Of all modern nanosensors using the principle of measuring variations in electric conductance, point-contact sensors stand out in having a number of original sensor properties not manifested by their analogues. The nontrivial nature of point-contact sensors is based on the unique properties of Yanson point contacts used as the sensing elements. The quantum properties of Yanson point contacts enable the solution of some of the problems that could not be solved using conventional sensors measuring conductance. In the present paper, we demonstrate this by showing the potential of quantum point-contact sensors to selectively detect components of a gas mixture in real time. To demonstrate the high efficiency of the proposed approach, we analyze the human breath, which is the most complex of the currently known natural gas mixtures with extremely low concentrations of its components. Point-contact sensors allow us to obtain a spectroscopic profile of the mixture. This profile contains information about the complete set of energy interactions occurring in the point contact/breath system when the breath constituents adsorb to and desorb from the surface of the point-contact conduction channel. With this information we can unambiguously characterize the analyzed system, since knowing the energy parameters is key to successfully identifying and modeling the physicochemical properties of various quantum objects. Using the point-contact spectroscopic profile of a complex gas mixture it is possible to get a functional dependence of the concentration of particular breath components on the amplitude of the sensor output signal. To demonstrate the feasibility of the proposed approach, we analyze the point-contact profiles from the breath of several patients and compare them with the concentrations of serotonin and cortisol in the body of each patient. The obtained results demonstrate that the proposed methodology allows one to get an effective calibration function for a non-invasive analysis of the level of serotonin and cortisol in the human body using the point-contact breath test. The present study indicates some necessary prerequisites for the design of fast detection methods using differential sensor analysis in real time, which can be implemented in various areas of science and technology, among which medicine is one of the most important.

Original fundamental properties of Yanson point contacts allow their application to research and technology development at a wide range of surrounding conditions. At low temperature these nanoobjects can be used as a main instrument of Yanson point-contact spectroscopy. At room temperature they can serve as a sensitive element of advanced nanosensors with excellent performance. The most important advantage of point-contact sensors in investigating complex gas media is the spectral nature of the response signal. The discovery of the spectral capabilities of point-contact sensors in the analysis of complex gas media allows us to speak in terms of spectral multifunctionality of Yanson point contacts and the expansion of the possibilities of their spectral application from the spectroscopy of electron-phonon interaction at low temperatures to spectroscopy of gaseous media at room temperatures. Using the spectral response of point-contact sensors, in this work we propose a new non-invasive method for the determination of melatonin, one of the important hormones characterizing the state of the human body. A series of procedures was proposed to find melatonin concentration in the human body as function of the response of a point-contact sensor to the action of the exhaled breath. It has been shown that the proposed method is accurate enough to be used for medical purposes in real time. The results of the study suggest that the problem of non-invasive determination of melatonin concentration in the human body can be successfully solved by using breath tests based on Yanson point contacts.

Significant progress in development of noninvasive diagnostic tools based on breath analysis can be expected if one employs a real-time detection method based on finding a spectral breath profile which would contain some energy characteristics of the analyzed gas mixture. Using the fundamental energy parameters of a quantum system, it is possible to determine with a high accuracy its quantitative and qualitative composition. Among the most efficient tools to measure energy characteristics of quantum systems are sensors based on Yanson point contacts. This paper reports the results of serotonin and melatonin detection as an example of testing the human hormonal background with point-contact sensors, which have already demonstrated their high efficiency in detecting carcinogenic strains of Helicobacter pylori and selective detection of complex gas mixtures. When comparing the values of serotonin and melatonin with the characteristic parameters of the spectral profile of the exhaled breath of each patient, high correlation dependences of the concentration of serotonin and melatonin with a number of characteristic parameters of the response curve of the point-contact sensor were found. The performed correlation analysis was complemented with the regression analysis. As a result, empiric regression relations were proposed to realize in practice the new non-invasive breath test for evaluation of the human hormonal background. Registration of the patient’s breath profile using point-contact sensors makes it possible to easily monitor the dynamics of changes in the human hormonal background and perform a quantitative evaluation of serotonin and melatonin levels in the human body in real time without invasive interventions (blood collection) and expensive equipment or reagents.

Molecular dynamics computer simulation with a Lennard–Jones potential is used to investigate the interaction of two identical substitutional impurity atoms in an hcp crystal lattice. Different atomic radii of the impurities atoms, interaction energy of the atoms and the lattice atoms, and initial distances between the impurity atoms at zero temperature and pressure. It is found that in a number of cases for small distances between the impurity atoms not exceeding five interatomic distances these atoms attract one another contrary to the well-known laws of the continuum theory of elasticity. Good agreement between the computational results and the theory of elasticity obtains for short distances between impurity atoms.

Two-dimensional crystals of bounded sizes formed by atoms with centrallysymmetric interaction between them (Lennard-Jones potential) are examined. Methodologies of molecular dynamics have established the atomic structure of clusters of approximately circular form with radii on the nanometer scale. Deviations of atomic configurations from the ideal lattice of a 2D crystal, caused both by the free boundary of a cluster and by the defects introduced into its center, dislocations and crowdions, are investigated. The values of the self-energy of these defects are calculated, and their dependencies on the cluster radius and the parameters of the potential of interatomic interaction are analyzed. Methodologies of continuum mechanics of crystals described the features of uniform elastic strain of 2D crystal circles and bands in comparison with deformation of 3D crystal spheres and rods. Two-dimensional analogues of the main characteristics of elasticity, namely the coefficient of compression, Young's modulus, shear modulus, and Poisson coefficient, as well as their connection with Lamé coefficients, are discussed. The dependencies of the enumerated parameters of elasticity on the parameters of the potential of interatomic interaction are established, and estimates for the effective sizes of kernels of dislocation and crowdion are derived.

The dynamics of a one-dimensional magnetic system in an external spatially localized high-frequency field were analyzed analytically (in the framework of perturbation theory and qualitative approach) and numerically. For the case of direct nonlinear resonance we found the dependence of local state amplitudes on the amplitude of the external field for different values of external field frequency and the damping parameter. Hysteresis character of the field dependence and the appearance of “instability windows”, where additional nutation of magnetic moments occurs, are also noted.

The spectral problem of the internal mode oscillations of a spin nanocluster in an anisotropic ferromagnetic chain placed a magnetic field has been solved exactly using the discrete Takeno-Homma model. A stability diagram on the plane of exchange and magnetic field parameters is constructed for spin clusters having arbitrary dimensions. Explicit expressions for the nanocluster internal mode oscillations are found, and their frequency dependences on the exchange and magnetic field parameters are calculated.

Noncollinear discrete domain walls in the Heisenberg anisotropic ferromagnetic chain under applied magnetic field and their small excitation spectra are studied analytically and numerically in the framework of the Takeno-Homma equation. The intersecting frequency dependences of localized excitations and continuous spectrum oscillations and the removal of the degeneracy by the magnetic field are revealed. The variational approach is proposed to describe the domain walls and to investigate their stability. It is shown that the obtained analytical expressions fit very well the numerical solutions. The total energy of static discrete domain walls and the Peierls energy barrier between them are found explicitly. The stability diagram for noncollinear domain walls on the plane of parameters of the exchange and the magnetic field is calculated, and it looks like the alternating stripes structure of stability regions of the bond-centered and site-centered discrete domain walls. This diagram feature is explained by the oscillating dependence of the Peierls energy barrier on the exchange and the magnetic field parameters.