David A. Berkley

Computer simulation of charge dynamics in electron‐irradiated polymer foils

A computer simulation is described which allows the study of charge motion in thin polymer films of the type used for electret transducers. The simulation operates with a variety of possible boundary conditions and can include nonlinear transport terms as well as time‐varying radiation‐induced conductivity. Electron‐irradiation parameters, including radiation‐induced conductivity and electron deposition profiles, are computed using a single‐scattering Monte Carlo model of the polymer. The time‐dependent charge‐transport equations are solved by direct discretization of the partial differential equations. Using a fast minicomputer, the charge‐transport solutions run approximately in real time for realistic polymer parameters. Results are discussed for open‐ and short‐circuit irradiation and for charge recall experiments.

HuMaNet: An experimental human-machine communications network based on ISDN wideband audio

A humans sensory capacity to assimilate, perceive, and react to information is much smaller than the capacity of modern transport facilities that convey the information. Moreover, the volume of information and the complexity of the terminal used to access the information can overwhelm people. The challenge, then, is to match an information systems capabilities to those of our senses. Recent advances in speech-processing technology have made natural voice — our preferred means for information exchange — feasible for human-machine communications. We describe an experimental network, called HuMaNet, that is implemented on commercial ISDN transport. The HuMaNet system uses speech-processing technology to make communications easier and more natural. Spoken commands control the system, which combines image and audio compression, database management, hands-free teleconferencing, and text-to-speech synthesis. Although HuMaNet is only in its initial phase, it has proved a remarkably habitable environment for human control of a complex computer and communications system.

Time‐dependent radiation‐induced conductivity in electron‐irradiated Teflon foils

The radiation‐induced conductivity (RIC) of 2.5×10−3 ‐cm‐thick Teflon was measured using partially penetrating electrons with an energy of 40 keV. The behavior of the external currents generated during irradiation is expressed by a ’’generalized box model.’’ We explain, with this model, the experimentally observed buildup and decay of the RIC by using a time‐dependent conductivity σ(t)=σ0 (1−et/τs), where σ0 is the steady‐state conductivity and τs is the time constant of the RIC buildup. The time sequence in which voltage and irradiation are applied is found to give significantly different time effects; for irradiation first, the induced conductivity reaches a final value when the voltage is applied, while with voltage first, the conductivity increases with time after the radiation is turned on. Measurements are complex because the nonirradiated region of the foil is entirely blocking for electrons while it allows transport of holes. The peak value of the induced current, and thus of the induced conductiv...

Removing reverberative echo components in speech signals

A system is disclosed for automatically reducing reverberation in typical voice telecommunications systems. This system uses center clipping levels adaptive to the level of reverberation input speech. In one configuration, the voiceband is divided into two sub-bands and center clipping occurs only for the lower band; costs are reduced with surprisingly little transmission quality sacrifice. Clipping-level holdover circuitry with exponential decay appears to work well for a large variety of reverberant enclosures.

Influence of intraocular pressure on corneal fluid pressure, tissue stress and thickness.

In this paper a simple, idealized model is defined for the mechanical structure of the cornea of a mammalian eye. The model consists of thin anterior (epithelium and Bowmans zone) and posterior (Descemets membrane and endothelium) layers, which form the front and back boundaries, respectively, of the main body—the stroma. The thin boundaries are assumed to be essentially force-free while the stroma, which is considered as a mixture of fluid and tissue, is able to take up forces (fluid pressure, tissue stress across the cornea and tension along the cornea). From this model the elastic state of the cornea is studied for varying intraocular pressure. A simple equation is derived that relates the intraocular pressure, the corneal fluid pressure and the thickness of the cornea. It is shown that, under certain conditions, an increased intraocular pressure leads to tissue compression on the posterior side of the stroma and tissue expansion on the anterior side. This may be related to observations showing increased scattering from only the anterior half of the rabbit stroma under increased intraocular pressure. If the high intraocular pressure persists for a long time the theory predicts an increase of the corneal thickness. This prediction seems to be supported by recent clinical experiments.

Constant hole schubweg in Teflon FEP (fluorinated ethylene propylene copolymer)

The hole schubweg (distance travelled between deep trapping events) in Teflon FEP (fluorinated ethylene propylene copolymer) is determined by measuring the mean depth of charge injected from the polymer surface, with various fields applied to the sample. It is found that the mean-depth of the injected charge after deep trapping is independent of the electrical field strength from 0.04 to 0.4 MV/cm. The lower value of 0.04 MV/cm is determined by the sensitivity of the method.

Integrated information modalities for human/machine communication: HuMaNet, an experimental system for conferencing

Abstract Ease of use is a major consideration as information systems become more sophisticated. A number of technologies for human/machine communication now permit natural interaction with complex systems for communication and computation. These technologies include automatic speech recognition, speech synthesis, audio and image compression, hands-free sound pickup, and hypertext methods for data base management. A digital teleconferencing system is described which integrates these information modalities for hands-free, voice-interactive operation. The system is implemented for voice, image, and data communication over public-switched commercial digital transport, namely, basic-rate ISDN.

Rate theory of radiation-induced conductivity of fluoroethylene propylene (FEP)

With the widespread use of dielectric materials in high-radiation environments the behavior of the radiation-induced conductivity of dielectrics has acquired considerable importance. Numerous authors have investigated the dielectric response to short, intense bursts of radiation. The long-time behavior of the induced conductivity of insulators determines the amount of charge build-up which has been observed in polymeric materials covering space satellites exposed to electronic radiation found in space [1].

A digital teleconferencing system with integrated modalities for human/machine communication: HuMaNet

The design and implementation of a digital teleconferencing system that integrates a number of speech technologies together with image and data facilities is described. The aim is to provide a variety of sophisticated communication features that are easy to learn and use. The system is called HuMaNet, for human-machine network. The system is controlled totally and interactively hands-free by natural speech. The system combines the technologies of speech recognition, text synthesis, and talker verification with autodirective microphone arrays, image compression, data, and hypertext management to provide high-quality audio and image conferencing. The present public-switched transport capacity provides 2B+D, or two 64 kB/s circuit-switched channels (2B), and one 16 Kb/s packet-switched channel (D).<<ETX>>

Computer simulation of charge dynamics in electron-irradiated polymer foils

Electron irradiation in a good dielectric, such as a Teflon polymer, both deposits electrons in the material and, simultaneously, induces significant conductivity. Considerable work has been done to understand the resulting transient (e.g. see refs. 1–7) and steady-state charge behavior (e.g. see refs. 8 and 9). Most theoretical studies have assumed uniform, time-indëpendent, induced conductivity and electron-beam current (implying a single electron range) in the irradiated region. Two recent exceptions are the numerical studies of Matsuoka et al.,10 Beers11 and, Gross and Leal Fereira12 who have relaxed the single electron-range assumption for time-independent parameters. Also, with the exception of Gross and Oliveira7,8 and a later paper by Aris, Davies and Lewis,9 previous work has treated linearized transport equations only.