This thesis examines the two state structure of the solar wind and its influence upon proton temperatures. To examine this question, data from the Helios spacecraft are examined. The results from the data are interpreted in light of several theoretical models of the solar wind. In particular, it is found that the interplanetary heating of the protons observed by Helios is consistent with models that rely on extended deposition of energy and momentum in the form of Alfvenic waves. Analysis shows that between 4-10% of the time the data are consistent with two fluid models which do not include extended deposition of energy and momentum. For the rest of the data, the magnetic fluctuations are analyzed and it is found that there is dissipation of wave energy. Calculations show that the heating required by the protons can be accounted for by the apparent dissipation of Alfvenic wave energy. The relationships of temperature to velocity, to number density, and to momentum flux are also examined and are found to be consistent with a bifurcation of the solar wind based upon Alfven waves. A qualitative scenario for the generation of the two state solar wind wherein all the energy for the solar wind comes from convection in the sun is discussed.

In this thesis we derive an analytical relationship between the Earth's magnetospheric potential drop and the ionospheric conductance by adopting a simple two-dimensional model of a magnetic field draping around the tail magnetopause. Two methods are used: (1) matching currents through the tail magnetopause and the Earth's ionosphere in analogy with the Alfven wing at the Jovian satellite Io, (2) minimizing the total power that the solar wind loses to the Earth's magnetosphere. We find, in both cases, that the magnetospheric potential drop, $\Delta\phi\sb{\rm is}$, is inversely proportional to the ionospheric conductance, $\Sigma\sb{\rm is}$, and we compare this result to the revised result of the numerical model of Fedder and Lyon (1987) and to the conclusions of Hill et al. (1976) and Hill (1984). Considering the derived proportionality factor as a 'magnetosheath conductance', $\Sigma\sb{\rm msh}$, we determine that the high-latitude tail magnetospheric 'driver' acts as a current generator as opposed to a voltage generator.

In this thesis, we study the barotropic stability of the Bickley jet on the $ beta$-plane in the context of the linear and weakly nonlinear theory. / In the linear theory, the normal mode approach is used where we introduce a small wavelike perturbation to the mean parallel flow to obtain the Rayleigh-Kuo equation. Together with its boundary conditions, this equation is solved as an eigenvalue problem. As a result, new linear unstable sinuous modes are obtained within the narrow region bounded by two known neutral modes. We also locate a sinuous neutral mode which is singular and radiating, near the stability limit of $ beta=-2$. / An integral part of the thesis involves the application of the weakly nonlinear theory. The temporal evolution of the perturbation amplitude about the varicose neutral mode is studied by means of the Landau equation. Consequently, the value of the Landau constant is deduced which indicates a frequency reduction to the linear perturbation.

A specially-designed plasma chamber was constructed to study the operating characteristics of a dc plasma transferred arc struck between a fluid convective cathode and a water-cooled anode. The plasmagen gas consisted of pure argon and arc lengths as high as 7 cm were studied. / The arc voltage increased markedly with arc length and with an increase in the inlet velocity of the argon flow past the cathode tip, and much less with an increase in current. The effect of the gas velocity was minor at low velocities (1 to 3 m/s) but became important at higher velocities (20 to 60 m/s). / Arc length and gas velocity were again the major factors in the distribution of the arc energy. For long arcs and at high gas velocities, the energy emitted by the arc to the wall of the chamber was dominant, while for short arcs the energy absorbed by the water-cooled anode was greater. In all cases, the fraction of the input energy absorbed by the water-cooled cathode, or leaving the system as sensible heat in the exit gas was small. At the anode, the major contribution was from electron recombination, with convection heat transfer from the plasma somewhat less. Direct radiation from the plasma to the anode surface was very small. The recombination of the electron stream occurred on a very small area of the anode ((TURN) 5 mm in diameter). In spite of the energetic water cooling, appreciable vaporization took place on that area. / Appropriate instrumentation permitted the measurement of the stagnation-pressure and pressure distribution on the anode, and that of total heat flux and radiative heat transfer. From the latter, it was estimated that the plasma temperature just above the anode was in the range 10,000 - 12,000 K. / Preliminary experiments with an anode consisting of molten copper showed that the arc root was no longer fixed, but moved around continuously. The arc was otherwise quite stable, and its operating characteristics differed little from those reported for solid anodes, in spite of the greater extent of metal vaporization.

Single solid-stat nanopores have been fabricated in free-standing layers of amorphous silicon nitride. Using a focused electron beam and a focused ion beam, diameters ranging from about 0.7 nm to a few hundred nanometerswere achieved. Structural relaxation of nanopores fabricated by focused electron beam was observed. Depending on the initial diameter and on the length of the nanopores, two distinct phases for the relaxation process were found. An experimental setup for themeasurement of pressure-driven mass flow of helium through a single nanopore was built. The conductance of nanopores with diameters ranging from 25 nm to 315 nm was measured. A semi-phenomenological model was developed and it was shown to quantitatively describe the conductance of fluid through a short cylindrical nanopore. / Des nanopores ont été fabriqués dans de minces couches suspendues de nitrure de silicium amorphe. En utilisant un faisceau d'électrons focalisé et un faisceau d'ions focalisé, des diamètres entre 0.7 nm et 315 nm ont été obtenus. La relaxation struturelle de nanopores fabriqués par faisceau focalisé d'électrons a été observée. Dépendamment du diamètre inital du nanopore et de sa longueur, deux phases distinctes ont été identifiées. Un montage expérimental permettant la mesure de l'écoulement de masse d'hélium causé par l'application d'une différence de pression a été réalisé. La mesure de conductance de nanopores ayant un diamètre compris entre 25 nm et 315 nm a été effectuée. Un simple modèle phénoménologique permet de décrire quantitativement l'écoulement de gaz dans un court nanopore cylindrique.

We compute, to next-to-leading order in perturbation theory, the rate of energy loss suffered by a heavy quark moving nonrelativistically in the quark-gluon plasma. This quantity is essentially a measure of the scattering rates of this quark against plasma constituents, and of their efficiency in slowing it down. The next-to-leading order correction is sensitive to the physics of overlapping scatterings, as well as to the self-interactions of gauge fields with small momenta (of order the electric screening scale). We find the next-to-leading order correction to be remarkably large, suggesting that the perturbative series is unreliable unless the coupling constant of the theory assumes unrealistically small values.

The energy cascade process in turbulent flows is studied. Kolmogorov inertial range theories are critically reviewed and the multifractal characterization is discussed. Multiplicative cascade models are compared to the energy dissipation field (EDF) measured in the atmosphere. Landau's objection to the 1941 Kolmogorov theory is extended to the predictions of statistical fluid mechanics. The hypothesis $ rm Delta v( lambda L) { buildrel{d} over=} lambda sp{1/3} Delta v(L)$ is rejected with a statistical test. The moments $ rm langle( log varepsilon(L)) sp{p} rangle,$ where $ varepsilon$(L) denotes the EDF averaged over a volume of size L, are shown to be gaussian. For the EDF: Convergence tests showed that the exponents $ tau$(q) were not reliable for q $<$ 0; the correlations obey $ rm langle( mu sb{x}( delta)) sp{p}( mu sb{x+ delta}( delta)) sp{q} rangle propto delta sp{ gamma(p,q)}$ but $ gamma$ does not always equal the value obtained with a multinomial measure; a privileged scale ration r $ approx$ 1/2 is suggested by the prefactor oscillations of the correlation function. The implications of these results for the modelling of the EDF are discussed.

Nonlinear processes, such as passive scalar fluctuations driven by the turbulent wind field, exhibit extreme variability over a wide range of space-time scales and intensifies. As a resuit, of the complexity of those fields, the theoretical treatment of turbulence is a long-standing challenge of fluid mechanics. An empirical study of stochastic fluctuations in atmospheric aerosol concentration using state of the art lidar data is the subject of this thesis. The statistics of the fluctuations in the scalar field are closely related to those of the turbulent Avind field. Initially, a detailed review of the treatments of such turbulent atmospheric fields that is commonly found in the littérature is given. The main strands of research relevant to a statistical understanding of atmospheric dynamics are (1) isotropic hydrodynamic turbulence in 2D and 3D (with extensions), (2) buoyancy driven flows (3) gravity wave theories, (4) closures, (5) direct numerical simulations. It is argued that all current approaches treat the anisotropy of the dynamics and the characteristic intermittency inappropriately. Already existing - albeit limited - empirical evidence is then used to motivate the relevance of Generalized Scale Invariance and the Unified Scaling Model (e.g. [Schertzer and Lovejoy, 1983, 1984, 1985]) Avhich models turbulent atmospheric fields as anisotropic multifractal cascade processes. This model implies the anisotropic multiscaling of the fields over the entire range of spatial scales and that variability increases algebraically downscale leading to a highly intermittent field.

We introduce and study new lattice gas models of hydrodynamics to simulate thermal fluids in non-equilibrium. The new approach consists in modifying the conventional Lattice Gas Cellular Automata method for fluids by removing the constraints of the Fermi exclusion principle and by introducing internal potential energy levels for the particles. These modifications allow the effective employment of Monte-Carlo dynamics for the evolution of the models, so that the temperature is defined in a natural way, and the introduction of interactions becomes straightforward. / Because the transport properties of fluids determine their behavior in non-equilibrium, we study in detail the effect of our modifications on transport coefficients. We derive expressions for these coefficients in two ways: from Chapman-Enskog expansions and from linear response theory. Because of the potential energy, the transport properties are more similar to those of real fluids than are conventional LGCA models with kinetic energy only: the bulk viscosity is non-zero and thermal diffusion is well defined over a range of densities and temperatures. / We construct several models to illustrate the advantages and implications of our approach. One model is used to study the local temperature distribution in a simulation of Rayleigh Benard convection. Another is used to introduce interactions between particles and to simulate the 1st order phase separation of a fluid into the regions of low and high density. This latter model is also used to study the dynamics of interfaces between the phases. We observe the effects of inertia at the interface and demonstrate that the mean square width of an initially flat interface scales as t3/2 for late times t.

The basic characteristics of a transferred arc argon plasma were determined. A cathode assembly suitable for transferring the electric arc to a molten metal bath or to a cooled anode was designed and constructed to produce the plasma in open air. It included provision for the injection of secondary gas into the arc column. / The measured electrical characteristics indicated that the sustained voltage depended strongly on the arc length and much less on current. The inlet gas velocity past the cathode tip was determined to be an important operating parameter, rather than the volumetric gas flowrate. / The measurement of the axial and radial profiles of temperature was effected with (+OR-) 8% accuracy by a novel diagnostic technique based on the determination of the variations in the outputs of a two-wavelength pyrometer that views a small section of the plasma, as the latter is swept rapidly by a blocking element. Temperatures up to 18,500 K were observed on the axis of the plasma column. / A sweeping microprobe was used to measure the axial and radial profiles of velocity. Velocities up to 190 m/s were recorded. The presence of a relatively colder flow surrounding the plasma column was detected. Mass and energy balances performed by taking this flow into account agreed with the measured input rates.