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Cacao is an economically important crop, since it provides the raw material for the multibillion dollar global chocolate industry. Yunnan Province is in the far southwestern region of China where tropical agriculture makes up a significant part of the provincial GDP. There is great potential for cacao production in Yunnan, given the rapid increase of chocolate consumption in China. Understanding the genetic background of available germplasm is essential for effective genebank management and crop genetic improvement. The objectives of this investigation were to assess the genetic identity of the cacao germplasm maintained in Yunnan, China; and to quantify the level of genetic diversity in comparison with available diversity in international collections. Using Single Nucleotide Polymorphism (SNP) markers, we genotyped the cacao collection maintained in the Xishuangbanna Tropical Botanical Garden in Yunnan. Multivariate analysis and Bayesian assignment test, using 150 reference cacao accessions, showed that these introduced cacao germplasm accessions have a narrow genetic background and were mostly comprised of Amelonado hybrids. Of the 88 Yunnan accessions, 59% of the parentage is contributed by Amelonado and 17% by two Upper Amazon Forastero populations. The study demonstrated that these introduced cacao germplasm accessions have a narrow genetic background thus lacking multiple sources of resistance to major cacao diseases. The present results therefore suggest that new introductions are needed to enrich genetic diversity in this collection. An improved germplasm collection would serve as a foundation for broader on-farm diversity for cacao cultivation in Yunnan, as well as in other tropical regions of China.

It has been suggested that ion foreshock waves originating in the solar wind upstream of the quasi-parallel (Q-||) shock can impact the planetary magnetosphere leading to standing shear Alfvén waves, i.e., the field line resonances (FLRs). In this paper, we carry out simulations of interaction between the solar wind and terrestrial magnetosphere under radial interplanetary magnetic field conditions by using a 3-D global hybrid model, and show the properties of self-consistently generated field line resonances through direct mode conversion in magnetospheric response to the foreshock disturbances for the first time. The simulation results show that the foreshock disturbances from the Q-|| shock can excite magnetospheric ultralow-frequency waves, among which the toroidal Alfvén waves are examined. It is found that the foreshock wave spectrum covers a wide frequency range and matches the band of FLR harmonics after excluding the Doppler shift effects. The fundamental harmonic of field line resonances dominates and has the strongest wave power, and the higher the harmonic order, the weaker the corresponding wave power. The nodes and anti-nodes of the odd and even harmonics in the equatorial plane are also presented. In addition, as the local Alfvén speed increases earthward, the corresponding frequency of each harmonic increases. The field-aligned current in the cusp region indicative of the possibly observable aurora is found to be a result of magnetopause perturbation which is caused by the foreshock disturbances, and a global view substantiating this scenario is given. Finally, it is found that when the solar wind Mach number decreases, the strength of both field line resonance and field-aligned current decreases accordingly.

Array signal processing is attractive for Global Navigation Satellite System (GNSS) applications, as the desired reception environments for GNSS are becoming more challenging, while users’ demands for high-accuracy positioning are growing. One goal of array signal processing is to find the direction of arrival (DOA) of the signal source. Several advanced techniques have been proposed to estimate the DOA, with the direction lock loop (DiLL) being a representative method. However, applying the DiLL in GNSS receivers is not straightforward. One reason for this is the low sensitivity of the utilized spatial correlation function in the angular region close to broadside within a linear antenna array. In order to address this problem, an improved DOA tracking technique is presented building on the traditional DiLL, i.e., the rotate-to-zero direction lock loop (RZ-DiLL). Simulations and live data validations show that the proposed RZ-DiLL avoids the low sensitivity issue of the traditional DiLL. Moreover, the experimental results show that compared to a single-antenna GNSS receiver, the RZ-DiLL-implemented GNSS array signal receiver provides an improved carrier-to-noise ratio and, in turn, improved position solutions.

Binary offset carrier (BOC) modulation technology is widely used in newly developed and modernized global navigation satellite systems. BOC signal offers superior performance over conventional binary phase-shift keying signal due to its sharp auto-correlation function. However, the main drawback of BOC signal tracking is the ambiguity problem caused by the presence of multiple side-peaks in the auto-correlation function. We derive a new analytical model to solve the ambiguity issue. Based on the derived analytical model, a code tracking algorithm that completely removes all ambiguities is introduced. Theoretical analysis and simulation show that the proposed technique significantly improves the multipath mitigation performance and code tracking accuracy in thermal noise over those of existing side-peaks-cancellation techniques.

Recent imager and radar observations in the nightside polar cap have shown evidence that polar cap patches are associated with localized flow channels. To understand how flow channels propagate from the dayside auroral oval into the polar cap, we use an all-sky imager in Antarctica and DMSP (F13, F15, F16, F17 and F18) to determine properties of density and flows associated with dayside polar cap patches. We identified 50 conjunction events during the southern winter seasons of 2007–2011. In a majority (45) of events, longitudinally narrow flow enhancements directed anti-sunward are found to be collocated with the patches, have velocities (up to a few km/s) substantially larger than the large-scale background flows (~500 m/s) and have widths comparable to patch widths (~400 km). While the patches start with poleward moving auroral forms (PMAFs) as expected, many PMAFs propagate azimuthally away from the noon over a few hours of MLT, resulting in formation of polar cap patches quite far away from the noon, as early as ~6 MLT. The MLT separation from the noon is found to be proportional to the IMF |By|. Fast polar cap flows of >~1500 m/s are predominantly seen during large IMF |By| and small |Bz|. The presence of fast, anti-sunward flow channels associated with the polar cap patches suggests that the flow channels form in the dayside auroral oval through transient reconnection and can be the source of flow channels propagating into the polar cap.

An experimental research was carried out to study the fluid mechanics of underwater supersonic gas jets. High pressure air was injected into a water tank through converging-diverging nozzles (Laval nozzles). The jets were operated at different conditions of over-, full- and under-expansions. The jet sequences were visualized using a CCD camera. It was found that the injection of supersonic air jets into water is always accompanied by strong flow oscillation, which is related to the phenomenon of shock waves feedback in the gas phase. The shock wave feedback is different from the acoustic feedback when a supersonic gas jet discharges into open air, which causes screech tone. It is a process that the shock waves enclosed in the gas pocket induce a periodic pressure with large amplitude variation in the gas jet. Consequently, the periodic pressure causes the jet oscillation including the large amplitude expansion. Detailed pressure measurements were also conducted to verify the shock wave feedback phenomenon. Three kinds of measuring methods were used, i.e., pressure probe submerged in water, pressure measurements from the side and front walls of the nozzle devices respectively. The results measured by these methods are in a good agreement. They show that every oscillation of the jets causes a sudden increase of pressure and the average frequency of the shock wave feedback is about 5–10 Hz.

The present paper describes experimental investigation on the flow pattern and hydrodynamic effect of underwater gas jets from supersonic and sonic nozzles operated in correct- and imperfect expansion conditions. The flow visualizations show that jetting is the flow regime for the submerged gas injection at a high speed in the parameter range under consideration. The obtained results indicate that high-speed gas jets in still water induce large pressure pulsations upstream of the nozzle exit and the presence of shock-cell structure in the over- and under-expanded jets leads to an increase in the intensity of the jet-induced hydrodynamic pressure.

The present paper describes a numerical two-way coupling model for shock-induced laminar boundary-layer flows of a dust-laden gas and studies the transverse migration of fine particles under the action of Saffman lift force. The governing equations are formulated in the dilute two-phase continuum framework with consideration of the finiteness of the particle Reynolds and Knudsen numbers. The full Lagrangian method is explored for calculating the dispersed-phase flow fields (including the number density of particles) in the regions of intersecting particle trajectories. The computation results show a significant reaction of the particles on the two-phase boundary-layer structure when the mass loading ratio of particles takes finite values.