In this paper, we discuss an abstraction method for Petri nets based on an equivalence of firing sequences of a specified subnet or a specified subset of transitions. Specifically, a method is presented to generate an equivalent net which preserves firing sequences of a specified subnet or a specified subset of transitions. The abstraction can be applied to an efficient behavioral analysis of concurrent systems constructed by composition of modules such as communication networks and Flexible Manufacturing Systems (FMS).

A continuous-wave ultrasonic Doppler system using wide field ultrasound transducers was applied to telemeter blood velocity from the carotid artery of exercising subjects. Velocity spectrogram was obtained by Hanning windowed fast Fourier transformation of the telemetered data. Distortion caused by a high-pass filter and transducers in the telemetry system was discussed in the paper. As the maximum Reynolds number in our experiment was 1478 which is smaller than the critical level of 2000, the blood flow should be laminar. Spatial velocity profiles were then reconstructed from the velocity spectrogram. In this paper, we defined a converging index Q of the velocity spectrum to measure the bluntness of the spatial velocity distribution across the blood vessel. Greater Q, the blunter the velocity profile will be. Simulation results for spatial velocity distributions of theoretical parabolic flow and Gaussian-distribution spectra with varied Q value showed that the cut-off effect by a high-pass filter of cut-off frequency fc=200Hz in our system could be ignored when the axial velocity is larger than 0.30 m/s and Q is greater than 2.0. Our experimental results, in contrast to those obtained from phantom systems by us and by Hein and O'Brien, indicate that the distribution of blood velocity is much blunter than previously thought. The Q index exceeded 10 during systole, whereas it was 0.5 in parabolic flow. The peak of Q index lagged behind that of axial blood velocity by approximately 0.02s. The phase delay of the Q index curve might be due to the time needed for the red blood cells to form the non-homogeneous distribution.

This paper discusses an all-optical tank circuit that uses the comb-shaped gain spectrum generated by a Brillouin amplifier. The theory of timing clock extraction is shown for two cases: with two gains and with three gains. In both cases, the waveform of the extracted timing clock is simulated. According to the simulation, unlike an ordinary tank circuit, the amplitude of the extracted clock is not constant even though the quality factor (Q) is infinite. The extracted clock is clearly influenced by the pattern of the original data stream if the Brillouin gain is finite. The ratio of the maximum extracted clock amplitude to the minimum extracted amplitude is calculated as a function of Brillouin gain. The detuning of the pump light frequency is also discussed. It induces not only changes in the Brillouin gain, but also phase shift in the amplified light. The relation between the frequency drift of the pump lights and the jitter of the extracted timing clock is shown, in both cases: two pump lights are used and three pump lights are used. It is numerically shown that when the all pump lights have the same frequency drift, i.e., their frequency separation is constant, the phase of the extracted clock is not influenced by the frequency drift of the pump lights. The operation principle is demonstrated at 5Gbit/s, 2.5Gbit/s, and 2Gbit/s using two pumping techniques. The parameters of quality factor and the suppression ratio in the baseband domain are measured. Q and the suppression ratio are found to be 160 and 28dB, respectively.

In this letter, we present the evaluation of an option-based learning algorithm, developed to perform a conflict-free allocation of calls among cars in a multi-car elevator system. We evaluate its performance in terms of the service time, its flexibility in the task-allocation, and the load balancing.

This paper proposes a constant-power adder based on multiple-valued logic and its application to cryptographic processors being resistant to side-channel attacks. The proposed adder is implemented in Multiple-Valued Current-Mode Logic (MV-CML). The important feature of MV-CML is that the power consumption can be constant regardless of input values, which makes it possible to prevent power-analysis attacks using dependencies between power consumption and intermediate values or operations of the executed cryptographic algorithms. In this paper, we focus on a multiple-valued Binary Carry-Save adder based on the Positive-Digit (PD) number system and its application to RSA processors. The power characteristic of the proposed design is evaluated with HSPICE simulation using 90 nm process technology. The result shows that the proposed design can achieve constant power consumption with lower performance overhead in comparison with the conventional binary design.

We performed numerical analyses on structure sensitive field emission properties of our proposing plasmon resonant photomixer (PRX) in the terahertz range. The photomixer incorporates doubly interdigitated grating strips for gate electrodes and a vertical resonator structure for realizing highly efficient terahertz emission even at room temperature. We investigated the dependence of total field emission properties of PRX's on their material and dimension parameters. Introduction of low-conductive gate electrodes and ac-coupled 2D periodic plasmon gratings with depleted connecting portions are effective for expanding its lower cutoff frequency. The cutoff frequency, which is around 1.0 THz in standard metal-gates configuration, is expanded to less than 500 GHz. The output intensity could also be amplified more than double. On the other hand, a shorter vertical cavity is effective for expanding its upper cutoff frequency, which is expanded close to vertical resonant frequency, while maintaining the lower cutoff frequency. The combination of these design rules can realize much broader bandwidth operation.

The wave absorber composed of cylindrical bars arranged periodically and metallic mesh for improving visibility is proposed for ETC, and characteristics of reflectivity and shielding effect are evaluated analytically and experimentally. As a result, reflectivity of -10 dB and shielding effect of -25 dB are obtained for circularly polarized wave when the gap between cylindrical bars is 30 mm. Therefore, realization of proposed wave absorber for installing between ETC lanes can be clarified.

Fabrication of 1.5 µm GaInAsP/InP laser by OMVPE on p-type substrate is reported. Low threshold current density (1.2 kA/cm2) was obtained by reduction of growth time in order to prevent Zn diffusion from substrate. CW operations at room temperature were obtained in buried heterostructure (BH) devices fabricated by OMVPE-LPE hybrid growth method. No degradation was observed after 2000 hours' aging test.

The choreography realization problem is a design challenge for systems based on service-oriented architecture. In our previous studies, we studied the problem on a case where choreography was given by one or two scenarios and was expressed by an acyclic relation of events; we introduced the notion of re-constructibility as a property of acyclic relations to be satisfied. However, when choreography is defined by multiple scenarios, the resulting behavior cannot be expressed by an acyclic relation. An event structure is composed of an acyclic relation and a conflict relation. Because event structures are a generalization of acyclic relations, a wider class of systems can be expressed by event structures. In this paper, we propose the use of event structures to express choreography, introduce the re-constructibility of event structures, and show a necessary condition for an event structure to be re-constructible.

We experimentally demonstrate transistor operation in a vertical p+-MoS2/n-HfS2 van der Waals (vdW) heterostructure configuration for the first time. The HfS2/MoS2 heterojunction transistor exhibits an ON/OFF ratio of 104 and a maximum drain current of 20 nA. These values are comparable with the corresponding reported values for vdW heterojunction TFETs. Moreover, we study the effect of atmospheric exposure on the subthreshold slope (SS) of the HfS2/MoS2 transistor. Unpassivated and passivated devices are compared in terms of their SS values and IDS-VGS hysteresis. While the unpassivated HfS2/MoS2 heterojunction transistor exhibits a minimum SS value of 2000 mV/dec, the same device passivated with a 20-nm-thick HfO2 film exhibits a significantly lower SS value of 700 mV/dec. HfO2 passivation protects the device from contamination caused by atmospheric moisture and oxygen and also reduces the effect of surface traps. We believe that our findings will contribute to the practical realization of HfS2-based vdW heterojunction TFETs.

Current-voltage characteristics of triple-barrier resonant tunneling diodes are theoretically analyzed taking phase breaking into account. The peak current in predicted using conventional theories is much smaller, typically by a factor of 1/3000 for a coherent length of 100 nm, than that measured because the incoherent tunneling process is neglected. We take both the coherent and the incoherent tunneling processes into account in the analysis and show that the product of the peak current and the voltage width at half maximum of the peak current is almost constant even when the phase coherent length varies between 50 and 1000 nm. The peak current density increases by two orders of magnitude in the model developed here.

Nuclear power plants require in-vessel inspections for soundness checks and preventive maintenance. One inspection procedure is visual testing (VT), which is based on video images of an underwater camera in a nuclear reactor. However, a lot of noise is superimposed on VT images due to radiation exposure. We propose a technique for improving the quality of those images by image processing that reduces radiation noise and enhances signals. Real-time video processing was achieved by applying the proposed technique with a parallel processing unit. Improving the clarity of VT images will lead to reducing the burden on inspectors.

This paper proposes a secure distributed transmission method that establishes multiple transmission routes in space to a destination. In the method, the transmitted information is divided into pieces of information by a secret-sharing method, and the generated pieces are separately transmitted to the destination through different transmission routes using individually-controlled antenna directivities. As the secret-sharing method can divide the transmitted information into pieces in such a manner that nothing about the original information is revealed unless all the divided pieces are obtained, the secrecy of the transmitted information is greatly improved from an information-theoretic basis. However, one problem is that it does not perform well in the vicinity around the receiver. This is due to the characteristics of distributed transmission that all distributed pieces of information must eventually gather at the destination; an eavesdropper can obtain the necessary pieces to reconstruct the original information. Then, this paper expands the distributed transmission method into a two-way communication scheme. By adopting the distributed transmission in both communication directions, a secure link can be provided as a feedback channel to enhance the secrecy of the transmitted information. The generation of the shared pieces of information is given with signal forms, and the secrecy of the proposed method is evaluated based on the signal transmission error rates as determined by computer simulation.

The first results of a field trial held in November 2000, of 1 Tbit/s (25 43 Gbit/s) unidirectional Wavelength Division Multiplexing (WDM) transmission, are presented. The field trial used a 43 Gbit/s/channel Optical Transport Network (OTN) interface prototype and standard Single Mode Fibers (SMFs) installed in the Nara area network of NTT West Corporation. The features of this field trial include the accommodation of multiple services such as GbE, STM-16 and OC-48. Error free operation of 25 channels with 100 GHz spacing over a 91 km standard SMF with Forward Error Correction (FEC) is verified for STM-16. A DV stream over IP over Ethernet as a tributary channel was also successfully transmitted.

This paper presents a new proof to a polynomial-time algorithm for determining whether a given embedded graph is a Delaunay graph, i. e. , whether it is topologically equivalent to a Delaunay triangulation. The problem of recognizing the Delaunay graph had long been open. Recently Hodgson et al. gave a combinatorial characterization of the Delaunay graph, and thus constructed the polynomial-time algorithm for recognizing the Delaunay graphs. Their proof is based on sophisticated discussions on hyperbolic geometry. On the other hand, this paper gives another and simpler proof based on primitive arguments on Euclidean geometry. Moreover, the algorithm is applied to study the distribution of non-Delaunay graphs.

It is well known that the electromagnetic interference (EMI) radiated from industrial, scientific and medical (ISM) apparatus seriously degrades the performance of wireless communication systems. In this paper, an ISM-band wireless local area network (WLAN) which employs a direct sequence-spread spectrum (DS-SS) system is designed to be sufficiently robust and reliable to operate in the presence of this EMI. To satisfy this goal, a technique to suppress EMI in the DS-SS system using a multicode transmission and an EMI observation channel is proposed. In the study, the EMI radiated from switching-type microwave ovens (MWO interference) which are ISM apparatus is concerned, and for a tractable investigation, a statistical model to represent MWO interference based on experimental measurement results is employed. As well known that MWO interference exhibits a bursty impulsive characteristic in time, a technique to transmit multiple long spreading codes (multicode transmission) is introduced for the DS-SS system to overcome the burstness of the interference. Moreover, inspired by the broadband in frequency of MWO interference, a technique to estimate the channel MWO interference by means of observing its levels in an adjacent channel is proposed, and this technique is applied to construct a multicode DS-SS receiver which can suppress the channel MWO interference. An evaluation of the bit error rate performance of the proposed multicode DS-SS system is conducted by computer simulation, and the numerical results demonstrate that the proposed DS-SS system can operate effectively even in the presence of MWO interference.

In this paper, we report the fabrication and device characteristics of InP/InGaAs double heterojunction bipolar transistors (DHBTs) with buried SiO2 wires. The SiO2 wires were buried in the collector and subcollector layers by metalorganic chemical vapor deposition toward reduction of the base-collector capacitance under the base electrode. A current gain of 22 was obtained at an emitter current density of 1.25 MA/cm2 for a DHBT with an emitter width of 400 nm. The DC characteristics of DHBTs with buried SiO2 wires were the same as those of DHBTs without buried SiO2 wires on the same substrate. A current gain cutoff frequency (fT) of 213 GHz and a maximum oscillation frequency (fmax) of 100 GHz were obtained at an emitter current density of 725 kA/cm2.

A GaInNAs alloy on GaAs substrate has been very promising for long-wavelength vertical-cavity surface-emitting lasers (VCSELs) as an active layer. In spite of many groups reported the excellent temperature characteristics of the threshold current of the GaInNAs/GaAs edge-emitting lasers, discussions of the temperature dependence of the lasing characteristics except threshold current is few. In this paper, temperature characteristics of GaInNAs lasers grown by chemical beam epitaxy (CBE) emitting at λ=1.27 µm and λ=1.30 µm were investigated in detail. The characteristic temperature (T0) ranging from 10 to 80 varies from 60 to 130 K and decreased with decreasing cavity length for shorter cavity (< 400 µm) devices. On the other hand, longer cavity (< 400 µm) devices show that the cavity length does not affect so much to T0. The internal losses did not increase with increasing temperature. On the other hand, internal quantum efficiencies decreased with increasing temperature. It is considered that non-radiative recombination center with large temperature dependence may influence the decrease of the internal quantum efficiency due to the insufficient crystal quality of GaInNAs layer. The transparency current densities were unchanged for all temperature range, however, the gain constants decreased with increasing temperature. Thus, the decrease of the gain constant is considered to be due to decreasing of gain. Unchanged both transparency current density and internal loss may also express that these temperature characteristics were not induced by carrier overflow but be done by decreasing of the gain. From the results, it is considered that the temperature dependence of the gain originated from the Fermi-Dirac distribution of carriers was dominant for the temperature characteristics of GaInNAs/GaAs lasers. Due to the temperature dependence on the gain, the T0 decreases with increasing mirror loss.

1.55µm GaInAsP/InP BH lasers with multiple p-n current blocking layer were fabricated entirely by low-pressure OMVPE. The undercut portions were filled in a manner similar to mass transport process. The laser shows a threshold current of 48 mA at 300 K under CW operation.

Gain and loss coefficients were determined for GaInAsP/InP (λg1.5 µm) grown by OMVPE from lasing characteristics. Crystal quality of OMVPE GaInAsP/InP was found to be substantially the same as those grown be LPE. Absorption losses of the quaternary active and the binary InP layers were estimated separately.