Identificação de dano baseada na totalidade da informação espectral: aplicações

O tema da identificação de dano (deteção e localização) em estruturas através de métodos não destrutivos recebeu, ao longo das últimas décadas, um interesse acrescido em resultado de um significativo número de estruturas monitorizadas, tais como pontes ou edifícios históricos de elevado interesse patrimonial. Vários métodos de identificação de dano têm sido sugeridos com base em alterações dos parâmetros dinâmicos (e.g. frequências naturais ou modos de vibração), sempre que a matriz de rigidez ou de massa seja alterada no sistema. Contudo, o problema da identificação de dano é complexo, não havendo, até ao momento, um método ou um conjunto de métodos que resolva o problema. O presente artigo apresenta um método de identificação baseado na utilização da totalidade da informação espetral dentro de uma gama de frequências de interesse, obtida por ensaios de vibração ambiente (sem medir as excitações). O método é aplicado a três casos de estudo. Os resultados demostram que o método baseado na utilização da totalidade da informação espectral poderá ser um importante contributo para a identificação do dano em estruturas

Structural monitoring and damage identification on a masonry chimney by a spectral-based identification technique

The present work deals with the damage identification of a historical masonry chimney located in Guimarães (Portugal), including a detailed survey, inspection and diagnosis. The chimney was object of a continuous monitoring campaign carried out to catch the evolution of the modal parameters and evaluate the success of the rehabilitation works planned after a lightning accident. Based on the dynamic features extracted from the OMA data, a damage identification analysis was performed making use of different damage identification techniques. Considering the explicit dependence of output-only power spectral densities on frequency contents, a spectral-based identification method was used to detect the damage. Finally, an appropriate localization index was defined combining evolutionary complex eigenvectors obtained from the decomposition of the power spectral density matrix. The results allow to conclude that the spectral-based dynamic identification method is a non-destructive tool able to capture the global behavior of a structure and may reveal itself of great help for exploring damage at an early stage in historical constructions

Broad N2H+ emission towards the protostellar shock L1157-B1

We present the first detection of N2H+ towards a low-mass protostellar outflow, namely the L1157-B1 shock, at about 0.1 pc from the protostellar cocoon. The detection was obtained with the IRAM 30-m antenna. We observed emission at 93 GHz due to the J = 1-0 hyperfine lines. The analysis of the emission coupled with the HIFI CHESS multiline CO observations leads to the conclusion that the observed N2H+(1-0) line originates from the dense (> 10^5 cm-3) gas associated with the large (20-25 arcsec) cavities opened by the protostellar wind. We find a N2H+ column density of few 10^12 cm-2 corresponding to an abundance of (2-8) 10^-9. The N2H+ abundance can be matched by a model of quiescent gas evolved for more than 10^4 yr, i.e. for more than the shock kinematical age (about 2000 yr). Modelling of C-shocks confirms that the abundance of N2H+ is not increased by the passage of the shock. In summary, N2H+ is a fossil record of the pre-shock gas, formed when the density of the gas was around 10^4 cm-3, and then further compressed and accelerated by the shock.Comment: ApJ, in pres

A spectrum-driven damage Identification technique: application and validation through the numerical simulation of the Z24 Bridge

The present paper focuses on a damage identification method based on the use of the second order spectral properties of the nodal response processes. The explicit dependence on the frequency content of the outputs power spectral densities makes them suitable for damage detection and localization. The well-known case study of the Z24 Bridge in Switzerland is chosen to apply and further investigate this technique with the aim of validating its reliability. Numerical simulations of the dynamic response of the structure subjected to different types of excitation are carried out to assess the variability of the spectrum-driven method with respect to both type and position of the excitation sources. The simulated data obtained from random vibrations, impulse, ramp and shaking forces, allowed to build the power spectrum matrix from which the main eigenparameters of reference and damage scenarios are extracted. Afterwards, complex eigenvectors and real eigenvalues are properly weighed and combined and a damage index based on the difference between spectral modes is computed to pinpoint the damage. Finally, a group of vibration-based damage identification methods are selected from the literature to compare the results obtained and to evaluate the performance of the spectral index.The authors would like to express their sincere gratitude to Prof. Dr. Guido De Roeck for sharing his information about the Z24 Bridge. The first author would also like to acknowledge the Italian Ministry of Education, Universities and Research (MIUR) for the Ph.D. scholarship provided

H_{2} adsorption on multiwalled carbon nanotubes at low temperatures and low pressures

We present an experimental study on H_{2} adsorption on multiwalled carbon nanotubes (MWCNTs) at low temperatures (12–30 K) and low pressures (2×10^{-5}  Torr) using the temperature programmed desorption technique. Our results show that the molecular hydrogen uptake increases nearly exponentially from 6×10^{-9}  wt. % at 24.5 K to 2×10^{-7}  wt. % at 12.5 K and that the desorption kinetics is of the first order. Comparative measurements indicate that MWCNTs have an adsorption capacity about two orders higher than that of activated carbon (charcoal) making them a possible candidate as hydrogen cryosorber for eventual applications in accelerators and synchrotrons

Spectral-based damage identification technique on an earthen mock-up construction tested on a shaking table

Conservation of ancient built heritage plays a leading role for modern societies. Knowledge about ancient building methods, essentially based on the use of natural materials such as earth, stone and wood, is fundamental to plan interventions aimed at preserving the architectural heritage. Due to the growing research on sustainable technologies, the interest in structural systems built using natural materials has been rising more and more. Taking an earthen mock-up construction as model, the paper focuses on the dynamic behaviour of such a system tested on a shaking table. Detailed descriptions of the model, its mechanical features, the seismic test performed and the damage pattern obtained are first presented. Then, the dynamic identification of the structure during damage occurrence is performed through the decomposition of the power spectral density matrix. Damage evolution and localization are also analyzed by an index based on the complex eigenvectors estimated from the matrix. Finally, comparisons between experimental and analytical results are addressed

Lamb meat colour stability as affected by dietary tannins

Twenty-one male Comisana lambs were divided into three groups at 45 days of age and were individually penned for 60 days. Seven lambs were fed a concentrate-based diet (C), seven lambs received the same concentrate with the addiction of tannins from quebracho (Schinopsis lorentzii; T), whereas the remaining animals were fed exclusively fresh vetch (Vicia sativa; H). Colour descriptors (a*, b* and H*) and metmyoglobin (MMb) percentages were measured on minced semimembranosus muscle over 14 days of refrigerated storage in a high oxygen atmosphere. Regardless of dietary treatment, meat redness decreased, while yellowness and hue angle increased (P < 0.001) over storage duration. However, higher a* values, lower b* values and lower H* values were observed in meat from both H- and T-fed animals as compared to meat from C-fed lambs (P = 0.012; P = 0.02; P = 0.003, respectively). Metmyoglobin formation increased over time (P < 0.001), but H diet resulted in lower metmyoglobin percentages than C diet (P = 0.007). We conclude that the inclusion of tannins into the concentrate improved meat colour stability compared to a tannin-free concentrate. Moreover, the protective effect of tannins against meat discolouration was comparable to that obtained by feeding lambs fresh herbage

Reproductive outcomes and fertility preservation strategies in women with malignant ovarian germ cell tumors after fertility sparing surgery

Malignant ovarian germ cell tumors are rare tumors that mainly affect patients of reproductive age. The aim of this study was to investigate the reproductive outcomes and fertility preservation strategies in malignant ovarian germ cell tumors after fertility-sparing surgery. Data in literature support that fertility-sparing surgery is associated with an excellent oncological outcome not only in early stages malignant ovarian germ cell tumors but also in advanced stages. Moreover, the possibility of performing conservative treatment should be considered even in case of relapse or advanced disease, given the high chemosensitivity. Indeed, available data have shown that menstrual function is maintained after platinum-based regimens in over 85–95% of patients with malignant ovarian germ cell tumors and rate of premature menopause reported in literature ranges between 3% and 7.4%, while premature ovarian failure rates are between 3.4% and 5%. Moreover, reproductive outcomes are about 80% with no increase in the risk of teratogenicity compared to general population. Therefore, conservative surgery for malignant ovarian germ cell tumors currently may represent a therapeutic option in patients who wish to preserve fertility but must be available for extended follow-up and after subscribing to informed consent

The Herschel HIFI water line survey in the low-mass proto-stellar outflow L1448

As part of the WISH (Water In Star-forming regions with Herschel) key project, we report on the observations of several ortho- and para-H2O lines performed with the HIFI instrument towards two bright shock spots (R4 and B2) along the outflow driven by the L1448 low-mass proto-stellar system, located in the Perseus cloud. These data are used to identify the physical conditions giving rise to the H2O emission and infer any dependence with velocity. These observations provide evidence that the observed water lines probe a warm (T_kin~400-600 K) and very dense (n 10^6 - 10^7 cm^-3) gas, not traced by other molecules, such as low-J CO and SiO, but rather traced by mid-IR H2 emission. In particular, H2O shows strong differences with SiO in the excitation conditions and in the line profiles in the two observed shocked positions, pointing to chemical variations across the various velocity regimes and chemical evolution in the different shock spots. Physical and kinematical differences can be seen at the two shocked positions. At the R4 position, two velocity components with different excitation can be distinguished, with the component at higher velocity (R4-HV) being less extended and less dense than the low velocity component (R4-LV). H2O column densities of about 2 10^13 and 4 10^14 cm^-2 have been derived for the R4-LV and the R4-HV components, respectively. The conditions inferred for the B2 position are similar to those of the R4-HV component, with H2O column density in the range 10^14 - 5 10^14 cm^-2, corresponding to H2O/H2 abundances in the range 0.5 - 1 10^-5. The observed line ratios and the derived physical conditions seem to be more consistent with excitation in a low velocity J-type shock with large compression rather than in a stationary C-shock, although none of these stationary models seems able to reproduce all the characteristics of the observed emission.Comment: Accepted for publication in A&

Water emission from the chemically rich outflow L1157

In the framework of the Herschel-WISH key program, several ortho-H2O and para-H2O emission lines, in the frequency range from 500 to 1700 GHz, were observed with the HIFI instrument in two bow-shock regions (B2 and R) of the L1157 cloud. The primary aim is to analyse water emission lines as a diagnostic of the physical conditions in the blue (B2) and red-shifted (R) lobes to compare the excitation conditions. A total of 5 ortho- and para-H216O plus one o-H218O transitions were observed in B2 and R with a wide range of excitation energies (27 K<=Eu<=215 K). The H2O spectra, observed in the two shocked regions, show that the H2O profiles are markedly different in the two regions. In particular, at the bow-shock R, we observed broad (~30 km s-1 with respect to the ambient velocity) red-shifted wings where lines at different excitation peak at different red-shifted velocities. The B2 spectra are associated with a narrower velocity range (~6 km s-1), peaking at the systemic velocity. The excitation analysis suggests, for B2, low values of column density NH2O <=5{\times}1013 cm-2, a density range of 105 <=nH2 <=107 cm-3, and warm temperatures (>=300 K). The presence of the broad red-shifted wings and multiple peaks in the spectra of the R region, prompted the modelling of two components. High velocities are associated with relatively low temperatures (~100K),NH2O{\simeq}5{\times}1012-5{\times}1013 cm-2 and densities nH2{\simeq}106-108 cm-3.Lower velocities are associated with higher excitation conditions with Tkin>=300 K, very dense gas (nH2 ~108 cm-3) and low column density (NH2O<5{\times}1013 cm-2).Comment: 9 pages, 8 figures, A&A in pres