1,535 research outputs found

    Polarization switching at the nanoscale in ferroelectric copolymer thin films

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    The polarization switching kinetics were measured at the nanoscale in continuous thin films of a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene. The dependence of the switching rate on voltage for a 54-nm thick film exhibits extrinsic nucleation and domain-growth type kinetics with no true threshold coercive field, and is qualitatively different from the behavior of an 18-nm thick film, which exhibits intrinsic switching kinetics, and a true threshold field. The results are consistent with studies of thin film capacitors of much larger area and with a recent refinement of the theory of the critical size for intrinsic switching

    Polarization imaging in ferroelectric polymer thin film capacitors by pyroelectric scanning microscopy

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    A Pyroelectric Scanning Microscopy system, which uses laser-induced thermal modulation for mapping the pyroelectric response, has been used to image a bipolar domain pattern in a ferroelectric polymer thin film capacitor. This system has achieved a resolution of 660±28 nm by using a violet laser and high f-number microscope objective to reduce the optical spot size, and by operating at high modulation frequencies to reduce the thermal diffusion length. The results agree well with a thermal model implemented numerically using finite element analysis

    Optical second harmonic generation probe of two-dimensional ferroelectricity

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    Optical second harmonic generation (SHG) is used as a noninvasive probe of two-dimensional (2D) ferroelectricity in Langmuir-Blodgett (LB) films of copolymer vinylidene fluoride with trifluorethylene. The surface 2D ferroelectric-paraelectric phase transition in the topmost layer of LB films and a thickness independent (almost 2D) transition in the bulk of these films are observed in temperature studies of SHG.Comment: 9 pages, 2 figures, Optics Letters, in prin

    More flexible brain activation underlies cognitive reserve in older adults

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    Abstract The goal of this study was to identify the brain mechanisms underlying cognitive reserve using a parametric n-back working memory (WM) task in a sample of healthy older adults. We first identified the WM-related activations associated with years of education and then tested whether these activations mitigated the detrimental impact of age on cognition. Thirty-nine older adults received a magnetic resonance imaging examination while completing an n-back task with different levels of WM load (0-, 1- vs. 2-back). Results show that more education is associated with lower activation of the left medial superior frontal gyrus (BA8) in the 1-back condition and a greater activation of the right caudate nucleus in the 2-back condition. The caudate and frontal activations are task-positive and task-negative regions, respectively. Moderation analyses indicate that the effect of age on performance is less detrimental in participants with higher caudate activation in the 2-back condition. Overall, these results suggest that cognitive reserve is explained by a superior ability to flexibly engage greater or novel activation as cognitive demand increases

    Talking about sex after traumatic brain injury: perceptions and experiences of multidisciplinary rehabilitation professionals

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    Purpose: Research indicates that although 50–60% of people who have had a traumatic brain injury (TBI) experience changes in sexual functioning, sexuality issues remain largely unaddressed in rehabilitation. This study aimed to explore rehabilitation professionals’ perceptions and experiences of discussing sexuality with service-users who have had a TBI. Method: Purposeful sampling was used to recruit 24 participants from two local National Health Service trusts and from a national charity. Four focus groups were conducted with pre-existing groups of professionals, using a semi-structured interview schedule. Focus group data were transcribed verbatim and analysed using thematic analysis. Results: Six main themes were derived from the analysis: (1) sexuality after TBI is a specialist issue; (2) sexuality is a sensitive subject; (3) practicalities of discussing sexuality; (4) roles and responsibilities; (5) dilemmas about risk and vulnerabilities; and (6) organisational and structural issues. Conclusions: Our findings suggest that a more proactive approach to addressing sexuality issues be taken by incorporating sexuality into assessments and by having sexuality information available for service-users. Support for professionals is also needed in the form of the development of policy, on-going training and supervision
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