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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Aspects of Bacterial Resistance to Silver

Sütterlin, Susanne January 2015 (has links)
Bacterial resistance to antibiotics has increased rapidly within recent years, and it has become a serious threat to public health. Infections caused by multi-drug resistant bacteria entail higher morbidity, mortality, and a burden to health care systems. The use of biocides, including silver compounds, may affect the resistance to both biocides and antibiotics and, thereby, can be a driving factor in this development. The aim of the following thesis was to investigate the frequency of silver resistance and the effects of silver exposure on bacterial populations being of clinical significance and from geographically different parts of the world. Furthermore, it explored the genetic background of silver resistance, and if silver could select directly or indirectly for antibiotic resistance. By a range of methods, from culture in broth to whole genome sequencing, bacterial populations from humans, birds and from the environment were characterized. The studies showed that sil genes, encoding silver resistance, occurred at a high frequency. Sil genes were found in 48 % of Enterobacter spp., in 41 % of Klebsiella spp. and in 21 % of all human Escherichia coli isolates with production of certain types of extended-spectrum beta-lactamases (CTX-M-14 and CTX-M-15). In contrast, silver resistance was not found in bird isolates or in bacterial species, such as Pseudomonas aeruginosa and Legionella spp., with wet environments as their natural habitat. One silver-resistant Enterobacter cloacae strain was isolated from a chronic leg ulcer after only three weeks of treatment with silver-based dressings. The in-vivo effects of these dressings were limited, and they failed to eradicate both Gram-positive and Gram-negative bacteria. The activity of silver nitrate in vitro was bacteriostatic on Gram-positive species such as S. aureus and bactericidal on Gram-negative species. In Enterobacteriaceae, sil genes were associated with silver resistance phenotypes in all but one case. Using whole genome sequencing, single nucleotide polymorphisms in the silS gene were discovered after silver exposure in isolates with expressed silver resistance. This resistance could co-select for resistance to beta-lactams, co-trimoxazole and gentamicin. The findings of this thesis indicate that silver exposure may cause phenotypic silver resistance, and it may reduce the susceptibility to mainly beta-lactams and select for bacteria with resistance to clinically important antibiotics.
2

Hegemony has his hand up again : examining masculinities and resistance when teaching about gender

Moore, Shannon Dawn Maree 11 1900 (has links)
This paper outlines interview based, qualitative research that was conducted with six male youth who were previously students in my Social Studies 11 class. Within two separate, semi-structured interviews, participants were asked to discuss student resistance to anti oppressive pedagogy that focused on gender, and their understanding of masculinities. The initial purpose of this research was to find a relationship, if any, between acts of student resistance and the construction of masculinities. Participant perceptions of masculinities evolved as the dominant theme within the interviews. These discussions revealed that student understandings of masculinity were often entrenched in hegemonic language, yet contradictions were exposed between their rote definitions and personal narratives. Further, the use of media as a discourse became a venue for complicating essentialist understandings of masculinity, and for exposing multiple, fluid, versions of masculinities. Within these discussions of multiplicity, race and sexuality became two intersections of identity that took precedence. Also the intersection of teacher identity and the reading of identity terms emerged as a salient interpretation for gender discussions in the classroom. Throughout this write-up of the research are methodological considerations surrounding power, the construction of masculinity and race, and the further entrenching of heteronormativity, in the form of methodological interludes. Finally, within the conclusion, I consider the implications for practice and future directions for research in masculinities.
3

Electrical resistivity of disordered metallic systems

Shalmon, Marina. January 1979 (has links)
No description available.
4

Variability in susceptibility of insect pests of stored products to insecticides.

Kumar, Virendra. January 1966 (has links)
Insect pests of public health importance were the first among which the development of highly insecticide resistant strains was shown to be widespread. More recently, numerous instances of resistance among economically important insect pests of growing crops have been revealed. The relative scarcity of reported resistance in stored-products pests is probably a reflection of fewer investigations and fewer instances of continued insecticidal controls. The possible development of resistance at a future date in stored-products pests and the chance that one might avoid such development if it can be foreseen should be adequate justification for the present investigation. It was felt that the occurrence of stored-products pests as isolated islands of population might enhance the selection of resistant strains locally and also allow their eradication if they are discovered, making this a worthwhile area for study. [...]
5

Hegemony has his hand up again : examining masculinities and resistance when teaching about gender

Moore, Shannon Dawn Maree 11 1900 (has links)
This paper outlines interview based, qualitative research that was conducted with six male youth who were previously students in my Social Studies 11 class. Within two separate, semi-structured interviews, participants were asked to discuss student resistance to anti oppressive pedagogy that focused on gender, and their understanding of masculinities. The initial purpose of this research was to find a relationship, if any, between acts of student resistance and the construction of masculinities. Participant perceptions of masculinities evolved as the dominant theme within the interviews. These discussions revealed that student understandings of masculinity were often entrenched in hegemonic language, yet contradictions were exposed between their rote definitions and personal narratives. Further, the use of media as a discourse became a venue for complicating essentialist understandings of masculinity, and for exposing multiple, fluid, versions of masculinities. Within these discussions of multiplicity, race and sexuality became two intersections of identity that took precedence. Also the intersection of teacher identity and the reading of identity terms emerged as a salient interpretation for gender discussions in the classroom. Throughout this write-up of the research are methodological considerations surrounding power, the construction of masculinity and race, and the further entrenching of heteronormativity, in the form of methodological interludes. Finally, within the conclusion, I consider the implications for practice and future directions for research in masculinities.
6

Evolution and molecular characterization of clinical respiratory macrolide-resistant Streptococcus pneumoniae in Canada

Wierzbowski, Aleksandra K. 11 January 2012 (has links)
The purpose of this thesis was to molecularly characterize macrolide-resistant S. pneumoniae (SPN) isolates in Canada between 1998 and 2008. The characterization involved looking at the multi-drug resistant phenotype (MDR), the mechanisms of macrolide resistance, the genetic relatedness, the serotype distribution and PCV7 vaccine coverage as well as the determination of presence of pili-virulence factors. The hypothesis of the study was that macrolide-resistant SPN will growingly be MDR, genetically related, piliated and consisting of serotypes not found in PCV7 vaccine. Over 1500 macrolide-resistant SPN isolates collected between 1998 and 2008 were studied. Macrolide-resistant isolates came from patients from all regions of Canada, and from all age groups. They came from slightly more males (60%) and slightly more in-patients (62%). Macrolide resistant SPN remained low at 8% during the first 4 years of the study, and started to increase reaching 22% by the end of the study in 2008 (p=0.001). Overall the most common mechanism of resistance was efflux mediated by mef(A) (51%), followed by target site modification mediated by erm(B) (36%). The efflux mediated macrolide resistance in S. pneumoniae was predominantly due to the presence of subtype E (95%), which was resistant to more antibiotic classes, and was genetically and serotypically more diverse than the A subtype. Isolates carrying both erm(B) and mef(A) macrolide resistance genes increased overtime from 1% (1998) to 19% (2008) (p=0.002). Serotype distribution showed a decrease in PCV7 vaccine coverage from 67% to 31% (p=0.0072). Isolates with non-PCV7 serotypes increased overtime from 33% to 57% (p=0.0152). Isolates with serotype 19A increased by 15% (p=0.005). They were found to be multi-drug resistant, carried both erm(B) and mef(A) subtype E macrolide resistance genes, and were genetically related. The presence of virulence factor pili-type 1 (PI-1) and pili-type 2 (PI-2) was found associated with these isolates, possibly contributing to its emergence. In conclusion, macrolide resistant SPN increased during the course of this study mostly due to emergence of multi-drug resistant, genetically related, piliated, 19A S. pneumoniae.
7

Evolution and molecular characterization of clinical respiratory macrolide-resistant Streptococcus pneumoniae in Canada

Wierzbowski, Aleksandra K. 11 January 2012 (has links)
The purpose of this thesis was to molecularly characterize macrolide-resistant S. pneumoniae (SPN) isolates in Canada between 1998 and 2008. The characterization involved looking at the multi-drug resistant phenotype (MDR), the mechanisms of macrolide resistance, the genetic relatedness, the serotype distribution and PCV7 vaccine coverage as well as the determination of presence of pili-virulence factors. The hypothesis of the study was that macrolide-resistant SPN will growingly be MDR, genetically related, piliated and consisting of serotypes not found in PCV7 vaccine. Over 1500 macrolide-resistant SPN isolates collected between 1998 and 2008 were studied. Macrolide-resistant isolates came from patients from all regions of Canada, and from all age groups. They came from slightly more males (60%) and slightly more in-patients (62%). Macrolide resistant SPN remained low at 8% during the first 4 years of the study, and started to increase reaching 22% by the end of the study in 2008 (p=0.001). Overall the most common mechanism of resistance was efflux mediated by mef(A) (51%), followed by target site modification mediated by erm(B) (36%). The efflux mediated macrolide resistance in S. pneumoniae was predominantly due to the presence of subtype E (95%), which was resistant to more antibiotic classes, and was genetically and serotypically more diverse than the A subtype. Isolates carrying both erm(B) and mef(A) macrolide resistance genes increased overtime from 1% (1998) to 19% (2008) (p=0.002). Serotype distribution showed a decrease in PCV7 vaccine coverage from 67% to 31% (p=0.0072). Isolates with non-PCV7 serotypes increased overtime from 33% to 57% (p=0.0152). Isolates with serotype 19A increased by 15% (p=0.005). They were found to be multi-drug resistant, carried both erm(B) and mef(A) subtype E macrolide resistance genes, and were genetically related. The presence of virulence factor pili-type 1 (PI-1) and pili-type 2 (PI-2) was found associated with these isolates, possibly contributing to its emergence. In conclusion, macrolide resistant SPN increased during the course of this study mostly due to emergence of multi-drug resistant, genetically related, piliated, 19A S. pneumoniae.
8

The impact of differential friction on curve negotiation speed

Pilgrim, Michael January 2014 (has links)
This thesis considers the impact of differential skid resistance between wheel paths on the speed at which a vehicle can safely negotiate a curve. Currently the New Zealand Transport Agency undertakes measurement of the co-efficient of friction on the state highway network by measuring both wheel paths, but taking the average value to represent the level of skid resistance available. Part of the basis for this approach is that modern cars have Electronic Stability Control that has historically been considered to negate the effects of any differential friction. Aside from straight line braking testing, little research has been done on the impacts of differential friction on curves. There are however a number of areas of research that can be related to this topic.By PC Crash simulation modeling, this research identifies that there are a number of gaps in our understanding of the relationship between vehicles maneuvering on a curve and the effect of varying skid resistance. It concludes that taking the average of the two values is not the same as considering them separately and, that as the difference in the co-efficient of friction between the wheel paths increases, the speed at which a vehicle can safely maneuver around a curve decreases. It has also been found that when Electronic Stability Control is used the speed at which the vehicle can safely maneuver around a curve decreases further.
9

Epidemiology of community-associated methicillin resistant staphylococcus aureus (CA-MRSA) infection in Hong Kong, 2007: a descriptive and analytical study

劉昌志, Lau, Cheong-chi. January 2008 (has links)
published_or_final_version / Community Medicine / Master / Master of Public Health
10

The status of resistance in Culex quinquefasciatus say (Diptera: culicidae) populations in Brazos and Harris Counties, Texas

Johnsen, Mark Miller 15 May 2009 (has links)
In 2002, West Nile virus was isolated for the first time in Harris County, Texas. The subsequent epidemic led the Harris County Mosquito Control Division to initiate an extensive spraying operation to suppress infected adult mosquitoes. The control program was aimed at the predominate disease-carrying mosquito for the southern United States, Culex quinquefasciatus Say. With the increase of insecticide pressure on the mosquito populations, the possibility of resistance was brought into question. A three year study using a vial bioassay test was conducted in Harris (2004-2005) and Brazos (2005-2006) counties to determine the resistance status of Cx. quinquefasciatus to the six chemicals (malathion, naled, resmethrin, permethrin, sumithrin, and pyrethrum) used most frequently in adult mosquito control programs. The resistance ratios acquired from the vial bioassay tests were mapped onto shapefiles for Harris and Brazos counties, which revealed clustering of areas with pyrethroid resistance mosquito populations in the northeastern, southeastern, and southwestern corners of Loop 610 in Harris County. An additional six-month preliminary study, involving six operational areas in Harris County and three in Brazos County, was conducted, demonstrating only minor fluctuations in the monthly resistance ratios occurring in both counties in 2005. A significant correlation was documented between the two years of resistance ratios for mosquitoes to the three pyrethroids in Harris County and all the insecticides except pyrethrum in Brazos County. A significant relationship was also found between the resmethrin resistance ratios and the number of spray events performed during the previous year and the malathion resistance ratios with the insecticide treatments conducted in the same year. The correlation analyses provide data used to predict areas where resistance can develop in the mosquito population, thus providing the control agency more data to plan future control tactics. The overall analysis indicated that Harris County has localized pockets of resistant mosquitoes; but, on a whole, it does not seem to have widespread resistance in its mosquito populations. The only resistance that was detected was in the mosquitoes tested against the three pyrethroids. Mosquitoes in Brazos County, which has no organized mosquito control, demonstrated county-wide susceptibility to all six insecticides tested.

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