Orientational Susceptibility and Elastic Constants Near the Nematic-Isotropic Phase Transition for Trimers with Terminal-Lateral-Lateral-Terminal Connections

Magnetically induced Freedericksz measurements were performed in the nematic liquid crystal phase to extract the elastic constants of a terminal-lateral-lateral-terminal trimer, i.e., a trimer in which the connections to the first and third mesogens are at the end of the mesogen and both attachments to the central mesogen are lateral. Polymeric liquid crystals based on this unit have negative Poisson ratios. Additionally, electric field Kerr measurements were performed in the isotropic phase to extract the orientational susceptibility. The elastic constants were found to be similar to values obtained for typical monomers, albeit with a slightly enhanced ratio K-33/K-11 and reduced ratio K-11/K-22 especially near the transition temperature. The temperature dependence of the susceptibility was found to deviate significantly from that of typical monomers. The observed behavior is discussed in terms of coupled order parameters representing the terminal and core mesogens of the molecule

Pretransitional Behavior Above the Nematic-Isotropic Phase Transition of an Auxetic Trimer Liquid Crystal

Static Light scattering and electric field-induced Kerr measurements were performed above the nematic-isotropic phase transition of a terminal-lateral-lateral-terminal negative Poisson ratio trimer. Far both measurements the inverse susceptibility was observed to be nearly linear with temperature, a result inconsistent with our previously reported Kerr data [Phys. Rev. E 58, 2041 (1998)]. [S1063-651X(99)11010-9]

Structures and Properties of Liquid-Crystalline Polymers Based on Laterally Attached Oligo \u3ci\u3ep\u3c/i\u3e-Phenylenes

The structures and properties of liquid‐crystalline polymers containing laterally attached p‐terphenyl and p‐pentaphenyl have been studied. In contrast to their mesogenic groups, that is, p‐terphenyl and p‐pentaphenyl, the polymers have much lower crystallinity and also lower nematic‐to‐isotropic transition temperatures. The significant depression in crystallinity can be attributed to flexible chain segments laterally attached to the oligo p‐phenylene rods, which prevent close packing of the rods and thus disrupt the crystallization. The destabilization of the liquid‐crystalline phase is due to the diluting effect of the flexible polymer backbones; that is, the concentration of the mesogenic groups is reduced. The polymer containing p‐pentaphenyl can still exhibit good solubility in common solvents and emit light at about 402 nm in the solvent tetrahydrofuran. In the solid state, the emission redshifts to 418 nm, which is fairly close to the blue‐light emission. An interdigitated packing structure of mesogenic groups has been proposed to represent the structure of the polymer in the oriented state. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3394–3402, 200

Spatial-Temporal Pattern and Influencing Factors of Land Ecological Carrying Capacity in The National Pilot Zones for Ecological Conservation in China

Improving land ecological carrying capacity (LECC) is important in accelerating the realization of national ecological civilization construction goals. Based on the panel data of the first batch of prefecture-level cities in the National Pilot Zones for Ecological Conservation initiative from 2005 to 2019, this study analyzes the spatial–temporal pattern of LECC using the improved ecological footprint model, Theil–Sen’s slope estimator and Mann–Kendall test, and investigates the influencing factors of LECC using the geodetector. Results show that the overall land ecological carrying status of each province tends to improve but also shows remarkable interprovincial differences in development trend, with Guizhou outperforming Jiangxi and Fujian in general. The pattern of LECC security has apparent regional heterogeneity. Most prefecture-level cities have high ecological pressure and uneven spatial distribution but slowly improve overall. The influencing factor of forest land coverage and population density has strong explanatory power on the LECC, and the interactions among the factors are enhanced. The four aspects of land ecological construction should be carried out. A first step is to strengthen land ecological management and optimize the land use practices actively. Second, modern technology is used to establish real-time monitoring and early warning systems for LECC security. Third, the two key factors of forest land coverage and population density should be focused on, and enhancing their positive interaction with industrial structure and arable land utilization rate. Finally, the experience of model construction should be promoted in the Non-national Pilot Zones for Ecological Conservation in China. The aim is to enhance the effectiveness of land ecology measures further and promote the construction of national ecological civilization in China

Spatial-Temporal Pattern and Influencing Factors of Land Ecological Carrying Capacity in The National Pilot Zones for Ecological Conservation in China

Improving land ecological carrying capacity (LECC) is important in accelerating the realization of national ecological civilization construction goals. Based on the panel data of the first batch of prefecture-level cities in the National Pilot Zones for Ecological Conservation initiative from 2005 to 2019, this study analyzes the spatial–temporal pattern of LECC using the improved ecological footprint model, Theil–Sen’s slope estimator and Mann–Kendall test, and investigates the influencing factors of LECC using the geodetector. Results show that the overall land ecological carrying status of each province tends to improve but also shows remarkable interprovincial differences in development trend, with Guizhou outperforming Jiangxi and Fujian in general. The pattern of LECC security has apparent regional heterogeneity. Most prefecture-level cities have high ecological pressure and uneven spatial distribution but slowly improve overall. The influencing factor of forest land coverage and population density has strong explanatory power on the LECC, and the interactions among the factors are enhanced. The four aspects of land ecological construction should be carried out. A first step is to strengthen land ecological management and optimize the land use practices actively. Second, modern technology is used to establish real-time monitoring and early warning systems for LECC security. Third, the two key factors of forest land coverage and population density should be focused on, and enhancing their positive interaction with industrial structure and arable land utilization rate. Finally, the experience of model construction should be promoted in the Non-national Pilot Zones for Ecological Conservation in China. The aim is to enhance the effectiveness of land ecology measures further and promote the construction of national ecological civilization in China

A Modular Cooperative Wall-Climbing Robot Based on Internal Soft Bone

Most existing wall-climbing robots have a fixed range of load capacity and a step distance that is small and mostly immutable. It is therefore difficult for them to adapt to a discontinuous wall with particularly large gaps. Based on a modular design and inspired by leech peristalsis and internal soft-bone connection, a bionic crawling modular wall-climbing robot is proposed in this paper. The robot demonstrates the ability to handle variable load characteristics by carrying different numbers of modules. Multiple motion modules are coupled with the internal soft bone so that they work together, giving the robot variable-step-distance functionality. This paper establishes the robotic kinematics model, presents the finite element simulation analysis of the model, and introduces the design of the multi-module cooperative-motion method. Our experiments show that the advantage of variable step distance allows the robot not only to quickly climb and turn on walls, but also to cross discontinuous walls. The maximum climbing step distance of the robot can reach 3.6 times the length of the module and can span a discontinuous wall with a space of 150 mm; the load capacity increases with the number of modules in series. The maximum load that N modules can carry is about 1.3 times the self-weight

Alternating Positive and Negative Feedback Control Model Based on Catastrophe Theories

In automatic control systems, negative feedback control has the advantage of maintaining a steady state, while positive feedback control can enhance some activities of the control system. How to design a controller with both control modes is an interesting and challenging problem. Motivated by it, on the basis idea of catastrophe theories, taking positive feedback and negative feedback as two different states of the system, an adaptive alternating positive and negative feedback (APNF) control model with the advantages of two states is proposed. By adaptively adjusting the relevant parameters of the constructed symmetric catastrophe function and the learning rule based on error and forward weight, the two states can be switched in the form of catastrophe. Through the Lyapunov stability theory, the convergence of the proposed adaptive APNF control model is proven, which indicates that system convergence can be guaranteed by selecting appropriate parameters. Moreover, we present theoretical proof that the negative feedback system with negative parameters can be equivalent to the positive feedback system with positive parameters. Finally, the results of the simulation example show that APNF control has satisfactory performance in response speed and overshoot

Meta-analysis of the potential role of extracorporeal shockwave therapy in osteonecrosis of the femoral head

Abstract Background We aimed to evaluate the role of extracorporeal shockwave therapy (ESWT) in improving osteonecrosis of the femoral head (ONFH). Methods We searched studies focusing on the role of ESWT in ONFH using PubMed, Embase, the Cochrane Library, WanFang, VIP, and CNKI databases updated up to July 28, 2017, without language restriction. Standardized mean difference (SMD) values and 95% confidence intervals (95% CIs) were pooled to compare the pain score and Harris hip score for ESWT treatment and other treatment strategies. Results Four articles, including 230 ONFH patients, were eligible for the meta-analysis. No significant differences were found in the pain score (SMD = − 1.0104; 95% CI − 2.3279–0.3071) and Harris hip score (SMD = 0.3717; 95% CI − 0.3125–1.0559) between the two groups before treatment. After treatment, significant differences were found between the experimental and control groups in the pain score (SMD = − 2.1148; 95% CI − 3.2332–0.9965) and Harris hip score (SMD = 2.1377; 95% CI 1.2875–2.9880). There were no significant differences in pain score before and after treatment between the two groups (SMD = − 0.7353; 95% CI − 2.1272–0.6566), but significant differences were found in the Harris hip score (SMD = 1.2969; 95% CI 0.7171–1.8767). Conclusion For patients at an early stage, ESWT may be safe and effective for relief of pain and improvement of motor function

The relationship between apolipoprotein genes polymorphisms and susceptibility to osteonecrosis of the femoral head: a meta-analysis

Abstract Background The objective of this study was to evaluate whether apolipoprotein gene polymorphisms confer susceptibility to osteonecrosis of the femoral head (ONFH). Methods The relevant literature was screened from databases of Pubmed, Embase, Wanfang, Weipu and China National Knowledge Internet (CNKI) until May, 2017. In addition, odds ratio (OR) and its corresponding 95% confidence interval (CI) were used as a measure of effect size for calculating effect size. Results Totally, six case-control studies were included in this meta-analysis. It revealed that ApoB-C7623T polymorphism frequency was increased in ONFH group than in control group under three genetic models, including allele model (T vs. C, OR = 4.5149, 95% CI: 1.6968–12.0134); additive model (TC vs. CC, OR = 6.2515, 95% CI: 2.0939–18.6640); and dominant model (TT + TC vs. CC, OR = 5.4998, 95% CI: 1.9246–15.7163). In addition, the increased risk of ONFH were related to ApoA1-rs1799837 polymorphism under additive model (AA vs. GG, OR = 1.4175, 95% CI: 1.0522–1.9096) and recessive model (AA vs. GG + AG, OR = 1.7727, 95% CI: 1.3399–2.3452). However, four ApoB rs1042031, rs693, 3’-VNTR and G12619A polymorphisms under the all genetic models were not associated with susceptibility to ONFH. Conclusion The T allele and TC genotype of ApoB-C7623T and AA genotype of ApoA1-rs1799837 may contribute to increase the risk of ONFH