Polarization loss in the organic ferroelectric trialkylbenzene-1,3,5-tricarboxamide (BTA).

We investigate the polarization loss in the archetypical molecular organic ferroelectric trialkylbenzene-1,3,5-tricarboxamide (BTA). We prove that the polarization loss is due to thermally activated R-relaxation, which is a collective reversal of the amide dipole moments in ferroelectric domains. By applying a weak electrostatic field both the polarization loss and the R-relaxation are suppressed, leading to an enhancement of the retention time by at least several orders of magnitude. Alternative loss mechanisms are discussed and ruled out. By operating the thin-film devices slightly above the crystalline to liquid crystalline phase transition temperature the retention time of one compound becomes more than 12 hours even in absence of supportive bias, which is among the longest reported so far for organic ferroelectric materials.

True ferroelectric switching in thin films of trialkylbenzene-1,3,5-tricarboxamide (BTA).

We have investigated the ferroelectric polarization switching properties of trialkylbenzene-1,3,5-tricarboxamide (BTA), which is a model system for a large class of novel organic ferroelectric materials. In the solid state BTAs form a liquid crystalline columnar hexagonal phase that provides long range order that was previously shown to give rise to hysteretic dipolar switching. In this work the nature of the polar switching process is investigated by a combination of dielectric relaxation spectroscopy, depth-resolved pyroelectric response measurements, and classical frequency- and time-dependent electrical switching. We show that BTAs, when brought in a homeotropically aligned hexagonal liquid crystalline phase, are truly ferroelectric. Analysis of the transient switching behavior suggests that the ferroelectric switching is limited by a highly dispersive nucleation process, giving rise to a wide distribution of switching times.

Asymmetric polarization and hysteresis behaviour in ferroelectric P(VDF-TrFE) (76 : 24) copolymer thin films spatially resolved via LIMM.

The concept of charge-polarization coupling in the ferroelectric copolymer PVDF-TrFE (poly[vinylidene fluoride-co-trifluoroethylene]) has been revisited by employing high resolution (<50 nm) pyroelectric depth profiling (LIMM). By virtue of probing the pyroelectric activity over the film thickness in the presence of a variable, external electrical field, the local ferroelectric response and spatially resolved hysteresis could be obtained. A large asymmetry was found between the positive and negative electrode-polymer interface. Differences in amplitude of polarization, contribution of interface charges and length scale of the polarization-free zone near the electrodes suggest a higher availability of compensation charges at the negative electrode that finally stabilize the local polarization. The resulting asymmetries in the polarization distribution are hence attributed to excess charges as a result of electron injection as a specific charge generation mechanism at the negative electrode.

Dielectric and specific heat relaxations in vapor deposited glycerol.

Recently [S. Capponi, S. Napolitano, and M. Wübbenhorst, Nat. Commun. 3, 1233 (2012)], vapor deposited glasses of glycerol have been found to recover their super-cooled liquid state via a metastable, ordered liquid (MROL) state characterized by a tremendously enhanced dielectric strength along with a slow-down of the relaxation rate of the structural relaxation. To study the calorimetric signature of this phenomenon, we have implemented a chip-based, differential AC calorimeter in an organic molecular beam deposition setup, which allows the simultaneous measurement of dielectric relaxations via interdigitated comb electrodes and specific heat relaxation spectra during deposition and as function of the temperature. Heating of the as-deposited glass just above the bulk Tg and subsequent cooling/reheating revealed a step-wise increase in cp by in total 9%, indicating unambiguously that glycerol, through slow vapour deposition, forms a thermodynamically stable glass, which has a specific heat as low as that of crystalline glycerol. Moreover, these glasses were found to show excellent kinetic stability as well as evidenced by both a high onset-temperature and quasi-isothermal recovery measurements at -75 °C. The second goal of the study was to elucidate the impact of the MROL state on the specific heat and its relaxation to the super-cooled state. Conversion of "MROL glycerol" to its "normal" (ordinary liquid, OL) state revealed a second, small (∼2%) increase of the glassy cp, a little gain (<10%) in the relaxed specific heat, and no signs of deviations of τcal from that of normal "bulk" glycerol. These findings altogether suggest that the MROL state in glycerol comprises largely bulk-type glycerol that coexist with a minor volume fraction (<10%) of PVD-induced structural anomalies with a crystal-like calorimetric signature. Based on the new calorimetric findings, we have proposed a new physical picture that assumes the existence of rigid polar clusters (RPCs) and conclusively explains the extraordinary high kinetic stability of the MROL state, its specific calorimetric signature, the enhanced strength, and apparent slow-down of the dielectric α-relaxation. In this new picture, the incredibly slow and strengthened dielectric response is ascribed to driven rotational diffusion of whole RPCs, a mechanism that perfectly couples to the relaxation time of the "normal" glycerol fraction. First considerations based on the strength and the retardation of the dielectric RPCs' response yield independently a size estimate for the RPCs in the order of 4-5 nm. Finally, we have discussed possible crystallisation and reorganisation effects, which give rise to pronounced out-of phase components of the specific heat at higher temperatures.

Image descriptions in early and mid-level vision: what kind of model is this and what kind of models do we really need?

In The utility of image descriptions in the initial stages of vision: A case study of printed text, Watt and Dakin (2010) describe a model that integrates mechanisms at both early and middle stages of visual processing, and provide a demonstration of the application of the model to the relational organization of printed text. In the following, we discuss a number of the merits of this approach, but argue that it is (at this stage) highly difficult to assess the utility of this model as a plausible description of human visual processing. First, we indicate that the authors' description of the model is underspecified. Second, we question the generalizability of the model. Third, we argue that the model needs to be directly compared to quantitative empirical data. Fourth, we argue that the model needs to be directly compared to alternative models.

Knowledge, skills and counselling behaviour of Belgian general practitioners on CPR-related issues.

General practitioners (GP) can identify potential cardiac arrest victims. They have the opportunity to inform cardiac patients and their families about the risk of sudden cardiac death and can motivate family members to attend a CPR-course. To study actual counselling practices concerning basic CPR-training a questionnaire was mailed to a representative sample of Belgian GPs (n = 1119). The level of CPR-training of the GPs was fairly good: 67% had received BLS training on a manikin and 63% had already attended a cardiac arrest event. A discrepancy was observed between the positive attitude towards CPR and the counselling of family members to attend a CPR-course (9%). GPs feared to inflict additional stress to the patient (32%) or the family (43%) or did not know where CPR courses were organised (37%). GPs are a primary target group for CPR-training and should learn how to counsel potential bystanders of a cardiac arrest to attend a CPR-course without inflicting additional anxiety on the patient or his family.