962 resultados para Ferroelectric memories


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Objective. The main purpose of the study was to examine whether emotion impairs associative memory for previously seen items in older adults, as previously observed in younger adults. Method. Thirty-two younger adults and 32 older adults participated. The experiment consisted of 2 parts. In Part 1, participants learned picture–object associations for negative and neutral pictures. In Part 2, they learned picture–location associations for negative and neutral pictures; half of these pictures were seen in Part 1 whereas the other half were new. The dependent measure was how many locations of negative versus neutral items in the new versus old categories participants remembered in Part 2. Results. Both groups had more difficulty learning the locations of old negative pictures than of new negative pictures. However, this pattern was not observed for neutral items. Discussion. Despite the fact that older adults showed overall decline in associative memory, the impairing effect of emotion on updating associative memory was similar between younger and older adults.

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Historical narratives help construct social identities, which are maintained through differentiation between in-groups and "others." In this article, we contend that Fatima Besnaci-Lancou's texts, as well as her reconciliation work—in which she enjoins Beurs and Harkis' offspring to write a new, inclusive, polyphonic narrative of the Algerian War—are an example of the positive use of textually mediated identity (re)construction. Her work suggests the possibility of implementing a moderate politics of empathetic recognition of the (often migration-related) memories of "others" so as to reinforce French national belongingness.

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The present study aimed to investigate the organization of autobiographical memory and to reveal how emotional knowledge for personal events is represented in autobiographical knowledge base. For these purposes, the event-cueing technique was employed (Brown & Schopflocher, 1998). Forty-six participants were provided eight retrieval cues and asked to generate a personal event related to each of them (i.e., cueing events). Following this, they responded to each cueing event by retrieving two personal episodes (i.e., cued events). The results indicated that cued events shared the life themes with cueing events, suggesting the thematic organization of autobiographical memory. We also found that the life themes of each personal episode determined types of emotional states with which they were associated. The implications for the affect and memory literature and the emotion regulation literature were discussed.

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We introduced photo-polymer networks into the various liquid crystalline phases of the antiferroelectric liquid crystal AS612 and studied the effects of these networks by measuring the temperature dependence of the Bragg wavelengths selectively reflected. After polymerization, the decrease in Bragg wavelengths with respect to the original values is consistent with a shorter helical pitch due to polymer network shrinkage. Also, by removing the liquid crystalline material, we are able to image the residual polymer network using scanning electron microscopy and polarized light microscopy. The polymer strands are a few microns thick and the networks show both chiral and non-chiral features.

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Cellular neural networks (CNNs) have locally connected neurons. This characteristic makes CNNs adequate for hardware implementation and, consequently, for their employment on a variety of applications as real-time image processing and construction of efficient associative memories. Adjustments of CNN parameters is a complex problem involved in the configuration of CNN for associative memories. This paper reviews methods of associative memory design based on CNNs, and provides comparative performance analysis of these approaches.

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The temperature dependence of the crystalline structure and the lattice parameters of Pb1-xLaxZr0.40Ti0.60O3 ferroelectric ceramic system with 0.00 x 0.21 was determined. The samples with x 0.11 show a cubic-to-tetragonal phase transition at the maximum dielectric permittivity, Tmax. Above this amount and especially for the x = 0.12 sample, a spontaneous phase transition from a relaxor ferroelectric state (cubic phase) to a ferroelectric state (tetragonal phase) is observed upon cooling below the Tmax. Unlike what has been reported in other studies, the x = 0.13, 0.14, and 0.15 samples, which present a more pronounced relaxor behavior, also presents a spontaneous normal-to-relaxor transition, indicated by a cubic to tetragonal symmetry below the Tmax. The origin of this anomaly has been associated with an increase in the degree of tetragonality, confirmed by the measurements of the X-ray diffraction patterns. The differential thermal analysis (DSC) measurements also confirm the existence of these phase transitions.

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For the first time, nanograined Pb(1-1.5x)La(x)TiO(3) ferroelectric ceramics, with x=0.2, were produced by a process based on a high-pressure densification technique (HPD) that eliminates the need of high-temperature sintering. Our results showed the production of workable dense ceramics with average grain size around 100 nm and free from secondary phase. Regarding the dielectric measurements, the samples showed satisfactory dielectric losses as well as remarkable diffusivity in the dielectric curves. Moreover, ferroelectric hysteresis measurements showed that samples produced by the HPD technique can stand high electric fields necessary to switch the polarization and thus to induce piezoelectric activity. Our results demonstrated clearly the viability of the proposed method to produce nanograined ferroelectric bulk ceramics, then opening the possibility of developing new technologies.

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Bi(4-x)La(x)Ti(3)O(12) (BLT) ceramics were prepared and studied in this work in terms of La(3+)-modified microstructure and phase development as well as electrical response. According to the results processed from X-ray diffraction and electrical measurements, the solubility limit (XL) of La(3+) into the Bi(4)Ti(3)O(12) (BIT) matrix was here found to locate slightly above x = 1.5. Further, La(3+) had the effect of reducing the material grain size, while changing its morphology from the plate-like form, typical of BIT ceramics, to a spherical-like one. The electrical results presented and discussed here also include the behavior of the temperature of the ferroelectric-paraelectric phase transition as well as the normal or diffuse and/or relaxor nature of this transition depending on the La(3+) content. (c) 2008 Elsevier Ltd. All fights reserved.

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Dielectric properties of BaTiO(3) ferroelectric ceramics were studied over wide frequency and temperature ranges. The materials showed complex dielectric behaviors, which included an anomalous increase of permittivity towards higher temperatures. Important, this property tended however to saturate to values that varied with grain-boundary density. Application of impedance spectroscopy and consideration of the series-layer model allowed a coherent discussion of these and other interesting observations from this work. In particular, analysis of the relationship existing in this model between macroscopic and microscopic dielectric properties rendered possible to account for grain vs. grain-boundary dielectric behaviors, in harmony with microstructure features, and to know the dielectric anomaly strength to be in fact expected from grain boundaries in such polycrystalline materials. (C) 2010 Elsevier Ltd. All rights reserved.

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Perovskite-structured Ba(0.90)Ca(0.10)(Ti(1-x)Zr(x))O(3) ceramics were prepared in this work and subsequently studied in terms of composition-dependent dielectric and high-resolution long-range order structural properties from 30 to 450 K. The dielectric response of these materials was measured at several frequencies in the range from 1 kHz to 1 MHz. Combining both techniques, including Rietveld refinement of the X-ray diffraction data, allowed observing that, when increasing Zr(4+) content, the materials change from conventional to diffuse and relaxor ferroelectric compounds, the transition occurring spontaneously at the x = 0.18 composition. Interestingly, this spontaneous transition turned out to be prevented for a further increase of Zr(4+). On the basis of all the dielectric and structural results processed, a phase diagram of this system is presented. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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Single-phase perovskite structure Pb(1-x)Ba(x)TiO(3) thin films (x = 0.30, 0.50 and 0.70) were deposited on Pt/Ti/SiO(2)/Si substrates by the spin-coating technique. The dielectric study reveals that the thin films undergo a diffuse type ferroelectric phase transition, which shows a broad peak. An increase of the diffusivity degree with the increasing Barium contents was observed, and it was associated to a grain decrease in the studied composition range. The temperature dependence of the phonon frequencies was used to characterize the phase transition temperatures. Raman modes persist above tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive. The origin of these modes was interpreted in terms of breakdown of the local cubic symmetry by chemical disorder. The absence of a well-defined transition temperature and the presence of broad bands in some interval temperature above FE-PE phase transition temperature Suggested a diffuse type phase transition. This result corroborates the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in these thin films. The leakage Current density of the PBT thin films was studied at different temperatures and the data follow the Schottky emission model. Through this analysis the Schottky barrier height values 0.75, 0.53 and 0.34 eV were obtained to the PBT70, PBT50 and PBT30 thin films, respectively. (C) 2008 Elsevier Ltd. All rights reserved.

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The Republic of Korea and Japan share a tumultuous history, but arguably no period has caused greater trauma in bilateral relations than the twentieth century. After Japan’s four-decade long colonial occupation of Korea, the two countries took two decades just to establish diplomatic relations. Subsequent interactions have remained seriously compromised by the memory of colonialism. This article reviews the tensions behind the tempestuous bilateral relationship, focusing on the depiction of Japan’s wartime past in school textbooks. We advance three suggestions for reconciliation: viewing reconciliation not as the restoration of a harmonious pre-conflict order, but as an ongoing, incomplete process; expanding promising bilateral dialogues; and accepting that there will always be differences between Korea and Japan, most notably with regard to representations of the past. Rather than being an inevitable source of conflict, these differences should contribute to an ongoing process of negotiation between the two neighbors.

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The current study addressed how the timing of interviews affected children's memories of unique and repeated events. Five- to six-year-olds (N= 125) participated in activities 1 or 4 times and were misinformed either 3 or 21 days after the only or last event. Although single-experience children were subsequently less accurate in the 21- versus 3-day condition, the timing of the misinformation session did not affect memories of repeated-experience children regarding invariant details. Children were more suggestible in the 21- versus 3-day condition for variable details when the test occurred soon after misinformation presentation. Thus, timing differentially affected memories of single and repeated events and depended on the combination of event-misinformation and misinformation-test delays rather than the overall retention interval.