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1

Metachromatic Agar-Diffusion Methods for Detecting Staphylococcal Nuclease Activity  

PubMed Central

Based on the metachromatic property of Toluidine Blue O, three, convenient agar-diffusion methods have been developed that enable detection of the nuclease of Staphylococcus aureus at concentrations as low as 0.005 ?g/ml in agar and broth cultures. The interactions of agar and deoxyribonucleic acid with Toluidine Blue O are discussed. Images

Lachica, R. V. F.; Genigeorgis, C.; Hoeprich, P. D.

1971-01-01

2

Improved agar diffusion method for detecting residual antimicrobial agents.  

PubMed

The improved agar diffusion method for determination of residual antimicrobial agents was investigated, and the sensitivities of various combinations of test organisms and assay media were determined using 7 organisms, 5 media, and 31 antimicrobial agents. Bacillus stearothermophilus and synthetic assay medium (SAM) showed the greatest sensitivity for screening penicillins (penicillin G and ampicillin). The combination of Bacillus subtilis and minimum medium (MM) was the most sensitive for tetracyclines (oxytetracycline and chlortetracycline), B. stearothermophilus and SAM or Micrococcus luteus and Mueller-Hinton agar (MHA) for detecting tylosin and erythromycin, B. subtilis and MHA for aminoglycosides (streptomycin, kanamycin, gentamicin, and dihydrostreptomycin), B. stearothermophilus and SAM for polyethers (salinomycin and lasalocid), and B. subtilis and MM or Clostridium perfringens and GAM for polypeptides (thiopeptin, enramycin, virginiamycin, and bacitracin). However, gram-negative bacterium Escherichia coli ATCC 27166 and MM were better for screening for colistin and polymixin-B. For detecting the synthetic drugs tested, the best combination was B. subtilis and MM for sulfonamides, E. coli 27166 and MM for quinolones (oxolinic acid and nalidixic acid), B. subtilis and MM for furans (furazolidone), and the bioluminescent bacterium Photobacterium phosphoreum and luminescence assay medium for chloramphenicol and oxolinic acid. The results showed that the use of four assay plates, B. stearothermophilus and SAM, B. subtilis and MM, M. luteus and MHA, and E. coli 27166 and MM, was superior to the currently available techniques for screening for residual antimicrobial agents in edible animal tissues. PMID:11252480

Tsai, C E; Kondo, F

2001-03-01

3

An Agar Diffusion Method for the Differentiation of Bacillus Anthracis.  

National Technical Information Service (NTIS)

A method of differentiating Bacillus anthracis from B. cereus and other aerobic spore-formers has been developed based on detection of protective antigen production by individual colonies on solid medium. Single colonies were obtained by inoculating the s...

L. Angelety G. G. Wright

1969-01-01

4

Comparison of microplate, agar drop and well diffusion plate methods for evaluating hemolytic activity of Listeria monocytogenes  

Microsoft Academic Search

th May, 2009 Hemolytic activity is an important characteristic for the differentiation of Listeria monocytogenes from apathogenic Listeria species within of conventional laboratory practices. We compared the efficacy of the agar well diffusion method with respect to two previously described methods such as the agar drop and microplate methods in quantifying hemolysis of L. monocytogenes cultures. The hemolytic activities of

M. L. Vaca Ruiz; P. G. Silva; A. L. Laciar

5

Inaccuracy of the disk diffusion method compared with the agar dilution method for susceptibility testing of Campylobacter spp.  

PubMed

The agar dilution method has been standardized by the CLSI for the susceptibility testing of Campylobacter species, and according to these standards, the disk diffusion method should be used only in screening for macrolide and ciprofloxacin resistance. Nevertheless, the disk diffusion test is currently widely used, since it is easy to perform in clinical microbiology laboratories. In this study, the disk diffusion method was compared to the agar dilution method by analyzing the in vitro activities of seven antimicrobial agents against 174 Campylobacter strains collected in Finland between 2003 and 2008. Recommendations of the CLSI were followed using Mueller-Hinton agar plates with 5% of sheep blood. For each strain, the disk diffusion tests were performed two to four times. Of the 33 erythromycin-resistant strains (MIC, ?16 ?g/ml), 24 (73%) constantly showed a 6-mm erythromycin inhibition zone (i.e., no inhibition), while for seven strains the inhibition zone varied from 6 to 44 mm in repeated measurements. Among the 141 erythromycin-susceptible strains (MIC, <16 ?g/ml), erythromycin inhibition zones varied between 6 and 61 mm. Of the 87 ciprofloxacin-resistant strains, 47 (54%) showed 6-mm inhibition zones, while 40 strains showed inhibition zones between 6 and 60 mm. Significant differences between the repetitions were observed in the disk diffusion for all antimicrobial agents and all strains except for the macrolide-resistant strains regarding the macrolides. For 17 (10%) strains, the variation in repeated measurements was substantial. These results show that the disk diffusion method may not be a reliable tool for the susceptibility testing of Campylobacter spp. Further studies are needed to assess whether the disk diffusion test could be improved or whether all susceptibilities of campylobacters should be tested using an MIC-based method. PMID:22075583

Lehtopolku, Mirva; Kotilainen, Pirkko; Puukka, Pauli; Nakari, Ulla-Maija; Siitonen, Anja; Eerola, Erkki; Huovinen, Pentti; Hakanen, Antti J

2011-11-09

6

A method for turbidimetric measurement of bacterial growth in liquid cultures and agar plug diffusion cultures, using standard test tubes  

Microsoft Academic Search

A method has been developed for turbidimetric measurement of bacterial growth in standard inexpensive test tubes with closures in-place. Liquid cultures and agar plug diffusion cultures can be assayed using an unmodified spectrophotometer. Growth curves of replicate cultures grown in test tubes, are reproducible with respect to similarity of curve shape, onset of logarithmic growth phase, and maximum growth.

K. J. Brown

1980-01-01

7

The antibacterial activity of sodium hypochlorite and chlorhexidine against Enterococcus faecalis: A review on agar diffusion and direct contact methods  

PubMed Central

Complete debridement and disinfection of the root canal system are fundamental requirements for successful endodontic treatment. Despite the morphological challenges of the internal root anatomy, root canal irrigants play an important role in the optimization of the root canal preparation, which is essentially a chemo-mechanical procedure. Enterococcus faecalis is one of the most resistant microorganisms that dominants the microbial ecosystem of persistent periradicular lesions in retreatment cases. For that reason, many in vitro and in vivo studies evaluated and compared the antibacterial activity of sodium hypochlorite and chlorhexidine at varying concentrations using different experimental models against this microorganism. However, many controversies with regard to the ideal irrigant and concentration do in fact exist. Hence, this review aims to discuss the antibacterial activity of these two main root canal irrigants against Enterococcus faecalis using the agar diffusion and direct contact methods and the possible modulating factors responsible for inconsistent findings among different studies. In addition, the disinfection potential of both chemical agents on gutta percha and Resilon cones are also discussed. The source of this review was conducted through an electronic literature search using PubMed database from December 1997 until December 2011, which analyze the related laboratory investigations of both irrigants, published in major endodontic journals.

Luddin, Norhayati; Ahmed, Hany Mohamed Aly

2013-01-01

8

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

PubMed Central

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 sp. (five species), Alternaria sp., Bipolaris spicifera, Fusarium sp. (three species), Mucor sp. (two species), Paecilomyces lilacinus, Rhizopus sp. (two species), and Scedosporium sp. (two species): (i) two media (supplemented Mueller-Hinton agar [2% dextrose and 0.5 ?g/ml methylene blue] and plain Mueller-Hinton [MH] agar), (ii) three incubation times (16 to 24, 48, and 72 h), and (iii) seven disks (amphotericin B and itraconazole 10-?g disks, voriconazole 1- and 10-?g disks, two sources of caspofungin 5-?g disks [BBL and Oxoid], and posaconazole 5-?g disks). MH agar supported better growth of all of the species tested (24 to 48 h). The reproducibility of zone diameters and their correlation with either MICs or MECs (caspofungin) were superior on MH agar (91 to 100% versus 82 to 100%; R, 0.71 to 0.93 versus 0.53 to 0.96 for four of the five agents). Based on these results, the optimal testing conditions for mold disk diffusion testing were (i) plain MH agar; (ii) incubation times of 16 to 24 h (zygomycetes), 24 h (Aspergillus fumigatus, A. flavus, and A. niger), and 48 h (other species); and (iii) the posaconazole 5-?g disk, voriconazole 1-?g disk, itraconazole 10-?g disk (for all except zygomycetes), BBL caspofungin 5-?g disk, and amphotericin B 10-?g (zygomycetes only).

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

2007-01-01

9

Comparison of agar dilution, broth microdilution, E-test, disk diffusion, and automated Vitek methods for testing susceptibilities of Enterococcus spp. to vancomycin.  

PubMed Central

An evaluation was undertaken to determine the optimal method for testing the susceptibilities of 100 clinical isolates and two reference strains of Enterococcus spp. to vancomycin in vitro. Six testing methods were studied by using the following media and incubation times: agar screen with the Synergy Quad Plate (Remel, Lenexa, Kans.), an in-house-prepared brain heart infusion (BHI) agar plate, and an in-house-prepared Mueller-Hinton (MH) agar plate, all incubated for 24 or 48 h; broth microdilution (Sensititre Just One Strip; AccuMed International, Inc., West Lake, Ohio) with BHI or cation-adjusted MH broth incubated for 24 or 48 h; agar dilution with BHI or MH agar incubated for 24 or 48 h; epsilometer test (E test; AB BioDisk, Solna, Sweden) with BHI or MH agar incubated for 24 or 48 h; disk diffusion with BHI or MH agar incubated for 24 or 48 h; and the automated Vitek method with the gram-positive susceptibility Staphylococcus aureus card and R02.03 software (bioMerieux, Inc., Hazelwood, Mo.). Growth failures occurred with MH media (n = 6) but not with BHI media. One growth failure occurred with the Vitek method. Results for each testing method for each Enterococcus strain were interpreted as susceptible, intermediate, or resistant according to current National Committee for Clinical Laboratory Standards (NCCLS) criteria and compared to the vancomycin resistance genotype (i.e., vanA, vanB, vanC-1, or vanC-2/3). For all methods, extension of the incubation time from 24 h to 48 h either produced no difference in the results or gave poorer results. The following methods produced no very major or major interpretive errors: broth microdilution with BHI media incubated for 24 h, agar dilution with BHI media incubated for 24 or 48 h, and E test with BHI media incubated for 24 or 48 h. Unacceptable frequencies of very major errors (> 1%) occurred with all methods for which MH media were used. Minor interpretive errors were frequent with all methods. These minor interpretive errors also occurred most frequently with Enterococcus strains with vanC genes, which encoded low-level vancomycin resistance (MIC < or = 8 microg/ml), as opposed to Enterococcus strains which possessed vanA or vanB genes, which encoded higher-level vancomycin resistance (MIC > or = 64 microg/ml). Modification of NCCLS breakpoints, especially for motile Enterococcus spp. (E. casseliflavus, E. flavescens, and E. gallinarum), may resolve this problem; however, in the current study, one E. faecalis strain and one E. faecium strain carried only the vanC gene. The agar screen method may also require reformulation. The current agar screen plate contains 6 microg of vancomycin per ml, which may not detect all low-level resistance associated with vanC genotypes. Nevertheless, the clinical significance of this low-level vancomycin resistance remains unknown.

Kohner, P C; Patel, R; Uhl, J R; Garin, K M; Hopkins, M K; Wegener, L T; Cockerill, F R

1997-01-01

10

Comparison of agar dilution, broth microdilution, E-test, disk diffusion, and automated Vitek methods for testing susceptibilities of Enterococcus spp. to vancomycin.  

PubMed

An evaluation was undertaken to determine the optimal method for testing the susceptibilities of 100 clinical isolates and two reference strains of Enterococcus spp. to vancomycin in vitro. Six testing methods were studied by using the following media and incubation times: agar screen with the Synergy Quad Plate (Remel, Lenexa, Kans.), an in-house-prepared brain heart infusion (BHI) agar plate, and an in-house-prepared Mueller-Hinton (MH) agar plate, all incubated for 24 or 48 h; broth microdilution (Sensititre Just One Strip; AccuMed International, Inc., West Lake, Ohio) with BHI or cation-adjusted MH broth incubated for 24 or 48 h; agar dilution with BHI or MH agar incubated for 24 or 48 h; epsilometer test (E test; AB BioDisk, Solna, Sweden) with BHI or MH agar incubated for 24 or 48 h; disk diffusion with BHI or MH agar incubated for 24 or 48 h; and the automated Vitek method with the gram-positive susceptibility Staphylococcus aureus card and R02.03 software (bioMerieux, Inc., Hazelwood, Mo.). Growth failures occurred with MH media (n = 6) but not with BHI media. One growth failure occurred with the Vitek method. Results for each testing method for each Enterococcus strain were interpreted as susceptible, intermediate, or resistant according to current National Committee for Clinical Laboratory Standards (NCCLS) criteria and compared to the vancomycin resistance genotype (i.e., vanA, vanB, vanC-1, or vanC-2/3). For all methods, extension of the incubation time from 24 h to 48 h either produced no difference in the results or gave poorer results. The following methods produced no very major or major interpretive errors: broth microdilution with BHI media incubated for 24 h, agar dilution with BHI media incubated for 24 or 48 h, and E test with BHI media incubated for 24 or 48 h. Unacceptable frequencies of very major errors (> 1%) occurred with all methods for which MH media were used. Minor interpretive errors were frequent with all methods. These minor interpretive errors also occurred most frequently with Enterococcus strains with vanC genes, which encoded low-level vancomycin resistance (MIC < or = 8 microg/ml), as opposed to Enterococcus strains which possessed vanA or vanB genes, which encoded higher-level vancomycin resistance (MIC > or = 64 microg/ml). Modification of NCCLS breakpoints, especially for motile Enterococcus spp. (E. casseliflavus, E. flavescens, and E. gallinarum), may resolve this problem; however, in the current study, one E. faecalis strain and one E. faecium strain carried only the vanC gene. The agar screen method may also require reformulation. The current agar screen plate contains 6 microg of vancomycin per ml, which may not detect all low-level resistance associated with vanC genotypes. Nevertheless, the clinical significance of this low-level vancomycin resistance remains unknown. PMID:9399530

Kohner, P C; Patel, R; Uhl, J R; Garin, K M; Hopkins, M K; Wegener, L T; Cockerill, F R

1997-12-01

11

Gentamicin diffusion in Mueller-Hinton agar plates from different manufacturers  

Microsoft Academic Search

Sir, The diameter of inhibition zones in agar diffusion suscept- ibility test is the result of several variables related to the antibiotic-bacterium pair, standard method and composi- tion of the medium.1 The evaluation of different lots of Mueller-Hinton agar (MHA) and the development and application of reference media in the agar diffusion test has been taken into consideration by the

C. Arcelloni; R. Vaiani; R. Paroni; H. S. Raffaele Milan

12

Comparison of agar disk diffusion, microdilution broth, and agar dilution for testing antimicrobial susceptibility of coagulase-negative staphylococci.  

PubMed Central

A collection of 120 oxacillin-susceptible and 120 oxacillin-resistant coagulase-negative staphylococci (CNS) from six tertiary care hospital laboratories were tested by agar disk diffusion, three microdilution broth systems (Sensititre, Dynatech, and Alpkem), and the Vitek AutoMicrobic system for comparison with reference agar dilution results. The antimicrobial agents tested were oxacillin, cefazolin, cefotaxime, cefuroxime, cefamandole, fusidic acid, rifampin, and vancomycin. Incubation was at 30 or 35 degrees C for 24, 48, and 72 h. The broth media were supplemented with 2% NaCl for some antimicrobial agents, and the agar dilution method was used with and without the addition of 4% NaCl. The CNS were identified to species by the method of Kloos and Schleifer. The results showed a lack of concordance between two hospitals with respect to oxacillin susceptibility testing by agar dilution with no NaCl supplement. The reasons are not clear but may be related to variations in media. The 4% NaCl supplement or extended incubation to 48 h eliminated this difference. The cefazolin and cefotaxime susceptibility results in the agar disk diffusion test were unreliable if accepted at face value. Cefamandole testing correlated well with the reference method regardless of the method used, and salt supplementation is not recommended. Most of the oxacillin-resistant CNS were resistant to the other beta-lactam drugs except cefamandole. Of 22 CNS resistant to cefamandole, 21 were S. haemolyticus.

Smith, J A; Henry, D A; Bourgault, A M; Bryan, L; Harding, G J; Hoban, D J; Horsman, G B; Marrie, T; Turgeon, P

1987-01-01

13

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.

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

14

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.

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

1999-01-01

15

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

16

A Specific Diffusible Antigen of Rinderpest Virus demonstrated by the Agar Double-Diffusion Precipitation Reaction  

Microsoft Academic Search

IN recent years diffusible antigens of many viruses have been demonstrated by the double-diffusion precipitation reaction in agar. Early attempts in this laboratory to demonstrate such antigens associated with rinderpest virus failed, probably because the convalescent bovine and rabbit sera used did not contain a sufficiently high concentration of antibody.

G. White

1958-01-01

17

Screening fungicides for use in fish culture: Evaluation of the agar plug transfer, cellophane transfer, and agar dilution methods  

USGS Publications Warehouse

The reliability, reproducibility, and usefulness of three screening methods -- the cellophane transfer, the agar plug transfer, and the agar dilution -- to screen aquatic fungicides were evaluated. Achlya flagellata and Saprolegnia hypogyna were exposed to 1, 10, and 100 mg/L of malachite green to test each method. The cellophane transfer and agar plug transfer techniques had similar reliability and reproducibility in rating fungicidal activity, and were both superior to the agar dilution technique. The agar plug transfer and agar dilution techniques adequately projected in vivo activity of malachite green, but the cellophane transfer technique overestimated its activity. Overall, the agar plug transfer technique most accurately rated the activity of malachite green and was the easiest test to perform. It therefore appears to be the method of choice for testing aquatic fungicides.

Bailey, Tom A.

1983-01-01

18

Antimicrobial Susceptibility Testing of Bacillus anthracis: Comparison of Results Obtained by Using the National Committee for Clinical Laboratory Standards Broth Microdilution Reference and Etest Agar Gradient Diffusion Methods  

Microsoft Academic Search

We determined the patterns of antimicrobial susceptibility of 65 isolates of Bacillus anthracis (50 historical and 15 recent U.S. clinical isolates) to nine antimicrobial agents using the National Committee for Clinical Laboratory Standards (NCCLS) broth microdilution reference method. The results for the 50 historical B. anthracis isolates obtained by the broth microdilution method were compared to those generated by the

M. Jasmine Mohammed; Chung K. Marston; Tanja Popovic; Robbin S. Weyant; Fred C. Tenover

19

Method for Measuring Changes in Surface Tension on Agar  

PubMed Central

The surface tension of agar surfaces was determined by measuring the contact angles formed by drops of various hydrophobic liquids on the surface and then calculating the composite surface free energy function by solving a series of simultaneous equations derived from these data. This method was used to measure the change in the surface tension of agar produced by the addition of various concentrations of albumin. The resulting curve was typical of the effect of increasing concentrations of surfactants on surface tension. The method was compared with other methods of determining surface tension of solids, and it was concluded that the technique used here provided the most reliable results.

Weisberg, David S.; Dworkin, Martin

1983-01-01

20

Diffusion of Methylene Blue in Phantoms of Agar Using a Photoacoustic Technique  

Microsoft Academic Search

In this work, the kinetics of diffusion of methylene blue in agar aqueous solution is studied using a photoacoustic technique.\\u000a Two agar phantoms solutions in water with a relation of mass\\/volume of 0.01% and 0.05% were analyzed. The study was performed\\u000a using a modified Rosencwaig photoacoustic cell that is enclosed by transparent windows, on both sides. The sample is deposited

L. Vilca-Quispe; J. J. Alvarado-Gil; P. Quintana; J. Ordonez-Miranda

2010-01-01

21

Tracer-diffusion of cobalt ions in sodium and potassium nitrates in agar gel  

Microsoft Academic Search

Tracer-diffusion of Co2+ ions is studied in agar gel in the presence of sodium and potassium nitrates at 25°C. The diffusion coefficient values at various electrolyte concentrations are compared with the corresponding theoretical values computed on the basis of Onsager's theory. The deviations from the theory are attributed to the various co-occurring effects in the diffusion medium. The activation energy

Mahendrakumar K. Patil

1986-01-01

22

The diffusion of gibberellins into agar and water during early germination of Pharbitis nil Choisy  

Microsoft Academic Search

Agar diffusion of imbibed seeds yielded significant amounts of diffusible Gibberellin-like substances. An analysis of the extractable and diffusible gibberellin-like substance, including an analysis of the remaining imbibition water of the seeds, indicated that a significant part of these gibberellin-like substances could be attributed to a net biosynthesis of these substances in the imbibing seeds. At the same time it

Gerard W. M. Barendse; Hans A. M. Gilissen

1977-01-01

23

Methods for identifying lipoxygenase producing microorganisms on agar plates  

PubMed Central

Plate assays for lipoxygenase producing microorganisms on agar plates have been developed. Both potassium iodide-starch and indamine dye formation methods were effective for detecting soybean lipoxygenase activity on agar plates. A positive result was also achieved using the ?-carotene bleaching method, but the sensitivity of this method was lower than the other two methods. The potassium iodide-starch and indamine dye formation methods were also applied for detecting lipoxygenase production by Trichoderma reesei and Pichia pastoris transformants expressing the lipoxygenase gene of the fungus Gaeumannomyces graminis. In both cases lipoxygenase production in the transformants could be identified. For detection of the G. graminis lipoxygenase produced by Aspergillus nidulans the potassium iodide-starch method was successful. When Escherichia coli was grown on agar and soybean lipoxygenase was applied on the culture lipoxygenase activity could clearly be detected by the indamine dye formation method. This suggests that the method has potential for screening of metagenomic libraries in E. coli for lipoxygenase activity.

2012-01-01

24

Immunodiagnosis of Paragonimiasis by Counterimmunoelectrophoresis and Agar Gel Diffusion.  

National Technical Information Service (NTIS)

The counterimmunoelectrophoresis (CIEP) technic is a rppid and accurate immunodiagnostic test for detecting paragonimiasis. 57 cases of paragonimiasis were examined by this method and all showed positive reactions. For comparison, their sera were also exa...

H. Xiaosu F. Ruiyuan H. Anqi Y. Heping T. Guangzhao

1980-01-01

25

Osmotic Dehydration of Foods in a Multicomponent Solution Part I. Lowering of Solute Uptake in Agar Gels: Diffusion Considerations  

Microsoft Academic Search

The composition of a multicomponent aqueous solution containing sugars and salts was studied in order to lower solute uptake during osmotic dehydration of an agar gel. A diffusion cell was used to obtain the effective diffusivity and the main diffusion coefficient of each solute in the presence of the others. The main diffusion coefficients were then expressed as a function

Z. Emam-Djomeh; G. Djelveh; J.-B. Gros

2001-01-01

26

Diffusion of Cesium Ions Labeled with 134 Cs in Agar Gel Containing Alkali Metal Iodides: Obstruction Effect and Activation Energy  

Microsoft Academic Search

The effect of some alkali metal iodides on the obstruction effect and activation energy for tracer-diffusion of cesium ions in an agar gel medium was studied using the zone-diffusion technique. It to be observed that both the extent of obstruction (?) and the activation energy (E) decrease with the increasing charge density of the cation of the supporting electrolyte. These

Narendra A. Gokarn; Nilima S. Rajurkar

2006-01-01

27

A modified agar pad method for mycobacterial live-cell imaging  

Microsoft Academic Search

Background  Two general approaches to prokaryotic live-cell imaging have been employed to date, growing bacteria on thin agar pads or\\u000a growing bacteria in micro-channels. The methods using agar pads 'sandwich' the cells between the agar pad on the bottom and\\u000a a glass cover slip on top, before sealing the cover slip. The advantages of this technique are that it is simple

Graham Joyce; Brian D Robertson; Kerstin J Williams

2011-01-01

28

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

2013-06-24

29

Smart approach to evaluate drug diffusivity in injectable agar-carbomer hydrogels for drug delivery.  

PubMed

Hydrogels are commonly studied for tissue engineering applications and controlled drug delivery. In order to evaluate their reliability as scaffolds and delivery devices, literature describes many release studies performed involving different analytical techniques. However, these experiments can be expensive, time-consuming, and often not reproducible. In this study, two injectable agar-carbomer-based hydrogels were studied, both being loaded with sodium fluorescein, a harmless fluorophore with a steric hindrance similar to many small drugs, such as for example steroids and other neuroprotecting agents. Starting from simple, traditional, and inexpensive release experiments, it was possible to indirectly estimate the self-diffusion coefficient (D) of loaded sodium fluorescein. Such a parameter was also directly measured in the gel matrix by means of high resolution magic angle spinning (HRMAS) diffusion-ordered spectroscopy NMR. Because of the agreement between the calculated values and those measured by HRMAS-NMR spectroscopy, the latter approach can be considered as a simple and fast alternative to long analytic procedures. PMID:21355616

Santoro, M; Marchetti, P; Rossi, F; Perale, G; Castiglione, F; Mele, A; Masi, M

2011-02-28

30

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

31

Analysis of Antibiotics Susceptibility of Old and Fresh ATCC Strain of Staphylococcus aureus by Standard Agar Diffusion Technique  

Microsoft Academic Search

A comparative study of an old and fresh ATCC strain of Staphylococcus aureus was carried out to determine the mechanism of antibiotic resistance of the old one, which had been preserved in lyophilized condition. Five different antibiotics having five different modes of action were used. They included amoxicillin, azithromycin, neomycin, ciprofloxacin and polymixin B. Agar diffusion technique was followed to

Marufa Zerin Akhter; Ibrahim Khalil; Priyanath Roy; Mir Mohammad Ibna Masud

2007-01-01

32

Activity of Retapamulin against Streptococcus pyogenes and Staphylococcus aureus Evaluated by Agar Dilution, Microdilution, E-Test, and Disk Diffusion Methodologies  

Microsoft Academic Search

The in vitro activity of retapamulin against 106 Staphylococcus aureus isolates and 109 Streptococcus pyogenes isolates was evaluated by the agar dilution, broth microdilution, E-test, and disk diffusion methodologies. Where possible, the tests were performed by using the CLSI methodology. The results of agar dilution, broth microdilution, and E-test (all with incubation in ambient air) for S. aureus yielded similar

Glenn A. Pankuch; Gengrong Lin; Dianne B. Hoellman; Caryn E. Good; Michael R. Jacobs; Peter C. Appelbaum

2006-01-01

33

Identification of Staphylococcal Enterotoxin by the Agar Precipitation Method.  

National Technical Information Service (NTIS)

Adoption of the method for obtaining and purifying the enterotoxin of staphylococcus No. 32/54-55 and production of homologous antitoxin has made it possible to carry out further serological tests in order to identify the enterotoxin of staphylococci in v...

M. Kalember-Radosavljevic

1966-01-01

34

Multicenter Evaluation of Ethambutol Susceptibility Testing of Mycobacterium tuberculosis by Agar Proportion and Radiometric Methods  

Microsoft Academic Search

Reproducibility of ethambutol (EMB) susceptibility test results for Mycobacterium tuberculosis has always been difficult for a variety of reasons, including the narrow range between the critical breakpoint for EMB resistance and the MIC for susceptible strains, borderline results obtained with the BACTEC 460TB method, the presence of microcolonies determined using the agar proportion (AP) method, and a lack of agreement

B. Madison; B. Robinson-Dunn; I. George; W. Gross; H. Lipman; B. Metchock; A. Sloutsky; G. Washabaugh; G. Mazurek; J. Ridderhof

2002-01-01

35

Comparison of Etest and Agar Dilution Method for Antimicrobial Susceptibility Testing ofFlavobacteriumIsolates  

Microsoft Academic Search

The Etest was evaluated as a possible alternative to the standard agar dilution method for susceptibility testing of nine antimicrobial agents against Flavobacterium species. In studies of 100 clinical isolates, the agreement between the MICs (61 log2dilution) obtained by the two methods was acceptable for cefotaxime, ceftazidime, amikacin, minocycline, ofloxacin, and ciprofloxacin (>90%). Conversely, the agreement between the results obtained

PO-REN HSUEH; JEN-CHYI CHANG; LEE-JENE TENG; PAN-CHYR YANG; SHEN-WU HO; WEI-CHUAN HSIEH; ANDKWEN-TAY LUH

1997-01-01

36

MODIFIED AGAR MEDIUM FOR DETECTING ENVIRONMENTAL SALMONELLAE BY THE MOST-PROBABLE-NUMBER METHOD  

EPA Science Inventory

Salmonellae in the environment remain a potential source of disease. Low numbers of salmonellae have been detected and enumerated from environmental samples by most probable number methods that require careful colony selection from plated agar medium. A modified xylose lysine bri...

37

Correlation of Neo-Sensitabs Tablet Diffusion Assay Results on Three Different Agar Media with CLSI Broth Microdilution M27-A2 and Disk Diffusion M44-A Results for Testing Susceptibilities of Candida spp. and Cryptococcus neoformans to Amphotericin B, Caspofungin, Fluconazole, Itraconazole, and Voriconazole  

Microsoft Academic Search

We compared the Neo-Sensitabs tablet assay to both reference M27-A2 broth microdilution and M44-A disk diffusion methods for testing susceptibilities of 110 isolates of Candida spp. and Cryptococcus neoformans to amphotericin B, caspofungin, fluconazole, itraconazole, and voriconazole. Neo-Sensitabs assay inhibition zone diameters in millimeters on three agars (Mueller-Hinton agar supplemented with 2% dextrose and 0.5 g\\/ml methylene blue (MGM), Shadomy

A. Espinel-Ingroff; E. Canton; D. Gibbs; A. Wang

2007-01-01

38

Modification of the Congo red agar method to detect biofilm production by Staphylococcus epidermidis.  

PubMed

Staphylococcus epidermidis in immunocompromised patients can cause bacteremia related to the use of catheter due to biofilm production. There are different phenotypic methods to detect biofilm formation. One method is based on culture in brain heart infusion agar (BHIA) containing sucrose and red Congo dye (original Congo red agar). Our group created a new CRA formula and we have confirmed its capacity to detect biofilm production in 210 S. epidermidis strains, including 76 (36.2%) icaAB gene-positive strains. Other parameters were also evaluated. The new CRA formula that gave the best results was BHIA with sucrose (5%), Congo red (0.08%), NaCl (1.5%), glucose (2%), and vancomycin (0.5 mg/mL) (vancomycin-modified CRA-CRAmod). The CRAmod plus vancomycin may be a promising tool and can help to determine the real participation of S. epidermidis in the infectious process. PMID:23313084

Kaiser, Thaís Dias Lemos; Pereira, Eliezer Menezes; Dos Santos, Kátia Regina Netto; Maciel, Ethel Leonor Noia; Schuenck, Ricardo Pinto; Nunes, Ana Paula Ferreira

2013-01-11

39

Agar Plate Method for Detection and Enumeration of Alkylbenzenesulfonate-Degrading Microorganisms  

PubMed Central

A simple method for detection and enumeration of alkylbenzenesulfonate (ABS)-degrading microorganisms by using agar plates was developed and used in microbiological studies of coastal marine and polluted river waters. The method depends upon the color responses of neutral red in alkaline medium. Neutral red changes from pink, when it enters into ABS micelles, to yellow, when the ABS is degraded, and does not form micelles. When neutral red-tris(hydroxymethyl)-aminomethane buffer solution and then cationic surfactant solution were sprayed onto the agar surface of ABS-nutrient agar cultures, transparent haloes appeared around the colonies of ABS-degrading microorganisms against a pink background. Viable counts of ABS-degrading bacteria isolated from both seawater and freshwater environments were considerably higher in polluted waters than in less polluted areas. Viable counts of ABS-degrading bacteria averaged 1.5 × 105/ml in samples from the surface water of polluted Tokyo Bay and 3.0 × 104/ml in samples from the surface water of polluted Tamagawa River but were fewer in number in samples from less polluted waters. Images

Ohwada, Kouichi

1975-01-01

40

Quantitative Assessment of Bactericidal Activities of ?-Lactam Antibiotics by Agar Plate Method  

PubMed Central

Quantitative bactericidal activities of ?-lactam antibiotics were determined by the agar plate method. Broth cultures, of which the colony-forming units were counted before the study, were inoculated on antibiotic-containing agar plates, utilizing a 10?3, 10?2, or 10?1 dilution or undiluted culture plated with each 0.001-ml calibrated loop. These plates were incubated at 37°C overnight, and the minimal drug concentration at which no bacterial growth was observed on the plates was defined as minimal inhibitory concentration. After this procedure, the agar surface was treated with ?-lactamase spray to inactivate the antibiotic. These plates were incubated again at 37°C overnight. The minimal drug concentration at which no evidence of bacterial growth was visible on the plates (resulting in a 100% kill) was defined as minimal bactericidal concentration. The lowest concentration which reduced the number of colony-forming units to 1/1,000 that in the original inoculum (resulting in a 99.9% kill) was defined as minimal lethal concentration. When compared for Escherichia coli, Klebsiella pneumoniae, Enterobacter sp., Serratia marcescens, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, alpha-hemolytic streptococcus (non-enterococcal), beta-hemolytic streptococcus, and enterococcus, the minimal bactericidal concentrations were generally several fold higher than the minimal inhibitory concentrations. Minimal lethal concentrations were virtually the same as minimal inhibitory concentrations for gram-negative strains; however, for some gram-positive strains, minimal lethal concentrations were higher than minimal inhibitory concentrations.

Masuda, Gohta; Tomioka, Susumu

1978-01-01

41

INTERLABORATORY EVALUATION OF MI AGAR AND THE US ENVIRONMENTAL PROTECTION AGENCY-APPROVED MEMBRANE FILTER METHOD FOR THE RECOVERY OF TOTAL COLIFORMS AND ESCHERICHIA COLI FROM DRINKING WATER  

EPA Science Inventory

A new membrane filter (MF) medium, MI agar, recently validated for use in recovering chlorine-damaged total coloiforms (TC) and Escherichia coli from drinking water, was compared to the US Environmental Protection Agency (EPA)-approved MF method(mEndo agar and nutrient agar suppl...

42

Studies on the utilisation of carbohydrates and krebs cycle intermediates by Rhizobia, using an agar plate method  

Microsoft Academic Search

An agar plate method for the testing of substrate utilisation is described, and is applied to 108 strains of bacteria belonging to the generaRhizobium andAgrobacterium. With this method, utilisation can be observed without misleading results due to the utilisation of amino acids and other substances present in the medium. Major differences in the utilisation of carbohydrates by the tested species

P. H. Graham

1964-01-01

43

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 Central

Abstract Data generated using different antimicrobial testing methods often have to be combined, but the equivalence of such results is difficult to assess. Here we compared two commonly used antimicrobial susceptibility testing methods, automated microbroth dilution and agar disk diffusion, for 8 common drugs, using 222 Salmonella isolates of serotypes Newport, Typhimurium, and 4,5,12:i-, which had been isolated from clinical salmonellosis cases among cattle and humans. Isolate classification corresponded well between tests, with 95% overall category agreement. Test results were significantly negatively correlated, and Spearman's correlation coefficients ranged from ?0.98 to ?0.38. Using Cox's proportional hazards model we determined that for most drugs, a 1?mm increase in zone diameter resulted in an estimated 20%–40% increase in the hazard of growth inhibition. However, additional parameters such as isolation year or serotype often impacted the hazard of growth inhibition as well. Comparison of economical feasibility showed that agar disk diffusion is clearly more cost-effective if the average sample throughput is small but that both methods are comparable at high sample throughput. In conclusion, for the Salmonella serotypes and antimicrobial drugs analyzed here, antimicrobial susceptibility data generated based on either test are qualitatively very comparable, and the current published break points for both methods are in excellent agreement. Economic feasibility clearly depends on the specific laboratory settings, and disk diffusion might be an attractive alternative for certain applications such as surveillance studies.

Cummings, Kevin J.; Warnick, Lorin D.; Schukken, Ynte H.; Siler, Julie D.; Grohn, Yrjo T.; Davis, Margaret A.; Besser, Tom E.; Wiedmann, Martin

2011-01-01

44

Quantification of gentamicin in Mueller–Hinton agar by high-performance liquid chromatography  

Microsoft Academic Search

The aim of this study was to optimise a method for gentamicin determination in an agar matrix and to investigate if and how agar composition can affect the gentamicin diffusion kinetics during the agar diffusion tests for antibiotics sensitivity. Gentamicin was separated by RP-HPLC and detected at 365 nm after pre-column derivatization with 1-fluoro-2,4-dinitrobenzene. Recovery (?79%), linearity (r2?0.997) and sensitivity

C. Arcelloni; B. Comuzzi; R. Vaiani; R. Paroni

2001-01-01

45

Some Basic Mathematical Methods of Diffusion Theory.  

National Technical Information Service (NTIS)

An introductory treatment of the fundamentals of diffusion theory is presented, starting with molecular diffusion and leading up to the statistical methods of turbulent diffusion. A multilayer diffusion model, designed to permit concentration and dosage c...

A. C. Giere

1977-01-01

46

An improved agar-plate method for studying root growth and response of Arabidopsis thaliana  

PubMed Central

Arabidopsis thaliana is a widely used model plant for plant biology research. Under traditional agar-plate culture system (TPG, traditional plant-growing), both plant shoots and roots are exposed to illumination, and roots are grown in sucrose-added medium. This is not a natural environment for the roots and may cause artifact responses. We have developed an improved agar-plate culture system (IPG, improved plant-growing) where shoots are illuminated but roots are grown in darkness without sucrose addition. Compared to TPG, IPG produced plants with significantly less total root length, lateral root length and root hair density, although their primary roots were longer. Root gravitropism, PIN2 (an auxin efflux carrier) abundance, H+ efflux or Ca2+ influx in root apexes, were weaker in IPG-grown roots than those in TPG-grown roots. We conclude that IPG offers a more natural way to study the root growth and response of Arabidopsis thaliana.

Xu, Weifeng; Ding, Guochang; Yokawa, Ken; Baluska, Frantisek; Li, Qian-Feng; Liu, Yinggao; Shi, Weiming; Liang, Jiansheng; Zhang, Jianhua

2013-01-01

47

Agar block smear preparation: a novel method of slide preparation for preservation of native fungal structures for microscopic examination and long-term storage.  

PubMed

We describe a novel method of fungal slide preparation named "agar block smear preparation." A total of 510 agar block smears of 25 fungal strains obtained from culture collections, 90 QC fungal strains, and 82 clinical fungal strains from our clinical microbiology laboratory, which included a total of 137 species of yeasts, molds, and thermal dimorphic fungi, were prepared and examined. In contrast to adhesive tape preparation, agar block smears preserved the native fungal structures, such as intact conidiophores of Aspergillus species and arrangements of conidia in Scopulariopsis brevicaulis. Furthermore, agar block smears allowed examination of fungal structures embedded in the agar, such as the ascomata with ascomal hairs in Chaetomium funicola; pycnidium of Phoma glomerata; the intercalary ovoidal chlamydospores arranged in chains of Fusarium dimerum; and the lateral, spherical chlamydospores arranged in pairs of Fusarium solani. After 1 year of storage, morphological integrity was found to have been maintained in 459 (90%) of the 510 agar block smears. After 3 years of storage, morphological integrity was found to have been maintained in 72 (71%) of the 102 smears prepared in 2006. Agar block smear preparation preserves the native fungal structures and allows long-term storage and examination of fungal structures embedded in the agar, hence overcoming the major drawbacks of adhesive tape preparation. The major roles of agar block smear should be diagnosis for difficult cases, accurate identification of fungal species for clinical management of patients and epidemiological studies, and long-term storage for transportation of slides and education purposes. PMID:20660221

Woo, Patrick C Y; Ngan, Antonio H Y; Chui, Hon-Kit; Lau, Susanna K P; Yuen, Kwok-Yung

2010-07-21

48

Production of toxic shock syndrome toxin 1 by Staphylococcus aureus as determined by tampon disk-membrane-agar method.  

PubMed Central

The influence of 17 commercially available tampons on production of toxic shock syndrome toxin 1 (TSST-1) by Staphylococcus aureus was investigated by using a tampon disk method. Filter membranes overlaying agar medium (with or without blood) in small petri dishes were spread inoculated with a TSST-1-producing strain of S. aureus. Disks cut from unrolled tampons were pressed and laid on the inoculated membranes; incubation was for 19 h at 37 degrees C with 5% CO2 in air. CFU on the membranes and in the disks were enumerated, and the presence of TSST-1 in the disks and in the agar layers was determined. Tampons made of different materials supported characteristic levels of cell growth and toxin production in the tampon. Colonization of the interface surface of the tampon disks was heavy. The number of CFU extracted from the tampon disks ranged from 5 X 10(10) to 82 X 10(10). There was little variation in the CFU recovered from the membranes ([1.9 +/- 0.4] X 10(11)). Sixty to 170 micrograms of TSST-1 was recoverable from the agar, with an additional 10 to 90 micrograms recoverable from tampon disks, depending on the type of tampon disk. The amount of toxin in the agar layer from the various tampon disks was relatively constant and indicated an important contribution of toxin from vaginal S. aureus cells not growing in the tampon. The main role of tampons in toxic shock syndrome may be that of providing a fibrous surface for heavy colonization and sufficient air for TSST-1 production.

Robbins, R N; Reiser, R F; Hehl, G L; Bergdoll, M S

1987-01-01

49

The Streamline Diffusion Method for Time Dependent Convection: Diffusion Problems with Small Diffusion.  

National Technical Information Service (NTIS)

A time stepping version of the streamline diffusion method, previously considered in the case of a stationary convection-diffusion problem with small diffusion, is introduced and analyzed. At each timestep the usual Galerkin method is applied to a modifie...

U. Naevert

1981-01-01

50

Comparison of Sorbitol MacConkey Agar and a Two-Step Method Which Utilizes Enzyme-Linked Immunosorbent Assay Toxin Testing and a Chromogenic Agar To Detect and Isolate Enterohemorrhagic Escherichia coli  

Microsoft Academic Search

Enterohemorrhagic Escherichia coli (EHEC) and specifically serotype O157:H7 are a significant cause of hemorrhagic gastrointestinal disease and the hemolytic uremic syndrome. Methods currently used in clinical microbiology labs, such as sorbitol-MacConkey (SMAC) agar, reliably detect only O157:H7. We have evaluated a two-step method that has the potential to identify and isolate all EHEC serotypes, including serotype O157: H7. This method

THOMAS J. NOVICKI; JUDY A. DALY; SUSAN L. MOTTICE; KAREN C. CARROLL

2000-01-01

51

Evaluation of Salmonella typhimurium, Yersinia enterocolitica and Staphylococcus aureus counts in apple juice with cinnamon, by conventional media and thin agar layer method  

Microsoft Academic Search

Pasteurized apple juice (pH 3.64) with cinnamon (0% and 0.3%) was inoculated with Salmonella typhimurium, Yersinia enterocolitica or enterotoxigenic Staphylococcus aureus at 104cfuml?1, and stored at 5°C and 20°C. Counts on tryptic soy agar (TSA), selective medium and thin agar layer (TAL) were determined at 1h and 1, 3, 7 and 14 days. The TAL method (selective medium overlaid with

J. Yuste; D. Y. C. Fung

2003-01-01

52

Optimization of the Agar-gel Method for Isolation of Migrating Ascaris suum Larvae From the Liver and Lungs of Pigs  

PubMed Central

Experiments on use of an agar-gel method for recovery of migrating Ascaris suum larvae from the liver and lungs of pigs were conducted to obtain fast standardized methods. Subsamples of blended tissues of pig liver and lungs were mixed with agar to a final concentration of 1% agar and the larvae allowed to migrate out of the agar-gel into 0.9% NaCl at 38°C. The results showed that within 3 h more than 88% of the recoverable larvae migrated out of the liver agar-gel and more than 83% of the obtained larvae migrated out of the lung agar-gel. The larvae were subsequently available in a very clean suspension which reduced the sample counting time. Blending the liver for 60 sec in a commercial blender showed significantly higher larvae recovery than blending for 30 sec. Addition of gentamycin to reduce bacterial growth during incubation, glucose to increase larval motility during migration or ice to increase sedimentation of migrated larvae did not influence larvae recovery significantly.

Saeed, I; Roepstorff, A; Rasmussen, T; H?g, M; Jungersen, G

2001-01-01

53

Comparison of agar-based methods for the isolation and enumeration of heterotrophic bacteria with the new multidose IDEXX SimPlate method.  

PubMed

Pour and spread plates are the conventional methods of choice for the isolation and enumeration of heterotrophic microorganisms in treated water supplies. The tests are performed at 22 degrees C and 37 degrees C for 72 h and 48 h respectively. Counts at 22 degrees C are associated with pollution of water systems from external sources, while counts at 37 degrees C are used as an indication of treatment plant performance and the deterioration of the general quality of water. Conventional methods using Yeast Extract Agar for a pour plate and R2A agar for a spread plate were compared with the multidose IDEXX SimPlate method for the isolation and enumeration of heterotrophic bacteria in water. SimPlate gave a significantly higher count on average than the conventional methods. The R2A method showed the next highest count, being significantly higher than Yeast Extract Agar. In addition, unlike the pour and spread plate methods, SimPlate was easier to use, reduced labour, and the test results were far easier to read. PMID:15318522

Vulindlu, M; Charlett, A; Surman, S; Lee, J V

2004-01-01

54

Advantages of functional single-cell isolation method over standard agar plate dilution method as a tool for studying denitrifying bacteria in rice paddy soil  

PubMed Central

We recently established a method for isolating functional single cells from environmental samples using a micromanipulator (Functional single-cell (FSC) isolation), and applied it to the study of denitrifying bacteria in rice paddy soil (Ashida et al. 2010. Appl Microbiol Biotechnol 85:1211–1217). To further examine the advantages and possible disadvantages of the FSC method, we isolated denitrifying bacteria from the same rice paddy soil sample using both FSC and standard agar plate dilution (APD) methods and compared in this study. The proportion of denitrifying bacteria in the total isolates was more than 6-fold larger with FSC isolation (57.1%) compared with the APD method (9.2%). Denitrifying bacteria belonging to Alphaproteobacteria and Bacilli were commonly isolated using both methods, whereas those belonging to Betaproteobacteria, which had been found to be active in the denitrification-inductive paddy soil, were isolated only with the FSC method. On the other hand, Actinobacteria were only isolated using the APD method. The mean potential denitrification activity of the FSC isolates was higher than that of the APD isolates. Overall, FSC isolation was confirmed to be an excellent method for studying denitrifying bacteria compared with the standard agar plate dilution method.

2012-01-01

55

Advantages of functional single-cell isolation method over standard agar plate dilution method as a tool for studying denitrifying bacteria in rice paddy soil.  

PubMed

We recently established a method for isolating functional single cells from environmental samples using a micromanipulator (Functional single-cell (FSC) isolation), and applied it to the study of denitrifying bacteria in rice paddy soil (Ashida et al. 2010. Appl Microbiol Biotechnol 85:1211-1217). To further examine the advantages and possible disadvantages of the FSC method, we isolated denitrifying bacteria from the same rice paddy soil sample using both FSC and standard agar plate dilution (APD) methods and compared in this study. The proportion of denitrifying bacteria in the total isolates was more than 6-fold larger with FSC isolation (57.1%) compared with the APD method (9.2%). Denitrifying bacteria belonging to Alphaproteobacteria and Bacilli were commonly isolated using both methods, whereas those belonging to Betaproteobacteria, which had been found to be active in the denitrification-inductive paddy soil, were isolated only with the FSC method. On the other hand, Actinobacteria were only isolated using the APD method. The mean potential denitrification activity of the FSC isolates was higher than that of the APD isolates. Overall, FSC isolation was confirmed to be an excellent method for studying denitrifying bacteria compared with the standard agar plate dilution method. PMID:22985609

Nishizawa, Tomoyasu; Tago, Kanako; Uei, Yusuke; Ishii, Satoshi; Isobe, Kazuo; Otsuka, Shigeto; Senoo, Keishi

2012-09-18

56

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

57

Performance of three chromogenic VRE screening agars, two Etest(®) vancomycin protocols, and different microdilution methods in detecting vanB genotype Enterococcus faecium with varying vancomycin MICs.  

PubMed

Frequencies of vanB-type Enterococcus faecium increased in Europe during the last years. VanB enterococci show various levels of vancomycin MICs even below the susceptible breakpoint challenging a reliable diagnostics. The performance of 3 chromogenic vancomycin-resistant enterococci (VRE) screening agars, 2 Etest® vancomycin protocols, and different microdilution methods to detect 129 clinical vanB E. faecium strains was investigated. Altogether, 112 (87%) were correctly identified as VanB-type Enterococcus by microdilution MICs. An Etest® macromethod protocol was more sensitive than the standard protocol while keeping sufficient specificity in identifying 15 vanA/vanB-negative strains. Three chromogenic VRE agars performed similarly with 121 (94%), 123 (95%), and 124 (96%) vanB isolates that grew on Brilliance™ VRE Agar, CHROMagar™ VRE, and chromID™ VRE agar, respectively. Using identical media and conditions, we did not identify different growth behaviour on agar and in broth. A few vanB strains showed growth of microcolonies inside the Etest® vancomycin inhibition zones, suggesting a VanB heteroresistance phenotype. PMID:22901792

Klare, Ingo; Fleige, Carola; Geringer, Uta; Witte, Wolfgang; Werner, Guido

2012-08-15

58

Radial diffusion method for determining tannin in plant extracts  

Microsoft Academic Search

Tannin in plant extracts can be determined by reacting the tannin with a protein and quantitating the precipitated complex. In the new assay described here, a tannin-containing solution is placed in a well in a protein-containing agar slab. As the tannin diffuses into the gel and complexes with protein, a visible ring of precipitation develops. The area of the ring

Ann E. Hagerman

1987-01-01

59

A cross comparison of QPCR to agar-based or defined substrate test methods for the determination of Escherichia coli and enterococci in municipal water quality monitoring programs  

Microsoft Academic Search

Molecular methods such as quantitative, real-time polymerase chain reaction (QPCR) are intended to shorten the period between sampling and publicly available results. Cross comparison studies in Racine, WI, USA evaluated QPCR against agar-based (US EPA Method 1600) and defined substrate (IDEXX Colilert-18®) methods for the detection and quantification of Escherichia coli and enterococci in a variety of aqueous environments (wastewater,

Jennifer S. Lavender; Julie L. Kinzelman

2009-01-01

60

Comparison between the BACTEC MGIT 960 system and the agar proportion method for susceptibility testing of multidrug resistant tuberculosis strains in a high burden setting of South Africa  

PubMed Central

Background The increasing problem of multi-drug-resistant (MDR) tuberculosis (TB) [ie resistant to at least isoniazid (INH) and rifampicin (RIF)] is becoming a global problem. Successful treatment outcome for MDR-TB depends on reliable and accurate drug susceptibility testing of first-line and second-line anti-TB drugs. Method Consecutive M. tuberculosis isolates identified as MDR-TB during August 2007 to January 2008 using the BACTEC MGIT 960 systems and the agar proportion method were included in this study. Susceptibility testing of MDR-TB isolates against ethambutol (EMB) and streptomycin (STR) as well as two second-line anti-TB drugs, kanamycin (KAN) and ofloxacin (OFX) was performed using the BACTEC MGIT 960 systems at a routine diagnostic laboratory. The results were compared to those obtained by the agar proportion method. Result The agreement between the BACTEC MGIT 960 system and the agar proportion method was 44% for EMB, 61% for STR and 89% for both KAN and OFX. The sensitivity and specificity of the BACTEC MGIT 960 system using the agar proportion method as a gold standard was 92% and 37% for EMB, 95% and 37% for STR, 27% and 97% for KAN and 84% and 90% for OFX, respectively. Conclusions The BACTEC MGIT 960 system showed acceptable sensitivity for EMB, STR, and OFX; however, the BACTEC MGIT 960 system was less specific for EMB and STR and demonstrated a low sensitivity for KAN. The lower agreement found between the two methods suggests the unreliability of the BACTEC MGIT 960 system for the drugs tested. The reasons for the lower agreement between the two methods need to be investigated and further studies are needed in this setting to confirm the study finding.

2012-01-01

61

Comparative study of disk diffusion and microdilution methods for evaluation of antifungal activity of natural compounds against medical yeasts Candida spp and Cryptococcus sp  

Microsoft Academic Search

Antifungal activity of natural products has been tested by adapting methods designed for synthetic drugs. In this study, two methods for the determination of antifungal activity of natural products, agar diffusion and broth microdilution, the CLSI reference methods for synthetic drugs, are compared and discussed. The microdilution method was more sensitive. The minimal inhibitory concentrations (MIC) of crude extracts, fractions

V. S. Bolzani; Maria José; Soares Mendes

62

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

Microsoft Academic Search

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

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

2006-01-01

63

Interlaboratory Evaluation of Etest Method for Testing Antifungal Susceptibilities of Pathogenic Yeasts to Five Antifungal Agents by Using Casitone Agar and Solidified RPMI 1640 Medium with 2% Glucose  

Microsoft Academic Search

An interlaboratory evaluation (two centers) of the Etest method was conducted for testing the antifungal susceptibilities of yeasts. The MICs of amphotericin B,fluconazole,flucytosine, itraconazole, and ketoconazole were determined for 83 isolates ofCandidaspp.,Cryptococcus neoformans, andTorulopsis glabrata. Two buffered (phosphate buffer) culture media were evaluated: solidified RPMI 1640 medium with 2% glucose and Casitone agar. MIC endpoints were determined after both 24

A. ESPINEL-INGROFF; M. PFALLER; M. E. ERWIN; N. JONES

1996-01-01

64

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

65

Virtual source method for diffuse optical imaging.  

PubMed

The Green's function for diffusive wave propagation can be obtained by utilizing the representation theorems of the convolution type and the correlation type. In this work, the Green's function is retrieved by making use of the Robin boundary condition and the representation theorems for diffusive media. The diffusive Green's function between two detectors for photon flux is calculated by combining detector readings due to point light sources and utilizing virtual light sources at the detector positions in optical tomography. Two dimensional simulations for a circular region with eight sources and eight detectors located on the boundary are performed using a finite element method to demonstrate the feasibility of virtual sources. The most important potential application would be the replacement of noisy measurements with synthetic measurements that are provided by the virtual sources. This becomes an important issue in small animal and human studies. In addition, the same method may also be used to reduce the imaging time. PMID:23852209

Erkol, Hakan; Unlu, Mehmet Burcin

2013-07-10

66

Multilevel adaptive methods for laminar diffusion flames  

Microsoft Academic Search

A multilevel adaptive method is applied to the numerical simulation of laminar diffusion flames. A local fine grid is embedded near the jet inlet of the simulation to provide increased resolution and accuracy. Computational results confirm that the multilevel local refinement process substantially increases local and global accuracy with little added cost.

C. Liu; Z. Liu; S. McCormick

1993-01-01

67

Effects of culture media on detection of methicillin resistance in Staphylococcus aureus and coagulase negative staphylococci by disc diffusion methods  

Microsoft Academic Search

AIMS--To test 10 culture media for their ability to detect resistance and sensitivity of staphylococci to methicillin by disc diffusion. METHODS--Fifty strains of Staphylococcus aureus and 135 strains of coagulase negative staphylococci were tested using Columbia, Diagnostic Sensitivity Test, Mueller Hinton, Sensitest and Iso-sensitest agars with and without 5% added sodium chloride. Cultures were examined after 18 and 40 hours

L M Milne; M R Crow; A G Emptage; J B Selkon

1993-01-01

68

Evaluation of Etest and Disk Diffusion Methods Compared with Broth Microdilution Antifungal Susceptibility Testing of Clinical Isolates of Candida spp. against Posaconazole  

Microsoft Academic Search

We performed Etest, disk diffusion, and broth microdilution susceptibility testing of 2,171 clinical isolates of Candida spp. against posaconazole. By using provisional breakpoints for comparison purposes only, the categorical agreement between the agar-based methods and broth microdilution results ranged from 93 to 98%, with <1% very major errors. The essential agreement (within 2 well dilutions) between the Etest and broth

Daniel J. Diekema; Shawn A. Messer; Richard J. Hollis; Linda B. Boyken; Shailesh Tendolkar; Jennifer Kroeger; Michael A. Pfaller

2007-01-01

69

Improved hydrophobic grid membrane filter method, using EF-18 agar, for detection of Salmonella in foods: collaborative study.  

PubMed

A collaborative study was carried out in 30 laboratories to validate improvements to the official final action hydrophobic grid membrane filter (HGMF) screening method for Salmonella in foods, 985.42, by comparing the performance of the improved HGMF method against that of the AOAC/BAM conventional culture method. Six products were included in the collaborative study: milk chocolate, raw deboned poultry meat, black pepper, soy flour, egg yolk powder, and nonfat dry milk. The raw deboned poultry meat was naturally contaminated with Salmonella, and the remaining 5 products were each inoculated in advance with low levels of individual Salmonella serotypes. The AOAC/BAM method produced 11 false negative results and the improved HGMF method produced 18 false negative results. The improved HGMF Salmonella method has been approved interim official first action for all foods to replace the HGMF official final action method, 985.42. PMID:2272997

Entis, P

70

Effects of culture media on detection of methicillin resistance in Staphylococcus aureus and coagulase negative staphylococci by disc diffusion methods.  

PubMed Central

AIMS--To test 10 culture media for their ability to detect resistance and sensitivity of staphylococci to methicillin by disc diffusion. METHODS--Fifty strains of Staphylococcus aureus and 135 strains of coagulase negative staphylococci were tested using Columbia, Diagnostic Sensitivity Test, Mueller Hinton, Sensitest and Iso-sensitest agars with and without 5% added sodium chloride. Cultures were examined after 18 and 40 hours of incubation. The diameter of the zone and its characteristics were recorded and these media were assessed for their ability to produce clear, readable zones of inhibition. Changes in the variables which determined resistance were investigated. Results were analysed allowing a zone diameter reduction of 8 mm and 10 mm compared with the control in addition to the standard 6 mm. RESULTS--Columbia agar with added sodium chloride supported the growth of all strains, detected the highest number of resistant strains, and was the easiest to read. Resistance was detected after 18 hours in most resistant strains, but some required 40 hours of incubation. There was poor agreement, however, on this medium (63-94%) between disc diffusion and the reference MIC method for sensitive strains. Allowing a greater reduction in zone size resulted in more agreement with sensitive strains but with consequently lowered detection of resistant strains. The other media showed some growth failures and more zones that were difficult to read. More resistance was detected when incubation was prolonged to 40 hours but this was consistently less than on Columbia agar with added salt. CONCLUSIONS--None of the media detected all of the resistant strains. Columbia agar with added salt was the most satisfactory medium in this respect, but it misidentified up to 37% of the sensitive strains as resistant. Methicillin susceptibility testing by disc diffusion testing is unreliable.

Milne, L M; Crow, M R; Emptage, A G; Selkon, J B

1993-01-01

71

Method 1600: 'Enterococci' in Water by Membrane Filtration Using membrane-Enterococcus Indoxyl-D-Glucoside Agar (mEI).  

National Technical Information Service (NTIS)

This method describes a membrane filter (MF) procedure for the detection and enumeration of the enterococci bacteria in water. Enterococci are commonly found in the feces of humans and other warm-blooded animals. Although some strains are ubiquitous and n...

2002-01-01

72

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

2008-09-23

73

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

74

Uncertainty of Thermal Diffusivity Measurements by Laser Flash Method  

Microsoft Academic Search

The laser-pulse method is a well-established nonsteady-state measurement technique for measuring the thermal diffusivity, a, of solid homogeneous isotropic opaque materials. BNM-LNE has developed its own bench based on the principle of this method in which the thermal diffusivity is identified according to the “partial time moments method.” Uncertainties of thermal diffusivity by means of this method have been calculated

B. Hay; J. R. Filtz; J. Hameury; L. Rongione

2005-01-01

75

Comparison of Neo-Sensitabs Tablet Diffusion Assay with CLSI Broth Microdilution M38-A and Disk Diffusion Methods for Testing Susceptibility of Filamentous Fungi with Amphotericin B, Caspofungin, Itraconazole, Posaconazole, and Voriconazole  

Microsoft Academic Search

We compared the Neo-Sensitabs tablet assay to both reference M38-A broth microdilution and disk diffusion methods for testing the susceptibility of 183 filamentous isolates to amphotericin B, caspofungin, itraconazole, posaconazole, and voriconazole. Neo-Sensitabs and disk assay inhibition zone diameters, in millimeters, were obtained on nonsupplemented Mueller-Hinton agar at 16 to 48 h. The reproducibility of zone diameters (i.e., the percentage

A. Espinel-Ingroff; E. Canton

2008-01-01

76

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

PubMed Central

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, ampicillin, 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 address issues encountered when clinical methods are used with environmental samples. Initial trials conducted using strains of E. coli with resistance to the selected antibiotics showed that this method was reproducible and accurate with respect to antibiotic resistance. Trials using wastewater effluent demonstrated the precision of the method, and the levels of resistance found in effluent were directly comparable to the levels of antibiotic resistance determined using the more traditional CLSI (formerly NCCLS) disk susceptibility test. All wastewater isolates growing on MI-R plates were confirmed to be resistant using the CLSI disk susceptibility test. Bacterial resistance to ampicillin (38% ± 4% overall), sulfamethoxazole, tetracycline (21% ± 3% overall), and ciprofloxacin (6% ± 1%) were found in wastewater effluent. A successful trial was also conducted with water collected from the Brisbane River, Australia. The levels of antibiotic resistance in E. coli ranged from 0 to 47% for ampicillin, from 0 to 24% for tetracycline, from 0 to 63% for sulfamethoxazole, and from 0 to 1% for ciprofloxacin, with the highest incidence of resistance associated with wastewater treatment plant discharges. This method has great potential for rapid and representative assessment of antibiotic resistance in E. coli and could allow increased sample analysis, resulting in greater confidence in spatial analysis in environmental studies.

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

2007-01-01

77

A nodal integral method for neutron diffusion in hexagonal geometry  

Microsoft Academic Search

We derive a new nodal method for the neutron diffusion equation using the Nodal Integral Method (NIM) formalism. The new approach is based on a coordinate transformation, reminiscent of that used in boundary fitted coordinates methods, to transform a general parallelogram into a rectangle. The transformed equation in this case contains a mixed derivative, in addition to the standard diffusion

Azmy

1991-01-01

78

Nodal integral method for neutron diffusion in hexagonal geometry.  

National Technical Information Service (NTIS)

We derive a new nodal method for the neutron diffusion equation using the Nodal Integral Method (NIM) formalism. The new approach is based on a coordinate transformation, reminiscent of that used in boundary fitted coordinates methods, to transform a gene...

Y. Y. Azmy

1991-01-01

79

Comparison of the Baird-Parker agar and 3M Petrifilm Staph Express Count plate methods for enumeration of Staphylococcus aureus in naturally and artificially contaminated foods.  

PubMed

The recently developed 3M Petrifilm Staph Express Count plate (PFSE) method was compared with the U.S. Food and Drug Administration Bacteriological Analytical Manual's Baird-Parker agar spread plate (B-P) method for enumeration of Staphylococcus aureus in naturally contaminated, mechanically separated poultry (MSP; n = 92) and raw milk (n = 12). In addition, mozzarella and Parmesan cheeses and hot-smoked rainbow trout and chub were surface inoculated with a three-strain mixture of S. aureus, stored at 5 degrees C, and periodically analyzed with both methods for numbers of S. aureus. For naturally contaminated raw milk and MSP samples, the PFSE method yielded counts that were not significantly different (P > 0.05) from counts obtained using the B-P method. From raw milk and MSP samples, 60% (21 of 35) and 55% (124 of 226), respectively, of confirmed (DNAse-positive) isolates from PFSE plates were identified by further testing as S. aureus. Corresponding S. aureus identification rates for isolates forming typical colonies on B-P plates were 53% (19 of 36) and 50% (125 of 248). For both methods, other staphylococci composed the vast majority of tested isolates that were not identified as S. aureus. For inoculated hot-smoked fish, S. aureus counts from the PFSE method were not significantly different from counts from the B-P method. Compared to the B-P method, significantly lower numbers of inoculated S. aureus were recovered using the PFSE method in analyses of mozzarella cheese stored 28 and 42 days at 4 degrees C. The PFSE and B-P methods were not significantly different for inoculated cheeses at all other sampling times. DNAse-positive isolates from PFSE analyses of inoculated cheeses and smoked fish were identified as S. aureus 98% (51 of 52) and 86% (36 of 42) of the time, respectively, as compared with 100% (58 of 58) and 95% (40 of 42) of the time for typical B-P isolates. Overall, the PFSE and B-P methods appeared to perform similarly in enumeration of S. aureus in animal-derived foods. PMID:14627298

Ingham, Steven C; Becker, Katie L; Fanslau, Melody A

2003-11-01

80

Comparison of colicine production and diffusion on different solid media  

Microsoft Academic Search

Using a freezing-thawing method for extracting colicine from solid media it has been shown that the choice of media for production and diffusion is important. Digest nutrient agar yielded the most colicine and peptone water agar the least. A factor in bacteriological peptone, but absent in a proteose peptone (Difco) and Neopeptone, was responsible for inhibiting production on peptone water

J. McGeachie; W. McCormick

1963-01-01

81

Enumeration of sublethally injured Escherichia coli O157:H7 ATCC 43895 and Escherichia coli strain B-41560 using selective agar overlays versus commercial methods.  

PubMed

Quality control procedures during food processing may involve direct inoculation of food samples onto appropriate selective media for subsequent enumeration. However, sublethally injured bacteria often fail to grow, enabling them to evade detection and intervention measures and ultimately threaten the health of consumers. This study compares traditional selective and nonselective agar-based overlays versus two commercial systems (Petrifilm and Easygel) for recovery of injured E. coli B-41560 and O157:H7 strains. Bacteria were propagated in tryptic soy broth (TSB), ground beef slurry, and infant milk formula to a density of 10(6) to 10(8) CFU/ml and then were stressed for 6 min either in lactic acid (pH 4.5) or heat shocked for 3 min at 60°C. Samples were pour plated in basal layers of either tryptic soy agar (TSA), sorbitol MacConkey agar (SMAC), or violet red bile agar (VRB) and were resuscitated for 4 h prior to addition of agar overlays. Other stressed bacteria were plated directly onto Petrifilm and Easygel. Results indicate that selective and nonselective agar overlays recovered significantly higher numbers (greater than 1 log) of acid- and heat-injured E. coli O157:H7 from TSB, ground beef, and infant milk formula compared with direct plating onto selective media, Petrifilm, or Easygel, while no significant differences among these media combinations were observed for stressed E. coli B-41560. Nonstressed bacteria from TSB and ground beef were also recovered at densities significantly higher in nonselective TSA-TSA and in VRB-VRB and SMAC-SMAC compared with Petrifilm and Easygel. These data underscore the need to implement food safety measures that address sublethally injured pathogens such as E. coli O157:H7 in order to avoid underestimation of true densities for target pathogens. PMID:23575132

Smith, Amanda R; Ellison, Alysha L; Robinson, Amanda L; Drake, Maryanne; McDowell, Susan A; Mitchell, James K; Gerard, Patrick D; Heckler, Rachel A; McKillip, John L

2013-04-01

82

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

83

Comparison of radon diffusion coefficients measured by transient-diffusion and steady-state laboratory methods  

SciTech Connect

A method was developed and used to determine radon diffusion coefficients in compacted soils by transient-diffusion measurements. A relative standard deviation of 12% was observed in repeated measurements with a dry soil by the transient-diffusion method, and a 40% uncertainty was determined for moistures exceeding 50% of saturation. Excellent agreement was also obtained between values of the diffusion coefficient for radon in air, as measured by the transient-diffusion method, and those in the published literature. Good agreement was also obtained with diffusion coefficients measured by a steady-state method on the same soils. The agreement was best at low moistures, averaging less than ten percent difference, but differences of up to a factor of two were observed at high moistures. The comparison of the transient-diffusion and steady-state methods at low moistures provides an excellent verification of the theoretical validity and technical accuracy of these approaches, which are based on completely independent experimental conditions, measurement methods and mathematical interpretations.

Kalwarf, D.R.; Nielson, K.K.; Rich, D.C.; Rogers, V.C.

1982-11-01

84

Variational methods in steady state diffusion problems  

SciTech Connect

Classical variational techniques are used to obtain accurate solutions to the multigroup multiregion one dimensional steady state neutron diffusion equation. Analytic solutions are constructed for benchmark verification. Functionals with cubic trial functions and conservational lagrangian constraints are exhibited and compared with nonconservational functionals with respect to neutron balance and to relative flux and current at interfaces. Excellent agreement of the conservational functionals using cubic trial functions is obtained in comparison with analytic solutions.

Lee, C.E.; Fan, W.C.P.; Bratton, R.L.

1983-01-01

85

A hermite finite element method for convection-diffusion equations  

NASA Astrophysics Data System (ADS)

This work addresses a technique to solve convection-diffusion problems based on Hermite interpolation. More specifically we extend to the case of these equations a Hermite finite element method providing flux continuity across interelement boundaries, shown to be a well-adapted tool for simulating purely diffusive phenomena [6]. The method can be viewed as a non trivial improved version of the lowest order Raviart-Thomas mixed method [4] and its extension to convection-diffusion problems proposed by Douglas and Roberts [2]. Convergence results are proven to hold, and comparative numerical results illustrate the good performance of the new method.

Ruas, V.; Trales, P.

2013-10-01

86

Molecular Diffusion Coefficients: Experimental Determination and Demonstration.  

ERIC Educational Resources Information Center

|Presented are laboratory methods which allow the demonstration and determination of the diffusion coefficients of compounds ranging in size from water to small proteins. Included are the procedures involving the use of a spectrometer, UV cell, triterated agar, and oxygen diffusion. Results including quantification are described. (CW)|

Fate, Gwendolyn; Lynn, David G.

1990-01-01

87

A radial basis functions method for fractional diffusion equations  

NASA Astrophysics Data System (ADS)

One of the ongoing issues with fractional diffusion models is the design of an efficient high-order numerical discretization. This is one of the reasons why fractional diffusion models are not yet more widely used to describe complex systems. In this paper, we derive a radial basis functions (RBF) discretization of the one-dimensional space-fractional diffusion equation. In order to remove the ill-conditioning that often impairs the convergence rate of standard RBF methods, we use the RBF-QR method [1,33]. By using this algorithm, we can analytically remove the ill-conditioning that appears when the number of nodes increases or when basis functions are made increasingly flat. The resulting RBF-QR-based method exhibits an exponential rate of convergence for infinitely smooth solutions that is comparable to the one achieved with pseudo-spectral methods. We illustrate the flexibility of the algorithm by comparing the standard RBF and RBF-QR methods for two numerical examples. Our results suggest that the global character of the RBFs makes them well-suited to fractional diffusion equations. They naturally take the global behavior of the solution into account and thus do not result in an extra computational cost when moving from a second-order to a fractional-order diffusion model. As such, they should be considered as one of the methods of choice to discretize fractional diffusion models of complex systems.

Piret, Cécile; Hanert, Emmanuel

2013-04-01

88

Optical Fiber Fabrication by the Out-Diffusion Method  

Microsoft Academic Search

Single-mode optical fibers with triangular index profile are successfully fabricated by a new fabrication technique, the ``out-diffusion method''. Evaporation and diffusion of fluorine by heating and subsequent collapsing of the fluorine-doped silica glass tubes result in formation of the core in the center of the collapsed preforms. Optical fibers with refractive index difference of 0.67% are obtained with an optical

Takeshi Kitagawa; Shuichi Shibata; Masaharu Horiguchi

1987-01-01

89

Comparison of regularization methods for human cardiac diffusion tensor MRI.  

PubMed

Diffusion tensor MRI (DT-MRI) is an imaging technique that is gaining importance in clinical applications. However, there is very little work concerning the human heart. When applying DT-MRI to in vivo human hearts, the data have to be acquired rapidly to minimize artefacts due to cardiac and respiratory motion and to improve patient comfort, often at the expense of image quality. This results in diffusion weighted (DW) images corrupted by noise, which can have a significant impact on the shape and orientation of tensors and leads to diffusion tensor (DT) datasets that are not suitable for fibre tracking. This paper compares regularization approaches that operate either on diffusion weighted images or on diffusion tensors. Experiments on synthetic data show that, for high signal-to-noise ratio (SNR), the methods operating on DW images produce the best results; they substantially reduce noise error propagation throughout the diffusion calculations. However, when the SNR is low, Rician Cholesky and Log-Euclidean DT regularization methods handle the bias introduced by Rician noise and ensure symmetry and positive definiteness of the tensors. Results based on a set of sixteen ex vivo human hearts show that the different regularization methods tend to provide equivalent results. PMID:19356971

Frindel, Carole; Robini, Marc; Croisille, Pierre; Zhu, Yue-Min

2009-01-20

90

Quality Control Guidelines for Amphotericin B, Itraconazole, Posaconazole, and Voriconazole Disk Diffusion Susceptibility Tests with Nonsupplemented Mueller-Hinton Agar (CLSI M51-A Document) for Nondermatophyte Filamentous Fungi?  

PubMed Central

Although Clinical and Laboratory Standards Institute (CLSI) disk diffusion assay standard conditions are available for susceptibility testing of filamentous fungi (molds) to antifungal agents, quality control (QC) disk diffusion zone diameter ranges have not been established. This multicenter study documented the reproducibility of tests for one isolate each of five molds (Paecilomyces variotii ATCC MYA-3630, Aspergillus fumigatus ATCC MYA-3626, A. flavus ATCC MYA-3631, A. terreus ATCC MYA-3633, and Fusarium verticillioides [moniliforme] ATCC MYA-3629) and Candida krusei ATCC 6258 by the CLSI disk diffusion method (M51-A document). The zone diameter ranges for selected QC isolates were as follows: P. variotii ATCC MYA-3630, amphotericin B (15 to 24 mm), itraconazole (20 to 31 mm), and posaconazole (33 to 43 mm); A. fumigatus ATCC MYA-3626, amphotericin B (18 to 25 mm), itraconazole (11 to 21 mm), posaconazole (28 to 35 mm), and voriconazole (25 to 33 mm); and C. krusei, amphotericin B (18 to 27 mm), itraconazole (18 to 26 mm), posaconazole (28 to 38 mm), and voriconazole (29 to 39 mm). Due to low testing reproducibility, zone diameter ranges were not proposed for the other three molds.

Espinel-Ingroff, A.; Canton, E.; Fothergill, A.; Ghannoum, M.; Johnson, E.; Jones, R. N.; Ostrosky-Zeichner, L.; Schell, W.; Gibbs, D. L.; Wang, A.; Turnidge, J.

2011-01-01

91

Diffusion through a Double-Sided Plate: Development of a Method to Study Alga-Bacterium Interactions  

PubMed Central

Bacteria and algae isolated from a wastewater oxidation pond were inoculated onto opposing surfaces of double-layer agar plates (Lutri plates) to determine the usefulness of such plates for studying microbial interactions. The altered growth characteristics of various algae depending on the species of bacteria on the adjacent medium surface indicated that there was diffusion of extracellular products through the agar, suggesting that this simple assay can be used for screening potential interactions of actively growing organisms. Images

Colwell, Frederick S.; Speidel, Harold K.

1985-01-01

92

A nodal integral method for neutron diffusion in hexagonal geometry  

SciTech Connect

We derive a new nodal method for the neutron diffusion equation using the Nodal Integral Method (NIM) formalism. The new approach is based on a coordinate transformation, reminiscent of that used in boundary fitted coordinates methods, to transform a general parallelogram into a rectangle. The transformed equation in this case contains a mixed derivative, in addition to the standard diffusion operator. We then apply the NIM formalism to the transformed equation and derive the discrete-variable balance equation and current continuity conditions. Finally, we transform the resulting expressions back into the original coordinate system, and manipulate them to obtain a single balance equation for the entire hexagon. 5 refs., 2 figs.

Azmy, Y.Y.

1991-01-01

93

Comparing in vitro activity of tigecycline by using the disk diffusion test, the manual microdilution method, and the VITEK 2 automated system.  

PubMed

Tigecycline is a broad spectrum antibiotic having activity against multiresistant isolates. In vitro susceptibility testing is difficult to perform with the use of traditional microbiological techniques. The aim of this study was to evaluate the disk diffusion test with three different Mueller-Hinton agar brands, and the Vitek 2 automated system in comparison with the standard broth microdilution method against 200 gram-negative isolates (Escherichia coil, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens and Acinetobacter baumannii). Among Enterobacteriaceae, the Becton Dickinson agar had the lowest rate of minor (32.5%) and major errors (3.8%). No very major errors were found. For A. baumanni, the rate of minor and major errors was lower. A high rate of agreement (94%) was found between the broth microdilution method and the Vitek 2 system. Our results show that there are important differences between agars used for the disk diffusion test, and that Vitek 2 is a valid tool for susceptibility testing in clinical laboratories. PMID:21180392

Leal Castro, A L; Buitrago Gutierrez, G; Ovalle, V; Cortes, J A; Alvarez, C A

94

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

95

Efficient stochastic Galerkin methods for random diffusion equations  

SciTech Connect

We discuss in this paper efficient solvers for stochastic diffusion equations in random media. We employ generalized polynomial chaos (gPC) expansion to express the solution in a convergent series and obtain a set of deterministic equations for the expansion coefficients by Galerkin projection. Although the resulting system of diffusion equations are coupled, we show that one can construct fast numerical methods to solve them in a decoupled fashion. The methods are based on separation of the diagonal terms and off-diagonal terms in the matrix of the Galerkin system. We examine properties of this matrix and show that the proposed method is unconditionally stable for unsteady problems and convergent for steady problems with a convergent rate independent of discretization parameters. Numerical examples are provided, for both steady and unsteady random diffusions, to support the analysis.

Xiu Dongbin [Department of Mathematics, Purdue University, 150 N. University Street, West Lafayette, IN 47907 (United States)], E-mail: dxiu@math.purdue.edu; Shen Jie [Department of Mathematics, Purdue University, 150 N. University Street, West Lafayette, IN 47907 (United States)], E-mail: shen@math.purdue.edu

2009-02-01

96

Unified multilayer diffusion model and application to diffusion experiment in porous media by method of chambers.  

PubMed

Diffusion coefficient is an important parameter for examining contaminant transport in the environment. Chamber methods (with or without external mixing devices) are the most popular methods for measuring effective diffusion coefficients in porous media (Deff) through air or water. The objectives of this paper were to apply simplified and unified analytical methods for both perfectly mixed and nonmixed (one- or two-) chamber systems and to examine how mixing affects the estimation of Deff. An analytical solution for a multilayer transient diffusion model was applied to the chamber methods without external mixing. By increasing the diffusion coefficient in reservoirs (D1 and D3) more than 10 times from the value for air or water (D0), the model was sufficient to approximate the well-mixed condition and, consequently, can be used to model transient diffusion in chamber systems with external mixing devices. We demonstrated that at long time Deff was related to the first eigenvalue (beta1) of a transcendental equation, which provided a quick method for determining Deff accurately from experimental data. The error caused by using the well-mixed approximation can be significant for a single-chamber system when there are no external mixing devices. This error increased rapidly with decreases in the experimental duration. A good fit for the concentration versus time curve could not be obtained forthe well-mixed solution, especially when sampling ports were near the boundary (x=0) and interface (x = l1). The proposed solutions are useful when the reservoir or chamber methods are used for measuring Deff and have wide applications in predicting contaminates transport in porous media and groundwater. PMID:19452895

Liu, Gang; Barbour, Lee; Si, Bing C

2009-04-01

97

Evaluation of Disk Diffusion and Etest Compared to Broth Microdilution for Antifungal Susceptibility Testing of Posaconazole against Clinical Isolates of Filamentous Fungi  

Microsoft Academic Search

We performed Etest, disk diffusion, and broth microdilution susceptibility testing of posaconazole against 146 clinical isolates of filamentous fungi. By using provisional breakpoints for comparison purposes only, categorical agreement between the results of the agar-based methods and those of broth microdilution were 96 to 98%, with no very major errors. These agar-based methods hold promise as simple and reliable methods

Shawn A. Messer; Daniel J. Diekema; Richard J. Hollis; Linda B. Boyken; Shailesh Tendolkar; Jennifer Kroeger; Michael A. Pfaller; Lucille A. Carver

2007-01-01

98

Stochastic operator-splitting method for reaction-diffusion systems.  

PubMed

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. PMID:23163359

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

2012-11-14

99

Solving Cauchy reaction-diffusion equation by using Picard method.  

PubMed

In this paper, Picard method is proposed to solve the Cauchy reaction-diffusion equation with fuzzy initial condition under generalized H-differentiability. The existence and uniqueness of the solution and convergence of the proposed method are proved in details. Some examples are investigated to verify convergence results and to illustrate the efficiently of the method. Also, we obtain the switching points in examples. PMID:23961376

Behzadi, Shadan Sadigh

2013-03-13

100

A heterogeneous finite element method in diffusion theory  

Microsoft Academic Search

A new Heterogeneous Finite Element Method (HFEM) is presented, which does not require prior assembly-level homogenization and which accounts for the leakage effect. The HFEM is developed in diffusion theory. The method is a Lagrange Finite Element Method, that uses basis functions that include fine mesh detail. The elementary basis functions are generated from fixed-boundary-flux fine mesh heterogeneous assembly calculations.

Eleodor Nichita; Farzad Rahnema

2003-01-01

101

Highly accurate method for the convection-diffusion equation  

Microsoft Academic Search

In this paper, we shall develop a new approach to implicit method for solving the convection-diffusion equation, which will exhibit several advantageous features: highly accurate, fast and with good results whatever the exact solution is too large i.e., the absolute error still very small. The stability region is discussed and the obtained results for a test problem is compared with

Hassan N. A. Ismail; Elsayed M. E. Elbarbary

1999-01-01

102

Range Image Segmentation by an Effective Jump-Diffusion Method  

Microsoft Academic Search

This paper presents an effective jump-diffusion method for segmenting a range image and its associated reflectance image in the Bayesian framework. The algorithm works on complex real-world scenes (indoor and outdoor), which consist of an unknown number of objects (or surfaces) of various sizes and types, such as planes, conics, smooth surfaces, and cluttered objects (like trees and bushes). Formulated

Feng Han; Zhuowen Tu; Song-Chun Zhu

2004-01-01

103

A Stabilization Method for the Hydrogen Diffusion Model in Materials  

Microsoft Academic Search

In this paper, we highlight the existence of some instability in finite element method appearing for high values of the Peclet number in the model of hydrogen diffusion in materials. A stabilization technique is used to overcome the instability problem and therefore improve this scheme. We manage to improve the scheme and decrease the instability, and we highlight the strong

Stephane Ndong-Mefane; Hiroshi Kanayama; Masao Ogino; M. F. El-Amin

2008-01-01

104

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

PubMed

The U.S. Food and Drug Administration's Bacteriological Analytical Manual recommends two enumeration methods for Bacillus cereus: (i) standard plate count method with mannitol-egg yolk-polymyxin (MYP) agar and (ii) a most-probable-number (MPN) method with tryptic soy broth (TSB) supplemented with 0.1% polymyxin sulfate. This study compared the effectiveness of MYP and MPN methods for detecting and enumerating B. cereus in raw and high-temperature, short-time pasteurized skim (0.5%), 2%, and whole (3.5%) bovine milk stored at 4°C for 96 h. Each milk sample was inoculated with B. cereus EZ-Spores and sampled at 0, 48, and 96 h after inoculation. There were no differences (P > 0.05) in B. cereus populations among sampling times for all milk types, so data were pooled to obtain overall mean values for each treatment. The overall B. cereus population mean of pooled sampling times for the MPN method (2.59 log CFU/ml) was greater (P < 0.05) than that for the MYP plate count method (1.89 log CFU/ml). B. cereus populations in the inoculated milk samples ranged from 2.36 to 3.46 and 2.66 to 3.58 log CFU/ml for inoculated milk treatments for the MYP plate count and MPN methods, respectively, which is below the level necessary for toxin production. The MPN method recovered more B. cereus, which makes it useful for validation research. However, the MYP plate count method for enumeration of B. cereus also had advantages, including its ease of use and faster time to results (2 versus 5 days for MPN). PMID:21375885

Harper, Nigel M; Getty, Kelly J K; Schmidt, Karen A; Nutsch, Abbey L; Linton, Richard H

2011-03-01

105

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

106

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

107

Thermal diffusivity of nonflat plates using the flash method.  

PubMed

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. PMID:21280851

Salazar, Agustín; Fuente, Raquel; Apiñaniz, Estibaliz; Mendioroz, Arantza

2011-01-01

108

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

109

Comparative Study of Responses to Neomycins B and C by Microbiological and Gas-Liquid Chromatographic Assay Methods  

PubMed Central

The relative responses of neomycins B and C have been determined by a microbiological agar-diffusion method, a turbidimetric method, and by a recently developed gas-liquid-chromatographic (GLC) method capable of separating the neomycin isomers. The ratios of response of neomycin C to neomycin B by the individual methods were as follows: agar-diffusion method, 1:3; turbidimetric method, 1:2.5; and GLC method, 1:1. When neomycin C is assumed to have 35% biological activity of neomycin B, the calculated drug contents of neomycin sulfate powders obtained by the GLC method correlated well with values obtained by the microbiological agar-diffusion assay method.

Tsuji, Kiyoshi; Robertson, John H.; Baas, Ruth; McInnis, D. J.

1969-01-01

110

A Numerical Method for Determining Diffusivity from Annealing Experiments  

NASA Astrophysics Data System (ADS)

Terrestrial analogs of lunar ilmenite (FeTiO3) have been implanted with solar-wind energy 4He at 4 keV and 3He at 3 keV using Plasma Source Ion Implantation (PSII). Isochronal annealing of the samples revealed thermally induced 4He evolution similar to the helium release of the Apollo 11 regoliths reported by Pepin, et. al., [1970]. These annealing experiments are analyzed with a three dimensional numerical method based on Fick's law for diffusion. An iterative method is used to calculate the diffusivity. The code uses an assumed diffusivity to calculate the amount of gas released during a temperature step. The initial depth profile of the implanted species is generated using the TRIM electronic stopping code [Ziegler, 1996]. The calculated value is compared to the measured value and a linear regression is used to calculate a new diffusivity until there is convergence within a specified tolerance level. The diffusivity as a function of temperature is then fitted to an Arrhenius equation. Analysis of results for 4 keV 4He on ilmenite shows two distinct regions of Arrehnius behavior with activation energies of 0.5 +/- 0.1 eV at emperatures below 800 deg C and 1.5 +/- 0.2 eV at temperatures from 800 deg C to 1100 deg C. Pepin, R. O., L. E. Nyquist, D. Phinney, and D. C. Black (1970) "Rare Gases in Apollo 11 Lunar Material," Proceedings of the Apollo 11 Lunar Science Conference, 2, pp. 1435-1454. Ziegler, J. P. (1996) SRIM Instruction Manual: The Stopping and Range of Ions in Matter, (Yorktown, New York: IBM - Research); based on Ziegler, J. P., J. P. Biersack and U. Littmark, The Stopping and Range of Ions in Solids, (New York: Pergamon Press, 1985).

Harris-Kuhlman, K. R.; Kulcinski, G. L.

1998-12-01

111

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

PubMed

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 extracted using different processes, were evaluated for their physical and chemical properties. The PA showed most desirable performances in terms of gel strength, gelling temperature, sulfate content and 3,6-anhydro-l-galactose content. Among the different processed agars, PA gel strength was 1913 g/cm2, the highest among the different processed agars, which increased 8.6% on the basis of the AA. Further we applied this new technique to extract agars from Gracilaria asiatica, and similar results were obtained with that of G. lemaneiformis. This indicates that the agar photobleaching extraction process is a feasible method for Gracilaria species and has a potential application. During the whole agar photobleaching extraction process the pigment content of G. lemaneiformis declined gradually and the TOC concentration in photobleaching solution increased along with the increase in the irradiation time. The mechanism of agar photobleaching could be elucidated by the photolysis theory. PMID:17765536

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

2007-08-31

112

BAM Media M20: Blood Agar  

Center for Food Safety and Applied Nutrition (CFSAN)

... Heat with agitation to dissolve agar. Autoclave 15 min at 121°C. Cool to 50°C. Add 5 ml defibrinated sheep red blood cells to 100 ml melted agar. ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

113

A diffusion accelerated solution method for the nonlinear characteristic scheme  

SciTech Connect

Recently the nonlinear characteristic scheme for spatially discretizing the discrete-ordinate equations was introduced. This scheme is accurate for both optically thin and optically thick spatial meshes and produces strictly positive angular and scalar fluxes. The nonlinear characteristic discrete-ordinate equations can be solved using the source iteration method; however, it is well known that the this method converges prohibitively slowly for optically thick problems with scattering ratios at or near unity. In this paper we describe a diffusion accelerated solution method for solving the nonlinear characteristic equations in slab geometry.

Wareing, T.A.; Walters, W.F.; Morel, J.E.

1995-02-01

114

A Numerically Stable Method for Integration of the Multicomponent Species Diffusion Equations  

Microsoft Academic Search

A diagonally implicit method is shown to be an effective method for integrating the multicomponent species conservation equations. The constitutive equation for multicomponent diffusion is recast into a form analogous to that for binary diffusion, except that the diffusion coefficient is replaced with a matrix of effective multicomponent diffusion coefficients. The resulting matrix has properties that allow the diagonal terms

William Wangard; David S. Dandy; Brian J. Miller

2001-01-01

115

Crosswind Smear and Pointwise Errors in Streamline Diffusion Finite Element Methods,  

National Technical Information Service (NTIS)

The streamline diffusion method is a finite element method for convection-dominated convection-diffusion problems which combines formal high accuracy with decent stability properties. The mathematical analysis of the method was started in Johnson and Naev...

C. Johnson A. H. Schatz L. B. Wahlbin

1987-01-01

116

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.

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

2009-01-01

117

Method 1600: Enterococci in Water by Membrane Filtration Using membrane-Enterococcus Indoxyl-Beta-D-Glucoside Agar (mEI), April 2005.  

National Technical Information Service (NTIS)

Method 1600 describes a membrane filter (MF) procedure for the detection and enumeration of the enterococci bacteria in water. This is a single-step method that is a modification of EPA Method 1106.1 (mE-EIA). Unlike the mE-EIA method, it does not require...

2005-01-01

118

The method of fundamental solutions with eigenfunctions expansion method for 3D nonhomogeneous diffusion equations  

Microsoft Academic Search

After the successful applications of the combination of the method of fundamental solutions (MFS), the method of particular solutions (MPS), and the eigenfunctions expansion method (EEM) to solve 2D homo- geneous and nonhomogeneous diffusion equations by Young et al. (Young et al., Numer Meth Part Differ Equat 22 (2006), 1173), this article intends to extend the same fundamental concepts to

D. L. Young; C. H. Chen; C. M. Fan; L. H. Shen

2009-01-01

119

Diffuse optical cortical mapping using the boundary element method  

PubMed Central

Cortical mapping, also called optical topography is a new medical imaging modality which allows the non-invasive investigation of the outer layers of the cortex. This technique is challenging and the geometry of the subject is very often over-simplified. We aim here to localize activated regions of an anatomically accurate brain. A Boundary Element Method is used for the forward model. The reconstruction of perturbations in the absorption coefficient is demonstrated in a geometrically realistic simulation and in vivo. These results show that diffuse optical imaging of the head can provide reliable activity maps when anatomical data is available.

Elisee, Josias; Gibson, Adam; Arridge, Simon

2011-01-01

120

Feasible method for routine surveillance culturing of stools from neutropenic patients.  

PubMed Central

This study was undertaken to develop an accurate, yet inexpensive, method for determining whether the bowel of a neutropenic patient is colonized with bacteria resistant to the antimicrobial agents used in empiric therapy. Selective agar media were prepared in which Mueller-Hinton agar or MacConkey agar were supplemented with one of the following antimicrobial agents: carbenicillin (16 micrograms/ml), gentamicin (4 micrograms/ml), or tobramycin (4 micrograms/ml). Moxalactam was incorporated initially at 16 micrograms/ml and subsequently at 8 micrograms/ml. Stools from neutropenic patients and bone marrow transplant recipients were inoculated on these media and on unsupplemented MacConkey agar. All bacteria that grew on the antibiotic-containing media were categorized as resistant to the supplementing drug; failure to detect an organism that did grow on the antibiotic-free MacConkey agar indicated susceptibility. These results were compared with those obtained for all isolates on all media by agar disk diffusion. There were 512 gram-negative enteric isolates from 320 stools obtained from 98 patients. The antibiotic-containing media suppressed the growth of 95% of bacteria that were identified as susceptible by agar disk diffusion. In detecting resistant organisms, the correlation between agar disk diffusion and direct stool screening with Mueller-Hinton agar ranged from 73 to 83%, and on MacConkey agar it ranged from 87 to 97%. The predictive value of a resistant result was 80 to 97% for the four antimicrobial agents when MacConkey agar was used. MacConkey agar performed better than Mueller-Hinton agar because of the greater ease of detecting different bacterial morphotypes. The cost of direct stool screening with antibiotic-supplemented MacConkey agar is approximately half the cost of routine methods of surveillance. Its cost and accuracy make the method a useful adjunct to the routine management of neutropenic patients.

Smith, J A; Sherlock, C H; Burdge, D R

1984-01-01

121

Method 1103.1: Escherichia coli (E. coli) in Water by Membrane Filtration Using membrane-Thermotolerant Escherichia coli Agar (mTEC), April 2005.  

National Technical Information Service (NTIS)

Method 1103.1 describes a membrane filter (MF) procedure for the detection and enumeration of Escherichia coli bacteria in ambient water. E. coli is a common inhabitant of the intestinal tract of warm-blooded animals, and its presence in water samples is ...

2005-01-01

122

Method 1600: Enterococci in Water by Membrane Filtration Using Membrane-Enterococcus Indoxyl-Beta-D-Glucoside Agar (mEI), July 2006.  

National Technical Information Service (NTIS)

The MF method provides a direct count of bacteria in water based on the development of colonies on the surface of the membrane filter (Reference 18.5). A water sample is filtered through the membrane which retains the bacteria. Following filtration, the m...

2006-01-01

123

BAM Media M97: Mannitol Salt Agar  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M97: Mannitol Salt Agar. January 2001. ... International Programs; News & Events; Training and Continuing Education; ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

124

Quality Control Limits for Posaconazole Disk Susceptibility Tests on Mueller-Hinton Agar with Glucose and Methylene Blue  

Microsoft Academic Search

An international collaborative study was performed in order to propose quality control limits for fluconazole disk diffusion susceptibility tests on Mueller-Hinton agar with 2% glucose and 0.5 g of methylene blue per ml. The supplements may be added before autoclaving the agar, or Mueller-Hinton agar plates may be flooded with a glucose-methylene blue solution. Replicate tests on both types of

S. Brown; M. Traczewski

2007-01-01

125

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.

2012-01-01

126

Simplified measurement of soil pH using an agar-contact technique  

Microsoft Academic Search

A method for the indirect measurement of soil-pH is described. This method allows the spatial arrangement of soil and rhizosphere to be conserved. The soil is brought into contact with a layer of agar, containing bromocresol purple. A nylon gauze is placed between soil and agar. For quantitative pH measurements, a micro-electrode is inserted into the agar after three hours

Jan W. M. Pijnenborg; T. A. Lie; A. J. B. Zehnder

1990-01-01

127

Convergence of a finite element method for the drift-diffusion semiconductor device equations: The zero diffusion case  

Microsoft Academic Search

In this paper a new explicit finite element method for numerically solving the drift-diffusion semiconductor device equations is introduced and analyzed. The method uses a mixed finite element method for the approximation of the electric field. A finite element method using discontinuous finite elements is used to approximate the concentrations, which may display strong gradients. The use of discontinuous finite

Bernardo Cockburn; Ioana Triandaf

1992-01-01

128

Monitoring Diffusion of Reptating Polymer Chains by Direct Energy Transfer Method: a Monte Carlo Simulation  

Microsoft Academic Search

A kinetic Monte Carlo method was used to simulate the diffusion of reptating polymer chains across the interface. A time-resolved fluorescence technique conjunction with direct energy transfer method was used to measure the extend of diffusion of dye labeled reptating polymer chains. The diffusion of donor and acceptor labeled polymer chains between adjacent compartments was randomly generated. The fluorescence decay

Erkan Tuzel; K. Batuhan Kisacikoglu; Onder Pekcan

2003-01-01

129

Parameter estimation method for flash thermal diffusivity with two different heat transfer coefficients.  

National Technical Information Service (NTIS)

Determining thermal diffusivity using flash diffusivity tests at high temperatures is investigated using parameter estimation. One aspect is development of a method for determining two different heat transfer coefficients, one at the heated face and one a...

J. V. Beck R. Dinwiddie

1995-01-01

130

Residual Agar Determination in Bacterial Spores by Electrospray Ionization Mass Spectrometry  

SciTech Connect

Presented here is an analytical method to detect residual agar from a bacterial spore sample as an indication of culturing on an agar plate. This method is based on the resolubilization of agar polysaccharide from a bacterial spore sample, enzymatic digestion, followed by electrospray ionization tandem mass spectrometry (ESI-MSn) analysis for detection of a specific agar fragment ion. A range of Bacillus species and strains were selected to demonstrate the effectiveness of this approach. The characteristic agar fragment ion was detected in the spores grown on agar that were washed from 1 to 5 times, irradiated or non-irradiated and not in the spores grown in broth. A sample containing approximately 108 spores is currently needed for confident detection of residual agar from culture on agar plates in the presence of bacterial spores with a limit of detection of approximately 1 ppm agar spiked into a broth-grown spore sample. The results of a proficiency test with 42 blinded samples are presented demonstrating the utility of this method with no false positives and only 3 false negatives for samples that were below the detection level of the method as documented.

Wahl, Karen L.; Colburn, Heather A.; Wunschel, David S.; Petersen, Catherine E.; Jarman, Kristin H.; Valentine, Nancy B.

2010-02-15

131

Three-dimensional paint projection weighting of diffuse and scattered illumination methods and apparatus  

US Patent & Trademark Office Database

Methods for rendering an object includes determining diffuse illumination values for object surface points, associating a 3D grid including vertices with the object, mapping object surface points to vertices, determining diffuse illumination values for vertices from the diffuse illumination values for object surface points, low pass filtering diffuse illumination values for the vertices to determine illumination compensation values for the vertices, determining illumination compensation values for the object surface points from the illumination compensation values for the vertices, and determining compensated diffuse illumination values for the object surface points from a weighted combination of the diffuse illumination values and illumination compensation values for the surface points.

2007-02-13

132

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

133

Recovery of Sublethally Injured Bacteria Using Selective Agar Overlays.  

ERIC Educational Resources Information Center

|This experiment subjects bacteria in a food sample and an environmental sample to conditions of sublethal stress in order to assess the effectiveness of the agar overlay method to recover sublethally injured cells compared to direct plating onto the appropriate selective medium. (SAH)|

McKillip, John L.

2001-01-01

134

Polymeric hydrogen diffusion barrier, high-pressure storage tank so equipped, method of fabricating a storage tank and method of preventing hydrogen diffusion  

DOEpatents

An electrochemically active hydrogen diffusion barrier which comprises an anode layer, a cathode layer, and an intermediate electrolyte layer, which is conductive to protons and substantially impermeable to hydrogen. A catalytic metal present in or adjacent to the anode layer catalyzes an electrochemical reaction that converts any hydrogen that diffuses through the electrolyte layer to protons and electrons. The protons and electrons are transported to the cathode layer and reacted to form hydrogen. The hydrogen diffusion barrier is applied to a polymeric substrate used in a storage tank to store hydrogen under high pressure. A storage tank equipped with the electrochemically active hydrogen diffusion barrier, a method of fabricating the storage tank, and a method of preventing hydrogen from diffusing out of a storage tank are also disclosed.

Lessing, Paul A. (Idaho Falls, ID)

2008-07-22

135

Growth kinetics of three species of Tetrahymena on solid agar  

SciTech Connect

A nutrient-agar method without liquid overlay has been developed for cultivation of ciliates. Three species of Tetrahymena-T. pyriformis strain W, T. rostrata strain UNI, and T. vorax strain V/sub 2/S, representing the 3 main groups of Tetrahymena species, were used; however the method should apply to other ciliates. Growth on the surface of the agar was facilitated by an optimal surface-to-volume ratio yielding a high density of ciliates and short generation times. At the highest density achieved, the cells became irregularly hexagonal and formed a monolayer tissue on the agar. Ciliates grown on agar were like those in liquid culture, typical oral ciliature, food-vacuole formation, and typical cortical patterns being retained. Advantages of this method include high cell density, easy recovery, and optimal O/sub 2/ supply. The organisms can also be cultivated on the surface of sterile cellulose-nitrate filters, facilitating in situ fixation and staining as well as transfer into different media by transfer of filters with cells, without prior centrifugation and resuspension.

Dobra, K.W.; McArdle, E.W.; Ehret, C.F.

1980-01-01

136

Efficient Method for Calculating Axial Diffusion Coefficients in Two-Dimensional Low Density Channel  

Microsoft Academic Search

An efficient calculation method of an axial diffusion coefficient which is applicable to multi-region and two-dimensional geometries has been developed. This diffusion coefficient which requires biquadratic numerical integration is quickly calculated by using a Good Lattice Point Method. Total computational time is about one-thirty hundredth that of Romberg's Method. The geometry dependency of axial diffusion coefficient is investigated. As a

Kaoru KOBAYASHI

1991-01-01

137

Stafilokoklarda Metisilin Direncinin Farkli Yöntemlerle Belirlenmesi ve Ço?ul Antibiyotik Direnci The Detection of Methicillin Resistance in Staphylococci by Different Methods and the Multiple Antibiotic Resistance  

Microsoft Academic Search

SUMMARY In the present study, we aimed to investigate the detection of methicillin resistance in clinically isolated Staphylococcus strains by different methods and to compare the specifity and sensitivity of these methods. We also tried to determine multiple antibiotic resistance in methicillin resistant Staphylococcus strains. Agar screening test (reference test), agar dilution test, disc diffusion test and automatised system (Sceptor?)

Yahya HAKGÜDENER; Serpil KAYA; M. Zahir BAKICI

138

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...

139

BAM Media M127: Potato Dextrose Agar  

Center for Food Safety and Applied Nutrition (CFSAN)

... Medium powder is available commercially but may require supplementing with extra agar to a final concentration of 20 g/liter. ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

140

Some Experiments With Agar-Grown Seedlings  

ERIC Educational Resources Information Center

Two percent agar gel is reported as a better medium for germination and growth studies. Students can be encouraged to undertake many simple experiments and make precise observations by using this medium. (PS)

Freeland, P. W.

1973-01-01

141

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

142

In Vitro Activity of Fosfomycin against a Collection of Clinical Pseudomonas aeruginosa Isolates from 16 Spanish Hospitals: Establishing the Validity of Standard Broth Microdilution as Susceptibility Testing Method.  

PubMed

The broth microdilution method for fosfomycin and Pseudomonas aeruginosa was assessed and compared with the approved agar dilution method in 206 genetically unrelated P. aeruginosa clinical isolates. Essential agreement between the two methods was 84%, and categorical agreement was 89.3%. Additionally, Etest and disk diffusion assays were performed. Results validate broth microdilution as a reliable susceptibility testing method for fosfomycin against P. aeruginosa. Conversely, unacceptable concordance was established between Etest and disk diffusion results with agar dilution results. PMID:23939889

Díez-Aguilar, María; Morosini, María-Isabel; Del Campo, Rosa; García-Castillo, María; Zamora, Javier; Cantón, Rafael

2013-08-12

143

FAST TRACK COMMUNICATION: The origin of Bohm diffusion, investigated by a comparison of different modelling methods  

NASA Astrophysics Data System (ADS)

'Bohm diffusion' causes the electrons to diffuse perpendicularly to the magnetic field lines. However, its origin is not yet completely understood: low and high frequency electric field fluctuations are both named to cause Bohm diffusion. The importance of including this process in a Monte Carlo (MC) model is demonstrated by comparing calculated ionization rates with particle-in-cell/Monte Carlo collisions (PIC/MCC) simulations. A good agreement is found with a Bohm diffusion parameter of 0.05, which corresponds well to experiments. Since the PIC/MCC method accounts for fast electric field fluctuations, we conclude that Bohm diffusion is caused by fast electric field phenomena.

Bultinck, E.; Mahieu, S.; Depla, D.; Bogaerts, A.

2010-07-01

144

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

Microsoft Academic Search

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

Sharon Dudley; Kathleen Ashe; Birgit Winther; J. Owen Hendley

2001-01-01

145

DRYING OF WATER GELS: DETERMINATION OF THE CHARACTERISTIC CURVE OF AGAR-AGAR  

Microsoft Academic Search

Agar-agar is a polysaccharide extracted as a hydrocolloid from red seaweed, whose gels are homogeneous, stable and transparent. The characterization of ternary equilibrium and mass transfer kinetics in the agar-water-air system is essential for designing operations in the extractive process as well as for ascertaining the behaviour of these gels and sols during evaporation. humectation and swelling.In this work, the

O. Iglesias; A. Garcia; M. Roques; J. L. Bueno

1993-01-01

146

Numerical Simulation of DAM Break by Adaptive Stencil Diffuse Interface Method  

NASA Astrophysics Data System (ADS)

This paper presents the application of an adaptive stencil diffuse interface method to the simulation of dam break problem. The adaptive stencil diffuse interface method is the combination of the diffuse interface method and a stencil adaptive algorithm, where the diffuse interface method is used as the solver, and the adaptive stencil refinement scheme is applied to improve the resolution around the interface so that the fine-scale interface behavior can be captured. In this paper, we use this method to simulate the dam break problem, study the dam height and leading edge position, and compare our results with the experiment data available in the literature. It is shown that the results using the adaptive stencil diffuse interface method agree very well with the experimental results.

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

147

Antimicrobial susceptibility testing of Helicobacter pylori comparison of E-test, broth microdilution, and disk diffusion for ampicillin, clarithromycin, and metronidazole  

Microsoft Academic Search

The optimal method for the determination of the minimum inhibitory concentration (MIC) of antimicrobials against Helicobacter pylori has not been established. The epsilometer agar diffusion gradient test (E-Test; AB Biodisk, Solna, Sweden) was compared with broth microdilution, the reference method, and disk diffusion for the antimicrobial susceptibility testing of 122 clinical isolates of H. pylori to ampicillin, clarithromycin, and metronidazole.

Charles Y. Hachem; Jill E. Clarridge; Rita Reddy; Robert Flamm; Dolores G. Evans; S. Ken Tanaka; David Y. Graham

1996-01-01

148

Developmental changes in the lateral diffusion of Leydig cell membranes measured by the FRAP method.  

PubMed

A simple method for isolation and fluorescence labelling of Leydig cells (L-cells) from rat testes was developed. Lateral diffusion coefficients of both lipid and protein membrane fluorescent probes were measured by the method of fluorescence recovery after photobleaching (FRAP). Age-dependent changes in diffusibility of membrane lipids and proteins were discovered. PMID:3653400

Zlatanov, I V; Foley, M; Birmingham, J; Garland, P B

1987-09-28

149

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

150

Some Extensions Of The Local Discontinuous Galerkin Method For Convection-Diffusion Equations In Multidimensions  

Microsoft Academic Search

The local discontinuous Galerkin method has been developed recently by Cockburn and Shu for convection-dominated convection-diffusion equations. In this paper, we extend the method to multidimensional equations with non-periodic boundary conditions, and with a positive semi-definite diffusion coecient which may depend on space and time. Stability and a priori error estimates are derived.

Bernardo Cockburn; Clint Dawson

1999-01-01

151

Gabor Feature Space Diffusion via the Minimal Weighted Area Method  

Microsoft Academic Search

Gabor feature space is elaborated for representation, process- ing and segmentation of textured images. As a first step of preprocessing of images represented in this space, we introduce an algorithm for Gabor feature space denoising. It is a geometric-based algorithm that applies diffusion-like equation derived from a minimal weighted area functional, introduced previously and applied in the context of stereo

Chen Sagiv; Nir A. Sochen; Yehoshua Y. Zeevi

2001-01-01

152

Application of logarithmic method to determine the thermal diffusivity of graphite and ceramics by laser flash method.  

National Technical Information Service (NTIS)

A new analytical method, logarithmic method, was applied to analyze the measurement method for thermal diffusivity by laser flash method and compared with other conventional analytical methods, t(sub 1/2) method and modified t(sub 1/2) method. Two kinds o...

H. Matsuo

1993-01-01

153

Multiparametric crystallography using the diversity of multiple scattering patterns for Bragg and diffuse waves. Method of standing diffuse waves  

NASA Astrophysics Data System (ADS)

The fundamentals of a new-generation crystallography developed by the authors, known as diffuse-dynamical multiparametric diffractometry (DDMD), are reviewed. Kovalchuk and Kohn, in their classic paper "X-ray standing waves—a new method of studying the structure of crystals" (Sov. Phys. Usp. 29 426 (1986)) provided theoretical and experimental justification for applying the method of X-ray standing waves to perfect crystals. The present paper discusses the results of extending their work to crystals with defects in which standing diffuse waves arise in addition to X-ray standing waves. The effect exerted by defects on the dynamical scattering pattern then depends on the diffraction conditions, thus creating a new phenomenon that manifests itself in a widely diverse diffuse-dynamical picture inherently impossible for kinematical scattering. By adjusting the diffraction conditions, this allows modifying the Bragg and diffuse wave fields (from running to standing), and hence changing the character of the field interaction with the crystal, with the result that experiments can provide sufficiently many various scattering patterns for the problem of unique mulliparametric diagnosis to be solved by treating the patterns collectively. Theoretical and experimental fundamentals of DDMD and the results of its practical application are discussed.

Molodkin, Vadim B.; Shpak, Anatolii P.; Kovalchuk, Mikhail V.; Machulin, Vladimir F.; Nosik, Valerii L.

2011-07-01

154

Generalized Steady-State Method for Solving 2-D Diffusion Systems.  

National Technical Information Service (NTIS)

The report describes massively parallel modelling of distributed parameter systems through the generalized steady-state method. This method is explained for 1-D and 2-D diffusion systems. It is illustrated that the arising models contain explicit parallel...

L. Dekker

1993-01-01

155

A review of diffusion tensor magnetic resonance imaging computational methods and software tools  

Microsoft Academic Search

In this work we provide an up-to-date short review of computational magnetic resonance imaging (MRI) and software tools that are widely used to process and analyze diffusion-weighted MRI data. A review of different methods used to acquire, model and analyze diffusion-weighted imaging data (DWI) is first provided with focus on diffusion tensor imaging (DTI). The major preprocessing, processing and post-processing

Khader M. Hasan; Indika S. Walimuni; Humaira Abid; Klaus R. Hahn

156

Oxygen diffusion in silicon oxide films produced by different methods  

Microsoft Academic Search

Thin films of silicon oxide were prepared on copper substrates using several techniques, such as DC sputtering, sol-gel and microwave decomposition of gases (SiH4 and O2). The sol-gel films were made using a conventional mixture of tetraethoxysilane (TEOS), water and ethanol, with various TEOS\\/water ratios. The oxygen diffusion coefficient is found from the thickness of the copper oxide layer formed

J. J Pérez-Bueno; R Ram??rez-Bon; Y. V Vorobiev; F. Espinozabeltran; J. Gonzalezhernandez

2000-01-01

157

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

Microsoft Academic Search

this paper, we study the Local Discontinuous Galerkin methods fornonlinear, time-dependent convection-diffusion systems. These methods are an extensionof the Runge-Kutta Discontinuous Galerkin methods for purely hyperbolicsystems to convection-diffusion systems and share with those methods their highparallelizability, their high-order formal accuracy, and their easy handling of complicatedgeometries, for convection dominated problems. It is proven that for scalarequations, the Local...

Bernardo Cockburn; Chi-Wang Shu

1998-01-01

158

Pigments of fly agaric (Amanita muscaria).  

PubMed

The complex pigment pattern of fly agaric (Amanita muscaria) cap skins has been studied by LC-DAD and mass spectrometry. Among the betaxanthins the corresponding derivatives of serine, threonine, ethanolamine, alanine, Dopa, phenylalanine and tryptophan are reported for the first time to contribute to the pigment pattern of fly agarics. Betalamic acid, the chromophoric precursor of betaxanthins and betacyanins, muscaflavin and seco-dopas were also detected. Furthermore, the red-purple muscapurpurin and the red muscarubrin were tentatively assigned while further six betacyanin-like components could not be structurally allocated. Stability studies indicated a high susceptibility of pigment extracts to degradation which led to rapid colour loss thus rendering a complete characterization of betacyanin-like compounds impossible at present. Taking into account these difficulties the presented results may be a starting point for a comprehensive characterization of the pigment composition of fly agarics. PMID:18274277

Stintzing, Florian; Schliemann, Willibald

159

[Angle reproducibility and surface roughness of stone casts obtained from combined agar-alginate impressions].  

PubMed

Angle reproducibility and surface roughness were compared among stone casts obtained from two agar-alginate impression methods; 1) conventional method in which an alginate mix was applied before gelation of agar, and 2) improved method in which an alginate mix was applied to gelled agar. Impressions of the rectangular parallel piped metal mold with a high accurate point angle was taken according to the above methods, and stone casts were obtained. Enlarged images of the angles of the casts were projected with an optical projector, and the defects of the point angle were traced. The area, the length and the circular-degree coefficient of the defects were determined using an image analysis system. The surface roughness of the stone casts was also measured. The stone casts prepared by the improved agar-alginate method had better angle reproducibility and the same surface roughness as that prepared by the conventional method. PMID:2135530

Ohta, T

1990-05-01

160

A local discontinuous Galerkin method for a doubly nonlinear diffusion equation arising in shallow water modeling  

Microsoft Academic Search

In this paper, we study a local discontinuous Galerkin (LDG) method to approximate solutions of a doubly nonlinear diffusion equation, known in the literature as the diffusive wave approximation of the shallow water equations (DSW). This equation arises in shallow water flow models when special assumptions are used to simplify the shallow water equations and contains as particular cases: the

Mauricio Santillana; Clint Dawson

2010-01-01

161

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

162

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

163

Migration of Chemotactic Bacteria in Soft Agar: Role of Gel Concentration  

PubMed Central

We study the migration of chemotactic wild-type Escherichia coli populations in semisolid (soft) agar in the concentration range C = 0.15–0.5% (w/v). For C?0.35%, expanding bacterial colonies display characteristic chemotactic rings. At C = 0.35%, however, bacteria migrate as broad circular bands rather than sharp rings. These are growth/diffusion waves arising because of suppression of chemotaxis by the agar and have not been previously reported experimentally to our knowledge. For C = 0.4–0.5%, expanding colonies do not span the depth of the agar and develop pronounced front instabilities. The migration front speed is weakly dependent on agar concentration at C < 0.25%, but decreases sharply above this value. We discuss these observations in terms of an extended Keller-Segel model for which we derived novel transport parameter expressions accounting for perturbations of the chemotactic response by collisions with the agar. The model makes it possible to fit the observed front speed decay in the range C = 0.15–0.35%, and its solutions qualitatively reproduce the observed transition from chemotactic to growth/diffusion bands. We discuss the implications of our results for the study of bacteria in porous media and for the design of improved bacteriological chemotaxis assays.

Croze, Ottavio A.; Ferguson, Gail P.; Cates, Michael E.; Poon, Wilson C.K.

2011-01-01

164

Green synthesis of gold nanoparticles of different sizes and shapes using agar-agar water solution and femtosecond pulse laser irradiation  

NASA Astrophysics Data System (ADS)

We report a method to create gold nanoparticles of different sizes and shapes using agar-agar water solution and irradiation with light from a xenon lamp, followed by ultrashort laser pulses. No additives, such as solvents, surfactants or reducing agents, were used in the procedure. Laser irradiation (laser ablation) was important to the reduction of the nanoparticles diameter and formation of another shapes. Distilled water was used as solvent and agar-agar (hydrophilic colloid extracted from certain seaweeds) was important for the stabilization of gold nanoparticles, avoiding their agglomeration. The formation of gold nanoparticles was confirmed with ultraviolet-visible absorption and TEM microscopy. The gold nanoparticles acquired spherical, prism, and rod shapes depending on the laser parameters. Variation of laser irradiation parameters as pulse energy, irradiation time and repetition rate was assessed. The relevant mechanisms contributing for the gold nanoparticles production are discussed.

Almeida de Matos, Ricardo; da Silva Cordeiro, Thiago; Elgul Samad, Ricardo; Dias Vieira, Nilson; Coronato Courrol, Lilia

2012-11-01

165

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

2013-05-06

166

Cation concentration variability of four distinct Mueller-Hinton agar brands influences polymyxin B susceptibility results.  

PubMed

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

Girardello, Raquel; Bispo, Paulo J M; Yamanaka, Tiago M; Gales, Ana C

2012-05-02

167

Screening for drug-resistant Candida yeasts with chromogenic agar.  

PubMed

We examined the utility of agar dilution to screen yeasts for reduced susceptibility to several newer antifungal drugs including echinocandins and azoles. We compared agar dilution susceptibility screening with the Clinical and Laboratory Standards Institute (CLSI) method for Candida isolates. We added echinocandins and azoles to CHROMagar Candida medium prior to its solidification. Assessment of resistance was based on growth characteristics, wherein decreased colony size in the presence of antifungal drugs was used as an indicator of susceptibility. Clinical Candida isolates of C. albicans, C. glabrata, C. parapsilosis, C. tropicalis, C. guilliermondii, C. lusitaniae, C. rugosa and C. dubliniensis were screened for drug susceptibility. Overall, antifungal susceptibility of the yeasts to anidulafungin, caspofungin, micafungin, posaconazole and voriconazole, determined using CHROMagar agar dilution, were shown to be 96, 80, 94, 90 and 97% as accurate, respectively, as those determined by the CLSI method, i.e., within one tube dilution of CLSI MICs. Categorical errors by percentage had a broader range. Major errors noted with anidulafungin, caspofungin and micafungin were 3, 6 and 0%, respectively, while very major errors were 15, 55 and 38%, respectively. Major errors with posaconazole and voriconazole were 12 and 0%, respectively, while very major errors were 0 and 22%, respectively, compared to CLSI standards. Most of the assessment errors were found with C. glabrata and C. parapsilosis. Agar dilution screening for drug susceptibility with the current panel of antifungal drugs is rapid, accurate and effective. However, the determination of resistance or non-susceptibility in yeasts may be more problematic, and may be species dependent. PMID:20109095

Kirkpatrick, William R; Zimmerman, Joseph D; Haikal, Fadi P; Broker, Michael J; Brockway, Erin; Fothergill, Annette W; McCarthy, Dora I; Patterson, Thomas F; Redding, Spencer W

2010-09-01

168

[Statistical methods of comparative genomic analysis based on diffusion processes].  

PubMed

Comparative genomics is a powerful tool of genome functional specificity predictions and investigation of evolution specificity. Background of a large field of bioinformatics investigations is a computation of different scores of sequences and comparing them with a threshold. Comparative genomic analysis involves scores comparing for orthological groups of genetic objects. In this paper we represent a statistical approach to comparative genomic analysis, that based on investigation of diffusion in sequence space determined by neutral evolution of sequences. Using this approach we represent several statistics for selection pressure estimation and analyze statistics for several biological problems. We formulate technology of statistics applying to obtain new biological information. This approach is represented as Java-class library. PMID:23755544

Soldatov, R A; Mironov, A A

169

Eulerian-Lagrangian Localized Adjoint Method for the Advection-Diffusion Equation.  

National Technical Information Service (NTIS)

The paper presents a space-time localized adjoint method (LAM) approximation for the advection-diffusion transport equation. The formulation is based on a space-time discretization in which specialized test functions are defined. These functions locally s...

M. A. Celia T. F. Russell I. Herera R. E. Ewing

1990-01-01

170

X-ray topography study of monocrystalline silicon wafers diffused with phosphorus by different methods  

NASA Astrophysics Data System (ADS)

To reduce the cost of the emitter diffusion process, there has been increasing interest to substitute the standard process of batch POCl3 emitter diffusion used in the silicon solar-cell manufacturing industry with in-line diffusion processes such as the spray-on and screen-printing process. For this reason, it is essential to study and compare the processes of different diffusion methods from the point of view of the crystalline quality of the final wafers. X-ray transmission topography was employed to characterize the possible precipitates and other microdefects generated in Czochralski-grown silicon (Cz Si) during the emitter diffusion process carried out by screen-printing, spray-on and the standard process, in which the emitter was provided by a liquid (POCl3) source. The results indicate that the phosphorus diffusion process influences the crystalline quality of the wafers and the efficiency of the external gettering process that takes place during phosphorus diffusion depends on the diffusion method employed.

Vallejo, B.; González-Mañas, M.; Caballero, M. A.

2013-11-01

171

A Robust and Efficient Method for Steady State Patterns in Reaction-Diffusion Systems  

PubMed Central

An inhomogeneous steady state pattern of nonlinear reaction-diffusion equations with no-flux boundary conditions is usually computed by solving the corresponding time-dependent reaction-diffusion equations using temporal schemes. Nonlinear solvers (e.g., Newton’s method) take less CPU time in direct computation for the steady state; however, their convergence is sensitive to the initial guess, often leading to divergence or convergence to spatially homogeneous solution. Systematically numerical exploration of spatial patterns of reaction-diffusion equations under different parameter regimes requires that the numerical method be efficient and robust to initial condition or initial guess, with better likelihood of convergence to an inhomogeneous pattern. Here, a new approach that combines the advantages of temporal schemes in robustness and Newton’s method in fast convergence in solving steady states of reaction-diffusion equations is proposed. In particular, an adaptive implicit Euler with inexact solver (AIIE) method is found to be much more efficient than temporal schemes and more robust in convergence than typical nonlinear solvers (e.g., Newton’s method) in finding the inhomogeneous pattern. Application of this new approach to two reaction-diffusion equations in one, two, and three spatial dimensions, along with direct comparisons to several other existing methods, demonstrates that AIIE is a more desirable method for searching inhomogeneous spatial patterns of reaction-diffusion equations in a large parameter space.

Lo, Wing-Cheong; Chen, Long; Wang, Ming; Nie, Qing

2012-01-01

172

A Robust and Efficient Method for Steady State Patterns in Reaction-Diffusion Systems.  

PubMed

An inhomogeneous steady state pattern of nonlinear reaction-diffusion equations with no-flux boundary conditions is usually computed by solving the corresponding time-dependent reaction-diffusion equations using temporal schemes. Nonlinear solvers (e.g., Newton's method) take less CPU time in direct computation for the steady state; however, their convergence is sensitive to the initial guess, often leading to divergence or convergence to spatially homogeneous solution. Systematically numerical exploration of spatial patterns of reaction-diffusion equations under different parameter regimes requires that the numerical method be efficient and robust to initial condition or initial guess, with better likelihood of convergence to an inhomogeneous pattern. Here, a new approach that combines the advantages of temporal schemes in robustness and Newton's method in fast convergence in solving steady states of reaction-diffusion equations is proposed. In particular, an adaptive implicit Euler with inexact solver (AIIE) method is found to be much more efficient than temporal schemes and more robust in convergence than typical nonlinear solvers (e.g., Newton's method) in finding the inhomogeneous pattern. Application of this new approach to two reaction-diffusion equations in one, two, and three spatial dimensions, along with direct comparisons to several other existing methods, demonstrates that AIIE is a more desirable method for searching inhomogeneous spatial patterns of reaction-diffusion equations in a large parameter space. PMID:22773849

Lo, Wing-Cheong; Chen, Long; Wang, Ming; Nie, Qing

2012-06-01

173

Detection of Agar, by Analysis of Sugar Markers, Associated with Bacillus Anthracis Spores, After Culture  

SciTech Connect

Detection of small quantities of agar associated with spores of Bacillus anthracis could provide key information regarding its source or growth characteristics. Agar, widely used in growth of bacteria on solid surfaces, consists primarily of repeating polysaccharide units of 3,6-anhydro-L-galactose (AGal) and galactose (Gal) with sulfated and O-methylated galactoses present as minor constituents. Two variants of the alditol acetate procedure were evaluated for detection of potential agar markers associated with spores. The first method employed a reductive hydrolysis step, to stabilize labile anhydrogalactose, by converting to anhydrogalactitol. The second eliminated the reductive hydrolysis step simplifying the procedure. Anhydrogalactitol, derived from agar, was detected using both derivatization methods followed by gas chromatography-mass spectrometry (GC-MS) analysis. However, challenges with artefactual background (reductive hydrolysis) or marker destruction (hydrolysis) lead to the search for alternative sugar markers. A minor agar component, 6-O-methyl galactose (6-O-M gal), was readily detected in agar-grown but not broth-grown bacteria. Detection was optimized by the use of gas chromatography-tandem mass spectrometry (GC-MS-MS). With appropriate choice of sugar marker and analytical procedure, detection of sugar markers for agar has considerable potential in microbial forensics.

Wunschel, David S.; Colburn, Heather A.; Fox, Alvin; Fox, Karen F.; Harley, William M.; Wahl, Jon H.; Wahl, Karen L.

2008-08-01

174

Note on coefficient matrices from stochastic Galerkin methods for random diffusion equations  

SciTech Connect

In a recent work by Xiu and Shen [D. Xiu, J. Shen, Efficient stochastic Galerkin methods for random diffusion equations, J. Comput. Phys. 228 (2009) 266-281], the Galerkin methods are used to solve stochastic diffusion equations in random media, where some properties for the coefficient matrix of the resulting system are provided. They also posed an open question on the properties of the coefficient matrix. In this work, we will provide some results related to the open question.

Zhou Tao, E-mail: tzhou@lsec.cc.ac.c [Institute of Computational Mathematics, The Chinese Academy of Sciences, Beijing 100190 (China); Tang Tao, E-mail: ttang@hkbu.edu.h [Department of Mathematics, Hong Kong Baptist University, Kowloon Tong (Hong Kong)

2010-11-01

175

Methods to determine slow diffusion coefficients of biomolecules. Applications to Engrailed 2, a partially disordered protein  

Microsoft Academic Search

We present new NMR methods to measure slow translational diffusion coefficients of biomolecules. Like the heteronuclear stimulated\\u000a echo experiment (XSTE), these new methods rely on the storage of information about spatial localization during the diffusion\\u000a delay as longitudinal polarization of nuclei with long T1 such as nitrogen-15. The new BEST-XSTE sequence combines features of Band-selective Excitation Short-Transient (BEST) and\\u000a XSTE

Rafal Augustyniak; Fabien Ferrage; Raphaël Paquin; Olivier Lequin; Geoffrey Bodenhausen

176

A spectral embedding method applied to the advection-diffusion equation  

SciTech Connect

In order to solve partial differential equations in complex geometries with a spectral type method, one describes an embedding approach which essentially makes use of Fourier expansions and boundary integral equations. For the advection-diffusion equation, the method is based on an efficient {open_quotes}Helmholtz solver,{close_quotes} the accuracy of which is tested by considering 1D and 2D advection-diffusion problem in a hexagonal geometry. 16 refs., 13 figs., 2 tabs.

Elghaoui, M.; Pasquetti, R. [Laboratoire J.A. Dieudonne, Nice (France)

1996-05-01

177

Convergence of a finite element method for the drift-diffusion semiconductor device equations  

Microsoft Academic Search

In this paper a new explicit finite element method for numerically solving the drift-diffusion semiconductor device equations is introduced and analyzed. The method uses a mixed finite element method for the approximation of the electric field. A finite element method using discontinuous finite elements is used to approximate the concentrations, which may display strong gradients. The use of discontinuous finite

Bernardo Cockburn; Ioana Triandaf

1992-01-01

178

High-Order Finite Difference Nodal Method for Neutron Diffusion Equation  

Microsoft Academic Search

A nodal method has been developed which accurately and rapidly solves the three-dimensional neutron diffusion equation in both Cartesian and hexagonal geometries.To reduce the number of unknowns in comparison with the interface current method in favor of short computation time and a small computer memory requirement, this method employs the finite difference method (FDM) as its global neutron balance solution

Kazuo AZEKURA; Kunitoshi KURIHARA

1991-01-01

179

Performance of ANL hexagonal-geometry nodal diffusion methods  

SciTech Connect

The DlF3D nodal scheme was the first widely used hexagonal-geometry extension of the transverse integration nodal approach. This scheme is extremely effective for its primary application (fast reactors), its accuracy typically being similar to that of finite difference (FD) solutions employing 24 triangular mesh per hexagon and a factor of {approximately} 5 finer axial mesh. For applications requiring a finer FD mesh, e.g., some thermal systems, the accuracy of DIF3D nodal is thus likely to be insufficient. This accuracy limitation stems from approximations made not only for within-node one-dimensional (1-D) (transverse-integrated) flux shapes but also for the corner-point fluxes that appear in the hexagonal-geometry relations between node-surface currents and 1-D fluxes. Thus unlike Cartesian geometry, use of the actual 1-D fluxes does not ensure exact flux-current coupling relations. This theoretical drawback of the transverse integration approach in hexagonal geometry can be avoided by employing multidimensional expansions for the within-node flux, as is done in the VARIANT variational nodal diffusion and transport capabilities recently implemented in DIF3D. Here we compare the performance of the DIM nodal and VARIANT options in the solution of fast and thermal reactor benchmark problems with homogenized assemblies and demonstrate the superior accuracy achievable with the VARIANT scheme.

Khalil, H.; Taiwo, T.A.; Yang, W.S.; Palmiotti, G. [Argonne National Lab., IL (United States)

1994-12-31

180

Quantum Diffusion Monte Carlo Method for strong field time dependent problems  

NASA Astrophysics Data System (ADS)

We formulate the Quantum Diffusion Quantum Monte Carlo (QDMC) method for the solution of the time-dependent Schr"odinger equation for atoms in strong laser fields. Unlike for the normal diffusion Monte Carlo the wave function is represented by walkers with two kinds or colors which solve two coupled and nonlinear diffusion equations. Those diffusion equations are coupled by the potentials similar to those introduced by Shay which must be added to Schr"odingers equation to obtain classical dynamics equivalent to the quantum mechanics [1]. The potentials are calculated semi-analytically similarly to smoothing methods of smooth particle electrodynamics (SPD) with Gaussian smoothing kernels. We apply this method to strong field two electron ionization of Helium. We calculate two electron double ionization rate in full six-dimensional configuration space quantum mechanically. Comparison with classical mechanics and the low dimensional grid models is also provided. 1cm [1] D. Shay, Phys. Rev A 13, 2261 (1976)

Kalinski, Matt

2006-05-01

181

Detection of siderophore production from several fungi and bacteria by a modification of chrome azurol S (CAS) agar plate assay  

Microsoft Academic Search

A well-known and widely used method for detection of siderophore production by microorganisms in solid medium is the universal chrome azurol S (CAS)-agar plate assay. However, the high toxicity of CAS-blue agar medium caused by the presence of a detergent impedes its utilization with many varieties of fungi and Gram-positive bacteria. To solve this problem, a modification of the CAS-agar

Adriane M. F. Milagres; Angela Machuca; Diovana Napoleão

1999-01-01

182

Evaluation of the direct and diffusion methods for the determination of fluoride content in table salt  

PubMed Central

Objective The aim of this study was to assess methods currently used for analyzing fluoridated salt in order to identify the most useful method for this type of analysis. Basic research design Seventy-five fluoridated salt samples were obtained. Samples were analyzed for fluoride content, with and without pretreatment, using direct and diffusion methods. Element analysis was also conducted in selected samples. Fluoride was added to ultra pure NaCl and non-fluoridated commercial salt samples and Ca and Mg were added to fluoride samples in order to assess fluoride recoveries using modifications to the methods. Results Larger amounts of fluoride were found and recovered using diffusion than direct methods (96%–100% for diffusion vs. 67%–90% for direct). Statistically significant differences were obtained between direct and diffusion methods using different ion strength adjusters. Pretreatment methods reduced the amount of recovered fluoride. Determination of fluoride content was influenced both by the presence of NaCl and other ions in the salt. Conclusion Direct and diffusion techniques for analysis of fluoridated salt are suitable methods for fluoride analysis. The choice of method should depend on the purpose of the analysis.

Martinez-Mier, E. Angeles; Soto-Rojas, Armando E.; Buckley, Christine M.; Margineda, Jorge; Zero, Domenick T.

2010-01-01

183

Development of advanced methods for analysis of experimental data in diffusion  

NASA Astrophysics Data System (ADS)

There are numerous experimental configurations and data analysis techniques for the characterization of diffusion phenomena. However, the mathematical methods for estimating diffusivities traditionally do not take into account the effects of experimental errors in the data, and often require smooth, noiseless data sets to perform the necessary analysis steps. The current methods used for data smoothing require strong assumptions which can introduce numerical "artifacts" into the data, affecting confidence in the estimated parameters. The Boltzmann-Matano method is used extensively in the determination of concentration - dependent diffusivities, D(C), in alloys. In the course of analyzing experimental data, numerical integrations and differentiations of the concentration profile are performed. These methods require smoothing of the data prior to analysis. We present here an approach to the Boltzmann-Matano method that is based on a regularization method to estimate a differentiation operation on the data, i.e., estimate the concentration gradient term, which is important in the analysis process for determining the diffusivity. This approach, therefore, has the potential to be less subjective, and in numerical simulations shows an increased accuracy in the estimated diffusion coefficients. We present a regression approach to estimate linear multicomponent diffusion coefficients that eliminates the need pre-treat or pre-condition the concentration profile. This approach fits the data to a functional form of the mathematical expression for the concentration profile, and allows us to determine the diffusivity matrix directly from the fitted parameters. Reformulation of the equation for the analytical solution is done in order to reduce the size of the problem and accelerate the convergence. The objective function for the regression can incorporate point estimations for error in the concentration, improving the statistical confidence in the estimated diffusivity matrix. Case studies are presented to demonstrate the reliability and the stability of the method. To the best of our knowledge there is no published analysis of the effects of experimental errors on the reliability of the estimates for the diffusivities. For the case of linear multicomponent diffusion, we analyze the effects of the instrument analytical spot size, positioning uncertainty, and concentration uncertainty on the resulting values of the diffusivities. These effects are studied using Monte Carlo method on simulated experimental data. Several useful scaling relationships were identified which allow more rigorous and quantitative estimates of the errors in the measured data, and are valuable for experimental design. To further analyze anomalous diffusion processes, where traditional diffusional transport equations do not hold, we explore the use of fractional calculus in analytically representing these processes is proposed. We use the fractional calculus approach for anomalous diffusion processes occurring through a finite plane sheet with one face held at a fixed concentration, the other held at zero, and the initial concentration within the sheet equal to zero. This problem is related to cases in nature where diffusion is enhanced relative to the classical process, and the order of differentiation is not necessarily a second--order differential equation. That is, differentiation is of fractional order alpha, where 1 ? alpha < 2. For alpha = 2, the presented solutions reduce to the classical second-order diffusion solution for the conditions studied. The solution obtained allows the analysis of permeation experiments. Frequently, hydrogen diffusion is analyzed using electrochemical permeation methods using the traditional, Fickian-based theory. Experimental evidence shows the latter analytical approach is not always appropiate, because reported data shows qualitative (and quantitative) deviation from its theoretical scaling predictions. Preliminary analysis of data shows better agreement with fractional diffusion analysis when compared to tr

Jaques, Alonso V.

184

Diffusion in Homicide: Exploring a General Method for Detecting Spatial Diffusion Processes  

Microsoft Academic Search

This article proposes a new method for examining dynamic changes in thespatial distribution of a phenomenon. Recently introduced exploratoryspatial data analysis (ESDA) techniques provide social scientists with anew set of tools for distinguishing between random and nonrandom spatialpatterns of events (Anselin, 1998). Existing ESDA measures, however, arestatic and do not permit comparisons of distributions of events in the samespace but

Jacqueline Cohen; George Tita

1999-01-01

185

[Precipitation of streptavidin complexes with biotinylated proteins in agar gel].  

PubMed

The effect of precipitation of complexes of streptavidin with biotinylated proteins under conditions of simple (according to Mancini) and double (according to Ouchterlony) radial diffusion in agar gel was studied. The position and form of precipitation lines depended primarily on the initial concentration of components and the degree of protein biotinylation. Free biotin, 1% SDS, and 6 M urea contained in the gel, as well as thermal denaturation of streptavidin inhibited the precipitate formation. Mannose, glucose, fucose, galactose, sucrose, and NaCl at high concentrations had no effect on biospecific precipitation. A model of interaction of streptavidin with biotinylated macromolecules is suggested, which accounts for the observed effect, and the prospects of practical application of the precipitation effect are discussed. PMID:19235518

Novakovski?, M E; Vashkevich, I I; Sviridov, O V

186

Operator splitting implicit integration factor methods for stiff reaction-diffusion-advection systems  

NASA Astrophysics Data System (ADS)

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.

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

2011-07-01

187

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.

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

2011-01-01

188

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

PubMed

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

2011-07-01

189

Pulse method for determining thermal diffusivity of poor heat conductors  

Microsoft Academic Search

Conclusions The above pulse method serves to obtain a simple design solution without the use of complicated systems. By using two specimens a good thermal contact with a required surface is obtained. This method is essential for nonmetallic materials (ceramics, glass, polymers, etc.). We used specimens in the form of plates, since this shape can be easily provided for the

B. N. Egorov; V. S. Kilesso

1969-01-01

190

Formal Methods Diffusion: Past Lessons and Future Prospects  

Microsoft Academic Search

Based on a study by Adelard (UK) commissioned by the German Bundesamt fuer Sicherheit in der Informationstechnik this paper\\u000a identifies crucial factors leading to the success or failure of the application of formal methods and provides ideas of improved\\u000a technology adoption perspectives by analysing the formal methods market.

Robin E. Bloomfield; Dan Craigen; Frank Koob; Markus Ullmann; Stefan Wittmann

2000-01-01

191

A novel method to measure diffusion coefficients in porous metal-organic frameworks.  

PubMed

We present a novel method to determine diffusion constants of small molecules within highly porous metal-organic frameworks (MOFs). The method is based on the recently proposed liquid-phase epitaxy (LPE) process to grow MOF thin films (SURMOFs) on appropriately functionalized substrates, in particular on organic surfaces exposed by thiolate-based self-assembled monolayers (SAMs). By applying the LPE-method to SAM-coated quartz crystals, the time-dependence of the mass-uptake of the MOF when exposing it to a gas is measured by a quartz-crystal microbalance (QCM). The homogenous nature of the SURMOFs together with their well-defined thickness allow to analyze the QCM-data using Fickian diffusion to yield the diffusion constant. We demonstrate the potential of this method for the case of pyridine diffusion within HKUST-1 (Cu(3)(BTC)(2)) MOF, for which the diffusion coefficient at room temperature is found to amount to 1.5 x 10(-19) m(2) s(-1). Assuming a Fickian diffusion and a hopping mechanism, we yield a binding energy of 0.78 eV of the pyridine to the Cu(2+) sites within the HKUST-1 MOF, a value in good agreement with the results of precise ab initio quantum chemistry calculations. PMID:20532258

Zybaylo, Olexandra; Shekhah, Osama; Wang, Hui; Tafipolsky, Maxim; Schmid, Rochus; Johannsmann, Diethelm; Wöll, Christof

2010-06-07

192

A method for determining optical properties of human tissues by measuring diffuse reflectance with CCD  

NASA Astrophysics Data System (ADS)

It is important to measure optical properties noninvasively, quickly and accurately in vivo for disease diagnostics and medical therapeutics. In this study, we measured the absorption coefficient and the reduced scattering coefficient of human tissues by measuring diffuse reflectance with CCD, examined the techniques involved, such as quantization of diffusion approximation theory, effective reverse fitting algorithm, and the data selection and processing method, and finally concluded about the accuracy of this method. The experimental results indicate that the error is less than or equal to 8% using the diffusion theory, under the condition that the reduced scattering coefficient is one order of magnitude greater than the absorption coefficient. The stability and precision of optical property measurements are significantly improved by using the multi-step iterative fitting method and using the ring areas to determine the diffuse reflectance center. The efficiency of reverse algorithm is greatly enhanced by selecting a one-dimensional array on the straight line crossing both the entry point and the diffusion center for fitting. The error of measured absorption coefficient and scattering coefficient of the Intralipid solution and human forearm tissues are less than 5% with our method. These results can provide important technical information for application of the diffusion theory.

Sun, P.; Yang, Run Q.; Xie, Feng H.; Ding, Jia Q.; Zhang, Fu Q.; Cao, Xian P.

2010-11-01

193

Microscopic derivation of causal diffusion equation using the projection operator method.  

PubMed

We derive a coarse-grained equation of motion of a number density by applying the projection operator method to a non-relativistic model. The derived equation is an integrodifferential equation and contains the memory effect. The equation is consistent with causality and the sum rule associated with the number conservation in the low momentum limit, in contrast to usual acausal diffusion equations given by using the Fick's law. After employing the Markov approximation, we find that the equation has the similar form to the causal diffusion equation. Our result suggests that current-current correlations are not necessarily adequate as the definition of diffusion constants. PMID:16196672

Koide, T

2005-08-29

194

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

195

Estimating distributed anatomical connectivity using fast marching methods and diffusion tensor imaging  

Microsoft Academic Search

A method is presented for determining paths of anatomical connection between regions of the brain using magnetic resonance diffusion tensor information. Level set theory, applied using fast marching methods, is used to generate three-dimensional time of arrival maps, from which connection paths between brain regions may be identified. The method is demonstrated in the normal brain and it is shown

Geoffrey J. M. Parker; Claudia A. M. Wheeler-Kingshott; Gareth J. Barker

2002-01-01

196

Nodal solution method of neutron diffusion equations using a high-order finite difference scheme  

Microsoft Academic Search

Nodal solution techniques based on an interface current method have been developed for efficient neutron diffusion calculations in Cartesian geometry. The success of these methods for analysis of light water reactors, particularly of pressurized water reactors, has prompted the development of analogous techniques for hexagonal geometry. At present, however, the methods are not as successful as in Cartesian geometry. This

Kazuo Azekura; Kunitoshi Kurihara

1989-01-01

197

Compact Finite Volume Methods for the Diffusion Equation.  

National Technical Information Service (NTIS)

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 ...

M. E. Rose

1989-01-01

198

A superfast-preconditioned iterative method for steady-state space-fractional diffusion equations  

NASA Astrophysics Data System (ADS)

Fractional diffusion equations model phenomena exhibiting anomalous diffusion that cannot be modeled accurately by the classical second-order diffusion equations. Because of the nonlocal property of fractional differential operators, the corresponding numerical methods have full coefficient matrices which require storage of O(N2) and computational cost of O(N3) for a problem of size N.We develop a superfast-preconditioned conjugate gradient squared method for the efficient solution of steady-state space-fractional diffusion equations. The method reduces the computational work from O(N2) to O(N log N) per iteration and reduces the memory requirement from O(N2) to O(N). Furthermore, the method significantly reduces the number of iterations to be mesh size independent.Preliminary numerical experiments for a one-dimensional steady-state diffusion equation with 213 nodes show that the fast method reduces the overall CPU time from 3 h and 27 min for the Gaussian elimination to 0.39 s for the fast method while retaining the accuracy of Gaussian elimination. In contrast, the regular conjugate gradient squared method diverges after 2 days of simulations and more than 20,000 iterations.

Wang, Hong; Du, Ning

2013-05-01

199

Hierarchical modeling of diffusive transport through nanochannels by coupling molecular dynamics with finite element method  

NASA Astrophysics Data System (ADS)

We present a successful hierarchical modeling approach which accounts for interface effects on diffusivity, ignored in classical continuum theories. A molecular dynamics derived diffusivity scaling scheme is incorporated into a finite element method to model transport through a nanochannel. In a 5 nm nanochannel, the approach predicts 2.2 times slower mass release than predicted by Fick’s law by comparing time spent to release 90% of mass. The scheme was validated by predicting experimental glucose diffusion through a nanofluidic membrane with a correlation coefficient of 0.999. Comparison with experiments through a nanofluidic membrane showed interface effects to be crucial. We show robustness of our discrete continuum model in addressing complex diffusion phenomena in biomedical and engineering applications by providing flexible hierarchical coupling of molecular scale effects and preserving computational finite element method speed.

Ziemys, A.; Kojic, M.; Milosevic, M.; Kojic, N.; Hussain, F.; Ferrari, M.; Grattoni, A.

2011-06-01

200

Diffusion-synthetic acceleration methods for the discrete-ordinates equations  

SciTech Connect

The diffusion-synthetic acceleration (DSA) method is an iterative procedure for obtaining numerical solutions of discrete-ordinates problems. The DSA method is operationally more complicated than the standard source-iteration (SI) method, but if encoded properly it converges much more rapidly, especially for problems with diffusion-like regions. In this article we describe the basic ideas beind the DSA method and give a (roughly chronological) review of its long development. We conclude with a discussion which covers additional topics, including some remaining open problems and the status of current efforts aimed at solving these problems.

Larsen, E.W.

1983-01-01

201

Algorithmes paralleles pour la resolution de l'equation de diffusion par des methodes elements finis et par les methodes nodales. (Parallel algorithms for solving the diffusion equation by finite elements methods and by nodal methods).  

National Technical Information Service (NTIS)

The aim of this work is to study methods for solving the diffusion equation, based on a primal or mixed-dual finite elements discretization and well suited for use on multiprocessors computers; domain decomposition methods are the subject of the main part...

F. Coulomb

1989-01-01

202

A New Multicomponent Diffusion Formulation for the Finite-Volume Method: Application to Convective Droplet Combustion  

Microsoft Academic Search

A new multicomponent formulation, appropriate for use with the finite-volume method, has been developed to describe mass diffusion velocities accurately. The new formulation is applied in a quasi-steady numerical model for n-heptane fuel droplet combustion in a forced-convection environment. Results obtained using the complete formulation are compared to the results obtained under various assumptions. Using a single binary diffusion coefficient

Daniel N. Pope; George Gogos

2005-01-01

203

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

204

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

205

Preparation and characterization of dysprosium-neodymium modified magnetic fluid coated by agar  

Microsoft Academic Search

The experiment used agar as a coating agent to manufacture dysprosium-neodymium modified water-based magnetic fluid coated by agar with the method of chemical co-precipitation when the two rare-earth element dysprosium and neodymium were precipitated with Fe3+ and Fe2+ together, which has high stability and a strong magnetic field. After the experimental research on all aspects of factors influencing the magnetic

Yuan Xing-hai; Liu Ru; Deng Yan-jun

2009-01-01

206

Low density, microcellular, dopable, agar/gelatin foams for pulsed power experiments  

SciTech Connect

Low-density, microcellular foams prepared from the natural polymers agar and gelatin have been developed for pulsed-power physics experiments. Numerous experiments were supported with foams having densities at or below 10 mg/cm{sup 3}. For some of the experiments, the agar/gelatin foam was uniformly doped with metallic elements using soluble salts. Depending on the method of preparation, cell sizes were typically below 10 microns and for one process were below 1.0 micron.

McNamara, W.F. [Orion International Technologies, Inc., Albuquerque, NM (United States); Aubert, J.H. [Sandia National Lab., Albuquerque, NM (United States)

1997-04-01

207

Operator Splitting Methods for Systems of Convection-Diffusion Equations: Nonlinear Error Mechanisms and Correction Strategies  

NASA Astrophysics Data System (ADS)

Many numerical methods for systems of convection-diffusion equations are based on an operator splitting formulation, where convective and diffusive forces are accounted for in separate substeps. We describe the nonlinear mechanism of the splitting error in such numerical methods in the one-dimensional case, a mechanism that is intimately linked to the local linearizations introduced implicitly in the (hyperbolic) convection steps by the use of an entropy condition. For convection-dominated flows, we demonstrate that operator splitting methods typically generate a numerical widening of viscous fronts, unless the splitting step is of the same magnitude as the diffusion scale. To compensate for the potentially damaging splitting error, we propose a corrected operator splitting (COS) method for general systems of convection-diffusion equations with the ability of correctly resolving the nonlinear balance between the convective and diffusive forces. In particular, COS produces viscous shocks with a correct structure also when the splitting step is large. A front tracking method for systems of conservation laws, which in turn relies heavily on a Riemann solver, constitutes an important part of our COS strategy. The proposed COS method is successfully applied to a system modeling two-phase, multicomponent flow in porous media and a triangular system modeling three-phase flow.

Karlsen, K. Hvistendahl; Lie, K.-A.; Natvig, J. R.; Nordhaug, H. F.; Dahle, H. K.

2001-11-01

208

The Diffusion of Evaluation Methods among Public Relations Practitioners.  

ERIC Educational Resources Information Center

|A study explored the relationships between public relations practitioners' organizational roles and the type of evaluation methods they used on the job. Based on factor analysis of role data obtained from an earlier study, four organizational roles were defined and ranked: communication manager, media relations specialist, communication liaison,…

Dozier, David M.

209

The Diffusion of Evaluation Methods among Public Relations Practitioners.  

ERIC Educational Resources Information Center

A study explored the relationships between public relations practitioners' organizational roles and the type of evaluation methods they used on the job. Based on factor analysis of role data obtained from an earlier study, four organizational roles were defined and ranked: communication manager, media relations specialist, communication liaison,…

Dozier, David M.

210

BAM Media M84: Liver-Veal-Egg Yolk Agar  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M84: Liver-Veal-Egg Yolk Agar. January 2001. Bacteriological Analytical Manual. M84 Liver-Veal-Egg Yolk Agar. ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

211

BAM Media M149: Triple Sugar Iron Agar (TSI)  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M149: Triple Sugar Iron Agar (TSI). January 2001. Bacteriological Analytical Manual. M149 Triple Sugar Iron Agar (TSI). ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

212

BAM Media M-198: mTEC Agar (BD # 233410)  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M-198: mTEC Agar (BD # 233410). February 2013. Bacteriological Analytical Manual. M198 mTEC Agar (BD # 233410). ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

213

BAM Media M152: Trypticase (Tryptic) Soy Agar  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M152: Trypticase (Tryptic) Soy Agar. January 2001. Bacteriological Analytical Manual. M152 Trypticase (Tryptic) Soy Agar. ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

214

BAM Media M182: Malt Extract Agar - (Yeasts and Molds) ...  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M182: Malt Extract Agar - (Yeasts and Molds) (MEAYM). January 2001. ... M182 Malt Extract Agar for Yeasts and Molds (MEAYM). ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

215

BAM Media M113: Nutrient Agar (for Bacillus cereus)  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M113: Nutrient Agar (for Bacillus cereus). January 2001. Bacteriological Analytical Manual. M113 Nutrient Agar (for Bacillus cereus). ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

216

BAM Media M139: Sorbitol-MacConkey Agar  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M139: Sorbitol-MacConkey Agar. January 2001. Bacteriological Analytical Manual. M139 Sorbitol-MacConkey Agar. ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

217

BAM Media M159: Trypticase Soy-Sheep Blood Agar  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M159: Trypticase Soy-Sheep Blood Agar. January 2001. Bacteriological Analytical Manual. M159 Trypticase Soy-Sheep Blood Agar. ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

218

BAM Media M191: Vibrio vulnificus sucrose Agar (VPSA)  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M191: Vibrio vulnificus sucrose Agar (VPSA). May 2004. Bacteriological Analytical Manual. M191 Vibrio vulnificus sucrose Agar (VPSA). ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

219

BAM Media M142: Staphylococcus Agar No. 110  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M142: Staphylococcus Agar No. 110. January 2001. Bacteriological Analytical Manual. M142 Staphylococcus Agar No. 110. ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

220

BAM Media M190: Vibrio vulnificus Agar (VVA)  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M190: Vibrio vulnificus Agar (VVA). May 2004. Bacteriological Analytical Manual. M190 Vibrio vulnificus Agar (VVA). Solution 1. ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

221

BAM Media M133: Sabouraud's Dextrose Broth and Agar  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M133: Sabouraud's Dextrose Broth and Agar. January 2001. Bacteriological ... Manual. M133 Sabouraud's Dextrose Broth and Agar. ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

222

The uses and limitations of disc diffusion in the antibiotic sensitivity testing of bacteria  

Microsoft Academic Search

Summary Disc diffusion in agar is a common method of testing the sensitivity of bacteria to antibiotics. A microorganism is judged sensitive or resistant according to the diameter of the zone of inhibition of cultural growth, which is then correlated statistically with the minimal inhibitory concentration (MIC). We have tested the closeness of this relationship by comparing 20,000 simultaneous measurements

H. Dickert; K. Machka; I. Braveny

1981-01-01

223

Depth image post-processing method by diffusion  

NASA Astrophysics Data System (ADS)

Multi-view three-dimensional television relies on view synthesis to reduce the number of views being transmitted. Arbitrary views can be synthesized by utilizing corresponding depth images with textures. The depth images obtained from stereo pairs or range cameras may contain erroneous values, which entail artifacts in a rendered view. Post-processing of the data may then be utilized to enhance the depth image with the purpose to reach a better quality of synthesized views. We propose a Partial Differential Equation (PDE)-based interpolation method for a reconstruction of the smooth areas in depth images, while preserving significant edges. We modeled the depth image by adjusting thresholds for edge detection and a uniform sparse sampling factor followed by the second order PDE interpolation. The objective results show that a depth image processed by the proposed method can achieve a better quality of synthesized views than the original depth image. Visual inspection confirmed the results.

Li, Yun; Sjöström, Mârten; Jennehag, Ulf; Olsson, Roger

2013-03-01

224

Violet red bile 2 agar for stressed coliforms.  

PubMed

Counts on a new, autoclave-sterilizable violet red bile (VRB-2) agar were compared with counts on freshly boiled VRB agar. Yields on VRB-2 agar averaged 217, 180, 130, and 112% of counts obtained on the control medium for samples of water, cottage cheese, frozen vegetables, and raw milk, respectively. The general principle used for the development of VRB-2 agar could be applied to many other kinds of selective plating media. PMID:1092265

Hartman, P A; Hartman, P S; Lanz, W W

1975-04-01

225

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

226

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

2013-06-19

227

Morphological development of Morchella conica mycelium on different agar media.  

PubMed

The present study presents the development of mycelium of Morchella conica where different concentration of sucrose added at different agar media. For this sucrose have been added as 0.25, 0.50, 0.75, 1.00 and 1.25% concentration to wheat agar potato dextrose agar malt extract agar and complete medium yeast agar The radial growth speed, morphologic specifications, radial growth radius and pigmentation of mycelium were taken as criteria, the development period of mycelium in wheat agar was completed in 4 days and mycelium were very thin. The colonization period of the mycelium was determined; 7 days in potato dextrose agar 5 days in malt extract agar and 5 days at complete medium yeast agar. The development of the mycelium; at potato dextrose agar was dense and circular; at malt extract agar and at completed medium yeast agar was rhizomorphic. Mycelium has developed very well at sucrose medium and formed creamy and light yellow pigmentation. PMID:20120503

Guler, P; Ozkaya, E G

2009-07-01

228

Comparison of Neo-Sensitabs Tablet Diffusion Assay with CLSI Broth Microdilution M38-A and Disk Diffusion Methods for Testing Susceptibility of Filamentous Fungi with Amphotericin B, Caspofungin, Itraconazole, Posaconazole, and Voriconazole?  

PubMed Central

We compared the Neo-Sensitabs tablet assay to both reference M38-A broth microdilution and disk diffusion methods for testing the susceptibility of 183 filamentous isolates to amphotericin B, caspofungin, itraconazole, posaconazole, and voriconazole. Neo-Sensitabs and disk assay inhibition zone diameters, in millimeters, were obtained on nonsupplemented Mueller-Hinton agar at 16 to 48 h. The reproducibility of zone diameters (i.e., the percentage of replicate zone diameters that were within 2 standard deviations of the means), their correlation with either MICs or minimum effective concentrations (for caspofungin only), and the categorical agreement were similar between tablet and disk assays (93 to 100% [R, >0.70] and 79 to 96%, respectively) with four of the five agents. The exceptions were the results for posaconazole tablets (R, 0.686; disk, 0.757; 84% categorical agreement for tablet and 96% for disk). These data suggest the potential value of the Neo-Sensitabs assay for testing 5-?g caspofungin and 1-?g voriconazole posaconazole tablets against all mold isolates, 8-?g itraconazole and 5-?g tablets against all mold isolates except zygomycetes, and 10-?g amphotericin B tablets against zygomycete isolates only.

Espinel-Ingroff, A.; Canton, E.

2008-01-01

229

Thin agar film for enhanced fungal growth and microscopic viewing in a new sealable fungal culture case.  

PubMed Central

This project was undertaken to find ways to enhance fungus colony maturation, to make viewing of fungal cultures easier, and to reduce disruption of the fungal structures to be observed for identification. Accordingly, a technique using a thin (0.2-mm) agar film that avoids problems inherent in traditional methods of fungal culture and identification was developed. In addition, to accommodate the 0.2-mm layer of agar film and a contiguous thicker 4-mm section of agar, a sealable fungal culture case that fits within microscope stage calipers and under the objective lenses was invented. The growth and identification of 28 organisms were evaluated in the sealable fungal culture cases and on double-pour agar plates by using potato dextrose agar in both. Compared with results obtained with the double-pour agar plates (rated as "good"), fungal growth and identification with the sealable fungal culture case were superior (rated as "excellent") (P < 0.05, chi-square test). The thin agar film limits excessive mycelial growth, while it often promotes complete sporulation or other forms of maturation of the fungal colony. More importantly, the thin agar film allows direct microscopic viewing of the developing fungal colonies. The portion of the sealable fungal culture case with the 4-mm layer of agar can be used for evaluation of colony pigment and texture. In conclusion, this new sealable fungal culture case allows direct viewing and earlier fungal species identification with greater intrinsic safety.

Hill, D R

1996-01-01

230

Agar-Gel Precipitin Technique in Anthrax Antibody Determinations1  

PubMed Central

A modification of the agar-gel precipitation inhibition technique of Thorne and Belton for detecting anthrax antibodies reduces inconsistency of visually determined end points on the same sera observed by different technicians. Determination of the minimal reacting concentrations of the anthrax antigen and antibody reagents, modifications of the visualization apparatus, methods for combining reagents, and length of incubation periods contribute to the ease of the end-point determinations and the uniformity of results. When compared with the previous technique, the modified procedure is less time-consuming while retaining satisfactory reproducibility, simplicity, specificity, and sensitivity. Images FIG. 1 FIG. 2

Ray, John G.; Kadull, Paul J.

1964-01-01

231

A rational high-order compact ADI method for unsteady convection–diffusion equations  

NASA Astrophysics Data System (ADS)

Based on a fourth-order compact difference formula for the spatial discretization, which is currently proposed for the one-dimensional (1D) steady convection–diffusion problem, and the Crank–Nicolson scheme for the time discretization, a rational high-order compact alternating direction implicit (ADI) method is developed for solving two-dimensional (2D) unsteady convection–diffusion problems. The method is unconditionally stable and second-order accurate in time and fourth-order accurate in space. The resulting scheme in each ADI computation step corresponds to a tridiagonal matrix equation which can be solved by the application of the 1D tridiagonal Thomas algorithm with a considerable saving in computing time. Three examples supporting our theoretical analysis are numerically solved. The present method not only shows higher accuracy and better phase and amplitude error properties than the standard second-order Peaceman–Rachford ADI method in Peaceman and Rachford (1959) [4], the fourth-order ADI method of Karaa and Zhang (2004) [5] and the fourth-order ADI method of Tian and Ge (2007) [23], but also proves more effective than the fourth-order Padé ADI method of You (2006) [6], in the aspect of computational cost. The method proposed for the diffusion–convection problems is easy to implement and can also be used to solve pure diffusion or pure convection problems.

Tian, Zhen F.

2011-03-01

232

Transport and diffusion of material quantities on propagating interfaces via level set methods  

Microsoft Academic Search

We develop theory and numerical algorithms to apply level set methods to problems involving the transport and diffusion of material quantities in a level set framework. Level set methods are computational techniques for tracking moving interfaces; they work by embedding the propagating interface as the zero level set of a higher dimensional function, and then approximate the solution of the

David Adalsteinsson; J. A. Sethian

2003-01-01

233

A nodal integral method for the neutron diffusion equation in cylindrical geometry  

SciTech Connect

This Summary reports recent progress in deriving and numerically implementing a nodal integral method (NIM) for solving the neutron diffusion equation in cylindrical, r-z, geometry. Comparisons of numerical solutions to two test problems with those obtained by the code EXTERMINATOR-2 indicate the superior accuracy of the nodal integral method solutions on much coarser meshes. 6 refs., 1 fig., 1 tab.

Azmy, Y.Y.

1987-01-01

234

Mimetic Finite Difference Methods for Maxwell's Equations and the Equations of Magnetic Diffusion - Abstract  

Microsoft Academic Search

We have constructed mimetic finite difference methods for both the TE and TM modes for 2-D Maxwell's curl equations and equations of magnetic diffusion with discontinuous coefficients on nonorthogonal, nonsmooth grids. The discrete operators were derived using the discrete vector and tensor analysis to satisfy discrete analogs of the main theorems of vector analysis. Because the finite difference methods satisfy

J. M. Hyman; M. Shashkov

2001-01-01

235

Evaluation of diffusion and dilution methods to determine the antibacterial activity of plant extracts  

Microsoft Academic Search

The aim of this study was to evaluate diffusion and dilution methods for determining the antibacterial activity of plant extracts and their mixtures. Several methods for measurement of the minimal inhibitory concentration (MIC) of a plant extract are available, but there is no standard procedure as there is for antibiotics. We tested different plant extracts, their mixtures and phenolic acids

Anja Klan?nik; Saša Piskernik; Barbara Jeršek; Sonja Smole Možina

2010-01-01

236

Flux expansion nodal method for solving multigroup neutron diffusion equations in hexagonal- z geometry  

Microsoft Academic Search

A flux expansion nodal method (FENM) has been developed to solve multigroup neutron diffusion equations in hexagonal-z geometry. In this method, the intranodal fluxes are expanded into a set of analytic basis functions for each group. In order to improve the nodal coupling relations, a new type of nodal boundary conditions is proposed, which requires the continuity of both the

Bangyang Xia; Zhongsheng Xie

2006-01-01

237

HEXPEDITE: A net current multigroup nodal diffusion method for hexagonal-z geometry  

Microsoft Academic Search

The feasibility of a nodal diffusion algorithm for hexagonal cores was first demonstrated by Duracz and by Lawrence. They implemented a polynomial method with partial currents for internode coupling. Following them, several authors introduced variants of the expansion technique. Wagner developed an analytical method; however, like all previous authors, he still used partial currents for internode coupling and a response

W. E. Fitzpatrick; A. M. Ougouag

1992-01-01

238

Meshfree explicit local radial basis function collocation method for diffusion problems  

Microsoft Academic Search

This paper formulates a simple explicit local version of the classical meshless radial basis function collocation (Kansa) method. The formulation copes with the diffusion equation, applicable in the solution of a broad spectrum of scientific and engineering problems. The method is structured on multiquadrics radial basis functions. Instead of global, the collocation is made locally over a set of overlapping

B. Sarler; R. Vertnik

2006-01-01

239

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

240

Continuous and Discontinuous Finite Element Methods for Convection-Diffusion Problems: A Comparison  

Microsoft Academic Search

We compare numerically the performance of a new continuous-discontinuous finite element method (CDFEM) for linear convection-diffusion equations with three well-known upwind finite element for- mulations, namely with the streamline upwind Petrov-Galerkin finite element method, the residual- free bubble method and the discontinuous Galerkin finite element method. The defining feature of the CDFEM is that it uses discontinuous approximation spaces in

Andrea Cangiani; Emmanuil H. Georgoulis; Max Jensen

241

Nodal solution method of neutron diffusion equations using a high-order finite difference scheme  

SciTech Connect

Nodal solution techniques based on an interface current method have been developed for efficient neutron diffusion calculations in Cartesian geometry. The success of these methods for analysis of light water reactors, particularly of pressurized water reactors, has prompted the development of analogous techniques for hexagonal geometry. At present, however, the methods are not as successful as in Cartesian geometry. This presentation proposes a nodal method that provides accuracy in both hexagonal and Cartesian geometries.

Azekura, Kazuo; Kurihara, Kunitoshi

1989-01-01

242

An investigation on the use of removal-diffusion theory for BNCT treatment planning: a method for determining proper removal-diffusion parameters.  

PubMed

This paper outlines a method for determining proper removal-diffusion parameters to be used in removal-diffusion theory calculations for the purpose of BNCT treatment planning. Additionally, this paper demonstrates that, given the proper choice of removal-diffusion parameters, removal-diffusion theory may provide an accurate calculation technique for determining absorbed dose distributions for the purpose of BNCT treatment planning. For a four-group, one-dimensional calculation in water, this method was used to determine values for the neutron scattering cross sections, neutron removal cross sections, neutron diffusion coefficients, and extrapolation distances. These values were then used in a one-dimensional DIF3D calculation. The results of the DIF3D calculation showed a maximum deviation of 2.5% from a MCNP calculation performed for the same geometry. PMID:11585220

Albertson, B J; Blue, T E; Niemkiewicz, J

2001-09-01

243

Tracer diffusion in an ordered alloy: application of the path probability and Monte Carlo methods  

SciTech Connect

Tracer diffusion technique has been extensively utilized to investigate diffusion phenomena and has contributed a great deal to the understanding of the phenomena. However, except for self diffusion and impurity diffusion, the meaning of tracer diffusion is not yet satisfactorily understood. Here we try to extend the understanding to concentrated alloys. Our major interest here is directed towards understanding the physical factors which control diffusion through the comparison of results obtained by the Path Probability Method (PPM) and those by the Monte Carlo simulation method (MCSM). Both the PPM and the MCSM are basically in the same category of statistical mechanical approaches applicable to random processes. The advantage of the Path Probability method in dealing with phenomena which occur in crystalline systems has been well established. However, the approximations which are inevitably introduced to make the analytical treatment tractable, although their meaning may be well-established in equilibrium statistical mechanics, sometimes introduce unwarranted consequences the origin of which is often hard to trace. On the other hand, the MCSM which can be carried out in a parallel fashion to the PPM provides, with care, numerically exact results. Thus a side-by-side comparison can give insight into the effect of approximations in the PPM. It was found that in the pair approximation of the CVM, the distribution in the completely random state is regarded as homogeneous (without fluctuations), and hence, the fluctuation in distribution is not well represented in the PPM. These examples thus show clearly how the comparison of analytical results with carefully carried out calculations by the MCSM guides the progress of theoretical treatments and gives insights into the mechanism of diffusion.

Sato, Hiroshi; Akbar, S.A.; Murch, G.E.

1984-01-01

244

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

PubMed

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

2013-03-01

245

A method for calculating the self-diffusion coefficients of molecules in multicomponent mixtures of liquids  

NASA Astrophysics Data System (ADS)

A method for calculating the self-diffusion coefficients of molecules in multicomponent liquid mixtures with arbitrary compositions was suggested. The method was based on the Stokes-Einstein equation and the assumption of the volume-additive character of the numerical multiplier in this equation. The self-diffusion coefficients of molecules of separate components in the individual state at infinite dilution in each of mixture components and dynamic viscosities of separate individual components and a mixture of a given composition are necessary and were used for calculations.

Arkhipov, V. P.

2011-03-01

246

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.

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

2008-01-01

247

Thermal Diffusivity Measurement for Thermal Spray Coating Attached to Substrate Using Laser Flash Method  

NASA Astrophysics Data System (ADS)

Ceramic-based thermal barrier coatings are used as heat and wear shields of gas turbine blades. There is a strong need to evaluate the thermal conductivity of coating for thermal design and use. The thermal conductivity of a bulk material is obtained as the product of thermal diffusivity, specific heat capacity, and density above room temperature in many cases. Thermal diffusivity and thermal conductivity are unique for a given material because they are sensitive to the structure of the material. Therefore, it is important to measure them in each sample. However it is difficult to measure the thermal diffusivity and thermal conductivity of coatings because coatings are attached to substrates. In order to evaluate the thermal diffusivity of a coating attached to the substrate, we have examined the laser flash method with the multilayer model on the basis of the response function method. We carried out laser flash measurements in layered samples composed of a CoNiCrAlY bond coating and a 8YSZ top coating by thermal spraying on a Ni-based superalloy substrate. It was found that the procedure using laser flash method with the multilayer model is useful for the thermal diffusivity evaluation of a coating attached to a substrate.

Akoshima, Megumi; Tanaka, Takashi; Endo, Satoshi; Baba, Tetsuya; Harada, Yoshio; Kojima, Yoshitaka; Kawasaki, Akira; Ono, Fumio

2011-11-01

248

Study of the diffusion of points defects in crystalline silicon using the kinetic ART method  

NASA Astrophysics Data System (ADS)

Because of the long-time scale involved, the activated diffusion of point defects is often studied in standard molecular dynamics at high temperatures only, making it more difficult to characterize complex diffusion mechanisms. Here, we turn to the study of point defect diffusion in crystalline silicon using kinetic ART (kART)[1-2], an off-lattice kinetic Monte Carlo method with on-the-fly catalog building based on the activation-relaxation technique (ART nouveau). By generating catalogs of diffusion mechanisms and fully incorporating elastic and off-lattice effects, kART is a unique tool for characterizing this problem. More precisely, using kART with the standard Stillinger-Weber potential we consider the evolution of crystalline cells with 1 to 4 vacancies and 1 to 4 interstitials at various temperatures and to provide a detailed picture of both the atomistic diffusion mechanisms and overall kinetics in addition to identifying special configurations such as a 2-interstitial super-diffuser. [4pt] [1] F. El-Mellouhi, N. Mousseau and L.J. Lewis, Phys. Rev. B. 78, 153202 (2008)[0pt] [2] L. K. Béland, P. Brommer, F. El-Mellouhi, J.-F. Joly and N. Mousseau, Phys. Rev. E 84, 046704 (2011).

Trochet, Mickael; Brommer, Peter; Beland, Laurent-Karim; Joly, Jean-Francois; Mousseau, Normand

2013-03-01

249

Extraction and Quantification of Solutes in Solidified Agar Culture Media  

PubMed Central

A method is described for determining the concentration of certain solutes in solidified culture media. The method is based upon the finding that under specified conditions the concentration of solute in an agar gel (Cg) is related to the concentration of solute in a centrifugally extracted gel supernatant (Cs) by the ratio, Cg/Cs, which is characteristic for each solute. The method avoids direct assays of the gels and instead involves assaying the supernatants from inoculated and uninoculated (control) gels with conventional liquid assay techniques and then calculating solute concentrations in the inoculated gels by use of the Cg/Cs ratios determined from the controls. Uninoculated agar gels containing known concentrations of various solutes and similar gels inoculated with Neurospora crassa or Escherichia coli were centrifuged at various times, and the supernatants were assayed for solute concentrations. The solute concentrations in the supernatants from the inoculated gels multiplied by the Cg/Cs ratios for those solutes determined at the same times for the uninoculated controls gave calculated solute concentrations in the inoculated gels. The differences between these calculated solute concentrations and those initially present in the inoculated gels indicated the amounts of solutes utilized from the gels by the microorganisms at various incubation times.

Buynitzky, Stephen J.; Howe, H. Branch; Shellhorse, Yovonne

1979-01-01

250

Control of the pattern of perithecium development in Sordaria fimicola on agar medium.  

PubMed

In a Sordaria fimicola (Rob.) Ces. and de Not. colony grown on agar medium in a petri plate, perithecia developed in a narrow band around the plate edge after the colony margin reached the edge. Physical wounding of the colony carried out shortly before or during the time perithecia were developing around the plate edge stimulated perithecium development in the wound area. Diffusion barriers were created by cutting small trenches in the agar parallel to the plate edge. The trenches were made at several different positions between the plate center and edge using cultures of several different ages, and the resultant distribution of perithecia along the trench edges suggested that the colony center and periphery produce diffusible inhibitors of perithecium development. These inhibitors may be responsible, in part, for the observed pattern of perithecium development in the colony. PMID:1158169

Pollock, R T

1975-06-01

251

Quantitative examination of a novel clustering method using magnetic resonance diffusion tensor tractography.  

PubMed

MR diffusion tensor imaging (DTI) can measure and visualize organization of white matter fibre tracts in vivo. DTI is a relatively new imaging technique, and new tools developed for quantifying fibre tracts require evaluation. The purpose of this study was to compare the reliability of a novel clustering approach with a multiple region of interest (MROI) approach in both healthy and disease (schizophrenia) populations. DTI images were acquired in 20 participants (n=10 patients with schizophrenia: 56+/-15 years; n=10 controls: 51+/-20 years) (1.5 T GE system) with diffusion gradients applied in 23 non-collinear directions, repeated three times. Whole brain seeding and creation of fibre tracts were then performed. Interrater reliability of the clustering approach, and the MROI approach, were each evaluated and the methods compared. There was high spatial (voxel-based) agreement within and between the clustering and MROI methods. Fractional anisotropy, trace, and radial and axial diffusivity values showed high intraclass correlation (p<0.001 for all tracts) for each approach. Differences in scalar indices of diffusion between the clustering and MROI approach were minimal. The excellent interrater reliability of the clustering method and high agreement with the MROI method, quantitatively and spatially, indicates that the clustering method can be used with confidence. The clustering method avoids biases of ROI drawing and placement, and, not limited by a priori predictions, may be a more robust and efficient way to identify and measure white matter tracts of interest. PMID:19159690

Voineskos, Aristotle N; O'Donnell, Lauren J; Lobaugh, Nancy J; Markant, Doug; Ameis, Stephanie H; Niethammer, Marc; Mulsant, Benoit H; Pollock, Bruce G; Kennedy, James L; Westin, Carl Fredrik; Shenton, Martha E

2008-12-29

252

Quantitative Examination of a Novel Clustering Method using Magnetic Resonance Diffusion Tensor Tractography  

PubMed Central

MR diffusion tensor imaging (DTI) can measure and visualize organization of white matter fibre tracts in vivo. DTI is a relatively new imaging technique, and new tools developed for quantifying fibre tracts require evaluation. The purpose of this study was to compare the reliability of a novel clustering approach with a multiple region of interest (MROI) approach in both healthy and disease (schizophrenia) populations. DTI images were acquired in 20 participants (n=10 patients with schizophrenia: 56 ± 15 years; n=10 controls: 51 ± 20 years) (1.5 Tesla GE system) with diffusion gradients applied in 23 non-collinear directions, repeated three times. Whole brain seeding and creation of fibre tracts were then performed. Interrater reliability of the clustering approach, and the MROI approach, were each evaluated and the methods compared. There was high spatial (voxel-based) agreement within and between the clustering and MROI methods. Fractional anisotropy, trace, and radial and axial diffusivity values showed high intraclass correlation (p<0.001 for all tracts) for each approach. Differences in scalar indices of diffusion between the clustering and MROI approach were minimal. The excellent interrater reliability of the clustering method and high agreement with the MROI method, quantitatively and spatially, indicates that the clustering method can be used with confidence. The clustering method avoids biases of ROI drawing and placement, and, not limited by a priori predictions, may be a more robust and efficient way to identify and measure white matter tracts of interest.

Voineskos, Aristotle N; O'Donnell, Lauren J; Lobaugh, Nancy J; Markant, Doug; Ameis, Stephanie H; Niethammer, Marc; Mulsant, Benoit H; Pollock, Bruce G; Kennedy, James L; Westin, Carl Fredrik; Shenton, Martha E

2009-01-01

253

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

Microsoft Academic Search

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

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

254

Carrier-diffusion measurements in silicon with a Fourier-transient-grating method  

NASA Astrophysics Data System (ADS)

Carrier-diffusion measurements in silicon using a newly developed Fourier-transient-grating technique is presented. The method uses a laser light pulse projected through a semitransparent grid pattern to excite a sinusoidal excess carrier grating within the sample. The interdiffusion of carriers is monitored by free-carrier absorption of a focused infrared probe beam. The grating is scanned across the probe beam and the spatial Fourier transform is calculated at each sampling time following the excitation pulse. The resulting Fourier spectrum shows a peak for a frequency corresponding to the grating period and the decay of the amplitude of this spatial-frequency component represents a characteristic grating erasure time, which is related to the carrier diffusivity. This Fourier-transient-grating method allows sensitive measurements of the carrier diffusivity over a broad range of injection levels, both in the minority carrier regime as well as for high-injection conditions including the transition between the two regimes. Here, measurement data are presented for silicon samples of various doping concentration and types for excess carrier injections in the range ~1012-1017 cm-3. At low densities of injected carriers, our measurement data are in agreement with generally accepted low-injection lattice-scattering mobility values showing the transition to the high-injection range according to ambipolar theory. However, at excess carrier concentrations exceeding 1015 cm-3, the diffusion coefficient is clearly reduced with respect to the ambipolar diffusivity (using constant electron and hole diffusivities) due to carrier-carrier scattering effects. This reduction is stronger above an injected carrier density of 1016 cm-3 than that predicted by many-body quantum theory [J. F. Young and H. M. van Driel, Phys. Rev. B 26, 2147 (1982)]. The diffusivity data, converted to mobilities using Einstein's relation, have also been compared to recent semiempiric drift-mobility models used for semiconductor device simulation.

Linnros, Jan; Grivickas, Vytautas

1994-12-01

255

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

256

Lattice Boltzmann method for multi-component, non-continuum mass diffusion  

NASA Astrophysics Data System (ADS)

Recently, there has been a great deal of interest in extending the lattice Boltzmann method (LBM) to model transport phenomena in the non-continuum regime. Most of these studies have focused on single-component flows through simple geometries. This work examines an ad hoc extension of a recently developed LBM model for multi-component mass diffusion (Joshi et al 2007 J. Phys. D: Appl. Phys. 40 2961) to model mass diffusion in the non-continuum regime. In order to validate the method, LBM results for ternary diffusion in a two-dimensional channel are compared with predictions of the dusty gas model (DGM) over a range of Knudsen numbers. A calibration factor based on the DGM is used in the LBM to correlate Knudsen diffusivity to pore size. Results indicate that the LBM can be a useful tool for predicting non-continuum mass diffusion (Kn > 0.001), but additional research is needed to extend the range of applicability of the algorithm for a larger parameter space. Guidelines are given on using the methodology described in this work to model non-continuum mass transport in more complex geometries where the DGM is not easily applicable. In addition, the non-continuum LBM methodology can be extended to three-dimensions. An envisioned application of this technique is to model non-continuum mass transport in porous solid oxide fuel cell electrodes.

Joshi, Abhijit S.; Peracchio, Aldo A.; Grew, Kyle N.; Chiu, Wilson K. S.

2007-12-01

257

Numerical Calculation Method for Three-Dimensional Flows in the Dump Diffuser of Gas Turbine Combustor.  

National Technical Information Service (NTIS)

A finite volume method for the solution of three-dimensional incompressible steady Navier-Stokes equations based on a general curvilinear coordinate system was employed to study characteristics of turbulent flow in the dump diffuser of a gas turbine combu...

Y. Ando M. Kawai Y. Sato H. Toh

1988-01-01

258

Preparation of roxithromycin-polymeric microspheres by the emulsion solvent diffusion method for taste masking  

Microsoft Academic Search

Microspheres of roxithromycin with Eudragit S100 and silica were prepared by the emulsion solvent diffusion method to mask the bitter taste of the antibiotic. The effect of different polymers and drug-polymer ratios on the taste masking and the characteristics of the microspheres were investigated. It was found that Eudragit S100 was the best for masking the unpleasant taste of roxithromycin

Yan Gao; Fu-de Cui; Ying Guan; Lei Yang; Yong-sheng Wang; Li-na Zhang

2006-01-01

259

Service Life of Fence Posts Treated by Double-Diffusion Methods.  

National Technical Information Service (NTIS)

Service-life tests indicate that Englemann spruce, lodgepole pine, and Rocky Mountain Douglas-fir fence posts treated by double-diffusion methods performed excellently after field exposure of 30 years with no failures. The test site was located in the sem...

D. C. Markstrom L. R. Gjovik

1999-01-01

260

Antimicrobial Susceptibility Testing of Acinetobacter spp. by NCCLS Broth Microdilution and Disk Diffusion Methods  

Microsoft Academic Search

Although both broth microdilution (BMD) and disk diffusion (DD) are listed by NCCLS as acceptable meth- ods for testing Acinetobacter spp. for antimicrobial susceptibility, few studies have compared the results gen- erated by the two methods. We tested 196 isolates of Acinetobacter spp. from nine U.S. hospitals and from the Centers for Disease Control culture collection by using BMD and

Jana M. Swenson; George E. Killgore; Fred C. Tenover

2004-01-01

261

DEVELOPMENT OF LOW-DIFFUSION FLUX-SPLITTING METHODS FOR DENSE GAS-SOLID FLOWS  

EPA Science Inventory

The development of a class of low-diffusion upwinding methods for computing dense gas-solid flows is presented in this work. An artificial compressibility/low-Mach preconditioning strategy is developed for a hyperbolic two-phase flow equation system consisting of separate solids ...

262

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

263

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 obtained in the prior art.

Rutherford, W.M.

1985-12-04

264

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

Microsoft Academic Search

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

J. Kramer; R. Jecl; L. Skerget

2008-01-01

265

Nonequilibrium statistical operator method: Generalized transport equations of diffusion-reaction processes  

Microsoft Academic Search

Generalized transport equations for description of diffusion-reaction processes in chemically active mixtures are obtained. The nonequilibrium statistical operator method by Zubarev is used and both strong and weak nonequilibrium processes are analyzed. In the approximation of the second order in fluctuations we get generalized equations of chemical kinetics for bimolecular reactions with generalized rate constants. In the case of spatial

P. P. Kostrobii; M. V. Tokarchuk; Y. A. Humenyuk

2003-01-01

266

Calculation of effective diffusion coefficient in even approximations of the surface pseudo source method  

SciTech Connect

The preference of even approximations of the surface pseudo source method for calculation of the diffusion coefficient is substantiated. The homogenization limit for the G{sub 0} approximation in the case of the cell size tending to zero is analytically proved.

Kovalishin, A. A., E-mail: kaa@adis.vver.kiae.ru; Laletin, N. I. [Russian Research Centre Kurchatov Institute (Russian Federation)

2011-12-15

267

Combined relaxation and displacement experiment: a fast method to acquire T2, diffusion and velocity maps.  

PubMed

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 separate T2 and displacement images with microscopic resolution can be obtained within minutes. The capability for 3D flow imaging is demonstrated. The sequence is then used to investigate forced detachment of a biofilm in a tube. PMID:15183357

Manz, Bertram

2004-07-01

268

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

PubMed

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. PMID:16173154

Chau, Jessica Furrer; Or, Dani; Sukop, Michael C

2005-08-01

269

A finite volume method for trace element diffusion and partitioning during crystal growth  

NASA Astrophysics Data System (ADS)

A finite volume method on a uniform grid is presented to compute the polythermal diffusion and partitioning of a trace element during the growth of a porphyroblast crystal in a uniform matrix and in linear, cylindrical and spherical geometry. The motion of the crystal-matrix interface and the thermal evolution are prescribed functions of time. The motion of the interface is discretized and it advances from one cell boundary to next as the prescribed interface position passes the cell center. The appropriate conditions for the flux across the crystal-matrix interface are derived from discrete mass conservation. Numerical results are benchmarked against steady and transient analytic solutions for isothermal diffusion with partitioning and growth. Two applications illustrate the ability of the model to reproduce observed rare-earth element patterns in garnets (Skora et al., 2006) and water concentration profiles around spherulites in obsidian (Watkins et al., 2009). Simulations with diffusion inside the growing crystal show complex concentration evolutions for trace elements with high diffusion coefficients, such as argon or hydrogen, but demonstrate that rare-earth element concentrations in typical metamorphic garnets are not affected by intracrystalline diffusion.

Hesse, Marc A.

2012-09-01

270

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

271

METHOD FOR REMOVAL OF LIGHT ISOTOPE PRODUCT FROM LIQUID THERMAL DIFFUSION UNITS  

DOEpatents

A method and apparatus are described for removing the lighter isotope of a gaseous-liquid product from a number of diffusion columns of a liquid thermal diffusion system in two stages by the use of freeze valves. The subject liquid flows from the diffusion columns into a heated sloping capsule where the liquid is vaporized by the action of steam in a heated jacket surrounding the capsule. When the capsule is filled the gas flows into a collector. Flow between the various stages is controlled by freeze valves which are opened and closed by the passage of gas and cool water respectively through coils surrounding portions of the pipes through which the process liquid is passed. The use of the dual stage remover-collector and the freeze valves is an improvement on the thermal diffusion separation process whereby the fraction containing the lighter isotope many be removed from the tops of the diffusion columns without intercolumn flow, or prior stage flow while the contents of the capsule is removed to the final receiver.

Hoffman, J.D.; Ballou, J.K.

1957-11-19

272

A new method for obtaining velocity and diffusivity from time-dependent distributions of a tracer via the maximum likelihood estimator for the advection-diffusion equation  

SciTech Connect

An inverse problem for the advection-diffusion equation is considered, and a method of maximum likelihood (ML) estimation is developed to derive velocity and diffusivity from time-dependent distributions of a tracer. Piterbarg and Rozovskii showed theoretically that the ML estimator for diffusivity is consistent ever in an asymptotic case of infinite number of observational spatial modes. In the present work, the ML estimator is studied based on numerical experiments with a tracer in a two-dimensional flow under the condition of a limited number of observations in space. The numerical experiments involve the direct and the inverse problems. For the former, the time evolution of a tracer is simulated using the Galerkin-type method-as a response of the conservation equation to stochastic forcing. In the inverse problem, the advection-diffusion equation is fitted to the simulated data employing the ML estimator. It is shown that the ML method allows us a method to estimate diffusion coefficient components D{sub x} and D{sub y} based on a short time series of tracer observations. The estimate of the diffusion anistropy, D{sub x}/D{sub y}, is shown to be even more robust than the estimate of the diffusivity itself. A comparison with an estimation technique based on the finite-difference approximation demonstrates advantages of the ML estimator. Finally, the ML method is employed for analysis of heat balance in the upper layer of the North Pacific in the winter. This application focuses on the heat diffusion anisotropy at the ocean mesoscale. 29 refs., 14 figs.

Ostrovskii, A.G. [Kyushu Univ., Kasuga (Japan); Piterbarg, L.I. [Univ. of Southern California, Los Angeles, CA (United States)

1997-05-15

273

A parameter-uniform Schwarz method for a coupled system of reaction-diffusion equations  

NASA Astrophysics Data System (ADS)

We consider an arbitrarily sized coupled system of one-dimensional reaction-diffusion problems that are singularly perturbed in nature. We describe an algorithm that uses a discrete Schwarz method on three overlapping subdomains, extending the method in [H. MacMullen, J.J.H. Miller, E. O'Riordan, G.I. Shishkin, A second-order parameter-uniform overlapping Schwarz method for reaction-diffusion problems with boundary layers, J. Comput. Appl. Math. 130 (2001) 231-244] to a coupled system. On each subdomain we use a standard finite difference operator on a uniform mesh. We prove that when appropriate subdomains are used the method produces [epsilon]-uniform results. Furthermore we improve upon the analysis of the above-mentioned reference to show that, for small [epsilon], just one iteration is required to achieve the expected accuracy.

Stephens, Meghan; Madden, Niall

2009-08-01

274

Self-diffusion measurements by a constant-relaxation method in strongly inhomogeneous magnetic fields  

NASA Astrophysics Data System (ADS)

The simple pulse sequence ?x-?1-2?y-?1+?2-2?y-?2-Hahnecho used to measure the self-diffusion coefficient /D under constant-relaxation condition, i.e., for ?1+?2=const. was investigated in the presence of strongly inhomogeneous static as well as radiofrequency magnetic fields. The encoding of the Hahn-echo amplitude by the pulse flip angle and diffusion was evaluated by taking into account the spatial distribution of the off-resonance field, the strength and orientation of the local field gradients, and the pulse flip angles by a computer simulation program. As input files, this program uses maps of static and radiofrequency fields, and the /D coefficient can be evaluated from the time dependence of the Hahn-echo amplitude. The method was applied to a mobile one-sided NMR sensor, NMR-MOUSE with a bar magnet by measuring /D for a series of liquids with different viscosities. The method was shown to be particularly useful for measuring /D of solvents in elastomers without the need for measurements of the transverse relaxation rates. The self-diffusion coefficient of toluene in a series of crosslinked natural rubber samples was measured and correlated with the crosslink density. Finally, the method was applied to measure the diffusion anisotropy of free water in bovine Achilles tendon.

Klein, M.; Fechete, R.; Demco, D. E.; Blümich, B.

2003-10-01

275

Elaboration of a Nodal Method to Solve the Steady State Multigroup Diffusion Equation. Study and Use of the Multigroup Diffusion Code DAHRA.  

National Technical Information Service (NTIS)

The subject is divided in two parts: In the first part a nodal method has been worked out to solve the steady state multigroup diffusion equation. This method belongs to the same set of nodal methods currently used to calculate the exact fission powers an...

A. Halilou A. Lounici

1981-01-01

276

Polynomial nodal method for solving neutron diffusion equations in hexagonal-z geometry  

Microsoft Academic Search

A polynomial nodal method is developed to solve few-group neutron diffusion equations in hexagonal-z geometry. The method is based on conformal mapping of a hexagon into a rectangle. The resulting equations are solved using a fourth-order expansion of the transverse-integrated neutron flux into orthogonal polynomials. The transverse leakage is represented using constant neutron currents at the faces of the internal

Vyacheslav G. Zimin; Denis M. Baturin

2002-01-01

277

A Spectral Embedding Method Applied to the Advection–Diffusion Equation  

Microsoft Academic Search

In order to solve partial differential equations in complex geometries with a spectral type method, one describes an embedding approach which essentially makes use of Fourier expansions and boundary integral equations. For the advection–diffusion equation, the method is based on an efficient “Helmholtz solver,” the accuracy of which is tested by considering 1D and 2D Helmholtz-like problems. Finally, the capabilities

M. Elghaoui; R. Pasquetti

1996-01-01

278

Three dimensional heterogeneous finite element method for static multi-group neutron diffusion  

Microsoft Academic Search

Because current full-core neutronic-calculations use two-group neutron diffusion and rely on homogenizing fuel assemblies, reconstructing pin powers from such a calculation is an elaborate and not very accurate process; one which becomes more difficult with increased core heterogeneity. A three-dimensional Heterogeneous Finite Element Method (HFEM) is developed to address the limitations of current methods by offering fine-group energy representation and

Elif Can Aydogdu

2010-01-01

279

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

2013-06-18

280

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

281

Osmotic Dehydration of Foods in a Multicomponent Solution Part II. Water Loss and Solute Uptake in Agar Gels and Meat  

Microsoft Academic Search

The composition of the solution defined in Part I of this study was tested and improved to obtain high water loss during the dehydration of an agar gel. This solution was used for osmotic dehydration of meat slices. A mathematical model based on Fick's law of diffusion was used to estimate the time course of the water profile in meat,

G. Djelveh; J.-B. Gros; Z. Emam-Djomeh

2001-01-01

282

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

283

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

PubMed

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

2013-01-14

284

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.

Gunn, B A

1984-01-01

285

Relativistic diffusion Monte Carlo method: zeroth-order regular approximation-diffusion Monte Carlo method in a spin-free formalism.  

PubMed

A diffusion Monte Carlo (DMC) method for the relativistic zeroth-order regular approximation (ZORA) is proposed. In this scheme, a novel approximate Green's function is derived for the spin-free ZORA Hamiltonian. Several numerical tests on atoms and small molecules showed that by combining with the relativistic cusp-correction scheme, the present approach can include both relativistic and electron-correlation effects simultaneously. The correlation energies recovered by the ZORA-DMC method are comparable with the nonrelativistic DMC results and superior to the coupled cluster singles and doubles with perturbative triples correction results when the correlation-consistent polarized valence triple-zeta Douglas-Kroll basis set is used. For the heavier CuH molecule, the ZORA-DMC estimation of its dissociation energy agrees with the experimental value within the error bar. PMID:23083144

Nakatsuka, Yutaka; Nakajima, Takahito

2012-10-21

286

Relativistic diffusion Monte Carlo method: Zeroth-order regular approximation-diffusion Monte Carlo method in a spin-free formalism  

NASA Astrophysics Data System (ADS)

A diffusion Monte Carlo (DMC) method for the relativistic zeroth-order regular approximation (ZORA) is proposed. In this scheme, a novel approximate Green's function is derived for the spin-free ZORA Hamiltonian. Several numerical tests on atoms and small molecules showed that by combining with the relativistic cusp-correction scheme, the present approach can include both relativistic and electron-correlation effects simultaneously. The correlation energies recovered by the ZORA-DMC method are comparable with the nonrelativistic DMC results and superior to the coupled cluster singles and doubles with perturbative triples correction results when the correlation-consistent polarized valence triple-zeta Douglas-Kroll basis set is used. For the heavier CuH molecule, the ZORA-DMC estimation of its dissociation energy agrees with the experimental value within the error bar.

Nakatsuka, Yutaka; Nakajima, Takahito

2012-10-01

287

Splitting Method for Solving the Coarse-Mesh Discretized Low-Order Quasi-Diffusion Equations  

SciTech Connect

In this paper, the development is presented of a splitting method that can efficiently solve coarse-mesh discretized low-order quasi-diffusion (LOQD) equations. The LOQD problem can reproduce exactly the transport scalar flux and current. To solve the LOQD equations efficiently, a splitting method is proposed. The presented method splits the LOQD problem into two parts: (a) the D problem that captures a significant part of the transport solution in the central parts of assemblies and can be reduced to a diffusion-type equation and (b) the Q problem that accounts for the complicated behavior of the transport solution near assembly boundaries. Independent coarse-mesh discretizations are applied: the D problem equations are approximated by means of a finite element method, whereas the Q problem equations are discretized using a finite volume method. Numerical results demonstrate the efficiency of the methodology presented. This methodology can be used to modify existing diffusion codes for full-core calculations (which already solve a version of the D problem) to account for transport effects.

Hiruta, Hikaru [North Carolina State University (United States); Anistratov, Dmitriy Y. [North Carolina State University (United States); Adams, Marvin L. [Texas A and M University (United States)

2005-02-15

288

A new diffusion nodal method based on analytic basis function expansion  

SciTech Connect

The transverse integration procedure commonly used in most advanced nodal methods results in some limitations. The first is that the transverse leakage term that appears in the transverse integration procedure must be appropriately approximated. In most advanced nodal methods, this term is expanded in a quadratic polynomial. The second arises when reconstructing the pinwise flux distribution within a node. The available one-dimensional flux shapes from nodal calculation in each spatial direction cannot be used directly in the flux reconstruction. Finally, the transverse leakage defined for a hexagonal node becomes so complicated as not to be easily handled and contains nonphysical singular terms. In this paper, a new nodal method called the analytic function expansion nodal (AFEN) method is described for both the rectangular geometry and the hexagonal geometry in order to overcome these limitations. This method does not solve the transverse-integrated one-dimensional diffusion equations but instead solves directly the original multidimensional diffusion equation within a node. This is a accomplished by expanding the solution (or the intranodal homogeneous flux distribution) in terms of nonseparable analytic basis functions satisfying the diffusion equation at any point in the node.

Noh, J.M.; Cho, N.Z. (Korea Advanced Institute of Science and Technology, Taejon (Korea, Democratic People's Republic of))

1993-01-01

289

Acanthamoeba on Sabouraud's agar from a patient with keratitis  

PubMed Central

A 25-year-old transgender patient came with complaints of watery discharge, red eye and photophobia in the left eye since 2 days. The patient had a history of wearing colored contact lenses since 4 years and cleaning the lens with tap water. Culture of lenses on Mac Conkey and blood agar yielded Klebsiella pneumoniae and Pseudomonas aeruginosa. Sabouroud's agar showed yeast cells and double-walled cysts of Acanthamoeba species. On further incubation of Sabouroud's agar, the cysts transformed to trophozoites. Parallel results were obtained on tap water agar. The previous therapy of moxifloxacin was changed to local Neosporin application.

Baradkar, Vasant; Samal, Badhuli; Mali, Swapna A; Kulkarni, Ketaki; Shastri, Jayanthi

2011-01-01

290

Acanthamoeba on Sabouraud's agar from a patient with keratitis.  

PubMed

A 25-year-old transgender patient came with complaints of watery discharge, red eye and photophobia in the left eye since 2 days. The patient had a history of wearing colored contact lenses since 4 years and cleaning the lens with tap water. Culture of lenses on Mac Conkey and blood agar yielded Klebsiella pneumoniae and Pseudomonas aeruginosa. Sabouroud's agar showed yeast cells and double-walled cysts of Acanthamoeba species. On further incubation of Sabouroud's agar, the cysts transformed to trophozoites. Parallel results were obtained on tap water agar. The previous therapy of moxifloxacin was changed to local Neosporin application. PMID:23508061

Baradkar, Vasant; Samal, Badhuli; Mali, Swapna A; Kulkarni, Ketaki; Shastri, Jayanthi

2011-07-01

291

Diffusion Systems for Evaluation of Biomineralization  

PubMed Central

A variety of in vitro study methods have been used to elucidate the roles of matrix molecules in biomineralization processes. Among these, gel diffusion-precipitation studies have proved to be an effective tool. This methodology is uniquely capable of characterizing the effects of matrix molecules on mineralization while only using very small quantities of material. Furthermore, gel methods have been extended for use as a mineralization assay system to characterize modified matrix molecules and synthetic analogues. Here we discuss the advantages and limitations of gelatin, agar, agarose, and other systems for studying the mechanisms of biomineralization.

Silverman, L.

2005-01-01

292

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.

Andualem, Berhanu; Gessesse, Amare

2013-01-01

293

Natural abundance-level measurement of the nitrogen isotopic composition of oceanic nitrate: an adaptation of the ammonia diffusion method  

Microsoft Academic Search

We have adapted the “ammonia diffusionmethod of nitrate extraction for natural-abundance level nitrogen isotopic measurement of oceanic nitrate. The method involves: (1) sample concentration (by boiling or evaporation); (2) conversion of nitrate to ammonia using Devarda's alloy; and (3) the gas-phase diffusion of ammonia onto an acidified glass fiber disk which is sandwiched between two porous Teflon membranes. We

D. M. Sigman; M. A. Altabet; R. Michener; D. C. McCorkle; B. Fry; R. M. Holmes

1997-01-01

294

Improved soft-agar colony assay in a fluid processing apparatus.  

PubMed

The standard method for quantitating bone marrow precursor cells has been to count the number of colony-forming units that form in semisolid (0.3%) agar. Recently we adapted this assay for use in hardware, the Fluid Processing Apparatus, that is flown in standard payload lockers of the space shuttle. When mouse or rat macrophage colony-forming units were measured with this hardware in ground-based assays, we found significantly more colony growth than that seen in standard plate assays. The improved growth correlates with increased agar thickness but also appears to be due to properties inherent to the Fluid Processing Apparatus. This paper describes an improved method for determining bone marrow macrophage precursor numbers in semisolid agar. PMID:10475256

Forsman, A D; Herpich, A R; Chapes, S K

1999-01-01

295

Methods to determine slow diffusion coefficients of biomolecules: applications to Engrailed 2, a partially disordered protein.  

PubMed

We present new NMR methods to measure slow translational diffusion coefficients of biomolecules. Like the heteronuclear stimulated echo experiment (XSTE), these new methods rely on the storage of information about spatial localization during the diffusion delay as longitudinal polarization of nuclei with long T(1) such as nitrogen-15. The new BEST-XSTE sequence combines features of Band-selective Excitation Short-Transient (BEST) and XSTE methods. By avoiding the saturation of all protons except those of amide groups, one can increase the sensitivity by 45% in small proteins. The new experiment which combines band-Selective Optimized Flip-Angle Short-Transient with XSTE (SOFAST-XSTE) offers an alternative when very short recovery delays are desired. A modification of the HSQC-edited version of the XSTE experiment offers enhanced sensitivity and access to higher resolution in the indirect dimension. These new methods have been applied to detect changes in diffusion coefficients due to dimerization or proteolysis of Engrailed 2, a partially disordered protein. PMID:21603954

Augustyniak, Rafal; Ferrage, Fabien; Paquin, Raphaël; Lequin, Olivier; Bodenhausen, Geoffrey

2011-05-21

296

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

2011-03-06

297

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

298

Corrections to linear methods for diffuse optical tomography using approximation error modelling  

PubMed Central

Linear reconstruction methods in diffuse optical tomography have been found to produce reasonable good images in cases in which the variation in optical properties within the medium is relatively small and a reference measurement with known background optical properties is available. In this paper we examine the correction of errors when using a first order Born approximation with an infinite space Green’s function model as the basis for linear reconstruction in diffuse optical tomography, when real data is generated on a finite domain with possibly unknown background optical properties. We consider the relationship between conventional reference measurement correction and approximation error modelling in reconstruction. It is shown that, using the approximation error modelling, linear reconstruction method can be used to produce good quality images also in situations in which the background optical properties are not known and a reference is not available.

Tarvainen, Tanja; Kolehmainen, Ville; Kaipio, Jari P.; Arridge, Simon R.

2010-01-01

299

Three-dimensional nodal diffusion and transport theory methods for hexagonal-z geometry  

SciTech Connect

Advanced nodal methods for the solution of the multigroup neutron diffusion and transport theory equations in three-dimensional hexagonal-z geometry are described. The code HEXNOD allows an accurate and efficient calculation of three-dimensional problems for fast reactors and high converter light water reactors. A unique capability of HEXNOD is the accurate solution of global three-dimensional neutron transport problems for fast reactors with very small computing times. The accuracy of the nodal diffusion and transport approximations is demonstrated by comparison with conventional finite difference methods and Monte Carlo calculations for a number of mathematical benchmark problems. Based on numerical results, it is concluded that the code HEXNOD is well suited for three-dimensional routine analysis of fast reactors and, in particular, as the neutronics module of the generalized quasi-static kinetics program HEXNODYN, which is currently being developed as part of the European accident code EAC-2.

Wagner, M.R. (Siemens AG, Erlangen (Germany, F.R.))

1989-12-01

300

Determination of the helium thermal diffusion coefficient in britholite using a NRA method: new results  

NASA Astrophysics Data System (ADS)

Dimensioning of actinides waste packages for long duration storage has to take into account helium production from natural decay and release rates from the material. For the latter, we propose here an improved method for the determination of the helium diffusion coefficient in britholite, to be used for minor actinides storage. This work is based on results we previously published using the classical three steps method: 3He implantation on a Van de Graaff facility, 3He profile determination analysing the protons resulting from the 3He(d,p)4He reaction in a nuclear microprobe, evolution of the helium profile during annealings. Taking explicitly into account the incident deuterons energy stragglings allows us to show that the implanted helium profiles are bimodal, each component leading to a different helium diffusion coefficient.

Gosset, Dominique; Trocellier, Patrick

2005-02-01

301

A hybrid preprocessing method using geometry based diffusion and elective enhancement filtering for pulmonary nodule detection  

NASA Astrophysics Data System (ADS)

The computer aided diagnostic (CAD) system has been developed to assist radiologist for early detection and analysis of lung nodules. For pulmonary nodule detection, image preprocessing is required to remove the anatomical structure of lung parenchyma and to enhance the visibility of pulmonary nodules. In this paper a hybrid preprocessing technique using geometry based diffusion and selective enhancement filtering have been proposed. This technique provides a unified preprocessing framework for solid nodule as well as ground glass opacity (GGO) nodules. Geometry based diffusion is applied to smooth the images by preserving the boundary. In order to improve the sensitivity of pulmonary nodule detection, selective enhancement filter is used to highlight blob like structure. But selective enhancement filter sometimes enhances the structures like blood vessel and airways other than nodule and results in large number of false positive. In first step, geometry based diffusion (GBD) is applied for reduction of false positive and in second step, selective enhancement filtering is used for further reduction of false negative. Geometry based diffusion and selective enhancement filtering has been used as preprocessing step separately but their combined effect was not investigated earlier. This hybrid preprocessing approach is suitable for accurate calculation of voxel based features. The proposed method has been validated on one public database named Lung Image Database Consortium (LIDC) containing 50 nodules (30 solid and 20 GGO nodule) from 30 subjects and one private database containing 40 nodules (25 solid and 15 GGO nodule) from 30 subjects.

Dhara, Ashis K.; Mukhopadhyay, Sudipta

2012-02-01

302

Characterization of non-diffusive transport in plasma turbulence via a novel Lagrangian method  

SciTech Connect

A novel method to probe and characterize the nature of the transport of passive scalars carried out by a turbulent flow is introduced. It requires the determination of two exponents which encapsulate the statistical and correlation properties of the component of interest of the Lagrangian velocities of the flow. Numerical simulations of a magnetically confined, near-critical turbulent plasma, known to exhibit superdiffusive radial transport, are used to illustrate the method. It is shown that the method can easily detect the change in the dynamics of the radial transport that takes place after adding to the simulations a (subdominant) diffusive channel of tunable strength.

Mier, Jose Angel [Universidad Carlos III, Madrid, Spain; Sanchez, Raul [ORNL; Garcia, Luis [Universidad Carlos III, Madrid, Spain; Carreras, Benjamin A [BACV Solutions, Inc., Oak Ridge; Newman, David E [University of Alaska

2008-01-01

303

Two-Dimensional Space-Time Dependent Multi-group Diffusion Equation with SLOR Method  

NASA Astrophysics Data System (ADS)

The research of two-dimensional space-time diffusion equations with SLOR (Successive-Line Over Relaxation) has been done. SLOR method is chosen because this method is one of iterative methods that does not required to defined whole element matrix. The research is divided in two cases, homogeneous case and heterogeneous case. Homogeneous case has been inserted by step reactivity. Heterogeneous case has been inserted by step reactivity and ramp reactivity. In general, the results of simulations are agreement, even in some points there are differences.

Yulianti, Y.; Su'Ud, Z.; Waris, A.; Khotimah, S. N.

2010-06-01

304

A variational meshfree method for solving time-discrete diffusion equations  

NASA Astrophysics Data System (ADS)

A meshfree method is developed for solving time-discrete diffusion equations that arise in models in brain research. Important criteria for a suitable method are flexibility with respect to domain geometry and the ability to work with very small moving sources requiring easy refinement possibilities. One part of the work concerns a meshfree discretization of the modified Helmholtz equation based on the related minimization problem and a local least-squares function approximation. In a second part, a node choosing algorithm is presented that moves around randomly distributed nodes for optimizing the node distribution and varying the node density as needed. The method is illustrated by two numerical tests.

Krottje, Johannes K.

2006-08-01

305

Consistent infinitesimal finite-element cell method for diffusion equation in unbounded medium  

Microsoft Academic Search

To calculate the unit-step response matrix of an unbounded medium for use in a time-domain analysis of unbounded medium-structure interaction for the diffusion equation, the consistent infinitesimal finite-element cell method is developed for the three-dimensional case. Its derivation is based on the finite-element formulation and on similarity. The discretization is only performed on the structure-medium interface, yielding a reduction of

Chongmin Song; John P. Wolf

1996-01-01

306

Angstrom methods applied to simultaneous measurements of thermal diffusivity and heat transfer coefficients: Part 1, Theory  

SciTech Connect

The authors present a method for simultaneous measurement of thermal diffusivity and local heat transfer coefficient based on a theory originally stated by Angstrom. They apply a sinusoidally varying thermal flux incident on one face of a one-dimensional specimen and convectively cool its opposite face. This results in a sinusoidally varying temperature on the cooled face with a measurable phase lag between the incident and transmitted waves that depends upon the material properties and the heat transfer coefficient.

Kosky, P.G.; Maylotte, D.H.; Gallo, J.P.

1999-11-01

307

The optimized order 2 method : Application to convection-diffusion problems  

Microsoft Academic Search

We present an iterative, non-overlapping domain decomposition method for solving the convection–diffusion equation. A reformulation of the problem leads to an equivalent problem, where the unknowns are on the boundary of the subdomains [F. Nataf, F. Rogier, E. de Sturler, in: A. Sequeira (Ed.), Navier–Stokes Equations on Related Nonlinear Analysis, Plenum Press, New York, 1995, pp. 307–377]. The solving of

C. Japhet; F. Nataf; F. Rogier

2001-01-01

308

Alternating direction implicit methods for two-dimensional diffusion with a non-local boundary condition  

Microsoft Academic Search

A new second-order finite difference technique based upon the Peaceman and Rachford (P - R) alternating direction implicit (ADI) scheme, and also a fourth-order finite difference scheme based on the Mitchell and Fairweather (M - F) ADI method, are used as the basis to solve the two-dimensional time dependent diffusion equation with non-local boundary conditions. The results of numerical experiments

M. Dehghan

1999-01-01

309

Three-dimensional nodal diffusion and transport theory methods for hexagonal-z geometry  

Microsoft Academic Search

Advanced nodal methods for the solution of the multigroup neutron diffusion and transport theory equations in three-dimensional hexagonal-z geometry are described. The code HEXNOD allows an accurate and efficient calculation of three-dimensional problems for fast reactors and high converter light water reactors. A unique capability of HEXNOD is the accurate solution of global three-dimensional neutron transport problems for fast reactors

1989-01-01

310

Synthesis of agar microparticles using temperature-controlled microfluidic devices for Cordyceps militaris cultivation.  

PubMed

A temperature-controlled microfluidic approach was developed for fabricating monodispersed agar beads with the potential to be a brand-new strategy for cultivating Cordyceps militaris. The proposed microfluidic system features a circulating water bath with precise temperature control (temperature deviation ?T<0.1°C). This device holds the promise of allowing us to develop a temperature-controlled system, characterized as simple, low cost, and easy to set up and use. The size-controllable agar beads were achieved by utilizing microfluidic emulsification in the cross-junction channel under temperature-controlled conditions. The flow conditions of the dispersed/continuous phases were adjusted to generate various sizes of agar beads. Our results show that the microparticles produced are as small as 176 ??m with a 95% particle size distribution within 5? ?m. The prepared agar microparticles performed well as a substrate for the cultivation of C. militaris. The proposed method could also be applied for encapsulating biomaterials, enzymes, drugs, catalysts, and nanoparticles into agar beads for biomedical applications. PMID:22012813

Lin, Yung-Sheng; Yang, Chih-Hui; Lu, Kang; Huang, Keng-Shiang; Zheng, Ying-Zhen

2011-10-20

311

The diffuse-scattering method for investigating locally ordered binary solid solutions  

SciTech Connect

Diffuse-scattering investigations comprise a series of maturing methods for detailed characterization of the local-order structure and atomic displacements of binary alloy systems. The distribution of coherent diffuse scattering is determined by the local atomic ordering, and analytical techniques are available for extracting the relevant structural information. An extension of such structural investigations, for locally ordered alloys at equilibrium, allows one to obtain pairwise interaction energies. Having experimental pairwise interaction energies for the various coordination shells offers one the potential for more realistic kinetic Ising modeling of alloy systems as they relax toward equilibrium. Although the modeling of atomic displacements in conjunction with more conventional studies of chemical ordering is in its infancy, the method appears to offer considerable promise for revealing additional information about the strain fields in locally ordered and clustered alloys. The diffuse-scattering methods for structural characterization and for the recovery of interaction energies are reviewed, and some preliminary results are used to demonstrate the potential of the kinetic Ising modeling technique to follow the evolution of ordering or phase separation in an alloy system.

Epperson, J.E. (Argonne National Lab., IL (United States)); Anderson, J.P. (LTV Steel Technology Center, Independence, OH (United States)); Chen, H. (Univ. of Illinois, Urbana, IL (United States). Materials Science and Engineering Dept.)

1994-01-01

312

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

313

A New FRAP/FRAPa Method for Three-Dimensional Diffusion Measurements Based on Multiphoton Excitation Microscopy  

PubMed Central

We present a new convenient method for quantitative three-dimensionally resolved diffusion measurements based on the photobleaching (FRAP) or photoactivation (FRAPa) of a disk-shaped area by the scanning laser beam of a multiphoton microscope. Contrary to previously reported spot-photobleaching protocols, this method has the advantage of full scalability of the size of the photobleached area and thus the range of diffusion coefficients, which can be measured conveniently. The method is compatible with low as well as high numerical aperture objective lenses, allowing us to perform quantitative diffusion measurements in three-dimensional extended samples as well as in very small volumes, such as cell nuclei. Furthermore, by photobleaching/photoactivating a large area, diffusion along the optical axis can be measured separately, which is convenient when studying anisotropic diffusion. First, we show the rigorous mathematical derivation of the model, leading to a closed-form formula describing the fluorescence recovery/redistribution phase. Next, the ability of the multiphoton FRAP method to correctly measure absolute diffusion coefficients is tested thoroughly on many test solutions of FITC-dextrans covering a wide range of diffusion coefficients. The same is done for the FRAPa method on a series of photoactivatable green fluorescent protein solutions with different viscosities. Finally, we apply the method to photoactivatable green fluorescent protein diffusing freely in the nucleus of living NIH-3T3 mouse embryo fibroblasts.

Mazza, Davide; Braeckmans, Kevin; Cella, Francesca; Testa, Ilaria; Vercauteren, Dries; Demeester, Jo; De Smedt, Stefaan S.; Diaspro, Alberto

2008-01-01

314

Growth of Desulfovibrio on the Surface of Agar Media.  

National Technical Information Service (NTIS)

Growth of Desulfovibrio desulfuricans (API strain) was found to take place in an atmosphere of hydrogen on the agar surface of complex media, including yeast extract (Difco), and Trypticase Soy Agar (BBL) without any added reducing agents. For growth on a...

W. P. Iverson

1966-01-01

315

Detection of extracellular proteases from microorganisms on agar plates  

Microsoft Academic Search

We present herein an improved assay for detecting the presence of extracellular proteases from microorganisms on agar plates. Using different substrates (gelatin, BSA, hemoglobin) incorporated into the agar and varying the culture medium composition, we were able to detect proteolytic activities from Pseudomonas aeruginosa, Micrococcus luteus and Serratia marcescens as well as the influence that these components displayed in the

Alane Beatriz Vermelho; Maria Nazareth Leal Meirelles; Andréa Lopes; Simone Dias Gonçalves Petinate; André Adriano Chaia; Marta Helena Branquinha

1996-01-01

316

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

317

The effects of connection reconstruction method on the interregional connectivity of brain networks via diffusion tractography.  

PubMed

Estimating the interregional structural connections of the brain via diffusion tractography is a complex procedure and the parameters chosen can affect the outcome of the connectivity matrix. Here, we investigated the influence of different connection reconstruction methods on brain connectivity networks. Specifically, we applied three connection reconstruction methods to the same set of diffusion MRI data, initiating tracking from deep white matter (method #1, M1), from the gray matter/white matter interface (M2), and from the gray/white matter interface with thresholded tract volume rather than the connection probability as the connectivity index (M3). Small-world properties, hub identification, and hemispheric asymmetry in connectivity patterns were then calculated and compared across methods. Despite moderate to high correlations in the graph-theoretic measures across different methods, significant differences were observed in small-world indices, identified hubs, and hemispheric asymmetries, highlighting the importance of reconstruction method on network parameters. Consistent with the prior reports, the left precuneus was identified as a hub region in all three methods, suggesting it has a prominent role in brain networks. PMID:21928316

Li, Longchuan; Rilling, James K; Preuss, Todd M; Glasser, Matthew F; Hu, Xiaoping

2011-09-16

318

Production of long-chain polyunsaturated fatty acids by monoxenic growth of labyrinthulids on oil-dispersed agar medium  

Microsoft Academic Search

A novel method is proposed for the production of long-chain polyunsaturated fatty acids (LCPUFA) by labyrinthulids. The method comprises a monoxenic culture with Psychlobacter phenylpyruvicus, using agar medium in which oil was dispersed. Soybean oil (SBO) was selected as the optimum material for an oil-dispersed agar medium. The labyrinthulids showed three-dimensional growth and an anastomosing ectoplasmic network in the SBO-dispersed

Y. Kumon; T. Yokochi; T. Nakahara; M. Yamaoka; K. Mito

2002-01-01

319

[Presumptive identification of Candida spp. and other clinically important yeasts: usefulness of Brilliance Candida Agar].  

PubMed

Fungal infections caused by yeasts have increased during the last decades and invasive forms represent a serious problem for human health. Candida albicans is the species most frequently isolated from clinical samples. However, other emerging yeast pathogens are increasingly responsible for mycotic infections, and some of them are resistant to some antifungal drugs. Consequently, it is necessary to have methods that can provide a rapid presumptive identification at species level. Numerous chromogenic agar media have been shown to be of value as diagnostic tools. We have compared a chromogenic medium, Brilliance Candida Agar, with CHROMagar Candida, the chromogenic medium most used in our country. A multicentre study was conducted in 16 Hospitals belonging to the Mycology Net of Buenos Aires City Government. A total of 240 yeast isolates were included in this research. The new chromogenic agar showed results very similar to those obtained with CHROMagar Candida. PMID:20346288

Alfonso, Claudia; López, Mónica; Arechavala, Alicia; Perrone, María Del Carmen; Guelfand, Liliana; Bianchi, Mario

2010-03-24

320

Improved diffusion methods for nitrogen and 15nitrogen analysis of Kjeldahl digests.  

PubMed

Simple methods are described that permit the use of either H3BO3 indicator solution or acidified filter disks to collect NH3 liberated by treatment of Kjeldahl digests with NaOH. These methods incorporate modifications to improve reliability, analytical capacity, and convenience. A semimicro digest was diluted to 25 mL with deionized water, and a 10 mL aliquot, containing up to 4 mg N (150 microg N for diffusions into acidified disks), was transferred to a shell vial, which was placed inside a 473 mL (1 pint) Mason jar containing 10 mL 10N NaOH. The NH3 liberated by overturning the vial was collected after 12 to 48 h at ambient temperature, or after 4 h at 45 to 50 degrees C on a hotplate, for quantitative and/or isotope-ratio analyses. With either H3BO3 indicator solution or acidified filter disks, recovery of diffused N was quantitative. Isotope-ratio analyses of diffused N from 15N-labeled chemical, plant, and soil samples were within 3% of analyses using steam distillation. PMID:11048842

Stevens, W B; Mulvaney, R L; Khan, S A; Hoeft, R G

321

Lateral heat flow method for thickness independent determination of thermal diffusivity  

NASA Astrophysics Data System (ADS)

A pulsed transient thermography method is described where a high-intensity light pulse is used to heat a long, uniform stripe on the surface of a plate. A high spatial resolution, high frame rate focal plane array infrared camera is used to monitor surface temperature. We explain the theoretical model and data analysis framework used to experimentally determine all three thermal diffusivity components from the temperature measurements. The analysis does not require any fitting to the temperature profile and is based on the creation of thermal time-of-flight (tof) images from the temperature data and the relationship between tof and the distance from the stripe edge. The in-plane components of thermal diffusivity are obtained without the need for thickness information. Experimental validation of this procedure was carried out using anisotropic carbon fiber reinforced polymer composites.

Tralshawala, Nilesh; Howard, Donald R.; Knight, Bryon; Plotnikov, Yuri; Ringermacher, Harry I.

2007-10-01

322

Improved diffusion methods for determination of inorganic nitrogen in soil extracts and water  

Microsoft Academic Search

Diffusion methods previously developed for inorganic-N analysis of soil extracts were modified to improve reliability, increase\\u000a the dynamic range, extend the scope of applications, and simplify the processing of samples for N-isotope analysis. In these\\u000a methods, the soil extract is treated with MgO, or MgO plus Devarda‘s alloy, in a 473-ml (1-pint) wide-mouth Mason jar to convert\\u000a NH4\\u000a +-N, NO3

R. L. Mulvaney; S. A. Khan; W. B. Stevens; C. S. Mulvaney

1997-01-01

323

Absorption spectroscopy of powdered materials using time-resolved diffuse optical methods.  

PubMed

In this paper a novel method, based on time-resolved diffuse optical spectroscopy, is proposed to measure the absorption of small amounts of nanostructured powder materials independent of scattering. Experimental validation, in the visible and near-infrared spectral range, has been carried out on India Inkparticles. The effectiveness of the technique to measure scattering-free absorption is demonstrated on carbon nanotubes. The comparison between the absorption spectra acquired by the proposed method and conventional measurements performed with a commercial spectrophotometer is discussed. PMID:23142900

D'Andrea, Cosimo; Obraztsova, Ekaterina A; Farina, Andrea; Taroni, Paola; Lanzani, Guglielmo; Pifferi, Antonio

2012-11-10

324

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

325

Solution of diffuser inlet velocity field of radial impeller centrifugal turbine pumps by means of the LDA method  

Microsoft Academic Search

The paper deals with velocity-field analysis of a centrifugal turbine pump with radial impellers and diffuser, and especially with the diffuser-inlet velocity field. The experimental model design, the design for the LDA-method application, methodology, and measurement results on static and dynamic velocity field properties are discussed.

M. Hrabovsky

1985-01-01

326

Solution of diffuser inlet velocity field of radial impeller centrifugal turbine pumps by means of the LDA method  

NASA Astrophysics Data System (ADS)

The paper deals with velocity-field analysis of a centrifugal turbine pump with radial impellers and diffuser, and especially with the diffuser-inlet velocity field. The experimental model design, the design for the LDA-method application, methodology, and measurement results on static and dynamic velocity field properties are discussed.

Hrabovsky, M.

327

Interstitial Air Pressure Dependence of Effective Thermal Conductivity and Diffusivity of Rajasthan Desert Sand Using Transient Hot-Strip Method  

Microsoft Academic Search

The transient hot strip (T H S) method used for the simultaneous measurement of effective thermal conductivity and diffusivity of loose granular two-phase materials at normal pressure and room temperature is now used for the measurement of effective thermal conductivity and diffusivity of Rajasthan Desert sand at different interstitial air pressure and room temperature. Experimental values of effective thermal conductivities

N. S. Saxena; M. A. Chohan; S. E. Gustafsson

1987-01-01

328

Numerical method in reproducing kernel space for an inverse source problem for the fractional diffusion equation  

NASA Astrophysics Data System (ADS)

We propose a new numerical method for reproducing kernel Hilbert space to solve an inverse source problem for a two-dimensional fractional diffusion equation, where we are required to determine an x-dependent function in a source term by data at the final time. The exact solution is represented in the form of a series and the approximation solution is obtained by truncating the series. Furthermore, a technique is proposed to improve some of the existing methods. We prove that the numerical method is convergent under an a priori assumption of the regularity of solutions. The method is simple to implement. Our numerical result shows that our method is effective and that it is robust against noise in L2-space in reconstructing a source function.

Wang, Wenyan; Yamamoto, Masahiro; Han, Bo

2013-09-01

329

Disk diffusion susceptibility testing of the Bacteroides fragilis group.  

PubMed Central

The susceptibilities of 225 isolates of the Bacteroides fragilis group to six antibiotics were determined by a new disk diffusion test in Wilkins-Chalgren agar and by the standard agar dilution method. For disk diffusion, the bacteria were directly suspended in saline and immediately swabbed onto 15-cm agar plates. Disks of cefoxitin (30 micrograms), chloramphenicol (30 micrograms), clindamycin (2 micrograms), moxalactam (30 micrograms), imipenem (10 micrograms), and ticarcillin (75 micrograms) were applied, and the plates were incubated at 37 degrees C in an anaerobic atmosphere. Zone sizes were measured at 24 h. The results of disk diffusion and agar dilution were compared by regression analysis by the method of least squares and by the error rate-bounded method. Zones were easily measured for 216 strains (96%). The correlation between the MICs and diameters of inhibition for cefoxitin, clindamycin, moxalactam, and ticarcillin was generally good. A correlation could not be established for chloramphenicol and imipenem, as there were too few resistant strains. With the recommended resistance breakpoints, the following susceptible and resistant zone diameter breakpoints could be established: cefoxitin, less than or equal to 19 and greater than or equal to 21 mm; clindamycin, less than or equal to 14 and greater than or equal to 18 mm; moxalactam, less than or equal to 21 and greater than or equal to 25 mm; and ticarcillin, less than or equal to 15 and greater than or equal to 16 mm. By applying these zone criteria, the percentage of false-susceptible strains was less than 1% and of false-resistant strains was less than 4% for the drugs tested.

Horn, R; Bourgault, A M; Lamothe, F

1987-01-01

330

Clonal growth of Blastocystis hominis in soft agar with sodium thioglycollate  

Microsoft Academic Search

The present report describes a method for establishment of colonies of Blastocystis hominis from single cells in soft agar. The percentage of colony-forming efficiency (% CFE = number of colonies grown \\/ number of\\u000a cells inoculated × 100) for the cultures was greatly improved by the addition of sodium thioglycollate. Five human Blastocystis isolates chosen for this study showed no

S. W. Tan; M. Singh; K. T. Thong; L. C. Ho; K. T. Moe; X. Q. Chen; G. C. Ng; E. H. Yap

1996-01-01

331

An electrochemical approach to monitor pH change in agar media during plant tissue culture  

Microsoft Academic Search

In this work, metal oxide microelectrodes were developed to monitor pH change in agar media during plant tissue culture. An antimony wire was produced by a new approach “capillary melt method”. The surface of the obtained antimony wire was oxidized in a potassium nitrate melt to fabricate an antimony oxide film for pH sensing. Characterization results show that the oxide

Min Wang; Yang Ha

2007-01-01

332

Performance of CHROMAGAR candida and BIGGY agar for identification of yeast species  

Microsoft Academic Search

BACKGROUND: The importance of identifying the pathogenic fungi rapidly has encouraged the development of differential media for the presumptive identification of yeasts. In this study two differential media, CHROMagar Candida and bismuth sulphite glucose glycine yeast agar, were evaluated for the presumptive identification of yeast species. METHODS: A total number of 270 yeast strains including 169 Candida albicans, 33 C.

Mine Yücesoy; Serhat Marol

2003-01-01

333

Differentiation of periosteal cells in muscle. An experimental study using the diffusion chamber method.  

PubMed

The osteo-chondrogenic capacity of the undifferentiated mesenchymal cells of the periosteum has been made use of in clinical reconstructive surgery. In the present investigation we studied the osteo-chondrogenic potency of free periosteal transplants in muscle using the diffusion chamber method. A total of 42 experimental and seven control rabbits aged four to six weeks were operated on. Periosteum was obtained from the anterior aspect of the left tibial bone by stripping. The grafts were placed in Nucleopore diffusion chambers with a pore size of 0.4 micron. The chambers were implanted in the anterior tibial and paraspinal muscles of the rabbit. Osteogenesis began after the second postoperative week and increased up to the 5-6 week interval when a plateau phase was reached. Chondrogenesis, which also began after the second postoperative week, reached two plateau phases; the first observed at 4-8 weeks and the second at 12-16 weeks. Neither bone nor cartilage formation could be observed outside the chambers. In the semi-open control chambers with only one end sealed, bone formed within the chamber as early as two weeks after transplantation and grew out into the adjacent connective tissue of muscle. It is noteworthy that the periosteal transplant retained its osteochondrogenic properties even when isolated in the diffusion chamber. The young age of the donor animals might have contributed to our findings. PMID:3252446

Jaroma, H J; Ritsilä, V A

1988-01-01

334

A new method for choosing the computational cell in stochastic reaction-diffusion systems  

PubMed Central

How to choose the computational compartment or cell size for the stochastic simulation of a reaction–diffusion system is still an open problem, and a number of criteria have been suggested. A generalized measure of the noise for finite-dimensional systems based on the largest eigenvalue of the covariance matrix of the number of molecules of all species has been suggested as a measure of the overall fluctuations in a multivariate system, and we apply it here to a discretized reaction–diffusion system. We show that for a broad class of first-order reaction networks this measure converges to the square root of the reciprocal of the smallest mean species number in a compartment at the steady state. We show that a suitably re-normalized measure stabilizes as the volume of a cell approaches zero, which leads to a criterion for the maximum volume of the compartments in a computational grid. We then derive a new criterion based on the sensitivity of the entire network, not just of the fastest step, that predicts a grid size that assures that the concentrations of all species converge to a spatially-uniform solution. This criterion applies for all orders of reactions and for reaction rate functions derived from singular perturbation or other reduction methods, and encompasses both diffusing and non-diffusing species. We show that this predicts the maximal allowable volume found in a linear problem, and we illustrate our results with an example motivated by anterior-posterior pattern formation in Drosophila, and with several other examples.

Kang, Hye-Won; Zheng, Likun; Othmer, Hans G.

2013-01-01

335

Equivalency testing of TTC Tergitol 7 agar (ISO 9308-1:2000) with five culture media for the detection of E. coli in water samples in Greece.  

PubMed

In this study ten laboratories in Greece compared the performance of reference method TTC Tergitol 7 Agar (with the additional test of beta-glucuronidase production) with five alternative methods, to detect E. coli in water, in line with European Water Directive recommendations. The samples were prepared by spiking drinking water with sewage effluent following a standard protocol. Chlorinated and non-chlorinated samples were used. The statistical analysis was based on the mean relative difference of confirmed counts and was performed in line with ISO 17994. The results showed that in total, three of the alternative methods (Chromocult Coliform agar, Membrane Lauryl Sulfate agar and Trypton Bilex-glucuronidase medium) were not different from TTC Tergitol 7 agar (TTC Tergitol 7 agar vs Chromocult Coliform agar, 294 samples, mean RD% 5.55; vs MLSA, 302 samples, mean RD% 1; vs TBX, 297 samples, mean RD% -2.78). The other two alternative methods (Membrane Faecal coliform medium and Colilert 18/ Quantitray) gave significantly higher counts than TTC Tergitol 7 agar (TTC Tergitol 7 agar vs MFc, 303 samples, mean RD% 8.81; vs Colilert-18/Quantitray, 76 samples, mean RD% 18.91). In other words, the alternative methods generated performance that was as reliable as, or even better than, the reference method. This study will help laboratories in Greece overcome culture and counting problems deriving from the EU reference method for E. coli counts in water samples. PMID:20057092

Mavridou, A; Smeti, E; Mandilara, G; Mandilara, G; Boufa, P; Vagiona-Arvanitidou, M; Vantarakis, A; Vassilandonopoulou, G; Pappa, O; Roussia, V; Tzouanopoulos, A; Livadara, M; Aisopou, I; Maraka, V; Nikolaou, E; Mandilara, G

2010-01-01

336

The Immunological Relationship of the Vaccinia and Pig Pox Viruses demonstrated by Gel Diffusion  

PubMed Central

The Ouchterlony double diffusion method in agar gel has been used to study the antigens of the vaccinia and pig pox viruses and their corresponding antibodies. The existence of a common antigenic constituent in the two viruses has been demonstrated. The sensitivity of the method was found to be adequate for sera giving complement fixation titres of 1/80. The complications arising from the presence of antibodies to heterologous (host) antigens are illustrated. ImagesFIG. 6FIG. 7

Datt, N. S.; Orlans, E. S.

1958-01-01

337

Modified nondestructive colorimetric method to evaluate the variability of oxygen diffusion rate through wine bottle closures.  

PubMed

Some modifications to a previous nondestructive colorimetric method that permits evaluation of the oxygen diffusion rate through wine closures were proposed. The method is based on the reaction of indigo carmine solution with oxygen and the tristimulus measurement of the consequent color change. Simplified preparation and measurement procedures were set up, allowing the analysis of a large number of samples simultaneously. The method was applied to the evaluation of the variability within the lot of 20 different types of stoppers (synthetic, produced by molding, and natural cork). The closures were tested at a storage temperature of 26 degrees C. With regard to oxygen permeability, the natural cork stopper showed a low homogeneity within the lot, especially during the first month after bottling, whereas the synthetic closure showed a greater steadiness in the performance. The limits of the colorimetric method were also analyzed, and three possible causes of degradation of the indigo carmine solution were identified: oxygen, light, and heat. PMID:20187636

Brotto, Laura; Battistutta, Franco; Tat, Lara; Comuzzo, Piergiorgio; Zironi, Roberto

2010-03-24

338

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.

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

2010-01-01

339

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

NASA Astrophysics Data System (ADS)

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®APOLLO3 is a registered trademark in France.1 neutronics code.

Jamelot, Erell; Ciarlet, Patrick

2013-05-01

340

A Novel Chromogenic Ester Agar Medium for Detection of Salmonellae  

Microsoft Academic Search

A novel agar medium, chromogenic Salmonella esterase (CSE) agar, for the differentiation of salmonellae is described. The agar contains peptones and nutrient extracts together with the following (grams per liter unless otherwise specified): 4-(2-(4-octanoyloxy-3,5-dimethoxyphenyl)-vinyl)-quinolinium-1-(propan-3-yl carboxylic acid) bromide (SLPA-octanoate; bromide form), 0.3223; lactose, 14.65; trisodium citrate dihydrate, 0.5; Tween 20, 3.0; ethyl 4-dimethylaminobenzoate, 0.035% (wt\\/vol), novobiocin, 70 mg liter 21 .

VENITIA M. COOKE; R. J. MILES; R. G. PRICE; A. C. RICHARDSON

1999-01-01

341

Method of diffusive gradients in thin films (DGT) compared with other soil testing methods to predict uranium phytoavailability.  

PubMed

The measurement of diffusive gradients in thin films (DGT) has been proposed as a surrogate for metal uptake by plants. A small-scale experiment was performed to test the predictive capacity of the DGT method with respect to uranium availability and uptake by ryegrass. Correlation analyses were performed to compare the results obtained with the DGT device with more conventional bioavailability indices - concentration of uranium in pore water or in selective extracts. Six soils with different uranium contamination history and with distinct soil characteristics were used for the availability tests and the uptake experiment. The four uranium bioavailability indices screened were highly correlated, indicating that at least partially comparable uranium pools were assessed. The uranium concentration in the pore water was a better predictor for uranium uptake by ryegrass than amounts of uranium recovered following extraction with 0.11 M CH3COOH or 0.4 M MgCl2, the fractions considered exchangeable according to, respectively, the BCR or NIST standardized sequential extraction methods. The DGT measured concentration, C(DGT), was also highly correlated with plant uptake but the significance level was sensitive to the value of the diffusion coefficient (pH depend or not) used to calculate C(DGT). From the results obtained it could not be concluded that the DGT method would have an additional value in assessing uranium bioavailability. PMID:17241652

Vandenhove, H; Antunes, K; Wannijn, J; Duquène, L; Van Hees, M

2007-01-22

342

Estimating Effective Vertical Diffusivity in Shallow Ponds by a Constrained Flux-Gradient Method  

NASA Astrophysics Data System (ADS)

Shallow ponds have been used to mitigate the deleterious effects of storm water run-off by acting as detention/retention basins that sequester run-off associated pollutants in sediments. Studies show that the retention efficiency of these systems can decrease over time as a result of the internal loading of nutrients/contaminants from the sediments back to the water column where they are available for export downstream. Quantifying the vertical transport of gases (down) and sediment derived materials (up) is vital to the modeling and understanding of the processes that contribute to the magnitude of internal loading. A critical parameter is the effective vertical diffusion coefficient: Kz=Dmolecular +Deddy (cm2 sec-1). The flux gradient method for estimating effective vertical thermal diffusivity has been applied with success in large lakes which undergo stratification cycles on seasonal or longer time scales. We offer a constrained version of the flux-gradient method that has been adapted for use in a shallow pond with a daily stratification cycle. The method employs heat as a tracer and assumes that transport in the face of a stable gradient is diffusive. By shrinking the spatial and temporal resolution of measurement to scales appropriate to the system of interest and carefully accounting for internal source and sink terms of heat (e.g solar radiation and sediment heat fluxes) we are able to calculate Kz as a function of time and depth during periods of stable stratification, i.e when the pond is not vertically well-mixed. Results show the magnitude of Kz varies from ca. 10-3 to 10-1 (cm2 sec-1) under stratified conditions depending primarily on the strength of stratification.

Bean, J. R.; Torgersen, T.

2004-12-01

343

cAMP diffusion in Dictyostelium discoideum: A Green's function method  

NASA Astrophysics Data System (ADS)

A Green’s function method is developed to approach the spatiotemporal equations describing the cAMP production in Dictyostelium discoideum, markedly reducing numerical calculations times: cAMP concentrations and gradients are calculated just at the amoeba locations. A single set of parameters is capable of reproducing the different observed behaviors, from cAMP synchronization, spiral waves and reaction-diffusion patterns to streaming and mound formation. After aggregation, the emergence of a circular motion of amoebas, breaking the radial cAMP field symmetry, is observed.

Calovi, Daniel S.; Brunnet, Leonardo G.; de Almeida, Rita M. C.

2010-07-01

344

Combination of Boundary Element Method and Finite Element Method in Diffuse Optical Tomography  

Microsoft Academic Search

This paper presents a new numerical method for optical tomography: the combined boundary element\\/finite element method (BEM-FEM), designed to tackle reconstructions in layered turbid media. The BEM-FEM focuses on the region of interest by creating a volume mesh and reconstructing in this region only. All other regions are treated as piecewise constant in a surface-integral approach. We validate the model

Josias Pierrick Elisee; Adam Gibson; Simon Arridge

2010-01-01

345

Advanced computational methods for nodal diffusion, Monte Carlo, and S(sub N) problems. Progress report, January 1, 1992--March 31, 1993.  

National Technical Information Service (NTIS)

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...

W. R. Martin

1993-01-01

346

Detection of decreased susceptibility to fluoroquinolones in Salmonella spp. by five different methods including real-time polymerase chain reaction (PCR)  

Microsoft Academic Search

Detection of Salmonella spp. isolates showing decreased susceptibility to fluoroquinolones has become important owing to the increasing prevalence of these strains and their association with treatment failure. Nalidixic acid agar dilution, nalidixic acid disk diffusion, MicroScan automated system and real-time polymerase chain reaction (PCR) (LightCycler) followed by melting temperature (Tm) analysis are compared with ciprofloxacin agar dilution as suitable methods

E. Aznar; T. Alarcon; B. Buendía; E. García-Peñuela; M. López-Brea

2007-01-01

347

3D modeling for solving forward model of no-contact fluorescence diffuse optical tomography method  

NASA Astrophysics Data System (ADS)

This paper presents detailed computational aspects of a new 3D modeling for solving the direct problem in a no-contact time-resolved Fluorescent Diffuse Optical Tomography (FDOT) method that rely on near-infrared scattered and fluorescent photons to image the optical properties and distribution of fluorescent probes in small laboratory animals. An optical scanner allowing performing in-vivo measurements in no-contact scheme was built in our laboratory and is presented. We use the three-dimensional Finite Element Method (FEM) to solve the coupled diffusion equations of excitation and fluorescence photons in highly scattering objects. The computed results allowed yielding photon density maps and the temporal profiles of photons on the surface of the small animal. Our 3D modeling of propagation of photons in the void space between the surface of the object and the detectors allows calculating the quantity of photons reaching the optodes. Simulations were carried-out on two test objects: a resin cylinder and a mouse phantom. The results demonstrate the potential applications of the method to pre-clinical imaging.

Nouizi, F.; Chabrier, R.; Torregrossa, M.; Poulet, P.

2009-07-01

348

Diffusion tensor imaging biomarkers for traumatic axonal injury: analysis of three analytic methods.  

PubMed

Traumatic axonal injury (TAI) is a common mechanism of traumatic brain injury not readily identified using conventional neuroimaging modalities. Novel imaging modalities such as diffusion tensor imaging (DTI) can detect microstructural compromise in white matter (WM) in various clinical populations including TAI. DTI-derived data can be analyzed using global methods (i.e., WM histogram or voxel-based approaches) or a regional approach (i.e., tractography). While each of these methods produce qualitatively comparable results, it is not clear which is most useful in clinical research and ultimately in clinical practice. This study compared three methods of analyzing DTI-derived data with regard to detection of WM injury and their association with clinical outcomes. Thirty patients with TAI and 19 demographically similar normal controls were scanned using a 3 Tesla magnet. Patients were scanned approximately eight months postinjury, and underwent an outcomes assessment at that time. Histogram analysis of fractional anisotropy (FA) and mean diffusivity showed global WM integrity differences between patients and controls. Voxel-based and tractography analyses showed significant decreases in FA within centroaxial structures involved in TAI. All three techniques were associated with functional and cognitive outcomes. DTI measures of microstructural integrity appear robust, as the three analysis techniques studied showed adequate utility for detecting WM injury. PMID:21070694

Marquez de la Plata, Carlos D; Yang, Fanpei Gloria; Wang, Jun Yi; Krishnan, Kamini; Bakhadirov, Khamid; Paliotta, Christopher; Aslan, Sina; Devous, Michael D; Moore, Carol; Harper, Caryn; McColl, Roderick; Munro Cullum, C; Diaz-Arrastia, Ramon

2010-11-12

349

The True Color of Yogi: An Accurate Method for Removing Diffuse Illumination from Multispectral Images of Mars  

NASA Astrophysics Data System (ADS)

We correct spectra of Yogi to remove diffuse illumination and show that the part of Yogi facing the wind is less red than other faces of the rock. Our method eliminates ambiguity in interpreting spectra obtained under Mars illumination conditions.

Stoker, C. R.; Rages, K.

2002-03-01

350

Calculation methods for ventricular diffusion-weighted imaging thermometry: phantom and volunteer studies.  

PubMed

A method for the measurement of temperature in the lateral ventricle using diffusion-weighted imaging (DWI) has been proposed recently. This method uses predetermined arbitrary thresholds, but a more objective method of calculation would be useful. We therefore compared four different calculation methods, two of which were newly created and did not require predetermined thresholds. A rectangular polyethylene terephthalate bottle (8?×?10?×?28?cm(3)) was filled with heated water (35.0-38.8?°C) and used as a water phantom. The DWI data of 23 healthy subjects (aged 26-75?years; mean?±?standard deviation, 50.13?±?19.1?years) were used for this study. The temperature was calculated using the following equation: T(°C)?=?2256.74/ln(4.39221/D)?-?273.15, where D is the diffusion coefficient. The mean ventricular temperature was calculated by four methods: two thresholding methods and two histogram curve-fitting methods. As a reference, we used the temperature measured at the tympanic membrane, which is known to be approximately 1?°C lower than the brain temperature. The averaged differences in temperature between mercury thermometry and classical predetermined thresholding methods for the water phantom were 0.10?±?0.42 and 0.05?±?0.41?°C, respectively. The histogram curve-fitting methods, however, yielded temperatures a little lower (averaged differences of -0.24?±?0.32 and -0.14?±?0.31?°C, respectively) than mercury thermometry. There was very little difference in temperature between tympanic thermometry and classical predetermined thresholding methods (+0.01 and -0.07?°C, respectively). In humans, however, the histogram curve-fitting methods yielded temperatures approximately 1?°C higher (+1.04?°C and +1.36?°C, respectively), suggesting that temperatures measured in this way more closely approximate the true brain temperature. The histogram curve-fitting methods were more objective and better matched the estimated brain temperature than did classical predetermined thresholding methods, although the standard deviation was wider in the former methods. PMID:21805517

Sakai, Koji; Yamada, Kei; Sugimoto, Naozo

2011-07-31

351

Nodal integral method for the neutron diffusion equation in cylindrical geometry  

SciTech Connect

The nodal methodology is based on retaining a higher a higher degree of analyticity in the process of deriving the discrete-variable equations compared to conventional numerical methods. As a result, extensive numerical testing of nodal methods developed for a wide variety of partial differential equations and comparison of the results to conventional methods have established the superior accuracy of nodal methods on coarse meshes. Moreover, these tests have shown that nodal methods are more computationally efficient than finite difference and finite-element methods in the sense that they require shorter CPU times to achieve comparable accuracy in the solutions. However, nodal formalisms and the final discrete-variable equations they produce are, in general, more complicated than their conventional counterparts. This, together with anticipated difficulties in applying the transverse-averaging procedure in curvilinear coordinates, has limited the applications of nodal methods, so far, to Cartesian geometry, and with additional approximations to hexagonal geometry. In this paper the authors report recent progress in deriving and numerically implementing a nodal integral method (NIM) for solving the neutron diffusion equation in cylindrical r-z geometry. Also, presented are comparisons of numerical solutions to two test problems with those obtained by the Exterminator-2 code, which indicate the superior accuracy of the nodal integral method solutions on much coarser meshes.

Azmy, Y.Y.

1987-01-01

352

Hybrid continuum-particle method for fluctuating lipid bilayer membranes with diffusing protein inclusions  

NASA Astrophysics Data System (ADS)

Biological membranes contain many types of embedded proteins whose collective organization and functions depend importantly on the mechanical interplay with the lipid bilayer. We introduce new methods at the level of individual proteins embedded within the bilayer in a manner closely related to the Immersed Boundary Method (Atzberger et al., 2007, [1], Peskin, 2002, [31]). Our approach accounts for the bidirectional coupling between the membranes and proteins, the elastic mechanics of the bilayer, the hydrodynamic interactions, and the thermal fluctuations. For proteins that induce curvature, we show that the bidirectional membrane-protein coupled dynamics has important consequences for the effective diffusivities of embedded proteins. We further show that collective effects arising from different area fractions and curvatures of the embedded proteins impact significantly membrane mechanics. The proposed modeling approach and computational methods are quite general and could be useful in the investigation of a wide variety of phenomena involving membrane-protein interactions.

Sigurdsson, Jon K.; Brown, Frank L. H.; Atzberger, Paul J.

2013-11-01

353

An ADI extrapolated Crank-Nicolson orthogonal spline collocation method for nonlinear reaction-diffusion systems  

NASA Astrophysics Data System (ADS)

An alternating direction implicit (ADI) orthogonal spline collocation (OSC) method is described for the approximate solution of a class of nonlinear reaction-diffusion systems. Its efficacy is demonstrated on the solution of well-known examples of such systems, specifically the Brusselator, Gray-Scott, Gierer-Meinhardt and Schnakenberg models, and comparisons are made with other numerical techniques considered in the literature. The new ADI method is based on an extrapolated Crank-Nicolson OSC method and is algebraically linear. It is efficient, requiring at each time level only O(N) operations where N is the number of unknowns. Moreover, it is shown to produce approximations which are of optimal global accuracy in various norms, and to possess superconvergence properties.

Fernandes, Ryan I.; Fairweather, Graeme

2012-08-01

354

High-order explicit-implicit numerical methods for nonlinear anomalous diffusion equations  

NASA Astrophysics Data System (ADS)

In this paper, the high-order finite difference/element methods for the nonlinear anomalous diffusion equations of subdiffusion and superdiffusion are developed, where the high-order finite difference methods are used to approximate the time-fractional derivatives and the finite element methods are used in the spatial domain. The stability and error estimates are proved for both cases of superdiffusion and subdiffusion. Numerical examples are provided to confirm the theoretical analysis. The present work was supported by the National Natural Science Foundation of China (No. 11372170), the grant of The First-class Discipline of Universities in Shanghai, the Key Program of Shanghai Municipal Education Commission (No. 12ZZ084), and the China Scholarship Council (No. 201206890032).

Zeng, F.; Li, C.; Liu, F.

2013-09-01

355

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

356

Automated counting of bacterial colony forming units on agar plates.  

PubMed

Manual counting of bacterial colony forming units (CFUs) on agar plates is laborious and error-prone. We therefore implemented a colony counting system with a novel segmentation algorithm to discriminate bacterial colonies from blood and other agar plates.A colony counter hardware was designed and a novel segmentation algorithm was written in MATLAB. In brief, pre-processing with Top-Hat-filtering to obtain a uniform background was followed by the segmentation step, during which the colony images were extracted from the blood agar and individual colonies were separated. A Bayes classifier was then applied to count the final number of bacterial colonies as some of the colonies could still be concatenated to form larger groups. To assess accuracy and performance of the colony counter, we tested automated colony counting of different agar plates with known CFU numbers of S. pneumoniae, P. aeruginosa and M. catarrhalis and showed excellent performance. PMID:22448267

Brugger, Silvio D; Baumberger, Christian; Jost, Marcel; Jenni, Werner; Brugger, Urs; Mühlemann, Kathrin

2012-03-20

357

Simultaneous measurement of the thermal conductivity and the thermal diffusivity of liquids by the transient hot-wire method  

Microsoft Academic Search

The paper describes a method and an instrument to measure the thermal conductivity and the thermal diffusivity of liquids simultaneously by the transient hot-wire method. Though the principle of this method has formerly been known, the practical application to fluids has been enabled only by high-precision measurement. In the present method, the thermal conductivity can be determined from the slope

Y. Nagasaka; A. Nagashima

1981-01-01

358

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

359

Rapid distinction between micrococci and staphylococci with furazolidone agars  

Microsoft Academic Search

Furazolidone agar proved to be a suitable medium for separating strains of the genera Micrococcus and Staphylococcus. 720 isolates (including 24 type strains) of gram- and catalase-positive cocci were tested for growth on tryptone soya and peptone agar with the addition of 50 µg\\/ml furazolidone. The results were compared with the classification obtained by the standard-O\\/F-test and by the test

K. E. yON RHEINBABEN; R. M. Hadlok

1981-01-01

360

Network-based diffusion analysis: a new method for detecting social learning  

PubMed Central

Social learning has been documented in a wide diversity of animals. In free-living animals, however, it has been difficult to discern whether animals learn socially by observing other group members or asocially by acquiring a new behaviour independently. We addressed this challenge by developing network-based diffusion analysis (NBDA), which analyses the spread of traits through animal groups and takes into account that social network structure directs social learning opportunities. NBDA fits agent-based models of social and asocial learning to the observed data using maximum-likelihood estimation. The underlying learning mechanism can then be identified using model selection based on the Akaike information criterion. We tested our method with artificially created learning data that are based on a real-world co-feeding network of macaques. NBDA is better able to discriminate between social and asocial learning in comparison with diffusion curve analysis, the main method that was previously applied in this context. NBDA thus offers a new, more reliable statistical test of learning mechanisms. In addition, it can be used to address a wide range of questions related to social learning, such as identifying behavioural strategies used by animals when deciding whom to copy.

Franz, Mathias; Nunn, Charles L.

2009-01-01

361

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

362

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. Steady or modulated illumination at several wavelengths provides the light excitation on the surface of the material to generate the SPV. A manually controlled or automatic servo system maintains a constant predetermined value of the SPV for each wavelength. A drop of a transparent electrolyte solution containing redox couples (preferably quinhydrone) having an oxidation-reduction potential (E) in the order of +0.6 to -1.65 volts couples the SPV to a measurement system. The drop of redox couple solution functions to create a liquid Schottky barrier at the surface of the material. Illumination light is passed through a transparent rod supported over the surface and through the drop of transparent electrolyte. The drop is held in the gap between the rod and the surface. Steady red light is also used as an optical bias to reduce deleterious space-charge effects that occur in amorphous silicon.

Moore, Arnold R. (Princeton, NJ)

1984-01-01

363

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. Steady or modulated illumination at several wavelengths provides the light excitation on the surface of the material to generate the SPV. A manually controlled or automatic servo system maintains a constant predetermined value of the SPV for each wavelength. A probe electrode immersed in an electrolyte solution containing redox couples (preferably quinhydrone) having an oxidation-reduction potential (E) in the order of +0.6 to -1.65 volts couples the SPV to a measurement system. The redox couple solution functions to create a liquid Schottky barrier at the surface of the material. The Schottky barrier is contacted by merely placing the probe in the solution. The redox solution is placed over and in contact with the material to be tested and light is passed through the solution to generate the SPV. To compensate for colored redox solutions a portion of the redox solution not over the material is also illuminated for determining the color compensated light intensity. Steady red light is also used as an optical bias to reduce deleterious space-charge effects that occur in amorphous silicon.

Moore, Arnold R. (Princeton, NJ)

1984-02-21

364

[The synergism of antifungals and essential oils against Candida spp. evaluated by a modified gradient-diffusion method].  

PubMed

The usefulness of modified method of MIC Test Strip, for determining the synergistic effect of essential oils in the liquid or volatile phase with fluconazole and voriconazole, was evaluated. Geranium oil used against C. albicans in agar dilution test, at a concentration of 1/2 MIC caused a drop in the value of fluconazole MIC from 12.0 mg/l to 0.064 mg/l and voriconazole from 0.125 mg/l to 0.006 mg/l. A similar effect of drug combinations with essential oils was obtained in the case of C. glabrata study. Volatile Clove oil and cytronelal, applied in subMIC concentrations, also caused a reduction offluconazole and voriconazole MICs. Thus, utility of this simple methods developed by us for testing the effectiveness of combinations of known drugs and new compounds with antifungal activity, has been confirmed. PMID:22184911

Rózalska, Barbara; Sadowska, Beata; Wieckowska-Szakiel, Marzena; Budzy?ska, Aleksandra

2011-01-01

365

One-sampling rebreathing method to measure diffusing capacity for CO.  

PubMed

To simplify the rebreathing method to obtain the pulmonary diffusing capacity for CO (DLCO), a one-sampling method was developed, combined with a simulation technique. The change in CO fraction in rebreathing air depends on the rebreathing volume (VRB), the dead space volume (VD), the gas volume in the lung-bag-system (VS) as well as the DLCO: Using the measured VRB, VD, and VS, the changes in CO fraction in bag and alveolar air were simulated by varying the DLCO, where the expired and inspired gas volumes were represented by a sinusoidal function of time. The DLCO was determined by checking the similarity between the simulated and measured CO fractions at the 7th expiratory period. To confirm the validity of the simulation method, two-sampling rebreathing and single breath methods were additionally carried out in 6 normal subjects in the sitting position. The DLCO measured by the simulation agreed well with that measured simultaneously by the two-sampling method. The DLCO measured by this method was also compatible with that obtained from the single breath method, when the dead space was excluded from the measured lung gas volume. PMID:3613279

Niizeki, K; Doi, K

1987-01-01

366

HEXPEDITE: A net current multigroup nodal diffusion method for hexagonal-z geometry  

SciTech Connect

The feasibility of a nodal diffusion algorithm for hexagonal cores was first demonstrated by Duracz and by Lawrence. They implemented a polynomial method with partial currents for internode coupling. Following them, several authors introduced variants of the expansion technique. Wagner developed an analytical method; however, like all previous authors, he still used partial currents for internode coupling and a response matrix solution approach. Very recently, another polynomial model with net currents expressed in terms of transverse-integrated fluxes and a nodal integral method based on coordinate transformations were presented. A transformation-group method was also introduced. In this paper, a hexagonal-z method similar in approach to that of the Cartesian geometry ILLICO is presented. The new method uses an analytical solution of the transverse-integrated equations, net currents for internode coupling, and a global coupling solution scheme different from that of the methods discussed earlier. An extension that treats explicitly the in-node spatial dependence of cross sections is also introduced.

Fitzpatrick, W.E. (Univ. of Illinois, Urbana (United States)); Ougouag, A.M. (Idaho National Engineering Lab., Idaho Falls (United States))

1992-01-01

367

Compact alternating direction implicit method for two-dimensional time fractional diffusion equation  

NASA Astrophysics Data System (ADS)

High-order compact finite difference scheme with operator splitting technique for solving two-dimensional time fractional diffusion equation is considered in this paper. A Grünwald-Letnikov approximation is used for the Riemann-Liouville time derivative, and the second order spatial derivatives are approximated by the compact finite differences to obtain a fully discrete implicit scheme. Alternating direction implicit (ADI) method is used to split the original problem into two separate one-dimensional problems. The local truncation error is analyzed and the stability is discussed by the Fourier method. The proposed scheme is suitable when the order of the time fractional derivative ? lies in the interval 12,1. A correction term is added to maintain high accuracy when ??0,12. Numerical results are provided to verify the accuracy and efficiency of the proposed algorithm.

Cui, Mingrong

2012-03-01

368

Diffusion Profiles of Fluorine in Archaeological Bones and Teeth. Their Use as a Possible Dating Method.  

National Technical Information Service (NTIS)

Measurements of radial fluorine profiles in bone and teeth sections with a nuclear microprobe show that the distribution is due to diffusion of fluoride ions inward from any exposed surface. Assuming simple diffusion and constant environment, the profile ...

P. H. Nelson

1984-01-01

369

A high-resolution abrasive method for determining diffusion profiles of sorbing radionuclides in dense argillaceous rocks.  

PubMed

The diffusion of (134)Cs(+) and (22)Na(+) in Opalinus Clay (OPA) was studied by in-diffusion laboratory experiments. The diffusive tracer profiles in the rock were determined using a high-resolution abrasive peeling method. The radionuclide activities in the grinding swarf were measured directly via gamma-spectrometry. By choosing the appropriate abrasive paper, a resolution down to 15 microm can be achieved. This is important when analysing strongly sorbing radionuclides such as tri- and tetravalent actinides that show steep, shallow diffusion profiles. In this study, a resolution between 20 and 90 microm was obtained which was sufficient for a good spatial resolution of the diffusion profiles. Both the effective diffusion coefficients and the distribution coefficients of the radionuclides could be determined by applying a single reservoir with decreasing source concentration analysis for a semi-infinite case. In the case of (22)Na(+), effective diffusion coefficients of D(e)=2.0 x 10(-11)m(2)s(-1) and D(e)=1.5 x 10(-11)m(2)s(-1) for Benken (Zurcher Weinland) OPA and Mont Terri OPA, respectively, were derived. The distribution coefficients were K(d)=3.1 x 10(-4) and 0.9 x 10(-4)m(3)kg(-1), respectively. For (134)Cs(+) the effective diffusion coefficients were higher, i.e. D(e)=3.1 x 10(-11)m(2)s(-1) for OPA from Benken and D(e)=3.0 x 10(-11)m(2)s(-1) for OPA from Mont Terri. The distribution coefficients determined were K(d)=0.16 m(3)kg(-1) for Benken and 0.23 m(3)kg(-1) for Mont Terri. Comparison of the data obtained for the weakly sorbing (22)Na(+) with those from earlier through-diffusion experiments showed that there is good agreement between the two methods. In the case of (134)Cs(+) such a comparison was not possible because through-diffusion data are not available. Because through-diffusion methods cannot be applied to strongly sorbing tracers in reasonable time periods, in-diffusion combined with high-resolution abrasive peeling offers an excellent alternative for measuring the diffusion properties of strongly sorbing tracers in dense argillaceous rocks. PMID:15866443

Van Loon, L R; Eikenberg, J

2005-03-21

370

Enhanced degradation of caffeine by immobilized cells of Pseudomonas sp. in agar–agar matrix using statistical approach  

Microsoft Academic Search

Previously, we isolated caffeine degrading Pseudomonas strain from soil of coffee plantation area, which could utilize caffeine as sole carbon and nitrogen source and could tolerate caffeine up to 20g\\/L. In this study, caffeine degradation by immobilized cells of this strain was investigated. Various matrices were considered and agar–agar was chosen based on degradation rate (0.08g\\/(Lh)), bead stability and reusability.

Sathyanarayana N. Gummadi; K. B. Ganesh; Devarai Santhosh

2009-01-01

371

Lattice Boltzmann methods for some 2-D nonlinear diffusion equations:Computational results  

SciTech Connect

In this paper we examine two lattice Boltzmann methods (that are a derivative of lattice gas methods) for computing solutions to two two-dimensional nonlinear diffusion equations of the form {partial derivative}/{partial derivative}t u = v ({partial derivative}/{partial derivative}x D(u){partial derivative}/{partial derivative}x u + {partial derivative}/{partial derivative}y D(u){partial derivative}/{partial derivative}y u), where u = u({rvec x},t), {rvec x} {element of} R{sup 2}, v is a constant, and D(u) is a nonlinear term that arises from a Chapman-Enskog asymptotic expansion. In particular, we provide computational evidence supporting recent results showing that the methods are second order convergent (in the L{sub 1}-norm), conservative, conditionally monotone finite difference methods. Solutions computed via the lattice Boltzmann methods are compared with those computed by other explicit, second order, conservative, monotone finite difference methods. Results are reported for both the L{sub 1}- and L{sub {infinity}}-norms.

Elton, B.H.; Rodrigue, G.H. (California Univ., Davis, CA (USA). Dept. of Applied Science Lawrence Livermore National Lab., CA (USA)); Levermore, C.D. (Arizona Univ., Tucson, AZ (USA). Dept. of Mathematics)

1990-01-01

372

A characteristic-based finite analytic method for solving the two-dimensional steady state advection-diffusion equation  

Microsoft Academic Search

This paper develops an improved finite analytic (FA) solution method to the advection-diffusion equation (ADE) for solving advection-dominated steady state transport problems. The FA method solves the ADE analytically in localized, discrete elements, with each element linked through local boundary conditions. Previous FA methods have suffered from complex solution formulations as well as from numerical dispersion stemming from inaccuracies in

Thomas Lowry; Shu-Guang Li

2002-01-01

373

A line source method for measuring the thermal conductivity and diffusivity of cylindrical specimens of rock and other poor conductors  

Microsoft Academic Search

A transient method for measuring with the same apparatus the thermal conductivity and diffusivity of a cylindrical rock specimen is described. The method involves heating the specimen by a wire placed in a shallow longitudinal saw cut. It may conveniently be used for measuring the variation of thermal properties with temperature. A complete theory of the method, including the effects

J C Jaeger; J H Sass

1964-01-01

374

Comparison and survey of finite difference methods for pricing American options under finite activity jump-diffusion models  

Microsoft Academic Search

Partial integro-differential formulations are often used for pricing American options under jump-diffusion models. A survey on such formulations and their numerical methods is presented. A detailed description of six efficient methods based on a linear complementarity formulation and finite difference discretizations is given. Numerical experiments compare the performance of these methods for pricing American put options under finite activity jump

Santtu Salmi; Jari Toivanen

2012-01-01

375

A MicroBioassay for Epilithon using Nutrient-Diffusing Artificial Substrata  

Microsoft Academic Search

A modification of the nutrient-diffusing substrata method was used to evaluate nutrient and invertebrate grazer effects on attached epilithic algae in an arctic river. An acid-cleaned porcelain or fused silica disk was melted into the opening of a small plastic, agar-filled vial, supplemented with water soluble materials. These materials were such that they would have an impact on the biomass

George G. Gibeau Jr; Michael C. Miller

1989-01-01

376

Hybrid Monte Carlo-Diffusion Method For Light Propagation in Tissue With a Low-Scattering Region  

NASA Astrophysics Data System (ADS)

The heterogeneity of the tissues in a head, especially the low-scattering cerebrospinal fluid (CSF) layer surrounding the brain has previously been shown to strongly affect light propagation in the brain. The radiosity-diffusion method, in which the light propagation in the CSF layer is assumed to obey the radiosity theory, has been employed to predict the light propagation in head models. Although the CSF layer is assumed to be a nonscattering region in the radiosity-diffusion method, fine arachnoid trabeculae cause faint scattering in the CSF layer in real heads. A novel approach, the hybrid Monte Carlo-diffusion method, is proposed to calculate the head models, including the low-scattering region in which the light propagation does not obey neither the diffusion approximation nor the radiosity theory. The light propagation in the high-scattering region is calculated by means of the diffusion approximation solved by the finite-element method and that in the low-scattering region is predicted by the Monte Carlo method. The intensity and mean time of flight of the detected light for the head model with a low-scattering CSF layer calculated by the hybrid method agreed well with those by the Monte Carlo method, whereas the results calculated by means of the diffusion approximation included considerable error caused by the effect of the CSF layer. In the hybrid method, the time-consuming Monte Carlo calculation is employed only for the thin CSF layer, and hence, the computation time of the hybrid method is dramatically shorter than that of the Monte Carlo method.

Hayashi, Toshiyuki; Kashio, Yoshihiko; Okada, Eiji

2003-06-01

377

Hybrid Monte Carlo-diffusion method for light propagation in tissue with a low-scattering region.  

PubMed

The heterogeneity of the tissues in a head, especially the low-scattering cerebrospinal fluid (CSF) layer surrounding the brain has previously been shown to strongly affect light propagation in the brain. The radiosity-diffusion method, in which the light propagation in the CSF layer is assumed to obey the radiosity theory, has been employed to predict the light propagation in head models. Although the CSF layer is assumed to be a nonscattering region in the radiosity-diffusion method, fine arachnoid trabeculae cause faint scattering in the CSF layer in real heads. A novel approach, the hybrid Monte Carlo-diffusion method, is proposed to calculate the head models, including the low-scattering region in which the light propagation does not obey neither the diffusion approximation nor the radiosity theory. The light propagation in the high-scattering region is calculated by means of the diffusion approximation solved by the finite-element method and that in the low-scattering region is predicted by the Monte Carlo method. The intensity and mean time of flight of the detected light for the head model with a low-scattering CSF layer calculated by the hybrid method agreed well with those by the Monte Carlo method, whereas the results calculated by means of the diffusion approximation included considerable error caused by the effect of the CSF layer. In the hybrid method, the time-consuming Monte Carlo calculation is employed only for the thin CSF layer, and hence, the computation time of the hybrid method is dramatically shorter than that of the Monte Carlo method. PMID:12790437

Hayashi, Toshiyuki; Kashio, Yoshihiko; Okada, Eiji

2003-06-01

378

Optimisation of the formulation of ?-carotene loaded nanostructured lipid carriers prepared by solvent diffusion method.  

PubMed

In this study, the optimised ?-carotene loaded nanostructured lipid carriers (NLC) were prepared using the solvent diffusion method. Response surface methodology (RSM) was employed in conjunction with a central composite design (CCD) to evaluate the effect of the preparation variables on particle size and ?-carotene stability to optimise the NLC formulation. Quadratic polynomial was the best fitted mathematical model for the experimental results. The statistical evaluations revealed that the lipid phase concentration and the surfactant concentration had significant effect on particle size of NLC. In addition, the influence of the liquid lipid to total lipid ratio and temperature on ?-carotene degradation was more important. The optimum formulations with minimum particle size (8-15 nm) and low ?-carotene degradation (0-3%) were derived from the fitted models and were experimentally examined which demonstrated a reasonable agreement between experimental and predicted values. Transition electron microscopy (TEM) observations exhibited spherical morphology of ?-carotene loaded NLC. PMID:23768336

Hejri, Abdolrasoul; Khosravi, Alireza; Gharanjig, Kamaladin; Hejazi, Mohammadamin

2013-03-07

379

New Chromogenic Agar Medium for the Identification of Candida spp.  

PubMed Central

A new chromogenic agar medium (Candida diagnostic agar [CDA]) for differentiation of Candida spp. is described. This medium is based on Sabouraud dextrose agar (Oxoid CM41) and contains (per liter) 40.0 g of glucose, 10.0 g of mycological peptone, and 15.0 g of agar along with a novel chromogenic glucosaminidase substrate, ammonium 4-{2-[4-(2-acetamido-2-deoxy-?-d-glucopyranosyloxy)-3-methoxyphenyl]-vinyl}-1-(propan-3-yl-oate)-quinolium bromide (0.32 g liter?1). The glucosaminidase substrate in CDA was hydrolyzed by Candida albicans and Candida dubliniensis, yielding white colonies with deep-red spots on a yellow transparent background after 24 to 48 h of incubation at 37°C. Colonies of Candida tropicalis and Candida kefyr were uniformly pink, and colonies of other Candida spp., including Candida glabrata and Candida parapsilosis, were white. CDA was evaluated by using 115 test strains of Candida spp. and other clinically important yeasts and was compared with two commercially available chromogenic agars (Candida ID agar [bioMerieux] and CHROMagar Candida [CHROMagar Company Ltd.]). On all three agars, colonies of C. albicans were not distinguished from colonies of C. dubliniensis. However, for the group containing C. albicans plus C. dubliniensis, both the sensitivity and the specificity of detection when CDA was used were 100%, compared with values of 97.6 and 100%, respectively, with CHROMagar Candida and 100 and 96.8%, respectively, with Candida ID agar. In addition, for the group containing C. tropicalis plus C. kefyr, the sensitivity and specificity of detection when CDA was used were also 100%, compared with 72.7 and 98.1%, respectively, with CHROMagar Candida. Candida ID agar did not differentiate C. tropicalis and C. kefyr strains but did differentiate members of a broader group (C. tropicalis, C. kefyr, Candida lusitaniae plus Candida guilliermondii); the sensitivity and specificity of detection for members of this group were 94.7 and 93.8%, respectively. In addition to the increased sensitivity and/or specificity of Candida detection when CDA was used, differentiation of colony types on CDA (red spotted, pink, or no color) was unambiguous and did not require precise assessment of colony color.

Cooke, Venitia M.; Miles, R. J.; Price, R. G.; Midgley, G.; Khamri, W.; Richardson, A. C.

2002-01-01

380

Modeling diffusion and phase transitions by a uniform-acceptance force-bias Monte Carlo method  

NASA Astrophysics Data System (ADS)

The uniform-acceptance force-bias Monte Carlo (UFMC) method [G. Dereli, Mol. Simul. 8, 351 (1992)] is a little-used atomistic simulation method that has strong potential as alternative or complementary technique to molecular dynamics (MD). We have applied UFMC to surface diffusion, amorphization, melting, glass transition, and crystallization, mainly of silicon. The purpose is to study the potential and the limitations of the method: to investigate its applicability, determine safe and effective values of the two UFMC parameters—a temperature and a maximum allowed atomic displacement per iteration step—that lead to reliable results for different types of simulations, assess the computational speed increase relative to MD, discover the microscopic mechanisms that make UFMC work, and show in what kind of simulations it can be useful and preferable over MD. It is found that in many simulations, UFMC can be a very efficient alternative to MD: it leads to analogous results in much fewer iteration steps. Due to the straightforward formalism of UFMC, it can be easily implemented in any MD code. Thus both methods can be combined and applied in turn, using UFMC for the acceleration of certain processes and MD for keeping precision and monitoring individual atom trajectories.

Timonova, Maria; Groenewegen, Jasper; Thijsse, Barend J.

2010-04-01

381

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

382

Data evaluation of laminar flow diffusion chamber nucleation experiments with different computational methods  

NASA Astrophysics Data System (ADS)

In order to evaluate the experimental data from laminar flow diffusion chamber (LFDC) experiments on homogeneous nucleation, an extensive postmeasurement computational analysis is required. The present work investigates the influence of the used computational methodology on the derived nucleation curves. To this end a reanalysis is made of previous LFDC experiments of 1-butanol nucleation in helium [D. Brus et al., J. Chem. Phys. 122, 214506 (2005)] using two different methods. The first method is based on single fluid heat and vapor transport in the carrier gas ignoring the aerosol processes, as commonly made in LFDC data evaluations. The second method is more comprehensive as is based on multidimensional computational fluid-particle dynamics. The calculations are made under the usual simplification of one-way coupling between fluid flow and particles, which is a valid approximation in most practical aerosols, while full aerosol dynamical effects are accommodated. Similar results were produced by the two methods. This finding corroborates the usual practice of omitting aerosol calculations in LFDC experimental data evaluation.

Mitrakos, D.; Ždímal, V.; Brus, D.; Housiadas, C.

2008-08-01

383

Development of an efficient multigrid method for the NEM form of the multigroup neutron diffusion equation  

NASA Astrophysics Data System (ADS)

Development of an improvement to the computational efficiency of the existing nested iterative solution strategy of the Nodal Exapansion Method (NEM) nodal based neutron diffusion code NESTLE is presented. The improvement in the solution strategy is the result of developing a multilevel acceleration scheme that does not suffer from the numerical stalling associated with a number of iterative solution methods. The acceleration scheme is based on the multigrid method, which is specifically adapted for incorporation into the NEM nonlinear iterative strategy. This scheme optimizes the computational interplay between the spatial discretization and the NEM nonlinear iterative solution process through the use of the multigrid method. The combination of the NEM nodal method, calculation of the homogenized, neutron nodal balance coefficients (i.e. restriction operator), efficient underlying smoothing algorithm (power method of NESTLE), and the finer mesh reconstruction algorithm (i.e. prolongation operator), all operating on a sequence of coarser spatial nodes, constitutes the multilevel acceleration scheme employed in this research. Two implementations of the multigrid method into the NESTLE code were examined; the Imbedded NEM Strategy and the Imbedded CMFD Strategy. The main difference in implementation between the two methods is that in the Imbedded NEM Strategy, the NEM solution is required at every MG level. Numerical tests have shown that the Imbedded NEM Strategy suffers from divergence at coarse- grid levels, hence all the results for the different benchmarks presented here were obtained using the Imbedded CMFD Strategy. The novelties in the developed MG method are as follows: the formulation of the restriction and prolongation operators, and the selection of the relaxation method. The restriction operator utilizes a variation of the reactor physics, consistent homogenization technique. The prolongation operator is based upon a variant of the pin power reconstruction methodology. The relaxation method, which is the power method, utilizes a constant coefficient matrix within the NEM non-linear iterative strategy. The choice of the MG nesting within the nested iterative strategy enables the incorporation of other non-linear effects with no additional coding effort. In addition, if an eigenvalue problem is being solved, it remains an eigenvalue problem at all grid levels, simplifying coding implementation. The merit of the developed MG method was tested by incorporating it into the NESTLE iterative solver, and employing it to solve four different benchmark problems. In addition to the base cases, three different sensitivity studies are performed, examining the effects of number of MG levels, homogenized coupling coefficients correction (i.e. restriction operator), and fine-mesh reconstruction algorithm (i.e. prolongation operator). The multilevel acceleration scheme developed in this research provides the foundation for developing adaptive multilevel acceleration methods for steady-state and transient NEM nodal neutron diffusion equations. (Abstract shortened by UMI.)

Al-Chalabi, Rifat M. Khalil

1997-09-01

384

A 1-D analytical method for estimating surface water-groundwater interactions and effective thermal diffusivity using temperature time series  

NASA Astrophysics Data System (ADS)

In order to manage surface water (SW) and groundwater (GW) as a single resource, it is necessary that the interactions between them are understood and quantified. Heat, as a natural tracer of water movement, is increasingly being used for this purpose. However, analytical methods that are commonly used are limited by uncertainties in the effective thermal diffusivity of the sediments at the SW-GW interface. We present a novel 1-D analytical method. It utilizes both the amplitude ratio and phase shift of pairs of temperature time series at the SW-GW interface to estimate the Darcy velocity. This eliminates both the need to specify a value for effective thermal diffusivity and the need for iteration. The method also allows for an estimation of effective thermal diffusivity, which can indicate periods where assumptions to the analytical solution are violated. Riverbed temperature data from the Murray Darling Basin (Australia) are used to illustrate the method.

McCallum, A. M.; Andersen, M. S.; Rau, G. C.; Acworth, R. I.

2012-11-01

385

High-order compact exponential finite difference methods for convection diffusion type problems  

NASA Astrophysics Data System (ADS)

A class of high-order compact (HOC) exponential finite difference (FD) methods is proposed for solving one- and two-dimensional steady-state convection diffusion problems. The newly proposed HOC exponential FD schemes have nonoscillation property and yield high accuracy approximation solution as well as are suitable for convection-dominated problems. The O(h4) compact exponential FD schemes developed for the one-dimensional (1D) problems produce diagonally dominant tri-diagonal system of equations which can be solved by applying the tridiagonal Thomas algorithm. For the two-dimensional (2D) problems, O(h4 + k4) compact exponential FD schemes are formulated on the nine-point 2D stencil and the line iterative approach with alternating direction implicit (ADI) procedure enables us to deal with diagonally dominant tridiagonal matrix equations which can be solved by application of the one-dimensional tridiagonal Thomas algorithm with a considerable saving in computing time. To validate the present HOC exponential FD methods, three linear and nonlinear problems, mostly with boundary or internal layers where sharp gradients may appear due to high Peclet or Reynolds numbers, are numerically solved. Comparisons are made between analytical solutions and numerical results for the currently proposed HOC exponential FD methods and some previously published HOC methods. The present HOC exponential FD methods produce excellent results for all test problems. It is shown that, besides including the excellent performances in computational accuracy, efficiency and stability, the present method has the advantage of better scale resolution. The method developed in this article is easy to implement and has been applied to obtain the numerical solutions of the lid driven cavity flow problem governed by the 2D incompressible Navier Stokes equations using the stream function-vorticity formulation.

Tian, Z. F.; Dai, S. Q.

2007-01-01

386

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

387

Examination of methods to determine free-ion diffusivity and number density from analysis of electrode polarization.  

PubMed

Electrode polarization analysis is frequently used to determine free-ion diffusivity and number density in ionic conductors. In the present study, this approach is critically examined in a wide variety of electrolytes, including aqueous and nonaqueous solutions, polymer electrolytes, and ionic liquids. It is shown that the electrode polarization analysis based on the Macdonald-Trukhan model [J. Chem. Phys. 124, 144903 (2006); J. Non-Cryst. Solids 357, 3064 (2011)] progressively fails to give reasonable values of free-ion diffusivity and number density with increasing salt concentration. This should be expected because the original model of electrode polarization is designed for dilute electrolytes. An empirical correction method which yields ion diffusivities in reasonable agreement with pulsed-field gradient nuclear magnetic resonance measurements is proposed. However, the analysis of free-ion diffusivity and number density from electrode polarization should still be exercised with great caution because there is no solid theoretical justification for the proposed corrections. PMID:23679415

Wang, Yangyang; Sun, Che-Nan; Fan, Fei; Sangoro, Joshua R; Berman, Marc B; Greenbaum, Steve G; Zawodzinski, Thomas A; Sokolov, Alexei P

2013-04-18

388

Mathematical basis for the measurement of absolute and fractional cardiac output with diffusible tracers by compartmental analysis methods  

SciTech Connect

Using compartmental analysis methods, a mathematical basis is given for the measurement of absolute and fractional cardiac output with diffusible tracers. Cardiac output is shown to be the product of the blood volume and the sum of the rate constants of tracer egress from blood, modified by a factor reflecting transcapillary diffusibility, the transfer fraction. The return of tracer to the blood and distant (intracellular) events are shown to play no role in the solution. Fractional cardiac output is the ratio of the rate constant of tracer egress from blood to an organ, divided by the sum of the egress constants from blood. Predominantly extracellular ions such as sodium or bromide are best suited for this technique, although theoretically any diffusible tracer whose compartmental model can be solved may be used. It is shown that fractional cardiac output is independent of the transfer fraction, and therefore can be measured accurately by tracers which are not freely diffusible.

Charkes, N.D.

1984-10-01

389

The radial diffusion method 1. Using intact cores to determine isotopic composition, chemistry, and effective porosities for groundwater in aquitards  

Microsoft Academic Search

A new method is described for the determination of the isotopic composition and chemistry of groundwater in aquitards. The effective porosities for each component can be determined concurrently. The method is based on diffusive exchange of water and solutes between groundwater in a cylindrical core of aquitard material and water in a reservoir placed along the axis of the cylinder.

G. van der Kamp; D. R. Van Stempvoort; L. I. Wassenaar

1996-01-01

390

The radial diffusion method .1. Using intact cores to determine isotopic composition, chemistry, and effective porosities for groundwater in aquitards  

Microsoft Academic Search

A new method is described for the determination of the isotopic composition and chemistry of groundwater in aquitards. The effective porosities for each component can be determined concurrently. The method is based on diffusive exchange of water and solutes between groundwater in a cylindrical core of aquitard material and water in a reservoir placed along the axis of the cylinder.

G. vanderKamp; D. R. vanStempvoort; L. I. Wassenaar

1996-01-01

391

The Radial Diffusion Method: 1. Using intact cores to determine isotopic composition, chemistry, and effective porosities for groundwater in aquitards  

Microsoft Academic Search

A new method is described for the determination of the isotopic composition and chemistry of groundwater in aquitards. The effective porosities for each component can be determined concurrently. The method is based on diffusive exchange of water and solutes between groundwater in a cylindrical core of aquitard material and water in a reservoir placed along the axis of the cylinder.

G. van der Kamp; D. R. Van Stempvoort; L. I. Wassenaar

1996-01-01

392

A simple and green analytical method for determination of glyphosate in commercial formulations and water by diffuse reflectance spectroscopy  

Microsoft Academic Search

This article describes a simple, inexpensive, and environmentally friendly method for the monitoring of glyphosate using diffuse reflectance spectroscopy. The proposed method is based on reflectance measurements of the colored compound produced from the spot test reaction between glyphosate and p-dimethylaminocinnamaldehyde (p-DAC) in acid medium, using a filter paper as solid support. Experimental designs were used to optimize the analytical

Aline Santana da Silva; Flávio Cesar Bedatty Fernandes; João Olímpio Tognolli; Leonardo Pezza; Helena Redigolo Pezza

2011-01-01

393

A method for measuring internal diffusion and equilibrium partition coefficients of volatile organic compounds for building materials  

Microsoft Academic Search

An experimental method for the determination of the internal diffusion coefficient (D) and partition coefficient (ke) of volatile organic compounds (VOCs) is developed for dry building materials (such as carpet, vinyl flooring, plywood, etc.). The method is used to determine D and ke for four VOCs (toluene, nonane, decane, and undecane ) through the backing material of a carpet specimen,

A. Bodalal; J. S. Zhang; E. G. Plett

2000-01-01

394

Simultaneous measurement of the thermal conductivity and thermal diffusivity of unconsolidated materials by the transient hot wire method  

Microsoft Academic Search

This paper describes a new design for the transient hot wire method that can obtain the thermal conductivity and thermal diffusivity of unconsolidated materials. In this method, the thermal conductivity is determined from the slope of the temperature rise versus time of an electrically heated wire. The temperature rise is detected as the unbalanced voltage of a precision Wheatstone bridge.

Greg C. Glatzmaier; W. Fred Ramirez

1985-01-01

395

Diffusion Tensor Imaging Biomarkers for Traumatic Axonal Injury: Analysis of Three Analytic Methods  

PubMed Central

Traumatic axonal injury (TAI) is a common mechanism of traumatic brain injury not readily identified using conventional neuroimaging modalities. Novel imaging modalities such as diffusion tensor imaging (DTI) can detect microstructural compromise in white matter (WM) in various clinical populations including TAI. DTI-derived data can be analyzed using global methods (i.e., WM histogram or voxel based approaches) or a regional approach (i.e., tractography). While each of these methods produce qualitatively comparable results, it is not clear which is most useful in clinical research and ultimately in clinical practice. This study compared three methods of analyzing DTI-derived data with regard to detection of WM injury and their association with clinical outcomes. Thirty patients with TAI and 19 demographically similar normal controls were scanned using a 3T magnet. Patients were scanned approximately eight months post-injury, and underwent an outcomes assessment at that time. Histogram analysis of FA and MD showed global WM integrity differences between patients and controls. Voxel-based and tractography analyses showed significant decreases in FA within centroaxial structures involved in TAI. All three techniques were associated with functional and cognitive outcomes. DTI measures of microstructural integrity appear robust, as the three analysis techniques studied showed adequate utility for detecting WM injury.

Marquez de la Plata, Carlos D.; Yang, Fanpei Gloria; Paliotta, Chris; Wang, Jun Yi; Krishnan, Kamini; Bakhadirov, Khamid; Aslan, Sina; Devous, Michael D.; Moore, Carol; Harper, Caryn; McColl, Roderick; Cullum, C. Munro; Diaz-Arrastia, Ramon

2011-01-01

396

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

NASA Astrophysics Data System (ADS)

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 this, allowing an automatic scanning of the whole frontier, the registration of data and computation. These surface temperatures constitute the boundary conditions of the heat equation solved in the domain of interest. The solution of the heat equation allows analyzing and controlling the temperature of every point belonging to the considered domain. This temperature distribution is controlled over the time with a period of the same order than the necessary time to obtain the frontier temperatures and at the end to contribute to the analysis of the thermal comfort. The study is done for the steady-state conditions under various weather situations. In this case the temperature depends only on space coordinates. With such procedure, we can have an idea about the time necessary to reach thermal equilibrium; time which has a great impact on the thermal comfort sensation. The results yielded by this method are compared with those given by others techniques used for temperature measurement. Finally, the method is used to access 3D temperature distribution for various geometric shapes.

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

2011-05-01

397

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

2011-02-03

398

Validation of the Delvotest SP NT. Performance Tested Methods(SM) 011102.  

PubMed

Delvotest SP NT is designed to test milk for the presence of antibacterial substances such as antibiotics. The test is made of an agar gel containing bacterial spores and a pH indicator. The milk sample is added onto the agar gel, and the test is placed for incubation at 64 degrees C. The principle of the test is based on the diffusion of possible inhibitory substances that may be present in the milk sample into the agar. This reduces growth and acid production by the test organism and delays or prevents the agar from changing color from purple to yellow. The present report includes all technical details about the Delvotest SP NT and the results of the validation study. The validation study demonstrates that the Delvotest SP NT conforms to the product performance claims and confirms the robustness of the test. The Delvotest SP NT is therefore granted Performance Tested Method(SM) certification. PMID:23451401

Hennart, Stephen L A; Faragher, John

399

Mean apparent propagator (MAP) MRI: a novel diffusion imaging method for mapping tissue microstructure.  

PubMed

Diffusion-weighted magnetic resonance (MR) signals reflect information about underlying tissue microstructure and cytoarchitecture. We propose a quantitative, efficient, and robust mathematical and physical framework for representing diffusion-weighted MR imaging (MRI) data obtained in "q-space," and the corresponding "mean apparent propagator (MAP)" describing molecular displacements in "r-space." We also define and map novel quantitative descriptors of diffusion that can be computed robustly using this MAP-MRI framework. We describe efficient analytical representation of the three-dimensional q-space MR signal in a series expansion of basis functions that accurately describes diffusion in many complex geometries. The lowest order term in this expansion contains a diffusion tensor that characterizes the Gaussian displacement distribution, equivalent to diffusion tensor MRI (DTI). Inclusion of higher order terms enables the reconstruction of the true average propagator whose projection onto the unit "displacement" sphere provides an orientational distribution function (ODF) that contains only the orientational dependence of the diffusion process. The representation characterizes novel features of diffusion anisotropy and the non-Gaussian character of the three-dimensional diffusion process. Other important measures this representation provides include the return-to-the-origin probability (RTOP), and its variants for diffusion in one- and two-dimensions-the return-to-the-plane probability (RTPP), and the return-to-the-axis probability (RTAP), respectively. These zero net displacement probabilities measure the mean compartment (pore) volume and cross-sectional area in distributions of isolated pores irrespective of the pore shape. MAP-MRI represents a new comprehensive framework to model the three-dimensional q-space signal and transform it into diffusion propagators. Experiments on an excised marmoset brain specimen demonstrate that MAP-MRI provides several novel, quantifiable parameters that capture previously obscured intrinsic features of nervous tissue microstructure. This should prove helpful for investigating the functional organization of normal and pathologic nervous tissue. PMID:23587694

Özarslan, Evren; Koay, Cheng Guan; Shepherd, Timothy M; Komlosh, Michal E; ?rfano?lu, M Okan; Pierpaoli, Carlo; Basser, Peter J

2013-04-13

400

Three-dimensional nodal diffusion and transport methods for the analysis of fast-reactor critical experiments  

SciTech Connect

This paper describes two new nodal methods for solving the multigroup neutron diffusion and transport equations in three-dimensional Cartesian geometry. These methods have been developed for the global analysis of fast-reactor critical experiments once cell-averaged multigroup cross sections for each matrix position or drawer have been computed using appropriate cell-homogenization procedures. Brief descriptions of the nodal diffusion and transport schemes are presented, along with results of two- and three-dimensional calculations for a current Zero Power Plutonium Reactor (ZPPR) configuration.

Lawrence, R.D.

1984-01-01

401

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

2013-10-01

402

Low-Temperature Thermal Diffusivity Measurement by Laser-Flash Method  

NASA Astrophysics Data System (ADS)

The pulse heating method has been developed for measuring the thermal diffusivity of solids at low temperatures. The experimental procedures were such that the front surface of a disk-shaped specimen was irradiated by a ruby-laser pulse (pulse width<1 msec), and the time variation of the temperature at the rear surface was detected by thin-film bolometers (sputtered gold film at higher temperatures and painted carbon film at lower temperatures) and was recorded by a sensitive high-speed electronic apparatus. The measurements were made at temperatures between 300 and 4.2 K, and the specimen used were polyethylene (60% crystallinity). The method to analyze the experimental data was precisely described. It was shown that the finite pulse-time effect could be ignored due to the short duration of the laser pulse, and that the consideration should be made on the heat loss from the specimen to its surroundings through the heat conduction, and also that an adequate choice of the bolometers was important especially at lower temperatures.

Kogure, Yoshiaki; Mugishima, Toshio; Hiki, Yosio

1986-10-01

403

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)

1997-03-01

404

Comparison of screening methods to identify methicillin-resistant Staphylococcus aureus  

Microsoft Academic Search

Screening methods to identify methicillin-resistantStaphylococcus aureus (MRSA) were compared using 96 isolates representing 17 distinct clones. The sensitivity of four commercial agglutination tests was determined in comparison to the tube coagulation test, and the results related to the presence of the coagulase gene. The broth screening test, agar dilution test and disc diffusion test were carried out, and the results

G. Kampf; K. Weist; S. Swidsinski; M. Kegel; H. Rtiden

1997-01-01

405

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

406

Preenrichment versus direct selective agar plating for the detection of Salmonella Enteritidis in shell eggs.  

PubMed

The relative effectiveness of two methods for the recovery of Salmonella Enteritidis (SE) from jumbo and medium shell eggs was compared. The first method used in the comparison consisted of a preenrichment of the sample, and the second method was developed by the U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS). Three bulk lots of blended, pooled eggs, each containing 220 liquid whole eggs that were thoroughly mixed manually were artificially inoculated with different levels of SE cells between approximately 10(0) and 10(3) CFU/ml. Twenty samples containing the contents of approximately 10 eggs each (by weight) were withdrawn from each of the inoculated bulk lots and incubated for 4 days at room temperature (ca. 23 degrees C). For the APHIS method, each sample was cultured by direct plating onto brilliant green (BG), brilliant green with novobiocin (BGN), xylose lysine desoxycholate (XLD), and xylose lysine agar Tergitol 4 (XLT4) agars. For the preenrichment method, 25-g portions from each pool were enriched in modified tryptic soy broth with 30 mg/liter of FeSO4. After 24 h of incubation, the preenrichments were subcultured to tetrathionate and Rappaport-Vassiliadis broths, and streaked to BG, BGN, bismuth sulfite, XLD, and XLT4 agar plates. SE isolates were confirmed biochemically and serologically. In all of the experiments, the preenrichment method recovered significantly more SE isolates (P < 0.05) of all the phage types and inoculum levels than did the APHIS method. From a total of 539 jumbo egg test portions analyzed, 381 (71%) were SE-positive by the preenrichment method and 232 (43%) were positive by the APHIS method. From a total of 360 medium egg test portions analyzed, 223 (62%) were SE-positive by the preenrichment method and 174 (48%) were positive by the APHIS method. The preenrichment method provided greater sensitivity for the isolation of SE in contaminated egg slurries than did the APHIS method. PMID:14503723

Valentín-Bon, I E; Brackett, R E; Seo, K H; Hammack, T S; Andrews, W H

2003-09-01

407

Comparison of the rheological and diffusion properties of some gelling agents and blends and their effects on shoot multiplication  

Microsoft Academic Search

The rheological and diffusion properties of blends of agar\\/guar gum, agar\\/Phytagel and Phytagel\\/guar gum were analysed and\\u000a compared to those properties of agar or Phytagel applied alone at two different gelling concentrations. Moreover, their effects\\u000a on the shoot multiplication of the apple scion Galaxy and two black locust clones (SF63, SF82) were studied, and their cost\\u000a benefits over agar were

Judit Dobránszki; Katalin Magyar-Tábori; Etelka Tombácz

408

Measurement of diffusion coefficient of tritium in alpha-phase of zirconium based on glow discharge implantation method  

SciTech Connect

A tritium implantation method based on a glow discharge of tritium gas was applied to the measurement of diffusion coefficient of tritium in alpha-phase of zirconium. The diffusion experiment was carried out in a temperature region from 673 K to 873K, and the diffusion coefficient of tritium was determined as follows, D / (cm{sup 2}/s) = 3.14x10{sup -3} exp (-42.7 RT / (kJ / mol)). The present data were in good agreement with our previous data, which were determined with an usual implantation method based on a nuclear reaction{sup 6}Li(n,{alpha})T. 12 refs., 2 figs., 1 tab.

Hashizume, Ken-ichi; Hatano, Yuji; Sakamoto, Kan; Sugisaki, Masayasu [Kyushu Univ., Fukuoka (Japan)

1995-10-01

409

A simple measurement of the Ni-63 diffusion profiles by residual activity method using a liquid scintillation counter  

NASA Astrophysics Data System (ADS)

A simple and sensitive technique based on a solid scintillator in place of the commonly used liquid scintillation (LS) cocktail has been developed to measure the low-energy surface radioactivity with the LS counter. As a test case, the method was applied to the successful determination of the nickel-63 self-diffusion profile in commercial purity nickel by means of the Gruzin?s residual activity method. On the same sample, the additional three methods of diffusion profile determination were used to compare with the proposed new method: (i) proportional counter activity detection, (ii) serial sectioning method and (iii) an integral sample measurement in LS cocktail. In conclusion, the strong and weak points are discussed for each method.

Rothová, V?ra

2013-11-01

410

Plating of isolated tobacco mesophyll protoplasts on agar medium  

Microsoft Academic Search

A technique was developed to derive cell and plant clones from isolated mesophyll protoplasts of tobacco. The protoplasts, plated on a fully defined agar medium, divided and grew actively forming visible colonies after one month of culture. Efficiency of colony formation depended on cell density and light condition during incubation. Under standard conditions, 60% of plated protoplasts formed colonies. Upon

Toshiyuki Nagata; Itaru Takebe

1971-01-01

411

Specific Identification of Fraction I-Positive Pasteurella pestis Colonies on Antiserum-Agar Plates  

PubMed Central

A method is described for the use of antiplague serum in Blood Agar Base plating media to detect fraction I-positive Pasteurella pestis. The antiserum was produced conveniently and in large volume in rabbits by use of Cutter plague vaccine combined with Freund's complete adjuvant. P. pestis colonies were specifically identified within 48 hr after plating by the presence of a precipitin ring surrounding each colony. The basis of the test was shown to be a precipitin reaction between fraction I antigen released from P. pestis colonies after chloroform vapor treatment and fraction I antibody present in the antiserum-agar medium. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5

Albizo, Johnnie M.; Surgalla, Michael J.

1968-01-01

412

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

2013-07-10

413

Testing the quality of magnetic gradient fields for studying self-diffusion processes by magnetic resonance methods  

NASA Astrophysics Data System (ADS)

Imaging techniques based on the principle of nuclear magnetic resonance (NMR) rank with the most advanced methods for studying chemical and biological properties of substances. Their universality makes them particularly suitable for use in a wide range of scientific branches. NMR has found significant application in medicine. The diffusion effects of water molecules in tissues reduce the magnitude of spin echo in NMR measuring methods. Based on the amplitude change in the image, the diffusion coefficients and their distribution in the specimen being measured can be calculated. MR images of an object weighted by diffusion coefficients require a defined sequence of gradient pulses and accurate knowledge of their time behaviour. Methods for measuring the diffusion coefficients require knowledge of the minimum length of leading and trailing edges, the defined magnitude of the magnetic field gradient being excited and also the symmetry of positive and negative gradient pulses (the zero integral of pulses of the same magnitude with opposite polarity). To determine the above characteristics of the time behaviour of gradient pulses of both polarities a simple measuring method was developed and experimentally tested on a tomograph with 4.7 T induction of the basic magnetic field. This method is based on the principle of measuring the instantaneous frequency of the MR signal in the presence of a gradient pulse subsequent to exciting a thin defined layer of the specimen under examination outside the gradient field centre.

Bartusek, Karel; Gescheidtova, Eva

2006-08-01

414

[Comparison of disk-diffusion method and PCR for detection of methicillin resistance in Staphylococcus aureus strains].  

PubMed

The aim of the study was to compare the disk-diffusion (oxacillin 1 microg, cefoxitin 30 microg) method and PCR for detection of methicillin-resistance in S. aureus. The investigation were carried out on 120 S. aureus strains isolated from clinical materials of patients hospitalized in the University Hospital at the L. Rydygier Collegium Medicum in Bydgoszcz, University of Nicolaus Copernicus in Toru?. Of the 120 S. aureus strains tested, 60 (50%) were mecA-positive by PCR. Consistency of results between oxacillin disk-difussion method and PCR amounted 92.5% and cefoxitin disk-diffusion method and PCR--98.3%. The oxacillin disk-difussion method falsely identified 3 (2.5%) strains as MSSA (sensitivity 95.0%) and 4 strains as MRSA (specificity 93.3%) in comparison with PCR. The cefoxitin disk-diffusion method falsely identified 2 (1.6%) strains as MSSA (sensitivity 96.7%) and there were no false resistant results (specificity 100%). Our results showed that in disk-diffusion tests, cefoxitin is a better than oxacillin for the identification of MRSA. PMID:17133901

Kaczmarek, Agnieszka; Budzy?ska, Anna; Miko?ajczyk, Dorota; Gospodarek, Eugenia

2006-01-01

415

Fabrication of microlens array diffuser films with controllable haze distribution by combination of breath figures and replica molding methods.  

PubMed

This work demonstrates the fabrication of a simple, low-cost microlens array (MLA) diffuser film with controllable haze distribution (diffusion effect) by a combination of "breath figures" (BFs) and micro-replica molding methods. Polystyrene (PS) molds obtained by BFs method contain concave, hexagonal packed air holes formed by the condensation of water vapor on cooling surfaces in a chamber in which relevant influence factors can be controlled. The sizes of the air holes in the BFs PS molds can be controlled by varying such factors as chamber temperature, chamber relative humidity, substrate temperature and others. The temperature distribution on the substrate affects the distribution of diameters of the air holes formed in a BFs PS mold. Convex PDMS (poly-dimethylsiloxane) MLAs were obtained by molding from the BFs PS molds. The focal lengths of MLAs were measured and compared with theoretical values. The diffusion effect of the diffuser films with MLAs of diameters 6 microm and 3 microm were compared. The results indicate that an MLA with a smaller diameter has a larger diffusion effect. PMID:19030084

Wu, Cheng Yi; Chiang, Ting Hsuan; Hsu, Chia Chen

2008-11-24

416

Inversion of diffusive transient electromagnetic data by a conjugate-gradient method  

NASA Astrophysics Data System (ADS)

Inversion of three-dimensional transient electromagnetic (TEM) data to obtain electrical conductivity and permeability can be done by a time-domain algorithm that extends to diffusive electromagnetic (EM) fields the imaging methods originally developed for seismic wavefields (Claerbout, 1971; Tarantola, 1984). The algorithm uses a conjugate-gradient search for the minimum of an error functional involving EM measurements governed by Maxwell's equations without displacement currents. The connection with wavefield imaging comes from showing that the gradient of the error functional can be computed by propagating the errors back into the model in reverse time and correlating the field generated by the backpropagation with the incident field at each point. These two steps (backpropagation and cross correlation) are the same ones used in seismic migration. The backpropagated TEM fields satisfy the adjoint Maxwell's equations, which are stable in reverse time. With magnetic field measurements the gradient of the error functional with respect to conductivity is the cross correlation of the backpropagated electric field with the incident electric field, whereas the gradient with respect to permeability is the cross correlation of the backpropagated magnetic field with the time derivative of the incident magnetic field. Tests on two-dimensional models simulating crosswell TEM surveys produce good images of a conductive block scatterer, with both exact and noisy data, and of a dipping conductive layer. Convergence, however, is slow.

Wang, Tsili; Oristaglio, Michael; Tripp, Alan; Hohmann, Gerald

1994-07-01

417

Continuous measurement of nitrous acid (HONO) in indoor environment using a diffusion scrubber and chemiluminescence method  

NASA Astrophysics Data System (ADS)

Recent study has demonstrated that the use of combustion appliances in indoor environments, e.g., gas stoves and heaters, results in significant concentrations of NO2 and nitrous acid (HONO). Indoor HONO is formed by both direct emissions from combustion processes and the heterogeneous reaction of NO2 with water vapor on surfaces present indoors. In this study in-situ instrument was constructed for measuring HONO concentration in both indoor and outdoor environments, utilizing diffusion scrubber and peroxynitrite-induced luminol chemiluminescent methods. We measured the HONO concentration under the conditions existing in living room of an apartment, along with NO, NO2, temperature, and relative humidity, to investigate the sources, chemical transformation, and lifetimes of nitrogen oxides and HONO. Some experiments investigated the emissions and transformations of nitrogen species from operation of unvented or vented gas appliance. Measurement data of NO, NO2, and HONO will be reported, and formation pathway of the HONO under the experimental conditions will also be discussed. In addition to measurement of indoor HONO, comparison of HONO measurements by luminol chemiluminescence and annular denuder integrated samples was made in outdoor environment. HONO in ambient air was sampled with annular denuders (Teflon-coated PM2.5 cyclone inlet followed by two Na2CO3-coated denuders coupled in series) operated at 16.7 L/min. Acknowledgement This study was supported by grant No. (# R01-2005-000-10775-0) from the Basic Research Program of the Korea Science and Engineering Foundation (KOSEF).

Park, S.; Hong, J.; Lee, J.; Cho, S.

2006-12-01

418

Cyclodextrins as stabilizers for the preparation of drug nanocrystals by the emulsion solvent diffusion method.  

PubMed

Cyclodextrins (CyDs) were employed as protective stabilizers for the preparation of surfactant-free nanocrystals of indomethacin (IMC) by using the emulsion solvent diffusion method. The effect of changing the type and concentration of CyDs on the formation of IMC nanocrystals was investigated. Dispersions were freeze-dried to characterize the size, shape, nanoparticle yield, crystallinity, and dissolution behavior of the obtained particles. Submicron-sized particles of IMC with average diameters in the range of 300-500 nm were obtained by incorporating alpha-, beta-, or gamma-CyD in the outer phase of the primary emulsions. Quantitative determination demonstrated that more than 80% of IMC was recovered as fine particles smaller than 0.8 microm. The powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) analyses of the freeze-dried samples confirmed the polymorphic change of IMC to the meta-stable form. A significant enhancement in the dissolution rate of IMC nanocrystals was observed when compared to the commercial powder. PMID:18325698

Makhlof, Abdallah; Miyazaki, Yuta; Tozuka, Yuichi; Takeuchi, Hirofumi

2008-01-20

419

Out-diffusion of Zn from Si: A method to study vacancy properties in Si  

NASA Astrophysics Data System (ADS)

We report out-diffusion experiments of Zn from homogeneously Zn-doped Si samples which were performed at 1107 °C. Depth distributions of Zn recorded by spreading-resistance profiling are accurately described on the basis of simultaneous contributions of the kick-out and dissociative diffusion mechanism. Analysis of the profiles reveals that Zn out-diffusion is mainly mediated by the dissociative mechanism. Fitting of Zn profiles yields data for the transport capacity of vacancies CVeqDV in Si and their thermal equilibrium concentration CVeq.

Giese, A.; Bracht, H.; Stolwijk, N. A.; Walton, J. T.

1998-06-01

420

METHOD OF AND APPARATUS FOR WITHDRAWING LIGHT ISOTOPIC PRODUCT FROM A LIQUID THERMAL DIFFUSION PLANT  

DOEpatents

An improved process and apparatus are described for removing enriched product from the columns of a thermal diffusion plant for separation of isotopes. In the removal cycle, light product at the top cf the diffusion columns is circulated through the column tops and a shipping cylinder connected thereto unttl the concertation of enriched product in the cylinder reaches the desired point. During the removal, circulation through the bottoms is blocked bv freezing. in the diffusion cycle, the bottom portion is unfrozen, fresh feed is distributed to the bottoms of the columns, ard heavy product is withdrawn from the bottoms, while the tops of the columns are blocked by freezing.

Dole, M.

1959-09-22

421

Finite element-boundary element method for advection-diffusion problems with variable advective fields and infinite domains.  

National Technical Information Service (NTIS)

In this paper a hybrid, finite element--boundary element method which can be used to solve for particle advection-diffusion in infinite domains with variable advective fields is presented. In previous work either boundary element, finite element, or diffe...

B. J. Driessen J. L. Dohner

1998-01-01

422

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

423

Prediction of drug dissolution profiles from tablets using NIR diffuse reflectance spectroscopy: A rapid and nondestructive method  

Microsoft Academic Search

A comparison between dissolution profiles obtained by using a dissolution apparatus (conventional method) and the NIR diffuse reflectance spectra of a series of clonazepam-containing batches is reported. Ten different formulations with fixed amount of clonazepam and varying proportions of excipients were analyzed at seven dissolution times and three different media. The percentages of dissolution of each sample were correlated with

Matheus P. Freitas; Andréia Sabadin; Leandro M. Silva; Fábio M. Giannotti; Débora A. do Couto; Edivan Tonhi; Renato S. Medeiros; Gislaine L. Coco; Valter F. T. Russo; José A. Martins

2005-01-01

424

A consistency check of three radar methods for monitoring eddy diffusion and energy dissipation rates through the tropopause  

Microsoft Academic Search

The capability of Stratosphere-Troposphere radars for estimating the energy dissipation rate ? and eddy diffusivity Kz is still strongly questioned because the methods proposed in the literature generally make use of assumptions not yet fully justified. In order to clarify this point, two assessment campaigns, using the high-resolution UHF PROUST radar, have been performed. Results obtained with both ``width'' and

D. Delage; R. Roca; F. Bertin; J. Delcourt; A. Crémieu; M. Massebeuf; R. Ney; P. Van Velthoven

1997-01-01

425

Catchment-scale vulnerability assessment of groundwater pollution from diffuse sources using the DRASTIC method: a case study  

Microsoft Academic Search

The catchment-scale groundwater vulnerability assessment that delineates zones representing different levels of groundwater susceptibility to contaminants from diffuse agricultural sources has become an important element in groundwater pollution prevention for the implementation of the EU Water Framework Directive (WFD). This paper evaluates the DRASTIC method using an ArcGIS platform for assessing groundwater vulnerability in the Upper Bann catchment, Northern Ireland.

Y. S. Yang; L. Wang

2010-01-01

426

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

427

DEVELOPMENT OF SPLIT-OPERATOR, PETROV-GALERKIN METHODS TO STIMULATE TRANSPORT AND DIFFUSION PROBLEMS  

EPA Science Inventory

The rate at which contaminants in groundwater undergo sorption and desorption is routinely described using diffusion models. uch approaches, when incorporated into transport models, lead to large systems of coupled equations, often nonlinear. his has restricted applications of co...

428

DEVELOPMENT OF SPLIT-OPERATOR, PETROV-GALERKIN METHODS TO SIMULATE TRANSPORT AND DIFFUSION PROBLEMS  

EPA Science Inventory

The rate at which contaminants in groundwater undergo sorption and desorption is routinely described using diffusion models. Such approaches, when incorporated into transport models, lead to large systems of coupled equations, often nonlinear. This has restricted applications of ...

429

A diffuse-interface method for simulating two-phase flows of complex fluids  

Microsoft Academic Search

Two-phase systems of microstructured complex fluids are an important class of engineering materials. Their flow behaviour is interesting because of the coupling among three disparate length scales: molecular or supra-molecular conformation inside each component, mesoscopic interfacial morphology and macroscopic hydrodynamics. In this paper, we propose a diffuse-interface approach to simulating the flow of such materials. The diffuse-interface model circumvents certain

P ENGTAO Y UE; J AMES J. F ENG

2004-01-01

430

A time-dependent method for characterizing the diffusion of 222Rn in concrete.  

PubMed

The porosity and diffusion length of concrete have been determined by measuring the time-dependent diffusion of radon through a thin slab of the material. One surface of the slab is exposed to a large, fixed radon concentration beginning at t = 0. The radon that diffuses out of a portion of the opposite surface is collected during several contiguous time intervals. The total activity collected over a set of intervals beginning at t = 0 and the steady-state flux of activity are used to calculate the porosity and diffusion length. As a test of these parameters, they are then used to predict the activity collected during other time intervals and for other sample thicknesses. Samples from two types of concrete were tested: one type yielded a porosity of 0.068 and a diffusion length of 12.6 cm; the respective values for the other were 0.32 and 16.9 cm. The predicted and experimental results agreed well, thereby verifying the assumption that concrete may be treated as a homogenous diffusion medium for radon. PMID:6885437

Zapalac, G H

1983-08-01

431

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

432

A finite analytic method for solving the 2-D time-dependent advection diffusion equation with time-invariant coefficients  

NASA Astrophysics Data System (ADS)

Difficulty in solving the transient advection diffusion equation (ADE) stems from the relationship between the advection derivatives and the time derivative. For a solution method to be viable, it must account for this relationship by being accurate in both space and time. This research presents a unique method for solving the time-dependent ADE that does not discretize the derivative terms but rather solves the equation analytically in the space time domain. The method is computationally efficient and numerically accurate and addresses the common limitations of numerical dispersion and spurious oscillations that can be prevalent in other solution methods. The method is based on the improved finite analytic (IFA) solution method [Lowry TS, Li S-G. A characteristic based finite analytic method for solving the two-dimensional steady-state advection diffusion equation. Water Resour Res 38 (7), 10.1029/2001WR000518] in space coupled with a Laplace transformation in time. In this way, the method has no Courant condition and maintains accuracy in space and time, performing well even at high Peclet numbers. The method is compared to a hybrid method of characteristics, a random walk particle tracking method, and an Eulerian Lagrangian Localized Adjoint Method using various degrees of flow-field heterogeneity across multiple Peclet numbers. Results show the IFALT method to be computationally more efficient while producing similar or better accuracy than the other methods.

Lowry, Thomas; Li, Shu-Guang

2005-02-01

433

Novel method for converting digital Fresnel hologram to phase-only hologram based on bidirectional error diffusion.  

PubMed

We report a novel and fast method for converting a digital, complex Fresnel hologram into a phase-only hologram. Briefly, the pixels in the complex hologram are scanned sequentially in a row by row manner. The odd and even rows are scanned from opposite directions, constituting to a bidirectional error diffusion process. The magnitude of each visited pixel is forced to be a constant value, while preserving the exact phase value. The resulting error is diffused to the neighboring pixels that have not been visited before. The resulting novel phase-only hologram is called the bidirectional error diffusion (BERD) hologram. The reconstructed image from the BERD hologram exhibits high fidelity as compared with those obtained with the original complex hologram. PMID:24104280

Tsang, P W M; Poon, T-C

2013-10-01

434

Investigations on the efficiency of cardiac-gated methods for the acquisition of diffusion-weighted images  

NASA Astrophysics Data System (ADS)

Diffusion-weighted images are inherently very sensitive to motion. Pulsatile motion of the brain can give rise to artifactual signal attenuation leading to over-estimation of the apparent diffusion coefficients, even with snapshot echo planar imaging. Such miscalculations can result in erroneous estimates of the principal diffusion directions. Cardiac gating can be performed to confine acquisition to the quiet portion of the cycle. Although effective, this approach leads to significantly longer acquisition times. On the other hand, it has been demonstrated that pulsatile motion is not significant in regions above the corpus callosum. To reduce acquisition times and improve the efficiency of whole brain cardiac-gated acquisitions, the upper slices of the brain can be imaged during systole, reserving diastole for those slices most affected by pulsatile motion. The merits and disadvantages of this optimized approach are investigated here, in comparison to a more standard gating method and to the non-gated approach.

Nunes, Rita G.; Jezzard, Peter; Clare, Stuart

2005-11-01

435

Comparison of chromogenic Biolog Rainbow agar Shigella/Aeromonas with xylose lysine desoxycholate agar for isolation and detection of Shigella spp. from foods.  

PubMed

Shigella outbreaks are widely reported throughout the world. However, it remains a challenge to isolate Shigella spp. from foods by using conventional microbiological media. The main objective of this study was to determine the effectiveness of a novel chromogenic medium, Rainbow agar Shigella/Aeromonas (Rainbow agar), for the isolation and detection of Shigella spp. in foods. All four Shigella species, S. sonnei, S. flexneri, S. dysenteriae, and S. boydii, were studied. Rainbow agar was compared with tryptic soy agar, xylose lysine desoxycholate agar (XLD), and Salmonella Shigella agar (SSA) for enumeration of Shigella spp. in pure culture. This chromogenic agar and XLD were also used to isolate Shigella spp. in artificially contaminated foods (4.8 log CFU/g of food), including lettuce, parsley, cilantro, spinach, potato salad, and shrimp. The inhibitory effect on Shigella growth by Rainbow agar was between that of XLD and SSA. All vegetables studied showed a moderately high background microflora on XLD and Rainbow agar. With artificially inoculated produce, Rainbow agar recovered about 1 to 2 log CFU more S. sonnei, S. dysenteriae, and S. boydii per g of food than did XLD. For potato salad and shrimp, which had low background microflora on Rainbow agar, Rainbow agar was slightly better in recovering Shigella spp. than XLD was in most cases. However, we found that the addition of streptomycin (6.25 mg/liter) to Rainbow agar could facilitate the isolation of Shigella in vegetables tested. In conclusion, Rainbow agar was a much more effective medium than was XLD for the isolation of Shigella spp. from foods. PMID:20819355

Zhang, Guodong; Lampel, Keith A

2010-08-01