Search Results - (Author, Cooperation:H. Irschik)

2012-08-04

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

DNA Polymerase III/*chemistry/drug effects ; Fluorescence Resonance Energy Transfer/methods ; *Gene Expression Regulation, Bacterial ; Protein Conformation ; *Transcription, Genetic

0005-2736

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Medicine

Physics

Electronic Resource

0005-2736

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Medicine

Physics

Electronic Resource

0167-7799

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Process Engineering, Biotechnology, Nutrition Technology

Electronic Resource

1432-0681

Key words thick plate ; vibrations ; frequency domain ; Kirchhoff plate ; membrane

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Summary Free and forced vibrations of moderately thick, transversely isotropic plates loaded by lateral forces and hydrostatic (isotropic) in-plane forces are analyzed in the frequency domain. Influences of shear, rotatory inertia, transverse normal stress and of a two-parameter Pasternak foundation are taken into account. First-order shear-deformation theories of the Reissner–Mindlin type are considered. These theories are written in a unifying manner using tracers to account for the various influencing parameters. In the case of a general polygonal shape of the plate and hard-hinged support conditions, the Reissner-Mindlin deflections are shown to coincide with the results of the classical Kirchhoff theory of thin plates. The background Kirchhoff plate, which has effective (frequency-dependent) stiffness and mass, is loaded by effective lateral and in-plane forces and by imposed fictitious “thermal” curvatures. These deflections are further split into deflections of linear elastic prestressed membranes with effective stiffness, mass and load. This analogy for the deflections is confirmed by utilizing D'Alembert's dynamic principle in the formulation of Lagrange, which yields an integral equation. Furthermore, the analogy is extended in order to include shear forces and bending moments. It is shown that in the static case, with no in-plane prestress taken into account, the stress resultants for certain groups of Reissner-type shear-deformable plates are identical with those resulting from the Kirchhoff theory of the background. Finally, results taken from the literature for simply supported rectangular and polygonal Mindlin plates are yielded and verified by analogy in a quick and simple manner.

Electronic Resource

0040-4039

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Chemistry and Pharmacology

Electronic Resource

1432-0681

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Summary An indirect boundary integral equation method for the solution of bending of Kirchhoff-plates with arbitrary temperature loading and convex, polygonal planform is presented. Clamped, simply supported and free boundaries are considered. The polygonal plate is embedded in a rectangular domain, thereby applying coincidence of boundaries as far as possible. Using Green's matrix of this basic domain, a vectorial boundary integral equation is derived, which has to be defined on part of the actual boundary only. Thus, the computational effort in the numerical solution is decreased, while the accuracy increases. Reduction to a scalar integral equation in the case of simply supported plates is achieved. The method is tested in example problems by considering parallelogram plates under various boundary conditions. In an appendix it is shown, how to use the method for Reissnertype plates with simple support under pressure loading.

Übersicht Es wird eine indirekte Randintegralgleichungsformulierung zur Behandlung des Biegungsproblems von Kirchhoffschen Platten mit konvexer, polygonaler Berandung unter beliebiger Temperaturbelastung vorgestellt. Dabei werden starr eingespannte, frei drehbar gelagerte und freie Ränder behandelt. Die polygonale Platte wird in einen rechteckigen Grundbereich eingebettet, wobei soweit wie möglich Übereinstimmung der Randbedingungen angestrebt wird. Unter Verwendung der Greenschen Matrix dieses Grundbereichs wird eine vektorielle Randintegralgleichung hergeleitet, welche nur mehr über einen Teil der tatsächlichen Berandung erstreckt werden muß. Auf diese Weise kann der Rechenaufwand bei der numerischen Lösung gering gehalten, aber die Genauigkeit gesteigert werden. Im Fall allseits frei drehbar gelagerter Platten gelingt weiters eine Reduktion zu einer skalaren Integralgleichung. Die Methode wird an Beispielen getestet, wobei Parallelogrammplatten mit verschiedenen Randbedingungen verwendet werden. Auf die Möglichkeit, das Verfahren zur Berechnung querbelasteter schubelastischer Platten vom Reissnerschen Typ mit Klemmschneidenlagerung heranzuziehen, wird in einem Anhang verwiesen.

Electronic Resource

1432-0924

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract Forced vibrations of moderately thick plates on two-parameter, Pasternak-type foundations are considered. Influence of plate shear and rotatory inertia are taken into account according to Mindlin. Excitations are of the force as well as of the support motion type. Formulation is in the frequency domain. An analogy to thin plates without foundations is given. This analogy to classical plate theory is complete in the case of polygonal plan-forms and hinged support conditions. In that case the higher order Mindlin-problem is reduced to two (second order) Helmholtz-Klein- Gordon boundary value problems. An advanced BEM using Green's functions of rectangular domains is applied to the latter, thereby satisfying boundary conditions exactly as far as possible. This problem oriented strategy provides the frequency response functions for the deflection of the undamped Mindlin plate with high numerical accuracy. Structural damping is built in subsequently, and Fast Fourier Transform is applied for calculation of the transient response.

Electronic Resource

1432-0924

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract The dynamic stability of plates subject to periodic in-plane forces is analyzed and the corresponding stability regions of the first and second order are calculated. Moderately thick plates are considered where the influence of shear and rotatory inertia is taken into account according to the Reissner–Mindlin theory. Plates of an arbitrary polygonal shape and simply supported boundaries are studied in detail. A two-parameter foundation of the plate is included. In-plane forces are assumed isotropic. This class of plates is characterized by the decoupling of the free flexural, thickness-shear and thickness-twist plate motions. The present contribution extends recent formulation derived by the authors, where the Reissner–Mindlin plate is modeled by a time-variant dynamic system of ODE's. The polygonal shape of the plate enters these Mathieu-type equations by means of the eigenvalues of second-order Helmholtz boundary value-problems via a proper membrane-analogy. Influence of shear and rotatory inertia is taken into account by tracers. In the present contribution, special emphasis is given to the calculation of the limits of the regions of instability in the p-P t plane (stability chart), where p defines the exciting frequency and P t the exciting force. In order to find the limits of the first and second order, suitable ansatz-functions are introduced. These ansatz-functions depend on the order of the regions, which are to be analyzed. The results are derived in a non-dimensional form and the two regions are graphically presented, compared and some parametric investigations are performed. In particular, the influence of the Helmholtz-eigenvalues, characterizing the specific shape of the plate, is studied. It is shown that an increase in the eigenvalue increases the domains of instability for each order and leads to a shift of the domains of instability towards higher frequencies.

Electronic Resource

1432-072X

Rhodospirillum rubum ; Membrane bound functions ; Bchl-levels ; NADH and succinate dependent electrontransport systems ; Photophosphorylation ; Light induced cytochrome reactions ; Cytochrome c 2 ; b-type cytochrome

Springer Online Journal Archives 1860-2000

Biology

Abstract The effects of transfer from low to high ligh intensity on membrane bound electrontransport reactions of Rhodospirillum rubrum were investigated. The experiments were performed with cultures which did not form bacteriochlorophyll (Bchl) for about two cell mass doublings during the initial phase of adaptation to high light intensity. Lack of Bchl synthesis causes a decrease of Bchl contents of cells and membranes. Also, the cellular amounts of photosynthetically active intracytoplasmic membranes decrease. In crude membrane fractions containing both cytoplasmic and intracytoplasmic membranes the initial activities of NADH oxidizing reactions increase only slightly (about 1.2 times) per protein, but the initial activities of succinate oxidizing reactions decrease (multiplied by a factor of 0.7). On a Bchl basis activities of NADH oxidizing reactions increase 3.4 times while activities of succinate dependent reactions increase 1.9 times. With isolated intracytoplasmic membranes activities of NADH as well as succinate dependent reactions increase to a comparable extent on a Bchl basis (about 1.8 times) and stay nearly constant on a protein basis. Cytochrome c oxidase responds like succinate dependent reactions. The data indicate that in cells growing under the conditions applied NADH oxidizing electron transport systems are incorporated into both, cytoplasmic and intracytoplasmic membranes, while incorporation of succinate oxidizing systems is confined to intracytoplasmic membranes only. Activities of photophosphorylation and succinate dependent NAD+ reduction in the light increase per Bchl about 1.8 times. On a Bchl basis increases of the fast light induced “on” reactions at 422 nm and increases of soluble cytochrome c 2 levels are comparable to increases of photophosphorylations and succinate dependent activities. But increases of slow light “off” reactions at 428 nm and of b-type cytochrome levels become three times greater then increases of cytochrome c 2 reactions and levels. These results infer that although electrontransport reactions of intracytoplasmic membranes change correlated to each other, Bchl, cytochrome c 2 and b-type cytochromes cellular levels are independent of each other. Furthermore, the data indicate that cytochrome c 2 rather than b-type cytochrome is involved with steps rate limiting for photophosphorylation.

Electronic Resource

1619-6937

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Summary A Berger-type approximation for large deflections of thermally loaded initially curved elastic plates is derived. In case of simply supported boundaries and arbitrary polygonal planforms, dimensionless solution is found in terms of Dirichlet's Helmholtz-eigenvalues of the given domain. Stability of this equilibrium solution is exemplarily discussed, showing bifurcation and snapping behaviour in the sense of a cusp catastrophe. Additionally, possibility of mode-jumping is indicated.

Electronic Resource

1619-6937

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Summary This paper is concerned with non-stationary random vibrations of yielding shear-wall buildings approximated by multi-degree-of-freedom elastic-plastic oscillators in the plastic hinge model. The initial strain formulation of plasticity is applied to render a linear system under effective and updated non-stationary random loading: Noting the complete analogy to a linear system driven by the earthquake excited ground acceleration as well as by the nonlinear drift processes, the excitation of the totally associated linear problem is alternated by assuming the power spectral density of the input to be given in the form of an effective envelope function including frequency dependence. This fictitious evolutionary excitation of the linear system with fixed stiffness and damping behaviour is taken into account using a time-stepping procedure.

Electronic Resource

1619-6937

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Summary An elastic-inelastic analogy is presented for dynamic biaxial bending of beams. Inelastic effects are treated as fictitious additional sources of self-stresses in the adjoint linear elastic structure of time-invariant stiffness. Thus, superposition applies and linear methods such as Green's functions and Duhamel's integral may be used in a convenient manner. Fictitious loadings themselves are determined from the inelastic material's law in a time-stepping procedure. As an example problem, a preloaded elastoplastic beam under harmonic excitation of support motion type is considered.

Electronic Resource

1619-6937

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Summary A membrane analogy is presented for eigenvalue problems of simply supported Mindlin plates of arbitrary polygonal planform. Influence of hydrostatic inplane forces and Pasternak-type foundation of the plate domain is taken into account. Analytical results are derived in a non-dimensional form, which — using the analogous membrane eigenvalues as parameters — is independent of the special shape of the plate.

Electronic Resource

1619-6937

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Summary This paper deals with a class of hybrid control systems for earthquake excited high raised buildings which consist of a passive base isolation and an additional active damper. The mechanical model of the building is a shear wall structure with nonlinear, hysteretic restoring forces. The differential geometric approach based on exterior differential systems is used to solve the disturbance decoupling problem for the mechanical model. Since the ideal controller is difficult to implement, a new control law is proposed. It solves the decoupling problem only approximately but its implementation is simple because only signals easy to measure are used. The stability is proved by means of the theory of Liapunov in combination with dissipative systems, and it turns out that the closed loop is robust with respect to all the variations of practical interest, too. Finally, computer simulations demonstrate the feasibility and efficiency of the discussed approach.

Electronic Resource

1619-6937

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Summary An advanced Boundary Element formulation for eigenvalue problems of membranes and plates is developed. Polygonal membranes are considered, and are embedded into a proper basic domain in order to satisfy boundary conditions exactly as far as possible. Hence, boundary integrals have to be applied at the not coinciding boundaries only. Eigenvalues of the underlying Dirichlet's Helmholtz problem are calculated from frequency response functions evaluated by that “method with Green's functions of finite domains”, and natural frequencies of corresponding membranes and simply supported plates are determined by analogy. A numerical investigation is performed for parallelogram Mindlin plates. Natural frequencies and critical buckling eigenvalues are graphically represented in a nondimensional form, where the influence of skew angle and plate thickness is studied.

Electronic Resource

1619-6937

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Summary This paper is concerned with flexural vibrations of composite plates, where piezoelastic layers are used to generate distributed actuation or to perform distributed sensing of strains in the plate. Special emphasis is given to the coupling between mechanical, electrical and thermal fields due to the direct piezoelectric effect and the pyroelectric effect. Moderately thick plates are considered, where the influence of shear and rotatory inertia is taken into account according to the kinematic approximations introduced by Mindlin. An equivalent single-layer theory is thus derived for the composite plates. It is shown that coupling can be taken into account by means of effective stiffness parameters and an effective thermal loading. Polygonal plates with simply supported edges are treated in some detail, where quasi-static thermal bending as well as free, forced and actuated vibrations are studied.

Electronic Resource

1619-6937

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Zusammenfassung Die Methode der Greenschen Funktion wurde in jüngster Zeit erfolgreich auf Probleme der ebenen Elastizitätstheorie angewendet. Dabei fanden Einflußfunktionen eines endlichen Grundbereiches einfacher geometrischer Form, der den gegebenen Bereich einschließt, Verwendung. Das Resultat dieser Formulierung ist ein Integralgleichungspaar, welches entlang dem Teil des Randes zu erstrecken ist, der nicht mit dem Rand des Grundbereiches bereits zusammenfällt. Eine allgemein gehaltene Formulierung der Biegelösung von Platten mit konvexem Grundriß unter beliebiger Belastung wird angegeben, wobei allerdings der Kürze halber eine Beschränkung auf polygonplatten erfolgt. Die Polygonplatte wird in einen Rechteckbereich eingebettet, wobei soviele Ränder wie möglich zusammenfallen sollen. Jene Randbedingungen des wirklichen Problems, welche dann noch nicht erfüllt sind, führen auf ein gekoppeltes Integralgleichungspaar für den Dichtefunktionsvektor, dessen Komponenten als im Grundbereich entlang der wirklichen Berandung verteilte Linienlasten und Linienmomente gedeutet werden. Damit wird der Kern zur korrespondierenden Greenschen Matrix. Weiters sind, nach Lösung der Integralgleichungen, Biegefläche und Spannungen des wirklichen Problems explizit bekannt. Die Lösung der Integralgleichungen erfolgt im allgemeinen numerisch. Die Methode wird an Beispielen getestet, wobei eine Trapezplatte unter verschiedenen Randbedingungen untersucht wird.

Summary Recently, the Green's function method has been applied successfully to problems of plane elasticity, using influence functions of some finite basic domain of simple geometrical shape, which contains the given one as a subdomain. The result of this formulation is a pair of integral equations, which have to be defined only along that part of the boundary not coinciding with the border of the basic domain. A rather general formulation for the solution of bending of plates of arbitrary convex planform and loading is presented, where, for the sake of brevity, plates of polygonal shape are considered. The polygonal plate is embedded in a rectangular domain, thereby applying coincidence of boundaries as far as possible. Those boundary conditions in the actual problem, which are not already satisfied, lead to a pair of coupled integral equations for a density function vector with components to be interpreted as line loads and moments distributed in the basic domain along the actual boundary. Thus, the kernel is the corresponding Green's matrix. Hence, having solved the integral equations, deflections and stresses in the actual problem are explicitly known. Solution of the integral equations is generally achieved by a numerical procedure. The method is tested in example problems by considering a trapezoidal plate under various boundary conditions.

Electronic Resource

1619-6937

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Summary A solution method for elastoplastic vibrating beams including damage accumulation is shown, where inelastic behavior of the structure is represented by an additional loading due to sources of selfstresses acting upon the linear elastic structure of time-invariant stiffness. Response due to this additional loading is evaluated using proper Green's functions. Thus, integral relations are set up, similar to Maysel's formula. Theory is applied to a two span sandwich beam with elastoplastic degrading flanges and elastic core material.

Electronic Resource

1573-269X

Composite beams ; physical non-linearity ; second-order theory ; vibrations ; beams with overhang

Springer Online Journal Archives 1860-2000

Mathematics

Abstract An efficient time-domain algorithm for plane non-linear flexural vibrations of multi-layered composite beams, which are driven into the inelastic range by severe transverse loadings, is presented. The influence of an axial static preload is considered in the sense of the quasi-linear second-order theory of structures. The inelastic parts of strain are treated as additional sources of selfstress in the linear elastic background-structure, driving the elastic response into the inelastic one. The efficiency of this exact formulation lies in the fact that linear solution techniques can be used in their most powerful form: Rubin's useful formulation for the quasi-static second-order transfer-matrix of linear elastic structures is applied in combination with modal analysis. Having in mind multi-metal beams, the classical lamination theory is assumed to be valid. Beams with overhang composed of ideal elastic-plastic and viscoplastic layers are studied as example structures. The fictitious sources of selfstress are calculated from the different material laws of the layers in a numerical time-stepping procedure, where a generalized midpoint-rule in combination with Crisfield's secant-Newton procedure is used.

Electronic Resource