High-Speed Micro-Particle Motion Monitoring Based on Continuous Single-Frame Multi-Exposure Technology.

The impact phenomena of solid micro-particles have gathered increasing interest across a wide range of fields, including space debris protection and cold-spray additive manufacturing of large, complicated structures. Effective motion monitoring is essential to understanding the impact behaviors of micro-particles. Consequently, a convenient and efficient micro-particle motion monitoring solution is proposed based on continuous single-frame multiple-exposure imaging technology. This method adopts a camera with excellent low-light performance coupled with high-frequency light-emitting diode (LED) flashes to generate short interval illumination. This technology can, in theory, achieve 1 million effective frames per second (fps) and monitor particles as small as 10 microns with speeds up to 12 km/s. The capabilities of the proposed method were validated by a series of micro-particle motion monitoring experiments with different particles sizes and materials under varying camera configurations. The study provides a feasible and economical solution for the velocity measurement and motion monitoring of high-speed micro-particles.

High Elongation and Transparent Nacre-Inspired PVA/MMT Nanocomposites.

Currently, high strength nacre-inspired PVA/MMT (polyvinyl alcohol/montmorillonite) nanocomposites with high MMT nanofiller content (50-70 wt%) have been constructed successfully. However, this seriously sacrifices the elongation and reduces the corresponding transparency. In this paper, high elongation and transparent PVA/MMT nanocomposites with high MMT content are prepared by the evaporation-induced assembly with the introduction of the micro-crosslinking. Results demonstrate that the micro-crosslinking can inhibit the formation of rod-shaped arrays, and contribute to a more ordered layered microstructure, where an elongation of 76.2% in 47.8 wt% MMT content nanocomposites is gained, nearly 19 times of that of non-crosslinked nanocomposites (ultimate strain is 4.1%). This provides a potential approach for compromise between high strength and excellent elongation at the same MMT content. Moreover, disappearance of rod-shaped arrays and resultant ordered layered microstructure make eventual films more transparent.

Investigations into the Role of Friction for Rigid Penetration into Concrete-Like Material Targets.

Currently, it appears that there is a lack of understanding related to the role of SSF, in the two-phase behavior of the deceleration history, which is an issue discussed recently in the impact dynamics field. This paper analytically and numerically focuses on the effect of SSF on the projectile deceleration characteristic of concrete-like targets. Firstly, the penetration process according to the two-phase feature of the projectile deceleration is revised, where analytical results indicate that the SSF has a phased feature corresponding to the two-phase behavior of the deceleration history. Furthermore, a series of numerical simulations are conducted to understand the role of SSF more clearly. Simulation results show a similar conclusion to the analyses of the two-phase penetration process; at the range below a certain critical striking velocity, adding friction can reproduce the experimental data; when exceeding the critical striking velocity, the simulated results without considering friction are closest to the experimental data. Hence, it could be gained that the role exchange between the SSF and the dynamic term contributes to the two-phase penetration behavior for concrete-like materials. This indicates that the sensitivity of SSF to the penetration process is one of the factors driving the two-phase feature.

New Algorithms for Autonomous Inertial Navigation Systems Correction with Precession Angle Sensors in Aircrafts.

This paper presents new algorithmic methods for accuracy improvement of autonomous inertial navigation systems of aircrafts. Firstly, an inertial navigation system platform and its nonlinear error model are considered, and the correction schemes are presented for autonomous inertial navigation systems using internal information. Next, a correction algorithm is proposed based on signals from precession angle sensors. A vector of reduced measurements for the estimation algorithm is formulated using the information about the angles of precession. Finally, the accuracy of the developed correction algorithms for autonomous inertial navigation systems of aircrafts is studied. Numerical solutions for the correction algorithm are presented by the adaptive Kalman filter for the measurement data from the sensors. Real data of navigation system Ts-060K are obtained in laboratory experiments, which validates the proposed algorithms.

Achieving nitrogen-doped carbon/MnO2 nanocomposites for catalyzing the oxygen reduction reaction.

The design and synthesis of cheaper and more stable catalysts with comparable electrocatalytic performance to commercial Pt/C towards the oxygen reduction reaction is of importance for their application in fuel cells and metal-air batteries. Herein, we report the generation of nitrogen-doped carbon/MnO2 nanocomposites via pyrolyzing the polypyrrole/MnO2 precursor that is obtained based on the direct redox reaction between polypyrrole and KMnO4. The achieved sample presents an onset and half-wave potential of -0.048 and -0.124 V vs. Hg/HgO, respectively, and a current retention of 93% after 20 000 s chronoamperometry measurement. Meanwhile, it shows stronger methanol tolerance, endowing it with great potential for the corresponding applications. The excellent oxygen reduction reaction catalytic activity originates from the synergistic effect between nitrogen-doped carbon and MnO2, where the former one is helpful for MnO2 to achieve a higher Mn3+/Mn4+ ratio and a higher number of oxygen vacancies, and the existence of the latter one is beneficial for generating a higher ID/IG ratio in the carbon layer. These both contribute to the achievement of large numbers of active sites for the electrocatalytic process.

Finite-Time Attitude Stabilization Adaptive Control for Spacecraft with Actuator Dynamics.

For the attitude stabilization of spacecraft with actuator dynamics, this paper proposed a finite-time control law. Firstly, the dynamic property of the actuator is analyzed by an example. Then, a basic control law is derived to achieve the finite-time stability using the double fast terminal sliding mode manifold. When there is no prior knowledge of time matrix of the actuator, an adaptive law is proposed to estimate the unknown information. An adaptive control law is derived to guarantee the finite-time convergence of the attitude, and a Lyapunov-based analysis is provided. Finally, simulations are carried out to demonstrate the effectiveness of the proposed control law to the attitude stabilization with the actuator dynamics. The results show that the high-precision attitude control performance can be achieved by the proposed scheme.

Rationally Designed Calcium Phosphate/Small Gold Nanorod Assemblies Using Poly(acrylic acid calcium salt) Nanospheres as Templates for Chemo-photothermal Combined Cancer Therapy.

Elaborately designed novel multifunctional therapeutic agents are highly desired for efficient cancer therapy. In this work, a new therapeutic nanoplatform based on calcium phosphate/small gold nanorod assemblies modified with methoxy-poly(ethylene glycol)-thiol (designated as PEGylated CaP/Au NR assemblies) is created via a mild, reproducible, and simple route for the first time. The obtained PEGylated CaP/Au NR assemblies possess many virtues including outstanding drug-loading capacity, excellent photothermal conversion efficiency (η, ∼38.5%), pH/near-infrared (NIR) dual-responsive release property, and good biocompatibility. After loading doxorubicin (DOX) in PEGylated CaP/Au NR assemblies, the DOX-loaded PEGylated CaP/Au NR assemblies can simultaneously supply intense heating effect and increased DOX release under 808 nm NIR laser, achieving excellent antitumor therapeutic effect in vitro and in vivo. Furthermore, the combination of DOX-loading and photothermal treatment upon PEGylated CaP/Au NR assemblies displays better therapeutic effect than single chemotherapy or photothermal therapy. Furthermore, the comprehensive methyl thiazolyl tetrazolium (MTT), hemolysis, and histological assays manifest no obvious toxicity of PEGylated CaP/Au NR assemblies. Our work elucidates the great prospect of PEGylated CaP/Au NR assemblies as a therapeutic agent for synergistic chemo-photothermal cancer therapy.

Controlling two-phase self-assembly of an adenine derivative on HOPG via kinetic effects.

Large-area self-assembled structures of a nucleobase adenine derivative were successfully realized through vacuum deposition. STM images reveal two types of structures, which could be regulated by substrate temperature and the evaporation rate, indicating the relevance of kinetic effects. The results are supported by computer simulations.

Temperature-dependent self-assembly of adenine derivative on HOPG.

Temperature-dependent self-assembly formed by the adsorption of the nucleobase adenine derivative on a graphite surface were investigated by in situ scanning tunneling microscopy (STM). The high-resolution STM images reveal two types of structures, α phase and ß phase, which are mainly driven by either hydrogen bonding or aromatic π-π interactions between adenine bases, respectively, as well as the interactions of alkyl chains. α-Phase structures can be transformed into ß-phase structures by increasing temperature. The reverse is true for decreasing temperature. This reflects structural stabilities resulting from the different interactions. Density functional theory (DFT) calculations were performed to characterize possible arrangements of adjacent adenine moieties systematically in terms of binding energies and structural properties. Via a systematic search algorithm, all possible network structures were determined on a microscopic level. In this way, it is possible to rationalize the structural parameters as found in the STM images.

Two-dimensional self-assembly of linear molecular rods at the liquid/solid interface.

We report on the synthesis and scanning tunneling microscopy (STM) studies of a series of linear molecular rods (1-5) comprising different numbers and/or spatial arrangements of perfluorinated benzene and benzene subunits interlinked with diacetylenes in the para position and decorated with or without terminal dodecyl chains. The molecules organize themselves into well-ordered 2D crystal structures at the liquid/solid interface through intermolecular and molecule-substrate interactions. Whereas the molecules substituted by dodecyl chains form the lamellar structures with alternating rigid core rows and alkyl chain rows, the unsubstituted ones change the orientation of the rigid backbones with respect to the lamellar axis. The molecular arrangement is not influenced by fluoro substituents on any phenyl ring of the backbone, which suggests that the interactions between the π-conjugated backbones are dominated by close packing rather than by the dipole moments of the rods or fluorine-based intermolecular interactions.

Effect of intermolecular dipole-dipole interactions on interfacial supramolecular structures of C3-symmetric hexa-peri-hexabenzocoronene derivatives.

Two-dimensional (2D) supramolecular assemblies of a series of novel C(3)-symmetric hexa-peri-hexabenzocoronene (HBC) derivatives bearing different substituents adsorbed on highly oriented pyrolytic graphite were studied by using scanning tunneling microscopy at a solid-liquid interface. It was found that the intermolecular dipole-dipole interactions play a critical role in controlling the interfacial supramolecular assembly of these C(3)-symmetric HBC derivatives at the solid-liquid interface. The HBC molecule bearing three -CF(3) groups could form 2D honeycomb structures because of antiparallel dipole-dipole interactions, whereas HBC molecules bearing three -CN or -NO(2) groups could form hexagonal superstructures because of a special trimeric arrangement induced by dipole-dipole interactions and weak hydrogen bonding interactions ([C-H···NC-] or [C-H···O(2)N-]). Molecular mechanics and dynamics simulations were performed to reveal the physics behind the 2D structures as well as detailed functional group interactions. This work provides an example of how intermolecular dipole-dipole interactions could enable fine control over the self-assembly of disklike π-conjugated molecules.

Two dimensional chiral networks emerging from the aryl-F...H hydrogen-bond-driven self-assembly of partially fluorinated rigid molecular structures.

Self-assembly of the partially fluorinated rigid molecules physisorbed at solution/graphite interface has been investigated by scanning tunneling microscopy. Upon adsorption, both the branched star-shaped compound 1 and the angulate rod 2 compromising diacetylene and acetylene interlinked benzene and pentafluorobezene formed two-dimensional chiral porous networks. The spontaneous formation of these architectures is likely attributed to the two effects: the compensation of the dipole moments of the branches and the formation of Ar-H...F hydrogen bonds. These results demonstrate that the immobilization of molecules at the liquid/solid interface can be driven by these weak intermolecular interactions instead of van der Waals interactions between alkyl chains and substrate.

A self assembled molecular zipper based on a perfluorophenyl-phenyl diacetylene motif.

The synthesis and characterization of a molecular rod consisting of a pentafluorophenyl and a para-dodecylphenyl subunit linked by a diacetylene and its large area self assembly into perfect parallel lines consisting of interlocked molecular rods are reported and discussed.

Tetradecylferrocene: ordered molecular array of an organometallic amphiphile in the crystal and in a two-dimensional assembled structure on a surface.

Tetradecylferrocene (4, Fc-(CH2)13CH3) was synthesized via lithiation of ferrocene by treatment with tert-butyl lithium, followed by alkylation with 1-bromotetradecane. Complex 4 forms a physisorbed ordered molecular monolayer on the surface of highly oriented pyrolytic graphite (HOPG) that was analyzed by scanning tunneling microscopy (STM). It features a lamellar structure with single rows of ferrocenyl moieties separating connecting areas formed by the long alkyl chains which are arranged parallel to each other. The ordering principle of 4 on the surface can be related to the arrangement of Fc-(CH2)13CH3 molecules in the three-dimensional crystal lattice.

Synthesis and surface properties of new ureas and amides at different interfaces.

The influence of the urea and amide group in the alkyl chain of methyl nonadecanoate on the surface properties is investigated and compared. For that purpose, the ureas CH3O2C-(CH2)m-NHCONH-(CH2)n-CH3 (n + m = 14) [1 (m = 2), 3 (m = 3), and 5 (m = 4)] and the amides CH3O2C-(CH2)m-NHCO-(CH2)n-CH3 (n + m = 15) [2(m = 2), 4 (m = 3), and 6 (m = 4)] were synthesized. The pi/A isotherms of the ureas show up to the attainable temperature of 313 K no LE phase, which indicates a very stable LC phase. The amides exhibit a two phase plateau region, with the exception of 2. The different behavior is connected with the hydrogen bond energies, which are stronger with the ureas in the LC than in the LE phase, whereas those of the amides have a similar strength in both phases. The effect of hydrogen bonds in self-assembled molecules of N,N'-dialkylurea CH3-(CH2)m-NHCONH-(CH2)n-CH3 (m + n = 14) [7 (n = 2)] was visualized by STM at the octylbenzene/graphite interface. Compound 7 forms a lamella structure with a periodicity of one molecule length. The tilt angle of 86 degrees +/- 2 degrees to the edge of the lamella points to a nearly orthogonal arrangement of the molecules. It indicates two equivalent bonds between the aza-hydrogens and the carbonyl oxygen. A similar arrangement is proposed for the LC phase of the ureas at the air/water interface.

Oligoethylene chains terminated by ferrocenyl end groups: synthesis, structural properties, and two-dimensional self-assembly on surfaces.

A series of unsaturated long-chain-bridged diferrocenes Fc-(CH2)n-CH=CH-(CH2)n-Fc (4 a-e) was synthesized by means of olefin metathesis. Subsequent catalytic hydrogenation furnished the saturated alpha,omega-bis-ferrrocenyl oligoethylene products Fc-(CH2)m-Fc (5). Members of both series formed highly ordered laminar structures at the highly oriented pyrolytic graphite (HOPG) solid/liquid interface or on the Ag(110) surface, which were characterized by STM. Details of the structural features of these ordered physisorbed surface assemblies of 4 and 5 were analyzed by comparison with DFT calculations on model systems and with the characteristic packing modes of these systems in the crystal.

STM study on quinacridone derivative assemblies: modulation of the two-dimensional structure by coadsorption with dicarboxylic acids.

We describe the two-dimensional (2D) assemblies of N,N'-dialkyl-substituted quinacridone derivatives on highly orientated pyrolytic graphite observed by scanning tunneling microscopy, and focus our discussion on whether the supramolecular organization can be modulated by the coadsorption of dicarboxylic acids. Our experiments have demonstrated that the quinacridone derivatives can form different 2D nanostructures when coadsorbed with dicarboxylic acids of different length at the liquid/graphite interface. Interestingly, N,N'-dihexadecyl-substituted quinacridone derivative alternately takes two different conformations in two columns for its coadsorption with pentadecanedioic acid and form a gridlike structure. It is shown that a cooperative effect of different interactions can be modulated by introducing guest molecule, leading to formation of different self-assembled nanostructures.

Supramolecular structures and assembly and luminescent properties of quinacridone derivatives.

The synthesis and single-crystal X-ray structures of two quinacridone derivatives, N,N'-di(n-butyl)quinacridone (1) and N,N'-di(n-butyl)-1,3,8,10-tetramethylquinacridone (2), are reported, and the 1H NMR, absorption, photoluminescent (PL), and electroluminescent (EL) characteristics are presented. Both these crystal structures are characterized by intermolecular pi...pi and hydrogen bonding interactions. The intermolecular pi...pi interactions lead to the formation of molecular columns in the solids of 1 and 2, and the interplanar contact distances between two adjacent molecules are 3.48 and 3.55 angstroms, respectively. Crystals of 1 display shorter intermolecular pi...pi contacts and higher density than 2. These results suggest that tighter intermolecular interactions exist in 1. The 1H NMR, absorption, and PL spectra of 1 and 2 in solutions exhibit concentration-dependent properties. The PL quantum yields of 1 in solutions decrease more quickly with the increase of concentration compared to that of 2 in solutions. For solid thin films of Alq3:1 (Alq3 = tris(8-hydroxyquinolinato)aluminum), emission intensities dramatically decrease and obvious red shifts are observed when the dopant concentration is above 4.2%, while for films of Alq3:2, a similar phenomenon occurs when the concentration is above 6.7%. EL devices with Alq3:1 as emitting layer only show high efficiencies (20.3-14.5 cd/A) within the narrow dopant concentration range of 0.5-1.0%. In contrast, high efficiencies (21.5-12.0 cd/A) are achieved for a wider dopant concentration range of 0.5-5.0% when Alq3:2 films are employed as emitting layer. The different PL and EL concentration-dependent properties of the solid thin films Alq3:1 and Alq3:2 are attributed to their different molecular packing characteristics in the solid state.

Influence of substituents on two-dimensional ordering of oligo(phenylene-ethynylene)s--a scanning tunneling microscopy study.

Two-dimensional (2D) assemblies of alkoxy-substituted oligo(phenylene-ethynylene)s bearing different substituents adsorbed on highly oriented pyrolytic graphite (HOPG) were studied by using scanning tunneling microscopy. It was found that the introduction of different endgroups or a biethynylene linkage into oligo(phenylene-ethynylene)s can significantly change their 2D ordering on HOPG. The carboxylic endgroups can direct the conjugated oligomers to form ordered lines through intermolecular hydrogen bonding. The possibility of controlling the 2D assemblies of conjugated molecules is of importance in designing organic optoelectronic devices.

Two- and three-dimensional molecular organization of Schiff-base derivatives.

We have designed and synthesized a series of Schiff base derivatives, and studied their structural features in two-dimensional (2D) and three-dimensional (3D) states by combining scanning tunneling microscopy (STM) and X-ray diffraction experiments. The Schiff-base derivatives with short alkyl chains crystallize easily, which allows a detailed structural analysis by X-ray diffraction. Due to the strong adsorbate-substrate interactions, those bases with long alkyl chains easily form 2D assemblies on highly oriented pyrolytic graphite (HOPG). The STM images indicate also that the introduction of two methoxy groups into the molecule can change the structure of these 2D assemblies as a result of the increased steric hindrances, for example: the Schiff-base derivative, bearing both methoxy groups and C16H33 tails, forms 2D Moiré patterns, and an alignment of pairing Schiff-base molecules may be easily resolved. Conversely, the Schiff base derivative, bearing solely C16H33 tails, forms 2D non-Moiré patterns. It is demonstrated that the 3D structural features result from the compromise of intermolecular interactions of different molecular moieties. However, there is one more factor, which also governs the 2D structure: the adsorbate-substrate interaction. The 3D crystal structure may thus help to understand many factors involved in the formation of 2D structures, and would be helpful for designing new molecular assemblies with tailoring functions.