Frequency Dependence of Aging, Rejuvenation and Memory in a disordered ferroelectric

We characterize in details the aging properties of the ferroelectric phase of K Ta_{1-x} Nb_x O_3 (KTN), where both rejuvenation and (partial) memory are observed. In particular, we carefully examine the frequency dependence of several quantities that characterize aging, rejuvenation and memory. We find a marked subaging behaviour, with an a.c. dielectric susceptiblity scaling as $\omega \sqrt{t_w}$, where $t_w$ is the waiting time. We suggest an interpretation in terms of pinned domain walls, much along the lines proposed for aging in a disordered ferromagnet, where both domain wall reconformations and overall (cumulative) domain growth are needed to rationalize the experimental findings.Comment: submitted to EPJ

Electrical and raman scattering studies of ZnO:P and ZnO:Sb thin films

A study on the structure, electrical and optical properties of ZnO thin films produced by r.f. magnetron sputtering and implanted either with phosphorous (P) or antimony (Sb) is reported in this work. Raman spectroscopy, X-ray diffraction, optical transmittance and Hall effect measurements have been employed to characterize the samples. X-ray diffraction and Raman scattering patterns confirm that, after a 500ºC annealing, the doped films keep a polycrystalline nature with (002) preferred orientation. These films are very transparent and Hall effect results show that all have p-type conduction, despite doping ion and dose. The electric resistivity reaches values of 0.012 (cm) and 0.042 (cm) for the P and Sb-doped samples, respectivel

Complementary eigenvalue problem in systems with frictional contact: the stiffness matrix for the contact nodes between different materials

This work addresses a numerical study of static equilibrium states of finite dimensional systems with frictional contact and its application to the particular problem of friction between two geological layers with different viscosity. Its formulation as a complementarity eigenproblem requires the building up of mass M and stiffness K matrices to solve the eigenvalue equations for the relative deformation of two contacting materials.Fundação para a Ciência e a Tecnologia (FCT

Special matrices for visco-elastic systems

In this work the evolution of visco-elastic systems under external stress is addressed. An approach as a mixed complementary eigenvalue problem to model the geological folding and asymmetric boudinage in the same direction is considered. A matricial dynamics equation that comprehends elasticity and viscosity matrices is presented. An algorithm to connect material points and to build the adjacency matrix has been developed. Numerical results for a set of 16 nodes are shown.Portuguese Funds through FCT - ’Fundação para a Ciência e a Tecnologia’, UID/MAT/00013/2013. European Union through the European Regional Development Fund, based on COMPETE 2020 (Programa Operacional da Competitividade e Internacionalização), project ICT (UID/GEO/04683/2013) with reference POCI-01-0145-FEDER-007690 and national funds provided by Fundação para a Ciência e Tecnologia. Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013.info:eu-repo/semantics/publishedVersio

Balance between viscous and elastic parameters for ductile materials flow under an overdamped regime

The evolution of less ductile layers embedded in a more ductile matrix under simple progressive shear in some geological structures, such as folding and asymmetric boudinage in the same direction, is a current trend in structural geology research. Aiming to study this subject, in this work a finite element method (FEM) is used to discretize a continuous medium as a point-mass model in which every node is subject to elastic and viscous forces. The dynamic equation of the present system takes into account both kinds of those forces driving the motion of each particle. In the herein developed model the system is subject to external shear forces applied to some nodes, resulting in a continuous flow of material. The balance between viscous and elastic constants is pursuit in order to characterize the evolution of the system.- The author Maria Antonia Forjaz acknowledges the funding supported by Portuguese Funds through FCT 'Fundacao para a Ciencia e a Tecnologia', UID/MAT/00013/2013. The author Jorge Pamplona is co-funded by the European Union through the European Regional Development Fund, based on COMPETE 2020 (Programa Operacional da Competitividade e Internacionalizacao), project ICT (UID/GEO/04683/2013) with reference POCI01-0145-FEDER-007690 and national funds provided by Fundacao para a Ciencia e Tecnologia. The authors Teresa de Lacerda-Aroso and Antonio Mario Almeida acknowledge the support of the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013

High-magnetic field lattice length changes in URu2Si2

We report high magnetic field (up to 45 T) c-axis thermal expansion and magnetostriction experiments on URu2Si2 single crystals. The sample length change associated with the transition to the hidden order phase becomes increasingly discontinous as the magnetic field is raised above 25 T. The re-entrant ordered phase III is clearly observed in both the thermal expansion and magnetostriction above 36 T, in good agreement with previous results. The sample length is also discontinuous at the boundaries of this phase, mainly at the upper boundary. A change in the sign of the coefficient of thermal-expansion is observed at the metamagnetic transition (B_M = 38 T) which is likely related to the existence of a quantum critical end point.Comment: 5 pages, 4 figures, to be published in PR

A versatile and compact capacitive dilatometer

We describe the design, construction, calibration, and operation of a relatively simple differential capacitive dilatometer suitable for measurements of thermal expansion and magnetostriction from 300 K to below 1 K with a low-temperature resolution of about 0.05 angstroms. The design is characterized by an open architecture permitting measurements on small samples with a variety of shapes. Dilatometers of this design have operated successfully with a commercial physical property measurement system, with several types of cryogenic refrigeration systems, in vacuum, in helium exchange gas, and while immersed in liquid helium (magnetostriction only) to temperatures of 30 mK and in magnetic fields to 45 T.Comment: 8 pages, incorporating 6 figures, submitted to Rev. Sci. Instru

Col-OSSOS: Colors of the Interstellar Planetesimal 1I/`Oumuamua

The recent discovery by Pan-STARRS1 of 1I/2017 U1 (`Oumuamua), on an unbound and hyperbolic orbit, offers a rare opportunity to explore the planetary formation processes of other stars, and the effect of the interstellar environment on a planetesimal surface. 1I/`Oumuamua's close encounter with the inner Solar System in 2017 October was a unique chance to make observations matching those used to characterize the small-body populations of our own Solar System. We present near-simultaneous g$^\prime$, r$^\prime$, and J photometry and colors of 1I/`Oumuamua from the 8.1-m Frederick C. Gillett Gemini North Telescope, and $gri$ photometry from the 4.2 m William Herschel Telescope. Our g$^\prime$r$^\prime$J observations are directly comparable to those from the high-precision Colours of the Outer Solar System Origins Survey (Col-OSSOS), which offer unique diagnostic information for distinguishing between outer Solar System surfaces. The J-band data also provide the highest signal-to-noise measurements made of 1I/`Oumuamua in the near-infrared. Substantial, correlated near-infrared and optical variability is present, with the same trend in both near-infrared and optical. Our observations are consistent with 1I/`Oumuamua rotating with a double-peaked period of $8.10 \pm 0.42$ hours and being a highly elongated body with an axial ratio of at least 5.3:1, implying that it has significant internal cohesion. The color of the first interstellar planetesimal is at the neutral end of the range of Solar System $g-r$ and $r-J$ solar-reflectance colors: it is like that of some dynamically excited objects in the Kuiper belt and the less-red Jupiter Trojans.Comment: Accepted to ApJ

Visco-elastic systems as a quadratic eigenvalue problem

In viscous materials systems, time and stress dependent instabilities often occur. The evolution of visco-elastic systems under external stress has already been modeled by applying matricial dynamic equations comprehending elasticity and viscosity matrices. In this study we report a novel formulation for such kind of systems as a nonlinear quadratic eigenvalue problem evolving from an already defined adjacency matrix. A four mass-spring damped system is presented as case study.The author Maria Antónia Forjaz acknowledges the funding supported by Portuguese Funds through FCT - ’Fundação para a Ciência e a Tecnologia’, UID/MAT/00013/2013. The author Jorge Pamplona is co-funded by the European Union through the European Regional Development Fund, based on COMPETE 2020 (Programa Operacional da Competitividade e Internacionalização), project ICT (UID/GEO/04683/2013) with reference POCI-01-0145-FEDER-007690 and national funds provided by Fundação para a Ciência e Tecnologia. The authors António Mário Almeida and T. de Lacerda–Arôso acknowledge the support of the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013.info:eu-repo/semantics/publishedVersio