Abstract. The study involved 300 elderly patients with chronic periapical periodontitis. The patients were randomly assigned into three groups. The treatment for group A used a Mtwo Ni-Ti rotary instrument combined with ultrasonic irrigation of a 2.5% NaOCl solution. The group B used the same instrument combined with ultrasonic irrigation of an active silver ion antibacterial solution. The group C used the same instrument combined with syringe irrigation of a 2.5% NaOCl solution. The root canal fillings were performed immediately after canal preparation. Twenty-four hours after the procedure, patients self-assessed pain levels according to the VAS table. The three groups returned after seven days so their postoperative acute reactions could be evaluated clinically. After six and twelve months, efficacy was evaluated. The self-assessed pain levels for group A and B were significantly lower than group C. The incidence of postoperative acute reactions after seven days for group A and B were significantly lower than those of group C. The effective rates after six and twelve months did not differ among these groups. The single-visit root canal treatment with a nickel-titanium rotary instrument combined with ultrasonic irrigation for elderly patients with chronic periapical periodontitis achieved short and long term efficacy and stability.
Because of their high ionic conductivity,
utilizing gel
polymer
electrolytes (GPEs) is thought to be an effective way to accomplish
high-energy-density batteries. Nevertheless, most GPEs have poor adaptability
to Ni-rich cathodes to alleviate the problem of inevitable rapid capacity
decay during cycling. Therefore, to match LiNi0.8Co0.1Mn0.1O2 (NCM811), we applied pentaerythritol
tetraacrylate (PETEA) monomers to polymerize in situ in a polyacrylonitrile
(PAN) membrane to obtain GPEs (PETEA-TCGG-PAN). The impedance variations
and key groups during the in situ polymerization of PETEA-TCGG-PAN
are investigated in detail. PETEA-TCGG-PAN with a high lithium-ion
transference number (0.77) exhibits an electrochemical decomposition
voltage of 5.15 V. Noticeably, the NCM811|PETEA-TCGG-PAN|Li battery
can cycle at 2C for 120 cycles with a capacity retention
rate of 89%. Even at 6C, the discharge specific capacity
is able to reach 101.47 mAh g–1. The combination
of LiF and Li2CO3 at the CEI interface is the
reason for the improved rate performance. Moreover, when commercialized
LFP is used as the cathode, the battery can also cycle stably for
150 cycles at 0.5C. PETEA and PAN can together foster
the transportation of Li+ with the construction of a fast
ion transport channel, making a contribution to stable charge–discharge
of the above batteries. This study provides an innovative design philosophy
for designing in situ GPEs in high-energy-density lithium metal batteries.
Columns of frame structures are the key load-bearing components and the exterior columns are susceptible to attack in terrorist blasts. When subjected to blast loads, the columns would suffer a loss of bearing capacity to a certain extent due to the damage imparted, which may induce the collapse of them and even cause the progressive collapse of the whole structure. In this paper, the high-fidelity physics-based finite element program LS-DYNA was utilized to investigate the dynamic behavior and damage characteristics of the widely used concrete-filled steel tube (CFST) columns subjected to blast loads. The established numerical model was calibrated with test data in open literatures. Possible damage modes of CFST columns under blast loading were analyzed, and the damage criterion based on the residual axial load capacity of the columns was adopted to assess the damage degree. A parametric study was conducted to investigate the effects of critical parameters such as blast conditions and column details on the damage degree of CFST columns. Based on the numerical simulation data, an empirical equation was proposed to estimate the variation of columns damage degree with the various parameters.
Compressive strength and tensile strength are important mechanical properties of concrete. The long-term strength of concrete under real service environment is an important parameter when evaluating existing buildings, which should also be properly considered in structural design. In this study, the relationship between compressive and splitting tensile strength of old concrete existing for long period under marine environment was investigated. At a deserted harbour, concrete cores samples were drilled by pairs in site. For each pair of samples, the two cores were drilled from the adjacent location and conducted to compressive, splitting tensile test, respectively. 48 compressive and splitting tensile strengths were finally obtained. From the test results, tensile strength presents general uptrend with compressive strength, and the two parameters are well positively correlated. Exponential model generally recommended by building codes or literatures is still capable of describing the relationship between compressive and tensile strength of old deteriorated concrete, when function parameters are properly determined. Based on statistical theory and the experimental result of this study, a method for predicting long-term tensile strength of concrete is developed and an example is given, which may provide a potential way to estimate long-term concrete strength under real marine environment.
External bonding of FRP laminates to the tension soffit of concrete members has become a popular method for flexural strengthening. However, the long-term field performance of FRP-strengthened RC members under service conditions is still a concern, and more work needs to be done. Based on concrete smeared-crack approach, this paper presents a finite-element (FE) model for predicting long-term behavior of FRP-strengthened RC beam, which considers the time-dependent properties of all components including the aging effect of concrete. According to the comparison between theoretical predictions and test results, the validity of the FE model is verified. The interfacial edge stresses in adhesive layer were determined through appropriate mesh refinement near the plate end, and their time-dependent characteristics were investigated. The results show that creep of concrete and epoxy resin cause significant variations of the edge stresses with time. According to the research in this paper, the FE approach is found to be able to properly simulate the long-term behavior of the FRP-strengthened beam and help us better understand the complex changes in the stress state occurring over time.
Dissertation writing is not only one of the major sections of practical abilities of English majors, but also one of the important channels to improve their comprehensive abilities. In the new era of internet and multi culture, the quality of English majors' dissertation is in the process of deceasing continuously due to various factors like the society, culture, educational context, etc, causing the malfunctions of dissertation writing. This paper analyzes the practical problems of English dissertation writing in the newly-built colleges in China, including its essence and expectations in college education and, provides some countermeasures for improving the quality of dissertation ecologically.
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