Stress tensor determination by modified hydraulic tests on pre-existing fractures:Method and stress constraints

The hydraulic testing of pre-existing fractures(HTPF)is one of the most promising in situ stress measurement methods,particularly for three-dimensional stress tensor determination.However,the stress tensor determination based on the HTPF method requires at least six tests or a minimum of 14-15 tests(under different conditions)for reliable results.In this study,we modified the HTPF method by considering the shear stress on each pre-existing fracture,which increased the number of equations for the stress tensor determination and decreased the number of tests required.Different shear stresses were attributed to different fractures by random sampling;therefore,the stress tensors were obtained by searching for the optimal solution using the least squares criterion based on the Monte Carlo method.Thereafter,we constrained the stress tensor based on the tensile strength criterion,compressive strength criterion,and vertical stress constraints.The inverted stress tensors were presented and analyzed based on the tensorial nature of the stress using the Euclidean mean stress tensor.Two stress-measurement campaigns in Weifang(Shandong Province,China)and Mercantour road tunnel(France)were implemented to highlight the validity and efficiency of the modified HTPF(M-HTPF)method.The results showed that the M-HTPF method can be applied for stress tensor inversion using only three to four tests on pre-existing fractures,neglecting the stress gradient.The inversion results were confined to relatively small distribution dispersions and were significantly reliable and stable due to the shear stresses on the fractures and the stress constraints employed.The M-HTPF method is highly feasible and efficient for complete stress tensor determination in a single borehole.

Influences of pre-existing fracture on ground deformation induced by normal faulting in mixed ground conditions

Physical model tests have been conducted by various researchers to investigate fault rupture propagation and ground deformation induced by bedrock faulting. However, the effects of pre-existing fracture on ground deformation are not fully understood. In this work, six centrifuge tests are reported to investigate the influence of pre-existing fracture on ground deformation induced by normal faulting in sand, clay and nine-layered soil with interbedded sand and clay layers. Shear box tests were conducted to develop a filter paper technique, which was adopted in soil model preparation to simulate the effects of pre-existing fracture in centrifuge tests. Centrifuge test results show that ground deformation mechanism in clay, sand and nine-layered soil strata is classified as a stationary zone, a shearing zone and a rigid body zone. Inclination of the strain localization is governed by the dilatancy of soil material. Moreover, the pre-existing fracture provides a preferential path for ground deformation and results in a scarp at the ground surface in sand. On the contrary, fault ruptures are observed at the ground surface in clay and nine-layered soil strata.

A method to model the effect of pre-existing cracks on P-wave velocity in rocks

Crack closure is one of the reasons inducing changes of P-wave velocity of rocks under compression.In this context,a method is proposed to investigate the relationships among P-wave velocity,pre-existing cracks,and confining pressure based on the discrete element method(DEM).Pre-existing open cracks inside the rocks are generated by the initial gap of the flat-joint model.The validity of the method is evaluated by comparing the P-wave velocity tested on a sandstone specimen with numerical result.As the crack size is determined by the diameter of particles,the effects of three factors,i.e.number,aspect ratio,and orientation of cracks on the P-wave velocity are discussed.The results show that P-wave velocity is controlled by the(i.e.number) of open micro-cracks,while the closure pressure is determined by the aspect ratio of crack.The reason accounting for the anisotropy of P-wave velocity is the difference in crack number in measurement paths.Both of the number and aspect ratio of cracks can affect the responses of P-wave velocity to the applied confining pressure.Under confining pressure,the number of open cracks inside rocks will dominate the lowest P-wave velocity,and the P-wave velocity of the rock containing narrower cracks is more sensitive to the confining pressure.In this sense,crack density is difficult to be back-calculated merely by P-wave velocity.The proposed method offers a means to analyze the effect of pre-existing cracks on P-wave velocity.

Damage and failure characteristics of rock similar materials with pre-existing cracks

In order to further study the damage and failure mechanism for rock similar materials,this study investigated the mechanical properties and failure characteristics,law of damage space development,and damage evolution characteristics for rock similar materials with pre-existing cracks of varying length under uniaxial compression load.The equipment used in this study is the self-developed YYW-Ⅱ strain controlled unconfined compression apparatus and the PCIE-8 acoustic emission monitoring system.Results show that,as the length of pre-existing crack increases:(1) the peak and residual strength reduces,and the peak axial strain and the strain during the initial compression phase increases;(2) the major failure mode is changed from shear failure to tensile failure along a vertical plane that passes the middle of the pre-existing crack;(3) The damage increases during the stable and accelerated development stage,and the effect of the pre-existing cracks is more during the accelerated development stage than the stable development stage.

Effects of pre-existing cracks and infillings on strength of natural rocks--Cases of sandstone, argillite and basalt

This study aims to examine the influence of pre-existing discontinuities on the strengths of four natural rocks of different origins.A series of unconfined compression tests was performed on specimens of two types of sandstones,argillite and basalt that contain open and filled cracks.It was found that the presence of cracks tends to decrease the overall strength for all studied rocks;however,the magnitude of strength reduction is related to the property of rock.The larger strength decrease was observed for the relatively harder argillite and basalt,compared to the softer sandstone.It was also found that the infill material could increase the strength of rock specimens,while the obtained strength depended on the characteristics of the fill material.

Seismic stability analysis of slopes with pre-existing slip surfaces

In analyzing seismic stability of a slope with upper bound limit analysis method, the slip surface is often assumed as a log-spiral or plane slip surface. However, due to the presence of a weak layer and unfavorable geological structural surface or a bedrock interface with overlying soft strata, the preexisting slip surface of the slope may be irregular and composed of a series of planes rather than strictly logspiral or plane shape. A computational model is developed for analyzing the seismic stability of slopes with pre-existing slip surfaces. This model is based on the upper bound limit analysis method and can consider the effect of anchor bolts. The soil or rock is deemed to follow the Mohr-Coulomb yield criterion. The slope is divided into multiple block elements along the slip surface. According to the displacement compatibility and the associated flow rule, a kinematic velocity field of the slope can be obtained computationally. The proposed model allows not only calculation of the rate of external work owing to the combined effect of self-weight and seismic loading, but also that of the energy dissipation rate caused by the slip surface, interfaces of block elements and anchorage effect of the anchors. Considering a direct relationship between the rate of external work and the energy dissipation rate, the expressions of yield acceleration and permanent displacement of anchored slopes can be derived. Finally, the validity of this proposed model is illustrated by analysis on three typical slopes. The results showed that the proposed model is more easily formulated and does not need to solve complex equations or time consuming iterations compared with previous methods based on the conditions of force equilibrium.

Relationship of Pre-Existing Maternal/Caregiver Acute Respiratory Infection in the Pattern and Risk of Acute Respiratory Infection among Infants in Rivers State, Nigeria

History of upper respiratory tract infection in the mother or siblings was associated with higher risk of acute lower respiratory tract infection in cases. Most upper respiratory tract infections were caused by viral pathogens and likely to occur in many members of the family. The study aimed to determine the existence and pattern of relationship between risk of acute respiratory infection (ARI) among infants and exposure to pre-existing maternal/caregiver acute respiratory tract infection. The study was designed as a community-based Nested case-control study of 1100 infants randomly selected from 12 communities out of 6 Local Government Areas of the 3 senatorial districts of Rivers State. A multistage random sampling technique was used in selecting the subjects up to the community level. Descriptive method was used to represent the characteristics of the subjects and the differences in ARI between exposed and unexposed infants were tested in a bivariate logistics regression at 5% level of significance. Odds ratio (OR) was used to interpret the size effect measures of ARI on exposure to pre-existing maternal/caregiver ARI differences. A total of 275 Cases of ARI and 825 controls were included in the study. Among exposed infants (N = 104), ARI cases were found to be higher n = 80 (76.9%) than in control n = 24 (23.1%). Whereas, among unexposed infants N = 991, ARI cases were found to be lower n = 195 (19.7%) than in control n = 796 (80.3%). For the exposed infants, the odds for ARI were 13.5 times significantly higher compared to those of their unexposed counterparts (OR-Unadjusted = 13.52, (p < 0.0001, 95% CI = 0.047 - 0.121)). The findings will widen the horizon in the etiological consideration of ARI among infants vis-à-vis exposure potential to pre-existing maternal/caregiver ARI via nursing care. Therefore, community-based sensitization programme on barrier nursing care techniques and personal hygiene practices should be on focus.

Influence of intermediate principal stress on failure mechanism of hard rock with a pre-existing circular opening

Based on particle flow theory, the influences of the magnitude and direction of the intermediate principal stress on failure mechanism of hard rock with a pre-existing circular opening were studied by carrying out true triaxial tests on siltstone specimen. It is shown that peak strength of siltstone specimen increases firstly and subsequently decreases with the increase of the intermediate principal stress. And its turning point is related to the minimum principal stress and the direction of the intermediate principal stress. Failure characteristic(brittleness or ductility) of siltstone is determined by the minimum principal stress and the difference between the intermediate and minimum principal stress. The intermediate principal stress has a significant effect on the types and distributions of microcracks. The failure modes of the specimen are determined by the magnitude and direction of the intermediate principal stress, and related to weakening effect of the opening and inhibition effect of confining pressure in essence: when weakening effect of the opening is greater than inhibition effect of confining pressure, the failure surface is parallel to the x axis(such as σ2=σ3=0 MPa); conversely, the failure surface is parallel to the z axis(such as σ2=20 MPa, σ3=0 MPa).

Oblique extension of pre-existing structures and its control on oil accumulation in eastern Bohai Sea

Based on 3D seismic data, the evolution mechanism and characteristics of faults were investigated to reveal the structural origin and its control on differential hydrocarbon accumulation through comprehensive analyses, including structure style analysis, fault activity analysis, analogue modelling and comparison among the wells. The complex fault system with differently trending faults resulted from strike-slip and rifting in Paleogene was partly activated, developed successively and stretched obliquely by the near-NS extensional stress field in Neogene. In the area little affected by pre-existing faults, new faults nearly perpendicular to the extension direction developed. The structural development in the study area was not caused by transpressional strike slip. Under the oblique extension effect of pre-existing faults, if the angle between the strike of pre-existing fault and the extensional direction is different, the strike-slip and extensional stresses are different in ratio. The larger the angle between the two is, the stronger the extensional component, the poorer the sealing ability of the fault, and the stronger the oil and gas migration capacity will be. Conversely, the smaller the angle between the two is, the stronger the strike-slip component, the better the sealing ability of the fault, and the poorer the oil and gas migration capacity will be. The accumulation condition analysis results considering the fault trend are in good agreement with the oil and gas shows in wells drilled in this area.

On the Reactivation of the Pre-Existing Normal Fault

The reactivation of pre-existing faults is a common phenomenon in a basin. This paper discusses the relationship between the pre-existing faults and the newly formed Coulomb shear fractures regarding pore fluid pressures. Based on the Coulomb fracture criterion and Byerlee frictional sliding criterion, an equation relating pore pressure coefficient (&lambda;e), minimum dip angle (αe) of the reactive pre-existing fault and the intersection point depth (z) between the pre-existing fault and a newly formed Coulomb shear fault in an extensional basin, is established in this paper. This equation enhanced the understanding on the reactivation of pre-existing faults and can be used to calculate paleo-pore fluid pressures. The bigger the pore fluid pressure in a pre-existing fault is, the less the minimum dip angle for a reactive pre-existing fault will be. The minimum dip angle is less in shallow area than that in deep area. This will be of significance in petroleum exploration and development.

On the Orientation of Fractures with Transpressional and Transtensional Wrenches in Pre-Existing Faults

The orientation of fractures with transpressional and transtensional wrenches in pre-existing faults has not been quantitatively determined. Based on Coulomb failure criterion and Byerlee’s frictional sliding criterion, this paper has indicated quantitative geometric relationships between the pre-existing fault and the local induced principal stress axes caused by the rejuvenation of the pre-existing fault. For a hidden pre-existing fault with some cohesion, the angles between the local induced principal stress axes and the pre-existing fault quantitatively vary with the applied stress and the cohesion coefficient, the ratio of the thickness of the cover layer to the thickness of the whole wrench body, whether transpressional or transtensional wrenches occur. For a surface pre-existing fault with zero cohesion, the angles between the pre-existing fault and the local induced principal stress axes are related to the rock inner frictional angle regardless of both the applied stress and the cohesion coefficient where transpressional wrenches occur, and the local induced maximum principal stress axis is identical with the applied maximum principal stress axis where transtensional wrenches occur. Therefore, the geometric relationships between the pre-existing faults and their related fractures are defined, because the local induced principal stress axes determine the directions of the related fractures. The results can be applied to pre-existing weak fabrics. They can help to understand and analyze wrench structures in outcrops or subsurface areas. They are of significance in petroleum exploration.

Mechanism investigation of pre-existing void-induced multi-modal electro-migration behavior

A multi-modal time-to-failure distribution for an electro-migration(EM) structure has been observed and studied from long duration in-situ EM experiment, for which the failure mechanism has been investigated and discussed comprehensively. The mixed EM failure behavior strongly suggest that the fatal voids induced EM failure appear at various locations along the EM structure. This phenomenon is believed to be highly related to the existence of pre-existing voids before EM stress. Meanwhile, the number and location of the pre-existing voids can influence the EM failure mode significantly. Based on our research, a potential direction to improve the EM lifetime of Cu interconnect is presented.

Pre-existing cirrhosis is associated with increased mortality of traumatic patients: Analysis of cases from a trauma center in East China

AIM:To determine the impact of cirrhosis on trauma patients and define the factors predicting death.METHODS:The data on patients admitted to the trauma center from January 2000-2005 were studied retrospectively.The clinical variables were recorded and compared to identify the factors differentiating cirrhotic trauma survivors from non survivors.Child's classification criteria were derived from the reviewed charts of cirrhotic trauma patients to evaluate their predictive value in cirrhotic trauma.Trauma registry was also used to generate a trauma control group by matching for age,sex,abbreviated injury score(AIS)over the same period of time.The outcome variables compared were mortality rate,time of ICU and hospital stay.Results were expressed as mean ± SD.These data were analyzed by SPSS.11.0 statistical software.Univariate analysis was performed to identify significant medical factors for survivor and non survivors subjected to chi-square test.Fisher's exact test and Student's t test were performed to determine the statistical difference between cirrhotic and control groups.P < 0.05 was considered statistically significant.RESULTS:Poor prognosis of traum patients was associated with one or more of the following findings:ascitcs,hyperbilirubinemia(more than 2 mg/dL),hypoalbuminemia(less than 3.5 mg/dL),and prolonged prothrombin time(more than 12.5 seconds).Although Child's classification was used to predict the outcome in cirrhotic patients undergoing portacaval shunt procedures,no significant difference was found in mortality rate as a function of Child's classification.CONCLUSION:Cirrhosis is associated with a highermortality,a longer time of ICU and hospital stay of trauma patients.It seems that treatment of trauma patients with pre-existing severe liver disease is a challenge to surgeons.

Relationship between the Pre-existing Active Kunlun Fault and Co-seismic Surface Ruptures Produced by the 2001 Mw 7.8 Central Kunlun Earthquake, China

Field investigations allow to constrain the co-seismic surface rupture zone of ～400 km with a strike-slip up to 16.3 m associated with the 2001 Mw 7.8 Central Kunlun earthquake that occurred along the western segmentof the Kunlun fault, northern Tibet. The co-seismic rupture structures are almost duplicated on the pre-existing fault traces of the Kunlun fault. The deformational characteristics of the co-seismic surface ruptures reveal that the earthquake had a nearly pure strike-slip mechanism. The geologic and topographic evidence clearly shows that spatialdistributions of the co-seismic surface ruptures are restricted by the pre-existing geological structures of the Kunlun fault.

Molecular dynamics study on mechanical behaviors of Ti/Ni nanolaminate with a pre-existing void

Metallic nanolaminated materials possess excellent mechanical properties due to their unique modulation structures and interfacial properties.However,how microdefects affect their mechanical properties is still uncertain.To evaluate the influences of void location(in the crystalline layer and the Ti/Ni interface),void diameter(d)and thickness of the intermediate layer(h)on overall tensile behaviors,various types of defective Ti/Ni nanolaminates with pre-existing void are established by the molecular dynamics method in this work.The results indicate that the strength and plastic deformation mechanisms are strongly dependent on those determinants.Yield stresses of Ti/Ni nanolaminates decrease distinctly with increasing void diameter,while peak stresses with a void in the crystalline layer decrease with increasing d/h.Different void locations lead eventually to disparate initial plastic deformation carriers around the void,and various evolutions in the microstructure of the defective Ti/Ni nanolaminates.The Ti/Ni interface plays a significant role in the tensile process.The semi-coherent interface impedes new grains and lattice dislocations from passing across the interface,while the incoherent interface facilitates dislocations generating and sliding along the interface,and absorbs the dislocations moving to the interface.The results also indicate that the strain rate significantly affects the evolution of the microstructure and the tensile properties of defective Ti/Ni nanolaminates.

Improved mass relations of mirror nuclei

In this study,we revisit the previous mass relations of mirror nuclei by considering 1/N-and 1/Z-dependent terms and the shell effect across a shell.The root-mean-squared deviation is 66 keV for 116 nuclei with neutron number N≥10,as com-pared with experimental data compiled in the AME2020 database.The predicted mass excesses of 173 proton-rich nuclei,including 98 unknown nuclei,are tabulated in the Supplemental Material herein with competitive accuracy.

The breaking of spin symmetry in the single-particle resonances in deformed nuclei

The exploration of spin symmetry (SS) in nuclear physics has been instrumental in identifying atomic nucleus structures.In this study,we solve the Dirac equation from the relativistic mean field (RMF) in complex momentum representation.We investigated SS and its breaking in single-particle resonant states within deformed nuclei,with a focus on the illustrative nucleus168Er.This was the initial discovery of a resonant spin doublet in a deformed nucleus,with the expectation of the SS approaching the continuum threshold.With increasing single-particle energy,the splitting of the resonant spin doublets widened significantly.This escalating splitting implies diminishing adherence to the SS,indicating a departure from the expected behavior as the energy levels increase.We also analyzed the width of the resonant states,showing that lower orbital angular momentum resonances possess shorter decay times and that SS is preserved within broad resonant doublets,as opposed to narrow resonant doublets.Comparing the radial density of the upper components for the bound-state and resonant-state doublets,it becomes evident that while SS is well-preserved in the bound states,it deteriorates in the resonant states.The impact of nuclear deformation (β_(2)) on SS was examined,demonstrating that an increase in β_(2) resulted in higher energy and width splitting in the resonant spin doublets,which is attributed to increased component mixing.Furthermore,the sensitivity of spin doublets to various potential parameters such as surface diffuseness (a),radius (R),and depth (Σ0) is discussed,emphasizing the role of these parameters in SS.This study provides valuable insights into the behavior of spin doublets in deformed nuclei and their interplay with the nuclear structure,thereby advancing our understanding of SS in the resonance state.

Systematic study on heavy-particle radioactivity of superheavy nuclei ^(297–300)119

In the current study,we examined every possible cluster-daughter combination in the heavy-particle decay of isotopes ^(297-300)119 and computed the decay half-lives using the modified generalized liquid drop model(MGLDM)with the preformation factor depending on the disintegration energy.The predicted half-life of every heavy cluster(Z_(C)≥32)was within the experimentally observable limits.These results aligned with the predictions of Poenaru et al.[Phys.Rev.Lett.107,062503(2011)]that superheavy nuclei(SHN)with Z>110 will release heavy particles with a penetrability comparable to or greater than theα-decay.The half-lives predicted using the MGLDM for clusters^(89)Rb,^(91)Rb,and^(92)Rb from parents^(297)119,^(299)119,and^(300)119,respectively,agreed with the predictions of Poenaru et al.[Eur.Phys.J.A 54,14(2018)].It was found that the isotopes of heavy clusters Kr,Rb,Sr,Pa,In,and Cd had half-lives comparable to theαhalf-life;and isotopes of clusters I,Xe,and Cs had the minimum half-life(10^(-14)s).These observations revealed the role of the shell closure(Z=82,N=82,and N=126)of the cluster and daughter nuclei in heavy-cluster radioactivity.We predicted that isotope ^(297,299)119 decayed by 4αdecay chains and isotope^(300)119 decayed by 6αdecay chains,while^(298)119 decayed by continuousαdecay chains.The predicted half-lives and modes of decay of the nuclei in the decay chains of^(297-300)119 agreed with the experimental data,proving the reliability of our calculations.The present study determined the most favorable heavy-cluster emissions from these nuclei and provided suitable projectile-target combinations for their synthesis.

On joint analysing XMM-NuSTAR spectra of active galactic nuclei

A recently released XMM-Newton note revealed a significant calibration issue between nuclear spectroscopic telescope array(NuSTAR)and XMM-Newton European Photon Imaging Camera(EPIC)and provided an empirical correction to the EPIC effective area.To quantify the bias caused by the calibration issue in the joint analysis of XMM-NuSTAR spectra and verify the effectiveness of the correction,in this work,we perform joint-fitting of the NuSTAR and EPIC-pn spectra for a large sample of 104 observation pairs of 44 X-ray bright active galactic nuclei(AGN).The spectra were extracted after requiring perfect simultaneity between the XMM-Newton and NuSTAR exposures(merging good time intervals(GTIs)from two missions)to avoid bias due to the rapid spectral variability of the AGN.Before the correction,the EPIC-pn spectra are systematically harder than the corresponding NuSTAR spectra by■subsequently yielding significantly underestimated cutoff energy E_(cut)and the strength of reflection component R when performing joint-fitting.We confirm that the correction is highly effective and can commendably erase the discrepancy in best-fitΓ,E_(cut),and R.We thus urge the community to apply the correction when joint-fitting XMM-NuSTAR spectra,but note that the correction is limited to 3–12 keV and therefore not applicable when the soft X-ray band data are included.Besides,we show that as merging GTIs from two missions would cause severe loss of NuSTAR net exposure time,in many cases,joint-fitting yields no advantage compared with utilizing NuSTAR data alone.Finally,We present a technical note on filtering periods of high background flares for XMM-Newton EPIC-pn exposures in the small window(SW)mode.

Opportunities for production and property research of neutron-rich nuclei around N=126 at HIAF

The study of nuclide production and its properties in the N=126 neutron-rich region is prevalent in nuclear physics and astrophysics research.The upcoming High-energy FRagment Separator(HFRS)at the High-Intensity heavy-ion Accelerator Facility(HIAF),an in-flight separator at relativistic energies,is characterized by high beam intensity,large ion-optical acceptance,high magnetic rigidity,and high momentum resolution power.This provides an opportunity to study the production and properties of neutron-rich nuclei around N=126.In this paper,an experimental scheme is proposed to produce neutron-rich nuclei around N=126 and simultaneously measure their mass and lifetime based on the HFRS separator;the feasibility of this scheme is evaluated through simulations.The results show that under the high-resolution optical mode,many new neutron-rich nuclei approaching the r-process abundance peak around A=195 can be produced for the first time,and many nuclei with unknown masses and lifetimes can be produced with high statistics.Using the time-of-flight corrected by the measured dispersive position and energy loss information,the cocktails produced from 208 Pb fragmentation can be unambiguously identified.Moreover,the masses of some neutron-rich nuclei near N=126 can be measured with high precision using the time-of-flight magnetic rigidity technique.This indicates that the HIAF-HFRS facility has the potential for the production and property research of neutron-rich nuclei around N=126,which is of great significance for expanding the chart of nuclides,developing nuclear theories,and understanding the origin of heavy elements in the universe.