Optoelectronic integration of a GaAs/AlGaAs bistable field effecttransistor (BISFET) and LED

The bistable field effect transistor (BISFET) is a novel inversion-channel switching device exhibiting abrupt current transitions and hysteresis in its output characteristics. The semiconductor structure of the BISFET is compatible with a range of electronic and optoelectronic devices. In this work, integration of a BISFET with an LED is reported. Both devices have been implemented on a single semiconductor substrate using a single fabrication sequence. The BISFET is used to current drive the LED. Abrupt transitions and hysteresis are seen in the optical output from the circuit in the range of gate voltage from 1.75 V to 1.9 V     

A strategy for designing error detection schemes for general datanetworks

The author presents a five-step methodology that provides insight into the order in which errors should be considered when designing an error detection scheme, which types of error detection mechanisms are most effective, and which layer should be responsible for detecting a given type of error     

Reciprocating flow ion exchange part II: Application to saline water softening

The “hardness” components in sea water can be considerably reduced by means of a new economical fixed bed technique called “Reciprocating Flow Ion Exchange”, when used in conjunction with a closed cycle exchanger-evaporator system. Removal of 87.9% of the calcium and 54.5% of the magnesium in sea water has been obtained with an overall flow rate of 5.0 U. S. g. p. m./sq. ft. Results from bench scale and a 5,000 g. p. d. pilot plant were identical. The virtually continuous cyclic steady-state process requires a small amount of exchanger (0.5 to 2% of the usual ion exchange methods, such as conventional fixed beds or fluidized beds). The effects of variation in operating parameters are discussed.     

High power pulsed lasers

Pulsed high power lasers can deliver sufficient energy on inertial fusion time scales (0.1–10 ns) to heat and compress DT fuel to fusion reaction conditions. Several laser systems have been examined for application to the fusion problem. Examples are Ndglass, CO₂, KrF, and I₂, etc. A great deal of developmental effort has been applied to the Ndglass laser and the CO₂ gas laser systems. These systems now deliver >10⁴ kJ and >20×10¹² W to inertial fusion targets. The Nova Ndglass laser is being constructed to provide >200 kJ and >200×10¹² W of 1 m radiation for fusion experimentation in the mid-1980s. For inertial fusion target gain, >100 times the laser input, it is expected that the laser must deliver 3–5 MJ of energy on the 10–20 ns time scale. This paper reviews the developments in laser technology and outlines approaches to construction of a 3–5 MJ driver.     

Mesoporous Silicon‐PLGA Composite Microspheres for the Double Controlled Release of Biomolecules for Orthopedic Tissue Engineering

In this study, poly(dl ‐lactide‐co‐glycolide)/porous silicon (PLGA/pSi) composite microspheres, synthesized by a solid‐in‐oil‐in‐water (S/O/W) emulsion method, are developed for the long‐term controlled delivery of biomolecules for orthopedic tissue engineering applications. Confocal and fluorescent microscopy, together with material analysis, show that each composite microsphere contained multiple pSi particles embedded within the PLGA matrix. The release profiles of fluorescein isothiocyanate (FITC)‐labeled bovine serum albumin (FITC‐BSA), loaded inside the pSi within the PLGA matrix, indicate that both PLGA and pSi contribute to the control of the release rate of the payload. Protein stability studies show that PLGA/pSi composite can protect BSA from degradation during the long term release. We find that during the degradation of the composite material, the presence of the pSi particles neutralizes the acidic pH due to the PLGA degradation by‐products, thus minimizing the risk of inducing inflammatory responses in the exposed cells while stimulating the mineralization in osteogenic growth media. Confocal studies show that the cellular uptake of the composite microspheres is avoided, while the fluorescent payload is detectable intracellularly after 7 days of co‐incubation. In conclusion, the PLGA/pSi composite microspheres offer an additional level of controlled release and could be ideal candidates as drug delivery vehicles for orthopedic tissue engineering applications.     

Extreme field-induced cyclotron mass variations in coupled double quantum wells

We observe deviations in the cyclotron effective mass m_c near the partial energy gap formed in strongly coupled GaAs double quantum wells (QWs) subject to in-plane magnetic fields B. In k-space, B shifts the two QW dispersion curves relative to one another, resulting in an anticrossing and opening the energy gap. This gives rise to large B-tunable distortions in the Fermi surface and density of states. This system is thus unique in that the Fermi surface and energy position of the gap can be controlled by sweeping B. Recently, Lyo has predicted that m_c undergoes large variations as the partial energy gap is moved through the Fermi level by B. By tilting our sample by a small angle θ, we introduce a small perpendicular magnetic field B, in addition to B, and analyze the temperature dependence of the resulting Shubnikov-de Haas oscillations to obtain m_c(B). Due to the strongly distorted dispersion near the gap, m_c is suppressed by more than a factor of 3 near the upper gap edge, and enhanced by 50% near the lower gap edge, in excellent agreement with the theory of Lyo. We also observe the quantum Hall effect in a double QW at a high, constant B.     

Results concerning the bandwidth of subliminal channels

In conjunction with a six-month research program on computer security, cryptology and coding theory hosted by the Isaac Newton Institute of Mathematical Sciences, University of Cambridge, Cambridge, U.K., a Workshop on information hiding was held from May 30 through June 1, 1996. This workshop was devoted to all aspects of information hiding - other than the usual cryptographic concealment of content, including steganography, subliminal channels, fingerprinting, covert channels, etc. Two surprising results pertaining to subliminal channels were presented or grew out of presentations made at this workshop. One is of interest to the secure communications protocol designer concerned with denying the use of subliminal channels, while the other is important to the designer, or user, of subliminal channels. The first raises the question of whether the notion of a “subliminal-free” communication channel is an oxymoron, i.e., is it possible to force the bandwidth of the subliminal channel to be truly zero? The second forces a more precise formulation of a conjecture the author had made that the bandwidth of a subliminal channel is logarithmically limited if the transmitter is unwilling to trust the subliminal receiver unconditionally. Motivated by these results, this paper reexamines the fundamental questions of the bandwidth available for subliminal communication as a function of the trust the transmitter has in the subliminal receiver and of a logically sound interpretation of the term “subliminal-free”     

The effect of varying barrier height on the operationalcharacteristics of 1.3-μm strained-layer MQW lasers

This paper presents an empirical study of the effects that barrier layer composition has on the operational characteristics of 1.3-μm-wavelength InGaAsP-InP multiquantum-well (MQW) strained-layer ridge-waveguide lasers. A systematic empirical investigation of how this design choice affects practical device operation was undertaken by examining threshold current, efficiency, and modal gain as a function of temperature in five different laser structures. The results of these studies indicate that small barrier heights improve device performance, despite the loss of electronic confinement in the shallow conduction band quantum wells. Indeed, it appears that carrier uniformity in the MQW structure may be improved by carrier redistribution due to thermal or tunneling effects, which in turn enhances the operation of the low barrier height structures