Comprehending narratives containing flashbacks: Evidence for temporally organized representations.

This study investigated the representations that readers construct for narratives describing a sequence of events. Participants read narratives describing 4 successive events in chronological order (Event 1, Event 2, Event 3, Event 4 [E1, E2, E3, E4] Experiment 1) or in nonchronological order with E1 being mentioned in a flashback (E2, E3, E1, E4; Experiments 2-4). The information about the duration of E2 was manipulated, and the mental accessibility of E1 was tested at the end of a passage. All 4 experiments showed that E1 was less accessible if the text implied that it occurred a relatively long time ago in the described world compared with when it occurred a shorter time ago. This result suggests that readers construct a temporally organized representation even if the text structure does not suggest such an organization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reaction behaviour of monomeric β-ketoesters

Summary Polymerizable enamines were synthesized by the reaction of 2-acetoacetoxyethyl methacrylate (AAEMA) with various aliphatic mono- and diamines. The enamines were characterized by elemental analyses, IR,¹H NMR and¹³C NMR spectroscopy. Radical polymerization of synthesized enamines yielded polymers with pendant enamine groups which were also prepared by the reaction of poly(AAEMA) with the corresponding amines.     

Active centers, catalytic behavior, symbiosis and redox properties of MoV(Nb,Ta)TeO ammoxidation catalysts

Selective as well as waste forming active centers were defined for MoVNbTeO and MoVTaTeO catalysts in the ammoxidation of propane to acrylonitrile and all catalytic functionalities were assigned to specific elements at the respective active centers. Symbiosis between M1 and M2 phases of these catalysts was observed, with phase cooperation being more extensive in the Nb than Ta containing compositions. The difference in catalytic effectiveness arises most likely because contact and surface area exposure of the two respective, cooperating phase pairs are not equal. The M1 phase of the catalysts is reducible by propane and ammonia in the absence of dioxygen and is regenerable to its original, fully oxidized state by dioxygen (air). No structural collapse is observed even after 120 C₃H₈ + NH₃ reduction pulses. The so induced reduction of the catalyst extends up to 70 layers deep. The product distribution over the first few pulses is very similar to that under catalytic conditions, supporting the concept that lattice oxygen is involved in the catalytic ammoxidation process. Therefore, the ammoxidation of paraffins is a redox process, as is of course the well-known olefin ammoxidation process.     

Superplasticity in eutectoid steel

A eutectoid steel exhibited abnormally large tensile extensibility in three quite dissimilar circumstances: i) micrograin plasticity, defined by a strain-rate sensitivity exponent m = 0.42, was found at 716°C for straining the ferrite-cementite aggregate at the rate è = 4.4 x 10^-3 min^-1, giving 133 pct elongation; ii) at a much greater strain rate, ε = 25 min^-1, superplasticity appeared in austenite strained at 927°C, giving 142 pct elongation; iii) a new type of transformation plasticity was predicted and experimentally verified: 490 pct elongation resulted from thermal cycling 21 times across Ae₁. Plastic stability analysis distinguishes it from micrograin plasticity by showing that it owes to strain-hard ening during plastically stable flow; hence, there are no restrictions ε or m. Furthermore, it is not necessary to perform the straining during the transformation, since the strain-hardening capacity can be regenerated by thermal cycling through the phase transformation if the transformation serves to recover the flow stress. Additional work showed that straining during austenitizing fails to increase m above pretransformation levels. Formerly Graduate Student, Syracuse University, Syracuse, N. Y.     

mRNA openers and closers: modulating AU-rich element-controlled mRNA stability by a molecular switch in mRNA secondary structure

Approximately 3 000 genes are regulated in a time-, tissue-, and stimulus-dependent manner by degradation or stabilization of their mRNAs. The process is mediated by interaction of AU-rich elements (AREs) in the mRNA's 3'-untranslated regions with trans-acting factors. AU-rich element-controlled genes of fundamentally different functional relevance depend for their activation on one positive regulator, HuR. Here we present a methodology to exploit this central regulatory process for specific manipulation of AU-rich element-controlled gene expression at the mRNA level. With a combination of single-molecule spectroscopy, computational biology, and molecular and cellular biochemistry, we show that mRNA recognition by HuR is dependent on the presentation of the sequence motif NNUUNNUUU in single-stranded conformation. The presentation of the HuR binding site in the mRNA secondary structure appears to act analogously to a regulatory on/off switch that specifically controls HuR access to mRNAs in cis. Based on this finding we present a methodology for manipulating ARE mRNA levels by actuating this conformational switch specifically in a target mRNA. Computationally designed oligonucleotides (openers) enhance the NNUUNNUUU accessibility by rearranging the mRNA conformation. Thereby they increase in vitro and endogenous HuR-mRNA complex formation which leads to specific mRNA stabilization (as demonstrated for TNFalpha and IL-2, respectively). Induced HuR binding both inside and outside the AU-rich element promotes functional IL-2 mRNA stabilization. This opener-induced mRNA stabilization mimics the endogenous IL-2 response to CD28 stimulation in human primary T-cells. We therefore propose that controlled modulation of the AU-rich element conformation by mRNA openers or closers allows message stabilization or destabilization in cis to be specifically triggered. The described methodology might provide a means for studying distinct pathways in a complex cellular network at the node of mRNA stability control. It allows ARE gene expression to be potentially silenced or boosted. This will be of particular value for drug-target validation, allowing the diseased phenotype to ameliorate or deteriorate. Finally, the mRNA openers provide a rational starting point for target-specific mRNA stability assays to screen for low-molecular-weight compounds acting as inhibitors or activators of an mRNA structure rearrangement.     

Stability-based validation of clustering solutions

Data clustering describes a set of frequently employed techniques in exploratory data analysis to extract "natural" group structure in data. Such groupings need to be validated to separate the signal in the data from spurious structure. In this context, finding an appropriate number of clusters is a particularly important model selection question. We introduce a measure of cluster stability to assess the validity of a cluster model. This stability measure quantifies the reproducibility of clustering solutions on a second sample, and it can be interpreted as a classification risk with regard to class labels produced by a clustering algorithm. The preferred number of clusters is determined by minimizing this classification risk as a function of the number of clusters. Convincing results are achieved on simulated as well as gene expression data sets. Comparisons to other methods demonstrate the competitive performance of our method and its suitability as a general validation tool for clustering solutions in real-world problems.