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Several studies concluded that deep reflection is infrequently reached in student portfolios. An explanation for these disappointing conclusions might be that motivation for portfolio reflection determines the quality of reflection. This study aimed to examine the relationship between motivation for using digital portfolios and reflection. Participants were 156 eleventh-grade students in secondary education, whose motivation for composing a digital portfolio was measured by the motivation part of the Motivated Strategies for Learning Questionnaire. Portfolios of 37 of the 156 students were examined in terms of the amount and nature of reflection by means of a coding scheme based on Mezirow's model of transformative learning. On average, one-fifth (19.5%) of the paragraphs in a portfolio contained reflection, and paragraphs with deep reflection were hardly found (0.8%). It was concluded that motivation for composing a portfolio was fair, but not related to the amount and nature of reflection. This exploratory study gives rise to further research into factors that might influence the quality of portfolio reflection. (Contains 5 tables.)

Discusses conceptual knowledge acquisition using computer simulation and describes a study of undergraduates that examined the role of metacognitive skillfulness and intellectual ability during initial inductive learning with a complex computer simulation. Results showed that metacognitive skillfulness was positively related to learning behavior and to scores on qualitative tests. (Author/LRW)

We present a systematic investigation of the oxidation properties of Si dots fabricated on a silicon-on-insulator (SOI) wafer. Dots with diameters varying from 9 to 81 nm were structured on a SOI wafer. These dots were oxidized in a dry oxygen atmosphere at 700, 850, and 1000 °C. The resulting structures were investigated using a side view transmission electron microscopy (TEM) technique in combination with energy filtered TEM. The dimensions of the residual Si and the grown SiO[sub 2] were then extracted from the micrographs and analyzed. The oxidation appears to be retarded as compared to the well-known planar oxidation. At 700 and 850 °C a self-limiting effect is observed as well as a clear pattern dependent oxidation at 850 and 1000 °C. We attribute these effects to stress buildup in the oxide. The critical stress, causing the self-limiting effect, is calculated using a model that considers the decrease of the reaction rate with increasing stress perpendicular to the Si surface. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which examined the influence of the implantation species on the steepness of the lateral potential of gallium arsenide/AlGaAs quantum wires fabricated by the implantation induced intermixing technique. Theoretical background; Materials and methods used; Results of the study.

In this article an overview will be given of the applications of Reflection-Contrast Microscopy (RCM). A short explanation of the antiflex and oblique illumination methods, used with RCM is presented. The advantage of using ultrathin sections for light microscopy with RCM is discussed. [ABSTRACT FROM AUTHOR]

A high-current annealing technique is used to fabricate nanogaps and hybrid diamond/graphite structures in boron-doped nanocrystalline diamond films. Nanometer-sized gaps down to ∼1 nm are produced using a feedback-controlled current annealing procedure. The nanogaps are characterized using scanning electron microscopy and electronic transport measurements. The structural changes produced by the elevated temperature, achieved by Joule heating during current annealing, are characterized using Raman spectroscopy. The formation of hybridized diamond/graphite structure is observed at the point of maximum heat accumulation. [ABSTRACT FROM AUTHOR]

Glomerulonephritis in BALB/c mice following infection with is characterized by albuminuria and glomerular deposition of immunoglobulins. Electron-dense deposits are present in the mesangium, as well as subendothelially and subepithelially along the glomerular capillary wall. In this study the nature of intracytoplasmic, electron-dense, round structures observed in glomerular endothelial cells was investigated by immunoelectron-microscopy and enzyme histochemistry. The presence of these structures was related in time with the development of proteinuria. Mice from the C57BL1O strain, which upon infection develop glomerular immune complexes without proteinuria, were examined as well. The results demonstrated that the first endothelial changes, occurring 3–4 weeks after infection, were swelling of endothelial cells containing intracytoplasmic, electron-dense, round structures. These changes were seen prior to the onset of proteinuria, and were not present in glomeruli of mice that did not develop proteinuria. The endothelial granules were shown to contain immunoglobulins and typical lysosomal enzymes, providing evidence for phagocytosis by the glomerular endothelial cells. Liver endothelial cells did not show comparable changes. Thus, local phagocytosis by glomerular endothelial cells is shown to be a specific event in the development of glomerular disease. [ABSTRACT FROM PUBLISHER]

We investigated the clearance kinetics and tissue distribution of different sized IgA in normal and macrophage-depleted rats. Rats were injected iv with liposomes containing dichloromethylcne diphosphonate (DMDP). DMDP treatment resulted in complete depletion of liver macrophages 24-48 h after administration. Normal and macrophage depleted rats were injected intravenously with monomeric, dimetic, polymeric or aggregated polymeric IgA (AIgA) and assessed for blood clearance and tissue distribution. In normal rats, clearance of IgA was size dependent, i.e. a faster clearance with increasing size. No differences in clearance kinetics were observed of the different sized IgA between normal and DMDP-treated rats. TCA non-precipitable radioactivity, a measure for degradation of IgA. was found in the circulation of normal and DMDP-treated rats after AIgA administration. The liver was the main organ responsible for the clearance of IgA in normal and DMDP-treated rats. Immunofluorescenee studies on liver biopsies indicated that AIgA was associated with Kupffer cells in normal rats. Electronmicroscopical studies revealed that the AIgA was internalized and located in vesicles in Kupffer cells. In DMDP-treated rats the AIgA was associated with endothelial cells and electron microscopy studies showed that this AIgA was taken up by endothelial cells. These data show that rat liver endothelial cells are able to bind, internalize and degrade AIgA in situations where Kupffer cells are absent, and that these cells may play an important role in the handling of AIgA and IgA-immune complexes. [ABSTRACT FROM AUTHOR]

We present a method to make Pt nanometer-spaced electrodes that are free of metallic particles and stable at ambient conditions. The nanogaps are fabricated using feedback-controlled electromigration to form few-atom contacts. When performing this procedure at elevated temperatures (>420 K), the Pt contacts undergo self-breaking so that nanometer separated electrode pairs are formed. Once cooled down to lower temperatures, the nanogaps stabilize and can be characterized in detail. We find that current-voltage characteristics can be well fitted to a Simmons model for tunneling and gap-size fluctuations at room temperature determined from these fits stay within 0.6 Å for at least 50 h. [ABSTRACT FROM AUTHOR]

We have studied the electrical transport through two adjacent double dot structures realized in Si-on-insulator material. The small dimensions of dots and the distance between the centers of the dots, here 100 nm, allow for dc measurements at 4.2 K. We demonstrate that although the structures are entirely doped, we are able to operate both double dot structures simultaneously in the double dot regime. Clear Coulomb blockade characteristics with a Coulomb blockade region of 20 mV are observed in both structures. Using gates, the number of electrons on each individual dot can be manipulated simultaneously. From the measured charging diagrams the capacitances between the gates and the dots are determined. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Uniformly doped single electron transistors nominally consisting of a single island and two silicon tunneling barriers have been fabricated on silicon-on-insulator material. Two operation regimes are found depending upon the gate voltages applied. The structure acts either as a multiple tunnel junction device or as a single electron transistor consisting of a single dot corresponding to the geometrical shape of the device. The multiple tunnel junction behavior is attributed to the formation of additional tunneling barriers, introduced into the structure by the high doping level. We demonstrate that these barriers can be removed by raising the Fermi level via the application of an appropriate gate voltage. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]