Tesi: "Effect of light on weeds"

1

Omami, Elizabeth Nabwile, of Western Sydney Hawkesbury University, of Agriculture Horticulture and Social Ecology Faculty e School of Horticulture. "Amaranthus retroflexus seed dormancy and germination responses to environmental factors and chemical stimulants". THESIS_FAHSE_HOR_Omami_E.xml, 1993. http://handle.uws.edu.au:8081/1959.7/66.

Testo completo

Abstract (sommario):

A large number of weed seeds in the soil persist because of seed dormancy, and depletion of the seed bank through manipulation of seed dormancy has been suggested as one of the goals in weed control. This study was designed to investigate some of the factors which control dormancy and germination in Amaranthus retroflexus seeds. Germination studies were conducted at different temperatures, and either in continuous white light or in the dark. Higher temperatures increased germination and, although light interacted with temperature, its effect on germination varied with the temperature. In an attempt to determine changes in dormancy during dry storage, two lots of seeds were stored dry at different temperatures. Loss in dormancy increased with an increase in storage temperature and duration, but the time required for maximum germination varied according to the seedlot. Seeds germinated to higher percentages at high temperatures, but storage at higher temperatures and for prolonged duration resulted in seeds gaining the ability to germinate at lower temperatures. Changes in dormancy under field conditions were also examined. Seeds were buried at different depths and for different durations and they all lost viability with time, but this loss was greater in surface-sown and shallowly buried seeds. Dormancy was broken during cold periods and induced as warmer periods progressed. The effects of chemical stimulants on dormancy and germination were investigated. The response of seeds to ethephon and nitrate were assessed at different temperatures either at continuous white light or in the dark. Germination increased with the concentration of the chemicals, and a greater response was observed at lower temperatures. The response to light varied depending on temperature
Master of Science (Hons)

Gli stili APA, Harvard, Vancouver, ISO e altri

2

Omami, Elizabeth Nabwile. "Amaranthus retroflexus seed dormancy and germination responses to environmental factors and chemical stimulants". Thesis, [S.l. : s.n.], 1993. http://handle.uws.edu.au:8081/1959.7/66.

Testo completo

Abstract (sommario):

A large number of weed seeds in the soil persist because of seed dormancy, and depletion of the seed bank through manipulation of seed dormancy has been suggested as one of the goals in weed control. This study was designed to investigate some of the factors which control dormancy and germination in Amaranthus retroflexus seeds. Germination studies were conducted at different temperatures, and either in continuous white light or in the dark. Higher temperatures increased germination and, although light interacted with temperature, its effect on germination varied with the temperature. In an attempt to determine changes in dormancy during dry storage, two lots of seeds were stored dry at different temperatures. Loss in dormancy increased with an increase in storage temperature and duration, but the time required for maximum germination varied according to the seedlot. Seeds germinated to higher percentages at high temperatures, but storage at higher temperatures and for prolonged duration resulted in seeds gaining the ability to germinate at lower temperatures. Changes in dormancy under field conditions were also examined. Seeds were buried at different depths and for different durations and they all lost viability with time, but this loss was greater in surface-sown and shallowly buried seeds. Dormancy was broken during cold periods and induced as warmer periods progressed. The effects of chemical stimulants on dormancy and germination were investigated. The response of seeds to ethephon and nitrate were assessed at different temperatures either at continuous white light or in the dark. Germination increased with the concentration of the chemicals, and a greater response was observed at lower temperatures. The response to light varied depending on temperature

Gli stili APA, Harvard, Vancouver, ISO e altri

3

Bigley, Richard Ernest. "Ecological physiology of conifer seedling and sapling suppression by, and release from, competing vegetation". Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28625.

Testo completo

Abstract (sommario):

The overall objective of this thesis was to improve our understanding of the light environment associated with two of the major deciduous competitors of commercial conifer seedlings in low elevation coastal British Columbia, and the physiological response of young conifers to specific environments and changes in the environment. Studies were conducted to investigate: 1) seasonal and herbicide-induced changes in the light regimes beneath the canopies of two brush species, 2) growth and physiology of seedlings of three conifer species in several different deciduous brush environments throughout the year, and 3) changes in the physiology and growth of suppressed conifer saplings when different methods and schedules were used to reduce shading from an overtopping red alder canopy. Seasonal changes in the light quantity and quality were documented within salmonberry (Rubus spectabilis Pursch) and below red alder (Alnus rubra Bong.) canopies. The prediction of light attenuation within salmonberry canopies using the Beer-Lambert law was good for foliated canopies using leaf area index, and defoliated canopies using stem area index. As salmonberry leaf area increased, the ratio of red to far-red light declined exponentially. Growth of grand fir (Abies qrandis (Dougl.) Forbes), western hemlock (Tsuga heterophylla (Raf.) Sarg.) and Douglas-fir (Pseudetsuga menziesii (Mirbel) Franco) seedlings decreased with increases in the canopy density of overtopping deciduous species. Physiological differences between conifer species and differences between overtopping canopy treatments declined in the autumn and winter. Based on the physiological measurements, suppression of the shade intolerant Douglas-fir seedlings was greatly reduced during the period that overtopping deciduous canopies were leafless. Animal damage reduces growth and probably increases the duration seedlings are under overtopping canopies. Suppressed Douglas-fir saplings released from overtopping by red alder canopies showed the greatest growth response when the alder canopies were removed in the spring; complete removal of the alder canopy during the summer had a predictably deleterious effect on the sapling physiology and growth. Herbicide injections resulted in a slower but predictable increase in conifer growth.
Forestry, Faculty of
Graduate

Gli stili APA, Harvard, Vancouver, ISO e altri

4

Ma, Li. "Ecophysiology of the effect of red to far-red light ratio on selected weed and crop species". Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/63174.

Testo completo

Abstract (sommario):

Plants growing in canopies are exposed to reduced light intensity as well as low red/far-red light ratios, a signal of impending competition. In order to advance our understanding of the eco-physiological role of red/far-red ratio in agroecosystems, growth chamber and greenhouse studies were conducted to investigate 1. the growth and morphological responses of common lamb’s-quarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.) and tomato (Solanum lycopersicum L.) to different red/far-red ratios, 2. how leaf optical properties at red (660 nm) and far-red (730 nm) wavelengths change with leaf position and plant development, and 3. if red/far-red ratio influences response of corn (Zea mays L.), lettuce (Lactuca sativa L.), and pigweed plants to UV-B radiation. Three red/far-red ratios were achieved by using supplemental far-red lamps in growth chambers, while maintaining the photosynthetically active radiation. Results showed that red/far-red ratio treatment influenced several growth and allometric parameters and tomato, lamb’s-quarters, and pigweed differed in this regard. This differential response among species suggests that fluctuations in the red/far-red ratio in canopies could impact inter-plant interactions among these species. Red/far-red ratio in a plant canopy is affected by leaf optical properties. A study of leaf optical properties of lamb’s-quarters, pigweed and tomato using a CI-710 Miniature Leaf Spectrometer showed that leaf optical properties changed with leaf position and plant development, which could modify the light environment in canopies comprising populations of these species. Interestingly, these species differed in this regard, suggesting differences in their ability to signal potential competition. Leaf optical properties, as well as leaf position and plant development effects, therefore, should be taken into consideration in assessing the eco-physiological functions of a vegetation cover. Effect of pre-exposure to low red/far-red ratio on plant susceptibility to UV-B radiation could impact plant interaction. However, my research showed that red/far-red ratio pre-treatment and the associated change in anthocyanin concentration did not alter the response of corn, lettuce and pigweed seedlings to enhanced UV-B radiation. This improves our understanding of the eco-physiological role of these environmental stressors in agro-ecosystems, where both red/far-red ratio and UV-B levels fluctuate.
Land and Food Systems, Faculty of
Graduate

Gli stili APA, Harvard, Vancouver, ISO e altri

5

Röhrig, Manfred. "Modelling the light competition between crops and weeds". [S.l. : s.n.], 1999. http://deposit.ddb.de/cgi-bin/dokserv?idn=956719619.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

6

Umeda, Kai. "Effect of Halosulfuron on Rotational Crops". College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2002. http://hdl.handle.net/10150/214957.

Testo completo

Abstract (sommario):

A field test was conducted to evaluate and determine the safety of halosulfuron on typical rotational crops such as lettuce, broccoli, spinach, onion, alfalfa, barley, field corn, and melons after an initial application on cantaloupes. Halosulfuron at 0.05 or 0.1 lb AI/A applied on cantaloupes did not detrimentally affect crop stand establishment, height, or whole plant fresh weights when alfalfa, barley, spinach, lettuce, onion, and broccoli were planted at approximately 4 to 5 MAT. Cantaloupes and field corn planted at 1 YAT were not affected in establishing a stand and in growing during the early season as height or vine lengths were measured. At 15 to 16 MAT, lettuce, onion, and broccoli were not affected in establishing a stand. Watermelon planted at 1 YAT exhibited slight stand reduction and crop injury with halosulfuron applied PREE. Alfalfa planted after PREE applications indicated slightly depressed height and yield compared to POST treatments and the untreated check. Spinach planted where POST applications were made on cantaloupes tended to show a slight reduction in fresh weight at 15 to 16 MAT. Halosulfuron does not appear to be a major deterrent to typical crop rotational schemes in the diverse desert agricultural systems.

Gli stili APA, Harvard, Vancouver, ISO e altri

7

Umeda, K., e N. Lund. "Effect of Prowl and Prefar Herbicides on Onions". College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2001. http://hdl.handle.net/10150/214935.

Testo completo

Abstract (sommario):

Significant onion height reduction was observed when Prowl (pendimethalin) and Prefar (bensulide) herbicide combinations were applied preemergence (PREE). The onions resumed growth but the height was still slightly reduced later in the growing season compared to the handweeded check and the standard herbicide treatment, Dacthal (DCPA). The onion crop stand emerged initially but later in the season, a significant crop stand reduction was observed for the higher rate of Prowl at 0.5 lb AI/A plus Prefar. A lower rate of Prowl at 0.25 lb AI/A plus Prefar also caused a reduction of the onion stand compared to the handweeded check or Dacthal.

Gli stili APA, Harvard, Vancouver, ISO e altri

8

Fillmore, Andrew Nathan. "Droplet Size Effect on Herbicide Used in Cereals to Control Dicotyledonous Weeds". Thesis, North Dakota State University, 2014. https://hdl.handle.net/10365/27419.

Testo completo

Abstract (sommario):

Experiments were conducted to evaluate the effect of droplet size on the efficacy of translocated and non-translocated herbicides. Translocated and non-translocated herbicides provided similar control when comparing droplet size effect on efficacy. Medium and very coarse droplet sizes gave the greatest visible injury whereas coarse-sized gave the lowest visible injury assessments for most species. However, droplet size generally did not affect contact herbicide efficacy. Overall, droplet size was not a strong factor contributing to herbicide efficacy and often, differences were only between herbicides. Non-ionic surfactant solutions measured by a Sympatec droplet analysis system gave the highest percent of volume in droplets <150?m compared to other adjuvants. The lowest percent of volume in droplets <150?m was a 0.5x rate. A liquid herbicide formulation gave the largest percent of volume in droplets <150?m whereas an emulsifiable concentrate formulation was lowest. Percent volume in droplets <150?m was often related to the solution VMD.

Gli stili APA, Harvard, Vancouver, ISO e altri

9

Harati, Ebrahim. "Fatigue strength of welds in 800 MPa yield strength steels : Effects of weld toe geometry and residual stress". Licentiate thesis, Högskolan Väst, Avd för tillverkningsprocesser, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-8009.

Testo completo

Abstract (sommario):

Nowadays there is a strong demand for lighter vehicles in order to increase the pay load. Through this the specific fuel consumption is decreased, the amount of greenhouse gases is lowered and the transport economy improved. One possibility to optimize the weight is to make the components from high strength steels and join them by welding. Welding is the main joining method for fabrication of a large proportion of all engineering structures. Many components experience fatigue loading during all or part of their life time and welded connections are often the prime location of fatigue failure.Fatigue fracture in welded structures often initiates at the weld toe as aconsequence of large residual stresses and changes in geometry acting as stress concentrators. The objective of this research is to increase the understanding of the factors that control fatigue life in welded components made from very high strength steels with a yield strength of more than 800 MPa. In particular the influences of the local weld toe geometry (weld toe radius and angle) and residual stress on fatigue life have been studied. Residual stresses have been varied by welding with conventional as well as Low Transformation Temperature (LTT) filler materials. The three non-destructive techniques Weld Impression Analysis (WIA), Laser Scanning Profiling (LSP) and Structured Light Projection (SLP) have been applied to evaluate the weld toe geometry.Results suggest that all three methods could be used successfully to measure the weld toe radius and angle, but the obtained data are dependent on the evaluation procedure. WIA seems to be a suitable and economical choice when the aim is just finding the radius. However, SLP is a good method to fast obtain a threedimensional image of the weld profile, which also makes it more suitable for quality control in production. It was also found that the use of LTTconsumables increased fatigue life and that residual stress has a relatively larger influence than the weld toe geometry on fatigue strength of welded parts.

Gli stili APA, Harvard, Vancouver, ISO e altri

10

Hewitt, Cade Alan. "Effect of row spacing and seeding rate on grain sorghum tolerance of weeds". Thesis, Kansas State University, 2015. http://hdl.handle.net/2097/19784.

Testo completo

Abstract (sommario):

Master of Science
Department of Agronomy
J. A. Dille
Weed control in grain sorghum has always presented a challenge to producers in the semi-arid Great Plains. Cultural control tactics such as narrowing of row spacings and increasing seeding rates can be effective control methods. The objective of this research was to determine the row spacing and seeding rates that maximizes yield while suppressing weeds. Grain sorghum row spacings of 25, 51, and 76-cm and seeding rates of 75,000, 100,000, 125,000, and 150,000 seeds ha[superscript]-1 were evaluated in Kansas at Beloit and Manhattan in 2013 and Beloit, Manhattan, and Hays in 2014. Grain sorghum growth and yield response were measured in response to natural weed communities. After evaluation, Beloit was considered a low weed pressure site while Manhattan and Hays were considered to be moderate and high weed pressure sites, respectively. Grain sorghum biomass was different while weed biomass was consistent across row spacings. Yield loss equations and profit functions were derived to determine the amount of grain yield and $ ha[superscript]-1 loss from each of the three locations. Yield and profit lost was greatest amongst weedy observations. Results indicated that grain sorghum grown on wide row spacings and seeding rates of 125,000 seeds ha[superscript]-1 out yielded all other treatments under a low weed pressure site (Beloit) and narrow row spacings out yielded wider spacings in moderate and high weed pressure sites (Manhattan and Hays). These results imply that a Kansas grain sorghum producer should evaluate potential weed pressure before determining a final row spacing and seeding rate.

Gli stili APA, Harvard, Vancouver, ISO e altri

11

Hayakawa, M., T. Kinoshita e A. I. Sanda. "Hadronic Light-by-Light Scattering Effect on Muon g -2". The American Physical Society, 1995. http://hdl.handle.net/2237/7156.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

12

Sampson, D. L. "The effect of tillage systems on weed control and botanical composition in forage corn /". Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63912.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

13

Hussein, Sultan Begna. "Agronomic and physiological aspects of competition for light between corn hybrids differing in canopy architecture and weeds". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0030/NQ64511.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

14

Begna, Sultan Hussein. "Agronomic and physiological aspects of competition for light between corn hybrids differing in canopy architecture and weeds". Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=35572.

Testo completo

Abstract (sommario):

The problems associated with short growing seasons has led to the development of leafy-reduced stature (LRS) corn hybrids. These hybrids have more leaf area above the ear, more rapid leaf area development, shorter stature, earlier maturity, and better responses to high plant populations and narrow spacings than conventional hybrids. Plants grown in a reduced light environment are limited in carbon assimilation and this, in turn, results in reductions in growth and development. A way to supplement the availability of photosynthate is injection of sucrose into plant stems. The objective of this thesis was to determine the ability of LRS corn plants to compete with weeds, and the reactions of weed species to the shade, including the relationships between weed growth (increase in biomass) and development (shape) under shaded conditions. Three years of field experiments (LRS and more conventional corn hybrids with both transplanted and naturally growing weeds) and two years of greenhouse work [weeds alone, C3 (lamb's quarters and velvetleaf) and C4 (redroot pigweed) in full sun or deep (75%) shade injected with 15% sucrose or not] were conducted. Yield reductions due to weed pressure were lower for LRS than other hybrids. Biomass production by both transplanted and naturally occurring weeds was up to 85% less under corn canopies than when grown without competition from corn. The biomass of C4 weeds was more reduced by competition with corn plants than that of C3 weeds. In spite of quick and early leaf development, leaves and other plant parts of LRS were not damaged excessively by mechanical (rotary hoeing) weed control. Both C3 and C4 weed plants produced more dry matter when injected with sucrose. Dry weights of sucrose injected shaded plants were not different from full sun uninjected plants. However, sucrose injection did not alter shading effects on development (distribution of biomass). Dry matter production and photosynthetic rates of C4 weeds were more reduced

Gli stili APA, Harvard, Vancouver, ISO e altri

15

Mykytyuk, O. Yu, О. І. Olar e T. V. Biryukova. "Effect of light on human health". Thesis, БДМУ, 2019. http://dspace.bsmu.edu.ua:8080/xmlui/handle/123456789/19204.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

16

Thomas, Dean Timothy. "Selective grazing by sheep to improve the control of weeds of crops". University of Western Australia. School of Animal Biology, 2006. http://theses.library.uwa.edu.au/adt-WU2006.0041.

Testo completo

Abstract (sommario):

[Truncated abstract] With the rapid development of multiple herbicide resistant weeds in crops, it is likely that an important role now exists for new grazing management strategies in farming systems to provide an integrated approach to weed management. In this thesis we examined the general hypothesis that sowing a legume of low preference by sheep relative to the target weeds of crops would improve the control of those weeds in a grazed pasture. To test this general hypothesis, legumes of low preference by Merino sheep were identified and a series of experiments conducted to determine the effect on pasture composition when these less preferred legumes were incorporated into a grazed pasture. We found a learned response that altered forage preference by sheep was important in determining the effectiveness of grazing to reduce seed set by weeds of crops. Investigations on this aspect of the grazing behaviour of sheep were a key part of this thesis. The short-term relative preference of Merino hoggets among 15 pasture legumes, 4 grain legumes and annual ryegrass was determined by offering adjacent monocultures of each of the forage genotypes to the sheep. The relative preference of the hoggets for each of the 20 forages was determined at three phases of plant growth from estimates of the amount of forage consumed. Sheep showed a low selective preference for Vetch (Vicia sativa L.), chickpea (Cicer arietinum L.), biserrula (Biserrula pelecinus L.), lotus (Lotus ornithopodioides L.) and snail medic (Medicago scutellata L.) cvs. Kelson and Sava at the vegetative phase of plant growth. An indoor method was also developed to test the relative preference of sheep among forages growing in pots. Using this method chickpea and snail medic, but not biserrula, were found to have a low relative preference by sheep at the vegetative phase.

Gli stili APA, Harvard, Vancouver, ISO e altri

17

Čepulienė, Rita. "Dynamics of accumulation of allelochemical compounds in oilseed rape and effect on agricultural crops and weeds". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20141230_175312-56329.

Testo completo

Abstract (sommario):

Research objective. The study was aimed to identify the dynamics of accumulation of phenolic compounds and glucosinolates in oilseed rape and the effect of different morphological parts of oilseed rape on agricultural plants and weeds. The goals of the studies. The following goals were set in order to reach the aim of the studies: 1. To identify the dynamics of accumulation of phenolic compounds in oilseed rapeduring vegetation. 2. To analyse composition of allelochemical compounds of different morphological parts of rape residues after harvesting and ascertain quantitative and qualitative changes of these compounds in rape residues that decomposed in the soil for a different period. 3. To ascertain the effect of different morphological parts of oilseed rape that remain immediately after harvesting on the germination, shoot height and root length of agricultural plants and weeds. 4. To ascertain the effect of different morphological parts of oilseed rape that decomposed in the soil for a different period on the germination, growth of shoots and roots of agricultural plants and weeds.
Tyrimų tikslas. Nustatyti fenolinių junginių ir gliukozinolatų kaupimosi rapsuose dinamiką bei rapsų skirtingų morfologinių dalių liekanų poveikį žemės ūkio augalams ir piktžolėms. Tyrimų uždaviniai: 1. Nustatyti fenolinių junginių kaupimosi dinamiką rapsuose vegetacijos metu. 2. Ištirti alelocheminių junginių sudėtį rapsų skirtingų morfologinių dalių liekanose po derliaus nuėmimo ir nustatyti jų kiekybinius ir kokybinius pokyčius skirtingą laiką dirvoje irusiose rapsų liekanose. 3. Nustatyti rapsų atskirų morfologinių dalių, liekančių iškart po derliaus nuėmimo, poveikį žemes ūkio augalų ir piktžolių sėklų dygimui, daigų aukščiui ir šaknų ilgiui. 4. Nustatyti skirtingą laiką dirvoje irusių rapsų morfologinių dalių poveikį žemės ūkio augalų ir piktžolių sėklų dygimui, daigų bei šaknų augimui.

Gli stili APA, Harvard, Vancouver, ISO e altri

18

Gwinner, Michael Christian. "High-performance light-emitting polymer field-effect transistors". Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610236.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

19

Doyle, Colleen Elizabeth. "Effect of Short-Term Light Exposure on Alertness". The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524088785098075.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

20

Lafont, O., S. M. H. Luk, P. Lewandowski, N. H. Kwong, P. T. Leung, E. Galopin, A. Lemaitre et al. "Controlling the optical spin Hall effect with light". AMER INST PHYSICS, 2017. http://hdl.handle.net/10150/623050.

Testo completo

Abstract (sommario):

The optical spin Hall effect is a transport phenomenon of exciton polaritons in semiconductor microcavities, caused by the polaritonic spin-orbit interaction, which leads to the formation of spin textures. The control of the optical spin Hall effect via light injection in a double microcavity is demonstrated. Angular rotations of the polarization pattern up to 22 degrees are observed and compared to a simple theoretical model. The device geometry is responsible for the existence of two polariton branches which allows a robust independent control of the polariton spin and hence the polarization state of the emitted light field, a solution technologically relevant for future spin-optronic devices. Published by AIP Publishing.

Gli stili APA, Harvard, Vancouver, ISO e altri

21

DiTommaso, Antonio. "Effect of the fungal pathogen, Colletotrichum coccodes (Wallr.) Hughes, on growth, reproduction and competitive ability of velvetleaf (Abutilon theophrasti Medik.)". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29012.

Testo completo

Abstract (sommario):

Field and growth bench experiments were performed to assess the effect of a selective fungal pathogen of Abutilon theophrasti (velvetleaf) on various aspects of intra- and interspecific competition between this vigorous agricultural weed and soybean (Glycine max). In the absence of the foliar pathogen, Colletotrichum coccodes, A. theophrasti and soybean responded differently to the presence of conspecies or to individuals of the other species. In pure stand, the deleterious effects of intraspecific competition on reproductive output were substantially greater for A. theophrasti than for soybean, especially at lower monoculture densities. In mixtures, however, A. theophrasti reproductive performance was markedly higher than at equivalent monoculture densities, particularly at the lower mixture densities. Soybean reproduction at these lower mixture densities (10 to 20 plants m$ sp{-2}$) was severely curtailed compared with reproductive output at equivalent pure stand densities. A. theophrasti reproductive output was limited more by the presence of conspecies than by the presence of soybean, whereas the opposite trend was observed for soybean. In pure stand, application of C. coccodes had limited impact on either A. theophrasti or soybean yield. However, application of the fungal pathogen in A. theophrasti monocultures caused significant (30-44%) aboveground biomass reductions within five weeks of inoculation, in two of the three years in one field study. Eight weeks following C. coccodes inoculation, A. theophrasti biomass within inoculated monoculture plots did not differ significantly from biomass within uninoculated control plots, although height hierarchies were significantly more developed. In mixtures, C. coccodes applications caused reductions in A. theophrasti growth and reproduction when provided with an adequate dew period. Alternatively, soybean yield losses within inoculated mixture plots were generally lower than for uninoculated control plots, althoug

Gli stili APA, Harvard, Vancouver, ISO e altri

22

Gaongalelwe, Motlhasedi Olebile. "Effect of delayed sowing and increased crop density on weed emergence and competition with wheat". Title page, table of contents and abstract only, 2002. http://web4.library.adelaide.edu.au/theses/09AFM/09afmg2118.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

23

Marmon, Jason Kendrick. "Light-matter interactions in semiconductor nanowires| Light-effect transistor and light-induced changes in electron-phonon coupling and electrical characteristics". Thesis, The University of North Carolina at Charlotte, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10243428.

Testo completo

Abstract (sommario):

This dissertation explores three related embodiments of light–matter interactions at the micro– and nano–scales, and is focused towards tangible device applications. The first topic provides a fundamentally different transistor or electronic switch mechanism, which is termed a light–effect transistor (LET). The LET, unlike exotic techniques, provides a practical and viable approach using existing fabrication processes. Electronic devices at the nanoscale operate within the ballistic regime, where the dominate source of energy loss comes from impurity scattering. As a LET does not require extrinsic doping, it circumvents this issue. Electron–phonon coupling, however, is the second largest source, and it is a pertinent and important parameter affecting electronic conductivity and energy efficiency, such as in LETs. The third topic is laser writing, or the use of a laser to perform post–growth modifications, to achieve specific optical and electrical characteristics.

A LET offers electronic–optical hybridization at the component level, which can continue Moore’s law to the quantum region without requiring a FET’s fabrication complexity, e.g., physical gate and doping, by employing optical gating and photoconductivity. Multiple independent gates are therefore readily utilized to achieve unique functionalities without increasing chip space. LET device characteristics and novel digital and analog applications, such as optical logic gates and optical amplification, are explored. Prototype cadmium selenide (CdSe) nanowire–based LETs show output and transfer characteristics resembling advanced FETs, e.g., on/off ratios up to ~1.0x10⁶ with a source-drain voltage of ~1.43 V, gate-power of ~260 nW, and a subthreshold swing of ~0.3 nW/decade (excluding losses). The LET platform offers new electronic–optical integration strategies and high speed and low energy electronic and optical computing approaches.

Electron–phonon coupling is typically studied as an intrinsic property, which is particularly important for electronic transport properties at the nanoscale, where controversy and even contradictory experimental and theoretical findings still persist. Zinc telluride (ZnTe) has important uses in optical or laser refrigeration, and the existing studies do not consider extrinsic effects, such as laser–forming tellurium–based species. Nanostructures, with their large surface–to–volume ratios, are more susceptible to extrinsic perturbations that ultimately effect coupling. In this dissertation, ZnTe is studied in bulk, thin film, and nanowire forms with primary focus on the latter. Raman spectroscopy under near resonant excitation is used to extract electron–phonon coupling strengths, which is obtained through the ratio of the first and second order Raman peaks, R =

I2LO/I1LO

(and is proportional to the Huang–Rhys factor). Laser–formation of tellurium–based species on ZnTe nanowires dynamically altered the ratio R from ~6-7 to 2.4 after laser processing, while tuning the (532 nm) laser power from a few microwatts to 150 microwatts (with constant optical exposure time) did not significantly impact the EPC strength. Other explored effects include size dependence, chemical effects (methanol exposure), and interface effects (e.g., at a gold–nanowire junction). The findings suggest that the previously reported size dependence in ZnTe was extrinsic in nature. Tunable coupling strengths also suggest the possibility of novel electronic and optoelectronic devices.

The electrical characteristic of CdSe nanowire M-S-M devices are shown to be tunable with laser illumination. As with any semiconductor material, sufficiently low optical powers produce stable and reproducible electrical properties, while higher optical powers and exposure times can induce laser modifications of the material. Drastic modification of electrical characteristics were observed, such as from converting an ohmic response (linear slope change) to rectified characteristics, and modification of both forward and reverse currents. Results suggest the potential to laser write wavelength–specific electronic functions that could be used in applications requiring wavelength discrimination, such as with night vision products. Using a combination of laser modification and device fabrication processes provides the ability to offer a menu of electrical behaviors using the same materials and fabrication processes.

Gli stili APA, Harvard, Vancouver, ISO e altri

24

Grant, Robert Wallace. "A UV Zeeman-effect polarizer". Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/24674.

Testo completo

Abstract (sommario):

It is shown that light emitted by mercury vapour at 253.7 nm can be polarized by passing the light through mercury absorption gas embedded in a magnetic field which is transverse to the direction of propagation of the light. The absorption lines of the mercury are split by the Zeeman effect, so that the absorber has an absorption coefficient which depends on both the polarization and wavelength of the transmitted light. A complete theory for the Hg²⁰² isotope is presented and the results are compared to measurements made with a natural mercury emitter and absorber. The observations are in qualitative agreement with the theory once isotope and hyperfine structure of the isotopes in natural mercury are included in the theory. Quantitative analysis was not possible because the emission line profiles could not be measured with the available equipment.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

Gli stili APA, Harvard, Vancouver, ISO e altri

25

Spooner, Nigel Antony. "The effect of light on the thermoluminescence of quartz /". Title page, contents and summary only, 1987. http://web4.library.adelaide.edu.au/theses/09SM/09sms764.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

26

Hollmark, Malin. "Absorbed dose and biological effect in light ion therapy". Doctoral thesis, Stockholm : Medical Radiation Physics, Stockholm university together with KI, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7756.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

27

Ladin, Loren Guerrero 1959. "Effect of ultraviolet light on reproduction in Hydra littoralis". Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277085.

Testo completo

Abstract (sommario):

The "DNA Damage Hypothesis" pertaining to the evolution of sex was tested using Hydra littoralis. DNA damage was produced by irradiating whole live hydra with ultraviolet light. A curve of uv light dosage vs. survival was constructed. Estimations of threshold fluence and LD50 were made from the survival curve. In four separate experiments, using various combinations of environmental temperatures, uv doses, and number of doses, frequencies of asexual and sexual reproduction were observed and compared. The hydra that received uv treatments did not show an increase in the consequent amount of sexual reproduction, and actually showed a decrease. An increase in the amount of sexual reproduction following DNA damage is predicted by the DNA damage hypothesis, therefore these results do not support this theory. The data was also used to make contradictory observations regarding the "stress hypothesis" for the occurrence of sexual reproduction in hydra.

Gli stili APA, Harvard, Vancouver, ISO e altri

28

Mirolo, Francesca. "The effect of light elements on metal/silicate partitioning". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:968b0001-4162-4439-9dc3-8b87a47137e0.

Testo completo

Abstract (sommario):

The accretion of the Earth was marked by the high-pressure segregation of most of its core, accompanied by dissolution of about 10% of one or more “light” elements into the metallic phase. Various light elements have been proposed including S, Si, C and O, with each having an effect on the partitioning behaviour of the trace elements. Metallurgical data indicate that dissolution of even small amounts of light elements in liquid Fe can have profound effects on the activities of some trace components. For instance, significant partitioning of Si into the core of the growing Earth should have affected the observed Mo content of the mantle (Ono-Nakazato et al., 2007). Here, I use the epsilon model of non-ideal interactions in Fe liquids (ε. I present interaction parameters (ε, derived from 1.5GPa, 1550-1650oC metal-silicate equilibration experiments, for W, Ni, Co and Mo in liquid Fe alloyed with C, and W, Ni, Co, Mo, Cu, Mn, Ag, Sb, Cd, In, Tl, Pb, Ga, Ge, Cr, V and Zn in liquid Fe alloyed with S. Additional epsilon values were taken from the steelmaking sourcebook when necessary. I used this new data in conjunction with published metal–silicate partitioning results to develop a model of continuous accretion and core segregation taking explicit account of the partitioning of Si (this study) and O (from Ozawa et al., 2008) between metal and silicate and their effects on metal–silicate partitioning of siderophile elements. The best model for explaining the Earth’s formation including the Mo:W ratio of the silicate Earth posits that the Earth’s oxidation state increased in steps from 1 to 6.26% FeO, increasing Si in the Earth’s core and the light elements C and S being added to the planet in the last ~20% of accretion material.

Gli stili APA, Harvard, Vancouver, ISO e altri

29

Stasinopoulos, Triantafyllos C. "Effect of light quality on growth of cultured tissues /". The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487687485811527.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

30

Khan, Ashfaq. "Near field effect of light interaction with transparent microspheres". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/near-field-effect-of-light-interaction-with-transparent-microspheres(9a2b46b0-ec0b-4f95-982a-35341d5d9ee1).html.

Testo completo

Abstract (sommario):

With the increasing demand for miniaturized devices there is a need for economic and reliable nano fabrication and nanoscopy techniques. This Thesis aims to improve the laser micro/nano patterning by contact particle lens array (CPLA) technique and also extend the CPLA technique to white light nanoscopy. CPLA has been used for patterning for nearly a decade. They have been used to fabricate bumps, bowls and user defined features on the surface of material. However, the CPLA method is limited to patterning of flat, smooth and hydrophilic substrates. Moreover, the particles can only be deposited once and are not recoverable. Thus the particles could not be used repeatedly. The thesis was aimed at transporting a monolayer to pattern curved, rough or hydrophobic surfaces. A Particle monolayer was formed on a smooth, flat and hydrophilic surface. The transportation of the particle monolayer was carried out by a flexible transparent (to the processing laser) sticky surface. The monolayer was adhered to the plastic and then peeled off and wrapped on the new surface. Laser processing was carried out by the laser passing through the sticky surface. The sticky surface and the adherent particles were peeled off and reused. The effect of the laser processing parameters (scan speed, power and fluence) was experimentally investigated. An understanding of the process was developed by numerical and analytical simulation. Analytical simulation was carried out by Mie and particle on surface (POS) theory which provided the near field distribution for a single particle. Detailed simulation, modelling the presence of resin, was conducted by finite integration technique (FIT). Coupled electromagnetic and thermal modelling was conducted to understand temporal temperature distribution in the near field. The Thesis also investigated the utilization of CPLA for extending the capability of a white light microscopy to nanoscopy. Nano scales features on a substrate were imaged by a standard white light microscope by observing through a CPLA deposited on its surface. The novelty of the work is that it uses a simple method to transport large area monolayer arrays of about 100 mm2 and utilize it for repeated (up to three times) patterning of substrates that were previously considered impossible to be patterned. The thesis also presents a novel method of nanoscopy by using CPLA.

Gli stili APA, Harvard, Vancouver, ISO e altri

31

Hankins, S. D. "The effect of precipitation on the performance of foliage-applied herbicides for the control of broad-leaved weeds". Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379852.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

32

Tsang, Yik Chong. "The effect of aberrations and light scatter on visual performance at photopic and mesopic light levels". Thesis, City University London, 2013. http://openaccess.city.ac.uk/2476/.

Testo completo

Abstract (sommario):

The Contrast Acuity Assessment (CAA) test was developed to assess the minimum spatial vision requirements for commercial pilots. The goal of the CAA test was for it to be sensitive to retinal image degradation in subjects who had undergone excimer laser refractive surgery. Increased aberrations and scattered light or abnormal processing of visual information in the retina and/or the visual pathway are the main causes of retinal image degradation. The purpose of this study was to further investigate the effect of aberrations, scatter and other parameters on the CAA test under photopic and mesopic conditions. This could help to provide explanations for previous CAA test results. The effect of contrast, stimulus onset time, pupil size and crowding on the CAA test was examined. This was in order to try to provide explanations for the decline in Landolt ring gap acuity over the central 5 degrees, as observed in previous CAA test results, which had shown a foveal dip to occur under photopic and mesopic conditions. Contrast Sensitivity was measured on eight subjects using 6 and 3 mm artificial pupils using the City University Contrast Sensitivity Test. A significant trend of decreasing contrast sensitivity with increased pupil size occurred for the middle and lower spatial frequencies (1.2 and 6.1 cpd), but not for the highest 19.1 cpd spatial frequency. The effects of using high contrast (125%) rather than low contrast (24%) CAA test targets were investigated, in combination with the use of artificial pupils of 6 mm and 3 mm. We concluded that low contrast could play a role in producing a foveal dip under photopic and mesopic conditions. The effect of crowding and stimulus onset time on the CAA Test was examined on 3 subjects, by reducing the contrast of the fixation guides under mesopic and photopic conditions and increasing stimulus onset time. This gave inconclusive results. No significant conclusions were drawn concerning the effect of crowding or stimulus onset time on the CAA foveal dip. The effect of aberrations on normal subjects on the photopic and mesopic CAA test was examined, to determine whether they may have influenced the foveal dip. 14 subjects were tested with natural pupils, under photopic conditions and 10 subjects, were tested under mesopic conditions. A Shack Hartmann aberrometer was used to take wavefront aberration measurements. No significant regressions were found between aberrations and foveal dip. We concluded that aberrations were probably not the cause of the foveal dip. Q value lenses consisting of Q = -2, Q = -1, Q = 0, Q = +1 and Q = +1.5 contact lenses were tested on subjects with natural pupils, to determine whether the CAA test could pick up larger non-physiological changes in aberrations. Large changes in visual performance were observed. Z (4,0) spherical aberration versus central CAA gap acuity was found to produce a significant quadratic regression under mesopic conditions. Seidel coma and Seidel astigmatism were also found to produce significant linear regressions. under photopic conditions. Scatter was measured in 4 subjects, using 6 mm and 3 mm artificial pupils, to determine whether scatter would increase with the larger pupil size. Linear regressions of scatter k’ versus foveal dip gave results which were not statistically significant. Scatter was measured for 3 subjects using the 5 different Q value contact lenses, to see if the Q values affected the scatter. The results were not statistically significant. The differences in scatter produced were found to be far less than the increase of scatter found in two subjects with pathological conditions. We concluded that scatter played an insignificant role in producing the foveal dip or changing visual performance with the use of Q value contact lenses. The project produced a systematic investigation of the parameters affecting the CAA test. A statistically significant association, described by a quadratic regression curve, exists between CAA mesopic gap acuity and Z (4,0) spherical aberration.

Gli stili APA, Harvard, Vancouver, ISO e altri

33

Orr, Danielle Jean. "The Effect of Refractive Error and Light Exposure on Red and Blue Light-Driven Pupil Responses". The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1491935483251647.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

34

Matelon, R. J. "The interaction of light with periodic magnetic structures". Thesis, Coventry University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289100.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

35

Merchant, Amethyst G. "The Light and Water Stress Tolerance of Two Invasive Legumes: Cytisus scoparius (Scotch broom) and Spartium junceum (Spanish broom)". Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/35429.

Testo completo

Abstract (sommario):

The ability of Cytisus scoparius L. and Spartium junceum L. to acclimate to different levels of light and water stress was studied to understand ecological constraints on distributions of these plants. A reaction norm experimental design was used to determine growth and physiological responses of each to imposed conditions.

Light treatments were stressful for both species. Increases in shade led to decreases in relative growth rates (RGR); however, light was more of a limiting factor for S. junceum because of the greater decrease in its growth rate at lowest light intensities. As light decreased, stem allocation increased in S. junceum. More differences in allocation to leaves and roots among light treatments were found in C. scoparius. Correspondingly, the greatest changes in photosynthetic characters were found in S. junceum stems and C. scoparius leaves. Differences in physiological traits did not prove to be acclimation to low light levels because quantum yield decreased when light decreased. Neither species exhibited rapid growth rates, normal allocation patterns, or proper adjustments of photosynthetic characters under light conditions below 50% full intensity.

Water treatments did not cause any critical changes in growth or physiology of either species. Neither species' RGR was greatly decreased. Water availability is more of a determining factor of growth for C. scoparius because of its continued, small decline in RGR as watering frequency decreased. Spartium junceum appeared to be better adapted to the imposed water treatments with its smaller number of leaves, leaf surface area, percentage leaf weight, specific leaf area, and leaf area / stem area ratio. Spartium junceum also displayed larger root / shoot ratios in drier conditions. The magnitude of these shifts was typically greater in C. scoparius, but the RGR of this species decreased more than that of S. junceum under drier conditions. More stress was imposed on C. scoparius because its lowest water potential measurements were 40% lower than those of S. junceum and below the water potential value at turgor loss point during midday hours. When water potential decreased, Spartium junceum showed signs of acclimation because stem photosynthesis increased and leaf photosynthesis decreased while C. scoparius did not adjust its rates of photosynthesis. Water treatments did not impose enough stress to cause osmotic adjustments. Performance under these light and water treatments explained the habitat preference of each to areas where these species have become invaders along the Pacific Coast of the Unites States.
Master of Science

Gli stili APA, Harvard, Vancouver, ISO e altri

36

Koppen, Camille. "Seeing the light: an exploration of the Colavita dominance effect". Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491283.

Testo completo

Abstract (sommario):

The Colavita effect provides a remarkable example of visual dominance, demonstrating that a visual stimulus can dominate a person's perception to such an extent that, on occasion, it appears to extinguish their perception of (or at least their ability to respond to) a concurrently-presented auditory stimulus. The aim of the experiments reported in this thesis was to investigate some of the key factors contributing to the Colavita visual dominance effect in order to gain a deeper understanding of its causes. The main findings reported in this thesis were that the Colavita visual dominance effect reflects a perceptually-based phenomenon (see Chapters 2, 3, and 8), and is modulated by the modality to which participants endogenously and/or exogenously attend (Chapter 4), and the stimulus that they perceived first (Chapter 5). The spatial and temporal separation between the auditory and visual stimuli both appear to modulate the Colavita effect (Chapters 5 and 6), however, the semantic congruency between them does not appear to affect the magnitude of the Colavita effect that emerges (Chapter 7). An explanation is put forward that describes the Colavita effect as follows: Participants' tendency to endogenously and/or exogenously direct their attention toward the visual modality results in the delayed perception of the auditory component of the bimodal stimulus. The auditory stimulus may therefore sometimes arrive at the primary stage of stimulus processing during the attentional dwell time of the visual stimulus. This may result in a difficulty in the consolidation and conscious report of the auditory stimulus because the processing of the visual stimulus temporarily occupies the participant's limited-capacity attentional resources, thus resulting in the decay of the information concerning the auditory stimulus. The empirical findings reported in this thesis advance several important conclusions regarding the mechanism of the Colavita effect which, in tum, may contribute toward a greater understanding of the wider area of visual dominance, and could also provide a potential springboard for the study of crossmodal extinction in normal participants.

Gli stili APA, Harvard, Vancouver, ISO e altri

37

Maddocks, Samantha Annice. "The effect of light quality on avian behaviour and welfare". Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364870.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

38

Zaumseil, Jana. "N-channel, ambipolar and light-emitting polymer field-effect transistors". Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613003.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

39

Mouland, Josh. "The effect of spatially patterned light on the suprachiasmatic nucleus". Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/the-effect-of-spatially-patterned-light-on-the-suprachiasmatic-nucleus(de2b1fff-2058-497e-948a-cc3811ffa39d).html.

Testo completo

Abstract (sommario):

The daily variation in background light intensity (irradiance) can entrain the endogenous clock in the suprachiasmatic nucleus (SCN) to the external environment. The only source of this photic information in mammals is the eye, which is primarily a visual organ. It is therefore highly specialised to detect high frequency spatiotemporal modulations. This together with the adaptation which occurs within the retina could be present difficulties when encoding global irradiance. This raises the question of whether spatial patterns, which are present in our everyday viewing, might affect the ability of the SCN to receive 'true irradiance' signals and entrain to the external environment. My first approach was to determine whether individual SCN cells might receive a 'true irradiance' signal. To this end I mapped and characterised the receptive field properties of SCN neurons using in vivo electrophysiology. Indeed a handful of neurons (full field cells) responded to light anywhere in the visual scene and thus may act as 'irradiance detectors'. However, the vast majority of cells only sampled local radiance from a limited area of the visual scene. Having mapped the receptive field properties it became clear that cells which sampled from a limited area of the visual scene would be sensitive to spatial contrast (patterns). To examine the effect of spatiotemporal contrast on the SCN I examined two SCN outputs: locomotor activity and neuronal firing rates. Although spatiotemporal modulation in light intensity could induce large amplitude oscillations in neuronal activity; the time averaged firing rate and locomotor activity, which are believed to be determined by irradiance, were largely unaffected by spatial patterns. This led to the conclusion that the SCN can multiplex photic information into information regarding irradiance, and spatial information by encoding them under different timescales. Melanopsin has been heralded as the key photopigment for encoding irradiance and entraining the SCN. However such experiments have been only performed using diffuse light stimuli. Here I investigated the role of melanopsin under natural viewing conditions which incorporated spatial patterns. Under such stimuli the SCN response can be almost entirely accounted for by the melanopic irradiance of the stimuli.

Gli stili APA, Harvard, Vancouver, ISO e altri

40

Mtintsilana, Asanda. "The effect of light on a rat model of depression". Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13205.

Testo completo

Abstract (sommario):

Includes bibliographical references.
Background: Depression is a debilitating mood disorder, negatively affecting an individual’s health and well-being. Despite this, the aetiology of depression remains poorly understood. Consistently, depression treatments are far from satisfactory due to limited efficacy and adverse side effects often associated with them, suggesting a need to improve the current animal models of depression in order to understand the basic mechanisms of the disorder. In an attempt to elucidate the pathophysiology of depression, a rodent model of depression (maternal separation, MS) is used to study the neurobiological mechanisms implicated in depression. However, MS alone produces inconsistent findings and often additional stressors are used to exaggerate the effects of MS. To create a more robust model of MS, MS rats were exposed to chronic constant light (CCL). However, contradictory findings have been reported with CCL. Aims: This study aimed to explore the effects of additional CCL in an MS model by measuring glutamate and potassium-stimulated [3H]DA release in the nucleus accumbens (NAc), testing the effects of CCL on serotonin (5-HT) levels in the hypothalamus and prefrontal cortex (PFC) and measuring ì-opioid receptor (MOR-1) levels in the NAc and orexin receptor (OXR-1 and OXR-2) levels in the PFC. Methods: In order to achieve these aims four experimental groups were chosen, out of which two groups; non-maternally separated (NMS) rats and maternally separated (MS) rats were exposed to CCL for 3 weeks during adolescence and the remaining two groups; NMS and MS rats were not subjected to CCL. At postnatal day 80 (adulthood), rats were decapitated and brain tissue collected for analysis of glutamate- and potassium-stimulated [3H]DA release in the NAc using in vitro superfusion. Serotonin levels in the hypothalamus and PFC were determined using Enzyme-Linked ImmunoSorbent Assay (ELISA). Western blot analysis was used to measure MOR-1 levels in the NAc, OXR-1 and OXR-2 in the PFC. Results: MS caused a significant decrease in glutamate-stimulated [3H]DA release in the NAc. In the NAc shell, CCL exposure revealed a trend towards a decrease in [3H]DA release in response to both glutamate- and potassiumstimulation. Moreover, in the hypothalamus NMS and MS rats subjected to CCL had significantly increased 5-HT levels compared to NMS and MS rats without xvii CCL exposure. In the PFC CCL had a significant effect on 5-HT levels and it was revealed that NMS CCL rats had decreased 5-HT levels compared to NMS rats. Similarly, MS CCL rats had significantly decreased 5-HT levels compared to NMS. MS and CCL did not have any significant effect on MOR-1 protein levels in the NAc. On the other hand, MS rats had increased OXR-1 and OXR-2 proteins levels in the PFC compared to NMS and MS CCL rats. Conclusion: MS decreased glutamate-stimulated [3H]DA release in the NAc. Serotonin levels in the hypothalamus and PFC were altered by the effects of MS and CCL. Furthermore, MS exposure increased OXR-1 and OXR-2 protein levels in the PFC. However, MS and CCL did not alter MOR-1 protein levels in the NAc. Therefore, this study has demonstrated that CCL exaggerated the effects of MS and created a more robust model of MS.

Gli stili APA, Harvard, Vancouver, ISO e altri

41

Rocha, Rui Jorge Miranda. "Effect of light on ex situ production of symbiotic corals". Doctoral thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/11777.

Testo completo

Abstract (sommario):

Doutoramento em Biologia
The increasing interest in coral culture for biotechnological applications, to supply the marine aquarium trade, or for reef restoration programs, has prompted researchers to optimize coral culture protocols, with emphasis to ex situ production. When cultured ex situ, the growth performance of corals can be influenced by several physical, chemical and biological parameters. For corals harbouring zooxanthellae, light is one of such key factors, as it can influence the photosynthetic performance of these endosymbionts, as well as coral physiology, survival and growth. The economic feasibility of ex situ coral aquaculture is strongly dependent on production costs, namely those associated with the energetic needs directly resulting from the use of artificial lighting systems. In the present study we developed a versatile modular culture system for experimental coral production ex situ, assembled solely using materials and equipment readily available from suppliers all over the world; this approach allows researchers from different institutions to perform truly replicated experimental set-ups, with the possibility to directly compare experimental results. Afterwards, we aimed to evaluate the effect of contrasting Photosynthetically Active Radiation (PAR) levels, and light spectra emission on zooxanthellae photochemical performance, through the evaluation of the maximum quantum yield of PSII (Fv/Fm) (monitored non-invasively and non-destructively through Pulse Amplitude Modulation fluorometry, PAM), chlorophyll a content (also determined non-destructively by using the spectral reflectance index Normalized Difference Vegetation Index, NDVI), photosynthetic and accessory pigments, number of zooxanthellae, coral survival and growth. We studied two soft coral species, Sarcophyton cf. glaucum and Sinularia flexibilis, as they are good representatives of two of the most specious genera in family Alcyoniidae, which include several species with interest for biotechnological applications, as well as for the marine aquarium trade; we also studied two commercially important scleractinian corals: Acropora formosa and Stylophora pistillata. We used different light sources: hydrargyrum quartz iodide (HQI) lamps with different light color temperatures, T5 fluorescent lamps, Light Emitting Plasma (LEP) and Light Emitting Diode (LED). The results achieved revealed that keeping S. flexibilis fragments under the same light conditions as their mother colonies seems to be photobiologically acceptable for a short-term husbandry, notwithstanding the fact that they can be successfully stocked at lower PAR intensities. We also proved that low PAR intensities are suitable to support the ex situ culture S. cf. glaucum in captivity at lower production costs, since the survival recorded during the experiment was 100%, the physiological wellness of coral fragments was evidenced, and we did not detect significant differences in coral growth. Finally, we concluded that blue light sources, such as LED lighting, allow a higher growth for A. formosa and S. pistillata, and promote significant differences on microstructure organization and macrostructure morphometry in coral skeletons; these findings may have potential applications as bone graft substitutes for veterinary and/or other medical uses. Thus, LED technology seems to be a promising option for scleractinian corals aquaculture ex situ.
O potencial dos corais como espécies emergentes com interesse para a aquacultura evidencia-se pela sua possível comercialização em três segmentos de mercado: a) aplicações biotecnológicas para pesquisa e exploração de novos compostos bioativos, b) aquariofilia marinha, e c) restauração de recifes de coral. Deste modo, o crescente interesse na aquacultura de corais conduziu a um esforço da comunidade científica para otimizar protocolos de cultivo, nomeadamente cultivo ex situ. O desempenho dos corais cultivados ex situ, em sistemas fechados com recirculação, pode ser afetado por diversos fatores físicos, químicos e biológicos. A iluminação representa um fator chave para o cultivo de corais que se caraterizem por um modo de vida em simbiose com dinoflagelados fotossintéticos (zooxantelas), uma vez que este fator influencia diretamente o desempenho destes endossimbiontes e, consequentemente, a fisiologia e crescimento do coral hospedeiro. A viabilidade económica de uma exploração aquícola está dependente do equilíbrio entre receitas e custos de produção, sendo que no caso do cultivo ex situ de corais, o custo relacionado com a utilização de sistemas de iluminação artificial influencia de forma preponderante o custo total de produção. No presente trabalho foi desenvolvido um sistema modular e versátil para o cultivo experimental de corais, recorrendo unicamente a materiais e equipamentos disponíveis no mercado á escala global; a utilização generalizada deste sistema permitirá a execução de desenhos experimentais estatisticamente robustos, bem como comparar de forma direta os resultados obtidos por diferentes equipas de investigação. Posteriormente foi avaliado o efeito de diferentes níveis de radiação fotossintética ativa (PAR – “Photosynthetically Active Radiation”), bem como diferentes espetros de emissão (comprimento de onda), na atividade fotossintética dos endossimbiontes (zooxantelas) de corais, recorrendo ao métodos não invasivo e não destrutivo designado como Fluorometria de Pulso Modulado (PAM – “Pulse Amplitude Modulation fluorometry”), para avaliar a eficiência fotoquímica do fotossistema II (Fv/Fm). Avaliou-se a concentração de clorofila a de forma indireta, através do cálculo do índice NDVI (“Normalized Difference Vegetation Index”) que resulta da reflectância espectral obtida de forma não invasiva e não destrutiva; para além do método mencionado realizaram-se análises para obtenção da concentração de pigmentos fotossintéticos e acessórios. Por fim, avaliou-se o efeito da luz na taxa de crescimento e percentagem de sobrevivência das espécies de corais estudadas. As variáveis independentes estudadas foram as diferentes fontes de iluminação artificial utilizadas para cultivo ex situ de corais, nomeadamente: lâmpadas de halogeneto metálico (HQI – “hydrargyrum quartz iodide”) com diferentes temperaturas de cor, lâmpadas T5 fluorescentes, lâmpadas de plasma (LEP – “Light Emitting Plasma”) e lâmpadas de LED (“Light Emitting Diode”). Estudaram-se duas espécies de corais moles, Sarcophyton cf. glaucum e Sinularia flexibilis, que representam dois dos géneros com mais espécies na família Alcyoniidae, onde se incluem numerosas espécies com interesse para a biotecnologia marinha e para o mercado da aquariofilia marinha; foram igualmente estudadas duas espécies de corais duros, Acropora formosa e Stylophora pistillata, comercialmente importantes para o mercado da aquariofilia marinha, e relevantes para ações de repovoamento nos recifes de coral. Demonstrámos através dos resultados das diferentes experiências realizadas, que a cicatrização e recuperação de fragmentos de S. flexibilis mantidos após fragmentação nas mesmas condições luminosas das colónias mãe dos fragmentos são aceitáveis, embora possam igualmente ser mantidos com sucesso em regimes luminosos com uma menor intensidade do valor de PAR. Ficou também demonstrado que o cultivo do coral S. cf. glaucum em regimes luminosos com uma baixa intensidade do valor de PAR é biologicamente viável, o que permite uma redução acentuada nos custos de produção associados á iluminação artificial. Finalmente, concluiu-se que a utilização de sistemas de iluminação que emitam nos comprimentos de onda na faixa de radiação azul proporciona taxas de crescimento mais elevadas aos corais A. formosa e S. pistillata, para além de promover alterações ao nível da organização das micro e macroestruturas que integram os exosqueletos destes corais, referidos como um biomaterial com potencial para aplicação biomédica em implantes ósseos ou reconstrução maxilo-facial. Ficou também provado neste estudo, que as novas tecnologias de iluminação (LED) são bastante promissoras para o cultivo ex situ de corais.

Gli stili APA, Harvard, Vancouver, ISO e altri

42

Generali, Gianluca <1977&gt. "Organic heterostructure approach for multifunctional light-emitting field-effect transistors". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3568/1/Generali_Gianluca_tesi.pdf.

Testo completo

Abstract (sommario):

The possibility of combining different functionalities in a single device is of great relevance for further development of organic electronics in integrated components and circuitry. Organic light-emitting transistors (OLETs) have been demonstrated to be able to combine in a single device the electrical switching functionality of a field-effect transistor and the capability of light generation. A novel strategy in OLET realization is the tri-layer vertical hetero-junction. This configuration is similar to the bi-layer except for the presence of a new middle layer between the two transport layers. This “recombination” layer presents high emission quantum efficiency and OLED-like (Organic Light-Emitting Diode) vertical bulk mobility value. The key idea of the vertical tri-layer hetero-junction approach in realizing OLETs is that each layer has to be optimized according to its specific function (charge transport, energy transfer, radiative exciton recombination). Clearly, matching the overall device characteristics with the functional properties of the single materials composing the active region of the OFET, is a great challenge that requires a deep investigation of the morphological, optical and electrical features of the system. As in the case of the bi-layer based OLETs, it is clear that the interfaces between the dielectric and the bottom transport layer and between the recombination and the top transport layer are crucial for guaranteeing good ambipolar field-effect electrical characteristics. Moreover interfaces between the bottom transport and the recombination layer and between the recombination and the top transport layer should provide the favourable conditions for the charge percolation to happen in the recombination layer and form excitons. Organic light emitting transistor based on the tri-layer approach with external quantum efficiency out-performing the OLED state of the art has been recently demonstrated [Capelli et al., Nat. Mater. 9 (2010) 496-503] widening the scientific and technological interest in this field of research.

Gli stili APA, Harvard, Vancouver, ISO e altri

43

Generali, Gianluca <1977&gt. "Organic heterostructure approach for multifunctional light-emitting field-effect transistors". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3568/.

Testo completo

Abstract (sommario):

The possibility of combining different functionalities in a single device is of great relevance for further development of organic electronics in integrated components and circuitry. Organic light-emitting transistors (OLETs) have been demonstrated to be able to combine in a single device the electrical switching functionality of a field-effect transistor and the capability of light generation. A novel strategy in OLET realization is the tri-layer vertical hetero-junction. This configuration is similar to the bi-layer except for the presence of a new middle layer between the two transport layers. This “recombination” layer presents high emission quantum efficiency and OLED-like (Organic Light-Emitting Diode) vertical bulk mobility value. The key idea of the vertical tri-layer hetero-junction approach in realizing OLETs is that each layer has to be optimized according to its specific function (charge transport, energy transfer, radiative exciton recombination). Clearly, matching the overall device characteristics with the functional properties of the single materials composing the active region of the OFET, is a great challenge that requires a deep investigation of the morphological, optical and electrical features of the system. As in the case of the bi-layer based OLETs, it is clear that the interfaces between the dielectric and the bottom transport layer and between the recombination and the top transport layer are crucial for guaranteeing good ambipolar field-effect electrical characteristics. Moreover interfaces between the bottom transport and the recombination layer and between the recombination and the top transport layer should provide the favourable conditions for the charge percolation to happen in the recombination layer and form excitons. Organic light emitting transistor based on the tri-layer approach with external quantum efficiency out-performing the OLED state of the art has been recently demonstrated [Capelli et al., Nat. Mater. 9 (2010) 496-503] widening the scientific and technological interest in this field of research.

Gli stili APA, Harvard, Vancouver, ISO e altri

44

Dumitru, Alina Gabriela. "Quantum theory of light scattering at finite temperature". Thesis, Nottingham Trent University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241832.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

45

Au, Yat-Yin. "Light scattering studies of metallic magnetic microstructures". Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1141842225.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

46

Buisson, Daniel Joseph. "Anatomical and morphological responses of papaya, Carica papaya L., to various light conditions". FIU Digital Commons, 1991. http://digitalcommons.fiu.edu/etd/1817.

Testo completo

Abstract (sommario):

Plants that develop under foliar shade encounter both low photosynthetically active radiation (PAR) and low red to far red ratios (R:FR). Both of these factors are important in determining developmental responses to shade. Papaya (Carica papaya L.) seedlings grown under filtered shade (low PAR and low R:FR) were compared with seedlings grown under neutral shade (low PAR with R:FR similar to that of full sunlight), and high light (moderate PAR with R:FR similar to that of full sunlight). The results indicated that papaya exhibits a light seeking strategy as evidenced by morphological and anatomical differences between treatments. Based on past research the results also indicate shade developmental responses in papaya to be phytochrome mediated.

Gli stili APA, Harvard, Vancouver, ISO e altri

47

Amat, Genís Albert. "Effect of visible and near-infrared light on adenosine triphosphate (atp)". Doctoral thesis, Universitat Rovira i Virgili, 2005. http://hdl.handle.net/10803/8715.

Testo completo

Abstract (sommario):

L' ATP es una molecula clau en el metabolisme cel.lular, actuant com a donador d'energia lliure i acoplant reaccions endergoniques i exergoniques. L'ATP es sintetitzat a la mitocondria en un proces anomenat fosforil.lacio oxidativa despres d'una serie de reaccions a la cadena de citocroms que es troba en la membrana interna de l'organel.la. La font d'energia necessaria per aquesta sintesi s'obte en les cel.lules animals dels nutrients de l'ingestio, i de la llum solar en les plantes. Existeix una via alternativa de sintesi d'ATP extramitocondrial, la glicolisi, que s'inicia amb la fosforilacio de la glucosa per l'enzim hexokinasa.
Interaccio llum-materia
L'energia electromagnetica l'ona de la qual oscil.la en una longitud d'ona de nanometres es anomenada llum. En aquestes frequencies, l'energia promou excitacio electronica de certs atoms i molecules. Existeix una interaccio diferent de la llum amb molecules, produida per el camp electromagnetic que per definicio la llum provoca en qualsevol medi. El camp electric resultant desplaca els electrons dels enllacos quimics produint una polaritzacio del medi sense que existeixi absorcio de l'energia. Aquest es un mecanisme interactiu que existeix sempre, i es l'unic que es dona en molecules que son transparents (no absorbeixen) per a una determinada frequencia de la llum, com es el cas de l'ATP per l'energia visible i infravermella propera.
Experiments, resultats i discussio
Quan l'ATP es excitat amb fotons ultraviolats, es produiex una fluorescencia en longituts d'ona visibles. L'io magnesi s'ha utilitzat per estudiar com la llum visible i infravermella propera produiex un desplacament de carregues electriques a la molecula d'ATP.
La construccio d'un interferometre de Michelson ha servit per observar l'interaccio no absortiva de la llum i l'ATP. La mesura directa de l'index de refraccio d'una solucio d'ATP dona informacio sobre les caracteristiques electriques del medi. L'observacio de que aquest index canvia despres d'irradiar la solucio amb longituds d'ona visibles i infravermelles properes, confirmen que la llum provoca canvis electrics significatius en l'ATP.
En aquest treball tambe s'ha estudiat el comportament bioquimic de l'ATP irradiat quant forma part de dues reaccions quimiques diferents: la de la luciferina-luciferasa i la de la hexoquinasa. En tots dos casos, l'us d'aquest ATP irradiat ha produit una alteracio dels parametres cinetics estudiats, V0 i k en la reaccio de la luciferina-luciferasa, i km i vmax en la reaccio de l'hexoquinasa.
Conclusions
Aquesta interaccio no absortiva de la llum amb l'ATP es la primera descrita per a una biomolecula. El mecanisme aporta noves dades per explicar els efectes observats en el metabolisme cel.lular despres de l'irradiacio d'organismes, teixits i cultius cel.lulars amb llum visible i infravermella propera.
ATP is a key molecule in cellular metabolism. In this thesis, I examined the effects of visible (635 and 655 nm) and near-infrared (810 and 830 nm) light on ATP in solution. I also examined were the biochemical behavior of light-exposed ATP in the luciferine-luciferase reaction and hexokinase reaction, the initial step in glycolysis that begins extra mithocondrial ATP synthesis. Irradiated groups in the luciferine-luciferase reaction showed an improvement in the kinetic parameters V0 and k, and more ATP molecules reacted with the enzyme when they were excited by light. When irradiated ATP was added to the hexokinase reaction, the experimental groups showed significant differences in the Michaelis-Menten kinetic parameters (km for ATP and vmax) and the rate of product synthesis was greater. Changes in both reactions were wavelength and dose dependant.
When ATP was excited with UV photons, it fluoresced. This fluorescence decreased when Mg2+ was added, probably because the ion binds the phosphates, which are the part of the molecule responsible for light emission. Irradiating the ATP-Mg2+ solution with 655 nm and 830 nm light increased the fluorescence resulting from a displacement of charges in the phosphor-oxygen bond that repels Mg2+.
The refraction of light in an ATP solution was observed by the Michelson interferometer and by directly measuring the refractive index. The refractive index changed after red and near-infrared light interaction due to a change in the electrical permittivity of the medium.
Since ATP in water is transparent to visible and near-infrared light, and is therefore not a chromophore for those wavelengths, I conclude that the observed light interaction with ATP is not due to photon absorption but to the electromagnetic disturbance produced by the light, which leads to a polarization of the dielectric molecule that is ATP.
This interaction of visible and near-infrared electromagnetic energy with ATP offers new perspectives for explaining light interaction at subcellular level.

Gli stili APA, Harvard, Vancouver, ISO e altri

48

Korger, Jan Verfasser], e Gerd [Akademischer Betreuer] [Leuchs. "Geometric Spin Hall Effect of Light / Jan Korger. Gutachter: Gerd Leuchs". Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2014. http://d-nb.info/107574475X/34.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

49

Chan, Chia-Hsin, e 詹佳欣. "Effects of 6 Weeks Light Response Training on Agility in Soft Tennis Player". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/bnw99b.

Testo completo

Abstract (sommario):

碩士
臺北市立大學
運動健康科學系碩士班
105
Background: In soft tennis, players only have limited time to make a decision right after opponents hit the ball till drop. Because the material of balls is softer and easier to change the shape, reaction and agility capability are quite important for the players. Purpose: To investigate the effects of 6-week light response training on agility, lower limbs power and skill-related physical fitness in soft tennis players. Methods: 22 soft tennis players were assigned to a light training group (LTG, n = 11) and a control group (CG, n = 11). All subjects participated in the 6 weeks agility training. LTG’s agility training protocol was intervened light simulation, but CG did not. The agility capability test, lower limbs strength, and skill-related fitness test were done before and after the training programme. Results: After 6-week agility training, the performance of agility, lower limbs power and lower limbs muscle strength have improved in both LTG and CG. In random change of direction agility test, LTG showed significant difference after training programme but CG did not. Conclusion: This finding indicated that 6-week agility training could not only significantly improve agility, lower limbs power, and lower limbs muscle strength, but also got a significant improvement on random change of direction agility test in LTG. Hence, we suggest that add this training protocol in while operating agility training in order to fit the footstep of soft tennis.

Gli stili APA, Harvard, Vancouver, ISO e altri

50

Röhrig, Manfred [Verfasser]. "Modelling the light competition between crops and weeds / von Manfred Röhrig". 1999. http://d-nb.info/956719619/34.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Tesi sul tema "Effect of light on weeds"

Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili