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Ti-6Al, Ti-6Al-2Mo and Ti-6Al-3Nb alloys were prepared to investigate the toughening effects of β stabilizers Mo and Nb on impact toughness and crack resistance of titanium alloys. Instrumented Charpy impact tests showed that the total impact absorbed energy of Ti-6Al-2Mo and Ti-6Al-3Nb (∼64 J) were two times higher than that of Ti-6Al (∼30 J), indicating the higher impact toughness of Ti-6Al-2Mo and Ti-6Al-3Nb alloys. Analysis of load-displacement curves revealed the similar crack initiation energy of Ti-6Al, Ti-6Al-2Mo and Ti-6Al-3Nb (15.4 J, 16.1 J and 15.0 J, respectively). However, the higher crack propagation energy of Ti-6Al-2Mo and Ti-6Al-3Nb (46.7 J and 48.3 J, respectively) were about three times higher than that of Ti-6Al (14.4 J), indicating the stronger resistance to crack propagation in Ti-6Al-2Mo and Ti-6Al-3Nb. Post-mortem analysis of impact samples demonstrated that the increased dislocation density and deformation twinning were mainly responsible for the stronger resistance to crack propagation in Ti-6Al-2Mo and Ti-6Al-3Nb. Due to the invisibility of dislocation activation and deformation twinning during the Charpy impact process, a mathematical model has been proposed to evaluate the effects of Al, Mo and Nb elements on dislocation mobility based on the Yu Rui-huang electron theory. Addition of Mo and Nb elements significantly improved the dislocation mobility in Ti-6Al-2Mo and Ti-6Al-3Nb compared to that in Ti-6Al alloy. Therefore, more dislocations were activated in Ti-6Al-2Mo and Ti-6Al-3Nb which supplied the larger plastic deformation under impact loading. A dislocation-based model also has been proposed to interpret the nucleation and propagation of deformation twinning under the impact loading. Dislocation pileup at α/β interfaces provided potential sites for nucleation of deformation twinning in Ti-6Al-2Mo and Ti-6Al-3Nb. Furthermore, deformation twinning facilitated the dislocation motion in α grains with hard orientations. The increased dislocation mobility and deformation twinning were responsible for the stronger crack resistance as well as the higher impact toughness of Ti-6Al-2Mo and Ti-6Al-3Nb alloys.

Nanotube coatings on titanium surfaces have favorable biocompatibility and structures and are widely used in local drug delivery. However, when a drug freely diffuses out of a nanotube, it leads to an explosive release, making the duration of action extremely short. In this study, a high concentration of vancomycin hydrochloride region similar to a dam was formed on a nanotube coating surface by exploiting the attraction of the electric charge generated by the energy conversion of the piezoelectric effect to vancomycin hydrochloride. The “dam” not only reduces the diffusion rate of vancomycin hydrochloride inside the nanotube into the dam and the diffusion rate of the dam to the outside but also forms a high concentration of vancomycin hydrochloride action region. The free diffusion rate of vancomycin hydrochloride loaded on the TiO2 @ BaTiO3 coaxial nanotubes was reduced by the piezoelectric effect, and the cumulative release of vancomycin hydrochloride for 7 days is reduced by 54.8%. The polarized vancomycin-containing coaxial nanotube coating has a long-lasting antibacterial effect on Staphylococcus aureus. The TiO2 @ BaTiO3 coaxial nanotubes loaded with vancomycin hydrochloride coating with piezoelectric properties has potential application value in controlled drug delivery.

Currently, δ-MnO2 is one of the popularly studied cathode materials for aqueous zinc-ion batteries (ZIBs) but impeded by the sluggish kinetics of Zn2+ and the Mn cathode dissolution. Here, we report our discovery in the study of crystalline/amorphous MnO2 (disordered MnO2), prepared by a simple redox reaction in the order/disorder engineering. This disordered MnO2 cathode material, having open framework with more active sites and more stable structure, shows improved electrochemical performance in 2 mol·L−1 ZnSO4/0.1 mol·L−1 MnSO4 aqueous electrolyte. It delivers an ultrahigh discharge specific capacity of 636 mA·h·g−1 at 0.1 A·g−1 and remains a large discharge capacity of 216 mA·h·g−1 even at a high current density of 1 A·g−1 after 400 cycles. Hence disordered MnO2 could be a promising cathode material for aqueous ZIBs. The storage mechanism of the disordered MnO2 electrode is also systematically investigated by structural and morphological examinations of ex situ, ultimately proving that the mechanism is the same as that of the δ-MnO2 electrode. This work may pave the way for the possibility of using the order/disorder engineering to introduce novel properties in electrode materials for high-performance aqueous ZIBs.

Since label noise can hurt the performance of supervised learning (SL), how to train a good classifier to deal with label noise is an emerging and meaningful topic in machine learning field. Although many related methods have been proposed and achieved promising performance, they have the following drawbacks: (1) They can lead to data waste and even performance degradation if the mislabeled instances are removed; and (2) the negative effect of the extremely mislabeled instances cannot be completely eliminated. To address these problems, we propose a novel method based on the capped ℓ1 norm and a graph-based regularizer to deal with label noise. In the proposed algorithm, we utilize the capped ℓ1 norm instead of the ℓ1 norm. The used norm can inherit the advantage of the ℓ1 norm, which is robust to label noise to some extent. Moreover, the capped ℓ1 norm can adaptively find extremely mislabeled instances and eliminate the corresponding negative influence. Additionally, the proposed algorithm makes full use of the mislabeled instances under the graph-based framework. It can avoid wasting collected instance information. The solution of our algorithm can be achieved through an iterative optimization approach. We report the experimental results on several UCI datasets that include both binary and multi-class problems. The results verified the effectiveness of the proposed algorithm in comparison to existing state-of-the-art classification methods.

Development of high-efficiency and low-cost electrocatalyst for oxygen evolution reaction (OER) is very important for use at alkaline water electrolysis. Metal-organic frameworks (MOF) provide a rich platform for designing multi-functional materials due to their controllable composition and ultra-high surface area. Herein, we report our findings in the development of amorphous nickel–cobalt bimetal-organic framework nanosheets with crystalline motifs via a simple “ligands hybridization engineering” strategy. These complexes’ ligands contain inorganic ligands (H2O and NO3−) and organic ones, hexamethylenetetramine (HMT). Further, we investigated a series of mixed-metal with multi-ligands materials as OER catalysts to explore their possible advantages and features. It is found that the Ni doping is an effective approach for optimizing the electronic configuration, changing lattice ordering degree, and thus enhancing activities of HMT-based electrocatalysts. Also, the crystalline-amorphous boundaries of various HMT-based electrocatalyst can be easily controlled by simply changing amounts of Ni-precursor added. As a result, the optimized ultrathin (Co, 0.3Ni)-HMT nanosheets can reach a current density of 10 mA cm−2 at low overpotential of 330 mV with a small Tafel slope of 66 mV dec−1. Our findings show that the electronic structure changes induced by Ni doping, 2D nanosheet structure, and MOF frameworks with multi-ligands compositions play critical roles in the enhancement of the kinetically sluggish electrocatalytic OER. The present study emphasizes the importance of ligands and active metals via hybridization for exploring novel efficient electrocatalysts.

In tube free bending forming technology, the springback behavior affects the bent tubes’ forming accuracy and quality. Thus, in this investigation, the springback behaviors of T2-Cu and AA6061-T6 tubes manufactured by free bending technology were studied experimentally and using finite element modeling. The bending radius of the formed tubes was measured in ABAQUS combined with the geometric calculation. After investigating the different A-values (sufficient length of deformation zone) of Cu and Al tubes, it was found that the higher the A-value, the higher the bending angle, the lower the bending radius, and the larger the springback angle. The changes of both bending and material properties affect the springback to specific values. The tube forming’s stress peak occurred in the forming segment, where the springback angle is the highest, and the outer springback is higher than the inner side at the same A-value and position. Under the same forming parameters, each section’s strain variation and springback angle in the bending process of T2-Cu tubes is higher than that of AA6061-T6 tubes. The simulation results were in remarkable agreement with those obtained from experimentation, proving the simulation’s reliability and accuracy.

For polylactide (PLA) toughening modification by rubbery materials, the toughness generally improved at the expense of lowered mechanical strength even after interfacial compatibilization. In this ...

In order to design magnetorheological elastomers (MREs) based craftsmanship for metal forming, a comprehensive study on the mechanical properties of MREs under triaxial compression is required. An experimental setup integrating free compression and triaxial compression is designed to characterize isotropic MREs specimens under compression mode. The results showed that the MREs specimen in mold had successively experienced free compression stage, transition stage and triaxial compression stage during the experiment. The stress-strain curves of the MREs specimen changed when the concentration of magnetic particles increased from 0 to 44.7%, and the strain required to reach the transition stage was reduced. The effect of magnetic flux density on the stress-strain curves of the MREs specimen depended on the concentration of magnetic particles. The measured data obtained at different strain rates revealed maximum changes of 15.7% and 0.096% in volume compression modulus and Poisson ratio, respectively, which occurred under the magnetic flux density of 200 mT and CIP concentrations of [Formula: see text]. In this study, through a set of experiments, the stress-strain curves of the MREs specimen under different concentrations was elucidated, and their effects on the volume compression modulus and Poisson ratio were discussed.

Relieving users from the burden of remembering and inputting authentication information explicitly, such as passwords/PINs and lock patterns, implicit authentication mechanisms have gained an increasing concern. When providing authentication, the existing implicit methods only depend on a specific behavior, such as typing on the screen, performing gestures, or taking a walk. However, in real applications, a user’s behavioral characteristics are also decided by the context where behavior is performed. Thus, those existing methods show limited authentication accuracy and usability. To address these issues, we propose CaIAuth, a reliable context-aware implicit authentication framework, which profiles users’ behavior and context characteristics in a holistic fashion. It observes the states of context-sensing entities for different smartphone usage patterns and builds a context-aware model to distinguish between legitimate users and illegal ones. We conducted extensive experiments to evaluate system performance with a large data set collected from 142 subjects. The experimental results show that our system achieves a low equal error rate (EER) (e.g., less 7%) and is resilient against common threats, including zero-effect attack and mimicry attack. In addition, CaIAuth achieves a low authentication delay and overhead.

Manufacturing thin-walled metallic bellow is a complicated forming process, and defects such as wrinkling, cracking, and over-thinning quickly occur because of the complex compressive and tensile stress state. To achieve high-quality products, it is crucial to study the forming characteristics and explore proper forming parameters in advance for a particular metallic bellow. Thus, this investigation is aimed at studying the effect of using the magnetorheological elastomer (MRE) forming medium and the axial feeding on the forming quality of thin-walled Inconel 718 bellow during the bulging process. The change of MRE’s mechanical properties is combined with the basic principle of the bulging process. The process of coupling three different axial loading paths and three magnetic field loading conditions was explored through finite element (FE) simulation. The results obtained from the FE simulation showed that the forming quality of the proposed thin-walled bellow is the best when the magnetic field intensity is 0.14 T, and the punch step length is 7 mm. The experimental results are in a remarkable agreement with those obtained from simulation, confirming the simulation’s validity.

Bone defect repair at load-bearing sites is a challenging clinical problem for orthopedists. Defect reconstruction with implants is the most common treatment; however, it requires the implant to have good mechanical properties and the capacity to promote bone formation. In recent years, the piezoelectric effect, in which electrical activity can be generated due to mechanical deformation, of native bone, which promotes bone formation, has been increasingly valued. Therefore, implants with piezoelectric effects have also attracted great attention from orthopedists. In this study, we developed a bioactive composite scaffold consisting of BaTiO3, a piezoelectric ceramic material, coated on porous Ti6Al4V. This composite scaffold showed not only appropriate mechanical properties, sufficient bone and blood vessel ingrowth space, and a suitable material surface topography but also a reconstructed electromagnetic microenvironment. The osteoconductive and osteoinductive properties of the scaffold were reflected by the proliferation, migration, and osteogenic differentiation of mesenchymal stem cells. The ability of the scaffold to support vascularization was reflected by the proliferation and migration of human umbilical vein endothelial cells and their secretion of VEGF and PDGF-BB. A well-established sheep spinal fusion model was used to evaluate bony fusion in vivo. Sheep underwent implantation with different scaffolds, and X-ray, micro-computed tomography, van Gieson staining, and elemental energy-dispersive spectroscopy were used to analyze bone formation. Isolated cervical angiography and visualization analysis were used to assess angiogenesis at 4 and 8 months after transplantation. The results of cellular and animal studies showed that the piezoelectric effect could significantly reinforce osteogenesis and angiogenesis. Furthermore, we also discuss the molecular mechanism by which the piezoelectric effect promotes osteogenic differentiation and vascularization. In summary, Ti6Al4V scaffold coated with BaTiO3 is a promising composite biomaterial for repairing bone defects, especially at load-bearing sites, that may have great clinical translation potential.

Voltage fluctuations caused output variation in the distributed energy system (such as solar, photovoltaic, and wind) produce flickers. The extraction of voltage flicker envelope parameters and accurate calculation of voltage flicker values are important for voltage flicker detection. Traditional digital filters need to be calculated according to the sampling frequency before they can be designed so that the flicker meter can only sample at a fixed frequency. To overcome the shortcomings of digital filters, a new method for measuring flickers is presented in this study. The proposed method uses analytical mode decomposition (AMD) based on spectral correction and a novel constructed mutual convolution window. The voltage flicker envelope can be extracted using an AMD method, which can replace the filter used in traditional methods, it can be analysed to obtain the corrected spectrum, which is based on an improved fast Fourier transform. The proposed method simplifies the voltage flicker detection process and exhibits high detection accuracy, which with lower detection relative error and stronger anti-interference ability. The simulation analysis and experimental results show that this approach can effectively overcome problems associated with voltage flicker measurements, such as single modulation wave frequency change and multi-frequency modulation wave fluctuation.

This paper investigates Posbist reliability theory for typical systems with multicomponents. This theory is based on possibility and binary-state assumptions. It works well under situations of insufficient data and epistemic uncertainty. When the lifetime of every component of a typical system is assumed unrelated and a normal, strictly convex fuzzy variable in some possibility space, the Posbist reliability is concretely derived where the exactly value can be obtained at any moment, unlike existing ones only given by a lower and upper bound. We numerically compare the Posbist reliability between typical systems of four types: series, parallel, series-parallel, and parallel-series. Moreover, numerical safety evaluations are given based on possibilistic and probabilistic models.

A sintering-free magnesium phosphate cement (MPC) with an arbitrary shape is potentially used as a bone implant material, especially with complex shapes. However, the high degradation rate of MPC may lead to the degradation of mechanical properties. In this study, graphene (G)/barium titanate (BT)/MPC composites were fabricated by introducing the piezoelectric phase BT and conductive phase G into MPC, which exhibited the piezoelectric effect after polarisation. The negative surface of the composite may attract Ca2+ and Mg2+ to mineralise rapidly, thereby reducing and improving its degradation rate and mechanical properties, respectively. The contents of additional G and BT were optimised. When BT and G contents were 50 mol% and 0.5 wt%, respectively, the piezoelectric coefficient of the composites increased to 6.31 pC/N, which is an increase of 421% without the addition of G. The results of in vitro degradation and mineralisation in simulated body fluids (SBF) showed that introducing BT and G could effectively slow down the degradation rate, promote mineralisation on the composite surface, and enhance the impact on bone integration.

Shortening the period of bone repair based on BaTiO 3 /hydroxyapatite(HA) composites with osteoconductivity and osteoinductivity is important. However, when the piezoelectric properties of composites are matched with natural bone, the content of non-degradable BaTiO 3 needs to reach 90%, which may not conducive to clinical application. The barium titanate content in the composite was reduced by doping Er 3+ into the BaTiO 3 of BaTiO 3 /HA composites with enhanced piezoelectric properties. The piezoelectric constant and compressive strength of composites increased with the increase of Er 3+ -doped barium titanate (BTEr) content. Appropriate piezoelectric stimulation can promote the growth of osteoblasts. 70% BTEr/30% HA is more beneficial to the proliferation of osteoblasts than 70% BaTiO 3 /30% HA.

The poor cycle stability and reversibility seriously hinder the widespread application of SnO2 materials as anodes for lithium-ion batteries (LIBs). A novel sandwich-architecture composite of Si-do...

Inositol polyphosphate 4-phosphatase type II (INPP4B) is a phosphoinositide phosphatase that plays complex roles in the pathogenesis of different tumors. We aimed to explore the expression, clinicopathological significance, and prognostic value of INPP4B in oral squamous cell carcinoma (OSCC). Tissue microarrays that included samples from 176 primary OSCCs, 42 normal mucosae, and 69 dysplastic tissues were used for immunostaining analyses of INPP4B protein. Aperio ScanScope CS scanner and aperio quantification software were used to scan the microarrays and score the staining, respectively. We also evaluated the correlation between INPP4B expression and clinical parameters, pathological grades, node-positive status, and immune-related markers. Expression of INPP4B was statistically significantly upregulated in human primary OSCC tissues compared with dysplastic and normal tissues. Additionally, we found that patients with strong expression of INPP4B had a statistically significantly poorer overall survival than patients with weak expression of INPP4B. Furthermore, our study indicated that expression of INPP4B in OSCC was positively associated with expression of p-S6Ser235/236 , p-CADSer1859 , and certain immune checkpoints (B7-H4, Galectin-9). Therefore, INPP4B may be an independent prognostic indicator for patients with OSCC, in which it might function as an oncoprotein.

The application of piezoelectric materials in bone repair is a hot topic because both positive and negative charge can promote the cells growth. However, the deposition process of apatite induced by piezoelectric materials with periodic loading is still not clear. In this work, TiO2–BaTiO3 coatings were prepared on medical titanium alloys by microarc oxidation and hydrothermal reactions. The TiO2 layer obtained by micro-arc oxidation participated in hydrothermal reaction to generate BaTiO3 on the surface of TiO2 layer. After electric field polarization, the coating was endowed with bioelectric activity similar to that of natural bone. Periodic mechanical loading was applied to the coatings using a cyclic stress loading device. It was found that the negative charge could attract Ca2+ to be gathered on the coating surface, thus obtaining a high deposition of apatite, increasing the Ca/P ratio and promoting the crystallinity of the apatite. In addition, the negative charge also changed the type of apatite growth units near the coating, resulting in the deposition of apatite in hexagonal flake shapes perpendicular to the coating.

Lane-Changing Decision (LCD) behavior is complex, dangerous, and varied by the Driver's Psychology (DP) and Driving Style (DS). For lacking the consideration of DP and DS, the existing LCD models cannot predict the LCD process varying with the drivers and traffic conditions accurately. To deal with the problems, a new LCD model coupling DP and DS, named DP&DS-LCD, is put forward. In the model, a psychological field model is constructed to represent the DP effect on the scene vehicles. And then, K-means and K-Nearest Neighbor (KNN) algorithm are respectively adopted in learning and recognition phases to recognize the current driving style pattern. Finally, based on the DP and DS, the multi-Grained Cascade Forest (gcForest) algorithm is applied to predict the LCD behavior. In experiments, DP&DS-LCD is compared with other three LCD models by using the opening I-80 database from Next Generation Simulation project (NGSIM). And the results showed that the DP&DS-LCD model achieved the best performance. Therefore, the DP&DS-LCD model is effective and could provide support for the decision of autonomous vehicles by predicting the surrounding vehicles' Lane-Changing (LC) behavior.

This paper focuses on the development of electric vehicle (EV) charging infrastructure in the UK, which is a vital part of the delivering ultra-low-emission vehicle (ULEV) and will transition into low emission energy systems in the near future. Following a brief introduction to global landscape of EV and its infrastructure, this paper presents the EV development in the UK. It then unveils the government policy in recent years, charging equipment protocols or standards, and existing EV charging facilities. Circuit topologies of charging infrastructure are reviewed. Next, three important factors to be considered in a typical site, i. e., design, location and cost, are discussed in detail. Furthermore, the management and operation of charging infrastructure including different types of business models are summarized. Last but not least, challenges and future trends are discussed.

This paper investigates Lyapunov and external stability of Caputo fractional order switching systems. It proves an estimation for the Caputo fractional order derivative of an arbitrary quadratic function whose variable is a function of time with the same differential properties as those given by the most recent smoothness result, and then establishes criteria on Lyapunov stability that bridge over existing difficulties. On the other hand, the equivalence between Caputo fractional order switching control systems and their diffusive realizations is shown. This together with a Lyapunov-like function proven to be well defined shows their advantages in solving the problem of external stability.

Cells communicate with each other via the transmission and reception of signal molecules. In this paper, we test our hypothesis that random cell motion can enhance cell-cell communication. We first conducted cell-tracking experiments to obtain motility parameters of endothelial cells, and then used the molecular communication framework to obtain the achievable rates at which cells can communicate. Our results show that random cell motion can benefit cell-cell communication when signal molecules that cells use are an order of magnitude less-diffusive than well-known vascular endothelial growth factors.

The intersection structure, composed of twin shield tunnels and a transverse passage, is ubiquitous in the metros around the world. However, the dynamic characteristics of this kind of intersection structure have not been studied a lot yet. By carrying out the corresponding model tests and numerical simulations, the dynamic characteristics of this kind of intersection structure are studied in this paper, which is very helpful for the determination of the ground vibration from this kind of underground structure. The results show that the vibration of the transverse passage is more severe than the main tunnel, manifested that the frequency response function (FRF) of the transverse passage has greater magnitudes than that of the main tunnel at the locations with the same distance from the vibration source. The peak frequencies of the acceleration responses at different locations of the intersection structure under the moving train load are all located in the frequency band 44.9–56.1 Hz where the corresponding 1/3 octave band spectra of FRF have the largest values in the considered frequency band 31.5–250 Hz, indicating that the natural frequencies of the intersection structure in the frequency band 44.9~56.1 Hz have significant influences on its acceleration responses below 250 Hz induced by the moving train.

Liuhuanggou bituminous coal (LBC) and its extraction residue (ER) were thermally dissolved sequentially in cyclohexane, toluene, and ethanol at 300 °C to obtain soluble portions (SPs) 1–3 (SP1-SP3) from the thermal dissolution (TD) In the total yield (TY) of 10.4% and SPs I-III (SPI-SPIII) from the TD in the TY of 4.9%, respectively. The SPs were analyzed by multiple analytical tools, including gas chromatograph/mass spectrometer (GC/MS), quadrupole exactive orbitrap mass spectrometer (QEOTMS), and Fourier transform infrared spectrometer. The analysis with GC/MS shows that normal alkanes are the most abundant in SPI, while arenes are predominant in SP1, SP2, and SPII. According to the analysis with QEOTMS, abundant heteroatom-containing organic species were concentrated into SP3 and SPIII with molecular masses of 150–750 u. The relative contents of N1 and N1O1 species are predominantly high in SPIII and SP3, respectively.

Efficient intracellular delivery of biomolecules into cells that grow in suspension is of great interest for biomedical research, such as for applications in cancer immunotherapy. Although tremendous effort has been expended, it remains challenging for existing transfer platforms to deliver materials efficiently into suspension cells. Here, we demonstrate a high-efficiency photothermal delivery approach for suspension cells using sharp nanoscale metal-coated tips positioned at the edge of microwells, which provide controllable membrane disruption for each cell in an array. Self-aligned microfabrication generates a uniform microwell array with three-dimensional nanoscale metallic sharp tip structures. Suspension cells self-position by gravity within each microwell in direct contact with eight sharp tips, where laser-induced cavitation bubbles generate transient pores in the cell membrane to facilitate intracellular delivery of extracellular cargo. A range of cargo sizes were tested on this platform using Ramos suspension B cells with an efficiency of84% for Calcein green (0.6 kDa) and45% for FITC-dextran (2000 kDa), with retained viability of96% and a throughput of100 000 cells delivered per minute. The bacterial enzyme β-lactamase (29 kDa) was delivered into Ramos B cells and retained its biological activity, whereas a green fluorescence protein expression plasmid was delivered into Ramos B cells with a transfection efficiency of58%, and a viability of89% achieved.

Background Glioblastoma mutliforme is the most common and has the poorest prognosis of any malignant tumor of the central nervous system. Luteolin, the most abundant xanthone extracted from vegetables and medicinal plants, has been shown to have treatment effects in various cancer cell types. Luteolin is however, hydrophobic and has poor biocompatibility, which leads to low bioavailability. Patients and methods In this study, folic acid modifiedpoly(ethylene glycol)-poly(e-caprolactone) (Fa-PEG-PCL) nano-micelles was used to encapsulate the luteolin, creating luteolin loaded PEG-PCL (Lut/Fa-PEG-PCL) micelles to treat glioma both in vitro and in vivo. Results When compared with the free luteolin and Lut/MPEG-PCL, Lut/Fa-PEG-PCL induced a significant cell growth inhibition and more apoptosis of GL261 cells both in vitro and in vivo. The safety assessment also showed no obvious side effects were observed in mice which were administrated with free luteolin or Lut/MPEG-PCL and Lut/Fa-PEG-PCL. Conclusion These results suggested Lut/Fa-PEG-PCL may be used as an excellent intravenously injectable formulation for the treatment and chemoprevention.

Scene images generally show the characteristics of large intra-class variety and high inter-class similarity because of complicated appearances, subtle differences, and ambiguous categorization. Hence, it is difficult to achieve satisfactory accuracy by using a single representation. For solving this issue, we present a comprehensive representation for scene recognition by fusing deep features extracted from three discriminative views, including the information of object semantics, global appearance, and contextual appearance. These views show diversity and complementarity of features. The object semantics representation of the scene image, denoted by spatial-layout-maintained object semantics features, is extracted from the output of a deep-learning-based multi-classes detector by using spatial fisher vectors, which can simultaneously encode the category and layout information of objects. A multi-direction long short-term memory-based model is built to represent contextual information of the scene image, and the activation of the fully connected layer of a convolutional neural network is used to represent the global appearance of scene image. These three kinds of deep features are then fused to draw a final conclusion for scene recognition. Extensive experiments are conducted to evaluate the proposed comprehensive representation on three benchmarks scene image database. The results show that the three deep features complement to each other strongly and are effective in improving recognition performance after fusion. The proposed method can achieve scene recognition accuracy of 89.51% on the MIT67 database, 78.93% on the SUN397 database, and 57.27% on the Places365 databases, respectively, which are better percentages than the accuracies obtained by the latest reported deep-learning-based scene recognition methods.

This paper studies the problem of exponential H ∞ synchronization of switching fuzzy systems with time-varying delay and impulses via maximum, minimum dwell time. The switching fuzzy model has locally Takagi and Sugeno (T–S) fuzzy models and switches them according to states, external variables and/or time. By introducing the concept of maximum, minimum dwell time and a modified two-side direction relation between the number of switchings and the maximum, minimum dwell time, a normal L 2 norm bound constraint is derived. By using the matrix decomposition method and reciprocal convex combination, and combining with the Wirtinger-based inequality, which gives a sharper upper bound than the Jensen's inequality, some new sufficient criteria are obtained to guarantee that the error system without impulses and with impulses is globally exponentially stable with an H ∞ performance index γ, respectively. Three illustrative examples are provided to show the effectiveness of the results.

Arbitrary patterning of micro-objects in liquid is crucial to many biomedical applications. Among conventional methodologies, acoustic approaches provide superior biocompatibility but are intrinsically limited to producing periodic patterns at low resolution due to the nature of standing waves and the coupling between fluid and structure vibrations. This work demonstrates a near-field acoustic platform capable of synthesizing high resolution, complex and non-periodic energy potential wells. A thin and viscoelastic membrane is utilized to modulate the acoustic wavefront on a deep, sub-wavelength scale by suppressing the structural vibration selectively on the platform. Using 3 MHz excitation (λ ∼ 500 μm in water), we have experimentally validated such a concept by realizing patterning of microparticles and cells with a line resolution of 50 μm (one tenth of the wavelength). Furthermore, massively parallel patterning across a 3 × 3 mm2 area has been achieved. This new acoustic wavefront modulation mechanism is powerful for manufacturing complex biologic products.

Colorectal cancer is one of the most common and malignant cancer in the world wide. Recently, combination of target therapy and chemotherapy has generated new promise for colorectal cancer. Apatinib mesylate is a novel and highly selective VEGFR-2 inhibitor, presented with an outstanding activity of anti-angiogensis, which has the potential for treating various tumors. As a traditional chemotherapeutic drug, docetaxel (Taxotere) is a widely used semisynthetic taxoid in solid tumors. In this study, Liposome and Methoxy poly(ethylene glycol)-poly(e-caprolactone) (MPEG-PCL) were constructed as drug delivery system for the delivery of apatinib (Lipo-Apa) and docetaxel (DOC/M), respectively. Co-administration of Lipo-Apa and DOC/M showed synergistically effects on inhibiting cell proliferation and inducing cell apoptosis of CT26 cells in vitro. Moreover, fibrin glue, as a biocompatible adherent hemostat, was used as a kind of vehicle for locally delivery of DOC/M in animal models, for achieving locally high concentration and prolonging releasing time. Combination of Lipo-Apa by gavage and locally delivery of DOC/M showed significantly improved anti-tumor activity in a subcutaneous xenograft model as well as in the abdominal metastasis model of colorectal cancer. In addition, promoted tumor apoptosis, inhibited proliferation and decreased tumor angiogenesis were presented by the co-administration. Finally, our study suggested that combination of oral administration of Lipo-Apa and locally delivery of DOC/M by fibrin glue, has the potential to be applied clinically in colorectal cancer therapy.

Polyvinylidene fluoride (PVDF) coating with piezoelectric properties was prepared on surface of titanium-based materials to improve the bio inertness of the surface. The surface of titanium-based materials with piezoelectric properties similar to human bone promotes the growth of osteoblasts. However, not only new bone growth but also osseointegration are observed in the process of bone repair. The hydrophobicity of PVDF coating is unfavorable for mineralization. In this study, a PVDF coating was prepared on the titanium surface by using titanium dioxide nanotubes as a transition layer, and PVDF was attached to the wall of the titanium dioxide nanotube. The contact angle of the polarized PVDF coating decreases from 108° to 47°, which indicates that it changes from hydrophobic to hydrophilic due to the reduction in surface energy and the effect of negative surface charge. After the coating is left for a period of time, its contact angle only increases by 20° due to the loss of negative surface charge. After a physiological loading is applied to the polarized PVDF coating, the durability of its surface hydrophilicity is maintained. The mineralization ability of the polarized PVDF coating after being immersed in simulated body fluid (SBF) for 1, 7, and 14 days is significantly higher than that of the unpolarized sample. The increase in mineralization ability is mainly due to the hydrophilicity of the surface and the attraction of negative charges to calcium ions. Notably, after the polarized PVDF coating is subjected to physiological load, the mineralization ability is further improved after being immersed in SBF for 14 days, and its surface is covered with a layer of bone-like apatite. The high mineralization ability of the PVDF coating on the titanium surface after polarization can promote osseointegration and therefore shorten the bone repair cycle. Accordingly, this coating has potential application value in the clinical treatment of bone defect repair in middle-aged and elderly people.

In this paper, we investigate the external stability and $H_{\infty }$ H ∞ control of switching systems with time-varying delay and impulse. First of all, a modified two-direction inequality (relation) between the switching numbers and the maximum, minimum dwell time is proposed. This new inequality is applied to proving the external stability of switching systems with delay and impulse consisting of subsystems with Hurwitz stable matrices of internal dynamics. By using this new inequality, a normal $L_{2}$ L 2 norm constraint is derived rather than weighted $L_{2}$ L 2 norm constraint. In addition, by a realizable switching law, the obtained result is extended to the switching systems comprised of subsystems with both Hurwitz stable and unstable matrices of internal dynamics. The results are finally applied to $H_{\infty }$ H ∞ control and illustrated by a numerical example.

By using a kernel method, Lepski and Willer establish adaptive and optimal $$L^p$$ risk estimations in the convolution structure density model in 2017 and 2019. They assume their density functions to be in a Nikol’skii space. Motivated by their work, we first use a linear wavelet estimator to obtain a point-wise optimal estimation in the same model. We allow our densities to be in a local and anisotropic Holder space. Then a data driven method is used to obtain an adaptive and near-optimal estimation. Finally, we show the logarithmic factor necessary to get the adaptivity.

Tissue engineering technology provides effective alternative treatments for tracheal reconstruction. The formation of a functional microvascular network is essential to support cell metabolism and ensure the long-term survival of grafts. However, given the lack of an identifiable vascular pedicle of the trachea that could be anastomosed to the blood vessels directly in the recipient's neck, successful tracheal transplantation faces significant challenges in rebuilding the adequate blood supply of the graft. Herein, we describe a one-step method to construct microvascularization of tissue-engineered trachea in orthotopic transplantation. Forty rabbit tracheae were decellularized using a vacuum-assisted decellularization (VAD) method. Histological appearance and immunohistochemical (IHC) analysis demonstrated efficient removal of cellular components and nuclear material from natural tissue, which was also confirmed by 4′-6-diamidino-2-phenylindole(DAPI) staining and DNA quantitative analysis, thus significantly reducing the antigenicity. Scanning electron microscopy (SEM), immunofluorescence (IF) analysis, GAG and collagen quantitative analysis showed that the hierarchical structures, composition and integrity of the extracellular matrix (ECM) were protected. IF analysis also demonstrated that basic fibroblast growth factor (b-FGF) was preserved during the decellularization process, and also exerted biocompatibility and proangiogenic properties by the chick chorioallantoic membrane(CAM) assay. Xenotransplantation assays indicated that the VAD tracheal matrix would no longer induced inflammatory reactions implanted in the body for 4 weeks after treated by VAD more than 16 h. Furthermore, we seeded the matrix with bone marrow-derived endothelial cells (BMECs) in vitro and performed in vivo tracheal patch repair assays to prove the biocompatibility and neovascularization of VAD-treated tracheal matrix, and the formation of a vascular network around the patch promoted the crawling of surrounding ciliated epithelial cells to the surface of the graft. We conclude that this natural VAD tracheal matrix is non-immunogenic and no inflammatory reactions in vivo transplantation. Seeding with BMECs on the grafts and then performing orthotopic transplantation can effectively promote the microvascularization and accelerate the native epithelium cells crawling to the lumen of the tracheal graft.

The retina is an internal part of the human eye that plays a crucial role in vision. Retinal vessel segmentation is an important basis for the identification and classification of Diabetic Retinopathy (DR), Age related macular degeneration (AMD)，Retinal Detachment, and other retinal diseases. At the same time, the morphological structure of retinal blood vessels can also be used to diagnose cardiovascular diseases, which is important for early diagnosis and prevention of exacerbation of the disease. There are already advanced state-of-the-art methods to help automatically segment and identify retinal vessel diseases. This paper presents the methods of the principle and applications of deep learning in retinal image analysis. We described various segmentation methods based on deep learning. Analyzing along with the limitations of each method. Finally, we proposed some suggestions for the improvement of retinal image analysis.

Targeted drug delivery systems have currently demonstrated considerable potential clinical benefits in cancer treatment. Curcumin has become a candidate anti-tumor drug for the therapy of glioblastoma multiforme (GBM) by increasing cell apoptosis and suppressing cell proliferation. In current research, we explored a novel targeted drug delivery system with a self-assembly measure by curcumin, MPEG-PLA and Fa-PEG-PLA. Compared with free curcumin and Cur/MPEG-PLA, Cur/Fa-PEG-PLA can remarkably suppress the growth of GL261 cells and promote apoptotic rate. Moreover, after the procession of tumor-bearing mice with curcumin/Fa-PEG-PLA complex, tumor growth in subcutaneous and intracranial tumor models were repressed via suppressing angiogenesis and facilitating apoptosis in vivo. The Curcumin/Fa-PEG-PLA nanoparticle may be a novel drug for the therapy of GBM.

Porous titanium scaffolds with centrosymmetric pore channels in the radial direction were fabricated by freeze-casting, and TiH2/H2O slurries with different TiH2 contents (20, 25, and 30 vol.%) were cast in a cylindrical metal mold. The cold sources at the bottom and side of the metal mold caused ice crystals to grow radially. The lamellar channels of the porous titanium scaffolds were arranged in centrosymmetric regular channels in the radial axis and afforded the higher radial fracture loading than that of porous titanium prepared by conventional unidirectional freezing. As load-bearing artificial implants, porous titanium scaffolds require high strength in other directions aside from the axial axis. The centrosymmetric regular pore channels can satisfy the clinical demands and improve the security in practical applications, particularly on organisms. The porous scaffold prepared by this method had no toxicity and had good biocompatibility.

Purpose: The purpose of this study was to investigate finite element biomechanical properties of the novel transpedicular transdiscal (TPTD) screw fixation with interbody arthrodesis technique in lumbar spine. Methods: An L4–L5 finite element model was established and validated. Then, two fixation models, TPTD screw system and bilateral pedicle screw system (BPSS), were established on the validated L4–L5 finite element model. The inferior surface of the L5 vertebra was set immobilised, and moment of 7.5 Nm was applied on the L4 vertebra to test the range of motion (ROM) and stress at flexion, extension, lateral bending and axial rotation. Results: The intact model was validated for prediction accuracy by comparing two previously published studies. Both of TPTD and BPSS fixation models displayed decreased motion at L4–L5. The ROMs of six moments of flexion, extension, left lateral bending, right lateral bending, left axial rotation and right axial rotation in TPTD model were 1.92, 2.12, 1.10, 1.11, 0.90 and 0.87°, respectively; in BPSS model, they were 1.48, 0.42, 0.35, 0.38, 0.74 and 0.75°, respectively. The screws' peak stress of above six moments in TPTD model was 182.58, 272.75, 133.01, 137.36, 155.48 and 150.50 MPa, respectively; and in BPSS model, it was 103.16, 129.74, 120.28, 134.62, 180.84 and 169.76 MPa, respectively. Conclusion: Both BPSS and TPTD can provide stable biomechanical properties for lumbar spine. The decreased ROM of flexion, extension and lateral bending was slightly more in BPSS model than in TPTD model, but TPTD model had similar ROM of axial rotation with BPSS model. The screws' peak stress of TPTD screw focused on the L4–L5 intervertebral space region, and more caution should be put at this site for the fatigue breakage. The translational potential of this article: Our finite element study provides the biomechanical properties of novel TPTD screw fixation, and promotes this novel transpedicular transdiscal screw fixation with interbody arthrodesis technique be used clinically. Keywords: Bilateral pedicle screw system, Biomechanics, Finite element, Lumbar arthrodesis, Transpedicular transdiscal screw

The effects of the annealing methods and annealing temperatures on the pore structures and mechanical properties of porous alumina were investigated. The amorphisation behavior and solidification behavior of the sucrose solutions during annealing were discussed. The pore morphology of porous alumina changed noticeably after uniform annealing. As annealing temperature increased from −25 ℃ to −5 ℃, the pore morphology of porous alumina changed gradually from irregular lamellar channels to circular channels. After directional annealing, the pore morphology of porous alumina was similar to that after uniform annealing; however, the uniformity of pore channels and the density of pore walls were increased. During directional annealing at −15℃, the compressive strength of porous alumina reached 58.8 MPa, which was 35% higher than that of unannealed porous alumina.

Porous titanium scaffolds with aligned lamellar pore channels and smooth inner walls were fabricated by directional freeze casting using aqueous TiH2 slurries. The formation of dendrites was inhibited by increasing the TiH2 content in slurry. The pore structures and compression strengths of porous titanium scaffolds that were made with different solid contents were characterized. The formation mechanism of aligned lamellar pore channels and the reason for the improvement of compression strength were analyzed. With increasing TiH2 content in slurry, the open porosity reduced from 38.57 to 29.03% while lamellar spacing decreased. Young’s modulus was decreased with the increasing open porosity. Directional lamellar pore channels were obtained by controlling the TiH2 content in slurry, which can reduce the number of branches and prevent stress concentrations during compression. Also, the porous titanium scaffolds prepared by this process had a good biocompatibility with osteoblasts.

The development of methods to obtain ceramic pigments with fluorescence characteristics or hyper-domain performance has attracted research interest. In this study, Er-doped and Er/Yb-codoped CoAl2O4 pigments were synthesized by co-precipitation. The influence of Er doping, Er/Yb codoping, and the doping contents on the colour, composition, and luminescence properties of CoAl2O4 pigments were investigated. Er doping did not significantly affect the phase composition and colour performance of the CoAl2O4 pigment. The upconversion effect was induced by excitation with a 950 nm laser. Er doping could enhance the upconversion luminescence intensity of the CoAl2O4 pigment. At a 1 mol.% Er doping content, all luminous intensities reached maximum values. The downconversion effect was observed after excitation with a 350 nm laser. The luminescence was blue, and slight differences in the luminescence intensity with different Er doping contents were observed. Yb2O3 was formed after Er/Yb was codoped at > 6 mol.% Yb doping content, thereby affecting the phase composition and colour performance of the CoAl2O4 pigment. The luminous intensity of red light (739 nm) was the strongest in all cases. The luminous intensities of all of the colours decreased to the minimum value at 9 mol.% Yb doping content compared with those at other doping contents. At 3 mol.% Yb doping content, the luminous intensities of all colours decreased to very low values (close to 0), and the quenching effect of Yb3+ was achieved using a 350 nm laser. Er/Yb-codoped CoAl2O4 pigments exhibited the upconversion luminescence effect under an infrared laser and inhibited visible-light reflection under an UV laser. This ceramic pigment can be developed further to obtain ceramic pigments with anti-counterfeit function.

Targeting nanoparticles to cancers for improved therapeutic efficacy and decreased side effects remains a popular concept in the past decades. Although the enhanced permeability and retention effect serves as a key rationale for all the currently commercialized nanoformulations, it does not enable uniform delivery of nanoparticles to all tumorous regions in all patients with sufficient quantities. Also, the increase in overall survival is often modest. Many factors may influence the delivering process of nanoparticles, which must be taken into consideration for the promise of nanomedicine in patients to be realized. Herein, we review the mechanisms and influencing factors during the delivery of cancer therapeutics and summarize current strategies that have been developed for the fabrication of smart drug delivery systems.

Equal channel angular pressing results in ultrafine-grained pure titanium (Ti) with superior mechanical properties and no harmful alloying elements, which is expected to replace pure Ti and Ti alloys as a new generation of biomedical implant materials. To further improve the bioactivity of Ti surfaces, porous titania coatings were prepared on ultrafine-grained Ti through micro-arc oxidation (MAO) in Ca-, P-, and Si-containing electrolyte. The effects of oxidation time on the surface morphology, wettability, and roughness of ultrafine-grained Ti after MAO were investigated. The cellular compatibility of the coatings was evaluated through a cytotoxicity experiment, cell proliferation assay, and examination of the adhesion behaviour of osteoblasts. The results indicate that the specimens after the MAO treatment showed higher surface energy, larger surface roughness, and could better promote adhesion and spreading of osteoblasts than those before the treatment. Additionally, the oxidation time has a pronounced influence on the surface microstructure and wettability of the coatings. As the oxidation time increases, the roughness and thickness of coating surface constantly increases. In the 9-min treatment, the coating with the highest surface energy exhibits the highest wettability. This in vitro cell experiment indicates that the cytotoxicity of ultrafine-grained Ti before and after MAO is grade 0. Compared with other specimens, the 9-min sample, which has the highest number of viable cells, markedly promotes incipient adhesion and later proliferation of osteoblasts, thus exhibiting highest bioactivity.

Lamellar porous alumina with graded structures was fabricated through a novel method of simultaneous centrifugal casting and directional freeze casting. Alumina particles in ceramic slurry moved outward from the center by centrifugal force and formed stable gradient distribution because of viscous resistance and electrostatic repulsion among particles. The porous and pore-size gradient structure were obtained after freeze drying. With increased rotational speed, the pore size of the lamellar pore channels also gradually increased. However, the sizes of the ice crystals and lamellar pores shrunk at 200 rpm due to the destabilization of laminar flow during ice-crystal growth. Compressive strength obviously improved with increased rotational speed, and that of the resulting porous ceramic was 2.3 times higher than that in the absence of centrifugation at 1000 rpm rotational speed.

A superoxide anion radical () electrochemical sensor based on a gold nanoparticle/[Fe(CN)6]4– anionic doped poly(3,4-ethylenedioxythiophene)/multiwalled carbon nanotube composite modified glassy ca...

We developed a highly efficient method for patterning cells by a novel and simple technique called lift-off cell lithography (LCL). Our approach borrows the key concept of lift-off lithography from microfabrication and utilizes a fully biocompatible process to achieve high-throughput, high-efficiency cell patterning with nearly zero background defects across a large surface area. Using LCL, we reproducibly achieved >70% patterning efficiency for both adherent and non-adherent cells with

CoAl 2 O 4 ceramic pigments produced by common methods have low chroma values, which limit their application in ceramic glazing, enamel glazing, and ceramic product printing. The colour stability of the ceramic pigments and changes upon high-temperature sintering are important factors, especially in 3D printing. In this study, CoAl 2 O 4 ceramic pigments were synthesized using a co-precipitation method and both the colouration mechanism and stability of CoAl 2 O 4 ceramic pigments were investigated. The Co content, Co ion valence, and coordination number were found to be important factors affecting the CoAl 2 O 4 ceramic pigments. When the Co content was excessively high, either Co 3+ was produced or Co 2+ entered the octahedron spaces of the spinel structure. The coordination field of the Co ions was consequently altered and the colour transitioned from blue to green. After sintering on substrates at 1300 °C, the brightness and chroma of obtained CoAl 2 O 4 coatings were superior to those of the pigment powders prior to sintering, and the colour of CoAl 2 O 4 with a relatively high Co/Al ratio changed from green to blue. The latter pigment may have formed a partially inverse spinel structure upon sintering at a high temperature. The probability of Co 2+ entering the octahedron spaces increased; concomitantly, the number of Co 2+ in the tetrahedron spaces decreased, resulting in an increase in the coordination number of Co. In addition, Co 3+ in the ceramic pigments was transformed into Co 2+ by deoxidation reactions during the coating sintering process, thereby increasing the chroma of blue CoAl 2 O 4 pigments.

It is of great importance to design and exploit high-efficiency low-cost electrocatalysts for the oxygen evolution reaction (OER) under mild conditions for applications. In this Article, we propose that formation of a thin amorphous Ni carbonate layer on Ni3N nanoarray supported on carbon cloth (Ni3N NA/CC) is an effective strategy to boost its OER activity in at near-neutral pH. When used as a 3D non-noble-metal OER electrocatalyst, the resulting core–shell Ni3N@Ni-Ci NA/CC displays superior catalytic activity with extremely small overpotential of 400 mV for 20 mA cm−2 in 1.0 M KHCO3 (bulk pH: 8.3). Moreover, it also exhibits considerable long-term electrochemical durability with its activity being preserved for at least 12 h. Conductive Ni3N nanoarray not only provides as the Ni source for in-situ electrochemical derivation of 3D Ni-Ci catalyst with high surface area, more exposed active sites and facilitated mass diffusion, but effectively prompts the electron transport from Ni-Ci shell to CC, enabling more efficient water oxidation electrocatalysis.

MoS2 becomes one of the ideal anode materials for lithium-ion batteries (LIBs) because of its unique two-dimensional layered structure and high theoretical capacity. However, the poor conductivity and volume change during reaction hinder its application. In this work, we demonstrate a two-step hydrothermal method to synthesis the unique structure of core–shell CoS2@MoS2 nanorods anchored on carbon cloth (CC). The one-dimensional Co(OH)2 nanowire array on CC forms a carbon-based framework, which increases the reaction surface area for subsequent in situ generation of MoS2. The MoS2 layer with rich holes enhances lithium storage capacity and increases the active sites. Compared with pure MoS2 electrode, CoS2@MoS2/CC (CMCC) exhibits a stronger electrochemical performance as a binder-free electrode for LIBs. The structure has a high discharge specific capacity of 1175 mA h g−1 at the current density of 0.1 A g−1. The further experiments prove that the CMCC structure has outstanding ion transport ability and low impedance characteristics, which are attributed to its special structure and the introduction of Co ions. The present work provides a new idea for the design of stable flexible electrode with high electrochemical performance for lithium-ion batteries.

Binary Ti-4(Nb, V, Fe) alloys were prepared to investigate the effects of β-stabilizers (Nb, V and Fe) on microstructure formation and mechanical properties of titanium alloys by using experimental and theoretical methods. Microstructure observations revealed that addition of Nb, V or Fe significantly tailored the microstructure under different heat-treated conditions, i.e., furnace-cooled (FC), air-cooled (FC) and water-quenched (WQ). The FC Ti–4(Nb, V, Fe) alloys exhibited the Widmanstatten microstructure and the AC samples showed the spheroidized microstructure. The WQ Ti–4Fe exhibited the microstructure composed of equiaxed β grains and nanoscale ω particles while the WQ Ti–4Nb and Ti–4V showed the martensite microstructure. Differentials of microstructure can be attributed to the effects of Nb, V and Fe elements on the phase stability and energy barrier of phase transformation according to the empirical electron theory (EET) of solids and molecules. Results of tensile tests showed that Nb, V and Fe significantly influenced the tensile properties under the different heat treatments. Both the WQ Ti–4Nb and Ti–4V showed the larger tensile strength than that of the FC and AC sample due to the stronger solid-solution and phase-interface strengthening in martensite structure. The WQ Ti–4Fe sample exhibited the largest tensile strength (1104 MPa) compared to that of the FC (754 MPa) and AC (981 MPa) samples due to the strongest solid-solution and phase-interface strengthening from the ω phase. By executing the methods of the empirical electron theory (EET) of solids and molecules, effects of β-stabilizers (Nb, V and Fe) on microstructure formation and mechanical properties of titanium alloys were revealed on the view of valence electron.