Biodegradability of cellulose fabrics

Biodegradability of cellulose fabrics was evaluated by use of a soil burial test, an activated sewage sludge test, and an enzyme hydrolysis. Surface changes after biodegradation were observed by optical microscopy. From X‐ray diffraction analysis (XRD), changes in the crystallinities and the internal structures as a result of degradation were also investigated. It was shown that biodegradability decreased in the following order: rayon > cotton ? acetate. Rayon fibers, which have a low crystallinity and a low degree of orientation, showed the highest biodegradability in most cases. However, in spite of its low crystallinity, acetate fibers exhibited very low biodegradability, probably because of the presence of hydrophobic groups in its structure. On the other hand, linen showed an inconsistent behavior in that it had the highest biodegradability in the soil burial test, but a lower biodegradability than that of cotton in the activated sewage sludge test. XRD analysis revealed that there was a slight increase in the crystallinity of linen, cotton, and rayon fabrics at the initial stage, but a continuous decrease thereafter. From the correlation analysis, it was revealed that the biodegradability of cellulose fabrics was closely related to the moisture regain of the fibers, which reflects the hydrophilicity and internal structure of the fibers at the same time. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 248–253, 2004     

Determining node duty cycle using Q-learning and linear regression for WSN

Wireless sensor network(WSN)is effective for monitoring the target environment,which consists of a large number of sensor nodes of limited energy.An efficient medium access control(MAC)protocol is thus imperative to maximize the energy efficiency and performance of WSN.The most existing MAC protocols are based on the scheduling of sleep and active period of the nodes,and do not consider the relationship between the load condition and performance.In this paper a novel scheme is proposed to properly determine the duty cycle of the WSN nodes according to the load,which employs the Q-leaming technique and function approximation with linear regression.This allows low-latency energy-efficient scheduling for a wide range of traffic conditions,and effectively overcomes the limitation of Q-learning with the problem of continuous state-action space.NS3 simulation reveals that the proposed scheme significantly improves the throughput,latency,and energy efficiency compared to the existing fully active scheme and S-MAC.     

Effect of yttrium on the stability of aluminide-yttrium composite coatings in a cyclic high-temperature hot-corrosion environment

A composite coating of aluminide-yttrium has shown excellent corrosion resistance in a cyclic high-temperature hot-corrosion environment. To understand the effect of yttrium on the stability of the composite coating, the specimens were prepared with various coating parameters of Y thickness, sequence of post heat treatment and surface condition before Y-ion plating. Performance of the composite coating was evaluated by isothermal oxidation and cyclic high-temperature hot corrosion. Isothermal-oxidation-test results show that the Y in the composite coating helps to form a thick and dense Al₂O₃ scale which is ductile and resistant to thermal stress. The Y in Al₂O₃ may act as a donor which leads to an increase in concentration of interstitial oxygen and, thus, increases in oxidation rate. The presence of Y₂O₃ and (Y, Al) O-type compounds in grain boundaries of Al₂O₃ and boundaries between the Al₂O₃ and NiAl effectively prohibits the fast diffusion of oxidants (such as O and S) and Al along grain boundaries. Consequently, it may induce slow diffusion through the matrix, and thus the corrosion resistance of the composite coating under cyclic hot corrosion increases substantially.     

Thermal stability of lamellar structure of PST crystal and lamellar boundary design for creep resistant TiAl alloy

The stability of lamellar structure is crucial for the creep resistance of TiAl alloys, but degradation of the lamellar structure is unavoidable at high temperatures. The degradation of the lamellar structure in PST crystals of Ti-48mol.%Al was studied during high temperature exposure (annealing and creep testing) to examine how to make a stable lamellar structure with high creep deformation resistance. Since the six orientation variants of γ lamellae are nucleated independently of the adjoining lamellae, pseudo twin and 120° rotational fault boundaries are most frequently observed at the initial stage of lamellar formation. The preferential removal of high energy (pseudo twin and 120° rotational fault) boundaries during the evolution of lamellar structure results in the highly probable appearance of a true twin boundary at a later stage of lamellar evolution. The coarsening of lamellar spacing and the spheroidization of the lamellae are the major degradation events occurring during creep deformation, and the migration of the lamellar boundaries brings both of them about. The lamellar structures of TiAl alloy contain four types of lamellar boundaries. The stability of the four types of boundaries decreases in the following order: γ/α₂ > true twin > pseudo twin > or=120° rotational fault boundaries. The γ/α₂ boundary has the highest stability (lowest mobility), and the high density of γ/α₂ boundaries is proposed to make a stable lamellar structure with good creep resistance. A material having the high density of γ/α₂ boundaries was produced through the heat treatment of a PST crystal in the α+γ two-phase regime. The excellent creep properties of the material were proven through creep tests of hard oriented PST crystals made of the material. This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials,” organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei University, Seoul, Korea on October 25–26, 2002.     

The influence of titanium on the electrochemical properties of the AB5-type metal hydrides

AB₅-type intermetallic compounds were prepared by arc-melting in argon atmosphere. The composition of a stoichiometric compound LaNi_3.6Al_0.4Co_0.7Mn_0.3 with a hexagonal CaCu₅ structure was varied by stoichiometric and nonstoichiometric addition of Ti. With the increase of the Ti y0.05 content in LaNi_3.6Al_0.4Co_0.7Mn_0.3Ti_y, the hydrogen storage capacity is enhanced, whereas when y=0.1–0.3, it is decreased. The discharge capacity and cyclability are increased considerably by addition of titanium in the range of 0.02–0.1 with a maximum value at about 0.1%. The highest maximum capacity is achieved for a nonstoichiometric addition of 0.05% Ti. The kinetic properties are also additionally improved by the formation of a titanium-rich second phase. This can explain the improvement of the capacity for alloys with low Ti content. The decrease in capacity for high Ti content was also correlated with the amount of the Ti-rich phase. Therefore, the improvement of kinetics are due to the catalytic effect, grain boundary diffusion effect or more pronounced alloy pulverization upon cycling. This study has been aimed to improve the electrode properties of a series of multicomponent LaNi_3.6Al_0.4Co_0.7Mn_0.3Ti_y (y=0.0, 0.02, 0.05, 0.1, 0.2, 0.3) alloys which have mutual complementary properties. All the prepared alloys have been subjected to analyses by EDS, SEM and XRD. In order to determine the hydrogen storage capacity, the pressure composition isotherms (P–C–T curves) have been used. The metal hydride electrodes were characterized by galvanostatic cycling test.     

Effect of minor elements on hot cracking susceptibility of austenitic stainless steel welds

This research evaluates the effects of Si, N and REM on the hot cracking behavior of specially designed austenitic stainless steels. Varestraint hot cracking tests and microstructural examination revealed that solidification cracking of 304 can be minimized by a suitable addition of Si, N and control of the solidification mode. Further, the addition of N to “fully” austenitic 316 weld metal decreased solidification cracking susceptibility. REM additions were also effective in reducing solidification and weld metal HAZ liquation cracking in 347, but was ineffective for reduction in base metal HAZ liquation cracking.     

Effect of low-cycle fatigue on the hot ductility of plain carbon steel

In a continuous casting steelmaking operation, the surface of a slab is under a condition that can be characterized as high-temperature, low-cycle fatigue in which the tensile and compressive stress is repeatedly developed. For this reason, for the evaluation of the hot ductility of a slab, considering the fatigue deformation is more feasible before a tensile or compressive test. In this study, the effects of low-cycle fatigue on the hot ductility of steels with a carbon content of 0.06–0.8 wt.% are investigated at various temperatures. For a carbon content of 0.06%, there were no significant differences between the RA values from a simple tensile test and those from a tensile test after fatigue deformation. The tendency of ductility deterioration with fatigue deformation is evident in 0.1 %C steel, and is due to the deformation-induced ferrite film that forms around the prior austenite grain. Conversely, high carbon steel containing 0.8 %C did not show a recovery of hot ductility in a low temperature region, and the specimen on which the tensile was measured after fatigue showed a higher hot ductility in the low temperature region, which is thought to result from the pearlite refinement effects. As the results obtained in this work showed noticeable differences in the hot ductility of carbon steel through the test conditions, it is suggested that for more accurate data, fatigue deformation be adopted in which the temperature range in an unbending operation is determined in the steelmaking factory.     

Magnesium interlayered diamond coating on silicon

Diamond thin films have been deposited using hot filament chemical vapour deposition technique on manually scratched p-Si(1 0 0) substrate, with and without magnesium interlayer. In spite of magnesium melting point being lower (T_m = 649 °C) than the growth temperature of the substrate (T_s  750 °C) used in these experiments, it was found that high quality diamond films could be grown on Mg covered substrate. A liquid substrate is probably generated during the diamond film growth. Raman spectroscopy analysis exhibited only the triply degenerate, zone centre optical phonon peak at 1333 cm⁻¹ indicating that nearly stress free crystallites were present. Broadening of the Raman peak (11.76 cm⁻¹) indicates that some small crystallites also are present. Scanning electron and atomic force microscopy accompanied by X-ray diffraction analysis where used to compare the details of diamond film growth directly on scratched Si(1 0 0) and Mg interlayered scratched Si(1 0 0) substrates.     

Micro-end-milling of single-crystal silicon

Ductile-regime machining of silicon using micro-end-mill is almost impossible because of the brittle properties of silicon, crystal orientation effects, edge radius of the cutter and the hardness of tool materials. Micro-end-milling can potentially be used to create desired three dimensional (3D) free form surface features using the ductile machining technology for single-crystal silicon. There is still a lack of fundamental understanding of micro-end-milling of single-crystal silicon using diamond-coated tool, specifically basic understanding of material removal mechanism, cutting forces and machined surface integrity in micro-scale machining of silicon. In this paper, further research to understand the chip formation mechanism was conducted. An analysis was performed to discover how the chips are removed during the milling process. Brittle and ductile cutting regimes corresponding to machined surfaces and chips are discussed. Experiments have shown that single-crystal silicon can be ductile machined using micro-end-milling process. Forces generated when micro-end-milling single-crystal silicon are used to determine the performance of the milling process. Experimental results show that the dependence of the cutting force on the uncut chip thickness can be well described by a polynomial function order n. As cutting regime becomes more brittle, the cutting force has more complex function.     

Frequent Interaction and Fast Feedback Predict Perceived Social Support: Using Crawled and Self‐Reported Data of Facebook Users

The present study examines if Facebooking can contribute to psychological well‐being and if so, which aspects of Facebook use could play a significant role. Matching crawled data with self‐reported data from mobile Facebook users, we found that more social interactions with Facebook friends and faster friends' reactions to a user's post contributed toFacebook user's perceived social support and ultimately alleviated loneliness. We also found that the association between frequency as well as speed of Facebook social interactions and psychological well‐being were more significant among those who were sensitive to other's behaviors and feelings than those who were not. The theoretical and practical implications of the findings, particularly regarding mobile communication context, are also discussed.