Transient Equilibrium Research Articles

18F-Fluciclovine (18F-FACBC) PET imaging of recurrent brain tumors

PurposeThe aim of our study was to investigate the efficacy of 18F-Fluciclovine brain PET imaging in recurrent gliomas, and to compare the utility of these images to that of contrast enhanced magnetic resonance imaging (MRI) and to [11C-methyl]-L-methionine (11C-Methionine) PET imaging. We also sought to gain insight into the factors affecting the uptake of 18F-FACBC in both tumors and normal brain, and specifically to evaluate how the uptake in these tissues varied over an extended period of time post injection.MethodsTwenty-seven patients with recurrent or progressive primary brain tumor (based on clinical and MRI/CT data) were studied using dynamic 18F-Fluciclovine brain imaging for up to 4 h. Of these, 16 patients also had 11C-Methionine brain scans. Visual findings, semi-quantitative analyses and pharmacokinetic modeling of a subset of the 18F-Fluciclovine images was conducted. The information derived from these analyses were compared to data from 11C-Methionine and to contrast-enhanced MRI.Results18F-Fluciclovine was positive for all 27 patients, whereas contrast MRI was indeterminate for three patients. Tumor 18F-Fluciclovine SUVmax ranged from 1.5 to 10.5 (average: 4.5 ± 2.3), while 11C-Methionine’s tumor SUVmax ranged from 2.2 to 10.2 (average: 5.0 ± 2.2). Image contrast was higher with 18F-Fluciclovine compared to 11C-Methionine (p < 0.0001). This was due to 18F-Fluciclovine’s lower background in normal brain tissue (0.5 ± 0.2 compared to 1.3 ± 0.4 for 11C-Methionine). 18F-Fluciclovine uptake in both normal brain and tumors was well described by a simple one-compartment (three-parameter: Vb,k1,k2) model. Normal brain was found to approach transient equilibrium with a half-time that varied greatly, ranging from 1.5 to 8.3 h (mean 2.7 ± 2.3 h), and achieving a consistent final distribution volume averaging 1.4 ± 0.2 ml/cc. Tumors equilibrated more rapidly (t1/2ranging from 4 to 148 min, average 57 ± 51 min), with an average distribution volume of 3.2 ± 1.1 ml/cc. A qualitative comparison showed that the rate of normal brain uptake of 11C-Methionine was much faster than that of 18F-Fluciclovine.ConclusionTumor uptake of 18F-Fluciclovine correlated well with the established brain tumor imaging agent 11C-Methionine but provided significantly higher image contrast. 18F-Fluciclovine may be particularly useful when the contrast MRI is non-diagnostic. Based on the data gathered, we were unable to determine whether Fluciclovine uptake was due solely to recurrent tumor or if inflammation or other processes also contributed.

Modeling Networks of Evolving Populations

The goal of this research is to devise a method of differential equation based modeling of evolution that can scale up to capture complex dynamics by enabling the inclusion of many—potentially thousands—of biological characteristics. Towards that goal, a mathematical model for evolution based on the well-established Fisher-Eigen process is built with a unique and efficient structure. The Fisher-Eigen partial differential equation (PDE) describes the evolution of a probability density function representing the distribution of a population over a phenotype space. This equation depends on the choice of a fitness function representing the likelihood of reproductive success at each point in the phenotype space. The Fisher-Eigen model has been studied analytically for simple fitness functions, but in general no analytic solution is known. Furthermore, with traditional numerical methods, the equation becomes exponentially complex to simulate as the dimensionality of the problem expands to include more phenotypes. For this research, a network model is synthesized and a set of ordinary differential equations (ODEs) is extracted based on the Fisher-Eigen PDE to describe the dynamic behavior of the system. It is demonstrated that, when juxtaposed with full numerical PDE simulations, this ODE model finds well-matched transient and precise equilibrium solutions. This prototype method makes modeling of high-dimensional data possible, allowing researchers to examine and even predict complex dynamic behavior based on a snapshot of a population. KEYWORDS: Evolutionary Modeling; Mathematical Biology; Network Dynamics; Ordinary Differential Equations; Partial Differential Equations; Fisher-Eigen model; Phenotype; Fitness Function

Cherenkov emission-based external radiotherapy dosimetry: I. Formalism and feasibility.

Cherenkov emission (CE)-based external beam dosimetry is envisioned to involve the detection of CE directly in water with placement of a high-resolution detector out of the field, avoiding perturbations encountered with traditional dosimeters. In this work, we lay out the groundwork for its implementation in the clinic and motivate CE-based dosimeter design efforts. To that end, we examine a formalism for broad-beam in-water CE-based dosimetry of external radiotherapy beams, design and test a Monte Carlo (MC) simulation framework for the calculation of CE-to-dose conversion factors used by the formalism, and demonstrate the experimental feasibility of this method. The formalism is conceptually analogous to ionization-based dosimetry and employs CE-to-dose conversion factors, , including only and all CE generated within polar angles θ±δθ on beam axis. The EGSnrc user code SPRRZnrc is modified to calculate , as well as CE spectral and angular distributions. The modified code is tested with monoenergetic parallel electrons on a thin water slab. Detector configurations are examined for broad 6-22MeV electron beams from a BEAMnrc TrueBeam model, with a focus on (4π detection), , and ( is the CE angle of relativistic electrons in water). We perform a relative experimental validation at with electron beams, using a simple detector design with spherical optics and geometrical optics approximation of the sensitive volume, which spans the water tank. Due to transient charged particle equilibrium, broad photon beams are generally less sensitive to beam quality, depth, and angle. For 0.1-50MeV electrons on a thin water slab, the code outputs CE photon spectral density per unit mass (calculated from dose and ) and angle in agreement with theory within ±0.03% and , respectively, corresponding to the output precision. The configuration was found impractical due to detection considerations. Detection at for small δθ exhibited beam quality dependence of the same order as well as strong superficial depth dependence. A 4π configuration ameliorates these effects. A more practical approach may employ a large numerical aperture. In comparing with literature, we find that these effects are less pronounced for broad photon beams in water, as expected. Measured relative at small δθ were within 1% of simulated factors (relative to their local average) for percent-depth CE (PDC) >50%. At other depths, deviations were in accordance with signal-to-noise, known detector limitations, and approximations. It was found that the CE spectrum is beam quality and depth invariant, while for electron beams the CE angular distribution is strongly dependent on beam quality and depth. However, the uncertainty of CE and PDC measurement at detection for small δθ due to deviations around δθ was shown to be ≤1% and <0.1% (k=1), respectively. The robustness to expected detector setup variations was found to result in ≤1% (k=1) local uncertainty contribution for PDC >50%. Based on our MC and experimental studies, we conclude that the CE-based method is promising for high-resolution, perturbation-free, three-dimensional dosimetry in water, with specific applications contingent on comprehensive detector development and characterization.

Transient radioactive equilibrium of 121mTe and 121Te and determination of their half-lives

[121mTe]-Tellurium and [121Te]-tellurium form a genetic mother/daughter pair in a transient radioactive equilibrium. Both nuclides are found as undesired byproducts in [123I]-iodide solution, a radionuclide established in radiopharmacy for synthesis of tracers with application in diagnostic nuclear medicine. Because these Te-isotopes affect the radionuclidic purity of the product and contribute to the overall dose for the patient, their half-lives must be known accurately in order for the dose calculations to be correct.For each of the two isotopes, literature reports several distinct, but inconsistent values for the respective half-life T1/2:121mTe: 125 d / ∼140 d / 154 d / 164 d // 121Te: ∼17 d / 19 d.ZAG Zyklotron AG is a commercial manufacturer of [123I]-sodium iodide and therefore it was a reasonable goal to add to literature an additional view on the half-lives of 121mTe and 121Te from long-time examination of retention samples and of quality control samples drawn from routine production. This work experimentally found T1/2 of 121mTe to be 165.1(7) d and T1/2 of 121Te to be 19.38(3) d. In addition, the transient radioactive equilibrium was examined closer with these values for the IT internal transition ratio of 121mTe.

Investigation into the mechanism of thin filament regulation by transient kinetics and equilibrium binding: Is there a conflict?

Striated muscle contraction occurs when myosin undergoes a lever-type structural change. This process (the power stroke) requires ATP and is governed by the thin filament, a complex of actin, tropomyosin, and troponin. The authors have used a fast-mixing instrument to investigate the mechanism of regulation. Such (pre-steady-state kinetic) experiments allow biochemical intermediates in a working actomyosin cycle to be monitored. The regulatory focal point is demonstrated to be the step that involves the departure of inorganic phosphate (i.e., AM-ADP-Pi → AM-ADP). This part of the cycle, which lies on the main kinetic pathway and coincides with the drive stroke, is maximally accelerated ∼100-fold by the combined association of ligands (Ca[II] and rigor myosin heads) with the thin filament. However, the observed ligand dependencies of the rates of Pi dissociation that are reported herein are at variance with predictions of models derived from experiments where ATP hydrolysis is not taking place (and myosin exists in a nonphysiological form). It is concluded that the principal influence of the thin filament is in setting the rate of Pi dissociation and that physiological levels of regulation are dependent upon the liganded state of the thin filament as well as the conformation of myosin.

Optimal timing of tau pathology imaging and automatic extraction of a reference region using dynamic [18F]THK5317 PET.

[18F]THK5317 is a PET tracer for in-vivo imaging of tau associated with Alzheimer's disease (AD). This work aimed to evaluate optimal timing for standardized uptake value ratio (SUVR) measures with [18F]THK5317 and automated generation of SUVR-1 and relative cerebral blood flow (R1) parametric images. Nine AD patients and nine controls underwent 90 min [18F]THK5317 scans. SUVR-1 was calculated at transient equilibrium (TE) and for seven different 20 min intervals and compared with distribution volume ratio (DVR; reference Logan). Cerebellar grey matter (MRI) was used as reference region. A supervised cluster analysis (SVCA) method was implemented to automatically generate a reference region, directly from the dynamic PET volume without the need of a structural MRI scan, for computation of SUVR-1 and R1 images for a scan duration matching the optimal timing. TE was reached first in putamen, frontal- and parietal cortex at 22 ± 4 min for AD patients and in putamen at 20 ± 0 min in controls. Over all regions and subjects, SUVR20–40-1 correlated best with DVR-1, R2 = 0.97. High correlation was found between values generated using MRI- and SVCA-based reference (R2 = 0.93 for SUVR20–40-1; R2 = 0.94 for R1). SUVR20–40 allows for accurate semi-quantitative assessment of tau pathology and SVCA may be used to obtain a reference region for calculation of both SUVR-1 and R1 with 40 min scan duration.

66. Results of a spectrometric analysis performed at the ASST Lariana on 223Ra-dichloruro Xofigo

Purpose BAYER has recently marketed a pharmaceutical named Xofigo, consisting of 223Ra-dichloride, for the treatment of metastatic bone lesions of castration-resistant prostate cancer. Its production modality consists of the neutron irradiation of a 226Ra target yielding 227Ac which, through intermediate steps, decays into 223Ra. In view of the possible presence of radionuclide impurities that may demand strong radiation protection requirements (e.g. 227Ac and 226Ra), a radiometric analysis of Xofigo was performed to rule out any contamination by other long-lived radioisotopes [1] . Methods The spectrometry system consisted of the GEM-20 P EG&G ORTEC Hyperpure Germanium detector, the ORTEC TRIUMP-PCI-8 k multichannel analyzer, the ORTEC GammaVision spectral analysis program, and two certified calibration point sources (152Eu and 241Am). A 0.2 ml volume of radiopharmaceutical (about 200 kBq activity) was inserted into a conical test tube and the gamma emission spectrum was acquired. The detection efficiency was calculated by a dedicated application (ORTEC ANGLE v.3.0), integrated with the GammaVision software. The spectral analysis was performed by means of a specific library, containing both expected and suspected radioisotopes. Results The spectral acquisitions (see Figure) and the related analysis (see Table) were repeated to test the reproducibility of the results and provided the following outcomes: the calculated 223Ra activity was (196 ± 9) kBq, in agreement with the one measured at sampling, and the 211Bi and 219Rn activities were absolutely compatible with the transient equilibrium condition with the 223Ra father. No radionuclides other than those expected were found above the minimum detectable activity (MDA). Conclusions Any significant presence of radioisotope contamination in the radiopharmaceutical sample and, consequently, of issues related to long-lived radionuclides, can be excluded, ensuring both the operator and the patient protection and the safe management of the radioactive waste. Download : Download high-res image (262KB) Download : Download full-size image

Coreflood Study of Effect of Surfactant Concentration on Foam Generation in Porous Media.

The propagation of foam in an oil reservoir depends on the creation and stability of the foam in the reservoir, specifically the creation and stability of foam films, or lamellae. As the foam propagates far from the injection well, superficial velocity and pressure gradient decrease with distance from the well. Experimental (Friedmann et al. Steam-foam mechanistic field trial in the midway-sunset field. SPERE. 1994, 9 (4), 297–304) and theoretical (Ashoori, et al. Roles of Transient and Local Equilibrium Foam Behaviour in Porous Media: Traveling Wave. Colloids Surf. A2011, 337 (1–3), 228–242). studies relate concerns about foam propagation at low superficial velocity to the minimum velocity or pressure gradient for foam generation near the well (Gauglitz et al. Foam Generation in Homogeneous Porous Media. Chem. Eng. Sci.2002, 57, 4037–4052; Rossen et al. Percolation Theory of Creation and Mobilization of Foams in Porous Media. AI Chem Eng. J.1990, 36, (8)). The objective of this work is to measure the impact of surfactant concentration and gas fractional flow on foam generation. Theory (Kam et al. Model for Foam Generation in Homogeneous Media. SPE J.2003, 8 (4): 417–42, SPE-87334-PA; Rossen 1990) relates foam generation to gas fractional flow and, indirectly, to the stability of foam films, or lamellae, which in turn depends on surfactant concentration (Apaydin et al. Surfactant Concentration and End Effects on Foam Flow in Porous Media. (Apaydin et al.Transp Porous Media. 2001, 43, 511–536). However, the link between foam generation and surfactant concentration has not been established experimentally. In our experiments, nitrogen foam is generated in a core of Bentheimer sandstone. The foam-generation experiments consist of measuring the minimum velocity for foam generation as a function of gas fractional flow at three surfactant concentrations well above the critical micelle concentration. Experimental results show that the minimum velocity for foam generation decreases with increasing liquid fraction, as shown by previous foam generation studies (Friedmann et al., 1994; Rossen and Gauglitz, 1990). Additionally, our results show that this velocity decreases with increasing surfactant concentration, far above the CMC. We also propose a workflow for screening out the experimental artifacts that can distort the trigger velocity.

The Implementation of the Gradual Movement of Sliding Blocks to a New Method for Evaluating the Seismic Stability of Slopes Reinforced by Geotextile

Evaluating the seismic stability of a rock slope typically involves searching for the minimum value of calculated safety factors (SF) for each supposed sliding block. Because only the transient equilibrium is evaluated, the likelihood of any slope failure can be deemed negligible if all the calculated SFs are greater than unity. However, even if some of the calculated SF are less than unity, it cannot be assumed that the slope will collapse. Recently, in the wake of extremely large earthquakes in Japan, the design earthquake standards for nuclear power plants (NPP) have been extended. After the experience of the 2011 off the Pacific coast of Tohoku Earthquake, the designer is expected to consider beyond design basis earthquakes to determine whether more can reasonably be done to reduce the potential for damage, especially where major consequences may ensue [IAEA (2011). IAEA international fact finding expert mission of the Fukushima dai-ichi NPP accident following the Great East Japan Earthquake and Tsunami, Mission report, IAEA]. With this in mind, the method employed to evaluate the seismic performance of the slope surrounding an NPP needs to be capable of doing more than determining the likelihood of failure: it must also consider the process toward failure in the event of an earthquake beyond the design basis. In this paper, a new evaluation flow which considers the failure process is proposed to evaluate the seismic performance of slopes surrounding an NPP. This is followed by confirming the validity of the concepts in the proposed flow chart by re-evaluating centrifuge tests in past literature and the numerical simulations designed for those tests.

A software tool for simulating contaminant transport and remedial effectiveness in sediment environments

Sediments have often acted as sinks for contaminants that possess strong affinity for solids near historical pollution sources. Mathematical models describing the evolution of contaminant concentrations in sediment environments provide a scientific basis for decision support and remediation design. Herein, novel software (CapSim) is introduced including processes relevant to natural attenuation and in-situ treatment and containment (capping). The tool has been used as a basis for remedial design at a number of sites throughout the United States. CapSim is built on the concept of an arbitrary number of layers that each exhibit traditional porous media transport processes including sorption (linear and non-linear, transient or local equilibrium), advection, diffusion, dispersion, multicomponent linked reactions and, critically, processes specific to the sediment-water interface including bioturbation of both solids and porewater, deposition, consolidation, and interaction with the overlying surface water. A summary of recent applications and selected simulations of key features are presented.

Regional times to equilibria and their impact on semi-quantification of [18F]AV-1451 uptake

The semi-quantitative estimate standardised uptake value ratios (SUVR) correlate well with specific binding of the tracer expressed as distribution volume ratios (DVR) for the tau positron emission tomography tracer [18F]AV-1451 uptake and are therefore widely used as proxy for tracer binding. With regard to tracer kinetic modelling, there exists a time point when SUVR deviates minimally from DVR, occurring when the specific binding reaches a transient equilibrium. Here, we have investigated whether the time to equilibrium affects the agreement between SUVR and DVR across different brain regions. We show that the time required to reach equilibrium differs across brain regions, resulting in region-specific biases. However, even though the 80–100 min post-injection time window did not show the smallest bias numerically, the disagreement between SUVR and DVR varied least between regions during this time. In conclusion, our findings suggest a regional component to the bias of SUVR related to the time to transient equilibrium of the specific binding. [18F]AV-1451 uptake should consequently be interpreted with some caution when compared across brain regions using this method of quantification. The commonly used time window 80–100 min post-injection shows the most consistent bias across regions and is recommended for semi-quantification of [18F]AV-1451.

Experimental study on combustion characteristics of an n-butanol-biodiesel droplet

This work was aimed to study droplet combustion which was a foundation of spray combustion. Combustion characteristics of BUT00 (pure biodiesel) and BUT50 (50% n-butanol and 50% biodiesel by mass) were investigated using droplet suspension technology under 1 bar and 900 K. One flame was observed for BUT00 while two flames were observed for BUT50. The flame of BUT00 underwent successively faint luminosity, bright luminosity, soot aggregate and soot spread. The first flame of BUT50 was faint and the second one was similar to that of BUT00 because they were caused by n-butanol and biodiesel combustion respectively. Before the auto-ignition of BUT00, (D/D0)2 was approximately unchanged at 1.0 and similarity degree (SD) was higher than 97%. Temperature growth rate (TGR) decreased first quickly and then slowly. After the auto-ignition of BUT00, (D/D0)2 sharply decreased and SD was in the range of 90–97%. The flame heating led to the increase of TGR. For BUT50, obvious fluctuations were found in (D/D0)2, SD and TGD. The SD of BUT50 was generally lower than 97%. The (D/D0)2 of BUT50 included transient heating, fluctuation evaporation and equilibrium evaporation phases. Some characteristic parameters were deterministic although (D/D0)2 in fluctuation evaporation phase was a non-deterministic process.

Cross-Scale Modeling of MnS Precipitation for Steel Solidification

One of the advantages of numerical simulations over traditional experimental methodologies is that they can synchronize nucleation, growth and coarsening during solidification from the point of view of microstructural analysis. However, the computational cost and accuracy are bottlenecks restricting simulation approaches. Here, two cellular automaton (CA) modules with different grid dimensions are coupled to form a cross-scale model in order to simulate MnS precipitation, accompanied by the matrix growth of dendrites during the solidification of a Fe-C-Mn-S steel, where the matrix growth is computed through the CA module with large grids based on the solute conservation and the undercooling of thermal, constitutional, and curvature, and increments of solid fraction of MnS are solved in combination with the transient thermodynamic equilibrium on the locally re-meshed grids once the MnS precipitation is formed. We utilize the cross-scale mode to illustrate MnS evolution in a solidifying matrix and explain the reason why it coexists in three shapes. Further, we study the effects of the content of elements Mn and S on MnS precipitation based on two continuously cast steel objects, with the factor of concentration product fixed as a constant. A re-precipitation of MnS is observed during the solidification of a system with a high content of Mn and low content of S. Simultaneous computation using cross-scale modeling can effectively save on computational resources, and the simulation results agree well with the experimental cases, which confirm its reliable accuracy.

A new puffing model for a droplet of butanol-hexadecane blends

A new model was developed to investigate the puffing process of a butanol-hexadecane droplet. The puffing model took into account all the key processes, including the surface evaporation, bubble formation, bubble growth and bubble breakup. The Rayleigh equation was modified to simulate the bubble growth inside a small droplet. The sub-models for surface evaporation and bubble growth were firstly verified against the previous experimental data. Then the droplet puffing experiments of butanol-hexadecane blends were conducted under 1 bar and 750 K condition using the droplet suspension technique to further verify the puffing model. Results showed that the puffing model well simulated three phases of BUT50 (50% butanol and 50% hexadecane by mass). The three phases were the transient heating, fluctuation evaporation and equilibrium evaporation phases. An extremely strong fluctuation and several weak fluctuations were observed during the fluctuation evaporation phase from the experimental normalized squared diameter. Due to the model hypotheses, these weak fluctuations were ignored and only the strong fluctuation was simulated in the present model. Furthermore, a significant turning point was observed in the experimental temperature curve when the droplet diameter had the strong fluctuation. The occurrence of the strong fluctuation was caused by the obvious bubble expansion inside the droplet. The numerical results showed that the significant heat absorption for the bubble expansion led to the turning point in the temperature curve.

Dynamics of capsules enclosing viscoelastic fluid in simple shear flow

Previous studies on capsule dynamics in shear flow have dealt with Newtonian fluids, while the effect of fluid viscoelasticity remains an unresolved fundamental question. In this paper, we report a numerical investigation of the dynamics of capsules enclosing a viscoelastic fluid and which are freely suspended in a Newtonian fluid under simple shear. Systematic simulations are performed at small but non-zero Reynolds numbers (i.e. $Re=0.1$) using a three-dimensional front-tracking finite-difference model, in which the fluid viscoelasticity is introduced via the Oldroyd-B constitutive equation. We demonstrate that the internal fluid viscoelasticity presents significant effects on the deformation behaviour of initially spherical capsules, including transient evolution and equilibrium values of their deformation and orientation. Particularly, the capsule deformation decreases slightly with the Deborah number De increasing from 0 to $O(1)$. In contrast, with De increasing within high levels, i.e. $O(1{-}100)$, the capsule deformation increases continuously and eventually approaches the Newtonian limit having a viscosity the same as the Newtonian part of the viscoelastic capsule. By analysing the viscous stress, pressure and viscoelastic stress acting on the capsule membrane, we reveal that the mechanism underlying the effects of the internal fluid viscoelasticity on the capsule deformation is the alterations in the distribution of the viscoelastic stress at low De and its magnitude at high De, respectively. Furthermore, we find some new features in the dynamics of initially non-spherical capsules induced by the internal fluid viscoelasticity. Particularly, the transition from tumbling to swinging of oblate capsules can be triggered at very high viscosity ratios by increasing De alone. Besides, the critical viscosity ratio for the tumbling-to-swinging transition is remarkably enlarged with De increasing at relatively high levels, i.e. $O(1{-}100)$, while it shows little change at low De, i.e. below $O(1)$.

Negative Cooperativity in the Interaction of Prostaglandin H Synthase-1 with the Competitive Inhibitor Naproxen Can Be Described as the Interaction of a Non-competitive Inhibitor with Heterogeneous Enzyme Preparation.

The kinetic mechanism of the interaction of nonsteroidal anti-inflammatory drugs (NSAIDs) with their main pharmacological target, prostaglandin H synthase (PGHS), has not yet been established. We showed that inhibition of PGHS-1 from sheep vesicular glands by naproxen (a representative of NSAIDs) demonstrates a non-competitive character with respect to arachidonic acid and cannot be described within a framework of the commonly used kinetic schemes. However, it can be described by taking into account the negative cooperativity of naproxen binding to the cyclooxygenase active sites of the PGHS-1 homodimer (the first naproxen molecule forms a more stable complex (K1 = 0.1 µM) with the enzyme than the second naproxen molecule (K2 = 9.2 µM)). An apparent non-competitive interaction of PGHS-1 with naproxen is due to slow dissociation of the enzyme-inhibitor complexes. The same experimental data could also be described using commonly accepted kinetic schemes, assuming that naproxen interacts was a mixture of two enzyme species with the inhibition constants Kα = 0.05 µM and Kβ = 18.3 µM. Theoretical analysis and numerical calculations show that the phenomenon of kinetic convergence of these two models has a general nature: when K2 >> K1, the kinetic patterns (for transient kinetics and equilibrium state) generated by the cooperative model could be described by a scheme assuming the presence of two enzyme forms with the inhibition constants Kα = K1/2, Kβ = 2·K2. When K2 << K1, the cooperative model can be presented as a scheme with two inhibitor molecules simultaneously binding to the enzyme with the observed inhibition constant K (K = K1·K2). The assumption on the heterogeneity of the enzyme preparation in relation to its affinity to the inhibitor can be used instead of the assumption on the negative cooperativity of the enzyme-inhibitor interactions for convenient and easy practical description of such phenomena in enzymology, biotechnology, pharmacology, and other fields of science.

Synthesis and Photophysical Properties of a Covalently Linked Porphyrin Chromophore–Ru(II) Water Oxidation Catalyst Assembly on SnO2 Electrodes

We describe here the preparation and surface photophysical properties of a covalently linked, chromophore-catalyst assembly between a phenyl phosphonate-derivatized pentafluorophenyl-substituted porphyrin and the water oxidation catalyst, [RuII(terpyridine)(2-benzimidazolylpyridine)(OH2)]2+, in a derivatized assembly of porph-RuII–OH22+. The results of nanosecond transient absorption measurements on nanoparticle SnO2 electrodes in aqueous acetate buffer at pH 4.7 are consistent with rapid electron injection into SnO2 with transfer of oxidative equivalents to the assembly. Electron transfer from the singlet excited state of the porphyrin to the conduction band of the electrode, SnO2(e–)|-porph+-RuII–OH22+, is favored as the porphyrin singlet excited state lies 0.44 eV above the SnO2 conduction band edge. Electron injection is rapid (⟨τinj⟩ < 10–8 s), and occurs with high efficiency. Based on measured redox potentials, following excitation and injection, intra-assembly oxidation of the catalyst, -porph+-RuII–OH22+ → -porph-RuIII–OH2+ + H+, is favored in the transient equilibrium state by 0.62 eV at pH 4.7. However, immediately after the flash, a distribution exists at the surface between isomers with SnO2(e–)|-porph+-RuII–OH22+ undergoing back electron transfer to the surface with an average lifetime of ⟨τ1⟩ ∼ 10–7 s and a slower component for back electron transfer from SnO2(e–)|-porph-RuIII–OH2+ with ⟨τ2⟩ ∼ 4 × 10–5 s.

Effect of ambient temperature on the puffing characteristics of single butanol-hexadecane droplet

Puffing characteristics of BUT50 (50% n-butanol and 50% n-hexadecane by mass) were investigated using the droplet suspension technology under 638, 688 and 738 K. Experimental results showed that BUT50 underwent transient heating, fluctuation evaporation and equilibrium evaporation phases under all ambient temperatures. In the fluctuation evaporation phase, the fluctuation frequency of 738 K was higher than that of 638 K. (Dmax/D0)2 of 738 K was lower than that of 638 K. Easy bubble rupture led to high fluctuation frequency and low (Dmax/D0)2 at 738 K. Three turning points were found in transient temperature growth rate at 638 and 738 K. Four characteristic droplet temperatures were analyzed, including droplet temperatures at the start (T1) and end (T2) of transient heating phase, at (Dmax/D0)2 (T3) and at the end of total lifetime (T4). T2 was slightly lower and T3 was slightly higher than the boiling point of n-butanol. T4 was lower than the boiling point of n-hexadecane. Furthermore, the transient heating duration (tTH), fluctuation evaporation duration (tFE) and total lifetime (tTL) decreased with increasing ambient temperature. The reduction of tFE played an important role in the decrease of tTL. The percentages of tTH/tTL and tFE/tTL were stable with increasing ambient temperature.

Recursive thoughts on the simulation of the flexible multibody dynamics of slender offshore structures

In this work, the floating frame of reference formulation is used to create a flexible multibody model of slender offshore structures such as pipelines and risers. It is shown that due to the chain-like topology of the considered structures, the equation of motion can be expressed in terms of absolute interface coordinates. In the presented form, kinematic constraint equations are satisfied explicitly and the Lagrange multipliers are eliminated from the equations. Hence, the structures can be conveniently coupled to finite element or multibody models of for example seabed and vessel. The chain-like topology enables the efficient use of recursive solution procedures for both transient dynamic analysis and equilibrium analysis. For this, the transfer matrix method is used. In order to improve the convergence of the equilibrium analysis, the analytical solution of an ideal catenary is used as an initial configuration, reducing the number of required iterations.

Hierarchical aging pathways and reversible fragile-to-strong transition upon annealing of a metallic glass former

The change of physical properties during aging and the associated microscopic dynamics of the Au49Cu26.9Si16.3Ag5.5Pd2.3 bulk metallic glass are investigated using a broad collection of laboratory and synchrotron-based techniques, such as differential- and fast-scanning calorimetry, thermomechanical testing, and x-ray photon correlation spectroscopy. We observe multiple decays in the enthalpy change during aging. This is reflected by a microscopic ordering consisting of distinct stationary dynamical regimes interconnected by abrupt aging processes. The stationary regimes are representative of states of local and transient equilibrium with increasingly higher activation energies. Furthermore, the aging study is conducted with the kinetically fragile frozen-in structure and the underlying fragile-to-strong transition is accessed by the ultra-viscous liquid state during annealing on a long-time scale and corresponds to the last observed enthalpy equilibration decay. The experimental work verifies, for the first time, that in a metallic glass forming system, the fragile-to-strong transition can also occur below the conventional glass transition temperature. Upon reheating, the reverse transformation, i.e. the strong-to-fragile transition, is observed with an entropy change of 0.19 J/(g-atom K), which is 2.4% of the entropy of fusion.