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We establish a direct route for the accurate determination of the solvent effect on the Krichevskii parameter of a solute, based solely on the contrasting solvation behavior of the solute in the desired solvent relative to that of the reference solvent, i.e., in terms of the distinct solvation Gibbs free energies of the solute and the corresponding Krichevskii parameters of an ideal gas solute in the pair of solvents. First, we illustrate the proposed approach in the determination of the H/D−solvent effect on the Krichevskii parameter of gaseous solutes in aqueous solutions, when the solvents are different isotopic forms (isotopomers) of water, and then, by generalizing the approach to any pair of solvents. For that purpose, we (a) identify the links between the standard solvation Gibbs free energy of the i−solute in the two involved solvent environments and the resulting Krichevskii parameters, (b) discuss the fundamentally based linear behavior between the Krichevskii parameter and the standard solvation Gibbs free energy of the i−solute in an α−solvent, and interpret two emblematic cases of solutions involving either an ideal gas solute or an i−solute behaving identically as the solvating species, as well as (c) provide a novel microstructural interpretation of the solvent effect on the Krichevskii parameter according to a rigorous characterization of the critical solvation as described by a finite unambiguous structure making/breaking parameter Siα∞(SR) of the i−solute in the pair of α−solvents.

In this article, we raise awareness about the misuses of frequently invoked criteria for structure making/breaking phenomena, resulting from the absence of any explicit cause–effect relationship between the proposed markers and the microstructural perturbation of the solvent induced by the solute. First, we support our assessment with rigorous molecular-based foundations to determine, directly and quantitatively, the solute-induced perturbation of the solvent structure leading to an unambiguous definition of a structure making/breaking event. Then, we highlight and discuss the sources of concealed ambiguities in two of the most frequently invoked structure making/breaking criteria, i.e., Hepler’s thermal expansivity-based and Jones–Dole’s B coefficient-based markers. Finally, we illustrate how the implementation of rigorous molecular-based arguments, in conjunction with the available experimental evidence on a variety of aqueous species at infinite dilution, rule out the validity of these two criteria as structure making/breaking markers and suggest their discontinuation to avoid the perpetuation of myths.

We analyzed the consistency, or lack thereof, of the conjectured connection between the sign of Jones-Dole's B-coefficient, or its isobaric-temperature derivative, and the structure-making/breaking ability of a solute in a dilute solution. We sought to shed light on some crucial issues, including (i) whether Jones-Dole's B-coefficient contains any embedded microstructural information, (ii) whether we can either assign any definite foundation to the widely used assumption about the sign of the B-coefficient and its structure-making/breaking trend or provide a rational justification for its use as a structure-making/breaking marker, and (iii) whether we actually need Jones-Dole's B-coefficient and its isobaric-temperature derivative as markers for the interpretation of structure-making/breaking trends. Thus, we first addressed the fundamental (statistical mechanical) microscopic to (thermodynamic) macroscopic foundations of a rigorous approach to the structure-making/breaking ability of a solute, regardless of the type of solvent or nature of the solute-solvent intermolecular interaction asymmetries, and its exact relationships to the resulting solution thermodynamics. Then, we derived the required conditions for the signs of the B-coefficient and/or its isobaric-temperature derivative to describe either a structure-making or a structure-breaking event, according to the actual solute-induced perturbation of the solvent microstructure, and consequently, tested the rationale underlying the B-based conjectured structure-making/breaking markers. Moreover, we invoked a well-known transition-state (TS) interpretation of the B-coefficient to connect it explicitly to the derived molecular-based structure-making/breaking signature and to find under which TS conditions the signs of the B-coefficient and its temperature derivative could describe the actual solute-induced perturbation of the solvent microstructure. We illustrated the actual structure-making/breaking behavior for a series of aqueous solutes over a wide range of solute-solvent intermolecular interaction asymmetries and compared their behavior against that predicted by Jones-Dole's based markers. This comparison, supported by rigorous thermodynamic arguments, highlighted the lack of uniqueness (or one-to-one correspondence) in the response of the B-based markers to the solute-solvent intermolecular interaction asymmetry, and therefore, their inadequacy as structure-making/breaking descriptors. Finally, we discuss the findings and provide a cautionary outlook on the use of the viscosity-based structural markers.

We analyzed the hydration behavior of alkyl-substituted urea osmolytes in terms of their deviation from Lewis-Randall solution ideality and characterized their structure-making/breaking tendency according to a proposed solvation formalism that provides a rigorous cause-effect connection between the system microstructure and its solution thermodynamic nonidealities. After a brief introduction of the rationale behind the use of Lewis-Randall over alternative solution ideality references, we (i) assessed the effect of the nature and type of alkyl substitution on the osmolyte-induced perturbation of the solution microstructure as a function of composition, (ii) analyzed their microstructural responses to changes in temperature and pressure, and (iii) demonstrated the structure-breaking nature of urea and the magnifying behavior of its alkyl-substituted osmolytes, whose trend follows the increasingly positive deviation of the osmolyte solutions from Lewis-Randall ideality. Then, we discussed the falsifiability of a pair of frequently used conjectured structure-making/breaking criteria, supported by the derived exact relationships between the structure-making/breaking parameter, the solution thermodynamic nonideality, and the osmotic second virial coefficient of the aqueous osmolytes. Finally, we provided an outlook on how the proposed approach could guide the quest for a truly (microstructural to free energy) causative explanation for the denaturation mechanism of proteins.

This work addresses the thermodynamic limiting behavior of dilute species in binary solutions as described by their excess chemical, mechanical and thermal partial molar properties M ˆ i E ( T P x i ) as well as the corresponding composition slopes [ ∂ M ˆ i L R ( T P x i ) / ∂ x i ] T P , where M ˆ i L R ( T P x i ) comprises the partial molar properties of systems describing the excess Gibbs free energy and the corresponding temperature- and pressure-derivative quantities. These quantities include the species partial molar Gibbs free energies according to Lewis-Randall (LR) description, and their volumes, enthalpies, entropies, and isobaric heat capacities. The analysis builds upon the recently proposed solvation formalism for dilute systems [J. Chem. Phys., 128 (2008); J. Chem. Phys., 148 (2018); Fluid Phase Equilib., 472 (2018)] and its scope includes (a) the identification of the microstructural signatures, macroscopic manifestation, as well as the interrelations between the species partial molar quantities M ˆ i L R ( T P x i ) [ ∂ M ˆ i L R ( T P x i ) / ∂ x i ] T P , and the apparent molar counterpart M ϕ ( T P x i ) at finite composition as well as at infinite dilution; (b) the development and testing of a method to describe the actual limiting M ˆ i L R ( T P x i → 0 ) behavior in terms of the corresponding value at the condition of solute saturation, i.e., M ˆ i L R ( T P x i = x i s a t ) ; (c) the illustration and discussion of some successful approximations for the accurate estimation of the limiting M ˆ i L R ( T P x i → 0 ) , and consequently, (d) the discussion of potential drawbacks underlying the composition regression of experimental data and subsequent extrapolation to infinite dilution.

This paper proposes a multimodal multiobjective Differential Evolution optimization algorithm (MMODE). The technique is conceived for deployment on problems with a Pareto multimodality, where the Pareto set comprises multiple disjoint subsets, all of which map to the same Pareto front. A new contribution is the formulation of a decision-variable preselection scheme that promotes diversity of solutions in both the decision and objective space. A new mutation-bound process is also introduced as a supplement to a classical mutation scheme in Differential Evolution methods, where offspring that lie outside the search bounds are given a second opportunity to mutate, hence reducing the density of individuals on the boundaries of the search space. New multimodal multiobjective test functions are designed, along with analytical expressions for their Pareto sets and fronts. Some test functions introduce more complicated Pareto-front shapes and allow for decision-space dimensions greater than two. The performance of the MMODE algorithm is compared with five other state-of-the-art methods. The results show that MMODE realizes superior performance by finding more and better distributed Pareto solutions.

We present a novel molecular thermodynamic framework for the unambiguous assessment of the reliability of modeling approximations, their internal consistency, and the compliance with fundamental limiting behaviors in the description of solvation phenomena of species at infinite dilution in fluid systems over wide ranges of state conditions and solute-solvent intermolecular asymmetries. The proposed aprioristic approach does not rely on any type of regression technique; its accuracy rests on the theoretical validity and self-consistency of the underlying core solvation formalism and the first principles of chemical thermodynamics already established for model systems for which we have available exact formal results, and its application leads to the identification, as well as the isolation of the sources of modeling deficiencies. To that end, we (i) set the foundations for a rigorous description of the solvation behavior of solutes at infinite dilution at the microscopic and concomitant macroscopic levels, (ii) advance a set of thermodynamic limiting conditions as required constraints for any model of infinitely dilute solutions, (iii) identify the microscopic signatures of the solvation phenomena in terms of solute-induced perturbations of the solvent microstructure, and (iv) invoke an exact fluctuation formalism of solutions to assess the predictive capability of some current density-based models of aqueous non-electrolyte solutions. According to the findings of this analysis, we suggest a novel fully molecular-based alternative for the thermodynamic description of solutions at infinite dilution involving wide ranges of state conditions and solute-solvent intermolecular asymmetry, including the ideal gas solute and the solute behaving as another solvent species. This approach, which functions at a self-consistent integral plus derivative level, would automatically comply with all required thermodynamic constraints.

As a single-hidden-layer feedforward neural network, an extreme learning machine (ELM) randomizes the weights between the input layer and the hidden layer as well as the bias of hidden neurons, and analytically determines the weights between the hidden layer and the output layer using the least-squares method. This paper proposes a two-hidden-layer ELM (denoted TELM) by introducing a novel method for obtaining the parameters of the second hidden layer (connection weights between the first and second hidden layer and the bias of the second hidden layer), hence bringing the actual hidden layer output closer to the expected hidden layer output in the two-hidden-layer feedforward network. Simultaneously, the TELM method inherits the randomness of the ELM technique for the first hidden layer (connection weights between the input weights and the first hidden layer and the bias of the first hidden layer). Experiments on several regression problems and some popular classification datasets demonstrate that the proposed TELM can consistently outperform the original ELM, as well as some existing multilayer ELM variants, in terms of average accuracy and the number of hidden neurons.

In this work, we have derived rigorous expressions for the thermodynamic description of the solvation behavior of a model solute in highly-compressible environments of a real solvent, in order to address the question posed in the title of this manuscript. Toward that end, we first provide the essential statistical thermodynamic foundations to support a fundamentally-based approach for the determination of the Krichevskii parameter of a solute in any solvent, based solely on the knowledge of the corresponding Henry's law constant. Second, we analyze the actual orthobaric-density behavior of ln Q ( T , P σ ) and T σ ln Q ( T , P σ ) , when Q = K D ∞ and Q = ( H i , j I S / f j o ) , for an infinitely dilute ideal gas solute in an aqueous solution, a system for which we have complete knowledge of its microscopic and thermodynamic behaviors. Third, we invoke these results to test the assumptions behind the modeling of the orthobaric-density dependence of the Henry's law constant, infinite dilution vapor-liquid distribution, and Ostwald coefficients of real solutes. Fourth, we discuss the implications underlying the interpretation of the regressed orthobaric-density slopes, the accuracy of the resulting effective Krichevskii parameters, and the extension of the current analysis to the orthobaric-density behavior for the corresponding Ostwald coefficient, T σ ln L i , j ∞ ( T , P σ ) . Finally, we show how the fundamentally-based orthobaric-density linear expressions of ln Q ( T , P σ ) for the three Q − quantities converge to the corresponding, empirically-found, T σ ln Q ( T , P σ ) asymptotic linear representations for near-critical infinitely dilute solutions.

Sparsity and reconstruction error are two main objectives to be optimized in sparse signal reconstruction. In this paper, sparse signals are reconstructed by optimizing these two objectives simultaneously. This reconstruction method mainly consists of three steps. First, a one-dimension-dominated method is used to find a uniformly distributed optimal compromise solution set between these two objectives. Second, the Iterative Half Thresholding method is employed to improve the sparsity. Third, a robust selection method is proposed to choose a final solution from the solution set. The proposed method is compared with eight sparse reconstruction algorithms on twelve sparse test instances. Experimental results show that the proposed algorithm is able to reconstruct both noisy and noiseless sparse signals. In addition, the effectiveness of the proposed algorithm is demonstrated in practical application instances.

A systematic method for the steady-state modeling of mass transport phenomena and electrochemical behavior focusing on the cathode side of a direct methanol fuel cell (DMFC) with an open-cathode design is presented and demonstrated using an experimental system. The architecture features an internal water-recovery technology that promotes back-convection of water from the cathode to the anode through a polymer electrolyte permeable membrane that includes laser-drilled holes. Eight adjustable modeling parameters are estimated from experimental data from a prototype system, and a model validation study shows that predictions of water venting rates and of cell voltage have errors better than 9 % when extrapolating to conditions not used for parameter estimation. Illustrations of the use of the model include an analysis of performance at various flow rates of feed air, operating temperatures and currents, and a prediction of the effect of alternative material designs for selected cell layers. The approach serves as a paradigm for the development of general models for open-cathode active-feed DMFC systems.

To attain the general form of stable coalition structure, this paper addressed the problem of retailers’ coalition stability in a two-stage supply chain consisting of one supplier and multiple retailers. A profit gain function was established via introducing market gain coefficient and coalition cost coefficient for different coalition structures. Based on the function, the profit of each retailer in all kinds of coalition structures was analysed, and the general feature of a stable coalition structure was attained by the largest consistent set method and the stable set method. Furthermore, some insights were obtained. For example, stable coalition structures are equidistributed or approximate equidistributed; with supplier’s cost increasing, the size of the retailers’ coalition increases. Finally, the above conclusions are verified by numerical simulation. The results of this paper provide a reference for retailers’ coalition in a supply chain, such as automobile or Information Technology supply chain.

A systematic method for modeling direct methanol fuel cells, with a focus on the anode side of the system, is advanced for the purpose of quantifying the methanol crossover phenomenon and predicting the concentration of methanol in the anode catalyst layer of a direct methanol fuel cell. The model accounts for fundamental mass transfer phenomena at steady state, including convective transport in the anode flow channel, as well as diffusion and electro-osmotic drag transport across the polymer electrolyte membrane. Experimental measurements of methanol crossover current density are used to identify five modeling parameters according to a systematic parameter estimation methodology. A validation study shows that the model matches the experimental data well, and the usefulness of the model is illustrated through the analysis of effects such as the choice fuel flow rate in the anode flow channel and the presence of carbon-dioxide bubbles.

We present a novel molecular-based approach for the determination of the osmotic second virial coefficients of gaseous solutes in dilute binary solutions, according to a recently proposed molecular thermodynamic formalism of gas solubility [A. A. Chialvo, J. Chem. Phys. 148, 174502 (2018) and Fluid Phase Equilib. 472, 94 (2018)]. We discuss relevant solvation fundamentals and derive new expressions including (i) the relations among infinite-dilution solvation quantities leading to a novel self-consistent route to the calculation of the osmotic second virial coefficients, (ii) the new microstructural interpretation of the resulting osmotic second virial coefficients based on Kirkwood-Buff integrals, the unambiguous discrimination between short- and long-range contributions, and their limiting behavior as the solvent approaches its critical conditions, (iii) new rigorous expressions for the calculation of the osmotic second virial coefficients using standard reference thermodynamic data, and (iv) their underlying interdependence based on the constrained state variable invoked in the density expansion. We then invoke the proposed formalism to shed some light on the inaccuracies behind current calculations of osmotic second virial coefficients from molecular theory and simulation as well as macroscopic correlations. To advance the microscopic understanding and illustrate the functional relationship between the osmotic second virial coefficients, Henry’s law constant, and the solute-solvent intermolecular asymmetry as a source of solution non-ideality, we use data for the microstructural and thermodynamic behavior of infinitely dilute Lennard-Jones systems obtained self-consistently via integral equations calculations. The newly derived relationships leading to the proposed formalism offer novel routes for the accurate determination of osmotic second virial coefficients of any type of solutes in dilute solutions regardless of the type and nature of the intermolecular interactions. However, for illustration purposes in the current work, we dealt with aqueous solutions of simple gases to exploit the abundance of standard thermodynamic data for the orthobaric Henry’s law constant and solute distribution coefficients, as well as the availability of results from molecular-based calculations and macroscopic correlations.We present a novel molecular-based approach for the determination of the osmotic second virial coefficients of gaseous solutes in dilute binary solutions, according to a recently proposed molecular thermodynamic formalism of gas solubility [A. A. Chialvo, J. Chem. Phys. 148, 174502 (2018) and Fluid Phase Equilib. 472, 94 (2018)]. We discuss relevant solvation fundamentals and derive new expressions including (i) the relations among infinite-dilution solvation quantities leading to a novel self-consistent route to the calculation of the osmotic second virial coefficients, (ii) the new microstructural interpretation of the resulting osmotic second virial coefficients based on Kirkwood-Buff integrals, the unambiguous discrimination between short- and long-range contributions, and their limiting behavior as the solvent approaches its critical conditions, (iii) new rigorous expressions for the calculation of the osmotic second virial coefficients using standard reference thermodynamic data, and (iv) their unde...

The reaction pathway and kinetics of CuGaSe2 formation were investigated by monitoring the phase evolution of temperature ramp annealed or isothermally soaked bilayer glass/GaSe/CuSe precursor film using time-resolved, in situ high-temperature X-ray diffraction. Bilayer GaSe/CuSe precursor films were deposited on alkali-free thin glass substrates in a migration-enhanced epitaxial deposition system. The initial CuSe phase begins to transform to b-Cu2� xSe at around 2301C, followed by CuGaSe2 formation accompanied by a decrease in the b-Cu2� xSe peak intensity at around 2601C. Both the parabolic and Avrami diffusion-controlled reaction models represented the experimental data very well over the entire temperature range (280–3701C) of the set of isothermal experiments with estimated activation energies of 115(716) and 124(719) kJ/mol, respectively. Transmission electron microscopy–energy-dispersive X-ray spectrometry (TEM–EDS) analysis suggests that CuGaSe2 forms at the interface of the initial GaSe and CuSe layers. r 2008 Elsevier B.V. All rights reserved.

A two-port vector network analyzer (VNA) can be used for measuring the differential-mode (or common-mode) S-parameters of an integrated circuit by combining on-wafer probes with 3-dB-coupling baluns (or power splitters). In such a measurement setup, the error networks from each port of the VNA to the device-under-test are three-port rather than the conventional two-port. This paper proposes a new set of an impedance standards and algorithm that can efficiently extract the full nine mixed-mode S-parameters of the three-port error network. For differential-mode measurements, the four differential-mode S-parameters are used for the calibration and the remaining five common- and cross-mode S-parameters are used for evaluating their associated measurement errors. By a minor variation, the proposed method can be used for characterizing the full nine mixed-mode S-parameters of the 3-dB-coupler embedded probe itself, providing a valuable tool in its development stage. The proposed method uses a pseudoinverse of an overdetermined matrix, by which it becomes tolerant to errors that occur when measuring the impedance standards.

In situ high-temperature X-ray diffraction was used to investigate the reaction mechanism and kinetics of CuGaSe2 formation from Cu–Ga precursors during selenization. The precursor films were deposited in a migration enhanced molecular beam epitaxial reactor on Mo-coated thin glass substrates. During the selenization CuSe forms in the temperature range of approximately 260 to 370 °C, and the onset of formation of CuGaSe2 occurred at approximately 300 °C. The kinetic analysis using a modified Avrami model suggests the formation of CuGaSe2 from selenization of Cu–Ga films follows a one-dimensional diffusion-controlled reaction with an apparent activation energy of 109 (± 7) kJ/mol.

A dynamic multi-swarm particle swarm optimizer (DMS-PSO) (This research is partially supported by National Natural Science Foundation of China (Grant No.61473266), and China Postdoctoral Science Foundation (Grant No. 2013M541990)) is implemented to tune the gain settings of PI controllers for an autonomous hybrid energy system consisting of wind-turbine, solar photovoltaic, diesel engine, and fuel cell generator, as well as an aqua electrolyzer and energy storage system. The system performance has been verified under three different conditions using experimental data. Simulation results show that the DMS-PSO achieves better suppression of frequency fluctuation than basic particle swarm optimizer and differential evolution algorithm.

Rapid thermal annealing (RTA), with fast ramp rate, was performed on several Cu(In,Ga)Se2 (CIGS) films and solar cells under various peak annealing temperatures and holding times. Characterizations were made on CIGS films and cells before and after RTA treatments to study effects of RTA on the CIGS film properties and cell performance. In addition, AMPS-1D device simulation program was used to study effects of defect density on the cell performance by fitting the experimental data of RTA-treated CIGS cells. The results show that RTA treatments under optimal annealing condition can provide significant improvements in the electrical properties of CIGS films and cell performance while preserving the film composition and microstructure morphology. r 2006 Elsevier B.V. All rights reserved.

The reaction pathway and kinetics of a-CuInSe2 formation from a glass/In2Se3/CuSe polycrystalline bilayer precursor film were investigated using time-resolved, in situ high-temperature X-ray diffraction. Bilayer glass/In2Se3/CuSe precursor films were deposited on thin glass substrates in a migration enhanced molecular beam epitaxial deposition system. These films were then temperature ramp annealed or isothermally soaked while monitoring the phase evolution. The initial In2Se3 and CuSe reactant phases were directly transformed to a-CuInSe2 without any detectable intermediate phase. Kinetic parameters were estimated using the Avrami and parabolic diffusion controlled reaction models. The parabolic reaction model fitted the experimental data better than the Avrami model over the entire temperature range (230‐290 8C) of the set of isothermal experiments, with an estimated activation energy of 162 (G5) kJ/mol. q 2005 Elsevier Ltd. All rights reserved.

The effect of a secondary copper selenide phase that appears during epitaxial growth of CuInSe2 (CIS) films on (1 0 0) GaAs substrates was investigated. CIS films with different copper to indium molar ratios were deposited on (1 0 0) GaAs substrates at 3601C by migration-enhanced epitaxy. Films grown under In-rich conditions were polycrystalline, whereas films grown with a Cu-rich composition were epitaxial, as evidenced by pole figure analysis, even when the copper composition was only slightly higher than the 1:1 Cu:In molar ratio. The epitaxial film growth followed a Stranski–Krastanov mode and contained both matrixand island regions. Grazing incidence XRD revealed a small amount of CIS with the Cu–Au-like structure near the surface of the island regions. A binary Cu–Se secondary phase aggregated near the surface in the island regions of the film, as determined by electron probe microanalysis (EPMA) before and after etching in 10% KCN. It is proposed that a Cu–Se phase present during the growth of Cu-rich CIS films enhances the mobility of adatoms on the substrate surface, allowing the film to grow epitaxially to a critical thickness. After that critical thickness is attained, the Cu–Se phase segregates at dislocation sites to nucleate the island regions. TEM-EDX scans of cross-sections also suggested a small amount of the Cu–Se secondary phase segregates on the film surface.

Pulsed non-melt laser annealing (NLA) has been used for the first time to modify near-surface defects and related junction properties in Cu(In,Ga)Se2 (CIGS) solar cells. CIGS films deposited on Mo/glass substrates were annealed using a 25 ns pulsed 248 nm laser beam at selected laser energy density in the range 20–60 mJ/cm2 and pulse number in the range 5–20 pulses. XRD peak narrowing and SEM surface feature size increase suggest near-surface structure changes. Dual-beam optical modulation (DBOM) and Hall-effect measurements indicate NLA treatment increases the effective carrier lifetime and mobility along with the sheet resistance. In addition, several annealed CdS/CIGS films processed by NLA were fabricated into solar cells and characterized by photo- and dark-J–V and quantum efficiency (QE) measurements. The results show significant improvement in the overall cell performance when compared to unannealed cells. The results suggest that an optimal NLA energy density and pulse number for a 25 ns pulse width are approximately 30 mJ/cm2 and 5 pulses, respectively. The NLA results reveal that overall cell efficiency of a cell processed from an unannealed film increased from 7.69% to 13.41% and 12.22% after annealing 2 different samples at the best condition prior to device processing.

The reaction kinetics for the formation of CuInSe2 thin films from a stacked bilayer precursor consisting of InSe and CuSe was studied by means of in situ high-temperature x-ray diffraction. In particular, the isothermal phase evolution of the glass/InSe/CuSe precursor was observed at different temperatures. The pathway produces a CuInSe2 diffusion barrier layer that also functions as a nucleation barrier. Hence, amorphous and crystalline phases simultaneously grow during isothermal processing. The shape of the time-resolved fractional reaction curve exhibits a deceleratory behavior, consistent with the presence of a diffusion-controlled reaction mechanism. Analyses based on Avrami and parabolic-rate laws were conducted. The Avrami exponent for each isothermal reaction is in the range 0.5–0.8, which indicates that the growth reaction is dominantly one-dimensional diffusion controlled. The estimated apparent activation energy for this reaction is 66.0 kJ/mol. The results based on the parabolic rate model a...

In this study the presence of an oil-soluble nonionic surfactant, Brij 30 (polyoxyethylene-4 lauryl ether), in an oil stain, or its addition to the stain through an oil-based solution or water-based mixture is shown to enhance, to a great extent, the spontaneous removal of the stain from a polyester fabric by inducing rollback and spontaneous emulsification phenomena. These findings lead to potential applications of Brij 30 as laundry pre-spotters for enhancement of the removal of tough stains. The effect of three key factors, namely, the surfactant type, the surfactant concentration, and the surfactant application protocol, on the effectiveness of spontaneous detergency was analyzed via ultraviolet-visible spectroscopy. The test fabrics were soiled with a stain composed of mineral oil plus orange OT dye [1-(o-tolylazo)-2-naphthol]. The results showed that all three factors were important for effective detergency. Brij 30 removed more than 80% w/w of the stain, whereas sodium dodecyl sulfate removed less than 24% w/w, and Brij 35 (polyoxyethylene-23 lauryl ether) was ineffective, removing less than 1% w/w. It was also observed that a low threshold concentration of Brij 30, approximately 0.2 mM, was required to spontaneously remove the oil stain, and that higher concentrations did not cause a significant enhancement of the effectiveness of soil removal. Brij 30 completed the detergency effect in less than 1 min, which may have beneficial implications regarding reduced energy consumption. Video microscopy studies revealed that at low Brij 30 surfactant concentrations, the mechanism for spontaneous oil removal proceeded predominantly via a rollback mechanism and that at higher concentrations, a spontaneous emulsification mechanism became progressively more important.

The Nyquist robust sensitivity margin is proposed as a new scalar indicator of robust stability that also provides a meaningful quantitative assessment of the worst sensitivity realized by the uncertain closed loop. After formulating and discussing in detail the underlying optimization problem required for the calculation of the margin, the approach is applied to the characterization of the robust stability of a closed-loop featuring a linear system with an affine uncertainty structure and a parametric uncertainty set described by a real rectangular polytope. The capabilities of the methodology are illustrated through examples, which include an approach for quantifying alternative robustness margins, such as a parametric stability margin. The computational algorithm is systematic and can be carried out with high numerical precision. Copyright © 2005 John Wiley & Sons, Ltd.