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In this paper, the bandgap characteristics of a missing rib lattice structure composed of beam elements are investigated by using the Floquet-Bloch theorem. The tuning of the width and position of the bandgap is achieved by changing the local structural parameters, i.e., the rotation angle, the short beam length, and the beam thickness. In order to expand the regulation of the bandgap, the influence of the material parameters of the crossed long beams inside the structure on the bandgap is analyzed. The results show that the mass density and stiffness of the structure have significant effects on the bandgap, while Poisson’s ratio has no effect on the bandgap. By analyzing the first ten bands of the reference unit cell, it can be found that the missing rib lattice structure generates multiple local resonance bandgaps for vibration reduction, and these bandgap widths are wider. The modal analysis reveals that the formation of the bandgap is due to the dipole resonance of the lattice structure, and this dipole resonance originates from the coupling of the bending deformation of the beam elements. In the band structure, the vibrational mode of the 9th band with a negative slope corresponds to a rotational resonance, which is different from that with the conventional negative slope formed by the coupling of two resonance modes. This study can provide a theoretical reference for the design of simple and lightweight elastic metamaterials, as well as for the regulation of bandgaps and the suppression of elastic waves.

Heart failure (HF) is a complex clinical syndrome that poses a major hazard to human health. Patients with different types of HF have great differences in pathogenesis and treatment options. Therefore, HF typing is of great significance for timely treatment of patients. In this paper, we proposed an automatic approach for HF typing based on heart sounds (HS) and convolutional recurrent neural networks, which provides a new non-invasive and convenient way for HF typing. Firstly, the collected HS signals were preprocessed with adaptive wavelet denoising. Then, the logistic regression based hidden semi-Markov model was utilized to segment HS frames. For the distinction between normal subjects and the HF patients with preserved ejection fraction or reduced ejection fraction, a model based on convolutional neural network and recurrent neural network was built. The model can automatically learn the spatial and temporal characteristics of HS signals. The results show that the proposed model achieved a superior performance with an accuracy of 97.64%. This study suggests the proposed method could be a useful tool for HF recognition and as a supplement for HF typing.

Molecular-level selectin-cluster of differentiation 44 (CD44) interactions are far from clear because of the complexity and diversity of CD44 glycosylation and isoforms expressed on various types of cells. By combining experimental measurements and simulation predictions, the binding kinetics of three selectin members to the recombinant CD44 were quantified and the corresponding microstructural mechanisms were explored, respectively. Experimental results showed that the E-selectin-CD44 interactions mainly mediated the firm adhesion of microbeads under shear flow with the strongest rupture force. P- and L-selectins had similar interaction strength but different association and dissociation rates by mediating stable rolling and transient adhesions of microbeads, respectively. Molecular docking and molecular dynamics (MD) simulations predicted that the binding epitopes of CD44 to selectins are all located at the side face of each selectin, although the interfaces denoted as the hinge region are between lectin and epidermal growth factor domains of E-selectin, Lectin domain side of P-selectin and epidermal growth factor domain side of L-selectin, respectively. The lowest binding free energy, the largest rupture force and the longest lifetime for E-selectin, as well as the comparable values for P- and L-selectins, demonstrated in both equilibration and steered MD simulations, supported the above experimental results. These results offer basic data for understanding the functional differences of selectin-CD44 interactions.

A one-dimensional mechanical lattice system with local resonators is proposed as an elastic metamaterial model, which shows negative mass and negative modulus under specific frequency ranges. The proposed representative units, consisting of accurately arranged rigid components, can generate controllable translational resonance and achieve negative mass and negative modulus by adjusting the local structural parameters. A shape memory polymer is adopted as a spring component, whose Young’s modulus is obviously affected by temperature, and the proposed metamaterials’ tunable ability is achieved by adjusting temperature. The effect of the shape memory polymer’s stiffness variation on the band gaps is investigated detailedly, and the special phenomenon of intersecting dispersion curves is discussed, which can be designed and controlled by adjusting temperature. The dispersion relationship of the continuum metamaterial model affected by temperature is obtained, which shows great tunable ability to manipulate wave propagation.

Hybrid circuit breaker (HCB) has shown good performance for interrupting dc fault current. However, a massive number of IGBTs in series is needed. These will lead to high costs and significant difficulty in balancing IGBT dynamic voltage. This paper proposes a bidirectional hybrid circuit breaker based on a cascaded half-bridge submodule structure to reduce the overall costs and implementation difficulty of HCB. The number of IGBTs is reduced by 50%, and the operating speed is fast enough. A model of a four-terminal modular multilevel converter (MMC) system with a proposed hybrid circuit breaker in different stages is developed to describe the fault blocking process more clearly. The performance of the proposed HCB is validated and compared with other HCB structure through both theoretical derivation and time-domain simulation.

Metastasis is one of the main causes of failure in the treatment of triple-negative breast cancer (TNBC). Abnormally estrogen level and activated platelets are the key driving forces for TNBC metastasis. Herein, an “ion/gas” bioactive nanogenerator (termed as IGBN), comprising a copper-based MOF and loaded cisplatin-arginine (Pt-Arg) prodrug is developed for metastasis-promoting tumor microenvironment reprogramming and TNBC therapy. The copper-based MOF not only serves as a drug carrier, but also specifically produces Cu2+ in tumors, which catalytic oxidizing estrogen to reduce estrogen levels in situ. Meanwhile, the rationally designed Pt-Arg prodrug reduced into cisplatin to significantly promote the generation of H2O2 in the tumor, then permitting self-augmented cascade NO gas generation by oxidizing Arg through a H2O2 self-supplied way, thus blocking platelet activation in tumor. We clarified that IGBN inhibited TNBC metastasis through local estrogen deprivation and platelets blockade, affording 88.4% inhibition of pulmonary metastasis in a 4T1 mammary adenocarcinoma model. Notably, the locally copper ion interference, NO gas therapy and cisplatin chemotherapy together resulted in an enhanced therapeutic efficacy in primary tumor ablation without significant toxicity. This “ion/gas” bioactive nanogenerator offers a robust and safe strategy for TNBC therapy. Graphical Abstract

Studying and analyzing the dynamic behavior of offshore wind turbines are of great importance to ensure the safety and improve the efficiency of such expensive equipments. In this work, a tapered beam model is proposed to investigate the dynamic response of an offshore wind turbine tower on the monopile foundation assembled with rotating blades in the complex ocean environment. Several environment factors like wind, wave, current, and soil resistance are taken into account. The proposed model is analytically solved with the Galerkin method. Based on the numerical results, the effects of various structure parameters including the taper angle, the height and thickness of the tower, the depth, and the diameter and the cement filler of the monopile on the fundamental natural frequency of the wind turbine tower system are investigated in detail. It is found that the fundamental natural frequency decreases with the increase in the taper angle and the height and thickness of the tower, and increases with the increase in the diameter of the monopile. Moreover, filling cement into the monopile can effectively improve the fundamental natural frequency of the wind turbine tower system, but there is a critical value of the amount of cement maximizing the property of the monopile. This research may be helpful in the design and safety evaluation of offshore wind turbines.

This work shows that a few-layer graphene with two highly-tensioned outermost layers exhibits negative effective mass and behaves like an elastic metamaterial. Actually, our simulations based on simple elastic membrane model confirm the existence of a bandgap in terahertz range within which a tensioned few-layer graphene exhibits remarkable vibration isolation: forced vibration will be highly restricted to a narrow region around the site of the applied excitation while all other parts of the graphene remain essentially static. The values of terahertz bandgap frequencies are determined by the van der Waals interaction coefficient between adjacent layers, while the width of the bandgap is determined by the number of inner layers. This research may provide new perspectives for designing and analyzing graphene-based metamaterials and nano-resonators with potential applications in high-frequency vibration controlling.

In this paper, a novel size-dependent functionally graded (FG) cylindrical shell model is developed based on the nonlocal strain gradient theory in conjunction with the Gurtin-Murdoch surface elasticity theory. The new model containing a nonlocal parameter, a material length scale parameter, and several surface elastic constants can capture three typical types of size effects simultaneously, which are the nonlocal stress effect, the strain gradient effect, and the surface energy effects. With the help of Hamilton’s principle and first-order shear deformation theory, the non-classical governing equations and related boundary conditions are derived. By using the proposed model, the free vibration problem of FG cylindrical nanoshells with material properties varying continuously through the thickness according to a power-law distribution is analytically solved, and the closed-form solutions for natural frequencies under various boundary conditions are obtained. After verifying the reliability of the proposed model and analytical method by comparing the degenerated results with those available in the literature, the influences of nonlocal parameter, material length scale parameter, power-law index, radius-to-thickness ratio, length-to-radius ratio, and surface effects on the vibration characteristic of functionally graded cylindrical nanoshells are examined in detail.

Lifang Cheng,1,2,&ast; Kangla Liao,2,&ast; Yingying Wang,2 Fajin Lv,1 Xingming Guo,3 Yineng Zheng,1 Jian Qin2 1Department of Radiology, The First Affiliated Hospital of Chongqing Medical University, Chongqing, 400016, People’s Republic of China; 2Department of Cardiology, The First Affiliated Hospital of Chongqing Medical University, Chongqing, 400016, People’s Republic of China; 3Key Laboratory of Biorheology Science and Technology, Ministry of Education, College of Bioengineering, Chongqing University, Chongqing, 400044, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Yineng Zheng; Jian Qin Tel/Fax +86-23-89012558Email yinengzheng@cqmu.edu.cn; hjqj2001@163.comBackground: This study aimed to investigate the correlation between the ratio of diastolic to systolic durations (D/S) and echocardiographic parameters of patients with chronic heart failure (CHF) and evaluate whether the D/S can be used as a supplementary biomarker for the classification of heart failure (HF) phenotypes.Methods: In total, 122 CHF patients with a left ventricular ejection fraction (LVEF) < 40%, 40%≤LVEF< 50%, or ≥ 50% were categorized as having HF with a reduced ejection fraction (HFrEF) (N=32), HF with a mid-range ejection fraction (HFmrEF) (N=21) or HF with a preserved ejection fraction (HFpEF) (N=69), respectively. All patients underwent echocardiography for assessment of nineteen structural and functional echocardiographic parameters and digital phonocardiography for the measurement of D/S. Spearman correlation was used to analyse the associations between the D/S and echocardiographic parameters. Multivariate logistic regression analysis was performed to examine the associations between the D/S and HF phenotypes, and receiver operating characteristic (ROC) curve analysis was employed to evaluate the predictive value of the D/S in the classification of HF phenotypes.Results: The D/S values of patients with HFrEF, HFmrEF and HFpEF were 1.32± 0.06, 1.44± 0.11 and 1.54± 0.08, respectively, which were significantly different (All P< 0.05). A close correlation between the D/S and LVEF was found (r=0.777, P< 0.001). The multivariate analysis indicated that the D/S was an independent risk factor for CHF phenotypes (OR=4.927, 95% CI 2.532– 9.587; P< 0.001). The area under the ROC curve for distinguishing between HFmrEF and HFpEF using the D/S was 0.764 (95% CI 0.707– 0.845; P < 0.001) and that for distinguishing between HFmrEF and HFrEF using the D/S was 0.821 (95% CI 0.755– 0.882; P < 0.001).Conclusion: The D/S was significantly associated with LVEF, and as LVEF decreased, the D/S tended to decrease, which could also serve as a noninvasive supplementary indicator for detecting systolic and diastolic dysfunction.Keywords: phonocardiogram, heart sounds, ratio of diastolic to systolic durations, D/S, chronic heart failure, CHF

Objective. Heart sounds can reflect detrimental changes in cardiac mechanical activity that are common pathological characteristics of chronic heart failure (CHF). The ACC/AHA heart failure (HF) stage classification is essential for clinical decision-making and the management of CHF. Herein, a machine learning model that makes use of multi-scale and multi-domain heart sound features was proposed to provide an objective aid for ACC/AHA HF stage classification. Approach. A dataset containing phonocardiogram (PCG) signals from 275 subjects was obtained from two medical institutions and used in this study. Complementary ensemble empirical mode decomposition and tunable-Q wavelet transform were used to construct self-adaptive sub-sequences and multi-level sub-band signals for PCG signals. Time-domain, frequency-domain and nonlinear feature extraction were then applied to the original PCG signal, heart sound sub-sequences and sub-band signals to construct multi-scale and multi-domain heart sound features. The features selected via the least absolute shrinkage and selection operator were fed into a machine learning classifier for ACC/AHA HF stage classification. Finally, mainstream machine learning classifiers, including least-squares support vector machine (LS-SVM), deep belief network (DBN) and random forest (RF), were compared to determine the optimal model. Main results. The results showed that the LS-SVM, which utilized a combination of multi-scale and multi-domain features, achieved better classification performance than the DBN and RF using multi-scale or/and multi-domain features alone or together, with average sensitivity, specificity, and accuracy of 0.821, 0.955 and 0.820 on the testing set, respectively. Significance. PCG signal analysis provides efficient measurement information regarding CHF severity and is a promising noninvasive method for ACC/AHA HF stage classification.

Based on the nonlocal strain gradient theory and surface elasticity theory, a unified size-dependent plate model is developed for buckling analysis of rectangular nanoplates. The developed model is capable of capturing nonlocal effect, strain gradient effect as well as surface energy effects simultaneously. Moreover, by selecting appropriate shape function, the present model can be reduced to not only Kirchhoff and Mindlin plate models but also various higher-order shear deformation plate models. The non-classical governing equations and associated boundary conditions are established by using the principle of minimum potential energy. Analytical solutions for critical buckling load of rectangular nanoplates under various boundary conditions are obtained. Verification of the proposed model is carried out by comparing the degenerated results with those reported in open literature. The effects of nonlocal parameter, material length scale parameter, geometric parameters, shear deformation and surface energy on the buckling behavior of rectangular nanoplates under different boundary conditions are discussed in detail. The numerical results show that the critical buckling load evaluated by nonlocal strain gradient theory is lower than that predicted by classical continuum theory when the nonlocal parameter is larger than the material length scale parameter, and is higher than that evaluated by classical continuum theory when the nonlocal parameter is smaller than the material length scale parameter. However, when taking surface effects into account, the critical buckling load is mainly affected by surface effects at large length-to-thickness ratio, and depends on the combined effects of nonlocality, strain gradient and surface energy at small length-to-thickness ratio.

The present paper investigates the small size effect on a localized transition zone in the merging of two wrinkles in constrained suspended graphene under in-plane shear. It is found the classical elasticity theory overestimates the wrinkle amplitude and wavelength in contrast with the results of atomistic simulation. The analytic formulations for the wrinkling hierarchy are obtained by using nonlocal plate theory. Here, this small size effect can be estimated by correct value of nonlocal parameter e0a = 1.9 nm. Besides, the orientation of graphene slightly influences the wrinkling hierarchy of graphene. The temperature effect is significant under small shear strain, while this effect is significant in the constrained edges and insignificant in the middle region under large strain. The occurrence of cracking is always in constrained edges, where the stress concentration releases in the wrinkling hierarchy. This work is expected to provide a better understanding of the mechanism of nanometer scale wrinkles.

To overcome endo/lysosomal restriction as well as to increase the clinical availability of nanomedicine, we report on a NIR stimuli-responsive nanoplatform based on mesoporous silica nanoparticles tethered with lipid bilayers (MSN@tLB) for chemotherapy and photodynamic dual-modality therapy. In this nanosystem, a hydrophilic drug molecule zoledronic acid (ZOL) was first incorporated into the MSN core with modifications of hyperbranched polyethylenimine (PEI). To prevent the leakage of the payload, the LB shell was covalently tethered onto the MSN core via the PEI cushion which can greatly enhance the stability of the LB. Meanwhile, a hydrophobic photosensitizer IR-780 iodide was introduced into the hydrophobic compartment to endow the system with photo-activation properties. The as-prepared MSN-ZOL@tLB-IR780 possesses high dispersion stability stemming from the LB, as well as negligible cytotoxicity. After cellular internalization and endo/lysosomal capture of the nanoparticles, photochemical internalization (PCI) mediated simultaneous cargo release and endo/lysosomal escape were achieved by local ROS production upon 808 nm irradiation, thus leading to highly efficient chemo-photodynamic therapy on cancer cells in vitro. Such a system presents a sophisticated platform that integrates biocompatibility, spatiotemporal control, NIR-responsiveness, and synergistic therapies to promote cancer therapy.

The present work aims to examine the metamaterial vibrational behavior of circular few-layer graphene sheets under layerwise tension forces. For this objective, a simplified three-membrane model is developed to simulate flexural vibration of tensioned circular few-layer graphene sheets, in which tensioned top and bottom layers are modeled as two elastic membranes while all less-tensioned or tension-free inner layers together are treated as a single membrane, and the three membranes are coupled through the van der Waals interaction between adjacent layers. Our results show that when the two outermost layers are highly tensioned but the inner layers are free of tension, circular few-layer graphene sheets exhibit negative effective mass within a certain terahertz frequency range. Moreover, such few-layer graphene sheets with negative effective mass demonstrate remarkable vibration isolation and vibration suppression. This research broadens our perspectives for designing and analyzing graphene-based metamaterials and resonators and could find potential application in nanoelectromechanical systems.

In this paper, size-dependent Kirchhoff and Mindlin plate models are developed to investigate the coupling effects of nonlocal stress, strain gradient and surface energy on the dynamic response of nanoplate. The nonlocal stress and strain gradient effects are captured by nonlocal strain gradient theory, while the surface energy effects are incorporated by surface elasticity theory. The governing equations of motion and related boundary conditions are derived from Hamilton's principle. Analytical solutions for the natural frequencies of simply supported nanoplate are obtained through the Navier approach. A good agreement between the results of the present models and those available in literatures are observed. Selected examples are presented to show the influences of nonlocal parameter, material length scale parameter, length-to-thickness ratio, aspect ratio, surface energy and shear deformation on the vibration behavior of nanoplate. It is found that for nanoplate with lower length-to-thickness ratio, the nonlocal stress, strain gradient and surface energy have remarkable influences on the vibration characteristic simultaneously. While surface effects play a dominant role in the vibration behavior for nanoplate with higher length-to-thickness ratio.

The study reports a multifunctional nanoplatform based on mesoporous silica coated gold nanorod (AuNR@MSN) to overcome biological barriers associating with nanocarrier for multiple enhanced photodynamic therapy (PDT) and photothermal therapy (PPT). Indocyanine green (ICG) was loaded into AuNR@MSN and end-capped with β-cyclodextrin (β-CD). Then, a peptide RLA ([RLARLAR] 2 ) with plasma membrane permeability and mitochondria-targeting capacity was anchored to AuNR@MSN via host-gust interaction. Subsequently, a charge-reversible polymer was introduced to endow stealth property. When the nanoplatform extravasates to tumor tissue, the weak acidity in tumor microenvironment could induce the dissociation of charge-reversible polymer and re-exposure of RLA peptide. Such a pH-mediated transition could facilitate the targeted accumulation of the nanoplatform in mitochondria. Upon singular 808 nm laser irradiation , the nanoplatform displayed enhanced PDT effect through the generation of reactive oxygen species (ROS) mediated by the local electric field of AuNR, plasmonic photothermal effect, and leakage of endogenous ROS by mitochondrion-targeted PDT. Meanwhile, local hyperthermia was generated by both ICG and AuNR for PPT. The in vitro and in vivo experiments demonstrated that the composite nanoplatform had good antitumor effect with minimal side effect. This work provides new insight into the development of new phototherapeutics for oncotherapy.

Buckling of a single ribbon is the simplest type of instability in mechanics. Recently postbuckling has been adopted in three-dimensional (3D) assembly technique to form diverse 3D architectures from planar precursors. amongst various structures, 3D serpentine structures are remarkable, especially in stretchable electronics and micro-electro-mechanical systems, as they provide ultra-low rigidity and high stretchability. Previous studies on those structures are mainly based on finite element analysis and individually focused on features such as the resonant frequency, critical compression for buckling and stretchability. A comprehensive theoretical model that fully reveals the mechanical behaviour of such structures and provides detailed information such as the displacement/rotation, curvature and strain distribution, is essential for applications that require a tailored structural design. Here an analytical model in very concise and explicit form is developed, showing that the postbuckling of serpentine structures obeys similar rules as that of a straight ribbon, with the effective torsional rigidity playing the role of the bending rigidity. The effective torsional rigidity involves not only the cross-sectional profile (ribbon width and thickness) but also the geometry parameters unique in the serpentine structures, which significantly enlarges the design space. Using serpentine structures of unidentical ribbons, an inverse design strategy is proposed to form various architectures buckled from planar precursors, without adopting spatial-varying cross-sectional thicknesses or widths as in previous works. A multi-directional strain sensor with ultra-low rigidity is also presented to demonstrate the application of the theoretical model. The above results also indicate that complexity (rich design space) and conciseness (simple rules) could coexist in 3D serpentine structures, which is rare in other structures formed by the mechanics-guided 3D assembly.

This paper studies the free vibration and dynamic stability characteristics of functionally graded composite multilayer microtubes reinforced with graphene platelets under axial mechanical load. The graphene platelets are assumed to be uniformly or gradiently distributed across the radial direction of the microtube, and the corresponding effective material properties are estimated by the modified Halpin-Tsai model and the rule of mixture. Based on the modified couple stress theory and a refined higher-order beam theory, a size-dependent multilayer tube model for the dynamic analysis is developed. By employing Hamiltons principle , the governing equations and associated boundary conditions are derived. Galerkin technique is applied to convert the governing partial differential equations into ordinary ones, from which the analytical solutions of natural frequencies and dynamic instability regions under different boundary conditions can be obtained. After verifying the accuracy of the proposed model, the influences of graphene platelets distribution pattern and weight fraction, microstructure effect, axial load as well as geometrical parameters on the free vibration and dynamic stability behaviors of functionally graded composite multilayer microtubes are investigated. It is found that distributing more graphene platelets in the outer layers but fewer in the inner layers has the best reinforcing effect for the composite microtubes.

The present paper shows that a carbon nanotube filled with a mass chain behaves like a metamaterial which exhibits negative effective mass density within a certain range of frequencies. Unlike the known elastic metamaterials proposed in literature which are all based on artificial design of their microstructure, a filled carbon nanotube offers an already fabricated metamaterial which exhibits negative effective mass density and achieves desirable metamaterial dynamic properties even without any artificial design of microstructure. To demonstrate metamaterial dynamic behaviors of such a filled carbon nanotube, a simple continuum model is used to study flexural vibration of a hinged filled carbon nanotube. It is confirmed that the locally resonant bandgap of a filled carbon nanotube is determined by the mass of the inserted mass chain and the van der Waals interaction coefficient between the inserted mass chain and the surrounding carbon nanotube, and the expected metamaterial behavior can be demonstrated by remarkable vibration isolation. Actually, our results show clearly that when the applied excitation frequency is within the bandgap, forced vibration of a filled carbon nanotube is highly restricted to a narrow region around the site of the applied external excitation whose width is only a few times the outer diameter of the carbon nanotube.

In present paper, a unified size-dependent high-order beam model which contains various higher-order shear deformation beam models as well as Euler–Bernoulli and Timoshenko beam models is developed to study the simultaneous effects of nonlocal stress and strain gradient on the bending and buckling behaviors of nanobeams by using the nonlocal strain gradient theory. For this objective, a nonlocal parameter is introduced to capture the nonlocal effect and a material length scale parameter is involved to evaluate the strain gradient effect. The governing equations and the associated boundary conditions are formulated by using Hamilton's principle. Navier's method is utilized to obtain the analytical solutions for bending and buckling of a simply supported nanobeam. The present model is validated by comparing the obtained results with those available in literature. The influences of nonlocal parameter, material length scale parameter, slenderness ratio and shear deformation on the bending and buckling behaviors of the nanobeam are examined in detail. Results reveal that within the framework of nonlocal strain gradient theory, results predicted by Timoshenko beam model and various higher-order beam models are almost same with some negligible differences. Moreover, it is found that the nanobeam could exhibit either stiffness-softening effect or stiffness-hardening effect, which depends on the relative magnitude of the nonlocal parameter and the material length scale parameter.

Graphene reinforced composites have attracted a great deal of attention in recent years due to their outstanding mechanical properties. The present work focuses on the size-dependent postbuckling characteristics of functionally graded (FG) graphene platelets reinforced composite (GPLRC) multilayer microtubes containing initial geometrical imperfection. It is assumed that the distribution of GPL reinforcements in microtubes is uniform or layer-wise change across the radial direction, and five typical distribution patterns (i.e., UD, FG-X, FG-O, FG-V and FG-A) are considered. Based on the modified couple stress theory and a refined higher-order beam theory, the non-classical governing equations with the account of von Karman geometrical non‐linearity for postbuckling analysis are derived by employing the principle of minimum potential energy and solved by using an analytical method. After validating the analytical solutions by comparing with results reported in the literature, the influences of various important parameters on the postbuckling of FG-GPLRC multilayer microtubes are investigated. It is found that the microstructure effect on the postbuckling behavior is significant when the outer radius of the microtube is comparable to the material length scale parameter. Moreover, the initial geometrical imperfection decreases the postbuckling load-carrying capacity at small deflection, but increases it at large deflection. Additionally, our results indicate that the FG-V distribution pattern produces the highest postbuckling load-carrying capacity for FG-GPLRC multilayer tubes, which differs from the cases for FG-GPLRC multilayer beams, plates and thin shells where the FG-X distribution pattern always has the best reinforcing effect. The present work could provide theoretical guidelines for the optimal design and safety assessment of graphene reinforced composite tubular structures, and may find potential application in microscale engineering devices and systems.

Nanoscale drug delivery systems (NDDS) have shown great potential in tumor treatment due to its unique advantages, especially its unique enhanced permeability and retention effect (EPR) in solid tumors. Therefore, NDDS have been extensively explored in recent years. However, current NDDS did not achieve satisfied clinical therapeutic effect against to tumor treatment. This is mainly ascribed to two reasons. One is that nanocarriers would inevitably encounter a series of physiological and pathological barriers in vivo , leading to low drug transport efficiency. The other is that tumor stroma pose a huge obstruction to tumor therapy, nanotherapeutics just focus on the tumor cells themselves are insufficient for complete tumor eradication. Here in this review, we first outlining sequential biological obstacles encountered by nanocarriers from three levels of blood, tumor tissue and tumor cells. Then, we give a detailed discussion of the role of tumor stroma, and highlight the therapeutic resistances mediated by tumor stroma. In light of these formidable barriers, we provide promising approaches to overcome each barrier or remodel stroma through innovative NDDS design. Finally, we give proposals and considerations of NDDS design, and then discuss several existing challenges and further opportunities of NDDS in clinical application. This review seeks to provide guidelines for optimizing NDDS design through mitigation of biological barriers to efficient tumor therapy.

Graphene has been expected to revolutionize the electronics, but suffered from its zero bandgap that will lead to an unacceptable leakage current in graphene-based transistors. Although a bandgap engineered graphene structure may have a bandgap, such bandgap is sensitively dependent on the geometry of the structure. Finding new two-dimensional (2D) semiconducting carbon allotropes is therefore extremely important for the new emerging all-carbon electronics. Based on first principles calculations, here we predict a new 2D semiconducting carbon allotrope, referred to as twin graphene. The allotrope has an intrinsic direct bandgap, very close to that of silicon and tunable by in-plane strain, indicating its great potential in nanoelectronics. The stability of twin graphene is carefully verified by both the first principles calculations and the molecular dynamics simulations. We determine also the mechanical properties of twin graphene, including the in-plane stiffness, Poisson’s ratio, shear stiffness and bending stiffness. Its excellent electronic and mechanical properties suggest that twin graphene may have a significant impact on many disciplines and fields related to nanotechnology.

A size-dependent sinusoidal shear deformation beam model is developed to investigate the free vibration of nanobeams based on the nonlocal strain gradient theory. The new model contains a nonlocal parameter and a material length scale parameter which can capture the size effect. The governing equations and boundary conditions are derived by employing Hamilton's principle. Navier's method is utilized to obtain analytical solutions for natural frequencies of simply supported nanobeams. The results are compared with other beam models and other classical and non-classical theories. Several numerical examples are presented to illustrate the effects of nonlocal parameter, material length scale parameter, slenderness ratio and shear deformation on the free vibration of nanobeams. It is found that natural frequencies predicted by the nonlocal strain gradient theory are higher than those predicted by nonlocal theory and lower than those obtained by strain gradient theory. When the length scale parameter is smaller than the nonlocal parameter, the nanobeam exerts a stiffness-softening effect. When the length scale parameter is larger than the nonlocal parameter, the nanobeam exerts a stiffness-hardening effect. Moreover, it is observed that the effect of shear deformation becomes more significant for nanobeams with lower values of slenderness ratios and for higher modes.