Controlled synthesis of Co₂C nanochains using cobalt laurate as precursor: Structure, growth mechanism and magnetic properties

Zhang, Yajing,Zhu, Yuan,Wang, Kangjun,Li, Da,Wang, Dongping,Ding, Fu,Meng, Dan,Wang, Xiaolei,Choi, Chuljin,Zhang, Zhidong Elsevier 2018 Journal of magnetism and magnetic materials Vol.456 No.-

<P><B>Abstract</B></P> <P>Cobalt carbides (Co<SUB>2</SUB>C and Co<SUB>3</SUB>C) nanocomposites exhibit interesting hard magnetic property, controlled synthesis of individual phase facilitates to clarify the magnetism of each, but it is difficult to obtain the single phase. We present a new approach to address this issue via a polyol refluxing process, using cobalt laurate as the precursor. The single phase Co<SUB>2</SUB>C magnetic nanochains self-assembled by nanoparticles are synthesized. The precursor is the key factor for controlling the growth kinetics of the Co<SUB>2</SUB>C nanochains. Cobalt, instead of cobalt carbides, is produced if cobalt chloride, acetate and acetylacetonate replace cobalt laurate as the precursor, respectively. The evolution of the growth process has been studied. In the formation of Co<SUB>2</SUB>C, first fcc-Co produces, then it transforms into Co<SUB>2</SUB>C by carbon diffusion process, and the produced carbon first exists in disordered state and then a small amount of them transforms into graphite. Saturation magnetization (<I>Ms</I>) of Co<SUB>2</SUB>C nanochains obtained at 300 °C for 20, 60, and 180 min are 27.1, 18.9, and 10.9 emu g<SUP>−1</SUP>, respectively. The decrease of <I>Ms</I> caused by increasing carbon content, and the carbon content are much larger than the stoichiometric ratio value of Co<SUB>2</SUB>C (9.2 wt%). The Co<SUB>2</SUB>C nanochains have mesoporous pore of 3.8 nm and the specific surface area of 48.6 m<SUP>2</SUP> g<SUP>−1</SUP>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The Co<SUB>2</SUB>C magnetic nanochains are synthesized using cobalt laurate as the precursor in TEG. </LI> <LI> The precursor of cobalt laurate is the key factor for controlling the growth kinetics of Co<SUB>2</SUB>C nanochains. </LI> <LI> Ms of Co<SUB>2</SUB>C nanochains obtained at 300 °C for 20, 60, and 180 min are 27.1, 18.9, and 10.9 emu g<SUP>−1</SUP>, respectively. </LI> <LI> The decrease of Ms is caused by increasing carbon content with increasing reaction time. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>We present a new approach to obtain single phase Co<SUB>2</SUB>C nanochains by using cobalt laurate as the precursor.</P> <P>[DISPLAY OMISSION]</P>

Excellent microwave absorption of FeCo/ZnO composites with defects in ZnO for regulating the impedance matching

Bao, Xiukun,Wang, Xiaolei,Zhou, Xinao,Shi, Guimei,Xu, Ge,Yu, Jin,Guan, Yinyan,Zhang, Yajing,Li, Da,Choi, Chuijin Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.769 No.-

<P><B>Abstract</B></P> <P>FeCo/ZnO composites have been successfully prepared through liquid-phase reduction process for the formation of FeCo polyhedrons and sequentially thermal decomposition of colloidal mixture of FeCo and Zn(Ac)<SUB>2</SUB>·2H<SUB>2</SUB>O under nitrogen atmospheres. ZnO nanoparticles are homogeneously deposited on the surface of FeCo polyhedrons and the level of oxygen-vacancy defects in ZnO can be elevated with the increase of ZnO content. By comparison with FeCo polyhedrons, FeCo/ZnO composites exhibit excellent microwave absorption. The optimal RL value can reach −34.8 dB at 14.8 GHz and effective bandwidth (RL < −10 dB) is 5.1 GHz in the frequency range of 12.4–17.5 GHz with a matching thickness of 1.5 mm. The integrated bandwidth with RL < −10 dB can reach 14.1 GHz covering 3.4–17.5 GHz. Theory analysis demonstrates the interfacial polarization, dipole polarization and high conductivity due to oxygen-vacancy defects in FeCo/ZnO composites contribute to enhancement of dielectric loss capacity, which is more favorable for impedance matching.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The preferable impedance matching of FeCo/ZnO composites can be achieved by regulating the ZnO content. </LI> <LI> The optimal reflection loss (RL) can reach −34.8 dB with a matching thickness of 1.5 mm. </LI> <LI> The effective bandwidth with RL < −10 dB achieve 14.1 GHz covering 3.4–17.5 GHz with integrated thickness of 1.5–5 mm. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Transmission characteristics in double and triple non-uniform magnetic barriers based on graphene

Yajing Li,Yong Guo 한국물리학회 2011 Current Applied Physics Vol.11 No.1

We evaluate the transmission and the conductance through double and triple non-uniform magnetic barriers in graphene-based nanostructures. The results indicate that non-uniform magnetic modulation results in rich transport properties. Compared with uniform double barrier magnetic structures, both the transmission and the conductance are drastically reduced through non-uniform ones. In the nonuniform triple magnetic barriers, the transmission and the conductance exhibit complicated oscillations,which vary with the width or the height of magnetic barriers. The non-uniformity introduced by altering the height and width of magnetic barriers have different effects on the transmission. For the magnetic barriers with different heights, the transmission is suppressed greatly in both low and high incident wave vector regions, while for the magnetic barriers with different widths, the obvious suppression occurs in the low incident wave vector region.

Segmentation of Slow Slip Events in South Central Alaska Possibly Controlled by a Subducted Oceanic Plateau

Li, Haotian,Wei, Meng,Li, Duo,Liu, Yajing,Kim, YoungHee,Zhou, Shiyong American Geophysical Union 2018 Journal of Geophysical Research: Solid Earth Vol.123 No.1

Loss Analysis and Soft-Switching Behavior of Flyback-Forward High Gain DC/DC Converters with a GaN FET

Li, Yan,Zheng, Trillion Q.,Zhang, Yajing,Cui, Meiting,Han, Yang,Dou, Wei The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.1

Compared with Si MOSFETs, the GaN FET has many advantages in a wide band gap, high saturation drift velocity, high critical breakdown field, etc. This paper compares the electrical properties of GaN FETs and Si MOSFETs. The soft-switching condition and power loss analysis in a flyback-forward high gain DC/DC converter with a GaN FET is presented in detail. In addition, a comparison between GaN diodes and Si diodes is made. Finally, a 200W GaN FET based flyback-forward high gain DC/DC converter is established, and experimental results verify that the GaN FET is superior to the Si MOSFET in terms of switching characteristics and efficiency. They also show that the GaN diode is better than the Si diode when it comes to reverse recovery characteristics.

Recent insights into autophagy and metals/nanoparticles exposure

Li Qiong,Feng Yajing,Wang Ruike,Liu Rundong,Ba Yue,Huang Hui 한국독성학회 2023 Toxicological Research Vol.39 No.3

Some anthropogenic pollutants, such as heavy metals and nanoparticles (NPs), are widely distributed and a major threat to environmental safety and public health. In particular, lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As), and mercury (Hg) have systemic toxicity even at extremely low concentrations, so they are listed as priority metals in relation to their significant public health burden. Aluminum (Al) is also toxic to multiple organs and is linked to Alzheimer’s disease. As the utilization of many metal nanoparticles (MNPs) gradually gain traction in industrial and medical applications, they are increasingly being investigated to address potential toxicity by impairing certain biological barriers. The dominant toxic mechanism of these metals and MNPs is the induction of oxidative stress, which subsequently triggers lipid peroxidation, protein modification, and DNA damage. Notably, a growing body of research has revealed the linkage between dysregulated autophagy and some diseases, including neurodegenerative diseases and cancers. Among them, some metals or metal mixtures can act as environmental stimuli and disturb basal autophagic activity, which has an underlying adverse health effect. Some studies also revealed that specific autophagy inhibitors or activators could modify the abnormal autophagic flux attributed to continuous exposure to metals. In this review, we have gathered recent data about the contribution of the autophagy/mitophagy mediated toxic effects and focused on the involvement of some key regulatory factors of autophagic signaling during exposure to selected metals, metal mixtures, as well as MNPs in the real world. Besides this, we summarized the potential significance of interactions between autophagy and excessive reactive oxygen species (ROS)-mediated oxidative damage in the regulation of cell survival response to metals/NPs. A critical view is given on the application of autophagy activators/inhibitors to modulate the systematic toxicity of various metals/MNPs.

The Clinical Manifestation, Executive Dysfunction, and Caregiver Strain in Subthreshold Attention-Deficit/Hyperactivity Disorder

Yajing Tang,Sunwei Qiu,Haimei Li,Feifei Si,Mengjie Zhao,Min Dong,Meirong Pan,Xinxin Yue,Lu Liu,Qiujin Qian,Yufeng Wang 대한신경정신의학회 2023 PSYCHIATRY INVESTIGATION Vol.20 No.9

Objective Subthreshold attention-deficit/hyperactivity disorder (ADHD) has been suggested to be a “morbid condition” which also needs medical attention.Methods The present study recruited 89 children with subthreshold ADHD (sADHD), 115 children with diagnosed ADHD (cADHD), and 79 healthy controls (HC) to explore the clinical manifestation, executive functions (EFs) of sADHD, and the caregiver strain. The clinical manifestation was evaluated through clinical interviews and parent-reports. Executive functions were assessed both experimentally and ecologically. Caregiver strain was measured by a parent-reported questionnaire.Results For the clinical manifestation, both sADHD and cADHD indicated impairments when compared with HC. The comorbidities and the scaled symptoms indicated that the externalizing behaviors were relatively less serious in sADHD than cADHD, whereas the internalizing behaviors between two groups were comparable. For ecological EFs, sADHD scored between cADHD and HC in inhibition and working memory. For experimental EFs, sADHD was comparable to cADHD in inhibition, shifting, and was worse than cADHD in verbal working memory. For the caregiver strain, all scores of sADHD were between that in cADHD and that in HC.Conclusion Our present findings supported the suggestion of subthreshold ADHD as “morbid condition,” which should be treated with caution in clinical practice, especially for the internalizing behaviors and some key components of EFs.

Dynamic colonization of gut microbiota and its influencing factors among the breast-feeding infants during the first two years of life

Li Ping,Chang Xuelian,Chen Xiaoyu,Tang Tiantian,Liu Yajing,Shang Yu,Qi Kemin 한국미생물학회 2022 The journal of microbiology Vol.60 No.8

The maturation of infant gut microbiota has lifelong implications on health, which has been proposed as the major events during the first year of life. However, little is known about their dynamic colonization and influencing elements among the first two-year infancy as well as into the adulthood. So based on the 16S rRNA sequencing data among 30 healthy breast-feeding mother-infant pairs with normal ranges of growth and development indicators from birth to two years old, the dynamic colonization of gut microbiota and its influencing factors were discussed using this birth cohort. Among these, we identified that the diversity of gut microbiota was significantly increased from six-month to two-year subgroups. The significantly dynamic trends of gut microbiota at the phylum (genus) level were that the percents of Firmicutes (Faecalibacterium, Blautia, Enterococcus, Subdoligranulum, Agathobacter, unidentified_Erysipelotrichaceae, Staphylococcus, unidentified_Ruminococcaceae, and Fusicatenibacter), Bacteroidetes and Verrucomicrobia were increased, while Actinobacteria (Bifidobacterium) and Proteobacteria (unidentified- Enterobacteriaceae and Klebsiella) were decreased with the increased ages from six months to two years old, which might simultaneously modulate the host pathways, such as the higher percents of chemoheterotrophy and fermentation, and lower percentages of nitrate_reduction, aerobic_chemoheterotrophy and so on. Furthermore, there were significant associations between maternal (milk microbiota, pre-pregnancy BMI, BMI increment during the pregnancy)/infant characteristics (BMI at birth and BMI gain), and the compositions of gut microbiota. However, no differences of gut microbiota were shown between the different sex and productive mode subgroups. Overall, the colonization of gut microbiota is significantly matured into the adulthood with the increased ages to two-years old and regulated by the above maternal/infant characteristics, which will provide a new direction for the host-gut microbiota interplay during the first two years of life.

Loss Analysis and Soft-Switching Behavior of Flyback-Forward High Gain DC/DC Converters with a GaN FET

Yan Li,Trillion Q. Zheng,Yajing Zhang,Meiting Cui,Yang Han,Wei Dou 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.1

Compared with Si MOSFETs, the GaN FET has many advantages in a wide band gap, high saturation drift velocity, high critical breakdown field, etc. This paper compares the electrical properties of GaN FETs and Si MOSFETs. The soft-switching condition and power loss analysis in a flyback-forward high gain DC/DC converter with a GaN FET is presented in detail. In addition, a comparison between GaN diodes and Si diodes is made. Finally, a 200W GaN FET based flyback-forward high gain DC/DC converter is established, and experimental results verify that the GaN FET is superior to the Si MOSFET in terms of switching characteristics and efficiency. They also show that the GaN diode is better than the Si diode when it comes to reverse recovery characteristics.

Investigation of the discharging behaviors of different doped silicon nanowires in alkaline Si-air batteries

Danshuo Chen,Yajing Li,Xiaochen Zhang,Sujuan Hu,Yingjian Yu 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.112 No.-

Compared with metal-air batteries, Si-air batteries have advantages on gravimetric/volumetric capacityand safety. This novel battery using flat Si wafer as anode has been preliminarily researched in recent tenyears. In this work, Si nanowires (NWs) have been fabricated on p < 100 > and n < 100 > Si wafers andtheir discharging behaviors under various operating conditions have been systematically analyzed comparedwith flat Si wafer anodes. Si NWs anodes universally exhibit longer discharge times than flat Siwafer anodes because of their larger specific surface areas and superior resistance to the passivationcaused by SiO2 deposition. It is also demonstrated that a KOH electrolyte concentration of 1.9 M is thelowest threshold for the p < 100 > Si anode at a current density of 0.03 mA/cm2, and the p < 100 > Si anodecan discharge for more than 400 h. Furthermore, n < 100 > Si NWs anodes performed best with a dischargetime of more than 500 h at higher current density of 0.05 mA/cm2 with an electrolyte concentrationof 6 M. This work can aid in understanding the electrochemical properties of silicon anodes withdifferent configurations and doping types in Si-air batteries and provide direction for the operation ofSi-air batteries at appropriate conditions.