Magnetic Weyl semimetal phase in a Kagomé crystal Liu, D F; Liang, A J; Liu, E K ...
Science (American Association for the Advancement of Science),
09/2019, Volume:
365, Issue:
6459
Journal Article
Peer reviewed
Open access
Weyl semimetals are crystalline solids that host emergent relativistic Weyl fermions and have characteristic surface Fermi-arcs in their electronic structure. Weyl semimetals with broken time ...reversal symmetry are difficult to identify unambiguously. In this work, using angle-resolved photoemission spectroscopy, we visualized the electronic structure of the ferromagnetic crystal Co
Sn
S
and discovered its characteristic surface Fermi-arcs and linear bulk band dispersions across the Weyl points. These results establish Co
Sn
S
as a magnetic Weyl semimetal that may serve as a platform for realizing phenomena such as chiral magnetic effects, unusually large anomalous Hall effect and quantum anomalous Hall effect.
Origami-inspired designs possess attractive applications to science and engineering (e.g. deployable, self-assembling, adaptable systems). The special geometric arrangement of panels and creases ...gives rise to unique mechanical properties of origami, such as reconfigurability, making origami designs well suited for tunable structures. Although often being ignored, origami structures exhibit additional soft modes beyond rigid folding due to the flexibility of thin sheets that further influence their behaviour. Actual behaviour of origami structures usually involves significant geometric nonlinearity, which amplifies the influence of additional soft modes. To investigate the nonlinear mechanics of origami structures with deformable panels, we present a structural engineering approach for simulating the nonlinear response of non-rigid origami structures. In this paper, we propose a fully nonlinear, displacement-based implicit formulation for performing static/quasi-static analyses of non-rigid origami structures based on ‘bar-and-hinge’ models. The formulation itself leads to an efficient and robust numerical implementation. Agreement between real models and numerical simulations demonstrates the ability of the proposed approach to capture key features of origami behaviour.
This paper explores the rate-energy (R-E) region of simultaneous wireless information and power transfer for MIMO broadcasting channel under the nonlinear radio frequency energy harvesting (EH) ...model. The goal is to characterize the tradeoff between the maximal energy transfer versus information rate. The separated EH and information decoding (ID) receivers and the co-located EH and ID receivers scenarios are considered. For the co-located receivers scenario, both time switching (TS) and power splitting (PS) receiver architectures are investigated. Optimization problems are formulated to derive the boundaries of the R-E region s for the considered systems. As the problems are nonconvex, we first transform them into equivalent ones and derive some semi-closed-form solutions, and then design efficient algorithms to solve them. Numerical results are provided to show the R-E region s of the systems, which provide some interesting insights. It is shown that all practical circuit specifications greatly affect the system R-E region. Compared with the systems under traditional linear EH model, the ones under the nonlinear EH model achieve smaller R-E region s due to the limitations of practical circuit features and also show very different R-E tradeoff behaviors.
Changes in two novel HBV serological markers, linearized hepatitis B surface antigen (HQ-HBsAg) and hepatitis B core-related antigen (HBcrAg), in the natural history of chronic hepatitis B (CHB) have ...not been well characterized. Serum HQ-HBsAg and HBcrAg levels of 404 Asian treatment-naïve CHB patients were analysed in a cross-sectional manner. Patients were categorized into five groups: immune tolerant (IT group, n = 52), immune clearance (IC group, n = 105), hepatitis B e antigen (HBeAg)-negative hepatitis (ENH group, n = 97), HBeAg-negative quiescent group (ENQ group, n = 95) and CHB with hepatitis B surface antigen (HBsAg) seroclearance (SC group, n = 55). HQ-HBsAg and HBcrAg were measured and correlated with HBV DNA, HBsAg, HBV genotype and clinical parameters. HQ-HBsAg showed good correlation with HBsAg, especially in the ENQ group (r = 0.874, p <0.001). Correlation of HQ-HBsAg with HBV DNA was less prominent and weakest in the ENH group (r = 0.268, p 0.008). HBcrAg correlated best with HBV DNA in the ENQ group (r = 0.537, p <0.001). In the ENQ group, 42.1% of patients had undetectable HBcrAg; this subgroup of patients, when compared with those with detectable HBcrAg, had significantly lower median HBV DNA (3.17/4.48 log IU/mL, p <0.001) and HBsAg (5.05/5.96 log mIU/mL, p <0.001) levels. Forty per cent of the SC group patients had detectable HQ-HBsAg and/or HBcrAg up to 42 months after HBsAg seroclearance. When comparing anti-HBs positivity and median time after HBsAg seroclearance in the SC group with and without detectable HQ-HBsAg/HBcrAg, there was no significant difference (22.7% and 36.4%, respectively, p 0.284, and 76.5 and 93.2 months, respectively, p 0.245). HQ-HBsAg and HBcrAg showed unique patterns of distribution throughout the five disease phases of CHB, including high detectability rates after HBsAg seroclearance, opening up different possibilities for their applicability.
Intracellular lipids are stored in lipid droplets (LDs) and metabolized by cytoplasmic neutral hydrolases to supply lipids for cell use. Recently, an alternative pathway of lipid metabolism through ...the lysosomal degradative pathway of autophagy has been described and termed lipophagy. In this form of lipid metabolism, LD triglycerides (TGs) and cholesterol are taken up by autophagosomes and delivered to lysosomes for degradation by acidic hydrolases. Free fatty acids generated by lipophagy from the breakdown of TGs fuel cellular rates of mitochondrial β-oxidation. Lipophagy therefore functions to regulate intracellular lipid stores, cellular levels of free lipids such as fatty acids and energy homeostasis. The amount of lipid metabolized by lipophagy varies in response to the extracellular supply of nutrients. The ability of the cell to alter the amount of lipid targeted for autophagic degradation depending on nutritional status demonstrates that this process is selective. Intracellular lipids themselves regulate levels of autophagy by unclear mechanisms. Impaired lipophagy can lead to excessive tissue lipid accumulation such as hepatic steatosis, alter hypothalamic neuropeptide release to affect body mass, block cellular transdifferentiation and sensitize cells to death stimuli. Future studies will likely identify additional mechanisms by which lipophagy regulates cellular physiology, making this pathway a potential therapeutic target in a variety of diseases.
Recent emphasis on green communications has generated great interest in the investigations of energy harvesting communications and networking. Energy harvesting from ambient energy sources can ...potentially reduce the dependence on the supply of grid or battery energy, providing many attractive benefits to the environment and deployment. However, unlike the conventional stable energy, the intermittent and random nature of the renewable energy makes it challenging in the realization of energy harvesting transmission schemes. Extensive research studies have been carried out in recent years to address this inherent challenge from several aspects: energy sources and models, energy harvesting and usage protocols, energy scheduling and optimization, implementation of energy harvesting in cooperative, cognitive radio, multiuser and cellular networks, etc. However, there has not been a comprehensive survey to lay out the complete picture of recent advances and future directions. To fill such a gap, in this paper, we present an overview of the past and recent developments in these areas and highlight a number of possible future research avenues.
The performance of four sections of a full-scale embankment constructed on soft soil is examined using a fully coupled and fully three-dimensional finite element analysis. The four sections had ...similar embankment loadings but different improvement options (one unimproved, one with pile-support only, one with a single layer geotextile-reinforced platform and pile-support, and one with two layers of geogrid-reinforced platform and pile-support). Like the field data, the numerical results show that the inclusion of piles decreases the settlement at the subsoil surface to 52% of that for the unimproved section, and the addition of a single layer of geotextile reinforcement (J = 800 kN/m) further reduced settlement to only 31% of that of the unimproved section. The effects of geosynthetic reinforcement and multiple layers of reinforcement on the performance of the pile-supported embankment are discussed. The relative load transfer is calculated using eight existing methods and they are compared with the field measurements and numerical results.
Commercially available activated carbon cloth electrodes are treated using nitric acid and ethylenediamine solutions, resulting in chemical surface charge enhanced carbon electrodes for capacitive ...deionization (CDI) applications. Surface charge enhanced electrodes are then configured in a CDI cell to examine their salt removal at a fixed charging voltage and both reduced and opposite polarity discharge voltages, and subsequently compared to the salt removal of untreated electrodes. Substantially improved salt removal due to chemical surface charge and the use of a discharge voltage of opposite sign to the charging voltage is clearly demonstrated in these CDI cycling tests, an observation which for the first time validates both enhanced CDI and extended-voltage CDI effects predicted by the Donnan model Biesheuvel et al., Colloids Interf. Sci. Comm., 10.1016/j.colcom.2015.12.001 (2016). Our experimental and theoretical results demonstrate that the use of carbon electrodes with optimized chemical surface charge can extend the CDI working voltage window through discharge voltages of opposite sign to the charging voltage, which can significantly enhance the salt adsorption capacity of CDI electrodes. Thus, in addition to carbon pore size distribution, chemical surface charge in carbon micropores is considered foundational for salt removal in CDI cells.
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•Improved salt removal due to chemical surface charge and a reduction in discharge voltage was observed.•The amphoteric Donnan model properly predicts salt removal for CDI cells.•Both the extended voltage CDI and enhanced CDI effects were validated.•Carbon surface charge significantly impacts salt removal in CDI cells.
Unmanned air vehicles (UAVs) can provide important communication advantages to ground-based wireless ad hoc networks. In this paper, the location and movement of UAVs are optimized to improve the ...connectivity of a wireless network. Four types of network connectivity are quantified: global message connectivity, worst-case connectivity, network bisection connectivity, and k -connectivity. The problems of UAV deployment and movement are formulated to improve the different types of connectivity. Both problems are NP -hard. For the deployment case, some heuristic adaptive schemes are proposed to yield simple but effective solutions. In addition, a closed-form solution for the two-node one-UAV case is provided. For k -connectivity, we propose an algorithm that improves connectivity using Delaunay triangulation. To optimize the UAV movement, an algorithm that tracks changes in the network topology is constructed. The simulation results show that by only deploying a single UAV, the global message network connectivity and the worst-case network connectivity can be improved by up to 109% and 60%, respectively. The network bisection connectivity and the k -connectivity can also be significantly improved.
In this paper, online convex optimization problem with time-varying constraints is studied from the perspective of an agent taking sequential actions. Both the objective function and the constraint ...functions are dynamic and unknown a priori to the agent. We first consider the scenario of the gradient feedback, in which, the values and gradients of the objective function and constraint functions at the chosen action are revealed after an action is submitted. We propose a computationally efficient online algorithm, which only involves direct closed-form computations at each time instant. It is shown that the algorithm possesses sublinear regret with respect to the dynamic benchmark sequence and sublinear constraint violations, as long as the drift of the benchmark sequence is sublinear, or in other words, the underlying dynamic optimization problems do not vary too drastically. Furthermore, we investigate the scenario of the bandit feedback, in which, after an action is chosen, only the values of the objective function and the constraint functions at several random points close to the action are announced to the agent. A bandit version of the online algorithm is proposed and we also establish its sublinear expected regret and sublinear expected constraint violations under the assumption that the drift of the benchmark sequence is sublinear. Finally, two numerical examples, namely online quadratic programming and online logistic regression, are presented to corroborate the effectiveness of the proposed algorithms and to confirm the theoretical guarantees.
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