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21.
Per definition, CSCL research deals with the data of individuals nested in groups, and the influence of a specific learning
setting on the collaborative process of learning. Most well-established statistical methods are not able to analyze such nested
data adequately. This article describes the problems which arise when standard methods are applied and introduces multilevel
modelling (MLM) as an alternative and adequate statistical approach in CSCL research. MLM enables testing interactional effects
of predictor variables varying within groups (for example, the activity of group members in a chat) and predictors varying
between groups (for example, the group homogeneity created by group members’ prior knowledge). So it allows taking into account
that an instruction, tool or learning environment has different but systematic effects on the members within the groups on
the one hand and on the groups on the other hand. The underlying statistical model of MLM is described using an example from
CSCL. Attention is drawn to the fact that MLM requires large sample sizes which are not provided in most CSCL research. A
proposal is made for the use of some analyses which are useful. 相似文献
22.
23.
Hong-long Chang Feng Zhang Ji-liang Ding Fang-lu Chen Shui-jin Hong Michael Kraft Wei-zheng Yuan 《Microsystem Technologies》2012,18(6):723-730
This paper presents a highly reliable macro to micro domain interconnection technology for microfluidic applications using Polydimethylsiloxane (PDMS) casting techniques. Characteristic to the interconnectors are long flanges fabricated in the PDMS film; therefore the contact area between PDMS and tubes is considerably increased compared to other interconnection technologies. Thus, both glass capillaries and Polytetrafluoroethylene (PTFE) tubes can be held in position very reliably and rigidly. To test the reliability of the interconnectors, PTFE tubes were successfully connected to microfluidic chips without the aid of any liquid adhesives. Both leakage and pull-out tests demonstrated the functionality and reliability of the PDMS interconnectors; no leakage was detected under a working pressure up to 400?kPa. A pull-out test yielded a pull-out force of 22.45?N. Furthermore, once a casting mould is fabricated, it can be re-used as a template repeatedly achieving a low cost technology and making it suitable for batch production. 相似文献
24.
Gadolinium-enhanced magnetic resonance angiography of the pelvis in patients with erectile impotence
Michael K. Stehling Libin Liu Gerhard Laub Kurt Fleischmann Ulrike Rohde 《Magma (New York, N.Y.)》1997,5(3):247-254
This study evaluted the potential of contrast-enhanced digital-subtraction magnetic resonance angiography (CE-DS-MRA) for
noninvasive angiographic delineation of the arterial supply of the penis in patients with erectile dysfunction. After induction
of an erection with prostaglandin E, a three-dimensional fast imaging with steady-state precision (FISP) sequence with TE
of 1.8–2 milliseconds, TR of 4.4–5 milliseconds, and flip angle of 40°–60° was used to obtain high-resolution angiograms of
the pelvis and penis during the injection of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) 0.3 mmol/kg body weight,
within 30–50 seconds. DS maximum intensity projections (MIPs) and multiplanar reconstructions (MPRs) were compared with clinical
work-up and directional Doppler ultrasound in 11 patients. In all 11 patients (100%), the arterial supply of the penis could
be delineated from the aortic bifurcation via the iliac and internal pudendal arteries to the dorsal and deep penile arteries.
Of the 22 internal pudendal arteries, 6 (27%) were occluded on CE-DS-MRA and 5 (23%) had stenoses, of which 4 (18%) were greater
than 50%. In 7 patients (64%) good correlation between CE-DS-MRA and clinical findings and/or Doppler ultrasound was found;
in 2 patients (18%), the correlation was moderate, and in 2 patients (18%) results were discrepant. In 6 patients (55%), MRA
provided additional information to the clinical and Doppler ultrasound work-up. CE-DS-MRA can delineate small sessels such
as the internal pudendal and penile arteries and thus has the potential to become a noninvasive angiography method in the
work-up of erectile impotence.
Supported by Siemens Medical Systems, Erlangen; Schering AG, Berlin; and Agfa-Gevaert AG, Leverkusen. 相似文献
25.
Gen Li Ulrike K. Müller Johan L. van Leeuwen Hao Liu 《Journal of the Royal Society Interface》2014,11(101)
Fish larvae may intercept their own wake during sharp turns, which might affect their escape performance. We analysed C-starts of larval zebrafish (Danio rerio, Hamilton, 1822) using a computational fluid dynamics approach that simulates free swimming (swimming trajectory is determined by fluid forces) by coupling hydrodynamics and body dynamics. The simulations show that fish may intercept their own wake when they turn by 100–180°. During stage 1 of a C-start, the fish generates a strong jet at the tail that is shed into the wake. During stage 2, the fish intercepts this wake. Counterfactual simulations showed that wake interception increased the lateral force on the fish and reduced the fish''s turning angle by more than 5°. Wake interception caused no significant acceleration tangential to the trajectory of the fish and did not affect total power output. While experimental and simulation evidence suggests that fish larvae can either undershoot or intercept but not overshoot their wake, our simulations show that larger fish might be able to avoid intercepting their wake by either under- or overshooting. As intercepting its own wake modifies the fish''s escape trajectory, fish should account for this effect when planning their escape route. 相似文献
26.
Benjamin W. Riblett Nicola L. Francis Margaret A. Wheatley Ulrike G. K. Wegst 《Advanced functional materials》2012,22(23):4920-4923
Successful spinal cord repair is thought to be promoted with hierarchically structured scaffolds. These should combine aligned porosity with additional linear features on the micrometer scale to guide axons across multiple length scales. Such scaffolds are generated through the carefully controlled directional solidification of an aqueous biopolymer solution, followed by lyophilization. Under specific freezing conditions this yields a highly regular and aligned lamellar architecture. This architecture exhibits uniform ridges of controlled height and width on the lamellar surface. These ridges run parallel to the pore axis, serving as secondary guidance features. The ridges are capable of linearly aligning 62.4% of chick dorsal root ganglia neurites to within ±10° of the ridge direction. Notably, neurites sprouting perpendicular to the ridge are guided into alignment with these microridged features. 相似文献
27.
Petra Fallier-Becker Maike Nieser Ulrike Wenzel Rainer Ritz Susan Noell 《International journal of molecular sciences》2016,17(8)
The astrocytic endfoot membranes of the healthy blood-brain barrier—contacting the capillary—are covered with a large number of the water channel aquaporin 4 (AQP4). They form orthogonal arrays of particles (OAPs), which consist of AQP4 isoform M1 and M23. Under pathologic conditions, AQP4 is distributed over the whole cell and no or only small OAPs are found. From cell culture experiments, it is known that cells transfected only with AQP4-M1 do not form OAPs or only small ones. We hypothesized that in astrocytomas the situation may be comparable to the in vitro experiments expecting an upregulation of AQP4-M1. Quantitative Real-time PCR (qRT-PCR) of different graded astrocytomas revealed an upregulation of both isoforms AQP4 M1 and M23 in all astrocytomas investigated. In freeze fracture replicas of low-grade malignancy astrocytomas, more OAPs than in high-grade malignancy astrocytomas were found. In vitro, cultured glioma cells did not express AQP4, whereas healthy astrocytes revealed a slight upregulation of both isoforms and only a few OAPs in freeze fracture analysis. Taken together, we found a correlation between the decrease of OAPs and increasing grade of malignancy of astrocytomas but this was not consistent with an upregulation of AQP4-M1 in relation to AQP4 M23. 相似文献
28.
Christina Schwind Jürgen Buder Ulrike Cress Friedrich W. Hesse 《Computers & Education》2012,58(2):787-796
The Web is a perfect backdrop for opinion formation as a multitude of different opinions is publicly available. However, the different opinions often remain unexploited: Learners prefer preference-consistent over preference-inconsistent information, a phenomenon called confirmation bias. Two experiments were designed to test whether technologies such as recommender systems can be used to overcome this bias. The role of preference-inconsistent recommendations was explored by comparing their influence to a condition with preference-consistent recommendations and to a control condition without recommendations. In Study 1, preference-inconsistent recommendations led to a reduction of confirmation bias and to a more moderate view of the controversial topic of neuro-enhancement. In Study 2, we found that preference-inconsistent recommendations stimulated balanced recall and divergent thinking. Together these studies showed that preference-inconsistent recommendations are an effective approach for reducing confirmation bias and stimulating divergent thinking. In conclusion, future research and practical implications are discussed. 相似文献
29.
Christina Skiera Panagiotis Steliopoulos Thomas Kuballa Ulrike Holzgrabe Bernd Diehl 《Journal of the American Oil Chemists' Society》2012,89(8):1383-1391
Within the course of lipid peroxidation, hydroperoxides are formed as primary products. They can be used as analytical markers
to assess the deterioration status of oils and fats. Here a new 1H-NMR assay to determine the hydroperoxide amount in edible oils is presented. We were able to show that the analytical performance
of the method is similar to that of the commonly used peroxide value (PV) according to Wheeler. A total of 290 edible oil
samples were analyzed using both methods. For some oil varieties considerable discrepancies were found between the results
obtained. In the case of black seed and olive oil, two substances could be identified that cause positive (black seed oil)
and negative (olive oils) deviations from the theoretical PV expected from the NMR values. 相似文献
30.
Back Cover: Mapping the Interactions of Selective Biochemical Probes of Antibody Conformation by Hydrogen–Deuterium Exchange Mass Spectrometry (ChemBioChem 11/2017)
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