Using a Stochastic Complexity Measure to Check the Efficient Market Hypothesis

The weak form of the Efficient Market Hypothesis (EMH) states that current market price reflects fully the information from past prices and rules out prediction based on price data alone. No recent test of time series of stock returns rejects this weak-form hypothesis. This research offers another test of the weak form of the EHM that leads to different conclusions for some time series.The stochastic complexity of a time series is a measure of the number of bits needed to represent and reproduce the information in the time series. In an efficient market, compression of the time series is not possible, because there are no patterns and the stochastic complexity is high. In this research, Rissanen's context tree algorithm is used to identify recurring patterns in the data, and use them for compression. The weak form of the EMH is tested for 13 international stock indices and for all the stocks that comprise the Tel-Aviv 25 index (TA25), using sliding windows of 50, 75, and 100 consecutive daily returns. Statistically significant compression is detected in ten of the international stock index series. In the aggregate, 60% to 84% of the TA25 stocks tested demonstrate compressibility beyond randomness. This indicates potential market inefficiency.     

A survey of recent advances in SAT-based formal verification

Dramatic improvements in SAT solver technology over the last decade and the growing need for more efficient and scalable verification solutions have fueled research in verification methods based on SAT solvers. This paper presents a survey of the latest developments in SAT-based formal verification, including incomplete methods such as bounded model checking and complete methods for model checking. We focus on how the surveyed techniques formulate the verification problem as a SAT problem and how they exploit crucial aspects of a SAT solver, such as application-specific heuristics and conflict-driven learning. Finally, we summarize the noteworthy achievements in this area so far and note the major challenges in making this technology more pervasive in industrial design verification flows.     

On the kinetics of AlH3 decomposition and the subsequent Al oxidation

Metal hydrides are used for hydrogen storage. AlH₃ shows a capacity to store about 10 wt% hydrogen. Its hydrogen is split-off in the temperature interval of 400–500 K. On dehydrogenation a nano-structured Al material emerges with specific surfaces up to 15–20 m²/g. The surface areas depend on the heating rate because of a temperature dependent crystallite growth. The resulting Al oxidizes up to 20–25% weight on air access forming an alumina passivation layer of 3–4 nm thickness on all exposed surfaces. The heat released from this Al oxidation induces a high risk to this type of hydrogen storage if the containment might be destroyed, accidentally. The kinetics of the dehydrogenation and the subsequent oxidation is investigated by methods of thermal analysis. A reaction scheme is confirmed which consists of a starting Avrami-Erofeev mechanism followed by formal 1st order oxidation on unlimited air access. The kinetic parameters, activation energies and pre-exponentials are evaluated and can be used to calculate the reaction progress. Together with the heat of the Al oxidation the overall heat release and the related rate can be estimated.     

Partial oxidation of methane in hollow‐fiber membrane reactors based on alkaline‐earth metal‐free CO2‐tolerant oxide

The U‐shaped alkaline‐earth metal‐free CO₂‐stable oxide hollow‐fiber membranes based on (Pr_0.9La_0.1)₂(Ni_0.74Cu_0.21Ga_0.05)O_4+δ (PLNCG) are prepared by a phase‐inversion spinning process and applied successfully in the partial oxidation of methane (POM) to syngas. The effects of temperature, CH₄ concentration and flow rate of the feed air on CH₄ conversion, CO selectivity, H₂/CO ratio, and oxygen permeation flux through the PLNCG hollow‐fiber membrane are investigated in detail. The oxygen permeation flux arrives at approximately 10.5 mL/min cm² and the CO selectivity is higher than 99.5% with a CH₄ conversion of 97.0% and a H₂/CO ratio of 1.8 during 140 h steady operation. The spent hollow‐fiber membrane still maintains a dense microstructure and the Ruddlesden‐Popper K₂NiF₄‐type structure, which indicates that the U‐shaped alkaline‐earth metal‐free CO₂‐tolerant PLNCG hollow‐fiber membrane reactor can be steadily operated for POM to syngas with good performance. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3587–3595, 2014     

Photo-vulcanization using thiol-ene chemistry: Film formation,morphology and network characteristics of UV crosslinked rubber latices

The photo-vulcanization with versatile thiol-ene chemistry represents an innovative approach to crosslink diene-rubber materials both in latex and in solid film state. In this work, the structure of elastomer-based thiol-ene networks and the morphology after film formation are studied in detail using electron microscopic techniques, atomic force microscopy and multiple-quantum solid-state NMR spectroscopy. Additionally, film formation properties and corresponding macroscopic properties of photo-vulcanized natural rubber (NR) latex and its synthetic counterpart, isoprene rubber (IR) latex, are determined in dependence on the curing procedure (pre- and post-vulcanization). The results reveal that thiol-ene cured elastomers comprise homogenously distributed crosslinks with a low amount of short chain defects. Whilst photochemically pre-cured NR latex particles provide coherent films, the film formation and mechanical properties of IR are strongly governed by the crosslink density of the latex particles. In film state, photo-vulcanization promotes narrow crosslink distributions and excellent tensile properties of both NR and IR.     

优化车门ECU功耗的新概念

<正>在现代汽车中,电子控制单元(ECU)的数量不断增长。现代电子零部件增加了许多功能可为驾驶员提供更多的信息和更舒适的环境,