Search results for "41"
showing 10 items of 3365 documents
On stiffness and damping of vibro-impact dynamics of backlash
2021
We consider the instantaneous stiffness and damping of the vibro-impact in a backlash pair. Opposed to the existing and mostly used models of the backlash, we address the problem of contact and separation, and the associated force propagation within a mechanical pair, from a viewpoint of the vibro-impact dynamics. We discuss the impact forces with the coefficient of restitution as a principal factor which shapes the transient backlash response.We show that a common approach to modeling the backlash by means of a dead-zone in a restoring force is unsuitable for correctly capturing the mechanical impact. We exemplary demonstrate a qualitative accord between an experimental backlash response a…
Exploring Affordances of an Online Environment : A Case-Study of Electronics Engineering Undergraduate Students’ Activity in Mathematics
2019
Online learning environments are being used for teaching and learning of mathematics at university level. Exploiting the potential of digital technology, these Internet-based environments administer computer-generated homework, assistance and feedback for students. This article presents a case-study of a small group of undergraduate engineering students’ learning activity in mathematics in an online environment. The study focuses on students’ interactions with the online environment to make sense of the affordances of this environment. Utilizing multiple sources of data aid in analyzing the intentional and the operational aspects of students’ interactions with several resources in this envi…
Critical aspects of student teachers’ conceptions of learning
2011
Abstract The aim of this phenomenographic study was to discover the educationally critical aspects of learning conceptions among health education student teachers (N = 20). The qualitative data consisted of written essays and semi-structured interviews. Six qualitatively distinctive conceptions of learning could be discerned, namely learning as 1) the reproduction of acquired health knowledge, 2) the application of health knowledge, 3) developing personal meanings on health matters, 4) the transformation of individual thinking, 5) personal growth, and 6) collective meaning-making. These qualitatively distinct categories were reflected through three themes, which embodied critical aspects: t…
Modular Breath Analyzer (MBA): Introduction of a Breath Analyzer Platform Based on an Innovative and Unique, Modular eNose Concept for Breath Diagnos…
2021
Exhaled breath analysis for early disease detection may provide a convenient method for painless and non-invasive diagnosis. In this work, a novel, compact and easy-to-use breath analyzer platform with a modular sensing chamber and direct breath sampling unit is presented. The developed analyzer system comprises a compact, low volume, temperature-controlled sensing chamber in three modules that can host any type of resistive gas sensor arrays. Furthermore, in this study three modular breath analyzers are explicitly tested for reproducibility in a real-life breath analysis experiment with several calibration transfer (CT) techniques using transfer samples from the experiment. The experiment …
Low-generation dendrimers with a calixarene core and based on a chiral C2-symmetric pyrrolidine as iminosugar mimics
2012
The preparation of low-generation dendrimers based on a simple calix[4]arene scaffold by insertion of the iminosugar-analogue C2-symmetric 3,4-dihydroxypyrrolidine is described. This methodology allows a rapid incorporation of a considerable number of iminosugar-like moieties in a reduced volume and in a well-defined geometry. The inclusion of alkali-metal ions (sodium and potassium) in the polar cavity defined by the acetamide moieties at the lower rim of the calixarene was demonstrated, which allows also the rigidification of the dendrimer structure and the iminosugar presentation in the clusters. The combination of the supramolecular properties of calixarenes with the advantage of a dend…
Hyper-reticulated calixarene polymers: a new example of entirely synthetic nanosponge materials
2018
New calixarene-based nanosponges (CaNSs), i.e., hyper-reticulated polymers constituted by calixarene monomer units joined by means of bis(1,2,3-trialzolyl)alkyl linkers, were synthesized, characterized and subjected to preliminary tests to assess their supramolecular absorption abilities towards a set of suitable organic guests, selected as pollutant models. The synthesis was accomplished by means of a CuAAC reaction between a tetrakis(propargyloxy)calix[4]arene and an alkyl diazide. The formation of the polymeric network was assessed by means of FTIR and 13C{1H} CP-MAS solid-state NMR techniques, whereas morphological characterization was provided by SEM microghaphy. The materials were pro…
Polyaminoazide mixtures for the synthesis of pH-responsive calixarene nanosponges
2019
Two mixtures of polyaminoazides were synthesized by a nucleophilic displacement strategy providing no separation of the components. The mixtures were adequately characterized by means of combined HR-ESIMS, FTIR and NMR techniques and, despite their complexity, they were successfully used to accomplish the subsequent preparation of pH-sensitive calixarene hyper-reticulated nanosponge materials. The desired responsivity to pH variations of the nanosponges obtained was verified by means of absorption tests on a set of organic pollutant model molecules.
Totalitarismo y lenguaje: el campo de concentración como espacio multilingüe y la figura del intérprete concentracionario
2020
espanolEn este trabajo se examinan las relaciones entre el poder absoluto y el lenguaje. Los campos de concentracion del regimen nacionalsocialista se entienden como el espacio donde se materializa la maxima expresion del totalitarismo. Al convertirse en sociedades forzadamente multilingues desde el inicio de la guerra, la lengua alemana puede convertirse, mas que nunca, en un instrumento mas de opresion al servicio del sistema: se deforma para convertirse practicamente en un protolenguaje violento yrudimentario, y su conocimiento por parte de los reclusos se relaciona siempre con las perspectivas de supervivencia. Ademas, se desarrolla una lengua franca que incorpora rasgos de varios idiom…
Analysis of Contact Traces of Cannabis by In-Tube Solid-Phase Microextraction Coupled to Nanoliquid Chromatography
2018
Because of its inherent qualities, in-tube solid-phase microextraction (IT-SPME) coupled on-line to nanoliquid chromatography (nanoLC) can be a very powerful tool to address the new challenges of analytical laboratories such as the analysis of traces of complex samples. This is the case of the detection of contact traces of drugs, especially cannabis. The main difficulties encountered in the analysis of traces of cannabis plants on surfaces are the low amount of sample available (typically <
Device-Based Measures of Sedentary Time and Physical Activity Are Associated With Physical Fitness and Body Fat Content
2020
Introduction/Purpose: Physical activity and sedentary time may associate with physical fitness and body composition. Yet, there exists some observational studies that have investigated the associations of device-based measures of sedentary time and physical activity (PA) with cardiorespiratory fitness (CRF) and body composition but associations with muscular fitness (MF) are less studied. Methods: Objective sedentary time and physical activity was measured by a hip worn accelerometer from 415 young adult men (age: mean 26, standard deviation 7 years). Cardiorespiratory fitness (VO2max) (CRF) was determined using a graded cycle ergometer test until exhaustion. Maximal force of lower extremit…