Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 109
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Opt Lett ; 45(3): 665, 2020 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-32004279

RESUMO

This publisher's note contains corrections to Opt. Lett.44, 2081 (2019)OPLEDP0146-959210.1364/OL.44.002081.

2.
Artigo em Inglês | MEDLINE | ID: mdl-32031283

RESUMO

The redox reaction of oxygen has been considered critical in controlling the electrochemical properties of Li-excessive layered oxide electrodes. However, conventional electrode materials without over-lithiation remain the most practical if their performance could be improved through rational approaches. Typically, cationic redox reactions are believed to dominate the electrochemical operations in conventional electrodes, and the involvement of anionic redox reactions, although proposed, is yet to be clarified through reliable characterizations. Here, we show unambiguous evidence of reversible anionic redox reactions in LiNi1/3Co1/3Mn1/3O2., with a detailed quantification on its reversibility upon electrochemical cycling. Two types of oxygen involvements are discussed. One is the typical involvement of O through hybridization with transition metals throughout the electrochemical operation; the other is the intrinsic O redox at high potentials, which is 75% reversible during initial cycling and 63% retained after 10 cycles. Our results clarify the reaction mechanism at high potentials in conventional layered electrodes involving both cationic and anionic reactions. Additionally, our combined characterizations indicate a critical role of transition-metals for oxygen redox activities and the optimism of utilizing reversible oxygen redox reactions in conventional layered oxides for high-capacity lithium-ion batteries.

3.
Artigo em Inglês | MEDLINE | ID: mdl-31961644

RESUMO

As a parent compound of Li-rich electrodes, Li2MnO3 exhibits high capacity during the initial charge; however, it suffers notoriously low Coulombic efficiency due to oxygen and surface activities. Here, we successfully optimize the oxygen activities toward reversible oxygen redox reactions by intentionally introducing protons into lithium octahedral vacancies in the Li2MnO3 system with its original structural integrity maintained. Combining structural probes, theoretical calculations, and resonant inelastic X-ray scattering results, a moderate coupling between the introduced protons and lattice oxygen at the oxidized state is revealed, which stabilizes the oxygen activities during charging. Such a coupling leads to an unprecedented initial Coulombic efficiency (99.2%) with a greatly improved discharge capacity of 302 mAh g-1 in the protonated Li2MnO3 electrodes. These findings directly demonstrate an effective concept for controlling oxygen activities in Li-rich systems, which is critical for developing high-energy cathodes in batteries.

4.
ACS Appl Mater Interfaces ; 12(5): 6688-6698, 2020 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-31912731

RESUMO

A combination of X-ray photoelectron/Auger electron spectroscopy and soft X-ray emission spectroscopy has been employed to investigate the impact of different alkali postdeposition treatments (PDTs) on the chemical structure of the (buried) CdS/Cu(In,Ga)Se2 heterojunction: the key interface in chalcopyrite-based thin-film solar cells. Chemical bath deposited (CBD) CdS layers of different thicknesses on NaF PDT (CIGSeNaF) and NaF + KF PDT (CIGSeNaF+KF) Cu(In,Ga)Se2 absorbers prepared at low temperature (to facilitate the use of flexible, e.g., polyimide, substrates) were studied. While we find the CdS/CIGSeNaF interface to be mainly free of significant chemical interaction, in the proximity of the CdS/CIGSeNaF+KF interface, an elemental redistribution involving Cd, In, K, S, and Se is revealed. For the early stages of the CBD-CdS process, our findings are in agreement with the conversion of the K-In-Se-type layer present on the CIGSeNaF+KF surface into a mixed Cd-In-(O,OH,S,Se)-type layer, probably having some Cd-In and (S,O)-Se composition gradients. For long CBD times-independent of employed PDT-we find the buffer material to be best described by a Cd(O,OH,S)-like species rather than by a pure CdS buffer. These findings shed light on the observed performance leap of corresponding CdS/CIGSeNaF+KF-based solar cells.

5.
Nat Mater ; 2020 Jan 20.
Artigo em Inglês | MEDLINE | ID: mdl-31959949

RESUMO

Despite the high energy density of lithium-rich layered-oxide electrodes, their real-world implementation in batteries is hindered by the substantial voltage decay on cycling. This voltage decay is widely accepted to mainly originate from progressive structural rearrangements involving irreversible transition-metal migration. As prevention of this spontaneous cation migration has proven difficult, a paradigm shift toward management of its reversibility is needed. Herein, we demonstrate that the reversibility of the cation migration of lithium-rich nickel manganese oxides can be remarkably improved by altering the oxygen stacking sequences in the layered structure and thereby dramatically reducing the voltage decay. The preeminent intra-cycle reversibility of the cation migration is experimentally visualized, and first-principles calculations reveal that an O2-type structure restricts the movements of transition metals within the Li layer, which effectively streamlines the returning migration path of the transition metals. Furthermore, we propose that the enhanced reversibility mitigates the asymmetry of the anionic redox in conventional lithium-rich electrodes, promoting the high-potential anionic reduction, thereby reducing the subsequent voltage hysteresis. Our findings demonstrate that regulating the reversibility of the cation migration is a practical strategy to reduce voltage decay and hysteresis in lithium-rich layered materials.

6.
ACS Omega ; 4(18): 17735-17740, 2019 Oct 29.
Artigo em Inglês | MEDLINE | ID: mdl-31681879

RESUMO

Controlling the surface is necessary to adjust the essential properties and desired functions of nanomaterials and devices. For nanostructured multivalent vanadium oxides, unwanted surface oxidation occurs at ambient atmosphere generally and needs to be suppressed or avoided. We describe the suppressed surface oxidation of VO2 nanostructures through blocking oxygen adsorption. During an enhanced photoinduced surface oxidation process, the increased oxidation states of vanadium in VO2 nanostructures are suppressed by the use of an inert atmosphere or coating. Intermediate oxidation states are observed, and an ALD-TiO2 coating has a good antioxidant capacity for preventing the formation of oxygen-enriched components. Such oxidation suppression is beneficial to improving the stability of VO2 nanostructures. Controllable surface oxidation helps us to understand the physical essentials of surface chemical reactions and achieve better control of surface functions and performances on correlated vanadium oxide nanostructures.

7.
Proc Natl Acad Sci U S A ; 116(47): 23473-23479, 2019 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-31685612

RESUMO

The layered oxide Na0.67CoO2 with Na+ occupying trigonal prismatic sites between CoO2 layers exhibits a remarkably high room temperature oxygen evolution reaction (OER) activity in alkaline solution. The high activity is attributed to an unusually short O-O separation that favors formation of peroxide ions by O--O- interactions followed by O2 evolution in preference to the conventional route through surface O-OH- species. The dependence of the onset potential on the pH of the alkaline solution was found to be consistent with the loss of H+ ions from the surface oxygen to provide surface O- that may either be attacked by solution OH- or react with another O-; a short O-O separation favors the latter route. The role of a strong hybridization of the O-2p and low-spin CoIII/CoIV π-bonding d states is also important; the OER on other CoIII/CoIV oxides is compared with that on Na0.67CoO2 as well as that on IrO2.

8.
Onco Targets Ther ; 12: 7489-7500, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31686854

RESUMO

Background/aims: 2-oxoglutarate dehydrogenase (OGDH) is the first rate-limiting E1 subunit of OGDH complex (OGDHC), which plays as a regulatory point in the cross-road of TCA cycle and glutamine metabolism. Until now, the role of OGDH in carcinogenesis has been unclear. Methods: In the present study, we determined the expression of OGDH in human gastric cancer (GC) tissues and cell lines by RT-qPCR, Western blotting and immunohistochemical staining respectively. The biological impacts of OGDH on cell growth and migration were explored through modulation OGDH expression in GC cells. Furthermore, mitochondrial functions and Wnt/ß-catenin signal were analyzed to elucidate the mechanism by which OGDH was involved in GC progression. Results: The results showed that the levels of OGDH mRNA and protein were significantly higher in GC tissues, which was positively correlated with clinicalpathological parameters of GC patients. OGDH inhibitor SP significantly suppressed GC cell viability. Modulation of OGDH had distinct effects on cell proliferation, cell cycle and cell migration in the GC cell lines AGS and BGC823. Overexpression of OGDH resulted in the downregulation of the EMT molecular markers E-cadherin and ZO-1, the upregulation of N-cadherin and claudin-1. OGDH deficiency had the opposite outcomes in GC cells. Meantime, OGDH knockdown cells showed decreased mitochondrial membrane potential, oxygen consumption rate, intracellular ATP product, and increased ROS level and NADP+/NADPH ratio. Consistently, overexpression of OGDH enhanced the mitochondrial function in GC cells. Furthermore, OGDH knockdown reduced the expressions of ß-catenin, slug and TCF8/ZEB1, and the downstream targets cyclin D1 and MMP9 in GC cells. OGDH overexpression facilitated the activation of Wnt/ß-catenin signal pathway. Additionally, overexpression of OGDH promoted tumorigenesis of GC cells in nude mice. Conclusion: Taken together, these results indicate that OGDH serves as a positive regulator of GC progression through enhancement of mitochondrial function and activation of Wnt/ß-catenin signaling.

9.
Nat Commun ; 10(1): 4975, 2019 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-31672984

RESUMO

Birnessite is a low-cost and environmentally friendly layered material for aqueous electrochemical energy storage; however, its storage capacity is poor due to its narrow potential window in aqueous electrolyte and low redox activity. Herein we report a sodium rich disordered birnessite (Na0.27MnO2) for aqueous sodium-ion electrochemical storage with a much-enhanced capacity and cycling life (83 mAh g-1 after 5000 cycles in full-cell). Neutron total scattering and in situ X-ray diffraction measurements show that both structural water and the Na-rich disordered structure contribute to the improved electrochemical performance of current cathode material. Particularly, the co-deintercalation of the hydrated water and sodium-ion during the high potential charging process results in the shrinkage of interlayer distance and thus stabilizes the layered structure. Our results provide a genuine insight into how structural disordering and structural water improve sodium-ion storage in a layered electrode and open up an exciting direction for improving aqueous batteries.

10.
Aging (Albany NY) ; 11(21): 9778-9793, 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31727867

RESUMO

Globally, epithelial ovarian cancer (EOC) is the most common gynecological malignancy with poor prognosis. The expression and oncogenic roles of ubiquitin specific peptidase 5 (USP5) have been reported in several cancers except EOC. In the current study, USP5 amplification was highly prevalent in patients with EOC and associated with higher mRNA expression of USP5. USP5 amplification and overexpression was positively correlated with poor prognosis of patients of ovarian serous carcinomas. Disruption of USP5 profoundly repressed cell proliferation by inducing cell cycle G0/G1 phase arrest in ovarian cancer cells. Additionally, USP5 knockdown inhibited xenograft growth in nude mice. Knockdown of USP5 decreased histone deacetylase 2 (HDAC2) expression and increased p27 (an important cell cycle inhibitor) expression in vitro and in vivo. The promoting effects of USP5 overexpression on cell proliferation and cell cycle transition, as well as the inhibitory effects of USP5 overexpression on p27 expression were mediated by HDAC2. Moreover, USP5 interacted with HDAC2, and disruption of USP5 enhanced the ubiquitination of HDAC2. HDAC2 protein was positively correlated USP5 protein, and negatively correlated with p27 protein in ovarian serous carcinomas tissues. Collectively, our data suggest the oncogenic function of USP5 and the potential regulatory mechanisms in ovarian carcinogenesis.

11.
Beilstein J Nanotechnol ; 10: 1833-1843, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31579080

RESUMO

A model is proposed to study the diffusion of non-equilibrium minority carriers under the influence of a piezo potential and to calculate the corresponding current-voltage (I-V) characteristics of a piezoelectric p-n junction exposed to mechanical loading. An effective solution to describe this non-equilibrium process has been put forward including two concepts: the influence of prestress loading on p-n junctions in a quasi-electrostatic thermal equilibrium and the perturbation of small fields superposed on the obtained quasi-electrostatic solutions. A few useful results are obtained through this loaded p-n junction model. Under a forward-bias voltage, a tensile (compressive) loading raises (reduces) the potential barrier of the space charge zone (SCZ), i.e., produces an equivalent reverse- (forward-) electric voltage on the SCZ. When a piezoelectric p-n junction is exposed to a reverse-bias voltage, the current density monotonically decreases with increasing reverse voltage and gradually approaches saturation. A bigger tensile (compressive) loading produces a smaller (larger) saturation current density. The appearance of an equivalent voltage on the SCZ induced by prestress indicates that the performance of a p-n junction with the piezo effect can be effectively tuned and controlled by mechanical loadings. Meanwhile, numerical results show that a loading location closer to the SCZ produces a stronger effect on the I-V characteristics of a piezoelectric p-n junction, implying that the tuning effect of mechanical loadings depends on how much influence of the deformation-induced electric field can reach the SCZ. Furthermore, it is also found that the deformation-induced electric field becomes weak with increasing doping because the higher doping is corresponding to the stronger electric leakage. Thus, the higher mechanical tuning performance on higher doped piezoelectric p-n junctions requires the prestress loadings to be applied closer to the interface of p- and n-zone. This study on a non-equilibrium process of piezoelectric p-n junctions has significance for piezotronics.

12.
J Am Chem Soc ; 141(30): 12079-12086, 2019 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-31287957

RESUMO

Li- and Mn-rich (LMR) layered cathode materials have demonstrated impressive capacity and specific energy density thanks to their intertwined redox centers including transition metal cations and oxygen anions. Although tremendous efforts have been devoted to the investigation of the electrochemically driven redox evolution in LMR cathode at ambient temperature, their behavior under a mildly elevated temperature (up to ∼100 °C), with or without electrochemical driving force, remains largely unexplored. Here we show a systematic study of the thermally driven surface-to-bulk redox coupling effect in charged Li1.2Ni0.15Co0.1Mn0.55O2. We for the first time observed a charge transfer between the bulk oxygen anions and the surface transition metal cations under ∼100 °C, which is attributed to the thermally driven redistribution of Li ions. This finding highlights the nonequilibrium state and dynamic nature of the LMR material at deeply delithiated state upon a mild temperature perturbation.

13.
Cancer Cell Int ; 19: 142, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31139019

RESUMO

Background: Esophageal squamous cell carcinoma (ESCC) is one of leading malignant cancers of gastrointestinal tract worldwide. Until now, the involved mechanisms during the development of ESCC are largely unknown. This study aims to explore the driven-genes and biological pathways in ESCC. Methods: mRNA expression datasets of GSE29001, GSE20347, GSE100942, and GSE38129, containing 63 pairs of ESCC and non-tumor tissues data, were integrated and deeply analyzed. The bioinformatics approaches include identification of differentially expressed genes (DEGs) and hub genes, gene ontology (GO) terms analysis and biological pathway enrichment analysis, construction and analysis of protein-protein interaction (PPI) network, and miRNA-gene network construction. Subsequently, GEPIA2 database and qPCR assay were utilized to validate the expression of hub genes. DGIdb database was performed to search the candidate drugs for ESCC. Results: Finally, 120 upregulated and 26 downregulated DEGs were identified. The functional enrichment of DEGs in ESCC were mainly correlated with cell cycle, DNA replication, deleted in colorectal cancer (DCC) mediated attractive signaling pathway, and Netrin-1 signaling pathway. The PPI network was constructed using STRING software with 146 nodes and 2392 edges. The most significant three modules in PPI were filtered and analyzed. Totally ten genes were selected and considered as the hub genes and nuclear division cycle 80 (NDC80) was closely related to the survival of ESCC patients. DGIdb database predicted 33 small molecules as the possible drugs for treating ESCC. Conclusions: In summary, the data may provide new insights into ESCC pathogenesis and treatments. The candidate drugs may improve the efficiency of personalized therapy in future.

14.
Opt Lett ; 44(8): 2081-2084, 2019 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-30985816

RESUMO

Detecting optical signatures of quantum phase transitions (QPT) in driven-dissipative systems constitutes a new frontier for many-body physics. Here we propose a practical idea to characterize the extensively studied phenomenon of photonic QPT, based on a many-body system composed of nitrogen-vacancy centers embedded individually in photonic crystal cavities, by detecting the critical behaviors of mean photon number, photon fluctuation, photon correlation, and emitted spectrum. Our results bridge these observables to the distinct optical signatures in different quantum phases and serve as good indicators and invaluable tools for studying dynamical properties of dissipative QPT.

15.
Faraday Discuss ; 216(0): 414-433, 2019 Jul 11.
Artigo em Inglês | MEDLINE | ID: mdl-31020294

RESUMO

Electronic and lattice contributions to picosecond time-resolved X-ray absorption spectra (trXAS) of CuO at the oxygen K-edge are analyzed by comparing trXAS spectra, recorded using excitation wavelengths of 355 nm and 532 nm, to steady-state, temperature-dependent XAS measurements. The trXAS spectra at pump-probe time-delays ≥150 ps are dominated by lattice heating effects. Insight into the temporal evolution of lattice temperature profiles on timescales up to 100s of nanoseconds after laser excitation are reported, on an absolute temperature scale, with a temporal sensitivity and a spatial selectivity on the order of 10s of picoseconds and 10s of nanometers, respectively, effectively establishing an "ultrafast thermometer". In particular, for the 532 nm experiment at ∼5 mJ cm-2 fluence, both the initial sample temperature and its dynamic evolution are well captured by a one-dimensional thermal energy deposition and diffusion model. The thermal conductivity k = (1.3 ± 0.4) W m-1 K-1 derived from this model is in good agreement with the literature value for CuO powder, kpowder = 1.013 W m-1 K-1. For 355 nm excitation, a quantitative analysis of the experiments is hampered by the large temperature gradients within the probed sample volume owing to the small UV penetration depth. The impact of the findings on mitigating or utilizing photoinduced lattice temperature changes in future X-ray free electron laser (XFEL) experiments is discussed.

16.
Nat Commun ; 10(1): 1650, 2019 04 09.
Artigo em Inglês | MEDLINE | ID: mdl-30967531

RESUMO

Despite the importance of studying the instability of delithiated cathode materials, it remains difficult to underpin the degradation mechanism of lithium-rich cathode materials due to the complication of combined chemical and structural evolutions. Herein, we use state-of-the-art electron microscopy tools, in conjunction with synchrotron X-ray techniques and first-principle calculations to study a 4d-element-containing compound, Li2Ru0.5Mn0.5O3. We find surprisingly, after cycling, ruthenium segregates out as metallic nanoclusters on the reconstructed surface. Our calculations show that the unexpected ruthenium metal segregation is due to its thermodynamic insolubility in the oxygen deprived surface. This insolubility can disrupt the reconstructed surface, which explains the formation of a porous structure in this material. This work reveals the importance of studying the thermodynamic stability of the reconstructed film on the cathode materials and offers a theoretical guidance for choosing manganese substituting elements in lithium-rich as well as stoichiometric layer-layer compounds for stabilizing the cathode surface.

17.
Expert Rev Mol Diagn ; 19(4): 313-324, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30907673

RESUMO

INTRODUCTION: Colorectal cancer (CRC) is one of the most common malignant tumors worldwide and contributes significantly to cancer-related deaths. Since CRC is largely asymptomatic until alarm features develop to advanced stages, the incidence and mortality rate of CRC is relatively high and increases year by year. Areas covered: This review mainly summarizes the recent advances of genetic, epigenetic, and proteomic molecular markers that may be used to predict the prognosis of CRC. Moreover, we made an introduction to immune biomarkers and emerging microbial biomarkers. We also discussed the recent movement of molecular pathological epidemiology (MPE) in the context of prognostic biomarkers. Finally, we discussed the pros and cons of various biomarkers for improving prognostic judgment. Expert opinion: A great number of molecular targets have been identified as prognostic markers for CRC. However, because of some limitations, the efficiency of these biomarkers is restricted in clinical application. Combining a panel of several approaches may present a promising alternative tool for clinical practice. Further large-scale clinical trials are required to validate the prognostic value of these biomarkers in clinical use.

18.
Nat Commun ; 10(1): 1278, 2019 03 20.
Artigo em Inglês | MEDLINE | ID: mdl-30894539

RESUMO

Although single-atomically dispersed metal-Nx on carbon support (M-NC) has great potential in heterogeneous catalysis, the scalable synthesis of such single-atom catalysts (SACs) with high-loading metal-Nx is greatly challenging since the loading and single-atomic dispersion have to be balanced at high temperature for forming metal-Nx. Herein, we develop a general cascade anchoring strategy for the mass production of a series of M-NC SACs with a metal loading up to 12.1 wt%. Systematic investigation reveals that the chelation of metal ions, physical isolation of chelate complex upon high loading, and the binding with N-species at elevated temperature are essential to achieving high-loading M-NC SACs. As a demonstration, high-loading Fe-NC SAC shows superior electrocatalytic performance for O2 reduction and Ni-NC SAC exhibits high electrocatalytic activity for CO2 reduction. The strategy paves a universal way to produce stable M-NC SAC with high-density metal-Nx sites for diverse high-performance applications.

19.
J Am Chem Soc ; 141(12): 4900-4907, 2019 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-30827112

RESUMO

The development of high energy electrode materials for lithium ion batteries is challenged by their inherent instabilities, which become more aggravated as the energy densities continue to climb, accordingly causing increasing concerns on battery safety and reliability. Here, taking the high voltage cathode of LiNi0.5Mn1.5O4 as an example, we demonstrate a protocol to stabilize this cathode through a systematic phase modulating on its particle surface. We are able to transfer the spinel surface into a 30 nm shell composed of two functional phases including a rock-salt one and a layered one. The former is electrochemically inert for surface stabilization while the latter is designated to provide necessary electrochemical activity. The precise synthesis control enables us to tune the ratio of these two phases, and achieve an optimized balance between improved stability against structural degradation without sacrificing its capacity. This study highlights the critical importance of well-tailored surface phase property for the cathode stabilization of high energy lithium ion batteries.

20.
Nat Mater ; 18(3): 256-265, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30718861

RESUMO

Reversible high-voltage redox chemistry is an essential component of many electrochemical technologies, from (electro)catalysts to lithium-ion batteries. Oxygen-anion redox has garnered intense interest for such applications, particularly lithium-ion batteries, as it offers substantial redox capacity at more than 4 V versus Li/Li+ in a variety of oxide materials. However, oxidation of oxygen is almost universally correlated with irreversible local structural transformations, voltage hysteresis and voltage fade, which currently preclude its widespread use. By comprehensively studying the Li2-xIr1-ySnyO3 model system, which exhibits tunable oxidation state and structural evolution with y upon cycling, we reveal that this structure-redox coupling arises from the local stabilization of short approximately 1.8 Å metal-oxygen π bonds and approximately 1.4 Å O-O dimers during oxygen redox, which occurs in Li2-xIr1-ySnyO3 through ligand-to-metal charge transfer. Crucially, formation of these oxidized oxygen species necessitates the decoordination of oxygen to a single covalent bonding partner through formation of vacancies at neighbouring cation sites, driving cation disorder. These insights establish a point-defect explanation for why anion redox often occurs alongside local structural disordering and voltage hysteresis during cycling. Our findings offer an explanation for the unique electrochemical properties of lithium-rich layered oxides, with implications generally for the design of materials employing oxygen redox chemistry.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA