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.     

Assessment of flavor volatiles of modified Iranian rice cultivars during the gelatinization process

A combined GC-MS with the headspace solid-phase microextraction (SPME) method has been employed for the analysis of the flavor volatiles of two modified Iranian rice cultivars during gelatinization. In order to optimize the different experimental parameters, the effect of fiber composition, water content of the rice samples, and equilibrium time were investigated. As a result, while gelatinization progresses, the amount of volatile compounds would increase as well. Therefore, a broad range of the flavor volatiles of rice could be extracted, concentrated, and identified. Altogether, 54 and 66 components were identified for HD5 and HD6 rice samples, respectively, of which 33 unique compounds were not detected previously. The identified volatile components in the modified cultivars belong to the chemical classes of aldehydes, ketones, alcohols, and heterocyclic compounds, phenolic compounds, and hydrocarbons.     

Methylmercury determination in biological samples using electrothermal atomic absorption spectrometry after acid leaching extraction

An efficient and sensitive method for the determination of methylmercury in biological samples was developed based on acid leaching extraction of methylmercury into toluene. Methylmercury in the organic phase was determined by electrothermal atomic absorption spectrometry (ETAAS). The methylmercury signal was enhanced and the reproducibility increased by formation of certain complexes and addition of Pd-DDC modifier. The complex of methylmercury with DDC produced the optimum analytical signal in terms of sensitivity and reproducibility compared to complexes with dithizone, cysteine, 1,10-phenanthroline, and diethyldithiocarbamate. Method performance was optimized by modifying parameters such as temperature of mineralization, atomization, and gas flow rate. The limit of detection for methylmercury determination was 0.015 μg g⁻¹ and the RSD of the whole procedure was 12% for human teeth samples (n=5) and 15.8% for hair samples (n=5). The method’s accuracy was investigated by using NIES-13 and by spiking the samples with different amounts of methylmercury. The results were in good agreement with the certified values and the recoveries were 88–95%.     

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.     

Preparation and characterization of nanocomposite,silica aerogel,activated carbon and its adsorption properties for Cd (II) ions from aqueous solution

A novel composite adsorbent, silica aerogel activated carbon was synthesized by sol-gel process at ambient pressure drying method. The composite was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Nitrogen adsorption/desorption isotherms (BET).In the present study, the mentioned adsorbent was used moderately for the removal of cadmium ions from aqueous solutions and was compared with two other adsorbents of cadmium, activated carbon and silica aerogel. The experiments of Cd adsorption by adsorbents were performed at different initial ion concentrations, pH of the solution, adsorption temperature, adsorbent dosage and contact time. Moreover, the optimum pH for the adsorption was found to be 6.0 with the corresponding adsorbent dosage level of 0.1 g at 60 °C temperature. Subsequently, the equilibrium was achieved for Cd with 120 min of contact time.Consequently, the results show that using this composite adsorbent could remove more than 60% of Cd under optimum experimental conditions. Langmuir and Freundlich isotherm model was applied to analyze the data, in which the adsorption equilibrium data were correlated well with the Freundlich isotherm model and the equilibrium adsorption capacity (q_e) was found to be 0.384 mg/g in the 3 mg/L solution of cadmium.     

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).

     

H-point standard additions method for simultaneous determination of sulfamethoxazole and trimethoprim in pharmaceutical formulations and biological fluids with simultaneous addition of two analytes

The applicability of H-point standard additions method (HPSAM) to the resolving of overlapping spectra corresponding to the sulfamethoxazole and trimethoprim is verified by UV-vis spectrophotometry. The results show that the H-point standard additions method with simultaneous addition of both analytes is suitable for the simultaneous determination of sulfamethoxazole and trimethoprim in aqueous media. The results of applying the H-point standard additions method showed that the two drugs could be determined simultaneously with the concentration ratios of sulfamethoxazole to trimethoprim varying from 1:18 to 16:1 in the mixed samples. Also, the limits of detections were 0.58 and 0.37 μmol L(-1) for sulfamethoxazole and trimethoprim, respectively. In addition the means of the calculated RSD (%) were 1.63 and 2.01 for SMX and TMP, respectively in synthetic mixtures. The proposed method has been successfully applied to the simultaneous determination of sulfamethoxazole and trimethoprim in some synthetic, pharmaceutical formulation and biological fluid samples.