Java语言及其虚拟机技术探讨

随着Internet的迅猛发展，Internet编程语言Java愈来愈成为计算机行业的焦点。本文在简述了Java的主要特点后，重点对Java最关键的技术──虚拟机进行了深入的探讨。     

Recursive simulation models of the semiconductor laser modulationcharacteristics for accurate performance evaluation of coherent opticalCPFSK systems

Modeling of the semiconductor laser nonuniform FM response and residual IM modulation is essential for the computer-aided design of coherent optical communication systems. This paper presents an accurate simulation model, in which the FM and IM responses are represented by recursive digital filters derived directly from measurements. A comparison with previous models of the bibliography reveals the advantages of the current approach. The proposed modeling procedure is applied in the case of a single-electrode DFB laser. This DFB model, in combination with a semi-analytical technique for the evaluation of the error probability, is used to study the influence of the modulation characteristics on the performance of a coherent heterodyne CPFSK system with differential receiver operating at 1 Gb/s. Theoretical and experimental results are in excellent agreement     

A 3-V, 2%-mW multibit current-mode ΣΔ DAC with 100 dBdynamic range

The area ratio of analog to digital for mixed-mode chip has been inversely proportional to the process design rule for a given dynamic range objective, in contradiction to the LSI trend. This paper presents a design approach to realize a high degree of size reduction with process design rules for analog circuitry and a signal processing architecture for digital circuitry. A five-level current-mode ΣΔ digital-to-analog converter (DAC) system reveals full scale total harmonic: distortion plus noise (THD+N) of -90 dB and dynamic-range of 100 dB at 3 V (low power of 22 mW). Analog-area down-scaling can be accomplished by this architecture to be 1.09 mm², using 0.6-μm double-poly double-metal (DPDM) CMOS. For the digital filter, a pipeline instruction sequence with multiplierless architecture also gives small area of 1.98 mm²     

Behavior of zirconium in the ZrOW(100) system at high temperature, studied by ISS, AES and work-function measurements

The behavior of zirconium atoms at the W(100) surface associated with oxygen adsorption at different sample temperatures has been studied by Auger electron spectroscopy (AES), ion scattering spectroscopy (ISS), and the relative change of the work function (Δф) measured by the onset of the secondary electron energy distribution. The results have revealed: (i) adsorption of zirconium onto the W(100) surface followed by the elevation of the sample temperature up to 1710 K in an oxygen partial pressure of 2.7 × 10⁻⁴ induces complete diffusion of zirconium atoms into the W(100) substrate; (ii) further exposure of oxygen induces co-existence of oxygen and tungsten on the surface at 1710 K, resulting in a work function of 4.37 eV; (iii) keeping the sample temperature at 1710 K, simple evacuation of the system has resulted in surface segregation of zirconium atoms to the surface to form a zirconium atomic layer on the top-most surface, reducing the work function to 2.7 eV. The results have revealed that this specific behavior of zirconium atoms at high temperature assures, with very good reproducibility, the highly stable performance and long service life of Zr---O/W(100)-emitters in practical use, even in a low vacuum of 10⁻⁶ Pa.     

Failure analysis of ULSI circuits using photon emission

A real-time failure analysis technique for ULSI circuits using photon emission is proposed. This technique utilizes a photon detection system combined with a circuit tester. Improved failure detection is achieved because the tester can bias arbitrary blocks in the ULSI chip. Detecting and correct process defects and design errors improves the reliability of the ULSI chip     

A 10 bit 20 MS/s 3 V supply CMOS A/D converter

A 10 bit CMOS A/D converter with 3 V power supply has been developed for being integrated into system VLSI's. In this A/D converter, redundant binary encoders named “twin encoders” enhance tolerance to substrate noise, together with employing differential amplifiers in comparators. The bias circuit using a replica of the amplifier is developed for biasing differential comparators with 3 V power supply. Subranging architecture along with a multilevel tree decoding structure improves dynamic performance of the ADC at 3 V power supply. The A/D converter is fabricated in double-polysilicon, double-metal, 0.8 μm CMOS technology. The experimental results show that the ADC operates at 20 MS/s and the twin encoders suppress the influence of substrate noise effectively. This ADC has a single power supply of 3 V, and dissipates 135 mW at 20 MS/s operation     

Multi-valued solutions and branch point singularities for nonlinear hyperbolic or elliptic systems

Multi-valued solutions are constructed for 2 × 2 first-order systems using a generalization of the hodograph transformation. The solution is found as a complex analytic function on a complex Riemann surface for which the branch points move as part of the solution. The branch point singularities are envelopes for the characteristics and thus move at the characteristic speeds. We perform an analysis of stability of these singularities with respect to perturbations of the initial data. The generic singularity types are folds, cusps, and nondegenerate umbilic points with non-zero 3-jet. An isolated singularity is generically a square root branch point corresponding to a fold. Two types of collisions between singularities are generic: At a “tangential” collision between two singularities moving at the same characteristic speed, a cube root branch point is formed, corresponding to a cusp. A “non-tangential” collision, between two square root branch points moving at different characteristic speeds, remains a square root branch point at the collision and corresponds to a nondegenerate umbilic point. These results are also valid for a diagonalizable n-th order system for which there are exactly two speeds. © 1993 John Wiley & Sons, Inc.     

Temporal integration method for image-processing-basedsuper-high-resolution image acquisition

The authors propose an image processing-based approach towards the development of a super-high-resolution image acquisition system. Imaging methods based on this approach can be classified into two main categories: a spatial integration imaging method and a temporal integration imaging method. With regard to the spatial integration imaging method, the authors have previously presented a method for acquiring an improved-resolution image by integrating multiple images taken simultaneously with multiple different cameras. They develop their work, aiming at a particular class of application where a user indicates a region of interest (ROI) on an observed image in advance, and apply a prototypal temporal integration imaging method. The prototypal temporal integration imaging method does not involve global image segmentation, but uses a subpixel registration algorithm which describes an image warp within the ROI, with subpixel accuracy, as a deformation of quadrilateral patches. The method then performs a subpixel registration by warping an observed image with the warping function recovered from the deformed quadrilateral patches. Experimental simulations demonstrate that the temporal integration imaging is promising as a basic means of high resolution imaging     

Design of wavelength-flattened coupler using a novel diagram

A novel diagram which describes the condition of 3 dB coupler is proposed. Using the proposed diagram, the design of a wavelength-flattened 3 dB directional coupler composed of a uniform coupled waveguide is investigated. Normalized waveguide parameters are introduced to characterize a five-layer planar waveguide. This enables us to generalize the discussion and to reduce the number of parameters required for characterizing a coupled waveguide. A broadband 3 dB coupler having 50±5% coupling ratio over a wavelength range of 1.1-1.7 μm is designed     

Decomposition methods: A new proof of convergence

We propose a new convergence proof of Adomian's technique based on properties of convergent series. Then we deduce some results about the speed of convergence of this method allowing us to solve nonlinear functional equations.