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1. Effect of Humidity on Friction and Wear—A Critical Review

   https://doi.org/10.3390/lubricants6030074  

   Chen, Zhe ; He, Xin ; Xiao, Chen ; Kim, Seong ( September 2018 , Lubricants)

   The friction and wear behavior of materials are not intrinsic properties, but extrinsic properties; in other words, they can drastically vary depending on test and environmental conditions. In ambient air, humidity is one such extrinsic parameter. This paper reviews the effects of humidity on macro- and nano-scale friction and wear of various types of materials. The materials included in this review are graphite and graphene, diamond-like carbon (DLC) films, ultrananocrystalline diamond (UNCD), transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), boric acid, silicon, silicon oxide, silicates, advanced ceramics, and metals. Details of underlying mechanisms governing friction and wear behaviors vary depending on materials and humidity; nonetheless, a comparison of various material cases revealed an overarching trend. Tribochemical reactions between the tribo-materials and the adsorbed water molecules play significant roles; such reactions can occur at defect sites in the case of two-dimensionally layered materials and carbon-based materials, or even on low energy surfaces in the case of metals and oxide materials. It is extremely important to consider the effects of adsorbed water layer thickness and structure for a full understanding of tribological properties of materials in ambient air. 

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2. Self‐Sorting of 10‐µm‐Long Single‐Walled Carbon Nanotubes in Aqueous Solution

   https://doi.org/10.1002/adma.201901641  

   Wang, Peng ; Barnes, Benjamin ; Wu, Xiaojian ; Qu, Haoran ; Zhang, Chiyu ; Shi, Yang ; Headrick, Robert J. ; Pasquali, Matteo ; Wang, YuHuang ( June 2019 , Advanced Materials)

   Single‐walled carbon nanotubes (SWCNTs) are a class of 1D nanomaterials that exhibit extraordinary electrical and optical properties. However, many of their fundamental studies and practical applications are stymied by sample polydispersity. SWCNTs are synthesized in bulk with broad structural (chirality) and geometrical (length and diameter) distributions; problematically, all known post‐synthetic sorting methods rely on ultrasonication, which cuts SWCNTs into short segments (typically <1 µm). It is demonstrated that ultralong (>10 µm) SWCNTs can be efficiently separated from shorter ones through a solution‐phase “self‐sorting”. It is shown that thin‐film transistors fabricated from long semiconducting SWCNTs exhibit a carrier mobility as high as ≈90 cm²V⁻¹s⁻¹, which is ≈10 times higher than those which use shorter counterparts and well exceeds other known materials such as organic semiconducting polymers (<1 cm²V⁻¹s⁻¹), amorphous silicon (≈1 cm²V⁻¹s⁻¹), and nanocrystalline silicon (≈50 cm²V⁻¹s⁻¹). Mechanistic studies suggest that this self‐sorting is driven by the length‐dependent solution phase behavior of rigid rods. This length sorting technique shows a path to attain long‐sought ultralong, electronically pure carbon nanotube materials through scalable solution processing.

    

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3. The upper ocean silicon cycle of the subarctic Pacific during the EXPORTS field campaign

   Brzezinski, Mark A. ; Varela, Diana E. ( February 2022 , Elementa)

   The contribution of diatoms to the production and export of organic carbon is highly modified in high-nutrient low-chlorophyll (HNLC) regions due to the decoupling of upper-ocean silicon and carbon cycling caused by low iron. The Si cycle and the role of diatoms in the biological carbon pump was examined at Ocean Station Papa (OSP) in the HNLC region of the northeastern subarctic Pacific during the NASA EX port Processes in the Ocean from RemoTe Sensing (EXPORTS) field study. Sampling occurred during the annual minimum in surface silicic acid concentration, [Si(OH)4 ]. Biogenic silica (bSi) concentrations were low being in the tens of nanomolar range despite high [Si(OH) 4 ], ~15 μM. On average the > 5.0 μm particle size fraction dominated Si dynamics accounting for 65% of bSi stocks and 81% of Si uptake compared to the small fraction (0.6 - 5.0 μm). Limitation of Si uptake was detected in the small, but not the large, size fraction. Small diatoms were co-limited with growth rate restricted by Fe and Si uptake restricted by [Si(OH) 4 ], whereas larger diatoms were only growth limited by Fe. About a third of silica production was exported out of the upper 100 m. The contribution of diatoms to carbon export (9 - 13%) was about twice their contribution to primary productivity (3 - 7%). The combination of low silica production, low diatom primary productivity and high bSi export efficiency at OSP was more similar to the dynamics in the subtropical gyres than to other HNLC regions. 

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4. Direct uptake of organically derived carbon by grass roots and allocation in leaves and phytoliths: 13C labeling evidence

   https://doi.org/10.5194/bg-13-1693-2016  

   Alexandre, Anne ; Balesdent, Jérôme ; Cazevieille, Patrick ; Chevassus-Rosset, Claire ; Signoret, Patrick ; Mazur, Jean-Charles ; Harutyunyan, Araks ; Doelsch, Emmanuel ; Basile-Doelsch, Isabelle ; Miche, Hélène ; et al ( January 2016 , Biogeosciences)

   In the rhizosphere, the uptake of low-molecular-weight carbon (C) and nitrogen (N) by plant roots has been well documented. While organic N uptake relative to total uptake is important, organic C uptake is supposed to be low relative to the plant's C budget. Recently, radiocarbon analyses demonstrated that a fraction of C from the soil was occluded in amorphous silica micrometric particles that precipitate in plant cells (phytoliths). Here, we investigated whether and to what extent organically derived C absorbed by grass roots can feed the C occluded in phytoliths. For this purpose we added ¹³C- and ¹⁵N-labeled amino acids (AAs) to the silicon-rich hydroponic solution of the grass Festuca arundinacea. The experiment was designed to prevent C leakage from the labeled nutritive solution to the chamber atmosphere. After 14 days of growth, the ¹³C and ¹⁵N enrichments (¹³C excess and ¹⁵N excess) in the roots, stems and leaves as well as phytoliths were measured relative to a control experiment in which no labeled AAs were added. Additionally, the ¹³C excess was measured at the molecular level, in AAs extracted from roots and stems and leaves. The net uptake of labeled AA-derived ¹³C reached 4.5 % of the total AA ¹³C supply. The amount of AA-derived ¹³C fixed in the plant was minor but not nil (0.28 and 0.10 % of total C in roots and stems/leaves, respectively). Phenylalanine and methionine that were supplied in high amounts to the nutritive solution were more ¹³C-enriched than other AAs in the plant. This strongly suggested that part of AA-derived ¹³C was absorbed and translocated into the plant in its original AA form. In phytoliths, AA-derived ¹³C was detected. Its concentration was on the same order of magnitude as in bulk stems and leaves (0.15 % of the phytolith C). This finding strengthens the body of evidences showing that part of organic compounds occluded in phytoliths can be fed by C entering the plant through the roots. Although this experiment was done in nutrient solution and its relevance for soil C uptake assessment is therefore limited, we discuss plausible forms of AA-derived ¹³C absorbed and translocated in the plant and eventually fixed in phytoliths, and implications of our results for our understanding of the C cycle at the soil–plant–atmosphere interface 

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5. Decoupling silicon metabolism from carbon and nitrogen assimilation poises diatoms to exploit episodic nutrient pulses in a coastal upwelling system

   https://doi.org/10.3389/fmars.2023.1291294  

   Maniscalco, Michael A. ; Brzezinski, Mark A. ; Krause, Jeffrey W. ; Thamatrakoln, Kimberlee ( November 2023 , Frontiers in Marine Science)

   Diatoms serve as the major link between the marine carbon (C) and silicon (Si) biogeochemical cycles through their contributions to primary productivity and requirement for Si during cell wall formation. Although several culture-based studies have investigated the molecular response of diatoms to Si and nitrogen (N) starvation and replenishment, diatom silicon metabolism has been understudied in natural populations. A series of deckboard Si-amendment incubations were conducted using surface water collected in the California Upwelling Zone near Monterey Bay. Steep concentration gradients in macronutrients in the surface ocean coupled with substantial N and Si utilization led to communities with distinctly different macronutrient states: replete (‘healthy’), low N (‘N-stressed’), and low N and Si (‘N- and Si-stressed’). Biogeochemical measurements of Si uptake combined with metatranscriptomic analysis of communities incubated with and without added Si were used to explore the underlying molecular response of diatom communities to different macronutrient availability. Metatranscriptomic analysis revealed that N-stressed communities exhibited dynamic shifts in N and C transcriptional patterns suggestive of compromised metabolism. Expression patterns in communities experiencing both N and Si stress imply that the presence of Si stress may partially ameliorate N stress and dampen the impact on organic matter metabolism. This response builds upon previous observations that the regulation of C and N metabolism is decoupled from Si limitation status, where Si stress allows the cell to optimize the metabolic machinery necessary to respond to episodic pulses of nutrients. Several well-characterized Si-metabolism associated genes were found to be poor molecular markers of Si physiological status; however, several uncharacterized Si-responsive genes were revealed to be potential indicators of Si stress or silica production.

    

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