# Saint Petersburg State University

• Saint Petersburg, Russia
Recent publications
Diode-pumped alkali lasers, possessing high efficiency and narrow linewidth, can provide feasible solutions for wavelength ranges difficult to reach by commercial lasers. In this study, we investigate a generation of coherent blue light (CBL) via four-wave mixing (FWM)-based up-conversion processes in cesium (Cs) vapor. A bichromatic pumping scheme with 852- and 917-nm lasers drives the Cs atoms to the 6D5/2 excited level, followed by cascaded decay of 6D5/2 → 7 P3/2 → 6 S1/2, producing 456-nm CBL under phase matching conditions. The fluorescence in multiple bands from blue to near- and far-infrared in the FWM process is demonstrated under different experimental conditions. To optimize the experimental parameters, we investigate the dependence of 456-nm CBL on the vapor temperature, frequency, and intensity of the two pump lasers. A maximum power of 2.94 mW is achieved with pump powers of 430 mW (for 852 nm) and 470 mW (for 917 nm). The corresponding conversion efficiency is 1.5%/W, three-fold higher than those in previous studies. Our results can contribute to fundamental research on atom—photon interactions and quantum metrology.
The paper studies a bounded symmetric operator Aε in L2(Rd) with(Aεu)(x)=ε−d−2∫Rda((x−y)/ε)μ(x/ε,y/ε)(u(x)−u(y))dy; here ε is a small positive parameter. It is assumed that a(x) is a non-negative L1(Rd) function such that a(−x)=a(x) and the moments Mk=∫Rd|x|ka(x)dx, k=1,2,3, are finite. It is also assumed that μ(x,y) is Zd-periodic both in x and y function such that μ(x,y)=μ(y,x) and 0<μ−⩽μ(x,y)⩽μ+<∞. Our goal is to study the limit behaviour of the resolvent (Aε+I)−1, as ε→0. We show that, as ε→0, the operator (Aε+I)−1 converges in the operator norm in L2(Rd) to the resolvent (A0+I)−1 of the effective operator A0 being a second order elliptic differential operator with constant coefficients of the form A0=−divg0∇. We then obtain sharp in order estimates of the rate of convergence.
Monoamine oxidase (MAO) are flavoenzymes that metabolize neurotransmitter, dietary and xenobiotic amines to their corresponding aldehydes with the production of hydrogen peroxide. Two isoforms, MAO-A and MAO-B, are expressed in humans and mammals, and display different substrate and inhibitor specificities as well as different physiological roles. MAO inhibitors are of much therapeutic value and are used for the treatment of neuropsychiatric and neurodegenerative disorders such as depression, anxiety disorders, and Parkinson’s disease. To discover MAO inhibitors with good potencies and interesting isoform specificities, the present study synthesized a series of 2,1-benzisoxazole (anthranil) derivatives and evaluated them as in vitro inhibitors of human MAO. The compounds were in most instances specific inhibitors of MAO-B with the most potent MAO-B inhibition observed for 7a (IC50 = 0.017 µM) and 7b (IC50 = 0.098 µM). The most potent MAO-A inhibition was observed for 3l (IC50 = 5.35 µM) and 5 (IC50 = 3.29 µM). It is interesting to note that 3-(2-aminoethoxy)-1,2-benzisoxazole derivatives, the 1,2-benzisoxazole, zonisamide, as well as the isoxazole compound, leflunomide, have been described as MAO inhibitors. This is however the first report of MAO inhibition by derivatives of the 2,1-benzisoxazole structural isomer. Graphical abstract
A novel series of cyclometalated platinum(II) complexes bearing acyclic diaminocarbene (ADC) ancillary ligands were designed and prepared. Their photophysical properties were systematically studied through experimental and theoretical investigations. All complexes exhibit green phosphorescence with a quantum efficiency of up to 45% in 2 wt% doped PMMA film at room temperature. The complexes are used as light-emitting dopants for organic light-emitting diode (OLED) fabrication. The devices displayed a green emission with a maximum current efficiency of 2.9 cd A-1 and a luminance of 2700 cd m-2. These results show that these cyclometalated platinum(II) complexes can be used as efficient green emitting components of OLED devices.
The phase formation of complex pyrochlores (space group Fd-3m) Bi2Mg(Zn)1–xNixTa2O9 was investigated during solid-phase synthesis. It was found that the pyrochlore phase precursor in all cases was α-BiTaO4. The pyrochlore phase synthesis reaction proceeds mainly at temperatures above 850–900 °C and consists in the interaction of bismuth orthotantalate with a transition element oxide. The influence of magnesium and zinc on the course of pyrochlore synthesis was revealed. The reaction temperatures of magnesium and nickel (800 and 750 °C, respectively) were determined. The change in the pyrochlore unit cell parameter depending on the synthesis temperature was analyzed for both systems. Nickel–magnesium pyrochlores are characterized by a porous dendrite-like microstructure with a grain size of 0.5–1.0 microns, and the porosity of the samples reaches 20 percent. The calcination temperature does not significantly affect the microstructure of the samples. Prolonged calcination of the preparations leads to the coalescence of grains with the formation of larger particles. Nickel oxide has a sintering effect on ceramics. The studied nickel–zinc pyrochlores are characterized by a low-porous dense microstructure. The porosity of the samples does not exceed 10%. The optimal conditions for obtaining phase-pure pyrochlores (1050 °C and 15 h) were determined.
The chemical composition (including B, Be, Li), the Raman spectrum and the crystal structure evolution (at the temperature range 27–1000 °C) of Mn-bearing, Bi-rich gadolinite subgroup mineral from the Jaguaraçu Pegmatite, Brazil (type-locality of minasgeraisite-(Y)) was studied. Elemental mapping revealed that the crystal being investigated has complex chemical zonation with various Bi (~8-24 wt.% Bi2O3), Ca (~8-10 wt.% CaO) and Y (~11-17 wt.% Y2O3) content. The sample in hand has all specific features of the chemical composition of minasgeraisite-(Y), except Ca excess and, thus, should be considered as hingganite-(Y). The Raman spectrum of the sample under study consists of the number of bands (140, 179, 243, 350, 446, 519, 559, 625, 902, 973, 3224, 3353, 3532 and 3763 cm–1) and is similar to that of hingganite-(Y) / -(Nd). Crystal structure refinement confirmed that the crystal in question should be considered as hingganite-(Y) and is in line with the previously obtained data on gadolinite subgroup minerals from the Jaguaraçu Pegmatite. High-temperature single crystal X-ray diffraction studies revealed that the mineral starts to decompose above 800 °C. We can conclude that beryllosilicates are most stable at high-temperature conditions within the gadolinite supergroup and that species with a higher M-site occupancy have higher stability upon heating.
We study bounded solutions to the fractional equation (-Δ)su+u-|u|q-2u=0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(-\Delta )^s u+u-|u|^{q-2}u=0$$\end{document} in Rn\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathbb R^n$$\end{document} for n≥2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$n\ge 2$$\end{document} and subcritical exponent q>2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$q>2$$\end{document}. Applying the variational approach based on concentration arguments and symmetry considerations which was introduced by Lerman, Naryshkin, Nazarov (Nonlinear Anal. 190:111590, 2020) we construct several types of solutions with various structures (radial, rectangular, triangular, hexagonal, quasi-periodic, breather type, etc.).
Industrial activity results in ton-scale production of calcium carbide and generation of a significant amount of calcium carbide residue (CCR), which is often disposed of in the environment as waste. CCR is an active chemical, and rain washes away alkali from sludge, changing the pH of soils and water and damaging the environment. In this work, we explored new opportunities for the utilization of CCR in view of the coming industrial uptake of digital design and additive technologies. Amazingly, CCR can be successfully used as a filler for the modification of 3D printed materials towards the introduction of hybrid organic/inorganic frameworks. A series of commercially available plastics (PLA, ABS, Nylon, PETG, SBS) were successfully used as matrices for CCR-based composite production with high CCR contents up to 28%. Tensile analyses showed increases in tensile strength and Young’s modulus of 9% and 60%, respectively. Moreover, in comparison with the pure plastics, the CCR-based materials better maintained the digitally designed shape (lower shrinkage). Importantly, CCR-filled materials are 3D printable, making them very promising components in the building sector. Considering the amount of already available CCR stored in the environment, this material is available in large quantities in the near future for hybrid materials, and anticipated opportunities exist in the additive manufacturing sector. The involvement of CCR in practical composite materials is equally important for environmental protection and reuse of already available multiple-ton wastes.
A novel ultra-high-entropy rare earth orthoferrite (UHE REO) of Sc1/16Y1/16La1/16Ce1/16Pr1/16Nd1/16Sm1/16Eu1/16Gd1/16Tb1/16Dy1/16Ho1/16Er1/16Tm1/16Yb1/16Lu1/16FeO3 nominal composition was successfully synthesized for the first time through a simple and efficient solution combustion approach. PXRD, Raman, and 57Fe Mössbauer spectroscopy confirmed the high chemical and phase purity of the synthesized UHE REO (hereafter denoted as ΣREFeO3), which belonged to the Pnma space group, typical of the perovskite-like rare earth orthoferrites. Despite the fact that the main X-ray reflections, vibration modes, and spectral Mössbauer components unambiguously indicate the single-phase nature of the sample, the results of SEM and TEM make it possible to establish the presence of a main (about 50 nm) and a minor ultrafine (about 10 nm) fraction of ΣREFeO3 nanoparticles. The bimodal size distribution of nanoparticles was also reflected in the magnetic behavior of this substance: the presence of several sextet components in the Mössbauer spectra, the hard single-domain magnetic nature of the main fraction of 50 nm UHE REO nanoparticles, and the superparamagnetic state of the minor fraction of 10 nm UHE REO nanoparticles. Thus, the unusual features of nanostructured ΣREFeO3 can potentially be used for the creation of new generations of transformers, magnetic memory systems, magnetic screens, radio devices, etc.
Molecular and stable isotope compositions of hydrate-bound gases collected from 59 hydrate-bearing sites between 2005 to 2019 in the southern and central sub-basins of Lake Baikal are reported. The δ²H of the hydrate-bound methane is distributed between − 310‰ and − 270‰, approximately 120‰ lower than its value in the marine environment, due to the difference in δ²H between the lake water and seawater. Hydrate-bound gases originate from microbial (primary and secondary), thermogenic, and mixed gas sources. Gas hydrates with microbial ethane (δ¹³C: − 60‰, δ²H: between − 310‰ and − 250‰) were retrieved at approximately one-third of the total sites, and their stable isotope compositions were lower than those of thermogenic ethane (δ¹³C: − 25‰, δ²H: − 210‰). The low δ²H of ethane, which has rarely been reported, suggests for the first time that lake water with low hydrogen isotope ratios affects the formation process of microbial ethane as well as methane. Structure II hydrates containing enclathrated methane and ethane were collected from eight sites. In thermogenic gas, hydrocarbons heavier than ethane are biodegraded, resulting in a unique system of mixed methane-ethane gases. The decomposition and recrystallization of the hydrates that enclathrate methane and ethane resulted in the formation of structure II hydrates due to the enrichment of ethane.
The main goal of this study was the elucidation of structures of products of oxidation of industrial hydrolysis lignin (HL) obtained in the system H2O2-H2SO4-H2O. It was found that the obtained oxidized hydrolysis lignin (OHL) contained structural fragments of muconic acid dilactone. The latter appeared as a result of the oxidation of aromatic ring of HL into unstable structures of 3,4-dihydroxyadipic acid, which are spontaneously cyclized into the corresponding fragments of muconic acid dilactone in acidic oxidative medium. Consequent reaction of OHL with aqueous sodium hydroxide (NaOH) led to the formation of sodium salt of OHL (Na-OHL), in which the muconic acid dilactone units of OHL opened into fragments of disodium salts of 3,4-dihydroxyadipic acid. The Na-OHL was transformed into the series of novel derivatives of lignins. Thus, the reaction of Na-OHL with thionyl chloride proceeded as a substitution of hydroxyl groups into chlorine atoms in the structure of OHL, that afforded chloro-derivative of OHL. The latter was transformed into amino-amide and ester-ether derivatives of OHL by nucleophilic substitution of chlorine atoms with amines and alcohols correspondingly.
The paper discusses the line profile asymmetry of the photon scattering process that arises naturally in quantum electrodynamics (QED). Based on precision spectroscopic experiments conducted on hydrogen atoms, we focus our attention on the two-photon 1s-2s transition. As one of the most precisely determined transition frequencies, it is a key pillar of optical frequency standards and is used in determining fundamental physical constants, testing physical principles, and searching constraints on new fundamental interactions. The results obtained in this work show the need to take into account the natural line profile asymmetry in precision spectroscopic experiments.
Metal foams, which are similar to other types of foam materials, are composed of solid material with a significant proportion of the volume consisting of pores. Although metal foams retain some of the properties of the original material, they also possess several advantageous characteristics such as low density and thermal conductivity, high specific stiffness, and porosity. As a result, metal foams are becoming increasingly popular for applications such as heat exchangers, soundproofing devices, and gas–liquid filters. Additive manufacturing has the potential to expand the production capabilities of foams by reducing materials consumption and the creation of complex geometry. This work demonstrates the possibility of direct 3D printing of metal foams made of titanium, aluminum, and aluminum-bronze using direct energy deposition and special parameters of the printing process. This method is superior to traditional methods in terms of cost and the absence of additional stages of preparation and post-processing. The open porosity of the foam can be easily changed by varying the laser power. The laser power in the range of 10 to 180 W along with rapid prototyping makes it possible to obtain metal foams of complex geometry with a high degree of open porosity (up to 50% for titanium and up to 30% for aluminum alloys), not inferior in quality to foams obtained by conventional methods. Moreover, by changing the printing modes, it is possible to adjust the structure of foam from uniform to columnar, increasing the thermal conductivity and insulating properties of the samples.
A comparative SEM study of palp sensory surfaces in 25 caddisfly species representing seven families reveals seven types of sensilla: long trichoid, blunt chaetoid, campaniform, mushroom-like pseudoplacoid, petaloid, thick basiconic and thin basiconic sensilla. Long trichoid and chaetoid sensilla are present on all segments of both pairs of palps. First and second segments of maxillary palps bear groups of long and sclerotised chaetoid sensilla on their medial surface. Other segments of maxillary palps and all segments of labial palps have shorter and thinner chaetoid sensilla mainly on their ventromedial surfaces. Campaniform sensilla usually occur on the first segment of labial palps and second segment of maxillary palps. Mushroom-like pseudoplacoid sensilla may occupy all palp segments or only distal ones. Petaloid sensilla form sensory fields on apical segments of both pairs of palps in most studied species. Thick basiconic sensilla occur only in apical sensory complexes on tips of maxillary and labial palps. A comparison with the Lepidoptera suggests the similarity in palp sensilla and conservative evolution of the palp surface. The reconstructed ground plan for the palp sensory surfaces in Trichoptera and Amphiesmenoptera is provided.
The main manifestations of COVID-19 are primarily interstitial pneumonia and respiratory failure. No less than 20% of patients have variable skin rashes, which try to be interpreted as markers and predictors of the peculiarities of the course of coronavirus infection. In addition, hair loss is a characteristic manifestation of COVID-19, and the salivary follicles are regarded as a target for SARS-CoV-2. The most common variants of alopecia in patients with a new coronavirus infection or vaccine-induced alopecia are acute telogenic, nondescript, and androgenetic alopecia. This review provides information on the most common variants of hair loss in patients with SARS-CoV-2 infection, the features of their manifestations, and possible mechanisms of development. Acute telogenic hair loss is the most common variant of SARS-CoV-2-induced alopecia, is characteristic of patients with subacute course of COVID-19 and can be combined with trichodynia, anosmia and aguvia, which are markers of nervous syste damage. Given the variability in the time of onset after infection, a heterogeneous pathogenesis of alopecia can be assumed. Nested alopecia after COVID-19 is often a relapse of the disease, its severity and frequency do not correlate with the severity of the infectious disease, and its prevalence in women indicates the importance of hormonal factors in its development. Androgenetic alopecia may be a predictor of high risk of infection, severe course, and recurrence of COVID-19. The first two variants of alopecia may be associated with COVID-19 vaccination, and the latter is a predictor of inadequate immune response to vaccine administration. The mechanisms of the damaging effects of SARS-CoV-2 on hair follicles have not been fully deciphered and are most likely complex, with different leading links in different types of hair loss. Deciphering these mechanisms may provide prerequisites for understanding the mechanisms of COVID-19 damage to other tissues and organs.
The results of studying the dielectric permittivity, the third harmonic coefficient, and the DTA signal for Al2O3 nanoporous matrices filled with rubidium nitrate are presented. A shift of the phase transition Tc ≈ 437 K by 3 K to the low-temperature region and an increase in the temperature hysteresis of the phase transition from 14 K for polycrystalline RbNO3 to 33 K for RbNO3 in the pores of the Al2O3 oxide film were found.
Subject. This article considers the reliability of reporting information as one of the most important qualitative characteristics that ensure the usefulness of accounting data to interested users to make management decisions. Objectives. The article aims to articulate an issue of the implemented methodology of research in the field of accounting, aimed at improving the reliability of accounting data. Methods. For the study, I used the methods of analysis, systematization, comparison, and logical generalization. Results. The article presents various definitions of the category of Fairness of Accounting Statements. It finds that compliance with the statutory regulations determines the boundaries of the accounting methodology. However, the statements do not reflect all the accounting events of the enterprise, and what is reflected is not always recorded correctly. In this regard, the perception of reporting data and the interpretation of the results of analysis by users may differ from the meaning implicit in the data, determined by the implemented accounting methodology. This kind of discrepancy between the content of accounting statements, determined by the accounting methodology, and the perception of these data by users can cause a situation that was defined by Russian academic economist, professor Yaroslav V. Sokolov (1938–2010) as the Paradox of Accounting. Quite a number of research papers are devoted to this problem, but most of them are not verified in practice. Conclusions and Relevance. The article concludes that the financial statements, in reality, cannot be reliable, since they are just a simplified model of the financial and operating activities of the enterprise. The results obtained can be considered as a determination of the directions of further research in the field of the Accounting Paradox Theory by Yaroslav V. Sokolov.
Phase-homogeneous LiFePO4 powders have been synthesized. The content of impurity crystalline phases was less than 0.1%, according to synchrotron diffractometry (SXRD) data. Anisotropic crystallite sizes L¯Vhkl were determined by XRD. A low resistance covering layer of mechanically strong ferric-graphite-graphene composite with impregnated ferric (Fe3+) particles < 10 nm in size increases the cycleability compared to industrial cathodes. In accordance with the corrosion model, the destruction of the Fe3+-containing protective layer of crystallites predominates at the first stage, and at the second stage Fe escapes into the electrolyte and to the anode. The crystallite size decreases due to amorphization that starts from the surface. The rate capability, Q(t), has been studied as a function of L¯Vhkl, of the correlation coefficients rik between crystallite sizes, of the Li diffusion coefficient, D, and of the electrical relaxation time, τel. For the test cathode with a thickness of 8 μm, the values of D = 0.12 nm2/s, τel = 8 s were obtained. To predict the dependence Q(t), it is theoretically studied in ranges closest to experimental values: D = 0.5 ÷ 0.03 nm2/s, τel = 8/1 s, average sizes along [010] L¯1 = 90/30 nm, averaged r¯ = 0/1.
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• School of Medicine
• Faculty of Physics
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• Department of Applied Ecology
• Laboratory of Macroecology and Biogeography of Invertebrates
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