Modified graphene‐based materials as effective catalysts for transesterification of rapeseed oil to biodiesel fuel

Production of biodiesel by the transesterification process using different modified graphene‐based materials as catalysts was studied.Solid acid graphene‐based samples were prepared by grafting sulfonic or phosphate groups on the surface of thermally reduced graphene oxide.The obtained materials were thoroughly characterized using scanning electron microscopy,X‐ray diffraction,thermogravimetric analysis,X‐ray photoelectron spectroscopy,N2 adsorption‐desorption measurements,potentiometric titration,elemental analysis,and Fourier transform infrared spectroscopy.The prepared catalysts were tested in the transesterification of rapeseed oil with methanol at 130°C under pressure,and their activities were compared to the performance of a commercially available heterogeneous acidic catalyst,Amberlyst‐15.All modified samples were active in the transesterification process;however,significant differences were observed in the yield of biodiesel,depending on the method of catalyst preparation and strength of the acidic sites.The highest yield of fatty acid methyl esters of 70%was obtained for thermally reduced graphene oxide functionalized with 4‐benzenediazonium sulfonate after 6 h of processing,and this result was much higher than that obtained for the commercial catalyst Amberlyst‐15.The results of the reusability test were also promising.

Enhanced thermal emission from metal-free,fully epitaxial structures with epsilon-near-zero InAs layers

We introduce a novel method to create mid-infrared(MIR)thermal emitters using fully epitaxial,metal-free structures.Through the strategic use of epsilon-near-zero(ENZ)thin films in InAs layers,we achieve a narrow-band,wide-angle,and p-polarized thermal emission spectra.This approach,employing molecular beam epitaxy,circumvents the complexities associated with current layered structures and yields temperature-resistant emission wavelengths.Our findings contribute a promising route towards simpler,more efficient MIR optoelectronic devices.

Revisting High-Resolution Schemes with van Albada Slope Limiter

Slope limiters play an essential role in maintaining the non-oscillatory behavior of high-resolution methods for nonlinear conservation laws.The family of minmod limiters serves as the prototype example.Here,we revisit the question of non-oscillatory behavior of high-resolution central schemes in terms of the slope limiter proposed by van Albada et al.(Astron Astrophys 108:76–84,1982).The van Albada(vA)limiter is smoother near extrema,and consequently,in many cases,it outperforms the results obtained using the standard minmod limiter.In particular,we prove that the vA limiter ensures the one-dimensional Total-Variation Diminishing(TVD)stability and demonstrate that it yields noticeable improvement in computation of one-and two-dimensional systems.

Non-Oscillatory Hierarchical Reconstruction for Central and Finite Volume Schemes

This is the continuation of the paper”Central discontinuous Galerkin methods on overlapping cells with a non-oscillatory hierarchical reconstruction”by the same authors.The hierarchical reconstruction introduced therein is applied to central schemes on overlapping cells and to finite volume schemes on non-staggered grids.This takes a new finite volume approach for approximating non-smooth solutions.A critical step for high-order finite volume schemes is to reconstruct a non-oscillatory high degree polynomial approximation in each cell out of nearby cell averages.In the paper this procedure is accomplished in two steps:first to reconstruct a high degree polynomial in each cell by using e.g.,a central reconstruction,which is easy to do despite the fact that the reconstructed polynomial could be oscillatory;then to apply the hierarchical reconstruction to remove the spurious oscillations while maintaining the high resolution.All numerical computations for systems of conservation laws are performed without characteristic decomposition.In particular,we demonstrate that this new approach can generate essentially non-oscillatory solutions even for 5th-order schemes without characteristic decomposition.

Double-Exponentially Decayed Photoionization in CREI Effect： Numerical Experiment on 3D H2^＋

On the platform of the 3D H2^＋ system, we perform a numerical simulation of its photoionization rate under excitation of weak to intense laser intensities with varying pulse durations and wavelengths. A novel method is proposed for calculating the photoionization rate： a double exponential decay of ionization probability is best suited for fitting this rate. Confirmation of the well-documented charge-resonance-enhanced ionization （CREI） effect at medium laser intensity and finding of ionization saturation at high light intensity corroborate the robustness of the suggested double-exponential decay process. Surveying the spatial and temporal variations of electron wavefunctions uncovers a mechanism for the double-exponentially decayed photoionization probability as onset of electron ionization along extra degree of freedom. Henceforth, the new method makes clear the origins of peak features in photoionization rate versus internuclear separation. It is believed that this multi-exponentially decayed ionization mechanism is applicable to systems with more degrees of motion.

Exact Timing of Returned Molecular Wavepacket

An ionizing wavepacket of electron will re-visit its parent molecular ion during photoionization by strong laser field. This scenario is associated with physical concepts such as molecular re-scattering/collision, interference, diffraction, molecular clock, and generation of XUV light via high-order harmonic generation. On the workbench of a reduced dimensionality model of molecular hydrogen ions irradiated by laser pulse of 0.01-10.0 a.u. intensities, one-cycle pulsewidth, and 800nm wavelength, by deploying a momentum operator on the time-dependent wavefunction of an ionizing wavepacket, we can determine, in a precise manner, the exact time instant for the re-visiting electron to come back to the cation position. The time value is 57.6% of an optical cycle of the exciting laser pulse. This result may be useful in attosecond pump-probe experiments or molecular clock applications.

Imaging Internuclear Separation of H^＋2 in Configuration Space： Reduced Dimensionality Model

We present a method for obtaining the internuclear separation of diatomic molecular ion H^＋2 irradiated by attosecond-duration laser pulse, by computing the probability flux of wavefunction pattern of photoelectron in configuration space. In contrast to earlier means of attosecond-scale time-gating or taking ratio of image data in momentum space, our alternative is characterized by experimental feasibility. The numerical results of a reduceddimensionality model on hydrogenic ions corroborated our method are obtained and can be generalized to more complex molecular systems for inferring bond length or bond angle information.

The Influence of Microscopic Fungi on Chromated Galvanized Zinc Coatings

A solution containing Cr(VI), Cr(NO3)3 and its complex with an organic acid as well as several commercial solutions containing Cr(III) complexes with an organic acid and additionally CO2+, F-, SO42- ions were used for the studies. Results of the studies obtained in the following commercial solutions: Likonda 2AT, Cr(NO3)3 + malonic acid;Likonda 3Cr5 and Likonda 3CrMC are discussed. Steel coated with chromated Zn coatings was contaminated by some microscopic fungi. The variety of fungi on chromated plates diminished, however the propagules of fungi did not disappear completely. The Likonda 3Cr5 solution diminishes fungi contamination on chromated steel most effectively. In water used to rinse the surface of chromated plates the number of fungi propagules was detected to be higher as compared to that on the plate surface. The least quantity of fungi propagules was detected in water used to rinse plates coated in the Likonda 3Cr5 solution. The main part of fungi detected on chromated plates treated in the Likonda 3Cr5 solution were the fungi of Cladosporium species (C.herbarum, C.cladosporioides). The latter species also dominated on chromated plates coated with zinc and treated with the other solution. It should be mentioned, that on these plates chromated in this solution, Actinomycetes of the Streptomyces group were abundant. After comparison of surfaces of the plates treated in four solutions it has been determined that the surface of the plates treated in the Likonda 3Cr5 passivation solution and exposed to modelling conditions changed least of all. It has been noticed that on the subject studied white porous rust accumulates, the intensity of this process on the surface studied determines both the probability of corrosion and the resistance of the used safety means to the external factors.

Profound Carrier-Envelope-Phase-Difference Effect on Photoionization Rate： Numerical Results on a Model Hydrogen Atom

We discuss importance of the carrier-envelope phase difference （CEPD） effect which would be encountered in real short laser pulses. By numerically simulating photoionization rate of a one-dimensional atomic hydrogen model irradiated by short light pulses, a profound CEPD effect on the photoionization rate is revealed, which might shed light on laser-atom interaction investigation. We also suggest that photoionization process might be exploited in return to measure CEPD values.

Two-Fluid Formulation of Lower-Hybrid Drift Instabilities in Current-Sheet Equilibrium with a Guide Field

Anonlocal two-fluid formulation has been constructed for describing lowerhybrid drift instabilities in current-sheet configuration with a finite guide magnetic field in the context of magnetic reconnection.As a benchmark and verification,a class of unstable modes with multiple eigenstates are found by numerical solutions with guide field turned off.It is found that the most unstable modes are the electrostatic,short-wavelength perturbations in the lower-hybrid frequency range,with wave functions localized at the edge of the current sheet where the density gradient reaches its maximum.It is also found that there exist electrostatic modes located near the center of the current sheet where the current density is maximum.These modes are lowfrequency,long-wavelength perturbations.Attempts will bemade to compare the current results with those from kinetic theory in the near future since the validity of the fluid theory ultimately needs to be checked with the more fundamental kinetic theory.

聚环氧乙烷在水和叔丁醇溶液中分子构型变化的研究

在聚合物溶液中,聚合物单体和溶剂分子之间的相互作用会影响聚合物高分子的尺寸和结构。本文使用动态光散射实验系统研究了聚环氧乙烷在水+TBA二元混合溶液中的分子尺寸变化,实验结果表明聚环氧乙烷分子会呈现出收缩-膨胀的奇异性构型变化。本文也系统分析了产生该现象的原因,依次分析了在二元混合溶液中可能对聚合物分子尺寸产生影响三个原因:溶剂非理想性影响(Shultz-Flory理论)、临界涨落影响以及水+醇溶液所呈现出来的奇异性性质。结合这三个因素,本文较好地解释了实验所观测到的奇异现象。

Direct extraction of topological Zak phase with the synthetic dimension

Measuring topological invariants is an essential task in characterizing topological phases of matter.They are usually obtained from the number of edge states due to the bulk-edge correspondence or from interference since they are integrals of the geometric phases in the energy band.It is commonly believed that the bulk band structures could not be directly used to obtain the topological invariants.Here,we implement the experimental extraction of Zak phase from the bulk band structures of a Su-Schrieffer-Heeger(SSH)model in the synthetic frequency dimension.Such synthetic SSH lattices are constructed in the frequency axis of light,by controlling the coupling strengths between the symmetric and antisymmetric supermodes of two bichromatically driven rings.We measure the transmission spectra and obtain the projection of the time-resolved band structure on lattice sites,where a strong contrast between the non-trivial and trivial topological phases is observed.The topological Zak phase is naturally encoded in the bulk band structures of the synthetic SSH lattices,which can hence be experimentally extracted from the transmission spectra in a fiber-based modulated ring platform using a laser with telecom wavelength.Our method of extracting topological phases from the bulk band structure can be further extended to characterize topological invariants in higher dimensions,while the exhibited trivial and non-trivial transmission spectra from the topological transition may find future applications in optical communications.

Constraint Preserving Schemes Using Potential-Based Fluxes I.Multidimensional Transport Equations

We consider constraint preserving multidimensional evolution equations.A prototypical example is provided by the magnetic induction equation of plasma physics.The constraint of interest is the divergence of the magnetic field.We design finite volume schemes which approximate these equations in a stable manner and preserve a discrete version of the constraint.The schemes are based on reformulating standard edge centered finite volume fluxes in terms of vertex centered potentials.The potential-based approach provides a general framework for faithful discretizations of constraint transport and we apply it to both divergence preserving as well as curl preserving equations.We present benchmark numerical tests which confirm that our potential-based schemes achieve high resolution,while being constraint preserving.