Graphical Representations of Speed: Obstacles Preservice K‐8 Teachers Experience

This study examines the difficulties college students experience when creating and interpreting graphs in which speed is one of the variables. Nineteen students, all preservice elementary or middle school teachers, completed an upper‐level course exploring algebraic concepts. Although all of these preservice teachers had previously completed several mathematics courses, including calculus, they demonstrated widespread misconceptions about the variable speed. This study identifies four cognitive obstacles held by the students, provides excerpts of their graphical constructions and verbal interpretations, and discusses potential causes for the confusion. In particular, misconceptions arose when students interpreted the behavior and nature of speed within a graphical context, as well as in situations where they were required to construct a graph involving speed as a variable. The study concludes by offering implications for the teaching and learning of speed and its interpretation within a graphical setting.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Efficient gene delivery in differentiated human embryonic stem cells

Human embryonic stem (hES) cells are capable of differentiating into pluralistic cell types, however, spontaneous differentiation generally gives rise to a limited number of specific differentiated cell types and a large degree of cell heterogeneity. In an effort to increase the efficiency of specified hES cell differentiation, we performed a series of transient transfection of hES cells with EGFP expression vectors driven by different promoter systems, including human cellular polypeptide chain elongation factor 1 alpha (hEF1alpha), human cytomegalo-virus, and chicken beta-actin. All these promoters were found to lead reporter gene expression in undifferentiated hES cells, but very few drug-selectable transfectants were obtained and failed to maintain stable expression of the transgene with either chemical or electroporation methods. In an attempt to increase transfection efficiency and obtain stable transgene expression, differentiated hES cells expressing both mesodermal and ectodermal markers were derived using a defined medium. Differentiated hES cells were electroporated with a hEF1alpha promoter-driven EGFP or human noggin expression vector. Using RT-PCR, immunocytochemistry and fluorescence microscopy, the differentiated hES cells transfected with foreign genes were confirmed to retain stable gene and protein expression during prolonged culture. These results may provide a new tool for introducing exogenous genes readily into hES cells, thereby facilitating more directed differentiation into specific and homogenous cell populations.     

Quantitation of plasma and biliary cefpiramide concentrations in human samples using high-performance liquid chromatography

Cefpiramide is frequently used to treat biliary infections. However, no bioanalytical method has been validated to quantitate cefpiramide in human samples, particularly in bile. Therefore, this study was conducted to develop a simple, selective and validated high-performance liquid chromatographic method to determine cefpiramide in human plasma and bile. A protein precipitation procedure was used to extract cefpiramide and cefoperazone (internal standard, IS) from 200 μl of plasma and bile. Utilizing a Capcell Pak C₁₈ column (4.6 × 250 mm), cefpiramide and IS were separated using the timed-gradient mobile phase consisting of 0.1 m sodium acetate (pH 5.2) and acetonitrile at a flow rate of 1 ml/min with photodiode array detector (wavelength set at 273 nm). The calibration curves showed linearity at concentrations ranging from 1 to 150 μg/ml in both plasma and bile (r² > 0.999). The within- and between-run coefficients of variation (CVs) for plasma samples were 0.570–4.43 and 1.10–2.76%, respectively; for bile samples, the within- and between-day precision (CV) was 0.814–6.34 and 2.05–4.00%, respectively. Our newly developed bioanalytical method was successfully employed to quantify cefpiramide concentrations in both plasma and bile at multiple time points in patients with acute cholangitis.     

Study on the Constituents of Roots of Aceriphyllum rossii

A new stereoisomer of a tetrahydrofuranoid lignan, acerifuranoid A ( 1 ), and two new oleanane‐type triterpenoids, aceriphyllic acids J and K ( 2 and 3 ), were isolated from the roots of Aceriphyllum rossii. Their structures were elucidated on the basis of spectroscopic analyses and chemical evidence. These isolated compounds exhibited weak cytotoxic activity against various cancer cell lines with IC₅₀>150 μM .     

A rapid technique to determine the internal area function of finite-length ducts using maximum length sequence analysis

This paper describes a rapid technique for reconstruction of the internal area function of a duct using blockage-induced eigenvalue shifts determined from eigenfrequencies measured under two sets of duct termination boundary conditions. A single broad band maximum length sequence (MLS) measurement of short duration is utilized to obtain the transfer function of the duct, which in turn can be utilized to determine its eigenvalue shifts and subsequently its internal area function using an inverse perturbation technique. The reconstruction results display the same order of accuracy as those obtained previously using swept sine measurements of extended duration. An expression for the determination of the area function is presented utilizing resonant frequency information alone, thus rendering duct length determination unnecessary. A computational routine further simplifies the process such that the accuracy of the technique could be ascertained for a range of configurations including longer ducts and ducts that initially have nonuniform internal cross section over their length. Development of a relationship between obstacle length and wavelength of the lowest eigenfrequency required for successful reconstruction is also described. This is an important result for longer ducts where measurement of lower eigenfrequencies may present problems using standard measurement equipment.     

A generalization of a theorem of Heins

Let be the family of holomorphic selfmaps of the unit disk in the complex plane . Heins established the continuity of the functional which assigns to ( denotes the identity map) either (i) the fixed point of or (ii) the limit of its iterations or (iii) if ( represents the boundary of ). Using an Abate extension of the Denjoy-Wolff lemma to strongly convex domains, we extend this result of Heins to selfmaps of strongly convex domains in with boundary.

     

Liquid–liquid extraction of neodymium (III) and europium (III) using synergic mixture of furosemide and tribenzylamine in benzyl alcohol

The extraction behavior of Nd(III) and Eu(III) with 0.05 mol dm⁻³ furosemide in benzyl alcohol as single acidic extractant and then with equimolar (0.05 mol dm⁻³) synergic mixture of furosemide as acidic extractant and tribenzylamine as neutral donor in benzyl alcohol has been studied from aqueous solutions of pH 1 to 6. The effect of various parameters and of various cations and anions on the extraction of these metal ions was investigated. The composition of the extracted adducts was determined by slope analysis method that came out to be [(M(FS)₂)⁺ (CH₃COO)⁻] and [M(FS)₃·3TBA] where M = Nd(III) and Eu(III).

     

Properties of self-assembled InAs quantum dots grown by various growth techniques

The properties of self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy on GaAs substrates were investigated. The surface properties of samples were monitored by reflection high-energy electron diffraction to determine growth. Photoluminescence (PL) and transmission electron microscope (TEM) were then used to observe optical properties and the shapes of the InAs-QDs. Attempts were made to grow InAs-QDs using a variety of growth techniques, including insertion of the InGaAs strained-reducing layer (SRL) and the interruption of In flux during QD growth. The emission wavelength of InAs-QDs embedded in a pure GaAs matrix without interruption of In flux was about 1.21 μm and the aspect ratio was about 0.21. By the insertion InGaAs SRL and interruption of In flux, the emission wavelength of InAs-QDs was red shifted to 1.37 μm and the aspect ratio was 0.37. From the PL and TEM analysis, the properties of QDs were improved, particularly when interruption techniques were used.