Synthesis and dielectric properties of polystyrene‐clay nanocomposite materials

Polystyrene‐clay nanocomposite (PsCN) materials were synthesized and their properties of crystallinity, thermal behavior, and dielectric characteristics were investigated. A polymerizable cationic surfactant, [2‐(dimethylamino)ethyl]triphenylphonium bromide, was used for the intercalation of montmorillonite (MMT). The organophilic MMT was prepared by Na⁺‐exchanged MMT and ammonium cations of a cationic surfactant in an aqueous medium. Organophilic styrene monomers were intercalated into the interlayer regions of organophilic clay hosts followed by a free‐radical polymerization. Exfoliation to 2 wt % MMT in the polystyrene (PS) matrix was achieved as revealed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Thermal properties by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were also studied. The dielectric properties of PsCNs in the form of film with clay loading from 1.0 to 5.0 wt % were measured under frequencies of 100 Hz–1 MHz at 25–70°C. A decreased dielectric constant and low dielectric loss were observed for PsCN materials. The dielectric response at low frequency that originated from dipole orientation was suppressed due to the intercalation of clay materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1368–1373, 2004     

A performance criterion for the depth estimation with application to robot visual servo control

This article deals with the depth observability problem of a robot visual system with a moving camera. In the visual system, the unknown depth of a feature point is estimated from the input of the camera velocity and the output of the image of the feature point. Although it is well known that the linear velocity of the camera must satisfy some constraints for successful depth estimation, this proposes a criterion to measure the performance of the depth estimation, which is a heuristic extension from an estimation result of a linear system. This performance criterion depends on both the image position and the linear velocity of the camera. Some simulation and experiment examples demonstrate and verify the proposed performance criterion. Furthermore, this criterion is used to develop a new visual servo control scheme that has good performance in both the depth estimation and the visual control. This control scheme is also verified by a simulation example. © 2001 John Wiley & Sons, Inc.     

Analysis of room temperature magnetic regenerative refrigeration

Results of a room temperature magnetic refrigeration test bed and an analysis using a computational model are presented. A detailed demonstration of the four sequential processes in the transient magnetocaloric regeneration process of a magnetic material is presented. The temperature profile during the transient approach to steady state operation was measured in detail. A 5 °C evolution of the difference of temperature between the hot end and the cold end of the magnetocaloric bed due to regeneration is reported. A model is developed for the heat transfer and fluid mechanics of the four sequential processes in each cycle of thermal wave propagation in the regenerative bed combined with the magnetocaloric effect. The basic equations that can be used in simulation of magnetic refrigeration systems are derived and the design parameters are discussed.     

Mathematics for reasoning about loop functions

The criticality of modern software applications, the pervasiveness of malicious code concerns, the emergence of third-party software development, and the preponderance of program inspection as a quality assurance method all place a great premium on the ability to analyze programs and derive their function in all circumstances of use and all its functional detail. For C-like programming languages, one of the most challenging tasks in this endeavor is the derivation of loop functions. In this paper, we outline the premises of our approach to this problem, present some mathematical results, and discuss how these results can be used as a basis for building an automated tool that derives the function of while loops under some conditions.     

A simpler analysis of Burrows–Wheeler-based compression

In this paper, we present a new technique for worst-case analysis of compression algorithms which are based on the Burrows–Wheeler Transform. We mainly deal with the algorithm proposed by Burrows and Wheeler in their first paper on the subject [M. Burrows, D.J. Wheeler, A block sorting lossless data compression algorithm, Technical Report 124, Digital Equipment Corporation, Palo Alto, California, 1994], called bw0. This algorithm consists of the following three essential steps: (1) Obtain the Burrows–Wheeler Transform of the text, (2) Convert the transform into a sequence of integers using the move-to-front algorithm, (3) Encode the integers using Arithmetic code or any order-0 encoding (possibly with run-length encoding).     

Differential cytokine regulation of natural killer cell-mediated necrotic and apoptotic cytotoxicity

Natural killer (NK) cells can kill target cells by either necrotic or apoptotic mechanisms. Using the 51Cr-release assay to measure necrotic death of target cells, neonatal NK cells had low NK activity (K562 targets) and high lymphokine-activated killer (LAK) activity (Daudi targets) compared with adult cells, as has been previously reported. Using a 125I-deoxyuridine (125I-UdR) release assay, cord cells were shown to also have higher apoptotic LAK activity against YAC-1 target cells. Interleukin-4 (IL-4) inhibited interleukin-2 (IL-2)-induced necrotic killing of target cells by adult effectors but had no such inhibitory effect on cord cells. In contrast, IL-4 inhibited both adult and cord LAK cytotoxicity of YAC-1 target cells by apoptotic mechanisms with higher suppression observed in cord cell preparations. Using a colorimetric substrate conversion assay, IL-2 induced higher, and IL-4 had a more significant suppressive effect on, cord cell granzyme B enzyme activity compared with adult cells, paralleling apoptosis cytotoxicity data. Co-culture of either adult or cord LAK cells with IL-4 had a similar inhibitory effect on granzyme B protein expression, as detected by Western blotting. In contrast, IL-4 did not inhibit perforin expression, thereby defining IL-4 as a cytokine that can differentially regulate the NK cell-mediated cytotoxicity processes of apoptosis and necrosis. The differential sensitivity of cord cells to cytokine regulation of cytotoxicity may also have implications for cord blood transplantations, as NK cells are known to function as an effector cell in both graft-versus-host disease and in the graft-versus-leukaemia phenomena.     

Digital simulation of flow patterns in the czochralski crystal-pulling process

A procedure is described for the numerical solution of the time-dependent equations governing the flow in a crystal-growth crucible. The molten crystal material is taken to be a Newtonian fluid with constant viscosity. The Boussinesq approximation is employed, i.e. compressibility is neglected except insofar as thermal expansion modifies the gravitational body force. Crucible rotation is the main driving force, but a series of numerical experiments suggests that buoyancy effects can modify appreciably the impurity-blending estimates obtained from an isothermal study.     

Economic potential of bioremediation using immobilized microalgae-based microbial fuel cells

Clean Technologies and Environmental Policy - The cathodic microalgae-based MFC converts the nutrients within wastewater and produces oxygen as oxygen supply for cathodic reactions, leading to the...     

Significant decreased dielectric constant and loss of polystyrene–clay nanocomposite materials by using long‐chain intercalation agent

Polystyrene–clay nanocomposite (PsCN) materials have been prepared by a free radical polymerization process. Montmorillonite (MMT), modified by two different organics, was investigated: one contains a short chain and three benzyl groups on the ammonium ion (DAETPB), while the other contains a long chain (HTAC). The organic modification determines the extent of exfoliation or intercalation of the materials. Exfoliation is more likely to occur using HTAC, as then the gallery of clay has been opened more due to the long chain structure. Exfoliation of MMT in polystyrene (PS) matrix was revealed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were employed to confirm the increased thermal stability of these PsCN materials. Dielectric properties of polystyrene‐clay nanocomposites, in the form of film with clay loading from 1.0 to 5.0 wt %, were measured under frequencies of 100 Hz～1 MHz at 25～70°C. Decreased dielectric constant and low dielectric loss were observed for PsCN materials. Especially, the decrease of dielectric constant was found to be related to the extent of exfoliation of clay. It is recognized that the confinement effect of clay results in the suppression of the dielectric response of the nanocomposite materials at low frequency. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2402–2410, 2004     

Effect of Magnetic Field Dynamics on the Copper‐Constantan Thermocouple Performance

Abstract

This paper presents some results of experimental research addressing the influence of magnetic field dynamics on the copper‐constantan thermocouple performance. There are challenges in measuring temperature by thermocouples in a time‐dependent magnetic field. Although there is considerable experience on the effect of a static magnetic field, there is a lack of awareness of the outcome of a varying field on thermocouple performance. We measured the accuracy of the thermocouple response in an alternating magnetic field for various operational parameters: frequency of the magnetic field, geometry, and length of the thermocouple wire in the field, and magnetic field strength. The effect of each of the operational parameters is discussed. Test results of temperature profile measure by a copper‐constantan thermocouple in a varying magnetic field system that was used in a room temperature magnetic refrigeration test bed are demonstrated.