This study was undertaken to gain a greater understanding of the growth mechanism of carbon nanoclusters. A set of carbon nanocluster samples prepared by three different methods and under different conditions was characterized with respect to morphology, structure, composition, and related properties. Electron microscopy characterization techniques were used to identify these features. The carbon nanoclusters prepared by conventional arc discharge, modified arc discharge, and catalytic CO disproportionation appear quite different on the surface, but have features in common that this study emphasizes. For the understanding of the growth mechanisms of carbon nanoclusters of different morphologies, the dependence of growth features on the major processing parameters--carbon supply and carbon activity, reaction temperature, gas type and partial pressure, composition and materials involved--was interpreted systematically in a comparative manner. For the encapsulation of foreign materials into carbon cages, the ratio of the supply of carbon and encapsulants, the dimensions and configurations of the electrodes, the flow of a buffer gas across the carbon source, the nature and surface area of materials to be encapsulated or acting as catalyst were recognized as the basic components of a process that lead to properties of as-made materials such as the size distribution of the clusters, the degree of the carbonization of the encapsulants, and the predominant presence of certain morphologies. Regarding the comparison of the structural stability of different morphologies, the results of the post deposition treatments such as elevated high temperature annealing, nitric acid erosion, and electron beam bombardment provide further insight into the properties of this novel family of materials. Operating in certain domains of the parameter space, carbon-coated ferromagnetic nanoparticles, single-walled nanotubes, cylindrical multi-walled nanotubes, and conical fish-bone filaments were produced and comparatively characterized. A tentative discussion with the aim of confirming, expanding or modifying some growth models that have emerged from the work of the past was given in this dissertation. It is expected that this broad-based comparative study will advance the understanding of the growth mechanism to a point where some of the technological promise of the carbon nanoclusters may be realized.

Lightning, a familiar phenomenon on Earth, may also occur at other times and locations in our solar system. It has been suggested as a mechanism for forming chondrules, millimeter-sized beads of glassy silicate found in primitive meteorites formed in the early solar system 4.5 billion years ago. It has also been detected in Voyager images of Jupiter, and there is evidence that it may occur on other planets as well, including Venus, Saturn and Neptune. The mechanism believed to produce lightning discharges on Earth, and possibly other planets, is charge production by collisions of ice particles, followed by gravitational separation of oppositely-charged large and small particles. This work examines the possibility of the occurrence of lightning discharges in the atmospheres of Jupiter and Neptune as well as in the protoplanetary nebula (PPN) of the early solar system by modeling charge separation and growth of the electric field. The model is also applied to the Earth as a test of its predictive power. It is found that the model can reproduce the correct timescale, particle charge and electric field magnitude seen in terrestrial lightning. The model also predicts lightning on Jupiter at the 3-5 bar level provided that the local water abundance is greater than the solar value. This is a much higher abundance than measured by the Galileo probe into Jupiter's atmosphere, which suggests that the water content measured by the probe does not apply to the entire planet. An application of the model to Neptune's water and NH₄SH clouds finds that lightning is unlikely in these clouds due to the large electric field required for electrical breakdown. Lightning may be possible in the overlying H₂S-NH₃ cloud provided that these substances can undergo collisional charge exchange with a magnitude at least 1% of that found in water ice. In the protoplanetary nebula, it appears that large-scale precipitation-induced lightning could not have occurred, due to the small mass density, low temperature and high electrical conductivity of the surroundings. This is a robust conclusion that does not depend sensitively on the values of the parameters involved.

With an always-increasing need for higher integration, the wireless industry poses challenges regarding miniaturization and high performance circuitry. In addition, the solutions require compatibility with the rest of the design for integration and manufacturing. The present work depicts the progress toward a novel, high quality, one-pole filter-resonator operating in the 5.6-5.8 GHz range. Quality factors up to 640 are demonstrated on Silicon planar structures with volume of 177 mm³. Further size reduction yielded a volume of 24.5 mm³ and a quality factor of 186.

No description available.

Increasing attention has been given to the preparation and study of compounds with linear chains of metal atoms surrounded by four ligands. The majority of linear trimetal complexes are supported by dpa, the anion of dipyridylamine, having the general formula M3(dpa)4X2, where X is typically a monoanion. It has been shown that the behavior of the trinuclear system is far more complicated than might have been expected. Specifically, both symmetrical and unsymmetrical chains can occur and the interpretation of the magnetic properties of certain compounds has been a challenging task. Present in this dissertation is the bulk of work completed on an exploration of syntheses and characterizations of linear trichromium and trinickel compounds with different types of tridentate ligands. These ligands include 2,6-bis(phenylamino)pyridine,H2BPAP, (the corresponding dianion of this is denoted by BPAP) and a set of five unsymmetrical formamidines with different organic substituents ranging from strong electron-donating groups, such as -OCH3, to electron-withdrawing groups, e.g., F. Ligands impact on the trimetal chain in various ways. In the case of the M3(BPAP)42- ions, there are no axial interactions because these anionic species do not attract electron donating ligands. Thus they have properties which are different from those of M3(dpa)4X2 molecules. Most notably, the Ni3(BPAP)42- ion is diamagnetic and all three nickel ions can be described as square-planar, low-spin NiII centers. ivWhen unsymmetrical formamidines are used to support linear trichromium chains with a Cl anion at each end, the separation between terminal chromium atoms is significantly longer (ca. 0.15 - 0.25) than those in trichromium compounds reported earlier. Moreover, the unsymmetrical formamidinates tend to support symmetrical trichromium chains, while the rest of the known tridentate ligands typically yield unsymmetrical Cr36+ chains. The synthesis and structural studies of trinickel compounds with unsymmetrical formamidines are also presented.

The debate over the origin of the ultrafast demagnetization has been intensively active for the past 16 years. Several microscopic mechanisms have been proposed but none has managed so far to provide direct and incontrovertible evidences of their validity. In this context I have proposed an approach based on spin dependent electron superdiffusion as the driver of the ultrafast demagnetization. Excited electrons and holes in the ferromagnetic metal start diffusing after the absorption of the laser photons. Being the material ferromagnetic, the majority and minority spin channels occupy very different bands. It is then not surprising that transport properties are strongly spin dependent. In most of the ferromagnetic metals, majority spin excited electrons have better transport properties than minority ones. The effect is that majority carriers are more efficient in leaving the area irradiated by the laser, triggering a net spin transport. Recent experimental findings are revolutionising the field by being incompatible with previously proposed models and showing uncontrovertibly the sign of spin superdiffusion. We have shown that spin diffusing away from a layer undergoing ultrafast demagnetization can be used to create an ultrafast increase of magnetization in a neighboring magnetic layer. We have also shown that optical excitation is not a prerequisite for the ultrafast demagnetization and that excited electrons superdiffusing from a non-magnetic substrate can trigger the demagnetization. Finally we have shown that it is possible to control the time shape of the spin currents created and developed a technique to detect directly spin currents in a contact-less way.  The impact of these new discoveries goes beyond the solution of the mystery of ultrafast demagnetization. It shows how spin information can be, not only manipulated, as shown 16 years ago, but most importantly transferred at unprecedented speeds. This new discovery lays the basis for a full femtosecond spintronics.

Using the focused ion beam sputtering capabilities of Scanning Ion Microscope with Polarization Analysis (SIMPA), arrays of regular shaped particles with sizes in the order of 10$\mu$m are produced from a 35nm thick $\rm Ni\sb{83}Fe\sb{17}$ film with in-plane uniaxial anisotropy, The aspect ratio of the particles range from bar-like (50:1) to island-like (1.4:1). Their magnetic properties are studied with longitudinal magneto-optical Kerr effect. Structures with different geometries are found to display fundamental differences in their magnetic behavior. Two types of geometry induced changes in the magnetization reversal process are discerned. These changes are found to agree with a theoretical model based on micromagnetic effects. Light is scattered into a regular diffraction pattern from these structures. The magneto-optical effects in the various spectral orders are examined; they are found to produce similar hysteresis curves as the specular beam.

Mathematical models of rabbit atrial and ventricular myocytes that are based on quantitative voltage clamp data from emzymatically isolated cardiac myocytes have been developed. These models are capable of accurately simulating the transmembrane ionic currents recorded in response to a step change in membrane potential (whole-cell voltage clamp response), the nonpropagated membrane action potential (MAP), and the frequency-dependent action potential waveshape changes occurring in response to variations in rate of stimulation. Rectangular pulse, ramp and action potential voltage-clamp measurements of the transmembrane ionic currents have allowed us to model a number of processes thought to be important during repolarization. These computations provide important biophysical insights into the electrophysiological activity of atrial and ventricular cells and their associated intra- and extracellular ionic concentration changes. The present model also has useful predictive capabilities. We have used the model to: (1) estimate the intracellular $Ca\sp{2+}$ transient in these myocytes and to compare the relative occupancy of the $Ca\sp{2+}$ binding sites in the contractile proteins with known cellular mechanical activity, and (2) predict the response of the atrial cell to potassium current blockade via $BaCl\sb2$ to the bathing medium.

Epitaxial films of hcp Tb(0001) on bcc W(110) substrates are prepared and their geometric, electronic and magnetic properties are studied. The atomic flatness and cleanness and the single-crystalline state of the W(110) substrates and the Tb films are checked using scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and low-energy and high-energy electron diffraction (LEED and RHEED). Using electron capture spectroscopy (ECS), the surface electron spin polarization of the Tb(0001) films is studied as a function of temperature. The topmost layer is found to order ferromagnetically below a surface Curie temperature T$\sb{\rm C\sb s}$ = 249.96 K, which lies above both the bulk Curie and Neel temperatures T$\sb{\rm C\sb b}$ = 220 K and T$\sb{\rm N\sb b}$ = 228 K, respectively, and exhibits strongly non-monotonic behavior close to 245 K. Novel critical behavior is observed near T$\sb{\rm C\sb s}$, suggesting strong surface anisotropies, in accord with a recently predicted and previously unobserved surface phase transition.

Two sensors that have been proposed for use on a space robot are cameras and radar. Considered individually, neither of these sensors provides enough information for a computer to derive a good surface description of a remote object. Their combination, however, can produce a complete surface model. The lack of atmosphere in space presents special problems for optical image sensors. Frequently, edges are lost in shadow and surface details are obscured by diffraction effects caused by specularly reflected light. An alternate sensor for space robotic applications is microwave radar. The polarized radar cross-section (RCS) is a simple, well-understood, microwave measurement that contains limited information about a scattering object's surface shape. These two data sets are fused through an error minimization procedure. First, an incomplete surface model is derived from the camera image. Next, the unknown characteristics of the surface are represented by some parameter. Finally, the correct value for this parameter is computed by iteratively generating theoretical predictions to the RCS and comparing them to the observed value. A theoretical RCS may be computed from the surface model in several ways. One such RCS prediction technique is the method of moments. The method of moments can be applied to an unknown surface only if some shape information is available from an independent source. Here, the camera image provides the necessary information. When the method of moments is used to predict the RCS, the error minimization algorithm will converge in most cases. By combining the microwave and optical information in this way, the shapes of some three-dimensional objects have been accurately recovered. Simulations and experiments were performed on plates, ellipsoids, and an arbitrary curved object. Simulations show that error in the recovered shapes is very small when the RCS measurement error is not too large. Experiments prove that the RCS can be measured within this tolerance. In general, this investigation has shown the usefulness of sensor fusion applied to the shape reconstruction problem in space. Furthermore, a specific framework has been developed and proved effective for integrating the two types of sensors that are typically found on space vehicles.