281 research outputs found
Quantitative and qualitative biogenic silicon analyses combining modern microscopical and spectroscopical methods
Numerous organisms comprising pro- and eukaryotes are evolutionarily adapted to synthesize siliceous structures (biosilicification). In terrestrial biogeosystems biogenic silicon (BSi) accumulation of phytogenic (BSi synthesized by plants), protistic (diatoms and testate amoeba), microbial (bacteria and fungi) and zoogenic (sponges) origin results in formation of corresponding BSi pools. Accumulation and recycling of BSi in terrestrial ecosystems influence fluxes of dissolved Si from the continents to the oceans, thus act as a filter in the global Si cycle. Although the biogenic control mechanism especially of phytogenic Si pools (phytoliths) has been generally recognized since decades quantitative information on other terrestrial BSi pools is rare. Additionally, information on physicochemical properties of the various siliceous structures are needed to better understand their dissolution kinetics. We used modern microscopical (laser scanning microscopy, LSM; Scanning electron microscopy with coupled energy-dispersive X-ray spectroscopy, SEM-EDX) and spectroscopical (micro-Fourier transform infrared spectroscopy, micro-FTIR) methods for quantitative and qualitative analyses of BSi structures. LSM was used to measure volumes and surface areas of BSi structures and corresponding surface-area-to-volume ratios (A:V ratios) were calculated as an indicator for the resistibility of these siliceous structures against dissolution. Volume measurements were also used for the quantification of BSi pools by multiplication of corresponding volumes with BSi density. SEM-EDX analyses provided information on the elemental composition of different BSi structures and with the help of micro-FTIR we were able to gain specific information about chemical bonding and molecular structures of BSi. These information will help us to understand in detail dissolution kinetics of various siliceous structures, thus their role in Si cycling
Cell surface properties of Pseudomonas stutzeri in the process of diesel oil biodegradation
Pseudomonas stutzeri, isolated from crude oil-contaminated soil, was used to degrade diesel oil. Of three surfactants, 120 mg rhamnolipids 1â1 significantly increased degradation of diesel oil giving 88% loss after 14 days compared to 54% loss without the surfactant. The system with rhamnolipids was characterised by relatively high particle homogeneity. However, the addition of saponins to diesel oil caused the cells to aggregate (the polydispersity index: 0.542) and the biodegradation of diesel oil was only 46%. The cell yield was 0.22 g lâ1
Detectability subspaces and observer synthesis for two-dimensional systems
The notions of input-containing and detectability subspaces are developed within the context of observer synthesis for two-dimensional (2-D) Fornasini-Marchesini models. Specifically, the paper considers observers which asymptotically estimate the local state, in the sense that the error tends to zero as the reconstructed local state evolves away from possibly mismatched boundary values, modulo a detectability subspace. Ultimately, the synthesis of such observers in the absence of explicit input information is addressed
On some aspects of the geometry of differential equations in physics
In this review paper, we consider three kinds of systems of differential
equations, which are relevant in physics, control theory and other applications
in engineering and applied mathematics; namely: Hamilton equations, singular
differential equations, and partial differential equations in field theories.
The geometric structures underlying these systems are presented and commented.
The main results concerning these structures are stated and discussed, as well
as their influence on the study of the differential equations with which they
are related. Furthermore, research to be developed in these areas is also
commented.Comment: 21 page
Finite-region stabilization via dynamic output feedback for 2-D Roesser models
Finite-region stability (FRS), a generalization of finite-time stability, has been used to analyze the transient behavior of discrete two-dimensional (2-D) systems. In this paper, we consider the problem of FRS for discrete 2-D Roesser models via dynamic output feedback. First, a sufficient condition is given to design the dynamic output feedback controller with a state feedback-observer structure, which ensures the closed-loop system FRS. Then, this condition is reducible to a condition that is solvable by linear matrix inequalities. Finally, viable experimental results are demonstrated by an illustrative example
Uptake of Hydrocarbon by Pseudomonas fluorescens (P1) and Pseudomonas putida (K1) Strains in the Presence of Surfactants: A Cell Surface Modification
The objective of this research was the evaluation of the effects of exogenous added surfactants on hydrocarbon biodegradation and on cell surface properties. Crude oil hydrocarbons are often difficult to remove from the environment because of their insolubility in water. The addition of surfactants enhances the removal of hydrocarbons by raising the solubility of these compounds. These surfactants cause them to become more vulnerable to degradation, thereby facilitating transportation across the cell membrane. The obtained results showed that the microorganism consortia of bacteria are useful biological agents within environmental bioremediation. The most effective amongst all, as regards biodegradation, were the consortia of Pseudomonas spp. and Bacillus spp. strains. The results indicated that the natural surfactants (rhamnolipides and saponins) are more effective surfactants in hydrocarbon biodegradation as compared to Triton X-100. The addition of natural surfactants enhanced the removal of hydrocarbon and diesel oil from the environment. Very promising was the use of saponins as a surfactant in hydrocarbon biodegradation. This surfactant significantly increases the organic compound biodegradation. In the case of those surfactants that could be easily adsorbed on cells of strains (e.g., rhamnolipides), a change of hydrophobicity to ca. 30â40% was noted. As the final result, an increase in hydrocarbon biodegradation was observed
An algorithm to study the nonnegativity, regularity and stability via state-feedbacks of singular systems of arbitrary index
This paper deals with singular systems of index k â„ 1. Our main
goal is to find a state-feedback such that the closed-loop system satis-
fies the regularity condition and it is nonnegative and stable. In order
to do that, the core-nilpotent decomposition of a square matrix is applied
to the singular matrix of the system. Moreover, if the Drazin
projector of this matrix is nonnegative then the previous decomposition
allows us to write the core-part of the matrix in a specific block
form. In addition, an algorithm to study this kind of systems via a
state-feedback is designed.This paper has been partially supported by Ministry of Education of Spain [grant number DGI MTM2010-18228].Herrero DebĂłn, A.; Francisco J. RamĂrez; Thome, N. (2014). An algorithm to study the nonnegativity, regularity and stability via state-feedbacks of singular systems of arbitrary index. Linear and Multilinear Algebra. 1-11. https://doi.org/10.1080/03081087.2014.904559S11
Geometric techniques for implicit two-dimensional systems
Geometric tools are developed for two-dimensional (2-D) models in an implicitFornasiniâMarchesini form. In particular, the structural properties of controlled and conditionedinvariance are defined and studied. These properties are investigated in terms ofquarter-plane causal solutions of the implicit model given compatible boundary conditions.The definitions of controlled and conditioned invariance introduced, along with the correspondingoutput-nulling and input-containing subspaces, are shown to be richer than theone-dimensional counterparts. The analysis carried out in this paper establishes necessaryand sufficient conditions for the solvability of 2-D disturbance decoupling problems andunknown-input observation problems. The conditions obtained are expressed in terms ofoutput-nulling and input-containing subspaces, which can be computed recursively in a finitenumber of steps
Improving the vibration suppression capabilities of a magneto-rheological damper using hybrid active and semi-active control
This paper presents a new hybrid active & semi-active control method
for vibration suppression in flexible structures. The method uses a combination of a
semi-active device and an active control actuator situated elsewhere in the structure
to suppress vibrations. The key novelty is to use the hybrid controller to enable
the magneto-rheological damper to achieve a performance as close to a fully active
device as possible. This is achieved by ensuring that the active actuator can assist
the magneto-rheological damper in the regions where energy is required. In addition,
the hybrid active & semi-active controller is designed to minimize the switching of the
semi-active controller. The control framework used is the immersion and invariance
control technique in combination with sliding mode control. A two degree-of-freedom
system with lightly damped resonances is used as an example system. Both numerical
and experimental results are generated for this system, and then compared as part
of a validation study. The experimental system uses hardware-in-the-loop to simulate
the effect of both the degrees-of-freedom. The results show that the concept is viable
both numerically and experimentally, and improved vibration suppression results can
be obtained for the magneto-rheological damper that approach the performance of an
active device
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