Densification mechanisms during hot pressing of ZrB2-20 vol.% SiC composite

The dominant densification mechanisms for hot pressing of ZrB2-20 vol.% SiC composite at different hot-pressing temperatures and pressures was identified. The dominant densification mechanisms were found to change over a very short temperature range. For hot pressing at 1700 degrees C, the dominant densification mechanism was found to be mechanically driven particle fragmentation and rearrangement only, whereas at 1850 degrees C a plastic flow mechanism started to become dominant after initial particle fragmentation and rearrangement. At 2000 degrees C, the dominant mechanism changed from plastic flow to grain boundary diffusion. (c) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Structural, iono and thermoluminescence properties of heavy ion (100 MeV Si7+) bombarded Zn2SiO4:Sm3+ nanophosphor

Structural, iono (IL) and thermoluminescence (TL) studies of Zn2SiO4:Sm3+ (1-5 mol%) nanophosphor bombarded with swift heavy ions in the fluence range 3.91 x 10(12)-21.48 x 10(12) cm(-2) have been carried out. The average crystallite sizes for pristine and ion irradiated for 3.91 x 10(12) ions cm(-2) and 21.48 x 10(12) ions cm(-2) were found to be 34, 26 and 20 nm. With increase of ion fluence, the intensity of XRD peaks decreases and FWHM increases. The peak broadening indicates the stress induced point/clusters defects produced due to heavy ion irradiation. IL studies were carried out for different Sm3+ concentrations in Zn2SiO4 by irradiating with ion fluence of 15.62 x 10(12) ions cm(-2). The characteristic emission peaks at similar to 562, 599, 646 and 701 nm were recorded by exciting Si7+ ions in the fluence range 3.91 x 10(12)-21.48 x 10(12) ions cm(-2). These peaks were attributed to (4)G(5/2)-> H-6(5/2) (562 nm), (4)G(5/2)-> H-6(7/2) (599 nm), (4)G(5/2)-> H-6(9/2) (646 nm), and (4)G(5/2)-> H-6(5/2) (701 nm) transitions of Sm3+. The highest emission was recorded at 3 mol% of Sm3+ doped Zn2SiO4. TL studies were carried out for 3 mol% Sm3+ concentration in the fluence range 3.91 x 10(12)-21.48 x 10(12) ions cm(-2). Two U glow peaks at 152 and 223 degrees C were recorded. The kinetic parameters (E, b, and s), were estimated using Chen's peak shape method. Simple glow curve structure (223 degrees C), highly resistive, increase in TL. intensity up to 19.53 x 10(12) ions cm(-2), simple trap distribution makes Zn2SiO4:Sm3+ (3 mol%) phosphor highly useful in radiation dosimetry.

Effect of zinc substitution on the nanocobalt ferrite powders for nanoelectronic devices

Zinc substituted cobalt ferrite powders {Co(1-x)ZnxFe2O4} (0.0 <= x <= 0.5) were prepared by the solution combustion method. The structural, morphological, magnetic and electrical properties of as synthesized samples were studied. Powder X-ray diffraction patterns reveals single phase, cubic spinel structure with space group No. Fd (3) over barm (227). As zinc concentration increases, the lattice constant increases and the crystallite size decreases. The minimum crystallite size of similar to 12 nm was observed for x = 0.5 composition. The synthesized ferrite compounds show ferrimagnetic behavior, with coercivity value of 10779 Oe (Hard ferrite) at 20 K and 1298 Oe (soft ferrite) at room temperature (RT). The maximum saturation magnetization recorded for the Co0.5Zn0.5Fe2O4 composition was 99.78 emu g(-1) and 63.83 emu g(-1) at 20 K and RT respectively. The dielectric parameters such as dielectric constant, loss tangent and AC conductivity were determined as a function of frequency at RT. The magnetic and dielectric properties of the samples illustrates that the materials were quite useful for the fabrication of nanoelectronic devices. (C) 2013 Elsevier B.V. All rights reserved.

Hydrothermal synthesis of Gd2O3:Eu3+ nanophosphors: Effect of surfactant on structural and luminescence properties

Various morphologies of Eu3+ activated gadolinium oxide have been prepared by hydrothermal method using hexadecylamine (HDA) as surfactant at different experimental conditions. The powder X-ray diffraction studies reveal as-formed product is hexagonal Gd(OH)(3):Eu3+ phase and subsequent heat treatment at 350 and 600 degrees C transforms to monoclinic GdOOH:Eu3+ and cubic Gd2O3:Eu3+ phases respectively. SEM pictures of without surfactant show irregular shaped rods along with flakes. However, in the presence of HDA surfactant, the particles are converted into rods of various sizes. The temperature dependent morphological evolution of Gd2O3:Eu3+ without and with HDA surfactant is studied. TEM micrographs of Gd(OH)(3):Eu3+ sample with HDA confirms smooth nanorods with various diameters in the range 20-100 nm. FTIR studies reveal that HDA surfactant plays an important role in conversion of cubic to hexagonal phases. Among these three phases, cubic phase Gd2O3:Eu3+ (lambda(ex) = 254 nm) show red emission at 612 nm corresponding to D-5(0)-> F-7(2) and is more efficient host than the monoclinic counterpart. The band gap for hexagonal Gd(OH)(3):Eu3+ is more when compared to monoclinic GdOOH:Eu3+ and cubic Gd2O3:Eu3+. (C) 2013 Elsevier B. V. All rights reserved.

Synthesis and luminescence properties of Sm3+ doped CaTiO3 nanophosphor for application in white LED under NUV excitation

CaTiO3:Sm3+ (1-11 mol%) nanophosphors were successfully synthesized by a low temperature solution combustion method LCS]. The structural and morphological properties of the phosphors were studied by using Powder X-ray diffractometer (PXRD), Fourier transform infrared (FTIR), X-ray photo electron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscopy (TEM). TEM studies indicate that the size of the phosphor is similar to 20-35 nm. Photoluminescence (PL) properties of Sm3+ (1-11 mol%) doped CaTiO3 for NUV excitation (407 nm) was studied in order to investigate the possibility of its use in White light emitting diode (WLED) applications. The emission spectra consists of intra 4f transitions of Sm3+, such as (4)G(5/2) -> H-6(5/2) (561 nm), (4)G(5/2) -> H-6(7/2) (601-611 nm), (4)G(5/2) -> H-6(9/2) (648 nm) and (4)G(5/2) -> H-6(11/2) (703 nm) respectively. Further, the emission at 601-611 nm show strong orange-red emission and can be applied to the orange-red emission of phosphor for the application for near ultra violet (NUV) excitation. Thermoluminescence (TL) of the samples irradiated with gamma source in the dose range 100-500 Gy was recorded at a heating rate of 5 degrees C s(-1). Two well resolved glow peaks at 164 degrees C and 214 degrees C along with shouldered peak at 186 degrees C were recorded. TL intensity increases up to 300 Gy and thereafter, it decreases with further increase of dose. The kinetic parameters namely activation energy (E), frequency factor (s) and order of kinetics were estimated and results were discussed in detail. (C) 2014 Elsevier B.V. All rights reserved.

Conformational Analysis of a 20-Membered Cyclic Peptide Disulfide from Conus virgo with a WPW Segment: Evidence for an Aromatic-Proline Sandwich

A novel peptide containing a single disulfide bond, CIWPWC (Vi804), has been isolated and characterised from the venom of the marine cone snail, Conus virgo. A precursor polypeptide sequence derived from complementary DNA, corresponding to the M-superfamily conotoxins, has been identified. The identity of the synthetic and natural peptide sequence has been established. A detailed analysis of the conformation in solution is reported for Vi804 and a synthetic analogue, (CIWPWC)-W-D ((D)W3-Vi804), in order to establish the structure of the novel WPW motif, which occurs in the context of a 20-membered macrocyclic disulfide. Vi804 exists exclusively in the cis W3P4 conformer in water and methanol, whereas (D)W3-Vi804 occurs exclusively as the trans conformer. NMR spectra revealed a W3P4 typeVI turn in Vi804 and a typeII turn in the analogue peptide, (D)W3-Vi804. The extremely high-field chemical shifts of the proline ring protons, together with specific nuclear Overhauser effects, are used to establish a conformation in which the proline ring is sandwiched between the flanking Trp residues, which emphasises a stabilising role for the aromatic-proline interactions, mediated predominantly by dispersion forces.

Eco-friendly green synthesis, structural and photoluminescent studies of CeO2:Eu3+ nanophosphors using E. tirucalli plant latex

The investigation involves preparation and photoluminescence properties of CeO2:Eu3+ (1-11 mol%) nano phosphors by eco-friendly green combustion route using Euphorbia tirucalli plant latex as fuel. The final product was characterized by powder X-ray diffraction (PXRD), Scanning electron microcopy (SEM) and Transmission electron microscopy (TEM). The PXRD and SEM results reveals cubic fluorite phase with flaky structure. The crystallite size obtained from TEM was found to be similar to 20-25 nm, which was comparable to W-H plots and Scherrer's method. Photoluminescence (PL) emission of all the Eu3+ doped samples shows characteristic bands arising from the transitions of D-5(0) -> F-5(J) (J = 0, 1, 2, 3, 4) manifolds under excitation at 373 and 467 nm excitation. The D-5(0) -> F-7(2) (613 nm) transition often dominate the emission spectra, indicating that the Eu3+ cations occupy a site without inversion center. The highest PL intensity was recorded for 9 mol% Eu3+ ions with 5 ml latex. PL quenching was observed upon further increase in Eu3+ concentration. The international commission on illumination (CIE) chromaticity co-ordinates were calculated from emission spectra, the values (x, y) were very close to national television system committee (NTSC) standard values of pure red emission. The results demonstrate that the synthesized phosphor material could be very useful for display applications. Further, the phosphor material prepared by this method was found to be non toxic, environmental friendly and could be a potential alternative to economical routes. (C) 2014 Elsevier B.V. All rights reserved.

Local spatial structure of forest biomass and its consequences for remote sensing of carbon stocks

Advances in forest carbon mapping have the potential to greatly reduce uncertainties in the global carbon budget and to facilitate effective emissions mitigation strategies such as REDD+ (Reducing Emissions from Deforestation and Forest Degradation). Though broad-scale mapping is based primarily on remote sensing data, the accuracy of resulting forest carbon stock estimates depends critically on the quality of field measurements and calibration procedures. The mismatch in spatial scales between field inventory plots and larger pixels of current and planned remote sensing products for forest biomass mapping is of particular concern, as it has the potential to introduce errors, especially if forest biomass shows strong local spatial variation. Here, we used 30 large (8-50 ha) globally distributed permanent forest plots to quantify the spatial variability in aboveground biomass density (AGBD in Mgha(-1)) at spatial scales ranging from 5 to 250m (0.025-6.25 ha), and to evaluate the implications of this variability for calibrating remote sensing products using simulated remote sensing footprints. We found that local spatial variability in AGBD is large for standard plot sizes, averaging 46.3% for replicate 0.1 ha subplots within a single large plot, and 16.6% for 1 ha subplots. AGBD showed weak spatial autocorrelation at distances of 20-400 m, with autocorrelation higher in sites with higher topographic variability and statistically significant in half of the sites. We further show that when field calibration plots are smaller than the remote sensing pixels, the high local spatial variability in AGBD leads to a substantial ``dilution'' bias in calibration parameters, a bias that cannot be removed with standard statistical methods. Our results suggest that topography should be explicitly accounted for in future sampling strategies and that much care must be taken in designing calibration schemes if remote sensing of forest carbon is to achieve its promise.

Evolution of deformation texture and magnetic properties in a nanocrystalline nickel-20 wt% cobalt alloy

The evolution of crystallographic texture in a nanocrystalline nickel-20 wt% cobalt alloy has been investigated for deformation up to large strains. The effect of texture on magnetic properties has been evaluated. The material shows characteristic copper-type texture at large strain levels. Microstructural examinations indicate that the evolution of texture is assisted by deformation-induced grain growth. The values of saturation magnetization and coercivity have been correlated with the crystallographic texture and grain size. (C) 2014 Elsevier B.V. All rights reserved.

Ligand 5,10,15,20-Tetra(N-methyl-4-pyridyl)porphine (TMPyP4) Prefers the Parallel Propeller-Type Human Telomeric G-Quadruplex DNA over Its Other Polymorphs

The binding of ligand 5,10,15,20-tetra(N-methyl-4-pyridyl)porphine (TMPyP4) with telomeric and genomic G-quadruplex DNA has been extensively studied. However, a comparative study of interactions of TMPyP4 with different conformations of human telomeric G-quadruplex DNA, namely, parallel propeller-type (PP), antiparallel basket-type (AB), and mixed hybrid-type (MH) G-quadruplex DNA, has not been done. We considered all the possible binding sites in each of the G-quadruplex DNA structures and docked TMPyP4 to each one of them. The resultant most potent sites for binding were analyzed from the mean binding free energy of the complexes. Molecular dynamics simulations were then carried out, and analysis of the binding free energy of the TMPyP4-G-quadruplex complex showed that the binding of TMPyP4 with parallel propeller-type G-quadruplex DNA is preferred over the other two G-quadruplex DNA conformations. The results obtained from the change in solvent excluded surface area (SESA) and solvent accessible surface area (SASA) also support the more pronounced binding of the ligand with the parallel propeller-type G-quadruplex DNA.

Photocytotoxic luminescent lanthanide complexes of DTPA-bisamide using quinoline as photosensitizer

Lanthanide complexes Ln(DTPAAQ)(DMF)] (1-3) (Ln - Pr (1), Eu (2), Tb (3), H(3)DTPAAQ - N, N `'-bis(3-amidoquinolyl) diethylenetriamine-N, N', N `'-triacetic acid, DMF - N, N-dimethylformamide) were studied for their structures, photophysical properties, DNA and protein binding, DNA photocleavage, photocytotoxicity and cellular internalization. The crystal structures of complexes Ln(DTPAAQ)(DMF)] (1-3) display a discrete mononuclear nine-coordinate {LnN(3)O(6)} tricapped-trigonal prism (TTP) coordination geometry. The europium and terbium complexes show strong luminescence properties in the visible region having a long luminescence lifetime (tau = 0.51-0.64 ms). The conjugated 3-aminoquinoline moieties act as efficient light harvesting antennae, which upon photoexcitation transfer their energy to Eu(III) or Tb(III) for their characteristic D-5(0) -> F-7(J) or D-5(4) -> F-7(J) f-f transitions respectively. The complexes display efficient binding affinity to DNA (K-b = 3.4 x 10(4) - 9.8 x 10(4) M-1) and BSA (KBSA = 3.03 x 10(4) - 6.57 x 10(4) M-1). Europium and terbium complexes give enhanced luminescence upon interacting with CT-DNA suggesting possible luminescence-based sensing applications for these complexes. Complexes 1-3 show moderate cleavage of supercoiled (SC) DNA to its nicked circular (NC) form on exposure to UV-A light of 312 nm involving formation of singlet oxygen (O-1(2)) and hydroxyl radicals (cOH) in type-II and photoredox pathways. Eu(III) and Tb(III) complexes exhibit remarkable photocytotoxicity with human cervical cancer cell line (HeLa) (IC50 = 20.7-28.5 mM) while remaining essentially noncytotoxic up to 150 mM in the dark. Complexes are nontoxic in nature thus suitable for designing cellular imaging agents. Fluorescence microscopy data reveal primarily cytosolic localization of the Eu(III) and Tb(III) complexes in HeLa cells.

Effect of potassium present in stratum corneum during non-invasive measurement of potassium in human subjects using reverse iontophoresis

Purpose: Reverse iontophoresis (RI) is one of the potential techniques used to monitor the concentration of various analytes in body fluids non -invasively. Transdermal extraction of potassium is investigated using RI. In the present work, the effect of potassium on stratum corneum (SC) during RI, feasibility of RI for continuous monitoring of potassium, and use of potassium as internal standard in RI, are investigated. Methods: Tape stripping experiment is carried out to find potassium concentration in SC. RI is carried out continuously for 180 min without passive diffusion and after passive diffusion for 60 min. Skin impedance measurements are done at 20 Hz and 20 kHz. Results: Potassium is found to be in the range 300-650 nmol/cm(2) on SC by tape stripping experiment. Correlation coefficient between blood potassium and extracted potassium through RI after passive diffusion (R-2 = 0.5870) is more than without passive diffusion (R-2 = 0.5117). The skin impedance measurement shows that RI has more effect on SC than superficial layer of SC during RI. Conclusion: The present investigations conclude that it is possible to monitor potassium continuously through RI and using potassium as internal standard in RI.

Structural Evolution and Property Changes in Nd_{60}Al_{10}Fe_{20}Co_{10} Bulk Metallic Glass During Crystallization

The structural evolution and property changes in Nd60Al10Fe20Co10 bulk metallic glass (BMG) upon crystallization are investigated by the ultrasonic method, x-ray diffraction, density measurement, and differential scanning calorimetry. The elastic constants and Debye temperature of the BMG are obtained as a function of annealing temperature. Anomalous changes in ultrasonic velocities, elastic constants, and density are observed between 600–750 K, corresponding to the formation of metastable phases as an intermediate product in the crystallization process. The changes in acoustic velocities, elastic constants, density, and Debye temperature of the BMG relative to its fully crystallized state are much smaller, compared with those of other known BMGs, the differences being attributed to the microstructural feature of the BMG.

Nd_(60)Al_(10)Fe_(20)Co_(10)金属玻璃的变形行为

利用材料测试系统(MTS)、X-Ray 衍射(XRD)和扫描电镜(SEM)等手段研究了Nd 基大块金属玻璃的变形行为和断裂特征。Nd 基大块金属玻璃样品在室温下是脆性断裂,大约在500 K 时变形模式从非均匀变形转变为均匀变形,在523 K 以上表现出显著的塑性变形。在5×10-4 m/s 的应变速率下,这种Nd 基大块金属玻璃材料在523 K~600 K 之间出现明显的屈服应力下降现象,随后进入1 种稳定的粘性流动状态,而且这种屈服下降现象与温度和应变速率有关。这种在过冷液相区的变形行为与其他大块金属玻璃变形特征相似。合金的这种塑性变形行为表明了其存在稳定的过冷液相区,同时对其变形行为的研究有助于进一步了解Nd 基大块金属玻璃的反常热稳定性。

Estudio preliminar sobre la utilización de la semilla de ayote (Cucurbita maxima) en el control de parasitos gastrointestinales en terneros de 3-8 meses de edad en la Hacienda San Emilio, Granada

El presente estudio se realizó con el objetivo de determinar si la semilla de ayote (Cucurbita maxima) fresca ejerce algún efecto en el control de parásitos gastrointestinales en terneros, el cual fue realizado en la Hacienda San Emilio ubicada en el Municipio de Diriomo, departamento de Granada, la temperatura del lugar oscila entre los 27-34ºC. La duración del experimento fue de 14 días a partir de la selección, identificación de los animales y aplicación de los tratamientos. En el estudio se utilizaron tablas de contingencia de variables dicotómicas: control total y reducción parasitaria como columnas y tratamientos como filas. Para el estudio se seleccionaron 20 animales entre los 3-8 meses de edad, estos se dividieron en 4 grupos constituidos por 5 animales para cada uno de los 4 tratamientos; Tratamiento 1: Doramectina 1% (10mg/50kg) SC, Tratamiento 2: semilla de ayote a dosis de 240 mg/kg/ día por 3 días PO, Tratamiento 3: semilla de ayote a dosis de 240mg/ kg por un día PO,Tratamiento 4: animales sin tratamiento. A los animales se les realizaron análisis coprológicos al inicio del estudio para identificar la familia de parásitos y la carga parasitaria. Los terneros fueron pesados e identificados para la aplicación de los tratamientos; posteriormente se realizó otro análisis coprológico con la técnica de Mc Master a los 14 días después del primer día de aplicación de los tratamientos. Se identificaron las familias Trichost rongylidae, Eimeriidae y Strongyloididae. Para la familia Eimeriidae demostró tener un mejor efecto el tratamiento con semilla de ayote; en lo que refiere a disminución de la carga parasitaria tanto la semilla de ayote como la doramectina resultaron efectivos en las familias Trichostrongylidae y Eimeriidae, mientras que en la familia Strongyloididae solo fue efectiva la doramectina. A través del análisis de costos se determinó que es económicamente factible la utilización de semilla de ayote en la Coccidiosis.