203 research outputs found
Thermal Properties of the Binary-Filler Composites with Few-Layer Graphene and Copper Nanoparticles
The thermal properties of an epoxy-based binary composites comprised of
graphene and copper nanoparticles are reported. It is found that the
"synergistic" filler effect, revealed as a strong enhancement of the thermal
conductivity of composites with the size-dissimilar fillers, has a well-defined
filler loading threshold. The thermal conductivity of composites with a
moderate graphene concentration of ~15 wt% exhibits an abrupt increase as the
loading of copper nanoparticles approaches ~40 wt%, followed by saturation. The
effect is attributed to intercalation of spherical copper nanoparticles between
the large graphene flakes, resulting in formation of the highly thermally
conductive percolation network. In contrast, in composites with a high graphene
concentration, ~40 wt%, the thermal conductivity increases linearly with
addition of copper nanoparticles. The electrical percolation is observed at low
graphene loading, less than 7 wt.%, owing to the large aspect ratio of
graphene. At all concentrations of the fillers, below and above the electrical
percolation threshold, the thermal transport is dominated by phonons. The
obtained results shed light on the interaction between graphene fillers and
copper nanoparticles in the composites and demonstrate potential of such hybrid
epoxy composites for practical applications in thermal interface materials and
adhesives.Comment: 25 pages, 4 figure
Quantitative Evaluation of the Carbon Hybridization State by Near Edge X-Ray Absorption Fine Structure Spectroscopy.
The characterization of the local bonding configuration of carbon in carbon-based materials is of paramount importance since the properties of such materials strongly depend on the distribution of carbon hybridization states, the local ordering, and the degree of hydrogenation. Carbon 1s near edge X-ray absorption fine structure (NEXAFS) spectroscopy is one of the most powerful techniques for gaining insights into the bonding configuration of near-surface carbon atoms. The common methodology for quantitatively evaluating the carbon hybridization state using C 1s NEXAFS measurements, which is based on the analysis of the sample of interest and of a highly ordered pyrolytic graphite (HOPG) reference sample, was reviewed and critically assessed, noting that inconsistencies are found in the literature in applying this method. A theoretical rationale for the specific experimental conditions to be used for the acquisition of HOPG reference spectra is presented together with the potential sources of uncertainty and errors in the correctly computed fraction of sp(2)-bonded carbon. This provides a specific method for analyzing the distribution of carbon hybridization state using NEXAFS spectroscopy. As an illustrative example, a hydrogenated amorphous carbon film was analyzed using this method, and showed good agreement with X-ray photoelectron spectroscopy (which is surface sensitive). Furthermore, the results were consistent with analysis from Raman spectroscopy (which is not surface sensitive), indicating the absence of a structurally different near-surface region in this particular thin film material. The present work can assist surface scientists in the analysis of NEXAFS spectra for the accurate characterization of the structure of carbon-based materials
Synthetic aperture radar and optical remote sensing image fusion for flood monitoring in the Vietnam lower Mekong basin: a prototype application for the Vietnam Open Data Cube
Flood monitoring systems are crucial for flood management and consequence mitigation in flood prone regions. Different remote sensing techniques are increasingly used for this purpose. However, the different approaches suffer various limitations, including cloud and weather effects (optical data), and low spatial resolution and poor colour presentation (synthetic aperture radar data). This study fuses two data types (Landsat and Sentinel-1) to overcome these limitations and produce better quality images for a prototype flood application in the Vietnam Open Data Cube (VODC). Visual and quantitative evaluation of fused image quality revealed improvement in the images compared with the original scenes. Ground-truth data was used to develop the study flood extraction algorithm and we found a good agreement between our results and SERVIR Mekong (a joint initiative by the US agency for International Development (USAID), National Aeronautics and Space Administration (NASA), Myanmar, Thailand, Cambodia, Laos and Vietnam) maps. While the algorithm is run on a personal computer (PC), it has a clear potential to be developed for application on a big data system
Novel role for polycystin-1 in modulating cell proliferation through calcium oscillations in kidney cells
Objectives: Polycystin-1 (PC1), a signalling receptor regulating Ca2+-permeable cation channels, is mutated in autosomal dominant polycystic kidney disease, which is typically characterized by increased cell proliferation. However, the precise mechanisms by which PC1 functions on Ca2+ homeostasis, signalling and cell proliferation remain unclear. Here, we investigated the possible role of PC1 as a modulator of non-capacitative Ca2+ entry (NCCE) and Ca2+ oscillations, with downstream effects on cell proliferation. Results and discussion: By employing RNA interference, we show that depletion of endogenous PC1 in HEK293 cells leads to an increase in serum-induced Ca2+ oscillations, triggering nuclear factor of activated T cell activation and leading to cell cycle progression. Consistently, Ca2+ oscillations and cell proliferation are increased in PC1-mutated kidney cystic cell lines, but both abnormal features are reduced in cells that exogenously express PC1. Notably, blockers of the NCCE pathway, but not of the CCE, blunt abnormal oscillation and cell proliferation. Our study therefore provides the first demonstration that PC1 modulates Ca2+ oscillations and a molecular mechanism to explain the association between abnormal Ca2+ homeostasis and cell proliferation in autosomal dominant polycystic kidney disease
Energy band diagram of device-grade silicon nanocrystals
This work was supported by the EPSRC (EP/K022237/1) and the Leverhulme International Network (IN-2012-136). SA would like to acknowledge the support of the Ulster University Vice-Chancellor's Research Studentship and CR that of the NI-DEL studentship.Device grade silicon nanocrystals (NCs) are synthesized using an atmospheric-pressure plasma technique. The Si NCs have a small and well defined size of about 2.3 nm. The synthesis system allows for the direct creation of thin films, enabling a range of measurements to be performed and easy implementation of this material in different devices. The chemical stability of the Si NCs is evaluated, showing relatively long-term durability thanks to hydrogen surface terminations. Optical and electrical characterization techniques, including Kelvin probe, ultraviolet photoemission spectroscopy and Mott-Schottky analysis, are employed to determine the energy band diagram of the Si NCs.Publisher PDFPeer reviewe
Ionic liquids as a neat lubricant applied to steel-steel contacts
This paper studies the use of 3 ionic liquids ([(NEMM)MOE][FAP], [BMP][FAP] and [BMP][NTf2]) as neat lubricant within steel-steel contact conditions. Tribological tests (at 40 and 100 C) were conducted in a HFRR tribometer and hence a complementary study was developed using a MTM tribometer. The wear surface on the discs was measured after the HFRR tests by confocal microscopy and also analyzed by SEM and XPS. The [BMP][NTf2] showed the lowest friction coefficient in the MTM and HFRR tests at 40 C but at 100 C its tribological behavior worsened due to its lowest viscosity. Similar results were found for wear behavior. Both antifriction and antiwear results were related to the tribofilms formation from the ECR and XPS measurements. © 2013 Elsevier Ltd
FAP- Anion Ionic Liquids Used in the Lubrication of a Steel–Steel Contact
This study compares the tribological behavior of two ionic liquids ([BMP][FAP] and [(NEMM)MOE][FAP]) used as oil additive for the lubrication of a steel–steel contact. Friction and wear experiments were performed using a HFRR test machine. Friction coefficient and electrical contact resistance were measured during the tests, and the wear surface was analyzed by confocal microscopy and XPS. The tribological results showed that both ionic liquids used as additive decrease friction and wear but the [BMP][FAP] had a better performance than the [(NEMM)MOE][FAP] due to its higher reactivity with the steel
Viral transduction of primary human lymphoma B cells reveals mechanisms of NOTCH-mediated immune escape
Hotspot mutations in the PEST-domain of NOTCH1 and NOTCH2 are recurrently identified in B cell malignancies. To address how NOTCH-mutations contribute to a dismal prognosis, we have generated isogenic primary human tumor cells from patients with Chronic Lymphocytic Leukemia (CLL) and Mantle Cell Lymphoma (MCL), differing only in their expression of the intracellular domain (ICD) of NOTCH1 or NOTCH2. Our data demonstrate that both NOTCH-paralogs facilitate immune-escape of malignant B cells by up-regulating PD-L1, partly dependent on autocrine interferon-? signaling. In addition, NOTCH-activation causes silencing of the entire HLA-class II locus via epigenetic regulation of the transcriptional co-activator CIITA. Notably, while NOTCH1 and NOTCH2 govern similar transcriptional programs, disease-specific differences in their expression levels can favor paralog-specific selection. Importantly, NOTCH-ICD also strongly down-regulates the expression of CD19, possibly limiting the effectiveness of immune-therapies. These NOTCH-mediated immune escape mechanisms are associated with the expansion of exhausted CD8+ T cells in vivo.© 2022. The Author(s)
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Multimorphic Materials: Spatially Tailoring Mechanical Properties via Selective Initiation of Interpenetrating Polymer Networks
Access to multimaterial polymers with spatially localized properties and robust interfaces is
anticipated to enable new capabilities in soft robotics, such as smooth actuation for advanced medical
and manufacturing technologies. Here, orthogonal initiation is used to create interpenetrating polymer
networks (IPNs) with spatial control over morphology and mechanical properties. Base catalyzes the
formation of a stiff and strong polyurethane, while blue LEDs initiate the formation of a soft and elastic
polyacrylate. IPN morphology is controlled by when the LED is turned „on‟, with large phase
separation occurring for short time delays (~1-2 minutes) and a mixed morphology for longer time
delays (>5 minutes), which was supported by dynamic mechanical analysis, small angle X-ray
scattering, and atomic force microscopy. Through tailoring morphology, tensile moduli and fracture
toughness can be tuned across ~1-2 orders of magnitude. Moreover, a simple spring model is used to
explain the observed mechanical behavior. Photopatterning produces “multimorphic” materials, where
morphology is spatially localized with fine precision (<100 µm), while maintaining a uniform chemical
composition throughout to mitigate interfacial failure. The fabrication of hinges represents a possible
use-case for multimorphic materials in soft robotics.This work was primarily supported by the National Science Foundation under Grant No. DMR-
2045336 (M.J.A., C. B., and Z.A.P., synthesis and mechanical characterization). Partial support was
provided from the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award
#DE-SC0022050 (N.P. and X. G., morphology characterization related to scattering and AFM-IR) and
through the Center for Materials for Water and Energy Systems (M-WET), an Energy Frontier
Research Center under Award #DE-SC0019272 (M.J.A. and B.D.F., nanoindentation characterization),
the National Science Foundation under Grant No. CMMI-2038512 (L.M.C., AFM fast force distance
mapping characterization), NSF Graduate Research Fellowship under Grant No. DGE-1610403 (M.J.A.), and the Robert A. Welch Foundation under Grant No. F-2007 (Z.A.P., partial materials and
supplies support). The authors acknowledge the use of shared research facilities supported in part
by the Texas Materials Institute and the Center for Dynamics and Control of Materials (NSF MRSEC)
under Grant No. DMR-1720595.Center for Dynamics and Control of Material
Tribological performance of tributylmethylammonium bis(trifluoromethylsulfonyl)amide as neat lubricant and as an additive in a polar oil
The ionic liquid (IL) tributylmethylammonium bis(trifluoromethylsulfonyl)amide ([N4441][NTf2]) was used as neat lubricant and as an additive (1.5 wt%) in a polar oil to study its friction and wear reducing properties. Tribological tests were completed for 90 minutes at room temperature and 100 °C in a reciprocating configuration at loads of 30 and 70 N, 10 Hz-frequency, and 4 mm stroke length. Wear volume was measured by confocal microscopy and the surface-IL interaction determined by XPS. The main findings were that neat IL showed the best tribological behavior; the IL-containing mixture behaved similar to the base oil regarding friction, however outperformed the antiwear behavior of the base oil under higher temperature; surface-IL chemical interaction was found mainly at 100 °C
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