Superconductivity in the PbO-type structure α-FeSe Hsu, Fong-Chi; Luo, Jiu-Yong; Yeh, Kuo-Wei ...
Proceedings of the National Academy of Sciences - PNAS,
09/2008, Letnik:
105, Številka:
38
Journal Article
Recenzirano
Odprti dostop
The recent discovery of superconductivity with relatively high transition temperature (Tc) in the layered iron-based quaternary oxypnictides LaO₁₋xFx FeAs by Kamihara et al. Kamihara Y, Watanabe T, ...Hirano M, Hosono H (2008) Iron-based layered superconductor LaO1-xFx FeAs (x = 0.05-0.12) with Tc = 26 K. J Am Chem Soc 130:3296-3297. was a real surprise and has generated tremendous interest. Although superconductivity exists in alloy that contains the element Fe, LaOMPn (with M = Fe, Ni; and Pn = P and As) is the first system where Fe plays the key role to the occurrence of superconductivity. LaOMPn has a layered crystal structure with an Fe-based plane. It is quite natural to search whether there exists other Fe based planar compounds that exhibit superconductivity. Here, we report the observation of superconductivity with zero-resistance transition temperature at 8 K in the PbO-type α-FeSe compound. A key observation is that the clean superconducting phase exists only in those samples prepared with intentional Se deficiency. FeSe, compared with LaOFeAs, is less toxic and much easier to handle. What is truly striking is that this compound has the same, perhaps simpler, planar crystal sublattice as the layered oxypnictides. Therefore, this result provides an opportunity to better understand the underlying mechanism of superconductivity in this class of unconventional superconductors.
This study reports that highly oxygen-deficient CeO2 nanoparticles (NPs) can be obtained without reduction treatment by using thermal decomposition method. Different amounts of surfactants are used ...to control the size of the NPs. The X-ray absorption near-edge spectra (XANES) indicate that the concentration of Ce3+ is higher than 20% for all NPs. It is also found that most Ce3+ locates at the surface. Magnetic-measurement results show that room-temperature ferromagnetism (FM) of the CeO2 is closely related to the concentration of Ce3+ at the surface (I s Ce3+ ). Saturation magnetization (M s) reaches the maximum value with an I s Ce3+ of about 40%; however, M s decreases when I s Ce3+ is raised further. The highest M s in this study is obtained from the sample without surfactant (M s = 0.12 emu/g). This is comparable with the results in other reports in which the CeO2 NPs were subjected to the reduction treatment. Notably, NPs become paramagnetic when I s Ce3+ reaches 48%. This study suggests that oxygen vacancy is essential for the formation of FM in CeO2 NPs. However, FM will be suppressed with excess oxygen deficiency. The effect of surfactant on the growth and the stoichiometry of the CeO2 particles will also be discussed in this report.
1 Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan; 2 Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung, Taiwan; and 3 Graduate ...Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan, Republic of China
Submitted 15 January 2008
; accepted in final form 4 March 2008
H + -ATPase-rich (HR) cells in zebrafish gills/skin were found to carry out Na + uptake and acid-base regulation through a mechanism similar to that which occurs in mammalian proximal tubular cells. However, the roles of carbonic anhydrases (CAs) in this mechanism in zebrafish HR cells are still unclear. The present study used a functional genomic approach to identify 20 CA isoforms in zebrafish. By screening with whole mount in situ hybridization, only zca2-like a and zca15a were found to be expressed in specific groups of cells in zebrafish gills/skin, and further analyses by triple in situ hybridization and immunocytochemistry demonstrated specific colocalizations of the two zca isoforms in HR cells. Knockdown of zca2-like a caused no change in and knockdown of zca15a caused an increase in H + activity at the apical surface of HR cells at 24 h postfertilization (hpf). Later, at 96 hpf, both the zca2-like a and zca15a morphants showed decreased H + activity and increased Na + uptake, with concomitant upregulation of znhe3b and downregulation of zatp6v1a (H + -ATPase A-subunit) expressions. Acclimation to both acidic and low-Na + fresh water caused upregulation of zca15a expression but did not change the zca2-like a mRNA level in zebrafish gills. These results provide molecular physiological evidence to support the roles of these two zCA isoforms in Na + uptake and acid-base regulation mechanisms in zebrafish HR cells.
ionocytes; Na + /H + exchanger; skin; gill; embryo
Address for reprint requests and other correspondence: P.-P. Hwang, Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan (e-mail: pphwang{at}gate.sinica.edu.tw )
Camphor is a terpene ketone with aromatic and volatile properties in nature derived from the bark of
Cinnamomum camphora
or synthesized from turpentine. Camphor exhibits various biological properties ...such as anti-microbial, anti-viral, anti-coccidial, and anti-cancer. It is also used as a form of topical medication for skin irritation, joint pain, and as a relief for itching from insect bites. However, even though the high dose of camphor has been documented to be toxic/lethal in humans in different studies, camphor’s developmental toxicity has not yet been explored, and its extensive mechanism of action is still unclear. In the present study, we aimed to assess the toxic effects of camphor in zebrafish embryos in the initial developmental stages. The obtained results demonstrated that a sub-lethal dose of camphor caused a decrease in hatching rate, body length, and substantial elevation in malformation rate on zebrafish embryos. On further observation, in the following time frame, curved body and pericardial edema of zebrafish were also observed. Furthermore, exposure to a sub-lethal dose of camphor was also able to trigger cardiotoxicity in zebrafish larvae. Later, on subsequent biochemical analysis, it was found that the antioxidant capacity inhibition and oxidative stress elevation that occurred after camphor exposure might be associated with the inhibition of total superoxide dismutase (SOD) activity and an increase in reactive oxygen species (ROS) and malondialdehyde (MDA) concentration. In addition, compared to the control group, several apoptotic cells in treated zebrafish were also found to be elevated. Finally, after further investigation on marker gene expressions, we conclude that the developmental toxicity of camphor exposure might be associated with apoptosis elevation and oxidative stress. Taken together, the current study provides a better understanding of the developmental toxicity of camphor on zebrafish, a promising alternative animal model to assess the developmental toxicity of chemical compounds.
1 Institute of Cellular and Organismic Biology, Academia Sinica, Taipei; 2 Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung; 3 Department of Bioscience Technology, ...Chung Yuang Christian University, Chung-Li, Taiwan. ROC
Submitted 1 December 2008
; accepted in final form 27 January 2009
H + -ATPase-rich (HR) cells in zebrafish are known to be involved in acid secretion and Na + uptake mechanisms in zebrafish gills/skin; however, little is known about how HR cells are functionally regulated. In the present work, we studied the roles of Drosophila glial cell missing ( gcm ), a cell fate-related transcription factor, in the differentiation and functional regulation of zebrafish HR cells. Zebrafish gcm 2 ( zgcm2 ) was found to begin expression in zebrafish embryos at 10 h postfertilization (hpf), and to be extensively expressed in gills but only mildly so in eyes, heart, muscles, and testes. By whole mount in situ hybridization, zgcm2 mRNA signals were found in a group of cells on the zebrafish yolk sac surface initially in the tail bud stage (10 hpf); they had disappeared at 36 hpf and thereafter appeared again in the gill region from 48 hpf. Double fluorescence in situ hybridization further demonstrated specific colocalization of zgcm2 mRNA in HR cells in zebrafish embryos. Knockdown of zgcm2 with a specific morpholino oligonucleotide caused the complete disappearance of HR cells with a concomitant decrease in H + activity at the apical surface of HR cells, but it did not affect the occurrence of Na + -K + -ATPase-rich cells. A decrease in the H + -ATPase subunit A ( zatp6v1a ) expression and no change in zgcm2 expression in zebrafish gills were seen from 12 h to 3 days after transfer to acidic fresh water, but a compensatory stimulation in the expressions of both genes appeared 4 days posttransfer. In conclusion, functional regulation of HR cells is probably achieved by enhancing cell differentiation via zGCM2 activation.
acid secretion; ionocytes; ion regulation; gills
Address for reprint requests and other correspondence: P. P. Hwang, Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 11529, Taiwan (e-mail: pphwang{at}gate.sinica.edu.tw )
As an animal's surface area expands during development, skin cell populations must quickly respond to maintain sufficient epithelial coverage. Despite much progress in understanding of skin cell ...behaviours in vivo
, it remains unclear how cells collectively act to satisfy coverage demands at an organismic level. Here we created a multicolour cell membrane tagging system, palmskin, to monitor the entire population of superficial epithelial cells (SECs) in developing zebrafish larvae. Using time-lapse imaging, we found that many SECs readily divide on the animal body surface; during a specific developmental window, a single SEC can produce a maximum of four progeny cells over its lifetime on the surface of the animal. Remarkably, EdU assays, DNA staining and hydroxyurea treatment showed that these terminally differentiated skin cells continue splitting despite an absence of DNA replication, causing up to 50% of SECs to exhibit reduced genome size. On the basis of a simple mathematical model and quantitative analyses of cell volumes and apical surface areas, we propose that 'asynthetic fission' is used as an efficient mechanism for expanding epithelial coverage during rapid growth. Furthermore, global or local manipulation of body surface growth affects the extent and mode of SEC division, presumably through tension-mediated activation of stretch-activated ion channels. We speculate that this frugal yet flexible mode of cell proliferation might also occur in contexts other than zebrafish skin expansion.
This study presented the superior superconductivity of Y-Ba-Cu-O (YBCO) bulk materials grown by using modified infiltration growth (IG) method with a small Sm-Ba-Cu-O crystal as seed. Compare to the ...bulks grown by melt-textured growth (MTG) method, IG bulk is denser and with finer second phase (Y2Ba1Cu1O5, Y211). In addition, remarkable peak effect was observed of the IG YBCO bulk material. Peak effect in Jc(H, T) is an distinctive property of RE-Ba-Cu-O (RE = rare earth element, e.g. Sm, Nd) superconductors. However, it is found that peak effect is unusual in Y-Ba-Cu-O material. In this study, magnetism measurements also show peak effect in Jc(H, T), especially at low temperatures. At 50 K, the peak position of Jc(H, T) was about 5 Tesla. Jc value of peak, Jc(peak, 50 K), is comparable to that of self-field, Jc(0, 50 K). On the other hand, it is noted that this effect is spatial-dependent, i.e. it only can be found in particular part of bulk. To interpret the mechanism of peak effect and the spatial-dependence, different microstructure analysis, which includes scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray absorption spectrum (XAS) were used. The results indicated that the composition is inhomogeneous throughout the bulk. Diffusion of Sm from seed to YBCO bulk was observed, which is believed to occur during high temperature, and thus changed the superconductivity. The inhomogeneity of microstructure was correlated to the spatial-dependent of peak effect. Finally, this study also demonstrates a possible way to introduce peak effect in YBCO materials and thus enhance the applications in high field regions.
This investigation demonstrates a strong dependence of the magnetism of CeO2 nanoparticles on the concentration of oxygen vacancies. A strong magnetic signal is over for a narrow range (0.1 < Ce3+/Ce ...< 0.2) of Ce3+ concentrations in the nanoparticles. Previous studies have determined that most of the vacancies are at the surface of the particle and, given particles of size 3–10 nm, the strong magnetic signal corresponds to an even narrower range of Ce3+ content at the surface (0.40 < Ce3+ surface/Cesurface < 0.45). X-ray magnetic circular dichroism (XMCD) measurement reveals that electrons in Ce bear magnetic moments while oxygen atoms do not respond magnetically indicating that the bounded magnetic polarons are more important to magnetism than is oxygen-mediated exchange.
PDF
