Catálogo de publicaciones - revistas

<jats:p>We describe simulations of lubrication by a hexadecane molecular lubricating film during the shearing process of a Cu-Zn alloy performed using the atomistic method. The results indicate that with increasing Zn contents, the interface slip between the alloy wall and the lubricating film first decreases and then increases, according to variations of the radius distribution function (RDF), while the interface slip reaches its lowest value of 0.12 during the shearing of CuZn30 alloy. We also discuss the relationship between interface roughness and the lubricating film. During film lubrication, the interface’s roughness effectively inhibits interfacial slip. For the convex contact model, the presence of the hexadecane lubricating film reduces the interfacial contact pressure from 11.9 GPa to 8.7 GPa and the friction coefficient from 0.81 to 0.52.</jats:p>

<jats:p>Silica-based planar lightwave circuit (PLC) devices can reduce transmission loss and cost in a quantum key distribution (QKD) system, and have potential applications in integration and production. A PLC-based quantum decoding integrated chip for multi-protocols is designed and fabricated, which is composed of variable optical splitters (VOSs), asymmetric Mach–Zehnder interferometers (AMZIs), and variable directional couplers (VDCs). Balanced pulse-pairs of four outputs are obtained simultaneously with measured delay times of 405 ps and 402 ps, respectively. The chip has advantages in achieving high interference visibility and low quantum bit error rate (QBER).</jats:p>

<jats:p>We build a double quantum-dot system with Coulomb coupling and aim at studying connections among the entropy production, free energy, and information flow. By utilizing concepts in stochastic thermodynamics and graph theory analysis, Clausius and nonequilibrium free energy inequalities are built to interpret local second law of thermodynamics for subsystems. A fundamental set of cycle fluxes and affinities is identified to decompose two inequalities by using Schnakenberg’s network theory. Results show that the thermodynamic irreversibility has energy-related and information-related contributions. A global cycle associated with the feedback-induced information flow would pump electrons against the bias voltage, which implements a Maxwell demon.</jats:p>

<jats:p>To address the problem that it is difficult to detect an intermediate frequency (IF) signal at the receiving end of a communication system under extremely low signal-to-noise ratio (SNR) conditions, we propose a stochastic resonance (SR)-enhanced sine-signal detection method based on the sign function. By analyzing the SR mechanism of the sine signal and combining it with the characteristics of a dual-sequence frequency-hopping (DSFH) receiver, a periodic stationary solution of the Fokker–Planck equation (FPE) with a time parameter is obtained. The extreme point of the sine signal is selected as the decision time, and the force law of the electromagnetic particles is analyzed. A receiving structure based on the sign function is proposed to maximize the output difference of the system, and the value condition of the sign function is determined. In order to further improve the detection performance, in combination with the central-limit theorem, the sampling points are averaged <jats:italic>N</jats:italic> times, and the signal-detection problem is transformed into a hypothesis-testing problem under a Gaussian distribution. The theoretical analysis and simulation experiment results confirm that when <jats:italic>N</jats:italic> is 100 and the SNR is greater than 20 dB, the bit-error ratio (BER) is less than 1.5 × 10<jats:sup>−2</jats:sup> under conditions in which the signal conforms to the optimal SR parameters.</jats:p>

<jats:p>As the competition for marine resources is increasingly fierce, the security of underwater acoustic communication has attracted a great deal of attention. The information and location of the communicating platform can be leaked during the traditional underwater acoustic communication technology. According to the unique advantages of chaos communication, we put forward a novel communication scheme using complex parameter modulation and the complex Lorenz system. Firstly, we design a feedback controller and parameter update laws in a complex-variable form with rigorous mathematical proofs (while many previous references on the real-variable form were only special cases in which the imaginary part was zero), which can be realized in practical engineering; then we design a new communication scheme employing parameter modulation. The main parameter spaces of the complex Lorenz system are discussed, then they are adopted in our communication scheme. We also find that there exist parametric attractors in the complex Lorenz system. We make numerical simulations in two channels for digital signals and the simulations verify our conclusions.</jats:p>

<jats:p>We propose and realize a new optical state selection method on a cesium atomic fountain clock by applying a two-laser 3–3′ optical pumping configuration to spin polarize atoms. The atoms are prepared in |<jats:italic>F</jats:italic> = 3, <jats:italic>m<jats:sub>F</jats:sub> </jats:italic> = 0〉 clock state with optical pumping directly after being launched up, followed by a pushing beam to push away the atoms remaining in the |<jats:italic>F</jats:italic> = 4〉 state. With a state selection efficiency exceeding 92%, this optical method can substitute the traditional microwave state selection, and helps to develop a more compact physical package. A Ramsey fringe has been achieved with this optical state selection method, and a contrast of 90% is obtained with a full width half maximum of 0.92 Hz. The short-term frequency stability of 6.8 × 10<jats:sup>−14</jats:sup> (<jats:italic>τ</jats:italic>/<jats:italic>s</jats:italic>)<jats:sup>−1/2</jats:sup> is acquired. In addition, the number of detected atoms is increased by a factor of 1.7 with the optical state selection.</jats:p>

<jats:p>It is essential to explore high efficient catalysts for nitrogen reduction in ammonia production. Based on the first-principles calculation, we find that B/g-C<jats:sub>2</jats:sub>N can serve as high performance photocatalyst in N<jats:sub>2</jats:sub> fixation, where single boron atom is anchored on the g-C<jats:sub>2</jats:sub>N to form B/g-C<jats:sub>2</jats:sub>N. With the introduction of B atom to g-C<jats:sub>2</jats:sub>N, the energy gap reduces from 2.45 eV to 1.21 eV and shows strong absorption in the visible light region. In addition, N<jats:sub>2</jats:sub> can be efficiently reduced on B/g-C<jats:sub>2</jats:sub>N through the enzymatic mechanism with low onset potential of 0.07 V and rate-determining barrier of 0.50 eV. The “acceptance-donation” interaction between B/g-C<jats:sub>2</jats:sub>N and N<jats:sub>2</jats:sub> plays a key role to active N<jats:sub>2</jats:sub>, and the BN<jats:sub>2</jats:sub> moiety of B/g-C<jats:sub>2</jats:sub>N acts as active and transportation center. The activity originates from the strong interaction between 1<jats:italic>π</jats:italic>1<jats:italic>π</jats:italic>* orbitals of N<jats:sub>2</jats:sub> and molecular orbitals of B/g-C<jats:sub>2</jats:sub>N, the ionization of 1<jats:italic>π</jats:italic> orbital and the filling of 1<jats:italic>π</jats:italic>* orbital can increase the N≡N bond length greatly, making the activation of N<jats:sub>2</jats:sub>. Overall, this work demonstrates that B/g-C<jats:sub>2</jats:sub>N is a promising photocatalyst for N<jats:sub>2</jats:sub> fixation.</jats:p>

<jats:p>X-ray emission from the collisions of 3 MeV Ar<jats:sup>11 +</jats:sup> ions with V, Fe, Co, Ni, Cu, and Zn is investigated. Both the x-rays of the target atom and projectile are observed simultaneously. The x-ray yield is extracted from the original count. The inner-shell ionization cross section is estimated by the binary encounter approximation model and compared with the experimental result. The remarkable result is that the Ar <jats:italic>K</jats:italic>-shell x-ray yield is diminished with the target atomic number increasing, which is completely opposite to the theoretical calculation. That is interpreted by the competitive consumption of the energy loss for the ionization of inner-shell electrons between the projectile and target atom.</jats:p>

<jats:p>We propose a simple pumping method to increase the effective population of cold atoms in the clock state and investigate the factors which affect the pumping efficiency in cold atom systems. We report the theory and demonstrate the corresponding experiment in an <jats:sup>87</jats:sup>Rb integrating sphere cold atom clock. The experimental results show that the population of cold atoms in the Zeeman sublevel |<jats:italic>F</jats:italic> = 2, <jats:italic>m<jats:sub>F</jats:sub> </jats:italic> = 0〉 is approximately 1.62 times that of the result using optical pumping alone. This method can also be applied to increase the effective population in any one of the target Zeeman sublevels in other cold atom systems.</jats:p>

<jats:p>We develop a numerical scheme for solving the one-dimensional (1D) time-dependent Schrödinger equation (TDSE), and use it to study the strong-field photoionization of the atomic hydrogen. The photoelectron energy spectra obtained for pulses ranging from XUV to near infrared are compared in detail to the spectra calculated with our well-developed code for accurately solving the three-dimensional (3D) TDSE. For XUV pulses, our discussions cover intensities at which the ionization is in the perturbative and nonperturbative regimes. For pulses of 400 nm or longer wavelengths, we distinguish the multiphoton and tunneling regimes. Similarities and discrepancies between the 1D and 3D calculations in each regime are discussed. The observed discrepancies mainly originate from the differences in the transition matrix elements and the energy level structures created in the 1D and 3D calculations.</jats:p>