Limit cycle bifurcations in resonant LC power inverters under zero current switching strategy

Nonlinear Dynamics - The dynamics of a DC-AC self-oscillating LC resonant inverter with a zero current switching strategy is considered in this paper. A model that includes both the series and the...     

Is the Pauli exclusion principle the origin of electron localisation?

ABSTRACT

In this work, we inquire into the origins of the electron localisation as obtained from the information content of the same-spin pair density, γ^{σ, σ}(r₂∣r₁). To this end, we consider systems of non-interacting and interacting identical Fermions contained in two simple 1D potential models: (1) an infinite potential well and (2) the Kronig–Penney periodic potential. The interparticle interaction is considered through the Hartree–Fock approximation as well as the configuration interaction expansion. Morover, the electron localisation is described through the Kullback–Leibler divergence between γ^{σ, σ}(r₂∣r₁) and its associated marginal probability. The results show that, as long as the adopted method properly includes the Pauli principle, the electronic localisation depends only modestly on the interparticle interaction. In view of the latter, one may conclude that the Pauli principle is the main responsible for the electron localisation.     

Lithium-functionalized germanene: A promising media for CO2 capture

Density functional theory (DFT) is employed to investigate the interactions of CO₂ gas molecules with pristine and lithium-functionalized germanene. It is discovered that although a single CO₂ molecule is weakly physisorbed on pristine germanene, a significant improvement on its adsorption energy is found by utilizing Li-functionalized germanene as the adsorbent. Excitingly, the moderate adsorption energy at high CO₂ coverage secures an easy release step. Moreover, the structure of Li-functionalized germanene can be fully recovered after removal of CO₂ gas molecules. Our results suggest that Li-functionalized germanene show promise for CO₂ sensing and capture with a storage capacity of 12.57 mol/kg.     

Sensitive and Profitable Electrochemical Detection of Uric Acid in the Presence of Dopamine with a Novel Carbon Paste Electrode Decorated with a Copper(II) Complex

A new microcomposite with copper(II) complex and carbon paste (Cu_C/CPE) was developed to determine the uric acid (UA) content in the presence of dopamine (DP) and was characterized via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and energy dispersive spectroscopy (EDS). The results showed high selectivity for UA compared with DP because the anodic peak currents for DP were near those of a CPE without Cu_c and were considerably increased for UA. The UA and DP increases were 86.9 % and 14.3 %, respectively, according to CV and 96.6 % and 25.5 %, respectively, according to square wave voltammetry (SWV) with the Cu_C/CPE. Moreover, the anodic peak separation for UA and DP was 0.17 V. With optimal parameters (pH, 3.3; adsorption time(t_ADS), 30 s;adsorption potential (E_ADS)_, 0.10 V), the anodic peak currents for UA were proportional to concentrations between 1.6 and 14.4 μmol L^?1 using standard solutions with UA concentrations ranging from 8.0–40.5 μmol L^?1 and real samples. The UA detection limit was 0.13 μmol L^?1. The new sensor was used to determine the UA contentin human urine samples, and the method was checked with a urine chemistry control from Bio‐Rad based on human urine spiked with quantities of UA and showed a recovery between 84 % and 106 % at concentrations below 10.0 μmol L^?1.     

Controlling Interfacial Charge Transfer and Fill Factors in CuO‐based Tandem Dye‐Sensitized Solar Cells

We designed and synthesized a series of novel electron‐accepting zinc(II)phthalocyanines (ZnPc) and probed them in p‐type dye sensitized solar cells (p‐DSSCs) by using CuO as photocathodes. By realizing the right balance between interfacial charge separation and charge recombination, optimized fill factors (FFs) of 0.43 were obtained. With a control over fill factors in p‐DSSCs in hand we turned our attemtion to t‐DSSCs, in which we combined for the first time CuO‐based p‐DSSCs with TiO₂‐based n‐DSSCs using ZnPc and N719. In the resulting t‐DSSCs, the V_OC of 0.86 V is the sum of those found in p‐ and n‐DSSCs, while the FF remains around 0.63. It is only the smaller J_scs in t‐DSSCs that limits the efficiency to 0.69 %.     

Electrochemical Studies of Inclusion Complex Formed Between Glutathione and β‐cyclodextrin‐modified Carbon Electrodes and its Application for Determination of Glutathione

In this work, the electrochemical determination of glutathione (GSH) using β‐cyclodextrin (β‐CD) modified carbon electrodes was carried out. Different methodologies were used to modify the electrodes. In the first part of this paper, we analyze and compare the ability of the electrodes to determine GSH using the different β‐CD‐modified electrodes and cyclic voltammetry. We found that the carbon paste electrode modified by potential sweeping was the best electrode for GSH determination; in addition, we found that an inclusion complex formed between β‐CD deposited on the electrode surface and GSH. The formation constant for this complex was 2498.54 M^?1 at 25 °C. Furthermore, we have also calculated thermodynamic parameters for the formation of the inclusion complex. In the second part of this paper, we analyze the effect of sweep rate and pH on the determination of GSH. The best results were obtained at a rate of 50 mV s^?1 and a pH of 2.2. The β‐CD‐modified carbon paste electrode exhibits a linear response in a concentration range of 20 to 157 µM with a sensitivity of 1083.65 µA mM^?1cm^?2 and a detection limit of 3.92 µM. Finally, the electrode was used to determine the GSH concentration in Eichhornia crassipes root extract, and the concentration determination accuracy was validated by a well‐known spectroscopic method.     

Combining Zinc Phthalocyanines,Oligo(p-Phenylenevinylenes), and Fullerenes to Impact Reorganization Energies and Attenuation Factors

A study on electron transfer in three electron donor-acceptor complexes is reported. These architectures consist of a zinc phthalocyanine (ZnPc) as the excited-state electron donor and a fullerene (C₆₀) as the ground-state electron acceptor. These complexes are brought together by axial coordination at ZnPc. The key variable in our design is the length of the molecular spacer, namely, oligo-p-phenylenevinylenes. The lack of appreciable ground-state interactions is in accordance with strong excited-state interactions, as inferred from the quenching of ZnPc centered fluorescence and the presence of a short-lived fluorescence component. Full-fledged femtosecond and nanosecond transient absorption spectroscopy assays corroborated that the ZnPc ⋅ ⁺-C₆₀ ⋅ ⁻ charge-separated state formation comes at the expense of excited-state interactions following ZnPc photoexcitation. At a first glance, the ZnPc ⋅ ⁺-C₆₀ ⋅ ⁻ charge-separated state lifetime increased from 0.4 to 86.6 ns as the electron donor-acceptor separation increased from 8.8 to 29.1 Å. A closer look at the kinetics revealed that the changes in charge-separated state lifetime are tied to a decrease in the electronic coupling element from 132 to 1.2 cm⁻¹, an increase in the reorganization energy of charge transfer from 0.43 to 0.63 eV, and a large attenuation factor of 0.27 Å⁻¹.     

Sublimation/Volatilisation Kinetics of 8-hydroxyquinolines and Their Nitro-derivatives

5-Nitro-8-hydroxyquinoline (B) and 5,7-dinitro-8-hydroxyquinoline (C) were obtained from nitration of 8-hydroxyquinoline (A) and purified in acetone medium and under heating in which the formation of (B) or (C) depends on the amount of HNO₃ added. TG curves present mass loss in only one step before and after the melting point (T _m =76°C (A) and 180°C (B)) in different proportions as a function of the heating rate, characterising the sublimation and the volatilisation processes, respectively. The thermal stability of the compounds follow the order: A (77°C)<B (121°C)<C (222°C). Kinetic parameters through TG curves, dynamic process, using heating rates of 1, 2.5, 5, 10 and 20°C min^ȡ1 , enabled to obtain the following increasing order to the activation energy values of the compounds: 80.4 (A), 102.0 (B) and 153.9 kJ mol⁻¹ (C). Other kinetic parameters as pre-exponential and half-lifetime were also estimated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis, characterization and photophysical properties of a SWNT-phthalocyanine hybrid

We report the synthesis, characterization and photophysical features of a new nanometer scale carbon nanostructure, that is, a single-wall carbon nanotube bearing phthalocyanine chromophores.