Weak Deformation Research Articles

Genesis of subglacial triangular‐shaped landforms (murtoos) formed by the Fennoscandian Ice Sheet

AbstractThe purpose of this paper is to describe the internal structure and composition of recently discovered subglacial landforms called “murtoos” in order to interpret their formative processes and depositional environment. So far, murtoos have only been reported from Finland and Sweden, but they probably exist in all areas covered by past ice sheets. Murtoos mainly occur in fields along subglacial meltwater routes or corridors in close relation to eskers and ribbed moraine tracts. Murtoos were excavated perpendicular to the long axes of the triangular murtoo heads in six locations. Murtoos were found to be composed of silt/clay‐poor, sandy and gravelly diamictons interbedded with sorted sediments, and are suggested to be produced by pulsed, highly sediment‐concentrated flows during weak glaciotectonic deformation, indicating effective pressure close to zero. Murtoos can be divided into three main depositional units: 1) the core, 2) the murtoo body and 3) the murtoo mantle. The initial deposition of murtoos took place in a network of low canals and conduits or cavities with fluctuating stream flow likely over 50 km from the ice margin. Murtoos reveal an increasing influence of subglacial meltwater flow in rapidly widening broad and low conduits with increasing sediment transport over short distances. The results of this work suggest that murtoos were formed time‐transgressively over yearly meltwater cycles in a semi‐distributed drainage system not recognised before, in which was high‐pressure porewater conditions with rapid mobilisation of subglacial saturated sediments, a critical factor in the development of semi‐efficient drainage. Murtoos are suggested as missing element between distributed and channelised drainage systems not included in current glaciohydrological models or even in the theoretical basis of glacial hydrology.

The Crustal Dynamics and Its Geological Explanation of the Three-Dimensional Co-Seismic Deformation Field for the 2021 Maduo MS7.4 Earthquake Based on GNSS and InSAR.

Three-dimensional deformation is an important input to explore seismic mechanisms and geodynamics. The GNSS and InSAR technologies are commonly used to obtain the co-seismic three-dimensional deformation field. This paper focused on the effect of calculation accuracy caused by the deformation correlation between the reference point and the points involved in the solution, to build a high-accuracy three-dimensional deformation field for a detailed geological explanation. Based on the variance component estimation (VCE) method, the InSAR LOS, azimuthal deformation, and the GNSS horizontal and vertical deformation were integrated to solve the three-dimensional displacement of the study area in combination with the elasticity theory. The accuracy of the three-dimensional co-seismic deformation field of the 2021 Maduo MS7.4 earthquake obtained by the method proposed in this paper, was compared with that obtained from the only InSAR measurements obtained using a multi-satellite and multi-technology approach. The results showed the difference in root-mean-square errors (RMSE) of the integration and GNSS displacement was 0.98 cm, 5.64 cm, and 1.37 cm in the east-west, north-south and vertical direction respectively, which was better than the RMSE of the method using only InSAR and GNSS displacement, which was 5.2 cm and 12.2 cm in the east-west, north-south, and no vertical direction. With the geological field survey and aftershocks relocation, the results showed good agreement with the strike and the position of the surface rupture. The maximum slip displacement was about 4 m, which was consistent with the result of the empirical statistical formula. It was firstly found that the pre-existing fault controlled the vertical deformation on the south side of the west end of the main surface rupture caused by the Maduo MS7.4 earthquake, which provided the direct evidence for the theoretical hypothesis that large earthquakes could not only produce surface rupture on seismogenic faults, but also trigger pre-existing faults or new faults to produce surface rupture or weak deformation in areas far from seismogenic faults. An adaptive method was proposed in GNSS and InSAR integration, which could take into account the correlation distance and the efficiency of homogeneous point selection. Meanwhile, deformation information of the decoherent region could be recovered without interpolation of the GNSS displacement. This series of findings formed an essential supplement to the field surface rupture survey and provided a novel idea for the combination of the various spatial measurement technologies to improve the seismic deformation monitoring.

Temporally probing the thermal phonon and charge transfer induced out-of-plane acoustical displacement of monolayer and bi-layer MoS2/GaN heterojunction

Acoustical behavior of semiconducting transition metal dichalcogenides determines the heat transfer pathway, and thus plays a crucial role in the electronics and optoelectronics design. In this research, van der Waals heterojunctions (vdWHs) consisting of transferred monolayer and bi-layer MoS2 on GaN substrate were studied. We observed an asymmetric bipolar acoustic strain wave with ∼5 ps duration, which describes the surface of substrate undergoing strong compressive deformation after weak tensile deformation in the out-of-plane direction. We developed a theory to explain the mechanisms responsible for the observed strain waveform in the vdWHs elastic system, and obtained the critical parameters of the carrier dynamics by temporal fitting. Our results not only report a coherent acoustic phonon generated in the vdWHs, which will complement our understanding of the thermal transfer at the 2D/substrate interface, but also provide information about the intrinsic properties in the vdWHs, which would benefit the design of the 2D-based devices in the future.

Polaron with quadratic electron-phonon interaction

We present a numerically exact study of a polaron with quadratic coupling to the oscillator displacement, or ${X}^{2}$ polaron, using two alternative methodological developments. Our results cover both antiadiabatic and adiabatic regimes and the entire range of electron-phonon coupling ${g}_{2}$, from the system's stability threshold at attractive ${g}_{2}=\ensuremath{-}1$ to arbitrary strong repulsion at ${g}_{2}\ensuremath{\gg}1$. The key properties of ${X}^{2}$ polarons prove dramatically different from their linear counterparts. They (i) are insensitive even to large quadratic coupling except in the antiadiabatic limit near the threshold of instability at attraction, (ii) depend only on the adiabatic ratio but are insensitive to the electron dispersion and dimension of space, and (iii) feature weak lattice deformations even at the instability point. Our results are of direct relevance to the properties of electrons at low densities in polar materials, including recent proposals for their superconducting states.

Paleoproterozoic high-pressure granulite facies metamorphism in the Yinshan Block, North China craton

The Yinshan Block located in the northern margin of the North China Craton (NCC) has been regarded as a typical Archean cratonic block, but it is argued whether the block had been affected by Paleoproterozoic tectonic and metamorphic events. This paper reports the late Paleoproterozoic high-pressure (HP) granulites for the first time from the Xiwulanbulang area in the Yinshan Block, and presents a systematic study on their petrography, mineral chemistry, phase equilibria modelling and zircon dating to confirm their metamorphic evolution and tectonic implications. Two representative samples contain the typical HP basic granulite assemblages involving garnet, clinopyroxene, plagioclase, amphibole and quartz, with garnet commonly occurring as coronae around clinopyroxene and plagioclase. Both samples show clockwise P–T paths with their peak conditions of ∼930 °C/∼15kbar (20NM01) and 970–980 °C/∼13.5 kbar (21NM05) respectively, constrained using the maximum Ti contents in amphibole and minimum anorthite (XAn) in the mantle of plagioclase on P–T pseudosections. Zircon dating yields a magmatic age of ∼ 2.3 Ga and metamorphic ages of ∼2.5 Ga and ∼1.8 Ga. The ∼2.3 Ga magmatic age represents the time of protolith gabbro crystallization, which can be comparative to the extension-related bimodal magmatism in the Khondalite Belt. The ∼ 1.8 Ga age was determined from metamorphic zircons that have flat HREE patterns with the presence of garnet, interpreted as the time of the post-peak cooling and uplifting of the HP granulite facies metamorphism. The ∼2.5 Ga is defined from the captured zircon grains by gabbroic intrusions from the country Neoarchean rocks. The HP granulite facies metamorphism registers a geothermal gradient of 19–20 °C/km, indicating a collision-related orogenic event that may have occurred at ∼1.85 Ga along the northern margin of the NCC. Therefore, the Yinshan Block may represent a weak deformation domain in the orogenic belt on the northern margin of the NCC.

Unravelling the impact of geological heterogeneities in the reservoir management. An integrated study of the deep-water Akpo field (Niger delta)

Geological and seismic data have been integrated to describe the impact of structural and sedimentological heterogeneities on fluid dynamics for one of the reservoirs (Reservoir X) of the Akpo field (deep offshore of Niger Delta). Akpo is a sinuous 4-way anticline formed because of strong deformation occurring within the over pressurized shales of the Akata Formation. Weak deformation may have started since 9 Ma; however, most of the strain associated with shortening was accumulated between ca 7 Ma and ca 3 Ma. The cumulative shortening has been estimated in the order of 4% (ca 400 m). From 3 Ma (during the latest stages of growth of the Akpo anticline) up to Present-day, the residual strain was taken up by oblique (right lateral strike-slip component) extensional faults, between 2 km and ca 15 km in length, organized into two main trends: N-dipping, ENE-WSW to NE-SW striking faults, and NNW-SSE striking faults mainly dipping to the east. These faults are segmented and have a maximum throw in the order of 70 m. Based on the architectural elements identified in this work, the Reservoir X of the Akpo field has been subdivided into three main intervals: a basal lobe (Interval 1a) and a related channel (Interval 1 b); two intermediate generations of meandering channels (Interval 2a and 2 b); and an upper and strongly erosional constructive channel (Interval 3). The 4D signal has been integrated to better understand the complex fluid flow within Reservoir X in time and space. The extensional faults play a role in baffling mainly in the central part of the field, where across-fault flow is likely to occur in correspondence with the spill points. Facies distribution and the nature of the contact between various reservoir intervals are also important because vertical and lateral communication between sand bodies can be complex. Levees or mud barriers can inhibit flow, impacting both efficiency of support between injectors and producers. On the other hand, sand-to-sand communication due to the strong erosional character of the contacts enhances dynamic connectivity between sands belonging to different reservoir intervals. As an example, even if sands belonging to Interval 3 totally erode (i.e. dynamically isolate) those of Interval 2 in the southern part of the field, in the northern sector the two reservoir intervals are in (vertical) communication as suggested by the 4D signal. A key result of this integrated work is that of documenting in detail the modes in which faults and sedimentary features impact fluid flow within and across reservoir intervals in a deep-water environment.

Quantification of the Writhe Number of the Evolution of Solar Filament Axes

Solar filament eruptions often show complex and dramatic geometric deformation that is highly relevant to the underlying physical mechanism triggering the eruptions. It is well known that the writhe of filament axes is a key parameter characterizing its global geometric deformation, but a quantitative investigation of the development of writhe during its eruption is still lacking. Here we introduce the Writhe Application Toolkit, which can be used to characterize accurately the topology of filament axes. This characterization is achieved based on the reconstruction and writhe number computation of three-dimensional paths of the filament axes from dual-perspective observations. We apply this toolkit to four dextral filaments located in the northern hemisphere with a counterclockwise (CCW) rotation during their eruptions. Initially, all these filaments possess a small writhe number (≤0.20) indicating a weak helical deformation of the axes. As the CCW rotation kicks in, their writhe numbers begin to decrease and reach large negative values. Combined with the extended Călugăreanu theorem, the absolute value of twist is deduced to decrease during the rotation. Such a quantitative analysis strongly indicates a consequence of the conversion of twist into writhe for the studied events.

Degradation of Typical Reverse Sand-Mudstone Interbedded Bank Slope Based on Multi-Source Field Experiments.

The bank slopes in the Three Gorges Reservoir area (TGRA) have experienced obvious deterioration under the action of the periodic fluctuations in the reservoir water level. Generally, laboratory tests have been used to reveal the evolution trend of the slope banks. However, this method has a certain degree of cross-scale problem, especially for the mechanical state in a complex environment. Therefore, in this study, we took the Yangjiaping bank slope in the TGRA as an example and proposed a comprehensive on-site detection method to further reveal the rock mass degradation phenomenon of this typical reverse sand-mudstone interbedded bank slope. Specifically, multi-scale laser scanning, cross-hole acoustic wave detection, and inclination measurements were performed to analyze the fractures, quality, and deformation of rocky banks. The results showed that the deterioration of the bank slope manifested as the expansion, deepening, and widening of the cracks, as well as the peeling off and loosening of rocky banks. Large-scale laser scanning revealed that the deterioration zone was deformed along large fracture zones and layers. Unlike limestone slopes, the intact sandstone underground might be degraded by changes in water. There are few inclinometers and no deformation or weak deformation, which requires long-term monitoring. The relevant research methods provide an important reference for determining the instability and failure trend of the reservoir bank slopes.

Role of pre-kinematic fluid-rock interactions on phase mixing, quartz recrystallization and strain localization in low-temperature granitic shear zones

This study explores the relative importance of fluid availability, temperature and mineral assemblage variations on the development of macro and microstructures in greenschist-facies shear zones of two granitoids of the Axial Zone (central Pyrenees) emplaced at the end of Variscan orogeny, at similar structural levels. The investigated shear zones formed during alpine compression at comparable temperature. In the Bielsa granitoid, deformation was distributed in a dense network of shear zones. Extensive mineralogical transformations resulted in variations in major, minor and rare earth element contents pointing to pre-kinematic hydrothermal alteration (at Permian-Triassic) at 270–350 °C and further alteration in fluid-abundant conditions during Alpine shearing. Quartz was fractured, exhibits weak plastic deformation and was weakly reworked, mainly by dissolution-reprecipitation. Strain was accommodated in the mica-rich matrix (40–50% vol. of mica). Mica significantly grew during pre-kinematic hydrothermal alteration. In the Maladeta granite, deformation was localized in sparse shear zones. Hydrothermal alteration occurred at similar to slightly higher temperature (280–380 °C). Elemental variation related to alteration was weaker, pointing to fluid-deficient conditions before and during Alpine compression. Limited fluid resulted in lower mica content (20–28% vol.) than in Bielsa. Quartz exhibits stronger intragrain plastic deformation, dynamic recrystallization by subgrain rotation and reworking by dissolution-reprecipitation and nucleation. Strain was accommodated by both quartz aggregates and mica-rich matrix. The transition from dominant brittle behavior of quartz to dynamic recrystallization by subgrain rotation occurred in a narrow range of 350–380 °C, well below 450 °C as generally described. The lower temperature and less hydrated conditions in Maladeta are in apparent contradiction with stronger quartz recrystallization and strain localization than in Bielsa. By promoting phyllosilicate growth and phase mixing before shearing, the metamorphic pre-conditioning of the granitic protolith appears to be the main factor controlling strain distribution at sample scales and differences in tectonic styles between the two massifs.

Cocycle deformations for weak Hopf algebras

In this paper we introduce a theory of multiplication alteration by two-cocycles for weak Hopf algebras. We show that, just like it happens for Hopf algebras, if H a weak Hopf algebra and H? its weak Hopf algebra deformation by a 2-cocycle ?, there is a braided monoidal category equivalence between the categories of left-right Yetter-Drinfel?d modules HYDH and H?YDH?. As a consequence we get in this context that the category Rep(D(H)) of left modules over the Drinfel?d double D(H) can be identified with the category Rep(D(H?)) of left modules over the Drinfel?d double D(H?).

Ultrastretchable Composite Organohydrogels with Dual Cross-Links Enabling Multimodal Sensing.

Building multiple cross-links or networks is a favorable way of diversifying applications of the hydrogels, which is also available for the organohydrogels prepared via the solvent replacement way. However, the situations become more complicated for organohydrogels due to the presence of replaced solvents. Therefore, the correlations between the multiple cross-links and final performance need to be better understood for the organohydrogels, which is vital for tailoring their inherent properties to expand final application scenarios. Polyacrylamide (PAM)/poly(vinyl alcohol) (PVA)/MXene composite organohydrogels with dual cross-links, namely, the covalently cross-linked PAM chains as the primary network and the physically cross-linked PVA/PAM chains with MXene particles as the secondary cross-links, were developed here for the study. The occurrence of the secondary cross-links plays multiple roles as sacrificial units endowing the system with ultrastretchability with an excellent strain-resistance effect and as temperature-sensitive units endowing the system with thermosensation ability with an outstanding temperature coefficient of resistance. Thus, the optimized sample can be used as a strain sensor with excellent environmental tolerance for detecting human motion as a pressure sensor to probe compression with weak deformation and as a thermal sensor to capture environmental temperature changes. This work provides valuable information on developing organohydrogels with superior performance for multimodal sensors.

Microstructure, mechanical properties and tear toughness of laser-welded DP980 dual phase steel

In this study, DP980 steel sheets were laser welded with a laser power of 4.5 kW and a welding speed of 4.5 m min−1. The microstructural evolution and mechanical properties of the welded joint and the effect of notch location on tear toughness were evaluated. Results show that the fusion zone (FZ) was composed of lath martensite, the hardness (276 HV) of the heat-affected zone (HAZ) was lower than that of the base metal (305 HV) resulting from martensite tempering. The welded specimens failed at the soft HAZ with a 98.4% joint efficiency during the tensile test, and the ultimate tensile strength of the as-recieved steel and welded joint was 1026 MPa and 1010 MPa, respectively. The tear energy of the FZ and HAZ was lower than DP980 base metal (BM). Thus, it is considered that the fracture toughness of the joint decreased after welding. The crack growth path of the FZ gradually deviated toward the HAZ during tearing due to the asymmetrical plastic zone at the crack tip. Compared with the ductile fracture of the base metal, the significant decrease in the fracture toughness of the welded joint is due to the weak deformation resistance of tempered martensite.

Comparative Analysis of the Drainage Effect Based on Improved Hydraulic Flushing Technology.

The composite structure coal seam composed of coal seams with strong and weak deformation is widely developed in the coalfields in Southwest and North China. The implementation of hydraulic flushing in soft coal stratification can effectively relieve the pressure and increase the permeability of coal seams, so it can improve the effect of underground gas drainage. Taking Xin'an Coal Mine, West Henan province, China, as an example, this paper discussed the influence of hydraulic flushing on the gas drainage effect in soft coal seam by means of field investigation, numerical simulation analysis, similar simulation, and field verification. As the same time, a fluid-solid coupling model of gas drainage based on layered hydraulic flushing technology is established, and the differences and reasons of the gas drainage effect after layered hydraulic flushing in soft and hard composite coal seams are discussed. The results show that (1) the gas concentration change of layered flushing boreholes intermittently rises rapidly, and there is no obvious law, while that of conventional flushing boreholes shows a regular attenuation trend. (2) According to the numerical simulation results, after 30 days of drainage, the effective drainage range of layered hydraulic flushing is 8.33 m3 higher than that of conventional hydraulic flushing. (3) There are not a few points where the single borehole concentration data of each row of layered flushing boreholes are in the high level. Meanwhile, the maximum concentration of all conventional flushing boreholes is less than 40%, except that one borehole can reach 70% at the beginning. (4) All of the average gas drainage concentration of single-row boreholes using layered flushing technology is greater than 20% in the vast majority of days, while that of the conventional flushing boreholes is only higher than 20% in row 5 and has only lasted for 2 days. The difference of the drainage effect is obvious.

Surface friction of subducting seamounts influences deformation of the accretionary wedge

Undulating topography on a subducting oceanic plate causes substantial deformation of the accretionary wedge. In particular, the subduction of a seamount is considered to induce 1) the development of landward concave topography such as reentrant and indented features, 2) compression within the accretionary wedge, and 3) disturbance of the primary thrust-sheet structures by uplift associated with the formation of multiple faults. However, according to previous seismic profiles, some subducting seamounts have provided suggestive evidence for weak wedge deformation rather than strong compression and uplift that were indicated in the previous model experiments. As the cross-sectional shape of an accretionary wedge is known to be strongly constrained by the internal and basal friction of the wedge, this study evaluates the effect of the frictional conditions of a subducting seamount on the deformation of the upper plate using analog experiments of two seamount models with low and high friction, respectively. Results show that subduction of a high-friction seamount causes continuous compression and uplift of the accretionary wedge, with the plate boundary fault zone composed of discontinuous multiple faults that offset vertically and partially overlapped to form a thick deformation zone. In contrast, a low-friction seamount is associated with a relatively thin wedge and a single plate boundary fault, which results in less compression compared with a high-friction seamount. During the subduction of a low-friction seamount, the accretionary wedge grows locally as the thickness of sediment on the seamount decreases, which has not been reported in previous studies. The wedge deformation pattern around the subducting Bennett Knoll Seamount in the Hikurangi Margin could be explained by the mechanism observed in the low-friction seamount subduction. From these results, we conclude that the frictional conditions on the seamount surface are a dominant control on the process of wedge deformation during the early stages of seamount subduction.

Strain hardening and stored energy in high-Mn austenitic based low-density steel

In the present study an attempt has been made to understand the high strain hardening in austenitic low-density steel using two full field measurements of temperature and strain on the sample during tensile deformation. Based on these measurements’ evolution of energy storage during deformation was calculated. High energy storage has been attributed to the interaction between dislocation groups belonging to different slip bands and destruction of short-range order (SRO) clusters. This in turn, dictates the range of the elastic stress field of slip bands. Furthermore, weak deformation heterogeneity ensued just after yield and continued with a fixed strain pattern up to facture. This did not result in macroscopic instability but manifested as microstructural heterogeneity in the form of micro-band and nano twins at later stages of deformation. A mathematical model of energy storage based on dislocation entrapment is discussed.

Sedimentary–tectonic interaction on the growth sequence architecture within the intraslope basins of deep-water Niger Delta Basin

This paper presents a 3D seismic-based case study from the deep-water Niger Delta Basin to investigate sedimentary–tectonic interaction on growth sequence architecture within the thrust-related intraslope or piggyback basins. Gravitational contraction in the lower continental slope had yielded a series of thrust faults and associated folds in the study area, which formed several piggyback basins. These basins were filled by a suite of growth sequences with varying stratigraphic architecture. Analysis of the 3D seismic data recognized three primary seismic facies types respectively as: convergent, draping and chaotic, which contain seven subtypes. These facies types are combined to form different filling successions for convergent or chaotic growth sequences. The convergent growth sequences mainly occur in the deep section of basin fills during strong gravitational deformation, and always began with convergent-baselapping strata succeeded by convergent-thinning strata, representing pond-to-bypass transition in the ponded-basin accommodation space. The chaotic growth sequences mainly occur in the shallow section of basin fills in response to weak gravitational deformation, and usually began with debris-flow deposits succeeded by channel-levee complexes, reflecting dominant erosion-bypass processes in the slope accommodation space. A dynamic fill-and-spill model considering relationship between episodic sedimentation rate and structural growth rate is proposed to explain the formative mechanisms of growth strata units and associated successions. Interaction between glaciation or deglaciation and sea-level change and gravitational deformation history are suggested to be the factor which resulted in the complex stratal stacking patterns, including progradational or retrogradational stacking patterns within convergent growth sequences, and progradational stacking patterns within chaotic growth sequences.

Texture formation in biomedical superelastic Ti – Zr – Nb alloys during rolling and subsequent heat treatment

Currently, low-modulus biocompatible Ti – Nb – Zr alloys are considered promising for medical applications. Superelasticity is a property that is mainly governed by the crystallographic direction in single crystals, i.e. by the predominant orientation of grains in polycrystalline objects. In order to control the crystallographic texture in products (such as foils), one should understand how it forms at various stages of thermomechanical processing. This paper compares the following alloys in terms of their crystallographic texture and how it forms: Ti –18Zr – 15Nb (18-15), Ti – 6Zr – 22Nb (22-6), Ti – 22Nb – (1–1.5)O (1O and 1.5O) (at.%). The composition of an alloy influences the stability of the initial β-phase, which tends to decrease with an increase in the concentration of Zr, which replaces Nb. A decreasing stability triggers martensitic transformations during rolling resulting in the formation of a weak blurry texture {112}<011>, as can be observed during deformation of alloy 18-15. Plastic deformation of a stable β-phase leads to the formation of a sharp twocomponent texture typical of BCC alloys: {110}<001> and {112}<011>, which develops during the rolling of alloys with oxygen and 22-6. Recrystallization of rolled foils (ε = 92%) at 650 оC for 0.5 h leads to sharpening of the texture components in the case of samples with a sharp deformation texture (22-6, 1O, 1 .5O) and to a change in texture in the case of samples with a weak deformation texture (18-15). Cyclic tensile tests conducted in three different directions revealed the presence of anisotropy in foils of all compositions. However, alloy 18-15 has the lowest anisotropy. An increase in the Zr concentration contributes to maximum reversible strain in the process of realizing superelasticity at room temperature. This research was funded by the Ministry of Science and Higher Education of the Russian Federation; Agreement No. 075-15-2021-1352.

Investigation on stability of large bedding slope affected by weak interlayer creep deformation

Investigation on stability of large bedding slope affected by weak interlayer creep deformation

Numerical simulation of strain localization through an integrated Cosserat continuum theory and strong discontinuity approach

In this paper, we propose a new numerical approach abbreviated as Cos-SDA for analyzing strain localization problems of geomaterials. The Cos-SDA is achieved by implanting the strong discontinuity approach (SDA) into the computational framework of the Cosserat continuum finite element approach (Cos-FEA). Through two numerical examples of plane strain compression test and slope stability, it is demonstrated that the Cos-SDA model can effectively simulate the entire progressive failure process of geomaterials from weak discontinuity to strong discontinuity. Cos-SDA can effectively alleviate the influence of mesh distortion in shear zone, and the numerical solution can still maintain convergence even under large deformation. Cos-FEA and Cos-SDA have much stiffer mechanical response than SDA-FEA since an internal length scale is introduced into the governing equations. In contrast, the SDA-FEA shows more conservative as the unmature bifurcation occurs and weak discontinuous stage is ignored in the numerical simulation, while Cos-FEA numerical results show an over-stiff mechanical response in the stage of post failure. Cos-SDA inherits the advantages of both SDA-FEA and Cos-FEA and neutralizes their mechanical responses, so it is more reasonable in simulating the progressive failure process from weak discontinuity deformation (strain localization) to strong discontinuity deformation (slip) occurring in geomaerials.

Successive neutron alignments in the yrast, negative-parity band of oblate-deformed Tl199

The negative-parity band structure built on the proton $h{}_{9/2}$ state in $^{199}\mathrm{Tl}$ has been established up to an excitation energy of 7 MeV and spin of (51/2)$\ensuremath{\hbar}$. The level scheme has been extended with the inclusion of fourteen new transitions de-exciting levels at high spin. The $\mathrm{\ensuremath{\Delta}}\mathit{I}=1$ $\ensuremath{\gamma}$ rays are found to be more prominently visible in the spectra when comparing to $\mathrm{\ensuremath{\Delta}}\mathit{I}=2$ transitions. Rotation alignments are evident at frequencies of 0.22 and 0.30 MeV with both being attributed to the breaking of pairs of neutrons in the $i{}_{13/2}$ subshell. Since $^{199}\mathrm{Tl}$ is expected to have weak oblate deformation, and lies in a transitional region where competing contributions to the spin are expected from collective rotation and the angular momentum of high-$j$ nucleons, calculations using both the principal axis cranking (PAC) and tilted axis cranking (TAC) formalisms have been performed to understand its structure. Both the PAC and TAC calculations are found to provide a satisfactory description of the evolution of excitation energies with spin. The PAC calculations give a good account of the experimental crossing frequencies and associated spins. The structure of the yrast, negative-parity band in $^{199}\mathrm{Tl}$ may be primarily understood in terms of the collective rotation of a moderately deformed oblate nucleus, along with contributions to the angular momentum from two pairs of rotation-aligned $i{}_{13/2}$ neutrons.