Effects of free convection and mass transfer on the flow past an impulsively moving infinite vertical circular cylinder

The effects of free convection and mass transfer are taken into account for the Stokes' problem of the flow near an impulsively moving infinite vertical circular cylinder. Expressions of the velocity, temperature, concentration and skin friction of the fluid in closed form are obtained by the Laplace transform technique. The results based on various values of the parameters Gr (Grashof number), Gm (modified Grashof number), Sc (Schmidt number) and Pr (Prandtl number) are given in graphical form. It will be seen that there is a rise in the velocity due to the presence of a foreign mass. But higher Sc yields the lower velocity and skin friction. As the radius of the circular cylinder approaches to infinite, the results presented in this paper agree with those of V.M. Soundalgekar's and C.K. Chen's etc. for the flow past an impulsively moving infinite vertical plate.     

Complex-subband transform for subband-based motionestimation/compensation and coding

This paper introduces the complex subband transform (CST) that can be applied for both subband signal decomposition and motion estimation, which are the two major processes in subband-based image sequence coding. In the experiments, we compare the CST-based subband motion compensation with conventional block matching motion compensation, and find that the former has (i) higher peak signal-to-noise ratio (PSNR) of the reconstructed images and (ii) lower prediction error entropy of the motion vectors.     

Photoactive Electro-Controlled Visual Perception Memory for Emulating Synaptic Metaplasticity and Hebbian Learning

In bionic technology, it has become an innovative process imitating the functionality and structuralism of human biological systems to exploit advanced artificial intelligent machines. Bionics plays a significant role in environmental protection, especially for its low energy loss. By fusing the concept of receptor-like sensing component and synapse-like memory, the photoactive electro-controlled optical sensory memory (PE-SM) is proposed and realized in a single device, which endows a simple methodology of reducing power consumption by photoactive electro-control. The PE-SM is the system built with the stacked atomically thick materials, in which rhenium diselenide serves as a robust photosensor, hexagonal boron nitride serves as a tunneling dielectric, and graphene serves as a charge-storage layer. With the features of the PE-SM, it performs synaptic metaplasticities under optical spikes. In addition, a simulated spiking neural network composed of 24 × 24 PE-SMs is further presented in an unsupervised machine learning environment, performing image recognition via the Hebbian rule. The PE-SM not only improves the neuromorphic computing efficiency but also simplifies the circuit-size structure. Eventually, the concept of photoactive electro-control can extend to other photosensitive 2D materials and provide a new approach of constructing either visual perception memory or photonic synaptic devices.     

Tunneling injection quantum-dot lasers with polarization-dependent photon-mediated carrier redistribution and gain narrowing

A theoretical and experimental study of a particular transverse-electric (TE) mode lasing mechanism of a tunneling injection InP quantum-dot (QD) laser is reported. In the experiment, the TE mode lasing action takes place at the first excited state of InP biaxially compressively strained QDs. This QD state is coupled to the ground state of two tensile-strained InGaP quantum wells (QWs) although the tensile-strained QW structure favors the transverse-magnetic (TM) polarization light emission. The measured TE and TM modal gain spectra show a typical QW gain evolution behavior at low injection currents, which can be theoretically modeled by the quasi-equilibrium of carrier distribution. When the injection current is increased near threshold, a TE gain narrowing and a simultaneous TM gain pinning are observed in the measured modal gain spectra, which cannot be explained via the quasi-equilibrium model. We propose a polarization-dependent photon-mediated carrier redistribution in the QD-coupled-QW structure to explain this TE and TM gain evolution behavior. When the injection current is just below threshold, the strong carrier depletion via stimulated emission due to coupling between the InP QD and InGaP QW states plays an important role in carrier redistribution, which depends on the optical transition energy and polarization. This concept of the polarization-dependent photon-mediated carrier redistribution explains the TE gain narrowing and TM gain pinning behavior. In addition, a coupled rate equation model is established, and the calculated polarization power ratio based on the coupled rate equations explains the experimental observation.     

Redshifting and broadening of quantum-well infrared photodetector'sresponse via impurity-free vacancy disordering

The partial intermixing of the well and barrier materials offers unique opportunities to shift locally the bandgap of quantum-well (QW) structures. We have demonstrated redshifting and broadening of the wavelength responses of bound-to-continuum GaAs and InP based quantum-well infrared photodetectors (QWIP's) after growth via impurity-free vacancy disordering (IFVD). A comprehensive set of experiments is conducted on QWIP's fabricated from both as-grown and multiple-quantum-well (MQW) structures. Compared to the as-grown detector, the peak spectral responses of the disordered detectors were shifted to longer wavelengths. The peak absolute response of the disordered GaAs based QWIP is lower by almost a factor of four. However, the responsivity characteristics of the disordered InP based QWIP show no major degradation. In general, with the spectral broadening taken into account, the overall performance of the disordered QWIP's has not dropped significantly. Thus, the postgrowth control of the QW composition profiles by impurity-free vacancy disordering offers unique opportunities to fine tune various aspects of a photodetector's response. Theoretical calculations of the absorption coefficient spectrum are in excellent agreement with the experimental data     

An optimal scheduling algorithm for testing interconnect using boundary scan

Systems will soon be built with ICs that conform with the IEEE 1149.1 boundary scan architecture. Due to the hierarchical nature of such systems, they may contain many boundary scan chains. These chains can be used to test the system, subsystem, and board interconnect. To reduce test time, the application of test vectors to these scan chains must be carefully scheduled. This article deals with problems related to finding an optimal schedule for testing interconnect. This problem is modeled using a directed graph. The following results are obtained: (1) upper and lower bounds on interconnect test time; (2) necessary and sufficient conditions for obtaining an optimal schedule when the graph is acyclic; (3) sufficient condition for obtaining an optimal schedule when the graph is cyclic; and (4) an algorithm for constructing an optimal schedule for any graph.This work was supported by Defense Advanced Research Projects Agency and monitored by the Office of Naval Research under contract No. N00014-87-K-0861. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the Defense Advanced Research Projects Agency or the U.S. Government.     

Defect Engineering in Ambipolar Layered Materials for Mode-Regulable Nociceptor

Defect engineering represents a significant approach for atomically thick 2D semiconductor material development to explore the unique material properties and functions. Doping-induced conversion of conductive polarity is particularly beneficial for optimizing the integration of layered electronics. Here, controllable doping behavior in palladium diselenide (PdSe₂) transistor is demonstrated by manipulating its adatom-vacancy groups. The underlying mechanisms, which originate from reversible adsorption/desorption of oxygen clusters near selenide vacancy defects, are investigated systematically via their dynamic charge transfer characteristics and scanning tunneling microscope analysis. The modulated doping effect allows the PdSe₂ transistor to emulate the essential characteristics of photo nociceptor on a device level, including firing signal threshold and sensitization. Interestingly, electrostatic gating, acting as a neuromodulator, can regulate the adaptive modes in nociceptor to improve its adaptability and perceptibility to handle different danger levels. An integrated artificial nociceptor array is also designed to execute unique image processing functions, which suggests a new perspective for extension of the promise of defect engineered 2D electronics in simplified sensory systems toward use in advanced humanoid robots and artificial visual sensors.     

A 1-17-GHz InGaP-GaAs HBT MMIC analog multiplier and mixer with broad-band input-matching networks

An InGaP-GaAs heterojunction bipolar transistor (HBT) analog multiplier/mixer monolithic microwave integrated circuit (MMIC) is developed that adopts a Gilbert-cell multiplier with broad-band input-matching networks to widen the bandwidth up to 17 GHz. This MMIC was fabricated using a commercially available 6-in InGaP-GaAs HBT MMIC process. It achieved a measured sensitivity of above 1100 V/W for an analog multiplier and a conversion gain of better than 9 dB for a mixer. It also demonstrated a lower corner frequency and noise than that of an InP HBT analog multiplier. The measured low-frequency noise was 10 nV/sqrt(Hz), which is about half of that of an InP HBT analog multiplier with a similar architecture. The corner frequency of the low-frequency noise was roughly estimated to be 15 kHz. The measured performance of this MMIC chip with gain-bandwidth-product (GBP) of 47 GHz rivals that of the reported GaAs-based analog multipliers and mixers. The high GBP result achieved by this chip is attributed to the HBT device performance and the broad-band input-matching network.