Kinetic and Binding Studies Reveal Cooperativity and Off-Cycle Competition for H-Bonding Catalysis with Silsesquioxane Silanols

The catalytic activity, kinetics, and quantification of H-bonding ability of incompletely condensed polyhedral oligomeric silsesquioxane (POSS) silanols are reported. POSS-triols, a homogeneous model for vicinal silica surface sites, exhibit enhanced H-bonding compared with other silanols and alcohols as quantified using a ³¹P NMR probe. Evaluation of a Friedel–Crafts addition reaction shows that phenyl-POSS-triol is active as an H-bond donor catalyst whereas other POSS silanols studied are not. An in-depth kinetic study (using RPKA and VTNA) highlights the concentration-dependent H-bonding behavior of POSS-triols, which is attributed to intermolecular association forming an off-cycle dimeric species. Binding constants provide additional support for reduced H-bond ability at higher concentrations, which is attributed to competitive association. POSS-triol self-association disrupts H-bond donor abilities relevant for catalysis by reducing the concentration of active monomeric catalyst.     

Effect of Printed Circuit Board Structures on Temperature-Dependent Gain Characteristics of RF Power Amplifier Chips

We fabricated and characterized heterojunction field effect transistor radio frequency (RF) power amplifier (PA) test fixtures, for wireless applications, with various printed circuit board (PCB) structures. The RF matching and bias circuits of the test fixtures were designed so that they had the same RF characteristics. The only source of the variation of the RF gain (S₂₁) was different thermal characteristics of each PCB. The values of the junction temperature (T_J) and the junction-to-ambient thermal resistance (R _{J A}) of each test fixture were shown to be changed as much as 80deg C and 30deg C / W, respectively, by the change of PCB structures. The change of Rja was shown to be originated from the change of the PCB thermal resistance, assuring that the structure of the PCB was the dominant factor in determining R _{J A} Finally, we obtained a universal relation between S₂₁ of the amplifier and Tj. This work suggests that thermal budget of PCB is as important as that of package in wireless RF equipments.     

The Island-Gate Varactor—A High-Q MOS Varactor for Millimeter-Wave Applications

A new accumulation MOS varactor with island-shaped poly gate layout is proposed to improve the quality factor ( Q-factor) at high frequency, which can be readily employed for CMOS-based millimeter-wave applications. Measured results up to 67 GHz show significant improvements in the Q-factor and the series resistance R_s over the conventional multi-finger MOS varactors with the same ground rule and gate area. The proposed island-gate MOS varactor is expected to improve the overall Q-factor of the LC tank of millimeter-wave oscillators.     

Study of normal breast tissue by in vivo volume localized proton MR Spectroscopy: variation of Water–Fat ratio in relation to the heterogeneity of the breast and the menstrual cycle

Purpose

To investigate the alterations in water–fat (W-F) ratio of the normal breast tissue of female volunteers as a function of the histological phases of the menstrual cycle.

Methods

Image-guided volume localized in vivo proton (¹H) magnetic resonance spectroscopy (MRS) at 1.5 T was carried out in the para-areolar region and the upper and lower quadrants of the normal breast tissue of volunteers (n=29; mean age 33.7±6 years) during five histological phases of the menstrual cycle.

Results

A W-F value of 0.90±0.41 was observed for the para-areolar region during the proliferative phase, which reduced to 0.46±0.21 and 0.45±0.25 during follicular and luteal phases, respectively. The value increased to 0.76±0.61 during secretory and to 0.87±0.37 during menstrual phases. No significant difference was observed in the W-F value for the upper and the lower quadrants of the breast during various phases of the menstrual cycle. However, the W-F ratio of the para-areolar region was significantly higher compared to the upper and the lower quadrants during all phases. This reflects the dependence of W-F value on the amount of glandular and adipose tissues and the heterogeneous nature of the breast.

Conclusions

Our results indicate that changes in the normal breast tissue characteristics occur due to physiological factors like menstrual cycle that strongly influences the W-F value especially the para-areolar region in a cyclic manner. Thus any assessment of breast pathology using W-F values should be carried out carefully taking into consideration the location of the tumor within the breast as well as the time of menstruation.     

Duality in generalized fractional programming via Farkas' lemma

For fractional programs involving several ratios in the objective function, a dual is introduced with the help of Farkas' lemma. Often the dual is again a generalized fractional program. Duality relations are established under weak assumptions. This is done in both the linear case and the nonlinear case. We show that duality can be obtained for these nonconvex programs using only a basic result on linear (convex) inequalities.     

Assignment of proton NMR spectrum of triglycidylether of para-aminophenol (TGPAP), using two-dimensional techniques: SUPERCOSY and J-resolved

One- and two-dimensional 400-MHz proton NMR experiments are reported for the epoxy resin monomer, triglycidylether of para-aminophenol (TGPAP). Assignment of the epoxy protons becomes difficult due to many overlapping signals from the glycidylamine and glycidylether regions. To solve this problem we employed the homonuclear proton shift-correlated (SUPERCOSY) and J-resolved two-dimensional techniques. The combination of these methods permits the complete elucidation of the complex spectrum.     

Predictive Congestion Control Protocol for Wireless Sensor Networks

Available congestion control schemes, for example transport control protocol (TCP), when applied to wireless networks, result in a large number of packet drops, unfair scenarios and low throughputs with a significant amount of wasted energy due to retransmissions. To fully utilize the hop by hop feedback information, this paper presents a novel, decentralized, predictive congestion control (DPCC) for wireless sensor networks (WSN). The DPCC consists of an adaptive flow and adaptive back-off interval selection schemes that work in concert with energy efficient, distributed power control (DPC). The DPCC detects the onset of congestion using queue utilization and the embedded channel estimator algorithm in DPC that predicts the channel quality. Then, an adaptive flow control scheme selects suitable rate which is enforced by the newly proposed adaptive backoff interval selection scheme. An optional adaptive scheduling scheme updates weights associated with each packet to guarantee the weighted fairness during congestion. Closed-loop stability of the proposed hop-by-hop congestion control is demonstrated by using the Lyapunov-based approach. Simulation results show that the DPCC reduces congestion and improves performance over congestion detection and avoidance (CODA) [3] and IEEE 802.11 protocols.     

Impact of Capillary-Driven Liquid Films on Salt Crystallization

Flow-through drying of ionic liquids in porous media can lead to super saturation and hence crystallization of salts. A model for the evolution of solid and liquid concentrations of salt, in porous media, due to evaporation by gas flow is presented. The model takes into account the impact of capillary-driven liquid film flow on the evaporation rates as well as the rate of transport of salt through those films. It is shown that at high capillary wicking numbers and high dimensionless pressure drops, supersaturation of brine takes place in the higher drying rate regions in the porous medium. This leads to solid salt crystallization and accumulation in the higher drying rate region. In the absence of wicking, there is no transport and accumulation of solid salt. Results from experiments of flow-through drying in rock cores are compared with model prediction of salt crystallization and accumulation.     

Analytical model and characterization of abnormally structured MOSFETs

Electrical characteristics of abnormally structured n-MOSFETs having uncontacted active regions are experimentally investigated using test devices with various gate widths. Linear resistance and saturation drain current of the devices are estimated by a simple schematic model, which consists of parallel-connected conventional devices having parasitic resistors. A comparison of experimental results of conventional and abnormal devices gives the parasitic resistance caused by abnormal active structure. The increment rate of the parasitic resistance depending on gate width shows two categories, which are logarithmic increment at narrow device and exponential increment at wider device. The performance degradation in the wider device is also explained by the reduction of effective channel area. The suggested model provides a physical analysis of the abnormal transistor and shows good agreement with the measured drain current in linear and saturation regions for both forward- and reverse-modes.