How concept images affect students’ interpretations of Newton's method

Knowing when students have the prerequisite knowledge to be able to read and understand a mathematical text is a perennial concern for instructors. Using text describing Newton's method and Vinner's notion of concept image, we exemplify how prerequisite knowledge influences understanding. Through clinical interviews with first-semester calculus students, we determined how evoked concept images of tangent lines and roots contributed to students’ interpretation and application of Newton's method. Results show that some students’ concept images of root and tangent line developed throughout the interview process, and most students were able to adequately interpret the text on Newton's method. However, students with insufficient concept images of tangent line and students who were unwilling or unable to modify their concept images of tangent line after reading the text were not successful in interpreting Newton's method.     

Structural influence on the 2D-conductivity of thin Au films

Thin gold films (60Å–500Å) are prepared simultaneously onto carbon coated quartz- and NaCl-crystals at different substrate temperatures (5 KT300 K) in uhv. For the Au-films condensed onto the quartz substrates the temperature dependence of the electrical resistivity is measured between 1.7 K and 300 K in situ. The corresponding Au-films condensed onto NaCl are removed and investigated in an EM. The observed hole and channel structures are related to the 2D-conductivity behavior.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Ion chromatographic determination of oxalate in plasma: correlation study with an enzymatic method

An ion chromatographic (IC) method for the determination of oxalate in plasma was developed. The method exploits a rapid and simple sample preparation step that substantially reduces the plasma chloride level to facilitate the oxalate determination. The chloride is removed as silver chloride by using a cation-exchange resin in the silver cation form. The dependence on chloride concentration and pH was evaluated. The oxalate recovery in plasma samples was found to be 93 ± 18% (n=4 trials) according to a standard addition study. A comparison of the IC method with an enzymatic method indicated that both methods measure the same oxalate concentration over the range examined, 5–300 μM. Furthermore, the comparison involved a correlation study that allowed cross-validation of the two methods, suggesting that neither is adversely affected by interferences. The detection limit of the IC method was 0.5 μM or 4.4 ng oxalate.     

Fast, easy, solvent-free, microwave-promoted Michael addition of anilines to α,β-unsaturated alkenes: synthesis of N-aryl functionalized β-amino esters and acids

The rapid, simple, microwave-promoted synthesis of N-aryl functionalized β-amino esters using Michael addition reactions is presented. Reactions are performed neat at 200 °C for 20 min and are catalyzed by acetic acid. The esters can be easily hydrolyzed to the corresponding N-aryl functionalized β-amino acids.     

Four-arm oligonucleotide Ni(II)-cyclam-centered complexes as precursors for the generation of supramolecular periodic assemblies

The development of a multiarm metal-centered DNA building block as a precursor for the construction of supramolecular assemblies has relied upon the preparation of a Ni(II)-1,4,8,11-tetrazacyclotetradecane ligand (cyclam) functionalized with four linkers. This complex can be incorporated into a support-bound DNA sequence and the remaining three linkers can then be elongated by DNA synthesis. The result is a Ni(II)-cyclam complex tethering four 20-mer DNA strands. This building block, designed to be tetrahedral in nature, can in principle be used to form tetrahedral assemblies. These assemblies can be designed to be of known size and composition or permitted to grow into complexes of essentially infinite size, ideally the macroscopic version of a crystal.     

Imaging and differentiation of mouse embryo tissues by ToF-SIMS

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) equipped with a gold ion gun was used to image mouse embryo sections and differentiate tissue types (brain, spinal cord, skull, rib, heart and liver). Embryos were paraffin-embedded and then deparaffinized. The robustness and repeatability of the method was determined by analyzing ten tissue slices from three different embryos over a period of several weeks. Using principal component analysis (PCA) to reduce the spectral data generated by ToF-SIMS, histopathologically identified tissue types of the mouse embryos can be differentiated based on the characteristic differences in their mass spectra. These results demonstrate the ability of ToF-SIMS to determine subtle chemical differences even in fixed histological specimens.     

Structural changes and chain radius of gyration in cold-drawn polyethylene after annealing: small- and wide-angle X-ray scattering and small-angle neutron scattering studies

Samples made from linear polyethylene were drawn at room temperature and subsequently annealed at high temperatures below the melting point. The structural changes of the crystalline lamellae and lamellar superstructures as well as the single chain radius of gyration were studied by means of combined small- and wide-angle X-ray scattering and small-angle neutron scattering (SANS). After drawing, the polymeric chain segments in the crystalline phase are preferentially oriented along the drawing direction with a high degree of orientation whereas the lamellae in the samples are found to be slightly sheared exhibiting oblique surfaces as evidenced by X-ray scattering. SANS indicates that the chains are highly elongated along the drawing direction. Annealing the deformed samples at temperatures where the mechanical alpha-process of polyethylene is active leads to a thickening of both crystalline lamellae and amorphous layers. The chains in the crystalline phase retain their high degree of orientation after annealing while the lamellae are sheared to a larger extent. In addition, there is also lateral growth of the crystalline lamellae during high-temperature annealing. Despite the structural changes of the crystalline and amorphous regions, there is no evidence for global chain relaxation. The global anisotropic shape of the chains is preserved even after prolonged annealing at high temperatures. The results indicate that the mobility of polyethylene chains-as seen, e.g., by 13C NMR-is a local phenomenon. The results also yield new insight into mechanical properties of drawn PE, especially regarding stress relaxation and creep mechanisms.     

The rotational spectrum and theoretical study of a dinuclear complex, MnRe(CO)(10)

The first rotational spectrum of a dinuclear complex, MnRe(CO)(10), has been obtained using a high-resolution pulsed beam microwave spectrometer. Sixty-four hyperfine components of the J=11-->J(')=12 and J=12-->J(')=13 rotational transitions were measured for two rhenium isotopomers. The B values obtained from the experiment are B=200.36871(18) MHz for the (187)Re isotopomer and B=200.5561(10) MHz for the (185)Re isotopomer. The measured rotational constants are in reasonably good agreement with the B values calculated from the x-ray diffraction structural data, and from theoretical calculations. The gas-phase Mn-Re bond distance is approximately 2.99 A, and the calculated value is only slightly longer. The experimental quadrupole coupling constant for the manganese atom is eQq(aa) ((55)Mn)=-16.52(5) MHz, and the corresponding quadrupole coupling constants for the two rhenium isotopomers are eQq(aa) ((187)Re)=370.4(4) MHz and eQq(aa) ((185)Re)=390.9(6) MHz. The quadrupole coupling constants were also determined from a variety of theoretical calculations, with very large Gaussian orbital bases. The best estimates, at a nonrelativistic level, are eQq(aa) ((55)Mn)=0.68 MHz and eQq(aa) ((187)Re)=327.6 MHz with a 874 GTO basis set, but the results are very basis set dependent, especially the sign of the Mn quadrupole coupling. Very slight bending of angles MnC(eq)O(eq) and ReC(eq)O(eq) angles is found in the calculations.