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      • KCI등재SCOPUS

        Use of supercritical methanol/carbon dioxide mixtures for biodiesel production

        María,Belén,García-Jarana,Jezabel,Sánchez-Oneto,Juan,Ramón,Portela,Lourdes,Casas,Casimiro,Mantell,Enrique,Martínez,de,la,Ossa 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.8

        The use of supercritical conditions for the production of biodiesel from both vegetables oils and waste-oils may be of great industrial interest because it can be carried out without those catalysts necessary in the conventional transesterification process, therefore avoiding a complex separation between the product and the catalyst. However, the use of supercritical alcohol requires higher operating temperatures and pressures. In this work, CO2 was added to the reaction mixture in order to reduce the operating conditions (temperature, pressure and molar ratio of alcohol to vegetable oil). The novelty of using CO2 may have two advantages: a possible combination of supercritical CO2 extraction of the oil and its subsequent transesterification reaction without CO2 depressurization, and a reduction of the supercritical temperature and pressure of the mixture. The effects of temperature (280-350 oC), pressure (140-280 bar), methanol- to-oil molar ratio (20-30), CO2-to-methanol molar ratio (0.05-0.2) and residence time (0-45minutes) on the yield of methyl esters (biodiesel) were studied in a batch reactor, obtaining in all cases a relatively low increase in the yield when CO2 was present in the medium. The yields of biodiesel were tested with three vegetable oils used as model compounds (palm, sunflower and borage), obtaining similar results.

      • SCIESCOPUSKCI등재

        Probabilistic Constrained Approach for Distributed Robust Beamforming Design in Cognitive Two-way Relay Networks

        Chen,,Xueyan,Guo,,Li,Dong,,Chao,Lin,,Jiaru,Li,,Xingwang,Cavalcante,,Charles,Casimiro Korean Society for Internet Information 2018 KSII Transactions on Internet and Information Syst Vol.12 No.1

        In this paper, we propose the distributed robust beamforming design scheme in cognitive two-way amplify-and-forward (AF) relay networks with imperfect channel state information (CSI). Assuming the CSI errors follow a complex Gaussian distribution, the objective of this paper is to design the robust beamformer which minimizes the total transmit power of the collaborative relays. This design will guarantee the outage probability of signal-to-interference-plus-noise ratio (SINR) beyond a target level at each secondary user (SU), and satisfies the outage probability of interference generated on the primary user (PU) above the predetermined maximum tolerable interference power. Due to the multiple CSI uncertainties in the two-way transmission, the probabilistic constrained optimization problem is intractable and difficult to obtain a closed-form solution. To deal with this, we reformulate the problem to the standard form through a series of matrix transformations. We then accomplish the problem by using the probabilistic approach based on two sorts of Bernstein-type inequalities and the worst-case approach based on S-Procedure. The simulation results indicate that the robust beamforming designs based on the probabilistic method and the worst-case method are both robust to the CSI errors. Meanwhile, the probabilistic method can provide higher feasibility rate and consumes less power.

      • SCIESCOPUSKCI등재

        Performance Analysis of NOMA-based Relaying Networks with Transceiver Hardware Impairments

        Deng,,Chao,Zhao,,Xiaoya,Zhang,,Di,Li,,Xingwang,Li,,Jingjing,Cavalcante,,Charles,Casimiro Korean Society for Internet Information 2018 KSII Transactions on Internet and Information Syst Vol.12 No.9

        In this paper, the performance of non-orthogonal multiple access (NOMA) dual-hop (DH) amplify-and-forward (AF) relaying networks is investigated, where Nakagami-m fading channel is considered. In order to cover more details, in our analysis, the transceiver hardware impairments at source, relay and destination nodes are comprehensively considered. To characterize the effects of hardware impairments brought in NOMA DH AF relaying networks, the analytical closed-form expressions for the exact outage probability and approximate ergodic sum rate are derived. In addition, the asymptotic analysis of the outage probability and ergodic sum rate at high signal-to-noise ratio (SNR) regime are carried out in order to further reveal the insights of the parameters for hardware impairments on the network performance. Simulation results indicate the performance of asymptotic ergodic sum rate are limited by levels of distortion noise.

      • KCI등재SCOPUS

        Preparation of polyphenol fine particles potent antioxidants by a supercritical antisolvent process using different extracts of Olea europaea leaves

        Antonio,Montes,Chandrasekar,Chinnarasu,Clara,Pereyra,Lourdes,Casas,María,Teresa,Fernández-Ponce,Casimiro,Mantell,Sangma,Pattabhi,Enrique,Martínez,de,la,Ossa 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.2

        Various extracts from olive leaves have been precipitated by a supercritical antisolvent (SAS) process to evaluate the possibility of producing polyphenol fine particles with controlled size and size distribution. Olive leaves were initially extracted with subcritical fluids using mixtures of CO2+ethanol at 10% and 50%, by pressurized liquid extraction (PLE) with water, ethanol and a hydroalcoholic mixture (50 : 50) (v/v), and also by conventional ethanol extraction (CE). PLE gave the extract with the highest yield and the best antioxidant activity. SAS precipitation was unsuccessful for the extracts obtained with pressurized water and with the hydroalcoholic mixture (50 : 50) (v/v). The SAS precipitates with the smallest particle sizes were produced from extracts obtained with subcritical fluids. The SAS precipitates obtained after the conventional ethanol extraction of olive leaves showed the best antioxidant activity.

      • KCI등재SCOPUS

        Performance Analysis of Two-Way Relay NOMA Systems with Hardware Impair-ments and Channel Estimation Errors

        ( Xinji Tian ), ( Qianqian Li ), ( Xingwang Li ), ( Hui Zhang ), ( Khaled Rabie ), ( Charles Casimiro Cavalcante ) 한국인터넷정보학회 2019 KSII Transactions on Internet and Information Syst Vol.13 No.11

        In this paper, we consider a two-way relay non-orthogonal multiple access (TWR-NOMA) system with residual hardware impairments (RHIs) and channel estimation errors (CEEs), where two group users exchange their information via the decode-and-forward (DF) relay by using NOMA protocol. To evaluate the performance of the considered system, exact analytical expressions for the outage probability of the two groups users are derived in closed-form. Moreover, the asymptotic outage behavior in the high signal-to-noise ratio (SNR) regime is examined and the diversity order is derived and discussed. Numerical simulation results verify the accuracy of theoretical analyses, and show that: i) RHIs and CEEs have a deleterious effects on the outage probabilities; ii) CEEs have significant effects on the performance of the near user; iii) Due to the RHIs, CEEs, inter-group interference and intra-group interference, there exists error floors for the outage probability.

      • KCI등재

        Green strategy to produce large core–shell affinity beads for gravity-driven API purification processes

        Raquel,Viveiros,Francisco,M.,Dias,Luisa,B.,Maia,William,Heggie,Teresa,Casimiro 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.54 No.-

        In this work, Molecular Imprinted Polymers (MIPs)-layered silica beads which have affinity for a model pharmaceutical impurity, acetamide (ACET) were developed using supercritical carbon dioxide (scCO2) technology. Silica beads were first functionalized using two different green strategies, grafting to (MPS/ EtOH in scCO2) and grafting from (plasma technology). These core beads were then used as seed particles in the synthesis, in scCO2 of a MIP layer. Dynamic binding tests were performed in order to evaluate the affinity of the resulting silica core – MIP shell beads to ACET and the efficiency of its removal from an active pharmaceutical ingredient – Beclomomethasone dipropionate (API) crude mixture. ACET was preferentially retained over analogue molecules, benzamide (BENZ) and pivalamide (PIV). The core–shell MIP beads were packed in a SPE column (396.5 mg in a 3 mL SPE tube) and evaluated as a potential gravity-driven purification device, enabling the removal of 100% of ACET whilst losing only 0.37% of API from a model mixture solution—10 mL of ACET and API (0.25 mg mL1 + 3.5 mg mL1).

      • SCIESCOPUSKCI등재

        An Improved Remote Sensing Image Fusion Algorithm Based on IHS Transformation

        Deng,,Chao,Wang,,Zhi-heng,Li,,Xing-wang,Li,,Hui-na,Cavalcante,,Charles,Casimiro Korean Society for Internet Information 2017 KSII Transactions on Internet and Information Syst Vol.11 No.3

        In remote sensing image processing, the traditional fusion algorithm is based on the Intensity-Hue-Saturation (IHS) transformation. This method does not take into account the texture or spectrum information, spatial resolution and statistical information of the photos adequately, which leads to spectrum distortion of the image. Although traditional solutions in such application combine manifold methods, the fusion procedure is rather complicated and not suitable for practical operation. In this paper, an improved IHS transformation fusion algorithm based on the local variance weighting scheme is proposed for remote sensing images. In our proposal, firstly, the local variance of the SPOT (which comes from French "Systeme Probatoire d'Observation dela Tarre" and means "earth observing system") image is calculated by using different sliding windows. The optimal window size is then selected with the images being normalized with the optimal window local variance. Secondly, the power exponent is chosen as the mapping function, and the local variance is used to obtain the weight of the I component and match SPOT images. Then we obtain the I' component with the weight, the I component and the matched SPOT images. Finally, the final fusion image is obtained by the inverse Intensity-Hue-Saturation transformation of the I', H and S components. The proposed algorithm has been tested and compared with some other image fusion methods well known in the literature. Simulation result indicates that the proposed algorithm could obtain a superior fused image based on quantitative fusion evaluation indices.

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