Attractor States and Quantum Instabilities in de Sitter Space

The asymptotic behavior of the energy–momentum tensor for a free quantized scalar field with mass m and curvature coupling in de Sitter space is investigated. It is shown that for an arbitrary, homogeneous, and isotropic, fourth-order adiabatic state for which the two-point function is infrared finite, T _ab approaches the Bunch–Davies de Sitter invariant value at late times if m ² + R > 0. In the case m = = 0, the energy–momentum tensor approaches the de Sitter invariant Allen–Folacci value for such a state. For m ² + R = 0 but m and not separately zero, it is shown that at late times T _ab grows linearly in terms of cosmic time leading to an instability of de Sitter space. The asymptotic behavior is again independent of the state of the field. For m ² + R < 0, it is shown that, for most values of m and , T _ab grows exponentially in terms of cosmic time at late times in a state dependent manner.     

Ordering Ambiguity Revisited via Position Dependent Mass Pseudo-Momentum Operators

Ordering ambiguity associated with the von Roos position dependent mass (PDM) Hamiltonian is considered. An affine locally scaled first order differential introduced, in Eq. (9), as a PDM-pseudo-momentum operator. Upon intertwining our Hamiltonian, which is the sum of the square of this operator and the potential function, with the von Roos d-dimensional PDM-Hamiltonian, we observed that the so-called von Roos ambiguity parameters are strictly determined, but not necessarily unique. Our new ambiguity parameters’ setting is subjected to Dutra’s and Almeida’s, Phys. Lett. A. 275 (2000) 25 reliability test and classified as good ordering. PACS numbers: 03.65.Ge, 03.65. Fd, 03.65.Ca     

Skeletal mechanism generation and analysis for n-heptane with CSP

We use a procedure based on the decomposition into fast and slow dynamical components offered by the Computational Singular Perturbation (CSP) method to generate automatically skeletal kinetic mechanisms for the simplification of the kinetics of n-heptane oxidation. The detailed mechanism of the n-heptane oxidation here considered has been proposed by Curran et al. and involves 561 species and 2538 reactions. After carrying out a critical assessment of important aspects of this procedure, we show that the comprehensive skeletal kinetic mechanisms so generated are able to reproduce the main features of n-heptane ignition at various initial pressures and temperatures and equivalence ratios. A by-product of the algorithm that generates the skeletal mechanisms is the identification of the network of important species and reactions at a given state of the kinetic system. The analysis of this network is carried out by resorting to a visual representation of the pathways at selected time instants of the ignition process. Visual inspection of the pathways enables the identification and comparison of the relevant kinetic processes as obtained at different ignition regimes. The graphs are generated by interfacing the model reduction procedure with the open-source package graphviz.     

Energy–momentum tensor on foliations

In this paper, we give a new lower bound for the eigenvalues of the Dirac operator on a compact spin manifold. This estimate is motivated by the fact that in its limiting case a skew-symmetric tensor (see Eq. (1.6)) appears that can be identified geometrically with the O’Neill tensor of a Riemannian flow, carrying a transversal parallel spinor. The Heisenberg group which is a fibration over the torus is an example of this case. Sasakian manifolds are also considered to be particular examples of Riemannian flows. Finally, we characterize the 3-dimensional case by a solution of the Dirac equation.     

Synthesis,molecular structure,photophysical properties and spectroscopic characterization of new 1D-magnesium(II) porphyrin-based coordination polymer

Research on Chemical Intermediates - Chemical preparation, X-ray diffraction, spectral and photophysical studies were performed for H2TPBP (5,10,15,20-tetrakis[4 (benzoyloxy)phenyl] porphyrin),...     

Highly Selective and Sensitive Electrochemical Determination of Ni(II) in Real Samples Based on Ion‐imprinted Polymer Technology

Nickel is one of the heavy metals which has been considered as a serious pollutant affecting the human health. Therefore, it is necessary to control its concentration in foods and drinks. Recently, ion‐imprinted polymer based electrochemical sensors have been attracted lots of attention due to their valuable selectivity and sensitivity toward target analytes. In this study, Ni(II)‐1,10‐phenanthroline complex was prepared in ethanol and added stepwise to the aqueous solution of dopamine, followed by pH adjustment for self‐polymerization of dopamine in alkaline conditions. During the polymerization process, Ni(II)‐imprinted polydopamine (Ni‐PDA) was formed due to effective interactions between polydopamine and 1,10‐phenanthroline ligands carrying Ni(II) ions. A thin film of Ni‐PDA was anchored on a glassy carbon electrode (GCE) through a simple casting procedure. After drying, the sensor was employed for the determination of Ni(II) ions by means of differential pulse voltammetry. Under optimum conditions, a linear calibration curve was obtained in the range 1–25 μM with the detection limit of 0.39 μM (S/N=3). Due to excellent selectivity to Ni(II) ions, the sensor was not suffered from the excess amount of interfering ions and used for Ni(II) determination in different water and tea samples.     

An Overview on Electrochemical Determination of Cholesterol

Cholesterol detection is of great significance in biomedical applications because it is a crucial biomarker for some diseases. It is the precursor of different biological compounds such as vitamin D, hormones, and bile acid, etc. The cholesterol level in blood correlated to various diseases such as hypolipoproteinaemia, septicaemia, malnutrition hypertension, anaemia, brain thrombosis and arteriosclerosis for instance its levels in the blood of more than 200 mg/dL, increase the risk of heart disease. It is also found in foods from animal origin such as milk, meat, cheese, egg and seafood. With respect to dietary reference value for cholesterol intake, most of food safety authorities recommended maximum intake 300 mg per day for adults. Consequently, cholesterol is considered as a critical indicator of clinical biochemistry and so introducing new techniques for determination of it in biological samples and food is important. In this review, Principles, methods and recent developments in electrochemical cholesterol sensors are reviewed. Special attention is given to the discussion on some problems and bottlenecks in areas of enzymatic cholesterol sensing and new advances in non‐enzymatic sensors.     

Discrete Hf18 Metal‐oxo Cluster as a Heterogeneous Nanozyme for Site‐Specific Proteolysis

The selective hydrolysis of proteins by non‐enzymatic catalysis is difficult to achieve, yet it is crucial for applications in biotechnology and proteomics. Herein, we report that discrete hafnium metal‐oxo cluster [Hf₁₈O₁₀(OH)₂₆(SO₄)₁₃?(H₂O)₃₃] ( Hf₁₈ ), which is centred by the same hexamer motif found in many MOFs, acts as a heterogeneous catalyst for the efficient hydrolysis of horse heart myoglobin (HHM) in low buffer concentrations. Among 154 amino acids present in the sequence of HHM, strictly selective cleavage at only 6 solvent accessible aspartate residues was observed. Mechanistic experiments suggest that the hydrolytic activity is likely derived from the actuation of Hf^IV Lewis acidic sites and the Brønsted acidic surface of Hf₁₈ . X‐ray scattering and ESI‐MS revealed that Hf₁₈ is completely insoluble in these conditions, confirming the HHM hydrolysis is caused by a heterogeneous reaction of the solid Hf₁₈ cluster, and not from smaller, soluble Hf species that could leach into solution.     

An aniline-based fiber coating for solid phase microextraction of polycyclic aromatic hydrocarbons from water followed by gas chromatography-mass spectrometry

A fiber coating from polyaniline (PANI) was electrochemically prepared and employed for solid phase microextraction (SPME) of some polycyclic aromatic hydrocarbons (PAHs) from water samples. The PANI film was directly electrodeposited on the platinum wire surface in sulfuric acid solution using cyclic voltammetry (CV) technique. The applicability of this coating was assessed employing a laboratory-made SPME device and gas chromatography with mass spectrometry (GC-MS) for the extraction of some PAHs from the headspace of aqueous samples. Application of wider potential range in CV led to a PANI with more stability against the temperature. The homogeneity and the porous surface structure of the film were examined by the scanning electron microscopy (SEM). The study revealed that this polymer is a suitable SPME fiber coating for extracting the selected PAHs. Important parameters influencing the extraction process were optimized and an extraction time of 40 min at 40 degrees C gave maximum peak area, when the aqueous sample was added with NaCl (20%, w/v). The synthesis of the PANI can be carried out conveniently and in a reproducible manner while it is rather inexpensive and stable against most of organic solvents. The film thickness of PANI can be precisely controlled by the number of CV cycles. The resulting thickness was roughly 20 microm after 20 cycles. At the optimum conditions, the relative standard deviation (RSD) for a double distilled water spiked with selected PAHs at ppb level were 8.80-16.8% (n = 3) and detection limits for the studied compounds were between 0.1-6 pg mL(-1). The performance of PANI was, also, compared with a commercial solid coated-based SPME fiber, carbowax/divinylbenzene (CW/DVB), under similar experimental conditions.     

Asymptotic Behavior of Positive Solutions of a Nonlinear Combined p-Laplacian Equation

For p > 1, we establish existence and asymptotic behavior of a positive continuous solution to the following boundary value problem $$\left\{\begin{array}{ll}\frac{1}{A} \left( A\Phi _{p}(u^{\prime})\right) ^{\prime}+a_{1}(r)u^{\alpha _{1}}+a_{2}(r)u^{\alpha _{2}}=0, \, {\rm in}\, (0,\infty ),\\ {\rm lim}_{r\rightarrow 0} A\Phi _{p}(u^{\prime})(r)=0, {\rm lim}_{r\rightarrow \infty } u(r)=0,\end{array}\right.$$ where \({\alpha _{1}, \alpha _{2} < p -1, \Phi _{p}(t) = t|t| ^{p-2},A}\) is a positive differentiable function and a ₁, a ₂ are two positive functions in \({C_{\rm loc}^{\gamma}((0, \infty )), 0 < \gamma < 1,}\) satisfying some appropriate assumptions related to Karamata regular variation theory. Also, we obtain an uniqueness result when \({\alpha _{1}, \alpha _{2} \in (1-p,p-1)}\) . Our arguments combine a method of sub and supersolutions with Karamata regular variation theory.