Catálogo de publicaciones - revistas

<jats:p>In the numerical studies of active particles, models consisting of a solid body and a fluid body have been well established and widely used. In this work, such an active Brownian particle (ABP) is realized in molecular dynamics (MD) simulations. Immersed in a fluid, each ABP consists of a head particle and a spherical phantom region of fluid where the flagellum of a microswimmer takes effect. Quantitative control over the orientational persistence time is achieved via an external stochastic dynamics. This control makes it possible to validate ABP’s diffusion property in a wide range of particle activity. In molecular description, the axial velocity of ABP exhibits a Gaussian distribution. Its mean value defines the active velocity which increases with the active force linearly, but shows no dependence on the rotational diffusion coefficient. For the active diffusion coefficient measured in free space, it shows semi-quantitative agreement with the analytical result predicted by a minimal ABP model. Furthermore, the active diffusion coefficient is also calculated by performing a quantitative analysis on the ABP’s distribution along <jats:italic>x</jats:italic> axis in a confinement potential. Comparing the active diffusion coefficients in the above two cases (in free space and in confinement), the validity of the ABP modeling implemented in MD simulations is confirmed. Possible reasons for the small deviation between the two diffusion coefficients are also discussed.</jats:p>

<jats:p>When chaotic systems are implemented on finite precision machines, it will lead to the problem of dynamical degradation. Aiming at this problem, most previous related works have been proposed to improve the dynamical degradation of low-dimensional chaotic maps. This paper presents a novel method to construct high-dimensional digital chaotic systems in the domain of finite computing precision. The model is proposed by coupling a high-dimensional digital system with a continuous chaotic system. A rigorous proof is given that the controlled digital system is chaotic in the sense of Devaney’s definition of chaos. Numerical experimental results for different high-dimensional digital systems indicate that the proposed method can overcome the degradation problem and construct high-dimensional digital chaos with complicated dynamical properties. Based on the construction method, a kind of pseudorandom number generator (PRNG) is also proposed as an application.</jats:p>

<jats:p>Considering an elastically coupled Brownian motors system in a two-dimensional traveling-wave potential, we investigate the effects of the angular frequency of the traveling wave, wavelength, coupling strength, free length of the spring, and the noise intensity on the current of the system. It is found that the traveling wave is the essential condition of the directed transport. The current is dominated by the traveling wave and varies nonmonotonically with both the angular frequency and the wavelength. At an optimal angular frequency or wavelength, the current can be optimized. The coupling strength and the free length of the spring can locally modulate the current, especially at small angular frequencies. Moreover, the current decreases rapidly with the increase of the noise intensity, indicating the interference effect of noise on the directed transport.</jats:p>

<jats:p>In recent years, clinical studies have found that acetone concentration in exhaled breath can be taken as a characteristic marker of diabetes. Metal–oxide–semiconductor (MOS) materials are widely used in acetone gas sensors due to their low cost, high sensitivity, fast response/recovery time, and easy integration. This paper reviews recent progress in acetone sensors based on MOS materials for diabetes diagnosis. The methods of improving the performance of acetone sensor have been explored for comparison, especially in high humidity conditions. We summarize the current excellent methods of preparations of sensors based on MOSs and hope to provide some help for the progress of acetone sensors in the diagnosis of diabetes.</jats:p>

<jats:p>Recent progresses on quantum control of cold atoms and trapped ions in both the scientific and technological aspects greatly advance the applications in precision measurement. Thanks to the exceptional controllability and versatility of these massive quantum systems, unprecedented sensitivity has been achieved in clocks, magnetometers, and interferometers based on cold atoms and ions. Besides, these systems also feature many characteristics that can be employed to facilitate the applications in different scenarios. In this review, we briefly introduce the principles of optical clocks, cold atom magnetometers, and atom interferometers used for precision measurement of time, magnetic field, and inertial forces. The main content is then devoted to summarize some recent experimental and theoretical progresses in these three applications, with special attention being paid to the new designs and possibilities towards better performance. The purpose of this review is by no means to give a complete overview of all important works in this fast developing field, but to draw a rough sketch about the frontiers and show the fascinating future lying ahead.</jats:p>

<jats:p>The nonradiative charge-transfer processes of Be<jats:sup>3+</jats:sup>(1s)/B<jats:sup>4+</jats:sup>(1s) colliding with He(1s<jats:sup>2</jats:sup>) are investigated by the quantum-mechanical molecular orbital close-coupling (QMOCC) method from 10 eV/u to 1800 eV/u. Total and state-selective cross sections are obtained and compared with other results available. Although the incident ions have the same number of electrons and collide with the same target, their cross sections are different due to the differences in molecular structure. For Be<jats:sup>3+</jats:sup>(1s) + He(1s<jats:sup>2</jats:sup>), only single-electron-capture (SEC) states are important and the total cross sections have a broad maximum around <jats:italic>E</jats:italic> = 150 eV/u. While for B<jats:sup>4+</jats:sup>(1s) + He(1s<jats:sup>2</jats:sup>), both the SEC and double-electron-capture (DEC) processes are important, and the total SEC and DEC cross sections decrease rapidly with the energy decreasing.</jats:p>

<jats:p>Up to now, at least 806 carbon allotropes have been proposed theoretically. Three interesting carbon allotropes (named <jats:italic>Pbam</jats:italic>-32, <jats:italic>P</jats:italic>6/<jats:italic>mmm</jats:italic>, and <jats:inline-formula> <jats:tex-math> <?CDATA $I\bar{4}3d$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>I</mml:mi> <mml:mover accent="true"> <mml:mn>4</mml:mn> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> <mml:mn>3</mml:mn> <mml:mi>d</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_9_093601_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) were recently uncovered based on a random sampling strategy combined with space group and graph theory. The calculation results show that they are superhard and remarkably stable compared with previously proposed metastable phases. This indicates that they are likely to be synthesized in experiment. We use the factor group analysis method to analyze their <jats:italic>Γ</jats:italic> -point vibrational modes. Owing to their large number of atoms in primitive unit cells (32 atoms in <jats:italic>Pbam</jats:italic>-32, 36 atoms in <jats:italic>P</jats:italic>6/<jats:italic>mmm</jats:italic>, and 94 atoms in <jats:inline-formula> <jats:tex-math> <?CDATA $I\bar{4}3d$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>I</mml:mi> <mml:mover accent="true"> <mml:mn>4</mml:mn> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> <mml:mn>3</mml:mn> <mml:mi>d</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_9_093601_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>), they have many Raman- and infrared-active modes. There are 48 Raman-active modes and 37 infrared-active modes in <jats:italic>Pbam</jats:italic>-32, 24 Raman-active modes and 14 infrared-active modes in <jats:italic>P</jats:italic>6/<jats:italic>mmm</jats:italic>, and 34 Raman-active modes and 35 Raman- and infrared-active modes in <jats:inline-formula> <jats:tex-math> <?CDATA $I\bar{4}3d$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>I</mml:mi> <mml:mover accent="true"> <mml:mn>4</mml:mn> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> <mml:mn>3</mml:mn> <mml:mi>d</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_9_093601_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. Their calculated Raman spectra can be divided into middle frequency range from 600 cm<jats:sup>−1</jats:sup> to 1150 cm<jats:sup>−1</jats:sup> and high frequency range above 1150 cm<jats:sup>−1</jats:sup>. Their largest infrared intensities are 0.82, 0.77, and 0.70 (D/Å)<jats:sup>2</jats:sup>/amu for <jats:italic>Pbam</jats:italic>, <jats:italic>P</jats:italic>6/<jats:italic>mmm</jats:italic>, and <jats:inline-formula> <jats:tex-math> <?CDATA $I\bar{4}3d$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>I</mml:mi> <mml:mover accent="true"> <mml:mn>4</mml:mn> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> <mml:mn>3</mml:mn> <mml:mi>d</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_9_093601_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, respectively. Our calculated results provide an insight into the lattice vibrational spectra of these sp<jats:sup>3</jats:sup> carbon allotropes and suggest that the middle frequency Raman shift and infrared spectrum may play a key role in identifying newly proposed carbon allotropes.</jats:p>

<jats:p>Compact atomic gravimeters are the potential next generation precision instruments for gravity survey from fundamental research to broad field applications. We report the calibration results of our home build compact absolute atomic gravimeter USTC-AG02 at Changping Campus, the National Institute of Metrology (NIM), China in January 2019. The sensitivity of the atomic gravimeter reaches <jats:inline-formula> <jats:tex-math><?CDATA $35.5\,{\rm {\mu}} {\rm{Gal}}/\sqrt{{\rm{Hz}}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>35.5</mml:mn> <mml:mspace width="0.25em" /> <mml:mo>μ</mml:mo> <mml:mi mathvariant="normal">Gal</mml:mi> <mml:mo>/</mml:mo> <mml:msqrt> <mml:mrow> <mml:mi mathvariant="normal">Hz</mml:mi> </mml:mrow> </mml:msqrt> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_9_093701_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> (1 μGal = 1 × 10<jats:sup>−8</jats:sup> m/s<jats:sup>2</jats:sup>) and its long-term stability reaches 0.8 μGal for averaging over 4000 seconds. Considering the statistical uncertainty, the dominant instrumental systematic errors and environmental effects are evaluated and corrected within a total uncertainty (2<jats:italic>σ</jats:italic>) of 15.3 μGal. After compared with the reference <jats:italic>g</jats:italic> value given by the corner cube gravimeter NIM-3A, the atomic gravimeter USTC-AG02 reaches the degree of equivalence of 3.7 μGal.</jats:p>

<jats:p>High precision atom interferometers have shown attractive prospects in laboratory for testing fundamental physics and inertial sensing. Efforts on applying this innovative technology to field applications are also being made intensively. As the manipulation of cold atoms and related matching technologies mature, inertial sensors based on atom interferometry can be adapted to various indoor or mobile platforms. A series of experiments have been conducted and high performance has been achieved. In this paper, we will introduce the principles, the key technologies, and the applications of atom interferometers, and mainly review the recent progress of movable atom gravimeters.</jats:p>

<jats:p>Metasurface is a kind of two-dimensional metamaterial with specially designed sub-wavelength unit cells. It consists of single-layer or few-layer stacks of planar structures and possesses certain superior abilities to manipulate the propagating electromagnetic waves, including the terahertz (THz) ones. Compared with the usual passive THz metasurfaces whose optical properties are difficult to be controlled after fabrication, the active materials are highly desirable to enable dynamic and tunable control of THz waves. In this review, we briefly summarize the progress of active THz metasurfaces, from their physical mechanisms on carrier concentration modulations, phase transitions, magneto-optical effects, etc., for various possible THz applications mainly with low-dimensional materials, vanadium dioxide films, and superconductors.</jats:p>