Qualitative Identification of Milk Fat from Chromatographic Data

The data on the amount of fatty acids in milk, animal, vegetable, and mixed fats were obtained by capillary gas–liquid chromatography. Statistical data on the concentrations of myristic, palmitic, stearic, oleic, linoleic, and linolenic acids in milk fat were considered as criteria of its natural origin. Concepts were formulated for the detection of a multicomponent adulterating additive of variable composition in a product containing variable amounts of the same components. A graphical interpretation of the results of the analysis was proposed based on the identification zone.     

Lines of Development of Seismic Prospecting in the 20th Century

The theory and practice of seismic prospecting are discussed. The period of its development is subdivided into two parts: the classical period up to the 70s years of the twentieth century and the modern technological period. Bibliography: 4 titles.     

Determination of ionol in oils in the presence of low-molecular-weight phenols using reversed-phase HPLC

A procedure was developed for extracting phenol-type antioxidants from oils. The extraction system consisted of isopropanol, 25% NH₃, water, and ammonium sulfate as a salting-out agent. The optimum conditions were found for determining ionol in the presence of phenol and alkylphenols in the isopropanol extract using reversed-phase HPLC with an UV-detector. The time of analysis was 55 min. The detection limits in oils (taking into account extraction preconcentration) were 0.0005 mg/L for phenol, 0.0006 mg/L for cresols, and 0.015 mg/L for ionol.     

Synthesis of monosubstituted 1,2,4,5-tetrazines – 3-amino-1,2,4,5-tetrazines

Chemistry of Heterocyclic Compounds - The substitution of pyrazolyl moiety in 3-(3,5-dimethyl-1H-pyrazol-1-yl)-1,2,4,5-tetrazine with N-nucleophiles provided a series of highnitrogen tetrazine...     

Periodic solutions of the quasilinear beam vibration equation with homogeneous boundary conditions

We prove the existence of infinitely many time-periodic solutions of the quasilinear beam vibration equation with homogeneous boundary conditions for the case in which the nonlinear term has power-law growth. We also prove the existence of at least one periodic solution provided that the nonlinear term satisfies the resonance-free condition.     

Some Aspects of the Effective Detection of Ammonium Nitrate-Based Explosives by Pulsed NQR Method

The nuclear quadrupole resonance (NQR) method has been applied to ammonium nitrate (AN)-based explosives, ANFO and REOGEL+, to find an optimized multi-pulse technique for effective detection. The relaxation parameters and signal intensities for nitrogen-14 lines of these substances were measured. The experimental results of applying the proposed multi-pulse technique in these samples are presented and convincingly demonstrate a path toward efficient detection. A detection using sequences of this character could be achieved over real-world scan volumes for screening of goods. It was proven that the cross-polarization technique can significantly enhance the NQR signal for AN-based explosives.     

Periodic Solutions of a Nonlinear Wave Equation with Nonconstant Coefficients

The existence of time-periodic solutions of a nonlinear equation for forced oscillations of a bounded string is proved when the d'Alembert operator has nonconstant coefficients and the nonlinear term has power-law growth.     

Periodic solutions of a quasilinear wave equation

We study the properties of wave operators satisfying the periodicity condition with respect to time and homogeneous boundary conditions of the third kind and of Dirichlet type. We prove the existence of a nontrivial periodic (in time) sine-Gordon solution with homogeneous boundary conditions of the third kind and of Dirichlet type. We obtain theorems on the existence of periodic solutions of a quasilinear wave equation with variable (in x) coefficients and a boundary condition of the third kind.     

Effect of the doping level on temperature bistability in a silicon wafer

The influence of the doping level on the effect of the temperature bistability in a silicon wafer upon radiative heat transfer between the wafer and the elements of the heating system is studied. Theoretical transfer characteristics are constructed for a silicon wafer doped with donor and acceptor impurities. These characteristics are compared with the transfer characteristics obtained during heating and cooling of wafers with the hole conduction (with dopant concentrations of 10¹⁵, 2 × 10¹⁶, and 3 × 10¹⁷ cm^?3) and electron conduction (with impurity concentrations of 10¹⁵ and 8 × 10¹⁸ cm^?3) in a thermal reactor of the rapid thermal annealing setup. It is found that the width and height of the hysteresis loop decrease with increasing dopant concentration and are almost independent of the type of conduction of the silicon wafer. The critical value of the impurity concentration of both types is 1.4 × 10¹⁷ cm^?3. For this concentration, the loop width vanishes, and the height corresponds to the minimal value of the temperature jump (～200 K). The mechanism of temperature bistability in the silicon wafer upon radiative heat transfer is discussed.