Beginners’ progress in early arithmetic in the Swedish compulsory school

This article focuses on spontaneous knowledge-building in the field of “the arithmetic of the child.” The aim is to investigate the conceptual progress of fifteen children during their early school years in the compulsory school. The study is based on the epistemology of radical constructivism and the methodology of “multiple clinical interviews”. A model of “the arithmetic of the child” elucidates mental structures used by the child in solving problems. The individual interviews are video-recorded. The results show that the children's solutions are compatible with the model. When the researcher adapts problems to the children's available concepts to bring out their capability, they all solve them in their own ways. Further, the conceptual levels of the children differ to a great extent at school start and do not all show conceptual progress after 2 years of traditional teaching. An implication for an alternative teaching process is suggested, namely “the arithmetic for the child”, accomplished in a triadic teaching process.     

Aroma WaterLOGSY: a fast and sensitive screening tool for drug discovery

One-dimensional NMR spectroscopy has proven to be a powerful technique for screening compound libraries in drug discovery. We report a novel water ligand-observed gradient spectroscopy (WaterLOGSY) pulse sequence, named Aroma WaterLOGSY, that selectively detects aromatic WaterLOGSY signals from compounds or ligands. In the Aroma WaterLOGSY, water magnetization is untouched after water excitation and utilizes the whole period of the remaining pulse sequence to relax back to the +z direction. Due to the phase cycling design, the water magnetization is allowed to relax for the period of two full scans before it gets inverted again. Therefore, the recycle delay can be significantly shortened. Within similar experimental time, Aroma WaterLOGSY shows approximately two times higher sensitivity than the standard scheme. This method also allows the use of non-deuterated reagents, thereby accelerating experimental set-up time for ligand-binding studies.     

Photoinduced electron transfer in Zn(II)porphyrin-bridge-Pt(II)acetylide complexes: variation in rate with anchoring group and position of the bridge

The synthesis and photophysical characterization of two sets of zinc porphyrin platinum acetylide complexes are reported. The two sets of molecules differ in the way the bridging phenyl-ethynyl unit is attached to the porphyrin ring. One set is attached via an ethynyl unit on the β position, while the other set is attached via a phenyl unit on the meso position of the porphyrin. These were compared with previously studied complexes where attachment was made via an ethynyl unit on the meso position. Femtosecond transient absorption measurements showed in all systems a rapid quenching of the porphyrin singlet state. Electron transfer is suggested as the quenching mechanism, followed by an even faster recombination to form both the porphyrin ground and triplet excited states. This is supported by the variation in quenching rate and porphyrin triplet yield with solvent polarity, and the observation of an intermediate state in the meso-phenyl linked systems. The different linking motifs between the dyads resulted in significant variations in electron transfer rates.     

Direct electrochemistry and bioelectrocatalysis of a class II non-symbiotic plant haemoglobin immobilised on screen-printed carbon electrodes

In this study, direct electron transfer (ET) has been achieved between an immobilised non-symbiotic plant haemoglobin class II from Beta vulgaris (nsBvHb2) and three different screen-printed carbon electrodes based on graphite (SPCE), multi-walled carbon nanotubes (MWCNT-SPCE), and single-walled carbon nanotubes (SWCNT-SPCE) without the aid of any electron mediator. The nsBvHb2 modified electrodes were studied with cyclic voltammetry (CV) and also when placed in a wall-jet flow through cell for their electrocatalytic properties for reduction of H₂O₂. The immobilised nsBvHb2 displayed a couple of stable and well-defined redox peaks with a formal potential (E°′) of ?33.5 mV (vs. Ag|AgCl|3 M KCl) at pH 7.4. The ET rate constant of nsBvHb2, k _s, was also determined at the surface of the three types of electrodes in phosphate buffer solution pH 7.4, and was found to be 0.50 s^?1 on SPCE, 2.78 s^?1 on MWCNT-SPCE and 4.06 s^?1 on SWCNT-SPCE, respectively. The average surface coverage of electrochemically active nsBvHb2 immobilised on the SPCEs, MWCNT-SPCEs and SWCNT-SPCEs obtained was 2.85?×?10^?10 mol cm^?2, 4.13?×?10^?10 mol cm^?2 and 5.20?×?10^?10 mol cm^?2. During the experiments the immobilised nsBvHb2 was stable and kept its electrochemical and catalytic activities. The nsBvHb2 modified electrodes also displayed an excellent response to the reduction of hydrogen peroxide (H₂O₂) with a linear detection range from 1 μM to 1000 μM on the surface of SPCEs, from 0.5 μM to 1000 μM on MWCNT-SPCEs, and from 0.1 μM to 1000 μM on SWCNT-SPCEs. The lower limit of detection was 0.8 μM, 0.4 μM and 0.1 μM at 3σ at the SPCEs, the MWCNT-SPCEs, and the SWCNT-SPCEs, respectively, and the apparent Michaelis–Menten constant, $ {\hbox{K}}_{\rm{M}}^{\rm{app}} $ , for the H₂O₂ sensors was estimated to be 0.32 mM , 0.29 mM and 0.27 mM, respectively.     

“Clickable” affinity ligands for effective separation of glycoproteins

In this paper, we present a new modular approach to immobilize boronic acid ligands that can offer effective separation of glycoproteins. A new “clickable” boronic acid ligand was synthesized by introducing a terminal acetylene group into commercially available 3-aminophenyl boronic acid. The clickable ligand, 3-(prop-2-ynyloxycarbonylamino)phenylboronic acid (2) could be easily coupled to azide-functionalized hydrophilic Sepharose using Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction under mild condition. Compared to other boronic acid affinity gels, the new affinity gel displayed superior effectiveness in separating model glycoproteins (ovalbumin and RNase B) from closely related bovine serum albumin and RNase A in the presence of crude Escherichia coli proteins. Because of the simplicity of the immobilization through “click chemistry”, the new ligand 2 is expected to not only offer improved glycoprotein separation in other formats, but also act as a useful building block to develop new chemical sensors for analysis of other glycan compounds.     

Transverse, tilting and cross-coupling stiffness of cylindrical rubber isolators in the audible frequency range—The wave-guide solution

Audio-frequency wave-guide models for antisymmetric dynamic stiffness of arbitrary long elastomer cylinders are presented. The locally non-mixed boundary conditions at the lateral and radial surfaces are simultaneously satisfied by using the modes corresponding to the dispersion relation for axial waves in cylinders satisfying the stress free boundary conditions at the curved radial boundaries, while the displacement conditions on the flat cylinder ends are satisfied by mode matching. The elastomer is modelled as nearly incompressible with deviatoric visco-elasticity based on a fractional derivative, standard linear solid embodying a Mittag-Leffler relaxation kernel, the main advantage being the minimum parameter number required to successfully model the material properties over a broad frequency band. The stiffness is found to depend strongly on frequency; displaying resonances and anti-resonances. The method is compared with and verified against finite element models. In addition, comparison to thin beam theories, i.e. Euler and Timoschenko theory and a simple shear model, is presented, illustrating the limitations of these models.     

Random laser action in bovine semen

Experiments using bovine semen reveal that the addition of a high-gain water soluble dye results in random laser action when excited by a Q-switched, frequency doubled, Nd:Yag laser. The data shows that the linewidth collapse of the emission is correlated to the sperm count of the individual samples, potentially making this a rapid, low sample volume approach to count determination.     

Graphene as a reversible spin manipulator of molecular magnets

One of the primary objectives in molecular nanospintronics is to manipulate the spin states of organic molecules with a d-electron center, by suitable external means. In this Letter, we demonstrate by first principles density functional calculations, as well as second order perturbation theory, that a strain induced change of the spin state, from S=1→S=2, takes place for an iron porphyrin (FeP) molecule deposited at a divacancy site in a graphene lattice. The process is reversible in the sense that the application of tensile or compressive strains in the graphene lattice can stabilize FeP in different spin states, each with a unique saturation moment and easy axis orientation. The effect is brought about by a change in Fe-N bond length in FeP, which influences the molecular level diagram as well as the interaction between the C atoms of the graphene layer and the molecular orbitals of FeP.     

Sub-nanometer distances and cluster shapes in dense hydrogen and in higher levels of hydrogen Rydberg matter by phase-delay spectroscopy

The inter-atomic distances in potassium clusters of Rydberg matter (RM) at excitation levels n _B = 4–8 were recently measured by phase-delay spectroscopy (Holmlid, J Nanopart Res 12: 273, 2010). Excitation levels n _B < 4 with shorter inter-atomic distances exist for hydrogen clusters, and distances down to 140 pm are now measured with this light-scattering method. The clusters studied have maximum dimensions from 0.3 nm up to several tens of nm, often being planar. A weak carbon dioxide laser beam interacts with the clusters in a tunable RM cavity. A strong fringe structure is observed as a function of the end-grating angular position. Delay lengths in the clusters are derived from the fringe structure, corresponding to twice the distance between rows or planes in the clusters. Good agreement with predicted and a few previously measured distances in excitation levels n _B = 1, 2, and 3 is found. Close-packing is the main structure both in planar and 3D clusters. Planar clusters are only observed for n _B = 1 and 3, while 3D clusters are found in excitation levels n _B = 1, 2 and 3. The cluster–cluster distance in stacks of planar clusters for n _B = 2 and 3 is now observed for the first time.