Optimization studies of single-transverse-mode 980 nm ridge-waveguide lasers

The paper presents a simple and efficient Mode-Solver-based method for determining the ridge profile that ensures stable single-transverse-mode operation in ridge waveguide lasers. A quantitative figure of merit, easily derived from the Mode Solver analysis of the structure, indicates the likelihood of single transverse modal behavior over the whole bias range. The transverse mode analysis performed with the in-house developed software has been compared with the results of the commercial simulation package LASTIP and with experiments. The simulation and experimental results have been used to derive processing guidelines for achieving a stable single-transverse-mode operation in ridge waveguide lasers.     

Impulse Control of One-Dimensional Ito Diffusions with an Expected and a Pathwise Ergodic Criterion

We consider the problem of controlling a general one-dimensional Ito diffusion by means of an impulse control process. The objective is to minimise a long-term expected criterion as well as a long-term pathwise criterion that penalise both deviations of the state process from a given nominal point and the use of impulsive control effort. In particular, each time the controller deploys an impulse to reposition the system's state, a fixed cost and a cost proportional to the impulse's size are incurred. We solve the resulting optimisation problems and we provide an explicit characterisation of an optimal control strategy under general assumptions. The control of a foreign exchange rate or an inflation rate presents a potential application of the model that we study.     

Homogeneity analysis of ion-implanted resonant tunnelling diodes for applications in digital logic circuits

A planar process for molecular beam epitaxy grown resonant tunnelling diodes (RTDs) in the GaAs/AlAs material system is presented and analysed with respect to the homogeneity of the diodes. The results can be correlated with a parameter sensitivity study based on quantum mechanical transport simulations. The homogeneity analysis reveals that our concept provides sufficient precision to fabricate RTDs suitable for application in robust digital logic circuits.     

Exponential instability of linear skew-product semiflows in terms of Banach function spaces

In this paper we obtain necessary and sufficient conditions for uniform exponential instability of linear skew-product semiflows in terms of Banach sequence spaces and Banach function spaces, respectively. We deduce the versions of some theorems due to Datko, Neerven, Przyluski, Rolewicz and Zabczyk, for the case of instability of linear skew-product semiflows.     

On Uniform Exponential Trichotomy of Evolution Operators in Banach Spaces

This paper presents necessary and sufficient conditions for uniform exponential trichotomy of nonlinear evolution operators in Banach spaces. Thus are obtained results which extend well-known results for uniform exponential stability in the linear case.      

European ring exercise on water toxicity using different bioluminescence inhibition tests based on Vibrio fischeri, in support to the implementation of the water framework directive

An inter-laboratory comparison exercise was conducted under the European Union funded project entitled: Screening Methods for Water Data Information in Support of the Implementation of the Water Framework Directive (SWIFT-WFD) and coordinated by the Consejo Superior de Investigaciones Científicas (CSIC), in order to evaluate the reproducibility of different toxicity tests based on the bioluminescence inhibition of Vibrio fischeri, for the rapid water toxicity assessment.For the first time, this type of exercise has been organized in Europe, and using different tests based on the same principle. In this exercise, 10 laboratories from 8 countries (Austria, Cyprus, Germany, Greece, Italy, Portugal, Romania, and Spain) took place, and a total number of 360 samples were distributed.During the exercise, six series of six samples were analyzed along 5 months. Every batch of samples was composed by three real samples and three standard solutions. The real samples were: a raw influent and the effluent of a wastewater treatment plant (WWTP), and a sample from a first settlement of the WWTP spiked with a mixture of toxicant standards.A final number of 330 (91.7%) samples was analyzed, 3300 values in duplicate were collected, and the results for each sample were expressed as the 50% effective concentration (EC₅₀) values calculated through five points of dilution inhibition curves, after 5 and 15 min of incubation times.A statistical study was initiated using 660 results. The mean values, standard deviations (σ), variances (σ²), and upper and lower warning limits (UWL and LWL) were obtained, using the EC₅₀ values calculated with the result from the participating laboratories.The main objectives of this toxicity ring study were to evaluate the repeatability (r) and reproducibility (R) when different laboratories conduct the test, the influence of complex matrix samples, the variability between different tests based on the same principle, and to determine the rate at which participating laboratories successfully completed tests initiated.In this exercise, the 3.93% toxicity values were outliers according with the Z-score values and the Dixon test. The samples with the greater number of outliers were those with the smallest variability coefficient, corresponding to the greater and the smaller toxicity level.No relation was found through the cluster analysis, between the final results and the different commercial devices involved. Testing by multiple commercial devices did not appear to reduce the precision of the results, and the variability coefficient for the exercise was nearby to the average value for past editions carried out at national level, where the different participants used the same commercial device.Stability of samples was also followed during the exercise. While statistical significance differences were not found for the greater part of samples, for the sample from the WWTP influent, a significant decrease of the toxicity value was found along this study. Nevertheless, this was a type of sample with a high toxicity level during all the exercise.On the other hand, in order to obtain the chemical characterization of real samples, those were analyzed by chromatographic techniques, using different sequential solid phase extraction (SSPE) procedures, followed by liquid chromatography coupled with mass spectrometry (LC-MS), and gas chromatography-mass spectrometry (GC-MS). Good agreement was found between the chemical analysis results and the toxicity level of the samples.     

Trends for nanotechnology development in China, Russia, and India

China, Russia, and India are playing an increasingly important role in global nanotechnology research and development (R&D). This paper comparatively inspects the paper and patent publications by these three countries in the Thomson Science Citation Index Expanded (SCI) database and United States Patent and Trademark Office (USPTO) database (1976–2007). Bibliographic, content map, and citation network analyses are used to evaluate country productivity, dominant research topics, and knowledge diffusion patterns. Significant and consistent growth in nanotechnology papers are noted in the three countries. Between 2000 and 2007, the average annual growth rate was 31.43% in China, 11.88% in Russia, and 33.51% in India. During the same time, the growth patterns were less consistent in patent publications: the corresponding average rates are 31.13, 10.41, and 5.96%. The three countries’ paper impact measured by the average number of citations has been lower than the world average. However, from 2000 to 2007, it experienced rapid increases of about 12.8 times in China, 8 times in India, and 1.6 times in Russia. The Chinese Academy of Sciences (CAS), the Russian Academy of Sciences (RAS), and the Indian Institutes of Technology (IIT) were the most productive institutions in paper publication, with 12,334, 6,773, and 1,831 papers, respectively. The three countries emphasized some common research topics such as “Quantum dots,” “Carbon nanotubes,” “Atomic force microscopy,” and “Scanning electron microscopy,” while Russia and India reported more research on nano-devices as compared with China. CAS, RAS, and IIT played key roles in the respective domestic knowledge diffusion.     

The deformation of flat connections and affine manifolds

Geodesically complete affine manifolds are quotients of the Euclidean space through a properly discontinuous action of a subgroup of affine Euclidean transformations. An equivalent definition is that the tangent bundle of such a manifold admits a flat, symmetric and complete connection. If the completeness assumption is dropped, the manifold is not necessarily obtained as the quotient of the Euclidean space through a properly discontinuous group of affine transformations. In fact the universal cover may no longer be the Euclidean space. The main result of this paper states that if a flat connection of a bundle can be properly deformed into a metric connection then its Euler class vanishes. This is a partial result toward an old question of Chern.     

Self‐Assembled Columnar Triazole Quartets: An Example of Synergistic Hydrogen‐Bonding/Anion–π Interactions

The self‐assembly of triazole amphiphiles was examined in solution, the solid state, and in bilayer membranes. Single‐crystal X‐ray diffraction experiments show that stacked protonated triazole quartets (T₄) are stabilized by multiple strong interactions with two anions. Hydrogen bonding/ion pairing of the anions are combined with anion–π recognition to produce columnar architectures. In bilayer membranes, low transport activity is observed when the T₄ channels are operated as H⁺/X^? translocators, but higher transport activity is observed for X^? in the presence of the K⁺‐carrier valinomycin. These self‐assembled superstructures, presenting intriguing structural behaviors such as directionality, and strong anion encapsulation by hydrogen bonding supported by vicinal anion–π interactions can serve as artificial supramolecular channels for transporting anions across lipid bilayer membranes.