Investigations of moiréartifacts induced by flux fluctuations in x-ray dark-field imaging

X-ray dark-field imaging using a grating interferometer has shown potential benefits for a variety of applications in recent years.X-ray dark-field image is commonly retrieved by using discrete Fourier transform from the acquired phasestepping data.The retrieval process assumes a constant phase step size and a constant flux for each stepped grating position.However,stepping errors and flux fluctuations inevitably occur due to external vibrations and/or thermal drift during data acquisition.Previous studies have shown that those influences introduce errors in the acquired phase-stepping data,which cause obvious moiréartifacts in the retrieved refraction image.This work investigates moiréartifacts in x-ray dark-field imaging as a result of flux fluctuations.For the retrieved mean intensity,amplitude,visibility and dark-field images,the dependence of moiréartifacts on flux fluctuation factors is theoretically derived respectively by using a first-order Taylor series expansion.Results of synchrotron radiation experiments verify the validity of the derived analytical formulas.The spatial frequency characteristics of moiréartifacts are analyzed and compared to those induced by phase-stepping errors.It illustrates that moiréartifacts can be estimated by a weighted mean of flux fluctuation factors,with the weighting factors dependent on the moiréphase and different greatly for each retrieved image.Furthermore,moiréartifacts can even be affected by object’s features not displayed in the particular contrast.These results can be used to interpret images correctly,identify sources of moiréartifacts,and develop dedicated algorithms to remove moiréartifacts in the retrieved multi-contrast images.

Spatial resolution and image processing for pinhole camera-based X-ray fluorescence imaging: a simulation study

Spatial resolution and image-processing methods for full-field X-ray fluorescence(FF-XRF)imaging using X-ray pinhole cameras were studied using Geant4simulations with different geometries and algorithms for image reconstruction.The main objectives were:(1)calculating the quantum efficiency curves of specific cameras,(2)studying the relationships between the spatial resolution and the pinhole diameter,magnification,and camera binning value,and(3)comparing image-processing methods for pinhole camera systems.Several results were obtained using a point and plane source as the X-ray fluorescence emitter and an array of 100×100 silicon pixel detectors as the X-ray camera.The quantum efficiency of a back-illuminated deep depletion(BI-DD)structure was above 30%for the XRF energies in the 0.8–9 keV range,with the maximum of 93.7%at 4 keV.The best spatial resolution of the pinhole camera was 24.7μm and 31.3 lp/mm when measured using the profile function of the point source,with the diameter of 20μm,magnification of 3.16,and camera bin of 1.A blind deconvolution algorithm with Gaussian filtering performed better than the Wiener filter and Richardson iterative methods on FF-XRF images,with the signal-to-noise ratio of 7.81 dB and improved signalto-noise ratio of 7.24 dB at the diameter of 120μm,magnification of 1.0,and camera bin of 1.

A mini-review on recent progress of new sensitizers for luminescence of lanthanide doped nanomaterials

Trivalent lanthanide(Ln2+)doped luminescent nanocrystals are promising for applications ranging from biosensor,lasing,super-resolution nanoscopy,information security and so on.Although the utility prospect is of great attractions,the light absorption of these lanthanide doped nanocrystals is inherently weak due to the electric dipole-forbidden 4f→4f transitions.Even worse,the quantum yields of upconverison nanocrystals are very low,which will unavoidably hinder their further applications.In a typical lanthanide luminescent nanosystem,both sensitizers as light absorption centers and activators as light emitting centers are necessary and important for desired luminescence properties.Among various sensitization systems,only Yb3+and Nd+are considered as the most efficient sensitizers.Thus,the corresponding excitation wavelengths are strictly limited around 980 and 808 nm.To enrich excitation wavelengths and boost luminescence intensity,exploring more sensitization units that possess larger absorption cross section,higher efficiency of energy transfer process and independent excitation is imperative and beneficial for the demands of different applications,such as broadened absorption in near infrared(NIR)region for higher conversion efficiency of solar cells,prolonged excitation wavelength to second near infrared windows region(NIR Ⅱ,1,000-1,700 nm)for in vivo fluorescence imaging with deeper tissue depth and higher spatial resolution,more orthogonal excitations and emissions to improve optical multiplexing,and so on.Therefore,in the review,we primarily conclude several major energy transfer mechanisms from sensitizers to activators.Then we present three kinds of sensitizers,including lanthanide ions,organic dyes and quantum dots(QDs),and introduce the newly designed sensitization system that allows us to exploit superior excitation wavelength and amplity luminescence intensity.Finally,several future challenges and opportunities for the sensitizing strategies are discussed in hope of directing and broadening the applications of lanthanide nanosystem.

Eu^(3+)-doped Bovine Serum Albumin-derived Carbon Dots for Ratiometric Fluorescent Detection of Tetracycline

The abuse of antibiotics has become a global concern,thus it is significant to develop simple antibiotic assays.Herein,a novel type of lanthanide-doped bovine serum albumin(BSA)derived carbon dots(BCDs)dubbed Eu-BCDs has been unveiled for ratiometric fluorescent detection of tetracycline(TC),which was formed from the one-step hydrothermal reaction of Eu^(3+)and BSA.Upon challenge with TC,the blue fluorescence of Eu-BCDs at 448 nm was gradually quenched due to the internal filtration effect,while the characteristic red fluorescence of Eu^(3+)at 618 nm was significantly enhanced owning to the antenna effect,leading to the ratiometric fluorescent detection of TC with fast response(2 min),a wide linear dynamic range(0-80μmol/L),and high selectivity and sensitivity(limit of detection(LOD)of 3 nmol/L).Moreover,Eu-BCDs can be successfully applied for the ratiometric fluorescent detection of TC in environmental and biological samples,such as river water,milk,honey and serum.The Eu-BCDs sensing platform would have great application potential in view of its simple preparation,rapid response,high sensitivity and good selectivity.

Learning Deep RGBT Representations for Robust Person Re-identification

Person re-identification(Re-ID)is the scientific task of finding specific person images of a person in a non-overlapping camera networks,and has achieved many breakthroughs recently.However,it remains very challenging in adverse environmental conditions,especially in dark areas or at nighttime due to the imaging limitations of a single visible light source.To handle this problem,we propose a novel deep red green blue(RGB)-thermal(RGBT)representation learning framework for a single modality RGB person ReID.Due to the lack of thermal data in prevalent RGB Re-ID datasets,we propose to use the generative adversarial network to translate labeled RGB images of person to thermal infrared ones,trained on existing RGBT datasets.The labeled RGB images and the synthetic thermal images make up a labeled RGBT training set,and we propose a cross-modal attention network to learn effective RGBT representations for person Re-ID in day and night by leveraging the complementary advantages of RGB and thermal modalities.Extensive experiments on Market1501,CUHK03 and Duke MTMC-re ID datasets demonstrate the effectiveness of our method,which achieves stateof-the-art performance on all above person Re-ID datasets.