Utilizamos um formalismo variacional, juntamente com técnicas diagramáticas, para estudar o comportamento termodinâmico do modelo de Ising com campo transverso na presença de interações de longo alcance. Obtivemos uma expressão para a suscetibilidade acima da temperatura crítica Tc. Tambem obtivemos uma forma analítica para a temperatura critica, que nos permite traçar gráficos de kTc/J em função de r/J - onde J e a constante de troca das interações de curto alcance e r é o campo transverso para valores fixos do número de coordenação da rede e da razão n entre as interações de longo e de curto alcance. Os nossos resultados aproximados para a suscetibilidade foram comparados com a expansão exata em serie de altas temperaturas. / We use a variational formalism, together with diagrammatic technique, to study the thermodynamic behaviour of the Ising model in a transverse field with the addition of long range interactions. We obtain an expression for the susceptibility above the transition temperature. Also, we obtain an analytic expression for the critical temperature, which allows the construction of kTc/J versus f/J curves (where J is the exchange parameter of the short range interactions and r is the transverse field) for fixed values of the coordination number of the lattice and of the ratio n between long and short range interactions. Our approximate results for the susceptibility are compared with the exact expansion in a high temperature series.

Neste trabalho fizemos um estudo do diagrama de fase no plano campo magnético (H) vs. temperatura (T) e temperaturas acima de 0,3 K dos sistemas mistos MN(BR IND. 1-x CL IND. x) IND. 24 H IND. 2O. A técnica experimental utilizada foi a medida da susceptibilidade magnética diferencial. Estudamos a dependência da temperatura de Néel, dos campos críticos e do diagrama de fase em função da concentração x. Os resultados mostram que alterando a concentração x de Cloro podemos controlar a anisotropia do sistema entre as anisotropias do Cloreto e Brometo puros. Desta maneira pudemos fazer um estudo experimental dos diagramas de fase em função do campo magnético, da temperatura e da anisotropia do sistema. / Differential magnetic susceptibility measurements were performed on single crystals of the mixed system MN(BR IND. 1-x CL IND. x) IND. 24 H IND. 2O, at temperatures (T) above 0.3 K and in the presence of an external magnetic (H) field . We studied the dependence of the Néel temperature, the critical fields and the magnetic phase diagram in the T vs. H plane on the concentration x. The results indicate that the anisotropy of the mixed systems can be changed between the values of the anisotropy of the Chloride and the Bromide by changing the concentration x of the Chloride. We used this fact to perform an experimental study of the dependence of the phase diagrams on temperature, magnetic field and anisotropy.

Neste trabalho fizemos um estudo do diagrama de fase no plano campo magnético (H) vs. temperatura (T) e temperaturas acima de 0,3 K dos sistemas mistos MN(BR IND. 1-x CL IND. x) IND. 24 H IND. 2O. A técnica experimental utilizada foi a medida da susceptibilidade magnética diferencial. Estudamos a dependência da temperatura de Néel, dos campos críticos e do diagrama de fase em função da concentração x. Os resultados mostram que alterando a concentração x de Cloro podemos controlar a anisotropia do sistema entre as anisotropias do Cloreto e Brometo puros. Desta maneira pudemos fazer um estudo experimental dos diagramas de fase em função do campo magnético, da temperatura e da anisotropia do sistema. / Differential magnetic susceptibility measurements were performed on single crystals of the mixed system MN(BR IND. 1-x CL IND. x) IND. 24 H IND. 2O, at temperatures (T) above 0.3 K and in the presence of an external magnetic (H) field . We studied the dependence of the Néel temperature, the critical fields and the magnetic phase diagram in the T vs. H plane on the concentration x. The results indicate that the anisotropy of the mixed systems can be changed between the values of the anisotropy of the Chloride and the Bromide by changing the concentration x of the Chloride. We used this fact to perform an experimental study of the dependence of the phase diagrams on temperature, magnetic field and anisotropy.

Utilizamos um formalismo variacional, juntamente com técnicas diagramáticas, para estudar o comportamento termodinâmico do modelo de Ising com campo transverso na presença de interações de longo alcance. Obtivemos uma expressão para a suscetibilidade acima da temperatura crítica Tc. Tambem obtivemos uma forma analítica para a temperatura critica, que nos permite traçar gráficos de kTc/J em função de r/J - onde J e a constante de troca das interações de curto alcance e r é o campo transverso para valores fixos do número de coordenação da rede e da razão n entre as interações de longo e de curto alcance. Os nossos resultados aproximados para a suscetibilidade foram comparados com a expansão exata em serie de altas temperaturas. / We use a variational formalism, together with diagrammatic technique, to study the thermodynamic behaviour of the Ising model in a transverse field with the addition of long range interactions. We obtain an expression for the susceptibility above the transition temperature. Also, we obtain an analytic expression for the critical temperature, which allows the construction of kTc/J versus f/J curves (where J is the exchange parameter of the short range interactions and r is the transverse field) for fixed values of the coordination number of the lattice and of the ratio n between long and short range interactions. Our approximate results for the susceptibility are compared with the exact expansion in a high temperature series.

Average characteristics of subsidence inversions associated with the Pacific High have only been documented for areas along the U.S. West Coast and over the tropical eastern North Pacific Ocean. This study, which is based on 3414 upper-air soundings for June through September of 1964 and 1965, shows the average summer season characteristics of the inversion from Tatoosh Island, Washington northward along the coast of the Gulf of Alaska. A comparison is also made with the subsidence inversion found over the eastern North Pacific Ocean from Johnston Island (17°N, 168.5°W) to Ocean Station PAPA (50°N, 145°W). Some of the more notable findings are: (a) a diurnal oscillation of the height of the inversion base exists, except in the regions of Yakutat and Anchorage, Alaska; (b) the height of the inversion increases with increasing latitude from Tatoosh Island to Anchorage; (c) the inversion thickness decreases from Tatoosh Island to Anchorage; (d) subsidence inversions are most pronounced over the California coast compared to any other location between Johnston Island and Anchorage. / Graduation date: 1978

Thesis (Ph.D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 27, 2007) Vita. Includes bibliographical references.

Thesis--M. Phil., University of Hong Kong, 1976.

The urbanization process alters the radiative, thermal, moisture and aerodynamic characteristics of a surface, which significantly affect the surface energy balance within the atmospheric boundary layer. Such modifications can lead to the so-called urban warming phenomenon, where the extent and rate of urban surface and air temperature is substantially higher than the corresponding rural region, which has caused serious concern in recent decades. However, the understanding of the causes of urban warming is incomplete, and the same applies to lack of effective mitigation strategies. Therefore, in order to have a complete understanding of the formation of urban warming, the present thesis focusses on the estimation of temporal variations of urban surface and air temperatures by using numerical simulations, analytical methods and field measurements. To better understand the mechanism(s) of urban surface temperature variation, a three-dimensional model that incorporates the energy exchange processes is first developed for a realistically complex city. In order to reduce the computational effort for the radiation heat transfer calculation, the compressed row storage scheme is applied, which permits the rigorous consideration of multiple reflections in a realistic urban area with hundreds of buildings. The developed surface energy balance model is then used to investigate the effects of the urban canopy geometry on urban albedo and surface temperature. The average urban albedo is less for a moderately compact city having high rise buildings with varying building heights than other cases. A cooler urban street surface temperature with smaller amplitude and earlier occurrence of the daily maximum temperature is observed in a high rise compact city than a low-rise sparse city. In order to understand quantitatively the causes of urban air warming, a new analytical zero-dimensional urban air temperature model is also developed, which is able to capture the features of the urban temperature variation. Results show that solar heat gain, evapotranspiration and the anthropogenic heat affect the mean air temperature, while heat storage and thermal convection affect the amplitude and phase shift of the daily cycle. A high-rise, high-density city generates low surface temperature, resulting in low air temperature during the day. The main conclusion of this study is that on the condition rural air temperature cycle is given, the mean temperature of the urban air and surface temperature is determined by the net heat gain and ventilation rate, and the amplitude and phase can be obtained from thermal storage and ventilation rate. Essentially, the net heat gain, thermal storage and ventilation are affected by urban morphology, and hence a city thermal environment can be designed. (419 words) / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Climatic fluctuation is putting Nigeria’s agriculture system under serious threat and stress. The study of the effect of climate change on agricultural productivity is critical given its impact in changing livelihood patterns in the country. Descriptive and co-integration analysis are the techniques used to analyze the Time series data used in this work. The finding demonstrates that the rate in agricultural productivity is persistently higher between 1981 and 1995, followed by a much lower growth rate in the 1996–2000 sub period. There was variation in the trend pattern of rainfall. Temperature was not relatively constant either. The Augmented Dickey-Fuller test for unit root revealed that agricultural productivity is not stationary and likewise the annual rainfall but became stationary after the differencing. Annual temperature on the other hand is stationary at its level. Temperature change was revealed to exert negative effect while rainfall change exerts positive effect on agricultural productivity. However previous year rainfall was negatively significant in affecting current year agricultural productivity. It is recommended that if agricultural productivity was to be increased and sustained, environmentally and agricultural sensitive technologies and innovations that can prevent climate fluctuation should be encouraged.

Graduation date: 1977