, engineered surfaces that serve as substrates for EUV optical devices are accomplished with grayscale exposure. The method of fabricating a multilevel EUV optical element includes: (a) providing a substrate; (b) depositing a layer of curable material on a surface of the substrate; (c) creating a relief profile in a layer of cured material from the layer of curable material wherein the relief profile comprises multiple levels of cured material that has a defined contour; and (d) depositing a multilayer reflection film over the relief profile wherein the film has an outer contour that substantially matches that of the relief profile. The curable material can comprise photoresist or a low dielectric constant material.
Advanced computational methods for nodal diffusion, Monte Carlo, and S(sub N) problems
NASA Astrophysics Data System (ADS)
Martin, W. R.
1993-01-01
This document describes progress on five efforts for improving effectiveness of computational methods for particle diffusion and transport problems in nuclear engineering: (1) Multigrid methods for obtaining rapidly converging solutions of nodal diffusion problems. An alternative line relaxation scheme is being implemented into a nodal diffusion code. Simplified P2 has been implemented into this code. (2) Local Exponential Transform method for variance reduction in Monte Carlo neutron transport calculations. This work yielded predictions for both 1-D and 2-D x-y geometry better than conventional Monte Carlo with splitting and Russian Roulette. (3) Asymptotic Diffusion Synthetic Acceleration methods for obtaining accurate, rapidly converging solutions of multidimensional SN problems. New transport differencing schemes have been obtained that allow solution by the conjugate gradient method, and the convergence of this approach is rapid. (4) Quasidiffusion (QD) methods for obtaining accurate, rapidly converging solutions of multidimensional SN Problems on irregular spatial grids. A symmetrized QD method has been developed in a form that results in a system of two self-adjoint equations that are readily discretized and efficiently solved. (5) Response history method for speeding up the Monte Carlo calculation of electron transport problems. This method was implemented into the MCNP Monte Carlo code. In addition, we have developed and implemented a parallel time-dependent Monte Carlo code on two massively parallel processors.
A High-Order Upwind Method for Convection-Diffusion Equations with the Newmann Boundary Condition
NASA Astrophysics Data System (ADS)
Zhao, Weidong
In this paper a high-order upwind finite difference method is studied for steady convection-diffusion problems with the Newmann boundary condition. Based on these equations in the conservation form, a conservative high-order upwind finite difference scheme on nonuniform rectangular partition is proposed. The scheme satisfies the maximum value principle and has a second-order error estimate in the discrete H1 norm. The method and its analysis apply to groundwater pollution and reservoir simulation problems. Keywords: convection-diffusion, high-order upwind method, error estimate
A First-Passage Kinetic Monte Carlo method for reaction–drift–diffusion processes
Mauro, Ava J.; Sigurdsson, Jon Karl; Shrake, Justin; Atzberger, Paul J.; Isaacson, Samuel A.
2014-02-15
Stochastic reaction–diffusion models are now a popular tool for studying physical systems in which both the explicit diffusion of molecules and noise in the chemical reaction process play important roles. The Smoluchowski diffusion-limited reaction model (SDLR) is one of several that have been used to study biological systems. Exact realizations of the underlying stochastic processes described by the SDLR model can be generated by the recently proposed First-Passage Kinetic Monte Carlo (FPKMC) method. This exactness relies on sampling analytical solutions to one and two-body diffusion equations in simplified protective domains. In this work we extend the FPKMC to allow for drift arising from fixed, background potentials. As the corresponding Fokker–Planck equations that describe the motion of each molecule can no longer be solved analytically, we develop a hybrid method that discretizes the protective domains. The discretization is chosen so that the drift–diffusion of each molecule within its protective domain is approximated by a continuous-time random walk on a lattice. New lattices are defined dynamically as the protective domains are updated, hence we will refer to our method as Dynamic Lattice FPKMC or DL-FPKMC. We focus primarily on the one-dimensional case in this manuscript, and demonstrate the numerical convergence and accuracy of our method in this case for both smooth and discontinuous potentials. We also present applications of our method, which illustrate the impact of drift on reaction kinetics.
Hiraguchi, Hisako; Nakagawa, Hisami; Kaketani, Masahiro; Hirose, Hideharu; Nishiyama, Minoru
2007-05-01
This study investigated the effects of disinfection of combined agar/alginate impressions on the dimensional accuracy of resultant stone casts. Impressions of a master cast designed to simulate an abutment tooth were prepared by combining each of two brands of cartridge-form agar impression materials with an alginate impression material. The impressions were immersed in 1% sodium hypochlorite for 10 minutes or 2% glutaraldehyde for 30 minutes. The remaining impressions were sprayed with these two disinfectants and then stored in sealed bags for 10, 30, 60, and 120 minutes. Stone casts obtained from the non-disinfected impressions were also prepared as control. Changes in diameter of the stone casts were then measured. Results indicated that storage for 10 minutes after spraying with 1% sodium hypochlorite was an appropriate disinfection method for combined agar/alginate impressions, as well as immersion in 1% sodium hypochlorite for 10 minutes. PMID:17694758
Hoffmann, Thomas; Dorrestein, Pieter C
2015-11-01
Matrix deposition on agar-based microbial colonies for MALDI imaging mass spectrometry is often complicated by the complex media on which microbes are grown. This Application Note demonstrates how consecutive short spray pulses of a matrix solution can form an evenly closed matrix layer on dried agar. Compared with sieving dry matrix onto wet agar, this method supports analyte cocrystallization, which results in significantly more signals, higher signal-to-noise ratios, and improved ionization efficiency. The even matrix layer improves spot-to-spot precision of measured m/z values when using TOF mass spectrometers. With this technique, we established reproducible imaging mass spectrometry of myxobacterial cultures on nutrient-rich cultivation media, which was not possible with the sieving technique. Graphical Abstract ᅟ. PMID:26297185
FUJIHARA, Masatoshi; TABUCHI, Hiroyuki; UEGAKI, Kaho
2015-01-01
To determine the appropriate method for isolating Salmonella enterica, we compared the growth of S. enterica serovars using three selective enrichment media. S. enterica was more successfully isolated from artificially contaminated fecal samples after enrichment in Hajna tetrathionate broth or modified semisolid Rappaport agar than in Rappaport broth. Since most bacteria (other than motile S. enterica) do not migrate on modified semisolid Rappaport agar, the growth characteristics of S. enterica can be interpreted easily and quickly. Two S. enterica isolates did not migrate on modified semisolid Rappaport agar, but did grow in Hajna tetrathionate broth, which suggests that the combined use of these selective enrichment media is appropriate for isolating S. enterica. PMID:26498402
NASA Astrophysics Data System (ADS)
Hoffmann, Thomas; Dorrestein, Pieter C.
2015-11-01
Matrix deposition on agar-based microbial colonies for MALDI imaging mass spectrometry is often complicated by the complex media on which microbes are grown. This Application Note demonstrates how consecutive short spray pulses of a matrix solution can form an evenly closed matrix layer on dried agar. Compared with sieving dry matrix onto wet agar, this method supports analyte cocrystallization, which results in significantly more signals, higher signal-to-noise ratios, and improved ionization efficiency. The even matrix layer improves spot-to-spot precision of measured m/z values when using TOF mass spectrometers. With this technique, we established reproducible imaging mass spectrometry of myxobacterial cultures on nutrient-rich cultivation media, which was not possible with the sieving technique.
Walker Diffusion Method for Calculation of Transport Properties of Finite Composite Systems
Van Siclen, Clinton D
2002-01-01
A heterogeneous medium may be represented by a scalar field of local transport coefficients (e.g., conductivity) or by a resistor network derived from that scalar field. In either case the effective (macroscopic) and local (microscopic) transport properties may be calculated by the walker diffusion method. Some sample calculations for disordered systems are presented to demonstrate the method.
The Galerkin/least-squares method for advective-diffusive equations
NASA Technical Reports Server (NTRS)
Hughes, T. J. R.; Franca, L. P.; Hulbert, G. M.; Johan, Z.; Shakib, F.
1988-01-01
Galerkin/least-squares finite-element methods are presented for advective-diffusive equations. Galerkin/least-squares represents a conceptual simplification of streamline-upwind Petrov-Galerkin methods, and is in fact applicable to a wide variety of other problem types. A convergence analysis and error estimates are presented. Some numerical results for compressible Navier-Stokes flows are presented.
A rational high-order compact ADI method for unsteady convection-diffusion equations
NASA Astrophysics Data System (ADS)
Tian, Zhen F.
2011-03-01
Based on a fourth-order compact difference formula for the spatial discretization, which is currently proposed for the one-dimensional (1D) steady convection-diffusion problem, and the Crank-Nicolson scheme for the time discretization, a rational high-order compact alternating direction implicit (ADI) method is developed for solving two-dimensional (2D) unsteady convection-diffusion problems. The method is unconditionally stable and second-order accurate in time and fourth-order accurate in space. The resulting scheme in each ADI computation step corresponds to a tridiagonal matrix equation which can be solved by the application of the 1D tridiagonal Thomas algorithm with a considerable saving in computing time. Three examples supporting our theoretical analysis are numerically solved. The present method not only shows higher accuracy and better phase and amplitude error properties than the standard second-order Peaceman-Rachford ADI method in Peaceman and Rachford (1959) [4], the fourth-order ADI method of Karaa and Zhang (2004) [5] and the fourth-order ADI method of Tian and Ge (2007) [23], but also proves more effective than the fourth-order Padé ADI method of You (2006) [6], in the aspect of computational cost. The method proposed for the diffusion-convection problems is easy to implement and can also be used to solve pure diffusion or pure convection problems.
NASA Technical Reports Server (NTRS)
Emery, A. F.; Johansson, O.; Lobo, M.; Abrous, A.
1988-01-01
Several different numerical methods for calculating diffuse radiation viewfactors are described. Each is applied to a range of surface configurations, from almost completely unobstructed to a dense set of intersecting surfaces. The speed, accuracy and unique characteristics are discussed in order to define optimal methods for different surface geometries.
The Local Discontinuous Galerkin Method for Time-Dependent Convection-Diffusion Systems
NASA Technical Reports Server (NTRS)
Cockburn, Bernardo; Shu, Chi-Wang
1997-01-01
In this paper, we study the Local Discontinuous Galerkin methods for nonlinear, time-dependent convection-diffusion systems. These methods are an extension of the Runge-Kutta Discontinuous Galerkin methods for purely hyperbolic systems to convection-diffusion systems and share with those methods their high parallelizability, their high-order formal accuracy, and their easy handling of complicated geometries, for convection dominated problems. It is proven that for scalar equations, the Local Discontinuous Galerkin methods are L(sup 2)-stable in the nonlinear case. Moreover, in the linear case, it is shown that if polynomials of degree k are used, the methods are k-th order accurate for general triangulations; although this order of convergence is suboptimal, it is sharp for the LDG methods. Preliminary numerical examples displaying the performance of the method are shown.
Method for site characterization of anisotropic diffuse illumination of photovoltaic systems
NASA Astrophysics Data System (ADS)
Russo, Juan M.; Zhang, Deming; Vorndran, Shelby; Gordon, Michael; Castillo, Jose; Brooks, Adria; Lonij, Vincent; Cronin, Alex; Kostuk, Raymond
2012-10-01
In this paper a method to characterize the anisotropy of diffuse illumination incident on photovoltaic systems is presented. PV systems are designed based on standard conditions in which only consider direct and isotropic diffuse illumination. Anisotropic illumination can cause the PV system output to step outside of the design specifications. A baffled multi-detector sensor system is described having a discrete set of azimuthal and declination angle combinations in order to constantly sample the irradiance and the incidence angle of the diffuse illumination in all zenith directions. The sensor was deployed in the Tucson Electric Power Solar Test Yard alongside with commercially available PV systems that are independently monitored. Constant and transient sources of anisotropic diffuse illumination, such as surface reflection and cloud edge effects respectively, are measured and modeled with ray tracing software. Results of the method are described for characterizing diffuse illumination at the TEP Solar Test Yard. Understanding the anisotropic diffuse illumination can potentially allow to more accurately predict PV system or to optimize energy harvesting of systems with non-standard mounting conditions as well as building integrated photovoltaic applications.
Laser interferometric method for determining the carrier diffusion length in semiconductors
Manukhov, V. V.; Fedortsov, A. B.; Ivanov, A. S.
2015-09-15
A new laser interferometric method for measuring the carrier diffusion length in semiconductors is proposed. The method is based on the interference–absorption interaction of two laser radiations in a semiconductor. Injected radiation generates additional carriers in a semiconductor, which causes a change in the material’s optical constants and modulation of the probing radiation passed through the sample. When changing the distance between carrier generation and probing points, a decrease in the carrier concentration, which depends on the diffusion length, is recorded. The diffusion length is determined by comparing the experimental and theoretical dependences of the probe signal on the divergence of the injector and probe beams. The method is successfully tested on semiconductor samples with different thicknesses and surface states and can be used in scientific research and the electronics industry.
Individual Differences and Fitting Methods for the Two-Choice Diffusion Model of Decision Making
Ratcliff, Roger; Childers, Russ
2015-01-01
Methods of fitting the diffusion model were examined with a focus on what the model can tell us about individual differences. Diffusion model parameters were obtained from the fits to data from two experiments and consistency of parameter values, individual differences, and practice effects were examined using different numbers of observations from each subject. Two issues were examined, first, what sizes of differences between groups can be obtained to distinguish between groups and second, what sizes of differences would be needed to find individual subjects that had a deficit relative to a control group. The parameter values from the experiments provided ranges that were used in a simulation study to examine recovery of individual differences. This study used several diffusion model fitting programs, fitting methods, and published packages. In a second simulation study, 64 sets of simulated data from each of 48 sets of parameter values (spanning the range of typical values obtained from fits to data) were fit with the different methods and biases and standard deviations in recovered model parameters were compared across methods. Finally, in a third simulation study, a comparison between a standard chi-square method and a hierarchical Bayesian method was performed. The results from these studies can be used as a starting point for selecting fitting methods and as a basis for understanding the strengths and weaknesses of using diffusion model analyses to examine individual differences in clinical, neuropsychological, and educational testing. PMID:26236754
Technology Transfer Automated Retrieval System (TEKTRAN)
Salmonella is a common cause of foodborne disease resulting from the consumption of contaminated food products. Although a direct plating method is widely used for presumptive positive screening of pathogenic Salmonella colonies on agar plates, it is labor-intensive, time-consuming and also prone to...
Prakash, Peralam Yegneswaran; Bhargava, Kanika
2016-04-01
The slide culture technique aids in the study of undisturbed microscopic morphological details of filamentous fungi. The existing methods for setting up of slide culture are quite cumbersome, time-consuming and require elaborate preparation. We describe a modified and easy to perform micro chamber agar spot slide culture technique. PMID:26924158
An asymptotic induced numerical method for the convection-diffusion-reaction equation
NASA Technical Reports Server (NTRS)
Scroggs, Jeffrey S.; Sorensen, Danny C.
1988-01-01
A parallel algorithm for the efficient solution of a time dependent reaction convection diffusion equation with small parameter on the diffusion term is presented. The method is based on a domain decomposition that is dictated by singular perturbation analysis. The analysis is used to determine regions where certain reduced equations may be solved in place of the full equation. Parallelism is evident at two levels. Domain decomposition provides parallelism at the highest level, and within each domain there is ample opportunity to exploit parallelism. Run time results demonstrate the viability of the method.
NASA Technical Reports Server (NTRS)
Penner, Reginald M.; Vandyke, Leon S.; Martin, Charles R.
1987-01-01
The current pulse E sub oc relaxation method and its application to the determination of diffusion coefficients in electrochemically synthesized polypyrrole thin films is described. Diffusion coefficients for such films in Et4NBF4 and MeCN are determined for a series of submicron film thicknesses. Measurement of the double-layer capacitance, C sub dl, and the resistance, R sub u, of polypyrrole thin films as a function of potential obtained with the galvanostatic pulse method is reported. Measurements of the electrolyte concentration in reduced polypyrrole films are also presented to aid in the interpretation of the data.
Calculation of the neutron diffusion equation by using Homotopy Perturbation Method
NASA Astrophysics Data System (ADS)
Koklu, H.; Ersoy, A.; Gulecyuz, M. C.; Ozer, O.
2016-03-01
The distribution of the neutrons in a nuclear fuel element in the nuclear reactor core can be calculated by the neutron diffusion theory. It is the basic and the simplest approximation for the neutron flux function in the reactor core. In this study, the neutron flux function is obtained by the Homotopy Perturbation Method (HPM) that is a new and convenient method in recent years. One-group time-independent neutron diffusion equation is examined for the most solved geometrical reactor core of spherical, cubic and cylindrical shapes, in the frame of the HPM. It is observed that the HPM produces excellent results consistent with the existing literature.
NUMERICAL METHODS FOR SOLVING THE MULTI-TERM TIME-FRACTIONAL WAVE-DIFFUSION EQUATION
Liu, F.; Meerschaert, M.M.; McGough, R.J.; Zhuang, P.; Liu, Q.
2013-01-01
In this paper, the multi-term time-fractional wave-diffusion equations are considered. The multi-term time fractional derivatives are defined in the Caputo sense, whose orders belong to the intervals [0,1], [1,2), [0,2), [0,3), [2,3) and [2,4), respectively. Some computationally effective numerical methods are proposed for simulating the multi-term time-fractional wave-diffusion equations. The numerical results demonstrate the effectiveness of theoretical analysis. These methods and techniques can also be extended to other kinds of the multi-term fractional time-space models with fractional Laplacian. PMID:23772179
An ink-diffusion-based rendering method for Chinese ink painting
NASA Astrophysics Data System (ADS)
Zhang, Yao; Miao, Zhenjiang; Liu, Yanghua; Zhou, Wei
2012-04-01
In non-photorealistic rendering (NPR), the Chinese ink painting style rendering is a traditional NPR skill of China. In this paper, we propose a method for image-based and ink-diffusion-based Chinese ink painting NPR. Users without painting experience can also convert a normal image to a Chinese ink painting automatically. As we known, ink is an important pigment for Chinese ink painting and the various ink shade effects on the painting are produced by ink mixed with water. In addition, the ink diffusion along the boundaries is a very important aspect of Chinese ink painting. In order to realize the effects described above, we present a Chinese ink painting NPR method based on ink diffusion. We use Mean Shift based image segmentation algorithm to preprocess the input image to get regions with different tones. Then, we detect the segmentation regions' edges letting the edge points to be the start points for diffusion. We set each point an ink value which is corresponding to its gray value. At the same time, a new algorithm simulating ink diffusion is proposed to make the segmentation image look like a black-ink painting. Results in this paper demonstrate our method is promising.
NASA Astrophysics Data System (ADS)
Bodammer, N. C.; Kaufmann, J.; Kanowski, M.; Tempelmann, C.
2009-02-01
Diffusion tensor tractography (DTT) allows one to explore axonal connectivity patterns in neuronal tissue by linking local predominant diffusion directions determined by diffusion tensor imaging (DTI). The majority of existing tractography approaches use continuous coordinates for calculating single trajectories through the diffusion tensor field. The tractography algorithm we propose is characterized by (1) a trajectory propagation rule that uses voxel centres as vertices and (2) orientation probabilities for the calculated steps in a trajectory that are obtained from the diffusion tensors of either two or three voxels. These voxels include the last voxel of each previous step and one or two candidate successor voxels. The precision and the accuracy of the suggested method are explored with synthetic data. Results clearly favour probabilities based on two consecutive successor voxels. Evidence is also provided that in any voxel-centre-based tractography approach, there is a need for a probability correction that takes into account the geometry of the acquisition grid. Finally, we provide examples in which the proposed fibre-tracking method is applied to the human optical radiation, the cortico-spinal tracts and to connections between Broca's and Wernicke's area to demonstrate the performance of the proposed method on measured data.
Development of Reference Materials for Thermal-Diffusivity Measurements by the Flash Method
NASA Astrophysics Data System (ADS)
Akoshima, M.; Abe, H.; Baba, T.
2015-12-01
The thermal conductivity of solid materials used for thermal simulations and thermal designs can be obtained as the product of thermal diffusivity, specific heat capacity, and bulk density in many cases. The thermal diffusivity is usually measured by the flash method, and the specific heat capacity is usually measured by differential scanning calorimetry. In order to obtain reliable thermal conductivities for strict thermal design, it is necessary to measure the thermal diffusivity using the flash method, a well-validated apparatus. Reference materials are an effective means for validation of most practical measurement apparatus. For the flash method, isotropic graphite was selected as a candidate reference material. A batch of isotropic graphite samples was prepared and characterized in detail in order to be a certified reference material for thermal-diffusivity measurement. The detailed characterization ensures the traceability of the measurement results to the international system of units (SI). A convenient reference material for thermal conductivity was also obtained by using the known thermal-diffusivity measurements, specific heat capacity, and density of the material.
Anandh, K R; Sujatha, C M; Ramakrishnan, S
2014-01-01
Ventricle enlargement is a useful structural biomarker for the diagnosis of Alzheimers Disease (AD). This devastating neurodegenerative disorder results in progression of dementia. Although AD results in the passive increment of ventricle volume, there exists a large overlap in the volume measurements of AD and normal subjects. Hence, shape based analysis of ventricle dilation is appropriate to detect the subtle morphological changes among these two groups. In this work, segmentation of ventricle in Alzheimer MR images is employed using level set method and anisotropic based diffusion filtering. Images considered for this study are preprocessed using filters. Anisotropic based diffusion filtering is employed to extract the edge map. This filtering performs region specific smoothing process using the diffusion coefficient as a function of image gradient. Filtered images are subjected to level set method which employs an improved diffusion rate equation for the level set evolution. Geometric features are extracted from the segmented ventricles. Results show that the diffusion filter could extract edge map with sharp region boundaries. The modified level set method is able to extract the morphological changes in ventricles. The observed morphological changes are distinct for normal and AD subjects (p < 0.0001). It is also observed that the sizes of ventricle in the AD subjects are noticeably enlarged when compared to normal subjects. Features obtained from the segmented ventricles are also clearly distinct and demonstrate the differences in the AD subjects. As ventricle volume and its morphometry are significant biomarkers, this study seems to be clinically relevant. PMID:25405438
NASA Astrophysics Data System (ADS)
Akoshima, Megumi; Tanaka, Takashi; Endo, Satoshi; Baba, Tetsuya; Harada, Yoshio; Kojima, Yoshitaka; Kawasaki, Akira; Ono, Fumio
2011-11-01
Ceramic-based thermal barrier coatings are used as heat and wear shields of gas turbine blades. There is a strong need to evaluate the thermal conductivity of coating for thermal design and use. The thermal conductivity of a bulk material is obtained as the product of thermal diffusivity, specific heat capacity, and density above room temperature in many cases. Thermal diffusivity and thermal conductivity are unique for a given material because they are sensitive to the structure of the material. Therefore, it is important to measure them in each sample. However it is difficult to measure the thermal diffusivity and thermal conductivity of coatings because coatings are attached to substrates. In order to evaluate the thermal diffusivity of a coating attached to the substrate, we have examined the laser flash method with the multilayer model on the basis of the response function method. We carried out laser flash measurements in layered samples composed of a CoNiCrAlY bond coating and a 8YSZ top coating by thermal spraying on a Ni-based superalloy substrate. It was found that the procedure using laser flash method with the multilayer model is useful for the thermal diffusivity evaluation of a coating attached to a substrate.
A hybrid transport-diffusion method for Monte Carlo radiative-transfer simulations
Densmore, Jeffery D. . E-mail: jdd@lanl.gov; Urbatsch, Todd J. . E-mail: tmonster@lanl.gov; Evans, Thomas M. . E-mail: tme@lanl.gov; Buksas, Michael W. . E-mail: mwbuksas@lanl.gov
2007-03-20
Discrete Diffusion Monte Carlo (DDMC) is a technique for increasing the efficiency of Monte Carlo particle-transport simulations in diffusive media. If standard Monte Carlo is used in such media, particle histories will consist of many small steps, resulting in a computationally expensive calculation. In DDMC, particles take discrete steps between spatial cells according to a discretized diffusion equation. Each discrete step replaces many small Monte Carlo steps, thus increasing the efficiency of the simulation. In addition, given that DDMC is based on a diffusion equation, it should produce accurate solutions if used judiciously. In practice, DDMC is combined with standard Monte Carlo to form a hybrid transport-diffusion method that can accurately simulate problems with both diffusive and non-diffusive regions. In this paper, we extend previously developed DDMC techniques in several ways that improve the accuracy and utility of DDMC for nonlinear, time-dependent, radiative-transfer calculations. The use of DDMC in these types of problems is advantageous since, due to the underlying linearizations, optically thick regions appear to be diffusive. First, we employ a diffusion equation that is discretized in space but is continuous in time. Not only is this methodology theoretically more accurate than temporally discretized DDMC techniques, but it also has the benefit that a particle's time is always known. Thus, there is no ambiguity regarding what time to assign a particle that leaves an optically thick region (where DDMC is used) and begins transporting by standard Monte Carlo in an optically thin region. Also, we treat the interface between optically thick and optically thin regions with an improved method, based on the asymptotic diffusion-limit boundary condition, that can produce accurate results regardless of the angular distribution of the incident Monte Carlo particles. Finally, we develop a technique for estimating radiation momentum deposition during the DDMC simulation, a quantity that is required to calculate correct fluid motion in coupled radiation-hydrodynamics problems. With a set of numerical examples, we demonstrate that our improved DDMC method is accurate and can provide efficiency gains of several orders of magnitude over standard Monte Carlo.
Study of the diffusion of points defects in crystalline silicon using the kinetic ART method
NASA Astrophysics Data System (ADS)
Trochet, Mickael; Brommer, Peter; Beland, Laurent-Karim; Joly, Jean-Francois; Mousseau, Normand
2013-03-01
Because of the long-time scale involved, the activated diffusion of point defects is often studied in standard molecular dynamics at high temperatures only, making it more difficult to characterize complex diffusion mechanisms. Here, we turn to the study of point defect diffusion in crystalline silicon using kinetic ART (kART), an off-lattice kinetic Monte Carlo method with on-the-fly catalog building based on the activation-relaxation technique (ART nouveau). By generating catalogs of diffusion mechanisms and fully incorporating elastic and off-lattice effects, kART is a unique tool for characterizing this problem. More precisely, using kART with the standard Stillinger-Weber potential we consider the evolution of crystalline cells with 1 to 4 vacancies and 1 to 4 interstitials at various temperatures and to provide a detailed picture of both the atomistic diffusion mechanisms and overall kinetics in addition to identifying special configurations such as a 2-interstitial super-diffuser.
A gradient random walk method for two-dimensional reaction-diffusion equations
Sherman, A. ); Mascagni, M. Inst. for Defense Analyses, Bowie, MD . Supercomputing Research Center)
1994-11-01
An extension to two space dimensions of the gradient random walk algorithm for reaction-diffusion equations is presented. This family of algorithms is related closely to the random vortex method of computational fluid dynamics. Although the computational cost is high, the method has the desirable features of being grid free and of automatically adapting to the solution by concentrating elements where the gradient is large. In addition, the method can be extended easily to more than two space dimensions. A key feature of the method is discretization in terms of the dependent, rather than independent, variable, giving it features in common with Lagrangian particle methods. The method is derived here and its application to some simple reaction-diffusion wave propagation problems is illustrated.
A domain decomposition method for time fractional reaction-diffusion equation.
Gong, Chunye; Bao, Weimin; Tang, Guojian; Jiang, Yuewen; Liu, Jie
2014-01-01
The computational complexity of one-dimensional time fractional reaction-diffusion equation is O(N²M) compared with O(NM) for classical integer reaction-diffusion equation. Parallel computing is used to overcome this challenge. Domain decomposition method (DDM) embodies large potential for parallelization of the numerical solution for fractional equations and serves as a basis for distributed, parallel computations. A domain decomposition algorithm for time fractional reaction-diffusion equation with implicit finite difference method is proposed. The domain decomposition algorithm keeps the same parallelism but needs much fewer iterations, compared with Jacobi iteration in each time step. Numerical experiments are used to verify the efficiency of the obtained algorithm. PMID:24778594
NASA Astrophysics Data System (ADS)
Zolotarev, V. M.
2014-04-01
Particular features of the application of Fourier-transform IR diffuse reflection spectroscopy methods to the in situ investigation of spectra of porous rough objects have been considered. The reciprocal influence of the scattering and absorption of porous objects on the formation of the impurity-band contour in the diffuse reflection spectrum when the impurity center is in the vicinity of the fundamental IR absorption band has been analyzed. Using methods of Fourier-transform IR diffuse reflection spectroscopy, processes of mineralization of fragments of mammoth tusks from a multilayer paleolithic site at Yudinovo (Bryansk oblast, Russia) and fragments of mammoth tusks from Yakutia (Russia) have been investigated. Particular features of mineralization processes (carbonate formation and silicification) on the surface and in the volume of objects at different conditions of their burial (humidity, temperature, soil acidity) have been studied.
Stability and error analysis of nodal expansion method for convection-diffusion equation
Deng, Z.; Rizwan-Uddin; Li, F.; Sun, Y.
2012-07-01
The development, and stability and error analyses of nodal expansion method (NEM) for one dimensional steady-state convection diffusion equation is presented. Following the traditional procedure to develop NEM, the discrete formulation of the convection-diffusion equation, which is similar to the standard finite difference scheme, is derived. The method of discrete perturbation analysis is applied to this discrete form to study the stability of the NEM. The scheme based on the NEM is found to be stable for local Peclet number less than 4.644. A maximum principle is proved for the NEM scheme, followed by an error analysis carried out by applying the Maximum principle together with a carefully constructed comparison function. The scheme for the convection diffusion equation is of second-order. Numerical experiments are carried and the results agree with the conclusions of the stability and error analyses. (authors)
A Domain Decomposition Method for Time Fractional Reaction-Diffusion Equation
Bao, Weimin; Tang, Guojian; Jiang, Yuewen; Liu, Jie
2014-01-01
The computational complexity of one-dimensional time fractional reaction-diffusion equation is O(N2M) compared with O(NM) for classical integer reaction-diffusion equation. Parallel computing is used to overcome this challenge. Domain decomposition method (DDM) embodies large potential for parallelization of the numerical solution for fractional equations and serves as a basis for distributed, parallel computations. A domain decomposition algorithm for time fractional reaction-diffusion equation with implicit finite difference method is proposed. The domain decomposition algorithm keeps the same parallelism but needs much fewer iterations, compared with Jacobi iteration in each time step. Numerical experiments are used to verify the efficiency of the obtained algorithm. PMID:24778594
Mavridou, A; Smeti, E; Mandilara, G; Mandilara, G; Boufa, P; Vagiona-Arvanitidou, M; Vantarakis, A; Vassilandonopoulou, G; Pappa, O; Roussia, V; Tzouanopoulos, A; Livadara, M; Aisopou, I; Maraka, V; Nikolaou, E; Mandilara, G
2010-01-01
In this study ten laboratories in Greece compared the performance of reference method TTC Tergitol 7 Agar (with the additional test of beta-glucuronidase production) with five alternative methods, to detect E. coli in water, in line with European Water Directive recommendations. The samples were prepared by spiking drinking water with sewage effluent following a standard protocol. Chlorinated and non-chlorinated samples were used. The statistical analysis was based on the mean relative difference of confirmed counts and was performed in line with ISO 17994. The results showed that in total, three of the alternative methods (Chromocult Coliform agar, Membrane Lauryl Sulfate agar and Trypton Bilex-glucuronidase medium) were not different from TTC Tergitol 7 agar (TTC Tergitol 7 agar vs Chromocult Coliform agar, 294 samples, mean RD% 5.55; vs MLSA, 302 samples, mean RD% 1; vs TBX, 297 samples, mean RD% -2.78). The other two alternative methods (Membrane Faecal coliform medium and Colilert 18/ Quantitray) gave significantly higher counts than TTC Tergitol 7 agar (TTC Tergitol 7 agar vs MFc, 303 samples, mean RD% 8.81; vs Colilert-18/Quantitray, 76 samples, mean RD% 18.91). In other words, the alternative methods generated performance that was as reliable as, or even better than, the reference method. This study will help laboratories in Greece overcome culture and counting problems deriving from the EU reference method for E. coli counts in water samples. PMID:20057092
Development of advanced methods for analysis of experimental data in diffusion
NASA Astrophysics Data System (ADS)
Jaques, Alonso V.
There are numerous experimental configurations and data analysis techniques for the characterization of diffusion phenomena. However, the mathematical methods for estimating diffusivities traditionally do not take into account the effects of experimental errors in the data, and often require smooth, noiseless data sets to perform the necessary analysis steps. The current methods used for data smoothing require strong assumptions which can introduce numerical "artifacts" into the data, affecting confidence in the estimated parameters. The Boltzmann-Matano method is used extensively in the determination of concentration - dependent diffusivities, D(C), in alloys. In the course of analyzing experimental data, numerical integrations and differentiations of the concentration profile are performed. These methods require smoothing of the data prior to analysis. We present here an approach to the Boltzmann-Matano method that is based on a regularization method to estimate a differentiation operation on the data, i.e., estimate the concentration gradient term, which is important in the analysis process for determining the diffusivity. This approach, therefore, has the potential to be less subjective, and in numerical simulations shows an increased accuracy in the estimated diffusion coefficients. We present a regression approach to estimate linear multicomponent diffusion coefficients that eliminates the need pre-treat or pre-condition the concentration profile. This approach fits the data to a functional form of the mathematical expression for the concentration profile, and allows us to determine the diffusivity matrix directly from the fitted parameters. Reformulation of the equation for the analytical solution is done in order to reduce the size of the problem and accelerate the convergence. The objective function for the regression can incorporate point estimations for error in the concentration, improving the statistical confidence in the estimated diffusivity matrix. Case studies are presented to demonstrate the reliability and the stability of the method. To the best of our knowledge there is no published analysis of the effects of experimental errors on the reliability of the estimates for the diffusivities. For the case of linear multicomponent diffusion, we analyze the effects of the instrument analytical spot size, positioning uncertainty, and concentration uncertainty on the resulting values of the diffusivities. These effects are studied using Monte Carlo method on simulated experimental data. Several useful scaling relationships were identified which allow more rigorous and quantitative estimates of the errors in the measured data, and are valuable for experimental design. To further analyze anomalous diffusion processes, where traditional diffusional transport equations do not hold, we explore the use of fractional calculus in analytically representing these processes is proposed. We use the fractional calculus approach for anomalous diffusion processes occurring through a finite plane sheet with one face held at a fixed concentration, the other held at zero, and the initial concentration within the sheet equal to zero. This problem is related to cases in nature where diffusion is enhanced relative to the classical process, and the order of differentiation is not necessarily a second--order differential equation. That is, differentiation is of fractional order alpha, where 1 ≤ alpha < 2. For alpha = 2, the presented solutions reduce to the classical second-order diffusion solution for the conditions studied. The solution obtained allows the analysis of permeation experiments. Frequently, hydrogen diffusion is analyzed using electrochemical permeation methods using the traditional, Fickian-based theory. Experimental evidence shows the latter analytical approach is not always appropiate, because reported data shows qualitative (and quantitative) deviation from its theoretical scaling predictions. Preliminary analysis of data shows better agreement with fractional diffusion analysis when compared to traditional square-root scaling. Although there is a large amount of work in the estimation of the diffusivity from experimental data, reported studies typically present only the analytical description for the diffusivity, without scattering. However, because these studies do not consider effects produced by instrument analysis, their direct applicability is limited. We propose alternatives to address these, and to evaluate their influence on the final resulting diffusivity values.
NASA Astrophysics Data System (ADS)
Zhang, X. Y.; Watson, E. B.; Cherniak, D. J.
2007-03-01
Like most other minerals, titanite rarely if ever forms perfect crystals. In addition to the point defects that might affect lattice diffusion, there may be extended line- or planar defects along which fast diffusion could occur. During the course of an experimental study of oxygen lattice diffusion in titanite, we found that almost all of the 18O uptake profiles produced in natural titanite crystals departed from the complementary error function solution expected for simple lattice diffusion with a constant surface concentration. Instead, they exhibited "tails" extending deeper into the samples than expected for simple lattice diffusion. The purpose of this contribution is to report on these features—described as "fast-paths" for oxygen diffusion—and outline a method for coping with them in extracting information from diffusion profiles. For both dry and hydrothermal experiments in which the "fast paths" are observed, 18O was used as the diffusant. In dry experiments, the source material was 18O-enriched SiO 2 powder, while 18O-enriched water was used for the hydrothermal experiments. Diffusive uptake profiles of 18O were measured in all cases by nuclear reaction analysis (NRA) using the 18O (p,α) 15N reaction [see Zhang X. Y., Cherniak D. J., and Watson E. B. (2006) Oxygen diffusion in titanite: lattice and fast-path diffusion in single crystals. Chem. Geol.235 105-123]. In our experiments, different sizes of "tails" (with varying 18O concentrations) were observed. Theoretically, under the same temperature and pressure conditions, the sizes of tails should be affected by two factors: the diffusion duration and the defect density. For the same experiment duration, the higher the defect density, the larger the "tail"; for the same defect densities, the longer the diffusion duration, the larger the "tail." The diffusion "tails" could be a result of either planar defects or one-dimensional "pipe" diffusion. AFM imaging of HF etched titanite surfaces confirmed that the etched features might be caused by either parallel planar defects or parallel pipe defects, but could not differentiate between these possibilities. Through theoretical calculations simulating the tailed diffusion profiles using reasonable assumptions of lattice diffusivities and fast-path diffusivities, and comparing these with tail features measured in our samples, it can be concluded that the "tails" observed in our experiments are caused by planar defects rather than pipe defects. A new method was developed for separating the "fast-path" contribution from the overall composite diffusion profile consisting of both "fast-path" and lattice diffusion. Through this process, the lattice diffusion coefficient could be determined, which is required to analyze the tail. The oxygen diffusion rates in the fast-paths were obtained by traditional graphical analysis methods, using the Whipple-Le Claire equation (for 2-D defects) assuming that the width of the fast-path is 1 nm. Two Arrhenius relations were obtained for the fast-path diffusion phenomenon, one for experiments under dry conditions, and the other for hydrothermal conditions:
Boral, Shilpi; Bohidar, H B
2012-06-21
A comprehensive study of hydration of polyanionic agar molecules in its solution and gel phase in glycerol-water binary solvent is reported. Raman spectroscopy results predict differential water structure arrangement for glycerol-water binary solvent, 0.02% (w/v) agar in glycerol solution and 0.3% (w/v) agar organogel. The 3200 cm(-1) Raman band pertaining to ice-like structure of water was found to increase in gel phase alike in glycerol-water solvent while it decreased in agar solutions with increase in glycerol concentration. In contrast, the partially structured water corresponding to the component 3310 cm(-1) of Raman spectra increased in agar solution, and decreased in gel phase similar to glycerol-water solvent case. We have explained these observations based on a simple model where the available oxygen to hydrogen atom ratio in a given solvent-polymer system uniquely defines hydration in solution and gel phases. The gelation concentration was found to increase from 0.18 (for water) to 0.22% (w/v) (50% v/v glycerol solution) as the glycerol concentration was raised. Correspondingly, the gelation temperature, T(g), showed a decline from 40 to 20 °C, and the gel melting temperature, T(m), revealed a reduction from 81 to 65 °C in the same glycerol concentration regime. Two distinctive features are evident here: (i) presence of glycerol as a cosolvent does not favor the gelation of agar as compared to water and (ii) agar organogels are softer than their hydrogels. A unique 3D phase diagram for the agar organogel is proposed. Circular dichroism data confirmed that the agar molecules retained their biological activity in these solvents. Thus, it is shown that thermo-mechanical properties of these organogels could be systematically tuned and adapted as per application requirement. PMID:22657388
New contactless method for thermal diffusivity measurements using modulated photothermal radiometry.
Pham Tu Quoc, S; Cheymol, G; Semerok, A
2014-05-01
Modulated photothermal radiometry is a non-destructive and contactless technique for the characterization of materials. It has two major advantages: a good signal-to-noise ratio through a synchronous detection and a low dependence on the heating power and the optical properties of the sample surface. This paper presents a new method for characterizing the thermal diffusivity of a material when the phase shift between a modulated laser power signal and the thermal signal of a plate sample is known at different frequencies. The method is based on a three-dimensional analytical model which is used to determine the temperature amplitude and the phase in the laser heating of the plate. A new simple formula was developed through multi-parametric analysis to determine the thermal diffusivity of the plate with knowledge of the frequency at the minimum phase shift, the laser beam radius r0 and the sample thickness L. This method was developed to control the variation of the thermal diffusivity of nuclear components and it was first applied to determine the thermal diffusivity of different metals: 304 L stainless steel, nickel, titanium, tungsten, molybdenum, zinc, and iron. The experimental results were obtained with 5%-10% accuracy and corresponded well with the reference values. The present paper also demonstrates the limit of application of this method for plate with thickness r0/100 ≤ L ≤ r0/2. The technique is deemed interesting for the characterization of barely accessible components that require a contactless measurement. PMID:24880399
New contactless method for thermal diffusivity measurements using modulated photothermal radiometry
NASA Astrophysics Data System (ADS)
Pham Tu Quoc, S.; Cheymol, G.; Semerok, A.
2014-05-01
Modulated photothermal radiometry is a non-destructive and contactless technique for the characterization of materials. It has two major advantages: a good signal-to-noise ratio through a synchronous detection and a low dependence on the heating power and the optical properties of the sample surface. This paper presents a new method for characterizing the thermal diffusivity of a material when the phase shift between a modulated laser power signal and the thermal signal of a plate sample is known at different frequencies. The method is based on a three-dimensional analytical model which is used to determine the temperature amplitude and the phase in the laser heating of the plate. A new simple formula was developed through multi-parametric analysis to determine the thermal diffusivity of the plate with knowledge of the frequency at the minimum phase shift, the laser beam radius r0 and the sample thickness L. This method was developed to control the variation of the thermal diffusivity of nuclear components and it was first applied to determine the thermal diffusivity of different metals: 304 L stainless steel, nickel, titanium, tungsten, molybdenum, zinc, and iron. The experimental results were obtained with 5%-10% accuracy and corresponded well with the reference values. The present paper also demonstrates the limit of application of this method for plate with thickness r0/100 ≤ L ≤ r0/2. The technique is deemed interesting for the characterization of barely accessible components that require a contactless measurement.
Liquid-phase thermal diffusion isotope separation apparatus and method having tapered column
Rutherford, W.M.
1985-12-04
A thermal diffusion counterflow method and apparatus for separating isotopes in solution in which the solution is confined in a long, narrow, vertical slit which tapers from bottom to top. The variation in the width of the slit permits maintenance of a stable concentration distribution with relatively long columns, thus permitting isotopic separation superior to that obtained in the prior art.
Liquid-phase thermal diffusion isotope separation apparatus and method having tapered column
Rutherford, William M.
1988-05-24
A thermal diffusion counterflow method and apparatus for separating isotopes in solution in which the solution is confined in a long, narrow, vertical slit which tapers from bottom to top. The variation in the width of the slit permits maintenance of a stable concentration distribution with relatively long columns, thus permitting isotopic separation superior to that obtainable in the prior art.
A moving mesh finite difference method for equilibrium radiation diffusion equations
Yang, Xiaobo; Huang, Weizhang; Qiu, Jianxian
2015-10-01
An efficient moving mesh finite difference method is developed for the numerical solution of equilibrium radiation diffusion equations in two dimensions. The method is based on the moving mesh partial differential equation approach and moves the mesh continuously in time using a system of meshing partial differential equations. The mesh adaptation is controlled through a Hessian-based monitor function and the so-called equidistribution and alignment principles. Several challenging issues in the numerical solution are addressed. Particularly, the radiation diffusion coefficient depends on the energy density highly nonlinearly. This nonlinearity is treated using a predictor–corrector and lagged diffusion strategy. Moreover, the nonnegativity of the energy density is maintained using a cutoff method which has been known in literature to retain the accuracy and convergence order of finite difference approximation for parabolic equations. Numerical examples with multi-material, multiple spot concentration situations are presented. Numerical results show that the method works well for radiation diffusion equations and can produce numerical solutions of good accuracy. It is also shown that a two-level mesh movement strategy can significantly improve the efficiency of the computation.
DEVELOPMENT OF LOW-DIFFUSION FLUX-SPLITTING METHODS FOR DENSE GAS-SOLID FLOWS
The development of a class of low-diffusion upwinding methods for computing dense gas-solid flows is presented in this work. An artificial compressibility/low-Mach preconditioning strategy is developed for a hyperbolic two-phase flow equation system consisting of separate solids ...
A moving mesh finite difference method for equilibrium radiation diffusion equations
NASA Astrophysics Data System (ADS)
Yang, Xiaobo; Huang, Weizhang; Qiu, Jianxian
2015-10-01
An efficient moving mesh finite difference method is developed for the numerical solution of equilibrium radiation diffusion equations in two dimensions. The method is based on the moving mesh partial differential equation approach and moves the mesh continuously in time using a system of meshing partial differential equations. The mesh adaptation is controlled through a Hessian-based monitor function and the so-called equidistribution and alignment principles. Several challenging issues in the numerical solution are addressed. Particularly, the radiation diffusion coefficient depends on the energy density highly nonlinearly. This nonlinearity is treated using a predictor-corrector and lagged diffusion strategy. Moreover, the nonnegativity of the energy density is maintained using a cutoff method which has been known in literature to retain the accuracy and convergence order of finite difference approximation for parabolic equations. Numerical examples with multi-material, multiple spot concentration situations are presented. Numerical results show that the method works well for radiation diffusion equations and can produce numerical solutions of good accuracy. It is also shown that a two-level mesh movement strategy can significantly improve the efficiency of the computation.
21 CFR 866.4600 - Ouchterlony agar plate.
Code of Federal Regulations, 2011 CFR
2011-04-01
... containing an agar gel used to examine antigen-antibody reactions. In immunodiffusion, antibodies and antigens migrate toward each other through gel which originally contained neither of these reagents. As...
21 CFR 866.4600 - Ouchterlony agar plate.
Code of Federal Regulations, 2010 CFR
2010-04-01
... containing an agar gel used to examine antigen-antibody reactions. In immunodiffusion, antibodies and antigens migrate toward each other through gel which originally contained neither of these reagents. As...
Numerical solution of a diffusion problem by exponentially fitted finite difference methods.
D'Ambrosio, Raffaele; Paternoster, Beatrice
2014-01-01
This paper is focused on the accurate and efficient solution of partial differential differential equations modelling a diffusion problem by means of exponentially fitted finite difference numerical methods. After constructing and analysing special purpose finite differences for the approximation of second order partial derivatives, we employed them in the numerical solution of a diffusion equation with mixed boundary conditions. Numerical experiments reveal that a special purpose integration, both in space and in time, is more accurate and efficient than that gained by employing a general purpose solver. PMID:26034665
Error diffusion method applied to design combined CSG-BSG element used in ICF driver
NASA Astrophysics Data System (ADS)
Zhang, Yixiao; Yao, Xin; Gao, Fuhua; Guo, Yongkang; Wang, Lei; Hou, Xi
2006-08-01
In the final optics assembly of Inertial Confinement Fusion (ICF) driver, Diffractive Optical Elements (DOEs) are applied to achieve some important functions, such as harmonic wave separation, beam sampling, beam smoothing and pulse compression etc. However, in order to optimize the system structure, decrease the energy loss and avoid the damage of laser induction or self-focusing effect, the number of elements used in the ICF system, especially in the final optics assembly, should be minimized. The multiple exposure method has been proposed, for this purpose, to fabricate BSG and CSG on one surface of a silica plate. But the multiple etch processes utilized in this method is complex and will introduce large alignment error. Error diffusion method that based on pulse-density modulation has been widely used in signal processing and computer generated hologram (CGH). In this paper, according to error diffusion method in CGH and partial coherent imaging theory, we present a new method to design coding mask of combine CSG-BSG element with error diffusion method. With the designed mask, only one exposure process is needed in fabricating combined element, which will greatly reduce the fabrication difficulty and avoid the alignment error introduced by multiple etch processes. We illustrate the designed coding mask for CSG-BSG element with this method and compare the intensity distribution of the spatial image in partial coherent imaging system with desired relief.
Diffuse interface methods for inverse problems: case study for an elliptic Cauchy problem
NASA Astrophysics Data System (ADS)
Burger, Martin; Løseth Elvetun, Ole; Schlottbom, Matthias
2015-12-01
Many inverse problems have to deal with complex, evolving and often not exactly known geometries, e.g. as domains of forward problems modeled by partial differential equations. This makes it desirable to use methods which are robust with respect to perturbed or not well resolved domains, and which allow for efficient discretizations not resolving any fine detail of those geometries. For forward problems in partial differential equations methods based on diffuse interface representations have gained strong attention in the last years, but so far they have not been considered systematically for inverse problems. In this work we introduce a diffuse domain method as a tool for the solution of variational inverse problems. As a particular example we study ECG inversion in further detail. ECG inversion is a linear inverse source problem with boundary measurements governed by an anisotropic diffusion equation, which naturally cries for solutions under changing geometries, namely the beating heart. We formulate a regularization strategy using Tikhonov regularization and, using standard source conditions, we prove convergence rates. A special property of our approach is that not only operator perturbations are introduced by the diffuse domain method, but more important we have to deal with topologies which depend on a parameter \\varepsilon in the diffuse domain method, i.e. we have to deal with \\varepsilon -dependent forward operators and \\varepsilon -dependent norms. In particular the appropriate function spaces for the unknown and the data depend on \\varepsilon . This prevents the application of some standard convergence techniques for inverse problems, in particular interpreting the perturbations as data errors in the original problem does not yield suitable results. We consequently develop a novel approach based on saddle-point problems. The numerical solution of the problem is discussed as well and results for several computational experiments are reported. In particular investigations of convergence rates support our theoretical findings.
NASA Technical Reports Server (NTRS)
Atkins, H. L.; Shu, Chi-Wang
2001-01-01
The explicit stability constraint of the discontinuous Galerkin method applied to the diffusion operator decreases dramatically as the order of the method is increased. Block Jacobi and block Gauss-Seidel preconditioner operators are examined for their effectiveness at accelerating convergence. A Fourier analysis for methods of order 2 through 6 reveals that both preconditioner operators bound the eigenvalues of the discrete spatial operator. Additionally, in one dimension, the eigenvalues are grouped into two or three regions that are invariant with order of the method. Local relaxation methods are constructed that rapidly damp high frequencies for arbitrarily large time step.
A CCD-ADI method for unsteady convection-diffusion equations
NASA Astrophysics Data System (ADS)
Sun, Hai-Wei; Li, Leonard Z.
2014-03-01
With a combined compact difference scheme for the spatial discretization and the Crank-Nicolson scheme for the temporal discretization, respectively, a high-order alternating direction implicit method (ADI) is proposed for solving unsteady two dimensional convection-diffusion equations. The method is sixth-order accurate in space and second-order accurate in time. The resulting matrix at each ADI computation step corresponds to a triple-tridiagonal system which can be effectively solved with a considerable saving in computing time. In practice, Richardson extrapolation is exploited to increase the temporal accuracy. The unconditional stability is proved by means of Fourier analysis for two dimensional convection-diffusion problems with periodic boundary conditions. Numerical experiments are conducted to demonstrate the efficiency of the proposed method. Moreover, the present method preserves the higher order accuracy for convection-dominated problems.
Kempka, S.N.; Strickland, J.H.
1993-08-01
A numerical method to simulate viscous diffusion of vorticity using vortex blobs (i.e., without a grid) is presented. The method consists of casting the effects of viscous diffusion into an effective ``diffusion velocity`` at which vortex blobs convect. The diffusion velocity was proposed previously by Ogami and Akamatsu, but they did not consider the effects of the divergence of the diffusion velocity. In fact, the diffusion velocity is highly non-solenoidal, which significantly affects the area over which a vortex blob diffuses. A formulation is presented that relates the area expansion to the diffusion velocity divergence. By taking into account the area expansion, more accurate simulations of diffusion are obtained, as demonstrated by a comparison of numerical and analytical diffusion solutions. Results from simulations show that vortex areas expand significantly in regions of large vorticity gradients. As a result of the area expansion, adjacent vortices remain overlapped, thereby maintaining smooth solution fields. The non-solenoidal diffusion velocity method is easily implemented in vortex blob algorithms, thus facilitating the development of vortex methods to simulate flows with finite Reynolds numbers.
Zemlianitskaia, E P; Kurbanova, I Z; Sergeeva, T I
1979-02-01
An express method for determination of antibiotic sensitivity in the strains of Cl. perfringens of type A using Soviet dry nutrient media and antibiotics is proposed. The criteria for estimation of the level of the antibiotic sensitivity of the causative agent of gas gangrene in short periods on the basis of comparison of the data of the antibiotic agar diffusion procedure and the antibiotic MIC were worked out. Twelve antibiotics and 45 collection strains of Cl. perfringens of type A were used in the experiment. The antibiotic agar diffusion method with the use of the nutrient media, microbial load and cultivation conditions developed by the authors is recommended for tentative determination of the antibiotic sensitivity in Cl. perfringens of type A for 4 hours. The use of the agar diffusion method and determination of the antibiotic MIC provided complete estimation of tha antibiotic sensitivity of Cl. perfringens of type A within not more than 24 hours. PMID:219770
NASA Technical Reports Server (NTRS)
Chau, Jessica Furrer; Or, Dani; Sukop, Michael C.; Steinberg, S. L. (Principal Investigator)
2005-01-01
Liquid distributions in unsaturated porous media under different gravitational accelerations and corresponding macroscopic gaseous diffusion coefficients were investigated to enhance understanding of plant growth conditions in microgravity. We used a single-component, multiphase lattice Boltzmann code to simulate liquid configurations in two-dimensional porous media at varying water contents for different gravity conditions and measured gas diffusion through the media using a multicomponent lattice Boltzmann code. The relative diffusion coefficients (D rel) for simulations with and without gravity as functions of air-filled porosity were in good agreement with measured data and established models. We found significant differences in liquid configuration in porous media, leading to reductions in D rel of up to 25% under zero gravity. The study highlights potential applications of the lattice Boltzmann method for rapid and cost-effective evaluation of alternative plant growth media designs under variable gravity.
NASA Astrophysics Data System (ADS)
Effenberger, F.
2014-09-01
Numerical solution methods for Stochastic Differential Equations (SDEs) have become an important tool to study charged particle transport, due to their simplicity and conformance with modern computer architecture. Their field of application ranges from the detailed calculation of solar energetic particle events to the cosmic ray transport in the outer heliosphere and in the Galaxy. At the heart of the applicability of SDEs to kinetic equations is the fundamental equivalence between the Fokker-Planck diffusion equation of parabolic type and an SDE involving a Wiener process to represent the stochastic Brownian motion of (pseudo-)particles. This equivalence has recently been extended to anomalous diffusion involving a Fokker-Planck equation of fractional order and generalized Lévy distributions. Numerical tests and applications of this approach to anomalous diffusion and future prospects of the SDE approach in the space physics context are outlined.
Zheng, Y.P.; Zhang, T.Y.
1998-12-31
In order to verify the results predicted by the model in Part 1 of this work, permeation experiments were conducted at room and high temperatures on fully-annealed-commercially-pure iron with two kinds of surface treatment, one group with plasma cleaning and presputtering and the other without it. The experimental results show that the diffusivity evaluated by the new model is independent of sample thickness and surface treatment, while the diffusivity evaluated by the time-lag model varies two orders of magnitude. The experimental results confirm that a fine surface treatment yields a low energy barrier for desorption. The energy barrier for either group is higher than the activation energy of diffusion. Consequently, the ratio of drift velocity through surface to that in bulk increases with increasing temperature and makes the time-lag method appropriate at elevated temperatures.
Novel front-surface thermal-diffusivity measurement method based on phase analysis
NASA Astrophysics Data System (ADS)
Braggiotti, Alberto; Marinetti, Sergio
2000-05-01
The technique described in this paper is for one-side thermal diffusivity measurement. A single stripe-shaped pulse provided by a flash lamp is used to heat the front surface of a specimen slab. Classical methods for estimating a parameter out of a distribution involve fitting the temperature distribution with its theoretical model. With the technique described in this paper the evolution of the temperature distribution along a line perpendicular to the heated stripe is analyzed in the frequency domain. An estimate of the thermal diffusivity is then obtained from comparison of the phase component behavior with an abacus similarly built from the theoretical model. This technique is valid for any shape of flash lamp pulse (i.e. laser spot), and can be used also for estimating the thermal diffusivity of anisotropic materials. The choice of the stripe shape is due to the limitations of the simulation environment used.
Quantitative comparison of reconstruction methods for intra-voxel fiber recovery from diffusion MRI.
Daducci, Alessandro; Canales-Rodríguez, Erick Jorge; Descoteaux, Maxime; Garyfallidis, Eleftherios; Gur, Yaniv; Lin, Ying-Chia; Mani, Merry; Merlet, Sylvain; Paquette, Michael; Ramirez-Manzanares, Alonso; Reisert, Marco; Reis Rodrigues, Paulo; Sepehrband, Farshid; Caruyer, Emmanuel; Choupan, Jeiran; Deriche, Rachid; Jacob, Mathews; Menegaz, Gloria; Prčkovska, Vesna; Rivera, Mariano; Wiaux, Yves; Thiran, Jean-Philippe
2014-02-01
Validation is arguably the bottleneck in the diffusion magnetic resonance imaging (MRI) community. This paper evaluates and compares 20 algorithms for recovering the local intra-voxel fiber structure from diffusion MRI data and is based on the results of the "HARDI reconstruction challenge" organized in the context of the "ISBI 2012" conference. Evaluated methods encompass a mixture of classical techniques well known in the literature such as diffusion tensor, Q-Ball and diffusion spectrum imaging, algorithms inspired by the recent theory of compressed sensing and also brand new approaches proposed for the first time at this contest. To quantitatively compare the methods under controlled conditions, two datasets with known ground-truth were synthetically generated and two main criteria were used to evaluate the quality of the reconstructions in every voxel: correct assessment of the number of fiber populations and angular accuracy in their orientation. This comparative study investigates the behavior of every algorithm with varying experimental conditions and highlights strengths and weaknesses of each approach. This information can be useful not only for enhancing current algorithms and develop the next generation of reconstruction methods, but also to assist physicians in the choice of the most adequate technique for their studies. PMID:24132007
METHOD FOR REMOVAL OF LIGHT ISOTOPE PRODUCT FROM LIQUID THERMAL DIFFUSION UNITS
Hoffman, J.D.; Ballou, J.K.
1957-11-19
A method and apparatus are described for removing the lighter isotope of a gaseous-liquid product from a number of diffusion columns of a liquid thermal diffusion system in two stages by the use of freeze valves. The subject liquid flows from the diffusion columns into a heated sloping capsule where the liquid is vaporized by the action of steam in a heated jacket surrounding the capsule. When the capsule is filled the gas flows into a collector. Flow between the various stages is controlled by freeze valves which are opened and closed by the passage of gas and cool water respectively through coils surrounding portions of the pipes through which the process liquid is passed. The use of the dual stage remover-collector and the freeze valves is an improvement on the thermal diffusion separation process whereby the fraction containing the lighter isotope many be removed from the tops of the diffusion columns without intercolumn flow, or prior stage flow while the contents of the capsule is removed to the final receiver.
Method of analyzing the influence of network structure on information diffusion
NASA Astrophysics Data System (ADS)
Nagata, Katsuya; Shirayama, Susumu
2012-07-01
Social phenomena are affected by the structure of networks consisting of personal relationships. In the present paper, the diffusion of information among people is examined. In particular, the relationship between the network structure and the dynamics is studied. First, several networks are generated using the proposed network model and other network models, such as the WS model and the KE model. By changing the parameters of the network models, networks with different structures are generated. The parameters of the network models determine the topology of the networks and the statistical indicators. Second, the role of network structure on information diffusion is investigated through numerical simulations using a simple information diffusion model of the networks. Two data mining methods are used to analyze the results. A neural network predicts the convergence rate and the time using six explanatory variables, and a decision tree reveals the statistical indicator that has a strong effect on the information diffusion. After these analyses, important statistical variables explaining the information diffusion are shown.
Data Assimilation Using a Variational Method for a 1D Radiation Belt Diffusion Model
NASA Astrophysics Data System (ADS)
Marchand, R.; Degeling, A. W.; O'Donnell, S.; Rankin, R.; Kabin, K.
2009-12-01
A variational data assimilation algorithm has been developed to incorporate electron flux time-series data from satellites into a simple one dimensional diffusion model for the radial transport of radiation belt electrons. The model developed assumes a power law scaling for the radial diffusion coefficient with L shell. The effectiveness of this method is investigated by means of a series of identical twin numerical experiments. This involves using the diffusion model to produce synthetic observations along various satellite trajectories. These observations are in turn used to estimate time-dependent parameters input to the diffusion model, which are compared against the values initially used. The data assimilation algorithm considers the time dependent source located at the outer boundary as a function to be determined. Using synthetic satellite electron flux observations, the algorithm computes a source function that, when used as an input to the diffusion model, most closely reproduces the synthetic observations in a least-squares sense. Observational errors are taken into account, and an estimate of the uncertainty in the output source function is also produced. This uncertainty is found to consistently reflect the quality of the source function estimation during identical twin numerical experiments. Initial tests indicate that the quality of the outer boundary source estimation is strongly dependent on the satellite location, indicating that the outer boundary source estimation becomes poor as information relating to the outer boundary contained in the observations is reduced. The potential of using this data assimilation method to estimate one or more parameters that determine the radial diffusion coefficient, and the possibility of determining whether physical processes affecting the observations are missing in the dynamical model will be discussed.
GPU-accelerated 3D neutron diffusion code based on finite difference method
Xu, Q.; Yu, G.; Wang, K.
2012-07-01
Finite difference method, as a traditional numerical solution to neutron diffusion equation, although considered simpler and more precise than the coarse mesh nodal methods, has a bottle neck to be widely applied caused by the huge memory and unendurable computation time it requires. In recent years, the concept of General-Purpose computation on GPUs has provided us with a powerful computational engine for scientific research. In this study, a GPU-Accelerated multi-group 3D neutron diffusion code based on finite difference method was developed. First, a clean-sheet neutron diffusion code (3DFD-CPU) was written in C++ on the CPU architecture, and later ported to GPUs under NVIDIA's CUDA platform (3DFD-GPU). The IAEA 3D PWR benchmark problem was calculated in the numerical test, where three different codes, including the original CPU-based sequential code, the HYPRE (High Performance Pre-conditioners)-based diffusion code and CITATION, were used as counterpoints to test the efficiency and accuracy of the GPU-based program. The results demonstrate both high efficiency and adequate accuracy of the GPU implementation for neutron diffusion equation. A speedup factor of about 46 times was obtained, using NVIDIA's Geforce GTX470 GPU card against a 2.50 GHz Intel Quad Q9300 CPU processor. Compared with the HYPRE-based code performing in parallel on an 8-core tower server, the speedup of about 2 still could be observed. More encouragingly, without any mathematical acceleration technology, the GPU implementation ran about 5 times faster than CITATION which was speeded up by using the SOR method and Chebyshev extrapolation technique. (authors)
Lu, Yao; Chan, Heang-Ping; Wei, Jun; Hadjiiski, Lubomir M
2013-02-01
Digital breast tomosynthesis (DBT) has strong promise to improve sensitivity for detecting breast cancer. DBT reconstruction estimates the breast tissue attenuation using projection views (PVs) acquired in a limited angular range. Because of the limited field of view (FOV) of the detector, the PVs may not completely cover the breast in the x-ray source motion direction at large projection angles. The voxels in the imaged volume cannot be updated when they are outside the FOV, thus causing a discontinuity in intensity across the FOV boundaries in the reconstructed slices, which we refer to as the truncated projection artifact (TPA). Most existing TPA reduction methods were developed for the filtered backprojection method in the context of computed tomography. In this study, we developed a new diffusion-based method to reduce TPAs during DBT reconstruction using the simultaneous algebraic reconstruction technique (SART). Our TPA reduction method compensates for the discontinuity in background intensity outside the FOV of the current PV after each PV updating in SART. The difference in voxel values across the FOV boundary is smoothly diffused to the region beyond the FOV of the current PV. Diffusion-based background intensity estimation is performed iteratively to avoid structured artifacts. The method is applicable to TPA in both the forward and backward directions of the PVs and for any number of iterations during reconstruction. The effectiveness of the new method was evaluated by comparing the visual quality of the reconstructed slices and the measured discontinuities across the TPA with and without artifact correction at various iterations. The results demonstrated that the diffusion-based intensity compensation method reduced the TPA while preserving the detailed tissue structures. The visibility of breast lesions obscured by the TPA was improved after artifact reduction. PMID:23318346
Yohem, K. H.; Slymen, D. J.; Bregman, M. D.; Meyskens, F. L.
1988-01-01
The radiation response of murine and human melanoma cells assayed in bilayer soft agar and monolayer was examined. Cells from the murine melanoma Cloudman S91 CCL 53.1 cell line and three human melanoma cell strains (C8146C, C8161, and R83-4) developed in our laboratory were irradiated by single dose X-rays and plated either in agar or on plastic. D0 values were the same within 95% confidence intervals for cells from the human melanoma cell strains C8146C, C8161, and R83-4 but were dissimilar for the murine cell line CCL 53.1 Dq values were different for all cells studied. The shape of the survival curve for all four melanomas was not identical for cells assayed in soft agar versus cells grown on plastic. This would indicate that apparent radiosensitivity was influenced by the method of assay although there were no apparent consistent differences between the curves generated by monolayer or bilayer soft agar assays. PMID:3348949
Quantitative evaluation of registration methods for atlas-based diffuse optical tomography
NASA Astrophysics Data System (ADS)
Wu, Xue; Eggebrecht, Adam T.; Culver, Joseph P.; Zhan, Yuxuan; Basevi, Hector; Dehghani, Hamid
2013-06-01
In Diffuse Optical Tomography (DOT), an atlas-based model can be used as an alternative to a subject-specific anatomical model for recovery of brain activity. The main step of the generation of atlas-based subject model is the registration of atlas model to the subject head. The accuracy of the DOT then relies on the accuracy of registration method. In this work, 11 registration methods are quantitatively evaluated. The registration method with EEG 10/20 systems with 19 landmarks and non-iterative point to point algorithm provides approximately 1.4 mm surface error and is considered as the most efficient registration method.
Application of Electrode Methods in Studies of Nitric Oxide Metabolism and Diffusion Kinetics
Liu, Xiaoping; Zweier, Jay L.
2012-01-01
Nitric oxide (NO) has many important physiological roles in the body. Since NO electrodes can directly measure NO concentration in the nM range and in real time, NO electrode methods have been generally used in laboratories for measuring NO concentration in vivo and in vitro. This review focuses on the application of electrode methods in studies of NO diffusion and metabolic kinetics. We have described the physical and chemical properties that need to be considered in the preparation of NO stock solution, discussed the effect of several interfering factors on the measured curves of NO concentration that need to be eliminated in the experimental setup for NO measurements, and provided an overview of the application of NO electrode methods in measuring NO diffusion and metabolic kinetics in solution and in biological systems. This overview covers NO metabolism by oxygen (O2), superoxide, heme proteins, cells and tissues. Important conclusions and physiological implication of these studies are discussed. PMID:23730264
Asgari, Setareh; Jahanshahi, Mohsen; Rahimpour, Ahmad
2014-09-26
In the present work a novel kind of dense nanoporous composite matrix for expanded bed application has been successfully first prepared with Nickel powder as a densifier and was covered with Agar-Agar layer as a skeleton, through the method of water-in-oil emulsification. Agar-Agar is a porous and inexpensive polymer. In order to fabricate cost-effective adsorbent with favorable qualities Agar-Agar polymer was used. Thereafter, the customized composite particle was modified by pseudo-affinity dye-ligand, Reactive Blue 4 (RB4), aimed at preparing a pseudo-affinity adsorbent (RB4-Agar-Ni) for bioprodut adsorption from aqueous solution. Bovine Serum Albumin (BSA) was selected as a model protein to investigate the adsorption behavior in batchwise and expanded bed chromatography, and the obtained results were evaluated with that of Streamline™ (Amersham-Pharmacia Biotech, Sweden). Spherical appearance and porous structure of composite particles were observed by the optical microscope (OM) and scanning electronic microscope (SEM). The results suggested that the matrices followed the logarithmic normal size distribution with the range of 65-300 μm and average diameter of 126.81-151.47 μm, proper wet density of 1.64-2.78 g/ml, water content of 62.74-34%, porosity of 98-90% and pore size of about 38-130 nm. For better comprehension of the impact of solid phase properties on the performance of the expanded bed, the expansion and hydrodynamic properties of a composite matrix with a series of densities was evaluated and estimated by the retention time distribution method (RTD) in an expanded bed and was compared with that of other matrices. According to obtained results the expansion factors under the same fluid velocity decreased by increasing the matrix density. Moreover, the axial dispersion coefficient (Dax) is the most appropriate parameter for evaluating the stability of expanded bed, on various operating conditions, such as different flow velocity, bed expansion degree, viscosity of the liquid phase and the density of adsorbent. It was observed that the application of matrix with high density was proper for high operation, fluid velocity, since the addition of densifier improves the rigidity of the matrix. Three momentous factors, pH, ionic strength and initial concentration of BSA were analyzed. The best results showed that the adsorption equilibrium isotherms seems to follow a typical Langmuir isotherm and also the maximum adsorption capacity (qm) of BSA on RB4-Agar-Ni (64.01 mg/ml adsorbent) was higher than that on RB4-Streamline commercial adsorbent (about 54 mg.ml adsorbent). Additionally kinetic adsorption processes were characterized by the pseudo-first-order and pseudo-second-order kinetics equations. The experimental data followed the pseudo-first-order kinetic equation. Also the breakthrough curves were investigated. It was found that dynamic binding capacity (DBC) decreased with increasing the flow rate and the values of DBC decreased from 21.08 to 11.15 mg/ml adsorbent when the density of composite beads increased from 1.64 to 2.78 g/ml. All results indicate that the prepared composite is promising for efficient bioproduct adsorption with good hydrodynamic characteristics, high stability and it is suitable for expanded bed usage as a cost-effective adsorbent. PMID:25152492
Tchitchekova, Deyana S.; Morthomas, Julien; Perez, Michel; Ribeiro, Fabienne; Ducher, Roland
2014-07-21
A novel method for accurate and efficient evaluation of the change in energy barriers for carbon diffusion in ferrite under heterogeneous stress is introduced. This method, called Linear Combination of Stress States, is based on the knowledge of the effects of simple stresses (uniaxial or shear) on these diffusion barriers. Then, it is assumed that the change in energy barriers under a complex stress can be expressed as a linear combination of these already known simple stress effects. The modifications of energy barriers by either uniaxial traction/compression and shear stress are determined by means of atomistic simulations with the Climbing Image-Nudge Elastic Band method and are stored as a set of functions. The results of this method are compared to the predictions of anisotropic elasticity theory. It is shown that, linear anisotropic elasticity fails to predict the correct energy barrier variation with stress (especially with shear stress) whereas the proposed method provides correct energy barrier variation for stresses up to ∼3 GPa. This study provides a basis for the development of multiscale models of diffusion under non-uniform stress.
Dating of black gel pen ink using the dissolution-diffusion method.
Li, Biao
2014-01-01
In many criminal and civil cases in China, the most commonly questioned documents are those written with gel pen ink. An important task for forensic document examiners is to identify whether two or more ink entries in one or more documents were written with the same ink type. The identification of the age of gel ink entries made poses an important and difficult problem for forensic document examiners. In this paper, a dissolution-diffusion method was successfully employed to estimate the relative age of gel ink entries by comparing dissolution-diffusion rates. Using extensive tests, the mixed solution of dimethyl formamide (DMF) and anhydrous ethanol proved to be a suitable solvent and was used to dissolve the dye of gel ink strokes made at different times. As preliminary findings of this study, calibration curves were created to indicate the relationship between the average dissolution-diffusion rate of soluble gel ink components and the age of gel ink entries stored under natural aging conditions. It was also determined that brands of gel inks, types of paper and thickness of gel ink strokes had varying impacts on estimating the dates of gel ink strokes. Experimental results showed that dissolution-diffusion method was applicable for determining the relative age of gel ink entries under certain conditions. PMID:24378312
NASA Astrophysics Data System (ADS)
Jiang, Tian; Zhang, Yong-Tao
2016-04-01
Implicit integration factor (IIF) methods were developed in the literature for solving time-dependent stiff partial differential equations (PDEs). Recently, IIF methods were combined with weighted essentially non-oscillatory (WENO) schemes in Jiang and Zhang (2013) [19] to efficiently solve stiff nonlinear advection-diffusion-reaction equations. The methods can be designed for arbitrary order of accuracy. The stiffness of the system is resolved well and the methods are stable by using time step sizes which are just determined by the non-stiff hyperbolic part of the system. To efficiently calculate large matrix exponentials, Krylov subspace approximation is directly applied to the implicit integration factor (IIF) methods. So far, the IIF methods developed in the literature are multistep methods. In this paper, we develop Krylov single-step IIF-WENO methods for solving stiff advection-diffusion-reaction equations. The methods are designed carefully to avoid generating positive exponentials in the matrix exponentials, which is necessary for the stability of the schemes. We analyze the stability and truncation errors of the single-step IIF schemes. Numerical examples of both scalar equations and systems are shown to demonstrate the accuracy, efficiency and robustness of the new methods.
Agar/collagen membrane as skin dressing for wounds.
Bao, Lei; Yang, Wei; Mao, Xuan; Mou, Shansong; Tang, Shunqing
2008-12-01
Agar, a highly hydrophilic polymer, has a special gel property and favorable biocompatibility, but moderate intension strength in an aqueous condition and a low degradation rate. In order to tailor both properties of mechanical intension and degradation, type I collagen was composited with agar in a certain ratio by drying at 50 degrees C or by a freeze-dry process. Glutaraldehyde was chosen as a crosslinking agent, and the most favorable condition for crosslinking was that the weight ratio of agar to glutaraldehyde was 66.7 and the pH value about 5. Dynamic mechanical analysis results showed that the single agar membrane had a modulus value between 640 MPa and 1064 MPa, but it was between 340 MPa and 819 MPa after being composited with type I collagen. It was discovered under an optical microscope that the pores were interconnected in the composite scaffolds instead of the honeycomb-like pores in a single type I collagen scaffold or the laminated gaps in a single agar scaffold. The results of an acute toxicity test disclosed that the composites were not toxic to mice although the composites were crosslinked with a certain concentration of glutaraldehyde. The results of gross examinations showed that when the composite membranes or scaffolds were applied to a repair rabbit skin lesion, the composites had a good repair effect without infection, liquid exudation or visible scar in the lesion covered with them. But in the control group, the autologous skin showed necrosis and there were a lot of scar tissues in the lesion site. H&E staining results showed that the repair tissue was similar to the normal one and very few scaffolds or membranes were left without degradation after 2 or 3 weeks. In conclusion, it is proved that type I collagen increases the toughness of the agar membrane, and the agar/type I collagen composites are promising biomaterials as wound dressings for healing burns or ulcers. PMID:19029613
Iterative Two- and One-Dimensional Methods for Three-Dimensional Neutron Diffusion Calculations
Lee, Hyun Chul; Lee, Deokjung; Downar, Thomas J.
2005-09-15
Two methods are proposed for solving the three-dimensional neutron diffusion equation by iterating between solutions of the two-dimensional (2-D) radial and one-dimensional (1-D) axial solutions. In the first method, the 2-D/1-D equations are coupled using a current correction factor (CCF) with the average fluxes of the lower and upper planes and the axial net currents at the plane interfaces. In the second method, an analytic expression for the axial net currents at the interface of the planes is used for planar coupling. A comparison of the new methods is made with two previously proposed methods, which use interface net currents and partial currents for planar coupling. A Fourier convergence analysis of the four methods was performed, and results indicate that the two new methods have at least three advantages over the previous methods. First, the new methods are unconditionally stable, whereas the net current method diverges for small axial mesh size. Second, the new methods provide better convergence performance than the other methods in the range of practical mesh sizes. Third, the spectral radii of the new methods asymptotically approach zero as the mesh size increases, while the spectral radius of the partial current method approaches a nonzero value as the mesh size increases. Of the two new methods proposed here, the analytic method provides a smaller spectral radius than the CCF method, but the CCF method has several advantages over the analytic method in practical applications.
Farzad Rahnema; Dingkang Zhang; Abderrafi Ougouag; Frederick Gleicher
2011-04-04
The main objective of this research is to develop an integrated diffusion/transport (IDT) method to substantially improve the accuracy of nodal diffusion methods for the design and analysis of Very High Temperature Reactors (VHTR). Because of the presence of control rods in the reflector regions in the Pebble Bed Reactor (PBR-VHTR), traditional nodal diffusion methods do not accurately model these regions, within which diffusion theory breaks down in the vicinity of high neutron absorption and steep flux gradients. The IDT method uses a local transport solver based on a new incident flux response expansion method in the controlled nodes. Diffusion theory is used in the rest of the core. This approach improves the accuracy of the core solution by generating transport solutions of controlled nodes while maintaining computational efficiency by using diffusion solutions in nodes where such a treatment is sufficient. The transport method is initially developed and coupled to the reformulated 3-D nodal diffusion model in the CYNOD code for PBR core design and fuel cycle analysis. This method is also extended to the prismatic VHTR. The new method accurately captures transport effects in highly heterogeneous regions with steep flux gradients. The calculations of these nodes with transport theory avoid errors associated with spatial homogenization commonly used in diffusion methods in reactor core simulators
On assessment of numerical methods for diffusion-combustion flow with fast chemistry
NASA Astrophysics Data System (ADS)
Funami, Yuki; Shimada, Toru
2012-11-01
Boundary-layer combustion, a major characteristic of a hybrid rocket engine, is a complex phenomenon of fluid dynamics and combustion. Its rate-limiting process is diffusion, whereas combustion reactions are generally very fast. One of numerical approaches for this is to solve simultaneously the Navier-Stokes equations with the transport equation for the mixture fraction. Chemical composition of the combustion gas can be determined by solving local chemical equilibrium for a given flow and mixture fraction fields. The governing equations for a diffusion-combustion flow with fast chemistry are characterized by the convective term, the diffusion term, and the chemical equilibrium calculation. As seen from the numerical methods for these, the convective-flux Jacobian and the numerical flux schemes, upwind higher precision approximation and limiter design, and chemical equilibrium calculation method. This study is focused especially on upwind higher precision approximation method. In this paper, by solving test problems such as quasi-one-dimensional hybrid rocket flow, assessment is made on a variety of numerical methods with respect to precision and convergence.
Andualem, Berhanu; Gessesse, Amare
2013-01-01
Objective To investigate and optimize microbial media that substitute peptone agar using brebra seed defatted flour. Methods 'Defatted process, inoculums preparation, evaluation of bacterial growth, preparation of cooked and hydrolyzed media and growth turbidity of tested bacteria were determined. Results Two percent defatted flour was found to be suitable concentration for the growth of pathogenic bacteria: Escherichia coli (ATCC 25922) (E. coli), Pseudomonas aeruginosa (ATCC 27853), Salmonella (NCTC 8385) and Shigella flexneri (ATCC 12022) (S. flexneri), while 3% defatted flour was suitable for Staphylococcus aureus (ATCC 25923) (S. aureus). E. coli (93±1) and S. flexneri (524±1) colony count were significantly (P≤0.05) greater in defatted flour without supplement than in supplemented medium. E. coli [(3.72×109±2) CFU/mL], S. aureus [(7.4×109±2) CFU/mL], S. flexneri [(4.03×109±2) CFU/mL] and Salmonella [(2.37×109±1) CFU/mL] in non-hydrolyzed sample were statistically (P≤0.05) greater than hydrolyzed one and commercial peptone agar. Colony count of Salmonella [(4.55×109±3) CFU/mL], S. flexneri [(5.40×109±3) CFU/mL] and Lyesria moncytogenes (ATCC 19116) [(5.4×109±3) CFU/mL] on raw defatted flour agar was significantly (P≤0.05) greater than cooked defatted flour and commercial peptone agar. Biomass of E. coli, S. aureus, Salmonella and Enterococcus faecalis in non-hydrolyzed defatted flour is highly increased over hydrolyzed defatted flour and commercial peptone broth. Conclusions The defatted flour agar was found to be better microbial media or comparable with peptone agar. The substances in it can serve as sources of carbon, nitrogen, vitamins and minerals that are essential to support the growth of microorganisms without any supplements. Currently, all supplements of peptone agar are very expensive in the market. PMID:24075344
Non-invasive measurements of tissue hemodynamics with hybrid diffuse optical methods
NASA Astrophysics Data System (ADS)
Durduran, Turgut
Diffuse optical techniques were used to measure hemodynamics of tissues non-invasively. Spectroscopy and tomography of the brain, muscle and implanted tumors were carried out in animal models and humans. Two qualitatively different methods, diffuse optical tomography and diffuse correlation tomography, were hybridized permitting simultaneous measurement of total hemoglobin concentration, blood oxygen saturation and blood flow. This combination of information was processed further to derive estimates of oxygen metabolism (e.g. CMRO 2) in tissue. The diffuse correlation measurements of blood flow were demonstrated in human tissues, for the first time, demonstrating continous, non-invasive imaging of oxygen metabolism in large tissue volumes several centimeters below the tissue surface. The bulk of these investigations focussed on cerebral hemodynamics. Extensive validation of this methodology was carried out in in vivo rat brain models. Three dimensional images of deep tissue hemodynamics in middle cerebral artery occlusion and cortical spreading depression (CSD) were obtained. CSD hemodynamics were found to depend strongly on partial pressure of carbon dioxide. The technique was then adapted for measurement of human brain. All optical spectroscopic measurements of CMRO2 during functional activation were obtained through intact human skull non-invasively. Finally, a high spatio-temporal resolution measurement of cerebral blood flow due to somatosensory cortex activation following electrical forepaw stimulation in rats was carried out with laser speckle flowmetry. New analysis methods were introduced for laser speckle flowmetry. In other organs, deep tissue hemodynamics were measured on human calf muscle during exercise and cuff-ischemia and were shown to have some clinical utility for peripheral vascular disease. In mice tumor models, the measured hemodynamics were shown to be predictive of photodynamic therapy efficacy, again suggesting promise of clinical utility. In total, the research has pioneered the development of diffuse optical measurements of blood flow, oxygenation and oxygen metabolism in a large range of research and clinical applications.
NASA Astrophysics Data System (ADS)
Kang, Q.; Chen, L.
2014-12-01
Although short-term production of unconventional gas depends on the area of contact created by hydraulic fracturing and connections with pre-existing natural fracture networks, sustainable recovery is limited by transfer of gas from nanoporous matrix into the fractures, because the permeability of hydraulic fractures is orders of magnitude higher than that of the shale matrix. Therefore, a fundamental understanding of hydrocarbon mobility in shale matrix is urgently needed for improving recovery efficiencies. Shale transport properties (diffusivity, permeability, and electronic conductivity), which are critical for understanding the fundamental transport mechanisms, are still poorly understood. There have been some studies using experimental techniques such as scanning electron microscopy (SEM) to visualize the nanoscale structures of shale. Due to the ultra-low porosity and permeability, it is difficult to experimentally investigate the fundamental transport processes inside the shale or accurately measure the transport properties. Advanced pore-scale numerical methods, e.g., the lattice Boltzman method (LBM) may provide an alternative approach. In the present study, three-dimensional nanoscale porous structures of shale are reconstructed based on SEM images of shale samples. Characterization analysis of the nanoscale reconstructed shale is performed, including determination of porosity, pore size distribution, specific surface area, and pore connectivity. The LBM flow model and diffusion model are adopted to simulate fluid flow and Knudsen diffusion in the reconstructed shale, respectively. Tortuosity, intrinsic permeability, and effective Knudsen diffusivity are numerically predicted. The tortuosity is much higher than what is commonly employed in Bruggeman equation. Correction of the intrinsic permeability by taking into consideration the contribution of Knudsen diffusion, which leads to the apparent permeability, is performed. The correction factor under different Knudsen number and pressure conditions are estimated and compared with existing corrections reported in the literature.
Hyperspectral imaging for detecting pathogens grown on agar plates
NASA Astrophysics Data System (ADS)
Yoon, Seung Chul; Lawrence, Kurt C.; Siragusa, Gregory R.; Line, John E.; Park, Bosoon; Windham, William R.
2007-09-01
This paper is concerned with the development of a hyperspectral imaging technique for detecting and identifying one of the most common foodborne pathogens, Campylobacter. Direct plating using agars is an effective tool for laboratory tests and analyses of microorganisms. The morphology (size, growth pattern, color, etc.) of colonies grown on agar plates has been widely used to tentatively differentiate organisms. However, it is sometimes difficult to differentiate target organisms like Campylobacters from other contaminants grown together on the same agar plates. A hyperspectral imaging system operating at the visible and near infrared (VNIR) spectral region from 400 nm to 900 nm was set up to measure spectral signatures of 17 different Campylobacter and non-Campylobacter subspecies. Protocols for culturing, imaging samples and for calibrating measured data were developed. The VNIR spectral library of all 17 organisms commonly encountered in poultry was established from calibrated hyperspectral images. A classification algorithm was developed to locate and identify Campylobacters, non-Campylobacter contaminants, and background agars with 99.29% accuracy. This research has a potential to be expanded to detect other pathogens grown on agar media.
An adaptive tau-leaping method for stochastic simulations of reaction-diffusion systems
NASA Astrophysics Data System (ADS)
Padgett, Jill M. A.; Ilie, Silvana
2016-03-01
Stochastic modelling is critical for studying many biochemical processes in a cell, in particular when some reacting species have low population numbers. For many such cellular processes the spatial distribution of the molecular species plays a key role. The evolution of spatially heterogeneous biochemical systems with some species in low amounts is accurately described by the mesoscopic model of the Reaction-Diffusion Master Equation. The Inhomogeneous Stochastic Simulation Algorithm provides an exact strategy to numerically solve this model, but it is computationally very expensive on realistic applications. We propose a novel adaptive time-stepping scheme for the tau-leaping method for approximating the solution of the Reaction-Diffusion Master Equation. This technique combines effective strategies for variable time-stepping with path preservation to reduce the computational cost, while maintaining the desired accuracy. The numerical tests on various examples arising in applications show the improved efficiency achieved by the new adaptive method.
Cu diffusion as an alternative method for nanopatterned CuTCNQ film growth
NASA Astrophysics Data System (ADS)
Capitán, M. J.; Álvarez, J.; Navío, C.; Miranda, R.
2016-05-01
In this paper we show by means of ‘in situ’ x-ray diffraction studies that CuTCNQ formation from Cu(solid)–TCNQ(solid tetracyanoquinodimethane) goes through Cu diffusion at room temperature. The film quality depends on the TCNQ evaporation rate. At low evaporation rate we get a single phase-I CuTCNQ film very well crystallized and well oriented. The film has a CuTCNQ(0 2 0) orientation. The film is formed by CuTCNQ nanorods of a very homogeneous size. The film homogeneity has also been seen by atomic force microscopy (AFM). The electronic properties of the film have been measured by x-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS). Thus, the Cu-diffusion method has arisen as a very simple, clean and efficient method to grow localized CuTCNQ nanorods on Cu, opening up new insights for technological applications.
Preparation of Eudragit L 100-55 enteric nanoparticles by a novel emulsion diffusion method.
Hao, Shilei; Wang, Bochu; Wang, Yazhou; Zhu, Liancai; Wang, Bin; Guo, Tingwang
2013-08-01
In this study, a novel emulsion diffusion method was used to prepare enteric Eudragit L100-55 nanoparticles by ultrasonic dispersion and diffusion solidification. Omeprazole was selected as the model drug. The prepared nanoparticles were in spherical shape and exhibited negative zeta potential. The Fourier transform infrared spectroscopy results indicated that no molecular interaction occurred between the drug molecule and polymer chain. In addition, the nanoparticles showed a strong pH-sensitive release in vitro. A mild cytotoxicity of nanoparticle was observed in the subsequent studies, and the particle cellular uptake study showed that the nanoparticles could be taken up by Caco-2 cells after 0.5h incubation. Our results indicated that the enteric Eudragit L 100-55 nanoparticle could be synthesized successfully via this ultrasonic solidification method, which also could be applied to prepare other pH-sensitive polymer nanoparticles. PMID:23537830
Surface preparation for determining diffusion length by the surface photovoltage method
Goodman, A.M.
1985-03-26
A method of treating the surface of a sample of n-type silicon material in preparation for measurements for determining the minority carrier diffusion length of the material by the surface photovoltage method comprises applying a strong oxidizing agent to an appropriately prepared surface of a semiconductor material such as silicon. The oxidizing agent is taken from the group consisting of potassium permanganate (KMnO/sub 4/), potassium dichromate (K/sub 2/Cr/sub 2/O/sub 7/), and ammonium dichromate ((NH/sub 4/)/sub 2/Cr/sub 2/O/sub 7/). The surface preparation assures a consistently large surface photovoltage that is stable during the surface photovoltage measurement for minority carrier diffusion length.
Does diffusion MRI tell us anything about the white matter? An overview of methods and pitfalls
ODonnell, Lauren J.; Pasternak, Ofer
2014-01-01
One key pitfall in diffusion magnetic resonance imaging (dMRI) clinical neuroimaging research is the challenge of understanding and interpreting the results of a complex analysis pipeline. The sophisticated algorithms employed by the analysis software, combined with the relatively non-specific nature of many diffusion measurements, lead to challenges in interpretation of the results. This paper is aimed at an intended audience of clinical researchers who are learning about dMRI or trying to interpret dMRI results, and who may be wondering Does dMRI tell us anything about the white matter? We present a critical review of dMRI methods and measures used in clinical neuroimaging research, focusing on the most commonly used analysis methods and the most commonly reported measures. We describe important pitfalls in every section, and provide extensive references for the reader interested in more detail. PMID:25278106
Cu diffusion as an alternative method for nanopatterned CuTCNQ film growth.
Capitán, M J; Álvarez, J; Navío, C; Miranda, R
2016-05-11
In this paper we show by means of 'in situ' x-ray diffraction studies that CuTCNQ formation from Cu(solid)-TCNQ(solid tetracyanoquinodimethane) goes through Cu diffusion at room temperature. The film quality depends on the TCNQ evaporation rate. At low evaporation rate we get a single phase-I CuTCNQ film very well crystallized and well oriented. The film has a CuTCNQ(0 2 0) orientation. The film is formed by CuTCNQ nanorods of a very homogeneous size. The film homogeneity has also been seen by atomic force microscopy (AFM). The electronic properties of the film have been measured by x-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS). Thus, the Cu-diffusion method has arisen as a very simple, clean and efficient method to grow localized CuTCNQ nanorods on Cu, opening up new insights for technological applications. PMID:27049286
Disk diffusion susceptibility testing of the Bacteroides fragilis group.
Horn, R; Bourgault, A M; Lamothe, F
1987-10-01
The susceptibilities of 225 isolates of the Bacteroides fragilis group to six antibiotics were determined by a new disk diffusion test in Wilkins-Chalgren agar and by the standard agar dilution method. For disk diffusion, the bacteria were directly suspended in saline and immediately swabbed onto 15-cm agar plates. Disks of cefoxitin (30 micrograms), chloramphenicol (30 micrograms), clindamycin (2 micrograms), moxalactam (30 micrograms), imipenem (10 micrograms), and ticarcillin (75 micrograms) were applied, and the plates were incubated at 37 degrees C in an anaerobic atmosphere. Zone sizes were measured at 24 h. The results of disk diffusion and agar dilution were compared by regression analysis by the method of least squares and by the error rate-bounded method. Zones were easily measured for 216 strains (96%). The correlation between the MICs and diameters of inhibition for cefoxitin, clindamycin, moxalactam, and ticarcillin was generally good. A correlation could not be established for chloramphenicol and imipenem, as there were too few resistant strains. With the recommended resistance breakpoints, the following susceptible and resistant zone diameter breakpoints could be established: cefoxitin, less than or equal to 19 and greater than or equal to 21 mm; clindamycin, less than or equal to 14 and greater than or equal to 18 mm; moxalactam, less than or equal to 21 and greater than or equal to 25 mm; and ticarcillin, less than or equal to 15 and greater than or equal to 16 mm. By applying these zone criteria, the percentage of false-susceptible strains was less than 1% and of false-resistant strains was less than 4% for the drugs tested. PMID:3481247
A modified evaluation method to reduce finite pulse time effects in flash diffusivity measurement
NASA Astrophysics Data System (ADS)
Tao, Ye; Yang, Liping; Zhong, Qiu; Xu, Zijun; Luo, Caiyun
2015-12-01
A modified evaluation method for laser flash is proposed. In this method, the moment of laser-heating cutoff time is considered as zero point. The penetration depth and formula equation of the sample temperature distribution are obtained with the approximate analytical solution before time zero (during laser heating) for the physical model of a continuously heated half-infinite, well-distributed sample. The weighted-average and approximate-equation methods are then used to quantitatively determine the laser effect depth, which leads to the formulation of a modified evaluation method in flash thermal diffusivity measurement. Results of the simulation calculations and experiments confirm the correctness of the modified method, which remarkably increases flash method applications. The modified method is applicable only to cases in which δ(x) does not exceed the sample thickness ( √{ 12 α τ 0 } ≤ L ) during laser heating.
A modified evaluation method to reduce finite pulse time effects in flash diffusivity measurement.
Tao, Ye; Yang, Liping; Zhong, Qiu; Xu, Zijun; Luo, Caiyun
2015-12-01
A modified evaluation method for laser flash is proposed. In this method, the moment of laser-heating cutoff time is considered as zero point. The penetration depth and formula equation of the sample temperature distribution are obtained with the approximate analytical solution before time zero (during laser heating) for the physical model of a continuously heated half-infinite, well-distributed sample. The weighted-average and approximate-equation methods are then used to quantitatively determine the laser effect depth, which leads to the formulation of a modified evaluation method in flash thermal diffusivity measurement. Results of the simulation calculations and experiments confirm the correctness of the modified method, which remarkably increases flash method applications. The modified method is applicable only to cases in which δ(x) does not exceed the sample thickness (√(12ατ0)≤L) during laser heating. PMID:26724057
A study on the comparison of median filter regularization methods in diffusion tensor MRI.
Kim, Sunghee; Kwon, Kiwoon; Park, Insung; Han, Bongsu; Kim, Dongyoun
2007-01-01
Diffusion Tensor Magnetic Resonance Imaging (DT-MRI) is a method which makes it possible to study non-invasively the architecture of axonal fibers in the central nervous system. Since eigenvectors obtained from DT-MRI usually contain noise, the calculated vector directions may be deviated from the real fiber orientation. Therefore, noise errors can be accumulated as fiber tract becomes longer in tractography of DT-MRI. We used three algorithms for computing matrix medians which are the Simple Median Method, the Gradient Descent Method, and the Successive Fermat Method, because matrix-valued median filters show excellent capabilities for structure-preserving denoising. The results of the Successive Fermat Method give better than those of the Simple Median Method and is faster and the performance is similar to those of the Gradient Descent Method. PMID:18002740
A hybrid method for efficient and accurate simulations of diffusion compartment imaging signals
NASA Astrophysics Data System (ADS)
Rensonnet, Gaëtan; Jacobs, Damien; Macq, Benoît; Taquet, Maxime
2015-12-01
Diffusion-weighted imaging is sensitive to the movement of water molecules through the tissue microstructure and can therefore be used to gain insight into the tissue cellular architecture. While the diffusion signal arising from simple geometrical microstructure is known analytically, it remains unclear what diffusion signal arises from complex microstructural configurations. Such knowledge is important to design optimal acquisition sequences, to understand the limitations of diffusion-weighted imaging and to validate novel models of the brain microstructure. We present a novel framework for the efficient simulation of high-quality DW-MRI signals based on the hybrid combination of exact analytic expressions in simple geometric compartments such as cylinders and spheres and Monte Carlo simulations in more complex geometries. We validate our approach on synthetic arrangements of parallel cylinders representing the geometry of white matter fascicles, by comparing it to complete, all-out Monte Carlo simulations commonly used in the literature. For typical configurations, equal levels of accuracy are obtained with our hybrid method in less than one fifth of the computational time required for Monte Carlo simulations.
A novel grating-imaging method to measure carrier diffusion coefficient in graphene
NASA Astrophysics Data System (ADS)
Chen, Ke; Wang, Yaguo; Akinwande, Deji; Bank, Seth; Lin, Jung-Fu
Similar to carrier mobility, carrier diffusion coefficient in graphene determines the response rate of future graphene-based electronics. Here we present a simple, sensitive and non-destructive technique integrated with ultrafast pump-probe spectroscopy to measure carrier diffusion in CVD-grown graphene. In the method, the pump and the probe beams pass through the same area of a photomask with metal strips i.e. a transmission amplitude grating, and get diffracted. The diffracted light is collected by an objective lens and focused onto the sample to generate carrier density grating. Relaxation of this carrier density grating is governed by both carrier recombination and carrier diffusion in the sample. Transient transmission change of the probe beams, which reflects this relaxation process, is recorded. The measured diffusion coefficients of multilayer and monolayer CVD-grown graphene are 2000cm2/s and 10000cm2/s, respectively, comparable with the reported values of epitaxial graphene and reduced graphene. This transmission grating technique can be used to measure carrier dynamics in versatile 2D materials.
NASA Astrophysics Data System (ADS)
Trochet, Mickaël; Béland, Laurent Karim; Joly, Jean-François; Brommer, Peter; Mousseau, Normand
2015-06-01
We study point-defect diffusion in crystalline silicon using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo method with on-the-fly catalog building capabilities based on the activation-relaxation technique (ART nouveau), coupled to the standard Stillinger-Weber potential. We focus more particularly on the evolution of crystalline cells with one to four vacancies and one to four interstitials in order to provide a detailed picture of both the atomistic diffusion mechanisms and overall kinetics. We show formation energies, activation barriers for the ground state of all eight systems, and migration barriers for those systems that diffuse. Additionally, we characterize diffusion paths and special configurations such as dumbbell complex, di-interstitial (IV-pair+2I) superdiffuser, tetrahedral vacancy complex, and more. This study points to an unsuspected dynamical richness even for this apparently simple system that can only be uncovered by exhaustive and systematic approaches such as the kinetic activation-relaxation technique.
NASA Astrophysics Data System (ADS)
Dhara, Ashis K.; Mukhopadhyay, Sudipta
2012-03-01
The computer aided diagnostic (CAD) system has been developed to assist radiologist for early detection and analysis of lung nodules. For pulmonary nodule detection, image preprocessing is required to remove the anatomical structure of lung parenchyma and to enhance the visibility of pulmonary nodules. In this paper a hybrid preprocessing technique using geometry based diffusion and selective enhancement filtering have been proposed. This technique provides a unified preprocessing framework for solid nodule as well as ground glass opacity (GGO) nodules. Geometry based diffusion is applied to smooth the images by preserving the boundary. In order to improve the sensitivity of pulmonary nodule detection, selective enhancement filter is used to highlight blob like structure. But selective enhancement filter sometimes enhances the structures like blood vessel and airways other than nodule and results in large number of false positive. In first step, geometry based diffusion (GBD) is applied for reduction of false positive and in second step, selective enhancement filtering is used for further reduction of false negative. Geometry based diffusion and selective enhancement filtering has been used as preprocessing step separately but their combined effect was not investigated earlier. This hybrid preprocessing approach is suitable for accurate calculation of voxel based features. The proposed method has been validated on one public database named Lung Image Database Consortium (LIDC) containing 50 nodules (30 solid and 20 GGO nodule) from 30 subjects and one private database containing 40 nodules (25 solid and 15 GGO nodule) from 30 subjects.
New contactless method for thermal diffusivity measurements using modulated photothermal radiometry
Pham Tu Quoc, S. Cheymol, G.; Semerok, A.
2014-05-15
Modulated photothermal radiometry is a non-destructive and contactless technique for the characterization of materials. It has two major advantages: a good signal-to-noise ratio through a synchronous detection and a low dependence on the heating power and the optical properties of the sample surface. This paper presents a new method for characterizing the thermal diffusivity of a material when the phase shift between a modulated laser power signal and the thermal signal of a plate sample is known at different frequencies. The method is based on a three-dimensional analytical model which is used to determine the temperature amplitude and the phase in the laser heating of the plate. A new simple formula was developed through multi-parametric analysis to determine the thermal diffusivity of the plate with knowledge of the frequency at the minimum phase shift, the laser beam radius r{sub 0} and the sample thickness L. This method was developed to control the variation of the thermal diffusivity of nuclear components and it was first applied to determine the thermal diffusivity of different metals: 304 L stainless steel, nickel, titanium, tungsten, molybdenum, zinc, and iron. The experimental results were obtained with 5%–10% accuracy and corresponded well with the reference values. The present paper also demonstrates the limit of application of this method for plate with thickness r{sub 0}/100 ≤ L ≤ r{sub 0}/2. The technique is deemed interesting for the characterization of barely accessible components that require a contactless measurement.
NASA Astrophysics Data System (ADS)
Lai, Yongzeng; Zeng, Yan; Xi, Xiaojing
2011-11-01
In this paper, we discuss control variate methods for Asian option pricing under exponential jump diffusion model for the underlying asset prices. Numerical results show that the new control variate XNCV is much more efficient than the classical control variate XCCV when used in pricing Asian options. For example, the variance reduction ratios by XCCV are no more than 120 whereas those by XNCV vary from 15797 to 49171 on average over sample sizes 1024, 2048, 4096, 8192, 16384 and 32768.
Method and apparatus for determining minority carrier diffusion length in semiconductors
Goldstein, Bernard; Dresner, Joseph; Szostak, Daniel J.
1983-07-12
Method and apparatus are provided for determining the diffusion length of minority carriers in semiconductor material, particularly amorphous silicon which has a significantly small minority carrier diffusion length using the constant-magnitude surface-photovoltage (SPV) method. An unmodulated illumination provides the light excitation on the surface of the material to generate the SPV. A manually controlled or automatic servo system maintains a constant predetermined value of the SPV. A vibrating Kelvin method-type probe electrode couples the SPV to a measurement system. The operating optical wavelength of an adjustable monochromator to compensate for the wavelength dependent sensitivity of a photodetector is selected to measure the illumination intensity (photon flux) on the silicon. Measurements of the relative photon flux for a plurality of wavelengths are plotted against the reciprocal of the optical absorption coefficient of the material. A linear plot of the data points is extrapolated to zero intensity. The negative intercept value on the reciprocal optical coefficient axis of the extrapolated linear plot is the diffusion length of the minority carriers.
Contribution to an effective design method for stationary reaction-diffusion patterns
Szalai, István; Horváth, Judit; De Kepper, Patrick
2015-06-15
The British mathematician Alan Turing predicted, in his seminal 1952 publication, that stationary reaction-diffusion patterns could spontaneously develop in reacting chemical or biochemical solutions. The first two clear experimental demonstrations of such a phenomenon were not made before the early 1990s when the design of new chemical oscillatory reactions and appropriate open spatial chemical reactors had been invented. Yet, the number of pattern producing reactions had not grown until 2009 when we developed an operational design method, which takes into account the feeding conditions and other specificities of real open spatial reactors. Since then, on the basis of this method, five additional reactions were shown to produce stationary reaction-diffusion patterns. To gain a clearer view on where our methodical approach on the patterning capacity of a reaction stands, numerical studies in conditions that mimic true open spatial reactors were made. In these numerical experiments, we explored the patterning capacity of Rabai's model for pH driven Landolt type reactions as a function of experimentally attainable parameters that control the main time and length scales. Because of the straightforward reversible binding of protons to carboxylate carrying polymer chains, this class of reaction is at the base of the chemistry leading to most of the stationary reaction-diffusion patterns presently observed. We compare our model predictions with experimental observations and comment on agreements and differences.
Song, Yun S; Steinrücken, Matthias
2012-03-01
The transition density function of the Wright-Fisher diffusion describes the evolution of population-wide allele frequencies over time. This function has important practical applications in population genetics, but finding an explicit formula under a general diploid selection model has remained a difficult open problem. In this article, we develop a new computational method to tackle this classic problem. Specifically, our method explicitly finds the eigenvalues and eigenfunctions of the diffusion generator associated with the Wright-Fisher diffusion with recurrent mutation and arbitrary diploid selection, thus allowing one to obtain an accurate spectral representation of the transition density function. Simplicity is one of the appealing features of our approach. Although our derivation involves somewhat advanced mathematical concepts, the resulting algorithm is quite simple and efficient, only involving standard linear algebra. Furthermore, unlike previous approaches based on perturbation, which is applicable only when the population-scaled selection coefficient is small, our method is nonperturbative and is valid for a broad range of parameter values. As a by-product of our work, we obtain the rate of convergence to the stationary distribution under mutation-selection balance. PMID:22209899
Contribution to an effective design method for stationary reaction-diffusion patterns
NASA Astrophysics Data System (ADS)
Szalai, István; Horváth, Judit; De Kepper, Patrick
2015-06-01
The British mathematician Alan Turing predicted, in his seminal 1952 publication, that stationary reaction-diffusion patterns could spontaneously develop in reacting chemical or biochemical solutions. The first two clear experimental demonstrations of such a phenomenon were not made before the early 1990s when the design of new chemical oscillatory reactions and appropriate open spatial chemical reactors had been invented. Yet, the number of pattern producing reactions had not grown until 2009 when we developed an operational design method, which takes into account the feeding conditions and other specificities of real open spatial reactors. Since then, on the basis of this method, five additional reactions were shown to produce stationary reaction-diffusion patterns. To gain a clearer view on where our methodical approach on the patterning capacity of a reaction stands, numerical studies in conditions that mimic true open spatial reactors were made. In these numerical experiments, we explored the patterning capacity of Rabai's model for pH driven Landolt type reactions as a function of experimentally attainable parameters that control the main time and length scales. Because of the straightforward reversible binding of protons to carboxylate carrying polymer chains, this class of reaction is at the base of the chemistry leading to most of the stationary reaction-diffusion patterns presently observed. We compare our model predictions with experimental observations and comment on agreements and differences.
Contribution to an effective design method for stationary reaction-diffusion patterns.
Szalai, István; Horváth, Judit; De Kepper, Patrick
2015-06-01
The British mathematician Alan Turing predicted, in his seminal 1952 publication, that stationary reaction-diffusion patterns could spontaneously develop in reacting chemical or biochemical solutions. The first two clear experimental demonstrations of such a phenomenon were not made before the early 1990s when the design of new chemical oscillatory reactions and appropriate open spatial chemical reactors had been invented. Yet, the number of pattern producing reactions had not grown until 2009 when we developed an operational design method, which takes into account the feeding conditions and other specificities of real open spatial reactors. Since then, on the basis of this method, five additional reactions were shown to produce stationary reaction-diffusion patterns. To gain a clearer view on where our methodical approach on the patterning capacity of a reaction stands, numerical studies in conditions that mimic true open spatial reactors were made. In these numerical experiments, we explored the patterning capacity of Rabai's model for pH driven Landolt type reactions as a function of experimentally attainable parameters that control the main time and length scales. Because of the straightforward reversible binding of protons to carboxylate carrying polymer chains, this class of reaction is at the base of the chemistry leading to most of the stationary reaction-diffusion patterns presently observed. We compare our model predictions with experimental observations and comment on agreements and differences. PMID:26117122
Computing quasi-linear diffusion coefficients using the delta-f particle-in-cell method
Austin, T. M.; Smithe, D. N.; Ranjbar, V.
2009-11-26
Linear wave codes AORSA and TORIC couple to the bounce-averaged nonlinear Fokker-Planck code CQL3D through quasi-linear diffusion coefficients. Both linear wave codes rely on the quasi-local approximation that includes only first-order parallel and perpendicular gradient variations of cyclotron frequency and ignores field line curvature along with temperature and density gradient effects. The delta-f particle-in-cell (DFPIC) method has been successfully used for simulating ion-cyclotron fast wave behavior. This method also permits particle behavior such as multiple pass resonance, banana orbits, and superadiabaticity. We present new work on generating quasi-linear diffusion coefficients using the DFPIC method that will permit the electromagnetic particle-in-cell (EMPIC) code, VORPAL, to couple to CQL3D and to compare to AORSA and TORIC. A new multiple weight delta-f approach will be presented that converts velocity derivatives to action derivatives and yields a full tensor quasi-linear diffusion coefficient.
Alemani, Davide; Chopard, Bastien; Galceran, Josep; Buffle, Jacques
2005-09-21
A new approach to numerically solve a reaction-diffusion system is given, specifically developed for complex systems including many reacting/diffusing species with broad ranges of rate constants and diffusion coefficients, as well as complicated geometry of reacting interfaces. The approach combines a Lattice Boltzmann (LB) method with a splitting time technique. In the present work, the proposed approach is tested by focusing on the typical reaction process between a metal ion M and a ligand L, to form a complex ML with M being consumed at an electrode. The aim of the paper is to systematically study the convergence conditions of the associated numerical scheme. We find that the combination of LB with the time splitting method allows us to solve the problem for any value of association and dissociation rate constant of the reaction process. Also, the method can be extended to a mixture of ligands. We stress two main points: (1) the LB approach is particularly convenient for the flux computation of M and (2) the splitting time procedure is very well suited for reaction processes involving association-dissociation rate constants varying on many orders of magnitude. PMID:16240048
Song, Yun S.; Steinrücken, Matthias
2012-01-01
The transition density function of the Wright–Fisher diffusion describes the evolution of population-wide allele frequencies over time. This function has important practical applications in population genetics, but finding an explicit formula under a general diploid selection model has remained a difficult open problem. In this article, we develop a new computational method to tackle this classic problem. Specifically, our method explicitly finds the eigenvalues and eigenfunctions of the diffusion generator associated with the Wright–Fisher diffusion with recurrent mutation and arbitrary diploid selection, thus allowing one to obtain an accurate spectral representation of the transition density function. Simplicity is one of the appealing features of our approach. Although our derivation involves somewhat advanced mathematical concepts, the resulting algorithm is quite simple and efficient, only involving standard linear algebra. Furthermore, unlike previous approaches based on perturbation, which is applicable only when the population-scaled selection coefficient is small, our method is nonperturbative and is valid for a broad range of parameter values. As a by-product of our work, we obtain the rate of convergence to the stationary distribution under mutation–selection balance. PMID:22209899
The diffuse-scattering method for investigating locally ordered binary solid solutions
Epperson, J.E. ); Anderson, J.P. ); Chen, H. . Materials Science and Engineering Dept.)
1994-01-01
Diffuse-scattering investigations comprise a series of maturing methods for detailed characterization of the local-order structure and atomic displacements of binary alloy systems. The distribution of coherent diffuse scattering is determined by the local atomic ordering, and analytical techniques are available for extracting the relevant structural information. An extension of such structural investigations, for locally ordered alloys at equilibrium, allows one to obtain pairwise interaction energies. Having experimental pairwise interaction energies for the various coordination shells offers one the potential for more realistic kinetic Ising modeling of alloy systems as they relax toward equilibrium. Although the modeling of atomic displacements in conjunction with more conventional studies of chemical ordering is in its infancy, the method appears to offer considerable promise for revealing additional information about the strain fields in locally ordered and clustered alloys. The diffuse-scattering methods for structural characterization and for the recovery of interaction energies are reviewed, and some preliminary results are used to demonstrate the potential of the kinetic Ising modeling technique to follow the evolution of ordering or phase separation in an alloy system.
Fly agaric (Amanita muscaria) poisoning, case report and review.
Satora, Leszek; Pach, Dorota; Butryn, Beata; Hydzik, Piotr; Balicka-Slusarczyk, Barbara
2005-06-01
Gathering and eating mushrooms and other plants containing psychoactive substances has become increasingly popular among young people experimenting with drugs. Dried fly agaric Amanita muscaria fruiting bodies were eaten by five young persons (18-21 years of age) at a party in order to evoke hallucinations. Visual and auditory hallucinations occurred in four of them, whereas a 18-year-old girl lost consciousness. The following morning, she went to the Clinic of Toxicology. Due to the fact that not all the active substances present in the fly agaric have been identified, and some of them have an effect after a period of latency, the patient was admitted for several days of observation during which check-up examinations were performed. After four days without any problems, she was discharged. The poisoning regressed with no organ complications. The remaining persons who had eaten the fly agaric were free from any complaints. PMID:15904689
A deterministic particle method for one-dimensional reaction-diffusion equations
NASA Technical Reports Server (NTRS)
Mascagni, Michael
1995-01-01
We derive a deterministic particle method for the solution of nonlinear reaction-diffusion equations in one spatial dimension. This deterministic method is an analog of a Monte Carlo method for the solution of these problems that has been previously investigated by the author. The deterministic method leads to the consideration of a system of ordinary differential equations for the positions of suitably defined particles. We then consider the time explicit and implicit methods for this system of ordinary differential equations and we study a Picard and Newton iteration for the solution of the implicit system. Next we solve numerically this system and study the discretization error both analytically and numerically. Numerical computation shows that this deterministic method is automatically adaptive to large gradients in the solution.
Agar-block microcosms for controlled plant tissue decomposition by aerobic fungi.
Schilling, Jonathan S; Jacobson, K Brook
2011-01-01
The two principal methods for studying fungal biodegradation of lignocellulosic plant tissues were developed for wood preservative testing (soil-block; agar-block). It is well-accepted that soil-block microcosms yield higher decay rates, fewer moisture issues, lower variability among studies, and higher thresholds of preservative toxicity. Soil-block testing is thus the more utilized technique and has been standardized by American Society for Testing and Materials (ASTM) (method D 1413-07). The soil-block design has drawbacks, however, using locally-variable soil sources and in limiting the control of nutrients external (exogenous) to the decaying tissues. These drawbacks have emerged as a problem in applying this method to other, increasingly popular research aims. These modern aims include degrading lignocellulosics for bioenergy research, testing bioremediation of co-metabolized toxics, evaluating oxidative mechanisms, and tracking translocated elements along hyphal networks. Soil-blocks do not lend enough control in these applications. A refined agar-block approach is necessary. Here, we use the brown rot wood-degrading fungus Serpula lacrymans to degrade wood in agar-block microcosms, using deep Petri dishes with low-calcium agar. We test the role of exogenous gypsum on decay in a time-series, to demonstrate the utility and expected variability. Blocks from a single board rip (longitudinal cut) are conditioned, weighed, autoclaved, and introduced aseptically atop plastic mesh. Fungal inoculations are at each block face, with exogenous gypsum added at interfaces. Harvests are aseptic until the final destructive harvest. These microcosms are designed to avoid block contact with agar or Petri dish walls. Condensation is minimized during plate pours and during incubation. Finally, inoculum/gypsum/wood spacing is minimized but without allowing contact. These less technical aspects of agar-block design are also the most common causes of failure and the key source of variability among studies. Video publication is therefore useful in this case, and we demonstrate low-variability, high-quality results. PMID:21339715
Differentiation of Candida dubliniensis from Candida albicans on Pal's Agar
Al Mosaid, Asmaa; Sullivan, Derek J.; Coleman, David C.
2003-01-01
Production of a hyphal fringe around colonies grown on Pal's agar (sunflower seed agar) at 30°C for 48 to 72 h provides a simple means of discriminating between isolates of C. dubliniensis and C. albicans with 100% accuracy. Of 128 C. dubliniensis isolates tested on this medium, all produced a hyphal fringe. In contrast, none of the 124 C. albicans isolates tested produced a hyphal fringe. Pal's medium has the added advantage of being prepared from inexpensive, readily available seeds. PMID:14532221
Arabski, Micha?; Wasik, S?awomir; Piskulak, Patrycja; G?d?, Natalia; Slezak, Andrzej; Kaca, Wies?aw
2011-01-01
The aim of this study was to analysis of antibiotics (ampicilin, streptomycin, ciprofloxacin or colistin) release from agarose gel by spectrophotmetry and laser interferometry methods. The interferometric system consisted of a Mach-Zehnder interferometer with a He-Ne laser, TV-CCD camera, computerised data acquisition system and a gel system. The gel system under study consists of two cuvettes. We filled the lower cuvette with an aqueous 1% agarose solution with the antibiotics at initial concentration of antibiotics in the range of 0.12-2 mg/ml for spectrophotmetry analysis or 0.05-0.5 mg/ml for laser interferometry methods, while in the upper cuvette there was pure water. The diffusion was analysed from 120 to 2400 s with a time interval of deltat = 120 s by both methods. We observed that 0.25-1 mg/ml and 0,05 mg/ml are minimal initial concentrations detected by spectrophotometric and laser interferometry methods, respectively. Additionally, we observed differences in kinetic of antibiotic diffusion from gel measured by both methods. In conclusion, the laser interferometric method is a useful tool for studies of antibiotic release from agarose gel, especially for substances are not fully soluble in water, for example: colistin. PMID:22046824
NASA Astrophysics Data System (ADS)
Chen, Li; Zhang, Lei; Kang, Qinjun; Viswanathan, Hari S.; Yao, Jun; Tao, Wenquan
2015-01-01
Porous structures of shales are reconstructed using the markov chain monte carlo (MCMC) method based on scanning electron microscopy (SEM) images of shale samples from Sichuan Basin, China. Characterization analysis of the reconstructed shales is performed, including porosity, pore size distribution, specific surface area and pore connectivity. The lattice Boltzmann method (LBM) is adopted to simulate fluid flow and Knudsen diffusion within the reconstructed shales. Simulation results reveal that the tortuosity of the shales is much higher than that commonly employed in the Bruggeman equation, and such high tortuosity leads to extremely low intrinsic permeability. Correction of the intrinsic permeability is performed based on the dusty gas model (DGM) by considering the contribution of Knudsen diffusion to the total flow flux, resulting in apparent permeability. The correction factor over a range of Knudsen number and pressure is estimated and compared with empirical correlations in the literature. For the wide pressure range investigated, the correction factor is always greater than 1, indicating Knudsen diffusion always plays a role on shale gas transport mechanisms in the reconstructed shales. Specifically, we found that most of the values of correction factor fall in the slip and transition regime, with no Darcy flow regime observed.
Chen, Li; Zhang, Lei; Kang, Qinjun; Viswanathan, Hari S; Yao, Jun; Tao, Wenquan
2015-01-01
Porous structures of shales are reconstructed using the markov chain monte carlo (MCMC) method based on scanning electron microscopy (SEM) images of shale samples from Sichuan Basin, China. Characterization analysis of the reconstructed shales is performed, including porosity, pore size distribution, specific surface area and pore connectivity. The lattice Boltzmann method (LBM) is adopted to simulate fluid flow and Knudsen diffusion within the reconstructed shales. Simulation results reveal that the tortuosity of the shales is much higher than that commonly employed in the Bruggeman equation, and such high tortuosity leads to extremely low intrinsic permeability. Correction of the intrinsic permeability is performed based on the dusty gas model (DGM) by considering the contribution of Knudsen diffusion to the total flow flux, resulting in apparent permeability. The correction factor over a range of Knudsen number and pressure is estimated and compared with empirical correlations in the literature. For the wide pressure range investigated, the correction factor is always greater than 1, indicating Knudsen diffusion always plays a role on shale gas transport mechanisms in the reconstructed shales. Specifically, we found that most of the values of correction factor fall in the slip and transition regime, with no Darcy flow regime observed. PMID:25627247
Chen, Li; Zhang, Lei; Kang, Qinjun; Viswanathan, Hari S.; Yao, Jun; Tao, Wenquan
2015-01-01
Porous structures of shales are reconstructed using the markov chain monte carlo (MCMC) method based on scanning electron microscopy (SEM) images of shale samples from Sichuan Basin, China. Characterization analysis of the reconstructed shales is performed, including porosity, pore size distribution, specific surface area and pore connectivity. The lattice Boltzmann method (LBM) is adopted to simulate fluid flow and Knudsen diffusion within the reconstructed shales. Simulation results reveal that the tortuosity of the shales is much higher than that commonly employed in the Bruggeman equation, and such high tortuosity leads to extremely low intrinsic permeability. Correction of the intrinsic permeability is performed based on the dusty gas model (DGM) by considering the contribution of Knudsen diffusion to the total flow flux, resulting in apparent permeability. The correction factor over a range of Knudsen number and pressure is estimated and compared with empirical correlations in the literature. For the wide pressure range investigated, the correction factor is always greater than 1, indicating Knudsen diffusion always plays a role on shale gas transport mechanisms in the reconstructed shales. Specifically, we found that most of the values of correction factor fall in the slip and transition regime, with no Darcy flow regime observed. PMID:25627247
Fixed and pulsed gradient diffusion methods in low-field core analysis.
Leu, Gabriela; Fordham, Edmund J; Hürlimann, Martin D; Frulla, Phil
2005-02-01
We review diffusion-weighted relaxation protocols for two-dimensional diffusion/relaxation time (D, T(2)) distributions and their application to fluid-saturated sedimentary rocks at low fields typical of oil-well logging tools (< or = 2 MHz for 1H). Fixed field gradient (FFG) protocols may be implemented in logging tools and in the laboratory; there, pulsed field gradient (PFG) protocols are also available. In either category, direct or stimulated echoes may be used for the diffusion evolution periods. We compare the results of several variant FFG and PFG protocols obtained on liquids and two contrasting sedimentary rocks. For liquids and rocks of negligible internal gradients (g(int)), results are comparable, as expected, for all the studied protocols. For rocks of strong g(int), protocol-dependent artifacts are seen in the joint (D, T2) distributions, consistent with the effects of the internal fields. For laboratory petrophysics, the PFG methods offer several advantages: (a) significantly improved signal-to-noise ratio and acquisition times for repetitions over many samples; (b) freedom from heteronuclear contamination when fluorinated liquids are used in core holders; and (c) a palette of variants--one comparable with the FFG--for the study of rocks of significant g(int). Given suitable hardware, both PFG and FFG methods can be implemented in the same bench-top apparatus, providing a versatile test bed for application in a petrophysical laboratory. PMID:15833632
Hierarchical clustering method for improved prostate cancer imaging in diffuse optical tomography
NASA Astrophysics Data System (ADS)
Kavuri, Venkaiah C.; Liu, Hanli
2013-03-01
We investigate the feasibility of trans-rectal near infrared (NIR) based diffuse optical tomography (DOT) for early detection of prostate cancer using a transrectal ultrasound (TRUS) compatible imaging probe. For this purpose, we designed a TRUS-compatible, NIR-based image system (780nm), in which the photo diodes were placed on the trans-rectal probe. DC signals were recorded and used for estimating the absorption coefficient. We validated the system using laboratory phantoms. For further improvement, we also developed a hierarchical clustering method (HCM) to improve the accuracy of image reconstruction with limited prior information. We demonstrated the method using computer simulations laboratory phantom experiments.
Properties of alloy steel powders produced by the method of diffusion impregnation (review)
Napara-Volgina, S.G.
1985-06-01
In their review of research on the properties of alloy steel powders produced by the method of diffusion impregnation, the authors systematize their data into three charts, one on the characteristics of charges and the recommended areas of use of powders, one on the chemical and particle size compositions and technological properties of the powders, and one on the fine crystalline structure of alloy powders of different compositions. The authors recommend the use of such powders, especially powder metallurgy constructional steels, produced by hot stamping and other methods providing high density.
Numerical methods of solving a system of multi-dimensional nonlinear equations of the diffusion type
NASA Technical Reports Server (NTRS)
Agapov, A. V.; Kolosov, B. I.
1979-01-01
The principles of conservation and stability of difference schemes achieved using the iteration control method were examined. For the schemes obtained of the predictor-corrector type, the conversion was proved for the control sequences of approximate solutions to the precise solutions in the Sobolev metrics. Algorithms were developed for reducing the differential problem to integral relationships, whose solution methods are known, were designed. The algorithms for the problem solution are classified depending on the non-linearity of the diffusion coefficients, and practical recommendations for their effective use are given.
Absorption spectroscopy of powdered materials using time-resolved diffuse optical methods.
D'Andrea, Cosimo; Obraztsova, Ekaterina A; Farina, Andrea; Taroni, Paola; Lanzani, Guglielmo; Pifferi, Antonio
2012-11-10
In this paper a novel method, based on time-resolved diffuse optical spectroscopy, is proposed to measure the absorption of small amounts of nanostructured powder materials independent of scattering. Experimental validation, in the visible and near-infrared spectral range, has been carried out on India Ink^{particles. The effectiveness of the technique to measure scattering-free absorption is demonstrated on carbon nanotubes. The comparison between the absorption spectra acquired by the proposed method and conventional measurements performed with a commercial spectrophotometer is discussed. PMID:23142900}
Galerkin finite element method for two-dimensional Riesz space fractional diffusion equations
NASA Astrophysics Data System (ADS)
Bu, Weiping; Tang, Yifa; Yang, Jiye
2014-11-01
In this article, a class of two-dimensional Riesz space fractional diffusion equations is considered. Some fractional spaces are established and some equivalences between fractional derivative spaces and fractional Sobolev space are presented. By the Galerkin finite element method and backward difference method, a fully discrete scheme is obtained. According to Lax-Milgram theorem, the existence and uniqueness of the solution to the fully discrete scheme are investigated. The stability and convergence of the scheme are also derived. Finally, some numerical examples are given for verification of our theoretical analysis.
A nodal expansion method for the neutron diffusion equation in cylindrical geometry
Komlev, O.G.; Suslov, I.R.
1995-12-31
A polynomial nodal expansion method (NEM) is applied to solve multigroup diffusion equations in cylindrical R-Z geometry, Fourth-order polynomials are used to approximate one dimensional (1D) transverse integrated fluxes. The special set of the basis functions is used in R-direction. The transverse integrated leakages are approximated by both constant and quadratic polynomials. Preliminary efficiency evaluation of the NEM is carried out for a fast breeder reactor (FBR) model problem. Results indicate computational efficiency of NEM in comparison with finite-difference method (FDM).
NASA Astrophysics Data System (ADS)
Zhu, Jianting; Ogden, Fred L.; Lai, Wencong; Chen, Xiangfeng; Talbot, Cary A.
2016-04-01
Vadose zone flow problems are usually solved from the Richards equation. Solution to the Richards equation is generally challenging because the hydraulic conductivity and diffusivity in the equation are strongly non-linear functions of water content. The finite water-content method was proposed as an alternative general solution method of the vadose zone flow problem for infiltration, falling slugs, and vadose zone response to water table dynamics based on discretizing the water content domain into numerous bins instead of the traditional spatial discretization. In this study, we develop an improved approach to the original finite water-content method (referred to as TO method hereinafter) that better simulates diffusive effects but retains the robustness of the TO method. The approach treats advection and diffusion separately and considers diffusion on a bin by bin basis. After discretizing into water content bins, we treat the conductivity and diffusivity in individual bins as water content dependent constant evaluated at given water content corresponding to each bin. For each bin, we can solve the flow equations analytically since the hydraulic conductivity and diffusivity can be treated as a constant. We then develop solutions for each bin to determine the diffusive water amounts at each time step. The water amount ahead of the convective front for each bin is redistributed among water content bins to account for diffusive effects. The application of developed solution is straightforward only involving algebraic manipulations at each time step. The method can mainly improve water content profiles, but has no significant difference for the total infiltration rate and cumulative infiltration compared to the TO method. Although the method separately deals with advection and diffusion, it can account for the coupling effects of advection and diffusion reasonably well.
NASA Astrophysics Data System (ADS)
Kaźmierczak-Bałata, Anna; Bodzenta, Jerzy; Trefon-Radziejewska, Dominika
2010-01-01
The use of a typical measuring cryostat with a standard temperature controller was proposed for investigation of the temperature dependence of the thermal diffusivity of transparent samples. The basic idea is to use the cryostat heater to control the mean sample temperature and to generate the thermal wave in it, simultaneously. Because of the relatively high thermal inertia of the system, the measurements are carried out at frequencies not exceeding 50 mHz. The periodic temperature disturbance in the sample was detected optically by the use of the mirage effect. The proposed method was used for determination of the thermal diffusivity of yttrium aluminum garnet single crystals in a temperature range from 20 °C to 200 °C.
Engle, Mark A.; Olea, Ricardo A.; O'Keefe, Jennifer M. K.; Hower, James C.; Geboy, Nicholas J.
2013-01-01
Coal fires occur in nature spontaneously, contribute to increases in greenhouse gases, and emit atmospheric toxicants. Increasing interest in quantifying coal fire emissions has resulted in the adaptation and development of specialized approaches and adoption of numerical modeling techniques. Overview of these methods for direct estimation of diffuse gas emissions from coal fires is presented in this paper. Here we take advantage of stochastic Gaussian simulation to interpolate CO2 fluxes measured using a dynamic closed chamber at the Ruth Mullins coal fire in Perry County, Kentucky. This approach allows for preparing a map of diffuse gas emissions, one of the two primary ways that gases emanate from coal fires, and establishing the reliability of the study both locally and for the entire fire. Future research directions include continuous and automated sampling to improve quantification of gaseous coal fire emissions.
A balancing domain decomposition method by constraints for advection-diffusion problems
Tu, Xuemin; Li, Jing
2008-12-10
The balancing domain decomposition methods by constraints are extended to solving nonsymmetric, positive definite linear systems resulting from the finite element discretization of advection-diffusion equations. A pre-conditioned GMRES iteration is used to solve a Schur complement system of equations for the subdomain interface variables. In the preconditioning step of each iteration, a partially sub-assembled finite element problem is solved. A convergence rate estimate for the GMRES iteration is established, under the condition that the diameters of subdomains are small enough. It is independent of the number of subdomains and grows only slowly with the subdomain problem size. Numerical experiments for several two-dimensional advection-diffusion problems illustrate the fast convergence of the proposed algorithm.
NASA Astrophysics Data System (ADS)
Kramer, J.; Jecl, R.; Škerget, L.
2008-09-01
In the present work, a Boundary Domain Integral Method, which has been already established for the solution of viscous incompressible fluid flow through porous media, is extended to capture compressible fluid flow in porous media. The presented numerical scheme was used for solving the problem of double diffusive natural convection in a square porous cavity heated from a side, while the horizontal walls are maintained at different concentrations. The Brinkman extension of Darcy equation is used to model the flow through porous medium. The velocity-vorticity formulation is employed enabeling the computation scheme to be partitioned into kinematic and kinetic parts. The results of double diffusive natural convection in porous cavity are presented in terms of velocity, temperature and concentration redistributions.
GPU-Accelerated Finite Element Method for Modelling Light Transport in Diffuse Optical Tomography
Schweiger, Martin
2011-01-01
We introduce a GPU-accelerated finite element forward solver for the computation of light transport in scattering media. The forward model is the computationally most expensive component of iterative methods for image reconstruction in diffuse optical tomography, and performance optimisation of the forward solver is therefore crucial for improving the efficiency of the solution of the inverse problem. The GPU forward solver uses a CUDA implementation that evaluates on the graphics hardware the sparse linear system arising in the finite element formulation of the diffusion equation. We present solutions for both time-domain and frequency-domain problems. A comparison with a CPU-based implementation shows significant performance gains of the graphics accelerated solution, with improvements of approximately a factor of 10 for double-precision computations, and factors beyond 20 for single-precision computations. The gains are also shown to be dependent on the mesh complexity, where the largest gains are achieved for high mesh resolutions. PMID:22013431
Thermal diffusivity measurement using the mode-mismatched photothermal lens method
NASA Astrophysics Data System (ADS)
Benitez, Miguel; Marcano, Aristides; Melikechi, Noureddine
2009-04-01
We report on a mode-mismatched pump-probe photothermal lens experiment aimed at determination of the thermal diffusivity coefficient of optical samples. In the scheme, the probe beam is collimated and the pump beam is focused. Using a Fresnel diffraction approximation, we show that under these conditions the time dependence of the signal does not depend on the Rayleigh parameters and waist positions of the light beams. This fact allows a more simple and reliable calibration of the experiment in comparison to other schemes. We conduct studies on liquid and solid samples that confirm the predictions of the model. Using the proposed method, we measure the thermal diffusivity coefficient of distilled water, ethanol, methanol, chloroform, nitrobenzene, ethylene glycol, and a solid piece of acrylic plastic. The results are in good agreement with previous measurements.
Numerical methods for one-dimensional reaction-diffusion equations arising in combustion theory
NASA Technical Reports Server (NTRS)
Ramos, J. I.
1987-01-01
A review of numerical methods for one-dimensional reaction-diffusion equations arising in combustion theory is presented. The methods reviewed include explicit, implicit, quasi-linearization, time linearization, operator-splitting, random walk and finite-element techniques and methods of lines. Adaptive and nonadaptive procedures are also reviewed. These techniques are applied first to solve two model problems which have exact traveling wave solutions with which the numerical results can be compared. This comparison is performed in terms of both the wave profile and computed wave speed. It is shown that the computed wave speed is not a good indicator of the accuracy of a particular method. A fourth-order time-linearized, Hermitian compact operator technique is found to be the most accurate method for a variety of time and space sizes.
Reddy, Ashok Kumar; Brahmaiah, Upputuri; Narayen, Nitesh; Reddy, Ravi Kumar; Reddy, Rupak Kumar; Chitta, Meghraj; Prasad, Srinivas; Swarup, Rishi; Mohiuddin, Syed Maaz; Reddy, Madhukar; Aasuri, Murali K; Murthy, B S R; Bhide, Milind; Ahmed, Sajid
2013-06-01
To compare the blood agar (BA), sabouraud dextrose agar (SDA) and chocolate agar (CA) for the isolation of fungi in patients with mycotic keratitis. Corneal Scrapings of 229 patients with clinically diagnosed microbial keratitis were inoculated on BA, SDA, CA. The culture media were evaluated for the rate and time taken for the fungal growth. Seventy six of 229 patients had fungal keratitis. Fungus grew on BA in 60/76(78.9 %), on SDA in 76/76 (100 %), on CA in 40/76(52.6 %) patients. The fungi which grew on BA (60/76) also grown on SDA at the same time. The colony morphologies of different fungi were better on SDA than BA/CA. Among the different culture media, SDA is essential for the isolation fungi in patients with mycotic keratitis. PMID:23196788
A tracer-based inversion method for diagnosing eddy-induced diffusivity and advection
NASA Astrophysics Data System (ADS)
Bachman, S. D.; Fox-Kemper, B.; Bryan, F. O.
2015-02-01
A diagnosis method is presented which inverts a set of tracer flux statistics into an eddy-induced transport intended to apply for all tracers. The underlying assumption is that a linear flux-gradient relationship describes eddy-induced tracer transport, but a full tensor coefficient is assumed rather than a scalar coefficient which allows for down-gradient and skew transports. Thus, Lagrangian advection and anisotropic diffusion not necessarily aligned with the tracer gradient can be diagnosed. In this method, multiple passive tracers are initialized in an eddy-resolving flow simulation. Their spatially-averaged gradients form a matrix, where the gradient of each tracer is assumed to satisfy an identical flux-gradient relationship. The resulting linear system, which is overdetermined when using more than three tracers, is then solved to obtain an eddy transport tensor R which describes the eddy advection (antisymmetric part of R) and potentially anisotropic diffusion (symmetric part of R) in terms of coarse-grained variables. The mathematical basis for this inversion method is presented here, along with practical guidelines for its implementation. We present recommendations for initialization of the passive tracers, maintaining the required misalignment of the tracer gradients, correcting for nonconservative effects, and quantifying the error in the diagnosed transport tensor. A method is proposed to find unique, tracer-independent, distinct rotational and divergent Lagrangian transport operators, but the results indicate that these operators are not meaningfully relatable to tracer-independent eddy advection or diffusion. With the optimal method of diagnosis, the diagnosed transport tensor is capable of predicting the fluxes of other tracers that are withheld from the diagnosis, including even active tracers such as buoyancy, such that relative errors of 14% or less are found.
Gogoi, Sudarshan; Borah, Himadri; Dutta, Rekha R; Puzari, Panchanan
2015-04-01
In this work, the diffusion of thiocholine ion into an enzyme-loaded polypyrrole film was evaluated by different methods, and the results were compared to identify the most suitable method. The enzyme-loaded polypyrrole film was coated with a thin layer of gelatin and gluteraldehyde so as to prevent enzyme leaching. Diffusion coefficients under normal and prepolarized conditions were calculated by five different methods, namely, the Cottrell method, the method of Peerce and Bard, the theoretical impedance model, the electrochemically stimulated conformational relaxation (ESCR) method, and the direct impedance measurement method. The theoretical model of Vortynstev was used to calculate the parameters from the impedance spectra using simplex technique in MATLAB. The results indicate that under normal unpolarized condition the ESCR method gives a diffusion coefficient close to that given by Vortynstev method, but under polarized conditions the Cottrell method can provide a better value of diffusion coefficient than ESCR. The diffusion coefficient of thiocholine in PPy composite film from an electrolytic background of phosphate buffer of pH 7.4 was found to be 1.00 × 10(-8) cm(2) s(-1) based on Vortynstev method. The mechanism of thiocholine diffusion into the positively charged/polarized matrix is attributed to be through the formation of a dinegative ion between thiocholine and phosphate anion via electrostatic attraction. PMID:25782026
Jenkins, R D; Stevens, S L; Craythorn, J M; Thomas, T W; Guinan, M E; Matsen, J M
1985-09-01
Disk diffusion susceptibility tests for enterococci are frequently modified by adding 5% sheep blood (SB) to Mueller-Hinton agar; the performance standards from the National Committee for Clinical Laboratory Standards sanction this addition. Susceptibility testing of aminoglycoside antibiotics is not recommended for enterococci; in actual practice, however, some laboratories do include aminoglycoside antibiotics routinely, and others may test upon request or in selected situations. In examining 50 clinical isolates of enterococci, SB-enriched Mueller-Hinton agar frequently gave enlarged zone sizes that falsely indicated susceptibility (72% for gentamicin and tobramycin), with the average increase in zone size being 6.3 and 7.6 mm, respectively. Comparison agar dilution MICs demonstrated uniform resistance, with or without added SB. The effect was shown to be caused by heme in concentrations as low as 0.03 micrograms/ml, which, when combined with aminoglycoside antibiotics, caused a synergistic growth inhibition of the enterococci, resulting in larger aminoglycoside antibiotic zones. We postulate that the heme effect is related to a catalytic cleavage of intracellular H2O2 and resultant lipid peroxidation. No other organism or antimicrobial agent tested demonstrated a similar effect, although other investigators have shown a similar phenomenon with the broad-spectrum cephalosporins. Because enterococci grow well and give accurate susceptibility results on Mueller-Hinton agar without SB supplementation and because of the spectrum of definable problems with a number of antimicrobial agents, we recommend that enterococci routinely be tested without SB. PMID:4044795
Hyperspectral Imaging for Detecting Pathogens Grown on Agar Plates
Technology Transfer Automated Retrieval System (TEKTRAN)
This paper is concerned with the development of a hyperspectral imaging technique for detecting and identifying one of the most common foodborne pathogens, Campylobacter. Direct plating using agars is an effective tool for laboratory tests and analyses of microorganisms. The morphology (size, growth...
Internal structure and thermo-viscoelastic properties of agar ionogels.
Sharma, Anshu; Rawat, Kamla; Solanki, Pratima R; Aswal, V K; Kohlbrecher, J; Bohidar, H B
2015-12-10
Ionic liquids (IL) can alter the physical properties of agar hydrogels. Rheology studies show that gels with wide range of storage moduli (gel strength) G0 values ranging from 1 to 20 KPa could be made in imidazolium based IL solutions where the IL concentration may not exceed 5% (w/v). Gelation and gel melting temperatures (tgel and Tm) could be altered by as much as ≈ 10 °C. Small angle neutron scattering studies revealed the presence of fibre bundles of agar double helices having typical length of 120 nm that increased to ≈ 180 nm under favorable conditions. These structures gain flexibility from the cladding of the agar bundles by IL molecules which in turn caused partial charge neutralization of its surface. Raman spectroscopy revealed differential hydration of these bundles. It was found that IL molecules with longer alkyl chain (more hydrophobic) altered the gel homogeneity, and changed its thermal and mechanical properties significantly. Therefore, customization of agar hydrogels in green solvent medium (IL solutions) widens the scope of its application potential that may include sensing. PMID:26428165
21 CFR 866.4600 - Ouchterlony agar plate.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Ouchterlony agar plate. 866.4600 Section 866.4600 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES IMMUNOLOGY AND MICROBIOLOGY DEVICES Immunology Laboratory Equipment and Reagents §...
21 CFR 866.4600 - Ouchterlony agar plate.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Ouchterlony agar plate. 866.4600 Section 866.4600 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES IMMUNOLOGY AND MICROBIOLOGY DEVICES Immunology Laboratory Equipment and Reagents §...
21 CFR 866.4600 - Ouchterlony agar plate.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Ouchterlony agar plate. 866.4600 Section 866.4600 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES IMMUNOLOGY AND MICROBIOLOGY DEVICES Immunology Laboratory Equipment and Reagents §...
Improving agar electrospinnability with choline-based deep eutectic solvents
Technology Transfer Automated Retrieval System (TEKTRAN)
One percent agar (% wt) was dissolved in the deep eutectic solvent (DES), (2-hydroxyethyl) trimethylammonium chloride/urea at a 1:2 molar ratio, and successfully electrospun into nanofibers. An existing electrospinning set-up, operated at 50 deg C, was adapted for use with an ethanol bath to collect...
Use of potato flakes agar in clinical mycology.
Rinaldi, M G
1982-06-01
A formulation comprised of commercially available potato flakes, glucose, and agar provides a medium which is inexpensive, is easily prepared, and is particularly useful for the identification of mold fungi encountered in the clinical mycology laboratory. The inclusion of appropriate antimicrobial agents results in a selective medium effective in the isolation and identification of medically important fungi. PMID:7050152
Özarslan, Evren; Westin, Carl-Fredrik; Mareci, Thomas H.
2016-01-01
The influence of Gaussian diffusion on the magnetic resonance signal is determined by the apparent diffusion coefficient (ADC) and tensor (ADT) of the diffusing fluid as well as the gradient waveform applied to sensitize the signal to diffusion. Estimations of ADC and ADT from diffusion-weighted acquisitions necessitate computations of, respectively, the b-value and b-matrix associated with the employed pulse sequence. We establish the relationship between these quantities and the gradient waveform by expressing the problem as a path integral and explicitly evaluating it. Further, we show that these important quantities can be conveniently computed for any gradient waveform using a simple algorithm that requires a few lines of code. With this representation, our technique complements the multiple correlation function (MCF) method commonly used to compute the effects of restricted diffusion, and provides a consistent and convenient framework for studies that aim to infer the microstructural features of the specimen. PMID:27182208
Liu, Changchun; Sadik, Mohamed M.; Mauk, Michael G.; Edelstein, Paul H.; Bushman, Frederic D.; Gross, Robert; Bau, Haim H.
2014-01-01
Real-time amplification and quantification of specific nucleic acid sequences plays a major role in medical and biotechnological applications. In the case of infectious diseases, such as HIV, quantification of the pathogen-load in patient specimens is critical to assess disease progression and effectiveness of drug therapy. Typically, nucleic acid quantification requires expensive instruments, such as real-time PCR machines, which are not appropriate for on-site use and for low-resource settings. This paper describes a simple, low-cost, reaction-diffusion based method for end-point quantification of target nucleic acids undergoing enzymatic amplification. The number of target molecules is inferred from the position of the reaction-diffusion front, analogous to reading temperature in a mercury thermometer. The method was tested for HIV viral load monitoring and performed on par with conventional benchtop methods. The proposed method is suitable for nucleic acid quantification at point of care, compatible with multiplexing and high-throughput processing, and can function instrument-free. PMID:25477046
Self-feeding MUSE: a robust method for high resolution diffusion imaging using interleaved EPI.
Zhang, Zhe; Huang, Feng; Ma, Xiaodong; Xie, Sheng; Guo, Hua
2015-01-15
Single-shot echo planar imaging (EPI) with parallel imaging techniques has been well established as the most popular method for clinical diffusion imaging, due to its fast acquisition and motion insensitivity. However, this approach is limited by the relatively low spatial resolution and image distortion. Interleaved EPI is able to break the limitations but the phase variations among different shots must be considered for artifact suppression. The introduction of multiplexed sensitivity-encoding (MUSE) can address the phase issue using sensitivity encoding (SENSE) for self-navigation of each interleave. However, MUSE has suboptimal results when the number of shots is high. To achieve higher spatial resolution and lower geometric distortion, we introduce two new schemes into the MUSE framework: 1) a self-feeding mechanism is adopted by using prior information regularized SENSE in order to obtain reliable phase estimation; and 2) retrospective motion detection and data rejection strategies are performed to exclude unusable data corrupted by severe pulsatile motions. The proposed method is named self-feeding MUSE (SF-MUSE). Experiments on healthy volunteers demonstrate that this new SF-MUSE approach provides more accurate motion-induced phase estimation and fewer artifacts caused by data corruption when compared with the original MUSE method. SF-MUSE is a robust method for high resolution diffusion imaging and suitable for practical applications with reasonable scan time. PMID:25451470
Liu, Changchun; Sadik, Mohamed M; Mauk, Michael G; Edelstein, Paul H; Bushman, Frederic D; Gross, Robert; Bau, Haim H
2014-01-01
Real-time amplification and quantification of specific nucleic acid sequences plays a major role in medical and biotechnological applications. In the case of infectious diseases, such as HIV, quantification of the pathogen-load in patient specimens is critical to assess disease progression and effectiveness of drug therapy. Typically, nucleic acid quantification requires expensive instruments, such as real-time PCR machines, which are not appropriate for on-site use and for low-resource settings. This paper describes a simple, low-cost, reaction-diffusion based method for end-point quantification of target nucleic acids undergoing enzymatic amplification. The number of target molecules is inferred from the position of the reaction-diffusion front, analogous to reading temperature in a mercury thermometer. The method was tested for HIV viral load monitoring and performed on par with conventional benchtop methods. The proposed method is suitable for nucleic acid quantification at point of care, compatible with multiplexing and high-throughput processing, and can function instrument-free. PMID:25477046
A diffuse-interface method for two-phase flows with soluble surfactants.
Teigen, Knut Erik; Song, Peng; Lowengrub, John; Voigt, Axel
2011-01-20
A method is presented to solve two-phase problems involving soluble surfactants. The incompressible Navier-Stokes equations are solved along with equations for the bulk and interfacial surfactant concentrations. A non-linear equation of state is used to relate the surface tension to the interfacial surfactant concentration. The method is based on the use of a diffuse interface, which allows a simple implementation using standard finite difference or finite element techniques. Here, finite difference methods on a block-structured adaptive grid are used, and the resulting equations are solved using a non-linear multigrid method. Results are presented for a drop in shear flow in both 2D and 3D, and the effect of solubility is discussed. PMID:21218125
Brotto, Laura; Battistutta, Franco; Tat, Lara; Comuzzo, Piergiorgio; Zironi, Roberto
2010-03-24
Some modifications to a previous nondestructive colorimetric method that permits evaluation of the oxygen diffusion rate through wine closures were proposed. The method is based on the reaction of indigo carmine solution with oxygen and the tristimulus measurement of the consequent color change. Simplified preparation and measurement procedures were set up, allowing the analysis of a large number of samples simultaneously. The method was applied to the evaluation of the variability within the lot of 20 different types of stoppers (synthetic, produced by molding, and natural cork). The closures were tested at a storage temperature of 26 degrees C. With regard to oxygen permeability, the natural cork stopper showed a low homogeneity within the lot, especially during the first month after bottling, whereas the synthetic closure showed a greater steadiness in the performance. The limits of the colorimetric method were also analyzed, and three possible causes of degradation of the indigo carmine solution were identified: oxygen, light, and heat. PMID:20187636
Fast non-overlapping Schwarz domain decomposition methods for solving the neutron diffusion equation
Jamelot, Erell; Ciarlet, Patrick
2013-05-15
Studying numerically the steady state of a nuclear core reactor is expensive, in terms of memory storage and computational time. In order to address both requirements, one can use a domain decomposition method, implemented on a parallel computer. We present here such a method for the mixed neutron diffusion equations, discretized with Raviart–Thomas–Nédélec finite elements. This method is based on the Schwarz iterative algorithm with Robin interface conditions to handle communications. We analyse this method from the continuous point of view to the discrete point of view, and we give some numerical results in a realistic highly heterogeneous 3D configuration. Computations are carried out with the MINOS solver of the APOLLO3® neutronics code.
Mueller-Klieser, W
1984-01-01
A method has been developed for the quantitative evaluation of oxygen tension (PO2) distributions in multicellular spheroids measured with O2-sensitive microelectrodes. The experimental data showed that multicellular tumor spheroids in stirred growth media were characterized by a diffusion-depleted zone surrounding the spheroids. This zone was elicited by an unstirred layer of medium next to the spheroid leading to a continuous decrease in the PO2 values from the bulk medium towards the spheroid surface. Theoretical considerations demonstrate that the volume-related O2 consumption rate, Q, in the spheroids can be assessed by measuring the PO2 gradient in the diffusion-depleted zone outside the spheroids. Accordingly, Krogh's diffusion constant, KS, in the spheroids can be determined through measuring the PO2 gradient within the spheroids. The results obtained suggest that multicellular spheroids represent useful in vitro tumor models for the experimental and theoretical analysis of the interrelationship among O2 supply to tumor cells, O2 metabolism in tumors tissue, and the responsiveness of cancer cells to treatment. PMID:6487734
NOTE A method for fat suppression in MRI based on diffusion-weighted imaging
NASA Astrophysics Data System (ADS)
Bendel, Peter; Schiffenbauer, Yael
2010-11-01
The diffusion coefficient of lipid molecules is usually much smaller than that of water, and it is demonstrated here how this difference can be exploited for robust fat suppression in magnetic resonance imaging (MRI). In contrast to the prevailing methods, diffusion-based fat suppression does not rely on chemical shift differences between water and lipids and can therefore be applied easily in low or inhomogeneous magnetic fields. It is also independent of relaxation times and can therefore be incorporated in experiments requiring conventional T1-weighted contrast. Diffusion-based fat suppression (DIFFSUP) consists of subtracting the signals acquired at low and high b-values, where the high b-value is ideally designed to achieve full suppression of the water and negligible attenuation of the lipid signal. Since high b-value images may be particularly affected by motion artifacts, a version of DIFFSUP incorporating first-order velocity compensation is also proposed and demonstrated. Results from phantoms and live mice at field strengths of 4.7 T and 1.0 T are presented.
A method to analyze the diffuse gamma-ray emission with the Fermi Large Area Telescope
Ackermann, Markus; Johannesson, Gueolaugur; Digel, Seth; Moskalenko, Igor V.; Reimer, Olaf; Porter, Troy; Strong, Andrew
2008-12-24
The Fermi Gamma-Ray Space Telescope with its main instrument the LAT is the most sensitive {gamma}-ray telescope in the energy region between 30 MeV and 100 GeV. One of the prime scientific goals of this mission is the measurement and interpretation of the diffuse Galactic and extragalactic {gamma}-ray emission. While not limited by photon statistics, this analysis presents several challenges: Instrumental response functions, residual background from cosmic rays as well as resolved and unresolved foreground {gamma}-ray sources have to be taken carefully into account in the interpretation of the data. Detailed modeling of the diffuse {gamma}-ray emission is being performed and will form the basis of the investigations. We present the analysis approach to be applied to the Fermi LAT data, namely the modeling of the diffuse emission components and the background contributions, followed by an all-sky maximum-likelihood fitting procedure. We also report on the performance of this method evaluated in tests on simulated Fermi LAT and real EGRET data.
Rani, G Usha; Mishra, Sumit; Pathak, Gopal; Jha, Usha; Sen, Gautam
2013-10-01
Synthesis of graft copolymers under the influence of microwave radiation alone is a rapid, efficient, clean, cheap, convenient, energy-saving and green method. Grafting of poly(2-hydroxyethylmethacrylate) on agar backbone was carried out under the influence of microwave radiation. The synthesis is optimized in terms of percentage grafting and intrinsic viscosity, by varying the microwave irradiation time and monomer (2-hydroxyethylmethacrylate) concentration. The synthesized graft copolymers have been characterized by intrinsic viscosity measurement, FTIR spectroscopy, UV-spectroscopy, elemental analysis (C, H, N, & S), thermal studies and scanning electron microscopy (SEM). Flocculation efficacy of the synthesized graft copolymers was studied in 0.25% kaolin and 1% coal fine suspension, through 'jar test' procedure. Further, flocculation efficacy of the best grade, coagulant (alum) and agar were studied for possible application in remediation of metals from river water. PMID:23850679
A new method for choosing the computational cell in stochastic reactiondiffusion systems
Kang, Hye-Won; Zheng, Likun; Othmer, Hans G.
2013-01-01
How to choose the computational compartment or cell size for the stochastic simulation of a reactiondiffusion system is still an open problem, and a number of criteria have been suggested. A generalized measure of the noise for finite-dimensional systems based on the largest eigenvalue of the covariance matrix of the number of molecules of all species has been suggested as a measure of the overall fluctuations in a multivariate system, and we apply it here to a discretized reactiondiffusion system. We show that for a broad class of first-order reaction networks this measure converges to the square root of the reciprocal of the smallest mean species number in a compartment at the steady state. We show that a suitably re-normalized measure stabilizes as the volume of a cell approaches zero, which leads to a criterion for the maximum volume of the compartments in a computational grid. We then derive a new criterion based on the sensitivity of the entire network, not just of the fastest step, that predicts a grid size that assures that the concentrations of all species converge to a spatially-uniform solution. This criterion applies for all orders of reactions and for reaction rate functions derived from singular perturbation or other reduction methods, and encompasses both diffusing and non-diffusing species. We show that this predicts the maximal allowable volume found in a linear problem, and we illustrate our results with an example motivated by anterior-posterior pattern formation in Drosophila, and with several other examples. PMID:22071651
Venter, J P; Mller, D G; du Plessis, J; Goosen, C
2001-05-01
In order to determine whether a drug shows the potential for percutaneous absorption, both in situ and in vitro studies are used. In vitro studies are good indicators of transdermal drug delivery, but the possibility exists that anatomical changes in excised skin can influence drug delivery. The aim of this study was to compare the in vitro Franz diffusion cell method with an in situ adapted diffusion cell method. A saturated aqueous solution of doxylamine succinate was used as model drug and the receptor phase was an isotonic Srensen buffered solution. The in vitro permeation studies were conducted using vertical Franz diffusion cells with nude mice skin. For in situ studies, a diffusion cell was implanted under the dorsal skin of a nude mouse, simulating the in vitro method. Both in situ and in vitro experiments were conducted over a period of 12 h during which samples were collected every 90 min. The mean steady-state flux from Franz diffusion cells was 0.164+/-0.045 microg/cm2/h and flux determined by the in situ method was 0.113+/-0.034 microg/cm2/h. A statistical significant difference existed between the permeation results of the in vitro and in situ experimental methods. A subjective, semi-quantitative assessment of histological changes to excised nude mouse skin was done using light microscopy. This showed that excised skin undergoes sub-lethal injury (necrosis) during in vitro experiments, which may lead to increased permeability of the drug. It was noticed that in vitro and in situ permeation results showed very close correlation until approximately 4.5 h after commencement of experiments, after which, the permeation through excised skin increased. It was assumed that cell necrosis occurred to such an extent after approximately 4.5 h, that the barrier function of the stratum corneum decreased and permeation of the drug increased. PMID:11297901
NASA Astrophysics Data System (ADS)
Frassinetti, L.; Olofsson, K. E. J.; Fridström, R.; Setiadi, A. C.; Brunsell, P. R.; Volpe, F. A.; Drake, J.
2013-08-01
A new method for the estimate of the wall diffusion time of non-axisymmetric fields is developed. The method based on rotating external fields and on the measurement of the wall frequency response is developed and tested in EXTRAP T2R. The method allows the experimental estimate of the wall diffusion time for each Fourier harmonic and the estimate of the wall diffusion toroidal asymmetries. The method intrinsically considers the effects of three-dimensional structures and of the shell gaps. Far from the gaps, experimental results are in good agreement with the diffusion time estimated with a simple cylindrical model that assumes a homogeneous wall. The method is also applied with non-standard configurations of the coil array, in order to mimic tokamak-relevant settings with a partial wall coverage and active coils of large toroidal extent. The comparison with the full coverage results shows good agreement if the effects of the relevant sidebands are considered.
Estimating Effective Vertical Diffusivity in Shallow Ponds by a Constrained Flux-Gradient Method
NASA Astrophysics Data System (ADS)
Bean, J. R.; Torgersen, T.
2004-12-01
Shallow ponds have been used to mitigate the deleterious effects of storm water run-off by acting as detention/retention basins that sequester run-off associated pollutants in sediments. Studies show that the retention efficiency of these systems can decrease over time as a result of the internal loading of nutrients/contaminants from the sediments back to the water column where they are available for export downstream. Quantifying the vertical transport of gases (down) and sediment derived materials (up) is vital to the modeling and understanding of the processes that contribute to the magnitude of internal loading. A critical parameter is the effective vertical diffusion coefficient: Kz=Dmolecular +Deddy (cm2 sec-1). The flux gradient method for estimating effective vertical thermal diffusivity has been applied with success in large lakes which undergo stratification cycles on seasonal or longer time scales. We offer a constrained version of the flux-gradient method that has been adapted for use in a shallow pond with a daily stratification cycle. The method employs heat as a tracer and assumes that transport in the face of a stable gradient is diffusive. By shrinking the spatial and temporal resolution of measurement to scales appropriate to the system of interest and carefully accounting for internal source and sink terms of heat (e.g solar radiation and sediment heat fluxes) we are able to calculate Kz as a function of time and depth during periods of stable stratification, i.e when the pond is not vertically well-mixed. Results show the magnitude of Kz varies from ca. 10-3 to 10-1 (cm2 sec-1) under stratified conditions depending primarily on the strength of stratification.
NASA Astrophysics Data System (ADS)
Pestiaux, A.; Krn, T.; Melchior, S.; Lambrechts, J.; Remacle, J. F.; Deleersnijder, E.; Fichefet, T.
2012-04-01
The discretization of the Gent-McWilliams velocity and isopycnal diffusion with a discontinuous Galerkin finite element method is presented. Both processes are implemented in an ocean model thanks to a tensor related to the mesoscale eddies. The antisymmetric part of this tensor is computed from the Gent-McWilliams velocity and is subsequently included in the tracer advection equation. This velocity can be constructed to be divergence-free. The symmetric part that describes the diapycnal and isopycnal diffusions requires a special treatment. A stable and physically sound isopycnal tracer diffusion scheme is needed. Here, an interior penalty method is chosen that enables to build stable diffusion terms. However, due to the strong anisotropy of the diffusion, the common-usual penalty factor by Ern et al. (2008) is not sufficient. A novel method for computing the penalty term of Ern is then proposed for diffusion equations when both the diffusivity and the mesh are strongly anisotropic. Two test cases are resorted to validate the methodology and two more realistic applications illustrate the diapycnal and isopycnal diffusions, as well as the Gent-McWilliams velocity.
Sinc-Chebyshev Collocation Method for a Class of Fractional Diffusion-Wave Equations
Mao, Zhi; Xiao, Aiguo; Yu, Zuguo; Shi, Long
2014-01-01
This paper is devoted to investigating the numerical solution for a class of fractional diffusion-wave equations with a variable coefficient where the fractional derivatives are described in the Caputo sense. The approach is based on the collocation technique where the shifted Chebyshev polynomials in time and the sinc functions in space are utilized, respectively. The problem is reduced to the solution of a system of linear algebraic equations. Through the numerical example, the procedure is tested and the efficiency of the proposed method is confirmed. PMID:24977177
The Galerkin finite element method for a multi-term time-fractional diffusion equation
NASA Astrophysics Data System (ADS)
Jin, Bangti; Lazarov, Raytcho; Liu, Yikan; Zhou, Zhi
2015-01-01
We consider the initial/boundary value problem for a diffusion equation involving multiple time-fractional derivatives on a bounded convex polyhedral domain. We analyze a space semidiscrete scheme based on the standard Galerkin finite element method using continuous piecewise linear functions. Nearly optimal error estimates for both cases of initial data and inhomogeneous term are derived, which cover both smooth and nonsmooth data. Further we develop a fully discrete scheme based on a finite difference discretization of the time-fractional derivatives, and discuss its stability and error estimate. Extensive numerical experiments for one- and two-dimensional problems confirm the theoretical convergence rates.
cAMP diffusion in Dictyostelium discoideum: A Green's function method
NASA Astrophysics Data System (ADS)
Calovi, Daniel S.; Brunnet, Leonardo G.; de Almeida, Rita M. C.
2010-07-01
A Green’s function method is developed to approach the spatiotemporal equations describing the cAMP production in Dictyostelium discoideum, markedly reducing numerical calculations times: cAMP concentrations and gradients are calculated just at the amoeba locations. A single set of parameters is capable of reproducing the different observed behaviors, from cAMP synchronization, spiral waves and reaction-diffusion patterns to streaming and mound formation. After aggregation, the emergence of a circular motion of amoebas, breaking the radial cAMP field symmetry, is observed.
Akhgari, Abbas; Sadeghi, Hasti; Dabbagh, Mohammad Ali
2014-01-01
Objective(s): The aim of this study was to improve flowability and compressibility characteristics of starch to use as a suitable excipient in direct compression tabletting. Quasi-emulsion solvent diffusion was used as a crystal modification method. Materials and Methods: Corn starch was dissolved in hydrochloric acid at 80°C and then ethanol as a non-solvent was added with lowering temperature until the formation of a precipitate of modified starch. Flow parameters, particle size and thermal behavior of the treated powders were compared with the native starch. Finally, the 1:1 mixture of naproxen and each excipient was tabletted, and hardness and friability of different tablets were evaluated. Results: Larger and well shaped agglomerates were formed which showed different thermal behavior. Treated starch exhibited suitable flow properties and tablets made by the treated powder had relatively high hardness. Conclusion: It was found that recrystallization of corn starch by quasi emulsion solvent diffusion method could improve its flowability and compressibility characteristics. PMID:25422746
Liu, Cong; Kolarik, Barbara; Gunnarsen, Lars; Zhang, Yinping
2015-10-20
Polychlorinated biphenyls (PCBs) have been found to be persistent in the environment and possibly harmful. Many buildings are characterized with high PCB concentrations. Knowledge about partitioning between primary sources and building materials is critical for exposure assessment and practical remediation of PCB contamination. This study develops a C-depth method to determine diffusion coefficient (D) and partition coefficient (K), two key parameters governing the partitioning process. For concrete, a primary material studied here, relative standard deviations of results among five data sets are 5%-22% for K and 42-66% for D. Compared with existing methods, C-depth method overcomes the inability to obtain unique estimation for nonlinear regression and does not require assumed correlations for D and K among congeners. Comparison with a more sophisticated two-term approach implies significant uncertainty for D, and smaller uncertainty for K. However, considering uncertainties associated with sampling and chemical analysis, and impact of environmental factors, the results are acceptable for engineering applications. This was supported by good agreement between model prediction and measurement. Sensitivity analysis indicated that effective diffusion distance, contacting time of materials with primary sources, and depth of measured concentrations are critical for determining D, and PCB concentration in primary sources is critical for K. PMID:26347992
Synthesis of metal-organic framework films by pore diffusion method
NASA Astrophysics Data System (ADS)
Murayama, Naohiro; Nishimura, Yuki; Kajiro, Hiroshi; Kishida, Satoru; Kinoshita, Kentaro; Tottori Univ Team; Nippon Steel; Sumitomo Metal Co. Collaboration; Tottori Integrated Frontier Resaerch Center (Tifrec) Collaboration; Tottori University Electronic Display Resaerch Center (Tedrec) Collaboration
Metal-organic frameworks (MOFs) presents high controllability in designing the nano-scale pore, and this enable molecular storages, catalysts, gas sensors, gas separation membranes, and electronic devices for next-generation. Therefore, a simple method for film synthesis of MOFs compared with conventional methods [1] is strongly required. In this paper, we provide pore diffusion method, in which a substrate containing constituent metals of MOF is inserted in solution that includes only linker molecules of MOF. As a result, 2D growth of MOF was effectively enhanced, and the formation of flat and dense MOF films was attained. The growth time, t, dependence of film thickness, d, can be expressed by the relation of d = Aln(t + 1) + B, where A and B are constants. It means that ionized coppers diffuse through the pores of MOFs and the synthesis reaction proceeds at the MOF/solvent interface. We demonstrated the fabrication of a HKUST-1/Cu-TPA hetero structure by synthesizing a Cu-TPA film continuously after the growth of a HKUST-1 film on the CuOx substrate.
An Ion Diffusion Method for Visualising a Solid-like Water Nanofilm
NASA Astrophysics Data System (ADS)
Wang, Ya; Duan, Zhiguang; Fan, Daidi
2013-12-01
A nano-thick solid-like water film on solid surfaces plays an important role in various fields, including biology, materials science, atmospheric chemistry, catalysis and astrophysics. Visualising the water nanofilm has been a challenge due to its dynamic nature and nanoscale thickness. Here we report an ion diffusion method to address this problem using a membrane formed with a BSA-Na2CO3 (BSA, bovine serum albumin) mixture. After a solid-like water nanofilm deposits onto the membrane, Na+ and CO32- ions diffuse into the film to form a solid Na2CO3 phase in its place. Consequently, the morphology of the nanofilm can be visualised by the space filled by the Na2CO3. Using this method, we successfully observed polygon-like, ribbon-like and spot-like nanofilms at 193 K, 253 K and room temperature, respectively. Our method may provide a tool for characterising confined water films ranging from a few nanometres to hundreds of nanometres in thickness.
An Ion Diffusion Method for Visualising a Solid-like Water Nanofilm
Wang, Ya; Duan, Zhiguang; Fan, Daidi
2013-01-01
A nano-thick solid-like water film on solid surfaces plays an important role in various fields, including biology, materials science, atmospheric chemistry, catalysis and astrophysics. Visualising the water nanofilm has been a challenge due to its dynamic nature and nanoscale thickness. Here we report an ion diffusion method to address this problem using a membrane formed with a BSA-Na2CO3 (BSA, bovine serum albumin) mixture. After a solid-like water nanofilm deposits onto the membrane, Na+ and CO32− ions diffuse into the film to form a solid Na2CO3 phase in its place. Consequently, the morphology of the nanofilm can be visualised by the space filled by the Na2CO3. Using this method, we successfully observed polygon-like, ribbon-like and spot-like nanofilms at 193 K, 253 K and room temperature, respectively. Our method may provide a tool for characterising confined water films ranging from a few nanometres to hundreds of nanometres in thickness. PMID:24336341
Pore size distribution of bioresorbable films using a 3-D diffusion NMR method.
Benjamini, Dan; Elsner, Jonathan J; Zilberman, Meital; Nevo, Uri
2014-06-01
Pore size distribution (PSD) within porous biomaterials is an important microstructural feature for assessing their biocompatibility, longevity and drug release kinetics. Scanning electron microscopy (SEM) is the most common method used to obtain the PSD of soft biomaterials. The method is highly invasive and user dependent, since it requires fracturing of the sample and then considers only the small portion that the user had acquired in the image. In the current study we present a novel nuclear magnetic resonance (NMR) method as an alternative method for estimation of PSD in soft porous materials. This noninvasive 3-D diffusion NMR method considers the entire volume of the specimen and eliminates the user's need to choose a specific field of view. Moreover, NMR does not involve exposure to ionizing radiation and can potentially have preclinical and clinical uses. The method was applied on four porous 50/50 poly(dl-lactic-co-glycolic acid) bioresorbable films with different porosities, which were created using the freeze-drying of inverted emulsions technique. We show that the proposed NMR method is able to address the main limitations associated with SEM-based PSD estimations by being non-destructive, depicting the full volume of the specimens and not being dependent on the magnification factor. Upon comparison, both methods yielded a similar PSD in the smaller pore size range (1-25μm), while the NMR-based method provided additional information on the larger pores (25-50μm). PMID:24534719
NASA Astrophysics Data System (ADS)
Mao, Bosi; Bentaleb, Ahmed; Louerat, Frédéric; Divoux, Thibaut; Snabre, Patrick
Numerous hydrogels are prepared by cooling down to ambient temperature, aqueous polymer solutions brought to a boil. Although the incubation time of the polymer solution at such a high temperature could be used as a tuning parameter, its impact on the subsequent gelation has been poorly investigated. Here we study the effect of prolonged heating at 80°C on a 1.5% wt solution of agar, a natural polysaccharide. The incubation time is varied from a few hours up to five days. We show that the agar sol. continuously degrades as the result of both the hydrolysis and the intermolecular oxidation of the polymer chains. Furthermore, electronic microscopy and X-ray diffraction experiments reveal that gels formed from older agar sols display an increasingly coarser microstructure composed of micron-sized aggregated pieces of polysaccharides, in contrast with the fibrous-like structure of gels made from fresh sols. Along with structural changes prolonged incubation time leads to weaker gels of lower shear elastic modulus. Finally, macro-indentation experiments coupled to direct visualization show that increasing the incubation time of the agar sol. decreases the yield strain of the gel by a factor of three, while the rupture scenario turns continuously from brittle to ductile-like. Acknowledging funding from BioMérieux & CNRS.
Norris, A.T. . Inst. for Computational Mechanics in Propulsion); Pope, S.B. . Sibley School of Mechanical and Aerospace Engineering)
1995-01-01
The velocity-dissipation-composition probability density function (pdf) method is used to model a turbulent CO/H[sub 2]/N[sub 2]-air-piloted jet diffusion flame in the regime of extinction. The thermochemistry is modeled by a three-scalar simplified formulation obtained by the intrinsic low-dimensional manifold (ILDM) method. Calculations are performed for five different jet velocities, and the scalar pdfs are compared with experimental data. Overall good agreement is obtained between the calculations and the experimental results, with the only significant difference being the high level of scatter in the experimental data compared with the pdf results: reasons for this difference are discussed. The pdf method is found to predict flame extinction at approximately the same jet velocity as that of the experiment. A small amount of local extinction is observed in the pdf results for the high-jet-velocity cases.
NASA Astrophysics Data System (ADS)
Fernandes, Ryan I.; Fairweather, Graeme
2012-08-01
An alternating direction implicit (ADI) orthogonal spline collocation (OSC) method is described for the approximate solution of a class of nonlinear reaction-diffusion systems. Its efficacy is demonstrated on the solution of well-known examples of such systems, specifically the Brusselator, Gray-Scott, Gierer-Meinhardt and Schnakenberg models, and comparisons are made with other numerical techniques considered in the literature. The new ADI method is based on an extrapolated Crank-Nicolson OSC method and is algebraically linear. It is efficient, requiring at each time level only O(N) operations where N is the number of unknowns. Moreover, it is shown to produce approximations which are of optimal global accuracy in various norms, and to possess superconvergence properties.
Diffused bounce-back condition and refill algorithm for the lattice Boltzmann method
NASA Astrophysics Data System (ADS)
Krithivasan, Siddharth; Wahal, Siddhant; Ansumali, Santosh
2014-03-01
A solid-fluid boundary condition for the lattice Boltzmann (LB) method, which retains the simplicity of the bounce-back method and leads to positive definite populations similar to the diffusive boundary condition, is presented. As a refill algorithm, it is proposed that quasi-equilibrium distributions be used to model distributions at fluid nodes uncovered due to solid movement. The method is tested for flow past an impulsively started cylinder and demonstrates considerable enhancement in the accuracy of the unsteady force calculation at moderate and high Reynolds numbers. Furthermore, via simulations, we show that momentum exchange procedure used in LB to compute forces is not Galilean invariant. A modified momentum exchange procedure is proposed to reduce the errors due to violation of Galilean invariance.
A comparison between the fission matrix method, the diffusion model and the transport model
Dehaye, B.; Hugot, F. X.; Diop, C. M.
2013-07-01
The fission matrix method may be used to solve the critical eigenvalue problem in a Monte Carlo simulation. This method gives us access to the different eigenvalues and eigenvectors of the transport or fission operator. We propose to compare the results obtained via the fission matrix method with those of the diffusion model, and an approximated transport model. To do so, we choose to analyse the mono-kinetic and continuous energy cases for a Godiva-inspired critical sphere. The first five eigenvalues are computed with TRIPOLI-4{sup R} and compared to the theoretical ones. An extension of the notion of the extrapolation distance is proposed for the modes other than the fundamental one. (authors)
NASA Astrophysics Data System (ADS)
Zendejas, Gerardo; Chiasson, Mike
This paper will propose and explore a method to enhance focal actors' abilities to enroll and control the many social and technical components interacting during the initiation, production, and diffusion of innovations. The reassembling and stabilizing of such components is the challenging goal of the focal actors involved in these processes. To address this possibility, a healthcare project involving the initiation, production, and diffusion of an IT-based innovation will be influenced by the researcher, using concepts from actor network theory (ANT), within an action research methodology (ARM). The experiences using this method, and the nature of enrolment and translation during its use, will highlight if and how ANT can provide a problem-solving method to help assemble the social and technical actants involved in the diffusion of an innovation. Finally, the paper will discuss the challenges and benefits of implementing such methods to attain widespread diffusion.
Plimpton, Steven J.; Sershen, Cheryl L.; May, Elebeoba E.
2015-01-01
This paper describes a method for incorporating a diffusion field modeling oxygen usage and dispersion in a multi-scale model of Mycobacterium tuberculosis (Mtb) infection mediated granuloma formation. We implemented this method over a floating-point field to model oxygen dynamics in host tissue during chronic phase response and Mtb persistence. The method avoids the requirement of satisfying the Courant-Friedrichs-Lewy (CFL) condition, which is necessary in implementing the explicit version of the finite-difference method, but imposes an impractical bound on the time step. Instead, diffusion is modeled by a matrix-based, steady state approximate solution to the diffusion equation. Moreover, presented in figure 1 is the evolution of the diffusion profiles of a containment granuloma over time.
Plimpton, Steven J.; Sershen, Cheryl L.; May, Elebeoba E.
2015-01-01
This paper describes a method for incorporating a diffusion field modeling oxygen usage and dispersion in a multi-scale model of Mycobacterium tuberculosis (Mtb) infection mediated granuloma formation. We implemented this method over a floating-point field to model oxygen dynamics in host tissue during chronic phase response and Mtb persistence. The method avoids the requirement of satisfying the Courant-Friedrichs-Lewy (CFL) condition, which is necessary in implementing the explicit version of the finite-difference method, but imposes an impractical bound on the time step. Instead, diffusion is modeled by a matrix-based, steady state approximate solution to the diffusion equation. Moreover, presented in figuremore » 1 is the evolution of the diffusion profiles of a containment granuloma over time.« less
A new method for apportionnement of diffuse nutrient sources of surface water contamination
NASA Astrophysics Data System (ADS)
Groenendijk, Piet; Mulder, Martin; Van Boekel, Erwin; Van der Bolt, Frank; Hendriks, Rob; Renaud, Leo
2014-05-01
Surface water quality has improved slightly in many regions of the Netherlands during the last decades, due to a reduction of the nutrient loads from point sources, but in most areas the concentrations do not meet the targets to comply with the objectives of the Water Framework Directive. Leaching from agricultural soils is currently the largest source. Quantitative insight into the contribution of the various land management related sources is necessary to discuss the responsibility of different authorities to further improve the quality. Such an understanding is also needed to assess the effects of mitigation measures. The STONE model was developed in 1998- 2000 aiming at the assessment of the effectiveness of Dutch policy measures to reduce nutrient loads to groundwater and surface waters from agricultural land. The process oriented model simulates the carbon, nitrogen and phosphorus cycles in soil and is capable to calculate N and P fluxes to surface waters. Due to the nature of the interdependent soil transformation processes, straight forward model runs don't yield in the relative contribution of the use of fertilizers and other diffuse sources to the total diffuse loads to surface waters. A new method was developed to reveal the relative contribution to surface water contamination of resp. the actual fertilization practise, the historical fertilizer excesses, the atmospheric deposition rates, the inputs by upward seeping water flow, the inputs by infiltrated surface water during summer time in polders and the natural soil release. The method is based on a linear proxy model of the STONE model. The coefficients were derived from the results of a sensitivity analysis. At the national level, the diffuse nitrogen and phosphorus load on surface waters due to the actual fertilization practise amounts to resp. 64% and 48% of the total diffuse loads from agricultural land. Deposition, the input by upward seeping water and the input by infiltrated surface water in polders amounts to less than 5% each. The release from soils, including the effect of historical nutrient surpluses, amounts to resp. 27% and 45% of nitrogen and phosphorus load from agricultural land. The method allows for a further distinction in the relative source contributions per land use, soil type and groundwater regime class. Although agriculture is one of the main contributors to surface water contamination, diminishing manure and fertilizer inputs will not result to a short time contamination reduction due to the long memory of the soil.
A sparse representation based method to classify pulmonary patterns of diffuse lung diseases.
Zhao, Wei; Xu, Rui; Hirano, Yasushi; Tachibana, Rie; Kido, Shoji
2015-01-01
We applied and optimized the sparse representation (SR) approaches in the computer-aided diagnosis (CAD) to classify normal tissues and five kinds of diffuse lung disease (DLD) patterns: consolidation, ground-glass opacity, honeycombing, emphysema, and nodule. By using the K-SVD which is based on the singular value decomposition (SVD) and orthogonal matching pursuit (OMP), it can achieve a satisfied recognition rate, but too much time was spent in the experiment. To reduce the runtime of the method, the K-Means algorithm was substituted for the K-SVD, and the OMP was simplified by searching the desired atoms at one time (OMP1). We proposed three SR based methods for evaluation: SR1 (K-SVD+OMP), SR2 (K-Means+OMP), and SR3 (K-Means+OMP1). 1161 volumes of interest (VOIs) were used to optimize the parameters and train each method, and 1049 VOIs were adopted to evaluate the performances of the methods. The SR based methods were powerful to recognize the DLD patterns (SR1: 96.1%, SR2: 95.6%, SR3: 96.4%) and significantly better than the baseline methods. Furthermore, when the K-Means and OMP1 were applied, the runtime of the SR based methods can be reduced by 98.2% and 55.2%, respectively. Therefore, we thought that the method using the K-Means and OMP1 (SR3) was efficient for the CAD of the DLDs. PMID:25821509
A Sparse Representation Based Method to Classify Pulmonary Patterns of Diffuse Lung Diseases
Xu, Rui; Tachibana, Rie; Kido, Shoji
2015-01-01
We applied and optimized the sparse representation (SR) approaches in the computer-aided diagnosis (CAD) to classify normal tissues and five kinds of diffuse lung disease (DLD) patterns: consolidation, ground-glass opacity, honeycombing, emphysema, and nodule. By using the K-SVD which is based on the singular value decomposition (SVD) and orthogonal matching pursuit (OMP), it can achieve a satisfied recognition rate, but too much time was spent in the experiment. To reduce the runtime of the method, the K-Means algorithm was substituted for the K-SVD, and the OMP was simplified by searching the desired atoms at one time (OMP1). We proposed three SR based methods for evaluation: SR1 (K-SVD+OMP), SR2 (K-Means+OMP), and SR3 (K-Means+OMP1). 1161 volumes of interest (VOIs) were used to optimize the parameters and train each method, and 1049 VOIs were adopted to evaluate the performances of the methods. The SR based methods were powerful to recognize the DLD patterns (SR1: 96.1%, SR2: 95.6%, SR3: 96.4%) and significantly better than the baseline methods. Furthermore, when the K-Means and OMP1 were applied, the runtime of the SR based methods can be reduced by 98.2% and 55.2%, respectively. Therefore, we thought that the method using the K-Means and OMP1 (SR3) was efficient for the CAD of the DLDs. PMID:25821509
Anjum, M F; Lemma, F; Cork, D J; Meunier, D; Murphy, N; North, S E; Woodford, N; Haines, J; Randall, L P
2013-12-01
The aim of this work was to develop a molecular method using loop-mediated isothermal amplification (LAMP) for detection of extended spectrum β-lactamase (ESBL)-producing Enterobacteriaceae from meat, and to compare it with different isolation agars and microarrays. LAMP assays were developed for CTX-M groups 1, 2, and 9 and OXA-10-like genes. Chicken, lamb, beef, pork, and turkey samples were spiked with 10, 100, and 1,000 cfu/gram using 8 strains of ESBL-producing Enterobacteriaceae (CTX-M sequence types 1, 2, 3, 14, 15, OXA-11, SHV-2, TEM-52) +/- a mix of competitor organisms. Samples were enriched overnight in buffered peptone water (BPW) +/- antibacterials before plating to CHROMagar CTX, OXOID ESBL Brilliance agar, and MacConkey agar with 1 mg/L cefotaxime. Selected BPW broths were also tested using LAMP assays, microarrays and using cefpodoxime discs on agar. For isolation/detection of ESBL producers from beef, pork, lamb, and turkey spiked with 10 or 100 cfu/gram ESBL (natural flora only), all agars and the LAMP assays showed 100% sensitivity and specificity for ESBL spike strains. For chicken samples, both LAMP and chromogenic agars showed improved sensitivity and specificity for isolation of ESBLs compared with MacConkey agar, particularly with competitor bacteria added. In comparison, the cefpodoxime disc method and microarray showed reduced sensitivity. PMID:24329955
Clark, R B; Sanders, C C; Pakiz, C B; Hostetter, M K
1988-01-01
In recent years, a number of clinical microbiology laboratories have isolated Pseudomonas aeruginosa with the unusual aminoglycoside disk diffusion result of resistance to both amikacin and gentamicin but susceptibility to tobramycin (ArGrTs). A total of 39 isolates of P. aeruginosa reported to have this resistance pattern were retested by the standard National Committee for Clinical Laboratory Standards disk diffusion procedure; 30 strains (77%) were confirmed to be ArGrTs. These 30 isolates were further examined for susceptibility to those aminoglycosides by agar dilution and broth micro- and macrodilution methods. Only 27, 27, and 23% of the isolates appeared to be ArGrTs by agar, broth microdilution, and broth macrodilution testing, respectively. Most of the remaining isolates were resistant to all three aminoglycosides when tested by broth dilution and resistant only to gentamicin when tested by agar dilution. The percentages of strains resistant to any particular aminoglycoside by agar dilution, broth microdilution, and broth macrodilution, respectively, were 43, 80, and 70 for amikacin, 97, 93, and 100 for gentamicin, 100, 100, and 100 for netilmicin, 30, 87, and 93 for sisomicin, and 13, 57, and 50 for tobramycin. These results indicate that strains showing the unusual aminoglycoside antibiogram are less susceptible to aminoglycosides in general and should probably be considered borderline resistant to all aminoglycosides. The efficacy of aminoglycosides in the treatment of infections produced by these strains is unknown. PMID:3134846
Co-precipitation with PVP and Agar to Improve Physicomechanical Properties of Ibuprofen
Maghsoodi, Maryam; Kiafar, Farhad
2013-01-01
Objective(s) : Ibuprofen is a problematic drug in tableting due to its viscoelastic properties. Additionally its high cohesivity results in low flowability. In this study, co-precipitation of ibuprofen with varying concentration of agar and PVP to optimize properties of Ibuprofen was carried out. Materials and Methods: Co-precipitates of ibuprofen- PVP or agar were prepared by solvent evaporation technique under vacuum condition. Differential scanning calorimetry (DSC), X -ray diffraction of powder (XRDP) and FT-IR spectroscopy were used to investigate the solid state characteristics of the co-precipitates. The dissolution behavior, flowability, particle size and compaction properties of various batches were also studied. Results: Co-precipitation of drug with agar led to a change in habit from needle to plate shape crystals, while drug –PVP co-precipitates had agglomerated structure and consisted of numerous crystals which had been aggregated together. The co-precipitates showed improved flow properties compared with ibuprofen alone. Precipitation of ibuprofen with these additives led to modification in the dissolution of the drug. Agar in 1% w/w improved slightly the dissolution rate of drug while PVP had a negative impact and led to reduction in the dissolution rate of drug to less than that of pure drug. The all obtained co-precipitates exhibited significantly improved tableting behavior compared with drug crystals alone. This may be due to this fact that, the polymer covering the drug particles increases and changes the nature of the surface area available for interparticulate bonds between particles. DSC, XRDP and FT-IR experiments showed that drug particles, in co-precipitates samples, did not undergo polymorphic modifications. Conclusion: The study highlights the influence of polymeric additives on crystallization process leading to modified performance. PMID:24250936
Co-precipitation with PVP and Agar to Improve Physicomechanical Properties of Ibuprofen
Maghsoodi, Maryam; Kiafar, Farhad
2013-01-01
Objective(s) : Ibuprofen is a problematic drug in tableting due to its viscoelastic properties. Additionally its high cohesivity results in low flowability. In this study, co-precipitation of ibuprofen with varying concentration of agar and PVP to optimize properties of Ibuprofen was carried out. Materials and Methods: Co-precipitates of ibuprofen- PVP or agar were prepared by solvent evaporation technique under vacuum condition. Differential scanning calorimetry (DSC), X -ray diffraction of powder (XRDP) and FT-IR spectroscopy were used to investigate the solid state characteristics of the co-precipitates. The dissolution behavior, flowability, particle size and compaction properties of various batches were also studied. Results: Co-precipitation of drug with agar led to a change in habit from needle to plate shape crystals, while drug –PVP co-precipitates had agglomerated structure and consisted of numerous crystals which had been aggregated together. The co-precipitates showed improved flow properties compared with ibuprofen alone. Precipitation of ibuprofen with these additives led to modification in the dissolution of the drug. Agar in 1% w/w improved slightly the dissolution rate of drug while PVP had a negative impact and led to reduction in the dissolution rate of drug to less than that of pure drug. The all obtained co-precipitates exhibited significantly improved tableting behavior compared with drug crystals alone. This may be due to this fact that, the polymer covering the drug particles increases and changes the nature of the surface area available for interparticulate bonds between particles. DSC, XRDP and FT-IR experiments showed that drug particles, in co-precipitates samples, did not undergo polymorphic modifications. Conclusion: The study highlights the influence of polymeric additives on crystallization process leading to modified performance. PMID:24250942
Payne, L N; Howes, K; Rennie, M; Bumstead, J M; Kidd, A W
1981-12-01
Lymphoblastoid cell lines derived from Marek's disease (MD) lymphomas have been established with difficulty by a number of workers. We have compared with conventional liquid culture methods the efficiency of a new technique for establishing lymphoid cell lines in which lymphoma cells were cultured initially in agar medium. Cells from 39/79 lymphomas gave rise to loose lymphoid colonies in the seeded agar after 7 days' incubation at 41 degrees C. Two types of macrophage colony also developed. When lymphoid colonies in agar were transferred to liquid culture, 23/39 gave rise to permanent lymphoid cell lines, compared with 8/33 comparable cultures initiated in liquid medium. Twenty-nine new cell lines have been developed from Rhode Island Red, line 6 and line 7 chickens. All carry T-cell markers and the MD tumour-associated surface antigen (MATSA) and showed variable but low responsiveness to lectin mitogens. The new cell lines, when first established, consisted mainly of small, lymphocytoid cells, but, after varying times, these changed into typical lymphoblastoid lines and an increased expression of an embryonic antigen was associated with this change. The lymphocytoid line cells were more slowly growing and density-dependent than were the lymphoblastoid cells, and lymphocytoid lines grew better at 41 degrees C and lymphoblastoid lines better at 37 degrees C. MD virus could be rescued from some of the lines but others appeared to be true non-producers. PMID:7199514
Numerical Modeling of Deep Mantle Convection: Advection and Diffusion Schemes for Marker Methods
NASA Astrophysics Data System (ADS)
Mulyukova, Elvira; Dabrowski, Marcin; Steinberger, Bernhard
2013-04-01
Thermal and chemical evolution of Earth's deep mantle can be studied by modeling vigorous convection in a chemically heterogeneous fluid. Numerical modeling of such a system poses several computational challenges. Dominance of heat advection over the diffusive heat transport, and a negligible amount of chemical diffusion results in sharp gradients of thermal and chemical fields. The exponential dependence of the viscosity of mantle materials on temperature also leads to high gradients of the velocity field. The accuracy of many numerical advection schemes degrades quickly with increasing gradient of the solution, while the computational effort, in terms of the scheme complexity and required resolution, grows. Additional numerical challenges arise due to a large range of length-scales characteristic of a thermochemical convection system with highly variable viscosity. To examplify, the thickness of the stem of a rising thermal plume may be a few percent of the mantle thickness. An even thinner filament of an anomalous material that is entrained by that plume may consitute less than a tenth of a percent of the mantle thickness. We have developed a two-dimensional FEM code to model thermochemical convection in a hollow cylinder domain, with a depth- and temperature-dependent viscosity representative of the mantle (Steinberger and Calderwood, 2006). We use marker-in-cell method for advection of chemical and thermal fields. The main advantage of perfoming advection using markers is absence of numerical diffusion during the advection step, as opposed to the more diffusive field-methods. However, in the common implementation of the marker-methods, the solution of the momentum and energy equations takes place on a computational grid, and nodes do not generally coincide with the positions of the markers. Transferring velocity-, temperature-, and chemistry- information between nodes and markers introduces errors inherent to inter- and extrapolation. In the numerical scheme that we use for this study, the velocity field is discretised using second order triangular elements, which gives second order accuracy of interpolation from grid-nodes to markers. A fourth order Runge-Kutta solver is used to compute marker-trajectories. We reevaluate the velocity field for each of the intermediate steps of the ODE-solver, rendering our advection scheme to be fourth-order accurate in time. We compare two different approaches for performing the thermal diffusion step. In the first, more conventional approach, the energy equation is solved on a static grid. For this grid, we use first-order triangular elements and a higher resolution than for the velocity-grid, to compensate for the lower order elements. The temperature field is transferred between grid-nodes and markers, and a subgrid diffusion correction step (Gerya and Yuen, 2003) is included to account for the different spatial resolutions of the markers and the grid. In the second approach, the energy equation is solved directly on markers. To do this, we compute a constrained Delaunay triangulation, with markers as nodes, at every time step. We wish to resolve the large range of spatial scales of the solution at lowest possible computational cost. In several existing codes this is achieved with dynamically adaptive meshes, which use high resolution in regions with high solution gradients, and vice versa. The numerical scheme used in this study can be extended to include a similar feature, by regenerating the thermal and mechanical grids in the course of computation, adapting them to the temperature and chemistry fields carried by the markers. We present the results of thermochemical convection simulations obtained using the schemes outlined above, as well as the results of the numerical benchmarks commonly used in the geodynamics community. The quality of the solutions, as well as the computational cost of our schemes, are discussed.
Zhang, Guodong; Lampel, Keith A
2010-08-01
Shigella outbreaks are widely reported throughout the world. However, it remains a challenge to isolate Shigella spp. from foods by using conventional microbiological media. The main objective of this study was to determine the effectiveness of a novel chromogenic medium, Rainbow agar Shigella/Aeromonas (Rainbow agar), for the isolation and detection of Shigella spp. in foods. All four Shigella species, S. sonnei, S. flexneri, S. dysenteriae, and S. boydii, were studied. Rainbow agar was compared with tryptic soy agar, xylose lysine desoxycholate agar (XLD), and Salmonella Shigella agar (SSA) for enumeration of Shigella spp. in pure culture. This chromogenic agar and XLD were also used to isolate Shigella spp. in artificially contaminated foods (4.8 log CFU/g of food), including lettuce, parsley, cilantro, spinach, potato salad, and shrimp. The inhibitory effect on Shigella growth by Rainbow agar was between that of XLD and SSA. All vegetables studied showed a moderately high background microflora on XLD and Rainbow agar. With artificially inoculated produce, Rainbow agar recovered about 1 to 2 log CFU more S. sonnei, S. dysenteriae, and S. boydii per g of food than did XLD. For potato salad and shrimp, which had low background microflora on Rainbow agar, Rainbow agar was slightly better in recovering Shigella spp. than XLD was in most cases. However, we found that the addition of streptomycin (6.25 mg/liter) to Rainbow agar could facilitate the isolation of Shigella in vegetables tested. In conclusion, Rainbow agar was a much more effective medium than was XLD for the isolation of Shigella spp. from foods. PMID:20819355
Method and apparatus for determining minority carrier diffusion length in semiconductors
Moore, Arnold R.
1984-01-01
Method and apparatus are provided for determining the diffusion length of minority carriers in semiconductor material, particularly amorphous silicon which has a significantly small minority carrier diffusion length using the constant magnitude surface-photovoltage (SPV) method. Steady or modulated illumination at several wavelengths provides the light excitation on the surface of the material to generate the SPV. A manually controlled or automatic servo system maintains a constant predetermined value of the SPV for each wavelength. A drop of a transparent electrolyte solution containing redox couples (preferably quinhydrone) having an oxidation-reduction potential (E) in the order of +0.6 to -1.65 volts couples the SPV to a measurement system. The drop of redox couple solution functions to create a liquid Schottky barrier at the surface of the material. Illumination light is passed through a transparent rod supported over the surface and through the drop of transparent electrolyte. The drop is held in the gap between the rod and the surface. Steady red light is also used as an optical bias to reduce deleterious space-charge effects that occur in amorphous silicon.
Method and apparatus for determining minority carrier diffusion length in semiconductors
Moore, Arnold R.
1984-02-21
Method and apparatus are provided for determining the diffusion length of minority carriers in semiconductor material, particularly amorphous silicon, which has a significantly small minority carrier diffusion length using the constant magnitude surface-photovoltage (SPV) method. Steady or modulated illumination at several wavelengths provides the light excitation on the surface of the material to generate the SPV. A manually controlled or automatic servo system maintains a constant predetermined value of the SPV for each wavelength. A probe electrode immersed in an electrolyte solution containing redox couples (preferably quinhydrone) having an oxidation-reduction potential (E) in the order of +0.6 to -1.65 volts couples the SPV to a measurement system. The redox couple solution functions to create a liquid Schottky barrier at the surface of the material. The Schottky barrier is contacted by merely placing the probe in the solution. The redox solution is placed over and in contact with the material to be tested and light is passed through the solution to generate the SPV. To compensate for colored redox solutions a portion of the redox solution not over the material is also illuminated for determining the color compensated light intensity. Steady red light is also used as an optical bias to reduce deleterious space-charge effects that occur in amorphous silicon.
Blood species identification using Near-Infrared diffuse transmitted spectra and PLS-DA method
NASA Astrophysics Data System (ADS)
Zhang, Linna; Zhang, Shengzhao; Sun, Meixiu; Wang, Zhennan; Li, Hongxiao; Li, Yingxin; Li, Gang; Lin, Ling
2016-05-01
Blood species identification is of great significance for blood supervision and wildlife investigations. The current methods used to identify the blood species are destructive. Near-Infrared spectroscopy method is known for its non-invasive properties. In this research, we combined Near-Infrared diffuse transmitted spectra and Partial Least Square Discrimination Analysis (PLS-DA) to identify three blood species, including macaque, human and mouse. Blind test and external test were used to assess the PLS-DA model. The model performed 100% accuracy in its identification between three blood species. This approach does not require a specific knowledge of biochemical features for each individual class but relies on a spectroscopic statistical differentiation of the whole components. This is the first time to demonstrate Near-Infrared diffuse transmitted spectra have the ability to identify the species of origin of blood samples. The results also support a good potential of absorption and scattering spectroscopy for species identification in practical applications for real-time detection.
A Simple and Efficient Diffuse Interface Method for Compressible Two-Phase Flows
Ray A. Berry; Richard Saurel; Fabien Petitpas
2009-05-01
In nuclear reactor safety and optimization there are key issues that rely on in-depth understanding of basic two-phase flow phenomena with heat and mass transfer. For many reasons, to be discussed, there is growing interest in the application of two-phase flow models to provide diffuse, but nevertheless resolved, simulation of interfaces between two immiscible compressible fluids – diffuse interface method (DIM). Because of its ability to dynamically create interfaces and to solve interfaces separating pure media and mixtures for DNS-like (Direct Numerical Simulation) simulations of interfacial flows, we examine the construction of a simple, robust, fast, and accurate numerical formulation for the 5-equation Kapila et al. [1] reduced two-phase model. Though apparently simple, the Kapila et al. model contains a volume fraction differential transport equation containing a nonlinear, non-conservative term which poses serious computational challenges. To circumvent the difficulties encountered with the single velocity and single pressure Kapila et al. [1] multiphase flow model, a 6-equation relaxation hyperbolic model is built to solve interface problems with compressible fluids. In this approach, pressure non-equilibrium is first restored, followed by a relaxation to an asymptotic solution which is convergent to the solutions of the Kapila et al. reduced model. The apparent complexity introduced with this extended hyperbolic model actually leads to considerable simplifications regarding numerical resolution, and the various ingredients used by this method are general enough to consider future extensions to problems involving complex physics.
Application of a Particle Method to the Advection-Diffusion-Reaction Equation
NASA Astrophysics Data System (ADS)
Paster, A.; Bolster, D.; Benson, D. A.
2012-12-01
A reaction between two chemical species can only happen if molecules collide and react. Thus, the mixing of a system can become a limiting factor in the onset of reaction. Solving for reaction rate in a well-mixed system is typically a straightforward task. However, when incomplete mixing kicks in, obtaining a solution becomes more challenging. Since reaction can only happen in regions where both reactants co-exist, the incomplete mixing may slow down the reaction rate, when compared to a well-mixed system. The effect of incomplete mixing upon reaction is a highly important aspect of various processes in natural and engineered systems, ranging from mineral precipitation in geological formations to groundwater remediation in aquifers. We study a relatively simple system with a bi-molecular irreversible kinetic reaction A+B → Ø where the underlying transport of reactants is governed by an advection-diffusion equation, and the initial concentrations are given in terms of an average and a perturbation. Such a system does not have an analytical solution to date, even for the zero advection case. We model the system by a Monte Carlo particle tracking method, where particles represent some reactant mass. In this method, diffusion is modeled by a random walk of the particles, and reaction is modeled by annihilation of particles. The probability of the annihilation is proportional to the reaction rate constant and the probability density associated with particle co-location. We study the numerical method in depth, characterizing typical numerical errors and time step restrictions. In particular, we show that the numerical method converges to the advection-diffusion-reaction equation at the limit Δt →0. We also rigorously derive the relationship between the initial number of particles in the system and the initial concentrations perturbations represented by that number. We then use the particle simulations of zero-advection system to demonstrate the well-known phenomena of incomplete mixing (Ovchinnikov-Zeldovich segregation). The numerical results of the particle-tracking simulations are compared to an approximate analytical solution and the late time discrepancy is explained. We also study, for a two dimensional system, how shear flow effects the reaction rate. We do so since shear flow is the simplest form of a spatially variable advection. For the shear flow system, we find that shear flow leads to better mixing of the system on one hand, and a surprising one dimensional segregation at late times, on the other hand. This is in contrast with zero-advection two-dimensional system, where the late time behavior is characterized by the formation of two-dimensional islands. References (Manuscripts in submission): Paster A., D. Bolster and D.A. Benson. Connecting the dots: application of a particle method to the diffusion-reaction equation. Submitted to Advances in Water Resources. Paster A., D. Bolster and D.A. Benson. Particle Tracking and the Diffusion-Reaction Equation. Submitted to Water Resources Research.
NASA Astrophysics Data System (ADS)
Marchetti, M.; Robinson, B. H.; Evangelou, M. W. H.; Vachey, A.; Schwitzguebel, J. P.; Bernier-Latmani, R.; Schulin, R.
2009-04-01
Trace elements (TE) are essential for humans and plants, but they may be toxic if their concentration is too high. For this reason, the management of TE in soils is very important. In some cases it may be necessary to increase the uptake of nutrients or TE by plants, for example in a biofortification perspective. Conversely, in some other cases TE uptake by plants should be decreased, for instance to avoid heavy metals entering the food chain via edible crops. Microorganisms living in the rhizosphere affect trace element (TE) uptake by plants. However, due to the complexity of this space and the variety of microorganisms that occur there, it is difficult to isolate the effect of any particular strain. To overcome this hurdle, we developed a system in which we grew plants under sterile conditions in agar and inoculated their rhizosphere with a single, well-defined microbial strain. For many years, agar has been used as a growth substrate for microorganisms and plant tissues. It is cheap, easy to use, and can be autoclaved to ensure its sterility. Because of its widespread use, an experiment conducted using this substrate can be reproduced under the same conditions in any laboratory. In contrast to soil, there is little interaction between the trace elements and the agar matrix. There are many studies investigating the influence of microorganisms on TE uptake by plants. However, so far only a small variety of microorganisms has been tested on few plant species. Therefore, the first objective of our research was to develop a method to rapidly screen a large variety of microorganisms on various plant species. Once this goal was achieved, we sought to study the effect of single, well-defined microbial strains on TE uptake by sunflower and wheat. The substrate for plants growth was a 10% agar solution prepared with modified Hoagland's solution and a TE solution containing 1 mg/kg Pb and molar equivalents of Cu, Ni and Zn. The agar solution was autoclaved and poured into sterile, transparent plastic boxes, whose lid was equipped with a filter allowing gas exchanges without contamination by external microorganisms. The seed surface was sterilised and the plants grew one week in agar before their rhizosphere was inoculated with LB broth containing a pure bacterial strain or agar plugs colonized by fungal hyphae. We tested 14 strains, with 5 replicates per treatment and a control where the system was inoculated with sterile LB broth. The plants grew for 2 weeks in a climate chamber and their shoots were analysed for their TEs by ICP-OES. Samples of agar and roots were collected to confirm microbial colonization of the rhizosphere, respectively sterile conditions in the control treatments. Concerning the method development, the plants grew without visible toxicity in all the boxes, and the analysis of root and agar samples indicated that the controls were sterile and the strains inoculated were growing along the roots. More than 90% of the TE and nutrients added to the system were in the liquid fraction of the agar medium, thus available for root uptake. The screening showed that the microorganisms in general decreased TE uptake by wheat and sunflower, although some of them had an opposite effect on the plants. However, with the same plant species, the microorganisms had a consistent effect on all TE tested, i.e. a given single strain caused the same effect (increase or decrease of TE uptake) on all TE tested. In sunflower, 3 microorganisms (Paenibacillus polymyxa, Pythium ultimum and Rhizoctonia solani) decreased Cu and Zn uptake by 50% compared to the control treatment. These three species are common soil microorganisms. All three are known to exude auxin, a phytohormone. This hormone can modify root morphology and physiology and thus may affect TE uptake by plants. R. solani and P. ultimum are root pathogens. Their effect was opposite to what we expected. If roots are damaged, TE should have flooded into the plant and accumulate in the tissues, but this was not the case. One explanation could be the biosorption of TE by these microorganisms, reducing the uptake by plant. Conversely to sunflower, none of the microorganisms tested showed a significant effect on TE uptake by wheat. With our research, we created an agar system allowing the screening of several microbial strains for their effect on plant TE uptake. Future work will involve screening of several other strains in a wide range of conditions in agar. A method validation with a pot experiment is also needed, as some interactions in this artificial rhizosphere may be different from those that would take place in soil. We will also pursue the investigation of two interesting mechanisms revealed by the screening: the effect of pathogens and phytohormone-exuding microorganisms on TE uptake by plants.
Gradient diffusion antibiotic susceptibility testing of potentially probiotic lactobacilli.
Charteris, W P; Kelly, P M; Morelli, L; Collins, J K
2001-12-01
Minimum inhibitory contentrations (MICs) of selected inhibitors of cell wall synthesis (benzylpenicillin, ampicillin, and vancomycin), protein synthesis (gentamicin, streptomycin, tetracycline, chloramphenicol, and erythromycin), and nucleic acid synthesis (co-trimoxazole, rifampicin, and metronidazole) were determined by gradient diffusion (E test; AB Biodisk, Solna, Sweden) on deMan, Rogosa, Sharpe (MRS) agar for Lactobacillus strain GG and 11 closely related, rapidly growing, facultatively anaerobic, potentially probiotic Lactobacillus rhamnosus strains. All strains were resistant to vancomycin (MIC90 > or = 256 microg/ml), co-trimoxazole (MIC90 > or = 32 microg/ml), metronidazole (MIC90 > or = 32 microg/ml), gentamicin (MIC90 > or = 128 microg/ml), and streptomycin (MIC90 > or = 256 microg/ml), and sensitive to pencillin G (MIC90 > 0.375 microg/ml), ampicillin (MIC90 > 0.750 microg/ml), rifampicin (MIC90 > 0.375 microg/ml), tetracycline (MIC90 > 1.5 microg/ml), chloramphenicol (MIC90 > 8 microg/ml), and erythromycin (MIC90 > 2 microg/ml). E test MICs were also determined for L. acidophilus National Collection of Food Bacteria (NCFB) 1748 and L. reuteri Deutsche Sammlung von Mikroorganismen 20016T by the inoculum application method recommended by the manufacturer (swabbing), with and without antibiotic prediffusion for 1 h at room temperature, and by an alternative inoculum application (agar overlay) method, without antibiotic prediffusion. Antibiotic prediffusion increased the MICs for penicillin G, ampicillin, tetracycline, and chloramphenicol by up to 2 log2 MIC dilutions without changing antibiotic susceptibility category. Agar overlay application also increased the MICs for these antibiotics as well as for gentamicin by up to 3 log2 MIC dilutions without changing antibiotic susceptibility category. Exact agreement between MICs determined by swab and agar overlay application without antibiotic prediffusion was strain dependent: 54.5% for strain DSM 20016T and 72.7% for strain NCFB 1748. The swab and agar overlay gradient diffusion methods provide a reliable basis for antibiotic susceptibility testing of rapidly growing, facultatively anaerobic lactobacilli, using MRS agar as test medium and are readily applicable for testing individual isolates as needed. PMID:11770631
Efficient method for near real-time diffuse optical tomography of the human brain
NASA Astrophysics Data System (ADS)
Wu, Xue; Eggebrecht, Adam T.; Ferradal, Silvina L.; Culver, Joseph P.; Dehghani, Hamid
2015-07-01
Previous studies have showed only regions with a sensitivity higher that 1% of the maximum value can affect the recovery result for diffuse optical tomography (DOT). Two methods of efficient sensitivity map generation based on Finite Element Models (FEM) are developed based on (1) reduced sensitivity matrix and (2) parallelisation process. Time and memory efficiency of these processes are evaluated and compared with conventional methods. It is shown that the computational time for a full head model containing 200k nodes is reduced from 3 hours to 48 minutes and the required memory is reduced from 5.5 GB to 0.5 GB. For a range of mesh densities up to 320k nodes, the required memory is improved by ~1000% and computational time by ~400% to allow near real-time image recovery.
Reprint of Domain decomposition multigrid methods for nonlinear reaction-diffusion problems
NASA Astrophysics Data System (ADS)
Arrarás, A.; Gaspar, F. J.; Portero, L.; Rodrigo, C.
2015-04-01
In this work, we propose efficient discretizations for nonlinear evolutionary reaction-diffusion problems on general two-dimensional domains. The spatial domain is discretized through an unstructured coarse triangulation, which is subsequently refined via regular triangular grids. Following the method of lines approach, we first consider a finite element spatial discretization, and then use a linearly implicit splitting time integrator related to a suitable decomposition of the triangulation nodes. Such a procedure provides a linear system per internal stage. The equations corresponding to those nodes lying strictly inside the elements of the coarse triangulation can be decoupled and solved in parallel using geometric multigrid techniques. The method is unconditionally stable and computationally efficient, since it avoids the need for Schwarz-type iteration procedures. In addition, it is formulated for triangular elements, thus yielding much flexibility in the discretization of complex geometries. To illustrate its practical utility, the algorithm is shown to reproduce the pattern-forming dynamics of the Schnakenberg model.
Compact alternating direction implicit method for two-dimensional time fractional diffusion equation
NASA Astrophysics Data System (ADS)
Cui, Mingrong
2012-03-01
High-order compact finite difference scheme with operator splitting technique for solving two-dimensional time fractional diffusion equation is considered in this paper. A Grünwald-Letnikov approximation is used for the Riemann-Liouville time derivative, and the second order spatial derivatives are approximated by the compact finite differences to obtain a fully discrete implicit scheme. Alternating direction implicit (ADI) method is used to split the original problem into two separate one-dimensional problems. The local truncation error is analyzed and the stability is discussed by the Fourier method. The proposed scheme is suitable when the order of the time fractional derivative γ lies in the interval {1}/{2},1. A correction term is added to maintain high accuracy when γ∈0,{1}/{2}. Numerical results are provided to verify the accuracy and efficiency of the proposed algorithm.
NASA Astrophysics Data System (ADS)
Oka, Chiemi; Ushimaru, Kazunori; Horiishi, Nanao; Tsuge, Takeharu; Kitamoto, Yoshitaka
2016-02-01
The present paper describes optimization of preparation conditions of a core-shell composite particle, and its heat generation by alternating magnetic fields. The composite particles are prepared with a modified emulsion solvent diffusion method, which is combined with Pickering emulsion stabilized by magnetic nanoparticles. In this method, the magnetic nanoparticles act as an emulsifier, and its amount and size are crucial to morphology of the composite particles. The magnetic nanoparticles of 8-9 nm would be strongly adsorbed at a liquid-liquid interface rather than the larger nanoparticles. At the optimized concentration of the magnetic nanoparticle’s suspension for the preparation, small and uniform composite particles are obtained since the amount of the nanoparticles is enough to prevent coalescence of droplets during the formation of the composites. The heat generation by alternating magnetic fields emerged certainly. This result suggests the composite particles have a property as a heat-generating carrier for hyperthermia treatment.
Bodor, Sándor; Zook, Justin M; Lindner, Erno; Tóth, Klára; Gyurcsányi, Róbert E
2008-05-01
The diffusion coefficients of active components in ion-selective membranes have a decisive influence on the life-time and detection limit of the respective ion-selective electrodes, as well as influencing the rate of polarization and relaxation processes of electrically perturbed ion sensors. Therefore, the rational design of mass transport controlled ion-selective electrodes with sub-nanomolar detection limits requires reliable data on the diffusion coefficients. We have implemented electrochemical methods for the quantitative assessment of both the diffusion coefficients of free ionophores and ion-ionophore complexes. The diffusion coefficients of the pH-sensitive chromoionophore ETH 5294 and the calcium-selective ionophore ETH 5234 were determined in plasticized PVC membranes with different PVC to plasticizer ratios. The diffusion coefficient of the free chromoionophore determined by a chronoamperometric method was validated with optical methods for a variety of membrane compositions. The calcium-selective ionophore ETH 5234 was used as a model compound to assess the diffusion coefficient of the ion-ionophore complex calculated from the time required for the complexes to cross a freshly prepared membrane during potentiometric ion-breakthrough experiments. The difference between the diffusion coefficients of the free ionophore ETH 5234 and the ion-ionophore complex was found to be significant and correlated well with the geometry of the respective species. PMID:18427685
[Technological aspects of agar-hydrocolloid impression materials].
Davidson, C L; Bekke-Hoekstra, I S
1979-01-01
Physical properties with clinical relevance has been tested on a number of agar hydrocolloid impression materials For 1 hour an almost perfect dimensional stability can be maintained when the impression is stored in water. Elasticity and strength are poor. Only the use of much bulk material may prevent damage during manipulation of the gel. The detail reproduceability meets all standards. A good compatibility with dental stone subsequently allows sharp details in the model. PMID:293792
Lattice Boltzmann methods for some 2-D nonlinear diffusion equations:Computational results
Elton, B.H.; Rodrigue, G.H. . Dept. of Applied Science Lawrence Livermore National Lab., CA ); Levermore, C.D. . Dept. of Mathematics)
1990-01-01
In this paper we examine two lattice Boltzmann methods (that are a derivative of lattice gas methods) for computing solutions to two two-dimensional nonlinear diffusion equations of the form {partial derivative}/{partial derivative}t u = v ({partial derivative}/{partial derivative}x D(u){partial derivative}/{partial derivative}x u + {partial derivative}/{partial derivative}y D(u){partial derivative}/{partial derivative}y u), where u = u({rvec x},t), {rvec x} {element of} R{sup 2}, v is a constant, and D(u) is a nonlinear term that arises from a Chapman-Enskog asymptotic expansion. In particular, we provide computational evidence supporting recent results showing that the methods are second order convergent (in the L{sub 1}-norm), conservative, conditionally monotone finite difference methods. Solutions computed via the lattice Boltzmann methods are compared with those computed by other explicit, second order, conservative, monotone finite difference methods. Results are reported for both the L{sub 1}- and L{sub {infinity}}-norms.
Convergence of methods for coupling of microscopic and mesoscopic reaction-diffusion simulations
NASA Astrophysics Data System (ADS)
Flegg, Mark B.; Hellander, Stefan; Erban, Radek
2015-05-01
In this paper, three multiscale methods for coupling of mesoscopic (compartment-based) and microscopic (molecular-based) stochastic reaction-diffusion simulations are investigated. Two of the three methods that will be discussed in detail have been previously reported in the literature; the two-regime method (TRM) and the compartment-placement method (CPM). The third method that is introduced and analysed in this paper is called the ghost cell method (GCM), since it works by constructing a "ghost cell" in which molecules can disappear and jump into the compartment-based simulation. Presented is a comparison of sources of error. The convergent properties of this error are studied as the time step Δt (for updating the molecular-based part of the model) approaches zero. It is found that the error behaviour depends on another fundamental computational parameter h, the compartment size in the mesoscopic part of the model. Two important limiting cases, which appear in applications, are considered: Δt → 0 and h is fixed; Δt → 0 and h → 0 such that √{ Δt } / h is fixed. The error for previously developed approaches (the TRM and CPM) converges to zero only in the limiting case (ii), but not in case (i). It is shown that the error of the GCM converges in the limiting case (i). Thus the GCM is superior to previous coupling techniques if the mesoscopic description is much coarser than the microscopic part of the model.
NASA Astrophysics Data System (ADS)
Jackson, Bob; Silgram, Martyn; Quinton, John
2010-05-01
Recent UK government-funded research has shown that compacted, unvegetated tramlines wheelings can represent an important source and transport pathway, which can account for 80% of surface runoff, sediment and phosphorus losses to edge-of-field from cereals on moderate slopes. For example, recent research found 5.5-15.8% of rainfall lost as runoff, and losses of 0.8-2.9 kg TP/ha and 0.3-4.8 T/ha sediment from tramline wheelings. When compaction was released by shallow cultivation, runoff was reduced to 0.2-1.7% of rainfall with losses of 0.0-0.2 kg TP/ha and 0.003-0.3 T/ha sediment respectively i.e. close to reference losses from control areas without tramlines. Recent independent assessments using novel tracer techniques have also shown that tramline wheelings can represent important sediment sources at river catchment scale. In response to these latest findings, a new project is now underway investigating the most cost-effective and practical ways of operationalising methods for managing tramline wheelings in autumn-sown cereal systems to reduce the risk of soil compaction from the autumn spray operation and the associated risk of surface runoff and diffuse pollution loss of sediment, phosphorus and nitrogen to edge of field. Research is focusing on the over-winter period when soils are close to field capacity and the physical protection of the soil surface granted by growing crop is limited. This paper outlines this new multi-disciplinary project and associated methodologies, which include hillslope-scale event-based evaluations of the effectiveness of novel mitigation methods on surface runoff and diffuse pollution losses to edge of field, assessments of the economic and practical viability of mitigation methods, and modelling the impact on water quality of implementation of the most promising techniques at both farm and catchment scale. The study involves a large consortium with 20 partners, including many industrial organisations representing tractor, crop sprayer, cultivator and tyre manufacturers, and the associated development and evaluation of novel tools for sustainable land management. Preliminary results from the first winter of monitoring focus on soil physics assessments (such as surface roughness, near-surface compaction, bulk density) and event-based losses associated with surface runoff. Research is initially investigating the relative importance of soil compaction, rather than the lack of vegetation cover, in accounting for the much greater losses of surface runoff, sediment and P loss identified down tramline wheelings compared to the uncompacted, cropped area. Treatments being investigated on three sites with contrasting soil textures and climatic regimes include: • The effect of correctly inflated, "Xeobib" low ground pressure tractor and sprayer tyres compared to conventional tyres and "common practice" tyre pressures • The effect of drilling the wheeling areas and using new GPS technology to guide spraying operations, compared to conventional practice of using undrilled tramline areas for that purpose. Subsequent monitoring periods will explore the cost-effectiveness of techniques to lift the soil compaction in the autumn using novel tools attached to the sprayer unit. Results from such applied, field scale cost-effectiveness studies provide evidence to help identify source areas of diffuse pollution, improve our process understanding of the response of soil systems to land management practices, and thereby support the targeting of practical pollution control measures across a range of soil types and climatic regimes. This project will provide practical recommendations to the farming industry, help inform farm scale evaluations of diffuse pollution risk such as the new Soil Protection Review recently introduced by the UK Department for the Environment Food and Rural Affairs (Defra), and yield data to help parameterise and refine diffuse pollution models used for policy support at a range of scales.
Lattice Boltzmann method for convection-diffusion equations with general interfacial conditions
NASA Astrophysics Data System (ADS)
Hu, Zexi; Huang, Juntao; Yong, Wen-An
2016-04-01
In this work, we propose an interfacial scheme accompanying the lattice Boltzmann method for convection-diffusion equations with general interfacial conditions, including conjugate conditions with or without jumps in heat and mass transfer, continuity of macroscopic variables and normal fluxes in ion diffusion in porous media with different porosity, and the Kapitza resistance in heat transfer. The construction of this scheme is based on our boundary schemes [Huang and Yong, J. Comput. Phys. 300, 70 (2015), 10.1016/j.jcp.2015.07.045] for Robin boundary conditions on straight or curved boundaries. It gives second-order accuracy for straight interfaces and first-order accuracy for curved ones. In addition, the new scheme inherits the advantage of the boundary schemes in which only the current lattice nodes are involved. Such an interfacial scheme is highly desirable for problems with complex geometries or in porous media. The interfacial scheme is numerically validated with several examples. The results show the utility of the constructed scheme and very well support our theoretical predications.
NASA Astrophysics Data System (ADS)
Nagasaka, Y.; Hatakeyama, T.; Okuda, M.; Nagashima, A.
1988-07-01
This article is devoted to the theory and experiment of the forced Rayleigh scattering method for measurement of thermal diffusivity of liquids which can be employed in the form of an instrument operated optically in a contact-free manner. The theoretical considerations included are: (1) effect of cell wall, (2) effect of dye, (3) effect of Gaussian beam intensity distribution, (4) effect of heating duration time, and (5) effect of coupled dye and wall for a heavily absorbing sample. The errors caused by inadequate setting of optical conditions are also analyzed: (1) effects of grating thickness and (2) effects of initial temperature amplitude. Experimental verifications of the theory have been carried out through the measurements on toluene and water as standard reference substances. As a result of these experiments and theory, the criteria for optimum measuring conditions became available. To demonstrate the applicability of the present theory and the apparatus, the thermal diffusivities of toluene and methanol have been measured near room temperature under atmospheric pressure. The accuracy of the present measurement is estimated to be ±3%.
On the diffuse interface method using a dual-resolution Cartesian grid
NASA Astrophysics Data System (ADS)
Ding, Hang; Yuan, Cheng-jun
2014-09-01
We investigate the applicability and performance of diffuse interface methods on a dual-resolution grid in solving two-phase flows. In the diffuse interface methods, the interface thickness represents a cut-off length scale in resolving the interfacial dynamics, and it was found that an apparent loss of mass occurs when the interface thickness is comparable to the length scale of flows [24]. From the accuracy and mass conservation point of view, it is desirable to have a thin interface in simulations. We propose to use a dual-resolution Cartesian grid, on which a finer resolution is applied to the volume fraction C than that for the velocity and pressure fields. Because the computation of C field is rather inexpensive compared to that required by velocity and pressure fields, dual-resolution grids can significantly increase the resolution of the interface with only a slight increase of computational cost, as compared to the single-resolution grid. The solution couplings between the fine grid for C and the coarse grid (for velocity and pressure) are delicately designed, to make sure that the interpolated velocity is divergence-free at a discrete level and that the mass and surface tension force are conserved. A variety of numerical tests have been performed to validate the method and check its performance. The dual-resolution grid appears to save nearly 70% of the computational time in two-dimensional simulations and 80% in three-dimensional simulations, and produces nearly the same results as the single-resolution grid. Quantitative comparisons are made with previous studies, including Rayleigh Taylor instability, steadily rising bubble, and partial coalescence of a drop into a pool, and good agreement has been achieved. Finally, results are presented for the deformation and breakup of three-dimensional drops in simple shear flows.
Radiative transfer equation modeling by streamline diffusion modified continuous Galerkin method
NASA Astrophysics Data System (ADS)
Long, Feixiao; Li, Fengyan; Intes, Xavier; Kotha, Shiva P.
2016-03-01
Optical tomography has a wide range of biomedical applications. Accurate prediction of photon transport in media is critical, as it directly affects the accuracy of the reconstructions. The radiative transfer equation (RTE) is the most accurate deterministic forward model, yet it has not been widely employed in practice due to the challenges in robust and efficient numerical implementations in high dimensions. Herein, we propose a method that combines the discrete ordinate method (DOM) with a streamline diffusion modified continuous Galerkin method to numerically solve RTE. Additionally, a phase function normalization technique was employed to dramatically reduce the instability of the DOM with fewer discrete angular points. To illustrate the accuracy and robustness of our method, the computed solutions to RTE were compared with Monte Carlo (MC) simulations when two types of sources (ideal pencil beam and Gaussian beam) and multiple optical properties were tested. Results show that with standard optical properties of human tissue, photon densities obtained using RTE are, on average, around 5% of those predicted by MC simulations in the entire/deeper region. These results suggest that this implementation of the finite element method-RTE is an accurate forward model for optical tomography in human tissues.
Comparison of EPI Distortion Correction Methods in Diffusion Tensor MRI Using a Novel Framework
Wu, M.; Chang, L.-C.; Walker, L.; Lemaitre, H.; Barnett, A.S.; Marenco, S.; Pierpaoli, C.
2016-01-01
Diffusion weighted images (DWIs) are commonly acquired with Echo-planar imaging (EPI). B0 inhomogeneities affect EPI by producing spatially nonlinear image distortions. Several strategies have been proposed to correct EPI distortions including B0 field mapping (B0M) and image registration. In this study, an experimental framework is proposed to evaluation the performance of different EPI distortion correction methods in improving DT-derived quantities. A deformable registration based method with mutual information metric and cubic B-spline modeled constrained deformation field (BSP) is proposed as an alternative when B0 mapping data are not available. BSP method is qualitatively and quantitatively compared to B0M method using the framework. Both methods can successful reduce EPI distortions and significantly improve the quality of DT-derived quantities. Overall, B0M was clearly superior in infratentorial regions including brainstem and cerebellum, as well as in the ventral areas of the temporal lobes while BSP was better in all rostral brain regions. PMID:18982621
Juozaitis, Arvydas; Willeke, Klaus; Grinshpun, Sergey A.; Donnelly, Jean
1994-01-01
To study impaction versus impingement for the collection and recovery of viable airborne microorganisms, three new bioaerosol samplers have been designed and built. They differ from each other by the medium onto which the bioaerosol particles are collected (glass, agar, and liquid) but have the same inlet and collection geometries and the same sampling flow rate. The bioaerosol concentrations recorded by three different collection techniques have been compared with each other: impaction onto a glass slide, impaction onto an agar medium, and impingement into a liquid. It was found that the particle collection efficiency of agar slide impaction depends on the concentration of agar in the collection medium and on the sampling time, when samples are collected on a nonmoving agar slide. Impingement into a liquid showed anomalous behavior with respect to the sampling flow rate. Optimal sampling conditions in which all three new samplers exhibit the same overall sampling efficiency for nonbiological particles have been established. Inlet and collection efficiencies of about 100% have been achieved for all three devices at a sampling flow rate of 10 liters/min. The new agar slide impactor and the new impinger were then used to study the biological factors affecting the overall sampling efficiency. Laboratory experiments on the total recovery of a typical environmental microorganism, Pseudomonas fluorescens ATCC 13525, showed that both sampling methods, impaction and impingement, provided essentially the same total recovery when relatively nonstressed microorganisms were sampled under optimal sampling conditions. Comparison tests of the newly developed bioaerosol samplers with those commercially available showed that the incorporation of our research findings into the design of the new samplers yields better performance data than data from currently available samplers. PMID:16349217
Protein diffusion coefficient measurements by laminar flow analysis: method and applications.
Walters, R R; Graham, J F; Moore, R M; Anderson, D J
1984-07-01
Laminar flow in an open tube leads to solute band spreading. This process is opposed by radial diffusion. The translational diffusion coefficient of a solute can be calculated from the band dispersion, tube length, and flow rate. No calibration is necessary. A simple apparatus was used to measure the diffusion coefficients of several small solutes and 18 proteins. Most results were within +/- 10% of literature values. Each determination required 7-90 min, depending on the magnitude of the diffusion coefficient. The amount of protein needed was approximately 25 micrograms. The diffusion coefficient data were useful for the estimation of molecular weights. PMID:6486405
Goodwin, C Rory; Xu, Risheng; Iyer, Rajiv; Sankey, Eric W; Liu, Ann; Abu-Bonsrah, Nancy; Sarabia-Estrada, Rachel; Frazier, James L; Sciubba, Daniel M; Jallo, George I
2016-03-01
Brainstem gliomas comprise 10-20% of all pediatric central nervous system (CNS) tumors and diffuse intrinsic pontine gliomas (DIPGs) account for the majority of these lesions. DIPG is a rapidly progressive disease with almost universally fatal outcomes and a median survival less than 12 months. Current standard-of-care treatment for DIPG includes radiation therapy, but its long-term survival effects are still under debate. Clinical trials investigating the efficacy of systemic administration of various therapeutic agents have been associated with disappointing outcomes. Recent efforts have focused on improvements in chemotherapeutic agents employed and in methods of localized and targeted drug delivery. This review provides an update on current preclinical and clinical studies investigating treatment options for brainstem gliomas. PMID:26849840
Boundary conditions of the lattice Boltzmann method for convection-diffusion equations
NASA Astrophysics Data System (ADS)
Huang, Juntao; Yong, Wen-An
2015-11-01
In this paper, we employ an asymptotic analysis technique and construct two boundary schemes accompanying the lattice Boltzmann method for convection-diffusion equations with general Robin boundary conditions. One scheme is for straight boundaries, with the boundary points locating at any distance from the lattice nodes, and has second-order accuracy. The other is for curved boundaries, has only first-order accuracy and is much simpler than the existing schemes. Unlike those in the literature, our schemes involve only the current lattice node. Such a "single-node" boundary schemes are highly desirable for problems with complex geometries. The two schemes are validated numerically with a number of examples. The numerical results show the utility of the constructed schemes and very well support our theoretical predications.
Scalable implicit methods for reaction-diffusion equations in two and three space dimensions
Veronese, S.V.; Othmer, H.G.
1996-12-31
This paper describes the implementation of a solver for systems of semi-linear parabolic partial differential equations in two and three space dimensions. The solver is based on a parallel implementation of a non-linear Alternating Direction Implicit (ADI) scheme which uses a Cartesian grid in space and an implicit time-stepping algorithm. Various reordering strategies for the linearized equations are used to reduce the stride and improve the overall effectiveness of the parallel implementation. We have successfully used this solver for large-scale reaction-diffusion problems in computational biology and medicine in which the desired solution is a traveling wave that may contain rapid transitions. A number of examples that illustrate the efficiency and accuracy of the method are given here; the theoretical analysis will be presented.
NASA Astrophysics Data System (ADS)
Huang, Juntao; Hu, Zexi; Yong, Wen-An
2016-04-01
In this paper, we present a kind of second-order curved boundary treatments for the lattice Boltzmann method solving two-dimensional convection-diffusion equations with general nonlinear Robin boundary conditions. The key idea is to derive approximate boundary values or normal derivatives on computational boundaries, with second-order accuracy, by using the prescribed boundary condition. Once the approximate information is known, the second-order bounce-back schemes can be perfectly adopted. Our boundary treatments are validated with a number of numerical examples. The results show the utility of our boundary treatments and very well support our theoretical predications on the second-order accuracy thereof. The idea is quite universal. It can be directly generalized to 3-dimensional problems, multiple-relaxation-time models, and the Navier-Stokes equations.
Fast optimization method based on the diffuser dot density for uniformity of the backlight module.
Huang, Bing-Le; Guo, Tai-Liang
2016-02-20
A fast optimization method based on the diffuser dot density (DDD) for uniformity of the backlight module (BLM) is proposed in the paper. First, the relationship between the efficiency of the light emerging and the DDD is analyzed, and then a simulation model that is employed to acquire a serial of simulating data is constructed. Second, a mathematic method to profit the relationship is adopted, and a polynomial relationship is derived. Finally, an algorithm to adjust the DDD and optimize the uniformity of the BLM based on the DDD is constructed. The simulation results prove that only by three times optimization, the uniformity of the BLM can reach 85.6%, and the experimental result indicates that the algorithm proposed in the paper can improve the uniformity rapidly. The final experimental result is that the uniformity of the third optimization reaches 77.4%, which satisfies the target 75% in the phase of designing the BLM. Compared to the conventional optimization method, the method can speed up the procedure and lower the expense of developing the BLM in fabricating the liquid-crystal display. PMID:26906605
NDRC: A Disease-Causing Genes Prioritized Method Based on Network Diffusion and Rank Concordance.
Fang, Minghong; Hu, Xiaohua; Wang, Yan; Zhao, Junmin; Shen, Xianjun; He, Tingting
2015-07-01
Disease-causing genes prioritization is very important to understand disease mechanisms and biomedical applications, such as design of drugs. Previous studies have shown that promising candidate genes are mostly ranked according to their relatedness to known disease genes or closely related disease genes. Therefore, a dangling gene (isolated gene) with no edges in the network can not be effectively prioritized. These approaches tend to prioritize those genes that are highly connected in the PPI network while perform poorly when they are applied to loosely connected disease genes. To address these problems, we propose a new disease-causing genes prioritization method that based on network diffusion and rank concordance (NDRC). The method is evaluated by leave-one-out cross validation on 1931 diseases in which at least one gene is known to be involved, and it is able to rank the true causal gene first in 849 of all 2542 cases. The experimental results suggest that NDRC significantly outperforms other existing methods such as RWR, VAVIEN, DADA and PRINCE on identifying loosely connected disease genes and successfully put dangling genes as potential candidate disease genes. Furthermore, we apply NDRC method to study three representative diseases, Meckel syndrome 1, Protein C deficiency and Peroxisome biogenesis disorder 1A (Zellweger). Our study has also found that certain complex disease-causing genes can be divided into several modules that are closely associated with different disease phenotype. PMID:26080386
NASA Astrophysics Data System (ADS)
Al-Chalabi, Rifat M. Khalil
1997-09-01
Development of an improvement to the computational efficiency of the existing nested iterative solution strategy of the Nodal Exapansion Method (NEM) nodal based neutron diffusion code NESTLE is presented. The improvement in the solution strategy is the result of developing a multilevel acceleration scheme that does not suffer from the numerical stalling associated with a number of iterative solution methods. The acceleration scheme is based on the multigrid method, which is specifically adapted for incorporation into the NEM nonlinear iterative strategy. This scheme optimizes the computational interplay between the spatial discretization and the NEM nonlinear iterative solution process through the use of the multigrid method. The combination of the NEM nodal method, calculation of the homogenized, neutron nodal balance coefficients (i.e. restriction operator), efficient underlying smoothing algorithm (power method of NESTLE), and the finer mesh reconstruction algorithm (i.e. prolongation operator), all operating on a sequence of coarser spatial nodes, constitutes the multilevel acceleration scheme employed in this research. Two implementations of the multigrid method into the NESTLE code were examined; the Imbedded NEM Strategy and the Imbedded CMFD Strategy. The main difference in implementation between the two methods is that in the Imbedded NEM Strategy, the NEM solution is required at every MG level. Numerical tests have shown that the Imbedded NEM Strategy suffers from divergence at coarse- grid levels, hence all the results for the different benchmarks presented here were obtained using the Imbedded CMFD Strategy. The novelties in the developed MG method are as follows: the formulation of the restriction and prolongation operators, and the selection of the relaxation method. The restriction operator utilizes a variation of the reactor physics, consistent homogenization technique. The prolongation operator is based upon a variant of the pin power reconstruction methodology. The relaxation method, which is the power method, utilizes a constant coefficient matrix within the NEM non-linear iterative strategy. The choice of the MG nesting within the nested iterative strategy enables the incorporation of other non-linear effects with no additional coding effort. In addition, if an eigenvalue problem is being solved, it remains an eigenvalue problem at all grid levels, simplifying coding implementation. The merit of the developed MG method was tested by incorporating it into the NESTLE iterative solver, and employing it to solve four different benchmark problems. In addition to the base cases, three different sensitivity studies are performed, examining the effects of number of MG levels, homogenized coupling coefficients correction (i.e. restriction operator), and fine-mesh reconstruction algorithm (i.e. prolongation operator). The multilevel acceleration scheme developed in this research provides the foundation for developing adaptive multilevel acceleration methods for steady-state and transient NEM nodal neutron diffusion equations. (Abstract shortened by UMI.)
A method for estimating the diffuse attenuation coefficient (KdPAR)from paired temperature sensors
Read, Jordan S.; Rose, Kevin C.; Winslow, Luke A.; Read, Emily Kara
2015-01-01
A new method for estimating the diffuse attenuation coefficient for photosynthetically active radiation (KdPAR) from paired temperature sensors was derived. We show that during cases where the attenuation of penetrating shortwave solar radiation is the dominant source of temperature changes, time series measurements of water temperatures at multiple depths (z1 and z2) are related to one another by a linear scaling factor (a). KdPAR can then be estimated by the simple equation KdPAR ln(a)/(z2/z1). A suggested workflow is presented that outlines procedures for calculating KdPAR according to this paired temperature sensor (PTS) method. This method is best suited for conditions when radiative temperature gains are large relative to physical noise. These conditions occur frequently on water bodies with low wind and/or high KdPARs but can be used for other types of lakes during time periods of low wind and/or where spatially redundant measurements of temperatures are available. The optimal vertical placement of temperature sensors according to a priori knowledge of KdPAR is also described. This information can be used to inform the design of future sensor deployments using the PTS method or for campaigns where characterizing sub-daily changes in temperatures is important. The PTS method provides a novel method to characterize light attenuation in aquatic ecosystems without expensive radiometric equipment or the user subjectivity inherent in Secchi depth measurements. This method also can enable the estimation of KdPAR at higher frequencies than many manual monitoring programs allow.
NASA Astrophysics Data System (ADS)
He, G. H.; Zhang, X. Z.; Wei, Z.; Dong, S. Q.; di, Z. Q.; Zhou, B. L.
1986-07-01
The laser pulse method can be successfully applied to the measurement of thermal diffusivity of isotropic materials subject to some assumptions. For anisotropic materials, this method is applicable to the measurement of principal thermal diffusivity only on the condition that there is no difference in direction between the principal axis and that of the temperature gradient. After analyzing the heat conduction process in an anisotropic solid, it has been shown that large errors in the measurement of thermal diffusivity would exist if the direction of the principal axis deviates inconspicuously from that of the temperature gradient. The experimental results of thermal diffusivity of highly oriented pyrolytic graphite (HOPG) samples with various deviation angles have been compared with the analytical results. The laser pulse method is not applicable to measurements on semitransparent pyrolytic boron nitride (PBN). We adopted a two-layer composite sample to measure the thermal diffusivity of PBN in the c direction and a particular graphite-PBN composite sample has been prepared which has a very low thermal resistance at the interface. The thermal diffusivity and thermal conductivity of PG (below 2300°C) and PBN (below 1000°C) are given.
NASA Astrophysics Data System (ADS)
Suzuki, Takuji; Terabe, Hiroki; Iida, Shimpei; Yamashita, Takashi; Nagashima, Yasuyuki
2014-09-01
We have developed a new method to study positron diffusion in metals. In this method, we observe positronium negative ions emitted from the sample surfaces after coating with alkali-metals to evaluate the yields of the positrons which return to the surfaces. γ-rays from the ions accelerated using an electric field are clearly distinguished from those emitted from pair-annihilation of positrons in the bulk or on the surface and self-annihilation of emitted positronium atoms. Reliable studies on positron diffusion in metals have been enabled by this method.
Diffusion approximation-based simulation of stochastic ion channels: which method to use?
Pezo, Danilo; Soudry, Daniel; Orio, Patricio
2014-01-01
To study the effects of stochastic ion channel fluctuations on neural dynamics, several numerical implementation methods have been proposed. Gillespie's method for Markov Chains (MC) simulation is highly accurate, yet it becomes computationally intensive in the regime of a high number of channels. Many recent works aim to speed simulation time using the Langevin-based Diffusion Approximation (DA). Under this common theoretical approach, each implementation differs in how it handles various numerical difficulties—such as bounding of state variables to [0,1]. Here we review and test a set of the most recently published DA implementations (Goldwyn et al., 2011; Linaro et al., 2011; Dangerfield et al., 2012; Orio and Soudry, 2012; Schmandt and Galán, 2012; Güler, 2013; Huang et al., 2013a), comparing all of them in a set of numerical simulations that assess numerical accuracy and computational efficiency on three different models: (1) the original Hodgkin and Huxley model, (2) a model with faster sodium channels, and (3) a multi-compartmental model inspired in granular cells. We conclude that for a low number of channels (usually below 1000 per simulated compartment) one should use MC—which is the fastest and most accurate method. For a high number of channels, we recommend using the method by Orio and Soudry (2012), possibly combined with the method by Schmandt and Galán (2012) for increased speed and slightly reduced accuracy. Consequently, MC modeling may be the best method for detailed multicompartment neuron models—in which a model neuron with many thousands of channels is segmented into many compartments with a few hundred channels. PMID:25404914
Khan, Ahmed Nawaz; Khar, Roop Krishen; Ajayakumar, P. V.
2016-01-01
Objective: The aim of present study was to establish near infrared-chemometric methods that could be effectively used for quality profiling through identification and quantification of amoxicillin (AMOX) in formulated capsule which were similar to commercial products. In order to evaluate a large number of market products easily and quickly, these methods were modeled. Materials and Methods: Thermo Scientific Antaris II near infrared analyzer with TQ Analyst Chemometric Software were used for the development and validation of the identification and quantification models. Several AMOX formulations were composed with four excipients microcrystalline cellulose, magnesium stearate, croscarmellose sodium and colloidal silicon dioxide. Development includes quadratic mixture formulation design, near infrared spectrum acquisition, spectral pretreatment and outlier detection. According to prescribed guidelines by International Conference on Harmonization (ICH) and European Medicine Agency (EMA) developed methods were validated in terms of specificity, accuracy, precision, linearity, and robustness. Results: On diffuse reflectance mode, an identification model based on discriminant analysis was successfully processed with 76 formulations; and same samples were also used for quantitative analysis using partial least square algorithm with four latent variables and 0.9937 correlation of coefficient followed by 2.17% root mean square error of calibration (RMSEC), 2.38% root mean square error of prediction (RMSEP), 2.43% root mean square error of cross-validation (RMSECV). Conclusion: Proposed model established a good relationship between the spectral information and AMOX identity as well as content. Resulted values show the performance of the proposed models which offers alternate choice for AMOX capsule evaluation, relative to that of well-established high-performance liquid chromatography method. Ultimately three commercial products were successfully evaluated using developed methods. PMID:27134469
Electrospinning of agar/PVA aqueous solutions and its relation with rheological properties
Technology Transfer Automated Retrieval System (TEKTRAN)
In this work, we report the successful fabrication of agar-based nanofibers by an electrospinning technique using water as the solvent media. A tubeless spinneret was attached inside the electrospinning chamber, operated at 50 deg C, to avoid agar gelation. Pure agar solution 1% (w/w) showed inadequ...
Inverse Monte Carlo method in a multilayered tissue model for diffuse reflectance spectroscopy
NASA Astrophysics Data System (ADS)
Fredriksson, Ingemar; Larsson, Marcus; Strömberg, Tomas
2012-04-01
Model based data analysis of diffuse reflectance spectroscopy data enables the estimation of optical and structural tissue parameters. The aim of this study was to present an inverse Monte Carlo method based on spectra from two source-detector distances (0.4 and 1.2 mm), using a multilayered tissue model. The tissue model variables include geometrical properties, light scattering properties, tissue chromophores such as melanin and hemoglobin, oxygen saturation and average vessel diameter. The method utilizes a small set of presimulated Monte Carlo data for combinations of different levels of epidermal thickness and tissue scattering. The path length distributions in the different layers are stored and the effect of the other parameters is added in the post-processing. The accuracy of the method was evaluated using Monte Carlo simulations of tissue-like models containing discrete blood vessels, evaluating blood tissue fraction and oxygenation. It was also compared to a homogeneous model. The multilayer model performed better than the homogeneous model and all tissue parameters significantly improved spectral fitting. Recorded in vivo spectra were fitted well at both distances, which we previously found was not possible with a homogeneous model. No absolute intensity calibration is needed and the algorithm is fast enough for real-time processing.
A reaction-diffusion model of the Darien Gap Sterile Insect Release Method
NASA Astrophysics Data System (ADS)
Alford, John G.
2015-05-01
The Sterile Insect Release Method (SIRM) is used as a biological control for invasive insect species. SIRM involves introducing large quantities of sterilized male insects into a wild population of invading insects. A fertile/sterile mating produces offspring that are not viable and the wild insect population will eventually be eradicated. A U.S. government program maintains a permanent sterile fly barrier zone in the Darien Gap between Panama and Columbia to control the screwworm fly (Cochliomyia Hominivorax), an insect that feeds off of living tissue in mammals and has devastating effects on livestock. This barrier zone is maintained by regular releases of massive quantities of sterilized male screwworm flies from aircraft. We analyze a reaction-diffusion model of the Darien Gap barrier zone. Simulations of the model equations yield two types of spatially inhomogeneous steady-state solutions representing a sterile fly barrier that does not prevent invasion and a barrier that does prevent invasion. We investigate steady-state solutions using both phase plane methods and monotone iteration methods and describe how barrier width and the sterile fly release rate affects steady-state behavior.
A model of cefoperazone tissue penetration: diffusion coefficient and protein binding.
Meulemans, A
1992-01-01
The apparent diffusion coefficient of a bound drug, cefoperazone, was studied. The protein binding of cefoperazone was studied by voltammetry, a technique which permitted instant measurements. The apparent diffusion coefficients were similar in agar and fibrin and lower in rat brain tissue. The influence of protein on the value of the apparent diffusion coefficient was negligible. The hypothesis that only the free drug diffuses was supported. The percentage of binding determined by voltammetry corresponded to the true concentration of drug which diffuses and is much lower than the percentage of binding determined by the ultrafiltration centrifugation method. This discrepancy could be explained by the rate of dissociation of the protein-drug complex. PMID:1605594
Atomistic study of diffusion-mediated plasticity and creep using phase field crystal methods
NASA Astrophysics Data System (ADS)
Berry, Joel; Rottler, Jörg; Sinclair, Chad W.; Provatas, Nikolas
2015-10-01
The nonequilibrium dynamics of diffusion-mediated plasticity and creep in materials subjected to constant load at high homologous temperatures is studied atomistically using phase field crystal (PFC) methods. Creep stress and grain size exponents obtained for nanopolycrystalline systems, m ≃1.02 and p ≃1.98 , respectively, closely match those expected for idealized diffusional Nabarro-Herring creep. These exponents are observed in the presence of significant stress-assisted diffusive grain boundary migration, indicating that Nabarro-Herring creep and stress-assisted boundary migration contribute in the same manner to the macroscopic constitutive relation. When plastic response is dislocation-mediated, power-law stress exponents inferred from dislocation climb rates are found to increase monotonically from m ≃3 , as expected for generic climb-mediated natural creep, to m ≃5.8 as the dislocation density ρd is increased beyond typical experimental values. Stress exponents m ≳3 directly measured from simulations that include dislocation nucleation, climb, glide, and annihilation are attributed primarily to these large ρd effects. Extrapolation to lower ρd suggests that m ≃4 -4.5 should be obtained from our PFC description at typical experimental ρd values, which is consistent with expectations for power-law creep via mixed climb and glide. The anomalously large stress exponents observed in our atomistic simulations at large ρd may nonetheless be relevant to systems in which comparable densities are obtained locally within heterogeneous defect domains such as dislocation cell walls or tangles.
Oxygen diffusion-concentration product in rhodopsin as observed by a pulse ESR spin labeling method.
Subczynski, W K; Renk, G E; Crouch, R K; Hyde, J S; Kusumi, A
1992-01-01
Permeation of molecular oxygen in rhodopsin, an integral membrane protein, has been investigated by monitoring the bimolecular collision rate between molecular oxygen and the nitroxide spin label using a pulse electron spin resonance (ESR) T1 method. Rhodopsin was labeled by regeneration with the spin-labeled 9-cis retinal analogue in which the beta-ionone ring of retinal is replaced by the nitroxide tetramethyl-oxypyrrolidine ring. The bimolecular collision rate was evaluated in terms of an experimental parameter W(x), defined as T1(-1)(air,x)--T1(-1)(N2,x) where T1's are the spin-lattice relaxation times of the nitroxide in samples equilibrated with atmospheric air and nitrogen respectively, which is proportional to the product of local oxygen concentration and local diffusion coefficient (transport). W-values at the beta-ionone binding site in spin-labeled rhodopsin are in the range of 0.02-0.13 microseconds-1, which are 10-60 times smaller than W's in water and 1.1-20 times smaller than in model membranes in the gel phase, indicating that membrane proteins create significant permeation resistance to transport of molecular oxygen inside and across the membrane. W(thereby the oxygen diffusion-concentration product) is larger in the meta II-enriched sample than in rhodopsin, indicating light-induced conformational changes of opsin around the beta-ionone binding site. W decreases with increase of temperature for both rhodopsin and meta II-enriched samples, suggesting that temperature-induced conformational changes take place in both samples. These changes were not observable using conventional ESR spectroscopy. It is concluded that W is a sensitive monitor of conformational changes of proteins. PMID:1330032
Bodzenta, Jerzy; Kaźmierczak-Bałata, Anna; Wokulska, Krystyna B; Kucytowski, Jacek; Łukasiewicz, Tadeusz; Hofman, Władysław
2009-03-01
Three crystals used in solid-state lasers, namely, yttrium aluminum garnet (YAG), yttrium orthovanadate (YVO(4)), and gadolinium calcium oxoborate (GdCOB), were investigated to determine the influence of dopants on their thermal diffusivity. The thermal diffusivity was measured by thermal wave method with a signal detection based on mirage effect. The YAG crystals were doped with Yb or V, the YVO(4) with Nd or Ca and Tm, and the GdCOB crystals contained Nd or Yb. In all cases, the doping caused a decrease in thermal diffusivity. The analysis of complementary measurements of ultrasound velocity changes caused by dopants leads to the conclusion that impurities create phonon scattering centers. This additional scattering reduces the phonon mean free path and accordingly results in the decrease of the thermal diffusivity of the crystal. The influence of doping on lattice parameters was investigated, additionally. PMID:19252616
Wang, Yangyang; Sun, Che-Nan; Fan, Fei; Sangoro, Joshua R; Berman, Marc; Greenbaum, Steve; Zawodzinski, Thomas; Sokolov, Alexei P
2013-01-01
Electrode polarization analysis is frequently used to determine free-ion diffusivity and number density in ionic conductors. In the present study, this approach is critically examined in a wide variety of electrolytes, including aqueous and nonaqueous solutions, polymer electrolytes, and ionic liquids. It is shown that the electrode polarization analysis based on theMacdonald-Trukhan model [J. Chem. Phys. 124, 144903 (2006); J. Non-Cryst. Solids 357, 3064 (2011)] progressively fails to give reasonable values of free-ion diffusivity and number density with increasing salt concentration. This should be expected because the original model of electrode polarization is designed for dilute electrolytes. An empirical correction method which yields ion diffusivities in reasonable agreement with pulsed-field gradient nuclear magnetic resonance measurements is proposed. However, the analysis of free-ion diffusivity and number density from electrode polarization should still be exercised with great caution because there is no solid theoretical justification for the proposed corrections.
Holographic method for investigating the diffusion of dye molecules in the polymer host
NASA Astrophysics Data System (ADS)
Wang, C. H.; Xia, J. L.
1990-02-01
Laser induced holographic grating relaxation studies of thymoquinone dissolved in amorphous poly(?-methyl styrene) have been carried out. The Onsager theory of mutual diffusion for binary and tertiary systems are utilized to analyze the shape of the diffraction intensity curve. Different line shapes that are associated with the relaxation of the diffraction intensity are interpreted in terms of the diffusion processes. Diffusion coefficients are obtained as a function of thymoquinone concentration from 0.3 to 20 wt. % at various temperatures. It is shown that at very low concentrations (less than 0.5%), the self-diffusion coefficients of the dye molecule and its photoproduct are obtained. Above 0.5% concentrations the diffusion coefficient rapidly increases with increasing dye concentration. The temperature dependence of the self-diffusion coefficient follows the Williams-Landel-Ferry equation, whereas the mutual diffusion coefficient at higher dye concentrations follows the Arrhenius equation. The self-diffusion coefficient rapidly decreases as the sample temperature is traversed across the glass transition temperature (Tg). However at finite dye concentrations there is no detectable effect owing to the onset of Tg on the mutual diffusion coefficient. The difference is attributed to the plasticizing effect of the dye molecules.
NASA Astrophysics Data System (ADS)
Zhong, Xinxin; Zhao, Yi; Cao, Jianshu
2014-04-01
The time-dependent wavepacket diffusion method for carrier quantum dynamics (Zhong and Zhao 2013 J. Chem. Phys. 138 014111), a truncated version of the stochastic Schrödinger equation/wavefunction approach that approximately satisfies the detailed balance principle and scales well with the size of the system, is applied to investigate the carrier transport in one-dimensional systems including both the static and dynamic disorders on site energies. The predicted diffusion coefficients with respect to temperature successfully bridge from band-like to hopping-type transport. As demonstrated in paper I (Moix et al 2013 New J. Phys. 15 085010), the static disorder tends to localize the carrier, whereas the dynamic disorder induces carrier dynamics. For the weak dynamic disorder, the diffusion coefficients are temperature-independent (band-like property) at low temperatures, which is consistent with the prediction from the Redfield equation, and a linear dependence of the coefficient on temperature (hopping-type property) only appears at high temperatures. In the intermediate regime of dynamic disorder, the transition from band-like to hopping-type transport can be easily observed at relatively low temperatures as the static disorder increases. When the dynamic disorder becomes strong, the carrier motion can follow the hopping-type mechanism even without static disorder. Furthermore, it is found that the memory time of dynamic disorder is an important factor in controlling the transition from the band-like to hopping-type motions.
Shibukawa, Atsushi; Okamoto, Atsushi; Takabayashi, Masanori; Tomita, Akihisa
2014-02-24
We propose a spatial cross modulation method using a random diffuser and a phase-only spatial light modulator (SLM), by which arbitrary complex-amplitude fields can be generated with higher spatial resolution and diffraction efficiency than off-axis and double-phase computer-generated holograms. Our method encodes the original complex object as a phase-only diffusion image by scattering the complex object using a random diffuser. In addition, all incoming light to the SLM is consumed for a single diffraction order, making a diffraction efficiency of more than 90% possible. This method can be applied for holographic data storage, three-dimensional displays, and other such applications. PMID:24663718
Sousa, Ana M M; Souza, Hiléia K S; Latona, Nicholas; Liu, Cheng-Kung; Gonçalves, Maria P; Liu, LinShu
2014-10-13
In the present paper, we test the suitability of ChCl/urea (DES-U) and ChCl/glycerol (DES-G) eutectic mixtures, each one prepared at 1:2 molar ratio, for the production of agar films. A three-step process is proposed: pre-solubilization of polymer in DES followed by compression-molding and subsequent drying. The mechanical properties, water resistance and microstructure of the films were evaluated at different polymer concentrations (i.e. 2-6%, w/w). DES-U showed by far, the best film forming ability. Agreeing with the diffusion and SEM data, films with the best mechanical properties were found at the lowest and highest agar concentrations (tensile strengths of 24.2-42 MPa and elongations of 15.4-38.9%). The water sorption and contact angle studies suggested increased hydrophilicity for the film containing the lowest concentration of agar. The use of choline chloride based ionic liquid analogues as solvent and plasticizer might be a promising tool for the development of new non-aqueous materials based on seaweed polysaccharides. PMID:25037344
NASA Astrophysics Data System (ADS)
Xu, Jing; Wu, Jian; Feng, Daming; Cui, Zhiming
Serious types of vascular diseases such as carotid stenosis, aneurysm and vascular malformation may lead to brain stroke, which are the third leading cause of death and the number one cause of disability. In the clinical practice of diagnosis and treatment of cerebral vascular diseases, how to do effective detection and description of the vascular structure of two-dimensional angiography sequence image that is blood vessel skeleton extraction has been a difficult study for a long time. This paper mainly discussed two-dimensional image of blood vessel skeleton extraction based on the level set method, first do the preprocessing to the DSA image, namely uses anti-concentration diffusion model for the effective enhancement and uses improved Otsu local threshold segmentation technology based on regional division for the image binarization, then vascular skeleton extraction based on GMM (Group marching method) with fast sweeping theory was actualized. Experiments show that our approach not only improved the time complexity, but also make a good extraction results.
Convergence analysis of two-node CMFD method for two-group neutron diffusion eigenvalue problem
NASA Astrophysics Data System (ADS)
Jeong, Yongjin; Park, Jinsu; Lee, Hyun Chul; Lee, Deokjung
2015-12-01
In this paper, the nonlinear coarse-mesh finite difference method with two-node local problem (CMFD2N) is proven to be unconditionally stable for neutron diffusion eigenvalue problems. The explicit current correction factor (CCF) is derived based on the two-node analytic nodal method (ANM2N), and a Fourier stability analysis is applied to the linearized algorithm. It is shown that the analytic convergence rate obtained by the Fourier analysis compares very well with the numerically measured convergence rate. It is also shown that the theoretical convergence rate is only governed by the converged second harmonic buckling and the mesh size. It is also noted that the convergence rate of the CCF of the CMFD2N algorithm is dependent on the mesh size, but not on the total problem size. This is contrary to expectation for eigenvalue problem. The novel points of this paper are the analytical derivation of the convergence rate of the CMFD2N algorithm for eigenvalue problem, and the convergence analysis based on the analytic derivations.
NASA Astrophysics Data System (ADS)
Ardeshirpour, Yasaman; Biswal, Nrusingh; Aguirre, Andres; Zhu, Quing
2011-04-01
In diffuse optical tomography (DOT), a typical perturbation approach requires two sets of measurements obtained at the lesion breast (lesion or target site) and a contra-lateral location of the normal breast (reference site) for image reconstruction. For patients who have a small amount of breast tissue, the chest-wall underneath the breast tissue at both sites affects the imaging results. In this group of patients, the perturbation, which is the difference between measurements obtained at the lesion and reference sites, may include the information of background mismatch which can generate artifacts or affect the reconstructed quantitative absorption coefficient of the lesion. Also, for patients who have a single breast due to prior surgery, the contra-lateral reference is not available. To improve the DOT performance or overcome its limitation, we introduced a new method based on an exogenous contrast agent and demonstrate its performance using animal models. Co-registered ultrasound was used to guide the lesion localization. The results have shown that artifacts caused by background mismatch can be reduced significantly by using this new method.
Bifurcation analysis of brown tide by reaction-diffusion equation using finite element method
Kawahara, Mutsuto; Ding, Yan
1997-03-01
In this paper, we analyze the bifurcation of a biodynamics system in a two-dimensional domain by virtue of reaction-diffusion equations. The discretization method in space is the finite element method. The computational algorithm for an eigenspectrum is described in detail. On the basis of an analysis of eigenspectra according to Helmholtz`s equation, the discrete spectra in regards to the physical variables are numerically obtained in two-dimensional space. In order to investigate this mathematical model in regards to its practical use, we analyzed the stability of two cases, i.e., hydranth regeneration in the marine hydroid Tubularia and a brown tide in a harbor in Japan. By evaluating the stability according to the linearized stability definition, the critical parameters for outbreaks of brown tide can be theoretically determined. In addition, results for the linear combination of eigenspectrum coincide with the distribution of the observed brown tide. Its periodic characteristic was also verified. 10 refs., 8 figs., 5 tabs.
Özarslan, Evren; Koay, Cheng Guan; Shepherd, Timothy M; Komlosh, Michal E; İrfanoğlu, M Okan; Pierpaoli, Carlo; Basser, Peter J
2013-09-01
Diffusion-weighted magnetic resonance (MR) signals reflect information about underlying tissue microstructure and cytoarchitecture. We propose a quantitative, efficient, and robust mathematical and physical framework for representing diffusion-weighted MR imaging (MRI) data obtained in "q-space," and the corresponding "mean apparent propagator (MAP)" describing molecular displacements in "r-space." We also define and map novel quantitative descriptors of diffusion that can be computed robustly using this MAP-MRI framework. We describe efficient analytical representation of the three-dimensional q-space MR signal in a series expansion of basis functions that accurately describes diffusion in many complex geometries. The lowest order term in this expansion contains a diffusion tensor that characterizes the Gaussian displacement distribution, equivalent to diffusion tensor MRI (DTI). Inclusion of higher order terms enables the reconstruction of the true average propagator whose projection onto the unit "displacement" sphere provides an orientational distribution function (ODF) that contains only the orientational dependence of the diffusion process. The representation characterizes novel features of diffusion anisotropy and the non-Gaussian character of the three-dimensional diffusion process. Other important measures this representation provides include the return-to-the-origin probability (RTOP), and its variants for diffusion in one- and two-dimensions-the return-to-the-plane probability (RTPP), and the return-to-the-axis probability (RTAP), respectively. These zero net displacement probabilities measure the mean compartment (pore) volume and cross-sectional area in distributions of isolated pores irrespective of the pore shape. MAP-MRI represents a new comprehensive framework to model the three-dimensional q-space signal and transform it into diffusion propagators. Experiments on an excised marmoset brain specimen demonstrate that MAP-MRI provides several novel, quantifiable parameters that capture previously obscured intrinsic features of nervous tissue microstructure. This should prove helpful for investigating the functional organization of normal and pathologic nervous tissue. PMID:23587694
Jayawardena, Asitha; Boardman, Allison; Cook, Thomas; Oprescu, Florin; Morcuende, Jose A
2011-01-01
This ethnographic study evaluated the use of low-bandwidth web-conferencing to enhance diffusion of a specific best practice, the Ponseti method to treat clubfoot, in three economically diverse countries in Latin America. A "Ponseti Virtual Forum" (PVF) was organized in Guatemala, Peru and Chile to examine the influences of economic level and telecommunication infrastructure on the effectiveness of tins approach. Across the three countries, a total of 14 different sites participated in the PVFs. Thirty-three Ponseti-trained practitioners were interviewed before and after each PVF, which included interactions with a Spanish-speaking Ponseti method expert. Semi-structured interviews, observations, and IP address data were triangulated and analyzed. The results demonstrated that 100% of the practitioners rated the sessions as very useful and that they would use this approach again. The largest obstacles to using PVFs were financial (7 out of 9 practitioners) in Guatemala; a lack of equipment and network access (6 out of 11) in Peru; and the organization and implementation of the conferences themselves (7 out of 9) in Chile. This study illustrates the usefulness of Ponseti Virtual Forums in Latin America. Health officials in Peru are currently developing a large-scale information session for traumatologists about the Ponseti method, while practitioners in Guatemala and Chile are organizing monthly scholarly meetings for physicians in remote areas. This initial feedback suggests that low-bandwidth web-conferencing can be an important vehicle for the dissemination of best practices, such as the Ponseti method, in developing countries. PMID:22096417
Adaptive meshless local maximum-entropy finite element method for convection-diffusion problems
NASA Astrophysics Data System (ADS)
Wu, C. T.; Young, D. L.; Hong, H. K.
2014-01-01
In this paper, a meshless local maximum-entropy finite element method (LME-FEM) is proposed to solve 1D Poisson equation and steady state convection-diffusion problems at various Peclet numbers in both 1D and 2D. By using local maximum-entropy (LME) approximation scheme to construct the element shape functions in the formulation of finite element method (FEM), additional nodes can be introduced within element without any mesh refinement to increase the accuracy of numerical approximation of unknown function, which procedure is similar to conventional p-refinement but without increasing the element connectivity to avoid the high conditioning matrix. The resulted LME-FEM preserves several significant characteristics of conventional FEM such as Kronecker-delta property on element vertices, partition of unity of shape function and exact reproduction of constant and linear functions. Furthermore, according to the essential properties of LME approximation scheme, nodes can be introduced in an arbitrary way and the continuity of the shape function along element edge is kept at the same time. No transition element is needed to connect elements of different orders. The property of arbitrary local refinement makes LME-FEM be a numerical method that can adaptively solve the numerical solutions of various problems where troublesome local mesh refinement is in general necessary to obtain reasonable solutions. Several numerical examples with dramatically varying solutions are presented to test the capability of the current method. The numerical results show that LME-FEM can obtain much better and stable solutions than conventional FEM with linear element.
A Simple Educational Method for the Measurement of Liquid Binary Diffusivities
ERIC Educational Resources Information Center
Rice, Nicholas P.; de Beer, Martin P.; Williamson, Mark E.
2014-01-01
A simple low-cost experiment has been developed for the measurement of the binary diffusion coefficients of liquid substances. The experiment is suitable for demonstrating molecular diffusion to small or large undergraduate classes in chemistry or chemical engineering. Students use a cell phone camera in conjunction with open-source image…
A Simple Educational Method for the Measurement of Liquid Binary Diffusivities
ERIC Educational Resources Information Center
Rice, Nicholas P.; de Beer, Martin P.; Williamson, Mark E.
2014-01-01
A simple low-cost experiment has been developed for the measurement of the binary diffusion coefficients of liquid substances. The experiment is suitable for demonstrating molecular diffusion to small or large undergraduate classes in chemistry or chemical engineering. Students use a cell phone camera in conjunction with open-source image
NASA Astrophysics Data System (ADS)
Mittelstaedt, Eric; Davaille, Anne; van Keken, Peter E.; Gracias, Nuno; Escartin, Javier
2010-10-01
Diffuse flow velocimetry (DFV) is introduced as a new, noninvasive, optical technique for measuring the velocity of diffuse hydrothermal flow. The technique uses images of a motionless, random medium (e.g., rocks) obtained through the lens of a moving refraction index anomaly (e.g., a hot upwelling). The method works in two stages. First, the changes in apparent background deformation are calculated using particle image velocimetry (PIV). The deformation vectors are determined by a cross correlation of pixel intensities across consecutive images. Second, the 2-D velocity field is calculated by cross correlating the deformation vectors between consecutive PIV calculations. The accuracy of the method is tested with laboratory and numerical experiments of a laminar, axisymmetric plume in fluids with both constant and temperature-dependent viscosity. Results show that average RMS errors are 5%-7% and are most accurate in regions of pervasive apparent background deformation which is commonly encountered in regions of diffuse hydrothermal flow. The method is applied to a 25 s video sequence of diffuse flow from a small fracture captured during the Bathyluck'09 cruise to the Lucky Strike hydrothermal field (September 2009). The velocities of the 10C-15C effluent reach 5.5 cm/s, in strong agreement with previous measurements of diffuse flow. DFV is found to be most accurate for approximately 2-D flows where background objects have a small spatial scale, such as sand or gravel.
NASA Astrophysics Data System (ADS)
Lin, Guoxing
2015-10-01
Inter-molecular multiple quantum coherence (iMQC) has important applications in NMR and MRI. However, the current theoretical methods still have some difficulties in analyzing the behavior of iMQC signal attenuation of pulsed field gradient diffusion experiments. In this paper, the iMQC diffusion experiments were analyzed by an effective phase shift diffusion equation (EPSDE) method, which is based on the idea that the accumulating phase shift (APS) can be viewed as the result of a diffusion process in virtual phase space (VPS) with effective diffusion coefficient K2(t) D (rad2/s) where K ( t ) = ∫0 t γ g ( t ' ) d t ' is a wavenumber and D is the physical diffusion coefficient of the spin carrier in the real space. The term K(ttot) z1 needs to be added to the APS when K(ttot) is not zero. Most of the time, K(ttot) equals zero. However, in iMQC experiments, the condition K(ttot) equaling zero or being non-zero for each spin depends on the gradient pulse setting. The signal attenuations of these two types of iMQC, zero or non-zero K(ttot), were analyzed in detail for free and restricted diffusions, which shows that there are significant differences between these two types of iMQC. Particularly, if an apparent diffusion coefficient Dapp is used to analyze the signal attenuation, it equals nD for zero K(ttot) which agrees with current theoretical and experimental reports, while for non-zero K(ttot), it equals (2n - 1) D which agrees with experimental results from the literature; there are no similar theoretical results reported for comparison. The result that Dapp equals (2n - 1) D is important because the higher value of Dapp means that non-zero K(ttot) iMQC can potentially provide more contrast and measure slower diffusion rates than zero K(ttot) iMQC. The EPSDE method provides a new way to analyze iMQC diffusion experiments.
Alemani, Davide; Chopard, Bastien; Galceran, Josep; Buffle, Jacques
2006-09-21
This paper studies the optimisation of a numerical model and a computer code to solve numerically reaction-diffusion processes in environmental or biological systems with complicated geometries and mixtures of reactions including time and spatial scales extending over several order of magnitude. In particular, we consider different grid refinement techniques in the framework of a lattice Boltzmann solver for reaction-diffusion systems. Two new grid refinement methods are proposed, which are both quantitatively good. The first method is based on the matching of the concentration profiles and fluxes across two adjacent sub-domains, while the second method is based on nested subgrids. The focus of our study is the trade off between accuracy and CPU time. We show how the different parameters of the method, such as the refinement factors, the location of the boundary between different grids or coupling methods at the interface affect the quality of the numerical solution and the efficiency of the method. PMID:17028701
NASA Astrophysics Data System (ADS)
Nguyen, Dang Van; Li, Jing-Rebecca; Grebenkov, Denis; Le Bihan, Denis
2014-04-01
The complex transverse water proton magnetization subject to diffusion-encoding magnetic field gradient pulses in a heterogeneous medium can be modeled by the multiple compartment Bloch-Torrey partial differential equation (PDE). In addition, steady-state Laplace PDEs can be formulated to produce the homogenized diffusion tensor that describes the diffusion characteristics of the medium in the long time limit. In spatial domains that model biological tissues at the cellular level, these two types of PDEs have to be completed with permeability conditions on the cellular interfaces. To solve these PDEs, we implemented a finite elements method that allows jumps in the solution at the cell interfaces by using double nodes. Using a transformation of the Bloch-Torrey PDE we reduced oscillations in the searched-for solution and simplified the implementation of the boundary conditions. The spatial discretization was then coupled to the adaptive explicit Runge-Kutta-Chebyshev time-stepping method. Our proposed method is second order accurate in space and second order accurate in time. We implemented this method on the FEniCS C++ platform and show time and spatial convergence results. Finally, this method is applied to study some relevant questions in diffusion MRI.
Nguyen, Dang Van; Li, Jing-Rebecca; Grebenkov, Denis; Le Bihan, Denis
2014-04-15
The complex transverse water proton magnetization subject to diffusion-encoding magnetic field gradient pulses in a heterogeneous medium can be modeled by the multiple compartment Bloch–Torrey partial differential equation (PDE). In addition, steady-state Laplace PDEs can be formulated to produce the homogenized diffusion tensor that describes the diffusion characteristics of the medium in the long time limit. In spatial domains that model biological tissues at the cellular level, these two types of PDEs have to be completed with permeability conditions on the cellular interfaces. To solve these PDEs, we implemented a finite elements method that allows jumps in the solution at the cell interfaces by using double nodes. Using a transformation of the Bloch–Torrey PDE we reduced oscillations in the searched-for solution and simplified the implementation of the boundary conditions. The spatial discretization was then coupled to the adaptive explicit Runge–Kutta–Chebyshev time-stepping method. Our proposed method is second order accurate in space and second order accurate in time. We implemented this method on the FEniCS C++ platform and show time and spatial convergence results. Finally, this method is applied to study some relevant questions in diffusion MRI.
Meulemans, A; Paycha, F; Hannoun, P; Vulpillat, M
1989-08-01
A method for determining diffusion coefficients of four antibiotics in extracellular tissue space according to Fick's law is described. This new method was applied to rat brain tissue and to agar. After diffusion of the antibiotic in one axis, the gradient concentration was determined with microvoltammetric electrodes. These microelectrodes (1 micron at the extreme tip) measured the free diffusible form of electroactive antibiotics in the extracellular brain space. Metronidazole, chloramphenicol succinate, cefsulodin, and piperacillin gave diffusion coefficients ranging from 0.1 x 10(-6) to 0.2 x 10(-6) cm2 . s-1 in tissue; chloramphenicol base, which is positively charged, gave a coefficient of 0.04 x 10(-6) cm2 . s-1. The coefficient ranged from 0.6 x 10(-6) to 1.2 x 10(-6) cm2 . s-1 in agar. These coefficients were used to simulate antibiotic concentrations in infectious sites and between capillaries by using a simple model of plane diffusion. PMID:2802555
Meulemans, A; Paycha, F; Hannoun, P; Vulpillat, M
1989-01-01
A method for determining diffusion coefficients of four antibiotics in extracellular tissue space according to Fick's law is described. This new method was applied to rat brain tissue and to agar. After diffusion of the antibiotic in one axis, the gradient concentration was determined with microvoltammetric electrodes. These microelectrodes (1 micron at the extreme tip) measured the free diffusible form of electroactive antibiotics in the extracellular brain space. Metronidazole, chloramphenicol succinate, cefsulodin, and piperacillin gave diffusion coefficients ranging from 0.1 x 10(-6) to 0.2 x 10(-6) cm2 . s-1 in tissue; chloramphenicol base, which is positively charged, gave a coefficient of 0.04 x 10(-6) cm2 . s-1. The coefficient ranged from 0.6 x 10(-6) to 1.2 x 10(-6) cm2 . s-1 in agar. These coefficients were used to simulate antibiotic concentrations in infectious sites and between capillaries by using a simple model of plane diffusion. PMID:2802555
Thickness Mapping of Eleven Retinal Layers Segmented Using the Diffusion Maps Method in Normal Eyes
Kafieh, Raheleh; Rabbani, Hossein; Abramoff, Michael D.; Sonka, Milan
2015-01-01
This study was conducted to determine the thickness map of eleven retinal layers in normal subjects by spectral domain optical coherence tomography (SD-OCT) and evaluate their association with sex and age. Mean regional retinal thickness of 11 retinal layers was obtained by automatic three-dimensional diffusion map based method in 112 normal eyes of 76 Iranian subjects. We applied our previously reported 3D intraretinal fast layer segmentation which does not require edge-based image information but rather relies on regional image texture. The thickness maps are compared among 9 macular sectors within 3 concentric circles as defined by ETDRS. The thickness map of central foveal area in layers 1, 3, and 4 displayed the minimum thickness. Maximum thickness was observed in nasal to the fovea of layer 1 and in a circular pattern in the parafoveal retinal area of layers 2, 3, and 4 and in central foveal area of layer 6. Temporal and inferior quadrants of the total retinal thickness and most of other quadrants of layer 1 were significantly greater in the men than in the women. Surrounding eight sectors of total retinal thickness and a limited number of sectors in layers 1 and 4 significantly correlated with age. PMID:25960888
Comparison of dialysis membrane diffusion samplers and two purging methods in bedrock wells
Imbrigiotta, T.E.; Ehlke, T.A.; Lacombe, P.J.; Dale, J.M.
2002-01-01
Collection of ground-water samples from bedrock wells using low-flow purging techniques is problematic because of the random spacing, variable hydraulic conductivity, and variable contamination of contributing fractures in each well's open interval. To test alternatives to this purging method, a field comparison of three ground-water-sampling techniques was conducted on wells in fractured bedrock at a site contaminated primarily with volatile organic compounds. Constituent concentrations in samples collected with a diffusion sampler constructed from dialysis membrane material were compared to those in samples collected from the same wells with a standard low-flow purging technique and a hybrid (high-flow/low-flow) purging technique. Concentrations of trichloroethene, cis-1,2-dichloroethene, vinyl chloride, calcium, chloride, and alkalinity agreed well among samples collected with all three techniques in 9 of the 10 wells tested. Iron concentrations varied more than those of the other parameters, but their pattern of variation was not consistent. Overall, the results of nonparametric analysis of variance testing on the nine wells sampled twice showed no statistically significant difference at the 95-percent confidence level among the concentrations of volatile organic compounds or inorganic constituents recovered by use of any of the three sampling techniques.
Method of coating the interior surface of hollow objects with a diffusion coating
Knowles, Shawn D.; Senor, David J.; Forbes, Steven V.; Johnson, Roger N.; Hollenberg, Glenn W.
2005-03-15
A method for forming a diffusion coating on the interior of surface of a hollow object wherein a filament, extending through a hollow object and adjacent to the interior surface of the object, is provided, with a coating material, in a vacuum. An electrical current is then applied to the filament to resistively heat the filament to a temperature sufficient to transfer the coating material from the filament to the interior surface of the object. The filament is electrically isolated from the object while the filament is being resistively heated. Preferably, the filament is provided as a tungsten filament or molybdenum filament. Preferably, the coating materials are selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Ge, Hg, In, K, Li, Mg, Mn, Na, Ni P, Pb, Pd, Pr, S, Sb, Sc, Se, Si, Sn, Sr, Te, Tl, Y, Yb, Zn, and combinations thereof. The invention additionally allows for the formation of nitrides, hydrides, or carbides of all the possible coating materials, where such compounds exist, by providing a partial pressure of nitrogen, hydrogen, hydrocarbons, or combination thereof, within the vacuum.
Thermal diffusivity of few-layers graphene measured by an all-optical method
NASA Astrophysics Data System (ADS)
Cabrera, H.; Mendoza, D.; Benítez, J. L.; Bautista Flores, C.; Alvarado, S.; Marín, E.
2015-11-01
We report on the measurement of the thermal diffusivity, D, of few-layers graphene obtained by chemical vapor deposition, using a noncontact optical microscopy method based on a mode mismatched thermal lens technique in a pump-probe two-laser beams configuration. It takes advantage of the coaxial counter propagating tightly focused excitation and collimated probe beams in an improved thermal lens microscopy setup. The obtained results: D = (6.5 ± 0.09) × 10-4 m2 s-1, D = (1.9 ± 0.07) × 10-4 m2 s-1 and D = (1.3 ± 0.05) × 10-4 m2 s-1 for four (on a glass slide), eight and sixteen graphene (freestanding) layers are reasonable values, as can be concluded from reported literature data.
A grey diffusion acceleration method for time-dependent radiative transfer calculations
Nowak, P.F.
1991-07-01
The equations of thermal radiative transfer describe the emission, absorption and transport of photons in a material. As photons travel through the material they are absorbed and re-emitted in a Planckian distribution characterized by the material temperature. As a result of these processes, the material can change resulting in a change in the Planckian emission spectrum. When the coupling between the material and radiation is strong, as occurs when the material opacity or the time step is large, standard iterative techniques converge very slowly. As a result, nested iterative algorithms have been applied to the problem. One algorithm, is to use multifrequency DSA to accelerate the convergence of the multifrequency transport iteration and a grey transport acceleration (GTA) followed by a single group DSA. Here we summarize a new method which uses a grey diffusion equation (GDA) to directly solve the multifrequency transport (S{sub N}) problem. Results of Fourier analysis for both the continuous and discretized equations are discussed and the computational efficiency of GDA is compared with the DSA and GTA nested algorithms. 5 refs., 1 fig., 1 tab.
Roberts, Elijah; Stone, John E.; Luthey-Schulten, Zaida
2013-01-01
Spatial stochastic simulation is a valuable technique for studying reactions in biological systems. With the availability of high-performance computing, the method is poised to allow integration of data from structural, single-molecule, and biochemical studies into coherent computational models of cells. Here we introduce the Lattice Microbes software package for simulating such cell models on high-performance computing systems. The software performs either well-stirred or spatially resolved stochastic simulations with approximated cytoplasmic crowding in a fast and efficient manner. Our new algorithm efficiently samples the reaction-diffusion master equation using NVIDIA GPUs and is shown to be two orders of magnitude faster than exact sampling for large systems while maintaining an accuracy of ∼0.1%. Display of cell models and animation of reaction trajectories involving millions of molecules is facilitated using a plug-in to the popular VMD visualization platform. The Lattice Microbes software is open source and available for download at http://www.scs.illinois.edu/schulten/lm. PMID:23007888
NASA Astrophysics Data System (ADS)
Park, S.; Hong, J.; Lee, J.; Cho, S.
2006-12-01
Recent study has demonstrated that the use of combustion appliances in indoor environments, e.g., gas stoves and heaters, results in significant concentrations of NO2 and nitrous acid (HONO). Indoor HONO is formed by both direct emissions from combustion processes and the heterogeneous reaction of NO2 with water vapor on surfaces present indoors. In this study in-situ instrument was constructed for measuring HONO concentration in both indoor and outdoor environments, utilizing diffusion scrubber and peroxynitrite-induced luminol chemiluminescent methods. We measured the HONO concentration under the conditions existing in living room of an apartment, along with NO, NO2, temperature, and relative humidity, to investigate the sources, chemical transformation, and lifetimes of nitrogen oxides and HONO. Some experiments investigated the emissions and transformations of nitrogen species from operation of unvented or vented gas appliance. Measurement data of NO, NO2, and HONO will be reported, and formation pathway of the HONO under the experimental conditions will also be discussed. In addition to measurement of indoor HONO, comparison of HONO measurements by luminol chemiluminescence and annular denuder integrated samples was made in outdoor environment. HONO in ambient air was sampled with annular denuders (Teflon-coated PM2.5 cyclone inlet followed by two Na2CO3-coated denuders coupled in series) operated at 16.7 L/min. Acknowledgement This study was supported by grant No. (# R01-2005-000-10775-0) from the Basic Research Program of the Korea Science and Engineering Foundation (KOSEF).
NASA Astrophysics Data System (ADS)
Ahadi, Amirhossein; Saghir, M. Ziad
2014-08-01
In this study, a Mach-Zehnder interferometer that is equipped with two lasers of different wavelengths was used to conduct high resolution measurements of concentration profiles of a ternary mixture inside a diffusion cell. Windowed Fourier transform along with an advanced unwrapping procedure was employed to extract the phase image from fringe images. Then the phase difference was obtained for a spatial resolution of 1920×1240. According to the measured refractive index profile, concentration contours of two components (out of three) were measured. Consequently, the concentration profile of the third components was calculated. Previously, the analytical solution for binary mixtures was used to estimate only the pure diffusion coefficients. In this study, for the first time, the refractive indices measured by two lasers along with the analytical solution for the ternary system, based on Fick's law, and an evolutionary algorithm (EA) known as a genetic algorithm (GA) were employed to measure the pure and cross diffusion coefficients of a transparent ternary mixture simultaneously. The optimization method to estimate diffusion coefficients was tested against various objective functions, and the best approach was that which was proposed herein. In order to validate the proposed measurement method, the experimental results of the Selectable Optical Diagnostics Instrument-Diffusion Coefficients in Mixtures (SODI-DCMIX1 project) on board the International Space Station (ISS) were analyzed using this technique and the obtained results were compared with previous techniques.
METHOD OF AND APPARATUS FOR WITHDRAWING LIGHT ISOTOPIC PRODUCT FROM A LIQUID THERMAL DIFFUSION PLANT
Dole, M.
1959-09-22
An improved process and apparatus are described for removing enriched product from the columns of a thermal diffusion plant for separation of isotopes. In the removal cycle, light product at the top cf the diffusion columns is circulated through the column tops and a shipping cylinder connected thereto unttl the concertation of enriched product in the cylinder reaches the desired point. During the removal, circulation through the bottoms is blocked bv freezing. in the diffusion cycle, the bottom portion is unfrozen, fresh feed is distributed to the bottoms of the columns, ard heavy product is withdrawn from the bottoms, while the tops of the columns are blocked by freezing.
Zhao, Yuechao; Chen, Junlin; Yang, Mingjun; Liu, Yu; Song, Yongchen
2016-05-01
In this study, magnetic resonance imaging (MRI) was used to dynamically visualize the diffusion process of CO2 in porous media saturated with liquid hydrocarbon. Based on the assumption of semi-infinite media, effective CO2 diffusivity was obtained directly by the nonlinear fitting of one MR profile during the diffusion process. These experimental findings obtained based on MRI method showed a close agreement with the conventional pressure-volume-temperature method. The novel MRI-based technique is a time-saving approach that can reduce the duration of CO2 diffusivity measurement more than 90%, and realize rapid and accurate measurement and estimation of CO2 diffusivity. PMID:26707850
NASA Astrophysics Data System (ADS)
Espejo, A.; Giráldez, J. V.; Vanderlinden, K.; Taguas, E. V.; Pedrera, A.
2014-08-01
Despite the well-accepted value of soil hydraulic properties for describing and modeling matter and energy fluxes in the unsaturated zone, their accurate measurement across scales is still a daunting task. The increasing availability of continuous soil water content measurements at discrete points in space, as provided by sensor networks, offers still unexplored possibilities for evaluating soil physical properties across landscapes. In this study, we propose a new method, based on the Bruce and Klute equation, to estimate effective soil water diffusivity from soil water profile data observed during continuous desiccation periods. An analytical expression is proposed for the diffusion-soil water relationship, assuming an exponential relationship between soil water content and the Boltzmann variable. The method has been evaluated using soil water profile data observed at inter-row and under canopy locations across a rainfed olive orchard in SW Spain. The spatial variability of the effective soil water diffusivity across the orchard was estimated. Different soil conditions under the tree canopies as compared to inter-row areas resulted in significantly different effective diffusivity relationships, reflecting the effect of trees on soil physical properties and water dynamics across olive orchards. The proposed method offers a suitable alternative to traditional laboratory methods and can be easily extended to estimate soil hydraulic conductivity and water retention curves.
Technology Transfer Automated Retrieval System (TEKTRAN)
Thermal conductivity and thermal diffusivity are two important physical properties essential for designing any food engineering processes. Recently a new transient plane-source method was developed to measure a variety of materials, but its application in foods has not been documented. Therefore, ...
The solid-phase diffusion coefficient (Dm) and material-air partition coefficient (Kma) are key parameters for characterizing the sources and transport of semivolatile organic compounds (SVOCs) in the indoor environment. In this work, a new experimental method was developed to es...
ERIC Educational Resources Information Center
Artun, Huseyin; Costu, Bayram
2013-01-01
The aim of this study was to explore a group of prospective primary teachers' conceptual understanding of diffusion and osmosis as they implemented a 5E constructivist model and related materials in a science methods course. Fifty prospective primary teachers' ideas were elicited using a pre- and post-test and delayed post-test survey consisting…
ERIC Educational Resources Information Center
Artun, Huseyin; Costu, Bayram
2013-01-01
The aim of this study was to explore a group of prospective primary teachers' conceptual understanding of diffusion and osmosis as they implemented a 5E constructivist model and related materials in a science methods course. Fifty prospective primary teachers' ideas were elicited using a pre- and post-test and delayed post-test survey consisting
A comparison of implicit numerical methods for solving the transient spherical diffusion equation
NASA Technical Reports Server (NTRS)
Curry, D. M.
1977-01-01
Comparative numerical temperature results obtained by using two implicit finite difference procedures for the solution of the transient diffusion equation in spherical coordinates are presented. The validity and accuracy of these solutions are demonstrated by comparison with exact analytical solutions.
Investigation to develop a method to apply diffusion barrier to high strength fibers
NASA Technical Reports Server (NTRS)
Veltri, R. D.; Paradis, R. D.; Douglas, F. C.
1975-01-01
A radio frequency powered ion plating process was used to apply the diffusion barriers of aluminum oxide, yttrium oxide, hafnium oxide and titanium carbide to a substrate tungsten fiber. Each of the coatings was examined as to its effect on both room temperature strength and tensile strength of the base tungsten fiber. The coated fibers were then overcoated with a nickel alloy to become single cell diffusion couples. These diffusion couples were exposed to 1093 C for 24 hours, cycled between room temperature and 1093 C, and given a thermal anneal for 100 hours at 1200 C. Tensile testing and metallographic examinations determined that the hafnium oxide coating produced the best high temperature diffusion barrier for tungsten of the four coatings.
DEVELOPMENT OF SPLIT-OPERATOR, PETROV-GALERKIN METHODS TO SIMULATE TRANSPORT AND DIFFUSION PROBLEMS
The rate at which contaminants in groundwater undergo sorption and desorption is routinely described using diffusion models. Such approaches, when incorporated into transport models, lead to large systems of coupled equations, often nonlinear. This has restricted applications of ...
Comparison between agar and methylcellulose cultures of human leukemic cells.
Kubota, K; Preisler, H D; Sagawa, K; Minowada, J
1981-08-01
A comparison was made between the agar and methylcellulose culture systems with respect to their ability to support the clonal growth of leukemic cells obtained from patients with acute myeloblastic leukemia, acute lymphoblastic leukemia, and chronic myelogenous leukemia in blastic crisis. The number of clusters and/or colonies formed and the morphology of the cells within them varied from patient to patient. Nevertheless, no significant difference between the two culture systems within given leukemic specimens was found. No significant differences were noted among three different conditioned media used as sources of colony-stimulating activity. Most of the cells within clusters and colonies were identified to be immature members of granulocyte-macrophage series or to be indistinguishable from the preculture leukemic blast cells by morphological and cell surface marker studies. Cells from myeloid crisis in chronic myelogenous leukemia grew well in the cultures, but cells from lymphoid crisis did not proliferate. PMID:6941851
Libra, J A; Sahlmann, C; Schuchardt, A; Handschag, J; Wiesmann, U; Gnirss, R
2005-01-01
The aeration systems of two full-scale, activated-sludge basins were compared during a period of three years, under the same operating conditions, using dynamic offgas testing. Only the material of the diffuser was different (membrane versus ceramic-tube diffusers). The investigation has shown that, although the membrane diffusers have higher initial standard-oxygen-transfer efficiency (alphaSOTE) and standard-aeration efficiency (alphaSAE), these decreased over time, while the alphaSAE of the ceramic diffusers started lower, but increased slightly over the whole period. A cost comparison makes clear how important it is to evaluate the aeration system under process conditions. The operating costs were the dominant factor (approximately 10x higher than capital costs), and operating costs were approximately 20% higher for membrane versus ceramic diffusers. The poor performance of the membrane-tube diffusers under process conditions could be explained on the basis of the actual alphaAE values in the basin, not the standardized values. PMID:16274078
An improved design method and experimental performance of two dimensional curved wall diffusers
NASA Technical Reports Server (NTRS)
Yang, T.; Hudson, W. G.; El-Nashar, A. M.
1972-01-01
A computer design program was developed to incorporate the suction slots in solving the potential flow equations with prescribed boundary conditions. Using the contour generated from this program two Griffith diffusers were tested having area ratios AR = 3 and 4. The inlet Reynolds number ranged from 600,000 to 7 million. It was found that the slot suction required for metastable operation depends on the sidewall suction applied. Values of slot suction of 8% of the inlet flow rate was required for AR = 4 with metastable condition, provided that enough sidewall suction was applied. For AR = 3, the values of slot suction was about 25% lower than those required for AR = 4. For nearly all unseparated test runs, the effectiveness was 100% and the exit flow was uniform. In addition to the Griffith diffusers, dump and cusp diffusers of comparable area ratios were built and tested. The results obtained from these diffusers were compared with those of the Griffith diffusers. Flow separation occurred in all test runs with the dump and cusp diffusers.
Taimouri, Vahid; Afacan, Onur; Perez-Rossello, Jeannette M.; Callahan, Michael J.; Mulkern, Robert V.; Warfield, Simon K.; Freiman, Moti
2015-01-01
Purpose: To evaluate the effect of the spatially constrained incoherent motion (SCIM) method on improving the precision and robustness of fast and slow diffusion parameter estimates from diffusion-weighted MRI in liver and spleen in comparison to the independent voxel-wise intravoxel incoherent motion (IVIM) model. Methods: We collected diffusion-weighted MRI (DW-MRI) data of 29 subjects (5 healthy subjects and 24 patients with Crohn’s disease in the ileum). We evaluated parameters estimates’ robustness against different combinations of b-values (i.e., 4 b-values and 7 b-values) by comparing the variance of the estimates obtained with the SCIM and the independent voxel-wise IVIM model. We also evaluated the improvement in the precision of parameter estimates by comparing the coefficient of variation (CV) of the SCIM parameter estimates to that of the IVIM. Results: The SCIM method was more robust compared to IVIM (up to 70% in liver and spleen) for different combinations of b-values. Also, the CV values of the parameter estimations using the SCIM method were significantly lower compared to repeated acquisition and signal averaging estimated using IVIM, especially for the fast diffusion parameter in liver (CVIV IM = 46.61 ± 11.22, CVSCIM = 16.85 ± 2.160, p < 0.001) and spleen (CVIV IM = 95.15 ± 19.82, CVSCIM = 52.55 ± 1.91, p < 0.001). Conclusions: The SCIM method characterizes fast and slow diffusion more precisely compared to the independent voxel-wise IVIM model fitting in the liver and spleen. PMID:25832079
NASA Astrophysics Data System (ADS)
Jagannath, Ravi Prasad K.; Yalavarthy, Phaneendra K.
2013-03-01
Typical image-guided diffuse optical tomographic image reconstruction procedures involve reduction of the number of optical parameters to be reconstructed equal to the number of distinct regions identified in the structural information provided by the traditional imaging modality. This makes the image reconstruction problem less ill-posed compared to traditional underdetermined cases. Still, the methods that are deployed in this case are same as those used for traditional diffuse optical image reconstruction, which involves a regularization term as well as computation of the Jacobian. A gradient-free Nelder-Mead simplex method is proposed here to perform the image reconstruction procedure and is shown to provide solutions that closely match ones obtained using established methods, even in highly noisy data. The proposed method also has the distinct advantage of being more efficient owing to being regularization free, involving only repeated forward calculations.
Rule, Toby D.; Cai, Wei; Wang, Hsin
2013-01-01
Because of its extremely high thermal conductivity, measuring the thermal conductivity or diffusivity of optical-grade diamond can be challenging. Various methods have been used to measure the thermal conductivity of thick diamond films. For the purposes of commercial quality control, the AC laser calorimetry method is appealing because it enables fairly rapid and convenient sample preparation and measurement. In this paper, the method is used to measure the thermal diffusivity of optical diamond. It is found that sample dimensions and measurement parameters are critical, and data analysis must be performed with great care. The results suggest that the method as it is applied to optical-grade diamond could be enhanced by a more powerful laser, higher frequency beam modulation, and post-processing based on 2D thermal simulation.
Ganesh, P; Kim, Jeongnim; Park, Changwon; Yoon, Mina; Reboredo, Fernando A; Kent, Paul R C
2014-12-01
Highly accurate diffusion quantum Monte Carlo (QMC) studies of the adsorption and diffusion of atomic lithium in AA-stacked graphite are compared with van der Waals-including density functional theory (DFT) calculations. Predicted QMC lattice constants for pure AA graphite agree with experiment. Pure AA-stacked graphite is shown to challenge many van der Waals methods even when they are accurate for conventional AB graphite. Highest overall DFT accuracy, considering pure AA-stacked graphite as well as lithium binding and diffusion, is obtained by the self-consistent van der Waals functional vdW-DF2, although errors in binding energies remain. Empirical approaches based on point charges such as DFT-D are inaccurate unless the local charge transfer is assessed. The results demonstrate that the lithium-carbon system requires a simultaneous highly accurate description of both charge transfer and van der Waals interactions, favoring self-consistent approaches. PMID:26583215
Tsang, P W M; Poon, T-C
2013-10-01
We report a novel and fast method for converting a digital, complex Fresnel hologram into a phase-only hologram. Briefly, the pixels in the complex hologram are scanned sequentially in a row by row manner. The odd and even rows are scanned from opposite directions, constituting to a bidirectional error diffusion process. The magnitude of each visited pixel is forced to be a constant value, while preserving the exact phase value. The resulting error is diffused to the neighboring pixels that have not been visited before. The resulting novel phase-only hologram is called the bidirectional error diffusion (BERD) hologram. The reconstructed image from the BERD hologram exhibits high fidelity as compared with those obtained with the original complex hologram. PMID:24104280
NASA Astrophysics Data System (ADS)
Toyoda, Takahiro; Sugiura, Nozomi; Masuda, Shuhei; Sasaki, Yuji; Igarashi, Hiromichi; Ishikawa, Yoichi; Hatayama, Takaki; Kawano, Takeshi; Kawai, Yoshimi; Kouketsu, Shinya; Katsumata, Katsuro; Uchida, Hiroshi; Doi, Toshimasa; Fukasawa, Masao; Awaji, Toshiyuki
2015-11-01
An improved vertical diffusivity scheme is introduced into an ocean general circulation model to better reproduce the observed features of water property distribution inherent in the deep Pacific Ocean structure. The scheme incorporates (a) a horizontally uniform background profile, (b) a parameterization depending on the local static stability, and (c) a parameterization depending on the bottom topography. Weighting factors for these parameterizations are optimally estimated based on the Green's function method. The optimized values indicate an important role of both the intense vertical diffusivity near rough topography and the background vertical diffusivity. This is consistent with recent reports that indicate the presence of significant vertical mixing associated with finite-amplitude internal wave breaking along the bottom slope and its remote effect. The robust simulation with less artificial trend of water properties in the deep Pacific Ocean illustrates that our approach offers a better modeling analysis for the deep ocean variability.
In vitro biocompatibility study of keratin/agar scaffold for tissue engineering.
Nayak, Kush Kumar; Gupta, Pratima
2015-11-01
The porous scaffold was fabricated from a binary blend of keratin/agar for tissue engineering. The miscibility of keratin and agar polymers into their blend was confirmed by Fourier transform infrared spectroscopy and X-ray diffractometer study. The scaffold fabricated from freeze extraction method resulted in a porous interconnected structure with apparent porosity 94.40±2.34%. Scanning electron microscopy study reveals the presence of interconnected pores with a pore size ranges from 50 to 300μm. The hydrophilic nature of the scaffold was confirmed by water retention capacity studies, which was observed 160±7.89%. The scaffold's tensile strength of 0.154±0.031MPa and percent of elongation at break with 16.33±2.52% justify its mechanical capability. The positive antimicrobial property and in vitro degradation was recorded for the fabricated scaffold. The in vitro biocompatibility study of the scaffolds confirms the attachment and proliferation of the cultured mammalian myofibroblast cell line. Negative cytotoxicity and a viable cell growth ensure that the fabricated scaffold can serve a potential source of biomaterial for tissue engineering and can be applicable for wound healing and skin regeneration. PMID:26188296
Visualization of Biosurfactant Film Flow in a Bacillus subtilis Swarm Colony on an Agar Plate
Kim, Kyunghoon; Kim, Jung Kyung
2015-01-01
Collective bacterial dynamics plays a crucial role in colony development. Although many research groups have studied the behavior of fluidic swarm colonies, the detailed mechanics of its motion remains elusive. Here, we developed a visualization method using submicron fluorescent beads for investigating the flow field in a thin layer of fluid that covers a Bacillus subtilis swarm colony growing on an agar plate. The beads were initially embedded in the agar plate and subsequently distributed spontaneously at the upper surface of the expanding colony. We conducted long-term live cell imaging of the B. subtilis colony using the fluorescent tracers, and obtained high-resolution velocity maps of microscale vortices in the swarm colony using particle image velocimetry. A distinct periodic fluctuation in the average speed and vorticity of flow in swarm colony was observed at the inner region of the colony, and correlated with the switch between bacterial swarming and growth phases. At the advancing edge of the colony, both the magnitudes of velocity and vorticity of flow in swarm colony were inversely correlated with the spreading speed of the swarm edge. The advanced imaging tool developed in this study would facilitate further understanding of the effect of micro vortices in swarm colony on the collective dynamics of bacteria. PMID:26343634
NASA Astrophysics Data System (ADS)
Hamdi, Amine; Miller, Eric L.; Boas, David; Franceschini, Maria A.; Kilmer, Misha E.
2005-03-01
Analysis of the quasi-sinusoidal temporal signals measured by a Diffuse Optical Tomography (DOT) instrument can be used to determine both quantitative and qualitative characteristics of functional brain activities arising from visual and auditory simulations, motor activities, and cognitive tasks performances. Once the activated regions in the brain are resolved using DOT, the temporal resolution of this modality is such that one can track the spatial evolution (both the location and morphology) of these regions with time. In this paper, we explore a state-estimation approach using Extended Kalman Filters to track the dynamics of functionally activated brain regions. We develop a model to determine the size, shape, location and contrast of an area of activity as a function of time. Under the assumption that previously acquired MRI data has provided us with a segmentation of the brain, we restrict the location of the area of functional activity to the thin, cortical sheet. To describe the geometry of the region, we employ a mathematical model in which the projection of the area of activity onto the plane of the sensors is assumed to be describable by a low dimensional algebraic curve. In this study, we consider in detail the case where the perturbations in optical absorption parameters arising due to activation are confined to independent regions in the cortex layer. We estimate the geometric parameters (axis lengths, rotation angle, center positions) defining the best fit ellipse for the activation area's projection onto the source-detector plane. At a single point in time, an adjoint field-based nonlinear inversion routine is used to extract the activated area's information. Examples of the utility of the method will be shown using synthetic data.
Brusa, Victoria; Piñeyro, Pablo E; Galli, Lucía; Linares, Luciano H; Ortega, Emanuel E; Padola, Nora L; Leotta, Gerardo A
2016-03-01
Shiga toxin-producing Escherichia coli (STEC) are foodborne pathogens, and beef cattle are recognized as the principal reservoir. The aims of this study were (1) to identify the most sensitive combination of selective enrichment broths and agars for STEC isolation in artificially inoculated ground beef samples, and (2) to evaluate the most efficient combination(s) of methods for naturally contaminated ground beef samples. A total of 192 ground beef samples were artificially inoculated with STEC and non-stx bacterial strains. A combination of four enrichment broths and three agars were evaluated for sensitivity, specificity, and positive predictive value for STEC isolation from experimentally inoculated samples. Enrichments with either modified tryptic soy broth (mTSB) containing 8 mg/L novobiocin (mTSB-8) or modified Escherichia coli (mEC) broth followed by isolation in MacConkey agar were the most sensitive combinations for STEC isolation of artificially inoculated samples. Independently, both enrichments media followed by isolation in MacConkey were used to evaluate ground beef samples from 43 retail stores, yielding 65.1% and 58.1% stx-positive samples by RT-PCR, respectively. No difference was observed in the isolate proportions between these two methods (8/25 [32%] and 8/28 [28.6%]). Identical serotypes and stx genotypes were observed in STEC strains isolated from the same samples by either method. In this study, no single enrichment protocol was sufficient to detect all STEC in artificially inoculated samples and had considerable variation in detection ability with naturally contaminated samples. Moreover, none of the single or combinations of multiple isolation agars used were capable of identifying all STEC serogroups in either artificially inoculated or naturally occurring STEC-contaminated ground beef. Therefore, it may be prudent to conclude that there is no single method or combination of isolation methods capable of identifying all STEC serogroups. PMID:26836701