Fabrication and optimization of a whiskerless Schottky barrier diode for submillimeter wave applications

The following accomplishments were made towards the goal of an optimized whiskerless diode chip for submillimeter wavelength applications. (1) Surface channel whiskerless diode structure was developed which offers excellent DC and RF characteristics, reduced shunt capacitance and simplified fabrication compared to mesa and proton isolated structures. (2) Reliable fabrication technology was developed for the surface channel structure. The new anode plating technology is a major improvement. (3) DC and RF characterization of the surface channel diode was compared with whisker contacted diodes. This data indicates electrical performance as good as the best reported for similar whisker contacted devices. (4) Additional batches of surface channel diodes were fabricated with excellent I-V and reduced shunt capacitance. (5) Large scale capacitance modelinng was done for the planar diode structure. This work revealed the importance of removing the substrate gallium arsenide for absolute minimum pad capacitance. (6) A surface channel diode was developed on quartz substrate and this substrate was completely removed after diode mounting for minimum parasitic capacitance. This work continues with the goal of producing excellent quality submillimeter wavelength planar diodes which satisfy the requirements of easy handling and robustness. These devices will allow the routine implementation of Schottky receivers into space-based applications at frequencies as high as 1 THz, and, in the future, beyond

A new method for the determination of thin film porosity

Internal reflection spectroscopy may be used to determine presence of water in thin film pores. Presence of water in such pores is function of relative humidity and pore size. Thus, one can determine pore size by controlling humidity. Fluids with surface tension different from that of water can be used to detect pores

The beginnings of geography teaching and research in the University of Glasgow: the impact of J.W. Gregory

J.W. Gregory arrived in Glasgow from Melbourne in 1904 to take up the post of foundation Professor of Geology in the University of Glasgow. Soon after his arrival in Glasgow he began to push for the setting up of teaching in Geography in Glasgow, which came to pass in 1909 with the appointment of a Lecturer in Geography. This lecturer was based in the Department of Geology in the University's East Quad. Gregory's active promotion of Geography in the University was matched by his extensive writing in the area, in textbooks, journal articles and popular books. His prodigious output across a wide range of subject areas is variably accepted today, with much of his geomorphological work being judged as misguided to varying degrees. His 'social science' publications - in the areas of race, migration, colonisation and economic development of Africa and Australia - espouse a viewpoint that is unacceptable in the twenty-first century. Nonetheless, that viewpoint sits squarely within the social and economic traditions of Gregory's era, and he was clearly a key 'Establishment' figure in natural and social sciences research in the first half of the twentieth century. The establishment of Geography in the University of Glasgow remains enduring testimony of J.W. Gregory's energy, dedication and foresight

Recent spectroscopic findings concerning clay/water interactions at low humidity: Possible applications to models of Martian surface reactivity

A feasibility study assessing the utility of the adaptation of near infrared correlation spectroscopy to quantifying iron and adsorbed water in some clay-based Mars soil analog materials (MarSAM's). The work was intended to constitute Phase 1 of an approach to identifying optical analytical wavelength regions, not only for important mineral classes, but for chemically active centers within them. Many of these centers are common to unrelated mineral classes and of disproportionate influence relative to the mineral structure as a whole in determining the surface reactivity of mineral surfaces. We previously reported linearity between reflectance and total iron and total moisture over a large range of both key variables. We also discovered interesting relationships between the intensity of iron bands and the relative humidity of the systems. These relationships were confirmed. We also show that, in the low humidity range, reflectance is linearly dependent on a different kind of water from that best representing the full humidity range (the kind of water associated, in clays, with surface acidity). These relationships and the sensitivity and capability of quantitation of near infrared data indicate high promise with the production of reactive surface intermediates of products of surface reactions

Experimental apparatus for investigation of fan aeroelastic instabilities in turbomachinery

The application, installation, and monitoring of dynamic strain gage instrumentation on the rotating fan blades for subsonic stalled flutter mode of the first fan rotor are described. The engine installation, the modifications to the engine controls to obtain off schedule operation of the fan, engine aerodynamic instrumentation, and general data acquisition systems are discussed

Phase Transitions in the Spin-Half J_1--J_2 Model

The coupled cluster method (CCM) is a well-known method of quantum many-body theory, and here we present an application of the CCM to the spin-half J_1--J_2 quantum spin model with nearest- and next-nearest-neighbour interactions on the linear chain and the square lattice. We present new results for ground-state expectation values of such quantities as the energy and the sublattice magnetisation. The presence of critical points in the solution of the CCM equations, which are associated with phase transitions in the real system, is investigated. Completely distinct from the investigation of the critical points, we also make a link between the expansion coefficients of the ground-state wave function in terms of an Ising basis and the CCM ket-state correlation coefficients. We are thus able to present evidence of the breakdown, at a given value of J_2/J_1, of the Marshall-Peierls sign rule which is known to be satisfied at the pure Heisenberg point (J_2 = 0) on any bipartite lattice. For the square lattice, our best estimates of the points at which the sign rule breaks down and at which the phase transition from the antiferromagnetic phase to the frustrated phase occurs are, respectively, given (to two decimal places) by J_2/J_1 = 0.26 and J_2/J_1 = 0.61.Comment: 28 pages, Latex, 2 postscript figure

Low-momentum ring diagrams of neutron matter at and near the unitary limit

We study neutron matter at and near the unitary limit using a low-momentum ring diagram approach. By slightly tuning the meson-exchange CD-Bonn potential, neutron-neutron potentials with various $^1S_0$ scattering lengths such as $a_s=-12070fm$ and $+21fm$ are constructed. Such potentials are renormalized with rigorous procedures to give the corresponding $a_s$-equivalent low-momentum potentials $V_{low-k}$, with which the low-momentum particle-particle hole-hole ring diagrams are summed up to all orders, giving the ground state energy $E_0$ of neutron matter for various scattering lengths. At the limit of $a_s\to \pm \infty$, our calculated ratio of $E_0$ to that of the non-interacting case is found remarkably close to a constant of 0.44 over a wide range of Fermi-momenta. This result reveals an universality that is well consistent with the recent experimental and Monte-Carlo computational study on low-density cold Fermi gas at the unitary limit. The overall behavior of this ratio obtained with various scattering lengths is presented and discussed. Ring-diagram results obtained with $V_{low-k}$ and those with $G$-matrix interactions are compared.Comment: 9 pages, 7 figure

Delayed phlegmon with gallstone fragments masquerading as soft tissue sarcoma.

Complications from lost gallstones after cholecystectomy are rare but varied from simple perihepatic abscess to empyema and expectoration of gallstones. Gallstone complications have been reported in nearly every organ system, although reports of malignant masquerade of retained gallstones are few. We present the case of an 87-year-old woman with a flank soft tissue tumor 4 years after laparoscopic cholecystectomy. The initial clinical, radiographic and biopsy findings were consistent with soft tissue sarcoma (STS), but careful review of her case in multidisciplinary conference raised the suspicion for retained gallstones rather than STS. The patient was treated with incisional biopsy/drainage of the mass, and gallstones were retrieved. The patient recovered completely without an extensive resectional procedure, emphasizing the importance of multidisciplinary sarcoma care to optimize outcomes for potential sarcoma patients