Microstructural evolution of injection molded gas- and water-atomized 316L stainless steel powder during sintering

The present study investigates the microstructural evolution and densification behavior of water- and gas-atomized 316L stainless steel powder. Dilatometry and quenching studies were conducted to determine the extent of densification and corresponding microstructural changes. Results indicate that water-atomized powder could be sintered to 97% of theoretical density, while gas-atomized powders could be sintered to near-full density. The difference in the densification behavior is examined in terms of the particle morphology, initial green density and the particle chemistry.     

Document image characterization using a multiresolution analysis of the texture: application to old documents

In this article, we propose a method of characterization of images of old documents based on a texture approach. This characterization is carried out with the help of a multi-resolution study of the textures contained in the images of the document. Thus, by extracting five features linked to the frequencies and to the orientations in the different areas of a page, it is possible to extract and compare elements of high semantic level without expressing any hypothesis about the physical or logical structure of the analyzed documents. Experimentation based on segmentation, data analysis and document image retrieval tools demonstrate the performance of our propositions and the advances that they represent in terms of characterization of content of a deeply heterogeneous corpus.     

Geospatial Analytics for COVID-19 Active Case Detection

Ever since the COVID-19 pandemic started in Wuhan, China, much research work has been focusing on the clinical aspect of SARS-CoV-2. Researchers have been leveraging on various Artificial Intelligence techniques as an alternative to medical approach in understanding the virus. Limited studies have, however, reported on COVID-19 transmission pattern analysis, and using geography features for prediction of potential outbreak sites. Predicting the next most probable outbreak site is crucial, particularly for optimizing the planning of medical personnel and supply resources. To tackle the challenge, this work proposed distance-based similarity measures to predict the next most probable outbreak site together with its magnitude, when would the outbreak likely to happen and the duration of the outbreak. The work began with preprocessing of 1365 patient records from six districts in the most populated state named Selangor in Malaysia. The dataset was then aggregated with population density information and human elicited geography features that might promote the transmission of COVID-19. Empirical findings indicated that the proposed unified decision-making approach outperformed individual distance metric in predicting the total cases, next outbreak location, and the time interval between start dates of two similar sites. Such findings provided valuable insights for policymakers to perform Active Case Detection.     

Six Birds with One Stone: Versatile Nanoporphyrin for Single-Laser-Triggered Synergistic Phototheranostics and Robust Immune Activation

Simultaneous photodynamic therapy (PDT) and photothermal therapy (PTT) can reduce the risks of drug leakage, body burden, and preparation complexity in traditional combination PDT/PTT. Here, a versatile nanoporphyrin (Pp18-lipos) self-assembled from lipid–purpurin 18 conjugates (Pp18-lipids) and pure lipids is presented. The as-prepared Pp18-lipos with 2 mol% Pp18-lipids can perform effective PDT and fluorescence imaging. The Pp18-lipos with 65 mol% Pp18 can perform potent PTT and photoacoustic imaging. The chelation of Mn²⁺ endows the Pp18-lipids-Mn²⁺ a high T₁-weighted magnetic resonance imaging contrast. Notably, pretreatment of low-dose PDT facilitates the endocytosis and tumor accumulation of Pp18-lipos, thus achieving synergistic PDT/PTT. Upon exposure to a single 705 nm-laser, the combination of PDT/PTT achieves a significantly higher tumor growth inhibition rate than PDT or PTT alone. In addition, it is found that the synergistic PDT/PTT triggers more potent anti-tumor immune response including tumor infiltration of immune cells and release of related cytokines.     

Do Images of Biskyrmions Show Type‐II Bubbles?

The intense research effort investigating magnetic skyrmions and their applications for spintronics has yielded reports of more exotic objects including the biskyrmion, which consists of a bound pair of counter‐rotating vortices of magnetization. Biskyrmions have been identified only from transmission electron microscopy images and have not been observed by other techniques, nor seen in simulations carried out under realistic conditions. Here, quantitative Lorentz transmission electron microscopy, X‐ray holography, and micromagnetic simulations are combined to search for biskyrmions in MnNiGa, a material in which they have been reported. Only type‐I and type‐II magnetic bubbles are found and images purported to show biskyrmions can be explained as type‐II bubbles viewed at an angle to their axes. It is not the magnetization but the magnetic flux density resulting from this object that forms the counter‐rotating vortices.     

NIR Biosensing of Neurotransmitters in Stem Cell‐Derived Neural Interface Using Advanced Core–Shell Upconversion Nanoparticles

Nondestructive neurotransmitter detection and real‐time monitoring of stem cell differentiation are both of great significance in the field of neurodegenerative disease and regenerative medicine. Although luminescent biosensing nanoprobes have been developed to address this need, they have intrinsic limitations such as autofluorescence, scattering, and phototoxicity. Upconversion nanoparticles (UCNPs) have gained increasing attention for various biomedical applications due to their high photostability, low auto‐fluorescent background, and deep tissue penetration; however, UCNPs also suffer from low emission intensities due to undesirable energy migration pathways. To address the aforementioned issue, a single‐crystal core–shell–shell “sandwich” structured UCNP is developed that is designed to minimize deleterious energy back‐transfer to yield bright visible emissions using low power density excitations. These UCNPs show a remarkable enhancement of luminescent output relative to conventional β‐NaYF4:Yb,Er codoped UCNPs and β‐NaYF4:Yb,Er@NaYF4:Yb “active shell” alike. Moreover, this advanced core–shell–shell UCNP is subsequently used to develop a highly sensitive biosensor for the ultrasensitive detection of dopamine released from stem cell‐derived dopaminergic‐neurons. Given the challenges of in situ detection of neurotransmitters, the developed NIR‐based biosensing of neurotransmitters in stem cell‐derived neural interfaces present a unique tool for investigating single‐cell mechanisms associated with dopamine, or other neurotransmitters, and their roles in neurological processes.     

A multi-angle spectrometer for automatic measurement of plant canopy reflectance spectra

The paper describes the design and operation of a multi-angle spectrometer (MAS) for automatic measurement of near-field spectral reflectances of plant canopies at hourly intervals. A novel feature of the instrument is a rotating periscope connected to a spectrometer via a fiber optic cable. Canopy reflectances are calculated for multiple view azimuths, at a single zenith angle from measurements of spectrometer dark current, incoming solar irradiance and reflected radiances. Spectral measurements are made between 300 and 1150 nm wavelength at a band-to-band spacing of 3 nm, and a bandwidth (full-width, half maximum) of 10 nm. Preliminary data analysis showed that the canopy reflectance model of Kuusk [Kuusk, A. (1995). A fast, invertible canopy reflectance model. Remote Sensing of Environment 51, 342-350] reproduced the observed large differences in visible and near-infrared (NIR) reflectances, but the model was unable to predict quantitatively the observed variations in the measured reflectance spectra with azimuth, particularly in the NIR. Discrepancies between model and measurements are likely due to the inhomogeneous nature of the forest canopy in contrast to the assumption of a uniformly absorbing turbid medium in the model. Measurements using the MAS can be used to investigate directional dependences of reflectance indices and for testing BRDF models used to separate geometrical and plant physiological contributions to the reflectance signals. The MAS provides continuous sampling of reflectance indices which can be compared with canopy properties such as chlorophyll content and photosynthetic capacity.