Long-term strength and durability parameters of lightweight concrete in hot regime: importance of initial curing

The paper presents results on strength development and durability of 35 and 50 MPa total lightweight concretes exposed to hot marine exposure conditions for a period of 7 years. An initial water curing of 7 days and subsequent seaside exposure was found more beneficial for the strength development of lightweight concrete. One day of initial curing and subsequent seaside exposure was not very conducive for the strength development. A marginal degradation in both the stiffness and the modulus of rupture of the concretes over the exposure period was observed. Likewise, the water penetrability of the two mixtures, for all the three initial curing regimes, increased over a period of 7 years. This establishes that the compressive strength of concrete is not synonymous with its durability. Overall, 3–7 days of initial water curing seems most desirable to enhance the durability of concrete exposed to hot salty marine exposure conditions.     

Heterogeneous photocatalysed degradation of 4-chlorophenoxyacetic acid in aqueous suspensions

The photocatalysed degradation of 4-chlorophenoxyacetic acid (4-CPA, 1) has been investigated in aqueous suspensions of titanium dioxide under a variety of conditions. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic analysis technique and depletion in total organic carbon (TOC) content as a function of irradiation time. The influence of various parameters such as, different types of titanium dioxide (TiO2) powders, pH, catalyst and substrate concentrations, and in the presence of electron acceptor such as hydrogen peroxide (H(2)O(2)) besides molecular oxygen has been investigated. The effects of these parameters on the degradation rates were found to be significant. The volatile degradation product 4-chlorophenol was analyzed by GC-MS technique and probable pathways for the formation of product has been proposed.     

Thermal management of power electronics modules packaged by a stacked-plate technique

The research presented in this paper is part of a multidisciplinary research program of the Center for Power Electronics Systems at Virginia Tech. The program supported by the Office of Naval Research focuses on the development of innovative technologies for packaging power electronics building blocks. The primary objective of this research is to improve package performance and reliability through thermal management, i.e., reducing device temperatures for a given power level. The task of thermal management involves considering trade-offs in the electrical design, package layout and geometry, materials selection and processing, manufacturing feasibility, and production cost. Based on the electrical design of a simple building block, samples of packaged modules, rated at 600 V and 3.3 kW, were fabricated using a stacked-plate technique, termed metal posts interconnected parallel plate structure (MPIPPS). The MPIPPS technique allows the power devices to be interconnected between two direct-bond copper substrates via the use of metal posts. Thermal modeling results on the MPIPPS packaged modules indicate that the new packaging technique offers a superior thermal management means for packaging power electronics modules.     

An innovative technique for packaging power electronic buildingblocks using metal posts interconnected parallel plate structures

Power electronics building blocks (PEBBs) are envisioned as integrated power modules consisting of power semiconductor devices, power integrated circuits, sensors, and protection circuits for a wide range of power electronics applications, such as inverters for motor drives and converters for power processing equipment. At the Center for Power Electronics Systems, we developed a topology for a basic building block-a two-switch two-diode half-bridge converter in totem-pole configuration with built-in gate-driver and protection circuitry, fiber-optic receiver/transmitter interface, and soft-switching capability. Based on the topology, a series of prototype modules, with 600 V, 3.3 kW rating, were fabricated using an innovative packaging technique developed for the program-metal posts interconnected parallel plate structure (MPIPPS). This new packaging technique uses direct attachment of bulk copper, not wire-bonding of fine aluminum wires, for interconnecting power devices. Electrical performance data of the packaged devices show that an air-cooled 15 kW inverter, operating from 400 V dc bus with 20 kHz switching frequency can be constructed by integrating three prototype modules, which is almost double what could be achieved with commercially packaged devices of the same rating     

Fluorinated siloxane amine oligomers

Fluorine‐containing siloxane oligomers were made from bis(aminopropyl)tetramethyldisiloxane and trimethyltris(trifluoropropyl)cyclotrisiloxane. These materials were characterized by IR spectroscopy, size exclusion chromatography, nonaqueous colorimetric end group titration, and ¹H‐NMR. The end groups of one oligomer were chemically modified for an increased NMR signal for molecular weight determination. The cyclic trimeric siloxane starting material was additionally studied via ¹³C‐, ²⁹Si‐, and ¹⁹F‐NMR. Two forms of it were used: a white solid obtained at room temperature, and a colorless liquid isolated at low temperature. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1315–1320, 2000     

Oral Squamous Cell Carcinoma Contributes to Differentiation of Monocyte-Derived Tumor-Associated Macrophages via PAI-1 and IL-8 Production

Tumor-associated macrophages (TAMs) promote cancer cell proliferation and metastasis, as well as anti-tumor immune suppression. Recent studies have shown that tumors enhance the recruitment and differentiation of TAMs, but the detailed mechanisms have not been clarified. We thus examined the influence of cancer cells on the differentiation of monocytes to TAM subsets, including CD163⁺, CD204⁺, and CD206⁺ cells, in oral squamous cell carcinoma (OSCC) using immunohistochemistry, flow cytometry, and a cytokine array. Furthermore, we investigated the effect of OSCC cells (HSC-2, SQUU-A, and SQUU-B cells) on the differentiation of purified CD14⁺ cells to TAM subsets. The localization patterns of CD163⁺, CD204⁺, and CD206⁺ in OSCC sections were quite different. The expression of CD206 on CD14⁺ cells was significantly increased after the co-culture with OSCC cell lines, while the expressions of CD163 and CD204 on CD14⁺ cells showed no change. High concentrations of plasminogen activator inhibitor-1 (PAI-1) and interleukin-8 (IL-8) were detected in the conditioned medium of OSCC cell lines. PAI-1 and IL-8 stimulated CD14⁺ cells to express CD206. Moreover, there were positive correlations among the numbers of CD206⁺, PAI-1⁺, and IL-8⁺ cells in OSCC sections. These results suggest that PAI-1 and IL-8 produced by OSCC contribute to the differentiation of monocytes to CD206⁺ TAMs.     

An electrochemically reduced graphene oxide-based electrochemical immunosensing platform for ultrasensitive antigen detection

We present an electrochemically reduced graphene oxide (ERGO)-based electrochemical immunosensing platform for the ultrasensitive detection of an antigen by the sandwich enzyme-linked immunosorbent assay (ELISA) protocol. Graphene oxide (GO) sheets were initially deposited on the amine-terminated benzenediazonium-modified indiun tin oxide (ITO) surfaces through both electrostatic and π-π interactions between the modified surfaces and GO. This deposition was followed by the electrochemical reduction of graphene oxide (GO) for preparing ERGO-modified ITO surfaces. These surfaces were then coated with an N-acryloxysuccinimide-activated amphiphilic polymer, poly(BMA-r-PEGMA-r-NAS), through π-π stacking interactions between the benzene ring tethered to the polymer and ERGO. After covalent immobilization of a primary antibody on the polymer-modified surfaces, sandwich ELISA was carried out for the detection of an antigen by use of a horseradish peroxidase (HRP)-labeled secondary antibody. Under the optimized experimental conditions, the developed electrochemical immunosensor exhibited a linear response over a wide range of antigen concentrations with a very low limit of detection (ca. 100 fg/mL, which corresponds to ca. 700 aM). The high sensitivity of the electrochemical immunosensor may be attributed not only to the enhanced electrocatalytic activity owing to ERGO but also to the minimized background current owing to the reduced nonspecific binding of proteins.     

Effects of argon and oxygen flow rate on water vapor barrier properties of silicon oxide coatings deposited on polyethylene terephthalate by plasma enhanced chemical vapor deposition

Plasma polymer coatings were deposited from hexamethyldisiloxane on polyethylene terephthalate (PET) substrates while varying the operating conditions, such as the Ar and O₂ flow rates, at a fixed radio frequency power of 300 W. The water vapor transmission rate (WVTR) of the untreated PET was 54.56 g/m²/day and was decreased after depositing the silicon oxide (SiO_x) coatings. The minimum WVTR, 0.47 g/m²/day, was observed at Ar and O₂ flow rates of 4 and 20 sccm, respectively, with a coating thickness of 415.44 nm. The intensity of the peaks for the Si-O-Si bending at 800-820 cm^− 1 and Si-O-Si stretching at 1000-1150 cm^− 1 varied depending on the Ar and O₂ flow rates. The contact angle of the SiO_x coated PET increased as the Ar flow rate was increased from 2 to 8 sccm at a fixed O₂ flow rate of 20 sccm. It decreased gradually as the oxygen flow rate increased from 12 to 28 sccm at a fixed Ar carrier gas flow rate. The examination by atomic force microscopy revealed a correlation of the SiO_x morphology and the water vapor barrier performance with the Ar and O₂ flow rates. The roughness of the deposited coatings increased when either the O₂ or Ar flow rate was increased.     

Stress-dependent thermal relaxation effects in micro-mechanical resonators

Thermal relaxation is a key factor in determining the quality factor of micro and nano resonators, which controls the energy dissipation through the coupling of the mechanical and thermal domains. While the literature contains approximate, exact and computational models for quantitative analysis of thermo-elastic coupling, very few techniques are available to ‘tune’ it without changing the material, geometry or operating conditions. In this paper, we develop an analytical model that considers a pre-stress in a flexural resonator to modify the thermal relaxation time and thus increase the quality factor. The effects of length-scale, pre-stress and geometry on the quality factor have been analyzed. The model predicts that significant improvement in terms of dimensionless quality factors is possible by tuning the pre-stress.