Central Composite Experiment Research Articles

Highly fluorescent carbon dots from peanut shells as potential probes for copper ion: The optimization and analysis of the synthetic process

The use of natural materials, a renewable resource, instead of chemicals as carbon precursors for simple synthesis of fluorescent carbon dots (FCDs) remains a significant challenge. Here, we report the preparation of FCDs with a photoluminescence (PL) quantum yield (QY) of 10.58% from peanut shells via one-pot pyrolysis treatment optimized by using a central composite experiment design. Optimum pyrolysis conditions were found to be 400 °C temperature, 4 h duration, and 70 g peanut shell weight. The as-prepared FCDs possess unique excitation-dependent behavior, good water dispersibility and high photostability. The results of Fourier transform infrared (FTIR) spectroscopy to analyze the pyrolytic process indicated the complete combustion of peanut shells happened at 3 and 4 h at 400 °C. The PL intensity of the FCDs was not always proportional to the corresponding QY value in our work due to the different amount of carbon-rich residues after the pyrolysis process. Fluorescence-quenching trials were conducted to analyze their sensitivity and selectivity in Cu2+ detection. The detection limit was found to be 4.8 μM. Our pyrolysis treatment of peanut shells for preparing FCDs is not only a green and facile method but also a means of recycling peanut shells.

Optimization of Lactoperoxidase and Lactoferrin Separation on an Ion-Exchange Chromatography Step

Lactoperoxidase (LP), which is a high-value minor whey protein, has recently drawn extensive attention from research scientists and industry due to its multiplicity of function and potential therapeutic applications. In this study, the separation and optimization of two similar-sized proteins, LP and lactoferrin (LF) were investigated using strong cation exchange column chromatography. A two-step optimization strategy was developed for the separation of LP and LF. Optimization was started with central composite design-based experiments to characterize the influences of different decision variables, namely, flow rate, length of gradient, and final salt concentration in the linear elution gradient step on the yield of LP. This was followed by a more accurate optimization of ion-exchange chromatography (IEC) separation of LP and LF based on an experimentally verified chromatographic model. The optimal operating points were found and the results were compared with validation experiments. Predictions respecting yield confirmed a very good agreement with experimental results with improved product purity.

A Canopy Density Model for Planar Orchard Target Detection Based on Ultrasonic Sensors.

Orchard target-oriented variable rate spraying is an effective method to reduce pesticide drift and excessive residues. To accomplish this task, the orchard targets’ characteristic information is needed to control liquid flow rate and airflow rate. One of the most important characteristics is the canopy density. In order to establish the canopy density model for a planar orchard target which is indispensable for canopy density calculation, a target density detection testing system was developed based on an ultrasonic sensor. A time-domain energy analysis method was employed to analyze the ultrasonic signal. Orthogonal regression central composite experiments were designed and conducted using man-made canopies of known density with three or four layers of leaves. Two model equations were obtained, of which the model for the canopies with four layers was found to be the most reliable. A verification test was conducted with different layers at the same density values and detecting distances. The test results showed that the relative errors of model density values and actual values of five, four, three and two layers of leaves were acceptable, while the maximum relative errors were 17.68%, 25.64%, 21.33% and 29.92%, respectively. It also suggested the model equation with four layers had a good applicability with different layers which increased with adjacent layers.

Passive isothermalisation of an exothermic reaction in flow using a novel “Heat Pipe Oscillatory Baffled Reactor (HPOBR)”

In this study, a heat pipe was integrated with a mesoscale oscillatory baffled reactor for the passive temperature control of an exothermic reaction. The thermal/chemical performance of this new Heat Pipe Oscillatory Baffled Reactor (HPOBR) was compared to a conventional jacketed OBR (JOBR) using central composite experiment designs for an imination reaction between benzaldehyde and n-butylamine, in the absence of solvent. The variables in the experimental designs were reactant net flow rate (Ren=4–20), fluid oscillation intensity (Reo=123–491) and heat pipe fill ratio (FR=11.5–26.5; methanol working fluid). In the JOBR, the fill ratio factor was replaced with jacket temperature (4–20°C). Both reactors were able to reduce the maximum reaction temperature below the butylamine boiling point in all experiments. Overall, a 20-fold reduction in reactant volume and 13-fold improvement in reaction rate were obtained in the HPOBR for this imination reaction, compared with the same reaction using a solvent. Advantages of the HPOBR demonstrated here are isothermal operation and passive thermal control. Both reactors offer accelerated reaction rates and the potential for screening exothermic reactions. The HPOBR is a novel reactor design that provides a new approach for achieving green chemistry through solventless operation.

Development and characterization of a high-solids deacetylation process

Dilute-acid pretreatment has proven to be a robust means of converting herbaceous feedstock to fermentable sugars. However, it also releases acetic acid, a known fermentation inhibitor, from acetyl groups present in the biomass. A mild, dilute alkaline extraction stage was implemented prior to acid pretreatment to separate acetic acid from the hydrolysate sugar stream. This step, termed deacetylation, improved the glucose and xylose yields from enzymatic hydrolysis and ethanol yields from fermentation of the sugars relative to the control experiments using dilute-acid pretreatment of native corn stover without deacetylation. While promising, deacetylation as it was historically practiced is conducted at low solids loadings, and at fixed conditions. Thus, many questions have been left unanswered, including the relationship between sodium hydroxide and solids loading, and acetate and xylan solubilization, as well as the impact of temperature and residence time on the process efficacy. A central composite experiment was designed to evaluate the impact of solids loading, sodium hydroxide loading, reaction time and temperature during deacetylation on the acetate and xylan solubilization of corn stover. Using the ANOVA test, it became apparent that neither of the responses was significantly impacted by the solids loading, while the reaction time was a minor factor—the responses were largely driven by reaction temperature and the sodium hydroxide loading. Based on the results, we successfully demonstrated the ability to transition the low-solids (10 % w/w) deacetylation process to a higher-solids process (30 % w/w) with minimal impact on the ability to extract acetate from biomass. Conditions were selected to minimize xylose loss during deacetylation, while also removing 70 % of acetyl groups. The impact of selected conditions on the enzymatic hydrolysis and fermentation was further investigated. Evaluation of the whole-process impact demonstrated that despite the upfront reduction in carbohydrate loss during deacetylation, the overall process sugar yields were depressed by the high-solids, low alkali process relative to the historical control. Consequently, ethanol titers were reduced, though strong fermentation performance was still observed, indicating that 70 % acetate removal is sufficient to depress acetic acid concentrations to a level that does not substantially inhibit ethanol fermentation by rZymomo nas.

Properties of mortars produced with reactivated cementitious materials

The production of reactivated cementitious materials is an option for the recycling of hydrated-cement-rich fines discarded during recycled aggregate production. Reactivation is based on a thermal process where calcium silicate hydrates present in the fines decompose forming new hydraulic compounds. In the reported study, materials reactivated at temperatures between 660 °C and 940 °C were characterized using X-Ray diffraction and particle size analysis, and evaluated as binders using a central composite experiment to model the effects of reactivation temperature and reactivated material substitution level on the flowability, compressive strength and expansion of mortar mixtures. Reactivation temperature effects correlated with the relative concentration of reactive phases, particularly a stabilized form of alpha'-C2S identified in the materials. Substitution effects depended on the supplementary material tested, and lacked significant interaction with reactivation temperature. In the region explored, mortars based on materials produced at 800 °C, 40% substituted by silica fume, achieved highest strength but lowest flowability.

An experimental investigation of design parameters for pico-hydro Turgo turbines using a response surface methodology

Millions of off-grid homes in remote areas around the world have access to pico-hydro (5 kW or less) resources that are undeveloped due to prohibitive installed costs ($/kW). The Turgo turbine, a hydroelectric impulse turbine generally suited for medium to high head applications, has gained renewed attention in research due to its potential applicability to such sites. Nevertheless, published literature about the Turgo turbine is limited and indicates that current theory and experimental knowledge do not adequately explain the effects of certain design parameters, such as nozzle diameter, jet inlet angle, number of blades, and blade speed on the turbine's efficiency. In this study, these parameters are used in a three-level (34) central composite response surface experiment. A low-cost Turgo turbine is built and tested from readily available materials and a second order regression model is developed to predict its efficiency as a function of each parameter above and their interactions. The effects of blade orientation angle and jet impact location on efficiency are also investigated and experimentally found to be of relatively little significance to the turbine. The purpose of this study is to establish empirical design guidelines that enable small hydroelectric manufacturers and individuals to design low-cost efficient Turgo Turbines that can be optimized to a specific pico-hydro site. The results are also expressed in dimensionless parameters to allow for potential scaling to larger systems and manufacturers.

Pyrolysis of spent coffee grounds using a screw-conveyor reactor

The fast pyrolysis of spent coffee grounds using a compact, transportable, screw conveyor reactor for producing bio-oil was studied. A two-factor, five-level, central composite response surface experiment was completed to formulate a statistical model that relates reactor temperature (429–550°C) and residence time (23–42s, controlled by the screw rotation rate) to bio-oil yield and quality. Regression analysis of model fits with experimental data showed that temperature and residence time had a significant effect (p<0.05) on bio-oil yield. Highest bio-oil yield (61.8%) was observed at 500°C while the highest char yield (20.6 % w/w) was produced at the lowest temperature of 429°C. Bio-oil yields increased with screw speed and decreasing residence time. The model predicted a maximum liquid yield of 61.7% and an accompanying char yield of 17.1% at 505°C (778K) and 70rpm. In addition to containing oxygenated organic compounds typical of bio-oils, spent coffee bio-oil also contains more hydrophobic compounds (>20% peak area) such as fatty acids, fatty acid esters, medium-chain paraffins, olefins, and caffeine. Because of the abundance of spent coffee grounds and the quality of its bio-oil, this waste stream offers potential as a valuable bioenergy feedstock.

Simulation and Experimental Research on Cutting Force of Turning Titanium Alloy

This paper mainly establishes a two-dimensional model about the YG8 carbide tool turning TC4 titanium alloy on the basis of ABAQUS. The cutting force of the simulation model was verified by the turning experiment, and the relationships of cutting force with cutting speed, feed rate and rake angle of cutting edge in the model were studied. A prediction model of main cutting force related to cutting speed, feed rate and rake angle was obtained by central composite experiment. Studies have shown that the difference between the cutting force acquired by simulation and by experiment was less than 10%; in a certain range, the cutting force increased with the feed rate, the cutting force decreased with the increase of cutting speed and rake angle, and the influence of feed rate to cutting force was most significant.

Optimal Immobilization ofβ-Galactosidase ontoκ-Carrageenan Gel Beads Using Response Surface Methodology and Its Applications

β-Galactosidase (β-gal) was immobilized by covalent binding on novel κ-carrageenan gel beads activated by two-step method; the gel beads were soaked in polyethyleneimine followed by glutaraldehyde. 22 full-factorial central composite experiment designs were employed to optimize the conditions for the maximum enzyme loading efficiency. 11.443 U of enzyme/g gel beads was achieved by soaking 40 units of enzyme with the gel beads for eight hours. Immobilization process increased the pH from 4.5 to 5.5 and operational temperature from 50 to 55°C compared to the free enzyme. The apparent K m after immobilization was 61.6 mM compared to 22.9 mM for free enzyme. Maximum velocity V max was 131.2 μmol·min−1 while it was 177.1 μmol·min−1 for free enzyme. The full conversion experiment showed that the immobilized enzyme form is active as that of the free enzyme as both of them reached their maximum 100% relative hydrolysis at 4 h. The reusability test proved the durability of the κ-carrageenan beads loaded with β-galactosidase for 20 cycles with retention of 60% of the immobilized enzyme activity to be more convenient for industrial uses.

Parameter Optimization for Enhancement of Ethanol Yield by Atmospheric Pressure DBD-Treated Saccharomyces cerevisiae

In this study, Saccharomyces cerevisiae (S. cerevisiae) was exposed to dielectric barrier discharge plasma (DBD) to improve its ethanol production capacity during fermentation. Response surface methodology (RSM) was used to optimize the discharge-associated parameters of DBD for the purpose of maximizing the ethanol yield achieved by DBD-treated S. cerevisiae. According to single factor experiments, a mathematical model was established using Box-Behnken central composite experiment design, with plasma exposure time, power supply voltage, and exposed-sample volume as impact factors and ethanol yield as the response. This was followed by response surface analysis. Optimal experimental parameters for plasma discharge-induced enhancement in ethanol yield were plasma exposure time of 1 min, power voltage of 26 V, and an exposed sample volume of 9 mL. Under these conditions, the resulting yield of ethanol was 0.48 g/g, representing an increase of 33% over control.

Finite Element Study on Micro Cutting Process of Guide Abrasive Wear

Two-dimensional finite element model is established by ABAQUS Explicit finite element analysis in this paper. It includes abrasive wear micro cutting process between pair of guide. Johnson-cook constitutive model is used to simulate the guide material deformation of wear process. Based on different sizes and different speed of grain, loading, cutting and unloading process are simulated by finite element, guide surface stress distribution and deformation condition are studied in the guide rail pair wear process. The simulation data is obtained by central composite experiments and regression model is gotten by MATLAB. The influence law of the particle radius and speed to guide residual compressive stress and deformation are gotten by the prediction model.

Influences of microwave vacuum puffing conditions on anthocyanin content of raspberry snack

Microwave technology is fit for the processing of berry products, but it may affect nutrition components of berry fruit. To improve the nutritional value of the berry products, the influences of microwave vacuum puffing conditions on the anthocyanin content of raspberry snack were investigated using central composite experiments. Results indicated that vacuum pressure had the most significant effect on the anthocyanins of berry snack, followed by the puffing time, microwave power, and initial moisture content. The interaction between microwave power and puffing time on the anthocyanins was extremely significant. Under microwave power of 2.68 kW and the puffing time of 81.00 s, the anthocyanin content of raspberry snack was retained at high level. The results can provide some technological basis for the berry fruit products processed with high quality.

Medium optimization of a hydrophilic solvent-stable protease from Serratia sp. SYBC H

Two statistical methods were used for medium optimization for a hydrophilic solvent-stable protease production by Serratia sp. SYBC H with duckweed as the nitrogen source. Orthogonal design was applied to find the significant variables, then response surface methodology (RSM), including Box–Behnken central composite experiments, was used to determine the optimal concentrations and interaction of the significant variables. Results demonstrated that duckweed powder, wheat flour, Tween 80, sodium chloride had significant effects on the solvent-stable protease production. The interaction between duckweed and wheat flour was significant. The optimal level of the variables for the maximum protease production was duckweed 43.9 g/L, wheat flour 20 g/L, sodium chloride 0.08 M, Tween 80 1% v/v, initial pH 11.0, and inoculum size 7% v/v. The maximum protease activity reached 1922.8 U/mL in the optimized medium, with about 18.3-fold higher than that in the unoptimized medium. Most importantly, the protease from Serratia sp. SYBC H has successfully catalyzed the specific acylation of sucrose in a two-solvent medium consisting of pyridine and n-hexane (1:1, v/v), and non-specific acylation of sucrose in anhydrous DMSO. These results demonstrated that the protease from Serratia sp. SYBC H is a solvent-stable protease and it could be an ideal biocatalyst for sugar esters syntheses in non-aqueous media.

Immobilization and stability of a Rhizopus oryzae lipase expressed in Pichia pastoris: Comparison between native and recombinant variants

The stability of a soluble extract containing a recombinant lipase from Rhizopus oryzae (Cursive) lipase (rROL) produced by Pichia pastoris (Cursive), as well as that for the commercial extract containing the lipase produced by the native organism (nROL), was investigated. The results showed higher residual activity values of the commercial protein compared with the recombinant one. Moreover, two different kinds of support, the polypropylene powder EP100 and Eupergit®C, were tested to immobilize the enzymes. The residual activity of the immobilizated derivatives was also tested to determine whether their stability was enhanced. The results showed a slight improvement in rROL using both supports but a decrease in nROL using Eupergit®C. The study of the residual activity of soluble and immobilized enzymes was performed by means of a central composite rotatable experiment design. In addition, EP100 adsorption isotherms were determined.

Cooling curves for the preliminary design of beef chillers

A multilayer two-dimensional model of beef carcass chilling using CFD-generated heat transfer coefficients was used to calculate the parameters of leg and shoulder cooling curves, assuming an exponential cooling model. A central composite experiment was designed to systematically vary air velocity, side weight and fat thickness. Comparison with experimental data suggests that the predicted characteristic time for the leg, and hence the cooling time to a given temperature, should be multiplied by a correction factor 1.07. The effects of airflow direction and of radiation heat transfer have been quantified. A correlation was proposed to estimate leg centre temperature from shoulder temperature. The shortcut formulae and methods presented here will be useful in the design and troubleshooting of industrial beef chillers. They could also be used in Monte Carlo simulations where a large number of samples are considered, to take into account random variations in product characteristics and operating conditions.

Developing and investigating of elastic ball burnishing tool

Burnishing, a plastic deformation process, is becoming more popular in satisfying the increasing demands of machine component performance and reliability. Thus, investigating the burnishing parameters in order to improve the product quality is especially crucial. The objective of this research is to evaluate the effect of different burnishing conditions on surface microhardness, surface roughness, and form accuracy. Orthogonal central composite experiment design was used to select the input parameters making them into the right order. Optimum burnishing parameters were established to minimize roughness and/or maximize surface hardening. Emperical formulas were developed to predict the surface microhardness and roughness of leaded brass obtained by burnishing under lubricated conditions.

Method development and validation for the analysis of didanosine using micellar electrokinetic capillary chromatography

A selective MEKC method was developed for the analysis of didanosine in bulk samples. Successful separation of didanosine from 13 of its potential impurities, derived from the various synthetic preparation procedures, was achieved. As CZE gave poor separation selectivity, MEKC was preferable. The use of EKC allowed achievement of the separation in a significantly shorter time than conventional HPLC. An anionic long-chain surfactant, lithium dodecyl sulfate (LiDS), was used as the pseudostationary phase and sodium tetraborate buffer as the aqueous phase. In order to obtain the optimal conditions and to test the method robustness, a central composite response surface modeling experiment was performed. The optimized electrophoretic conditions include the use of an uncoated fused-silica capillary with a total length of 40 cm and an ID of 50 microm, a BGE containing 40 mM sodium tetraborate and 110 mM LiDS at pH 8.0, an applied voltage of 18.0 kV, and the capillary temperature maintained at 15 degrees C. The method was found to be robust. The parameters for validation such as linearity, precision, and sensitivity are also reported. Three commercial bulk samples were analyzed with this system.

Optimization of Rubber Wood Drying by Response Surface Method and Multiple Contour Plots

By adopting the central-composite experiment design, the response surface methodology was used to optimize operating conditions of rubber wood drying. The independent variables are initial moisture content of rubber wood, and three drying environment parameters namely, temperature, relative humidity, and air velocity. The investigating responses are final moisture content, drying time, and energy consumption. The restriction of the optimization is the designated final moisture content, which is not greater than 16%. The third-order polynomial models with transformed responses were developed from experiment data to generate 3-D response surfaces and contour plots. The analysis of variance (ANOVA) was performed to identify the significant parameters affecting the rubber wood drying. Drying temperature and holding relative humidity are those two influential operating parameters that significantly control the final moisture of rubber wood and affect the drying time and energy. The multiple contour plots of drying responses show that the optimum operating regions are located mainly at high temperature drying zone. The high temperature drying practice can save energy and drying time by 44 and 25% respectively, in comparison to the conventional temperature drying.

Experimental study of workpiece-level variability in blind-via electroplating

The acid copper electroplating process for the manufacture of printed wire boards was studied by statistical techniques. The objectives of this study were to investigate the effects of process and product parameters on the workpiece-level uniformity during the acid copper plating of blind vias and to explore the minimization of the deposit thickness variation. The parameters studied were the concentrations of copper sulphate, sulphuric acid and additive, average current density (ACD), electrode separation (ES), the aspect ratio and the depth ratio of the via holes. Multifactor two-level factorial and the central composite rotatable five-level experiments were designed and conducted sequentially to generate statistical process models. Only the average current density and the electrode separation were found to be significant. A second-order model was then developed for the process in the proximity of the optimum region and verified experimentally to locate the optimum combinations of ACD and ES with respect to minimum thickness variability across the whole workpiece. Post-optimal analysis showed that the optimum solution was more sensitive to the electrode separation than the average current density.