X-ray lensless optics and ptychography
X-ray lensless optics and ptychography
A. S. Busarov$^1$, P. Yu. Glagolev$^2$, N. L. Popov$^1$
One of the tasks of modern optical methods is the most complete description of the objects and light fields under study. For example, the materials under study must be characterized not only by absorption, but also by refraction, and the light fields behind the object and near the detector - not only by intensity, but also by phase. The 1972 work of Gershberg and Saxton was the first attempt to accomplish this task without using any optical elements, relying only on a quadratic detector and a computer simulating the propagation of electromagnetic waves. Today, such lensless imaging methods are used in a wide range of wavelengths, from terahertz to hard x-rays. The purpose of this work is to give a brief introduction to the theory of lensless methods as applied to the X-ray wavelength range. The results of experiments on lensless imaging of test objects, recently performed at the Lebedev Physical Institute using lasers, are also presented.
Show AbstractAssessment of dynamic disorder in DNA oligonucleotides using low-frequency Raman spectroscopy
Assessment of dynamic disorder in DNA oligonucleotides using low-frequency Raman spectroscopy
A. Yu. Sosorev$^{1,2,3}$, O. D. Parashchuk$^1$, A. A. Trubitsyn$^1$, N. O. Dubinets$^{2,4}$, I. V. Chicherin$^1$, D. Yu. Parashuk$^{1,2}$
The degree of DNA compaction in various regions of the cell nucleus determines whether the corresponding genes should be expressed, and whether other important cellular processes, such as DNA replication and repair, should take place. However, approaches to the experimental assessment of the compactness of DNA in cell nuclei, as well as its indicator, dynamic disorder — thermal fluctuations in the position and mutual orientation of molecular fragments — are practically not developed. In this paper, using single-stranded oligonucleotides guanine and cytosine, as well as their double-stranded combination as an example, we show that dynamic disorder in DNA can be estimated using low-frequency Raman spectroscopy. For the first time, the Raman spectra of oligonucleotides were measured in a wide range including the low-frequency and high-frequency regions. It was found that the low-frequency Raman intensity is maximal for single-stranded oligocytosine and minimal in double-stranded oligonucleotide, in full agreement with the magnitude of dynamic disorder estimated from the molecular dynamics simulations. The results obtained indicate the prospects of using low-frequency Raman spectroscopy to assess the dynamic disorder and compactness of DNA. It is expected that the use of such a technique should contribute to the understanding of key cellular processes and their underlying physical mechanisms, which is necessary for the development of advanced methods of molecular biophysics and cell biology.
Show AbstractSecond harmonic generation in structures with inhomogeneous magnetization distribution
Second harmonic generation in structures with inhomogeneous magnetization distribution
I. A. Kolmychek, V. B. Novikov, A. I. Maydykovskiy, T. V. Murzina
The study of the interaction of laser radiation with ferromagnetic materials is not only an inexhaustible source of new effects, but also provides an opportunity to study magnetic media at the micro- and macro-scale. This is especially important for the development of modern technologies to produce structures with fundamentally new magnetic and optical properties that can’t be observed in natural materials. The review presents the results of studies of nonlinear optical effects in ferromagnetic nano- and microstructures, as well as films of different compositions. The unique capabilities of nonlinear-optical diagnostics of anisotropic, vortex, exchange-biased magnetic structures, visualization of the micromagnetic structure of the surface layers of ferrite garnets, based both on the high sensitivity of the optical second harmonic generation method to the magnetic state of nanostructures and interfaces, and on the symmetry properties of high-order magnetization-induced susceptibility tensor have been demonstrated.
Show AbstractEffects of wind on deep convection in Lake Baikal during the autumnal thermal bar
Effects of wind on deep convection in Lake Baikal during the autumnal thermal bar
B. O. Tsydenov, N. S. Trunov, V. V. Churuksaeva, D. V. Degi
The results of numerical modeling of processes of deep convection in Lake Baikal during the autumnal thermal bar are presented. Analysis of the space---time distributions of temperature under different wind conditions was conducted on an example of the Boldakov River---Maloye More Strait cross-section which is characterised by the great depths. Simulations have shown the effectiveness of wind only in the upper 250 m layers. However, cabbeling instability generated by the thermal bar can lead to convective mixing to a depth of ~600 m.
Show AbstractInvestigation of $1^-_1$ excited states of even-even nuclei
Investigation of $1^-_1$ excited states of even-even nuclei
R. V. Jolos, E. A. Kolganova
General information on the structure and properties of the first excited $1^-$ states of even-even nuclei is given. Poorly-studied characteristics of $1^-$ states which are of interest for study within the framework of the research program at the Compton source of monochromatic gamma rays of ICPM INOC are discussed.
Show AbstractThe laser-electron source of X-ray radiation (from the opening statement at workshop dedicated to the 85th anniversary of B.S. Ishkhanov in SINP MSU on October 26, 2023)
The laser-electron source of X-ray radiation (from the opening statement at workshop dedicated to the 85th anniversary of B.S. Ishkhanov in SINP MSU on October 26, 2023)
I. A. Artyukov$^1$, A. V. Vinogradov$^1$, V. I. Shvedunov$^{1,2}$
The work, as well as the seminar at which it was reported, is devoted to the memory of the outstanding physicist-nuclear scientist, professor of Moscow State University B.S. Ishkhanov, namely his contribution to the research and development of LEXG - laser-electronic X-ray generators. Relevance and prospects of this direction are connected with «gap» between two existing types of X-ray sources: on the one hand - X-ray tubes, and on the other - electronic accelerators, storage rings and free electrons lasers. It’s about a huge difference in their bundle characteristics, cost, scale, energy consumption, etc. The history of modern projects abroad, as well as the LEXG project of MSU - Jilin University, led by Prof. B.S. Ishkhanov, are briefly presented. From the point of view of their applications, the LEXG designs can be divided into two types with different scale of the devices. The first is the use of serial X-ray tubes and the second is radiation medicine, nuclear technology and nuclear physics research. International conferences on LEXG have been held since 2008. The list of these is given in the Annex to the article.
Show AbstractField emission from point diamond cathodes under continuous laser irradiation
Field emission from point diamond cathodes under continuous laser irradiation
V. I. Kleshch, I. R. Anderzhanov, R. R. Ismagilov, A. N. Obraztsov
The presented study investigates the impact of continuous laser irradiation in the visible range on the field emission properties of diamond needle-like micro-sized crystallites with a nanometer tip radius. The measurements were carried out in a vacuum diode configuration with a flat metal anode using DC voltage source. It was found that the field emission current increased under illumination, showing a direct correlation with the radiation power. The relative increase in current under the action of laser irradiation is determined by the parameters of the dark current-voltage characteristic and reaches its maximum value in the region corresponding to the minimum increase in dark current with voltage. It is shown that the most likely mechanism for the increase in current is a change in the electrical resistance of the diamond microneedle as a result of absorption of laser radiation in the presence of electron levels located in the band gap of the diamond associated with impurities or structural defects in the near surface layer of the diamond microneedle.
Show AbstractElectric dipole polarizability of magic nuclei
Electric dipole polarizability of magic nuclei
N. N. Arsenyev, A. P. Severyukhin
The correlations between the electric dipole polarizability and neutron skin thickness are studied by the magic nuclei~$^{40,48}$Ca, $^{68,78}$Ni, $^{132}$Sn, and $^{208}$Pb. The strength distribution of the $E1$~transitions is calculated within the random phase approximation model based on the Skyrme nuclear energy density functional. A comparison with the experimental data has allowed us to constrain the value of the nuclear symmetry energy $J=30-37$~MeV.
Show AbstractThe tardigrade radioprotective protein Dsup (damage suppressor) is resistant\\ to~high doses of ionizing radiation
The tardigrade radioprotective protein Dsup (damage suppressor) is resistant\\ to~high doses of ionizing radiation
M. P. Zarubin$^1$, A. F. Nizamieva$^{1,2}$, S. I. Alexeev$^1$, S. V. Mitrofanov$^1$, Yu. E. Gorshkova$^{1,2}$, E. V. Kravchenko$^1$
The unique Dsup protein of the tardigrade Ramazzottius varieornatus increases resistance to radiation and oxidative stress in various species of organisms and in human cell culture. According to modeling data, Dsup forms a complex with DNA with an intermolecular distance of ~4 Å, as a result of which DNA is less damaged by reactive oxygen species formed during exposure to radiation. However, the stability of the Dsup protein itself under the influence of ionizing radiation remains unclear, which is important for assessing its radioprotective potential and understanding the molecular mechanisms of the action of this protein under conditions of high doses of radiation. In this work, the radiation degradation of the Dsup protein after γ-ray irradiation by small-angle X-ray scattering (SAXS) and protein electrophoresis in polyacrylamide gel under denaturing conditions (SDS-PAGE) was studied for the first time. It has been shown that, in contrast to the control bovine serum albumin, the spatial and structural characteristics of the Dsup protein remain almost unchanged even when exposed to high doses of radiation (5 and 10 kGy), which suggests its high radiation stability.
Show AbstractA model of surface nanorelief formation under gas cluster ion beam irradiation
A model of surface nanorelief formation under gas cluster ion beam irradiation
D. R. Bessmertniy, A. E. Ieshkin
A model for the evolution of surface nanorelief under irradiation with gas cluster ions is proposed. The model is based on consideration of individual collisions of clusters with a surface. The amount of substance sputtered from the collision area and the efficiency of its redeposition onto other surface elements are determined. The performance of the model is shown when compared with experimental data. The stages of smoothing of a harmonic relief are studied. A new measure of the effectiveness of surface smoothing is proposed.
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