Catálogo de publicaciones - revistas

<jats:p>A series of Au films with different nominal deposition thickness <jats:italic>d</jats:italic> were fabricated on ionic liquid surfaces by thermal evaporation at room temperature, taken as surface-enhanced Raman scattering (SERS) substrates. Au atoms deposited on the liquid surfaces can diffuse and aggregate randomly and eventually form films with ramified structure, which consist of nanoparticles (NPs). There are amounts of ultrasmall (∼ 1 nm or smaller) nanogaps among the Au NPs, which can dramatically enhance Raman signal. Raman spectra of R6G were investigated with the assistance of the Au films. The results indicate that the Au films with higher thickness possess better SERS performance when 5.0 ≤ <jats:italic>d</jats:italic> ≤ 30.0 nm. A random distribution model of Au NPs was used in the finite-difference time-domain method and the simulation results are in good agreement with the experimental findings.</jats:p>

<jats:p>Why heavily parameterized neural networks (NNs) do not overfit the data is an important long standing open question. We propose a phenomenological model of the NN training to explain this non-overfitting puzzle. Our linear frequency principle (LFP) model accounts for a key dynamical feature of NNs: they learn low frequencies first, irrespective of microscopic details. Theory based on our LFP model shows that low frequency dominance of target functions is the key condition for the non-overfitting of NNs and is verified by experiments. Furthermore, through an ideal two-layer NN, we unravel how detailed microscopic NN training dynamics statistically gives rise to an LFP model with quantitative prediction power.</jats:p>

<jats:p>Radiative energy losses are very important in regulating the cosmic ray electron and/or positron (CRE) spectrum during their propagation in the Milky Way. Particularly, the Klein–Nishina (KN) effect of the inverse Compton scattering (ICS) results in less efficient energy losses of high-energy electrons, which is expected to leave imprints on the propagated electron spectrum. It has been proposed that the hardening of CRE spectra around 50 GeV observed by Fermi-LAT, AMS-02, and DAMPE could be due to the KN effect. We show in this work that the transition from the Thomson regime to the KN regime of the ICS is actually quite smooth compared with the approximate treatment adopted in some previous works. As a result, the observed spectral hardening of CREs cannot be explained by the KN effect. It means that an additional hardening of the primary electrons spectrum is needed. We also provide a parameterized form for the accurate calculation of the ICS energy-loss rate in a wide energy range.</jats:p>

<jats:p>Imperfections in practical detectors, including limited detection efficiency, and inherent electronic noise, can seriously decrease the transmission distance of continuous-variable measurement-device-independent quantum key distribution systems. Owing to the difficulties inherent in realizing a high-efficiency fiber homodyne detector, challenges still exist in continuous-variable measurement-device-independent quantum key distribution system implementation. We offer an alternative approach in an attempt to solve these difficulties and improve the potential for system implementation. Here, a novel practical detector modeling method is utilized, which is combined with a one-time shot-noise-unit calibration method for the purpose of system realization. The new modeling method benefits greatly from taking advantage of one-time shot-noise-unit calibration methods, such as measuring electronic noise and shot noise directly to a novel shot-noise unit, so as to eliminate the statistical fluctuations found in previous methods; this makes the implementation of such systems simpler, and the calibration progress more accurate. We provide a simulation of the secret key rate versus distance with different parameters. In addition, the minimal detection efficiency required at each distance, as well as the contrast between the two methods, are also shown, so as to provide a reference in terms of system realization.</jats:p>

<jats:p>We propose a one-dimensional optical lattice model to simulate and explore two-dimensional topological phases with ultracold atoms, considering the phases of the hopping strengths as an extra dimension. It is shown that the model exhibits nontrivial phases, and corresponding two chiral-edge states. Moreover, we demonstrate the connections between changes in the topological invariants and the Dirac points. Furthermore, the topological order detected by the particle pumping approach in cold atoms is also investigated. The results obtained here provide a feasible and flexible method of simulating and exploring high-dimensional topological phases in low-dimension systems via the controllable phase of the hopping strength.</jats:p>

<jats:p>The exact reconstruction of many-body quantum systems is one of the major challenges in modern physics, because it is impractical to overcome the exponential complexity problem brought by high-dimensional quantum many-body systems. Recently, machine learning techniques are well used to promote quantum information research and quantum state tomography has also been developed by neural network generative models. We propose a quantum state tomography method, which is based on a bidirectional gated recurrent unit neural network, to learn and reconstruct both easy quantum states and hard quantum states in this study. We are able to use fewer measurement samples in our method to reconstruct these quantum states and to obtain high fidelity.</jats:p>

<jats:p>We numerically investigate the transport of a passive colloidal particle in a periodic array of planar counter-rotating convection rolls, at high Péclet numbers. It is shown that an external bias, oriented parallel to the array, produces a huge excess diffusion peak, in cases where bias and advection drag become comparable. This effect is not restricted to one-dimensional convection geometries, and occurs independently of the array’s boundary conditions.</jats:p>

<jats:p>We propose to use transverse momentum <jats:italic>p</jats:italic> <jats:sub>T</jats:sub> distribution of <jats:italic>J</jats:italic>/<jats:italic>ψ</jats:italic> production at the future Electron Ion Collider (EIC) to explore the production mechanism of heavy quarkonia in high energy collisions. We apply QCD and QED collinear factorization to the production of a <jats:inline-formula> <jats:tex-math><?CDATA $c\bar{c}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>c</mml:mi> <mml:mover accent="true"> <mml:mi>c</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_38_4_041201_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> pair at high <jats:italic>p</jats:italic> <jats:sub>T</jats:sub>, and non-relativistic QCD factorization to the hadronization of the pair to a <jats:italic>J</jats:italic>/<jats:italic>ψ</jats:italic>. We evaluate <jats:italic>J</jats:italic>/<jats:italic>ψ</jats:italic> <jats:italic>p</jats:italic> <jats:sub>T</jats:sub>-distribution at both leading and next-to-leading order in strong coupling, and show that production rates for various color-spin channels of a <jats:inline-formula> <jats:tex-math><?CDATA $c\bar{c}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>c</mml:mi> <mml:mover accent="true"> <mml:mi>c</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_38_4_041201_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> pair in electron-hadron collisions are very different from that in hadron-hadron collisions, which provides a strong discriminative power to determine various transition rates for the pair to become a <jats:italic>J</jats:italic>/<jats:italic>ψ</jats:italic>. We predict that the <jats:italic>J</jats:italic>/<jats:italic>ψ</jats:italic> produced in electron-hadron collisions is likely unpolarized, and the production is an ideal probe for gluon distribution of colliding hadron (or nucleus). We find that the <jats:italic>J</jats:italic>/<jats:italic>ψ</jats:italic> production is dominated by the color-octet channel, providing an excellent probe to explore the gluon medium in large nuclei at the EIC.</jats:p>

<jats:p>The remaining uncertainties in relation to isovector nuclear interactions call for reliable experimental measurements of isovector probes in finite nuclei. Based on the Bayesian analysis, although neutron-skin thickness data or isovector giant dipole resonance data in <jats:sup>208</jats:sup>Pb can constrain only one isovector interaction parameter, correlations among other parameters can also be built. Using combined data for both the neutron-skin thickness and the isovector giant dipole resonance helps to significantly constrain all isovector interaction parameters; as such, it serves as a useful methodology for future research.</jats:p>