Experimental study on the effect of water absorption level on rockburst occurrence of sandstone

To investigate the mechanism of rockburst prevention by spraying water onto the surrounding rocks,15 experiments are performed considering different water absorption levels on a single face.High-speed photography and acoustic emission(AE)system are used to monitor the rockburst process.The effect of water on sandstone rockburst and the prevention mechanism of water on sandstone rockburst are analyzed from the perspective of energy and failure mode.The results show that the higher the ab-sorption degree,the lower the intensity of the rockburst after absorbing water on single side of sand-stone.This is reflected in the fact that with the increase in the water absorption level,the ejection velocity of rockburst fragments is smaller,the depth of the rockburst pit is shallower,and the AE energy is smaller.Under the water absorption level of 100%,the magnitude of rockburst intensity changes from medium to slight.The prevention mechanism of water on sandstone rockburst is that water reduces the capacity of sandstone to store strain energy and accelerates the expansion of shear cracks,which is not conducive to the occurrence of plate cracking before rockburst,and destroys the conditions for rockburst incubation.

Mechanical Study of Nano⁃ceramic Thermal Barrier Coatings by the Equation of Phonon Radiative Transfer

Temperature filed,thermal stress,especially tensile stress and J⁃integral are important for thermal barrier coatings(TBCs)under thermal shock.At the micro⁃and nano⁃scale,the energy transport mechanisms are significantly different from those at the macro⁃scale.The temperature fields,which are obtained by combining the Equation of Phonon Radiative Transport(EPRT)(for the nano⁃scale ceramic TBCs)and the Fourier law(for the substrate),are used as the thermal loading in the thermal stress and J⁃integral of an edge in the TBCs analysis by the finite element method.The temperature field and thermal stresses as well as J⁃integral are compared with those which are calculated by applying the Fourier law to both the TBCs and the substrate.The influence of the physical heat properties of the TBCs on the temperature field and thermal stress and J⁃integral have been analyzed in this paper.It is concluded that the temperature,thermal stress,including the tensile and compressive components,and J⁃integral which are calculated with the EPRT,are lower than that calculated with the Fourier law in the TBCs.Moreover,thermal stress in the TBCs increase with increasing phonon speed and relaxation time,but J⁃integral at the crack tip is in the opposite.

The Compactions of Elasto-Plastic and Visco-Plastic Granular Assemblies

In this paper, the compactions of the elasto-plastic and the visco-plastic granular assemblies are simulated using the finite element method. Governing equations for motion and deformation for particles, including coupling of rigid body motion and deformation for deformable bodies, are investigated. An implicit discrete element method for block systems is developed to make visco-plastic analysis for the assemblies. Among particles, three different contact types, cohering, rubbing and sliding, are taken into account. To verify accuracy and efficiency of the numerical method, some numerical example is simulated and the results are in a satisfactory agreement with the solutions in literatures. The effects of frictional condition, the initial solid volume ratio, the number of particles in the assembly, and different types of compact- tion on the compaction of the elasto-plastic and the visco-plastic aggregates are investigated. It is demonstrated that the effect of frictional condition, the initial solid volume ratio, the number of particles in the assembly, and different types of compaction on the global behavior of the elasto-plastic the visco-plastic granular assemblies under compacting are considerable. The numerical model is extended to simulate the compaction of aggregates consisting of mixed particles of different viscous incompressible materials. It is indicated that, with minor modification, the method could be used in a variety of problems that can be represented using granular media, such as asphalt, polymers, aluminum, snow, food product, etc.

An Improved Empirical Mode Decomposition for Power Analysis Attack

Correlation power analysis(CPA) has become a successful attack method about crypto-graphic hardware to recover the secret keys. However, the noise influence caused by the random process interrupts(RPIs) becomes an important factor of the power analysis attack efficiency, which will cost more traces or attack time. To address the issue, an improved method about empirical mode decomposition(EMD) was proposed. Instead of restructuring the decomposed signals of intrinsic mode functions(IMFs), we extract a certain intrinsic mode function(IMF) as new feature signal for CPA attack. Meantime, a new attack assessment is proposed to compare the attack effectiveness of different methods. The experiment shows that our method has more excellent performance on CPA than others. The first and the second IMF can be chosen as two optimal feature signals in CPA. In the new method, the signals of the first IMF increase peak visibility by 64% than those of the tradition EMD method in the situation of non-noise. On the condition of different noise interference, the orders of attack efficiencies are also same. With external noise interference, the attack effect of the first IMF based on noise with 15dB is the best.

High speed laser cladding as a new approach to prepare ultra-high temperature ceramic coatings

Ultra-high temperature ceramic(UHTC)coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation.This study provides a new approach to fabricate UHTC coatings with high speed laser cladding(HSLC)technology,and places more emphasis on investigating the formation mechanism,phase compositions,and mechanical properties of HSLC-UHTC coatings.Results show that a well-bonded interface between the coating and the tantalum alloy substrate can be formed.The coating is mainly composed of(Zr,Ta)C ceramic solid solution phase with a content of higher than 90% by volume and Ta(W)metal solid solution phase.At a relatively high powder feeding rate,the ZrC ceramic phase appears in the coating while a dense ZrC UHTC top layer with a thickness of up to~50μm is successfully fabricated.As for the mechanical properties of the HSLC coatings,the fracture toughness of the coating decreases with the increase of powder feeding rate.The increase of carbide solid solution phase can significantly improve the high temperature microhardness(552.7±1.8 HV0.5@1000℃).The innovative design of HSLC ZrC-based coatings on refractory alloys accomplishes continuous transitions on microstructure and properties from the substrate to the UHTC top layer,which is a very promising candidate scheme for thermal protection coating.

Flexible piezoelectret film sensor for noncontact mechanical signal capture by multiple transmission media

Mechanical signal capture without physical contact has emerged as a highly promising research field and attracted tremendous attention due to its prosperous applications in household medical care,lifestyle monitoring and remote operation,offering users high level of safety,convenience and comfort.Moreover,noncontact sensing is ideal to maximize the immersive user experience in the human–machine interaction(HMI),eliminating interference to human activities and mechanical fatigue to the sensor,simultaneously.Herein,we report a self-powered flexible sensor integrated with irradiation cross-linked polypropylene(IXPP)piezoelectret film for noncontact sensing,featuring multi-functions to detect mechanical signals transmitted through solid,liquid and gaseous media and would facilitate their versatile practical applications.The folded-structure configuration of the sensor facilitates the improvement of the noncontact sensing sensitivity.For solid media,such as the rectangular wooden stick used in this study,the sensor can detect mechanical stimulus exerted at a distance of 100 cm.A system detection sensitivity up to 57 pC/kPa with a low detection limit of 0.6 kPa is achieved at a noncontact distance of 10 cm.Even when partly or completely immersed in water,the sensor effectively traces movement signals of human bodies underwater,demonstrating great advantages for non-inductive aquatic fitness training monitoring.Furthermore,due to the low acoustic impedance of piezoelectret film,speech recognition through gaseous medium is also achieved.We further introduce application demonstrations of the developed film sensors to monitor exercise postures and physiological signals without direct contact between human body and the sensor,displaying great potential to be incorporated into future smart electronics.This study commendably expands the application scope of piezoelectret materials,which will have profound implications for exploring novel intelligent human–machine interactions.

Experimental investigation on acoustic emission precursor of rockburst based on unsupervised machine learning method

The key to achieving rockburst warning lies in the understanding of rockburst precursors.Considering the cor-relation characteristics of rockburst acoustic emission(AE)parameters,a self-organizing map neural network(SOMNN)based method for rockburst precursor inversion was proposed.The feature of this method lies in a cyclic data segmentation iteration process based on the thinking of“interference signal screening”,“key signal extraction”,and“precursor signal inversion”.The rationality of this method has been verified in three groups of rockburst experiments.The results revealed that rockburst AE precursor signals consist of a series of signals characterized by long duration,high energy,low average frequency,high energy amplitude,and low peak fre-quency.Subsequently,potential value in long term rockburst warning of the precursor obtained in this study was shown via the comparison of conventional precursors.Finally,a preliminary interpretation for rockburst pre-cursor was proposed under the framework of AE parameters physical significance,and it is revealed that AE precursor signals are likely linked to the creation of large-scale tensile cracks before rockburst.

State of the art review of the large deformation rock bolts

Rock bolting technique is an important reinforcement measure in the geotechnical engineering practice.New rock bolts have been continuously emerging through the development of rock supporting technology.Complex conditions,such as high crustal stress,extremely soft rock,and strong mining disturbance often occur in the deep mining,resulting in large deformation of the surrounding rock masses.Since the deformation of traditional rock bolts is generally below 200 mm,failure often occurs to the rock bolts because of insufficient deformability.To effectively control the large deformation of surrounding rock masses caused by complex conditions,it is necessary to develop large deformation rock bolts with high constant resistance,also called energy-absorbing bolts.This paper systematically reviews the development of large deformation rock bolts and the structure,energy absorption mechanism,anchorage performance,and mechanical properties of several typical large deformation rock bolts.The advantages and disadvantages of existing large deformation rock bolts are compared and the concept of constant resistance large deformation support is introduced.

Fracture model for the prediction of the electrical percolation threshold in CNTs/Polymer composites

In this paper, we propose a 3D stochastic model to predict the percolation threshold and the effective electric conductivity of CNTs/Polymer composites. We consider the tunneling effect in our model so that the unrealistic interpenetration can be avoided in the identification of the conductive paths between the CNTs inside the polymer. The results are shown to be in good agreement with reported experimental data.

Structural mechanism of a dual-functional enzyme Dgp A/B/C as both a C-glycoside cleaving enzyme and an O-to C-glycoside isomerase

The C-glycosidic bond that connects the sugar moiety with aglycone is difficult to be broken or made due to its inert nature.The knowledge of C-glycoside breakdown and synthesis is very limited.Recently,the enzyme Dgp A/B/C cascade from a human intestinal bacterium PUE was identified to specifically cleave the C-glycosidic bond of puerarin(daidzein-8-C-glucoside).Here we investigated how puerarin is recognized and oxidized by Dgp A based on crystal structures of Dgp A with or without substrate and biochemical characterization.More strikingly,we found that apart from being a C-glycoside cleaving enzyme,Dgp A/B/C is capable of efficiently converting O-to C-glycoside showing the activity as a structure isomerase.A possible mechanistic model was proposed dependently of the simulated complex structure of Dgp B/C with 3’’-oxo-daidzin and structure-based mutagenesis.Our findings not only shed light on understanding the enzyme-mediated C-glycosidic bond breakage and formation,but also may help to facilitate stereospecific C-glycoside synthesis in pharmaceutical industry.

SARS-CoV-2 spike host cell surface exposure promoted by a COPI sorting inhibitor

Via an insufficient coat protein complex I(COPI)retrieval signal,the majority of SARSCo V-2 spike(S)is resident in host early secretory organelles and a tiny amount is leaked out in cell surface.Only surface-exposed S can be recognized by B cell receptor(BCR)or anti-S therapeutic monoclonal antibodies(m Abs)that is the trigger step for B cell activation after S m RNA vaccination or infected cell clearance by S m Abs.Now,a drug strategy to promote S host surface exposure is absent.Here,we first combined structural and biochemical analysis to characterize S COPI sorting signals.A potent S COPI sorting inhibitor was then invented,evidently capable of promoting S surface exposure and facilitating infected cell clearance by S antibody-dependent cellular cytotoxicity(ADCC).Importantly,with the inhibitor as a probe,we revealed Omicron BA.1 S is less cell surface exposed than prototypes because of a constellation of S folding mutations,possibly corresponding to its ER chaperone association.Our findings not only suggest COPI is a druggable target against COVID-19,but also highlight SARS-Co V-2 evolution mechanism driven by S folding and trafficking mutations.

黄曲霉毒素B1降解菌的筛选及在玉米贮藏中的应用

【目的】本研究分离筛选出一株对黄曲霉既有抑制作用又能降解其毒素的拮抗细菌菌株,并将其应用于玉米中的黄曲霉污染防治研究。【方法】试验通过平板筛选法结合玉米活体筛选法对黄曲霉毒素B1 (AFB1)的拮抗细菌进行初筛,以AFB1的降解率和抑制率为指标进行复筛。【结果】分离到的菌株对黄曲霉菌的抑制率为79.20%,对1μg/mL的黄曲霉毒素B1的降解率为68.39%。贮藏期玉米含水量在15%–30%时,该菌株对黄曲霉污染的抑制率与玉米含水量成反比,即玉米含水量在15%时其抑制率达92.46%,玉米含水量在30%时其抑制率为19.41%。玉米含水量在28%时,菌株对黄曲霉污染玉米的防治效果达到36.39%。【结论】筛选出的拮抗菌株为枯草芽孢杆菌,该菌株不仅对黄曲霉菌有抑制作用,而且能减少AFB1对玉米的污染。

Design and application of friction pair surface modification coating for remanufacturing

Friction,wear,and contact fatigue are the main causes of energy loss,material waste,and equipment failure.The aim of remanufacturing is to repair and modify the damaged equipment surface,and the surface coating is the major material that allows the remanufactured parts to be used in a new round of operation.Thus,the design and preparation of surface coatings are very important to repair,strengthen,or modify the friction pairs,in order to ensure long-term operation of the remanufactured parts.Recent1y,a lot of research on designing and preparing friction pair surface modification coatings has been conducted by the National Key Laboratory for Remanufacturing (NKLR).The research conducted achieved the following goals:the mechanism of micro/nano multilayer surface modification coatings with long-term efficacy life was revealed,and the corresponding design considerations and preparation methods of nanocrystalline micro tribological coatings were innovatively developed.A series of new 'two-step' processes to prepare sulfide solid lubricating coatings were developed.The competitive failure mechanism of the surface coating in simultaneous wear and fatigue conditions was revealed,and some composite coatings with dual properties of wear resistance and fatigue resistance were prepared.Based on the stress distribution of friction surface contact areas and the piezoelectric effect,a failure warning intelligent coating is designed and developed.These coatings have been successfully applied to critical friction components,such as the spindle of large centrifugal compressors,engine cylinder piston components,and driver gear pairs.

3D fracture modelling and limit state analysis of prestressed composite concrete pipes

In this manuscript,we study fracture of prestressed cylindrical concrete pipes.Such concrete pipes play a major role in tunneling and underground engineering.The structure is modelled fully in 3D using three-dimensional continuum elements for the concrete structure which beam elements are employed to model the reinforcement.This allows the method to capture important phenomena compared to a pure shell model of concrete.A continuous approach to fracture is chosen when concrete is subjected to compressive loading while a combined continuous-discrete fracture method is employed in tension.The model is validated through comparisons with experimental data.

Modeling Frequency- and Temperature-Invariant Dissipative Behaviors of Randomly Entangled Carbon Nanotube Networks under Cyclic Loading

Recent experiments have shown that entangled networks of carbon nanotubes exhibit temperature- and frequency-invariant dissipative behaviors under cyclic loading. We have performed coarse-grained molecular dynamics simulations which show that these intriguing phenomena can be attributed to the unstable attachments/detachments between individual carbon nanotubes induced by van der Waals interactions. We show that this behavior can be described by a triboelastic constitutive model. This study highlights the promise of carbon nanomaterials for energy absorption and dissipation under extreme conditions.

Generalized valuations on MTL-algebras

In this paper,we study some kinds of generalized valuations on MTL-algebras,discuss the relationship between the cokernel of generalized valuations and types of filters on MTL-algebras.Then,we give some equivalent characterizations of positive implicative generalized valuations on MTL-algebras.Finally,we characterize the structure theory of quotient MTL algebras based on the congruence relation,which is constructed by generalized valuations.The results of this paper not only generalize related theories of generalized valuations,but also enrich the algebraic conclusion of probability measure,on algebras of triangular norm based fuzzy logic.