Using Micro-CT Scanning to Quantitative Characterize Porosity in High Pressure Die Castings and Semi-Solid Castings

Porosity is one of the main defects that limits the performance of castings. Porosity in aluminum castings can originate from several sources, including the volumetric shrinkage occurring during solidification, the precipitation of dissolved hydrogen, and entrapment of gasses such as air, boiling water, vaporized lubricants, etc. Traditional methods of identifying and measuring porosity in castings include 2D x-rays, sectioning and polishing, and Archimedes density measurements, but none of these provide a satisfactory quantitative estimate of the size, total volume and distribution of the pores. X-ray CT scanning is a relatively new method that generates not only a 3-dimensional view of the size and distribution of the pores, but can also provide quantitative information of the volume, surface area, size, shape and position of each pore within a casting. Micro-CT scanning is a specialized sub-category of CT scanning, which provides excellent resolution of fine porosity (a resolution limit of 4 microns in one of the case-stores presented in this paper), but it should be noted that the resolution limit in CT scanning techniques is related to sample size. This paper describes results from micro-CT scanning studies of two high pressure die castings and a semi-solid casting, and provides quantitative data on the total porosity content, and the porosity distribution. The paper will also demonstrate the capabilities of the micro-CT scanning process to provide a quantitative comparison of the porosity content in these different types of aluminum castings.

Fluorescent Probes for STED Optical Nanoscopy

Progress in developing fluorescent probes, such as fluorescent proteins, organic dyes, and fluorescent nanoparticles, is inseparable from the advancement in optical fluorescence microscopy. Super-resolution microscopy, or optical nanoscopy, overcame the far-field optical resolution limit, known as Abbe’s diffraction limit, by taking advantage of the photophysical properties of fluorescent probes. Therefore, fluorescent probes for super-resolution microscopy should meet the new requirements in the probes’ photophysical and photochemical properties. STED optical nanoscopy achieves super-resolution by depleting excited fluorophores at the periphery of an excitation laser beam using a depletion beam with a hollow core. An ideal fluorescent probe for STED nanoscopy must meet specific photophysical and photochemical properties, including high photostability, depletability at the depletion wavelength, low adverse excitability, and biocompatibility. This review introduces the requirements of fluorescent probes for STED nanoscopy and discusses the recent progress in the development of fluorescent probes, such as fluorescent proteins, organic dyes, and fluorescent nanoparticles, for the STED nanoscopy. The strengths and the limitations of the fluorescent probes are analyzed in detail.

Small-scale topographic irregularities on Phobos: image and numerical analyses for MMX mission

The mothership of the Martian Moons eXploration (MMX) will perform the first landing and sampling on the surface of Phobos. For the safe landing, the 2.1-m-wide mothership of the MMX should find a smooth surface with at most 40 cm topographic irregularity, however, whose abundance or even existence is not guaranteed based on current knowledge. We studied the highest resolution (a few meters per pixel) images of Phobos for possible topographic irregularities in terms of boulder (positive relief feature) and crater distributions. We find that the spatial number densities of positive relief features and craters can vary significantly, indicating that the surface irregularities vary significantly over the entire surface. We extrapolate the size-frequency distributions of positive relief features to evaluate the surface roughness below the image resolution limit. We find that the probabilities that topographic irregularities are < 40 cm for the areas of 4 × 4 m and 20 × 20 m are > 33% and < 1% for boulder-rich areas and > 88% and > 13% for boulder-poor areas, respectively, even for the worst-case estimates. The estimated probabilities largely increase when we reduce the assumed number of positive relief features, which are more realistic cases. These indicate high probabilities of finding a smooth enough place to land on Phobos’ surface safely. Graphical Abstract

Resolution capability of resist patterns and throughput using alkaline treatment under ultrasonic irradiation

Alkaline treatment of the photoresist under ultrasonic irradiation has been investigated to improve the resolution capability of resist patterns with higher throughput. The selectively dissolved phenol resin for the combination of the alkaline treatment with ultrasonic irradiation was increased by 2.3 times compared to the solely alkaline treatment. The sensitizing effect of naphthoquinone diazide (sensitizer) based on phenol was increased to 0.46 against dip treatment of 0.31. As a result, resist sensitivity was increased to 26% and the resolution capability was drastically improved. Consequently, the 0.5 μm line and space resist patterns were resolved completely with fine profile by using the photoresist with a 0.7 μm resolution limit together with g-line exposure machine with a 0.6 μm resolution limit. As a consequence, a high throughput of 25 wafers/min was achieved, which was more than 25 times higher than that of electron beam (EB) lithography.

Quantifying Scatter in Galaxy Formation at the Lowest Masses

We predict the stellar mass–halo mass (SMHM) relationship for dwarf galaxies, using simulated galaxies with peak halo masses of M peak = 1011 M ⊙ down into the ultra-faint dwarf range to M peak = 107 M ⊙. Our simulated dwarfs have stellar masses of M star = 790 M ⊙ to 8.2 × 108 M ⊙, with corresponding V-band magnitudes from −2 to −18.5. For M peak > 1010 M ⊙, the simulated SMHM relationship agrees with literature determinations, including exhibiting a small scatter of 0.3 dex. However, the scatter in the SMHM relation increases for lower-mass halos. We first present results for well-resolved halos that contain a simulated stellar population, but recognize that whether a halo hosts a galaxy is inherently mass resolution dependent. We thus adopt a probabilistic model to populate “dark” halos below our resolution limit to predict an “intrinsic” slope and scatter for the SMHM relation. We fit linearly growing log-normal scatter in stellar mass, which grows to more than 1 dex at M peak = 108 M ⊙. At the faintest end of the SMHM relation probed by our simulations, a galaxy cannot be assigned a unique halo mass based solely on its luminosity. Instead, we provide a formula to stochastically populate low-mass halos following our results. Finally, we show that our growing log-normal scatter steepens the faint-end slope of the predicted stellar mass function.

Doppler Slicing for Ultrasound Super-Resolution Without Contrast Agents

Much of the information needed for diagnosis and treatment monitoring of diseases like cancer and cardiovascular disease is found at scales below the resolution limit of classic ultrasound imaging. Recently introduced vascular super-localization methods provide more than a ten-fold improvement in spatial resolution by precisely estimating the positions of microbubble contrast agents. However, most vascular ultrasound scans are currently performed without contrast agents due to the associated cost, training, and post-scan monitoring. Here we show that super-resolution ultrasound imaging of dense vascular structures can be achieved using the natural contrast of flowing blood cells. Instead of relying on separable targets, we used Fourier-based decomposition to separate signals arising from the different scales of vascular structures while removing speckle noise using multi-ensemble processing. This approach enabled the use of compressed sensing for super-resolution imaging of the underlying vascular structures, improving resolution by a factor of four. Reconstruction of ultrafast mouse brain scans revealed details that could not be resolved in regular Doppler images, agreeing closely with bubble-based super-localization microscopy of the same fields of view. By combining multi-ensemble Doppler acquisitions with narrowband Fourier decomposition and computational super-resolution imaging, this approach opens new opportunities for affordable and scalable super-resolution ultrasound imaging.

Microfluidic Platform combined with a Dark Field Imaging System for Quantification of E. coli Contamination in Water

In this paper, we present a method for detecting and quantifying pathogens in water samples. The method proposes a portable dark field imaging and analysis system for quantifying E. coli concentrations in water after being labeled with magnetic particles. The system utilizes the tracking of moving micro/nano objects close to or below the optical resolution limit confined in small sample volumes (~ 10 µl). In particular, the system analyzes the effect of volumetric changes due to bacteria conjugation to magnetic microparticles (MP) on their Brownian motion while being suspended in liquid buffer solution. The method allows for a simple inexpensive implementation and the possibility to be used as point-of-need testing system. Indeed, a work-ing prototype is demonstrated with the capacity of quantifying E. coli colony forming units (CFU) at a range of 1x10³ - 6x10³ CFU/mL.

Identifying influential spreaders in complex networks by an improved gravity model

Identification of influential spreaders is still a challenging issue in network science. Therefore, it attracts increasing attention from both computer science and physical societies, and many algorithms to identify influential spreaders have been proposed so far. Degree centrality, as the most widely used neighborhood-based centrality, was introduced into the network world to evaluate the spreading ability of nodes. However, degree centrality always assigns too many nodes with the same value, so it leads to the problem of resolution limitation in distinguishing the real influences of these nodes, which further affects the ranking efficiency of the algorithm. The k-shell decomposition method also faces the same problem. In order to solve the resolution limit problem, we propose a high-resolution index combining both degree centrality and the k-shell decomposition method. Furthermore, based on the proposed index and the well-known gravity law, we propose an improved gravity model to measure the importance of nodes in propagation dynamics. Experiments on ten real networks show that our model outperforms most of the state-of-the-art methods. It has a better performance in terms of ranking performance as measured by the Kendall’s rank correlation, and in terms of ranking efficiency as measured by the monotonicity value.

What are the distinguishing features and size requirements of biomolecular condensates and their implications for RNA-containing condensates?

Exciting recent work has highlighted that numerous cellular compartments lack encapsulating lipid bilayers (often called “membraneless organelles”), and that their structure and function are central to the regulation of key biological processes, including transcription, RNA splicing, translation and more. These structures have been described as “biomolecular condensates” to underscore that biomolecules can be significantly concentrated in them. Many condensates, including RNA granules and processing bodies, are enriched in proteins and nucleic acids. Biomolecular condensates exhibit a range of material states from liquid- to gel-like, with the physical process of liquid-liquid phase separation implicated in driving or contributing to their formation. To date, in vitro studies of phase separation have provided mechanistic insights into the formation and function of condensates. However, the link between the often micron-sized in vitro condensates with nanometer-sized cellular correlates has not been well established. Consequently, questions have arisen as to whether cellular structures below the optical resolution limit can be considered biomolecular condensates. Similarly, the distinction between condensates and discrete dynamic hub complexes is debated. Here we discuss the key features that define biomolecular condensates to help understand behaviors of structures containing and generating RNA.