• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 2676
  • 864
  • 307
  • 303
  • 220
  • 179
  • 66
  • 37
  • 35
  • 32
  • 32
  • 26
  • 23
  • 19
  • 17
  • Tagged with
  • 5824
  • 618
  • 593
  • 460
  • 453
  • 435
  • 408
  • 375
  • 353
  • 281
  • 271
  • 268
  • 267
  • 267
  • 263
  • 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.
41

Interactions between density dependence and dispersal

Fowler, Michael S. January 2002 (has links)
No description available.
42

A comparative study of methods of assessing hydrodynamic drag reducing polymers

McIlwrath, J. C. January 1978 (has links)
No description available.
43

Denitrification within riverine systems of north-east England

Pattinson, Sarah N. January 1999 (has links)
This study was undertaken to investigate denitrification and nitrous oxide production in sediments and the key environmental factors influencing these within selected river systems of the LOIS (Land-Ocean Interaction Study) area in North-East England and southern Scotland. Seasonal and spatial trends were evident in both environmental and denitrification data measured monthly for 1.5 years along the Swale-Ouse system from source to tidal limits. Denitrification, measured in sediment cores using acetylene inhibition and expressed by unit area of sediment, increased with distance from source down to freshwater tidal limits. Results from a supplementary survey of the freshwater tidal reaches of the Yorkshire Ouse showed a decrease from the tidal limits. Denitrification activity showed a spring (March to May) peak, particularly in the lowland sites. The highest rate (883±134 µmol N m(^-2) h(^-1)) was measured on the River Wiske, a highly eutrophic lowland tributary to the Swale. A high degree of colinearity was evident between environmental variables, although a significant relationship between denitrification, nitrate and temperature was found through multiple regression. For comparison, measurements were made in the less populated Tweed river system. The seasonal and spatial trends evident in both the environmental and denitrification data from the River Tweed, under a more limited sampling programme, were generally consistent with those observed in the Swale-Ouse system. An intensive field investigation of 50 river sites showed that both potential denitrification rate and N(_2)O production in sediment slurries were positively correlated with nitrate water concentration, sediment water content and percentage of fine (<100 µm) sediment particles. An experimental study investigating the kinetic parameters for denitrification, found that sediment cores taken along the Swale-Ouse exhibited a saturation type curve with added nitrate. Apparent affinity and estimates of apparent maximum velocity for mixed populations of denitrifying bacteria showed an increase on moving downstream and were highest on the Wiske.
44

The novel synthesis of aldehyde insect sex pheromones

Carter, Charles Ross January 1999 (has links)
No description available.
45

F/A-18 Data Reduction at the Naval Air Warfare Center, China Lake, California

Smith, Darren C. 10 1900 (has links)
International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California / The current F/A-18 data reduction/analysis system is incapable of meeting increased customer demands. A new system has been developed and is based on new technologies. In the process of developing the new system, the design team had to divorce themselves from the current system and consider what the ideal system would consist of. This was accomplished with great success in the areas of timeliness of data turn around, customer satisfaction, and increased efficiency.
46

The Use of Aerobic Running in the Reduction of Anxiety

Allen, Geoffrey H. 05 1900 (has links)
This investigation was concerned with the potential effectiveness of an aerobic running program in the reduction of anxiety. Anxiety was defined in this investigation as a subject's score on the Taylor Manifest Anxiety Scale (TMAS).
47

Catalytic Amide Reductions under Hydrosilylation Conditions

Volkov, Alexey January 2016 (has links)
This thesis covers the development of catalytic methodologies for the mild and chemoselective reductions of amides. The first part of the thesis describes the use of a Fe(II)/NHC catalyst for the deoxygenation of aromatic tertiary amides to corresponding amines. The protocol is characterized by low catalyst loading, mild reaction conditions and the use of air and moisture stable polymethylhydrosilaxane (PMHS) as the hydride source. The second part concerns the development of a protocol for the room temperature deoxygenation of a wide range of tertiary amides to amines using catalytic amounts of Et2Zn and LiCl together with PMHS. The system displayed high levels of chemoselectivity tolerating various reducible groups such as nitro, nitrile, and olefin functionalities, and was shown to be applicable for the reduction of aromatic, heteroaromatic and aliphatic tertiary amides. The attempts to expand the scope of the Fe-based protocol to accommodate benzylic tertiary amides led to the development of a transition metal-free catalytic system based on KOtBu for the formation of enamines. The final products constitute an important class of precursors for a wide range of valuable compounds in organic chemistry. Moreover, avoiding the use of transition metals in the protocol allowed the desired products to be obtained without the hazardous metal contaminants. The last chapter of the thesis describes the Mo(CO)6-catalyzed hydrosilylation of amides. The Mo-based catalyst was proven to mediate the deoxygenation of α,β-unsaturated tertiary and secondary amides to the corresponding allylamines without reduction of the olefinic bonds. Further development of the catalytic system revealed an unprecedented chemoselectivity in the hydrosilylation of aromatic and certain aliphatic tertiary amides in the presence of a variety of reducible groups along with aldehydes and imines that were tolerated for the first time. Moreover, it was possible to control the reaction outcome by variation of the reaction temperature to obtain either amines or aldehydes as the major products. The synthetic utility of the developed Mo(CO)6-catalyzed protocols was further demonstrated in the synthesis of the pharmaceuticals Naftifine and Donepezil.
48

Electrochemical reduction of diphenyldiazomethane

January, James Richard, 1950- January 2011 (has links)
Vita. / Digitized by Kansas Correctional Industries
49

The catalytic reduction of nitric oxide with ammonia/

Walker, John William January 1974 (has links)
No description available.
50

Optimised reduction of the radiated noise from the casing of a constant speed gearbox

Shen, Anne, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW January 2008 (has links)
This thesis presents a comprehensive methodology for predicting and minimising the noise radiated from a constant speed gearbox assembly by means of attaching optimally placed stiffening ribs on the casing. The procedure involves building an FE model of the gearbox, which is updated using modal parameters extracted from a modal test. This is followed by synthesis of the required FRFs with respect to the forcing degrees-of-freedom. The forces, which are assumed to act only at the bearings are identified from these FRFs and the measured operational velocities of the casing. The identified forces are then used to excite the updated FE model to re-calculate the vibration velocities. A boundary element method is used to calculate the final radiated sound power to be compared with that measured. The same forces are used later to excite the modified gearbox casing to determine the improvement given by optimised modification. The optimisation study minimises the vibration energy of the casing in 10% bands around critical frequencies, in this case the first two harmonics of the gearmesh frequency. To allow for errors in the model, the excitation is by white noise, so as to produce wide stop bands, rather than minimising the response at particular frequencies. The vibration energy is weighted for radiation efficiency, A-weighting, and relative source strength in the bands. The final optimal stiffener layout is validated through a final vibration and acoustic calculation on the updated gearbox model using the forces identified in the earlier steps. The study of one particular gearbox concludes that i) the proposed hybrid optimisation scheme produces a theoretical effective noise reduction of 3 dBA for the total sound power. ii) Because the gearmesh harmonics were targeted, a further 5 dB improvement was effectively gained by eliminating the tonal penalty which otherwise applied. iii) From plate studies it was demonstrated that the stiffening ribs could be attached using epoxy cement (to avoid welding) and that the properties of the cemented joint could be determined by model updating after attaching one rib, so as to obtain a better prediction of the final optimised result.

Page generated in 0.1892 seconds