A Recognition Algorithm of VGPO Jamming Based on Discrete Chirp-Fourier Transform

This paper addresses the recognition problem of velocity gate pull-off (VGPO) jamming from the target echo signal for the velocity-based tracking system. The discrete chirp-Fourier transform (DCFT) is studied in this paper to jointly estimate the chirp rates and frequencies of the target and jamming signals. Firstly, the scaling characteristic of the DCFT algorithm is explored. Then we focus on the quantitative effect of the VGPO jamming signal by analyzing the jointly estimated results in each pulse. The quantitative effect indicates that, as long as the estimated frequency is unchanged, the relationship between the estimated chirp rate and the pulse numbers is similar to the relationship between the frequency offset of VGPO jamming and the time. Finally, by utilizing the joint estimated results in each pulse repetition interval and calculating the mean square to variance ratio (MSVR) of the normalized estimated chirp rate, the VGPO jamming can be recognized. Simulation results show that the jamming signal and the target echo become distinguishable with the proposed feature. Comparing to the existing works, the proposed method can correctly recognize the jamming signal with lower jamming-to-noise ratio (JNR) 5dB with less data needed, which means it can work effectively in the early stage of interference implementation and shows great potential in practical applications.

A Recognition Algorithm of VGPO Jamming Based on Discrete Chirp-Fourier Transform

We address the recognition problem of velocity gate pull-off (VGPO) jamming from the target echo signal for the velocity automatic tracking system. To this end, we resort to the discrete chirp-Fourier transform (DCFT) to jointly estimate the chirp rates and frequencies of the target and jamming signals. Firstly, the scaling characteristic of the DCFT algorithm is explored. Then we highlight the quantitative effect of the VGPO jamming signal by analyzing the jointly estimated result in each pulse. The effective effect indicates that the relationship between the estimated chirp rate and the pulse is similar to that between the frequency offset of VGPO jamming and the time when the estimated frequency is unchanged. Finally, by utilizing the analytical result and extracting the feature of the mean square to variance ratio (MSVR) of the normalized estimated chirp rate, the VGPO jamming can be recognized. Simulation results show that, for a time when the estimated frequency is unchanged, the MSVR of VGPO jamming decreases with the pulse numbers increases, and is always larger than that of a target which is steady. Comparing to other methods, the proposed method can correctly recognize the jamming signal with jamming-to-noise ratio (JNR) 5dB which shows better recognition performance, and is also effective within a shorter period.

Pulse Design for Ultra Wideband System Based on Generalized Gaussian Pulse

In order to improve the detection performance of ultra wideband (UWB) system, a nonlinear scaling UWB pulse based on generalized Gaussian pulse (GGP) was proposed in this paper. Then wideband ambiguity function (WBAF) of the pulse was derived and analyzed to show the relationship between its range ambiguity function and nonlinear scaling characteristic parameters. The simulation demonstrate that such UWB pulse can achieve the thumbtack WBAF, low side lobes and high range resolution can be achieved by increasing modulation frequency offset and decreasing modulation frequency. The simulation result can provide theoretic guidance to UWB pulse design.

Multiple Citrus Viroids in Citrus from Japan and Their Ability to Produce Exocortis-Like Symptoms in Citron

Sequential polyacrylamide gel electrophoresis analyses showed many viroid-like RNAs in samples collected from citrus trees in Japan. Reverse transcription polymerase chain reaction and sequencing analyses of the amplified fragments verified that they were derived from variants of six citrus viroids, Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd) including CVd-I-LSS (a distinct variant of CBLVd), Hop stunt viroid, Citrus viroid III, Citrus viroid IV, and Citrus viroid OS. The samples induced symptoms with variable severity in Arizona 861-S1 ‘Etrog’ citrons (Citrus medica L.) likely due to the varying accumulation patterns produced by the different viroids. Some of the symptoms caused by the samples harboring the citrus viroids other than CEVd were as severe as those caused by CEVd. Some source citrus trees showing the severe bark scaling characteristic of exocortis disease in trifoliate orange (Poncirus trifoliata (L.) Raf.) rootstocks contained only citrus viroids other than CEVd in complex. This indicates that certain exocortis-like diseases in Japan were caused by some combination of citrus viroids not including CEVd.

The gravitational interchange instability for perpendicular density gradients

The analouge of the Reyleigh–Taylor instability (the gravitational interchange mode) for an infinitely conducting, approximately one-dimensional plane plasma slab is examined when the gravitational acceleration g is taken to be perpendicular to the equalibrium density gradient δp0. In contrast with the ‘classical’ situation (where g is aligned with δp0), it is found for a current layer with Magnetic shear that there is no instability threshold equivalent to the ‘classical’ situation (where g is aligned with δp0), it is found for a current layer with magnetic shear that there is no instability threshold equivalent to the Suydam criterion: the mode is unstable for all values of |δp0|. In the weak shear limit the growth rate of the instability is shown to exhibit the familiar (g|δp0|/p0)img; scaling characteristic of the gravitational interchange mode.

On the Space-Time Structure of Human Interlimb Co-Ordination

In three experiments we show, using behavioural measures of movement outcome, as well as movement trajectory information and resultant kinematic profiles, that there is a strong tendency for the limbs to be co-ordinated as a unitary structure even under conditions where the movements are of disparate difficulty. Environmental constraints (an obstacle placed in the path of one limb, but not in the other) are shown to modulate the space-time behaviour of both limbs (Experiment II). Our results obtain for symmetrical (Experiment I) as well as asymmetrical movements that involve non-homologous muscle groups (Experiment III). These findings suggest that in multi-joint limb movements, the many degrees of freedom are organised to function temporarily as a single coherent unit that is uniquely specific to the task demands placed on it. For movements in general, and two-handed movements in particular, such units are revealed in a partitioning of the relevant force demands for each component (a force scaling characteristic) and a preservation of the internal “topology” of the action, as indexed by the relative timing among components. These features, as well as systematic deviations from perfect synchrony between the limbs can be rationalised by a model that assumes the limbs behave qualitatively like non-linear oscillators.