Tuning the resonance in high-temperature superconducting terahertz metamaterials

In this Letter, we present resonance properties in terahertz metamaterials consisting of a split-ring resonator array made from high-temperature superconducting films. By varying the temperature, we observe efficient metamaterial resonance switching and frequency tuning. The results are well reproduced by numerical simulations of metamaterial resonance using the experimentally measured complex conductivity of the superconducting film. We develop a theoretical model that explains the tuning features, which takes into account the resistive resonance damping and additional split-ring inductance contributed from both the real and imaginary parts of the temperature-dependent complex conductivity. The theoretical model further predicts more efficient resonance tuning in metamaterials consisting of a thinner superconducting split-ring resonator array, which are also verified in subsequent experiments.     

Hawking radiation and black hole spectroscopy in Hořava–Lifshitz gravity

Hawking radiation from the black hole in Ho?ava–Lifshitz gravity is discussed by a reformulation of the tunneling method given in Banerjee and Majhi (2009) [17]. Using a density matrix technique the radiation spectrum is derived which is identical to that of a perfect black body. The temperature obtained here is proportional to the surface gravity of the black hole as occurs in usual Einstein gravity. The entropy is also derived by using the first law of black hole thermodynamics. Finally, the spectrum of entropy/area is obtained. The latter result is also discussed from the viewpoint of quasi-normal modes. Both methods lead to an equispaced entropy spectrum, although the value of the spacing is not the same. On the other hand, since the entropy is not proportional to the horizon area of the black hole, the area spectrum is not equidistant, a finding which also holds for the Einstein–Gauss–Bonnet theory.     

Effect of Cold Atmospheric Plasma Jet and Gamma Radiation Treatments on Gingivobuccal Squamous Cell Carcinoma and Breast Adenocarcinoma Cells

Surgery, chemotherapy and radiotherapy, the conventional treatment modalities of cancer though successful are limited by presence of residual tumor cells, toxic side-effects and treatment resistance, thus raising the need for investigating other novel approaches. Here, we have used a cold atmospheric plasma (CAP) jet and assessed the in vitro efficacy in gingivobuccal squamous cell carcinoma (GB-SCC) – ITOC-03, breast adenocarcinoma—MCF7 and HEK293 cells. Cells lines were subjected to varying doses of ionizing radiation (0, 2, 4, 6, 8 Gy) and CAP jet treatment (0, 60, 180, 240, 300 s). CAP jet treatment showed time dependent increase in H₂O₂ and NO₂^? concentration. Cell viability assay showed potent effect of CAP jet on all three cell lines in comparison to radiation treatment, while helium gas treatment showed minimal inhibitory effect. Irradiated, CAP jet and helium gas treated cells showed loss of nucleic acid features, 788 cm^?1 and 1340 cm^?1 in Raman spectra, indicating DNA damage. Principal Component Analysis (PCA) showed distinct classification of CAP-treated and control cells, while Principal Component – Linear Discriminant Analysis (PC-LDA) based classification of Raman spectra showed ITOC-03 and HEK293 cells to be sensitive to CAP jet and radiation treatment in comparison to MCF7 cells. Collectively, cell viability assay and Raman spectroscopy have shown potent effect of CAP jet in GB-SCC and breast adenocarcinoma cells.

     

A Rational Approach Towards Determination of Optical Ionicity and Non-covalent Interactions in Fullerene-Calix[4]arene Host-Guest Complexes

The present article reports the host-guest complexation of a calix[4]arene derivative, namely 4-iso-propyl-calix[4]arene (1), with fullerenes (both C₆₀ and C₇₀) in toluene and benzonitrile solutions. It is observed that the charge-transfer (CT) absorption bands are located in the ground state for the C₆₀ and C₇₀ complexes of 1. By utilizing the CT absorption bands, various important physicochemical parameters like the oscillator strength, resonance energy, transition dipole moment, electronic coupling element and solvent reorganization energies have been estimated for the C₆₀-1 and C₇₀-1 complexes. The CT transition energy is very helpful for determining the vertical ionization potential of 1 in solution. Jobs method of continuous variation was used to establish 1:1 stoichiometry for the fullerene complexes of 1. The most fascinating feature of the present study is that 1 binds C₇₀ preferentially compared to C₆₀ as obtained from binding constant (K) data. The effect of solvent on the complexation of fullerenes (C₆₀ and C₇₀) with 1 is clearly observed from the trend in the K values: in toluene and whereas in benzonitrile, and . Molecular mechanics force field (MMMF) calculations reveal fascinating features regarding the binding pattern of fullerenes towards 1 in vacuo in terms of enthalpy of formation. MMMF calculations establish that during C₇₀-1 complexation, C₇₀ is directed in an end-on manner rather than the traditional side-on pattern.     

Spectrophotometric study of the supramolecular complexes of [60]- and [70]Fullerenes with biscalix[6]arene and crown[4]calix[6]arene

[60]- and [70]Fullerenes have been shown to form 1:1 supramolecular complexes with bis[2-(5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41-pentahydroxycalix[6]arenyl-oxy ethyl ether) (1) and 5,11,17,23,29,35-hexa-tert-butyl-37,38,40,41-tetra hydroxyl-39,42-(crown-4)calix[6]arene (2) in CHCl3 medium by electronic absorption spectroscopy. Formation constants (K) of the complexes of [60]- and [70]fullerenes with 1 and 2 have been determined at room temperature from which free energy of formation values of the complexes have been estimated. The very high formation constant value of [60]fullerene/1 complex (5900 dm3 mol-1) in indicative of formation of inclusion complex. Moreover, PM3 calculations reveal that intermolecular interaction between [60]fullerene and 1 proceeds through quite deep energy molecular orbital.     

Reactions of sulfur(IV) with an octahedral manganese(IV) complex of 1,8-bis(2-hydroxy benzamido)-3,6-diaza octane: the role of phenolate–amide–amine coordination

The Mn^IV complex of tetra-deprotonated 1,8-bis(2-hydroxybenzamide)-3,6-diazaoctane (Mn^IVL) engrossed in phenolate-amido-amine coordination is reduced by HSO₃⁻ and SO₃²⁻ in the pH range 3.15–7.3 displaying biphasic kinetics, the Mn^IIIL⁻ being the reactive intermediate. The Mn^IIIL⁻ species has been characterized by u.v.–vis. spectra {λ _max, (ε, dm³ mol⁻¹ cm⁻¹): 285(15 570), 330 sh (7570), 469(6472), 520 sh (5665), pH=5.42}. SO₄²⁻ was the major oxidation product of S^IV; dithionate is also formed (18 ± 2% of [Mn^IV]_T) which suggests that dimerisation of SO₃^−• is competitive with its fast oxidation by Mn^IV/III. The rates and activation parameters for Mn^IVL + HSO₃⁻ (SO₃²⁻) → Mn^IIIL⁻; Mn^IIIL⁻ + HSO₃⁻ (SO₃²⁻) → Mn^IIL²⁻ are reported at 28.5–45.0 °C (I=0.3 mol dm⁻³, 10% (v/v) MeOH + H₂O). Reduction by SO₃²⁻ is ca. eight times faster than by HSO₃⁻ both for Mn^IVL and Mn^IIIL⁻. There was no evidence of HSO₃⁻/SO₃²⁻ coordination to the Mn centre indicating an outer sphere (ET) mechanism which is further supported by an isokinetic relationship. The self exchange rate constant (k₂₂) for the redox couple, Mn^IIIL⁻/Mn^IVL (1.5 × 10⁶ dm³ mol⁻¹ s⁻¹ at 25 °C) is reported.     

Novel Schiff bases–based thiophenes: Design,synthesis and biological evaluation

2-amino-5-(3-fluoro-4-methoxyphenyl)thiophene-3-carbonitrile derivatives have been synthesized from 1-(3-fluoro-4-methoxyphenyl)ethanone, malononitrile, mild base, and sulfur powder using the Gewald method through a multistep reaction sequence. The structures of newly synthesized compounds were established on the basis of their elemental analyses, IR, ¹H NMR, ¹³C NMR, and mass spectral data, and then synthesized compounds were screened for their in vitro antimicrobial activity. Among them, derivatives 3b (thiphene), 3f (pyrazole), and 3d (halogen) showed good activity and remaining derivatives exhibited moderate activity.     

Valence and origin of metal-insulator transition in Mn doped SrRuO3 studied by electrical transport, X-ray photoelectron spectroscopy and LSDA+U calculation

We have studied the valence and electronic properties of Mn doped SrRuO₃ using electrical transport measurement, X-ray photoelectron spectroscopy (XPS) and local (spin) density approximation plus Coulomb interaction strength calculation (LSDA+U). The resistivity data revealed that the system undergoes transition from metal to insulator at the critical Mn doping level, x∼0.2, which is accompanied by the structural transition from orthorhombic to tetragonal crystal symmetry. Besides, the significant reduction of the spectral weight at the coherent zone (0.8 eV) of the valence band is observed for x>0.2. The core XPS spectra suggest that both the transition elements exist in the mixed ionic pair, Ru⁺⁴/Ru⁺⁵↔Mn⁺³/Mn⁺⁴. The detail analysis of the results suggests that the Coulomb correlation effect in conjugation with localization of the charge carriers predominate over the mixed ionic pair effect and responsible for the metal-insulator transition in the series.     

Polymerization of methyl methacrylate initiated by Mn(III)–glycerol redox system

The kinetics of thermal polymerization of methyl methacrylate initiated by the redox system Mn(III)–glycerol was studied in aqueous sulfuric acid in the temperature range of 30–40°C, and the rates of polymerization, R_p, and Mn³⁺ disappearance, etc., were measured. The effect of certain water-miscible organic solvents and certain cationic and anionic surfactants on the rates of polymerization has been investigated. A mechanism involving the formation of a complex between Mn³⁺ and glycerol whose decomposition yields the initiating free radical with the polymerization being terminated by the metal ion has been suggested.     

Chemical Composition and Antioxidant Activity of the Leaf Essential Oil of Schefflera venulosa

Chemistry of Natural Compounds -