A correlation for the estimation of critical micellization concentrations and temperatures of polyols in aqueous solutions

An empirical correlation is presented for the estimation of critical micellization concentrations (CMC) and critical micellization temperatures (CMT) for poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymers in aqueous solutions. The CMC and CMT are expressed as a function of the polyol molecular weight, composition, and temperature (for CMC determination) or concentration (in the case of CMT). The correlation was developed from experimental CMT data for a set of 12 polyols that covered a wide range of molecular weights (2900–14600) and poly(ethylene oxide) contents (30–80 wt%) and is based on a simple expression for the standard free energy of micellization. Such a correlation should be useful to practitioners of the field as it allows easy prediction of CMC and CMT for a wide range of polyols with a minimal number of input parameters.     

System level performance evaluation of MIMO and SISO OFDM-based WLANs

In this paper we investigate the system level performance of an Orthogonal Frequency Division Multiplexing (OFDM) Wireless LAN network enhanced through Multiple-Input Multiple-Output (MIMO) techniques and compare it to the performance of the conventional Single-Input Single-Output (SISO) network. The MIMO scheme we apply is closed loop power allocation based on Singular Value Decomposition (SVD). The above investigations are carried out by means of a software based simulation platform. In order to characterize the system level performance accurately, a suitable link-to-system interface based on channel capacity has been developed. The performance evaluation is achieved by monitoring the average system throughput and the percentage of satisfied users. Extensive system level simulations have been carried out that prove the superiority of MIMO techniques especially for heavy traffic load conditions.     

Search Algorithms for Subdatatype-Based Multimedia Retrieval

Recently, researchers have mainly been interested only in the search for data content that are globally similar to the query and not in the search for inside data items. This paper presents an algorithm, called a generalized virtual node (GVN) algorithm, to search for data items where parts (subdatatype) are similar to the incoming query. We call this subdatatype-based multimedia retrieval. Each multimedia datatype, such as image and audio is represented in this paper as a k-dimensional signal in the spatio-temporal domain. A k-dimensional signal is transformed into characteristic features and these features are stored in a hierarchical multidimensional structure, called the k-tree. Each node on the k-tree contains partial content corresponding to the spatial and/or temporal positions in the data. The k-tree structure allows us to build a unified retrieval model for any types of multimedia data. It also eliminates unnecessary comparisons of cross-media querying. The experimental results of the use of the new GVN algorithm for subaudio and subimage retrievals show that it takes much less retrieval times than other earlier algorithms such as brute-force and the partial-matching algorithm, while the accuracy is acceptable.     

Walsh Orthogonal Functions in Geometrical Feature Extraction

Walsh functions are used in designinq a feature extraction algorithm. The ?axis-symmetry? property of the Walsh functions is used to decompose geometrical patterns. An axissymmetry (a.s.)-histogram is obtained from the Walsh spectrum of a pattern by adding the squares of the spectrm coefficients that correspond to a given a.s.-number ? and plotting these against ?. Since Walsh transformation is not positionally invariant, the sequency spectrum does not specify the pattern uniquely. This disadvantage is overcome by performing a normalization on the input pattern through Fourier transformation. The a.s.-histogram is obtained from the Walsh spectrum coefficients of the Fourier-normalized rather than the original pattern. Such histogram contains implicit information about symmetries, periodicities, and discontinuities present in a figure. It is shown that a.s.-histograms result in great dimensionality reduction in the feature space, which leads to a computationally simpler classification task, and that patterns which differ only in translations or 90° rotation have equal a.s.-histograms.     

A new control design for multiterminal HVDC systems using optimal entire eigenstructure assignment

Contents This paper presents a new method of control design for multiterminal HVDC systems. The proposed design approach applies the optimal entire eignestructure assignment technique developed for optimal state feedback controls of multi-input linear systems in order to achieve predetermined response characteristics. The feedback-gains are computed to assign the closed-loop eigenvalues of the HVDC system at any specified distinct modes and simultaneously minimize an appropriate linear quadratic (LQ) performance index. Therefore, the controller design takes into account the dynamics of the DC transmission system, making possible the regulation of the current at the remote terminals, and at the same time assures both stability with predetermined duration of transient response and minimum system effort. A computer simulation of an integrated ac/dc power system is used to demonstrate the effectiveness of the proposed design since in all simulated cases the transient response for typical disturbances appears desirable, showing fast damping characteristics without significant overshoots or oscillations.

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Eine neue Regelmethode für HGÜ-Systeme mit mehreren Unterwerken optimaler Eigenstruktur

Übersicht Diese Arbeit befaßt sich mit einer neuen Regelmethode für HGÜ-Systeme mit mehreren Unterwerken. Die vorgeschlagene Regelstrategie basiert auf der Technik der optimalen Eigenstruktur. Die für optimale Zustandsregelung von linearen Systemen mit vielen Eingängen entwickelt worden ist, um eine vorgeschriebene Antwort zu erreichen. Die Verstärkungsfaktoren werden berechnet, um die Eigenwerte des Regelkreises des HGÜ-Systems bei beliebig gewünschten Höhen zu ermitteln und gleichzeitig ein geeignetes lineares quadratisches Kriterium zu minimieren. Somit berücksichtigt die Regelbemessung die Dynamik des Gleichstromübertragungssystems und ermöglicht die Stromregelung in entfernten Unterwerken. Ebenfalls wird Stabilität des Systems unter Vorbestimmung der Dauer der Transienten Antwort und Minimierung der Systembelastung gesichert. Es wird eine Computersimulation eines ac/dc-Systems durchgeführt, um die Effektivität der vorgeschlagenen Methode zu demonstrieren. In sämtlichen Fällen zeight die transiente Antwort typischer Störungen schnelle Dämpfung ohne merkbare Überhöhungen und Schwingungen.

     

Design of a reduced order observer for optimal decentralizedcontrol of HVDC systems

The authors present a novel approach to the design of decentralized optimal controls for integrated power systems. The approach involves the decomposition of the integrated system into interconnected subsystems and the independent control of each subsystem, considering the interactions at the interconnection points as unknown disturbances. The design of a reduced-order observer, capable of reconstructing the inaccessible states of the system and the unknown disturbances, and the integration of this observer into the overall control loop are presented. As an example, an optimal current regulator for HVDC system is presented to demonstrate the effectiveness of the proposed approach     

Size- and shape-controlled synthesis of colloidal gold through autoreduction of the auric cation by poly(ethylene oxide)-poly(propylene oxide) block copolymers in aqueous solutions at ambient conditions

Gold nanoparticles with an average diameter in the range 5-20?nm have been synthesized from hydrogen tetrachloroaureate (III) hydrate (HAuCl(4)·3H(2)O) in air-saturated aqueous PEO-PPO-PEO block copolymer solutions at ambient temperature in the absence of any other reducing agent (PEO: poly(ethylene oxide), PPO: poly(propylene oxide)). The particle size was controlled by the block copolymer concentration and PEO and PPO block lengths. Our findings indicate that longer PEO blocks lead to an increase in particle size because of an increase in reaction activity. Adsorption of PO segments on gold nanoparticles seems to prevent particle growth from aggregation, and results in small particle size and high colloidal stability. An increase of the HAuCl(4) concentration causes a change in the particle shape from spherical to triangular or hexagonal nanoplates.     

Error Performance of Digital Modulation Schemes with MRC Diversity Reception over η-μ Fading Channels

This paper provides exact-form expressions for the average symbol error probability (ASEP) of various digital modulation schemes with maximal ratio combining (MRC) diversity over L independent, not necessarily identically distributed (n.i.d.) eta-mu fading channels. The derived expressions are given in terms of the Lauricella and Appell hypergeometric functions and include several others available in the literature such as those for Nakagami-m and Hoyt. General asymptotic ASEP expressions are also derived for all the considered modulation schemes which provide useful insights regarding the factors affecting the performance of the considered system.     

Self-Assembly of Polyethylene Glycol Ether Surfactants in Aqueous Solutions: The Effect of Linker between Alkyl and Ethoxylate

The aqueous self-assembly behavior of two homologous series of poly(ethylene oxide) (PEO)-containing nonionic surfactants based on a C₁₀-Guerbet hydrophobe is reported. The two families of surfactants, alkyl ethoxylates and alkyl alkoxylates, are commercially available from BASF under the trade name Lutensol® XP-series and XL-series, respectively. The latter incorporate propylene oxide (PO) units in the surfactant chain. Dye solubilization was used to determine the critical micellization concentration (CMC) of each surfactant at 22 and 50 °C. The PO-containing alkyl alkoxylates displayed lower CMC values, which were also more sensitive to temperature. The Gibbs free energy, enthalpy, and entropy of micellization were computed from the CMC data and used to identify the contribution of each surfactant moiety (alkyl chain, PO unit, and PEO block) in controlling the CMC. The micellization properties are compared with compositionally similar surfactants with linear alkyl chains, yielding information about the effects of the Guerbet alkyl chain on micellization. Isothermal titration calorimetry was also used to characterize the CMC and enthalpy of micellization which generally compare well with the dye solubilization results. Cloud point data reveal nonmonotonic relationships for the Lutensol® surfactants with respect to composition, unlike linear alkyl chain surfactants. Finally, dilute solution viscosity measurements performed on some Lutensol® surfactants show a change in the slope, suggesting a structural change that tends to be more pronounced for surfactants with longer PEO blocks. The data presented herein enhance the understanding of surfactant structure–property relationships required for industrial formulation.