Catálogo de publicaciones - revistas

<jats:p>A numerical model is developed by coupling the cellular automaton (CA) method and the lattice Boltzmann method (LBM) to simulate the dendritic growth of Al–Cu alloy in both two and three dimensions. An improved decentered square algorithm is proposed to overcome the artificial anisotropy induced by the CA cells and to realize simulation of dendritic growth with arbitrary orientations. Based on the established CA-LBM model, effects of forced convection and gravity-driven natural convection on dendritic growth are studied. The simulation results show that the blocking effect of dendrites on melt flow is advanced with a larger number of seeds. The competitive growth of the converging columnar dendrites is determined by the interaction between heat flow and forced convection. Gravity-driven natural convection leads to highly asymmetric growth of equiaxed dendrites. With sinking downwards of the heavy solute, chimney-like or mushroom-like solute plumes are formed in the melt in front of the columnar dendrites when they grow along the gravitational direction. More details on dendritic growth of Al–Cu alloy under convection are revealed by 3D simulations.</jats:p>

<jats:p>Rapid single flux quantum (RSFQ) circuits are a kind of superconducting digital circuits, having properties of a natural gate-level pipelining synchronous sequential circuit, which demonstrates high energy efficiency and high throughput advantage. We find that the high-throughput and high-speed performance of RSFQ circuits can take the advantage of a hardware implementation of the encryption algorithm, whereas these are rarely applied to this field. Among the available encryption algorithms, the advanced encryption standard (AES) algorithm is an advanced encryption standard algorithm. It is currently the most widely used symmetric cryptography algorithm. In this work, we aim to demonstrate the SubByte operation of an AES-128 algorithm using RSFQ circuits based on the SIMIT Nb03 process. We design an AES <jats:italic>S</jats:italic>-box circuit in the RSFQ logic, and compare its operational frequency, power dissipation, and throughput with those of the CMOS-based circuit post-simulated in the same structure. The complete RSFQ <jats:italic>S</jats:italic>-box circuit costs a total of 42237 Josephson junctions with nearly 130 Gbps throughput under the maximum simulated frequency of 16.28 GHz. Our analysis shows that the frequency and throughput of the RSFQ-based <jats:italic>S</jats:italic>-box are about four times higher than those of the CMOS-based <jats:italic>S</jats:italic>-box. Further, we design and fabricate a few typical modules of the <jats:italic>S</jats:italic>-box. Subsequent measurements demonstrate the correct functioning of the modules in both low and high frequencies up to 28.8 GHz.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Carbyne, as the truly one-dimensional carbon allotrope with <jats:italic>sp</jats:italic>-hybridization, has attracted significant interest in recent years, showing potential applications in next-generation molecular devices due to its ultimate one-atom thinness. Various excellent properties of carbyne have been predicted, however, free-standing carbyne sample is extremely unstable and the corresponding experimental researches and modifications are under-developed compared to other known carbon allotropes. The synthesis of carbyne has been slowly developed for the past decades. Recently, there have been several breakthroughs in <jats:italic>in-situ</jats:italic> synthesis and measurement of carbyne related materials, as well as the preparation of ultra-long carbon chains toward infinite carbyne. These progresses have aroused widespread discussion in the academic community. In this review, the latest approaches in the synthesis of <jats:italic>sp</jats:italic> carbon are summarized. We then discuss its extraordinary properties, including mechanical, electronic, magnetic, and optical properties, especially focusing on the regulations of these properties. Finally, we provide a perspective on the development of carbyne.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We experimentally realize a two-dimensional (2D) single-layer ultracold gases for $^{87}$Rb by dynamically tuning the periodicity of a standing wave, known as accordion lattice. In order to load $^{87}$Rb Bose-Einstein condensate into single dark fringe node of the blue detuning optical lattice, we reduce the lattice periodicity from 26.7 $\mu$m to 3.5 $\mu$m with the help of an accousto-optic deflector (AOD) to compress the three dimensional BEC adiabatically into a flat and uniform quasi-2D single-layer. We describe the experimental procedure of the atoms loading into the accordion lattice in detail and present the characteristics of quasi-2D ultracold gases. This setup provides an important platform for studying in- and out-of equilibrium physics, phase transition and 2D topological matter.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigated the photon emission spectra on Ag(111) surface excited by tunneling electrons using a low temperature scanning tunneling microscope in ultrahigh vacuum. Characteristic plasmon modes were illustrated as a function of the bias voltage. The one electron excitation process was revealed by the linear relationship between the luminescence intensity and the tunneling current. Luminescence enhancement is observed in the tunneling regime for the relatively high bias voltages, as well as at the field emission resonance with bias voltage increased up to 9 V. Presents of a silver (Ag) nanoparticle in the tunneling junction results in an abnormally strong photon emission at the high field emission resonances, which is explained by the further enhancement due to coupling between the localized surface plasmon and the vacuum. The results are of potential value for applications where ultimate enhancement of photon emission is desired.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magneto-acoustic tomography with current injection (MAT-CI) belongs to hybrid imaging, under the excitation of the static magnetic field, the thermoacoustic effect and the Lorentz force effect will exist at the same time. Therefore, the detected signal is a mixed signal generated by the simultaneous action of two effects, but the influence of excitation parameters on the two effects is different. In this paper, for different conductivity objects, the proportion of thermoacoustic signal (TA) and magneto-acoustic signal (MA) in mixed signal is quantitatively analyzed from the three aspects: the magnetic induction intensity, pulse excitation and injection current polarity. Experimental and simulation analysis show that the intensity ratio of MA to TA is not affected when the conductivity varies from 0.1S/m to 1.5S/m and other conditions remain unchanged. When the amplitude of the pulse excitation and the strength of the magnetic induction are different, the growth rates of MA and TA are different, which has a significant impact on the proportion of the two signals in the mixed signal. At the same time, due to the Lorentz force effect, MA is affected by the polarity of the injected current and the direction of the static magnetic field. The combination of the static magnetic field and the injected current can not only distinguish the two signals in the mixed signal, but also effectively enhance the intensity of the mixed signal, and improve the quality of the reconstructed image.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The magnetic and magnetocaloric (MCE) of the amorphous <jats:italic>RE</jats:italic> <jats:sub>55</jats:sub>Co<jats:sub>30</jats:sub>Al<jats:sub>10</jats:sub>Si<jats:sub>5</jats:sub>(<jats:italic>RE</jats:italic> = Er and Tm) ribbons were systematically investigated in this paper. Compounds with <jats:italic>R</jats:italic> = Er and Tm undergo a second order magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) around Curie temperature <jats:italic>T</jats:italic> <jats:sub>C</jats:sub> ~ 9.3 K and 3 K, respectively. For Er<jats:sub>55</jats:sub>Co<jats:sub>30</jats:sub>Al<jats:sub>10</jats:sub>Si<jats:sub>5</jats:sub> compound, an obvious magnetic hysteresis and thermal hysteresis were observed at low field below 6 K, possibly due to spin-glass behavior. Under the field change of 0-5 T, the maximum values of magnetic entropy change (−Δ<jats:italic>S</jats:italic> <jats:sub> <jats:italic>M</jats:italic> </jats:sub> <jats:sup> <jats:italic>max</jats:italic> </jats:sup>) reach as high as 15.6 J/kg K and 15.7 J/kg K for Er<jats:sub>55</jats:sub>Co<jats:sub>30</jats:sub>Al<jats:sub>10</jats:sub>Si<jats:sub>5</jats:sub> and Tm<jats:sub>55</jats:sub>Co<jats:sub>30</jats:sub>Al<jats:sub>10</jats:sub>Si<jats:sub>5</jats:sub> compounds, corresponding refrigerant capacity (<jats:italic>RC</jats:italic>) values are estimated as 303 J/kg and 189 J/kg, respectively. The large MCE makes amorphous <jats:italic>RE</jats:italic> <jats:sub>55</jats:sub>Co<jats:sub>30</jats:sub>Al<jats:sub>10</jats:sub>Si<jats:sub>5</jats:sub> (<jats:italic>RE</jats:italic> = Er and Tm) alloys become very attractive magnetic refrigeration materials in the low-temperature region.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Quantum key distribution provides an unconditional secure key sharing method in theory, but the imperfect factors of practical devices will bring security vulnerabilities. In this paper, we characterize the imperfections of the sender and analyze the possible attack strategies of Eve. Firstly, we present a quantized model for distinguishability of decoy states caused by intensity modulation. Besides, considering that Eve may control the preparation of states through hidden variables, we evaluate the security of preparation in practical QKD scheme based on the weak-randomness model. Finally, we analyze the influence of the distinguishability of decoy state to secure key rate, for Eve may conduct the beam splitting attack and control the channel attenuation of different parts. Through the simulation, it can be seen that the secure key rate is sensitive to the distinguishability of decoy state and weak randomness, especially when Eve can control the channel attenuation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Quantum metrology provides a fundamental limit on the precision of multi-parameter estimation, called the Heisenberg limit, which has been achieved in noiseless quantum systems. However, for systems subject to noises, it is hard to achieve this limit since noises are inclined to destroy quantum coherence and entanglement. In this paper, a combined control scheme with feedback and quantum error correction (QEC) is proposed to achieve the Heisenberg limit in the presence of spontaneous emission, where the feedback control is used to protect a stabilizer code space containing an optimal probe state and an additional control is applied to eliminate the measurement incompatibility among three parameters. Although an ancilla system is necessary for the preparation of the optimal probe state, our scheme does not require the ancilla system to be noiseless. In addition, the control scheme in this paper has a low-dimensional code space. For the three components of a magnetic field, it can achieve the highest estimation precision with only a 2-dimensional code space, while at least a 4-dimensional code space is required in the common optimal error correction protocols.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A novel 4H-SiC trench IGBT with a controllable hole-extracting (CHE) path is proposed and investigated in this paper. The CHE path is controlled by metal semiconductor gate (MES gate) and metal oxide semiconductor gate (MOS gate) in p-shield region. The grounded p-shield region can significantly suppress the high electric field around gate oxide in SiC devices, but it weakens the conductivity modulation in the SiC trench IGBT by rapidly sweeping out holes. This effect can be eliminated by introducing CHE path. The CHE path is pinched off by the high gate bias voltage in on-state to maintain high conductivity modulation and obtain a comparatively low on-state voltage (<jats:italic>V</jats:italic> <jats:sub>ON</jats:sub>). During the turn-off transient, the CHE path is formed, which contributes to a decreased turn-off loss (<jats:italic>E</jats:italic> <jats:sub>OFF</jats:sub>). Based on numerical simulation, the <jats:italic>E</jats:italic> <jats:sub>OFF</jats:sub> of the proposed IGBT is reduced by 89% compared with the conventional IGBT at same <jats:italic>V</jats:italic> <jats:sub>ON</jats:sub> and the <jats:italic>V</jats:italic> <jats:sub>ON</jats:sub> of the proposed IGBT is reduced by 50% compared to the grounded p-shield IGBT at same <jats:italic>E</jats:italic> <jats:sub>OFF</jats:sub>. In addition, the average power reduction for the proposed device can be 51.0 % to 81.7 % and 58.2% to 72.1% with its counterparts at a wide frequency range of 500 Hz to 10 kHz, revealing a great improvement of frequency characteristics.</jats:p>