34 research outputs found

    Advances in ab-initio theory of Multiferroics. Materials and mechanisms: modelling and understanding

    Full text link
    Within the broad class of multiferroics (compounds showing a coexistence of magnetism and ferroelectricity), we focus on the subclass of "improper electronic ferroelectrics", i.e. correlated materials where electronic degrees of freedom (such as spin, charge or orbital) drive ferroelectricity. In particular, in spin-induced ferroelectrics, there is not only a {\em coexistence} of the two intriguing magnetic and dipolar orders; rather, there is such an intimate link that one drives the other, suggesting a giant magnetoelectric coupling. Via first-principles approaches based on density functional theory, we review the microscopic mechanisms at the basis of multiferroicity in several compounds, ranging from transition metal oxides to organic multiferroics (MFs) to organic-inorganic hybrids (i.e. metal-organic frameworks, MOFs)Comment: 22 pages, 9 figure

    Pain Symptoms Accompanying Chronic Poststernotomy Pain: A Pilot Study

    No full text
    Objective. Despite the technical developments in surgical procedures, chronic poststernotomy pain (CPSP) is still very common. Many theories for its cause have been proposed in the literature, but the etiology is still not clear. Pain along the sternal scar and in the upper extremities (sometimes accompanied with paresthesia) persists in about 30% of cases. These symptoms have been regarded as two separate complications. This study investigated all pain symptoms in patients following sternotomy. Design. Retrospective pilot study. Setting. Outpatient clinic at the Leiden University Medical Center. Patients. A cohort of patients who underwent open heart surgery by median sternotomy between January 1, 2004 and January 1, 2006. Interventions. A questionnaire was completed by 631 patients, and a selected sample of 277 patients was examined for pain of the head, neck, back, and chest and upper extremities. Outcome Measures. All pain locations were compared in two groups: 189 patients with sternal pain and 88 patients without sternal pain. Results. We found that pain and muscular tenderness in the investigated areas unrelated to the chest wall incision were significantly more common in patients with sternal pain compared to the nonsternal pain group. No surgical or demographic factors with the exception of female gender were consistent predictors of sternal pain. Conclusion. CPSP is an extensive pain syndrome. Sternal pain is frequently accompanied by pain of the head, neck, back, and upper extremities. Further research on the possible etiology is warranted

    Differences in chunking behavior between young and older adults diminish with extended practice

    Get PDF
    Previous research found reduced motor chunking behavior in older adults compared to young adults. However, it remains unclear whether older adults are unable to use a chunking strategy or whether they are just slower in developing them. Our goal was to investigate the effect of extended practice on the development of chunking behavior in healthy older adults. A group of young and a group of healthy older adults between 74 and 85 years of age visited the lab on 2 days. A sequence of 3 and a sequence of 6 elements were both practiced 432 times in a discrete sequence production task. We found that age differences in chunking behavior, as measured by the difference between initiation and execution of the sequence, diminish with extended practice. Furthermore, in older, but not in young adults, slow responses that are often interpreted as the first response of a next motor chunk were associated with a finger that was also slow during performance of the random sequences. This finding calls for more attention to biomechanical factors in future theory about aging and sequence learning

    Pain Symptoms Accompanying Chronic Poststernotomy Pain: A Pilot Study

    No full text
    Objective. Despite the technical developments in surgical procedures, chronic poststernotomy pain (CPSP) is still very common. Many theories for its cause have been proposed in the literature, but the etiology is still not clear. Pain along the sternal scar and in the upper extremities (sometimes accompanied with paresthesia) persists in about 30% of cases. These symptoms have been regarded as two separate complications. This study investigated all pain symptoms in patients following sternotomy. Design. Retrospective pilot study. Setting. Outpatient clinic at the Leiden University Medical Center. Patients. A cohort of patients who underwent open heart surgery by median sternotomy between January 1, 2004 and January 1, 2006. Interventions. A questionnaire was completed by 631 patients, and a selected sample of 277 patients was examined for pain of the head, neck, back, and chest and upper extremities. Outcome Measures. All pain locations were compared in two groups: 189 patients with sternal pain and 88 patients without sternal pain. Results. We found that pain and muscular tenderness in the investigated areas unrelated to the chest wall incision were significantly more common in patients with sternal pain compared to the nonsternal pain group. No surgical or demographic factors with the exception of female gender were consistent predictors of sternal pain. Conclusion. CPSP is an extensive pain syndrome. Sternal pain is frequently accompanied by pain of the head, neck, back, and upper extremities. Further research on the possible etiology is warranted.Cardiolog

    Similar Representations of Sequence Knowledge in Young and Older Adults: A Study of Effector Independent Transfer

    Get PDF
    Older adults show reduced motor performance and changes in motor skill development. To better understand these changes, we studied differences in sequence knowledge representations between young and older adults using a transfer task. Transfer, or the ability to apply motor skills flexibly, is highly relevant in day-to-day motor activity and facilitates generalization of learning to new contexts. By using movement types that are completely unrelated in terms of muscle activation and response location, we focused on transfer facilitated by the early, visuospatial system. We tested 32 right-handed older adults (65–75) and 32 young adults (18–30). During practice of a discrete sequence production task, participants learned two six-element sequences using either unimanual key-presses (KPs) or by moving a lever with lower arm flexion-extension (FE) movements. Each sequence was performed 144 times. They then performed a test phase consisting of familiar and random sequences performed with the type of movements not used during practice. Both age groups displayed transfer from FE to KP movements as indicated by faster performance on the familiar sequences in the test phase. Only young adults transferred their sequence knowledge from KP to FE movements. In both directions, the young showed higher transfer than older adults. These results suggest that the older participants, like the young, represented their sequences in an abstract visuospatial manner. Transfer was asymmetric in both age groups: there was more transfer from FE to KP movements than vice versa. This similar asymmetry is a further indication that the types of representations that older adults develop are comparable to those that young adults develop. We furthermore found that older adults improved less during FE practice, gained less explicit knowledge, displayed a smaller visuospatial working memory capacity and had lower processing speed than young adults. Despite the many differences between young and older adults, the ability to apply sequence knowledge in a flexible way appears to be partly preserved in older adults
    corecore