The influence of the motion of a rotor grid on a stator grid

Summary In this paper we have used the method of characteristics developed for two dimensional unsteady flow problems to study a simplified axial turbine problem. The system consists of two sets of blades —the guiding vanes which are fixed and the rotor blades which move perpendicular to these vanes. The initial undisturbed constant flow in the system is perturbed by introducing a small velocity normal to the rotor blades to simulate a slight constant inclination. The resulting perturbed flow is periodic after the first three cycles. We have studied the perturbed density distribution throughout the system during a period.

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Der Einfluß der Bewegung eines Laufschaufelgitters auf ein Leitschaufelgitter

Zusammenfassung In der vorliegenden Arbeit wird das Charakteristikenverfahren für zweidimensionale instationäre Strömungen auf ein Problem der Axialturbinen angewandt. Das System besteht aus zwei Gitterreihen, den feststehenden Leitschaufeln und den hierzu senkrecht bewegten Laufschaufeln. Die anfangs ungestörte konstante Strömung wird gestört, indem den Laufschaufeln eine geringe Normalgeschwindigkeit erteilt wird, um eine konstante Anstellung zu simulieren. Die gestörte Strömung ist periodisch nach den ersten drei Perioden. Berechnet wurde das gestörte Dichtefeld während einer Periode.

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List of Symbols d distance between guide vanes - angle of inclination of rotor blades - W ₀ constant velocity of rotor blades perpendicular to the guide vanes - U ₀ initial steady streaming parallel flow between the guiding vanes - V _p velocity perpendicular to the rotor blades to simulate inclination of the blades - x coordinate parallel to the guide vanes - y coordinate perpendicular to the guide vanes - t time - u, v velocity componente inx, y directions, respectively - a ₀ undisturbed sound velocity in the system - a perturbed sound velocity - M ₀=U ₀/a ₀ nondimensional quantity corresponding toU ₀ - N ₀=W ₀/a ₀ nondimensional quantity corresponding toW ₀ - V ₀=V _p0/a ₀ nondimensional quantity corresponding toV _p0 - nondimensional coordinates corresponding tox, y, t, respectively - nondimensional quantity corresponding toa - nondimensional quantities corresponding tou, v respectively With 5 FiguresThis work was done during the award of an Alexander Von Humboldt Fellowship at the DFVLR-Aerodynamische Versuchsanstalt, Institut für Strömungsmechanik, Göttingen, Federal Republic of Germany.     

A formally verified application-level framework for real-time scheduling on POSIX real-time operating systems

We present a framework, called meta scheduler, for implementing real-time scheduling algorithms. The meta scheduler is a portable middleware layer component designed for implementations over POSIX-compliant operating systems. It accommodates pluggable real-time scheduling algorithms while offering the flexibility of platform independence - the singular underlying OS requirement is the now nearly ubiquitous POSIX compliance. The versatility of pluggable schedulers positions the meta scheduler for deployment in an interoperable heterogeneous real-time environment. We present the design of the meta scheduler and outline its implementation. Furthermore, we present a mechanized correctness verification using the UPPAAL model checker. Prototype implementation of the meta scheduler over QNX Neutrino real-time operating system demonstrates high performance and a small footprint.     

An Automatic Presence Service for Low Duty-Cycled Mobile Sensor Networks

We consider providing presence service for duty-cycled wireless sensor networks through a multihop approach. The presence service is to ensure automatic network monitoring by which each node would know whether the sink node is reachable or not. Towards providing such presence service, we tackle three problems: 1) efficient neighbor discovery due to not-always-awake nature of duty-cycling and the mobile environment, 2) light presence message passing from the sink node to all reachable nodes given broadcasting is expensive and difficult in an embedded duty-cycling network, and 3) automatic network monitoring if there is node failure and network partition. In our protocol, in order to save power consumption, an online node which is reachable from the sink node only book-keeps the broadcast schedule of its parent in a breadth-first-search spanning tree in order to trace the online status all along. The offline node which is not reachable from the sink node stays awake periodically based on quorum-based wakeup scheduling, and probes the beacons which may come from online nodes. The presence protocol can automatically detect link failure or network partition, and it can also automatically recover online status for each sensor node if there is a path to the sink node, which is significant for applications that are sensitive to end-to-end latency constraints. The presence protocol proposed is implemented through a layered approach so that it is independent from any specific MAC and routing protocols. We make extensive simulations in order to validate the energy efficiency and reliability of our design.     

A Differential CMOS Current-Mode Variable Gain Amplifier with Digital dB-Linear Gain Control

A novel CMOS variable gain amplifier operating on current signals with a dB-linear gain control is presented. The gain control is achieved by multiplying a digitally synthesized exponentially varying control current signal by a differential input signal in the current domain. A current amplifier at the output sets the gain to the desired level. Current-mode operation allows for a reduced supply voltage by minimizing the voltage swing at the low impedance nodes of the circuit. Multiple circuit realizations for various blocks are presented allowing for designs meeting different constraints. Experimental realization of the variable gain amplifier shows the validity of the presented approach.     

Design of Dual-Band Beam Switching Array for Adaptive Antenna Applications Using Hybrid Directional Coupler and E-Shape Slot Radiator

Wireless Personal Communications - Applications of wireless sensor networks (WSNs) are increasing tremendously to facilitate and establish a link between the physical world and information system....     

Tokens vs. Signals: On Conformance between Formal Models of Dataflow and Hardware

Designing hardware often involves several types of modeling and analysis, e.g., in order to check system correctness, to derive performance properties such as throughput, to optimize resource usages (e.g., buffer sizes), and to synthesize parts of a circuit (e.g., control logic). Working directly with low-level hardware models such as finite-state machines (FSMs) to answer such questions is often infeasible, e.g., due to state explosion. Instead, designers often use dataflow models such as SDF and CSDF, which are more abstract than FSMs, and less expensive to use since they come with more efficient analysis algorithms. However, dataflow models are only abstractions of the real hardware, and often omit critical information. This raises the question, when can one say that a certain dataflow model faithfully captures a given piece of hardware? The question is of more than simply academic interest. Indeed, as illustrated in this paper, dataflow-based analysis outcomes may sometimes be defensive (e.g., buffers that are too big) or even incorrect (e.g., buffers that are too small). To answer the question of faithfully capturing hardware using dataflow models, we develop a formal conformance relation between the heterogeneous formalisms of (1) finite-state machines with synchronous semantics, typically used to model synchronous hardware, and (2) asynchronous processes communicating via queues, used as a formal model for dataflow. The conformance relation preserves performance properties such as worst-case throughput and latency.     

Fabrication and characterization of poly(methyl methacrylate)/CaCu3Ti4O12 composites

Composites comprising Poly(Methyl Methacrylate) (PMMA) and CaCu₃Ti₄O₁₂ (CCTO) via melt mixing followed by hot pressing were fabricated. These were characterized using X‐ray diffraction, thermo gravimetric, scanning electron microscopy, and Impedance analyzer for their structural, morphology, and dielectric properties. Composites were found to have better thermal stability than that of pure PMMA. The composite, with 38 Vol % of CCTO (in PMMA), exhibited remarkably low dielectric loss at high frequencies and the low frequency relaxation is attributed to the space charge polarization/MWS effect. Theoretical models were employed to rationalize the dielectric behavior of these composites. At higher temperatures, the relaxation peak shifts to higher frequencies, due to the merging of both β and α relaxations into a single dielectric dispersion peak. The AC conductivity in the high frequency region was attributed to the electronic polarization. POLYM. ENG. SCI., 54:551–558, 2014. © 2013 Society of Plastics Engineers     

A comparative study of the effects of three galactomannans on the functionality of extruded pea–rice blends

The present study evaluated the effects of three galactomannans on the physical and nutritional characteristics, and sensory acceptability of pea–rice based extruded products, targeted as nutritional snacks. A base blend of 70:30 pea and rice fortified with guar gum (GG), locust bean gum (LBG) and fenugreek gum (FG), at 5%, 10%, 15% and 20%, was extruded at pre-determined optimum processing conditions. All three gums resulted in good expanded products. Increasing the inclusion levels of gums, however, had no effect (P > 0.05) on the degree of expansion. Addition of 5% GG and LBG reduced (P < 0.05) the hardness, while the inclusion of GG and LBG at levels higher than 5%, and all inclusion levels of FG, increased (P < 0.05) the hardness of extruded products. Relative to other treatments, FG produced extrudates that were harder and crispier. The mean scores of sensory evaluation indicated that all products containing gums up to 15% were within the acceptable range. Extrusion increased (P < 0.001) the soluble fibre content and decreased the insoluble fraction; the magnitude of these changes were greater in GG and FG. The addition of 15% gums in the pea–rice blend reduced (P < 0.05) the glycaemic index to less than 55. Overall, the data suggest that all three galactomannans could be incorporated up to 15% in a pea–rice blend to develop nutritious, organoleptically acceptable, extruded snack products with low glycaemic index.     

Yttrium aluminum garnet powders by nitrate decomposition and nitrate–urea solution combustion reactions—a comparative study

Precursors for yttrium aluminum garnet (Y₃Al₅O₁₂—YAG) were synthesized by simple decomposition of concentrated aqueous solution of nitrates and combustion of concentrated aqueous solution of nitrates with urea on a heater. The precursor formed by the former reaction was granules of agglomerated powder while that from the latter reaction was a voluminous and porous sponge-like mass. Both precursors were ground to powders and subjected to detailed thermogravimetric–differential thermal analysis and X-ray diffraction studies. The precursor from the simple decomposition of nitrates exhibited a total loss in weight of about 18% in stages (25 to 300 °C and 300 to 600 °C) accompanied by endotherms—characterized as processes of dehydration of absorbed moisture and decomposition of residual nitrates, respectively. The as formed precursor and that heated to 820 °C were amorphous. Crystallization to YAG phase occurred from an amorphous oxide characterized by an exotherm above 820 °C with no loss of weight. The precursor from nitrate–urea combustion reaction was found to exhibit a weight loss of 2.5% accompanied by a shallow endotherm in the range of 25 to 300 °C—characterized as the process of dehydration of absorbed moisture. No further weight loss or heat effect was noticed, confirming it to be chemically pure YAG. This as formed precursor was found to be crystalline YAG. The difference in chemical composition of the precursors formed by these two reactions is attributed to the difference in the actual reaction temperatures during their formation—lower reaction temperature for the endothermic decomposition of nitrates and higher reaction temperature for the exothermic combustion associated with the formation of a bright flame. The morphology of the precursor powder formed by the former reaction exhibited only cracks while that of the precursor from the latter reaction exhibited pores and voids. The precursor from the former reaction was calcined at 1100 °C to form into chemically pure YAG. Zeta potential variation with pH for the aqueous suspensions of the crystalline YAG powders from both the reactions exhibited a maximum value in the range of 40 to 50 mV around a pH of 4, indicating stability of these dispersions towards coagulation at this pH. Particle size distribution of wet ground powders (slurries with 20%, v/v, solid at a pH of 4) showed that the powder from combustion reaction could be formed into a finer size than that from simple nitrate decomposition, indicating the agglomerates of combustion reaction were softer.