In this work, we present a new coprime array structure termed thinned coprime array (TCA), which exploits the redundancy in the structure of existing coprime array and achieves the same virtual ...aperture and degrees of freedom (DOFs) as the conventional coprime array with much fewer number of sensors. In comparison to other sparse arrays, thinned coprime arrays possess more unique lags (total number of difference co-arrays) than the nested arrays, while the number of consecutive lags (connected co-arrays) generated is close to 75% of the consecutive lags of the nested arrays with hole-free co-arrays. The resulting structure is much sparser and the number of sensor pairs with small separation is significantly reduced. Theoretical properties and proofs are provided and simulations are presented to demonstrate its robustness against heavy levels of mutual coupling using compressive sensing based direction of arrival estimation as well as certain additional desirable characteristics.
Topological semimetals are three-dimensional topological states of matter, in which the conduction and valence bands touch at a finite number of points, i.e., the Weyl nodes. Topological semimetals ...host paired monopoles and antimonopoles of Berry curvature at the Weyl nodes and topologically protected Fermi arcs at certain surfaces. We review our recent works on quantum transport in topological semimetals, according to the strength of the magnetic field. At weak magnetic fields, there are competitions between the positive magnetoresistivity induced by the weak anti-localization effect and negative magnetoresistivity related to the nontrivial Berry curvature. We propose a fitting formula for the magnetoconductivity of the weak anti-localization. We expect that the weak localization may be induced by inter-valley effects and interaction effect, and occur in double-Weyl semimetals. For the negative magnetoresistance induced by the nontrivial Berry curvature in topological semimetals, we show the dependence of the negative magnetoresistance on the carrier density. At strong magnetic fields, specifically, in the quantum limit, the magnetoconductivity depends on the type and range of the scattering potential of disorder. The high-field positive magnetoconductivity may not be a compelling signature of the chiral anomaly. For long-range Gaussian scattering potential and half filling, the magnetoconductivity can be linear in the quantum limit. A minimal conductivity is found at the Weyl nodes although the density of states vanishes there.
Using the Feynman diagram techniques, we derive the finite-temperature conductivity and magnetoconductivity formulas from the quantum interference and electron-electron interaction, for a ...three-dimensional disordered Weyl semimetal. For a single valley of Weyl fermions, we find that the magnetoconductivity is negative and proportional to the square root of magnetic field at low temperatures, as a result of the weak antilocalization. By including the contributions from the weak antilocalization, Berry curvature correction, and Lorentz force, we compare the calculated magnetoconductivity with a recent experiment. The weak antilocalization always dominates the magnetoconductivity near zero field, thus gives one of the transport signatures for Weyl semimetals. In the presence of strong intervalley scattering and correlations, we expect a crossover from the weak antilocalization to weak localization. In addition, we find that the interplay of electron-electron interaction and disorder scattering always dominates the conductivity at low temperatures and leads to a tendency to localization. Finally, we present a systematic comparison of the transport properties of single-valley Weyl fermions, 2D massless Dirac fermions, and 3D conventional electrons.
Neural stem cells (NSCs), capable of ischemia‐homing, regeneration, and differentiation, exert strong therapeutic potentials in treating ischemic stroke, but the curative effect is limited in the ...harsh microenvironment of ischemic regions rich in reactive oxygen species (ROS). Gene transfection to make NSCs overexpress brain‐derived neurotrophic factor (BDNF) can enhance their therapeutic efficacy; however, viral vectors must be used because current nonviral vectors are unable to efficiently transfect NSCs. The first polymeric vector, ROS‐responsive charge‐reversal poly(2‐acryloyl)ethyl(p‐boronic acid benzyl)diethylammonium bromide (B‐PDEA), is shown here, that mediates efficient gene transfection of NSCs and greatly enhances their therapeutics in ischemic stroke treatment. The cationic B‐PDEA/DNA polyplexes can effectively transfect NSCs; in the cytosol, the B‐PDEA is oxidized by intracellular ROS into negatively charged polyacrylic acid, quickly releasing the BDNF plasmids for efficient transcription and secreting a high level of BDNF. After i.v. injection in ischemic stroke mice, the transfected NSCs (BDNF‐NSCs) can home to ischemic regions as efficiently as the pristine NSCs but more efficiently produce BDNF, leading to significantly augmented BDNF levels, which in turn enhances the mouse survival rate to 60%, from 0% (nontreated mice) or ≈20% (NSC‐treated mice), and enables more rapid and superior functional reconstruction.
The first nonviral gene carrier, reactive‐oxygen‐species‐responsive charge‐reversal poly(2‐acryloyl)‐ethyl(p‐boronic acid benzyl)diethylammonium bromide (B‐PDEA), is shown to mediate efficient gene transfection to neural stem cells (NSCs). When BDNF gene plasmids are used, the transfected NSCs homing to the ischemic regions increase animal survival and reconstruct functions.
This paper applies the extended MFDFA method to analyze the volatility characteristics, multifractal features and asymmetry in EU carbon emission permits trading market(EUA) and the main Chinese ...carbon emission permits market including HBEA, SZA and GDEA. We divided the EUA market into three stages according to the phased construction plan of European commission. The empirical analysis shows that the fluctuation in the second and third stage of EUA market presents a long-term memory feature. However, there is obvious anti-persistent characteristics in the volatility of three main Chinese carbon emission permits trading markets and the first stage in EUA market. The multifractal degree in three main Chinese carbon emission permits trading markets is less than that in the first stage of EUA market, but far greater than the second and third stages. We also verified that the HBEA market has the weakest volatility and the least multifractal degree among three Chinese markets, and whose validity is second to the third stage of EUA market. In addition, the fluctuation of the EU and Chinese carbon emission permits trading markets are asymmetric. The EUA market has stronger reaction to good news, while Chinese carbon emission permits trading market still displays the leverage effect which verifies the volatility is more sensitive to the bad news in the second and third stages. Therefore, the results powerfully demonstrate that the Chinese carbon emission permits trading market is less mature and highly dynamic, which is similar to the level of first stage of EUA market. The volatility in Chinese markets is strong, and exists much noise in the system. So, the efficiency in Chinese markets is weaker than EU. Chinese markets are still far from maturity and efficiency.
•The market price volatility does not possess the significant long-term memory characteristics, it shows up the anti-persistent features.•With the development of the EUA market, the multifractal characteristics become weaker and weaker, and the reaction of the market price fluctuation to information become weaker as well.•The market asymmetry reflects the reaction of the price volatility to the positive and negative information.
A large negative magnetoresistance (NMR) is anticipated in topological semimetals in parallel magnetic fields, demonstrating the chiral anomaly, a long-sought high-energy-physics effect, in ...solid-state systems. Recent experiments reveal that the Dirac semimetal Cd3As2 has the record-high mobility and positive linear magnetoresistance in perpendicular magnetic fields. However, the NMR has not yet been unveiled. Here we report the observation of NMR in Cd3As2 microribbons in parallel magnetic fields up to 66% at 50 K and visible at room temperatures. The NMR is sensitive to the angle between magnetic and electrical fields, robust against temperature and dependent on the carrier density. The large NMR results from low carrier densities in our Cd3As2 samples, ranging from 3.0 × 10(17) cm(-3) at 300 K to 2.2 × 10(16) cm(-3) below 50 K. We therefore attribute the observed NMR to the chiral anomaly. In perpendicular magnetic fields, a positive linear magnetoresistance up to 1,670% at 14 T and 2 K is also observed.
A magnetoconductivity formula is presented for the surface states of a magnetically doped topological insulator. It reveals a competing effect of weak localization and weak antilocalization in ...quantum transport when an energy gap is opened at the Dirac point by magnetic doping. It is found that, while random magnetic scattering always drives the system from the symplectic to the unitary class, the gap could induce a crossover from weak antilocalization to weak localization, tunable by the Fermi energy or the gap. This crossover presents a unique feature characterizing the surface states of a topological insulator with the gap opened at the Dirac point in the quantum diffusion regime.
Converting CO2 into chemical fuels with a photocatalyst and sunlight is an appealing approach to address climate deterioration and energy crisis. Metal complexes are superb candidates for CO2 ...reduction due to their tunable catalytic sites with high activity. The coupling of metal complexes with organic photosensitizers is regarded as a common strategy for establishing photocatalytic systems for visible-light-driven CO2 reduction. While most of the organic photosensitizers generally contain precious metals and are available through onerous synthetic routes, their large-scale application in the photocatalysis is limited. Halide perovskite nanocrystals (NCs) have been considered as one of the most promising light-harvesting materials to replace the organic photosensitizers due to their tunable light absorption range, low cost, abundant surface sites, and high molar extinction coefficient. Herein, we demonstrate a facile strategy to immobilize Ni(terpy)22+ (Ni(tpy)) on inorganic ligand-capped CsPbBr3 NCs and to apply this hybrid as a catalyst for visible-light-driven CO2 reduction. In this hybrid photocatalytic system, the Ni(tpy) can provide specific catalytic sites and serve as electron sinks to suppress electron–hole recombination in the CsPbBr3 NCs. The CsPbBr3-Ni(tpy) catalytic system achieves a high yield (1724 μmol/g) in the reduction of CO2 to CO/CH4, which is approximately 26-fold higher than that achieved with the pristine CsPbBr3 NCs. This work has developed a method for enhancing the performance of photocatalytic CO2 reduction by immobilizing metal complexes on perovskite NCs. The methodology we present here provides a new platform for utilizing halide perovskite NCs for photocatalytic applications.
Berry phase physics is closely related to a number of topological states of matter. Recently discovered topological semimetals are believed to host a nontrivial π Berry phase to induce a phase shift ...of ±1/8 in the quantum oscillation (+ for hole and - for electron carriers). We theoretically study the Shubnikov-de Haas oscillation of Weyl and Dirac semimetals, taking into account their topological nature and inter-Landau band scattering. For a Weyl semimetal with broken time-reversal symmetry, the phase shift is found to change nonmonotonically and go beyond known values of ±1/8 and ±5/8, as a function of the Fermi energy. For a Dirac semimetal or paramagnetic Weyl semimetal, time-reversal symmetry leads to a discrete phase shift of ±1/8 or ±5/8. Different from the previous works, we find that the topological band inversion can lead to beating patterns in the absence of Zeeman splitting. We also find the resistivity peaks should be assigned integers in the Landau index plot. Our findings may account for recent experiments in Cd_{2}As_{3} and should be helpful for exploring the Berry phase in various 3D systems.
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