Effects of thermal creep of prestressed steel on post‐tensioned concrete slabs in and after fire

The effects of thermal creep of prestressed steel on post‐tensioned concrete slabs in and after fire were investigated based on an existing thermal creep model and calibrated parameters in this paper. A nonlinear finite element model was built up employing ABAQUS package, taking into account frictionless contact behaviour between prestressed steel tendons and surrounding concrete. The nonlinear material behaviour of concrete and prestressed steel at elevated temperatures was taken into account, where three material models for prestressed steel were adopted with or without considering thermal creep, and based on the model from EN 1992‐1‐2. The finite element model developed was verified against experimental results from the literature, showing that the model considering thermal creep was more accurate. Then the fire resistance period and responses of post‐tensioned concrete slabs in and after fire were investigated based on the verified model. Ignoring thermal creep underestimated the fire resistance period but overestimated the residual tendon stresses. The model from EN 1992‐1‐2 achieved nearly the same effects as the model considering thermal creep in fire but might yield inaccurate evaluation of residual tendon stresses. The model considering thermal creep worked well under fire and in the post‐fire conditions yielding reasonable predictions.     

Optimization of culture condition for ACEI and GABA production by lactic acid bacteria

Abstract: Gamma‐aminobutyric acid (GABA) and angiotensin‐converting enzyme inhibitor (ACEI) are compounds which can influence hypertension. The goal of this study is to optimize the culture condition for GABA and ACEI production by Lactobacillus plantarum NTU 102 fermented skim milk. In this study, we used 3‐factor‐3‐level Box–Behnken design combining with response surface methodology, where the 3 factors represent the concentration of skim milk, the concentration of monosodium glutamate, and culture temperature. Best conditions for GABA and ACEI production differed. The results indicated that L. plantarum NTU 102 produced the highest combined levels of GABA and ACEI at 37 °C, in milk having 8% to 12% nonfat solids supplemented with 0.6% to 1% MSG. Agitation of the medium during fermentation had no effect on GABA or ACEI production but extended incubation (up to 6 d) increases levels of the bioactive compounds. L. plantarum NTU 102 fermented products may be a potential functional food source for regulating hypertension.     

Influence of ventilation arrangements on particle removal in industrial cleanrooms with various tool coverage

This paper aims to investigate the influence of comparative ventilation arrangements (wall-return, locally balanced ceiling-return, and four-way ceiling-return) on the airflow distribution and particle fates within cleanrooms of ISO cleanliness class 7 with various tool coverage ratios (0%, 38%, and 60%). Computational fluid dynamics (CFD) was employed to analyze and compare the influence of the three ventilation arrangements on concentrations for particles of various sizes (diameters ranging from 0.01 to 100 μm) in the cleanrooms. The techniques of Eulerian and Lagrangian in CFD were employed for solving the continuous fluid and tracking the particle trajectory, respectively. The outcomes from this study suggested that particle removal rates for the given cleanrooms were significantly affected by the tool coverage ratios, the design of ventilation, and the particle sizes of concerns. In the cases of heavy tool coverage, the locally balanced ceiling-return ventilation arrangements can minimize the need for the relocation of the production lines and layouts of the production tools in cleanrooms, and may provide viable solutions to effective contamination without compromising contamination effectiveness or efficiency.     

Prediction of optimum reaction conditions for the thermo‐tolerant acetylxylan esterase from Neocallimastix patriciarum using the response surface methodology

BACKGROUND: Xylan is the second most abundant renewable polysaccharide in nature and also represents an important industrial substrate. The complete degradation of xylan requires the combination of several types of xylanolytic enzymes, including endo‐β‐1,4‐xylanases, β‐xylosidases, and acetylxylan esterases. As a biocatalyst, xylanolytic enzymes with good thermal stability are of great interest, therefore, a thermo‐tolerant acetylxylan esterase, AxeS20E, was investigated. RESULTS: The cDNA encoding the carbohydrate esterase (CE) domain of AxeS20E from Neocallimastix patriciarum was expressed in Escherichia coli as a recombinant His₆ fusion protein. The recombinant AxeS20E protein was obtained after purification by immobilized metal ion‐affinity chromatography. Response surface modeling (RSM) combined with central composite design (CCD) and regression analysis were then employed for the planned statistical optimization of the acetylxylan esterase activities of AxeS20E. The optimal conditions for the highest activity of AxeS20E were observed at 54.6 °C and pH 7.8. Furthermore, AxeS20E retained more than 85% of its initial activity after 120 min of heating at 80 °C. CONCLUSIONS: The results suggested that RSM combined with CCD and regression analysis were effective in determining optimized temperature and pH conditions for the enzyme activity of AxeS20E. The results also proved AxeS20E was thermo‐tolerant and might be a good candidate for various biotechnological applications. Copyright © 2009 Society of Chemical Industry     

Unified feature analysis in JPEG and JPEG 2000-compressed domains

Retrieving images compressed by different algorithms typically involves a pre-processing operation to decompress them onto the spatial domain from which features are extracted for further analysis. Our objective is to investigate common features that can be found in JPEG-compressed and JPEG 2000-compressed images so that image indexing can be done directly in their respective compressed domains. A fundamental difference between JPEG and JPEG 2000 is their transforms; the former uses a block-based discrete cosine transform (BDCT) while the latter uses a wavelet transform (WT). Direct comparison on BDCT blocks and WT subbands cannot reveal their relationship. By employing our proposed subband-filtering model, the BDCT coefficients can be concatenated to form structures similar to WT subbands. Our theoretical studies show that the concatenated BDCT and WT filters share common characteristics in terms of passband regions, magnitude and energy spectra. In particular, their low-pass filters are identical for Haar wavelets and highly similar for other wavelet kernels. Despite the fact that compression can affect features that can be extracted, our experimental results confirm that common features can always be extracted from JPEG- and JPEG 2000-compressed domains irrespective of the values of the compression ratio and the types of WT kernels used. As a result, similar JPEG-compressed and JPEG 2000-compressed images can be retrieved from one another without requiring a full decompression.     

Development of digital image correlation method to analyse crack variations of masonry wall

The detection of crack development in a masonry wall forms an important study for investigating the earthquake resistance capability of the masonry structures. Traditionally, inspecting the structure and documenting the findings were done manually. The procedures are time-consuming, and the results are sometimes inaccurate. Therefore, the digital image correlation (DIC) technique is developed to identify the strain and crack variations. This technique is non-destructive for inspecting the whole displacement and strain field. Tests on two masonry wall samples were performed to verify the performance of the digital image correlation method. The phenomena of micro cracks, strain concentration situation and nonuniform deformation distribution which could not have been observed preciously by manual inspection are successfully identified using DIC. The crack formation tendencies on masonry wall can be observed at an earlier stage by this proposed method. These results show a great application potential of the DIC technique for various situations such as inspecting shrinkage-induced cracks in fresh concrete, masonry and reinforced concrete structures, and safety of bridges.     

A Fully Integrated MIMO Multiband Direct Conversion CMOS Transceiver for WLAN Applications (802.11n)

802.11n is the latest offering from the IEEE standard committee tasked with enabling and enhancing WLAN systems. This standard utilizes several techniques to offer a much larger rate versus range than the legacy WLAN systems. A single-chip multiband direct-conversion CMOS MIMO transceiver (2times2) targeted for WLAN applications is presented. This transceiver is capable of satisfying the requirements of the draft 802.1 In standard and achieves PHY rates of > 270 Mb/s. The receivers and transmitters achieve an EVM of better than -41 dB (0.9%) and -40 dB (1.0%) operating in legacy g and a modes, respectively. From a 1.8 V supply and with both cores operating, the chip draws 275 mA in RX mode and 280 mA in TX mode.     

2D-numerical analysis of hydraulic fracturing in heterogeneous geo-materials

A geo-material failure process analysis (F-RFPA2D), considering the coupling of stress distribution, fluid flow, and element damage evolution, is used to investigate the mechanisms of crack initiation and propagation around a 2-D cylindrical cavity in heterogeneous stiff soils during hydraulic fracturing. A large number of numerical analysis on hydraulic fracturing in stiff soil with pre-existing injection cavity have been carried out to study the mechanism of hydraulic fracturing in stiff soil. In addition, the characteristic of acoustic emission (AE) due to hydraulic fractures are studied by numerical simulations. The results provide a better understanding of the crack initiation and propagation mechanisms during hydrofracturing. The simulation software package can be a powerful tool for study of soil behavior during hydraulic fractures.     

Real-time GA-based rescheduling approach for the pre-sewing stage of an apparel manufacturing process

In this paper, a real-time segmentation rescheduling (RSR) approach using genetic algorithms to handle the production planning and scheduling problem in dynamic apparel manufacturing environment is proposed. Experiments based on the actual production data were conducted to validate the performance of the RSR approach. The experimental results indicated that the makespan and the influence caused by the change of schedule could be minimised.