Moscow University Physics Bulletin最新文献

In this work, an automatic thermoregulation system for biosensors based on field-effect transistors with a nanowire channel is demonstrated, providing full control and maintenance of the required temperature regime in bioanalytical analyses. The system elements, including field-effect transistors with a nanowire channel, temperature sensors, and heaters, were fabricated on a single silicon crystal using electron beam lithography, reactive ion etching, and high-vacuum deposition techniques. Unique electronics for temperature control and maintenance were developed. The dependence of thermometer readout on heating power was measured, which is in good agreement with the results of numerical simulation. A demonstration of a thermoregulation system with PID-feedback, ensuring the establishment of a desired temperature in the range from 30 to 70({}^{circ})C within 18 s in a liquid medium, was carried out. A demonstration of a thermoregulation system for detecting nucleic acids was performed using synthetic single-stranded DNA, representing a gene fragment from the bacterium Escherichia coli. The minimum detectable response was observed for a sample with a concentration of 3 fM.

This paper presents a prototype of an infrared photometer, created at the Sternberg Astronomical Institute, Lomonosov Moscow State University (SAI MSU), based on the commercial infrared module Gavin-615A. The operating spectral range of the photometer is 3–5 (mu)m. Investigations of the photometer’s detector have shown that its parameters coincide with those stated by the manufacturer. The nonlinearity of the detector does not exceed ({sim}5%) across the entire signal range, and coefficients for correction functions were determined. Additionally, we determined the readout noise (textrm{RN}=1200pm 210e^{-}), the conversion coefficient (textrm{GAIN}=520pm 9e^{-}/)ADU, the signal magnitude of the bias frame (textrm{BIAS}=960.5pm 2.2) ADU, and the dark current ({approx}(9.3pm 1.1)times 10^{6}e^{-})/s, which is the sum of the detector’s dark current and the radiation from the entrance window of the detector module. The value of dark current was measured at a window temperature of (6^{circ})C. Observations commenced with the photometer at the 2.5-m telescope of the Caucasian Mountain Observatory of MSU, with the first results presented in this paper. The unvignetted field of view was (30^{primeprime}). In the (M) band under good atmospheric conditions, an image quality close to the diffraction limit was achieved. Images of a star with brightness (L=7.96) and (M=6.78) were obtained over the 20-s exposure time and a (textrm{SNR}sim 10) ratio. It is shown that at high image quality with (textrm{SNR}=3) and exposure of 20 s it is possible to observe stars up to (Lsim) 9({}^{m}) and (Msim 8^{m}). The main module of the photometer was also used in measurements of the sky background brightness.

A model for the evolution of surface nanorelief under irradiation with gas cluster ions is proposed. The model is based on the consideration of individual cluster collisions with a surface. The amount of material sputtered from the collision area and the efficiency of its redeposition on other surface elements are determined. The model’s performance is demonstrated through comparison with experimental data. The stages of smoothing the model harmonic relief are investigated. A new measure of surface smoothing efficiency is proposed.

As demonstrated by a three-dimensional geodynamo model, during reversals and excursions of the geomagnetic field, with small amplitudes of heat sources, there occurs attenuation not only of the dipolar magnetic field but also of the high harmonic field. In this scenario, the Earth’s magnetosphere can be significantly smaller than previously expected, and correspondingly, the amount of radiation that penetrates the Earth could be greater.

The previously proposed method of molecular dynamics modelling for the sputter deposition of thin films from metal targets has been adapted for the case of dielectric targets and applied to silicon dioxide films. The possibility of the ejection from targets of not only silicon atoms but also clusters with oxygen atoms is taken into account by adding O=Si=O molecules to the flow of deposited atoms. Atomistic film clusters have been obtained at high-energy and low-energy sputter deposition with various percentages of molecules in the flow of deposited atoms. The values of the stress tensor components have been calculated. Compressive stresses are observed at high-energy deposition, while tensile stresses are observed at low-energy deposition. The absolute values of the diagonal components of the stress tensor increase with the increasing proportion of molecules in the flow of deposited atoms.

The spatio-temporal dynamics of plasma in a symmetrical dual-frequency 81 MHz/1.76 MHz capacitive discharge under the influence of a low-frequency 1.76 MHz field has been studied. Using phase-resolved optical emission spectroscopy, the dynamics of argon and xenon emission intensity in the plasma was obtained. Measurements of the electron energy probability function (EEPF) at the center of the discharge were performed using a Langmuir probe, and electron density measurements were made using a hairpin probe. The main result is the dynamics of the intensity ratios of selected argon and xenon lines under different conditions: at pressures of 40, 200, and 400 mTorr, low-frequency voltage amplitudes of 100, 200, and 400 V, and input power at 81 MHz of 3 and 15 W. The dynamics of high-energy electrons was investigated based on a two-temperature approximation of the electron energy probability function.

In recent times, Monte Carlo simulations are gaining widespread recognition as the most precise tool for calculating particle interactions with matter. In this study, we investigated two primary aspects. Firstly, we examined how the average excitation energy of water ((I_{W})) influences the location of the Bragg peak (BP). Secondly, we used the particle and heavy ion transport code system (PHITS) to study the Bragg curve of ({}^{12})C ion beam having an energy of 200 MeV/u in three different mediums: water, soft tissue, and bone. Lastly, we examined the impact of secondary particles on the overall dose. Our findings indicate that the average excitation energy of water strongly influences the position of the BP. The tail dose beyond the BP primarily results from secondary fragments of the primary carbon ion beams. Furthermore, the PHITS code accurately reproduces the measured Bragg curves.

Studying single cells opens opportunities for understanding many biological processes and, as a consequence, plays an important role in the development of biomedicine. Scanning ion conductance microscopy (SICM) and nanopipette systems for the analysis of single cells represent a powerful tool for investigating the morphological, mechanical, and biochemical features of living cells with nanometer spatial resolution under near-natural conditions. Over the last decades, SICM has shown great success in studying and manipulating single cells, and the noncontact nature of the system, combined with the unique features of nanopipettes used as probes, has opened new possibilities for the application of such systems in biomedical applications. This review reflects the latest trends and directions in the development of SICM and nanopipette systems for the single-cell analysis.

The goal of this study is to investigate the effect and influence of cross-sections data, implemented in DOSXYZnrc Monte Carlo code, on the dose distributions data such as beam dose profiles and percentage depth dose, and it influences on the efficiency. This study was performed in tow phases: the commissioning of Phase Space files generated by SATURNE 43 for 12 MV and the analysis of these Phase Space files by using different cross section implemented DOSXYZnrc code. A SATURNE 43 linear accelerator head’s has been modeled with BEAMnrc Monte Carlo code to simulate a 12 MV photon beam on a square field size of (times 10) cm({}^{2}). Phase Space files for the SATURNE 43 photon beam were created by using the EGSnrc BEAMnrc system. The Phase Space files was scored below the botom jaws and used as input in simulation using DOSXYZnrc. The calculated results established that the percentage depth dose curves, beam profiles dose and efficiency are less sensitive to photon, pair, and Bremsstrahlung cross-sections data available in DOSXYZnrc code.

We study the electromagnetic contribution to the processes of elastic scattering of neutrinos on nucleons. In our formalism, the electromagnetic charge, magnetic, electric, and anapole form factors of neutrinos, both of diagonal and transition types in the mass basis, are taken into account. When treating the nucleon electromagnetic vertex, we consider not only the charge and magnetic form factors of the nucleon but also its electric and anapole form factors. We analyze the possible effects of the neutrino magnetic moment in the elastic neutrino–nucleon scattering and how they can be distinguished from the effects of strange quarks contributing to the weak neutral current form factor of the nucleon.