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The mechanical behavior of 66 carbon-fibre-reinforced polymer (CFRP)-confined concrete-filled steel tubular (CFST) short columns and 42 non-CFRP-confined CFST short columns under axial compression are studied. The typical failure modes and load–displacement curves of the specimen are obtained, and the stress mechanisms of the specimen are analysed. The effects of fiber-reinforced polymer (FRP) layers, core concrete strength and cross-section forms on the axial mechanical properties of CFST short columns are discussed. The test results show that there is a positive correlation between the improvement coefficient of bearing capacity and the confinement effect coefficient of FRP. Based on the superposition principle, the bearing capacity calculation formulas of circular and square CFST columns without CFRP confinement are proposed. On this basis, taking the confinement effect of FRP into account, the calculation formula of axial bearing capacity of FRP-confined CFST short columns is proposed. The comparison between the calculated values of the model and the measured values of the experiments shows that the model has good prediction effect.

The poor stability of peptides against trypsin largely limits their development as potential antibacterial agents. Here, to obtain a peptide with increased trypsin stability and potent antibacterial activity, TICbf-14 derived from the cationic peptide Cbf-14 was designed by the addition of disulfide-bridged hendecapeptide (CWTKSIPPKPC) loop. Subsequently, the trypsin stability and antimicrobial and antibiofilm activities of this peptide were evaluated. The possible mechanisms underlying its mode of action were also clarified. The results showed that TICbf-14 exhibited elevated trypsin inhibitory activity and effectively mitigated lung histopathological damage in bacteria-infected mice by reducing the bacterial counts, further inhibiting the systemic dissemination of bacteria and host inflammation. Additionally, TICbf-14 significantly repressed bacterial swimming motility and notably inhibited biofilm formation. Considering the mode of action, we observed that TICbf-14 exhibited a potent membrane-disruptive mechanism, which was attributable to its destructive effect on ionic bridges between divalent cations and LPS of the bacterial membrane. Overall, TICbf-14, a bifunctional peptide with both antimicrobial and trypsin inhibitory activity, is highly likely to become an ideal candidate for drug development against bacteria.

Since the beampattern has the characteristics of range-angle dependence, frequency diverse array multiple-input multiple-output (FDA-MIMO) radar has a good application prospect. There have been many studies to improve the performance of the beampattern by optimizing the frequency offset. However, on the basis of fully understanding the time parameters, the relationship between the array element frequency offset and the beampattern performance still needs to be clarified. Based on a new FDA-MIMO radar framework, this paper presents an analytical solution of the beampattern, which removes the influence of the time parameter. Taking the minimum main lobe as the objective function, an analytical method for solving a better frequency offset is given. Then, a method of using the window function was proposed to reduce the high side lobes of the range dimension. Comparing with the existing FDA radar beampattern design methods, it can achieve a more focusing beampattern. The simulation results verify the correctness of the theory.

Antimicrobial peptides (AMPs), which hold tremendous promise in overcoming the emergence of drug resistance, are limited in wide clinical applications due to their instability, especially against trypsin. Herein, we designed six peptide mutants based on the cathelicidin CATHPb2, followed by screening. Pb2-1, which showed the best activity against drug-resistant bacteria among these mutants, was selected to be combined with the trypsin inhibitory loop ORB-C to obtain two hybrid peptides: PCL-1 and Pb2-1TI. Notably, both of the hybrid peptides exhibited a remarkable enhancement in trypsin resistance compared with Pb2-1. The tests showed that PCL-1 displayed broad-spectrum antimicrobial activity that was superior to that of Pb2-1TI. In addition, PCL-1 had relatively lower cytotoxicity than Pb2-1TI towards the L02 and HaCaT cell lines and negligible hemolysis, as well as tolerance to high concentrations of salt, extreme pH, and temperature variations. In vivo, PCL-1 effectively improved the survival rate of mice that were systemically infected with drug-resistant Escherichia coli through efficient bacterial clearance from the blood and organs. With regard to mode of action, PCL-1 damaged the integrity of the bacterial cell membrane and attached to the membrane surface while bound to bacterial genomic DNA to eventually kill the bacteria. Altogether, the trypsin-resistant peptide PCL-1 is expected to be a candidate for the clinical treatment of bacterial infections.

A multiple‐input multiple‐output (MIMO) radar with frequency diverse array (FDA) produces a range‐angle‐dependent steering vector, which can suppress the deceptive jamming in joint range‐angle domain. This in turn complicates the task of radar jamming. With the emergence and development of digital radio frequency memory (DRFM), radar electronic jamming technique has entered the age of coherent jamming. Based on the analysis of the superiority of the FDA‐MIMO radar in cancelling the deceptive jammers, a novel range gate pull‐off method via DRFM against FDA‐MIMO radar is proposed. Compared with the traditional deceptive jamming methods, the proposed method cannot be suppressed due to the mismatch in range. In particular, even the anti‐jamming methods based on power domain cease to be effective. The effectiveness of the proposed scheme in jamming the tracking performance of the FDA‐MIMO radar is demonstrated via computer simulations.

Infections induced by fungi, especially the drug-resistant fungi, are difficult clinical problems. Conventional antifungal treatment is effective but due to resistance, treatment failure, and treatment-related toxicity, there is a need for new antifungal drugs. In this study, SA-2 (YYRRLLRVLRRRW) was derived from Cystatin-SA, a saliva protein with a molecular weight of 14 kDa. Meanwhile, the structure-activity of SA-2 and its mutants was also studied. We detected the antimicrobial activity and cytotoxicity of SA-2 and found that SA-2 had a low cytotoxicity toward mammalian cells but a good inhibitory effect on Candida albicans (C. albicans) and Cryptococcus neoformans (C. neoformans), with MIC values of 16-64 μg/mL and 8-32 μg/mL, respectively. Interestingly, SA-2 effectively killed fluconazole-resistant C. neoformans and C. albicans within 12 h. This antifungal activity against fluconazole-resistant fungi was comparable to that of amphotericin B. In addition, the C. neoformans-infected mice model was established to evaluate the anti-infective activity of SA-2 in vivo. Results showed that SA-2 significantly reduced the counts of fungi in lung and brain tissues to protect fluconazole-resistant C. neoformans-infected mice from death without changing mice body weights. Moreover, the dramatically increased pro-inflammatory cytokines TNF-α, IL-6 and IL-1β induced by intranasal infection of C. neoformans could be obviously declined due to the treatment of SA-2, which may be attributed to the elimination of C. neoformans in time in the infected tissue. For the mode of actions underlying SA-2 against C. neoformans, we found that the cationic peptide SA-2 could adhere to the negatively charged fungal cell membrane to increase the surface potential of C. neoformans in a dose-dependent manner, and finally disrupted the integrity of fungal cell membrane, reflecting as a 60% positive rate of propidium iodide uptake of C. neoformans cells after SA-2 (4 × MIC) treatment. Our study indicated that SA-2 has the potential to develop as a new therapeutic agent against infection induced by drug-resistant fungi.

The cryptographic chip in system must be evaluated for side channel leakage detection before coming into service. However, the existing evaluation technology is too inefficient. This letter decomposes the variance of the traces of power consumption into variance of the sensitive variable and noise to estimate the signal-to-noise (SNR). According to the relationship between the success rate (SR) of the power analysis attack, SNR and conditional mutual information, the minimum number of traces is computable to evaluate the information leakage of the cryptographic chip. This method effectively estimates the minimum number of power traces when the SNR of power consumption is greater than 0.1. When the SNR is less than 0.1, the result calculated by this method is consistent with the change trend of the simulation, which means that the result also evaluates the ability of cryptographic chip to resist power analysis attacks. The method improves the evaluation efficiency by at least 60000 times compared with the simulation of CPA.

Recently, unmanned aerial vehicle (UAV) has made significant progress, which raises new challenges in electromagnetic (EM) protection. The UAV positioning module is sensitive to electromagnetic interference (EMI) but few works have been reported on its immunity testing. In this letter, an equivalent dynamic test system is designed based on the bulk current injection (BCI) method, in order to test the UAV positioning module under working state. A forward system is designed and implemented which is capable of bringing in the GPS signal for the positioning module. The immunity test is carried out and a series of functional failures have been observed. The immunity characteristics of the working-state positioning module is obtained which shows its susceptibility from 450MHz to 800MHz. Finally, an equivalent dynamic test is conducted, showing the influence of EMI on the ability of detecting GPS signals and the horizontal dilution of precision (HDOP) of the positioning module.

A polysaccharide (ESPS) purified from Eupolyphaga sinensis Walker by ion exchange chromatography and gel chromatography was investigated, including its structure characterization and antitumor activity. The results showed that ESPS was composed of rhamnose, fucose, arabinose, xylose, glucose, and galactose in a molar ratio of 7.4: 3.1: 13.9: 9.3: 39.7: 26.5, with the mean weight (Mw) of 2.14 × 104 Da; the main chain of ESPS was mainly composed of → 4) - α - D - Glcp - (1 → and → 3) - β - D - Galp - (1 →, and the side chains were connected to the main chain through the O-6 atom of glucose and O-4 and O-6 atom of galactose. In addition, ESPS promoted the lymphocyte proliferation and inhibited liver cancer cells growth through enhancing lymphocyte activity in vitro, mainly NK cells. Moreover, ESPS markedly stimulated immunity in H22-bearing mice by increasing the spleen and thymus indices and effectively inhibited H22 cell growth in vivo. These data indicated that ESPS was a polysaccharide component possessing high anti-hepatocellular carcinoma activity, representing a potential immunotherapy candidate for the treatment of liver cancer.

Honeysuckle has been used in the treatment of influenza virus infection for thousands of years in China. However, its main active components and the functional mechanisms remain to be elucidated. Here, four honeysuckle extracts, including acids extract, flavonoids extract, total extract and acids-flavonoids mixture, were prepared to clarify the main active antiviral components. The cytopathic effect reduction assay showed that all the four extracts inhibited the replication of influenza viruses H1N1, H3N2 and the oseltamivir-resistant mutant strain H1N1-H275Y. The acids-flavonoids mixture had the strongest inhibitory effects in vitro with EC(50) values of 3.8, 4.1, and > 20 μg/mL against H1N1, H3N2 and H1N1-H275Y, respectively, showing competitive antiviral activity with oseltamivir and ribavirin. Honeysuckle acids extract also showed the most significant antiviral activity in vivo. Oral administration of the acids extract at a dosage of 600 mg/kg/d effectively alleviated viral pneumonia, maintained body weight and improved the survival rate to 30% of the mice infected with a lethal dose of H1N1. The results of time-of-drug addition experiment and neuraminidase (NA) inhibition assay showed that honeysuckle extracts had a broad-spectrum inhibitory effect against influenza virus NAs. The flavonoid extract showed the strongest inhibitory effect on the NA of influenza virus H7N9 with an IC(50) of 24.7 μg/mL. These results suggested that these extracts might exert their antiviral activity by suppressing the release of influenza viruses. Briefly, our findings demonstrate that acids and flavonoids extracts of honeysuckle are the major antiviral active components, and the acids extract has the potential to be developed into an antiviral agent against influenza virus, especially for oseltamivir-resistant viruses.

Antibiotics resistance is one of the most significant public health threats globally. Strategies that strengthen host defenses to control pathogen infection has become a hot research field. Macrophages are part of early host defense mechanisms, and are activated via host pattern recognition receptors (PRRs), such as Toll-like receptor 4 (TLR4), which then facilitates phagocytosis and elimination of invading pathogens. However, few activators of PRRs have been approved for clinical use because of their toxic effects. This study aimed to investigate whether Strongylocentrotus nudus eggs polysaccharide (SEP), a non-toxic extract from seafood, contributes to host defense against bacterial infection. Results showed that SEP promoted bacterial clearance by enhancing phagocytosis by macrophages during E. coli infection in vitro, but was inhibited by TLR4 specific inhibitor TAK-242, STAT3 inhibitor Stattic or blockade of CD64. In addition, SEP protected mice from E. coli induced mortality, reduced pulmonary inflammation and inhibited dissemination of bacteria to organs, while TAK-242 retarded the protection of SEP. Overall, SEP strengthened innate host defense and improved the outcome in bacterial infection, suggesting that SEP could be used as a potential immunomodulator in host-directed therapies.

Hepatitis B virus (HBV) infection remains a major global threat to human health worldwide. Recently, the Chinese medicines with antiviral properties and low toxicity have been a concern. In our previous study, Eupolyphaga sinensis Walker polysaccharide (ESPS) has been isolated and characterized, while its antiviral effect on HBV remained unclear. The anti-HBV activity of ESPS and its regulatory pathway were investigated in vitro and in vivo. The results showed that ESPS significantly inhibited the production of HBsAg, HBeAg, and HBV DNA in the supernatants of HepG2.2.15 in a dose-dependent manner; HBV RNA and core protein expression were also decreased by ESPS. The in vivo studies using HBV transgenic mice further revealed that ESPS (20 and 40 mg/kg/2 days) significantly reduced the levels HBsAg, HBeAg, and HBV DNA in the serum, as well as HBV DNA and HBV RNA in mice liver. In addition, ESPS activated the Toll-like receptor 4 (TLR4) pathway; elevated levels of IFN-β, TNF-α, and IL-6 in the serum were observed, indicating that the anti-HBV effect of ESPS was achieved by potentiating innate immunity function. In conclusion, our study shows that ESPS is a potential anti-HBV ingredient and is of great value in the development of new anti-HBV drugs.

Cbf-14 (RLLRKFFRKLKKSV), a designed antimicrobial peptide derived from the cathelicidin family, is effective against drug-resistant bacteria. Structurally related peptide impurities in peptide medicines probably have side effects or even toxicity, thus impurity profiling research during the entire production process is indispensable. In this study, a simple liquid chromatography-high-resolution mass spectrometry (LC-HRMS) method using a quadrupole time-of-flight (Q-TOF) mass spectrometer was developed for separation, identification, and characterization of structurally related peptide impurities in Cbf-14. A total of one process-related impurity and thirty-two degradation products were identified, and seven of them have been synthesized and confirmed. These impurities have not been declared in custom synthetic peptides. The degradation products were divided into five categories: fifteen Cbf-14 hydrolysates, five Cbf-14 isomers, four acetyl-Cbf-14 isomers, two aldimine derivatives, and six oxidized impurities. Combined with the peptide synthesis and the stress-testing studies, the origins and the formation mechanisms of these impurities were elucidated, which provides a unique insight for the follow-up quality study of Cbf-14 and other peptide products.

Defects such as voids, pores, and joints will transform into big scale cracks in the rock of tunnel surrounding under dynamic load like blasting and earthquake. In this paper, three kinds of symmetrical cracks were chosen as an example, and experiments and numerical simulations were conducted to study the effect of symmetric cracks on a blast-induced crack. The relationship of main crack propagation characteristic and distribution of symmetrical cracks was investigated. Some circular specimens using two kinds of material, PMMA and sandstone, including a center hole charged with a detonator and pre-existing cracks were used in the experiments. The test system consisted of an oscilloscope and an ultradynamic strain amplifier and crack propagation gauges (CPGs) were employed in monitoring propagation velocity. AUTODYN code was applied in numerical simulation to investigate the propagation behavior of main crack between symmetrical cracks. Linear equation of state and a modified major principal stress failure criterion was utilized to describe the status of rock material. Based on experimental and numerical results, it can be concluded that (1) the pre-existing symmetrical cracks have arrest effect on main crack propagation, (2) compressive stress in y-direction plays very important roles in crack arrest, and (3) the spacing of parallel cracks has a great influence on crack propagation length and velocity.

Background It has been reported that lncRNA growth arrest-specific transcript 5 (GAS5) interacts with miR-21, which plays critical roles in osteoporosis. The involvement of GAS5 in osteoporosis was investigated in this study. Methods Expression levels of GAS5 and miR-21 in plasma of both osteoporosis patients and healthy controls were determined by RT-qPCR. Diagnostic values of GAS5 and miR-21 for osteoporosis were analyzed by ROC curve analysis. Overexpression experiments were used to assess the interactions between GAS5 and miR-21. The roles of GAS5 and miR-21 in the apoptosis of osteoclasts were investigated by cell apoptosis assay. Results The present study aimed to investigate the roles of GAS5 in osteoporosis. The results showed that GAS5 was upregulated, while miR-21 was downregulated in plasma of osteoporosis patients. Expression levels of GAS5 and miR-21 were inversely correlated across plasma samples from osteoporosis patients but not the plasma samples from the controls. Altered expression of GAS5 and miR-21 distinguished osteoporosis patients from the controls. In osteoclasts, overexpression of GAS5 led to downregulation of miR-21, while overexpression of miR-21 did not affect the expression of GAS5. Overexpression of GAS5 led to promoted apoptosis of osteoclasts, while overexpression of miR-21 led to suppressed apoptosis of osteoclasts. In addition, overexpression of miR-21 attenuated the enhancing effects of overexpressing GAS5 on cell apoptosis. Conclusion GAS5 is upregulated in osteoporosis and may downregulate miR-21 to promote the apoptosis of osteoclasts.

In this paper, the electromagnetic interference and temperature coupling on MOS transistor is analyzed. The temperature controlled platform that combined with the standardized direct power injection method is designed for experimental measurement. Then the temperature effect on MOS device is considered into the conducted electromagnetic immunity model of input/output element (IOE) for typical field programmable gate array. Meanwhile, the proposed immunity model ICIM-CI-T (integrated circuits immunity model-conducted immunity-temperature), which is based on ICIM-CI, is built to predict the influence of thermal effect on the electromagnetic immunity of IOE. Finally, the validation of the ICIM-CI-T model is verified by experimental measurements, and both simulation and measurement results fit very well at different temperatures. Moreover, it is also observed that temperature exerts different effects on the immunity characteristic of IOE with the change of radio frequency interference frequency.

High-quality Pb(Zr0.52Ti0.48)O3 (PZT) thin film was fabricated by pulsed laser deposition on flexible mica substrates. X-ray diffraction results showed that the growth of PZT thin film is extended along (001) preferred orientation without any other secondary phases. The electrical properties measurements show that the flexible PZT thin films possess excellent ferroelectric and piezoelectric properties. The remnant polarization (2Pr) and the piezoelectric coefficient (d33) were measured to be 32 μC/cm2 and 15 pm/V, respectively, when the flexible thin film was unbending. Furthermore, the flexible PZT thin films exhibit high stability under mechanical bending. The saturated polarization and dielectric constant of PZT capacitors decrease when the capacitors change from the central area to the edge under a certain bending state. This was interpreted based on the out-of-plane tensile strain change for each capacitor.

Under static loading, crack propagation processes are a dynamic process due to very high propagation speeds. For fine-grained concrete material under static loading, the crack propagation speed can reach 723.7 m/s, thus the crack propagation process under static loading actually can be considered as a dynamic issue, not a static issue. Crack propagations with a rapid speed are extremely unfavorable to the stability of concrete structures. Therefore, it is of significance to study the dynamic fracturing of concrete structure under static loading. Three-point bending (TPB) tests were conducted by using concrete specimens. A novel test system coupled with crack propagation gauges (CPGs) and strain gauges (SGs) was utilized to measure the crack speed and the initiation loads. The experimental results show that crack propagation velocities are not a constant and the propagation toughness of fine-grained concrete varies with the crack tip displacement. The initiation toughness is higher than the propagation toughness.

Hepatitis B virus (HBV) infection remains a major global threat to human health worldwide. Recently, the Chinese medicines with antiviral properties and low toxicity have been a concern. In our previous study

The lack of detect technology hinders the understanding of host-guest (H-G) chemical properties for thiolate-protected tiara-like structural nanoclusters (Mn(SR)2n). In this work, NMR spectroscopy is demonstrated as a powerful tool to probe the H-G structure of Mn(SR)2n both experimentally and theoretically. A low-field shifting and wide chemical shift (CS) signal of the H nucleus in CH2Cl2 is observed in the NMR spectrum of the mixture of CH2Cl2 and Pd8(PET)16 (PET is 2-phenylethanethiol), agreeing with the theoretical results that a deshielding area appears in the central cavity of Pd8(SR)16. All Mn(SR)2n own similar nucleus-independent chemical shift maps and deshielding cavities, which means that the H nucleus in small molecules trapped by Mn(SR)2n should have consistent low-field shifted CSs. However, such a phenomenon was only observed in the NMR spectrum of the mixed solution of Pd8(SR)16 and CH2Cl2, indicating that Pd8(SR)16 is the only one in the series of Pdn(SR)2n (n = 4~16) analogues that can capture a CH2Cl2, the H-G properties of Mn(SR)2n are highly dependent on their cavity sizes, and a guest molecule only inserts into the matching cavity of Mn(SR)2n. We anticipate that the realization of such convenient probe strategy will give a deeper understanding of the H-G properties of Mn(SR)2n.

During radar detection, the adaptive beamforming technique needs to create nulls to resist the interference. When the interference appears within the mainlobe, the main detection beam will become distorted. To solve this problem, a new method for the covariance matrix reconstruction is proposed for the mainlobe maintenance problem, and a worst-case performance optimization (WCPO) algorithm with enhanced waveform robustness is obtained. Its integration is performed over a known region without the target information to obtain the improved covariance matrix, which is then brought into the convex optimization equation to solve for the weight vector. Simulation results show that the output signal-to-noise ratio of this algorithm is higher than that of the conventional WCPO algorithm with a robust beam for the same signal-to-noise ratio. It can also effectively eliminate the primary lobe offset and secondary lobe elevation problems.

Steering acid fracturing is a new way which can significantly increase oil and gas production. However, it is still unknown how to appropriately use steering acid in carbonate reservoir. Therefore, four true tri-axial acid fracturing experiments were carried out to study fracture initiation and propagation during steering acid fracturing. The experimental results reveal the following. 1. The results of the acid fracturing are easily affected by natural vugs, which can change the direction of the acid-etched fracture propagation. When there are few vugs in the reservoir, the steering acid etches the surface of the acid-etched fractures and forms crowds of acid-etched vugs. 2. When using high pumping rate, it is easy for the steering acid to plug the top of the acid-etched fracture and force the fracture to change its propagation direction. 3. The acid will etch the fracture surface, which results in a strong conductivity. The acid-etching phenomenon is obvious in the area near the wellbore and the turning area. The steering acid etches multiple channels with high conductivities rather than etching the entire area of the fracture surface. 4. Acid fatigue fracturing can effectively reduce the fracturing pressure. However, when using this method, there will be few acid-etched vugs in the area far from the wellbore. When acid is used as fracturing fluid, it would react with the carbonate, and form complex fracture networks.

In view of the functional failure or safety of the key components of the Software defined radio (SDR) communication link caused by electromagnetic pulse, the electromagnetic sensitivity of the lower noise amplifier (LNA) in radio frequency front end is discussed in this manuscript. By analyzing the electromagnetic topology and coupling mechanism of interference to typical SDR communication links, the equivalent circuit of LNA is designed. ADS is used to simulate and analyze the electromagnetic sensitivity of LNA in radio frequency front end to extract the sensitivity threshold to electromagnetic pulse. The behavior characteristics of the pole current signal of the Pseudomorphic High Electron Mobility Transistor (PHEMT), key part of the LNA, is studied, and the damage model of different stages of PHEMT is established. The equivalent electromagnetic sensitivity model of LNA is finally obtained and analyzed by simulation. The results show that the PHEMT characteristic model can well reflect the damage characteristics of LNA at all levels.

Incorporating reversible dynamic linkages into the polymer networks endows traditional thermosets with recyclability and reprocessability. However, the facile preparation of recyclable polymer networks with suitable stability and acceptable cost is still a challenge. Among various dynamic linkages, ionic bonds promise a rational dynamic linkage in virtue of suitable stability and facile chemical synthesis. In this study, dynamic ionic bonds were incorporated into the waterborne polyacrylate to form adaptable polymer networks. The carboxyl groups of waterborne polyacrylate provide hydrophilicity and crosslinking sites. Metal salts were added into polyacrylate emulsion to obtain crosslinked polyacrylate via solution casting process. This crosslinking strategy has improved the solvent resistance, creep resistance and tensile strength of linear polyacrylates. The effect of metal cation crosslinking on the water resistance depends on the carboxyl content of linear polyacrylate. Subsequently the mechanical property of pristine and recycled crosslinked polyacrylate was evaluated. Polyacrylate networks crosslinked by divalent metal zinc cation show superior tensile strength and recyclability. Anions of zinc salts have an obvious influence on the enhancement and recyclability of obtained polyacrylate networks. Polyacrylate crosslinked by zinc acetate shows optimal comprehensive performance and application prospect. In addition, the shape memory effect of polyacrylate crosslinked by metal salt zinc acetate was investigated. The shape fixity ratio and shape recovery ratio were 99.8% and 84.9%, respectively. This strategy promises great prospect in designing and preparing customizable high performance recyclable smart thermosets.

Concrete structures usually contain cracks or microcracks. Under dynamic loading, such as impacts, blasts and earthquakes, these cracks may initiate and propagate, weakening concrete strength and structure’s stability. It is thus necessary to carry out the research on the crack dynamic fracture behavior and to develop crack arresting technique for cracked concrete structures under dynamic loads. In this study, impact tests were performed using a drop-weight impact device. A single crack emanating from a semicircle and a V-shaped bottom (SCESVB) specimen was proposed. The V-shaped bottom has the function of arrest on the propagation of the pre-crack. Crack propagation gauges (CPGs) were used to measure crack propagation parameters. Three angles 120°, 150° and 180° were designed for the V-shaped bottom of the SCESVB specimens. The crack propagation behavior was simulated by the finite difference code AUTODYN, and the dynamic stress intensity factor (DSIF) was calculated by the finite element code ABAQUS. The critical DSIF was determined by the crack initiation time and the propagation time measured by the CPG. The experimental and numerical simulation results show that the SCESVB specimen is suited to studying crack propagation behavior and crack arresting behavior for concrete under dynamic loads. During the crack propagation process, the crack may arrest in a short time, and the critical DSIF at initiation is higher than that at propagation for the concrete.

Utilization of renewable biomass to prepare phase change material (PCM) that can reversibly store renewable thermal energy is of great interest. Castor oil with functional hydroxyl groups is especially attractive for the preparation of polymeric materials. In this work, a novel castor oil-based polyurethane-acrylate oligomer (COPUA) was firstly synthesized through a two-step condensation reaction. Followed by in situ polymerization of COPUA in the presence of palmitic acid (PA), a novel biomass-based form-stable PCM was prepared, in which renewable PA serves as phase change functional ingredient and castor oil-based crosslinking network acts as encapsulation material. Tailoring the mass ratio of PA and COPUA provides the ultimate encapsulation ratio (70%) of PA in form-stable PCM. The chemical structure, crystalline property, thermal property of form-stable PCM were characterized using Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, differential scanning calorimetry and thermogravimetric. Those results demonstrate that the prepared form-stable PCM possesses that good thermal storage capacity with the phase change enthalpy reaches 141.2 J g−1. Accelerated thermal cycling test was also performed to illustrate the thermal reliability of form-stable PCM.

For the purpose of improving the accuracy and effectiveness of acid fracturing design for carbonate reservoirs with developed natural fractures, an acidizing fluid flow and reaction model taking the multiple leak-off effect of natural fracture, wormhole and matrix into account was established according to the liquid phase reaction equilibrium principle and the local reaction equilibrium principle after the dynamic change of fracture geometry in the process of fracture created by prepad fluid was simulated in the classical pseudo-three dimensional mathematical model of fracture propagation. Then, the acid fracturing stimulation of a case well on site was taken as an example. The newly developed model was used to simulate the filtration process of acidizing fluid in fractures and the dynamic etching morphology of acidic rocks during the acidizing fluid injection of prepad acid fracturing. The effective length of etched fractures was determined by analyzing the concentration change of acidizing fluid along the direction of hydraulic fracture length and the threshold concentration of residual acidizing fluid comprehensively, and then it was compared with the interpretation result of pressure buildup test. And the following research results were obtained. First, in the process of acid fracturing in fractured–porous reservoirs, the acidizing fluid filtration velocity along the direction of fracture length is not constant and the filtration velocity curve fluctuates in a serrated shape. And the acidizing fluid filtration velocity where etched wormholes meet natural fractures is commonly higher than that in matrix. Second, acidizing fluid is lost seriously and the effective distance of acidizing fluid gets short significantly during the acid fracturing of fractured–porous reservoirs. Third, acid fracturing in the verification well is remarkable in blockage removing and stimulation, and its well test interpretation results are consistent with the simulation interpretation results provided by the newly developed mathematical model. It is indicated that this newly developed model is reliable. In conclusion, the mathematical model of prepad acid fracturing which considers multiple leak-off effect is more suitable for acid fracturing simulation of fractured–porous reservoirs. Keywords: Carbonate rock, Reservoir, Natural facture, Wormhole, Prepad acid fracturing, Acidizing fluid filtration, Effective fracture length, Fractured–porous, Acid fracturing simulation

A facile strategy of incorporating dynamic carboxylic zinc ion interactions into traditional linear polymers was developed to achieve the recyclability of crosslinked polymers. For newly synthesized polymers, pendant carboxyl can be incorporated into polymer chains during the synthesis process and subsequently crosslinked with zinc acetate. For commercial thermoplastics with only C–C bonds in the backbone, reactive processing offers an alternative approach to prepare vitrimers. This strategy is expected to be an effective approach for high performance recyclable polymer systems.

To distinguish the dielectric surface breakdown from the atmospheric breakdown, one method for atmospheric breakdown experiment by loading dielectric focusing lens is proposed. The focusing characteristics of dielectric focusing lens are investigated for the microwave frequency on the order of 1.3GHz to 9.3GHz, the lens focal length on the order of 0.3m to 0.9m and the dielectric constant on the order of 0.3 to 0.9. Simulations show that higher frequency, shorter focal length, and fitter dielectric constant result in better focus effect that the rising and falling edges of electric field strength change faster near the focus which is closer to the theoretical value. A dielectric focusing lens for the S-band is optimally designed with the polytetrafluoroethylene of 0.32m thickness, 0.6m diameter, and 0.4m focal length. The focus indicator of dielectric lens is measured and the atmospheric breakdown experiment is carried out. The experimental values of atmospheric breakdown are consistent with the theoretical values. The electric field strength with the lens at the focus is 5-6 times greater than that without focusing lens. The image of atmospheric breakdown by the dielectric lens focusing method experiment is clearer than that by the direct radiation method.