Piezoelectric composite cements: Towards the development of self-powered and self-diagnostic materials

Piezoresistivity is the most commonly used sensing principle in cement-based smart composites for strainmonitoring applications. Nonetheless, the need for external electric power to conduct electrical resistivity measurements restricts the scalability of this technology, especially when implemented in remote structures. To address this issue, this manuscript thoroughly analyses the piezoelectric properties of cement composites doped with reduced graphene oxide (rGO) and evaluates their potential as self-powered strain sensors. To do so, a comprehensive methodology involving voltammetry measurements, open circuit potential determination, and uniaxial compression testing is developed to determine the piezoelectric coefficients of charge �33 and voltage �33. Furthermore, a novel circuital model for signal processing of the electromechanical response is developed and experimentally validated in terms of time series of output voltage, resistance, and the generated electric power. The developed methodology is applied to laboratory samples manufactured following two different filler dispersion methods. The presented results evidence that samples prepared by ultrasonic cleaner dispersion achieve optimal properties, with a piezoelectric charge coefficient of 1122.28 ± 246.67 pC/N, about 47 times greater than previously reported composites in the literature. Unlike piezoresistive cement-based composites, a remarkable nonlinear correlation between the fractional change in the intrinsic resistance of the material and the applied mechanical strain has been observed. Instead, a considerable linearity (R 2 = 0.96) between the externally applied mechanical strain and the generated (piezoelectric) electric power has been found, which suggests the great potential of the latter for conducting off-the-grid strain monitoring applications

First-principles study of electronic, vibrational, elastic, and magnetic properties of FeF 2 as a function of pressure

We report systematic ab initio calculations of the electronic band structure, phonon dispersion relation, and the structural characterization of FeF 2 in the rutile (P 4 2 /mnm) structure as well as in several high-pressure phases by means of the generalized gradient approximation (GGA) + U approximation. Using the phonon dispersion relations, we calculated the Gibbs free energy and evaluated the phase transitions at 300 K, at which most experimental measurements are performed. Calculated Raman and infrared vibrational modes, lattice parameters, and electronic structure for all considered crystalline structures are compared with available experimental data. Our calculations show that at 5.33 GPa, the FeF 2 undergoes a second-order proper ferroelastic phase transition, rutile → CaCl 2 -type structure. This result is supported by the softening of the elastic shear module C s in the rutile phase, the softening (hardening) of the B 1g (A g ) Raman active mode in the rutile (CaCl 2 -type) structure near the transition pressure, and the decrease of the square of the spontaneous strain e ss from the CaCl 2 -type structure. This demonstrates that the rutile → CaCl 2 -type phase transition is driven by the coupling between the Raman active B 1g mode and shear modulus C s . At 8.22 GPa, the CaCl 2 -type structure undergoes a first-order phase transition to the P bca phase, a distorted fcc P a3 phase with a volume reduction of V ≈ 7%, as reported in experiments. Upon further increase of the pressure, the P bca phase transforms to a F mmm phase othorhombic center-type structure at ∼20.38 GPa, with V ≈ 2.5%. Finally, at 25.05 GPa, there is a phase transition to the orthorhombic cotunnite structure (P nma space group), with V ≈ 5.8%, which is stable up to 45 GPa, the largest considered pressure. The coordination number for the Fe ion in each phase is 6, 6, 6, 8, and 9 for rutile, CaCl 2 -type, P bca, F mmm, and cotunnite structures, respectively. The evolution of the band gap, phonon frequencies, and magnetic moment of Fe ion as a function of the applied pressure is reported for all studied phases. The exchange constants J 1 , J 2 , and J 3 , calculated for rutile and the lowest Gibbs free-energy high-pressure phases, are reported

Ferromagnetic behavior of ultrathin manganese nanosheets

Ferromagnetic behaviour has been observed experimentally for the first time in nanostructured Manganese. Ultrathin ($\sim$ 0.6 nm) Manganese nanosheets have been synthesized inside the two dimensional channels of sol-gel derived Na-4 mica. The magnetic properties of the confined system are measured within 2K-300K temperature range. The confined structure is found to show a ferromagnetic behaviour with a nonzero coercivity value. The coercivity value remains positive throughout the entire temperature range of measurement. The experimental variation of susceptibility as a function of temperature has been satisfactorily explained on the basis of a two dimensional system with a Heisenberg Hamiltonian involving direct exchange interaction.Comment: 13 pages, 9 figure

Confinement Effects in Antiferromagnets

Phase equilibrium in confined Ising antiferromagnets was studied as a function of the coupling (v) and a magnetic field (h) at the surfaces, in the presence of an external field H. The ground state properties were calculated exactly for symmetric boundary conditions and nearest-neighbor interactions, and a full zero-temperature phase diagram in the plane v-h was obtained for films with symmetry-preserving surface orientations. The ground-state analysis was extended to the H-T plane using a cluster-variation free energy. The study of the finite-T properties (as a function of v and h) reveals the close interdependence between the surface and finite-size effects and, together with the ground-state phase diagram, provides an integral picture of the confinement in anisotropic antiferromagnets with surfaces that preserve the symmetry of the order parameter.Comment: 10 pages, 8 figures, Accepted in Phys. Rev.

Measurement of the vortex core in sub-100 nm Fe dots using polarized neutron scattering

We use polarized neutron scattering to obtain quantitative information about the magnetic state of sub-100 nm circular magnetic dots. Evidence for the transition from a single domain to a vortex state, as a function of the dot diameter and magnetic field, is found from magnetization curves and confirmed by micromagnetic and Monte-Carlo simulations. For 20 nm-thick Fe dots with diameters close to 60 nm, the vortex is the ground state. The magnetization of the vortex core (140 ± 50 emu/cm3) and its diameter (19 ± 4 nm) obtained from polarized neutron scattering are in agreement with simulations

Epidemiological and some clinical characteristics of neuroblastoma in Mexican children (1996–2005)

<p>Abstract</p> <p>Background</p> <p>Neuroblastoma (NB) is the principal tumor of the sympathetic nervous system in children under one year of age. The incidence in developed countries is greater than that in developing countries. The aim of this article is to present the epidemiological and some clinical characteristics of Mexican children with NB.</p> <p>Methods</p> <p>A population-based, prolective study, with data obtained from the Childhood Cancer Registry of the Instituto Mexicano de Seguro Social. Statistical analysis: The simple frequencies of the variables of the study and the annual average incidence (per 1,000,000 children/years) by age and sex were obtained. The trend was evaluated by calculating the annual percentage of change. The curves of Kaplan-Meyer were employed for the survival rate and the log-rank test was used to compare the curves.</p> <p>Results</p> <p>Of a total of 2,758 children with cancer registered during the period from 1996–2005, 72 (2.6%) were identified as having Group IV, defined according to the International Classification of Childhood Cancer. The incidence for NB was 3.8 per 1,000,000 children/year; NB was highest in the group of children under one year of age, followed by the group of children between the ages 1–4 years (18.5 and 5.4 per 1,000,000 children/years, respectively). The male/female ratio was 1.1 and there was no trend toward an increase. The time of diagnosis was 26 days (median), but varied according to the stage at diagnosis. Stages III and IV were presented in 88% of the cases. There was no association between the stage, the age at time of diagnosis, or the histological pattern. The overall five-year survival rate was 64%; the patients with stage I, II, III, or IVs did not die; and the five-year survival rate of cases in Stage IV was 40%.</p> <p>Conclusion</p> <p>It is possible that the low incidence of neuroblastoma in Mexican children is due to the difficulty in diagnosing the cases with the best prognosis, some of which could have had spontaneous regression. There was no trend to an increase; the majority of the cases were diagnosed in the advanced stages; and the overall five-years survival rate was similar to that for developed countries.</p

Characterising the KMP-11 and HSP-70 recombinant antigens' humoral immune response profile in chagasic patients

11 pages, 6 figures.-- The pre-publication history for this paper can be accessed here: http://www.biomedcentral.com/1471-2334/9/186/pre pubBackground: Antigen specificity and IgG subclass could be significant in the natural history of Chagas' disease. The relationship between the different stages of human Chagas' disease and the profiles of total IgG and its subclasses were thus analysed here; they were directed against a crude T. cruzi extract and three recombinant antigens: the T. cruzi kinetoplastid membrane protein-11 (rKMP-11), an internal fragment of the T. cruzi HSP-70 protein192-433, and the entire Trypanosoma rangeli HSP-70 protein. Methods: Seventeen Brazilian acute chagasic patients, 50 Colombian chronic chagasic patients (21 indeterminate and 29 cardiopathic patients) and 30 healthy individuals were included. Total IgG and its subtypes directed against the above-mentioned recombinant antigens were determined by ELISA tests. Results: The T. cruzi KMP-11 and T. rangeli HSP-70 recombinant proteins were able to distinguish both acute from chronic chagasic patients and infected people from healthy individuals. Specific antibodies to T. cruzi crude antigen in acute patients came from IgG3 and IgG4 subclasses whereas IgG1 and IgG3 were the prevalent isotypes in indeterminate and chronic chagasic patients. By contrast, the specific prominent antibodies in all disease stages against T. cruzi KMP-11 and T. rangeli HSP-70 recombinant antigens were the IgG1 subclass.This work was supported by Colciencias Research project No. 1203-333- 18692. IDF was supported by Colciencias and the Universidad Javeriana's Young Researcher 2008 Programme (Bogotá, Colombia). MCT and MCL were supported by P06-CTS-02242 Grant from PAI (Junta de Andalucia) and RICET-RD06/0021-0014, Spain. MS received financial support from the Brazilian agency - CNPq.Peer reviewe