Accepted
Study on the relationship between hydrogen bond network dynamics of water and its terahertz spectrum
, , Received Date: 2021-09-17
Abstract +
Water is an active matrix of life. Understanding the terahertz absorption spectrum of water is the prerequisite for the application of terahertz technology in biomedicine. The choice of terahertz frequency is essential for achieving the biological effects of terahertz with high efficiency and low energy consumption. The complex hydrogen bond network of water makes it have a broad terahertz absorption peak. Therefore, it is necessary to study the relationship between the dynamics of the hydrogen bond network of water and its terahertz absorption spectrum. However, research in this field is still lacking. Using molecular dynamics simulation methods, this article studied the terahertz absorption spectra of different water models at room temperature and pressure. Furthermore, taking the temperature as a variable, we explored the dependence of the terahertz absorption spectrum of water on the strength of the hydrogen bond network. We found that rising temperature makes the terahertz absorption spectrum of the hydrogen bond network red-shift, indicating that the center frequency of the spectrum strongly correlates with the strength of the hydrogen bond. Further studies showed that there is a linear relationship between the hydrogen bond lifetime of water and the center frequency of vibration absorption peak of the hydrogen bond network. The mechanism underlying can be disclosed by the analogy of the hydrogen bonds in the hydrogen bond network to springs with the help of the spring oscillator model. These findings are promising for deepening the understanding of the complex hydrogen bond network dynamics in water and promoting the study of
, , Received Date: 2021-09-24
Abstract +
Methane hydrate (so-call flammable ice) has a large variety of advantages such as wide distribution, large resource reserves, high energy density, being clean and pollution-free, etc. Thus, it has attracted extensive attention since been discovered. Unfortunately, it brings many difficulties during exploitation, which mainly involves in the dissolution of caged methane hydrate. As a result, in this paper we explore this decomposition under the specific THz electromagnetic stimulation through molecular dynamics simulations. In analyzing the vibrational spectrum of the hydrogen-bond network in methane hydrate, we find a specific absorption peak which whereas does not exist in the bulk water. By introducing a THz wave at this specific frequency to the methane hydrate, we discover that the field stimulus breaks the original hydrogen-bond network, lowers the coordinate number of water molecules for the methane, and ultimately free the methane from the water cages. The F4 ordered parameters further validates the phase change from the crystal water to liquid water under the same THz field irritation. We have also proved the specifity of this peak absorption frequency with remarkable superiority over other frequencies in decomposing the methane hydrate. Our findings support the viability of non-thermally dissolving methane hydrate, which is promising to promote the exploitation efficiency and development of new energy sources in the future.
, , Received Date: 2021-01-14
Abstract +
$ \theta $$ \phi $ increase, some energy levels increase and tend to change linearly, and other energy levels first decrease and then increase. If the limit values of the non-commutative parameters are taken as follows:, $ \theta \to 0 $ and $ \phi \to 0 $ , then the noncommutative energy spectra will be consistent with the energy spectra of the two-dimensional harmonic oscillator in the commutative space in general. On the other hand, the energy levels will split under the influence of coupling parameters. Moreover, the degree to which the energy levels split can increase as the kinds of couplings in the system increase. It is found that the coordinate coupling parameter $ \eta $ and the momentum coupling parameter $ \sigma $ have the same influence on the energy levels, but the coordinate momentum cross-coupling parameter $ \kappa $ has less influence on the energy levels than $ \eta $ and $ \sigma $ . Overall, the above results are completely different from those of two-dimensional oscillator in the usual commutative space, which is degenerated except for the ground state.">The ideas of noncommutative space originate from the research on time-space coordinate on an extremely small scale. Subsequently, the noncommutative space has gradually attracted some attention. The researchers started to explore noncommutative effect in some other fields. With the establishment of noncommutative quantum mechanics, it becomes significant to explore the noncommutative effect of exactly solvable models. The kinds of harmonic oscillators are very important and fundamental models in physics. But in noncommutative phase space, coordinate and coordinate are noncommutative, and momentum and momentum are also noncommutative. These results in the difficulty in obtaining the energy spectra of oscillators systems. In this paper the quantum properties of a two-dimensional coupling harmonic oscillator in noncommutative phase space are studied. Firstly, the Hamiltonian of the system is constructed, which includes all possible coupling types, namely, coordinate-coordinate coupling, momentum-momentum coupling, and coordinate-momentum cross-coupling. Secondly, the explicit expression of the noncommutative energy spectrum for the Hamiltonian is obtained by using the invariant eigen-operator method. In this work it is shown explicitly that the changes in the energy levels are related to the noncommutative parameters and coupling parameters. Thirdly, the effects of coupling parameters and non-commutative parameters on the energy spectra are analyzed in detail in the form of graphs. The results show that the energy levels under the influence of non-commutative parameters are non-degenerated. As the values of non-commutation parameters $ \theta $ and $ \phi $ increase, some energy levels increase and tend to change linearly, and other energy levels first decrease and then increase. If the limit values of the non-commutative parameters are taken as follows:, $ \theta \to 0 $ and $ \phi \to 0 $ , then the noncommutative energy spectra will be consistent with the energy spectra of the two-dimensional harmonic oscillator in the commutative space in general. On the other hand, the energy levels will split under the influence of coupling parameters. Moreover, the degree to which the energy levels split can increase as the kinds of couplings in the system increase. It is found that the coordinate coupling parameter $ \eta $ and the momentum coupling parameter $ \sigma $ have the same influence on the energy levels, but the coordinate momentum cross-coupling parameter $ \kappa $ has less influence on the energy levels than $ \eta $ and $ \sigma $ . Overall, the above results are completely different from those of two-dimensional oscillator in the usual commutative space, which is degenerated except for the ground state.
, , Received Date: 2021-07-01
Abstract +
The precise, uniform and constant wireless transmission of electromagnetic power to multiple targets in a local finite space is a scientific problem to be solved urgently. Aiming at this problem, this paper proposes an automatic zone selection channel matching method based on time reversal (TR) technique which has the spatio-temporal focusing characteristics. The proposed method can not only adaptively compensate the channel differences at different targets based on the contribution rate of the multipath signals, but also dynamically divide the working range of the time reversal mirror (TRM) elements to eliminate the mutual influences between different targets through the use of the distance coefficient. While improving the accuracy of energy focusing, the proposed method also solves the problem that non-uniform microwave power transmission (MPT) of multiple targets, and therefore it achieves constant, uniform and long-time MPT of multi-targets.
, , Received Date: 2021-04-27
Abstract +
Muon scattering imaging technology can be used to detect nuclear material and is of considerable significance in nuclear safety. However, it is difficult to distinguish special nuclear materials from high-Z objects effectively by using the existing muon scattering imaging technologies. Muon-induced neutrons emitted from special nuclear materials can help to identify the existence of special nuclear materials. However, this method has long imaging time and low imaging quality. Multi-modal imaging of muon uses both the information about scattering muons penetrating the material and the information about muons stopped by material and generating secondary induced neutrons, which can overcome the shortcomings of single imaging method effectively. The detection model is set up based on Geant4. The simulation programs of muon imaging in coincidence with muon induced neutrons, scattering imaging of muon, and multi-modal imaging of muon are developed by using Cosmic-ray Shower Library as particle source, and the imaging algorithms are implemented respectively on the basis of the simulated data. Two imaging models are designed for muon scattering imaging. The first one is a single 235U cube, and the second one is composed of four cubes, namely 235U cube, 239Pu cube, lead cube and aluminum cube. This simulation has completed muon scattering imaging of single cube and four cubes. In the part of muon imaging in coincidence with muon induced neutrons, the neutronic gain of the HEU (90% 235U) plate, LEU (20% 235U) plate, and DU (0.2% 235U) plate, as well as the relationship between the neutronic gain of these three uranium plates and the energy and charged properties of the muon are obtained by simulation, and then two imaging models are set up. The first one is composed of four cubes, namely 235U cube, 239Pu cube, lead cube, and aluminum cube, and the other is comprised of multilayer nuclear components. The 2D and 3D reconstruction results of multi-objects and multilayer nuclear components are obtained through muon imaging in coincidence with muon induced neutrons. Then the multi-modal imaging of muon for three cubes is realized in the presence or absence of iron shielding shell. The imaging capabilities are compared with the muon scattering imaging capacities and muon imaging capacities in coincidence with muon induced neutrons. Simulation studies indicate that multi-modal imaging of muon based on scattering and secondary induced neutrons can effectively combine the advantages of every single imaging method. The multi-modal imaging of muon can take advantage of available information more efficiently, which is helpful in improving the imaging quality. Multi-modal imaging of muon not only has the advantages of short imaging time and high imaging quality, but also can distinguish special nuclear material from other high-Z materials clearly, which is vital for detecting special nuclear materials.
, , Received Date: 2021-03-19
Abstract +
In recent years, industries such as mobile consumer electronics and electric vehicles have been developing rapidly, and they have been hunting for lithium batteries with high energy density, high safety and stability, to alleviate the range anxiety and improve their stability over long term operations. These make all-solid-state lithium batteries very attractive and they have been under intense investigations. However, the development of high-performance all-solid-state lithium batteries requires an in-depth understanding of their charging and discharging mechanism as well as their performance degradation mechanism, along with the evolution of the microstructures, phase compositions, chemical states and their distributions, etc., inside the battery and at the interface. This paper summarizes the basic principles, functions, and the representative progress in the investigation of the dynamic process and failure mechanism of the electrode material and interface in the solid-state lithium battery in the working condition and real electrochemical process, with typical in-situ characterization techniques, including in-situ microscopy (in-situ scanning electron microscopy (SEM), in-situ transmission electron microscopy (TEM)), in-situ X-ray technology (in-situ X-ray diffraction (XRD)), in-situ X-ray photoelectron spectroscopy (XPS), in-situ near-edge structure X-ray absorption spectroscopy (XANES), in-situ X-ray tomography), in-situ neutron technology (in-situ neutron diffraction (ND), In situ neutron depth profiling (NDP)) and in situ spectroscopy technology (in situ Raman spectroscopy, in situ nuclear magnetic resonance (NMR) and in situ nuclear magnetic resonance imaging (MRI)), etc. We also discussed the application of future advanced in-situ characterization techniques in the investigation of all-solid-state lithium batteries.
, , Received Date: 2021-07-30
Abstract +
In this paper, the propagation properties of partially coherent power-exponent-vortex beam have been studied. Firstly, the propagation model of partially coherent power-exponent-vortex beam was established. Then, the propagation properties of partially coherent power-exponent-vortex beams in free space and ABCD optical system have simulated. The results show that when power-exponent-vortex beams propagated in free space, the topological charge, power exponent and coherence length have a great influence on the distribution of light intensity, and the area of light spot gradually increases with the increase of propagation distance; when the beam propagated in the focusing system, the changes of topological charge and power exponent will affect the light intensity distribution, while the coherence length has little effect on the overall intensity distribution of the beam, only the quality of the spot. The research results of this paper reveal the propagation properties of partially coherent power-exponent-vortex beam, which will lay a theoretical foundation for its application in optical capture and other fields, and has important significance for promoting the theory and application of optical field manipulation.
, , Received Date: 2021-07-16
Abstract +
Two dimensional magnetic material which has been rapidly developed in recent years, has potential application in the development of spintronic devices. In order to understand the magnetic properties of two-dimensional magnetic materials, it is necessary to comprehend the magnetic interaction which is estimated by the exchange parameters between the magnetic atoms. The calculation of the magnetic exchange parameters is based on the first-principle. The commonly used method to calculate the exchange parameters is energy-mapping method. However, this method has some disadvantages. This paper derives the spin-spiral dispersion relationship under the Heisenberg interaction and the Dzyaloshinskii-Moriya (DM) interaction through the generalized Bloch condition of three kinds of two-dimensional magnetic structures: a tetragonal structure, a hexagonal structure in which the cell contains one magnetic atom, a hexagonal structure in which the cell contains two magnetic atoms. We calculate magnetic exchange parameters of some materials through the first principle. These materials are: MnB、VSe2、MnSTe、Cr2I3Cl3. MnSTe and Cr2I3Cl3 are two-dimensional Janus materials, which means they have space-reversal symmetry broken, so there is DM interaction in the system.
, , Received Date: 2021-07-15
Abstract +
In this paper, a metamaterial structure with a double-layer split square ring and a double C-shaped structure is designed, which has dual-band electromagnetically induced transparency effects in the terahertz band. This structure has transmission peaks at 1.438 THz and 1.699 THz. Through the analysis of the surface current distribution, the reasons for the dual-band electromagnetically induced transparency are discussed. The effect of the designed metamaterial on the transmission window when the opening size of the open square ring and the distance of the double C-shaped structure and the incident angle are changed is studied. At the incident angle, the transmission spectrum of the designed material changes greatly, showing high sensitivity to angle. The research results show that the structure has potential application prospects in angle sensors and other fields.
, , Received Date: 2021-04-26
Abstract +
The spin effect of bound magnetopolaron in an anisotropic quantum dot is studied with Pekar variational method. The expression of the ground state energy of the bound magnetopolaron is obtained through theoretical derivation. The relationship between the ground state energy of the polaron and the transverse effective confinement length, the longitudinal effective confinement length, the magnetic field cyclotron resonance frequency, and the Coulomb bound potential are discussed, respectively. Due to the crystal structural inversion asymmetry and the time inversion asymmetry, the polaron energy experiences Rashba spin-orbit splitting and Zeeman splitting. Under the strong and weak magnetic fields, we discussed the dominant position of Zeeman effect and Rashba effect, respectively. Due to the presence of phonons and impurities, the polaron is more stable than the bare electron state.
, , Received Date: 2021-03-02
Abstract +
The adsorption and desorption behaviors of ammonia on TaC(0001) surface have been studied by employing spin-polarized density function theory calculations. The surface energy calculation results show that TaC (0001) terminating with Ta is the most stable surface. According to the optimized structural and energetic properties, it was found that NH3 prefers to adsorb on the top site, whereas NH2, H prefer to adsorb on the triple hcp site and NH, N prefer on the triple fcc site. In addition, three transition states were found for analyzing the mechanism of dehydrogenation of NH3, and the N recombination reaction was also considered. The results show that the desorption of nitrogen atoms is the rate-determining step in the overall reaction. Finally, in order to further elucidate the mechanism of NH3 adsorption and dissociation on the surface of Ta-TaC, the electronic structure of the most stable adsorption position was analyzed from the perspective of charge density distribution and electron density of states. The results of electronic structure calculation show that NH3 molecule is adsorbed on the surface through the mixture of 2PZ orbital of N atom and 5dZ2 orbital of substrate Ta. With the progress of dehydrogenation, the charge transfer phenomenon becomes more and more serious. The charge transfer between adsorbate and substrate plays an important role in accelerating NH3 dehydrogenation catalytic process.
, , Received Date: 2021-06-21
Abstract +
There have been some theoretical studies on the high pressure phase transition behavior of BaF2, while in most cases the authors pay main attention to the optical and electrical properties of BaF2 with increasing pressure. To date, there is still a lack of theoretical explanation for the hysteresis phenomenon of high-pressure phase of BaF2 when the pressure was released. In addition, the pressure-dependent behavior of the BaF2 band gap is still controversial, and there are few studies dealing with its high-pressure Raman spectra. Therefore, first principles were used to make a supplementary calculation of the high pressure behavior of BaF2. For a given pressure P and temperature T, the thermodynamic stable phase has the lowest Gibbs free energy. The calculations are performed at zero temperature and hence, the Gibbs free energy becomes equal to the enthalpy. Thus, the variation of enthalpy was calculated as a function of pressure to study the high-pressure phase stability of BaF2 based on density functional theory as implemented in the Vienna ab initio simulation package (VASP). The results show that BaF2 undergoes two structural phase transitions from Fm3m(cubic) to Pnma(orthorhombic) and then to P63/mmc(hexagonal) with increasing pressure, and the transition pressures are 3.5 and 18.3 GPa, respectively. By calculating the evolution of lattice constant with the pressure, it was found that at about 15 GPa (near the second phase transition pressure), the lattice constants of the Pnma structure show abnormal behavior (a slight increase in bo and a slight decrease in ao). We suggest that this behavior leads to the reduction of the band gap by analyzing the calculated results of Pnma structure of other materials. The Pnma structure completely transformed to P63/mmc structure at about 20 GPa. By analyzing the phonon dispersion curves of BaF2 as a function of pressure, the structural stability information of the material can also be obtained. Then the density functional perturbation theory (DFPT) was used to calculate the phonon dispersion curves of BaF2 by VASP code and Phonopy code. The hysteresis phenomenon of the P63/mmc structure, when the pressure was released, is explained by phonon soft mode. The results predict that the P63/mmc structure can be stabilized at least to 80 GPa.
, , Received Date: 2021-08-11
Abstract +
The thermal transport properties of porous graphene nanoribbons were studied by non-equilibrium Green's function method. The results show that due to the existence of nano-pores, the thermal conductance of porous graphene nanoribbons is much lower than that of graphene nanoribbons. At room temperature, the thermal conductance of zigzag porous graphene nanoribbons is only 12% of that of zigzag graphene nanoribbons of the same size. This is due to the phonon localization caused by the nano-pores in the porous graphene nanoribbons. In addition, the thermal conductance of porous graphene nanoribbons has remarkable anisotropy. At the same size, the thermal conductance of armchair porous graphene nanoribbons is about 2 times higher than that of zigzag porous graphene nanoribbons. This is because the phonon locality in the zigzag direction is stronger than that in the armchair direction, and even part of the frequency phonons are completely localized.
, , Received Date: 2021-04-05
Abstract +
A large high altitude air shower observatory (LHAASO) located at Daocheng in Sichuan province, China, with an altitude up to 4410 m above the sea level, takes the function of hybrid technology to detect cosmic rays. It is composed of three sub-arrays: a 1.3 km2 ground-based particle detector array (KM2A) for γ-ray astronomy and cosmic ray physics, a 78000 m2 water Cherenkov detector array (WCDA) for γ-ray astronomy, and 18 wide field-of-view air Cherenkov/fluorescence telescopes array (WFCTA) for cosmic ray physics. As the major array of LHAASO, KM2A is composed of 5195 electromagnetic particle detectors (EDs, each with 1 m2) and 1188 muon detectors (MDs, each with 36 m2). In the ground-based experiments, there are two common independent data acquisition systems, corresponding to the shower and scaler operation modes. Up to now, the KM2A array operates only in shower mode with the primary energy threshold of about 10 TeV. In the scaler mode, it is not necessary for too many detectors to be hit at the same time. The energy threshold of the experiment can be greatly lowered. In order to learn more about the scaler mode in LHAASO-KM2A, we adopt the CORSIKA 7.5700 to study the cascade processes of extensive air showers in the atmosphere, and employ the G4KM2A (based on Geant4) to simulate the detector responses. The KM2A-ED array is divided into dozens of clusters. For one cluster (composed of 64 EDs), the event rates of showers having a number of fired EDs ≥ 1, 2, 3, 4 (in a time coincidence of 100 ns) are recorded. The average rates of the four multiplicities are ~88 kHz, ~1400 Hz, ~220 Hz, and ~110 Hz, respectively. The particle multiplicities m ≥ 3 are almost completely due to cosmic ray secondary particles. The corresponding primary energies and effective areas are also given in this paper. According to our simulations, the energy threshold of the scaler mode can be lowered to 100 GeV, and the effective areas reach up to ~ 100 m2. The simulation results in this work are helpful in the online triggering with the scaler mode, and provide information for the subsequent data analysis in LHAASO-KM2A.
, , Received Date: 2021-03-29
Abstract +
HTL-free carbon-based perovskite solar (PSCs) batteries have the advantages of low cost, simple preparation steps, and high stability, and have broad application prospects. However, the direct contact between the carbon electrode and the active layer causes the photoelectric conversion efficiency of the device to be generally lower than that of other metal electrode perovskite solar cells. Therefore, it is necessary to add a hole-transport layer between the perovskite layer and the electrode to improve the charge transport efficiency and optimize the performance. Poly(3-hexylthiophene) has excellent photoelectric properties and is regarded as one of the suitable hole transport materials for perovskite solar cells. In this paper, P3HT is used as the hole transport layer of the device. Compared with the traditional organic hole-transport layer Spiro-OMeTAD, the P3HT has the advantages of low cost and easy manufacture. However, in the current devices with using P3HT as the hole transport layer, due to the characteristics of the surface morphology and molecular ordering of the P3HT film, the carrier mobility in the film itself is low, resulting in unsatisfactory device performance. Studies have shown that the surface morphology and molecular arrangement of the P3HT film can be changed by doping, and the migration rate of charge-carriers inside the film can be accelerated, thereby improving the photovoltaic performance of the solar cell. In this paper, a printing process is used to print carbon paste on the hole transport layer as the electrode of the device, and spin coating is used to prepare the transport layer. And through the method of doping 1,8-diiodooctane (DIO) in P3HT to optimize the device performance, the photoelectric conversion efficiency of the carbon-based perovskite solar cell is improved, the mobility of holes is improved, and the transportation of electrons is blocked. The reduced interface recombination, the improved interface contact between the carbon electrode and the device, the increased short-circuit current Jsc and the fill factor FF lead the photoelectric conversion efficiency of the device to increase from 14.06% to 15.11%. We test the light stability of the device under the 1000-h continuous illumination in a nitrogen atmosphere, and the conversion efficiency of the device remains above 98%, indicating that the addition of DIO into P3HT improves not only the photoelectric conversion efficiency of the device, but also the stability.
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