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Glass-ceramic is a typical hard and brittle material that is difficult to machine. In order to improve the surface quality of laser-assisted fast tool servo machining optical free-form surface of glass-ceramic, the effects of spindle speed, feed speed, piezoelectric frequency and laser power on the surface roughness were investigated. Firstly, the Taguchi method (TM) was used to establish the orthogonal experiment, and the contribution rate of each machining parameter to the surface roughness was obtained through variance and signal-to-noise ratio (S/N) analysis. The order of the influence degree of each parameter on the surface roughness is as follows: laser power > spindle speed > feed speed > piezoelectric frequency. The optimal machining parameter combinations obtained for the TM experiment are as follows: spindle speed 50 rpm, feed speed 0.01 mm rev−1, piezoelectric frequency 8 Hz, laser power 75 W. The range of surface roughness reduction obtained by comparing laser-assisted machining (LAM) with pure fast tool servo (FTS) machining is 38.75%∼58.77%. The Box-Behnken Design (BBD) in response surface methodology (RSM) was used to design experiments and a regression model for surface roughness was established through RSM. The deviation between the surface roughness predicted by the regression equation and the experimental value is less than ±6%. The influence law of various machining parameters on surface roughness was studied through three-dimensional response surface. RSM optimized the minimum surface roughness with a desirability of 99.43%. The optimal combination of machining parameters optimized through RSM is as follows: spindle speed 53.71 rpm, feed speed 0.02 mm rev−1, piezoelectric frequency 6.73 Hz, laser power 72 W. This paper is the first to combine LAM with FTS for machining optical free-form surface of glass-ceramic. This study provides a reference for laser-assisted fast tool servo machining and the research methods of surface quality.

In recent years, there are more and more space complex operational tasks such as the maintenance and assembly of on-orbit aircraft. Traditional robot planning and control methods require precise dynamic models, which are difficult to accommodate to on-orbit assembly operations in extreme space environments. Typical space operation tasks, such as plug and pull operation, whose control strategy can be artificially designed. Being artificially designed by combining the output control strategy and deep reinforcement learning algorithm, which can simplify the training difficulty of deep reinforcement learning, making the learning process more efficient and training results better. In this paper, a deep Residual reinforcement learning algorithm combined with a heuristic control strategy is constructed to complete the space mechanical arm assembly operation training in a highly realistic simulation environment. Based on the experimental data, the Residual deep reinforcement-learning algorithm designed in this paper shows the performance of rapid convergence and can complete the on-orbit assembly operation task with a high probability.

Visual guidance based on cooperative target is one of the most commonly used approaches in the field of space in-orbit service, such as spacecraft rendezvous and docking and satellite maintenance. Considering the limited space hardware resources, it is necessary to design an embedded image processing algorithm to meet the special needs of space recognition, such as small memory consumption and fast recognition speed. Therefore, aiming at the classic three-point cooperative target, recognition, and pose estimation algorithm is designed in this paper based on mono-vision. In this method, a fast inflection point detection method is designed, and the contour is divided into several edges with a single feature, which improves the accuracy of circle recognition. Finally, the relative pose of the target coordinate system can be obtained quickly and accurately by P3P. The algorithm has low complexity and can realize fast recognition with small memory, even with limited space-grade hardware resources. The effectiveness of the proposed method is verified by experiments.

Long-form document matching is an important direction in the field of natural language processing and can be applied to tasks such as news recommendation and text clustering. However, long-form document matching suffers from noisiness and sparsity of semantic information in long text. Using short-form document matching methods on a long-form matching problem is not satisfactory. Long-form document matching has attracted the attention of researchers, who have proposed many effective methods. Methods for matching long texts can be divided into three categories: traditional bag-of-words-based models, traditional deep learning-based models, and pre-training-based models. This study reviews typical methods of long-form document matching, analyzes their advantages and disadvantages, and discusses possible future developments.

As an important part of composite insulator, glass fiber reinforced polymer (GRP) rod needs to bear the main mechanical and keep certain insulation performance. The void in the material is key factor to the performance of GRP rod. The void with larger size could affect the electric field distribution significantly and lead to the “Lantern-like” heating. In this paper, the structure of void in GRP rod is studied by 3D X-ray microscope. It is found that the void dimensions in the GRP rod is generally less than 300μm, but the interconnection of linear hole makes the length of the void increase significantly. For the GRP rod with high porosity, the length of connection hole is hard to be detected directly by the existing technology, but it could be calculated based on the diameter of the hole. Based on the calculation method, the dimensions of void in GRP rod could be inspected by the observation of section using optical microscope.

Referring to GB/T 18386-2017, the impact of NEDC, WLTC and CLTC on the energy consumption of pure electric vehicle is simulated and analysed. Combined with the characteristic parameters of the driving cycles, from the perspective of energy flow loss of each system of the vehicle, the influences of driving cycles on the energy consumption of each part of the vehicle and the working efficiency of the power components are analyzed in detail, and the internal mechanism of the influence rule of driving cycles on energy consumption is revealed. Based on the CLTC, the effects of load mass, ambient temperature and air conditioning on the energy consumption of the electric vehicle are explored. The research results show that the electric vehicle has the longest driving range and the lowest energy consumption under CLTC; as the loading quality increases, the driving range decreases, and the energy consumption per 100 kilometers increases; test temperature and the air conditioner have a great influence on the driving range, especially in the low temperature environment.

With the intensification of global warming, spatiotemporal variations in the climate and their mechanisms have received increasing attention. Currently, the relationship between regional precipitation regime, large-scale circulation, and topography, particularly in high-altitude areas such as the Qinghai–Tibet Plateau, are not well understood. Herein, the spatial and temporal variability in the annual and intra-annual (wet and dry periods) precipitation at 33 stations in the Three-River Headwaters (TRH) region from 1967 to 2016 are analysed. Moreover, the empirical orthogonal function and wavelet transform coherence methods are used to analyse the relationships between the different modes of precipitation change and 14 atmospheric circulation indices. The following results were obtained. (1) The mean annual precipitation and mean dry period precipitation significantly increased over the studied period. Annual and intra-annual precipitation showed a spatial southeast-to-northwest decreasing trend. (2) Two main patterns of precipitation were observed during the studied period: a dominant pattern with high- and low-value centres located in southeast and northwest TRH, respectively, and a dipole pattern with more precipitation over southwest TRH and less precipitation over northeast TRH. (3) Precipitation had a negative correlation with latitude, positive correlation with longitude, and nonlinear relationship with elevation. (4) Precipitation changes over various parts of the studied domain were determined based on changes in the weather systems affecting the area, with different indices being correlated with different components during different times of the year.

3D bioprinting is an emerging biofabrication process for the production of adherent cell-based products, including engineered tissues and foods. While process innovations are rapidly occurring in the area of process monitoring, which can improve fundamental understanding of process-structure-property relations as well as product quality by closed-loop control techniques, in-line sensing of the bioink composition remains a challenge. Here, we report that hollow multifunctional fibers enable in-line impedimetric sensing of bioink composition and exhibit selectivity for real-time classification of cell type, viability, and state of differentiation during bioprinting. Continuous monitoring of the fiber impedance magnitude and phase angle response from 102 to 106 Hz during microextrusion 3D bioprinting enabled compositional and quality analysis of alginate bioinks that contained fibroblasts, neurons, or mouse embryonic stem cells (mESCs). Fiber impedimetric responses associated with the bioinks that contained differentiated mESCs were consistent with differentiation marker expression characterized by immunocytochemistry. 3D bioprinting through hollow multifunctional fiber impedimetric sensors enabled classification of stem cells as stable or randomly differentiated populations. This work reports an advance in monitoring 3D bioprinting processes in terms of in-line sensor-based bioink compositional analysis using fiber technology and provides a non-invasive sensing platform for achieving future quality-controlled bioprinted tissues and injectable stem-cell therapies.

The correlation between crystal chemistry characteristics and dispersion performance of Ca-montmorillonite with different layer charge density was studied. The four kinds of purified montmorillonite were characterized by XRD, XRF, FTIR, SEM, TEM, BET, TG-DTG, Zeta potential, and Molecular dynamics simulation (MD). The XRD analysis results show that the d(001) value of the four kinds of Ca-montmorillonite are 1.51 nm, 1.51 nm, 1.53 nm, and 1.50 nm, respectively, and the calculation results of layer charge density show that the semi-unit cell charge density are 0.38, 0.53, 0.61, and 0.69, respectively. The charge density is positively correlated with the mass content of MgO. The FTIR analysis results show that with the increase of layer charge density, the couple vibration wave number of Si–O–Mg and Mg–O move towards the high frequency region, from 464.70 cm−1 to 466.36 cm−1 and from 517.12 cm−1 to 520.41 cm−1. The SEM analysis results show that the higher layer charge density of montmorillonite, the worse exfoliation between layers and the thicker layer thickness, The images of TEM show that montmorillonites are mainly composed of a clearly layered structure. The results of BET show that with the increase of charge density, the BET surface area, micropore area and total pore volume gradually increase from 32.69 m2 g−1 to 64.50 m2 g−1, from 4.87 m2 g−1 to 18.24 m2 g−1, and from 0.06 cm3 g−1 to 0.12 cm3 g−1 , respectively, while PSDs and pore diameter decrease from 7.88 nm to 1.74 nm, and from 7.65 nm to 5.47 nm. The results of TG and DTG show that with the increase of charge density, the removal temperature of free water and inter-layer water increase from 80 °C to 100 °C and 139 °C to 155 °C, respectively. The simulation results of MD show that with the increase of layer charge density, the number of hydrogen bonds increase from 186 to 271 and the adsorption energy increases from −1467.11 to −1874.32 kcal mol−1. The particle size increases from 701 nm(Mt1) to 1576 nm(Mt4) with the layer charge density, and the absolute value of Zeta potential, colloidal value and expansion capacity of montmorillonites suspension decrease with the increase of the layer charge density, which further indicates that the dispersion of montmorillonites decrease with the increase of layer charge density.

This paper introduces digital twin models for machining parts based on key features and gives the modeling method. In this paper we propose three layers structure of the digital twin model, including geometric layer, data layer and document layer, in order to make machining process optimization and quality prediction. The digital twin model realizes the expression of physical parts in digital space and the information correlation with theoretical processing features. Besides, this paper also analyzes the potential application scenarios and development trends of digital twin models of machined parts.

In this study, the microstructure of Ti(C, N)-based cermet was improved by adding β-cobalt (face-centered cubic) and (Ti, W, Mo, Ta)(C, N) solid solution powder to prepare micro-nano Ti(C, N)-based cermet powder. In order to improve the comprehensive properties of the material. Firstly, the Co powder with face-centered cubic structure was obtained by the solid-phase reaction of high-energy ball milling, and its plastic deformation resistance was higher than that of Co powder with dense hexagonal structure. Secondly, The powder of (Ti, W, Mo, Ta)(C, N)solid solution was obtained by mechanical alloying and high-temperature carbonization under the atmosphere of N2. And the two were applied to the micro-nano Ti(C, N)-based cermet powder, and finally the properties of cermet powder were compared with that of ordinary cermet powder. The results show that the microstructure of micro-Ti(C, N)-based cermet powder prepared in this study is a double-core rim structure, that is, the structure of black core white rim and gray core white rim. This structure can effectively prevent crack of the expansion. The strength and toughness of cermet materials are greatly improved, which is beneficial to the improvement of comprehensive properties of cermet materials.

In order to improve the accuracy of accelerator mass spectrometry (AMS) measurement for 182Hf/180Hf, a series of measurements have been taken in the AMS laboratory at the China Institute of Atomic Energy (CIAE). The major ones include the instantaneous monitoring of 180HfF−5 current, testing the stability of transmission, the alternate measurements of an unknown sample and standard, and the origin identification and minimization of background 182W. The experimental details and the improvement in the measurement accuracy, as well as some useful suggestions for better satisfying the requirements of certain practical applications, are presented in this paper.

The ratio of 36Cl/Cl can determine the exposure age of surface rocks and monitor the secular equilibrium of 36Cl of sedimentary and igneous rock in groundwater. Due to the uncertainty effects of different chemical separation processes for removing 36S, there is a high degree of uncertainty in 36Cl accelerator mass spectrometry (AMS) measurements if the ratio of 36Cl/Cl is lower than 10−14. A 36Cl AMS higher sensitivity measurement has been set up by using a ΔE-Q3D method at the China Institute of Atomic Energy (CIAE). The performances of ΔE-Q3D method for 36Cl-AMS measurement had been systemically studied. The experimental results show that the ΔE-Q3D method has a higher isobar suppression factor. Taking advantage of direct removing 36S, the sample preparation can be simplified and the uncertainty effects of different chemical separation processes can be reduced in 36Cl AMS measurements.

Acrylic fiber manufacturing wastewater, containing a wider range of pollutants, high concentration of refractory organics, poisonous and harmful matters, was significant to treat from the effluents of wastewater treatment plants (WWTPs). In this work, a Fenton reactor was employed for advanced treatment of the WWTP effluents. An orthogonal test and a parametric study were carried out to determine the effect of the main operating conditions and the Fenton process attain excellent performance on the degradation of pollutants under an optimal condition of ferrous dosage was 6.25 mM, hydrogen peroxide was 75 mM and initial pH value was 3.0 in 90 min reaction time. The removal efficiency of COD, TOC, NH4 +-N and TN reached from 45% to 69%. Lastly, as a teaching advice, the Fenton reactor was used in practicing teaching nicely.

In the recent charts of the nuclides an accepted half-life of 79Se is only an upper limit, < 6.5 × 104 a. In this letter, A new half-life of 79Se has been measured to be (1.13 ± 0.17) × 106 a. The number of 79Se atoms was determined from measured 79Se/Se ratios with the accelerator mass spectrometry technique and the decay rate of 79Se was determined by counting the emitted β rays with a liquid scintillation spectrometer.

Following the intense studies on topological insulators, significant efforts have recently been devoted to the search for gapless topological systems. These materials not only broaden the topological classification of matter but also provide a condensed matter realization of various relativistic particles and phenomena previously discussed mainly in high energy physics. Weyl semimetals host massless, chiral, low-energy excitations in the bulk electronic band structure, whereas a symmetry protected pair of Weyl fermions gives rise to massless Dirac fermions. We employed scanning tunneling microscopy/spectroscopy to explore the behavior of electronic states both on the surface and in the bulk of topological semimetal phases. By mapping the quasiparticle interference and emerging Landau levels at high magnetic field in Dirac semimetals Cd$_3$As$_2$ and Na$_3$Bi, we observed extended Dirac-like bulk electronic bands. Quasiparticle interference imaged on Weyl semimetal TaAs demonstrated the predicted momentum dependent delocalization of Fermi arc surface states in the vicinity of the surface-projected Weyl nodes.

Minimally invasive image guided surgery (IGS) has been increasingly used in interventional radiology. One of the key technologies in IGS is tracking the surgical instruments during operation, which makes it possible to visualize the position and orientation relationships between the tumor and the puncture needle based on the 3D model reconstructed from pre-operative images. In order to improve the accuracy of instruments tracking, and simplify registration process, we proposed a registration method based on virtual frame. The registration was performed in two steps. In the first stage, the rigid frame registration using the iterative closest point algorithm was completed by the producer when the surgery system was installed and debugged in the operating room, during which a standard transformation matrix from real space to model space was obtained. In the second stage, getting more than three points from the patient's skin and converting them to the image space using the matrix acquired in the first step, and then working out the transformation matrix between the converted points and the corresponding points in the image space, the rotation and translation parameters were calculated by the second matrix and were used to adjust the model's location and pose. This intra-operative registration was completed by surgeons. In the surgery system, we employed the electromagnetic measurement system to locate the puncture needle, and it was calibrated by laser tracker to improve the position accuracy. Contrasting experiments were conducted to verify the effectiveness of the registration method. The results showed that the accuracy of conventional paired-point-based registration method was 0.85 ± 0.10 mm, while the proposed registration method was 0.44 ± 0.07 mm, indicating that the proposed registration method could improve the registration quality.

With the development of traffic systems, some issues such as traffic jams become more and more serious. Efficient traffic flow theory is needed to guide the overall controlling, organizing and management of traffic systems. On the basis of the cellular automata model and the traffic flow model with look-ahead potential, a new cellular automata traffic flow model with negative exponential weighted look-ahead potential is presented in this paper. By introducing the negative exponential weighting coefficient into the look-ahead potential and endowing the potential of vehicles closer to the driver with a greater coefficient, the modeling process is more suitable for the driver's random decision-making process which is based on the traffic environment that the driver is facing. The fundamental diagrams for different weighting parameters are obtained by using numerical simulations which show that the negative exponential weighting coefficient has an obvious effect on high density traffic flux. The complex high density non-linear traffic behavior is also reproduced by numerical simulations.

Determining the local structure of catalyst materials is critical for understanding the mechanism of enhanced electrochemical activity in semiconductor electrode. Here, using X-ray absorption fine structure (XAFS) spectra, we reveal that the local disorder structure is formed for the mixed-phase Co3O4 nanowire arrays due to the interaction between the phases of Co3O4 and Co2(OH)2CO3. Comparing to pure Co3O4 nanowire arrays, the mixed phase sample is richer in Co2+ and the electronic structure is changed by the local structure, which are demonstrated by the X-ray absorption near-edge structure (XANES) spectra. It is deduced that the mixed-phase Co3O4 nanowire arrays with abundant Co2+ sites provide more redox centres in electrochemical reaction than the pure Co3O4 nanowire arrays.

We studied the influence of heat treatment time on the optical, thermal, electrical, and mechanical properties of strontium barium niobate (Sr1−xBaxNb2O6; hereafter SBN) piezoelectric glass-ceramics with tungsten bronze-type structure, which have good piezoelectric properties and are important lead-free piezoelectric materials. We found that the best heat treatment time is 4 h. The properties of the prepared materials are better than that of SBN ceramics and the glass-ceramic growth is faster than the SBN crystal when the heat treatment time of the SBN piezoelectric glass-ceramic is controlled, reducing the preparation costs greatly.

This paper describes the preparation of a piezoelectric glass ceramic material from potassium sodium niobate (K0.5Na0.5NbO3; KNN) using a novel melting method. The effects of the subsequent heat-treatment on the optical, thermal, electrical, and mechanical properties of the material are carefully examined, and its crystal structure and surface morphology are characterized respectively by x-ray diffraction and scanning electron microscopy. This new material has a much higher piezoelectric coefficient (163 pCN−1) than traditional piezoelectric ceramics (131 pCN−1). On this basis therefore, a strategy for the future study and development of lead-free KNN-based piezoelectric glass ceramics is proposed.

The determination of uranium isotopic composition in trace samples is important in different fields. A new measurement method that uses an accelerator mass spectrometry (AMS) technique has been developed for the analysis of uranium isotopic ratios in ultra-trace uranium samples at the China Institute of Atomic Energy. As a result, about 5-nanogram level uranium samples analyzed with AMS is achieved.

Engineered hollow nanoparticles have exhibited their potential in nanotechnology applications, but so far the investigation of the deformation mechanisms for these hollow particles during the sintering process has rarely been reported. Hence, a comparative study of both solid and hollow spherical silver nanoparticles with different sizes under different heating rates of laser sintering is conducted systematically in this paper, based on molecular dynamics simulations. An interesting phenomenon is observed where the temperature for fast neck growth shows an inverse trend in all the hollow nanoparticle pairs at an ultrahigh heating rate, which is quite different from that known in the solid particle cases. This finding implies that besides the size and heating rate, the nanoparticle geometry could also play an important role in the sintering process. At a low heating rate, the plastic deformation combined with structural reconfigurations induced by the lattice sliding in the hollow shells is found to be an important mechanism during the heating process. At an ultrahigh heating rate, the transition from fcc crystal directly to disordered structure from both outside and inside surfaces becomes more dominant than the structural reconfiguration with lattice defects, which is facilitated by the introduction of the inner free surfaces in hollow nanoparticles. The entire hollow particle pairs thus show an obvious tendency to coalesce and melt at a lower temperature level than with a low heating rate.

Molecular dynamics simulations were performed to study the influence of system size on wave propagation and deformation patterns in 〈1 0 0〉/{1 0 0} copper nanobars with square cross-section under symmetric longitudinal impact loading. Nanobars of longitudinal length 100a with cross-sectional edge lengths h = 10a, 20a, and 40a were impacted on both ends by flyers of size 20a × h × h, where a is the Cu unit cell length, and impact speed 500 m s−1. For reference, quasi-infinite slab samples with periodic cross-sectional edge lengths 10a and 40a were also studied. It was found that the wave propagation speed increases with increasing cross-sectional area and eventually approaches the value obtained for a quasi-infinite sample. Extensive plasticity occurs across the entire length of the nanobars, whereas the quasi-infinite samples remain in the elastic regime and exhibit a vibrating (ringing) behaviour. The deformation pattern in the nanobars is strongly dependent on the cross-sectional area. For the nanobar with h = 10a the material fully reorients from 〈1 0 0〉/{1 0 0} to 〈1 1 0〉/{1 1 1} with few stacking faults and twins. Material in the nanobar with h = 20a does not reorient completely; the local crystal deformation is mediated mainly by a partial dislocation activity leading to predominantly non-intersecting stacking faults and twins. Nanobars with h = 40a exhibit behaviour similar to that for the h = 20a case but with greater propensity for intersecting stacking faults.

It has been claimed that the half-life of radioactive nuclides embedded in metals may be significantly affected by the screening of quasi-free electrons provided by the metals, especially at the cryogenic temperature. We determine the α-decay half-life values of 210Po in high purity metallic bismuth at 4.2 K and 293 K. The results show that the α-decay half-life of 210Po at T = 4.2 K is about (24 ± 8)% shorter than that at room temperature.

We report the ferroelectric, dielectric and piezoelectric properties of a dense and crack-free lead zirconate titanate (Pb(Zr0.52Ti0.48)O3, PZT) thick film containing micro- and nano-crystalline particles. The results show that these electrical properties are dependent strongly on the annealing temperature and film thickness. For the different-annealing-temperature and different-thickness films, the higher-annealing-temperature thicker ones show the larger remnant polarization and smaller coercive field. The dielectric results show that relative dielectric constant achieves the largest value at annealing temperature of 700°C, and increases with the increasing film thickness. For the piezoelectric properties, the longitudinal piezoelectric coefficient increases linearly with the film thickness increasing and the 4-μm-thick PZT film shows the largest value of about 200.65 pC/N. Therefore, the PZT thick films present good electric properties and enlarged potential in MEMS applications.

The long-lived isotope 53Mn cosmogenically produced in situ is a very useful indicator for geochronological dating. A new 53Mn accelerator-mass-spectrometry (AMS) measurement method is developed based on the HI-13 Tandem Accelerator and ΔE-Q3D detection system at China Institute of Atomic Energy. The performance of 53Cr isobar separation and suppression is tested by a series of 53Mn standards and commercial MnO samples. The results show that the ΔE-Q3D detection system brought about an overall suppression factor of more than 107 for the interfering isobar 53Cr.

We investigated whether implantation of vascular bundles or sensory nerves affected the expression of calcitonin gene-related peptide type I receptor (CGRP1R) and neuropeptide Y1 receptor (NPY1R) in tissue-engineered bone. We implanted osteogenically induced bone marrow mesenchymal stem cells (BMSCs) with β-tricalcium phosphate (β-TCP) as the scaffold material either with sensory nerve tracts (group I, n = 18), vascular bundles (group II, n = 18) or alone (group III, n = 18) to repair a 1.2 cm femur defect in the rabbit. Better osteogenesis was observed by x-ray and histology in groups I and II than in group III at 4, 8 and 12 weeks. Within the new bone, the mRNA levels of the two neuropeptide receptors determined by real-time PCR increased through week 8, and then gradually decreased (P < 0.05). Expression of the neuropeptide receptors determined by immunohistochemistry was lowest at 4 weeks (P < 0.05) and was higher in group II than in group I (P < 0.05). Expression was significantly higher in groups I and II than in group III at all time points. We conclude that implanting vascular bundles into tissue-engineered bone can significantly improve the early expression of CGRP1R and NPY1R. In contrast, implantation of sensory nerves did not show the same dramatic effect as implantation of vascular bundles.

The effect of loading path on the mechanical behaviour of single crystalline copper nanowires is investigated with molecular dynamics simulations. Different loading conditions including pre-tensile torsion and pre-torsional tension at different temperatures are taken into consideration. It is found that elastic pre-loading conditions can induce a distinct weakening on the resistance against plastic deformation under later applied loads. Meanwhile, coupled thermal and pre-loading effect can also facilitate the transformation from elasticity to plasticity. Formations of fivefold twins are observed in copper nanowires subjected to the loading path with tension after pre-torsion. These fivefold twins all form at the necking stage before fracture, and are found to be pre-torsion- and size-dependent but insensitive to the change in temperature and cross-sectional shape. The results reported here indicate that the loading path effect on the mechanical behaviour plays an important role in the formation of some special microstructures such as multiple twins in metallic nanowires.

The length, loading rate and thermal effects on the torsional response of hollow copper nanowires are investigated with molecular dynamics simulation. Evolution of atomic configuration is studied, which shows that partial dislocations nucleated from the surfaces accommodate the plastic deformation of the nanowires under torsion. With the increase in torsional angle, necking appears and the corresponding cross-section transforms from a hollow square to a solid circle. Meanwhile, atomic rearrangement from being amorphous to fcc occurs, which becomes more obvious at higher loading rates. To understand the relation between material and geometrical instabilities, the torsional buckling mode is also investigated and found to strongly depend on both wire length and temperature.

Near-infrared (NIR)-to-visible upconversion fluorescent nanoparticles were synthesized and used for imaging and targeted delivery of small interfering RNA (siRNA) to cancer cells. Silica-coated NaYF(4) upconversion nanoparticles (UCNs) co-doped with lanthanide ions (Yb/Er) were synthesized. Folic acid and anti-Her2 antibody conjugated UCNs were used to fluorescently label the folate receptors of HT-29 cells and Her2 receptors of SK-BR-3 cells, respectively. The intracellular uptake of the folic acid and antibody conjugated UCNs was visualized using a confocal fluorescence microscope equipped with an NIR laser. siRNA was attached to anti-Her2 antibody conjugated UCNs and the delivery of these nanoparticles to SK-BR-3 cells was studied. Meanwhile, a luciferase assay was established to confirm the gene silencing effect of siRNA. Upconversion nanoparticles can serve as a fluorescent probe and delivery system for simultaneous imaging and delivery of biological molecules.