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1.
Org Lett ; 26(27): 5799-5804, 2024 Jul 12.
Article in English | MEDLINE | ID: mdl-38953705

ABSTRACT

Herein, we disclose a photoinduced radical cascade cyclization of alkynes with sulfinates via a novel EDA complex for the synthesis of various 3-sulfonylindoles and vinyl sulfone oxindoles, which are crucial motifs in medicinal and biological chemistry. The reaction proceeds under mild, photocatalyst- and transition-metal-free conditions, featuring operational simplicity, broad substrate scope, and easy scalability. Mechanistic studies reveal that the reaction is initiated with a photoinduced intermolecular charge transfer from sulfinates to N-sulfonamides, generating a sulfonyl radical followed by an N-centered radical, thus enabling the cascade cyclization process.

2.
J Am Chem Soc ; 146(21): 14745-14753, 2024 May 29.
Article in English | MEDLINE | ID: mdl-38742738

ABSTRACT

We herein describe a Ni-catalyzed formal hydroamidation of readily available α,ß-unsaturated carbonyl compounds to afford valuable chiral ß-amino acid derivatives (up to >99:1 e.r.) using dioxazolones as a robust amino source. A wide range of alkyl-substituted olefins conjugated to esters, amides, thioesters, and ketones were successfully amidated at the ß-position with excellent enantioselectivity for the first time. Combined experimental and computational mechanistic studies supported our working hypothesis that this unconventional ß-amidation of unsaturated carbonyl substrates can be attributed to the polar-matched migratory olefin insertion of an (amido)(Cl)NiII intermediate, in situ generated from the dioxazolone precursor.

3.
Biometrics ; 80(2)2024 Mar 27.
Article in English | MEDLINE | ID: mdl-38567733

ABSTRACT

Brain-effective connectivity analysis quantifies directed influence of one neural element or region over another, and it is of great scientific interest to understand how effective connectivity pattern is affected by variations of subject conditions. Vector autoregression (VAR) is a useful tool for this type of problems. However, there is a paucity of solutions when there is measurement error, when there are multiple subjects, and when the focus is the inference of the transition matrix. In this article, we study the problem of transition matrix inference under the high-dimensional VAR model with measurement error and multiple subjects. We propose a simultaneous testing procedure, with three key components: a modified expectation-maximization (EM) algorithm, a test statistic based on the tensor regression of a bias-corrected estimator of the lagged auto-covariance given the covariates, and a properly thresholded simultaneous test. We establish the uniform consistency for the estimators of our modified EM, and show that the subsequent test achieves both a consistent false discovery control, and its power approaches one asymptotically. We demonstrate the efficacy of our method through both simulations and a brain connectivity study of task-evoked functional magnetic resonance imaging.


Subject(s)
Brain , Magnetic Resonance Imaging , Humans , Time Factors , Magnetic Resonance Imaging/methods , Brain/diagnostic imaging , Brain/physiology
4.
PLoS Genet ; 20(3): e1011196, 2024 Mar.
Article in English | MEDLINE | ID: mdl-38466721

ABSTRACT

Hematophagous mosquitoes require vertebrate blood for their reproductive cycles, making them effective vectors for transmitting dangerous human diseases. Thus, high-intensity metabolism is needed to support reproductive events of female mosquitoes. However, the regulatory mechanism linking metabolism and reproduction in mosquitoes remains largely unclear. In this study, we found that the expression of estrogen-related receptor (ERR), a nuclear receptor, is activated by the direct binding of 20-hydroxyecdysone (20E) and ecdysone receptor (EcR) to the ecdysone response element (EcRE) in the ERR promoter region during the gonadotropic cycle of Aedes aegypti (named AaERR). RNA interference (RNAi) of AaERR in female mosquitoes led to delayed development of ovaries. mRNA abundance of genes encoding key enzymes involved in carbohydrate metabolism (CM)-glucose-6-phosphate isomerase (GPI) and pyruvate kinase (PYK)-was significantly decreased in AaERR knockdown mosquitoes, while the levels of metabolites, such as glycogen, glucose, and trehalose, were elevated. The expression of fatty acid synthase (FAS) was notably downregulated, and lipid accumulation was reduced in response to AaERR depletion. Dual luciferase reporter assays and electrophoretic mobility shift assays (EMSA) determined that AaERR directly activated the expression of metabolic genes, such as GPI, PYK, and FAS, by binding to the corresponding AaERR-responsive motif in the promoter region of these genes. Our results have revealed an important role of AaERR in the regulation of metabolism during mosquito reproduction and offer a novel target for mosquito control.


Subject(s)
Aedes , Receptors, Steroid , Animals , Female , Humans , Aedes/genetics , Aedes/metabolism , Ecdysone/metabolism , Mosquito Vectors/genetics , Receptors, Cytoplasmic and Nuclear/genetics , Receptors, Cytoplasmic and Nuclear/metabolism , Homeostasis/genetics , Insect Proteins/genetics , Insect Proteins/metabolism
5.
Molecules ; 28(23)2023 Nov 27.
Article in English | MEDLINE | ID: mdl-38067522

ABSTRACT

Poly(vinyl chloride) (PVC) is widely used in various fields and requires the use of thermal stabilizers to enhance its thermal stability during processing because of its poor thermal stability. Layered double hydroxides (LDHs) are widely considered to be one kind of highly efficient and environmentally friendly PVC thermal stabilizer. To investigate the thermal stabilizing process of layered double hydroxides (LDHs) in PVC resin, PVC and MgAl-LDHs powders with different interlayer anions (CO32-, Cl-, and NO3-) were physically mixed and aged at 180 °C. The structure of LDHs at different aging times was studied using XRD, SEM, and FT-IR. The results show that the thermal stabilizing process of LDHs on PVC mainly has three stages. In the first stage, the layers of LDHs undergo a reaction with HCl, which is released during the thermal decomposition of PVC. Subsequently, the ion exchange process occurs between Cl- and interlayer CO32-, resulting in the formation of MgAl-Cl-LDHs. Finally, the layers of MgAl-Cl-LDHs react with HCl slowly. During the thermal stabilizing process of MgAl-Cl-LDHs, the peak intensity of XRD reduces slightly, and no new XRD peak emerges. It indicates that only the first step happens for MgAl-Cl-LDHs. The TG-DTA analysis of LDHs indicates that the interaction of LDHs with different interlayer anions has the following order: NO3- < CO32- < Cl-, according to the early coloring in the thermal aging test of PVC composites. The results of the thermal aging tests suggest that LDHs with a weak interaction between interlayer anions and layers can enhance the early stability of PVC significantly. Furthermore, the thermal aging test demonstrates that LDHs with high HCl absorption capacities exhibit superior long-term stabilizing effects on PVC resin. This finding provides a valuable hint for designing an LDHs/PVC resin with a novel structure and excellent thermal stability.

6.
J Am Stat Assoc ; 118(543): 2158-2170, 2023.
Article in English | MEDLINE | ID: mdl-38143786

ABSTRACT

Thanks to its fine balance between model flexibility and interpretability, the nonparametric additive model has been widely used, and variable selection for this type of model has been frequently studied. However, none of the existing solutions can control the false discovery rate (FDR) unless the sample size tends to infinity. The knockoff framework is a recent proposal that can address this issue, but few knockoff solutions are directly applicable to nonparametric models. In this article, we propose a novel kernel knockoffs selection procedure for the nonparametric additive model. We integrate three key components: the knockoffs, the subsampling for stability, and the random feature mapping for nonparametric function approximation. We show that the proposed method is guaranteed to control the FDR for any sample size, and achieves a power that approaches one as the sample size tends to infinity. We demonstrate the efficacy of our method through intensive simulations and comparisons with the alternative solutions. our proposal thus makes useful contributions to the methodology of nonparametric variable selection, FDR-based inference, as well as knockoffs.

7.
Medicine (Baltimore) ; 102(46): e34868, 2023 Nov 17.
Article in English | MEDLINE | ID: mdl-37986280

ABSTRACT

The aim of this study was to retrospectively analyze the clinical efficacy and safety of Qingfei Paidu granules (QFPG) combined with non-drug therapy of traditional Chinese medicine (TCM) in treating patients with asymptomatic coronavirus disease 2019 (COVID-2019). A total of 450 patients admitted to the wards of Chongming Changxing Island isolation site from April 1 to 18, 2022 were retrospectively analyzed and divided into 3 groups according to the treatment that they received. W1 was not treated (control group), and W2 was given QFPG (TCM treatment), W3 (TCM combined with TCM non-drug therapy) was treated with QFPG, five-element music therapy and Gong. We retrospectively analyzed the medical history data, including general information, time of first turning negative, length of hospital stays, number of cases classified as mild or ordinary, number of cases with adverse events/adverse reactions. The conversion to negative time of the 3 groups was 6.50, 4.40, and 3.81 days, respectively, and there were significant differences among the 3 groups (P < .001). The hospital duration in the 3 groups was 8.45, 5.72, and 5.53 days, respectively, and there were significant differences among the 3 groups (P < .001). The number of adverse events W1 (5/150, 3.3%), W2 (8/150, 5.3%), and W3 (4/150, 2.7%) was consistent among the 3 groups (P > .05). QFPG with TCM non-drug therapy is effective in patients with asymptomatic COVID-2019, which can effectively shorten the time to double negative and reduce the proportion of patients with mild disease.


Subject(s)
COVID-19 , Drugs, Chinese Herbal , Humans , Medicine, Chinese Traditional , Retrospective Studies , SARS-CoV-2 , Drugs, Chinese Herbal/therapeutic use , COVID-19 Drug Treatment , Asymptomatic Diseases
8.
J Phys Condens Matter ; 35(40)2023 Jul 10.
Article in English | MEDLINE | ID: mdl-37379853

ABSTRACT

Binary ruthenium dioxide (RuO2) has gradually attracted much attention in condensed matter physics and material sciences due to its various intriguing physical properties, such as strain-induced superconductivity, anomalous Hall effect, collinear anti-ferromagnetism, etc. However, its complex emergent electronic states and the corresponding phase diagram over a wide temperature range remain unexplored, which is critically important to understanding the underlying physics and exploring its final physical properties and functionalities. Here, through optimizing the growth conditions by using versatile pulsed laser deposition, high-quality epitaxial RuO2thin films with clear lattice structure are obtained, upon which the electronic transport is investigated, and emergent electronic states and the relevant physical properties are unveiled. Firstly, at a high-temperature range, it is the Bloch-Grüneisen state, instead of the common Fermi liquid metallic state, that dominates the electrical transport behavior. Moreover, the recently reported anomalous Hall effect is also revealed, which confirms the presence of the Berry phase in the energy band structure. More excitingly, we find that above the superconductivity transition temperature, a new positive magnetic resistance quantum coherent state with an unusual dip as well as an angel-dependent critical magnetic field emerges, which can be attributed to the weak antilocalization effect. Lastly, the complex phase diagram with multiple intriguing emergent electronic states over a wide temperature range is mapped. The results greatly promote the fundamental physics understanding of the binary oxide RuO2and provide guidelines for its practical applications and functionalities.

9.
ChemSusChem ; 16(16): e202300350, 2023 Aug 21.
Article in English | MEDLINE | ID: mdl-37198136

ABSTRACT

Lithium-ion battery cathode materials suffer from bulk and interfacial degradation issues, which negatively affect their electrochemical performance. Oxide coatings can mitigate some of these problems and improve electrochemical performance. However, current coating strategies have low throughput, are expensive, and have limited applicability. In this article, we describe a low-cost and scalable strategy for applying oxide coatings on cathode materials. We report synergistic effects of these oxide coatings on the performance of aqueously processed cathodes in cells. The SiO2 coating strategy developed herein improved mechanical, chemical, and electrochemical performance of aqueously processed Ni-, Mn- and Co-based cathodes. This strategy can be used on a variety of cathodes to improve the performance of aqueously processed Li-ion cells.

10.
Chem Asian J ; 18(6): e202201305, 2023 Mar 14.
Article in English | MEDLINE | ID: mdl-36696069

ABSTRACT

Developing a fast and highly active oxygen evolution reaction (OER) catalyst to change energy kinetics technology is essential for making clean energy. Herein, we prepare three-dimensional (3D) hollow Mo-doped amorphous FeOOH (Mo-FeOOH) based on the precatalyst MoS2 /FeC2 O4 via in situ reconstruction strategy. Mo-FeOOH exhibits promising OER performance. Specifically, it has an overpotential of 285 mV and a durability of 15 h at 10 mA cm-2 . Characterizations indicate that Mo was included inside the FeOOH lattice, and it not only modifies the electronic energy levels of FeOOH but also effectively raises the inherent activity of FeOOH for OER. Additionally, in situ Raman analysis indicates that FeC2 O4 gradually transforms into the FeOOH active site throughout the OER process. This study provides ideas for designing in situ reconstruction strategies to prepare heteroatom doping catalysts for high electrochemical activity.

11.
Insect Sci ; 30(1): 81-94, 2023 Feb.
Article in English | MEDLINE | ID: mdl-35633120

ABSTRACT

Hormones control the reproductive development of Aedes aegypti mosquitoes. The adult male reproductive process and mating behavior require adequate nutrients and energy. Understanding the molecular mechanism linking hormones, energy metabolism, and reproduction in male mosquitoes is important. In this study, we found that the size of the male accessory gland, an essential part of the male reproductive system, gradually increased after eclosion. However, it was significantly reduced in male mosquitoes deficient in methoprene-tolerant (Met), the receptor of juvenile hormone. Likewise, egg hatchability of females that mated with Met-depleted males showed the same downward trend. The mRNA level of the gene encoding accessory gland protein, l-asparaginase (ASNase), was reduced in Met dsRNA-treated males. Electrophoretic mobility shift assay and quantitative reverse transcription-PCR results revealed that Met was capable of binding directly to the promoter of ASNase and activated its transcription. RNA interference of ASNase in males resulted in the reduction of egg hatchability of the females with which they mated. These results showed that Met influenced the fecundity of male mosquitoes by directly upregulating the expression of the ASNase gene. Moreover, the levels of triacylglycerol and the sizes of lipid droplets were decreased by 72-78 h after eclosion in the fat body cells, whereas both of them increased in Met-depleted male mosquitoes, indicating that Met knockdown reduced lipid catabolism. These data demonstrate that Met might influence the egg hatchability of females by regulating lipid metabolism and the development of the male accessory gland in male mosquitoes.


Subject(s)
Aedes , Female , Male , Animals , Aedes/genetics , Juvenile Hormones/metabolism , Asparaginase/metabolism , Methoprene , Lipid Metabolism , Triglycerides/metabolism , Insect Proteins/genetics
12.
Zhongguo Zhong Yao Za Zhi ; 47(17): 4560-4564, 2022 Sep.
Article in Chinese | MEDLINE | ID: mdl-36164860

ABSTRACT

Animal medicine is a large category of Chinese medicinecommonly used in clinical practice and has important scientific and therapeutic value. Animal medicine isscarcer than herbal medicine. In recent years, with the vigorous development of traditional Chinese medicine(TCM),the contradiction between the increasing industrial demand andsupply of scarce and even endangered medicinal animals has become increasingly prominent. The continuous lack of medicinal animal resources affects the clinical demandandalso causes serious damage to the ecological environment. Only relying on artificial breeding is not enough to alleviate the current condition of depletion. In the face of this dilemma, it is a major challenge for the current industrial development to protect animal resources and meet clinical and industrial needs with "available medicines". The application of substitutes for animal medicines isthe key focus to alleviate this problem, and it is also the key scientific issue to be solved urgently in the modernization of TCM. This paper summarizedand reviewedthe history, current situation, strategies, and methods of animal medicinesubstitution and put forward the point of view of "similar chemical characteristics, similar efficacy, and higher safety" to provide references for scientific substitution and resource protection of rare animals.


Subject(s)
Drugs, Chinese Herbal , Plants, Medicinal , Animals , Drugs, Chinese Herbal/therapeutic use , Medicine, Chinese Traditional , Plant Breeding , Research Design
13.
RSC Adv ; 12(24): 15373-15377, 2022 May 17.
Article in English | MEDLINE | ID: mdl-35693244

ABSTRACT

Thermal insulation materials are highly desirable for several applications ranging from building envelopes to thermal energy storage systems. A new type of low-cost insulation material called hollow silica particles (HSPs) was recently reported. The present work presents an HSP-based stand-alone composite that has very low thermal conductivity and is highly stable to moisture.

14.
J Am Chem Soc ; 144(22): 10064-10074, 2022 06 08.
Article in English | MEDLINE | ID: mdl-35621341

ABSTRACT

Intramolecular alkyne hydroamidation represents a straightforward approach for the access to synthetically valuable cyclic enamides. Despite some advances made in this realm, the ability to attain a precise regiocontrol still remains challenging, especially for endo cyclization that leads to six-membered and larger azacyclic rings. Herein, we report a NiH-catalyzed intramolecular hydroamidation of alkynyl dioxazolones that allows for an excellent endo selectivity, thus affording a range of six- to eight-membered endocyclic enamides with a broad scope. Mechanistic investigations revealed that Ni(I) catalysis is operative in the current system, proceeding via regioselective syn-hydronickelation, alkenylnickel E/Z isomerization, and Ni-centered inner-sphere nitrenoid transfer. In particular, the key alkenylnickel isomerization step, which previously lacked mechanistic understandings, was found to take place through the η2-vinyl transition state. The synthetic value of this protocol was demonstrated by diastereoselective modifications of the obtained endocyclic enamides to highly functionalized δ-lactam scaffolds.


Subject(s)
Alkynes , Catalysis , Cyclization , Isomerism , Stereoisomerism
15.
Polymers (Basel) ; 13(19)2021 Sep 24.
Article in English | MEDLINE | ID: mdl-34641077

ABSTRACT

In this paper, a basalt fiber surface was treated with coupling agent KH-550 and hydrochloric acid, and the basalt fiber polymer-modified active powder concrete (RPC) material was prepared. There are significant differences in material composition and properties between basalt fiber polymer-modified RPC and ordinary concrete, and the structural design calculation (cracking moment and normal section bending bearing capacity) of an ordinary reinforced concrete beam is no longer applicable. Thus, mechanical parameters such as displacement and strain of reinforcement basalt fiber polymer-modified RPC beams subjected to four-point bending were tested. The excellent compressive and tensile strengths of basalt fiber polymer-modified RPC were fully utilized. The tensile strength of basalt fiber polymer-modified RPC in the tensile zone of the beam was considered in the calculation of normal section bending bearing capacity of reinforcement basalt fiber polymer-modified RPC beams. The results showed that the measured values of the cracking moment and ultimate failure bending moment of reinforcement basalt fiber polymer-modified RPC beams were in good agreement with the calculated values. The established formulas for cracking moment and normal section bending bearing capacity can provide references for the design of reinforcement basalt fiber polymer-modified RPC simply supported beam and promote the wide application of basalt fiber polymer-modified RPC materials in practical engineering.

16.
J Am Chem Soc ; 143(15): 5867-5877, 2021 04 21.
Article in English | MEDLINE | ID: mdl-33834777

ABSTRACT

The formal hydroamination/hydroamidation utilizing metal hydride is an appealing synthetic tool for the construction of valuable nitrogen-containing compounds from unsaturated hydrocarbons. While significant advances have been made for the functionalizations of alkenes in this realm, the direct hydroamidation of alkynes remains rather limited due to the high feasibility of the key metal-alkenyl intermediate to choose other reaction pathways. Herein, we report a NiH-catalyzed strategy for the hydroamidation of alkynes with dioxazolones, which allows convenient access to synthetically useful secondary enamides in (E)-anti-Markovnikov or Markovnikov selectivity. The reaction is viable for both terminal and internal alkynes and is also tolerant with a range of subtle functional groups. With H2O found as an essential component for high catalyst turnovers, the involvement of inner-sphere nitrenoid transfer is proposed that outcompetes an undesired semireduction process, thus representing the first example to show the competence of Ni catalysis for metal-nitrenoid formation from dioxazolones.

17.
PeerJ ; 9: e10841, 2021.
Article in English | MEDLINE | ID: mdl-33763297

ABSTRACT

BACKGROUND: Topspin is one of the most attacking stroke in table tennis sport. The aim of this research was to investigate the kinematic characteristics of the lower limb (driving leg) during topspin forehand loop in different playing level table tennis athletes. METHODS: Ten male table tennis athletes performed topspin forehand loop shots with maximal force to hit the ball that was played by a professional table tennis coach. The three-dimensional Vicon motion analysis system was used to capture the kinematic information. RESULTS: The key findings from this research indicate that there were no significant differences in motion time between elite athletes (EA) and medium athletes (MA) during the entire phase (P = 0.784). EA showed significantly less knee (P < 0.001) as well as hip (P < 0.001) flexion in the BS stage when contrasted to MA, with a significant larger ankle varus (P = 0.003) as well as eversion (P < 0.001) than MA in the BS and FS phase, respectively. EA displayed a significant larger angular changing rate of ankle dorsiflexion (P < 0.001) and varus (P < 0.001) in the BS stage with ankle plantar flexion as well as eversion during the FS stage, with a significant larger ankle internal rotation (P = 0.003) and external rotation (P < 0.001) than MA in the BS and FS phase, respectively. Furthermore, EA showed significantly larger ankle dorsiflexion (P = 0.001) as well as plantarflexion (P < 0.001) ROM in the BS and FS phase respectively compared with MA. CONCLUSION: Ankle activities in the all plane displayed significant differences in kinematic characteristics between EA and MA. MA should pay attention to the function that ankle played in the kinetic chain, such as training the lower limb muscle rapid reaction ability to improve the energy transfer efficiency and capability of the kinetic chain.

18.
Biomed Environ Sci ; 34(1): 83-88, 2021 Jan 20.
Article in English | MEDLINE | ID: mdl-33531111

ABSTRACT

Pneumoconiosis, an interstitial lung disease that occurs from breathing in certain kinds of damaging dust particles, is a major occupational disease in China. Patients diagnosed with occupational pneumoconiosis can avail of free medical treatment, whereas patients without a diagnosis of occupational diseases cannot not claim free medical treatment in most provinces from the government before 2019. This study aimed to analyze the priority of medical facility selection and its influencing factors among patients with pneumoconiosis. A total of 1,037 patients with pneumoconiosis from nine provinces in China were investigated. The health service institutions most frequently selected by the patients were county-level hospitals (37.5%). The main reason for the choice was these hospitals' close distance to the patients' homes (47.3%). The factors for the choice of health care institutions were living in the eastern region ( OR = 2.91), living in rural areas ( OR = 2.10), silicosis diagnosis ( OR = 2.44), employment in private enterprises ( OR = 2.91), smoking ( OR = 2.69), and quit smoking ( OR = 3.98). The diagnosis, treatment, and rehabilitation therapy of pneumoconiosis should be enhanced in primary medical institutions.


Subject(s)
Patient Acceptance of Health Care/statistics & numerical data , Pneumoconiosis/therapy , Adult , Aged , China , Female , Hospitals , Humans , Insurance Coverage , Male , Middle Aged , Rural Population , Silicosis , Smoking
19.
Nanomaterials (Basel) ; 10(10)2020 Oct 21.
Article in English | MEDLINE | ID: mdl-33096903

ABSTRACT

The urban environment is facing serious problems caused by automobile exhaust pollution, which has led to a great impact on human health and climate, and aroused widespread concern of the government and the public. Nano titanium dioxide (TiO2), as a photocatalyst, can be activated by ultraviolet irradiation and then form a strong REDOX potential on the surface of the nano TiO2 particles. The REDOX potential can degrade the automobile exhaust, such as nitrogen oxides (NOx) and hydrocarbons (HC). In this paper, a photocatalytic environmentally friendly pervious concrete (PEFPC) was manufactured by spraying nano TiO2 on the surface of it and the photocatalytic performance of PEFPC was researched. The nano TiO2 particle size, TiO2 dosage, TiO2 spraying amount, and dispersant dosage were selected as factors to investigate the efficiency of photocatalytic degradation of automobile exhaust by PEFPC. Moreover, the environmental scanning electron microscope (ESEM) was used to evaluate the distribution of nano TiO2 on the surface of the pervious concrete, the distribution area of nano TiO2 was obtained through Image-Pro Plus, and the area ratio of nano TiO2 to the surface of the pervious concrete was calculated. The results showed that the recommended nano TiO2 particle size is 25 nm. The optimum TiO2 dosage was 10% and the optimum dispersant dosage was 5.0%. The photocatalytic performance of PEFPC was best when the TiO2 spraying amount was 333.3 g/m2. The change in the photocatalytic ratio of HC and NOx is consistent with the distribution area of nano TiO2 on the surface of the pervious concrete. In addition, the photocatalytic performance of PEFPC under two light sources (ultraviolet light and sunlight) was compared. The results indicated that both light sources were able to stimulate the photocatalytic performance of PEFPC. The research provided a reference for the evaluation of automobile exhaust removal performance of PEFPC.

20.
Sensors (Basel) ; 20(18)2020 Sep 17.
Article in English | MEDLINE | ID: mdl-32957669

ABSTRACT

This paper presented a laboratory investigation for analyzing the natural frequency response of reinforced concrete (RC) beams affected by steel corrosion. The electrochemical acceleration technique induced the corroded RC beams until the predetermined value of the steel corrosion ratio was achieved. Then, the natural frequency responses of the corroded beams were tested utilizing piezoelectric acceleration sensors. The damage states of the corroded beams were assessed through the measurement of crack parameters and the equivalent elastic modulus of the beams, which aims to clarify the fundamental characteristics of the dynamic response for the corroded RC beam with the increased steel corrosion ratio. The results revealed that steel corrosion reduces the bending stiffness of the RC beams and, thus, reduces the modal frequency. The variation of natural frequency can identify the corrosion damage even if no surface cracking of the RC beam, and the second-order frequency should be more indicative of the damage scenario. The degradations of stiffness and the natural frequency were estimated in this study by the free vibration equation of a simply supported beam, and a prediction method for the RC beam's residual service life was established. This study supports the use of variations in natural frequency as one diagnostic indicator to evaluate the health of RC bridge structures.

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