Operation of fiber-grating semiconductor laser (FGL) has been stabilized by using the semiconductor optical amplifier which has a simple slant-waveguide structure. The emission wavelength, which depends on a temperature, shows hysteresis. Employing the directly modulated FGL at 2.5 Gb/s, transmission over 400 km in standard optical fiber has been successfully achieved.

Multi-input floating gate differential amplifier (FGDA) is proposed which can perform any convolution operation with differential structure and feedback loop. All operations are in the voltage mode. Only one terminal is required for the negative feedback which can suppress distortions due to mismatches of active elements. Possible applications include intelligent image sensor, where fully parallel DCT operation can be performed. A prototype chip is fabricated which is functional. A preliminary test result is reported.

The application of photonic technologies to packet switching offers the potential of very large switch capacity in the terabit per second range. The merging of packet switching with photonic technologies opens up the possibility of packet switching in transparent photonic media, in which packets remain in optical form without undergoing optoelectronic conversion. This paper reviews recent work on photonic packet switching. Different approaches to photonic packet switching and key design issues are discussed.

To enhance the extinction ratio (ER) of NRZ-to-inverted-RZ converter based on cross-gain compression of a semiconductor optical amplifier (SOA), a modified terahertz optical asymmetric demultiplexer (TOAD) is cascaded. ER is improved from 1.6-6.7 dB to 5.4-14.5 dB, depending on the intensity of input optical NRZ signal. The proposed NRZ-to-inverted-RZ converter enhances and regulates ER to a high value (14.5 dB) for very wide optical NRZ signal intensity range.

Recently, mobile computing has received much attention from database community. Sharing information among mobile users is one of the most challenging issues in mobile computing due to user mobility. Replication is a promising technique to this issue. However, adopting replication into mobile computing is a non-trivial task, since we are still facing other problems such as the lack in disk capacity and wireless network bandwidth used by mobile users. We have proposed a dynamic replica allocation strategy called User Majority Replica Allocation (UMRA) that is well suited to the modern architecture of mobile computing environment while avoiding such problems mentioned above. In this paper, we propose two relocation decision policies for UMRA and we provide a cost analysis for them. We also provide a cost analysis for another replica allocation strategy called Static Replica Allocation (SRA) for a comparison purpose.

The tera-bit order capacity of ultrahigh-speed and wide-band networks will become necessary to provide highly advanced multimedia services. In conventional networks, electronic circuits limit the speed capability of the networks. Consequently, all-optical networks are essential to realize ultrahigh-speed and wide-band communications. In this paper, we propose the configuration of an all-optical code division multiplexing (CDM) switching network based on self-routing principles and the structure of a nonlinear all-optical switching device as one of the key components for the network. We show that the required performances of the optical devices used in the CDM switching fabric are lower than those used in the TDM and illustrate the basic transmission characteristics of the switching device utilizing FD-BPM. To evaluate the multiplexing performance, we demonstrate the maximum number of channels under an error-free condition and the BER characteristics when the Gold sequence is applied as one of the CDM code sets, and show that the network of the sub-tera-bit order capacity is realizable by adopting TDM, WDM and CDM technologies. We also illustrate the packet assembly method suitable for self-routing transmissions and one of network architectures where the proposed switching fabric can be exploited.

Operation of fiber-grating semiconductor laser (FGL) has been stabilized by using the semiconductor optical amplifier which has a simple slant-waveguide structure. The emission wavelength, which depends on a temperature, shows hysteresis. Employing the directly modulated FGL at 2.5 Gb/s, transmission over 400 km in standard optical fiber has been successfully achieved.

Given two terms and their rewriting rules, an unreachability problem proves the non-existence of a reduction sequence from one term to another. This paper formalizes a method for solving unreachability problems by abstraction; i. e. , reducing an original concrete unreachability problem to a simpler abstract unreachability problem to prove the unreachability of the original concrete problem if the abstract unreachability is proved. The class of rewriting systems discussed in this paper is called β rewriting systems. The class of β rewriting systems includes very important systems such as semi-Thue systems and Petri Nets. Abstract rewriting systems are also a subclass of β rewriting systems. A β rewriting system is defined on axiomatically formulated base structures, called β structures, which are used to formalize the concepts of "contexts" and "replacement," which are common to many rewritten objects. Each domain underlying semi-Thue systems, Petri Nets, and other rewriting systems are formalized by a β structure. A concept of homomorphisms from a β structure (a concrete domain) to a β structure (an abstract domain) is introduced. A homomorphism theorem (Theorem1)is established for β rewriting systems, which states that concrete reachability implies abstract reachability. An unreachability theorem (Corollary1) is also proved for β rewriting systems. It is the contraposition of the homomorphism theorem, i. e. , it says that abstract unreachability implies concrete unreachability. The unreachability theorem is used to solve two unreachability problems: a coffee bean puzzle and a checker board puzzle.

The security of the ElGamal-type signature scheme is based on the difficulty of solving a discrete logarithm problem. If a random value that is introduced in the signing procedure is small, then the time for generating signature can be reduced. This strategy is particularly advantageous when a signer uses a smart card. In this paper, we show that the secret key can be computed efficiently if the random value is less than O(q) where q is the order of the generator.

This paper describes a new floating-point divider (FDIV), in which the key features of redundant binary circuits and an asynchronous clock scheme reduce the delay time and area penalty. The redundant binary representation of +1 = (1, 0), 0 = (0, 0), -1 = (0,1) is applied to the all mantissa division circuits. The simple and unified representation reduces circuit delay for the quotient determination. Additionally, the local clock generator circuit for the asynchronous clock scheme eliminates clock margin overhead. The generator circuit guarantees the worst delay-time operation by the feedback loop of the replica delay paths via a C-element. The internal iterative operation by the asynchronous scheme and the modified redundant-binary addition/subtraction circuit keep the area small. The architecture design avoids extra calculation time for the post processes, whose main role is to produce the floating-point status flags. The FDIV core using proposed technologies operates at 42. 1 ns with 0.35 µm CMOS technology and triple metal interconnections. The small core of 13.5 k transistors is laid-out in a 730µm 910 µm area.

Detecting security flaws is important in order to keep the database secure. A security flaw in object-oriented databases means that a user can infer the result of an unpermitted method only from permitted methods. Although a database management system enforces access control by an authorization, security flaws can occur under the authorization. The main aim of this paper is to show an efficient decision algorithm for detecting a security flaw under a given authorization. This problem is solvable in polynomial time in practical cases by reducing it to the congruence closure problem. This paper also mentions the problem of finding a maximal subset of a given authorization under which no security flaw exists.

This paper studies the problem of testing concurrent systems considered as blackboxes and specified using asynchronous Communicating Finite State Machines. We present an approach to derive test cases for concurrent systems in a succinct and formal way. The approach addresses the state space explosion problem by introducing a causality relation model and the concept of logical time to express true concurrency and describe timing constraints on events. The conformance relation between test cases and trace observed from the real system is defined, and a new test architecture as well as a test case application is presented according to the conformance relation defined. To improve verdict capability of test cases, the approach is enhanced by relaxing the unit-time assumption to any natural number. And a computationally efficient algorithm for the enhanced approach is presented and the algorithm is evaluated in terms of computational efficiency and verdict capability. Finally the approach is generalized to describe timing constraints by any real numbers.

Simple expressions for constriction resistance of multitude conducting spots were analytically formulated by Greenwood. These expressions, however, include some approximations. Nakamura presented that the constriction resistance of one circular spot computed using the BEM is closed to Maxwell's exact value. This relative error is only e=0. 00162 [%]. In this study, the constriction resistances of two, five and ten conducting spots are computed using the boundary element method (BEM), and compared with those obtained using Greenwood's expressions. As the conducting spots move close to each other, the numerical deviations between constriction resistances computed using Greenwood's expressions and the BEM increase. As a result, mutual resistance computed by the BEM is larger than that obtained from Greenwood's expressions. The numerical deviations between the total resistances computed by Greenwood's expressions and that by the BEM are small. Hence, Greenwood's expressions are valid for the total constriction resistance calculation and can be applied to problems where only the total resistance of two contact surfaces, such as a relay and a switch, is required. However, the numerical deviations between the partial resistances computed by Greenwood's expression and that by the BEM are very large. The partial resistance calculations of multitude conducting spots are beyond the applicable range of Greenwood's expression, since Greenwood's expression for constriction resistance of two conducting spots is obtained by assuming that the conducting spots are equal size. In particular, the deviation between resistances of conducting spots, which are close to each other, is very large. In the case of partial resistances which are significant in semiconductor devices, Greenwood's expressions cannot be used with high precision.

Connector contact resistance may become unstable if fretting occurs. Such motions result in the formation of insulating oxides on the surface of base metal contacts or organic polymers on contacts made of platinum group metals. These degradations are termed fretting corrosion and frictional polymerization, respectively. Motion may be caused by external vibration or fluctuating temperature. The lower the frequency of movement, the fewer the number of cycles to contact failure. Increasing the contact normal load or reducing the amplitude of movement may stabilize the connection. Tin and palladium and many of their alloys are especially prone to fretting failure. Tin mated to gold is worse than all-tin contacts. Gold and high gold-silver alloys that are softer when mated to palladium stabilize contact resistance since these metals transfer to the palladium during fretting; but flash gold coatings on palladium and palladium nickel offer marginal improvement for the gold often quickly wears out. Dissimilar metal contact pairs show behaviors like that of the metal which predominates on the surface by transfer. Contact lubricants can often prevent fretting failures and may even restore unlubricated failed contacts to satisfactory service.

This letter addresses how to set SIR targets higher than normally required, in order to mitigate the effect of signal-to-interference ratio (SIR) measurement error included in power control steps. We find that scaling up the SIR targets by 1 dB is conformable to resisting SIR measurement error for code division multiple access (CDMA) mobile systems.

Analysis of frequency-dependent lossy transmission lines is very important for designing the high-speed VLSI, MCM and PCB. The frequency-dependent parameters are always obtained as tabulated data. In this paper, a new curve fitting technique of the tabulated data for the moment matching technique in the interconnect analysis is presented. This method based on Chebyshev interpolation enhances the efficiency of the moment matching technique.

The importance of technology retargeting for hard IPs is getting increased. However, recent advances in process technologies make layout reuse too complicated to be done by conventional compactors. As an efficient approach, this paper proposes a flexible layout abstraction model and a new layout synthesis algorithm. The synthesis algorithm provides a concurrent procedure of detailed wiring, compaction, and transistor layout generation by using a scan line to get better layout results than conventional compactors. We have applied this method to the technology retargeting of actual cell layouts and have achieved quite good results comparable to hand-crafted designs.

The mapping from a global routing to a feasible detailed routing in a number of 2D array routing structures has been shown to be an NP-complete problem. These routing structures include the Xilinx style routing architecture, as well as architectures with significantly higher switching flexibility. In response to this complexity, a different class of FPGA routing structures called Greedy Routing Architectures (GRAs) have been proposed. On GRAs, optimally routing each switch box, in a specified order, leads to an optimal chip routing. Because routing each switch box takes polynomial time, the mapping problem on GRAs can be solved in polynomial time. In particular, an H-tree GRA with W2+2W switches per switch box (SpSB) and a 2D array GRA with 4W2+2W SpSB have been proposed. In this paper, we improve on these results by introducing an H-tree GRA with W2/2+2W SpSB and a 2D array GRA with 3.5W2+2W SpSB. These new GRAs have the same desirable mapping properties of the previously described GRAs, but use fewer switches.

This paper reports on an Intelligent CASE tool, applicable in a structured programming phase, or from detailed design to coding. This is automation of the bottom level in the hierarchical design process of detailed design and coding, where the largest man-hours are consumed. The main idea is that human designers use a CASE tool for the initial design of a software system, and the design knowledge is automatically acquired from the structured charts and stored in the knowledge base. The acquired design knowledge may be reused in designs. By reusing it, a similar software system may be designed automatically. It has been shown that knowledge acquired in this way has a Logarithmic Learning Effect. Based on this, a quantitative evaluation of productivity is made. By accumulating design experiences (e. g. 10 times), more than 80% of the detailing designs are performed automatically, and productivity increases by up to 4 times. This tool features universality, an essentially zero start-up cost for automatic design, and a substantial increase in software productivity after enough experiences have been accumulated. This paper proposes a new basic idea and its implementation, a quantitative evaluation applying techniques from Industrial Engineering, which proves the effectiveness of the proposed system.

A method is proposed for deriving a traffic characteristics model that can be used to forecast the traffic volume for intelligent telecommunication services. A sort of regression analysis with dummy variables is used to represent the service quantitatively and to construct the traffic characteristics model. Recursive least squares estimation, which is a special case of the Kalman filter, is applied to the traffic characteristics model to forecast the traffic volume. In the proposed modeling and forecasting, qualitative factors representing a certain service attribute are selected and using an information criterion, the model with the best fit is identified as the most suitable forecasting model. Numerical results using practical observation data showed that the proposed method produces an accurate forecast and is thus effective for practical use.