In order to explore the potential application of graphene oxide (GO) in the field of metalworking fluid, GO was synthesized by improved Hummers' method, followed by edge-functionalization with n-octanylamine, and Pickering emulsions based on functionalized GO were constructed. The oil-water interfacial behaviors of functionalized GO at liquid-liquid interfaces, together with the tribological behaviors of GO-based Pickering emulsions at solid-liquid interfaces were respectively studied. The interfacial tension of functionalized GO at different oil-water interfaces was studied by full-automatic interfacial tension tester. And the interfacial lubricating properties of GO-based Pickering emulsions on CoCrMo alloy and 304 stainless steel were studied by UMT-tribolab and white light interferometer. To clarify the lubricating mechanism of GO-based Pickering emulsions, the composition of lubricating films on metal friction pairs was analyzed by Micro-Raman and XPS. The results show that the friction-reducing properties of GO-based Pickering emulsions are better than that of base emulsion, and alkylamine functionalized GO shows better lubrication performance on CoCrMo alloy than on that 304 stainless steel. Compared with base emulsion, when the friction counterpart is CoCrMo alloy, GO emulsion can reduce the average friction coefficient and the steel ball wear rate by 35.9% and 46.7% respectively, while Oct-N-GO emulsion can reduce the average friction coefficient (COF) and the wear rate of steel ball by 48.7% and 73.0% respectively. The mechanism analysis shows that the good interfacial wettability of functionalized GO enables its Pickering emulsion to form a better interfacial lubricating film on metal surfaces. The alkylamine chains at GO edges are more prone to be sheared during friction, which reduces the interfacial shear force and results in reducing friction. At the same time, the lubricating film formed by Oct-N-GO contains higher content of C-O-C/C-OH and C=O, which can adsorb or fill the metal surfaces and play an anti-wear role.
Pure copper tensile bars were produced by conventional die casting (HPDC) and vacuum-assist die casting (VADC) processes. Porosity and mechanical properties were investigated by using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray computed tomography (XCT) and tensile tester. Results show that porosities including gas porosity and shrinkage porosity could be observed in copper castings. Since the application of vacuum could reduce filling related gas entrapment and facilitate solidification due to the increased heat transfer between metal and die, both number and size of the entrapped gases, as well as shrinkage porosities were significantly reduced in vacuum-assist die castings of pure copper. The porosity fraction decreased from 2.243% to 0.875% compared with that of the conventional die casting. Besides, mechanical properties were improved significantly, i.e., by 15% for ultimate tensile strength and three times for elongation.
A novel linear time-periodic (LTP) model for advanced PLLs is presented, demonstrating superior accuracy over the conventional linear time-invariant (LTI) models. Applying eigenvalues analysis, a general parameter design procedure is proposed and the effect of voltage unbalance is investigated. The effectiveness of the theoretical analysis is verified by time-domain simulation results.
Sildenafil is known to reduce cardiac hypertrophy through cGMP-dependent protein kinase (cGK) activation. Studies have demonstrated that cGK has a central switching role in modulating vascular smooth muscle cell (VSMC) phenotype in response to vascular injury. Here, we aimed to examine the effects of cGK activation by sildenafil on neointimal formation and platelet aggregation. After vascular injury, neointimal hyperplasia in rat carotid arteries was significantly reduced in the sildenafil-treated group. This effect of sildenafil was accompanied by the reduction of viability and migration of VSMCs. Further experiments showed that the increased cGK activity by sildenafil inhibited platelet-derived growth factor-induced phenotype change of VSMCs from a contractile form to a synthetic one. Conversely, the use of cGK inhibitor or gene transfer of dominant-negative cGK reversed the effects of sildenafil, increasing viability of VSMCs and neointimal formation. Interestingly, sildenafil significantly inhibited platelet aggregation induced by ADP or thrombin. This effect was reversed by cGK inhibitor, suggesting that sildenafil inhibits platelet aggregation via cGK pathway. This study demonstrated that sildenafil inhibited neointimal formation and platelet aggregation via cGK pathway. These results suggest that sildenafil could be a promising candidate for drug-eluting stents for the prevention of both restenosis and stent thrombosis.
As the heart of next-generation air transportation systems, the automatic dependent surveillance-broadcast (ADS-B) is becoming a substitute for the radar, because it can enhance flight safety by requiring aircraft to regularly broadcast their precise geographic positions. Despite its promise, the lack of security mechanisms, e.g., not providing data encryption and message authentication, is a significant barrier to realistically deploy this new technology. While many methods have been proposed for ADS-B security, they can deal with either privacy or integrity unilaterally, and also need to change current ADS-B standards. In this paper, we present a new cryptographic solution to ADS-B security by first carefully exploiting some cryptographic primitives, and then adapting them to the air traffic-monitoring scenario. In contrast to previous approaches, our proposed solution is not only of high compatibility with existing protocols of ADS-B, but also lightweight for congested data links and resource-constraint avionics. Furthermore, it can also tolerate package loss and disorder that frequently occur in ADS-B wireless broadcast networks, making the proposed solution easy-to-deploy and practical. Security analysis shows that our proposal simultaneously achieves the confidentiality and authenticity of ADS-B messages. In addition, performance evaluation also demonstrates the efficiency of communication and computation for the proposal by using flight data of OpenSky-a sensor network that covers Central Europe aiming at gathering ADS-B flight data. Finally, the deployment in a real airport environment also proves the effectiveness of our solution.
Recently online learning algorithm is applied to time series prediction with missing data without the strict assumption on the noise terms. The existing algorithm only uses the observed data to predict time series, which does not impute the missing data and costs most time to count the number of common missing observation in any two sub-sequences of time series with constant length. In this paper, we consider online learning algorithm for time series prediction with missing data, which use the estimated values to impute the missing data. We firstly propose an online algorithm for the standard autoregressive (AR) model with missing data. In addition, the length of coefficients vector is added to utilize more previous time series data under an improper setting. On this basis, two sparse online learning algorithms are proposed, one is for alpha-exp-concave loss functions and the other is for general loss functions. Our theorem guarantees the algorithms to approach the performance of the best AR coefficients vector in hindsight. Furthermore, we conduct a set of experiments on real data to show that our algorithm can achieve much the same error compared to the state-of-the-art algorithm and need less time.
As content is transmitted in content-driven manner in the content-centric network (CCN), it does not require any host address; therefore, it is infeasible to establish a traditional secure channel between hosts. Securing the content transmission in the CCN is a challenging problem. We solve this problem with the content-based encryption, where the encryption key is associated with the content itself, and the private decryption keys are distributed to the authorized consumers. To deal with the security requirements for content-based encryption, we define a security model that captures the key existential unforgeability and semantic security. We then propose a content-based encryption scheme with short ciphertexts, which is proven to be strong key existentially unforgeable and semantically secure in the standard model. We apply the scheme to construct a secure content transmission protocol in the CCN, which captures the security properties of content confidentiality, integrity, resistance to replay attacks and resistance to key forgery attacks. The performance analysis shows that our protocol is efficient for large content transmission.
The analysis of the small-signal stability of converter-based microgrids is well established, but the existing deterministic approaches cannot fully capture the impact of random parameters resulting from complex converter control structures and stochastic operation scenarios. Accurate assessment of the relevance of different parameters can facilitate efficient modeling, online monitoring and control design of the microgrids. In this paper, a global sensitivity analysis (GSA) framework is proposed to identify the most relevant parameters that affect the small-signal stability of converter-based microgrids. First, the systematic approach to derive the complete small-signal state-space model of the microgrid is introduced and the stability index is defined. Then, the system operating states, the control and the network parameters are chosen as input variables, and the priority ranking procedure based on GSA is explained. Next, the Levenberg-Marquardt based power flow calculation is adopted to determine the steady-state operation point. The polynomial chaos expansion and the low-rank approximation methods are introduced into the GSA to further improve computation efficiency. Finally, the proposed methodology is applied to an exemplary microgrid. The critical parameters influencing the system small-signal stability are identified, and the results are compared with those of the conventional local sensitivity analysis. The correctness and effectiveness of the proposed methodology are verified by real-time simulation results.
Corrugated lead halide 2D perovskites are an emerging class of intrinsic broadband white-light emitters. Recently, we reported first-generation ultrastable cationic lead halide emitters, overcoming the air/moisture sensitivity of perovskites. Herein, the crystal engineering of cationic lead bromide layers realized a 4-fold improvement of photoluminescence quantum efficiency (PLQE) over our previous materials. The PLQE is stepwise increased by enhancing the structural deformation from inorganic slabs as well as the quantum confinement effect from organic pillaring spacers. Upon continuous near-UV irradiation (>360 nm) under atmospheric conditions, [Pb4Br6][O2C(CH2)(6)CO2] exhibits undiminished broadband photoemission with a PLQE of 8.2% for at least 30 days. Variable-temperature photophysics studies and density functional theory calculations indicate the enhanced PLQE is largely attributed to the formation of self-trapped excitons (Pb-2(3+) and Br-2(-)) originating from strong electron-phonon coupling in cationic bromoplumbate layers.
Magnetic silica nanoparticles (MSNPs) were prepared and applied for the first time as a matrix in MALDI MS for analysis of small thermally labile biomolecules including oligosaccharides, amino acids, peptides, nucleosides, and ginsenosides. The matrix was characterized by scanning electron microscopy and UV-vis spectroscopy. It displays good performance in analyses of such biomolecules in the positive ion mode. In addition, the method generates significantly less energetic ions compared to the use of carbon nanotubes or graphene-assisted LDI MS and thus produces intact molecular ions with little or no fragmentation. In addition, the MSNPs have better surface homogeneity and better salt tolerance and cause lower noise. It is assumed that the soft ionization observed when using MSNPs as a matrix is due to the specific surface area and the homogenous surface without large clusters. The matrices were applied to the unambiguous identification and relative quantitation of the water extract of Panax ginseng roots. Any false-positive results as obtained when using graphene and carbon nanotubes as a matrix were not observed.
Many of the sandstones at cultural heritage sites around the world are susceptible to chemical weathering, and long-term monitoring of the chemical weathering would be of great value for heritage conservation and would also provide reference data for environmental protection policies and projects. Reflectance spectroscopy is a potential tool for monitoring sandstone weathering due to its non-destructive characteristics. In this paper, we present the results of an investigation into the reflectance spectra of sandstones at the Yungang Grottoes, China, where the sandstones are variously fresh, calcite-dissolved, or argillitic-altered. We found several spectral absorptions, including those at 490, 675, 900, 1410, 1918, 2205, 2330, 2350, and 2380 nm. The absorptions at 490, 675, and 900 nm are related to hematite cement, while that at 2330 nm is associated with calcite cement. The absorptions at 1410, 2205, 2350, and 2380 nm are induced by the Al-OH vibration of kaolinite, and that at 1918 nm is related to crystal water. The calcite-dissolved sandstones have lower absorption intensities at 2330 nm than fresh sandstones, and the argillitic-altered sandstones have lower absorption intensities at 490, 675, and 900 nm than the fresh sandstones. In the 1st-derivative reflectance plots, the absorption peaks at similar to 1400 nm shift towards shorter wavelengths with increasing kaolinite contents. The spectral features of the fresh, calcite-dissolved, and argillitic-altered sandstones are all different, and this means they can be distinguished spectroscopically, which demonstrates the usefulness of reflectance spectroscopy for the long-term monitoring of sandstone weathering in the Yungang Grottoes.
Integrating ratiometric photoelectrochemical (PEC) techniques with paper microfluidics to construct a ratiometric PEC paper analytical device for practical application is often restricted by the grave dependence of ratiometric assay on photoactive materials and low mass-transfer rates of the paper channel. Herein, a universal donor/ acceptor-induced ratiometric PEC paper analytical device with a hollow double-hydrophilic-walls channel (HDHC) was fabricated for high-performance microRNA-141 (miRNA-141) quantification. Concretely, a photoanode and photocathode were integrated on the paper-based sensing platform in which the photocathode served as a biosensing site for the pursuit of higher selectivity. For formulation of a cascading signal amplification strategy, a unique duplex-specific nuclease-induced target recycling reaction was engineered for the output of a double amount of all useful DNA linkers instead of conventional output of only one available DNA product, which could guarantee the output of abundant DNA linkers with the initiation of a cascade of hybridization chain reaction on both the trunk and branch in the presence of miRNA-141. Then the formed dendriform polymeric DNA duplex structures were further decorated with glucose oxidase (GO(x))-mimicking gold nanoparticles by the electrostatic interaction to form a branchy gold tree (BGT). Profiting from the perfect GOx-mimicking activity of BGT and high mass-transfer rates of HDHC, the cathodic photocurrent from Ag2S/Cu2O hybrid structure was in a "signal off" state while the anodic photocurrent from graphene quantum dots (GQDs) and Ag-2 Se QDs cosensitized ZnO nanosheets was in a "signal on" state because BGT-catalyzed glucose oxidation reaction evoked the consumption of dissolved O-2 as an electron acceptor and the generation of H2O2 as an electron donor. With calculation of the ratio of two photocurrent intensities, the quantitative detection of miRNA-141 was achieved with high sensitivity, accuracy, and reliability.
Theoretical calculations were combined with experiments to explore the photoelectric catalytic performance of MSe2/SnO2 (M = Mo, W) nanocomposites. The electronic structures of the composites were studied by density functional theory(DFT) calculation. Compared with SnO2 material (1.070 eV), the band gap values of MSe2/SnO2 (M = Mo, W) nanocomposites were significantly reduced to 0.133 and 0.008 eV, respectively. Population analysis suggested that the charges transferred between upper MSe2 (M = Mo, W) and underlying SnO2, which could improve the photoelectric catalytic performance of SnO2 materials. Thus, the MSe2/SnO2 (M = Mo, W) nanocomposites were synthesized by hydrothermal method and characterized by XRD. Electrodeposition was conducted to prepare the corresponding electrodes with Fluorine-doped Tin Oxide (FTO) conductive glass to test the photoelectric catalytic performance. The experimental results showed that the photocurrents of the MSe2/SnO2 (M = Mo, W) nanocomposites were 4.8 and 3.0 mu A/cm(2), respectively, and the electrochemical impedance was both smaller than that of SnO2 material. Therefore, the MSe2/SnO2 (M = Mo, W) nanocomposites are good photoelectric catalytic materials.
The newly invented triboelectric nanogenerator (TENG) shows a significant potential to be a powerful technology for converting mechanical energy into electricity as a complementary usage for solving our future energy demanded for micro- and macro- grid. However, packaging and robustness are critical factors for TENG toward practical applications since the performance of TENG is affected by environmental conditions such as humidity. Here, a full-packaged waterwheel-like rolling triboelectric-electromagnetic hybrid nanogenerator (TEHNG) for harvesting mechanical energy in harsh environment has designed. The integrated silicone rubber-magnet rods and electrodes laminated by a layer of nylon film, which worked as the triboelectric material, are used to fabricate a rolling friction free-standing triboelectric layer mode triboelectric nanogenerator (RFS-TENG) and combining with copper coils subtly, electromagnetic generator (EMG) is achieved. The rolling friction causes almost no damage to the triboelectric layers and there is no obvious normalized current decay found after 3-days continuous working at 0.5 Hz. Thus, this novel design makes the TEHNG easier to be packaged, and prevent from water interference revealing a superior robustness. It is also found that the developed TEHNG broadens the working frequency range as TENG can work more effectively for converting the mechanical energy at lower-frequencies less than 5 Hz energy scavenging while EMG can work much better at higher-frequencies above 5 Hz. Moreover, combining with hand shaking and water wheel, the device can be demonstrated to collect the energy of handy and water-flow flexibly. Furthermore, using current output signals of the EMG, a self-powered wireless frequency and revolution sensor systems are also demonstrated. This work presents a new platform of hybrid generator for harvesting mechanical energy in harsh environments with several desirable features such as the broadened frequency bands, better portability and for building up self-powered wireless sensor systems.
The newly invented triboelectric nanogenerator (TENG) is deemed to be a more efficient strategy than an electromagnetic generator (EMG) in harvesting low-frequency (<2 Hz) water wave energy. Various TENGs with different structures and functions for blue energy have been developed, which can be roughly divided into two types: liquid-solid contact electrification TENGs and fully enclosed solid-solid contact electrification TENGs. Robustness and packaging are critical factors in the development of TENGs toward practical applications. Furthermore, for fully enclosed TENGs, the requirements and costs of packaging are very high, and they can difficult to disassemble after enclosed, if there is something wrong with the devices. Herein, a nonencapsulative pendulum-like paper based hybrid nanogenerator for energy harvesting is designed, which mainly consists of three parts, one solar panel, two paper based zigzag multilayered TENGs, and three EMG units. This unique structure reveals the superior robustness and a maximum peak power of zigzag multilayered TENGs up to 22.5 mW is realized. Moreover, the device can be used to collect the mechanical energy of human motion in hand shaking. This work presents a new platform of hybrid generators toward energy harvesting as a portable practical power source, which has potential applications in navigation and lighting.