Engineering students' understanding of equilibrium and stability

Engineering students in control courses have been observed to lack an understanding of equilibrium and stability, both of which are crucial concepts in this discipline. The introduction of these concepts is generally based on the study of \classical" examples from Newtonian mechanics supplemented with a control system. Equilibrium and stability are approached in di erent ways at the various stages of a typical engineering syllabus: at the beginning, they are mostly dealt with from a static point of view, for example in mechanics, and are subsequently handled through dynamic analysis in control courses. In general, there is little clari cation of the di erences between these concepts or the ways in which they are linked. We believe that this leads to much confusion and incomprehension among engineering students. Several studies have shown that students encounter di culties when presented with simple familiar or academic static equilibrium cases in mechanics. Our study investigates students' conceptions and misconceptions about equilibrium and stability through a series of questions about several innovative non-static situations. It reveals that the understanding of these notions is shaken when the systems being studied are placed in inertial or non-inertial moving reference frames. The students in our study were particularly uncertain about the existence of unstable equilibrium positions and had di culty in differentiating between the two concepts. The results suggest that students use a velocity-based approach to explain such situations. A poor grasp of the above fundamental concepts may result from previous learning experiences. More speci cally, certain di culties seem to be directly linked to a lack of understanding of these concepts, while others are related to misconceptions arising from everyday experiences and the inappropriate use of physical examples in primary school

Démarches d’investigation en sciences et construction du savoir

National audienceDepuis plusieurs années, les démarches dites «d’investigation» sont mises en avant dans les programmes scolaires en mathématiques et en sciences expérimentales. Depuis septembre 2013, les lycéens arrivant dans l’enseignement supérieur ont été initiés à ces démarches, en particulier à l’école primaire et au collège. Lors du minicolloque «Enseignement» du congrès général de la SFP 2013, nous nous sommes centrés sur ce nouveau «profil» d’étudiant qui nécessite d’être connu des enseignants du supérieur, en particulier concernant les démarches scientifiques

Transition from Casimir to van der Waals force between macroscopic bodies

The transition of van der Waals to Casimir forces between macroscopic gold surfaces is investigated by Atomic Force Microscopy in the plane-sphere geometry. It was found that the transition appears to take place at separations about 10 % the plasma wavelength for evaporated gold surfaces, which compares to theoretical predictions by incorporation of experimental optical data and roughness corrections. Moreover, the force data allow estimation of the Hamaker constant AH in the van der Waals regime, which is in good agreement with the Lifshitz theory predictions (even if roughness corrections are taken into account) and former surface force apparatus measurements.Comment: 12 pages, 3 figure

Head-to-head comparison between F-18-DOPA PET/CT and Ga-68-DOTA-peptide PET/CT in detecting intestinal neuroendocrine tumours:A systematic review and meta-analysis

Objective: The imaging of intestinal neuroendocrine tumours (NETs) relies on functional PET tracers; these tumours can be studied by means of both Ga-68-DOTA-peptides and F-18-DOPA PET/CT. As yet, it is unclear which of these two modalities offers the better sensitivity. We therefore conducted a meta-analysis to assess the available data. Design: PubMed, CENTRAL, Scopus and Web of Science were searched for studies comparing the sensitivity of Ga-68-DOTA-peptides and F-18-DOPA PET/CT; papers up to February 2021 were considered. Patients and Measurements: In each study, we considered sensitivity in terms of patient-based (PBA), region-based (RBA) and lesion-based analysis (LBA) and pooled the results yielded by each tracer. Multidisciplinary follow-up served as the standard of truth. Results: Of the 636 records identified, 6 articles published between 2008 and 2021 were finally selected, and 112 intestinal NET patients were included. The pooled sensitivity of F-18-DOPA PET/CT was 83%, 89% and 95% on PBA, RBA and LBA, respectively. Ga-68-DOTA peptide PET/CT showed sensitivity of 88%, 92% and 82% on PBA, RBA and LBA, respectively. No significant differences were found between the two tracers on PBA and RBA. By contrast, a clear trend towards significance in favour of F-18-DOPA PET/CT was identified on LBA. The presence of a significant difference in favour of F-18-DOPA PET/CT was confirmed in a subgroup analysis conducted only on the most recent and largest studies. In all three analyses, mild-to-high heterogeneity was found, while no publication bias was observed. Conclusion: Both F-18-DOPA PET/CT and Ga-68-DOTA-peptide PET/CT are reliable diagnostic procedures in patients with intestinal NETs. However, in terms of lesion detection, a non-negligible difference in favour of F-18-DOPA PET/CT was observed. Thus, the use of F-18-DOPA PET/CT could be considered as a first-line molecular procedure in intestinal NETs

The fcc-bcc crystallographic orientation relationship in AlxCoCrFeNi high-entropy alloys

This paper concentrates on the crystallographic-orientation relationship between the various phases in the Al-Co-Cr-Fe-Ni high-entropy alloys. Two types of orientation relationships of bcc phases (some with ordered B2 structures) and fcc matrix were observed in Al0.5CoCrFeNi and Al0.7CoCrFeNi alloys at room temperature: (1 -1 0)(bcc)//(200)(fcc), [CM](bcc)//[001](fcc), (b) (1 -1 1)B2//(2 - 2 0)(fcc), [011]B2//[11 root 2](fcc). (C) 2016 Elsevier B.V. All rights reserved.</p

Hard-yet-tough high-vanadium hierarchical composite coating:Microstructure and mechanical properties

In this work, we report a high-vanadium hierarchical coating prepared on the surface of nodular cast iron substrate by a low-cost plasma transferred arc (PTA) surface alloying process. The coating consists of a graded layer with an alloyed zone (AZ) rich in submicron sized granular (V-Ti-Nb-Cr-Mo) composite carbides on top of intermediate melted zone characterized by refined ledeburite and martensite. The dense spherical particles in the AZ are FCC structured MC-type (M = V, Ti and Nb) carbides which tend to aggregate while M7C3 and M2C carbides nucleate on MC. The super-lattice V8C7 maintains its cube-on-cube orientation relationship with TiC. The hardness of the AZ is 9.6 +/- 1.0 GPa, similar to 4 times that of the substrate. Nano- and micro-indentations point at a superior strength-toughness in the AZ, where cracks are deflected and bridged by the spherical MC carbides in a compressive residue stress state. The fracture mode appears to be rather ductile in the AZ whereas brittle failure appears in both the melted zone and substrate. TEM and EDS results confirm that such a micro architecture design, assisted by the rapid solidification rate of the PTA process, concurrently activates various strengthening micromechanisms including the precipitation hardening and grain refinement

Surface roughness evolution of nanocomposite thin films

An analysis of dynamic roughening and smoothening mechanisms of thin films grown with pulsed-dc magnetron sputtering is presented. The roughness evolution has been described by a linear stochastic equation, which contains the second- and fourth-order gradient terms. Dynamic smoothening of the growing interface is explained by ballistic effects resulting from impingements of ions to the growing thin film. These ballistic effects are sensitive to the flux and energy of impinging ions. The predictions of the model are compared with experimental data, and it is concluded that the thin film roughness can be further controlled by adjusting waveform, frequency, and width of dc pulses

Protective films on complex substrates of thermoplastic and cellular elastomers:Prospective applications to rubber, nylon and cork

Deposition of thin films is an appropriate methodology to enhance the performance of a material by modification of its surface, while keeping the properties of the bulk largely unaffected. However, a practical implementation becomes less straightforward when dealing with sensitive or complex substrates, for instance, those which cannot be subjected to harsh treatments, such as cleaning and etching, or extreme deposition conditions, like high temperatures, and ion impingement et cetera. This paper concentrates on deposition processing of complex substrates. In particular, it discusses the deposition of two types of protective coatings (diamond-like carbon (DLC) films against friction and wear, and TiO2 films against UV light) on three types of thermoplastic and cellular elastomers (rubber, nylon and cork). It is demonstrated that a successful protection of thermoplastic elastomers against wear with DLC films can be attained, after a thorough adaptation of the procedure to the characteristics of the specific substrate. In addition, the paper reports the very first depositions on a cellular elastomer like cork by vapor deposition methods, including Atomic Layer Deposition (ALD)