SiGe HMODFET "KAIST" micropower model and amplifier realization

The recently published small-signal KAIST model is used successfully to fit the measured RF characteristics of a novel SiGe n-HMODFET device operating at micropower levels and extracted small-signal model parameters for this device under micropower operation are presented here for the first time. This model is then used to predict the performance of a simple micropower amplifier (sub 300-/spl mu/W total power consumption), realized in SiGe technology, and a comparison of modeled versus measured data is included.     

Fabrication and performance of parallel-addressed InGaN micro-LED arrays

High-performance, two-dimensional arrays of parallel-addressed InGaN blue micro-light-emitting diodes (LEDs) with individual element diameters of 8, 12, and 20 /spl mu/m, respectively, and overall dimensions 490 /spl times/490 /spl mu/m, have been fabricated. In order to overcome the difficulty of interconnecting multiple device elements with sufficient step-height coverage for contact metallization, a novel scheme involving the etching of sloped-sidewalls has been developed. The devices have current-voltage (I-V) characteristics approaching those of broad-area reference LEDs fabricated from the same wafer, and give comparable (3-mW) light output in the forward direction to the reference LEDs, despite much lower active area. The external efficiencies of the micro-LED arrays improve as the dimensions of the individual elements are scaled down. This is attributed to scattering at the etched sidewalls of in-plane propagating photons into the forward direction.     

Recent developments in the synthesis and discovery of oligosaccharides and glycoconjugates for the treatment of disease

The development of the first automated oligosaccharide synthesizer, along with new methods for screening carbohydrate ligand arrays is likely to lead to a rapid acceleration in both our ability to synthesize these molecules, and understand the roles of oligosaccharides and glycoconjugates in biology. Consequently we may uncover new avenues for therapeutic intervention more rapidly. These recent developments are very important since our understanding of the role of glycoconjugates in nature has traditionally fallen far behind that of the other biopolymers such as proteins and nucleic acids as the formation of, for example, glycosylated proteins is not template driven. The chemical synthesis of oligosaccharides and glycoconjugates has provided us with new potential cancer vaccines, antibiotics and new biotechnological tools. Glycobiologists have employed many such tools to uncover new signalling roles for oligosaccharides and glycoconjugates. In this review we aim to highlight some emerging methods for glycoconjugate assembly and screening, and discuss innovative approaches to glycoconjugate based drug design and delivery, all of which are, and will continue to be, fruitful avenues for medicinal chemistry research.     

Constrained Drying of Aqueous Yttria-Stabilized Zirconia Slurry on a Substrate. I: Drying Mechanism

Aqueous yttria-stabilized zirconia slurry was cast on a substrate to form wet coatings. Both weight loss and thickness reduction were measured, during the drying process. Lateral drying was observed by in situ monitoring of the coating surface. The drying kinetics were classified as an initial constant rate period (CRP), followed by a falling rate period (FRP). Thickness reduction occurred in the CRP stage, and was uneven across the coating because of lateral flow. As tensile stresses developed within the coating because of the constrained volume shrinkage, crack formation and propagation occurred in the FRP stage and affected the drying rate.     

Fabrication of optical fibre nanowires and their optical and mechanical characterisation

It is demonstrated for the first time that long nanowires with radii as small as 30 nm can be manufactured with a conventional coupler fabrication rig. The temporal deterioration of nanowire optical properties has been studied and correlated with its mechanical behaviour. The original transmission properties have been restored by a post-fabrication treatment.     

The role of modelling in identifying drug targets for diseases of the cell cycle.

The cell cycle is implicated in diseases that are the leading cause of mortality and morbidity in the developed world. Until recently, the search for drug targets has focused on relatively small parts of the regulatory network under the assumption that key events can be controlled by targeting single pathways. This is valid provided the impact of couplings to the wider scale context of the network can be ignored. The resulting depth of study has revealed many new insights; however, these have been won at the expense of breadth and a proper understanding of the consequences of links between the different parts of the network. Since it is now becoming clear that these early assumptions may not hold and successful treatments are likely to employ drugs that simultaneously target a number of different sites in the regulatory network, it is timely to redress this imbalance. However, the substantial increase in complexity presents new challenges and necessitates parallel theoretical and experimental approaches. We review the current status of theoretical models for the cell cycle in light of these new challenges. Many of the existing approaches are not sufficiently comprehensive to simultaneously incorporate the required extent of couplings. Where more appropriate levels of complexity are incorporated, the models are difficult to link directly to currently available data. Further progress requires a better integration of experiment and theory. New kinds of data are required that are quantitative, have a higher temporal resolution and that allow simultaneous quantitative comparison of the concentration of larger numbers of different proteins. More comprehensive models are required and must accommodate not only substantial uncertainties in the structure and kinetic parameters of the networks, but also high levels of ignorance. The most recent results relating network complexity to robustness of the dynamics provide clues that suggest progress is possible.     

Two-step parameter extraction procedure with formal optimization for physics-based circuit simulator IGBT and p-i-n diode models

A practical and accurate parameter extraction method is presented for the Fourier-based-solution physics-based insulated gate bipolar transistor (IGBT) and power diode models. The goal is to obtain a model accurate enough to allow switching loss prediction under a variety of operating conditions. In the first step of the extraction procedure, only one simple clamped inductive load test is needed for the extraction of the six parameters required for the diode model and of the 12 and 15 parameters required for the nonpunch-through (NPT) and punch-through (PT) IGBT models, respectively. The second part of the extraction procedure is an automated formal optimization step that refines the parameter estimation. Validation with experimental results from various structures of IGBT demonstrates the accuracy of the proposed IGBT and diode models and the robustness of the parameter extraction method.     

PV system sizing using observed time series of solar radiation

Sizing represents an important part of photovoltaic system design. This paper describes a sizing procedure based on the observed time series of solar radiation. Using a simple geometrical construction, the sizing curve is determined as a superposition of contributions from individual climatic cycles of low daily solar radiation. Unlike the traditional methods based on loss-of-load probability, the reliability of supply enters in this method through the length of the time series of data used in the analysis. The method thus resembles techniques used in other branches of engineering where extreme values are considered as functions of certain recurrence intervals.     

Emissions from distributed vs. centralized generation: The importance of system performance

Distributed generation (DG) offers a number of potential benefits, but questions remain about environmental performance. Air emissions from five key DG technologies; gas engines, diesel engines, gas turbines, micro-turbines, and fuel cells, were systematically compared with total energy supply systems based on centralized gas turbines (CCGT) and coal steam turbines plus distributed heating (DH) using gas-fired boilers. Based on emissions and operational factors from existing commercially marketed DG-CHP technologies, combined heat and power (CHP) applications are considered, which are remotely monitored and operated as base-load supply. Emissions results are characterized using heat-to-power ratios (HPRs), which concisely describe different types of energy demand under different applications or seasonal conditions. At an HPR of zero (i.e. the special case of electricity-only), CCGT with DH gives the lowest emissions portfolio, but at HPR values typical for buildings in the United States, efficiency advantages ensure gas-fired combustion DG-CHP technologies become broadly competitive across the range of key emissions. Fuel cell DG-CHP provides a very low emissions portfolio, but at a significant cost premium. At higher HPR values, emissions from heat supply can become a key issue, leading to the surprising finding that some combustion-based DG-CHP systems have lower total emissions than fuel cell-based systems. Based on these insights, the paper concludes with a discussion of streamlined yet rigorous regulatory approaches for DG-CHP technologies.     

Renewable energies and the poor: niche or nexus?

Renewable energies are considered as an essential element of any strategy for sustainable energy development. The poor in the developing world without access to modern energies are regarded as a major market for renewable energies. This short paper attempts to analyse whether such a niche is backed by any economic logic and whether renewable energy and the poor nexus could be a strategy for success. The paper suggests that contrary to the common belief, the economic logic behind the niche is unsound and that the nexus is not a recipe for success.