Swelling-Based Chemical Sensing With Unmodified Optical Fibers

We use distributed fiber optic strain sensing to examine swelling of the fiber's polymer coating.The distributed sensing technique that uses unmodified low-cost...     

Selective laser ablation of SiNx layers on textured surfaces for low temperature front side metallizations

For an alternative front side metallization process without screen printing of metal paste the selective opening of the front surface anti‐reflection coating could be realized by laser ablation. A successful implementation of this scheme requires direct absorption of the laser light within the anti‐reflection coating, since the emitter underneath must not be damaged severely. Additionally, the ablation must be feasible on textured surfaces. In this paper, we show that laser light with a wavelength of 355 nm and a pulse length of approximately 30 ns is absorbed directly by a typical silicon nitride anti‐reflection coating. Based on lifetime measurements on ablated samples it is shown that a damage free laser ablation of SiN_x layers on planar surfaces is possible. The characteristic ablation structure on textured surfaces is explained and quantified by rigorous coupled wave analysis (RCWA) simulations. Finally, high efficiency solar cells with a standard emitter (R_sh approx. 50 Ω/sq) have been processed using laser ablation of the silicon nitride anti‐reflection coating. These cells show efficiencies of up to 19·1%, comparable to the reference solar cells using photolithographically opened contact areas. Copyright © 2008 John Wiley & Sons, Ltd.     

Screening and Characterization of Lactobacillus sp. from the Water of Cassava’s Fermentation for Selection as Probiotics

The present study aimed to evaluate selected probiotic properties of Lactobacilli isolated from the water of submerged cassava fermentation. Following Lactobacilli isolation, isolates were screened for their antimicrobial activity. Acid and bile tolerances, bile salt hydrolase (Bsh) activity spectrum were assessed. Among the 113 isolates obtained, 16 showed a broad antimicrobial activity spectrum against the indicator microorganisms. From these 16, 12 were found acid and bile resistant. They hydrolyzed glycoconjugated or tauroconjugated bile salts. From the four bile Bsh genes screened, only Bsh-Lp1 was found in five isolates. They identified as Lactobacillus paraplantarum, Lactobacillus paracasei, Lactobacillus brevis, and Lactobacillus plantarum. Based on the principal component analysis, L. paracasei 62L, L. plantarum 85L and 86L were selected as the most promising strains. These results suggest that water from submerged cassava fermentation can be a source of Lactobacilli with high probiotic potential.     

Programs with lists are counter automata

We address the problem of verifying programs manipulating one-selector linked data structures. We propose and study in detail an application of counter automata as an accurate abstract model for this problem. We let control states of the counter automata correspond to abstract heap graphs where list segments without sharing are collapsed, and use counters to keep track of the number of elements in these segments. As a significant theoretical result, we show that the obtained counter automata are bisimilar to the original programs. Moreover, from a practical point of view, our translation allows one to apply efficient automatic analysis techniques and tools developed for counter automata (integer programs) in order to verify both safety as well as termination of list-manipulating programs. As another theoretical contribution, we prove that if the control of the generated counter automata does not contain nested loops (i.e., these automata are flat), both safety and termination are decidable for the original programs. Subsequently, we generalise our counter-automata-based model to keep track of ordering properties over lists storing ordered data. Finally, we show effectiveness of our approach by verifying automatically safety as well as termination of several sorting programs.     

State of the art versus classical clustering for unsupervised word sense disambiguation

This paper ultimately discusses the importance of the clustering method used in unsupervised word sense disambiguation. It illustrates the fact that a powerful clustering technique can make up for lack of external knowledge of all types. It argues that feature selection does not always improve disambiguation results, especially when using an advanced, state of the art method, hereby exemplified by spectral clustering. Disambiguation results obtained when using spectral clustering in the case of the main parts of speech (nouns, adjectives, verbs) are compared to those of the classical clustering method given by the Naïve Bayes model. In the case of unsupervised word sense disambiguation with an underlying Naïve Bayes model feature selection performed in two completely different ways is surveyed. The type of feature selection providing the best results (WordNet-based feature selection) is equally being used in the case of spectral clustering. The conclusion is that spectral clustering without feature selection (but using its own feature weighting) produces superior disambiguation results in the case of all parts of speech.     

Ethernet PON (ePON): Design and Analysis of an Optical Access Network

With the expansion of services offered over the Internet, the last mile bottleneck problems continue to exacerbate. A passive optical network (PON) is a technology viewed by many as an attractive solution to this problem. In this study, we propose the design and analysis of a PON architecture which has an excellent performance-to-cost ratio. This architecture uses the time-division multiplexing (TDM) approach to deliver data encapsulated in Ethernet packets from a collection of optical network units (ONUs) to a central optical line terminal (OLT) over the PON access network. The OLT, in turn, is connected to the rest of the Internet. A simulation model is used to analyze the systems performance such as bounds on packets delay and queue occupancy. Then, we discuss the possibility of improving the bandwidth utilization by means of timeslot size adjustment, and by packet scheduling.     

Double Charge Transfer Dominates in Carrier Localization in Low Bandgap Sites of Heterogeneous Lead Halide Perovskites

Heterogeneous organic-inorganic halide perovskites possess inherent non-uniformities in bandgap that are sometimes engineered and exploited on purpose, like in quasi-2D perovskites. In these systems, charge carrier and excitation energy migration to lower-bandgap sites are key processes governing luminescence. The question, which of them dominates in particular materials and under specific experimental conditions, still remains unanswered, especially when charge carriers comprise excitons. In this study transient absorption (TA) and transient photoluminescence (PL) techniques are combined to address the excited state dynamics in quasi-2D and other heterogeneous perovskite structures in broad temperature range, from room temperature down to 15 K. The data provide clear evidence that charge carrier transfer rather than energy migration dominates in heterogeneous quasi-2D perovskite films.     

Encapsulation of Noble Metal Nanoparticles through Seeded Emulsion Polymerization as Highly Stable Plasmonic Systems

The implementation of plasmonic nanoparticles in vivo remains hindered by important limitations such as biocompatibility, solubility in biological fluids, and physiological stability. A general and versatile protocol is presented, based on seeded emulsion polymerization, for the controlled encapsulation of gold and silver nanoparticles. This procedure enables the encapsulation of single nanoparticles as well as nanoparticle clusters inside a protecting polymer shell. Specifically, the efficient coating of nanoparticles of both metals is demonstrated, with final dimensions ranging between 50 and 200 nm, i.e., sizes of interest for bio‐applications. Such hybrid nanocomposites display extraordinary stability in high ionic strength and oxidizing environments, along with high cellular uptake, and low cytotoxicity. Overall, the prepared nanostructures are promising candidates for plasmonic applications under biologically relevant conditions.     

Eclipse Pulsed Laser Deposition for Damage‐Free Preparation of Transparent ZnO Electrodes on Top of Organic Solar Cells

Pulsed laser deposited gallium doped zinc oxide (ZnO:Ga) is reported as transparent top electrode for organic solar cells. In contrast to standard coating techniques, prone to harm organic sublayers and leading to strongly reduced device efficiencies, eclipse pulsed laser deposition (PLD) in argon atmosphere is identified as compatible, nonharmful deposition method for ZnO:Ga, even on top of sensitive organic material. Although PLD is not yet ready for mass production, the experiments reveal and solve crucial process limitations, e.g., droplet impacts, which might be useful also for high yield deposition methods. Optimized ZnO:Ga top electrodes achieve a high mean transparency in the visible spectral range of T_vis = 82.7% and a reasonable sheet resistance of R_S = 83 Ω sq^?1. The organic photovoltaic devices prepared with this electrode obtained an efficiency of η = 2.9%, almost equal to the efficiency of reference samples using a state‐of‐the‐art metal top contact (η = 3.0%). The investigations here demonstrate the successful deposition of transparent conductive oxides as top electrode for organic devices and open a new path towards the combination of metal oxides and organic semiconductors.