An Approach to Analyse Phase Synchronization in Oscillator Networks with Weak Coupling

We study phase synchronization in oscillator networks through phase reduced method. The dynamics of networks is reduced to phase equations by this method. Analysing the phase equations through the master stability function method, one obtains that the oscillators with identical frequency can be in-phase synchronized by weak balanced coupling. Similarly, the problem of frequency synchronization of oscillators with different frequencies is transformed to the existence of a locally asymptotically stable equilibrium of the phase error system.     

过渡层结构和生长工艺条件对Si基GaN的影响

为了提高MOCVD外延硅基GaN材料的质量，在硅（111）衬底上以HT-AlN为缓冲层，在缓冲层上再生长变组份过渡层后外延生长GaN。过渡层为多层复合结构，分为高温变组分AlGaN、GaN、低温AlN、高温变组分AlGaN。在高温生长AlGaN和GaN层中插入一层低温生长AlN以缓解降温过程中应力对厚GaN层的影响，为了缓慢释放热应力、采用合适的慢降温工艺。当外延层的厚度小于1．7微米时GaN外延层无龟裂，而厚度不断增加时，GaN外延层产生龟裂。本文研究了AlN缓冲层生长温度、高温变组分AlGaN生长过程中生长时间的变化对所生长GaN材料的影响。采用三维视频显微镜、高分辨率双晶X射线衍射（DCXRD）、扫描电子显微镜（SEM）、原子力显微镜（AFM）和室温光致荧光光谱（RT-PL）对样品进行了测试分析。测试结果表明所研制的硅基GaN表面光亮、平整，过渡层的引入有利于降低外延层中应力，提高GaN结晶质量。     

Dynamics of network motifs in genetic regulatory networks

Network motifs hold a very important status in genetic regulatory networks. This paper aims to analyse the dynamical property of the network motifs in genetic regulatory networks. The main result we obtained is that the dynamical property of a single motif is very simple with only an asymptotically stable equilibrium point, but the combination of several motifs can make more complicated dynamical properties emerge such as limit cycles. The above-mentioned result shows that network motif is a stable substructure in genetic regulatory networks while their combinations make the genetic regulatory network more complicated.     

Synchronization between Different Networks

Synchronization between two networks with different topology structures and different dynamical behaviours is studied. These two different networks are driving and responding networks, respectively. Under the preconditions that the driving network gets synchronization, we give the conditions for the responding network to be synchronized to the same dynamics as the driving network with the help of the open-plus-closed-loop method. Then a example is given to verify the validity of the theoretical results.     

Ni/ITO与p型GaN的欧姆接触

通过环形传输线方法(CTLM),电流-电压(I-V)曲线、光学透过率、表面形貌等手段,研究了N i层厚度和N i层的高温退火对N i/ITO与p型氮化镓接触特性的影响,探讨了N i/ITO-p-GaN欧姆接触的形成机制,提出了低温氧化N i金属层的方法。获得接触电阻率(cρ)小于9.5×10-5Ω.cm2,透过率达到74%(470 nm)的N i/ITO-p-GaN电极。     

Si(111)衬底上GaN的MOCVD生长

利用LP-MOCVD在Si（111）衬底上,以高温AIN为缓冲层,分别用低温GaN（LT-GaN）和偏离化学计量比富Ga高温GaN（HT-GaN）为过渡层外延生长六方相GaN薄膜。采用高分辨率双晶X射线衍射（DCXRD）,扫描电子显微镜（SEM）,原子力显微镜（AFM）和室温光致荧光光谱（RT-PL）进行分析。结果表明,有偏离化学计量比富Ga HT-GaN为过渡层生长的GaN薄膜质量和光致荧光特性均明显优于以LT-GaN为过渡层生长的GaN薄膜,得到GaN（0002）和（1012）的DCXRD峰,其半峰全宽（FWHM）分别为698s和842s,室温下的光致荧光光谱在361nm处有一个很强的发光峰,其半峰全宽为44．3meV。     

Control schemes for synchronizing two subnetworks with weak couplings

In this paper, we propose a well-designed network model with a parameter and study full and partial synchronization of the network model based on the stability analysis. The network model is composed of a star-coupled subnetwork and a globally coupled subnetwork. By analyzing the special coupling configuration, three control schemes are obtained for synchronizing the network model. Further analysis indicates that even if the inner couplings in each subnetwork are very weak, two of the control schemes are still valid. In particular, if the outer coupling weight parameter θ is larger than (n2 2n)/4, or the subnetwork size n is larger than θ2, the two subnetworks with weak inner couplings can achieve synchronization. In addition, the synchronizability is independent of the network size in case of 0 < θ < n/(n + 1). Finally, we carry out some numerical simulations to confirm the validity of the obtained control schemes. It is worth noting that the main idea of this paper also applies to any network consisting of a dense subnetwork and a sparse network.