Cell theory, as formulated by Theodor Schwann in 1839, introduced the idea that the cell is the main structural unit of living nature. Later, in solving the problem of cell multiplication, Rudolf ...Virchow expanded the cell theory with a postulate: all cells only arise from pre-existing cells. But what did the very first cell arise from? This paper proposes extending the Virchow's law by the assumption that between the nonliving protocell and the first living cell the continuity of fundamental physical properties (the principle of invariance of physical properties) is preserved. The protocell is understood here as a cell-shaped physical system on the basis of the self-organized biologically significant prebiotic macromolecules, primarily peptides, having a potential to transform into the living cell. Biophase is considered as the physical basis of the membraneless protocell, the internal environment of which is separated from the external environment due to the phase of adsorbed water. The evidence is given that the first protocells may have been formed on the basis of intrinsically disordered peptides. Data on the similarity of the physical properties of living cells and the following model systems are given: protein and artificial polymer solutions, coacervate droplets, and ion-exchange resin granules. Available data on the similarity of the physical properties of cell models and living cells allow us to rephrase the Virchow's postulate as follows: the physical properties of a living cell could only arise from pre-existing physical properties of the protocell.
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The results of computational experiments for determining the effect of a mode I surface fatigue crack cross-sectional shape in a rectangular cantilever beam on the characteristics of its free and ...forced bending vibrations with varying cross-sectional dimensions of the crack and its longitudinal position are presented. Finite-element models of beams with 8-node 3D finite elements were developed for carrying out investigations. Three types of a breathing crack cross-section were considered: rectangular, triangular, and trapezoidal one, with the solution of a contact problem to ensure the non-penetration of crack edges. Plots of relative change in the natural frequency of vibration, the amplitudes of the first and second harmonics and their ratios at the main, super- and subharmonic resonances versus the shape, relative area and location of the crack were obtained. It is shown that when bending vibrations of the beam with a rectangular crack, are excited along the axis Oy, there arise displacements only in the direction of driving force, while in the case of triangular and trapezoidal cracks, there arise additional displacements along the axis of minimum stiffness, Oz. It was found that the change in the natural frequency of the beam, as well as the ratio of the amplitudes of dominant harmonics during the recording of vibrations along the excitation axis at the main, super- and subharmonic resonances increase with increasing relative area of the crack cross-section. Under this condition, their largest value was characteristic of a rectangular crack, and the smallest of a triangular one. It was noted that a characteristic indicator of the asymmetric shape of the crack was the appearance of vibrations in the plane perpendicular to the excitation plane.
Carbon films were fabricated on oxidized silicon substrates coated by treated bi-layer catalyst film using a chemical vapor deposition (CVD) method with a short-time acetylene inflow. The films ...consisted of carbon nanotubes and bundles of them, and graphene-like carbon nanostructures. Unusually high magnetic field sensitivity (3000Ω/T) obtained from Hall measurements was observed in the films. The effect of scaling the size of the Hall sensor from carbon films on its magnetic field sensitivity has been investigated. The sensitivity of the Hall sensor with an active area size of 0.13×0.13µm2 was found to be 1140Ω/T, which is much higher than reported in the literature. This carbon material is promising for the fabrication of Hall effect sensors of submicron size.
•Carbon films were grown by CVD method with a short-time acetylene inflow.•The films consisted of CNT and bundles of them, and graphene-like carbon structures.•Magnetic field sensitivity of 3000Ω/T was observed in the carbon films.•The Hall sensor with an active area size of 0.13×0.13μm2 had S=1140Ω/T.
Cross-linking of polysaccharides by metal ions provides polymer gels highly required by industrial applications. In this article, we study the rheological properties and microstructure of solutions ...of a stiff anionic polysaccharide xanthan cross-linked by chromium (III) ions, and we demonstrate that their properties are highly sensitive to the preparation pH. Stable gels are obtained in a wide range of pH from 2.4 to 7.8. The maximum elastic modulus is observed for the gels made at pH 6.3, and by freeze-fracture transmission electron microscopy it is shown that they are characterized by the most dense network structure. However, out of this pH interval, no gelation is observed. At low pH (< 2.4) it is due to high protonation of carboxylic groups of xanthan preventing their interaction with chromium ions, and to the disappearance of oligomeric ions, which are effective in cross-linking. At high pH (> 7.8) the absence of gelation is caused by the transformation of reactive chromium ions into insoluble chromium hydroxide. At the same time, for the gels initially formed at pH 6.3, subsequent change of pH to strongly acidic (1.4) or basic (8.9) medium does not affect appreciably their properties, meaning that chromium cross-links are stable once they are formed. These observations open a reliable route to produce polysaccharide gels with required mechanical properties in a wide pH range where they initially cannot be prepared. It is also shown that the increase of pH to 6.3 of the initially ungelled solution prepared at pH 1.5 results in gelation. This effect offers a facile way for delayed gelation of polysaccharides, which is especially required by oil industry.
The mechanism of synthesis of yttrium-aluminum garnet Y
3
Al
5
O
12
(YAG) from a mixture of yttrium and ammonium carbonates NH
4
Y(CO
3
)
2
∙H
2
O with aluminum and ammonium hydroxycarbonates NH
4
...AlCO
3
(OH)
2
is shown to be different from the mechanism of synthesis from a mixture of hydrated yttrium and aluminum oxides. Calcination of a mixture of hydrated oxides leads to the formation of both Y
3
Al
5
O
12
(YAG) and the impurity phases Y
4
Al
2
O
9
and YAlO
3
, whereas monophase YAG is formed after a mixture of carbonates undergoes calcination. The difference in the mechanism of YAG synthesis is probably due to the difference in particle sizes formed after carbonates and hydrated oxides undergo calcination.
A theoretical study is performed of the interaction between spin current in a strongly spin-orbit-coupled platinum (Pt) conductor and a spin wave in ferromagnetic layers of yttrium iron garnet (YIG) ...with periodic modulation of their thickness under conditions of Bragg resonances and interlayer bond. It is shown that the conditions for two Bragg resonances in the first Brillouin zone in the spin wave spectrum are satisfied in the YIG/Pt/YIG sandwich structure. The spin current in Pt allows the frequency tuning of resonances and control over the depth of the spin wave band gap corresponding to the resonance conditions.
This work is devoted to the study of the composition and structure of thin “spin-on glass” films and xerogels prepared from silica sols containing platinum and palladium compounds, both separately ...and together. The thickness and concentration distribution of Pt/Pd nanoparticles (NPs) in silica films depending on the concentration of precursors of platinum and palladium in silica sols were determined using the method of X-ray reflectometry. The composition and size of Pt/Pd nanoparticles formed in xerogels and thin films were determined in the nanometer and submicron ranges by means of atomic force and transmission electron microscopy of high resolution as well as by means of X-ray diffraction analysis. It was also determined that bimetallic Pt/Pd nanoparticles possess a common crystal lattice forming clusters with the structure of a mixed alloy type.
Highlights
Pt/Pd NPs with bimetallic crystal lattices form from TEOS-derived sols doped with Pt and Pd.
The size of Pt/Pd bimetallic NPs formed in films is 5–6 nm and of the ones formed in xerogels–10–18 nm.
A Pt and Pd concentration gradient is detected in 30–40 nm-thick doped silica films.
Pt/Pd crystallites up to 70 nm in size form at the meso level as well.
This work is devoted to the determination of vibrodiagnostic indicators of the presence of symmetric and annular breathing cracks in cantilever beams at their nonlinear longitudinal vibrations. The ...results of determining the vibrodiagnostic indicators of the presence of cracks, namely, the relative change in the fundamental frequency of longitudinal vibration and the ratio of the amplitudes of the dominant harmonics at the fundamental and superharmonic resonances for different depths and locations of cracks, are presented. To carry out computational studies, various computational models were developed, namely, with concentrated and distributed parameters, beam and volumetric finite element (FE) models, and methods for their research. The use of the model with concentrated parameters consists of the analytical determination of the nonlinearity parameter of the system, which takes into account the change in the stiffness of the system in the presence of damage and is determined by changing the potential deformation energy of the beam due to the opening of the crack during oscillations. The determination of vibrodiagnostic indicators of the presence of a crack using a model with distributed parameters is carried out by solving the differential equation of forced longitudinal vibrations of the second order, where the crack is represented as a section of the beam with a reduced cross-sectional area. The numerical analysis of vibrations of the objects of study with a breathing crack is carried out using the developed beam and volumetric FE models. In the beam FE model, the breathing crack is modeled by a finite element with variable stiffness, and in the volumetric model, it is represented as a mathematical section with the setting of contact interaction conditions for its banks. The main dependences of vibrodiagnostic indicators of the presence of cracks on their parameters are obtained analytically using a model with concentrated parameters and numerically using a beam FE model. To confirm the reliability of the obtained dependences, their individual values are compared with the data obtained for the volumetric FE model, which obviously describes the stress–strain state in the vicinity of the crack most accurately among the proposed models but at the same time requires more computational resources. The obtained numerical dependences of the ratio of the amplitudes of the dominant harmonics of displacements at the main resonance from the place of vibration registration are characterized by fractures in the vicinity of the crack and therefore can be used to determine the location of the crack. According to the results of the analysis of the obtained dependences, it was found that it is practically impossible to determine the location of the crack in this case, since the results obtained for the relative location of the crack in the range from 0.1 to 0.5 are close in values, and the dependences of the vibrodiagnostic indicator on the place of registration of vibrations at superharmonic resonance are uniform and have no fractures.
The amino acid sequences of the coat proteins (CPs) of the potexviruses potato virus X (PVX) and alternanthera mosaic virus (AltMV) share ~40% identity. The N-terminal domains of these proteins ...differ in the amino acid sequence and the presence of the N-terminal fragment of 28 residues (∆N peptide) in the PVX CP. Here, we determined the effect of the N-terminal domain on the structure and physicochemical properties of PVX and AltMV virions. The circular dichroism spectra of these viruses differed significantly, and the melting point of PVX virions was 10-12°C higher than that of AltMV virions. Alignment of the existing high-resolution 3D structures of the potexviral CPs showed that the RMSD value between the C
α
-atoms was the largest for the N-terminal domains of the two compared models. Based on the computer modeling, the ∆N peptide of the PVX CP is fully disordered. According to the synchrotron small-angle X-ray scattering (SAXS) data, the structure of CPs from the PVX and AltMV virions differ; in particular, the PVX CP has a larger portion of crystalline regions and, therefore, is more ordered. Based on the SAXS data, the diameters of the PVX and AltMV virions and helix parameters in solution were calculated. The influence of the conformation of the PVX CP N-terminal domain and its position relative to the virion surface on the virion structure was investigated. Presumably, an increased thermal stability of PVX virions vs. AltMV is provided by the extended N-terminal domain (ΔN peptide, 28 amino acid residues), which forms additional contacts between the adjacent CP subunits in the PVX virion.
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