We report capacitive measurements of the hysteresis and avalanche properties of $\sp4$He in Nuclepore. Hysteresis was measured on global loops and subloops for Nuclepore with 30 nm and 200 nm diameter pores. Subloops exhibit the property of return point memory, but subloops between the same chemical potential end points were not congruent. The failure of congruence showed that the Preisach model, in which the pores do not interact, does not describe this system. Modification of the Preisach model to allow for pore intersection within the membrane resulted in qualitative agreement with the data. Using a model for hystersis by Mason which included pore-pore interactions, we calculated the pore size distribution for Nuclepore. Close examination of the primary desorption curve resulted in the observation of large groups of pores draining together. This was the first observation of avalanches in the draining of fluid from a porous material. The properties of the avalanches were documented for 200 nm and 30 nm pore diameter Nuclepore. Using two capacitors on the same Nuclepore substrate, we found that avalanche events were spatially extended involving a low density of pores. With a composite porous/nonporous sample we showed that pore coupling occurred via the superfluid $\sp4$He film.

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We have measured the viscosity of a dilute mixture of 3He in 4He at temperatures from 5 to 100 mK and in magnetic fields of 0.35, 2.01 and 8.76 T using a vibrating wire viscometer. Subject to our choice of calibration function, the data at 0.35 T is in good agreement with theory. Due to an interaction of our viscometer with the magnetic field the motion of the wire at 2.01 and 8.76 T is not understood; however, the 2.01 T data can be brought into agreement with the 0.35 T data by adjusting a geometrical constant. An increase in the low temperature viscosity between 2.01 and 8.76 T is in qualitative agreement with theory (using an alternate choice of calibration function a decrease in viscosity between 2.01 and 8.76 T is observed).

Tesis para optar al grado de Magíster en Ciencias, Mención Física / Los plasmas son comunes en diferentes sistemas astronómicos. Una parte importante de estos plasmas están en el régimen no colisional, en que el camino libre medio de las partículas que lo componen es más grande que el tamaño del sistema. Un ejemplo de este tipo de objetos es el disco de acreción que se encuentra en las cercanías del agujero negro ubicado en el centro de la Vía Láctea, Sagitario A* (Sgr A*). Por su baja colisionalidad, se espera que el plasma en Sgr A* no siga una distribución de Maxwell-Boltzmann. Además, por la mayor eficiencia radiativa de los electrones, es también esperable que estos tengan menor temperatura que los iones. El grado en que se calientan los electrones en un sistema no colisional, así como su espectro de energía, tienen importantes consecuencias observacionales. Existen diversos mecanismos que pueden transferir energía a los electrones. Entre ellos están: reconexión magnética, interacción onda-partícula, y viscosidad anisotrópica. En esta tesis nos enfocamos en el calentamiento de electrones por medio de la interacción onda partícula y por calentamiento viscoso. Para ello realizamos simulaciones ``particle-in-cell'' (o PIC) de un plasma no colisional, magnetizado y sujeto a un cizalle permanente. Este cizalle produce una amplificación del campo magnético, obteniéndose así una anisotropía de presión en las particulas, debido a la invarianza adiabatica de su momento magnetico. Esta anisotropía produce inestabilidades cinéticas en el plasma, las que propagan ondas en escalas del radio de Larmor de las partículas. Algunos ejemplos relevantes para nuestro estudio son las inestabilidades de whistler e ion-ciclotrón. Estas inestabilidades pueden resonar preferentemente con los electrones e iones, respectivamente, otorgando o quitando energía a las partículas. Realizamos simulaciones con moderadas razones de masa entre iones y electrones, para estudiar a los electrones en el régimen cinético. Consideramos consistentemente el régimen no-lineal y cuasi-estacionario de las inestabilidades. Estudiamos el calentamiento de los electrones, y se encontró que estos se calientan principalmente por viscosidad. Sin embargo, se encontró un calentamiento extra, el que es transferido desde los iones a los electrones debido a la interacción de estos últimos con las ondas ion-ciclotrón (las que a su vez son principalmente producidas por los iones). Este calentamiento extra aumenta con la magnetización y disminuye al aumentar la razón de masa y la temperatura de los iones. Además, la componente no térmica del espectro de energía de los electrones se ve fuertemente modificada cuando el radio de Larmor de estos es similar al de los iones. Esta componente no térmica se asemeja bastante a lo que se infiere de observaciones de sistemas como Sgr A*. Nuestro trabajo nos permitió entonces encontrar condiciones que facilitan el calentamiento y aceleración no térmica de electrones debido a la transferencia de energía entre iones y electrones en plasmas no colisionales.

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Municipal solid waste (MSW) management strategies typically include a combination of three approaches, recycling, combustion, and landfill disposal. In the US approximately 54% of the generated MSW was landfilled in 2008, mainly because of its simplicity and cost-effectiveness. However, landfills remain a major concern due to potential landfill gas (LFG) emissions, generated from the chemical and biological processes occurring in the disposed waste. The main components of LFG are methane (50-60%) and carbon dioxide (40-50%). Although LFG poses a threat to the environment, if managed properly it is a valuable energy resource due to the methane content. Currently there are over 550 active LFG to energy (LFGTE) facilities in the US, producing renewable energy from LFG. A major challenge in designing/operating a LFGTE facility is the uncertainty in LFG generation rate predictions. LFG generation rates are currently estimated using models that are dependent upon the waste disposal history, moisture content, cover type, and gas collection system, which are associated with significant uncertainties. The objectives of this research were to:  Evaluate various approaches of estimating LFG generation and to quantify the uncertainty of the model outcomes based on case-study analysis,  Present a methodology to predict long-term LFGTE potential under various operating practices on a regional scale, and  Investigate costs and benefits of emitting vs. collecting LFG emissions with regards to operation strategies and regulations. iii The first-order empirical model appeared to be insensitive to the approach taken in quantifying the model parameters, suggesting that the model may be inadequate to accurately describe LFG generation and collection. The uncertainty values for the model were, in general, at their lowest within five years after waste placement ended. Because of the exponential nature, the uncertainty increased as LFG generation declined to low values decades after the end of waste placement. A methodology was presented to estimate LFGTE potential on a regional scale over a 25-year timeframe with consideration of modeling uncertainties. The methodology was demonstrated for the US state of Florida, and showed that Florida could increase the annual LFGTE production by more than threefold by 2035 through installation of LFGTE facilities at all landfills. Results showed that diverting food waste could significantly reduce fugitive LFG emissions, while having minimal effect on the LFGTE potential. Estimates showed that with enhanced landfill operation and energy production practices, LFGTE power density could be comparable to technologies such as wind, tidal, and geothermal. More aggressive operations must be considered to avoid fugitive LFG emissions, which could significantly affect the economic viability of landfills. With little economic motivation for US landfill owners to voluntarily reduce fugitive emissions, regulations are necessary to increase the cost of emitting GHGs. In light of the recent economic recession, it is not likely that a carbon tax will be established; while a carbon trading program will enforce emission caps and provide a tool to offset some costs and improve emission-reduction systems. Immediate action establishing a iv US carbon trading market with carbon credit pricing and trading supervised by the federal government may be the solution. Costs of achieving high lifetime LFG collection efficiencies are unlikely to be covered with revenues from tipping fee, electricity sales, tax credits, or carbon credit trading. Under scenarios of highly regulated LFG emissions, sustainable landfilling will require research, development, and application of technologies to reduce the marginal abatement cost, including:  Diverting rapidly decomposable waste to alternative treatment methods,  Reducing fugitive emissions through usage daily/intermediate covers with high oxidation potential,  Increasing the lifetime LFG collection efficiency, and  Increasing LFG energy value – for instance by producing high-methane gas through biologically altering the LFG generation pathway

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