High-resolution Digital Images Research Articles

SPhaseStation: a whole slide quantitative phase imaging system based on dual-view transport of intensity phase microscopy.

Whole slide imaging scans a microscope slide into a high-resolution digital image, and it paves the way from pathology to digital diagnostics. However, most of them rely on bright-field and fluorescence imaging with sample labels. In this work, we designed sPhaseStation, which is a dual-view transport of intensity phase microscopy-based whole slide quantitative phase imaging system for label-free samples. sPhaseStation relies on a compact microscopic system with two imaging recorders that can capture both under and over-focus images. Combined with the field of view (FoV) scan, a series of these defocus images in different FoVs can be captured and stitched into two FoV-extended under and over-focus ones, which are used for phase retrieval via solving the transport of intensity equation. Using a 10× micro-objective, sPhaseStation reaches the spatial resolution of 2.19µm and obtains the phase with high accuracy. Additionally, it acquires a whole slide image of a 3m m×3m m region in 2min. The reported sPhaseStation could be a prototype of the whole slide quantitative phase imaging device, which may provide a new perspective for digital pathology.

Computer vision-based statistical crack quantification for concrete structures

This paper newly proposed a computer vision-based crack quantification algorithm using a statistical approach. Recently, high-resolution digital images have been effectively utilized for automated crack width and length evaluation on concrete structures. However, cracks are often difficult to accurately measure by randomly distributed and complex shapes. To overcome the technical limitation, a novel statistical crack quantification algorithm is proposed and experimentally validated through concrete structures in this paper. First, cracks on digital images are automatically detected using a deep semantic segmentation network. Then, multi-branched cracks are separated into single cracks through crack map generation. Each separated crack length and width is calculated by the Euclidean distance transform algorithm. Finally, crack width is presented as a representative value with a statistical confidence interval. The quantitative crack evaluation results for width and length were successfully compared with the actual field measurement values by average differences of 18.07% and − 26.28%, respectively.

Quantitative investigation of strain partitioning and failure mechanism in ultrafine grained medium Mn steel through high resolution digital image correlation

Ultrafine grained medium Mn steel exhibits simultaneous high strength and ductility, however, often showing Lüders deformation and discontinuous yielding phenomena. The connections between martensite transformation and Lüders deformation as well as the localized failure behavior are quantitatively investigated through high resolution digital image correlation, enabled by nanoscale strain distribution and microstructural alignment. At a low global tensile strain level, strain localization happens in austenite domain resulted from a sequential slip deformation and martensite transformation, which then triggers the yielding of ferrite by generating thin strain channels to connect adjacent hotspots. This microscopic deformation mode promotes the formation of macroscopic deformation bands, resulting in Lüders band initiation and propagation. When increasing the applied load, the externally imposed strain is accommodated by ferrite instead, resulting in pronounced strain partitioning. The triple grains boundary having no further strain hardening capacity is favorable for void initiation and propagation.

Light-Matter Interactions Revealing Load-Induced Phase Mobility in Elastomers.

Elastomers with segmental microstructure are a fascinating class of shock-tolerant and impact-resistant materials. However, their technological potential remains untapped due to a vague understanding of the molecular contributions to their superior mechanical behavior. Herein, in situ light-matter interactions, to reveal the extent of microstructural mobility by temporally exploiting molecular processes during creep response, are leveraged. The segmental microstructure comprises aromatic hard domains embedded within an aliphatic soft matrix. High-resolution digital image correlation reveals the development of strain striations, mild anisotropy, and the mechanisms responsible for domain mobility, where the rate of hard segment mobility is found to be 60% slower than that of the soft segment. Terahertz spectral analyses pinpoint the contributions of interchain hydrogen bonding of the hard segments and their significant conformational changes by observing spectral features at ≈1.2THz and ≈1.67THz. Moreover, the domain mobility is examined using experimental and computational light scattering approaches, uncovering dynamic scattering and elucidating the difference in the complex refractive index of the soft and hard segments. The study unlocks the pathway for quantitative measurements of elusive molecular mobility and conformational changes during mechanical loading and sheds light on the origin of the shock tolerance in some elastomeric polymers with segmental microstructure.

The effect of Mn containing dispersoids on the distribution of slip and fracture mode in Al-Mg-Si-Mn alloys

Improvements in the fracture performance of Al-Mg-Si extrusions are required to meet the demands of the automotive market. The fracture mode and the associated ductility results from competition between transgranular and intergranular fracture paths where intersection of slip bands and grain boundaries plays a significant role. In this study, the distribution of plastic strain within grains for microstructures with different spacings of Mn dispersoids was quantified using high resolution digital image correlation. It was observed that plastic strain was organized into slip bands where the magnitude of local shear strain decreased with reduced inter particle spacing of the dispersoids. It is proposed that this leads to a lower stress concentration on the grain boundary, decreasing the propensity for intergranular fracture. This was consistent with the findings that intergranular fracture was dominant in the dispersoid free material whereas low and high densities of dispersoids gave rise to a transgranular fracture mode.

Histopathological evaluation of Onchocerca volvulus nodules by microscopy and by digital image analysis for the study of macrofilaricidal drug efficacy.

Novel drugs or drug combinations that kill or permanently sterilize adult Onchocerca volvulus worms would be very helpful for treatment and elimination of onchocerciasis. In absence of a reliable biomarker for viable adult worms, histopathological assessment of worms within onchocercal nodules is a standard method to determine macrofilaricidal activity. The goal of the present study was to determine the agreement between two independent experts in the analysis of nodule sections and to assess the value of digital imaging as a means of standardizing the analysis. Two expert microscopists independently assessed 605 nodules by direct microscopy. At least two sections with two different stains hematoxylin & eosin (H&E, APR immunostain) of paraffin-embedded, ethanol-fixed whole-nodule cross-sections were analyzed. After variables were identified prone to observer discrepancies, we performed a second study to compare consolidated results for 100 nodules obtained by the two readers by microscopy and by analysis of scanned, high resolution digital images (20x magnification). The last data set analyzed was a quality panel of 100 nodules that has been previously examined by microscopy, and included additional immunostains for Wolbachia endobacteria. These slides were digitalized, read by the two assessors and results were compared with original microscopy results. The degree of agreement between assessors varied for different parameters. Agreement for female worm counts in nodules was approximately 80%, while agreement regarding female worm viability was 98%. There were no major differences observed between results obtained by microscopy or digital images. Good agreement for important parameters was also observed for the nodules of the quality panel. Nodule analysis by experienced microscopists was reproducible with regard to important parameters such as identification of living female worms or detection of normal embryogenesis. Assessments varied more for other parameters, and we recommend continued use of two independent readers for detailed analyzes. Analysis of scanned images provided similar results to direct microscopy. This facilitates training and comparison of nodule findings by readers in different locations. Analysis of high quality digital images that can be viewed remotely should improve the quality and availability of nodule assessments that are primary endpoints for onchocerciasis clinical trials.

Quantification of Slip Band Distribution in Polycrystals: An Automated Fast Fourier Transform Decomposition Approach.

Plastic deformation is accumulated in slip bands in a wide variety of engineering alloys. Multiple material and loading conditions impact their distribution and degree of slip localization, but these effects are rarely quantified. To tackle this, the current work introduces a fast Fourier transform (FFT) decomposition method and applies it to a tensile-loaded polycrystalline nickel-based superalloy imaged via high-resolution digital image correlation and electron backscatter diffraction. This approach identifies active slip planes over the FFT images of individual grains and performs inverse transforms such that slip band traces with shared orientations are isolated. This technique enabled the largest quantification of slip band spacings and in-plane strains to date, with a total of 6,557 slip bands detected. The results show that the slip band spacings increase with grain size, with no evident dependence on grain orientation and Schmid factor. Slip bands are found to develop similar spacings along different octahedral planes and continue to spread over larger regions of the grain as the resolved shear stress of the active slip system increases. The FFT decomposition technique, which could be employed with multiple microscopy techniques, will allow for much-needed large-scale quantitative studies of slip localization.

Overcoming The Taxonomic Impediment: An Action Plan For India

Insect taxonomy in India has been on a terminal decline and the unknown and undocumented insects of India face the threat of extinction before they are formally described due to climate change, habitat destruction and other anthropogenic factors. Ways to overcome the so called ‘Taxonomic impediment’, loosely defined as the lack of experts and funds and other resources for taxonomic research, are briefly discussed in the Indian context. A combination of concise morphological descriptions, high resolution digital imaging and open access web publishing with at least minimum molecular characterization (COI sequences) appears to be an ideal way to promote fast track documentation of Indian insects. Needless to add, increased funding and opportunities for insect taxonomy is the foremost requirement to further the cause of insect taxonomy in India. For this, insect taxonomic services should be recognized as a major input in agricultural pest management technology by ICAR and state agricultural universities.

In-situ characterization and multiscale finite element analyses for thermomechanical behavior of 3D woven composites

Thermal stress concentration, induced by the mismatch of coefficients of thermal expansion (CTE), contributes significantly to fatigue and failure of composites. We demonstrated the practicality of fiber Bragg grating sensors and high-resolution digital image correlation technique for in-situ characterization of thermal strain field evolution in 3D angle-interlocked woven composites (3DAWC). Multiscale representative volume element (RVE) models were constructed for studying its steady-state and transient-state thermomechanical behaviors. We found the CTE mismatch causes stress localization at the interface and it exhibits a periodic distribution within the 3DAWC, which attributes to its 3D architecture. Stresses and strains concentrate mainly on the sharp interfaces close to the diamond-shaped yarns and the resin-rich areas, respectively. The thermal stress in the resin reaches a maximum of 22 MPa around Tg, close to half of its yield stress. The macroscopic homogenized CTEs calculated from the RVE model in thickness and in warp directions are greater than those of each component. Transient analysis reveals that the non-uniform temperature field induced by heat transfer effects has little effect on maximum stress values in each component.

Enhanced mechanical strength in hot-rolled La-Fe-Si/Fe magnetocaloric composites by microstructure manipulation

La-Fe-Si-based alloys possess a giant magnetocaloric effect due to the sharp itinerant-electron metamagnetic transition. However, the relatively poor mechanical strength of these alloys impedes their practical application in the magnetic refrigeration system. In this study, we employed hot rolling to manipulate the microstructure, and thus to improve the mechanical strength of LaFe11.6Si1.4/Fe composites. The microstructure and magnetic phase transition behavior have been systematically investigated by X-ray tomography, high-resolution transmission electron microscope and digital image correlation technique. We found that the bending strength of the hot-rolled LaFe11.6Si1.4/Fe reached up to 176 MPa, which is about 26% higher than the non-rolled one. The refinement of the α-Fe particles plays a key role in hindering crack propagation and enhancing the mechanical strength of the hot-rolled sample. Additionally, the reduction of the La-rich phase and large-size pores is found to be beneficial to the mechanical strength enhancement. The hot-rolled composite shows a sharp metamagnetic transition with a maximum magnetic entropy change of 17 J kg−1 K−1 for 2 T magnetic field change. This study demonstrates that microstructure manipulation based on hot rolling is a feasible approach to improve the mechanical strength of La-Fe-Si materials.

Mechanical behavior of polycrystals: Coupled in situ DIC-EBSD analysis of pure copper under tensile test

Understanding the mechanisms at the microstructure scale is of great importance for modeling the behavior of materials at different scales. To this end, digital image correlation (DIC) is an effective measurement method for evaluating the strains generated by various loading conditions. The objective of this paper is to describe the experimental setup and the use of high resolution digital image correlation (HRDIC) during in situ Scanning Electron Microscope (SEM) tests in order to provide a coupling between polycrystalline modeling and experiment in the near future. The HRDIC technique is used to evaluate the tensile behavior of a pure copper polycrystal at room temperature. Several magnitudes are investigated in order to discuss the representativeness of the results with respect to the macroscopic scale. The selected image correlation parameters are discussed regarding the ability of the technique to define inter- and intra- granular strain heterogeneities. Finally, based on EBSD analyzes, the impact of grain orientation on the mechanical behavior is discussed. The Schmid factor, calculated from a macroscopic stress, appears to be the determining factor concerning the orientation of the location bands. On the other hand, it is not sufficient to define the mean strains in the grains.

Toward digital histopathological assessment in surgery for central nervous system tumors using stimulated Raman histology.

Intraoperative neuropathological assessment with conventional frozen sections supports the neurosurgeon in optimizing the surgical strategy. However, preparation and review of frozen sections can take as long as 45 minutes. Stimulated Raman histology (SRH) was introduced as a novel technique to provide rapid high-resolution digital images of unprocessed tissue samples directly in the operating room that are comparable to conventional histopathological images. Additionally, SRH images are simultaneously and easily accessible for neuropathological judgment. Recently, the first study showed promising results regarding the accuracy and feasibility of SRH compared with conventional histopathology. Thus, the aim of this study was to compare SRH with conventional H&E images and frozen sections in a large cohort of patients with different suspected central nervous system (CNS) tumors. The authors included patients who underwent resection or stereotactic biopsy of suspected CNS neoplasm, including brain and spinal tumors. Intraoperatively, tissue samples were safely collected and SRH analysis was performed directly in the operating room. To enable optimal comparison of SRH with H&E images and frozen sections, the authors created a digital databank that included images obtained with all 3 imaging modalities. Subsequently, 2 neuropathologists investigated the diagnostic accuracy, tumor cellularity, and presence of diagnostic histopathological characteristics (score 0 [not present] through 3 [excellent]) determined with SRH images and compared these data to those of H&E images and frozen sections, if available. In total, 94 patients with various suspected CNS tumors were included, and the application of SRH directly in the operating room was feasible in all cases. The diagnostic accuracy based on SRH images was 99% when compared with the final histopathological diagnosis based on H&E images. Additionally, the same histopathological diagnosis was established in all SRH images (100%) when compared with that of the corresponding frozen sections. Moreover, the authors found a statistically significant correlation in tumor cellularity between SRH images and corresponding H&E images (p < 0.0005 and R = 0.867, Pearson correlation coefficient). Finally, excellent (score 3) or good (2) accordance between diagnostic histopathological characteristics and H&E images was present in 95% of cases. The results of this retrospective analysis demonstrate the near-perfect diagnostic accuracy and capability of visualizing relevant histopathological characteristics with SRH compared with conventional H&E staining and frozen sections. Therefore, digital SRH histopathology seems especially useful for rapid intraoperative investigation to confirm the presence of diagnostic tumor tissue and the precise tumor entity, as well as to rapidly analyze multiple tissue biopsies from the suspected tumor margin. A real-time analysis comparing SRH images and conventional histological images at the time of surgery should be performed as the next step in future studies.

Effect of in-lath slip strength on the strain partitioning in a dual-phase steel investigated by high-resolution digital image correlation and crystal plasticity simulations

In this study, the effect of different modeling hypotheses for the plastic deformation of lath martensite was investigated through an integrated experimental–numerical approach. The local plastic strain distribution of a dual-phase steel with a coarse microstructure was quantified by high-resolution digital image correlation analysis. The same area was reproduced in a crystal plasticity finite element model using the electron backscatter diffraction measurement of the specimen surface prior deformation. Different modeling hypotheses in terms of in-lath and out-of-lath slip strength as well as boundary and bulk elements were explored. It was found that early plastic deformation in lath martensite grains predominantly took place at various interfaces in the form of slip bands parallel to the in-lath slip planes in blocks exhibiting high in-lath Schmid factor. A comparison between experiment and simulations suggested that assuming a lower strength and hardening rate for in-lath slip systems of boundary elements better reproduced the plastic strain fields in martensite grains. However, the different models showed limited effect on the strain distribution within ferrite grains and on the local stress–strain path at void nucleation sites. This suggested that the main factor affecting early strain concentration and subsequent damage initiation in ferrite grains was the phase morphology and strength contrast.

Role of microstructure heterogeneity on deformation behaviour in additive manufactured Ti-6Al-4V

The influence of two different bi-lamellar microstructures, with varied volume fractions of primary alpha lamellae (αp) and secondary alpha lamellae (αs), on the mechanical performance of laser powder bed fusion fabricated Ti-6Al-4V has been investigated. A low and high αp volume fraction variant was created by different solution heat treatment temperatures. Scanning transmission electron microscopy (STEM) was performed on both materials to give a comprehensive assessment of the local microstructure and element partitioning effects. Deformation experiments, combined with high resolution digital image correlation (HRDIC), enabled a detailed comparison of 2D slip patterns at progressive strain increments during tensile loading, with the underlying microstructure collected using electron backscattering diffraction based grain orientation mapping. In both microstrural variants, shear strain was mainly observed in the coarse αp lamellae, suggesting that the constituent was softer than the fine αs regions. This strength difference is not attributed to potential different levels of Al-based solid solution strengthening as a result of element partitioning. Instead, the strength difference was attributed to the fine β ligaments formed in-between the αs during ageing. The low αp volume fraction variant, i.e. high-volume fraction of αs, displayed a significant increase in yield strength compared to the high αp volume fraction variant without compromising ductility through increased heterogeneous plasticity and an enhanced strain hardening rate.

Simultaneous enhancement of strength and ductility for AZ31 magnesium alloy by pre-twinning induced heterostructure

Pre-twinning was used to tailor the strength and ductility of AZ31 magnesium alloy. Simultaneous enhancements in both ductility and strength were achieved in the AZ31 after the introducing of a high fraction of twin-matrix pairs. The slip trace analysis indicated that although the area-weighted average global Schmid factors (SFs) were not significantly changed, much more non-basal slip was activated in the pre-twinned sample compared with that in the as-received sample, which was beneficial to achieving higher work hardening and obtaining higher uniform elongation. The high-resolution digital image correlation (DIC) combined with ex-situ electron backscatter diffraction (EBSD) characterization revealed that the uniformity of the grain-size scale strain distribution was improved and the local strain concentration at the boundary was reduced during the loading as result of the extra activated non-basal slip, which delayed intergranular crack initiation and increased ductility. The activation of much non-basal slip with high critical resolved shear stress, the hetero-deformation, and the fine equivalent grain size caused the strengthening of the AZ31 sample with a high fraction of twin-matrix pair interfaces. These results imply that tailoring the twin-matrix interface density is an effective strategy to achieve excellent strength-ductility combinations in HCP metals.

High-resolution mapping of the strain heterogeneity in heterogeneous and homogeneous structured Mg 13Gd alloy

The hetero-deformation induced (HDI) stress can effectively promote extra strengthening and strain hardening behavior, which originates from the heterogenous deformation between soft and hard domains. How to quantitatively evaluate the strain heterogeneity at the micron and sub-micron scales remains a great challenge during deformation incompatibility. In this study, the strain evolution at grain level of heterogeneous (HES) and homogeneous-structured (HOS) Mg 13Gd (wt%) alloy was characterized by high-resolution digital image correlation. Both HES and HOS samples show strain heterogeneity related to the physical slip bands inside grains, and the magnitude of local deformation in grain level is much higher than the macroscopic strain, especially at grain boundaries. The HOS sample can also generate HDI stress due to the remarkable difference in Schmid factor and lower geometrical compatibility factor between adjacent grains. The formation of dispersed strain bands in the coarse grains with hard orientation of the HES sample contributes to strain delocalization behavior and the improvement of strain hardening capacity. These results provide us with a new insight for heterostructured design of Mg alloys on a more microscopic scale. • The strain evolution at grain level of heterogeneous and homogeneous-structured Mg 13Gd (wt%) alloy was characterized by high-resolution digital image correlation. • The heterogeneous and homogeneous-structured sample showed strain heterogeneity, and the magnitude of local deformation in grain level was much higher than the macroscopic strain, especially at grain boundaries. • The homogeneous-structured sample can also generate the hetero-deformation induced stress due to the remarkable difference in Schmid factor and lower geometrical compatibility factor between adjacent grains. • The formation of dispersed strain bands in the coarse grains of the heterogeneous-structured sample contributed to strain delocalization behavior as well as the improvement of strain hardening capacity.

Precipitate mediated plasticity at twin boundary in Nickel-based superalloy

Twin boundaries (TBs) were reported to be the vulnerable site for strain localization in Nickel-based superalloys, but the mechanistic origin of localized plasticity is obscure and the effect from precipitates is still controversial. To clarify the role of γ″ in the localized plasticity, in-situ high-resolution digital image correlation (HRDIC) coupled with correlative multiscale characterizations were employed to reveal the microstructural strain evolution of Inconel 718 superalloy with different γ″ sizes. Pronounced localized plasticity and strain localization were observed at TBs in all samples regardless of the γ″ size, and the governing factor for the localized plasticity is the maximum Schmid factor associated with TBs. It is found that the formation of symmetric V-shaped γ″ along TBs results in easy channels for dislocation slip by destructing the precipitation strengthening adjacent to TBs, which takes the responsibility for the severe localized plasticity at TBs regardless of the γ″ size, and the size of γ″ only determines the distance between the localized slip bands and TBs.

Palaeohydrology from the Northern Salado River, a lower Parana river tributary (Argentina)

Palaeofloods and drainage palaeostage can be approached from sedimentological, stratigraphical, geomorphological, geodetic, and geophysical information. This allows us to supply pre-instrumental and historical data and to assess a particular flood-prone area. It has been proved that the study of Late Holocene fluvial sediments is valuable source to estimate 1 × 102-1x103yr. scale occurrence and long-term recurrence of maximum events. The geological evidence of palaeofloods in lowlands in Central Argentina may reveal higher discharges likely occurred in the near past.In this work, we attempt to identify sedimentological evidence of past floods in Late Holocene sediments from the northern Salado River (NSR), an important tributary of the lower Paraná River basin (Chaco-Pampean plain region). In the yr. 2003, the lower reaches of the NSR recorded an extreme flood event that provoked a disaster in Santa Fe, a city of 500,000 inhabitants located at the river mouth.Considering the importance of this event, we developed a geomorphometry methodology for discriminating different levels of fluvial terraces and flood indicators in a representative area of the NSR, using multi-scale resolution Digital Elevation Model (DEM) data. Descriptions of flood-associated fluvial landforms and sedimentological stratigraphic attributes were performed in the field. High-resolution geodetic information and digital optical images were obtained from UAV photogrammetry. Ground Penetrating Radar (GPR) cross-sections were achieved and addressed to detect extreme flood evidence. A geomorphometric routine was applied to simulate the extreme flood scenarios, based on the data obtained from the field. The map resulting from the simulation was compared to satellite images recorded in the yr. 2003 extreme flood. A series of slackwater deposits and other palaeostage indicators (SWD-PSI) showed elevations higher than those reached over the yr. 2003 extraordinary flood (instrumentally recorded) and in the yr. 1914 historic flood event. The geomorphometric simulation of a flood event, calibrated from these diagnostic landforms, allowed us to extend the flood-prone area beyond the boundaries of the current active floodplain and channel. The integrative methodology enabled the mapping of areas potentially prone to flooding. The estimations of the discharges associated to the inferred palaeofloods could be 50–80% larger than the maximum events historically documented and instrumentally measured.

A multi-task deep learning framework for perineural invasion recognition in gastric cancer whole slide images

Perineural invasion (PNI) is the process of neoplastic invasion of the nerves and is a prognostic factor in gastric cancer. However, such examination is a labor-intensive task in high-resolution digital pathological images. To alleviate this problem, we propose a multi-task deep learning-based framework to highlight diagnostically significant PNI regions in whole slide images (WSIs) of human gastric cancer tissue sections. The proposed framework includes a gastric cancer segmentation model, neural detection model, and PNI decision-making module, which realizes the segmentation of the gastric cancer region while completing the task of identifying PNI. Adequate comparative experiments were performed on our own gastric cancer PNI dataset called GC-PNI. Experiments have shown that our proposed model can effectively diagnose PNI with a high sensitivity of 0.972 and a specificity of 0.933, illustrating the potential of this practical application.

Heterogeneous slip localization in an additively manufactured 316L stainless steel

Additively manufactured 316L stainless steels display significantly higher yield strength than their as-cast or wrought counterparts. This is associated with the micro-scale cellular structure and complex grain and sub-grain structure, resulting from high cooling rates occurring during the additive manufacturing process. The consequences of these peculiar microstructural features on plastic localization early in the plastic regime at the sub-grain scale are investigated. The plastic localization involved during monotonic deformation of conventional and additive manufactured 316L stainless steels is investigated using high-resolution digital image correlation. Significant heterogeneous slip localization is observed in the additively manufactured 316L stainless steels compared to the wrought 316L stainless steels. The cellular structure and low-angle grain boundaries are observed to control the incipient plasticity. In addition, slip localization characteristics indicate that the additional strengthening in the AM material is mainly related to the cellular structure acting as a dislocation forest-type obstacle.