共查询到20条相似文献,搜索用时 0 毫秒
1.
Quantum-enhanced positioning and clock synchronization 总被引:5,自引:0,他引:5
A wide variety of positioning and ranging procedures are based on repeatedly sending electromagnetic pulses through space and measuring their time of arrival. The accuracy of such procedures is classically limited by the available power and bandwidth. Quantum entanglement and squeezing have been exploited in the context of interferometry, frequency measurements, lithography and algorithms. Here we report that quantum entanglement and squeezing can also be employed to overcome the classical limits in procedures such as positioning systems, clock synchronization and ranging. Our use of frequency-entangled pulses to construct quantum versions of these protocols results in enhanced accuracy compared with their classical analogues. We describe in detail the problem of establishing a position with respect to a fixed array of reference points. 相似文献
2.
Periodic somite segmentation in vertebrate embryos is controlled by the 'segmentation clock', which consists of numerous cellular oscillators. Although the properties of a single oscillator, driven by a hairy negative-feedback loop, have been investigated, the system-level properties of the segmentation clock remain largely unknown. To explore these characteristics, we have examined the response of a normally oscillating clock in zebrafish to experimental stimuli using in vivo mosaic experiments and mathematical simulation. We demonstrate that the segmentation clock behaves as a coupled oscillator, by showing that Notch-dependent intercellular communication, the activity of which is regulated by the internal hairy oscillator, couples neighbouring cells to facilitate synchronized oscillation. Furthermore, the oscillation phase of individual oscillators fluctuates due to developmental noise such as stochastic gene expression and active cell proliferation. The intercellular coupling was found to have a crucial role in minimizing the effects of this noise to maintain coherent oscillation. 相似文献
3.
《天津理工大学学报》2017,(3):40-44
随着数字电子系统设计的快速发展,FPGA(现场可编程门阵列)在一些实际应用系统中通常包含有多个不同时钟,而系统功能实现的前提就是要完成数据在多个不同的时钟域之间进行传输,通常会产生亚稳态危害,为了较小亚稳态风险,本文分析了在跨时钟域时系统可能出现的亚稳态问题,提出了在FPGA工程设计中实现不同时钟域间的数据同步方法,对异步FIFO缓存法做了重点介绍.读写地址指针均采用了格雷码的形式,格雷码的特点是的相邻元之间每一次只有一位数据发生变化,所以系统的亚稳态风险会减小,通过Modelsim软件的仿真,验证了异步FIFO的应用可以有效的解决数据的跨时钟域传输问题. 相似文献
4.
Involvement of Notch and Delta genes in spider segmentation 总被引:6,自引:0,他引:6
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通信双方基于时钟漂移破坏协议信息同步问题,提出了一种在时钟漂移下协议信息保持同步的方式。文中首先介绍了现在常用的处理方式,并分析了在时钟漂移下协议同步保持原理,最后根据协议设计在系统设备中进行了验证,证明该方式具备抗时钟漂移的能力。 相似文献
6.
《华东师范大学学报(自然科学版)》2016,(6)
针对正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)采样时钟同步问题,提出了一种适合于软件无线电(Software-.Defined Radio,SDR)接收机的全数字实现方案.该方案的整体结构基于经典的Gardner环路,借助联合迭代估计算法来进行误差的动态跟踪,并通过对接收信号进行异步重采样来实现采样时钟误差的实时校正.误差检测环节不仅能消除载波频率误差的影响,还可以在维持环路的响应速度的同时提高误差检测的精度.误差校正环节利用一种简单的动态延迟技术来对信号重采样进行直接控制,尽管增加了一些处理延迟,但能使重采样过程平稳进行.理论分析和仿真结果表明,新的采样时钟同步方案在多径信道环境中能有效工作,算法的性能优于其他同类算法. 相似文献
7.
Acetylation-dependent regulation of endothelial Notch signalling by the SIRT1 deacetylase 总被引:1,自引:0,他引:1
Guarani V Deflorian G Franco CA Krüger M Phng LK Bentley K Toussaint L Dequiedt F Mostoslavsky R Schmidt MH Zimmermann B Brandes RP Mione M Westphal CH Braun T Zeiher AM Gerhardt H Dimmeler S Potente M 《Nature》2011,473(7346):234-238
Notch signalling is a key intercellular communication mechanism that is essential for cell specification and tissue patterning, and which coordinates critical steps of blood vessel growth. Although subtle alterations in Notch activity suffice to elicit profound differences in endothelial behaviour and blood vessel formation, little is known about the regulation and adaptation of endothelial Notch responses. Here we report that the NAD(+)-dependent deacetylase SIRT1 acts as an intrinsic negative modulator of Notch signalling in endothelial cells. We show that acetylation of the Notch1 intracellular domain (NICD) on conserved lysines controls the amplitude and duration of Notch responses by altering NICD protein turnover. SIRT1 associates with NICD and functions as a NICD deacetylase, which opposes the acetylation-induced NICD stabilization. Consequently, endothelial cells lacking SIRT1 activity are sensitized to Notch signalling, resulting in impaired growth, sprout elongation and enhanced Notch target gene expression in response to DLL4 stimulation, thereby promoting a non-sprouting, stalk-cell-like phenotype. In vivo, inactivation of Sirt1 in zebrafish and mice causes reduced vascular branching and density as a consequence of enhanced Notch signalling. Our findings identify reversible acetylation of the NICD as a molecular mechanism to adapt the dynamics of Notch signalling, and indicate that SIRT1 acts as rheostat to fine-tune endothelial Notch responses. 相似文献
8.
单向时延测量的实时时钟同步算法 总被引:1,自引:0,他引:1
对已有分段聚类算法进行改进,使用软件方法对单向时延序列进行分析,在线检测时钟调整位置.采用变宽度的滑动窗方法对单向时延数据进行过滤,减少时间序列大小,同时保证时钟调整位置信息不丢失.使用自底向上算法对时间序列进行线性分段,检测时钟调整或时钟频率跳变点,算法的时间复杂度大大降低.针对在线时钟同步的要求,为了消除滑动窗不具有离线算法的全局寻优缺点,提出使用基于滑动窗自底向上算法的实时单向时延时钟同步算法.实际测试实验表明:该算法大大降低了时间复杂度并提高了分段精度. 相似文献
9.
The ELF3 zeitnehmer regulates light signalling to the circadian clock 总被引:24,自引:0,他引:24
The circadian system regulates 24-hour biological rhythms and seasonal rhythms, such as flowering. Long-day flowering plants like Arabidopsis thaliana, measure day length with a rhythm that is not reset at lights-off, whereas short-day plants measure night length on the basis of circadian rhythm of light sensitivity that is set from dusk, early flowering 3 (elf3) mutants of Arabidopsis are aphotoperiodic and exhibit light-conditional arrhythmias. Here we show that the elf3-7 mutant retains oscillator function in the light but blunts circadian gating of CAB gene activation, indicating that deregulated phototransduction may mask rhythmicity. Furthermore, elf3 mutations confer the resetting pattern of short-day photoperiodism, indicating that gating of phototransduction may control resetting. Temperature entrainment can bypass the requirement for normal ELF3 function for the oscillator and partially restore rhythmic CAB expression. Therefore, ELF3 specifically affects light input to the oscillator, similar to its function in gating CAB activation, allowing oscillator progression past a light-sensitive phase in the subjective evening. ELF3 provides experimental demonstration of the zeitnehmer ('time-taker') concept. 相似文献
10.
Periodic notch inhibition by lunatic fringe underlies the chick segmentation clock 总被引:15,自引:0,他引:15
The segmented aspect of the vertebrate body plan first arises through the sequential formation of somites. The periodicity of somitogenesis is thought to be regulated by a molecular oscillator, the segmentation clock, which functions in presomitic mesoderm cells. This oscillator controls the periodic expression of 'cyclic genes', which are all related to the Notch pathway. The mechanism underlying this oscillator is not understood. Here we show that the protein product of the cyclic gene lunatic fringe (Lfng), which encodes a glycosyltransferase that can modify Notch activity, oscillates in the chick presomitic mesoderm. Overexpressing Lfng in the paraxial mesoderm abolishes the expression of cyclic genes including endogenous Lfng and leads to defects in segmentation. This effect on cyclic genes phenocopies inhibition of Notch signalling in the presomitic mesoderm. We therefore propose that Lfng establishes a negative feedback loop that implements periodic inhibition of Notch, which in turn controls the rhythmic expression of cyclic genes in the chick presomitic mesoderm. This feedback loop provides a molecular basis for the oscillator underlying the avian segmentation clock. 相似文献
11.
The Drosophila eye, a paradigm for epithelial organization, is highly polarized with mirror-image symmetry about the equator. The R3 and R4 photoreceptors in each ommatidium are vital in this polarity; they adopt asymmetrical positions in adult ommatidia and are the site of action for several essential genes. Two such genes are frizzled (fz) and dishevelled (dsh), the products of which are components of a signalling pathway required in R3, and which are thought to be activated by a diffusible signal. Here we show that the transmembrane receptor Notch is required downstream of dsh in R3/R4 for them to adopt distinct fates. By using an enhancer for the Notch target gene Enhancer of split mdelta, we show that Notch becomes activated specifically in R4. We propose that Fz/Dsh promotes activity of the Notch ligand Delta and inhibits Notch receptor activity in R3, creating a difference in Notch signalling capacity between R3 and R4. Subsequent feedback in the Notch pathway ensures that this difference becomes amplified. This interplay between Fz/Dsh and Notch indicates that polarity is established through local comparisons between two cells and explains how a signal from one position (for example, the equator in the eye) could be interpreted by all ommatidia in the field. 相似文献
12.
Arteries and veins are anatomically, functionally and molecularly distinct. The current model of arterial-venous identity proposes that binding of vascular endothelial growth factor to its heterodimeric receptor--Flk1 and neuropilin 1 (NP-1; also called Nrp1)--activates the Notch signalling pathway in the endothelium, causing induction of ephrin B2 expression and suppression of ephrin receptor B4 expression to establish arterial identity. Little is known about vein identity except that it involves ephrin receptor B4 expression, because Notch signalling is not activated in veins; an unresolved question is how vein identity is regulated. Here, we show that COUP-TFII (also known as Nr2f2), a member of the orphan nuclear receptor superfamily, is specifically expressed in venous but not arterial endothelium. Ablation of COUP-TFII in endothelial cells enables veins to acquire arterial characteristics, including the expression of arterial markers NP-1 and Notch signalling molecules, and the generation of haematopoietic cell clusters. Furthermore, ectopic expression of COUP-TFII in endothelial cells results in the fusion of veins and arteries in transgenic mouse embryos. Thus, COUP-TFII has a critical role in repressing Notch signalling to maintain vein identity, which suggests that vein identity is under genetic control and is not derived by a default pathway. 相似文献
13.
Androutsellis-Theotokis A Leker RR Soldner F Hoeppner DJ Ravin R Poser SW Rueger MA Bae SK Kittappa R McKay RD 《Nature》2006,442(7104):823-826
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15.
Recent evidence indicates that growing blood-vessel sprouts consist of endothelial cells with distinct cell fates and behaviours; however, it is not clear what signals determine these sprout cell characteristics. Here we show that Notch signalling is necessary to restrict angiogenic cell behaviour to tip cells in developing segmental arteries in the zebrafish embryo. In the absence of the Notch signalling component Rbpsuh (recombining binding protein suppressor of hairless) we observed excessive sprouting of segmental arteries, whereas Notch activation suppresses angiogenesis. Through mosaic analysis we find that cells lacking Rbpsuh preferentially localize to the terminal position in developing sprouts. In contrast, cells in which Notch signalling has been activated are excluded from the tip-cell position. In vivo time-lapse analysis reveals that endothelial tip cells undergo a stereotypical pattern of proliferation and migration during sprouting. In the absence of Notch, nearly all sprouting endothelial cells exhibit tip-cell behaviour, leading to excessive numbers of cells within segmental arteries. Furthermore, we find that flt4 (fms-related tyrosine kinase 4, also called vegfr3) is expressed in segmental artery tip cells and becomes ectopically expressed throughout the sprout in the absence of Notch. Loss of flt4 can partially restore normal endothelial cell number in Rbpsuh-deficient segmental arteries. Finally, loss of the Notch ligand dll4 (delta-like 4) also leads to an increased number of endothelial cells within segmental arteries. Together, these studies indicate that proper specification of cell identity, position and behaviour in a developing blood-vessel sprout is required for normal angiogenesis, and implicate the Notch signalling pathway in this process. 相似文献
16.
Differential Notch signalling distinguishes neural stem cells from intermediate progenitors 总被引:1,自引:0,他引:1
During brain development, neurons and glia are generated from a germinal zone containing both neural stem cells (NSCs) and more limited intermediate neural progenitors (INPs). The signalling events that distinguish between these two proliferative neural cell types remain poorly understood. The Notch signalling pathway is known to maintain NSC character and to inhibit neurogenesis, although little is known about the role of Notch signalling in INPs. Here we show that both NSCs and INPs respond to Notch receptor activation, but that NSCs signal through the canonical Notch effector C-promoter binding factor 1 (CBF1), whereas INPs have attenuated CBF1 signalling. Furthermore, whereas knockdown of CBF1 promotes the conversion of NSCs to INPs, activation of CBF1 is insufficient to convert INPs back to NSCs. Using both transgenic and transient in vivo reporter assays we show that NSCs and INPs coexist in the telencephalic ventricular zone and that they can be prospectively separated on the basis of CBF1 activity. Furthermore, using in vivo transplantation we show that whereas NSCs generate neurons, astrocytes and oligodendrocytes at similar frequencies, INPs are predominantly neurogenic. Together with previous work on haematopoietic stem cells, this study suggests that the use or blockade of the CBF1 cascade downstream of Notch is a general feature distinguishing stem cells from more limited progenitors in a variety of tissues. 相似文献
17.
Hellström M Phng LK Hofmann JJ Wallgard E Coultas L Lindblom P Alva J Nilsson AK Karlsson L Gaiano N Yoon K Rossant J Iruela-Arispe ML Kalén M Gerhardt H Betsholtz C 《Nature》2007,445(7129):776-780
In sprouting angiogenesis, specialized endothelial tip cells lead the outgrowth of blood-vessel sprouts towards gradients of vascular endothelial growth factor (VEGF)-A. VEGF-A is also essential for the induction of endothelial tip cells, but it is not known how single tip cells are selected to lead each vessel sprout, and how tip-cell numbers are determined. Here we present evidence that delta-like 4 (Dll4)-Notch1 signalling regulates the formation of appropriate numbers of tip cells to control vessel sprouting and branching in the mouse retina. We show that inhibition of Notch signalling using gamma-secretase inhibitors, genetic inactivation of one allele of the endothelial Notch ligand Dll4, or endothelial-specific genetic deletion of Notch1, all promote increased numbers of tip cells. Conversely, activation of Notch by a soluble jagged1 peptide leads to fewer tip cells and vessel branches. Dll4 and reporters of Notch signalling are distributed in a mosaic pattern among endothelial cells of actively sprouting retinal vessels. At this location, Notch1-deleted endothelial cells preferentially assume tip-cell characteristics. Together, our results suggest that Dll4-Notch1 signalling between the endothelial cells within the angiogenic sprout serves to restrict tip-cell formation in response to VEGF, thereby establishing the adequate ratio between tip and stalk cells required for correct sprouting and branching patterns. This model offers an explanation for the dose-dependency and haploinsufficiency of the Dll4 gene, and indicates that modulators of Dll4 or Notch signalling, such as gamma-secretase inhibitors developed for Alzheimer's disease, might find usage as pharmacological regulators of angiogenesis. 相似文献
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19.
针对陈氏混沌系统提出了两种同步方案:全局同步和不确定参数的自适应同步.基于李亚普诺夫稳定性理论,研究了关于线性反馈耦合全局同步的一般性标准;对于参数未知或不确定的陈氏混沌系统,通过设计适当的控制器和参数自适应律,实现了两种陈氏混沌系统的自适应同步.仿真结果表明:两种同步均能实现陈氏混沌系统指数渐近同步,且同步效果良好,可应用于其他系列混沌系统. 相似文献
20.
首先通过全局分岔图和吸引子图对所研究的Mathieu方程的动力学行为进行了分析.在此基础上,对该方程的混沌同步进行了研究.利用主动同步方法实现了2个不同初值的Mathieu方程间的自同步,同时利用该方法实现了Mathieu方程与非线性陀螺系统间的异结构同步.数值仿真验证了该方法对实现Mathieu方程混沌同步的有效性. 相似文献