Steady-state Experiments Research Articles

Substituent and solvent effects on spectroscopic properties of 2-amino-1,3-dicyano-5,6,7,8-tetrahydronaphthalene derivatives

In this article, we report the photophysical properties of six, newly synthesized donor-substituted 2-amino-1,3-dicyano-5,6,7,8-tetrahydronaphthalene fluorophores. The steady-state and time-resolved spectroscopic experiments have been used to investigate the substituent and solvent effects on the locally excited (LE) and intramolecular charge transfer (ICT) emission. We demonstrate that the spectroscopic characteristics (fluorescence quantum yields, fluorescence decay times, radiative rate constants, and ground and excited state dipole moments) of the studied D–A dyes, as well as the reorganization energies characterizing the solute–solvent interactions and intramolecular torsion motions greatly depend on different substituents and microenvironment. On the basis of the experimental results and our previous quantum-chemical calculations, it was shown that two emitting charge transfer states: non-relaxed (ICT)NR and relaxed (ICT)R exist in six biphenyl derivatives dissolved in polar solvents (e.g., THF), whereas in non-polar medium (MCH) the existence of two emissive states have been attributed to non-relaxed and relaxed, locally excited state ((LE)NR, (LE)R).

Electron-Donating Behavior of Few-Layer Graphene in Covalent Ensembles with Electron-Accepting Phthalocyanines

We describe herein the first example of highly exfoliated graphene covalently linked to electron accepting phthalocyanines. The functionalization of the nanocarbon surface with alkylsulfonyl phthalocyanines was attained by means of a "click" chemistry protocol. The new ensemble was fully characterized (thermogravimetric analysis, atomic force microscopy, transmission electron microscopy and Raman, as well as ground-state absorption) and was studied in terms of electron donor-acceptor interactions in the ground and in the excited state. In particular, a series of steady-state and time-resolved spectroscopy experiments demonstrated photoinduced electron transfer from the graphene to the electron-accepting phthalocyanines. This is the first example of an electron donor-acceptor nanoconjugate, that is, few-layer graphene/phthalocyanine, pinpointing the uncommon electron donating character of graphene.

Recovery and concentration of buoyant cenospheres using an Inverted Reflux Classifier

Cenospheres are hollow, low-density particles found in power station fly ash. They have many commercially-useful properties which make them a valuable by-product. However, recovering cenospheres from fly ash is difficult due to their low concentration and fine size. Experiments were performed to test the novel approach of using an Inverted Reflux Classifier. In this configuration, the particles are fluidised by adding wash water from above which helps to wash any entrained dense material from the overhead product. Inclined channels are mounted at the base to minimise the loss of buoyant cenospheres in the waste underflow stream.Experiments were performed at both laboratory scale (80mm×100mm cross-section) and pilot scale (300mm×300mm cross section) using mixtures of cenospheres and silica, all nominally less than 100μm in size. In batch tests, the bed expansion behaviour of the positively-buoyant cenospheres in the Inverted Reflux Classifier was found to be analogous to the behaviour of negatively-buoyant particles in the standard configuration. Continuous steady-state experiments were performed using feeds with suspension solids concentration varying from 0.3 to 9.5wt.% solids and a buoyant cenosphere grade of 0.5 to 65wt.%, with a range of fluidisation wash water rates, and degree of volume reduction (ratio of volumetric feed to product rate). Both units delivered high recoveries and product grades. An increase in volume reduction (decreasing overflow rate for a given feed rate), caused a drop in recovery and an improvement in grade. The throughput advantage compared to a conventional teetered (fluidised) bed separator was over 30 in some cases. Both laboratory and pilot-scale units displayed similar behaviour and the results were also consistent with existing correlations for negatively-buoyant particles in the standard Reflux Classifier. Hence this technology has clear potential for recovering and concentrating cenospheres from fly ash.

Experimental and Theoretical Investigation on Excited State Intramolecular Proton Transfer Coupled Charge Transfer Reaction of Baicalein

The excited state intramolecular proton transfer (ESIPT) coupled charge transfer of baicalein has been investigated using steady-state spectroscopic experiment and quantum chemistry calculations. The absence of the absorption peak from S1 excited state both in the experimental and calculated absorption spectra indicates that S1 is a dark state. The dark excited state S1 results in the very weak fluorescence of solid baicalein in the experiment. The frontier molecular orbital and the charge difference densities of baicalein show clearly that the S1 state is a charge-transfer state whereas the S2 state is a locally excited state. The only one stationary point on the potential energy profile of excited state suggests that the ESIPT reaction of baicalein is a barrierless process.

End capped polyenic structures as visible light sensitive photoinitiators for polymerization of vinylethers

Nine new photoinitiating systems based on a combination of new and established dyes (having an end capped polyenic structure) with an iodonium salt have been synthesized and tested for the polymerization of divinylether and epoxy monomers upon a visible light exposure. They exhibit a strong absorption in the 350–650 nm range which well matches the visible light emission of different convenient visible light sources. Interestingly, very soft irradiation conditions can be employed. Excellent polymerization profiles have been obtained from selected dye iodonium salt combinations using a halogen amp or a laser diode à 457 nm. The chemical mechanisms associated with these novel photoinitiating systems are investigated by steady-state photolysis and ESR experiments.

Comparative Genome-Scale Reconstruction of Gapless Metabolic Networks for Present and Ancestral Species

We introduce a novel computational approach, CoReCo, for comparative metabolic reconstruction and provide genome-scale metabolic network models for 49 important fungal species. Leveraging on the exponential growth in sequenced genome availability, our method reconstructs genome-scale gapless metabolic networks simultaneously for a large number of species by integrating sequence data in a probabilistic framework. High reconstruction accuracy is demonstrated by comparisons to the well-curated Saccharomyces cerevisiae consensus model and large-scale knock-out experiments. Our comparative approach is particularly useful in scenarios where the quality of available sequence data is lacking, and when reconstructing evolutionary distant species. Moreover, the reconstructed networks are fully carbon mapped, allowing their use in 13C flux analysis. We demonstrate the functionality and usability of the reconstructed fungal models with computational steady-state biomass production experiment, as these fungi include some of the most important production organisms in industrial biotechnology. In contrast to many existing reconstruction techniques, only minimal manual effort is required before the reconstructed models are usable in flux balance experiments. CoReCo is available at http://esaskar.github.io/CoReCo/.

Non-uniqueness, Numerical Artifacts, and Parameter Sensitivity in Simulating Steady-State and Transient Foam Flow Through Porous Media

The uniqueness and sensitivity of foam modeling parameters are crucial for simulating foam flow through porous media. In the absence of oil in the porous medium, the local-equilibrium foam model investigated in this work uses three parameters to describe the foam quality dependence: $$fmmob,\, fmdry$$ , and $$epdry$$ . Even for a specified value of $$epdry$$ , in some cases, two pairs of $$fmmob$$ and $$fmdry$$ values can experimentally match measured transition foam quality ( $$f_\mathrm{g}^{t}$$ ) and transition foam apparent viscosity ( $$\mu _\mathrm{foam,app}^t$$ ). This non-uniqueness can be broken by limiting the solution such that $$fmdry$$ is smaller than the transition water saturation ( $$S_\mathrm{w}^t$$ ). In addition, a three-parameter fit using all experimental data of apparent viscosity versus foam quality was developed to simultaneously estimate $$fmmob,\, fmdry$$ , and $$epdry$$ . However, a better strategy is to conduct and match a transient experiment, in addition to steady-state experiments, in which a gas displaces the surfactant solution at 100 % water saturation. This transient foam quality scans the entire range of fractional flow, and the values of the foam parameters that best match the experiment can be uniquely determined. The numerical artifact of pressure oscillations in simulating this transient foam process was investigated by comparing the finite difference algorithm with the method of characteristics. Sensitivity analyses indicated that the estimated foam parameters were highly dependent on the parameters used for the water and gas relative permeabilities. In particular, the water relative permeability exponent and connate water saturation are important.

INCA: a computational platform for isotopically non-stationary metabolic flux analysis

13C flux analysis studies have become an essential component of metabolic engineering research. The scope of these studies has gradually expanded to include both isotopically steady-state and transient labeling experiments, the latter of which are uniquely applicable to photosynthetic organisms and slow-to-label mammalian cell cultures. Isotopomer network compartmental analysis (INCA) is the first publicly available software package that can perform both steady-state metabolic flux analysis and isotopically non-stationary metabolic flux analysis. The software provides a framework for comprehensive analysis of metabolic networks using mass balances and elementary metabolite unit balances. The generation of balance equations and their computational solution is completely automated and can be performed on networks of arbitrary complexity.

Development and validation of a virtual soot sensor: Part 1: steady-state engine operation

The reduction of the emission limits has lead to an increased complexity of the ECU calibration process and to the need for expensive aftertreatment methods in order to fulfil the legislated limits. Integrating feedback of the Particulate Matter (PM) and NO x emissions into the engine management could make fulfilment of legislation easier and reduce the complexity of the necessary calibration process. Since production type PM sensors for raw emission feedback are not available, a virtual soot sensor (VSS) has been developed. The VSS is a mean value soot model which provides predictions for the PM in real-time (cycle resolved). Its inputs are ECU variables and characteristic values of the heat release rate which are obtained on-line from in-cylinder pressure measurement. The structure of the VSS has been derived from optical kL-measurement data, i.e. from representative, crank angle resolved evolutions of the in-cylinder PM (3-color pyrometry). The model is structured into three consecutive phases which represent the in-cylinder PM evolution and is calibrated with measurements of the exhaust PM concentration of a standard engine operating map only. The three phases correspond to an initial phase where formation of PM dominates, a phase when formation and oxidation are roughly in balance, and a phase during which oxidation dominates. For steady state experiments, the VSS shows an excellent correlation with the exhaust gas soot (respectively elementary carbon) concentration that has been measured with a photo-acoustic soot sensor (PASS). In addition a reasonable ratio between soot formation and soot oxidation is reproduced.

Adding Regulation to Cross-Bridge Muscle Models

For over fifty years, cross-bridge models have helped us understand muscle contraction. These models describe both steady state and transient force measurements. Being computationally efficient, they allow parameter estimation from data fits. Unfortunately, they only apply to maximal activation. At sub-maximal activation, tropomyosin inhibits myosin binding. If a myosin molecule binds to actin, it locally displaces tropomyosin thereby facilitating the binding of adjacent myosin. Since myosin and actin are arranged in filaments, cooperativity violates the mean-field approximation. This approximation is fundamental to any cross-bridge model, so models of activation typically use Monte-Carlo methods. Such models, though useful for some applications, are orders of magnitude slower than cross-bridge models and so parameter estimation is difficult. To address this problem, we have developed a method to efficiently incorporate activation into cross-bridge models.The basis of our theory is that, at sub-maximal activation, some parts of the thin filament are locally active, while the rest is inactive. A set of differential equations can keep track of these locally activated regions as they form, grow, shrink and disappear. Inside these active regions, myosin obeys a cross-bridge model; outside these active regions, myosin remains unbound. We have validated this model by comparisons to Monte-Carlo simulations. The model successfully fits both steady state and transient experiments at all levels of activation. We have compared the model to measurements of in vitro motility at low calcium and low ATP (rigor activation), showing that the model reproduces the measurements, and can estimate parameters of activation. This parameter estimation is possible because the model is roughly 10,000-fold faster than Monte-Carlo simulations. We are now fitting the model to experiments performed under conditions of variable calcium and ATP. This work represents a step toward a complete multi-scale description of muscle contraction.

Organic semiconductor core–shell nanoparticles designed through successive solvent displacements

The concept of sequential nanoprecipitation is developed to generate organic semiconductor core–shell nanoparticles with P3HT core and PCBM shell. Steady-state photoluminescence experiments on such nanoparticles enable the estimation of the exciton diffusion length at ∼14 nm.

Chapter Eighteen - Real-Time Assessment of the Metabolic Profile of Living Cells with Genetically Encoded NADH Sensors

Redox metabolism plays a critical role in multiple pathophysiological settings, including oncogenesis and tumor progression. Until recently, however, our knowledge of key redox processes in living systems was limited by the lack of an adequate methodology to monitor redox potential. Nicotinamide adenine dinucleotide, in its reduced (NADH) and oxidized (NAD(+)) forms, is perhaps the most important small molecule in the redox metabolism of mammalian cells. We have previously developed a series of genetically encoded fluorescent sensors allowing for the quantification of intracellular NADH. Here, we present experimental components and considerations that are required to perform a standardized quantification of intracellular NADH based on these probes. Moreover, we present the initial calibration experiments necessary to obtain reliable data from this approach, we detail a protocol to measure intracellular NADH levels in steady-state kinetic experiments, and we provide consideration on the processing of data. Among various applications, this technique is suitable for the study of redox alterations in malignant cells.

One-step production of long-chain hydrocarbons from waste-biomass-derived chemicals using bi-functional heterogeneous catalysts

In this study, we demonstrate the production of long-chain hydrocarbons (C8+) from 2-methylfuran (2MF) and butanal in a single step reactive process by utilizing a bi-functional catalyst with both acid and metallic sites. Our approach utilizes a solid acid for the hydroalkylation function and as a support as well as a transition metal as hydrodeoxygenation catalyst. A series of solid acids was screened, among which MCM-41 demonstrated the best combination of activity and stability. Platinum nanoparticles were then incorporated into the MCM-41. The Pt/MCM-41 catalyst showed 96% yield for C8+ hydrocarbons and the catalytic performance was stable over four reaction cycles of 20 hour each. The reaction pathways for the production of long-chain hydrocarbons is probed with a combination of infrared spectroscopy and steady-state reaction experiments. It is proposed that 2MF and butanal go through hydroalkylation first on the acid site followed by hydrodeoxygenation to produce the hydrocarbon fuels.

Effect of Turbulence Intensity on Cross-Injection Film Cooling at a Stepped or Smooth Endwall of a Gas Turbine Vane Passage

This study is concerned with a film cooling technique applicable to the protection of the endwalls of a gas turbine vane. In the experiments, cross-injection coolant flow from two-row, paired, inclined holes with nonintersecting centerlines was utilized. The test model is a scaled two-half vane. The levels of turbulence intensity used in the experiments are T.I. = 1.8%, 7%, and 12%. Other parameters considered in the film cooling experiments include three inlet Reynolds numbers (9.20 × 104, 1.24 × 105, and 1.50 × 105), three blowing ratios (0.5, 1.0, and 2.0), and three endwall conditions (smooth endwall and stepped endwall with forward-facing or backward-facing step). Thermochromic liquid crystal (TLC) technique with steady-state heat transfer experiments was used to obtain the whole-field film cooling effectiveness. Results show that, at low turbulence intensity, increasing Reynolds number decreases the effectiveness in most of the vane passage. There is no monotonic trend of influence by Reynolds number at high turbulence intensity. The effect of blowing ratio on the effectiveness has opposite trends at low and high turbulence levels. Increasing turbulent intensity decreases the effectiveness, especially near the inlet of the vane passage. With a stepped endwall, turbulence intensity has only mild effect on the film cooling effectiveness.

Dynamics of the Lever-Arm Swing in Myosin V

Myosins utilize a conserved structural mechanism to convert the energy from ATP hydrolysis to a large swing in the force generating lever-arm. However, there remains an ongoing controversy about the kinetics of lever-arm swing in relation to the steps in the ATPase cycle. To address this question we have developed a novel FRET system in myosin V (MV) that utilizes several donor-acceptor pairs to examine the dynamics of lever arm motion. MV containing a single IQ motif and an N-terminal (NT) tetracysteine site was labeled with the bisarsenical dye FlAsH (MV.NT.FlAsH). The first IQ motif of MV.NT.FlAsH was exchanged either with IAANS labeled CaM, a donor, or QSY-9 labeled CaM, a non-fluorescent acceptor. Steady-state and transient kinetic experiments reveal a decrease in FRET upon ATP binding (recovery stroke) in both donor-acceptor pairs. We utilized transient kinetic experiments to demonstrate that upon mixing the MV.ADP.Pi complex with actin there was a FRET increase that occurred in two phases, and the fast and slow phases correlated well with the release rates of Pi and ADP, respectively. We also labeled the upper-50kDa tetracysteine site with FlAsH (MV.U50.FlAsH) and exchanged the QSY labeled CaM on to the first IQ motif. We observed structural changes during ATP binding that were very similar to the MV.NT.FlAsH results. During actin-activated product release we observed two-phases, a rapid increase in FRET followed by a slower decrease in FRET, which correlated well with ADP release. We find that the force generating motion of the lever arm occurs in two steps which are closely coupled to the product release steps. Our results also indicate that the conformational changes in the lever arm associated with the power stroke may follow a unique pathway that is not simply the reversal of the recovery stroke.

Characterisation of water-oil drainage process through a reservoir rock sample by digital core analysis

Oil-water relative permeability and capillary pressure of a water-wet digital core are computed using the finite-volume/volume of fluid method and mimicking traditional laboratory steady-state experiments carried out on a water saturated sample. Commercial software is used for immiscible multiphase fluid flow simulations, carried out on a low-cost multicore workstation, and the porescale data are upscaled to derive relative permeability and capillary pressure curves as function of water saturation. The digital sample is obtained by high resolution X-ray computed tomography scanning.

Biogas Plasticization Coupled Anaerobic Digestion: The Anaerobic Pump Stoichiometry

This paper presents the stoichiometry section of a bioenergetics investigation into the biogas plasticization of wastewater sludge using the Anaerobic Pump (TAP). Three residue samples, an input substrate and two residual products, were collected from two side by side operated AD systems, a conventional continuous flow and stirred reactor, and TAP, and submitted for elemental and calorimetric analyses. The elemental compositions of the residues were fitted to a heterotrophic metabolism model [1] for both systems. To facilitate balanced stoichiometric models, a simple "cell" correction computation separates measured residual composites into "real" residual composition and cell growth (C5H7NO2) components. The elemental data and model results show that the TAP stage II residual composition (C1H0.065O0.0027N0.036) was nearly devoid of hydrogen and oxygen, leaving only fixed carbon and cells grown as the composition of the remaining mass. This quantitative evidence supports prior measurements of very high methane yields from TAP stage II reactor during steady-state experiments [2]. All performance parameters derived from the stoichiometric model(s) showed good agreement with measured steady-state averaged values. These findings are strong evidence that plasticization-disruption (TAP) cycle is the mechanism responsible for the observed increases in methane yield. The accuracy achieved by the stoichiometry models qualifies them for thermodynamic analysis to obtain potentials and bioconversion efficiencies. How applied pressure causes matrix conformation changes triggered by a functional consequence (plasticization and disruption) is this study's essential focus.

Fluid flow numerical experiments of faulted porous carbonates, Northwest Sicily (Italy)

A methodology to assess the effects of structural heterogeneities below seismic resolution in porous carbonate grainstones on reservoir performance during production is developed by integrating structural analysis, power law distributions, up-scaling, and numerical techniques. The novelty of the methodology consists of accounting for the buffering effects on permeability caused by compactive and cataclastic deformation bands. By using this methodology, a 3D deterministic field analogue and a 3D Discrete Fracture Network (DFN) representations of the reservoir/aquifer were built first, and then single-phase, steady-state fluid flow numerical experiments in an equivalent porous medium framework were performed. The field analogue is located along the Northwestern coast of Sicily (Italy) where Lower Pleistocene porous carbonate grainstones are crosscut by a strike-slip fault system. This fault system is made up of two conjugate sets of strike-slip shear structures recognized as single compactive shear bands (CSB), zones of compactive shear bands (ZB) and well-developed faults (DF), with discrete slip surfaces and cataclastic material. The permeability of these structures is up to three orders of magnitude less than the surrounding porous carbonate rocks. The fluid flow numerical experiments have been performed on the two aforementioned reservoir/aquifer descriptions to assess the effect of Sub-Seismic Resolutions Faults (SSRF), such as those observed in the outcrops, on fluid flow during production from a well, injection production in Enhanced Oil Recovery (EOR), and up-scaling to large cell size for regional flow simulation. Comparison of draw-down modeling in the DFN and the deterministic models show that results are similar with the exception of wells located in areas of intense strain localization with ZB and DF. The use of the DFN model is therefore an acceptable representation of the heterogeneities induced by SSRF in a reservoir/aquifer. Results of numerical computations show that, in structurally complex areas, SSRF-related ZB and DF might represent a drilling risk because they can enhance draw-down during production and EOR activities.

Mathematical Model to Predict Skin Concentration after Topical Application of Drugs

Skin permeation experiments have been broadly done since 1970s to 1980s as an evaluation method for transdermal drug delivery systems. In topically applied drug and cosmetic formulations, skin concentration of chemical compounds is more important than their skin permeations, because primary target site of the chemical compounds is skin surface or skin tissues. Furthermore, the direct pharmacological reaction of a metabolically stable drug that binds with specific receptors of known expression levels in an organ can be determined by Hill’s equation. Nevertheless, little investigation was carried out on the test method of skin concentration after topically application of chemical compounds. Recently we investigated an estimating method of skin concentration of the chemical compounds from their skin permeation profiles. In the study, we took care of “3Rs” issues for animal experiments. We have proposed an equation which was capable to estimate animal skin concentration from permeation profile through the artificial membrane (silicone membrane) and animal skin. This new approach may allow the skin concentration of a drug to be predicted using Fick’s second law of diffusion. The silicone membrane was found to be useful as an alternative membrane to animal skin for predicting skin concentration of chemical compounds, because an extremely excellent extrapolation to animal skin concentration was attained by calculation using the silicone membrane permeation data. In this chapter, we aimed to establish an accurate and convenient method for predicting the concentration profiles of drugs in the skin based on the skin permeation parameters of topically active drugs derived from steady-state skin permeation experiments.

Influence of the receiver’s back surface radiative characteristics on the performance of a heat-pipe evacuated-tube solar collector

The receiver’s back surface radiative characteristics of a heat-pipe evacuated-tube solar collector (ETSC) may have a significant influence on its performance. This influence is generally related to the back surface emissivity and temperature; however it has been not studied previously. This paper firstly presents a heat transfer model for the ETSC, which is then derived to characterize the relationship between the heat loss and the back surface emissivity of the ETSC. A steady state experiment has been also performed to measure the heat loss of ETSC with different back surface emissivity values. The experimental results indicate that the heat loss of the ETSC increases with the increase of the back surface emissivity, but the rate of increase differs for different operation temperatures. When the back surface emissivity increases from 0.03 to 0.12, the heat loss of ETSC only increases by 31% when the operation temperature is below 100°C, but the heat loss will increase to 96% when the operation temperature is over 200°C. This means that the change of back surface emissivity can significantly affect the performance of the ETSC at higher temperature but affect little at lower temperature. Based on this, a novel method by performing roughness treatment on the receiver’s back surface is proposed to solve the overheating problem of ETSC in summer. Two solar water heaters including 6 ETSCs with standard and roughness-treated tubes were tested under real weather condition. Experiment reveals that when the water temperature in tank is below 60°C, the two solar water heaters own similar temperature change. But when the temperature is over 80°C, the solar water heater with roughness-treated tube shows obviously lower temperature increase than that with standard tube. Therefore, it is very effective to prevent overheating of some solar water heaters used in high latitudes in summer by increasing the receiver’s back surface roughness.