Impact sensitivities of energetic materials: Exploring the limitations of a model based only on structural formulas

Using a comprehensive set of drop weight impact test data (h₅₀) newly compiled from literature for 308 materials, a recent approach to predict impact sensitivities of nitro compounds is generalized to most explosive substances of interest. Compared to previous ones, this procedure is more thoroughly validated and exhibits a good predictive value. Furthermore, it yields new insight into the physical mechanisms involved, explaining for instance the unexpected desensitization of some oxygen-deficient triazoles upon nitration.     

Robust skin detection in real-world images

Human skin detection in images is desirable in many practical applications, e.g., human–computer interaction and adult-content filtering. However, existing methods are mainly suffer from confusing backgrounds in real-world images. In this paper, we try to address this issue by exploring and combining several human skin properties, i.e. color property, texture property and region property. First, images are divided into superpixels, and robust skin seeds and background seeds are acquired through color property and texture property of skin. Then we combining color, region and texture properties of skin by proposing a novel skin color and texture based graph cuts (SCTGC) to acquire the final skin detection results. Comprehensive and comparative experiments show that the proposed method achieves promising performance and outperforms many state-of-the-art methods over publicly available challenging datasets with a great part of hard images.     

组合式火箭爆破器系统飞行性算法研究

为提高爆炸带的展直率,确保火箭爆破器的破障效果,建立二维有限质点模型对火箭爆破器系统的飞行特性进行研究。根据力学方程、运动方程和几何连续方程,通过时间差分法对各质点的力学参数进行数值计算,并结合实验工况对火箭爆破器系统在空中飞行的力学特性进行计算分析。结果表明:在主动段中,火箭拖拽爆炸带加速运动,爆炸带保持直线拉直状态;爆炸带全部拉出后,由于阻力伞的作用,爆炸带的内力较大,仍能维持在展直状态;进入被动段后,随着火箭及爆炸带速度的下降,阻力伞对爆炸带的拉力随之下降,爆炸带在越过最高点后,下落的阶段容易发生弯曲。     

Mechanical behavior of cold-water fish gelatin gels crosslinked with 1,4-butanediol diglycidyl ether

In this work, chemical crosslinking with 1,4-butanediol diglycidyl ether (BDDGE) is used as strategy to enhance mechanical performance of fish gelatin (FG) gels in order to meet the properties' range of mammalian gelatin physical gels. Joint analysis of free amino groups, swelling ratio, and total soluble material indicates that crosslinking degree increases with increasing FG concentration and it is favored by a 0.2 BDDGE/FG ratio. Increasing crosslinking degree enhances gel indentation strength and shear modulus (μ) while decreases fracture toughness (G_IC). Measured μ and G_IC values lies within the range exhibited by mammalian gelatin physical gels, but the relationship between these parameters is opposite. This is due to the different fracture mechanisms occurring in chemically crosslinked and physical gels.     

Output feedback tracking control for rigid body attitude via immersion and invariance angular velocity observers

A novel immersion and invariance (I&I) angular velocity observer is presented for the attitude tracking control of a rigid body with the lack of angular rate. Global exponential convergence of angular velocity estimate errors are guaranteed by an innovative filter design for the estimates' Euclidean norm. The proposed method requires fewer filter states compared with existing I&I angular velocity observer designs, which achieves a simpler closed-loop structure (dynamic reduction). The observer synthesis and convergence are independent of the control torque, which leads to much convenience in establishing “separation property” when combining a proportional-derivative attitude tracking controller driven by angular velocity estimates. A rigorous stability analysis is provided to ensure the (almost) global asymptotic convergence of the overall closed-loop tracking errors, and several numerical simulations are carried out to demonstrate the effectiveness of the combined implementation of proposed angular velocity observer and full-state feedback attitude tracking controller.     

Effect of Pluronic F127 on the 3D pore morphology of poly(N-isopropylacrylamide-co-acrylic acid) hydrogels and their nitric oxide release from S-nitrosoglutathione

Changing the pore morphology of hydrogels can be an effective strategy to modulate their drug release profiles. Herein, Pluronic F127 was used to change the three-dimensional pore morphology of crosslinked poly(N-isopropylacrylamide-co-acrylic acid) (P[NIPAm-co-AAc]) hydrogels. F127 reduced the pore diameters from 20 ± 4 to 2.9 ± 0.4 μm and from 11 ± 1 to 1.4 ± 0.4 μm in hydrogels synthesized at 8 and 30°C, respectively. Small-angle X-ray scattering indicates that the segregation of the F127 during the polymerization process induces F127 phase transitions from unimers (at 8°C) or cubic-packed micelles (at 30°C) to a lamellar structure. P(NIPAm-co-AAc) hydrogels charged with S-nitrosoglutathione (GSNO), released nitric oxide (NO) spontaneously during hydration. The decrease in the pore diameter led to a twofold to threefold increase in the rate of water absorption and a fourfold to sixfold increase in the rate of NO release of the hydrogels. F127 can be used to change the pore morphology of P(NIPAm-co-AAc) hydrogels, with concomitant changes in their rate of hydration and NO release from GSNO, opening a new perspective for their use in topical NO delivery.     

亲水性PET共混材料的制备及性能研究

以机械共混法制备亲水性聚对苯二甲酸乙二醇酯（PET）共混材料，并通过接触角测定仪、差示扫描量热仪(DSC)和电子万能材料试验机等对共混材料的亲水性能、热性能和力学性能等进行研究与分析。结果表明，亲水处理剂聚乙二醇（PEG）、聚丙烯酸钠（PAAS）、聚乙烯吡咯烷酮（PVP）均能改善PET的亲水性能，影响PET的结晶性能，但亲水处理剂对PET的力学性能影响较小，其中PET/PEG共混材料的亲水性最优；随着PEG含量的增加，PET/PEG共混材料的亲水性先逐渐增强，当PEG含量高于5 %后，共混材料的亲水性变化很小；且PET的结晶度随着PEG的加入呈现先增大后减小的趋势。     

Rheological properties and gel characteristics of polysaccharides from fruit-bodies of Sparassis crispa

Rheological properties and gel characteristics of Sparassis crispa polysaccharides (SCPs) were investigated under various concentrations, temperature, pH, salt concentrations, and sucrose concentrations. SCP solutions behaved as shear thinning pseudoplastic fluids; apparent viscosity increased with concentrations but decreased with extreme conditions and was highest for 1% SCPs at 80 ℃ under neutral conditions; 5% SCPs solutions formed a hysteresis loop and exhibited thixotropic properties. By oscillatory measurements, SCPs were viscoelastic materials. 0.5% and 1% SCPs solutions exhibited viscous behavior at low frequency and enhanced elastic property with the oscillation frequency increased. With the concentration increased to 3% and 5%, the elastic property was predominant in solutions and exhibited gel-like behavior. SCPs gel textural properties and water holding capacity increased with concentration (to 20%) and decreased with salinity, extreme sucrose, and pH. 10% SCPs gels were optimized at 10% sucrose in neutral conditions. Thus, these results implied SCPs had the potential utilization as a new hydrocolloid source in food industries.     

分子筛协同有机磷酸盐改性聚丙烯性能的研究

采用直接混合法制得等规聚丙烯(iPP)/分子筛体系和iPP/有机磷酸盐成核剂(NA11)/分子筛体系,研究不同种类分子筛在不同含量下对iPP结晶温度及力学性能的影响,进而研究不同分子筛在低含量下协同有机磷酸盐对iPP体系成核性能的影响,从动力学角度解释了提升原因。结果表明,单独添加分子筛制得的iPP体系,随着分子筛含量的增加,结晶性能和力学性能得到显著提升,不同分子筛对iPP性能的影响不同,ZSM-5型分子筛在含量为5%(质量分数,下同)以上具有促进iPPβ晶型生成的效果;采用直接混合法制得的不同分子筛复配有机磷酸酯钠盐NA11成核剂可提升iPP的力学性能;特别是当0.1%NA11和0.1%4A型分子筛一起添加到iPP中时,可在保证iPP具有较好刚性的同时兼具有良好的韧性,使iPP的弯曲模量提高35.2%、冲击强度提高14.4%,从而达到促进iPP材料刚韧平衡的效果。     

Effects of nisin concentration on properties of gelatin film-forming solutions and their films

The addition of nisin into a gelatin matrix can change properties of the film. The aim of this work was to develop gelatin-based films containing different nisin concentrations in order to study their influence on the film's antimicrobial and physical properties and their rheological properties as a film-forming solution (FFS). The FFS was characterised by rheological assays, and the gelatin-based active films were characterised and assessed by the effects of nisin concentrations on their various properties, including antimicrobial activity. Nisin's concentration affected not only its viscoelastic properties of FFS but also its film solubility in water, film surface roughness and light barrier. The addition of nisin also slightly modified the water contact angle and the mechanical properties of the gelatin films. Finally, the films demonstrated activity against Staphylococcus aureus and Listeria monocytogenes at concentrations above 56 mg of nisin g⁻¹ of gelatin.