In-Situ Nuclear Magnetic Resonance Investigation of Strain, Temperature, and Strain-Rate Variations of Deformation-Induced Vacancy Concentration in Aluminum

Critical strain to serrated flow in solid solution alloys exhibiting dynamic strain aging (DSA) or Portevin–LeChatelier effect is due to the strain-induced vacancy production. Nuclear magnetic resonance (NMR) techniques can be used to monitor in situ the dynamical behavior of point and line defects in materials during deformation, and these techniques are nondestructive and noninvasive. The new CUT-sequence pulse method allowed an accurate evaluation of the strain-enhanced vacancy diffusion and, thus, the excess vacancy concentration during deformation as a function of strain, strain rate, and temperature. Due to skin effect problems in metals at high frequencies, thin foils of Al were used and experimental results correlated with models based on vacancy production through mechanical work (vs thermal jogs), while in situ annealing of excess vacancies is noted at high temperatures. These correlations made it feasible to obtain explicit dependencies of the strain-induced vacancy concentration on test variables such as the strain, strain rate, and temperature. These studies clearly reveal the power and utility of these NMR techniques in the determination of deformation-induced vacancies in situ in a noninvasive fashion.

The orientation dependence of dislocation slip in NaCl single crystals

Results are presented of investigations into the role of dislocation motion in deforming NaCl single crystals, using the technique of pulsed N.M.R. In particular, the spin-locking pulse sequence is used to measure T 1p, which is the spin-lattice relaxation time in the presence of a resonant r.f. magnetic field. T 1p, depends strongly on the mean free path L which is covered by the dislocations during successive jumps between obstacles in their glide plane. The mean free path is determined in crystals compressed in different directions, in which cases either the {110} or the {100} planes are primarily activated. It is shown that both the mean free path, measured as a function of strain rate and of the applied stress, and the work hardening differ remarkably for the two different primary slip planes. The magnitude of the mean free path is compared with the mean distance between dislocations in the crystal and the activation length of dislocations at obstacles, as obtained from mechanical stress relaxation experiments

ORDERING IN CuNiZn ALLOYS

Par microscopie électronique et en mesurant la variation de résistivité les auteurs ont étudié quatre alliages de structure c.f.c., de composition Cu2NiZn, Cu3Zn, Ni3Zn et CuNi2Zn. La cinétique de grossissement isotherme de domaines ordonnés dans Cu2NiZn suit une loi [MATH] = Ktn avec n voisin de 0,3. Il n'existe pas d'ordre à grande distance dans les alliages Cu3Zn et Ni3Zn même après de longs recuits de mise en ordre aux températures de 61 et 110°C respectivement. Les micrographies en champ sombre fondamental de l'alliage CuNi2Zn présentent un fort "clustering".Electron microscopy and electrical resistivity have been used in a comparative study of Cu2NiZn, Cu3Zn, Ni3Zn and CuNi2Zn. Quantitative measurements on the kinetics of domain growth in ordered Cu2NiZn have been made and a t1'3 law is observed for the growth process. Alloys near the composition Cu3Zn and Ni3Zn do not show long range order even after long anneals at 61 and 110°C respectively. Dark field micrographs of CuNi2Zn using a fundamental reflection indicate strong clustering

Dislocation dynamics in alkali halide single crystals investigated by nuclear spin relaxation measurements

La résonance magnétique nucléaire est appliquée à l'étude de la variation de la vitesse des dislocations avec la contrainte de compression appliquée dans des cristaux d'halogénures alcalins. T1ρ a été mesurée en fonction du taux [MATH] de la déformation plastique. La route moyenne des dislocations mobiles a été déterminée. Nous indiquons les résultats des expériences sur de différents noyaux, sur de différentes orientations des cristaux et sur des températures différentes.Dislocations moving at various velocities in deforming alkali halide single crystals were studied using the technique of pulsed nuclear magnetic resonance. The spin lattice relaxation rate in the rotating frame is measured as a function of the plastic deformation rate [MATH]. From this the mean free path of mobile dislocations can be determined. The results for different resonant nuclei, different crystal orientations with respect to the crystal axis and different temperatures are presented

The mean free path of mobile dislocations in doped NaCl single crystals measured by N.M.R. between room temperature and 300°C

The mean free path of mobile dislocations has been measured by determining the spin–lattice relaxation rate of deforming NaCl single crystals as a function of temperature and of the concentration of Ca2+ impurities. The latter may influence the magnitude of the mean free path, but this depends to a large extent on the point-defect configuration. The degree of association and the mobility of the point defects has been studied by measuring the spin–lattice relaxation rate without deforming the samples. On the other hand, the distribution of dislocations also varies with temperature, and this affects the mobility of dislocations too. The work-hardening rate of the crystals is compared with the mean free path as a function of temperature, and it is shown that both quantities have extremes under the influence of competitive mechanisms such as an enhanced thermal activation of dislocations at obstacles, an increasing mobility of point defects and an increasing number of intersections of mobile dislocations with dislocation dipoles

The new normal: Chronic stay in the paediatric ICU

Advances in treatment options have resulted in a growing population of children who require chronic medical support in order to survive: children with medical complexity (CMC). Their complex medical needs are not easily met outside the hospital. The gap between the protective hospital environment and home proves to be extensive, which is why it is extremely challenging for this particular group of patients and their families to make that transition. In this case report, on the background of a child with medical complexity who endured an extremely lengthy admission to the paediatric intensive care unit (PICU), we will elaborate on the changes that are occurring in PICUs worldwide due to the growing CMC population as well as a transitional care unit as a possible intervention for this pressing issue

Marfan syndrome in adolescence: adolescents' perspectives on (physical) functioning, disability, contextual factors and support needs

Although essential for providing optimal adolescent patient support, knowledge of the impact of Marfan syndrome in adolescence is limited. To explore adolescents’ perceived impact of Marfan syndrome on (physical) functioning (activities, participation), disability (limitations, restrictions), contextual factors and support needs, we interviewed 19 adolescents with Marfan syndrome. Audio-recordings were transcribed, coded and analysed using thematic analysis. Identified themes were “difficulties in keeping up with peers” and “being and feeling different from peers”. Furthermore, an adolescent Marfan syndrome-specific International Classification of Functioning, Disability and Health for Children and Youth (ICF-CY) model derived from the data describing the adolescent perceived impact of Marfan syndrome on functioning, disability and its contextual factors. Adolescents perceived problems in keeping up with peers in school, sports, leisure and friendships/relationships, and they could not meet work requirements. Moreover, participants perceived to differ from peers due to their appearance and disability. Contextual factors: coping with Marfan syndrome, self-esteem/image, knowledge about Marfan syndrome, support from family/friends/teachers, ability to express needs and peer-group acceptation acted individually as barrier or facilitator for identified themes

Physical Functioning After Admission to the PICU: A Scoping Review

Objectives: To conduct a scoping review to 1) describe findings and determinants of physical functioning in children during and/or after PICU stay, 2) identify which domains of physical functioning are measured, 3) and synthesize the clinical and research knowledge gaps. Data Sources: A systematic search was conducted in PubMed, Embase, Cumulative Index to Nursing and Allied Health Literature, and Cochrane Library databases following the Preferred Reporting Items for Systematic Reviews and Meta-analyses extension for Scoping Reviews guidelines. Study Selection: Two investigators independently screened and included studies against predetermined criteria. Data Extraction: One investigator extracted data with review by a second investigator. A narrative analyses approach was used. Data Synthesis: A total of 2,610 articles were identified, leaving 68 studies for inclusion. Post-PICU/hospital discharge scores show that PICU survivors report difficulties in physical functioning during and years after PICU stay. Although sustained improvements in the long-term have been reported, most of the reported levels were lower compared with the reference and baseline values. Decreased physical functioning was associated with longer hospital stay and presence of comorbidities. A diversity of instruments was used in which mobility and self-care were mostly addressed. CONCLUSIONS: The results show that children perceive moderate to severe difficulties in physical functioning during and years after PICU stay. Longitudinal assessments during and after PICU stay should be incorporated, especially for children with a higher risk for poor functional outcomes. There is need for consensus on the most suitable methods to assess physical functioning in children admitted to the PICU