Catálogo de publicaciones - revistas

<jats:p>Majorana fermions have been predicted to exist at the edge states of a two-dimensional topological superconductor. We fabricated single quintuple layer (QL) Bi<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub>/FeTe heterostructure with the step-flow epitaxy method and studied the topological properties of this system by using angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. We observed the coexistence of robust superconductivity and edge states on the single QL Bi<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub> islands which can be potential evidence for topological superconductor.</jats:p>

<jats:p>Field-driven magnetic domain wall propagation in ferromagnetic nanostrips with trapezoidal cross section has been systematically investigated by means of micromagnetic simulation. Asymmetric dynamic behaviors of domain wall, depending on the propagation direction, were observed under an external magnetic field. When the domain walls propagate in the opposite direction along the long axis of the nanostrip, the Walker breakdown fields as well as the average velocities are different. The asymmetric landscape of demagnetization energies, which arises from the trapezoidal geometry, is the main origin of the asymmetric propagation behavior. Furthermore, a trapezoid-cross-section nanostrip will become a nanotube if it is rolled artificially along its long axis, and thus a two-dimensional transverse domain wall will become a three-dimensional one. Interestingly, it is found that the asymmetric behaviors observed in two-dimensional nanostrips with trapezoidal cross section are similar with some dynamic properties occurring in three-dimensional nanotubes.</jats:p>

<jats:p>We perform a computational simulation of light emissions from two sonoluminescent bubbles in water. Our simulation includes the radii of two bubbles, radiation acoustic pressures, and light emission spectra by numerically solving the pulsing equations of a two-bubble system and the equations of gas dynamics. The simulation results demonstrate that the motion of each bubble in the two-bubble system is restrained because of the radiation acoustic pressures from the other pulsing bubble. The restrained oscillation of a bubble with a small ambient radius is stronger than that of a bubble with a large ambient radius under the same driving acoustic pressure. This effect increases when the distance between the two bubbles decreases. When compared to single-bubble sonoluminescence, the interaction between two bubbles leads to generation of different spectral characteristics.</jats:p>

<jats:p>In this study, the effects of quantum dot size on the binding energy, radiative lifetime, and optical absorption coefficient of exciton state in both GaN/Al<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Ga<jats:sub>1−<jats:italic>x</jats:italic> </jats:sub>N core/shell and Al<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Ga<jats:sub>1−<jats:italic>x</jats:italic> </jats:sub>N/GaN inverted core/shell quantum dot structures are studied. For the GaN/Al<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Ga<jats:sub>1−<jats:italic>x</jats:italic> </jats:sub>N core/shell structure, the variation trend of binding energy is the same as that of radiation lifetime, both of which increase first and then decrease with the increase of core size. For Al<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Ga<jats:sub>1−<jats:italic>x</jats:italic> </jats:sub>N/GaN inverted core/shell structure, the binding energy decreases first and then increases with core size increasing, and the trends of radiation lifetime varying with core size under different shell sizes are different. For both structures, when the photon energy is approximately equal to the binding energy, the peak value of the absorption coefficient appears, and there will be different peak shifts under different conditions.</jats:p>

<jats:p>Inspired by recent discoveries of the quasi-Josephson effect in shunted nanowire devices, we propose a superconducting nanowire interference device in this study, which is a combination of parallel ultrathin superconducting nanowires and a shunt resistor. A simple model based on the switching effect of nanowires and fluxoid quantization effect is developed to describe the behavior of the device. The current–voltage characteristic and flux-to-voltage conversion curves are simulated and discussed to verify the feasibility. Appropriate parameters of the shunt resistor and inductor are deduced for fabricating the devices.</jats:p>

<jats:p>Transient receptor potential vanilloid subtype 1 (TRPV1) is a polymodel sensory receptor and can be activated by moderate temperature (≥ 43 °C). Though extensive researches on the heat-activation mechanism revealed some key elements that participate in the heat-sensation pathway, the detailed thermal-gating mechanism of TRPV1 is still unclear. We investigate the heat-activation process of TRPV1 channel using the molecular dynamics simulation method at different temperatures. It is found that the favored state of the supposed upper gate of TRPV1 cannot form constriction to ion permeation. Oscillation of S5 helix originated from thermal fluctuation and forming/breaking of two key hydrogen bonds can transmit to S6 helix through the hydrophobic contact between S5 and S6 helix. We propose that this is the pathway from heat sensor of TRPV1 to the opening of the lower gate. The heat-activation mechanism of TRPV1 presented in this work can help further functional study of TRPV1 channel.</jats:p>

<jats:p>The circadian clock is a self-sustained biological oscillator which can be entrained by environmental signals. The cyanobacteria circadian clock is the simplest one, which is composed of the proteins KaiA, KaiB and KaiC. The phosphorylation/dephosphorylation state of KaiC exhibits a circadian oscillator. KaiA and KaiB activate KaiC phosphorylation and dephosphorylation respectively. CikA competing with KaiA for the same binding site on KaiB affects the phosphorylation state of KaiC. Quinone is a signaling molecule for entraining the cyanobacterial circadian clock which is oxidized at the onset of darkness and reduced at the onset of light, reflecting the environmental light–dark cycle. KaiA and CikA can sense external signals by detecting the oxidation state of quinone. However, the entrainment mechanism is far from clear. We develop an enhanced mathematical model including oxidized quinone sensed by KaiA and CikA, with which we present a detailed study on the entrainment of the cyanobacteria circadian clock induced by quinone signals. We find that KaiA and CikA sensing oxidized quinone pulse are related to phase advance and delay, respectively. The time of oxidized quinone pulse addition plays a key role in the phase shifts. The combination of KaiA and CikA is beneficial to the generation of entrainment, and the increase of signal intensity reduces the entrainment phase. This study provides a theoretical reference for biological research and helps us understand the dynamical mechanisms of cyanobacteria circadian clock.</jats:p>

<jats:p>A feasible neuron model can be effective to estimate the mode transition in neural activities in a complex electromagnetic environment. When neurons are exposed to electromagnetic field, the continuous magnetization and polarization can generate nonlinear effect on the exchange and propagation of ions in the cell, and then the firing patterns can be regulated completely. The conductivity of ion channels can be affected by the temperature and the channel current is adjusted for regulating the excitability of neurons. In this paper, a phototube and a thermistor are used to the functions of neural circuit. The phototube is used to capture external illumination for energy injection, and a continuous signal source is obtained. The thermistor is used to percept the changes of temperature, and the channel current is changed to adjust the excitability of neuron. This functional neural circuit can encode the external heat (temperature) and illumination excitation, and the dynamics of neural activities is investigated in detail. The photocurrent generated in the phototube can be used as a signal source for the neural circuit, and the thermistor is used to estimate the conduction dependence on the temperature for neurons under heat effect. Bifurcation analysis and Hamilton energy are calculated to explore the mode selection. It is found that complete dynamical properties of biological neurons can be reproduced in spiking, bursting, and chaotic firing when the phototube is activated as voltage source. The functional neural circuit mainly presents spiking states when the photocurrent is handled as a stable current source. Gaussian white noise is imposed to detect the occurrence of coherence resonance. This neural circuit can provide possible guidance for investigating dynamics of neural networks and potential application in designing sensitive sensors.</jats:p>

<jats:p>We report on the temperature-dependent Schottky barrier in organic solar cells based on PTB7:PC<jats:sub>71</jats:sub>BM. The ideality factor is found to increase with temperature decreasing, which is explained by a model in which the solar cell is taken as Schottky barrier diode. Accordingly, the dark current in the device originates from the thermally emitted electrons across the Schottky barrier. The fittings obtained with the thermal emission theory are systematically studied at different temperatures. It is concluded that the blend/Ca/Al interface presents great inhomogeneity, which can be described by 2 sets of Gaussian distributions with large zero bias standard deviations. With the decrease of temperature, electrons favor going across the Schottky barrier patches with lower barrier height and as a consequence the ideally factor significantly increases at low temperature.</jats:p>

<jats:p>A GaN-based pin neutron detector with a <jats:sup>6</jats:sup>LiF conversion layer was fabricated, and can be used to detect thermal neutrons. Measurement of the electrical characteristic of the GaN-based pin neutron detector showed that the reverse leakage current of the neutron detector was reduced significantly after deposition of a <jats:sup>6</jats:sup>LiF conversion layer on the detector surface. The thermal neutrons used in this experiment were obtained from an <jats:sup>241</jats:sup>Am–Be fast neutron source after being moderated by 100-mm-thick high-density polyethylene. The experimental results show that the detector with 16.9-μm thick <jats:sup>6</jats:sup>LiF achieved a maximum neutron detection efficiency of 1.9% at a reverse bias of 0 V, which is less than the theoretical detection efficiency of 4.1% calculated for our GaN neutron detectors.</jats:p>