First-Row Transition-Metal Cations (Co2+, Ni2+, Mn2+, Fe2+) and Graphene (Oxide) Composites: From Structural Properties to Electrochemical Applications

Composites of graphene (oxide) (GO) and first-row transition-metal cations (Co²⁺, Ni²⁺, Mn²⁺, Fe²⁺) are prepared by mixing GO and aqueous metal salt solutions. The amount of metal cation bound to GO nanosheets is calculated by using inductively coupled plasma mass spectrometry (ICP-MS) and the possible binding sites of the metals are investigated by means of attenuated total reflectance infrared (ATR-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. Electrodes loaded with the metal/GO composites are prepared by a simple drop-casting technique without any binders or conductive additives. The effect of electrochemical reduction on the structure of the composite electrodes is investigated by Raman spectroscopy, XPS, X-ray diffraction (XRD) analysis, and field emission scanning electron microscopy (FESEM). A detailed electrochemical characterization is performed for the utilization of the composite electrodes for electrochemical capacitors and possible oxygen reduction reaction electrocatalysts by cyclic voltammetry (CV) and rotating disk electrode measurements. The highest areal capacitance is achieved with the as-deposited Fe/GO composite (38.7 mF cm⁻² at 20 mV s⁻¹). In the cyclic stability measurements, rCo/GO, rNi/GO, rMn/GO, and rFe/GO exhibit a capacitance retention of 44, 1.1, 73, and 87 % after 3000 cycles of CV at 100 mV s⁻¹, respectively.     

Approaching a large deviation theory for complex systems

Nonlinear Dynamics - Membership function identification is the basis for solving the fuzzy control problems. In order to complete the fuzzification process and reflect the dynamic quality of the...     

Ground state and phonon spectrum of NiSi2

We have studied structural, electronic, elastic and dynamical properties of NiSi₂ by employing the plane wave pseudopotential method based on density functional theory within the local density approximation. The calculated lattice constant, bulk modulus and first-order pressure derivative of the bulk modulus are reported and compared with earlier available experimental and theoretical calculations. Numerical first-principles calculations of the elastic constants were used to calculate C₁₁, C₁₂ and C₄₄ for NiSi₂. The calculated electronic band structure has been compared with angle-resolved photoemission spectroscopy experimental data along the [100] and [111] symmetry directions. A linear response approach to density functional theory is used to derive the phonon dispersion curves and phonon partial density of states. Atomic displacement patterns for NiSi₂ at the Γ, X and L symmetry points are also presented.     

Natural‐Product‐Inspired Aminoepoxybenzoquinones Kill Members of the Gram‐Negative Pathogen Salmonella by Attenuating Cellular Stress Response

Gram‐negative bacteria represent a challenging task for antibacterial drug discovery owing to their impermeable cell membrane and restricted uptake of small molecules. We herein describe the synthesis of natural‐product‐derived epoxycyclohexenones and explore their antibiotic activity against several pathogenic bacteria. A compound with activity against Salmonella Typhimurium was identified, and the target enzymes were unraveled by quantitative chemical proteomics. Importantly, two protein hits were linked to bacterial stress response, and corresponding assays revealed an elevated susceptibility to reactive oxygen species upon compound treatment. The consolidated inhibition of these targets provides a rationale for antibacterial activity and highlights epoxycyclohexenones as natural product scaffolds with suitable properties for killing Gram‐negative Salmonella.     

Synthesis, characterization and thermal behavior of 1,1-dialkyl-3-(4-(3,3-dialkylthioureidocarbonyl)-benzoyl)thiourea and its Cu(II), Ni(II), and Co(II) complexes

We report the synthesis, characterization, and thermal behavior of 1,1-diethyl-3-(4-(3,3-diethylthioureidocarbonyl)benzoyl)thiourea, 1,1-di-n-propyl-3-(4-(3,3-di-n-propylthioureido carbonyl)benzoyl)thiourea and 1,1-di-n-butyl-3-(4-(3,3-di-n-butylthioureidocarbonyl)benzoyl)thiourea and their Ni(II), Cu(II), and Co(II) complexes. The structure of the prepared compounds was determined by elemental analysis, FT-IR, ¹H NMR spectroscopy and mass spectrometry. The ligands are coordinated to metal atoms in a bidentate manner yielding an essentially neutral complex of the type M₃L₃. Thermal decomposition of related compounds was investigated by DTA and TG techniques. The pyrolytic end product was identified by X-ray powder diffraction method. The text was submitted by the authors in English.     

Evolution of magnetic and structural properties of TiO2 with Co-doping

This paper presents the phase formations and magnetic properties of Co-doped TiO₂ synthesized by the colloidal and ammonium nitrate melt techniques (ANMT). The phase formations and ferromagnetic properties were studied with XRD and SQUID magnetometry. Crystallization of the TiO₂ rutile lattice was completed at 1000 °C and that was preserved during annealing up to 1300 °C. For the samples annealed at 1200 °C, elemental analysis has shown that the colloidal technique leads to a single-phase rutile with cobalt concentration of almost nothing even in the initially 0.5 mol Co-added samples. Further increase of annealing temperature results in the appearance of other Ti-phases in addition to the rutile. On the other hand, it is quite interesting that these samples show ferromagnetic behavior. The samples synthesized by the ANMT method contain larger amounts of Co compared to the colloidal technique.     

Linking the viscous and vacancy behavior of high molecular weight hydrocarbons

A new theoretical model that was recently purposed for zero-shear viscosity has now been extended to the three-branch alkanes with pentyl, hexyl, or phenyl attachments. The model links the equilibrium theory of Simha-Somcynsky (SS) statistical thermodynamics of liquids and the transport theory of Eyring Significant Structure (ESS). The predicted quantity of hole fraction as a measure of the free volume, computed from the SS equation of state, plays a primary role in the theory to combine the both theories. The experimental PVT data from 310 to 408 K temperature and 0.1 to 344.5 MPa pressure range have been used. The proportionality constants of the activation energy and the transmission coefficient have been calculated for each species separately and they are in expected trend with the substituted ring structure. Satisfactory agreement in prediction of viscosity from the hole fraction has been obtained.     

Lower degree bounds for modular vector invariants

Let be a finite group of order divisible by a prime acting on an vector space where is the field with elements and . Consider the diagonal action of on copies of This note sharpens a lower bound for for groups which have an element of order whose Jordan blocks have sizes at most 2.

     

Two-step numerical procedure for complex permittivity retrieval of dielectric materials from reflection measurements

A two-step measurement procedure has been proposed for measurement of complex permittivity of dielectric materials using one-port reflection measurements. In the procedure, as a first step, a graphical method is applied to analyze on the complex reflection-coefficient plane the general pattern of dielectric behavior of the sample. Then, as a second step, optimization algorithms are utilized for retrieving electrical properties of samples. The procedure requires measurement of complex reflection scattering parameters of at least two samples with different lengths. It has been validated by X-band measurements of three polyvinyl chloride samples with lengths 5, 10, and 20 mm.