The effects of melamine on gas production (GP) kinetics, methane (CH4) production and fermentation of diets differing in forage content (low-forage (LF) diet: 200 g/kg and high-forage (HF) diet: ...800 g/kg) by rumen micro-organisms in vitro were studied using batch cultures. Rumen contents were collected from three Simmental×Luxi crossbred beef cattle. Melamine was added to the incubation bottles to achieve final concentration of 0 (control), 2, 6, 18, 54, 162 and 484 mg/kg of each diet. Cumulative GP was continuously measured in an automated gas recording instrument during 72 h of incubation, while fermentation gas end-products were collected to determine molar proportions of carbon dioxide (CO2), CH4 and hydrogen gas (H2) in manually operated batch cultures. Differences in GP kinetics and fermentation gases were observed in response to the nature of the diets incubated. Although melamine addition did not affect GP kinetics and fermentation gas pattern compared to the control, the increase of melamine addition stimulated the yield of CH4 by decreasing CO2, especially during the fermentation of the HF diet. The concentrations of ammonia nitrogen (N), amino acid N and microbial N in culture fluids were greater in the fermentation of LF- than HF diets, and these concentrations were increased by the increase of melamine addition after 72-h fermentation. The concentrations of total volatile fatty acids (VFA) were greater in HF than LF diets. The addition of melamine decreased total VFA concentrations and this response was greater in HF than LF diet fermentations. Melamine addition did not affect molar proportions of acetate, butyrate, propionate and valerate compared with the control; however, branched-chain VFA production, which was lower in the HF than the LF diet, was increased by the melamine addition, especially in the HF diet fermentation. The ratio of non-glucogenic to glucogenic acids was lower in the HF than the LF diet, but it was not affected by melamine addition. In brief, the greater reduction in the rate and extent of rumen fermentation found for the HF diet in comparison with the LF diet suggested that rumen fermentation rate and extent in vitro depended mainly on the nature of the incubated substrate, and that they could be further inhibited by the increase of melamine addition.
In this study, the insertion of both Al and Cr atoms into SiC matrix has been experimentally evidenced by X-ray diffraction, Raman scattering, elements analysis and magnetic measurements. Structure ...analysis showed that (Al, Cr)-codoped SiC has a single-phase 4H-crystal structure and no trace of any other impurity phases were detected. Raman scattering showed that several new features appeared in (Al, Cr)-codoped 4H-SiC: (1) the vanishing of the folded longitudinal-optical phonons modes-plasmon coupling (FLOPC) modes with
x=(
q/
q
B)=0; (2) an obvious absorbing peak was found in Si
1−
x−
y
Al
x
Cr
y
C with
y=0.0203
at%; (3) folded transverse-optical (FTO) mode shifts to high frequency and linewidths full widths at half maximum (FWHM) decrease with increase in Cr content. Magnetic properties characterizations showed that weak ferromagnetism order is established. With increase in Cr content, the magnetization decreased. No clear influence of Al doping on the magnetic properties of codoped 4H-SiC is evidenced while the magnetic origin should be ascribed to be induced by Cr. It is speculated that doping Cr elements at Si sites destroy the effective coupling of the spins induced by Al doping. The major role of Al is to stabilize the codoped crystal structure as 4H-single-phase.
► We found that codoping Al and Cr elements can also be realized in SiC lattice. ► No traces of any other impurities phase were detected by various characterizations means. ► In other words, codoping strategy of using (Al, TM) elements is useful to approach natural magnetic properties of TM-doped SiC.
On the basis of a size-dependent cohesive energy model originally proposed for spherical nanoparticles, we develop an analytical model for the first time to determine the size- and shape-dependent ...catalytic activation energy of platinum nanoparticles through the introduction of a shape factor. The catalytic activation energy E a(λ,D) was found to decrease with the decreasing size D or increasing shape factor λ, where the size effect is the principle factor and the shape effect is secondary. For platinum nanoparticles with the same size, the order is E a(cube) > E a(sphere) > E a(octahedron) > E a(tetrahedron) because λtetrahedron > λoctahedron > λsphere > λcube. The accuracy of the developed model was verified by the available experimental results.
► FCG rate decreases and FCG lives increase with the increase of laser energy. ► The reductions of FCG rate by LP in initial and final FCG stage are analyzed. ► Fatigue striation spacing of FCG ...region decreases with the increase of laser energy. ► Numerical model of FCG rate and FCG lives under RS induced by LP is established. ► Reasonable agreements are obtained between experimental and numerical results.
Effects of laser energy on fatigue crack growth (FCG) properties of 6061-T6 aluminum alloy subjected to multiple laser peening (LP) were investigated. LP experiments and typical FCG experiments were performed on the compact tension (CT) samples. In order to reveal the enhancement mechanism of laser energy on FCG properties through residual stress (RS), a numerical model of effective stress intensity factor (SIF) was established. The results showed that compressive RS induced by LP can effectively decrease FCG rate and increase FCG lives of CT samples. The experimental results and numerical analysis correlated with each other.
The hardness and the elastic modulus of Cu films with thickness (@it) and grain size (@id) have been investigated by nanoindentation tests. The @id and the indentation depth increase linearly with ...the increase in @@it.@ The hardness rises with the decrease in @it, whereas the elastic modulus is independent of @it and it is about 20% less than conventional coarse-grained Cu. The enhanced hardness is attributed to the smaller @id and the indentation depth. The analysis of load-displacement curves indicates that the scope of the critical shear stress for different thick Cu films ranges from 3.2 to 4.1 GPa, which is similar to the theoretical shear stress of single crystalline Cu. The present results are explained by the dislocation mediated mechanism even if @id reaches about 16.4 nm for the Cu film with @it = 180 nm.
Nanoindentation creep tests were carried out at the maximum indentation load from 500 to 9000
μN to study the indentation size effect (ISE) on the creep behavior of amorphous, nanocrystalline (NC) ...bcc and NC tetragonal Ta films. For NC bcc and tetragonal Ta films, the creep strain rate
ε
˙
decreases and stress exponent
n increases with enhanced peak loads or indent depth, and are therefore both indentation size dependent. However, an inverse ISE on
ε
˙
and
n is found for amorphous Ta films. The difference of the ISE is attributed to the distinct creep deformation process. Several creep mechanisms including self-diffusion along the indenter/specimen interface, grain boundary diffusion and sliding, and dislocation climb have been introduced to interpret the ISE for NC Ta films. The inverse ISE on amorphous Ta films is explained by the shear transformation zone theory.
The laser peening coverage areas over the central-hole of Ti–6Al–4V alloy specimens can significantly affect the final rupture morphologies, including the FCI location, crack front, and even the ...fatigue striation spacing (FSS). Display omitted
•Residual stress trends induced by LP with different coverage areas were revealed.•Fatigue fracture microstructures induced by LP with different coverage areas was studied.•Evolution of FCI and FCG as well as dislocations was systematically demonstrated.•Strengthening mechanism of residual stress and surface nanocrystallization was investigated.
Laser peening (LP) with different coverage areas was carried out on Ti–6Al–4V titanium alloy specimens. Residual stresses, fatigue lives and fracture morphologies of specimens subjected to LP were analyzed. The LP-induced compressive residual stresses under different coverage areas were revealed in the superficial layer. The results show that LP coverage area has significant effect on fatigue response and fracture behavior. The decreased fatigue striation spacing and increased dislocations observed in the treated specimens further confirmed the effect of LP on decelerating fatigue crack growth (FCG). In addition, the strengthening mechanism of LP-induced compressive residual stress and surface nanocrystallization was theoretically investigated.
The evolution of interfacial structures and creep behavior of Cu/Ta multilayers at room temperature were investigated as the individual layer thickness (hL) varies from 2.5 to 100nm. The interface ...structures exhibit different configurations at different length scales. The main crystal phase in Ta layers changes from α-Ta to β-Ta with the increase of hL from 5 to 10nm, and amorphous regions appear at the interface when hL=25nm. These variations affect the creep behaviors deeply. The creep stress exponent (n) increases with the decreasing hL and reaches maximum at hL=5nm. According to the variation of n values, the creep behavior is dominated by the dislocation climb from the grain boundaries in Cu layers to the heterogeneous interfaces between two constituent when decreasing the hL. In addition, the change of Ta phases also contributes a lot to the stress exponent at several nanometer scale.
In this paper, we prepared alloying Ti/Ni multilayers through changing modulation periods (λ) and subsequent annealing. Strain rate sensitivity of the multilayers was investigated by nanoindentation. ...It was found that the multilayer became full alloying with the highest value of hardness at λ=5.4nm. Both the alloying degree and the corresponding hardness are remarkable dependent on λ. Only the multilayers accompanied by obvious stress-induced pop-in events exhibit negative strain rate sensitivity resulted from stress-induced martensitic transformation, while hardness of the other multilayers does not change with strain rate. In addition, the critical load for the first pop-in increases with strain rate, meaning that larger stress is needed to induce martensitic transformation at higher strain rate.
Abstract
The Lobster Eye Imager for Astronomy (LEIA), a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe mission, was successfully launched onboard the SATech-01 satellite of the ...Chinese Academy of Sciences on 2022 July 27. In this paper, we introduce the design and on-ground test results of the LEIA instrument. Using state-of-the-art Micro-Pore Optics (MPO), a wide field of view of 346 square degrees (18.°6 × 18.°6) of the X-ray imager is realized. An optical assembly composed of 36 MPO chips is used to focus incident X-ray photons, and four large-format complementary metal-oxide semiconductor (CMOS) sensors, each of size 6 cm × 6 cm, are used as the focal plane detectors. The instrument has an angular resolution of 4′–8′ (in terms of FWHM) for the central focal spot of the point-spread function, and an effective area of 2–3 cm
2
at 1 keV in essentially all the directions within the field of view. The detection passband is 0.5–4 keV in soft X-rays and the sensitivity is 2–3 × 10
−11
erg s
−1
cm
−2
(about 1 milliCrab) with a 1000 s observation. The total weight of LEIA is 56 kg and the power is 85 W. The satellite, with a design lifetime of 2 yr, operates in a Sun-synchronous orbit of 500 km with an orbital period of 95 minutes. LEIA is paving the way for future missions by verifying in flight the technologies of both novel focusing imaging optics and CMOS sensors for X-ray observation, and by optimizing the working setups of the instrumental parameters. In addition, LEIA is able to carry out scientific observations to find new transients and to monitor known sources in the soft X-ray band, albeit with limited useful observing time available.
