极端温度下CRTS Ⅰ型板式无砟轨道CA砂浆受压伤损试验

CA砂浆是一种温度敏感性材料,温度变化将直接影响其受压承载的性能。为了研究极端温度对CA砂浆性能产生的影响,将CRTSⅠ型CA砂浆分别放在-50、-40、-30、20、40、60、80℃环境下进行单轴压缩试验,分析CA砂浆在不同极端温度下受压的规律以及伤损特性。结果表明:随着温度的升高,CA砂浆的抗压强度和弹性模量变小,并利用模量-温度曲线更直观地表现出CA砂浆由脆性逐渐转变为塑性,同时给出了受温度影响的CA砂浆温度-抗压强度的经验公式。以切线模量的变化来判断CA砂浆的温度损伤程度,分析CA砂浆温度损伤规律和伤损槛值随温度的变化规律,随着温度的升高,CA砂浆损伤应力槛值减小,当温度增大到一定时,CA砂浆的应力槛值与抗压强度的比值RC受温度的影响不是很明显。

Dynamic mechanical properties and instability behavior of layered backfill under intermediate strain rates

To obtain dynamic mechanical properties and failure rule of layered backfill under strain rates from10to80s-1,impactloading test on layered backfill specimens(LBS)was conducted by using split Hopkinson pressure bar system.The results indicatethat positive correlation can be found between dynamic compressive strength and strain rate,as well as between strength increasefactor and strain rate.Dynamic compressive strength of LBS gets higher as the arithmetic average cement-sand ratio increases.Compared with static compressive strength,dynamic compressive strength of LBS is enhanced by11%to163%.In addition,theenergy dissipating rate of LBS lies between that of corresponding single specimens,and it decreases as the average cement contentincreases.Deformation of LBS shows obvious discontinuity,deformation degree of lower strength part of LBS is generally higherthan that of higher strength part.A revised brittle fracture criterion based on the Stenerding-Lehnigk criterion is applied to analyzingthe fracture status of LBS,and the average relevant errors of the3groups between the test results and calculation results are4.80%,3.89%and4.66%,respectively.

Bearing characteristics and fatigue damage mechanism of multi-pillar system subjected to different cyclic loads

Aiming to investigate the fatigue damage mechanism and bearing characteristics of multi-pillar system under cyclic loading,a series of axial cyclic loading tests with different cyclic amplitudes were carried out on triple-pillar marble specimens.The acoustic emission(AE)and digital image correlation(DIC)were jointly applied to monitoring and recording damage evolution and failure behavior of each pillar,which reproduced the cataclysmic instability process of underground pillar groups.Experimental results indicated that the cyclic amplitude exceeding the threshold of damage initiation weakened the resistance to deformation,resulting in obvious release of dissipated energy and the reduction of bearing capacity.Conversely,after low-amplitude cyclic loading,both the pre-peak bearing capacity and the post-peak ductility of the pillar system increased due to the compaction of initial defects,indicating that the peak bearing capacity was closely related to the extent of pre-peak fatigue damage.The axial strain of each pillar was measured by DIC virtual extensometer to present the damage extent during cyclic loading phase.Meanwhile,fracture evolution of typical load drop points was also characterized by transverse strain fields(εxx),and observations showed that the damage extent of key pillar undergoing high-amplitude cyclic loads was more serious and violent,accompanied by the ejection of rock debris and loud noises.

CT IDENTIFICATION OF THE MECHANIC CHARACTERISTICS OF DAMAGE PROPAGATION OF ROCK

The computerized tomography technique is applied to study the damage propagation of rock for the first time in this paper. CT values and their distribution regularity of damage propaga-tion of rock are analyzed in detail. The relation between CT values and stresses (strains) of the damage propagation of rock is then discussed. This provides the foundation for establishing the constitutive relation of damage propagation of rock.

Mechanical properties of deep sandstones under loading rate effect

The advance speed of the working face in coal mines can significantly affect the fluctuation frequency of abutment pressure in front of the coal body.Moreover,it has a certain correlation with the change of axial loading rate in coal and rock mechanics test.Therefore,uniaxial compression tests under various loading rates of 0.05,0.1,0.15,0.25,0.5 MPa/s were conducted using 2000 kN triaxial testing machine and PCI-2 acoustic emission test system to study the loading rate effect on the mechanical properties of deep sandstones.The results show that 1)the peak strength and elastic modulus of the deep sandstone increase with the loading rate increasing;2)with the loading rate increasing,the deep sandstone transforms from plastic-elastic-plastic to plastic-elastic and moreover,the failure mode gradually transfers from type I to type III;3)With the loading rate increasing,the total input strain energy,elastic strain energy,and dissipated strain energy generally increase;4)the damage variable presents the evolution characteristics of inverted“S”shape with time,and with the loading rate increasing,the damage degree of the deep sandstone is aggravated.The conclusion obtained can provide the theoretical basis for the stability control of the surrounding rock in deep engineering.

Biomechanical characteristics of an anterior cruciate ligament injury in javelin throwing

Purpose： The purpose of this study was to understand the mechanism of an anterior cruciate ligament （ACL） injury in javelin throwing and javelin throwing techniques relevant to this ACL injury. Methods： The patient in this study was an elite female javelin thrower who completed the first three trials and sustained a non-contact ACL injury on her left knee in the fourth trial of javelin throwing during a recent track and field meet. Three-dimensional kinematic data were collected in the injury and non-injury trials. The kinematic data of 52 male and 54 female elite javelin throwers were obtained from a javelin throwing biomechanical database. Results： The patient had greater forward center of mass velocity and less vertical center of mass velocity after the first 25% of the delivery phase in the injury trial compared to non-injury trials. The patient had less left knee flexion angle and angular velocity but similar left knee valgus and internal rotation angles during the first 21% of the delivery phase in the injury trial compared to non-injury trials. The video images showed an obvious tibia anterior translation at the 30% of the delivery phase in the injury trial. The left knee flexion angle and angular velocity at the time of the left foot landing and the maximal left knee flexion angle during the delivery phase were not significantly correlated to the official distance for 52 male and 54 female elite javelin throwers. Conclusion： The ACL injury in this study occurred during the first 30% of the delivery phase, most likely during the first 25% of the delivery phase. A stiff landing of the left leg with a small knee flexion angle was the primary contributor to this injury. Javelin throwers may have a soft left leg landing with a flexed knee, which may help them prevent ACL injuries without compromising performance.

Analysis of the mechanic characteristics of the damage propagation of rock under triaxial stress condition

The advanced computerized tomography is applied to study the damage propagation of rock. The real time CT scanning is carried out to the damage propagation of rock under triaxial stress condition. The damage propagation constitutive relation of rock under triaxial stress condition is analyzed at last.

Attenuation law of explosive stress wave in damaged rock mass

The attenuation regularity of explosion stress waves in damaged rocks is discussed according to physical and geometric attenuation of waves in this paper. The relation between numerical decrement and damaged parameter is given and the results have an important significance to design and control blasting effect accurately in a concrete rock.

Seismic Damage Characteristics of the Wenchuan Great Earthquake on May 12,2008 and Suggestions for Disaster Prevention

The paper introduces the tectonic background, focal mechanism and distribution of aftershock of the Wenchuan earthquake on May 12,2008. The earthquake is considered to be the result of long-term interaction between the eastward movement of the Bayan Har Block and the Sichuan Basin. Most of the earthquake energy was released in an area （the seismic source body） 330kin long,52km wide and 20km deep over 100s. Energy release in the source body was extremely uneven, and strong ground motion in the epicenter area shows obvious asymmetrical character in the time and space scale. The high-intensity area is distributed along the source body, and the intensity distribution bears an obvious anomalous characteristic. The investigation results indicate that more than 90 percent of casualties caused by this earthquake were in the areas of intensity IX or above. Houses, schools and hospitals etc. suffered serious damage. Lifelines such as transportation, water conservation etc. also suffered significant damage. Besides, earthquake-triggered avalanches, landslides, mud-rock flows and so on were extremely serious. The tremendous earthquake disaster highlighted the deficiencies in disaster prevention and mitigation management, scientific earthquake research, technology and application of earthquake disaster prevention, and publicity of earthquake preparedness and disaster reduction.

Replication of M13 single-stranded DNA bearing a sitespecific ethenocytosine lesion by Escherichia coil cell extracts

Previous investigation on the mutagenic effects of 3,N4-Ethenocytosine (εC), a nonpairing DNA lesion,revealed the existence of a novel SOS-independent inducible mutagenic mechanism in E. coli termed UVM for UV modulation of mutagenesis. To investigate whether UVM is mediated by an alteration of DNA replication, we have set up an in vitro replication system ill which phage M13 viral single-stranded DNA bearing a single site-specific (εC) residue is replicated by soluble protein extracts from E. coli cells. Replication products were analyzed by agarose gel electrophoresis and the frequency of translesion synthesis was determined by restriction endonuclease analyses. Our data indicate that DNA replication is strongly inhibited by εC, but that translesion DNA synthesis does occur in about 14% of the replicated DNA molecules. These results are very similar to those observed previously in vivo, and suggest that this experimental system may be suitable for evaluating alterations in DNA replication in UVM-induced cells.

STUDY ON THE DAMAGE CONSTITUTIVE RELATION OF ROCK UNDER UNIAXIAL STRESS CONDITION

The damage propagation constitutive relation of rock under uniaxial stress condition is studied by CT scanning in this paper. Damage variables of rock are calculated using CT scanning method and Lemaitre’s equivalent strain hypothesis respecively, the damage propagation constitutive relation of rock is discussed.

Three-Step Damage Identification Method Based on Dynamic Characteristics

A three-step damage identification method based on dynamic characteristics is proposed to improve the structure reliability and security and avoid serious accident. In the proposed method, the frequency and difference of modal curvature(DMC) are used as damage indexes. Firstly, the detection of the occurrence of damage is addressed by the frequency or the square of frequency change. Then the damage location inside the structure is measured by the DMC. Finally, with the stiffness reduction rate as a damage factor, the amount of damage is estimated by the optimization algorithm. The three-step damage identification method has been validated by conducting the simulation on a cantilever beam and the shaking table test on a submerged bridge. The results show that the method proposed in this paper can effectively solve the damage identification problem in theory and engineering practice.

Functional expression of opioid receptor-like receptorand its endogenous specific agonist nociceptin/orphanin FQ during mouse embryogenesis

Expression of opioid receptor-like receptor (ORL1)and its endogenous peptide agonist nociceptin/orphaninFo (N/OFQ) during mouse embryogenesis have been investigated. Transcripts of ORL1 and N/OFQ were detected by RT-PCR in mouse brain of day 8 embryo (E8)and the expression continued afterwards. Northern blotanalysis revealed abundant expression of ORL1 at postnatal day 1 (P1) and N/OFQ at E17 and P1 in the brain butnone was detected in other embryonic tissues. The presence of functional ORL1 in mouse embryonic brain wasalso confirmed by specific binding of [3H] N/OFQ (kd=1.3±0.5 nM and Bmax = 72±9 fmol/mg protein) as wellas by N/OFQ-stimulated G protein activation.

Rheological properties of surrounding rock in deep hard rock tunnels and its reasonable support form

Second lining stability, which is the last protection in tunnel engineering, is critically important. The theological properties of the surrounding rock heavily affect second lining stability. In this work, we used laboratory triaxial compressive rheological limestone tests to study nonlinear creep damage characteristics of surrounding rock mass in construction projects. We established a nonlinear creep damage constitutive model for the rock mass, as well as a constitutive model numerical implementation made by programming. Second, we introduced a new foam concrete with higher compression performance and good ductility and studied its mechanical properties through uniaxial and triaxial tests. This concrete was used as the filling material for the reserved deformation layer between the primary support and second lining. Finally, we proposed a high efficiency and accuracy staged optimization method. The minimum reserved deformation layer thickness was established as the optimization goal, and the presence of plastic strain in the second lining after 100 years of surrounding rock creep was used as an evaluation index. Reserved deformation layer thickness optimization analysis reveals no plastic strain in the second lining when the reserved deformation minimum thickness layer is 28.50 cm. The results show that the new foam concrete used as a reserved deformation layer filling material can absorb creep deformation of surrounding rock mass, reduce second lining deformation that leads to plastic strain, and ensure long-term second lining stability.

Investigation of Combination Characteristic of Damage Location and Intensity in Arch Using Wavelet Coefficient

Arch is a typical complex structure comparing with beam and plate in bridge system. This paper investigates the damage characteristic combining the crack location with the crack intensity in arch. Initially, the first four displacement modes of intact and different damaged arch are simulated and the displacement mode changes are obtained. Next, the wavelet transformation is applied to the displacement mode changes in arch and wavelet coefficients at damage loci are picked. Finally, the damage index including damage location and damage intensity in arch is provided and plotted. The results show that wavelet coefficient module maximum of mode changes can be the damage indicator and is influenced by damage location and damage intensity. The damage indicator is proportional to the damage intensity and present monotonic trend according to damage location which depend on the mode order. At the same time, the large modulus maximum corresponds to small damage combination of location and intensity in the first four modes.

Biologic characteristics of fibroblast cells cultured from the knee ligaments

To culture fibroblast cells from th e knee ligaments and to study the biological characteristics of these cells. Methods: Cells of the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL) from New Zealand white rabbit were cultured in vitro. Cellular growth and expression of the collagen were analyzed. Moreover, a n in vitro wound closure model was established and the healing of the ACL and th e MCL cells was compared. Results: Maximal growth for all these cells were obtained with Dulbeccos modified Eagles medium supplemented with 10% fetal bovine serum, b ut RPMI 1640 and Hams F12 media were not suitable to maintain these cells. Mor p hology of both ACL and MCL cells from New Zealand white rabbit was alike in vitr o, but the MCL cells grew faster than the ACL cells. Both cell types produced si milar amount of collagen in culture, but the ratio of collage type Ⅰ to type Ⅲ produced by ACL cells was higher than that produced by MCL cells. Wound closure assay showed that at 36 hours after injury, cell free zones created in the ACL cultures were occupied partially by the ACL cells; in contrast, the wounded zon e in the MCL cultures was almost completely covered by the cells.Conclusions: Although the ACL cells and the MCL cells from New Zealand white rabbit show similar appearance in morphology in culture, the cellu lar growth and the biochemical synthesis of collagen as well as the healing in v itro were significantly different. These differences in intrinsic properties of the two types of cells in vitro might contribute to the differential healing pot entials of these ligaments in vivo.

Acoustic emission characterization methods of damage modes identification on carbon fiber twill weave laminate

In order to get a deep understanding of composite failure mechanisms, the new advanced signal processing methodologies are established for the analysis of the large number of acoustic emission (AE) data obtained from the quasi-static tension test of carbon fiber twill weave composite. For this purpose, AE signals have been collected and post-processed for tension test, and are analyzed with three signal processing methods: Empirical Mode Decomposition (EMD), Hilbert-Huang Transform (HHT) and modified energy entropy algorithm. AE signals can be decomposed into a set of Intrinsic Mode Functions (IMF) components, results from this study reveal that the peak frequency of IMF components based on Fast Fourier Transform (FFT) corresponds to different damage mechanisms of composite. HHT of AE signals can clearly express the frequency distribution of IMF component in time-scale in different damage stages, and can calculate accurate instantaneous frequency for damage modes recognition. The energy entropy based on EMD is introduced to act as a new relevant descriptor of composite damage modes in order to improve the characterization and the discrimination of the damage mechanisms.

Selection of real earthquake accelerograms for structural dynamic analysis and energy evaluation

Real earthquake accelerograms are used in structural dynamic analysis.The criteria for record database establishment,record screening,selection principle,scaling adjustment,and sampling size are discussed in the present paper.An optimized selection method using coupled genetic and greedy algorithms is proposed,and energy input characteristics for the records which are selected only through matching acceleration design spectrum are analyzed.Using the proposed method,the mean and target spectra can reach a good agreement within a period range of interest.The dispersion among the response spectra of the different records is small,and the tolerance of the spectrum value corresponding to each period in the important period scope can be controlled more strictly than the specified limit.If the structural cumulative damage or structures with energy-dissipation components are considered,the records selected using the method that only match the acceleration design spectrum are not applicable.In this case,the selection method that considers the energy input demand is recommended.

Clinical characteristics of 96 patients with drug-induced acute liver failure:a comparison between Traditional Chinese and Western Medicine

OBJECTIVE: To compare the causes, clinical symptoms, laboratory test results, and prognosis in patients with acute liver failure(ALF) induced by traditional Chinese medicines(TCM) and by Western Medicines(WM).METHODS: The medical histories of patients who were diagnosed with drug-induced ALF(DALF)(n =96) after hospitalization in the 302 Military Hospital between January 2010 and December 2015 were retrospectively examined.RESULTS: Fifty-eight of the 96 DALF patients(60.4%) had a hepatocellular pattern of DALF, 16 patients(16.7%) had a cholestatic pattern, and 22 patients(22.9%) had a mixed pattern. DALF resolved in 24 patients(25.0%). Twenty-five patients(26.0%)developed chronic liver injury, 43 patients(44.8%)died, and 4 patients(4.2%) underwent liver transplantation. There were 42 ALF patients(43.8%) who received WM, and 32 ALF patients(33.3%) who received TCM. TCM-induced ALF patients had a higher average age [42.4 ± 18.4) vs(33.5 ± 17.9) years,P = 0.04] and higher creatinine and urine nitrogen levels [(155.2 ± 108.8) vs(97.5 ± 130.4) mmol/L, P =0.047;(9.1 ± 7.7) vs(4.3 ± 5.0) mmol/L, P = 0.002, respectively]. Patients with TCM-induced ALF exhibited an increased risk of renal injury [odds ratio(OR),3.75; 95% confidence interval(CI), 1.330-10.577].The 14 patients with TCM-induced ALF who died exhibited higher creatinine levels than the 18 patients with TCM-induced ALF patients who survived[(218.7 ± 111.6) vs(105.8 ± 78.4) mmol/L, P =0.002]. They were also more likely to exhibit ascites(85.7% vs 44.4%, P = 0.017) and hepatorenal syndrome(78.6% vs 22.2%, P = 0.002).CONCLUSION: TCM-induced ALF was more likely to be accompanied by renal injury than was WM-induced ALF, especially in TCM-induced ALF patients who died.

Biomechanical behavior of brain injury caused by sticks using finite element model and Hybrid-III testing

Objective： To study the biomechanical mechanism of head injuries beaten with sticks, which is common in the battery or assaultive cases.Methods： In this study, the Hybrid-III anthropomorphic test device and finite element model （FEM） of the total human model for safety （THUMS） head were used to determine the biomechanical response of head while being beaten with different sticks. Total eight Hybrid-III tests and four finite element simulations were conducted. The contact force, resultant acceleration of head center of gravity, intracranial pressure and von Mises stress were calculated to determine the different biomechanical behavior of head with beaten by different sticks.Results： In Hybrid-III tests, the stick in each group demonstrated the similar kinematic behavior under the same loading condition. The peak values of the resultant acceleration for thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group were 203.4 g, 221.1 g, 170.5 g and 122.2 g respectively. In finite element simulations, positive intracranial pressure was initially observed in the frontal comparing with negative intracranial pressure in the contra-coup site. Subsequently the intracranial pressure in the coup site was decreasing toward negative value while the contra-coup intracranial pressure increasing toward positive values.Conclusions： The results illustrated that the stiffer and larger the stick was, the higher the von Mises stress, contact force and intracranial pressure were. We believed that the results in the Hybrid-III tests and THUMS head simulations for brain injury beaten with sticks could be reliable and useful for better understanding the injury mechanism.