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J T Connor

Publications and source records attributed to J T Connor.

11 recordsLinked to original sources
PubMed1998

Hybrid bilayer membranes in air and water: infrared spectroscopy and neutron reflectivity studies.

In this report we describe the fabrication and characterization of a phospholipid/alkanethiol hybrid bilayer membrane in air. The bilayer is formed by the interaction of phospholipid with the hydrophobic surface of a self-assembled alkanethiol monolayer on gold. We have characterized the resulting hybrid bilayer membrane in air using atomic force microscopy, spectroscopic ellipsometry, and reflection-absorption infrared spectroscopy. These analyses indicate that the phospholipid added is one monolayer thick, is continuous, and exhibits molecular order which is similar to that observed for phospholipid/phospholipid model membranes. The hybrid bilayer prepared in air has also been re-introduced to water and characterized using neutron reflectivity and impedance spectroscopy. Impedance data indicate that when moved from air to water, hybrid bilayers exhibit a dielectric constant and thickness that is essentially equivalent to hybrid bilayers prepared in situ by adding phospholipid vesicles to alkanethiol monolayers in water. Neutron scattering from these samples was collected out to a wave vector transfer of 0.25 A(-1), and provided a sensitivity to changes in total layer thickness on the order of 1-2 A. The data confirm that the acyl chain region of the phospholipid layer is consistent with that observed for phospholipid-phospholipid bilayers, but suggest greater hydration of the phospholipid headgroups of HBMs than has been reported in studies of lipid multilayers.

Lipid Bilayers↗
PubMed1997

A constrained neural network Kalman filter for price estimation in high frequency financial data.

In this paper we present a neural network extended Kalman filter for modeling noisy financial time series. The neural network is employed to estimate the nonlinear dynamics of the extended Kalman filter. Conditions for the neural network weight matrix are provided to guarantee the stability of the filter. The extended Kalman filter presented is designed to filter three types of noise commonly observed in financial data: process noise, measurement noise, and arrival noise. The erratic arrival of data (arrival noise) results in the neural network predictions being iterated into the future. Constraining the neural network to have a fixed point at the origin produces better iterated predictions and more stable results. The performance of constrained and unconstrained neural networks within the extended Kalman filter is demonstrated on "Quote" tick data from the $/DM exchange rate (1993-1995).

Algorithms↗
PubMed1997

Improved option pricing using artificial neural networks and bootstrap methods.

A hybrid neural network is used to predict the difference between the conventional option-pricing model and observed intraday option prices for stock index option futures. Confidence intervals derived with bootstrap methods are used in a trading strategy that only allows trades outside the estimated range of spurious model fits to be executed. Whilst hybrid neural network option pricing models can improve predictions they have bias. The hybrid option-pricing bias can be reduced with bootstrap methods. A modified bootstrap predictor is indexed by a parameter that allows the predictor to range from a pure bootstrap predictor, to a hybrid predictor, and finally the bagging predictor. The modified bootstrap predictor outperforms the hybrid and bagging predictors. Greatly improved performance was observed on the boundary of the training set and where only sparse training data exists. Finally, bootstrap bias estimates were studied.

Algorithms↗
PubMedDate not supplied

The artificial kidney in North America: George Murray and the Canadian connection.

Approximately 50 years after the Scottish chemist Thomas Graham described the process of selective diffusion in solutions (dialysis) in 1861, a Johns Hopkins University team led by John J. Abel purified animal blood using celloidin membranes. Termed "vividiffusion" by Abel, these limited but successful experiments were abandoned in 1914. The most successful artificial kidney machine was later devised by Willem J. Kolff in Holland during the early 1940s; this basic design later developed into a commercially successful venture in America. Other mechanical hemodialysis equipment was also invented, such as that of Canadian surgeon George Murray (1894-1976), who devised the first artificial kidney machine in North America in 1946. Blood to be filtered was gently pumped through a vertical helical coil of cellulose acetate tubing (the dialyzing membrane) placed in a salt-buffered tapwater solution. Four patients were treated in this manner, all of whose blood was purified; however, two of this group later died due to chronic kidney problems. Murray's artificial kidney was never developed commercially owing to Kolff's more efficacious design and, it is contended here, due to the failure of Canadians to capitalize on domestic technological innovations. It is also suggested that as it is an example of simultaneous invention, a further exploration of the artificial kidney might reveal insights into the historical development of modern medical technology.

Canada↗