Numerical investigation of obstacle's effect on the performance of proton-exchange membrane fuel cell: studying the shape of obstacles.

Fuel cells are the technology through which chemical energy can be converted to electricity and heat. They perform the conversion with no contamination. Hence, they have become a significant source of clean power in today's modern life. That being said, it is really crucial that every source of power provides a high and stable amount of efficiency, and it should be considered when it comes to developing PEM fuel cell technology as well. One of the most important parameters in applying such fuel cells is the layout and dimensions of the flow field designed for the reactors on the bipolar plates of the fuel cell and its improvement. In the current research, for the best geometry dimension and arrangement of obstacles, four types of obstacle including triangular, cylindrical, square and trapezoidal are simulated. The obtained results show that the triangular obstacle has the best performance in terms of the produced current density and pressure drop. The results reveal that at the constant voltage of 0.6 V, the current density in the flow field with triangular and square obstacles is increased more than 80% in comparison to cylindrical and trapezoidal types. Finally, the fuel cell with triangular and square obstacles as the optimum flow field is designed, manufactured and tested.

Numerical investigation of dimensions and arrangement of obstacle on the performance of PEM fuel cell.

The fuel cell is an electrochemical energy converter which converts the chemical energy from a fuel into electricity and heat and has been able to introduce itself as a source of clean power in the world over the past few decades. One of the major technical challenges in the development of PEM fuel cell technology is to achieve high and stable efficiency. One of the key parameters in designing this type of fuel cell is the shape and dimensions of reactors flow field channels on the bipolar plates. In this research, the obstacle is simulated by selecting the obstacle geometry in the channel path, and after choosing the best range (height), the best obstacle width is analyzed to have better performance. The simulation is done for the non-obstacle case and obstacles with 0.5, 1, 1.5 and 2 mm heights and 0.9, 1.8, 2.7 and 3.6 mm widths, respectively. The obtained results for PEMFC show that the height of 1.5 mm and the width of 3.6 mm have the highest impact on the fuel cell efficiency regarding species consumption, pressure drop and current density. Once the proper dimensions of the obstacle have been determined, different arrangements of the obstacle and their effect on the fuel cell efficiency are investigated, and the best arrangement is selected.

High rate of detection of mixed infections of Plasmodium vivax and Plasmodium falciparum in South-East of Iran, using nested PCR.

Sistan and Baluchestan province, South-East of Iran, has been reported as an endemic area of malaria [Sadrizadeh B. Malaria in the world, in the eastern Mediterranean region and in Iran: Review article. WHO/EMRO Report 2001: 1-13.]. The main objective of this research was to perform rapid and correct diagnoses of malaria infection. Blood specimens were collected from 140 suspected volunteers. The Giemsa-stained slides examination and nested PCR for amplification of the Plasmodium small subunit ribosomal genes (ssrRNA) were utilized. The results demonstrated 118 out of 140 cases (84.3%) positive for malaria parasites, including 60.7%, 20.7% and 2.9% as having Plasmodium vivax (P.v), Plasmodium falciparum (P.f) and mixed infections (P.v+P.f), respectively by microscopy. The nested PCR detected malaria parasites in 134 samples (94.3%), consisting of 51.4% P.v, 12.6% P.f and 29.3% mixed infections. The PCR analysis detected 37 cases of mixed infections more than that of the routine microscopy. These results suggested that there are a considerable number of cases with mixed infections in the study area that mainly remain undiagnosed by microscopy. It is also concluded that the nested PCR is a suitable complement to microscopy for accurate specific diagnosis of malaria species in field.

A continuing survey of drug-resistant tuberculosis, New York City, April 1994.

BACKGROUND: A 1991 survey showed high levels of drug resistance among tuberculosis patients in New York, NY. As a result, the tuberculosis control program was strengthened, including expanded use of directly observed therapy and improved infection control. METHODS: We collected isolates from every patient in New York City with a positive culture for Mycobacterium tuberculosis during April 1994; results were compared with those in the April 1991 survey. RESULTS: From 1991 to 1994, the number of patients decreased from 466 to 332 patients. The percentage with isolates resistant to 1 or more antituberculosis drugs decreased from 33% to 24% (P < .01); with isolates resistant to at least isoniazid decreased from 26% to 18% (P < .05); and with isolates resistant to both isoniazid and rifampin decreased from 19% to 13% (P < .05). The number of patients with isolates resistant to both isoniazid and rifampin decreased by more than 50%. Among never previously treated patients, the percentage with resistance to 1 or more drugs decreased from 22% in 1991 to 13% in 1994 (P < .05). The number of patients with consistently positive culture results for more than 4 months decreased from 130 to 44. A history of antituberculosis treatment was the strongest predictor of drug resistance (odds ratio = 3.1; P < .001). Human immunodeficiency virus infection was associated with drug resistance among patients who never had been treated for tuberculosis. CONCLUSIONS: Drug-resistant tuberculosis declined significantly in New York City from 1991 to 1994. Measures to control and prevent tuberculosis were associated with a 29% decrease in the proportion of drug resistance and a 52% decrease in the number of patients with multidrug-resistant tuberculosis.

A comparative study of different Leishmania tropica isolates from Iran: correlation between infectivity and cytochemical properties.

Five isolates of Leishmania tropica from southwest Iran were studied to identify correlates among human disease, animal infectivity, and surface biochemistry. Clinical patterns of the disease in humans differed. One striking strain, LT-249, produced a small dry lesion which did not heal during four years of observation. Infectivity of these L. tropica for mice was correlated with lectin agglutination patterns and interaction with macrophages. There was also a significant difference among the five isolates regarding infectivity for BALB/c mice; isolate LT-249 was not infective whereas all the others were. All isolates agglutinated with Concanavalin A (Con A), Ricinus communis and soybean agglutinin but not with four other lectins listed. However, Leishmania isolate LT-249 showed much poorer agglutination with all lectins than did the other four isolates. Two isolates were selected for detailed study of attachment to macrophages, one, LT-249, which was not infective and one, LT-252, which was infective for BALB/c mice. The number of promastigotes which attached to macrophages in vitro was the same, but the mechanism of attachment differed since only the LT-252 bound predominantly by Con A-mannose receptor interaction. These results indicate a correlation among animal infectivity, lectin agglutination, and promastigote-macrophage attachment. In particular one isolate of L. tropica which caused prolonged infection in humans was not infective in BALB/c mice, showed poor agglutination with lectins, and bound to macrophages by a different mechanism than did other isolates from the same region.

Persistent diarrhea caused by Isospora belli: therapeutic response to pyrimethamine and sulfadiazine.

A 54-year-old human immunodeficiency virus (HIV)-positive homosexual man developed overwhelming watery diarrhea and marked weight loss over a 3-week period. Although Entamoeba histolytica and other nonpathogenic enteric protozoa were observed along with Isospora belli in this patient's stool specimens, they were promptly eradicated after metronidazole (flagyl) treatment. The presence of I. belli oocysts in various stages of development in the stool and clinical symptoms related to Isospora infection persisted for 10 more months despite treatment with combined chemotherapeutic agents. Clinical and parasitiological resolution was ultimately achieved through an 8-week course of pyrimethamine and sulfadiazine.

First report on Anopheles fluviatilis U in southeastern Iran.

Anopheles fluviatilis James, one of the malaria vectors in Iran, is a complex of at least three cryptic species provisionally designated as species S, T and U. These species are morphologically indistinguishable at any stage of their life cycle and can be identified only by the examination of species-specific fixed inversions in the polytene chromosomes. Recently, sequence analysis of 28S D3 and second internal transcribed spacer (ITS2) regions of ribosomal DNA has revealed 7 haplotypes of S, U, T1, T2, Y, X and V within the complex. Identification of the cryptic species of the complex is of paramount importance in a disease control program due to contrasting differences in their vectorial efficiency, preference for feeding on humans and resting behavior. In this study we analyzed the sequence of 28S D3- and ITS2-rDNA loci to identify the species composition of the An. fluviatilis complex in Jiroft and Chabahar districts, two of the most important endemic malaria foci in southeastern corner of Iran. The ITS2 sequence analysis revealed that all of the An. fluviatilis specimens were identical to the Y/T2 haplotype of An. fluviatilis T, whereas D3 sequence analysis revealed presence of species T in Jiroft and species U in Chabahar district. It is the first report of species U in Iran.

A new perspective on and re-assessment of SAG2 locus as the tool for genetic analysis of Toxoplasma gondii isolates.

SAG2 locus, the coding gene of the P22 protein, has been widely used for the molecular epidemiology of Toxoplasma gondii and characterization of the parasite isolates with two separate polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) processes. To re-assess the resolution power and suitability of this genetic marker for molecular characterization of the parasite isolates, a number of 27 Toxoplasma strains from different zymodeme patterns were used in the present study. Both codon and non-codon regions of the SAG2 locus of all 27 strains were amplified and subjected to sequencing and nucleotide alignment. Nucleotide variations clustered the three major genotypes (I, II and III). Some minor genotypes, unidentifiable by SAG2-RFLP, could be identified by sequence comparison. However, there were other genotypes that could not be differentiated from the major types due to having identical sequences. This suggests that a remarkable number of field isolates representing several minor types will be miss-clustered with the major types by using the traditional SAG2-PCR-RFLP method. It was concluded that this technique seems not to be suitable for Toxoplasma population study. Thus, the utilization of more variable markers and other discriminatory methods are also recommended.

[Contributions to the micromorphology of the miracidium of Schistosoma mansoni. I. Fine structure of the tegument and its "associated structures" (author's transl)]. / Beiträge zur Mikromorphologie der Miracidien von Schistosoma mansoni. I. Feinstruktur des Teguments und dessen "Begleitorganellen".

The body wall of the miracidium of S. mansoni has been studied by light and electron microscope. It has been found that the tegument layer contains so-called membrane-bound bodies. The tegument layer will be separated from muscle layer by means of a basal membrane. Special attention was focused on the associated structures of the tegument; these are cilia, microvilli-like appendices amounting to six in number at our test-organisms and finally two types of sensory papillae on the so-called terebratorium. After treatment of the miracidium in antiserum, fine granulated precipitate was formed around the cilia.

Diarrhea caused by a Cyanobacterium-like organism.

Seven cases of watery diarrhea of explosive onset, three of them ending within two weeks, are discussed. The cause of diarrhea is believed to be the presence of an organism called Cyanobacteriumlike organism. These are non-refractile, spherical bodies, 8-9 micrometers in diameter, which take on a faint to deep pink color after modified kinyoun acid-fast staining. Risk factors such as travel to and from warm regions, and water as a possible source of infection are briefly discussed.

Rifampin-monoresistant tuberculosis in New York City, 1993-1994.

All New York City patients whose cultures yielded Mycobacterium tuberculosis with isolated resistance to rifampin in 1993 and 1994 were included in this study. Of the 96 patients, 48 (50%) had primary resistance, 32 (33%) had acquired resistance, and 16 (17%) had unclassified resistance; 66% had histories of illicit drug use, and 79% were infected with human immunodeficiency virus (HIV). The median time to emergence of resistance was 40 weeks among the 32 patients with acquired resistance. Each of the HIV-infected patients with acquired resistance (cases, n = 29) was matched to two HIV-infected patients who had disease due to fully susceptible M. tuberculosis (controls, n = 58). In multivariate analysis, factors associated with the emergence of rifampin resistance were as follows: a sputum smear positive for acid-fast bacilli, advanced immunosuppression, and nonadherence to therapy.

Alga associated with diarrhea in patients with acquired immunodeficiency syndrome and in travelers.

Spherical bodies resembling coccidian oocysts and measuring 8.0 to 9.0 microns in diameter were seen in the stools of eight persons with explosive, watery diarrhea. Seven had recently traveled to tropical countries, mostly in the Caribbean, and four had acquired immunodeficiency syndrome. The structures were easily discernible in wet mounts by light microscopy and contained variable numbers of granular inclusions, but were refractory to, or stained partially with, 12 commonly used laboratory stains. Electron microscopy revealed an outer fibrillar coat, a thin cell wall, granules, and organelles which were not surrounded by membranes. One type of organelle was similar to the thylakoid photosynthesizing organelles of blue-green algae (cyanobacteria). These findings indicate that the bodies may be a species of blue-green algae.

Emergence of fluoroquinolone-resistant tuberculosis in New York City.

22 patients infected with fluoroquinolone-resistant Mycobacterium tuberculosis in New York City were identified between January, 1991, and November, 1993. In 16 patients resistance arose as a result of inadequate or inappropriate treatment. 6 patients had primary infection with fluoroquinolone-resistant organisms; 5 acquired the organisms nosocomially. Seven distinct patterns of restriction-fragment length polymorphism were identified in isolates from 21 patients. Fluoroquinolones should be restricted to patients with multidrug-resistant disease or intolerance to other antituberculosis drugs. All patients with multidrug-resistant tuberculosis should be on directly observed therapy.

Multicenter laboratory validation of susceptibility testing of Mycobacterium tuberculosis against classical second-line and newer antimicrobial drugs by using the radiometric BACTEC 460 technique and the proportion method with solid media.

In a large multicenter study involving six major study sites in the United States, Canada, and Europe, the susceptibilities of 272 Mycobacterium tuberculosis strains to classical second-line antituberculosis (anti-TB) drugs (capreomycin, cycloserine, ethionamide, and kanamycin) and newer compounds (amikacin, clofazimine, ofloxacin, and rifabutin) were determined by the radiometric BACTEC 460 procedure and the conventional proportion method on Middlebrook 7H10 agar. Previously established critical concentrations for classical second-line anti-TB drugs were compared with several concentrations in liquid medium to establish equivalence. MICs of newer compounds determined in liquid medium were either the same or up to four times lower than those determined in agar medium. After establishing critical concentrations (breakpoints) in the extended testing of clinical isolates, we obtained an excellent overall correlation between the two systems, with no errors with amikacin, kanamycin, and ofloxacin and very few major or very major errors with the other drugs; however, for cycloserine, no breakpoint concentration could be recommended due to repeatedly inconsistent results by both methods. Based on these data we conclude that the BACTEC 460 procedure is a simple and rapid method requiring 4 to 8 days on average to generate accurate antimicrobial susceptibility testing (AST) results for eight anti-TB drugs other than those considered primary ones. These data not only fill a major gap of knowledge regarding the critical test concentrations of secondary anti-TB drugs but also provide a baseline for future evaluations of M. tuberculosis AST with the more recently developed, nonradiometric broth-based culture systems.

Multicenter evaluation of the BACTEC MGIT 960 system for recovery of mycobacteria.

We evaluated the BACTEC MGIT 960 system, which is a fully automated, noninvasive system for the growth and detection of mycobacteria with a capacity to incubate and continuously monitor 960 7-ml culture tubes. We studied 3,330 specimens, 2,210 respiratory and 1,120 nonrespiratory specimens, collected from 2,346 patients treated at six sites. Processed specimens were inoculated into the BACTEC MGIT 960 and BACTEC 460 TB systems, as well as onto Lowenstein-Jensen slants and Middlebrook 7H11/7H11 selective plates. From all culture systems, a total of 362 isolates of mycobacteria were recovered; these were recovered from 353 specimens collected from 247 patients. The greatest number of isolates of mycobacteria (289, or 80% of the 362 isolates) was recovered with the BACTEC MGIT 960, followed by the BACTEC 460 TB (271, or 75%) and solid media (250, or 69%). From all culture systems a total of 132 isolates of Mycobacterium tuberculosis complex were recovered. The greatest number of isolates of M. tuberculosis complex was recovered when liquid medium was combined with conventional solid media; the number recovered with BACTEC 460 TB plus solid media was 128 (97%), that recovered with BACTEC MGIT 960 plus solid media was 121 (92%), that recovered with BACTEC 460 TB was 119 (90%) and that recovered with all solid media combined was 105 (79%). The recovery with BACTEC MGIT 960 alone was 102 (77%). The mean times to detection (TTD) for M. tuberculosis complex were 14.4 days for BACTEC MGIT, 15.2 days for BACTEC 460 TB, and 24.1 days for solid media. The numbers of isolates of Mycobacterium avium complex (MAC) recovered were 172 (100%) for all systems, 147 (85%) for BACTEC MGIT 960, 123 (72%) for BACTEC 460 TB, and 106 (62%) for all solid media combined. The TTD for MAC in each system were 10.0 days for BACTEC MGIT 960, 10.4 days for BACTEC 460 TB, and 25.9 days for solid media. Breakthrough contamination rates (percentages of isolates) for each of the systems were 8.1% for BACTEC MGIT 960, 4.9% for BACTEC 460 TB, and 21.1% for all solid media combined.