bluuebunny/crossref_metadata_2025 huggingface dataset:
Challenges, solutions and research priorities for sustainable rangelands
Authors: Nielsen Uffe N. , Stafford-Smith Mark , Metternicht Graciela I. , Ash Andrew , Baumber Alex , Boer Matthias M. , Booth Sandy , Burnside Don , Churchill Amber C. , El Hassan Marwan , Friedel Margaret H. , Godde Cecile M. , Kelly Dana , Kelly Mick , Leys John F. , McDonald Sarah E. , Maru Yiheyis T. , Phelps David G. , Ridges Malcolm , Simpson Geoff , Traill Barry , Walker Brian , Waters Cathleen M. , Whyte Angus W.
Published: November 2020

Australia’s rangeland communities, industries, and environment are under increasing pressures from anthropogenic activities and global changes more broadly. We conducted a horizon scan to identify and prioritise key challenges facing Australian rangelands and their communities, and outline possible avenues to address these challenges, with a particular focus on research priorities. We surveyed participants of the Australian Rangeland Society 20th Biennial Conference, held in Canberra in September 2019, before the conference and in interactive workshops during the conference, in order to identify key challenges, potential solutions, and research priorities. The feedback was broadly grouped into six themes associated with supporting local communities, managing natural capital, climate variability and change, traditional knowledge, governance, and research and development. Each theme had several sub-themes and potential solutions to ensure positive, long-term outcomes for the rangelands. The survey responses made it clear that supporting ‘resilient and sustainable rangelands that provide cultural, societal, environmental and economic outcomes simultaneously’ is of great value to stakeholders. The synthesis of survey responses combined with expert knowledge highlighted that sustaining local communities in the long term will require that the inherent social, cultural and natural capital of rangelands are managed sustainably, particularly in light of current and projected variability in climate. Establishment of guidelines and approaches to address these challenges will benefit from: (i) an increased recognition of the value and contributions of traditional knowledge and practices; (ii) development of better governance that is guided by and benefits local stakeholders; and (iii) more funding to conduct and implement strong research and development activities, with research focused on addressing critical knowledge gaps as identified by the local stakeholders. This requires strong governance with legislation and policies that work for the rangelands. We provide a framework that indicates the key knowledge gaps and how innovations may be implemented and scaled out, up and deep to achieve the resilience of Australia’s rangelands. The same principles could be adapted to address challenges in rangelands on other continents, with similar beneficial outcomes.
Health care access, health care utilisation and sexual orientation disclosure among Black sexual minority men in the Deep South
Authors: He Ying , Dangerfield II Derek T. , Fields Errol L. , Dawkins Milton R. , Turpin Rodman E. , Johnson Damon , Browne Dorothy C. , Hickson DeMarc A.
Published: November 2020

Background
Black gay, bisexual, and other sexual minority men (BSMM) account for 39.1% of new HIV infections among men who have sex with men and 78.9% of newly diagnosed cases among Black men. Health care access, health care utilisation and disclosing sexuality to providers are important factors in HIV prevention and treatment. This study explored the associations among sexual orientation disclosure, health care access and health care utilisation among BSMM in the Deep South. Methods:Secondary analysis of existing data of a population-based study in Jackson, Mississippi, and Atlanta, Georgia, was conducted among 386 BSMM. Poisson regression models were used to estimate prevalence ratios (PR) between sexual orientation disclosure to healthcare providers, health care access and health care utilisation. Results:The mean (±s.d.) age of participants was 30.5 ± 11.2 years; 35.3% were previously diagnosed with HIV and 3.7% were newly diagnosed with HIV. Two-thirds (67.2%) self-identified as homosexual or gay; 70.6% reported being very open about their sexual orientation with their healthcare providers. After adjustment, BSMM who were not open about their sexual orientation had a lower prevalence of visiting a healthcare provider in the previous 12 months than those who were very open with their healthcare provider (PR 0.42; 95% confidence interval 0.18–0.97). Conclusion:Clinics, hospitals and other healthcare settings should promote affirming environments that support sexuality disclosure for BSMM.
Characteristics of sequential activity in networks with temporally asymmetric Hebbian learning
Authors: Gillett Maxwell , Pereira Ulises , Brunel Nicolas
Published: November 2020

Significance

Sequential activity is a prominent feature of many neural systems, in multiple behavioral contexts. Here, we investigate how Hebbian rules lead to storage and recall of random sequences of inputs in both rate and spiking recurrent networks. In the case of the simplest (bilinear) rule, we characterize extensively the regions in parameter space that allow sequence retrieval and compute analytically the storage capacity of the network. We show that nonlinearities in the learning rule can lead to sparse sequences and find that sequences maintain robust decoding but display highly labile dynamics to continuous changes in the connectivity matrix, similar to recent observations in hippocampus and parietal cortex.
The Tupí-Guaraní language family
Authors: Ferraz Gerardi Fabrício , Reichert Stanislav
Published: November 2020

Attempts to classify Tupí-Guaraní languages have so far been inconsistent with archaeological evidence and ignored information from historical sources. The case of Tupinambá is most illustrative in this regard. Using both Bayesian phylogenetic analysis and a stochastic algorithm that reconstructs phylogenetic trees by relying on maximum likelihood estimation, we suggest a new internal classification of the Tupí-Guaraní branch. The results of the analyses are in accordance with the most recent genetic research on Tupían populations and challenge previous classifications by suggesting, among others, that Tupinambá should not be considered a ‘Guaraní’ language.
The word order of negation in the history of Basque
Authors: Salaberri Iker
Published: November 2020

This article investigates word order changes in negated periphrastic constructions in the history of Basque. A number of linguistic variables are argued to correlate with these changes: the negative particleezis increasingly focalized in main clauses, the innovative patternnegative particle – auxiliary verb –main verballows for more syntactic flexibility than the conservative one, and the word order changes do not progress at equal rates in all clause subtypes. Genre issues are also considered, including the hypothesis that the loss of the conservative ordermain verb – negative particle – auxiliary verbof main clauses occurs first in texts close to oral language. Moreover, it is argued that eastern dialects are more innovative than western dialects and that efforts towards standardization of the language have slowed down this case of word order change.
Use and acquisition of mouth actions in L2 sign language learners
Authors: Mesch Johanna , Schönström Krister
Published: November 2020

This article deals with L2 acquisition of a sign language, examining in particular the use and acquisition of non-manual
mouth actions performed by L2 learners of Swedish Sign Language. Based on longitudinal data from an L2 learner corpus, we describe the
distribution, frequency, and spreading patterns of mouth actions in sixteen L2 learners at two time points. The data are compared with nine
signers of an L1 control group.

The results reveal some differences in the use of mouth actions between the groups. The results are specifically related
to the category of mouthing borrowed from spoken Swedish. L2 signers show an increased use of mouthing compared to L1 signers. Conversely,
L1 signers exhibit an increased use of reduced mouthing compared with L2 signers. We also observe an increase of adverbial mouth gestures
within the L2 group. The results are discussed in relation to previous findings, and within the framework of cross-linguistic influence.
A new chapter in the CD8 T reg story
Authors: Cantor Harvey , Kim Hye-Jung
Published: November 2020

CD8+ T reg cells play an important role in the maintenance of self-tolerance and can inhibit the development of autoimmune disease. In this issue of JEM, Mishra et al. (https://doi.org/10.1084/jem.20200030) reveal that TGF-β signaling and an Eomes-dependent genetic program contribute to CD8 T reg cell differentiation and function.
Ultrafast dynamics of 2-thiouracil investigated by time-resolved Auger spectroscopy
Authors: Lever F , Mayer D , Picconi D , Metje J , Alisauskas S , Calegari F , Düsterer S , Ehlert C , Feifel R , Niebuhr M , Manschwetus B , Kuhlmann M , Mazza T , Robinson M S , Squibb R J , Trabattoni A , Wallner M , Saalfrank P , Wolf T J A , Gühr M
Published: November 2020

We present time-resolved ultraviolet-pump x-ray probe Auger spectra of 2-thiouracil. An ultraviolet induced shift towards higher kinetic energies is observed in the sulfur 2p Auger decay. The difference Auger spectra of pumped and unpumped molecules exhibit ultrafast dynamics in the shift amplitude, in which three phases can be recognized. In the first 100 fs, a shift towards higher kinetic energies is observed, followed by a 400 fs shift back to lower kinetic energies and a 1 ps shift again to higher kinetic energies. We use a simple Coulomb-model, aided by quantum chemical calculations of potential energy states, to deduce a C–S bond expansion within the first 100 fs. The bond elongation triggers internal conversion from the photoexcited S2 to the S1 state. Based on timescales, the subsequent dynamics can be interpreted in terms of S1 nuclear relaxation and S1-triplet internal conversion.
Identifications of extreme ultraviolet spectra of Br-like to Ni-like neodymium ions using an electron beam ion trap
Authors: Suzuki C , Dipti  , Yang Y , Gall A , Silwal R , Sanders S , Naing A , Tan J , Takacs E , Ralchenko Yu
Published: November 2020

Accurate extreme ultraviolet spectra of open N-shell neodymium (Nd) ions were recorded at the electron beam ion trap facility of the National Institute of Standards and Technology. The measurements were performed for nominal electron beam energies in the range of 0.90 keV to 2.31 keV. The measured spectra were then compared with the spectra simulated by a collisional-radiative model utilizing atomic data produced with a fully relativistic atomic structure code. Consequently, 59 lines from Br-like to Ni-like Nd ions were unambiguously identified, most of which were newly assigned in this study. The wavelengths of 9 known lines from Ni-, Cu- and Zn-like Nd ions were in excellent agreement with previous measurements.
Double-plate calibration for coil capacitance effect and application in high-frequency eddy-current testing
Authors: Xu Jin , Lei Yinzhao
Published: November 2020

In high-frequency eddy-current testing, the coil impedance is often seriously affected by the capacitance effect, while the existing calibration method only corrects the capacitive couplings within the coil itself and ignores the coupling between the coil and the conductor. Combined with the equivalent circuit, a correction method for both the capacitive couplings is proposed using single-plate calibration. Furthermore, considering the skin effect at high frequencies, which leads to the calculation error of coil impedance, a modified impedance is introduced in the equivalent circuit and the double-plate calibration is presented. Using the two proposed methods and the existing calibration method, the experimental values of the coil impedance were respectively corrected when the coil was on a single-coated plate (titanium coating and TiAl6V4 titanium alloy substrate), and compared with the theoretical values between 1 and 100 MHz. The results show a sequentially improved correction effect of the existing calibration method, single-plate calibration, and double-plate calibration. Combined with the Levenberg–Marquardt method, the double-plate calibration was applied to the parameter measurement of the conductive plate with tens of micrometer coating. Through analyzing the sensitivity function of each tested parameter, we employed the inductance to calculate the substrate conductivity at hundreds of kilohertz and the resistance to calculate the coating thickness and conductivity at tens of megahertz. The parameters of three single-coated plates with coating thicknesses of 23 μm, 32 μm and 52 μm were respectively tested, and the results show that the relative measurement errors of all parameters are less than 15%.
Synthesis of deep red emitting Cu–In–Zn–Se/ZnSe quantum dots for dual-modal fluorescence and photoacoustic imaging
Authors: Sheng Yang , Li Shuai , Sun Yixin , Zhang Rong , Zhao Xinyu , Tan Mei Chee
Published: November 2020

CuInSe2 quantum dots (QDs) are one of the most important Cd-free fluorescent probes; they usually exhibited low fluorescence intensity, suggesting that a considerable amount of absorbed photon energy was lost as heat. In this study we aimed to improve the fluorescence intensity of CuInSe2 QDs and investigate their photoacoustic (PA) signal resulting from the heat dissipation, which was previously rarely reported. Cu–In–Zn–Se/ZnSe QDs were synthesized by adopting two strategies of Zn doping and ZnSe shell growth. It was found that there was an upper limit for Zn concentration beyond which the fluorescence intensity began to decrease. In addition, a blue shift of the emission peak of Cu–In–Zn–Se/ZnSe QDs was observed at high concentrations of ZnSe precursor due to the diffusion of excessive Zn. To prepare the dual-modal fluorescence and PA imaging probe, poly(maleic anhydride-alt-1-octadecene) (PMAO) modified with polyethylene glycol (PEG) was coated on the QDs, which led to a slight reduction in fluorescence. Cellular labeling on HeLa cells was performed to demonstrate the utility of these probes for fluorescence imaging. We further studied the in vitro PA imaging capabilities of the Cu–In–Zn–Se/ZnSe/PMAO-g-PEG nanoparticles, which showed a distinct PA signal beyond 1.0 mg ml−1. The current work demonstrated that a moderate amount of Zn doping is necessary for enhancing fluorescence and there is a limit beyond which the fluorescence will be diminished. We also demonstrated the proof of concept that Cu–In–Zn–Se/ZnSe QDs are able to serve as a potential PA imaging contrast agent.
Tunable parametric amplification of a graphene nanomechanical resonator in the nonlinear regime
Authors: Su Zi-Jia , Ying Yue , Song Xiang-Xiang , Zhang Zhuo-Zhi , Zhang Qing-Hang , Cao Gang , Li Hai-Ou , Guo Guang-Can , Guo Guo-Ping
Published: November 2020

Parametric amplification is widely used in nanoelectro-mechanical systems to enhance the transduced mechanical signals. Although parametric amplification has been studied in different mechanical resonator systems, the nonlinear dynamics involved receives less attention. Taking advantage of the excellent electrical and mechanical properties of graphene, we demonstrate electrical tunable parametric amplification using a doubly clamped graphene nanomechanical resonator. By applying external microwave pumping with twice the resonant frequency, we investigate parametric amplification in the nonlinear regime. We experimentally show that the extracted coefficient of the nonlinear Duffing force α and the nonlinear damping coefficient η vary as a function of external pumping power, indicating the influence of higher-order nonlinearity beyond the Duffing (∼x
3) and van der Pol (∼

x

2

d
x

d
t

) types in our device. Even when the higher-order nonlinearity is involved, parametric amplification still can be achieved in the nonlinear regime. The parametric gain increases and shows a tendency of saturation with increasing external pumping power. Further, the parametric gain can be electrically tuned by the gate voltage with a maximum gain of 10.2 dB achieved at the gate voltage of 19 V. Our results will benefit studies on nonlinear dynamics, especially nonlinear damping in graphene nanomechanical resonators that has been debated in the community over past decade.
Extreme value distributions of observation recurrences
Authors: Caby Th , Faranda D , Vaienti S , Yiou P
Published: November 2020

We study analytically and numerically the extreme value distribution of observables defined along the temporal evolution of a dynamical system. The convergence to the Gumbel law of observable recurrences gives information on the fractal structure of the image of the invariant measure by the observable. We provide illustrations on idealized and physical systems.
On some rigorous aspects of fragmented condensation
Authors: Dimonte Daniele , Falconi Marco , Olgiati Alessandro
Published: November 2020

In this paper we discuss some aspects of fragmented condensation from a mathematical perspective. We first propose a simple way of characterizing finite fragmentation. Then, inspired by recent results of semiclassical analysis applied to bosonic systems with infinitely many degrees of freedom, we address the problem of persistence of fragmented condensation. We show that the latter occurs in interacting systems, in the mean-field regime, and in the limit of large gap of the one-body Hamiltonian.
Vertical GaN power rectifiers: interface effects and switching performance
Authors: Yang Shu , Han Shaowen , Sheng Kuang
Published: November 2020

The emergence of free-standing GaN substrates enables the development of vertical GaN-on-GaN devices with high-power ratings and high frequencies. The Schottky interface plays an important role in determining the current transport mechanisms and the forward/reverse electrical performance of the vertical GaN Schottky barrier diodes. Moreover, given its direct bandgap and ultrashort minority carrier lifetime, it is of particular interest and importance to evaluate the fast switching performance of the vertical GaN power rectifiers. In this paper, we discuss the technology, physical mechanisms and characterizations of vertical GaN power rectifiers with high-quality interfaces and fast switching performances, including: (a) accurate characterization and carrier transport mechanisms of the Schottky interface; (b) Schottky interface engineering with optimized post-metallization annealing and a tunneling-enhancement layer; (c) fast reverse recovery performance that is characterized by high-speed board-level tests. The investigations and analysis on the interface effects and switching performance of the vertical GaN power rectifiers are valuable for high-efficiency and high-frequency power electronics applications.
Ponderomotively assisted ionization injection in plasma wakefield accelerators
Authors: Zeng Ming , de la Ossa Alberto Martinez , Osterhoff Jens
Published: November 2020

An injection scheme is proposed to realize electron trapping in sub-relativistic plasma wakefield accelerators. A laser under oblique angle of incidence ionizes a dopant gas in plasma and ponderomotively accelerates the released electrons into the direction of wake propagation. This process enables electron trapping in the wakefield even for a wakefield potential below the trapping threshold. We study the scheme theoretically and by means of particle-in-cell (PIC) simulations to demonstrate high-quality beam formation and acceleration with sub-micrometer normalized emittances and sub-percent uncorrelated energy spreads.
Constraints on neutrino mass in the scenario of vacuum energy interacting with cold dark matter after Planck 2018
Authors: Li Hai-Li , Zhang Jing-Fei , Zhang Xin
Published: November 2020

In this work, we investigate the constraints on the total neutrino mass in the scenario of vacuum energy interacting with cold dark matter (abbreviated as IΛCDM) by using the latest cosmological observations. We consider four typical interaction forms, i.e.

Q
=
β
H

ρ

de

,

Q
=
β
H

ρ

c

,

Q
=
β

H

0

ρ

de

, and

Q
=
β

H

0

ρ

c

, in the IΛCDM scenario. To avoid the large-scale instability problem in interacting dark energy models, we employ the extended parameterized post-Friedmann method for interacting dark energy to calculate the perturbation evolution of dark energy in these models. The observational data used in this work include the cosmic microwave background (CMB) measurements from the Planck 2018 data release, the baryon acoustic oscillation (BAO) data, the type Ia supernovae (SN) observation (Pantheon compilation), and the 2019 local distance ladder measurement of the Hubble constant H
0 from the Hubble Space Telescope. We find that, compared with those in the ΛCDM+

∑

m

ν

model, the constrains on

∑

m

ν

are looser in the four IΛCDM+

∑

m

ν

models. When considering the three mass hierarchies of neutrinos, the constraints on

∑

m

ν

are tightest in the degenerate hierarchy case and loosest in the inverted hierarchy case. In addition, in the four IΛCDM+

∑

m

ν

models, the values of coupling parameter β are larger using the CMB+BAO+SN+H
0 data combination than that using the CMB+BAO+SN data combination, and β > 0 is favored at more than 1σ level when using CMB+BAO+SN+H
0 data combination. The issue of the H
0 tension is also discussed in this paper. We find that, compared with the ΛCDM+

∑

m

ν

model, the H
0 tension can be alleviated in the IΛCDM+

∑

m

ν

model to some extent.
Sputtering of the beryllium tungsten alloy Be2W by deuterium atoms: molecular dynamics simulations using machine learned forces
Authors: Chen L. , Kaiser A. , Probst M. , Shermukhamedov S.
Published: November 2020

Material erosion and fuel retention will limit the life and the performance of thermonuclear fusion reactors. In this work, sputtering, reflection and retention processes are atomistically modeled by simulating the non-cumulative sputtering by deuterium projectiles on a beryllium–tungsten alloy surface. The forces for the molecular dynamics trajectories were machine learned from density functional theory with a neural network architecture. Our data confirms and supplements previous results for simulated sputtering rates. In the non-cumulative scenario we simulate, we did not observe reaction mechanisms leading to swift chemical sputtering. Thus, our sputtering rates at low impact energies are smaller than in comparable non-cumulative studies. The sputtering yields of the Be2W alloy are generally lower than those of pure beryllium. We found a strong dependence of the sputtering yield on the incident angle with an increase by about a factor of 3 for larger incident angles at 100 eV impact energy. In the pristine surface, a large majority of the impacting hydrogen projectiles at perpendicular impact remains in the surface.
Uncertainty and complementarity: two key notions in Paul Busch’s studies at the heart of quantum mechanics
Authors: Lahti Pekka
Published: November 2020

The problem of approximate joint measurement of complementary observables, like position and momentum, and the relevance of the uncertainty relations to that question were at the heart of the investigations of Paul Busch into the foundations of quantum mechanics. A good third of his published work dealt with this and closely related questions. This paper is an attempt to survey some of the steps taken in that research starting with Paul’s first papers on the subject matter in the early 1980’s and reaching its height in recent years.
Quantum incompatibility from the viewpoint of entanglement theory
Authors: Heinosaari Teiko
Published: November 2020

In this essay I discuss certain analogies between quantum incompatibility and entanglement. It is an expanded version of my talk presented at Mathematical Foundations of Quantum Mechanics in memoriam Paul Busch, held in York in June 2019.
Subspace constraints for joint measurability
Authors: Kiukas Jukka
Published: November 2020

The structure of quantum effects, positive operators of norm at most one, played a central role in the work of Paul Busch on uncertainty, complementarity, and joint measurability in quantum measurement theory. Here we focus on one aspect of this structure, called “strength of an effect along a ray” [Lett. Math. Phys. 47 329 (1999)], presenting a few observations not explicit in the existing literature. In fact, the strength function turns out to be useful for characterising positivity and complementarity of quantum effects of a suitable block matrix form, and for studying extensions of joint measurements defined on a subspace of codimension one.
Sequential measurements and entropy
Authors: Schmidt Heinz-Jürgen , Gemmer Jochen
Published: November 2020

We sketch applications of the so-called J-equation to quantum information theory concerning fundamental properties of the von Neumann entropy. The J-equation has recently be proposed as a sort of progenitor of the various versions of the Jarzynski equation. It has been derived within a general framework of sequential measurements that is slightly generalised here.
A relational perspective on the Wigner-Araki-Yanase theorem
Authors: Loveridge Leon
Published: November 2020

We present a novel interpretation of the Wigner-Araki-Yanase (WAY) theorem based on a relational view of quantum mechanics. Several models are analysed in detail, backed up by general considerations, which serve to illustrate that the moral of the WAY theorem may be that in the presence of symmetry, a measuring apparatus must fulfil the dual purpose of both reflecting the statistical behaviour of the system under investigation, and acting as a physical reference system serving to define those quantities which must be understood as relative.
Localizability and elementary particles
Authors: Jaeger Gregg
Published: November 2020

The well-definedness of particles of any kind depends on the limits, approximations, or other conditions that may or may not be involved, for example, whether there are interactions and whether ostensibly related energy is localizable. In particular, their theoretical status differs between its non-relativistic and relativistic versions: One can properly define interacting elementary particles in single-system non-relativistic quantum mechanics, at least in the case of non-zero mass systems; by contrast, one is severely challenged to define even these properly in the relativistic quantum field theories that now underlie the study of particle physics. Here, the impact of localizability on this status is reviewed in relation to the work of Paul Busch on positive operator valued measures that significantly probes the relevance of quantum unsharpness to it.
Comparison of entangling protocols in ABC-type spin chains
Authors: Estarellas Marta P , Spiller Timothy P , D’Amico Irene
Published: November 2020

In this contribution we consider an advantageous building block with potential for various quantum applications: a device based on coupled spins capable of generating and sharing out an entangled pair of qubits. Our model device is a dimerized spin chain with three weakly coupled embedded sites (defects). Three different entangling protocols were proposed for this chain in [1] and [2], one producing a Cluster state building block and two generating a Bell state, depending on the initial state injection. Here we compare the robustness of such protocols as quantum entangling gates against different types of fabrication (static energy fluctuations) and operation (timing injection delays) errors.
Paul Busch: Contributions to Quantum Theory
Authors: Colbeck Roger , Loveridge Leon , Weigert Stefan
Published: November 2020

A bibliography of Paul Busch’s scientific contributions is presented.
Accurate numerical determination of a self-preserving quantum vortex ring
Authors: Zuccher Simone , Caliari Marco
Published: November 2020

We compute simultaneously the translational speed, the magnitude and the phase of a quantum vortex ring for a wide range of radii, within the Gross–Pitaevskii model, by imposing its self preservation in a co-moving reference frame. By providing such a solution as the initial condition for the time-dependent Gross–Pitaevskii equation, we verify a posteriori that the ring’s radius and speed are well maintained in the reference frame moving at the computed speed. Convergence to the numerical solution is fast for large values of the radius, as the wavefunction tends to that of a straight vortex, whereas a continuation technique and interpolation of rough solutions are needed to reach convergence as the ring tends to a disk. Comparison with other strategies for generating a quantum ring reveals that all of them seem to capture quite well the translational speed, whereas none of them seems to preserve the radius with the accuracy reached in the present work.
An approximate method for evaluating the fracture process zone near mode II dynamic crack tip
Authors: Ji Chenmeng , Qi Chengzhi
Published: November 2020

Fracture process zone is the key for understanding the nonlinear fracture of quasi-brittle materials. Evaluation of the shape and size of fracture process zone near mode II dynamic crack tip is still a problem unsolved completely at present. The analytical methods for study on dynamic crack like integral transformation method and Wiener-hopf method are not easy to be used to calculate the stress fields near dynamic crack tip. So far the studies on fracture process zone near dynamic crack tip mostly focused on the experimental and numerical simulations. An approximate method for evaluating the shape and the size of fracture process zone is proposed and the feasibility of the new method is demonstrated by comparing with the results calculated based on the well-known stress fields. The shape and size of the fracture process zone near the mode II dynamic crack tip in dependence on crack propagation velocity are determined based on the approximate method. The results show that the areas of fracture process zone calculated based on the new method are nearly the same with the results calculated based on the well-known stress fields under plane stress condition and plane strain condition by the Von Mises criterion. The approximate method can provide a good reference for determination of the fracture process zone near mode II dynamic crack tip since no analytic method has been found for evaluating the fracture process zone near dynamic crack tip to the authors’ knowledge. The fracture process zone near mode II dynamic crack tip is distributed symmetrically with respect to crack plane and increases with the crack propagation velocity. The area of fracture process zone changes more rapidly when the Rayleigh wave velocity is approached. The areas of fracture process zone calculated under plane stress condition are bigger than these calculated under plane strain condition.
Stress distribution model of hard and brittle mud shale based on hydration damage
Authors: Liu Hailong , Xie Tao , Chen Zhuo , Lin Hai , Huo Hongbo
Published: November 2020

Hard and brittle shale developed in the middle and deep layers of the Bohai Sea cause severe challenges in drilling. During the drilling process, drilling fluid easily penetrates the rock along the microcracks, which leads to the deterioration of the mechanics and strength parameters of the rock. This consequently changes the stress distribution in the borehole wall. In addition, the fluid seepage hydrates the rock, which affects the relationship between the change in water content at any position and at any time in the rock mass is solved. The hydration equivalent of the elastic modulus is regarded as damage evolution, and a damage tensor considering hydration is introduced. A constitutive relationship of hard and brittle mud shale considering the effect of hydration damage is established, and the stress distribution around the well of the hard and brittle mudstone under non-uniform stress is solved by a semi-numerical and semi-analytical method. In addition, the influence law of hydration damage on the stress distribution around the well is analyzed. Taking an 8-1/2-inch section of an exploratory well in the Bozhong 19-6 gas field as an example, the stress distribution and collapse pressure analysis of the well bore revealed that after the section of the well was drilled for 100 h, the formation stiffness caused by hydration damage significantly decreased and borehole instability occurred inside the borehole wall. The risk of collapse was greater in the direction of the smallest in situ stress. The effect of hydration expansion on the stress distribution was limited, showing only a slight effect on the tangential stress near the well wall. The collapse of hard and brittle mud shale is mainly related to deterioration of the rock stiffness performance and strength parameters caused by hydration damage. The section incurred a short period of collapse, in which the maximum diameter expansion rate was equivalent to 5.9%, and the density of drilling fluid used on site was relatively low. Therefore, the density of the drilling fluid should be appropriately increased to enhance its sealing properties. The model reveals the hydration collapse mechanism of hard and brittle shale to a certain extent, which provides a theoretical basis for the safe and efficient drilling in similar formations.
A Modified Elastic Plate Model for the Thickness of Reinforced Soil of Shield Tunnel End
Authors: Tingshuai Sun , Kezhi Song , Teng Huang , Junhao Luo , Sukun Zhuang
Published: November 2020

The soil body of the shield end could be unstable and should be reinforced, and its thickness affects the stability and economy of engineering. The existing elastic thin plate model was too conservative for design. A modified elastic plate model was proposed for the calculation. Based on elastic finite element analysis data, optimal fitting was conducted for the proposed elastic model, and the coefficients of the model were obtained. A case study showed that the elastic thin plate model is too conservative when used to calculate the thickness of the reinforced soil body. The actual reinforced thickness in practice is between the values of the elastic thin plate model and the modified elastic plate model.
Real-time drilling rate prediction method of reaming while drilling based on mechanical specific energy
Authors: Ma Guoxin , Du Xu , Chen Xuyue , Hong Yuqun , Wang An , Zhang Fengxi
Published: November 2020

Reaming while drilling (RWD) is a drilling technique that uses a reamer and a pilot bit to expand the size of an open hole segment to be larger than the inner diameter of an upper casing string while fully drilling, especially in deep wells. This technique reduces the number of trips and is highly efficient and widely used in deep wells, ultra-deep wells, small clearance wells, and side-drilling and complex well conditions. However, in the actual operation process, the mismatching between the pilot bit and reamer often leads to slippage, string vibration, and low-quality borehole.In this paper, based on the mechanical specific energy model and the RWD weight distribution model, combined with the drilling weight, torque, and formation confined compressive strength at the interface of the pilot bit and reamer, a real-time rate of penetration (ROP) prediction model suitable for RWD is derived. Through the analysis of the downhole condition of the RWD operation, reasonable drilling parameters are determined and a set of real-time RWD performance prediction and optimization algorithm is proposed.Studies show that during the RWD operation, the size of the pilot bit and reamer and the shape of the cutter have an enormous influence on ROP. When drilling in different formations, the excellent cooperation among the pilot bit, reamer, and formation is the key to improve ROP and bottom hole assembly stability. How to optimize the bit and reamer to drill with the same ROP and predict the ROP is the focus of this paper.Field logging data test the ROP prediction model and real-time optimization method, and the results indicate that the ROP prediction model has high precision, small error, and high timeliness, which can fully meet the requirements of field engineering. This model can guide the selection of the bit, reamer, and drilling parameters in RWD, which is of considerable significance to RWD.
Estimation of micromechanical strength of brittle rocks under compression
Authors: Xiaozhao Li , Chengzhi Qi , Zhushan Shao
Published: November 2020

A unified micro-macro method is proposed to estimate short-term, long-term, and shear strength of rocks under compression. This method is formulated by combining the wing microcrack model, subcritical crack growth law, Mohr–Coulomb failure criterion, and crack–strain relation. The short-term strength is predicted by the theoretical stress–strain relationship caused by microcrack growth. The stress states for a given creep failure time and long-term strength are analyzed using the proposed theoretical three-level creep evolution relationship. Moreover, the shear strength is reviewed by the proposed predictive method for shear failure. Correlation of short-term, long-term, and shear strength is closely analyzed, and the effects of crack size, crack friction, and fracture toughness on short-term, long-term, and shear strength are discussed.
Analysis of the effect of dam impoundment at the Baihetan site using coupled fluid-mechanical elasto-plastic simulations
Authors: Hou Jin , Xu Jianrong , Meng Guotao , Chu Weijiang , Cheng Zhao , Detournay Christine , Cundall Peter
Published: November 2020

Contractional valley deformation is a phenomenon quite specific to high dams in the southwest of China. Numerical simulations with coupling of stress and seepage were performed to study the mechanisms of valley deformation after impoundment and to determine whether and when valley contraction could develop at the Baihetan site. The initial generic study highlighted two competing mechanisms, a “Mattress Effect” and a “Swelling Effect”, associated with dam impoundment. The comprehensive FLAC3D model incorporates detailed rock mass property values, a grout curtain, an impounding plan, and the drainage volumes. The large-scale coupled seepage-mechanical simulations show that the convergence mechanism is activated by fluid diffusion in the valley. At sites upstream and up to about 400 m downstream of the dam, the valley deformation occurs shortly after the impoundment water level is raised; this behaviour reflects the impact of the mattress effect caused by the weight change of the standing impoundment water. However, deformation also occurs during periods when the impoundment level remains the same; this behaviour is caused by the large-scale water seepage associated with pore-pressure changes under and around the dam in the valley banks. The maximum convergence along the monitoring lines does not exceed 5 cm in the simulations, where affected by the presence of faults and bedding planes.
Rock Breaking Mechanism and Drilling Performance of Harmonic Vibro-Impact Drilling
Authors: Li Siqi , Tian Shenglei , Li Wei , Huan Zhao , Ling Xin , Zhuolun Li
Published: November 2020

An improved model of displacement response of rock considering damping is proposed and the energy response model is further presented. Then, the rock breaking mechanism under harmonic vibro-impact is investigated based on the displacement response and energy response. Furthermore, the numerical simulations are conducted to analyze the principal stress of rock and drilling characteristics in axial and torsional directions under harmonic vibro-impact. Finally, the performance of the harmonic vibro-impact drilling technology is verified by the field application. Based on the analysis undertaken, it can be concluded that the periodic harmonic impact force makes the rock subjected to more tensile stress and continuous damage accumulation, which causes the efficient rock breakage. What’s more, the harmonic vibro-impact can also alleviate the stick-slip effect and bounce phenomenon of drill bit to a certain extent. Our investigations confirm that the harmonic vibro-impact can achieve the purpose of rate of penetration (ROP) improvement.
Experimental study on creep characteristics of anchorage rock with cracks under cable pulling condition
Authors: Sun Xiaoming , Cui Li , Hu Jiangchun , Zhang Yong
Published: November 2020

The creep characteristics of anchorage rock mass with cracks are the basis for the stability control of anchorage rock and current research hotspots. Relying on the Muzhailing soft rock tunnel project, the anchorage segment is taken as the research object, numerical simulation as the main method is used to systematically study the instantaneous and creep mechanical properties of rock with different crack combinations under the condition of cable pulling, the results show that: 1) Under instantaneous pulling conditions, the effective anchorage range is funnel-shaped, and the maximum value of the maximum shear stress(MSS) appears at the front end of the anchorage rock, while under long-term pulling conditions, the effective anchorage range is uniform along the cable axis distribution, the maximum value of the MSS appears at the end of the cable; 2) Cracks with specific combinations can expand the anchorage range along the axial direction and slow down the shear failure at the front end of the anchorage rock, which is especially obvious for the anchorage rock under instantaneous pulling conditions 3) The optimal number of cracks and the specific area can be obtained by the "virtual intersection method". For the instantaneous MSS and the creep MSS, there is an obvious 45° crack angle effect. The research results are intended to provide a reference for further probing the creep mechanism of anchorage rock with complex crack combinations.
A simple elastoplastic dynamic constitutive model of saturated structural soft clay
Authors: Feng Shuangxi , Lei Huayang , Qi Ziyang
Published: November 2020

The dynamic constitutive relation of soil is widely applied to the ground design of marine structure and infrastructure in offshore geotechnical engineering. Increasing evidence from marine geotechnical design has shown that the traditional dynamic constitutive model has uncertain theories, many parameters, and complexity. Therefore, it is urgent to overcome these limitations and develop a simple and practical elastoplastic dynamic constitutive relation for the saturated structural soft clay. A simple dynamic constitutive relation with 5 parameters was proposed in this study, which can reflect the strain accumulation, hysteretic characteristics and cyclic degradation of the stress-strain for structural soft clay. First, the Drucker-Prager model was selected as the bounding surface, hardening modulus equation was established by the hardening law, interpolation function and structural strength coefficient. Then, the incremental stress-strain relationship was derived based on the incremental theory. The UMAT subroutine was compiled by FORTRAN language. Finally, the cyclic triaxial test and numerical simulation were carried out, and the stress-strain relationship was analyzed. The research results showed that the test results were in good agreement with the prediction results of the model.
Impact of reservoir heterogeneity on fluid injection-induced fault slip: insights from numerical simulation
Authors: Wang Zineng , Huang Xin , Huang Zhaoqin , Wang Xiaoguang , Lei Qinghua
Published: November 2020

In order to meet the growing energy demand worldwide, the technology of hydraulic fracturing for shale gas extraction has been rapidly developed and applied in recent years. However, man-made fluid injection has also caused several problems of high societal concern such as induced earthquakes. The focus of this paper is on the process of induced fault activation in shale reservoirs caused by hydraulic stimulation activities. We constructed a two-dimensional numerical model representing the horizontal cross-section of a faulted reservoir and simulated important coupled hydro-mechanical processes during fluid injection. We parameterized our model with the site investigation data of an actual shale gas project including in-situ stress, rock properties and injection protocol, etc. We represented the natural fault zone as a geological composite involving a fault core and a damage zone consisting of a set of subsidiary fractures parallel to the fault strike. We coupled the solid deformation and fault displacement with Darcy-type fluid flow based on poroelasticity principles and hydro-mechanical constitutive relationships. The heterogeneous nature of the permeability of the shale formation is mimicked by a random field model governed by a log-normal probability density function and directional correlation lengths, such that we can explore the impact of reservoir heterogeneity on the fault slip behaviour. In addition, we also studied the effects of fault length, dip angle and injection point-to-fault distance on the fault slip. Specifically, we analysed the link between fault slip and fluid flow field, permitting the capture of fluid movement in the heterogeneous faulted reservoir, the temporal and spatial evolution of preferential flow channels and their consequences on induced fault slip. The results of this research have important implications for understanding the triggering processes and mechanisms of fault slip during shale gas exploitation as well as many other injection-related engineering activities.
Numerical simulation on post-earthquake debris flows: A case study of the Chutou gully in Wenchuan, China
Authors: Liu Bo , Hu Xiewen , He Kun , Wu Mingyang , Huang Tao
Published: November 2020

Since the 2008 Wenchuan earthquake, post-earthquake debris flows have severely threatened people’s lives and the safety of public transit facilities, making particularly crucial to understand their formation mechanism. We focused on the Chutou gully debris flow and analyzed its formation mechanism based on field investigations and satellite images. The main inducing factor of this debris flow was a continuous heavy rainfall that exceeded the threshold of the study area: this, combined with the large amount of loose material created by the earthquake, dramatically promoted the volume and hazard degree of the debris flow. The three-dimensional debris flow simulation software RAMMS, based on an improved Voellmy–Salm fluid model, was used to simulate the movement process of the Chutou gully debris flow. The calibrated Coulomb friction (μ) and viscous turbulent friction (ξ) coefficients in the study area were 0.225 and 180 m/s2, respectively. The simulation results revealed the post-earthquake debris flow mechanism in terms of flow height, velocity, flow rate, and deposition area. The results of the numerical simulation were in good agreement with those of the field investigations. In particular, it was found that the peak flow of debris flow upstream of the Chutou gully was shorter in duration than the one upstream; however, due to the convergence of the branch gully, the downstream peak flow of debris flow increased significantly, while a large amount of solid material stranded downstream of the channel. Notably, this process is prone to occur again. This study proposes a new post-earthquake debris flow evaluation method, and its results are of reference value for the design of debris flow prevention engineering in meizoseismal areas.