Anticircular high performance thin-layer chromatography

The principal analytical details for the third of three possible modes in high performance thin-layer chromatography are given, namely the anticircular mode. Separation is achieved by allowing the mobile phase to enter the plate layer on a precise outer circle line, from where it flows towards the centre with nearly constant speed. This technique is theoretically and practically the fastest of all three possible in HPTLC. It permits maximum sample capacity with a minimum of time, layer and mobile phase consumption. It is therefore the most economical HPTLC technique. A new carrier-free mobile phase transfer principle is used. The conditions for qualitative and quantitative analysis are good: repeatability, reproducibility and accuracy of routine TLC analyses are superior to those achieved by the classical trough technique. The specially narrow spot-path in anticircular HPTLC facilitates automated quantitation. Compared with the linear and circular modes, the anticircular mode shows better separation and significantly increased sensitivity at higher Rf-values. The drawback, however, is that the separation power (expressed by the separation number) is lower compared with the other two modes.     

Electronic structure modeling of InAs/GaSb superlattices with hybrid density functional theory

The application of first-principles calculations holds promise for greatly improving our understanding of semiconductor superlattices. Developing a procedure to accurately predict band gaps using hybrid density functional theory lays the groundwork for future studies investigating more nuanced properties of these structures. Our approach allows a priori prediction of the properties of SLS structures using only the band gaps of the constituent materials. Furthermore, it should enable direct investigation of the effects of interface structure, e.g., intermixing or ordering at the interface, on SLS properties. In this paper, we present band gap data for various InAs/GaSb type-II superlattice structures calculated using the generalized Kohn-Sham formulation of density functional theory. A PBE0-type hybrid functional was used, and the portion of the exact exchange was tuned to fit the band gaps of the binary compounds InAs and GaSb with the best agreement to bulk experimental values obtained with 18% of the exact exchange. The heterostructures considered in this study are 6 monolayer (ML) InAs/6 ML GaSb, 8 ML InAs/8 ML GaSb and 10 ML InAs/10 ML GaSb with deviations from the experimental band gaps ranging from 3% to 11%.     

Stabilization of E-type antiferromagnetic ordering in La and Y substituted orthorhombic LuMnO3: A first-principles study

We carry out first principles density functional theory calculations of non-lone pairs, namely, La and Y substituted orthorhombic LuMnO₃, to verify the generality of symmetry breaking effects observed in the lone pair cations substituted orthorhombic rare earth manganites. Our calculations revealed that similar to lone pair cations ordering at the A-site of LuMnO₃, non-lone pair cations ordering also results in the lowering of the symmetry thereby proving that the symmetry breaking with A-site ordering is a generic effect. Interestingly, we were able to stabilize the large radius La substituted LuMnO₃ into an E-type antiferromagnetic (E-AFM) phase, in contrast to the normally expected A-type antiferromagnetic (A-AFM) phase of large radius rare earth manganites such as LaMnO₃.     

Green chemistry: the emergence of a transformative framework

Abstract

Since the Twelve Principles of Green Chemistry were formulated in the 1990s, there have been tremendous successes in developing new products and processes to be more compatible with human health, the environment, and sustainability goals. This review gives a sampling of research successes from the last 20years, including advances in synthetic efficiency, application of alternative synthetic methods, use of less hazardous solvents and reagents, and development of renewable resources for chemical feedstocks. The future of green chemistry will depend on innovations that consolidate and integrate these achievements that have been made, using all Twelve Principles as a framework for intentional design. Designing for sustainability and reduced hazard should not be viewed as constraining, but rather as providing the freedom to explore and invent, bridging continents and scientific disciplines to create new solutions.     

Convergence of a strong variational algorithm for relaxed controls involving a distributed optimal control problem of parabolic type 1

In this paper, we consider a class of Optimal Control problems involving first boundary value problems of parabolic type. A strong variational algorithm has been obtained for solving this class of optimal control problems in a paper by the author and D. W. Reid. It was also shown that any L∞ accumulation points of control sequences generated by the algorithm satisfy a necessary condition for optimality. Since such accumulation points need not exist, it is shown in this paper that control sequences generated by the algorithm always have accumulation points in the sense of control measure, and these accumulation points satisfy a necessary condition for optimality for the corresponding relaxed control problem.     

Heat flux calorimetry in intermetallic compound–H2(g) systems: heat measurements and modeling in the low pressures range

A heat conduction calorimeter has been used to determine enthalpies of solid–gas reactions in systems, such as intermetallic compounds–H₂(g). It is shown that the significance of the heat measurements must be carefully analyzed by controlling several parameters, which may influence the heat transfer conditions during the absorption and desorption reactions.

For this type of reaction, the measured heat flow is strongly dependent on the heat transfers through the gas phase in the low pressure range (Knudsen regime). It is demonstrated, experimentally and confirmed with simple models, that heat measurements can provide erroneous enthalpies due to our inability to account for the unavoidable modifications of the heat losses in the transition region. Experiments were carried out on the ZrNi–H₂ system.     

Banach 空间中一阶脉冲积分-微分方程初值问题整体解的存在性

通过逐段应用推广的Darbo不动点定理,在较弱的条件下,给出了实Banach空间中一阶脉冲积分-微分方程初值问题整体解的存在性,改进了一些已有的结果.     

A nonconvex dissipative system and its applications (I)

In order to study the uniformly translating solution of some non-linear evolution equations such as the complex Ginzburg–Landau equation, this paper presents a qualitative analysis to a Duffing–van der Pol non-linear oscillator. Monotonic property of the bounded exact solution is established based on the construction of a convex domain. Under certain parametric choices, one first integral to the Duffing–van der Pol non-linear system is obtained by using the Lie symmetry analysis, which constitutes one of the bases for further work of obtaining uniformly translating solutions of the complex Ginzburg–Landau equation. Dedicated to Professor G. Strang on the occasion of his 70th birthday     

Anisotropy of second-order nonlinear optical susceptibilities of arsenic triiodide-sulfur addition complex: AsI3 · 3S8

We report the anisotropic linear and second-order nonlinear optical (NLO) properties of arsenic triiodide-octa-sulfur (1:3) adduct, AsI₃ · 3S₈, which spontaneously crystallizes in the trigonal rhombohedral non-centrosymmetric space group R3m. The trigonal symmetry of the AsI₃ · 3S₈ molecule coincides with the crystal symmetry. The crystals are optically uniaxial with n_o/n_e of about 1.2 and show dichroism at the UV-visible wavelengths. Second harmonic generation (SHG) tensor elements were determined from Maker fringes measured with an Nd:YAG laser (∼10 ns pulse, 1064 nm). The coefficient d_222,eff = 32.0 pm/V for the light polarized parallel to the layers of iodine and sulfur atoms in the AsI₃ · 3S₈ crystal ab plane is markedly larger than d₃₃₃ = 11.6 pm/V for the polarization of light parallel to the crystal c axis. The anisotropy parameter, defined as the d_222,eff/d₃₃₃ ratio, is about 2.7 for the AsI₃ · 3S₈ crystal, smaller than that for the isomorphous CHI₃ · 3S₈ crystal (7.3) but larger than for the SbI₃ · 3S₈ crystal (0.7). Highly anisotropic components of the first hyperpolarizability tensor of an AsI₃ · 3S₈ molecule, β, were derived from the quadratic nonlinear susceptibility tensor of the crystal.     

Energy-efficient power allocation in cell-free massive MIMO with zero-forcing: First order methods

In this paper, the downlink of cell-free massive multiple-input multiple-output (MIMO) with zero-forcing processing is considered. To maximize the system energy efficiency (EE), we design power allocation algorithms taking into account imperfect channel state information, hardware, and backhaul power consumption. The total EE optimization problem is nonconvex, which traditionally is solved by the successive convex approximation framework which involves second order cone programs (SOCPs). As such methods have high complexity, the run time is extremely long, especially in large-scale systems with thousands of access points (APs) and users. To overcome this problem, in this paper, we propose to apply two computationally efficient methods, namely proximal gradient (PG) method and accelerated proximal gradient (APG) method to solve the considered problem. Numerical results show that, compared to the conventional SOCPs approximation methods, our proposed methods achieve the same performance while the run time is much smaller.