Natural Time Research Articles

Identifying impending failure in heterogeneous materials: A study on acoustic emission time series

In the present paper, precursors to identify impending failure in heterogeneous materials are investigated by analyzing Acoustic Emission (AE) time series. Three main approaches are considered: (1) long-range correlations using the Hurst (H) analysis, (2) Natural Time (NT) analysis, and (3) a proposed Method of Critical Fluctuations-Based (MCF-B) approach. The above approaches are employed to data collected from an experimental AE test on a concrete cubic specimen subjected to an axial compression loading. The results indicate that: persistent long-range correlations tend towards near-random behavior prior to imminent failure; critical regions, characterized by the convergence of natural time parameters, show a direct correlation with imminent increments in the acoustic emission activity and the structure's collapse; the proposed MCF-B approach as precursor, is capable to identify critical states, being the results in agreement with those from NT and Hurst analysis.

Is it time for job quality? Conceptualising temporal arrangements in new models of homecare.

Time is a key organising principle in the formal provision of care to older people in their own homes. It is used when delivering homecare services, calculating fees and care staff's pay entitlement. Research in the UK highlights how the predominant service model of compartmentalising care into pre-defined tasks, delivered in strictly scheduled time-based units, offers poor quality jobs, characterised by low pay, insecure and tightly controlled work. Our case study research of 'new models' of homecare however, found variation in the way time measures were operationalised. Drawing from Thompson's (1967, Past & Present, 38, 56-97) conceptualisation of clock-time (where care work is controlled by external measures of time) and nature's time (where care work is performed through internal notions of time) as a lens, we examine how service delivery models and job quality are temporally connected through homecare work. Through our analysis, we exemplify how the use of strict time-based measures can limit care work according to nature's time. We also consider the potential of ambitemporality-the accommodation of clock and nature's time-in organising service delivery as a means of enriching job quality. Finally, we discuss the pertinent implications of conceiving job quality in homecare work through a temporal lens.

Toward an Ecosocialist Degrowth

We are facing today the most pronounced and remarkable of all contradictions: that between what ecosocialist Ian Angus calls "capital's time" and "nature's time." As a result, a series of intertwined ecological and social crises have come together, posing existential threats to life on the planet. Everywhere, life, both human and nonhuman, is threatened, and the dangers of the imposition of capital's time on nature's time accelerate decade by decade at levels scarcely imaginable.

The Evolution of Preseismic Patterns Related to the Central Crete (Mw6.0) Strong Earthquake on 27 September 2021 Revealed by Multiresolution Wavelets and Natural Time Analysis

On 27 September 2021, a shallow earthquake with focal depth of 10 km and moment magnitude Mw6.0 occurred onshore in central Crete (Greece). The evolution of possible preseismic patterns in the area of central Crete before the Mw6.0 event was investigated by applying the method of multiresolution wavelet analysis (MRWA), along with that of natural time (NT). The monitoring of preseismic patterns by critical parameters defined by NT analysis, integrated with the results of MRWA as the initiation point for the NT analysis, forms a promising framework that may lead to new universal principles that describe the evolution patterns before strong earthquakes. Initially, we apply MRWA to the interevent time series of the successive regional earthquakes in order to investigate the approach of the regional seismicity towards critical stages and to define the starting point of the natural time domain. Then, using the results of MRWA, we apply the NT analysis, showing that the regional seismicity approached criticality for a prolonged period of ~40 days before the occurrence of the Mw6.0 earthquake, when the κ1 natural time parameter reached the critical value of κ1 = 0.070, as suggested by the NT method.

Seismicity Patterns Prior to the Thessaly (Mw6.3) Strong Earthquake on 3 March 2021 in Terms of Multiresolution Wavelets and Natural Time Analysis

On 3 March 2021, a strong, shallow earthquake of moment magnitude, Mw6.3, occurred in northern Thessaly (Central Greece). To investigate possible complex correlations in the evolution of seismicity in the broader area of Central Greece before the Mw6.3 event, we apply the methods of multiresolution wavelet analysis (MRWA) and natural time (NT) analysis. The description of seismicity evolution by critical parameters defined by NT analysis, integrated with the results of MRWA as the initiation point for the NT analysis, forms a new framework that may possibly lead to new universal principles that describe the generation processes of strong earthquakes. In the present work, we investigate this new framework in the seismicity prior to the Mw6.3 Thessaly earthquake. Initially, we apply MRWA to the interevent time series of the successive regional earthquakes in order to investigate the approach of the regional seismicity at critical stages and to define the starting point of the natural time domain. Then, we apply the NT analysis, showing that the regional seismicity approached criticality a few days before the occurrence of the Mw6.3 earthquake, when the κ1 natural time parameter reached the critical value of κ1 = 0.070.

Statistical and Criticality Analysis of the Lower Ionosphere Prior to the 30 October 2020 Samos (Greece) Earthquake (M6.9), Based on VLF Electromagnetic Propagation Data as Recorded by a New VLF/LF Receiver Installed in Athens (Greece).

In this work we present the statistical and criticality analysis of the very low frequency (VLF) sub-ionospheric propagation data recorded by a VLF/LF radio receiver which has recently been established at the University of West Attica in Athens (Greece). We investigate a very recent, strong (M6.9), and shallow earthquake (EQ) that occurred on 30 October 2020, very close to the northern coast of the island of Samos (Greece). We focus on the reception data from two VLF transmitters, located in Turkey and Israel, on the basis that the EQ’s epicenter was located within or very close to the 5th Fresnel zone, respectively, of the corresponding sub-ionospheric propagation path. Firstly, we employed in our study the conventional analyses known as the nighttime fluctuation method (NFM) and the terminator time method (TTM), aiming to reveal any statistical anomalies prior to the EQ’s occurrence. These analyses revealed statistical anomalies in the studied sub-ionospheric propagation paths within ~2 weeks and a few days before the EQ’s occurrence. Secondly, we performed criticality analysis using two well-established complex systems’ time series analysis methods—the natural time (NT) analysis method, and the method of critical fluctuations (MCF). The NT analysis method was applied to the VLF propagation quantities of the NFM, revealing criticality indications over a period of ~2 weeks prior to the Samos EQ, whereas MCF was applied to the raw receiver amplitude data, uncovering the time excerpts of the analyzed time series that present criticality which were closest before the Samos EQ. Interestingly, power-law indications were also found shortly after the EQ’s occurrence. However, it is shown that these do not correspond to criticality related to EQ preparation processes. Finally, it is noted that no other complex space-sourced or geophysical phenomenon that could disturb the lower ionosphere did occur during the studied time period or close after, corroborating the view that our results prior to the Samos EQ are likely related to this mainshock.

‘There is no time’: Agri-food internal migrant workers in Morocco's tomato industry

Agri-industrial production is supported by the agriculture–migration nexus, in which industrial-scale horticultural production relies on migrant workers. In this article I consider the time-related pressures on workers who are internal migrants from rural regions of Morocco. My account illustrates how workers are impacted by the demands from consumers for fresh food, year round, as well as by the rhythms of nature, and of social reproduction. I use concepts from EP Thompson's depiction of the transition from rural to factory work to describe the tensions in agricultural production at industrial scale for foreign markets. The concepts used are nature's time (related to seasonality, weather, daylight) and industrial time (of the market), and I adjoin to this the category of social-reproductive time in order to show these three time-related pressures function together. The identification of this threefold time-pressure on migrant workers in agri-food production builds on the recent attention of scholars to seasonality as a conceptual lens, and the identification of rhythms to highlight intersectional inequalities in the everyday. The paper is based on ethnographic and interview data from the Moroccan region of Chtouka Aït Baha, from which tomatoes and other crops are produced at industrial scale for export. I find that, together, the three temporal pressures lead to workers suffering exhaustion and finding themselves far from mobile and available to move with the seasons; rather, they are ‘locked in’ to this low-wage sector.

Evidence of critical dynamics in various electromagnetic precursors

A wide variety of electromagnetic phenomena possibly related with earthquake (EQ) preparation processes have been reported in the literature during the last few decades. An interesting aspect in their study is the time series analysis of the related observables aiming at the investigation of any embedded dynamics. In this review article we focus on the study of fracto-electromagnetic emissions (fracto-EME) at the MHz band, the ultra-low frequency (ULF) magnetic field variations (<3 Hz) and the subionospheric very low frequency (VLF) propagation anomalies. We present recent analysis results for these electromagnetic signals using two independent methods which are known for their ability to uncover critical dynamics, the recently proposed method of critical fluctuations (MCF) and the natural time (NT) analysis method. Our results show that all three considered electromagnetic signals present critical characteristics from a few weeks up to a few days before the main shock occurrence. On the other hand, signatures for the departure from the critical (highly symmetrical) state towards a low symmetry state, a state during which there is high localization of the EQ preparatory process, have been identified in specific cases for the MHz fracto-EME as well as for the ULF magnetic field variations. Based on a multidisciplinary analysis, a four-stage model of EQ dynamics by means of fracto-EME in the MHz and kHz bands has recently been proposed. The hypothesis that the precursors considered in this article emerge during the spatially extensive phase of EQ preparation, which corresponds to the first stage of the abovementioned four-stage model, as well as their relation with the foreshock seismic activity are discussed.

Criticality Hidden in Acoustic Emissions and in Changing Electrical Resistance during Fracture of Rocks and Cement-Based Materials.

Acoustic emissions (AE) due to microcracking in solid materials permit the monitoring of fracture processes and the study of failure dynamics. As an alternative method of integrity assessment, measurements of electrical resistance can be used as well. In the literature, however, many studies connect the notion of criticality with AE originating from the fracture, but not with the changes in the electrical properties of materials. In order to further investigate the possible critical behavior of fracture processes in rocks and cement-based materials, we apply natural time (NT) analysis to the time series of AE and resistance measurements, recorded during fracture experiments on cement mortar (CM) and Luserna stone (LS) specimens. The NT analysis indicates that criticality in terms of electrical resistance changes systematically precedes AE criticality for all investigated specimens. The observed greater unpredictability of the CM fracture behavior with respect to LS could be ascribed to the different degree of material homogeneity, since LS (heterogeneous material) expectedly offers more abundant and more easily identifiable fracture precursors than CM (homogenous material). Non-uniqueness of the critical point by varying the detection threshold of cracking events is apparently due to finite size effects which introduce deviations from the self-similarity.

Natural Time Analysis of Global Navigation Satellite System Surface Deformation: The Case of the 2016 Kumamoto Earthquakes.

In order to have further evidence of the atmospheric oscillation channel of the lithosphere-atmosphere-ionosphere coupling (LAIC), we have studied criticality in global navigation satellite system (GNSS) surface deformation as a possible agent for exciting atmospheric gravity waves (AGWs) in the atmosphere and GNSS fluctuations in the frequency range of AGWs with the use of the natural time (NT) method. The target earthquake (EQ) is the 2016 Kumamoto EQ with its main shock on 15 April 2016 (M = 7.3, universal time). As the result of the application of the NT method to GNSS data, we found that for the one-day sampled GNSS deformation data and its fluctuations in two AGW bands of 20–100 and 100–300 min, we could detect a criticality in the period of 1–14 April, which was one day to two weeks before the EQ. These dates of criticalities are likely to overlap with the time periods of previous results on clear AGW activity in the stratosphere and on the lower ionospheric perturbation. Hence, we suggest that the surface deformation could be a possible candidate for exciting those AGWs in the stratosphere, leading to the lower ionospheric perturbation, which lends further support to the AGW hypothesis of the LAIC process.

Health Monitoring of Medieval Masonry Towers by an Acoustic Emission Approach

Non-destructive tests were performed to assess cracking evolution in two medieval masonry buildings, Sineo and Asinelli towers rising respectively in the Cities of Alba and Bologna, in Italy. As regards the case study of Alba, in situ compressive flat-jack tests on small-sized elements of the tower were conducted in conjunction with acoustic emission (AE) monitoring. At the same time, crack patterns taking place in large volumes of the tower were likewise monitored through the AE technique.As for the case study of Bologna, a masonry wall of the Asinelli tower was monitored during a period of intense seismic activity. The observed correlation between the AE activity in the monitored structural element and local earthquakes points out a significant dependence of deterioration processes in the tower on the action of nearby earthquakes.In both cases, the trends of two evolutionary parameters, the b-value and the natural time (NT) variance κ1, were derived from the AE time series to identify the approach of the monitored structures to a critical state in relation to the earthquake occurrence.

On Possible Electromagnetic Precursors to a Significant Earthquake (Mw = 6.3) Occurred in Lesvos (Greece) on 12 June 2017.

This paper reports an attempt to use ultra-low-frequency (ULF) magnetic field data from a space weather monitoring magnetometer array in the study of earthquake (EQ) precursors in Greece. The data from four magnetometer stations of the HellENIc GeoMagnetic Array (ENIGMA) have been analyzed in the search for possible precursors to a strong EQ that occurred south of Lesvos Island on 12 June 2017, with magnitude Mw = 6.3 and focal depth = 12 km. The analysis includes conventional statistical methods, as well as criticality analysis, using two independent methods, the natural time (NT) method and the method of critical fluctuations (MCF). In terms of conventional statistical methods, it is found that the most convincing ULF precursor was observed in the data of ULF (20–30 mHz) depression (depression of the horizontal component of the magnetic field), which is indicative of lower ionospheric perturbation just 1 day before the EQ. Additionally, there are indications of a precursor in the direct ULF emission from the lithosphere 4 days to 1 day before the EQ. Further study in terms of NT analysis identifies criticality characteristics from 8 to 2 days before the EQ both for lithospheric ULF emission and ULF depression, while MCF reveals indications of criticality in all recorded magnetic field components, extending from 10 to 3 days before the EQ. Beyond the recordings of the geomagnetic stations of ENIGMA, the recordings of the fracto-electromagnetic emission stations of the HELlenic Seismo-ElectroMagnetics Network (ELSEM-Net) in Greece have been analyzed. The MHz recordings at the station that is located on Lesvos Island presented criticality characteristics (by means of both NT analysis and MCF) 11 days before the EQ, while a few days later (7–6 days before the EQ), the kHz recordings of the same station presented tricritical behavior. It is noted that the magnetosphere was quiet for a period of two weeks before the EQ and including its occurrence.

Natural time analysis on the ultra-low frequency magnetic field variations prior to the 2016 Kumamoto (Japan) earthquakes

On 15 April 2016 a very strong and shallow earthquake (EQ) (MW=7.0, depth ∼ 10 km) occurred in Southwest Japan under the city of Kumamoto, while two very strong foreshocks (MW=6.2 and MW=6.0) preceded by about one day. The Kumamoto EQs being very catastrophic, have already attracted much attention among the scientific community in a quest for understanding the generation mechanism, as well as for reporting any preseismic anomalies in various observables and assessing the effectivity of the current early warning systems. In the present article we report precursory behavior of the ground-based observed ultra-low frequency (ULF) magnetic field variations before the Kumamoto EQs. By analyzing specific ULF magnetic field characteristics in terms of the recently introduced natural time (NT) analysis method, we identified that ULF magnetic field variations presented critical features from 2 weeks up to 1 month before the Kumamoto EQs. Specifically, the ULF magnetic field characteristics Fh, Fz, Dh and δDep were analyzed. The first two represent variations of the horizontal and vertical components of the geomagnetic field. The third and fourth characteristics correspond to the depression (decrease) and a relative depression of the horizontal magnetic field variations, respectively. The latter depends on the degree of ionospheric disturbance. All of them were found to reach criticality before the Kumamoto EQs; however, in different time periods for each characteristic.

Critical features revealed in acoustic and electromagnetic emissions during fracture experiments on LiF

Acoustic emissions (AE) and electromagnetic emissions (EME) are produced during the fracture of solids permitting the monitoring of fracture processes and the study of fracture dynamics. In the literature there have been reported many attempts to connect the AE originating from the fracture of materials with the notion of criticality. Although there is an extended study of the AE during the fracture of a material and its relevance with the notion of criticality, this is not the case for the EME. In order to further investigate the possible critical behavior of fracture processes through AE and EME, we proceed here to the analysis of AE and EME time series using the recently proposed method of natural time (NT). We focus on the analysis of simultaneously acquired AE and EME time series, recorded during fracture experiments on LiF (non-irradiated and irradiated) specimens. The natural time analysis indicates that criticality is reached by both fracture-induced emissions, reflecting the critical behavior of the associated fracture processes. Moreover, it is found that both non-irradiated and irradiated LiF specimens exhibit similar behavior: the AE reach criticality earlier than EME, while EME reach criticality just before the global fracture.

Recent seismic activity at Cephalonia (Greece): a study through candidate electromagnetic precursors in terms of non-linear dynamics

Abstract. The preparation process of two recent earthquakes (EQs) that occurred in Cephalonia (Kefalonia), Greece, ((38.22° N, 20.53° E), 26 January 2014, Mw = 6.0, depth ∼ 20 km) and ((38.25° N, 20.39° E), 3 February 2014, Mw = 5.9, depth ∼ 10 km), respectively, is studied in terms of the critical dynamics revealed in observables of the involved non-linear processes. Specifically, we show, by means of the method of critical fluctuations (MCF), that signatures of critical, as well as tricritical, dynamics were embedded in the fracture-induced electromagnetic emissions (EMEs) recorded by two stations in locations near the epicentres of these two EQs. It is worth noting that both the MHz EMEs recorded by the telemetric stations on the island of Cephalonia and the neighbouring island of Zante (Zakynthos) reached a simultaneously critical condition a few days before the occurrence of each earthquake. The critical characteristics embedded in the EME signals were further verified using the natural time (NT) method. Moreover, we show, in terms of the NT method, that the foreshock seismic activity also presented critical characteristics before each event. Importantly, the revealed critical process seems to be focused on the area corresponding to the western Cephalonia zone, following the seismotectonic and hazard zoning of the Ionian Islands area near Cephalonia.

The Nature of Time, by Ulrich Meyer.

In 1908 Hermann Minkowski began an address to a congress of German natural scientists and physicians with the following now-famous words: ‘Henceforth space by itself and time by itself are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality’. This union is known, reasonably enough, as space–time , and the investigation of the nature and structure of space–time has been central to the development of the general theory of relativity, one of the two foundational theories of current physics. In the other foundational theory, quantum mechanics, space and time generally appear quite distinct, and even in the context of relativity theory some physicists still maintain that time (independently of space) is the bedrock reality while others claim time is a mere emergent phenomenon. Minkowski’s prophecy has not as yet been fully vindicated, even on its home turf. In other fields, like philosophy, space and time are still considered separately. We have a Philosophy of Time Society, for instance, but not a Philosophy of Space Society. Philosophical investigations of time are typically pursued quite independently of any consideration of space. One might think that philosophers are just retrograde in this respect, but one remarkable line of thought in Ulrich Meyer’s book, The Nature of Time ( NT ), is a series of arguments with the upshot that space and time must be considered quite distinct. Space is a manifold or collection of three-dimensional points but time is something else entirely. Time, or the set of times, is in Meyer’s view more like the set of possible worlds of modal logic than the set of time points that Minkowski imagined would be folded into space–time.

Multiresolution wavelets and natural time analysis before the January–February 2014 Cephalonia (Mw6.1 & 6.0) sequence of strong earthquake events

On January 26 and February 3, 2014, Cephalonia Island (Ionian Sea, Greece) was struck by two strong, shallow earthquakes (moment magnitudes Mw6.1 and Mw6.0, respectively) that ruptured two sub-parallel, strike-slip faults, with right-lateral kinematics. The scope of the present work is to investigate the complex correlations of the earthquake activity that preceded the Mw6.1 event in the broader area of the Cephalonia Island and identify possible indications of critical stages in the evolution of the earthquake generation process. We apply the recently introduced methods of Multiresolution Wavelet Analysis (MRWA) and Natural Time (NT) analysis and for the first time we combine their results in a joint approach that may lead to universal principles in describing the evolution of the earthquake activity as it approaches a major event. In particular, the initial application of MRWA on the inter-event time series indicates a time marker 12days prior to the major event. By using this time as the initiation point of the NT analysis, the critical stage of seismicity, where the κ1 parameter reaches the critical value of κ1=0.070, is approached few days before the occurrence of the Mw6.1 earthquake.

Relics: travels in nature's time machine

Relics: travels in nature's time machine

Wildlife tourism: the intangible, psychological benefits of human–wildlife encounters

This article presents the results of an ethnographic study of wildlife tourists. The findings reveal the commonalities and complexities of the wildlife experience during wildlife encounters at home and while on holiday. Nature's design, performance and immense biodiversity initiate an emotional response of awe, wonder and privilege that unlocks ecocentric and anthropomorphic connections to wild animals and a feeling that is ‘beyond words’. There is time to stand and stare, and contemplate. Nature and wildlife are not only spatial events but also temporal ones. In this liminal, embodied space of a wildlife encounter, socially constructed modern fast time dissipates and is replaced by stillness and nature's time whereby participants are totally absorbed in the spectacle. All thought and action is concentrated on the moment. This provokes a deep sense of well-being that transcends the initial encounter leading to spiritual fulfilment and psychological health benefits. The implications of this research has relevance to environmental conservation particularly the recognition that conserving habitats and wildlife has an intrinsic connection to the future well-being of the human population who are part of the ecosystem and not separate from it.

Not All Worlds Are Stages

The stage theory is a four-dimensional account of persistence motivatedby the worm theory's inability to account for our intuitions in thecases involving coinciding objects. Like the worm theory, it claimsthat there are objects spread out in time, but unlike the worm theory,it argues that these spacetime worms are not familiar particulars liketables and chairs. Rather, familiar particulars are the instantaneoustemporal slices of worms. In order to explain our intuitions that particulars persist for more than an instant, the stage theory drawson the counterpart theory of modal possibilism, which it is supposedto parallel. In this paper I show how the stage theory presupposes thattime can be divided into instants, which I call the atomistic view oftime. I do this by laying out an alternative theory of the nature oftime, the gunky view, and show that if time is gunky the stage theorycollapses into the worm theory. The deeper problem is that the merepossibility of gunky time would cause the stage theory's parallels topossibilism to break down. I therefore conclude that the stage theoryis committed to the view that time is necessarily atomistic. Finally,in the last section I argue that the fact that the stage theory rulesout a priori the possibility of time being gunky gives us reason toreject it as an account of persistence.