Entrainment of a population of synthetic genetic oscillators

Biological clocks are self-sustained oscillators that adjust their phase to the daily environmental cycles in a process known as entrainment. Molecular dissection and mathematical modeling of biological oscillators have progressed quite far, but quantitative insights on the entrainment of clocks are relatively sparse. We simultaneously tracked the phases of hundreds of synthetic genetic oscillators relative to a common external stimulus to map the entrainment regions predicted by a detailed model of the clock. Synthetic oscillators were frequency-locked in wide intervals of the external period and showed higher-order resonance. Computational simulations indicated that natural oscillators may contain a positive-feedback loop to robustly adapt to environmental cycles.     

Electron coherence in a melting lead monolayer

We used angle-resolved photoemission spectroscopy to measure the electronic dispersion and single-particle spectral function in a liquid metal. A lead monolayer supported on a copper (111) surface was investigated as the temperature was raised through the melting transition of the film. Electron spectra and momentum distribution maps of the liquid film revealed three key features of the electronic structure of liquids: the persistence of a Fermi surface, the filling of band gaps, and the localization of the wave functions upon melting. Distinct coherence lengths for different sheets of the Fermi surface were found, indicating a strong dependence of the localization lengths on the character of the constituent atomic wave functions.     

榧树天然群体中种子表型特征与化学成分的变异分析

对安徽省黄山市天然榧树Torreya grandis群体内种子表型性状和化学成分的变异进行分析研究,为优良榧树种质资源收集、品种选育及榧树遗传研究奠定基础。结果表明:①种蒲质量、种蒲横径、种蒲纵径、种核横径、种核纵径、种核质量、种形指数、核形指数和出核率的变幅分别为5.24～12.23 g,1.963～3.018 cm,2.255～3.685 cm,1.438～2.270 cm,2.009～3.208 cm,2.30～5.19 g,0.695～0.902,0.555～0.823,34.80%～66.49%;②营养成分粗脂肪、淀粉和蛋白质的质量分数变幅分别为232.96～425.54 g·kg-1,59.95～114.40 g·kg-1和153.22～231.85 g·kg-1;矿质元素磷、钾、钙、镁、铜、锌、锰和镉的变幅分别为0.81～2.29 g·kg-1,23.90～53.72 g·kg-1,80.18～224.38 mg·kg-1,765.84～798.57 mg·kg-1,8.10～31.60 mg·kg-1,40.43～128.00 mg·kg-1,1.45～23.32 mg·kg-1,0.01～0.11 mg·kg-1;多数单株样品砷和铅呈现未检出状态;③种蒲质量、种蒲横径、种蒲纵径、种核横径、种核纵径及种核质量两两之间极显著正相关(P<0.01);种蒲和种核的形状与质量的关系无规律;种蒲质量与种形指数、种核质量与核形指数之间无明显的相关关系,而种核质量与种形指数之间存在显著的负相关关系(P<0.05);出核率与种蒲横径、种蒲纵径、种核横径、种核纵径均存在极显著的负相关(P<0.01),与种核指数极显著正相关(P<0.01),与种形指数无显著的相关关系;3种营养成分质量分数之间不存在任何的相关关系,除粗脂肪与种核质量间存在显著的负相关关系外(P<0.05),营养成分与种子表型性状及矿质元素间不存在相关关系。钾与镁、铜与磷、铜与锰的质量分数间均存在显著的正相关(P<0.01);锰的质量分数与种形指数和核形指数间呈极显著正相关(P<0.01)。     

Mesoscopic phase coherence in a quantum spin fluid

Mesoscopic quantum phase coherence is important because it improves the prospects for handling quantum degrees of freedom in technology. Here we show that the development of such coherence can be monitored using magnetic neutron scattering from a one-dimensional spin chain of an oxide of nickel (Y2BaNiO5), a quantum spin fluid in which no classical static magnetic order is present. In the cleanest samples, the quantum coherence length is 20 nanometers, which is almost an order of magnitude larger than the classical antiferromagnetic correlation length of 3 nanometers. We also demonstrate that the coherence length can be modified by static and thermally activated defects in a quantitatively predictable manner.     

Synchronized oscillation in coupled nanomechanical oscillators

We report measurements of synchronization in two nanomechanical beam oscillators coupled by a mechanical element. We charted multiple regions of frequency entrainment or synchronization by their corresponding Arnold's tongue diagrams as the oscillator was driven at subharmonic and rational commensurate frequencies. Demonstration of multiple synchronized regions could be fundamentally important to neurocomputing with mechanical oscillator networks and nanomechanical signal processing for microwave communication.     

Temperature as a universal resetting cue for mammalian circadian oscillators

Environmental temperature cycles are a universal entraining cue for all circadian systems at the organismal level with the exception of homeothermic vertebrates. We report here that resistance to temperature entrainment is a property of the suprachiasmatic nucleus (SCN) network and is not a cell-autonomous property of mammalian clocks. This differential sensitivity to temperature allows the SCN to drive circadian rhythms in body temperature, which can then act as a universal cue for the entrainment of cell-autonomous oscillators throughout the body. Pharmacological experiments show that network interactions in the SCN are required for temperature resistance and that the heat shock pathway is integral to temperature resetting and temperature compensation in mammalian cells. These results suggest that the evolutionarily ancient temperature resetting response can be used in homeothermic animals to enhance internal circadian synchronization.     

Periodicity and chaos in coupled nonlinear oscillators

A system of coupled tunnel diode relaxation oscillators shows a variety of complex periodic states as the external voltage is varied. The existence of chaotic or nonperiodic states is more dependent on the nature of the coupling than on the number of degrees of freedom. A simple but accurate numerical model shows many of the phenomena observed experimentally.     

Neuronal coherence as a mechanism of effective corticospinal interaction

Neuronal groups can interact with each other even if they are widely separated. One group might modulate its firing rate or its internal oscillatory synchronization to influence another group. We propose that coherence between two neuronal groups is a mechanism of efficient interaction, because it renders mutual input optimally timed and thereby maximally effective. Modulations of subjects' readiness to respond in a simple reaction-time task were closely correlated with the strength of gamma-band (40 to 70 hertz) coherence between motor cortex and spinal cord neurons. This coherence may contribute to an effective corticospinal interaction and shortened reaction times.     

中国芦花鸡中出现马立克氏病

首次报道了中国特有鸡种--芦花鸡马立克氏病的发病情况.山东某养殖场散养的芦花鸡,于开产前出现颜面苍白,机体进行性消瘦,瘫痪,最后衰竭死亡,死亡率达10%.经大体剖检发现,病鸡的内脏器官有不同程度的增大,在肝、肾等器官出现散在的肿瘤样结节,经组织学检查发现,增生的病灶中心为多种细胞成分,包括大、中、小淋巴细胞和网状细胞.用I型马立克氏病(Marek's disease , MD) 的特异性引物132 bpr(132 bp repeat)进行PCR检测,阳性率为88.9%(8/9);3 个阳性PCR产物测序,其基因序列与MDVGA原型株的同源性分别为95.89%、97.96%和97.52%,上述检测表明此肿瘤是由MDV感染引起的.     

Communication through a diffusive medium: coherence and capacity

Coherent wave propagation in disordered media gives rise to many fascinating phenomena as diverse as universal conductance fluctuations in mesoscopic metals and speckle patterns in light scattering. Here, the theory of electromagnetic wave propagation in diffusive media is combined with information theory to show how interference affects the information transmission rate between antenna arrays. Nontrivial dependencies of the information capacity on the nature of the antenna arrays are found, such as the dimensionality of the arrays and their direction with respect to the local scattering medium. This approach provides a physical picture for understanding the importance of scattering in the transfer of information through wireless communications.     

Resetting central and peripheral circadian oscillators in transgenic rats

In multicellular organisms, circadian oscillators are organized into multitissue systems which function as biological clocks that regulate the activities of the organism in relation to environmental cycles and provide an internal temporal framework. To investigate the organization of a mammalian circadian system, we constructed a transgenic rat line in which luciferase is rhythmically expressed under the control of the mouse Per1 promoter. Light emission from cultured suprachiasmatic nuclei (SCN) of these rats was invariably and robustly rhythmic and persisted for up to 32 days in vitro. Liver, lung, and skeletal muscle also expressed circadian rhythms, which damped after two to seven cycles in vitro. In response to advances and delays of the environmental light cycle, the circadian rhythm of light emission from the SCN shifted more rapidly than did the rhythm of locomotor behavior or the rhythms in peripheral tissues. We hypothesize that a self-sustained circadian pacemaker in the SCN entrains circadian oscillators in the periphery to maintain adaptive phase control, which is temporarily lost following large, abrupt shifts in the environmental light cycle.     

Rotational coherence and a sudden breakdown in linear response seen in room-temperature liquids

Highly energized molecules normally are rapidly equilibrated by a solvent; this finding is central to the conventional (linear-response) view of how chemical reactions occur in solution. However, when a reaction initiated by 33-femtosecond deep ultraviolet laser pulses is used to eject highly rotationally excited diatomic molecules into alcohols and water, rotational coherence persists for many rotational periods despite the solvent. Molecular dynamics simulations trace this slow development of molecular-scale friction to a clearly identifiable molecular event: an abrupt liquid-structure change triggered by the rapid rotation. This example shows that molecular relaxation can sometimes switch from linear to nonlinear response.     

Quantum coherence in an optical modulator

Semiconductor quantum well electroabsorption modulators are widely used to modulate near-infrared (NIR) radiation at frequencies below 0.1 terahertz (THz). Here, the NIR absorption of undoped quantum wells was modulated by strong electric fields with frequencies between 1.5 and 3.9 THz. The THz field coupled two excited states (excitons) of the quantum wells, as manifested by a new THz frequency- and power-dependent NIR absorption line. Nonperturbative theory and experiment indicate that the THz field generated a coherent quantum superposition of an absorbing and a nonabsorbing exciton. This quantum coherence may yield new applications for quantum well modulators in optical communications.     

Chromosomal aberrations in a population of ground squirrels

Chromosomes were analyzed from a population of Spermophilus beldingi that included an adult female and three juveniles from the same burrow. All animals had a diploid number of 30. The adult and a juvenile female from the burrow had identical aberrant karyotypes containing an unpaired submetacentric and a minute metacentric chromosome. A familial aberration involving an X chromosome, without phenotypic alteration, is most probable.     

Frequent recombination in a saltern population of Halorubrum

Sex and recombination are driving forces in the evolution of eukaryotes. Homologous recombination is known to be the dominant process in the divergence of many bacterial species. For Archaea, the only direct evidence bearing on the importance or natural occurrence of homologous recombination is anecdotal reports of mosaicism from comparative genomic studies. Genetic studies, however, reveal that recombination may play a significant role in generating diversity among members of at least one archaeal group, the haloarchaea. We used multi-locus sequence typing to demonstrate that haloarchaea exchange genetic information promiscuously, exhibiting a degree of linkage equilibrium approaching that of a sexual population.     

Emerging chirality in artificial spin ice

Artificial spin ice, made up of planar nanostructured arrays of simple ferromagnetic bars, is a playground for rich physics associated with the spin alignment of the bars and spin texture associated with the magnetic frustration at the bar vertices. The phase diagram is exotic, showing magnetic monopole-like defects and liquid and solid phases of spins arranged in loop states with predicted chiral order. We show that magnetotransport measurements in connected honeycomb structures yield the onset of an anomalous Hall signal at 50 kelvin. The temperature scale can be attributed to the long-range dipolar ice phase. The topological Hall signal arises because chiral loops form at the sample edges, indicating a generic route to exotic states via nanoarray edge structure.