Gyroid‐Structured 3D ZnO Networks Made by Atomic Layer Deposition

3D continuous ZnO morphologies with characteristic feature sizes on the 10 nm length scale are attractive for electronic device manufacture. However, their synthesis remains a challenge because of the low crystallization temperature of ZnO. Here, we report a method for the robust and reliable synthesis of fully crystalline 3D mesoporous ZnO networks by means of atomic layer deposition (ALD) of ZnO into a self‐assembled block copolymer template. By carefully optimizing the processing conditions we are able to synthesize several‐micrometer‐thick layers of mesoporous ZnO networks with a strut width of 30 nm. Two 3D mesoporous morphologies are manufactured: a periodic gyroid structure and a random worm‐like morphology. Exploiting the ALD property to conformally coat complex surfaces of high aspect ratio, the channel network of a 3D continuous channel network of a self‐assembled block copolymer is replicated into ZnO. X‐ray photoemission spectroscopy and x‐ray diffraction measurements reveal that the chemical composition of the mesoporous structures is uniform and consists of wurtzite‐ZnO throughout the film. Scanning electron microscopy reveals an average pore dimension of 30 nm. The potential of this material for a hybrid photovoltaic application is demonstrated by the manufacture of a poly(3‐hexylthiophene)/ZnO solar cell.     

Experimental Study of a Ka-Band Cylindrical Open Resonator

A study of the electrodynamical properties of a Ka-band gyrotron open resonator was experimentally conducted. Experiments were accomplished to measure resonant frequencies and their respective loaded quality factors for TE modes in the frequency range from 26 to 40 GHz. In particular, a perturbation technique was used to determine the axial, radial and azimuthal electric field profiles, as an identification method of the TE₀₂₁ mode operating around 35 GHz. In any experimental event, good agreement with the values predicted by theory was found.     

A Simplified Internet Routing Architecture

This paper studies the effect of disaggregation on the size of the routing table in the Internet’s Default Free Zone (DFZ). Current practises for traffic balancing and protection against prefix hijacking in the Internet are based in disaggregating prefixes that cause an increase in size of the Internet’s core routing table. I propose an algorithm to assess their effect on the table size of these techniques. This algorithm is applied on routing tables collected by the RIPE’s Routing Repository between January 2001 and February 2011. The results show that before 2010, the IPv4 addressing space was gradually getting more fragmented. This trend is slowing down since the beginning of 2010, possibly as the result of the economic downturn. In the second part of this paper, I propose an alternative architecture that allows local Traffic Engineering configurations but keeps their effects from spreading over the Internet and outline an implementation for this architecture on a Linux platform.     

Lethal effect of electric fields on isolated ventricular myocytes

Defibrillator-type shocks may cause electric and contractile dysfunction. In this study, we determined the relationship between probability of lethal injury and electric field intensity ($E$ ) in isolated rat ventricular myocytes, with emphasis on field orientation and stimulus waveform. This relationship was sigmoidal with irreversible injury for $E ≫ hbox{50 V/cm}$ . During both threshold and lethal stimulation, cells were twofold more sensitive to the field when it was applied longitudinally (versus transversally) to the cell major axis. For a given $E$, the estimated maximum variation of transmembrane potential ( $Delta V_{max }$) was greater for longitudinal stimuli, which might account for the greater sensitivity to the field. Cell death, however, occurred at lower maximum $Delta V_{max }$ values for transversal shocks. This might be explained by a less steep spatial decay of transmembrane potential predicted for transversal stimulation, which would possibly result in occurrence of electroporation in a larger membrane area. For the same stimulus duration, cells were less sensitive to field-induced injury when shocks were biphasic (versus monophasic). Ours results indicate that, although significant myocyte death may occur in the $E$ range expected during clinical defibrillation, biphasic shocks are less likely to produce irreversible cell injury.      

Pruning the Volterra Series for Behavioral Modeling of Power Amplifiers Using Physical Knowledge

This paper presents an efficient and effective approach to pruning the Volterra series for behavioral modeling of RF and microwave power amplifiers. Rather than adopting a pure "black-box" approach, this model pruning technique is derived from a physically meaningful block model, which has a clear linkage to the underlying physical behavior of the device. This allows all essential physical properties of the PA to be retained, but significantly reduces model complexity by removing unnecessary coefficients from the general Volterra series. A reduced-order model of this kind can be easily extracted from standard time/frequency-domain measurements or simulations, and may be simply implemented in system-level simulators. A complete physical analysis and a systematic derivation are presented, together with both computer simulations and experimental validations     

New Alternatives to the Estimation Problem in Hardware-Software Codesign of Complex Embedded Systems: The H.261 Video Co-dec Case Study

As Codesign problems become larger and more realistic, the required time to estimate their solutions turns into an important bottleneck. This paper presents a new approach to improve the traditional estimation techniques, in order to avoid this drawback. The presented method has been successfully tested on a large experimental benchmark, attaining quality levels close to those provided by the Synopsys Behavioral Compiler. Finally, a case study based on the standard H.261 video co-dec is described, proving the convenience of the technique on real-life situations. The obtained results show a significant improvement in the process time, while keeping the good precision and fidelity levels that the traditional estimation models usually offer.     

Lead‐Free Polycrystalline Ferroelectric Nanowires with Enhanced Curie Temperature

Ferroelectrics are important technological materials with wide‐ranging applications in electronics, communication, health, and energy. While lead‐based ferroelectrics have remained the predominant mainstay of industry for decades, environmentally friendly lead‐free alternatives are limited due to relatively low Curie temperatures (T _C) and/or high cost in many cases. Efforts have been made to enhance T _C through strain engineering, often involving energy‐intensive and expensive fabrication of thin epitaxial films on lattice‐mismatched substrates. Here, a relatively simple and scalable sol–gel synthesis route to fabricate polycrystalline (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ nanowires within porous templates is presented, with an observed enhancement of T _C up to ≈300 °C as compared to ≈90 °C in the bulk. By combining experiments and theoretical calculations, this effect is attributed to the volume reduction in the template‐grown nanowires that modifies the balance between different structural instabilities. The results offer a cost‐effective solution‐based approach for strain‐tuning in a promising lead‐free ferroelectric system, thus widening their current applicability.     

Epitope-Imprinted Nanoparticles as Transforming Growth Factor-β3 Sequestering Ligands to Modulate Stem Cell Fate

Growth factors (GFs) are biomolecules with potent biological effects but inherent limitations hinder their potential as therapeutic agents and cell culture supplements in tissue engineering and regenerative medicine (TERM). Biomaterials that sequester endogenous GFs by affinity binding might circumvent such limitations and thus are being increasingly investigated. Here, molecularly imprinted nanoparticles (MINPs) are proposed as specific abiotic ligands for GFs. As a proof of concept, a conformational epitope of transforming growth factor-β3 (TGF-β3) is designed and surface imprinted onto polyacrylamide-based nanoparticles by inverse microemulsion polymerization. It is found that, depending on the polymerization mixture composition, MINPs can recognize and preferentially bind TGF-β3, either in noncompetitive assays or from a complex human fluid (platelet lysate). Substrates functionalized with MINPs are then used for 2D culture of adipose-derived stem cells. Remarkably, gene and protein expression profiles show a marked upregulation of SOX-9, suggesting activation of TGF-β3 signaling pathways without requiring supplementation with exogenous GF. Likewise, culturing these cells in pellets incorporating MINPs previously incubated with platelet lysate results in higher collagen II-rich matrix deposition, compared to pellets incorporating non-imprinted nanoparticles. In summary, results suggest MINPs can be used as cost-effective, stable, and scalable alternative abiotic GF ligands to guide cell fate in TERM applications.     

Control mechanisms to improve the robustness of mpeg-2 based communications over ATM networks

Audio-visual and other multimedia services are seen as an important source of traffic for ATM networks. Due to the statistical multiplexing schemes used by ATM networks, cells are exposed to delays, jitters and losses. These phenomena affect the quality of the service provided to the video-based applications. In this paper, we introduce a set of control mechanisms at different levels of the protocol architecture. These mechanisms have been particularly tailored to better support MPEG-2-based video communications applications using ATM networks as their underlying transmission mechanism. We show that the use of errorconcealment mechanisms prove more effective when supplemented by a structured set of protocol mechanisms. We study the impact of cell losses on the quality of MPEG-2 video sequences and provide an evaluation of the quality of the decoded video as perceived by the end user. Our results demonstrate the effectiveness of the proposed protocol architecture in improving the quality of service provided to the video application.     

Non‐Geminate Recombination as the Primary Determinant of Open‐Circuit Voltage in Polythiophene:Fullerene Blend Solar Cells: an Analysis of the Influence of Device Processing Conditions

The physical origin of the open‐circuit voltage in bulk heterojunction solar cells is still not well understood. While significant evidence exists to indicate that the open‐circuit voltage is limited by the molecular orbital energies of the heterojunction components, it is clear that this picture is not sufficient to explain the significant variations which often occur between cells fabricated from the same heterojunction components. We present here an analysis of the variation in open‐circuit voltage between 0.4–0.65 V observed for a range of P3HT/PCBM solar cells where device deposition conditions, electrode structure, active‐layer thickness and device polarity are varied. The analysis quantifies non‐geminate recombination losses of dissociated carriers in these cells, measured under device operating conditions. It is found that at open‐circuit, losses due to non‐geminate recombination are sufficiently large that other loss pathways may effectively be neglected. Variations in open‐circuit voltage between different devices are shown to arise from differences in the rate coefficient for non‐geminate recombination, and from differences in the charge densities in the photoactive layer of the device. The origin of these differences is discussed, particularly with regard to variations in film microstructure. By separately quantifying these differences in rate coefficient and charge density, and by application of a simple physical model based upon the assumption that open‐circuit is reached when the flux of charge photogeneration is matched by the flux of non‐geminate recombination, we are able to calculate correctly the open‐circuit voltage for all the cells studied to within an accuracy of ±5 mV.