We derive an $N$-fold Darboux transformation for the nonlinear Schrödinger equation coupled to a multiple self-induced transparency system, which is applicable to optical fiber communications in the erbium-doped medium. The $N$-soliton, $N$-breather and $N$th-order rogue wave solutions in the compact determinant representations are derived using the Darboux transformation and limit technique. Dynamics of such solutions from the first- to second-order ones are shown.

We explore the impact of distributional fairness degree and entanglement degree on the cooperation between different players by investigating a modified prisoner's dilemma game. We not only introduce a new concept of distributional fairness degree, but also obtain the cooperation conditions for overcoming dilemma in terms of fairness and entanglement inequalities. It is demonstrated that distributional fairness can be of fundamental importance to promote cooperation with the help of quantum entanglement.

The specific emitter identification (SEI) technique determines the unique emitter of a given signal by using some external feature measurements of the signal. It has recently attracted a great deal of attention because many applications can benefit from it. This work addresses the SEI problem using two methods, namely, the normalized visibility graph entropy (NVGE) and the normalized horizontal visibility graph entropy (NHVGE) based on treating emitters as nonlinear dynamical systems. Firstly, the visibility graph (VG) and the horizontal visibility graph (HVG) are used to convert the instantaneous amplitude, phase and frequency of received signals into graphs. Then, based on the information captured by the VG and the HVG, the normalized Shannon entropy (NSE) calculated from the corresponding degree distributions are utilized as the rf fingerprint. Finally, four emitters from the same manufacturer are utilized to evaluate the performance of the two methods. Experimental results demonstrate that both the NHVGE-based method and NVGE-based method are quite effective and they perform much better than the method based on the normalized permutation entropy (NPE) in the case of a small amount of data. The NVGE-based method performs better than the NHVGE-based method since the VG can extract more information than the HVG does. Moreover, our methods do not distinguish between the transient signal and the steady-state signal, making it practical.

From 1540 inelastic interactions of 3.7 A GeV $^{16}$O projectile with emulsion nuclei, we select samples of 87 and 61 events carefully due to interactions of neutron (n) and singly charged particles ($Z=1$), respectively. New results concerning the topology of such events are investigated. The average multiplicities of secondary relativistic particles that appear as shower tracks for n and $Z=1$ stay more or less constant when compared with analogous data on p-Em at similar energy. The multiplicity distributions and the average values of the various secondary charged particles are studied and compared with the corresponding predictions by the cascade evaporation model. The results assume that the n or $Z=1$ from $^{16}$O collide peripherally with an emulsion target and are considered as an expansion to the N-N collisions.

We experimentally study the spin exchange collision in ultracold $^{40}$K Fermi gases. The quadratic Zeeman shift, trap potential and temperature of atomic cloud will influence on the spin changing dynamics. Dependences of the spin components populations on the external bias magnetic field, the optical trap depth and the temperature of atomic cloud are experimentally investigated. The spin exchange from the initial states to the final state are observed for different initial states. This work shows an interesting process of reaching equilibrium by redistribution among the spin states with the spin exchange collision in an ultracold large-spin Fermi gas.

$^{40}$K is one of the most important atomic species for ultra-cold atomic physics. Due to the extremely low concentration (0.012%) of $^{40}$K in natural abundance of potassium, most experiments use 4–10% enriched potassium source, which have greatly suffered from the extremely low annual production and significant price hikes in recent years. Using naturally abundant potassium source, we capture $5.4\times10^{6}$ cold $^{40}$K atoms with the help of a high performance of two-dimensional magneto-optical trap (2D$^{+}$ MOT), which is almost three orders of magnitude greater than previous results without the 2D$^{+}$ MOT. The number of the $^{40}$K atoms is sufficient for most ultra-cold $^{40}$K experiments, and our approach provides an ideal alternative for the field.

Fano-like quantum routing of single photons in a system with two waveguides coupled to two collocated atoms is investigated theoretically. Using a full quantum theory in real space, photonic scattering amplitudes along four ports of the waveguide network are analytically obtained. It is shown that, by adjusting the atomic dipole-dipole interaction, an evident Fano-line shape emerges in the scattering spectra of the single-dot configuration system. Moreover, Fano resonance can also be achieved by varying the atom-waveguide coupling strength and atomic detuning, in the presence of the atomic dipole-dipole interaction. Therefore, the atomic dipole-dipole interaction may be utilized as a possible way to control spectral Fano-like resonance. The feasibility with the experimental waveguide channels is also discussed.

Beam steering in implant defined coherently coupled vertical cavity surface emitting laser (VCSEL) arrays is simulated using the FDTD solution software. Angular deflection dependent on relative phase differences among elements, inter-element spacing, element size and emitted wavelength is analyzed detailedly and systematically. We design and fabricate 1$\times$2 implant defined VCSEL arrays for optimum beam steering performance. Electronically controlled beam steering with a maximum deflection angle of 1.6$^{\circ}$ is successfully achieved in the 1$\times$2 VCSEL arrays. The percentage of the power in the central lobe is above 39% when steering. The results show that the steering is controllable. Compared with other beam steering methods, the fabrication process is simple and of low cost.

Second-harmonic generation in Nd$^{3+}$:SBN crystal with needle-like ferroelectric with aperiodic domain structures is investigated. Two pairs of second harmonic (SH) waves appearing in lines are observed in unpoled Nd$^{3+}$:SBN crystals with aperiodic needle-like domains. A pair of SH waves emit from the exit face, whose intensities are angle-dependent. The angular dependence is corresponding to the spatial frequency spectrum of the aperiodic domain structure. Another pair of SH waves emit from both the side surfaces, which are mainly the scattered SH waves by needle-like domain walls and obey the theory of Rayleigh scattering.

The titanium oxide (TiO$_{2}$) nanotubes have attracted attention for their use in dye-sensitized solar cells as photoanode. In this study semiconducting cadmium sulfide (CdS) nanoparticles are grown on top opened TiO$_{2}$ nanotubes arrays by radio-frequency magnetron sputtering. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and diffuse reflection spectra are used to study structural, morphological and optical properties of the CdS/TiO$_{2}$ bilayer.

Effects of Ti addition on the microstructures and mechanical properties of AlCrFeNiMo$_{0.5}$Ti$_{x}$ ($x=0$, 0.25, 0.4, 0.5, 0.6, 0.75) high entropy alloys (HEAs) are investigated. All these HEAs of various Ti contents possess dual BCC structures, indicating that Ti addition does not induce the formation of any new phase in these alloys. As Ti addition $x$ varies from 0 to 0.75, the Vickers hardness (HV) of the alloy system increases from 623.7 HV to 766.2 HV, whereas the compressive yield stress firstly increases and then decreases with increasing $x$ above 0.5. Meanwhile, the compressive ductility of the alloy system decreases with Ti addition. The AlCrFeNiMo$_{0.5}$Ti$_{0.6}$ and AlCrFeNiMo$_{0.5}$Ti$_{0.75}$ HEAs become brittle and fracture with very limited plasticity. In the AlCrFeNiMo$_{0.5}$Ti$_{x}$ HEAs, the AlCrFeNiMo$_{0.5}$ HEA possesses the highest compressive fracture strength of 4027 MPa and the largest compressive plastic strain of 27.9%, while the AlCrFeNiMo$_{0.5}$Ti$_{0.5}$ HEA has the highest compressive yield strength of 2229 MPa and a compressive plastic strain of 10.1%. The combination of high strength and large plasticity of the AlCrFeNiMo$_{0.5}$Ti$_{x}$ ($x=0$, 0.25, 0.4, 0.5) HEAs demonstrates that this alloy system is very promising for engineering applications.

Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-speciality grout. Dicalcium silicate (Ca$_{2}$SiO$_{4})$ is the primary constituent of a number of different types of cement. The $\beta$-Ca$_{2}$SiO$_{4}$ phase is metastable at room temperature and will transform into $\gamma$-Ca$_{2}$SiO$_{4}$ at 663 K. In this work, Portland cement is annealed at a temperature of 950 K under pressures in the range of 0–5.5 GPa. The high pressure experiments are carried out in an apparatus with six anvil tops. The effect of high pressure on the obtaining nano-size $\beta$-Ca$_{2}$SiO$_{4}$(C$_{2}$S) process is investigated by x-ray diffraction and transmission electron microscopy. Experimental results show that the grain size of the C$_{2}$S decreases with the increase of pressure. The volume fraction of the C$_{2}$S phase increases with the pressure as the pressure is below 3 GPa, and then decreases ($P>3$ GPa). The nano-effect is very important to the stabilization of $\beta$-Ca$_{2}$SiO$_{4}$. The mechanism for the effects of the high pressure on the annealing process of the Portland cement is also discussed.

The organic-inorganic hybrid perovskite CH$_{3}$NH$_{3}$PbI$_{3}$ has attracted significant interest for its high performance in converting solar light into electrical power with an efficiency exceeding 20%. Unfortunately, chemical stability is one major challenge in the development of CH$_{3}$NH$_{3}$PbI$_{3}$ solar cells. It was commonly assumed that moisture or oxygen in the environment causes the poor stability of hybrid halide perovskites, however, here we show from the first-principles calculations that the room-temperature tetragonal phase of CH$_{3}$NH$_{3}$PbI$_{3}$ is thermodynamically unstable with respect to the phase separation into CH$_{3}$NH$_{3}$I + PbI$_{2}$, i.e., the disproportionation is exothermic, independent of the humidity or oxygen in the atmosphere. When the structure is distorted to the low-temperature orthorhombic phase, the energetic cost of separation increases, but remains small. Contributions from vibrational and configurational entropy at room temperature have been considered, but the instability of CH$_{3}$NH$_{3}$PbI$_{3}$ is unchanged. When I is replaced by Br or Cl, Pb by Sn, or the organic cation CH$_{3}$NH$_{3}$ by inorganic Cs, the perovskites become more stable and do not phase-separate spontaneously. Our study highlights that the poor chemical stability is intrinsic to CH$_{3}$NH$_{3}$PbI$_{3}$ and suggests that element-substitution may solve the chemical stability problem in hybrid halide perovskite solar cells.

The self-consistent ab initio calculations based on the density functional theory approach using the full potential linear augmented plane wave method are performed to investigate both the electronic and magnetic properties of the NiFe compound. Polarized spin within the framework of the ferromagnetic state between magnetic ions is considered. Also, magnetic moments considered to lie along (001) axes are computed. The Monte Carlo simulation is used to study the magnetic properties of NiFe. The transition temperature $T_{\rm C}$, hysteresis loop, coercive field and remanent magnetization of the NiFe compound are obtained using the Monte Carlo simulation.

A series of boron- and phosphorus-doped silicon wafers are used to prepare a series of doped silicon nanocrystals (nc-Si) by high-energy ball milling with carboxylic acid-terminated surface. The sizes of the nc-Si samples are demonstrated to be $ < $5 nm. The doping levels of the nc-Si are found to be nonlinearly dependent on the original doping level of the wafers by x-ray photoelectron spectroscopy measurement. It is found that the nonlinear doping process will lead to the nonlinear chemical passivation and photoluminescence (PL) intensity evolution. The doping, chemical passivation and PL mechanisms of the doped nc-Si samples prepared by mechanochemical synthesis are analyzed in detail.

Designing new two-dimensional (2D) semiconductors with novel topological characters is highly desirable for further material innovation. We propose a theoretical design of a stable 2D inorganic material, namely, borane, which is jointly stabilized by traditional B–B localized and unique B–H–B delocalized chemical bonds. In borane, the bonding natures along different directions are distinguishing, which lead to huge differences in mechanical strengths of 142.73 and 97.47 N/m for $a$ and $b$ directions, respectively. In a unit cell, each hydrogen atom binds to two boron atoms forming a three-center-two-electron (3c-2e) bridge bond B–H–B. This can be considered as an extension of diborane molecules from 0D to 2D. The collaboration of localized and delocalized chemical bonds endows borane with high structural stability, as indicated by its favorable cohesive energy, high mechanical strength, absence of imaginary modes in the phonon spectrum, and moderate melting point. Remarkably, borane has a fascinating electronic property featured with a Dirac-like ring in the electronic band structure. The unique bonding nature and electronic property in borane would attract intensive interests in both theory and experiment.

We demonstrate the fabrication of a single electron transistor device based on a single ultra-small silicon quantum dot connected to a gold break junction with a nanometer scale separation. The gold break junction is created through a controllable electromigration process and the individual silicon quantum dot in the junction is determined to be a Si$_{170}$ cluster. Differential conductance as a function of the bias and gate voltage clearly shows the Coulomb diamond which confirms that the transport is dominated by a single silicon quantum dot. It is found that the charging energy can be as large as 300 meV, which is a result of the large capacitance of a small silicon quantum dot ($\sim$1.8 nm). This large Coulomb interaction can potentially enable a single electron transistor to work at room temperature. The level spacing of the excited state can be as large as 10 meV, which enables us to manipulate individual spin via an external magnetic field. The resulting Zeeman splitting is measured and the $g$ factor of 2.3 is obtained, suggesting relatively weak electron-electron interaction in the silicon quantum dot which is beneficial for spin coherence time.

A high intrinsic quality factor ($Q_{0}$) of a superconducting radio-frequency cavity is beneficial to reducing the operation costs of superconducting accelerators. Nitrogen doping (N-doping) has been demonstrated as a useful way to improve $Q_{0}$ of the superconducting cavity in recent years. N-doping researches with 1.3 GHz single cell cavities are carried out at Peking University and the preliminary results are promising. Our recipe is slightly different from other laboratories. After 250 μm polishing, high pressure rinsing and 3 h high temperature annealing, the cavities are nitrogen doped at 2.7–4.0 Pa for 20 min and then followed by 15 μm electropolishing. Vertical test results show that $Q_{0}$ of a 1.3 GHz single cell cavity made of large grain niobium has increased to $4\times10^{10}$ at 2.0 K and medium gradient.

The screening dependence of superconducting state parameters ($\lambda$, $\mu^{\ast}$, $T_{\rm c}$, $\alpha$ and $N_{0}V$) of six alloys of aluminium doped MgB$_{2}$ systems are studied in the BCS–Eliashberg–McMillan framework by employing five forms of dielectric screening function, viz. random phase approximation (RPA), Harrison, Geldart and Vosko (GV), Hubbard and Overhauser in conjunction with Ashcroft's potential. It is observed that electron-phonon coupling strength $\lambda$ and Coulomb pseudopotential $\mu^{\ast}$ are quite sensitive to the form of dielectric screening, whereas transition temperature $T_{\rm c}$, isotope effect exponent $\alpha$ and effective interaction strength $N_{0}V$ show weak dependence on the form of dielectric screening function. It is found that the RPA form of dielectric screening function yields the best results for transition temperature $T_{\rm c}$ for all alloys of the Mg-Al-B system. The results obtained using GV screening are much higher than the experimental results. This shows that all the four dielectric screenings used here almost describe superconductivity in all the alloys of the Mg-Al-B system, but the GV screening is not suitable for such an alloy system.

Thermodynamic properties of the mixed spin-1 and spin-1/2 Ising–Heisenberg model are studied on a honeycomb lattice using a new approach in the mean-field approximation to analyze the effects of longitudinal $D_z$ and transverse $D_x$ crystal fields. The phase diagrams are calculated in detail by studying the thermal variations of the order parameters, i.e., magnetizations and quadrupole moments, and compared with the literature to assess the reliability of the new approach. It is found that the model yields both second- and first-order phase transitions, and tricritical points. The compensation behavior of the model is also investigated for the sublattice magnetizations, and longitudinal and transverse quadrupolar moments. The latter type of compensation is observed in the literature but its possible importance is overlooked.

The elastocaloric effect of PbTiO$_{3}$ thin films with 180$^{\circ}$ domain structure is studied using the phase field method. The influence of external stress $\sigma_{33}$, misfit strain $u_{\rm m}$ and domain wall energy on the adiabatic temperature change ($\Delta T_{\sigma})$ at room temperature are carried out. The calculation results indicate that $|{\Delta T_\sigma}|$ increases as $|{\sigma_{33}}|$ or $|{u_{\rm m}}|$ increases. The largest $\Delta T_{\sigma}$ value of $-$7.8 K is obtained at $\sigma_{33}=2$ GPa and $u_{\rm m}=-0.02$. Furthermore, the domain switching behaviors under different gradient coefficients are different, and finally affect the elastocaloric effect in PTO thin films. These results could provide a guide to choose the substrate and the preparation process in experiments.

Co(II) doped ZnTe nanowires are prepared by a thermal evaporation method. The power and temperature dependent micro-photoluminescence spectra of single nanowire demonstrate the double bands near its band edge, and the ferromagnetism behavior for these nanowires is identified. The occurrence of excitonic magnetic polaron (EMP) can account for the second emission band for its higher binding energy and ferromagnetic coupling. This EMP formation in a nanostructure will facilitate to realize magnetic modulation on confined excitons and will find new applications for spinpolarized nanophotonic devices.

Using density functional theory calculations, we investigate the tetragonal distortion, electronic structure and magnetic property of Pt$_{2}$MnSn. The results indicate that, when the volume-conserving tetragonal distortion occurs, the energy minimum appears at $c/a=0.84$, and the energy difference between the minimum and cubic phase is as high as 107 meV/f.u. Thus from the point of view of thermodynamics, martensitic transformation may occur in Pt$_{2}$MnSn with decreasing the temperature. The electronic structure of its cubic and martensitic phases also approves this. Moreover, both the cubic and tetragonal phases of Pt$_{2}$MnSn are ferromagnetic structures and their total magnetic moments are 4.26 $\mu_{_{\rm B}}$ and 4.12 $\mu_{_{\rm B}}$, respectively.

To achieve the enhancement and manipulation of light absorption in graphene within the visible and near infrared regions, a design consists of high-contrast gratings and two evanescently coupled slabs with graphene monolayer is demonstrated. The operation principle and design process of the proposed structure are analyzed using the coupled mode theory, which is confirmed by the rigorous coupled wave analysis. It is proved that the absorptance of graphene monolayer can be greatly enhanced to unity. The thickness of grating and slab layers can significantly change the line width and resonant mode position in the absorption spectra. Furthermore, high tunability in amplitude and bandwidth of the absorption spectra can be achieved by controlling the structural parameters of the hybrid structure. The proposed devices could be efficiently exploited as tunable and selective absorbers, and could be allowed to realize other two-dimensional materials-based selective photo-detectors.

We report an Al$_{0.25}$Ga$_{0.75}$N/GaN based lateral field emission device with a nanometer scale void channel. A $\sim$45 nm void channel is obtained by etching out the SiO$_{2}$ sacrificial dielectric layer between the semiconductor emitter and the metal collector. Under an atmospheric environment instead of vacuum conditions, the GaN-based field emission device shows a low turn-on voltage of 2.3 V, a high emission current of $\sim$40 $\mu$A (line current density 2.3 mA/cm) at a collector bias $V_{\rm C}=3$ V, and a low reverse leakage of 3 nA at $V_{\rm C}=-3$ V. These characteristics are attributed to the nanometer scale void channel as well as the high density of two-dimensional electron gas in the AlGaN/GaN heterojunction. This type of device may have potential applications in high frequency microelectronics or nanoelectronics.

A new silicon-on-insulator (SOI) trench lateral double-diffused metal oxide semiconductor (LDMOS) with a reduced specific on-resistance $R_{\rm on,sp}$ is presented. The structure features a non-depleted embedded p-type island (EP) and dual vertical trench gate (DG) (EP-DG SOI). First, the optimized doping concentration of drift region is increased due to the assisted depletion effect of EP. Secondly, the dual conduction channel is provided by the DG when the EP-DG SOI is in the on-state. The increased optimized doping concentration of the drift region and the dual conduction channel result in a dramatic reduction in $R_{\rm on,sp}$. The mechanism of the EP is analyzed, and the characteristics of $R_{\rm on,sp}$ and breakdown voltage (BV) are discussed. Compared with conventional trench gate SOI LDMOS, the EP-DG SOI decreases $R_{\rm on,sp}$ by 47.1% and increases BV from 196 V to 212 V at the same cell pitch by simulation.