Students’ emergent articulations of uncertainty while making informal statistical inferences

Research on informal statistical inference has so far paid little attention to the development of students?? expressions of uncertainty in reasoning from samples. This paper studies students?? articulations of uncertainty when engaged in informal inferential reasoning. Using data from a design experiment in Israeli Grade 5 (aged 10?C11) inquiry-based classrooms, we focus on two groups of students working with TinkerPlots on investigations with growing sample size. From our analysis, it appears that this design, especially prediction tasks, helped in promoting the students?? probabilistic language. Initially, the students oscillated between certainty-only (deterministic) and uncertainty-only (relativistic) statements. As they engaged further in their inquiries, they came to talk in more sophisticated ways with increasing awareness of what is at stake, using what can be seen as buds of probabilistic language. Attending to students?? emerging articulations of uncertainty in making judgments about patterns and trends in data may provide an opportunity to develop more sophisticated understandings of statistical inference.     

中低变质程度煤显微组分结构的13 C-NMR研究

利用13C-NMR核磁共振技术对中低变质程度煤显微组分（镜质组和惰质组）的分子结构进行了研究,计算了5种煤9个显微组分的13C-NMR结构参数,获得了样品的结构特征及变化规律。结果表明,惰质组结构中芳构化程度要高于镜质组;脂碳数量则少于镜质组,芳环上的烷烃侧链也没有镜质组长;随着煤变质程度的提高,煤分子中芳构化程度不断提高,但惰质组的芳香度随变质程度变化的规律明显不如镜质组;在中低变质阶段,对煤化进程起主导作用的的是芳构化作用而不是环缩合作用,但在惰质组中脂碳断裂形成芳环的现象不明显。惰质组中含氧官能团的总量要低于同等变质程度的镜质组。     

Effect of Confinement on Proton‐Transfer Reactions in Water Nanopools

Proton transfer from the photoacid 8‐hydroxy‐1,3,6‐pyrenetrisulfonic acid (HPTS) to water is studied in reverse micelles with ionic (AOT=sodium dioctyl sulfosuccinate) and non‐ionic (BRIJ‐30=polyoxyethylene(4)lauryl ether) surfactants. The dynamics are studied by probing the transient electronic absorption and transient vibrational absorption, both with sub‐picosecond resolution. The reverse micelle sizes range from approximately 1.6 to 5.5 nm in diameter. For both surfactants it is found that the rate of proton transfer decreases with decreasing reverse micelle size, regardless of surfactant. In addition, for AOT reverse micelles, a fraction of the photoacid molecules exhibit non‐radiative decay, preventing proton transfer.     

Mapping the Relationship between Glycosyl Acceptor Reactivity and Glycosylation Stereoselectivity

The reactivity of both coupling partners—the glycosyl donor and acceptor—is decisive for the outcome of a glycosylation reaction, in terms of both yield and stereoselectivity. Where the reactivity of glycosyl donors is well understood and can be controlled through manipulation of the functional/protecting‐group pattern, the reactivity of glycosyl acceptor alcohols is poorly understood. We here present an operationally simple system to gauge glycosyl acceptor reactivity, which employs two conformationally locked donors with stereoselectivity that critically depends on the reactivity of the nucleophile. A wide array of acceptors was screened and their structure–reactivity/stereoselectivity relationships established. By systematically varying the protecting groups, the reactivity of glycosyl acceptors can be adjusted to attain stereoselective cis‐glucosylations.     

Novel potentiometric and optical silver ion-selective sensors with subnanomolar detection limits

Ten Ag⁺-selective ionophores have been characterized in terms of their potentiometric selectivities and complex formation constants in solvent polymeric membranes. The compounds with π-coordination show much weaker interactions than those with thioether or thiocarbamate groups as the coordinating sites. Long-term studies with the best ionophores show that the lower detection limit of the best Ag⁺ sensors can be maintained in the subnanomolar range for at least 1 month. The best ionophores have also been characterized in fluorescent microspheres. The so far best lower detection limits of 3 × 10⁻¹¹ M (potentiometrically) and 2 × 10⁻¹¹ M Ag⁺ (optically) are found with bridged thiacalixarenes.     

Enantioselective synthesis of chiral porphyrin macrocyclic hosts and kinetic enantiorecognition of viologen guests

The construction of macromolecular hosts that are able to thread chiral guests in a stereoselective fashion is a big challenge. We herein describe the asymmetric synthesis of two enantiomeric C₂-symmetric porphyrin macrocyclic hosts that thread and bind different viologen guests. Time-resolved fluorescence studies show that these hosts display a factor 3 kinetic preference (ΔΔG^‡_on = 3 kJ mol⁻¹) for threading onto the different enantiomers of a viologen guest appended with bulky chiral 1-phenylethoxy termini. A smaller kinetic selectivity (ΔΔG^‡_on = 1 kJ mol⁻¹) is observed for viologens equipped with small chiral sec-butoxy termini. Kinetic selectivity is absent when the C₂-symmetric hosts are threaded onto chiral viologens appended with chiral tails in which the chiral moieties are located in the centers of the chains, rather than at the chain termini. The reason is that the termini of the latter guests, which engage in the initial stages of the threading process (entron effect), cannot discriminate because they are achiral, in contrast to the chiral termini of the former guests. Finally, our experiments show that the threading and de-threading rates are balanced in such a way that the observed binding constants are highly similar for all the investigated host–guest complexes, i.e. there is no thermodynamic selectivity.

Chiral guests display kinetic stereoselective threading through chiral porphyrin cages if their chirality is located at the chain ends and not in the centers, supporting the previously reported entron effect of threading.     

Phosphate‐Binding Characteristics and Selectivity Studies of Bifunctional Organotin Carriers

The selective recognition of the orthophosphate anion by a series of bifunctional Lewis acidic organotin compounds is investigated. The binding affinity of these carriers to anions, as measured by NMR titrations in CH₂Cl₂ obeyed the potentiometric selectivity order phosphate > sulfate > perchlorate, and provided the corresponding complex‐formation constants. More accurate calculations of these values were obtained by the segmented‐sandwich‐membrane method performed directly inside the liquid polymeric membrane. These carriers were also studied potentiometrically in polymeric liquid membranes. The results indicate that (PhBr₂Sn)₂CH₂ is 2 to 5 orders of magnitude more selective towards phosphate over other oxoanions. These results set the ground for the development of a new series of highly selective anions carriers with a wide range of possible applications.     

An additional symmetry in the Weinberg-Salam model

An additional Z₆ symmetry hidden in the fermion and Higgs sectors of the Standard Model has been found recently. It has a singular nature and is connected to the centers of the SU(3) and SU(2) subgroups of the gauge group. A lattice regularization of the Standard Model was constructed that possesses this symmetry. In this paper, we report our results on the numerical simulation of its electroweak sector.