The tapered matrix amplifier: a low-power high-gain broadband amplifier

A new distributed amplifier topology that offers greatly reduced power consumption is presented. The tapered matrix amplifier (TMA) originates from the combination of transmission line tapering and matrix cascading of distributed amplifiers. The design of a TMA is however complicated by contrasting requirements of the tapered lines, the lumped line approximation and the parasitics of the circuit components. Therefore, a pragmatic design approach leveraging circuit optimization is proposed to handle these complexities. As a proof of concept, a prototype broadband amplifier was implemented in a 90 nm bulk CMOS process. It features an average gain of 15.8 dB over the pass-band, stretching from DC to 22 GHz, while consuming only 12.9 mW of DC power. The average noise figure in the pass-band is 5.4 dB, and the average IIP3 is ?7.3 dBm. The die area occupied by the amplifier is only 0.31 mm². In addition, it is shown that the prototype design can be easily adapted for high linearity while keeping the increase in power consumption to a minimum.     

Papain-specific activating esters in aqueous dipeptide synthesis

Enzymatic peptide synthesis has the potential to be a viable alternative for chemical peptide synthesis. Because of the increasing commercial interest in peptides, new and improved enzymatic synthesis methods are desirable. In recently developed enzymatic strategies such as substrate mimetic approaches and enzyme-specific activation, use of the guanidinophenyl ester (OGp) group has been shown to suffer from some drawbacks. OGp esters are sensitive to spontaneous chemical hydrolysis and the group is expensive to synthesize and therefore not suitable for large-scale applications. On the basis of earlier computational studies, we hypothesized that OGp might be replaceable by simpler ester groups to make the enzyme-specific activation approach to peptide bond formation more accessible. To this end, a set of potential activating esters (Z-Gly-Act) was designed, synthesized, and evaluated. Both the benzyl (OBn) and the dimethylaminophenyl (ODmap) esters gave promising results. For these esters, the scope of a model dipeptide synthesis reaction under aqueous conditions was investigated by varying the amino acid donor. The results were compared with those obtained from a previous study of Z-X(AA) -OGp esters. Computational docking analysis of the set of esters was performed in order to provide insight into the differences in the reactivities of all the potential activating esters. Finally, selected ODmap- and OBn-activated amino acids were applied in the synthesis of two biologically active dipeptides on preparative scales.     

A 5.8-GHz Quadrature Cross-Coupled Oscillator

This paper describes the implementation of a quadrature cross-coupled relaxation oscillator to be used in an OFDM RF front-end transceiver. A prototype of the oscillator was realized in a SiGe BiCMOS technology, and an oscillation frequency of 5.8 GHz was obtained which is 1/6 of the maximum f _T of the bipolar transistors. The circuit performance is evaluated by simulation and by experiment.     

A stepwise development and validation of a RANS based CFD modelling approach for the hydraulic and thermal-hydraulic analyses of liquid metal flow in a fuel assembly

The demand of reliable and clean energy at affordable prices poses a formidable challenge to the world. The initiatives from various international organizations reserve an important role for liquid metal cooled reactor systems. Assessment of such reactors usually involves unconventional thermal-hydraulics. Consequently, Reynolds Averaged Navier Stokes (RANS) based Computational Fluid Dynamics (CFD) approaches are expected to play a vital role along with various ongoing experiments for the design and the safe operation of these nuclear reactors. One of the major issues is the heat transport in the fuel assembly by the liquid metal. The known difficulties in heat transfer experiments, especially with liquid metals, necessitate the application of RANS in computing details of flow and temperature distribution.Considering these aspects, a four step approach is described in the current paper. As a first step, the heat transfer in a liquid metal flow inside a heated tube is analyzed using a RANS approach and then compared with some of the empirical correlations. The computed Nusselt number reveals the required development length of the thermal boundary layer in liquid metal. Furthermore, these simulations reveal the need of further assessment of this approach and all the existing correlations, and the care that should be taken while applying one of these correlations. In the second step, numerical simulations of the flow of heavy liquid metal around a heated rod in an annular cavity confirm that a RANS strategy can be employed in liquid metal flows. Furthermore, a comparison between computed and experimental non-dimensional axial temperature at the heated rod surface shows that among the considered turbulence models the use of a Baseline-Reynolds Stress Model (BSL-RSM) with automatic wall treatment (AWT) can be preferred for complex geometries. This is also demonstrated in the third step by computing the flow distribution in a triangular arrangement of a fuel assembly and by comparing with an existing hydraulics experiment in rod-bundle. These analyses reveal that the use of the BSL-RSM turbulence model with AWT allows prediction of the cross-flow in this rod-bundle. As the forth and last step, the integral TEGENA (TEmperatur- und GEschwindigkeitsverteilungen in Stabbündel mit turbulenter NAtriumströmung) experiment has been selected for further assessment of RANS based CFD approach in computing both the flow and temperature field. A comparison with literature demonstrates that the use of symmetric boundary condition in such a tightly packed parallel rod-bundle leads to a distorted flow field. The experimentally and the computationally obtained temperature field at a plane in the outlet reveal its acceptable predictive capability. Furthermore, application of two different Reynolds Stress Models yields almost the same temperature distribution as a result of the use of simple first-order gradient model for the turbulent heat fluxes. Consequently, these four steps support the use of this modelling approach for investigating the heat transport in (heavy) liquid metals. Finally, the preferred RANS approach has been applied for thermal-hydraulic evaluation in the square arrangement of a bare rod-bundle as is to be employed in the European Lead-cooled reactor System (ELSY). Also, the influence of rod pitch-to-diameter ratio has been analyzed by numerically re-arranging these rods in the different square lattice. Moreover, arranging the bare rods in triangular lattice at the different rod pitch-to-diameter ratios shows the effect of the square and triangular lattice in thermal-hydraulics. Lastly, comparisons with some of the existing heat transfer correlations for the triangular and the rectangular lattice allows us to identify preferred correlations for these lattice arrangements of bare and liquid metal cooled rod-bundles.     

Speed choice and mental workload of elderly cyclists on e-bikes in simple and complex traffic situations: A field experiment

To study the speed choice and mental workload of elderly cyclists on electrical assisted bicycles (e-bikes) in simple and complex traffic situations compared to these on conventional bicycles, a field experiment was conducted using two instrumented bicycles. These bicycles were identical except for the electric pedal support system. Two groups were compared: elderly cyclists (65 years of age and older) and a reference group of cyclists in middle adulthood (between 30 and 45 years of age). Participants rode a fixed route with a length of approximately 3.5 km on both bicycles in counterbalanced order. The route consisted of secluded bicycle paths and roads in a residential area where cyclist have to share the road with motorized traffic. The straight sections on secluded bicycle paths were classified as simple traffic situations and the intersections in the residential area where participants had to turn left, as complex traffic situations. Speed and mental workload were measured. For the assessment of mental workload the peripheral detection task (PDT) was applied. In simple traffic situations the elderly cyclists rode an average 3.6 km/h faster on the e-bike than on the conventional bicycle. However, in complex traffic situations they rode an average only 1.7 km/h faster on the e-bike than on the conventional bicycle. Except for the fact that the cyclists in middle adulthood rode an average approximately 2.6 km/h faster on both bicycle types and in both traffic conditions, their speed patterns were very similar. The speed of the elderly cyclists on an e-bike was approximately the speed of the cyclists in middle adulthood on a conventional bicycle. For the elderly cyclist and the cyclists in middle adulthood, mental workload did not differ between bicycle type. For both groups, the mental workload was higher in complex traffic situations than in simple traffic situations. Mental workload of the elderly cyclists was somewhat higher than the mental workload of the cyclists in middle adulthood. The relatively high speed of the elderly cyclists on e-bikes in complex traffic situations and their relatively high mental workload in these situations may increase the accident risk of elderly cyclist when they ride on an e-bike.     

Optimal blackouts: Empirical results on reducing the social cost of electricity outages through efficient regional rationing

The demand and supply of electricity must always balance. If supply falls short of demand, then price increases or voluntary demand reductions might help to maintain the balance in the system. Should these prove insufficient, then rationing is necessary. Rationing means interrupting the electricity delivery to certain areas or specific electricity users in order to preserve system stability. Since the cost of an interruption differs among electricity users, the social cost of different rationing mechanisms varies. This paper explores the cost difference between efficient regional rationing (minimizing social costs by rationing regions with low costs first) and random rationing (not taking into account social costs). For this the value of lost load calculations of De Nooij et al. [De Nooij, M., Bijvoet, C.C., Koopmans, C.C., (2007). The value of supply security: The costs of power interruptions: Economic input for damage reduction and investment in networks. Energy Economics, 29 (2), 277–295.] are refined. For the Netherlands, it is shown that efficient rationing can reduce social costs by 42 to 93%.     

Action semantic knowledge about objects is supported by functional motor activation.

The present study assessed the functional organization of action semantics by asking subjects to categorize pictures of an actor holding objects with a correct or incorrect grip at either a correct or incorrect goal location. Overall, reaction times were slower if the object was presented with an inappropriate posture, and this effect was stronger for goal violations compared with grip violations (Experiment 1). In addition, the retrieval of action semantics was found accompanied by the implicit activation of motor representations. Body-related objects (e.g., cup) were classified faster when a movement toward the subject’s body was required, whereas world-related objects (e.g., pincers) were responded to faster with a movement in the opposite direction (Experiments 2 and 3). In contrast, when subjects were required to retrieve only visual semantics (Experiment 4), no interference effects of postural information were observed, and motor representations were only partially activated. These findings suggest that action semantics can be accessed independently from visual semantics and that the retrieval of action semantics is supported by functional motor activation reflecting the prototypical use of an object. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Many-body Physics of a Quantum Fluid of Exciton-Polaritons in a Semiconductor Microcavity

Some recent results concerning nonlinear optics in semiconductor microcavities are reviewed from the point of view of the many-body physics of an interacting photon gas. Analogies with systems of cold atoms at thermal equilibrium are drawn, and the peculiar behaviours due to the non-equilibrium regime pointed out. The richness of the predicted behaviours shows the potentialities of optical systems for the study of the physics of quantum fluids.     

From Footprints to Animation

A method of using footprints as a basis for generating animated locomotion is proposed. An optimization process is used to maximize the physical plausibility and perceived comfort of a motion which is constrained to match given footprint and timing information. The proposed method creates plausible walking, turning, leaping, and running motions for bipedal figures at interactive rates. Autonomous motions are generated using a planning algorithm which dynamically generates new footprints and the associated new motions.