Catálogo de publicaciones - revistas

<jats:p>We report pulsed laser diode (LD) end-pumped acoustic <jats:italic>Q</jats:italic>-switched Tm:YAG laser, Tm:LuAG laser, and Tm:LuYAG laser and the physical properties and spectra of Tm:YAG, Tm:LuAG, and Tm:LuYAG are analyzed. The Tm:LuYAG laser is pumped by 785-nm and 788-nm pulses separately, and is compared with Tm:YAG laser. Different output energy values and output wavelengths of Tm:LuAYG lasers pumped by LDs with different wavelengths are obtained and compared with each other. When the repetition frequency is 100 Hz, the pulsed Tm:YAG laser has single pulse energy of 15.9 mJ, pulse width of 126.7 ns, and the center wavelength of 2013.36 nm, and the pulsed Tm:LuAG laser possesses single pulse energy of 11.8 mJ, pulse width of 252.4 ns, and the center wavelength of 2023.65 nm, and the pulsed Tm:LuYAG laser output energy values are 12.32 mJ and 12.25 mJ with the slope efficiencies of 12.5% and 11.85%, the center wavelengths of 2017.89 nm and 2027.11 nm, respectively, while the pump sources are 785-nm and 788-nm pulsed LDs, respectively.</jats:p>

<jats:p>We present nonlinear spectra of four-level ladder cesium atoms employing 6<jats:italic>S</jats:italic> <jats:sub>1/2</jats:sub> → 6<jats:italic>P</jats:italic> <jats:sub>3/2</jats:sub>→ 7<jats:italic>S</jats:italic> <jats:sub>1/2</jats:sub> → 30<jats:italic>P</jats:italic> <jats:sub>3/2</jats:sub> scheme of a room temperature vapor cell. A coupling laser drives Rydberg transition, a dressing laser couples two intermediate levels, and a probe laser optically probes the nonlinear spectra via electromagnetically induced transparency (EIT). Nonlinear spectra are detected as a function of coupling laser frequency. The observed spectra exhibit an enhanced absorption (EA) signal at coupling laser resonance to Rydberg transition and enhanced transmission (ET) signals at detunings to the transition. We define the enhanced absorption (transmission) strength, <jats:italic>H</jats:italic> <jats:sub>EA</jats:sub> (<jats:italic>H</jats:italic> <jats:sub>ET</jats:sub>), and distance between two ET peaks, <jats:italic>γ</jats:italic> <jats:sub>ET</jats:sub>, to describe the spectral feature of the four-level atoms. The enhanced absorption signal <jats:italic>H</jats:italic> <jats:sub>EA</jats:sub> is found to have a maximum value when we vary the dressing laser Rabi frequency <jats:italic>Ω</jats:italic> <jats:sub>d</jats:sub>, corresponding Rabi frequency is defined as a separatrix point, <jats:italic>Ω</jats:italic> <jats:sub>d<jats:sub>Se</jats:sub> </jats:sub>. The values of <jats:italic>Ω</jats:italic> <jats:sub>d<jats:sub>Se</jats:sub> </jats:sub> and further <jats:italic>η</jats:italic> = <jats:italic>Ω</jats:italic> <jats:sub>d<jats:sub>Se</jats:sub> </jats:sub>/<jats:italic>Ω</jats:italic> <jats:sub>c</jats:sub> are found to depend on the probe and coupling Rabi frequency but not the atomic density. Based on <jats:italic>Ω</jats:italic> <jats:sub>d<jats:sub>Se</jats:sub> </jats:sub>, the spectra can be separated into two regimes, weak and strong dressing ranges, <jats:italic>Ω</jats:italic> <jats:sub>d</jats:sub> ≲ <jats:italic>Ω</jats:italic> <jats:sub>d<jats:sub>Se</jats:sub> </jats:sub> and <jats:italic>Ω</jats:italic> <jats:sub>d</jats:sub> ≳ <jats:italic>Ω</jats:italic> <jats:sub>d<jats:sub>Se</jats:sub> </jats:sub>, respectively. The spectroscopies display different features at these two regimes. A four-level theoretical model is developed that agrees well with the experimental results in terms of the probe-beam absorption behavior of Rabi frequency-dependent dressed states.</jats:p>

<jats:p>We theoretically investigate a two-cavity optomechanical system in which each optical cavity couples to a mechanical resonator via radiation pressure force, and the two optical cavities couple to each other via a distant waveguide. Our study shows that the multiple optomechanically induced transparency can be observed from the output field at the probe frequency. The number and width of the transparent windows can be tuned by the classical driving power <jats:italic>P<jats:sub>l</jats:sub> </jats:italic>. We also analyze the distance of the two outermost transparency windows, which shows a linear relation with the parameters <jats:italic>P<jats:sub>l</jats:sub> </jats:italic> and <jats:italic>λ</jats:italic>. Our approach is feasible for controlling multipartite induced transparency, which represents a valuable step towards quantum networks with photonic and phononic circuits.</jats:p>

<jats:p>The van der Waals (vdW) heterostructures of bilayer transition metal dichalcogenide obtained by vertically stacking have drawn increasing attention for their enormous potential applications in semiconductors and insulators. Here, by using the first-principles calculations and the phonon Boltzmann transport equation (BTE), we studied the phonon transport properties of WS<jats:sub>2</jats:sub>/WSe<jats:sub>2</jats:sub> bilayer heterostructures (WS<jats:sub>2</jats:sub>/WSe<jats:sub>2</jats:sub>-BHs). The lattice thermal conductivity of the ideal WS<jats:sub>2</jats:sub>/WSe<jats:sub>2</jats:sub>-BHs crystals at room temperature (RT) was 62.98 W/mK, which was clearly lower than the average lattice thermal conductivity of WS<jats:sub>2</jats:sub> and WSe<jats:sub>2</jats:sub> single layers. Another interesting finding is that the optical branches below 4.73 THz and acoustic branches have powerful coupling, mainly dominating the lattice thermal conductivity. Further, we also noticed that the phonon mean free path (MFP) of the WS<jats:sub>2</jats:sub>/WSe<jats:sub>2</jats:sub>-BHs (233 nm) was remarkably attenuated by the free-standing monolayer WS<jats:sub>2</jats:sub> (526 nm) and WSe<jats:sub>2</jats:sub> (1720 nm), leading to a small significant size effect of the WS<jats:sub>2</jats:sub>/WSe<jats:sub>2</jats:sub>-BHs. Our results systematically demonstrate the low optical and acoustic phonon modes-dominated phonon thermal transport in heterostructures and give a few important guidelines for the synthesis of van der Waals heterostructures with excellent phonon transport properties.</jats:p>

<jats:p>The car-following behavior can be influenced by its driver’s backward-looking effect. Especially in traffic congestion, if vehicles adjust the headway by considering backward-looking effect, the stability of traffic flow can be enhanced. A model of car-following behavior considering backward-looking effect was built using visual information as a stimulus. The critical stability conditions were derived by linear and nonlinear stability analyses. The results of parameter sensitivity analysis indicate that the stability of traffic flow was enhanced by considering the backward-looking effect. The spatiotemporal evolution of traffic flow of different truck ratios and varying degrees of backward-looking effect was determined by numerical simulation. This study lays a foundation for exploring the complex feature of car-following behavior and making the intelligent network vehicles control rules more consistent with human driver habits.</jats:p>

<jats:p>We investigate how the barb of bird feathers is changed along both the rachis and barb. To investigate the microstructures and the mechanical behaviors of barbs, a series of barbs are manually cut from an eagle’s primary feather to observe the cross sections. A <jats:italic>λ</jats:italic>-like cross section with a tiny hook is observed at the right feet at each section. Afterwards, a measurement of the setup system is developed to evaluate the leakage ratio of a feather followed by a numerical predicting approach based on the CFD method. It is found that the air leakage increases linearly against the pressure, and the predicted results coincide well with the experimental results. Finally, the influences of leakage of the flight feather on both steady and unsteady aerodynamics are studied.</jats:p>

<jats:p>The flow separation control over an NACA 0015 airfoil using continuous alternating current (AC) dielectric barrier discharge (DBD) plasma actuator is investigated experimentally and numerically. This work is intended to report some observations made from our experiment, to which little attention is paid in the previous studies, but which is thought to be important to the understanding of control of complex flow separation with AC DBD. To this end, the response of separated flow to AC plasma actuation is visualized through the time-resolved particle image velocimetry (PIV) measurement, whereas numerical simulation is carried out to complement the experiment. The flow control process at chord-based Reynolds number (<jats:italic>Re</jats:italic>) of 3.31 × 10<jats:sup>5</jats:sup> is investigated. It is found that the response of external flow to plasma forcing is delayed for up to tens of milliseconds and the delay time increases with angle of attack increasing. Also observed is that at the intermediate angle of attack near stall, the forced flow features a well re-organized flow pattern. However, for airfoil at high post-stall angle of attack, the already well suppressed flow field can recover to the massively separated flow state and then reattach to airfoil surface with the flow pattern fluctuating between the two states in an irregular manner. This is contrary to one’s first thought that the forced flow at any angles of attack will become well organized and regular, and reflects the complexity of flow separation control.</jats:p>

<jats:p>Based on a set of experimental databases of turbulent boundary layers obtained from particle image velocimetry in the streamwise-wall-normal plane at friction-velocity-based Reynolds number <jats:italic>Re<jats:sub>τ</jats:sub> </jats:italic> = 612, the influence of uniform momentum zones (UMZs) on the skin-friction drag is investigated. The skin-friction drag is measured by the single-pixel ensemble correlation method. The results show that the velocity fields with the number of UMZs larger than the mean value have a relatively low skin-friction drag, while the velocity fields with the number of UMZs less than the mean value have a relatively high skin-friction drag. By analyzing the statistical characteristics of UMZs, the dynamic correlation between the UMZs and skin-friction drag is explored. The velocity fields with a low number of UMZs present a sweep event. These sweep motions intensify the small-scale Reynolds shear stress in the near-wall region by modulation effects. The enhancement of small-scale Reynolds shear stress is the direct reason for the high skin-friction drag. Increasing the proportion of velocity fields with high UMZs amount may be a direction to reduce the skin-friction drag within the TBL.</jats:p>

<jats:p>We study some nonlinear waves in a viscous plasma which is confined in a finite cylinder. By averaging the physical quantities on the radial direction in some cases, we reduce this system to a simple one-dimensional model. It seems that the effects of the bounded geometry (the radius of the cylinder in this case) can be included in the damping coefficient. We notice that the amplitudes of both Korteweg–de Vries (KdV) solitary waves and dark envelope solitary waves decrease exponentially as time increases from the particle-in-cell (PIC) simulation. The dependence of damping coefficient on the cylinder radius and the viscosity coefficient is also obtained numerically and analytically. Both are in good agreement. By using a definition, we give a condition whether a solitary wave exists in a bounded plasma. Moreover, some of potential applications in laboratory experiments are suggested.</jats:p>

<jats:p>This paper presents the evolution of the electronegativity with the applied power during the E to H mode transition in a radio frequency (rf) inductively coupled plasma (ICP) in a mixture of Ar and O<jats:sub>2</jats:sub>. The densities of the negative ion and the electron, as well as their ratio, <jats:italic>i.e.</jats:italic>, the electronegativity, are measured as a function of the applied power by laser photo-detachment combined with a microwave resonance probe, under different pressures and O<jats:sub>2</jats:sub> contents. Meanwhile, the optical emission intensities at Ar 750.4 nm and O 844.6 nm are monitored via a spectrograph. It was found that by increasing the applied power, the electron density and the optical emission intensity show a similar trench, <jats:italic>i.e.</jats:italic>, they increase abruptly at a threshold power, suggesting that the E to H mode transition occurs. With the increase of the pressure, the negative ion density presents opposite trends in the E-mode and the H-mode, which is related to the difference of the electron density and energy for the two modes. The emission intensities of Ar 750.4 nm and O 844.6 nm monotonously decrease with increasing the pressure or the O<jats:sub>2</jats:sub> content, indicating that the density of high-energy electrons, which can excite atoms, is monotonically decreased. This leads to an increase of the negative ion density in the H-mode with increasing the pressure. Besides, as the applied power is increased, the electronegativity shows an abrupt drop during the E- to H-mode transition.</jats:p>