The propagation of high-energy cosmic rays is influenced by the time-varying heliospheric magnetic field embedded in the solar wind, and by the geomagnetic field. To penetrate through this geomagnetic field, they must have a rigidity that exceeds the geomagnetic cutoff rigidity for a given position on the earth. In the atmosphere, the primary cosmic rays interact with atmospheric nuclei, to form a cascade of secondary particles. Neutron monitors record these secondary cosmic rays, mainly the neutrons, with energies about a decade higher than detected by most spacecraft. Since neutron monitors are integral detectors, each with its own detection efficiency, energy spectra cannot readily be derived from their observations. One way to circumvent this is by conducting latitudinal surveys with mobile neutron monitors. Another way is to use the worldwide stationary neutron monitor network, but then the counting rates of these monitors must be normalised sufficiently accurate against one another. For this reason two portable calibration neutron monitors were built at the Potchefstroom campus of the North-West University and completed in 2002. To achieve sufficient calibration accuracy, several properties of the calibrator are investigated in this work. Effects such as atmospheric pressure variations, diurnal variations, short-term scintillations, and multiplicity, contribute to the fluctuations of the counting rate of a neutron monitor. Due to these effects, the coefficient of variation of the calibrator is determined to be -40% larger than the Poisson deviation. The energy response of the calibrator over the cutoff rigidity interval from the poles to the equator is investigated, with the result that it is almost 4% larger than that of a standard 3NM64 neutron monitor. It is also determined that not only the calibrator, but also the stationary NM64 and IGY neutron monitors, have fairly large instrumental temperature sensitivity, which must be accounted for in calibration procedures. Furthermore, the calibrator has a large sensitivity to the type of surface beneath it, influencing its counting rate by as much as 5%. This investigation is incomplete and requires further experimentation before the calibration of the stationary neutron monitors can start. When calibrations of a significant number of the worldwide neutron monitors are done, their intensity spectra as derived from differential response functions, will provide experimental data for modulation studies at rigidities above 1 GV. / Thesis (Ph.D. (Physics))--North-West University, Potchefstroom Campus, 2006.

The propagation of high-energy cosmic rays is influenced by the time-varying heliospheric magnetic field embedded in the solar wind, and by the geomagnetic field. To penetrate through this geomagnetic field, they must have a rigidity that exceeds the geomagnetic cutoff rigidity for a given position on the earth. In the atmosphere, the primary cosmic rays interact with atmospheric nuclei, to form a cascade of secondary particles. Neutron monitors record these secondary cosmic rays, mainly the neutrons, with energies about a decade higher than detected by most spacecraft. Since neutron monitors are integral detectors, each with its own detection efficiency, energy spectra cannot readily be derived from their observations. One way to circumvent this is by conducting latitudinal surveys with mobile neutron monitors. Another way is to use the worldwide stationary neutron monitor network, but then the counting rates of these monitors must be normalised sufficiently accurate against one another. For this reason two portable calibration neutron monitors were built at the Potchefstroom campus of the North-West University and completed in 2002. To achieve sufficient calibration accuracy, several properties of the calibrator are investigated in this work. Effects such as atmospheric pressure variations, diurnal variations, short-term scintillations, and multiplicity, contribute to the fluctuations of the counting rate of a neutron monitor. Due to these effects, the coefficient of variation of the calibrator is determined to be -40% larger than the Poisson deviation. The energy response of the calibrator over the cutoff rigidity interval from the poles to the equator is investigated, with the result that it is almost 4% larger than that of a standard 3NM64 neutron monitor. It is also determined that not only the calibrator, but also the stationary NM64 and IGY neutron monitors, have fairly large instrumental temperature sensitivity, which must be accounted for in calibration procedures. Furthermore, the calibrator has a large sensitivity to the type of surface beneath it, influencing its counting rate by as much as 5%. This investigation is incomplete and requires further experimentation before the calibration of the stationary neutron monitors can start. When calibrations of a significant number of the worldwide neutron monitors are done, their intensity spectra as derived from differential response functions, will provide experimental data for modulation studies at rigidities above 1 GV. / Thesis (Ph.D. (Physics))--North-West University, Potchefstroom Campus, 2006.

<p>In the largest known investigation to date of the prevalence of resilience following experiences of child maltreatment, a statewide, longitudinal sample of maltreated children was used to measure the prevalence of resilience, defined in this study as consistent competence over time and across multiple domains of functioning within the academic setting. In response to the relative paucity of resilience research using large samples, multiple domains of functioning, and longitudinal data, the current study measured resilience in a sample of over 150,000 children who were reported to child protective services agencies for suspected maltreatment. Functioning was measured within three distinct domains (academic performance, special education, and behavioral functioning) across a time period of up to 7 years. A sample of over 450,000 children with no known maltreatment history was used to compare relative rates of consistent competence over time and examine any differential effects on competence across groups. Approximately 18% of maltreated children exhibited consistently competent functioning in all domains across all available years of data, whereas approximately 35% of nonmaltreated children demonstrated consistent competence. County-level introduction of differential response policies investigating children's reported maltreatment was found to promote higher rates of competent functioning. In addition, relative levels of government expenditures in children's counties on two popular statewide early childhood programs (Smart Start and More At Four) were found to predict competent functioning for maltreated and nonmaltreated children alike. These findings suggest that child welfare policies aimed at identifying and assisting high-risk families in need of services and support and community programs targeted at improving children's early development and school readiness hold promise for improving adaptive functioning among maltreated children at high risk for experiencing difficulties in the school environment.</p> / Dissertation

Made available in DSpace on 2015-03-26T13:36:44Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1982474 bytes, checksum: 1612e19e8ad39e9083e77817292c4d1a (MD5) Previous issue date: 2013-02-27 / The auxins IAA (indole-3-acetic, natural), 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid, the latter two synthetic) were sprayed on corn (Zea mays, monocot) and beans (Phaseolus vulgaris, dicot), in order to investigate some differential responses of the two plant groups as associated to ethylene metabolism. Corn plants treated with the auxins did not produce ethylene, not exhibiting also any senescence symptom. Beans plants, on the other hand, produced large amounts of ethylene following treatment with auxins. Aminoethoxyvinylglycine (AVG) plus Co2+ (ethylene biosynthesis inhibitors) were not able to relieve the epinasty, drying and leaf wrinkling effects in bean plants, but leaf yellowing was considerebly reduced, suggesting this was an ethylene effect. Following spraying with auxins, corn plants showed no production of 1-aminocyclopropane-1-carboxylic acid (ACC), a response shown by beans plants. Therefore in the monocot, auxins seemed not to induce the expression of ACC synthase (ACS) or its activity. When treated with ACC, corn plants failed to produce any trace of ethylene, unlikely bean plants. This suggested that in monocot, auxins seemed also not to induce the expression or activity of ACC oxidase (ACO) or the enzyme is not activated. Potassium ferrocyanide, employed as a source of cyanide ions, was much more toxic to bean plants than to corn and so the monocot seemed to be more resistant than bean plants. Maximum quantum yield of photosystem II (Fv/Fm) and photosynthetic pigments contents kept unchanged in corn plants treated with the auxins. Bean plants showed significant decreases in both variables following spraying with 2,4-D and 2,4,5-T. Decreases in chlorophyll contents in bean plants treated with 2,4-D and 2,4,5-T correlated well with leaf chlorosis what was shown to be due to a more pronounced fall of chlorophyll contents rather than to an increase in carotenoid contents. The xanthophylls (neoxanthin, violaxanthin and anteraxantina) also showed a higher degradation than the alpha and beta carotenes in bean plants treated with 2,4-D and 2,4,5-T. When AVG and Co2+ were supplied together with auxin, no appreciable decrease in either the Fv/Fm ratio or pigment contents was observed, with the exception of alpha carotene. Also the ratio of chlorophyll a to chlorophyll b was also larger in bean plants treated with 2,4-D and 2,4,5-T than in the plants treated with 2,4-D and 2,4,5-T plus AVG and Co2+. The ratio of chlorophyll a to chlorophyll b did not show any significance in bean plants upon treatment with IAA. / As auxinas AIA (ácido indol-3-acético, natural), 2,4-D (ácido 2,4-diclorofenoxiacético) e 2,4,5-T (ácido 2,4,5-triclorofenoxiacético, as duas últimas sintéticas) foram aplicadas em plantas de milho (Zea mays, monocotiledônea) e feijão (Phaseolus vulgaris, dicotiledônea), visando investigarem-se algumas respostas diferenciais dos dois grupos em relação ao metabolismo do etileno. Plantas de milho tratadas com as auxinas não produziram etileno e não exibiram quaisquer sintomas de senescência e epinastia. O feijão produziu bastante etileno após tratamento. Quando se utilizou aminoetoxivinilglicina (AVG) mais Co2+ (inibidores da biossíntese de etileno), a epinastia das plantas de feijão foi mantida mas o amarelecimento das plantas mostrou-se reduzido, deduzindo-se ser o amarelecimento um sintoma da ação do etileno. Após pulverização com as auxinas, o milho não exibiu produção do ácido 1-carboxílico-1- amino-ciclopropano (ACC), fato observado no feijão. Assim, na monocotiledônea, as auxinas parecem não induzir a expressão da sintase do ACC (ACS) ou, pelo menos, sua atividade. Quando tratadas com o ACC, as plantas de milho não produziram qualquer traço de etileno, ao contrário as plantas de feijão. Daí deduzir-se que na monocotiledônea, as auxinas parecem também não induzir a expressão ou atividade da oxidase do ACC (ACO) ou a enzima não é ativada. Empregando-se K4Fe(CN)6 como fonte de íons cianeto, as plantas de milho pareceram se mostrar mais resistentes à intoxicação do que as plantas de feijão. O rendimento quântico máximo de fotossistema II (razão Fv/Fm) e os níveis dos pigmentos fotossintéticos não sofreram alterações em plantas de milho tratadas com as auxinas. As plantas de feijão mostraram quedas significativas em ambas variáveis após pulverização com 2,4-D e 2,4,5-T, mas não com o AIA. A redução nos níveis das clorofilas em plantas de feijão tratadas com 2,4-D e 2,4,5-T relacionou-se com a clorose observada, desde que ocorreu uma degradação mais acentuada das clorofilas do que dos carotenoides. As xantofilas (neoxantina, anteraxantina e violaxantina) também sofreram uma degradação mais acentuada do que o alfa e beta caroteno em plantas de feijão tratadas com 2,4-D e 2,4,5-T. Quando AVG e Co2+ foram fornecidos conjuntamente com as auxinas, não ocorreu queda na razão Fv/Fm e nem no nível dos pigmentos, com exceção do alfa caroteno. A razão entre clorofila a e clorofila b também mostrou-se maior nas plantas de feijão tratadas com 2,4-D e 2,4,5-T do que nas plantas tratadas com 2,4-D e 2,4,5-T mais AVG e Co2+. Nas plantas tratadas com AIA o aumento na razão entre clorofila a e clorofila b não foi significativo.

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