NanoLAB Triboprobe: Characterizing Dynamic Wear, Friction and Fatigue at the Nanoscale

In-situ transmission electron microscopy (TEM) has developed rapidly over the last decade. In particular, with the inclusion of scanning probes in TEM holders, allows both mechanical and electrical testing to be performed whilst simultaneously imaging the microstructure at high resolution. In-situ TEM nanoindentation and tensile experiments require only an axial displacement perpendicular to the test surface. However, here, through the development of a novel in-situ TEM triboprobe, other surface characterisation experiments are now possible, with the introduction of a fully programmable 3D positioning system. Programmable lateral displacement control allows scratch tests to be performed at high resolution with simultaneous imaging of the changing microstructure. With the addition of repeated cyclic movements, both nanoscale fatigue and friction experiments can also now be performed. We demonstrate a range of movement profiles for a variety of applications, in particular, lateral sliding wear. The developed NanoLAB TEM triboprobe also includes a new closed loop vision control system for intuitive control during positioning and alignment. It includes an automated online calibration to ensure that the fine piezotube is controlled accurately throughout any type of test. Both the 3D programmability and the closed loop vision feedback system are demonstrated here.

Detección del movimiento cíclico estacional en edificios históricos por métodos topográficos

[ES] Para más información véase el trabajo LDGP_mem_003-2: "Estudio topográfico de las deformaciones del conjunto arquitectónico de la iglesia de Nuestra Señora de la Blanca (Agoncillo, La Rioja) [Julio 2007 – Octubre 2009]", http://hdl.handle.net/10810/7050

Comparison of cyclic fatigue and torsional resistance in reciprocating single-file systems and continuous rotary instrumentation systems

As compared with continuous rotary systems, reciprocating motion is believed to increase the fatigue resistance of NiTi instruments. We compared the cyclic fatigue and torsional resistance of reciprocating single-file systems and continuous rotary instrumentation systems in simulated root canals. Eighty instruments from the ProTaper Universal, WaveOne, MTwo, and Reciproc systems (n = 20) were submitted to dynamic bending testing in stainless-steel simulated curved canals. Axial displacement of the simulated canals was performed with half of the instruments (n = 10), with back-and-forth movements in a range of 1.5 mm. Time until fracture was recorded, and the number of cycles until instrument fracture was calculated. Cyclic fatigue resistance was greater for reciprocating systems than for rotary systems (P < 0.05). Instruments from the Reciproc and WaveOne systems significantly differed only when axial displacement occurred (P < 0.05). Instruments of the ProTaper Universal and MTwo systems did not significantly differ (P > 0.05). Cyclic fatigue and torsional resistance were greater for reciprocating systems than for continuous rotary systems, irrespective of axial displacement.

String Quartet n degrees 02 by Villa-Lobos: a dialogue with the cyclic form of Franck, Debussy and Ravel

This article investigates Villa-Lobos's String Quartet n degrees 02, an early work by this composer, written according cyclic sonata principles, as developed by Cesar Franck and systematized by Vincent d'Indy. Another important source are the string quartets composed by Franck (1889), Debussy (1893) and Ravel (1903), which possibly served as compositional models to Villa-Lobos. In this light, the themes of the Exposition in the first movement were analyzed and this procedure reveals some harmonic and rhythmic aspects throughout all the other movements.

Movements in gesture interfaces

There is a mismatch between the kinds of movements used in gesture interfaces and our existing theoretical understandings of gesture. We need to re-examine the assumptions of gesture research and develop theory more suited to gesture interface design. In addition to improved theory, we need to develop ways for participants in the process of design to adapt, extend and develop theory for their own design contexts. Gesture interface designers should approach theory as a contingent resource for design actions that is responsive to the needs of the design process.

Cyclic strain disrupts endothelial network formation on Matrigel

Most forms of tissue healing depend critically on revascularisation. In soft tissues and in vitro, mechanical stimuli have been shown to promote vessel-forming activity. However, in bone defects, increased interfragmentary motion impairs vascular regeneration. Because these effects seem contradictory, we aimed to determine whether a range of mechanical stimuli exists in which angiogenesis is favoured. A series of cyclic strain magnitudes were applied to a Matrigel-based “tube formation” assay and the total lengths of networks formed by human microvascular endothelial cells measured at 24 h. Network lengths were reduced at all strain levels, compared to unstretched controls. However, the levels of pro-angiogenic matrix metalloproteases-2 and -9 in the corresponding conditioned media were unchanged by strain, and vascular endothelial growth factor was uniformly elevated in stretched conditions. By repeating the assay with the addition of conditioned media from mesenchymal stem cells cultivated in similar conditions, paracrine stimuli were shown to increase network lengths, but not to alter the negative effect of cyclic stretching. Together, these results demonstrate that directly applied periodic strains can inhibit endothelial organisation in vitro, and suggest that this may be due to physical disruption rather than biochemical modulation. Most importantly, the results indicate that the straining of endothelial cells and their assembly into vascular-like structures must be studied simultaneously to adequately characterise the mechanical influence on vessel formation.

Increasing stochastic perturbations enhances acquisition and learning of complex sport movements

Traditionally, the aquisition of skills and sport movement has been characterised by numerous repetitions of presumed model movement pattern to be acquired by learners. This approach has been questioned by research identifying the presence of individualised movement patterns and the low probability of occurrence of two identical movements within and between individuals. In contrast, the differential learning approach claims advantage for incurring variability in the learning process by adding stochastic perturbations during practice. These ideas are exemplified by data from a high jump experiment which compared the effectiveness of classical and a differential training approach with pre-post test design. Results showed clear advantages for the group with additional stochastic perturbation during the aquisition phase in comparison to classically trained athletes. Analogies to similar phenomenological effects in the neurobiological literature are discussed.

Eye-movements and visual imagery : a working memory approach to the treatment of post-traumatic stress disorder

It has been claimed that the symptoms of post-traumatic stress disorder (PTSD) can be ameliorated by eye-movement desensitization-reprocessing therapy (EMD-R), a procedure that involves the individual making saccadic eye-movements while imagining the traumatic event. We hypothesized that these eye-movements reduce the vividness of distressing images by disrupting the function of the visuospatial sketchpad (VSSP) of working memory, and that by doing so they reduce the intensity of the emotion associated with the image. This hypothesis was tested by asking non-PTSD participants to form images of neutral and negative pictures under dual task conditions. Their images were less vivid with concurrent eye-movements and with a concurrent spatial tapping task that did not involve eye-movements. In the first three experiments, these secondary tasks did not consistently affect participants' emotional responses to the images. However, Expt 4 used personal recollections as stimuli for the imagery task, and demonstrated a significant reduction in emotional response under the same dual task conditions. These results suggest that, if EMD-R works, it does so by reducing the vividness and emotiveness of traumatic images via the VSSP of working memory. Other visuospatial tasks may also be of therapeutic value.

Influence of presbyopic corrections on driving-related eye and head movements

Purpose: To investigate whether wearing different presbyopic vision corrections alters the pattern of eye and head movements when viewing and responding to driving-related traffic scenes. Methods: Participants included 20 presbyopes (mean age: 56.1 ± 5.7 years) who had no experience of wearing presbyopic vision corrections, apart from single vision (SV) reading spectacles. Each participant wore five different vision corrections: distance SV lenses, progressive addition spectacle lenses (PAL), bifocal spectacle lenses (BIF), monovision (MV) and multifocal contact lenses (MTF CL). For each visual condition, participants were required to view videotape recordings of traffic scenes, track a reference vehicle, and identify a series of peripherally presented targets. Digital numerical display panels were also included as near visual stimuli (simulating the visual displays of a vehicle speedometer and radio). Eye and head movements were measured, and the accuracy of target recognition was also recorded. Results: The path length of eye movements while viewing and responding to driving-related traffic scenes was significantly longer when wearing BIF and PAL than MV and MTF CL (both p ≤ 0.013). The path length of head movements was greater with SV, BIF, and PAL than MV and MTF CL (all p < 0.001). Target recognition and brake response times were not significantly affected by vision correction, whereas target recognition was less accurate when the near stimulus was located at eccentricities inferiorly and to the left, rather than directly below the primary position of gaze (p = 0.008), regardless of vision correction. Conclusions: Different presbyopic vision corrections alter eye and head movement patterns. The longer path length of eye and head movements and greater number of saccades associated with the spectacle presbyopic corrections may affect some aspects of driving performance.