Showing papers by "Xiao Dong Chen published in 2009"

Effects of pulsed electric fields (PEF) treatment on physicochemical properties of potato starch.

Abstract: Potato starch–water suspensions (8.0%, w/w) were subjected to pulsed electric fields (PEF) treatment at 30 kV·cm − 1 , 40 kV·cm − 1 and 50 kV·cm − 1 , respectively. The physicochemical properties of PEF-treated potato starch samples were investigated using scanning electron microscopy (SEM), laser scattering technique, X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and the Brabender rheological method, with native potato starch as reference. It has been concluded from SEM analysis that dissociation and damage of PEF-treated potato starch granules appeared. Some granules aggregated with each other and showed gel-like structures. It was revealed from particle size analysis that there was an obvious increase of the granule size after PEF treatment. This has been attributed to the aggregation among granules. It was also demonstrated from other analysis that relative crystallinity, gelatinization temperatures, gelatinization enthalpy, peak viscosity as well as breakdown viscosity of modified samples all decreased with increasing electric field strength. Industrial relevance In this study, the effect of PEF treatment (up to 50 kV·cm − 1 ) on physicochemical properties of potato starch has been investigated. The results from SEM images showed that dissociation, denaturation and damage of potato starch granules had been induced by the PEF treatments. Some of granule fragments showed gel-like structures, and congregated with each other or with other starch granules. Laser scattering measurements of particle size revealed that an obvious increase of granule size under electric field strength of 50 kV·cm − 1 , which was attributed to the aggregation of the starch granules. The X-ray diffraction pattern showed an obvious loss of crystalline structure after the PEF treatment at 50 kV·cm − 1 , which induced a trend of transformation from crystal to non-crystal in potato starch granules. DSC analysis showed a decrease in gelatinization temperatures ( T o and T p ) and gelatinization enthalpy (Δ H gel ) with increasing electric field strength. Brabender rheological method has been used to show that the peak viscosity and breakdown viscosity decrease with increasing electric field strength of PEF treatment. All the results reveal that the PEF treatment can lead to an intragranular molecular rearrangement of potato starch granules, which induces changes of various physicochemical properties of the treated starch thus may endow it some new characteristics and functions. This phenomena may warrant further more detailed study.

A Small Printed Quasi-Self-Complementary Antenna for Ultrawideband Systems

Abstract: A novel and simple ultrawideband (UWB) printed quasi-self-complementary antenna is presented. The proposed antenna, which is fed by a microstrip line, has been demonstrated to provide an ultrawide 10-dB impedance bandwidth with satisfactory radiation properties. It also features both physically and electrically small dimensions, 16 mm times 25 mm in a physical size and 0.24lambda in an electrical size, respectively. The key parameters that affect the performance of the antenna are investigated. A good agreement is achieved between the simulation and the measurement.

Numerical Study of the Drying Process of Different Sized Particles in an Industrial-Scale Spray Dryer

Abstract: Development of high-performance spray dryers that are more energy efficient and are able to produce high-quality milk powders is very important for the future of the dairy powder industry. Understanding and optimization of the exiting dryers are also of great value. Computational fluid dynamics is a powerful tool to simulate and help understanding the characteristics of spray drying and to introduce potentially improved designs. The present study has concentrated on the multiphase flow in an industrial-scale spray dryer using the CFD package FLUENT. A Eulerian-Lagrangian approach is used in the simulations. A new drying model, REA model, for milk particles has been implemented for the first time in a CFD application. The numerical results match well with the plant data. It is argued that the “reflecting wall” boundary condition produced more physically correct results for normal dryer operation than the “escaping wall” boundary condition. The second one is an oversimplification. The influences of the part...

Thermomechanical property of rice kernels studied by DMA.

Abstract: The thermomechanical property of the rice kernels was investigated using a dynamic mechanical analyzer (DMA). The length change of rice kernels with a loaded constant force along the major axis direction was detected during temperature scanning. The thermomechanical transition occurred in rice kernels when heated. The transition temperatures were determined as 47°C, 50°C and 56°C for the medium-grain rice with the moisture contents of 18.1%, 16.0% and 12.5% (wet basis), respectively. Length change of the rice kernels increased with the increase of the temperature and moisture content. Among the four rice varieties investigated, the results showed that the thermomechanical property was not significantly affected by variety.

Effects of Incubation Temperature, Starter Culture Level and Total Solids Content on the Rheological Properties of Yogurt

Abstract: The effects of incubation temperature (35-45oC), starter culture level (0.003-0.006%, w/v), and milk total solids content (12.32-15.68%, w/v) on the rheological properties of yogurt were investigated using central composite rotatable design (CCRD) and response surface methodology (RSM). Gelation time during milk fermentation and apparent viscosity of yogurt stored for 3 days were the rheological parameters studied. The results revealed that the gelation time and apparent viscosity of yogurt were significantly affected (P < 0.1) by incubation temperature, starter culture level, and total solids. Incubation temperature had the greatest influence on the gelation time. Higher temperature led to shorter gelation time, but resulted in lower apparent viscosity of yogurt. Apparent viscosity of yogurt was mainly affected by total solids. Higher apparent viscosities were also obtained at lower incubation temperature.

A composite reaction engineering approach to drying of aqueous droplets containing sucrose, maltodextrin (DE6) and their mixtures

Abstract: Recently, several studies have been published on the spray drying of sucrose and other low-molecular-weight sugars which are typically sticky materials. Sticky materials can not be processed under normal drying conditions and may require addition of high-molecular-weight carbohydrates such as maltodextrin. Predicting appropriate drying conditions are however difficult due to the unavailability of drying kinetics. In this article, we have formulated the drying kinetics model using the reaction engineering approach (REA) for the drying of aqueous sucrose and aqueous maltodextrin (DE6) droplets. The relative activation energy was empirically obtained based on experimental measurements. To model the drying of droplets containing both solutes (sucrose and maltodextrin), a new "composite" REA has been established and presented here for the first time. Results demonstrated that the composite REA forms a reliable framework to model the drying of aqueous solutions of pure carbohydrates and their mixtures.

A Three-Dimensional Numerical Study of the Gas/Particle Interactions in an Industrial-Scale Spray Dryer for Milk Powder Production

Abstract: Gas/particle interaction plays an important role in modern spray dryers and may have influences on wall deposition, agglomeration, powder degradation, etc. In the present study, the three-dimensional (3-D) transient multiphase flow in an industrial-scale spray dryer has been investigated using the CFD package FLUENT. The Eulerian–Lagrangian approach and two-way coupling method were used in the simulations. The reaction engineering approach (REA model) for milk particles has been implemented. Some new characteristics of the gas flow pattern and the particle behavior (e.g., temperature–time profiles) were identified from the numerical results; for example, the milk particles flow in such a way that makes the central jet oscillation more nonlinear. The discrete phase enhances the turbulence near the air/droplet inlet but damps it downstream. The transient turbulent flow causes significant uncertainties in the particle tracking, which presented some challenges in simulations. The study has highlighted the imp...

Effect of high-dose methylprednisolone treatment on Th17 cells in patients with multiple sclerosis in relapse.

Abstract: Objectives – Growing evidences have suggested that Th17 cells are involved in the pathogenic mechanisms of multiple sclerosis (MS) Treatment with high-dose intravenous methylprednisolone (IVMP) has beneficial effects on functional recovery in patients with MS during relapse The present study was designed to analyze the influences of IVMP on Th17 cells in patients with MS after a 5-day high-dose IVMP treatment Materials and methods – Th17 cell count and the production of IL-17 in peripheral blood mononuclear cells (PBMCs) were measured using flow cytometry and ELISA respectively Quantitative real-time PCR was performed to analyze the mRNA expression of Th17 cell-related factors (IL-17, RORc and IL-23R) in PBMCs Results – A significant reduction in IL-17 production and Th17 cells count in PBMCs was found in patients with MS after IVMP treatment Moreover, the expression of IL-17, IL-23R and RORc mRNA decreased significantly after IVMP treatment Conclusions – Treatment with methylprednisolone has a suppressive effect on Th17 cells and may be related to its clinical efficiency

Effects of Drying Methods on the Release Kinetics of Vitamin B12 in Calcium Alginate Beads

Abstract: The aim of this article was to investigate the morphology, swelling properties, and respective drug release kinetics of vitamin B12–loaded calcium alginate beads prepared by oven (air), vacuum, and freeze drying. The initial particle size was 1 mm. The mean bead sizes of dried Ca-alginate beads were 0.7, 0.8, and 0.9 mm for oven-, vacuum-, and freeze-dried beads, respectively. The surface morphology of the dried beads was affected by the different drying methods applied. Oven- and vacuum-dried beads shrank in size, and more cracks appeared on the surface of oven-dried beads. Freeze-dried beads almost retained the same size prior to drying; however, the surface was rougher and highly porous. The swelling profiles were also affected by the drying methods, whereby freeze-dried beads showed the fastest solvent uptake at the start of the experiment. The release data of the dried Ca-alginate beads were treated with first-order, Higuchi, Korsmeyer, and Peppas kinetic models. The data for oven and vacuum seemed t...

Ultra wideband powerline communication (PLC) above 30 MHz

Abstract: A novel study of ultra wideband (UWB) communication over the indoor powerline channel, in a wide frequency range up to 1 GHz is presented. An exhaustive measurement campaign was conducted on a test bed that replicated the environment of an indoor powerline network. The aim of this study was to observe and analyse the transmission and noise properties of such a broadband powerline channel. A time domain channel model has been used to study the broadband channel response of the powerline. Measurement and modelling results show that the indoor powerline channel provides a communication link in the 50-550 MHz frequency range. Channel capacity is greatly enhanced by exploiting the 500 MHz bandwidth. The conclusions of this study indicate that gigabit per second data rate transmission are possible over the indoor powerline channel in 50-550 MHz.

Inactivation Kinetics of Yeast Cells during Infrared Drying

Abstract: In this study, aqueous yeast suspensions were used to investigate the effects of drying (in an infrared heating environment) on the survival of yeast. The processes were modeled mathematically using a range of kinetics rate equations. The model parameters for each kinetic rate expression were obtained using a Matlab optimization procedure and the more suitable models describing the inactivation processes were identified. In order to provide the data for model validation, experiments were conducted using freshly prepared yeast suspensions. Additional experiments were also performed that further demonstrate the protective effects of sucrose and skim milk solids on yeast survival during drying. The simple Arrhenius equation was found to be a good model for predicting yeast survival during the control experiments, when heat was applied without dehydration occurring. Models incorporating both temperature and moisture content were more effective in describing yeast inactivation during drying. The model that gav...

The impact of various drying kinetics models on the prediction of sample temperature-time and moisture content-time profiles during moisture removal from stratum corneum

Abstract: An attempt has been made here to model the moisture transport kinetics across porcine stratum corneum. Samples of porcine skin were dissected in the form of ‘thin layers’ (i.e. stratum corneum) of dimensions of 11.3 × 11.3 mm (70–200 μm thick). These layers were dried in a laboratory convection air dryer at 37 °C (normal human body temperature). The changes in weights of the samples were noted. The weight loss data was then converted in terms of moisture content (dry basis) and were monitored over time. Thereafter they were fitted against an empirical equation notably the Page model (Model 1) and the solution generated by the Fickian diffusion equation (Model 2). The current paper demonstrates the effectiveness of these two models in prediction of the sample temperature during drying. Furthermore, it also demonstrates the variation in spatial distribution of moisture content within the skin sample when moisture content and temperature dependency are introduced in the diffusivity. Such findings are important especially when developing skin multi-compartment physiologically based pharmacokinetic (PBPK) models to assess transdermal permeation of various hydrophilic penetrants.

Engineering Data of Diameter Change during Air Drying of Milk Droplets with 40 wt% Initial Solids Content

Abstract: Spray drying of liquid food droplets is one of the primary means of manufacturing food powders today. Modeling this process requires single-droplet drying modeling, and droplet size change during drying is one part of such modeling. Some experimental data of milk droplet diameter change at 20 and 30 wt% are reported in literature.[ 1 ] Data are not available at higher solid contents, which are of interest to the industry. We now report the experimental results of the effects of drying conditions on milk droplet size change (using projected area diameter as the parameter) using the glass filament technique, complimented by video imaging analysis software. Under the constant drying air conditions for solids content of 40 wt%, and for both skim and whole milk, the droplet diameter changes were correlated using the previous model of Lin and Chen.[ 1 ] With previous data together, the shrinkage coefficients were correlated against solids content.

A Simple Nongravimetric Technique for Measurement of Convective Drying Kinetics of Single Droplets

Abstract: In this article, a method is presented to measure the moisture content of single droplets/particles under air convection based on accurate measurement of the droplet/particle diameter and temperature. Experiments on droplets/particles of aqueous glucose were conducted as an example, and the results obtained support validity of such a method.

High power Terahertz generation by using vacuum electronic technology

Abstract: With the fast development of Terahertz (THz) related technologies, more and more applications, such as high bandwidth communications, radar, and secure detection, which require higher power, more reliable THz radiation sources. There are different approaches to generate THz radiation. In this paper, we mainly focus on the vacuum electronic technology, which has the potential to provide a sufficient high power to facilitate a wide range of THz applications.

Environment effects and system performance characterisation of GPS antennas for mobile terminals

Abstract: The GPS antenna on mobile terminals suffers from multipath effects owing to reflection, diffraction and scattering of the incident wave in a radio environment. A traditional approach to evaluate the GPS antenna performance in a real multipath environment is therefore insufficient. Presented is a new technique to characterise these environmental effects and the system performance of GPS antennas on mobile terminals.

Study on Creep Properties of Japonica Cooked Rice and Its Relationship with Rice Chemical Compositions and Sensory Evaluation

Abstract: Creep properties of four varieties japonica cooked rice were tested using a dynamic mechanical analyzer (DMA Q800). The creep curve was described by Burgers model. The creep process of japonica cooked rice mainly consisted of retarded elastic deformation, R and viscous flow deformation, V, and negligible instantaneous elastic deformation, E. The retarded elastic modulus, E2, relaxation time, τ , and the viscosity coefficient, η1, of the cooked rice according to the Burger model were estimated through nonlinear regression. The effect of the chemical compositions on the rheological parameters based on creep behavior of cooked rice was assessed. Correlation analysis indicated that the retarded elastic modulus, E2, had positive correlations with protein (r = 0.952, P = 0.048). The relaxation time, τ , had negative correlation with protein content (r = -0.909, P = 0.091). The viscosity coefficient, η1, was negatively correlated to amylose (r = -0.915, P = 0.085). The analysis between creep parameters and sensory evaluation showed that the viscosity coefficient, η1, positively correlated to stickiness and total evaluation of cooked rice. So it can be used to evaluate the eating quality of cooked rice.

Measurement and simulation of powerline channel using OFDM for UWB communication

Abstract: This paper presents the study of the UWB (Ultra Wideband) transmission characteristics over household powerline in a very high frequency band, from 50 MHz to 550 MHz. The characteristics of indoor powerline channels are examined for its use in UWB Communication in both measurements and software simulations. Firstly, broadband channel characteristics are measured in both frequency and time domain, followed by system level simulation of BER performance versus 0 / b E N . This paper presents a concept of utilising the MB-OFDM UWB model for broadband powerline communication. Results indicate that high data rate transmission is possible, by exploiting the powerline channel for UWB signal transmission in 50 – 500 MHz.

Effects of encapsulation process parameters of calcium alginate beads on Vitamin B12 drug release kinetics

Abstract: Calcium alginate beads were prepared by ionotropic gelation of droplet of an alginate solution containing Vitamin B12, followed by oven air drying at 70° C. The beads were characterized by a light microscope and in vitro drug release in phosphate buffer saline (PBS) solution (pH 7.4) maintained at 37° C in order to simulate intestinal fluid conditions. The effect of drug configuration within a bead, various process factors on the bead morphology and drug release properties was investigated. The experimental results indicated that altering the polymer to drug loading ratio, alginate, Vitamin B12 concentration and flow rates affected the Vitamin B12 release rates. The addition of chitosan to the polymer matrix was found to have a significant impact on the rate of release, as it slowed down the release of Vitamin B12. It has also been found that some combinations of the parameters mentioned above, thermal effects in particular, were able to create the clear wall-core structures, and it is envisaged that one can apply those combinations or at least adopt the overall trend in a more advanced equipment to achieve controlled releasing drug micro-capsules. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

Miniaturised antennas for UWB communications

Abstract: A brief review on our recent work on the miniaturised UWB antennas is presented. Three compact designs of UWB antennas are exemplified to illustrate their respective features and operations.