High Relative Density Research Articles

Process of Pure Copper Fabricated by Selective Laser Melting (SLM) Technology under Moderate Laser Power with Re-Melting Strategy.

Pure copper (Cu) material, because of its high thermal conductivity, can be 3D printed to fabricate effective thermal management components. However, in the selective laser melting (SLM) process, due to copper's high optical reflectivity, Cu-based parts need to be printed using high laser power. In this study, we demonstrated 3D printing with a re-melting strategy is able to fabricate high-density and low-surface-roughness pure copper parts using only a moderate laser (350 W) power. The effect of the re-scan to initial scan speed ratio on the printing quality resulting from the re-melting strategy is discussed. The re-melting strategy is likened to a localized annealing process that promotes the recrystallization of the newly formed copper microstructures on the re-scan path. Given a hatch spacing of 0.06 mm and a powder layer thickness of 0.05 mm, Cu samples with 93.8% density and low surface roughness (Sa~22.9 μm) were produced using an optimized scan speed of 200 mm/s and a re-scanning speed of 400 mm/s, with a laser power of 350 W. Our work provides an approach to optimize the laser power for printing pure copper 3D parts with high relative density (low porosity) and low surface roughness while ensuring the lifetime stability of the part. The re-melting strategies have broad implications in 3D printing and are particularly relevant for metals with high reflectivity, such as pure copper.

Structural, dielectric, and impedance properties of BiFeO3-GdFeO3 ceramics

The 0.8BiFeO3-0.2GdFeO3 (BFO-GFO) relaxor ferroelectric ceramics were synthesized by solid-state reaction method. Rietveld refinement revealed the co-existence of rhombohedral structure (space group, R3c) and orthorhombic phase (space group, Pn21a). High theoretical relative density (∼98%), significant ferroelectricity (Ps = 4.2 μC/cm2, Pr = 1.8 μC/cm2) and high Currie temperature (522 K−663 K) are measured. High diffuseness behavior with ΔTm = 112 K, γ = ∼1.7–1.9, and full width half maximum of TFWHM = 200 K, reveal excellent relaxor ferroelectric of ceramics. Correlated barrier hopping model (CBH) was used to explain the characteristic of conductivity by fitting the density of stats near Fermi level. Impedance spectrum analysis and the calculated activation energy revealed the ionization of oxygen vacancies contributes the conductance of grains and grain boundaries, respectively.

Microstructure and mechanical properties of pseudo binary eutectic Al–Mg2Si alloy processed by laser powder bed fusion

The traditional wrought Al–Mg–Si alloys fabricated via laser powder bed fusion (LPBF) are prone to hot cracks, unless adding grain refiners in as-LPBFed Al alloys. In this work, the Al-9.6 wt.%Mg-4.9 wt.%Si (equivalent to pseudo binary eutectic Al-13.3 wt.%Mg2Si) alloy with low solidification range and hot-cracking susceptibility was successfully processed by LPBF. The as-LPBFed alloys have reached a high relative density of 99.3% at the VED of 129.6 J/mm3. The microstructures were featured by fine α-Al grains and cellular eutectic Mg2Si, accompanied by a high number density of dislocations, coherent GP zone and α-Al12(Fe,Mn)3Si phases. The as-LPBFed Al-13.3Mg2Si alloy exhibited the high ultimate tensile strength of 557 MPa, yield strength of 439 MPa and elongation of 2.9%. In addition to the grain refinement and dislocation strengthening, the strength enhancement is mainly ascribed to the dispersion strengthening from the divorced nanosized eutectic Mg2Si. The results demonstrate that manipulation of alloys at near eutectic composition is effective to achieve high strength Al–Mg–Si alloys processed by LPBF.

Microstructural and mechanical property evolution of a nuclear zirconium-4 alloy fabricated via laser powder bed fusion and annealing heat treatment

ABSTRACT Zirconium (Zr) alloys are widely used in nuclear energy because of their excellent mechanical properties and low thermal neutron absorption cross-section. This work investigated the printability, microstructure, and mechanical properties of Zr-4 alloy additively manufactured by laser powder bed fusion (LPBF) for the first time. The effect of annealing temperature on the microstructural and the mechanical property evolution of the printed Zr-4 alloy was studied. The results exhibited that the Zr-4 alloy with a high relative density of 99.77% was obtained using optimised printing parameters. With an increase in the annealing temperature, the formed α phase of the Zr-4 alloy changed from an acicular shape to a coarse-twisted shape, and finally to an equiaxed shape. Such microstructure change endowed the alloy with a high compressive strength of 2130 MPa and compressive strain of 36%. When the annealing temperature exceeded 700°C, Zr x (Fe2Cr) compounds were precipitated, strengthening the alloy by pinning effect. These findings provide valuable guidance for the manufacture of geometrically complex Zr alloy parts for nuclear power applications.

Friction and dry sliding wear of Al–Fe–Cr quasicrystals with multi-reinforcements by laser powder bed fusion

A specially designed Al–Fe–Cr alloy with a rapid solidification-induced multi-scaled heterogeneous composite structure was manufactured using a laser powder bed fusion (LPBF) process with a high relative density (over 99.7%) and defect-free features. From the aspect of a single molten pool, the LPBF processed sample presents three regions with distinct composite structures: i) inner laser fusion zone (LFZ); ii) molten pool boundary (MPB) and iii) heat-affected zone (HAZ). For instance, spherical Al–Fe–Cr quasicrystals with sizes ranging from 100 to 300 nm inside ultrafine cellular structures are observed in the laser fusion zone. In contrast, the molten pool boundary exhibits a microstructure containing coarse flower-like quasicrystal particles and rectangular θ-Al13(Fe, Cr)2-4 particles. Moreover, the finer reinforcements in the heat-affected zone are spherical, rectangular or structureless and disperse in the α-Al matrix. This heterogeneous structure can be attributed to the graded temperature and solidification rate inside a single molten pool during LPBF processing. The tribological performance of the QC-reinforced aluminum matrix nanocomposites was comparatively investigated on a ball-on-disc reciprocating tribometer (UMT Tribo), in which the coefficient of friction was recorded. The results show that the LPBF-processed sample presents a stable friction coefficient (0.548) from mild to severe loads with a higher wear resistance of 3.704 × 10- 4mm3/(N*m) than the other LPBF-processed Al alloys. The worn surface morphology analysis shows that the wear mechanism presents a duplex wear mechanism of adhesive and oxidation wear.

Structural and electrical studies of B3+-and-In3+-ion co-doped Li1.3Al0.3Ti1.7(PO4)3 solid electrolytes

In this study, B3+ and In3+ ions were co-doped at the Al3+ sites of Li1.3Al0.3Ti1.7(PO4)3 electrolyte using a solid-state reaction with the goal of obtaining electrolytes with remarkable Li-ion conductivities. B3+-ion doping enhanced the densification of Li1.3Al0.3-yByTi1.7(PO4)3 electrolytes, and Li1.3Al0.22B0.08Ti1.7(PO4)3 electrolyte delivered the highest relative density of 97.6%. Subsequent In3+-ion doping further enhanced densification, and Li1.3Al0.21B0.08In0.01Ti1.7(PO4)3 electrolyte delivered the highest relative density of 98.2%. However, the electrolyte densification diminished rapidly upon further increasing the In3+-ion content. The peaks in the X-ray diffraction patterns of the Li1.3Al0.3-yByTi1.7(PO4)3 and Li1.3Al0.22-xB0.08InxTi1.7(PO4)3 electrolytes were indexed to rhombohedral NASICON-type LiTi2(PO4)3 with the space group R3¯c with trace amounts of LiTiPO5 secondary phase. Upon incorporating In3+ ions into the lattice of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte, the cell volume and the transport channels for Li+ ions were expanded, while B3+-ion incorporation slightly contracted the cell. The scanning electron microscopy and Raman spectroscopy results indicated that B3+-ion substitution into the Li1.3Al0.3Ti1.7(PO4)3 lattice to obtain Li1.3Al0.3-yByTi1.7(PO4)3 electrolytes, which led to the increase in the structural order of the lattices and promoted the formation of microstructures with superior crystallinity and smaller and more uniform grain sizes. Further, B3+ and In3+-ions co-doped Li1.3Al0.22-xB0.08InxTi1.7(PO4)3 electrolytes showed lower structural order, larger grain size, lower grain-size uniformity, and more pore contents than those of undoped Li1.3Al0.3Ti1.7(PO4). The ionic conductivities of the Li1.3Al0.3-yByTi1.7(PO4)3 electrolytes increased with increasing concentration of B3+-ion dopant and reached a maximum of 8.35× 10−4 S/cm for Li1.3Al0.22B0.08Ti1.7(PO4)3. Among the Li1.3Al0.22-xB0.08InxTi1.7(PO4)3 electrolytes, Li1.3Al0.21B0.08In0.01Ti1.7(PO4)3 presented the highest ionic conductivity of 1.08 × 10−3 S/cm, which was closely correlated to its high relative density. The contribution of electronic conductivity to total conductivity was found to be trivial.

Enhanced electrochemical properties of NASICON-type Na3Zr2Si2PO12 solid electrolytes with Tb3+-ions-assisted sintering

The new-type NZSP solid-state electrolytes with enhanced ion transport properties were synthesized by using lanthanide rare-earth Tb3+ ions assisted-sintering. The Na3+xZr2-xTbxSi2PO12 (x = 0, 0.1, 0.2, 0.3, 0.4) solid-state electrolytes were characterized by X-ray diffraction analysis, scanning electron microscopy, and AC impedance testing. The effects of different Tb3+ contents on the phase composition, microstructure morphology, and electrochemical performance were investigated. The results showed that both Na3Zr2Si2PO12 and Na3Tb(PO4)2 phases are formed in the solid electrolytes by Tb3+-ions-assisted sintering. The formation of a new phosphate phase regulates the Si/P ratio of the dominant electric phase, enhances the Na+ occupation, and helps to enhance the mobility of sodium ions. The introduction of an appropriate amount of Tb3+ ions has a soldering-like effect, which can effectively improve the densification of ceramics and further improve the ionic conductivity by promoting grain fusion and reducing the grain boundary concentration. At room temperature, the ceramic with the composition Na3.2Zr1.8Tb0.2Si2PO12 exhibits a high relative density of 97.03% and the highest ionic conductivity of 6.32 × 10−4 S·cm−1 and with a low activation energy of 0.22 eV. In addition, the Na3Tb(PO4)2 grain boundaries phase with low electronic conductivity can limit the transfer of electrons and reduce the electronic conductivity of the NASICON electrolytes, so that the tolerance of solid-state electrolytes against Na dendrite growth is strongly enhanced. The Tb3+-ion-assisted sintering strategy can provide a valuable reference for improving the electrochemical performance of fast ion conductors.

Far from equilibrium ultrafast high‐temperature sintering of ZrO2–SiO2 nanocrystalline glass–ceramics

AbstractUltrafast high‐temperature sintering (UHS) is a novel sintering technique with ultrashort firing cycles (e.g., a few tens of seconds). The feasibility of UHS has been validated on several ceramics and metals; however, its potential in consolidating glass–ceramics has not yet been demonstrated. In this work, an optimized carbon‐free UHS was utilized to prepare ZrO2–SiO2 nanocrystalline glass–ceramics (NCGCs). The phase composition, grain size, densification behavior, and microstructures of NCGCs prepared by UHS were investigated and compared with those of samples sintered by pressureless sintering. Results showed that NCGCs with a high relative density (～95%) can be obtained within ～50 s discharge time by UHS. The UHS processing not only hindered the formation of ZrSiO4 and cristobalite but also enhanced the stabilization of t‐ZrO2. Meanwhile, owing to the ultrashort firing cycles, the UHS technology allowed the NCGCs to be consolidated in a far from equilibrium state. The NCGCs showed a microstructure of spherical monocrystalline ZrO2 nanocrystallites embedded in an amorphous SiO2 matrix.

Characterization of negative thermal expansion material Zr2-xTixWP2O12 with MgO

In this study, it is executed to obtain [Formula: see text] ([Formula: see text], 0.10, 0.15, 0.20) ceramics with high relative density, 0–0.9 wt% MgO was added as a sintering aid. The influence of MgO amount and relative density on the coefficient of thermal expansion for [Formula: see text] was also investigated. Pure and monophase of Zr[Formula: see text]Ti[Formula: see text]WP2O[Formula: see text] with MgO has been obtained and MgO used sintering aid was doped in the crystal. The coefficients of thermal expansion of the 0.9 wt% MgO-doped sample and MgO-free sample were [Formula: see text] ppm/K and [Formula: see text] ppm/K, respectively. This result suggests that doping of MgO does not have an influence on the coefficient of thermal expansion. In other words, adding MgO increases sintering properties without change in the coefficient of thermal expansion.

Study of densification mechanism of Si3N4 added with MgO by spark plasma sintering

Spark plasma sintering, as a novel powder solidification technology, is applied in this study to sinter Si3N4/MgO powder. The highest relative density [Formula: see text] of 97.14% and Vickers hardness of 1650[Formula: see text]HV are obtained at a soaking temperature of 1750∘C. A steady-state creep mode is utilized to study the densification mechanism of the Si3N4/MgO powder by computing its densification rate [Formula: see text] and further effective stress exponent [Formula: see text] in the soaking period. The results show that [Formula: see text] at soaking temperatures ranging between 1600∘C and 1650∘C, which indicates that its densification mechanism is grain boundary sliding. By contrast, [Formula: see text] at the aforementioned constant soaking temperature ranges indicates that its densification mechanism transformed into dislocation climb-dominated creep. With the soaking temperature further increasing to 1700–1750∘C, the densification mechanism is revealed to be grain boundary diffusion at [Formula: see text]. In addition, the activation densification [Formula: see text] of the Si3N4/MgO powder is calculated to be 206[Formula: see text]kJ/mol at soaking temperatures ranging between 1600∘C and 1650∘C under the determined [Formula: see text].

A PRELIMINARY SURVEY OF TREE SPECIES DIVERSITY: A CASE STUDY OF FEDERAL UNIVERSITY WUKARI

The impact of anthropogenic activities on tree species diversity of a selected sub-sample of the Federal University Wukari Campus comprising of four sampling Sites (A, B, C and D) was investigated using the Shannon-Wiener, Margalefs and Menhinik diversity indices. Tree felling is the commonest human activity. The infrastructural developments and anthropogenic activities among the four sampling sites ranges from low to high. A total of 203 individual tree species of 20 species from 15 families was encountered in the study area. The dominant families were Arecaceace, Fabaceae, Anacardiaceae, Lamiaceae and Moraceae. Elaies guineensis (80) was the most dominant tree species with the highest relative density (RD) of 39.4% at Site D while the lowest RD of 0.49 were encountered at Sites A, B and C. The most abundant tree species were Elaies guineensis and Mangifera indica due to their economic importance. About 35% of the trees were exotic while 65% were native. A high Shannon-Wiener index value of 0.78 and Margalefs index value of 14.869 were observed. Analysis of the diversity indices of the 20 species reveals the sensitivity of the Shannon-Wiener index than the Margalefs index, though the two indices shows relative diversity of tree species according to their ranges. The high population size of the indigenous trees with higher economic uses is a strong indicator of loss of tree genetic resources that play critical roles in local diversification of the ecosystems to make them more resilient for what is to come with respect to climate change regulation.

Facile Production Method of PbS Nanoparticles via Mechanical Milling of Galena Ore

In this research, some physical properties such as the density, specific heat capacity, and micro-hardness of galena ore lumps purchased from the public market were determined. The microscopic study, using the scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), confirmed that the as-received galena ore was mostly lead sulfide (PbS). The XRD pattern of the galena powder also elucidated that all the peaks were assigned to PbS. In addition, the as-received galena was roughly crushed, and fine-milled using a high-vibration milling machine with tungsten carbide rings. Nanoscale particles of about 90 nm were produced in a very short milling time of around 15 min. The obtained nanoscale powder was well investigated in the SEM at low and high magnifications to assess the exact range of particle size. Meanwhile, the SEM was employed to investigate the microstructure of sintered samples, where a part of the milled galena powder was compacted and sintered at 700 °C for 2 h. Again, the result of this investigation proved the formation of PbS with even smaller grain size compared with the grain size of the starting galena ore. A high relative sinter density of approximately 97% for galena powder was achieved by sintering under vacuum.

Monotonic and cyclic undrained behaviour and liquefaction resistance of pumiceous, non-plastic sandy silt

Experimental data related to the mechanical behaviour of crushable pumiceous soils are limited compared with those for hard-grained soils. The main focus of previous studies has been on pumiceous sands, whereas pumiceous silts have not been investigated to date. In this paper, several series of monotonic and cyclic triaxial tests were performed to investigate the undrained behaviour and liquefaction resistance of a natural volcanic-ash derived, non-plastic pumiceous silt from northern New Zealand. Particle crushing due to sample reconstitution and triaxial testing was analysed by quantifying the changes in grain-size parameters and pumice contents. The main results can be summarized as follows. (1) The pumiceous silt showed a contractive response, even at medium to high relative densities, leading to high flow liquefaction susceptibility. (2) When subjected to cyclic undrained loading, the silt exhibited similar trends in terms of excess pore water pressure and axial strain accumulation to those established for hard-grained soils as opposed to those for pumiceous sands. (3) The liquefaction resistance of both medium-dense and dense samples was within the lower range compared to published cyclic resistance curves of both hard-grained soils and pumiceous sands. (4) The material did not undergo significant particle crushing after testing. Result (4) was considered to be the main factor that contributed to the fact that, in general, the cyclic undrained behaviour of the pumiceous silt was close to the trends established for those of hard-grained soils.

Dynamics of stochastic-constrained particles

Prior studies have focused on the overall behavior of randomly moving particle swarms. However, the characteristics of the stochastic-constrained particles that form ubiquitously within these swarms remain oblivious. This study demonstrates a generalized diffusion equation for stochastic-constrained particles that considers the velocity and location aggregation effects observed from their parent particle swarm (i.e., a completely random particle swarm). This equation can be approximated as the form of Schrödinger equation in the microcosmic case (low relative density) and describe the dynamics of the total mass distribution in the macrocosmic case (high relative density). The predicted density distribution of the particle swarm in the stable aggregation state is consistent with the total mass distribution of massive, relaxed galaxy clusters (at least in the range of r<r_{textrm{s}}), preventing cuspy problems in the empirical Navarro–Frenk–White profile. This study opens a window to observe the dynamics of stochastic-constrained particles from a third perspective, from which the aggregation effect of particles without gravitation can be saw.

Effect of Zr4+ on Lithium-Ion Conductivity of Garnet-Type Li5+xLa3(Nb2−xZrx)O12 Solid Electrolytes

Garnet-type structured electrolytes are considered a key technology for the next generation of lithium-ion batteries such as all-solid-state batteries. Cubic Garnet-type solid oxides with composition Li5+xLa3(Nb2−xZrx)O12 (x between 0 and 1.5) were synthesized by solid-state reaction and sintered by spark plasma sintering. Powder characterization indicates the formation of solid solution with high chemical homogeneity and spherical particles. High relative densities (&gt;96%) were obtained by spark plasma sintering at 950 °C for 10 min and pressure application of 50 MPa. Although the formation of secondary phase La2Zr2O7 was identified by the X-ray diffraction patterns of Zr-doped pellets, it has been eliminated for x = 0.75 and 1 by conventional heat treatment at 850 °C for 1 h. High ionic conductivity values were attained for x ≥ 0.75, reaching a maximum value in the order of 10−4 S.cm−1 at 25 °C with activation energy of 0.38 eV. The results indicated that Zr4+ promoted significant increasing of the lithium-ion conductivity by lowering the activation energy.

Spark plasma sintering of translucent polycrystalline α/β‐silicon nitride ceramics with Y2O3 additive

Translucent polycrystalline α/β‐silicon nitride ceramics had been fabricated for the first time by spark plasma sintering from α-Si3N4 starting powder with 2 wt% Y2O3. It aimed to investigate the influence of process parameters on the phase evolution, microstructural development, and mechanical properties of sintered ceramics. The increase in sintering temperature from 1750 °C to 1800 °C under 25 MPa considerably raised relative density, promoted α-β phase transformation, increased hardness and fracture toughness values, and exhibited translucency in the visible region. Furthermore, the highest relative density (98%), hardness (∼HV: 14.9 GPa), fracture toughness (∼9.8 MPa m1/2) values, and a higher degree of translucency were achieved with the increment of uniaxial pressure from 25 to 50 MPa at 1750 °C. These results indicated that translucent polycrystalline α/β‐silicon nitride ceramics, produced by liquid phase assisted spark plasma sintering at 1750 °C under 50 MPa, can be used as transparent armors and visible windows under harsh conditions.

Effect of CaO additive on the densification of MgO and MgO-YGAG:Ce ceramics

Highly transparent MgO ceramic was prepared by hot isostatic pressing (HIP) technique of vacuum-sintered MgO compact using CaO as the sintering additive. Densification process of MgO ceramic is significantly enhanced by doping 0.5 at% CaO at the vacuum-sintering temperature of 1100–1350 °C. By subsequent HIP sintering at 1650 °C, the relative density of 0.5% CaO-doped MgO ceramic vacuum-sintered at 1350 °C increases from 94.67% to 99.97%. It attains high in-line transmittance of 70.78% at 600 nm and 87.59% at 6000 nm, respectively. Meanwhile, the thermal conductivity reaches 53.2 W/(m∙K), demonstrating that CaO-doped MgO is a promising candidate material as the secondary phase of phosphor composite ceramics. Herein, 0.5% CaO-doped MgO-YGAG:Ce (Y2.82Gd0.18Al5O12:Ce) composite ceramic with stable binary-phase structure, high relative density of 99.1% and thermal conductivity of 32.6 W/(m∙K) was synthesized by vacuum-sintering at 1350 °C and the luminescence performance under blue laser excitation was evaluated.

Development of Fe-Mn-Si-Cr-Ni shape memory alloy with ultrahigh mechanical properties and large recovery strain by laser powder bed fusion

This work systematically studied the effect of volumetric energy density E on the densification, microstructures, tensile mechanical properties, and shape memory performance of a Fe-Mn-Si-Cr-Ni shape memory alloy (SMA) fabricated by laser powder bed fusion (L-PBF). An E of 90–265 J/mm3 is suggested to fabricate the Fe-Mn-Si-Cr-Ni SMA with minor metallurgical defects and a high relative density of above 99%. The increase in E can promote the formation of the primary γ austenite and the solid phase transformation from the primary δ ferrite to the γ austenite, which helps to achieve a nearly complete γ austenitic microstructure. The increase in E also contributes to fabricating the Fe-Mn-Si-Cr-Ni SMA with superior comprehensive mechanical properties and shape memory performance by L-PBF. The Fe-Mn-Si-Cr-Ni SMA with a combination of good ductility of around 30%, high yield strength of above 480 MPa, an ultrahigh ultimate tensile strength of above 1 GPa, and large recovery strain of about 6% was manufactured by L-PBF under a high E of 222–250 J/mm3. The good shape memory effect, excellent comprehensive mechanical properties, and low cost of Fe-Mn-Si-Cr-Ni SMAs, as well as the outstanding ability to fabricate complex structures of L-PBF technology, provide a solid foundation for the design and fabrication of novel intelligent structures.

Manufacturing and Characterization of Dental Crowns Made of 5-mol% Yttria Stabilized Zirconia by Digital Light Processing.

We herein report manufacturing of dental crowns made of 5-mol% yttria partially stabilized zirconia (5Y-PSZ) with desired mechanical properties, optical translucency and dimensional accuracy using digital light processing (DLP). To this end, all processing parameters were carefully controlled and optimized. First, 5Y-PSZ particles with a bimodal distribution were prepared via calcination of as-received granules and subsequent ball-milling and then used to formulate 5Y-PSZ suspensions with a high solid loading of 50 vol% required for high densification after sintering. Dispersant content was also optimized. To provide high dimensional accuracy, initial dimensions of dental crowns for 3D printing were precisely determined by considering increase and decrease in dimensions during photopolymerization and sintering, respectively. Photopolymerization time was also optimized for a given layer thickness of 50 μm to ensure good bonding between layers. A multi-step debinding schedule with a slow heating rate was employed to avoid formation of any defects. After sintering at 1500 °C for 2 h, 5Y-PSZ could be almost fully densified without noticeable defects within layers and at interfaces between layers. They had high relative densities (99.03 ± 0.39%) with a high cubic phase content (59.1%). These characteristics allowed for achievement of reasonably high mechanical properties (flexural strength = 625.4 ± 75.5 MPa and Weibull modulus = 7.9) and % transmittance (31.4 ± 0.7%). In addition, 5Y-PSZ dental crowns showed excellent dimensional accuracy (root mean square (RMS) for marginal discrepancy = 44.4 ± 10.8 μm and RMS for internal gap = 22.8 ± 1.6 μm) evaluated by the 3D scanning technique.

Region-wise analysis of beef cow movements in Japan.

Animal movement is an important factor in the transmission of animal infectious diseases. A better understanding of movement patterns is therefore necessary for developing effective control measures against disease spread. In Japan, a cattle tracing system was established in 2003, following a bovine spongiform encephalopathy epidemic, and the information on all cattle movements has been stored in a national database maintained by the National Livestock Breeding Center. Using these data, we previously analyzed the movement of dairy cows, concluding that heterogeneities in cattle movement are associated with regional and seasonal factors. In the present study, we aimed to identify specific factors affecting the regional and seasonal movement patterns of beef cows in Japan. From April 2012 to March 2017, 797,553 farm-to-farm movement events were recorded. We analyzed movements by month and by cattle age and looked at the frequency of movement within and between seven regions spanning the national territory. Our results show that calf movement peaked at 9-10 months old; these movements were considered to be via the market and were frequent within and between regions. For inter-regional movements, Kyushu region was the top producer of calves for calf trading markets throughout Japan. With regard to intra-regional movements, round-trip movements for summer grazing were observed in May and October for cattle of various ages in the northern regions, especially Hokkaido and Tohoku. Moreover, the movements of Japanese Shorthorn breeds in Tohoku region exhibited consistent annual peaks in May and October/November, in accordance with their seasonal breeding practice. In the areas with high relative densities of dairy cows, such as Hokkaido, the shipping of newborn beef calves produced via embryo transfer to dairy cows was also observed. Overall, understanding the patterns of beef cow movement will help develop effective disease surveillance measures, such as pre-movement inspections focused on specific regions and types of movement.