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The Cu-Sn-C system P/M alloys were sintered by laser. The influence of laser sintering on the properties of the laser-sintered materials was investigated. The properties, such as the density, impact toughness, hardness and wear resistance of the laser-sintered materials are desirable. A maximum impact toughness of 11.7 J/cm2 was achieved and the wear resistance of the laser-sintered materials was tremendously increased compared with conventional sintering. The green compact made from Cu-Sn-C powders, with a thickness of 10 mm, can be penetratively sintered by using a suitable processing condition. The laser sintering was characterised by a thermal cycle which was accomplished in a relatively short time, resulting in a relatively high temperature (950 °C). The curves showing temperature profiles for the top surface and bottom of the laser-sintered specimen were recorded by thermocouples. Differences in temperatures between the top surface and bottom were very small, less than 60 °C. Some intermetallics/phases such as α-Cu, Cu31Sn8(δ), Cu4Sn(e) and Cu6Sn5(η) were most readily produced in the laser-sintered materials and their distributions were more homogeneous than conventional sintering, owing to the better flow ability of the melt caused by a relatively high sintering temperature. The behaviour of diffusion between Cu and Sn was also studied by means of simulation diffusion couple.

Gate matrix layout problem plays an important role in integrated circuit design, but its optimization is NP-hard. In this paper, typical gate layout problem is analysed and adapted to neural network representation, furthermore the simulated results are given.

Green Compact Laser Sintering (GCLS) is a new technique for sintering powder metallurgical components by laser irradiation. After mixing; powders are pressed into a green compact; which can then be sintered by laser irradiation. The properties of powder metallurgical alloys for GCLS and conventional sintering are compared.

A new approach to calculate fault detection probabilities is presented. Fault-free simulation is used in the approach. The quantities of controllability and observability are defined as probabilities of controlling and observing the nodes in the circuit. The probability distribution of random signals on the circuit nodes is analyzed, and it is proved that controllability is in normal distribution. Thus the unbiasing estimation of the fault detection probability can be obtained. According to the concept of observability, we deal with the fan-out nodes. The fault coverages for actual circuits obtained from this approach agree favorably with the fault simulation results.

The ZL108 Al-Si alloy containing rare earth was melted with a CO2 2 kW laser. The maximum microhardness values of the laser-melted zone (LMZ) was shifted back by 2 h in the microhardness-time curve and 20 °C in the microhardness-temperature curve, as compared with conventional treatment materials in the given range. The LMZ had better structural stability at the elevated temperature than that of the conventional materials. Stacking faults were found in the resolidified aluminium, and were identified to be intrinsic. Both structural stability and the existence of the stacking faults were related to Ce supersaturation in the resolidified aluminium.

To solve the problem of deficiency detecting, it is necessary to detect the wall thickness of pipe rapidly, continuously, successively and accurately. For that purpose, this paper introduces a dynamic testing facility for on-line high-speed inspection of underground oil or gas transportation pipelines. The facility consists of a high-energy multi-channel ultrasonic focusing probe, a water-spraying coupler and a computer testing software developed in VC++ 6.0. Compared with the traditional testing methods, the system can not only probe the wall thickness of rigid tube material continuously by using multi-channel ultrasonic probes, but with the affiliated computer testing software it can also display curves of thickness in multi-graphs and give out warning when it exceeds the standard range. Furthermore the data can be stored and searched conveniently. Experiment has indicated many advantages in the equipment. Firstly, its detecting speed reaches 25m/min. Secondly, its testing accuracy is high. The accuracy is ±0.1mm, and the pipeline wall that can be tested by the equipment is more than 10% of the thickness and the pipeline ektexine that can be tested is more than 12.5% of the thickness. Especially, the experimental results conform to requirement of the latest API-5CT standards. Thirdly, it has credible detecting capability.

In this paper, a multi-channel MAC protocol that supports multiple traffics will be presented. The dynamic channel selection scheme by receiver decision is implemented and the number of the data channel is independent of the network topology. An adaptive back off algorithm is employed to provide service differentiation for delay sensitive and best-effort traffic. The simulation results have shown that it can support multiple traffics and provide a certain QoS guarantee.

Ad hoc network is expected to play a major role in future wideband wireless access to the Internet. The dual mode system that multi-hop network overlaid with a cellular structure is more and more attractive for researchers. However, routing is important for such networks due to the dynamic nature of network topology and the resource constraints. To maximize the resource utilization and minimize the network transfer delay along the path, the shortest path with minimum hops approach is often adopted. However, the quality of wireless channel among the mobile nodes is time varying due to fading, shadowing and path loss. Considering adaptive channel coding and modulation scheme, the channel state can be characterized by different link throughput. In this paper, a channel adaptive routing (CHAR) is presented. The CHAR transform link throughput into the channel quality factor and finds the shortest routing according to the channel quality measure. Simulation results show that the proposed routing may reduce the average transfer delay and increase the packet deliver rate.

A new kind of method, which can be used in WCDMA mobile communication system to determine the insert frequency of the pilot symbols, is proposed here. The pilot symbols are used to estimate the channel parameters and implement the coherent demodulation of data. Performance difference between the pilot symbol aided coherent demodulation (PSACD) and the ideal coherent demodulation can be used as a criterion to determine the insert frequency of the pilot symbol. Thus these provide the basement for a new frame structure which has advantages over the conventional one. Performance comparison between the new and conventional frame structure is evaluated by computer simulation.

A GFC protocol with adaptive feedback control mechanism is suggested. The mechanism is advantageous because it can dynamically alleviate the traffic of each priority at UNI when the quality of service of that priority is deteriorating.

A synchronous chaotic spread-spectrum CDMA system is presented. In the system, we use an open flow coupled-chaotic sequence as the signature sequence. This coupled map lattices has a long chaotic transient and can be recovered easily. The autocorrelation and cross-correlation properties of the chaotic sequences are investigated and compared to m and Gold sequences. Finally, the error probabilities of the proposed system are analyzed.

A new procedure is proposed for resolving multipaths for the wireless channel. This method uses antenna arrays at the base station to estimate the direction of arrival (DOA) of the multipaths. Beams are formed in the specific DOAs. Thus the significant paths can be separated from one another and then fed into the fingers of a RAKE type receiver. Each finger is adaptively adjusted for delay to achieve optimum combining. We show that such enhancement greatly improves the system performance. Results of preliminary simulation studies are also presented.

In this paper, a quick repeated learning rule, which is based on the Hebb rule and the Hamming distance distribution of the pattern set to be learned, is studied. With the help of the proposed learning rule, not only can the learned patterns be addressable, but an attraction basin with a predetermined radius is established for each attractor.

Aluminium and its alloys have been known as kinds of materials with high stacking-fault energy. It is therefore difficult to find stacking faults or twins in them. It was shown by our early studies that apart from a pearlite-like A1-Si eutectoid structure [1], a large amount of stacking faults [2] was found in laser-melted A1-Si alloy containing rare earths (RE). Following these results, we performed experiments with both the same material as in [1, 2] and laser-melted material coated with alloy powder containing RE. A twin structure was observed by transmission electron microscopy (TEM). The purpose of this letter is to display the twin morphology and to discuss possible mechanisms for twin formation. The materials used for laser melting were divided into two groups. The composition of the first group (FG) was (wt %): 12 Si, 1.23 Cu, 0.5 Mn, 0.93 Mg, 1.0 Fe and 0.1 RE. The RE contained 10 wt% Ce, the remainder being A1. The second group (SG) were prepared from laser alloying. Alloy powder was predeposited on the surface of the material, which was similar to the first material but without RE. The powder contained (wt %): 55 A1, 25 Si, 10 Cr and 10 RE (Ce-rich). Laser melting or alloying was carried out with an HG1-CO2 laser. The output power was 2.8 kW and the beam diameter 5 mm with a scanning speed of 54 mms -1 . Slices for TEM were cut from laser-melted alloyed zones with a thickness of 0.4 mm parallel to the melted surface. After thinning by a series of SiC papers, the thin foils were then thinned by ion-miiling or electrolyte (5% perchloric acid and 75% ethanol). A model H-800 TEM was employed to study microstructure, operated at 200 kV. The laser melted/alloyed region was 0.8 mm deep and 4.0ram wide, and the secondary dendritic distance of the melted region ranged from approximately 2 to 3.5 ram. Growth of the eutectic and 0~-A1 was based on the interface between liquid and solid (matrix). The growth direction of ol-A1 was in agreement with [0 0 1] orientation. Fig. 1 shows the o~-A1 and AI-Si eutectic for the laser-melted region (FG). The typical twin morphology in o~-A1 is shown in Fig. 2a and b, using brightand dark-field techniques. The electron diffraction pattern and its

The wear resistance of both laser melted and conventionally quenched 1·0%C tool steel has been investigated. From unlubricated wear tests, the abrasion resistance of laser treated material was found to be superior to that of conventionally treated material, both in the as treated condition and after a range of tempering treatments (room temperature at 300°C), as a result of the presence of retained austenite.MST/1326

A scheme combining interference cancellation and an adaptive antenna is proposed. It can mitigate multiple access interference even if the interference signal arrives at the antenna array at the same angle as the desired signal. SIR (ratio of signal to interference) of the system is analyzed. Numerical results show a good performance improvement of such system.

Based on the three-valued characteristic of Gold codes, a kind of improved Gold code, which is biased with a constant direct current on a Gold code, is proposed. We call it the biased Gold code. From the analysis and simulation, we can see that its correlation characteristics are improved. According to the results of simulation, the BER performance of the system with a biased Gold code is superior to that of the traditional Gold code system.

A CDMA system model combined with adaptive antenna and RAKE structure is built. Analytical results of BER under different imperfection situations are induced. It is shown the performance of such a receiver is good under lower Eb/No. System performance affected by power control deviation, channel parameter estimation and code phase error is analyzed.