Chirality‐specific lift forces of helix under shear flows: Helix perpendicular to shear plane

Chiral objects in shear flow experience a chirality‐specific lift force. Shear flows past helices in a low Reynolds number regime were studied using slender‐body theory. The chirality‐specific lift forces in the vorticity direction experienced by helices are dominated by a set of helix geometry parameters: helix radius, pitch length, number of turns, and helix phase angle. Its analytical formula is given. The chirality‐specific forces are the physical reasons for the chiral separation of helices in shear flow. Our results are well supported by the latest experimental observations.     

Enrico Ferri’s Scientific Socialism: A Marxist Interpretation of Herbert Spencer’s Organic Analogy

Spencer’s evolutionary philosophy is usually identified with right-wing doctrines such as individualism, laissez-faire liberalism and even conservatism. Since he himself defended similar positions, it is perhaps not surprising that the study of the political interpretations of his ideas has drawn relatively little attention. In this article I propose to examine a rather atypical reading of Spencer’s organic analogy, though definitely not a marginal one: Enrico Ferri’s Marxist doctrine of Scientific Socialism. Ferri is not a figure unknown to scholars interested in the political aspects of the evolutionary debate. Nonetheless, the relation between his theory and Spencer’s bio-sociology – notably the complex dialectic of themes such as “the struggle for existence” versus “class struggle,” or “evolution” versus “revolution” – has not yet received full-length analysis. In my study I investigate the diffusion of Spencer’s ideas in Italy and their impact on the new “positivist” sciences of psychology and sociology inasmuch as these questions are essential to understanding Ferri’s position. Throughout, I stress the importance of the intellectual and political context in the process of appropriation of ideas that led to this unexpected shift in meaning.¹ Spencer, 1843, 1851, 1879–1893, 1884.     

Crystal structure and Raman studies of dsFP483, a cyan fluorescent protein from Discosoma striata

To better understand the diverse mechanisms of spectral tuning operational in fluorescent proteins (FPs), we determined the 2.1-Å X-ray structure of dsFP483 from the reef-building coral Discosoma. This protein is a member of the cyan class of Anthozoa FPs and exhibits broad, double-humped excitation and absorbance bands, with a maximum at 437-440 nm and a shoulder at 453 nm. Although these features support a heterogeneous ground state for the protein-intrinsic chromophore, peak fluorescence occurs at 483 nm for all excitation wavelengths, suggesting a common emissive state. Optical properties are insensitive to changes in pH over the entire range of protein stability. The refined crystal structure of the biological tetramer (space group C2) demonstrates that all protomers bear a cis-coplanar chromophore chemically identical with that in green fluorescent protein (GFP). To test the roles of specific residues in color modulation, we investigated the optical properties of the H163Q and K70M variants. Although absorbance bands remain broad, peak excitation maxima are red shifted to 455 and 460 nm, emitting cyan light and green light, respectively. To probe chromophore ground-state features, we collected Raman spectra using 752-nm excitation. Surprisingly, the positions of key Raman bands of wild-type dsFP483 are most similar to those of the neutral GFP chromophore, whereas the K70M spectra are more closely aligned with the anionic form. The Raman data provide further evidence of a mixed ground state with chromophore populations that are modulated by mutation. Possible internal protonation equilibria, structural heterogeneity in the binding sites, and excited-state proton transfer mechanisms are discussed. Structural alignments of dsFP483 with the homologs DsRed, amFP486, and zFP538-K66M suggest that natural selection for cyan is an exquisitely fine-tuned and highly cooperative process involving a network of electrostatic interactions that may vary substantially in composition and arrangement.     

Structure of the N-terminal Mlp1-binding domain of the Saccharomyces cerevisiae mRNA-binding protein, Nab2

Nuclear abundant poly(A) RNA-binding protein 2 (Nab2) is an essential yeast heterogeneous nuclear ribonucleoprotein that modulates both mRNA nuclear export and poly(A) tail length. The N-terminal domain of Nab2 (residues 1-97) mediates interactions with both the C-terminal globular domain of the nuclear pore-associated protein, myosin-like protein 1 (Mlp1), and the mRNA export factor, Gfd1. The solution and crystal structures of the Nab2 N-terminal domain show a primarily helical fold that is analogous to the PWI fold found in several other RNA-binding proteins. In contrast to other PWI-containing proteins, we find no evidence that the Nab2 N-terminal domain binds to nucleic acids. Instead, this domain appears to mediate protein:protein interactions that facilitate the nuclear export of mRNA. The Nab2 N-terminal domain has a distinctive hydrophobic patch centered on Phe73, consistent with this region of the surface being a protein:protein interaction site. Engineered mutations within this hydrophobic patch attenuate the interaction with the Mlp1 C-terminal domain but do not alter the interaction with Gfd1, indicating that this patch forms a crucial component of the interface between Nab2 and Mlp1.     

后路椎弓根螺钉内固定结合后外侧植骨融合治疗胸腰椎骨折的临床观察

目的：观察后路椎弓根螺钉内固定结合后外侧植骨融合治疗胸腰椎骨折的临床效果及安全性。方法：回顾性分析2010年6月-2012年4月在我院脊柱骨科住院治疗的71例胸腰脊椎骨折患者,所有患者随机被分成2组,治疗组38例接受采用后路椎弓根螺钉内固定结合后外侧植骨融合治疗,对照组33例接受传统椎弓根螺钉内固定。术后对患者椎体前缘高度、脊柱Cobb’s角、腰背痛、神经功能恢复情况、内固定并发症等方面进行手术效果的评价。结果：治疗组术后及随诊患者的椎体前、后缘高度的比值与对照组相比,均有统计学差异（P〈0．05）;治疗组术后及随诊患者的Cobb’s角较对照组明显减小,差异有统计学意义（P〈0．05）,治疗组手术时间与对照组相比差异有统计学意义（P〈0．05）;两组患者医疗费用、神经功能改善筝级相互比较,无统计学意义咿0．05）。结论：后路复位椎弓根螺钉内固定结合后外侧植骨融合治疗胸腰椎骨折的临床疗效确切。     

A reciprocal connection factor for assessing knee-joint function

In the knee joint, interactions between instantaneous kinetics and kinematics associated with ligamentous and articular tissues are not fully understood. These structures may be represented by the instantaneous screw axis ($) (ISA) and static force vectors ($′). Geometric changes to the joint structure affecting motion have not been fully explained, especially after surgical reconstruction and replacement procedures. The ISA offers a joint-characterisation approach, which is dependent on the combined forces of ligaments, articular contacts and muscles. The standard four-bar linkage model in the sagittal plane demonstrates that the normal contact force and the lines of action of the cruciate ligaments always intersect at the centre of rotation of the joint. A kinematic knee model in which the articular surfaces in the lateral and medial compartments as well as the isometric fascicles in the engaged ligaments may be represented as five constraints in a one-degree-of-freedom parallel spatial mechanism. This study provides a theoretical foundation to elucidate the role of each of these elements in the control of the ISA. A recourse to the principle of virtual work explained through d'Alembert's principle for reducing a dynamics problem to an instantaneous static scenario allows screws to be applied to the biomechanics of human motion. The principle of reciprocity links these approaches together to explain the transmitting load between the tibia and the femur as well as the relative motion within the knee joint. A principal clinical implication of this study is the introduction of the reciprocal connection factor to evaluate knee kinematics and kinetics in one simple term, allowing the quantitative assessment of the outcome of knee-joint treatment and rehabilitation methods.     

An approximate model for cancellous bone screw fixation

This paper presents a finite element (FE) model to identify parameters that affect the performance of an improved cancellous bone screw fixation technique, and hence potentially improve fracture treatment. In cancellous bone of low apparent density, it can be difficult to achieve adequate screw fixation and hence provide stable fracture fixation that enables bone healing. Data from predictive FE models indicate that cements can have a significant potential to improve screw holding power in cancellous bone. These FE models are used to demonstrate the key parameters that determine pull-out strength in a variety of screw, bone and cement set-ups, and to compare the effectiveness of different configurations. The paper concludes that significant advantages, up to an order of magnitude, in screw pull-out strength in cancellous bone might be gained by the appropriate use of a currently approved calcium phosphate cement.     

Syntheses, structures, luminescent and magnetic properties of a novel class of metal complexes constructed from 2-(2-pyridyl)benzimidazole and 5-hydroxy-1,3-benzenedicarboxylic acid

Four novel metal coordination polymers, [Zn(2-PBIM)(OH-BDC)]_n (1), [Cd(2-PBIM)(OH-BDC)]_n (2), [Mn(2-PBIM)(OH-BDC)]_n·1.5nH₂O (3), [Cu(2-PBIM)(OH-BDC)]_n·nH₂O (4) [2-PBIM = 2-(2-pyridyl)benzimidazole; OH-H₂BDC = 5-hydroxy-1,3-benzenedicarboxylic acid], have been synthesized under hydrothermal conditions and structurally characterized by single crystal X-ray diffraction analysis, elemental analysis, IR spectroscopy, and thermogravimetric analysis. Compound 1 possesses left-handed screw (M-helix) and right-handed screw (P-helix) chains that are further connected though intermolecular hydrogen bonds and π-π stacking interactions resulting in a three-dimensional (3D) network. Compound 2 has a two-dimensional metal-organic framework which is connected into a 3D network by intermolecular hydrogen bonds and π-π stacking interactions. Compounds 3 and 4 are isostructural and possess one-dimensional (1D) channels. Free 2-PBIM and OH-H₂BDC ligands and complexes 1, 2 show fluorescent emissions in the visible and near-infrared region. Magnetic susceptibility measurements indicate that both 3 and 4 exhibit antiferromagnetic coupling between adjacent center atoms.     

右美托咪定复合丙泊酚全麻在腰椎管减压、椎弓根钉内固定植骨、融合术中的应用

目的:观察右美托咪定复合丙泊酚全麻在腰椎管减压、椎弓根钉内固定植骨融合术中的应用价值。方法:将2015年7月至2019年8月于我院手术治疗84例腰椎退行性疾病患者按随机数字表法分为观察组和对照组,每组42例。观察组于麻醉诱导前静脉泵入0.5μg/kg右美托咪定并在术中以0.2μg/kg·h麻醉维持,对照组于麻醉诱导前静脉泵入生理盐水。对比两组麻醉诱导前(T0)、诱导后(T1)、插管后1 min(T2)和5 min(T3)、拔管1 min(T4)和5 min(T5)的心率(HR)、收缩压(SBP)及舒张压(DBP)的数值,同时记录患者的手术时间、苏醒时间、瑞芬太尼用量及12 h内吗啡用量。比较各时间点VAS评分及不良反应的发生率。结果:与T0比较,两组患者T1时HR、SBP、DBP均显著降低(P<0.05),与T1比较,两组患者T2、T3和T4时HR、SBP、DBP均显著升高(P<0.05),观察组在T3、T4和T5时HR、SBP、DBP均显著降低(P<0.05)。观察组患者各时间点VAS评分及瑞芬太尼用量和24 h吗啡用量均显著低于对照组(P<0.05),观察组患者不良反应发生率显著低于对照组(P<0.05)。结论:右美托咪定复合丙泊酚全麻能够维持术中血液动力学稳定,减少术中麻醉药物和术后镇痛药物用量,改善术后镇痛效果,且不良反应少。     

椎旁肌退变与短节段腰椎融合内固定术后螺钉松动的相关性分析

摘要 目的：分析椎旁肌退变与短节段腰椎融合内固定术后螺钉松动的相关性。方法：回顾性分析2018年6月至2020年6月广州市番禺区中医院行短节段腰椎融合内固定术治疗的251例腰椎退行性疾病患者的临床资料，根据术后螺钉松动情况分为松动组（n=47）和对照组（n=204）。收集患者的临床资料，对比两组椎间植骨融合情况、螺钉直径、螺钉长度、螺钉椎内长度、椎旁肌的肌肉相对总横截面积（rtCSA）和脂肪浸润程度（FI）。应用多因素logistic回归分析短节段腰椎融合内固定术后螺钉松动发生的危险因素，并描绘受试者工作特征（ROC）曲线检验危险因素预测短节段腰椎融合内固定术后螺钉松动的效能。结果：251例患者平均随访时间（24.16±7.28）个月，其中47例患者在最终随访时发生螺钉松动，总体松动率18.73%。两组性别、骨密度比较差异有统计学意义（P＜0.05）。与对照组相比，松动组的多裂肌FI增高（P＜0.05）。与对照组相比，松动组的竖脊肌rtCSA减少，竖脊肌FI增高（P＜0.05）。多因素logistic回归分析显示竖脊肌FI较高是短节段腰椎融合内固定术后螺钉松动发生的独立危险因素，而竖脊肌rtCSA较高、骨密度较高则是保护因素（P＜0.05）。ROC曲线分析显示：骨密度、竖脊肌rtCSA、竖脊肌FI等3指标单独及联合应用时：ROC-AUC（0.95CI）分别为0.708（0.446～0.971）、0.736（0.495～0.951）、0.648（0.335～0.965）、0.842（0.719～0.957）。联合应用预测效能较高。结论：竖脊肌的退变是短节段腰椎融合内固定术后螺钉松动的危险因素。当骨密度＜-3.00 g/cm²、竖脊肌rtCSA＜1.45%及FI＞35.00%时，提示术后发生螺钉松动的可能性大，可作为短节段腰椎融合内固定术后评价螺钉松动风险的参考指标。