Search

Leaf skeletonization represents a distinctive form of insect feeding behavior. It commonly occurs in angiosperm leaves after their initial appearance during the Early Cretaceous. This type of feeding behavior rarely has been documented in pre-Mesozoic fossils. We describe the earliest evidence of insect-skeletonized leaves of Dictyophyllum nathorstii Zeiller, affi li- ated with the extant fern family Dipteridaceae in the Late Triassic Yipinglang fl ora from southwestern China. The skeletonization generally is located adjacent to the pinna rachilla of the distal free portion of the leaf. In the skeletonized area, the interveinal tissue is com- pletely removed, exposing the pinna rachilla, pinnule midveins, and lateral veins. Most non- vascular tissue has been removed between the vascular bundles, the latter forming polygo- nal meshes of varying size. Our report of insect-mediated skeletonization of fern leaves from southwestern China fi lls a spatiotemporal gap in the published data on the paleogeographi- cal distribution and stratigraphic occurrence of plant-arthropod associations, and indicates an antagonistic relationship between a fern host and its insect herbivore.

The purpose of this paper is to analyze the amplitude and phase modulation effect incurred by the rotating transmit antenna in passive bistatic radar, which result in pulses loss and phase reversals within the direct-path pulse train. The processing loss mechanisms of signal to noise ratio (SNR) and offsets in target Doppler measurements caused by the pulses loss and phase reversals are described. The expressions of the peak output of cross-ambiguity function are derived to evaluate SNR loss in the presence of pulses loss or/and phase reversals. Simulation results show that the maximum SNR loss is about 3.5 dB, and the SNR loss curves for various Doppler frequencies and different number of lost pulses are conformed to the theoretical analysis. The SNR loss gets progressively worse with increasing target Doppler frequency. The frequency estimation error increases with target Doppler frequency and lost pulse number, up to a worst case of about 0.75 of a Doppler cell.

Passive bistatic coherent radar system operates with distinct non-cooperative transmitter and receiver located at different sites. In such spatial separation, the receiving system needs to independently solve the problem of time and phase synchronization via direct-path signal. The impact of time synchronization error was explored and solved in passive bistatic coherent radar. The common model of digital sampling process is introduced to illustrate the effect of time synchronization error (TSE). The periodicity of relative sample instant variation of each pulse is deduced. Then, normalized interference power (NIP) is defined to evaluate the potential impact of TSE. The NIP expressions are derived when the difference between the adjacent relative sample instant is uniform distribution or Gaussian distribution. It is found that there are new spurious frequency components and the detection performance is decreased in the case of asynchronous sampling. At the same time, the analytical Doppler frequency bias expression caused by TSE is presented. Theoretical results are confirmed by simulation in the cases of different periods of relative sampling instant.

To study the effect of Guishen Pill (GSP) on expression levels of Oct-4, MVH, and Egr-1 in mice with diminished ovarian reserve (DOR).Totally 40 female C57BL/6J mice were randomly divided into 4 groups, the normal control group, the model group, the GSP group, and the dehydroepiandrosterone (DHEA) group, 10 in each group. Pregnant mare serum gonadotropin (PMSG), human chorionic gonadotropin (HCG), and prostaglandin F2α (PGF2α) were sequentially administrated to produce superovulation. The DOR model was established by exposing to ozone inhalation. Mice in the GSP group were intragastrically administered with GSP at 0.3 mL. Those in the DHEA group were intragastrically administered with DHEA at 0.3 mL. Equal volume of normal saline was intragastrically administered to mice in the normal control group and the model group. All mice wer treated for 21 days. Serum levels of estrogen (E2), progestogen (P), and anti-Müllerian hormone (AMH) were measured by ELISA. Changes of Oct-4, anti-AMH, and early growth response gene-1 (Egr-1) mRNA in ovaries were dtected by Real-time PCR.Compared with the model group, serum levels of E2, P, and AMH, as well as contents of estrogen receptor (ER), progestogen receptor (PR), MVH, and Oct-4 mRNA significantly increased in the GSP group and the DHEA group (P0.05).GSP could improve expression levels of Oct-4, MVH, and Egr-1 mRNA in DOR mice and their ovarian function.

Recently, some scholars suggested that it is important to keep a stablehemodynamic state and prevent the stress responses in geriatric patients undergoing total hip replacement (THR). We conducted this randomized prospective study to observe anesthetic potency of unilateral spinal anesthesia and stress response to it in geriatric patients during THR. We compared the effect of unilateral spinal and bilateral spinal on inhibition of stress response through measuring Norepinephrine (NE), epinephrine (E) and cortisol (CORT). Plasma concentrations of NE, E and CORT were determined in blood samples using ELISA (enzyme-linked immunosorbent assays) at three time points: To (prior to anesthesia) T1 (at the time point of skin closure), T2 (twenty-four hours after the operation). Sixty patients were randomly divided into two groups: group A (unilateral spinal anesthesia) and group B (conventional bilateral spinal anesthesia). 7.5tymg of hypobaric bupivacaine were injected into subarachnoid cavity at group A and 12mg hypobaric bupivacaine were given at group B. The onset time of sensory and motor block, loss of pinprick sensation, degree of motor block, regression of sensory and motor blocks and hemodynamic changes were also recorded. These data were used to evaluate anesthetic potency of spinal anesthesia. The results of this experiment show that unilateral spinal anesthesia can provide restriction of sensory and motor block, minimize the incidence of hypotension and prevent the stress responses undergoing THR. It is optimal anesthesia procedure for geriatric patients by rapid subarachnoid injection of small doses of bupivacaine.

The purpose of this paper is to analysis the amplitude modulation effect caused by the rotating transmit antenna pattern, which results in pulses loss within the direct-path pulse train. The loss mechanisms of signal to noise ratio (SNR) were discussed for these modulation phenomena. The analytical expression of the peak output of cross-ambiguity function was derived, which correspond to the cases of pulses loss occurrence. Simulation results show that the maximum SNR loss is less than 4 dB in the worst case, and the SNR loss curves for various Doppler frequencies and different number of pulse loss are conformed to the theoretical analysis. The worst Doppler frequency estimation bias is about 0.75 times the frequency resolution cell when there is no ambiguity in Doppler estimation.

This paper explored the transmit antenna scanning modulation effect on the signal to noise ratio (SNR) loss in a noncooperative illuminator based bistatic radar. The general expression of normalized filed pattern for widely used antenna was analyzed. The direct-path signal and target echo modulated by the transmit antenna, which is mechanically scanned in azimuth, were described. Mathematical representations for direct-path signal and target echo were proposed with respect to the analytical expression of antenna’s pattern. The SNR loss of the coherent integration via cross-correlation processing was derived. The relationship between SNR loss and SNRs of direct-path channel and target echo channel was evaluated. The simulation result shows that the SNR loss caused by antenna modulation can be ignored if the average SNR in direct path is greater than 15 dB. However, the SNR loss deteriorates rapidly if the visual angle becomes larger. Some suggestions on choosing the IF bandwidth and data selection were presented.

Passive bistatic coherent radar system operates with distinct non-cooperative transmitter and receiver located at different sites. In such spatial separation, the critical issues in attempting to operate a bistatic system with a noncooperative illuminator are target location and its observability, which were explored and solved in this paper. The solution to the bistatic triangle for target range from the receiver requires calculating the azimuth of the direct path pulse, which allows accurate measurement of the bistatic range to the target and computation of target slant range. Finally, the observability of the system was demonstrated.

In passive bistatic radar system, the receiver needs to independently solve the problem of frequency synchronization via the fluctuating direct-path signal. Under the circumstance, it is difficult to achieve highly accurate frequency synchronization since the instantaneous frequency measurement accuracy depends on the signal to noise ratio of the direct-path signal. In this paper, we focused on the impact of FSE on passive bistatic radar system. Since the imbalance between the in-phase(I) and quadrature(Q) component is a function of frequency, the imperfection arises from FSE in digital I and Q components has been introduced. The integration loss was calculated with respect to amplitude and phase imbalance factors. An analysis that explains how the extraneous components generated is presented. Then NIP was defined to evaluate the impact of FSE in quantity. Simulation results demonstrated that the interference frequencies caused by FSE will deteriorate the performance of weak target detection and parameter estimation.

The aim of this research is to develop techniques for bistatic ISAR as applied to target imaging. A scheme of an independent bistatic receiving system without dedicated data links was carried out under the support of national science foundation. The research defined a system configuration and assesses its potential performance via modeling. It was developed to support pulse compression of wideband waveforms for applications. The associated implementation issues introduced by electro-optical component characteristics were discussed. Coherent detection was used to implement difference mixing for subsequent digital processing. This system is independent since it requires no timing control signals for synchronization provided by illuminators, but the necessary reference signal is intercepted from the radar's sidelobe emissions.