Sub-millimeter Scale Research Articles

Ultrabright and Highly Polarity‐Sensitive NIR‐I/NIR‐II Fluorophores for the Tracking of Lipid Droplets and Staging of Fatty Liver Disease

AbstractVisualizing the progression of fatty liver disease in vivo is of great significance in biomedical research of fatty liver, but hindered by the lack of suitable approaches with deep penetration, high specificity, and real‐time observability for fatty liver imaging. Herein, two bright NIR‐I/NIR‐II fluorophores with D–π–A–π–D structures are designed and synthesized for fatty liver tracking in vivo. Such fluorophores show an ultrahigh quantum yield of 49.2% and 17.3% at the emission maximum of 930 and 975 nm, respectively. Most interestingly, these two fluorophores display ultrasensitive fluorescence response (over 100‐fold enhancement) toward the variations of environment polarity. Accordingly, further doping of these fluorophores into amphiphilic organic matrix allows the formation of ultrabright NIR‐I/NIR‐II fluorescent nanoprobes for high‐resolution fluorescence imaging of the vessels. Additionally, with the assistance of such nanoprobes and NIR‐II fluorescence imaging, real‐time monitoring of heartbeat rate and the respiratory rate, accurate identification, and imaging‐guided surgery of the submillimeter scale lymph nodes are successfully realized. Moreover, the as‐designed fluorophores show superior performance for indicating lipid droplets (LDs) in living cells. Ultimately, precise monitoring of fatty liver with NIR‐I/NIR‐II fluorescent LDs probe is first confirmed, demonstrating the possibility for staging fatty liver disease with a contact‐free method.

A Method and Analysis to Enable Efficient Piezoelectric Transducer-Based Ultrasonic Power and Data Links for Miniaturized Implantable Medical Devices.

Acoustic links for implantable medical devices (implants) have gained attention primarily because they provide a route to wireless deep-tissue systems. The miniaturization of the implants is a key research goal in these efforts, nominally because smaller implants result in less acute tissue damage. Implant size in most acoustic systems is limited by the piezoelectric bulk crystal used for power harvesting and data communication. Further miniaturization of the piezocrystal can degrade system power transfer efficiency and data transfer reliability. Here, we present a new method for packaging the implant piezocrystal; the method maximizes power transfer efficiency ( η ) from the acoustic power at the piezo surface to the power delivered to the electrical load and information transfer across the acoustic link. Our method relies on placing piezo-to-substrate anchors to the piezo regions where the vibrational displacement of the mode of interest is zero. To evaluate our method, we investigated packaged 1×1×1 mm3 piezocrystals assembled with different sized anchors. Our results show that reducing the anchor size decreases anchor loss and thus improves piezo quality factor (Q). We also demonstrate that this method improves system electromechanical coupling. A strongly coupled, high-Q piezo with properly sized and located anchors is demonstrated to achieve significantly higher η and superior data transfer capability at resonance. Overall, this work provides an analysis and generic method for packaging the implant piezocrystal that enables the design of efficient acoustic power and data links, which provides a path toward the further miniaturization of ultrasonic implants to submillimeter scales.

Tracing Carbonate Formation, Serpentinization, and Biological Materials With Micro-/Meso-Scale Infrared Imaging Spectroscopy in a Mars Analog System, Samail Ophiolite, Oman.

Visible‐shortwave infrared (VSWIR) imaging spectrometers map composition remotely with spatial context, typically at many meters‐scale from orbital and airborne data. Here, we evaluate VSWIR imaging spectroscopy capabilities at centimeters to sub‐millimeter scale at the Samail Ophiolite, Oman, where mafic and ultramafic lithologies and their alteration products, including serpentine and carbonates, are exposed in a semi‐arid environment, analogous to similar mineral associations observed from Mars orbit that will be explored by the Mars‐2020 rover. At outcrop and hand specimen scales, VSWIR spectroscopy (a) identifies cross‐cutting veins of calcite, dolomite, magnesite, serpentine, and chlorite that record pathways and time‐order of multiple alteration events of changing fluid composition; (b) detects small‐scale, partially altered remnant pyroxenes and localized epidote and prehnite that indicate protolith composition and temperatures and pressures of multiple generations of faulting and alteration, respectively; and (c) discriminates between spectrally similar carbonate and serpentine phases and carbonate solid solutions. In natural magnesite veins, minor amounts of ferrous iron can appear similar to olivine's strong 1‐μm absorption, though no olivine is present. We also find that mineral identification for carbonate and serpentine in mixtures with each other is strongly scale‐ and texture‐dependent; ∼40 area% dolomite in mm‐scale veins at one serpentinite outcrop and ∼18 area% serpentine in a calcite‐rich travertine outcrop are not discriminated until spatial scales of <∼1–2 cm/pixel. We found biological materials, for example bacterial mats versus vascular plants, are differentiated using wavelengths <1 μm while shortwave infrared wavelengths >1 μm are required to identify most organic materials and distinguish most mineral phases.

Sub-millimetre scale Van der Waals single-crystal MoTe2 for potassium storage: Electrochemical properties, and its failure and structure evolution mechanisms

Potassium-ion batteries (KIBs) are competent candidates for next-generation energy-storage systems due to the source abundance, cost efficiency, and high energy density from comparable electrode potential to lithium. However, developing practical electrode materials for KIBs is still in its infancy, and the electrochemical reaction mechanisms for a specific material are far from clear. Here, MoTe2, due to the merits of sizeable ion-intercalation interlayer spacing of Van der Waals-type material, superior electron conductivity of its metal-semimetal characteristics to wildly studied MoS2, was for the first time investigated as the working electrode for potassium storage. The potassiation/depotassiation mechanisms were unravelled, combining electrochemical analysis, ex-situ scanning electron microscope (SEM), ex-situ transmission electron microscope (TEM) and in-situ X-ray diffraction. Sub-millimetre single-crystal MoTe2 displayed a high volumetric capacity of 792.4 mAh cm−3 at initial depotassiation and maintained a gravimetric specific capacity of 210 mAh g−1 at 100 mA g−1. It decayed rapidly after 25 cycles caused by the deactivation of active electrode material from the irreversible crystalline cracking and structure evolution during the electrochemical cycling. At initial potassiation, 2H-MoTe2 was irreversibly converted to 1T-MoTe2 and then further converted to potassium telluride. And at initial depotassiation over 2.5 V (vs. K/K+), a tentative K-Mo-Te compound with R-3H Cs4Mo18Te20 structure was formed and soon irreversibly converted to K2Te3 under following potassiation. Meanwhile, the stepwise reversible conversion of K2Te3-KTe-K5Te3 predominates the continuous electrochemical processes after the initial discharge/charge. Apart from the potential application for potassium-ion batteries, the conversion mechanisms amongst potassium tellurides also provide instructions for upcoming potassium-tellurium batteries.

European Association of Nuclear Medicine October 20-23, 2021 Virtual.

Aim/Introduction: Over the last decades, the use of 18F-FDG has taken a pivotal role in oncological diagnosis, staging and follow-up. While endless research has shown the clinical importance of 18F-FDG, we remain unaware how 18F-FDG behaves in and around human malignancies on a submillimetric scale. Unfortunately, as glucose metabolism is an active process, pathological assessment of relevant protein markers was found to be inadequate in correctly predicting 18F-FDG-uptake. Technological improvements are resulting in increasing spatial resolution for PET-scanners, therefore an urgent understanding of 18F-FDG-distribution on these higher resolutions is required. Materials and Methods: In the current study, we developed a methodology that enabled direct coregistration of the radioactivity-distribution in a surgically resected specimen with histopathological assessment. Patients were injected with 4 MBq/kg of 18F-FDG prior to the initiation of standard of care surgical oncological resection. After resection of the malignancy, the surgical specimen was imaged using preclinical micro-PET and -CT devices with a spatial resolution of 800µm and 50µm, respectively. After imaging, the specimen was freshly sliced into thin slices of approximately 2mm by a pathologist. One slice was snap-frozen and frozen sections were imaged using an autoradiographic flm overnight. Following the imaging, frozen sections were stained with standard hematoxylin and eosin staining. Pathological results were overlayed with the results of 18F-FDG PET/CT and autoradiography to coregister the histopathological and imaging results. Results: We performed this methodology on a total of four patients with cutaneous squamous cell carcinoma (n=2), angiosarcoma (n=1) and thyroid medullary carcinoma (n=1). While the mean time between injection and autoradiography was 3h49, we were able to image sufcient radioactivity to directly coregister the results with the clinical pathological frozen sections. All regions with identifed malignant tissue displayed increased 18F-FDG-uptake. However, uptake was not limited to these regions, as a similar increased uptake was identifed in adjacent benign sebaceous glands. Interestingly, we also identifed a heterogeneous 18F-FDGuptake in separate clusters of malignant tissue, which could partly be explained by the cluster’s amount of peritumoral infammatory cells. Conclusion: To the best of our knowledge, these results are the frst to describe direct coregistration of 18F-FDG with the gold standard of histopathology in any human malignancy. These heterogeneous results display an important diversity in metabolic activity between diferent tumor and peritumoral tissues. The use of this methodology could increase our understanding of radiotracer distribution in human diseases on a previously unprecedented scale in clinical nuclear medicine.

Magnetization transfer weighted EPI facilitates cortical depth determination in native fMRI space

The increased availability of ultra-high field scanners provides an opportunity to perform fMRI at sub-millimeter spatial scales and enables in vivo probing of laminar function in the human brain. In most previous studies, the definition of cortical layers, or depths, is based on an anatomical reference image that is collected by a different acquisition sequence and exhibits different geometric distortion compared to the functional images. Here, we propose to generate the anatomical image with the fMRI acquisition technique by incorporating magnetization transfer (MT) weighted imaging. Small flip angle binomial pulse trains are used as MT preparation, with a flexible duration (several to tens of milliseconds), which can be applied before each EPI segment without constraining the acquisition length (segment or slice number). The method's feasibility was demonstrated at 7T for coverage of either a small slab or the near-whole brain at 0.8 mm isotropic resolution. Tissue contrast was found to be similar to that obtained with a state-of-art anatomical reference based on MP2RAGE. This MT-weighted EPI image allows an automatic reconstruction of the cortical surface to support laminar analysis in native fMRI space, obviating the need for distortion correction and registration.

Phi-OTDR Based On-Line Monitoring of Overhead Power Transmission Line

The overhead power transmission line, as an important component of equipment for long-distance power transmission, is threatened by icing and galloping, which will lead to equipment troubles and cause huge economic loss. Thus, there is a great need for on-line monitoring for transmission lines. Because the photoelectric composite cable, such as optical fiber composite overhead ground wire (OPGW) is widely used, it is possible to introduce distributed optical fiber sensors (DOFS) into transmission line status monitoring. Common schemes based on DOFS usually offer low sensing density and are hard to realize global awareness, while phase sensitive optical time domain reflectometry (Φ-OTDR), as a DOFS that has the characteristic of distributed sensing, is hoping to address the limitation. In this paper, by establishing mathematical models, proposing analytical method, and building demonstration devices to analyze the dynamic strain characteristics of overhead power transmission line, an Φ-OTDR based on-line monitoring scheme of transmission line status is presented and experimentally proved for the first time. The estimation error of sag is less than 5.8% on centimeter scale, and the estimation error of ice thickness is no more than 10.84% on sub-millimeter scale, which gives an accurate description of transmission line status and provides strong support for early warning of transmission line failures.

Estimation of low-cycle fatigue damage of sputtered Cu thin films at the micro scale using deep learning

Herein, we propose a method to estimate fatigue damage of a thin metal film at the micro scale with high accuracy. With progress in the miniaturization of flexible printed circuits, estimation of damage at the micro scale is required to improve the reliability of industrial processing. Despite this necessity, it has been difficult to accurately evaluate the damage at the micro scale using conventional tests. Therefore, we focus on the use of microscopic images for damage estimation based on the correlation between damage and surface morphology, such as cracks. However, image-based analytical estimation by physical modeling is extremely difficult because of the complexity of the morphology. Therefore, the proposed method is based on image recognition using deep learning. In particular, VGG19-based transfer learning was implemented. An L2-constrained softmax loss developed for face recognition was used, as the diversity of textures in the microscopic images was lower than that used for general object detection. As a result, the proposed method was able to accurately estimate the fatigue damage at the micro scale, which was at the submillimeter scale. The average estimation error was reduced to 15% of that obtained using the binarization method, indicating the L2-constrained softmax loss method to be highly effective. Although verification under a broad range of fatigue conditions is required for a more general evaluation, it was concluded that the proposed method is effective for evaluating the damage of thin metal films of flexible printed circuits at the micro scale.

Unexpected thermo-elastic effects in liquid glycerol by mechanical deformation

It is commonly accepted that shear waves do not propagate in a liquid medium. The shear wave energy is supposed to dissipate nearly instantaneously. This statement originates from the difficulty to access “static” shear stress in macroscopic liquids. In this paper, we take a different approach. We focus on the stability of the thermal equilibrium while the liquid (glycerol) is submitted to a sudden shear strain at sub-millimeter scale. The thermal response of the deformed liquid is unveiled. The liquid exhibits simultaneous and opposite bands up to about +0.04 to −0.04 °C temperature variation, while keeping the global thermal balance unchanged. The sudden thermal changes and the long thermal relaxation highlight the ability of the liquid to convert the step strain energy in non-uniform thermodynamic states. The thermal effects depend nearly linearly on the amplitude of the deformation supporting the hypothesis of a shear wave propagation (elastic correlations) extending up to several hundreds micrometers. This new physical effect can be explained in terms of the underlying phonon physics of confined liquids, which unveils a hidden solid-like response with many similarities to glassy systems.

Submillimeter constraints for non-Newtonian gravity from spectroscopy

In this work, we consider the Yukawa-type and power-type non-Newtonian corrections, which induce amplification of the gravitational interaction on submillimeter scales, and analytically calculate deviations produced by the atomic gravitational field on the energy levels of hydrogen-like ions. Analyzing ionic transitions between Rydberg states, we derive prospective constraints for non-Newtonian corrections. It is shown that the results also provide stronger constraints, due to the high accuracy for Rydberg transition measures into the optical spectrum frequency range, than the current empirical bounds following from Casimir force measurements.

Effective elastic modulus of an intact cornea related to indentation behavior: A comparison between the Hertz model and Johnson-Kendall-Roberts model

In this study, a macro-indentation test on the submillimeter scale was performed to analyze the indentation behavior of an intact cornea under physiological pressures. The Hertz and Johnson-Kendall-Roberts (JKR) models were employed to solve the elastic modulus (E) of the intact cornea. The relevant detailed analysis showed that the JKR model, which accounted for the contribution from the adhesion energy, could be used to obtain the E values that were more than two-folds of those obtained from the Hertz model, which only considered the external force. Compared with the uniaxial tension test in vitro, unlike the elastic Hertz-model, the E values under physiological pressures that were obtained with the JKR model were between the lower and upper limits of corneal material. This phenomenon indicated that the JKR model could be used to obtain reasonably effective E values of an intact cornea under physiological pressures.

A High-Temperature Digital Image Correlation Method and its Application on Strain Measurement of Film Cooling Holes

In this paper, a digital image correlation (DIC) method is developed and applied on film cooling holes in the submillimeter scale in high temperature. Compared with the traditional DIC method, the speckle patterning method and the optical system are improved. In detail, a kind of high temperature-resistant black paint is selected as the basecoat, and the white ZrO2 particles are evenly distributed on the specimen using high-pressure splashing method. Besides, to eliminate the radiation effect of the high-temperature specimen, the blue light source is used to illuminate the specimen, and the optical bandpass filter is placed in front of the camera to allow the blue light passing. In order to verify the DIC method, the strain measurement on a specimen with single skew hole is performed. The relative error in high temperature of the maximum strain between the measurement results and the numerical simulation results given by the finite element method (FEM) is 12%. The strain concentration factor of the single skew hole is measured as 1.83. Finally, the developed method is applied to the strain measurement of the structure with multiple film cooling holes in 870°C. The X-shape strain distribution can be observed at the hole with maximum stress, which suggests that the strain field of multiple holes has coupling effect. In addition, the strain concentration factor of multiple film cooling holes increases to 2.34.

Sensitivity Enhancement of Ultrahigh-Order Mode Based Magnetic Field Sensor via Vernier Effect and Coarse Wavelength Sampling

A methodology combining the asymmetrical metal-cladding waveguide (aSMCW) excited ultrahigh-order modes and coarse wavelength induced Vernier effect is theoretically proposed to enhance the sensitivity of the magnetic field sensor. In our aSMCW structure, a transparent glass SF11 with a sub-millimeter scale thickness is selected as the guiding layer, whose magnetically modulated refractive index leads to a variation of resonant wavelength. By controlling the sampling interval of tunable laser, the Vernier effect assisted resonant wavelength shift is more distinguishable and the sensitivity is enhanced about 20 times. Our sensitivity enhancement method is low cost since the optical spectrum analyzer (OSA) with a fine resolution is needless.

Towards in situ U–Pb dating of dolomite

Abstract. Recent U–Pb dating by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has demonstrated that reasonable precision (3 %–10 %, 2σ) can be achieved for high-resolution dating of texturally distinct calcite phases. Absolute dating of dolomite, for which biostratigraphy and traditional dating techniques are very limited, remains challenging, although it may resolve many fundamental questions related to the timing of mineral-rock formation by syngenetic, diagenesis, hydrothermal, and epigenetic processes. In this study we explore the possibility of dating dolomitic rocks via recent LA-ICP-MS dating techniques developed for calcite. The in situ U–Pb dating was tested on a range of dolomitic rocks of various origins from the Cambrian to Pliocene age – all of which are from well-constrained stratigraphic sections in Israel. We present imaging and chemical characterization techniques that provide useful information on interpreting the resulting U–Pb ages and discuss the complexity of in situ dolomite dating in terms of textural features that may affect the results. Textural examinations indicate zonation and mixing of different phases at the sub-millimeter scale (&lt; 1 µm), and thus Tera–Wasserburg ages represent mixed dates of early diagenesis and some later epigenetic dolomitization event(s). We conclude that age mixing at the sub-millimeter scale is a major challenge in dolomite dating that needs to be further studied and note the importance of matrix-matched standards for reducing uncertainties of the dated material.

Laminar fMRI using T2-prepared multi-echo FLASH

Functional magnetic resonance imaging (fMRI) using blood oxygenation level dependent (BOLD) contrast at a sub-millimeter scale is a promising technique to probe neural activity at the level of cortical layers. While gradient echo (GRE) BOLD sequences exhibit the highest sensitivity, their signal is confounded by unspecific extravascular (EV) and intravascular (IV) effects of large intracortical ascending veins and pial veins leading to a downstream blurring effect of local signal changes. In contrast, spin echo (SE) fMRI promises higher specificity towards signal changes near the microvascular compartment. However, the T2-weighted signal is typically sampled with a gradient echo readout imposing additional T2’-weighting.In this work, we used a T2-prepared (T2-prep) sequence with short GRE readouts to investigate its capability to acquire laminar fMRI data during a visual task in humans at 7 T. By varying the T2-prep echo time (TEprep) and acquiring multiple gradient echoes (TEGRE) per excitation, we studied the specificity of the sequence and the influence of possible confounding contributions to the shape of laminar fMRI profiles. By fitting and extrapolating the multi-echo GRE data to a TEGRE = 0 ms condition, we show for the first time laminar profiles free of T2’-pollution, confined to gray matter. This finding is independent of TEprep, except for the shortest one (31 ms) where hints of a remaining intravascular component can be seen. For TEGRE > 0 ms a prominent peak at the pial surface is observed that increases with longer TEGRE and dominates the shape of the profiles independent of the amount of T2-weighting. Simulations show that the peak at the pial surface is a result of static EV dephasing around pial vessels in CSF visible in GM due to partial voluming. Additionally, another, weaker, static dephasing effect is observed throughout all layers of the cortex, which is particularly obvious in the data with shortest T2-prep echo time. Our simulations show that this cannot be explained by intravascular dephasing but that it is likely caused by extravascular effects of the intracortical and pial veins. We conclude that even for TEGRE as short as 2.3 ms, the T2’-weighting added to the T2-weighting is enough to dramatically affect the laminar specificity of the BOLD signal change. However, the bulk of this corruption stems from CSF partial volume effects which can in principle be addressed by increasing the spatial resolution of the acquisition.

In vivo human whole-brain Connectom diffusion MRI dataset at 760\u2009\xb5m isotropic resolution

We present a whole-brain in vivo diffusion MRI (dMRI) dataset acquired at 760 μm isotropic resolution and sampled at 1260 q-space points across 9 two-hour sessions on a single healthy participant. The creation of this benchmark dataset is possible through the synergistic use of advanced acquisition hardware and software including the high-gradient-strength Connectom scanner, a custom-built 64-channel phased-array coil, a personalized motion-robust head stabilizer, a recently developed SNR-efficient dMRI acquisition method, and parallel imaging reconstruction with advanced ghost reduction algorithm. With its unprecedented resolution, SNR and image quality, we envision that this dataset will have a broad range of investigational, educational, and clinical applications that will advance the understanding of human brain structures and connectivity. This comprehensive dataset can also be used as a test bed for new modeling, sub-sampling strategies, denoising and processing algorithms, potentially providing a common testing platform for further development of in vivo high resolution dMRI techniques. Whole brain anatomical T1-weighted and T2-weighted images at submillimeter scale along with field maps are also made available.

Voxelated three-dimensional miniature magnetic soft machines via multimaterial heterogeneous assembly.

Small-scale soft-bodied machines that respond to externally applied magnetic field have attracted wide research interest because of their unique capabilities and promising potential in a variety of fields, especially for biomedical applications. When the size of such machines approach the sub-millimeter scale, their designs and functionalities are severely constrained by the available fabrication methods, which only work with limited materials, geometries, and magnetization profiles. To free such constraints, here, we propose a bottom-up assembly-based 3D microfabrication approach to create complex 3D miniature wireless magnetic soft machines at the milli- and sub-millimeter scale with arbitrary multimaterial compositions, arbitrary 3D geometries, and arbitrary programmable 3D magnetization profiles at high spatial resolution. This approach helps us concurrently realize diverse characteristics on the machines, including programmable shape morphing, negative Poisson's ratio, complex stiffness distribution, directional joint bending, and remagnetization for shape reconfiguration. It enlarges the design space and enables biomedical device-related functionalities that are previously difficult to achieve, including peristaltic pumping of biological fluids and transport of solid objects, active targeted cargo transport and delivery, liquid biopsy, and reversible surface anchoring in tortuous tubular environments withstanding fluid flows, all at the sub-millimeter scale. This work improves the achievable complexity of 3D magnetic soft machines and boosts their future capabilities for applications in robotics and biomedical engineering.

Tensor Domain Averaging in Diffusion Imaging of Small Animals to Generate Reliable Tractography

Testing on small animal models is roughly the only path to transfer science-based knowledge to human use. More avidly than other human organs, we study the brain through animal models due to the complexity of experimenting directly on human subjects, even at a cellular level where the skull makes tissue sampling harder than in any other organ. Thanks to recent technological advances in imaging, animals do not need to be sacrificed. Magnetic resonance, in particular, favors long-term analysis and monitoring since its methods do not perturb the organ functions nor compromise the metabolism of the animals. Neurons' integrity is now indirectly visible under specialized mechanisms that use water displacement to track static boundaries. Although these water diffusion methods have proven to be successful in detecting neuronal structure at the submillimeter scale, they yield noisy results when applied to the resolutions required by small animals or when facing low myeline contents as in neonates and young children. This manuscript presents a strategy to display neuronal trending representations that follow the corticospinal tract's pathway and neuronal integrity in small rodents. The strategy is the foundation to study human neurodegenerative diseases and neurodevelopment as well.

Laser-Induced Breakdown Spectroscopy (LIBS) characterization of granular soils: Implications for ChemCam analyses at Gale crater, Mars

The Curiosity rover has been characterizing mineralogical and chemical compositions of Gale crater soils on Mars since 2012. Given its sub-millimeter scale of analysis, the ChemCam instrument is well suited to study the composition of soil constituents. However, the interpretation of LIBS data on soils in the martian environment is complicated by the large diversity of particle sizes (from dust to sand), combined with the unknown physical arrangement of their mineral constituents (i.e., the type of grain mixtures). For example, martian soils contain a significant amount of X-ray amorphous materials whose physical form remains unclear. In this study, we reproduced martian soil analyses in the laboratory to understand how the LIBS technique can provide specific insights into the physical and chemical properties of granular soils. For this purpose, different types of samples were studied with various ranges of grain sizes, mimicking two possible mixtures that may occur in martian soils: mechanical mixtures of two populations of grains made of distinct chemical compositions; and material forming a compositionally distinct coating at the surface of grains. Our results, also supported by in situ ChemCam data, demonstrate that both the sizes and the type of mixture of soil particles have a strong influence on the LIBS measurement. For mechanical mixtures of two populations of grains larger than 125–250 μm, the scatter of the data provides information about the chemical composition of the end-members. On the other hand, the chemistry recorded by LIBS for grains with surface coatings is fully dominated by the outer material for grains smaller than 500 μm in diameter. This is due to the small penetration depth of the laser (~0.3–1.5 μm per shot), combined with the ejection of small grains at each shot, which leads to a constant replenishment of fresh material. This experimental work will thus improve our understanding of martian soils analyzed by ChemCam, and more broadly, will benefit LIBS studies of granular materials.

Sulfobetaine Hydrogels with a Complex Multilength-Scale Hierarchical Structure.

Hydrogels with a hierarchical structure were prepared from a new highly water-soluble crosslinker N,N,N',N'-tetramethyl-N,N'-bis(2-ethylmethacrylate)-propyl-1,3-diammonium dibromide and from the sulfobetaine monomer 2-(N-3-sulfopropyl-N,N-dimethyl ammonium)ethyl methacrylate. The free radical polymerization of the two compounds is rapid and yields near-transparent hydrogels with sizes up to 5 cm in diameter. Rheology shows a clear correlation between the monomer-to-crosslinker ratio and the storage and loss moduli of the hydrogels. Cryo-scanning electron microscopy, low-field nuclear magnetic resonance (NMR) spectroscopy, and small-angle X-ray scattering show that the gels have a hierarchical structure with features spanning the nanometer to the sub-millimeter scale. The NMR study is challenged by the marked inhomogeneity of the gels and the complex chemical structure of the sulfobetaine monomer. NMR spectroscopy shows how these complications can be addressed via a novel fitting approach that considers the mobility gradient along the side chain of methacrylate-based monomers.