Biological and technical variables affecting immunoassay recovery of cytokines from human serum and simulated vaginal fluid: a multicenter study

The increase of proinflammatory cytokines in vaginal secretions may serve as a surrogate marker of unwanted inflammatory reaction to microbicide products topically applied for the prevention of sexually transmitted diseases, including HIV-1. Interleukin (IL)-1beta and IL-6 have been proposed as indicators of inflammation and increased risk of HIV-1 transmission; however, the lack of information regarding detection platforms optimal for vaginal fluids and interlaboratory variation limit their use for microbicide evaluation and other clinical applications. This study examines fluid matrix variants relevant to vaginal sampling techniques and proposes a model for interlaboratory comparisons across current cytokine detection technologies. IL-1beta and IL-6 standards were measured by 12 laboratories in four countries, using 14 immunoassays and four detection platforms based on absorbance, chemiluminescence, electrochemiluminescence, and fluorescence. International reference preparations of cytokines with defined biological activity were spiked into (1) a defined medium simulating the composition of human vaginal fluid at pH 4.5 and 7.2, (2) physiologic salt solutions (phosphate-buffered saline and saline) commonly used for vaginal lavage sampling in clinical studies of cytokines, and (3) human blood serum. Assays were assessed for reproducibility, linearity, accuracy, and significantly detectable fold difference in cytokine level. Factors with significant impact on cytokine recovery were determined by Kruskal-Wallis analysis of variance with Dunn's multiple comparison test and multiple regression models. All assays showed acceptable intra-assay reproducibility; however, most were associated with significant interlaboratory variation. The smallest reliably detectable cytokine differences ( P < 0.05) derived from pooled interlaboratory data varied from 1.5- to 26-fold depending on assay, cytokine, and matrix type. IL-6 but not IL-1beta determinations were lower in both saline and phosphate-buffered saline as compared to vaginal fluid matrix, with no significant effect of pH. The (electro)chemiluminescence-based assays were most discriminative and consistently detected <2-fold differences within each matrix type. The Luminex-based assays were less discriminative with lower reproducibility between laboratories. These results suggest the need for uniform vaginal sampling techniques and a better understanding of immunoassay platform differences and cross-validation before the biological significance of cytokine variations can be validated in clinical trials. This investigation provides the first standardized analytic approach for assessing differences in mucosal cytokine levels and may improve strategies for monitoring immune responses at the vaginal mucosal interface.     

Analysis of reliability and optimization of ESD protection devices supported by modeling and simulation

An analysis of electrostatic discharge (ESD) protection structures supported by advanced 2-D mixed mode electro-thermal device and circuit simulation with calibrated electro-physical models to increase the reliability of protected IC’s is presented. The critical temperature as a criterion of device destruction is defined and experimentally verified. Numerical simulation and visualization of the internal electro-physical properties of the analyzed structures during a very short ESD pulse considerably improved the understanding of their physical behavior and contributes to a proper design and optimization of doping and geometry of the analyzed ESD protection devices. The analyzed devices are designed as protection against Human Body Model (HBM) and International Electromechanical Commission model (IEC) 61000-4-2 with very high robustness. The obtained results are shown on two examples. Modification of the device layout by splitting the cathode contact of the ESD diode into two parts allowing area reduction with improved electrical characteristics is the subject of the first example. The influence of doping fluctuations on the device robustness is presented in the second example. Different triggering and failure mechanisms of the diode and transistor structure during HBM and IEC pulse are presented.     

Modeling of CrSi2-Si and MoSi2-Si Schottkybarrier contacts

Forward and reverse l-V characteristics measured on CrSi₂ -Si and MoSi₂Si Schottky structures were compared with simulated ones. While the CrSi₂-Si shows the typical non-ideal I-V characteristics of a reverse biased Schottky contact, the MoSi₂-Si exhibit the nearly ideal forward and reverse I-V characteristics. The model for numerical simulation involves the clearly defined boundary conditions which combines the thermionic-emission/diffusion theory with the generation recombination theory and has the closed form     

Gate leakage current in GaN-based mesa- and planar-type heterostructure field-effect transistors

The excessive gate leakage current of the planar- and mesa-type InAlN/GaN heterostructure field-effect transistors (HFETs) is evaluated. It is found that the gate current of the mesa-type HFETs is higher than that of the planar devices, particularly at low biases. Analyses of the gate current considering different transport mechanisms yielded identical thermionic currents (i.e., an identical Schottky barrier height) but a significantly higher leakage component in the mesa-type HFETs than in the planar devices. This additional current component observed in the mesa-type devices shows a nearly ohmic behavior. Mapping by the electron-beam induced current technique confirms an enhanced current located under the expanded gate contact and on the part of the mesa-sidewall, where the gate contact is placed. Two-dimensional simulation of the device structure shows that considerable part of the gate leakage current flows through the GaN buffer layer. These results underline the importance of a proper design of the device structure and layout (i.e., the use of planar structure with device insulation prepared by ion implantation rather than by mesa technique), and of the preparation of the GaN buffer (it should be semi-insulating) in order to fabricate reliable, low leakage current GaN-based HFETs.     

Temperature dependence of InAs/GaAs quantum dots solar photovoltaic devices

This paper presents the temperature dependence measurements characterisation of several InAs/GaAs quantum dots （QDs） solar cell devices. The devices with cylindrical geometry were fabricated and characterised on-wafer under 20 suns in a temperature range from 300°K to 430°K. The temperature dependence parameters such as open circuit voltage, short circuit density current, fill factor and efficiency are studied in detail. The increase of temperature produces an enhancement of the short circuit current. However, the open circuit voltage is degraded because the temperature increases the recombination phenomena involved, as well as reducing the effective band gap of the semiconductor.     

High-temperature performance of AlGaN/GaN HFETs and MOSHFETs

Performance of AlGaN/GaN HFETs and Al₂O₃/AlGaN/GaN MOSHFETs at the elevated temperatures up to 425 °C was investigated. Static output and transfer characteristics were measured and the saturation drain current, the peak transconductance and the series conductance as a function of temperature were evaluated. All these characteristic features of HFETs and MOSHFETs decreased with increased temperature. At 425 °C the devices exhibited ∼30% of their saturation drain current, peak transconductance and series conductance evaluated at room temperature. The device performance at elevated temperatures follows exactly the T^x dependence with a power x = −1.5. This indicates that the temperature dependence of the mobility of channel electrons due to phonon scattering is the predominant effect describing high-temperature performance of AlGaN/GaN HFETs and MOSHFETs.     

Unified tunnelling-diffusion theory for Schottky and very thin MOS structures

We derive general formulae for calculating the transport of free charge carriers in a MOS structure with a thin insulating layer. In particular, we obtain relationships for boundary concentrations of free charge carriers on the insulator–semiconductor interface and for the current densities flowing through the MOS structure. Our direct tunnelling-diffusion approach makes the well known thermionic emission–diffusion theory for the Schottky interface applicable also to metal–insulator–semiconductor barriers with a very thin insulator layer. We demonstrate how direct tunnelling through the insulating layer and drift–diffusion of free charge carriers in the semiconductor affect the I–V and C–V curves and the boundary concentrations needed to numerically solve the continuity equations.     

Identification of the crystalline-phases in thin pentacene layers by Raman spectroscopy

We investigated the different crystallographic phases in thin pentacene layers by the micro-Raman spectroscopy. For the first time we have determined the presence of orthorhombic, thin film and triclinic bulk phase in thin pentacene layers by the micro-Raman polarization spectroscopy, which were confirmed by XRD measurements.