Z曲线的理论研究

DNA序列与正四面体(RT)中的映象点(D格点)具有对应关系．一系列D格点形成晶格(D晶格)．D晶格证明是面心立方晶格,并揭示了D格点的空间分布规律．在此基础上得到Z曲线的一些特性,如Z曲线束具有S4群的对称性。Z曲线均在最大正四面体的内切球内等等．     

线粒体遗传密码及基因组遗传密码的对称分析

病毒、细菌和真核生物的氨基酸编码都使用相同的遗传密码,表明它们可能有共同的来源。但人和牛的线粒体的遗传密码和基因组的遗传密码相比,出现以下不同;（1）ATA编码甲硫氮酸M而不是异亮氨酸I。（2）TGA不再是终止密码子X而编码色氨酸W。（3）AGA和AGG不再是精氨酸R的密码子而变为终止密码子X。应用高维空间拓扑分析的方法,对线粒体遗传密码和基因组遗传密码的6维编码空间进行对称性分析,得到如下结果：（1）线粒体遗传密码的起始密码子是2个而不是1个。（2）线粒体遗传密码的终止密码子是4个而不是3个。（3）线粒体遗传密码空间只有2、4、6三种偶数简并度而没1、3两种奇数简并度,表明其对称度较高。（4）线粒体遗传密码空间除丝氨酸S分成两个平行的子空间之外,终止密码子X亦分成两个平行的子空间,表明其连通度较低。（5）线粒体遗传密码一基因组遗传密码相比,共有3个简并平面出现变异,即：1001λλ（M和I）,011λ1λ（W和X）,以及1011λλ（S和X或S和R）。（6）基因组遗传密码的1、3两种奇数简并度可能来源于线粒体遗传密码的1001λλ平面和011λ1λ平面的对称性破缺。对线粒体遗传密码变异的生物学意义及遗传密码的起源进行了分析和讨论。     

Proposing a new index to quantify instantaneous symmetry during manual wheelchair propulsion

Propelling a manual wheelchair (MWC) is a strenuous task that causes upper limb musculoskeletal disorders (MSD) in a large proportion of MWC users. Although most studies on MWC propulsion biomechanics assume that MWC propulsion is a relatively symmetric task, recent literature suggests that this is the case only when the assessed outcome measures are averaged over long periods of time, and not over short periods (i.e., instantaneously). No method is currently available to assess instantaneous symmetry. In this work, we present the Instantaneous Symmetry Index (ISI), a new method that quantifies how a variable has been instantaneously asymmetric during a selected time period. Thirteen experienced MWC users propelled on different cross slopes of 0%, 2%, 4%, 6% and 8%. As the cross slope is increased, the upper hand produced less propulsive moments and the lower hand produced more propulsive movements. This has been reflected in the ISI, which increased from 0.20 (0% slope) to 0.84 (8% slope) with a Spearman׳s coefficient of 0.90. The ISI has great potential to evaluate the ability of a user to propel symmetrically and synchronously, and will be a relevant measure to include in future studies on the impact of MWC propulsion asymmetry on MSD risk.     

How symmetric are metal-on-metal hip resurfacing patients during gait? Insights for the rehabilitation

Metal-on-metal hip resurfacing patients demonstrate hip biomechanics closer to normal in comparison to total hip arthroplasty during gait. However, it is not clear how symmetric is the gait of hip resurfacing patients. Biomechanical data of 12 unilateral metal-on-metal hip resurfacing participants were collected during gait at a mean time of 45 months (SD 24) after surgery. Ankle, knee, hip, pelvis and trunk kinematics and kinetics of both sides were measured with a motion and force-capture system. Principal component analysis and mean hypothesis’ tests were used to compare the operated and healthy sides. The operated side had prolonged ankle eversion angle during late stance and delayed increased ankle inversion angle during early swing (p = 0.008; effect size = 0.70), increased ankle inversion moment during late stance (p = 0.001; effect size = 0.78), increased knee adduction angle during swing (p = 0.044; effect size = 0.57), decreased knee abduction moment during stance (p = 0.05; effect size = 0.40), decreased hip range of motion in the sagittal plane (p = 0.046; effect size = 0.56), decreased range of hip abduction moment during stance (p = 0.02; effect size = 0.63), increased hip range of motion in the transverse plane (p = 0.02; effect size = 0.62), decreased hip internal rotation moment during the transition from loading response to midstance (p = 0.001; effect size = 0.81) and increased trunk ipsilateral lean (p = 0.03; effect size = 0.60). Therefore, hip resurfacing patients have some degree of asymmetry in long term, which may be related to hip weakness and decreased range of motion, to foot misalignments and to strategies implemented to reduce loading on the operated hip. Interventions such as muscle strengthening and stretching, insoles and gait feedback training may help improving symmetry following hip resurfacing.     

Spontaneous deadlock breaking on amoeba-based neurocomputer

Any artificial concurrent computing system involves a potential risk of “deadlock” that its multiple processes sharing common computational resources are stuck in starved conditions, if simultaneous accesses of the processes to the resources were unconditionally permitted. To avoid the deadlock, it is necessary to set up some form of central control protocol capable of appropriately regulating the resource allocation. On the other hand, many decentralized biological systems also perform concurrent computing based on interactions of components sharing limited amounts of available resources. Despite the absence of a central control unit, they appear to be free from the deadlock implying their death, as long as they are alive. Should we consider that biological computing paradigms are essentially different from artificial ones? Here we employ a photosensitive amoeboid cell known as a model organism for studying cellular information processing and construct an experimental system to explore how the amoeba copes with deadlock-like situations induced by optical feedback control. The feedback control is implemented by a recurrent neural network algorithm for leading the amoeba to solve a particular constraint satisfaction problem. We show that the amoeba is capable of breaking through the deadlock-like situations because its oscillating cellular membrane spontaneously produces a wide variety of spatiotemporal patterns. The result implies that our system can be developed to a neurocomputer that works as logical circuit, associative memory device, combinatorial optimization problem solver, and chaotic computer capable of spontaneous transition among multiple solutions.     

The origins of asymmetry in the folding transition states of protein L and protein G

Topology has been shown to be an important determinant of many features of protein folding; however, the delineation of sequence effects on folding remains obscure. Furthermore, differentiation between the two influences proves difficult due to their intimate relationship. To investigate the effect of sequence in the absence of significant topological differences, we examined the folding mechanisms of segment B1 peptostreptococcal protein L and segment B1 of streptococcal protein G. These proteins share the same highly symmetrical topology. Despite this symmetry, neither protein folds through a symmetrical transition state. We analyzed the origins of this difference using theoretical models. We found that the strength of the interactions present in the N-terminal hairpin of protein L causes this hairpin to form ahead of the C-terminal hairpin. The difference in chain entropy associated with the formation of the hairpins of protein G proves sufficient to beget initiation of folding at the shorter C-terminal hairpin. Our findings suggest that the mechanism of folding may be understood by examination of the free energy associated with the formation of partially folded microstates.     

A careful physical analysis of gas bubble dynamics in xylem

Many studies have confirmed that cavitation in xylem is caused by air bubbles. Recently Shen et al. (Tree Physiol. 22 (2002) R655), analysed the expansion of a pre-existent bubble in xylem and one formed by air seeding. The present paper makes a further analysis of bubble expansion by the equilibrium criterion of the Helmholtz function. It has been proved that when xylem pressure P'l decreases to a special value P'l* from a value higher than, or equal to, or lower than -Po (Po is atmospheric pressure), an air bubble in xylem can grow up steadily, corresponding to minimums of the Helmholtz function F(r). As soon as P'l is lower than P'l*, since F(r) will be a decreasing function when P'l < P'l*, resulting in non-equilibrium of the bubble, it will break inducing a cavitation event. The analysis is consistent with the results of mechanism. Given P'l > or = -3Po, if an air bubble could enter a conduit, it would be in a stable equilibrium. When P'l < -3Po an air bubble entering a conduit will be in an unstable equilibrium. As the water further vaporizes, it will break at once. This is the case to which the former published formula P'l = -2sigma/rp is applicable.     

Aurora-A Breaks Symmetry in Contractile Actomyosin Networks Independently of Its Role in Centrosome Maturation

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Using force sensing insoles to predict kinetic knee symmetry during a stop jump

Knee kinetic asymmetries are present during jump-landings in athletes returning to sport following anterior cruciate ligament (ACL) reconstruction, and are associated with an increased risk for sustaining a second ACL injury. The loadsol® is a wireless load sensing insole that can be used in non-laboratory settings. The purpose of this study was to determine if the loadsol® could be used to predict knee extension moment and power symmetry during a bilateral stop jump task in healthy recreational athletes. Forty-two uninjured recreational athletes completed seven bilateral stop jumps. During each landing, the loadsol® (100 Hz) measured plantar load while 3D ground reaction forces (1920 Hz) and lower extremity kinematics (240 Hz) were collected simultaneously. Peak impact force, loading rate, and impulse were quantified using the loadsol® and peak knee extension moment, average knee extension moment, and total knee work was quantified using the laboratory instrumentation. Limb symmetry indices were quantified for each outcome measure. Multivariate backwards regressions were used to determine if loadsol® symmetry could predict knee kinetic symmetry. Intraclass correlation coefficients (ICCs) and Bland-Altman plots were used to determine the agreement and error between predicted and actual knee kinetic symmetry. Loadsol® impulse and peak impact force symmetry significantly predicted kinetic knee symmetry and explained 42–61% of its variance. There was good agreement (ICCs = 0.742–0.862) between predicted and actual knee kinetic symmetry, and the error in the predicted outcomes range from ±18 to ±43. These results support using the loadsol® to screen for kinetic symmetries during landing in athletes following ACL reconstruction.