Search

Composites LiNi0.5Mn1.5O4-NiO nanosticks were prepared by a simple molten salt route of adding MnSO4 to molten LiNO3, NaNO3 and slightly excess NiSO4·6H2O. Field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) investigations revealed that one-dimensional composites LiNi0.5Mn1.5O4-NiO nanosticks were generated in a large quantity. The result of dc and ac magnetisation, as well as magnetic hysteresis measurements, shows that three different magnetic phases, i.e. ferrimagnetic, antiferromagnetic (AFM) and spin-glass-like (SGL) phases may coexist in LiNi0.5Mn1.5O4-NiO nanocomposites. Furthermore, magnetic measurements suggest that the exchange bias (EB) effect was obtained at low temperature. [ABSTRACT FROM AUTHOR]

The low quantum yield (~10-5) has restricted practical use of photoluminescence (PL) from MoS2 composed of a few layers, but the quantum confinement effects across two-dimensional planes are believed to be able to boost the PL intensity. In this work, PL from 2 to 9 nm MoS2 quantum dots (QDs) is excluded from the solvent and the absorption and PL spectra are shown to be consistent with the size distribution. PL from MoS2 QDs is also found to be sensitive to aggregation due to the size effect. [ABSTRACT FROM AUTHOR]

Regulation of magnetism and half-metallicity has attracted much attention because of its potential in spintronics. The magnetic properties and electronic structure of graphitic carbon nitride (g-C4N3) with external strain are determined theoretically based on the density function theory and many-body perturbation theory (G0W0). Asymmetric deformation induced by uniaxial strain not only regulates the magnetic characteristics but also leads to a transformation from half-metallicity to metallicity. However, this transition cannot occur in the structure with symmetric deformation induced by biaxial strain. Our results suggest the use of strain engineering in metal-free spintronics applications. [ABSTRACT FROM AUTHOR]

p-type ultrathin 3C-SiC nanocrystals are coated on heat-treated n-type TiO2 nanotube arrays formed by electrochemical etching of Ti sheets to produce heterostructured photocatalysts. Depending on the amounts of 3C-SiC nanocrystals on the TiO2 nanotubes, photocatalytic degradation of organic species can be enhanced. The intrinsic electric field induced by the heterojunction promotes separation of the photoexcited electrons-holes in both the TiO2 nanotubes and 3C-SiC nanocrystals. Hence, holes can more effectively travel to the surface of 3C-SiC nanocrystals and there are more electrons on the surface of TiO2 nanotubes consequently forming more ·O2- and ·OH species to degrade organic molecules. [ABSTRACT FROM AUTHOR]

Raman spectra acquired from spherical SnO2 nanocrystals prepared by pulsed laser ablation and hydrothermal synthesis exhibit three oxygen-vacancy-related Raman modes at 234, 573, and 618 cm−1. The peak location and intensity vary with annealing temperature under O2 finally approaching those of bulk materials. Density functional calculation discloses that the three Raman modes stem from subbridging, in-plane, and bridging oxygen vacancies, respectively. Raman spectra can thus be used to discern different types of oxygen vacancies in SnO2 nanocrystals. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Two novel cyano-bridged complexes, {[Cu(men)2][Ni(CN)4] n ( 1) (men = N,N′-dimethyl-ethylenediamine) and [Mn(bpy)2]4[Mo(CN)8]2·0.5MeOH·0.75H2O ( 2) (bpy = 2,2′-bipyridine) have been synthesized and structurally characterized by IR spectroscopy and X-ray crystallography. The complex 1 has onedimensional zigzag chain structure in which the Ni atom is coordinated by four cyanide groups, and the Cu atom is surrounded by four nitrogen atoms of the two men ligands in equatorial plane and two nitrogen atoms of the bridging cyanide in axial positions; the Cu centre is in a distorted octahedral environment. Owing to weak interactions, complex 1 is self-assembled into two-dimensional network via N-H...N hydrogen bonds. In 2, the basic structural unit is centrosymmetric and contains four Mn centers connected by two octacyanomolybdates via eight cyanide bridges. Each Mo atom is linked via four cyanide groups to four Mn, and the other four cyanide groups are terminal. From X-ray single crystal analysis (room temperature), 1 crystallizes in monoclinic space group P21/ n with a = 6.7332(7) Å, b = 13.9248(15) Å, c = 9.0869(10) Å, β = 98.4030(10)°, V = 843.05(16) Å3, Z = 2; 2 crystallizes in monoclinic space group P21/ n with a = 13.886(6) Å, b = 24.116(11) Å, c = 15.263(7) Å, β = 90.175(6)°, V = 5111(4) Å3, Z = 2. [ABSTRACT FROM AUTHOR]

By experimentally examining and theoretically analyzing the Raman spectra of SixGe1−xnanocrystal-embedded silica films, we show that the 430 cm−1Si–Si optical phonon mode can be used as a fingerprint to identify the existence of local silicon cluster nanostructures inside SixGe1−xnanocrystals with high silicon content. [ABSTRACT FROM AUTHOR]

Ge0.54Si0.46 alloy nanocrystals (NCs) with different twinning structures are synthesized by magnetron sputtering followed by high temperature (>1100 °C) annealing and rapid cooling. The local strain induced by rapid cooling enables neighboring NCs to coalesce quickly. Because of insufficient time to form individual structures, a leading twinning interface forms inevitably in the interior of the NCs. The twinning NCs with large surface free energies reconstruct for energy optimization at high temperature. Consequently, the twinning layer thickness shrinks slowly, finally transforming into untwined stable NCs with the lowest surface free energy. Our experimental observations are corroborated by theoretical calculation. [ABSTRACT FROM AUTHOR]

The Ge–Ge optical phonon peak at 300 cm-1 acquired from amorphous SiO2 films embedded with Ge nanocrystals by Raman scattering is sensitive to the Si content. When the Si concentration is high, a thin GeSi interfacial layer forms around the Ge nanocrystals. A tensile stress is produced to partially offset the compressive stress imposed by the SiO2 matrix on the Ge nanocrystals, consequently downshifting the frequency of the optical phonon and increasing its linewidth. Theoretical calculation based on phonon confinement and compressive effects discloses that the interfacial layer plays a crucial role in the optical phonon behavior. [ABSTRACT FROM AUTHOR]

Amorphous foliaceous SiO2 helical nanobelts with equidistant alternating bright and dark stripes are synthesized using thermal evaporation. A very thin polar crystalline layer spontaneously formed on the nanobelt surface stabilizes the twist and the internal shear stress imbalance induces the periodic reconstruction. The periodic bright and dark stripes disappear slowly with growth time because the polar crystalline SiO2 layers are covered slowly by an amorphous layer. The polar surface-driven mechanism, which can adequately explain the appearance and disappearance of the periodic fringes, is verified theoretically. [ABSTRACT FROM AUTHOR]

A theoretical analysis is performed for photoexcitation of carriers from a quantum well state into a superlattice subband. The parameters of the device structure are chosen so that (a) the first excited state of the quantum well lies within the lowest subband of the superlattice and (b) the lowest subband is narrow. The degeneracy of the first excited state with the subband provides resonant enhancement of photoexcitation into the subband while the subband extrema provide long-wavelength and short-wavelength cutoffs. The response band and bandwidth can be tailored and there is the possibility of high-temperature operation associated with the narrow band response. [ABSTRACT FROM AUTHOR]

In order to investigate the association between polymorphisms in genes encoding metabolizing enzymes (CYP1A1-MspI, EC-SOD (extracellular superoxide dismutase), GSTT1, GSTM1, ALDH2), cigarette and alcohol consumption, and the risk of oral squamous cell carcinoma, we conducted a prospective case-control study comprised of 750 individuals with oral squamous cell carcinoma (OSCC) and 750 healthy individuals. Data about smoking and drinking habits were collected along with other demographic and clinical information. Peripheral blood samples were collected for DNA extraction, and polymerase chain reaction (PCR) and PCR-RFLP (restriction fragment length polymorphism) were used to determine genotypes of CYP1A1, EC-SOD, GSTT1, GSTM1, ALDH2. The results showed that smoking and alcohol consumption were significantly more common among patients than controls (p <0.05). There were significant differences in the genotype distribution for each locus between groups, with the CYP1A1 (m2/ m2), EC-SOD (C/G), GSTT1 [-], GSTM1 [-] and ALDH2 (non G/G) genotypes being more common among patients (p <0.05). Furthermore, the majority of patients had at least two or more variant genotypes, while controls had one or no variant genotype (p <0.05). Finally, multiple variant genotypes combined with smoking, drinking, or both smoking and drinking significantly increased the risk of OSCC, with greater increase for heavier smoking/drinking. In brief, genetic polymorphism of CYP1A1, EC-SOD, GSTT1, GSTM1, and ALDH2 and smoking and drinking history are closely associated with susceptibility to OSCC. [ABSTRACT FROM AUTHOR]

Islet amyloid polypeptide (IAPP) is an amyloidogenic protein associated with pancreatic beta-cell loss in type 2 diabetes. For in vitro studies, human IAPP oligomers can lead to formation of either non-toxic amyloid fibrils or toxic oligomers, the latter causing beta-cell apoptosis. To date, the correlation of oligomerization of IAPP and beta-cell loss in type 2 diabetic mellitus (DM) remains to be elucidated. Pancreas specimens were obtained from autopsies of 6 male human LAPP transgenic mice and 11 human adults (Type 2 DM subjects: n=5, male=2, age=78.6±6.6 years; non-DM control subjects: n--6, male=3, age=80.0±8.2 years). Oligomer depositions were detected by immunostaining with oligomer-specific polyclonal antibody. Fibrillar amyloid was detected by IAPP antibody and thioflavin-T. Mitochondria and oxidative phosphorylation were identified with anti-mitochondria and anti-cytochrome oxidase monoclonal antibodies respectively. All 6 hIAPP transgenic mice developed diabetes with a fasting blood glucose level of 11.9±.5mM by 4 months of age. At 2 months when fasting blood glucose was mildly elevated at 6.5±0.2mM, pancreatic islets showed oligomer deposition without fibrillar amyloid. In human pancreas, normal islets of control group were virtually negative for oligomer deposition. In islets with reduced numbers of β-cells, oligomer deposits were increased. Oligomers were deposited in a scattered manner which was accompanied by discrete fibrillar amyloid plaque. In islets with absence of β-cells, oligomers were intermixed with IAPP fibrillar amyloid. Islet cells with intracellular oligomers showed diminished staining of mitochondria and oxidative phosphorylation. These results suggest that, oligomerization of IAPP is associated with β-cell apoptosis due to mitochondrial depletion and compromised oxidative phosphorylation. In conclusion, the oligomerization of IAPP precedes the development of diabetes and the formation of fibrillar amyloid. [ABSTRACT FROM AUTHOR]

To characterize the pancreatic beta-cell function during oral glucose tolerance test (OGTT), 25 male Zucker lean rats with body weight of 200.8±4.1 [± SE] grams received oral glucose 2.5 g/kg. Every five animals were sacrificed at 0, 15, 30, 60, and 120 minutes of OGTT time points. Serum insulin was measured with a rot-specific ELISA kit and pancreas specimens were double immunostained with beta-cell hormones of insulin and amylin (islet amyloid polypeptide, IAPP). Fasting blood glucose levels were not different among the five groups of animals (0 minute, 4.7±0.2 mM; 15 minute, 5.2±0.4 mM; 30 minute, 5.0±0.3 mM; 60 minute, 5.1±0.3 mM; 120 minute, 5.3±0.3 mM; ANOVA p=0.651). Blood glucose levels of OGTT 15 minute (7.5±0.8 mM), 30 minute (7.7±0.5 mM) and 60 minute (7.6+0.5 mM) were higher than those of 0 minute (4.7±0.2 mM) and 120 minute (5.6±0.3 mM). Similarly, serum insulin levels of 15 minute (229.0±134.2pM), 30 minute (113.2±34.4 pM), and 60 minute (64.2±20.4 pM) were higher than those of 0 minute (42.0±3.2 pM) and 120 minute (38.2±1.3 pM). Compared with islet beta-cells in the fasting state, islet beta-cells during OGTT had an enhanced immunoreactivity of insulin and amylin at 15 minute and 60 minute but a decreased degranulation at 30 minute. Islet beta-cells of OGTT 0 minute and 120 minute showed similar immunoreactivity of insulin and amylin. The extra-islet cells expressing insulin and amylin accounted for about 12% of the total pancreatic beta-cells and showed no remarkable changes during OGTT. These data suggest that 1) islet beta-cells and extra-islet beta-cells are heterogeneous in response to glucose challenge, 2) insulin and amylin are partner islet hormones in glucose homeostasis, 3) islet beta-cells have at least two phases of degranulation and secretion during a two-hour OGTT. [ABSTRACT FROM AUTHOR]