Underwater acoustic spiral wavefront transducer with low phase directionality error.

The phase and azimuth angle of acoustic spiral wavefronts are linearly related. Based on this phase directionality of spiral wavefronts, the complex azimuth determination of the positioning of unmanned underwater vehicles can be converted into simple phase acquisition processes, where the azimuth determination accuracy is influenced by the phase directionality error of a spiral wavefront transducer. This study proposes a spiral wavefront transducer that improves the underwater positioning accuracy.

Robust multi-angle structured illumination lensless microscopy via illumination angle calibration.

Multi-angle structured illumination lensless (MASIL) microscopy enables high-resolution image recovery over a large field of view. Successful image recovery of MASIL microscopy, however, relies on an accurate knowledge of the multi-angle illumination. System misalignments and slight deviations from the true illumination angle may result in image artifacts in reconstruction.

Research and Fabrication of Broadband Ring Flextensional Underwater Transducer.

At present, high-speed underwater acoustic communication requires underwater transducers with the characteristics of low frequency and broadband. The low-frequency transducers also are expected to be low-frequency directional for realization of point-to-point communication. In order to achieve the above targets, this paper proposes a new type of flextensional transducer which is constructed of double mosaic piezoelectric ceramic rings and spherical cap metal shells.

Underwater Spiral Wave Sound Source Based on Phased Array with Three Transducers.

This paper realizes an underwater spiral wave sound source by using three omni-directional spherical transducers with three different phases. The pressure distribution of the sound field for a phased array is derived using the superposition theory of sound field. The generation of spiral wave field is presented, the relationship between the performance of phased array sound field and the array parameters is analyzed, and also verified by the finite element method (FEM).

Spiral Sound Wave Transducer Based on the Longitudinal Vibration.

A spiral sound wave transducer comprised of longitudinal vibrating elements has been proposed. This transducer was made from eight uniform radial distributed longitudinal vibrating elements, which could effectively generate low frequency underwater acoustic spiral waves. We discuss the production theory of spiral sound waves, which could be synthesized by two orthogonal acoustic dipoles with a phase difference of 90 degrees.

Publisher Correction: The early history of wheat in China from C dating and Bayesian chronological modelling.

In the version of this Article originally published, the x and y axis labels in Fig. 1 were switched over; the correct labels are: 'Longitude (° N)' on the x axis, and 'Latitude (° E)' on the y axis. This figure has now been amended in all versions of the Article.

The early history of wheat in China from C dating and Bayesian chronological modelling.

Wheat is regarded as one of the most important West Asian domesticates that were introduced into Late Neolithic/Early Bronze Age China. Despite a growing body of archaeological data, the timing and routes of its dispersal remain controversial. New radiocarbon (C) dating evidence from six archaeological sites in the Shandong and Liaoning Peninsulas and Bayesian modelling of available C data from China suggest that wheat appeared in the lower Yellow River around 2600 Before Common Era (BCE), followed by Gansu and Xinjiang around 1900 BCE and finally occurred in the middle Yellow River and Tibet regions by 1600 BCE.