Parametric Study on the Interface Layer of Renovation Solutions for Orthotropic Steel Bridge Decks

Abstract: The article presents renovation solutions for orthotropic steel bridge decks consisting of bonding a second steel plate to the existing steel deck in order to reduce the stresses and enlarge the life span of the orthotropic bridge deck. Two solutions for the interface layer between the existing deck plate and the second steel plate are presented: thin epoxy (bonded system) and thick polyurethane (sandwich system). A parametric study based on analytical solutions is carried out on flexural behavior of beams representing the renovation solutions. The influence of geometrical, mechanical and structural parameters on the stiffness and stress reduction factor of the system is studied. Maximum values of stiffness and stress reduction are achieved when maximizing the interface layer thickness and minimizing the second steel plate thickness with in certain practical limits. Based on the weight restrictions one can choose the most efficient interface layer regarding thickness and mechanical properties.     

Evaluating vector data type usage in OpenCL kernels

Open Computing Language (OpenCL) is an open, functionally portable programming model for a large range of highly parallel processors. To provide users with access to the underlying platforms, OpenCL has explicit support for features such as local memory and vector data types (VDTs). However, these are often low‐level, hardware‐specific features, which can be detrimental to performance on different platforms. In this paper, we focus on VDTs and investigate their usage in a systematic way. First, we propose two different approaches (inter‐vdt and intra‐vdt) to use VDTs in OpenCL kernels, and show how to translate scalar OpenCL kernels to vectorized ones. After obtaining vectorized code, we evaluate the performance effects of using VDTs with two types of benchmarks: micro‐benchmarks and macro‐benchmarks. With micro‐benchmarks, we study the execution model of VDTs and the role of the compiler‐aided vectorizer on five devices. With macro‐benchmarks, we explore the changes of memory access patterns before and after using VDTs, and the resulting performance impact. Not only our evaluation provides insights into how OpenCL's VDTs are mapped on different processors, but it also indicates that using such data types introduces changes in both computation and memory accesses. Based on the lessons learned, we discuss how to deal with performance portability in the presence of VDTs. Copyright © 2014 John Wiley & Sons, Ltd.     

The impact of alkali elements on the degradation of CIGS solar cells

Unencapsulated CIGS solar cells with high and low contents of sodium (Na) and potassium (K) were simultaneously exposed to damp heat and illumination. The solar cells with a high alkali (Na, K) content exhibited higher initial conversion efficiencies, but degraded severely within 100 h, while the alkali poor samples kept relatively stable performance under damp heat and illumination. The degradation of the samples with a high alkali content resulted in the formation of sodium rich spots on the top ZnO:Al surface of the samples. This is likely caused by light‐induced Na⁺ migration via the grain boundaries in the absorber to the depletion region, where the Na⁺ accumulated. This allowed subsequent Na⁺ transport through the depletion region due to the lowering of the internal electric field caused both by the Na⁺ accumulation and illumination. The migration resulted in the formation of shunt paths, which reduced the shunt resistance and open circuit voltage. Furthermore, ingression of water into the ZnO:Al is expected to be responsible for a slow but steady increase in series resistance for both high and low alkali solar cells. Additionally, sodium migration led to a severe increase of the series resistance in case of alkali rich samples. Copyright © 2015 John Wiley & Sons, Ltd.     

On optimal filters with maximum number of constraints on amplitude and phase characteristics

For optimal filters specified amplitude and phase (or group delay) characteristics, it is required that all the free parameters of the transfer function be used for the approximation. To achieve this requirement, the number of constraints on the amlitude and phase characteristics is defined first on general interpolation bases. Constant or arbitrarily prescribed lowpass or bandpass group delay and amplitude characteristics are approximated in the maximally flat, ripple or mixed sense for lumped filters, whereas highpass and band rejection characteristics are also considered for distributed or sampled data filters. The relationship between the number of free parameters and the number of amplitude and phase constraints for a given degree is derived for non-reciprocal as well as for reciprocal lossy and reciprocal reactant cases. Conditions are derived for the distribution of free parameters between the passband and stopband amplitude and phase characteristics for transfer functions with Hurwitzian denominator and also for monotonic amplitude characteristics in the transition band. Some published separate and simultaneous approximation methods are evaluated and compared on the above bases. It is pointed out that some of these methods do not satisfy the above requirements, although the optimal solution would exhibit higher performances.     

Nonsmooth stabilizability and feedback linearization of discrete-time nonlinear systems

We consider the problem of stabilizing a discrete-time nonlinear system using a feedback which is not necessarily smooth. A sufficient condition for global dynamical stabilizability of single-input triangular systems is given. We obtain conditions expressed in terms of distributions for the nonsmooth feedback triangularization and linearization of discrete-time systems. Relations between stabilization and linearization of discrete-time systems are given.     

Substituent distribution within cross-linked and hydroxypropylated sweet potato starch and potato starch

Revealing the substituents distribution within starch can help to understand the changes of starch properties after modification. The distribution of substituents over cross-linked and hydroxypropylated sweet potato starch was investigated and compared with modified potato starch. The starches were cross-linked with sodium trimetaphosphate and/or hydroxypropylated with propylene oxide. The native and modified starches were gelatinized and hydrolysed by pullulanase, β-amylase, α-amylase and a combination of pullulanase, α-amylase and amyloglucosidase. The hydrolysates were analysed by HPSEC, HPAEC and MALDI-TOF mass spectrometry. Cross-linking had only a slight effect on the enzymatic hydrolysis, where hydroxypropylation evidently limited the enzymatic hydrolysis. The results obtained suggest that the hydroxypropyl substituents are not distributed regularly over the starch chains. Although the average substitution was around 2 hydroxypropyl groups per 10 glucose units, in the enzyme digests of hydroxypropylated starches, oligomer fragments of 10–15 glucose units, carrying 5–8 hydroxypropyl groups, were identified. It is hypothesised that higher levels of substituents are present in the amorphous regions and periphery of clusters of starch granules. This is the first time that the location of hydroxypropyl groups within sweet potato starch has been examined in this detail. Despite significant differences in granule architecture between starches from potato and sweet potato, similar patterns of hydroxypropylation have been found.     

Positron annihilation and nano-indentation analysis of irradiation effects on the microstructure and hardening of A508-3 steels used in Chinese HTGR

The irradiation and annealing behavior of Chinese A508-3 reactor pressure vessel (RPV) steel (0.04 wt% Cu) after 3 MeV Fe-ion irradiation ranging from 0.1 to 20 dpa at room temperature (called RTRPV) and high temperature (250?°C, called HTRPV) was studied by positron annihilation Doppler broadening (PADB) spectroscopy and nano-indentation hardness. PADB showed that the density of vacancy-type defects was higher for low-temperature irradiations. The higher hardness was found after high-temperature irradiation because of the formation of solute clusters during irradiation. Positron annihilation measurements revealed the interaction and clustering of vacancies with solute clusters which were introduced by Fe-ion irradiation. For both RTRPVs and HTRPVs, the positron defect parameter and positron diffusion length showed the recovery of the irradiation-induced defects. Total recovery was observed after annealing at 450 °C.