Effects of cell correlations in a matched-filter PN codeacquisition for direct-sequence spread-spectrum systems

Rapid pseudonoise (PN) code acquisition with matched-filter correlators has been very popular in direct-sequence (DS) spread-spectrum systems. Conventionally, the analysis of this acquisition method is based on the assumption that the detections among cells are independent. However, there may be strong correlations among cell detections for the case that the cell size is less than a chip duration. In this paper, the mean acquisition time performance of the acquisition method is analyzed with the cell correlations being taken into account. Numerical results show that depending on the threshold value and other system parameters, the effect of cell correlations may be over 20% of the mean acquisition time for signal-to-noise ratios (SNR) of practical interest. The analytical results are substantiated by computer simulations     

On the corrosion behaviour of newly developed biodegradable Mg-based metal matrix composites produced by in situ reaction

Biodegradable Mg-based metal matrix composite (Mg-MMC) reinforced by MgO ceramics and Mg–Zn intermetallics were prepared by in situ reaction using a powder mixture of pure magnesium and 20 wt% ZnO as raw materials. The corrosion behaviour of Mg-MMC was evaluated by electrochemical measurements and immersion tests in Hanks’ solution. Results show that the newly developed Mg-MMC is composed of α-Mg matrix and uniformly distributed MgO ceramic and Mg–Zn intermetallics in matrix as reinforcements. The Mg-MMC possesses a corrosion behaviour comparable to pure magnesium and exhibits enhanced improvement in mechanical properties and corrosion resistance.     

Fabrication of diamond micro-structures by ink-jet printed diamond seeding and microwave plasma assisted chemical vapor deposition

Ink-jet printing has the advantage of easy formation of micro-patterns on rigid as well as flexible surfaces without needing conventional lithographic processes. By means of printing in selected areas, diamond seeding in designed patterns and areas is achieved. Properly designed ink with a desirable composition helps the formation of patterned structures with tailored functions. Ink containing nano-diamond particles was designed and used to print micro-structures, which were applied for further CVD growth of diamond by means of microwave plasma CVD. Promising applications of this technique are discussed.     

Identification of a threshold value for the DEMATEL method using the maximum mean de-entropy algorithm to find critical services provided by a semiconductor intellectual property mall

To deal with complex problems, structuring them through graphical representations and analyzing causal influences can aid in illuminating complex issues, systems, or concepts. The DEMATEL method is a methodology which can confirm interdependence among variables and aid in the development of a chart to reflect interrelationships between variables, and can be used for researching and solving complicated and intertwined problem groups. The end product of the DEMATEL process is a visual representation—the impact-relations map—by which respondents organize their own actions in the world. In order to obtain a suitable impact-relations map, an appropriate threshold value is needed to obtain adequate information for further analysis and decision-making. In the existing literature, the threshold value has been determined through interviews with respondents or judged by the researcher. In most cases, it is hard and time-consuming to aggregate the respondents and make a consistent decision. In addition, in order to avoid subjective judgments, a theoretical method to select the threshold value is necessary. In this paper, we propose a method based on the entropy approach, the maximum mean de-entropy algorithm, to achieve this purpose. Using a real case to find the interrelationships between the services of a Semiconductor Intellectual Property Mall as an example, we will compare the results obtained from the respondents and from our method, and show that the impact-relations maps from these two methods could be the same.     

Channel Assignment and Hand-off Policies in Cluster-Based Micro/ Picocellular Wireless Networks

In this paper, we consider cluster-based micro/picocellular networks with overlapped cell-clusters. Channel assignment and hand-off policies are essential and important policies in cellular wireless networks. The issue of how different channel assignment and hand-off policies in the overlapped areas affect the overall system performance has not yet been studied in the literature. This paper provides a thorough study and understanding of this issue. We propose two cluster channel assignment policies, namely, partitioned and shared cluster channel assignment policies, and two hand-off policies, namely, boundary and early hand-off policies. The proposed cluster channel assignment policies and hand-off policies are combined to obtain three different strategies, namely, partitioned-boundary, partitioned-early, and shared-boundary strategies. Extensive simulations are used to study the performance of the strategies. Our results show that the partitioned-early and shared-boundary strategies produce significantly lower hand-off dropping and forced termination probabilities than the partitioned-boundary strategy. The partitioned-early and shared-boundary strategies yield similar performance.     

Continuous-flow particle and cell separations in a serpentine microchannel via curvature-induced dielectrophoresis

Particle and cell separations are critical to chemical and biomedical analyses. This study demonstrates a continuous-flow electrokinetic separation of particles and cells in a serpentine microchannel through curvature-induced dielectrophoresis. The separation arises from the particle size-dependent cross-stream dielectrophoretic deflection that is generated by the inherent electric field gradients within channel turns. Through the use of a sheath flow to focus the particle mixture, we implement a continuous separation of 1 and 5 μm polystyrene particles in a serpentine microchannel under a 15 kV/m DC electric field. The effects of the applied DC voltages and the serpentine length on the separation performance are examined. The same channel is also demonstrated to separate yeast cells (range in diameter between 4 and 8 μm) from 3 μm particles under an electric field as low as 10 kV/m. The observed focusing and separation processes for particles and cells in the serpentine microchannel are reasonably predicted by a numerical model.     

Adaptive frame synchronization for surveillance system across a heterogeneous network

As mobile techniques are booming, the surveillance function is extended from a stationary mode to a mobile mode. In a heterogeneous network environment, cameras and viewers are located in different networks so that frame synchronization may span across diverse network domains with different transmission capabilities. The mismatch of transmission capabilities may affect the viewing continuity and playback liveness between cameras and viewers. In the article, we propose an adaptive frame synchronization mechanism for frame capturing at cameras based on the network condition to improve the frame synchronization between two sides across a heterogeneous network. Based on a brief theoretical analysis of the asynchronization effect for video communication in a heterogeneous network environment, the proposed adaptive pause time mechanism can be an effective solution to relieve the asynchronization effect in the unmatched transmission rate situation. The evaluation results show that the proposed scheme can achieve a shorter time delay between the captured frames at the camera site and the viewer site.     

Removal of chlorophenols from aqueous solution by fly ash

Fly ash from coal-fired thermal power plants can be used for the removal of 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP) with enthalpy changes of about -3 kcal/mol. The amounts of 2-CP and 2,4-DCP removed are affected by the pH value of the solution. The efficiency of removal improves when the pH value is less than the pK(a) values of 2-CP and 2,4-DCP, respectively. The adsorbed amount of chlorophenol by fly ash is also affected by particle diameter, carbon content, and the specific surface area of the ash used in this study. As expected, more adsorption takes place with fly ash of higher carbon content and larger specific surface area. Moreover, the adsorbed amount of chlorophenol is not influenced by the matrix in the wastewater, as shown by studying the removal of 2-CP and 2, 4-DCP in wastewater from a synthetic fiber plant. Chlorophenols in the wastewater were also removed efficiently through a fly ash column, with breakthrough times being inversely proportional to flow rates.     

Flow visualizations and heat transfer measurements for a rotating pin-fin heat sink with a circular impinging jet

This work experimentally investigated the fluid flow and heat transfer behaviors of jet impingement onto the rotating heat sink. Air was used as impinging coolant, while the square heat sinks with uniformly in-line arranged 5 × 5 and 9 × 9 pin-fins were employed. The side length (L) of the heat sink equaled 60 mm and was fixed. Variable parameters were the relative length of the heat sink (L/d = 2.222 and 4.615), the relative distance of nozzle-to-fin tip (C/d = 0–11), the jet Reynolds number (Re = 5019–25,096) and the rotational Reynolds number (Re_r = 0–8114). Both flow characteristics of stationary and rotating systems were illustrated by the smoke visualization. Besides, the results of heat transfer indicate that, for a stationary system with a given air flow rate, there was a larger average Nusselt number (Nu₀) for the 9 × 9 pin-fin heat sink with L/d = 4.615 and C/d = 11. For a rotating system, a bigger Re_r meant a more obvious heat transfer enhancement (Nu_Ω/Nu₀) in the case of smaller Re, but Nu_Ω/Nu₀ decreased with increasing Re. In this work, Nu_Ω/Nu₀ in L/d = 2.222 is higher than in L/d = 4.615; among the systems in L/d = 2.222, bigger Nu_Ω/Nu₀ exists in the case of C/d = 9–11, but among the systems in L/d = 4.615, bigger Nu_Ω/Nu₀ exists in the case of C/d = 1–3. Finally, according to the base of Nu_Ω/Nu₀ ? 1.1, the criterion of the substantial rotation was suggested to be Re_r/Re ? 1.154.     

Modeling VOC Emissions in the High-Purity Oxygen Activated Sludge Process

Mass balances for volatile organic compounds (VOCs) were added to a structured mathematical model of the high-purity oxygen activated sludge (HPO-AS) process. The model was sized to correspond to two large existing HPO-AS treatment plants. The stripping of ten different VOCs was modeled and compared to stripping from conventional air activated sludge process. The results show that the covered aeration tanks can reduce stripping by more than 90%, depending on the specific VOC. If biodegradation is considered, the HPO-AS process degrades more than the conventional process due to the higher liquid-phase concentrations that result because of reduced stripping. The increase in biodegradation depends on the VOCs degradability but should increase to nearly 100% for highly volatile but biodegradable VOCs.