Object wave reconstruction by phase-plate transmission electron microscopy

A method is described for the reconstruction of the amplitude and phase of the object exit wave function by phase-plate transmission electron microscopy. The proposed method can be considered as in-line holography and requires three images, taken with different phase shifts between undiffracted and diffracted electrons induced by a suitable phase-shifting device. The proposed method is applicable for arbitrary object exit wave functions and non-linear image formation. Verification of the method is performed for examples of a simulated crystalline object wave function and a wave function acquired with off-axis holography. The impact of noise on the reconstruction of the wave function is investigated.     

Combined removal of chlorinated ethenes and heavy metals by zerovalent iron in batch and continuous flow column systems

The combined removal of chlorinated ethenes and heavy metals from a simulated groundwater matrix by zerovalent iron (ZVI) was investigated. In batch, Ni (5-100 mg L(-1)) enhanced trichloroethene (TCE, 10 mg L(-1)) reduction by ZVI (100 g L(-1)) due to catalytic hydrodechlorination by bimetallic Fe0/Ni0. Cr(VI) or Zn (5-100 mg L(-1)) lowered TCE degradation rates by a factor of 2 to 13. Cr(VI) (100 mg L(-1)) in combination with Zn or Ni (50-100 mg L(-1)) inhibited TCE degradation. Addition of 20% H2(g) in the headspace, or of Zn (50-100 mg L(-1)), enhanced TCE removal in the presence of Ni and Cr(VI). Sorption of Zn to ZVI alleviated the Cr(VI) induced inhibition of bimetallic Fe0/Ni0 apparently due to release of protons necessary for TCE hydrodechlorination. In continuous ZVI columns treating tetrachloroethene (PCE, 1-2 mg L(-1)) and TCE (10 mg L(-1)), and a mixture of the metals Cr(VI), Zn(II), and Ni(II) (5 mg (L-1)), the PCE removal efficiency decreased from 100% to 90% in columns operated without heavy metals. The PCE degradation efficiency remained above 99% in columns receiving heavy metals as long as Ni was present. The findings of this study indicate the feasibility and limitations of the combined treatment of mixtures of organic and inorganic pollutants by ZVI.     

On the Fastest Vickrey Algorithm

We investigate the algorithmic performance of Vickrey-Clarke-Groves mechanisms in the single item case. We provide a formal definition of a Vickrey algorithm for this framework, and give a number of examples of Vickrey algorithms. We consider three performance criteria, one corresponding to a Pareto criterion, one to worst-case analysis, and one related to first-order stochastic dominance. We show that Pareto best Vickrey algorithms do not exist and that worst-case analysis is of no use in discriminating between Vickrey algorithms. For the case of two bidders, we show that the bisection auction stochastically dominates all Vickrey algorithms. We extend our analysis to the study of weak Vickrey algorithms and winner determination algorithms. For the case of two bidders, we show that the One-Search algorithm stochastically dominates all column monotonic weak Vickrey algorithms and that a suitably adjusted version of the bisection algorithm, the WD bisection algorithm, stochastically dominates all winner determination algorithms. The WD bisection algorithm Pareto dominates all column monotonic winner determination algorithms in the n bidder case.     

Monolithic integration of an InGaAsP-InP MQW laser/waveguide using a twin-guide structure with a mode selection layer

We demonstrate a monolithically integrated 1.55-/spl mu/m wavelength InGaAsP-InP multiple-quantum-well (MQW) laser with a passive Y-branch waveguide in a vertical twin-waveguide structure. To reduce the sensitivity of the device performance characteristics to laser cavity length and variations in the layer structure, we introduce an In/sub 0.53/Ga/sub 0.47/As absorption, or "loss" layer. This layer eliminates the propagation of the even mode, while having minimal effect on the odd mode. The threshold current densities and differential efficiencies of the devices are unaffected by the loss layer. A record high coupling efficiency of 45% from the laser to the external passive waveguide is obtained.     

Optimal experiment design for nonlinear dynamic (bio)chemical systems using sequential semidefinite programming

Optimal experiment design (OED) for parameter estimation in nonlinear dynamic (bio)chemical processes is studied in this work. To reduce the uncertainty in an experiment, a suitable measure of the Fisher information matrix or variance–covariance matrix has to be optimized. In this work, novel optimization algorithms based on sequential semidefinite programming (SDP) are proposed. The sequential SDP approach has specific advantages over sequential quadratic programming in the context of OED. First of all, it guarantees on a matrix level a decrease of the uncertainty in the parameter estimation procedure by introducing a linear matrix inequality. Second, it allows an easy formulation of E‐optimal designs in a direct optimal control optimization scheme. Finally, a third advantage of SDP is that problems involving the inverse of a matrix can be easily reformulated. The proposed techniques are illustrated in the design of experiments for a fed‐batch bioreactor and a microbial kinetics case study. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1728–1739, 2014     

Fuel cell propulsion in small fixed-wing unmanned aerial vehicles: Current status and research needs

Fuel cells are considered the most promising path to increased endurance of electric-powered small unmanned aircraft. Recent progress in fuel cell technology and hydrogen storage has resulted in several demonstrator platforms with formidable endurance. However, further research and development is needed to transition to widespread use. To help guide this changeover this paper presents a comprehensive overview of recent research activities, and highlights research challenges and opportunities. Firstly, benefits of fuel cells for unmanned vehicle propulsion are covered, and some challenges are identified. An overview of some notional demonstrator vehicles is given next to provide a panoramic view of progress made and the current state-of-the-art. Following this, research in fuel storage technology and hybridisation efforts are separately surveyed and discussed. Finally, some recommended future research areas are identified before conclusions are drawn.     

Models for Wireless Data Communications in Indoor Train Environment

The provisioning of wireless data services in the railway environment will become increasingly important for train operators and train constructors in the upcoming years. In this paper, we present models to predict train-to-wayside wireless data communications characteristics in terms of throughput, jitter, and packet loss predictions for 2G/3G networks. To this end, an extensive measurement campaign is carried out along a Belgian Intercity railway track. Based on these measurements, we apply a multiple regression, window mean, and autoregressive model. We find that the window mean model is recommended for the prediction of throughput and jitter, while the multiple regression model is more favorable for the prediction of packet loss. The implementation of these predictions in train-to-wayside communication systems can enhance the provisioning of seamless network connection necessary for a wide variety of data services.