Zone Center Research Articles

Управление противопожарными расстояниями от стоянки автотранспортного средства до зданий, сооружений промышленного назначения

The analysis was carried out concerning the regulatory requirements for fire safety aimed at preventing the spread of fire from the parking lot of motor vehicles to various buildings and structures located on the territory of industrial use, as well as an analysis of fires on the motor vehicles. The need is shown related to applying a calculation estimate of the possibility of ignition of a fire-hazardous irradiated material from the effect of a radiated heat flux during a fire for establishing a fire-prevention distance. To assess the fulfillment of fire safety requirements aimed at preventing the spread of fire with the subsequent establishment of a fire-prevention distance from the parking lot of motor vehicles, it is required to implement the calculated scenarios. Scenarios should consider the type (body, opening), the location of the surface (front, rear, side) and its calculated values, the number of motor vehicles, the burning and irradiated materials with their calculated values, the location of the irradiated material relative to the radiating surface (centered, perpendicular, outside zone center). They are based on the mechanism of ignition of the irradiated material from the action of a radiant heat flux during the combustion of a motor vehicle. The practical use of this technique will allow to simulate the threat of propagation of the radiated heat flux to nearby protection objects, to establish a safe distance from the parking of motor vehicles to various buildings and structures for industrial purposes, and to make decisions on the compliance of protection objects with fire safety requirements. To carry out calculations to determine the safe fire-prevention distance from the parking lots of motor vehicles, a computer program was developed for the computer “Assessment of the safe distance from the boundaries of open areas of motor vehicles”. Its practical application will significantly simplify the procedure associated with the assessment of compliance with fire safety requirements aimed at preventing the spread of fire from the parking lot of the motor vehicle to buildings and structures for industrial purposes and will allow to set the value of the safe fire distance between them.

Age Determination of the Azov Anchovy Engraulis encrasicolus maeoticus (Engraulidae) Based on the Otolith Image Analysis

To specify the age determination of the Azov anchovy Engraulis encrasicolus maeoticus, the length of otoliths of the age 0+ fish and the radii of annual rings in the otoliths of individuals of different age groups have been analysed. The otoliths of 380 fish caught in the Sea of Azov in October–November 2018 and off the northwestern coast of the Caucasus in February 2019 have been analyzed. The ImageJ software has been used for measuring the maximum otolith length and plotting the reflected light intensity profiles along the length of the otolith transect. In the fingerlings (0+) with an average total length of 70.9 ± 6.7 mm, in October–November, the otolith radius averaged 0.95 ± 0.08 mm, while in February, with an average 66.6 ± 10.6 mm, it was 0.86 ± 0.15 mm. In the smallest fish (48–55 mm), the distance from the core of the otolith to the edge of the white opaque zone varied from 0.54 to 0.72 mm (on average, 0.63 ± 0.04 mm). According to the averaged data, the radii to the center of the dark hyaline zone of otoliths for different age groups of anchovy are: R1, 0.94 ± 0.09; R2, 1.23 ± 0.08; and R3, 1.40 ± 0.07 mm. The present study is aimed at developing automatic methods for determining the age of fish from light intensity profile peaks on otolith images.

Inelastic Neutron Scattering Study of Phonon Dispersion Relation in Higher Manganese Silicides

We report inelastic neutron scattering (INS) measurements of the phonon dispersion relation in higher manganese silicides (HMSs). A large ingot of HMS is synthesized using a slow cooling method, which is found to have Mn15Si26 as the primary phase. The sample is composed of highly oriented crystallites as confirmed by a neutron pole-figure study and thermal conductivity data. Our INS results are mostly consistent with earlier experimental and theoretical phonon studies in HMS, including the presence of a low-lying twisting mode. However, some discrepancies are also observed. Most notably, a 5 meV gap at the zone center and the softer dispersion relation of the low-lying twisting mode. We discuss the potential origins of these observations and their implications for the thermal properties of HMS.

Phonon transition across an isotopic interface

Isotopic mixtures result in distinct properties of materials such as thermal conductivity and nuclear process. However, the knowledge of isotopic interface remains largely unexplored mainly due to the challenges in atomic-scale isotopic identification. Here, using electron energy-loss spectroscopy in a scanning transmission electron microscope, we reveal momentum-transfer-dependent phonon behavior at the h−10BN/h-11BN isotope heterostructure with sub-unit-cell resolution. We find the phonons’ energy changes gradually across the interface, featuring a wide transition regime. Phonons near the Brillouin zone center have a transition regime of ~3.34 nm, whereas phonons at the Brillouin zone boundary have a transition regime of ~1.66 nm. We propose that the isotope-induced charge effect at the interface accounts for the distinct delocalization behavior. Moreover, the variation of phonon energy between atom layers near the interface depends on both of momentum transfer and mass change. This study provides new insights into the isotopic effects in natural materials.

Spatial distribution characteristics of plumes induced by femtosecond laser ablation of silicon in vacuum

The spatial distribution characteristics of plumes induced by femtosecond laser ablation of silicon in vacuum are studied by using spectroscopy. The plume spatial distribution clearly shows two zones with different characteristics. The center of the first zone is at a distance of approximately 0.5 mm from the target. Silicon ionic radiation, recombination radiation, and bremsstrahlung mainly occur in this zone, causing an exponential decay with a decay constant of approximately 0.151–0.163 mm. The second zone with a greater area, whose center is at a distance of approximately 1.5 mm from the target, follows the first zone. In this zone, the radiation from silicon atoms and electron-atom collisions dominates, leading to an allometric decay with an allometric exponent of approximately − 1.475 to − 1.376. In the second zone, the electron density spatial distribution is approximately arrowhead-shaped, which is potentially induced by collisions between ambient molecules and the particles in front of the plume. These results indicate that both the recombination effect and expansion effect play important roles and compete with each other in plumes. The recombination effect is dominant near the silicon surface, causing exponential decay. As the distance increases, the electron density decreases exponentially by recombination, causing a more intense expansion effect.

A cross-sectional survey on the allocation of nursing human resources in burn centers in China

Objective: To investigate the allocation of nursing human resources in burn centers in China. Methods: A cross-sectional survey was conducted. Using a self-designed questionnaire, a survey was carried out from January to March 2022 to investigate the January to December 2021 status of 39 burn centers in China that met the inclusion criteria based on six strategic regions and other regions, including the hospital grade and the region, the number of nurses and opening beds in the burn centers and burn intensive care units (BICUs), the age, working seniority in burn specialty, educational background, professional title, personnel employment, and turnover of nurses and training of newly recruited nurses in the burn centers. Results: This survey covered 30 provinces, municipalities, and autonomous regions in China (excluding Hong Kong Special Administrative Region, Macao Special Administrative Region, and Taiwan region of China). A total of 39 questionnaires were collected, all of which were valid. The 39 burn centers were located in 38 tertiary A hospitals and 1 tertiary B hospital, with 26 burn centers in strategic areas. The nurse/bed ratio of burn centers in the Greater Bay Area of Guangdong, Hong Kong, and Macao was the highest, while the nurse/bed ratio of burn centers in border ethnic minority area was the lowest. Except for the Chengdu-Chongqing Economic Circle, BICUs had been set up in burn centers in other regions. Among the 39 burn centers, the percentage of nurses aged 25 to 34 years was 51.21% (738/1 441), the percentage of nurses worked in burn specialty for less than 5 years was 31.16% (449/1 441), the percentage of nurses with bachelor's degree was 69.74% (1 005/1 441), and the percentage of nurses with nursing professional title was 44.14% (636/1 441), which were the highest. There were significant differences in the employment of nurses, the percentage of permanent nurses in burn centers in the collaborative development zone of Beijing-Tianjin-Hebei was 82.48% (113/137), while the percentage of permanent nurses in burn centers in important military strategic area was only 9.42% (34/361); the turnover rate of nurses was 9.03% (143/1 584), among which the turnover rate of nurses was 18.14% (80/441) in burn centers in important military strategic area. The training for newly recruited nurses in 39 burn centers was mainly based on the guidance of senior nurses and the pre-job education+specialist training. Conclusions: The burn nursing human resources in strategic areas in China are seriously insufficient and unevenly distributed, with unstable nurse team and lack of standardized specialist training. In particular, the nursing human resources in BICUs need to be equipped and supplemented urgently.

Effect of magnetic order on longitudinal Tomonaga-Luttinger liquid spin dynamics in weakly coupled spin- 12 chains

The quantum many-body interactions in one-dimensional spin-$\frac{1}{2}$ systems are subject to Tomonaga-Luttinger liquid (TLL) physics, which predict an array of multiparticle excitations that form continua in momentum-energy space. Here we use inelastic neutron spectroscopy to study the TLL spin dynamics in ${\mathrm{SrCo}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$, a compound which contains weakly coupled spin-$\frac{1}{2}$ chains of Co atoms, at 0.05 K and in a longitudinal magnetic field up to 9.0 T. The measurements were performed above 3.9 T, where the ground-state N\'eel antiferromagnetic (AFM) order is completely suppressed and the multiparticle excitations are exclusively of the TLL type. In this region and below 7.0 T, the longitudinal TLL mode---psinon/antipsinon (P/AP)---is unexpectedly well described by a damped harmonic oscillator (DHO) while approaching the zone center defining the static spin-spin correlations. A non-DHO-type, continuumlike signal is seen at higher fields, but deviations from the ideal one-dimensional TLL still remain. This change in the P/AP mode coincides with the phase transition between the longitudinal spin density wave (LSDW) and transverse AFM order. Inside the LSDW state, the DHO-type P/AP spectral weight increases and the linewidth broadens as the magnetic order parameter decreases. These results reveal the impact of three-dimensional magnetic order on the TLL spin dynamics; they call for beyond-mean-field treatment for the interchain exchange interactions.

Anisotropic Phonon Scattering and Thermal Transport Property Induced by the Liquid-like Behavior of AgCrSe2.

Superionic conductors exhibiting a periodic crystalline lattice and liquid-like ionic conductivity have emerged as promising materials in energy-conversion devices. Herein, we have investigated the interplay among anharmonic lattice dynamics, thermal conduction, and ultrafast atomic diffusion across the superionic transition of AgCrSe2. We show that the thermal conductivity (κ) contributions from convection and conduction-convection interactions increase simultaneously due to the gradual fluidization of Ag atoms, leading to a temperature-independent κ in the superionic state. We demonstrate a non-Peierls type thermal transport behavior induced by the strong lattice anharmonicity of Ag atoms, which promotes a nontrivial wave-like phonon tunneling in the normal state of AgCrSe2. Our current fluctuation analysis demonstrates an anisotropic phonon-liquid scattering behavior that the in-plane nondispersive transverse acoustic (TA) phonons near the zone boundary collapse, while the zone center and boundary TA phonons in the direction perpendicular to the liquid-like flow of Ag atoms survive.

First-principles study of structural, electronic and vibrational properties of bulk and monolayer TiS2

In this paper the structural, electronic and vibrational properties of 3D bulk and 2D layer of TiS2 are studied. The PBE-GGA ansatz in the density functional theory together with the van der Waals interaction are considered deploying the plane wave pseudopotential method. The properties such as lattice parameters, elastic constants, bulk modulus, electronic band structure and the density of states of the ground state of hexagonal 3D bulk and 2D layered TiS2 are presented. The vibrational frequencies at the centre of the Brillouin zone are also reported. Effect of strain is seen on the electronic properties of the monolayers of TiS2. The results of the structural, electronic and vibrational properties are well in agreement with the available experimental results. The study finds that both bulk and monolayer TiS2 are semimetals with a small overlapping of bands near Fermi level. The band overlapping increases in the bulk TiS2 on applying pressure. The magnitude of phonon vibration frequencies increases with pressure. The monolayer TiS2 becomes metal when negative strain (compression) along xy plane is applied. On the contrary positive strain (tensile) opens an indirect bandgap in the monolayer TiS2.

Magnetic phase diagrams of the pyrochlore-based magnets: Landau theory

The family of crystals with a pyrochlore lattice, including pyrochlores, spinels, and Laves phases (C15) is a fertile playground for the discovery and scientific study of exotic magnetic properties as well as search for new technological applications. In this work a possible magnetically long-range ordered phases derived from the archetypical pyrochlore lattice were studied within the Landau phase transition theory. A group-theoretical analysis reveals the existence of 20 low symmetrical phases, generated by the magnetic order parameters associated with the center of the Brillouin zone. For each of these phases, the symmetry-related magnetic and structural parameters were determined and discussed in detail. We extend this analysis by means of the thermodynamic theory: on the ground of the sixth-degree thermodynamic potential phase diagrams of the spin-ordered pyrochlore-based magnets are constructed in the exchange approximation. It is shown that an essential feature of all studied phase diagrams is the existence of singular elements: multiphase points, multicritical points of different types, lines of phase transitions of both the first and second order.

Experimental observations of communication in blackout, topological waveguiding and Dirac zero-index property in plasma sheath.

The plasma sheath causes the spacecraft's communication signal to attenuate dramatically during the re-entry period, which seriously threatens the astronauts. However, valid experimental protocols have not been obtained hitherto. To realize the propagation of electromagnetic waves in negative permittivity background of the plasma sheath, alumina columns are embedded in the plasma background to form plasma photonic crystals, which can support the coupling of evanescent waves between the alumina columns. We experimentally demonstrate the realization of communication in blackout scenario by achieving a complete passing band in the plasma cutoff region. For high frequency communications in the plasma sheath, electromagnetic wave propagation based on topological edge states is also experimentally demonstrated. Furthermore, we realize a triply-degenerate Dirac cone formed dynamically at the center of the Brillouin zone by modulating the electron density, where electromagnetic wave exhibits high transmittance and does not experience phase accumulation at the Dirac point. Our work thus not only provides an effective approach to overcome the communication blackout problem, but the design can also be served as a promising experimental platform to explore topological electromagnetic phenomena.

A study on convection in molten zone of aluminum alloy during Fe/Al resistance spot welding

Aluminum alloys are increasingly being applied to automobile bodies to reduce the weight of automobiles. In joining steel materials and aluminum alloys using resistance spot welding(RSW), it is important to control the state of intermetallic compounds due to the temperature at the joining interface. In other words, in RSW of Fe/Al dissimilar materials, it is necessary to clarify the heating and cooling phenomena of the interface temperature during joining. Although the convection behavior of the molten aluminum alloy is thought to influence the temperature distribution at the joining interface, there are no studies that have directly observed this phenomenon. In this study, convection in molten zone of aluminum alloy during RSW of steel and aluminum alloy is discussed. Direct observations were attempted in order to clarify the convection behavior of the molten aluminum alloy in RSW of steel and aluminum alloy. The main feature of this experiment is that a real-scale test piece and an RSW apparatus used in actual production were used to observe convection during actual production. The observation experiments were conducted using synchrotron radiation X-ray at SPring-8. During welding, the specimens were irradiated with synchrotron radiation X-ray, and convection was observed from the behavior of tracer particles placed on the specimens. As a results, three types of convection were observed: radial outward convection from the center of the molten zone at the joining interface, convection from the edge of the molten zone toward its center, and weak circulating convection at the edge of the molten zone. And, small convection velocities were generated at the edge of the molten zone. Furthermore, the convection velocity inside the molten zone was calculated to be approximately 1.75 m/s. In addition, it was shown that there is a correlation between convection behavior and the shape of the molten zone.

Emergence of Dirac cone in CsPbBr3 perovskite-based two-dimensional photonic crystals

In this paper, it has been proposed that all-inorganic perovskite materials can be used to design and fabricate two-dimensional (2D) photonic crystals. The theoretical study performed here shows that these perovskite-based 2D photonic crystals exhibit a Dirac cone dispersion. In this study, cesium lead bromide (CsPbBr3) having rectangular shapes of varying widths (50, 100, and 150 nm) and a fixed height of 300 nm are arranged in a regular manner with a lattice constant of 500 nm. The pattern of these photonic crystals exhibits C4v symmetry. It has been observed when these perovskite materials, arranged in a rectangular shape, are having a certain dimension; they display a Dirac cone dispersion at the centre of the Brillouin zone at a frequency close to peta-hertz. Further, these photonic crystals are used to manipulate the propagation of electromagnetic (EM) waves of frequency ∼4 × 1014 Hz. Near this frequency, the photonic crystals respond as a nearly zero refractive index material, which allows passing EM waves even in presence of an obstacle. This study can be expanded to design and fabricate two-dimensional photonic crystals based on various perovskite materials.

Influence of interlayer temperature on microstructure and mechanical properties of TiAl alloys in wire and arc additive manufacturing

TiAl intermetallics have attracted widespread attention in the aerospace and automotive fields. This study focuses on the in-situ fabrication of TiAl alloys by auxiliary wire gas metal arc (GMA) additive manufacturing in which pure Ti and Al wires are melted to form a eutectic molten pool. The effects of interlayer temperature on forming characteristics, microstructure, and mechanical properties of TiAl alloys were studied, i.e., 30, 170, 330, and 500 °C. As the interlayer temperature increases, the macro-cracks gradually disappear, the layer width increases, and the layer height decreases. The center and lower parts of the homogeneous zone in the middle region present dendritic and interdendritic γ phases. However, these parts exhibit equiaxed α2/γ nearly-lamellar colonies and massive γm phase at an interlayer temperature of 500 °C. The thicknesses of α2/γ fully-lamellar colonies in the homogeneous zone increase as the interlayer temperature increases. With the increasing interlayer temperature, the total average microhardness first decreases and then increases, the compressive strength mainly presents a decreasing trend, and the compression rate increases first and then decreases. The maximal compressive strengths in the vertical and horizontal directions are 1802.5 and 1814.3 MPa, respectively. By changing the interlayer temperature from 30 to 330 °C, the compression rates in both directions increase by 11.8 % and 13.4 %, respectively.

Magma transport along structural boundaries in the upper crust: insights from broad-band magnetotelluric constraints on the structure beneath Unzen volcano, Japan

SUMMARY Unzen volcano, located on Shimabara Peninsula, Nagasaki, Japan, is an active volcano that has been intensively monitored since 1989, one year before the most recent eruption in 1990–1995. Previous earthquake and surface deformation studies have revealed that magma is transported obliquely from a magma reservoir beneath Tachibana Bay, to the west of Shimabara Peninsula. Here, we conduct broad-band magnetotelluric (MT) surveys at 99 sites around Shimabara Peninsula to investigate the crustal structure beneath Unzen volcano that is related to magma migration. A 3-D resistivity model that is constructed from 25 broad-band MT sites and 45 telluric sites shows a broad high-resistivity zone beneath Shimabara Peninsula and low-resistivity zones to the west and east of the peninsula. An unexpected observation is the spatial alignment of the high-resistivity zone with a seismic low-velocity zone (LVZ) at 3–15 km depth. Quantitative analysis indicates this high-resistivity zone contains < 0.7 per cent melt under the assumption that the melt is stored in a good porosity network, while < 11 per cent melt in relatively poor pore network. We infer this high-resistivity, LVZ to be a highly crystallized mush zone (HCMZ) with low permeability. The hypocentres and pressure sources of the 1990–1995 eruption are distributed along the boundary between the high- and low-resistivity zones beneath the western part of the peninsula. We therefore conclude that the magma migrated along a structural boundary that possessed a relatively high permeability. Previous studies have suggested that eruptible magma is usually transported vertically upward through the centre of the mush zone, whereas the present results reveal that magma can be transported along the upper boundary of an HCMZ.

Dynamic vapor and keyhole behavior, and equiaxed dendrite formation in blue laser processing of copper

A coupled Cu vapor and keyhole numerical model including a simple virtual mesh refinement method was developed to investigated the Cu vapor and keyhole behavior in blue laser processing of a copper material. Electron backscatter diffraction (EBSD) was adopted to measure the crystal structure of the fusion zone. The Cu vapor mainly flowed upwards above the keyhole, while some downward flows were observed inside the keyhole. The recoil force and Marangoni stress caused the melt at the keyhole wall to flow downwards, and the Marangoni stress caused the melt at the pool edge to flow outwards. Owing to the multiple reflections and high absorption rate, the total blue laser energy efficiency can be as high as 83.1%. The EBSD, numerical and theoretical results indicated that the blue laser favored the fine equiaxed dendrite formation in the center of the fusion zone, which was attributed to the higher value of the cooling rate G × R, where G is the temperature gradient and R is the solidification rate, and the lower value of G/R at this location, unlike the previously studied infrared laser processing case.

In search of Pca21 phase ferroelectrics

In recent years, hafnia-based ferroelectrics have attracted enormous attention due to their capability of maintaining ferroelectricity below 10 nm thickness and excellent compatibility with microelectronics flow lines. However, the physical origin of their ferroelectricity is still not fully clear, although it is commonly attributed to a polar Pca21 orthorhombic phase. The high-temperature paraelectric phases (the tetragonal phase or the cubic phase) do not possess a soft mode at the Brillouin zone center, thus the ferroelectric distortion has to be explained in terms of trilinear coupling among three phonon modes in the tetragonal phase. It is necessary to explore new materials with possible ferroelectricity due to the polar Pca21 phase, which in turn should be very helpful in evaluating the microscopic theory for ferroelectric hafnia. In this work, based on the idea of the Materials Genome Engineering, a series of hafnia-like ferroelectrics have been found, exemplified by LaSeCl, LaSeBr, LuOF and YOF, which possess adequate spontaneous polarization values and also relatively favorable free energies for the polar phase. Their common features and individual differences are discussed in detail. In particular, a promising potential ferroelectric material, Pca21 phase LuOF, is predicted and recommended for further experimental synthesis and investigation.

Two-dimensional Dirac fermions in a mass superlattice

We study two-dimensional (2D) Dirac fermions in the presence of a periodic mass term alternating between positive and negative values along one direction. This scenario could be realized for a graphene monolayer or for the surface states of topological insulators. The low-energy physics is governed by chiral Jackiw-Rebbi modes propagating along zero-mass lines, with the energy dispersion of the Bloch states given by an anisotropic Dirac cone. By means of the transfer matrix approach, we obtain exact results for a piecewise constant mass superlattice. On top of Bloch states, two different classes of boundary and/or interface modes can exist in a finite-size geometry or in a nonuniform electrostatic potential, respectively. We compute the dispersion relation for both types of boundary and interface modes, which originate either from states close to the superlattice Brillouin zone (BZ) center or, via a Lifshitz transition, from states near the BZ boundary. In the presence of a potential step, we predict that the interface modes, the Bloch wave functions, and the electrical conductance will sensitively depend on the step position relative to the mass superlattice.

Overcoming the strength-ductility trade-off in additive manufactured AlSi10Mg plates by friction stir welding at a low rotational speed

The main problem in post-treatment of laser powder bed fusion (L-PBF) AlSi10Mg is the sharp reduction in strength when the ductility enhances, i.e. the problem of strength-ductility trade-off. Friction stir welding (FSW) at a low rotational speed of 200 rpm was employed to join AlSi10Mg plate produced by laser-powder bed fusion in conjunction with overcoming the strength-ductility trade-off. The microstructure, texture, and mechanical properties of the as-built and friction stir welded samples were examined. FSW resulted in the elimination of porosities, formation of ultrafine-grains with an average grain size of 0.7 μm, increment in dislocation density and Taylor factor, and fragmentation of Si particles. In addition, after FSW, B/B¯ and C shear texture components were mainly formed in the center of the stir zone, while at the shoulder-dominated zone the A1∗(111)[1¯1¯2] and A2∗(111)[112¯] components might be formed. The main grain structure formation mechanism was continuous dynamic recrystallization occurring by a gradual increase in misorientation of low angle grain boundaries and geometrically dynamic recrystallization. Consequently, tensile elongation was enhanced by ≈173%, while a negligible decrease in strength (≈9%) was observed. During tensile loading, the joint was fractured from the stir zone by the initiation of cracks from the surface of the sample, resulting in a bimodal dimple structure.

Exploring and machine learning structural instabilities in 2D materials

We address the problem of predicting the zero-temperature dynamical stability (DS) of a periodic crystal without computing its full phonon band structure. Here we report the evidence that DS can be inferred with good reliability from the phonon frequencies at the center and boundary of the Brillouin zone (BZ). This analysis represents a validation of the DS test employed by the Computational 2D Materials Database (C2DB). For 137 dynamically unstable 2D crystals, we displace the atoms along an unstable mode and relax the structure. This procedure yields a dynamically stable crystal in 49 cases. The elementary properties of these new structures are characterized using the C2DB workflow, and it is found that their properties can differ significantly from those of the original unstable crystals, e.g., band gaps are opened by 0.3 eV on average. All the crystal structures and properties are available in the C2DB. Finally, we train a classification model on the DS data for 3295 2D materials in the C2DB using a representation encoding the electronic structure of the crystal. We obtain an excellent receiver operating characteristic (ROC) curve with an area under the curve (AUC) of 0.90, showing that the classification model can drastically reduce computational efforts in high-throughput studies.