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In this paper, a metamaterial electromagnetic energy harvester constructed via the capacitive loading of metal circular split rings is presented. Each energy-harvesting cell is loaded with a resistance that imitates the input impedance of a rectifier circuit. Specifically, the metamaterial energy harvester has high selective harvesting for left- and right-handed circularly polarized waves. Here, the energy absorption is mostly induced by the resistive load; thus, effective energy harvesting can be achieved. Moreover, the proposed energy harvester exhibits a high-efficiency harvesting for right-handed circularly polarized waves over a wide range of incident angles. Further, a transmission line model is adopted to interpret the energy harvesting mechanism, which shows that a good impedance matching and low dielectric loss can further enhance the harvesting efficiency. To demonstrate the design, a 15 15 unit-cell prototype is fabricated and measured, and the measured results reasonably agree with the simulated ones. [ABSTRACT FROM AUTHOR]

Ahigh performance metamaterial device for electromagnetic energy harvesting is presented. The unit cell of the metamaterial device consists of four identical omega ring resonators arranged in rotational symmetry, and each omega ring is loaded with a 50 Ω resistor that mimics the input impedance of a rectifier circuit. A proof-of-concept prototype is designed for operation at the frequency of 5.8 GHz. Here, the efficient energy harvesting is validated by the energy dissipated in each resistor. Based on the full absorption concept, the metamaterial device achieves a harvesting efficiency up to 93.1% under normal incidence. In addition, the energy harvester shows polarization independent and wide-angle incident frequency responses with good harvesting characteristics over the entire operating range. The surface current distribution is analyzed to gain an insight into the energy harvesting mechanism. Moreover, the harvester prototype is manufactured and measured, and the simulated and measured results are in good agreement. Due to the enhanced electromagnetic energy harvesting efficiency, the proposed device is a good candidate for microwave power transmission. [ABSTRACT FROM AUTHOR]

In this study, the design, realization, and characterization of an ultrathin triple-band polarization-insensitive wide-angle metamaterial absorber are reported. The metamaterial absorber comprises a periodic array of modified six-fold symmetric snowflakeshaped resonators with strip spiral line load, which is printed on a dielectric substrate backed by a metal ground plane. It is shown that the absorber exhibits three distinct near-unity absorption peaks, which are distributed across C, X, Ku bands, respectively. Owing to the six-fold symmetry, the absorber is insensitive to the polarization of the incident radiation. In addition, the absorber shows excellent absorption performance over wide oblique incident angles for both transverse electric and transverse magnetic polarizations. Simulated surface current and field distributions at the three absorption peaks are demonstrated to understand the absorption mechanism. Particularly, the absorption modes come from the fundamental and high-order dipole resonances. Furthermore, the experimental verification of the designed absorber is conducted, and the measured results are in reasonable agreement with the simulated ones. The proposed ultrathin (∼0.018λ0, λ0 corresponding to the lowest peak absorption frequency) compact (0.168λ0×0.168λ0 corresponding to the area of a unit cell) absorber enables potential applications such as stealth technology, electromagnetic interference and spectrum identification. [ABSTRACT FROM AUTHOR]

Continuous theoretical and technological progress in the face of increasing expectations for quality health care has transformed the surgical paradigm. The authors systematically review these historical trends and propose the novel paradigm of "precision surgery," featuring certainty-based practice to ensure the best result for each patient with multiobjective optimization of therapeutic effectiveness, surgical safety, and minimal invasiveness. The main characteristics of precision surgery may be summarized as determinacy, predictability, controllability, integration, standardization, and individualization. The strategy of precision in liver surgery is to seek a balance of maximizing the removal of the target lesion, while maximizing the functional liver remnant and minimizing surgical invasiveness. In this article, the authors demonstrate the application of precision approaches in specific settings in complex liver surgery. They propose that the concept of precision surgery should be considered for wider application in liver surgery and other fields as a step toward the ultimate goal of perfect surgery. [ABSTRACT FROM AUTHOR]

We have performed first principles density functional theory method simulations on electronic structures of B, N, Co, P, and Bi doped C60 solids. Our electronic structure simulations show that boron, phosphorous, and cobalt doped face-centered cubic (FCC) C60 solids have the electronic structures of n-type semiconductors. Nitrogen doped FCC C60 solid has an electronic structure similar to those of a p-type semiconductor. P doped C60 is a potential good candidate in thermoelectric application. For Bi doped C60, a transformation from n-type to p-type semiconductor and gradually to metal, which corresponding to the Bi:C60 dopant ratio at 1:60, 2:60, and 3:60, respectively, can be seen from our electronic density of states (DOS) analysis. There are volume contraction and charge transfer increasing in the 2:60 of Bi doped C60 results compared with those of 1:60 Bi doped C60 case. The charge transfer at a tetrahedral site is as three times larger as that of octahedral site. For the concentration of Bi doped C60 higher than 3:60, the system is expected to be a superconductor. [ABSTRACT FROM AUTHOR]

Solitary intrahepatic biliary cyst (SIBC) is a rare disease, and due to the lack of adequate understanding of it, SIBC is often misdiagnosed as simple liver cyst (SLC), which in turn affects the therapeutic effect. In order to arouse more attention to SIBC, combined with clinical experience in our center, this study specifically screened 3 representative cases of SIBC, and conducted a comprehensive retrospective analysis of their clinical characteristics, diagnosis and treatment process. Combined with the relevant literature, the diagnosis and treatment process of SIBC is widely discussed. [ABSTRACT FROM AUTHOR]

First principles density functional theory — based (GW) method — was used to simulate the electronic structure of the novel iron-based superconductor K0.8Fe2Se2. The calculated band gap of K0.8Fe2Se2 at the Γ point is 0.15 eV, which is significantly lower than the 0.61 eV of vacancy free crystal KFe2Se2. The d-orbital of Fe atom is overlapped with the p-orbital of Se atom. Charge density analysis shows strong lattice distortion and vacancy related electric dipole and quadruple near the K vacancy. The reflectivity is anisotropic in three coordinate directions. [ABSTRACT FROM AUTHOR]

We examine the possibility of nitrogen-doped C60 fullerene (N-C60) as a cathode catalyst for hydrogen fuel cells. We use first-principles spin-polarized density functional theory calculations to simulate the electrocatalytic reactions on N-C60. The first-principles results show that an O2 molecule can be adsorbed and partially reduced on the N–C complex sites (Pauling sites) of N-C60 without any activation barrier. Through a direct pathway, the partially reduced O2 can further react with H+ and additional electrons and complete the water formation reaction (WFR) with no activation energy barrier. In the indirect pathway, reduced O2 reacts with H+ and additional electrons to form H2O molecules through a transition state (TS) with a small activation barrier (0.22-0.37 eV). From an intermediate state to a TS, H+ can obtain a kinetic energy of ∼0.95-3.68 eV, due to the Coulomb electric interaction, and easily overcome the activation energy barrier during the WFR. The full catalytic reaction cycles can be completed energetically, and N-C60 fullerene recovers to its original structure for the next catalytic reaction cycle. N-C60 fullerene is a potential cathode catalyst for hydrogen fuel cells. [ABSTRACT FROM AUTHOR]

Some sufficient conditions for the asymptotic stability of cellular neural networks with time delay are derived using the Lyapunov–Krasovskii stability theory for functional differential equations as well as the linear matrix inequality (LMI) approach. The analysis shows how some well-known results can be refined and generalized in a straightforward manner. Moreover, the stability criteria obtained are delay-independent. They are less conservative and restrictive than those reported so far in the literature, and provide a more general set of criteria for determining the stability of delayed cellular neural networks. [ABSTRACT FROM AUTHOR]

The issues of the physical layer security are studied, where one transmitter (Alice), one full-duplex (FD) legitimate receiver (Bob) and one multi-antenna jammer (Charlie) are considered to defend against multiple passive and non-colluding eavesdroppers (Eves), for multiple-input multiple-output wiretap channels. With the assumption that the complete channel state information (CSI) for main channels and the statistical CSI for Eves' channels are available, an improved secrecy transmission design is proposed to minimise the secrecy outage probability (SOP), under the minimum secrecy rate requirement. In addition to integrating artificial noise aided transmit beamforming and multi-antenna cooperative jammer to impair Eves' channels, which is widely used in many existing works, a FD legitimate receiver is applied together to further enhance physical layer security. Based on the basic probability theory and convex optimisation, the accurate closed-form expression of the SOP is derived, and the impacts on secrecy performance are described, including the qualities of main channels, the Alice's transmit power and the number of Eves. Numerical results show that the proposed scheme using the FD Bob can significantly enhance the system security, as compared with that employing the half-duplex Bob. [ABSTRACT FROM AUTHOR]

Lithium-brine is an important potential source of lithium. Much research and investigation has been carried out aimed at lithium recovery from brine. Although the distribution and occurrence status of lithium in brine have important implications for lithium recovery, few reports had correlated to this issue. In this article, a study was carried out to explore the lithium migration behavior during brine evaporation and KCl production process at Qarhan Salt Lake. The occurrence status of lithium both in fresh mined brine and residual brine after evaporation were also speculated by means of lithium concentration evaluation and theoretical calculation based on the Pitzer electrolyte solution theory. Results showed that, for Qarhan brine mined from the Bieletan region, most lithium was enriched in the residual brine during the brine evaporation process. The concentration of lithium in the residual brine could be more than 400 mg/L. More than 99.93% lithium ions in residual brine exist in free ions state and lithium does not precipitate from brine with a density of 1.3649 g/mL. The results also revealed that lithium concentration in wastewater discharged from KCl plants can reach a level of 243.8 mg/L. The investigation results provide a theoretical basis for comprehensive development and utilization of lithium resources in Qarhan Salt Lake. [ABSTRACT FROM AUTHOR]

We report that the resistance of a chemical vapor deposition (CVD) grown graphene film transferred onto an SiO2 substrate increases to higher saturation values upon exposure to light of decreasing wavelength from the visible to ultraviolet. Light in the visible range causes a slight increase of up to 10% in saturation resistance. A significant increase in resistance is found starting at about 400 nm. The saturation resistance approaches up to 3 times the original resistance at 254 nm after 5 min. When the light is removed, the resistance falls to its original value with a time constant of several days. The effect is not observed for samples of CVD-grown graphene films on SiO2 that have been heated in vacuum at 600 ºC, nor single-crystal graphene mechanically exfoliated onto SiO2. We attribute the effect to photo dissociation of interfacial molecules such as H2O adsorbed between the CVD-grown film and SiO2 substrate at grain boundaries in the film. [ABSTRACT FROM AUTHOR]

This paper presents a novel compact dual-band and dual-polarized complementary split-ring resonator (CSRR)-fed substrate-integrated waveguide (SIW) cavity-backed fractal patch antenna for wireless energy harvesting and communication. The proposed antenna is composed of a Giuseppe Peano fractal radiation patch with a backed SIW cavity. To enhance the bandwidth and minimize the dimensions, the CSRR structure is designed to feed the Giuseppe Peano fractal patch orthogonally. A prototype of the proposed antenna is simulated, fabricated and measured. The proposed antenna exhibits good directionality and high cross-polarization level with especially compact size. [ABSTRACT FROM AUTHOR]

Surfactin originated from genus Bacillus is composed of a heptapeptide moiety bonded to the carboxyl and hydroxyl groups of a ß-hydroxy fatty acid and it can be chemically modified to prepare the derivatives with different structures, owing to the existence of two free carboxyl groups in its peptide loop. This article presents the chemical modification of surfactin esterified with three different alcohols, and nine novel surfactin derivatives have been separated from products by the high performance liquid chromatography (HPLC). The novel derivatives, identified with Fourier transform infrared spectroscopy (FT-IR) and electrospray ionization mass spectrometry (ESI-MS), are the mono-hexyl-surfactin C14 ester, mono-hexyl-surfactin C15 ester, mono-2-methoxy-ethyl-surfactin C14 ester, di-hexyl-surfactin C14 ester, di-hexyl-surfactin ester C15, di-2-methoxy-ethyl-surfactin ester C14, di-2-methoxy-ethyl-surfactin ester C15, di-6-hydoxyl-hexyl-surfactin C14 ester and, di-6-hydoxyl-hexyl-surfactin C15 ester. The reaction conditions for esterification were optimized and the dependence of yields on different alcohols and catalysts were discussed. This study shows that esterification is one of the most efficient ways of chemical modification for surfactin and it can be used to prepare more derivatives to meet the needs of study in biological and interfacial activities. [ABSTRACT FROM AUTHOR]

It is well-believed that below a certain particle size, grain boundarymediated plastic deformation (e.g., grain rotation, grain boundary sliding and diffusion) substitutes for conventional dislocation nucleation and motion as the dominant deformation mechanism. However, in situ probing of grain boundary processes of ultrafine nanocrystals during plastic deformation has not been feasible, precluding the direct exploration of the nanomechanics. Here we present the in situ texturing observation of bulk-sized platinum in a nickel pressure medium of various particle sizes from 500 nm down to 3 nm. Surprisingly, the texture strength of the same-sized platinum drops rapidly with decreasing grain size of the nickel medium, indicating that more active grain rotation occurs in the smaller nickel nanocrystals. Insight into these processes provides a better understanding of the plastic deformation of nanomaterials in a few-nanometer length scale. [ABSTRACT FROM AUTHOR]

The size of nanocrystals provides a limitation on dislocation activity and associated stress-induced . deformation. Dislocation-mediated plastic deformation is expected to become inactive below a critical particle size, which has been proposed to be between 10 and 30 nanometers according to computer simulations and transmission electron microscopy analysis. However, deformation experiments at high pressure on polycrystalline nickel suggest that dislocation activity is still operative in 3-nanometer crystals. Substantial texturing is observed at pressures above 3.0 gigapascals for 500-nanometer nickel and at greater than 11.0 gigapascals for 20-nanometer nickel. Surprisingly, texturing is also seen in 3-nanometer nickel when compressed above 18.5 gigapascals. The observations of pressure-promoted texturing indicate that under high external pressures, dislocation activity can be extended down to a few-nanometers-length scale. [ABSTRACT FROM AUTHOR]

Pressed bulk samples of C60 doped with P, Co, Al, and Bi have been investigated for their thermoelectric properties. These samples show extremely low thermal conductivity, typically in the range of 0.1–0.3 W/Km at room temperature. The Seebeck coefficients of Co, Al, and Bi doped C60 solids are in the tens of μV/K; however, for P doped C60 samples, a very large Seebeck coefficient in the order of 103 μV/K was observed. The value of the Seebeck coefficient seems to depend sensitively on the P concentration and changes sign upon annealing at 100 °C. Ab initio density functional theory calculations show that the calculated electronic structures and the activation energies strongly depend on the dopants in C60 solids. The high Seebeck coefficient in studied P doped C60 is due to the system’s unique dopant and concentration. [ABSTRACT FROM AUTHOR]