Nano-octahedra of cobalt ferrite CoxFe3???xO4 (1?≤?x?<?2), with a broad size distribution around 15–20 nm, were synthesized by a hydrothermal method using nitrates as precursors. For the first time, single-phased nano-octahedra of cobalt-rich ferrite CoxFe3???xO4 (x?=?1.5) were synthesized. The nano-octahedra are crystallized in a normal spinel structure, with tetrahedral sites occupied by Co2+. This specific octahedral shape was obtained with anionic, cationic, and nonionic surfactants. The nature of the surfactant influenced the chemical composition of the powder and the size of the nano-octahedra. The {100} truncation of the octahedra is more pronounced for the small particles. For the first time, single-phased nanoparticles with as much as x?=?1.8 cobalt were synthesized with ethylene glycol as solvent. These nanoparticles, around 8 nm in size, have no specific shape and possess a lacunar spinel structure similar to maghemite. The samples were characterized by X-ray diffraction, transmission electron microscopy, and energy-dispersive spectroscopy.
One-dimensional Ce3+-doped Li4Ti5O12 (Li4Ti5?xCexO12, x?=?0, 0.01, 0.02, and 0.05) sub-microbelts with the width of approximately 500 nm and thickness of about 200 nm have been synthesized via the facile electrospinning method. The structure and morphology of the as-prepared samples are characterized by XRD, TEM, SEM, BET, HRTEM, XPS, and AFM. Importantly, one-dimensional Li4Ti5O12 sub-microbelts can be well preserved with the introduction of Ce3+ ions, while CeO2 impurity is obtained when x is greater than or equal to 0.02. The comparative experiments prove that Ce3+-doped Li4Ti5O12 electrodes exhibit the brilliant electrochemical performance than undoped counterpart. Particularly, the reversible capacity of Li4Ti4.98Ce0.02O12 electrode reaches up to 139.9 mAh g?1 and still maintains at 132.6 mAh g?1 even after 100 cycles under the current rate of 4 C. The superior lithium storage properties of Li4Ti4.98Ce0.02O12 electrode could be attributed to their intrinsic structure advantage as well as enhanced overall conductivity.
Protein complexes that mediate secretion and adhesion are located on the plasma membrane of pancreatic β cells. Neuroligins and their binding partners, the neurexins, are among these complexes. β cell maturation and physiologically regulated insulin secretion, as a response to high levels of blood glucose, are dependent on their three-dimensional (3D) arrangement. Both insulin secretion and the proliferation rates of β cells dramatically increase when β cells are co-cultured with clusters of a member of the neuroligin family: NL-2. A membranal protein, such as NL-2, has very limited drugability owing to its low biostability and bioavailability. Thus, based on in silico modeling, a short NL-2 peptide (HSA-28), which was able to mimic NL-2-positive effects on β cells, was designed, as we described in previous publication. However, the peptide was active only as a cluster, created by the covering the maghemite (γ-Fe2O3)-based nanoparticles (NPs) with limited biocompatibility. In this brief communication, we will show that conjugation of HSA-28 to biocompatible hydrogel NPs exhibits an impressive protective effect on INS-1E β cells under oxidative stress and induces their proliferation rate via augmentation of PDX1 nuclear translocation. The diameter of coated by the peptide NPs was 206?±?63 nm (DLS) and 114?±?27 nm (cryo-TEM). This significant change in size can be explained by the very hydrophilic character of the proteinoid NPs, inducing adsorption of many water molecules on their surface, which are accounted only by the DLS. The ability of biocompatible hydrogel NPs to prevent apoptosis and increase β cell mass might be used for developing novel β cell protective therapies.
A simple solid-state method has been applied to synthesize Ni/reduced graphene oxide (Ni/rGO) nanocomposite under ambient condition. Ni nanoparticles with size of 10–30 nm supported on reduced graphene oxide (rGO) nanosheets are obtained through one-pot solid-state co-reduction among nickel chloride, graphene oxide, and sodium borohydride. The Ni/rGO nanohybrid shows enhanced catalytic activity toward the reduction of p-nitrophenol (PNP) into p-aminophenol compared with Ni nanoparticles. The results of kinetic research display that the pseudo-first-order rate constant for hydrogenation reaction of PNP with Ni/rGO nanocomposite is 7.66 × 10?3 s?1, which is higher than that of Ni nanoparticles (4.48 × 10?3 s?1). It also presents superior turnover frequency (TOF, 5.36 h?1) and lower activation energy (Ea, 29.65 kJ mol?1) in the hydrogenation of PNP with Ni/rGO nanocomposite. Furthermore, composite catalyst can be magnetically separated and reused for five cycles. The large surface area and high electron transfer property of rGO support are beneficial for good catalytic performance of Ni/rGO nanocomposite. Our study demonstrates a simple approach to fabricate metal-rGO heterogeneous nanostructures with advanced functions.
We consider on a bounded domain \(\Omega \subset {\mathbb{R}}^N\) , the Schrödinger operator ? Δ ? V supplemented with Dirichlet boundary solutions. The potential V is either the critical inverse square potential V(x) = (N ? 2)2/4|x|?2 or the critical borderline potential V(x) = (1/4)dist(x, ?Ω)?2. We present explicit asymptotic estimates on the eigenvalues of the critical Schrödinger operator in each case, based on recent results on improved Hardy–Sobolev type inequalities. 相似文献
The paper deals with the processes of photoburning and dark recovery of the photoluminescence (PL) yield of a “core-shell”-type hybrid nanoparticles Si/SiOx (npSi/SiOx) after exposure to laser light with a wavelength of 405 nm and power density of 0.05–1 W/cm2. The PL of npSi/SiOx occurs after excitation of nanocrystalline Si core and subsequent energy transfer to the luminescent oxygen-deficient centers (ODC) in the SiOx shell of a nanoparticle. These photoburning effects linearly depend on the power density of the exciting laser light, and the dynamics of the photoburning of PL is significantly non-exponential: the burning rate strongly drops during the exposure. The stop of laser exposure of npSi/SiOx is accompanied by a slow dark recovery of the quantum efficiency of PL up to its initial level. We have demonstrated the possibility of controlling the photosensibility of npSi/SiOx through changing the electron affinity of the environment. We have also proposed a physical mechanism that explains the observed photoburning and subsequent dark recovery of npSi/SiOx PL based on the existence of “traps” for electrons residing in the SiOx shell, where the electrons come as a result of tunneling from the excited ODC. The limiting time for this process is the lifetime of PL of ODC ranging from 10?5 to 10?4 s. The drop of the burning rate during exposure is caused by a strong difference in tunneling probabilities for different pairs of “ODC-trap”. The dark back tunneling of an electron from a trap to the original ODC occurs significantly (7–10 orders of magnitude) slower than the direct tunneling due to higher energy barrier.
Graphical abstract Dark recovery of photoluminescence efficiency of Si nanoparticles following laser burning in three surrounding media differing in electron affinity
Amphiphilic gold nanoparticles (AuNPs) functionalized with mixed monolayers consisting of hydrophobic and hydrophilic ligands find widespread applications in biosensing, drug delivery, and bioimaging. One important aspect of amphiphilic AuNPs in such applications is the tuning of the surface properties of these AuNPs by modifying the composition of the ligands. In this study, well-dispersed AuNPs as individuals with mixed monolayers of hydrophobic and hydrophilic ligands were synthesized and the ratios of hydrophilic and hydrophobic ligands on the AuNP surfaces with varying ligand lengths were investigated by electrostatic titration. We demonstrated that longer hydrophobic ligands have higher affinity for the AuNP surface, and that the relative ligand length plays an important role in determining the maximum hydrophobic coverage on the AuNP surface at which the ratio of the amount of hydrophobic to that of hydrophilic ligands on the AuNP surface is the largest, for AuNPs to remain as individuals. We expect that the AuNPs synthesized with diverse ratios of hydrophobic and hydrophilic ligands on the surface can be useful in biological applications.
On a smooth bounded domain \(\Omega \subset {\bf {\rm R}}^N\) we consider the Schrödinger operators ? Δ ? V, with V being either the critical borderline potential V(x) = (N ? 2)2/4 |x|?2 or V(x) = (1/4) dist(x, ?Ω)?2, under Dirichlet boundary conditions. In this work we obtain sharp two-sided estimates on the corresponding heat kernels. To this end we transform the Schrödinger operators into suitable degenerate operators, for which we prove a new parabolic Harnack inequality up to the boundary. To derive the Harnack inequality we have established a series of new inequalities such as improved Hardy, logarithmic Hardy Sobolev, Hardy-Moser and weighted Poincaré. As a byproduct of our technique we are able to answer positively to a conjecture of E. B. Davies. 相似文献
Novel water-soluble anionic p-tert-butylthiacalix[4]arene with propanesulfonate fragments has been synthesized. Alkylation of the lower rim of thiacalix[4]arene in the presence of NaH/THF led to cone conformation instead of the expected 1,3-alternate conformer due to metal template effect. The presence of supramolecular associates at the critical micelle concentration of 1.65 · 10?5 M were investigated in aqueous solutions by a combination of different techniques (DLS and conductivity). It was observed that the macrocyclic platform decreases the CMC by tenfold as compared with non-macrocycle analogs. A simple approach for the design of stable monodisperse Ag-based nanoaggregates (near 95 nm) containing ionic Ag and organic ligand–thiacalix[4]arene sulfo derivative in water has been developed. Self-assembled fractal hybrid nanodendrites consisting of water-soluble anionic (thia)calix[4]arenes and Ag+ have been obtained in a single step under mild conditions.
This work uses linear and looped RGDfV sequences attached to the surface of small (1.8 nm in diameter) gold nanoparticles (AuNPs) to enhance the radiosensitizating effects of Cilengitide, a cyclic RGDf (NMe)V pentapeptide that targets αvβ3 integrin which is overexpressed in certain cancers. Following synthesis and purification, the AuNPs were evaluated in vitro against HUVEC, H460, and MCF7 cells in clonogenic assays using a 137Cs irradiator. Untargeted AuNPs induced no significant dose enhancement factors (DEFs) in any of the cell types when compared to radiation treatment alone, whereas all evaluated AuNPs functionalized with targeting peptides performed at least as well as controls (irradiation after Cilengitide treatment). The observed DEFs also suggest that cyclizing the linear peptides into more spatially constrained, looped structures may facilitate target binding. These greater dose enhancements merit future in vivo studies of drug-AuNP conjugates to assess the ability of the nanostructures to provide an improved therapeutic benefit over treatment with drug candidates and radiation alone.
Highly dispersed anisotropic Ag nanostructures were synthesized within the channels of 3-aminopropyltrimethoxysilane (APTMS)-modified mesoporous SBA-15 for catalyzing the reduction of p-dinitrobenzene, p-nitrophenol, and p-nitroacetophenone, respectively. A green templating process without involving any reducing agent, by varying the amount (1–10 wt.%) of Ag loading followed by calcination at 350 °C under H2 led to change in the morphology of Ag nanoparticles from nanospheres (~7–8 nm) to nanorods (aspect ratio ~12–30 nm) without any deformation in mesoporous sieves. In comparison to white bare SBA-15, gray-colored samples were formed with Ag impregnation exhibiting absorption bands at 484 and 840 nm indicating the formation of anisotropic Ag nanostructures within mesoporous matrix. TEM and FE-SEM micrographs confirmed the presence of evenly dispersed Ag nanostructures within as well as on the surface of mesoporous matrix. AFM studies indicated a small decrease in the average roughness of SBA-15 from 20.59 to 19.21 nm for 4 wt.% Ag/m-SBA-15, illustrating the encapsulation of majority of Ag nanoparticles in the siliceous matrix and presence of small amount of Ag nanoparticles on the mesoporous support. Moreover, due to plugging of mesopores with Ag, a significant decrease in surface area from 680 m2/g of SBA-15 to 385 m2/g was observed. The Ag-impregnated SBA-15 catalyst displayed superior catalytic activity than did bare SBA-15 with 4 wt.% Ag-loaded catalyst exhibiting optimum activity for selective reduction of p-nitrophenol to p-aminophenol (100 %), p-nitroacetophenone to p-aminoacetophenone (100 %), and p-dinitrobenzene to p-nitroaniline (87 %), with a small amount of p-phenylenediamine formation.
Graphical abstract This paper demonstrates the spontaneous formation of uniformly dispersed Ag nanospecies of various morphologies (nanospheres, size ~7–8 nm and nanorods, aspect ratio ~12–30 nm), both within as well as on the surface of the mesoporous SBA-15, as a function of increased Ag loading. Surface structural and other physiochemical properties of Ag/m-SBA-15 nanocomposites were considerably influenced w.r.t change in Ag loading. Ag/m-SBA-15 nanocomposites with 4 wt.% Ag loading exhibited the highest selectivity (87 %) for the selective reduction of p-dinitrobenzene to p-nitroaniline and 100 % selectivity for p-nitrophenol to p-aminophenol and p-nitroacetophenone to p-aminoacetophenone, respectively.
For a two-dimensional Schrödinger operator HαV = ?Δ ?αV with the radial potential V(x) = F(|x|), F(r) ≥ 0, we study the behavior of the number N?(HαV) of its negative eigenvalues, as the coupling parameter α tends to infinity. We obtain the necessary and sufficient conditions for the semi-classical growth N?(HαV) = O(α) and for the validity of the Weyl asymptotic law. 相似文献
We link the Boundary Control Theory and the Titchmarsh-Weyl Theory. This provides a natural interpretation of the A?amplitude due to Simon and yields a new efficient method to evaluate the Titchmarsh-Weyl m?function associated with the Schrödinger operator H = ??x2 + q(x) on L2(0, ∞) with Dirichlet boundary condition at x = 0. 相似文献
Voltammetric dealloying is employed here to investigate the correlations between catalytic performance and surface composition and structure, taking ethanol oxidation reaction (EOR) on Pd-Cu alloy surface as a case study. First, home-made PdCu/C with a mean particle size of ca. 3.11?±?0.6 nm is dealloyed by repetitive potential cycling in 0.5 M H2SO4. With dealloying cycles rising, the Cu component is gradually leached out and the corresponding Pd/Cu atomic ratio gradually increases from ca. 2.1 to 4.0; meanwhile, SEM images display that Pd-rich porous shell is formed due to dealloying-induced surface structural rearrangement, being verified by the appearance of ear-like peaks at ??0.015 V (vs. SCE) in CVs collected in 0.5 M H2SO4; furthermore, XPS spectra indicate that core-level binding energies of Pd 3d5/2 first positively shift to 336.1 eV and then oppositively move down to 334.9 eV, indicating that the d-band center of Pd composition is modulated by the dealloying treatment. Moreover, the voltammetric peak current densities for EOR follow the order of PdCu/C-DA15?>?as-prepared PdCu/C ??>?PdCu/C-DA30 ? commercial Pd/C ? PdCu/C-DA75, due to the modest downshift of Pd d-band center resulted by charge transfer and surface atomic rearrangement. In addition, the EOR durability gradually decays with the continuous loss of Cu, indicating that electro-oxidation of surface species also follows the so-called bi-functional mechanism. This work might provide some new insights into the catalysis enhancement by tuning the surface/interfacial structure of catalysts.
Graphical abstract The voltammetric peak current densities for ethanol oxidation on home-made PdCu/C catalysts gradually decrease with the dealloying cycles rising, suggesting that the surface voltammetric dealloyment could effectively modulate the surface composition and structure, so as to tune the catalytic performance.
The temperature-dependent field cooling (FC) and zero-field cooling (ZFC) magnetizations, i.e., MFC and MZFC, measured under different magnetic fields from 500 Oe to 20 kOe have been investigated on two exchange–spring CoFe2O4/CoFe2 composites with different relative content of CoFe2. Two samples exhibit different magnetization reversal behaviors. With decreasing temperature, a progressive freezing of the moments in two composites occurs at a field-dependent irreversible temperature Tirr. For the sample with less CoFe2, the curves of ?d(MFC ? MZFC)/dT versus temperature T exhibit a broad peak at an intermediate temperature T2 below Tirr, and the moments are suggested not to fully freeze till the lowest measuring temperature 10 K. However, for the ?d(MFC ? MZFC)/dT curves of the sample with more CoFe2, besides a broad peat at an intermediate temperature T2, a rapid rise around the low temperature T1~15 K is observed, below which the moments are suggested to fully freeze. Increase of magnetic field from 2 kOe leads to the shift of T2 and Tirr towards a lower temperature, and the shift of T2 is attributable to the moment reversal of CoFe2O4.
Graphical abstract CoFe2O4/CoFe2 composites with different relative content of CoFe2 were prepared by reducing CoFe2O4 in H2 for 4 h (S4H) and 8 h (S8H). The temperature-dependent FC and ZFC magnetizations, i.e., MFC and MZFC, under different magnetic fields from 500 Oe to 20 kOe have been investigated. Two samples exhibit different magnetization reversal behaviors. With decreasing temperature, a progressive freezing of the moments in two composites occurs at field-dependent irreversible temperature Tirr. For the S4H sample, the curves of ?d(MFC ? MZFC)/dT versus temperature T exhibit a broad and field-dependent relaxing peak at T2 below Tirr (figure a), and the moments were suggested not to fully freeze till the lowest measuring temperature 10 K. However, for the S8H sample, it exhibits the reentrant spin-glass state around 50 K, as evidenced by a peak in the MFC curve (inset in figure b) and as a result of the cooperative effects of the random anisotropy of CoFe2O4, exchange–spring occurring at the interface of CoFe2O4 and CoFe2 together with the inter-particle dipolar interaction (figure c); in ?d(MFC ? MZFC)/dT curves, besides a broad relaxing peat at T2, a rapid rise around the low-temperature T1~15 K is observed, below which the moments are suggested to fully freeze. Increase of magnetic field from 2 kOe leads to the shift of T2 and Tirr towards a lower temperature, and the shift of T2 is attributable to the moment reversal of CoFe2O4.
Single-phase solid solutions of Sm2 ? xCexCuO4 + δ (0.05 ≤ x ≤ 0.20) with tetragonal structure are synthesized using acetate combustion followed by sintering at 1373 K for 10 h. X-ray powder diffraction and transmission electron microscopy studies confirmed the formation of solid solution in a single phase. Maximum conductivity (σ = 96.0 ± 0.5 S cm?1 at 973 K) giving composition Sm1.90Ce0.10CuO4 offers the minimum activation energy (Ea = 0.32 ± 0.004 eV) among all prepared compositions. Lowest cathode polarization resistance (Rp = 3.92 ± 0.07 Ω cm2 at 973 K) and activation energy (Ea = 1.12 ± 0.03 eV) values across the measured temperature range are obtained for Sm1.90Ce0.10CuO4. The impedance data fitted well to the Gerischer model indicates that a chemical-electrochemical-chemical-type reaction occurred at the mixed electronic-ionic conducting cathode. 相似文献
FexAg1?x granular thin-films, with the atomic Fe concentration, x, ranging from 0 up to 0.5, were deposited by dc magnetron co-sputtering. The giant magnetoresistance (GMR) intensity is maximum at xI = 0.32, while the maximum of GMR efficiency, γ, i.e., the change of GMR intensity for a unit change of reduced squared magnetization, is observed at xγ = 0.26. Owing to the spin-dependent scattering features, the GMR intensity and γ depend on both the concentration and the arrangement of the magnetic material. Therefore, to explain the difference between xI and xγ and to understand how the structural properties affect the magnetoresistive behaviour, we performed magnetization, Mössbauer and X-ray diffraction measurements as a function of x. X-ray data indicate that the granular films exhibit three different regimes: for x < 0.2, they can be described as a Fe–Ag solid solution; for 0.2 < x < 0.32 the Fe–Ag solid solution is still observed and very small Fe precipitates are found; finally, for x > 0.32, a Fe–Ag saturated solid solution is detected, containing bcc Fe clusters whose size is about 10 nm. Differently, for all the concentrations, magnetization data show the presence of Fe precipitates, whose size increases with x, and the Mössbauer investigation confirms this picture. We find that the samples grown at x = xγ display the finest Fe dispersion within the Ag matrix, as the Fe–Ag solid solution is nearly at saturation and the Fe cluster size is of the order of a few nanometers; this arrangement possibly maximizes the magnetic/non-magnetic interface extension thus enhancing the GMR efficiency. If x is slightly increased, the increase in total Fe content compensates the GMR efficiency reduction, so the GMR intensity maximum is observed. 相似文献
First-principles calculations of the electronic and optical properties of the bulkInxGa1 ? xN alloys aresimulated within the framework of full-potential linearized augmented plane-wave (FP-LAPW)method. To this end, a sufficiently adequate approach, namely modified Becke-Johnson(mBJLDA) exchange correlation potential is employed for calculating the energy band gapand optical absorption of InGaN-based solar cells systems. The quantities such as theenergy gap, density of states, imaginary part of dielectric function, refractive index andabsorption coefficient are determined for the bulkInxGa1?xN alloys, in thecomposition range from x = 0 to x = 1. It is found thatthe indium composition robustly controls the variation of band gap. From the examinationof the density of states and optical absorption ofInxGa1?xN ternary alloys,the energy gaps are significantly reduced for largest In concentration. The computed bandgaps vary nonlinearly with the composition x. It is also surmised thatthe significant variation in the band gaps elaborated via the experimental crystallinegrowth process, is originated by altering the In composition. Interestingly, it isworthwhile to perform InGaN solar cells alloys with improved efficiencies, because oftheir entire energy gap variation from 0.7 to 3.3 eV. 相似文献
Based on the Heisenberg model including single-site uniaxial anisotropy and using aGreen’s function technique we studied the influence of size and composition effects on theCurie temperature TC, saturationmagnetization MS and coercivityHC of spherical nanoparticles with astructural formulaMe1?xZnxFe2O4,Me = Ni, Cu, Co, Mn. It is shown that for x = 0.4–0.5and d = 10–20 nm these nanoparticles have aTC = 315 K and are suitable for aself-controlled magnetic hyperthermia. 相似文献
In this paper, a gate-all-around junctionless tunnel field effect transistor (JLTFET) based on heterostructure of compound and group III–V semiconductors is introduced and simulated. In order to blend the high tunneling efficiency of narrow band gap material JLTFETs and the high electron mobility of III–V JLTFETs, a type I heterostructure junctionless TFET adopting Ge–AlxGa1?xAs–Ge system has been optimized by numerical simulation in terms of aluminum (Al) composition. To improve device performance, we considered a nanowire structure, and it was illustrated that high-performance logic technology can be achieved by the proposed device. The optimal Al composition founded to be around 20 % (x = 0.2). The numerical simulation results demonstrate that the proposed device has low leakage current IOFF of ~1.9 × 10?17, ION of 4 µA/µm, ION/IOFF current ratio of 1.7 × 1011 and subthreshold swing SS of 12.6 mV/decade at the 40 nm gate length and temperature of 300 K. 相似文献
