Search

Nanoscale polymeric thin films are widely used in diverse applications such as energy devices, flexible electronics and biosensors, where a satisfactory mechanical performance is of vital importance to realize their full functionality. It has been evidenced that the elastic properties of polymer films are often strongly affected by their thickness; however, the underlying mechanism of this phenomenon, especially a thorough understanding at the microscopic level, has yet to be achieved. Here we established a coarse-grained molecular dynamics (CGMD) based computational framework, combining with experimental verifications, aiming to reveal the conformational origin of the stiffening behavior of crosslinked polymeric thin films. By imposing systematic controls over the polymer network structures, we found that the bi-axial modulus changes are essentially consequent of the alteration of polymer conformations. A unified theory was then proposed, to quantitatively clarify the correlation between the elastic properties of the system and the distributional variations of the chain end-to-end distances, with predicting a significant hardening effect on top of the conventional entropic elasticity with largely uncoiled chains. Adopting processing protocols inspired by the modeling, our experiments showed that PDMS films at approximately the same thickness may exhibit a two order of magnitude difference in their moduli. The good agreement between experiments and simulations illustrated our findings as an effective guideline for tailoring the elastic properties of polymer films at nanoscale.

Substituted 2,1,3-benzothiadiazole (BTD) is a widely used electron acceptor unit for functional organic semiconductors. Difluorination or annulation on the 5,6-position of the benzene ring is among the most adapted chemical modifications to tune the electronic properties, though each sees its own limitations in regulating the frontier orbital levels. Herein, a hitherto unreported 5,6-annulated BTD acceptor, denoted as ssBTD, is designed and synthesized by incorporating an electron-withdrawing 2-(1,3-dithiol-2-ylidene)malononitrile moiety via aromatic nucleophilic substitution of the 5,6-difluoroBTD (ffBTD) precursor. Unlike the other reported BTD annulation strategies, this modification leads to the simultaneous decrease in both frontier orbital energies, a welcoming feature for photovoltaic applications. Incorporation of ssBTD into conjugated polymers results in materials boasting broad light absorption, dramatic solvatochromic and thermochromic responses (>100 nm shift and a band gap difference of ∼0.28 eV), and improved crystallinity in the solid state. Such physical properties are in accordance with the combined electron-withdrawing effect and significantly increased polarity associated with the ssBTD unit, as revealed by detailed theoretical studies. Furthermore, the thiolated ssBTD imbues the polymer with ambipolar charge transport property, in contrast to the ffBTD-based polymer, which transports holes only. While the low mobilities (10-4 to 10-5 cm2 V-1 s-1) could be further optimized, detailed studies validate that the thioannulated BTD is a versatile electron-accepting unit for the design of functional stimuli-responsive optoelectronic materials.

An ultra-high performance liquid chromatography coupled with quadrupole Orbitrap mass spectrometry (UHPLC-Q-Orbitrap/MS)-based metabolomics method was applied to investigate the chemome diversity of Schisandra chinensis fructus (SF) and its processed products, including vinegar-processed Schisandra (VS), wine-processed Schisandra (WS), and honey-processed Schisandra (HS). A clear classification among four Schisandra products was observed in the score plot of the partial least-squares discriminant analysis (PLS-DA) model, then 28 marker compounds were selected and identified. The content of most marker compounds in VS and WS was increased compared with that in SF, and the lowest content was observed in HS, then the high-performance liquid chromatography (HPLC) analysis was performed to confirm the change trends. These results suggested the chemical composition variation occurs in different Schisandra products, and the marker compounds selected in this study will be useful for the quality evaluation of Schisandra products.

Container technology is an emerging virtualization technology that is more efficient and lightweight than virtual machines. This technology is becoming increasingly popular. However, containers are vulnerable to attackers due to various security issues. It is necessary to build trust between users and their containers, as well as between a remote party and the container in the untrusted container environment. The existing trusted computing technologies build a trust chain from hardware to the running operating system. In this paper, we extend the trust chain to containers and build trust in the container environment. We first boot the computer to a trusted operating system. The trusted OS then verifies programs running on the OS to improve security. We design the well-formed signature list to help users to authorize container executables and modify the Linux kernel to verify executables running in containers. Therefore, the user is able to control what programs can run in his containers and trust the containers. Our approach generates a measurement list and creates a vTPM for each container. A remote party can request the measurement list based on our container state challenge protocol. As a result, a remote party is able to know the container state and decide whether to trust the container. We also implement the executables measurement and verification mechanism and evaluate the performance. The results show the container start delay is no more than 3% of the normal container start time and the overhead to measure and verify executables is no more than 1 us in most cases, which is reasonably efficient.

Optoelectronic devices based on metal halide perovskites, including solar cells and light-emitting diodes, have attracted tremendous research attention globally in the last decade. Due to their potential to achieve high carrier mobilities, organic-inorganic hybrid perovskite materials can enable high-performance, solution-processed field-effect transistors (FETs) for next-generation, low-cost, flexible electronic circuits and displays. However, the performance of perovskite FETs is hampered predominantly by device instabilities, whose origin remains poorly understood. Here, perovskite single-crystal FETs based on methylammonium lead bromide are studied and device instabilities due to electrochemical reactions at the interface between the perovskite and gold source-drain top contacts are investigated. Despite forming the contacts by a gentle, soft lamination method, evidence is found that even at such "ideal" interfaces, a defective, intermixed layer is formed at the interface upon biasing of the device. Using a bottom-contact, bottom-gate architecture, it is shown that it is possible to minimize such a reaction through a chemical modification of the electrodes, and this enables fabrication of perovskite single-crystal FETs with high mobility of up to ≈15 cm2 V-1 s-1 at 80 K. This work addresses one of the key challenges toward the realization of high-performance solution-processed perovskite FETs.

Since the discovery of graphene, two-dimensional (2D) materials have received continuous attention and carried out in-depth exploration and development due to their excellent properties. With the exploration of the preparation of new 2D materials, one began to consider the synergistic effects produced by the in-plane junction and interlayer stacking to compensate for the defects of a single material and obtain some new properties. Matching the lattice structure to achieve specific functionalization, or using van der Waals force to achieve stacking, helps to introduce a new degree of freedom by combining different 2D materials, and open a new window for the research and practical application of 2D materials.From the perspective of atomic manufacturing, in this article we introduce the controllable preparation and optoelectronic applications of 2D planar and van der Waals heterojunction materials. First, we briefly introduce the common 2D materials such as graphene, hexagonal boron nitride, transition metal dichalcogenides and black phosphorus used in the preparation of heterojunctions and related concepts of heterojunctions. Second, we review, in principle, the commonly used characterization methods including scanning probe-based techniques, spectrum-based, electron-based imaging techniques and others. Third, we summarize the preparation methods of planar and vertical heterojunctions. Basically, mechanical transfer method such as wet or dry method can be used to produce various vertical heterostructures of 2D materials, but usually lack the scalability. On the other hand, chemical vapor deposition method provides a scalable route to producing the planar heterostructure and vertical structure of 2D materials. Several strategies have been developed to produce various heterostructures. In addition, the recent development of twist-angle and quasi-crystalline bi-layer graphene is briefly reviewed. Fourth, the properties and applications of 2D van der Waals heterostructures such as field-effect transistor, light emitting diode, solar cell, flexible optoelectronic devices and plasmonic applications are introduced. Finally, the problems in the field are discussed, and the outlook is provided.

With the development of offshore oil and gas exploitation intensifies, FPSO which having many advantages can better adapt to the complicated environment of deep sea in numerous offshore platform. Due to the hull prone to resonance phenomenon, FPSO has more intense motion compared to other platforms. Therefore, the main challenge of FPSO in the deep sea operation is to design effective mooring system. This paper introduced the dynamic response analysis methods of FPSO system. Time domain method of coupling analysis was used. Dynamic responses of catenary and taut inner tower FPSO system were calculated respectively. According to the current mooring system development, the article compared and analyzed catenary mooring system and taut mooring system. Moreover, the results indicated that the position ability and mooring strength of taut mooring system whose intermediate material is polyester are better than that of catenary mooring system on the premise that satisfies API specification at the same time.

We present a high accuracy, high reliability, high security, low power consumption micro blasting system for smart blasting network. The system consists of a MEMS semiconductor bridge (SCB) as electro-pyrotechnic initiator to ignite the explosive materials, a MEMS switch group as security device to increase the security, a micro application-specific integrated circuit (ASIC) as controller to control all the components and a streamlined peripheral circuit. The system is particularly suitable for accurate directional blasting at large surface and underground operations or other complex environments.

Ultrasensitive room temperature real-time NO2 sensors are highly desirable due to potential threats on environmental security and personal respiratory. Traditional NO2 gas sensors with highly operated temperatures (200–600 °C) and limited reversibility are mainly constructed from semiconducting oxide-deposited ceramic tubes or inter-finger probes. Herein, we report the functionalized graphene network film sensors assembled on an electrospun three-dimensional (3D) nanonetwork skeleton for ultrasensitive NO2 sensing. The functional 3D scaffold was prepared by electrospinning interconnected polyacrylonitrile (PAN) nanofibers onto a nylon window screen to provide a 3D nanonetwork skeleton. Then, the sulfophenyl-functionalized reduced graphene oxide (SFRGO) was assembled on the electrospun 3D nanonetwork skeleton to form SFRGO network films. The assembled functionalized graphene network film sensors exhibit excellent NO2 sensing performance (10 ppb to 20 ppm) at room temperature, reliable reversibility, good selectivity, and better sensing cycle stability. These improvements can be ascribed to the functionalization of graphene with electron-withdrawing sulfophenyl groups, the high surface-to-volume ratio, and the effective sensing channels from SFRGO wrapping onto the interconnected 3D scaffold. The SFRGO network-sensing film has the advantages of simple preparation, low cost, good processability, and ultrasensitive NO2 sensing, all advantages that can be utilized for potential integration into smart windows and wearable electronic devices for real-time household gas sensors.

A MEMS switch based on electro-thermal and electro-explosion has been packaged before its humidity test, temperature shock test and ballistic shock test are taken. Some devices failed after the tests. The analysis of such a device is given in this paper.

Catalytic hydrolysis of biomass over solid catalysts can be one of the most efficient pathways for a future sustainable society dependent on cellulose biomass. In this work metal–organic framework MIL-53(Al) without any functionalization was directly employed as an efficient heterogeneous catalyst for the hydrolysis of carboxymethyl cellulose (CMC) to 5-hydroxymethyl-furaldehyde (5-HMF) in aqueous phase. A 5-HMF molar yield of 40.3% and total reducing sugar (TRS) molar yield of 54.2% were obtained with water as single solvent at 473 K for 4 h. The catalyst could be reused three times without losing activity to a greater extent. With the remarkable advantages such as the use of water as single solvent and MIL-53(Al) as a novel heterogeneous green catalyst, the work provides a new platform for the production of value added chemicals and liquid fuels from biomass.

Background subtraction is widely used in detecting moving objects in a static scene, which requires a fixed camera, and a static background. Most background subtract algorithms require the illumination changing slowly, so can be tracked and updated. If the illumination changes fast and non-monotony, many algorithms fail. Here we research one special condition in changing illumination: single continuous varying illumination. This scene can be seen indoor or in the dark or in underground architecture. We advance a new algorithm based on the illumination factor (BSIF-background subtraction based on illumination factor), it can relative precisely get the moving objects in this scene.

The aim of this research is to reconstruct a metaphysical interpretation of the philosophy of history with regard to the spirit of historical thinking. The spirit of historical thinking is to emphasize the relation between what happened in the past and historical thinking about the past in the present. However, current philosophies of history, which are largely epistemologically oriented, have not adequately explored this relation. In order to investigate the relation between past and present, I refer to an Aristotelian philosophy of practice and politics, and adapt it to the domain of the philosophy of history, and argue the case for a metaphysical science of history. A metaphysical science of history contains two primary parts. They are the part on physis and the part on technê/phronēsis. With regard to physis that metaphysically investigates the natural generating progress of entities, I argue that the existence of historical events can be understood as a natural developing progress in which the events are ordered in a chronological sequence. Such chronological sequence is essentially the physis of history in the metaphysical sense (I characterize it as ‘Ordnungszeit’). For the part on technê/phronēsis, I demonstrate that Aristotelian knowing is for itself an action of knowing, which is located beyond a given temporal position in the past to both the past and the thinking present, and indicates the fundamental Beingness of history (I characterize it as ‘Geschehenszeit’). Finally I conclude that the historical eudaimonia, namely the pursuing of the completeness of historical knowledge, is the final presentation of actualizing Geschehenszeit, as it bridges the past and the present in accordance to the spirit of historical thinking.