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The efficiency and power density of ultralow-voltage (<1 V) high-current output dc transformers (DCXs) are limited by the losses and footprint area of the high-current windings. High-frequency current cancellation and power switches and high-current winding heterogeneous integration methods are proposed to reduce the length, area, and losses of high-current windings. With the proposed current-cancellation-based heterogeneous integration method, most of the high-current printed circuit board (PCB) windings of the transformer are replaced by power switches and capacitors, and almost zero PCB winding is achieved for the high-current secondary windings of the DCX. As a result, both power density and efficiency are improved significantly. A 36-V-to-0.75-V/150-A output DCX with a 48:1 turns-ratio transformer is designed and implemented with the four-layer PCB. A peak efficiency of 94.1% is achieved, while the power density of the high-frequency transformer in the DCX is 0.66 A/mm2.

Al–Cu–Mg alloy hemispherical components can be widely utilized in gyroscope navigation systems by virtue of low density, high deformability and fatigue strength. However, the nonuniformity in residual stress and microstructure of the component after deep drawing may lead to a complex microstructural evolution under the temperature environment, thereby decreasing the navigation precision. In this work, the evolution of grain sizes, dislocations, second phases and mechanical properties of Al–Cu–Mg alloy hemispherical components were evaluated under a temperature field. From the edge to the central part of the component, the grain size first decreased and then increased, while the hardness and residual stress first increased and then decreased. With the extension of exposure time, the dislocation density decreased and the coarsened Al2CuMg phases appeared, while the grain size of the component remained stable. Furthermore, the dislocation density declined faster and Al2CuMg phases precipitated rapider in the die fillet area in comparison with the situation at the bottom of the hemisphere. The higher dislocation density could provide more nucleation sites for Al2CuMg phases. Thereafter, more dislocations were consumed, thus accelerating the reduction of stored energy and lattice distortion under the temperature field. As a result, investigating the microstructural stability and mechanical properties of Al–Cu–Mg alloy hemispherical components can make a contribution to fabricating highly stabilized navigation devices to be further applied in the field of space exploration.

Due to its excellent deformability and high tensile strength, Ti–Zr–Nb alloy is promising in the field of aerospace and national defense. However, the relatively low stability of microstructure with temperature variation restricts its further application in navigation system. In this work, the microstructure evolution and mechanical properties of Ti–Zr–Nb alloy is investigated after an annealing treatment. When the annealing temperature increases, we observe the microstructure experiences recovery, recrystallization, reduction of dislocation density, refinement of α′-prime martensite phases and dissolution of ω-phases. These behaviors lead to the release of distortion energy, and thus the improvement of microstructural stability of Ti–Zr–Nb alloy. In the meantime, mechanical properties maintain after the enhancement of microstructural stability. Therefore, the propose annealing process can improve the microstructural stability and keep the good mechanical properties of Ti–Zr–Nb alloy in further aerospace application.

One-pot synthesis of continuously compositionally intermetallic graded material is desirable for the industries, but has proven to be difficult, as each constituent layer presents distinct crystal structure and microstructure. In this work, we demonstrate that a continuously compositionally Ti/Al intermetallic graded material can be successfully fabricated by a well-controlled laser parameter and powder feeding speed. Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), micro-area X-ray diffraction analysis (XRD), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) are utilized in characterizing the resulting graded material and its structural signatures. Results show that Ti5Si3, Ti3Al, TiAl, TiAl3and Ti7Al5Si12form from the Ti6Al4V side to AlSi10Mg side. Clear phase interface can be seen from SEM and TEM, but no macroscopic cracks appear on the graded or phase boundaries. The elemental distribution indicates the microstructure of gradually changes from initial network structure to columnar and dendritic structure from Ti6Al4V to AlSi10Mg. The hardness of the prepared Ti/Al graded material displays a parabolic shape with a maximum in the middle layers. Our findings suggest that continuously compositionally Ti6Al4V/AlSi10Mg intermetallic graded material could be synthesized in one time through laser powder deposition, and the continuously microstructure and hardness implies its application potential in aerospace, especially in the field of space debris protection.

Garments protective against chemical warfare agents (CWAs) or accidently released toxic chemicals must block the transport of toxic gases/vapors for a substantial time and allow moisture transport for breathability. These demands are challenging: either the barriers block CWAs effectively but have poor breathability or barriers have excellent breathability but cannot block CWAs well. Existing protective garments employ large amounts of active carbon, making them quite heavy. Metal–organic framework (MOF)-based adsorbents are being investigated as sorbents for CWAs. Breathable laminate of graphene oxide (GO) flakes supported on a porous membrane reduces permeation rates of CWA simulants substantially. We developed a multilayered membrane-based flexible barrier: GO laminate-based membrane over a MOF nanocrystal-filled expanded polytetrafluorethylene (ePTFE) membrane having submicrometer pores. The GO laminate-based layer developed a steady breakthrough concentration level almost 2 orders of magnitude below the usual breakthrough level. This highly reduced level of CWA was blocked by the MOF nanocrystal-filled membrane substrate layer over a highly extended period. We demonstrated the blocking of CWAs, mustard (HD), soman (GD), a sarin simulant [dimethyl methyl phosphonate (DMMP)], and ammonia for an extended period while the moisture transmission rate was substantial. The times for complete blockage of ammonia, HD, GD, and DMMP were 2750 min, 1075 min, 176 min, and 7 days, respectively. This remarkable performance resulted from a very low steady-state penetrant permeation through GO-laminate membrane and substantial penetrant sorption by MOF nanocrystals; furthermore, both layers show high moisture vapor transmission.

We consider arrays of coupled nonlinear optical cavities subject to coherent optical injection. These devices are described by the discrete generalized Lugiato–Lefever equation. We predict that stable three-dimensional localized structures, often called discrete light bullets, and clusters of them may form in the output of the coupled optical resonators. We consider both anomalous and normal dispersion and show that it results in the generation of, respectively, bright and dark discrete light bullets.

Ultrafast all-optical switches have attracted considerable attention for breaking through the speed limitation of electric devices. However, ultrafast and high-efficiency all-optical switches based on two-dimensional (2D) materials can be achieved due to their strong nonlinear optical response and ultrafast carrier dynamic. For this reason, we propose the pump-probe method to achieve an ultrafast optical switcher with a response time of 192 fs and a switching energy of 800 nJ by using transition metal carbide (Nb2C). The response time and switching energy are far smaller than that of the all-optical device based on the saturable absorption effect of 2D materials. It is believed that the Nb2C-based all-optical switch provides a novel idea to achieve a high-performance all-optical device and has the potential for application in high-speed photonics processing.

Germanium phosphide (GeP), a rising star of novel two-dimensional (2D) material composed of Group IV–V elements, has been extensively studied and applied in photonics thanks to its broadband optical absorption, strong light–matter interaction and flexible bandgap structure. Here, we show the strong nonlinear optical (NLO) properties of 2D GeP nanoflakes in the broadband range with open-aperture Z-scan technique to explore the performance of 2D GeP microfiber photonic devices (GMPDs) in near-infrared (near-IR) and mid-infrared (mid-IR) ultrafast photonics. Our results suggest that employing the GMPD as an optical device in an erbium-doped fiber laser (EDFL) system results in ultrashort pulses and rogue waves (RWs) at 1.55 μm. Likewise, by the incorporation of GMPD into a thulium-doped fiber laser (TDFL) system, stable ultrashort pulse operation is also achieved at 2.0 μm. We expect these findings to be an excellent GMPD that can be applied in mode-locked fiber lasers to open up new avenues for its development and application in ultrafast photonics.

MXene is a promising two-dimensional (2D) material that is widely used in electro-photonic devices due to its unique properties. In this contribution, V2CTx, a novel MXene, was employed as a saturable absorber (SA) for hybrid passively mode-locked fiber lasers. An ultra-stable and self-starting mode-locked laser system with low threshold can be achieved using V2CTxnanosheets and nonlinear polarization evolution (NPE). Signal to noise ratio increased 13 dB compared with using only NPE SA. A 72 fs pulse duration is easily achieved from this hybrid mode-locked fiber laser system. To the best of our knowledge, this is the shortest pulse duration generated from the Yb-doped mode-locked fiber lasers using a hybrid or 2D SAs. This study proves that MXene V2CTxnanosheets can be developed as suitable SAs and served as potential advanced ultrafast photonic devices in the future.

We report on the experimental observation of dual-wavelength dissipative soliton operation of a fiber laser with net anomalous cavity dispersion. Different from the dual- or multi-wavelength soliton operation of fiber lasers where mode locking is used to initiate soliton formation, no mode locking occurs in our fiber laser. Instead, soliton formation is through the dissipative mechanism caused by the effective gain bandwidth limitation. Either dual-wavelength scalar, or vector, or induced dissipative solitons are experimentally obtained. Their robustness is experimentally confirmed.

Optical modulation technique plays a crucial role in photonics technologies, and there is an ever-increasing demand for broadband and ultrafast optical modulation in the era of artificial intelligence. All-optical modulation is known to be able to operate in an ultrafast way and has a broadband response, showing great potential in applications for ultrafast information processing and photonic computing. Two-dimensional (2D) materials with exotic optoelectronic properties bring tremendous new opportunities for all-optical modulators with excellent performance, which have attracted lots of attention recently. In this review, we cover the state-of-art all-optical modulation based on 2D materials, including graphene, transitional metal dichalcogenides, phosphorus, and other novel 2D materials. We present the operations mechanism of different types of all-optical modulators with various configurations, such as fiber-integrated and free-space ones. We also discuss the challenges and opportunities faced by all-optical modulation, as well as offer some future perspectives for the development of all-optical modulation based on 2D materials.

Nowadays, as the combination of water pollution and water shortage causes severe environmental and social issues, the special wettable materials, which can be selectively wetted by either water or oil, attract tremendous attention for high-efficiency separation of oil–water mixtures. Herein, we prepare a phenolic-resin-based sponge composed of intertwined nanofibers via a simple hydrothermal method. The wettability of the as-prepared polymer is tuned readily by controlling only the hydrothermal temperature. In the case of the hydrothermal temperature below 210 °C, the polymer sponge demonstrates superhydrophilic and underwater superoleophobic properties, affording the separation of oil-in-water emulsions. However, as the hydrothermal temperature increases above 220 °C, the resulting bulk phenolic-resin-based material becomes superhydrophobic and underoil superhydrophobic, realizing a high filtration flux of 6147 L m–2h–1for the separation of water-in-oil emulsions driven by an external pressure of 40 kPa. This provides a feasible platform for future practical applications. The wettability transition depending on the hydrothermal temperature is discussed in terms of the reaction mechanism. In addition, the stability and breakthrough pressure are also addressed from the viewpoints of thermodynamic and fluid mechanics, respectively.

The correlation between the properties of the parent rock (PR) and the manufactured sand (MS) is poorly understood. In this study, eight groups of PR, crushed rock (CR), and MS were selected in the lithofacies analysis, where their mechanical properties and hazardous substances were investigated. The results show that the hazardous substances and alkali activities of PR and CR facilitated the prediction of whether the properties of MS met the specification requirements. Moreover, MS exhibited higher water absorption, greater crushing indices and soundness loss than PR and CR. Further, large mineral grains and diorite xenoliths and mica in granite led to higher brittleness and lower UCS than tuff (97MPa vs. 121-151MPa).

A novel route is developed to synthesize highly uniform N-doped porous carbon spheres (NCS) with a tailorable size ranging from 86 to 205 nm depending on their precursors of phenolic-resin-based analogues. Solid-state NMR and FTIR spectra confirm that the as-synthesized polymer spheres are composed of typical phenolic resin. After activation treatment with KOH, the NCS with a diameter of 86 nm possesses a high surface area of 1462 m2g–1coupled with hierarchical (micro and meso) pore structures. Upon these advantages, the prepared carbon sample endows the supercapacitor with high specific capacitance up to 247 F g–1at 1 A g–1with excellent rate performance and high cycling stability. Also, the specific energy density is 6.74 Wh kg–1at a current density of 0.1 A g–1. Therefore, the as-prepared uniform N-doped porous carbon spheres represent a promising candidate for an efficient electrode material.

Uniaxial compression acoustic emission (AE) tests were conducted on low-strength molybdenum ore (LSMO) to investigate its deformation and failure laws and AE characteristics. The stress–strain curve and AE parameter data of LSMOs were obtained by uniaxial compression AE test, and the relationships of stress, AE parameter, amplitude fractal dimension, and AE bvalue with loading time were analyzed accordingly to obtain the general law of their deformation and failure and a series of AE characteristics. The research shows that under the action of uniaxial stress, the failure mode of LSMOs mainly shows brittle failure, and the failure form mainly shows monoclinic shear failure. The stress–strain curve shows obvious plastic-elastic deformation, the plastic deformation time is long, and the division of each stage of deformation failure is not obvious. The simultaneous occurrence of large surges in ringing count and energy to higher orders of magnitude can be used as precursor information for failure destabilization of LSMOs. The evolution process of AE parameters of LSMO corresponds well with its deformation and failure process, and the variation pattern of ringing counts and energy shows a high consistency. With increasing stress, the amplitude correlation dimension and bvalue are mainly in the form of "falling-rising-falling-fluctuating". The results of the study can provide some theoretical basis for the assessment of the stability of the mine surrounding rock and the determination of a reasonable and effective reinforcement plan.

Inverse-Gaussian apodized fiber Bragg gratings (IGAFBGs) are numerically studied using the transfer matrix method and fabricated by the commonly used phase-mask scanning technique in a single-step scanning process. The IGAFBG can serve as a dual-wavelength passband filter, whose wavelength spacing can be continuously tuned by introducing a tunable chirp through applying a strain gradient in principle. Also, an IGAFBG with identical dual passbands having 0.144nm wavelength spacing is experimentally achieved. We also show that an IGAFBG can act as a multipassband filter with varied free spectral ranges (FSRs), and the largest FSR variation of this IGAFBG is nearly seven times more than that in a comparable FBG pair filter. An IGAFBG with varied FSRs of ∼16.125, ∼12.25, ∼8.5, and ∼6.375GHz is fabricated. This multipassband varying-FSR IGAFBG filter can find applications in step-tunable microwave generations.

We demonstrate observation and dynamics of unique soliton pulsation regime in an ultrafast fiber laser at 1.7 μm. It is found that with either single-soliton pulse or multiple-soliton pulses in cavity the laser emission could exhibit periodic intensity and shot-to-shot spectra variations as measured based on the dispersive Fourier transformation (DFT) technique. Further, detailed studies turned out that the soliton pulsation can comprise numerous small pulses with random intensities, exhibiting chaotic characteristics. Besides, all the pulses within the multiple solitons possess identical pulsation period. In addition, despite of the fact that the temporal intervals between the multiple solitons are on the order of tens of nanoseconds among them, their pulsations demonstrate excellent synchronicity. The experimental observations are further revealed by numerical simulations. These results can provide insights into ways to optimize designs of laser sources and open up new potential for generation of pulsating solitons in ultrafast fiber lasers at different wavelengths. [ABSTRACT FROM AUTHOR]

In this study, the mechanisms of environmentally relevant doses of Cu and Zn mixtures influencing lipid deposition and metabolism were investigated in freshwater teleost yellow catfish Pelteobagrus fulvidraco(2 months old, 4.95 (t0.01 g, mean ± SEM). Our study indicated that waterborne Cu exposure increased lipid content, while Zn activated lipophagic flux and alleviated Cu-induced lipid accumulation. Yellow catfish hepatocytes treated with Zn or Zn + Cu activated autophagy-specific lipophagy, decreased lipid storage, and increased nonesterified fatty acid (NEFA) release, suggesting a causal relationship between lipophagy and lipid droplet (LD) breakdown under Zn and Zn + Cu conditions. Our further investigation found that Beclin1 deacetylation by sirtuin 1 (SIRT1) was required for Zn- and Zn + Cu-induced lipophagy and lipolysis, and lysine residues 427 and 434 were key sites for Beclin1 deacetylation. Taken together, these findings show that the Zn-induced deacetylation of Beclin1 promotes lipophagy as an important pathway to alleviate Cu-induced lipid accumulation in fish, which reveals a previously unidentified mechanism for understanding the antagonistic effects of Cu and Zn on metabolism at their environmentally relevant concentrations. Our results highlight the importance of combined exposure when the biological effects of heavy metals are evaluated during environmental risk assessments.

We show analytically and numerically that a practically realizable first-order optical Hilbert transformer (OHT) can simultaneously function as a negative/positive first-order temporal optical differentiator (OD) in the stopband and a broadband ±90° phase shifter in the passbands. An integrated-optic OHT based on a four-tap finite impulse response filter is designed using the Remez iteration algorithm and is numerically verified.

In this work, the generation of polarization domain wall (PDW) dark pulses in a thulium-doped fiber laser system at 2 μm was experimentally explored. The fiber ring laser incorporates a segment of multimode fiber as saturable absorber, with a 50 m length of highly nonlinear fiber (HNLF) integrated to enhance the nonlinear effects. It was observed that the central wavelength and repetition frequency of the PDW dark pulses are 1876 nm and 3.16 MHz, respectively. The characteristics of the PDWs, including their intensity and splitting, were significantly influenced by the pump power and polarization states. Additionally, the phenomenon of elastic collisions between solitons and domain walls within the laser cavity was successfully captured, marking a new observation in thulium-doped fiber lasers. The dynamics of PDWs at 2 μm were found to be consistent with those at 1550 nm, enhancing the understanding of pulse dynamics across different wavelength regions. • Experimental observation of Polarization Domain Wall dynamics in a 2 μm thulium-doped fiber laser • Pump power and polarization states significantly influence the characteristics of PDWs. • Novel documentation of elastic collisions between solitons and domain walls • Consistent PDW dynamics observed between 2 μm and 1550 nm wavelength regions [ABSTRACT FROM AUTHOR]

We consider coupled weakly birefringent cavities filled-in with nonlinear Kerr material and subject to linearly polarized optical injection. Light propagation in such a system is described by a system of discrete Lugiato–Lefever-type equations for each linear polarization component of the electric field into each cavity, coupled by the cross-phase modulation terms and the neighboring waveguides field overlap integrals. We demonstrate that this system supports stable three-dimensional vector localized structures often called discrete vector light bullets. We consider both anomalous and normal dispersion and show that it results in the generation of, respectively, bright and dark discrete vector light bullets. Due to the polarization multistability of the system, we demonstrated coexisting light bullets with polarization at the light bullets peaks as different as predominantly linear to predominantly circular. We have shown that chaotic spatio-temporal dynamics can be realized even for such an injection strengths for which the light bullets distribution in the system is stationary by increasing the coupling strength C between the cavities. [ABSTRACT FROM AUTHOR]

We demonstrate the real-time dynamics of a unique pulsating soliton state featuring noisy behaviors in a mid-infrared ultrafast fiber laser at 2 μm. By virtue of the time-stretch dispersive Fourier transform method, the pulsating behaviors of the noisy solitons are investigated. We find that the noisy pulsating solitons are characterized by a special optical spectrum. The shot-to-shot spectra and pulse energy of these pulsating noisy pulses can evolve periodically with the roundtrips. Besides, the real-time optical spectra within a single period exhibit irregular fluctuations in terms of the spectral profile and intensity, suggesting that the pulsating solitons are made up of noisy wave packets with chaotic features. These results can further enrich the pulsating soliton dynamics and also give new insights into the nonlinear pulse dynamics of mid-infrared ultrafast fiber lasers. [ABSTRACT FROM AUTHOR]