Two monuments in Portugal are being monitoring by the University of Minho: the Clock Tower of Mogadouro and the Church of Jerónimos Monastery, in Lisbon. Vibration sensors and temperature and relative air humidity sensors are installed in the two monuments. Operational modal analysis is being used to estimate the modal parameters, followed by statistical analysis to evaluate the environmental effects on the dynamic response. The aim is to explore damage assessment in masonry structures at an early stage by vibration signatures as a part of a heath monitoring process to preserve the historical constructions. The paper presents all the preceding dynamic analysis steps before the monitoring task, which includes the installation of the monitoring system, the system identification and subsequent FE model updating analysis, the automatic modal identification and the investigation of the influence of the environment on the identified modal parameters.

The LisbOn KInetics Boltzmann (LoKI-B) is an open-source simulation tool (https://github. com/IST-Lisbon/LoKI) that solves a time and space independent form of the two-term electron Boltzmann equation, for non-magnetised non-equilibrium low-temperature plasmas excited by DC/HF electric fields from different gases or gas mixtures. LoKI-B was developed as a response to the need of having an electron Boltzmann solver easily addressing the simulation of the electron kinetics in any complex gas mixture (of atomic/molecular species), describing first and second-kind electron collisions with any target state (electronic, vibrational and rotational), characterized by any user-prescribed population. LoKI-B includes electron-electron collisions, it handles rotational collisions adopting either a discrete formulation or a more convenient continuous approximation, and it accounts for variations in the number of electrons due to nonconservative events by assuming growth models for the electron density. On input, LoKI-B defines the operating work conditions, the distribution of populations for the electronic, vibrational and rotational levels of the atomic/molecular gases considered, and the relevant sets of electron-scattering cross sections obtained from the open-access website LXCat (http://lxcat. net/). On output, it yields the isotropic and the anisotropic parts of the electron distribution function (the former usually termed the electron energy distribution function), the electron swarm parameters, and the electron power absorbed from the electric field and transferred to the different collisional channels. LoKI-B is developed with flexible and upgradable object-oriented programming under MATLAB ® , to benefit from its matrix-based architecture, adopting an ontology that privileges the separation between tool and data. This topical review presents LoKI-B and gives examples of results obtained for different model and real gases, verifying the tool against analytical solutions, benchmarking it against numerical calculations, and validating the output by comparison with available measurements of swarm parameters.

This paper presents a systematic characterization of capacitively-coupled radio-frequency hydrogen discharges, produced within a parallel plate cylindrical setup at different rf applied voltages (V rf = 50 − 600 V), frequencies (f = 13.56 − 40.56 MHz), and pressures (p = 0.2 − 1 torr). A twodimensional, time-dependent fluid model for charged particle transport is self-consistently solved coupled to a homogeneous kinetic model for hydrogen, including vibrationally excited molecular species and electronically excited atomic species. Numerical simulations are compared with experimental measurements of various plasma parameters. A good quantitative agreement is found between simulations and experiment for the coupled electrical power and the plasma potential. The model underestimates the values of the electron density, the self-bias potential, and the H(n=1) atom density with respect to measurements, but agrees with experiment when predicting that all these parameters increase with either V rf , f , or p. The dissociation degree is about 10 −3 for the work conditions considered. Simulations adopt a wall-recombination probability for H atoms that was experimentally measured, thus accounting for surface modification with discharge operating conditions. Results show the key role played by the atomic wall-recombination mechanism in plasma description.

This paper presents a systematic characterization of pure hydrogen capacitively coupled discharges, produced in a parallel plate cylindrical setup. A two-dimensional, time-dependent fluid model is used to describe the production, transport, and destruction of electrons and positive ions H ϩ , H 2 ϩ , and H 3 ϩ , at different frequencies ͑13.56-60 MHz͒, pressures ͑0.2-8 Torr͒, rf applied voltages ͑50-450 V͒ and geometric dimensions ͑1.6-12.8 cm radii and 1.6-6.4 cm interelectrode distances͒. A good agreement is found between calculation results and experimental measurements for the coupled electrical power, the plasma potential, and the self-bias potential, at various frequencies and rf applied voltages. However, the model generally underestimates the electron density with respect to its measured values. The paper discusses different space-time events, such as the development of double-ionization structures or the occurrence of field inversion and field reversal phenomena. The dependencies on pressure and frequency of the time-average electric field distribution are analyzed and related to the electron displacement within space-charge sheaths. This study is later used to understand the variations of the hydrogen dissociation rate, with changes in discharge operating conditions. The influence of reactor dimensions on the spatial profiles of the plasma potential, the rf electric field, the electron density, and the electron mean energy are analyzed in terms of discharge symmetry. An investigation of the space-time averaged rf electric field variations, with changes in the applied voltage, pressure, and geometric dimensions is carried out. These variations are shown to follow a universal similarity curve, if an adequate normalization is used when plotting the rf electric field as a function of pressure. This innovative representation of rf discharges allows a univocal definition of a reactor working point, for given operating conditions.

This paper uses experiments and modelling to study capacitively coupled radio-frequency (rf) discharges in pure nitrogen, at 13.56 MHz frequency, 0.1-1 mbar pressures and 2-30 W coupled powers. Experiments performed on two similar (not twin) setups, existing in the LATMOS and the GREMI laboratories, include electrical and optical emission spectroscopy (OES) measurements. Electrical measurements give the rf-applied and the direct-current-self-bias voltages, the effective power coupled to the plasma and the average electron density. OES diagnostics measure the intensities of radiative transitions with the nitrogen second-positive and first-negative systems, and with the 811.5 nm atomic line of argon (present as an actinometer). Simulations use a hybrid code that couples a two-dimensional time-dependent fluid module, describing the dynamics of the charged particles (electrons and positive ions N + 2 and N + 4 ), and a zero-dimensional kinetic module, describing the production and destruction of nitrogen (atomic and molecular) neutral species. The coupling between these modules adopts the local mean energy approximation to define space-time-dependent electron parameters for the fluid module and to work out space-time-averaged rates for the kinetic module. The model gives general good predictions for the self-bias voltage and for the intensities of radiative transitions (both average and spatially resolved), underestimating the electron density by a factor of 3-4.

A two-dimensional (r, z) time-dependent fluid model was developed and used to describe a dc planar magnetron discharge with cylindrical symmetry. The transport description of the charged species uses the corresponding first three moments of the Boltzmann equation: continuity, momentum transfer and mean energy transfer (the last one only for electrons), coupled with the Poisson equation. An original method is proposed to treat the transport equations. Electron and ion momentum transport equations are reduced to the classical drift-diffusion expression for the fluxes since the presence of the magnetic field is introduced as an additional part in the electron flux, while for ions an effective electric field was considered. Thus, both continuity and mean energy transfer equations are solved in a classical manner. Numerical simulations were performed considering argon as a buffer gas, with a neutral pressure varying between 5 and 30 mTorr, for different voltages applied on the cathode. Results obtained for densities of the charged particle, fluxes and plasma potential are in good agreement with those obtained in previous studies.

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Direct current magnetron sputtering was used to produce AlN x O y thin films, using an aluminum target, argon and a mixture of N 2 +O 2 (17:3) as reactive gases. The partial pressure of the reactive gas mixture was increased, maintaining the discharge current constant. Within the two identified regimes of the target (metallic and compound), four different tendencies for the deposition rate were found and a morphological evolution from columnar towards cauliflower-type, ending up as dense and featureless-type films. The structure was found to be Al-type (face centered cubic) and the structural characterization carried out by X-ray 2 diffraction and transmission electron microscopy suggested the formation of an aluminumbased polycrystalline phase dispersed in an amorphous aluminum oxide/nitride (or oxynitride) matrix. This type of structure, composition, morphology and grain size, were found to be strongly correlated with the electrical response of the films, which showed a gradual transition between metallic-like responses towards semiconducting and even insulating-type behaviors. A group of films with high aluminum content revealed a sharp decrease of the temperature coefficient of resistance (TCR) as the concentration ratio of non-metallic/aluminum atomic ratio increased. Another group of samples, where the non-metallic content became more important, revealed a smooth transition between positive and negative values of TCR. In order to test whether the oxynitride films have a unique behavior or simply a transition between the typical responses of aluminum and of those of the correspondent nitride and oxide, the electrical properties of the ternary oxynitride system were compared with AlN x and AlO y systems, prepared in similar conditions.