Transmission characteristics of finite-width conductor-backedcoplanar waveguide

This paper presents theoretical and experimental results for a finite-width conductor-backed coplanar waveguide (FW-CBCPW). The guiding characteristics of FW-CBCPW are investigated first by the rigorous method of mode matching. An FW-CBCPW through line is then placed within a test fixture commonly used in laboratories, and the scattering parameters of the through line are obtained theoretically by approximating the FW-CBCPW as a simple system of coupled transmission lines. Experimental results are shown to agree very well with the theoretical ones. In particular, the anomalous behavior observed in the transmission characteristic of the through line is related to the resonant phenomenon of the terminated side planes which are short-circuited at both input and output ends due to the test fixture. Finally, a technique of mode suppression in the side-plane regions is suggested for the improvement of signal transmission over a broad band of frequency spectrum. The effects of extra higher order modes on the transmission characteristics at high frequencies are also discussed     

Exploratory factor analysis of MRI brain structure measures in schizophrenia

Much of the literature shows various regional structural brain abnormalities in schizophrenia, but the complexity and variability of brain makes it difficult to determine how these regions are related. Statistical methods which estimate factors underlying patterns of covariance have not been widely used, but could be useful for analyzing such complex data. We applied exploratory and confirmatory factor analysis procedures to specific cortical and subcortical regional brain volume measures from MRI data in 60 normal and 44 schizophrenic subjects. Basal ganglia, heteromodal cortical gray, and medial temporal lobe factors were present in both the normal and the schizophrenia groups. The factor structure observed in the normal group showed a high degree of bilateral symmetry which is present but disrupted in the schizophrenia group. In the bilateral data, the disruption is most pronounced with medial and lateral temporal lobe structures including entorhinal cortex and anterior and posterior superior temporal gyri. There was a significant correlation between the basal ganglia factor and the heteromodal cortical gray factor in the normal group that was not present in the schizophrenia group. In the unilateral data, left posterior superior temporal gyrus did not load onto any factor in the schizophrenia group. Confirmatory factor analyses showed significant differences between the two groups in factor structure. A number of specific brain regions are affected in schizophrenia, and structural relationships between groups of regions also are abnormal. The results suggest that heteromodal dorsolateral prefrontal and superior temporal cortical gray regions are structurally related, whereas inferior parietal cortical gray is less so. These results should be viewed as preliminary as the ratio of parameters to subjects was relatively low, and replication is needed. However, the results demonstrate the potential utility of latent structure methods such as factor analysis in study of complex relationships in neuropsychiatric data.     

The effect of uniaxial stress on the periodic morphology of coherent gamma prime precipitates in nickel-base superalloy crystals

The periodic morphology of cube shaped, coherent γ ′ [Ni₃(Al, Ti)] precipitates in a representative nickel-base superalloy single crystal is shown to be influenced by the application of a 〈100〉 oriented uniaxial stress during annealing at elevated temperature. Furthermore, the stress annealed γ′ morphologies depend on the stress sense. Tensile and compressive stress annealing result in a directional coarsening of precipitates, and then agglomeration to form γ ′ precipitate plates with broad faces aligned perpendicular to the stress axis and precipitate parallelepipeds with long axes parallel to the stress axis, respectively. In explaining the morphological changes that occur during stress annealing, we consider two driving forces: i) a driving force due to changes in the stress-free shape of the specimen, and ii) a driving force due to changes in the effective modulus of the specimen. The first, which depends on a difference in the elastic constants and the lattice parameters of the two phases, is apparently the dominant driving force for the observed morphological changes in a stress annealed superalloy. The second, which depends only on a difference in elastic constants, may be important in alloys with elastically soft, incoherent inclusions such as pores. Formerly Section Supervisor, Advanced Materials Research and Development Laboratory, Pratt & Whitney Aircraft.     

Induced liquid phase mixing due to bubble motion at low gas velocity

Liquid phase mixing induced by gas bubbles at low gas velocities was studied experimentally. An experimental technique based on the principle of spectrophotometry was developed and applied in the experimental work. Experimental evidence suggests that the mixing phenomenon can be described as a diffusive process characterized by an effective diffusivity which is found to be a linear function of superficial gas velocity.     

Bilayer film model for the interaction between adsorption and bacterial activity in granular activated carbon columns part I: Formulation of equations and their numerical solutions

The diffusion-reaction film model proposed by Andrews and Tien (1981) for the interaction between adsorption and bacterial activities in carbon columns was generalized. The microbial film was assumed to be composed of two regions of distinctively different microbial activity, depending on the presence or absence of dissolved oxygen. Governing equations were derived to describe the dynamics of the carbon columns in which the interaction between adsorption and bacterial growth and methods for solving these equations were developed.     

Resonant phenomena in conductor-backed coplanar waveguides(CBCPW's)

A thorough and systematic investigation of resonant phenomena in conductor-backed coplanar waveguides (CBCPWs) is reported. A rigorous three dimensional full-wave space-domain integral equation method accompanied by an S-parameter extraction technique is used. A series of measurements has been conducted to confirm the theoretical results. A patch-resonator model and a microstriplike (MSL) model are employed to understand the origin of resonance existing in one of the test circuits. The 3-D program is also invoked by displaying the current distributions to help visualize how the CBCPW test circuits work at both through and resonant states. The results obtained validate the conclusions drawn for the patch-resonator model and the MSL model     

Effect of axial conduction and metal-helium heat transfer on the local stability of superconducting composite media

The growth or collapse of a local normal zone in a superconducting winding structure saturated with single phase liquid helium (composite superconductor) is studied analytically. The history of a given temperature disturbance is derived from the solution to the transient heat conduction equation in a one-dimensional infinite solid with temperature dependent rate of internal heat generation, communicating laterally with a channel filled with stagnant helium. The combined diffusion by axial heat conduction and lateral heat transfer to the helium channel and its effect on the collapse or growth behaviour of a local disturbance is presented analytically. The paper develops a theoretical criterion for local stability (recovery) expressed in terms of dimensionless groups accounting for heat generation in the normal zone, metal axial conduction cooling, lateral cooling provided by the helium channel and, most importantly, the amount and spatial extent of the sudden release of energy responsible for the local disturbance.     

The migrational characteristics of the cusp-oriented α/κ interface in the Cu-Si system

The mobility of the coherentα/κ boundaries in the copper-silicon system was studied in a Cu plus 5.16 wt pct Si alloy with a lamellar microstructure. A new resistometric technique was employed to study the isothermal kinetics ofα/κ interphase boundary migration as a function of driving force at two reaction temperatures, 702° and 568°C. The driving force was shown to be linearly related to the temperature change, δT, and the experimental results show that the functional relationship between mobility and δT exhibits an initial linear dependence followed by a sharp rise in mobility at higher values of δT. Upquench and down-quench results were found to be equivalent, implying that the mechanism for boundary motion is independent of whether the boundary is moving into theα or into theκ phase. The results demonstrate that theα/κ interface does not move normal to itself by the long range bulk diffusion of silicon at low values of δT during the initial periods of the reaction times. A pole mechanism with its associated dislocation node configuration, consisting ofa/2〈112〉 andc[00.1] pole dislocations anda/6〈112〉 transformation partial, is proposed as the mechanism for the migration of the coherent fcc/hcp boundary in the range of small δT. The results obtained at the different reaction temperatures are consistent with the mechanism proposed, and quantitative agreement exists between the experimental and predicted mobilities. The sharp rise in mobility at larger values of δT could not be explained in terms of the pole mechanism. Attempts to rationalize this behavior in terms of a two dimensional nucleation model were not successful since unrealistically low values of surface energy would be required. Formerly with Carnegie-Mellon University Formerly Professor, Carnegie-Mellon University This paper is based on a portion of the Ph.D. Thesis submitted by J. K. TIEN to the Department of Metallurgy and Materials Science, Carnegie-Mellon University, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Metallurgy and Materials Science.