A unified model for the dynamics of driven ribbon with strain and magnetic order parameters

We develop a unified model to explain the dynamics of driven one dimensional ribbon for materials with strain and magnetic order parameters. We show that the model equations in their most general form explain several results on driven magnetostrictive metallic glass ribbons such as the period doubling route to chaos as a function of a dc magnetic field in the presence of a sinusoidal field, the quasiperiodic route to chaos as a function of the sinusoidal field for a fixed dc field, and induced and suppressed chaos in the presence of an additional low amplitude near resonant sinusoidal field. We also investigate the influence of a low amplitude near resonant field on the period doubling route. The model equations also exhibit symmetry restoring crisis with an exponent close to unity. The model can be adopted to explain certain results on magnetoelastic beam and martensitic ribbon under sinusoidal driving conditions. In the latter case, we find interesting dynamics of a periodic one orbit switching between two equivalent wells as a function of an ac magnetic field that eventually makes a direct transition to chaos under resonant driving condition. The model is also applicable to magnetomartensites and materials with two order parameters. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4790845]

Green synthesis of polysaccharide/gold nanoparticle nanocomposite: An efficient ammonia sensor

A low cost eco-friendly method for the synthesis of gold nanoparticles (AuNPs) using guar gum (GG) as a reducing agent is reported. The nanoparticles obtained are characterized by UV-vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Based on these results, a potential mechanism for this method of AuNPs synthesis is discussed. GG/AuNPs nanocomposite (GG/AuNPs NC) was exploited for optical sensor for detection of aqueous ammonia based on surface plasmon resonance (SPR). It was found to have good reproducibility, response times of similar to 10 s and excellent sensitivity with a detection limit of 1 ppb (parts-per-billion). This system allows the rapid production of an ultra-low-cost GG/AuNPs NC-based aqueous ammonia sensor.

Charge transport and magnetic properties of coaxial composite fibrils of polypyrrole/multiwall carbon nanotubes at low temperature

We report the low temperature electrical and magnetic properties of polypyrrole (PPy)/multiwall carbon nanotube (MWNT) coaxial composite fibrils synthesized by the electro-polymerization method. The iron-filled MWNTs were first grown by chemical vapor deposition of a mixture of liquid phase organic compound and ferrocene by the one step method. Then the PPy/MWNT fibrils were prepared by the electrochemical polymerization process. Electron microscopy studies reveal that PPy coating on the surface of nanotube is quite uniform throughout the length. The temperature dependent electrical resistivity and magnetization measurements were done from room temperature down to 5 and 10 K, respectively. The room temperature resistivity (rho) of PPy/MWNT composite fibril sample is similar to 3.8 Omega m with resistivity ratio R-5 K/R-300 K] of similar to 300, and the analysis of rho(T) in terms of reduced activation energy shows that resistivity lies in the insulating regime below 40 K. The resistivity varies according to three dimensional variable range hopping mechanism at low temperature. The magnetization versus applied field (M-H loop) data up to a field of 20 kOe are presented, displaying ferromagnetic behavior at all temperatures with enhanced coercivities similar to 680 and 1870 Oe at room temperature and 10 K, respectively. The observation of enhanced coercivity is due to significant dipolar interaction among encapsulated iron nanoparticles, and their shape anisotropy contribution as well.

Insight into morphology changes of nanoparticle laden droplets in acoustic field

Hollow structures with unique morphologies form due to particle agglomeration in acoustically levitated nanofluid functional droplets when subjected to external heating. The final diameter of the structure depends only on the ratio of agglomeration to evaporation time scales for various nanoparticle laden droplets, and not on the type of the suspended particles. These time scales depend only on nanoparticle concentration. This valuable information may be exploited to form microstructures with desired properties from ceramic compounds. Phase diagrams for alumina and silica droplets indicate the transition from a bowl to ring structure depending on concentration.

Magnetic and transport relaxation property of La0.85Sr0.15CoO3 single crystals

Here, we present a comprehensive investigation of the dc magnetization and magnetotransport studies on La0.85Sr0.15CoO3 single crystals grown by the optical float zone method. The spin freezing temperature in the ac susceptibility study shifts to lower value at higher dc field and this is well described by the de Almeida-Thouless line which is the characteristic of SG behavior. The Magnetotransport study shows that the sample exhibits a huge negative MR of similar to 70% at 10 K which monotonically decreases with the increase in temperature. Besides, the magnetization and the resistivity relaxation give strong indication that the MR scales with sample's magnetization. In essence, all the present experimental findings evidence the SG behavior of La0.85Sr0.15CoO3 single crystals.

Surfactant free, non-aqueous method, for the deposition of ZnO nanoparticle thin films on Si(100) substrate with tunable ultraviolet (UV) emission

We report, strong ultraviolet (UV) emission from ZnO nanoparticle thin film obtained by a green synthesis, where the film is formed by the microwave irradiation of the alcohol solution of the precursor. The deposition is carried out in non-aqueous medium without the use of any surfactant, and the film formation is quick (5 min). The film is uniform comprising of mono-disperse nanoparticles having a narrow size distribution (15-22 nm), and that cover over an entire area (625 mm(2)) of the substrate. The growth rate is comparatively high (30-70 nm/min). It is possible to tune the morphology of the films and the UV emission by varying the process parameters. The growth mechanism is discussed precisely and schematic of the growth process is provided.

Anomalous magnetic behavior of La0.6Sr0.4MnO3 nano-tubes constituted with 3-12 nm particles

Uniform La0.6Sr0.4MnO3 (LSMO) nanotubes of an average diameter 180 nm were synthesized by a modified sol-gel method employing nanochannel porous anodic alumina templates. The nanotubes were characterized chemically and structurally by XRD, SEM, EDX, and TEM. Postannealed (700 degrees C for 1 h hour) nanotubes were found to be polycrystalline from XRD and SAED studies. To get further insight into the nanotube structure, HRTEM studies were done, which revealed that obtained LSMO nanotubes were structurally constituted with nanoparticles of 3-12 nm size. These constituent nanoparticles were randomly aligned and self-knitted to build the nanotube wall. Investigation of magnetic properties at this structured nanoscale revealed remarkable irreversibility between the zero field cooling (ZFC) and field cooling (FC) magnetization curves accompanied with a peak in the ZFC curve indicating spin-glass-like behavior. Structural defects and compositional variations at surfaces and grain-boundaries of constituent nanoparticles might be responsible for this anomalous magnetic behavior.

Effect of TiO2 on electrical and magnetic properties of Ni0.35Cu0.12Zn0.35Fe2O4 synthesized by the microwave-hydrothermal method

The nanocomposites of xTiO(2)+(1-x)Ni0.53Cu0.12Zn0.35Fe2O4 (where 0 <= x >= 1) were prepared using microwave hydrothermal (M H) method at 165 degrees C/45 min. The as-synthesized powders were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The particle size of the powder varies from 18 to 35 nm. The as prepared powders were densified at 500 degrees C/30 min using microwave sintering method. The sintered composites were characterized by XRD and scanning electron microscopy (SEM). The bulk densities of the present composites were increasing with the addition of TiO2. The grain sizes of all the composite vary between 65 nm and 90 nm. The addition of TiO2 to ferrite increased the dielectric properties (epsilon' and epsilon `') also the resonant frequency of all the composites was found to be greater than 1 GHz. The imaginary part of permeability mu `' was found to increase with an increase of TiO2.

Characterization and magnetic response of multiwall carbon nanotubes filled with iron nanoparticles of different aspect ratios

Three samples of multiwall carbon nanotubes (MWCNT) TF200, TF150 and TF100, where T and F stand for toluene and ferrocene respectively, and numeral denotes the amount (mg) of ferrocene] filled with iron-nanoparticles (Fe-NPs) of different aspect ratios are grown by chemical vapor deposition of toluene-ferrocene mixture. Energy dispersive X-ray analysis shows a systematic variation in the intensities of peak corresponding to Fe, indicating that Fe is present in different amounts in the three MWCNT samples. The lengths of Fe-NPs lie in the range of 200-250; 80-120; and 30-40 nm for TF200, TF150 and TF100, respectively, as estimated statistically from transmission electron microscopy micrographs. However, the diameter of the encapsulated Fe-NPs does not vary significantly for different samples and is 20-30 nm for all samples. Hysteresis loop measurements on these MWCNT samples were done at 10, 150 and 300 K up to an applied field of 1.5 T. At 10 K, values of coercivity are 2584, 2315, and 2251 Oe for TF200, TF150 and TF100 respectively. This is attributed to the strong shape anisotropy of the Fe-NPs and significant dipolar interactions between them. Further, M-H loops reveal that saturation magnetization of TF200 is almost four times that of TF100 at all temperatures.

Interplay of structural distortions, dielectric effects and magnetic order in multiferroic GdMnO3

Multiferroic materials are characterized by simultaneous magnetic and ferroelectric ordering making them good candidates for magneto-electrical applications. We conducted thermal expansion and magnetostriction measurements in magnetic fields up to 14 T on perovskitic GdMnO3 by highresolution capacitive dilatometry in an effort to determine all longitudinal and transversal components of the magnetostriction tensor. Below the ordering temperature T (N) = 42 K, i.e., within the different complex (incommensurate or complex) antiferromagnetic phases, lattice distortions of up to 100 ppm have been found. Although no change of the lattice symmetry occurs, the measurements reveal strong magneto-structural phenomena, especially in the incommensurate sinusoidal antiferromagnetic phase. A strong anisotropy of the magnetoelastic properties was found, in good agreement with the type and propagation vector of the magnetic structure. We demonstrate that our capacitive dilatometry can detect lattice expansion effects and changes of the dielectric permittivity simultaneously because the sample is housed inside the capacitor. A separation of both effects is possible by shielding the sample. Dielectric transitions could be detected by this method and compared to the critical values of H and T in the magnetic phase diagram. Dielectric changes measured at 1 kHz excitation frequency are detected in GdMnO3 at about 180 K, and between 10 K and 25 K in the canted antiferromagnetic structure which is characterized by a complex magnetic order on both the Gd- and Mn-sites.

Structural and magnetic properties of SmCo5/Co exchange coupled nanocomposite thin films

We investigated the structural and magnetic properties of SmCo5/Co exchange coupled nanocomposite thin films grown by magnetron sputtering from Sm and Co multitargets successively. The growth of the films was carried out at elevated substrate temperature followed by in situ annealing. On Si (100) substrate, X-ray diffraction confirms the formation of textured (110) SmCo5 hard phase, whereas on MgO (110) substrate, the diffraction pattern shows the epitaxial growth of SmCo5 phase with crystalline orientation along 100] direction. Secondary Ion Mass Spectroscopy reveals the structural transformation from multilayered (Sm/Co) to SmCo5/Co nano-composite films due to high reactivity of Sm at elevated temperature. Transmission electron microscopy indicates the existence of nanocrystalline phase of SmCo5 along with unreacted Co. Observed single phase behavior in magnetic hysteresis measurements indicates well exchange coupling between the soft and the hard phases in these nano-composite films. For samples with samarium layer thickness, t(sm)=3.2 nm and cobalt layer thickness, t(Co)= 11.4 nm, the values of (BH)(max) were obtained as 20.1 MGOe and 12.38 MGOe with H-c value similar to 3.0 kOe grown on MgO and Si substrates, respectively.

Engineering Gold Nanoparticle Interaction by PAMAM Dendrimer

Bare faceted gold nanoparticles (AuNPs) have a tendency to aggregate through a preferred attachment of the 111] surfaces. We have used fully atomistic classical molecular dynamics simulations to obtain a quantitative estimate of this surface interaction using umbrella sampling (US) at various temperatures. To tune this surface interaction, we use polyamidoamine (PAMAM) dendrimer to coat the gold surface under various conditions. We observe a spontaneous adsorption of the protonated as well as nonprotonated PAMAM dendrimer on the AuNP surface. The adsorbed dendrimer on the nanoparticle surface strongly alters the interaction between the nanoparticles. We calculate the interaction between dendrimercoated AuNPs using US and show how the interaction between two bare faceted AuNPs can be tuned as a function of dendrimer concentration and charge (pH dependent) With appropriate choice of the dendrimer concentration and charge, two strongly interacting AuNPs can be made effectively noninteracting. Our simulation results demonstrate a strategy to tune the nanoparticle interaction, which can help in engineering self-assembly of such nanoparticles.

Influence of magnetic field on the compressive behavior of carbon nanotube with magnetic nanoparticles

Carbon nanotubes (CNT) in their cellular like micro-structure have presented an excellent mechanical energy absorption capacity. Although, several efforts have been progressed to modify the CNT structure for further enhancing their energy absorption capacity but yet no report has revealed the effect of magnetic field on the mechanical behavior of as-grown CNT mat that contains magnetic iron nanoparticles in the form of decorated nanoparticles on the surface or filled inside core of the CNT. We report a significant impact of the presence of magnetic content that modifies the mechanical behavior of the entangled CNT mat in the presence of an external magnetic field. The energy absorption capacity doubles when magnetic field was applied in the radial direction of the CNT mat under uniaxial compression. (C) 2013 AIP Publishing LLC.

Classification of Vehicles Using Magnetic Field Angle Model

This paper presents an efficient approach to the modeling and classification of vehicles using the magnetic signature of the vehicle. A database was created using the magnetic signature collected over a wide range of vehicles(cars). A sensor dependent approach called as Magnetic Field Angle Model is proposed for modeling the obtained magnetic signature. Based on the data model, we present a novel method to extract the feature vector from the magnetic signature. In the classification of vehicles, a linear support vector machine configuration is used to classify the vehicles based on the obtained feature vectors.

Solution nuclear magnetic resonance structure of the GATase subunit and structural Basis of the interaction between GATase and ATPPase subunits in a two-subunit-type GMPS from methanocaldococcus jannaschii

The solution structure of the monomeric glutamine amidotransferase (GATase) subunit of the Methanocaldococcus janaschii (Mj) guanosine monophosphate synthetase (GMPS) has been determined using high-resolution nuclear magnetic resonance methods. Gel filtration chromatography and N-15 backbone relaxation studies have shown that the Mj GATase subunit is present in solution as a 21 kDa (188-residue) monomer. The ensemble of 20 lowest-energy structures showed root-mean-square deviations of 0.35 +/- 0.06 angstrom for backbone atoms and 0.8 +/- 0.06 angstrom for all heavy atoms. Furthermore, 99.4% of the backbone dihedral angles are present in the allowed region of the Ramachandran map, indicating the stereochemical quality of the structure. The core of the tertiary structure of the GATase is composed of a seven-stranded mixed beta-sheet that is fenced by five alpha-helices. The Mj GATase is similar in structure to the Pyrococcus horikoshi (Ph) GATase subunit. Nuclear magnetic resonance (NMR) chemical shift perturbations and changes in line width were monitored to identify residues on GATase that were responsible for interaction with magnesium and the ATPPase subunit, respectively. These interaction studies showed that a common surface exists for the metal ion binding as well as for the protein-protein interaction. The dissociation constant for the GATase-Mg2+ interaction has been found to be similar to 1 mM, which implies that interaction is very weak and falls in the fast chemical exchange regime. The GATase-ATPPase interaction, on the other hand, falls in the intermediate chemical exchange regime on the NMR time scale. The implication of this interaction in terms of the regulation of the GATase activity of holo GMPS is discussed.