Theory and method of dual-energy x-ray grating phase-contrast imaging

The principle of dual-energy x-ray grating phase-contrast imaging(DEPCI) is clarified by using the theory of x-ray interference and Fresnel diffraction. A new method of retrieving phase from the two interferograms is proposed for DEPCI,and its feasibility is verified via simulation. Finally, the proposed method applied to DEPCI experiment demonstrates the effectiveness of the method. This paper lays the theoretical foundation for performance optimization of DEPCI and the further integration of DEPCI and computed tomography.

Fiber-coupler-based microfluidic system for trapping of DNA biomolecules

A miniature fiber-coupler-based microfluidic system is proposed for trapping of DNA biomolecules. The loop-shaped fiber-coupler is fabricated by using flame tapering technique and integrated in a microfluidic channel. Probe-DNA immobilized on the fiber-coupler surface enables specific recognition of target DNA sequences and effectively facilitates the trapping of target DNA molecules. The binding characteristics of biomolecules on the fiber-coupler surface have been theoretically analyzed and experimentally demonstrated. Experimental results indicate that the spectral response of the loop-shaped fiber coupler immobilized with probe DNA exhibits a red-shift with the trapping of the DNA biomolecules. The proposed microfluidic system possesses such desirable merits as simple structure, label-free method and high integration, which make it a promising candidate for applications in molecular biology and related bioengineering areas.

Influence of In-N Clusters on Band Gap Energy of Dilute Nitride In_xGa_(1-x)N_yAs_(1-y)

The In-N clusters form in the dilute nitride InxGa1-xNy As1-yalloys after annealing.It is found that the formation of the In-N clusters not only raises the N levels lying above the conduction band minimum(CBM)of In GaA s,but also raises the N levels below the CBM of In GaA s,leading to the variation of the impurity-host interaction.The blueshift of the band gap energy is relative to the variation of the impurity-host interaction.In order to describe the blueshift of the band gap energy due to the formation of the In-N clusters,a model is developed.It is found that the model can describe the blueshift of the band gap energy well.In addition,it is found the blueshift of the band gap energy due to the atom interdiffusion at the interface can be larger than that due to the formation of the In-N clusters.

Blood cell counting based on U-Net++ and YOLOv5

Clinical information about a variety of disorders is available through blood cell counting,which is usually done by manual methods.However,manual methods are complex,time-consuming and susceptible to the subjective experience of inspectors.Although many efforts have been made to develop automated blood cell counting algorithms,the complexity of blood cell distribution and the highly overlapping nature of some red blood cells(RBCs) remain significant challenges that limit the improvement of analytical accuracy.Here,we proposed an end-to-end method for blood cell counting based on deep learning.Firstly,U-Net++ was used to segment the whole blood cell image into several regions of interest(ROI),and each ROI contains only one single cell or multiple overlapping cells.Subsequently,YOLOv5 was used to detect blood cells in each ROI.Specifically,we proposed several strategies,including fine classification of RBCs,adaptive adjustment for non-maximal suppression(NMS) threshold and blood cell morphology constraints to improve the accuracy of detection.Finally,the detection outcomes for each ROI were combined and superimposed.The results show that our method can effectively address the issue of high overlap and precisely segment and detect blood cells,with a 98.18% accuracy rate for blood cell counting.

Washed microbiota transplantation vs.manual fecal microbiota transplantation:clinical findings,animal studies and in vitro screening

Fecal microbiota transplantation(FMT)by manual preparation has been applied to treat diseases for thousands of years.However,this method still endures safety risks and challenges the psychological endurance and acceptance of doctors,patients and donors.Population evidence showed the washed microbiota preparation with microfiltration based on an automatic purification system followed by repeated centrifugation plus suspension for three times significantly reduced FMT-related adverse events.This washing preparation makes delivering a precise dose of the enriched microbiota feasible,instead of using the weight of stool.Intraperitoneal injection in mice with the fecal microbiota supernatant obtained after repeated centrifugation plus suspension for three times induced less toxic reaction than that by the first centrifugation following the microfiltration.The toxic reactions that include death,the change in the level of peripheral white blood cells,and the proliferation of germinal center in secondary lymphoid follicles in spleen were noted.The metagenomic next-generation sequencing(NGS)indicated the increasing types and amount of viruses could be washed out during the washing process.Metabolomics analysis indicated metabolites with pro-inflammatory effects in the fecal microbiota supernatant such as leukotriene B4,corticosterone,and prostaglandin G2 could be removed by repeated washing.Near-infrared absorption spectroscopy could be served as a rapid detection method to control the quality of the washingprocess.In conclusion,this study for the first time provides evidence linking clinical findings and animal experiments to support that washed microbiota transplantation(WMT)is safer,more precise and more quality-controllable than the crude FMT by manual.

Spectral analysis of photo-induced delayed luminescence from mesenchymal stem cells for label-free cell viability assessment

In this work,the spectral properties of the photo-induced delayed luminescence(DL)from mesenchymal stem cells(MSCs)and their correlation with cell viability were investigated using the single photon counting combined with band-pass filters.The results show that the DL of MSCs has a broad spectral distribution,which covers from 300 nm to 650 nm at least.The DL spectrum is not evenly distributed,but mainly distributed in the range from 400 nm to 550 nm.In addition,the DL spectral distribution remains stable during the DL decay process.Compared with the DL spectra of MSCs with high viability(>80%),those of MSCs with low viability(<30%)show a significant red-shift,referring to the increase in the proportion of 572—650 nm band and the decrease in the proportions of both 315—436 nm band and 413—500 nm band.Furthermore,the degree of the DL spectral red-shift exhibits a monotonous change as MSCs’viability decreases,and thus can be used as an important indicator for the cell viability assessment.

An on-line fiber cutting-welding method for the fabrication of Fabry-Perot micro-cavity

A Fabry-Perot micro-cavity is fabricated by on-line fiber cutting-welding method.The asymmetrical fiber Fabry-Perot micro-cavity is designed and produced by cutting a standard single-mode fiber and welding the fiber end with the core-offset structure.The length of the Fabry-Perot micro-cavity could be controlled within a certain range of accuracy based on the on-line fiber cutting-welding method.According to this method,a micro-machined Fabry-Perot micro-cavity with a length of about 147μm is achieved and its spectral characteristic is also investigated in our experiment.This proposed method is suitable to produce a micro-fiber-optic structure with improved and controlled precision,which is attractive for the fiber processing field.Moreover,the fabricated Fabry-Perot micro-cavity also has potential application in the microfluidic system and biochemical detection area.

Dual-demodulation large-scope high-sensitivity refractive index sensor based on twin-core PCF

In this paper, a refractive index(RI) sensor based on the twin-core photonic crystal fiber(TC-PCF) is presented. Introducing the rectangular array in the core area makes the PCF possible to obtain high birefringence and low confinement loss over the wavelength range from 0.6 μm to 1.7 μm. Therefore, the core region can enhance the interaction between the core mode and the filling material. We studied theoretically the evolution characteristics of the birefringence and operating wavelength corresponding to the strongest polarization point under the condition of filling the rectangular array with RI matching fluid range from 1.33 to 1.41. Simulation results reveal that the proposed TC-PCF has opposite evolutions of change rates between the B and wavelength, and the maximum RI sensing sensitivities of 1.809× 10-2 B/RIU and 8 700 nm/RIU at low and high RI infill are obtained respectively, which means that the TC-PCF features of dual-parameter demodulation for the RI sensing can maintain a high refractive index sensing sensitivity within a large scope of RI ranging from 1.33 to 1.41. Compared with the results of single-parameter demodulation, it is an optimized method to improve the sensitivity of low refractive index sensors, which has great application potency in the field of biochemical sensing and detection.

An improved U-Net for cell confluence estimation

Cell confluence is an important metric to determine the growth and the best harvest time of adherent cells. At present, the evaluation of cell confluence mainly relies on experienced labor, and thus it is not conducive to the automated cell culture. In this paper, we proposed an improved U-Net algorithm(called DU-Net) for the segmentation of adherent cells. First, the general convolution was replaced by the dilated convolution to expand the receptive fields for feature extraction. Then, the convolutional layers were combined with the batch normalization layers to reduce the dependence of the network on initialization. As a result, the segmentation accuracy and F1-score of the proposed DU-Net for adherent cells with low confluence(<50%) reached 96.94% and 93.87%, respectively, and for those with high confluence(≥50%), they reached 98.63% and 98.98%, respectively. Further, the paired t-test results showed that the proposed DU-Net was statistically superior to the traditional U-Net algorithm.

Nitrogen air lasing induced by multiple filaments array

Air lasing emission by launching intense ultrafast laser pulses in atmosphere has recently attracted increasing interest in the ultrafast laser science and atmospheric science fields,especially for remote sensing techniques.We demonstrated the fluorescence emissions at 337 nm,357 nm and 391 nm induced by multiple filaments using four kinds of step phase plates.Our results have indicated that the fluorescence signal has been amplified as it propagates along the filament through amplified spontaneous emission(ASE),and the fluorescence intensity is also enhanced in the backward direction via multiple filaments.Furthermore,the gain coefficient through ASE is increased with the number of filaments.

Laser-tuned whispering gallery modes in silica microbubble resonator integrated with iron oxide particles

A 473-nm-laser-tuned whispering gallery mode(WGM) silica microbubble resonator integrated with iron oxide particles is demonstrated in this paper. Owing to the photo-induced thermal effect, the WGM resonance wavelength could be tuned by adjusting laser power density of the illuminating light absorbed by the iron oxide particles. A wavelength tuning sensitivity of 0.03 nm/(mW·mm^(-2)) and a tuning range of 0.18 nm are experimentally achieved. Moreover, the influence of ambient temperature on the WGM spectral characteristics is experimentally studied, and a silica-microbubble-based reference scheme is demonstrated to compensate for the temperature-caused resonance wavelength variation. The proposed laser-tuned microresonator has great potential in optical modulation and high-precision optical filtering applications.

Intermodal interference based refractive index sensor employing elliptical core photonic crystal fiber

A refractive index(RI)sensor based on elliptical core photonic crystal fiber(EC-PCF)has been proposed.The asymmetric elliptical core introduces the polarization-dependent characteristics of the fiber core modes.The performances of intermodal interference between the intrinsic polarization fiber core modes are investigated by contrast in two interferometers based on the Mach-Zehnder(M-Z)and Sagnac interference model.In addition,the RI sensing characteristics of the two interferometers are studied by successively filling the three layers air holes closest to the elliptical core in the cladding.The results show that the M-Z interference between LP_(01)and LP_(11)mode in the same polarized direction is featured with the incremental RI sensing sensitivity as the decreasing interference length,and the infilled scope around the elliptical core has a weak correlation with the RI sensing sensitivity.Due to the high birefringence of LP11 mode,the Sagnac interferometer has better RI sensing performance,the maximum RI sensing sensitivity of 12000 nm/RIU is achieved under the innermost one layer air holes infilled with RI matching liquid of RI=1.39 at the pre-setting EC-PCF length of 12 cm,which is two orders of magnitude higher than the M-Z interferometer with the same fiber length.The series of theoretical optimized analysis would provide guidance for the applications in the field of biochemical sensing.