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1

Comparison of disc diffusion & E test methods with agar dilution for antimicrobial susceptibility testing of Haemophilus influenzae  

Microsoft Academic Search

Methods: A total of 46 isolates of H. influenzae from various invasive sites were included as test strains. Antimicrobial susceptibility testing was performed by Kirby-Bauer disc diffusion method for ampicillin, chloramphenicol, trimethoprim-sulphamethoxazole (TMP-SMZ) and cefotaxime. Minimum Inhibitory Concentration (MIC) determination was performed by E test and agar dilution for the same set of antimicrobials. All tests were performed on Haemophilus

Anand Manoharan; Rekha Pai; V. Shankar; Kurien Thomas; M. K. Lalitha

2003-01-01

2

Multicenter Evaluation of a New Disk Agar Diffusion Method for Susceptibility Testing of Filamentous Fungi with Voriconazole, Posaconazole, Itraconazole, Amphotericin B, and Caspofungin  

Microsoft Academic Search

The purpose of this study was to correlate inhibition zone diameters, in millimeters (agar diffusion disk method), with the broth dilution MICs or minimum effective concentrations (MECs) (CLSI M38-A method) of five antifungal agents to identify optimal testing guidelines for disk mold testing. The following disk diffusion testing parameters were evaluated for 555 isolates of the molds Absidia corymbifera, Aspergillus

A. Espinel-Ingroff; B. Arthington-Skaggs; N. Iqbal; D. Ellis; M. A. Pfaller; S. Messer; M. Rinaldi; A. Fothergill; D. L. Gibbs; A. Wang

2007-01-01

3

Comparison of Microscan Broth Microdilution, Synergy Quad Plate Agar Dilution, and Disk Diffusion Screening Methods for Detection of High-Level Aminoglycoside Resistance in Enterococcus Species  

Microsoft Academic Search

We compared the dried MicroScan microdilution panel, Synergy Quad plate agar dilution, and high-potency disk diffusion screening methods for the detection of high-level aminoglycoside resistance in 815 enterococcal bloodstream isolates. Agreement between the three methods was 99% when testing for high-level gentamicin resistance and 96% when testing for high-level streptomycin resistance.

David R. Murdoch; Lizzie J. Harrell; Susan M. Donabedian; Marcus J. Zervos; L. Barth Reller

2003-01-01

4

Agar Disk Diffusion (Bauer-Kirby) Tests with Various Fastidious and Nonfastidious Reference (ATCC) Strains: Comparison of Several Agar Media  

Microsoft Academic Search

Several agar media (Mueller-Hinton agar, MHA; diagnostic sensitivity test agar, DSTA; Schaedler agar, SchA; Todd-Hewitt agar with added yeast extract, THYA; Wilkins-Chalgren agar, WCA) were compared using the Bauer-Kirby agar disk diffusion test against six nonfastidious quality control strains: Staphylococcus aureus ATCC 25923 and ATCC 29213, Escherichia coli ATCC 25922 and ATCC 35218, Pseudomonas aeruginosa ATCC 27853, and Enterococcus faecalis

Walter H. Traub; Birgit Leonhard

1994-01-01

5

Diffusion of sucrose and dextran through agar gel membranes.  

PubMed

Mass transfer limitations severely impede the performance of bioreactions involving large molecules by gel-entrapped microorganisms. This paper describes a quantitative investigation of such diffusional limitations in agar gel membranes. Sucrose and commercial dextran fractions with (weight-average) molecular weights ranging from 10,000 to 2,000,000 Da were used as standard diffusants. For all tested solutes but sucrose, the values of the agar/water partition coefficients highlighted steric hindrance at the entrance of the membrane pores. The effective diffusivity of sucrose in agar was similar to that in water. All dextran fractions, however, displayed restricted diffusion in the agar membranes. Their effective diffusivities were a decreasing function of the agar content of the gel membrane (0.5, 1.0, or 1.5% w/v). The effective diffusivity in a given membrane decreased as the molecular weight of the diffusing molecule increased. T500 (Mw = 470,000 Da) and T2000 (Mw = 1,950,000 Da) fractions were unable to diffuse through 1.0 or 1.5% agar membranes. The diffusion data did not agree with the classical (Renkin) model for a hard sphere diffusing through a cylindrical pore. These results are discussed in terms of gel and diffusant characteristics. PMID:7505595

Lebrun, L; Junter, G A

1993-12-01

6

Antibiotic Susceptibility Testing (Agar Disk Diffusion and Agar Dilution) of Clinical Isolates of Enterococcus faecalis and E. faecium: Comparison of Mueller-Hinton, Iso-Sensitest, and Wilkins-Chalgren Agar Media  

Microsoft Academic Search

Forty-two isolates of Enterococcus faecalis and 56 isolates of Enterococcus faecium, including 8 vancomycin-resistant strains, were examined for comparative susceptibility to 27 antimicrobial drugs with the agar dilution method, employing Mueller-Hinton (MHA), Iso-Sensitest (ISTA), and Wilkins-Chalgren (WCA) agar. The Bauer-Kirby agar disk diffusion method was used to comparatively test 24 of the agents in parallel. The enterococci yielded better growth

Walter H. Traub; Udo Geipel; Birgit Leonhard

1998-01-01

7

Evaluation of interpretive criteria of agar dilution and disk diffusion susceptibility tests for Neisseria gonorrhoeae.  

PubMed

Using strains of Neisseria gonorrhoeae from Western New York, the National Committee for Clinical Laboratory Standards' (NCCLS) interpretive criteria for disk diffusion susceptibility testing was evaluated on chocolate-Mueller-Hinton agar (CMH) and GC agar. The reference method for comparison was the NCCLS agar dilution minimum inhibitory concentration (MIC) method. Even though the zone sizes were significantly smaller on the CMH agar, the interpretations were not significantly different on either GC or CMH agars except for tetracycline. On the CMH agar, the number of tetracycline-resistant strains was greater than on GC agar: 3% of the strains failed to grow on CMH agar and 4% did not produce interpretable zone sizes for ceftriaxone. Therefore, the use of CMH is not recommended. There was a significant difference between the interpretative criteria of the MIC and the disk diffusion method only for tetracycline. Therefore, the NCCLS zone-diameter interpretation criteria for tetracycline does not seem applicable for N. gonorrhoeae isolates in the Buffalo, New York, area. PMID:7924210

Altaie, S S; Moore, L S; Dryja, D; Furness, K

1994-03-01

8

Comparative Evaluation of the VITEK 2, Disk Diffusion, Etest, Broth Microdilution, and Agar Dilution Susceptibility Testing Methods for Colistin in Clinical Isolates, Including Heteroresistant Enterobacter cloacae and Acinetobacter baumannii Strains?  

PubMed Central

Increasing antibiotic resistance in gram-negative bacteria has recently renewed interest in colistin as a therapeutic option. The increasing use of colistin necessitates the availability of rapid and reliable methods for colistin susceptibility testing. We compared seven methods of colistin susceptibility testing (disk diffusion, agar dilution on Mueller-Hinton [MH] and Isosensitest agar, Etest on MH and Isosensitest agar, broth microdilution, and VITEK 2) on 102 clinical isolates collected from patient materials during a selective digestive decontamination or selective oral decontamination trial in an intensive-care unit. Disk diffusion is an unreliable method to measure susceptibility to colistin. High error rates and low levels of reproducibility were observed in the disk diffusion test. The colistin Etest, agar dilution, and the VITEK 2 showed a high level of agreement with the broth microdilution reference method. Heteroresistance for colistin was observed in six Enterobacter cloacae isolates and in one Acinetobacter baumannii isolate. This is the first report of heteroresistance to colistin in E. cloacae isolates. Resistance to colistin in these isolates seemed to be induced upon exposure to colistin rather than being caused by stable mutations. Heteroresistant isolates could be detected in the broth microdilution, agar dilution, Etest, or disk diffusion test. The VITEK 2 displayed low sensitivity in the detection of heteroresistant subpopulations of E. cloacae. The VITEK 2 colistin susceptibility test can therefore be considered to be a reliable tool to determine susceptibility to colistin in isolates of genera that are known not to exhibit resistant subpopulations. In isolates of genera known to (occasionally) exhibit heteroresistance, an alternative susceptibility testing method capable of detecting heteroresistance should be used. PMID:17646414

Lo-Ten-Foe, Jerome R.; de Smet, Anne Marie G. A.; Diederen, Bram M. W.; Kluytmans, Jan A. J. W.; van Keulen, Peter H. J.

2007-01-01

9

Agar Underlay Method for Recovery of Sublethally Heat-Injured Bacteria  

PubMed Central

A method of recovering sublethally heat-injured bacteria was developed. The procedure (termed the agar underlay method) uses a nonselective agar underlaid with a selective medium. In a two-chambered petri dish, the Lutri plate (LP), a nonselective agar is inoculated with a population of sublethally heat-injured bacteria. After a 2-h repair incubation period, selective agar is added to the bottom chamber of the LP and incubated. By diffusing through the nonselective top agar, selective agents from the underlay medium impart selectivity to the system. By the agar underlay method, recovery rates of the heat-injured food-borne pathogens Escherichia coli O157:H7 and Salmonella typhimurium were not different (P > 0.05) from recovery rates determined with nonselective media. Sublethally heat-injured cells (60°C for 1.5 min in buffer or 80°C for 30 s on meat surfaces) grew and produced a typical colony morphology and color reaction when the agar underlay procedure was used with the appropriate respective selective agars. Unlike agar overlay methods for injury repair, the agar underlay procedure allows the typical selective-medium colony morphology to develop and allows colonies to be more easily picked for further characterization. Higher recovery rates of heat-injured fecal enterococci from bovine fecal samples and total coliforms from animal waste lagoons were obtained by the agar underlay method with selective agars than by direct plating on the respective selective media. PMID:10583985

Kang, D. H.; Siragusa, G. R.

1999-01-01

10

Bioactivity auantification of a novel antimicrobial peptide by agar diffusion bioassay  

Microsoft Academic Search

Recently, antimicrobial peptides (AMP) produced by bacteria, called bacteriocins, have attracted a great deal of attention as biopreservatives in the application of agri-food industry. Extensive industrial uses and research studies require an accurate and precise method for the quantification of novel AMP in food samples, fermentation broth and other media. In this work, an agar diffusion bioassay was developed for

Li Xingfeng; Wang Zhixin; Dong Xinying; Wang Guangxian; Jia Yingmin

2011-01-01

11

Which is Better for Disc Diffusion Assays of Essential Oils—IsoSensitest or Nutrient Agar?  

Microsoft Academic Search

The disc diffusion assay is often used for screening of essential oils for antimicrobial activity. In this paper we describe an investigation into whether differences exist in the zone of inhibition obtained with two agar types; IsoSensitest and nutrient agar. Standard disc diffusion assay was performed using both agar types using three essential oils against two bacteria and one yeast.

Therese Moon; Heather Ma Cavanagh; Jenny M. Wilkinson

2006-01-01

12

An image analysis system: an objective and accurate alternative for reading the agar diffusion test.  

PubMed

A computerized image analysis system (IAS) has been used to develop a new method for reading the agar diffusion test automatically. In four experiments a total of 88 porcine plasma and 95 urine samples were screened for oxytetracycline by the agar diffusion test. The inhibition zones were measured by hand and by the IAS directly from the bioassay plate and by the IAS from the photo-negative taken from the plate. Both methods were positively correlated with the hand method for plasma (0.9716, 0.9669) and urine (0.9878, 0.9731) in the range tested for 0.1 to 2.0 micrograms/ml. Moreover, the coefficient of variation and the day-to-day-variation amounted to 1.72% and 1.47% respectively, for the method by hand and 1.10, 1.54% and 0.27, 0.38% respectively, for the IAS methods. It is concluded that the IAS method is an objective and accurate alternative for reading the agar diffusion test. PMID:8196092

Schoevers, E J; Terlou, M; Pijpers, A; Verheijden, J H

1994-02-01

13

Performance of the EUCAST disk diffusion method, the CLSI agar screen method, and the Vitek 2 automated antimicrobial susceptibility testing system for detection of clinical isolates of Enterococci with low- and medium-level VanB-type vancomycin resistance: a multicenter study.  

PubMed

Different antimicrobial susceptibility testing methods to detect low-level vancomycin resistance in enterococci were evaluated in a Scandinavian multicenter study (n=28). A phenotypically and genotypically well-characterized diverse collection of Enterococcus faecalis (n=12) and Enterococcus faecium (n=18) strains with and without nonsusceptibility to vancomycin was examined blindly in Danish (n=5), Norwegian (n=13), and Swedish (n=10) laboratories using the EUCAST disk diffusion method (n=28) and the CLSI agar screen (n=18) or the Vitek 2 system (bioMérieux) (n=5). The EUCAST disk diffusion method (very major error [VME] rate, 7.0%; sensitivity, 0.93; major error [ME] rate, 2.4%; specificity, 0.98) and CLSI agar screen (VME rate, 6.6%; sensitivity, 0.93; ME rate, 5.6%; specificity, 0.94) performed significantly better (P=0.02) than the Vitek 2 system (VME rate, 13%; sensitivity, 0.87; ME rate, 0%; specificity, 1). The performance of the EUCAST disk diffusion method was challenged by differences in vancomycin inhibition zone sizes as well as the experience of the personnel in interpreting fuzzy zone edges as an indication of vancomycin resistance. Laboratories using Oxoid agar (P<0.0001) or Merck Mueller-Hinton (MH) agar (P=0.027) for the disk diffusion assay performed significantly better than did laboratories using BBL MH II medium. Laboratories using Difco brain heart infusion (BHI) agar for the CLSI agar screen performed significantly better (P=0.017) than did those using Oxoid BHI agar. In conclusion, both the EUCAST disk diffusion and CLSI agar screening methods performed acceptably (sensitivity, 0.93; specificity, 0.94 to 0.98) in the detection of VanB-type vancomycin-resistant enterococci with low-level resistance. Importantly, use of the CLSI agar screen requires careful monitoring of the vancomycin concentration in the plates. Moreover, disk diffusion methodology requires that personnel be trained in interpreting zone edges. PMID:24599985

Hegstad, Kristin; Giske, Christian G; Haldorsen, Bjørg; Matuschek, Erika; Schønning, Kristian; Leegaard, Truls M; Kahlmeter, Gunnar; Sundsfjord, Arnfinn

2014-05-01

14

Comparison of Disk Diffusion and Agar Dilution Methods for Erythromycin, Ciprofloxacin, and Tetracycline Susceptibility Testing of Campylobacter coli and for Tetracycline Susceptibility Testing of Campylobacter jejuni subsp. jejuni?  

PubMed Central

With disk diffusion, the following zone diameters are suggested to be resistant and susceptible breakpoints, respectively: for susceptibility testing of Campylobacter coli, no inhibition zone and 15 mm or more for erythromycin, and 20 mm or less and 25 mm or more for ciprofloxacin, in the absence or presence of an inhibition zone around the nalidixic acid disk; and for susceptibility testing of C. coli and Campylobacter jejuni, 20 mm or less and 26 mm or more for tetracycline. PMID:18838597

Gaudreau, Christiane; Girouard, Yves; Gilbert, Huguette; Gagnon, Josée; Bekal, Sadjia

2008-01-01

15

CAS agar diffusion assay for the measurement of siderophores in biological fluids.  

PubMed

We developed a simple and universal method, by modifying the universal CAS (Chrome azurol S) assay, measuring siderophores in various biological fluids. We named the assay as CAS agar diffusion (CASAD) assay. CAS plate devoid of nutrients was prepared by using Bacto-agar (1.5%, w/v) as a matrix. Holes with 5-mm-diameter were punched on the CAS agar plate. Each hole was added by 35 microl of the test fluids containing Desferal that was twofold serially diluted. After incubating at 37 degrees C or room temperature for 4-8 h, the size of orange haloes formed around the holes was measured. The size of orange haloes correlated well with the concentration of Desferal in all the biological fluids tested in this study. CASAD assay showed consistent results in wide pH range from 5 to 9. Addition of iron to the test fluids containing Desferal decreased the size of orange haloes in a dose-dependent manner, which suggests that the CASAD assay detects only iron non-bound siderophore. These results suggest that CASAD assay would serve as a simple, stable, and highly reproducible test for screening and quantitative siderophore analysis in biological fluids. PMID:11166103

Shin, S H; Lim, Y; Lee, S E; Yang, N W; Rhee, J H

2001-02-01

16

Metronidazole susceptibility testing for Helicobacter pylori: comparison of disk, broth, and agar dilution methods and their clinical relevance.  

PubMed Central

Since the methods for metronidazole susceptibility testing of Helicobacter pylori have not been standardized or validated, we compared three methods that are used to test the metronidazole susceptibilities of 25 isolates of H. pylori. Specifically, we examined the methods of Steer's replicator agar dilution, tube broth microdilution, and modified Kirby-Bauer disk diffusion. The metronidazole disk zone sizes obtained by the disk diffusion method correlated well (r = 0.74) with the MICs obtained by the agar dilution method. Afterward, the disk diffusion method was used to characterize the metronidazole susceptibilities of 44 isolates of H. pylori. Dual therapy (bismuth and metronidazole) proved to be highly effective against metronidazole-susceptible strains (81.6% eradication rate) but fared poorly against resistant strains (16.7% eradication rate; P < 0.01). Using agar dilution testing, we validated the modified Kirby-Bauer disk diffusion method for metronidazole susceptibility testing of H. pylori and conclude that it is practical, accurate, and clinically applicable. PMID:8370723

DeCross, A J; Marshall, B J; McCallum, R W; Hoffman, S R; Barrett, L J; Guerrant, R L

1993-01-01

17

An extension of the Coconut Cream Agar method to screen Penicillium citrinum isolates for citrinin production.  

PubMed

A simple and rapid screening method was developed for the detection of citrinin in fungal cultures using Coconut Cream Agar (CCA) described previously for detecting aflatoxin and ochratoxin A. Fifteen isolates of Penicillium citrinum were inoculated onto CCA and incubated at 25 and 30°C for 10 days. All isolates produced a distinct yellow green fluorescence on CCA when the reverse side of the agar plates were viewed under long wavelength UV light. Detection was optimal at 25°C after four to 5 days of incubation. Isolates positive by the CCA method also tested positive for citrinin production by the TLC agar plug method after growth on CCA, Czapek yeast extract agar and yeast extract sucrose agar. Control cultures were negative by both methods, indicating that the CCA Petri dish method was suitable for screening cultures for citrinin production. PMID:23682683

Mohamed, S; Flint, S; Palmer, J; Fletcher, G C; Pitt, J I

2013-09-01

18

Agar and broth dilution methods to determine the minimal inhibitory concentration (MIC) of antimicrobial substances  

Microsoft Academic Search

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

Irith Wiegand; Kai Hilpert; Robert E W Hancock

2008-01-01

19

SEROLOGY OF THE SOLUBLE ANTIGENS OF CLOSTRIDIUM PERFRINGENS TYPES A-F BY AGAR-GEL DIFFUSION  

PubMed Central

Ellner, Paul D. (University of Vermont, Burlington) and Carolyn D. Bohan. Serology of the soluble antigens of Clostridium perfringens types A–F by agar-gel diffusion. J. Bacteriol. 83:284–296. 1962.—A serological study by agar-gel diffusion of the soluble antigens of 39 strains of the Clostridium perfringens group has shown them to be extremely heterogeneous. Strain variation occurred within the six types, and common antigens shared among the six types were frequently observed. Attempts to produce type-specific sera by absorption were unsuccessful, due to incomplete removal of common antibodies. Images PMID:13890020

Ellner, Paul D.; Bohan, Carolyn D.

1962-01-01

20

Larva currens: The Usefulness of the Agar Plate Method  

Microsoft Academic Search

Creeping eruption caused by Strongyloides stercoralis is called larva currens, while those caused by other parasites are called larva migrans. To detect the parasite, the direct smear method was used. However, this method is not very sensitive in detecting S. stercoralis. A 62-year-old male with polyarteritis nodosa cutanea had an erythematous creeping eruption in various regions, such as his lumbar

T. Iwamoto; M. Kitoh; K. Kayashima; T. Ono

1998-01-01

21

Preparation and characterization of bio-nanocomposite films of agar and silver nanoparticles: laser ablation method.  

PubMed

Silver nanoparticles (AgNPs) were prepared by a laser ablation method and composite films with the AgNPs and agar were prepared by solvent casting method. UV-vis absorbance test and transmission electron microscopy (TEM) analysis results revealed that non-agglomerated spherical AgNPs were formed by the laser ablation method. The surface color of the resulting agar/AgNPs films exhibited the characteristic plasmonic effect of the AgNPs with the maximum absorption peaks of 400-407 nm. X-ray diffraction (XRD) test results also exhibited characteristic AgNPs crystals with diffraction peaks observed at 2? values of 38.39°, 44.49°, and 64.45°, which were corresponding to (111), (200), and (220) crystallographic planes of face-centered cubic (fcc) silver crystals, respectively. Thermogravimetric analysis (TGA) results showed that thermal stability of the agar/AgNPs composite films was increased by the inclusion of metallic silver. Water vapor barrier properties and surface hydrophobicity of the agar/AgNPs films increased slightly with the increase in AgNPs content but they were not statistically significant (p>0.05), while mechanical strength and stiffness of the composite films decreased slightly (p<0.05). The agar/AgNPs films exhibited distinctive antimicrobial activity against both Gram-positive (Listeria monocytogenes) and Gram-negative (Escherichia coli O157:H7) bacterial pathogens. PMID:24528754

Rhim, Jong-Whan; Wang, Long-Feng; Lee, Yonghoon; Hong, Seok-In

2014-03-15

22

Quantitative dual-probe microdialysis: evaluation of [3H]mannitol diffusion in agar and rat striatum.  

PubMed

Dual-probe microdialysis was used to study interstitial diffusion in the rat brain. A radiolabelled tracer, (3H]mannitol, was continuously infused at different concentrations via a probe acutely implanted into the striatum of an anaesthetized male rat or into a dilute agar gel. Samples were collected by a second probe placed 1 mm away from the first, and the recovered [3H]mannitol was measured by liquid scintillation counting. In the striatum, the delivery of [3H]mannitol was counteracted by its removal from the extracellular space by passive uptake into cells and clearance into the microcirculation, causing the diffusion profile to approach quasi steady-state levels within 2 h. Diffusion data from brain and agar were analysed using a mathematical model. The apparent (effective) diffusion coefficient for [3H]mannitol was D* = 2.9 x 10(-6) cm2/s, the effective volume fraction alpha* = 0.30 and the clearance rate constant kappa= 2.3 x 10(-5)/s. A tortuosity, lambda = 1.81, and penetration distance r = 4.2 mm, were calculated. We conclude that, using dual-probe microdialysis, parameters reflecting geometric and dynamic tissue properties may be obtained using appropriate mathematical analysis. Quantitative dual-probe microdialysis will be valuable in characterizing interstitial diffusion and the clearance processes underpinning volume transmission in the brain. PMID:12067240

Höistad, Malin; Chen, Kevin C; Nicholson, Charles; Fuxe, Kjell; Kehr, Jan

2002-04-01

23

Colony morphotype on Sabouraud-triphenyltetrazolium agar: a simple and inexpensive method for Candida subspecies discrimination.  

PubMed Central

A new method of Candida subspecies discrimination on Sabouraud-triphenyltetrazolium agar is reported. Five hundred sixty-two strains of Candida and Torulopsis glabrata, previously identified by conventional mycological methods, were studied. Each strain received a three-letter code and a number based on its colonial morphology. Sixteen morphotypes were found for Candida albicans, 6 were found for Candida parapsilosis, 4 were found for both Candida guilliermondii and Candida krusei, and 12 were found for Candida tropicalis. None of the 56 T. glabrata strains studied grew on this agar. A reproducibility of 95% was found for C. albicans. The simplicity and low cost could make this method useful for typing Candida spp. Images PMID:1400981

Quindos, G; Fernandez-Rodriguez, M; Burgos, A; Tellaetxe, M; Cisterna, R; Ponton, J

1992-01-01

24

A simple and rapid semiquantitative method for measuring cellulase activity in agar media.  

PubMed

A simple and rapid semiquantitative technique for the determination of fungal cellulytic activities in solid (agar slant) media has been developed. This method is a combination of Congo-red staining widely used for qualitative cellulase detection and common cellulase activity tests. Previous investigation on the adsorptive effect of cellulose content of media showed that the real enzyme activity values can be measured with minimum loss by means of agar discs cut from the most active zones of slants visualized by Congo-red staining. Different cellulase activity tests (FPase, CMCase and beta-glucosidase by PNPG-method) of seven cellulolytic fungal strains were investigated by this technique. Data give information on the different enzyme profiles of the species. The method can be regarded as very simple and suitable for simultaneous rapid comparison of cellulase components of greater series of fungal strains from agar slant cultures. It can also be used in the case of fungi unable to grow in liquid cultures. PMID:7542535

Jakucs, E; Várallyay, E

1995-01-01

25

Tentative interpretive standards for agar disk diffusion antimicrobial susceptibility testing of cefoperazone.  

PubMed Central

Cefoperazone is a new cephalosporin with a very wide spectrum of activity, including activity against Pseudomonas aeruginosa. It has less activity on enterococci and Acinetobacter. Of the 459 selected bacterial strains tested in this study, only 1.5% (7 strains and 6 genera) had minimum inhibitory concentrations of greater than or equal to 128 micrograms/ml. For a minimum inhibitory concentration breakpoint of less than or equal to 32 micrograms/ml (susceptible), we recommend that the disk diffusion test be done with a 75-micrograms disk and breakpoints of greater than or equal to 18 mm for susceptible, 15 to 17 mm for intermediate, and less than or equal to 14 mm for resistant. Diffusion tests using these criteria yielded only 1.1% very major or major errors. PMID:6212595

Thornsberry, C; Barry, A L; Jones, R N; Baker, C N; Badal, R E

1982-01-01

26

Comparison of Rosco Neo-Sensitabs with Oxoid paper disks in EUCAST disk diffusion antimicrobial susceptibility testing on Mueller-Hinton agar.  

PubMed

This study compared Neo-Sensitabs with Oxoid paper disks using the European Committee on Antimicrobial Susceptibility Testing (EUCAST) disk diffusion antimicrobial susceptibility test on Mueller-Hinton agar. The EUCAST-recommended quality control strains (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 29213 and Enterococcus faecalis ATCC 29212) (Part I) and clinical isolates (Part II) were investigated. In Part I of the study, 27 combinations of antimicrobial agents were tested on four quality control strains repeatedly up to 60 times and zone diameters of tablets and disks were compared. In Part II of the study, 351 clinical isolates were included to cover a broad range of species, as well as resistance mechanisms. In Part I, four major deviations (>1 mm outside quality control ranges) were observed with Neo-Sensitabs. In one case with P. aeruginosa ATCC 27853 (meropenem), there was a corresponding major deviation (2 mm) with the Oxoid disk. The three remaining major deviations with Neo-Sensitabs were observed with meropenem (2 mm) in E. coli ATCC 25922 and with ciprofloxacin (2 mm) and gentamicin (3 mm) in P. aeruginosa ATCC 27853. For Oxoid disks, there were only minor deviations (=1 mm outside quality control ranges) in these three cases. In Part II, there were six discrepancies, susceptible versus resistant, in 3,533 comparisons between the two methods with the clinical isolates. The Rosco Neo-Sensitabs appear to be a possible alternative to Oxoid paper disks for EUCAST disk diffusion antimicrobial susceptibility testing on Mueller-Hinton agar. PMID:23232977

Justesen, U S; Acar, Z; Olsson, K; Jensen, T G; Kerrn, M B; Skov, R L; Gahrn-Hansen, B

2013-05-01

27

Agar disk diffusion and automated microbroth dilution produce similar antimicrobial susceptibility testing results for Salmonella serotypes Newport, Typhimurium, and 4,5,12:i-, but differ in economic cost.  

PubMed

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

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

28

VIDAS Salmonella (SLM) assay method EasySLM with ChromID Salmonella (SM2) Agar. Performance Tested Method 020901.  

PubMed

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

Johnson, Ronald; Mills, John; Colón-Reveles, Judith

2009-01-01

29

Comparison of sensititre dried microtitration trays with a standard agar method for determination of minimum inhibitory concentrations of antimicrobial agents.  

PubMed Central

A total of 222 clinical isolates were used to test the accuracy of Sensititre dried microtitration trays for determining minimum inhibitory concentrations (MICs) of antimicrobial agents. In comparison with an agar dilution technique, 89.5% of all the pairs of results were within one doubling dilution. The 2,420 pairs of MIC results with finite values gave a corresponding figure of 86.8%. Exclusion of sulfisoxazole results, which demonstrated a significant interlaboratory variation in accuracy, raised this value to 89.1%. Very good differentiation of beta-lactamase-producing strains of Staphylococcus aureus (24 of 24 giving an MIC greater than or equal to 0.25 micrograms/ml) and Haemophilus influenzae (3 of 3 giving an MIC greater than or equal to 32 micrograms/ml) was obtained with the Sensititre system. This method also clearly distinguished erythromycin-resistant S. aureus strains (7 of 7 giving an MIC greater than 32 micrograms/ml) from the susceptible strains (26 of 28 giving an MIC less than or equal to 0.5 microgram/ml plus 1 strain at 1.0 microgram/ml and 1 at 2.0 micrograms/ml). Sensititre offers an accurate and convenient method of determining MICs comparable to those obtained with the agar dilution procedure, with the advantage of an extended shelf life when stored at room temperature. PMID:6972192

Reeves, D S; Holt, A; Bywater, M J; Wise, R; Logan, M N; Andrews, J M; Broughall, J M

1980-01-01

30

Evaluation of the thin agar layer method for the recovery of pressure-injured and heat-injured Listeria monocytogenes.  

PubMed

A sublethally injured bacterial cell has been defined as a cell that survives a stress such as heating, freezing, acid treatment, or other antimicrobial intervention but can repair the cellular damage exerted by the stressor and later regain its original ability to grow. Consequently, sublethally injured cells are not likely to be included in conventional enumeration procedures, which could result in unrealistically low counts unless efforts are made to encourage recovery of the injured cells before enumeration. The objective of this study was to evaluate the use of the thin agar layer (TAL) method for the recovery of pressure-injured and heat-injured Listeria monocytogenes in a tryptic soy broth with 0.6% yeast extract system. Pressure injury consisted of treatment of a culture of mixed L. monocytogenes strains with high hydrostatic pressure at 400 or 600 MPa for 1 s, 2 min, 4 min, or 6 min at a process temperature of 12±2 °C. Heat injury consisted of treatment of a culture of mixed L. monocytogenes strains at 60±1 °C for 3, 6, or 9 min. Growth media were tryptic soy agar (TSA) with 0.6% yeast extract, modified Oxford medium (MOX), and TAL, which consisted of a 7-ml layer of TSA overlaid onto solidified MOX. Counts of viable L. monocytogenes on TAL were higher than those on MOX in the heat-injury experiment but not in the pressure-injury experiment. Therefore, the effectiveness of the TAL method may be specific to the type of injury applied to the microorganism and should be investigated in a variety of cellular injury scenarios. PMID:24780340

Lavieri, Nicolas A; Sebranek, Joseph G; Cordray, Joseph C; Dickson, James S; Jung, Stephanie; Manu, David K; Mendonça, Aubrey F; Brehm-Stecher, Byron F; Stock, Joseph; Stalder, Kenneth J

2014-05-01

31

Novel Method for Rapid Assessment of Antibiotic Resistance in Escherichia coli Isolates from Environmental Waters by Use of a Modified Chromogenic Agar  

Microsoft Academic Search

We validated a novel method for screening Escherichia coli resistance to antibiotics in environmental samples using modified Difco MI agar (Becton Dickinson) impregnated with selected antibiotics (tetracycline, ampi- cillin, cephalexin, and sulfamethoxazole), termed MI-R. This method combines an existing rapid assessment technique for E. coli enumeration with clinical reference data for breakpoint analysis of antibiotic resistance and was developed to

A. J. Watkinson; G. R. Micalizzi; J. R. Bates; S. D. Costanzo

2007-01-01

32

Generalizing the finite element method: Diffuse approximation and diffuse elements  

Microsoft Academic Search

This paper describes the new “diffuse approximation” method, which may be presented as a generalization of the widely used “finite element approximation” method. It removes some of the limitations of the finite element approximation related to the regularity of approximated functions, and to mesh generation requirements. The diffuse approximation method may be used for generating smooth approximations of functions known

B. Nayroles; G. Touzot; P. Villon

1992-01-01

33

Comparing the mannitol-egg yolk-polymyxin agar plating method to the three tube most probable number method for enumeration of bacillus cereus spores in raw and high-temperature-short-time pasteurized milk.  

E-print Network

??The Food and Drug Administration’s Bacteriological Analytical Manual recommends two enumeration methods for Bacillus spp.: 1) standard plating method using mannitol-egg yolk-polymyxin (MYP) agar and… (more)

Harper, Nigel Murray

2009-01-01

34

Mathematical Methods for Diffusion MRI Processing  

Microsoft Academic Search

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).

C. Lengleta; J. S. W. Campbellc; G. Harof Descoteauxe; P. Savadjievd; D. Wassermanng; A. Anwanderi

35

Mathematical Methods for Diffusion MRI Processing  

PubMed Central

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

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

36

Short report: an agar plate method for culturing hookworm larvae: analysis of growth kinetics and infectivity compared with standard coproculture techniques.  

PubMed

An agar plate (AP) method has been developed for culturing infectious larvae of the hookworm Ancylostoma ceylanicum. The third-stage larvae reared using the AP method displayed similar morphology to those cultured using Baermann or Harada-Mori coproculture techniques. The yield of viable larvae from the AP method (50%) was comparable to that of the Baermann (47%), and both were superior to Harada-Mori (2.1%). Third-stage larvae cultured by the AP method established patent infection in naturally permissive laboratory hosts, although the yield of adult worms was reduced compared with animals infected with L3 obtained by Baermann culture. The AP method is useful for defining growth requirements for hookworm development, as well as characterizing the effects of bacterially expressed compounds on hookworm larvae in vivo. PMID:18165527

Reiss, Daniel; Harrison, Lisa M; Bungiro, Richard; Cappello, Michael

2007-12-01

37

Demonstrating Diffusion  

ERIC Educational Resources Information Center

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)

Foy, Barry G.

1977-01-01

38

Diffusion Monte Carlo Method on Curved Manifolds  

Microsoft Academic Search

We present a stochastic approach to solving the many-body Schrödinger equation on curved manifolds with general metric. The method is based on the Diffusion Monte Carlo (DMC) technique, modified to include `quantum corrections' into the propagator which appear due to the curvature. As an illustration of our method we apply it to the quantum Hall effect, using the spherical geometry

V. Melik-Alaverdian; N. E. Bonesteel; G. Ortiz

1997-01-01

39

Screening of lactic acid bacteria for reducing power using a tetrazolium salt reduction method on milk agar.  

PubMed

Reducing activity is a physiological property of lactic acid bacteria (LAB) of technological importance. We developed a solid medium with tetrazolium dyes enabling weakly and strongly reducing LAB to be discriminated. It was used to quantify populations in a mixed culture (spreading method) and screen strains (spot method). PMID:23063698

Michelon, Damien; Tachon, Sybille; Ebel, Bruno; De Coninck, Joëlle; Feron, Gilles; Gervais, Patrick; Yvon, Mireille; Cachon, Rémy

2013-02-01

40

Correlation between Microdilution, E-test, and Disk Diffusion Methods for Antifungal Susceptibility Testing of Posaconazole against Candida spp.  

PubMed Central

Agar-based antifungal susceptibility testing is an attractive alternative to the microdilution method. We examined the correlation between the microdilution, E-test, and disk diffusion methods for posaconazole against Candida spp. A total of 270 bloodstream isolates of Candida spp. with a broad range of posaconazole MICs were tested using the CLSI M27-A2 method for microdilution, as well as the M-44A method and E-test methods for agar-based testing on Mueller-Hinton agar supplemented with 2% glucose and 0.5 ?g of methylene blue. MICs and inhibitory zone diameters at the prominent growth reduction endpoint were recorded at 24 and 48 h. The Candida isolates included Candida albicans (n = 124), C. parapsilosis (n = 44), C. tropicalis (n = 41), C. glabrata (n = 36), C. krusei (n = 20), C. lusitaniae (n = 3), and C. dubliniensis (n = 2). The overall concordance (i.e., the percentage of isolates within two dilutions) between the E-test and microdilution was 64.8% at 24 h and 82.6% at 48 h. When we considered an arbitrary breakpoint of ?1 ?g/ml, the agreement between the E-test and microdilution methods was 87.8% at 24 h and 93.0% at 48 h. The correlation of MICs with disk diffusion zone diameters was better for the E-test than the microdilution method. Zone correlation for diameters produced by the disks of two manufacturers was high, with a Pearson test value of 0.941 at 24 h. The E-test and microdilution MICs show good concordance and interpretative agreement. The disk diffusion zone diameters are highly reproducible and correlate well with both the E-test and the microdilution method, making agar-based methods a viable alternative to microdilution for posaconazole susceptibility testing. PMID:16757605

Sims, Charles R.; Paetznick, Victor L.; Rodriguez, Jose R.; Chen, Enuo; Ostrosky-Zeichner, Luis

2006-01-01

41

Hektoen Enteric Agar Protocol  

NSDL National Science Digital Library

Hektoen enteric agar is a selective and differential media for the recovery of enteric gram-negative rods from mixed microbiota.  The growth of gram-positive organisms and nonpathogenic enteric coliforms is inhibited through the use of bile salts and dyes, allowing intestinal pathogens, such as Salmonella and Shigella, to be more easily recovered.  The media can also differentiate between organisms that produce H2S and those that do not due to the presence of an iron-containing compound.  The use and interpretation of growth on this media is discussed in this protocol.

American Society For Microbiology;

2010-11-11

42

A rapid and easy method for the detection of microbial cellulases on agar plates using gram's iodine.  

PubMed

Screening for cellulase-producing microorganisms is routinely done on carboxymethylcellulose (CMC) plates. The culture plates are flooded either with 1% hexadecyltrimethyl ammonium bromide or with 0.1% Congo red followed by 1 M NaCl. In both cases, it takes a minimum of 30 to 40 minutes to obtain the zone of hydrolysis after flooding, and the hydrolyzed area is not sharply discernible. An improved method is reported herein for the detection of extracellular cellulase production by microorganisms by way of plate assay. In this method, CMC plates were flooded with Gram's iodine instead of the reagents just mentioned. Gram's iodine formed a bluish-black complex with cellulose but not with hydrolyzed cellulose, giving a sharp and distinct zone around the cellulase-producing microbial colonies within 3 to 5 minutes. The new method is rapid and efficient; therefore, it can be easily performed for screening large numbers of microbial cultures of both bacteria and fungi. This is the first report on the use of Gram's iodine for the detection of cellulase production by microorganisms using plate assay. PMID:18810533

Kasana, Ramesh Chand; Salwan, Richa; Dhar, Hena; Dutt, Som; Gulati, Arvind

2008-11-01

43

Development of an eco-friendly agar extraction technique from the red seaweed Gracilaria lemaneiformis  

Microsoft Academic Search

The red seaweed, Gracilaria lemaneiformis growing as an aquaculture bioremediator along the coasts of Liaodong Peninsula, China, was investigated for the agar production. An eco-friendly method called agar photobleaching extraction process was developed for the benefit of workers’ health and safety of the environment. The native agar (NA), alkali-modified agar (AA), chemical-bleached agar (CA) and photobleached agar (PA), which were

Haiyan Li; Xingju Yu; Yan Jin; Wei Zhang; Yuanling Liu

2008-01-01

44

Evaluation of disk diffusion methods to detect low-level ?-lactamase-negative ampicillin-resistant Haemophilus influenzae.  

PubMed

We evaluated the efficacy of disk diffusion methods for detection of low-level ?-lactamase-negative ampicillin-resistant (low-BLNAR) Haemophilus influenzae. Four hundred and seventy unselected, recent clinical isolates were tested with ampicillin (10 ?g), cefaclor (30 ?g) and cefuroxime (30 ?g) on iso-Sensitest agar enriched with nicotinamide adenine dinucleotide (NAD) and horse blood [ST agar; Swedish Reference Group for Antibiotics (SRGA) guidelines], and on chocolate agar (in-house guidelines). Selected isolates (n = 147) were subjected to partial sequencing of the ftsI gene. Forty-seven strains (10.0%) were genotypically identified as low-BLNAR, which was confirmed by determination of minimal inhibitory concentration (MIC) using microbroth dilution method: only low level resistance to ampicillin was detected [MIC ?1 ?g/mL; MIC(50) = 0.5 ?g/mL, implying susceptibility by Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antibiotic Susceptibility Testing (EUCAST) interpretative criteria]. The MIC of cefuroxime varied between 1 and 4 ?g/mL (MIC(50) = 2 ?g/mL), indicating susceptibility to cefuroxime by CLSI but not by EUCAST guidelines. Disk diffusion methods were able to discriminate low-BLNAR H. influenzae from the wild-type population with sensitivities ranging from 87% to 98% and specificities from 96% to 99%. Cefaclor was found to be superior to cefuroxime and ampicillin. Cefaclor zone diameter breakpoints of 30/29 and 23/22 mm are suggested for ST agar and chocolate agar, respectively. PMID:21569097

Nørskov-Lauritsen, Niels; Ridderberg, Winnie; Erikstrup, Lise T; Fuursted, Kurt

2011-06-01

45

Comparison of direct and modified direct complement-fixation and agar-gel precipitin methods in detecting chlamydial antibody in wild birds.  

PubMed

Detection of chlamydial antibody in serums of wild birds was compared for the following methods: direct complement-fixation (DCF), modified DCF (MDCF), and agar-gel precipitin (AGP). The birds species used were great-tailed grackles (Cassidix mexicanus), common grackles (Quiscalus quiscula), brown-headed cowbirds (Molothrus ater), bronzed cowbirds (Tangavius aeneus), and mourning doves (Zenaida macroura). The birds were either inoculated with an isolate of Chlamydia psittaci obtained originally from turkeys or kept as uninoculated cagemates. DCF detected antibody in most inoculated common grackles, mourning doves, and brown-headed cowbirds. It was unreliable, however, for great-tailed grackles and bronzed cowbirds inoculated intramuscularly. MDCF method detected antibody in all inoculated birds except 1 mourning dove, and gave higher titers than did DCF. AGP detected antibody in all inoculated brown-headed cowbirds and all mourning doves, 1 inoculated and 1 exposed great-tailed grackle, and none of the other 2 species. Chlamydiae were apparently transmitted to the uninoculated great-tailed and common grackles and mourning doves, for antibody was detected by all 3 methods in these species kept as uninoculated cagemates. PMID:100098

Grimes, J E; Page, L A

1978-01-01

46

Direct Sampling Method for Diffusive Optical Tomography  

E-print Network

In this work, we are concerned with the diffusive optical tomography (DOT) problem in the case when only one or two pairs of Cauchy data is available. We propose a simple and efficient direct sampling method (DSM) to locate inhomogeneities inside a homogeneous background and solve the DOT problem in both full and limited aperture cases. This new method is easy to implement and less expensive computationally. Numerical experiments demonstrate its effectiveness and robustness against noise in the data. This provides a new promising numerical strategy for the DOT problem.

Yat Tin Chow; Kazufumi Ito; Keji Liu; Jun Zou

2014-10-06

47

Agar medium for gas-liquid chromatography of anaerobes.  

PubMed

This study evaluates a method of performing gas-liquid chromatography (GLC) by direct extraction of fatty acids from agar for identification of clinically significant anaerobic bacteria. The potential use of agar cultures for GLC was studied by comparing chromatograms of 117 clinically isolated anaerobes grown in peptone yeast glucose broth and chopped meat carbohydrate broth, and on enriched brucella blood agar. For 98 of 117 anaerobes, fatty acid patterns from agar cultures were similar to those in broth. Significant differences were only found with Streptococcus intermedius, Clostridium perfringens, Clostridium tertium, and Actinomyces species, which produced less of certain fatty acids on agar than in broth. Results of this study indicate that GLC of short chain fatty acids produced on agar medium by anaerobes, combined with simple tests such as Gram's stain and colonial morphology, may allow fir direct presumptive genus identification from an initial pure agar culture. PMID:3940426

Pankuch, G A; Appelbaum, P C

1986-01-01

48

Carbapenem Disks on MacConkey Agar in Screening Methods for Detection of Carbapenem-Resistant Gram-Negative Rods in Stools  

PubMed Central

Direct plating of simulated stool specimens on MacConkey agar (MCA) with 10-?g ertapenem, meropenem, and imipenem disks allowed the establishment of optimal zone diameters for the screening of carbapenem-resistant Gram-negative rods (CRGNR) of ?24 mm (ertapenem), ?34 mm (meropenem), and ?32 mm (imipenem). PMID:23135936

Blackburn, Julie; Tsimiklis, Catherine; Lavergne, Valery; Pilotte, Josee; Grenier, Sophie; Gilbert, Andree; Lefebvre, Brigitte; Tremblay, Cecile; Bourgault, Anne-Marie

2013-01-01

49

Improved spatial direct method with gradient-based diffusion to retain full diffusive fluctuations  

NASA Astrophysics Data System (ADS)

The spatial direct method with gradient-based diffusion is an accelerated stochastic reaction-diffusion simulation algorithm that treats diffusive transfers between neighboring subvolumes based on concentration gradients. This recent method achieved a marked improvement in simulation speed and reduction in the number of time-steps required to complete a simulation run, compared with the exact algorithm, by sampling only the net diffusion events, instead of sampling all diffusion events. Although the spatial direct method with gradient-based diffusion gives accurate means of simulation ensembles, its gradient-based diffusion strategy results in reduced fluctuations in populations of diffusive species. In this paper, we present a new improved algorithm that is able to anticipate all possible microscopic fluctuations due to diffusive transfers in the system and incorporate this information to retain the same degree of fluctuations in populations of diffusing species as the exact algorithm. The new algorithm also provides a capability to set the desired level of fluctuation per diffusing species, which facilitates adjusting the balance between the degree of exactness in simulation results and the simulation speed. We present numerical results that illustrate the recovery of fluctuations together with the accuracy and efficiency of the new algorithm.

Koh, Wonryull; Blackwell, Kim T.

2012-10-01

50

Improved spatial direct method with gradient-based diffusion to retain full diffusive fluctuations  

PubMed Central

The spatial direct method with gradient-based diffusion is an accelerated stochastic reaction-diffusion simulation algorithm that treats diffusive transfers between neighboring subvolumes based on concentration gradients. This recent method achieved a marked improvement in simulation speed and reduction in the number of time-steps required to complete a simulation run, compared with the exact algorithm, by sampling only the net diffusion events, instead of sampling all diffusion events. Although the spatial direct method with gradient-based diffusion gives accurate means of simulation ensembles, its gradient-based diffusion strategy results in reduced fluctuations in populations of diffusive species. In this paper, we present a new improved algorithm that is able to anticipate all possible microscopic fluctuations due to diffusive transfers in the system and incorporate this information to retain the same degree of fluctuations in populations of diffusing species as the exact algorithm. The new algorithm also provides a capability to set the desired level of fluctuation per diffusing species, which facilitates adjusting the balance between the degree of exactness in simulation results and the simulation speed. We present numerical results that illustrate the recovery of fluctuations together with the accuracy and efficiency of the new algorithm. PMID:23083152

Koh, Wonryull; Blackwell, Kim T.

2012-01-01

51

Fastidious anaerobe agar compared with Wilkins-Chalgren agar, brain heart infusion agar, and brucella agar for susceptibility testing of Fusobacterium species.  

PubMed Central

Fastidious anaerobe agar supported the growth of 82 strains of fusobacteria better than brain heart infusion agar, brucella agar, and Wilkins-Chalgren agar. Fastidious anaerobe agar showed less hazing and fewer tailing endpoints with beta-lactam antibiotics. Whole-blood supplementation improved the performance of all media. Wilkins-Chalgren agar without blood failed to support the growth of 17% of the strains. All Fusobacterium ulcerans strains were resistant to clindamycin. PMID:2073122

Brazier, J S; Goldstein, E J; Citron, D M; Ostovari, M I

1990-01-01

52

Fastidious anaerobe agar compared with Wilkins-Chalgren agar, brain heart infusion agar, and brucella agar for susceptibility testing of Fusobacterium species.  

PubMed

Fastidious anaerobe agar supported the growth of 82 strains of fusobacteria better than brain heart infusion agar, brucella agar, and Wilkins-Chalgren agar. Fastidious anaerobe agar showed less hazing and fewer tailing endpoints with beta-lactam antibiotics. Whole-blood supplementation improved the performance of all media. Wilkins-Chalgren agar without blood failed to support the growth of 17% of the strains. All Fusobacterium ulcerans strains were resistant to clindamycin. PMID:2073122

Brazier, J S; Goldstein, E J; Citron, D M; Ostovari, M I

1990-11-01

53

Agar degradation by microorganisms and agar-degrading enzymes.  

PubMed

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 ?-(1,4) and ?-(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-?-agarase, ?-agarase, and ?-porphyranase. Although, in a broad sense, many other agarases are involved in complete hydrolysis of agar, most of those identified are ?-agarases. In this article we review agarolytic microorganisms and their agar-hydrolyzing systems, covering ?-agarases as well as ?-agarases, ?-neoagarobiose hydrolases, and ?-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

Chi, Won-Jae; Chang, Yong-Keun; Hong, Soon-Kwang

2012-05-01

54

Abilities of the mCP Agar Method and CRENAME Alpha Toxin-Specific Real-Time PCR Assay To Detect Clostridium perfringens Spores in Drinking Water  

PubMed Central

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

Maheux, Andree F.; Berube, Eve; Boudreau, Dominique K.; Villeger, Romain; Cantin, Philippe; Boissinot, Maurice; Bissonnette, Luc

2013-01-01

55

A Diffusion Synthetic Acceleration Method for Block Adaptive Mesh Refinement  

Microsoft Academic Search

A prototype two-dimensional Diffusion Synthetic Acceleration (DSA) method on a Block-based Adaptive Mesh Refinement (BAMR) transport mesh has been developed. The Block-Adaptive Mesh Refinement Diffusion Synthetic Acceleration (BAMR-DSA) method was tested in the PARallel TIme-Dependent SN (PARTISN) deterministic transport code. The BAMR-DSA equations are derived by differencing the DSA equation using a vertex-centered diffusion discretization that is diamond-like and may

R. C. Ward; R. S. Baker; J. E. Morel

2005-01-01

56

Development of the EUCAST disk diffusion antimicrobial susceptibility testing method and its implementation in routine microbiology laboratories.  

PubMed

With the support of ESCMID and European countries, EUCAST has developed a disk diffusion test with zone diameter breakpoints correlated with the EUCAST clinical MIC breakpoints. The development of the EUCAST disk diffusion method and quality control criteria are described, together with guidance on quality control and implementation of the method in clinical microbiology laboratories. The method includes the use of Mueller-Hinton agar without supplements for non-fastidious organisms and with 5% mechanically defibrinated horse blood and 20 mg/L ?-NAD for fastidious organisms, a standardized inoculum resulting in confluent growth, an incubation time of 16-20 h, a reading guide on how to read zone diameters on individual species-agent combinations and zone diameter breakpoints calibrated to the EUCAST clinical MIC breakpoints. EUCAST recommendations are described in detail and updated regularly on the EUCAST website (http://www.eucast.org). PMID:24131428

Matuschek, E; Brown, D F J; Kahlmeter, G

2014-04-01

57

Diffuse-Interface Methods in Fluid Mechanics  

NASA Technical Reports Server (NTRS)

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.

Anderson, D. M.; McFadden, G. B.; Wheeler, A. A.

1997-01-01

58

Development of a selective agar plate for the detection of Campylobacter spp. in fresh produce.  

PubMed

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

Yoo, Jin-Hee; Choi, Na-Young; Bae, Young-Min; Lee, Jung-Su; Lee, Sun-Young

2014-10-17

59

Domain Decomposition Method for the Advection-Diffusion Equation.  

National Technical Information Service (NTIS)

The report describes a model study for domain decomposition for the incompressible Navier-Stokes equations using the two-dimensional advection-diffusion equation. Three types of domain decomposition methods are investigated. They are: The Schwarz method; ...

E. Brakkee, P. Wilders

1994-01-01

60

Thermal characterization of magnetically aligned carbonyl iron/agar composites.  

PubMed

Composites of magnetic particles into polymeric matrices have received increasing research interest due to their capacity to respond to external magnetic or electromagnetic fields. In this study, agar from Gelidium robustum has been chosen as natural biocompatible polymer to build the matrix of the magnetic carbonyl iron particles (CIP) for their uses in biomedical fields. Heat transfer behavior of the CIP-agar composites containing different concentrations (5, 10, 15, 20, 25 and 30% w/w) of magnetically aligned and non-aligned CIP in the agar matrix was studied using photothermal radiometry (PTR) in the back-propagation emission configuration. The morphology of the CIP-agar composites with aligned and non-aligned CIP under magnetic field was also evaluated by scanning electron microscopy (SEM). The results revealed a dominant effect of CIP concentration over the alignment patterns induced by the magnetic field, which agrees with the behavior of the thermal diffusivity and thermal conductivity. Agar served as a perfect matrix to be used with CIP, and CIP-agar composites magnetically aligned at 20% CIP concentration can be considered as promising 'smart' material for hyperthermia treatments in the biomedical field. PMID:24274482

Diaz-Bleis, D; Vales-Pinzón, C; Freile-Pelegrín, Y; Alvarado-Gil, J J

2014-01-01

61

Diffusion via space discretization method to study the concentration dependence of self-diffusivity under confinement.  

PubMed

The concentration dependence of self-diffusivity is investigated by means of a novel method, extending our previously developed second-order Markov process model to periodic media. Introducing the concept of minimum-crossing surface, we obtain a unique decomposition of the self-diffusion coefficient into two parameters with specific physical meanings. Two case studies showing a maximum in self-diffusivity as a function of concentration are investigated, along with two cases where such a maximum cannot be present. Subsequently, the method is applied to the large cavity pore network of the ITQ-1 (Mobil tWenty tWo, MWW) zeolite for methane (displaying a maximum in self-diffusivity) and carbon dioxide (no maximum), explaining the diffusivity trend on the basis of the evolution of the model parameters as a function of concentration. PMID:20387922

Sant, Marco; Papadopoulos, George K; Theodorou, Doros N

2010-04-01

62

Diffusion via space discretization method to study the concentration dependence of self-diffusivity under confinement  

NASA Astrophysics Data System (ADS)

The concentration dependence of self-diffusivity is investigated by means of a novel method, extending our previously developed second-order Markov process model to periodic media. Introducing the concept of minimum-crossing surface, we obtain a unique decomposition of the self-diffusion coefficient into two parameters with specific physical meanings. Two case studies showing a maximum in self-diffusivity as a function of concentration are investigated, along with two cases where such a maximum cannot be present. Subsequently, the method is applied to the large cavity pore network of the ITQ-1 (Mobil tWenty tWo, MWW) zeolite for methane (displaying a maximum in self-diffusivity) and carbon dioxide (no maximum), explaining the diffusivity trend on the basis of the evolution of the model parameters as a function of concentration.

Sant, Marco; Papadopoulos, George K.; Theodorou, Doros N.

2010-04-01

63

A Method for Identifying Diffusive Trajectories with Stochastic Models  

NASA Astrophysics Data System (ADS)

Single particle tracking is a tool that is being increasingly used to study diffusive or dispersive processes in many branches of natural science. Often the ability to collect these trajectories experimentally or produce them numerically outpaces the ability to understand them theoretically. On the other hand many stochastic models have been developed and continue to be developed capable of capturing complex diffusive behavior such as heavy tails, long-range correlations, nonstationarity, and combinations of these things. We describe a computational method for connecting particle trajectory data with stochastic models of diffusion. Several tests are performed to demonstrate the efficacy of the method, and the method is applied to polymer diffusion, RNA diffusion in E. coli, and RAFOS dispersion in the Gulf of Mexico.

O'Malley, D.; Vesselinov, V. V.; Cushman, J. H.

2014-09-01

64

A hybrid transport-diffusion method for 2D transport problems with diffusive subdomains  

NASA Astrophysics Data System (ADS)

In this paper we present a computational method based on the Simple Corner Balance (SCB) scheme for solving 2D transport problems in diffusive media. It utilizes decomposition of spatial domain into transport and diffusive subregions. This methodology uses the low-order equations of the Second-Moment (SM) method for the first two angular moments of the transport solution. These low-order SM equations are solved globally. The high-order transport solution is computed only in transport subregions. The transport boundary conditions at interfaces with neighbouring diffusion subregions are formulated using asymptotic analysis of SCB. We apply the quasidiffusion (Eddington) tensor to evaluate transport effects in the problem domain and determine spatial ranges of diffusive subregions. Numerical results are presented. They demonstrate the accuracy of the developed methodology for the SCB scheme.

Stehle, Nicholas D.; Anistratov, Dmitriy Y.; Adams, Marvin L.

2014-08-01

65

Comparison of Supplemented Brucella Agar and Modified Clostridium difficile Agar for Antimicrobial Susceptibility Testing of Clostridium difficile  

PubMed Central

Background Antimicrobial susceptibility testing (AST) of Clostridium difficile is increasingly important because of the rise in resistant strains. The standard medium for the AST of C. difficile is supplemented Brucella agar (sBA), but we found that the growth of C. difficile on sBA was not optimal. Because active growth is critical for reliable AST, we developed a new, modified C. difficile (mCD) agar. C. difficile grew better on mCD agar than on sBA. Methods C. difficile isolates were collected from patients with healthcare-associated diarrhea. sBA medium was prepared according to the CLSI guidelines. Homemade mCD agar containing taurocholate, L-cysteine hydrochloride, and 7% horse blood was used. For 171 C. difficile isolates, we compared the agar dilution AST results from mCD agar with those from sBA. Results No significant differences were observed in the 50% minimal inhibitory concentration (MIC50) and 90% minimal inhibitory concentration (MIC90) of clindamycin (CLI), metronidazole (MTZ), moxifloxacin (MXF), piperacillin-tazobactam (PTZ), and rifaximin (RIX), but the values for vancomycin (VAN) were two-fold higher on mCD agar than on sBA. The MICs of CLI, MXF, and RIX were in 100% agreement within two-fold dilutions, but for MTZ, VAN, and PTZ, 13.7%, 0.6%, and 3.1% of the isolates, respectively, were outside the acceptable range. Conclusions The MIC ranges, MIC50 and MIC90, were acceptable when AST was performed on mCD agar. Thus, mCD agar could be used as a substitute medium for the AST of C. difficile. PMID:25368819

Kim, Gye Hyeong; Kim, Jieun; Pai, Hyunjoo

2014-01-01

66

Streamline diffusion methods for Fermi and Fokker-Planck equations  

Microsoft Academic Search

We derive error estimates in certain weighted L2-norms for the streamline diffusion and discontinuous Galerkin finite element methods for steady state, energy dependent, Fermi and Fokker-Planck equations in two space dimensions, giving error bounds of order O(h), for the weighted current function J, as in the convection dominated convection-diffusion problems, with J ? H (?) and h being the quasi-uniform

Mohammad Asadzadeh

1997-01-01

67

An explicit high order method for fractional advection diffusion equations  

NASA Astrophysics Data System (ADS)

We propose a high order explicit finite difference method for fractional advection diffusion equations. These equations can be obtained from the standard advection diffusion equations by replacing the second order spatial derivative by a fractional operator of order ? with 1method through consistency and stability. The order of convergence varies between two and three and for advection dominated flows is close to three. Although the method is conditionally stable, the restrictions allow wide stability regions. The analysis is confirmed by numerical examples.

Sousa, Ercília

2014-12-01

68

A stable transient boundary element method (BEM) for diffuser scattering  

Microsoft Academic Search

Boundary element methods (BEM) may be used to model scattering from hard rigid surfaces such as diffusers. They have the advantage over volumetric methods that only the surface need be meshed and the surface velocity potential found. Unlike the more widely used single frequency methodology, transient BEM discretizes integral equations to produce an iterative system that is marched on in

Jonathan A. Hargreaves; Trevor J. Cox

2005-01-01

69

Adaptive diffusion smoothing: A diffusion-based method to reduce IMRT field complexity  

SciTech Connect

Inverse-planned intensity modulated radiation therapy (IMRT) is often able to achieve complex treatment planning goals that are unattainable with forward three-dimensional (3D) conformal planning. However, the common use of IMRT has introduced several new challenges. The potentially high degree of modulation in IMRT beams risks the loss of some advantages of 3D planning, such as excellent target coverage and high delivery efficiency. Previous attempts to reduce beam complexity by smoothing often result in plan degradation because the smoothing algorithm cannot distinguish between areas of desirable and undesirable modulation. The purpose of this work is to introduce and evaluate adaptive diffusion smoothing (ADS), a novel procedure designed to preferentially reduce IMRT beam complexity. In this method, a discrete diffusion equation is used to smooth IMRT beams using diffusion coefficients, automatically defined for each beamlet, that dictate the degree of smoothing allowed for each beamlet. This yields a method that can distinguish between areas of desirable and undesirable modulation. The ADS method has been incorporated into our optimization system as a weighted cost function penalty, with two diffusion coefficient definitions designed to promote: (1) uniform smoothing everywhere or (2) smoothing based on cost function gradients with respect to the plan beamlet intensities. The ADS method (with both coefficient types) has been tested in a phantom and in two clinical examples (prostate and head/neck). Both types of diffusion coefficients produce plans with reduced modulation and minimal dosimetric impact, but the cost function gradient-based coefficients show more potential for reducing beam modulation without affecting dosimetric plan quality. In summary, adaptive diffusion smoothing is a promising tool for ensuring that only the necessary amount of beam modulation is used, promoting more efficient and accurate IMRT planning, QA, and delivery.

Matuszak, Martha M.; Larsen, Edward W.; Jee, Kyung-Wook; McShan, Daniel L.; Fraass, Benedick A. [Departments of Radiation Oncology and Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan 48109 (United States); Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan 48109 (United States); Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109 (United States)

2008-04-15

70

Leapfrog/finite element method for fractional diffusion equation.  

PubMed

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

Zhao, Zhengang; Zheng, Yunying

2014-01-01

71

Hair Sheep Blood, Citrated or Defibrinated, Fulfills All Requirements of Blood Agar for Diagnostic Microbiology Laboratory Tests  

PubMed Central

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

Yeh, Ellen; Pinsky, Benjamin A.; Banaei, Niaz; Baron, Ellen Jo

2009-01-01

72

Stochastic operator-splitting method for reaction-diffusion systems  

NASA Astrophysics Data System (ADS)

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.

Choi, TaiJung; Maurya, Mano Ram; Tartakovsky, Daniel M.; Subramaniam, Shankar

2012-11-01

73

The Flux-integral Method for Multidimensional Convection and Diffusion  

NASA Technical Reports Server (NTRS)

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).

Leonard, B. P.; Macvean, M. K.; Lock, A. P.

1994-01-01

74

Development of a Disk Diffusion Method for Testing Moraxella catarrhalis Susceptibility Using Clinical and Laboratory Standards Institute Methods: a SENTRY Antimicrobial Surveillance Program Report?  

PubMed Central

Currently, there is no Clinical and Laboratory Standards Institute (CLSI) disk diffusion method for testing Moraxella catarrhalis susceptibility. We examined 318 clinical strains of M. catarrhalis obtained as part of the SENTRY (Asia-Pacific) Antimicrobial Surveillance Program, plus two ATCC strains. MICs were determined by the CLSI standard broth microdilution method, and zone diameters were determined on Mueller-Hinton agar incubated in 5% CO2. All strains were examined for the presence of BRO-1 and BRO-2 ?-lactamases by using molecular techniques. Tentative zone diameter interpretive criteria were successfully developed for 19 antimicrobial agents, including nine ?-lactams, using current MIC interpretive criteria where available or wild-type cutoff values where no prior criteria were available. The proposed interpretive criteria were highly accurate, with ?0.7% very major (falsely susceptible) and ?1.0% major (falsely resistant) errors, respectively. PMID:19458179

Bell, Jan M.; Turnidge, John D.; Jones, Ronald N.

2009-01-01

75

Asymptotic Diffusion Accelerated Discontinuous Finite Element Methods for Transport Problems  

NASA Astrophysics Data System (ADS)

The diffusion synthetic acceleration (DSA) method has emerged as a powerful tool for accelerating the iterative convergence rate of discrete-ordinate transport calculations. However, in multi-dimensional geometries, only the diamond-differenced scheme has been efficiently solved by the DSA procedure. More advanced and accurate schemes, such as the discontinuous finite element schemes, have not been efficiently solved by DSA because applying the standard DSA procedure results in a large, complicated system of equations that cannot be collapsed into an efficiently solvable discrete diffusion equation. Here we present a new procedure for diffusion -accelerating certain discontinuous finite element schemes for slab and x-y geometry discrete-ordinates problems. The novel aspect of this procedure is that the discretized diffusion problem is derived from an asymptotic expansion of the discrete transport problem. The motivation for this procedure is that the resulting diffusion problem is relatively "simple" and easily solvable. The asymptotic expansion also shows that these discontinuous finite element schemes are highly accurate for diffusive problems with optically thick spatial meshes. Therefore, these schemes possess two very desirable properties: they are very accurate for all problems with optically thin meshes and diffusive problems with optically thick meshes, and they are efficiently solved by a diffusion-synthetic acceleration procedure. Specifically, we consider the conventional and lumped linear discontinuous schemes in slab geometry and a certain lumped bilinear discontinuous scheme in x-y geometry. In slab geometry, the new "asymptotic" DSA procedure is very efficient for problems that contain either isotropic scattering or linearly-anisotropic scattering. In x-y geometry, this procedure is very efficient provided the spatial cells do not have large aspect ratios and the system does not have highly anisotropic scattering. Also, the resulting discrete diffusion equation has a very simple five-point stencil with a one-point removal term and is very efficiently solved by the multigrid method. We provide numerical results that demonstrate the high level of accuracy and rapid convergence of the new methods.

Wareing, Todd Arlin

76

A mixed finite element method for nonlinear diffusion equations  

Microsoft Academic Search

We propose a mixed finite element method for a class of nonlinear diffusion equations, which is based on their interpretation as gradient flows in optimal transportation metrics. We introduce an appropriate linearization of the optimal transport problem, which leads to a mixed symmetric formulation. This formulation preserves the maximum principle in case of the semi-discrete scheme as well as the

Martin Burger; JOS ´ E A. CARRILLO; Marie-Therese Wolfram

2010-01-01

77

Pulse Method for the Measurement of Thermal Diffusivity of Metals  

Microsoft Academic Search

A pulse method for measuring thermal diffusivitity of metals has been developed. The temperature in an effectively infinite rod is zero everywhere up to the time t=0, when a very short heat pulse is introduced in the plane x=0. The subsequent temperature histories of several points at different distances from x=0 are recorded, and from these data the thermal diffusivity

Edwin L. Woisard

1961-01-01

78

Methods for diffusive relaxation in the Pn equation  

SciTech Connect

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.

Hauck, Cory D [Los Alamos National Laboratory; Mcclarren, Ryan G [Los Alamos National Laboratory; Lowrie, Robert B [Los Alamos National Laboratory

2008-01-01

79

Thermal diffusivity of nonflat plates using the flash method  

SciTech Connect

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.

Salazar, Agustin; Fuente, Raquel; Apinaniz, Estibaliz; Mendioroz, Arantza [Departamento de Fisica Aplicada I, Escuela Tecnica Superior de Ingenieria, Universidad del Pais Vasco, Alameda Urquijo s/n, 48013 Bilbao (Spain)

2011-01-15

80

Boundary particle method for Laplace transformed time fractional diffusion equations  

NASA Astrophysics Data System (ADS)

This paper develops a novel boundary meshless approach, Laplace transformed boundary particle method (LTBPM), for numerical modeling of time fractional diffusion equations. It implements Laplace transform technique to obtain the corresponding time-independent inhomogeneous equation in Laplace space and then employs a truly boundary-only meshless boundary particle method (BPM) to solve this Laplace-transformed problem. Unlike the other boundary discretization methods, the BPM does not require any inner nodes, since the recursive composite multiple reciprocity technique (RC-MRM) is used to convert the inhomogeneous problem into the higher-order homogeneous problem. Finally, the Stehfest numerical inverse Laplace transform (NILT) is implemented to retrieve the numerical solutions of time fractional diffusion equations from the corresponding BPM solutions. In comparison with finite difference discretization, the LTBPM introduces Laplace transform and Stehfest NILT algorithm to deal with time fractional derivative term, which evades costly convolution integral calculation in time fractional derivation approximation and avoids the effect of time step on numerical accuracy and stability. Consequently, it can effectively simulate long time-history fractional diffusion systems. Error analysis and numerical experiments demonstrate that the present LTBPM is highly accurate and computationally efficient for 2D and 3D time fractional diffusion equations.

Fu, Zhuo-Jia; Chen, Wen; Yang, Hai-Tian

2013-02-01

81

Method of making gas diffusion layers for electrochemical cells  

DOEpatents

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.

Frisk, Joseph William (Oakdale, MN); Boand, Wayne Meredith (Lino Lakes, MN); Larson, James Michael (Saint Paul, MN)

2002-01-01

82

Enhancement of the ultrasound images by modified anisotropic diffusion method.  

PubMed

Speckle is a primary factor which degrades the contrast resolution and masks the meaningful texture information present in an ultrasound image. Its presence severely hampers the interpretation and analysis of ultrasound images. When speckle reduction technique is applied for visual enhancement of ultrasound images, it is to be kept in mind that blurring associated with speckle reduction should be less and fine details are properly enhanced. With these points in consideration, the modified speckle reduction anisotropic diffusion (MSRAD) method is proposed in the present study to improve the visual quality of the ultrasound images. In the proposed MSRAD method, the four neighboring pixel template in speckle reduction anisotropic diffusion (SRAD) method of Yu and Acton (IEEE Trans Image Process 11:1260-1270, 2002) have been replaced by a new template of larger number of neighboring pixels to calculate the diffusion term. To enhance visual quality of ultrasound images, nonquadratic regularization (Yu and Yadegar, Proceedings of the IEEE international conference on image processing, 2006) is incorporated with MSRAD method and accordingly changes in parameter settings have been made. The performance of MSRAD method was evaluated using clinical ultrasound images, interpretation by the medical experts and results of MSRAD method by subjective and objective criteria. PMID:20574722

Mittal, Deepti; Kumar, Vinod; Saxena, Suresh Chandra; Khandelwal, Niranjan; Kalra, Naveen

2010-12-01

83

Split operator method for fluorescence diffuse optical tomography using anisotropic diffusion regularisation with prior anatomical information  

PubMed Central

Fluorescence diffuse optical tomography (fDOT) is an imaging modality that provides images of the fluorochrome distribution within the object of study. The image reconstruction problem is ill-posed and highly underdetermined and, therefore, regularisation techniques need to be used. In this paper we use a nonlinear anisotropic diffusion regularisation term that incorporates anatomical prior information. We introduce a split operator method that reduces the nonlinear inverse problem to two simpler problems, allowing fast and efficient solution of the fDOT problem. We tested our method using simulated, phantom and ex-vivo mouse data, and found that it provides reconstructions with better spatial localisation and size of fluorochrome inclusions than using the standard Tikhonov penalty term. PMID:22091447

Correia, Teresa; Aguirre, Juan; Sisniega, Alejandro; Chamorro-Servent, Judit; Abascal, Juan; Vaquero, Juan J.; Desco, Manuel; Kolehmainen, Ville; Arridge, Simon

2011-01-01

84

Perturbation Methods for Non-Markovian Quantum State Diffusion Equation  

E-print Network

Two perturbation methods for the non-Markovian quantum state diffusion (NMQSD) equation are investigated. The first perturbation method under investigation is based on a functional expansion of the NMQSD equation, while the second one expands the NMQSD equation in terms of the coupling strength. We have compared the advantages of the two methods based on bipartite systems where the accuracy of both perturbation methods can be examined by comparing the approximations with the exact solutions. Additionally, we provide an analytical solution for a special family of system's initial states, and the entanglement dynamics is discussed based on this solution.

Jie Xu; Xinyu Zhao; Jun Jing; Lian-Ao Wu; Ting Yu

2014-07-16

85

Novel integral method for the convection-diffusion heat equation  

SciTech Connect

Motivated by the desire to implement accurate and efficient nodal methods into thermal-hydraulics production codes, a nodal integral method (NIM) has been developed for the linear steady-state convection-diffusion heat equation and solved iteratively. Current NIMs for convection-diffusion problems employ direct solvers such as Newton-Raphson, rather then iterative schemes, which make them less suitable for use in large-scale production codes that use iterations between momentum and energy modules. The NIM developed here, for a given velocity field, solves the energy equation iteratively, making it possible to implement it as a module in production codes. The simple iterative scheme for the NIM described here converges very well and the method has a 0(h[sup 2]) error.

Michael, E.P.E.; Dorning, J.J.; Rizwan-uddin (Univ. of Virginia, Charlottesville, VA (United States)); Gelbard, E.M. (Argonne National Lab., IL (United States))

1993-01-01

86

Adsorptive removal of methylene blue by agar: effects of NaCl and ethanol  

PubMed Central

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

2012-01-01

87

Support Operators Method for the Diffusion Equation in Multiple Materials  

SciTech Connect

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.

Winters, Andrew R. [Los Alamos National Laboratory; Shashkov, Mikhail J. [Los Alamos National Laboratory

2012-08-14

88

ILLICO; A nodal neutron diffusion method for modern computer architectures  

Microsoft Academic Search

A nodal multigroup neutron diffusion method for modern computer architectures has been developed and implemented in the ILLICO code. Vectorization and parallelization strategies that are successful in speeding up modern nodal computations on commercially available supercomputers have been identified and applied. Realistic three-dimensional benchmark problems can be solved in the vectorized mode in >0.73 s (33.86 Mflops). Vector-concurrent implementations are

H. L. Rajic; A. M. Ougouag

1989-01-01

89

The determination of molecular diffusion coefficients by the barometric method  

Microsoft Academic Search

The binary molecular diffusion coefficients D\\u000a AB of a vaporizing liquid in gases under atmospheric conditions were measured by the new simple barometric method. A change\\u000a in the pressure of a vapor-gas mixture in a closed cell was determined as a function of time. Under experimental conditions,\\u000a one can also find partial saturated vapor pressures of substances. The deviations of

O. A. Kashirskaya; V. A. Lotkhov; V. V. Dil’man

2008-01-01

90

Newton-Krylov methods applied to nonequilibrium radiation diffusion  

SciTech Connect

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.

Knoll, D.A.; Rider, W.J.; Olsen, G.L.

1998-03-10

91

A diffusive information preservation method for small Knudsen number flows  

SciTech Connect

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.

Fei, Fei; Fan, Jing, E-mail: jfan@imech.ac.cn

2013-06-15

92

Diffusion  

NSDL National Science Digital Library

Diffusion is the net movement of particles from areas of high concentration (number of particles per unit area) to low concentration. In this activity, students use a molecular dynamics model to view the behavior of diffusion in gases and liquids.

Consortium, The C.

2011-12-11

93

Lattice Boltzmann method for double-diffusive natural convection  

NASA Astrophysics Data System (ADS)

A lattice Boltzmann method for double-diffusive natural convection is presented. The model combines a multicomponent lattice Boltzmann scheme with a finite-difference solution of the energy equation to simulate natural convection caused by gradients in temperature and concentration. The model is validated both in two and three dimensions, and the agreement with literature data is satisfactory. A case study of thermosolutal convection of air in a cubical enclosure with horizontal thermal and solutal gradients is presented, exhibiting a rich variety of flow structures.

Verhaeghe, F.; Blanpain, B.; Wollants, P.

2007-04-01

94

Lattice Boltzmann method for double-diffusive natural convection.  

PubMed

A lattice Boltzmann method for double-diffusive natural convection is presented. The model combines a multicomponent lattice Boltzmann scheme with a finite-difference solution of the energy equation to simulate natural convection caused by gradients in temperature and concentration. The model is validated both in two and three dimensions, and the agreement with literature data is satisfactory. A case study of thermosolutal convection of air in a cubical enclosure with horizontal thermal and solutal gradients is presented, exhibiting a rich variety of flow structures. PMID:17501014

Verhaeghe, F; Blanpain, B; Wollants, P

2007-04-01

95

Bacterial pathogens of otitis media and sinusitis: detection in the nasopharynx with selective agar media.  

PubMed

Carriage rates for the bacterial pathogens associated with otitis media (Streptococcus pneumoniae [SP], Hemophilus influenzae [HI], and Moraxella catarrhalis [MC]) are of interest. Culture on three selective agars was compared with culture on two standard agars to determine the more accurate method for detection of these species in the nasopharynx of healthy children. Weekly samples were obtained in winter from 18 healthy children (ages 1 through 9 years) as part of a longitudinal study. A 0.1-mL sample of 116 nasopharyngeal aspirate/washes was inoculated onto each of five agars. Two were standard (sheep blood and chocolate), and three were selective (blood with gentamicin for SP; chocolate with vancomycin, bacitracin, and clindamycin for HI; blood with amphotericin B, vancomycin, trimethoprim, and acetazolamide for MC). One technician read the standard plates and another the selective; both were blinded to the results of the other. SP was found in 44% of samples with selective agar versus 25% with standard agar; HI was found in 31% with selective versus 9% with standard; MC was found in 56% with selective versus 37% with standard. Overall, 80% of samples had one or more pathogens detected with selective agars as compared with 58% with standard agars (P =.0004). Selective agars were more accurate than standard agars for detecting otitis pathogens in the nasopharynx, where they are a common part of normal flora in healthy children. PMID:11709658

Dudley, S; Ashe, K; Winther, B; Hendley, J O

2001-11-01

96

Diffuse optical methods for assessing breast cancer chemotherapy  

NASA Astrophysics Data System (ADS)

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.

Tromberg, Bruce J.

2014-03-01

97

On matrix diffusion: formulations, solution methods and qualitative effects  

NASA Astrophysics Data System (ADS)

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 ?m2RmDm / Lm2, whereas late-time behavior (long tracer tests) depends only on ?mRm, 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 ?m2RmDm / Lm2, alors que le comportement à long terme (traçages de longue durée) ne dépend que de ?mRm, 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 ?m2RmDm / Lm2, mientras que el de tiempos largos depende sólo de ?mRm, 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

Carrera, Jesús; Sánchez-Vila, Xavier; Benet, Inmaculada; Medina, Agustín; Galarza, Germán; Guimerà, Jordi

98

Methods for Diffusive Relaxation in the $P_N$ Equations  

SciTech Connect

This study will investigate several numerical methods for modeling the transfer of neutral particles through a material medium, such as neutrons within a nuclear reactor. In a kinetic description, the particle evolution is governed by a transport equation, generally of the form (1.1) {partial_derivative}{sub t}F + v {center_dot} {del}{sub x}F = C(F). Here x {element_of} {Omega} {contained_in} R{sup 3} is a spatial coordinate, v {element_of} R{sup 3} is a velocity coordinate, t {ge} 0 is time, and the function F = F(x, v, t) is the non-negative distribution of particles in position-velocity phase space. The left-hand side of (1.1) describes the evolution of F along inertial trajectories, while the collision operator C on the right-hand side describes particle interactions with the medium via scattering and absorption/emission processes. Typically, there exists a diffusion limit for (1.1) in which F is approximated by a non-negative scalar function of space and time that satisfies a standard diffusion equation. This approximation is valid when collision processes dominate; i.e., when the mean free path between collisions is small compared to macroscopic variations in the system. Because collisions drive particles into equilibrium with the surrounding medium, long time scales (relative to the collision process) are required in order to observe diffusion dynamics. A common approach to solving (1.1) is with moment methods. In the moment approach, one tracks the evolution of a finite number of velocity moments of F. These moments, which are functions of space and time only, can then be used to reconstruct an approximation of F. Their evolution is approximated by a system of partial differential equations that are derived directly from (1.1). The exact form of these equations and the reconstruction of F is known as the closure problem. A basic requirement of any closure is that the resulting moment system has the same diffusion limit as the transport equation (1.1). Moment equations play an important role in so-called transition regimes, where collisions are frequent enough to impose macroscopic structure onto a particle system, but not frequent enough to validate the diffusion limit. Roughly speaking, as the number of particle interactions decreases, the system becomes less organized and more moments are needed for an accurate approximation of F. Thus simulations of multiscale transport phenomena can use moment equations in three fundamental ways: (1) As stand-alone models, with the flexibility to improve accuracy by adding more moments; (2) As preconditioners for more complicated models that may suffer from numerical stiffness; (3) In hybrid schemes that select components from a hierarchy of models in such a way as to maximize efficiency for a given level of accuracy. Thus additional moments, which can become computationally expensive, are used only in regimes where they are needed. For numerical simulations, the hyperbolic nature of many moment systems and the parabolic nature of the diffusion approximation are not always compatible. In such cases, the simulation of multi-scale problems with multiple temporal and spatial scales can be a challenge. In practice, there is a need for hyperbolic solvers that can handle shocks and discontinuities associated with streaming regimes (when the collisions are less frequent), but also behave like standard diffusion solvers in diffusive regimes. In particular, a hyperbolic solver should, in a specific asymptotic limit, reduce to a discretization of the relevant diffusion equation. This is the so-called asymptotic preserving property [27]. Unfortunately, hyperbolic solvers use numerical dissipation to capture discontinuities, and unless formulated carefully, this dissipation increases as the system approaches the diffusion limit. At some point in this limit process, the numerical dissipation dominates the actual physical diffusion in the system. Consequently, one may generate results which appear very well resolved, but are far from accurate. Another drawback of conventional hyperbolic so

Hauck, Cory D [ORNL; Lowrie, Robert B. [Los Alamos National Laboratory (LANL); Ryan, McClarren [Texas A& M University

2009-01-01

99

A review of chemical diffusion: Criticism and limits of simplified methods for diffusion coefficient calculation  

Microsoft Academic Search

A review of the physics and modelling of mass diffusion involving different gaseous chemical species is firstly proposed. Both accurate and simplified models for mass diffusion involve the calculation of individual species diffusion coefficients. Since these are computationally expensive, in CFD they are commonly estimated by assuming constant Lewis or Schmidt numbers for each chemical species. The constant Lewis number

E. Giacomazzi; F. R. Picchia; N. Arcidiacono

2008-01-01

100

Compact finite volume methods for the diffusion equation  

NASA Technical Reports Server (NTRS)

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.

Rose, Milton E.

1989-01-01

101

Stencil adaptive diffuse interface method for simulation of two-dimensional incompressible multiphase flows  

Microsoft Academic Search

Diffuse interface method is becoming a more and more popular approach for simulation of multiphase flows. As compared to other solvers, it is easy to implement and can keep conservation of mass and momentum. In the diffuse interface method, the interface is not considered as a sharp discontinuity. Instead, it treats the interface as a diffuse layer with a small

L. Ding; C. Shu; H. Ding; N. Zhao

2010-01-01

102

Physical-mechanical properties of agar/?-carrageenan blend film and derived clay nanocomposite film.  

PubMed

Binary blend films with different mixing ratio of agar and ?-carrageenan were prepared using a solution casting method with and without nanoclay and the effect of their composition on the mechanical, water vapor barrier, and water resistance properties was tested. The tensile strength (TS) of the ?-carrageenan film was greater than that of agar film. The water vapor permeability (WVP) of the agar film was lower than that of ?-carrageenan film, the swelling ratio (SR) and water solubility (WS) of ?-carrageenan film were higher than those of agar film. Each property of the binary blend films varied proportionately depending on the mixing ratio of each component. The XRD result indicated that the nanocomposite with agar/?-carrageenan/clay (Cloisite(®) Na(+)) was intercalated. Consequently, the mechanical strength, water vapor barrier properties, and water contact angle (CA) were significantly (P < 0.05) improved through nanocomposite formation. PMID:23170836

Rhim, Jong-Whan

2012-12-01

103

Physicochemical and morphological properties of plasticized poly(vinyl alcohol)-agar biodegradable films.  

PubMed

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 (?E) 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

Madera-Santana, T J; Freile-Pelegrín, Y; Azamar-Barrios, J A

2014-08-01

104

A Critical Study of Agglomerated Multigrid Methods for Diffusion  

NASA Technical Reports Server (NTRS)

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.

Nishikawa, Hiroaki; Diskin, Boris; Thomas, James L.

2011-01-01

105

A Critical Study of Agglomerated Multigrid Methods for Diffusion  

NASA Technical Reports Server (NTRS)

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.

Thomas, James L.; Nishikawa, Hiroaki; Diskin, Boris

2009-01-01

106

Electro-osmosis in gel -Application to Agar-Agar Fabien Cherblanc, Jer^ome Boscus, Jean-Claude Benet  

E-print Network

Electro-osmosis in gel - Application to Agar-Agar Fabien Cherblanc, J´er^ome Boscus, Jean-Claude B-engineering as a reference material, Agar-Agar gel is the focus of an experimental investigation concerning the electro-osmosis from liquid phase transport phenomena that take place in porous media (osmosis, electro-osmosis

Paris-Sud XI, Université de

107

A novel method for effective diffusion coefficient measurement in gas diffusion media of polymer electrolyte fuel cells  

NASA Astrophysics Data System (ADS)

A novel method for measuring effective diffusion coefficient of porous materials is developed. The oxygen concentration gradient is established by an air-breathing proton exchange membrane fuel cell (PEMFC). The porous sample is set in a sample holder located in the cathode plate of the PEMFC. At a given oxygen flux, the effective diffusion coefficients are related to the difference of oxygen concentration across the samples, which can be correlated with the differences of the output voltage of the PEMFC with and without inserting the sample in the cathode plate. Compared to the conventional electrical conductivity method, this method is more reliable for measuring non-wetting samples.

Yang, Linlin; Sun, Hai; Fu, Xudong; Wang, Suli; Jiang, Luhua; Sun, Gongquan

2014-07-01

108

Methicillin-Resistant Staphylococcus aureus (MRSA) Detection: Comparison of Two Molecular Methods (IDI-MRSA PCR Assay and GenoType MRSA Direct PCR Assay) with Three Selective MRSA Agars (MRSA ID, MRSASelect, and CHROMagar MRSA) for Use with Infection-Control Swabs  

Microsoft Academic Search

Methicillin-resistant Staphylococcus aureus (MRSA) is an increasing problem. Rapid detection of MRSA-colo- nized patients has the potential to limit spread of the organism. We evaluated the sensitivities and specificities of MRSA detection by two molecular methods (IDI-MRSA PCR assay and GenoType MRSA Direct PCR assay) and three selective MRSA agars (MRSA ID, MRSASelect, and CHROMagar MRSA), using 205 (101 nasal,

S. J. van Hal; D. Stark; B. Lockwood; D. Marriott; J. Harkness

2007-01-01

109

A novel agar formulation for isolation and direct enumeration of Vibrio vulnificus from oyster tissue.  

PubMed

A new selective and differential medium, Vibrio vulnificus X-Gal (VVX), was developed for direct enumeration of V. vulnificus (Vv) from oyster samples. This agar utilizes cellobiose and lactose as carbon sources, and the antibiotics colistin and polymyxin B as selective agents. Hydrolysis of 5-bromo-4-chloro-3-indolyl- beta-d-galactopyranoside (x-gal), used in the agar as a lactose analog, produces an insoluble blue dye that makes lactose positive colonies easily distinguishable from any non-lactose fermenting bacteria. Various bacterial species were spot plated onto thiosulfate-citrate-bile salts-sucrose agar (TCBS), and CHROMagar Vibrio, two vibrio-specific selective agars, non-selective agar, and VVX to compare selectivity of VVX to other widely used media. A V. vulnificus pure culture was serially diluted on VVX and non-selective agar to determine the VVX percent recovery. Water and oyster samples were spread plated on VVX agar and allowed to incubate for 16-18 h at 33 °C. Blue and white colonies from VVX agar were picked and screened by end point PCR for the Vv hemolysin vvhA. VVX agar showed a significant improvement over TCBS and CHROMagar at preventing non-target growth. There was an 87.5% recovery compared to non-selective plating and a 98% positivity rate of blue colonies picked from oyster tissue plating. The findings suggest that this new agar is a fast, distinctive, and accurate method for enumeration of V. vulnificus from the environment. PMID:23660708

Griffitt, Kimberly J; Grimes, D Jay

2013-08-01

110

SPACETIME FINITE ELEMENT METHODS FOR SURFACE DIFFUSION WITH APPLICATIONS TO  

E-print Network

­up of the body into a necklace of beads. The results of finite element calculations are compared governing diffusion in the surface of a body of revolution. The schemes share with the partial differential in an isotropic and homogeneous solid body by mass diffusion within the body's bounding surface S. We employ

111

An efficient semi-coarsening multigrid method for variable diffusion problems in cylindrical  

E-print Network

coefficient diffusion prob- lem written in cylindrical coordinates on a 3D domain = { (r, , z) | 0 An efficient semi-coarsening multigrid method for variable diffusion problems in cylindrical for solving the three-dimensional variable coefficient diffusion equa- tion in cylindrical coordinates

Wu, Chin-Tien

112

PRECONDITIONING A MIXED DISCONTINUOUS FINITE ELEMENT METHOD FOR RADIATION DIFFUSION  

SciTech Connect

We propose a multilevel preconditioning strategy for the iterative solution of large sparse linear systems arising from a finite element discretization of the radiation diffusion equations. In particular, these equations are solved using a mixed finite element scheme in order to make the discretization discontinuous, which is imposed by the application in which the diffusion equation will be embedded. The essence of the preconditioner is to use a continuous discretization of the original, elliptic diffusion equation for preconditioning the discontinuous equations. We have found that this preconditioner is very effective and makes the iterative solution of the discontinuous diffusion equations practical for large problems. This approach should be applicable to discontinuous discretizations of other elliptic equations. We show how our preconditioner is developed and applied to radiation diffusion problems on unstructured, tetrahedral meshes and show numerical results that illustrate its effectiveness.

JAMES S. WARSA; MICHELE BENZI; TODD A. WAREING; JIM E. MOREL

2002-06-18

113

Nonconforming streamline-diffusion-finite-element-methods for convection-diffusion problems  

Microsoft Academic Search

Summary.   We analyze nonconforming finite element approximations of streamline-diffusion type for solving convection-diffusion problems.\\u000a Both the theoretical and numerical investigations show that additional jump terms have to be added in the nonconforming case\\u000a in order to get the same order of convergence in L as in the conforming case for convection dominated problems. A rigorous error analysis supported by numerical

V. John; JML Maubach; L. Tobiska

1997-01-01

114

Migration of chemotactic bacteria in soft agar: role of gel concentration  

E-print Network

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 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.

O. A. Croze; G. P. Ferguson; M. E. Cates; W. C. K. Poon

2011-01-26

115

Water vapor adsorption isotherms of agar-based nanocomposite films.  

PubMed

Adsorption isotherms of agar and agar/clay nanocomposite films prepared with different types of nanoclays, that is, a natural montmorillonite (Cloisite Na(+) ) and 2 organically modified montmorillonites (Cloisite 30B and Cloisite 20A), were determined at 3 different temperatures (10, 25, and 40 °C). The water vapor adsorption behavior of the nanocomposite films was found to be greatly influenced with the type of clay. The Guggenheim-Anderson-de Boer (GAB) isotherm model parameters were estimated by using both polynomial regression and nonlinear regression methods and it was found that the GAB model fitted adequately for describing experimental adsorption isotherm data for the film samples. The monolayer moisture content (m(o) ) of the film samples was also greatly affected by the type of nanoclay used, that is, m(o) of nanocomposite films was significantly lower than that of the neat agar film. Nanocomposite films prepared with hydrophobic nanoclays (Cloisite 30B and Cloisite 20A) exhibited lower m(o) values than those prepared with hydrophilic nanoclay (Cloisite Na(+) ). PMID:22417601

Rhim, Jong-Whan

2011-10-01

116

Cation Concentration Variability of Four Distinct Mueller-Hinton Agar Brands Influences Polymyxin B Susceptibility Results  

PubMed Central

Polymyxins have been the only alternative therapeutic option for the treatment of serious infections caused by multidrug-resistant Acinetobacter baumannii or Pseudomonas aeruginosa isolates. For this reason, it is of crucial importance that susceptibility tests provide accurate results when testing these drug-pathogen combinations. In this study, the effect of cation concentration variability found on different commercial brands of Mueller-Hinton agar (MHA) for testing polymyxin B susceptibility was evaluated. The polymyxin B susceptibilities determined using Etest and disk diffusion were compared to those determined by the CLSI reference broth microdilution method. In general, the polymyxin B MIC values were higher when determined by Etest than when determined by broth microdilution against both A. baumannii and P. aeruginosa isolates. A high very major error rate (10%) was observed, as well as a trend toward lower MICs, compared to those determined by broth microdilution when the Merck MHA was tested by Etest. Poor essential agreement rates (10 to 70%) were observed for P. aeruginosa when all MHA brands were tested by Etest. Although an excellent categorical agreement rate (100%) was seen between the disk diffusion and broth microdilution methods for P. aeruginosa, larger zones of inhibition were shown obtained using the Merck MHA. The high cation concentration variability found for the MHA brands tested correlated to the low accuracy, and discrepancies in the polymyxin B MICs were determined by Etest method, particularly for P. aeruginosa isolates. PMID:22553247

Bispo, Paulo J. M.; Yamanaka, Tiago M.; Gales, Ana C.

2012-01-01

117

Diffusion  

NSDL National Science Digital Library

Diffusion is the movement of particles from an area of high concentration to an area of low concentration. The molecules move until equilibrium is reached. If a perfume is sprayed on one side of the room, the perfume molecules will eventually spread out all over the room until there are equal concentrations of the molecules throughout the space.

Christopher Thomas (None;)

2006-11-09

118

Agar Medium for Differential Enumeration of Lactic Streptococci1  

PubMed Central

An agar medium containing arginine and calcium citrate as specific substrates, diffusible (K2HPO4) and undiffusible (CaCO3) buffer systems, and bromocresol purple as the pH indicator was developed to differentiate among lactic streptococci in pure and mixed cultures. Milk was added as the sole source of carbohydrate (lactose) and to provide growth-stimulating factors. Production of acid from lactose caused developing bacterial colonies to seem yellow. Subsequent arginine utilization by Streptococcus lactis and S. diacetilactis liberated ammonia, resulting in a localized pH shift back toward neutrality and a return of the original purple indicator hue. The effects of production of acid from lactose and ammonia were fixed around individual colonies by the buffering capacity of CaCO3. After 36 hr at 32 C in a candle oats jar, colonies of S. cremoris were yellow, whereas colonies of S. lactis and S. diacetilactis were white. S. diacetilactis, on further incubation, utilized suspended calcium citrate, and, after 6 days, the citrate-degrading colonies exhibited clear zoning against a turbid background, making them easily distinguishable from the colonies of the other two species. The medium proved suitable for quantitative differential enumeration when compared with another widely used general agar medium for lactic streptococci. Images PMID:16349952

Reddy, M. S.; Vedamuthu, E. R.; Washam, C. J.; Reinbold, G. W.

1972-01-01

119

AEROSOL SIZE MEASUREMENT BY ELECTRICAL MOBILITY AND DIFFUSION ANALYSIS - A COMPARISON OF METHODS  

EPA Science Inventory

The principle of the electrical aerosol analyzer method is reviewed and the diffusion battery method is described in detail. An appendix explains the basis of the calculations used. The diffusion battery method is complicated by counting losses of very small particles, inherent t...

120

Syneresis and delayed detachment in agar plates  

E-print Network

Biogels made of crosslinked polymers such as proteins or polysaccharides behave as porous soft solids and store large amount of solvent. These gels undergo spontaneous aging, called syneresis that consists in the shrinkage of the gel matrix and the progressive expulsion of the solvent, which eventually leads to the gel detachment from its container. Here we report on the syneresis phenomena in agar plates that consist in Petri dishes filled with a gel mainly composed of agar. Direct observations and speckle pattern correlation analyses allow us to rationalize the delayed detachment of the gel from the sidewall of the Petri dish. The detachment time $t^*$ is mainly controlled by the gel minimum thickness $e_{min}$ along the periphery of the plate: $t^*$ increases as a robust function of $e_{min}$ that neither depends on the age of the gel nor on any previous mass loss. Time-resolved correlation spectroscopy reveals that the speckle decorrelation rate increases a few hours before $t^*$ and that the gel detachment can be anticipated. This work provides quantitative observables to predict the shelf life of agar plates and highlights the key role of the competition between the syneresis and the gel adhesion to the wall in the detachment process.

Thibaut Divoux; Bosi Mao; Patrick Snabre

2014-10-30

121

A hidden pitfall in the preparation of agar media undermines microorganism cultivability.  

PubMed

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-27(T) 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

Tanaka, Tomohiro; Kawasaki, Kosei; Daimon, Serina; Kitagawa, Wataru; Yamamoto, Kyosuke; Tamaki, Hideyuki; Tanaka, Michiko; Nakatsu, Cindy H; Kamagata, Yoichi

2014-12-15

122

Diffusion  

NSDL National Science Digital Library

Since the advent of the internet, a number of artists and related organizations have become interested in utilizing the web to promulgate new forms of artistic creation and their subsequent dissemination. Supported by the Arts Council of England, these Diffusion eBooks are essentially pdf files that readers can download, print out and make into booklets. As the site suggests, "the Diffusion format challenges conventions of interactivity-blending the physical and the virtual and breaking the dominance of mouse and screen as the primary forms of human computer interaction...the format's aim is to take the reader away from the screen and computer and engage them in the process of production." There are a number of creative booklets available here for visitors, complete with instruction on how to assemble them for the desired effect. For anyone with even a remote interest in the possibilities afforded by this rather curious new form of expression, this website is worth a look.

123

Susceptibilities of 201 Anaerobes to Erythromycin, Azithromycin, Clarithromycin, and Roxithromycin by Oxyrase Agar Dilution and E test Methodologies  

Microsoft Academic Search

The susceptibility of 201 anaerobes to erythromycin, azithromycin, clarithromycin, and roxithromycin was tested by agar dilution and E test methods by using a commercially available plate and dish system (OxyDish) to provide anaerobic conditions. Plates were incubated for 48 h. MICs for 50% of strains tested and MICs for 90% of strains tested by agar dilution and E test methods

S. K. SPANGLER; M. R. JACOBS; C. APPELBAUM

1995-01-01

124

A Multiresolution Method for Parameter Estimation of Diffusion Processes  

PubMed Central

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.

Kou, S. C.; Olding, Benjamin P.; Lysy, Martin; Liu, Jun S.

2014-01-01

125

Multilevel methods for transport equations in diffusive regimes  

NASA Technical Reports Server (NTRS)

We consider the numerical solution of the single-group, steady state, isotropic transport equation. An analysis by means of the moment equations shows that a discrete ordinate S(sub N) discretization in direction (angle) with a least squares finite element discretization in space does not behave properly in the diffusion limit. A scaling of the S(sub N) equations is introduced so that the least squares discretization has the correct diffusion limit. For the resulting discrete system a full multigrid algorithm was developed.

Manteuffel, Thomas A.; Ressel, Klaus

1993-01-01

126

Multiscale Finite-Difference-Diffusion-Monte-Carlo Method for Simulating Dendritic Solidification  

Microsoft Academic Search

We present a novel hybrid computational method to simulate accurately dendritic solidification in the low undercooling limit where the dendrite tip radius is one or more orders of magnitude smaller than the characteristic spatial scale of variation of the surrounding thermal or solutal diffusion field. The first key feature of this method is an efficient multiscale diffusion Monte Carlo (DMC)

Mathis Plapp; Alain Karma

2000-01-01

127

A Level Set Method for Anisotropic Geometric Diffusion in 3D Image Processing  

E-print Network

A Level Set Method for Anisotropic Geometric Diffusion in 3D Image Processing Tobias PreuÃ?er. A noisy 3D echocardiographical dataset (top left) is evolved by isotropic Perona Malik diffusion (top and Martin Rumpf Abstract--A new morphological multiscale method in 3D image process- ing is presented which

Preusser, Tobias

128

Atomic diffusion theory challenging the Cahn-Hilliard method  

NASA Astrophysics Data System (ADS)

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.

Nastar, M.

2014-10-01

129

Comparative evaluation of chromogenic agar medium and conventional culture system for isolation and presumptive identification of uropathogens  

PubMed Central

Objective: Urine is the most frequent specimen received for culture/sensitivity by clinical laboratories. The microbiological performance of HiCrome UTI agar medium was compared with Blood agar and MacConkey agar for isolation and presumptive identification of bacteria from urine culture. Methods: A total of 443 consecutively collected midstream and/or catheter-catch urine samples from patients attending the Islami Bank Medical College Hospital, Rajshahi, Bangladesh during January to December, 2012 were cultured. Urine samples showing pus cells ? 5/HPF were inoculated on to Blood agar (BA), MacConkey agar (MAC) and HiCrome UTI agar (CA) media simultaneously and incubated overnight aerobically at 370C. Rate of isolation and presumptive identification of bacterial species were compared for different media. Results: Culture yielded a total of 199 bacterial isolates from 189 (42.67%) positive plates including 179 (40.40%) unimicrobial and 10 (2.26%) polymicrobial (mixed growth of pair of bacteria) growths. Both HiCrome UTI agar and Blood agar media supported 100% growths while 151 (75.88%) growths were observed on MacConkey agar. The rate of presumptive identification was found significantly higher on HiCrome UTI agar (97.49%) than MAC agar (67.34%) (P<0.001) as primary urine culture medium. Of 199 isolates, E. coli was found to be the leading uropathogen isolated from 118 (59.30%) samples with its presumptive identification rate of 95.76%, 93.22% and 5.93% on CA, MAC and BA respectively. All 10 (100%) polymicrobial growths were demonstrated distinctly on CA against only 01(10%) on each BA and MAC. Conclusion: HiCrome UTI agar was found to be more useful as primary urine culture medium in both higher rate of isolation and presumptive identification of uropathogens in comparison to conventional media. Its inherent characteristics in demonstrating polymicrobial growth and ease of rapid identification by distinct colony colour are unique.

Akter, Laila; Haque, Rezwana; Salam, Md. Abdus

2014-01-01

130

Diffusion NMR methods applied to xenon gas for materials study.  

PubMed

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. PMID:12807139

Mair, R W; Rosen, M S; Wang, R; Cory, D G; Walsworth, R L

2002-12-01

131

Diffusion NMR methods applied to xenon gas for materials study  

NASA Technical Reports Server (NTRS)

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.

Mair, R. W.; Rosen, M. S.; Wang, R.; Cory, D. G.; Walsworth, R. L.

2002-01-01

132

Ultrasonic backscatter coefficients for weakly scattering, agar spheres in agar phantoms  

PubMed Central

Applicability of ultrasound phantoms to biological tissue has been limited because most phantoms have generally used strong scatterers. The objective was to develop very weakly scattering phantoms, whose acoustic scattering properties are likely closer to those of tissues and then compare theoretical simulations and experimental backscatter coefficient (BSC) results. The phantoms consisted of agar spheres of various diameters (nominally between 90 and 212 ?m), containing ultrafiltered milk, suspended in an agar background. BSC estimates were performed at two institutions over the frequency range 1–13 MHz, and compared to three models. Excellent agreement was shown between the two laboratory results as well as with the three models. PMID:20707460

King, Michael R.; Anderson, Janelle J.; Herd, Maria-Teresa; Ma, Darryl; Haak, Alexander; Wirtzfeld, Lauren A.; Madsen, Ernest L.; Zagzebski, James A.; Oelze, Michael L.; Hall, Timothy J.; O’Brien, William D.

2010-01-01

133

Evaluation of Three Techniques for Detection of Low-Level Methicillin-Resistant Staphylococcus aureus (MRSA): a Disk Diffusion Method with Cefoxitin and Moxalactam, the Vitek 2 System, and the MRSA-Screen Latex Agglutination Test  

PubMed Central

Very-low-level methicillin-resistant Staphylococcus aureus (MRSA), or class 1 MRSA, is often misdiagnosed as methicillin-susceptible S. aureus (MSSA). We evaluated the performances of three methods for detection of low-level methicillin resistance: the disk diffusion method using the cephamycin antibiotics cefoxitin and moxalactam, the Vitek 2 system (bioMérieux), and the MRSA-screen test (Denka). Detection of the mecA gene by PCR was considered to be the “gold standard.” We also determined the sensitivity of the oxacillin disk diffusion method with 5- and 1-?g disks and that of the Oxascreen agar assay with 6 mg of oxacillin liter?1 for detection of MRSA. We compared the distributions of MICs of oxacillin and cefoxitin by the E-test (AB Biodisk), and those of moxalactam by dilutions in agar, for MRSA and MSSA isolates. The 152 clinical isolates of S. aureus studied were divided into 69 MSSA (mecA-negative) and 83 MRSA (mecA-positive) isolates, including 63 heterogeneous isolates and 26 class 1 isolates (low-level resistance). The cefoxitin and moxalactam disk diffusion tests detected 100% of all the MRSA classes: cefoxitin inhibition zone diameters were <27 mm, and moxalactam inhibition zone diameters were <24 mm. The Vitek 2 system and the MRSA-screen test detected 94 and 97.6% of all MRSA isolates, respectively. The sensitivities of the 5- and 1-?g oxacillin disks were 95.2 and 96.4%, respectively, whereas that of the Oxascreen agar screen assay was 94%. All of the tests except the 1-?g oxacillin disk test were 100% specific. For the class 1 MRSA isolates, the sensitivity of the Vitek 2 test was 92.3%, whereas those of the MRSA-screen test and the disk diffusion method with cefoxitin and moxalactam were 100%. Therefore, the cefoxitin and moxalactam disk diffusion methods were the best-performing tests for routine detection of all classes of MRSA. PMID:12149327

Felten, Annie; Grandry, Bernadette; Lagrange, Philippe Henri; Casin, Isabelle

2002-01-01

134

Exact on-lattice stochastic reaction-diffusion simulations using partial-propensity methods  

NASA Astrophysics Data System (ADS)

Stochastic reaction-diffusion systems frequently exhibit behavior that is not predicted by deterministic simulation models. Stochastic simulation methods, however, are computationally expensive. We present a more efficient stochastic reaction-diffusion simulation algorithm that samples realizations from the exact solution of the reaction-diffusion master equation. The present algorithm, called partial-propensity stochastic reaction-diffusion (PSRD) method, uses an on-lattice discretization of the reaction-diffusion system and relies on partial-propensity methods for computational efficiency. We describe the algorithm in detail, provide a theoretical analysis of its computational cost, and demonstrate its computational performance in benchmarks. We then illustrate the application of PSRD to two- and three-dimensional pattern-forming Gray-Scott systems, highlighting the role of intrinsic noise in these systems.

Ramaswamy, Rajesh; Sbalzarini, Ivo F.

2011-12-01

135

Comparative Study for Determination of Mycobacterium tuberculosis Susceptibility to First- and Second-Line Antituberculosis Drugs by the Etest Using 7H11, Blood, and Chocolate Agar?  

PubMed Central

We investigated the performance of blood and chocolate agar as alternatives to Middlebrook 7H11 agar for testing the susceptibility of Mycobacterium tuberculosis to first-and second-line drugs by the Etest method. A total of 39 strains of M. tuberculosis including 22 multidrug-resistant M. tuberculosis strains and 17 susceptible strains were tested. In conclusion, our results showed that chocolate agar gave insufficient growth, needing up to 21 days of incubation, while results on blood agar were comparable to those on Middlebrook 7H11 agar and can be further explored as an alternative for Etest-based susceptibility testing of M. tuberculosis. PMID:18945843

Coban, Ahmet Yilmaz; Bilgin, Kemal; Uzun, Meltem; Akgunes, Alper; Yusof, Anne; Durupinar, Belma

2008-01-01

136

A multigrid Newton-Krylov method for flux-limited radiation diffusion  

SciTech Connect

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.

Rider, W.J.; Knoll, D.A.; Olson, G.L.

1998-09-01

137

Finite element methods for time-dependent convectiondiffusionreaction equations with small diffusion  

E-print Network

of the flow fields in 2D or performing simu- lations in 3D (on coarser grids) led to a piling up to the size of the flow field. That means, the convection­diffusion­reaction equations are convectionFinite element methods for time-dependent convection­diffusion­reaction equations with small

John, Volker

138

A fully implicit method for 3D quasi-steady state magnetic advection-diffusion.  

SciTech Connect

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.

Siefert, Christopher; Robinson, Allen Conrad

2009-09-01

139

Cosmic-ray diffusion modeling: Solutions using variational methods  

NASA Astrophysics Data System (ADS)

The diffusion of energetic particles in turbulent magnetic fields is usually described via the two-point, two-time velocity correlation function. A variational principle is used to determine the characteristic function that results from the Fourier-transformed correlation function. Both for a linear approximation and for the wave vector set to zero, explicit solutions are derived that depend on the Fokker-Planck coefficient of pitch-angle scattering. It is shown that, for an isotropic form of the Fokker-Planck coefficient, the characteristic function is divergent, which can be remedied only by using a Fokker-Planck coefficient that is finite at all pitch angles.

Tautz, R. C.; Lerche, I.

2013-05-01

140

Experimental Verification to Obtain Intrinsic Thermal Diffusivity by Laser-Flash Method  

NASA Astrophysics Data System (ADS)

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.

Akoshima, M.; Hay, B.; Neda, M.; Grelard, M.

2013-05-01

141

Recovery of spores of Clostridium botulinum in yeast extract agar and pork infusion agar after heat treatment.  

PubMed Central

Yeast extract agar, pork infusion agar, and modifications of these media were used to recover heated Clostridium botulinum spores. The D- and z-values were determined. Two type A strains and one type B strain of C. botulinum were studied. In all cases the D-values were largest when the spores were recovered in yeast extract agar, compared to the D-values for spores recovered in pork infusion agar. The z-values for strains 62A and A16037 were largest when the spores were recovered in pork infusion agar. The addition of sodium bicarbonate and sodium thioglycolate to pork infusion agar resulted in D-values for C. botulinum 62A spores similar to those for the same spores recovered in yeast extract agar. The results suggest that sodium bicarbonate and sodium thioglycolate should be added to recovery media for heated C. botulinum spores to obtain maximum plate counts. PMID:335970

Odlaug, T E; Pflug, I J

1977-01-01

142

A Local Incident Flux Response Expansion Transport Method for Coupling to the Diffusion Method in Cylindrical Geometry  

SciTech Connect

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.

Dingkang Zhang; Farzad Rahnema; Abderrafi M. Ougouag

2013-09-01

143

Eigenfunction methods in magnetospheric radial-diffusion theory  

NASA Technical Reports Server (NTRS)

Complete sets of orthonormal basis functions constructed according to a generalization of the quantum-mechanical WKB approximation can be used to generate a nearly-diagonal matrix representation of the radial-transport operator for ring-current ions in the presence of radial diffusion and charge exchange. The resulting eigenfunctions (constructed by weighting the basis functions in proportion to the respective components of the eigenvectors of the matrix representation) and eigenvalues provide a spatial and temporal description of the evolving phase-space density during and following a magnetospheric disturbance (e.g., a magnetic storm). A linear superposition of the basis functions can also be used to eliminate any discrepancy between the steady-state solution of the transport equation and the appropriate WKB approximation of this steady-state solution.

Schulz, Michael

1986-01-01

144

Complex diffusion Monte-Carlo method: test by the simulation of the 2D fermions  

Microsoft Academic Search

On the base of the diffusion Monte-Carlo method we develop the method allowing to simulate the quantum systems with complex wave function. The method is exact and there are no approximations on the simulations of the module and the phase of the system's wave function. In our method averaged value of any quantity have no direct contribution from the phase

B. Abdullaev; M. Musakhanov; A. Nakamura

2001-01-01

145

Accurate determination of specific heat at high temperatures using the flash diffusivity method  

NASA Technical Reports Server (NTRS)

The flash diffusivity method of Parker et al. (1961) was used to measure accurately the specific heat of test samples simultaneously with thermal diffusivity, thus obtaining the thermal conductivity of these materials directly. The accuracy of data obtained on two types of materials (n-type silicon-germanium alloys and niobium), was + or - 3 percent. It is shown that the method is applicable up to at least 1300 K.

Vandersande, J. W.; Zoltan, A.; Wood, C.

1989-01-01

146

The simulation of transport processes using the method of molecular dynamics. Self-diffusion coefficient  

Microsoft Academic Search

The possibility is investigated of using the method of molecular dynamics for calculating the self-diffusion coefficient of\\u000a liquids and gases. The exactness of calculation of the autocorrelation function of the velocity of molecules and of the self-diffusion\\u000a coefficient is systematically estimated. The characteristic errors of the method are analyzed. Correlations are constructed\\u000a which enable one to reduce the effect made

V. Ya. Rudyak; A. A. Belkin; D. A. Ivanov; V. V. Egorov

2008-01-01

147

Evaluation of CP Chromo Select Agar for the enumeration of Clostridium perfringens from water.  

PubMed

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

Manafi, Mammad; Waldherr, Kerstin; Kundi, Michael

2013-10-01

148

Chocolate agar, a differential medium for gram-positive cocci.  

PubMed Central

Reactions incurred on chocolate agar by gram-positive cocci were correlated with species identity. Darkening and clearing of the medium was usually associated with the species Staphylococcus epidermidis, Staphylococcus aureus, Staphylococcus simulans, and Streptococcus faecalis. Yellowing of chocolate agar was associated with alpha-hemolytic species of Streptococcus. The study demonstrated that reactions occurring on chocolate agar are useful in identifying gram-positive cocci. PMID:6490866

Gunn, B A

1984-01-01

149

Antimicrobial potentials of Mentha longifolia by disc diffusion method.  

PubMed

This study was conducted for the assessment of the antimicrobial activities of different solvents extracted samples from the aerial parts of Mentha longifolia against ten microbial species through the disc diffusion assay using two different concentrations of 1 and 2 mg disc1. All extracts from Mentha longifolia showed different ranges of antimicrobial activities. Butanol and ethyl acetate fractions showed inhibitory activities against all microbial species. Methanol fraction showed inhibitory effects against all the tested microbial species except Salmonella typhi. Salmonella typhi was also not controlled by methanol, petroleum ether and dichloromethane extracted samples. The most susceptible gram positive bacteria was Bacillus atropheus and Bacillus subtilis and were inhibited by all extracts and Staphylococus aureus was least susceptible among gram positive bacteria. Klebsiella pneumoniae was the most susceptible gram negative bacterium and Salmonella typhi was highly resistant among the gram negative bacteria. Erwinia carotovora and Agrobacterium tumefaciene were susceptible to all fractions. All fractions showed antifungal activities against Candida albicans except water extracted samples. PMID:25015464

Bakht, Jehan; Shaheen, Salma; Shafi, Mohammad

2014-07-01

150

Sol state formation and melting of agar gels rheological study  

NASA Astrophysics Data System (ADS)

The effect of temperature and molecular weight, on the conformational properties of agar aqueous solutions is reported. Equations of the viscosity agar solutions for different concentrations, and molecular weight, are given. The thermoreversible sol gel transition in agar gel is studied by small deformation oscillatory measurements of storage G? and loss modulus G?. The gelation and melting temperatures are given for different concentrations and molecular weights. Gelation enthalpies are calculated by the Ferry-Eldrige model, effect of nature and molecular weight of agar are discussed.

Lahrech, Kh.; Safouane, A.; Peyrellasse, J.

2005-12-01

151

21 CFR 866.4600 - Ouchterlony agar plate.  

Code of Federal Regulations, 2010 CFR

...AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES IMMUNOLOGY AND MICROBIOLOGY DEVICES Immunology Laboratory Equipment and Reagents § 866.4600 Ouchterlony agar plate. (a)...

2010-04-01

152

21 CFR 866.4600 - Ouchterlony agar plate.  

Code of Federal Regulations, 2013 CFR

...AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES IMMUNOLOGY AND MICROBIOLOGY DEVICES Immunology Laboratory Equipment and Reagents § 866.4600 Ouchterlony agar plate. (a)...

2013-04-01

153

Operator Splitting Implicit Integration Factor Methods for Stiff Reaction-Diffusion-Advection Systems  

PubMed Central

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

Zhao, Su; Ovadia, Jeremy; Liu, Xinfeng; Zhang, Yong-Tao; Nie, Qing

2011-01-01

154

Mass production of spores of lactic acid-producing Rhizopus oryzae NBRC 5384 on agar plate.  

PubMed

Mass production of sporangiospores (spores) of Rhizopus oryzae NBRC 5384 (identical to NRRL 395 and ATCC 9363) on potato-dextrose-agar medium was studied aiming at starting its L(+)-lactic acid fermentation directly from spore inoculation. Various parameters including harvest time, sowed spore density, size of agar plate, height of air space, and incubation mode of plate (agar-on-bottom or agar-on-top) were studied. Ordinarily used shallow Petri dishes were found out to be unsuitable for the full growth of R. oryzae sporangiophores. In a very wide range of the sowed spore density, the smaller it was, the greater the number of the harvested spores was. It was also interesting to find out that R. oryzae grown downward vertically with a deep air space in an agar-on-top mode gave larger amount of spores than in an agar-on-bottom mode at 30°C for 7-day cultivation. Scale-up of the agar plate culture from 26.4 to 292 cm(2) was studied, resulting in the proportional relationship between the number of the harvested spores/plate and the plate area in the deep Petri dishes. The number of plates of 50 cm in diameter needed for 100 m(3) industrial submerged fermentation started directly from 2 × 10(5) spores/mL inoculum size was estimated as about 6, from which it was inferred that such a fermentation would be feasible. Designing a 50 cm plate and a method of spreading and collecting the spores were suggested. Bioprocess technological significance of the "full-scale industrial submerged fermentation started directly from spore inoculation omitting pre-culture" has been discussed. PMID:23658025

Yamane, Tsuneo; Tanaka, Ryosuke

2013-01-01

155

Production of microbial medium from defatted brebra (Milletia ferruginea) seed flour to substitute commercial peptone agar  

PubMed Central

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

Andualem, Berhanu; Gessesse, Amare

2013-01-01

156

Antileishmanial activity of drug infused mini-agar plates on Leishmania donovani promastigotes.  

PubMed

Drug infused mini agar plates were found to be a better alternative of broth dilution method in the determination of antileishmanial susceptibility of two commonly used drugs, Sodium antimony gluconate and Amphotericin B against Leishmania donovani promastigotes. These two drugs were used here as models for antileishmanial compounds. The stability of the drugs in the stored agar plates was also tested for six months and found that they were same as fresh plates. Determination of antileishmanial susceptibility of Leishmania donovani promastigotes to compounds of screening by this method is quite inexpensive, simple to perform even in under-sophisticated laboratories of developing countries where the disease is endemic. PMID:21399608

Muniaraj, M; Sinha, P K; Das, P

2010-12-01

157

A coarse-mesh nodal method-diffusive-mesh finite difference method  

SciTech Connect

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.

Joo, H.; Nichols, W.R.

1994-05-01

158

Method of applying a cerium diffusion coating to a metallic alloy  

DOEpatents

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).

Jablonski, Paul D. (Salem, OR); Alman, David E. (Benton, OR)

2009-06-30

159

A new method of optimal design for a two-dimensional diffuser by using dynamic programming  

NASA Technical Reports Server (NTRS)

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.

Gu, Chuangang; Zhang, Moujin; Chen, XI; Miao, Yongmiao

1991-01-01

160

First-Order Hyperbolic System Method for Time-Dependent Advection-Diffusion Problems  

NASA Technical Reports Server (NTRS)

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.

Mazaheri, Alireza; Nishikawa, Hiroaki

2014-01-01

161

Method of fluxless brazing and diffusion bonding of aluminum containing components  

NASA Technical Reports Server (NTRS)

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.

Featherston, A. B.; Okelly, K. P. (inventors)

1976-01-01

162

Combined relaxation and displacement experiment: a fast method to acquire T 2, diffusion and velocity maps  

Microsoft Academic Search

A fast method for quantitative imaging of T2 and displacement (flow and diffusion) is presented. The pulse sequence combines multi-PGSE NMR with multi-echo acquisition and compensates for flow effects in the read gradient and diffusion during multi-echo trains. The impact of the gradient pulses in a multi-echo train on the signal phase and amplitude is discussed. It is shown that

Bertram Manz

2004-01-01

163

Practical method of diffusion-welding steel plate in air  

NASA Technical Reports Server (NTRS)

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.

Holko, K. H.; Moore, T. J.

1971-01-01

164

Comments on use of a disk diffusion method with cefoxitin (30 µg) to detect of methicillin-resistant Staphylococcus aureus  

Microsoft Academic Search

In their evaluation of the cefoxitin disk diffusion method compared to the gold standard PCR for the detection of the mecA gene in 155 clinical isolates of Staphylococcus aureus screened for the methicillin resistance profile, Cauwelier et al. [1] found that cefoxitin disk diffusion proved better than the oxacillin disk diffusion method. At the Sant Parmanand Hospital in New Delhi,

S. C. Arya; S. Kapoor; N. Agarwal; R. Bhasin; S. George

2004-01-01

165

Washington State University: Defects and Diffusion studied by Hyperfine Methods  

NSDL National Science Digital Library

The Hyperfine Interactions Laboratory at Washington State University addresses its research of "how solids are affected by mechanical, thermal, chemical, or irradiation treatment" with atom-scale resolution. Students and researchers can discover their nuclear hyperfine interactions methods. To learn about the Laboratory's research, users can find detailed descriptions, pictures, publications, meeting abstracts, and more. The website features undergraduate, graduate, postdocs, and visiting scientist research opportunities. Users can also find out about the International Conference on Hyperfine Interactions held in August 2004.

166

Comparison of agar based media for primary isolation of Helicobacter pylori.  

PubMed Central

AIMS--To determine the best medium for the primary isolation of Helicobacter pylori. METHODS--Sixty six gastric mucosal biopsy specimens frozen in 1 ml Cysteine Albimi media with 20% glycerol from 22 histologically proven H pylori infected patients were cultured on brain heart infusion agar (BHIA) with 7% fresh whole defibrinated horse blood, egg yolk agar (EYA), Columbia blood agar-cyclodextrin agar (CBA-Cd), and commercial trypticase soy agar (TSA) supplemented with 5% sheep blood. RESULTS--Successful primary isolation of H pylori was 96% with BHIA, 78% with TSA, 64% for EYA, and 32% with CBA-Cd. Colonies appeared earlier on BHIA (4.7 +/- 0.1 days, 5.3 +/- 0.4 days, 5.3 +/- 0.4 days, and 7.1 +/- 0.9 days for BHIA, TSA, EYA, and CBA-Cd) and there were more colonies on BHIA than on CBA-Cd, EYA or TSA (599 +/- 88, 104 +/- 66, 260 +/- 107, and 358 +/- 89, respectively). CONCLUSIONS--Success of a medium for passage of isolates apparently does not reliably predict usefulness for primary isolation. Freshly made BHIA with 7% horse blood medium is recommended for primary isolation. However, the easily obtainable TSA media would be the best alternative for routine clinical laboratories with no access to BHIA. Images PMID:7560195

Hachem, C Y; Clarridge, J E; Evans, D G; Graham, D Y

1995-01-01

167

Advanced computational methods for nodal diffusion, Monte Carlo, and S(sub N) problems  

NASA Astrophysics Data System (ADS)

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.

Martin, W. R.

1993-01-01

168

Accelerated molecular dynamics and equation-free methods for simulating diffusion in solids.  

SciTech Connect

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.

Deng, Jie; Zimmerman, Jonathan A.; Thompson, Aidan Patrick; Brown, William Michael (Oak Ridge National Laboratories, Oak Ridge, TN); Plimpton, Steven James; Zhou, Xiao Wang; Wagner, Gregory John; Erickson, Lindsay Crowl

2011-09-01

169

A method of online quantitative interpretation of diffuse reflection profiles of biological tissues  

NASA Astrophysics Data System (ADS)

We have developed a method of combined interpretation of spectral and spatial characteristics of diffuse reflection of biological tissues, which makes it possible to determine biophysical parameters of the tissue with a high accuracy in real time under conditions of their general variability. Using the Monte Carlo method, we have modeled a statistical ensemble of profiles of diffuse reflection coefficients of skin, which corresponds to a wave variation of its biophysical parameters. On its basis, we have estimated the retrieval accuracy of biophysical parameters using the developed method and investigated the stability of the method to errors of optical measurements. We have showed that it is possible to determine online the concentrations of melanin, hemoglobin, bilirubin, oxygen saturation of blood, and structural parameters of skin from measurements of its diffuse reflection in the spectral range 450-800 nm at three distances between the radiation source and detector.

Lisenko, S. A.; Kugeiko, M. M.

2013-02-01

170

Flow injection analysis simulations and diffusion coefficient determination by stochastic and deterministic optimization methods.  

PubMed

Stochastic and deterministic simulations of dispersion in cylindrical channels on the Poiseuille flow have been presented. The random walk (stochastic) and the uniform dispersion (deterministic) models have been used for computations of flow injection analysis responses. These methods coupled with the genetic algorithm and the Levenberg-Marquardt optimization methods, respectively, have been applied for determination of diffusion coefficients. The diffusion coefficients of fluorescein sodium, potassium hexacyanoferrate and potassium dichromate have been determined by means of the presented methods and FIA responses that are available in literature. The best-fit results agree with each other and with experimental data thus validating both presented approaches. PMID:23845484

Kucza, Witold

2013-07-25

171

A First-Passage Kinetic Monte Carlo method for reaction-drift-diffusion processes  

NASA Astrophysics Data System (ADS)

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.

Mauro, Ava J.; Sigurdsson, Jon Karl; Shrake, Justin; Atzberger, Paul J.; Isaacson, Samuel A.

2014-02-01

172

Determination of O-Isopropyl Methylphosphonic Acid in Living Microorganism-Agar Matrixes using ION Chromatography\\/Conductivity Detection  

Microsoft Academic Search

A direct anion exchange ion chromatography (IC)-based method for the detection of the chemical warfare (CW) agent degradation product, O-isopropyl methylphosphonic acid (IMPA) in agar medium has been developed. This is the first report of the development and validation of an IC-based method for the analysis of IMPA in a microorganism and agar matrix. In these experiments, IMPA served as

Alaa-Eldin F. Nassar; Samuel V. Lucas; Susan A. Thomas

1999-01-01

173

The Local Discontinuous Galerkin Method for Time-Dependent Convection-Diffusion Systems  

NASA Technical Reports Server (NTRS)

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.

Cockburn, Bernardo; Shu, Chi-Wang

1997-01-01

174

A finite difference method with non-uniform timesteps for fractional diffusion equations  

NASA Astrophysics Data System (ADS)

An implicit finite difference method with non-uniform timesteps for solving the fractional diffusion equation in the Caputo form is proposed. The method allows one to build adaptive methods where the size of the timesteps is adjusted to the behavior of the solution in order to keep the numerical errors small without the penalty of a huge computational cost. The method is unconditionally stable and convergent. In fact, it is shown that consistency and stability implies convergence for a rather general class of fractional finite difference methods to which the present method belongs. The huge computational advantage of adaptive methods against fixed step methods for fractional diffusion equations is illustrated by solving the problem of the dispersion of a flux of subdiffusive particles stemming from a point source.

Yuste, Santos B.; Quintana-Murillo, Joaquín

2012-12-01

175

EVALUATION OF THE FRONT-FIXING METHOD CAPABILITIES FOR NUMERICAL MODELLING OF DIFFUSION IN MOVING SYSTEMS  

Microsoft Academic Search

Application of a finite difference front fixing method to various problems with moving boundaries and non- linear material properties is discussed. Advantages and implementation problems of the method are highlighted. Particular attention is given to conservation properties of the algorithm and accurate solutions close to the moving boundaries. The algorithm is tested using a well-known solution of the plane diffusion

I. O. Golosnoy; J. K. Sykulski

176

A Penalty Method for American Options with Jump Diffusion Y. d'Halluin  

E-print Network

A Penalty Method for American Options with Jump Diffusion Processes Y. d'Halluin , P.A. Forsyth , and G. Labahn March 9, 2003 Abstract The fair price for an American option where the underlying asset complementarity problem. We develop an implicit discretization method for pricing such American options. The jump

Labahn, George

177

The Dual Gravimetric Hot-Air Method for Measuring Soil Water Diffusivity  

Microsoft Academic Search

The hot-air method provides rapid measurement of a soil's unsatu- rated hydraulic diffusivity function. The original method consists of blowing hot air across one end of a soil column for a short period, and then quickly extruding, dissecting, and oven drying the soil to provide the soil water content profile, which is used to calculate the soil's un- saturated hydraulic

J. S. Tyner; L. M. Arya; W. C. Wright

2006-01-01

178

Nanoscale simulation of shale transport properties using the lattice Boltzmann method: permeability and diffusivity  

E-print Network

Porous structures of shales are reconstructed based on scanning electron microscopy (SEM) images of shale samples from Sichuan Basin, China. Characterization analyzes of the nanoscale reconstructed shales are performed, including porosity, pore size distribution, specific surface area and pore connectivity. The multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) fluid flow model and single-relaxation-time (SRT) LBM diffusion model are adopted to simulate the fluid flow and Knudsen diffusion process within the reconstructed shales, respectively. Tortuosity, intrinsic permeability and effective Knudsen diffusivity are numerically predicted. The tortuosity is much higher than that 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 are estimated and compared with existing corrections re...

Chen, Li; Kang, Qinjun; Yao, Jun; Tao, Wenquan

2014-01-01

179

Remedy for the fermion sign problem in the diffusion Monte Carlo method for few fermions with antisymmetric diffusion process  

Microsoft Academic Search

We suggest an exact approach to help remedy the fermion sign problem in diffusion quantum Monte Carlo simulations. The approach is based on an explicit suppression of symmetric modes in the Schrödinger equation by means of a modified stochastic diffusion process (antisymmetric diffusion process). We introduce this algorithm and illustrate it on potential models in one dimension (1D) and show

Yuriy Mishchenko

2006-01-01

180

Assessment of Etest as an Alternative to Agar Dilution for Antimicrobial Susceptibility Testing of Neisseria gonorrhoeae  

PubMed Central

We studied whether the Etest can be used as an alternative to agar dilution to determine antimicrobial susceptibilities of ceftriaxone, cefixime, and cefpodoxime in Neisseria gonorrhoeae surveillance. One hundred fifteen clinical and laboratory isolates of N. gonorrhoeae were tested following the Clinical Laboratory Improvement Amendments (CLIA)-approved CLSI standard agar dilution method and, separately, by the Etest according to the manufacturer's recommendations. The MICs were determined and compared. Ten laboratory-generated mutants were used to simulate substantially nonsusceptible specimens. The Etest and agar dilution methods were well correlated. Statistical tests produced regression R2 values of 88%, 82%, and 85% and Pearson correlation coefficients of 92%, 91%, and 92% for ceftriaxone, cefixime, and cefpodoxime, respectively. When paired comparisons were made, the two tests were 88.7%, 80%, and 87% within 1 log2 dilution from each other for ceftriaxone, cefixime, and cefpodoxime, respectively. The within-2-log2 agreements were 99.1%, 98.3%, and 94.8% for ceftriaxone, cefixime, and cefpodoxime, respectively. Notwithstanding the good correlations and the within-2-log2 general agreement, the Etest results produced slightly lower MICs than the agar dilution results. In conclusion, we found that the Etest can be effectively used as an alternative to agar dilution testing to determine the susceptibility of N. gonorrhoeae to ceftriaxone, cefixime, and cefpodoxime, although we recommend further research into extremely resistant isolates. For isolates within the typical range of clinical MICs, reexamination of the Etest interpretation of susceptible and nonsusceptible categories would likely allow for successful transition from agar dilution to the Etest. PMID:24554750

Taylor, Thomas H.; Pettus, Kevin; Trees, David

2014-01-01

181

NUMERICAL METHODS FOR SOLVING THE MULTI-TERM TIME-FRACTIONAL WAVE-DIFFUSION EQUATION  

PubMed Central

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

Liu, F.; Meerschaert, M.M.; McGough, R.J.; Zhuang, P.; Liu, Q.

2013-01-01

182

Coagulase-Negative Staphylococci: Comparison of Phenotypic and Genotypic Oxacillin Susceptibility Tests and Evaluation of the Agar Screening Test by Using Different Concentrations of Oxacillin  

Microsoft Academic Search

This study evaluated the oxacillin susceptibilities of 152 coagulase-negative staphylococcal (CoNS) strains of 12 species by disk diffusion; agar dilution; E-test; the slide latex agglutination test (Slidex MRSA Detection test; bioMerieux S\\/A, Paris, France); the agar screening test with 1, 2, 4, or 6 g of oxacillin per ml and incubation for 24 or 48 h; and detection of the

Rosana B. R. Ferreira; Natalia L. P. Iorio; Karoline L. Malvar; Ana Paula; F. Nunes; Leila S. Fonseca; Carla C. R. Bastos; Katia R. N. Santos

2003-01-01

183

Oxygen self-diffusion “fast-paths” in titanite single crystals and a general method for deconvolving self-diffusion profiles with “tails”  

NASA Astrophysics Data System (ADS)

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,?) 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:

Zhang, X. Y.; Watson, E. B.; Cherniak, D. J.

2007-03-01

184

Preparation of poly(?-lactide-co-glycolide) nanoparticles by modified spontaneous emulsification solvent diffusion method  

Microsoft Academic Search

Purpose: The objectives of this study were to establish a new preparation method for poly(DL-lactide-co-glycolide) (PLGA) nanoparticles by modifying the spontaneous emulsification solvent diffusion (SESD) method and to elucidate the mechanism of nanoparticle formation on the basis of the phase separation principle of PLGA and poly(vinyl alcohol) (PVA) in the preparation system. Methods: PLGA nanoparticles were prepared by the modified-SESD

Hideki Murakami; Masao Kobayashi; Hirofumi Takeuchi; Yoshiaki Kawashima

1999-01-01

185

A Domain Decomposition Method for Time Fractional Reaction-Diffusion Equation  

PubMed Central

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

Bao, Weimin; Tang, Guojian; Jiang, Yuewen; Liu, Jie

2014-01-01

186

A domain decomposition method for time fractional reaction-diffusion equation.  

PubMed

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

Gong, Chunye; Bao, Weimin; Tang, Guojian; Jiang, Yuewen; Liu, Jie

2014-01-01

187

Investigation of the mineralization process of biosystems by IR diffuse reflection spectroscopy methods  

NASA Astrophysics Data System (ADS)

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.

Zolotarev, V. M.

2014-04-01

188

A deterministic Lagrangian particle separation-based method for advective-diffusion problems  

NASA Astrophysics Data System (ADS)

A simple and robust Lagrangian particle scheme is proposed to solve the advective-diffusion transport problem. The scheme is based on relative diffusion concepts and simulates diffusion by regulating particle separation. This new approach generates a deterministic result and requires far less number of particles than the random walk method. For the advection process, particles are simply moved according to their velocity. The general scheme is mass conservative and is free from numerical diffusion. It can be applied to a wide variety of advective-diffusion problems, but is particularly suited for ecological and water quality modelling when definition of particle attributes (e.g., cell status for modelling algal blooms or red tides) is a necessity. The basic derivation, numerical stability and practical implementation of the NEighborhood Separation Technique (NEST) are presented. The accuracy of the method is demonstrated through a series of test cases which embrace realistic features of coastal environmental transport problems. Two field application examples on the tidal flushing of a fish farm and the dynamics of vertically migrating marine algae are also presented.

Wong, Ken T. M.; Lee, Joseph H. W.; Choi, K. W.

2008-12-01

189

Determination of moisture diffusivity in porous materials using gamma-method  

Microsoft Academic Search

In the present paper, results of an experimental gamma ray study of moisture transfer processes in porous material are reported. Evolution of moisture profiles in porous concrete samples during sorption and capillary moistening has been examined. Measured moisture profiles were used to determine, by the Boltzmann–Matano method, the coefficient of moisture diffusion versus moisture content of the material under various

M. I. Nizovtsev; S. V. Stankus; A. N. Sterlyagov; V. I. Terekhov; R. A. Khairulin

2008-01-01

190

Simulation of gaseous diffusion in partially saturated porous media under variable gravity with lattice Boltzmann methods  

E-print Network

variable gravity conditions hampers progress in selection and design of effective plant growth systems. Our of the lattice Boltzmann method for rapid and cost-effective evaluation of alternative plant growth media designs gravity conditions may impact the effec- tive gaseous diffusion coefficient of plant growth media, thereby

Shor, Leslie McCabe

191

Hybrid LSDA\\/Diffusion Quantum Monte-Carlo Method for Spin Sequences in Vertical Quantum Dots  

Microsoft Academic Search

We present an new hybrid Diffusion Quantum Monte-Carlo (DQMC)\\/Local Spin Density Approximation (LSDA) method, to compute the electronic structure of vertical quantum dots (VQD). The exact many-body electronic configuration is computed with a realistic confining potential. Our model confirms the atomic-like model of 2D shell structures obeying Hund's rule already predicted by LSDA.

P. Matagne; T. Wilkens; J. P. Leburton; R. Martin

2002-01-01

192

Slow Diffusion of Macromolecular Assemblies by a New Pulsed Field Gradient NMR Method  

E-print Network

temperature. The method was illustrated by application to a water-soluble complex of tOmpA, the hydrophobic-1 , consistent with measurements by size exclusion chromatography and by ultracentrifugation of the molecules during the diffusion interval. It is shown in this paper that the duration of this interval can

193

A method for predicting non-uniform steady sound fields within spaces bounded by diffusive surfaces  

Microsoft Academic Search

A method for predicting non-uniform steady sound fields within spaces bounded by diffusive surfaces is presented. The definitions of the basic physical quantities employed as well as a detailed description of the methodology application are reported. An experimental verification of the model is conducted through measurements of the sound field due to a point source within rectangular ducts of different

C Cianfrini; M Corcione; D. M Fontana

1998-01-01

194

An objective method for regularization of fiber orientation distributions derived from diffusion-weighted MRI  

Microsoft Academic Search

Spherical deconvolution is an elegant method by which the orientation of crossing fibers in the brain can be estimated from a diffusion-weighted MRI measurement. However, higher resolution of fiber directions comes at the cost of higher susceptibility to noise. In this study, we describe the use of linear regularization of the fiber orientation distribution function by Damped Singular Value Decomposition.

Ken E. Sakaie; Mark J. Lowe

2007-01-01

195

An analytical method for determining the temperature dependent moisture diffusivities of pumpkin seeds during drying process  

Microsoft Academic Search

This paper presents an analytical method, which determines the moisture diffusion coefficients for the natural and forced convection hot air drying of pumpkin seeds and their temperature dependence. In order to obtain scientific data, the pumpkin seed drying process was investigated under both natural and forced hot air convection regimes. This paper presents the experimental results in which the drying

Ahmet Can

2007-01-01

196

Errors of optical vitreous silica heat diffusivity determination by pulse method  

NASA Astrophysics Data System (ADS)

The accuracy appraisal of thermophysical characteristics determination of optical vitreous silica was carried out by a pulse method by comparison of numerical solution results of problem of a non-stationary temperature sample field at collimated laser impulse of final duration impact on its surface and reference values of heat diffusivity.

Katz, M. D.

2014-08-01

197

A Level Set Method for Anisotropic Geometric Diffusion in 3D Image Processing  

Microsoft Academic Search

A new morphological multiscale method in 3D image processing is presented which combines the image processing methodology based on nonlinear diffusion equations and the theory of geometric evolution prob- lems. Its aim is to smooth level sets of a 3D image while simultaneously preserving geometric features such as edges and corners on the level sets. This is obtained by an

Martin Rumpf

2000-01-01

198

A hybrid, infrared thermography: heat diffusion equation, method for the 3D air-temperature measurement  

Microsoft Academic Search

The question of how to map the 3D indoor temperature by infrared thermography is solved by a hybrid method which is a combination of infrared thermography and the well known heat diffusion equation. The idea is to use infrared thermography to get the surface temperature of each frontier of the 3D domain of interest. A suitable procedure is devoted to

F. B. Djupkep Dizeu; X. Maldague; A. Bendada; E. Grinzato; P. Bison

2011-01-01

199

Liquid-phase thermal diffusion isotope separation apparatus and method having tapered column  

DOEpatents

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.

Rutherford, William M. (Dayton, OH)

1988-05-24

200

A simultaneous characterization of thermal conductivity and diffusivity of polymer materials by a periodic method  

Microsoft Academic Search

A periodic method is used to determine simultaneously both thermal conductivity and diffusivity of various polymer materials at room temperature. The sample is placed between two metallic plates and temperature modulation is applied on the front side of one of the metallic plates. The temperature at the front and rear sides of both plates is measured and the experimental transfer

Abderrahim Boudenne; Laurent Ibos; Evelyne Gehin; Yves Candau

2004-01-01

201

Formation of nanostructured Re–Cr–Ni diffusion barrier coatings on Nb superalloys by TVA method  

Microsoft Academic Search

Nanostructured Re–Cr–Ni multiple component film was chosen as a diffusion barrier layer and was prepared by the original thermionic vacuum arc (TVA) method. It uses an electron beam emitted by an externally heated cathode (a filament which is grounded) and accelerated by the high anodic voltage. The electron beam can evaporate the anode materials as much as to create a

C. P. Lungu; I. Mustata; G. Musa; A. M. Lungu; V. Zaroschi; K. Iwasaki; R. Tanaka; Y. Matsumura; I. Iwanaga; H. Tanaka; T. Oi; K. Fujita

2005-01-01

202

MRI Phantoms – Are There Alternatives to Agar?  

PubMed Central

The suitability of different gelling agents as MRI phantoms was evaluated in terms of homogeneity, gel stability and reproducibility. Time and effort for preparation were also taken into account. The relaxation times of various gel compositions were estimated. Carbomer-980 and Carbopol-974P were determined to be promising novel phantom materials. These gelling agents are readily available, inexpensive and easy to handle given that thermal treatment is not required. Furthermore, the viscoelasticity of their polymer network is pH-dependent. With such characteristics, it was even possible to embed sensitive objects and retrieve them after testing. This was demonstrated with a fiber phantom for Diffusion Weighted MRI applications. Since Carbomer-980 and Carbopol-974P are non-hazardous, they are also suitable for multimodal setups (e.g., MRI as well as ultrasonic imaging). PMID:23940563

Hellerbach, Alexandra; Schuster, Verena; Jansen, Andreas; Sommer, Jens

2013-01-01

203

Walker diffusion method for calculation of transport properties of composite materials  

SciTech Connect

The morphology of a multiphase microstructure greatly influences the macroscopic transport properties of the composite material. These properties are shown to be related to the diffusion coefficient of a random (nonbiased) walker. The proper diffusion rules are found by considering an isomorphic image of the microstructure in which distinct populations of walkers correspond to the phase domains, with the walker density of a population proportional to the transport coefficient of the corresponding domain. To demonstrate the method, it is applied to disordered two-phase percolating composites. {copyright} {ital 1999} {ital The American Physical Society}

DeW. Van Siclen, C. [Idaho National Engineering and Environmental Laboratory, Idaho Falls, Idaho 83415 (United States)] [Idaho National Engineering and Environmental Laboratory, Idaho Falls, Idaho 83415 (United States)

1999-03-01

204

Analysis of Preconditioning and Relaxation Operators for the Discontinuous Galerkin Method Applied to Diffusion  

NASA Technical Reports Server (NTRS)

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.

Atkins, H. L.; Shu, Chi-Wang

2001-01-01

205

A new method of measuring hydrogen diffusivity by hydrogen permeation technique. 2: Experimental studies  

SciTech Connect

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.

Zheng, Y.P.; Zhang, T.Y. [Hong Kong Univ. of Science and Technology, Kowloon (Hong Kong). Dept. of Mechanical Engineering

1998-12-31

206

Power spectra methods for a stochastic description of diffusion on deterministically growing domains  

NASA Astrophysics Data System (ADS)

A central challenge in developmental biology is understanding the creation of robust spatiotemporal heterogeneity. Generally, the mathematical treatments of biological systems have used continuum, mean-field hypotheses for their constituent parts, which ignores any sources of intrinsic stochastic effects. In this paper we consider a stochastic space-jump process as a description of diffusion, i.e., particles are able to undergo a random walk on a discretized domain. By developing analytical Fourier methods we are able to probe this probabilistic framework, which gives us insight into the patterning potential of diffusive systems. Further, an alternative description of domain growth is introduced, with which we are able to rigorously link the mean-field and stochastic descriptions. Finally, through combining these ideas, it is shown that such stochastic descriptions of diffusion on a deterministically growing domain are able to support the nucleation of states that are far removed from the deterministic mean-field steady state.

Woolley, Thomas E.; Baker, Ruth E.; Gaffney, Eamonn A.; Maini, Philip K.

2011-08-01

207

Energetic Particle Transport with Stochastic Differential Equations: General Methods and the Extension to Anomalous Diffusion Regimes  

NASA Astrophysics Data System (ADS)

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.

Effenberger, F.

2014-09-01

208

Simulation of gaseous diffusion in partially saturated porous media under variable gravity with lattice Boltzmann methods  

NASA Technical Reports Server (NTRS)

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.

Chau, Jessica Furrer; Or, Dani; Sukop, Michael C.; Steinberg, S. L. (Principal Investigator)

2005-01-01

209

A rapid method for determining apparent diffusion coefficients in Chalk and other consolidated porous media  

NASA Astrophysics Data System (ADS)

SummaryThe development of a method for the determination of the apparent diffusion coefficient, DA, for chloride in saturated Chalk cores is described. The method is rapid compared with other approaches, taking typically less than 24 h for a single determination. Cylindrical Chalk cores approximately 25 mm high by 25 mm in diameter, which are routinely used in porosity and permeability measurements and which had been pre-equilibrated with a 200 mg/L chloride solution, were sealed at both ends and attached to a slowly rotating spindle suspended in a reservoir. A chloride ion-selective electrode (ISE) connected to a data logger was used to record chloride diffusion out of the core. DA was estimated by analysing the change in chloride concentration in the reservoir with time. Diffusion coefficients were estimated for six Chalk samples from a range of Chalk lithologies. Sample porosities for these Chalks ranged from 32% to 48% and gas permeabilities from 0.3 to 8.2 × 10 -9 m 2. The DA was found to vary from 3.1 to 8.7 × 10 -10 m 2/s, a similar range to that observed by others. A bromide ISE was also used on one sample and found to give a similar DA to that obtained for chloride. This approach, which combines a rigorous mathematical model of diffusion with a relatively simple practical method, could easily be adapted for other ions and for other consolidated porous media.

Gooddy, Daren C.; Kinniburgh, David G.; Barker, John A.

2007-09-01

210

A semi-discrete finite element method for a class of time-fractional diffusion equations  

E-print Network

As fractional diffusion equations can describe the early breakthrough and the heavy-tail decay features observed in anomalous transport of contaminants in groundwater and porous soil, they have been commonly employed in the related mathematical descriptions. These models usually involve long-time range computation, which is a critical obstacle for its application, improvement of the computational efficiency is of great significance. In this paper, a semi-analytical method is presented for solving a class of time-fractional diffusion equations which overcomes the critical long-time range computation problem of time fractional differential equations. In the procedure, the spatial domain is discretized by the finite element method which reduces the fractional diffusion equations into approximate fractional relaxation equations. As analytical solutions exist for the latter equations, the burden arising from long-time range computation can effectively be minimized. To illustrate its efficiency and simplicity, four examples are presented. In addition, the method is employed to solve the time-fractional advection-diffusion equation characterizing the bromide transport process in a fractured granite aquifer. The prediction closely agrees with the experimental data and the heavy-tail decay of anomalous transport process is well-represented.

HongGuang Sun; Wen Chen; K. Y. Sze

2011-09-03

211

Oxygen self-diffusion ``fast-paths'' in titanite single crystals and a general method for deconvolving self-diffusion  

E-print Network

lattice diffusion. The purpose of this contribution is to report on these features--described as ``fast profiles. For both dry and hydrothermal experiments in which the ``fast paths'' are observed, 18 O was used was used for the hydrothermal experiments. Diffusive uptake profiles of 18 O were measured in all cases

Watson, E. Bruce

212

A numerical algorithm for the diffusion equation using 3D FEM and the Arnoldi method  

Microsoft Academic Search

In this paper we introduce a new computational method for solving the diffusion equation. In particular, we construct a “generalized” state-space system and compute the impulse response of an equivalent truncated state-space system. In this effort, we use a 3D finite element method (FEM) to obtain the state-space system. We then use the Arnoldi iteration to approximate the state impulse

Qing Su; Vassilis L. Syrmos; D. Y. Y. Yun

1999-01-01

213

Numerical Integration in the Discontinuous Galerkin Method for Nonlinear Convection-Diffusion Problems in 3D  

Microsoft Academic Search

In this paper the discontinuous Galerkin finite element method is used for the space-semidiscretization of a nonlinear nonstationary\\u000a convection-diffusion problem in three dimensions. As in practical computations integrals appearing in the forms defining the\\u000a approximate solution are evaluated with the use of quadrature formulae, the effect of numerical integration in the method\\u000a is studied. An estimate of the error caused

V. Sobotíková

214

Preparation of PLGA nanoparticles containing estrogen by emulsification–diffusion method  

Microsoft Academic Search

Nano-sized poly (d,l lactide-co-glycolide) (PLGA) particles, widely used as a biodegradable polymeric carrier, containing estrogen were prepared employing emulsification–diffusion method. Estrogen was chosen as a model drug. The preparation method consists of emulsifying a solution of polymer and drug in the aqueous phase containing stabilizer, previously saturated, followed by adding excess water. Influence of process variables on the mean particle

Hye-Young Kwon; Jun-Young Lee; Sung-Wook Choi; Yangsoo Jang; Jung-Hyun Kim

2001-01-01

215

Method of analyzing the influence of network structure on information diffusion  

NASA Astrophysics Data System (ADS)

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.

Nagata, Katsuya; Shirayama, Susumu

2012-07-01

216

Studies of the accuracy of time integration methods for reaction-diffusion equations  

NASA Astrophysics Data System (ADS)

In this study we present numerical experiments of time integration methods applied to systems of reaction-diffusion equations. Our main interest is in evaluating the relative accuracy and asymptotic order of accuracy of the methods on problems which exhibit an approximate balance between the competing component time scales. Nearly balanced systems can produce a significant coupling of the physical mechanisms and introduce a slow dynamical time scale of interest. These problems provide a challenging test for this evaluation and tend to reveal subtle differences between the various methods. The methods we consider include first- and second-order semi-implicit, fully implicit, and operator-splitting techniques. The test problems include a prototype propagating nonlinear reaction-diffusion wave, a non-equilibrium radiation-diffusion system, a Brusselator chemical dynamics system and a blow-up example. In this evaluation we demonstrate a "split personality" for the operator-splitting methods that we consider. While operator-splitting methods often obtain very good accuracy, they can also manifest a serious degradation in accuracy due to stability problems.

Ropp, David L.; Shadid, John N.; Ober, Curtis C.

2004-03-01

217

GPU-accelerated 3D neutron diffusion code based on finite difference method  

SciTech Connect

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)

Xu, Q.; Yu, G.; Wang, K. [Dept. of Engineering Physics, Tsinghua Univ. (China)

2012-07-01

218

A diffusion-based truncated projection artifact reduction method for iterative digital breast tomosynthesis reconstruction  

PubMed Central

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

Lu, Yao; Chan, Heang-Ping; Wei, Jun; Hadjiiski, Lubomir M

2014-01-01

219

A diffusion-based truncated projection artifact reduction method for iterative digital breast tomosynthesis reconstruction  

NASA Astrophysics Data System (ADS)

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.

Lu, Yao; Chan, Heang-Ping; Wei, Jun; Hadjiiski, Lubomir M.

2013-02-01

220

Implicit finite difference solution for time-fractional diffusion equations using AOR method  

NASA Astrophysics Data System (ADS)

In this paper, we derive an implicit finite difference approximation equation of the one-dimensional linear time fractional diffusion equations, based on the Caputo's time fractional derivative. Then this approximation equation leads the corresponding system of linear equation, which is large scale and sparse. Due to the characteristics of the coefficient matrix, we use the Accelerated Over-Relaxation (AOR) iterative method for solving the generated linear system. One example of the problem is presented to illustrate the effectiveness of AOR method. The numerical results of this study show that the proposed iterative method is superior compared with the existing one weighted parameter iterative method.

Sunarto, A.; Sulaiman, J.; Saudi, A.

2014-04-01

221

Quantitative evaluation of registration methods for atlas-based diffuse optical tomography  

NASA Astrophysics Data System (ADS)

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.

Wu, Xue; Eggebrecht, Adam T.; Culver, Joseph P.; Zhan, Yuxuan; Basevi, Hector; Dehghani, Hamid

2013-06-01

222

Application of Electrode Methods in Studies of Nitric Oxide Metabolism and Diffusion Kinetics  

PubMed Central

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

Liu, Xiaoping; Zweier, Jay L.

2012-01-01

223

One-week 96-well soft agar growth assay for cancer target validation.  

PubMed

Soft agar growth, used to measure cell anchorage-independent proliferation potential, is one of the most important and most commonly used assays to detect cell transformation. However, the traditional soft agar assay is time-consuming, labor-intensive, and plagued with inconsistencies due to individual subjectivity. It does not, therefore, meet the increasing demands of today's oncology drug target screening or validation processes. This report describes an alternative 96-well soft agar growth assay that can function as a replacement for the traditional method and overcomes the aforementioned limitations. It offers the following advantages: a shortened assay duration (1 week instead of 4 weeks) that makes transient transfection or treatment possible; plate reader quantification of soft agar growth (measuring cloning efficiency and colony size); and a significant reduction in required labor. Higher throughput also makes it possible to process large numbers of samples and treatments simultaneously and in a much more efficient manner, while saving precious workspace and overall cost. PMID:15152603

Ke, Ning; Albers, Aaron; Claassen, Gisela; Yu, De-hua; Chatterton, Jon E; Hu, Xiuyuan; Meyhack, Bernd; Wong-Staal, Flossie; Li, Qi-Xiang

2004-05-01

224

Is inclusion of Sabouraud dextrose agar essential for the laboratory diagnosis of fungal keratitis?  

PubMed Central

Purpose: To determine whether the inclusion of Sabouraud dextrose agar (SDA) is essential in the diagnosis of fungal keratitis. Materials and Methods: Corneal scrapings of 141 patients with microbial keratitis were smeared and cultured. Sheep blood agar (BA), chocolate agar (CA), SDA, non-nutrient agar (NNA) with Escherichia coli overlay, and brain heart infusion broth (BHI) were evaluated for time taken for growth and cost. The media were also evaluated experimentally for rate of growth and time taken for identification. Results: Twenty-six of 39 patients positive for fungus in corneal scrapings by microscopy were culture-positive. Fungus grew on BA in 22/39, on CA in 18/39, on SDA in 17/39, on NNA in 17/39, and on BHI in 13/39 cases. Growth on SDA was higher in ulcers with larger infiltrate (6/18 versus 9/13, P = 0.04). Estimated saving with inclusion of only BA/CA was Rs. 600 per patient. Performance of all media was similar in in vitro experiment although the characteristic spores and color were seen earlier on SDA. Conclusion: Fungal keratitis can be reliably confirmed on BA or CA, which support growth of both bacteria and fungus. PMID:20534916

Das, Sujata; Sharma, Savitri; Kar, Sarita; K Sahu, Srikant; Samal, Bikash; Mallick, Aparajita

2010-01-01

225

Diffuse surface calibration method to improve accuracy and dynamic range of aerosol elastic light scattering measurements  

NASA Astrophysics Data System (ADS)

A new method to calibrate detectors for elastic light scattering (ELS) measurement based on diffuse scattering from a Lambertian surface is presented. The method produces a calibration signal that is approximately seven orders of magnitude larger than a propane gas Rayleigh scattering calibration. The method also allows for calibration of detectors such as photodiodes, which are not sensitive enough to detect Rayleigh scattering for calibration but possess characteristics desirable for the measurement of soot ELS. Since the method is only suitable for backward scattering calibrations, transfer of calibration data from a backward- to a forward-oriented detector is accomplished with a secondary laser and integrating sphere. In demonstration experiments, calibration constants for photomultiplier tube (PMT) detectors obtained using both Rayleigh scattering and diffuse surface scattering agreed within experimental uncertainties as did measurements of in-flame scattering coefficients obtained with PMTs and photodiodes. However, achievable uncertainties with the diffuse-surface calibration approach were significantly reduced. More importantly, by enabling the use of photodiode detectors in ELS measurements, the new method facilitates operation at higher photon fluxes resulting in improved signal-to-noise ratios, reduced influence of photon shot noise, and the ability to achieve higher dynamic range in transient measurements.

Crosland, B. M.; Johnson, M. R.; Thomson, K. A.

2013-03-01

226

Dating of black gel pen ink using the dissolution-diffusion method.  

PubMed

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

Li, Biao

2014-01-01

227

An Advanced Integrated Diffusion/Transport Method for the Design, Analysis and Optimization of the Very-High-Temperature Reactors  

SciTech Connect

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

Farzad Rahnema; Dingkang Zhang; Abderrafi Ougouag; Frederick Gleicher

2011-04-04

228

A Comparison of Two Methods Used for Measuring the Antagonistic Activity of Bacillus Species  

Microsoft Academic Search

In this study, we have aimed to determine antagonistic effects of various Bacillus against representatives of Gram (+) and Gram (?) bacteria, (Staphylococcus aureus TISTR 517 and Escherichia coli TISTR 887) with a comparison between the cross streak method and agar well diffusion method. Both methods used in the experiment gave better inhibition results on the S. aureus TISTR 517

Monthon LERTCANAWANICHAKUL

2008-01-01

229

An Explicit Finite Difference Method and a New von Neumann-Type Stability Analysis for Fractional Diffusion Equations  

Microsoft Academic Search

Abstract. A numerical method for solving the fractional diffusion equation, which could also be easily extended to other fractional partial differential equations, is considered. In this paper we combine the forward time centered space (FTCS) method, well known for the numerical integration of ordinary diffusion equations, with the Gr¨ unwald–Letnikov discretization of the Riemann–Liouville derivative to obtain an explicit FTCS

S. B. Yuste; L. Acedo

2005-01-01

230

A novel model for diffusion based release kinetics using an inverse numerical method.  

PubMed

We developed and analyzed an inverse numerical model based on Fick's second law on the dynamics of drug release. In contrast to previous models which required two state descriptions of diffusion for long- and short-term release processes, our model is valid for the entire release process. The proposed model may be used for identifying and reducing experimental errors associated with measurements of diffusion based release kinetics. Knowing the initial and boundary conditions, and assuming Fick's second law to be appropriate, we use the methods of Lagrange multiplier along with least-square algorithms to define a cost function which is discretized using finite difference methods and is optimized so as to minimize errors. Our model can describe diffusion based release kinetics for static and dynamic conditions as accurately as finite element methods, but results are obtained in a fraction of CPU time. Our method can be widely used for drug release procedures and for tissue engineering/repair applications where oxygenation of cells residing within a matrix is important. PMID:21382735

Mohammadi, Hadi; Herzog, Walter

2011-10-01

231

Non-invasive measurements of tissue hemodynamics with hybrid diffuse optical methods  

NASA Astrophysics Data System (ADS)

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.

Durduran, Turgut

232

Surface preparation for determining diffusion length by the surface photovoltage method  

SciTech Connect

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.

Goodman, A.M.

1985-03-26

233

Comparison of NRC goniometric and integrating sphere methods for realizing an absolute diffuse reflectance scale  

NASA Astrophysics Data System (ADS)

At the National Research Council of Canada (NRC), the scale of diffuse spectral reflectance in the UV and visible range is realized using an integrating sphere method known as the Modified Sharp-Little method and has been wellcharacterized and validated. More recently, a gonioreflectometer has been designed to capture the bidirectional reflectance of reflecting objects. This system incorporates a diode-array spectroradiometer and is prone to non-linearity errors. In this paper the magnitude of this non-linearity error is evaluated using several diffusely reflecting materials by comparing the angular-integrated reflection indicatrix measured with the gonioreflectometer with results obtained using a transfer spectrophotometer that is traceable to the sphere-based NRC Absolute Reflectometer.

Baribeau, Réjean; Zwinkels, Joanne

2012-10-01

234

Hyperspectral imaging for detecting pathogens grown on agar plates  

NASA Astrophysics Data System (ADS)

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.

Yoon, Seung Chul; Lawrence, Kurt C.; Siragusa, Gregory R.; Line, John E.; Park, Bosoon; Windham, William R.

2007-09-01

235

Accurate numerical schemes based on the lattice Boltzmann methods for multi-dimensional diffusion equations  

NASA Astrophysics Data System (ADS)

We propose accurate explicit numerical schemes based on the lattice Boltzmann (LB) method for multi-dimensional diffusion equations. In LB schemes, the velocity models D2Q9 and D2Q13 are used for two-dimensional equations and D3Q19 and D3Q25 for three-dimensional equations. We introduce free parameters that characterize the weight of the equilibrium distribution functions to reduce numerical errors. Consistency analysis through the fourth-order Chapman-Ensgok expansion of the distribution functions gives an approximate diffusion equation with error terms up to fourth-order. The relaxation parameter and weight parameters are determined so that second-order error terms are eliminated in the approximate equation. Stability analysis shows that we can find a relaxation parameter so that each of the presented schemes is stable for given diffusion coefficients and discretizing parameters. Numerical experiments for the isotropic and anisotropic benchmark problems show that the presented schemes derived from the velocity models D2Q13 and D3Q25 are useful for numerical simulations of practical problems governed by two- and three-dimensional diffusion equations, respectively. In particular, schemes in which the value of the relaxation parameter is set to be 1 demonstrate a fourth-order accuracy under the stability condition.

Suga, Shinsuke

2014-11-01

236

Spin-orbit induced backflow in neutron matter with auxiliary field diffusion Monte Carlo method  

Microsoft Academic Search

The energy per particle of zero-temperature neutron matter is investigated, with particular emphasis on the role of the LsS interaction. An analysis of the importance of explicit spin-orbit correlations in the description of the system is carried out by the auxiliary field diffusion Monte Carlo method. The improved nodal structure of the guiding function, constructed by explicitly considering these correlations,

L. Brualla; S. Fantoni; A. Sarsa; K. E. Schmidt; S. A. Vitiello

2003-01-01

237

Computing quasi-linear diffusion coefficients using the delta-f particle-in-cell method  

SciTech Connect

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.

Austin, T. M.; Smithe, D. N.; Ranjbar, V. [Tech-X Corporation, 5621 Arapahoe Ave., Suite A, Boulder, CO 80303 (United States)

2009-11-26

238

A new method for measuring the diffusion coefficient in a gas phase.  

PubMed

A new and fast method for measuring the diffusion coefficients of binary gas mixtures using ion mobility spectrometry (IMS) has been developed. In this method, the sample is injected as a short pulse into the flowing drift gas, forming a Gaussian concentration profile inside the drift region. This Gaussian cloud is irradiated with a fast moving swarm of electrons to create negative ions. The flash of electrons is so short that the negative ions do not move much during the exposure time. The ions then drift toward the detector, where they are collected. The collected ion signal pattern reflects the spatial distribution of the sample inside the cloud at the time of exposure. This is repeated in intervals of 300-400 ms to monitor the spatial spreading of the molecules in the drift region. Consecutive IMS spectra show the evolution of the cloud over time. The collected spectra are fit to Gaussian functions to extract diffusion coefficients. Using this method, the diffusion coefficient of O(2), CHCl(3), and C(2)H(2)Cl(2) were measured, and the results are in good agreement with the previously reported experimental data. PMID:16986857

Rouholahnejad, Fereshteh; Tabrizchi, Mahmoud

2006-09-28

239

Method and apparatus for determining minority carrier diffusion length in semiconductors  

DOEpatents

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.

Goldstein, Bernard (Princeton, NJ); Dresner, Joseph (Princeton, NJ); Szostak, Daniel J. (Mercerville, NJ)

1983-07-12

240

THE PONSETI METHOD IN LATIN AMERICA: INITIAL IMPACT AND BARRIERS TO ITS DIFFUSION AND IMPLEMENTATION  

PubMed Central

The Ponseti method for correcting clubfoot is a safe, effective, and minimally invasive treatment that has recently been implemented in Latin America. This study evaluates the initial impact and unique barriers to the diffusion of the Ponseti method throughout this region. Structured interviews were conducted with 30 physicians practicing the Ponseti method in three socioeconomically diverse countries: Chile, Peru and Guatemala. Since learning the Ponseti method, these physicians have treated approximately 1,740 clubfoot patients, with an estimated 1,705 (98%) patients treated using the Ponseti method, and 35 (2%) patients treated using surgical techniques. The barriers were classified into the following themes: physician education, health care system of the country, culture and beliefs of patients, physical distance and transport, financial barriers for patients, and parental compliance with the method. The results yielded several common barriers throughout Latin America including lack of physician education, physical distance to the treatment centers, and financial barriers for patients. Information from this study can be used to inform, and to implement and evaluate specific strategies to improve the diffusion of the Ponseti method for treating clubfoot throughout Latin America. PMID:22096416

Boardman, Allison; Jayawardena, Asitha; Oprescu, Florin; Cook, Thomas; Morcuende, Jose A

2011-01-01

241

A deterministic particle method for one-dimensional reaction-diffusion equations  

NASA Technical Reports Server (NTRS)

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.

Mascagni, Michael

1995-01-01

242

Photothermal characterization of the gelation process in Gelidium robustum Agar  

NASA Astrophysics Data System (ADS)

Agar is a hydrophilic colloid formed by polysaccharides, whose ability to form reversible gels simply by cooling hot aqueous solutions is the most important property and can be regarded as the prototype and model for all gelling systems. In this paper the evolution of the gelation process of agar obtained from algae of the species Gelidium robustum, using the photopyroelectric technique is reported. It is shown that thermal effusivity increase when the agar is cooled, reaching a maximum value around 37°C. The increase in thermal effusivity can be related to the increasing of the bondings in the gel as temperature decreases, reaching the maximum at the gelation point. The decrease of the thermal effusivity at lower temperature could be due to the syneresis process involving a gradual release of water after gelation.

Freile-Pelegrín, Y.; Bante, J.; Alvarado-Gil, J. J.; Yánez-Limón, J. M.

2005-06-01

243

Spatially adaptive stochastic numerical methods for intrinsic fluctuations in reaction-diffusion systems  

NASA Astrophysics Data System (ADS)

Stochastic partial differential equations are introduced for the continuum concentration fields of reaction-diffusion systems. The stochastic partial differential equations account for fluctuations arising from the finite number of molecules which diffusively migrate and react. Spatially adaptive stochastic numerical methods are developed for approximation of the stochastic partial differential equations. The methods allow for adaptive meshes with multiple levels of resolution, Neumann and Dirichlet boundary conditions, and domains having geometries with curved boundaries. A key issue addressed by the methods is the formulation of consistent discretizations for the stochastic driving fields at coarse-refined interfaces of the mesh and at boundaries. Methods are also introduced for the efficient generation of the required stochastic driving fields on such meshes. As a demonstration of the methods, investigations are made of the role of fluctuations in a biological model for microorganism direction sensing based on concentration gradients. Also investigated, a mechanism for spatial pattern formation induced by fluctuations. The discretization approaches introduced for SPDEs have the potential to be widely applicable in the development of numerical methods for the study of spatially extended stochastic systems.

Atzberger, Paul J.

2010-05-01

244

Agar-Block Microcosms for Controlled Plant Tissue Decomposition by Aerobic Fungi  

PubMed Central

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

Schilling, Jonathan S.

2011-01-01

245

Agar-block microcosms for controlled plant tissue decomposition by aerobic fungi.  

PubMed

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

Schilling, Jonathan S; Jacobson, K Brook

2011-01-01

246

Charcoal-Yeast Extract Agar: Primary Isolation Mediumfor Legionella pneumophila  

Microsoft Academic Search

Charcoal-yeast extract agar isa new bacteriological mediumthatsupports excellent growth oftheLegionella pneumophila. Itresults frommodifications madeinan existing L.pneumophila medium,F-Gagar.Yeastextract, instead of an acidhydrolysate ofcasein, servesastheprotein source.Beefextractives and starch are notadded. Activated charcoal (Norit A or Norit SG)isincluded at 0.20%(wt\\/vol). Comparison ofcharcoal-yeast extract andF-Gagars showedthat a greater numberofcolony-forming units ofL.pneumophila was recovered from astandardized tissue inoculum on charcoal-yeast extract agar(4.35 x 106colony- forning

JAMES C. FEELEY; ROBERT J. GIBSON; GEORGE W. GORMAN; NANCY C. LANGFORD; J. KAMILE RASHEED; DON C. MACKEL; WILLIAM B. BAINE

1979-01-01

247

Stability of Antibiotics and Chemotherapeutics in Agar Plates  

PubMed Central

The stability of chemotherapeutic agents incorporated into agar plates was studied by comparison of minimum inhibitory concentrations on fresh and stored plates and by direct bioassay of the chemotherapeutic agar plates. Plates were stored in sealed bags at 4 C. No loss of bioactivity was demonstrated after 30 days of storage in plates containing methicillin, erythromycin, cephalothin, tetracycline, chloramphenicol, kanamycin, streptomycin, polymyxin B, or nalidixic acid. Penicillin G, ampicillin, and nitrofurantoin showed statistically significant losses of activity after 4 weeks. None of the chemotherapeutics tested showed significant loss in activity after 1 week. PMID:5485725

Ryan, Kenneth J.; Needham, Gerald M.; Dunsmoor, Carol L.; Sherris, John C.

1970-01-01

248

Numerical methods of solving a system of multi-dimensional nonlinear equations of the diffusion type  

NASA Technical Reports Server (NTRS)

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.

Agapov, A. V.; Kolosov, B. I.

1979-01-01

249

Galerkin finite element method for two-dimensional Riesz space fractional diffusion equations  

NASA Astrophysics Data System (ADS)

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.

Bu, Weiping; Tang, Yifa; Yang, Jiye

2014-11-01

250

Analysis of splitting methods for reaction-diffusion problems using stochastic calculus  

NASA Astrophysics Data System (ADS)

We consider linear and nonlinear reaction-diffusion problems, and their time discretization by splitting methods. We give probabilistic interpretations of the splitting schemes, and show how these representations allow us to give error bounds for the deterministic propagator under weak hypothesis on the reaction part. To show these results, we only use the Ito formula, and basic properties of solutions of stochastic differential equations. Eventually, we show how probabilistic representations of splitting schemes can be used to derive ``hybrid'' numerical schemes based on Monte Carlo approximations of the splitting method itself.

Faou, Erwan

2009-09-01

251

Fixed and pulsed gradient diffusion methods in low-field core analysis.  

PubMed

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

Leu, Gabriela; Fordham, Edmund J; Hürlimann, Martin D; Frulla, Phil

2005-02-01

252

GPU-Accelerated Finite Element Method for Modelling Light Transport in Diffuse Optical Tomography  

PubMed Central

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

Schweiger, Martin

2011-01-01

253

Boundary Domain Integral Method for Double Diffusive Natural Convection in Porous Media Saturated with Compressible Fluid  

NASA Astrophysics Data System (ADS)

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.

Kramer, J.; Jecl, R.; Škerget, L.

2008-09-01

254

Calculating diffusion and permeability coefficients with the oscillating forward-reverse method  

NASA Astrophysics Data System (ADS)

The forward-reverse or FR method is an efficient bidirectional work method for determining the potential of mean force w(z) and also supposedly gives in principle the position-dependent diffusion coefficient D(z). Results from a variation called the OFR (oscillating FR) method suggest inconsistencies in the D(z) values when calculated as prescribed by the FR method. A new steering protocol has thus been developed and applied to the OFR method for the accurate determination of D(z) and also provides greater convergence for w(z) in molecular dynamics simulations. The bulk diffusion coefficient for water was found to be (6.03±0.16)×10-5 cm2/s at 350 K with system size dependence within the statistical error bars. Using this steering protocol, D(z) and w(z) for water permeating a dipalmitoylphosphatidylcholine (DPPC) bilayer were determined. The potential of mean force is shown to have a barrier of peak height, wmax/(kBT)=8.4, with a width of about 10 Å on either side from the membrane center. The diffusion constant is shown to be highest in the core region of the membrane [peak value ˜(8.0±0.8)×10-5 cm2/s], lowest in the head-group region [minimum value ˜(2.0±0.3)×10-5 cm2/s], and to tend toward the bulk value as the water molecule leaves the membrane. The permeability coefficient P for H2O in DPPC was determined using the simulated D(z) and w(z) to give values of (0.129±0.075) cm/s at 323 K and (0.141±0.043) cm/s at 350 K. The results show more spatial detail than results presented in previous work while reducing the computational and user effort.

Holland, Bryan W.; Gray, Chris G.; Tomberli, Bruno

2012-09-01

255

Calculating diffusion and permeability coefficients with the oscillating forward-reverse method.  

PubMed

The forward-reverse or FR method is an efficient bidirectional work method for determining the potential of mean force w(z) and also supposedly gives in principle the position-dependent diffusion coefficient D(z). Results from a variation called the OFR (oscillating FR) method suggest inconsistencies in the D(z) values when calculated as prescribed by the FR method. A new steering protocol has thus been developed and applied to the OFR method for the accurate determination of D(z) and also provides greater convergence for w(z) in molecular dynamics simulations. The bulk diffusion coefficient for water was found to be (6.03±0.16)×10(-5) cm2/s at 350 K with system size dependence within the statistical error bars. Using this steering protocol, D(z) and w(z) for water permeating a dipalmitoylphosphatidylcholine (DPPC) bilayer were determined. The potential of mean force is shown to have a barrier of peak height, wmax/(kBT)=8.4, with a width of about 10 Å on either side from the membrane center. The diffusion constant is shown to be highest in the core region of the membrane [peak value ?(8.0±0.8)×10(-5) cm2/s], lowest in the head-group region [minimum value ?(2.0±0.3)×10(-5) cm2/s], and to tend toward the bulk value as the water molecule leaves the membrane. The permeability coefficient P for H2O in DPPC was determined using the simulated D(z) and w(z) to give values of (0.129±0.075) cm/s at 323 K and (0.141±0.043) cm/s at 350 K. The results show more spatial detail than results presented in previous work while reducing the computational and user effort. PMID:23031053

Holland, Bryan W; Gray, Chris G; Tomberli, Bruno

2012-09-01

256

Preparation of Agar-Agar from the Red Seaweed Pterocladia capillacea off the Coast of Alexandria, Egypt  

PubMed Central

The effect of different treatments on the quality of agar produced from Pterocladia has been studied, and the conditions for the production of material of good quality have been standardized. In the modified process, sun-bleached seaweed was washed well in water, soaked for 24 h, and then ground to a pulp and rinsed again in water. The pulp was then extracted with water (weed-to-water ratio, 1:30) under pressure for 2 h after adjusting the pH to 6 by the addition of acetic acid. The agar gel, after freeze thawing, was bleached with NaClO before drying in a current of hot air. Pretreatment of the seaweed with alkali at 80°C for 2 h prior to extraction was found to improve the quality of agar to a very great extent. PMID:16345175

Rao, A. V.; Bekheet, Inaam A.

1976-01-01

257

Development of a pure diffusion quantum Monte Carlo method using a full generalized Feynman-Kac formula. I. Formalism  

Microsoft Academic Search

This paper presents systematic developments in the previously initiated line of research concerning a quantum Monte Carlo (QMC) method based on the use of a pure diffusion process corresponding to some reference function and a generalized Feynman–Kac path integral formalism. Not only mean values of quantum observables, but also response properties are expressed using suitable path integrals involving the diffusion

Michel Caffarel; Pierre Claverie

1988-01-01

258

CO diffusion on Pt(111) with time-resolved infrared-pulsed molecular beam methods: Critical tests and analysis  

Microsoft Academic Search

The microscopic diffusion of CO on stepped Pt(111) crystal surfaces has been investigated with pulsed molecular beam–time-resolved surface infrared methods. Following a rapid exposure to CO, we record the time evolution of the CO surface vibrational spectra as the CO diffuse from the initial random distribution to the thermodynamically favored step sites. The data are simulated with a model that

J. E. Reutt-Robey; D. J. Doren; Y. J. Chabal; S. B. Christman

1990-01-01

259

Quantifying water diffusion in high-viscosity and glassy aqueous solutions using a Raman isotope tracer method  

NASA Astrophysics Data System (ADS)

Recent research suggests that under certain temperature and relative humidity conditions atmospheric aerosol may be present in the form of a glassy solid. In order to understand the impacts that this may have on aerosol-cloud interactions and atmospheric chemistry, knowledge of water diffusion within such aerosol particles is required. Here, a method is described in which Raman spectroscopy is used to observe D2O diffusion in high-viscosity aqueous solutions, enabling a quantitative assessment of water diffusion coefficients, Dwater, as a function of relative humidity. Results for sucrose solutions compare well with literature data at 23.5 ± 0.3 °C, and demonstrate that water diffusion is slow (Dwater ~5 × 10-17 m2 s-1), but not arrested, just below the glass transition at a water activity of 0.2. Room temperature water diffusion coefficients are also presented for aqueous levoglucosan and an aqueous mixture of raffinose, dicarboxylic acids and ammonium sulphate: at low humidity, diffusion is retarded but still occurs on millisecond to second timescales in atmospherically relevant-sized particles. The effect of gel formation on diffusion in magnesium sulfate solutions is shown to be markedly different from the gradual decrease in diffusion coefficients of highly viscous liquids. We show that using the Stokes-Einstein equation to determine diffusion timescales from viscosity leads to values which are more than 5 orders of magnitude too big, which emphasises the need to make measurements of diffusion coefficients. In addition, comparison of bounce fraction data for levoglucosan with measured diffusion data reveals that even when particles bounce the diffusion timescales for water are a fraction of a second for a 100 nm particle. This suggests a high bounce fraction does not necessarily indicate retarded water diffusion.

Price, H. C.; Murray, B. J.; Mattsson, J.; O'Sullivan, D.; Wilson, T. W.; Baustian, K. J.; Benning, L. G.

2014-04-01

260

A self-organizing Lagrangian particle method for adaptive-resolution advection-diffusion simulations  

NASA Astrophysics Data System (ADS)

We present a novel adaptive-resolution particle method for continuous parabolic problems. In this method, particles self-organize in order to adapt to local resolution requirements. This is achieved by pseudo forces that are designed so as to guarantee that the solution is always well sampled and that no holes or clusters develop in the particle distribution. The particle sizes are locally adapted to the length scale of the solution. Differential operators are consistently evaluated on the evolving set of irregularly distributed particles of varying sizes using discretization-corrected operators. The method does not rely on any global transforms or mapping functions. After presenting the method and its error analysis, we demonstrate its capabilities and limitations on a set of two- and three-dimensional benchmark problems. These include advection-diffusion, the Burgers equation, the Buckley-Leverett five-spot problem, and curvature-driven level-set surface refinement.

Reboux, Sylvain; Schrader, Birte; Sbalzarini, Ivo F.

2012-05-01

261

A diffuse-interface method for two-phase flows with soluble surfactants  

PubMed Central

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

Teigen, Knut Erik; Song, Peng; Lowengrub, John; Voigt, Axel

2010-01-01

262

Fast non-overlapping Schwarz domain decomposition methods for solving the neutron diffusion equation  

SciTech Connect

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.

Jamelot, Erell [Commissariat à l’Énergie Atomique et aux Énergie Alternatives, CEA Saclay, 91191 Gif-sur-Yvette Cedex (France)] [Commissariat à l’Énergie Atomique et aux Énergie Alternatives, CEA Saclay, 91191 Gif-sur-Yvette Cedex (France); Ciarlet, Patrick, E-mail: patrick.ciarlet@ensta.fr [POEMS Laboratory, CNRS-INRIA-ENSTA UMR 7231, ENSTA ParisTech 32, Boulevard Victor, 75739 Paris Cedex 15 (France)] [POEMS Laboratory, CNRS-INRIA-ENSTA UMR 7231, ENSTA ParisTech 32, Boulevard Victor, 75739 Paris Cedex 15 (France)

2013-05-15

263

Maintenance of leptospira species in leptospira vanaporn wuthiekanun agar.  

PubMed

The maintenance of Leptospira species in liquid or semisolid medium is time-consuming and at risk of contamination due to the needs of routine subculture and dark field microscopy. Using Leptospira Vanaporn Wuthiekanun (LVW) agar, we maintained 100 pathogenic Leptospira isolates for 12 months without the need for subculture and confirmed the viability of all isolates by the naked eye. PMID:25253789

Wuthiekanun, Vanaporn; Amornchai, Premjit; Langla, Sayan; Oyuchua, Malinee; Day, Nicholas P J; Limmathurotsakul, Direk

2014-12-01

264

[Poisoning with deadly agaric (Amanita virosa). Symptoms, diagnosis and treatment].  

PubMed

Amatoxin poisonings are uncommon in Norway. We describe a case where a young couple was poisoned after accidental ingestion of Amanita virosa (deadly agaric). After hospital treatment they recovered without serious damage to the liver. We briefly review the biological actions of amatoxins, discuss the symptoms and signs of amatoxin poisoning in detail, and outline current recommendations on therapy. PMID:2363148

Madsen, S; Jenssen, K M

1990-05-30

265

Localized axial Green's function method for the convection-diffusion equations in arbitrary domains  

NASA Astrophysics Data System (ADS)

A localized axial Green's function method (LAGM) is proposed for the convection-diffusion equation. The axial Green's function method (AGM) enables us to calculate the numerical solution of a multi-dimensional problem using only one-dimensional Green's functions for the axially split differential operators. This AGM has been developed not only for the elliptic boundary value problems but also for the steady Stokes flows, however, this paper is concerned with the localization of the AGM. This localization of the method is needed for practical purpose when computing the axial Green's function, specifically for the convection-diffusion equation on a line segment that we call the local axial line. Although our focus is mainly on the convection-dominated cases in arbitrary domains, this method can solve other cases in a unified way. Numerical results show that, despite irregular types of discretization on an arbitrary domain, we can calculate the numerical solutions using the LAGM without loss of accuracy even in cases of large convection. In particular, it is also shown that randomly distributed axial lines are available in our LAGM and complicated domains are not a burden.

Lee, Wanho; Kim, Do Wan

2014-10-01

266

Local DG method using WENO type limiters for convection-diffusion problems  

NASA Astrophysics Data System (ADS)

The local discontinuous Galerkin (LDG) method is a spatial discretization procedure for convection-diffusion equations, which employs useful features from high resolution finite volume schemes, such as the exact or approximate Riemann solvers serving as numerical fluxes and limiters, which is termed as Runge-Kutta LDG (RKLDG) when TVD Runge-Kutta method is applied for time discretization. It has the advantage of flexibility in handling complicated geometry, h- p adaptivity, and efficiency of parallel implementation and has been used successfully in many applications. However, the limiters used to control spurious oscillations in the presence of strong shocks are less robust than the strategies of essentially non-oscillatory (ENO) and weighted ENO (WENO) finite volume and finite difference methods. In this paper, we investigated RKLDG methods with WENO and Hermite WENO (HWENO) limiters for solving convection-diffusion equations on unstructured meshes, with the goal of obtaining a robust and high order limiting procedure to simultaneously obtain uniform high order accuracy and sharp, non-oscillatory shock transition. Numerical results are provided to illustrate the behavior of these procedures.

Zhu, Jun; Qiu, Jianxian

2011-05-01

267

A method to analyze the diffuse gamma-ray emission with the Fermi Large Area Telescope  

SciTech Connect

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.

Ackermann, Markus; Johannesson, Gueolaugur; Digel, Seth; Moskalenko, Igor V.; Reimer, Olaf [W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94305 (United States); Porter, Troy [Santa Cruz Institute for Particle Physics, Department of Physics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States); Strong, Andrew [Max-Planck-Institut fur Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching (Germany)

2008-12-24

268

Synthesis and applications of poly(2-hydroxyethylmethacrylate) grafted agar: a microwave based approach.  

PubMed

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

Rani, G Usha; Mishra, Sumit; Pathak, Gopal; Jha, Usha; Sen, Gautam

2013-10-01

269

Discretizing the Gent-McWilliams velocity and isopycnal diffusion with a discontinuous Galerkin finite element method  

NASA Astrophysics Data System (ADS)

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.

Pestiaux, A.; Kärnä, T.; Melchior, S.; Lambrechts, J.; Remacle, J. F.; Deleersnijder, E.; Fichefet, T.

2012-04-01

270

Spin-orbit induced backflow in neutron matter with auxiliary field diffusion Monte Carlo method  

NASA Astrophysics Data System (ADS)

The energy per particle of zero-temperature neutron matter is investigated, with particular emphasis on the role of the L?S interaction. An analysis of the importance of explicit spin-orbit correlations in the description of the system is carried out by the auxiliary field diffusion Monte Carlo method. The improved nodal structure of the guiding function, constructed by explicitly considering these correlations, lowers the energy. The proposed spin-backflow orbitals can also be conveniently used in the Green’s function Monte Carlo calculations of light nuclei.

Brualla, L.; Fantoni, S.; Sarsa, A.; Schmidt, K. E.; Vitiello, S. A.

2003-06-01

271

CCMR: Method Development of Dynamic Mass Diffusion Monte Carlo using Lennard-Jones Clusters  

NSDL National Science Digital Library

The Lennard-Jones clusters, clusters of inert particles have a long history of being studied. Many algorithms have been proposed and used with a varying level of success from "basin hopping" [1] to âgreedy searchâ [2]. Despite these achievements, the Lennard-Jones potential continues to be a widely studied model. Not only is it a good test case for new particle structure algorithms, but it is still an interesting model that we can yet learn from. In this project we proposed to study these cluster using a method never before attempted: dynamic mass diffusion Monte Carlo.

Craig, Helen A.

2007-08-29

272

Sinc-Chebyshev Collocation Method for a Class of Fractional Diffusion-Wave Equations  

PubMed Central

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

Mao, Zhi; Xiao, Aiguo; Yu, Zuguo; Shi, Long

2014-01-01

273

An Ion Diffusion Method for Visualising a Solid-like Water Nanofilm  

PubMed Central

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

Wang, Ya; Duan, Zhiguang; Fan, Daidi

2013-01-01

274

A simultaneous characterization of thermal conductivity and diffusivity of polymer materials by a periodic method  

NASA Astrophysics Data System (ADS)

A periodic method is used to determine simultaneously both thermal conductivity and diffusivity of various polymer materials at room temperature. The sample is placed between two metallic plates and temperature modulation is applied on the front side of one of the metallic plates. The temperature at the front and rear sides of both plates is measured and the experimental transfer function is calculated. The theoretical thermal heat transfer function is calculated by the quadrupole method. Thermal conductivity and diffusivity are simultaneously identified from both real and imaginary parts of the experimental transfer function. The thermophysical parameters of several polymer samples (PTFE, PVDF and PA11) with different thicknesses (respectively, 5 mm, 2 mm and 300 µm) were studied and compared with values from the literature. The values identified for the thermal parameters are in good agreement with values from the literature for PTFE and PVDF samples; however, we show that the method reaches its limit for the thinner PA11 sample, owing to inadequacy of the thermal model.

Boudenne, Abderrahim; Ibos, Laurent; Gehin, Evelyne; Candau, Yves

2004-01-01

275

An Ion Diffusion Method for Visualising a Solid-like Water Nanofilm  

NASA Astrophysics Data System (ADS)

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.

Wang, Ya; Duan, Zhiguang; Fan, Daidi

2013-12-01

276

Modification of flow and compressibility of corn starch using quasi-emulsion solvent diffusion method  

PubMed Central

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.

Akhgari, Abbas; Sadeghi, Hasti; Dabbagh, Mohammad Ali

2014-01-01

277

Quantifying water diffusion in high-viscosity and glassy aqueous solutions using a Raman isotope tracer method  

NASA Astrophysics Data System (ADS)

Recent research suggests that under certain temperature and relative humidity conditions atmospheric aerosol may be present in the form of a glassy solid. In order to understand the impacts that this may have on aerosol-cloud interactions and atmospheric chemistry, knowledge of water diffusion within such aerosol particles is required. Here, a method is described in which Raman spectroscopy is used to observe D2O diffusion in high-viscosity aqueous solutions, enabling a quantitative assessment of water diffusion coefficients, Dwater, as a function of relative humidity. Results for sucrose solutions compare well with literature data at 23.5 ± 0.3 °C, and demonstrate that water diffusion is slow (Dwater~5 ×10-17m2s-1), but not arrested, just below the glass transition. Room temperature water diffusion coefficients are also presented for aqueous levoglucosan and an aqueous mixture of raffinose, dicarboxylic acids and ammonium sulphate: at low humidity, diffusion is retarded but still occurs on millisecond to second timescales in atmospherically relevant-sized particles. The effect of gel formation on diffusion in magnesium sulfate solutions is shown to be markedly different from the gradual decrease in diffusion coefficients of highly viscous liquids. We show that using the Stokes-Einstein equation to determine diffusion timescales from viscosity leads to values which are more than five orders of magnitude too big, which emphasises the need to make measurements of diffusion coefficients. In addition, comparison of bounce fraction data for levoglucosan with measured diffusion data reveals that even when particles bounce the equilibration timescales for water are a fraction of a second for a 100 nm particle. This suggests a high bounce fraction does not necessarily indicate retarded water diffusion.

Price, H. C.; Murray, B. J.; Mattsson, J.; O'Sullivan, D.; Wilson, T. W.; Baustian, K. J.; Benning, L. G.

2013-11-01

278

Validation of a flow-injection-gas diffusion method for total volatile basic nitrogen determination in seafood products  

Microsoft Academic Search

A potentiometric flow-injection method, using a gas-diffusion cell, is described for the determination of total volatile basic nitrogen (TVB-N) in seafood products. The method was based on the change of the potential of a tungsten oxide electrode when volatile basic compounds, liberated from the fish extract sample, diffuses via a permeable membrane into a phosphate buffer acceptor stream and locally

Anissa Dhaouadi; Lotfi Monser; Saloua Sadok; Nafaâ Adhoum

2007-01-01

279

Operator splitting methods for degenerate convection–diffusion equations II: numerical examples with emphasis on reservoir simulation and sedimentation  

Microsoft Academic Search

We present an accurate numerical method for a large class of scalar, strongly degenerate convection–diffusion equations. Important subclasses are hyperbolic conservation laws, porous medium type equations, two-phase reservoir flow equations, and strongly degenerate equations coming from the recent theory of sedimentation–consolidation processes. The method is based on splitting the convective and the diffusive terms. The nonlinear, convective part is solved

Helge Holden; Kenneth Hvistendahl Karlsen; Knut-Andreas Lie

2000-01-01

280

A new method for apportionnement of diffuse nutrient sources of surface water contamination  

NASA Astrophysics Data System (ADS)

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.

Groenendijk, Piet; Mulder, Martin; Van Boekel, Erwin; Van der Bolt, Frank; Hendriks, Rob; Renaud, Leo

2014-05-01

281

Numerical Modeling of Deep Mantle Convection: Advection and Diffusion Schemes for Marker Methods  

NASA Astrophysics Data System (ADS)

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.

Mulyukova, Elvira; Dabrowski, Marcin; Steinberger, Bernhard

2013-04-01

282

Characterization of biogenic iron oxides collected by the newly designed liquid culture method using diffusion chambers.  

PubMed

We designed a new culture method for neutrophilic iron-oxidizing bacteria using liquid medium (i) to study the formation and mineralogical characteristics of biogenic iron oxides (BIOS) and (ii) to apply BIOS to various scientific and engineering applications. An iron-oxidizing bacterium, Mariprofundus ferrooxydans PV-1(T) (ATCC, BAA-1020), was cultured using a set of diffusion chambers to prepare a broad anoxic-oxic interface, upon which BIOS formation is typically observed in natural environments. Iron oxide precipitates were generated in parallel with bacterial growth. A scanning electron microscopy analysis indicated that the morphological features of the iron oxide precipitates in the medium (in vitro BIOS) were similar to those of BIOS collected from natural deep-sea hydrothermal environments in the Northwest Eifuku Seamount field in the northern Mariana Arc (in situ BIOS). Further chemical speciation of both the in vitro and in situ BIOS was examined with X-ray absorption fine structure (XAFS). A bulk XAFS analysis showed that the minerals in both BIOS were mainly ferrihydrite and oligomeric stages of amorphous iron oxyhydroxides with edge-sharing octahedral linkages. The amount of in vitro BIOS produced with the diffusion-chamber method was greater than those produced previously with other culture methods, such as gel-stabilized gradient and batch liquid culture methods. The larger yields of BIOS produced with the new culture method will allow us to clarify in the future the mineralization mechanisms during bacterial growth and to examine the physicochemical properties of BIOS, such as their adsorption to and coprecipitation with various elements and substances. PMID:24382149

Kikuchi, S; Makita, H; Takai, K; Yamaguchi, N; Takahashi, Y

2014-03-01

283

TOPICAL REVIEW: Applications of field-theoretic renormalization group methods to reaction diffusion problems  

NASA Astrophysics Data System (ADS)

We review the application of field-theoretic renormalization group (RG) methods to the study of fluctuations in reaction-diffusion problems. We first investigate the physical origin of universality in these systems, before comparing RG methods to other available analytic techniques, including exact solutions and Smoluchowski-type approximations. Starting from the microscopic reaction-diffusion master equation, we then pedagogically detail the mapping to a field theory for the single-species reaction kA ? ellA(ell < k). We employ this particularly simple but non-trivial system to introduce the field-theoretic RG tools, including the diagrammatic perturbation expansion, renormalization and Callan-Symanzik RG flow equation. We demonstrate how these techniques permit the calculation of universal quantities such as density decay exponents and amplitudes via perturbative epsi = dc - d expansions with respect to the upper critical dimension dc. With these basics established, we then provide an overview of more sophisticated applications to multiple species reactions, disorder effects, Lévy flights, persistence problems and the influence of spatial boundaries. We also analyse field-theoretic approaches to non-equilibrium phase transitions separating active from absorbing states. We focus particularly on the generic directed percolation universality class, as well as on the most prominent exception to this class: even-offspring branching and annihilating random walks. Finally, we summarize the state of the field and present our perspective on outstanding problems for the future.

Täuber, Uwe C.; Howard, Martin; Vollmayr-Lee, Benjamin P.

2005-04-01

284

A Simple and Efficient Diffuse Interface Method for Compressible Two-Phase Flows  

SciTech Connect

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.

Ray A. Berry; Richard Saurel; Fabien Petitpas

2009-05-01

285

Co-precipitation with PVP and Agar to Improve Physicomechanical Properties of Ibuprofen  

PubMed Central

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

Maghsoodi, Maryam; Kiafar, Farhad

2013-01-01

286

Co-precipitation with PVP and Agar to Improve Physicomechanical Properties of Ibuprofen  

PubMed Central

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

Maghsoodi, Maryam; Kiafar, Farhad

2013-01-01

287

Application of a Particle Method to the Advection-Diffusion-Reaction Equation  

NASA Astrophysics Data System (ADS)

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 ?t ?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.

Paster, A.; Bolster, D.; Benson, D. A.

2012-12-01

288

Evaluation of method of preparation of passive diffusion tubes for measurement of ambient nitrogen dioxide.  

PubMed

This study was carried out in response to suggestions that the measurement of NO(2) by Palmes-type passive diffusion tubes (PDT) is affected by the method of preparation of the triethanolamine (TEA) absorbent coating on the grids. The following combinations of factors were investigated: TEA solvent (acetone or water), volume composition of TEA in solvent (50% or 20%), and grid coating method (dipping in solution prior to assembly or pipetting solution on after assembly). Duplicate PDTs prepared by each of the 8 methods were exposed in parallel, in urban air, for a total of 80 separate 1 week exposures. NO(2) concentrations derived from PDTs prepared by pipetting methods were significantly less precise than concentrations from dipping methods, with mean RSDs for duplicate measurements of 13.8% and 8.5%, respectively (n= 316 each category). Pipetting methods using solutions of 50% TEA composition were particularly imprecise (mean RSD 17.2%). Data from PDTs prepared by pipetting methods were systematically more poorly correlated with each other and with data from co-located chemiluminescence analysers, than corresponding data from PDTs prepared by dipping methods, indicating that more consistent accuracy was also obtained by the latter PDTs. The statistical evidence suggested that PDTs prepared by pipetting 50% TEA in water generally gave lower NO(2) concentrations. Although this is in agreement with a previous study, it is also possible that such an observation here may be a statistical artefact given the demonstrably poorer precision of this method. The general tendency of PDTs to show positive bias in NO(2) measurement in urban air in 1 week exposures was again evident in this study (mean biases at roadside and urban centre locations of +35% (n= 475) and +18% (n= 112), respectively) consistent with augmentation of within-tube NO(2) flux by chemical reaction between co-diffusing NO and O(3). Overall, it is recommended that the pipetting method of PDT grid preparation is avoided, or at least investigated further, because of the apparent degradation in precision and accuracy of NO(2) measurement. Potential reasons for the effect are discussed. PMID:14737464

Hamilton, Richard P; Heal, Mathew R

2004-01-01

289

A numerical method to calculate the muon relaxation function in the presence of diffusion  

NASA Astrophysics Data System (ADS)

We present an accurate and efficient method to calculate the effect of random fluctuations of the local field at the muon, for instance in the case of muon diffusion, within the framework of the strong collision approximation. The method is based on a reformulation of the Markovian process over a discretized time base, leading to a summation equation for the muon polarization function which is solved by discrete Fourier transform. The latter is formally analogous, though not identical, to the integral equation of the original continuous-time model, solved by Laplace transform. With real-case parameter values, the solution of the discrete-time strong collision model is found to approximate the continuous-time solution with excellent accuracy even with a coarse-grained time sampling. Its calculation by the fast Fourier transform algorithm is very efficient and suitable for real time fitting of experimental data even on a slow computer.

Allodi, G.; De Renzi, R.

2014-11-01

290

Numerical Method Using Cubic B-Spline for a Strongly Coupled Reaction-Diffusion System  

PubMed Central

In this paper, a numerical method for the solution of a strongly coupled reaction-diffusion system, with suitable initial and Neumann boundary conditions, by using cubic B-spline collocation scheme on a uniform grid is presented. The scheme is based on the usual finite difference scheme to discretize the time derivative while cubic B-spline is used as an interpolation function in the space dimension. The scheme is shown to be unconditionally stable using the von Neumann method. The accuracy of the proposed scheme is demonstrated by applying it on a test problem. The performance of this scheme is shown by computing and error norms for different time levels. The numerical results are found to be in good agreement with known exact solutions. PMID:24427270

Abbas, Muhammad; Majid, Ahmad Abd.; Md. Ismail, Ahmad Izani; Rashid, Abdur

2014-01-01

291

Gradient diffusion antibiotic susceptibility testing of potentially probiotic lactobacilli.  

PubMed

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

Charteris, W P; Kelly, P M; Morelli, L; Collins, J K

2001-12-01

292

Comparison of Two Disc Diffusion Methods with Minimum Inhibitory Concentration for Antimicrobial Susceptibility Testing of Neisseria Gonorrhoeae Isolates  

PubMed Central

Background: A few studies are available comparing either minimum inhibitory concentration (MIC) values with the Clinical and Laboratory Standards Institute (CLSI) disc diffusion method or MIC with the Australian Gonococcal Surveillance Program (AGSP) method. Aim: This study was conducted with the aim to identify the most feasible and cost-effective method for antimicrobial susceptibility testing of Neisseria gonorrhoeae. Materials and Methods: Antimicrobial susceptibility testing of N. gonorrhoeae was performed using, in parallel, the E-test for MIC determination and disc diffusion by CLSI and AGSP techniques, and were compared. Susceptibility to penicillin, ciprofloxacin, tetracycline, ceftriaxone and spectinomycin and cefixime were determined by CSLI and AGSP method and Kappa statistics used to analyse the data with SPSS software. Results: All isolates were susceptible to ceftriaxone and spectinomycin by three methods. Ninety-nine (99%) strains were resistant to ciprofloxacin, while 1% showed intermediate susceptibility to ciprofloxacin by all methods. Statistically, there was a moderate level of agreement between the methods for penicillin. Conclusion: All three methods gave reproducible results. Although the media used in the disc diffusion by the AGSP method is easy and cheap to prepare, the CLSI method of disc diffusion testing is recommended for susceptibility testing of gonococcal isolates because of its feasibility and 100% accuracy, with MIC by E-test as the reference method. PMID:24971225

Khaki, P; Sharma, A; Bhalla, P

2014-01-01

293

Evaluation of enrichment, storage, and age of blood agar medium in relation to its ability to support growth of anaerobic bacteria.  

PubMed

By measuring the colony size of a variety of anaerobic bacteria isolated from clinical specimens, an evaluation was made of the benefits derived from the addition of several enrichments to blood agar medium commonly used for the growth of anaerobes. Similar methods were used to study the effects of various storage conditions and age of the medium. The results were compared with those obtained on freshly prepared and enriched blood agar plates as well as commercially available blood agar plates. Freshly prepared and enriched blood agar was found to give substantially larger colonies than could be grown on commercially obtained blood agar plates when both were inoculated and incubated under identical conditions. Storage of plating media under CO2 for periods of up to 72 h had only a minor effect on the growth of the anaerobic bacteria studied, but longer periods of storage under CO2 resulted in a less efficient plating medium. Nonenriched brain heart infusion (BHI) was found to be a better basal medium than Trypticase soy agar (TSA) medium. Colony size on fully enriched BHI blood agar plates was greater than nonenriched BHI greater than nonenriched TSA greater than commercially prepared nonenriched TSA plates. The data suggest that freshness of the plates may be as important as using rich media. PMID:11226

Hanson, C W; Martin, W J

1976-11-01

294

Measurement of the thermal diffusivity of liquids by the forced Rayleigh scattering method: Theory and experiment  

NASA Astrophysics Data System (ADS)

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%.

Nagasaka, Y.; Hatakeyama, T.; Okuda, M.; Nagashima, A.

1988-07-01

295

Use of Sodium Polyanethol Sulfonate in the Preparation of 5% Sheep Blood Agar Plates  

PubMed Central

An alternative method to defibrinating sheep blood for use in bacteriological media is described. The new procedure incorporates sodium polyanethol sulfonate in a concentration of 0.05% (vol/vol). In testing 117 bacterial and fungal isolates, no significant differences were found with respect to adequate growth, pigment production, hemolytic reactions, and other physical attributes. Further tests demonstrate that the sodium polyanethol sulfonate in sheep blood agar plates does not cause any aberrations in zone sizes around disks used in antibiotic susceptibility tests. Consequently, the method represents a suitable alternative to the use of defibrinated sheep blood in the preparation of bacteriological media. PMID:4210729

Wasilauskas, Benedict L.; Floyd, Julia; Roberts, T. Richard

1974-01-01

296

A multigrid Newton-Krylov method for multimaterial equilibrium radiation diffusion  

SciTech Connect

The authors focus on a fully implicit, nonlinearly converged, solution of multimaterial equilibrium radiation diffusion problems. The nonlinear method of solution is a Newton-Krylov (generalized minimum residual, GMRES) method preconditioned by a multigrid method. The multigrid iteration matrix results from a Picard-type linearization of the governing equations. The governing equation is highly nonlinear with the principal forms of nonlinearity found in the fourth-order dependence of the radiation energy on temperature, the temperature dependence of the opacity, and flux limiting. The efficiency of both the linear and nonlinear iterative techniques is investigated. With the realistic time step control the solution of the linear system does not scale linearly with multigrid as might be expected from theory. In contrast, the authors find that the use of multigrid to precondition a Newton-Krylov (GMRES) method provides a robust, scalable solution for the nonlinear system. Also only through converging the nonlinearities within a time step does the solution method achieve its design accuracy.

Rider, W.J.; Knoll, D.A.; Olson, G.L. [Los Alamos National Lab., NM (United States)] [Los Alamos National Lab., NM (United States)

1999-06-10

297

On the diffuse interface method using a dual-resolution Cartesian grid  

NASA Astrophysics Data System (ADS)

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.

Ding, Hang; Yuan, Cheng-jun

2014-09-01

298

Comparison of teicoplanin disk diffusion and broth microdilution methods against clinical isolates of Staphylococcus aureus and S. epidermidis  

PubMed Central

The CLSI M100-S19 document has recommended the disuse of vancomycin disks for staphylococci and informed that studies on the action of teicoplanin in disk-diffusion testing should be performed. We describe the comparison of two methods, disk diffusion and broth microdilution, for determining teicoplanin susceptibility in clinical isolates of staphylococci. Overall results showed an aggregation rate of 96.8%; Staphylococcus aureus showed total agreement while S. epidermidis showed 93.8% of agreement. According to these local results, disk diffusion can still be employed to teicoplanin susceptibility determination for staphylococci in our institution. PMID:24031750

Camargo, Carlos Henrique; Mondelli, Alessandro Lia; Boas, Paulo Jose Fortes Villas

2011-01-01

299

Comparison of teicoplanin disk diffusion and broth microdilution methods against clinical isolates of Staphylococcus aureus and S. epidermidis.  

PubMed

The CLSI M100-S19 document has recommended the disuse of vancomycin disks for staphylococci and informed that studies on the action of teicoplanin in disk-diffusion testing should be performed. We describe the comparison of two methods, disk diffusion and broth microdilution, for determining teicoplanin susceptibility in clinical isolates of staphylococci. Overall results showed an aggregation rate of 96.8%; Staphylococcus aureus showed total agreement while S. epidermidis showed 93.8% of agreement. According to these local results, disk diffusion can still be employed to teicoplanin susceptibility determination for staphylococci in our institution. PMID:24031750

Camargo, Carlos Henrique; Mondelli, Alessandro Lia; Bôas, Paulo José Fortes Villas

2011-10-01

300

The accuracy and stability of an implicit solution method for the fractional diffusion equation  

Microsoft Academic Search

We have investigated the accuracy and stability of an implicit numerical scheme for solving the fractional diffusion equation. This model equation governs the evolution for the probability density function that describes anomalously diffusing particles. Anomalous diffusion is ubiquitous in physical and biological systems where trapping and binding of particles can occur. The implicit numerical scheme that we have investigated is

T. A. M. Langlands; B. I. Henry

2005-01-01

301

Investigation of roughness cross correlation in a Ni\\/C multilayer mirror by X-ray diffuse scattering method  

Microsoft Academic Search

The possibility of applying X-ray diffuse scattering for studying roughness in multilayer X-ray mirrors, including the correlation\\u000a of roughnesses of neighboring interfaces (roughness cross-correlation) is considered. It is shown that the reliability and\\u000a informativeness of this method can be improved by rejecting the classical experimental schemes and using alternative schemes\\u000a in which not only the intensity of diffuse scattering itself,

N. V. Kovalenko; S. V. Mytnichenko; V. A. Chernov

2003-01-01

302

Impaction onto a Glass Slide or Agar versus Impingement into a Liquid for the Collection and Recovery of Airborne Microorganisms  

PubMed Central

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

Juozaitis, Arvydas; Willeke, Klaus; Grinshpun, Sergey A.; Donnelly, Jean

1994-01-01

303

Methicillin-resistant coagulase-negative staphylococci (MRCoNS) by disk diffusion method.  

PubMed

The antimicrobial susceptibility of 80 coagulase-negative staphylococci (CoNS) isolates from surgical wound, pus from infected skin lesions, burn exudates and diabetic ulcer exudates of patients in Mymensingh Medical College Hospital, Bangladesh, was evaluated in order to see their pattern of antimicrobial resistance. The study was carried out in the department of Microbiology, Mymensingh Medical College during the period from July 2009 to May 2011. The 80 CoNS isolates were subjected to antimicrobial susceptibility to relevant antibiotics including oxacillin by disk diffusion method. Out of 80 CoNS isolates, the highest number were resistant to oxacillin 36(45%), followed by gentamicin 32(40%), cefuroxime 25(31%), ceftriaxone 24(30%) and ciprofloxacin 18(22%). All isolates of CoNS were sensitive to imipenem and vancomycin. As MRCoNS were found multidrug resistant, therefore, antibiotic sensitivity must be done prior to treatment in infections caused by these species. PMID:23715340

Rahman, A; Hossain, M A; Paul, S K; Sultana, S; Haque, N; Kabir, M R; Hoque, S M

2013-04-01

304

IN-VITRO CHARACTERIZATION OF GASTRORETENTIVE MICROBALLOONS PREPARED BY THE EMULSION SOLVENT DIFFUSION METHOD  

PubMed Central

Microballoons floatable on JPXIII No.1 solution were developed as a dosage form capable of floating in the stomach. Microballoons were prepared by the emulsion solvent diffusion method using enteric acrylic and other polymers with drug in a mixture of dichloromethane and ethanol. It was found that preparation temperature determined the formation of cavity inside the microsphere and the surface smoothness, determining the floatability and the drug release rate of the microballoons. The correlation between the buoyancy of microballoons and their physical properties, e.g. apparent density and roundness of microballoons were elucidated. The drug loading efficiency of microballoons was also determined. The optimum loading amount of metformin in the microballoons was found to impart ideal floatable properties to the microballoons. By fitting the data into zero order, first order and Highuchi model it was concluded that the release followed zero order release. PMID:22247832

Yadav, Akash; Jain, Dinesh Kumar

2010-01-01

305

InP synthesis by the synthesis, solute diffusion (SSD) method using glassy-carbon crucibles  

SciTech Connect

An Indium Phosphide (InP) Synthesis system by the Synthesis, Solute Diffusion (SSD) method has been built. It provides high purity InP charges with low carrier densities (3 {times} 10{sup 14} to 2 {times} 10{sup 15} cm{sup {minus}3}) to be used as starting material for InP single-crystal Liquid Encapsulated Czochralski (LEC) growth. Glassy-carbon is a refractory material with low vapor pressure that can be moulded in various forms and sizes. Indeed the glassy-carbon crucible is reusable after the synthesis because InP does not stick to its walls. Preliminary electrical characteristics measurements showed residual carrier concentration below 3 {times} 10{sup 15} cm{sup {minus}3}. These results are comparable with those achieved utilizing quartz crucibles. The features denoted makes glassy-carbon an interesting alternative in comparison with quartz and PBN crucibles.

Miskys, C.R.; Oliveira, C.E.M. de; Carvalho, M.M.G. de [UNICAMP-IFGW-DFA-LPD, Campinas, Sao Paulo (Brazil)

1996-12-31

306

A systematic investigation of reflectance diffuse optical tomography using nonlinear reconstruction methods and continuous wave measurements  

PubMed Central

We conducted a systematic investigation of the reflectance diffuse optical tomography using continuous wave (CW) measurements and nonlinear reconstruction algorithms. We illustrated and suggested how to fine-tune the nonlinear reconstruction methods in order to optimize target localization with depth-adaptive regularizations, reduce boundary noises in the reconstructed images using a logarithm based objective function, improve reconstruction quantification using transport models, and resolve crosstalk problems between absorption and scattering contrasts with the CW reflectance measurements. The upgraded nonlinear reconstruction algorithms were evaluated with a series of numerical and experimental tests, which show the potentials of the proposed approaches for imaging both absorption and scattering contrasts in the deep targets with enhanced image quality.

Yuan, Zhen; Zhang, Jiang; Wang, Xiaodong; Li, Changqing

2014-01-01

307

A Lagged Diffusivity Method for Computing Total Variation Regularized Fluid Flow  

SciTech Connect

There is a great deal of recent work using optical flow methods for analyzing the dynamics of fluids, and much attention has been paid to developing regularization schemes for variational approaches that are consistent with the physics of fluid flow. In this work we show that using total variation to regularize two different kinds of optical flow functionals leads to very good flow field reconstructions for the kinds of dynamical structures that appear in fluid flow. The first optical flow functional is the classical component-based conservation of intensity, and the second approach is to reconstruct the potential of the flow, rather than the flow components. In the two cases, total variation regularization corresponds to imposing different scientific priors on the solution, which we compute using a variation of the Lagged Diffusivity Fixed Point Iteration. Numerical details are presented, and the results are demonstrated on synthetic data and on a data-driven oceanic flow model.

Basnayake, R.; Luttman, A.; Bollt, E.

2013-03-01

308

In-vitro characterization of gastroretentive microballoons prepared by the emulsion solvent diffusion method.  

PubMed

Microballoons floatable on JPXIII No.1 solution were developed as a dosage form capable of floating in the stomach. Microballoons were prepared by the emulsion solvent diffusion method using enteric acrylic and other polymers with drug in a mixture of dichloromethane and ethanol. It was found that preparation temperature determined the formation of cavity inside the microsphere and the surface smoothness, determining the floatability and the drug release rate of the microballoons. The correlation between the buoyancy of microballoons and their physical properties, e.g. apparent density and roundness of microballoons were elucidated. The drug loading efficiency of microballoons was also determined. The optimum loading amount of metformin in the microballoons was found to impart ideal floatable properties to the microballoons. By fitting the data into zero order, first order and Highuchi model it was concluded that the release followed zero order release. PMID:22247832

Yadav, Akash; Jain, Dinesh Kumar

2010-01-01

309

An anatomically driven anisotropic diffusion filtering method for 3D SPECT reconstruction  

NASA Astrophysics Data System (ADS)

In this study, we aim to reconstruct single-photon emission computed tomography images using anatomical information from magnetic resonance imaging as a priori knowledge about the activity distribution. The trade-off between anatomical and emission data is one of the main concerns for such studies. In this work, we propose an anatomically driven anisotropic diffusion filter (ADADF) as a penalized maximum likelihood expectation maximization optimization framework. The ADADF method has improved edge-preserving denoising characteristics compared to other smoothing penalty terms based on quadratic and non-quadratic functions. The proposed method has an important ability to retain information which is absent in the anatomy. To make our approach more stable to the noise-edge classification problem, robust statistics have been employed. Comparison of the ADADF method is performed with a successful anatomically driven technique, namely, the Bowsher prior (BP). Quantitative assessment using simulated and clinical neuroreceptor volumetric data show the advantage of the ADADF over the BP. For the modelled data, the overall image resolution, the contrast, the signal-to-noise ratio and the ability to preserve important features in the data are all improved by using the proposed method. For clinical data, the contrast in the region of interest is significantly improved using the ADADF compared to the BP, while successfully eliminating noise.

Kazantsev, Daniil; Arridge, Simon R.; Pedemonte, Stefano; Bousse, Alexandre; Erlandsson, Kjell; Hutton, Brian F.; Ourselin, Sébastien

2012-06-01

310

[Mechanical properties of nickel-titanium alloy wire developed by the diffusion method].  

PubMed

The present study was conducted to investigate mechanical properties of the nickel-titanium (Ni-Ti) alloy wire developed by the diffusion method, in comparison with the previous Ni-Ti wires. Two types of the wire, work hardening and super elastic wires, were used for three experiments; three-point bending test, tension test and torque test. The following findings were obtained. 1. A newly developed work hardening wire exhibited lower force level with a generous reduction of force at various wire deflections, in comparison with the previous work hardening Ni-Ti wires. It was also found that tension strength and extension ratio of this wire were greater, and its modulus of longitudinal elasticity was smaller than those of the previous wires, indicating high resistibility to breakage. 2. A super elastic wire, developed by the diffusion method, showed similar pattern of force reduction associated with varying wire deflections, although magnitude of force was slightly larger than those of the previous super elastic wires. 3. An interesting finding was that force and its reduction with various deflections were varied by controlling how the wire was ligated onto a bracket, which was more obvious in the work hardening type of the present Ni-Ti wire. 4. Magnitudes of force exerted by Ni-Ti wires were around 200 gf at a deflection of 2 mm with an interbracket distance of 7 mm, and seemed to be beyond an optimal orthodontic force for anterior teeth. A further refinement is expected in terms of improving mechanical properties and/or developing finer wires. PMID:2488929

Sakuda, M; Tanne, K; Araki, K; Kinami, H; Ishibe, H; Kokubu, K

1989-12-01

311

Development of a method to study positron diffusion in metals by the observation of positronium negative ions  

NASA Astrophysics Data System (ADS)

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. ?-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.

Suzuki, Takuji; Terabe, Hiroki; Iida, Shimpei; Yamashita, Takashi; Nagashima, Yasuyuki

2014-09-01

312

Fabrication of agar-gel microelectrodes and their application in the study of ion transfer across the agar–water ? 1,2-dichloroethane interface  

Microsoft Academic Search

In this paper, we describe a simple procedure to make agar-gel microelectrodes by filling micropipettes. These microelectrodes were used to study K+ transfer across the agar–water?1,2-dichloroethane interface facilitated by dibenzo-18-crown-6 (DB18C6), and the transfer of tetraethylammonium (TEA+). The results observed were similar to those obtained at micro-liquid?liquid interfaces. The effect of various amounts of agar in the aqueous phase was

Yuehong Tong; Peng Sun; Zhiquan Zhang; Yuanhua Shao

2001-01-01

313

Diffusion approximation-based simulation of stochastic ion channels: which method to use?  

PubMed

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

Pezo, Danilo; Soudry, Daniel; Orio, Patricio

2014-01-01

314

Diffusion approximation-based simulation of stochastic ion channels: which method to use?  

PubMed Central

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.

Pezo, Danilo; Soudry, Daniel; Orio, Patricio

2014-01-01

315

A new method for the measurement of the diffusivity of carbon in alpha-iron using an electrochemical cell  

Microsoft Academic Search

A new method has been employed to measure the diffusivity of carbon in alpha iron. The method involves the measurement of ionic current of a carbon concentration cell which employs an iron cylinder as the anode. The design of the cell is such that when a constant external potential is applied, the ionic current is determined by the concentration polarization

S. Rajendran Pillai; Indira Gandhi

1995-01-01

316

Method qualification and application of diffusion interaction parameter and virial coefficient.  

PubMed

This research focused on evaluation and application of two methods in studying weak protein-protein interactions, i.e. diffusion interaction parameter (KD) and second virial coefficient (B22), both of which are first-order coefficients of protein interactions. Although the plate-based KD method successfully distinguished KD values with relatively large difference in a pH ranging study, it failed to make a consistent statistical decision to determine close interactions as shown by the comprehensive ANOVA analysis. We also validated the DLS-based B22 method by using a model protein lysozyme. The dramatic change of solution appearance for lysozyme as a function of NaCl concentration highlighted the importance of B22 in understanding protein interactions. Moreover, B22 measurement for a MAb fragment suggested a more repulsive protein interaction in histidine buffer than in citrate buffer. The coefficient of variation was <10% when B22 was on an order of magnitude of 10(-4) L mmol/g(2) in contrast to >30% when it approached 10(-5) L mmol/g(2). In this research, we also made an attempt to study protein-protein interactions in concentrated MAb fragment solutions (e.g. >50 mg/mL). Our data suggested that such interactions could be empirically modeled by high-order virial expansions. PMID:24095715

Shi, Shuai; Uchida, Makiko; Cheung, Jason; Antochshuk, Valentyn; Shameem, Mohammed

2013-11-01

317

A model of cefoperazone tissue penetration: diffusion coefficient and protein binding.  

PubMed Central

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

Meulemans, A

1992-01-01

318

Author's personal copy Agar chemical hydrogel electrode binder for fuel-electrolyte-fed  

E-print Network

Author's personal copy Agar chemical hydrogel electrode binder for fuel-electrolyte-fed fuel cells­acid direct ethanol fuel cell Agar chemical hydrogel Electrode binder a b s t r a c t This work reports on the synthesis and application of a novel, cost-effective and environmentally friendly agar chemical hydrogel

Zhao, Tianshou

319

FAST MONTE CARLO SIMULATION METHODS FOR BIOLOGICAL REACTION-DIFFUSION SYSTEMS IN SOLUTION AND ON SURFACES  

PubMed Central

Many important physiological processes operate at time and space scales far beyond those accessible to atom-realistic simulations, and yet discrete stochastic rather than continuum methods may best represent finite numbers of molecules interacting in complex cellular spaces. We describe and validate new tools and algorithms developed for a new version of the MCell simulation program (MCell3), which supports generalized Monte Carlo modeling of diffusion and chemical reaction in solution, on surfaces representing membranes, and combinations thereof. A new syntax for describing the spatial directionality of surface reactions is introduced, along with optimizations and algorithms that can substantially reduce computational costs (e.g., event scheduling, variable time and space steps). Examples for simple reactions in simple spaces are validated by comparison to analytic solutions. Thus we show how spatially realistic Monte Carlo simulations of biological systems can be far more cost-effective than often is assumed, and provide a level of accuracy and insight beyond that of continuum methods. PMID:20151023

KERR, REX A.; BARTOL, THOMAS M.; KAMINSKY, BORIS; DITTRICH, MARKUS; CHANG, JEN-CHIEN JACK; BADEN, SCOTT B.; SEJNOWSKI, TERRENCE J.; STILES, JOEL R.

2010-01-01

320

Bifurcation analysis of brown tide by reaction-diffusion equation using finite element method  

SciTech Connect

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.

Kawahara, Mutsuto; Ding, Yan [Chuo Univ., Tokyo (Japan)] [Chuo Univ., Tokyo (Japan)

1997-03-01

321

Quantification of Al-goethite from diffuse reflectance spectroscopy and magnetic methods  

NASA Astrophysics Data System (ADS)

As one of the most abundant iron oxides in soils, the presence and nature of goethite is controlled by the soil conditions and burial history. The visible diffuse reflectance spectroscopy (DRS) is a useful tool for quantifying goethite. However, aluminium (Al) substitution for goethite is very common in soils and the effects of Al content on the DRS properties of goethite have not been fully resolved. In this study, two series of Al substituted goethites (Al-goethite) and 20 Chinese loess/palaeosol samples were investigated using both DRS and magnetic methods to test the feasibility of quantifying Al-goethite with the DRS method. Results show that the peak positions and amplitudes of the goethite DRS band are significantly influenced by Al substitution. Specifically, the goethite concentration proxy, the amplitude of the DRS band, is relatively stable only when Al substitution ranged between about 4 and 16 mol per cent. Practically, in order to resolve the difficulty in measuring Al content in natural samples, the unblocking temperature (Tb) is proposed as the proxy for Al substitution of goethite. When Tb of Al-goethite was above 250 K, the amplitude of DRS can be used to reliably trace the goethite concentration variation in natural samples. For example, the DRS spectra for the Chinese loess-palaeosol samples support the idea that only haematite is enhanced via pedogenesis. In contrast, the origin of goethite seems to be mostly related to the aeolian inputs.

Jiang, Zhaoxia; Liu, Qingsong; Colombo, Claudio; Barrón, Vidal; Torrent, José; Hu, Pengxiang

2014-01-01

322

Adaptive meshless local maximum-entropy finite element method for convection-diffusion problems  

NASA Astrophysics Data System (ADS)

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.

Wu, C. T.; Young, D. L.; Hong, H. K.

2014-01-01

323

DIFFUSION OF INNOVATION: ENHANCING THE DISSEMINATION OF THE PONSETI METHOD IN LATIN AMERICA THROUGH VIRTUAL FORUMS  

PubMed Central

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

Jayawardena, Asitha; Boardman, Allison; Cook, Thomas; Oprescu, Florin; Morcuende, Jose A

2011-01-01

324

Gellan gum as a substitute for agar in leptospiral media.  

PubMed Central

An albumin polysorbate semisolid medium (Ellinghausen McCullough Johnson Harris medium) gelled with gellan gum (Gelrite; Kelco Div., Merck & Co., Inc.) compared favorably with conventional agar media for the cultivation of both pathogenic and saprophytic leptospires. The gellan gum medium supported the growth of all 18 leptospiral strains studied which included an array of serovars with various fastidious growth characteristics. Gellan gum medium was also used advantageously as a long-term maintenance medium; 9- to 12-month-old cultures still contained viable organisms. The colonial growth in gellan gum plating medium of six representative strains was consistent with previously described colonial growth on agar plating media. In addition, gellan gum medium appeared to be an excellent medium for the recovery of leptospires from the blood, liver, and kidneys of hamsters experimentally infected with a virulent Leptospira interrogans serovar bataviae strain. As few as 1 to 10 organisms in the infective tissue could be recovered in semisolid Ellinghausen McCullough Johnson Harris-gellan gum medium. The antigenicity did not appear to be affected by growth in gellan gum medium. The hamster-virulent strain of L. interrogans serovar bataviae isolated from a moribund hamster maintained its virulence after 10 sequential passages in gellan gum medium. Gellan gum medium can be a valuable adjunct to currently used cultural procedures. Images PMID:3754265

Rule, P L; Alexander, A D

1986-01-01

325

Enumeration of heterotrophic bacteria in water for dialysis: Comparison of the efficiency of reasoner'2 agar and plate count agar.  

PubMed

Due to the fact the incubation conditions may influence the microbiological evaluation of water for dialysis, the objective of the present study was the comparison of the efficiency of R2A and PCA media in the enumeration of heterotrophic bacteria in 193 samples of water collected in dialysis clinics from 12 cities in São Paulo, between October and December 2007. Results showed counts significantly greater in R2A, suggesting that enumeration should be carried out in R2A, suggesting that enumeration should be carried out in R2A agar associated with longer incubation times, because of the greater sensitivity. PMID:24031456

Bugno, Adriana; Almodóvar, Adriana Aparecida Buzzo; Pereira, Tatiana Caldas

2010-01-01

326

GENERATION OF DYNAMIC STANDARD TEST ATMOSPHERES FOR AROMATIC COMPOUNDS BY USING THE DIFFUSION VIAL METHOD  

Microsoft Academic Search

A diffusion vial was calibrated to generate standard test atmospheres for benzene, toluene, ethylbenzene, and styrene. The vial was placed into a temperature-controlled chamber in a standards generator, and the diffusion rates for the test compounds were experimentally determined by mass loss and time. The test concentration data were correlated by using a gas chromatograph that was previously calibrated with

Brian Worthington; Allan R. Rey

1991-01-01

327

Diffusion coefficients for LMFBR cells calculated with MOC and Monte Carlo methods  

Microsoft Academic Search

The present work discusses the calculation of the diffusion coefficient of a lattice of hexagonal cells, with both “sodium present” and “sodium absent” conditions. Calculations are performed in the framework of lattice theory (also known as fundamental mode approximation). Unlike the classical approaches, our heterogeneous leakage model allows the calculation of diffusion coefficients under all conditions, even if planar voids

W. F. G. van Rooijen; G. Chiba

2011-01-01

328

A novel method for computing effective diffusivity: Application to helium implanted ?-Fe thin films  

NASA Astrophysics Data System (ADS)

The effective diffusivity of helium in thin iron films is quantified using spatially resolved stochastic cluster dynamics and object kinetic Monte Carlo simulations. The roles of total displacement dose (in DPA), damage rate, helium to DPA ratio, layer thickness, and damage type (cascade damage vs Frenkel pair implantation) on effective He diffusivity are investigated. Helium diffusivity is found to decrease with increasing total damage and decreasing damage rate. Arrhenius plots show strongly increased helium diffusivity at high temperatures, high total implantation, and low implantation rates due to decreased vacancy and vacancy cluster concentrations. At low temperatures, effective diffusivity is weakly dependent on foil thickness while at high temperatures, narrower foils prevent defect accumulation by releasing all defects at the free surfaces. Helium to DPA ratio is not shown to strongly change helium diffusivity in the range of irradiation conditions simulated. Frenkel pair implantation is shown to cause higher effective diffusivity and more complex diffusion mechanisms than cascade implantation. The results of these simulations indicate that the differences in damage rates between implantation experiments and fission or fusion environments may result in differences in the final microstructure.

Dunn, Aaron; Agudo-Merida, Laura; Martin-Bragado, Ignacio; McPhie, Mathieu; Cherkaoui, Mohammed; Capolungo, Laurent

2014-05-01

329

A Simple Educational Method for the Measurement of Liquid Binary Diffusivities  

ERIC Educational Resources Information Center

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…

Rice, Nicholas P.; de Beer, Martin P.; Williamson, Mark E.

2014-01-01

330

3D Lagrangian turbulent diffusion of dust grains in a protoplanetary disk: method and first applications  

E-print Network

In order to understand how the chemical and isotopic compositions of dust grains in a gaseous turbulent protoplanetary disk are altered during their journey in the disk, it is important to determine their individual trajectories. We study here the dust-diffusive transport using lagrangian numerical simulations using the the popular "turbulent diffusion" formalism. However it is naturally expressed in an Eulerian form, which does not allow the trajectories of individual particles to be studied. We present a simple stochastic and physically justified procedure for modeling turbulent diffusion in a Lagrangian form that overcomes these difficulties. We show that a net diffusive flux F of the dust appears and that it is proportional to the gas density ({\\rho}) gradient and the dust diffusion coefficient Dd: (F=Dd/{\\rho}\\timesgrad({\\rho})). It induces an inward transport of dust in the disk's midplane, while favoring outward transport in the disk's upper layers. We present tests and applications comparing dust diff...

Charnoz, Sebastien; Aleon, Jérôme; Moreira, Manuel

2011-01-01

331

A generalized diffusion model for growth of nanoparticles synthesized by colloidal methods.  

PubMed

A nanoparticle growth model is developed to predict and guide the syntheses of monodisperse colloidal nanoparticles in the liquid phase. The model, without any a priori assumptions, is based on the Fick's law of diffusion, conservation of mass and the Gibbs-Thomson equation for crystal growth. In the limiting case, this model reduces to the same expression as the currently accepted model that requires the assumption of a diffusion layer around each nanoparticle. The present growth model bridges the two limiting cases of the previous model i.e. complete diffusion controlled and adsorption controlled growth of nanoparticles. Specifically, the results show that a monodispersion of nanoparticles can be obtained both with fast monomer diffusion and with surface reaction under conditions of small diffusivity to surface reaction constant ratio that results is growth 'focusing'. This comprehensive description of nanoparticle growth provides new insights and establishes the required conditions for fabricating monodisperse nanoparticles critical for a wide range of applications. PMID:24491334

Wen, Tianlong; Brush, Lucien N; Krishnan, Kannan M

2014-04-01

332

A new method of determination of minority carrier diffusion length in the base region of silicon solar cells  

SciTech Connect

A new method of determination of the minority carrier diffusion length (L) in the base region of an n[sup +]-p-p[sup +] silicon solar cell using the spectral response of the cell in a middle wavelength ([lambda]) range is presented. The minority carrier diffusion length (L) in the base region of an n[sup +]-p or n[sup +]-p-p[sup +] silicon solar cell has a profound effect on the solar cell performance. In this paper the authors report a new method of determination of diffusion length using the middle wavelength spectral response (MWSR) of the cell. It has been developed using a model of n[sup +]-p-p[sub +] silicon solar cells given by Singh and Jain and making some simplifying assumptions. It is equally applicable to cells with d/L > 2.5 and d/L < 2.5. In the following they give the theoretical basis of the method and present the result of the measurement of diffusion length of a few N[sup +]-p-p[sup +] silicon solar cells with d/L in the range 1.3--4.1 by using this method and the LWSR method.

Basu, P.K.; Singh, S.N.; Arora, N.K.; Chakravarty, B.C. (National Physical Lab., New Delhi (India))

1994-03-01

333

A finite elements method to solve the Bloch-Torrey equation applied to diffusion magnetic resonance imaging  

NASA Astrophysics Data System (ADS)

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

2014-04-01

334

New experimental method to measure pure and cross diffusion coefficients of transparent ternary mixtures using Mach-Zehnder interferometry  

NASA Astrophysics Data System (ADS)

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.

Ahadi, Amirhossein; Saghir, M. Ziad

2014-08-01

335

Comparative evaluation of the E test, agar dilution, and broth microdilution for testing susceptibilities of Helicobacter pylori strains to 20 antimicrobial agents.  

PubMed Central

The Epsilometer test (E test; AB Biodisk, Solna, Sweden), a new quantitative technique for the determination of antimicrobial susceptibility, was compared to reference methods (agar dilution and broth microdilution) for the antimicrobial susceptibility testing of Helicobacter pylori. Seventy-one H. pylori strains isolated from patients with duodenal ulcers were tested against 20 antimicrobial agents. The E test and the agar dilution method were carried out on Mueller-Hinton agar; the broth microdilution method was performed with Mueller-Hinton broth. The E-test results showed excellent correlation with the agar dilution results, with 91.3 and 98.8% agreement within 1 and 2 log2 dilution steps, respectively, in a total of 1,350 tests. The correlation between the E-test results and the broth microdilution results was slightly higher, with 91.6 and 99.1% agreement within 1 and 2 log2 dilution steps, respectively, in a total of 1,317 tests. There were six major errors and two very major errors by the metronidazole E test compared to the results obtained by reference methods. Excellent agreement between E-test, agar dilution, and broth microdilution results was found for resistance to erythromycin (8%), clarithromycin (6%), and tetracycline (6%). Our results confirm that the E test is comparable to standardized methods for susceptibility testing. Therefore, the E test is a reliable and alternative method for testing H. pylori susceptibility to a wide range of antimicrobial agents in clinical practice. PMID:9196205

Piccolomini, R; Di Bonaventura, G; Catamo, G; Carbone, F; Neri, M

1997-01-01

336

Lattice Microbes: high-performance stochastic simulation method for the reaction-diffusion master equation  

PubMed Central

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

Roberts, Elijah; Stone, John E.; Luthey-Schulten, Zaida

2013-01-01

337

A grey diffusion acceleration method for time-dependent radiative transfer calculations  

SciTech Connect

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.

Nowak, P.F.

1991-07-01

338

The two-regime method for optimizing stochastic reaction–diffusion simulations  

PubMed Central

Spatial organization and noise play an important role in molecular systems biology. In recent years, a number of software packages have been developed for stochastic spatio-temporal simulation, ranging from detailed molecular-based approaches to less detailed compartment-based simulations. Compartment-based approaches yield quick and accurate mesoscopic results, but lack the level of detail that is characteristic of the computationally intensive molecular-based models. Often microscopic detail is only required in a small region (e.g. close to the cell membrane). Currently, the best way to achieve microscopic detail is to use a resource-intensive simulation over the whole domain. We develop the two-regime method (TRM) in which a molecular-based algorithm is used where desired and a compartment-based approach is used elsewhere. We present easy-to-implement coupling conditions which ensure that the TRM results have the same accuracy as a detailed molecular-based model in the whole simulation domain. Therefore, the TRM combines strengths of previously developed stochastic reaction–diffusion software to efficiently explore the behaviour of biological models. Illustrative examples and the mathematical justification of the TRM are also presented. PMID:22012973

Flegg, Mark B.; Chapman, S. Jonathan; Erban, Radek

2012-01-01

339

Comparison of dialysis membrane diffusion samplers and two purging methods in bedrock wells  

USGS Publications Warehouse

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.

Imbrigiotta, T. E.; Ehlke, T. A.; Lacombe, P. J.; Dale, J. M.

2002-01-01

340

Effect of the 5E Model on Prospective Teachers' Conceptual Understanding of Diffusion and Osmosis: A Mixed Method Approach  

ERIC Educational Resources Information Center

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…

Artun, Huseyin; Costu, Bayram

2013-01-01

341

Engineering Instruction In Nondestructive Testing Of Materials (NDT) Using The Capillary Diffusion Method  

NSDL National Science Digital Library

In a great majority of educational cases, testing of materials in the laboratory implies destructive techniques consisting of using universal testing machines (UTMs), where materials are brought to a failure condition under tension, compression, shear, bending or torsion. Common objectives associated with these types of tests are: the evaluation of materials moduli of elasticity and rigidity, yield strength, strain, ultimate strength, etc. In engineering practice, however, in-situ nondestructive testing (NDT) of materials are highly preferable, in order to evaluate rapidly the condition, failure potential, usefulness and serviceability of engineering materials. Thus, nondestructive testing of materials ought to be an essential ingredient of engineering education and training, since it plays a significant role in design, manufacturing and evaluation of engineering equipment. This paper presents an inexpensive, simple and effective method to convey to engineering students the underlying principles of NDT, based on an innovative technique referred to as Capillary Diffusion Method (CDM), which is classified within the category of non-destructive Penetrant Testing (PT). CDM is relatively unknown in the United States, but, it has been used for several years in the former Soviet Union, and more recently, in the Russian Federation. CDM proves to be quite versatile and considerably faster than conventional PT techniques used in the U.S. In this paper, the underlying science behind the CDM technique is discussed in detail, as well as, the academic benefits and educational potential derived from the inclusion of CDM in engineering academic curriculum. Mathematical, graphical and numerical documentation are presented in order to substantiate the suitability of CDM as an educational tool to teach Nondestructive Testing in engineering programs such as: Mechanical engineering, Chemical engineering, Civil engineering, Aeronautical, Aerospace engineering, Power Plant Engineering, and Nuclear engineering.

Berezkina, Nadezda; Leipunsky, Ilya; Lopez, Guido

2009-08-11

342

Elemental composition of Physarum compressum Alb. et Schw. sporocarps and their structures cultivated on rabbit dung and agar substrates.  

PubMed

The elemental composition of spores, peridium walls, and lime nodes of Physarum compressum sporocarps, cultivated on rabbit dung as a natural growing environment for the slime mold and on artificial agar medium, was compared to evaluate differences that may be dependent on substrates. Whole fruiting bodies and samples of both experimental media were extracted with nitric acid or Parr digest bomb, respectively, and analyzed by means of total X-ray reflection fluorescence (TXRF). Electron probe microanalysis (EPMA) of spores, peridium walls, and lime nodes structure was carried out with the scanning electron microscope equipped with energy-dispersive spectrometer. Because of minute sizes and roughness of investigated structures, Monte Carlo simulations were utilized to establish analytical conditions of EPMA. Biological and geological standards were used in the quantification of element concentrations. According to TXRF, the fruiting bodies from agar medium revealed lower concentrations of K, Ca, Cr, Mn, and Fe in relation to fruiting bodies from the dung, reflecting elemental relationships in the experimental media. According to EPMA, the highest Ca concentration was found in the lime nodes followed by the peridium and the spores. Culturing of the slime molds on the rabbit dung indicated higher concentration of Ca in the lime nodes and peridium walls when compared with those obtained from the sporocarps grown on agar media. The opposite relation was found for the spores. The concentration of Na, Mg, P, S, and Cl was generally lower in all structures of the sporocarps harvested from the dung than from the agar medium. K was in higher concentration in analyzed structures from dung than from agar. Different element uptake (except for Ca and K) was revealed by the two methods: TXRF and EPMA. PMID:20981759

Janik, Paulina; Tylko, Grzegorz; Ostachowicz, Beata; Turnau, Katarzyna

2010-12-01

343

Investigation to develop a method to apply diffusion barrier to high strength fibers  

NASA Technical Reports Server (NTRS)

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.

Veltri, R. D.; Paradis, R. D.; Douglas, F. C.

1975-01-01

344

Accelerated stochastic and hybrid methods for spatial simulations of reaction diffusion systems  

NASA Astrophysics Data System (ADS)

Spatial distributions characterize the evolution of reaction-diffusion models of several physical, chemical, and biological systems. We present two novel algorithms for the efficient simulation of these models: Spatial ?-Leaping ( S?-Leaping), employing a unified acceleration of the stochastic simulation of reaction and diffusion, and Hybrid ?-Leaping ( H?-Leaping), combining a deterministic diffusion approximation with a ?-Leaping acceleration of the stochastic reactions. The algorithms are validated by solving Fisher's equation and used to explore the role of the number of particles in pattern formation. The results indicate that the present algorithms have a nearly constant time complexity with respect to the number of events (reaction and diffusion), unlike the exact stochastic simulation algorithm which scales linearly.

Rossinelli, Diego; Bayati, Basil; Koumoutsakos, Petros

2008-01-01

345

Mathematical Methods for Diffusion MRI Processing C. Lengleta,b,,1  

E-print Network

in the orthogonal orientations. Measuring, at each voxel, the effect of water diffusion on the MR signal in a number used to study a wide range of neurological disorders such as cerebro-vascular diseases, multiple scle

346

Evaluation of New Vitek 2 Card and Disk Diffusion Method for Determining Susceptibility of Staphylococcus aureus to Oxacillin?  

PubMed Central

Detection of methicillin resistance in Staphylococcus aureus is a challenge, especially low-level resistance, which is often misdiagnosed. The aim of this study was to compare the diagnostic accuracies of the automated Vitek 2 system and disk diffusion tests, using cefoxitin and moxalactam, for the detection of methicillin resistance in S. aureus strains. Four sets of genotypically diverse isolates were selected from a national reference collection, including mecA-negative S. aureus isolates (n = 56), hospital-acquired (n = 88) and community-acquired (n = 40) S. aureus isolates, and heterogeneous methicillin-resistant S. aureus isolates (n = 29). Oxacillin susceptibility was tested by the Vitek 2 system with the AST P549 card and by disk diffusion methods using 10, 30, and 60 ?g cefoxitin and 30 ?g moxalactam. Oxacillin resistance was confirmed by PCR for the mecA gene. The overall sensitivities for oxacillin resistance detection were 97.5% for the Vitek 2 automated system, 98.7% for 60-?g cefoxitin and moxalactam disk diffusion, and 99.6% for 10- and 30-?g cefoxitin disks, respectively. Methicillin-susceptible S. aureus isolates were correctly reported as susceptible by all methods. The median times for methicillin testing were 7 h for the Vitek 2 system versus 24 h for disk diffusion methods. In conclusion, the cefoxitin and moxalactam disk diffusion methods and the Vitek 2 automated system are highly accurate methods for methicillin resistance detection, including a range of representative Belgian methicillin-resistant S. aureus strains and unusual strains exhibiting cryptic or low-level oxacillin resistance. PMID:18550733

Roisin, Sandrine; Nonhoff, Claire; Denis, Olivier; Struelens, Marc J.

2008-01-01

347

Measuring thermal diffusivity of mechanical and optical grades of polycrystalline diamond using an AC laser calorimetry method  

SciTech Connect

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.

Rule, Toby D. [II-VI Incorporated; Cai, Wei [ORNL; Wang, Hsin [ORNL

2013-01-01

348

Efficient gradient-free simplex method for estimation of optical properties in image-guided diffuse optical tomography  

NASA Astrophysics Data System (ADS)

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.

Jagannath, Ravi Prasad K.; Yalavarthy, Phaneendra K.

2013-03-01

349

a New Method for Measuring Diffusion Coefficient of Gases in Liquids by Plif  

NASA Astrophysics Data System (ADS)

Gas-liquid mass transfer is a major issue in engineering processes such as wastewater treatment or biogas production since this phenomenon is directly linked to their design and efficiency. In recent years, much research has been done in this area but some gaps still remain in our knowledge of gas-liquid transfer, in particular concerning molecular diffusivity. The determination of molecular diffusivity is commonly based on empirical correlations, such as the widely used Wilke and Chang13 expression, valid under specific conditions and with relatively high uncertainties. In the present work, an innovative and promising technique is proposed to determine diffusion coefficients of gases in liquids. This technique is based on visualizing and quantifying oxygen diffusion across a flat gas-liquid interface, in a Newtonian medium, using planar laser induced fluorescence (PLIF) with inhibition. Particle image velocimetry (PIV) experiments were conducted to confirm the hydrodynamic flow field in the liquid phase. Results included the visualization of oxygen diffusion over time, and the quantification of this visualization. The oxygen diffusivity thus determined is in agreement with values found in the literature.

Jimenez, Mélanie; Dietrich, Nicolas; Hebrard, Gilles

350

An improved design method and experimental performance of two dimensional curved wall diffusers  

NASA Technical Reports Server (NTRS)

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.

Yang, T.; Hudson, W. G.; El-Nashar, A. M.

1972-01-01

351

Preliminary Report on the Development of a Diffusion-in-Gel Method for the Diagnosis of Ram Epididymitis  

PubMed Central

A simple gel-diffusion technique is described for the diagnosis of ram epididymitis caused by Brucella ovis. The results are shown to be very similar to those obtained by the complement-fixation test, which is currently the standard method of diagnosis. The method is suitable for use in the field and is expected to facilitate the control of ram epididymitis in areas where laboratory facilities are not available. Images PMID:4985433

Myers, Donald M.; Siniuk, Alicia A.

1970-01-01

352

A numerical algorithm for the diffusion equation using 3D FEM and the Arnoldi method [human tissue cells detection  

Microsoft Academic Search

We introduce a computational method for solving the photon diffusion equation in an unusual human cells detection problem. In particular, we construct a “generalized” state-space system and compute the impulse response of an equivalent truncated state-space system. We use a 3D finite element method (FEM) to obtain the state space system. Secondly, we use the Arnoldi iteration to approximate the

Qing Su; Vassilis L. Syrmos; David Y. Y. Yun

1999-01-01

353

Evaluation of eight agar media for the isolation of shiga toxin-Producing Escherichia coli.  

PubMed

The growth characteristics of 96 shiga toxin-producing Escherichia coli (STEC) strains representing 36 different O-types (including priority O types O26, O45, O103, O111, O121, O145 and O157) on commercial and in-house agar media were studied. The ability of the strains to grow on agar media with varying selective supplement formulations was evaluated using MacConkey Agar (MAC); Rainbow® Agar O157 (RBA); Rainbow® Agar O157 with manufacturer-recommended selective supplements (RBA-NT); Rainbow® Agar O157 with USDA-recommended selective supplements (RBA-USDA); CHROMagar STEC™ (CH STEC); Tryptone Bile agar containing cefixime and tellurite (TBA-CT); Tryptone Bile agar containing cefixime, tellurite, eosin and methylene blue (TBA-EM); and VTEC agar. All of the strains were able to grow on MAC, RBA and VTEC agar, whereas a number of strains (including some non-O157 priority O types) were unable to grow on the highly selective media CH STEC, RBA-NT, RBA-USDA, TBA-EM and TBA-CT. Only RBA-NT and CH STEC exhibited significant inhibition of background flora from ground beef enrichment. Significant inhibition of background flora from beef trim enrichment was observed with RBA-NT, RBA-USDA, CH STEC, TBA-EM and VTEC agar. With exception of E. coli O157, several different colony morphologies were observed on the differential plating media among strains of the same O type, indicating that this colony morphology is not a reliable means of identifying target STEC. These results suggest that an approach to maximize the recovery of target STEC from beef enrichment cultures is dual plating on lesser (RBA, MAC, VTEC agar) and more highly (RBA-NT, CH STEC) selective agars. PMID:24211606

Gill, Alexander; Huszczynski, George; Gauthier, Martine; Blais, Burton

2014-01-01

354

Preparation and characterization of solid lipid nanoparticles containing cyclosporine by the emulsification-diffusion method  

PubMed Central

Solid lipid nanoparticles (SLNs) have been used for carrying different therapeutic agents because they improve absorption and bioavailability. The aim of the study was to prepare lipidic nanoparticles containing cyclosporine (CyA) by the emulsification-diffusion method and to study their physicochemical stability. Glyceryl behenate (Compritol® ATO 888) and lauroyl macrogolglycerides (Gelucire® 44/14) were used as carrier materials. Nanoparticles with good stability were obtained with Gelucire®, while it was difficult to obtain stable systems with Compritol®. Systems with Gelucire® were characterized by particle size, Z-potential, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), entrapment efficiency and in vitro release. Particle size and Z-potential were evaluated for at least three months. With a high CyA content (?60 mg) in Gelucire® SLNs, variations in size were greater and particle size also increased over time in all batches; this effect may have been caused by a probable expulsion of the drug due to the lipid’s partial rearrangement. While the Z-potential decreased 10 mV after three months, this effect may be explained by the superficial properties of the drug that make the molecules to be preferably oriented at the solid-liquid interface, causing a change in the net charge of the particle. SEM confirmed size and shape of the nanoparticles. DSC studies evidenced that CyA affects the lipid structure by a mechanism still unknown. The entrapment efficiency was higher than 92%, and CyA release from SLNs was relatively fast (99.60% in 45 min). PMID:20856836

Urban-Morlan, Zaida; Ganem-Rondero, Adriana; Melgoza-Contreras, Luz Maria; Escobar-Chavez, Jose Juan; Nava-Arzaluz, Maria Guadalupe; Quintanar-Guerrero, David

2010-01-01

355

Use of the Chrome Azurol S Agar Plate Technique To Differentiate Strains and Field Isolates of Rhizobium leguminosarum biovar trifolii.  

PubMed

Identification of Rhizobium and Bradyrhizobium strains and especially of indigenous isolates continues to be one of the major difficulties associated with competition studies. Because there is no universally accepted method, the method of choice depends on preference, experience, and equipment. Here, an agar plate technique was used to distinguish strains and field isolates of Rhizobium leguminosarum biovar trifolii to provide a basis for identifying nodule occupants in further competition studies. A rapid plate technique, based on differential growth characteristics, complements other techniques such as serological reactions, particularly when antisera cross-react with nonhomologous strains. The technique involves culturing strains and isolates on chrome azurol S agar. Although similar responses were observed among some strains, the response was highly reproducible and was considered an ideal complementary technique used in conjunction with serological procedures. Strains with similar responses could often be differentiated by varying media components, such as the source of carbon. PMID:16347877

Ames-Gottfred, N P; Christie, B R; Jordan, D C

1989-03-01

356

Comparison of diffusion- and pumped-sampling methods to monitor volatile organic compounds in ground water, Massachusetts Military Reservation, Cape Cod, Massachusetts, July 1999-December 2002  

USGS Publications Warehouse

To evaluate diffusion sampling as an alternative method to monitor volatile organic compound (VOC) concentrations in ground water, concentrations in samples collected by traditional pumped-sampling methods were compared to concentrations in samples collected by diffusion-sampling methods for 89 monitoring wells at or near the Massachusetts Military Reservation, Cape Cod. Samples were analyzed for 36 VOCs. There was no substantial difference between the utility of diffusion and pumped samples to detect the presence or absence of a VOC. In wells where VOCs were detected, diffusion-sample concentrations of tetrachloroethene (PCE) and trichloroethene (TCE) were significantly lower than pumped-sample concentrations. Because PCE and TCE concentrations detected in the wells dominated the calculation of many of the total VOC concentrations, when VOC concentrations were summed and compared by sampling method, visual inspection also showed a downward concentration bias in the diffusion-sample concentration. The degree to which pumped- and diffusion-sample concentrations agreed was not a result of variability inherent within the sampling methods or the diffusion process itself. A comparison of the degree of agreement in the results from the two methods to 13 quantifiable characteristics external to the sampling methods offered only well-screen length as being related to the degree of agreement between the methods; however, there is also evidence to indicate that the flushing rate of water through the well screen affected the agreement between the sampling methods. Despite poor agreement between the concentrations obtained by the two methods at some wells, the degree to which the concentrations agree at a given well is repeatable. A one-time, well-bywell comparison between diffusion- and pumped-sampling methods could determine which wells are good candidates for the use of diffusion samplers. For wells with good method agreement, the diffusion-sampling method is a time-saving and cost-effective alternative to pumped-sampling methods in a long-term monitoring program, such as at the Massachusetts Military Reservation.

Archfield, Stacey A.; LeBlanc, Denis R.

2005-01-01

357

An Alternative Method for Solving the Diffusion Equation under Approximation B in Electron-Photon Cascade Theory  

NASA Astrophysics Data System (ADS)

A new analytical formulation is proposed to solve the diffusion equation under Approximation B in electron-photon cascade theory. The Suzuki-Trotter formula, analytical continuation of the hypergeometric function, and product integration are introduced. By using these methods the usual series solutions are obtained, and summation of the infinite series for arbitrary values of the energy E is performed by using the method of Prony's interpolation. As E --> 0, the infinite sum for the electron component turns out to be the function of K1(s, -s) used in the usual cascade theory, and a logarithmic divergence arises for the photon component. Use of Prony's method makes it possible to derive the energy spectra as well as the track length distributions and the transition curves. Our numerical results agree well with previous authors' as expected. Our analytical approach provides a general framework for solving other diffusion equations containing non-commutative operators in different contexts.

Nii, N.

1998-03-01

358

Simulation of diffuse photon migration in tissue by a Monte Carlo method derived from the optical scattering of spheroids.  

PubMed

A Monte Carlo method was derived from the optical scattering properties of spheroidal particles and used for modeling diffuse photon migration in biological tissue. The spheroidal scattering solution used a separation of variables approach and numerical calculation of the light intensity as a function of the scattering angle. A Monte Carlo algorithm was then developed which utilized the scattering solution to determine successive photon trajectories in a three-dimensional simulation of optical diffusion and resultant scattering intensities in virtual tissue. Monte Carlo simulations using isotropic randomization, Henyey-Greenstein phase functions, and spherical Mie scattering were additionally developed and used for comparison to the spheroidal method. Intensity profiles extracted from diffusion simulations showed that the four models differed significantly. The depth of scattering extinction varied widely among the four models, with the isotropic, spherical, spheroidal, and phase function models displaying total extinction at depths of 3.62, 2.83, 3.28, and 1.95 cm, respectively. The results suggest that advanced scattering simulations could be used as a diagnostic tool by distinguishing specific cellular structures in the diffused signal. For example, simulations could be used to detect large concentrations of deformed cell nuclei indicative of early stage cancer. The presented technique is proposed to be a more physical description of photon migration than existing phase function methods. This is attributed to the spheroidal structure of highly scattering mitochondria and elongation of the cell nucleus, which occurs in the initial phases of certain cancers. The potential applications of the model and its importance to diffusive imaging techniques are discussed. PMID:24085080

Hart, Vern P; Doyle, Timothy E

2013-09-01

359

New method and installation for rapid determination of radon diffusion coefficient in various materials.  

PubMed

The mathematical apparatus and the experimental installation for the rapid determination of radon diffusion coefficient in various materials are developed. The single test lasts not longer than 18 h and allows testing numerous materials, such as gaseous and liquid media, as well as soil, concrete and radon-proof membranes, in which diffusion coefficient of radon may vary in an extremely wide range, from 1·10(-12) to 5·10(-5) m(2)/s. The uncertainty of radon diffusion coefficient estimation depends on the permeability of the sample and varies from about 5% (for the most permeable materials) to 40% (for less permeable materials, such as radon-proof membranes). PMID:24412813

Tsapalov, Andrey; Gulabyants, Loren; Livshits, Mihail; Kovler, Konstantin

2014-04-01

360

Antimicrobial susceptibility testing of dermatophytes--comparison of the agar macrodilution and broth microdilution tests.  

PubMed

Fifty dermatophyte strains, recently obtained from clinical material, belonging to 4 different species were examined for their susceptibility to 5 systemic or topical antimycotic agents using both an agar macrodilution and a broth microdilution test. Antimycotics compared were griseofulvin, itraconazole, sertaconazole, terbinafine and ciclopiroxolamine. A comparison of the minimum inhibitory concentrations (MIC) clearly showed differences between the two test methods applied. For all 5 antimycotics, MIC data were three- to seventy-fold lower in the microdilution test system. These differences, depending on the test method, have to be taken into account when comparing MIC data in the literature or when relating the in vitro data to the tissue concentrations determined in vivo. PMID:9444406

Niewerth, M; Splanemann, V; Korting, H C; Ring, J; Abeck, D

1998-01-01

361

Laboratory evaluation of different agar media for isolation of carbapenem-resistant Acinetobacter spp.  

PubMed

The optimal method for surveillance of carbapenem-resistant Acinetobacter spp. (CRAB) is unknown. A collection of CRAB strains (n?=?42), carbapenem-susceptible strains (CSAB), and non-Acinetobacter strains (n?=?18) was used to evaluate six laboratory surveillance methods: MacConkey (MAC), MAC?+?1 ?g/ml imipenem (MAC-IPM), minimal salts agar?+?1 % acetate (MSA), MSA with IPM disk (MSA-IPM), CHROMagarKPC, and CHROMagar Acinetobacter with CR102 (CHROMAcineto). CHROMAcineto was 100 % sensitive and specific. CHROMagarKPC and MAC-IPM were highly sensitive (>95 %), but their specificity was substantially hampered by the breakthrough growth of CSAB. MSA was unsuitable for CRAB detection. CHROMAcineto is a promising medium for CRAB detection and warrants further clinical evaluation. PMID:24865248

Moran-Gilad, J; Adler, A; Schwartz, D; Navon-Venezia, S; Carmeli, Y

2014-11-01

362

Domain Decomposition Method for Diffuse Optical Kiwoon Kwona, Il-young Sona, and Birsen Yazicia  

E-print Network

photon propagation in highly scattering media is the frequency- domain photon diffusion equation derived coefficients that minimize the error between the measured photon density function and the approximated one from a simplifying assumptions applied to photon transport equation. Based on this forward model

Yazici, Birsen

363

A rebreathing method for measuring lung volume, diffusing capacity and cardiac output in conscious small animals  

Microsoft Academic Search

We developed a multiple gas rebreathing technique for measuring lung diffusing capacity (DLCO), lung volume (VL) and cardiac output simultaneously in conscious spontaneously breathing small animals. Lung volume was measured from the dilution of methane (CH4) or sulfur hexafluoride (SF6) and verified independently by a helium washout technique. Cardiac output and DLCO were estimated from the uptake of acetylene and

Cuneyt Yilmaz; Robert L. Johnson; Connie C. W. Hsia

2005-01-01

364

Oxygen quantification methods and application to the determination of oxygen diffusion and solubility coefficients in food  

Microsoft Academic Search

Oxygen solubility and diffusivity in food are two key parameters to understand and quantify the impact of oxygen on food oxidation. A limiting step to the acquisition of these data is the availability and feasibility of methodologies to quantify oxygen content in food and especially in solid foods, even though some recent and significant progress has been made in this

C. Pénicaud; S. Peyron; N. Gontard; V. Guillard

2011-01-01

365

Oxygen Quantification Methods and Application to the Determination of Oxygen Diffusion and Solubility Coefficients in Food  

Microsoft Academic Search

Oxygen solubility and diffusivity in food are two key parameters to understand and quantify the impact of oxygen on food oxidation. A limiting step to the acquisition of these data is the availability and feasibility of methodologies to quantify oxygen content in food and especially in solid foods, even though some recent and significant progress has been made in this

C. Pénicaud; S. Peyron; N. Gontard; V. Guillard

2012-01-01

366

A novel quantitative method for evaluating diffuse in-stent narrowing at follow-up angiography.  

PubMed

A new quantitative parameter, diffuse index (DI), was proposed to evaluate objectively whether in-stent restenosis is diffuse or focal in nature. A total of 343 patients (346 lesions) with Wiktor-GX, AVE MS-II, or JOMED stents were evaluated at follow-up angiography. According to the QCA-CMS definition, lesion length is derived from the 100% reference diameter function (RDF). By moving the RDF downward, the lesion length, LL(x), at each percentage x of the RDF can be calculated. We have defined the DI by the ratio of this calculated length LL(x) and the total stent length, SL, in other words, DI = [LL(x)/SL]. The percentage plaque area (% PA) was calculated by dividing the plaque area by the sum of the plaque area and luminal area within the stent. An excellent correlation was found between the DI at 88% RDF and the % PA in all three stents (r > 0.88). The individual correlation curves were nearly identical, independent of the type of stent. Furthermore, based on the overall data, the combination of a DI > 0.8 and % PA > 30% correlated with a high incidence of subsequent major adverse cardiac events (13/25 = 52%). From these data, it can be concluded that the diffuse index is a new objective quantitative parameter to describe whether in-stent restenosis is of focal or diffuse nature. PMID:11747154

Ishii, Y; van Weert, A W; Hekking, E; de Marie, K; ter Horst, J; Oemrawsingh, P V; Reiber, J H

2001-11-01

367

An anatomically driven anisotropic diffusion filtering method for 3D SPECT reconstruction  

Microsoft Academic Search

In this study, we aim to reconstruct single-photon emission computed tomography images using anatomical information from magnetic resonance imaging as a priori knowledge about the activity distribution. The trade-off between anatomical and emission data is one of the main concerns for such studies. In this work, we propose an anatomically driven anisotropic diffusion filter (ADADF) as a penalized maximum likelihood

Daniil Kazantsev; Simon R Arridge; Stefano Pedemonte; Alexandre Bousse; Kjell Erlandsson; Brian F Hutton; Sébastien Ourselin

2012-01-01

368

A novel speckle reduction and contrast enhancement method based on fuzzy anisotropic diffusion  

Microsoft Academic Search

Two major problems of ultrasound imaging are low-contrast and speckle noise. Traditionally, before speckle reduction, an enhancement algorithm is employed to improve the quality of the image. However, the noise is enhanced as well. To overcome this drawback, we introduce a novel fuzzy anisotropic diffusion approach for speckle reduction and contrast enhancement. Maximum fuzzy entropy principle is used to map

Yingtao Zhang; H. D. Cheng; Jiawei Tian; Jianghua Huang

2010-01-01

369

Some new discretization and adaptation and multigrid methods for 2-D 3-T diffusion equations  

Microsoft Academic Search

In the simulation of laser-driven implosion of a fuel capsule in inertial confinement fusion experiments, a system of two-dimensional diffusion equations coupled with electron, iron and photon temperature are widely used to approximately describe the process of energy across multiple materials and the exchange of energy among electrons, irons and photons. The numerical solution of such equations is always challenging

Jun Jiang; Yunqing. Huang; Shi Shu; Shi Zeng

2007-01-01

370

Traveling wave solutions of density-dependent nonlinear reaction-diffusion equation via the extended generalized Riccati equation mapping method  

NASA Astrophysics Data System (ADS)

Analytical entire traveling wave solutions to the 1+1 density-dependent nonlinear reaction-diffusion equation via the extended generalized Riccati equation mapping method are presented in this paper. This equation can be regarded as an extension case of the Fisher-Kolmogoroff equation, which is used for studying insect and animal dispersal with growth dynamics. The analytical solutions are then used to investigate the effect of equation parameters on the population distribution.

Kengne, Emmanuel; Saydé, Michel; Ben Hamouda, Fathi; Lakhssassi, Ahmed

2013-11-01

371

Norm-conserving diffusion Monte Carlo method and diagrammatic expansion of interacting drude oscillators: Application to solid xenon  

Microsoft Academic Search

The quantum Drude oscillator (QDO) model, which allows many-body polarization and dispersion to be treated both on an equal footing and beyond the dipole limit, is investigated using two approaches to the linear scaling diffusion Monte Carlo (DMC) technique. The first is a general purpose norm-conserving DMC (NC-DMC) method wherein the number of walkers, N , remains strictly constant thereby

Andrew Jones; Andrew Thompson; Jason Crain; Martin H. Müser; Glenn J. Martyna

2009-01-01

372

Separation method of hole trapping and interface trap generation and their roles in NBTI reaction-diffusion model  

Microsoft Academic Search

In this study, we propose a systematic method to separate the hole trapping from measured V1 shift, thus giving the ideal interface trap generation behavior without measurement disturbance. Three stages of interface trap generation have been illustrated with the analytical H-H2 NBTI reaction-diffusion model, and the hole trapping has also been verified with its voltage-enhanced and temperature-insensitive properties. Finally, the

J. H. Lee; W. H. Wu; A. E. Islam; M. A. Alam; A. S. Oates

2008-01-01

373

Diffusion Geometry Diffusion Geometry  

E-print Network

Diffusion Geometry Diffusion Geometry for High Dimensional Data Matthew J. Hirn July 3, 2013 #12;Diffusion Geometry Introduction Embedding of closed curve Figure: Left: A closed, non-self-intersecting curve in 3 dimensions. Right: Its embedding as a circle. #12;Diffusion Geometry Introduction Cartoon

Hirn, Matthew

374

EULERIAN-LAGRANGIAN LOCALIZED ADJOINT METHOD FOR THE ADVECTION-DIFFUSION EQUATION  

EPA Science Inventory

Many numerical methods use characteristic analysis to accommodate the advective component of transport. uch characteristic methods include Eulerian-Lagrangian methods (ELM), modified method of characteristics (MMOC), and operator splitting methods. eneralization of characteristic...

375

AN EULERIAN-LAGRANGIAN LOCALIZED ADJOINT METHOD FOR THE ADVECTION-DIFFUSION EQUATION  

EPA Science Inventory

Many numerical methods use characteristic analysis to accommodate the advective component of transport. Such characteristic methods include Eulerian-Lagrangian methods (ELM), modified method of characteristics (MMOC), and operator splitting methods. A generalization of characteri...

376

Theory of the generalized chloride mass balance method for recharge estimation in groundwater basins characterised by point and diffuse recharge  

NASA Astrophysics Data System (ADS)

Application of the conventional chloride mass balance (CMB) method to point recharge dominant groundwater basins can substantially under-estimate long-term average annual recharge by not accounting for the effects of localized surface water inputs. This is because the conventional CMB method ignores the duality of infiltration and recharge found in karstic systems, where point recharge can be a contributing factor. When point recharge is present in groundwater basins, recharge estimation is unsuccessful using the conventional CMB method with, either unsaturated zone chloride or groundwater chloride. In this paper we describe a generalized CMB that can be applied to groundwater basins with point recharge. Results from this generalized CMB are shown to be comparable with long-term recharge estimates obtained using the watertable fluctuation method, groundwater flow modelling and Darcy flow calculations. The generalized CMB method provides an alternative, reliable long-term recharge estimation method for groundwater basins characterised by both point and diffuse recharge.

Somaratne, N.; Smettem, K. R. J.

2014-01-01

377

Visualization of Thermal Distribution Caused by Focused Ultrasound Field in an Agar Phantom  

NASA Astrophysics Data System (ADS)

Ultrasound waves have been widely used not only in medical diagnostic systems but also in medical treatment. There has been increasing interest in the thermal distribution caused by ultrasound waves. In this study, using thermochromic particles, a visualization method was suggested in a mimic phantom for organic materials. By blending various thermochromic particles with different critical temperatures, the thermal field distribution in the phantom could be observed. The effect of a concave-type ultrasound transducer on the temperature distribution in an agar phantom mixed with thermochromic particles was observed. The temperature distribution corresponded to changes in the brightness distribution of gray. It was confirmed that the thermal distribution pattern in the vicinity of the focal area varies with the time exposure to ultrasound waves.

Kim, Jungsoon; Kim, Moojoon; Ha, Kanglyeol

2011-07-01

378

Intrauterine device for laser light diffusion and method of using the same  

DOEpatents

An improved device for delivery of photoenergy from a light source, such as a laser, into a uterine cavity for photodynamic therapy is comprised of a plurality of optic fibers, which are bundled together and inserted into the uterine cavity by means of a uterine cannula. The cannula is positioned within the uterine cavity at a preferred location and then withdrawn thereby allowing the plurality of optic fibers to splay or diverge one from the other within the cavity. Different portions of the distal tip of the optic fiber is provided with a light diffusing tip, the remainder being provided with a nondiffusing tip portion. The fiber optic shape, as well as the segment which is permitted to actively diffuse light through the tip, is selected in order to provide a more uniform exposure intensity of the photo energy or at least sufficient radiation directed to each segment of the uterine walls. 5 figs.

Tadir, Y.; Berns, M.W.; Svaasand, L.O.; Tromberg, B.J.

1995-12-26

379

Intrauterine device for laser light diffusion and method of using the same  

DOEpatents

An improved device for delivery of photoenergy from a light source, such as a laser, into a uterine cavity for photodynamic therapy is comprised of a plurality of optic fibers, which are bundled together and inserted into the uterine cavity by means of a uterine cannula. The cannula is positioned within the uterine cavity at a preferred location and then withdrawn thereby allowing the plurality of optic fibers to splay or diverge one from the other within the cavity. Different portions of the distal tip of the optic fiber is provided with a light diffusing tip, the remainder being provided with a nondiffusing tip portion. The fiber optic shape, as well as the segment which is permitted to actively diffuse light through the tip, is selected in order to provide a more uniform exposure intensity of the photo energy or at least sufficient radiation directed to each segment of the uterine walls.

Tadir, Yona (Irvine, CA); Berns, Michael W. (Trabuco Canyon, CA); Svaasand, Lars O. (Trondheim, NO); Tromberg, Bruce J. (Irvine, CA)

1995-01-01

380

A cryostatic setup for the low-temperature measurement of thermal diffusivity with the photothermal method  

SciTech Connect

A cryostatic setup is described to perform photothermal deflection measurements from room temperature to 77 K. The setup uses gaseous nitrogen as a medium where the photodeflection is produced. The ability of the system to work is demonstrated presenting some measurements of thermal diffusivity of high-temperature superconductor samples and of yttrium-iron garnets with variable aluminum content. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Bertolotti, M. [Dipartimento di Energetica, Universita di Roma ``La Sapienza,`` Via Scarpa 16, 00161 Roma (Italy)] [Dipartimento di Energetica, Universita di Roma ``La Sapienza,`` Via Scarpa 16, 00161 Roma (Italy); [GNEQP of CNR (Italy); [INFM (Italy); Liakhou, G. [Technical University of Moldova, Stephan Cel Mare, 277012 Kishinev, Moldova (??)] [Technical University of Moldova, Stephan Cel Mare, 277012 Kishinev, Moldova (??); Li Voti, R.; Paoloni, S.; Sibilia, C. [Dipartimento di Energetica, Universita di Roma ``La Sapienza,`` Via Scarpa 16, 00161 Roma (Italy)] [Dipartimento di Energetica, Universita di Roma ``La Sapienza,`` Via Scarpa 16, 00161 Roma (Italy); [GNEQP of CNR (Italy); [INFM (Italy); Sparvieri, N. [ALENIA, Via Tiburtina Km 12.4, 00131 Roma (Italy)] [ALENIA, Via Tiburtina Km 12.4, 00131 Roma (Italy)

1995-12-01

381

An operator splitting method for the advection diffusion reaction equation for problems in porous flow  

NASA Astrophysics Data System (ADS)

In this work we consider an operator splitting numerical scheme for advection dominated material flow equation as given by the advection-diffusion-reaction equation. A model for multiphase flow is used to motivate the model under investigation. Dynamically consistent and positivity preserving nonstandard finite difference schemes are used to handle the split subproblems. Numerical simulations are presented to test the convergence of the split scheme.

Chapwanya, M.; Lubuma, J. M.-S.

2013-10-01

382

A self-normalized, full time-resolved method for fluorescence diffuse optical tomography.  

PubMed

A full time-resolved scheme that has been previously applied in diffuse optical tomography is extended to time-domain fluorescence diffuse optical tomography regime, based on a finite-element-finite-time-difference photon diffusion modeling and a Newton-Raphson inversion framework. The merits of using full time-resolved data are twofold: it helps evaluate the intrinsic performance of time-domain mode for improvement of image quality and set up a valuable reference to the assessment of computationally efficient featured-data-based algorithms, and provides a self-normalized implementation to preclude the necessity of the scaling-factor calibration and spectroscopic-feature assessments of the system as well as to overcome the adversity of system instability. We validate the proposed methodology using simulated data, and evaluate its performances of simultaneous recovery of the fluorescent yield and lifetime as well as its superiority to the featured-data one in the fidelity of image reconstruction. PMID:18711549

Gao, Feng; Zhao, Huijuan; Zhang, Limin; Tanikawa, Yukari; Marjono, Andhi; Yamada, Yukio

2008-08-18

383

Investigation of a diffuse optical measurements-assisted quantitative photoacoustic tomographic method in reflection geometry  

PubMed Central

Abstract. Photoacoustic tomography provides the distribution of absorbed optical energy density, which is the product of optical absorption coefficient and optical fluence distribution. We report the experimental investigation of a novel fitting procedure that quantitatively determines the optical absorption coefficient of chromophores. The experimental setup consisted of a hybrid system of a 64-channel photoacoustic imaging system with a frequency-domain diffused optical measurement system. The fitting procedure included a complete photoacoustic forward model and an analytical solution of a target chromophore using the diffusion approximation. The fitting procedure combines the information from the photoacoustic image and the background information from the diffuse optical measurements to minimize the photoacoustic measurements and forward model data and recover the target absorption coefficient quantitatively. 1-cm-cube phantom absorbers of high and low contrasts were imaged at depths of up to 3.0 cm. The fitted absorption coefficient results were at least 80% of their true values. The sensitivities of this fitting procedure to target location, target radius, and background optical properties were also investigated. We found that this fitting procedure was most sensitive to the accurate determination of the target radius and depth. Blood sample in a thin tube of radius 0.58 mm, simulating a blood vessel, was also studied. The photoacoustic images and fitted absorption coefficients are presented. These results demonstrate the clinical potential of this fitting procedure to quantitatively characterize small lesions in breast imaging. PMID:22734743

Xu, Chen; Kumavor, Patrick D.; Aguirre, Andres; Zhu, Quing

2012-01-01

384

Investigation of a diffuse optical measurements-assisted quantitative photoacoustic tomographic method in reflection geometry.  

PubMed

Photoacoustic tomography provides the distribution of absorbed optical energy density, which is the product of optical absorption coefficient and optical fluence distribution. We report the experimental investigation of a novel fitting procedure that quantitatively determines the optical absorption coefficient of chromophores. The experimental setup consisted of a hybrid system of a 64-channel photoacoustic imaging system with a frequency-domain diffused optical measurement system. The fitting procedure included a complete photoacoustic forward model and an analytical solution of a target chromophore using the diffusion approximation. The fitting procedure combines the information from the photoacoustic image and the background information from the diffuse optical measurements to minimize the photoacoustic measurements and forward model data and recover the target absorption coefficient quantitatively. 1-cm-cube phantom absorbers of high and low contrasts were imaged at depths of up to 3.0 cm. The fitted absorption coefficient results were at least 80% of their true values. The sensitivities of this fitting procedure to target location, target radius, and background optical properties were also investigated. We found that this fitting procedure was most sensitive to the accurate determination of the target radius and depth. Blood sample in a thin tube of radius 0.58 mm, simulating a blood vessel, was also studied. The photoacoustic images and fitted absorption coefficients are presented. These results demonstrate the clinical potential of this fitting procedure to quantitatively characterize small lesions in breast imaging. PMID:22734743

Xu, Chen; Kumavor, Patrick D; Aguirre, Andres; Zhu, Quing

2012-06-01

385

Evaluation of Mueller-Hinton-agar as a simple medium for the germ tube production of Candida albicans and Candida dubliniensis.  

PubMed

Candida albicans is the most frequently isolated yeast species from clinical specimens. A classical rapid presumptive differentiation from non-albicans species is based on its ability to produce germ tubes after incubation in human serum. The only non-albicans Candida species producing germ tubes is Candida dubliniensis. In this study, we evaluated Mueller-Hinton-agar (MH-agar) as a medium for germ tube formation of C. albicans and C. dubliniensis. A total of 859 yeast isolates from stool samples, including 632 strains of C. albicans, 10 C. dubliniensis and 217 other yeast strains from 20 different species, were grown on Sabouraud glucose (2%) agar at 37 degrees C for 24-72 h. Species were identified by standard methods. For the germ tube test (GTT), an inoculum from a single colony was streaked onto a MH-agar plate and covered by a sterile coverslip. After incubation at 37 degrees C for 2 h, the MH plates were examined using a light microscope at x200. The GTT was positive in 578 of 632 C. albicans strains (sensitivity 91.5%), in six of 10 C. dubliniensis strains (sensitivity 60.0%), and in none of the other yeast strains. MH-agar is a suitable medium for the GTT and the presumptive identification of C. albicans. It is safer to use than human serum and is widely available in microbiology laboratories. PMID:18399901

Rimek, Dagmar; Fehse, Brigitte; Göpel, Petra

2008-05-01

386

Detection of cellulase activity in polyacrylamide gels using Congo red-stained agar replicas.  

PubMed

Bands that have cellulolytic activity are visualized after polyacrylamide gel electrophoresis by laying the slab gel on top of a thin sheet of 2% agar containing 0.1% carboxymethylcellulose. After a suitable incubation time, zones of carboxymethylcellulose hydrolysis are revealed by staining the agar replica with Congo red. PMID:6193735

Béguin, P

1983-06-01

387

Evaluation of a chromogenic agar for detection of group B streptococcus in pregnant women.  

PubMed

We compared ChromID Strepto B agar (STRB; bioMérieux, Inc.), a selective and differential medium for group B streptococcus, with culture using neomycin-nalidixic acid agar (NNA) and LIM broth. STRB alone was more sensitive (87.7%) than NNA alone (79.0%), while each had a sensitivity of 100% when used in conjunction with LIM broth. PMID:20592154

Craven, Robin R; Weber, Carol J; Jennemann, Rebecca A; Dunne, W Michael

2010-09-01

388

Caprylate-thallous agar medium for selectively isolating Serratia and its utility in the clinical laboratory.  

PubMed Central

A defined agar medium (hereinafter designated caprylate-thallous [CT5 agar) containing 0.01% yeast extract, 0.1% caprylic (n-octanoic) acid, and 0.025% thallous sulfate is highly selective for all Serratia species and effectively discriminates against most non-Serratia strains likely to be in the same habitats. The selectivity of CT agar is demonstrated by the very high efficiency of colony formation (mean, 80.7% of that on a nonselective complex medium) on CT agar by known Serratia strains and the very low efficiency of colony formation (close to zero) on CT agar by bacterial strains known not to be Serratia. The utility of this medium in actual clinical laboratory practice is demonstrated by the more rapid and higher recovery of Serratia on this selective medium as compared to conventional procedures of in-tandem runs of 513 consecutive urine, feces, and sputum specimens. Pigmented and nonpigmented Serratia strains deliberately added to fecal specimens can be selectively and quantitatively recovered on CT agar. CT agar compares favorably with, or in some cases is an improvement over, other selective media which have been recommended for isolating Serratia. This selective CT agar medium could be quite useful in ecological surveys, especially those related to hospital-acquired infections. PMID:972193

Starr, M P; Grimont, P A; Grimont, F; Starr, P B

1976-01-01

389

The powerful combination of ion-milling method for XTEM preparation: Application to a diffusion barrier coating on Nb substrate  

NASA Astrophysics Data System (ADS)

The sample preparation of coating system for use in a transmission electron microscope (TEM) is a thoroughly challenging process of viewing samples at the nano-level scale. Two different ion milling methods have be taken, argon ion slicer (AIS) and focused ion beam (FIB) which have the ability to reveal many of the characteristics of how thin films form. This Method has been applied to investigate cross-sectional structure of Re-based diffusion barrier coating on Nb substrate. The detailed micro-nano structure of coating specimen presented several crystal defects such as dislocations, stacking faults, voids and cracks.

Sugiarti, Eni; Wang, Youming; Ohnuki, Somei

2012-06-01

390

Polyamide-thallium selenide composite materials via temperature and pH controlled adsorption-diffusion method  

NASA Astrophysics Data System (ADS)

Composite materials based on III-VI elements are promising in designing efficient photoelectronic devices, such as thin film organic-inorganic solar cells. In this work, TlSe composite materials were synthesized on a model polymer polyamide using temperature and pH controlled adsorption-diffusion method via (a) selenization followed by (b) the exposure to the group III metal (Tl) salt solution and their surface morphological, chemical and crystalline phase information was determined with particular focus on their corresponding structure-optical property relationship. XRD analysis yielded a complex crystalline phase distribution which correlated well with the optical and surface morphological properties measured. pH 11.3 and 80 °C yielded well defined, low structural disorder composite material surface. After annealing in N2 at 100 °C, polycrystalline PA-TlxSey composite materials yielded a single TlSe phase due to the enhanced diffusion and reaction of thallium ions into the polymer. The method described here can be used to synthesize variety of binary III-VI compounds diffused into the polymer at relatively low temperatures and low overall cost, thus providing for a flexible synthesis route for novel composite solar energy harvesting materials.

Ivanauskas, Remigijus; Samardokas, Linas; Mikolajunas, Marius; Virzonis, Darius; Baltrusaitis, Jonas

2014-10-01

391

Speckle contrast optical spectroscopy, a non-invasive, diffuse optical method for measuring microvascular blood flow in tissue.  

PubMed

We introduce a new, non-invasive, diffuse optical technique, speckle contrast optical spectroscopy (SCOS), for probing deep tissue blood flow using the statistical properties of laser speckle contrast and the photon diffusion model for a point source. The feasibility of the method is tested using liquid phantoms which demonstrate that SCOS is capable of measuring the dynamic properties of turbid media non-invasively. We further present an in vivo measurement in a human forearm muscle using SCOS in two modalities: one with the dependence of the speckle contrast on the source-detector separation and another on the exposure time. In doing so, we also introduce crucial corrections to the speckle contrast that account for the variance of the shot and sensor dark noises. PMID:25136500

Valdes, Claudia P; Varma, Hari M; Kristoffersen, Anna K; Dragojevic, Tanja; Culver, Joseph P; Durduran, Turgut

2014-08-01

392

Fast computation of diffuse reflectance in optical coherence tomography using an importance sampling-based Monte Carlo method  

NASA Astrophysics Data System (ADS)

Computer simulations of light transport in multi-layered turbid media are an effective way to theoretically investigate light transport in tissue, which can be applied to the analysis, design and optimization of optical coherence tomography (OCT) systems. We present a computationally efficient method to calculate the diffuse reflectance due to ballistic and quasi-ballistic components of photons scattered in turbid media, which represents the signal in optical coherence tomography systems. Our importance sampling based Monte Carlo method enables the calculation of the OCT signal with less than one hundredth of the computational time required by the conventional Monte Carlo method. It also does not produce a systematic bias in the statistical result that is typically observed in existing methods to speed up Monte Carlo simulations of light transport in tissue. This method can be used to assess and optimize the performance of existing OCT systems, and it can also be used to design novel OCT systems.

Lima, Ivan T., Jr.; Kalra, Anshul; Hernández-Figueroa, Hugo E.; Sherif, Sherif S.

2012-03-01

393

Rheological and structural characterization of agar/whey proteins insoluble complexes.  

PubMed

Complex coacervation between whey proteins and carboxylated or highly sulphated polysaccharides has been widely studied. The aim of this work was to characterise a slightly sulphated polysaccharide (agar) and whey protein insoluble complexes in terms of yield, composition and physicochemical properties as well as to study their rheological behaviour for better understanding their structure. Unlike other sulphated polysaccharides, complexation of agar and whey protein at pH 3 in the absence of a buffering agent resulted in a coacervate that was a gel at 20°C with rheological properties and structure similar to those of simple agar gels, reinforced by proteins electrostatically aggregated to the agar network. The behaviour towards heat treatment was similar to that of agar alone, with a high thermal hysteresis and almost full reversibility. In the presence of citrate buffer, the result was a "flocculated solid", with low water content (75-81%), whose properties were governed by protein behaviour. PMID:24906765

Rocha, Cristina M R; Souza, Hiléia K S; Magalhães, Natália F; Andrade, Cristina T; Gonçalves, Maria Pilar

2014-09-22

394

The soft agar clonogenicity and characterization of cells obtained from human solid tumors by mechanical and enzymatic means.  

PubMed

A two-step procedure for releasing cells from solid tumors has been applied to specimens of human melanoma, sarcoma, lung, colon, and breast carcinoma. The first population released mechanically has been compared with the population subsequently released enzymatically in tests of dye exclusion, ribonucleoside triphosphate pool sizes, intactness of DNA, and clonogenicity in soft agar. While greater numbers of dye-excluding cells are released in the enzymatic step, and these cells have higher ribonucleoside triphosphate pools and more intact DNA, both populations contain clonogenic cells in approximately equal numbers. Several semisolid media were employed in tests of clonogenicity, and all methods employing an agar underlayer appeared satisfactory and approximately equivalent in cloning efficiency. The methyl cellulose upper layer system facilitated implanting of pooled colonies into nude mice, which resulted in growth in the nude host and marked increase in cloning efficiency when the cells were replanted into soft agar-methyl cellulose plates. A comparison of four different areas of individual tumor specimens was made with cells released enzymatically and measuring cell yield, dye exclusion, ATP pool size, and uptake and metabolism of 5-fluoropyrimidines. Only relatively small variations were seen from one area to the next, with trypan blue exclusion exhibiting the least variation, and metabolism of fluorinated pyrimidines showing the most. PMID:7032739

Slocum, H K; Pavelic, Z P; Kanter, P M; Nowak, N J; Rustum, Y M

1981-01-01

395

Effect of Crystal Defects on Minority Carrier Diffusion Length in 6H SiC Measured Using the Electron Beam Induced Current Method.  

National Technical Information Service (NTIS)

We report values of minority carrier diffusion length in n-type 6H SiC measured using a planar Electron Beam Induced Current (EBIC) method. Values of hole diffusion length in defect free regions of n-type 6H SiC, with a doping concentration of 1.7El7 1/cu...

M. Tabib-Azar

1997-01-01

396

First and Second-Order Diffusive Methods for Rapid, Coarse, Distributed Load Balancing  

Microsoft Academic Search

.    We consider the following general problem modeling load balancing in a variety of distributed settings. Given an arbitrary\\u000a undirected connected graph G=(V,E) and a weight distribution w\\u000a \\u000a \\u000a \\u000a 0\\u000a \\u000a on the nodes, determine a schedule to move weights across edges in each step so as to (approximately) balance the weights\\u000a on the nodes. We focus on diffusive schedules for

S. Muthukrishnan; Bhaskar Ghosh; Martin H. Schultz

1998-01-01

397

Multiparameter Screening on SlipChip Used for Nanoliter Protein Crystallization Combining Free Interface Diffusion and Microbatch Methods  

SciTech Connect

This paper describes two SlipChip-based approaches to protein crystallization: a SlipChip-based free interface diffusion (FID) method and a SlipChip-based composite method that simultaneously performs microbatch and FID crystallization methods in a single device. The FID SlipChip was designed to screen multiple reagents, each at multiple diffusion equilibration times, and was validated by screening conditions for crystallization of two proteins, enoyl-CoA hydratase from Mycobacterium tuberculosis and dihydrofolate reductase/thymidylate synthase from Babesia bovis, against 48 different reagents at five different equilibration times each, consuming 12 {micro}L of each protein for a total of 480 experiments using three SlipChips. The composite SlipChip was designed to screen multiple reagents, each at multiple mixing ratios and multiple equilibration times, and was validated by screening conditions for crystallization of two proteins, enoyl-CoA hydratase from Mycobacterium tuberculosis and dihydrofolate reductase/thymidylate synthase from Babesia bovis. To prevent cross-contamination while keeping the solution in the neck channels for FID stable, the plates of the SlipChip were etched with a pattern of nanowells. This nanopattern was used to increase the contact angle of aqueous solutions on the surface of the silanized glass. The composite SlipChip increased the number of successful crystallization conditions and identified more conditions for crystallization than separate FID and microbatch screenings. Crystallization experiments were scaled up in well plates using conditions identified during the SlipChip screenings, and X-ray diffraction data were obtained to yield the protein structure of dihydrofolate reductase/thymidylate synthase at 1.95 {angstrom} resolution. This free-interface diffusion approach provides a convenient and high-throughput method of setting up gradients in microfluidic devices and may find additional applications in cell-based assays.

Li, Liang; Du, Wenbin; Ismagilov, Rustem F. (UC)

2010-08-04

398

Calibration of scattering and absorption properties of a liquid diffusive medium at NIR wavelengths. Time-resolved method  

NASA Astrophysics Data System (ADS)

In this paper, a general method to calibrate the absorption coefficient of an absorber and the reduced scattering coefficient of a liquid diffusive medium, based on time-resolved measurements, is reported. An exhaustive analysis of the error sources affecting the estimation is also performed. The method has been applied with a state-of-the-art time-resolved instrumentation to determine the intrinsic absorption coefficient of Indian ink and the reduced scattering coefficient of Intralipid-20%, with a standard error smaller than 1% and 2%, respectively. Finally, the results have been compared to those retrieved for the same compounds by applying a continuous wave method recently published, obtaining an agreement within the error bars. This fact represents a cross validation of the two independent calibration methods.

Spinelli, Lorenzo; Martelli, Fabrizio; Farina, Andrea; Pifferi, Antonio; Torricelli, Alessandro; Cubeddu, Rinaldo; Zaccanti, Giovanni

2007-05-01

399

Method for producing components with internal architectures, such as micro-channel reactors, via diffusion bonding sheets  

DOEpatents

This invention relates to a method for producing components with internal architectures, and more particularly, this invention relates to a method for producing structures with microchannels via the use of diffusion bonding of stacked laminates. Specifically, the method involves weakly bonding a stack of laminates forming internal voids and channels with a first generally low uniaxial pressure and first temperature such that bonding at least between the asperites of opposing laminates occurs and pores are isolated in interfacial contact areas, followed by a second generally higher isostatic pressure and second temperature for final bonding. The method thereby allows fabrication of micro-channel devices such as heat exchangers, recuperators, heat-pumps, chemical separators, chemical reactors, fuel processing units, and combustors without limitation on the fin aspect ratio.

Alman, David E. (Corvallis, OR); Wilson, Rick D. (Corvallis, OR); Davis, Daniel L. (Albany, OR)

2011-03-08

400

Diffuse Optical Tomography for Brain Imaging: Continuous Wave Instrumentation and Linear Analysis Methods  

NASA Astrophysics Data System (ADS)

Diffuse optical tomography (DOT) is a functional brain imaging technique that measures cerebral blood oxygenation and blood volume changes. This technique is particularly useful in human neuroimaging measurements because of the coupling between neural and hemodynamic activity in the brain. DOT is a multichannel imaging extension of near-infrared spectroscopy (NIRS). NIRS uses laser sources and light detectors on the scalp to obtain noninvasive hemodynamic measurements from spectroscopic analysis of the remitted light. This review explains how NIRS data analysis is performed using a combination of the modified Beer-Lambert law (MBLL) and the diffusion approximation to the radiative transport equation (RTE). Laser diodes, photodiode detectors, and optical terminals that contact the scalp are the main components in most NIRS systems. Placing multiple sources and detectors over the surface of the scalp allows for tomographic reconstructions that extend the individual measurements of NIRS into DOT. Mathematically arranging the DOT measurements into a linear system of equations that can be inverted provides a way to obtain tomographic reconstructions of hemodynamics in the brain.

Giacometti, Paolo; Diamond, Solomon G.

401

Improved Diffuse Boundary Condition for the DSBGK Method to Eliminate the Unphysical Density Drift  

E-print Network

An improved diffuse boundary condition, where the number flux of the incoming real molecules on the wall surface is calculated using the molecular variables rather than the cell's macroscopic variables, is proposed to eliminate the unphysical density drift, which was observed in the previous DSBGK simulation of the lid-driven problem but disappears in the channel flow problem because of the density constraint imposed at the open boundaries. Consequently, the efficient time-average process is valid for sampling all quantities of interest in closed as well as open problems. When the driven velocity of the lid-driven problem is only one micrometer per second that is realistic in the micro-electro-mechanical systems or pore-scale flows of the shale gas, we suggest to use the original boundary condition because the density drift during a very long time interval becomes unperceivable when the perturbation is tiny. Thus, the original diffuse boundary condition, which contains much less stochastic noise than the impr...

Li, Jun

2014-01-01

402

Nonequilibrium scheme for computing the flux of the convection-diffusion equation in the framework of the lattice Boltzmann method.  

PubMed

In this paper, we propose a local nonequilibrium scheme for computing the flux of the convection-diffusion equation with a source term in the framework of the multiple-relaxation-time (MRT) lattice Boltzmann method (LBM). Both the Chapman-Enskog analysis and the numerical results show that, at the diffusive scaling, the present nonequilibrium scheme has a second-order convergence rate in space. A comparison between the nonequilibrium scheme and the conventional second-order central-difference scheme indicates that, although both schemes have a second-order convergence rate in space, the present nonequilibrium scheme is more accurate than the central-difference scheme. In addition, the flux computation rendered by the present scheme also preserves the parallel computation feature of the LBM, making the scheme more efficient than conventional finite-difference schemes in the study of large-scale problems. Finally, a comparison between the single-relaxation-time model and the MRT model is also conducted, and the results show that the MRT model is more accurate than the single-relaxation-time model, both in solving the convection-diffusion equation and in computing the flux. PMID:25122408

Chai, Zhenhua; Zhao, T S

2014-07-01

403

A novel improved method for analysis of 2D diffusion relaxation data—2D PARAFAC-Laplace decomposition  

NASA Astrophysics Data System (ADS)

This paper demonstrates how the multi-linear PARAFAC model can with advantage be used to decompose 2D diffusion-relaxation correlation NMR spectra prior to 2D-Laplace inversion to the T2- D domain. The decomposition is advantageous for better interpretation of the complex correlation maps as well as for the quantification of extracted T2- D components. To demonstrate the new method seventeen mixtures of wheat flour, starch, gluten, oil and water were prepared and measured with a 300 MHz nuclear magnetic resonance (NMR) spectrometer using a pulsed gradient stimulated echo (PGSTE) pulse sequence followed by a Carr-Purcell-Meiboom-Gill (CPMG) pulse echo train. By varying the gradient strength, 2D diffusion-relaxation data were recorded for each sample. From these double exponentially decaying relaxation data the PARAFAC algorithm extracted two unique diffusion-relaxation components, explaining 99.8% of the variation in the data set. These two components were subsequently transformed to the T2- D domain using 2D-inverse Laplace transformation and quantitatively assigned to the oil and water components of the samples. The oil component was one distinct distribution with peak intensity at D = 3 × 10 -12 m 2 s -1 and T2 = 180 ms. The water component consisted of two broad populations of water molecules with diffusion coefficients and relaxation times centered around correlation pairs: D = 10 -9 m 2 s -1, T2 = 10 ms and D = 3 × 10 -13 m 2 s -1, T2 = 13 ms. Small spurious peaks observed in the inverse Laplace transformation of original complex data were effectively filtered by the PARAFAC decomposition and thus considered artefacts from the complex Laplace transformation. The oil-to-water ratio determined by PARAFAC followed by 2D-Laplace inversion was perfectly correlated with known oil-to-water ratio of the samples. The new method of using PARAFAC prior to the 2D-Laplace inversion proved to have superior potential in analysis of diffusion-relaxation spectra, as it improves not only the interpretation, but also the quantification.

Tønning, Erik; Polders, Daniel; Callaghan, Paul T.; Engelsen, Søren B.

2007-09-01

404

[Study on nondestructive rapid identification method of foods containing trans-fatty acids using diffuse near infrared spectroscopy].  

PubMed

A rapid nondestructive method for identifying intact foods containing trans fatty acids (TFA) using diffuse near infrared spectroscopy (NIR) was proposed in the present paper. The diffuse Fourier transform near infrared (FT-NIR) spectra of intact samples were collected by fiber probe, and the reference data of TFA content were determined by Chinese standard method GB/T 22110-2008 (gas chromatography (GC) method). In this work, all the samples were classified into two categories: foods with TFA and foods without TFA according to the TFA content of the foods. The identification models were established by different supervised pattern recognition algorithms including partial least square discriminant analysis (PLSDA), support vector machine (SVM), soft independent modeling of class analogy (SIMCA) and K-nearest neighbor method (KNN) etc. The performances of the established models employing different algorithms, data pretreatments and wavelength bands were compared. The results show that PLSDA and SVM algorithms have the ability of identifying intact foods with TFA, and the performance of identification models established by PLSDA is better than that of SVM. The PLSDA models established by the wavelength bands of 4 138-4 428, 5 507-5 963 and 7 794-8 960 cm(-1) which were pretreated with pretreatment methods of auto scaling and second derivative have the best performance. The correct classification percentages of its calibration and validation set are 96.4% and 88%, respectively, which indicates that this method is feasible for the identification of foods with TFA. This NIR method above mentioned has the characteristics of rapidness, non-destruction and easy operation due to the elimination of sample pretreatment such as oil extraction and grinding, therefore it is very suitable for on-line and in-site detection application. PMID:24555372

An, Xue-Song; Song, Chun-Feng; Yuan, Hong-Fu; Xie, Jin-Chun; Li, Xiao-Yu

2013-11-01

405

Development of glucosidase agar for the confirmation of water-borne Enterococcus.  

PubMed

Analysis of 56 river water samples by the Enterolert defined substrate technique, and standard m-Enterococcus agar isolation followed by confirmation, indicated that after 24 h incubation. Enterolert significantly underestimated the true numbers of enterococci. Extending Enterolert incubatioin to 36 h improved detection but also revealed false positives. These findings prompted the development of a novel confirmation medium we have termed glucosidase agar, which was prepared by dissolving Enterolert substrate in 2% (w/v) bacteriological agar. Analysis of 1,043 colonies arising on m-Enterococcus agar from 280 freshwater, marine and sewage effluent samples, demonstrated that 2-4 h incubation on glucosidase agar was a rapid and accurate means of confirming presumptive enterococci, when compared to standard confirmation procedures that take 48 h. The combination of primary isolation on m-Enterococcus agar followed by confirmation on glucosidase agar permits maximum recovery of Enteroccus whilst effectively eliminating false positives/negatives and provides a reliable alternative use of the Enterolert defined substrate technology. PMID:11791856

Adcock, P W; Saint, C P

2001-12-01

406

Novel diffusion-dilution method for release of semiochemicals: Testing pheromone component ratios on western pine beetle.  

PubMed

Each of the pheromone components of the Western pine beetle,Dendroctonus brevicomis LeC. (Coleoptera: Scolytidae), exo-brevicomin (E) and frontalin (F), were released in the forest at various ratios 0.01?1, 0.1?1, or 1?1 to a constant dose of the opposite component (E or F) plus the host monoterpene myrcene (M), which were each released at 1.5 mg/day. The components were released by a new method that combines the principles of chemical diffusion through a tube with mole percentage dilution of the chemical. Both sexes ofD. brevicomis were attracted similarly at comparable ratios (and release rates) of E or F and showed similar logarithmic relationships (r (2)=0.92?0.99). The bark beetle predator,Temnochila chlorodia (Mannerheim) (Coleoptera: Trogositidae) was apparently less sensitive to E thanD. brevicomis, being relatively less attracted to amounts of E equivalent to that released by 70 females, while none were attracted to that from seven females (while this rate still attracted significant numbers of conspecifics). The apparent insensitivity of bark beetles to extreme ratios between pheromone components in contrast to moths is discussed. The advantages of the diffusion-dilution method of releasing semiochemicals compared to previous methods of absorbents, wicks, capillary tubes, and semipermeable plastic membranes are also discussed. PMID:24277005

Byers, J A

1988-01-01

407

Evaluation of a central-difference-like method for the solution of the convection-diffusion equation  

SciTech Connect

For the numerical solution of the transport equation that describes the convection and diffusion of various physical quantities (e.g., momentum, heat, and material concentrations) first-order upwind schemes are widely used. For example, first order upwind differencing is used in codes like COMMIX and PHOENICS. These schemes are simple and always give oscillation-free and physically plausible solutions. However, due to false diffusion, at high Peclet numbers their accuracy on practical meshes is poor. In previous work, a central-difference-like method was presented that even with a coarse mesh produces oscillation-free solutions and of superior accuracy than the upwind scheme. For the evaluation of this method, previous work used the test problem of Smith and Hutton for Peclet numbers ranging from 10 to {infinity}. To further evaluate this method, in this work results are presented from its application to another benchmark problem of computational fluid dynamics. This problem is laminar isothermal flow in a square cavity driven by a sliding lid. 7 refs., 1 fig.

Tzanos, C.P.

1990-01-01

408

A new method of measuring hydrogen diffusivity by hydrogen permeation technique . 1: Theoretical modeling  

SciTech Connect

A new model on hydrogen permeation is proposed, considering absorption and desorption processes on the sample surfaces. Analytical solution, satisfying the flux continuity rather than the concentration boundary conditions, is derived from the model. Drift velocity through surface and drift velocity in bulk are introduced and their ratio determines the validity of the time-lag model. When the ratio of drift velocity through surface over that in bulk approaches infinity, the proposed model is reduced to the time-lag one. The diffusivity and the drift velocity through surface can be evaluated by fitting the entire normalized permeation curve. The obtained results can predict the effects of temperature, sample thickness and energy barriers of absorption and desorption on the permeation process. The thickness effect occurred in using the time-lag model is well explained by the effects of absorption and desorption on the permeation process.

Zhang, T.Y.; Zheng, Y.P. [Hong Kong Univ. of Science and Technology, Kowloon (Hong Kong). Dept. of Mechanical Engineering

1998-12-31

409

Nonlinear variants of the TR/BDF2 method for thermal radiative diffusion  

SciTech Connect

We apply the Trapezoidal/BDF2 (TR/BDF2) temporal discretization scheme to nonlinear grey radiative diffusion. This is a scheme that is not well-known within the radiation transport community, but we show that it offers many desirable characteristics relative to other second-order schemes. Several nonlinear variants of the TR/BDF2 scheme are defined and computationally compared with the Crank-Nicholson scheme. It is found for our test problems that the most accurate TR/BDF2 schemes are those that are fully iterated to nonlinear convergence, but the most efficient TR/BDF2 scheme is one based upon a single Newton iteration. It is also shown that neglecting the contributions to the Jacobian matrix from the cross-sections, which is often done due to a lack of smooth interpolations for tabular cross-section data, has a significant impact upon efficiency.

Edwards, Jarrod D. [Department of Nuclear Engineering, 129 Zachry Engineering Center, TAMU 3133, Texas A and M University, College Station, Texas 77843 (United States); Morel, Jim E., E-mail: morel@tamu.ed [Department of Nuclear Engineering, 129 Zachry Engineering Center, TAMU 3133, Texas A and M University, College Station, Texas 77843 (United States); Knoll, Dana A. [Fluid Dynamics and Solid Mechanics Group T-3, Los Alamos National Laboratory, P.O. Box 1663, MS B216, Los Alamos, NM 87545 (United States)

2011-02-20

410

Thermal Diffusivity Measurements of Oxide and Metallic Melts at High Temperature by the Laser Flash Method  

NASA Astrophysics Data System (ADS)

The importance of heat transfer properties such as thermal conductivity or thermal diffusivity of various materials at high temperature is strongly emphasized, in parallel with recent progress in surface technology for several electronic devices. Such importance has been well recognized in many pyrometallurgical processes related to plant design and accurate control of continuous casting in steelmaking. For example, heat transfer properties of molten salts are essential to design applications to heat transfer fluids for fusion reactors, breeder reactors, and thermal energy storage systems. Then, thermal property data of molten salts with sufficient reliability are strongly required to select an optimum composition of salt mixture for the desired condition [1]. We also need thermal property data of molten iron at elevated temperature and continuous casting powder melts consisting of various oxide components; SiO2, CaO, MgO, Al2O3, etc. for further improving the present continuous casting process for steel [2].

Shibata, Hiroyuki; Ohta, Hiromichi; Waseda, Yoshio

411

The effect of hydrogen bonding on the diffusion of water in n-alkanes and n-alcohols measured with a novel single microdroplet method.  

PubMed

While the Stokes-Einstein (SE) equation predicts that the diffusion coefficient of a solute will be inversely proportional to the viscosity of the solvent, this relation is commonly known to fail for solutes, which are the same size or smaller than the solvent. Multiple researchers have reported that for small solutes, the diffusion coefficient is inversely proportional to the viscosity to a fractional power, and that solutes actually diffuse faster than SE predicts. For other solvent systems, attractive solute-solvent interactions, such as hydrogen bonding, are known to retard the diffusion of a solute. Some researchers have interpreted the slower diffusion due to hydrogen bonding as resulting from the effective diffusion of a larger complex of a solute and solvent molecules. We have developed and used a novel micropipette technique, which can form and hold a single microdroplet of water while it dissolves in a diffusion controlled environment into the solvent. This method has been used to examine the diffusion of water in both n-alkanes and n-alcohols. It was found that the polar solute water, diffusing in a solvent with which it cannot hydrogen bond, closely resembles small nonpolar solutes such as xenon and krypton diffusing in n-alkanes, with diffusion coefficients ranging from 12.5x10(-5) cm(2)/s for water in n-pentane to 1.15x10(-5) cm(2)/s for water in hexadecane. Diffusion coefficients were found to be inversely proportional to viscosity to a fractional power, and diffusion coefficients were faster than SE predicts. For water diffusing in a solvent (n-alcohols) with which it can hydrogen bond, diffusion coefficient values ranged from 1.75x10(-5) cm(2)/s in n-methanol to 0.364x10(-5) cm(2)/s in n-octanol, and diffusion was slower than