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1.
Noora Virtanen Ville Nevalainen Taru Lehtinen Satu Mikkola 《Journal of Physical Organic Chemistry》2007,20(1):72-82
Transesterification of a phosphodiester bond of RNA models has been studied in various buffer solutions, under neutral and slightly alkaline conditions in H2O and D2O. The results show that imidazole is the only buffer system where a clear buffer catalysis on the cleavage of a phosphodiester bond is observed. The rate enhancement in sulphonic acid buffers is smaller, and a sulphonate base, particularly, is inactive as a catalyst. The rate‐enhancing effect of imidazole is, however, catalytic, and the catalytic inactivity of sulphonate buffers can be attributed to their structure and/or charge. The catalysis by imidazole is a complex system which, in addition to first‐order reactions, involves a process that shows a second‐order dependence in imidazole concentration. The latter reaction becomes significant in acidic imidazole buffers (pH < pKa), as the buffer concentration increases. The kinetic solvent deuterium isotope effect kH/kD, referring to first‐order catalysis by imidazole base, is 2.3 ± 0.3. That referring to second‐order catalysis is most probably much larger, but an accurate value could not be obtained. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
2.
Nonlinear Dynamics - The absolute nodal coordinate formulation (ANCF) is a nonlinear finite element approach proposed for the large deformation dynamics analysis of beam- and plate/shell-type... 相似文献
3.
Mikkola S 《Organic & biomolecular chemistry》2004,2(5):770-776
The hydrolysis of diadenosine 5',5'-triphosphate to AMP and ADP has been studied over a wide pH-range. Under acidic conditions the reaction shows a first-order dependence on the hydronium ion concentration. Below pH 3 the rate-increase begins to level off. From pH 6 to 9 the hydrolysis is slow and pH-independent. Base-catalysed hydrolysis is observed in NaOH-solutions. Under alkaline conditions an intramolecular nucleophilic attack on the phosphate producing 3',5'-cAMP is also observed, but it is slower than the intermolecular reaction. Depurination of the adenosine moieties competes with the hydrolysis both under acidic and alkaline conditions, but the mechanisms are different. The temperature-dependence of the hydrolysis of Ap(3)A and the depurination of adenosine moieties were studied under acidic conditions, and the activation parameters of the reactions were calculated. The results of the work reflect the fact that the negatively charged polyphosphate group is very resistant towards nucleophilic attack. An efficient catalysis is only observed under acidic conditions, where the phosphate group becomes protonated. General acids or bases did not catalyse the hydrolysis. Furthermore, hydroxide ion catalysed cleavage is only observed at high base concentrations and other negatively charged nucleophiles did not attack the phosphate groups of diadenosine polyphosphates. 相似文献
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5.
M. J. Mikkola 《International Journal of Non》1989,24(6):499-508
The principle of stationary complementary energy for geometrically non-linear problems of beams and trusses is considered. The functional of complementary energy is formulated in terms of force quantities. The stationary conditions describe the conditions of compatibility of the structure. The applications include the problem of elastica, a truss, and a bending problem by use of beam elements. 相似文献
6.
Nonlinear Dynamics - Dynamic simulation of mechanical systems can be performed using a multibody system dynamics approach. The approach allows to account systems of other physical nature, such as... 相似文献
7.
In this article we prove a representation theorem for functions, such that the realization formula is spectrally minimal in the following sense: the spectrum of the main operator in the realization intersects the unit circle precisely at those
points where the given function has no holomorphic extension. We also extend this result to operator-valued H
∞ functions.
Received: March 12, 2007. Revised: April 12, 2007. Accepted: May 7, 2007. 相似文献
8.
Henrik Ebel Marko K. Matikainen Vesa-Ville Hurskainen Aki Mikkola 《Nonlinear dynamics》2017,88(2):1075-1091
This study thoroughly examines various higher-order three and four-node beam elements for use in the absolute nodal coordinate formulation (ANCF). The paper carefully investigates which potential benefits and drawbacks the utilization of higher-order ANCF beam elements without in-slope vectors has in the case of the usage of full three-dimensional elasticity. When the elastic forces for shear-deformable ANCF beam elements are calculated using full three-dimensional elasticity—especially in the form of the St. Venant–Kirchhoff material law—Poisson locking severely deteriorates the accuracy of the numeric results. As shown in this paper, an existing approach to preventing this locking phenomenon for three-node beam elements can still produce unsatisfying results in load cases involving bidirectional bending. The results of this study show that enriching the polynomial basis used to approximate the beam kinematics provides a natural solution to this issue. As will be seen, these findings for three-node elements can also be extended to four-node elements. When using a sufficient approximation order in transverse directions, satisfying accuracy can be achieved both in conventional one-dimensional bending and in the above-mentioned bidirectional load case. 相似文献
9.
Mikkola JP Toukoniitty B Toukoniitty E Aumo J Salmi T 《Ultrasonics sonochemistry》2004,11(3-4):233-239
The effect of power ultrasound has been studied in the hydrogenation of 1-phenyl-1,2-propanedione (enantioselective hydrogenation) and linoleic acid (fat hardening). Furthermore the hydrogenation of d-xylose to xylitol and citral to citronellal and citronellol were studied under the influence of acoustic irradiation. We have investigated the effect of on-line acoustic irradiation of these heterogeneously catalysed liquid-gas-solid systems in which it was found to counter-effect catalyst deactivation, increase the reaction velocity and to enhance the selectivity of various heterogeneously catalysed reactions. 相似文献
10.
Kalle M. Mikkola 《Integral Equations and Operator Theory》2006,55(2):249-271
A finite-dimensional linear time-invariant system is output-stabilizable if and only if it satisfies the finite cost condition, i.e., if for each initial state there exists at least one L2 input that produces an L2 output. It is exponentially stabilizable if and only if for each initial state there exists at least one L2 input that produces an L2 state trajectory. We extend these results to well-posed linear systems with infinite-dimensional input, state and output
spaces. Our main contribution is the fact that the stabilizing state feedback is well posed, i.e., the map from an exogenous input (or disturbance) to the feedback, state and output signals is continuous in Lloc2 in both open-loop and closed-loop settings. The state feedback can be chosen in such a way that it also stabilizes the I/O
map and induces a (quasi) right coprime factorization of the original transfer function. The solution of the LQR problem has
these properties. 相似文献