Efekat niske početne pH vrednosti hranljive podloge na rast bele topole in vitro

The effect of low initial medium pH on shoot and root development of five white poplar (Populus alba L.) genotypes was tested. The shoot height, fresh mass of shoots per jar, dry mass of shoots per jar, number of roots, as well as the length of the longest root were measured and final pH of the media determined, after 35 days of culture in vitro. Three initial pH values of the medium were tested: 3.0, 4.0 and 5.5 as control. Agar solidification at pH 3.0 was not achieved after sterilization in autoclave, but it was successful after sterilizing in a microwave oven. The obtained results indicate that the tested genotypes are able to significantly influence the changes of media pH during culture. The effect of differences among the examined media was significant for biomass accumulation and final media pH. Generally, significantly higher values of fresh and dry shoot mass, shoot height and the longest root length were recorded on a medium with initial pH 3.0 then on a standard medium with pH 5.5.The implications of the obtained results for the improvement of in vitro propagation of white poplars are discussed.U istraživanju je testiran efekat niske početne pH vrednosti hranljive podloge na razvoj izbojaka i korena pet genotipova bele domaće topole (Populus alba L.). Nakon 35 dana kultivacije u kulturi in vitro mereni su visina izbojaka, sveža masa izbojaka po teglici, suva masa izbojaka po teglici, broj korenova, dužina najdužeg korena i određena je konačna pH vrednost hranljive podloge. Tri početne vrednosti pH medijuma - 3,0, 4,0 i 5,5- ispitane su kao standardna pH vrednost medijuma (kontrola). Problemi sa očvršćavanjem podloge kod podloga sa niskom početnom pH nakon sterilizacije, prevaziđene su sterilizacijom podloge u mikrotalasnoj pećnici. Dobijeni rezultati ukazuju na to da ispitivani genotipovi imaju mogućnost da utiču na promenu pH podloge tokom uzgoja u kulturi in vitro. Većina ispitivanih genotipova bele topole ostvarila je značajno bolji rast i razvoj izbojka i korenovog sistema, kao i akumulaciju biomase na podlozi sa početnom vrednošću pH. U radu se diskutuje o implikacijama dobijenih rezultata za poboljšanje in vitro razmnožavanja bele topole

Ni-Pd-Al2O3 catalyst supported on reticulated ceramic foam for dry methane reforming

In the present study, Ni-Pd/Al2O3 catalyst supported on α-Al2O3 based foam was prepared and evaluated in the dry methane reforming process. Corresponding metal chlorides were deposited to the foam surface by impregnation of the foam with ultrasonically aerosolized salt solutions at 473 K and drying at that temperature. Calcination step was excluded and the catalyst was reduced at very low temperature - 533 K. The reforming experiment lasted for 3 h, with standing time of 1 h at the following temperatures: 873, 973 and 1023 K. Conclusions on selectivity, catalytic activity and stability were reached on the basis of CO and H2 yields

Fractional-order PD control design for active vibration control of smart structures

Smart structures are obtained by integration of actuators, sensors and controllers into conventional structures and they play an important role in the field of active vibration control, especially in aerospace engineering. Certain elements of a smart structure possess viscoelastic properties which can be modeled by using fractional calculus. The fractional-order model of a smart structure implies the necessity of using fractional order controllers instead of integer order controllers. This paper deals with design of the fractional-order proportionalderivative (PD) controller with robust stability and disturbance rejection. The transfer function of the fractionalorder PD controller is parameterized, and these parameters are found by using of the Particle swarm optimization method minimizing a cost function related to the H����� norm. The fractional-order model of the smart structure is found by experimental identification by using the frequency response method. In order to represent the efficiency of the proposed controller, obtained results are compared with the corresponding results in the case when an integer-order PD controller is applied

Fractional-order PD control design for active vibration control of smart structures

Smart structures are obtained by integration of actuators, sensors and controllers into conventional structures and they play an important role in the field of active vibration control, especially in aerospace engineering. Certain elements of a smart structure possess viscoelastic properties which can be modeled by using fractional calculus. The fractional-order model of a smart structure implies the necessity of using fractional order controllers instead of integer order controllers. This paper deals with design of the fractional-order proportionalderivative (PD) controller with robust stability and disturbance rejection. The transfer function of the fractionalorder PD controller is parameterized, and these parameters are found by using of the Particle swarm optimization method minimizing a cost function related to the H����� norm. The fractional-order model of the smart structure is found by experimental identification by using the frequency response method. In order to represent the efficiency of the proposed controller, obtained results are compared with the corresponding results in the case when an integer-order PD controller is applied

Effect of piezoelectric fiber-reinforced composite (PFRC) actuator orientation on controllability of antisymmetric composite plates for active vibration control

Piezoelectric materials have a wide range of application on the active vibration control of flexible structures as actuators and sensors due to its inverse and direct piezoelectric effect. In order to increase performance of active vibration control, piezoelectric fibers are stacked into single layer composite, making piezoelectric fiber-reinforced composite (PFRC) actuator and sensor. These actuators and sensors are used for active vibration control of a thin-walled structures, placing them at the surface of the structure. Since that, control performances depend on sizes, positions and orientations of PFRC actuators and sensors. The aim of this paper is to investigate the effect of PFRC actuator orientation and position (top or bottom) on controllability of cross-ply and angle-ply antisymmetric composite plates for active vibration control. Depending on layers' orientation, composite laminates possess coupling behavior (bending-stretching, bending-shear coupling). Since antisymmetric laminates possess bending-stretching coupling behavior, the effect of this behavior on controllability will be also discussed

The exact natural frequency solution of a free axialbending vibration problem of a non-uniform AFG cantilever beam with a tip body

In this paper we present the solution of exact equations of motion for coupled axial and bending vibrations of a non-uniform axially functionally graded (AFG) cantilever beam with a body of which mass center is eccentrically displaced in axial and transverse direction with respect to the beam’s end. The Euler-Bernoulli beam theory is implemented to model behavior of the beam under axial and transverse in-plane vibrations. Based on the paper [1], that is supported by results publish in the paper [2] authors confirm the obtained results of natural frequencies of the AFG cantilever beam, when boundary conditions define the vibration coupling. The modified symbolic-numeric method of initial parameters presented in [3] is implemented in computing natural frequencies of the beam. This method is expanded to solve axial-bending vibration problems, with respect to the one presented in the literature [3] for the problem of the vibration of a cantilever beam. Some minor deviations in the obtained results may be noticed with respect to those obtained in [1], yet all within a tolerance domain due to the computational precision

Comparison of various optimization criteria for actuator placement for active vibration control of smart composite beam

Position of piezoelectric actuators and sensors on a smart structure directly affects the control performances of a smart structure. In order to improve efficiency of active vibration control of a smart structure, optimization of piezoelectric actuators and sensors placement has been performed. There are various optimization criteria for optimal placement of piezoelectric actuator. The ‘state-of-the-art’ of optimization criteria is presented in [1]. The aim of this paper is to compare control effectiveness of smart composite cantilever beam, where optimal configurations of actuator-sensor pairs were found by using four optimization criteria (LQR based optimization, grammian matrices, performance index and fuzzy optimization strategy). The problem is formulated as multi-input-multi-output (MIMO) model. The beam is discretized by using the finite element method (FEM). The particle swarm optimization (PSO) method is used to find optimal configurations for each configuration

Effect of piezoelectric fiber-reinforced composite (PFRC) actuator orientation on controllability of antisymmetric composite plates for active vibration control

Piezoelectric materials have a wide range of application on the active vibration control of flexible structures as actuators and sensors due to its inverse and direct piezoelectric effect. In order to increase performance of active vibration control, piezoelectric fibers are stacked into single layer composite, making piezoelectric fiber-reinforced composite (PFRC) actuator and sensor. These actuators and sensors are used for active vibration control of a thin-walled structures, placing them at the surface of the structure. Since that, control performances depend on sizes, positions and orientations of PFRC actuators and sensors. The aim of this paper is to investigate the effect of PFRC actuator orientation and position (top or bottom) on controllability of cross-ply and angle-ply antisymmetric composite plates for active vibration control. Depending on layers' orientation, composite laminates possess coupling behavior (bending-stretching, bending-shear coupling). Since antisymmetric laminates possess bending-stretching coupling behavior, the effect of this behavior on controllability will be also discussed

The exact natural frequency solution of a free axialbending vibration problem of a non-uniform AFG cantilever beam with a tip body

In this paper we present the solution of exact equations of motion for coupled axial and bending vibrations of a non-uniform axially functionally graded (AFG) cantilever beam with a body of which mass center is eccentrically displaced in axial and transverse direction with respect to the beam’s end. The Euler-Bernoulli beam theory is implemented to model behavior of the beam under axial and transverse in-plane vibrations. Based on the paper [1], that is supported by results publish in the paper [2] authors confirm the obtained results of natural frequencies of the AFG cantilever beam, when boundary conditions define the vibration coupling. The modified symbolic-numeric method of initial parameters presented in [3] is implemented in computing natural frequencies of the beam. This method is expanded to solve axial-bending vibration problems, with respect to the one presented in the literature [3] for the problem of the vibration of a cantilever beam. Some minor deviations in the obtained results may be noticed with respect to those obtained in [1], yet all within a tolerance domain due to the computational precision