A method for magnetizing curve identification in rotor fluxoriented induction machines

Operation of an indirect rotor flux oriented induction machine in the field weakening region is usually realized by varying the rotor flux reference in inverse proportion to the speed of rotation. In order to provide the correct stator d-axis current reference at all speeds, it is necessary to incorporate the inverse magnetizing curve of the machine in the controller. The paper proposes an experimental method for identifying the inverse magnetizing curve, specifically developed for the type of vector controlled drives described. The method utilizes the same indirect vector controller and PWM inverter that are used in subsequent normal operation of the drive. It requires that the machine can run under no-load conditions and that the fundamental component of the stator voltage can be measured. The simplicity and accuracy of the method make it well suited for use during commissioning of the drive. The method is verified by extensive experimentation     

Solidification of Hydrogen Clusters

The solidification of small parahydrogen clusters is studied. In such aggregates, where according to some Authors superfluid properties may be present, the principal antagonist of superfluidity is solidification. In this paper we investigate under what conditions solidification either cannot occur at all, or would occur only in times much longer than the lifetime of the cluster. Due to surface melting effects (enhanced by the van der Waals forces) the exterior layers of the cluster do not solidify. As far as the inner core is concerned, the solidification times depend notoriously strongly on the exact values of the parameters; they also depend strongly on the thickness of the molten layer. Nucleation implies a barrier, which in principle can be overcome either by thermal fluctuations (at relatively high temperatures) or by tunneling (at very low temperatures). Although a better knowledge of the physical properties of parahydrogen (especially the solid–liquid interface energy and the chemical potential of the two phases) is required, we confirm that in both cases the nucleation times can be exceedingly long.     

Mechanistic Analysis of an Engineered Enzyme that Catalyzes the Formose Reaction

An enzyme that catalyzes the formose reaction, termed “formolase”, was recently engineered through a combination of computational protein design and directed evolution. We have investigated the kinetic role of the computationally designed residues and further characterized the enzyme's product profile. Kinetic studies illustrated that the computationally designed mutations were synergistic in their contributions towards enhancing activity. Mass spectrometry revealed that the engineered enzyme produces two products of the formose reaction—dihydroxyacetone and glycolaldehyde—with the product profile dependent on the formaldehyde concentration. We further explored the effects of this product profile on the thermodynamics and yield of the overall carbon assimilation from the formolase pathway to help guide future efforts to engineer this pathway.     

Mobile Design as Neighborhood Acupuncture: Activating the Storytelling Networks of South Los Angeles

Abstract

A delicate touch is required to empower neighborhoods using civic media. Funding is persistently scarce. Especially in marginalized neighborhoods, blunt designs can be counterproductive and even entrench complex problems. New metaphors may be needed to guide design and empower local neighborhoods. Urban acupuncture is used as the basis for this study, emphasizing a light-touch strategy that has shown success in Brazil with urban transit, and more recently in Europe with urban design. We specifically propose “neighborhood acupuncture” to address the local level, tapping the sociology of place-based communication. To investigate the implications for systematic design, a case study is probed in South Los Angeles using mobile media for community mapping. Using qualitative methods, three tactics were investigated for the potential to “poke” the network into action, including one to bridge diverse storytelling networks. Each tactic ultimately seeks to build the capacity for collective action around neighborhood issues. Acupuncture is broadly argued to sustain two design shifts: first to help approach neighborhoods as ecosystems, and second, to design for circulation rather than any single technology platform.     

Two-Tier,Scalable and Highly Resilient Key Predistribution Scheme for Location-Aware Wireless Sensor Network Deployments

We propose a probabilistic key predistribution scheme for wireless sensor networks, where keying materials are distributed to sensor nodes for secure communication. We use a two-tier approach in which there are two types of nodes: regular nodes and agent nodes. Agent nodes are more capable than regular nodes. Our node deployment model is zone-based such that the nodes that may end up with closer positions on ground are grouped together. The keying material of nodes that belong to different zones is non-overlapping. However, it is still possible for nodes that belong to different zones to communicate with each other via agent nodes when needed. We give a comparative analysis of our scheme through simulations and show that our scheme provides good connectivity figures at reasonable communication cost by using minimal flooding in key distribution. Moreover, we show that our scheme is scalable such that no extra overhead in incurred in case of increased number of nodes and sensor field size. Most importantly, simulation results show that our scheme is highly resilient to node captures.     

Optimization of pH value and aluminium sulphate quantity in the chemical treatment of molasses

The aim of this investigation was to find the optimal working conditions for the chemical treatment of molasses that guarantee coagulation and precipitation of undesired macromolecules. Twenty experiments were performed, within the limits: 3.5pH8.5 and 0.1 mol Al/lc0.5 mol Al/l, on samples of molasses treated with Al₂(SO₄)₃ as a precipitant. The efficiency of the treatment was controlled through measuring both the zeta potential and solution absorbance at 560 nm. By analysing the experimental results, it was concluded that the optimum lies within reduced limits of: 4pH7 and 0.2 mol Al/lc0.4 mol Al/l, which covers nine experimental points. Based on these measurements, a mathematical model of absorbance changes was defined, in terms of pH and Al₂(SO₄)₃ quantity. The model was taken as the objective function, and the optimal calculated values were obtained: pH=5.3 and c=0.34 mol Al/l. They guarantee a minimal absorbance value of: 0.124 at 560 nm.     

The influence of structure order on the kinetics of dehydroxylation of kaolinite

The structural order of kaolinite is an important factor that shows a substantial effect on the processes which take place during the thermal treatment of kaolin. The influence of structural order on the dehydroxylation process was investigated by simultaneous thermogravimetry and differential thermal analysis (TG-DTA). The thermal analysis was performed on the samples with gradually decreasing structural order prepared by milling procedure. The apparent activation energy of dehydroxylation process decreases with decreasing structural order according to the exponential function. The extrapolation of experimental data leads to the estimation of apparent activation energy of 76.6 kJ mol^?1 and of frequency factor of 0.12 × 10⁴ s^?1 related to completely disordered form of kaolinite, while the ordered form shows the apparent activation energy of 216.17 kJ mol^?1 and the frequency factor of 9.26 × 10⁴ s^?1. The relationships between features such as the infrared pattern of treated material, the degree of structural order and the apparent activation energy were established.     

Impact of dynamic cross-saturation on accuracy of saturatedsynchronous machine models

Cross-saturation effect in synchronous machines has been a subject of considerable attention. Inclusion of the cross-saturation in the machine model has two consequences. The first one, called here “steady-state cross-saturation”, consists of dependence of the steady-state d-q axis magnetizing inductances on the currents in both axes. The second one, termed here “dynamic cross-saturation”, is the existence of nonzero elements in the system matrix, that describe cross coupling between d- and q-axis. Dynamic cross-saturation appears in all the saturated machine models, regardless of the selected set of state-space variables, with the exception of the winding flux linkage state-space model. The aim of this paper is to compare behavior of various models when dynamic cross-saturation is neglected. It is shown that the impact of dynamic cross-saturation on accuracy depends on the selected set of state-space variables. In the majority of cases omission of dynamic cross-saturation leads to very inaccurate results. However, it is found that for one particular class of models, omission of dynamic cross-saturation has practically no impact on accuracy. These models therefore fully describe the complete saturation effect by means of only continuous variation of the d-q axis magnetizing inductances