Pyrolysis of peat: Product yield and characterization

Pyrolysis of peat obtained from Yeniça?a, Bolu, Turkey was conducted in a fixed-bed tube furnace under various conditions, and variations in the structure of the char, tar and gas products were examined. The chars produced were studied by proximate and ultimate analyses. The maximum tar yield of 20.41% was obtained at a heating rate of 20 °C/min, a temperature of 450 °C, a sweeping gas flow rate of 100 ml/min and a 0.5–2.0 mm size range. The chemical composition of the tar was examined by elemental analysis, FTIR spectroscopy, ¹H-NMR spectroscopy and column chromatography. The chemical composition of the tar with dense aliphatic structure was established to be CH_1.22O_0.25N_0.02. The composition of the gases obtained at a heating rate of 20 °C/min for the 0.5–2.0 mm size range was examined by gas chromatography.     

Effect of hydrophobic hexafluoroisopropylidene group on the water sorption behaviors of rigid poly(p‐phenylene pyromellitimide) polyimide thin films

We prepared poly(p‐phenylene pyromellitimide) (PMDA–PDA), poly(p‐phenylene 4,4′‐hexafluoroisopropylidene diphthalimide), and their copolyimides with various compositions to explore the relationship between the water sorption and structure. The water sorption behaviors were gravimetrically investigated as a function of composition and temperature and interpreted with a Fickian diffusion model in films. Overall, the water sorption behaviors were strongly dependent on the changes in morphological structure, which originated from the variations in composition. When the content of the bulky hexafluoroisopropylidene group (6FDA) was increased, the water uptake decreased from 5.80 to 3.18 wt %, whereas the diffusion coefficient increased from 3.6 × 10^?10 to 11.3 × 10^?10 cm²/s. The relatively high water uptake in the PMDA–PDA polyimide film was successfully healed by the incorporation of 6FDA, which may have resulted from the increases in the intermolecular packing order and hydrophobicity. The degree of orientation and crystallinity, which are in‐plane characteristics, were directly correlated to the diffusion coefficient and activation energy in the polyimide film. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3442–3446, 2003     

Growth Mechanisms for SiC–AlN Solid Solution Crystals Prepared by Combustion Synthesis

AlN–SiC solid solution particles with a variety of morphologies including faceted polyhedrons with or without ledges; hexagonal platelets; hexagonal columns with a hexagonal plate or a pyramidal cap; and interpenetrating cones, have been found in the combustion products of a mixture of Al, Si, and carbon black under a nitrogen pressure of 10 MPa. Combustion temperature (the growth temperature of crystals) is the most important factor controlling the morphology of crystals formed in the combustion product. When temperatures are close to the melting point of the solid solutions, a small driving force for nucleation and long distances of surface migration make nucleation on the basal plane difficult, and thus the solid solution particles tend to grow as platelets. Supersaturation is the second key factor influencing crystal growth. At relatively low temperatures, a low supersaturation at the large pores renders nucleation difficult and the solid solution particles tend to grow as platelets. At relatively low temperatures and high supersaturation, a relatively high driving force for nucleation and short mean distances of surface migration promote the growth of AlN–SiC solid solutions as polyhedrons. The formation of the ledges on the polyhedral particles is attributed to the differences in the evaporation rates and the deposition rates between Al and Si. At relatively low temperatures and an intermediate supersaturation, the solid solution particles grow as prismatic columns. The formation of the prismatic columns with a hexagonal plate, or a pyramidal cap, is attributed to a sudden change of temperature during combustion. A possible growth mechanism for the AlN–SiC solid solution cones is proposed.     

Rheological behavior of two-phase polymer melts

Rheological behavior of dispersed two-phase polymer melts has been investigated by means of a capillary rheometer. The two-phase systems chosen for study were blends of two polymers: high-density polyethylene and polystyrene, which are incompatible in the molten state. In order to investigate the state of dispersion, photographs were taken of the microstructure of extrudate samples, showing that the polystyrene forms long fibers or droplets as a discrete phase dispersed in the polyethylene which forms a continuous phase. Measurements were made of the axial pressure distributions of the two-phase molten polymers flowing through circular tubes, which permit one, according to the theory advanced by Han, to determine viscous and elastic properties of the melts. Also measured was melt die swell ratio. It has been found from the two independent experimental techniques that there exist a maximum and/or minimum elastic property at a certain blending ratio, and that the elastic property decreases first with L/D ratio of a capillary and then levels off.     

Manufacturing and foaming of high melt viscosity of polypropylene by using electron beam radiation technology

The high melt viscosity of polypropylene was studied by grafting bifunctional monomers, 1,6‐hexanediol diacrylate (HDDA) and tripropylene glycol diacrylate (TPGDA), onto homopolypropylene (HPP) and random ter‐polypropylene (RTPP) under electron‐beam irradiation. Creation of the high‐melt‐viscosity polypropylene was possible at low radiation dosage and low monomer content, under a prohibition of both radiation degradation and homopolymerization. TPGDA monomer was more effective in increasing the melt viscosity of HPP compared with RTPP, whereas HDDA monomer was more effective for enhancing the melt viscosity of RTPP. Such different effects of monomers on melt viscosity may arise from different monomer structures, namely, TPGDA has additional three methyl groups, but HDDA has no methyl groups. Electron‐beam radiation technology, on an increase of the melt viscosity, was much more effective in HPP than RTPP, when compared with virgin polymers. Modified RTPP and HPP with high melt viscosity were capable of foaming with numerous fine cells, of which the modified HPP with 1.5 mmol TPGDA and 0.5 kGy could create more spherical foam cells and its bending strength was 1.5 times more than that of the foamed RTPP. POLYM. ENG. SCI., 46:431–437, 2006. © 2006 Society of Plastics Engineers.     

Efective Object Identification and Association by Varying Coverage Through RFID Power Control简

This paper presents an effective power scheduling strategy for energy efficient multiple objects identification and association. The proposed method can be utilized in many heterogeneous surveillance systems with visual sensors and RFID （radio-frequency identification） readers where energy efficiency as well as association rate are critical Multiple objects positions and trajectory estimates are used to decide the power level of RFID readers. Several key parameters including the time windows and the distance separations are defined in the method in order to minimize the effects of RFID coverage uncertainty. The power cost model is defined and incorporated into the method to minimize energy consumption and to maximize association performance. The proposed method computes the power cost using the range of the outermost position for possible single association and group associations at every sampling time. An RFID reader is activated with the proper coverage range when the power cost for the current time is lower than the power cost for the next time sample. The simplicity of the power cost model relieves the problematic combinatorial comparisons in multiple object cases. The performance comparison simulation with the minimum and maximum energy consumption shows that the proposed method achieves fast single associations with less energy consumption. Finally, the realistic comparison simulation with the fixed range RFID readers demonstrates that the proposed method outperforms the fixed ranges in terms of single association rate and energy consumption.     

Communicating Is Crowdsourcing: Wi-Fi Indoor Localization with CSI-Based Speed Estimation

Numerous indoor localization techniques have been proposed recently to meet the intensive demand for location-based service (LBS). Among them, the most popular solutions are the Wi-Fi fingerprint-based approaches. The core challenge is to lower the cost of fingerprint site-survey. One of the trends is to collect the piecewise data from clients and establish the radio map in crowdsourcing manner. However the low participation rate blocks the practical use. In this work, we propose a passive crowdsourcing channel state information (CSI) based indoor localization scheme, C²IL. Despite a crowdsourcing based approach, our scheme is totally transparent to the client and the only requirement is to connect to our 802.11n access points (APs). C²IL is built upon an innovative method to accurately estimate the moving speed solely based on 802.11n CSI. Knowing the walking speed of a client and its surrounding APs, a graph matching algorithm is employed to extract the received signal strength (RSS) fingerprints and establish the fingerprint map. For localization phase, we design a trajectory clustering based localization algorithm to provide precise real-time indoor localization and tracking. We develop and deploy a practical working system of C²IL in a large office environment. Extensive evaluations indicate that the error of speed estimation is within 3%, and the localization error is within 2 m at 80% time in a very complex indoor environment.     

机载前视风切变检测气象雷达的研究进展

机载气象雷达是商业飞机强制安装的机载电子设备,可以称得上是“双眼 ”,它对于保障飞行安全具有举足轻重的作用。目前,机载气象雷达关键技术尚掌握在国外 生 产厂商手中。本文从机载气象雷达系统和机载气象雷达涉及的信号处理技术（包括降水目标 检测、湍流检测和低空风切变检测、地杂波抑制等）两个方面论述了机载气象雷达的发展历 程,指出了其中的关键技术和尚待解决的问题。最后,本文针对下一代具有增强型检测能力的 机载气象雷达系统及其相关技术进行了评述。     

Effect of water pretreatment on CO<Subscript>2</Subscript> capture using a potassium-based solid sorbent in a bubbling fluidized bed reactor

A bubbling fluidized bed reactor was used to study CO₂ capture from flue gas by using a potassium-based solid sorbent, sorbKX35 which was manufactured by the Korea Electric Power Research Institute. A dry sorbent, sorbKX35, consists of K₂CO₃ for absorption and supporters for mechanical strength. To increase initial CO₂ removal, some amount of H₂O was absorbed in the sorbent before injecting simulated flue gas. It was possible to achieve 100% CO₂ removal for more than 10 minutes at 60°C and a residence time of 2 s with H₂O pretreatment. When H₂O pretreatment time was long enough to convert K₂CO₃ of sorbKX35 into K₂CO₃ · 1.5H₂O, CO₂ removal was excellent. The results obtained in this study can be used as basic data for designing and operating a large scale CO₂ capture process with two fluidized bed reactors. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Buckling of jets in electrospinning

Various buckling instabilities of electrospinning jets were observed and compared with the buckling instabilities of uncharged fluid jets. Buckling instability arises due to jet compression at impingement on a collector surface and occurs independently of the electrical bending instability. The velocity, diameter, density and viscosity of the electrospinning jets are the key factors that determine the buckling frequency. The electrically charged jets impinging onto grounded, horizontal or inclined (wedge-like) electrodes moving laterally at a constant velocity are studied experimentally. Straight and bending (electrospinning) jets emerge at short and sufficiently long inter-electrode distances, respectively. The experiments show that both straight segment and bending jets, when impinging onto a counter-electrode, buckled and produced patterns of meandering deposits. In the case of bending electrospun jets these short-length buckling patterns were superimposed on the bending loops found in the deposits. Buckling-related and bending-related morphologies are easily distinguishable. The buckling patterns have frequencies of the order of 10⁵-10⁶ Hz, whereas the bending loops are formed at the frequencies of the order of 10³ Hz. The deposited buckling patterns include sinuous, zigzag-like, figures-of-eight, recurring curves, coiled and other structures that resembled many patterns created by uncharged jets of highly viscous fluids impinging a hard flat surface. In addition, several new morphologies which were not observed before with uncharged jets were found. The experimentally measured frequencies of the buckling patterns were compared to the theoretical predictions and a reasonable agreement was found.