A simple, bioinspired approach to effectively prevent the restacking of chemically converted graphene sheets in multilayered films is presented. The method enables the creation of a new generation of ...supercapacitors that combine high energy density, high power density, and high operation rates.
Filtering images of more than one channel are challenging in terms of both efficiency and effectiveness. By grouping similar patches to utilize the self-similarity and sparse linear approximation of ...natural images, recent nonlocal and transform-domain methods have been widely used in color and multispectral image (MSI) denoising. Many related methods focus on the modeling of group level correlation to enhance sparsity, which often resorts to a recursive strategy with a large number of similar patches. The importance of the patch level representation is understated. In this paper, we mainly investigate the influence and potential of representation at patch level by considering a general formulation with a block diagonal matrix. We further show that by training a proper global patch basis, along with a local principal component analysis transform in the grouping dimension, a simple transform-threshold-inverse method could produce very competitive results. Fast implementation is also developed to reduce the computational complexity. The extensive experiments on both the simulated and real datasets demonstrate its robustness, effectiveness, and efficiency.
Porous yet densely packed carbon electrodes with high ion-accessible surface area and low ion transport resistance are crucial to the realization of high-density electrochemical capacitive energy ...storage but have proved to be very challenging to produce. Taking advantage of chemically converted graphene's intrinsic microcorrugated two-dimensional configuration and self-assembly behavior, we show that such materials can be readily formed by capillary compression of adaptive graphene gel films in the presence of a nonvolatile liquid electrolyte. This simple soft approach enables subnanometer scale integration of graphene sheets with electrolytes to form highly compact carbon electrodes with a continuous ion transport network. Electrochemical capacitors based on the resulting films can obtain volumetric energy densities approaching 60 watt-hours per liter.
With the rapid development of mobile electronics and electric vehicles, future electrochemical capacitors (ECs) need to store as much energy as possible in a rather limited space. As the core ...component of ECs, dense electrodes that have a high volumetric energy density and superior rate capability are the key to achieving improved energy storage. Here, the significance of and recent progress in the high volumetric performance of dense electrodes are presented. Furthermore, dense yet porous electrodes, as the critical precondition for realizing superior electrochemical capacitive energy, have become a scientific challenge and an attractive research focus. From a pore‐engineering perspective, insight into the guidelines of engineering the pore size, connectivity, and wettability is provided to design dense electrodes with different porous architectures toward high‐performance capacitive energy storage. The current challenges and future opportunities toward dense electrodes are discussed and include the construction of an orderly porous structure with an appropriate gradient, the coupling of pore sizes with the solvated cations and anions, and the design of coupled pores with diverse electrolyte ions.
Dense yet porous electrodes with high volumetric performance are the key to achieving superior electrochemical capacitive energy storage. Significant research breakthroughs in the volumetric performance of dense electrodes are presented. In particular, an insight into the guidelines of pore engineering is provided, to allow the design of dense electrodes toward high‐performance energy storage.
TVA: A DoS-Limiting Network Architecture Xiaowei Yang; Wetherall, D.; Anderson, T.
IEEE/ACM transactions on networking,
12/2008, Letnik:
16, Številka:
6
Journal Article
Recenzirano
We motivate the capability approach to network denial-of-service (DoS) attacks, and evaluate the traffic validation architecture (TVA) architecture which builds on capabilities. With our approach, ...rather than send packets to any destination at any time, senders must first obtain ldquopermission to sendrdquo from the receiver, which provides the permission in the form of capabilities to those senders whose traffic it agrees to accept. The senders then include these capabilities in packets. This enables verification points distributed around the network to check that traffic has been authorized by the receiver and the path in between, and hence to cleanly discard unauthorized traffic. To evaluate this approach, and to understand the detailed operation of capabilities, we developed a network architecture called TVA. TVA addresses a wide range of possible attacks against communication between pairs of hosts, including spoofed packet floods, network and host bottlenecks, and router state exhaustion. We use simulations to show the effectiveness of TVA at limiting DoS floods, and an implementation on Click router to evaluate the computational costs of TVA. We also discuss how to incrementally deploy TVA into practice.
The intrinsic catalytic activity at 10 mA cm−2 for oxygen evolution reaction (OER) is currently working out at overpotentials higher than 320 mV. A highly efficient electrocatalyst should possess ...both active sites and high conductivity; however, the loading of powder catalysts on electrodes may often suffer from the large resistance between catalysts and current collectors. This work reports a class of bulk amorphous NiFeP materials with metallic bonds from the viewpoint of electrode design. The materials reported here perfectly combine high macroscopic conductivity with surface active sites, and can be directly used as the electrodes with active sites toward high OER activity in both alkaline and acidic electrolytes. Specifically, a low overpotential of 219 mV is achieved at the geometric current density 10 mA cm−2 in an alkaline electrolyte, with the Tafel slope of 32 mV dec−1 and intrinsic overpotential of 280 mV. Meanwhile, an overpotential of 540 mV at 10 mA cm−2 is attained in an acidic electrolyte and stable for over 30 h, which is the best OER performance in both alkaline and acidic media. This work provides a different angle for the design of high‐performance OER electrocatalysts and facilitates the device applications of electrocatalysts.
A class of bulk amorphous NiFeP materials that perfectly combines high macroscopic conductivity with surface active sites is developed toward high activity for oxygen evolution reaction in both alkaline and acidic electrolytes. The synergistic effect of coordinatively unsaturated Ni, Fe, and P constitutes the highly active sites, while the high macroscopic conductivity facilitates the charge transfer from catalyst surface to current collector.
Fluorine doped single crystal Ni-rich cathode material with excellent electrochemical properties were successfully synthesized. X-ray diffraction (XRD) revealed that the fluorine substitution process ...did not change the hexagonal layer structure, but it promoted the unit cell expanded along the c-direction which was conductive to improving the kinetic of Li+ transmission. Energy dispersive X-ray Spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) further proved the fluorine doped into the cathode material, which simultaneously triggered partial Ni3+ reduction to Ni2+. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) demonstrated that fluorine substitution can effectively decrease polarization and suppress migration resistance of lithium ions. The lithium ions diffusion rate (DLi+) indicated that lithium ions migrated more smoothly in fluoride doped sample. Both the substitution effects of fluorine and short migration path way for lithium ions in single crystal particles account for excellent electrochemical performance of the Ni-rich lithium cathode material. This study provided some new thought into synthesis of high performance fluorine doped single crystal Ni-rich lithium cathode materials.
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•The single crystal morphology provides short migration path for Li+ ions.•F-doped into the cathode material triggers partial Ni3+ reduction to Ni2+.•Lithium ions migrate more smoothly in F-doped single crystal material.•Both F-doping and single crystal morphology account for excellent performance.
To explore the refinement mechanism of long period stacking ordered (LPSO) phases and its impact on mechanical properties, a typical Mg97Y2Zn1 alloy with α-Mg/LPSO binary microstructure prepared by ...multi-pass ECAP was systematically investigated. The obtained results indicate that during severe deformation the network 18R phase undergoes a three-step refining process, which includes kinking, zigzagging, and breaking. Lamellar 14H is precipitated first during early ECAP, and then is refined during further ECAP following a similar refining sequence of 18R phase. Moreover, a two-step dynamic recrystallization (DRX) is activated during deformation. In early passes of ECAP, DRX is promoted by 18R kinking through particle-stimulated nucleation (PSN) mechanism, and the precipitation of 14H lamellas suppresses DRX process in this period. After 14H lamellas became kinked, zigzagged and broken with more ECAP passes, the refined 14H accelerates the second step DRX process through PSN mechanism. In addition, owing to the significantly refined microstructures, both the strength and ductility of ECAP alloys increase. The ductility of ECAP alloy is improved remarkably with increasing ECAP passes. However, the increasing range of strength declines with further passes of ECAP, as the size of 18R stripes decreases gradually in the bimodal microstructures.
•A two-step dynamic recrystallization for Mg97Y2Zn1 alloy during SPD is proposed.•18R LPSO promotes the first-step DRX in early passes of ECAP.•14H LPSO promotes the second-step DRX in later period of ECAP.•Refined microstructure contributes more to enhancement of ductility than strength.
The support vector machine (SVM) has provided higher performance than traditional learning machines and has been widely applied in real-world classification problems and nonlinear function estimation ...problems. Unfortunately, the training process of the SVM is sensitive to the outliers or noises in the training set. In this paper, a common misunderstanding of Gaussian-function-based kernel fuzzy clustering is corrected, and a kernel fuzzy c-means clustering-based fuzzy SVM algorithm (KFCM-FSVM) is developed to deal with the classification problems with outliers or noises. In the KFCM-FSVM algorithm, we first use the FCM clustering to cluster each of two classes from the training set in the high-dimensional feature space. The farthest pair of clusters, where one cluster comes from the positive class and the other from the negative class, is then searched and forms one new training set with membership degrees. Finally, we adopt FSVM to induce the final classification results on this new training set. The computational complexity of the KFCM-FSVM algorithm is analyzed. A set of experiments is conducted on six benchmarking datasets and four artificial datasets for testing the generalization performance of the KFCM-FSVM algorithm. The results indicate that the KFCM-FSVM algorithm is robust for classification problems with outliers or noises.
Harmonia axyridis is a voracious predator, a biological control agent, and one of the world most invasive insect species. The advent of next-generation sequencing platforms has propelled ...entomological research into the genomics and post-genomics era. Real-time quantitative PCR (RT-qPCR), a primary tool for gene expression analysis, is a core technique governs the genomic research. The selection of internal reference genes, however, can significantly impact the interpretation of RT-qPCR results. The overall goal of this study is to identify the reference genes in the highly invasive H. axyridis. Our central hypothesis is that the suitable reference genes for RT-qPCR analysis can be selected from housekeeping genes. To test this hypothesis, the stability of nine housekeeping genes, including 18S, 28S, ACTB, ATP1A1, GAPDH, HSP70, HSP90, RP49, and ATP6V1A, were investigated under both biotic (developmental time, tissue and sex), and abiotic (temperature, photoperiod, in vivo RNAi) conditions. Gene expression profiles were analyzed by geNorm, Normfinder, BestKeeper, and the ΔCt method. Our combined results recommend a specific set of reference genes for each experimental condition. With the recent influx of genomic information for H. axyridis, this study lays the foundation for an in-depth omics dissection of biological invasion in this emerging model.
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