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During shale gas exploration, natural fractures in shale reservoirs may be induced by cyclic loads frequently encountered in different geological processes, including tectonic movements, seismic actions, and artificial construction interference (vertical and horizontal wells drilling and cyclic hydraulic fracturing). In this paper, experiments and PFC2D simulations are conducted to investigate the mechanical response and mechanism of shale specimens under cyclic loading and unloading. Using the experimental and simulation results, the strength and deformation characteristics and strain energy and damage evolutions during the cyclic loading-unloading process are quantified and analyzed. The damage variable characterized by plastic deformation, deformation modulus, and dissipated energy is thoroughly analyzed. Based on the PFC2D simulation, the micro-crack distribution and evolution are further studied, and the results can reflect the experiments well and reveal the damage mechanism under cyclic loading. Furthermore, the experiments and simulations indicate that the degree of fatigue damage is closely related to the number of cycles the specimens undergo, and a small number of cycles may not have a distinct effect on the strength.

The permeability of shale reservoirs is an important parameter in evaluating the feasibility of shale gas commercial exploitation. The influence of structural anisotropy, bedding planes, and effective stress is of great significance to the permeability of shale reservoirs; thus, a further study on the permeability of shale rock containing bedding planes and fractures is necessary. In this paper, to investigate the gas conductivity of shale rock in different bedding directions and fracture surfaces, permeability tests were conducted on the intact specimens with different bedding inclinations and specimens containing fractures of Longmaxi shale. The pulse decay method is adopted in the determination of the intact shale specimen, and the steady-state method is adopted to measure the permeability of fractured shale specimen. Combined with experiments and theoretical analysis, the anisotropic characteristics of the permeability of intact shale specimens and the permeability of fractured specimens under the applying of effective stress are studied. The permeability of the two kinds of shale specimens decreased exponentially with the increase in effective stress. The main controlling factors on permeability were studied, besides, the flow characteristic of fluid inside the rock with bedding plane or sandwich structures were described. Furthermore, a new model was proposed to describe the anisotropy of rock permeability characteristics. As for shale specimen contains fracture, the function between its equivalent permeability and fracture permeability was derived, as well as the function between equivalent permeability and effective stress, and the function between fracture permeability and effective stress.

Atomically dispersed iron–nitrogen–carbon (Fe–N–C) catalysts have emerged as the most promising alternative to the expensive Pt-based catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs), however suffer from low site density of active Fe-N4 moiety and limited mass transport during the catalytic reaction. To address these challenges, we report a three-dimensional (3D) metal–organic frameworks (MOF)-derived Fe–N–C single-atom catalyst. In this well-designed Fe–N–C catalyst, the micro-scale interconnected skeleton, the nano-scale ordered pores and the atomic-scale abundant carbon edge defects inside the skeleton significantly enhance the site density of active Fe-N4 moiety, thus improving the Fe utilization in the final catalyst. Moreover, the combination of the above mentioned micro- and nano-scale structures greatly facilitates the mass transport in the 3D Fe–N–C catalyst. Therefore, the multiscale engineered Fe–N–C single-atom catalyst achieves excellent ORR performance under acidic condition and affords a significantly enhanced current density and power density in PEMFC. Our findings may open new opportunities for the rational design of Fe–N–C catalysts through multiscale structural engineering.

Recently, the CDF collaboration reported a new measurement of the $W$ boson mass $M_W = 80.4335 \pm 0.0094$ GeV, which shows a $\sim 7\sigma$ deviation from the standard model prediction $80.3545 \pm 0.0057$ GeV obtained by the electroweak (EW) global fit. This deviation can be explained by new physics generating moderate EW oblique parameters $S$, $T$, and $U$. In this work, we use the loop corrections induced by some extra EW multiplets to explain the CDF $M_W$ anomaly. The lightest neutral particle in the multiplets can also serve as a candidate of cold dark matter (DM). We consider two such models, namely singlet-triplet scalar DM and singlet-doublet fermionic DM models, and perform numerical scans to find the parameter points accounting for the $M_W$ anomaly. The constraints from the correct DM thermal relic density and direct detection are also taken into account. We find the parameter points simultaneously interpreting the $M_W$ anomaly and satisfying the DM requirements in the former model, but do not find such parameter points in the latter model., Comment: 23 pages, 5 figures; v3: matches version accepted for publication in Phys. Rev. D

International audience; Abstract In order to reveal the nature of dark matter, it is crucial to detect its non-gravitational interactions with the standard model particles. The traditional dark matter searches focused on the so-called weakly interacting massive particles. However, this paradigm is strongly constrained by the null results of current experiments with high precision. Therefore there is a renewed interest of searches for heavy dark matter particles above TeV scale. The Large High Altitude Air Shower Observatory (LHAASO) with large effective area and strong background rejection power is very suitable to investigate the gamma-ray signals induced by dark matter annihilation or decay above TeV scale. In this document, we review the theoretical motivations and background of heavy dark matter. We review the prospects of searching for the gamma-ray signals resulted from dark matter in the dwarf spheroidal satellites and Galactic halo for LHAASO, and present the projected sensitivities. We also review the prospects of searching for the axion-like particles, which are a kind of well motivated light pseudo-scalars, through the LHAASO measurement of the very high energy gamma-ray spectra of astrophysical sources.

At present, shale gas plays a significant role in hydrocarbon reservoirs. Hydraulic fracturing is generally employed in the exploration and exploitation of shale gas. Economic and efficient hydraulic fracturing, known as volume fracturing, is largely associated with formation characteristics, including anisotropy and brittleness in rocks. Further research on the mechanical properties of rocks, particularly the anisotropy and brittleness behavior of shale, using hydraulic fracturing would be of practical significance. In this study, shale specimens were collected from an outcrop of the lower Silurian Longmaxi formation at Sichuan Basin in southwestern China, which is the most significant exploration area for unconventional gas in China. To better understand the size, type, and shape of brittle minerals, the matrix type (and rock texture), mineral composition, and microstructure of the shale matrix were tested through X-ray diffraction analysis and scanning electron microscopy. Furthermore, the anisotropic behavior of shale specimens, including strength, deformation, and failure behaviors, was tested and analyzed under conventional triaxial compression. In addition, the brittleness characteristics of shale specimens at different bedding inclinations under different confining pressures were analyzed based on the stress–strain curve characteristic and energy balance. Different brittleness indices, including a new one proposed in this study, were used to evaluate the brittleness of shale. The impacts of anisotropy and confining pressure on brittleness were discussed in detail. When compared with other brittleness indices, the proposed brittleness index demonstrates improved effectiveness and reflects the impact of confining pressure on brittleness significantly well. The relationship between brittleness and the failure mode was revealed using the new brittleness index, and the decreasing order of brittleness was concluded as follows: tensile splitting along bedding plane mode > tensile splitting through bedding plane mode > shear along bedding plane mode > shear through bedding plane mode.

Metallic materials with unique surface structure have attracted much attention due to their unique physical and chemical properties. However, it is hard to prepare bulk metallic materials with special crystal faces, especially at the nanoscale. Herein, we report an efficient method to adjust the surface structure of a Cu plate which combines ion implantation technology with the oxidation-etching process. The large number of vacancies generated by ion implantation induced the electrochemical oxidation of several atomic layers in depth; after chemical etching, the Cu(100) planes were exposed on the surface of the Cu plate. As a catalyst for acid hydrogen evolution reaction, the Cu plate with (100) planes merely needs 273 mV to deliver a current density of 10 mA/cm

We propose that the interaction between the axionlike particles (ALPs) and photons can be a possible origin of optical circular polarization (CP) in blazars. Given that there is no definite detection of optical CP at $\sim0.1\%$ level, a rough limit on ALP-photon coupling can be obtained, specifically $g_{a\gamma}\cdot B_\mathrm{T0}\lesssim7.9\times10^{-12}~\mathrm{G\cdot GeV}^{-1}$ for $m_{a}\lesssim 10^{-13}~\mathrm{eV}$, depending on the magnetic field configuration of the blazar jet. Obviously, for the blazar models with a larger magnetic field strength, such as hadronic radiation models, this constraint could be more stringent. We also perform a dedicated analysis of the tentative observations of optical CP in two blazars, namely 3C 66A and OJ 287, and we find that these observations could be explained by the ALP-photon mixing with $g_{a\gamma} \sim 10^{-11}~\mathrm{GeV}^{-1}$. As an outlook, our analysis can be improved by further research on the radiation models of blazars and high-precision joint measurements of optical CP and linear polarization., Comment: 15 pages, 9 figures, 4 tables

As a well-motivated dark matter candidate, axions can be detected through the axion-photon resonant conversion in the magnetospheres of magnetic white dwarf stars or neutron stars. In this work, we utilize Omega Centauri, which is the largest globular cluster in the Milky Way and is suggested to be the remnant core of a dwarf galaxy, to probe the axion dark matter through radio signals that originate from all the neutron stars and magnetic white dwarf stars in it. With 100 hours of observation, the combination of SKA phase 1 and LOFAR can effectively probe the parameter space of the axion-photon coupling $g_{a\gamma}$ up to $10^{-14}\sim 10^{-15}~\text{GeV}^{-1}$ for the axion mass range of $0.1\sim 30 ~\mu\text{eV}$. Depending on the choice of neutron star evolution model, this limitation is two or three and a half orders of magnitude higher than that of the single neutron star or magnetic white dwarf., Comment: 22 pages, 8 figs, and 2 tables; Phys Rev D accepted version

Axion as one of the promising dark matter candidates can be detected through narrow radio lines emitted from the magnetic white dwarf stars. Due to the existence of the strong magnetic field, the axion may resonantly convert into the radio photon (Primakoff effect) when it passes through a narrow region in the corona of the magnetic white dwarf, where the plasma frequency is equal to the axion mass. We show that for the magnetic white dwarf WD 2010+310, the future experiment SKA phase 1 with 100 hours of observation can effectively probe the parameter space of the axion-photon coupling gaγ up to ∼10−12 GeV−1 for the axion mass range of 0.2∼3.7 μeV. Note that in the low mass region (ma≲1.5 μeV), the WD 2010+310 could give greater sensitivity than the neutron star RX J0806.4-4123.

FeTe

In this paper, the strength and deformation behavior of transversely isotropic composite rock-like material, which consists of a hard rock-like material and a weak rock-like material, are first investigated under different confining pressures by using a rock triaxial testing system. The triaxial compression results show that the composite rock-like material shows distinct anisotropy, the strength shows a “U” type variation with respect to the inclination angle, and the apparent friction angle value and cohesion value show dispersion with respect to the inclination angle. With the advance of scientific instrumentation, X-ray computed tomography (CT) scanning has been used as a powerful inspection tool and has been applied to many fields for non-destructive structure and failure analysis. After the compression tests, a Nanotom 160 high-resolution micro-CT was employed to investigate the failure mechanism of transversely isotropic composite rock-like material on the micro-level. The 3D volume renders are in good agreement with the actual surface crack photographs of transversely isotropic composite specimens, which demonstrating that X-ray micro-CT scanning can be used to explore the damage of rock-like material. The internal crack distribution and damage can be clearly observed from the vertical and horizontal cross-section images of 3D volume renders. It further reveals that the failure mode of transversely isotropic composite rock-like specimens is transformed from tensile failure at low inclination angles to shear slippage at medium inclination angles. The impact of confining pressure on the failure mode and crack distribution from the 3D volume renders, which is also discussed, reveals that the mechanical properties of hard and weak rock materials are the key to control the crack distribution with increasing confining pressure.

Bedding planes or layers can have a serious effect on the mechanical behaviour of shale rock. Fractures occurring along bedding planes form a fracture network in shale hydraulic fracturing; thus, the tensile strength and fracture mode are important for hydraulic fracturing design. In this research, shale disk specimens are prepared and analysed under Brazilian test conditions. During the test, a 3D digital image correlation system (DIC) is employed to capture surface deformation, and an AE sensor and strain observation system are, respectively, used to record the AE event and central strain of the shale disk during the failure process. A new inherently anisotropic model is established with a banded-particle model and smooth joint model using the particle flow code (PFC2D). The laboratory test result shows that the Brazilian tensile strength (BTS) value decreased gradually along with bedding inclination, which corresponds to a trend of the decrease of the strength over the entire interval, but it is a rather systematic decrease, approximating a linear variation. By considering the specimen after failure, three types of fracture patterns are observed: arc fracture (AF) through outside the central part, central fracture along the loading direction (LA) and mixed fracture patterns of the two. The DIC and central strain observation systems confirm that the split fractures do not always propagate along the diametrical loading direction, which means that the traditional isotropic elastic theory no longer works for layered shale. The micro-level failure behaviour and mechanism are analysed by PFC simulation. The PFC simulation reveals that the rock matrix tensile fracture and shear fracture along bedding plane are the main fracture pattern of shale disk specimens under the Brazilian test. The bedding inclination and interlayer bonding force play a very important role in the anisotropic behaviour of the shale.

This paper presents a discrete element modeling (DEM) with particle flow code 2D (PFC2D) for simulating the mechanical behavior of artificial transversely isotropic rock under uniaxial compression. The DEM model is established with the approach of synthetic rock mass (SRM) modeling, i.e. embedding joints of weak plane to the bonded particle model (BPM) of intact rock for simulating the joint rock. Sensitivity of joint micro-parameters is analyzed to provide references for calibrating micro-parameters of artificial transversely isotropic rock in PFC2D. The uniaxial compression test of DEM model displays U-shape variation of uniaxial compressive strength (UCS) along with bedding angle which is same to that of artificial transversely isotropic rock, a non-ignorable diversity in UCS value compared with the artificial transversely isotropic rock is also presented, while the normalized values of them are of well-matching. The obtained information of type, counts and distribution of micro-crack in PFC2D after DEM model failure indicate a remarkable impact on failure behavior of transversely isotropic rock, which cannot be surveyed in laboratory test. Farther more, the bond force field and particle displacement field reveal that separation zones caused by tension arise at bedding angle below 45°, while the shear zone occurs at bedding angle above 45°.

In natural rock masses, joints or flaws usually occur in sets that are more or less parallel and regularly spaced. Many problems occurred in tunnel engineering mainly result from the failure of joints or faults because they are weaker compared with the rock matrix. Therefore, it is important to study the interaction of joints with the tunnel, as well as the interactions between themselves. In this research, rock-like specimens of non-persistent jointed rock masses containing a circular hole are prepared and tested under uniaxial compression. The test results show that the peak strength and elastic modulus of the non-persistent jointed rock specimens display a “U” type variation with respect to the joint inclination. The multiple joints can be simplified and regarded as a combination of three types of two-joints relative location, and the crack coalescence types and failure modes are in accordance with the classic crack coalescence types of the two joints. The crack coalescence between the joints and a circular hole can be categorized into three modes with respect to the joint inclination. The Discrete Element Method (DEM) model of the jointed rock specimen that contains a circular hole is established in particle flow code 2D (PFC2D). The simulation results show a good agreement with the experiment results. Furthermore, the displacement fields at the crack zones reveal that the coalescence of joints is mainly caused by tensile cracks and that shear slipping cracks easily occur at the sidewalls of the circular hole. By comparing the parallel-bond force fields in jointed models containing a circular hole with no a circular hole, it is shown that the circular hole can change the stress state at the top and bottom. The joints at a joint inclination of 90° have the smallest effect on the mechanical behavior of the rock specimen.

To investigate the role of fissure angle and heat treatment temperature on the mechanical properties and deformation failure behavior, uniaxial compression tests were carried out on granite specimens containing a single fissure. Using stress–strain curves, the peak strength, peak strain, and elastic modulus of the one-fissured granite specimens were analyzed in detail. The mechanical parameters are closely related to the fissure angle and the high temperature. As the fissure angle increases from 0° to 90°, the peak strength and elastic modulus first decrease and then increase, while the peak strain increases slowly. However, the peak strength and elastic modulus first increase and then decrease, while the peak strain first decreases and then increases with increasing treatment temperature. During the experiments, the crack evolution process and acoustic emission (AE) counts were obtained using real-time photography and the AE monitoring technique. In the granite specimens containing a pre-existing fissure, large AE counts are clearly observed before the peak strength, which indicates crack initiation and propagation. The accumulated AE count first increases slowly, but is followed by a sharp increase, with increasing deformation. The AE events in the one-fissured specimen also depend on the heat treatment temperature. As the temperature increases, the rate of increase of the accumulated AE count curve is reduced. Finally, using a digital image correlation method, the full fields of surface deformation were obtained for the entire testing process. In addition, the local strain around the pre-existing fissure was measured using strain gauges. The full strain field and local strain concentration are discussed to describe the fracture mechanism of brittle granite.

In this work, we investigate the axion-like particle (ALP)-photon oscillation effect in the spectra of the blazar Markarian 421 (Mrk 421) using 4.5 years of the Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ) and Fermi Large Area Telescope (Fermi-LAT) data. These data are collected during the common operation time, which cover ten activity phases of Mrk 421. No significant ALP-photon oscillation effect is confirmed. On the other hand, not all the observations of the ten phases can be individually used to set the 95% confidence level ($\rm C.L.$) constraint on the ALP parameter space. However, the constraint can be significantly improved if the analyses for the ten phases are combined. We find that the upper limit at 95% $\rm C.L.$ on the ALP-photon coupling $g_{a\gamma}$ set by the ARGO-YBJ and Fermi-LAT observations of Mrk 421 is within $\sim [2\times 10^{-11}, \ 6\times 10^{-11}] \rm \, GeV^{-1}$ for the ALP mass of $\sim 5\times 10^{-10}$ eV $\lesssim m_a \lesssim 5\times 10^{-7}\, \rm eV$., Comment: 10 pages, 8 figures

Construction of 2D transition metal dichalcogenide (TMD)-based epitaxial heterostructures with different compositions is important for various promising applications, including electronics, photonics, and catalysis. However, the rational design and controlled synthesis of such kind of heterostructures still remain challenge, especially for those consisting of layered TMDs and other non-layered materials. Here, a facile one-pot, wet-chemical method is reported to synthesize Cu

New physics could be explored through loop effects by the precision measurements at the Circular Electron Positron Collider due to its clean collision environment and high luminosity. In this work, we focus on two dark matter models that involve additional electroweak fermionic multiplets. We calculate their one-loop corrections to five processes, i.e. $e^+e^- \to \mu^+\mu^-, ~Zh, ~ZZ, ~W^+W^-$, and $Z\gamma$, and investigate the corresponding signatures at CEPC with the projected sensitivity. We find that the detectable parameter regions of these processes are complementary. The combined analysis shows that the mass of dark matter $m_{\chi^0_1}$ in these two models can be probed up to $ \sim 150~\mathrm{GeV}$ and $\sim 450$ GeV at a 95\% confidence level, respectively., Comment: 15 pages, 5 figures

The TeV $\gamma$-ray halo around the Geminga pulsar is an important indicator of cosmic-ray (CR) propagation in the local zone of the Galaxy as it reveals the spatial distribution of the electrons and positrons escaping from the pulsar. Considering the intricate magnetic field in the interstellar medium (ISM), it is proposed that superdiffusion model could be more realistic to describe the CR propagation than the commonly used normal diffusion model. In this work, we test the superdiffusion model in the ISM around the Geminga pulsar by fitting to the surface brightness profile of the Geminga halo measured by HAWC. Our results show that the chi-square statistic monotonously increases as $\alpha$ decreases from 2 to 1, where $\alpha$ is the characteristic index of superdiffusion describing the degree of fractality of the ISM and $\alpha=2$ corresponds to the normal diffusion model. We find that model with $\alpha, Comment: 11 pages, 4 figures, 1 table

We investigate the solar modulation effect with the long time cosmic ray proton and helium spectrum measured by AMS-02 on the time scale of a Bartels rotation (27 days) between May 2011 and May 2017. The time-span covers the negative heliospheric magnetic field polarity cycle, the polarity reversal period and the positive polarity cycle. The unprecedented accuracy of AMS-02 observation data provide a good opportunity to improve the understanding of the time dependent solar modulation effect. In this work, a two-dimensional solar modulation model is used to compute the propagation of cosmic rays in the heliosphere. Some important ingredients of the model which reflect the global heliospherical environment are taken from the observations. The propagation equation is numerically solved with the pubic Solarprop code. We find that the drift effect is suppressed during the high solar activity period but nearly recovered in the first half of 2017. The time-dependent rigidity dependence of the mean free path is critical to reproduce the observations between August 2012 and October 2015., 23 pages, 3 tables, 8 figures

This study prepared transversely isotropic rock-like specimens in three groups of layer thickness ratios, alternating with two kinds of rock-like materials. The conventional triaxial compression tests confirm mechanical difference of the two rock-like materials. The velocities of ultrasonic wave (longitudinal wave VP) are measured for each transversely isotropic rock-like specimen before uniaxial compressive test, the results present an anisotropic behavior with the degree of longitudinal wave velocity anisotropy (VPmax/VPmin) of the three groups of transversely isotropic rock-like specimens are 1.44, 1.08 and 1.09, respectively. The uniaxial compression test indicates that the strength variation of the three groups of transversely isotropic rock-like specimens are “U-shaped”, with the degree of strength anisotropy (σcmax/σcmin) are 2.35, 4.42 and 2.08, respectively. An empirical failure criterion introduced by Jaeger and modified by Donath predicts the failure strength of transversely isotropic rock-like specimen well. The acoustic emission result shows that the AE ringing count is significant to the surface crack extending. The failure pattern of transversely isotropic rock-like specimens can be classified into one of the following three modes: (a) tensile-split along the core axes when small bedding angle (0°, 15°, 30°), (b) shear-sliding along the bedding plane when major bedding angle (45°, 60°, 75°) and (c) split along the vertical bedding plane when bedding angle of 90°.

The hardening and softening features in the DAMPE proton spectrum are very likely to be originated from a nearby supernova remnant (SNR). The proton spectrum from the nearby SNR is required to be very hard below $\approx10$ TeV. To reproduce this feature, we illustrate that anomalously slow-diffusion zone for cosmic rays (CRs) must be existed in the local interstellar medium (ISM) after also taking the dipole anisotropy of CRs into account. Assuming that the diffusion coefficient is homogeneous in the nearby ISM, we show that the diffusion coefficient is constrained to the magnitude of $10^{26}$ cm$^2$ s$^{-1}$ when normalized to 1 GeV, which is about 100 times smaller than the average value in the Galaxy. We further discuss the spatial distribution of the slow diffusion and find two distinct possibilities. In one case, the SNR is several hundred of parsecs away from the solar system, meanwhile both the SNR and the solar system are required to be included in a large slow-diffusion zone. The homogeneous diffusion belongs to this case. In the other case, the SNR is very close with a distance of $\sim50$ pc and the slow-diffusion zone is only limited around the SNR. The required diffusion coefficient is further smaller in the latter case. This work provides a new way of studying the CR diffusion in the local ISM., 8 pages, 5 figures, 1 table

We investigate the axion like particle (ALP)-photon oscillation effect in the high energy $\gamma$-ray spectra of PG 1553+113 and PKS 2155-304 measured by Fermi-LAT and H.E.S.S.. The choice of extragalactic background light (EBL) model, which induces the attenuate effect in observed $\gamma$-ray spectra, would affect the ALP implication. For the ordinary EBL model that prefers a null hypothesis, we set constraint on the ALP-photon coupling constant at 95% C.L. as $g_{a\gamma}\lesssim 5\times 10^{-11} ~\rm{GeV}^{-1}$ for the ALP mass $\sim 10$ neV. We also consider the CIBER observation of the cosmic infrared radiation, which shows an excess at the wave wavelength of $\sim 1~\mu$m after the substraction of foregrounds. The high energy gamma-rays from extragalactic sources at high redshifts would suffer from a more significant attenuate effect caused by this excess. In this case, we find that the ALP-photon oscillation would improve the fit to the observed spectra of PKS 2155-304 and PG 1553+113 and find a favored parameter region at 95% C.L.., Comment: 8 pages, 7 figures, 1 table

The geometry and orientation of cavities in a rock mass has a significant influence on the failure mechanism and fracture propagation. The theoretical study of these behaviors is of great importance to enable fundamental understanding of unstable failure in rock mechanics. A very limited number of experimental studies have been conducted for sandstone specimens containing oval cavities. Sensitive parameters include the short axis (b) to long axis (a) ratio. Here, we enhance the present understanding of crack coalescence behavior around an oval cavity by applying uniaxial compression tests to sandstone cores containing manually inserted single oval cavity, combined with photographic and acoustic emission monitoring. The b:a ratio was varied from 1/4 to 1/1, thus the cross-sectional cavity shape evolved from oval to a fully circular opening. The experimental results showed that the stress-strain curves of specimens containing cavities exhibited multiple stress reductions prior to peak strength, which led to a sudden increase in the accumulated AE count-rate. As the b:a ratio was increased, the uniaxial compressive strength, crack initiation stress and peak strain of cavity specimens all decreased linearly. Tensile fractures, shear fractures, and compound shear-tensile fractures were all observed to emanate from the cavities. Compared to the intact specimen, the failure mode of cavity specimens comprised a mixture of tensile and shear cracks, emanating from the tips (or surfaces) of the oval cavity. For specimen with a cavity angle of 45°, when the b:a ratio was below 1/2, no tensile crack from the surface of short axis was initiated, whereas tensile crack was observed clearly after b:a = 1/2. This study not only increases our understanding of mechanical failure behavior in fractured rock, but also enhances our knowledge of underground tunneling or roadway stability.

The Fermi-LAT detects no significant anisotropy of the cosmic-ray (CR) electrons and positrons ($e^-+e^+$) with seven years of data, which provides the strongest restriction to the $e^-+e^+$ anisotropy up to now. As next generation CR observatory, HERD is expected to have a better capability of anisotropy detection than Fermi-LAT. In this paper, we discuss several models aimed to explain the AMS-02 data by the present and future anisotropy measurements. We find that the upper limits of Fermi-LAT disfavor Vela SNR as the dominant source in sub-TeV, while other cases that remain safe under the constraint of Fermi-LAT are expected to be distinguished from each other by HERD. We then discuss the possibilities of remarkable TeV spectral features, and test the corresponding anisotropies. We find the conditions under which the TeV model can have a prominent spectral feature and avoid the constraint of Fermi-LAT at the same time. Furthermore, the expected performance of HERD is sensitive enough to detect the anisotropies of all these TeV models, and even for the case of a featureless TeV spectrum. Thus HERD may play a crucial part in the study of the origin of cosmic electrons and positrons., 12 pages, 8 figures, 4 tables, accepted for publication in MNRAS

As a typical inherently anisotropic rock, layered sandstones can differ from each other in several aspects, including grain size, type of material, type of cementation, and degree of compaction. An experimental study is essential to obtain and convictive evidence to characterize the mechanical behavior of such rock. In this paper, the mechanical behavior of a layered sandstone from Xuzhou, China, is investigated under uniaxial compression and Brazilian test conditions. The loading tests are conducted on 7 sets of bedding inclinations, which are defined as the angle between the bedding plane and horizontal direction. The uniaxial compression strength (UCS) and elastic modulus values show an undulatory variation when the bedding inclination increases. The overall trend of the UCS and elastic modulus values with bedding inclination is decreasing. The BTS value decreases with respect to the bedding inclination and the overall trend of it is approximating a linear variation. The 3D digital high-speed camera images reveal that the failure and fracture of a specimen are related to the surface deformation. Layered sandstone tested under uniaxial compression does not show a typical failure mode, although shear slip along the bedding plane occurs at high bedding inclinations. Strain gauge readings during the Brazilian tests indicate that the normal stress on the bedding plane transforms from compression to tension as the bedding inclination increases. The stress parallel to the bedding plane in a rock material transforms from tension to compression and agrees well with the fracture patterns; “central fractures” occur at bedding inclinations of 0°–75°, “layer activation” occurs at high bedding inclinations of 75°–90°, and a combination of the two occurs at 75°.

Powered by inexhaustible solar energy, photoelectrochemical (PEC) hydrogen/ammonia production and reduction of carbon dioxide to high added‐value chemicals in eco‐friendly and mild conditions provide a highly attractive solution to carbon neutrality. Recently, substantial advances have been achieved in PEC systems by improving light absorption and charge separation/transfer in PEC devices. However, less attention is given to the atomic design of photoelectrocatalysts to facilitate the final catalytic reactions occurring at photoelectrode surface, which largely limits the overall photo‐to‐energy conversion of PEC system. Fundamental catalytic mechanisms and recent progress in atomic design of PEC materials are comprehensively reviewed by engineering of defect, dopant, facet, strain, and single atom to enhance the activity and selectivity. Finally, the emerging challenges and research directions in design of PEC systems for future photo‐to‐energy conversions are proposed., Photoelectrochemical hydrogen/ammonia generation and carbon dioxide reduction offer more opportunities for carbon neutrality. In this review, recent progress in the atomic design of PEC materials for enhanced surficial catalysis is reviewed from the aspects of defect, dopant, facet, strain, and single atom engineering. Emerging challenges and research directions for the design of future photo‐to‐energy devices are also proposed.

Rationale: The COVID-19 pandemic is spreading around the world and the leading cause of death is rapidly progressive respiratory failure because of lung damage and consolidation. Lung transplantation is the last line of treatment for chronic end-stage lung diseases. There were several cases of lung transplantation reported in patients with COVID-19 pneumonia. However, anesthetic management of lung transplantation in this subpopulation is rare. We report the anesthetic and perioperative management of lung transplantation in a patient with COVID-19 pneumonia. Patient concerns: A 70-year-old man with a 7-day history of fever was diagnosed with COVID-19 pneumonia. His throat swab was positive for COVID-19, but negative for other common viruses. Chest radiography showed multiple inflammatory foci in both lungs. By day 5, he presented respiratory distress. Computed tomography (CT) scan showed progressive deterioration of both lungs. Starting on day 7, SARS-CoV-2 RNA in bronchoalveolar lavage samples were continuously negative. However, his lung condition deteriorated. By day 17, a veno-venous extracorporeal membrane oxygenation (ECMO) was initiated. After 10 days of ECMO support, the patient's lung condition did not improve. CT scan revealed bilateral parenchymal consolidation with pulmonary fibrosis and hydrothorax. Diagnosis: Irreversible lung function loss induced by COVID-19 pneumonia. Interventions: Bilateral transplantation was performed because the patient's lung condition did not improve and CT scan revealed parenchymal consolidation with pulmonary fibrosis after 10 days of ECMO support. Thirty-six hours after the surgery, ECMO was discontinued. A percutaneous transluminal coronary angioplasty and a stent implantation were performed because of acute coronary syndrome and myocardial ischemia 4 days postoperatively. Outcomes: The patient remained hospitalized because of requirements for intermittent assisted ventilation via tracheostomy. Lessons: This case further supports the consideration that lung transplantation can potentially be the successful therapy for these patients who have developed irreversible lung function lose due to COVID-19 pneumonia. However, most critical patients with COVID-19 are older individuals with various comorbidities, which present new anesthetic challenges.

Owing to their high extinction coefficient and moderate band gap, cadmium chalcogenides are known as common semiconductors for photoelectric conversion. Nevertheless, no ideal cadmium chalcogenide with proper band structure is available yet for photoelectrochemical hydrogen evolution. In this work, we modified the band structure of CdTe via alloying with Se to achieve a ternary compound (CdSe0.8Te0.2) with n-type conduction, a narrower band gap, and a more negative band position compared to those of CdSe and CdTe. This novel material exhibits strong light absorption over a wider spectrum range and generates more vigorous electrons for hydrogen reduction. As a result, a photoelectrode based on nanoflake arrays of the new material could achieve a photocurrent density 2 times that of its CdSe counterpart, outperforming similar materials previously reported in the literature. Moreover, the quick transfer of holes achieved in the novel material was found to depress photocorrosion processes, which led to improv...

Cadmium sulfide was popularly utilized as a light harvesting material for photoelectrochemical (PEC) water splitting, however, the drawback of poor durability limits its practical application. Herein, we show that a catalytically active and chemically inert cadmium indium sulfide (CdIn2S4) can improve the stability and even photocurrent of a CdS photoelectrode.

It is fascinating and challenging to endow conventional materials with unprecedented properties. For instance, cadmium sulfide (CdS) is an important semiconductor with excellent light response; however, its potential in gas-sensing was underestimated owing to relatively low chemical activity and poor electrical conductivity. Herein, we demonstrate that an ideal architecture, ultrathin nanoflake arrays (NFAs), can improve significantly gas-sensing properties of CdS material. The CdS NFAs are grown directly on the interdigitated electrode to expose large surface area. Their thickness is reduced below the double Debye length of CdS, permitting to achieve a full depletion of carriers. Particularly, the prepared CdS nanoflakes are enclosed with high-energy {0001} facets exposed, which provides more active sites for gas adsorption. Moreover, the NFAs exhibit the light-trapping effect, which further enhances their gas sensitivity. As a result, the as-prepared CdS NFAs demonstrate excellent gas-sensing and light-response properties, thus being capable of dual gas and light detection.