The ELF4 gene controls circadian rhythms and flowering time in Arabidopsis thaliana

Many plants use day length as an environmental cue to ensure proper timing of the switch from vegetative to reproductive growth. Day-length sensing involves an interaction between the relative length of day and night, and endogenous rhythms that are controlled by the plant circadian clock. Thus, plants with defects in circadian regulation cannot properly regulate the timing of the floral transition. Here we describe the gene EARLY FLOWERING 4 (ELF4), which is involved in photoperiod perception and circadian regulation. ELF4 promotes clock accuracy and is required for sustained rhythms in the absence of daily light/dark cycles. elf4 mutants show attenuated expression of CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), a gene that is thought to function as a central oscillator component. In addition, elf4 plants transiently show output rhythms with highly variable period lengths before becoming arrhythmic. Mutations in elf4 result in early flowering in non-inductive photoperiods, which is probably caused by elevated amounts of CONSTANS (CO), a gene that promotes floral induction.     

A resetting signal between Drosophila pacemakers synchronizes morning and evening activity

The biochemical machinery that underlies circadian rhythms is conserved among animal species and drives self-sustained molecular oscillations and functions, even within individual asynchronous tissue-culture cells. Yet the rhythm-generating neural centres of higher eukaryotes are usually composed of interconnected cellular networks, which contribute to robustness and synchrony as well as other complex features of rhythmic behaviour. In mammals, little is known about how individual brain oscillators are organized to orchestrate a complex behavioural pattern. Drosophila is arguably more advanced from this point of view: we and others have recently shown that a group of adult brain clock neurons expresses the neuropeptide PDF and controls morning activity (small LN(v) cells; M-cells), whereas another group of clock neurons controls evening activity (CRY+, PDF- cells; E-cells). We have generated transgenic mosaic animals with different circadian periods in morning and evening cells. Here we show, by behavioural and molecular assays, that the six canonical groups of clock neurons are organized into two separate neuronal circuits. One has no apparent effect on locomotor rhythmicity in darkness, but within the second circuit the molecular and behavioural timing of the evening cells is determined by morning-cell properties. This is due to a daily resetting signal from the morning to the evening cells, which run at their genetically programmed pace between consecutive signals. This neural circuit and oscillator-coupling mechanism ensures a proper relationship between the timing of morning and evening locomotor activity.     

Adjustment to climate change is constrained by arrival date in a long-distance migrant bird

Spring temperatures in temperate regions have increased over the past 20 years, and many organisms have responded to this increase by advancing the date of their growth and reproduction. Here we show that adaptation to climate change in a long-distance migrant is constrained by the timing of its migratory journey. For long-distance migrants climate change may advance the phenology of their breeding areas, but the timing of some species' spring migration relies on endogenous rhythms that are not affected by climate change. Thus, the spring migration of these species will not advance even though they need to arrive earlier on their breeding grounds to breed at the appropriate time. We show that the migratory pied flycatcher Ficedula hypoleuca has advanced its laying date over the past 20 years. This temporal shift has been insufficient, however, as indicated by increased selection for earlier breeding over the same period. The shift is hampered by its spring arrival date, which has not advanced. Some of the numerous long-distance migrants will suffer from climate change, because either their migration strategy is unaffected by climate change, or the climate in breeding and wintering areas are changing at different speeds, preventing adequate adaptation.     

Circadian rhythms in olfactory responses of Drosophila melanogaster.

The core mechanism of circadian timekeeping in arthropods and vertebrates consists of feedback loops involving several clock genes, including period (per) and timeless (tim). In the fruitfly Drosophila, circadian oscillations in per expression occur in chemosensory cells of the antennae, even when the antennae are excised and maintained in isolated organ culture. Here we demonstrate a robust circadian rhythm in Drosophila in electrophysiological responses to two classes of olfactory stimuli. These rhythms are observed in wild-type flies during light-dark cycles and in constant darkness, but are abolished in per or tim null-mutant flies (per01 and tim01) which lack rhythms in adult emergence and locomotor behaviour. Olfactory rhythms are also abolished in the per 7.2:2 transgenic line in which per expression is restricted to the lateral neurons of the optic lobe. Because per 7.2:2 flies do not express per in peripheral oscillators, our results provide evidence that peripheral circadian oscillators are necessary for circadian rhythms in olfactory responses. As olfaction is essential for food acquisition, social interactions and predator avoidance in many animals, circadian regulation of olfactory systems could have profound effects on the behaviour of organisms that rely on this sensory modality.     

Coupled oscillators control morning and evening locomotor behaviour of Drosophila

Daily rhythms of physiology and behaviour are precisely timed by an endogenous circadian clock. These include separate bouts of morning and evening activity, characteristic of Drosophila melanogaster and many other taxa, including mammals. Whereas multiple oscillators have long been proposed to orchestrate such complex behavioural programmes, their nature and interplay have remained elusive. By using cell-specific ablation, we show that the timing of morning and evening activity in Drosophila derives from two distinct groups of circadian neurons: morning activity from the ventral lateral neurons that express the neuropeptide PDF, and evening activity from another group of cells, including the dorsal lateral neurons. Although the two oscillators can function autonomously, cell-specific rescue experiments with circadian clock mutants indicate that they are functionally coupled.     

Computational approaches to cellular rhythms

Oscillations arise in genetic and metabolic networks as a result of various modes of cellular regulation. In view of the large number of variables involved and of the complexity of feedback processes that generate oscillations, mathematical models and numerical simulations are needed to fully grasp the molecular mechanisms and functions of biological rhythms. Models are also necessary to comprehend the transition from simple to complex oscillatory behaviour and to delineate the conditions under which they arise. Examples ranging from calcium oscillations to pulsatile intercellular communication and circadian rhythms illustrate how computational biology contributes to clarify the molecular and dynamical bases of cellular rhythms.     

Synchronization and rhythmic processes in physiology

Complex bodily rhythms are ubiquitous in living organisms. These rhythms arise from stochastic, nonlinear biological mechanisms interacting with a fluctuating environment. Disease often leads to alterations from normal to pathological rhythm. Fundamental questions concerning the dynamics of these rhythmic processes abound. For example, what is the origin of physiological rhythms? How do the rhythms interact with each other and the external environment? Can we decode the fluctuations in physiological rhythms to better diagnose human disease? And can we develop better methods to control pathological rhythms? Mathematical and physical techniques combined with physiological and medical studies are addressing these questions and are transforming our understanding of the rhythms of life.     

摩托车发动机VVT系统控制策略的分析

针对中小排量摩托车发动机的特点,研制了可切换双进气正时参数VVT系统．以一维CFD计算为基础,建立了摩托车发动机VVT系统的循环仿真模型。在此基础上,对发动机怠速低负荷、中等负荷、低转速高负荷、高转速高负荷不同工况条件下VVTL（Variable Valve Timing and Lifting）运行模式的控制策略进行了详细探讨．结合JH125摩托车发动机所进行的研究表明,VVT系统可以在各种不同工况下实现发动机动力性、经济性以及排放性能的有效提高．     

蜜蜂生物节律研究进展

 生物节律主要指有机体生命活动的内在节律性。蜜蜂生物节律受到其社会性的影响,从而参与许多复杂行为的调控。与果蝇相比,蜜蜂的生物节律与哺乳动物更相似。工蜂和蜂王的生物节律表现出高度的可塑性。例如,工蜂的昼夜节律受其劳动分工形式的调控,并通过与幼蜂的直接接触来调节,哺育蜂昼夜照料幼虫,在行为或时钟基因表达方面没有昼夜节律变化。从蜜蜂的社会性、蜜蜂生物节律产生的分子机制、神经基础、研究方法、可塑性、蜜蜂的睡眠等方面综述了蜜蜂生物节律的研究进展。     

基于DHWPT的脑电基本节律特征提取

脑电中不同类型的基本节律在不同生理条件下特征不同,有效提取这些特征对于实现脑电定量分析具有重要作用。简要分析了谐波小波独特的优势,研究了基于离散谐波小波包方法精确提取脑电基本节律的问题,得到了两种反映节律特征的量化参数:单个导联上各节律在某时刻的频带能量比例(FBER-S)和某一导联脑电信号在某一频段内的能量占所有导联在该频段内能量的百分比(FBER-A)。对临床病例数据分析表明,这两种特征参数呈现的特点与确诊病例的病症特点吻合得很好,说明它们能够作为临床诊断和长时程脑电监护的有效辅助诊断依据。     

擒纵机构参数对钟表机构的计时散布影响研究

针对某弹药定时机构计时散布大的问题,应用理论分析和计算机仿真的方法,研究了尺寸因素对计时的影响问题.在对钟表机构动力学理论分析的基础上,通过对机构进行三维建模和动力学仿真,得出了部分擒纵机构参数对钟表机构计时精度的影响.结果表明,擒纵轮齿顶圆直径与擒纵轮轴与摆轴中心距对钟表机构计时的散布影响较大.     

Dynamics of Mid-Palaeocene North Atlantic rifting linked with European intra-plate deformations

The process of continental break-up provides a large-scale experiment that can be used to test causal relations between plate tectonics and the dynamics of the Earth's deep mantle. Detailed diagnostic information on the timing and dynamics of such events, which are not resolved by plate kinematic reconstructions, can be obtained from the response of the interior of adjacent continental plates to stress changes generated by plate boundary processes. Here we demonstrate a causal relationship between North Atlantic continental rifting at approximately 62 Myr ago and an abrupt change of the intra-plate deformation style in the adjacent European continent. The rifting involved a left-lateral displacement between the North American-Greenland plate and Eurasia, which initiated the observed pause in the relative convergence of Europe and Africa. The associated stress change in the European continent was significant and explains the sudden termination of a approximately 20-Myr-long contractional intra-plate deformation within Europe, during the late Cretaceous period to the earliest Palaeocene epoch, which was replaced by low-amplitude intra-plate stress-relaxation features. The pre-rupture tectonic stress was large enough to have been responsible for precipitating continental break-up, so there is no need to invoke a thermal mantle plume as a driving mechanism. The model explains the simultaneous timing of several diverse geological events, and shows how the intra-continental stratigraphic record can reveal the timing and dynamics of stress changes, which cannot be resolved by reconstructions based only on plate kinematics.     

Research and Implementation of SDH Retiming Mechanism

Synchronization is becoming more and more important with thelarge deployment of SDH network. Retiming， a new means of timing reference transfer means， is presented. The specifications and implementation of retiming mechanism are also discussed. The benefits that were brought by retiming mechanism are also analyzed.