Current Controlled Relaxation Oscillations in Ge_2Sb_2Te_5-Based Phase Change Memory Devices

The relaxation oscillation of the phase change memory （PCM） devices based on the Ge2Sb2Te5 material is investigated by applying square current pulses. The current pulses with different amplitudes could be accurately given by the independently designed current testing system. The relaxation oscillation across the PCM device could be measured using an oscilloscope. The oscillation duration decreases with time, showing an inner link with the shrinking threshold voltage Vth. However, the relaxation oscillation would not terminate until the remaining voltage Von reaches the holding voltage Vh. This demonstrates that the relaxation oscillation might be controlled by Von. The increasing current amplitudes could only quicken the oscillation velocity but not be able to eliminate it, which indicates that the relaxation oscillation might be an inherent behavior for the PCM cell.

Stability and multistability of synchronization in networks of coupled phase oscillators

Coupled phase oscillators usually achieve synchronization as the coupling strength among oscillators is increased beyond a critical value. The stability of synchronous state remains an open issue. In this paper, we study the stability of the synchronous state in coupled phase oscillators. It is found that numerical integration of differential equations of coupled phase oscillators with a finite time step may induce desynchronization at strong couplings. The mechanism behind this instability is that numerical accumulated errors in simulations may trigger the loss of stability of the synchronous state.Desynchronization critical couplings are found to increase and diverge as a power law with decreasing the integral time step. Theoretical analysis supports the local stability of the synchronized state. Globally the emergence of synchronous state depends on the initial conditions. Other metastable ordered states such as twisted states can coexist with the synchronous mode. These twisted states keep locally stable on a sparse network but lose their stability when the network becomes dense.

Dual transponder ranging performance in the presence of oscillator phase noise

A dual transponder carrier ranging method can be used to measure inter-satellite distance with high precision by combining the reference and the to-and-fro measurements. Based on the differential techniques, the oscillator phase noise, which is the main error source for microwave ranging systems, can be significantly attenuated. Further, since the range measurements are derived on the same satellite, the dual transponder ranging system does not need a time tagging system to synchronize the two satellites. In view of the lack of oscillator noise analysis on the dual transponder ranging model, a comprehensive analysis of oscillator noise effects on ranging accuracy is provided. First, the dual transponder ranging system is described with emphasis on the detailed analysis of oscillator noise on measurement precision. Then, a high-fidelity numerical simulation approach based on the power spectrum density of an actual ultra-stable oscillator is carried out in both frequency domain and time domain to support the presented theoretical analysis. The simulation results under different conditions are consistent with the proposed concepts, which makes the results reliable. Besides, the results demonstrate that a high level of accuracy can be achieved by using this oscillator noise cancelation-oriented ranging method.

The Ott-Antonsen Ansatz in Globally Coupled Phase Oscillators

The Ott-Antonsen ansatz provides a powerful tool in investigating synchronization among coupled phase oscil- lators. However, previous works using the ansatz only focused on the evolution of the order parameter and the information on desynchronized oscillators is less discussed. In this work, we show that the Ott-Antonsen ansatz can also be applied to investigate the desynchronous dynamics in coupled phase oscillators. Studying the original Kuramoto model and two of its variants, we find that the dynamics of α（ω）, the coefficient in the Fourier series of the probability density, can give most of the information on the synchronization, for example, the threshold of natural frequency delimiting the oscillators synchronized and desychronized by the mean field, the formulation of the effective frequency ωe （ω） of desynchronous oscillators, and the structure of the graph ωe （ω）.

Clustering and Synchronization in an Array of Repulsively Coupled Phase Oscillators

Clustering and synchronization in an array of repulsively coupled phase oscillators are numerically in-vestigated.It is found that oscillators are divided into several clusters according to the symmetry in the structure.Synchronization occurs between oscillators in each cluster,while those oscillators belonging to different clusters remainasynchronous.Such synchronization may collapse for all clusters when the dynamics of only one oscillator is alteredproperly.The synchronous state may return back after a short period of transient process.This is determined by thestrength of the oscillator altered.Its application in the communication of one-to-several is suggested.

Synchronization Dynamics in a System of Multiple Interacting Populations of Phase Oscillators

We study the synchronization dynamics in a system of multiple interacting populations of phase oscillators. Using the dimensionality-reduction technique of Ott and Antonsen, we explore different types of synchronization dynamics when the incoherent state becomes unstable. We find that the inter-population coupling is crucial to the synchronization. When the intra-population interaction is repulsive, the local synchronization can still be maintained through the inter-population coupling. For attractive inter-population coupling, the local order parameters in different populations are of in-phase while the local synchronization are of anti-phase for repulsive inter-population coupling.

Microwave Oscillator Phase Noise Requirement for TD-SCDMA Wireless Communication Systems

In time division synchronous code division multiple access （TD-SCDMA） wireless communication systems, QPSK or 8PSK has been employed to support high data rate services and high efficiency in available bandwidth. The performance of such systems is affected by the phase noise of the microwave local oscillator. The phase noise model of synthesizer and the RF transceiver model for the phase noise effect are proposed for applications of TD-SCDMA systems. The relationship between the power spectral density （PSD） and root mean square （RMS） phase error is given. Then, the error vector magnitude （EVM） performance is analytically evaluated by using the single side band （SSB） phase noise. Theoretical results show agreement with those obtained by measurement data and therefore can be used to derive the TD-SCDMA system performance.

Contribution of El Nino amplitude change to tropical Pacific precipitation decline in the late 1990s

Equatorial central Pacific precipitation experienced a prominent decline in the late 1990 s.This change was previously attributed to a La Nina-like mean sea surface temperature(SST)change in the Pacific Ocean associated with a phase switch of the Interdecadal Pacific Oscillation.Here,using a series of model experiments,the authors reveal that the El Nino-related interannual SST anomalies contributed largely to the precipitation decrease over the equatorial central Pacific.This El Nino SST effect was due to the change in the amplitude of El Nino events in the late 1990 s.The 1980-98 decade had more large-amplitude El Nino events than the 1999-2014 decade.The nonlinear precipitation response to SST anomalies resulted in a larger decadal mean precipitation in the 1980-98 decade than in the 1999-2014 decade.The results highlight the importance of El Nino amplitude change in future climate change related to global warming.

Influence of oscillator phase on oscillation frequency and sensitivity of an electrode-separated piezoelectric sensor

Theoretical consideration was proposed for the influences of the oscillator phase on the response nature of an electrode-separated piezoelectric sensor (ESPS) to liquid properties and verified experimentally. For the oscillators with different phases, the oscillation frequency of the ESPS may increase, maintain nearly constant or decrease with increasing conductivity in low conductivity solutions. The sensitivity of response to density and viscosity increases slightly with increasing oscillator phase. The response to permittivity depends hardly on the oscillator phase. In addition, the dependence of the oscillation frequency of the ESPS on the supply voltage of the oscillator was explained. The ESPS was used to determine atropine sulfate with a detection limit of 1.6x10(-7) mol/L.

60 GHz SIW Steerable Antenna Array in LTCC

In this paper, we present a 60 GHz substrate-integrated waveguide fed-steerable low-temperature cofired ceramics array. The antenna is suitable for transmitting and receiving on the 60 GHz wireless personal area network frequency band. The wireless system can be used for HDTV, high-data-rate networking up to 4.5 GBit/s, security and surveillance, and similar applications.

Synchronization of Phase Oscillators in Networks with Certain Frequency Sequence

Synchronization of Kuramoto phase oscillators arranged in real complex neural networks is investigated. It is shown that the synchronization greatly depends on the sets of natural frequencies of the involved oscillators. The influence of network connectivity heterogeneity on synchronization depends particularly on the correlation between natural frequencies and node degrees. This finding implies a potential application that inhibiting the effects caused by the changes of network structure can be bManced out nicely by choosing the correlation parameter appropriately.

Entangled chimeras in nonlocally coupled bicomponent phase oscillators:From synchronous to asynchronous chimeras

Chimera states,a symmetry-breaking spatiotemporal pattern in nonlocally coupled identical dynamical units,have been identified in various systems and generalized to coupled nonidentical oscillators.It has been shown that strong heterogeneity in the frequencies of nonidentical oscillators might be harmful to chimera states.In this work,we consider a ring of nonlocally coupled bicomponent phase oscillators in which two types of oscillators are randomly distributed along the ring:some oscillators with natural.frequency w1 and others with w2.In this model,the heterogeneity in frequency is measured by frequency mismatch|w1-w2|between the oscillators in these two subpopulations.We report that the nonlocally coupled bicomponent phase oscillators allow for chimera states no matter how large the frequency mismatch is.The bicomponent oscillators are composed of two chimera states,one supported by oscillators with natural frequency wI and the other by oscillators with natural frequency w2.The two chimera states in two subpopulations are synchronized at weak frequency mismatch,in which the coberent oscillators in thern share similar mean phase velocity,and are desynchronized at large frequency mismatch,in which the coherent oscillators in different subpopulations have distinct mean phase velocities.The synchronization-desynchronization transition between chimera states in these two subpopulations is observed with the increase in the frequency mismatch.The observed phenomena are theoretically analyzed by passing to the continuum limit and using the Ott-Antonsen approach.

Effects of frustration on explosive synchronization

In this study, we consider the emergence of explosive synchronization in scale-free networks by considering the Kuramoto model of coupled phase oscillators. The natural frequencies of oscillators are assumed to be correlated with their degrees and frustration is included in the system. This assumption can enhance or delay the explosive transition to synchronization. Interestingly, a de-synchronization phenomenon occurs and the type of phase transition is also changed. Furthermore, we provide an analytical treatment based on a star graph, which resembles that obtained in scale-free networks. Finally, a self-consistent approach is implemented to study the de-synchronization regime. Our findings have important implications for controlling synchronization in complex networks because frustration is a controllable parameter in experiments and a discontinuous abrupt phase transition is always dangerous in engineering in the real world.

Dynamics of clustering patterns in the Kuramoto model with unidirectional coupling

We study the synchronization transition in the Kuramoto model by considering a unidirectional cou- pling with a chain structure. The microscopic clustering features are characterized in the system. We identify several clustering patterns for the long-time evolution of the effective frequencies and reveal the phase transition between them. Theoretically, the recursive approach is developed in order to ob- tain analytical insights; the essential bifurcation schemes of the clustering patterns are clarified and the phase diagram is illustrated in order to depict the various phase transitions of the system. Fur- thermore, these recursive theories can be extended to a larger system. Our theoretical analysis is in agreement with the numerical simulations and can aid in understanding the clustering patterns in the Kuramoto model with a general structure.

Evidence for a Dirac nodal-line semimetal in SrAs_3

Dirac nodal-line semimetals with the linear bands crossing along a line or loop, represent a new topological state of matter. Here, by carrying out magnetotransport measurements and performing first-principle calculations, we demonstrate that such a state has been realized in high-quality single crystals of SrAs_3.We obtain the nontrivial ∏ Berry phase by analysing the Shubnikov-de Haas quantum oscillations. We also observe a robust negative longitudinal magnetoresistance induced by the chiral anomaly.Accompanying first-principles calculations identifies that a single hole pocket enclosing the loop nodes is responsible for these observations.

A low power CMOS VCO using inductive-biasing with high performance FoM

A novel voltage-controlled oscillator（VCO） topology with low voltage and low power is presented. It employed the inductive-biasing to build a feedback path between the tank and the MOS gate to enhance the voltage gain from output nodes of the tank to the gate node of the cross-coupled transistor. Theoretical analysis using timevarying phase noise theory derives closed-form symbolic formulas for the 1/f^2 phase noise region, showing that this feedback path could improve the phase noise performance. The proposed VCO is fabricated in TSMC 0.13 m CMOS technology. Working under a 0.3 V supply voltage with 1.2 m W power consumption, the measured phase noise of the VCO is –119.4 d Bc/Hz at 1 MHz offset frequency from the carrier of 4.92 GHz, resulting in an Fo M of 192.5 d Bc/Hz.