Universal Stabilizer Research Articles

Antioxidant properties of some plant extracts and effect of their addition on the oxidation stability of biodiesel

The extracts from the leaves of Deschampsia antarctica É. Desv., Camelina sativa (L.) Crantz, and Camellia japonica L. plants, as well as from defatted Camelina sativa and Silybum marianum seedcakes were investigated as potential additives for improvement of biodiesel stability against oxidation. Composition of the extracts was studied by means of HPLC, and antioxidant properties were evaluated using the Folin-Ciocalteu assay and the DPPH test. The oxidation of biodiesel was monitored during the accelerated procedure at 43C, with the changes in the acid number of biodiesel samples being the criteria of this process. In spite of significant distinctions in the content of various phenolic compounds, all the extracts were found to possess high antioxidant activity and decelerate biodiesel oxidation by 9-26%. The data did not reveal a directly proportional relationship between the antioxidants content in the extract, on the one hand, and the enhancement in biodiesel stability, on the other hand; various extracts had different influence on the behaviour of biodiesel from rape and Camelina seed oils. The results obtained are consistent with the assumption that there is no universal stabilizer for different types of biodiesel and indicate the prospects on searching for novel antioxidants of natural origin to inhibit oxidative processes.

Universal Adaptive Stabilization-Based Trend Filtering for Impending Battery Voltage Collapse Detection

Battery operated devices are common in everyday life. Deciding when a warning for impending battery voltage collapse should be triggered is not trivial. This letter develops an impending battery terminal voltage collapse detection system using a universal adaptive stabilizer (UAS) and a well-known trend filter. This eliminates requiring knowledge of battery model parameter values, or initial state-of-charge (SOC). The proposed approach overcomes the need for extensive training when compared to using neural-networks based techniques. Also, the developed trend filter when used with a UAS, eliminates the need for selecting windows of data to be processed. This is advantageous compared to earlier work, which uses a different trend filtering mechanism, because selection of window sizes is not straightforward. Further, the approach used in this letter shows that the UAS based technique is implementable on a cell phone. Associated mathematical results, and experimental data from such an implementation are presented. Additionally, the technique is also applied to other larger capacity Li-ion batteries showing its versatility. The developed technique can also be used to detect when the state-of-health (SOH) of a Li-ion battery is about to enter an unsafe region.

Organic Amines as Targeting Stabilizer at the Polymer/Fullerene Interface for Polymer:PC 61 BM Solar Cells

Herein, it is demonstrated that a small amount (0.05% in weight ratio) of polyethyleneimine (PEI) can effectively suppress the “burn‐in” degradation of both PTB7‐Th:PC61BM and P3HT:PC61BM cells, similar to the piperazine derivatives, suggesting that organic amines can serve as universal stabilizer in polymer:PC61BM solar cells. Light‐induced electron spin resonance (LESR) spectroscopy measurement shows a higher ESR signal intensity of PC61BM anions in 0.2% PEI‐doped film than in 1% piperazine‐doped film. Moreover, no piperazine is detected in a 10% (w/w) piperazine‐doped film by gas chromatography–mass spectrometry (GSMS). These results suggest that the residual piperazine in the blend film is very low, which can be understood by the high volatility of piperazine. Quantum calculations are performed on the intermolecular binding energy (EB) between polymer (using model repeating units), PC61BM, and piperazine molecules. Results reveal that piperazine prefers to localize at the polymer:fullerene interface by complexing with PC61BM (in P3HT:PC61BM) or PTB7‐Th (in PTB7‐Th:PC61BM system), which indicates that the photo dimerization of PC61BM which causes the “burn‐in” degradation of polymer:fullerene solar cells mainly happens at the donor/acceptor interface, and the organic amine serves as the targeting stabilizer at the interface.

Permanent magnet DC motor parameters estimation via universal adaptive stabilization

This paper presents a quick and effective adaptive estimation methodology for parameters estimation of a permanent magnet (PM) DC motor. The proposed technique uses a universal adaptive stabilizer (UAS). This technique estimates PMDC motor parameters in a single experimental run using input voltage, current and speed. Over time, due to aging and wear, a motor’s parameters values do not match those in the datasheet. Mathematical proofs, experimental results supporting the proposed approach are presented. Despite the persistence of excitation condition not being imposed, the proposed technique produces good results, and is verified in earlier work on Li-ion battery parameters estimation.

Universal Adaptive Stabilizer Based Optimization for Li-Ion Battery Model Parameters Estimation: An Experimental Study

This paper proposes a two-stage universal adaptive stabilizer (UAS)-based optimization technique for an accurate and efficient estimation of Li-ion battery model parameters. The first stage utilizes an UAS-based adaptive parameters estimation (APE) technique to acquire an initial estimate of battery model parameters. The second stage utilizes one of the three different optimization techniques, i.e., fmincon , particle swarm optimization (PSO), and hybrid PSO to improve the accuracy of battery model parameters obtained by the APE. The parameters estimated by the APE help in reducing the search space interval required by the optimization technique, thus reducing the computation time of the optimization process. Intensive computer simulation and experimentation are performed to estimate the battery terminal voltage using the estimated parameters. The accuracy of estimated battery parameters is evaluated by comparing the estimated and measured battery terminal voltage. The results show that the accuracy of the battery model parameters obtained by the optimization techniques alone is poor, and the required computation time is high. The accuracy of parameters obtained by UAS-based APE is good with very low computation time, while it is best when UAS-based APE is used in combination with the PSO, or hybrid PSO optimization techniques while requiring an intermediate amount of computation time.

Synthetic capacity does not predict elasmobranchs' ability to maintain trimethylamine oxide without a dietary contribution

Trimethylamine oxide (TMAO) is an organic osmolyte and universal protein stabilizer. Its role as a cytoprotectant is particularly important in ureosmotic elasmobranchs that accumulate high levels of urea, a macromolecular perturbant. Feeding is a key component in the turnover and maintenance of these nitrogenous compounds. However, previous studies examining TMAO regulation have been largely completed using starved individuals, when nitrogen balance is altered. Here, under fed conditions, we test the importance of dietary TMAO on long-term maintenance in three elasmobranch species with differing endogenous synthetic capacities. Smoothhounds (Mustelus canis), spiny dogfish (Squalus acanthias), and little skates (Leucoraja erinacea) exhibited species- and tissue-specific differences in their ability to conserve TMAO when fed a low TMAO diet for 56days. Smoothhounds, a species with the capacity for endogenous production, exhibited a decrease in muscle TMAO. Spiny dogfish and little skates, species with no reported ability for synthesis, exhibited decreases in plasma and liver TMAO, respectively. Our findings are contrary to previous starvation studies demonstrating constant levels of TMAO for up to 56days in elasmobranchs. Further, the previously reported synthetic capacity of these species did not correlate with their ability to conserve TMAO and cannot be used to predict a species reliance on dietary contributions for prolonged maintenance. It is possible that all species rely to a degree on absorption of TMAO from the diet or that alternate synthetic or regulatory pathways play a larger role than previously thought.

Waypoint Following for Differentially Driven Wheeled Robots with Limited Velocity Perturbations

In this paper a unified motion control strategy dedicated for the waypoint following task realized by a differentially driven robot is presented. It is assumed that the vehicle moves with limited velocities and accelerations in order to reduce excessive slip and skid effects. In order to include operational constraints, a motion planner is combined with a universal stabilizer taking advantage of transverse functions. To improve tracking precision translated transverse functions are deployed and a new adaptive technique for the controller tuning is proposed. During the motion planning stage an auxiliary trajectory connecting points in the configuration space and satisfying assumed phase constraints is generated. The resulting motion execution system has been implemented on a laboratory-scale skid-steering mobile robot, which served as platform for experimental validation of presented algorithms.

Fast Track Approval of Therapeutic Blood Substitutes

Fast Track Approval of Therapeutic Blood Substitutes

Simultaneous stabilization: Construction of a universal stabilizer for linear plants with delay with the use of spectral reducibility

We consider the problem of the construction of a common stabilizing controller for a family of k linear stationary nth-order plants with commensurable delays in the controls and the state variables. Our approach to stabilization is based on the construction of a common two-loop stabilizer. The controller of the first (internal) loop solves the problem of reducing each plant of the family to a finite spectrum, and the controller of the second (external) contour solves the stabilization problem.

Simultaneous stabilization of linear dynamic plants by the variable-structure controller

Consideration was given to the design of a unique controller with state feedback stabilizing the finite family of linear dynamic plants of identical orders. It was proposed to use for that the variable-structure controllers giving rise to sliding modes in the closed-loop systems. Constructive existence conditions for a universal variable-structure stabilizer of the given finite family of dynamic plants were formulated.

A FRACTIONAL ORDER UNIVERSAL HIGH GAIN ADAPTIVE STABILIZER

In this paper, a fractional order universal high gain adaptive stabilizer is proposed which guarantees the Lp stability of fractional order multiple–input and multiple–output (MIMO) systems with finite control effort. The boundedness of the control gain for the fractional order universal adaptive strategy is discussed for fractional order MIMO systems, and an upper bound of the control gain is presented for fractional order single-input and single-output (SISO) systems. Some advantages of the discussed fractional order universal adaptive stabilizer are demonstrated in numerical simulations, such as the overshoots of system outputs can be efficiently reduced by decreasing the fractional order of the universal adaptive stabilizer without significantly increasing the system gains.

Thermal Destabilization of Stem Bromelain by Trehalose

Trehalose, a naturally occurring osmolyte, is considered as a universal protein stabilizer. We investigated the effect of the disaccharides, trehalose and sucrose, on the thermal stability and conformation of bromelain. To our surprise, bromelain in the presence of 1 M trehalose/sucrose was destabilized under thermal stress. The average Tm values as determined by UV spectroscopy and CD spectropolarimetry decreased by 5 degrees and 7 degrees C for bromelain in 1 M sucrose or trehalose solutions, respectively. The enzyme was also found to inactivate faster at 60 degrees C in the presence of these osmolytes. The tertiary and secondary structure of bromelain undergoes small changes in the presence of sucrose/trehalose. Studies on the binding of these osmolytes with the native and the heat denatured enzyme revealed that sucrose/trehalose lead to preferential hydration of the denatured bromelain as compared to the native one, hence stabilizing more the denatured conformation. This is perhaps the first report on the destabilization of a protein by trehalose.

A universal iterative learning stabilizer for a class of MIMO systems

Design of iterative learning control (ILC) often requires some prior knowledge about a system's control matrix. In some applications, such as uncalibrated visual servoing, this kind of knowledge may be unavailable so that a stable learning control cannot always be achieved. In this paper, a universal ILC is proposed for a class of multi-input multi-output (MIMO) uncertain nonlinear systems with no prior knowledge about the system control gain matrix. It consists of a gain matrix selector from the unmixing set and a learned compensator in a form of the positive definite discrete matrix kernel, corresponding to rough gain matrix probing and refined uncertainty compensating, respectively. Asymptotic convergence for a trajectory tracking within a finite time interval is achieved through repetitive tracking. Simulations and experiments of uncalibrated visual servoing are carried out in order to verify the validity of the proposed control method.

Counteracting Osmolyte Trimethylamine N-Oxide Destabilizes Proteins at pH below Its pKa: MEASUREMENTS OF THERMODYNAMIC PARAMETERS OF PROTEINS IN THE PRESENCE AND ABSENCE OF TRIMETHYLAMINE N-OXIDE

Earlier studies have reported that trimethylamine N-oxide (TMAO), a naturally occurring osmolyte, is a universal stabilizer of proteins because it folds unstructured proteins and counteracts the deleterious effects of urea and salts on the structure and function of proteins. This conclusion has been reached from the studies of the effect of TMAO on proteins in the pH range 6.0-8.0. In this pH range TMAO is almost neutral (zwitterionic form), for it has a pK(a) of 4.66 +/- 0.10. We have asked the question of whether the effect of TMAO on protein stability is pH-dependent. To answer this question we have carried out thermal denaturation studies of lysozyme, ribonuclease-A, and apo-alpha-lactalbumin in the presence of various TMAO concentrations at different pH values above and below the pK(a) of TMAO. The main conclusion of this study is that near room temperature TMAO destabilizes proteins at pH values below its pK(a), whereas it stabilizes proteins at pH values above its pK(a). This conclusion was reached by determining the T(m) (midpoint of denaturation), delta H(m) (denaturational enthalpy change at T(m)), delta C(p) (constant pressure heat capacity change), and delta G(D) degrees (denaturational Gibbs energy change at 25 degrees C) of proteins in the presence of different TMAO concentrations. Other conclusions of this study are that T(m) and delta G(D) degrees depend on TMAO concentration at each pH value and that delta H(m) and the delta C(p) are not significantly changed in presence of TMAO.

Obstructions to the Existence of Universal Stabilizers for Smooth Control Systems

This paper states necessary conditions for the existence of “universal stabilizers” for smooth control systems. Roughly speaking, given a control system and a set {\cal U} of reference input functions, by “universal stabilizer” we mean a continuous feedback law that stabilizes the state of the system asymptotically to any of the reference trajectories produced by (arbitrary) inputs in {\cal U}. For an example, consider Brockett’s nonholonomic integrator, with {\cal U} representing a set of uniformly bounded, piecewise continuous functions of time. This system’s state can be asymptotically stabilized to any reference trajectory provided the latter is persistently exciting (PE). By contrast, for constant trajectories (i.e., equilibria), which are not PE, asymptotic stabilization is impossible by means of continuous pure-state feedback, in view of Brockett’s obstruction. However, since this obstruction can be circumvented by the use of time-varying state feedback, one might reasonably expect to be able to design a (time-varying) continuous control law capable of asymptotically stabilizing the state to arbitrary reference trajectories, be they PE or not. Surprisingly, a consequence of the results in this paper is that, for systems with nonholonomic constraints frequently found in control applications, if {\cal U} contains reference functions that are not PE, then the “universal stabilization” problem cannot be solved, even if time-varying feedback is used.

Why Is Trehalose an Exceptional Protein Stabilizer?: AN ANALYSIS OF THE THERMAL STABILITY OF PROTEINS IN THE PRESENCE OF THE COMPATIBLE OSMOLYTE TREHALOSE

Trehalose, a naturally occurring osmolyte, is known to be an exceptional stabilizer of proteins and helps retain the activity of enzymes in solution as well as in the freeze-dried state. To understand the mechanism of action of trehalose in detail, we have conducted a thorough investigation of its effect on the thermal stability in aqueous solutions of five well characterized proteins differing in their various physico-chemical properties. Among them, RNase A has been used as a model enzyme to investigate the effect of trehalose on the retention of enzymatic activity upon incubation at high temperatures. 2 m trehalose was observed to raise the transition temperature, Tm of RNase A by as much as 18 degrees C and Gibbs free energy by 4.8 kcal mol-1 at pH 2.5. There is a decrease in the heat capacity of protein denaturation (DeltaCp) in trehalose solutions for all the studied proteins. An increase in the DeltaG and a decrease in the DeltaCp values for all the proteins points toward a general mechanism of stabilization due to the elevation and broadening of the stability curve (DeltaG versus T). A direct correlation of the surface tension of trehalose solutions and the thermal stability of various proteins has been observed. Wyman linkage analysis indicates that at 1.5 m concentration 4-7 molecules of trehalose are excluded from the vicinity of protein molecules upon denaturation. We further show that an increase in the stability of proteins in the presence of trehalose depends upon the length of the polypeptide chain. The pH dependence data suggest that even though the charge status of a protein contributes significantly, trehalose can be expected to work as a universal stabilizer of protein conformation due to its exceptional effect on the structure and properties of solvent water compared with other sugars and polyols.

Universal stabilization of feedforward nonlinear systems

In recent years, many important results on global stabilization of feedforward nonlinear systems have been proposed. However, in all previous results, to develop a global stabilizer, one must know some a priori information on system nonlinearities. For example, it is required that the system nonlinearities be known, or be bounded by known functions, or be linearly parametrized, or satisfy some high order growth rate condition, etc. The contribution of this paper is proposing a universal global stabilizer design for a class of feedforward systems, which does not require a priori knowledge of system nonlinearities.

A design method of universal adaptive stabilizer

A design method of universal adaptive stabilizers for processes with unknown degrees and unknown signs of high-frequency gains, and with uncertain relative degree r, r+1 or r+2 (r/spl isin/ N), is presented. This is an extension of Marse's universal stabilizers where the relative degrees are uncertain but known to be one or two. It is shown that single adaptive control schemes with six tuning parameters can deal with enlarged uncertainties of relative degrees.

Biomechanics and functional anatomy of the upper ankle.

Dorsoplantar motion in the upper ankle joint is around one "transverse" rotational axis. In relation to the lower leg this axis is oblique joining the tips of the malleoli. Talocrural motion is highly precise compared to other human joints. Most of the stability and undisturbed motion in the loaded joint is afforded by the intimate osteocartilagineous contact. The rule of the collateral ligaments is secondary stabilisation, buffering of abnormal stresses and centering the talus in the extremes of motion. The posterior talofibular ligament is the universal lateral stabilizer, the deep portion of the deltoid ligament is the predominant medial ligament structure. Ligament tension without strain and under valgusabduction load as a rule makes only a difference in a quantitative way. Under varusadduction-stress load patterns are usually changed. Fibula and the distal syndesmotic ligaments, in the presence of valgusabduction- and external rotation stress, predominate over the medial joints structures. Remaining joint steps, especially in Volkmanns triangle (posterior malleolus) are prearthritic deformities. Nevertheless primary traumatic lesion of the cartilage has a major prognostic meaning. In cadaver joints as in vivo permanent lesions of only a singular fasciculus of the deltoid or lateral collateral ligament result in clearly detectable motion abnormalities. Concerning clinical therapy at present as in the past complete reconstruction of all that damaged singular structures must be claimed for. There is generally only a small tolerance against instability and malposition in the upper ankle joint. Even after one hundred years of research today factors defining the individual breadth of tolerance are not fully understood. In the presence of treatment regimes, that stood the test of time, it is therefore difficult to recommend treatment alternatives, relaying on individual biomechanical tolerance.

Weak Maps and Stabilizers of Classes of Matroids

LetFbe a field and letNbe a matroid in a class N ofF-representable matroids that is closed under minors and the taking of duals. ThenNis anF-stabilizer for N if every representation of a 3-connected member of N is determined up to elementary row operations and column scaling by a representation of any one of itsN-minors. The study of stabilizers was initiated by Whittle. This paper extends that study by examining certain types of stabilizers and considering the connection with weak maps.The notion of a universal stabilizer is introduced to identify the underlying matroid structure that guarantees thatNwill be anF′-stabilizer for N for every fieldF′ over which members of N are representable. It is shown that, just as withF-stabilizers, one can establish whether or notNis a universal stabilizer for N by an elementary finite check. IfNis a universal stabilizer for N, we determine additional conditions onNand N that ensure that ifNis not a strict rank-preserving weak-map image of any matroid in N, then no connected matroid in N with anN-minor is a strict rank-preserving weak-map image of any 3-connected matroid in N.Applications of the theory are given for quaternary matroids. For example, it is shown thatU2,5is a universal stabilizer for the class of quaternary matroids with noU3,6-minor. Moreover, ifM1andM2are distinct quaternary matroids withU2,5-minors but noU3,6-minors andM1is connected whileM2is 3-connected, thenM1is not a rank-preserving weak-map image ofM2.