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111.
Resolution and uniqueness of estimated parameters of a model of thin filament regulation in solution
Srboljub M. Mijailovich Xiaochuan Li Juan C. del Álamo R. Hugh Griffiths Vojislav Kecman Michael A. Geeves 《Computational Biology and Chemistry》2010,34(1):19-33
The estimation of chemical kinetic rate constants for any non-trivial model is complex due to the nonlinear effects of second order chemical reactions. We developed an algorithm to accomplish this goal based on the Damped Least Squares (DLS) inversion method and then tested the effectiveness of this method on the McKillop–Geeves (MG) model of thin filament regulation. The kinetics of MG model is defined by a set of nonlinear ordinary differential equations (ODEs) that predict the evolution of troponin–tropomyosin–actin and actin–myosin states. The values of the rate constants are estimated by integrating these ODEs numerically and fitting them to a series of stopped-flow pyrene fluorescence transients of myosin-S1 fragment binding to regulated actin in solution. The accuracy and robustness of the estimated rate constants are evaluated for DLS and two other methods, namely quasi-Newton (QN) and simulated annealing (SA). The comparison of these methods revealed that SA provides the best estimates of the model parameters because of its global optimization scheme. However it converges slowly and does quantify the uniqueness of the estimated parameters. On the other hand the QN method converges rapidly but only if the initial guess of the parameters is close to the optimum values, otherwise it diverges. Overall, the DLS method proves to be the most convenient method. It converges fast and was able to provide excellent estimates of kinetic parameters. Furthermore, DLS provides the model resolution matrix, which quantifies the interdependence of model parameters thereby evaluating the uniqueness of their estimated values. This property is essential for estimating of the dependence of the model parameters on experimental conditions (e.g. Ca2+ concentration) when it is assessed from noisy experimental data such as pyrene fluorescence from stopped-flow transients. The advantages of the DLS method observed in this study should be further examined in other physicochemical systems to firmly establish the observed effectiveness of DSL vs. the other parameter estimation methods. 相似文献
112.
We prove that a system of linear inequalities with interval-valued data is weakly solvable (each system obtained by fixing coefficeints in the intervals prescribed has a solution) if and only if it is strongly solvable (all such systems have a solution in common) and desribe an algorithm for checking strong solvability. 相似文献
113.
Ákos Császár 《Acta Mathematica Hungarica》2005,108(4):351-354
Summary In the paper [5], several operations on generalized topologies are considered. They are not monotone in general, but an old result on monotonicity may be sharpened. 相似文献
114.
A new characterisation method is described using the new theoretical model for erbium-doped silica fibre lasers (EDSFLs) based
on the energy conservation principle. Using this method, we obtained absorption and emission coefficients for the lasing wavelength
at lasing operating conditions. After that, an experimental procedure to deduce the spectral profiles of the absorption and
emission coefficients is also presented. This procedure allows us to obtain the values of these parameters for the whole fluorescence
spectrum through measurements of gain profiles under the lasing operation. Once the absorption and emission coefficients are
known, the new model can be applied and a comparison with experimental results for two different laser configurations is shown.
The theoretical model is proved to be accurate and in addition some equations are developed to allow the design and optimisation
of EDSFLs.
This revised version was published online in March 2005. In the previous version, the published online date was missing 相似文献
115.
116.
De Araújo Álvaro Alberto Roussos Sevastianos 《Applied biochemistry and biotechnology》2002,98(1-9):311-318
A technique was established to study ectomycorrhizal fungi on agar media. Petri dishes, 60 mm in diameter, containing 10 mL
of culture medium covered with a cellophane disk were used for easy collection of the mycelium after growth. For analysis
of fungal biomass production, a sterilized cellophane sheet was placed on the medium’s surface. Inoculation was achieved by
placing a mycelial block onto the center of the cellophane sheet and then incubating at 25°C in the dark. Colony radial growth
was measured and biomass dry wt was determined. Fresh mycelia were homogenized with 10 mL of acetate buffer (pH 5.5) for enzyme
analysis. A crude extract was obtained by adding all culture medium to 90 mL of distilled water and homogenizing in a Potter.
Reducing sugars, enzyme concentration, and pH were determined. Three fungal strains, Suillus collinitus, Pisosithus arrhizus, and Hebeloma cylindrosporum, were grown in different culture media (potato dextrose agar or Pintro’s medium). Parameters measured over time included
glucose concentration, phosphatase activity, biomass, and pH. 相似文献
117.
118.
119.
This work addresses the adsorption of benzothiophene (BT), as a model heterocyclic and aromatic sulphur compound present in
road fuels, over agglomerated zeolites with faujasite structure. Several adsorbents based on zeolites with FAU structure have
been prepared with different Si/Al molar ratios and exchange cations and then agglomerated. The influence of the zeolite basicity
has been studied, both in equilibrium and dynamic liquid phase adsorption experiments. Basicity of the adsorbent increased
as the Si/Al molar ratio and the electronegativity of the exchange cation decreased. In equilibrium experiments, the affinity
towards the adsorbent increased as the Si/Al molar ratio decreased, showing the highest affinity for exchanged low silica
X zeolites with medium basicity (A-KLSX-02). Dynamic experiments showed that the less zeolite basicity, the higher fractional
bed utilization and adsorption capacity at breakthrough time. Besides, zeolites with high basicity did not reach the equilibrium
capacity due to the low diffusivity of BT into the micropores. Thermogravimetric analyses of the spent adsorbents showed a
stronger BT adsorption onto the more basic zeolites. As main conclusion, adsorbents with medium basicity could present the
best performance in fuel desulphurization due to their high affinity with sulphur compounds, although diffusion problems should
be taken into account. 相似文献
120.
Ghizlane Choukrani Jimena Álvarez Freile Natasha Ustyanovska Avtenyuk Wei Wan Kerstin Zimmermann Edwin Bremer Lars Dähne 《Particle & Particle Systems Characterization》2021,38(7):2100012
Nanoparticles may limit off-tumor/on-target ubiquitous activation of signaling by protein-based drugs. However, many challenges still exist in the design of a nanoparticle for protein delivery. In this study, conditions to establish vaterite nanoparticles as a pH-sensitive drug delivery system (DDS) for encapsulated protein drugs are comprehensively evaluated. Low coprecipitation pH of vaterite and protein prevents protein denaturation and yields high loading efficiency. Unprotected vaterite recrystallizes in aqueous solutions within 3 h to calcite and releases the loaded protein completely, but surface-modified particles with carboxyl groups containing polymers prove stable for more than 5 months. Notably, modification of vaterite with sulfonated polymers increases the loading of cationic proteins by a multiple. A system is developed for vaterite exposure to (pH) conditions under body-like-flow rates, with the dissolution of vaterite and simultaneous release of active proteins at tumor microenvironmental pH reaching up to 80% and only 20% at physiological pH within 2 h. Importantly, the immunomodulatory protein tumor necrosis factor preserves its native structure and fully retains functional activity in vitro after release from the particles. In conclusion, the studies described here provide a framework for the development of vaterite-based DDS as a carrier for bioactive protein-based therapeutics. 相似文献