arXiv subjects

Jie Zhang

Publications and source records attributed to Jie Zhang.

1,177 records · Page 66Linked to original sources

arXiv2008

A Statistical Study on Solar Active Regions Producing Extremely Fast Coronal Mass Ejections

We present a statistical result on the properties of solar source regions that have produced 57 fastest front-side coronal mass ejections (CMEs) (speed 1500 km/s) occurred from 1996 June to 2007 January. The properties of these fast-CME-producing regions, 35 in total, are compared with those of all 1143 active regions (ARs) in the period studied. An automated method, based on SOHO/MDI magnetic synoptic charts, is used to select and characterize the ARs. For each AR, a set of parameters are derived including the areas (positive, negative and total, denoted by A_P, A_N and A_T respectively), the magnetic fluxes (positive, negative and total, F_P, F_N and F_T respectively), the average magnetic field strength (B_avg), quasi-elongation (e) characterizing the overall shape of the AR, the number and length of polarity inversion lines (PILs, or neutral lines, N_PIL and L_PIL respectively), and the average and maximum of magnetic gradient on the PILs (GOP_avg and GOP_max respectively). Our statistical analysis shows a general trend between the scales of an AR and the likelihood of producing a fast CME, i.e., the larger the geometric size (A_T), the larger the magnetic flux (F_T), the stronger the magnetic field (B_avg), and/or the more complex the magnetic configuration (N_PIL and L_PIL), then the higher the possibility of producing a fast CME. When all ARs are sorted into three equally-numbered groups with low, middle and high values of these parameters, we find that, for all these AR parameters, more than 60% of extremely fast CMEs are from the high-value group. The two PIL parameters are the best indicators of producing fast CMEs, with more than 80% from the high value group.

astro-ph↗

arXiv2007

Single-cycle megawatt terahertz pulse generation from a wavelength-scale plasma oscillator driven by ultrashort laser pulses

The tremendous applications of terahertz (THz) spectroscopy and imaging require THz sources in different parameters. We propose a novel scheme to generate single-cycle powerful THz pulses by ultrashort intense laser pulses incident obliquely on a tenuous plasma slab of few THz wavelengths in thickness. This is made possible by driving a large amplitude electron plasma wave in the plasma slab, thus producing a net transient current at the plasma surfaces. Theory and simulations show that such a THz source is capable of providing megawatt power and field strength of MV/cm, which may open up new horizons for nonlinear THz science and applications.

physics.plasm-ph↗

arXiv2007

Asymptotically pivotal statistic for surrogate testing with extended hypothesis

The method of surrogate data provides a framework for testing observed data against a hierarchy of alternative hypotheses. The aim of applying this method is to exclude the possibility that the data are consistent with simple linear explanations before seeking complex nonlinear causes. However, in recent time the method has attracted considerable criticism, largely as a result of ambiguity about the formation of the underlying null hypotheses, or about the power of the chosen statistic. In this communication we show that by employing a special family of ranks statistics these problems can be avoided and the method of surrogate data placed of a firm statistical foundation.

nlin.CD↗

arXiv2006

Marangoni Convection in Binary Mixtures

Marangoni instabilities in binary mixtures are different from those in pure liquids. In contrast to a large amount of experimental work on Marangoni convection in pure liquids, such experiments in binary mixtures are not available in the literature, to our knowledge. Using binary mixtures of sodium chloride/water, we have systematically investigated the pattern formation for a set of substrate temperatures and solute concentrations in an open system. The flow patterns evolve with time, driven by surface-tension fluctuations due to evaporation and the Soret effect, while the air-liquid interface does not deform. A shadowgraph method is used to follow the pattern formation in time. The patterns are mainly composed of polygons and rolls. The mean pattern size first decreases slightly, and then gradually increases during the evolution. Evaporation affects the pattern formation mainly at the early stage and the local evaporation rate tends to become spatially uniform at the film surface. The Soret effect becomes important at the later stage and affects the mixture for a large mean solute concentration where the Soret number is significantly above zero. The strength of convection increases with the initial solute concentration and the substrate temperature. Our findings differ from the theoretical predictions in which evaporation is neglected.

physics.flu-dyn↗

arXiv2006

Exact nonparametric inference for detection of nonlinear determinism

We propose an exact nonparametric inference scheme for the detection of nonlinear determinism. The essential fact utilized in our scheme is that, for a linear stochastic process with jointly symmetric innovations, its ordinary least square (OLS) linear prediction error is symmetric about zero. Based on this viewpoint, a class of linear signed rank statistics, e.g. the Wilcoxon signed rank statistic, can be derived with the known null distributions from the prediction error. Thus one of the advantages of our scheme is that, it can provide exact confidence levels for our null hypothesis tests. Furthermore, the exactness is applicable for finite samples with arbitrary length. We demonstrate the test power of this statistic through several examples.

nlin.CD↗

arXiv2005

Optimal phase space projection for noise reduction

In this communication we will re-examine the widely studied technique of phase space projection. By imposing a time domain constraint (TDC) on the residual noise, we deduce a more general version of the optimal projector, which includes those appearing in previous literature as subcases but does not assume the independence between the clean signal and the noise. As an application, we will apply this technique for noise reduction. Numerical results show that our algorithm has succeeded in augmenting the signal-to-noise ratio (SNR) for simulated data from the Rössler system and experimental speech record.

nlin.CD↗

arXiv2005

Experimental Synchronization of Independent Entangled Photon Sources

Realistic linear quantum information processing necessitates the ability to synchronously generate entangled photon pairs either at the same or at distant locations. Here, we report the experimental realization of synchronized generation of independent entangled photon pairs. The quality of synchronization is confirmed by observing a violation of Bell's inequality with 3.2 standard deviations in an entanglement swapping experiment. The techniques developed in our experiment will be of great importance for future linear optical realization of quantum repeaters and quantum computation.

quant-ph↗