1200 V 4H-SiC Bipolar Junction Transistors with A Record β of 70

A common current gain of 70 has been achieved in 4H-SiC bipolar junction transistors (BJTs) at room temperature, which is the highest among those reported. BJTs having an active area of 4 mm × 4 mm exhibit a specific on-resistance of 6.3 mΩ cm² at 25°C, which increases to 17.4 mΩ cm² at 250°C. BV_CEO (the breakdown voltage from collector to emitter with open base) and BV_CBO (the breakdown voltage from collector to base with open emitter) of 1200 V were observed at <5 μA leakage currents at all temperatures up to 250°C. Dynamic characteristics were measured using the IXYS RF/Directed Energy IXDD415 gate driver evaluation board to drive the BJT. A collector current (I _C) rise time at turn-on of 32 ns was measured with a 1.6 A gate current provided to support the collector current of 63 A. An I _C fall time at turn-off of 16 ns was achieved.     

Design of a high-speed CMOS multi-bit quantizer for continuous-time Delta-Sigma Modulator applications

Digital front-end receivers realize direct conversion of an analog signal to digital form at intermediate frequencies (IF), simplifying the overall system design and alleviating the problems associated with IF mixers. The trend is to eliminate any RF/analog mixers and digitize the RF signal as near as possible to the antenna. In order to digitize directly the analog input signal, a high dynamic-range and high-speed ADC is needed. Continuous-Time Bandpass Delta-Sigma Modulator can meet these requirements, using high-performance multi-bit quantizers. This article presents the design of a high-speed CMOS Analog-to-Digital Converter (ADC) which can be used as a quantizer in Continuous-Time Delta-Sigma Modulator. It is designed in a 130 nm CMOS technology from STMicroelectronics. The main features of the ADC are 3-bit resolution with 4 GHz sampling rate in a 0.8–2 GHz bandwidth.     

Effects of substrate shape, curvature and roughness on thin heteroepitaxial films of Pt on Au(1 1 1)

The growth of thin (1–10 nm) films of Pt on Au(1 1 1) was studied in order to understand and clarify differences in growth mode observed in ultra-high vacuum (UHV) studies and in electrochemical deposition studies. It was found that on flat Au(1 1 1), Pt grows in a layer-by-layer growth mode, but if the gold substrate is exposed to an acidic environment prior to Pt deposition, then the substrate becomes nanoscopically rough (islanded) and Pt growth follows a pseudo-Stranski–Krastanov (SK) growth mode in which an initially thin wetting layer becomes rougher with increasing film thickness. An analysis of curvature effects on epitaxial growth mode shows that thermodynamic curvature effects involving surface stress are negligible for the Pt/Au(1 1 1) system. Rather, the apparent SK growth is linked to kinetic effects associated with inhomogeneous in-plane elastic relaxation of Pt films on rough surfaces that drive Pt atoms from pits to the tops of islands in the early stages of growth. Implications for the control of epitaxial film roughness are discussed.     

Application of cellulose acetate butyrate-based membrane for osmotic drug delivery

The release rate of drugs from an OROS^® is controlled by semipermeable membranes composed typically of cellulose acetate (CA) with various flux enhancers. Cellulose acetate butyrate (CAB) was identified as a viable alternative. The CAB membrane matched the CA membrane in robustness but had superior drying properties, offering particular advantages for thermolabile formulations. Studies were conducted to characterize CAB membrane properties with respect to performance of OROS^® systems. Four different membrane formulations with varying plasticizer type and concentration were investigated. The CAB based membranes exhibited superior drying characteristics and similar functionality to the CA:polyethylene glycol (PEG) membranes used as a control. A linear relationship was observed between the level of flux enhancer and release rate. The stability of the membrane was evaluated based on release profiles after system storage at various conditions. The CAB membranes appeared to have stability comparable to the standard CA membrane. A linear relationship between membrane weight and release rate as well as the time required to release 90% of a drug from the system [T₉₀] for a model formulation was observed. In conclusion, the newly identified alternative membrane composition allows for the use of thinner membranes, thereby reducing cost of goods, coating time and, most importantly, membrane drying time.     

Many-body interaction analysis: algorithm development and application to large molecular clusters

A completely automated algorithm for performing many-body interaction energy analysis of clusters (MBAC) [M. J. Elrodt and R. J. Saykally, Chem. Rev. 94, 1975 (1994); S. S. Xantheas, J. Chem. Phys. 104, 8821 (1996)] at restricted Hartree-Fock (RHF)/MA Plesset 2nd order perturbation theory (MP2)/density functional theory (DFT) level of theory is reported. Use of superior guess density matrices (DM's) for smaller fragments generated from DM of the parent system and elimination of energetically insignificant higher-body combinations, leads to a more efficient performance (speed-up up to 2) compared to the conventional procedure. MBAC approach has been tested out on several large-sized weakly bound molecular clusters such as (H(2)O)(n), n=8, 12, 16, 20 and hydrated clusters of amides and aldehydes. The MBAC results indicate that the amides interact more strongly with water than aldehydes in these clusters. It also reconfirms minimization of the basis set superposition error for large cluster on using superior quality basis set. In case of larger weakly bound clusters, the contributions higher than four body are found to be repulsive in nature and smaller in magnitude. The reason for this may be attributed to the increased random orientations of the interacting molecules separated from each other by large distances.     

Effects of conformational stability and geometry of guanidinium display on cell entry by beta-peptides

We have used our ability to control beta-peptide secondary structure in order to explore the effects of conformational stability and geometry of guanidinium display on cell entry. Both of these factors affect the rate and relative amount of beta-peptide accumulation in the cytoplasm and nucleus of live HeLa cells. These beta-peptides do not show significant differences in cell surface binding, implying that structure and guanidinium display are important in a later step in cell entry than initial surface binding.     

Mono- and binuclear cyclometallated palladium(II) complexes containing bridging (N,O-) and terminal (N-) imidate ligands: air stable, thermally robust and recyclable catalysts for cross-coupling processes

Novel dinuclear cyclometallated palladium complexes [{Pd(mu-NCO)(C circumflex accent N)}(2)], containing asymmetric imidato -NCO- bridging units have been synthesised [C circumflex accent N = 7,8-benzoquinolyl; -NCO- = succinimidate (1c), phthalimidate (1a-3a) or maleimidate (3c)]. The reaction of these complexes, and the previously reported analogous imidate precursors containing a phenylazophenyl (1a-3a) or 2-pyridylphenyl (1b-3b) backbone, with tertiary phosphines provides novel mononuclear N-bonded imidate derivatives of the general formula [Pd(C circumflex accent N)(imidate)(L)][L = PPh(3), P(4-F-C(6)H(4))(3) or P(4-MeO-C(6)H(4))(3)]. The single crystal structures of [Pd(azb)(phthalimidate)(P(4-MeO-C(6)H(4))(3))](9a) and [Pd(bzq)(phthalimidate)(PPh(3))](7c) have been established. Dinuclear complexes (1a-3a, 1b-3b, 1c-3c) demonstrate outstanding thermal stability in the solid-state, as shown by thermoanalytical techniques. A marked influence of bridging imidate groups on the initial decomposition temperature is observed. The dinuclear and mononuclear derivatives are shown to be active catalysts/precatalysts for the Suzuki-Miyaura cross-coupling reactions of aryl bromides with aryl boronic acids, and the Sonogashira reactions of aryl halides with phenyl acetylene (in the presence and absence of Cu(I) salts). The conversions appear to be dependent, to some extent, on the type of imidate ligand, suggesting a role for these pseudohalides in the catalytic cycle in both cross-coupling processes. Lower catalyst loadings in 'copper-free' Sonogashira cross-couplings favour higher turnover frequencies. We have further determined that these catalysts may be recycled using a poly(ethylene oxide)(PEO)/methanol solvent medium in Suzuki-Miyaura cross-coupling. Once the reaction is complete, product extraction into a hexane/diethyl ether mixture (1 : 1, v/v) gives cross-coupled products in good yields (with purity > 95%). The polar phase can then be re-used several times without appreciable loss of catalytic activity.     

A Locally Adaptive Multimode Photodetector Circuit

Photodetection circuits form the first stage of the artificial image acquisition process. The image acquisition circuits discussed in this paper pertain to circuits fabricated in a standard CMOS process. Such circuits offers advantages such as random access to a pixel, faster readout, integration of processing circuitry on the same die, low voltage and low power dissipation, and lower cost over the conventional Charge Coupled Device (CCD) process. We describe a new locally adaptive multimode photodetector circuit. The advantages of the circuit are local adaptation, wide dynamic range, excellent sensitivity, and large output voltage swing. The circuit was fabricated in the 2 CMOS process through MOSIS. Simulation and experimental results of the circuit are given.     

Interplay between intensity standardization and inhomogeneity correction in MR image processing

Image intensity standardization is a postprocessing method designed for correcting acquisition-to-acquisition signal intensity variations (nonstandardness) inherent in magnetic resonance (MR) images. Inhomogeneity correction is a process used to suppress the low frequency background nonuniformities (inhomogeneities) of the image domain that exist in MR images. Both these procedures have important implications in MR image analysis. The effects of these postprocessing operations on improvement of image quality in isolation has been well documented. However, the combined effects of these two processes on MR images and how the processes influence each other have not been studied thus far. In this paper, we evaluate the effect of inhomogeneity correction followed by standardization and vice-versa on MR images in order to determine the best sequence to follow for enhancing image quality. We conducted experiments on several clinical and phantom data sets (nearly 4000 three-dimensional MR images were analyzed) corresponding to four different MRI protocols. Different levels of artificial nonstandardness, and different models and levels of artificial background inhomogeneity were used in these experiments. Our results indicate that improved standardization can be achieved by preceding it with inhomogeneity correction. There is no statistically significant difference in image quality obtained between the results of standardization followed by correction and that of correction followed by standardization from the perspective of inhomogeneity correction. The correction operation is found to bias the effect of standardization. We demonstrate this bias both qualitatively and quantitatively by using two different methods of inhomogeneity correction. We also show that this bias in standardization is independent of the specific inhomogeneity correction method used. The effect of this bias due to correction was also seen in magnetization transfer ratio (MTR) images, which are naturally endowed with the standardness property. Standardization, on the other hand, does not seem to influence the correction operation. It is also found that longer sequences of repeated correction and standardization operations do not considerably improve image quality. These results were found to hold for the clinical and the phantom data sets, for different MRI protocols, for different levels of artificial nonstandardness, for different models and levels of artificial inhomogeneity, for different correction methods, and for images that were endowed with inherent standardness as well as for those that were standardized by using the intensity standardization method. Overall, we conclude that inhomogeneity correction followed by intensity standardization is the best sequence to follow from the perspective of both image quality and computational efficiency.