John W. Schwegler

Visualizing multivariate functions, data, and distributions

The problem of visualizing a scalar-dependent variable that is a function of many independent variables is addressed, focusing on cases with three or more independent variables. A hierarchical axis using different metrics for each independent variable is used, as are hierarchical data symbols. The technique is described for the case in which each independent variable is sampled in a regular grid or lattice-like fashion (that is, in equal increments), but it can be generalized to a variety of less restrictive domains. Rather than presenting a formal mathematical description, the authors use a visual means of describing the technique for a simple three-dimensional data case, and then demonstrate by example how to extend it to higher dimensions. It is demonstrated that these techniques for plotting scalar fields on an N-dimensional lattice work for such data visualization tasks as the location of maxima, minima, saddle points, and other features, as well as for visually fitting multivariate data and the visual determination of dominant and weak or irrelevant variables.<<ETX>>

Salicylate-induced changes in cat auditory nerve activity.

The purpose of this study was to measure, in the cat, spontaneous auditory nerve (AN) activity before and after injection with sodium salicylate. Ten cats were anesthetized, and the AN and round window (RW) were surgically exposed. Electrodes were applied to allow recording from three channels, including bipolar electrodes and monopolar electrodes located directly on the auditory nerve, in addition to an RW electrode. Spectral averaging of the spontaneous activity was performed before and during salicylate treatment. An increase in spectral activity near 200 Hz was noted in all cats by 3 hours after salicylate injection. This activity was present in bipolar, monopolar, and RW records, and was temporarily diminished or eliminated by injection of lidocaine. No such spectral changes were found in saline-injected control animals. These results show promise of developing a noninvasive, objective, quantitative measure of tinnitus for studies in animals and in man.

Visualization and analysis of multi-variate data: a technique for all fields

A technique is presented for plotting large multivariate data sets that involves the mapping of n independent variable dimensions on to a single hierarchical horizontal axis with a single dependent variable being plotted on the vertical axis. The emphasis is on visual statistical analysis of either discrete variables or continuous variables that have been sampled on, or binned to, a regular n-dimensional lattice. The general applicability of the technique is discussed, and ways are explored of representing the hierarchical data-driven symbols that are particularly well suited to a variety of visual analysis tasks.<<ETX>>

The origin of the human auditory brain-stem response wave II

Auditory brain-stem responses (ABRs) were recorded from human subjects undergoing neurosurgical procedures which exposed the auditory nerve. Scalp recordings indicated that the latency of the negativity between waves I and II (In) and the latency of positive peak II (IIp) were shorter when the nerve was suspended in air than when the nerve was submerged in cerebrospinal fluid or saline, while earlier and later waves remained unaffected. These results could not be attributed to changes in stimulus or recording parameters or conduction velocity. Computational and somatosensory experimental evidence of stationary potentials generated by physical properties of the volume conductor, including changes in conductivity or geometry, are presented to develop a model of wave IIp generation. The results of this study suggest that wave IIp (and probably In) are manifestations of current flux asymmetries across conductivity boundaries created by the temporal bone-cerebrospinal fluid intradural space-brain-stem interfaces. The current flux asymmetries are generated as the propagating auditory nerve action potential crosses the conductivity boundaries. These results also indicate that the physical characteristics of the volume conductor and neural pathways must be considered when interpreting surface recorded evoked potentials.

Visualizing a scalar field on an N-dimensional lattice

The authors address the problem of visualizing a scalar dependent variable which is a function of many independent variables. In particular, cases where the number of independent variables is three or greater are discussed. A new hierarchical method of plotting that allows one to interactively view millions of data points with up to 10 independent variables is presented. The technique is confined to the case where each independent variable is sampled in a regular grid or lattice-like fashion, i.e., in equal increments. The proposed technique can be described in either an active or a passive manner. In the active view the points of the N-dimensional independent variables lattice are mapped to a single horizontal axis in a hierarchical manner, while in the passive view an observer samples the points of the N-dimensional lattice in a prescribed fashion and notes the values of the dependent variable. In the passive view a plot of the dependent variable versus a single parametric variable, which is simply the sampling number, forms the multidimensional graph.<<ETX>>

Preparation of YBa 2 Cu 3 O 7− x using barium hydroxide flux

High quality bulk YBa 2 Cu 3 O 7− x was synthesized by fusing stoichiometric amounts of yttrium and copper nitrates and barium hydroxide in air, using an ordinary Bunsen burner. The starting materials go through a short-lived liquid phase yielding a solid black product which was subsequently heat treated (900 °C, 18–24 h in air, followed by 500 °C, 5 h in O 2 ). These materials were greater than 99% phase pure with CuO as the only other phase and they exhibited a transition temperature of 92 K, a 15.5% perfect diamagnet response (field cooled). This synthesis represents an improvement over the much more labor and time intensive conventional methods in that it allows high quality materials of various compositions to be prepared quickly.

Preparation of YBa 2 Cu 3 O 7− x precursors from a fused eutectic of sodium and potassium hydroxides

A method for preparing YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} from the simultaneous thermal decomposition of the nitrates of yttrium, barium, and copper in an anhydrous fused eutectic of sodium and potassium hydroxide is described. This method eliminates the need for any mechanical grinding or the introduction of carbon containing anions. Products formed are fine powders ({similar to}1 {mu}m) having mole ratios 1.00 Y:2.00 Ba:3.06 Cu. X-ray diffraction analysis reveal that the initial products are Y(OH){sub 3}, BaO{sub 2}, and CuO, which when air calcinated/ oxygen annealed at 900--950 {degree}C form the superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}}. A mechanism is postulated for product formation as a function of reaction conditions.

Ten Minute Preparation Of Yba2Cu3O7−x Using Barium Hydroxide

High quality bulk YBa 2 CuO x−7 was synthesized by fusing stoichiometric amounts of yttrium and copper nitrates and barium hydroxide, in air, using an ordinary Bunsen burner. The starting materials go through a short-lived liquid phase yielding a solid black product which was subsequently heat treated, (900 C, 18–24 h, in air, followed by 500 C, 5 h., in O 2 ). These materials were greater than 99% phase pure with CuO as the only other phase and they exhibited a transition temperature of 92 K, a 15.5% perfect diamagnetic response (field cooled), 76% (zero field cooled). This synthesis represents an improvement over the much more labor and time intensive conventional methods in that it allows high quality materials of various compositions to be prepared quickly