Catálogo de publicaciones - revistas

<jats:p>X-ray speckle tracking based methods can provide results with best reported angular accuracy up to 2 nrad. However, duo to the multi-frame requirement for phase retrieval and the possible instability of the x-ray beam, mechanical and background vibration, the actual accuracy will inevitably be degraded by these time-dependent fluctuations. Therefore, not only spatial position, but also temporal features of the speckle patterns need to be considered in order to maintain the superiority of the speckle-based methods. In this paper, we propose a parallel acquisition method with advantages of real time and high accuracy, which has potential applicability to dynamic samples imaging as well as on-line beam monitoring. Through simulations, we demonstrate that the proposed method can reduce the phase error caused by the fluctuations to 1% at most compared with current speckle tracking methods. Meanwhile, it can keep the accuracy deterioration within 0.03 nrad, making the high theoretical accuracy a reality. Also, we find that waveforms of the incident beam have a little impact on the phase retrieved and will not influence the actual accuracy, which relaxes the requirements for speckle-based experiments.</jats:p>

<jats:p>The Jaynes–Cummings model with or without rotating-wave approximation plays a major role to study the interaction between atom and light. We investigate the Jaynes–Cummings model beyond the rotating-wave approximation. Treating the counter-rotating terms as periodic drivings, we solve the model in the extended Floquet space. It is found that the full energy spectrum folded in the quasi-energy bands can be described by an effective Hamiltonian derived in the high-frequency regime. In contrast to the <jats:italic>Z</jats:italic> <jats:sub>2</jats:sub> symmetry of the original model, the effective Hamiltonian bears an enlarged <jats:italic>U</jats:italic>(1) symmetry with a unique photon-dependent atom-light detuning and coupling strength. We further analyze the energy spectrum, eigenstate fidelity and mean photon number of the resultant polaritons, which are shown to be in accordance with the numerical simulations in the extended Floquet space up to an ultra-strong coupling regime and are not altered significantly for a finite atom-light detuning. Our results suggest that the effective model provides a good starting point to investigate the rich physics brought by counter-rotating terms in the frame of Floquet theory.</jats:p>

<jats:p>With the rapid demand for underwater optical communication (UOC), studies of UOC degradation by oceanic turbulence have attached increasing attention worldwide and become a research hot-spot in recent years. Previous studies used a simplified and inaccurate oceanic turbulence spectrum, in which the eddy diffusivity ratio between temperature and salinity is assumed to be unity and the outer scale of turbulence is assumed to be infinite. However, both assumptions are not true in most of the actual marine environments. In this paper, based on the Rytov theory in weak turbulence, we derive analytical expressions of “the aperture-averaged scintillation index” (SI) for both plane and spherical waves, which can clearly demonstrate how SI is influenced by several key factors in UOC. Then, typical fade statistics of the UOC system in weak turbulence is discussed including the probability of fade, the expected number of fades per time, the mean fade time, signal-to-noise ratio and bit error rate. Our results show that spherical wave is preferable in the UOC system in weak turbulence compared to plane wave, and the aperture-averaged effect has a significant impact on UOC system’s performance. Our results can be used to determine those key parameters for designing the UOC system over reasonable ranges.</jats:p>

<jats:p>There is always need for secure transmission of information and simultaneously compact-size photonic circuits. This can be achieved if surface plasmon-polaritons (SPPs) are used as source of information, and the reduced hacking as the transmission phenomenon. In this article, an SPP-based reduced hacking scheme is presented at interface between atomic medium and metallic conductor. The SPP propagation is manipulated with conductivity of the metal. The delay or advance of the SPP is found to create nanosecond time gap which can be used for storing and sending the information safely. The reduced hacking is further modified with conductivity of the metal and the control parameters of the atomic medium.</jats:p>

<jats:p>Time-resolved radial uniformity of pulse-modulated inductively coupled O<jats:sub>2</jats:sub>/Ar plasma has been investigated by means of a Langmuir probe as well as an optical probe in this paper. The radial uniformity of plasma has been discussed through analyzing the nonuniformity factor <jats:italic>β</jats:italic> (calculated by the measured <jats:italic>n</jats:italic> <jats:sub>e</jats:sub>, lower <jats:italic>β</jats:italic> means higher plasma radial uniformity). The results show that during the active-glow period, the radial distribution of <jats:italic>n</jats:italic> <jats:sub>e</jats:sub> exhibits an almost flat profile at the beginning phase, but it converts into a parabola-like profile during the steady state. The consequent evolution for <jats:italic>β</jats:italic> is that when the power is turned on, it declines to a minimum at first, and then it increases to a maximum, after that, it decays until it keeps constant. This phenomenon can be explained by the fact that the ionization gradually becomes stronger at the plasma center and meanwhile the rebuilt electric field (plasma potential and ambipolar potential) will confine the electrons at the plasma center as well. Besides, the mean electron energy (〈 <jats:italic>ε</jats:italic> 〉<jats:sub>on</jats:sub>) at the pulse beginning decreases with the increasing duty cycle. This will postpone the plasma ignition after the power is turned on. This phenomenon has been verified by the emission intensity of Ar (<jats:italic>;</jats:italic> = 750.4 nm). During the after-glow period, it is interesting to find that the electrons have a large depletion rate at the plasma center. Consequently, <jats:italic>n</jats:italic> <jats:sub>e</jats:sub> forms a hollow distribution in the radial direction at the late stage of after-glow. Therefore, <jats:italic>β</jats:italic> exhibits a maximum at the same time. This can be attributed to the formation of negative oxygen ion (O<jats:sup>−</jats:sup>) at the plasma center when the power has been turned off.</jats:p>

<jats:p>We experimentally investigate effects of W<jats:sup>6+</jats:sup> occupying the sites of Sc<jats:sup>3+</jats:sup> in the unit cell of Sc<jats:sub>2</jats:sub>W<jats:sub>3</jats:sub>O<jats:sub>12</jats:sub> (Sc<jats:sub>8</jats:sub>W<jats:sub>12</jats:sub>O<jats:sub>48</jats:sub>) on the structure, vibration and thermal expansion. The composition and structure of the doped sample (Sc<jats:sub>6</jats:sub>W<jats:sub>2</jats:sub>)W<jats:sub>12</jats:sub>O<jats:sub>48 ± <jats:italic>δ</jats:italic> </jats:sub> (with two W<jats:sup>6+</jats:sup> occupying two sites of Sc<jats:sup>3+</jats:sup> in the unit cell of Sc<jats:sub>8</jats:sub>W<jats:sub>12</jats:sub>O<jats:sub>48</jats:sub>) are analyzed and identified by combining the x-ray photoelectron spectroscopy and the synchronous x-ray diffraction with first-principles calculations based on density functional theory. Results show that the crystal with even W<jats:sup>6+</jats:sup> occupying even Sc<jats:sup>3+</jats:sup> in the unit cell is stable and maintains the orthorhombic structure at room temperature. The structure of the doped sample is similar to that of Sc<jats:sub>2</jats:sub>W<jats:sub>3</jats:sub>O<jats:sub>12</jats:sub>, and with even W occupying even positions of Sc in the unit cell and constituting the WO<jats:sub>6</jats:sub> octahedra. Raman analyses show that the doped sample possesses stronger W–O bonds and wider Raman linewidths than those of Sc<jats:sub>2</jats:sub>W<jats:sub>3</jats:sub>O<jats:sub>12</jats:sub>. The sample doped with W also exhibits intrinsic negative thermal expansion in the measured range of 150 K–650 K.</jats:p>

<jats:p>We study the properties of Bose–Einstein condensates under a non-Hermitian spin–orbit coupling (SOC), induced by a dissipative two-photon Raman process. We focus on the dynamics of the condensate at short times, when the impact of decoherence induced by quantum jumps is negligible and the dynamics is coherently driven by a non-Hermitian Hamiltonian. Given the significantly modified single-particle physics by dissipative SOC, the interplay of non-Hermiticity and interaction leads to a quasi-steady-state phase diagram different from its Hermitian counterpart. In particular, we find that dissipation can induce a phase transition from the stripe phase to the plane-wave phase. We further map out the phase diagram with respect to the dissipation and interaction strengths, and finally investigate the stability of quasi-steady states through the time-dependent dissipative Gross–Pitaevskii equation. Our results are readily accessible based on standard experiments with synthetic spin–orbit couplings.</jats:p>

<jats:p>Experimentally synthesized MoSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub> (<jats:italic>Science</jats:italic> <jats:bold>369</jats:bold> 670 (2020)) is a piezoelectric semiconductor. Here, we systematically study the large biaxial (isotropic) strain effects (0.90–1.10) on electronic structures and transport coefficients of monolayer MoSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub> by density functional theory (DFT). With <jats:italic>a</jats:italic>/<jats:italic>a</jats:italic> <jats:sub>0</jats:sub> from 0.90 to 1.10, the energy band gap firstly increases, and then decreases, which is due to transformation of conduction band minimum (CBM). Calculated results show that the MoSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub> monolayer is mechanically stable in the considered strain range. It is found that the spin-orbital coupling (SOC) effects on Seebeck coefficient depend on the strain. In unstrained MoSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub>, the SOC has neglected influence on Seebeck coefficient. However, the SOC can produce important influence on Seebeck coefficient, when the strain is applied, for example, 0.96 strain. The compressive strain can change relative position and numbers of conduction band extrema (CBE), and then the strength of conduction bands convergence can be enhanced, to the benefit of n-type <jats:italic>ZT</jats:italic> <jats:sub>e</jats:sub>. Only about 0.96 strain can effectively improve n-type <jats:italic>ZT</jats:italic> <jats:sub>e</jats:sub>. Our works imply that strain can effectively tune the electronic structures and transport coefficients of monolayer MoSi<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub>, and can motivate farther experimental exploration.</jats:p>

<jats:p>Structural properties of the organic-inorganic hybrid (C<jats:sub>2</jats:sub>H<jats:sub>5</jats:sub>NH<jats:sub>3</jats:sub>)<jats:sub>2</jats:sub>CuCl<jats:sub>4</jats:sub> (EA<jats:sub>2</jats:sub>CuCl<jats:sub>4</jats:sub>) have been investigated by means of x-ray powder diffraction and Rietveld analysis. A structural phase transition from <jats:italic>Pbca</jats:italic> to <jats:italic>Aba2</jats:italic> occurs at <jats:italic>T</jats:italic> <jats:sub>4</jats:sub> = 240 K, which results in a paraelectric–ferroelectric phase transition. The release of the Jahn–Teller distortion with increasing temperature toward <jats:italic>T</jats:italic> <jats:sub>4</jats:sub> is revealed by the structural analysis.</jats:p>

<jats:p>It is commonly realized that polydispersity may significantly affect the surface modification properties of polymer brush systems. In light of this, we systematically study morphologies of bidisperse polyelectrolyte brush grafted onto a spherical nanocolloid in the presence of trivalent counterions using molecular dynamics simulations. Via varying polydispersity, grafting density, and solvent selectivity, the effects of electrostatic correlation and excluded volume are focused, and rich phase behaviors of binary mixed polyelectrolyte brush are predicted, including a variety of pinned-patch morphologies at low grafting density and micelle-like structures at high grafting density. To pinpoint the mechanism of surface structure formation, the shape factor of two species of polyelectrolyte chains and the pair correlation function between monomers from different polyelectrolyte ligands are analyzed carefully. Also, electrostatic correlations, manifested as the bridging through trivalent counterions, are examined by identifying four states of trivalent counterions. Our simulation results may be useful for designing smart stimuli-responsive materials based on mixed polyelectrolyte coated surfaces.</jats:p>