Synthesis of α-hydroxy-ω-amino poly(ethylene oxide) and its use in reaction injection moulding (RIM)

Summary Computer simulations show that oligomers with two different terminal groups with dissimilar reactivities for isocyanates give a delayed viscosity rise in polyurethanes. This is a desired behaviour for RIM processes. Therefore, an -hydroxy--amino poly(ethylene oxide) (HAPEO) has been prepared. The synthesis was carried out by the ethoxylation of 2-hydroxyethyl phthalimide as a blocked amine. Hydrazinolysis appears to be the best way to obtain the deblocked oligomer. The product properties were compared with an oligomeric diamine ether (Jeffamine D2000). The gel time of HAPEO (M_n=500) and JAD2000 (M_n=2000) was the same (2 sec.). The product with HAPEO had a higher modulus, a comparable impact and tensile strength and a lower elongation at break.     

Geochemistry and flooding as determining factors of plant species composition in Dutch winter-flooded riverine grasslands

Dutch water policy aims for more frequent, controlled flooding of river valley floodplains to avoid unwanted flooding elsewhere; in anticipation of increased flooding risks resulting from climate changes. Controlled flooding usually takes place in winter in parts of the valleys which had not been subject to flooding in the last decades. It may thus affect existing nature with its conservation values. The goal of this study was to clarify the geochemical and hydrological factors determining plant species composition of winter-flooded river valley grasslands. A correlative study was carried out in 43 sites in 13 Dutch river valley floodplains, with measurements of flooding regime, vegetation composition, soil nutrients and soil pH status. With the use of canonical correspondence analysis (CCA) the plant species composition was investigated in relation to the geochemical variables and the winter winter-flooding regime. We found that the distributions of target species and non-target species were clearly correlated with geochemical characteristics and flooding regime. Clustering of sites within the CCA plots has led us to distinguish between four types of winter flooding in our areas: floodplains with (a) accumulating rain water, (b) low groundwater levels flooded with river water, (c) discharging groundwater and (d) high groundwater levels flooded with river water. Our major conclusions are (1) the winter groundwater level of winter-flooded grasslands was important for evaluating the effects of winter flooding on the geochemistry and plant species composition, and (2) winter winter-flooding effects were largely determined by the nature of the flooding. A high frequency of flooding particularly favoured a small set of common plant species. In areas with groundwater seepage, winter flooding may provide geochemical conditions suitable for diverse vegetation types with rare species. Rainwater flooded sites appeared less suitable for most target species.     

Model Checking Markov Chains with Actions and State Labels

In the past, logics of several kinds have been proposed for reasoning about discrete-time or continuous-time Markov chains. Most of these logics rely on either state labels (atomic propositions) or on transition labels (actions). However, in several applications it is useful to reason about both state properties and action sequences. For this purpose, we introduce the logic as CSL which provides a powerful means to characterize execution paths of Markov chains with actions and state labels. asCSL can be regarded as an extension of the purely state-based logic CSL (continuous stochastic logic). In asCSL, path properties are characterized by regular expressions over actions and state formulas. Thus, the truth value of path formulas depends not only on the available actions in a given time interval, but also on the validity of certain state formulas in intermediate states. We compare the expressive power of CSL and asCSL and show that even the state-based fragment of asCSL is strictly more expressive than CSL if time intervals starting at zero are employed. Using an automaton-based technique, an asCSL formula and a Markov chain with actions and state labels are combined into a product Markov chain. For time intervals starting at zero, we establish a reduction of the model checking problem for asCSL to CSL model checking on this product Markov chain. The usefulness of our approach is illustrated with an elaborate model of a scalable cellular communication system, for which several properties are formalized by means of asCSL formulas and checked using the new procedure     

Functional imaging of the heart

The 11 papers in this special issue focus on the functional imaging of the heart and the rapid progression of all modalities towards 4-D imaging.     

Sequential and Distributed Model Checking of Petri Net Specifications

In this paper we present algorithms for model checking CTL over systems specified as Petri nets. We present sequential as well as distributed model checking algorithms. The algorithms rely on an explicit representation of the system state space, but do not require the transition relation to be explicitly available; it is recomputed whenever required. This approach allows us to model check very large systems, with hundreds of millions of states, in a fast and efficient way. Furthermore, our distributed algorithms scale very well, as they show efficiencies in the range of 80 to 100%.     

Spatial power fluctuation correlations in urban rooftop photovoltaic systems

In this paper, we investigate the spatial dependence of variations in power output of small residential solar photovoltaic (PV) systems in a densely populated urban area (≈100km²) in and around Utrecht, the Netherlands. Research into the geo‐statistical behavior of this kind of randomly spaced collection of PV systems is complementary to other studies in the field of compact regularly spaced MW‐scale PV plants. Fluctuations in power output between PV systems are correlated up to a certain decorrelation length. Decorrelation is reached (within 1 − e⁻³≈95%) in an exponential model and the spatial scale ranges from 100 m to approx. 15 km, with a mean value 0.34(±0.2), 2.6(±0.3), and 5.0(±0.5) km for measurement time step of the time series of respectively 1, 5, and 15 min. These length scales are typical for an urban environment and is important for reduction of variability in aggregated output variability of PV systems. Furthermore, the distance‐independent variability still itself was found to be strictly linearly dependent on daily mean variability values. This is a good validation of the decorrelation of inter‐system ramp rate correlation over distances longer than the characteristic decorrelation length. Copyright © 2014 John Wiley & Sons, Ltd.     

Compact polarization-independent Mach-Zehnder space switch combining carrier depletion and the quantum confined Stark effect

We have developed an n-doped InGaAs-InAsP quantum well between InP, which is suited for a polarization-independent Mach-Zender interferometric (MZI) space switch operating at 1.55 /spl mu/m. The InAsP is compressively strained and the InGaAs is tensile strained for polarization independence and for strain balancing. The important boundary condition for the design of this structure is the waveguide loss, which we limit to 0.6 dB/cm, and the crosstalk due to imbalance in the MZI, which we limit to <-30 dB. To reduce the size of the phase shifting region, while imposing this boundary condition, we combine the quantum confined Stark effect (QCSE) effect and the carrier-depletion effect by using an n-doped quantum well. The QCSE was first optimized for an undoped InGaAs-InAsP quantum well. A polarization independent /spl Delta/n of 7.8/spl middot/10/sup -4/ at 100 kV/cm was obtained at the expense of 0.2-dB/cm excess waveguide loss and 0.1-dB/mm electroabsorption loss. The carrier-depletion effect in a 2/spl middot/10/sup 11/cm/sup -2/-doped QW increases /spl Delta/n with a factor 2.6 to 2/spl middot/10/sup -3/, at the expense of 0.4-dB/cm free-carrier absorption-induced waveguide loss. The combination of the QCSE and carrier depletion results in a phase-shifter length of 0.46 mm for an MZI in push-pull configuration.     

Light-activated switching based on light-induced band-structure modifications

We have investigated the mechanism of light-induced band-structure modifications to be employed in light-activated switching devices. This mechanism has been studied in a specially designed modulation doped GaAs/Al_xGa_1−xAs heterostructure by means of photoluminescence spectroscopy at low temperatures. It is related to the build-up of photogenerated carriers in the heterostructure, thereby changing the band structure. We show that this mechanism can be employed in a light-activated all-optical switch or a light-activated all-optical modulator with an expected contrast ratio of 27:1.     

Model-checking algorithms for continuous-time Markov chains

Continuous-time Markov chains (CTMCs) have been widely used to determine system performance and dependability characteristics. Their analysis most often concerns the computation of steady-state and transient-state probabilities. This paper introduces a branching temporal logic for expressing real-time probabilistic properties on CTMCs and presents approximate model checking algorithms for this logic. The logic, an extension of the continuous stochastic logic CSL of Aziz et al. (1995, 2000), contains a time-bounded until operator to express probabilistic timing properties over paths as well as an operator to express steady-state probabilities. We show that the model checking problem for this logic reduces to a system of linear equations (for unbounded until and the steady-state operator) and a Volterra integral equation system (for time-bounded until). We then show that the problem of model-checking time-bounded until properties can be reduced to the problem of computing transient state probabilities for CTMCs. This allows the verification of probabilistic timing properties by efficient techniques for transient analysis for CTMCs such as uniformization. Finally, we show that a variant of lumping equivalence (bisimulation), a well-known notion for aggregating CTMCs, preserves the validity of all formulas in the logic.