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<jats:p>Fluidics is one of the most historic subjects that are well-established over centuries on the macroscopic scale. In recent years, fluid detection using a number of micro/nano scale devices has been achieved. However, the interaction of microfluid and solid devices on micro/nano-meter scale still lacks in-depth research. We demonstrate a practical nanomechanical detector for microfluidics via a string resonator with high <jats:italic>Q</jats:italic>-factor, suspended over a hole. This device is placed under a jet nozzle with several microns of diameter, and the interaction between the micro-gas flow and the resonator is observed by monitoring the variation of the fundamental frequency and the quality factor. Moreover, we manage to measure the fluctuations of the micro-gas flow on the nanomechanical resonator by means of stochastic resonance. This work manifests a potential platform for detecting dynamical fluid behaviors at microscopic scale for novel fluid physics.</jats:p>

<jats:p>The Auger decay for the many-electron Xe<jats:sup>+</jats:sup> (4<jats:inline-formula> <jats:tex-math><?CDATA ${p}_{3/2}^{-1}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>p</mml:mi> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_38_2_023201_ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>) state is studied in detail, using multistep approaches. It is found that the single Auger decay channels are primarily Coster–Kronig processes, which is in accord with other theoretical and experimental results. The double and triple Auger decays result primarily from cascade processes, i.e., the sequential two-step and three-step Auger decay, and as such, the contributions from direct processes can be neglected. Level-to-level rates for single, double, and triple decays are obtained, based on which comprehensive Auger electron spectra and ion yields are obtained. Our decay paths and Auger electron spectra are in agreement with the experimental analysis [Hikosaka <jats:italic>et al.</jats:italic>, Phys. Rev. A 76 (2007) 032708], and our ion yield ratios (Xe<jats:sup>2+</jats:sup>: Xe<jats:sup>3+</jats:sup>: Xe<jats:sup>4+</jats:sup> = 4.6 : 87.0 : 8.4) are also in line with their values (5.0 : 86.0 : 9.0). However, with respect to the ion yield ratios, a discrepancy still remains among the experimental and theoretical results. Taking into account the complexity of Xe’s electronic structure, further, more detailed experiments are still required.</jats:p>

<jats:p>The plasmonic nanocavity is an excellent platform for the study of light matter interaction within a sub-diffraction volume under ambient conditions. We design a structure of plasmonic tweezers, which can trap molecular J-aggregates and also serve as a plasmonic cavity with which to investigate strong light matter interaction. The optical response of the cavity is calculated via finite-difference time-domain methods, and the optical force is evaluated based on the Maxwell stress tensor method. With the help of the coupled oscillator model and virtual exciton theory, we investigate the strong coupling progress at the lower level of excitons, finding that a Rabi splitting of 230 meV can be obtained in a single exciton system. We further analyze the relationship between optical force and model volume in the coupling system. The proposed method offers a way to locate molecular J-aggregates in plasmonic tweezers for investigating optical force performance and strong light matter interaction.</jats:p>

<jats:p>Near-field thermophotovoltaic systems functioning at 400–900 K based on graphene-hexagonal-boron-nitride heterostructures and thin-film InSb p–n junctions are investigated theoretically. The performances of two near-field systems with different emitters are examined carefully. One near-field system consists of a graphene-hexagonal-boron-nitride-graphene sandwiched structure as the emitter, while the other system has an emitter made of the double graphene-hexagonal-boron-nitride heterostructure. It is shown that both systems exhibit higher output power density and energy efficiency than the near-field system based on mono graphene-hexagonal-boron-nitride heterostructure. The optimal output power density of the former device can reach 1.3 × 10<jats:sup>5</jats:sup> W/m<jats:sup>2</jats:sup>, while the optimal energy efficiency can be as large as 42% of the Carnot efficiency. We analyze the underlying physical mechanisms that lead to the excellent performances of the proposed near-field thermophotovoltaic systems. Our results are valuable toward high-performance moderate temperature thermophotovoltaic systems as appealing thermal-to-electric energy conversion (waste heat harvesting) devices.</jats:p>

<jats:p>Symmetry plays fundamental role in physics and the nature of symmetry changes in non-Hermitian physics. Here the symmetry-protected scattering in non-Hermitian linear systems is investigated by employing the discrete symmetries that classify the random matrices. The even-parity symmetries impose strict constraints on the scattering coefficients: the time-reversal (<jats:italic>C</jats:italic> and <jats:italic>K</jats:italic>) symmetries protect the symmetric transmission or reflection; the pseudo-Hermiticity (<jats:italic>Q</jats:italic> symmetry) or the inversion (<jats:italic>P</jats:italic>) symmetry protects the symmetric transmission and reflection. For the inversion-combined time-reversal symmetries, the symmetric features on the transmission and reflection interchange. The odd-parity symmetries including the particle-hole symmetry, chiral symmetry, and sublattice symmetry cannot ensure the scattering to be symmetric. These guiding principles are valid for both Hermitian and non-Hermitian linear systems. Our findings provide fundamental insights into symmetry and scattering ranging from condensed matter physics to quantum physics and optics.</jats:p>

<jats:p>Pitch is the most important auditory perception characteristic of sound with respect to speech intelligibility and music appreciation, and corresponds to a frequency of sound stimulus. However, in some cases, we can perceive virtual pitch, where the corresponding frequency component does not exist in the stimulating sound. This virtual pitch contains a deviation from the de Boer pitch shift formula, which is known as second pitch shift. It has been theoretically suggested that nonlinear dynamics in the cochlea or in the neural network produce a nonlinear resonance with a frequency corresponding to the virtual pitch; however, there is no direct experimental observation to support this theory. The second virtual pitch shift, expressed via basilar membrane nonlinear vibration temporal patterns, and consistent with psychoacoustic experiments, is observed <jats:italic>in situ</jats:italic> in the cochlea via laser interferometry.</jats:p>

<jats:p>Tuning the thermal conductivity of silicon nanowires (Si-NWs) is essential for realization of future thermoelectric devices. The corresponding management of thermal transport is strongly related to the scattering of phonons, which are the primary heat carriers in Si-NWs. Using the molecular dynamics method, we find that the scattering of phonons from internal body defects is stronger than that from surface structures in the low-porosity range. Based on our simulations, we propose the concept of an exponential decay in thermal conductivity with porosity, specifically in the low-porosity range. In contrast, the thermal conductivity of Si-NWs with a higher porosity approaches the amorphous limit, and is insensitive to specific phonon scattering processes. Our findings contribute to a better understanding of the tuning of thermal conductivity in Si-NWs by means of patterned nanostructures, and may provide valuable insights into the optimal design of one-dimensional thermoelectric materials.</jats:p>

<jats:p>We conduct extensive research into the structures of Be<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Zn<jats:sub>1 – <jats:italic>x</jats:italic> </jats:sub>O ternary alloys in a pressure range of 0–60 GPa, using the <jats:italic>ab initio</jats:italic> total energy evolutionary algorithm and total energy calculations, finding several metastable structures. Our pressure-composition phase diagram is constructed using the enthalpy results. In addition, we calculate the electronic structures of the Be<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Zn<jats:sub>1 – <jats:italic>x</jats:italic> </jats:sub>O structures and investigate the bandgap values at varying pressures and Be content. The calculated results show that the bandgap of the Be<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Zn<jats:sub>1 – <jats:italic>x</jats:italic> </jats:sub>O ternary alloys increases with an increase in Be content at the same pressure. Moreover, the bandgap of the Be<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Zn<jats:sub>1 – <jats:italic>x</jats:italic> </jats:sub>O ternary alloys increases with the increasing pressure with fixed Be content. At the same Be content, the formation enthalpy of the Be<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Zn<jats:sub>1 – <jats:italic>x</jats:italic> </jats:sub>O ternary alloys first decreases, then increases with the increasing pressure.</jats:p>

<jats:p>Pressure evolution of local structure and vibrational dynamics of the perovskite-type relaxor ferroelectric single crystal of 0.935(Na<jats:sub>0.5</jats:sub>Bi<jats:sub>0.5</jats:sub>)TiO<jats:sub>3</jats:sub>-0.065BaTiO<jats:sub>3</jats:sub> (NBT-6.5BT) is systematically investigated via <jats:italic>in situ</jats:italic> Raman spectroscopy. The pressure dependence of phonon modes up to 30 GPa reveals two characteristic pressures: one is at around 4.6 GPa which corresponds to the rhombohedral-to-tetragonal phase transition, showing that the pressure strongly suppresses the coupling between the off-centered A- and B-site cations; the other structural transition involving the oxygen octahedral tilt and vibration occurs at pressure ∼13–15 GPa with certain degree of order-disorder transition, evidenced by the abnormal changes of intensity and FWHM in Raman spectrum.</jats:p>

<jats:p>The properties of six kinds of intrinsic point defects in monolayer GeS are systematically investigated using the “transfer to real state” model, based on density functional theory. We find that Ge vacancy is the dominant intrinsic acceptor defect, due to its shallow acceptor transition energy level and lowest formation energy, which is primarily responsible for the intrinsic p-type conductivity of monolayer GeS, and effectively explains the native p-type conductivity of GeS observed in experiment. The shallow acceptor transition level derives from the local structural distortion induced by Coulomb repulsion between the charged vacancy center and its surrounding anions. Furthermore, with respect to growth conditions, Ge vacancies will be compensated by fewer n-type intrinsic defects under Ge-poor growth conditions. Our results have established the physical origin of the intrinsic p-type conductivity in monolayer GeS, as well as expanding the understanding of defect properties in low-dimensional semiconductor materials.</jats:p>