A novel polarization converter based on the band-stop frequency selective surface

A dual-passband single-polarized converter based on the band-stop frequency selective surface(FSS)with a low radar cross-section(RCS)is designed in this article.The unit cell of the proposed converter is formed by a polarization layer attached to the band-stop frequency selective surface.The simulation results reveal that the co-polarization reflection coefficients below-10 d B are achieved in 3.82–13.64 GHz with a 112.4%fractional bandwidth(the ratio of the signal bandwidth to the central frequency).Meanwhile,a polarization conversion band is realized from 8.14 GHz to 9.27 GHz with a polarization conversion ratio which is over 80%.Moreover,the 1 d B transmission window is obtained in two nonadjacent bands of 3.42–7.02 GHz and 10.04–13.91 GHz corresponding to the relative bandwidths of 68.9%and 32.3%,respectively.Furthermore,the radar cross-section of the designed structure can be reduced in the wideband from 2.28 GHz to 14 GHz,and the 10 d B RCS reduction in the range of 4.10–13.35 GHz is achieved.In addition,the equivalent circuit model of this converter is established,and the simulation results of the Advanced Design System(ADS)match well with those of CST Microwave Studio(CST).The archetype of the designed converter is manufactured and measured.The experiment results match the simulation results well,which proves the reliability of the simulation results.     

Preparation of Polycaprolactone Tissue Engineering Scaffolds by Improved Solvent Casting/Particulate Leaching Method

The classic solvent casting/particulate leaching method to fabricate PCL scaffolds was improved by using a centrifugal technology, a direct bonding process in preparing salt matrices and a technology of vacuum treatment under heating in the desolvation process. Series operations of preshaping, centrifuging, casting and desolvating were employed during the scaffold's manufacture. The scaffold's properties were characterized including micro‐structures, pore dimensions, porosity and hydrophilicity. The results show that centrifugal technology can improve the pore uniformity of scaffolds. In the bonding process, well‐interconnected porous structures were formed if water content was between 2～7%. The distribution of pore dimensions was from 10 to 80 μm, and the porosities were about 89%. Generally, the porosities formed by vacuum treatment at high temperature are greater than those formed by vacuum treatment at ambient temperature in the desolvation process. The fabricated porous PCL scaffolds with good elasticity and desired thickness could be a good choice for application in soft tissue engineering.     

Solubility of a High Molecular-Weight Bacterial Cellulose in Lithium Chloride/N,N-dimethylacetamide Solution

High molecular-weight bacterial cellulose (BC) was found to be soluble in a lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) solvent system with a maximal concentration of 3 wt% if an activation procedure was performed beforehand. The granular BC was not favored and had to be ground to powders before dissolution. To facilitate subsequent dissolution, an activation procedure consisting of stewing the BC samples at 45°C–50°C in DMAc containing dissolved KMnO₄ was adopted. It was found that a swelling temperature of 45°C was preferred, for about 4 h, but continuous, constant temperature heating during dissolving procedure was unfavorable, possibly due to the instability of the intermediate complex formed between the Li⁺ ion and the carbonyl oxygen of DMAc. However, the BC sample would be gradually dissolved if placed at room temperature for a long enough time.     

Preparation and Characterization of Gelatin–Poly(L-lactic) Acid/Poly(hydroxybutyrate-co-hydroxyvalerate) Composite Nanofibrous Scaffolds

Poly(L-lactic) acid (PLLA) scaffolds, prepared by electrospinning technology, have been suggested for use in tissue engineering. They remain a challenge for application in biological fields due to PLLA's slow degradation and hydrophobic nature. We describe PLLA, PLLA/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), and PLLA/PHBV/gelatin (Gt) composite nanofiberous scaffolds (Gt–PLLA/PHBV) electrospun by changing the electrospinning technology. The morphologies and hydrophilicity of these fibers were characterized by scanning electron microscopy (SEM) and water contact angle measurement. The results showed that the addition of PHBV and Gt resulted in a decrease in the diameters and their distribution and greatly improved the hydrophilicity. The in-vitro degradation test indicated that GT–PLLA/PHBV composite scaffolds exhibited a faster degradation rate than PLLA and PLLA/PHBV scaffolds. Dermal fibroblasts viabilities on nanofibrous scaffolds were characterized by [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide] (MTT) assay and cell morphologies after 7 days culture. Results indicated that the GT–PLLA/PHBV composite nanofibers showed the highest bioactivity among the three scaffolds and increased with increasing time. The SEM images of cells/scaffolds composite materials showed the GT–PLLA/PHBV composite nanofibers enhanced the dermal fibroblasts's adhesion, proliferation, and spreading. It is suggested that the nanofibrous composite scaffolds of GT–PLLA/PHBV composites would be a promising candidate for tissue engineering scaffolds.     

Absorption and quantitative characteristics of C-H bond and O-H bond of NIR

The previous study mainly focused on the interpretation of the relationship between absorption characteristics and quantitative contribution in each near-infrared (NIR) frequency range. Furthermore, the absorption characteristics of NIR mainly cover overtones and combinations of molecular vibrations such as CH, OH, SH, and NH bonds. And it has been know that NIR wavelengths of C-H bond and O-H bond are assigned to different radio frequencies. This paper was intended to investigate the absorption characteristics of bond C-H and O-H bonds in NIR spectral range. Water and acetone which correspond to O-H and C-H bonds have been selected as typical solvents, as well as solutes. Calibration models were established using partial least square regression (PLS) and multiple linear regression (MLR). The parameter of the model were optimized by different spectral pretreatment methods. The result showed that the model set by Savitzky-Golay smooth (SG) in the spectral region of 810–1100 nm could successfully make accurate predictions. Short wave-NIR region has been discovered as optimum characteristic absorption of C-H and O-H bonds.     

Order conditions for RKN methods solving general second-order oscillatory systems

This paper proposes and investigates the multidimensional extended Runge-Kutta-Nyström (ERKN) methods for the general second-order oscillatory system y″ + My = f(y, y′) where M is a positive semi-definite matrix containing implicitly the frequencies of the problem. The work forms a natural generalization of our previous work on ERKN methods for the special system y″ + My = f(y) (H. Yang et al. Extended RKN-type methods for numerical integration of perturbed oscillators, Comput. Phys. Comm. 180 (2009) 1777–1794 and X. Wu et al., ERKN integrators for systems of oscillatory second-order differential equations, Comput. Phys. Comm. 181 (2010) 1873–1887). The new ERKN methods, with coefficients depending on the frequency matrix M, incorporate the special structure of the equation brought by the term My into both internal stages and updates. In order to derive the order conditions for the ERKN methods, an extended Nyström tree (EN-tree) theory is established. The results of numerical experiments show that the new ERKN methods are more efficient than the general-purpose RK methods and the adapted RKN methods with the same algebraic order in the literature.     

Long-Time Oscillatory Energy Conservation of Total Energy-Preserving Methods for Highly Oscillatory Hamiltonian Systems

For an integrator when applied to a highly oscillatory system,the near conservation of the oscillatory energy over long times is an important aspect.In this paper,we study the long-time near conservation of oscillatory energy for the adapted average vector field(AAVF)method when applied to highly oscillatory Hamiltonian systems.This AAVF method is an extension of the average vector field method and preserves the total energy of highly oscillatory Hamiltonian systems exactly.This paper is devoted to analysing another important property of AAVF method,i.e.,the near conservation of its oscillatory energy in a long term.The long-time oscillatory energy conservation is obtained via constructing a modulated Fourier expansion of the AAVF method and deriving an almost invariant of the expansion.A similar result of the method in the multi-frequency case is also presented in this paper.     

Matrix optimization based Euclidean embedding with outliers

Euclidean embedding from noisy observations containing outlier errors is an important and challenging problem in statistics and machine learning. Many existing methods would struggle with outliers due to a lack of detection ability. In this paper, we propose a matrix optimization based embedding model that can produce reliable embeddings and identify the outliers jointly. We show that the estimators obtained by the proposed method satisfy a non-asymptotic risk bound, implying that the model provides a high accuracy estimator with high probability when the order of the sample size is roughly the degree of freedom up to a logarithmic factor. Moreover, we show that under some mild conditions, the proposed model also can identify the outliers without any prior information with high probability. Finally, numerical experiments demonstrate that the matrix optimization-based model can produce configurations of high quality and successfully identify outliers even for large networks.

     

A Camptothecin‐Grafted DNA Tetrahedron as a Precise Nanomedicine to Inhibit Tumor Growth

Most chemotherapeutics are hydrophobic molecules and need to be converted into hydrophilic form before administration. Based on the excellent hydrophilicity and programmability of DNA, now, a general strategy to construct a precise drug‐containing DNA framework for cancer treatment is reported. In this novel drug delivery system, carbonethyl bromide‐modified camptothecin (CPT) is employed to directly react with phosphorothioate (PS) modified DNAs, resulting in the formation of chemotherapeutics‐grafted DNAs with a responsive disulfide linkage. By tuning the number and site of PS modifications on DNA strands, hydrophilicity of the obtained DNA‐drug conjugates (DDCs) can be regulated to retain their aqueous solubility and capability of molecular recognition. Subsequently, programmable DNA nanotechnology enables the self‐assembly of a precise drug‐containing tetrahedral framework with stimuli‐responsive feature and enhanced antitumor efficacy both in vitro and in vivo.