Thermal modeling of a shell and tube type evaporator with R404A

In this study, the two‐phase heat‐transfer coefficient of R404A inside horizontal tubes is analyzed through the evaporator's overall heat‐transfer coefficient, obtained using the effectiveness—Number of Transfer Units thermal design approach. This method constitutes an approximation that can be used in the evaporator's thermal design with an attempt to break some of the initial assumptions established in the heat exchanger thermal design method development. For the analysis, an experimental refrigeration system that is commercially available is built up with a shell and tube evaporator. All the experiments are performed at different evaporator pressures (270, 570 kPa), evaporator temperatures (?20, 0°C) and cooling water temperatures (20, 40°C). For these parameters, overall heat‐transfer coefficient of the heat exchanger is found in the range of 0.05–0.35 kW °C^?1. Copyright © 2010 John Wiley & Sons, Ltd.     

Distributed collaborative camera actuation for redundant data elimination in wireless multimedia sensor networks

Given the high cost of processing and communicating the multimedia data in wireless multimedia sensor networks (WMSNs), it is important to reduce possible data redundancy. Therefore, camera sensors should only be actuated when an event is detected within their vicinity. In the meantime, the coverage of the event should not be compromised. In this paper, we propose a low-cost distributed actuation scheme which strives to turn on the least number of cameras to avoid possible redundancy in the multimedia data while still providing the necessary event coverage. The basic idea of this scheme is the collaboration of camera sensors that have heard from scalar sensors about an occurring event to minimize the possible coverage overlaps. This is done by either counting the number of scalar sensors or determining the event boundaries with scalar sensors. Through simulation, we show how the distributed scheme performs in terms of coverage under several centralized and random deployment schemes. We also compare the performance with the case when all the cameras in the vicinity are actuated and when blockages in the region exist.     

Effect of Ice Sheet on Stochastic Response of Offshore Wind Turbine–Seawater–Soil Interaction Systems Subjected to Random Seismic Excitation

To investigate the effect of the presence of surrounding ice sheet on the stochastic response of offshore wind turbines subjected to random seismic excitation, this research uses a three-dimensional, numerical, finite-element model that includes viscous boundaries. The model of the ice–seawater–offshore wind turbine–soil interaction system uses the Lagrangian fluid (displacement-based) and solid-quadrilateral-isoparametric finite elements. Random seismic excitation from a filtered white-noise model and applied to each support point of the three-dimensional finite-element model of the coupled interaction system provides the experimental environment. A parametric study examines the effects of both the presence of and variation in mechanical and geometric properties of the surrounding ice sheet on the stochastic response of offshore wind turbines. The investigation also includes the effect of the wind turbine’s wall thickness in relation to the ice sheet on the stochastic seismic response of the coupled interaction system.     

Modification of ITO surface using aromatic small molecules with carboxylic acid groups for OLED applications

4-[(3-Methylphenyl)(phenyl)amino]benzoic acid (MPPBA) was synthesized in order to facilitate the hole-injection in Organic Light Emitting Diodes (OLED). MPPBA was applied to form self-assembled monolayer (SAM) on indium tin oxide (ITO) anode to align energy-level at the interface between organic semiconductor material (TPD) and inorganic anode (ITO) in OLED devices. The modified surface was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). KPFM was used to measure the surface potential and work function between the tip and the ITO surface modified by SAM technique using MPPBA. The OLED devices (ITO/MPPBA/TPD/Alq₃/Al) fabricated with SAM-modified ITO substrates showed lower turn-on voltages and enhanced diode current compare to the OLED devices fabricated with bare ITO substrates.     

Ferrimagnetic Skyrmions in Topological Insulator/Ferrimagnet Heterostructures

Magnetic skyrmions are topologically nontrivial chiral spin textures that have potential applications in next-generation energy-efficient and high-density spintronic devices. In general, the chiral spins of skyrmions are stabilized by the noncollinear Dzyaloshinskii–Moriya interaction (DMI), originating from the inversion symmetry breaking combined with the strong spin–orbit coupling (SOC). Here, the strong SOC from topological insulators (TIs) is utilized to provide a large interfacial DMI in TI/ferrimagnet heterostructures at room temperature, resulting in small-size (radius ≈ 100 nm) skyrmions in the adjacent ferrimagnet. Antiferromagnetically coupled skyrmion sublattices are observed in the ferrimagnet by element-resolved scanning transmission X-ray microscopy, showing the potential of a vanishing skyrmion Hall effect and ultrafast skyrmion dynamics. The line-scan spin profile of the single skyrmion shows a Néel-type domain wall structure and a 120 nm size of the 180° domain wall. This work demonstrates the sizable DMI and small skyrmions in TI-based heterostructures with great promise for low-energy spintronic devices.     

Ab initio study of structural,elastic and vibrational properties of praseodymium chalcogenides

The plane-wave pseudopotential approach to the density-functional theory within the GGA approximation implemented in Vienna Ab-initio Simulation Package (VASP) code have been used to calculate structural, elastic and lattice dynamical properties of praseodymium chalcogenides: PrS, PrSe and PrTe. The structural properties are performed in five different crystal structures: NaCl (space group Fm3m(225)), CsCl (space group Pm3m(221)), ZB (space group F43m(216)), WC (space group P6m2(187)) and CuAu (P4/mmm(123)). Our results showed that these chalcogenides are stable in NaCl phase which are in agreement with the experimental works. The phonon dispersion curves are showed that the gap between the optic and acoustic branches decreases on going from PrS to PrTe. We have also estimated some thermodynamical properties such as entropy and heat capacity at the temperature range 0–1000 K.     

A survey of visual sensor network platforms

Recent developments in low-cost CMOS cameras have created the opportunity of bringing imaging capabilities to sensor networks. Various visual sensor platforms have been developed with the aim of integrating visual data to wireless sensor applications. The objective of this article is to survey current visual sensor platforms according to in-network processing and compression/coding techniques together with their targeted applications. Characteristics of these platforms such as level of integration, data processing hardware, energy dissipation, radios and operating systems are also explored and discussed.     

Processes and apparatus developments in industrial waterjet applications

This paper is based on an abrasive waterjet cutting process that helps solve problems in processing of modern hard-to-cut materials, enabling wider industrial application. A detailed explanation of the recent developments in the main components of abrasive waterjet systems are given. Factors such as water pressure, grain diameters of abrasive feed rate, and traverse speed influencing surface roughness and depth of cut are studied using experimental data. Taking account of industrial applications, advantages–disadvantages, and limitations of the process are assessed.     

Thickness-dependent glass transition temperature of hydroxyethyl cellulose thin films based on dielectric properties

Hydroxyethyl cellulose (HEC) thin films with a molecular weight of 720,000 g/mol deposited by thermal evaporation in a thickness range of 250, 500, and 750 nm were measured in a frequency range of 1–10⁵ Hz and a temperature range of 233–373 K for dielectric characterization with increments of 10 K. Dielectric results were used to derive and evaluate the glass transition temperature and ductility, which are essential parameters for structural analysis. Results showed that the thickness of HEC thin films was an effective parameter on dielectric and structural properties. Because of the increasing thickness, the dielectric constant has values between 22 and 143 at 1 kHz, and glass transition temperature and ductility change between 211–175 K and 15–20, respectively. Based on the literature and the compatible results, the main effect of these variations could be dead layers and voids in structure. The effect of the dead layer gave an important idea about the adjustability of mechanical properties of HEC thin films depending on the thickness. In this way, it would be possible to use these thin films deposited from HEC with 720,000 g/mol molecular weight, especially in drug delivery, electrophoresis technologies, biomedical devices, and coverage applications.