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• TiN is a highly effective grain refiner for additive manufacture (AM) of 316 steel. • δ-ferrite is the primary solid phase during AM of the 316 steel. • Grain refinement in the TiN-inoculated 316 steel was inherited from the refinement of δ-ferrite. • Grain refinement led to dislocation-based deformation mechanism in the TiN-inoculated 316 steel. • TiN inoculation led to the superior strength-ductility synergy in the 316 steel. As a potent grain refiner for steel casting, TiN is now widely used to refine γ-austenite in steel additive manufacturing (AM). However, the refining mechanism of TiN during AM remains unclear despite intensive research in recent years. This work aims to boost our understanding on the mechanism of TiN in refining the γ-austenite in AM-fabricated 316 stainless steel and its corresponding effect on the mechanical behaviour. Experimental results show that addition of 1 wt.% TiN nanoparticles led to complete columnar-to-equiaxed transition and significant refinement of the austenite grains to ∼2 µm in the 316 steel. Thermodynamic and kinetic simulations confirmed that, despite the rapid AM solidification, δ-ferrite is the primary solid phase during AM of the 316 steel and γ-austenite forms through subsequent peritectic reaction or direct transformation from the δ-ferrite. This implies that the TiN nanoparticles actually refined the δ-ferrite through promoting its heterogenous nucleation, which in turn refined the γ-austenite. This assumption is verified by the high grain refining efficiency of TiN nanoparticles in an AM-fabricated Fe-4 wt.%Si δ-ferrite alloy, in which δ-ferrite forms directly from the melt and is retained at room temperature. The grain refinement is attributed to the good atomic matching between δ-ferrite and TiN. Grain refinement in the 316 steel through 1 wt.% TiN inoculation not only eliminated the property anisotropy but also led to a high strain-hardening rate upon plastic deformation and thereby a superior strength-ductility synergy with yield strength of 561 MPa, tensile strength of 860 MPa and elongation of 48%. [Display omitted] [ABSTRACT FROM AUTHOR]

• High performance Cu matrix Fe particle reinforced nanocomposite was fabricated. • Fast cooling and small solidification units in L-PBF suppressed the segregation. • Incorporating 8 wt.% Fe into pure Cu promoted heterogeneous nucleation of Cu grains. • Ageing enabled the nanoprecipitation of coarser BCC α-Fe and smaller FCC γ-Fe. • FCC γ-Fe with a diameter of 10-35 nm exhibited coherent interfaces with the Cu matrix. Liquid-liquid phase separation, and the resulted solute segregation, during conventional solidification have been a long-term challenge to produce copper (Cu)-iron (Fe) immiscible composites with high strength and high conductivity. The present work reports an effective solution to this issue through laser powder bed fusion (L-PBF) in-situ alloying of Cu-8 wt.% Fe. Microstructure observation showed that the fast cooling within micron-scale melt pools fully eliminated the Fe segregation and therefore the L-PBF fabricated nanocomposite achieved the homogeneous microstructure, which featured equiaxed fine grains around 1 µm in size. Ageing of the nanocomposite at 600°C for 1 h enabled precipitation of two types of nanoparticles. One is coarser Fe nanoprecipitates with body-centered cubic (BCC) structure and diameter of 100-300 nm, mainly distributing along grain boundaries. The other is smaller Fe nanoprecipitates with face-centered cubic (FCC) structure and diameter of 10-35 nm, being observed within the grains and having coherent interfaces with the Cu matrix. As a result, the aged Cu-Fe nanocomposite achieved tensile strength of 462.9±6.6 MPa with 30.4%±1.7% elongation to failure and 74.5% IACS (International Annealed Copper Standard) electrical conductivity. The formation mechanisms of the nanoprecipitates and the strengthening mechanisms of the nanocomposite are discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel cost-effective compositionally complicated alloy was designed and fabricated. • Nanoprecipitates-decorated heterogeneous lamella structure was produced by thermomechanical process. • The alloy with heterogeneous lamella structure demonstrated a comparable tensile property. • The formation mechanism of the heterogeneous lamella structure and the associated strengthening mechanisms was revealed. A heterogeneous lamella (HL) design strategy was applied to manipulate mechanical properties of a new cost-effective Fe 35 Ni 35 Cr 25 Mo 5 compositionally complicated alloy (CCA). The HL structure was produced by single-step heat treatment (800 °C for 1 h) after cold rolling. This HL structure consists of alternative lamellae regions of coarse-grained FCC matrix (5‒20 μm), and regions containing ultra-fine grains or subgrains (200‒500 nm) together with nanoprecipitates (20‒500 nm) and annealing twins. As compared with other cost-effective CCAs, the 800 °C annealed sample with HL structure demonstrated a comparable tensile property, with yield strength over 1.0 GPa and total elongation of ~13%. Formation of the annealing twins and nanoprecipitates decorated HL structure was a result of the concurrent partial recrystallization and precipitation of σ phase at the shear bands with a high density of lattice defects (e.g. high-density dislocation walls and deformation twins). The latter restricted the growth of recrystallized grains, leading to the formation of ultrafine subgrains within the HL structure. The high yield strength resulted from the multistage hetero-deformation induced (HDI) strengthening and precipitation strengthening associated with heterogeneous lamella structures containing nanoprecipitates. The ductility was originated from the coexistence of multiple deformation mechanisms, which started with dislocation slip and formation of stacking faults at the initial stage, followed by nano-twinning at the higher strain level. This HL design strategy, comprising composition and thermomechanical process designs, and the resultant microstructure tuning, open a broader window for the development of cost-effective CCAs with enhanced performance. [Display omitted] [ABSTRACT FROM AUTHOR]

Pancreatic islet transplantation remains a promising approach to the treatment of type 1 diabetes. Unfortunately, graft failure continues to occur because of immunologic rejection, despite the use of potent immunosuppressive [...]

Understanding the densification behaviours and formation mechanisms of defects are essential to fabricate high quality and high strength aluminium components using selective laser melting (SLM) technology. In this work, the effects of laser power and scanning speed on the densification, defects evolution and their formation mechanisms in a SLMed 2024 aluminium (Al) alloy were investigated in consideration of the corresponding laser energy input, melting mode transition and microstructural evolution. The results showed that optimizing the processing parameters effectively reduced the porosity level below 1% by avoiding the lack of fusion and keyhole melting mode, and minimizing the gas pores. However, optimization of the processing parameters could not eliminate the columnar structure associated with the SLMed 2024 Al alloy, which contributed to the hot-tearing cracks in the SLMed parts. It was found that the dependence of porosity formation on SLM processing parameters was contrary to the crack density. Hence, to further improve the SLM-processability of the 2024 Al alloy it is necessary to develop SLM methods in order avoid the hot-cracking within the optimized processing parameter window associated with the minimum porosity formation. [ABSTRACT FROM AUTHOR]

• The Fe 35 Ni 25 Cr 25 Mo 15 eutectic high entropy alloy (HEA) is a pseudo eutectic alloy. • The pseudo eutectic HEA consists of Mo-Cr enriched σ phase and Fe-Ni enriched FCC phase. • Spheroidization behaviour commenced above 800 °C. • Instability of the lamellar structure at elevated temperature results from migration of high-density faults. • Spheroidization treatment was invalid for the ductility improvement of brittle pseudo-eutectic HEA. A cost-effective Fe-enriched eutectic high-entropy alloy (EHEA), Fe 35 Ni 25 Cr 25 Mo 15 , was designed and prepared to avoid the use of expensive Co that is commonly used in HEAs. However, the as-cast Fe-enriched EHEA was associated with brittleness. The present work aims to evaluate the possibility and feasibility of spheroidization of the lamellar structure of the EHEA in order to improve the ductility. Due to the high cooling rate of arc-melting, the as-melted Fe 35 Ni 25 Cr 25 Mo 15 EHEA was found to be a pseudo eutectic alloy comprised of alternant σ phase (Cr 0.22 Mo 0.18 Fe 0.6 -type intermetallic) and face centred cubic (FCC) phase. The lamellar structure in the Fe-enriched EHEA remained stable up to 800 °C. The instability of the lamellar structure occurred at temperatures over 800 °C, which was resulted from migration of high-density faults (i.e. lamellar termination and ledges in the lamellae). However, the Fe 35 Ni 25 Cr 25 Mo 15 EHEA still exhibited brittleness even after spheroidization at 1100 °C for 168 h due to the formation of the hard and brittle σ matrix in the pseudo Fe 35 Ni 25 Cr 25 Mo 15 EHEA as a result of decomposition of the lamellar structure. Therefore, in contrast to the softening of traditional eutectic alloys, spheroidization treatment was considered as invalid to improve the ductility of pseudo-eutectic HEA with high fraction of intermetallic phase. The present work provides a valuable reference for those who aim to improve the ductility of brittle EHEA through spheroidization. [ABSTRACT FROM AUTHOR]

Quantum state joining has been recently experimentally demonstrated [C. Vitelli et al., Nat. Photon. 7, 521 (2013)] which can transfer two input photonic qubits into a photonic ququart. Here, we revisit these processes from a hybrid point of view. By exploring (he giant optical circular birefringence induced by quantum-dot spins in one-sided optical microcavities, we introduce some deterministic joining schemes including two quantum-dot spin joining, hybrid photon and quantum-dot spin joining, and two-photon joining. The input quantum information is represented by one photon with polarization and spatial mode degrees of freedom (DOFs). These schemes are also adapted to the inverse processes called quantum state splitting because all the joining procedures are unitary and do not require projection and feed-forward steps. The fused photon is convenient for realizing elementary logic gates such as the controlled-NOT (CNOT) gate, SWAP gate, and Toffoli gate. These hybrid fusion and splitting schemes provide flexible synthesis of the quantum-dot spin and photon in quantum applications. The transmission superiority of photons and storage superiority of the quantum-dot spin may be combined for quantum network communication or quantum computations. [ABSTRACT FROM AUTHOR]

Multiqubit quantum gates are natural quantum operations derived from various decompositions of quantum evolutions. Recently, linear-depth quantum circuits were proposed for an arbitrary n-qubit Toffoli gate with ancillary qubits [M. Saeedi and M. Pedram, Phys. Rev. A 87, 062318 (2013)]. Their circuits are based on an equivalent representation of the not gate regardless of the global phase. However, we find that this equivalence cannot be extended to the controlled-not gate or the n-qubit Toffoli gate. By reevaluating their circuits, we argue that their linear-depth quantum circuits could realize the joint operations of an n-qubit Toffoli gate and an n-qubit phase-flip gate. [ABSTRACT FROM AUTHOR]

A single photon encoded in both the spin and the orbital angular momentum has recently been experimentally demonstrated [X.-L. Wang et al., Nature 518, 516 (2015)] with linear optics using the hyperentangled state, which can be viewed as a bipartite four-dimensional (ququart) entanglement. Here, we investigate this process from a general point of view. By exploring a controlled phase flip induced by atomic ensembles in one-side optical microcavities, we propose teleportations of general ququart systems including a two-atomic-ensemble system, a two-polarized-photon system, one photon with the polarization and spatial degrees of freedom (DOFs), and a hybrid photon-ensemble system using two hyperentangled photons. The output information may also be encoded by different physical systems up to the special requirements of a receiver. These schemes are also adapted to teleportation of a ququart system with only phases or real probability amplitudes, which is beyond previous superdense teleportation [Nature Commun. 6, 7185 (2015)]. With these restrictions, half of the classical communication cost may be saved and experimental complexities are also reduced. Our theoretical schemes are feasible in modern physics and show the possibilities of transferring complex quantum systems for scalable quantum applications. [ABSTRACT FROM AUTHOR]

The influence of group-velocity-dispersion (GVD) effects on the propagation of femtosecond laser pulses in air at different pressures is investigated by numerically solving the extended nonlinear Schrödinger equation. It is observed that GVD has a great influence on the collapse distance Lc of the self-focusing short laser pulses when the pressure is relatively high (e.g., 10 atm), in which case the semiempirical formula describing the collapse distance of self-focusing laser pulse [Dawes and Marburger, Phys. Rev. 179, 862 (1969)] is no longer applicable, while GVD has little influence on the self-focusing process of longer laser pulses. Through the results of numerical simulations as well as analytical analysis, we lind that the initial duration of the laser pulse is the main factor that determines the GVD effect on the propagation and the increase of the pressure and pulse compression during the propagation enhance this effect. The spectral data show that GVD also influences the spectrum broadening in high-pressure cases. [ABSTRACT FROM AUTHOR]

During femtosecond filamentation in air, nitrogen molecules and corresponding molecular ions undergo dissociation due to the high intensity of laser pulses, generating nitrogen atoms and atomic ions. The generated atoms and atomic ions emit luminescence in the UV range, which superposes on those emissions for the neutral and ionic nitrogen molecules. Here we report on a significant difference between the emission behavior of the 391-nm line and the other spectral lines under different pump laser polarizations. We attribute this difference to the contribution of the atomic ions to the luminescence emission around 391 nm. The difference becomes more evident in tightly focusing cases, providing an indirect but effective evidence for the dissociation of nitrogen molecular ions. [ABSTRACT FROM AUTHOR]

Introduction: The COVID-19 pandemic has received broad public attention and has been subject to social media discussion since the beginning of 2020. Previous research has demonstrated that framing could influence perception and behaviors of audience members in the mass media. The question addressed in this paper concerns which information frame is best for reporting negative news (eg, deaths) and positive news (eg, recoveries or cures) related to the outbreak of COVID-19., Methods: During the Spring Festival holidays of 2020 in China, we investigated a sample of 8170 participants' risk perceptions and emotional responses to the pandemic, and their willingness to forward updates when the information is presented in different frames by using a 2 (domain: living [good news] vs dying [bad news]) × 2 (count: absolute vs relative) × 2 (population base: excluding population base vs including population base) × 2 (content: text-only vs text-plus-graphic) mixed factorial design, with the first factor being a within-subjects factor and the last three being between-subjects factors., Results: Results indicated that (1) participants were more willing to forward good news (eg, cures) than bad news (eg, deaths); (2) when reporting bad news, the inclusion of the "population base" was effective in minimizing negative emotions; (3) when reporting good news, excluding the "population base" was more effective than including it in order to maximize positive emotions; (4) a text-plus-graphic frame worked better than a text-only frame in lowering the level of risk perception and negative emotions., Discussion: This study is relevant to how individuals and organizations communicate information about this viral pandemic and the probable impact of this news on the general public., Competing Interests: All authors declare no competing interests., (© 2021 Kuang et al.)