13 results on '"Lyall N"'
Search Results
2. Chemical Evolution of the Exceptional Arctic Stratospheric Winter 2019/2020 Compared to Previous Arctic and Antarctic Winters
- Author
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Wohltmann, Ingo, von der Gathen, Peter, Lehmann, Ralph, Deckelmann, Holger, Manney, G. L., Davies, J., Tarasick, D., Jepsen, N., Kivi, R., Lyall, N., Rex, Markus, Wohltmann, Ingo, von der Gathen, Peter, Lehmann, Ralph, Deckelmann, Holger, Manney, G. L., Davies, J., Tarasick, D., Jepsen, N., Kivi, R., Lyall, N., and Rex, Markus
- Abstract
The winter 2019/2020 showed the lowest ozone mixing ratios ever observed in the Arctic winter stratosphere. It was the coldest Arctic stratospheric winter on record and was characterized by an unusually strong and long-lasting polar vortex. We study the chemical evolution and ozone depletion in the winter 2019/2020 using the global Chemistry and Transport Model ATLAS. We examine whether the chemical processes in 2019/2020 are more characteristic of typical conditions in Antarctic winters or in average Arctic winters. Model runs for the winter 2019/2020 are compared to simulations of the Arctic winters 2004/2005, 2009/2010, and 2010/2011 and of the Antarctic winters 2006 and 2011, to assess differences in chemical evolution in winters with different meteorological conditions. In some respects, the winter 2019/2020 (and also the winter 2010/2011) was a hybrid between Arctic and Antarctic conditions, for example, with respect to the fraction of chlorine deactivation into HCl versus ClONO2, the amount of denitrification, and the importance of the heterogeneous HOCl + HCl reaction for chlorine activation. The pronounced ozone minimum of less than 0.2 ppm at about 450 K potential temperature that was observed in about 20% of the polar vortex area in 2019/2020 was caused by exceptionally long periods in the history of these air masses with low temperatures in sunlight. Based on a simple extrapolation of observed loss rates, only an additional 21-46 h spent below the upper temperature limit for polar stratospheric cloud formation and in sunlight would have been necessary to reduce ozone to near zero values (0.05 ppm) in these parts of the vortex.
- Published
- 2021
3. Two-weight estimates for singular and strongly singular integral operators
- Author
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Kokilashvili, V., Lyall, N., and Meskhi, A.
- Published
- 2007
- Full Text
- View/download PDF
4. Near-Complete Local Reduction of Arctic Stratospheric Ozone by Severe Chemical Loss in Spring 2020
- Author
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Wohltmann, I., Von Der Gathen, P., Lehmann, R., Maturilli, M., Deckelmann, H., Manney, G. L., Davies, J., Tarasick, D., Jepsen, N., Kivi, R., Lyall, N., and Rex, M.
- Abstract
In the Antarctic ozone hole, ozone mixing ratios have been decreasing to extremely low values of 0.01–0.1 ppm in nearly all spring seasons since the late 1980s, corresponding to 95–99% local chemical loss. In contrast, Arctic ozone loss has been much more limited and mixing ratios have never before fallen below 0.5 ppm. In Arctic spring 2020, however, ozonesonde measurements in the most depleted parts of the polar vortex show a highly depleted layer, with ozone loss averaged over sondes peaking at 93% at 18 km. Typical minimum mixing ratios of 0.2 ppm were observed, with individual profiles showing values as low as 0.13 ppm (96% loss). The reason for the unprecedented chemical loss was an unusually strong, long-lasting, and cold polar vortex, showing that for individual winters the effect of the slow decline of ozone-depleting substances on ozone depletion may be counteracted by low temperatures.
- Published
- 2020
- Full Text
- View/download PDF
5. Near complete local reduction of Arctic stratospheric ozone by severe chemical loss in spring 2020
- Author
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Wohltmann, Ingo, von der Gathen, Peter, Lehmann, Ralph, Maturilli, Marion, Deckelmann, Holger, Manney, G. L., Davies, J., Tarasick, D., Jepsen, N., Kivi, R., Lyall, N., Rex, Markus, Wohltmann, Ingo, von der Gathen, Peter, Lehmann, Ralph, Maturilli, Marion, Deckelmann, Holger, Manney, G. L., Davies, J., Tarasick, D., Jepsen, N., Kivi, R., Lyall, N., and Rex, Markus
- Abstract
In the Antarctic ozone hole, ozone mixing ratios have been decreasing to extremely low values of 0.01–0.1 ppm in nearly all spring seasons since the late 1980s, corresponding to 95–99% local chemical loss. In contrast, Arctic ozone loss has been much more limited and mixing ratios have never before fallen below 0.5 ppm. In Arctic spring 2020, however, ozonesonde measurements in the most depleted parts of the polar vortex show a highly depleted layer, with ozone loss averaged over sondes peaking at 93% at 18 km. Typical minimum mixing ratios of 0.2 ppm were observed, with individual profiles showing values as low as 0.13 ppm (96% loss). The reason for the unprecedented chemical loss was an unusually strong, long-lasting, and cold polar vortex, showing that for individual winters the effect of the slow decline of ozone-depleting substances on ozone depletion may be counteracted by low temperatures.
- Published
- 2020
6. Near‐Complete Local Reduction of Arctic Stratospheric Ozone by Severe Chemical Loss in Spring 2020
- Author
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Wohltmann, I., primary, Gathen, P., additional, Lehmann, R., additional, Maturilli, M., additional, Deckelmann, H., additional, Manney, G. L., additional, Davies, J., additional, Tarasick, D., additional, Jepsen, N., additional, Kivi, R., additional, Lyall, N., additional, and Rex, M., additional
- Published
- 2020
- Full Text
- View/download PDF
7. COVID-19 Crisis Reduces Free Tropospheric Ozone Across the Northern Hemisphere.
- Author
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Steinbrecht W, Kubistin D, Plass-Dülmer C, Davies J, Tarasick DW, von der Gathen P, Deckelmann H, Jepsen N, Kivi R, Lyall N, Palm M, Notholt J, Kois B, Oelsner P, Allaart M, Piters A, Gill M, Van Malderen R, Delcloo AW, Sussmann R, Mahieu E, Servais C, Romanens G, Stübi R, Ancellet G, Godin-Beekmann S, Yamanouchi S, Strong K, Johnson B, Cullis P, Petropavlovskikh I, Hannigan JW, Hernandez JL, Diaz Rodriguez A, Nakano T, Chouza F, Leblanc T, Torres C, Garcia O, Röhling AN, Schneider M, Blumenstock T, Tully M, Paton-Walsh C, Jones N, Querel R, Strahan S, Stauffer RM, Thompson AM, Inness A, Engelen R, Chang KL, and Cooper OR
- Abstract
Throughout spring and summer 2020, ozone stations in the northern extratropics recorded unusually low ozone in the free troposphere. From April to August, and from 1 to 8 kilometers altitude, ozone was on average 7% (≈4 nmol/mol) below the 2000-2020 climatological mean. Such low ozone, over several months, and at so many stations, has not been observed in any previous year since at least 2000. Atmospheric composition analyses from the Copernicus Atmosphere Monitoring Service and simulations from the NASA GMI model indicate that the large 2020 springtime ozone depletion in the Arctic stratosphere contributed less than one-quarter of the observed tropospheric anomaly. The observed anomaly is consistent with recent chemistry-climate model simulations, which assume emissions reductions similar to those caused by the COVID-19 crisis. COVID-19 related emissions reductions appear to be the major cause for the observed reduced free tropospheric ozone in 2020., (© 2021. The Authors.)
- Published
- 2021
- Full Text
- View/download PDF
8. Rab14 regulates maturation of macrophage phagosomes containing the fungal pathogen Candida albicans and outcome of the host-pathogen interaction.
- Author
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Okai B, Lyall N, Gow NA, Bain JM, and Erwig LP
- Subjects
- Animals, Bone Marrow Cells, Candida albicans pathogenicity, Cathepsins biosynthesis, Cell Line, Green Fluorescent Proteins genetics, Host-Pathogen Interactions immunology, Immune Evasion, Lysosomal-Associated Membrane Protein 1 biosynthesis, Lysosomes immunology, Lysosomes microbiology, Mice, Mice, Inbred C57BL, Phagosomes genetics, Phagosomes immunology, Phagosomes microbiology, RNA Interference, RNA, Small Interfering, rab GTP-Binding Proteins genetics, rab5 GTP-Binding Proteins immunology, rab7 GTP-Binding Proteins, Candida albicans immunology, Hyphae immunology, Macrophages immunology, Phagocytosis immunology, rab GTP-Binding Proteins immunology
- Abstract
Avoidance of innate immune defense is an important mechanism contributing to the pathogenicity of microorganisms. The fungal pathogen Candida albicans undergoes morphogenetic switching from the yeast to the filamentous hyphal form following phagocytosis by macrophages, facilitating its escape from the phagosome, which can result in host cell lysis. We show that the intracellular host trafficking GTPase Rab14 plays an important role in protecting macrophages from lysis mediated by C. albicans hyphae. Live-cell imaging of macrophages expressing green fluorescent protein (GFP)-tagged Rab14 or dominant negative Rab14, or with small interfering RNA (siRNA)-mediated knockdown of Rab14, revealed the temporal dynamics of this protein and its influence on the maturation of macrophage phagosomes following the engulfment of C. albicans cells. Phagosomes containing live C. albicans cells became transiently Rab14 positive within 2 min following engulfment. The duration of Rab14 retention on phagosomes was prolonged for hyphal cargo and was directly proportional to hyphal length. Interference with endogenous Rab14 did not affect the migration of macrophages toward C. albicans cells, the rate of engulfment, the overall uptake of fungal cells, or early phagosome processing. However, Rab14 depletion delayed the acquisition of the late phagosome maturation markers LAMP1 and lysosomal cathepsin, indicating delayed formation of a fully bioactive lysosome. This was associated with a significant increase in the level of macrophage killing by C. albicans. Therefore, Rab14 activity promotes phagosome maturation during C. albicans infection but is dysregulated on the phagosome in the presence of the invasive hyphal form, which favors fungal survival and escape., (Copyright © 2015 Okai et al.)
- Published
- 2015
- Full Text
- View/download PDF
9. Where do rural women obtain postabortion care? The case of Uttar Pradesh, India.
- Author
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Johnston HB, Ved R, Lyall N, and Agarwal K
- Subjects
- Counseling, Female, Health Services Accessibility, Health Services Research, Humans, India, Abortion, Legal adverse effects, Aftercare, Rural Population, Women's Health Services organization & administration
- Abstract
Context: Although Indian law permits abortion for a broad range of social and medical indications, millions of unsafe and illegal abortions and countless subsequent complications occur annually. Nonetheless, in the central Indian state of Uttar Pradesh, few women with abortion complications are reported to seek care at registered private and public health facilities. Information is needed about where rural women seek care for abortion complications and about the quality of care they receive., Methods: Qualitative data were collected in 1999 in four villages in rural Uttar Pradesh. The study team conducted community mapping exercises, focus group discussions with female and male community members, and in-depth interviews with women of reproductive age and with postabortion care providers., Results: Postabortion care is widely available in the villages studied, largely from untrained or inappropriately trained providers. Because village-level providers are the front line of care for many women, abortion complications may be exacerbated rather than alleviated, appropriate care delayed and the cost of treatment increased. Village-level postabortion care does not include family planning and contraceptive counseling services or links to reproductive and other health services., Conclusions: : Existing village-level postabortion care services are inadequate. There is an urgent need to increase women's access to higher-quality postabortion care. This can be done by simultaneously engaging village-level providers in the formal system of postabortion care service delivery, as appropriate, and addressing the prevailing social and cultural mores that discourage women with abortion complications from seeking higher-level care.
- Published
- 2003
- Full Text
- View/download PDF
10. UTI: a new approach to its diagnosis.
- Author
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Hafiz S and Lyall N
- Subjects
- Anti-Bacterial Agents therapeutic use, Humans, Pakistan, Recurrence, Urinary Tract Infections drug therapy, Urinary Tract Infections microbiology, Anti-Bacterial Agents urine, Practice Patterns, Physicians' standards, Urinary Tract Infections urine
- Abstract
The incidence of urinary tract infection in our community is studied taking into consideration the indiscriminate and inappropriate use of antimicrobial agents and describing a simple method which could be adopted to evaluate samples of urine for the presence of antimicrobial agents. It reveals that 42.9% individuals were actually on antimicrobial agents and had sufficient levels in their urine to inhibit growth of the most common causative agent of urinary tract infection.
- Published
- 1989
11. Neisseria meningitidis storage identification and MIC determination.
- Author
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Hafiz S, Lyall N, and Alam M
- Subjects
- Preservation, Biological, Neisseria meningitidis drug effects
- Abstract
The significance Minimum Inhibitory Concentration (MIC) of determination for Meningococci is described and according to the present study a shift in the sensitivity of Meningococcus is occurring, local isolates show higher Minimum Inhibitory Concentration for Chloramphenicol and Azactam. Strains of Meningococcus can successfully be stored in a domestic freezer.
- Published
- 1989
12. Reliable and realistic approach to sensitivity testing.
- Author
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Hafiz S, Lyall N, Punjwani S, and Zaidi SQ
- Subjects
- In Vitro Techniques, Microbial Sensitivity Tests, Anti-Bacterial Agents pharmacology, Bacteria drug effects
- Abstract
Antibiotic testing by Disc was compared with Break-Point method using 535 clinical isolates; Disc sensitivity method was carried out in the routine way using the disc provided by pharmaceutical company. Break-point sensitivity was done by incorporating the substrate into solid medium, the results obtained showed greater resistance by Break-point which appears to be more realistic in the light of indiscriminate usage of antibiotic. The method is simple, cost effective, reliable and realistic (JPMA 39 : 94, 1989).
- Published
- 1989
13. Legionella pneumophila: laboratory diagnosis in developing countries like Pakistan.
- Author
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Hafiz S, Hamedani P, Lyall N, Ali J, Memon R, Ali S, Ali M, and Ansari M
- Subjects
- Colony Count, Microbial, Developing Countries, Fluorescent Antibody Technique, Humans, Legionella immunology, Legionella isolation & purification, Legionnaires' Disease immunology, Legionnaires' Disease microbiology, Pakistan, Predictive Value of Tests, Sputum immunology, Sputum microbiology, Legionnaires' Disease diagnosis
- Abstract
Three hundred random sputum samples were collected for analysis from cases of mild to severe respiratory infections and screened for Legionella pneumophila by both the culture method and also the direct fluorescent antigen test. In one third of the cases, blood specimen was also collected and screened for Legionella serum antibodies. With the direct fluorescent test it was possible to identify Legionella in 9% of the samples while the culture gave positive results in 4.3% of cases. Diagnostic antibody titers (1:256) were obtained in 12% of the samples while another 12% cases showed serum antibody titers of 1:64 to 1:128. In Pakistan where antibiotics are used extensively, the direct fluorescent examination of sputum samples gives more accurate diagnosis of Legionella cases than the culture method.
- Published
- 1989
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