Shallow-marine testate amoebae with internal structures from the Lower Devonian of China.

Testate amoebae, a polyphyletic protist group inhabiting a wide variety of extant ecosystems, have evolved as far back as early Neoproterozoic. However, their fossil record is discontinuous and biased toward empty shells. Here, we report an arcellinid testate amoeba species, Cangwuella ampulliformis gen. nov., sp. nov., from a shallow-marine community in the Early Devonian of Guangxi, southwestern China. With the aid of scanning electron microscopy and X-ray micro-tomography, we find that the shell of our testate amoeba contains some acetabuliform structures. Although such configuration does not match exactly with the known internal structures in extant testate amoebae, our fossils highlight the potential of exploring the ecological relationships between fossil testate amoebae and their associated organisms, and increase our knowledge on the diversity of testate amoebae in Early Devonian environments.

Quadriwave lateral shearing interferometry based on double birefringent crystals of beam displacer.

A quadriwave lateral shearing interferometry (QWLSI) is proposed based on double birefringent crystals of a beam displacer (DBCs-BD). The DBCs-BD is formed by adopting two birefringent crystals of a polarization beam displacer (PBD), which can generate the lateral shearing interference waves of four beams of overlapped replicas in the DBCs-BD orthogonal directions. When the replica waves are overlapped incident to the analyzer, and the direction of the transmission axis is set as 45° or 135°, the QWLSI's polarization interferogram can be obtained. The high-precision phase can be obtained by simple spectrum denoising and performing the Fourier transform of the resulting interferogram. We deduce the principle of QWLSI in detail, and the wavefront distribution can be achieved by the phase calculation. The experiment shows that the DBCs-BD-QWLSI exhibits feasibility and high precision.

Optimization of wavefront reconstruction accuracy for conjugate shift differential absolute testing.

The conjugate shift differential method, based on Fourier transforms, is critical for surface error testing of high-precision optical elements. However, this common approach is also prone to periodic spectrum loss. As such, this paper proposes conjugate double shift differential (CDSD) absolute testing, which can effectively compensate for spectrum loss and achieve accurate wavefront reconstructions. Spectrum loss in the single shift differential method is analyzed through a study of the Fourier reconstruction process. A calculation model for the proposed CDSD method is then established and constraint conditions for shift quantities are provided by analyzing double shear effects observed in transverse shear interference. Finally, the reconstruction accuracies of various spectrum compensation methods are compared. Results showed that spectrum loss became more evident with increasing shift amounts. However, the CDSD method produced the smallest measurement error compared with conventional direct zero filling and adjacent point averaging, suggesting our approach could effectively improve absolute shape measurement accuracy for planar optical elements.

Improving the phase reconstruction accuracy of simultaneous phase-shifted lateral shearing interferometry using a polarization redundant sub-region interpolation method.

In a simultaneous phase-shifted lateral shearing interferometry, a division of focal plane polarization camera is generally used as the phase-shifting device. However, acquiring simultaneous phase-shift interferograms in a single frame suffers from a lack of spatial resolution, significantly affecting the phase reconstruction accuracy. A polarization redundant sub-region interpolation (PRSI) method is proposed to solve this problem. This interpolation method distinguishes smooth regions from stripe fringe regions by calculating the polarization redundancy error of the synchronous phase shift interferogram. After sub-regional processing, resolution reconstruction is performed in the smoothed area using a fast convolutional bilinear interpolation method. In the streak detail region, the resolution reconstruction is performed based on the strength of the correlation between the orthogonal and non-orthogonal polarization channels crossing the streak region. The PRSI method can quickly reconstruct the lost pixels and accurately recover the stripe detail information. Experiment results show that the proposed interpolation method outperforms the existing dominant methods in terms of visual reconstruction effect and quantitative index of phase reconstruction.

New insights into the South China Lower Devonian flora based on fossils from Hezhang, Guizhou Province.

The Early Devonian flora of South China is composed of many endemic members and has been studied mainly based on Yunnan materials. We in this study report a new Lower Devonian plant locality, recognize four sub-regions of the Early Devonian flora from South China and furthermore demonstrate these plants' distribution pattern and probable dispersal route. The new finds of plant fossils are from the Lower Devonian of Hezhang County, Guizhou Province, and include Zosterophyllopsida Demersatheca and Euphyllophytopsida Pauthecophyton. Demersatheca contigua, consisting of cylindrical strobili with four longitudinal rows of sporangia decussately arranged, shows great similarities to the plant from Yunnan and Guangxi localities. Pauthecophyton hezhangensis sp. nov. has distinct fertile units with grouped sporangia and each unit with two or three fusiform sporangia. The new locality belongs to the Guizhou sub-region and shares some taxa with the eastern Yunnan and Cathaysia sub-regional floras within South China, in which the shared plant members are distributed around the epicontinental sea. We suggest that the Guizhou sub-region might act as a bridge during plant dispersal from eastern Yunnan to Cathaysia Oldland in the Early Devonian. This article is part of the theme issue 'The impact of Chinese palaeontology on evolutionary research'.

Morphology and Nomenclature of Barsassia (Lycopsida) from the Middle Devonian of West Junggar, Xinjiang, China.

Morphology and nomenclature are essential issues of botany, in which both extant and fossil plant taxa follow the same nomenclature code. Devonian (419.2-358.9 Ma) herbaceous lycopsid Barsassia, one of the earliest coal-forming plants in geological history, possesses a characteristic, easily recognized, step-like stem and has been thought to be an index fossil for dating and correlating the Middle Devonian strata, especially those in the paleoblocks of Siberia, Kazakhstan, Xinjiang, and North China. Here, we systematically study the Devonian lycopsid Barsassia in terms of its morphology and nomenclature, based on the new materials from the Middle Devonian Hujiersite Formation of West Junggar, Xinjiang, China, and the International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code). Barsassia ornata is determined as the type species of the genus, and a neotype is designated for that name. Barsassia ornata consists of fan- or rectangular-shaped leaves with awl-shaped or finger-like distal tips. Its leaves are pseudo-whorls and imbricately arranged on the stem surface forming distinct step-like structure.

Measurement investigation of an off-axis aspheric surface via a hybrid compensation method.

To measure the profile of an off-axis aspheric surface with large asphericity or lateral displacement, a hybrid compensation method is employed to realize a null test. First, the hybrid compensation method is simulated in MATLAB by using a fold sphere mirror and a computer-generated hologram (CGH) to compensate for the primary aberration and residual high-order aberration, respectively. For contrast, the hybrid compensation method is also simulated in Zemax by using dummy glass. Through comparing the simulation results from MATLAB and Zemax, the test CGH fringe positions from the two results are well matched. Then, the fold sphere mirror and CGH optical elements are designed and fabricated for an actual hybrid compensation measurement system, and the auto-collimation method is also used to detect the same off-axis aspheric surface. To ensure the correctness of the experiment, the result of actual hybrid compensation testing is contrasted with that of the auto-collimation method. Experiments show that the results obtained by the two methods are consistent, which indicates that this kind of hybrid compensation is an effective and accurate method for measurement of off-axis aspheric surfaces.

Position error correction of large-aperture aspherical in-position measurement.

An improved mathematical model of aspherical in-position measurement calibration is proposed in this paper, including hardware and software methods. The hardware method is used in rough calibration, but it is not precise enough. Then, the software method is chosen to further reduce the error. Simulation experiments are performed to demonstrate the effectiveness of this improved approach. Lastly, the model is verified through the testing of a concave aspheric surface. The experiment results show that the measurement errors of mirror after data processing can be reduced about 2 µm.