Generalized Fourth-Order Decompositions of Imaginary Time Path Integral: Implications of the Harmonic Oscillator

The imaginary time path integral formalism offers a powerful numerical tool for simulating thermodynamic properties of realistic systems. We show that, when second-order and fourth-order decompositions are employed, they share a remarkable unified analytic form for the partition function of the harmonic oscillator. We are then able to obtain the expression of the thermodynamic property and the leading error terms as well. In order to obtain reasonably optimal values of the free parameters in the generalized symmetric fourth-order decomposition scheme, we eliminate the leading error terms to achieve the accuracy of desired order for the thermodynamic property of the harmonic system. Such a strategy leads to an efficient fourth-order decomposition that produces third-order accurate thermodynamic properties for general systems.     

Theoretical study of surface plasmons coupling in transition metallic alloy 2D binary grating

The excitation of a surface plasmon polariton (SPP) wave on a metal–air interface by a 2D diffraction grating is numerically investigated. The grating consists of homogeneous alloys of two metals of a formula A_xB_1−x, or three metals of a formula A_xB_yC_z, where A, B and C could be silver (Ag), copper (Cu), gold (Au) or aluminum (Al).It is observed that all the alloys of two metals present a very small change of surface plasmon resonance (SPR) irrespective of composition x. Moreover, the addition of 25% of Al to two metals alloy is insufficient to change the SPR curves. The influence of the different grating parameters is discussed in details using rigorous coupled-wave analysis (RCWA) method. Furthermore, the SPR is highly dependent on grating periods (d_x and d_y) and the height of the grating h. The results reveal that d_x= d_y= 700 nm, h=40 nm and duty cycle w=0.5 are the optimal parameters for exciting SPP.     

Soluble Congeners of Prior Insoluble Shape-Persistent Imine Cages

One of the most applied reaction types to synthesize shape-persistent organic cage compounds is the imine condensation reaction and it is assumed that the formed cages are thermodynamically controlled products due to the reversibility of the imine condensation. However, most of the synthesized imine cages reported are formed as precipitate from the reaction mixture and therefore rather may be kinetically controlled products. There are even examples in literature, where resulting cages are not soluble at all in common organic solvents to characterize or study their formation by NMR spectroscopy in solution. Here, a triptycene triamine containing three solubilizing n-hexyloxy chains has been used to synthesize soluble congeners of prior insoluble cages. This allowed us to study the formation as well as the reversibility of cage formation in solution by investigating exchange of building blocks between the cages and deuterated derivatives thereof.     

New q‐Hermite polynomials: characterization,operators algebra and associated coherent states

This paper addresses a construction of new q‐Hermite polynomials with a full characterization of their main properties and corresponding raising and lowering operator algebra. The three‐term recursive relation as well as the second‐order differential equation obeyed by these new polynomials are explicitly derived. Relevant operator actions, including the eigenvalue problem of the deformed oscillator and the self‐adjointness of the related position and momentum operators, are investigated and analyzed. The associated coherent states are constructed and discussed with an explicit resolution of the induced moment problem. The phase collapse in a q‐deformed boson system is studied.     

Direct sunlight responsive Ag–ZnO heterostructure photocatalyst: Enhanced degradation of rhodamine B

The catalytic activity of Ag–ZnO heterostructure on the photocatalytic degradation of rhodamine B was investigated. It demonstrated that Ag–ZnO heterostructure exhibited an enhanced photocatalytic activity compared to pure ZnO nanoparticles under direct sunlight. The possible factors to the photocatalytic acitivity of the sample were explored, including Ag content, dispersity and calcination temperature. It was shown that the sample dispersed by PVP, with 5% mol ratio Ag content, calcined at 400 °C showed the highest photocatalytic acitivity and this catalyst was reusable.     

Ferroelectric phase transition and optical performance of PLZnNZT transparent ceramics

Lead-based Pb_0.97La_0.02(Zn_1/3Nb_2/3)_0.3(Zr_0.53Ti_0.47)_0.7O₃ (PLZnNZT) transparent ceramics with the addition of 2 wt% excess PbO were prepared by hot-pressing sintering method. The hot-pressing sintered PLZnNZT ceramics exhibit dense and large-grained microstructure, and perovskite structure with distorted cubic-like symmetry. The ceramics exhibit normal ferroelectric-like dielectric behavior with slightly diffused ferroelectric phase transition characteristic. The PLZnNZT ceramics exhibit fully developed, symmetric and saturated P–E hysteresis loop and large piezoelectric constant d₃₃, being 468 pC/N. The ceramics with 120 μm thickness exhibit maximum transmittance of 53% at 850 nm when Fresnel losses was not included, almost totally transparent in the mid IR region (2500–5600 nm), and low-lying optical band gap energy E_g of 3.23 eV. Three diffused Raman bands centering around 240 cm⁻¹, 560 cm⁻¹ and 750 cm⁻¹ are observed by micro-Raman spectroscopy, which can be attributed to F2g [BO₆] bending vibration, A1g [BO₆] stretching vibration and “soft mode” mixed by the bending and stretching vibrations, respectively, confirming the normal ferroelectric-like characteristic.     

BaCO3 mediated modifications in structural and magnetic properties of natural nanoferrites

Preparing M-type barium hexaferrite and improving the magnetic response of natural ferrites by incorporating barium carbonate (BaCO₃) is ever-demanding. Series of barium carbonate doped ferrites with composition (100−x)Fe₃O₄·xBaCO₃ (x=0, 10, 20, 30 wt%) are prepared through solid state reaction method and sintered gradually at temperatures of 800 and 1000 °C. Nanoparticles of natural ferrite and commercial BaCO₃ are used as raw materials. Impacts of BaCO3 on structural and magnetic properties of these synthesized ferrites are inspected. The obtained ferrites are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) at room temperature. Uniform barium hexaferrite particles in terms of both morphology and size are not achieved. The average crystallite size of BaFe₁₂O₁₉ is observed to be within 30–600 nm. The sintering process results phase transformation from Fe₃O₄ (magnetite) to α-Fe₂O₃ (hematite) and the formation of hexagonal barium ferrite crystals. The occurrence of barium crystal is found to enhance with the increase of BaCO₃ concentrations up to 20 wt% and suddenly drop at 30 wt%. Saturation and remanent magnetization of the doped ferrites are significantly augmented up to 16.37 and 8.92 emu g⁻¹, respectively compared to their pure counterpart. Furthermore, the coercivity field is slightly decreased as BaCO₃ concentrations are increased. BaCO₃ mediated improvements in the magnetic response of natural ferrites are demonstrated.     

Green synthesis and characterization of Au@Pt core–shell bimetallic nanoparticles using gallic acid

In this study, we developed a facile and benign green synthesis approach for the successful fabrication of well-dispersed urchin-like Au@Pt core–shell nanoparticles (NPs) using gallic acid (GA) as both a reducing and protecting agent. The proposed one-step synthesis exploits the differences in the reduction potentials of AuCl₄⁻ and PtCl₆²⁻, where the AuCl₄⁻ ions are preferentially reduced to Au cores and the PtCl₆²⁻ ions are then deposited continuously onto the Au core surface as a Pt shell. The as-prepared Au@Pt NPs were characterized by transmission electron microscope (TEM); high-resolution transmission electron microscope (HR-TEM); scanning electron microscope (SEM); UV-vis absorption spectra (UV-vis); X-ray diffraction (XRD); Fourier transmission infrared spectra (FT-IR). We systematically investigated the effects of some experimental parameters on the formation of the Au@Pt NPs, i.e., the reaction temperature, the molar ratios of HAuCl₄/H₂PtCl₆, and the amount of GA. When polyvinylpyrrolidone K-30 (PVP) was used as a protecting agent, the Au@Pt core–shell NPs obtained using this green synthesis method were better dispersed and smaller in size. The as-prepared Au@Pt NPs exhibited better catalytic activity in the reaction where NaBH₄ reduced p-nitrophenol to p-aminophenol. However, the results showed that the Au@Pt bimetallic NPs had a lower catalytic activity than the pure Au NPs obtained by the same method, which confirmed the formation of Au@Pt core–shell nanostructures because the active sites on the surfaces of the Au NPs were covered with a Pt shell.     

A novel ammonia-assisted method for the direct synthesis of Mn3O4 nanoparticles at room temperature and their catalytic activity during the rapid degradation of azo dyes

In this study, we prepared trimanganese tetroxide nanoparticles from MnCl₂ solution in an ammonia atmosphere using a new surfactant-free method at room temperature. We analyzed and characterized the effects of different processing conditions, such as the concentrations of manganese and the ammonia source, as well as the reaction time, on the structure, purity, and morphology of the products using powder X-ray diffraction (XRD), scanning electron microscopy, and Fourier transformation infrared spectroscopy (FTIR) techniques. The XRD and FTIR analyses confirmed that the prepared products comprised single phase Mn₃O₄. At room temperature, the paramagnetic characteristics were also verified by vibrating sample magnetometry. Furthermore, we tested the catalytic activity of the nanoparticles during the degradation of methyl orange and Congo red, which are organic pollutants. Our experiments demonstrated the rapid color removal and reduction in the chemical oxygen demand (>70% and >50% within 10 min, respectively) using aqueous solutions of azo dyes.     

High pressure studies using two-stage diamond micro-anvils grown by chemical vapor deposition

Ultra-high static pressures have been achieved in the laboratory using a two-stage micro-ball nanodiamond anvils as well as a two-stage micro-paired diamond anvils machined using a focused ion-beam system. The two-stage diamond anvils’ designs implemented thus far suffer from a limitation of one diamond anvil sliding past another anvil at extreme conditions. We describe a new method of fabricating two-stage diamond micro-anvils using a tungsten mask on a standard diamond anvil followed by microwave plasma chemical vapor deposition (CVD) homoepitaxial diamond growth. A prototype two-stage diamond anvil with 300?µm culet and with a CVD diamond second stage of 50?µm in diameter was fabricated. We have carried out preliminary high pressure X-ray diffraction studies on a sample of rare-earth metal lutetium sample with a copper pressure standard to 86?GPa. The micro-anvil grown by CVD remained intact during indentation of gasket as well as on decompression from the highest pressure of 86?GPa.