Some radiological features of the lumbar spine of 84 patients with spastic diplegia were compared with 50 control subjects. The average age of the patients was 20.1 years (3 to 39). Spondylolysis of the fifth lumbar vertebra was found in 21%, four times more frequently than in normal subjects. No patient under nine years of age had spondylolysis and the frequency increased with age. The average angle of lumbar lordosis in spastic patients in the standing position was greater than in normal subjects, and increased with age. The patients had a decreased sacrofemoral angle which caused an increase in Ferguson's angle and explained the increased angle of lumbar lordosis.

SUMMARYOrthogonal frequency division multiplexing (OFDM) communication systems have great advantages, such as high spectrum efficiency and robustness against multipath fading. In order to enhance the advantages, this paper investigates an efficient utilization of both diversity combining and higher-level modulation (adaptive modulation) with a repetition code on the frequency domain in the OFDM systems. The repetition coded OFDM systems can achieve an improvement of performance with such a simple structure as one pair of transmit/receive antennas. In this paper, we derive simple closed-form equations for bit error probability (BEP) and throughput, and then improvements of those performances in the proposed OFDM systems are verified by both theoretical analysis and Monte Carlo simulation.

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SUMMARYBoth adaptive modulation and diversity combining are attractive techniques to combat fading and these two can be applicable to each digital-modulated symbol in OFDM transmission. In this letter, aiming to combat severe fading more effectively than the adaptive modulation, we theoretically analyze the benefit of a frequency diversity scheme within one OFDM symbol, which is a simple kind of coded OFDM (COFDM) based on IEEE 802.16 protocols. A simple closed form equation of bit error rate (BER) is derived, and then the advantages of correlated diversity gain and interference suppression by the diversity scheme are verified by both theoretical analysis and Monte Carlo simulation.

Orthogonal frequency division multiplexing (OFDM) systems can avoid the eãect of multipath fading by absorbing delayed waves into guard interval. But as the eãect of delayed waves over guard interval becomes stronger, it causes the bit error rate (BER) performance in OFDM systems to be more degraded. This paper proposes the approximate derivation method of the BER in DQPSK/OFDM systems over frequency selective fading channels. In this study, we will derive the approximate equation of the BER with diãerential coding/diãerential detection in the time domain. We conårm that the BER derived from the proposed approximate equation coincides with that by computer simulation even when such parameters as the Doppler frequency shift, the delay spread, the Rician factor and so on are varied. I. INTRODUCTIONOrthogonal frequency division multiplexing (OFDM) systems have attracted considerable attention in the recent past because of its robustness against multipath fading (frequency-selective fading) and high spectrum eé-ciency. The futures have warranted the designation of OFDM as a standard transmission technique for various services, for example, forth generation mobile communications systems, digital terrestrial TV broadcasting and high speed wireless LAN.Besides the above appealing properties, however, OFDM systems suãer severe performance degradation from the impacts of Doppler frequency shift and delayed waves caused by multipath transmission because of the co-channel interference and the inter-carrier interference (ICI) in OFDM systems [1]- [3].We have already derived the approximate equation of the bit error rate (BER) in DQPSK/OFDM systems over frequency non-selective Nakagami-Rice and Rayleigh fading channels in [4]. We evaluated the performance degradation caused by the impact of Doppler frequency shift f D T s , where f D is the maximum Doppler frequency and T s is a symbol duration. OFDM systems can avoid the interference caused by multipath fading by absorbing delayed

Abstract.A halftoning technique that uses a simple GA has proven to be very effective to generate high quality halftone images. Recently, the two major drawbacks of this conventional halftoning technique with GAs, i.e. it uses a substantial amount of computer memory and processing time, have been overcome by using an improved GA (GA-SRM) that applies genetic operators in parallel putting them in a cooperative-competitive stand with each other. The halftoning problem is a true multiobjective optimization problem. However, so far, the GA based halftoning techniques have treated the problem as a single objective optimization problem. In this work, the improved GA-SRM is extended to a multiobjective optimization GA to generate simultaneously halftone images with various combinations of gray level and spatial resolution. Simulation results verify that the proposed scheme can effectively generate several high quality images simultaneously in a single run reducing even further the overall processing time.

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