Dual-band tunable negative refractive index metamaterial with F-Shape structure

This paper presents a negative refractive index tunable metamaterial based on F-Shape structure which is capable of achieving dual-band negative permeability and permittivity, thus dual-band negative refractive index. An electromagnetic simulation was performed and effective media parameters were retrieved. Numerical investigations show clear existence of two frequency bands in which permeability and permittivity both are negative. The two negative refractive index bandwidths are from 23.8 GHz to 24.1 GHz and from 28.3 GHz to 34.9 GHz, respectively. The geometry of the structure is simple so it can easily be fabricated. The proposed structure can be used in multiband and broad band devices, as the band range in second negative refractive index region is 7 GHz, for potential applications instead of using complex geometric structures and easily tuned by varying the separation between the horizontal wires.     

Interactions of thioflavin T with serum albumins: Spectroscopic analyses

The interaction of thioflavin T (ThT) with serum albumins from four different mammalian species i.e. human, bovine, porcine and rabbit, has been investigated by circular dichroism (CD), fluorescence spectroscopy and ITC. The binding constant (K) for HSA was found to be 9.9 × 10⁴ M⁻¹, 4.3 × 10⁴ M⁻¹ for RSA, 1.07 × 10⁴ M⁻¹ for PSA and 0.3 × 10⁴ M⁻¹ for BSA and the number of binding sites (n) were 1.14, 1.06, 0.94 and 0.8, respectively, which is very significant. By using unfolding pathway of HSA in the presence of urea, domain II of HSA has been assigned to possess binding site of ThT. Its binding constant is comparable to many drugs that bind at domain II of HSA, like salicylate, warfarin, digitoxin, etc. Acting force between HSA and ThT is showing that both hydrophobic and electrostatic forces have contributed for the interaction. ΔG_binding, ΔH and ΔS were calculated to be −28.46 kJ mol⁻¹, −3.50 kJ mol⁻¹ and 81.04 J K⁻¹ mol⁻¹, respectively. The data described here will help to increase our understanding about the interaction of ThT with native proteins. The results also indicate that care must be taken while using ThT as a probe for detecting amyloid fibrils.     

Pentacyclic triterpenoids from the aerial parts of Lantana camara

Three new pentacyclic triterpenoids, camaryolic acid (1), methylcamaralate (2) and camangeloyl acid (3) and six known compounds beta-sitosterol 3-O-beta-D-glucopyranoside (4), octadecanoic acid (5), docosanoic acid (6), palmitic acid (7), camaric acid (8) and lantanolic acid (9) were isolated from the aerial parts of Lantana camara. Structures of the new compounds were elucidated by spectroscopic and chemical methods.     

Studies on the sensitivity of yttrium by electrothermal atomization from metallic and metal-carbide surfaces of a heated graphite atomizer in atomic absorption spectrometry

Atomization of yttrium in tube-type electrothermal atomizers was studied using various atomization surfaces: pyrocoated graphite surface, carbidized graphite surface and tantalum or tungsten metal surfaces. Carbidizing of pyrocoated graphite tubes with other carbide-forming metals (Ta, Zr or La) produces refractory metal-carbide surfaces thereby preventing the carbide-forming yttrium to come in physical contact with the reactive graphite surface. The result is an enhancement in the analytical sensitivity (peak height absorbance) of yttrium. The atomization of Y from a metal surface (Ta or W) gives better analytical sensitivity, lower atomization temperature, and negligible memory effect compared with those from metal-carbidized surfaces.     

Mechanism of yttrium atom formation in electrothermal atomization from metallic and metal-carbide surfaces of a heated graphite atomizer in atomic absorption spectrometry

Mechanism of Y atom formation from pyrocoated graphite, tantalum and tungsten metal surfaces of a graphite tube atomizer has been studied and a mechanism for the formation for Y atoms is proposed for the first time. The following is the mechanism of yttrium atom formation regardless of whether the atomizing surface is pyrolytic graphite, tantalum or tungsten metal.

     

Dielectric permittivity of nickel ferrites at microwave frequencies 1 MHz to 1.8 GHz

NiFe₂O₄ prepared via the sol–gel technique were pre-sintered at 900 °C and synthesized at different sintering temperatures from 1,000 °C to 1,200 °C at 100 °C intervals. The samples were characterized for microwave dielectric properties. These samples were measured using Agilent Impedance/Material Analyzer at frequencies 1 MHz to 1.8 GHz. Results showed a decrease in the dielectric constant and loss factor with frequency except at the turning point, around 150 MHz, where the loss factor showed a gradual increase. However, both the dielectric constant and loss factor increase with increasing sintering temperature. The grain size and density also increased with increasing sintering temperature, but the porosity and grain boundary density showed a decrease. This paper was presented at the International Conference on Solid State Science and Technology 2006, Kuala Terengganu, Malaysia, Sept. 4–6, 2006.     

Analytical Analysis of Different Karats of Gold Using Laser Induced Breakdown Spectroscopy (LIBS) and Laser Ablation Time of Flight Mass Spectrometer (LA-TOF-MS)

Laser induced breakdown spectroscopy (LIBS) coupled with a laser ablation time of flight mass spectrometer (LA-TOF-MS) has been developed for discrimination/analysis of the precious gold alloys cartage. Five gold alloys of Karats 18K, 19K, 20K, 22K and 24K having certified composition of gold as 75, 79, 85, 93 and 99.99% were tested and their precise elemental compositions were determined using the laser produced plasma technique. The plasma was generated by focusing beam of a Nd:YAG laser on the target in air and its time integrated emission spectra were registered in the range 250–870 nm. The calibration free LIBS technique (CF-LIBS) was used for the quantitative determination of the constituent elements present in different Karats of gold. Elemental compositions of these gold alloys were also determined using a Laser Ablation time of flight mass spectrometer (LA-TOF-MS). The LIBS limit of detection was calculated from the calibration curves for copper, silver and gold. Results of CF-LIBS and LA-TOF-MS are in excellent agreement with the certified values. It is demonstrated that LIBS coupled with LA-TOF-MS is an efficient technique that can be used to analyze any precious alloys in a fraction of a second.     

Ultrasonic velocities, densities, viscosities, electrical conductivities, Raman spectra, and molecular dynamics simulations of aqueous solutions of Mg(OAc)2 and Mg(NO3)2: Hofmeister effects and ion pair formation

The ultrasonic velocities, densities, viscosities, and electrical conductivities of aqueous solutions of magnesium nitrate and magnesium acetate have been measured from dilute to saturation concentrations at 0 < or = t/degrees C < or = 50. The temperature derivative of the isentropic compressibility, kappa(s), became zero at 2.28 and 2.90 mol kg(-1) for Mg(OAc)2 and Mg(NO3)2 solutions, respectively, at 25 degrees C. The total hydration numbers of the dissolved ions were estimated to be, respectively, 24.3 and 19.2 at these concentrations. Differences in kappa(s) for various M2+ salts, using the present and literature data, correlated with reported M2+-OH2 bond lengths and to a lesser extent with cationic charge densities (ionic radii). The influence of anions on kappa(s) appears to follow the Hofmeister series and also correlates approximately with the anionic charge density. Substantial differences between Mg(OAc)2(aq) and Mg(NO3)2(aq) occur with respect to their structural relaxation times (derived from compressibility and viscosity data) and their electrical conductivities. These differences were attributed to a much greater ion association in Mg(OAc)2 solutions. Raman spectra recorded at 28 degrees C confirmed the presence of various types of contact ion pairs including mono- and bidentate complexes in Mg(OAc)2(aq). In Mg(NO3)2(aq), only noncontact ion pairs appear to be formed even at high concentrations. The experimental results are supported by molecular dynamics simulations, which also reveal the much stronger tendency of OAc- compared to NO3- to associate with Mg2+ in aqueous solutions. The simulations also allow an evaluation of the ion-ion and ion-water radial distribution functions and cumulative sums and provide a molecular picture of ion hydration in Mg(OAc)2(aq) and Mg(NO3)2(aq) at varying concentrations.     

Viscosities and Refractive Indices of Binary Mixtures of Dimethylsulphoxide with Some Aromatic Hydrocarbons at Different Temperatures: An Experimental and Theoretical Study

The viscosities, η, and refractive indices, n, of pure dimethylsulphoxide (DMSO), benzene, toluene, o‐xylene, m‐xylene, p‐xylene and mesitylene, and those of their 54 binary mixtures, with DMSO as common component, covering the whole composition range have been measured at 298.15, 303.15, 308.15, 313.15, and 318.15 K. From the experimental data, the deviations in viscosity, Δη and deviations in molar refraction, ΔR_m have been calculated. The variation of these parameters with composition and temperature of the mixtures have been discussed in terms of molecular interaction in these mixtures. The effect of the number and position of the methyl groups in these aromatic hydrocarbons on molecular interactions in these mixtures has also been discussed. The free energies, ΔG^*, enthalpies, ΔH^* and entropies, ΔS^* of activation of viscous flow have also been obtained by using Eyring viscosity equation. The ΔH^* values were found independent of temperature. The dependence of these thermodynamic parameters on composition of the mixtures has been discussed. Further, the viscosities and refractive indices of these binary mixtures were calculated theoretically from pure component data by using various empirical and semi‐empirical relations and the results were compared with the experimental findings.