First-principles calculations of nitrogen-doped antimony triselenide: A prospective material for solar cells and infrared optoelectronic devices

This study is focused on calculation of the electronic structure and optical properties of non-metal doped Sb2Se3 using the first-principles method. One and two N atoms are introduced to Sb and Se sites in a Sb₂Se₃ crystal. When one and two N atoms are introduced into the Sb₂Se₃ lattice at Sb sites, the electronic structure shows that the doping significantly modifies the bandgap of Sb₂Se₃ from 1.11 eV to 0.787 and 0.685 eV, respectively. When N atoms are introduced to Se sites, the material shows a metallic behavior. The static dielectric constants ε1(0) for Sb₁₆Se₂₄, Sb₁₅N₁Se₂₄, Sb₁₄N₂Se₂₄, Sb₁₆Se₂₃N₁, and Sb₁₆Se₂₂N₂ are 14.84, 15.54, 15.02, 18.9, and 39.29, respectively. The calculated values of the refractive index n(0) for Sb₁₆Se₂₄, Sb₁₅N₁Se₂₄, Sb₁₄N₂Se₂₄, Sb₁₆Se₂₃N₁, and Sb₁₆Se₂₂N₂ are 3.83, 3.92, 3.86, 4.33, and 6.21, respectively. The optical absorbance and optical conductivity curves of the crystal for N-doping at Sb sites show a significant redshift towards the short-wave infrared spectral region as compared to N-doping at Se sites. The modulation of the static refractive index and static dielectric constant is mainly dependent on the doping level. The optical properties and bandgap narrowing effect suggest that the N-doped Sb₂Se₃is a promising new semiconductor and can be a replacement for GaSb due to its very similar bandgap and low cost.     

Chromatographic component of identification of the transformation products of 1,1-dimethylhydrazine in the presence of sulfur

The gas-chromatographic retention indices of the products of 1,1-dimethylhydrazine transformations in the presence of sulfur allows one to confirm and, in ceratin cases, make more exact the results of their gas chromatography-mass spectrometry identification. Features of identification of new compounds, including 1,1-dimethyl-2-thioxohydrazine are discussed.     

Pattern recognition of Inductively Coupled Plasma Atomic Emission Spectroscopy of human scalp hair for discriminating between healthy and Hepatitis C patients

Inductively Coupled Plasma Atomic Emission Spectroscopy measurements of six trace elements were performed on the scalp hair of 155 donors, 73 of which have been diagnosed with Hepatitis C and 82 Controls. Principal Components Analysis (PCA) was employed to visualise the separation between groups and show the relationship between the elements and the diseased state. Pattern recognition methods for classification involving Quadratic Discriminant Analysis and Partial Least Squares Discriminant Analysis (PLS-DA) were applied to the data. The number of significant components for both PCA and PLS were determined using the bootstrap. The stability of training set models were determined by repeatedly splitting the data into training and test sets and employing visualisation for two components models: the percent classification ability (CC), predictive ability (PA) and model stability (MS) were computed for test and training sets.     

On the general nonlinear self-adjoint eigenvalue problem for systems of ordinary differential equations with singularities

A nonlinear self-adjoint eigenvalue problem for the general linear system of ordinary differential equations is examined on an unbounded interval. A method is proposed for the approximate reduction of this problem to the corresponding problem on a finite interval. Under the assumption that the initial data are monotone functions of the spectral parameter, a method is given for determining the number of eigenvalues lying on a prescribed interval of this parameter. No direct calculation of eigenvalues is required in this method.