The Failure of the Strong Pumping Lemma for Multiple Context-Free Languages

Seki et al. (Theor. Comput. Sci. 88(2):191–229, 1991) showed that every m-multiple context-free language L is weakly 2m-iterative in the sense that either L is finite or L contains a subset of the form \(\{ u_{0} w_{1}^{i} u_{1} \cdots w_{2m}^{i} u_{2m} \mid i \in \mathbb {N}\}\) , where w ₁?w _2n ≠ε. Whether every m-multiple context-free language L is 2m-iterative, that is to say, whether all but finitely many elements z of L can be written as z=u ₀ w ₁ u ₁?w _2m u _2m with w ₁?w _2m ≠ε and \(\{ u_{0} w_{1}^{i} u_{1} \cdots w_{2m}^{i} u_{2m} \mid i \in \mathbb {N}\} \subseteq L\) , has been open. We show that there is a 3-multiple context-free language that is not k-iterative for any k.     

Quantifying the evolution of TTCN-3 as a language

Ten years of maintenance, nine published revisions of the standards for the Testing and Test Control Notation version 3 (TTCN-3), more than 500 change requests since 2006, and 10 years of activity on the official TTCN-3 mailing list add up to a rich history, not unlike that of many successful Open Source Software (OSS) projects. In this article, we contemplate TTCN-3 in the context of software evolution and examine its history quantitatively. We mined the changes in the textual content of the standards, the data in change requests from the past 5 years, and the mailing list archives from the past 10 years. In addition, to characterize the use of the TTCN-3 we investigated the meta-data of the contributions at the TTCN-3 User Conference, and the use of language constructs in a large-scale TTCN-3 test suite. Based on these data sets, we first analyze the amount, density, and location of changes within the different parts of the standard. Then, we analyze the activity and focus of the user community and the maintenance team in both the change request management system and the official TTCN-3 mailing list. Finally, we analyze the distribution of contributions at the TTCN-3 User Conference across different topics over the past 8 years and construct use anomalies during the development of a large-scale test suite. Our findings indicate that the TTCN-3 is becoming increasingly stable as the overall change density and intensity, as well as the number of change requests are decreasing, despite the monotonous increase in the size of the standards.     

Proline versus charge concept for protein stabilization against proteolytic attack

The virtue of the so-called ‘proline concept’ andthe ‘charge concept’ for stabilizing protease-susceptibleregions of a protein structure was compared on bovine pancreaticribonuclease A. Alanine 20 and serine 21, both of whichare located in a loop that is susceptible to the unspecificproteases subtilisin Carlsberg, subtilisin BPN', proteinaseK and elastase, were replaced with proline or lysine by site-directedmutagenesis. The rate constant of proteolysis was decreasedby up to three orders of magnitude for the proline mutants dependingon the site of the mutation and the protease used. In contrast,substitution by lysine increased the proteolytic resistanceby only one order of magnitude characterizing the ‘prolineconcept’ as superior to the ‘charge concept’.Although the four applied proteases are considered to be unspecific,the degree of stabilization of the ribonuclease molecule variedconsiderably, indicating the impact of individual differencesin their substrate specificity on the proteolytic resistanceand degradation pathway of the target protein. Received May 12, 2003; revised October 23, 2003; accepted October 30, 2003     

Synthesis of end-branched poly(ethylene glycol)s by aqueous atom transfer radical polymerization

Summary This article reports the synthesis of novel hydrophilic end-branched poly(ethylene glycol)s, in aqueous media by atom transfer radical polymerization (ATRP). Poly(ethylene glycol)s with molecular weights 10,000 and 16,000 were end-functionalized and used as bifunctional initiators for the polymerization of a poly(ethylene glycol) macromonomer with a molecular weight of 2,000 (PEGMA), either by aqueous ATRP or in a watedmethanol (l/l V/V) mixture. For both macroinitiators a DP of 10 was the target, giving an average of 5 branches in each end. The rates of polymerization were of the same order of magnitude when the polymerizations were initiated by either of the two macroinitiators in watedmethanol (l/l V/V). When a bifunctional oligo(ethy1ene glycol) initiator (M_n = 600) was used to study the polymerization of PEGMA in water/methanol a reduction in the rate of polymerization was observed indicating an influence of the molecular weight of the initiator on the rate of polymerization. Received 25 Maich 2002/Revised 8 November 2002/Accepted 8 November 2002 Correspondence to Jorgen Kops     

Hydroisomerization of Renewable and Fossil n-Alkanes over Bifunctional Dealuminated ZSM-5 Catalysts

The hydroisomerization of two long-chain n-alkane mixtures was investigated over bifunctional Pt/H-ZSM-5 catalysts before and after dealumination of preshaped zeolite/binder pellets. The hydroisomerization over the dealuminated catalysts leads to more isomers and less cracking products. Consequently, higher ratios of multi- to mono-branched isomerization products are formed as expected for large- rather than medium-pore zeolites. This indicates a higher availability of space in the vicinity of the active sites and provides an attractive route to make medium-pore zeolites suitable for upgrading higher boiling hydrocarbon feeds.     

Crack growth angle prediction of an internal crack under mixed mode load for unfilled elastomer using the strain energy density factor

This article investigates the prediction of the crack growth angle of an existing internal crack under mixed mode loading at the crack tip for an unfilled ethylene propylene diene terpolymer rubber (EPDM). For the realization of mixed mode loading, the cracks of the uniaxial loaded specimens were oriented with different angles to the loading direction. The energy density factor was used as a potential criterion for determining the crack growth angle. The determination of the strain energy density factor was carried out simulatively in Abaqus. The second-order Ogden model was used to describe the rubber-like material behavior. The relative local minimum of the strain energy density factor provides the possible growth angle. The experimental investigations show that the initial cracks grow orthogonally to the loading direction for the different crack orientation angles. For the crack orientation angle parallel to the load direction, the crack growth was observed because the strong stretching of the specimen caused strong necking in the crack region. The crack growth for the remaining crack orientation angles were induced due to shear loading at the crack tip. The predictive angle of different crack orientation angles shows very good accordance to the measured crack growth angles.     

纵向旋转切削加工对环形零件畸变的影响

通过旋转试验和有限元分析介绍了工件在切削加工过程中产生的畸变情况，分析了工件的装夹方式、切削速度、切削深度和进刀量对100Cr6钢环圆度的影响。通过去应力退火释放冷加工诱发的残余应力后工件的圆度与切削参数有关。另外测试了被试验环的表面残余应力，其表面残余应力与装夹方式有关。将测量的装夹力作为计算参数输入，通过有限元分析方法测试了装夹方式对工件变形的影响。协同测量结果示出了装夹方式影响工件变形的一个主要因素，表面残余应力与工件的径向变形有关，最大的拉伸应力位于夹口位置。旋转切削试验结果表明，提高切削速度圆度会稍有增加；随着切削深度的加大，圆度呈下降趋势，尽管切削力增加了；进给量的增加会导致更高的切削力，因此圆度值也增加；常规的去应力退火可使被加工环的圆度值增加。     

Think,feel, bid: the impact of environmental conditions on the role of bidders’ cognitive and affective processes in auction bidding

Environmental conditions and the interplay of cognitive and affective processes both exert influences on bidding behavior. This paper brings the above together, considering how the (external) auction environment determines the impact of (internal) cognitive and affective processes on bidding behavior, assessed in comparison to the optimal bid. Two aspects of the auction environment were considered, namely auction dynamics (low: first-price sealed-bid auction, high: Dutch auction) and value uncertainty (low, high). In a laboratory experiment, we assess bidders’ cognitive workload and emotional arousal through physiological measurements. We find that higher auction dynamics increase the impact of emotional arousal on bid deviations, but not that of cognitive workload. Higher value uncertainty, conversely, increases the impact of cognitive workload on bid deviations, but not that of emotional arousal. Taken together, the auction environment is a critical factor in understanding the nature of the underlying decision process and its impact on bids.     

What can possibly go wrong? Anticipatory work in space operations

This paper explores how different forms of anticipatory work contribute to reliability in high-risk space operations. It is based on ethnographic field work, participant observation and interviews supplemented with video recordings from a control room responsible for operating a microgravity greenhouse at the International Space Station (ISS). Drawing on examples from different stages of a biological experiment on the ISS, we demonstrate how engineers, researchers and technicians work to anticipate and proactively mitigate possible problems. Space research is expensive and risky. The experiments are planned over the course of many years by a globally distributed network of organizations. Owing to the inaccessibility of the ISS, every trivial detail that could possibly cause a problem is subject to scrutiny. We discuss what we label anticipatory work: practices constituted of an entanglement of cognitive, social and technical elements involved in anticipating and proactively mitigating everything that might go wrong. We show how the nature of anticipatory work changes between planning and the operational phases of an experiment. In the planning phase, operators inscribe their anticipation into technology and procedures. In the operational phase, we show how troubleshooting involves the ability to look ahead in the evolving temporal trajectory of the ISS operations and to juggle pre-planned fixes along these trajectories. A key objective of this paper is to illustrate how anticipation is shared between humans and different forms of technology. Moreover, it illustrates the importance of including considerations of temporality in safety and reliability research.