The influence of teaching methodologies in the assimilation of density concept in primary teacher trainees

Density is one of the most misunderstood concepts amongst the most basic scientific ones, although it is studied even from the earlier academic stages. This is the reason teachers must know its implications as well as possible, including not only the classical definition or what students called "formula" (density is equal to mass divided by volume) but also the concept itself (that is, an intensive matter property). According to this concern, the current research focuses its interest in studying how different teaching methodologies have different outputs in the learning process of pre-service primary teachers. The main aim of this research is to compare the learning results of a control group (n = 84), where mainly oral-based expositions were used as the teaching instrument, with an experimental group (n = 109), where the main educative tool were laboratory activities. The results show statistically significant differences (p < 0.05) between both methodologies and reveal the existence of difficulties in the conceptual and experimental understanding of the concept of density. Although those students that were submitted to hands-on activities presented a significant better comprehension of the density idea, the persistence of misconceptions regarding this scientific relevant concept is also confirmed at university level.

HPLC determination of ciprofloxacin, cloxacillin, and ibuprofen drugs in human urine samples

This paper reports, for the first time, a liquid chromatographic method for the simultaneous determination of three frequently co-administered active principles, two antibiotics, ciprofloxacin (CIPRO) and cloxacillin (CLOXA) belonging to the fluoroquinolones and beta-lactam families, respectively, and ibuprofen (IBU), a non-steroidal anti-inflammatory drug. The chromatographic separation was performed on a C-18 analytical column, using isocratic elution with methanol-acetonitrile-pH 3 formate buffer (CT = 0.1 M) (15:12:73, v/v/v) for 3 min and, after that, a linear gradient with methanol-acetonitrile (88:12, v/v) for 8 min. Several absorption spectra were obtained for each peak using a DAD detector. Chromatograms at the maximum absorption wavelength for each analyte, 220 nm for both IBU and CLOXA, and 280 nm for CIPRO were selected as the most suitable. The proposed chromatographic method requires about 15 min per sample. The presence of a urine background was tested and no interference was found. The method was satisfactorily applied to the determination of CIPRO, CLOXA, and IBU, in fortified urine, and in urine samples from a patient undergoing treatment with these three active principles, among others. Limits of quantification in urine were 1.00, 1.70, and 2.87 microg/mL for CIPRO, CLOXA, and IBU, respectively.

Interference-free analysis using three-way fluorescence data and the parallel factor model. Determination of fluoroquinolone antibiotics in human serum

Three-way fluorescence data and multivariate calibration based on parallel factor analysis (PARAFAC) are combined for the simultaneous quantitation of three fluoroquinolone anitibiotics (norfloxacin, enoxacin, and ofloxacin) in human serum samples. The three analytes can be adequately determined with limits of detection of 0.2, 3.0, and 0.5 microg L(-1), respectively, with minimum experimental effort. The selected analytical methodology fully exploits the so-called second-order advantage of the employed three-way data, allowing obtaining individual concentrations of calibrated analytes in the presence of any number of uncalibrated (serum) components. In contrast to PARAFAC, less satisfactory results were obtained with a multidimensional partial least-squares (nPLS) model trained with the same calibration set.

Development of arachnoid villi and granulations in man

The superior sagittal sinus and confluens sinuum of 27 fetuses and newborns ranging from postmenstrual intervals of 26-54 weeks were studied by scanning electron microscopy and histology. 26-week specimens showed oval depressions in the final portions of tributary veins to the sinus. Histologically there were arachnoid tissue clusters within the dural wall. The walls of the depressions were more irregular by the 30th week. Arachnoid villi were apparent by the 35th week and granulations were observed after the 39th weeks. The granulations increased in complexity as development proceeded.