Distribution Of Peak Frequencies Research Articles

Distribution of peak frequency and omnipolar voltage in electrograms across the atrial body and thoracic veins in a normal heart.

The innovative peak frequency mapping facilitates the quantification of electrogram sharpness. However, reference values for normal atrial tissue are currently undefined. In this study, we explored the distribution of peak frequency and omnipolar peak-to-peak voltage (V-max) in a normal heart. Twenty-two patients with structurally normal heart were included. Either the right atrium (RA) and superior vena cava (SVC) or the left atrium (LA) and pulmonary veins (PVs) were mapped during sinus rhythm. In total, 13,654 points in the RA and 4143 points in the SVC from 15 patients and 4662 points in the LA and 2761 points in PVs from 7 patients were analyzed. The correlation between peak frequency and V-max was weak (R = 0.223). The median peak frequency was larger in the SVC than in the RA (441 [358-524] Hz vs. 358 [291-441] Hz, P < 0.0001) and in PVs than in the LA (346 [253-441] Hz vs. 323 [262-397] Hz, P < 0.0001). Conversely, the median V-max was smaller in the SVC than in the RA (1.96 [0.77-3.75] mV vs. 4.11 [2.10-6.83] mV, P < 0.0001) and in PVs than in the LA (1.16 [0.33-3.17] mV vs. 4.42 [2.63-6.84] mV, P < 0.0001). More than 95% of peak frequencies were > 174Hz in the RA and > 185Hz in the LA, and > 95% of V-maxes were > 0.52 and > 1.07mV in the RA and LA, respectively. Given the limited correlation between peak frequency and V-max, and recognizing their potential to provide distinct information, they can be used complementarily. Employing these parameters to extract varied insights can provide comprehensive understandings of tissue characteristics.

Contribution for the knowledge of the Alcochete-Pinhal Novo-Setúbal fault (Portugal) using ReMi and H/V Tests

The city of Setúbal is situated 30 km southeast of Lisbon, Portugal, and has experienced significant impacts from various earthquakes, including the one that occurred in 1858. This earthquake serves as an example of a nearby earthquake that caused significant social and structural damage, reaching a intensity of IX-VIII on the Modified Mercalli scale. Despite an average recurrence period of 3000–11000 years, as suggested by several authors, the Alcochete-Pinhal Novo-Setúbal fault (APSF) could potentially cause significant social, structural and economic impacts in future events. Several authors have reported on the APSF with slight variations in its outline, as it traverses multiple urbanized areas. The aim of this study was to locate the APSF in the Setúbal region and, to the best extent possible, determine its orientation and vertical offsets. 24 passive refraction microtremor tests (ReMi) and 145 horizontal-to-vertical (H/V) spectral ratios were employed to compute the variation of transverse wave velocity (VS) with depth and to compute the fundamental frequency (F0) and other natural frequency (F1) of the soils when present. Horizontal sections of VS and the spatial distribution of peak frequencies reveal alignments that can be related to the presence of the APSF fault zone. Considering all the alignments identified in this paper, two areas with distinct orientations for the APSF zone were proposed: one with a NNE-SSW strike and another with a NNW-SSE orientation. The lower values calculated for the fault plane dip (maximum of 5º) in the APSF area suggest a minimal vertical displacement, potentially corresponding to a strike-slip fault.

Characterization of the damage mechanism in CFRP composites under mode I based on comprehensive analysis of AE signals

This study utilises several methods centred on acoustic emission (AE) waveform characteristics to conduct in-depth analysis of the damage mechanism of composite materials under mode I. Combined with the peak frequency statistics and continuous wavelet transform (CWT) of AE signals, three damage modes of laminated composites during loading are identified. The cumulative energy of three damage modes separated by variational modal decomposition (VMD) is used to characterize their damage evolution process. Based on the findings, delamination and fiber–matrix debonding are proven to be the dominant damage mechanisms for mode I. The comprehensive analysis results from AE's accumulated energy, peak frequency distribution, CWT, VMD, and sentry function can accurately detect the onset time of delamination in laminates. The equivalent crack length is calculated by the load value determined at the initial time of delamination, and the strain energy release rate calculated by the load value and crack length at this time is used as the interlaminar fracture toughness value of mode I. This research method will provide a new idea for the damage tolerance analysis of mode I delamination in laminated structures.

Acoustic emission characteristic of sandstone and sandstone like material under multi-path loading.

Using spline interpolation to select proportions of similar materials, a comparative analysis of the fracturing behavior of sandstone specimens and similar material specimens was conducted through Brazilian splitting tests under multi-path loading. The study revealed that during stepwise loading, both sandstone and similar materials exhibited memory effects and plastic deformation. However, under constant velocity loading, the relationship between force and displacement in sandstone showed linearity after compaction. Employing MATLAB optimization algorithms for the inversion of acoustic emission event information, the distribution of fracture points, and the evolution of cracks were analyzed. The findings indicated that under stepwise loading, both sandstone and similar materials exhibited banded distribution of peak frequencies, with sandstone concentrated in the mid-low-frequency range and similar materials leaning towards the low-frequency range. The amplitude-frequency characteristics of acoustic emission signals suggested that initially, sandstone produced low-frequency, low-amplitude signals. As cracks developed, these signals gradually transformed into high-frequency, high-amplitude signals, ultimately leading to macroscopic failure. The ringing counts and b-values of sandstone displayed an approximate "W" shape distribution, with a subsequent decrease in b-values during final failure. In contrast, the acoustic emission counts were inversely related to b-values. Similar materials exhibited slightly more acoustic emission counts than sandstone, with relatively lower b-values. The crack development process of both sandstone and similar materials was confirmed through these observations. From the perspective of section initiation and local damage, sandstone and similar materials exhibited similar failure characteristics. The proportions of quartz sand: cement: water = 9:1:0.9 in similar materials demonstrated the most similar characteristics to sandstone in terms of mechanical loading, acoustic emission features, and failure morphology. This suggests that these similar materials can be used as substitutes for sandstone in analogous simulation experiments. The study provides theoretical support for understanding rock fracture mechanisms, offers guidance for the selection and proportioning of similar materials, and holds significance for predicting and controlling rock fracture behavior in engineering applications.

Efficacy of Iminoctadine Trialbesilate and Trifloxystrobin in Inhibiting and Controlling Pear Powdery Mildew (Phyllactinia pyri) in Hebei Province, China.

Pear powdery mildew (PPM), caused by Phyllactinia pyri, is one of the most serious diseases affecting production in the Hebei pear-growing region of China. Iminoctadine trialbesilate and trifloxystrobin are known to have broad-spectrum activity against a wide range of plant pathogens, including P. pyri. A total of 105 P. pyri strains were isolated from 11 cities in Hebei Province from 2017 to 2019. Iminoctadine trialbesilate and trifloxystrobin significantly inhibited P. pyri growth. Microscopic observation showed that P. pyri mycelia had different degrees of desiccation and that the conidial cell contents had been released. The sensitivities of 60 P. pyri strains to iminoctadine trialbesilate and trifloxystrobin were determined in vitro, and the average EC50 values were 0.5773 ± 0.0014 and 1.2038 ± 0.0010 μg/ml, respectively. The average EC50 values for 85 and 75% of the strains with continuous single peak frequency distributions were 0.4534 ± 0.0012 and 0.8124 ± 0.0039 μg/ml, respectively. These data could be used as the baseline sensitivities of P. pyri to these two fungicides. The maximum difference multiples of the sensitivities of P. pyri strains from the different cities to iminoctadine trialbesilate and trifloxystrobin were 13.5- and 17.2-fold, respectively. Cluster analysis showed that there was no significant correlation between P. pyri sensitivity and geographical origin. The field efficacies in controlling PPM were higher than 85%. These findings can improve how we monitor iminoctadine trialbesilate and trifloxystrobin resistance and improve application efficiency.

Fracture mechanical properties and identification of principal stress direction from the rock frequency domain

The characterization of rock instability precursors and the identification of principal stress direction are essential for the safety construction of underground engineering. This study explores the characterization of rock instability precursors from the frequency domain and identification of principal stress direction by the anisotropy of frequency variation. The results show that the dense distribution of peak frequency and frequency centroid in the high frequency domain, along with an increase in peak frequency bandwidth and a decrease in mean frequency centroid value, can be used as frequency domain criteria for rockburst prediction and early warning. Both peak frequency and frequency centroid are effective monitoring parameters for rock instability. The anisotropic frequency centroid variation can be used to identify the principal stress direction, and a process is proposed. This paper not only offers a valuable complement to existing methods for rock instability precursor and principal stress direction identification, but also provides a new analytical method for stability monitoring in rock engineering.

The Characterization and Evaluation of the Soluble Triggering Receptor Expressed on Myeloid Cells-like Transcript-1 in Stable Coronary Artery Disease.

Platelets play crucial roles in the development and progression of coronary artery disease (CAD). The triggering receptor expressed in myeloid cells-like transcript-1 (TLT-1) is stored in platelet α granules, and activated platelets release a soluble fragment (sTLT-1). We set out to better characterize the constituent amino acids of sTLT-1 and to evaluate sTLT-1 for use as a biomarker in patients with stable CAD. We evaluated sTLT-1 release using immunoprecipitation and mass spectrometry and employed statistical methods to retrospectively correlate sTLT-1 concentrations, utilizing ELISA in plasma samples from 1510 patients with documented stable CAD. We identified TLT-1 residues to 133 in platelet releasates. ADAM17 cuts TLT-1, suggesting that S136 is the C-terminal amino acid in sTLT-1. Our results revealed that for CAD patients, sTLT-1 levels did not differ significantly according to primary outcomes of death or major cardiac event; however, patients with left ventricular (LV) dysfunction had significantly lower plasma sTLT-1 levels as compared to those with normal LV function (981.62 ± 1141 pg/mL vs. 1247.48 ± 1589 pg/mL; p = 0.003). When patients were stratified based on sTLT-1 peak frequency distribution (544 pg/mL), a significant association with congestive heart failure was identified (OR = 2.94; 1.040-8.282; p = 0.042), which could be explained by LV dysfunction.

Microzonation study around Lake Toba, North Sumatra, Indonesia based on horizontal – vertical spectral ratio

Lake Toba, North Sumatra, Indonesia, is one of the biggest calderas in the world. The area is also prone to earthquake damage because of the tectonic activity due to its location in the subduction zone of Indo-Australian and Eurasian Plates. In recent years, Lake Toba has become one of the most attractive tourist destinations in Indonesia. Hence, the Indonesian government has been considering infrastructure development in this region. The region vulnerability cause by soil amplification due to the earthquake activity can be quantitatively investigated. We carried out a microzonation analysis around Lake Toba using Horizontal-Vertical (H/V) Spectral Ratio method. A total of about 30 short-period seismometers around Lake Toba were used for the analysis. We estimated several parameters that may define some soil characteristics, such as H/V peak amplitudes, peak frequencies, average shear wave velocity of 30 m depth (Vs30), and vulnerability index (Kg). Spatial distribution of peak frequencies and Vs30 suggest that the region may fall into sites SC and SD showing characteristics of dense to stiff soil. We also observed areas with a high vulnerability index (Kg > 20), which may indicate the high possibility of soil vulnerability due to strong earthquakes. The findings may provide preliminary results or sources for future geophysical, geological, and geotechnical analysis for disaster risk reduction in this high-risk region.

The role of superficial and deep layers in the generation of high frequency oscillations and interictal epileptiform discharges in the human cortex

Describing intracortical laminar organization of interictal epileptiform discharges (IED) and high frequency oscillations (HFOs), also known as ripples. Defining the frequency limits of slow and fast ripples. We recorded potential gradients with laminar multielectrode arrays (LME) for current source density (CSD) and multi-unit activity (MUA) analysis of interictal epileptiform discharges IEDs and HFOs in the neocortex and mesial temporal lobe of focal epilepsy patients. IEDs were observed in 20/29, while ripples only in 9/29 patients. Ripples were all detected within the seizure onset zone (SOZ). Compared to hippocampal HFOs, neocortical ripples proved to be longer, lower in frequency and amplitude, and presented non-uniform cycles. A subset of ripples (≈ 50%) co-occurred with IEDs, while IEDs were shown to contain variable high-frequency activity, even below HFO detection threshold. The limit between slow and fast ripples was defined at 150 Hz, while IEDs’ high frequency components form clusters separated at 185 Hz. CSD analysis of IEDs and ripples revealed an alternating sink-source pair in the supragranular cortical layers, although fast ripple CSD appeared lower and engaged a wider cortical domain than slow ripples MUA analysis suggested a possible role of infragranularly located neural populations in ripple and IED generation. Laminar distribution of peak frequencies derived from HFOs and IEDs, respectively, showed that supragranular layers were dominated by slower (< 150 Hz) components. Our findings suggest that cortical slow ripples are generated primarily in upper layers while fast ripples and associated MUA in deeper layers. The dissociation of macro- and microdomains suggests that microelectrode recordings may be more selective for SOZ-linked ripples. We found a complex interplay between neural activity in the neocortical laminae during ripple and IED formation. We observed a potential leading role of cortical neurons in deeper layers, suggesting a refined utilization of LMEs in SOZ localization.

Acoustic Emission Characteristics of the Water Weakening Effect on Cretaceous Weakly Cemented Sandstone

Rock mass stability is often affected by water–rock interaction in underground engineering construction. Cretaceous sandstones often have weak cementation, low strength and strong water-holding capacity, and their rock mass strength is easily weakened by these activities. In this paper, the uniaxial compressive strength (UCS) and tensile strength (TS) of weakly cemented Cretaceous sandstones from different sedimentary facies under natural and saturated conditions were tested, and the loading process was monitored by the acoustic emission (AE) technique. The results show that the existence of water obviously weakened the mechanical properties of weakly cemented sandstone. The UCS and TS of saturated braided river facies sandstone decreased to 41.24% and 35.95% of their natural states, respectively, while those of desert facies sandstone decreased to 32.90% and 26.98% of their natural states, respectively. The AE characteristics of sandstone from different sedimentary facies were similar during loading due to weakening by water, including a decrease in cumulative AE energy, b-value fluctuation and reduction in the peak frequency distribution range. Fracture in the Brazilian splitting test was mainly due to the rapid initiation and coalescence of microcracks near the peak point. However, in the uniaxial compression test, the macro fractures were caused by many microcracks that occurred continuously during loading and finally connected. The high quartz and low feldspar contents strengthened the mechanical properties of braided fluvial facies sandstone compared to those of desert facies sandstone and lessened the effect of water weakening.

Contribution to the seismic microzonation of Lisbon based on the integration of geological, geophysical, and geotechnical data

Lisbon has been affected by several moderate to strong earthquakes that caused considerable damage and produced significant economic and social impacts (e.g., the November 1st, 1755, earthquake). Studies on the potential damage due to a seismic event have been done considering Lisbon's moderate to high seismic hazard, but the seismic site effects have not yet been investigated at the city scale. The local ground conditions can locally modify the characteristics of surface seismic motion.Based on a multidisciplinary dataset composed of surface geology, a geotechnical database, and a geophysical database that compiles all the available geophysical tests carried out in Lisbon, an integrated approach to seismic ground characterisation was performed.A regression analysis of the shear-wave velocity values compiled in the geophysical database was done for each geological unit. The peak frequency distribution in the city, assessed from the ambient vibration measurements, showed a pattern in peak frequency variation. It decreases from the oldest to the most recent geological formations that outcrop in the SW-NE direction. Three zones based on peak frequency value distribution were proposed.An estimation of the impedance contrast depths was computed through two processes, considering the previous results: (i) the shallower contrast depth was assessed through a sharp variation of NSPT values available in the geotechnical database, and (ii) the deeper contrast depth was estimated based on geology data and deep borehole information. The results showed that for the upper ∼100 m of depth, a consistent relationship between the contrasts identified through different data was obtained, even if uncertainty increased with depth.

Seismic and ionospheric disturbances caused by the 3 September 2017 underground nuclear test in North Korea

We investigated lithospheric and ionospheric disturbances caused by the 3 September 2017 underground nuclear test (UNT) in North Korea based on data from networks of seismic stations and GPS/GLONASS receivers. We analyzed frequency composition of longitudinal and surface waves detected at more than 40 seismic stations. Low frequencies (∼0.45 ± 0.21 Hz) were found to prevail in the spectrum of longitudinal waves. For both types of waves, frequencies decreased with distance according to the power law. Analysis revealed two trends in the spatial distribution of peak frequencies. First, high and mid-frequencies (0.14–0.50 Hz) are typical for the continental landmass regions, and low frequencies of surface waves (0.13 Hz and below) are more common for the regions adjacent to fringe seas. Second, uneven frequency variations of seismic waves for different azimuths relative to the UNT epicenter (frequencies subside rapidly in the east, southeast, and southwest directions from the epicenter; towards the continental landmass inner parts, frequency variation is much slower). Records of longitudinal waves made at different distances from the epicenter allowed estimating the size of the focal area. Analysis of data from GPS/GLONASS receiving stations near the Korean Peninsula revealed ionospheric disturbances that were most likely caused by UNT. The ionospheric disturbances started to be detected ∼ 8 min after UNT and were observed for about 5 hrs. During the first 1.5–2 hrs after UNT, travelling ionospheric disturbances (TID) were recorded; they propagated from the epicenter at ∼ 600, 250 and 133 m/s. These TIDs had periods of 1–10.5 min and could be associated with acoustic waves induced in the Earth's atmosphere by the underground nuclear test. After TID passage over the UNT site, there was a long-lived (more than 3.5 hrs) region of non-travelling perturbations of ionospheric plasma with the velocity about 7 m/s. This velocity describes not so much the disturbance travel, but the time when the “receiver – satellite” line of sight (LOS) crosses the disturbance. This region can possibly occur due to the formation of standing waves in the atmosphere, development of plasma instabilities or penetration into the ionosphere of an anomalous electric field generated by radioactive substances leaked out onto the surface.

Surrounding gas composition affects the calling song development in the two-spotted cricket (Gryllus bimaculatus).

Male crickets emit acoustic signals (i.e., songs) by chirping using their forewings. Although the mechanisms and adaptive functions of these songs are well studied, knowledge about how songs develop within a generation is relatively scarce. Our previous work demonstrated a stable peak frequency at 5.7 kHz in the calling songs recorded from mature adult male crickets (Gryllus bimaculatus). In the present study, we monitored changes in the frequency component over time from the sexual maturity stage (early adult stage). We recorded 300 calling songs from a pool of 122 adults. The peak frequency distribution was lower and unstable (i.e., greater coefficient of variance) in the early adult stage. The mean peak frequency was 4.9 kHz on day 3, but gradually converged to 5.8 kHz over the 2-week adult stage. Immature adult males (emitting immature songs) produced an appropriately tuned song with a peak frequency of 5.8 kHz in an environment of 80% helium and 20% oxygen. These results suggest that the frequency component of the calling song is acquired during the early to mid-adult stage, and may be related to sexual maturation in males. Findings from the helium substitution experiment revealed that physical resistance from surrounding gas molecules negatively affect the stability of male singing, and that muscle development and forewing hardening may contribute to the maturation of singing, suggesting that females may adaptively select sexually mature males based on song traits.

Acoustic Emission Damage Detection during Three-Point Bend Testing of Short Glass Fiber Reinforced Composite Panels: Integrity Assessment

In this study, an acoustic emission (AE) technique was used as a passive non-destructive tool to detect the damage progress in short glass fiber-reinforced composite panels. AE detection was conducted during three-point bend tests, thus illustrating the flexural damage accumulation for composite panels with different sizes and fiber volume content. To demonstrate the universality of the employed integrity assessment methodology, AE data was detected using different timing parameters and two different transducer types, i.e., medium-band and wide-band frequency sensors. The AE waveform classification presented in this study is based on peak frequency distributions. Frequency bands that are associated with certain failure mechanisms, including matrix micro-cracking, fiber debonding, delamination, and fiber breakage, were obtained from the technical literature. Through this investigation, the concept of cumulative signal strength (CSS) and cumulative rise time versus peak amplitude ratio (CRA) as AE output parameters are shown to facilitate integrity assessment for the employed complex composite material system. Significant jumps in CSS and CRA curves could be correlated to critical strain levels and distinct damage events in the composite panels subjected to flexural loading.

Increased asymmetry of pit‐over‐peak statistics with landscape smoothing

AbstractThe local extremes (i.e., peaks and pits) of the landscape‐elevation field play a critical role in the energy, water, and nutrient distribution of a region, but their statistical distributions in relation to landscape evolution have received limited research attention. In this work, we first explain how the spatial correlation structure of the elevation field affects the counts and frequency distributions of local extremes. We then analyze local extremes statistics for eight mountainous landscapes worldwide with diverse hydroclimatic forcings and geologic histories using 24 digital elevation models and compare them with complex terrain of the Erythraeum Chaos region on Mars. The results reveal that the spherical covariance structure captures the observed spatial correlation in these cases, with the peak frequency distribution agreeing well with the elevation frequency distribution. The ratio of the pit‐over‐peak (POP) count is linked to the degree to which the pit and peak frequency distributions match, and carries the mark of landscape aging. The relationship between the geomorphic development stage (quantified by the reduced fatness of the slope‐distribution tail) and the deviation of POP values from unity in old mountainous landscapes confirms that the evolution towards smoother topographies is atypically accompanied by reduced pit counts distinctive of organized valley and ridge patterns.

Frequency distribution of pollutant concentrations over Indian megacities impacted by the COVID-19 lockdown.

The megacities experience poor air quality frequently due to stronger anthropogenic emissions. India had one of the longest lockdowns in 2020 to curb the spread of COVID-19, leading to reductions in the emissions from anthropogenic activities. In this article, the frequency distributions of different pollutants have been analysed over two densely populated megacities: Delhi (28.70° N; 77.10° E) and Kolkata (22.57° N; 88.36° E). In Delhi, the percentage of days with PM2.5 levels exceeding the National Ambient Air Quality Standards (NAAQS) between 25 March and 17 June dropped from 98% in 2019 to 61% in 2020. The lockdown phase 1 brought down the PM10 (particulate matter having an aerodynamic diameter ≤ 10 μm) levels below the daily NAAQS limit over Delhi and Kolkata. However, PM10 exceeded the limit of 100 μgm−3 during phases 2–5 of lockdown over Delhi due to lower temperature, weaker winds, increased relative humidity and commencement of limited traffic movement. The PM2.5 levels exhibit a regressive trend in the highest range from the year 2019 to 2020 in Delhi. The daily mean value for PM2.5 concentrations dropped from 85–90 μgm−3 to 40–45 μgm−3 bin, whereas the PM10 levels witnessed a reduction from 160–180 μgm−3 to 100–120 μgm−3 bin due to the lockdown. Kolkata also experienced a shift in the peak of PM10 distribution from 80–100 μgm−3 in 2019 to 20–40 μgm−3 during the lockdown. The PM2.5 levels in peak frequency distribution were recorded in the 35–40 μgm−3 bin in 2019 which dropped to 15–20 μgm−3 in 2020. In line with particulate matter, other primary gaseous pollutants (NOx, CO, SO2, NH3) also showed decline. However, changes in O3 showed mixed trends with enhancements in some of the phases and reductions in other phases. In contrast to daily mean O3, 8-h maximum O3 showed a reduction over Delhi during lockdown phases except for phase 3. Interestingly, the time of daily maximum was observed to be delayed by ~ 2 h over Delhi (from 1300 to 1500 h) and ~ 1 h over Kolkata (from 1300 to 1400 h) almost coinciding with the time of maximum temperature, highlighting the role of meteorology versus precursors. Emission reductions weakened the chemical sink of O3 leading to enhancement (120%; 11 ppbv) in night-time O3 over Delhi during phases 1–3.Supplementary InformationThe online version contains supplementary material available at 10.1007/s11356-021-16874-z.

Study on the Acoustic Emission Characteristics of Different Rock Types and Its Fracture Mechanism in Brazilian Splitting Test

In order to investigate the relationship between rock microfracture mechanism and acoustic emission (AE) signal characteristic parameters under split loads, the MTS322 servo-controlled rock mechanical test system was employed to carry out the Brazilian split tests on granite, marble, sandstone, and limestone, while FEI Quanta-200 scanning electron microscope system was employed to carry out the analysis of fracture morphology. The results indicate that different scales of mineral particle, mineral composition, and discontinuity have influence on the fracture characteristics of rock, as well as the b-value. The peak frequency distribution of the AE signal has obvious zonal features, and these distinct peak frequencies of four types of rock fall mostly in ranges of 0–100 kHz, 100–300 kHz, and above 300 kHz. Due to the different rock properties and mineral compositions, the proportions of peak frequencies in these intervals are also different among the four rocks, which are also acting on the b-value. In addition, for granite, the peak frequencies of AE signals are mostly distributed above 300 kHz for granite, marble, and limestone, which mainly derive from the internal fracture of k-feldspar minerals; for marble, the AE signals with peak frequency are mostly distributed in over 300 kHz, which mainly derive from the internal fracture of dolomite minerals and calcite minerals; AE signals for sandstone are mostly distributed in the range of 0–100 kHz, which mainly derive from the internal fracture of quartz minerals; for limestone, the AE signals with peak frequency are mostly distributed in over 300 kHz, which mainly derive from the internal fracture of granular-calcite minerals. The relationship between acoustic emission signal frequency of rock fracture and the fracture scale is constructed through experiments, which is of great help for in-depth understanding of the scaling relationship of rock fracture.

Influence of Freeze-Thaw Cycles on Acoustic Emission Characteristics of Granite Samples under Triaxial Compression

Understanding the acoustic emission (AE) characteristics of rocks that have undergone freeze-thaw cycling is of great significance for the use of AE technology to monitor the stability of rock masses in cold regions. A series of freeze-thaw cycling experiments and triaxial compression AE tests of granite samples were performed. The results show that, with an increasing number of freeze-thaw cycles, the P-wave velocity and peak AE intensity of granite show a substantial downward trend. The AE ringing counts during triaxial compression can be divided into three stages: abrupt period, calm period, and failure period. The overall change of the characteristic AE signal of granite samples that underwent different freeze-thaw cycles is the same. The AE signal during the destruction of granite occurs in clear dual dominant frequency bands. The peak frequency increases with increasing load time, and this trend becomes less clear as the number of freeze-thaw cycles increases. Overall, the peak frequency distribution tends to change from high to low with an increasing number of freeze-thaw cycles. The results provide basic data for rock mass stability monitoring and prediction, which is of great significance for engineering construction and management in cold regions.

Investigation of the Effects of Freeze-Thaw Cycles on Geomechanical and Acoustic Characteristics of Tuff Specimens under Different Stress Paths

In the process of development and construction of open-pit mine slope in the high altitude and cold area, freeze-thaw (F-T) cycles have an important impact on rock engineering structure. F-T cycles lead to the decrease in physical and mechanical properties of rock, which is closely related to the stability of open-pit slope. In this paper, the influence of F-T cycles on geomechanical and acoustic emission (AE) characteristics of tuff specimens under different stress paths was studied by using F-T cycle treatment, in situ AE monitoring, and uniaxial loading test. The results indicated that under the same stress path, the cumulative AE count/energy of rock samples subjected to F-T cycles was less than that of rock samples not subjected to F-T cycles. The peak frequency distribution of AE signal during the loading process of rock specimen presented the phenomenon of frequency bands. The width of the low-frequency band of the rock samples subjected to F-T cycles was larger than that of the rock samples under the natural state. The frequency and width of the high-frequency band of the rock samples subjected to F-T cycles were larger than those of the rock samples under the natural state. The rock samples subjected to F-T cycles had higher plastic strain than those without F-T cycles. According to the uniaxial compression test results of F-T rock samples under different stress paths, the peak stress and peak strain have little change, but the AE characteristics were obviously different.

Experimental study on acoustic emission frequency characteristics of granite under different cyclic loading and unloading

In Granite acoustic emission tests were performed during three different cyclic loading and unloading processes. The relationship between the acoustic emission frequency distribution pattern and the loading and unloading mode of granite during the cyclic loading and unloading process was discussed. The distribution pattern of the peak frequency with the stress evolution is analyzed qualitatively and quantitatively. Studies have shown that: in the first cycle of loading and unloading at each stage of the three cyclic loading and unloading processes, the acoustic emission ringing count and peak frequency are significantly increased, which has a significant Kaiser effect. It proves that the Kaiser effect essentially remembers the extent of the damage inside the rock previously. In the process of loading and unloading in the fourth stage cycle, the AE ring count showed a “U”-shaped change law, showing a significant Felicity effect. Comparing the three different cyclic loading and unloading modes, with the increase of the lower limit stress, the stress amplitude decreases, and the AE ringing count corresponding to the lower limit stress value of the unloading gradually decreases, and the peak frequency distribution shows more dense or concentrated characteristics. At the beginning of the third stage cycle, the proportion of high frequency band (140∼162kHz) gradually decreased, and the proportion of lower frequency band (11-18kHz) gradually increased. With the increase of the lower limit of cyclic loading and unloading, the lower frequency band (11-18kHz) in the fourth-stage cyclic loading and unloading process takes up a higher proportion, even as high as 95%. It indicates that the rock samples at this stage mainly undergo large-scale failure, and the rock samples are in a critical failure state. These provide the basis for exploring the evolution mechanism of rock mechanical behavior and the prediction method of instability and damage.