Separation of Damping and Velocity Strain Dependencies using an Ultrasonic Monochromatic Excitation

International audiencePrecise knowledge of the dependence of elastic modulus and Q factor on the amplitude of excitation is a prerequisite for the development and validation of models to explain the hysteresis observed in qua-sistatic experiments for various media, i.e., the different deformations at the same applied stress observed when stress change rate is positive or negative. Separation of different contributions to dynamic nonlin-earity (e.g., those due to nonequilibrium effects, often termed conditioning) and independent estimation of nonlinearities originated by the strain dependence of velocity and the damping factor are required, which is often not possible with standard approaches. Here we propose and validate a method that, measuring the response of a sample to a monochromatic excitation at different amplitudes, allows fast, continuous, and quasi-real-time monitoring of the dependence of the material elastic properties on amplitude: dynamic elastic modulus (related with velocity through density) and Q factor of the mechanical resonances (related with wave-amplitude attenuation parameters)

Separation of Damping and Velocity Strain Dependencies using an Ultrasonic Monochromatic Excitation

Precise knowledge of the dependence of elastic modulus and Q-factor on amplitude of excitation is a prerequisite for the development and validation of models to explain the hysteresis observed in quasi-static experiments for various media, i.e. the different deformations at the same applied stress observed when stress change rate is positive or negative. Separation of different contributions to dynamic nonlinearity (e.g those due to non equilibrium effects, often termed conditioning) and independent estimation of nonlinearities originated by the strain dependence of velocity and damping factor are required, which is often not possible with standard approaches. Here we propose and validate a method which, measuring the response of a sample to a monochromatic excitation at different amplitudes, allows fast, continuous and quasi real-time monitoring of the dependence of the material elastic properties on amplitude: dynamic elastic modulus (related with velocity through density) and Q-factor of the mechanical resonances (related with wave amplitude attenuation parameter

Exploiting Slow Dynamics Effects for Damage Detection in Concrete

Nonlinear ultrasonic techniques have been developed over the last decades to detect the presence of damage in materials of interest in the field of civil engineering, such as concrete or mortar. The dependence on the strain amplitude of measurable quantities, such as wave velocity, damping factor, resonance frequency, etc. is normally considered a qualitative indicator of the presence of defects at the microstructural level. The experimental approaches proposed have the advantage of being sensitive to small variations in the sample microstructure and are therefore more adapted to detect the presence of small cracks or damaged areas with respect to traditional linear ultrasonic techniques. However, nonlinear methods are difficult to implement, since they usually require a calibrated experimental set-up which also behaves linearly at high amplitudes of excitation. The slow dynamics features, typical of the hysteresis generated by damage, have been given much less attention as a tool for damage detection even though their quantification is often less demanding in terms of an experimental set-up. Here, we provide the first evidence of how recovery, which is part of the slow dynamics process, is sensitive to the presence of damage in concrete samples and thus could be considered as an easy-to-measure nonlinear indicator for Structural Health Monitoring purposes

"Experimental evidence of correlations between conditioning and relaxation in hysteretic elastic media"

Consolidated granular materials and materials with damage at the microstructural level exhibit anomalous elastic behavior even when excited by low-amplitude elastic waves. Their response is given by a combination of slow- and fast-dynamics effects which, as their definition implies, act on very different time scales. In particular, conditioning (a transition to an elastic state dependent on the strain amplitude) and relaxation (full recovery of the elastic properties when the strain is removed) have been observed in different materials and under different dynamic excitations. An experimental parametric analysis of the phenomenon, aiming to establish correlations between the effects on different elastic physical properties (wave velocity and attenuation coefficient) and between the evolution of conditioning and relaxation is proposed here, with the goal of better characterizing slow dynamics and allowing one to go beyond the phenomenological description of elastic hysteresis currently available. At the same time, by studying different materials, we wish to highlight the possibility of using slow dynamics as an additional tool for materials characterization

Suicidal Behavior and Psychological Distress in University Students: A 12-Nation Study. Archives of Suicide Research

This study investigated the prevalence of suicidal behavior and psychological distress in university students across 12 nations. A total of 5572 university students from 12 countries were surveyed about suicide ideation, suicide attempts and psychological distress by means of a self-administered questionnaire. Almost 29% of the samples reported having contemplated suicide and 7% reported attempting suicide. Of the total sample, 51.1% scored above the General Health Questionnaire-12 ≥ 3 cut-off point, 41.6% above the GHQ-12 ≥ 4 cut-off point, and 33.8% scored above the GHQ-12 ≥ 5 cut-off point. While odds of suicide ideation were elevated in Austria and the UK, reduced ORs were detected for China, Italy, Saudi Arabia, Tunisia, and Turkey. Similarly, while odds of suicide attempt were high in Jordan, Palestine, Saudi Arabia, and to some extent in Turkey, reduced ORs were observed for Austria, China, Italy, Japan and the USA. Elevated ORs for psychological distress were seen in Japan, Jordan, Palestine, Saudi Arabia, Tunisia and Turkey but reduced ORs were noted in Austria, China, Iran, Italy and the USA. Psychological distress was strongly associated with reports of suicide ideation and attempts. Suicide ideation, suicide attempt and psychological distress are common in university students but their rates vary depending on the sociocultural context. Due attention should be devoted to the mental health needs of young adults enrolled in higher educational institutions and more cross-cultural research is warranted to better understand the etiology of the observed intersocietal variations in suicidal behavior and psychological distress

Cross - national comparisons of attitudes towards suicide and suicidal persons in university students from 12 countries

This paper reports the results of a comparative investigation of attitudes to suicide and suicidal persons in 5,572 university students from 12 countries. Participants filled out two scales measuring attitudes towards suicide and suicidal persons, a measure of psychological distress together with the questions about suicidal behavior. Results showed that the highest suicide acceptance scores were observed in Austrian, UK, Japanese and Saudi Arabian samples and the lowest scores were noted in Tunisian, Turkish, Iranian and Palestinian samples. While the highest social acceptance scores for a suicidal friend were noted in Turkish, US, Italian and Tunisian samples, the lowest scores were seen in Japanese, Saudi Arabian, Palestinian and Jordanian samples. Compared to participants with a suicidal past, those who were never suicidal displayed more internal barriers against suicidal behavior. Men were more accepting of suicide than women but women were more willing to help an imagined suicidal peer. Participants with accepting attitudes towards suicide but rejecting attitudes towards suicidal persons reported more suicidal behavior and psychological distress, and were more often from high suicide rate countries and samples than their counterparts. They are considered to be caught in a fatal trap in which most predominant feelings of suicidality such as hopelessness or helplessness are likely to occur. We conclude that in some societies such as Japan and Saudi Arabia it might be difficult for suicidal individuals to activate and make use of social support systems

The Role of Religion on Suicidal Behavior, Attitudes and Psychological Distress in University Students: A Multinational Study

The purpose of this study was to determine the association of religion to suicidal behavior, attitudes and psychological distress in 5572 students from 12 countries by means of a self-report questionnaire. Our results showed that an affiliation with Islam was associated with reduced risk for suicide ideation, however affiliating with Orthodox Christianity and no religion was related to increased risk for suicide ideation. While affiliating with Buddhism, Catholic religion and no religion associated with lowered risk for attempting suicide, affiliation with Islam was related to heightened risk for attempting suicide. Affiliation with Hinduism, Orthodox Christianity, Protestantism, Catholicism, other religions and with no religion was associated with decreased risk for psychological distress but those reported affiliating with Islam evinced greater risk for psychological distress. The associations of the strength of religious belief to suicidal ideation and attempts were in the expected direction for most but it had a positive relation in respondents affiliating with Catholicism and other religions. Students reporting affiliation with Islam, Orthodox religion and Buddhism were the least accepting of suicide but they displayed a more confronting interpersonal style to an imagined peer with a suicidal decision. It was concluded that the protective function of religion in educated segments of populations (university students) and in university students residing in Muslim countries where freedom from religion is restricted or religion is normative and/or compulsory is likely to be limited. Our findings suggest that public policies supporting religious freedom may augment the protective function of religion against suicide and psychological distress

Is Individualism Suicidogenic? Findings From a Multinational Study of Young Adults From 12 Countries

The associations of individualistic versus collectivistic value orientations with suicidal ideation and attempts, attitudes towards suicide and towards suicidal individuals, and psychological distress were investigated across 12 nations (N = 5572 university students). We expected differential associations of value orientations with suicidal behavior and moderating effects of the prevailing value orientations in the various countries. Findings showed that intermediate levels of individualism appeared protective against suicide attempts across all investigated nations, but that, otherwise, there seemingly are no universal associations of individualism and collectivism with suicidal behaviors. High collectivism was associated with less suicidal ideation only in individualistic countries. Low individualism appeared to be a risk factor for suicidal ideation specifically in Muslim collectivistic cultures, whereas high individualism in Asian collectivistic cultures. Collectivistic values are uniformly associated with less permissive attitudes to suicide, whereas individualistic values with a more stigmatized view of suicidal behavior. Both individualistic and collectivistic values were associated with socially accepting attitudes to a suicidal peer, helping a suicidal friend, and emotional involvement. The associations of individualistic and collectivistic values with disapproving attitudes to suicidal disclosure were complex. Beliefs in punishment after death for suicide, seeing suicide as mental illness, and emotional involvement with a suicidal friend were lower in high-suicide-rate countries. These evidence patterns are discussed in the light of related research evidence, along with directions for future research in this area