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1

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

2

Serological Comparison of the Three Morphological Phases of Coccidioides Immitis by the Agar Gel Diffusion Method.  

National Technical Information Service (NTIS)

Hyperimmune sera against spherules and against arthrospores of Coccidioides immitis were prepared by inoculation of rabbits. The antibody content of these sera was studied by the agar gel diffusion method. It was observed that antispherule pooled sera for...

M. E. Landay R. W. Wheat N. F. Conant E. P. Lowe

1966-01-01

3

[Use of the agar diffusion precipitation method for detecting rotavirus antigen].  

PubMed

The possibility of rotavirus detection in feces of patients with acute enteric diseases by the agar gel diffusion (AGD) test was studied. The effectiveness of this method was compared with that of the standard method, direct electron microscopy. Both methods showed good correlation of the results, but the AGD test is methodically much simpler which recommends it for diagnosis of rotavirus infection. Rotavirus-specific hyperimmune calf serum may by used as a serological diagnostic preparation for the detection of human rotavirus antigen. PMID:3026098

Gracheva, N M; Demidova, S A; Blokhina, T A; Avakov, A A; Eliseeva, I Ia

1986-01-01

4

Antimicrobial susceptibility of flavobacteria as determined by agar dilution and disk diffusion methods.  

PubMed Central

A total of 106 clinical isolates of flavobacteria, including 41 isolates of Flavobacterium meningosepticum, 59 of Flavobacterium indologenes, and 6 of Flavobacterium odoratum were collected from January 1992 to December 1995 from patients in Taiwan. The in vitro activities of antimicrobial agents were determined concomitantly by the standard agar dilution and disk diffusion methods. More than 90% of the flavobacterial isolates were resistant to cephalothin, cefotaxime, ceftriaxone, moxalactam, aztreonam, imipenem, aminoglycosides, erythromycin, and glycopeptides. The majority of F. meningosepticum isolates were susceptible to piperacillin and to minocycline but resistant to ceftazidime, with MICs at which 90% of the isolates are inhibited being 8, 4, and > 128 microg/ml, respectively. Approximately half of the F. indologenes isolates were susceptible to piperacillin, cefoperazone, ceftazidime, and minocycline, with MICs at which 50% of the isolates are inhibited being 4, 16, 8, and 4 microg/ml, respectively. The majority of F. odoratum isolates were resistant to all the antimicrobial agents tested except minocycline, to which five of six isolates were susceptible. With least-squares regression analysis and error rate-bounded analysis methods, the following resistant and susceptible zone diameter breakpoints were established: < or = 12 and > or = 17 mm, respectively, for piperacillin against F. meningosepticum and F. indologenes; < or = 13 and > or = 18 mm, respectively, for ceftazidime against F. meningosepticum and F. indologenes, < or = 17 and > or = 21 mm, respectively, for ofloxacin against F. indologenes; < or = 16 and > or = 20 mm, respectively, for ciprofloxacin against F. meningosepticum. Valid breakpoints for the disk diffusion method could not be established for cefoperazone and ofloxacin against F. meningosepticum and for minocycline against F. meningosepticum and F. indologenes due to a poor correlation coefficient for the regression line or for cefoperazone and ciprofloxacin against F. indologenes due to the presence of remarkable error rates.

Chang, J C; Hsueh, P R; Wu, J J; Ho, S W; Hsieh, W C; Luh, K T

1997-01-01

5

Comparison of Agar Dilution, Broth Dilution, Cylinder Plate and Disk Diffusion Methods for Evaluation of Anti-leishmanial Drugs on Leishmania promastigotes  

PubMed Central

Background Leishmaniases are a group of diseases caused by Leishmania parasites. Growing of drug unresponsiveness in leishmaniasis patients necessitates the development of new drugs and accordingly a suitable assay is needed for evaluation of any modalities. The aim of this study was to compare four drug assays methods, agar dilution, broth dilution, cylinder plate and disk diffusion, for evaluation of anti-leishmanial drugs on Leishmania promastigotes, using glucantime as a currently available drug for treatment of leishmaniasis. Methods For broth dilution method, different concentration of glucantime was added to the parasite culture (promastigotes of Leishmania), while in cylinder plate method wells were punched in agar gel and filled with different concentration of drug and zone of inhibition was measured in each well. In disk diffusion method, the parasites were cultivated on the surface of agar; filter paper disks were enriched with various concentration of glucantime and were placed on the surface of agar. In agar dilution method, various concentrations of drug were incorporated onto blood agar and the parasites were cultivated on the surface of the agar. Results A direct correlation was found between the drug concentration and size of inhibitory zones in cylinder plate and disk diffusion methods. These two drug assays methods provided much better performance in comparison with broth and agar dilution methods. Conclusion Cylinder plate and disk diffusion methods seem to be acceptable methods for susceptibility testing of anti-leishmanial compounds on Leishmania promastigotes.

Mohammadzadeh, T; Sadjjadi, SM; Habibi, P; Sarkari, B

2012-01-01

6

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

7

Multicenter evaluation of a new disk agar diffusion method for susceptibility testing of filamentous fungi with voriconazole, posaconazole, itraconazole, amphotericin B, and caspofungin.  

PubMed

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 microg/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-microg disks, voriconazole 1- and 10-microg disks, two sources of caspofungin 5-microg disks [BBL and Oxoid], and posaconazole 5-microg 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-microg disk, voriconazole 1-microg disk, itraconazole 10-microg disk (for all except zygomycetes), BBL caspofungin 5-microg disk, and amphotericin B 10-microg (zygomycetes only). PMID:17428932

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

2007-06-01

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

Diffusion of sucrose and dextran through agar gel membranes.  

PubMed

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

Lebrun, L; Junter, G A

1993-12-01

10

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

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

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

2007-10-01

11

Application of the Agar-Agar Electrophoretic Method to Isolation of Soluble Proteins in Nerve Tissue.  

National Technical Information Service (NTIS)

A method of electrophoresis using agar-agar in lieu of filtering paper in order to lessen protein adsorption was investigated. Satisfactory results were obtained in the isolation of the proteins of nerve tissue. The agar also made it possible to demonstra...

A. V. Palladin N. M. Polyakova

1964-01-01

12

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

13

Evaluation of Mannitol Salt Agar for Detection of Oxacillin Resistance in Staphylococcus aureus by Disk Diffusion and Agar Screening  

PubMed Central

Mannitol salt agar was evaluated for detection of oxacillin resistance in 136 Staphylococcus aureus isolates. All mecA-positive isolates (n = 54) were correctly categorized as oxacillin resistant by the disk diffusion test (1-?g disk; zone diameter, <16 mm); the specificity was 97.6%. Agar screening (2 ?g of oxacillin per ml) revealed a sensitivity of 98.1% and a specificity of 95.1%.

Kampf, Gunter; Lecke, Christoph; Cimbal, Ann-Katrin; Weist, Klaus; Ruden, Henning

1998-01-01

14

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

15

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

16

Does elevating silver content in zinc-based glass polyalkenoate cements increase their antibacterial efficacy against two common bacteria using the agar gel diffusion method?  

PubMed

The authors have previously shown that it is possible to incorporate silver into a soda-zinc-silicate glass and subsequently form a glass polyalkenoate cement from it. The objective of the research described herein is to determine if incremental increases in the silver content of these glass polyalkenoate cements will increase their antibacterial efficacy against gram-positive and gram-negative bacteria using the accepted spread plate method. Four glass polyalkenoate cements were formulated; three contained increasing amounts of silver incorporated into them (cements A, B, and C, containing 0.33?mol%, 0.66?mol%, and 0.99?mol% silver, respectively) and a fourth contained no silver, which acted as a control (control cement). The handling properties of the glass polyalkenoate cements were evaluated, where working times were around 2?min and setting times ranged from 1?h 17?min to 2?h 41?min. Inductively coupled plasma atomic emission spectroscopy was employed to determine silver ion release with cement maturation for up to 14 days. The majority of silver ions were released within the first 24?h, with up to 2?mg/L cumulative ion release recorded up to 14 days. The antibacterial properties of the coatings were evaluated against Staphylococcus aureus and Pseudomonas aeruginosa bacteria. The silver-glass polyalkenoate cements exhibited antibacterial effect against both bacterial strains. The maximum inhibition zones recorded against S. aureus was 14.8?mm (SD?±?1.11) and against P. aeruginosa was 20.6?mm (SD?±?0.81). Cement B had a greater antibacterial effect compared to cement A, however, cements B and C had comparable antibacterial effects after 14 days even though cement C contained 0.33?mol% more silver than B. This indicates that by increasing the silver content in these cements, the antibacterial efficacy increases to a point, but there is a threshold where further silver ion release does not increase the antibacterial effect. PMID:22262577

Coughlan, A; Breed, S M; Ashraf, C; Cardinale, J A; Hall, M M; Towler, M R

2013-03-01

17

Infrared thermography analysis of thermal diffusion induced by RF magnetic field on agar phantoms loaded with magnetic nanoparticles  

NASA Astrophysics Data System (ADS)

Recently, several treatments for fighting malignant tumors have been designed. However these procedures have well known inconveniences, depending on their applicability, tumor size and side effects, among others. Magnetic hyperthermia is a safe, non-invasive method for cancer therapy. This treatment is applied via elevation of target tissue temperature by dissipation of heat from Magnetic Nanoparticles (MNPs), previously located within the tumor. The induction of heat causes cell death and therefore the removal of the tumor. In this work the thermal diffusion in phantoms of agar loaded with magnetic nanoparticles (MNPs) is studied using the infrared thermography technique, which is widely used in biology/medicine (e.g. skin temperature mapping). Agar is one of the materials used to simulate different types of body tissues, these samples are known as "phantoms". Agar is of natural origin, low cost and high degree of biocompatibility. In this work the agar gel was embedded with MNPs by coprecipitation and placed in an alternating magnetic field radiation. As a consequence, the energy from the radiation source is dissipated as heat and then transferred from the MNP to the gel, increasing its temperature. For the temperature analysis, the samples of agar gel were stimulated by RF magnetic field generated by coils. Heating was measured with infrared thermography using a Thermovision A20M infrared camera. Thermographic images allowed obtaining the dependence of thermal diffusion in the phantom as a function of the magnitude of the applied RF magnetic field and the load of magnetic particles.

Bante-Guerra, Jose; Macías, J. D.; Caballero-Aguilar, L.; Vales-Pinzón, C.; Alvarado-Gil, J. J.

2013-02-01

18

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

19

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

20

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

21

Nonspecific Precipitation of Serum Proteins by Sodium Lauryl Sulfate in Agar Diffusion and Immunoelectrophoresis  

PubMed Central

The anionic detergent sodium lauryl sulfate (SLS), in a final concentration of 0.1% and greater, reacted with whole serum in agar diffusion and immunoelectrophoresis to form artifactual precipitin lines. These lines occurred when either Ionagar or agarose was used as the supporting gel and were not affected by the presence of urea and 2-mercaptoethanol. Analytic chemical tests confirmed that the precipitating agent is SLS, and staining techniques showed that the detergent precipitates both protein and lipoprotein components of whole serum. Multiple artifactual precipitin lines occurred with a wide variety of animal sera, and a single line formed with human 7S immunoglobulin. Hence, in agar diffusion studies in which SLS is present in the test system, these artifactual lines may be easily misinterpreted as true antigen-antibody precipitin reactions. Images

Palmer, E. L.; Martin, M. L.; Hierholzer, J. C.; Ziegler, D. W.

1971-01-01

22

An agar diffusion comparison of the antimicrobial effect of calcium hydroxide at five different concentrations with three different vehicles.  

PubMed

The purpose of this study was to determine if varying the percent (by weight) of aqueous calcium hydroxide or using different vehicles had an effect on its antibacterial efficacy against common endodontic pathogens in a pour plate/traditional streak agar diffusion model. Mixtures of calcium hydroxide powder and sterile saline in 40, 50 and 60 percent concentrations and the commercial preparations UltraCal XS and Vitapex were tested against six known endodontic pathogens with an agar diffusion method. Each medicament was placed in one of five wells, in each of 10 agar plates (n = 10), for cultures of each bacterial species. Zones of inhibition were measured after 48 hours incubation for aerobes and 96 hours incubation for anaerobes. Multiple one-way analyses of variance and post-hoc Student Neuman Keuls evaluated the data at alpha = 0.05. Larger zones of inhibition were consistently observed for higher concentrations of calcium hydroxide with statistical significance among the bacteria, particularly between 40% and 60%. Vitapex had significantly smaller zones of inhibition than all other medicaments and 35% UltraCal XS with methylcellulose was nearly as effective as 50% Ca(OH)(2) in inhibitory activity. Formulations containing 50-60% Ca(OH)(2) or 35% Ca(OH)(2) with aqueous methylcellulose are recommended as endodontic interappointment medicaments. PMID:18793931

Blanscet, Michael L; Tordik, Patricia A; Goodell, Gary G

2008-10-01

23

Antibiotic susceptibility testing (agar disk diffusion and agar dilution) of clinical isolates of Enterococcus faecalis and E. faecium: comparison of Mueller-Hinton, Iso-Sensitest, and Wilkins-Chalgren agar media.  

PubMed

Forty-two isolates of Enterococcus faecalis and 56 isolates of Enterococcus faecium, including 8 vancomycin-resistant strains, were examined for comparative susceptibility to 27 antimicrobial drugs with the agar dilution method, employing Mueller-Hinton (MHA), Iso-Sensitest (ISTA), and Wilkins-Chalgren (WCA) agar. The Bauer-Kirby agar disk diffusion method was used to comparatively test 24 of the agents in parallel. The enterococci yielded better growth on ISTA and WCA. However, WCA completely antagonized co-trimoxazole and, though less, fosfomycin. Importantly, WCA slightly reduced the activities of teicoplanin (minimal inhibitory concentrations, MICs, raised up to twofold) and vancomycin (MICs raised two- to fourfold) against enterococci and staphylococcal quality control strains. Therefore, WCA was judged unsuitable for susceptibility testing of enterococci. For E. faecalis no discrepancies between agar dilution MICs and inhibition zone diameters were encountered with augmentin, ampicillin, ampicillin-sulbactam, chloramphenicol, mupirocin, oxacillin, teicoplanin, and co-trimoxazole. Overall, MHA yielded fewer very major (category I) and major (category II) discrepancies than ISTA. However, numerous minor (category III), slight (category IV), minimal (category V), and/or negligible (category VI) discrepancies were encountered with ciprofloxacin, doxycycline, erythromycin, fosfomycin, fusidic acid, meropenem, ofloxacin and rifampin. With respect to E. faecium, only cefotaxime, mupirocin, oxacillin, and teicoplanin yielded nondiscrepant results. Several very major (I) and major (II) discrepancies were observed with augmentin, ampicillin, ampicillin-sulbactam, doxycycline, fusidic acid, imipenem, and penicillin G. Minor discrepancies (categories III-VI) were particularly numerous with augmentin, chloramphenicol, ciprofloxacin, doxycycline, and piperacillin. The largest numbers of negligible (VI) discrepancies were noted with fosfomycin, fusidic acid, and ofloxacin. It is recommended to test one cephalosporin (cefuroxime or the like) in parallel for educational purposes and to exclude fosfomycin, fusidic acid, and rifampin from test batteries because of the wide scatter of test results. The large number of minimal (V) discrepancies of ciprofloxacin against E. faecalis, the numerous minor (III) and slight (IV) discrepancies of chloramphenicol against E. faecium, and the not insignificant number of very major (I) and minor (III) discrepancies observed with meropenem against isolates of E. faecalis necessitated proposals for new disk intermediate susceptibility criteria. PMID:9681198

Traub, W H; Geipel, U; Leonhard, B

1998-01-01

24

Diagnosis of Rhodococcus equi infection in foals by the agar gel diffusion test with protein antigen.  

PubMed

A protein antigen that reacted in the agar gel diffusion (AGD) test and which had equi factor(s) activity, was partially purified from the culture supernatant of Rhodococcus equi by successive column chromatography on diethylaminoethyl cellulose and Sepharose 4B. Employing a standard foal serum, the concentration of this antigen was adjusted for the AGD test. Optimal dilutions of the antigen reacted in the AGD test with sera from foals naturally infected with serologically different R. equi. The antigen prepared was considered suitable for use in field surveys of R. equi infection. Accordingly, four groups of sera were tested: those from 18 foals diagnosed as being infected with R. equi, those from 54 control foals with culture-negative R. equi pneumonia, arthritis or cellulitis, those from 46 diseased foals suspected of having R. equi infection and those from 51 clinically normal foals. A positive precipitation reaction was observed with sera from 100% of the first group, 69.5% of the third group and 17.7% of the fourth group. A negative reaction was obtained with sera from 100% of the second group. PMID:3125665

Nakazawa, M; Isayama, Y; Kashiwazaki, M; Yasui, T

1987-10-01

25

Sensitivity testing of veterinary pathogens with a semi-automatic image analysis system compared with tablet diffusion and agar dilution tests.  

PubMed

Recently a commercial computer-controlled image analysis system (IAS) was introduced to measure automatically the diameters of inhibition zones in the agar diffusion test. However, there is little information on the precision of this method. In the present study clinical isolates of Salmonella spp. (N = 104), Escherichia coli (N = 100), Pasteurella spp. (N = 99), Actinobacillus pleuropneumoniae (N = 85), porcine streptococci (N = 100), and Staphylococcus aureus (N = 95) were tested in the agar diffusion test, using nineteen different antibiotics in tablets. All inhibition zone diameters were first measured by a laboratory technician and then by the IAS. Although the zone diameters of all bacteria-antibiotic combinations measured by the IAS and those measured by the laboratory technician showed a significant positive correlation, the size of the inhibition zone diameters measured by the technician and the IAS differed significantly in 59% of the combinations. However, these differences were very small and may have no clinical relevance. The IAS was also used to calculate minimum inhibitory concentrations (MIC values) from the zone diameters. In 82% of the bacteria-antibiotic combinations MIC values calculated by the IAS showed a significant positive correlation with MIC values obtained with the reference agar dilution test. However, in 92% of the bacteria-antibiotic combinations, the calculated MIC values differed significantly from the reference values. In some cases these differences were so large that they could be of clinical relevance. The IAS was unable to measure the diameter of inhibition zones of porcine streptococci properly, due to poor contrast. We concluded that when tablets are used as antibiotic carriers the IAS accurately measures the diameter of inhibition zones for bacteria species that give good contrast between the agar and bacterial growth. MIC values determined with the IAS were only indicative of those determined with the reference agar dilution test. PMID:10427635

Mevius, D J; Veldman, K T; van der Pal, R H; van Zijderveld, F G

1999-06-01

26

Diagnostic accuracy assessment of Sensititre and agar disk diffusion for determining antimicrobial resistance profiles of bovine clinical mastitis pathogens.  

PubMed

Determining the accuracy and precision of a measuring instrument is pertinent in antimicrobial susceptibility testing. This study was conducted to predict the diagnostic accuracy of the Sensititre MIC mastitis panel (Sensititre) and agar disk diffusion (ADD) method with reference to the manual broth microdilution test method for antimicrobial resistance profiling of Escherichia coli (n = 156), Staphylococcus aureus (n = 154), streptococcal (n = 116), and enterococcal (n = 31) bovine clinical mastitis isolates. The activities of ampicillin, ceftiofur, cephalothin, erythromycin, oxacillin, penicillin, the penicillin-novobiocin combination, pirlimycin, and tetracycline were tested against the isolates. Diagnostic accuracy was determined by estimating the area under the receiver operating characteristic curve; intertest essential and categorical agreements were determined as well. Sensititre and the ADD method demonstrated moderate to highly accurate (71 to 99%) and moderate to perfect (71 to 100%) predictive accuracies for 74 and 76% of the isolate-antimicrobial MIC combinations, respectively. However, the diagnostic accuracy was low for S. aureus-ceftiofur/oxacillin combinations and other streptococcus-ampicillin combinations by either testing method. Essential agreement between Sensititre automatic MIC readings and MIC readings obtained by the broth microdilution test method was 87%. Essential agreement between Sensititre automatic and manual MIC reading methods was 97%. Furthermore, the ADD test method and Sensititre MIC method exhibited 92 and 91% categorical agreement (sensitive, intermediate, resistant) of results, respectively, compared with the reference method. However, both methods demonstrated lower agreement for E. coli-ampicillin/cephalothin combinations than for Gram-positive isolates. In conclusion, the Sensititre and ADD methods had moderate to high diagnostic accuracy and very good essential and categorical agreement for most udder pathogen-antimicrobial combinations and can be readily employed in veterinary diagnostic laboratories. PMID:21270215

Saini, V; Riekerink, R G M Olde; McClure, J T; Barkema, H W

2011-04-01

27

Agar barrier method for removal of yeast and other fungal contamination from Leishmania promastigotes culture  

PubMed Central

The present study explains a novel method of Leishmania promastigotes culture decontamination. The method is based on motility of Leishmania promastigotes across agar barrier which facilitates decontamination from yeast and other non motile contamination. This is inexpensive, easy, rapid and reliable physical method and is able to save valuable isolates in culture.

Gupta, Anil Kumar; Narayan, Shyam; Singh, Shubhankar Kumar; Thakur, Ajit Kumar; Das, Pradeep

2012-01-01

28

Evaluation of PCR-based screening for vancomycin-resistant enterococci compared with a chromogenic agar-based culture method.  

PubMed

Rapid detection of vancomycin-resistant enterococci (VRE) infection is very important for control and prevention of nosocomial spread of these bacteria. A multiplex PCR method for rapid screening of VRE has recently been developed. We performed a prospective study of VRE screening tests to compare the performance of PCR to that of a chromogenic agar-based culture method. From January to December 2009, a total of 8815 rectal swab specimens were tested simultaneously for VRE by VRE selective culture and by PCR. The specimens were inoculated onto ChromID VRE agar containing 8 µg vancomycin ml?¹ and examined after 24 and 48 h of incubation. Identification and antibiotic susceptibility tests were performed using the automated VITEK-2 system and a supplementary E-test and disk diffusion test. Detection of the vanA and vanB genes was performed with the Seeplex VRE detection kit. Specimens were inoculated in enterococcosel broth for 16-24 h before PCR for enrichment of VRE. VRE were isolated from 741 of the 8815 specimens by chromogenic agar-based culture (8.4?%). vanA and vanB genotypes were detected in 758 (8.6?%) and 3 (0.03?%) specimens, respectively, by multiplex PCR. Sensitivity, specificity, positive predictive value and negative predictive value of PCR for detection of VRE were 98.2?%, 99.6?%, 95.7?%, and 99.8?%. No VRE were isolated from vanB-positive specimens. The overall performance of PCR is comparable to that of a chromogenic agar-based culture method for screening of VRE, so PCR could be an alternative or supportive method for effective control of nosocomial VRE infection. PMID:21459908

Seo, Ja Young; Kim, Pyung-Whan; Lee, Jang-Ho; Song, Jae-Hoon; Peck, Kyong-Ran; Chung, Doo-Ryeon; Kang, Cheol-In; Ki, Chang-Seok; Lee, Nam Yong

2011-07-01

29

Agar plate method for rapid screening of rhizobium for tolerance to acid-aluminum stress  

SciTech Connect

An agar plate method has been developed for the rapid, preliminary screening of large numbers of rhizobia for tolerance to acidity and aluminum (acid-Al). Media containing pH indicators are used, and distinguish true tolerance from cases where growth depends on a previous pH shift. Strains which were highly tolerant or sensitive to acid Al on agar behaved similarly in defined liquid media. Strains that formed dry, pinpoint colonies were more sensitive to acid-Al than those that formed large, gummy colonies.

Ayanaba, A.; Asanuma, S.; Munns, D.N.

1983-01-01

30

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...

31

Efficacy of the thin agar layer method for the recovery of stressed Cronobacter spp. (Enterobacter sakazakii).  

PubMed

Cronobacter spp. (Enterobacter sakazakii) are emerging opportunistic pathogens for all age groups, and are of particular concern when it comes to infants. Prior to contaminating food, the organism may be exposed to a variety of stresses, leading to a generation of sublethally injured cells that may not be detected by selective media unless a protracted recovery period is included in the isolation procedure. This study evaluated the efficacy of the thin agar layer (TAL) method for the recovery of Cronobacter cells that had been exposed to various stress conditions. Five strains of C. sakazakii and C. muytjensii were exposed to starvation, heat, cold, acid, alkaline, chlorine, or ethanol, with or without further exposure to desiccation stress. The recovery of the stressed cells was determined on tryptone soy agar (TSA; nonselective control medium), violet red bile glucose agar (VRBGA; selective agar), Druggan-Forsythe-Iversen (DFI; selective agar), and TAL media (viz., VRBGA overlaid with TSA, and DFI overlaid with TSA). Regardless of stress type, there were no significant differences among the recoveries of stressed desiccated Cronobacter spp. cultures on TSA, DFI+TSA, and VRBGA+TSA, but there was significantly less recovery on VRBGA. The recovery of prestressed desiccated Cronobacter spp. on DFI+TSA was similar to that on TSA, whereas the recovery on VRBGA+TSA was lower. DFI+TSA performed better than VRBGA+TSA did in differentiating Cronobacter spp. within mixed bacterial cultures. The results of this study suggest the use of the TAL method DFI+TSA as an improved method for the direct recovery of stressed Cronobacter spp. PMID:21067681

Osaili, Tareq M; Al-Nabulsi, Anas A; Shaker, Reyad R; Al-Holy, Murad M; Al-Haddaq, Mohammed S; Olaimat, Amin N; Ayyash, Mutamed M; Al Ta'ani, Mahmoud K; Forsythe, Stephen J

2010-10-01

32

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

PubMed

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

Jakucs, E; Várallyay, E

1995-01-01

33

STUDIES ON THE AGAROPHYTE, GRACILARIA EDULIS - EXPERIMENTAL FIELD CULTIVATION AND METHODS OF lMPROVING YIELD AND QUALITY OF AGAR  

Microsoft Academic Search

Abstraa : Preliminary investigations on the extraction of phycocolloids from five common red algae of Sri Lanka revealed that Gracilaria edulis forms a suitable source for the production of agar. This coupled with the relative abundance of this species prompted the investigations on the cultivation of this alga and on the methods of extraction of agar from this species. Vegetative

A. SIVAPALAN; K. THEIVENDIRARAJAH

34

Comparison of manual mycobacteria growth indicator tube and epsilometer test with agar proportion method for susceptibility testing of Mycobacterium tuberculosis.  

PubMed

Background and Objectives: Antimycobacterial susceptibility tests take weeks, and delayed therapy can lead to spread of Mycobacterium tuberculosis. Therefore, rapid, accurate and cost-effective methods are required for proper therapy selection. In this study, the Mycobacteria growth indicator tube (MGIT) and epsilometer test (Etest) methods were compared to the agar proportion method for susceptibility testing of Mycobacterium tuberculosis. Materials and Methods: The susceptibility tests against isoniazid (INH), rifampin (RIF), streptomycin (STM) and ethambutol (ETM) of 51 M. tuberculosis complex isolates were analyzed by the MGIT, Etest and agar proportion methods. Results: The concordance between MGIT/Etest and agar proportion methods was 98% for INH and 100% for RIF, STM, ETM. There were not statistically significant differences in results of the susceptibility tests between MGIT/Etest and the reference agar proportion method. Conclusion: The results have shown that MGIT and Etest methods can be used instead of the agar proportion method, because these two methods are more rapid and easier than the agar proportion method. PMID:25008821

Karabulut, N; Bayraktar, B; Bulut, Y

2014-01-01

35

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...

36

Development of a molecular method for the rapid discrimination of red seaweeds used for agar production  

Microsoft Academic Search

In Tunisia, agar is produced from the species Gracilaria verrucosa. Other species, such as Gracilariopsis sp. which have a very similar morphology to Gracilaria, can be harvested in a mixture with Gracilaria with the result that the quantity and quality of agar extracted is different than initially expected. In this study, we tested the use of ITS sequences from 5.8s

Yolaine Joubert; Leïla Ben Abdeladhim; Jamel Ksouri; Joël Fleurence

2009-01-01

37

Effect of two aerosolization methods on the release of fungal propagules from a contaminated agar surface.  

PubMed

The effect of perpendicular and swirling aerozolization methods on the release of fungal fragments and spores from agar surface was studied. Three fungal species (Aspergillus versicolor, Cladosporium cladosporioides, Penicillium chrysogenum) were selected for the tests as they commonly occur indoors, create different hyphae structure when they grow on surfaces, and have different spore shapes, aerodynamic sizes, and formation mechanisms. As the tested surface, Petri dishes filled with malt extract agar, separately inoculated with fungal strains and cultivated to obtain an abundant and even growth were used. For the purpose of these experiments, a new aerosolization chamber was built in which HEPA-filtered air stream responsible for fungal propagule release was either perpendicularly directed towards the contaminated surface or set in swirling motion above it. The experiments were conducted at 2 air velocities, typical for outdoor environment (11.6 m/s) and ventilation ducts (29.1 m/s). Concentrations and size distributions of released fragments and spores were measured using an optical particle counter. The results showed that the propagule release depends on the direction (swirling motion was able to release up to 3.4 × 10(5) fragments and 3 × 10(5) spores from 1 cm( 2) of contaminated surface, i.e. significantly more than the perpendicularly directed air stream), velocity (the higher the swirling air velocity applied, the higher the number of released propagules) of the air stream above the contaminated surface, and varied due to the taxonomical species origin (the higher number of particulates was released by Aspergillus colonies). Hence, the efficient control of both microbial fragments and spores, not only in the air, but also in their source should be an integral part of the quality control procedure. PMID:22742802

Górny, Rafa? L; ?awniczek-Wa?czyk, Anna

2012-01-01

38

Susceptibility of Moraxella catarrhalis to 21 antimicrobial drugs: validity of current NCCLS criteria for the interpretation of agar disk diffusion antibiograms.  

PubMed

Ninety-four clinical isolates of Moraxella catarrhalis were examined for susceptibility to 21 antimicrobial drugs; 67 isolates (= 71.3%) produced beta-lactamase(s). In terms of antibiotic resistance, the number of isolates resistant to penicillin G, ampicillin, and cotrimoxazole were 56, 32, and 1, respectively. The number of isolates with intermediate susceptibility to penicillin G, ampicillin, ciprofloxacin, ofloxacin, cotrimoxazole, and fosfomycin were 11, 34, 1, 2, 2, and 47, respectively. All 94 isolates proved susceptible to ampicillin + 10 micrograms/ml of sulbactam, amoxicillin + 4 micrograms/ml of clavulanic acid, cefuroxime, cefotaxime, cefepime, cefepime, cefixime, imipenem, meropenem, chloramphenicol, doxycycline, tetracycline, fusidic acid, erythromycin, clarithromycin, and rifampin, as based on currently valid NCCLS criteria, where applicable. There were no very major or major discrepancies between agar dilution and agar disk diffusion test results. There were only a few minor discrepancies between test results, specifically: penicillin G (category IV = 4, category VI = 1); ampicillin (category IV = 4, category V = 1, category VI = 7), amoxicillin + clavulanic acid (category III = 11), cotrimoxazole (category IV = 1, category V = 1, category VI = 1), ciprofloxacin (category V = 1), and ofloxacin (category VI = 2). The sole exception was fosfomycin, with a total of 25 minor discrepancies encountered (category III = 14, category V = 9, category VI = 2). Wilkins-Chalgren agar compared favorably with Mueller-Hinton agar following examination with 11 selected antimicrobial drugs against 31 representative isolates of M. catarrhalis. PMID:9142455

Traub, W H; Leonhard, B

1997-01-01

39

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

40

Self-Diffusion of Co2+ Ions in CoBr2, CoI2 and Electrolyte-Diffusion of ZnSO4 in Agar Gel Medium  

Microsoft Academic Search

Self-diffusion of Co2+ ions in CoBr2 and CoI2 is reported in the concentration range of 10–5 to 0.25M in 1% agar gel at 25 °C. The deviations observed between the experimental and theoretical values of diffusion coefficients are explained by considering different types of interactions occurring in the ion-gel water system. The applicability of the transition state theory to the

S. F. Patil; P. R. Patil

2000-01-01

41

Serological typing of Ureaplasma urealyticum isolates from urethritis patients by an agar growth inhibition method.  

PubMed

An agar growth inhibition method for serotyping Ureaplasma urealyticum is described, and the results of applying this method to serotyping 338 strains of the organism are presented. The serotyped strains consisted of cloned isolates from male patients with primary and recurrent nongonococcal urethritis (NGU), isolates from symptomatic patients with other genitourinary tract infections and disorders, and isolates from asymptomatic carriers of U. urealyticum in the genitourinary tract (controls). Among 122 male patients with NGU, serotype 4 was associated most frequently (52%) with this disease at Camp Lejeune, N.C. Seventeen percent of the isolates were type 2. The remaining isolates consisted of types 1, 3, 6, and 8 and accounted for 6 to 9% each of the serotypes isolated from the NGU group. Types 5 and 7 were not isolated. Among 91 symptomatic patients with other genitourinary tract infections and disorders, U. urealyticum type 4 also was associated most frequently (37%) with these disorders. The remaining isolates, represented by types 1, 2, 3, 6, 7, and 8, accounted for 9 to 15% each of the types isolated from this group. Type 5 was not isolated. Among 125 symptomfree carriers of U. urealyticum in the genitourinary tract, type 8 was recovered most frequently (30%), whereas type 4 was isolated next most frequently (24%). The remaining isolates consisted of types 1, 2, 3, 5, and 6 and accounted for 2 to 15% each in this asymptomatic control group. Type 7 was not isolated. Of the present eight serotypes of U. urealyticum studied in this investigation, type 4 was associated most frequently with disease (NGU) and certain other disorders of the genitourinary tract at Camp Lejeune. A previously unknown association of U. urealyticum with frequently abacteriuric, unexplained pyuria (with or without urethral pruritus and dysuria) is reported, suggesting the existence of asymptomatic Ureaplasma urethritis. PMID:730828

Shepard, M C; Lunceford, C D

1978-11-01

42

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  

Microsoft Academic Search

A new membrane filter (MF) medium, MI agar, recently validated for use in recovering chlorine-damaged total coliforms (TC) and Escherichia coli from drinking water, was compared to the US Environmental Protection Agency (EPA)-approved MF method (mEndo agar and nutrient agar supplemented with 4-methylumbelliferyl-?-d-glucuronide) in a collaborative study. Six wastewater-spiked Cincinnati tap water samples, containing three different concentrations of E. coli

Kristen P. Brenner; Clifford C. Rankin; Manohari Sivaganesan

1996-01-01

43

Discordance in the minimal inhibitory concentrations of ertapenem for Enterobacter cloacae: Vitek 2 system versus Etest and agar dilution methods.  

PubMed

Our objective was to compare the ertapenem minimal inhibitory concentrations (MICs) for Enterobacter cloacae isolates categorized intermediate or resistant to ertapenem when measured with the Vitek 2 system, with the MICs for these isolates when measured by two methods performed in agar medium: the Etest and agar plate dilution method (APDM). Overall, 50 E. cloacae isolates were included in the study. The mean MIC of ertapenem was 2.92±1.77?g/ml according to the Vitek 2 system, 0.94±0.84?g/ml according to the Etest strips, and 0.93±0.62?g/ml according to the APDM. Furthermore, the MICs determined by the Vitek 2 system were higher than the MICs determined by the two other methods for 96% of strains. Lastly, according to the Etest strips and APDM, 42% of E. cloacae were susceptible to ertapenem. No carbapenemase was identified by the screening method used. Using the Vitek 2 system to determine ertapenem MICs for E. cloacae can have potential consequences in terms of additional carbapenemase-detecting tests and antimicrobial therapy. It would be interesting to determine if the Vitek 2 system is more effective for the detection of carbapenemase producers with low-level carbapenem resistance than the two methods performed in agar medium. PMID:24183718

Pailhoriès, Hélène; Cassisa, Viviane; Lamoureux, Claudie; Chesnay, Adélaïde; Lebreton, Cyrielle; Lemarié, Carole; Kempf, Marie; Mahaza, Chetaou; Joly-Guillou, Marie-Laure; Eveillard, Matthieu

2014-01-01

44

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

45

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

PubMed

A method modification study was conducted for the VIDAS Salmonella (SLM) assay (AOAC Performance Tested Method 020901) using the EasySLM method to validate a matrix extension for peanut butter. The VIDAS EasySLM method is a simple enrichment procedure compared to traditional Salmonella methods, requiring only pre-enrichment and a single selective enrichment media, Salmonella Xpress 2 (SX2) broth. SX2 replaces the two selective broths in traditional methods and eliminates the M broth transfer, incubation, and subsequent pooling of M broths prior to VIDAS assay. The validation study was conducted under the AOAC Research Institute Emergency Response Validation program. VIDAS SLM was compared to the U.S. Food and Drug Administration's Bacteriological Analytical Manual (FDA-BAM) method for detection of S. enterica ser. Typhimurium in peanut butter. All peanut butter samples were prepared, blind-coded, and shipped to the method developers' laboratory by Q Laboratories. In addition, Q Laboratories performed most probable number and reference method analyses on peanut butter samples. The VIDAS EasySLM ChromID Salmonella (SM2) Agar was previously validated in the Performance Tested Methods program for the detection of Salmonella in roast beef, raw ground pork, turkey, pork sausage, raw chicken breast, dry pet food, whole milk, ice cream, bagged spinach, shrimp (raw, peeled), raw cod, spent irrigation water, pecans, peanut butter, dry pasta, cake mix, ground black pepper, nonfat dry milk, liquid eggs, cantaloupe, and orange juice. In the matrix extension study for peanut butter, the VIDAS EasySLM method was shown to be equivalent to the appropriate reference culture procedure using both buffered peptone water pre-enrichment and the FDA-BAM lactose pre-enrichment in the two-step enrichment method with SX2 media. The current study extends the validation to include peanut butter. PMID:20166608

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

2009-01-01

46

Method 1603: Escherichia coli (E. coli) in Water by Membrane Filtration Using Modified Membrane-Thermotolerant Escherichia coli Agar (Modified mTEC), July 2006.  

National Technical Information Service (NTIS)

Method 1603 is a revised membrane filter (MF) procedure, a single-step method that uses one medium, modified mTEC Agar, and does not require the transfer of the membrane filter to another medium or other substrate.

2006-01-01

47

Electro-osmosis in gels: Application to Agar-Agar  

NASA Astrophysics Data System (ADS)

Widely used in food- and bio-engineering as a reference material, Agar-Agar gel is the focus of an experimental investigation concerning the electro-osmosis phenomenon. After presenting the experimental methods, one trial is discussed in detail. A fair reproducibility of results is obtained, and the averaged electro-osmotic permeability is provided. This value lies in the range generally measured on various kind of soils, even if Agar-Agar gel does not share any micro-structural characteristics with soils. To cite this article: F. Cherblanc et al., C. R. Mecanique 336 (2008).

Cherblanc, Fabien; Boscus, Jérôme; Bénet, Jean-Claude

2008-10-01

48

Assessment of Antibiotic Susceptibility of Ureaplasma urealyticum from Prostitutes and Outpatient Clinic Patients Using the E-Test and Agar Dilution Method  

Microsoft Academic Search

In this study, a total of 647 vaginal discharge samples were examined. Ureaplasma urealyticum growth was seen in 68 samples (10.5%). The antibiotic sensitivity of 30 types of U.urealyticum was determined with the E-test and agar dilution method. With the agar dilution method, all types were sensitive to ciprofloxacin and ofloxacin (MIC 0.94 ?g\\/ml), tetracycline (MIC 0.125 ?g\\/ml) and doxycycline

Hüseyin Çakan; Erdal Polat; Bekir Kocazeybek; Pelin Öcal; Mustafa Aslan

2003-01-01

49

[Comparison Of Agar-Gel Diffusion Tests, Counterimmunoelectrophoresis And Enzyme-Linked Immunosorbent Assay In The Sera Of Skin Test Positives For Paragonimiasis  

PubMed

Agar-gel diffusion test (AGD), counterimmunoelectrophoresis (CIEP) and enzyme-linked immunosorbent assay(ELISA) were examined with the sera of skin test positives for paragonimiasis. The crude antigen(Paragonimus whole worm extracts: protein concentration, 7.56mg/ml) and human sera were used in AGD and CIEP. And in ELISA test, diluted antigen with 1:40,000 of crude antigen and diluted sera with 1:100, 1:200 were used in the test. The positive identical ratio between AGD and CIEP reactions is 98 % and negative identical ratio is 100 %. One or three precipitin bands are observed in AGD. One to seven precipitin bands are also revealed in CIEP. Especially, deeply stained bands are observed in CIEP than those of AGD. The positive identical ratios between AGD and ELISA tests are 96 % in 1:100 diluted sera, and 94 % in 1:200 diluted sera. But the negative identical ratios between AGD and ELISA tests are 97 % and 99 % respectively in 1:100 and 1:200 diluted sera. The positive identical ratios between CIEP and ELISA tests are 98 % and 96 % respectively in 1:100 and 1:200 diluted sera, but also 97 % and 99 % in 1:100 and 1:200. Control sera, such as clonorchiasis, amoebiasis and toxoplasmosis, revealed all negatives with Paragonimus antigen in AGD, CIEP and ELISA tests. By above results, ELISA was most sensitive, next CIEP and AGD. But AGD test appears to be more useful when used to crude antigen without cross reaction with other parasitic infections. CIEP test is basically equal in terms of precipitin reaction, but CIEP is able to be detected more sensitively and rapidly though less simple in handiwork than AGD. Consequently, three methods for immunological tests of paragonimiasis have good correlations with one another. Also, each of these has both merits and demerits in immunological test for paragonimiasis. But the ELISA test was proved to be the most sensitive and convenient tool for mass screening test, especially in case of using purified antigen. PMID:12902659

Lee, Ok Ran; Choi, Won Young

1983-12-01

50

Generalizing the finite element method: Diffuse approximation and diffuse elements  

Microsoft Academic Search

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

B. Nayroles; G. Touzot; P. Villon

1992-01-01

51

Evaluation of the Thin Agar Layer Method for the Recovery of Pressure-Injured and Heat-Injured Listeria monocytogenes.  

PubMed

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

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

2014-05-01

52

Method 1603: 'Escherichia coli' (E. coli) in Water by Membrane Filtration Using Modified membrane-Thermotolerant 'Escherichia coli' Agar (mTEC).  

National Technical Information Service (NTIS)

The method describes a revised Escherichia coli membrane filter (MF) procedure, a single-step method that uses one medium, modified mTEC Agar, and does not require the transfer of the membrane filter to another medium or other substrate. The modified medi...

2002-01-01

53

A cell suspension agar diffusion test using Neutral Red release to assess the relative irritancy potential of cosmetic ingredients and formulations.  

PubMed

Synopsis An established cytotoxicity test for plastic materials in medical devices has been adapted and used to assess the relative potential irritancy of cosmetic ingredients and formulations during product development. Serum-free medium containing a novel protein supplement supported growth in suspension of LS mouse fibroblast cells. Release of the vital dye Neutral Red from pre-loaded cells suspended in agar was the endpoint. Test substances and reference standards were applied to a central well cut into the agar, a sensitive method which allowed accurate dose application and yielded consistent results. Relative irritancy potential was measured quantitatively by comparing the diameters of the clear zones of damaged cells which surround the central well. The test has been used with raw materials such as surfactants, preservatives and herbal extracts, as well as finished products ranging from shampoos and conditioners to creams, lotions and coloured cosmetics. The method is practical, versatile, reproducible and economic to use. Résumé Un test de cytotoxicité utilisé pour la détection de toxines dans les plastiques des appareils médicaux a été adapté pour prévenir le potentiel d'irritation relative. Le point mesuré est la libération de la teinture vitale rouge neutre des cellules chargées au préalable, résultant de l'incubation avec des substances tests. La mesure des diamétres de la zone claire de dilutions sequentielles de substances tests permet de calculer l'irritation potentielle d'un produit testé par rapport à un standard. Parmi les modifications, on a pu constater à l'aide d'une ligne de cellules en suspension dérivées de fibroblastes de souris L-929, la pousse en milieu sans sérum pour éviter les produits d'abattoir. A la place du sérum de veau, on a ajouté au milieu une nouvelle protéine innovatrice supportant la pousse normale en suspension. Durant la procédure de test les cellules se trouvaient en suspension dans une solution agar et les substances tests ont été appliquées sur une cellule centrale bien délimitéc sur la gélose plutôt qu'à l'aide d'un disque de papier filtre. L'application par une cellule centrale était plus sensible qu'avec un disque, permettant l'application d'une dose précise et fournissant des résultats plus fiables. Le test modifié a été utilisé sur une période de 4 ans pour des matiéres premières telles que tensioactifs, conservateurs et extraits de plantes, ainsi que des formules de shampooings, savons, lotions hydratantes et cosmétiques colorés. Ces produits ont étéévalués sur des panels de volontaires, et les produits testés sont commercialisés depuis 2 ans au moins. Le test est un moyen pratique, versatile, reproductible et économique de calculer le potentiel d'irritation relative d'une gamme de produits et ingrédients cosmktiques. PMID:19272118

Butler, N J; Langley, G R; Winwood, J

1993-02-01

54

Methods for serotyping nasopharyngeal isolates of Haemophilus influenzae: slide agglutination, Quellung reaction, countercurrent immunoelectrophoresis, latex agglutination, and antiserum agar.  

PubMed Central

Nasopharyngeal isolates of H. influenzae were typed by the slide agglutination test, the Quelling reaction, the latex agglutination test, countercurrent immunoelectrophoresis, and the antiserum agar test. These tests gave essentially comparable results, with countercurrent immunoelectrophoresis and latex agglutination being slightly more sensitive. Cross-reactive problems encountered with latex agglutination and the expense of performing countercurrent immunoelectrophoresis or the antiserum agar test made these tests less practical than the slide agglutination test to identify single strains that were already isolated. The Quellung reaction and slide agglutination were the most rapid tests used to type an organism. For mass screening of multiple samples, countercurrent immunoelectrophoresis was the simplest technique. The antiserum agar test was slow but was the best technique to screen nasopharyngeal swab cultures to identify the presence of any encapsulated strains in the mixed flora. Whether any of the above techniques were as sensitive as the immunofluorescence test was not evaluated in this study. Images

Ingram, D L; Collier, A M; Pendergrass, E; King, S H

1979-01-01

55

AgarCyto: A Novel Cell-processing Method for Multiple Molecular Diagnostic Analyses of the Uterine Cervix  

Microsoft Academic Search

SUMMARY In diagnostic cytology, it has been advocated that molecular techniques will improve cytopathological diagnosis and may predict clinical course. Ancillary molecular techniques, however, can be applied only if a sufficient number of preparations are made from a single cell sample. We have developed the AgarCyto cell block procedure for multi- ple molecular diagnostic analyses on a single scraping from

Harold M. J. Kerstens; Johanna C. M. Robben; Pino J. Poddighe; Willem J. G. Melchers; Henk Boonstra; Merryn V. E. Macville; Antonius G. J. M. Hanselaar

56

A Statistical Comparison of Analyst Accuracy and Speed in Counting Standard Methods Agar Plates Within Selected Colony Count Ranges.  

National Technical Information Service (NTIS)

Agar plates, prepared from serially diluted food homogenate and containing from 30-300 colonies per plate, are used by food microbiology testing laboratories to estimate the microbial population of food samples. Six analysts counted plates with 0-<400 col...

J. T. Fruin T. M. Hill J. B. Clarke J. L. Fowler

1976-01-01

57

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

58

Comparison of a novel MPN method against the yeast extract agar (YEA) pour plate method for the enumeration of heterotrophic bacteria from drinking water.  

PubMed

This study compared the Quanti-Disc most probable number (MPN) test for heterotrophic bacteria from drinking water with the widely used yeast extract agar (YEA) pour plate method. The Quanti-Disc test module contains 50 reaction wells in which a medium has been pre-deposited. The medium contains a suite of three fluorogenic enzyme substrates selected for the detection of enzymes expressed widely by heterotrophic bacteria. The MPN of heterotrophic bacteria is calculated from the number of fluorescing reaction wells after incubation of a sample. Quanti-Disc and the YEA pour plate method were compared according to guidance on comparing methods given in United Kingdom national guidance and ISO 17994:2004. The two methods were also challenged with reference strains and isolates of heterotrophic bacteria from drinking water. This indicated that heterotrophic bacteria commonly encountered in drinking water are detected by both the YEA pour plate method and Quanti-Disc. Analysis of data from split water samples (723 for 37 degrees C tests and 872 for 22 degrees C tests) from nine geographically diverse laboratories in England and Wales demonstrated that the Quanti-Disc method is equivalent to the YEA pour plate method for the analysis of heterotrophic bacteria from drinking and similar waters at 37 degrees C, and superior to YEA for the analysis at 22 degrees C. The Quanti-Disc method is a simple and efficient alternative method for the enumeration of heterotrophic bacteria from drinking water. PMID:18534656

Sartory, David P; Gu, Haoyi; Chen, Chun-Ming

2008-07-01

59

Inverse diffusion methods for data peak separation.  

PubMed

Previous methods for separation of overlapping data peaks include geometrical assessment and Fourier deconvolution. On the basis of inverse diffusion theory, we present new separation methods suitable for convenient programming and rapid calculation of Gaussian area contributions. Both continuum and discrete inverse diffusion models are described. Example computations are given for biological data: density gradient centrifugation, isoelectric focusing electrophoresis, and high-pressure liquid chromatography. PMID:3434792

Crandall, R; McClellan, M; Arch, S; Doenias, J; Piper, R

1987-11-15

60

Correlation between E-Test, Disk Diffusion, and Microdilution Methods for Antifungal Susceptibility Testing of Fluconazole and Voriconazole  

Microsoft Academic Search

The activities of fluconazole and voriconazole against isolates of Candida spp. (n 400) were tested by the E-test, disk diffusion, and the National Committee for Clinical Laboratory Standards (NCCLS) M27-A2 broth microdilution-based reference methods. More than 96% of isolates found to be susceptible to fluconazole by the reference method were identified as susceptible by the agar-based methods. Lesser degrees of

Madonna J. Matar; Luis Ostrosky-Zeichner; Victor L. Paetznick; Jose R. Rodriguez; Enuo Chen; John H. Rex

2003-01-01

61

Bacteria holding times for fecal coliform by mFC agar method and total coliform and Escherichia coli by Colilert-18 Quanti-Tray method.  

PubMed

Bacteria holding-time experiments of up to 62 h were performed on five surface-water samples from four urban stream sites in the vicinity of Atlanta, GA, USA that had relatively high densities of coliform bacteria (Escherichia coli densities were all well above the US Environmental Protection Agency criterion of 126 colonies (100 ml)(-1) for recreational waters). Holding-time experiments were done for fecal coliform using the membrane filtration modified fecal coliform (mFC) agar method and for total coliform and E. coli using the Colilert-18 Quanti-Tray method. The precisions of these analytical methods were quantified. Precisions determined for fecal coliform indicated that the upper bound of the ideal range of counts could reasonably be extended upward and would improve precision. For the Colilert-18 method, analytical precisions were similar to the theoretical precisions for this method. Fecal and total coliform densities did not change significantly with holding times up to about 27 h. Limited information indicated that fecal coliform densities might be stable for holding times of up to 62 h, whereas total coliform densities might not be stable for holding times greater than about 27 h. E. coli densities were stable for holding times of up to 18 h--a shorter period than indicated from a previous studies. These results should be applicable to non-regulatory monitoring sampling designs for similar urban surface-water sample types. PMID:19165613

Aulenbach, Brent T

2010-02-01

62

Bacteria holding times for fecal coliform by mFC agar method and total coliform and Escherichia coli by Colilert??-18 Quanti-Tray ?? method  

USGS Publications Warehouse

Bacteria holding-time experiments of up to 62 h were performed on five surface-water samples from four urban stream sites in the vicinity of Atlanta, GA, USA that had relatively high densities of coliform bacteria (Escherichia coli densities were all well above the US Environmental Protection Agency criterion of 126 colonies (100 ml)???-???1 for recreational waters). Holding-time experiments were done for fecal coliform using the membrane filtration modified fecal coliform (mFC) agar method and for total coliform and E. coli using the Colilert??-18 Quanti-Tray ?? method. The precisions of these analytical methods were quantified. Precisions determined for fecal coliform indicated that the upper bound of the ideal range of counts could reasonably be extended upward and would improve precision. For the Colilert??-18 method, analytical precisions were similar to the theoretical precisions for this method. Fecal and total coliform densities did not change significantly with holding times up to about 27 h. Limited information indicated that fecal coliform densities might be stable for holding times of up to 62 h, whereas total coliform densities might not be stable for holding times greater than about 27 h. E. coli densities were stable for holding times of up to 18 h-a shorter period than indicated from a previous studies. These results should be applicable to non-regulatory monitoring sampling designs for similar urban surface-water sample types. ?? 2009 Springer Science+Business Media B.V.

Aulenbach, B. T.

2010-01-01

63

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

64

Interlaboratory Comparison of Agar Dilution and Etest Methods for Determining the MICs of Antibiotics Used in Management of Neisseria meningitidis Infections  

PubMed Central

Previous studies have shown that there is considerable variation in the methods and media used to determine the susceptibility of Neisseria meningitidis to antimicrobial agents in different countries. In this study, national and regional reference laboratories used a standardized methodology to determine the MICs of antibiotics used in the management of meningococcal infection. Fourteen laboratories participated in the study, determining the susceptibility to penicillin G, rifampin, cefotaxime, ceftriaxone, ciprofloxacin, and ofloxacin of a collection of 17 meningococci, of which 11 strains were previously defined as having intermediate resistance to penicillin (PenI) by sequencing and restriction fragment length polymorphism analysis of the penA gene. The MIC was determined by agar dilution and Etest with Mueller-Hinton agar (MH), MH supplemented with sheep blood (MH+B), and MH supplemented with heated (chocolated) blood. Several laboratories encountered problems obtaining confluent growth with unsupplemented MH. MH+B was considered to give the most congruent and reproducible results among the study laboratories. The modal MIC for MH+B for each antibiotic and method was calculated to define the MIC consensus, allowing assessment of each individual laboratory's data in relation to the others. The agreement in each antibiotic/method/medium combination was defined as the percentage of laboratories with a result within one dilution of the modal result. For the whole study, an agreement of 90.6% was observed between agar dilution and Etest methods. The agreement in each laboratory/antibiotic/method combination ranged from 98.2% to 69.7%, with six laboratories demonstrating agreement higher than 90% and 11 more than 80%. The ability of the laboratories to detect the PenI isolates ranged from 18.2% to 100%. The apparent difficulty in interpreting susceptibility to rifampin, particularly with the Etest method, is very interesting.

Vazquez, Julio A.; Arreaza, Luisa; Block, Colin; Ehrhard, Ingrid; Gray, Stephen J.; Heuberger, Sigrid; Hoffmann, Steen; Kriz, Paula; Nicolas, Pierre; Olcen, Per; Skoczynska, Anna; Spanjaard, Lodewijk; Stefanelli, Paola; Taha, Muhamed-Kheir; Tzanakaki, Georgina

2003-01-01

65

Clustering method for estimating principal diffusion directions  

PubMed Central

Diffusion tensor magnetic resonance imaging (DTMRI) is a non-invasive tool for the investigation of white matter structure within the brain. However, the traditional tensor model is unable to characterize anisotropies of orders higher than two in heterogeneous areas containing more than one fiber population. To resolve this issue, high angular resolution diffusion imaging (HARDI) with a large number of diffusion encoding gradients is used along with reconstruction methods such as Q-ball. Using HARDI data, the fiber orientation distribution function (ODF) on the unit sphere is calculated and used to extract the principal diffusion directions (PDDs). Fast and accurate estimation of PDDs is a prerequisite for tracking algorithms that deal with fiber crossings. In this paper, the PDDs are defined as the directions around which the ODF data is concentrated. Estimates of the PDDs based on this definition are less sensitive to noise in comparison with the previous approaches. A clustering approach to estimate the PDDs is proposed which is an extension of fuzzy c-means clustering developed for orientation of points on a sphere. MDL (Minimum description length) principle is proposed to estimate the number of PDDs. Using both simulated and real diffusion data, the proposed method has been evaluated and compared with some previous protocols. Experimental results show that the proposed clustering algorithm is more accurate, more resistant to noise, and faster than some of techniques currently being utilized.

Nazem-Zadeh, Mohammad-Reza; Jafari-Khouzani, Kourosh; Davoodi-Bojd, Esmaeil; Jiang, Quan; Soltanian-Zadeh, Hamid

2012-01-01

66

Clustering method for estimating principal diffusion directions.  

PubMed

Diffusion tensor magnetic resonance imaging (DTMRI) is a non-invasive tool for the investigation of white matter structure within the brain. However, the traditional tensor model is unable to characterize anisotropies of orders higher than two in heterogeneous areas containing more than one fiber population. To resolve this issue, high angular resolution diffusion imaging (HARDI) with a large number of diffusion encoding gradients is used along with reconstruction methods such as Q-ball. Using HARDI data, the fiber orientation distribution function (ODF) on the unit sphere is calculated and used to extract the principal diffusion directions (PDDs). Fast and accurate estimation of PDDs is a prerequisite for tracking algorithms that deal with fiber crossings. In this paper, the PDDs are defined as the directions around which the ODF data is concentrated. Estimates of the PDDs based on this definition are less sensitive to noise in comparison with the previous approaches. A clustering approach to estimate the PDDs is proposed which is an extension of fuzzy c-means clustering developed for orientation of points on a sphere. MDL (Minimum description length) principle is proposed to estimate the number of PDDs. Using both simulated and real diffusion data, the proposed method has been evaluated and compared with some previous protocols. Experimental results show that the proposed clustering algorithm is more accurate, more resistant to noise, and faster than some of techniques currently being utilized. PMID:21642005

Nazem-Zadeh, Mohammad-Reza; Jafari-Khouzani, Kourosh; Davoodi-Bojd, Esmaeil; Jiang, Quan; Soltanian-Zadeh, Hamid

2011-08-01

67

Mimetic Finite Difference Methods for Diffusion Equations  

Microsoft Academic Search

This paper reviews and extends the theory and application of mimetic finite difference methods for the solution of diffusion problems in strongly heterogeneous non-isotropic materials. These difference operators satisfy the fundamental identities, conservation laws and theorems of vector and tensor calculus on nonorthogonal, nonsmooth, structured and unstructured computational grids. We provide explicit approximations for equations in two dimensions with discontinuous

J. Hyman; J. Morel; M. Shashkov; S. Steinberg

2001-01-01

68

Mimetic Finite Difference Methods for Diffusion Equations  

Microsoft Academic Search

This paper reviews and extends the theory and application of mimetic finite difference methods for the solution of diffusion problems in strongly heterogeneous anisotropic materials. These difference operators satisfy the fundamental identities, conservation laws and theorems of vector and tensor calculus on nonorthogonal, nonsmooth, structured and unstructured computational grids. We provide explicit approximations for equations in two dimensions with discontinuous

J. Hyman; J. Morelb; M. Shashkova; S. Steinberg

2002-01-01

69

Comparison of Radon Diffusion Coefficients Measured by Transient-Diffusion and Steady-State Laboratory Methods.  

National Technical Information Service (NTIS)

A method was developed and used to determine radon diffusion coefficients in compacted soils by transient-diffusion measurements. A relative standard deviation of 12 percent was observed in repeated measurements with a dry soil by the transient-diffusion ...

D. R. Kalkwarf K. K. Nielson D. C. Rich V. C. Rogers

1982-01-01

70

The Growth of Steroidobacter agariperforans sp. nov., a Novel Agar-Degrading Bacterium Isolated from Soil, is Enhanced by the Diffusible Metabolites Produced by Bacteria Belonging to Rhizobiales  

PubMed Central

An agar-degrading bacterium was isolated from soil collected in a vegetable cropping field. The growth of this isolate was enhanced by supplying culture supernatants of bacteria belonging to the order Rhizobiales. Phylogenetic analysis based on 16S rRNA gene sequences indicated the novel bacterium, strain KA5–BT, belonged to the genus Steroidobacter in Gammaproteobacteria, but differed from its closest relative, Steroidobacter denitrificans FST, at the species level with 96.5% similarity. Strain KA5–BT was strictly aerobic, Gram-negative, non-motile, non-spore forming, and had a straight to slightly curved rod shape. Cytochrome oxidase and catalase activities were positive. The strain grew on media containing culture supernatants in a temperature range of 15–37°C and between pH 4.5 and 9.0, with optimal growth occurring at 30°C and pH 6.0–8.0. No growth occurred at 10 or 42°C or at NaCl concentrations more than 3% (w/v). The main cellular fatty acids were iso–C15:0, C16:1?7c, and iso–C17:1?9c. The main quinone was ubiquinone-8 and DNA G+C content was 62.9 mol%. In contrast, strain FST was motile, did not grow on the agar plate, and its dominant cellular fatty acids were C15:0 and C17:1?8c. Based on its phylogenetic and phenotypic properties, strain KA5–BT (JCM 18477T = KCTC 32107T) represents a novel species in genus Steroidobacter, for which the name Steroidobacter agariperforans sp. nov. is proposed.

Sakai, Masao; Hosoda, Akifumi; Ogura, Kenjiro; Ikenaga, Makoto

2014-01-01

71

The in-vitro susceptibilities of vaginal lactobacilli to four broad-spectrum antibiotics, as determined by the agar dilution and E test methods.  

PubMed

The minimum inhibitory concentrations (MICs) of cefaclor, co-amoxiclav, clarithromycin and ciprofloxacin for 59 strains of vaginal lactobacilli were determined by both the reference agar dilution and E test methods. With the exception of clarithromycin, there was poor correlation between the results obtained by the two techniques. This was most apparent for the beta-lactams studied, the MICs of cefaclor as determined by the E test being particularly difficult to define. The stability of antimicrobial gradients in the E test may cause problems when testing slow-growing bacteria and/or organisms which grow only under anaerobic conditions. Accordingly, only those MICs determined by the agar dilution method are reported. The percentages of susceptible isolates were as follows: clarithromycin, 100; co-amoxiclav, 100; cefaclor, 20; and ciprofloxacin, 4. The administration of antimicrobials, such as ciprofloxacin and cefaclor, which have poor activities in vitro against lactobacilli, may therefore be advantageous to the host because it allows the protective effects of the normal vaginal flora to be preserved. PMID:7559189

Herra, C M; Cafferkey, M T; Keane, C T

1995-06-01

72

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.  

PubMed

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, stormwater, and surface water). Regulatory outcomes were also compared based on choice of indicator and method. Positive correlation was seen between QPCR cell equivalents and viable cells through the wastewater treatment process and in all surface water samples (river or freshwater bathing beach) but not in direct stormwater discharge. For surface water samples, correlation improved with the application of a site-specific corrective factor, with regulatory action correctly predicted 98% of the time at bathing beaches. This study suggests the potential utility of QPCR for certain water quality monitoring applications. PMID:19717179

Lavender, Jennifer S; Kinzelman, Julie L

2009-11-01

73

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

74

Standardized methods and quality control limits for agar and broth microdilution susceptibility testing of Mycoplasma pneumoniae, Mycoplasma hominis, and Ureaplasma urealyticum.  

PubMed

An international multilaboratory collaborative study was conducted to develop standard media and consensus methods for the performance and quality control of antimicrobial susceptibility testing of Mycoplasma pneumoniae, Mycoplasma hominis, and Ureaplasma urealyticum using broth microdilution and agar dilution techniques. A reference strain from the American Type Culture Collection was designated for each species, which was to be used for quality control purposes. Repeat testing of replicate samples of each reference strain by participating laboratories utilizing both methods and different lots of media enabled a 3- to 4-dilution MIC range to be established for drugs in several different classes, including tetracyclines, macrolides, ketolides, lincosamides, and fluoroquinolones. This represents the first multilaboratory collaboration to standardize susceptibility testing methods and to designate quality control parameters to ensure accurate and reliable assay results for mycoplasmas and ureaplasmas that infect humans. PMID:22915608

Waites, Ken B; Duffy, Lynn B; Bébéar, Cécile M; Matlow, Anne; Talkington, Deborah F; Kenny, George E; Totten, Patricia A; Bade, Donald J; Zheng, Xiaotian; Davidson, Maureen K; Shortridge, Virginia D; Watts, Jeffrey L; Brown, Steven D

2012-11-01

75

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

Microsoft Academic Search

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

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

1982-01-01

76

Evaluation of an automated agar plate streaker.  

PubMed Central

An automated agar plate streaker was evaluated. The Autostreaker mechanizes the agar plate streaking process by providing storage for plates, labeling and streaking one or more plates for either isolation or quantitation, and stacking in one of several racks for subsequent incubation. Results showed the Autostreaker to produce agar plates with well-separated colonies and accurate colony counts. A total of 1,930 clinical specimens were processed either in parallel with manual methods or solely by the Autostreaker. Technologist acceptance of machine-streaked plates was outstanding. Images

Tilton, R C; Ryan, R W

1978-01-01

77

Extraction of agar from Gelidium sesquipedale (Rhodopyta) and surface characterization of agar based films.  

PubMed

The chemical structure of the agar obtained from Gelidium sesquipedale (Rhodophyta) has been determined by (13)C nuclear magnetic resonance ((13)C NMR) and Fourier transform infrared spectroscopy (FTIR). Agar (AG) films with different amounts of soy protein isolate (SPI) were prepared using a thermo-moulding method, and transparent and hydrophobic films were obtained and characterized. FTIR analysis provided a detailed description of the binding groups present in the films, such as carboxylic, hydroxyl and sulfonate groups, while the surface composition was examined using X-ray photoelectron spectroscopy (XPS). The changes observed by FTIR and XPS spectra suggested interactions between functional groups of agar and SPI. This is a novel approach to the characterization of agar-based films and provides knowledge about the compatibility of agar and soy protein for further investigation of the functional properties of biodegradable films based on these biopolymers. PMID:24274535

Guerrero, P; Etxabide, A; Leceta, I; Peñalba, M; de la Caba, K

2014-01-01

78

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

PubMed

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

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

2008-11-01

79

Hektoen Enteric Agar Protocol  

NSDL National Science Digital Library

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

American Society For Microbiology;

2010-11-11

80

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

81

Spectral methods for atmospheric diffusion modeling  

Microsoft Academic Search

The rate of diffusion of a cloud depends on cloud dimensions. As the cloud enlarges, larger eddies come into play and the rate of diffusion increases. The turbulent diffusion process is scale-dependent. The gradient-transfer theory (K-theory) is only appropriate when the dimensions of the dispersed material are much larger than the size of the turbulent eddies. Introduction of a spectral

Ruwim Berkowicz

1984-01-01

82

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

NASA Astrophysics Data System (ADS)

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

Koh, Wonryull; Blackwell, Kim T.

2012-10-01

83

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

PubMed Central

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

Koh, Wonryull; Blackwell, Kim T.

2012-01-01

84

Troubleshooting in the Analysis of Hexachlorocyclohexane Isomers in Agar-Agar Culture Media  

Microsoft Academic Search

A method to determine hexachlorocyclohexane isomers (HCHs) in agar-agar culture media was developed in order to study the bioremediation potential of these compounds. Spiked culture medium samples (0.5 g) were finely chopped and then extracted with 20 ml of hexane:ethyl acetate (80:20) in an ultrasonic bath during 30 min and analyzed by gas chromatography and electron capture detection (GC-ECD). Analytical

M. Barriada-Pereira; M. J. González-Castro; S. Muniategui-Lorenzo; P. López-MahÍa; D. Prada-RodrÍguez; E. Fernández-Fernández

2007-01-01

85

Automatic agar tray inoculation device  

NASA Technical Reports Server (NTRS)

Automatic agar tray inoculation device is simple in design and foolproof in operation. It employs either conventional inoculating loop or cotton swab for uniform inoculation of agar media, and it allows technician to carry on with other activities while tray is being inoculated.

Wilkins, J. R.; Mills, S. M.

1972-01-01

86

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

PubMed Central

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

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

2013-01-01

87

Adaptive streamline diffusion finite element methods for stationary convection-diffusion problems  

SciTech Connect

Adaptive finite element methods for stationary convection-diffusion problems are designed and analyzed. The underlying discretization scheme is the Shock-capturing Streamline Diffusion method. The adaptive algorithms proposed are based on a posteriori error estimates for this method leading to reliable methods in the sense that the desired error control is guaranteed. A priori error estimates are used to show that the algorithms are efficient in a certain sense. 19 refs.

Eriksson, K.; Johnson, C.

1993-01-01

88

Diffuse-Interface Methods in Fluid Mechanics  

NASA Technical Reports Server (NTRS)

The authors review the development of diffuse-interface models of hydrodynamics and their application to a wide variety of interfacial phenomena. The authors discuss the issues involved in formulating diffuse-interface models for single-component and binary fluids. Recent applications and computations using these models are discussed in each case. Further, the authors address issues including sharp-interface analyses that relate these models to the classical free-boundary problem, related computational approaches to describe interfacial phenomena, and related approaches describing fully-miscible fluids.

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

1997-01-01

89

Nodal Polynomial Expansion Method to Solve the Multigroup Diffusion Equations.  

National Technical Information Service (NTIS)

The methodology of the solutions of the multigroup diffusion equations and uses the Nodal Polynomial Expansion Method is covered. The EPON code was developed based upon the above mentioned method for stationary state, rectangular geometry, one-dimensional...

R. D. M. Ribeiro

1983-01-01

90

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

91

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

PubMed Central

We first determined the analytical specificity and ubiquity (i.e., the ability to detect all or most strains) of a Clostridium perfringens-specific real-time PCR (rtPCR) assay based on the cpa gene (cpa rtPCR) by using a bacterial strain panel composed of C. perfringens and non-C. perfringens Clostridium strains. All non-C. perfringens Clostridium strains tested negative, whereas all C. perfringens strains tested positive with the cpa rtPCR, for an analytical specificity and ubiquity of 100%. The cpa rtPCR assay was then used to confirm the identity of 116 putative C. perfringens isolates recovered after filtration of water samples and culture on mCP agar. Colonies presenting discordant results between the phenotype on mCP agar and cpa rtPCR were identified by sequencing the 16S rRNA and cpa genes. Four mCP?/rtPCR+ colonies were identified as C. perfringens, whereas 3 mCP+/rtPCR? colonies were identified as non-C. perfringens. The cpa rtPCR was negative with all 51 non-C. perfringens strains and positive with 64 of 65 C. perfringens strains. Finally, we compared mCP agar and a CRENAME (concentration and recovery of microbial particles, extraction of nucleic acids, and molecular enrichment) procedure plus cpa rtPCR (CRENAME + cpa rtPCR) for their abilities to detect C. perfringens spores in drinking water. CRENAME + cpa rtPCR detected as few as one C. perfringens CFU per 100 ml of drinking water sample in less than 5 h, whereas mCP agar took at least 25 h to deliver results. CRENAME + cpa rtPCR also allows the simultaneous and sensitive detection of Escherichia coli and C. perfringens from the same potable water sample. In itself, it could be used to assess the public health risk posed by drinking water potentially contaminated with pathogens more resistant to disinfection.

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

2013-01-01

92

A Bayesian method with reparameterization for diffusion tensor imaging  

NASA Astrophysics Data System (ADS)

A multi-tensor model with identifiable parameters is developed for diffusion weighted MR images. A new parameterization method guarantees the symmetric positive-definiteness of the diffusion tensor. We set up a Bayesian method for parameter estimation. To investigate properties of the method, Monte Carlo simulated data from three distinct DTI direction schemes have been analyzed. The multi-tensor model with automatic model selection has also been applied to a healthy human brain dataset. Standard tensor-derived maps are obtained when the single-tensor model is fitted to a region of interest with a single dominant fiber direction. High anisotropy diffusion flows and main diffusion directions can be shown clearly in the FA map and diffusion ellipsoid map. For another region containing crossing fiber bundles, we estimate and display the ellipsoid map under the single tensor and double-tensor regimes of the multi-tensor model, suitably thresholding the Bayes factor for model selection.

Zhou, Diwei; Dryden, Ian L.; Koloydenko, Alexey; Li, Bai

2008-04-01

93

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

94

48 CFR 401.371 - AGAR Advisories.  

Code of Federal Regulations, 2010 CFR

... 4 2009-10-01 2009-10-01 false AGAR Advisories. 401.371 Section 401.371 ...Agency Acquisition Regulations 401.371 AGAR Advisories. The SPE may issue AGAR Advisories, consistent with the policies of...

2009-10-01

95

48 CFR 401.371 - AGAR Advisories.  

Code of Federal Regulations, 2010 CFR

... 4 2010-10-01 2010-10-01 false AGAR Advisories. 401.371 Section 401.371 ...Agency Acquisition Regulations 401.371 AGAR Advisories. The SPE may issue AGAR Advisories, consistent with the policies of...

2010-10-01

96

Alternative Transrectal Prostate Imaging: A Diffuse Optical Tomography Method  

Microsoft Academic Search

This paper presents a transrectal dual-modality near-infrared (NIR) diffuse optical tomography technique coupled with ultrasonography that provides an integrated method for detecting prostate cancer (PCa). The study that provides an alternative transrectal prostate imaging system stems from the perceived inadequacy of conventional transrectal ultrasound (TRUS) in PCa imaging. The transrectally applied diffuse optical tomography aims to characterize the spatially resolved

Daqing Piao; Kenneth E. Bartels; Zhen Jiang; Gilbert Reed Holyoak; Jerry W. Ritchey; Guan Xu; Charles F. Bunting; Gennady Slobodov

2010-01-01

97

A microfluidic method to measure small molecule diffusion in hydrogels.  

PubMed

Drug release from a fluid-contacting biomaterial is simulated using a microfluidic device with a channel defined by solute-loaded hydrogel; as water is pumped through the channel, solute transfers from the hydrogel into the water. Optical analysis of in-situ hydrogels, characterization of the microfluidic device effluent, and NMR methods were used to find diffusion coefficients of several dyes (model drugs) in poly(ethylene glycol) diacrylate (PEG-DA) hydrogels. Diffusion coefficients for methylene blue and sulforhodamine 101 in PEG-DA calculated using the three methods are in good agreement; both dyes are mobile in the hydrogel and elute from the hydrogel at the aqueous channel interface. However, the dye acid blue 22 deviates from typical diffusion behavior and does not release as expected from the hydrogel. Importantly, only the microfluidic method is capable of detecting this behavior. Characterizing solute diffusion with a combination of NMR, optical and effluent methods offer greater insight into molecular diffusion in hydrogels than employing each technique individually. The NMR method made precise measurements for solute diffusion in all cases. The microfluidic optical method was effective for visualizing diffusion of the optically active solutes. The optical and effluent methods show potential to be used to screen solutes to determine if they elute from a hydrogel in contact with flowing fluid. Our data suggest that when designing a drug delivery device, analyzing the diffusion from the molecular level to the device level is important to establish a complete picture of drug elution, and microfluidic methods to study such diffusion can play a key role. PMID:24411384

Evans, Stephanie M; Litzenberger, Andrew L; Ellenberger, Anne E; Maneval, James E; Jablonski, Erin L; Vogel, Brandon M

2014-02-01

98

Two new methods of determining radon diffusion in fish otoliths  

Microsoft Academic Search

Otoliths are bony structures found in the ears of fish and used in the210Pb\\/226Ra dating method for age determination. This paper checks the assumption that222Rn is not lost from or added to orange roughy fish otoliths by diffusion, which would invalidate the technique. The first method of monitoring diffusion relies on measuring the gamma activity of daughter radionuclides. Otoliths were

N. E. Whitehead; R. G. Ditchburn

1995-01-01

99

Agar degradation by microorganisms and agar-degrading enzymes.  

PubMed

Agar is a mixture of heterogeneous galactans, mainly composed of 3,6-anhydro-L-galactoses (or L-galactose-6-sulfates) D-galactoses and L-galactoses (routinely in the forms of 3,6-anhydro-L-galactoses or L-galactose-6-sulfates) alternately linked by ?-(1,4) and ?-(1,3) linkages. It is a major component of the cell walls of red algae and has been used in a variety of laboratory and industrial applications, owing to its jellifying properties. Many microorganisms that can hydrolyze and metabolize agar as a carbon and energy source have been identified in seawater and marine sediments. Agarolytic microorganisms commonly produce agarases, which catalyze the hydrolysis of agar. Numerous agarases have been identified in microorganisms of various genera. They are classified according to their cleavage pattern into three types-?-agarase, ?-agarase, and ?-porphyranase. Although, in a broad sense, many other agarases are involved in complete hydrolysis of agar, most of those identified are ?-agarases. In this article we review agarolytic microorganisms and their agar-hydrolyzing systems, covering ?-agarases as well as ?-agarases, ?-neoagarobiose hydrolases, and ?-porphyranases, with emphasis on the recent discoveries. We also present an overview of the biochemical and structural characteristics of the various types of agarases. Further, we summarize and compare the agar-hydrolyzing systems of two specific microorganisms: Gram-negative Saccharophagus degradans 2-40 and Gram-positive Streptomyces coelicolor A3(2). We conclude with a brief discussion of the importance of agarases and their possible future application in producing oligosaccharides with various nutraceutical activities and in sustainably generating stock chemicals for biorefinement and bioenergy. PMID:22526785

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

2012-05-01

100

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

101

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

102

Thermal characterization of magnetically aligned carbonyl iron/agar composites.  

PubMed

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

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

2014-01-01

103

Immobilization of pectin degrading enzyme from Bacillus licheniformis KIBGE IB-21 using agar-agar as a support.  

PubMed

Pectinase from Bacillus licheniformis KIBGE IB-21 was immobilized in agar-agar matrix using entrapment technique. Effect of different concentrations of agar-agar on pectinase immobilization was investigated and it was found that maximum immobilization was achieved at 3.0% agar-agar with 80% enzyme activity. After immobilization, the optimum temperature of enzyme increased from 45 to 50 °C and reaction time from 5 to 10 minutes as compared to free enzyme. Due to the limited diffusion of high molecular weight substrate, K(m) of immobilized enzyme slightly increased from 1.017 to 1.055 mg ml(-1), while Vmax decreased from 23,800 to 19,392 ?M min(-1) as compared to free enzyme. After 120 h entrapped pectinase retained their activity up to 82% and 71% at 30 °C and 40 °C, respectively. The entrapped pectinase showed activity until 10th cycle and maintain 69.21% activity even after third cycle. PMID:24507327

Rehman, Haneef Ur; Aman, Afsheen; Zohra, Raheela Rahmat; Qader, Shah Ali Ul

2014-02-15

104

Assessment of Diffusion Operators in a Novel Moving Particle Method  

Microsoft Academic Search

In this study, solution effectiveness is assessed to gether with its accuracy and required computational cost for three diffusion operators in a newly developed moving-particle method (MPPM) to simulate incompressible flow. The salient feature in the present particle method is the insertion of a pressure mesh within the computational particle cloud to deal with the pressure-related operators in governing equations.

Yao-Hsin Hwang

2012-01-01

105

Exact solutions of nonlinear diffusion equations by variational iteration method  

Microsoft Academic Search

In this paper, He’s variational iteration method is applied to obtain exact solutions of some nonlinear diffusion equations. The variational iteration method is used to construct correction functionals using general Lagrange multipliers identified optimally via the variational theory, and the initial approximations can be freely chosen with unknown constants. The solutions obtained are compared with those obtained by the Adomian

A. Sadighi; D. D. Ganji

2007-01-01

106

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

107

Leapfrog/Finite Element Method for Fractional Diffusion Equation  

PubMed Central

We analyze a fully discrete leapfrog/Galerkin finite element method for the numerical solution of the space fractional order (fractional for simplicity) diffusion equation. The generalized fractional derivative spaces are defined in a bounded interval. And some related properties are further discussed for the following finite element analysis. Then the fractional diffusion equation is discretized in space by the finite element method and in time by the explicit leapfrog scheme. For the resulting fully discrete, conditionally stable scheme, we prove an L 2-error bound of finite element accuracy and of second order in time. Numerical examples are included to confirm our theoretical analysis.

Zhao, Zhengang; Zheng, Yunying

2014-01-01

108

The Validation of Complete Fourier Direct MR Method for Diffusion MRI via Biological and Numerical Phantoms  

PubMed Central

The equations of the Complete Fourier Direct (CFD) MR model are explicitly derived for diffusion weighted NMR experiments. The CFD–MR theory is validated by comparing a biological phantom constructed from nerve bundles and agar gel with its numerical implementation. The displacement integral distribution function estimated from the experimental data is in high agreement with the numerical phantom. CFD–MR’s ability to estimate accurately and fully spin diffusion properties demonstrated here, provides the experimental validation of the theoretical CFD–MR model.

Ozcan, Alpay; Quirk, James D.; Wang, Yong; Wang, Qing; Sun, Peng; Spees, William M.; Song, Sheng-Kwei

2012-01-01

109

Stochastic operator-splitting method for reaction-diffusion systems  

NASA Astrophysics Data System (ADS)

Many biochemical processes at the sub-cellular level involve a small number of molecules. The local numbers of these molecules vary in space and time, and exhibit random fluctuations that can only be captured with stochastic simulations. We present a novel stochastic operator-splitting algorithm to model such reaction-diffusion phenomena. The reaction and diffusion steps employ stochastic simulation algorithms and Brownian dynamics, respectively. Through theoretical analysis, we have developed an algorithm to identify if the system is reaction-controlled, diffusion-controlled or is in an intermediate regime. The time-step size is chosen accordingly at each step of the simulation. We have used three examples to demonstrate the accuracy and robustness of the proposed algorithm. The first example deals with diffusion of two chemical species undergoing an irreversible bimolecular reaction. It is used to validate our algorithm by comparing its results with the solution obtained from a corresponding deterministic partial differential equation at low and high number of molecules. In this example, we also compare the results from our method to those obtained using a Gillespie multi-particle (GMP) method. The second example, which models simplified RNA synthesis, is used to study the performance of our algorithm in reaction- and diffusion-controlled regimes and to investigate the effects of local inhomogeneity. The third example models reaction-diffusion of CheY molecules through the cytoplasm of Escherichia coli during chemotaxis. It is used to compare the algorithm's performance against the GMP method. Our analysis demonstrates that the proposed algorithm enables accurate simulation of the kinetics of complex and spatially heterogeneous systems. It is also computationally more efficient than commonly used alternatives, such as the GMP method.

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

2012-11-01

110

Stochastic operator-splitting method for reaction-diffusion systems  

PubMed Central

Many biochemical processes at the sub-cellular level involve a small number of molecules. The local numbers of these molecules vary in space and time, and exhibit random fluctuations that can only be captured with stochastic simulations. We present a novel stochastic operator-splitting algorithm to model such reaction-diffusion phenomena. The reaction and diffusion steps employ stochastic simulation algorithms and Brownian dynamics, respectively. Through theoretical analysis, we have developed an algorithm to identify if the system is reaction-controlled, diffusion-controlled or is in an intermediate regime. The time-step size is chosen accordingly at each step of the simulation. We have used three examples to demonstrate the accuracy and robustness of the proposed algorithm. The first example deals with diffusion of two chemical species undergoing an irreversible bimolecular reaction. It is used to validate our algorithm by comparing its results with the solution obtained from a corresponding deterministic partial differential equation at low and high number of molecules. In this example, we also compare the results from our method to those obtained using a Gillespie multi-particle (GMP) method. The second example, which models simplified RNA synthesis, is used to study the performance of our algorithm in reaction- and diffusion-controlled regimes and to investigate the effects of local inhomogeneity. The third example models reaction-diffusion of CheY molecules through the cytoplasm of Escherichia coli during chemotaxis. It is used to compare the algorithm's performance against the GMP method. Our analysis demonstrates that the proposed algorithm enables accurate simulation of the kinetics of complex and spatially heterogeneous systems. It is also computationally more efficient than commonly used alternatives, such as the GMP method.

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

2012-01-01

111

The flux-integral method for multidimensional convection and diffusion  

NASA Technical Reports Server (NTRS)

The flux-integral method is a procedure for constructing an explicit, single-step, forward-in-time, conservative, control volume update of the unsteady, multidimensional convection-diffusion equation. The convective plus diffusive flux at each face of a control-volume cell is estimated by integrating the transported variable and its face-normal derivative over the volume swept out by the convecting velocity field. This yields a unique description of the fluxes, whereas other conservative methods rely on nonunique, arbitrary pseudoflux-difference splitting procedures. The accuracy of the resulting scheme depends on the form of the subcell interpolation assumed, given cell-average data. Cellwise constant behavior results in a (very artificially diffusive) first-order convection scheme. Second-order convection-diffusion schemes correspond to cellwise linear (or bilinear) subcell interpolation. Cellwise quadratic subcell interpolants generate a highly accurate convection-diffusion scheme with excellent phase accuracy. Under constant-coefficient conditions, this is a uniformly third-order polynomial interpolation algorithm (UTOPIA).

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

1994-01-01

112

Parametric level set reconstruction methods for hyperspectral diffuse optical tomography  

PubMed Central

A parametric level set method (PaLS) is implemented for image reconstruction for hyperspectral diffuse optical tomography (DOT). Chromophore concentrations and diffusion amplitude are recovered using a linearized Born approximation model and employing data from over 100 wavelengths. The images to be recovered are taken to be piecewise constant and a newly introduced, shape-based model is used as the foundation for reconstruction. The PaLS method significantly reduces the number of unknowns relative to more traditional level-set reconstruction methods and has been show to be particularly well suited for ill-posed inverse problems such as the one of interest here. We report on reconstructions for multiple chromophores from simulated and experimental data where the PaLS method provides a more accurate estimation of chromophore concentrations compared to a pixel-based method.

Larusson, Fridrik; Fantini, Sergio; Miller, Eric L.

2012-01-01

113

Finite Volume Methods for Diffusion Convection Equations on General Meshes  

Microsoft Academic Search

IntroductionFinite volume methods have been extensively used for industrial problems,in the case of hyperbolic equations, elliptic equations or coupled systems ofequations. The advantage of finite volume schemes using non structured meshesis clear for convection diffusion equations: on one hand, the stability and convergenceproperties of the finite volume scheme (using an upwind choice forthe convective flux) ensure a robust scheme for

Raphaèle Herbin

1996-01-01

114

Thermal Diffusivity Measurement by a Radial Heat Flow Method.  

National Technical Information Service (NTIS)

A method is presented whereby the thermal diffusivity of a solid is measured by observing the temperature excursion which results from a radial flow of heat. The radial heat flow is produced by the instantaneous deposition of energy on a disk region of on...

A. B. Donaldson R. E. Taylor

1975-01-01

115

Comparison of spiral gradient and conventional agar dilution for susceptibility testing of anaerobic bacteria.  

PubMed Central

Antimicrobial susceptibility tests were performed on brucella laked blood agar with 340 isolates and 14 antimicrobial agents by the standard agar dilution technique and the spiral gradient technique in which antibiotic concentrations were established by diffusion from the agar surface. For comparison, spiral gradient MICs were determined by calculating antimicrobial concentrations at growth endpoints and rounding up to the next twofold incremental concentration. The cumulative percentage of strains susceptible at the breakpoint determined from spiral gradient data was within 10%, generally, of the percentage of strains susceptible at the breakpoint determined from agar dilution data. The overall agreement between the two techniques (within one doubling dilution) was 90.6%. The spiral gradient agar dilution technique is a reasonable alternative to the conventional agar dilution technique for susceptibility testing of anaerobic bacteria. Images

Wexler, H M; Molitoris, E; Jashnian, F; Finegold, S M

1991-01-01

116

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

117

[Evaluation of the ChromID ESBL agar for the detection of ESBL-positive Enterobacteriaceae and vancomycin-resistant enterococcus isolates from urine cultures].  

PubMed

Extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae strains are frequent causative agents both in community-acquired infections and in nosocomial infections. The newly developed ChromID ESBL agar (bioMerieux, Marcy I'Etoile, France) is a chromogenic medium that helps rapid identification of ESBL-positive Enterobacteriaceae species from the clinical samples. The aim of this study was to evaluate the performance of ChromID ESBL agar in the rapid identification of ESBL-positive pathogens from the urine samples of the patients with urinary tract infections. A total of 672 urine samples (437 outpatients, 235 inpatients) were included in the study. All of the samples were inoculated simultaneously to 5% sheep blood agar, McConkey agar and ChromID ESBL agar media, and evaluated after incubation at 37°C for 18-24 hours. Gram-negative pathogens were tested for ESBL both by the standard combined double-disk diffusion (CDD) method using ceftazidime and cefotaxime disks and by doubledisk synergy (DDS) test. Among 672 urine cultures, 199 yielded microbial growth in routine media (sheep blood agar and/or McConkey agar), whereas 57 yielded bacterial growth in ChromID ESBL agar. When CDD method was accepted as the reference method according to Clinical and Laboratory Standards Institute (CLSI) recommendations, the sensitivity, specificity, positive and negative predictive values for ChromID ESBL agar for the detection of ESBL-positive bacteria in urinary tract infections were estimated as 97%, 92.9%, 89.1%, and 98.1%, respectively. Additionally, we also discovered that Chrom ID ESBL agar could detect vancomycin-resistant enterococci (VRE) as well as ESBL-positive bacteria, in our study. In order to investigate this observation we inoculated a total of 203 stock strains of Enterococcus spp. (118 vancomycin-sensitive, 85 vancomycin-resistant) to this medium. None of the vancomycinsensitive Enterococcus spp. did grow in ChromID ESBL medium, while 83 of the 85 resistant isolates (97.6%) did grow in the medium. As a result, it was concluded that ChromID ESBL agar medium was advantageous since it led to the growth of VRE and ESBL-positive Enterobacteriaceae isolates in different colors and helped in early identification of these two problematic bacteria. We thought that especially early detection of VRE will accelerate the establishment of necessary measures to prevent the nosocomial spread of this microorganism. PMID:22399167

Al??kan, Hikmet Eda; Colako?lu, Sule; Turunç, Tuba; Demiro?lu, Yusuf Ziya

2012-01-01

118

Method for fast pulsed thermal diffusivity measurements in thin films  

SciTech Connect

A modification of the pulse heating technique for thermal diffusivity measurements is described for use with thin vapor deposited coatings. This method uses a capacitive storage pulsed power system to resistively heat thin substrates in a 20 microsecond time interval to temperatures within the 1000 to 3000/sup 0/K range. The rapid heating allows not only the study of thin coatings, but also allows data unperturbed by sample changes to be collected on materials which experience gradual restructuring or mass loss at high temperatures. Samples in this work are prepared as vapor deposited films on the substrate before the test. These films, with high-electrical resistivity relative to the substrate, are heated primarily by thermal diffusion after the electrical pulse. This diffusion is observed by a fast infrared optical pyrometer system imaged on the coating surface. The observed surface temperature behavior is then compared to solutions of the heat transfer equations in which the thermal diffusivity is parametrically adjusted to match the experimental profiles. A family of such experiments for Sc and ScD/sub x/ films ranging from 5 to 10 microns thick are discussed and compared with previous thermal diffusivity data. The present work extends to temperatures well above previous measurements for these materials.

Benson, D.A.; Miller, G.D.

1981-01-01

119

Method of making gas diffusion layers for electrochemical cells  

DOEpatents

A method is provided for making a gas diffusion layer for an electrochemical cell comprising the steps of: a) combining carbon particles and one or more surfactants in a typically aqueous vehicle to make a preliminary composition, typically by high shear mixing; b) adding one or more highly fluorinated polymers to said preliminary composition by low shear mixing to make a coating composition; and c) applying the coating composition to an electrically conductive porous substrate, typically by a low shear coating method.

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

2002-01-01

120

Evaluation of Amorphous Diffusion Bonding by Nonlinear Ultrasonic Method  

Microsoft Academic Search

The characteristic of bond interface in amorphous diffusion bonding, of which evaluation is impossible by conventional method, was quantitatively evaluated by the second harmonic amplitude. Steel bars were bonded with Ni-based amorphous film. Conventional ultrasonic method, e.g. the echo height reflected from bond interface, could not identify samples manufactured at different bonding temperatures 1050, 1150 and 1250°C. Therefore, nonlinear ultrasonic

Y. Ohara; K. Kawashima; R. Yamada; H. Horio

2004-01-01

121

Enhancement of the ultrasound images by modified anisotropic diffusion method.  

PubMed

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

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

2010-12-01

122

An Agar Agar Chamber for the Study of Electromagnetic Waves in an Inhomogeneous Medium.  

National Technical Information Service (NTIS)

A medium for the propagation of electromagnetic waves whose dielectric constant or loss tangent has a prescribed profile was fabricated by using a large quantity of agar agar in simulation chambers. The dielectric constant of the agar agar could be change...

K. Iizuka

1968-01-01

123

Conventional Agar-Based Culture Method, and Nucleic Acid Amplification Test (NAAT) of the cppB Gene for Detection of Neisseria gonorrhea in Pregnant Women Endocervical Swab Specimens  

PubMed Central

Background Neisseria gonorrhea is the etiological agent of the sexually transmitted disease (STD) gonorrhea, and primarily infects the mucous membranes of the urethra, endocervix, pharynx or rectum of females which may result in substantial morbidity. N. gonorrhea also causes disseminated infection, with complications that may result in ectopic pregnancy, tubal infertility, chronic pelvic pain or maternal transmission of gonorrhea, and also increases susceptibility to HIV. Objectives In the present investigation, we used conventional agar-based culture method, and nucleic acid amplification of CCPB gene for detection of Neisseria gonorrhea in endocervical swabs samples collected from pregnant women studied Patients and Methods Endocervical swabs specimens for this study were obtained from 1100 pregnant women who presented to Shiraz (Iran) Hospitals from 2009 to 2011. In the present investigation we used conventional agar-based culture method, and nucleic acid amplification test (NAAT) of CCPB gene for detection of Neisseria gonorrhea in endocervical swabs samples collected from pregnant women studied. From each pregnant woman two endocervical swabs were taken: one swab placed in tubes containing phosphate buffered saline for Polymerase Chain Reaction, and the other to inoculate on culture media. Results Among 1100 endocervical swabs examined, 13 (1.18%) samples had positive results by polymerase chain reaction (PCR) on Neisseria gonorrhea CCPB gene. All endocervical swabs culture had negative results for Neisseria gonorrhea. 84 (7%) of the women had vaginal discharge, in whom PCR on endocervical swabs of these individuals had negative findings. Conclusions Nucleic acid amplification tests (NAATs) are very appropriate in detection of infected individuals. Detection techniques such as NAATs are independent of bacterial viability, and have a potential to limit false negative samples, therefore, in our country, the application of different laboratory diagnosis methods including NAATs with culture as gold standard for determination antimicrobial susceptibility is essential.

Hassanzadeh, Parvin; Mardaneh, Jalal; Motamedifar, Mohammad

2013-01-01

124

Background and Mathematical Analysis of Diffusion MRI Methods  

PubMed Central

The addition of a pair of magnetic field gradient pulses had initially provided the measurement of spin motion with nuclear magnetic resonance (NMR) techniques. In the adaptation of DW-NMR techniques to magnetic resonance imaging (MRI), the taxonomy of mathematical models is divided in two categories: model matching and spectral methods. In this review, the methods are summarized starting from early diffusion weighted (DW) NMR models followed up with their adaptation to DW MRI. Finally, a newly introduced Fourier analysis based unifying theory, so-called Complete Fourier Direct MRI, is included to explain the mechanisms of existing methods.

Ozcan, Alpay; Wong, Kenneth H.; Larson-Prior, Linda; Cho, Zang-Hee; Mun, Seong K.

2013-01-01

125

Chitosan Microparticles Prepared by the Simple Emulsification-Diffusion Method  

Microsoft Academic Search

Biodegradable chitosan microparticles were prepared by a water-in-oil emulsion solvent diffusion method without any surfactants. Aqueous chitosan solution and ethyl acetate were used as the water and oil phases, respectively. The chitosan microparticles; with spherical, deflated, and hollow shapes, could be fabricated from different chitosan concentrations. Chitosan microparticle matrices were sponge-like. The particle sizes increased with the chitosan concentration and

Nualchai Kotsaeng; Jesada Karnchanajindanun; Yodthong Baimark

2010-01-01

126

Diffusely reflecting paints including polytetrafluoroethylene and method of manufacture  

NASA Technical Reports Server (NTRS)

The invention pertains to a high diffuse, reflective paint comprising an alcohol soluble binder, polytetrafluoroethylene (TFE) and an alcohol for coating a substrate and forming an optical reference with a superior Lambertian characteristic. A method for making the paint by first mixing the biner and alcohol, and thereafter by mixing in outgassed TFE is described. A wetting agent may be employed to aid the mixing process.

Schutt, J. B.; Shai, M. C. (inventors)

1985-01-01

127

Method 1603: Escherichia coli (E. coli) in Water by Membrane Filtration Using Modified membrane-Thermotolerant Escherichia coli Agar (Modified mTEC), April 2005.  

National Technical Information Service (NTIS)

Method 1603 describes a membrane filter (MF) procedure for the detection and enumeration of Escherichia coli bacteria in ambient waters and disinfected wastewaters. This method is a single-step modification of EPA Method 1103.1 ( mTEC). Unlike the mTEC me...

2005-01-01

128

Some A Posteriori Error Estimates of the Finite-Difference Streamline-Diffusion Method for Convection-Dominated Diffusion Equations  

Microsoft Academic Search

In this paper, some a posteriori error estimates of the finite-difference streamline-diffusion method for one- and two-dimensional time-dependent convection-dominated diffusion equations are presented, which can be used to reasonably adjust space mesh. Numerical results show that this method of local refinement is feasible and effective.

Tong Kang; Dehao Yu

2001-01-01

129

Kopplung Finiter Methoden fuer Transport-Diffusions-Probleme (Coupling of Finite Methods for Transport-Diffusion Problems).  

National Technical Information Service (NTIS)

Discretization methods for the treatment of transport diffusion problems in fluid mechanics are presented. The general formulation and theoretical fundamentals of a class of discretization methods for such problems are given. A semidiscrete approximation ...

D. Albrecht

1989-01-01

130

Diffusion  

NSDL National Science Digital Library

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

Consortium, The C.

2011-12-11

131

A diffusive information preservation method for small Knudsen number flows  

NASA Astrophysics Data System (ADS)

The direct simulation Monte Carlo (DSMC) method is a powerful particle-based method for modeling gas flows. It works well for relatively large Knudsen (Kn) numbers, typically larger than 0.01, but quickly becomes computationally intensive as Kn decreases due to its time step and cell size limitations. An alternative approach was proposed to relax or remove these limitations, based on replacing pairwise collisions with a stochastic model corresponding to the Fokker-Planck equation [J. Comput. Phys., 229, 1077 (2010); J. Fluid Mech., 680, 574 (2011)]. Similar to the DSMC method, the downside of that approach suffers from computationally statistical noise. To solve the problem, a diffusion-based information preservation (D-IP) method has been developed. The main idea is to track the motion of a simulated molecule from the diffusive standpoint, and obtain the flow velocity and temperature through sampling and averaging the IP quantities. To validate the idea and the corresponding model, several benchmark problems with Kn ˜ 10-3-10-4 have been investigated. It is shown that the IP calculations are not only accurate, but also efficient because they make possible using a time step and cell size over an order of magnitude larger than the mean collision time and mean free path, respectively.

Fei, Fei; Fan, Jing

2013-06-01

132

A diffusive information preservation method for small Knudsen number flows  

SciTech Connect

The direct simulation Monte Carlo (DSMC) method is a powerful particle-based method for modeling gas flows. It works well for relatively large Knudsen (Kn) numbers, typically larger than 0.01, but quickly becomes computationally intensive as Kn decreases due to its time step and cell size limitations. An alternative approach was proposed to relax or remove these limitations, based on replacing pairwise collisions with a stochastic model corresponding to the Fokker–Planck equation [J. Comput. Phys., 229, 1077 (2010); J. Fluid Mech., 680, 574 (2011)]. Similar to the DSMC method, the downside of that approach suffers from computationally statistical noise. To solve the problem, a diffusion-based information preservation (D-IP) method has been developed. The main idea is to track the motion of a simulated molecule from the diffusive standpoint, and obtain the flow velocity and temperature through sampling and averaging the IP quantities. To validate the idea and the corresponding model, several benchmark problems with Kn ? 10{sup ?3}–10{sup ?4} have been investigated. It is shown that the IP calculations are not only accurate, but also efficient because they make possible using a time step and cell size over an order of magnitude larger than the mean collision time and mean free path, respectively.

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

2013-06-15

133

Enhanced isolation of Serpulina hyodysenteriae by using sliced agar media.  

PubMed Central

A method has been developed for separating Serpulina hyodysenteriae, a large spirochete and the causative agent of swine dysentery (SD), from other fecal anaerobic bacteria in rectal and colonic swabs. This was done by cutting the blood agar in parallel cuts and streaking perpendicular to the cuts in the center of the petri dish. Migration of S. hyodysenteriae from the central streak was apparent by the presence of strong beta-hemolysis along the edges of the cuts. If only S. hyodysenteriae migrated in the cut, they migrated to the end of the cut. However, if both motile bacteria and S. hyodysenteriae migrated in the cut, the motile bacteria migrated to the end of the cut where they formed colonies and the S. hyodysenteriae located along the edges of the cut between the colonies of motile bacteria and the central streak. Although motile bacteria were present where S. hyodysenteriae located, the growth of the motile bacteria was partially inhibited since they rarely formed visible colonies and were low in number. The cut in the agar was thought to improve traction for the serpentine movement of the S. hyodysenteriae and for the flagellar movement of the motile bacteria. Use of sliced blood agar was superior to conventionally streaked blood agar in that (i) it was easier to see strong beta-hemolysis on sliced agar; (ii) frequently, a confirmatory diagnosis could be made using only one petri dish with sliced agar, thereby saving time and media; (iii) S. hyodysenteriae could sometimes be isolated free of other bacteria; and (iv) sliced agar was more effective in isolating S. hyodysenteriae from swine with chronic diarrhea and nondiarrhetic carriers of SD in which the shedding of S. hyodysenteriae was low.

Olson, L D

1996-01-01

134

Test Methods for 'Escherichia coli' in Drinking Water: EC Medium with Mug Tube Procedure. Nutrient Agar with Mug Membrane Filter Procedure.  

National Technical Information Service (NTIS)

Two analytical methods for measuring the bacteriological quality of drinking water are described. They are approved for determining compliance of public water systems with the National Primary Drinking Water Regulations. The presence of Escherichia coli i...

R. H. Bordner

1991-01-01

135

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

136

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

137

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

138

Method 1106.1: Enterococci in Water by Membrane Filtration Using membrane-Enterococcus-Esculin Iron Agar (mE-EIA), April 2005.  

National Technical Information Service (NTIS)

Method 1106.1 describes a membrane filter (MF) procedure for the detection and enumeration of the enterococci bacteria in ambient water. The enterococci bacteria are commonly found in the feces of humans and other warm-blooded animals. Although some strai...

2005-01-01

139

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

National Technical Information Service (NTIS)

This method describes a membrane filter (MF) procedure for the detection and enumeration of Escherichia coli. Because the bacterium is a natural inhabitant only of the intestinal tract of warm-blooded animals, its presence in water samples is an indicatio...

2002-01-01

140

Method 1103.1: Escherichia coli (E. coli) in Water by Membrane Filtration Using Membrane-Thermotolerant Escherichia coli Agar (mTEC), March 2010.  

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 18.4). A water sample is filtered through the membrane which retains the bacteria. After filtration, the membr...

2010-01-01

141

Method 1103.1: Escherichia coli (E. coli) in Water by Membrane Filtration Using Membrane-Thermotolerant Escherichia coli Agar (mTEC), 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 18.4). A water sample is filtered through the membrane which retains the bacteria. After filtration, the membr...

2006-01-01

142

On matrix diffusion: formulations, solution methods and qualitative effects  

NASA Astrophysics Data System (ADS)

Matrix diffusion has become widely recognized as an important transport mechanism. Unfortunately, accounting for matrix diffusion complicates solute-transport simulations. This problem has led to simplified formulations, partly motivated by the solution method. As a result, some confusion has been generated about how to properly pose the problem. One of the objectives of this work is to find some unity among existing formulations and solution methods. In doing so, some asymptotic properties of matrix diffusion are derived. Specifically, early-time behavior (short tests) depends only on ?m2RmDm / Lm2, whereas late-time behavior (long tracer tests) depends only on ?mRm, and not on matrix diffusion coefficient or block size and shape. The latter is always true for mean arrival time. These properties help in: (a) analyzing the qualitative behavior of matrix diffusion; (b) explaining one paradox of solute transport through fractured rocks (the apparent dependence of porosity on travel time); (c) discriminating between matrix diffusion and other problems (such as kinetic sorption or heterogeneity); and (d) describing identifiability problems and ways to overcome them. RésuméLa diffusion matricielle est un phénomène reconnu maintenant comme un mécanisme de transport important. Malheureusement, la prise en compte de la diffusion matricielle complique la simulation du transport de soluté. Ce problème a conduit à des formulations simplifiées, en partie à cause de la méthode de résolution. Il s'en est suivi une certaine confusion sur la façon de poser correctement le problème. L'un des objectifs de ce travail est de trouver une certaine unité parmi les formulations et les méthodes de résolution. C'est ainsi que certaines propriétés asymptotiques de la diffusion matricielle ont été dérivées. En particulier, le comportement à l'origine (expériences de traçage courtes) dépend uniquement du terme ?m2RmDm / Lm2, alors que le comportement à long terme (traçages de longue durée) ne dépend que de ?mRm, et non pas du coefficient de diffusion matricielle ou de la forme et de la taille des blocs. Ceci est toujours vrai pour le temps moyen d'arrivée. Ces propriétés permettent: (a) d'analyser le comportement de la diffusion matricielle; (b) d'expliquer un paradoxe du transport de soluté dans les roches fracturées (la dépendance apparente entre la porosité et le temps de transit); (c) de faire la distinction entre la diffusion matricielle et d'autres problèmes, tels que la sorption cinétique ou l'hétérogénéité et (d) de décrire les problèmes d'identification et les façons de les résoudre. Resumen La difusión en la matriz está reconocida en la actualidad como un importante mecanismo de transporte de solutos. Desgraciadamente, tener en cuenta este proceso complica las simulaciones de transporte. Esto ha llevado a una serie de formulaciones simplificadas, motivadas en parte por el propio método de solución. Como resultado, se ha producido cierta confusión respecto a cuál es la manera adecuada de formular el problema. Uno de los objetivos de este trabajo es encontrar una cierta unidad entre las formulaciones existentes y los métodos de solución, lo que conduce a algunas propiedades asintóticas de la difusión en la matriz; específicamente, se comprueba que el comportamiento para tiempos cortos depende únicamente del parámetro ?m2RmDm / Lm2, mientras que el de tiempos largos depende sólo de ?mRm, y no del coeficiente de difusión en la matriz o del tamaño o forma del bloque. Esto último también es cierto, en todos los casos, respecto al tiempo medio de llegada (definido como el valor esperado de la distribución de tiempos de llegada). Estas propiedades son útiles para: (a) analizar el comportamiento cualitativo de la difusión en la matriz; (b) explicar una de las paradojas del transporte de solutos en medios fracturados, la aparente dependencia entre porosidad y tiempo de llegada; (c) discriminar entre difusión en la matriz y otros problemas, como las reacciones con cinética

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

143

Diffuse optical methods for assessing breast cancer chemotherapy  

NASA Astrophysics Data System (ADS)

In his talk, "Diffuse Optical Methods for Assessing Breast Cancer Chemotherapy," SPIE Fellow Bruce Tromberg (Beckman Laser Institute and Medical Clinic) describes a method combining frequency domain photon migration, essentially a method of tracking photon motion in tissue, with a NIR spectroscopy technique using 850nm LEDs. The result is a scatter corrected absorption spectra. The technique takes advantage of elevated blood and water levels and decreased lipid levels in the presence of tumors to provide a more accurate mapping of the breast, allowing more effective treatment. Tromberg's team recently completed their first full mapping of the breast and have taken the instrument from a standalone unit to a portable one suitable for travel. In addition to providing feedback to enhance breast cancer treatment, Tromberg expects that this technique will be applicable in treating other forms of cancer as well.

Tromberg, Bruce J.

2014-03-01

144

Methods for Diffusive Relaxation in the $P_N$ Equations  

SciTech Connect

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

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

2009-01-01

145

Agar Concentration in Counting Clostridium Colonies.  

National Technical Information Service (NTIS)

Decreasing the agar concentration of a counting medium from the usual 1.5% resulted in larger colonies with less interference from gas in Clostridium botulinum 115B and C. sporogenes PA 3679. Optimal agar concentration was 0.65% for C. botulinum with 24-h...

C. Eller L. Rogers E. S. Wynne

1966-01-01

146

Compact finite volume methods for the diffusion equation  

NASA Technical Reports Server (NTRS)

The paper describes an approach to treating initial-boundary-value problems by finite volume methods in which the parallel between differential and difference arguments is closely maintained. By using intrinsic geometrical properties of the volume elements, it is possible to describe discrete versions of the div, curl, and grad operators which lead, using summation-by-parts techniques, to familiar energy equations as well as the div curl = 0 and curl grad = 0 identities. For the diffusion equation, these operators describe compact schemes whose convergence is assured by the energy equations and which yield both the potential and the flux vector with second-order accuracy. A simplified potential form is especially useful for obtaining numerical results by multigrid and ADI methods.

Rose, Milton E.

1989-01-01

147

Compact finite volume methods for the diffusion equation  

NASA Technical Reports Server (NTRS)

An approach to treating initial-boundary value problems by finite volume methods is described, in which the parallel between differential and difference arguments is closely maintained. By using intrinsic geometrical properties of the volume elements, it is possible to describe discrete versions of the div, curl, and grad operators which lead, using summation-by-parts techniques, to familiar energy equations as well as the div curl = 0 and curl grad = 0 identities. For the diffusion equation, these operators describe compact schemes whose convergence is assured by the energy equations and which yield both the potential and the flux vector with second order accuracy. A simplified potential form is especially useful for obtaining numerical results by multigrid and alternating direction implicit (ADI) methods. The treatment of general curvilinear coordinates is shown to result from a specialization of these general results.

Rose, Milton E.

1989-01-01

148

Multigrid methods for numerical simulation of laminar diffusion flames  

NASA Technical Reports Server (NTRS)

This paper documents the result of a computational study of multigrid methods for numerical simulation of 2D diffusion flames. The focus is on a simplified combustion model, which is assumed to be a single step, infinitely fast and irreversible chemical reaction with five species (C3H8, O2, N2, CO2 and H2O). A fully-implicit second-order hybrid scheme is developed on a staggered grid, which is stretched in the streamwise coordinate direction. A full approximation multigrid scheme (FAS) based on line distributive relaxation is developed as a fast solver for the algebraic equations arising at each time step. Convergence of the process for the simplified model problem is more than two-orders of magnitude faster than other iterative methods, and the computational results show good grid convergence, with second-order accuracy, as well as qualitatively agreement with the results of other researchers.

Liu, C.; Liu, Z.; Mccormick, S.

1993-01-01

149

The physicochemical property characterization of agar acetate.  

PubMed

A series of agar acetates with different degree of substitution (DS) were prepared, and their properties were determined and analyzed. The results showed that the gelling temperature, the gel melting temperature, the gel strength, the gel hardness, the gel fracturability, the gel springiness and the solution apparent viscosity of agar acetates all decreased except that their gel cohesiveness increased with the increase of DS. The variation process of agar molecules in solution from coil to helix could be also observed by measuring solution optical rotation in a lower concentration at which even the solution could not form a gel. The gel skeleton structures of agar acetates were of porous network structures, and the pores became smaller and denser with the increase of DS. After acetylation, the water holding capacity of the agar was improved, but its thermal stability was lowered. PMID:24906725

Xia, Kai; Liu, Xin; Zhao, Jingkun; Zhang, Xiaodong

2014-09-22

150

A Critical Study of Agglomerated Multigrid Methods for Diffusion  

NASA Technical Reports Server (NTRS)

Agglomerated multigrid techniques used in unstructured-grid methods are studied critically for a model problem representative of laminar diffusion in the incompressible limit. The studied target-grid discretizations and discretizations used on agglomerated grids are typical of current node-centered formulations. Agglomerated multigrid convergence rates are presented using a range of two- and three-dimensional randomly perturbed unstructured grids for simple geometries with isotropic and highly stretched grids. Two agglomeration techniques are used within an overall topology-preserving agglomeration framework. The results show that multigrid with an inconsistent coarse-grid scheme using only the edge terms (also referred to in the literature as a thin-layer formulation) provides considerable speedup over single-grid methods but its convergence deteriorates on finer grids. Multigrid with a Galerkin coarse-grid discretization using piecewise-constant prolongation and a heuristic correction factor is slower and also grid-dependent. In contrast, grid-independent convergence rates are demonstrated for multigrid with consistent coarse-grid discretizations. Actual cycle results are verified using quantitative analysis methods in which parts of the cycle are replaced by their idealized counterparts.

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

2009-01-01

151

A Critical Study of Agglomerated Multigrid Methods for Diffusion  

NASA Technical Reports Server (NTRS)

Agglomerated multigrid techniques used in unstructured-grid methods are studied critically for a model problem representative of laminar diffusion in the incompressible limit. The studied target-grid discretizations and discretizations used on agglomerated grids are typical of current node-centered formulations. Agglomerated multigrid convergence rates are presented using a range of two- and three-dimensional randomly perturbed unstructured grids for simple geometries with isotropic and stretched grids. Two agglomeration techniques are used within an overall topology-preserving agglomeration framework. The results show that multigrid with an inconsistent coarse-grid scheme using only the edge terms (also referred to in the literature as a thin-layer formulation) provides considerable speedup over single-grid methods but its convergence deteriorates on finer grids. Multigrid with a Galerkin coarse-grid discretization using piecewise-constant prolongation and a heuristic correction factor is slower and also grid-dependent. In contrast, grid-independent convergence rates are demonstrated for multigrid with consistent coarse-grid discretizations. Convergence rates of multigrid cycles are verified with quantitative analysis methods in which parts of the two-grid cycle are replaced by their idealized counterparts.

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

2011-01-01

152

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 Central

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.

Diez-Aguilar, Maria; del Campo, Rosa; Garcia-Castillo, Maria; Zamora, Javier; Canton, Rafael

2013-01-01

153

Simple procedure for preparation of bluetongue virus and epizootic hemorrhagic disease virus antigens for agar gel immunodiffusion.  

PubMed

A simplified procedure was developed for preparing soluble antigen from two related orbiviruses, bluetongue and epizootic hemorrhagic disease viruses, for agar gel immunodiffusion. The antigens gave excellent results in both micro-agar gel diffusion (agar gel precipitin) and macro-agar gel diffusion (bluetongue immunodiffusion). Minor modification in the spatial arrangement of reference antisera, commonly utilized in the agar gel immunodiffusion tests, was employed to reduce the possible development of false-positive reactions. The procedures for antigen preparation were inexpensive and did not require elaborate filtration or high-speed centrifugation. Stability of antigen preparations at 5 degrees C was excellent (in excess of 3 years for bluetongue virus and 2 years for epizootic hemorrhagic disease virus). PMID:6140269

Stott, J L; Osburn, B I

1983-12-01

154

Tween 40-based precipitate production observed on modified chromogenic agar and development of biological identification kit for Malassezia species.  

PubMed

We developed a simple identification kit for nine species of Malassezia (M. furfur, M. slooffiae, M. sympodialis, M. restricta, M. obtusa, M. globosa, M. pachydermatis, M. dermatis, and M. japonica) based on their biological features. This method utilizes Tween 40-based precipitate production on modified chromogenic agar (CHROMagar) Malassezia medium, growth on specific agars (Sabouraud's dextrose agar, Cremophor EL agar, Tween 60-esculin agar), and catalase reactions. This identification kit was verified with 11 type and reference strains of nine Malassezia species. An additional 26 clinical isolates were also successfully identified using the kit and the results were confirmed by molecular biological analysis. PMID:16702101

Kaneko, Takamasa; Makimura, Koichi; Sugita, Takashi; Yamaguchi, Hideyo

2006-05-01

155

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

156

Characterization of physicochemical properties of carboxymethyl agar.  

PubMed

A series of carboxymethyl agars (CMAs) with different degree of substitution (DS) were prepared, and their properties were determined and analyzed. The results showed that with the increase of DS, the dissolving temperature, the gelling temperature, the gel melting temperature, the gel strength, the gel hardness, the gel fracturability, and the solution apparent viscosity of CMA all decreased, except that its gel cohesiveness and gel springiness increased. The variation process of agar molecules in solution from coil to helix could be observed by measuring the optical rotation of the solution at such a low concentration, at which even the solution could not form a gel. The gel skeleton microstructures of both agar and CMA were of porous network structure, and the pore size of CMA became smaller and denser with the increase of its DS. After carboxymethylation, the agar hygroscopicity was improved, but its thermal stability was lowered. PMID:25037374

Cao, Mingzhao; Liu, Xin; Luan, Jimei; Zhang, Xiaodong

2014-10-13

157

Natural porous agar materials from macroalgae.  

PubMed

Porous agar materials have been prepared from marine macroalgae species using a simple microwave-assisted extraction/drying methodology, providing a new family of polysaccharide derived porous solids. The microwave-assisted extraction allows a more efficient and less time-consuming extraction of the polysaccharide compared to conventional extraction protocols based on conventional heating. DRIFT and (13)C NMR results indicated that the internal agar structure (based on d-galactose and 3,6-anhydro-l-galactose linked units) was preserved after the extraction methodology, which opens a wide range of future possibilities and applications for this new family of porous polysaccharides. The extracted agar materials, which have already applications per se due to their high purities, could be subsequently transformed into a novel family of attractive mesoporous agar materials that could be used as natural templates for the production of nanocrystals of metal oxides. PMID:23399188

Francavilla, Matteo; Pineda, Antonio; Lin, Carol S K; Franchi, Massimo; Trotta, Pasquale; Romero, Antonio A; Luque, Rafael

2013-02-15

158

Differentiation of Candida dubliniensis from Candida albicans on rosemary extract agar and oregano extract agar.  

PubMed

Candida dubliniensis is a recently described pathogenic species which shares many phenotypic features with Candida albicans and therefore, may be misidentified in microbiological laboratories. Because molecular methods can be onerous and unfeasible in routine mycological laboratories with restricted budgets such as those in developing countries, phenotypic techniques have been encouraged in the development of differential media for the presumptive identification of these species. We examined the colony morphology and chlamydospore production of 30 C. dubliniensis isolates and 100 C. albicans isolates on two new proposed media: rosemary (Rosmarinus officinalis) extract agar (REA) and oregano (Origanum vulgare) extract agar (OEA). These substrates are traditionally used as spices and medicinal herbs. In both of these media, all C. dubliniensis isolates (100%) showed rough colonies with peripheral hyphal fringes and abundant chlamydospores after 24 to 48 hr of incubation at 25 degrees C. In contrast, under the same conditions, all isolates of C. albicans (100%) showed smooth colonies without hyphal fringes or chlamydospores. In conclusion, REA and OEA offer a simple, rapid, and inexpensive screening media for the differentiation of C. albicans and C. dubliniensis. PMID:18484650

de Loreto, Erico Silva; Pozzatti, Patrícia; Alves Scheid, Liliane; Santurio, Deise; Morais Santurio, Janio; Alves, Sydney Hartz

2008-01-01

159

21 CFR 866.4600 - Ouchterlony agar plate.  

Code of Federal Regulations, 2010 CFR

...2009-04-01 2009-04-01 false Ouchterlony agar plate. 866.4600 Section 866.4600...and Reagents § 866.4600 Ouchterlony agar plate. (a) Identification. An ouchterlony agar plate for clinical use is a device...

2009-04-01

160

21 CFR 866.4600 - Ouchterlony agar plate.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 false Ouchterlony agar plate. 866.4600 Section 866.4600...and Reagents § 866.4600 Ouchterlony agar plate. (a) Identification. An ouchterlony agar plate for clinical use is a device...

2010-04-01

161

Comparison of Four Selective Agars for the Isolation of Pseudomonads  

PubMed Central

Significant differences were found between Dettol (chloroxylenol) agar, nalidixic acid-cetrimide agar, and two other cetrimide-containing agars used for the isolation of small numbers of pseudomonads.

Hart, A.; Kite, Atricia E.

1977-01-01

162

The Quasi-Diffusion method for solving transport problems in planar and spherical geometries  

Microsoft Academic Search

The Quasi-Diffusion (QD) method [1]–[3] is a nonlinear algorithm for solving linear transport problems. Because the QD method utilizes both a transport sweep and a diffusion calculation within each iteration, it is operationally more complex than the Source Iteration (SI) method, which utilizes only a transport sweep within each iteration. However, the QD method often converges rapidly and with high

M. M. Miften; Edward W. Larsen

1993-01-01

163

Determination of the concentration dependence of polyelectrolyte diffusion coefficients by application of the Boltzmann gradient method  

Microsoft Academic Search

The concentration dependence of a polyelectrolyte diffusion coefficient in aqueous low salt solution (KCl, 1 mM) is determined from a single dynamic gradient experiment. The Boltzmann method is applied to calculate the diffusion coefficient. A special diffusion cell is constructed that minimizes aberrations in the optical detection of the polyion concentration profile. Bovine serum albumin (BSA) is chosen as a

A. T. Wagner; H.-H. Kohler

2008-01-01

164

Measurement of Cupric and Zincate Ion Diffusivities Using the Capillary Method.  

National Technical Information Service (NTIS)

Diffusion coefficients of four binary electrolyte systems were measured using the capillary-reservoir method. The four systems are: 1.0 molar KC1 in aqueous solution diffusing into H2O; 0.01 molar ZnO in 40% KOH solution diffusing into 40% KOH; 0.05 molar...

J. Gendler L. Nanis M. Litt

1974-01-01

165

Numerical transport and diffusion methods in radiative transfer  

SciTech Connect

A numerical discretization scheme, in both space and time, is considered for the equation of radiative transfer and its corresponding diffusion approximation. Numerical results are presented for radiation penetration into a cold slab driven by a constant incident surface intensity. A comparison of results is made among solutions obtained from the discretization of the radiative transfer equation, a flux-limited diffusion approximation, and the classical diffusion approximation. By numerically studying the properties of the flux-limited diffusion approximation, we conclude that the treatment of the nonlinearities in such a description can significantly affect the results. Different iteration strategies of such nonlinearities are discussed and benchmark data for the converged solution are presented in three different time regimes. Finally, we conclude from this analysis that flux limiting is an important factor in solving these types of problems and must be included in an diffusive description.

Szilard, R.H.; Pomraning, G.C. (California Univ., Los Angeles, CA (United States). School of Engineering and Applied Science)

1992-11-01

166

A numerical method for characterizing the time-dependent diffusion of radon in a porous material  

SciTech Connect

This paper describes an experimental test of radon diffusion through a porous material, and a model created to calculate such diffusion. The material studied was Zeolite 4A, which was pressed into slab form, for used in diffusion measurements. The model is based on a nonlinear least squares and Marquardt method. The model has the advantage of giving diffusion results while the system is still in the transient state, and also offering a simpler calculational procedure.

Tasi, S.C.; Hsu, C.N. (National Tsing Hua Univ., Taiwan (Taiwan, Province of China))

1993-12-23

167

Improvement of the homotopy perturbation method for solving nonlinear diffusion equations  

NASA Astrophysics Data System (ADS)

In this paper, the homotopy perturbation method (HPM) is improved to solve nonlinear diffusion equations. Nonlinear diffusion equations are the most important equations in mathematical physics. By applying this improvement (IHPM), exact solutions are obtained for some important physical processes of power-law diffusivities. To illustrate the method, some examples are provided. The convergence of the method is also considered. The results show the efficiency and accuracy of the IHPM.

Jafari, M. A.; Aminataei, A.

2010-07-01

168

Validation of the diffusion-barrier charcoal canister method  

Microsoft Academic Search

A six-month study was conducted by the Technical Measurements Center, US Department of Energy Grand Junction Projects Office, to evaluate the accuracy and reliability of indoor radon measurements using an intermittent diffusion-barrier charcoal canister sampling protocol. Diffusion-barrier charcoal canisters (DBCC) were exposed for seven days in sixteen occupied residences each week during the 26-week study. The radon concentrations measured by

D. E. Martz; J. L. George; S. T. Mamich; G. H. Jr. Langner

1989-01-01

169

Preparation and characterization of agar/clay nanocomposite films: the effect of clay type.  

PubMed

Agar-based nanocomposite films with different types of nanoclays, such as Cloisite Na+, Cloisite 30B, and Cloisite 20A, were prepared using a solvent casting method, and their tensile, water vapor barrier, and antimicrobial properties were tested. Tensile strength (TS), elongation at break (E), and water vapor permeability (WVP) of control agar film were 29.7±1.7 MPa, 45.3±9.6%, and (2.22±0.19)×10(-9) g·m/m2·s·Pa, respectively. All the film properties tested, including transmittance, tensile properties, WVP, and X-ray diffraction patterns, indicated that Cloisite Na+ was the most compatible with agar matrix. TS of the nanocomposite films prepared with 5% Cloisite Na+ increased by 18%, while WVP of the nanocomposite films decreased by 24% through nanoclay compounding. Among the agar/clay nanocomposite films tested, only agar/Cloisite 30B nanocomposite film showed a bacteriostatic function against?Listeria monocytogenes. PMID:21535851

Rhim, Jong-Whan; Lee, Soo-Bin; Hong, Seok-In

2011-04-01

170

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

PubMed

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

Rhim, Jong-Whan

2012-12-01

171

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

PubMed

The effects of the addition of glycerol (GLY) on the physicochemical and morphological properties of poly(vinyl alcohol) (PVA)-agar films were reported. PVA-agar films were prepared by solution cast method, and the addition of GLY in PVA-agar films altered the optical properties, resulting in a decrease in opacity values and in the color difference (?E) of the films. Structural characterization using Fourier transformation infrared (FTIR) spectroscopy and X-ray diffraction (XRD) indicated that the presence of GLY altered the intensity of the bands (from 1200 to 800cm(-1)) and crystallinity. The characterization of the thermal properties indicated that an increase in the agar content produces a decrease in the melting temperature and augments the heat of fusion. Similar tendencies were observed in plasticized films, but at different magnification. The formulation that demonstrated the lowest mechanical properties contained 25wt.% agar, whereas the formulation that contained 75wt.% agar demonstrated a significant improvement. The water vapor transmission rate (WVTR) and surface morphology analysis demonstrated that the structure of PVA-agar films is reorganized upon GLY addition. The physicochemical properties of PVA-agar films using GLY as a plasticizer provide information for the application of this formulation as packaging material for specific food applications. PMID:24875313

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

2014-08-01

172

Analysis and application of the IIPG method to quasilinear nonstationary convection-diffusion problems  

NASA Astrophysics Data System (ADS)

We develop a numerical method for the solution of convection-diffusion problems with a nonlinear convection and a quasilinear diffusion. We employ the so-called incomplete interior penalty Galerkin (IIPG) method which is suitable for a discretization of quasilinear diffusive terms. We analyse a use of the IIPG technique for a model scalar time-dependent convection-diffusion equation and derive hp a priori error estimates in the L2-norm and the H1-seminorm. Moreover, a set of numerical examples verifying the theoretical results is performed. Finally, we present a preliminary application of the IIPG method to the system of the compressible Navier-Stokes equations.

Dolejsí, Vít

2008-12-01

173

Apparatus and method for measuring thermal diffusivity using the flash method  

US Patent & Trademark Office Database

The present invention relates to an apparatus and method for measuring thermal diffusivity using the flash method. The apparatus includes: a laser generator 60 for generating a flash beam 30; a measurement sample 10 having graphite layers 20 formed on front and rear surfaces thereof, through which the flash beam 30 passes; an infrared sensor 70 disposed at the rear of the measurement sample 10 for measuring a temperature and time at the rear surface of the measurement sample 10 from heat 40 dissipated from the measurement sample 10; and operation means 80 for performing an operation based on an output signal of the infrared sensor 70.

2011-07-12

174

Membrane-assisted culture of fungal mycelium on agar plates for RNA extraction and pharmacological analyses.  

PubMed

Fungal mycelium grown in liquid culture is easy to harvest for RNA extraction and gene expression analyses, but liquid cultures often develop rather heterogeneously. In contrast, growth of fungal mycelium on agar plates is highly reproducible. However, this biological material cannot be harvested easily for downstream analyses. This article describes a PVDF (polyvinylidene difluoride) membrane-assisted agar plate culture method that enables the harvest of mycelium grown on agar plates. This culture method leads to a strongly reduced variation in gene expression between biological replicates and requires less growth space as compared with liquid cultures. PMID:24607793

Lange, Mario; Müller, Carolin; Peiter, Edgar

2014-05-15

175

Numerical methods for control and games of regime-switching diffusion systems: Algorithms, analysis, and computations  

Microsoft Academic Search

This work is concerned with numerical methods for controlled regime-switching diffusions. Numerical methods using Markov chain approximation techniques are developed for stochastic control problems, and two-player differential game problems. ^ In the stochastic control problem, the approximating Markov chain has two components: One component is an approximation to the diffusion, whereas the other keeps track of the regimes. A new

Qingshuo Song

2006-01-01

176

An error analysis of white matter tractography methods: synthetic diffusion tensor field simulations  

Microsoft Academic Search

White matter tractography using diffusion tensor MR images is a promising method for estimating the pathways of white matter tracts in the human brain. The success of this method ultimately depends upon the accuracy of the white matter tractography algorithms. In this study, a Monte Carlo simulation was used to investigate the impact of SNR, tensor anisotropy, and diffusion tensor

Mariana Lazar; Andrew L. Alexander

2003-01-01

177

Application of He's variational iteration method for solving the Cauchy reaction–diffusion problem  

Microsoft Academic Search

In this paper, the solution of Cauchy reaction–diffusion problem is presented by means of variational iteration method. Reaction–diffusion equations have special importance in engineering and sciences and constitute a good model for many systems in various fields. Application of variational iteration technique to this problem shows the rapid convergence of the sequence constructed by this method to the exact solution.

Mehdi Dehghan; Fatemeh Shakeri

2008-01-01

178

The variational iteration method: A powerful scheme for handling linear and nonlinear diffusion equations  

Microsoft Academic Search

In this work, we introduce a framework for obtaining exact solutions to linear and nonlinear diffusion equations. Exact solutions are developed for some diffusion processes of power law diffusitivies. He’s variational iteration method (VIM) is used for analytic treatment of these equations. The powerful VIM method is capable of handling both linear and nonlinear equations in a direct manner.

Abdul-Majid Wazwaz

2007-01-01

179

Calcium diffusion: A new dating method for archeological materials  

Microsoft Academic Search

Investigation of calcium migration across clay-cement interfaces in building bricks and other similar artifacts ranging in age from about 68 to 3,800 yr shows that calcium diffusion coefficients in the samples' clay layers are equivalent in all of the artifacts studied to date. Consequently, the age of the samples may be estimated from the distance that calcium migrated from the

Carol Waddell; John C. Fountain

1984-01-01

180

The Split Bregman Method for Image Diffusion on Implicit Surfaces  

Microsoft Academic Search

Image diffusion on implicit surfaces is solved by the concepts of intrinsic gradient and intrinsic divergence along with the expression of implicit surfaces using zero level set of a continuous signed distance function. But the finite difference scheme of the relevant gradient descent equations is complex and its computation efficiency is low. The Split Bregman algorithm for the nonlinear variational

Zengfang Zhao; Weibo Wei; Zhenkuan Pan; Cuiping Wang; Shen Hu

2010-01-01

181

Chemical Methods of Control  

NSDL National Science Digital Library

In this lab, learners evaluate the relative effectiveness of various chemical substances (i.e. garlic powder, bathroom cleaner, mouthwash, etc.) as antimicrobial agents. Learners use the agar diffusion method to determine "zones of inhibition." This lesson guide includes background information, questions for learners, and additional activity ideas.

Fran Slowiczek, Ed D.; Peters, Pamela M.

2009-01-01

182

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

183

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

184

Interpolation-free monotone finite volume method for diffusion equations on polygonal meshes  

Microsoft Academic Search

We developed a new monotone finite volume method for diffusion equations. The second-order linear methods, such as the multipoint flux approximation, mixed finite element and mimetic finite difference methods, are not monotone on strongly anisotropic meshes or for diffusion problems with strongly anisotropic coefficients. The finite volume (FV) method with linear two-point flux approximation is monotone but not even first-order

K. Lipnikov; D. Svyatskiy; Y. Vassilevski

2009-01-01

185

Nondestructive in-line monitoring method for diffusion process control in InP  

Microsoft Academic Search

We report a non-destructive in-line monitoring method developed for Cd diffusion into InP on SACM-APD structure. Photocurrent vs voltage measurement are taken directly via proving diffused diodes on a wafer. We demonstrate that there is linear correlation between punch-through voltages Vpt on the photo I-V curves and diffusion depth measured by SIMS and Polaron profiles. It has been established that

Yahong Y. Qian; Chris Pawlowicz; Vlad Temchenko; Christina Elliott; Andrew Woodard; Tedeusz Bryskiewicz; Kim Kirkwood; Kevin Hewitt

2003-01-01

186

Examination of three methods for studying ion diffusion in cement pastes, mortars and concrete  

Microsoft Academic Search

Three laboratory techniques for studying ion diffusion in hydrated cement pastes, mortars and concrete are described and compared.\\u000a In the first method, concentration profiles are produced by analysing material sampled at various distances from the surface\\u000a exposed to the selected ion, after various periods of exposure. The second technique employs a diffusion cell and calculation\\u000a of an effective diffusion coefficient

N. R. Buenfeld; J. B. Newman

1987-01-01

187

Water vapor adsorption isotherms of agar-based nanocomposite films.  

PubMed

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

Rhim, Jong-Whan

2011-10-01

188

Agar Medium for Differential Enumeration of Lactic Streptococci1  

PubMed Central

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

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

1972-01-01

189

Determination of diffusion lengths in silicon by an X-ray method  

NASA Technical Reports Server (NTRS)

By calibrating X-ray machine with cells of known diffusion lengths, measurements on test cells can be madeate rate of one every two minutes with standard deviation of less than two percent. test cells are compared with calibration cells whose diffusion lengths have been measured by an electron beam method.

Lamneck, J. H., Jr.

1970-01-01

190

[Utilization of tomato juice agar (V8 agar) in the presumptive identification of Candida dubliniensis].  

PubMed

We evaluated the capacity of tomato juice agar (V8 agar) to differentiate Candida dubliniensis from Candida albicans based on chlamydospore production. Candida albicans (n= 93) and Candida dubliniensis (n= 26) were studied; 100% of Candida dubliniensis showed chlamydospores and in 92.5% of Candida albicans isolates these elements were absent. These results suggest this medium as an alternative tool for presumptive differentiation between these species. PMID:16501777

Alves, Sydney Hartz; Linares, Carlos Eduardo; Loreto, Erico Silva de; Rodrigues, Magnus; Thomazi, Diego I; Souza, Felipe; Santurio, Janio M

2006-01-01

191

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

NASA Astrophysics Data System (ADS)

There is a need to obtain highly reliable values of thermophysical properties. The thermal conductivity of solids is often calculated from the thermal diffusivity, specific heat, and density, respectively, measured by the laser-flash method, differential scanning calorimetry, and Archimedes' method. The laser-flash method is one of the most well-known methods for measuring the thermal diffusivity of solids above room temperature. This method is very convenient to measure the thermal diffusivity without contact in a short time. On the other hand, it is considered as an absolute reference measurement method, in particular, because only measurements of basic quantities such as time, temperature, length, and electrical quantities are required, and because the uncertainty of measurement can be analytically evaluated. However, it could be difficult in some cases to obtain reliable thermal-diffusivity values. The measurement results can indeed depend on experimental conditions; in particular, the pulse heating energy. A procedure to obtain the intrinsic thermal-diffusivity value was proposed by National Metrology Institute of Japan (NMIJ). Here, "intrinsic" means unique for the material, independent of measurement conditions. In this method, apparent thermal-diffusivity values are first measured by changing the pulse heating energy at the same test temperature. Then, the intrinsic thermal diffusivity is determined by extrapolating these apparent thermal diffusivities to a zero energy pulse. In order to verify and examine the applicability of the procedure for intrinsic thermal-diffusivity measurements, we have measured the thermal diffusivity of some materials (metals, ceramics) using the laser-flash method with this extrapolation procedure. NMIJ and Laboratoire National de Metrologie et d'essais (LNE) have laser-flash thermal-diffusivity measurement systems that are traceable to SI units. The thermal diffusivity measured by NMIJ and LNE on four materials shows good agreement, although they used different measurement systems and different analysis methods of the temperature-rise curve. Experimental verification on the procedure was carried out using the measured results. Some problems and considered solutions for laser-flash thermal-diffusivity measurements are discussed.

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

2013-05-01

192

Fabrication and characterization of oxygen - Diffused titanium using spectroscopy method.  

PubMed

A thin native oxide film that forms on the titanium surface makes contact with the bone tissue has been considered to be of great importance to successful osseointegration. The study investigated oxygen-diffused grade 2 titanium obtained by introducing oxygen into the titanium crystal lattice using thermal treatment in fluidized bed performed at 610°C and 640°C in 6, 8, 12h. The thermal treatment at different temperatures and different times led to the formation of a TiO2 rutile film on the titanium surface and a concentration gradient of oxygen into titanium (XRD/GID analyses and GDOS results). Moreover Raman spectroscopy results showed that the TiO2 film on the surface titanium was composed of two oxides (TiO2), i.e. anatase and rutile, for the analyzed variants of heat treatment. The aim of the present study was to establish the optimum conditions for obtaining oxygen-diffused TiO2 film. The results obtained in the study demonstrated that the use of a fluidized bed for titanium oxidation processes allows for obtaining uniform oxide layers with good adhesion to the substrate, thus improving the titanium surface to suit biomedical applications. PMID:25008161

Lubas, M; Sitarz, M; Jasinski, J J; Jelen, P; Klita, L; Podsiad, P; Jasinski, J

2014-12-10

193

Validation of the diffusion-barrier charcoal canister method  

SciTech Connect

A six-month study was conducted by the Technical Measurements Center, US Department of Energy Grand Junction Projects Office, to evaluate the accuracy and reliability of indoor radon measurements using an intermittent diffusion-barrier charcoal canister sampling protocol. Diffusion-barrier charcoal canisters (DBCC) were exposed for seven days in sixteen occupied residences each week during the 26-week study. The radon concentrations measured by the DBCCs were compared to radon concentrations measured by triplicate sets of four different types of alpha-track monitors and integrated hourly radon concentrations measured by a Pylon Model AB-5 continuous radon monitor. The results were also compared with radon-daughter concentrations measured in these same residences by an Eberline WLM-1 working level monitor. Excellent agreement was observed between the integrated mean radon concentrations measured by the DBCCs compared with the six-month alpha-track results, and between the weekly DBCC readings and average weekly radon concentrations measured by the Pylon radon monitors. An intermittent sampling protocol employing six weekly DBCC measurements spaced approximately every two months throughout the year should provide estimates of the average annual indoor radon concentrations that meet the criteria established for the Grand Junction Remedial Action Program. 9 refs., 17 figs., 9 tabs.

Martz, D.E.; George, J.L.; Mamich, S.T.; Langner, G.H. Jr.

1989-05-01

194

Diffusion zone formation in aluminized MAR-247 from Bi-velocity Phase Field Method  

NASA Astrophysics Data System (ADS)

The Bi-velocity Phase Field Method (BPFM), which allows a quantitative description of diffusion mass transport in multi-phase materials, is presented and applied to simulate formation of a diffusion zone in aluminized MAR-247. The method links the bi-velocity Darken approach with the phase-field model in which the diffusion zone is quantitatively characterized by phase volume fractions. Accordingly, composition dependent diffusivities in a two-phase region are defined. The present method allows calculation of element-distribution profiles and volume fractions of the phases across a diffusion couple. Hence, a diffusion path can be determined for three component systems and, besides, the average stress field and entropy production during diffusion can be calculated. An example of the application of BPFM in the modeling of high-temperature reactive diffusion in an AlCrNi ternary system is presented. The simulated results are compared with experimental data obtained in aluminization of MAR-247 by the chemical vapor deposition process.

Wierzba, Bartek; Tkacz-?miech, Katarzyna

2013-03-01

195

[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

2009-01-01

196

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

197

Automatic surface inoculation of agar trays.  

NASA Technical Reports Server (NTRS)

Description of a machine and technique for the automatic inoculation of a plastic tray containing agar media with a culture, using either a conventional inoculation loop or a cotton swab. The design of the machine is simple, it is easy to use, and it relieves the operator from the manual task of streaking cultures. The described technique makes possible the visualization of the overall qualitative and, to some extent, quantitative relationships of various bacterial types in a sample tested.

Wilkins, J. R.; Mills, S. M.; Boykin, E. H.

1972-01-01

198

A method for optimizing the cosine response of solar UV diffusers  

NASA Astrophysics Data System (ADS)

Instruments measuring global solar ultraviolet (UV) irradiance at the surface of the Earth need to collect radiation from the entire hemisphere. Entrance optics with angular response as close as possible to the ideal cosine response are necessary to perform these measurements accurately. Typically, the cosine response is obtained using a transmitting diffuser. We have developed an efficient method based on a Monte Carlo algorithm to simulate radiation transport in the solar UV diffuser assembly. The algorithm takes into account propagation, absorption, and scattering of the radiation inside the diffuser material. The effects of the inner sidewalls of the diffuser housing, the shadow ring, and the protective weather dome are also accounted for. The software implementation of the algorithm is highly optimized: a simulation of 109 photons takes approximately 10 to 15 min to complete on a typical high-end PC. The results of the simulations agree well with the measured angular responses, indicating that the algorithm can be used to guide the diffuser design process. Cost savings can be obtained when simulations are carried out before diffuser fabrication as compared to a purely trial-and-error-based diffuser optimization. The algorithm was used to optimize two types of detectors, one with a planar diffuser and the other with a spherically shaped diffuser. The integrated cosine errors—which indicate the relative measurement error caused by the nonideal angular response under isotropic sky radiance—of these two detectors were calculated to be f2=1.4% and 0.66%, respectively.

Pulli, Tomi; Kärhä, Petri; Ikonen, Erkki

2013-07-01

199

Diffusion Rate Tomography for Time Domain Electromagnetic Induction Methods  

NASA Astrophysics Data System (ADS)

Although it is now routine to invert near-surface electromagnetic induction data in terms of ground conductivity, geoelectromagnetic inversion remains an open research problem because of its intrinsic non-uniqueness and the need to balance computational efficiency with recovering models bearing some resemblance to real geologic structure. The most popular approach for fitting electromagnetic data is analogous to seismic full-waveform inversion. Whether the data are in the time- or frequency-domain, a model is sought which recovers either the amplitude and phase, or the transient response of some measured waveform. However, imperfect knowledge of the source waveform has the potential to erroneously introduce unwarranted geologic structure in the final recovered earth model. Hence, we explore here an alternative approach that mitigates these effects in highly attenuated electromagnetic data. Rather than inverting for the full waveform response, Diffusion Rate Tomography (DiRT) is based on inverting for the arrival time of some key, diagnostic feature in the measured data. This procedure eliminates any error introduced by incomplete knowledge of the source amplitude due to miscalibration, instrument drift, or battery drainage. Time-domain electromagnetic sounding experiments conducted with a horizontal loop transmitter and offset receiver coil provide a useful test of the concept. As induced eddy currents from the transmitter diffuse beneath the receiver, a polarity change occurs in the vertical component of the observed magnetic field. This polarity change (or zero crossing) is our invertible diagnostic, and given a range of offsets between the transmitter and receiver antennae, the zero-crossing moveout curve constitutes the data we invert. Examples of DiRT for a range of geologic settings will be presented and compared against results from smooth, full-waveform inversion. Interestingly, although DiRT works on fewer data than the full-waveform inversion, there is strong similarity in the recovered models, suggesting future work in examining redundancy in electromagnetic data or optimal regularization schemes.

Kazlauskas, E. M.; Weiss, C. J.

2010-12-01

200

A direct O( N log 2 N) finite difference method for fractional diffusion equations  

NASA Astrophysics Data System (ADS)

Fractional diffusion equations model phenomena exhibiting anomalous diffusion that can not be modeled accurately by the second-order diffusion equations. Because of the nonlocal property of fractional differential operators, the numerical methods have full coefficient matrices which require storage of O( N2) and computational cost of O( N3) where N is the number of grid points. In this paper we develop a fast finite difference method for fractional diffusion equations, which only requires storage of O( N) and computational cost of O( N log 2 N) while retaining the same accuracy and approximation property as the regular finite difference method. Numerical experiments are presented to show the utility of the method.

Wang, Hong; Wang, Kaixin; Sircar, Treena

2010-10-01

201

Bilinear Forms for the Recovery-Based Discontinuous Galerkin Method for Diffusion.  

National Technical Information Service (NTIS)

The present paper introduces bilinear forms that are equivalent to the recovery-based discontinuous Galerkin formulation introduced by Van Leer in 2005. The recovery method approximates the solution of the diffusion equation in a discontinuous function sp...

B. Van Leer M. H. Van Raalte

2007-01-01

202

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

203

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

204

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

205

Application of He's variational iteration method for solving the reaction-diffusion equation with ecological parameters  

Microsoft Academic Search

He’s variational iteration method is applied to the search for the solution of the reaction–diffusion problem with ecological parameters. The method is extremely simple and concise, and comparison with the Adomian method reveals that the present method is an attracting mathematical tool.

D. D. Ganji; G. A. Afrouzi; R. A. Talarposhti

2007-01-01

206

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

207

Chemical structure and quality of agars from Gracilaria  

Microsoft Academic Search

Agar polymers synthesized by species of the genus Gracilaria constitute a complex mixture of molecules, containing several extremes in structure. Sulphate hemi-esters, methyl ethers\\u000a and pyruvic ketals can alter in a number of ways the structural regularity of agar based on strictly 3-O-linked ?-l-galactopyranose and 4-O-linked ?-l-galactopyranose residues. In comparison with agars from Gelidium and Pterocladia, agars from Gracilaria can

Erminio Murano

1995-01-01

208

Report: Antimicrobial potentials of Mentha longifolia by disc diffusion method.  

PubMed

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

Bakht, Jehan; Shaheen, Salma; Shafi, Mohammad

2014-07-01

209

Agars from three species of Gracilaria (Rhodophyta) from Yucatán Peninsula  

Microsoft Academic Search

Gracilaria cervicornis, Gracilaria blodgettii and Gracilaria crassissima growing along the coasts of Yucatán were investigated for their agar content. The effect of different concentrations of NaOH in the alkali treatment was evaluated. The three species of Gracilaria produced agars, both native and alkali treated, with different properties confirming the heterogeneity of the agar polymers in this genera. G. cervicornis produces

Y. Freile-Pelegr??n; E. Murano

2005-01-01

210

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.

211

Numerical study of water diffusion in biological tissues using an improved finite difference method  

PubMed Central

An improved finite difference (FD) method has been developed in order to calculate the behaviour of the nuclear magnetic resonance signal variations caused by water diffusion in biological tissues more accurately and efficiently. The algorithm converts the conventional image-based finite difference method into a convenient matrix-based approach and includes a revised periodic boundary condition which eliminates the edge effects caused by artificial boundaries in conventional FD methods. Simulated results for some modelled tissues are consistent with analytical solutions for commonly used diffusion-weighted pulse sequences, whereas the improved FD method shows improved efficiency and accuracy. A tightly coupled parallel computing approach was also developed to implement the FD methods to enable large-scale simulations of realistic biological tissues. The potential applications of the improved FD method for understanding diffusion in tissues are also discussed.

Xu, Junzhong; Does, Mark D; Gore, John C

2009-01-01

212

COMPARISON OF THE RECOVERIES OF ESCHERICHIA COLI AND TOTAL COLIFORMS FROM DRINKING WATER BY THE MI AGAR METHOD AND THE U.S. ENVIRONMENTAL PROTECTION AGENCY-APPROVED MEMBRANE FILTER METHOD  

EPA Science Inventory

Drinking water regulations under the Final Coliform Rule require that total coliform-positive drinking water samples be examined for the presence of Escherichia coli or fecal coliforms. The current U.S. Environmental Protection Agency-approved membrane filter (MF) method for E. c...

213

A Multigrid Newton-Krylov Method for Multimaterial Equilibrium Radiation Diffusion1  

Microsoft Academic Search

We focus on a fully implicit, nonlinearly converged, solution of multimaterial equilibrium radiation diffusion problems. The nonlinear method of solution is a Newton-Krylov (generalized minimum residual, GMRES) method preconditioned by a multigrid method. The multigrid iteration matrix results from a Picard-type linearization of the governing equations. The governing equation is highly nonlinear with the principal forms of nonlinearity found in

William J. Rider; Dana A. Knoll; Gordon L. Olsony

1999-01-01

214

A Multigrid Newton–Krylov Method for Multimaterial Equilibrium Radiation Diffusion  

Microsoft Academic Search

We focus on a fully implicit, nonlinearly converged, solution of multimaterial equilibrium radiation diffusion problems. The nonlinear method of solution is a Newton–Krylov (generalized minimum residual, GMRES) method preconditioned by a multigrid method. The multigrid iteration matrix results from a Picard-type linearization of the governing equations. The governing equation is highly nonlinear with the principal forms of nonlinearity found in

William J Rider; Dana A Knoll; Gordon L Olson

1999-01-01

215

Field Evaluation of a Diffusive Sampler for Monitoring Formaldehyde in Air: A Comparison of Methods  

Microsoft Academic Search

This field study was conducted to evaluate the performance of the SKC Passive Bubbler (SKC Inc., Eighty Four, Pennsylvania) in monitoring formaldehyde in a working environment. For comparison, a traditional pump and impinger method, National Institute for Occupational Safety and Health (NIOSH) Method 3500, was used as the reference method. Two approaches were used for the field evaluation of diffusive

John R. Kollman

1994-01-01

216

Study of acid diffusion behaves form PAG by using top coat method  

NASA Astrophysics Data System (ADS)

Our past research on measurements of simulation parameters for ArF resists focused on establishing methods for measuring the following parameters:[1]-[4] • Development parameters[1] • PEB parameters[2] • Dill's ABC parameters[3] • Quencher parameter[4] We entered these parameters into a lithography simulator and performed ArF resist simulations.We then explored ways to optimize the ArF resist material and process. This paper reports on our study of methods for measuring the diffusion length of acid generated from PAG during exposures. In our experiment, we applied a PAG-containing top coat (TC) material (second layer) to a PAG-free ArF resist (first layer), then performed the exposure and PEB processes. The acid generated in the TC during the exposure diffused into the ArF resist in the lower layer (first layer) when PEB was performed. The process of developing this sample removed the TC in the second layer and the parts of the first layer into which the acid had diffused.We obtained the acid diffusion length based on the quantity of film removed by the development. We calculated the acid diffusion coefficient after varying the exposure value and repeating the measurement. For this report, we also performed measurements to determine how differences in PAG anion size, amount of quencher additive, and PEB temperature affected the acid diffusion coefficient.We entered the measurements obtained into the PROLITH simulator and explored the effects of acid diffusion on pattern profile.

Sekiguchi, Atsushi; Matsumoto, Yoko

2014-03-01

217

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

218

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

219

Defect structure of zinc doped silicon studied by X-ray diffuse scattering method  

NASA Astrophysics Data System (ADS)

The results of investigation of microdefects (MDs) in Zn doped n-type Si by X-ray diffuse scattering (XRDS) method are presented. Experimental samples were made by a high-temperature diffusion annealing of Zn with subsequent quenching and tempering. The crystal lattice of the samples is found to contain spherical MDs of vacancy type and plane shape MDs of interstitial type with average radius about 0,1 and 2 ?m. The MDs average radius and their type depend on Zn doping level and thermal treatment after compensation diffusion.

Shcherbachev, Kirill D.; Privezentsev, Vladimir V.

2009-12-01

220

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

NASA Technical Reports Server (NTRS)

A new method for predicting the optimal velocity distribution on the wall of a two dimensional diffuser is presented. The method uses dynamic programming to solve the optimal control problem with inequality constraints of state variables. The physical model of optimization is designed to prevent the separation of the boundary layer while approaching the maximum pressure ratio in a diffuser of a specified length. The computational results are in fair agreement with the experimental ones. Optimal velocity distribution on a diffuser wall is said to occur when the flow decelerates quickly at first and then smoothly, while the flow is near separation, but always protected from it. The optimal velocity distribution can be used to design the contour of the diffuser.

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

1991-01-01

221

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

222

Stable and low diffusive hybrid upwind splitting methods  

NASA Technical Reports Server (NTRS)

We introduce in this paper a new concept for upwinding: the Hybrid Upwind Splitting (HUS). This original strategy for upwinding is achieved by combining the two previous existing approaches, the Flux Vector (FVS) and Flux Difference Splittings (FDS), while retaining their own interesting features. Indeed, our approach yields upwind methods that share the robustness of FVS schemes in the capture of nonlinear waves and the accuracy of some FDS schemes in the capture of linear waves. We describe here some examples of such HUS methods obtained by hybridizing the Osher approach with FVS schemes. Numerical illustrations are displayed and will prove in particular the relevance of the HUS methods we propose for viscous calculations.

Coquel, Frederic; Liou, Meng-Sing

1992-01-01

223

Method of fluxless brazing and diffusion bonding of aluminum containing components  

NASA Technical Reports Server (NTRS)

A method of diffusion bonding and fluxless brazing of aluminum containing components is reported. The aluminum surfaces are freed of any aluminum oxide coating and are coated with a polymeric sealer which can be thermally removed leaving essentially no residue. The polymeric sealer is being removed in a substantially oxygen free environment, and the aluminum components are then being brazed or diffusion bonded without the use of a flux to remove oxide coating.

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

1976-01-01

224

Oxygen diffusion in silica glass prepared by the sol–gel method  

Microsoft Academic Search

The oxygen diffusion constants for SiO2 coatings, prepared by the sol–gel method, were determined from Auger depth profile and Raman measurements. To do that, the coatings were deposited on copper substrates, and isothermally treated at various temperatures in air. The oxygen diffusion through the glass coating formed an oxide layer at the copper\\/SiO2 interface. The treatment times, at a given

F. J Garc??a-Rodr??guez; F Pérez-Robles; A Manzano-Ram??rez; Y. V Vorobiev; J González-Hernández

1999-01-01

225

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

Microsoft Academic Search

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).

Ray A. Berry; Richard Saurel; Fabien Petitpas

2009-01-01

226

Thermal Diffusivity Measurements of Refractory Metals as Candidate Reference Materials by the Laser Flash Method  

Microsoft Academic Search

A working group for standardization has organized to establish the Japanese Industrial Standard (JIS) for thermal diffusivity measurements of metals in the temperature range of 300–1700 K by the laser flash method. As candidate reference materials with high purity, high-temperature stability, and easy-to-get on a commercial basis, tantalum, niobium, and molybdenum have been selected. Thermal diffusivity values of the specimens, cut

N. Araki; T. Baba; H. Ohta; M. Ogawa; K. Shinzato; Y. Takasaki; K. Hosono; T. Yamane; D. W. Tang

2005-01-01

227

Practical method of diffusion-welding steel plate in air  

NASA Technical Reports Server (NTRS)

Method is ideal for critical service requirements where parent metal properties are equaled in notch toughness, stress rupture and other characteristics. Welding technique variations may be used on a variety of materials, such as carbon steels, alloy steels, stainless steels, ceramics, and reactive and refractory materials.

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

1971-01-01

228

Integrodifference methods with applications to diffusion and optical propagation  

Microsoft Academic Search

A new general procedure is described for deriving efficient, highly accurate finite-difference schemes. A differential operator is replaced by an exact system of integrodifference equations. The derivative appears inside the integrals, and its various interpolations lead to explicit or implicit approximate formulas. The method is especially useful for nonuniform partitions and for differential operators with variable, singular, or even quasilinear

Greene

1975-01-01

229

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

230

Advanced computational methods for nodal diffusion, Monte Carlo, and S[sub N] problems  

SciTech Connect

This document describes progress on five efforts for improving effectiveness of computational methods for particle diffusion and transport problems in nuclear engineering: (1) Multigrid methods for obtaining rapidly converging solutions of nodal diffusion problems. A alternative line relaxation scheme is being implemented into a nodal diffusion code. Simplified P2 has been implemented into this code. (2) Local Exponential Transform method for variance reduction in Monte Carlo neutron transport calculations. This work yielded predictions for both 1-D and 2-D x-y geometry better than conventional Monte Carlo with splitting and Russian Roulette. (3) Asymptotic Diffusion Synthetic Acceleration methods for obtaining accurate, rapidly converging solutions of multidimensional SN problems. New transport differencing schemes have been obtained that allow solution by the conjugate gradient method, and the convergence of this approach is rapid. (4) Quasidiffusion (QD) methods for obtaining accurate, rapidly converging solutions of multidimensional SN Problems on irregular spatial grids. A symmetrized QD method has been developed in a form that results in a system of two self-adjoint equations that are readily discretized and efficiently solved. (5) Response history method for speeding up the Monte Carlo calculation of electron transport problems. This method was implemented into the MCNP Monte Carlo code. In addition, we have developed and implemented a parallel time-dependent Monte Carlo code on two massively parallel processors.

Martin, W.R.

1993-01-01

231

Comparison of different methods for collection of volatile chemical markers from fungi  

Microsoft Academic Search

Volatile metabolites from Penicillium vulpinum, cultured on Czapek yeast autolysate agar and broth, were collected by three different methods: (1) diffusive sampling from headspace, (2) purging and trapping of headspace gases, and (3) steam distillation extraction (SDE) of biomass and liquid medium. The qualitative nature and semiquantitative amounts of mainly unsaturated compounds like mono- and sesquiterpenes collected by diffusive sampling

Thomas Ostenfeld Larsen; Jens Christian Frisvad

1995-01-01

232

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

PubMed

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

Kucza, Witold

2013-07-25

233

A new method for cancer detection based on diffusion reflection measurements of targeted gold nanorods  

PubMed Central

This paper presents a new method for cancer detection based on diffusion reflection measurements. This method enables discrimination between cancerous and noncancerous tissues due to the intense light absorption of gold nanorods (GNRs), which are selectively targeted to squamous cell carcinoma head and neck cancer cells. Presented in this paper are tissue-like phantom and in vivo results that demonstrate the high sensitivity of diffusion reflection measurements to the absorption differences between the GNR-targeted cancerous tissue and normal, noncancerous tissue. This noninvasive and nonionizing optical detection method provides a highly sensitive, simple, and inexpensive tool for cancer detection.

Ankri, Rinat; Peretz, Vital; Motiei, Menachem; Popovtzer, Rachela; Fixler, Dror

2012-01-01

234

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

Microsoft Academic Search

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

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

2006-01-01

235

Protein diffusion in agarose hydrogel in situ measured by improved refractive index method  

Microsoft Academic Search

The accurate knowledge of the diffusion behavior of protein within biomimetic hydrogel matrix at body temperature has a great implication for the design of efficient controlled release protein-base drug delivery devices. In this paper, we improved our previous in situ refractive index method with great temperature-controlled capability. For the first time, this newly improved method was employed to study the

Songmiao Liang; Jian Xu; Lihui Weng; Hongjun Dai; Xiaoli Zhang; Lina Zhang

2006-01-01

236

Immunoglobulin determination evaluation of the results of immunoelectrophoretic analysis and the radial diffusion method  

Microsoft Academic Search

A comparative study was made of the results of immunoglobulin determination in sera using immunoelectrophoresis and the radial diffusion method of Mancini. The results indicated that, except for certain ranges of immunoglobulin concentration (low, normal or slightly increased) the data obtained by immunoelectrophoresis are unreliable and do not correlate with the values obtained by the Mancini method.

Ben J. M. Zegers; H. Poen; J. W. Stoop; R. E. Ballieux

1968-01-01

237

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

238

Analytical Methods of Solving a Set of Multigroup Diffusion Equations for Homogeneous Reactors. Review.  

National Technical Information Service (NTIS)

A review of the Soviet and foreign literature on analytical methods of solving a set of multigroup diffusion equations for homogeneous reactors is given over the period from 1950 to 1971. The methods of power series expansion and iteration-over-source are...

E. S. Glushkov N. A. Petushkova

1977-01-01

239

Analytical solution of a fractional diffusion equation by variational iteration method  

Microsoft Academic Search

In the present paper the Analytical approximate solution of a fractional diffusion equation is deduced with the help of powerful Variational Iteration method. By using an initial value, the explicit solutions of the equation for different cases have been derived, which accelerate the rapid convergence of the series solution. The present method performs extremely well in terms of efficiency and

S. Das

2009-01-01

240

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

NASA Technical Reports Server (NTRS)

In this paper, we study the Local Discontinuous Galerkin methods for nonlinear, time-dependent convection-diffusion systems. These methods are an extension of the Runge-Kutta Discontinuous Galerkin methods for purely hyperbolic systems to convection-diffusion systems and share with those methods their high parallelizability, their high-order formal accuracy, and their easy handling of complicated geometries, for convection dominated problems. It is proven that for scalar equations, the Local Discontinuous Galerkin methods are L(sup 2)-stable in the nonlinear case. Moreover, in the linear case, it is shown that if polynomials of degree k are used, the methods are k-th order accurate for general triangulations; although this order of convergence is suboptimal, it is sharp for the LDG methods. Preliminary numerical examples displaying the performance of the method are shown.

Cockburn, Bernardo; Shu, Chi-Wang

1997-01-01

241

Method for site characterization of anisotropic diffuse illumination of photovoltaic systems  

NASA Astrophysics Data System (ADS)

In this paper a method to characterize the anisotropy of diffuse illumination incident on photovoltaic systems is presented. PV systems are designed based on standard conditions in which only consider direct and isotropic diffuse illumination. Anisotropic illumination can cause the PV system output to step outside of the design specifications. A baffled multi-detector sensor system is described having a discrete set of azimuthal and declination angle combinations in order to constantly sample the irradiance and the incidence angle of the diffuse illumination in all zenith directions. The sensor was deployed in the Tucson Electric Power Solar Test Yard alongside with commercially available PV systems that are independently monitored. Constant and transient sources of anisotropic diffuse illumination, such as surface reflection and cloud edge effects respectively, are measured and modeled with ray tracing software. Results of the method are described for characterizing diffuse illumination at the TEP Solar Test Yard. Understanding the anisotropic diffuse illumination can potentially allow to more accurately predict PV system or to optimize energy harvesting of systems with non-standard mounting conditions as well as building integrated photovoltaic applications.

Russo, Juan M.; Zhang, Deming; Vorndran, Shelby; Gordon, Michael; Castillo, Jose; Brooks, Adria; Lonij, Vincent; Cronin, Alex; Kostuk, Raymond

2012-10-01

242

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

243

Solution of the Advection-diffusion Equation using the Differential Quadrature Method  

Microsoft Academic Search

Differential Quadrature Method (DQM) to integrate the one-dimensional Advection-diffusion Equation (ADE) is presented. This\\u000a method was applied to two examples and the results were compared with the performance of the Explicit Finite Difference Method\\u000a (EFDM) and Implicit Finite Differences Method (IFDM). Based on the comparison with the exact solution, and both the explicit\\u000a and implicit finite difference solutions, it was

Birol Kaya

2010-01-01

244

Thermal diffusivity measurements at high temperatures by the radial flash method  

NASA Astrophysics Data System (ADS)

The flash method has been extended to measure thermal diffusivity in the radial direction at high temperatures, and in the presence of substantial radiation heat losses. Radial effects in this instance, arise because only a small portion of the front surface of the sample is exposed to the energy source. The present effort complements a recently published study in which thermal diffusivity was measured in the axial direction. In that study, substantial radial heat flow and axial radiation heat losses were experienced. Both methods were used to test the same samples of an isotropic material (POCO AXM-5Q graphite) and an anisotropic material (reactor-grade graphite). Results show that thermal diffusivity in the radial direction can be measured for both isotropic and anisotropic material without accounting for the large radiation heat losses. These results are also compared with those based on the conventional flash method using smaller samples.

Chu, F. I.; Taylor, R. E.; Donaldson, A. B.

1980-01-01

245

The numerical and experimental study of photon diffusion inside biological tissue using boundary integral method  

NASA Astrophysics Data System (ADS)

In this study, the diffusion of photons in turbid media, like biological tissue has been studied. Due to scattering and absorption of photons in such media, the study of photon propagation in biological tissue is complicated. The several numerical methods have been presented to simulate the behavior of diffused photons. Recently, Boundary Integral Method (BIM) has been offered to simulate photon migration inside biological tissues. This method has advantage, e.g. lower computational time in compared with other numerical methods. In this study, the accuracy and precision of BIM compares with another numerical method like Monte Carlo technique and finite difference method, and also the calculated results obtained by BIM and Monte Carlo method evaluate with measured results. Furthermore, the effects of scattering and absorption coefficient of tissue on the measured signal are studied.

Ansari, Mohammad Ali; Alikhani, Saeid; Mohajerani, Ezeddin; Massudi, Reza

2012-03-01

246

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

PubMed

The European Directive on drinking water quality has included mCP agar as the reference method for recovering Clostridium perfringens from drinking waters. In the present study, three media (mCP, TSCF and CP Chromo Select Agar) were evaluated for recovery of C. perfringens in different surface water samples. Out of 139 water samples, using a membrane filtration technique, 131 samples (94.2%) were found to be presumptively positive for C. perfringens in at least one of the culture media. Green colored colonies on CP Chromo Select Agar (CCP agar) were counted as presumptive C. perfringens isolates. Out of 483 green colonies on CCP agar, 96.3% (465 strains, indole negative) were identified as C. perfringens, and 15 strains (3.1%) were indole positive and were identified as Clostridium sordellii, Clostridium bifermentans or Clostridium tetani. Only 3 strains (0.6%) gave false positive results and were identified as Clostridium fallax, Clostridium botulinum, and Clostridium tertium. Variance analysis of the data obtained shows statistically no significant differences in the counts obtained between media employed in this work. The mCP method is very onerous for routine screening and bacterial colonies could not be used for further biochemical testing. The colonies on CCP and TSCF were easy to count and subculture for confirmation tests. TSCF detects sulfite-reducing clostridia, including species other than C. perfringens, and in some cases excessive blackening of the agar frustrated counting of the colonies. If the contamination was too high, TSCF did not consistently produce black colonies and as a consequence, the colonies were white and gave false negative results. On the other hand, the identification of typical and atypical colonies isolated from all media demonstrated that CCP agar was the most useful medium for C. perfringens recovery in water samples. PMID:23816139

Manafi, Mammad; Waldherr, Kerstin; Kundi, Michael

2013-10-01

247

Polyacrylamide grafted Agar: synthesis and applications of conventional and microwave assisted technique.  

PubMed

Polyacrylamide grafted Agar (Ag-g-PAM) has been successfully synthesized by conventional method and microwave assisted method. The former method employs ceric ammonium nitrate (CAN) as the free radical initiator while the latter uses the combination of ceric ammonium nitrate (CAN) and microwave irradiation. The synthesized graft copolymers have been characterized by elemental analysis (C, H, N, O and S), FTIR spectroscopy, intrinsic viscosity measurement and scanning electron micrograph (SEM); taking agar as a reference. Flocculation efficacy of synthesized graft copolymers was studied in kaolin suspension and in waste water through 'Jar test' procedure. In the present investigation, we have observed that polyacrylamide grafted agar synthesized by microwave assisted technique shows superior properties than conventional technique. These properties are reported in terms of intrinsic viscosity, flocculation efficacy and pollutant load reduction of waste water. PMID:22840002

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

2012-10-01

248

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

PubMed Central

In this paper, the multi-term time-fractional wave-diffusion equations are considered. The multi-term time fractional derivatives are defined in the Caputo sense, whose orders belong to the intervals [0,1], [1,2), [0,2), [0,3), [2,3) and [2,4), respectively. Some computationally effective numerical methods are proposed for simulating the multi-term time-fractional wave-diffusion equations. The numerical results demonstrate the effectiveness of theoretical analysis. These methods and techniques can also be extended to other kinds of the multi-term fractional time-space models with fractional Laplacian.

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

2013-01-01

249

An asymptotic induced numerical method for the convection-diffusion-reaction equation  

NASA Technical Reports Server (NTRS)

A parallel algorithm for the efficient solution of a time dependent reaction convection diffusion equation with small parameter on the diffusion term is presented. The method is based on a domain decomposition that is dictated by singular perturbation analysis. The analysis is used to determine regions where certain reduced equations may be solved in place of the full equation. Parallelism is evident at two levels. Domain decomposition provides parallelism at the highest level, and within each domain there is ample opportunity to exploit parallelism. Run time results demonstrate the viability of the method.

Scroggs, Jeffrey S.; Sorensen, Danny C.

1988-01-01

250

Determination of diffusion coefficients in polypyrrole thin films using a current pulse relaxation method  

NASA Technical Reports Server (NTRS)

The current pulse E sub oc relaxation method and its application to the determination of diffusion coefficients in electrochemically synthesized polypyrrole thin films is described. Diffusion coefficients for such films in Et4NBF4 and MeCN are determined for a series of submicron film thicknesses. Measurement of the double-layer capacitance, C sub dl, and the resistance, R sub u, of polypyrrole thin films as a function of potential obtained with the galvanostatic pulse method is reported. Measurements of the electrolyte concentration in reduced polypyrrole films are also presented to aid in the interpretation of the data.

Penner, Reginald M.; Vandyke, Leon S.; Martin, Charles R.

1987-01-01

251

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

252

Monte Carlo-based diffusion tensor tractography with a geometrically corrected voxel-centre connecting method  

NASA Astrophysics Data System (ADS)

Diffusion tensor tractography (DTT) allows one to explore axonal connectivity patterns in neuronal tissue by linking local predominant diffusion directions determined by diffusion tensor imaging (DTI). The majority of existing tractography approaches use continuous coordinates for calculating single trajectories through the diffusion tensor field. The tractography algorithm we propose is characterized by (1) a trajectory propagation rule that uses voxel centres as vertices and (2) orientation probabilities for the calculated steps in a trajectory that are obtained from the diffusion tensors of either two or three voxels. These voxels include the last voxel of each previous step and one or two candidate successor voxels. The precision and the accuracy of the suggested method are explored with synthetic data. Results clearly favour probabilities based on two consecutive successor voxels. Evidence is also provided that in any voxel-centre-based tractography approach, there is a need for a probability correction that takes into account the geometry of the acquisition grid. Finally, we provide examples in which the proposed fibre-tracking method is applied to the human optical radiation, the cortico-spinal tracts and to connections between Broca's and Wernicke's area to demonstrate the performance of the proposed method on measured data.

Bodammer, N. C.; Kaufmann, J.; Kanowski, M.; Tempelmann, C.

2009-02-01

253

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

NASA Astrophysics Data System (ADS)

Like most other minerals, titanite rarely if ever forms perfect crystals. In addition to the point defects that might affect lattice diffusion, there may be extended line- or planar defects along which fast diffusion could occur. During the course of an experimental study of oxygen lattice diffusion in titanite, we found that almost all of the 18O uptake profiles produced in natural titanite crystals departed from the complementary error function solution expected for simple lattice diffusion with a constant surface concentration. Instead, they exhibited "tails" extending deeper into the samples than expected for simple lattice diffusion. The purpose of this contribution is to report on these features—described as "fast-paths" for oxygen diffusion—and outline a method for coping with them in extracting information from diffusion profiles. For both dry and hydrothermal experiments in which the "fast paths" are observed, 18O was used as the diffusant. In dry experiments, the source material was 18O-enriched SiO 2 powder, while 18O-enriched water was used for the hydrothermal experiments. Diffusive uptake profiles of 18O were measured in all cases by nuclear reaction analysis (NRA) using the 18O (p,?) 15N reaction [see Zhang X. Y., Cherniak D. J., and Watson E. B. (2006) Oxygen diffusion in titanite: lattice and fast-path diffusion in single crystals. Chem. Geol.235 105-123]. In our experiments, different sizes of "tails" (with varying 18O concentrations) were observed. Theoretically, under the same temperature and pressure conditions, the sizes of tails should be affected by two factors: the diffusion duration and the defect density. For the same experiment duration, the higher the defect density, the larger the "tail"; for the same defect densities, the longer the diffusion duration, the larger the "tail." The diffusion "tails" could be a result of either planar defects or one-dimensional "pipe" diffusion. AFM imaging of HF etched titanite surfaces confirmed that the etched features might be caused by either parallel planar defects or parallel pipe defects, but could not differentiate between these possibilities. Through theoretical calculations simulating the tailed diffusion profiles using reasonable assumptions of lattice diffusivities and fast-path diffusivities, and comparing these with tail features measured in our samples, it can be concluded that the "tails" observed in our experiments are caused by planar defects rather than pipe defects. A new method was developed for separating the "fast-path" contribution from the overall composite diffusion profile consisting of both "fast-path" and lattice diffusion. Through this process, the lattice diffusion coefficient could be determined, which is required to analyze the tail. The oxygen diffusion rates in the fast-paths were obtained by traditional graphical analysis methods, using the Whipple-Le Claire equation (for 2-D defects) assuming that the width of the fast-path is 1 nm. Two Arrhenius relations were obtained for the fast-path diffusion phenomenon, one for experiments under dry conditions, and the other for hydrothermal conditions:

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

2007-03-01

254

Evaluation of Agar-Based Medium with Sheep Sera for Testing of Drug Susceptibility of Mycobacterium tuberculosis to Isoniazid, Rifampin, Ethambutol, and Streptomycin  

PubMed Central

The performance of sheep sera instead of sheep blood in agar-based media was investigated for susceptibility testing of Mycobacterium tuberculosis against primary drugs. The levels of agreement between agar-based medium supplemented with sheep sera and the proportion method on Middlebrook 7H11 agar as the reference method for determining susceptibility to isoniazid (INH), rifampin (RIF), ethambutol (EMB), and streptomycin (STR) were 98.4, 98.4, 95.3, and 100%, respectively.

Uzun, Meltem; Bozdogan, Bulent

2013-01-01

255

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

256

Use of the diffusion gradient thin film method to measure trace metals in fresh waters at low ionic strength  

Microsoft Academic Search

The diffusion gradients in thin films (DGT) method was investigated and used to measure trace metal concentrations in river water. The principle of DGT is that trace metal ions diffuse through a thin polyacrylamide gel film (the diffusion gel layer) and are subsequently immobilised and concentrated on a layer of Chelex-100 resin embedded in another polyacrylamide gel film (the resin

Mohammed Reza Sangi; Michael J. Halstead; Keith A. Hunter

2002-01-01

257

Numerical simulation of diffusion MRI signals using an adaptive time-stepping method  

NASA Astrophysics Data System (ADS)

The effect on the MRI signal of water diffusion in biological tissues in the presence of applied magnetic field gradient pulses can be modelled by a multiple compartment Bloch-Torrey partial differential equation. We present a method for the numerical solution of this equation by coupling a standard Cartesian spatial discretization with an adaptive time discretization. The time discretization is done using the explicit Runge-Kutta-Chebyshev method, which is more efficient than the forward Euler time discretization for diffusive-type problems. We use this approach to simulate the diffusion MRI signal from the extra-cylindrical compartment in a tissue model of the brain gray matter consisting of cylindrical and spherical cells and illustrate the effect of cell membrane permeability.

Li, Jing-Rebecca; Calhoun, Donna; Poupon, Cyril; Le Bihan, Denis

2014-01-01

258

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

NASA Astrophysics Data System (ADS)

Particular features of the application of Fourier-transform IR diffuse reflection spectroscopy methods to the in situ investigation of spectra of porous rough objects have been considered. The reciprocal influence of the scattering and absorption of porous objects on the formation of the impurity-band contour in the diffuse reflection spectrum when the impurity center is in the vicinity of the fundamental IR absorption band has been analyzed. Using methods of Fourier-transform IR diffuse reflection spectroscopy, processes of mineralization of fragments of mammoth tusks from a multilayer paleolithic site at Yudinovo (Bryansk oblast, Russia) and fragments of mammoth tusks from Yakutia (Russia) have been investigated. Particular features of mineralization processes (carbonate formation and silicification) on the surface and in the volume of objects at different conditions of their burial (humidity, temperature, soil acidity) have been studied.

Zolotarev, V. M.

2014-04-01

259

Characterization of bionanocomposite films prepared with agar and paper-mulberry pulp nanocellulose.  

PubMed

Crystallized nanocellulose (CNC) was separated from paper-mulberry (Broussonetia kazinoki Siebold) bast pulp by sulfuric acid hydrolysis method and they were blended with agar to prepare bionanocomposite films. The effect of CNC content (1, 3, 5 and 10wt% based on agar) on the mechanical, water vapor permeability (WVP), and thermal properties of the nanocomposites were studied. Changes of the cellulose fibers in structure, morphology, crystallinity, and thermal properties of the films were evaluated using FT-IR, TEM, SEM, XRD, and TGA analysis methods. The CNC was composed of fibrous and spherical or elliptic granules of nano-cellulose with sizes of 50-60nm. Properties of agar film such as mechanical and water vapor barrier properties were improved significantly (p<0.05) by blending with the CNC. The tensile modulus and tensile strength of agar film increased by 40% and 25%, respectively, in the composite film with 5wt% of CNC, and the WVP of agar film decreased by 25% after formation of nanocomposite with 3wt% of CNC. The CNC obtained from the paper-mulberry bast pulp can be used as a reinforcing agent for the preparation of bio-nanocomposites, and they have a high potential for the development of completely biodegradable food packaging materials. PMID:24906782

Reddy, Jeevan Prasad; Rhim, Jong-Whan

2014-09-22

260

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

PubMed

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

Yamane, Tsuneo; Tanaka, Ryosuke

2013-01-01

261

Evaluation of the Disk Diffusion Method Compared to the Microdilution Method in Susceptibility Testing of Anidulafungin against Filamentous Fungi?  

PubMed Central

Susceptibility testing of anidulafungin (AFG) against 32 mold isolates showed an excellent correlation between disk diffusion (DD) and broth microdilution methods. Based on our data, a 2-?g disk of AFG and a 24-h reading time might represent the best parameters for AFG DD testing against filamentous fungi.

Maida, Carmelo Massimo; Milici, Maria Eleonora; Trovato, Laura; Oliveri, Salvatore; Amodio, Emanuele; Spreghini, Elisabetta; Scalise, Giorgio; Barchiesi, Francesco

2008-01-01

262

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

Microsoft Academic Search

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

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

2007-01-01

263

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

264

Comparison of three gracilarioids: growth rate, agar content and quality  

Microsoft Academic Search

Three gracilarioid species, Gracilariopsis bailiniae and Gracilaria tenuistipitata from Vietnam and Gracilaria gracilis from Russia, were studied in order to determine whether Gracilaria gracilis might be a superior species for cultivation in brackish-water ponds for agar production compared with the Vietnamese species.\\u000a The effects of different salinity levels on the growth rate and agar production as well as agar properties

Anna V. Skriptsova; Yulia V. Nabivailo

2009-01-01

265

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

266

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

267

Preliminary Evaluation of a Semisolid Agar Antifungal Susceptibility Test for Yeasts and Molds  

Microsoft Academic Search

This report presents a semisolid agar antifungal susceptibility (SAAS) method for the rapid susceptibility screening of yeasts and molds. The reproducibility and accuracy of the SAAS method were assessed by com- paring the MICs of amphotericin B and fluconazole obtained for 10 candidate quality control (QC) American Type Culture Collection yeast strains in >15 replicates with those found by six

HARRIET PROVINE; SUSAN HADLEY

2000-01-01

268

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

269

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

270

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 ...

271

A method for measuring effective radon diffusion coefficients in radon barriers by using modified Lucas cells  

Microsoft Academic Search

Radon proof barriers are used for lowering of radon transport from the soil into the house and the determination of the radon diffusion coefficient is an important parameter to be determined in order to design the minimal thickness of the radon proof insulation. A method has been developed in our laboratory by using modified Lucas cells connected to a radon

L. S. Quindos Poncela; P. L. Fernandez; J. Gomez Arozamena; C. Sainz Fernandez

2005-01-01

272

New contactless method for thermal diffusivity measurements using modulated photothermal radiometry  

NASA Astrophysics Data System (ADS)

Modulated photothermal radiometry is a non-destructive and contactless technique for the characterization of materials. It has two major advantages: a good signal-to-noise ratio through a synchronous detection and a low dependence on the heating power and the optical properties of the sample surface. This paper presents a new method for characterizing the thermal diffusivity of a material when the phase shift between a modulated laser power signal and the thermal signal of a plate sample is known at different frequencies. The method is based on a three-dimensional analytical model which is used to determine the temperature amplitude and the phase in the laser heating of the plate. A new simple formula was developed through multi-parametric analysis to determine the thermal diffusivity of the plate with knowledge of the frequency at the minimum phase shift, the laser beam radius r0 and the sample thickness L. This method was developed to control the variation of the thermal diffusivity of nuclear components and it was first applied to determine the thermal diffusivity of different metals: 304 L stainless steel, nickel, titanium, tungsten, molybdenum, zinc, and iron. The experimental results were obtained with 5%-10% accuracy and corresponded well with the reference values. The present paper also demonstrates the limit of application of this method for plate with thickness r0/100 ? L ? r0/2. The technique is deemed interesting for the characterization of barely accessible components that require a contactless measurement.

Pham Tu Quoc, S.; Cheymol, G.; Semerok, A.

2014-05-01

273

Circular diffuse scattering of akermanite studied by the optical diffraction method  

Microsoft Academic Search

Circular diffuse scattering appears when the incommensurate phase of akermanite transforms partly to either the normal phase or the commensurate phase by exchanging Ca atoms for larger alkali-earth atoms such as Sr or by exchanging Mg atoms for larger atoms such as Fe and\\/or by increasing the temperature. The scattering effect has been investigated by using an optical diffraction method.

K. Iishi; K. Hagiya; M. Ohmasa

1994-01-01

274

Exploring technology diffusion and classification of business methods: Using the patent citation network  

Microsoft Academic Search

Among the many technology forecasting indicators, patents and patent citations are useful and important indicators. The more frequently a certain patent is cited by subsequent patents, the more the related technology can be said to be diffused, implying that the technology is more widely applied and thus more valuable. This paper analyzes the business methods technology which retrieves patents from

Shann-Bin Chang; Kuei-Kuei Lai; Shu-Min Chang

2009-01-01

275

New contactless method for thermal diffusivity measurements using modulated photothermal radiometry.  

PubMed

Modulated photothermal radiometry is a non-destructive and contactless technique for the characterization of materials. It has two major advantages: a good signal-to-noise ratio through a synchronous detection and a low dependence on the heating power and the optical properties of the sample surface. This paper presents a new method for characterizing the thermal diffusivity of a material when the phase shift between a modulated laser power signal and the thermal signal of a plate sample is known at different frequencies. The method is based on a three-dimensional analytical model which is used to determine the temperature amplitude and the phase in the laser heating of the plate. A new simple formula was developed through multi-parametric analysis to determine the thermal diffusivity of the plate with knowledge of the frequency at the minimum phase shift, the laser beam radius r0 and the sample thickness L. This method was developed to control the variation of the thermal diffusivity of nuclear components and it was first applied to determine the thermal diffusivity of different metals: 304 L stainless steel, nickel, titanium, tungsten, molybdenum, zinc, and iron. The experimental results were obtained with 5%-10% accuracy and corresponded well with the reference values. The present paper also demonstrates the limit of application of this method for plate with thickness r0/100 ? L ? r0/2. The technique is deemed interesting for the characterization of barely accessible components that require a contactless measurement. PMID:24880399

Pham Tu Quoc, S; Cheymol, G; Semerok, A

2014-05-01

276

Development and Validation of a Microbiological Agar Assay for Determination of Orbifloxacin in Pharmaceutical Preparation  

PubMed Central

Orbifloxacin is a fluoroquinolone with broad-spectrum antimicrobial activity, and belongs to the third generation of quinolones. Regarding the quality control of medicines, a validated microbiological assay for determination of orbifloxacin in pharmaceutical formulations has not as yet been reported. For this purpose, this paper reports the development and validation of a simple, sensitive, accurate and reproducible agar diffusion method to quantify orbifloxacin in tablet formulations. The assay is based on the inhibitory effect of orbifloxacin upon the strain of Staphylococcus aureus ATCC 25923 used as test microorganism. The results were treated statistically by analysis of variance and were found to be linear (r = 0.9992) in the selected range of 16.0–64.0 ?g/mL, precise with relative standard deviation (RSD) of repeatability intraday = 2.88%, intermediate precision RSD = 3.33%, and accurate (100.31%). The results demonstrated the validity of the proposed bioassay, which allows reliable orbifloxacin quantitation in pharmaceutical samples and therefore can be used as a useful alternative methodology for the routine quality control of this medicine.

Cazedey, Edith C. L.; Salgado, Herida R. N.

2011-01-01

277

Preconditioned time-difference methods for advection-diffusion-reaction equations  

SciTech Connect

Explicit time differencing methods for solving differential equations are advantageous in that they are easy to implement on a computer and are intrinsically very parallel. The disadvantage of explicit methods is the severe restrictions placed on stepsize due to stability. Stability bounds for explicit time differencing methods on advection-diffusion-reaction problems are generally quite severe and implicit methods are used instead. The linear systems arising from these implicit methods are large and sparse so that iterative methods must be used to solve them. In this paper we develop a methodology for increasing the stability bounds of standard explicit finite differencing methods by combining explicit methods, implicit methods, and iterative methods in a novel way to generate new time-difference schemes, called preconditioned time-difference methods.

Aro, C.; Rodrigue, G. [California Univ., Davis, CA (United States). Dept. of Applied Science]|[Lawrence Livermore National Lab., CA (United States); Wolitzer, D. [California State Univ., Hayward, CA (United States). Dept. of Mathematics and Computer Science

1994-01-01

278

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

2011-11-01

279

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

PubMed Central

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

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

1995-01-01

280

Antimicrobial and physical-mechanical properties of agar-based films incorporated with grapefruit seed extract.  

PubMed

The use of synthetic petroleum based packaging films caused serious environmental problems due to their difficulty in recycling and poor biodegradability. Therefore, present study was aimed to develop natural biopolymer-based antimicrobial packaging films as an alternative for the synthetic packaging films. As a natural antimicrobial agent, grapefruit seed extract (GSE) has been incorporated into agar to prepare antimicrobial packaging film. The films with different concentrations of GSE were prepared by a solvent casting method and the resulting composite films were examined physically and mechanically. In addition, the films were characterized by FE-SEM, XRD, FT-IR and TGA. The incorporation of GSE caused increase in color, UV barrier, moisture content, water solubility and water vapor permeability, while decrease in surface hydrophobicity, tensile strength and elastic modulus of the films. As the concentration of GSE increased from 0.6 to 13.3 ?g/mL, the physical and mechanical properties of the films were affected significantly. The addition of GSE changed film microstructure of the film, but did not influence the crystallinity of agar and thermal stability of the agar-based films. The agar/GSE films exhibited distinctive antimicrobial activity against three test food pathogens, such as Listeria monocytogenes, Bacillus cereus and Escherichia coli. These results suggest that agar/GSE films have potential to be used in an active food packaging systems for maintaining food safety and extending the shelf-life of the packaged food. PMID:24507339

Kanmani, Paulraj; Rhim, Jong-Whan

2014-02-15

281

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

NASA Technical Reports Server (NTRS)

Liquid distributions in unsaturated porous media under different gravitational accelerations and corresponding macroscopic gaseous diffusion coefficients were investigated to enhance understanding of plant growth conditions in microgravity. We used a single-component, multiphase lattice Boltzmann code to simulate liquid configurations in two-dimensional porous media at varying water contents for different gravity conditions and measured gas diffusion through the media using a multicomponent lattice Boltzmann code. The relative diffusion coefficients (D rel) for simulations with and without gravity as functions of air-filled porosity were in good agreement with measured data and established models. We found significant differences in liquid configuration in porous media, leading to reductions in D rel of up to 25% under zero gravity. The study highlights potential applications of the lattice Boltzmann method for rapid and cost-effective evaluation of alternative plant growth media designs under variable gravity.

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

2005-01-01

282

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

283

Quantitative comparison of reconstruction methods for intra-voxel fiber recovery from diffusion MRI.  

PubMed

Validation is arguably the bottleneck in the diffusion magnetic resonance imaging (MRI) community. This paper evaluates and compares 20 algorithms for recovering the local intra-voxel fiber structure from diffusion MRI data and is based on the results of the "HARDI reconstruction challenge" organized in the context of the "ISBI 2012" conference. Evaluated methods encompass a mixture of classical techniques well known in the literature such as diffusion tensor, Q-Ball and diffusion spectrum imaging, algorithms inspired by the recent theory of compressed sensing and also brand new approaches proposed for the first time at this contest. To quantitatively compare the methods under controlled conditions, two datasets with known ground-truth were synthetically generated and two main criteria were used to evaluate the quality of the reconstructions in every voxel: correct assessment of the number of fiber populations and angular accuracy in their orientation. This comparative study investigates the behavior of every algorithm with varying experimental conditions and highlights strengths and weaknesses of each approach. This information can be useful not only for enhancing current algorithms and develop the next generation of reconstruction methods, but also to assist physicians in the choice of the most adequate technique for their studies. PMID:24132007

Daducci, Alessandro; Canales-Rodríguez, Erick Jorge; Descoteaux, Maxime; Garyfallidis, Eleftherios; Gur, Yaniv; Lin, Ying-Chia; Mani, Merry; Merlet, Sylvain; Paquette, Michael; Ramirez-Manzanares, Alonso; Reisert, Marco; Reis Rodrigues, Paulo; Sepehrband, Farshid; Caruyer, Emmanuel; Choupan, Jeiran; Deriche, Rachid; Jacob, Mathews; Menegaz, Gloria; Pr?kovska, Vesna; Rivera, Mariano; Wiaux, Yves; Thiran, Jean-Philippe

2014-02-01

284

Diffusion method for the determination of acid-volatile sulfides (AVS) in sediment  

Microsoft Academic Search

A simplified procedure using diffusion and a sulfide ion selective electrode is described for measuring acid-volatile sulfides (AVS) in sediment. This method yielded at least 10% more AVS than the more common purge-and-trap method. The quantity of AVS (based on dry mass of sediment) was found to be dependent on acid concentration and on mass of wet sediment. The mean

Henry Brouwer; Tom P. Murphy

1994-01-01

285

Multigrid Newton–Krylov method for radiation in diffusive semitransparent media  

Microsoft Academic Search

We present a fast multigrid solver for simplified PN (SPN) approximations to the diffusive radiation in non-grey semitransparent media. The method consists on reformulating the equations as a nonlinear fixed point problem in the temperature only. Given a mesh hierarchy, time and space discretizations are performed using second-order implicit and finite differencing methods, respectively. At each mesh level, a Newton–Krylov

2007-01-01

286

Newton-Krylov methods applied to a system of convection-diffusion-reaction equations  

Microsoft Academic Search

We study the application of Newton-Krylov methods for the steady-state solution of the tokamak edge plasma fluid equations. This highly nonlinear system of two-dimensional convection-diffusion-reaction partial differential equations describes the boundary layer of a tokamak fusion reactor. These equations are characterized by multiple time and spatial scales. We use Newton's method to linearize the nonlinear system of equations resulting from

D. A. Knoll; P. R. McHugh

1995-01-01

287

Diffusion-Thermal Methods for Recovering Radionuclides from Solid Reactor and Cyclotron Targets: An Outlook  

Microsoft Academic Search

Various methods for recovering radionuclides from solid reactor, cyclotron targets wereanalyzed, namely: (a) cocrystallization and adsorption, (b) extraction and chromatography, (c) interphaseexchange in amalgam-solution systems, and (d) high-temperature gas thermal chromatography (sublimation, treatment of irradiated targets in oxygen or hydrogen flow). Major attention was given to diffusion-thermal methods. General dependences of physicochemical behavior of impurity transmutation radionuclides in irradiated metals

I. E. Alekseev

2003-01-01

288

A Modified Fuzzy C-Means Classification Method Using a Multiscale Diffusion Filtering Scheme  

PubMed Central

A fully automatic, multiscale fuzzy c-means (MsFCM) classification method for MR images is presented in this paper. We use a diffusion filter to process MR images and to construct a multiscale image series. A multiscale fuzzy C-means classification method is applied along the scales from the coarse to fine levels. The objective function of the conventional fuzzy c-means (FCM) method is modified to allow multiscale classification processing where the result from a coarse scale supervises the classification in the next fine scale. The method is robust for noise and low-contrast MR images because of its multiscale diffusion filtering scheme. The new method was compared with the conventional FCM method and a modified FCM (MFCM) method. Validation studies were performed on synthesized images with various contrasts and on the McGill brain MR image database. Our MsFCM method consistently performed better than the conventional FCM and MFCM methods. The MsFCM method achieved an overlap ratio of greater than 90% as validated by the ground truth. Experiments results on real MR images were given to demonstrate the effectiveness of the proposed method. Our multiscale fuzzy c-means classification method is accurate and robust for various MR images. It can provide a quantitative tool for neuroimaging and other applications.

Wang, Hesheng; Fei, Baowei

2009-01-01

289

Growth of Desulfovibrio on the Surface of Agar Media.  

National Technical Information Service (NTIS)

Desulfovibrio desulfuricans (API strain) was grown in an atmosphere of hydrogen on the agar surface of complex media, including yeast extract (Difco) and trypticase soy agar (BBL). Sodium lactate was required in the medium for the organism to grow on a 2%...

W. P. Iverson

1965-01-01

290

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

291

Hyperspectral imaging for detecting pathogens grown on agar plates  

Microsoft Academic Search

This paper is concerned with the development of a hyperspectral imaging technique for detecting and identifying one of the most common foodborne pathogens, Campylobacter. Direct plating using agars is an effective tool for laboratory tests and analyses of microorganisms. The morphology (size, growth pattern, color, etc.) of colonies grown on agar plates has been widely used to tentatively differentiate organisms.

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

2007-01-01

292

The concentration and pH dependent diffusion of 137Cs in compacted bentonite by using capillary method  

Microsoft Academic Search

The ‘in-diffusionmethod was used to study the diffusion behavior of radionuclide 137Cs in compacted bentonite using a capillary. The results (distribution coefficient, Kd, apparent and effective diffusion coefficients, Da and De) derived from the capillary method are in good agreement with the literature data, and fit the Fick’s second law very well. The experiments were carried out at 3.3×10?3

Xiangke Wang; Xiaoli Tan; Changlun Chen; Lei Chen

2005-01-01

293

Application of numerical methods for diffusion-based modeling of skin permeation.  

PubMed

The application of numerical methods for mechanistic, diffusion-based modeling of skin permeation is reviewed. Methods considered here are finite difference, method of lines, finite element, finite volume, random walk, cellular automata, and smoothed particle hydrodynamics. First the methods are briefly explained with rudimentary mathematical underpinnings. Current state of the art numerical models are described, and then a chronological overview of published models is provided. Key findings and insights of reviewed models are highlighted. Model results support a primarily transcellular pathway with anisotropic lipid transport. Future endeavors would benefit from a fundamental analysis of drug/vehicle/skin interactions. PMID:22261307

Frasch, H Frederick; Barbero, Ana M

2013-02-01

294

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

PubMed

In many criminal and civil cases in China, the most commonly questioned documents are those written with gel pen ink. An important task for forensic document examiners is to identify whether two or more ink entries in one or more documents were written with the same ink type. The identification of the age of gel ink entries made poses an important and difficult problem for forensic document examiners. In this paper, a dissolution-diffusion method was successfully employed to estimate the relative age of gel ink entries by comparing dissolution-diffusion rates. Using extensive tests, the mixed solution of dimethyl formamide (DMF) and anhydrous ethanol proved to be a suitable solvent and was used to dissolve the dye of gel ink strokes made at different times. As preliminary findings of this study, calibration curves were created to indicate the relationship between the average dissolution-diffusion rate of soluble gel ink components and the age of gel ink entries stored under natural aging conditions. It was also determined that brands of gel inks, types of paper and thickness of gel ink strokes had varying impacts on estimating the dates of gel ink strokes. Experimental results showed that dissolution-diffusion method was applicable for determining the relative age of gel ink entries under certain conditions. PMID:24378312

Li, Biao

2014-01-01

295

Comparison of the Etest and the Sensititre Colorimetric Methods with the NCCLS Proposed Standard for Antifungal Susceptibility Testing of Aspergillus Species  

Microsoft Academic Search

The susceptibilities of 25 clinical isolates of Aspergillus fumigatus, A. flavus, A. terreus, A. nidulans, and A. ustus to itraconazole and amphotericin B were determined by an agar diffusion-dilution method (the Etest method) and a colorimetric broth microdilution method (the Sensititre method); and the results were compared with those obtained by the NCCLS proposed standard M-38P method for antifungal susceptibility

Joseph Meletiadis; Johan W. Mouton; Jacques F. G. M. Meis; Bianca A. Bouman

296

Comparison of the Etest and the Sensititre Colorimetric Methods with the NCCLS Proposed Standard for Antifungal Susceptibility Testing of Aspergillus Species  

Microsoft Academic Search

The susceptibilities of 25 clinical isolates of Aspergillus fumigatus, A. flavus, A. terreus, A. nidulans, and A. ustus to itraconazole and amphotericin B were determined by an agar diffusion-dilution method (the Etest method) and a colorimetric broth microdilution method (the Sensititre method); and the results were compared with those obtained by the NCCLS proposed standard M-38P method for antifungal susceptibility

Joseph Meletiadis; Johan W. Mouton; Jacques F. G. M. Meis; Bianca A. Bouman; Paul E. Verweij

2002-01-01

297

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

298

An Analysis Method of the Fiber Tractography of Corpus Callosum in Autism Based on Diffusion Tensor Imaging Data  

Microsoft Academic Search

OBJECTIVE: A new method of segmentation and fiber tractography of corpus callosum in diffusion tensor imaging (DTI) is provided, and applied in the study of children with high functioning autism. METHOD: Diffusion tensor imaging data has been used to analyze the fiber tractography of corpus callosum, which has been manually extracted out and subdivided into five subregions in the scheme

Xiaoyan Ke; Shanshan Hong; Tianyu Tang; Haiqing Huang; Bing Zou; Huiguo Li; Yueyue Hang; Zuhong Lu

2008-01-01

299

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

300

A Monte Carlo based nodal diffusion model for criticality analysis, and, Application of high-order cross section homogenization method to two-group nodal diffusion  

Microsoft Academic Search

In the first part, an accurate and fast computational method is presented as an alternative to the Monte Carlo or deterministic transport theory codes currently used to determine the subcriticality of spent fuel storage lattices. The method is capable of analyzing storage configurations with simple or complex lattice cell geometry. It is developed based on two-group nodal diffusion theory, with

Germina Ilas

2002-01-01

301

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

SciTech Connect

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. [Physics Department, University of Lampung (UNILA), Jl. Sumantri Brojonegoro No. 1 Bandar Lampung (Indonesia); Su'ud, Z.; Waris, A.; Khotimah, S. N. [Physics Department, Bandung Institute of Technology (ITB), Jl. Ganesha 10 Bandung (Indonesia)

2010-06-22

302

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

PubMed

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 that major white matter tracts may be elucidated and that multiple connections and tract branching are allowed. Maps of connectivity between brain regions are also determined. Four options are described for estimating the degree of connectivity between regions. PMID:12071621

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

2002-05-01

303

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

304

A numerical method for determination of moisture transfer coefficient according to the diffusion moisture profiles  

Microsoft Academic Search

For a set of the measured diffusion moisture profiles, a numerical method for determination of moisture transfer coefficient\\u000a D(w, t) is suggested. The transfer coefficient is found as a sum of the degree $$\\u000ap_0 w^{p(t)} \\u000a$$ and exponential $$\\u000aAe^{\\\\mu (w - v_0 )} \\u000a$$ functions of the moisture concentration w, as opposite to the previous works. The exponent

E. Pavlusová; M. Pavlus; I. Sarhadov; I. V. Amirkhanov; T. P. Puzynina; I. V. Puzynin

2008-01-01

305

Test of the Cross Correlation Method for Efficient Single Crystal Diffuse Neutron Scattering with Elastic Discrimination  

NASA Astrophysics Data System (ADS)

Single crystal diffuse scattering provides a powerful probe of the complex disorder associated with many emergent phenomena of great interest. It provides a determination not only of the local distortions around a point defect but also of the length scale and morphology of short-range order on the nanoscale. However, obtaining accurate models of the local structure usually demands measurements over large volumes of reciprocal space with sufficiently high momentum and energy resolution. In order to overcome limitations of current instrumentation, we propose to utilize the cross-correlation method at pulsed neutron sources. This concept that combines the high efficiency of white-beam Laue diffraction for measuring large volumes of reciprocal space with energy discrimination produced by the use of a statistical chopper is currently being implemented in a dedicated instrument, Corelli , under construction at the Spallation Neutron Source. Here, we present our detailed investigation of the effectiveness of this method for measuring weak diffuse signals, based on full experiment simulations as well as actual measurements of the diffuse scattering from powder and single crystal samples obtained utilizing the cross correlation method on a prototype instrument.

Rosenkranz, Stephan; Castellan, John Paul; Vitt, Rich; Osborn, Raymond; Riedel, Rick; Ruiz-Rodriguez, Mariano; Funk, Loren

2013-03-01

306

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

SciTech Connect

Linear wave codes AORSA and TORIC couple to the bounce-averaged nonlinear Fokker-Planck code CQL3D through quasi-linear diffusion coefficients. Both linear wave codes rely on the quasi-local approximation that includes only first-order parallel and perpendicular gradient variations of cyclotron frequency and ignores field line curvature along with temperature and density gradient effects. The delta-f particle-in-cell (DFPIC) method has been successfully used for simulating ion-cyclotron fast wave behavior. This method also permits particle behavior such as multiple pass resonance, banana orbits, and superadiabaticity. We present new work on generating quasi-linear diffusion coefficients using the DFPIC method that will permit the electromagnetic particle-in-cell (EMPIC) code, VORPAL, to couple to CQL3D and to compare to AORSA and TORIC. A new multiple weight delta-f approach will be presented that converts velocity derivatives to action derivatives and yields a full tensor quasi-linear diffusion coefficient.

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

2009-11-26

307

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

NASA Astrophysics Data System (ADS)

Linear wave codes AORSA and TORIC couple to the bounce-averaged nonlinear Fokker-Planck code CQL3D through quasi-linear diffusion coefficients. Both linear wave codes rely on the quasi-local approximation that includes only first-order parallel and perpendicular gradient variations of cyclotron frequency and ignores field line curvature along with temperature and density gradient effects. The delta-f particle-in-cell (DFPIC) method has been successfully used for simulating ion-cyclotron fast wave behavior. This method also permits particle behavior such as multiple pass resonance, banana orbits, and superadiabaticity. We present new work on generating quasi-linear diffusion coefficients using the DFPIC method that will permit the electromagnetic particle-in-cell (EMPIC) code, VORPAL, to couple to CQL3D and to compare to AORSA and TORIC. A new multiple weight delta-f approach will be presented that converts velocity derivatives to action derivatives and yields a full tensor quasi-linear diffusion coefficient.

Austin, T. M.; Smithe, D. N.; Ranjbar, V.

2009-11-01

308

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

309

Comparison of ChromID Agar and Clostridium difficile Selective Agar for Effective Isolation of C. difficile from Stool Specimens  

PubMed Central

Background ChromID Clostridium difficile agar (IDCd; bioMérieux SA, France) is a recently developed chromogenic medium for rapid and specific isolation of C. difficile. We compared the performance of IDCd with that of Clostridium difficile Selective Agar (CDSA). Methods A total of 530 fresh stool specimens were collected from patients with clinical signs compatible with C. difficile infection, and cultures for C. difficile were performed on IDCd and CDSA. C. difficile colonies were identified by spore staining, odor, use of an ANI identification test kit (bioMérieux SA), and multiplex PCR for tcdA, tcdB, and tpi. Results The concordance rate between IDCd and CDSA was 90.6% (480/530). The positivity rates on IDCd on days 1 and 2 (55.6% and 85.0%, respectively) were significantly higher than those on CDSA (19.4% and 75.6%, respectively) (P<0.001 for day 1 and P=0.02 for day 2), but the detection rates on IDCd and CDSA on day 3 were not different (89.4% vs. 82.8%, P=0.0914). On day 3, the recovery rates for non-C. difficile isolates on IDCd and CDSA were 30.2% (160/530) and 22.1% (117/530), respectively (P=0.0075). Clostridium spp. other than C. difficile were the most prevalent non-C. difficile isolates on both media. Conclusions The culture positivity rates on IDCd and CDSA were not different on day 3 but IDCd may allow for rapid and sensitive detection of C. difficile within 2 days of cultivation.

Lee, Eun Joo

2014-01-01

310

Susceptibility testing by E-test and agar dilution of 30 strains of Legionella spp. isolated in Portugal.  

PubMed

OBJECTIVE: To evaluate the activity of erythromycin, roxithromycin, ciprofloxacin, doxycycline, sulfamethoxazole trimethoprim and rifampin against 32 strains of Legionella spp. under different testing conditions. METHODS: Minimum inhibitory concentrations (MICs) were determined by the E-test (Ab Biodisk, Solna, Sweden) and agar dilution reference technique (National Committee for Clinical Laboratory Standards (NCCLS), 1990) on two different media, buffered charcoal yeast extract agar (BCYE-alpha) and buffered yeast extract agar (BYE-alpha), under 48- and 72-h incubation, without CO2. RESULTS: All the antimicrobial agents were inhibited by BCYE-alpha agar. The MIC90 values on BYE-alpha were lower than those on BCYE-alpha but the variation factor was not the same: ciprofloxacin and rifampin, followed by erythromycin, suffered the greatest inhibition by the charcoal in the culture medium. Except for ciprofloxacin and rifampin, the 72-h MIC90 readings were always higher than the 48-h results whenever the agar dilution method was used. The E-test results showed slight variations with some, but not all, antibiotics. The most active agents against the 32 Legionella strains tested were rifampin and ciprofloxacin. CONCLUSIONS: BCYE-alpha is not suitable for susceptibility testing of Legionella spp. The E-test method on BYE-alpha agar with 48-h incubation is recommended. PMID:11864134

Marques, Teresa; Piedade, Júlia

1997-06-01

311

Physics-based preconditioning and the Newton-Krylov method for non-equilibrium radiation diffusion  

SciTech Connect

An algorithm is presented for the solution of the time dependent reaction-diffusion systems which arise in non-equilibrium radiation diffusion applications. This system of nonlinear equations is solved by coupling three numerical methods, Jacobian-free Newton-Krylov, operator splitting, and multigrid linear solvers. An inexact Newton's method is used to solve the system of nonlinear equations. Since building the Jacobian matrix for problems of interest can be challenging, the authors employ a Jacobian-free implementation of Newton's method, where the action of the Jacobian matrix on a vector is approximated by a first order Taylor series expansion. Preconditioned generalized minimal residual (PGMRES) is the Krylov method used to solve the linear systems that come from the iterations of Newton's method. The preconditioner in this solution method is constructed using a physics-based divide and conquer approach, often referred to as operator splitting. This solution procedure inverts the scalar elliptic systems that make up the preconditioner using simple multigrid methods. The preconditioner also addresses the strong coupling between equations with local 2 x 2 block solves. The intra-cell coupling is applied after the inter-cell coupling has already been addressed by the elliptic solves. Results are presented using this solution procedure that demonstrate its efficiency while incurring minimal memory requirements.

Mousseau, V.A.; Knoll, D.A.; Rider, W.J.

2000-05-20

312

Fabrication of graded-index plastic optical fiber by the diffusion-assisted coextrusion method  

NASA Astrophysics Data System (ADS)

Recently, plastic optical fibers (POFs) have drawn significant attention as high-speed transmission media due to their advantages over conventional glass optical fibers such as flexibility and durability. In addition, Grade-Index (GRIN) POFs with smoothly varying refractive indices provide increased data transmission speeds suitable for the short-distance communications such as local area networking or home networking. In this research, the diffusion-assisted coextrusion process is introduced as a method to fabricate GRIN POFs. In this process, two or more polymeric materials containing additives for refractive index modification are fed separately into a coextrusion die where a concentric multi-layer structure is formed. Subsequently, the diffusion of additives take places in a diffusion zone creating a non-equilibrium concentration profile, hence the refractive index profile. A theoretical analysis for the prediction of the refractive index profile obtainable by this process indicates that it is difficult to obtain a near-parabolic refractive index profile with the tubular flow design unless a very large residence time in the diffusion zone is provided. However, significant changes in the refractive index profile can be induced by adopting a multi-layer approach and an annulus flow design. Furthermore, the bandwidth estimated by the ray analysis indicates that even a small variation of the refractive index profile created by the additive diffusion can result in a significant increase in the bandwidth. To verify the findings from theoretical analysis, poly(methyl methacrylate)-base GRIN POFs with diphenyl sulfide and diphenyl sulfoxide as refractive index-modifying dopants were prepared and the effects of various operating conditions such as melt temperatures, flow rates and core-cladding interface positions were investigated. The dopant concentration profile, thus the refractive index profile, characterized by FT-IR spectroscopy, has been shown to be controllable by adjusting the material and/or process variables. Through the theoretical analysis and experimental verifications, it was shown that bandwidth over 700 MHz at a 100 m distance could be obtained by this method, suggesting that the diffusion-assisted coextrusion process is a viable method to fabricate a high bandwidth GRIN POF that is applicable for short-distance communications.

Sohn, In-Sung

313

Egg yolk emulsion agar, a new medium for the cultivation of Helicobacter pylori.  

PubMed Central

We developed a new agar, egg yolk emulsion (EYE) agar, for cultivation of Helicobacter pylori. EYE agar contains Columbia agar base (Oxoid), 10% EYE (Oxoid), 1% IsoVitaleX (BBL), and 40 mg of Triphenyleteraxolium chloride (Sigma) per liter. We compared EYE agar with the following agars: (i) brain heart infusion agar-7% horse blood-1% IsoVitaleX (GDW agar; C. S. Goodwin, E. D. Blincow, J. R. Warren, T. E. Waters, C. R. Sanderson, and L. Easton, J. Clin. Pathol. 38:1127-1131, 1985), (ii) brain heart infusion agar-10% horse serum-0.2% charcoal-1% yeast extract-40 mg of triphenyltetrazolium chloride per liter (GLU agar; Y. Glupczynski, M. Labbe, and F. Thiabaumont, p. 3-6, in F. Megraud and H. Lamouliatte, ed., Gastroduodenal Pathology and Campylobacter pylori, 1989), (iii) Columbia agar with 7% lysed horse blood (D&M agar; J. C. Dent and C. A. M. McNulty, Eur. J. Clin. Microbiol. Infect. Dis. 7:555-558, 1988), and (iv) brain heart infusion agar-10% EYE-1% IsoVitaleX (BHIE agar). H. pylori CFU counts, expressed as average percentages of maximum growth, were as follows: EYE agar, 96; GDW agar. 76; BHIE agar, 57; D&M agar, 52; and GLU agar, 23. Colony counts for EYE agar were significantly higher than for GDW agar (P = 0.027), BHIE agar (P = 0.005), D&M agar (P = 0.0001), and GLU agar (P less than 0.0001). EYE agar also had higher CFU counts than two commercial chocolate media; the EYE agar count was 80%, versus 33% for BBL chocolate medium and 63% for Remel chocolate medium.

Westblom, T U; Madan, E; Midkiff, B R

1991-01-01

314

Egg yolk emulsion agar, a new medium for the cultivation of Helicobacter pylori.  

PubMed

We developed a new agar, egg yolk emulsion (EYE) agar, for cultivation of Helicobacter pylori. EYE agar contains Columbia agar base (Oxoid), 10% EYE (Oxoid), 1% IsoVitaleX (BBL), and 40 mg of Triphenyleteraxolium chloride (Sigma) per liter. We compared EYE agar with the following agars: (i) brain heart infusion agar-7% horse blood-1% IsoVitaleX (GDW agar; C. S. Goodwin, E. D. Blincow, J. R. Warren, T. E. Waters, C. R. Sanderson, and L. Easton, J. Clin. Pathol. 38:1127-1131, 1985), (ii) brain heart infusion agar-10% horse serum-0.2% charcoal-1% yeast extract-40 mg of triphenyltetrazolium chloride per liter (GLU agar; Y. Glupczynski, M. Labbe, and F. Thiabaumont, p. 3-6, in F. Megraud and H. Lamouliatte, ed., Gastroduodenal Pathology and Campylobacter pylori, 1989), (iii) Columbia agar with 7% lysed horse blood (D&M agar; J. C. Dent and C. A. M. McNulty, Eur. J. Clin. Microbiol. Infect. Dis. 7:555-558, 1988), and (iv) brain heart infusion agar-10% EYE-1% IsoVitaleX (BHIE agar). H. pylori CFU counts, expressed as average percentages of maximum growth, were as follows: EYE agar, 96; GDW agar. 76; BHIE agar, 57; D&M agar, 52; and GLU agar, 23. Colony counts for EYE agar were significantly higher than for GDW agar (P = 0.027), BHIE agar (P = 0.005), D&M agar (P = 0.0001), and GLU agar (P less than 0.0001). EYE agar also had higher CFU counts than two commercial chocolate media; the EYE agar count was 80%, versus 33% for BBL chocolate medium and 63% for Remel chocolate medium. PMID:1890184

Westblom, T U; Madan, E; Midkiff, B R

1991-04-01

315

Experimental determination of the diffusion coefficient in two-dimensions in ferrous sulphate gels using the finite element method  

Microsoft Academic Search

A novel two-dimensional finite element method for modelling the diffusion which occurs in Fricke or ferrous sulphate type\\u000a radiation dosimetry gels is presented. In most of the previous work, the diffusion coefficient has been estimated using simple\\u000a one-dimensional models. This work presents a two-dimensional model which enables the diffusion coefficient to be determined\\u000a in a much wider range of experimental

C. Baldock; P. J. Harris; A. R. Piercy; B. Healy

2001-01-01

316

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

Microsoft Academic Search

The diffusion of 134Cs+ and 22Na+ 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 ?-spectrometry. By choosing the appropriate abrasive paper, a resolution down to 15?m can be achieved. This is important

L. R. Van Loon; J. Eikenberg

2005-01-01

317

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

NASA Technical Reports Server (NTRS)

We derive a deterministic particle method for the solution of nonlinear reaction-diffusion equations in one spatial dimension. This deterministic method is an analog of a Monte Carlo method for the solution of these problems that has been previously investigated by the author. The deterministic method leads to the consideration of a system of ordinary differential equations for the positions of suitably defined particles. We then consider the time explicit and implicit methods for this system of ordinary differential equations and we study a Picard and Newton iteration for the solution of the implicit system. Next we solve numerically this system and study the discretization error both analytically and numerically. Numerical computation shows that this deterministic method is automatically adaptive to large gradients in the solution.

Mascagni, Michael

1995-01-01

318

Rapid distinction between micrococci and staphylococci with furazolidone agars.  

PubMed

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 microgram/ml furazolidone. The results were compared with the classification obtained by the standard-O/F-test and by the test system of Schleifer and Kloos. For routine identification and separation of staphylococci from micrococci a peptone agar with 20 microgram furazolidone/ml is recommended. PMID:7018395

von Rheinbaben, K E; Hadlok, R M

1981-03-01

319

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

320

A Mesh-Free Method for the Simulation of Magnetic Diffusion  

NASA Astrophysics Data System (ADS)

Magnetohydrodynamics (MHD) plays an important role in various physical systems at large and small scales. Recently, mesh-free methods such as Smoothed Particle Magnetohydrodynamics [1] (SPMHD) have been developed to study these systems by simulating magnetic fields in the presence of conducting media. However, these methods currently do not incorporate realistic models for electrical resistivity, which can significantly affect the dynamics of the system by introducing magnetic diffusion, thereby altering the field's topology. We describe a Meshless Local Petrov Galerkin (MLPG) method that solves such magnetic diffusion problems using local weak forms composed of mesh-free shape functions. This MLPG method accommodates inhomogeneous and anisotropic electrical resistivity models and allows the magnetic field to be evolved implicitly in time. We have assembled several test problems of interest in order to verify the method. Ultimately, we aim to combine this MLPG method with a form of SPMHD in order to treat realistic resistive magnetohydrodynamic systems. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. [1] D. J. Price, J. J. Monaghan, Mon. Not. Roy. Astr. Soc. Volume 348 Issue 1 pp. 123-138 (2004)

Johnson, Jeffrey; Owen, Michael

2007-11-01

321

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

SciTech Connect

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

Atzberger, Paul J. [University of California, Department of Mathematics, Santa Barbara, CA 93106 (United States)], E-mail: atzberg@math.ucsb.edu

2010-05-01

322

Boundaries and breakdowns: applying Agar's concept of ethnography to observations in a pediatric clinic.  

PubMed

This paper discusses a methodology for observing and describing interactions between clinicians and patients in an inner-city pediatric clinic serving families of diverse ethnicity. The framework is derived from Michael Agar's concept of ethnography as an interpretive, problem-resolving method. In Agar's model, the participant-observer moves cognitively and analytically from focusing on breakdown (awareness of a problem in understanding) to resolution (applying knowledge structures or schemas to bounded phenomena or strips) and ultimately to coherence. This framework applies not only to describing what the ethnographer does, but also stages in the clinician's efforts to communicate. Awareness of repeated breakdowns allows the ethnographer to document fundamental differences in expectations and premises that affect communication between clinician and patient. Two major types of breakdowns are discussed: those occurring between clinic staff and families, and those occurring between staff and ethnographer. Terminological and analytical modifications of Agar's method are recommended to reflect more accurately the ethnographer's degree of involvement in the communication breakdown (active resolution versus passive resolution). The paper concludes that Agar's model provides a useful structure for developing a systematic ethnographic language that can readily be demonstrated and communicated to clinicians. PMID:10278578

McElroy, A; Jezewski, M A

1986-01-01

323

A discussion on validity of the diffusion theory by Monte Carlo method  

NASA Astrophysics Data System (ADS)

Diffusion theory was widely used as a basis of the experiments and methods in determining the optical properties of biological tissues. A simple analytical solution could be obtained easily from the diffusion equation after a series of approximations. Thus, a misinterpret of analytical solution would be made: while the effective attenuation coefficient of several semi-infinite bio-tissues were the same, the distribution of light fluence in the tissues would be the same. In order to assess the validity of knowledge above, depth resolved internal fluence of several semi-infinite biological tissues which have the same effective attenuation coefficient were simulated with wide collimated beam in the paper by using Monte Carlo method in different condition. Also, the influence of bio-tissue refractive index on the distribution of light fluence was discussed in detail. Our results showed that, when the refractive index of several bio-tissues which had the same effective attenuation coefficient were the same, the depth resolved internal fluence would be the same; otherwise, the depth resolved internal fluence would be not the same. The change of refractive index of tissue would have affection on the light depth distribution in tissue. Therefore, the refractive index is an important optical property of tissue, and should be taken in account while using the diffusion approximation theory.

Peng, Dong-Qing; Li, Hui; Xie, Shusen

2008-12-01

324

New method for the simultaneous determination of diffusion and adsorption of dyes in silica hydrogels.  

PubMed

The fine tuning of porosity in sol gel based devices makes possible the design of novel applications in which the transport of molecules through the oxide gel plays a crucial role. In this work we develop a new method for the simultaneous analysis of diffusion and adsorption of small diffusing probes, as anionic and cationic dyes, through silica mesoporous hydrogels synthesized by sol-gel. The novelty of the work resides in the simplicity of acquisition of the experimental data (by means of a desk scanner) and further mathematical modeling, which is in line with high throughput screening procedures, enabling rapid and simultaneous determination of relevant diffusion and adsorption parameters. Net mass transport and adsorption properties of the silica based hydrogels were contrasted to dye adsorption isotherms and textural characterization of the wet gels by SAXS, as well as that of the corresponding aerogels determined by Field Emission Scanning Electron Microscopy (FESEM) and N2 adsorption. Thus, the validation of the results with well-established characterization methods demonstrates that our approach is robust enough to give reliable physicochemical information on these systems. PMID:24776668

Perullini, Mercedes; Jobbágy, Matías; Japas, María Laura; Bilmes, Sara A

2014-07-01

325

Network simulation method applied to models of diffusion-limited gas bubble dynamics in tissue  

NASA Astrophysics Data System (ADS)

In this work the Network Simulation Method is used to study decompression sickness (DCS) in human subjects after diving and/or flying exposures. Bubble dynamics models suitable for these applications assume the bubble to be either contained in an unstirred tissue (two-region model) or surrounded by a boundary layer within a well stirred tissue (three-region model). The main results are obtained using the three-region model of gas bubble dynamics, which consists of a bubble and a well-stirred tissue region with an intervening unperfused diffusion region previously assumed to have a constant thickness and uniform gas diffusivity. Spatial discretization is used to numerically solve the diffusion equation considering the transitory term, where programming does not involve manipulation of the sophisticated mathematical software that is inherent in other numerical methods. The technique in question is always stable and convergent. Different effects (among them, tissue volume, initial bubble radius, surface tension of intercellular fluid and boundary layer thickness) are studied and plotted.

Zueco, Joaquín; Hernández-González, A.

2010-08-01

326

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

2000-01-01

327

Adaptive Mesh Refinement for the Nodal Integral Method and Application to the Convection-Diffusion Equation  

SciTech Connect

The nodal integral method (NIM) has been developed for several problems, including the Navier-Stokes equations, the convection-diffusion equation, and the multigroup neutron diffusion equations. The coarse-mesh efficiency of the NIM is not fully realized in problems characterized by a wide range of spatial scales; however, the combination of adaptive mesh refinement (AMR) capability with the NIM can recover the coarse-mesh efficiency by allowing high degrees of resolution in specific localized areas where it is needed and using a lower resolution everywhere else. Furthermore, certain features of the NIM can be fruitfully exploited in the application of the AMR process. Here, a general approach to couple nodal schemes with AMR is outlined and then applied to the convection-diffusion (energy) equation. For the recirculating flow problem studied, the total number of nodes required by the NIM-AMR to yield approximately the same level of accuracy is a factor of 6 smaller than the total number of nodes required by the NIM without AMR. These results show that, for problems characterized by a range of spatial scales, the nodal efficiency can be recovered by coupling the nodal method with adaptive mesh refinement capability.

Torej, Allen J.; Rizwan-Uddin

2001-06-17

328

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

NASA Technical Reports Server (NTRS)

The principles of conservation and stability of difference schemes achieved using the iteration control method were examined. For the schemes obtained of the predictor-corrector type, the conversion was proved for the control sequences of approximate solutions to the precise solutions in the Sobolev metrics. Algorithms were developed for reducing the differential problem to integral relationships, whose solution methods are known, were designed. The algorithms for the problem solution are classified depending on the non-linearity of the diffusion coefficients, and practical recommendations for their effective use are given.

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

1979-01-01

329

Direct estimation of diffuse gaseous emissions from coal fires: current methods and future directions  

USGS Publications Warehouse

Coal fires occur in nature spontaneously, contribute to increases in greenhouse gases, and emit atmospheric toxicants. Increasing interest in quantifying coal fire emissions has resulted in the adaptation and development of specialized approaches and adoption of numerical modeling techniques. Overview of these methods for direct estimation of diffuse gas emissions from coal fires is presented in this paper. Here we take advantage of stochastic Gaussian simulation to interpolate CO2 fluxes measured using a dynamic closed chamber at the Ruth Mullins coal fire in Perry County, Kentucky. This approach allows for preparing a map of diffuse gas emissions, one of the two primary ways that gases emanate from coal fires, and establishing the reliability of the study both locally and for the entire fire. Future research directions include continuous and automated sampling to improve quantification of gaseous coal fire emissions.

Engle, Mark A.; Olea, Ricardo A.; O'Keefe, Jennifer M. K.; Hower, James C.; Geboy, Nicholas J.

2013-01-01

330

A balancing domain decomposition method by constraints for advection-diffusion problems  

SciTech Connect

The balancing domain decomposition methods by constraints are extended to solving nonsymmetric, positive definite linear systems resulting from the finite element discretization of advection-diffusion equations. A pre-conditioned GMRES iteration is used to solve a Schur complement system of equations for the subdomain interface variables. In the preconditioning step of each iteration, a partially sub-assembled finite element problem is solved. A convergence rate estimate for the GMRES iteration is established, under the condition that the diameters of subdomains are small enough. It is independent of the number of subdomains and grows only slowly with the subdomain problem size. Numerical experiments for several two-dimensional advection-diffusion problems illustrate the fast convergence of the proposed algorithm.

Tu, Xuemin; Li, Jing

2008-12-10

331

Agar Gel Precipitin-Inhibition Technique for Histoplasmosis Antibody Determinations.  

National Technical Information Service (NTIS)

The agar gel precipitin-inhibition techniques of Ray, Kadull and Shay have been modified to detect Histoplasma capsulatum antibodies in sera from human clinical cases and experimental animals infected with this organism. With the modified procedure antibo...

J. G. Ray

1967-01-01

332

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

333

A noninvasive method for measuring the velocity of diffuse hydrothermal flow by tracking moving refractive index anomalies  

Microsoft Academic Search

Diffuse flow velocimetry (DFV) is introduced as a new, noninvasive, optical technique for measuring the velocity of diffuse hydrothermal flow. The technique uses images of a motionless, random medium (e.g., rocks) obtained through the lens of a moving refraction index anomaly (e.g., a hot upwelling). The method works in two stages. First, the changes in apparent background deformation are calculated

Eric Mittelstaedt; Anne Davaille; Peter E. van Keken; Nuno Gracias; Javier Escartin

2010-01-01

334

Comparison of laboratory methodologies for evaluating radiostrontium diffusion in soils: Planar-source versus half-cell methods  

Microsoft Academic Search

A planar-source method, initially designed to obtain diffusion coefficients in compacted clay, is adapted here to determine the apparent diffusion coefficient (Da) of radiostrontium in soils representative of the Spanish territory. Experiments were carried out by varying the moisture content (Fmoist), and bulk dry density (?bulk) of the soil samples, in order to study the influence of these soil packing

D. Aldaba; M. García-Gutiérrez; A. Rigol; M. Vidal

2010-01-01

335

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

336

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

337

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

PubMed Central

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

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

2010-01-01

338

Clinical evaluation of a novel chromogenic agar dipslide for diagnosis of urinary tract infections.  

PubMed

The performance of a novel dipslide (DipStreak; Novamed, Israel) consisting of chromogenic agar (Uriselect 3; Sanofi Pasteur, France) and blood agar media was evaluated prospectively and compared to that of conventional urine culture for the diagnosis of urinary tract infection. A total of 1070 clean-catch urine specimens obtained from 251 hospitalized patients and 819 outpatients were processed. The overall performance of the DipStreak was as follows: sensitivity, 95.7%; specificity, 99.2%; agreement, 89.8%; accuracy, 98%; positive predictive value, 98.5%; and negative predictive value, 97.7%. A total of 270 urine specimens were positive by both DipStreak and conventional culture. The chromogenic agar allowed rapid identification of organisms in 211 (78.1%) cultures, while isolates in the other 59 (21.9%) cultures remained unidentified. The results indicate that the DipStreak device coupled with the Uriselect 3 agar represents a convenient and accurate method for inoculation of urine specimens, quantitation of bacteria, diagnosis of significant bacteriuria, and presumptive identification of isolates. PMID:11057503

Yagupsky, P; Rider, M; Peled, N

2000-09-01

339

In vitro growth of bioactive nanostructured apatites via agar-gelatin hybrid hydrogel.  

PubMed

Biomimetic synthesis of bone-like carbonated apatite with good biocompatibility is a promising strategy for the development of novel biomaterials for bone engineering applications. Most research efforts have been focused on only protein-based or only polysaccharide-based template for synthesis of apatite minerals. To understand the cooperative roles of gelatin and polysaccharide playing in the biomineralization, agar hydrogel, gelatin and agar-gelatin hybrid hydrogel were respectively introduced as mineralization matrix for the in vitro growth of apatite in the study. It was shown that bundle-like carbonated apatite was successfully prepared in agar-gelatin hybrid hydrogel for the first time, through the interaction between apatite and matrix macromolecule under physiological temperature. Moreover, the in vitro biocompatibility of the prepared nanostructured apatite crystals was investigated using CCK-8 assay and alkaline phosphatase activity of osteoblast-like MC3T3-E1. Compared with HA synthesized by traditional method, the obtained apatite in agar-gelatin hybrid hydrogel could provide significantly higher cell viability and alkaline phosphatase activity. Through the study, we could better understand the role of gelatin and polysaccharide in bone formation process, and the product is a promising candidate to be used in bone tissue engineering. PMID:24266253

Deng, Yi; Zhao, Xianghui; Zhou, Yongsheng; Zhu, Peizhi; Zhang, Li; Wei, Shicheng

2013-12-01

340

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

341

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

SciTech Connect

Studying numerically the steady state of a nuclear core reactor is expensive, in terms of memory storage and computational time. In order to address both requirements, one can use a domain decomposition method, implemented on a parallel computer. We present here such a method for the mixed neutron diffusion equations, discretized with Raviart–Thomas–Nédélec finite elements. This method is based on the Schwarz iterative algorithm with Robin interface conditions to handle communications. We analyse this method from the continuous point of view to the discrete point of view, and we give some numerical results in a realistic highly heterogeneous 3D configuration. Computations are carried out with the MINOS solver of the APOLLO3® neutronics code.

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

2013-05-15

342

High-order mimetic finite difference method for diffusion problems on polygonal meshes  

NASA Astrophysics Data System (ADS)

The mimetic finite difference (MFD) methods mimic important properties of physical and mathematical models. As a result, conservation laws, solution symmetries, and the fundamental identities of the vector and tensor calculus are held for discrete models. The MFD methods retain these attractive properties for full tensor coefficients and arbitrary polygonal meshes which may include non-convex and degenerate elements. The existing MFD methods for solving diffusion-type problems are second-order accurate for the conservative variable (temperature, pressure, energy, etc.) and only first-order accurate for its flux. We developed new high-order MFD methods which are second-order accurate for both scalar and vector variables. The second-order convergence rates are demonstrated with a few numerical examples on randomly perturbed quadrilateral and polygonal meshes.

Gyrya, Vitaliy; Lipnikov, Konstantin

2008-10-01

343

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

Jamelot, Erell; Ciarlet, Patrick

2013-05-01

344

Finite difference methods for the time fractional diffusion equation on non-uniform meshes  

NASA Astrophysics Data System (ADS)

Since fractional derivatives are integrals with weakly singular kernel, the discretization on the uniform mesh may lead to poor accuracy. The finite difference approximation of Caputo derivative on non-uniform meshes is investigated in this paper. The method is applied to solve the fractional diffusion equation and a semi-discrete scheme is obtained. The unconditional stability and H1 norm convergence are proved. A fully discrete difference scheme is constructed with space discretization by compact difference method. The error estimates are established for two kinds of nonuniform meshes. Numerical tests are carried out to support the theoretical results and comparing with the method on uniform grid shows the efficiency of our methods. Moreover, a moving local refinement technique is introduced to improve the temporal accuracy of numerical solution.

Zhang, Ya-nan; Sun, Zhi-zhong; Liao, Hong-lin

2014-05-01

345

Usefulness of Chromogenic CromoCen® AGN agar medium for the identification of the genus Aeromonas: Assessment of faecal samples.  

PubMed

Selective screening media for the detection and identification of Aeromonas strains are needed to guide primary isolation procedures in the clinical laboratory. This study compared the selective CromoCen® AGN chromogenic agar medium for the detection and identification of Aeromonas strains that were isolated from various samples against the conventional selective agar media that are commonly used for the isolation of this organism in food, environmental and clinical samples. The Miles and Misra and ecometric methods were used to evaluate the microbiological performance of CromoCen® AGN chromogenic agar medium, which was shown to be satisfactory. A total of 14 reference Aeromonas strains, 44 wild strains and 106 clinical stool specimens were examined using both non-chromogenic selective agars that are commonly used for Aeromonas isolation and CromoCen® AGN agar. The latter exhibited 94.73% sensitivity and 100% specificity for the various samples. On CromoCen® AGN agar medium, Aeromonas formed colonies with light green, greenish and salmon pigments with or without a surrounding wide transparent zone (halo) of 2-3mm in diameter around the entire border. This medium is recommended for the isolation and potential identification of the Aeromonas genus. PMID:22561188

Aguilera-Arreola, M G; Portillo-Muñoz, M I; Rodríguez-Martínez, C; Castro-Escarpulli, G

2012-08-01

346

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

NASA Astrophysics Data System (ADS)

The discretization of the Gent-McWilliams velocity and isopycnal diffusion with a discontinuous Galerkin finite element method is presented. Both processes are implemented in an ocean model thanks to a tensor related to the mesoscale eddies. The antisymmetric part of this tensor is computed from the Gent-McWilliams velocity and is subsequently included in the tracer advection equation. This velocity can be constructed to be divergence-free. The symmetric part that describes the diapycnal and isopycnal diffusions requires a special treatment. A stable and physically sound isopycnal tracer diffusion scheme is needed. Here, an interior penalty method is chosen that enables to build stable diffusion terms. However, due to the strong anisotropy of the diffusion, the common-usual penalty factor by Ern et al. (2008) is not sufficient. A novel method for computing the penalty term of Ern is then proposed for diffusion equations when both the diffusivity and the mesh are strongly anisotropic. Two test cases are resorted to validate the methodology and two more realistic applications illustrate the diapycnal and isopycnal diffusions, as well as the Gent-McWilliams velocity.

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

2012-04-01

347

MRI Phantoms - Are There Alternatives to Agar?  

PubMed Central

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

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

2013-01-01

348

A comparative study of an in situ adapted diffusion cell and an in vitro Franz diffusion cell method for transdermal absorption of doxylamine.  

PubMed

In order to determine whether a drug shows the potential for percutaneous absorption, both in situ and in vitro studies are used. In vitro studies are good indicators of transdermal drug delivery, but the possibility exists that anatomical changes in excised skin can influence drug delivery. The aim of this study was to compare the in vitro Franz diffusion cell method with an in situ adapted diffusion cell method. A saturated aqueous solution of doxylamine succinate was used as model drug and the receptor phase was an isotonic Sörensen buffered solution. The in vitro permeation studies were conducted using vertical Franz diffusion cells with nude mice skin. For in situ studies, a diffusion cell was implanted under the dorsal skin of a nude mouse, simulating the in vitro method. Both in situ and in vitro experiments were conducted over a period of 12 h during which samples were collected every 90 min. The mean steady-state flux from Franz diffusion cells was 0.164+/-0.045 microg/cm2/h and flux determined by the in situ method was 0.113+/-0.034 microg/cm2/h. A statistical significant difference existed between the permeation results of the in vitro and in situ experimental methods. A subjective, semi-quantitative assessment of histological changes to excised nude mouse skin was done using light microscopy. This showed that excised skin undergoes sub-lethal injury (necrosis) during in vitro experiments, which may lead to increased permeability of the drug. It was noticed that in vitro and in situ permeation results showed very close correlation until approximately 4.5 h after commencement of experiments, after which, the permeation through excised skin increased. It was assumed that cell necrosis occurred to such an extent after approximately 4.5 h, that the barrier function of the stratum corneum decreased and permeation of the drug increased. PMID:11297901

Venter, J P; Müller, D G; du Plessis, J; Goosen, C

2001-05-01

349

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

350

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

351

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

PubMed Central

This paper is devoted to investigating the numerical solution for a class of fractional diffusion-wave equations with a variable coefficient where the fractional derivatives are described in the Caputo sense. The approach is based on the collocation technique where the shifted Chebyshev polynomials in time and the sinc functions in space are utilized, respectively. The problem is reduced to the solution of a system of linear algebraic equations. Through the numerical example, the procedure is tested and the efficiency of the proposed method is confirmed.

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

2014-01-01

352

Advances in direct methods in LEED: the diffuse LEED pattern as a hologram  

NASA Astrophysics Data System (ADS)

The direct analysis of the standard diffraction techniques used routinely to determine surface structures is one of the key points for their future. We emphasize that a diffuse low-energy electron diffraction (DLEED) pattern may not only be used in a conventional way, but may also be reinterpreted as a hologram. This provides a rapid new direct method in LEED, and allows to get directly geometrical information without the necessity of an expensive trial-and-error search. We discuss how different parameters may influence the holographic reconstruction process.

de Andres, Pedro L.

1992-05-01

353

Pore size distribution of bioresorbable films using a 3-D diffusion NMR method.  

PubMed

Pore size distribution (PSD) within porous biomaterials is an important microstructural feature for assessing their biocompatibility, longevity and drug release kinetics. Scanning electron microscopy (SEM) is the most common method used to obtain the PSD of soft biomaterials. The method is highly invasive and user dependent, since it requires fracturing of the sample and then considers only the small portion that the user had acquired in the image. In the current study we present a novel nuclear magnetic resonance (NMR) method as an alternative method for estimation of PSD in soft porous materials. This noninvasive 3-D diffusion NMR method considers the entire volume of the specimen and eliminates the user's need to choose a specific field of view. Moreover, NMR does not involve exposure to ionizing radiation and can potentially have preclinical and clinical uses. The method was applied on four porous 50/50 poly(dl-lactic-co-glycolic acid) bioresorbable films with different porosities, which were created using the freeze-drying of inverted emulsions technique. We show that the proposed NMR method is able to address the main limitations associated with SEM-based PSD estimations by being non-destructive, depicting the full volume of the specimens and not being dependent on the magnification factor. Upon comparison, both methods yielded a similar PSD in the smaller pore size range (1-25?m), while the NMR-based method provided additional information on the larger pores (25-50?m). PMID:24534719

Benjamini, Dan; Elsner, Jonathan J; Zilberman, Meital; Nevo, Uri

2014-06-01

354

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

NASA Astrophysics Data System (ADS)

A nano-thick solid-like water film on solid surfaces plays an important role in various fields, including biology, materials science, atmospheric chemistry, catalysis and astrophysics. Visualising the water nanofilm has been a challenge due to its dynamic nature and nanoscale thickness. Here we report an ion diffusion method to address this problem using a membrane formed with a BSA-Na2CO3 (BSA, bovine serum albumin) mixture. After a solid-like water nanofilm deposits onto the membrane, Na+ and CO32- ions diffuse into the film to form a solid Na2CO3 phase in its place. Consequently, the morphology of the nanofilm can be visualised by the space filled by the Na2CO3. Using this method, we successfully observed polygon-like, ribbon-like and spot-like nanofilms at 193 K, 253 K and room temperature, respectively. Our method may provide a tool for characterising confined water films ranging from a few nanometres to hundreds of nanometres in thickness.

Wang, Ya; Duan, Zhiguang; Fan, Daidi

2013-12-01

355

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

PubMed Central

A nano-thick solid-like water film on solid surfaces plays an important role in various fields, including biology, materials science, atmospheric chemistry, catalysis and astrophysics. Visualising the water nanofilm has been a challenge due to its dynamic nature and nanoscale thickness. Here we report an ion diffusion method to address this problem using a membrane formed with a BSA-Na2CO3 (BSA, bovine serum albumin) mixture. After a solid-like water nanofilm deposits onto the membrane, Na+ and CO32? ions diffuse into the film to form a solid Na2CO3 phase in its place. Consequently, the morphology of the nanofilm can be visualised by the space filled by the Na2CO3. Using this method, we successfully observed polygon-like, ribbon-like and spot-like nanofilms at 193?K, 253?K and room temperature, respectively. Our method may provide a tool for characterising confined water films ranging from a few nanometres to hundreds of nanometres in thickness.

Wang, Ya; Duan, Zhiguang; Fan, Daidi

2013-01-01

356

Analytical expressions for the NMR apparent diffusion coefficients in an anisotropic system and a simplified method for determining fiber orientation.  

PubMed

NMR measurements of anisotropic diffusion were studied using a three-dimensional random-walk model. It was found that the apparent diffusion coefficient can be expressed in a canonical form as the product of a diagonal matrix, an orthonormal rotation matrix, and a vector representing the encoding magnetic field gradient. The diffusion coefficient can be interpreted as the sum of the corresponding coefficients measured along the principal diffusion axes, weighted by the squares of the directional cosines of the encoding direction with respect to the principal axes. The analysis revealed that determining the orientation of anisotropy, in a cylindrically symmetric system, requires a minimum of four diffusion measurements. A special pulse sequence which minimized gradient cross-terms and possible restricted diffusion effects was used to characterize diffusion anisotropy in cut chicken gizzards. Diffusion coefficients parallel to the muscle fibers were found to be approximately two to three times larger than those in the transverse direction. Furthermore, the method was successful in detecting the angular change when the sample was rotated by 30 degrees. Results indicate that the proposed approach to measure fiber orientation is valid and may be used to improve the time efficiency of diffusion anisotropy measurements. PMID:7476078

Hsu, E W; Mori, S

1995-08-01

357

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

358

A comparison between the fission matrix method, the diffusion model and the transport model  

SciTech Connect

The fission matrix method may be used to solve the critical eigenvalue problem in a Monte Carlo simulation. This method gives us access to the different eigenvalues and eigenvectors of the transport or fission operator. We propose to compare the results obtained via the fission matrix method with those of the diffusion model, and an approximated transport model. To do so, we choose to analyse the mono-kinetic and continuous energy cases for a Godiva-inspired critical sphere. The first five eigenvalues are computed with TRIPOLI-4{sup R} and compared to the theoretical ones. An extension of the notion of the extrapolation distance is proposed for the modes other than the fundamental one. (authors)

Dehaye, B.; Hugot, F. X.; Diop, C. M. [Commissariat a l'Energie Atomique et aux Energies Alternatives, Direction de l'Energie Nucleaire, Departement de Modelisation des Systemes et Structures, CEA DEN/DM2S, PC 57, F-91191 Gif-sur-Yvette cedex (France)] [Commissariat a l'Energie Atomique et aux Energies Alternatives, Direction de l'Energie Nucleaire, Departement de Modelisation des Systemes et Structures, CEA DEN/DM2S, PC 57, F-91191 Gif-sur-Yvette cedex (France)

2013-07-01

359

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

360

Investigation of the accuracy of the spectral photocurrent method for the determination of minority carrier diffusion length  

NASA Astrophysics Data System (ADS)

The non-scanning, junction-based photocurrent method is one of many techniques that have been devised to determine the minority carrier diffusion length in semiconductor materials. The accuracy of this method is the subject of this paper and the investigation focuses on the theoretical equation that relates the diffusion length to the measured photocurrent produced by a Schottky barrier diode. Specifically, the investigation concentrates on a commonly used assumption in the derivation of this equation, which is that carriers arriving at the edge of the depletion region are swept away from the depletion edge toward the surface barrier at a velocity that is much greater than the diffusion velocity. The subsequent analysis and the results presented in this paper are based on experiments using p-type GaN. The results obtained from numerical simulations show that both velocities have comparable magnitude and the assumption in question is technically incorrect, especially when the diffusion length is very short, as is common for p-type GaN. However, further analysis also shows that in practice this does not adversely affect the accuracy of the diffusion values calculated. In fact, when the diffusion length is very short, the common equation results in calculated diffusion length values that are more accurate compared to those derived from the more detailed equation. This is an indirect consequence of the choice of the effective depletion width and hence, the relative proportion of the drift and diffusion currents.

Wee, D.; Parish, G.; Nener, B.

2012-04-01

361

An electron beam induced current method of determining minority carrier diffusion lengths in thin film solar cells  

Microsoft Academic Search

Minority carrier diffusion lengths were determined on both sides of the Cu(x)S\\/CdS heterojunction in polycrystalline thin film solar cells by an electron beam induced current (EBIC) method. This method uses a beam of electrons about 250 A in diameter to generate excess electron-hole pairs (EHP) in local regions of the cell. The average diffusion distance of the carriers is characterized

J. J. Oakes; I. G. Greenfield; L. D. Partain

1975-01-01

362

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

363

Generating quasi-linear diffusion coefficients using the delta-f PIC method  

NASA Astrophysics Data System (ADS)

Linear wave codes, AORSA and TORIC, used by the SciDAC Center for Simulation of Wave-Plasma Interaction couple to the bounce-averaged nonlinear Fokker-Planck code CQL3D through quasi-linear diffusion coefficients. Both AORSA and TORIC rely on the quasi-local approximation that only includes first-order parallel and perpendicular gradient variations of cyclotron frequency and ignores field line curvature along with temperature and density gradient effects. Previously, the delta-f particle-in-cell (DFPIC) method has been used for simulating ion-cyclotron fast wave behavior. Particle behavior such as multiple pass resonance, banana orbits, and superadiabaticity can also be examined with this method. We present recent results on using eqdisk fusion data to generate quasi-linear diffusion coefficients that permit the VORPAL code to compare to AORSA and TORIC and to eventually couple to CQL3D. The results are generated for a single toroidal mode using DFPIC simulations in RZ geometry.

Austin, Travis; Smithe, David; Wrobel, Matthew; Ranjbar, Vahid

2009-05-01

364

An artificial nonlinear diffusivity method for supersonic reacting flows with shocks  

NASA Astrophysics Data System (ADS)

A computational approach for modeling interactions between shocks waves, contact discontinuities and reactions zones with a high-order compact scheme is investigated. To prevent the formation of spurious oscillations around shocks, artificial nonlinear viscosity [A.W. Cook, W.H. Cabot, A high-wavenumber viscosity for high resolution numerical method, J. Comput. Phys. 195 (2004) 594-601] based on high-order derivative of the strain rate tensor is used. To capture temperature and species discontinuities a nonlinear diffusivity based on the entropy gradient is added. It is shown that the damping of 'wiggles' is controlled by the model constants and is largely independent of the mesh size and the shock strength. The same holds for the numerical shock thickness and allows a determination of the L2 error. In the shock tube problem, with fluids of different initial entropy separated by the diaphragm, an artificial diffusivity is required to accurately capture the contact surface. Finally, the method is applied to a shock wave propagating into a medium with non-uniform density/entropy and to a CJ detonation wave. Multi-dimensional formulation of the model is presented and is illustrated by a 2D oblique wave reflection from an inviscid wall, by a 2D supersonic blunt body flow and by a Mach reflection problem.

Fiorina, B.; Lele, S. K.

2007-03-01

365

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

366

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

367

An O( N log 2N) alternating-direction finite difference method for two-dimensional fractional diffusion equations  

NASA Astrophysics Data System (ADS)

Fractional diffusion equations model phenomena exhibiting anomalous diffusion that cannot be modeled accurately by the second-order diffusion equations. Because of the nonlocal property of fractional differential operators, the numerical methods for fractional diffusion equations often generate dense or even full coefficient matrices. Consequently, the numerical solution of these methods often require computational work of O( N3) per time step and memory of O( N2) for where N is the number of grid points. In this paper we develop a fast alternating-direction implicit finite difference method for space-fractional diffusion equations in two space dimensions. The method only requires computational work of O( N log 2N) per time step and memory of O( N), while retaining the same accuracy and approximation property as the regular finite difference method with Gaussian elimination. Our preliminary numerical example runs for two dimensional model problem of intermediate size seem to indicate the observations: To achieve the same accuracy, the new method has a significant reduction of the CPU time from more than 2 months and 1 week consumed by a traditional finite difference method to 1.5 h, using less than one thousandth of memory the standard method does. This demonstrates the utility of the method.

Wang, Hong; Wang, Kaixin

2011-09-01

368

Electrochemical methods for the determination of the diffusion coefficient of ionophores and ionophore-ion complexes in plasticized PVC membranes.  

PubMed

The diffusion coefficients of active components in ion-selective membranes have a decisive influence on the life-time and detection limit of the respective ion-selective electrodes, as well as influencing the rate of polarization and relaxation processes of electrically perturbed ion sensors. Therefore, the rational design of mass transport controlled ion-selective electrodes with sub-nanomolar detection limits requires reliable data on the diffusion coefficients. We have implemented electrochemical methods for the quantitative assessment of both the diffusion coefficients of free ionophores and ion-ionophore complexes. The diffusion coefficients of the pH-sensitive chromoionophore ETH 5294 and the calcium-selective ionophore ETH 5234 were determined in plasticized PVC membranes with different PVC to plasticizer ratios. The diffusion coefficient of the free chromoionophore determined by a chronoamperometric method was validated with optical methods for a variety of membrane compositions. The calcium-selective ionophore ETH 5234 was used as a model compound to assess the diffusion coefficient of the ion-ionophore complex calculated from the time required for the complexes to cross a freshly prepared membrane during potentiometric ion-breakthrough experiments. The difference between the diffusion coefficients of the free ionophore ETH 5234 and the ion-ionophore complex was found to be significant and correlated well with the geometry of the respective species. PMID:18427685

Bodor, Sándor; Zook, Justin M; Lindner, Erno; Tóth, Klára; Gyurcsányi, Róbert E

2008-05-01

369

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

NASA Astrophysics Data System (ADS)

A reaction between two chemical species can only happen if molecules collide and react. Thus, the mixing of a system can become a limiting factor in the onset of reaction. Solving for reaction rate in a well-mixed system is typically a straightforward task. However, when incomplete mixing kicks in, obtaining a solution becomes more challenging. Since reaction can only happen in regions where both reactants co-exist, the incomplete mixing may slow down the reaction rate, when compared to a well-mixed system. The effect of incomplete mixing upon reaction is a highly important aspect of various processes in natural and engineered systems, ranging from mineral precipitation in geological formations to groundwater remediation in aquifers. We study a relatively simple system with a bi-molecular irreversible kinetic reaction A+B ? Ø where the underlying transport of reactants is governed by an advection-diffusion equation, and the initial concentrations are given in terms of an average and a perturbation. Such a system does not have an analytical solution to date, even for the zero advection case. We model the system by a Monte Carlo particle tracking method, where particles represent some reactant mass. In this method, diffusion is modeled by a random walk of the particles, and reaction is modeled by annihilation of particles. The probability of the annihilation is proportional to the reaction rate constant and the probability density associated with particle co-location. We study the numerical method in depth, characterizing typical numerical errors and time step restrictions. In particular, we show that the numerical method converges to the advection-diffusion-reaction equation at the limit ?t ?0. We also rigorously derive the relationship between the initial number of particles in the system and the initial concentrations perturbations represented by that number. We then use the particle simulations of zero-advection system to demonstrate the well-known phenomena of incomplete mixing (Ovchinnikov-Zeldovich segregation). The numerical results of the particle-tracking simulations are compared to an approximate analytical solution and the late time discrepancy is explained. We also study, for a two dimensional system, how shear flow effects the reaction rate. We do so since shear flow is the simplest form of a spatially variable advection. For the shear flow system, we find that shear flow leads to better mixing of the system on one hand, and a surprising one dimensional segregation at late times, on the other hand. This is in contrast with zero-advection two-dimensional system, where the late time behavior is characterized by the formation of two-dimensional islands. References (Manuscripts in submission): Paster A., D. Bolster and D.A. Benson. Connecting the dots: application of a particle method to the diffusion-reaction equation. Submitted to Advances in Water Resources. Paster A., D. Bolster and D.A. Benson. Particle Tracking and the Diffusion-Reaction Equation. Submitted to Water Resources Research.

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

2012-12-01

370

Hyperspectral imaging for detecting pathogens grown on agar plates  

NASA Astrophysics Data System (ADS)

This paper is concerned with the development of a hyperspectral imaging technique for detecting and identifying one of the most common foodborne pathogens, Campylobacter. Direct plating using agars is an effective tool for laboratory tests and analyses of microorganisms. The morphology (size, growth pattern, color, etc.) of colonies grown on agar plates has been widely used to tentatively differentiate organisms. However, it is sometimes difficult to differentiate target organisms like Campylobacters from other contaminants grown together on the same agar plates. A hyperspectral imaging system operating at the visible and near infrared (VNIR) spectral region from 400 nm to 900 nm was set up to measure spectral signatures of 17 different Campylobacter and non-Campylobacter subspecies. Protocols for culturing, imaging samples and for calibrating measured data were developed. The VNIR spectral library of all 17 organisms commonly encountered in poultry was established from calibrated hyperspectral images. A classification algorithm was developed to locate and identify Campylobacters, non-Campylobacter contaminants, and background agars with 99.29% accuracy. This research has a potential to be expanded to detect other pathogens grown on agar media.

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

2007-09-01

371

Bifurcation Analysis of Brown Tide by Reaction Diffusion Equation Using Finite Element Method  

NASA Astrophysics Data System (ADS)

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 analysed the stability of two cases, i.e., hydranth regeneration in the marine hydroid Tubulariaand 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.

Kawahara, Mutsuto; Ding, Yan

1997-03-01

372

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

PubMed Central

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

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

2014-01-01

373

Flow cytometric analysis of E. coli on agar plates: implications for recombinant protein production.  

PubMed

Recombinant protein production in bacterial hosts is a commercially important process in the pharmaceutical industry. Optimisation of such processes is of critical importance for process productivity and reproducibility. Here, flow cytometry methods were developed to assess characteristics of bacteria during two process steps that are infrequently studied: agar plate culture and liquid culture set-up. During storage on agar plates, three discrete populations of varying green fluorescence intensity were observed along with a progressive shift of cells from the high green fluorescence population to an intermediate green fluorescence population, observed to be due formation of amyloid inclusion bodies. The dynamics of cellular fluorescence and scatter properties upon setup of liquid cultures were also assessed. These methods have the potential to improve the development of fermentation set-up, a currently little-understood area. PMID:24652548

Wyre, Chris; Overton, Tim W

2014-07-01

374

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

PubMed Central

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

Khaki, P; Sharma, A; Bhalla, P

2014-01-01

375

Fly agaric (Amanita muscaria) poisoning, case report and review.  

PubMed

Gathering and eating mushrooms and other plants containing psychoactive substances has become increasingly popular among young people experimenting with drugs. Dried fly agaric Amanita muscaria fruiting bodies were eaten by five young persons (18-21 years of age) at a party in order to evoke hallucinations. Visual and auditory hallucinations occurred in four of them, whereas a 18-year-old girl lost consciousness. The following morning, she went to the Clinic of Toxicology. Due to the fact that not all the active substances present in the fly agaric have been identified, and some of them have an effect after a period of latency, the patient was admitted for several days of observation during which check-up examinations were performed. After four days without any problems, she was discharged. The poisoning regressed with no organ complications. The remaining persons who had eaten the fly agaric were free from any complaints. PMID:15904689

Satora, Leszek; Pach, Dorota; Butryn, Beata; Hydzik, Piotr; Balicka-Slusarczyk, Barbara

2005-06-01

376

Testing the U-Th/4He dating method on carbonates I. Helium diffusion  

NASA Astrophysics Data System (ADS)

Corals and other carbonates, such as speleothems, are important climatic-change proxies which need to be precisely dated for paleoclimatic reconstructions. Yet, U-Th disequilibrium method is applicable up to ca. 500 ka old carbonates. Calcite is difficult to date precisely by U-Pb method because of the low U amounts often found and difficulties in correcting for the common lead. Radiogenic 4He produced by decay of 238U and 235U incorporated into carbonates is a potential chronometer of Quaternary, and possibly Tertiary, corals and speleothems. However, several limitations exist for this method, related to the few data on the He diffusion [1] and on the alpha recoil effect in carbonate minerals. We decided to measure 4He by step heating in carbonate samples dated previously by U-Th disequilibrium: a coral (Scleractinia) from Cape Verde dated at 125 ka; a stalagmite from Patagonia dated at 128 ka; and two hydrothermal travertines from the Ziz Valley in Morocco with ages ? 500 ka. A one cm3 of each sample was cut by saw, crushed, washed and sieved to 80-100?m and 100-125?m fractions. Crushed samples (0.5 to 1 gram) were loaded in a vacuum crucible and 4He extracted by step heating. Previous step heating experiments on a sub-Arctic flowstone suggested that 4He is mainly released between 400 and 600°C [2]. However, the first coral sample heated at 100°C steps, showed a release pattern profile with 4He mainly released between 200 and 400°C. Measured 4He amount of 2.05 x 10-8 (±0.03% 1?) ccSTP/g and U content of 2.7 ppm yield a U-4He age of 62.5 ka, lower than that obtained by U-Th disequilibrium. Data were not precise enough to calculate diffusion parameters using the Arrhenius diagram. The second step-heating pyrolysis of the coral using 50°C-steps indicated that all 4He is released between 250 and 350°C. The measured 4He amount was 2.27 x 10-8 (±0.04% 1?) ccSTP/g, yielding an age of 83 ka, again lower compared to that obtained by U-Th disequilibrium. The data were plotted on an Arrhenius diagram and the activation energy (E) and the ln(D0/a2) value were determined to be 26.2±3.7 kcal mol-1K-1 and 12.7±3.4 cm2 s-1. These values are in agreement with those of [1] for crinoids (E = 30.0±2.6; ln(D0/a2) = 11±2). Using our values, we estimated a diffusion coefficient for carbonate at ambient temperature (20°C) of 3.16 x 10-19 cm2 s-1. Assuming that all crushed material had an initial spherical shape and applying appropriate diffusion equations, the He fraction lost by the coral in the last 125 ka would be only 1 % of the total amount. Assuming a plane sheet (to better represent the septate structure of the coral) with a thickness ranging from 100 ?m to 1 mm, then the He fraction lost could reach 83% of the total, without taking into account the probable loss of He by ? recoil through the surface. These calculations suggests that more complex diffusion models need to be developed to test whether He is readily lost from the structure of corals in a short geological timescale. [1] Copeland, P. et al. (2007) Geochim. Cosmochim. Acta 71, 4488-4511. [2] Agosta, S. et al. (2011) GAC-MAC Annual Meeting, Ottawa (abstr.)

Pinti, D. L.; Ghaleb, B. G.; Sano, Y.; Blanchette, S.; Mathouchanh, E.; Takahata, N.

2012-12-01

377

An artificial nonlinear diffusivity method for supersonic reacting flows with shocks  

NASA Astrophysics Data System (ADS)

A computational approach for modeling interactions between shocks waves, contact discontinuities and reactions zones with a high order compact scheme is investigated. To prevent the formation of spurious oscillations around shocks, artificial nonlinear viscosity [1], based on high-order derivative of the strain rate tensor is used. To capture temperature and species discontinuities a nonlinear diffusivity based on the entropy gradients is added. The damping of `wiggles' is controlled by the model constants and is largely independent of the mesh size and the shock strength. The same holds for the numerical shock thickness and allows a determination of the L2 error. In the shock tube problem, with fluids of different initial entropy separated by the diaphragm, an artificial diffusivity is required to accurately capture the contact surface. Finally, the method is applied to a CJ detonation wave and to multi-dimensional flows including 2-D oblique wave reflection and a jet in a supersonic cross-flow.[1] Cook & Cabot, J. Comput. Phys. 203 (2005)

Fiorina, Benoit; Lele, Sanjiva K.

2005-11-01

378

A Monte Carlo based nodal diffusion model for criticality analysis, and, Application of high-order cross section homogenization method to two-group nodal diffusion  

NASA Astrophysics Data System (ADS)

In the first part, an accurate and fast computational method is presented as an alternative to the Monte Carlo or deterministic transport theory codes currently used to determine the subcriticality of spent fuel storage lattices. The method is capable of analyzing storage configurations with simple or complex lattice cell geometry. It is developed based on two-group nodal diffusion theory, with the nodal cross sections and discontinuity factors determined from continuous-energy Monte Carlo simulations of each unique node (spent fuel assembly type). Three different approaches are developed to estimate the node-averaged diffusion coefficient. The applicability and the accuracy of the nodal method are assessed in two-dimensional geometry through several benchmark configurations typical at Savannah River Site. It is shown that the multiplication constant of the analyzed configurations is within 1% of the MCNP results. In the second part, the high-order cross section homogenization method, recently developed by McKinley and Rahnema, is implemented in the context of two-group nodal diffusion theory. The method corrects the generalized equivalence theory homogenization parameters for the effect of the core environment. The reconstructed fine-mesh (fuel pin) flux and power distributions are a natural byproduct of this method. The method was not tested for multigroup problems, where it was assumed that the multigroup flux expansion in terms of the perturbation parameter is a convergent series. Here the applicability of the method to two-group problems is studied, and it is shown that the perturbation expansion series converges for the multigroup case. A two-group nodal diffusion code with a bilinear intra-nodal flux shape is developed for the implementation of the high-order homogenization method in the context of the generalized equivalence theory. The method is tested by using as a benchmark a core configuration typical of a BWR in slab geometry, which has large variations in the flux distribution across the core. There is a very good agreement between the nodal calculation and the fine-mesh reference calculation: the node-integrated group flux is within 0.5% of the reference solution in all nodes. The reconstructed fine-mesh flux (or equivalently the power distribution) in the core approximates the reference value very well.

Ilas, Germina

379

Mixed finite element method for generalized convection-diffusion equations based on an implicit characteristic-based algorithm  

Microsoft Academic Search

Summary  A mixed finite element method for generalized convection-diffusion equations is proposed. The primitive variable with its\\u000a spatial gradient and the diffusion flux are interpolated as independent variables. The variational (weak) form of the governing\\u000a equations is given on the basis of the extended Hu-Washizu three-field variational principle. The mixed element is formulated\\u000a with stabilized one point quadrature scheme and particularly

W. Wu; X. Li

2007-01-01

380

Agar from two coexisting species of Gracilaria (Gracilariaceae) from the Mexican Caribbean Agar de dos especies coexistentes de Gracilaria (Gracilariaceae) del Caribe mexicano  

Microsoft Academic Search

Gracilaria cornea and G. crassissima are similar species that coexist at Bajo Pepito in the Mexican Caribbean. Differences in agar properties from both species were determined for two reproductive categories: carposporic and undetermined, the latter mainly composed of tetrasporophytes. Agar yield (AY), agar gel strength (GS), 3,6-anhydrogalactose content (AG) and sulfate content (S) of native and alkali-treated agar were determined

Julio Espinoza-Avalos; Enrique Hernández-Garibay; José A. Zertuche-González

2003-01-01

381

A high-order mimetic method on unstructured polyhedral meshes for the diffusion equation  

NASA Astrophysics Data System (ADS)

We present a new family of mimetic finite difference schemes for solving elliptic partial differential equations in the primal form on unstructured polyhedral meshes. These mimetic discretizations are built to satisfy local consistency and stability conditions. The consistency condition is an exactness property, i.e., the mimetic schemes are exact when the solution is a polynomial of an assigned degree. The stability condition ensures the well-posedness of the method. The degrees of freedom are the solution moments on mesh faces and inside mesh cells. Higher order schemes are built using higher order moments. The developed schemes are verified numerically on diffusion problems with constant and spatially variable (possibly, discontinuous) tensorial coefficients.

Lipnikov, K.; Manzini, G.

2014-09-01

382

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

PubMed Central

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

Yadav, Akash; Jain, Dinesh Kumar

2010-01-01

383

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

PubMed

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. PMID:22617131

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

2012-06-21

384

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

385

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

386

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

PubMed

Synthesis of graft copolymers under the influence of microwave radiation alone is a rapid, efficient, clean, cheap, convenient, energy-saving and green method. Grafting of poly(2-hydroxyethylmethacrylate) on agar backbone was carried out under the influence of microwave radiation. The synthesis is optimized in terms of percentage grafting and intrinsic viscosity, by varying the microwave irradiation time and monomer (2-hydroxyethylmethacrylate) concentration. The synthesized graft copolymers have been characterized by intrinsic viscosity measurement, FTIR spectroscopy, UV-spectroscopy, elemental analysis (C, H, N, & S), thermal studies and scanning electron microscopy (SEM). Flocculation efficacy of the synthesized graft copolymers was studied in 0.25% kaolin and 1% coal fine suspension, through 'jar test' procedure. Further, flocculation efficacy of the best grade, coagulant (alum) and agar were studied for possible application in remediation of metals from river water. PMID:23850679

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

2013-10-01

387

A meshless method based on moving Kriging interpolation for a two-dimensional time-fractional diffusion equation  

NASA Astrophysics Data System (ADS)

Fractional diffusion equations have been the focus of modeling problems in hydrology, biology, viscoelasticity, physics, engineering, and other areas of applications. In this paper, a meshfree method based on the moving Kriging interpolation is developed for a two-dimensional time-fractional diffusion equation. The shape function and its derivatives are obtained by the moving Kriging interpolation technique. For possessing the Kronecker delta property, this technique is very efficient in imposing the essential boundary conditions. The governing time-fractional diffusion equations are transformed into a standard weak formulation by the Galerkin method. It is then discretized into a meshfree system of time-dependent equations, which are solved by the standard central difference method. Numerical examples illustrating the applicability and effectiveness of the proposed method are presented and discussed in detail.

Ge, Hong-Xia; Cheng, Rong-Jun

2014-04-01

388

An anisotropic diffusion method for denoising dynamic susceptibility contrast-enhanced magnetic resonance images  

NASA Astrophysics Data System (ADS)

The purpose of this study was to present an application of a novel denoising technique for improving the accuracy of cerebral blood flow (CBF) images generated from dynamic susceptibility contrast-enhanced magnetic resonance imaging (DSC-MRI). The method presented in this study was based on anisotropic diffusion (AD). The usefulness of this method was firstly investigated using computer simulations. We applied this method to patient data acquired using a 1.5 T MR system. After a bolus injection of Gd-DTPA, we obtained 40-50 dynamic images with a 1.32-2.08 s time resolution in 4-6 slices. The dynamic images were processed using the AD method, and then the CBF images were generated using pixel-by-pixel deconvolution analysis. For comparison, the CBF images were also generated with or without processing the dynamic images using a median or Gaussian filter. In simulation studies, the standard deviation of the CBF values obtained after processing by the AD method was smaller than that of the CBF values obtained without any processing, while the mean value agreed well with the true CBF value. Although the median and Gaussian filters also reduced image noise, the mean CBF values were considerably underestimated compared with the true values. Clinical studies also suggested that the AD method was capable of reducing the image noise while preserving the quantitative accuracy of CBF images. In conclusion, the AD method appears useful for denoising DSC-MRI, which will make the CBF images generated from DSC-MRI more reliable.

Murase, Kenya; Yamazaki, Youichi; Shinohara, Masaaki; Kawakami, Kazunori; Kikuchi, Keiichi; Miki, Hitoshi; Mochizuki, Teruhito; Ikezoe, Junpei

2001-10-01

389

A new method for estimating the coefficients of diffusion and emanation of radon in the soil.  

PubMed

This paper describes a new method for determining the basic parameters of soil - diffusion and emanation coefficients related to the transfer of radon in the soil matrix, which are very useful for testing models, based on diffusion and characteristics of various soil matrices regarding the dangers of radon. The method is based on the measurement of radon in soil air on two small depths, differing twice. The paper presents the results of the determination of the parameters for covering loams and clays of Tomsk (Russian Federation), obtained by this method. PMID:24787671

Ryzhakova, Nadezhda K

2014-09-01

390

Basic principles for the development of a common standardised method for determining the radon diffusion coefficient in waterproofing materials.  

PubMed

Paper presents the principles for unified test methods for determining the radon diffusion coefficient in waterproof materials in order to increase the accuracy, repeatability and reproducibility of the results. We consider this very important, because an assessment of the radon diffusion coefficient is required by several national technical standards when waterproofing acts as a radon-proof membrane. The requirements for key parameters for one test method performed under non-stationary conditions and for two methods performed under stationary conditions are described in this paper. PMID:22245288

Jiránek, Martin; Rovenská, Kate?ina

2012-04-01

391

Development and Validation of a Successful Microbiological Agar Assay for Determination of Ceftriaxone Sodium in Powder for Injectable Solution  

PubMed Central

Ceftriaxone sodium is a cephalosporin with broad-spectrum antimicrobial activity and belongs to the third generation of cephalosporins. Regarding the quality control of medicines, a validated microbiological assay for the determination of ceftriaxone sodium in powder for injectable solution has not been reported yet. This paper reports the development and validation of a simple, accurate and reproducible agar diffusion method to quantify ceftriaxone sodium in powder for injectable solution. The assay is based on the inhibitory effect of ceftriaxone sodium on the strain of Bacillus subtilis ATCC 9371 IAL 1027 used as test microorganism. The results were treated statistically by analysis of variance and were found to be linear (r = 0.999) in the selected range of 15.0–60.0 ?g/mL, precise with a relative standard deviation (RSD) of repeatability intraday = 1.40%, accurate (100.46%) and robust with a RSD lower than 1.28%. The results demonstrated the validity of the proposed bioassay, which allows reliable ceftriaxone sodium quantitation in pharmaceutical samples and therefore can be used as a useful alternative methodology for the routine quality control of this medicine.

Alessio, Patricia V.; Salgado, Herida R. N.

2012-01-01

392

A modified method for diffusive monitoring of 3-ethenylpyridine as a specific marker of environmental tobacco smoke  

NASA Astrophysics Data System (ADS)

A previously introduced method for monitoring environmental tobacco smoke (ETS) was further validated. The method is based on diffusive sampling of a vapour-phase marker, 3-ethenylpyridine (3-EP), with 3 M passive monitors (type 3500). Experiments were done in a dynamic chamber to assess diffusive sampling in comparison with active sampling in charcoal tubes or XAD-4 tubes. The sampling rate for 3-EP collected on the diffusive sampler was 23.1±0.6 mL min -1. The relative standard deviation for parallel samples ( n=6) ranged from 4% to 14% among experiments ( n=9). No marked reverse diffusion of 3-EP was detected nor any significant effect of relative humidity at 20%, 50% or 80%. The diffusive sampling of 3-EP was validated in field measurements in 15 restaurants in comparison with 3-EP and nicotine measurements using active sampling. The 3-EP concentration in restaurants ranged from 0.01 to 9.8 ?g m -3, and the uptake rate for 3-EP based on 92 parallel samples was 24.0±0.4 mL min -1. A linear correlation ( r=0.98) was observed between 3-EP and nicotine concentrations, the average ratio of 3-EP to nicotine being 1:8. Active sampling of 3-EP and nicotine in charcoal tubes provided more reliable results than sampling in XAD-4 tubes. All samples were analysed using gas chromatography-mass spectrometry after elution with a 15% solution of pyridine in toluene. For nicotine, the limit of quantification of the charcoal tube method was 4 ng per sample, corresponding to 0.04 ?g m -3 for an air sample of 96 L. For 3-EP, the limit of quantification of the diffusive method was 0.5-1.0 ng per sample, corresponding to 0.04-0.09 ?g m -3 for 8 h sampling. The diffusive method proved suitable for ETS monitoring, even at low levels of ETS.

Kuusimäki, Leea; Peltonen, Kimmo; Vainiotalo, Sinikka

393

Isolation and detection of extended spectrum ?-lactamase (ESBL)-producing enterobacteriaceae from meat using chromogenic agars and isothermal loop-mediated amplification (LAMP) assays.  

PubMed

The aim of this work was to develop a molecular method using loop-mediated isothermal amplification (LAMP) for detection of extended spectrum ?-lactamase (ESBL)-producing Enterobacteriaceae from meat, and to compare it with different isolation agars and microarrays. LAMP assays were developed for CTX-M groups 1, 2, and 9 and OXA-10-like genes. Chicken, lamb, beef, pork, and turkey samples were spiked with 10, 100, and 1,000 cfu/gram using 8 strains of ESBL-producing Enterobacteriaceae (CTX-M sequence types 1, 2, 3, 14, 15, OXA-11, SHV-2, TEM-52) +/- a mix of competitor organisms. Samples were enriched overnight in buffered peptone water (BPW) +/- antibacterials before plating to CHROMagar CTX, OXOID ESBL Brilliance agar, and MacConkey agar with 1 mg/L cefotaxime. Selected BPW broths were also tested using LAMP assays, microarrays and using cefpodoxime discs on agar. For isolation/detection of ESBL producers from beef, pork, lamb, and turkey spiked with 10 or 100 cfu/gram ESBL (natural flora only), all agars and the LAMP assays showed 100% sensitivity and specificity for ESBL spike strains. For chicken samples, both LAMP and chromogenic agars showed improved sensitivity and specificity for isolation of ESBLs compared with MacConkey agar, particularly with competitor bacteria added. In comparison, the cefpodoxime disc method and microarray showed reduced sensitivity. PMID:24329955

Anjum, M F; Lemma, F; Cork, D J; Meunier, D; Murphy, N; North, S E; Woodford, N; Haines, J; Randall, L P

2013-12-01

394

Transferring a Bacterial Culture to an Agar Slant  

NSDL National Science Digital Library

This video from CUNY Kingsborough Community College describes how to transfer a bacterial culture to an agar slant. The brief demonstration is described step by step and would be easy to replicate in a laboratory setting. Running time for the video is 0:34.

2013-06-28

395

Direct Cloning of Human Ovarian Carcinoma Cells in Agar1  

Microsoft Academic Search

We have recently developed an in vitro assay for human tumor stem cells that permits cloning of human ovarian adenocarcinoma cells in soft agar. Tumor colonies grew from both effusions and biopsies from 85% of 31 ovarian cancer patients. The cloning efficiency did not vary with the histology of the tumor. Growth was induced with medium conditioned by the adherent

Anne W. Hamburger; Sydney E. Salmon; Mary B. Kim; Jeff M. Trent; Barbara J. Soehnlen

396

Unconditionally stable diffusion-synthetic acceleration methods for the slab geometry discrete ordinates equations. Part 1: Theory  

Microsoft Academic Search

The authors consider the slab geometry discrete ordinates equations, with the weighted diamond, linear characteristic, linear discontinuous, and linear moments spatial differencing schemes. For each differencing scheme we derive a diffusion-synthetic, source-correction acceleration method which, for model (infinite medium, isotropic scattering, constant cross section, constant mesh spacing) problems, unconditionally reduces the spectral radius of the iteration method from the unaccelerated

1982-01-01

397

A Variation of the Method Using the Simulation of a Diffusion Process to Characterize the Shapes of Plane Figures  

Microsoft Academic Search

This is a variation of a previously presented method (1) for characterizing the shapes of plane figures. In addition to retaining the advantages of the original method, this variant includes one more: It is no longer necessary to halt a (simulated) diffusion process during the transient stage; that is, before arriving at an equilibrium. On the contrary, the longer the

Osvaldo Skliar; V ´ õctor Medina

398

Inverse Monte Carlo method in a multilayered tissue model for diffuse reflectance spectroscopy  

NASA Astrophysics Data System (ADS)

Model based data analysis of diffuse reflectance spectroscopy data enables the estimation of optical and structural tissue parameters. The aim of this study was to present an inverse Monte Carlo method based on spectra from two source-detector distances (0.4 and 1.2 mm), using a multilayered tissue model. The tissue model variables include geometrical properties, light scattering properties, tissue chromophores such as melanin and hemoglobin, oxygen saturation and average vessel diameter. The method utilizes a small set of presimulated Monte Carlo data for combinations of different levels of epidermal thickness and tissue scattering. The path length distributions in the different layers are stored and the effect of the other parameters is added in the post-processing. The accuracy of the method was evaluated using Monte Carlo simulations of tissue-like models containing discrete blood vessels, evaluating blood tissue fraction and oxygenation. It was also compared to a homogeneous model. The multilayer model performed better than the homogeneous model and all tissue parameters significantly improved spectral fitting. Recorded in vivo spectra were fitted well at both distances, which we previously found was not possible with a homogeneous model. No absolute intensity calibration is needed and the algorithm is fast enough for real-time processing.

Fredriksson, Ingemar; Larsson, Marcus; Strömberg, Tomas

2012-04-01

399

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

SciTech Connect

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

Wang, Yangyang [ORNL; Sun, Che-Nan [Oak Ridge National Laboratory (ORNL); Fan, Fei [ORNL; Sangoro, Joshua R [ORNL; Berman, Marc [Hunter College of the City University of New York; Greenbaum, Steve [Hunter College of the City University of New York; Zawodzinski, Thomas [University of Tennessee, Knoxville (UTK); Sokolov, Alexei P [ORNL

2013-01-01

400

Out-diffusion of Zn from Si: A method to study vacancy properties in Si  

Microsoft Academic Search

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

A. Giese; H. Bracht; N. A. Stolwijk; J. T. Walton

1998-01-01

401

Diffuse Attenuation Coefficient of Downwelling Irradiance: An Evaluation of Remote Sensing Methods  

NASA Technical Reports Server (NTRS)

The propagation of downwelling irradiance at wavelength lambda from surface to a depth (z) in the ocean is governed by the diffuse attenuation coefficient, K(sup -)(sub d)(lambda). There are two standard methods for the derivation of K(sup -)(sub d)(lambda) in remote sensing, which both are based on empirical relationships involving the blue-to-green ratio of ocean color. Recently, a semianalytical method to derive K(sup -)(sub d)(lambda) from reflectance has also been developed. In this study, using K(sup -)(sub d)(490) and K(sup -)(sub d)(443) as examples, we compare the K(sup -)(sub d)(lambda) values derived from the three methods using data collected in three different regions that cover oceanic and coastal waters, with K(sup -)(sub d)(490) ranging from approximately 0.04 to 4.0 per meter. The derived values are compared with the data calculated from in situ measurements of the vertical profiles of downwelling irradiance. The comparisons show that the two standard methods produced satisfactory estimates of K(sup -)(sub d)(lambda) in oceanic waters where attenuation is relatively low but resulted in significant errors in coastal waters. The newly developed semianalytical method appears to have no such limitation as it performed well for both oceanic and coastal waters. For all data in this study the average of absolute percentage difference between the in situ measured and the semianalytically derived K(sup -)(sub d) is approximately 14% for lambda = 490 nm and approximately 11% for lambda = 443 nm.

Lee, Zhong-Ping; Darecki, Miroslaw; Carder, Kendall L.; Davis, Curtiss O.; Stramski, Dariusz; Rhea, W. Joseph

2005-01-01

402

Coherent quantum transport in disordered systems: II. Temperature dependence of carrier diffusion coefficients from the time-dependent wavepacket diffusion method  

NASA Astrophysics Data System (ADS)

The time-dependent wavepacket diffusion method for carrier quantum dynamics (Zhong and Zhao 2013 J. Chem. Phys. 138 014111), a truncated version of the stochastic Schrödinger equation/wavefunction approach that approximately satisfies the detailed balance principle and scales well with the size of the system, is applied to investigate the carrier transport in one-dimensional systems including both the static and dynamic disorders on site energies. The predicted diffusion coefficients with respect to temperature successfully bridge from band-like to hopping-type transport. As demonstrated in paper I (Moix et al 2013 New J. Phys. 15 085010), the static disorder tends to localize the carrier, whereas the dynamic disorder induces carrier dynamics. For the weak dynamic disorder, the diffusion coefficients are temperature-independent (band-like property) at low temperatures, which is consistent with the prediction from the Redfield equation, and a linear dependence of the coefficient on temperature (hopping-type property) only appears at high temperatures. In the intermediate regime of dynamic disorder, the transition from band-like to hopping-type transport can be easily observed at relatively low temperatures as the static disorder increases. When the dynamic disorder becomes strong, the carrier motion can follow the hopping-type mechanism even without static disorder. Furthermore, it is found that the memory time of dynamic disorder is an important factor in controlling the transition from the band-like to hopping-type motions.

Zhong, Xinxin; Zhao, Yi; Cao, Jianshu

2014-04-01

403

Determining pre- and syn-eruptive timescales by diffusion methods: case studies from the Oruanui super-eruption  

NASA Astrophysics Data System (ADS)

Diffusion methods permit investigation of timescales of short-lived processes occurring in magmatic systems before, and in some cases during, eruption. We here present three case studies from the 25.4 ka Oruanui super-eruption looking at diffusion in a variety of minerals that reflects a spectrum of timescales. At one end of the spectrum, the diffusion of Li is exceedingly rapid. Diffusion distances of >100 microns in quartz and plagioclase can be attained in minutes at magmatic conditions. Strong diffusion appears to be induced in the very latest stages of magmatic ascent across most quartz and plagioclase crystals and is interpreted to be due to changes in the melt structure and fluid-melt equilibrium during decompression. With corrections for adiabatic expansion and post-eruptive cooling, the magma ascent rate from depths corresponding to the critical pressure is constrained to be up to 21 m/s. Determining timescales here requires corrections of raw data for local anorthite contents, although Li diffusion itself appears to be largely independent of composition. Fe-Ti oxides can retain significant zonation of Fe and Ti abundance for only a matter of days at magmatic conditions, making them ideal for thermometry to establish pre-eruptive conditions. However, observation of zonation in magnetite grains can be used to infer timescales of processes occurring over days before eruption. Magnetites from the phase 7 Oruanui eruption deposits show zoning, reflecting events which occurred in the hours before quenching of the host pumice. In combination with field and textural evidence, we interpret these events to result from syn-eruptive infiltration of hot mafic magma into Oruanui rhyolite. Diffusion in this scenario is straightforward to model in one dimension but requires consideration of ambient fO2. Structural ions in silicate minerals typically diffuse much more slowly, and so yield information on long-lived and persistent processes. Fe-Mg interdiffusion in orthopyroxene is more complex than either Fe-Ti in magnetite or Li in feldspars and quartz. The diffusion coefficient is both composition- and oxygen fugacity-dependent and so a finite difference model would typically be used to model the diffusion behaviour. Here, we show how a specially-constructed spreadsheet can accurately fit and model diffusion profiles based on certain diffusion laws. Results obtained for Oruanui orthopyroxenes suggest residence times in the range of 300 to 1000 years, reflecting the timescale over which the eruptible portion of the Oruanui magma body was assembled (see also ASR Allan et al. in session V046).

Morgan, D. J.; Allan, A. S.; Charlier, B. L.; Wilson, C. J.

2012-12-01

404

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

PubMed

Objective(s) : Ibuprofen is a problematic drug in tableting due to its viscoelastic properties. Additionally its high cohesivity results in low flowability. In this study, co-precipitation of ibuprofen with varying concentration of agar and PVP to optimize properties of Ibuprofen was carried out. Materials and Methods: Co-precipitates of ibuprofen- PVP or agar were prepared by solvent evaporation technique under vacuum condition. Differential scanning calorimetry (DSC), X -ray diffraction of powder (XRDP) and FT-IR spectroscopy were used to investigate the solid state characteristics of the co-precipitates. The dissolution behavior, flowability, particle size and compaction properties of various batches were also studied. Results: Co-precipitation of drug with agar led to a change in habit from needle to plate shape crystals, while drug -PVP co-precipitates had agglomerated structure and consisted of numerous crystals which had been aggregated together. The co-precipitates showed improved flow properties compared with ibuprofen alone. Precipitation of ibuprofen with these additives led to modification in the dissolution of the drug. Agar in 1% w/w improved slightly the dissolution rate of drug while PVP had a negative impact and led to reduction in the dissolution rate of drug to less than that of pure drug. The all obtained co-precipitates exhibited significantly improved tableting behavior compared with drug crystals alone. This may be due to this fact that, the polymer covering the drug particles increases and changes the nature of the surface area available for interparticulate bonds between particles. DSC, XRDP and FT-IR experiments showed that drug particles, in co-precipitates samples, did not undergo polymorphic modifications. Conclusion: The study highlights the influence of polymeric additives on crystallization process leading to modified performance. PMID:24250942

Maghsoodi, Maryam; Kiafar, Farhad

2013-04-01

405

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

PubMed

Objective(s) : Ibuprofen is a problematic drug in tableting due to its viscoelastic properties. Additionally its high cohesivity results in low flowability. In this study, co-precipitation of ibuprofen with varying concentration of agar and PVP to optimize properties of Ibuprofen was carried out. Materials and Methods: Co-precipitates of ibuprofen- PVP or agar were prepared by solvent evaporation technique under vacuum condition. Differential scanning calorimetry (DSC), X -ray diffraction of powder (XRDP) and FT-IR spectroscopy were used to investigate the solid state characteristics of the co-precipitates. The dissolution behavior, flowability, particle size and compaction properties of various batches were also studied. Results: Co-precipitation of drug with agar led to a change in habit from needle to plate shape crystals, while drug -PVP co-precipitates had agglomerated structure and consisted of numerous crystals which had been aggregated together. The co-precipitates showed improved flow properties compared with ibuprofen alone. Precipitation of ibuprofen with these additives led to modification in the dissolution of the drug. Agar in 1% w/w improved slightly the dissolution rate of drug while PVP had a negative impact and led to reduction in the dissolution rate of drug to less than that of pure drug. The all obtained co-precipitates exhibited significantly improved tableting behavior compared with drug crystals alone. This may be due to this fact that, the polymer covering the drug particles increases and changes the nature of the surface area available for interparticulate bonds between particles. DSC, XRDP and FT-IR experiments showed that drug particles, in co-precipitates samples, did not undergo polymorphic modifications. Conclusion: The study highlights the influence of polymeric additives on crystallization process leading to modified performance. PMID:24250936

Maghsoodi, Maryam; Kiafar, Farhad

2013-04-01

406

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

PubMed Central

Objective(s) : Ibuprofen is a problematic drug in tableting due to its viscoelastic properties. Additionally its high cohesivity results in low flowability. In this study, co-precipitation of ibuprofen with varying concentration of agar and PVP to optimize properties of Ibuprofen was carried out. Materials and Methods: Co-precipitates of ibuprofen- PVP or agar were prepared by solvent evaporation technique under vacuum condition. Differential scanning calorimetry (DSC), X -ray diffraction of powder (XRDP) and FT-IR spectroscopy were used to investigate the solid state characteristics of the co-precipitates. The dissolution behavior, flowability, particle size and compaction properties of various batches were also studied. Results: Co-precipitation of drug with agar led to a change in habit from needle to plate shape crystals, while drug –PVP co-precipitates had agglomerated structure and consisted of numerous crystals which had been aggregated together. The co-precipitates showed improved flow properties compared with ibuprofen alone. Precipitation of ibuprofen with these additives led to modification in the dissolution of the drug. Agar in 1% w/w improved slightly the dissolution rate of drug while PVP had a negative impact and led to reduction in the dissolution rate of drug to less than that of pure drug. The all obtained co-precipitates exhibited significantly improved tableting behavior compared with drug crystals alone. This may be due to this fact that, the polymer covering the drug particles increases and changes the nature of the surface area available for interparticulate bonds between particles. DSC, XRDP and FT-IR experiments showed that drug particles, in co-precipitates samples, did not undergo polymorphic modifications. Conclusion: The study highlights the influence of polymeric additives on crystallization process leading to modified performance.

Maghsoodi, Maryam; Kiafar, Farhad

2013-01-01

407

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

408

Micro-analysis by near-infrared diffuse reflectance spectroscopy with chemometric methods.  

PubMed

Great attention has been paid to near-infrared diffuse reflectance spectroscopy (NIRDRS) due to its practicability in analyzing real complex samples. However, the application of the technique in micro-analysis is badly restricted by its low sensitivity or high detection limit. In this study, the possibility of achieving the sensitive detection of micro-components using NIRDRS with the help of chemometric methods is studied with two experimental datasets. The results show that a very high sensitivity can be obtained when the noise and the variant background are minimized. Quantitative determination of low concentrations of pesticides and trace Cr(3+) in solutions is achieved by using preconcentration and chemometric approaches to minimize the noise and background. The absolute prediction error of the method can be as low as 7.6 ?g for the pesticide and 28.6 ?g for Cr(3+). These quantities are equivalent to 76 ng mL(-1) and 286 ng mL(-1) if 100 mL of solution are used for the analysis. PMID:24029879

Liu, Yan; Ning, Yu; Cai, Wensheng; Shao, Xueguang

2013-11-01

409

Artifact reduction method in ultrasound-guided diffuse optical tomography using exogenous contrast agents  

NASA Astrophysics Data System (ADS)

In diffuse optical tomography (DOT), a typical perturbation approach requires two sets of measurements obtained at the lesion breast (lesion or target site) and a contra-lateral location of the normal breast (reference site) for image reconstruction. For patients who have a small amount of breast tissue, the chest-wall underneath the breast tissue at both sites affects the imaging results. In this group of patients, the perturbation, which is the difference between measurements obtained at the lesion and reference sites, may include the information of background mismatch which can generate artifacts or affect the reconstructed quantitative absorption coefficient of the lesion. Also, for patients who have a single breast due to prior surgery, the contra-lateral reference is not available. To improve the DOT performance or overcome its limitation, we introduced a new method based on an exogenous contrast agent and demonstrate its performance using animal models. Co-registered ultrasound was used to guide the lesion localization. The results have shown that artifacts caused by background mismatch can be reduced significantly by using this new method.

Ardeshirpour, Yasaman; Biswal, Nrusingh; Aguirre, Andres; Zhu, Quing

2011-04-01

410

DSA Image Blood Vessel Skeleton Extraction Based on Anti-concentration Diffusion and Level Set Method  

NASA Astrophysics Data System (ADS)

Serious types of vascular diseases such as carotid stenosis, aneurysm and vascular malformation may lead to brain stroke, which are the third leading cause of death and the number one cause of disability. In the clinical practice of diagnosis and treatment of cerebral vascular diseases, how to do effective detection and description of the vascular structure of two-dimensional angiography sequence image that is blood vessel skeleton extraction has been a difficult study for a long time. This paper mainly discussed two-dimensional image of blood vessel skeleton extraction based on the level set method, first do the preprocessing to the DSA image, namely uses anti-concentration diffusion model for the effective enhancement and uses improved Otsu local threshold segmentation technology based on regional division for the image binarization, then vascular skeleton extraction based on GMM (Group marching method) with fast sweeping theory was actualized. Experiments show that our approach not only improved the time complexity, but also make a good extraction results.

Xu, Jing; Wu, Jian; Feng, Daming; Cui, Zhiming

411

Artifact reduction method in ultrasound-guided diffuse optical tomography using exogenous contrast agents  

PubMed Central

In diffuse optical tomography (DOT), a typical perturbation approach requires two sets of measurements obtained at the lesion breast (lesion or target site) and a contra-lateral location of the normal breast (reference site) for image reconstruction. For patients who have a small amount of breast tissue, the chest-wall underneath the breast tissue at both sites affects the imaging results. In this group of patients, the perturbation, which is the difference between measurements obtained at the lesion and reference sites, may include the information of background mismatch which can generate artifacts or affect the reconstructed quantitative absorption coefficient of the lesion. Also, for patients who have a single breast due to prior surgery, the contra-lateral reference is not available. To improve the DOT performance or overcome its limitation, we introduced a new method based on an exogenous contrast agent and demonstrate its performance using animal models. Co-registered ultrasound was used to guide the lesion localization. The results have shown that artifacts caused by background mismatch can be reduced significantly by using this new method.

Ardeshirpour, Yasaman; Biswal, Nrusingh; Aguirre, Andres; Zhu, Quing

2011-01-01

412

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

2013-09-01

413

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

NASA Astrophysics Data System (ADS)

In this paper, a meshless local maximum-entropy finite element method (LME-FEM) is proposed to solve 1D Poisson equation and steady state convection-diffusion problems at various Peclet numbers in both 1D and 2D. By using local maximum-entropy (LME) approximation scheme to construct the element shape functions in the formulation of finite element method (FEM), additional nodes can be introduced within element without any mesh refinement to increase the accuracy of numerical approximation of unknown function, which procedure is similar to conventional p-refinement but without increasing the element connectivity to avoid the high conditioning matrix. The resulted LME-FEM preserves several significant characteristics of conventional FEM such as Kronecker-delta property on element vertices, partition of unity of shape function and exact reproduction of constant and linear functions. Furthermore, according to the essential properties of LME approximation scheme, nodes can be introduced in an arbitrary way and the continuity of the shape function along element edge is kept at the same time. No transition element is needed