The Time Domain Electromagnetic Method (TDEM) survey is one of the several geophysical exploration methods. In the conventional TDEM survey, an induction coil is used as the magnetometer. However, the measurement depth is limited to about 500 m. Using high Tc SQUIDs, there are expectations of large bandwidth and high sensitivity for the TDEM. We developed the high Tc SQUID TDEM system. We have reduced the system noise by developing a 20 mm20 mm step-edge type direct coupled SQUID and a low noise direct readout flux locked loop (FLL) circuit. We have also improved the slew rate, optimizing the parameter of the FLL circuit. Consequently, the system noise of less than 0.2 pT/Hz1/2 at 1 kHz was achieved in the earth's magnetic field. The slew rate was 7.3 mT/sec. We conducted field trials and confirmed that the TDEM using high Tc SQUIDs obtains information of deeper region with high precision compared with the TDEM using induction coils.

Multichannel superconducting quantum interference device (SQUID) systems based on double relaxation oscillation SQUIDs (DROS) were developed for measuring magnetocardiography (MCG) and magnetoencephalography (MEG) signals. Since DROS provides large flux-to-voltage transfer coefficients, about 10 times larger than the DC SQUIDs, direct readout of the SQUID output was possible using compact room-temperature electronics. Using DROSs, we fabricated two types of multichannel systems; a 37-channel magnetometer system with circular sensor distribution for measuring radial components of MEG signals, and two planar gradiometer systems of 40-channel and 62-channel measuring tangential components of MCG or MEG signals. The magnetometer system has external feedback to eliminate magnetic coupling with adjacent channels, and reference vector magnetometers were installed to form software gradiometers. The field noise of the magnetometers is around 3 fT/ at 100 Hz inside a magnetically shielded room. The planar gradiometer systems have integrated first-order gradiometer in thin-film form with a baseline of 40 mm. The magnetic field gradient noise of the planar gradiometers is about 1 fT/cm/ at 100 Hz. The planar gradiometers were arranged to measure field components tangential to the body surface, providing efficient measurement of especially MCG signals with smaller sensor coverage than the conventional normal component measurements.

This paper compares the throughput performance employing hybrid automatic repeat request (ARQ) packet combining, i.e., Chase combining, and Incremental redundancy, considering the frequency diversity effect in the broadband forward-link channel for Orthogonal Frequency and Code Division Multiplexing (OFCDM) packet wireless access achieving a peak throughput above 100 Mbps. Simulation results show that the achievable throughput at the average received signal energy per symbol-to-background noise power spectrum density ratio (Es/N0) of 0 and 6 dB employing Incremental redundancy is increased by approximately 35 and 30% compared to that using Chase combining for QPSK and 16QAM data modulation schemes with the coding rate of R = 1/2, respectively, considering a large frequency diversity effect in a 12-path exponential decayed Rayleigh fading channel, since the reduced variations in the received signal level in a broadband channel bring about a larger coding gain in Incremental redundancy. We also show that when adaptive modulation and channel coding (AMC) is applied, Incremental redundancy is superior to Chase combining since the large coding gain is effective in achieving a large time diversity gain for a low number of retransmissions such as M = 1 or 2 for a maximum Doppler frequency up to fD = 400 Hz. It is demonstrated, nevertheless, that the total throughput when employing Incremental redundancy associated with a near optimum MCS set according to the channel conditions becomes almost identical to that using Chase combining when a large number of retransmissions, M, is allowed, such as M = 10, owing to time diversity along with frequency diversity.

The facility layout problem is one of the most fundamental quadratic assignment problems in operations research. In this paper, we present an improved genetic algorithm for solving the facility layout problem. In our computational model, we propose several improvements to the basic genetic procedures including conditional crossover and mutation. The performance of the proposed method is evaluated on some benchmark problems. Computational results showed that the improved genetic algorithm is capable of producing high-quality solutions.

In this Letter, a frequency-domain pre-rake transmission is presented for a direct sequence spread spectrum with time division duplex (DSSS/TDD) system under a frequency-selective fading channel. The mathematical relationship between frequency-domain and time-domain pre-rake transmissions is discussed. It is confirmed by the computer simulation that, similar to the time-domain pre-rake transmission, frequency-domain pre-rake transmission can improve the bit error rate (BER) performance. The frequency-domain pre-rake transmission shows only slight performance degradation compared to the frequency-domain rake reception for large SF.

This paper presents a new fast and robust circle extraction method that is capable of extracting circles from images with complicated backgrounds. It is not based on the Hough transform (HT) that requires a time-consuming voting process. The proposed method uses a least-squares circle fitting algorithm for extracting circles. The arcs are fitted by extended digital lines that are extracted by a fast line extraction method. The proposed method calculates accurate circle parameters using the fitted arcs instead of evidence histograms in the parameter space. Tests performed on various real-world images show that the proposed method quickly and accurately extracts circles from complicated and heavily corrupted images.

This paper proposes a new method of example-based query generation for spontaneous speech. Along with modeling the information flows of human dialogues, the authors have designed a system that allows users to retrieve information while driving a car. The system refers to the dialogue corpus to find an example that is similar to input speech, and it generates a query from the example. The experimental results for the prototype system show that 1) for transcribed text input, it provides the correct query in about 64% of cases and the partially collect query in about 88% 2) it has the ability to create correct queries for the utterances not including keywords, compared with the conventional keyword extraction method.

Since the interference is quite related to the performance of CDMA cellular systems, it is necessary to estimate Other-Cell-Interference Factor (OCIF). Here, starting from OCIF calculation for an aeronautical communication system, we investigate the forward link performance of data packet transmission in which the capacity, throughput and delay of the system are measured. To the numerical results, one can see that the performance of the aeronautical communication system is worse than that for terrestrial cellular systems and also depends logarithmically on both the cell radius and height.

There is a possibility that individuals ingest contaminants that have been accidentally mixed with food because processed foods have become very common. Therefore a detection method of small contaminants in food and pharmaceuticals is required. High-Tc SQUID detection systems for metallic contaminants in foods and drugs have been developed for safety purposes. We developed two systems; one large system is for meat blocks and the other small system is for powdered drugs or packaged foods. Both systems consist of SQUID magnetometers, a permanent magnet for magnetization and a belt conveyor. All samples were magnetized before measurements and detected by high Tc SQUIDs. As a result, we successfully detected small syringe needles with a length of 2 mm in a meat block and a stainless steel ball as small as 0.3 mm in diameter.

Magnetic immunoassays utilizing magnetic marker and high Tc superconducting quantum interference device (SQUID) have been performed. In this magnetic method, binding-reaction between an antigen and its antibody is detected by measuring the magnetic field from the magnetic marker. First, we discuss the magnetic property of the marker, and show that Fe3O4 particles with diameter of 25 nm can be used for remanence measurement. We also show a design of the SQUID for sensitive detection of the magnetic signal from the marker. Next, we developed a measurement system utilizing the SQUID and a reaction chamber with very low magnetic contamination. Finally, we conducted an experiment on the detection of the biological materials called IL8 and IgE. At present, a few atto-mol of IL8 and IgE has been detected, which shows the high sensitivity of the present method.

Power distribution in multilayered periodic waveguides is first analyzed by longitudinal modal transmission-line theory (L-MTLT). Novel effective characteristic impedances of the equivalent network for TE and TM modes are then derived, and a symmetrical grating guide with three layers is rigorously evaluated to clarify the validity of our approach. Excellent agreement between our results and the results due to other methods indicates that our approach is able to not only reveal all the physical meaning embedded in the multilayered and multi-sectional periodic waveguides, but also predict various possible Bragg regimes rigorously and simply.

In this paper, we propose a new algorithm for calculating the exact poles of the admittance matrix of RLCG interconnects. After choosing dominant poles and corresponding residues, each element of the exact admittance matrix is approximated by partial fraction. A procedure to obtain the residues that guarantee the passivity is also provided, based on experimental studies. In the procedure the residues are calculated by using the least squares method so that the partial fraction matches each element of the exact admittance matrix in the frequency-domain. From the partial fraction representation, the asymptotic equivalent circuit models which can be easily simulated with SPICE are synthesized. It is shown that an efficient model-order reduction is possible for short-length interconnects.

In MC-CDMA, the data rate can be increased by reducing the spreading factor SF or by allowing multicode transmission. In this paper, we examine by computer simulations which gives a better bit error rate (BER) performance--lower SF or multicode operation--when high level modulation is used in addition to error control coding. For a coded system in a frequency selective channel, there is a trade-off among frequency diversity gain due to spreading, improved coding gain due to better frequency interleaving effect and orthogonality distortion. It is found that for QPSK, the performance of OFDM (MC-CDMA with SF = 1) is almost the same as that of a fully spread MC-CDMA system. However, for 16QAM and 64QAM, the BER performance is better for lower SF unlike the uncoded system, wherein higher SF gives a better BER.

We show that the necessary and sufficient condition for the existence of a balanced quatrefoil decomposition of the complete multigraph λKn is n 9 and λ(n - 1) 0 (mod 24). Decomposition algorithms are also given.

To the authors' knowledge, there are not many cryptosystems proven to be as difficult as or more difficult than the discrete logarithm problem. Concerning problems related to the discrete logarithm problem, there are problems called the double discrete logarithm problem and the e-th root of the discrete logarithm problem. These two problems are likely to be difficult and they have been utilized in cryptographic protocols such as verifiable secret sharing scheme and group signature scheme. However, their exact complexity has not been clarified, yet. Related to the e-th root of the discrete logarithm problem, we can consider a square root of the discrete logarithm problem. Again, the exact complexity of this problem has not been clarified, yet. The security of cryptosystems using these underlying problems deeply depends on the difficulty of these underlying problems. Hence it is important to clarify their difficulty. In this paper we prove reductions among these fundamental problems and show that under certain conditions, these problems are as difficult as or more difficult than the discrete logarithm problem modulo a prime.

We consider space division multiplexing in a MIMO-OFDM system for high data rate transmission. Channel estimation is very important for suppressing interference and demultiplexing signals. In a wireless LAN system such as IEEE 802.11a, only a few training symbols are inserted in each subcarrier. First, we propose a channel estimation method for a MIMO-OFDM system with two training symbols per subcarrier. The basic idea is to estimate the time-domain channel responses between the transmit and receive antennas. The array response vectors for each subcarrier are calculated by applying a fast Fourier transform to them. We then can obtain the adaptive weights to cancel the interference. We show that employing training symbols having a lower condition number of the matrix used for the channel estimation improves the estimation accuracy. Furthermore, we show the bit error rate for several signal detection schemes using the above estimated channel. It is shown that an ordered successive detection based on an MMSE criterion has excellent performance, that is, it can achieve higher-speed transmissions with a lower transmit power.

This paper describes implementation and performance evaluation of simple SDM-COFDM (Space Division Multiplexed-Coded Orthogonal Frequency Division Multiplexing) prototype over fading MIMO (Multi-Input Multi-Output) channel in order to achieve higher frequency utilization efficiency. It employs ZF (Zero Forcing) type detection scheme for SDM transmission to reduce hardware implementation complexity, where ZF type detection scheme needs to only multiply the received data by the estimated inverse propagation coefficient matrix at each OFDM subcarrier. Moreover, in order to improve the performance degradation due to the increase of the transmitted data length per frame in fast fading environments, the inverse matrix tracking using STC (Space-Time Coded) pilot is proposed and implemented in the prototype. Experimental results show that the prototype with 22 antennas achieves about 90% increase of the frequency utilization efficiency compared to the SISO (Single-Input Single-Output) transmission.

Similar to direct sequence code division multiple access (DS-CDMA), site diversity can be applied to a multicarrier-CDMA (MC-CDMA) cellular system to improve the bit error rate (BER) performance for a user with weak received signal power, thus resulting in an increased link capacity. In this paper, the downlink site diversity reception using frequency-domain equalization based on minimum mean square error (MMSE) is considered for a MC-CDMA cellular system. A set of active base stations to be involved in the site diversity operation is determined based on the received signal power measurement by a mobile station. Downlink capacity with site diversity is evaluated by computer simulation. The impacts of path loss exponent and shadowing loss standard deviation on the site diversity effect are discussed. Furthermore, the performance improvement by antenna diversity reception is discussed.

Unloaded Q of a dielectric image resonator is discussed based on the electromagnetic field distribution. It is shown that a partial air gap and a dielectric sheet with low permittivity between the dielectric resonator and the shield case reduce both the dielectric loss and the conductor loss. Especially, reduction of the conductor loss is significant, since the magnetic field distribution moves from the conductor to the upper part of resonator. A half-cut image resonator with an air gap and dielectric spacer is simulated and measured. The unloaded Q of the dielectric resonator with low dielectric loss is improved by about two times from that of original image resonator.

We present two new parallel algorithms for extending the domain of a UOWHF. The first algorithm is complete binary tree based construction and has less key length expansion than Sarkar's construction which is the previously best known complete binary tree based construction. But only disadvantage is that here we need more key length expansion than that of Shoup's sequential algorithm. But it is not too large as in all practical situations we need just two more masks than Shoup's. Our second algorithm is based on non-complete l-ary tree and has the same optimal key length expansion as Shoup's which has the most efficient key length expansion known so far. Using the recent result, we can also prove that the key length expansion of this algorithm and Shoup's sequential algorithm are the minimum possible for any algorithms in a large class of "natural" domain extending algorithms. But its parallelizability performance is less efficient than complete tree based constructions. However if l is getting larger, then the parallelizability of the construction is also getting near to that of complete tree based constructions. We also give a sufficient condition for valid domain extension in sequential domain extension.