Catálogo de publicaciones - revistas

<jats:p>A radial cascaded composite ultrasonic transducer is analyzed. The transducer consists of three short metal tubes and two radially polarized piezoelectric ceramic short tubes arranged alternately along the radial direction. The short metal tubes and the piezoelectric ceramic short tubes are connected in parallel electrically and in series mechanically, which can multiply the input sound power and sound intensity. Based on the theory of plane stress, the electro-mechanical equivalent circuit of radial vibration of the transducer is derived firstly. The resonance/anti-resonance frequency equation and the expression of the effective electromechanical coupling coefficient are obtained. Excellent electromechanical characteristics are determined by changing the radial geometric dimensions. Two prototypes of the transducers are designed and manufactured to support the analytical theory. It is concluded that the theoretical resonance/anti-resonance frequencies are consistent with the numerical and experimental results. When <jats:italic>R</jats:italic> <jats:sub>2</jats:sub> is at certain values, both the anti-resonance frequency and effective electromechanical coupling coefficient corresponding to the second mode have maximal values. The radial cascaded composite ultrasonic transducer is expected to be used in the fields of ultrasonic water treatment and underwater acoustics.</jats:p>

<jats:p>We use the label-free microsphere-assisted microscopy to image low-contrast hexagonally close-packed polystyrene nanoparticle arrays with diameters of 300 and 250 nm. When a nanoparticle array is directly placed on a glass slide, it cannot be distinguished. If a 30-nm-thick Ag film is deposited on the surface of a nanoparticle array, the nanoparticle array with nanoparticle diameters of 300 and 250 nm can be distinguished. In addition, the Talbot effect of the 300-nm-diameter nanoparticle array is also observed. If a nanoparticle sample is assembled on a glass slide deposited with a 30-nm-thick Ag film, an array of 300-nm-diameter nanoparticles can be discerned. We propose that in microsphere-assisted microscopy imaging, the resolution can be improved by the excitation of surface plasmon polaritons (SPPs) on the sample surface or at the sample/substrate interface, and a higher near-field intensity due to the excited SPPs would benefit the resolution improvement. Our study of label-free super-resolution imaging of low-contrast objects will promote the applications of microsphere-assisted microscopy in life sciences.</jats:p>

<jats:p>High-order harmonics from helium atom in the orthogonally two-color (OTC) laser field are investigated by solving the two-dimensional time-dependent Schrödinger equation. Non-integer high-order harmonics are obtained in some ratio of frequencies of two components. Pure odd and even harmonics from atoms could be separated in two components by adjusting the ratio of frequencies in OTC scheme, and the resolution of harmonics is improved at the same time. The physical mechanism is explained by the periodicity of dipole. With the same intensity of the incident laser, the intensity of the high-order harmonics from the OTC field scheme is improved by three orders of magnitude compared to the monochromatic laser field scheme. A theoretical scheme is provided for experimentally achieving improving energy resolution and separation of pure odd and even harmonics in atoms. Also, we provide a means for improving harmonic intensity.</jats:p>

<jats:p>We use feedback wavefront shaping technology to realize the multi-point uniform light focusing in three-dimensional (3D) space through scattering media only by loading the optimal mask once. General 3D spatial focusing needs to load the optimal mask multiple times to realize the spatial movement of the focal point and the uniformity of multi-point focusing cannot be guaranteed. First, we investigate the effects of speckle axial correlation and different axial distances on 3D spatial multi-point uniform focusing and propose possible solutions. Then we use our developed non-dominated sorting genetic algorithm suitable for 3D spatial focusing (S-NSGA) to verify the experiment of multi-point focusing in 3D space. This research is expected to have potential applications in the fields of optical manipulation and optogenetics.</jats:p>

<jats:p>We implement an experimental study for the generation of wideband tunable femtosecond laser with a home-made power-scaled mode-locked fiber oscillator as the pump source. By coupling the sub-100 fs mode-locked pulses into a nonlinear photonic crystal fiber (NL-PCF), the exited spectra have significant nonlinear broadening and cover a spectra range of hundreds of nm. In experiment, by reasonably optimizing the structure parameters of NL-PCF and regulating the power of the incident pulses, femtosecond laser with tuning range of 900–1290 nm is realized. The research approach promotes the development of femtosecond lasers with center wavelengths out of the traditional laser gain media toward the direction of simplicity and ease of implementation.</jats:p>

<jats:p>Shell structures have increasingly widespread applications in biomedical ultrasound fields such as contrast agents and drug delivery, which requires the precise prediction of the acoustic radiation force under various circumstances to improve the system efficiency. The acoustic radiation force exerted by a zero-order quasi-Bessel–Gauss beam on an elastic spherical shell near an impedance boundary is theoretically and numerically studied in this study. By means of the finite series method and the image theory, a zero-order quasi-Bessel–Gauss beam is expanded in terms of spherical harmonic functions, and the exact solution of the acoustic radiation force is derived based on the acoustic scattering theory. The acoustic radiation force function, which represents the radiation force per unit energy density and per unit cross-sectional surface, is especially investigated. Some simulated results for a polymethyl methacrylate shell and an aluminum shell are provided to illustrate the behavior of acoustic radiation force in this case. The simulated results show the oscillatory property and the negative radiation force caused by the impedance boundary. An appropriate relative thickness of the shell can generate sharp peaks for a polymethyl methacrylate shell. Strong radiation force can be obtained at small half-cone angles and the beam waist only affects the results at high frequencies. Considering that the quasi-Bessel–Gauss beam possesses both the energy focusing property and the non-diffracting advantage, this study is expected to be useful in the development of acoustic tweezers, contrast agent micro-shells, and drug delivery applications.</jats:p>

<jats:p>With Zn substitution to the three-dimensional antiferromagnetically ordered barlowite Cu<jats:sub>4</jats:sub>(OH)<jats:sub>6</jats:sub>FBr, Cu<jats:sub>3</jats:sub>Zn(OH)<jats:sub>6</jats:sub>FBr shows no magnetic phase transition down to 50 mK, and the system is suggested to be a two-dimensional kagomé quantum spin liquid [<jats:italic>Chin. Phys. Lett.</jats:italic> <jats:bold>34</jats:bold> 077502 (2017)]. A key issue to identify such phase diagram is the exact chemical formula of the substituted compound. With Cu <jats:italic>L</jats:italic>-edge x-ray absorption spectrum (XAS) combined with the MultiX XAS calculations, we evaluate the Cu concentration in a nominal Cu<jats:sub>3</jats:sub>Zn(OH)<jats:sub>6</jats:sub>FBr sample. Our results show that although the Cu concentration is 2.80, close to the expected value, there is 34% residual Cu occupation in intersite layers between kagomé layers. Thus the Zn substitution of the intersite layers is not complete, and likely it intrudes the kagomé layers.</jats:p>

<jats:p>Understanding the mechanism of coalescence-induced self-propelled jumping behavior provides distinct insights in designing and optimizing functional coatings with self-cleaning and anti-icing properties. However, to date self-propelled jumping phenomenon has only been observed and studied on superhydrophobic surfaces, other than those hydrophobic surfaces with weaker but fairish water-repellency, for instance, vulcanized silicon rubber (RTV) coatings. In this work, from the perspective of thermodynamic-based energy balance aspect, the reason that self-propelled jumping phenomenon does not happen on RTV coatings is studied. The apparent contact angles of droplets on RTV coatings can be less than the theoretical critical values therefore cannot promise energy surplus for the coalesced droplets onside. Besides, on RTV and superhydrophobic surfaces, the droplet-size dependent variation characteristics of the energy leftover from the coalescence process are opposite. For the droplets coalescing on RTV coatings, the magnitudes of energy dissipations are more sensitive to the increase in droplet size, compared to that of released surface energy. While for superhydrophobic coatings, the energy generated during the coalescence process can be more sensitive than the dissipations to the change in droplet size.</jats:p>

<jats:p>Proton transfer plays a key role in the applications of advanced energy materials as well as in the functionalities of biological systems. In this work, based on the transfer matrix method, we study the quantum effects of proton transfer in a series of one-dimensional (1D) model potentials and numerically calculate the quantum probability of transferring across single and double barriers (wells). In the case of single barriers, when the incident energies of protons are above the barrier height, the quantum oscillations in the transmission coefficients depend on the geometric shape of the barriers. It is found that atomic resonant tunneling (ART) not only presents in the rectangular single well and rectangular double barriers as expected, but also exists in the other types of potential wells and double barriers. For hetero-structured double barriers, there is no resonant tunneling in the classical forbidden zone, i.e., in the case when the incident energy (<jats:italic>E</jats:italic> <jats:sub>i</jats:sub>) is lower than the barrier height (<jats:italic>E</jats:italic> <jats:sub>b</jats:sub>). Furthermore, we have provided generalized analysis on the characteristics of transmission coefficients of hetero-structured rectangular double barriers.</jats:p>

<jats:p>Using density functional theory, we investigate the vibrational properties and polarization-resolved Raman spectra of <jats:italic>α</jats:italic>-PtO<jats:sub>2</jats:sub> and obtain the Raman tensor and angle-dependent Raman intensity of <jats:italic>α</jats:italic>-PtO<jats:sub>2</jats:sub>. It is found that the polar plot of A<jats:sub>1g</jats:sub> mode in parallel polarization configuration is useful in identifying the orientation of the crystal. The Raman intensity of the E<jats:sub>g</jats:sub> mode is about five times stronger than that of the A<jats:sub>1g</jats:sub> mode. The Raman intensity is about three times stronger when the wave vector of the incident light is in <jats:italic>x</jats:italic> or <jats:italic>y</jats:italic> direction than in <jats:italic>z</jats:italic> direction. Our work will help the material scientists to characterize the <jats:italic>α</jats:italic>-PtO<jats:sub>2</jats:sub> and to identify its orientation by comparing the experimental spectra with our result.</jats:p>