By this report, we described the synthesis of graphene (1 wt%) reinforced copper matrix composites (Cu-GNS) by using the mechanical milling and the hot pressing. The structure and morphology of the ...few layer graphene nanosheets (GNS) reinforced copper matrix composites were discussed with the X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques, respectively. The influence of the mechanical milling on the microstructure was analyzed. The chemical compatibility and successful formation of the composites were confirmed by the X-ray diffraction studies. The consolidation of the powders was performed by using vacuum hot-press sintering (at 600 and 700 °C). The hardness and electrical conductivity were discussed with respect to the sintering temperatures. An improvement in the electrical conductivity around 22% for 1 wt% graphene reinforced Cu when compared with the pure Cu matrix consolidated at 600 °C was observed. The importance of lower sintering temperature and higher applied load in the consolidation (600 °C, 30 MPa for 30 min) to obtain the Cu-GNS composites with improved physical, mechanical and electrical properties was emphasized.
•Loading of graphene led to the 22% of rise in electrical conductivity of the Cu.•Graphene induced lubrication led to the predominance of the fracture.•Relative density exhibited an increment with graphene loading.•Low sintering temperature and high applied load are optimal for consolidation.
We present the first results from a reverberation-mapping campaign undertaken during the first half of 2012, with additional data on one active galactic nucleus (AGN) (NGC 3227) from a 2014 campaign. ...Our main goals are (1) to determine the black hole masses from continuum-Hβ reverberation signatures, and (2) to look for velocity-dependent time delays that might be indicators of the gross kinematics of the broad-line region. We successfully measure Hβ time delays and black hole masses for five AGNs, four of which have previous reverberation mass measurements. The values measured here are in agreement with earlier estimates, though there is some intrinsic scatter beyond the formal measurement errors. We observe velocity-dependent Hβ lags in each case, and find that the patterns have changed in the intervening five years for three AGNs that were also observed in 2007.
A Survey of Herbig Ae/Be Multiplicity Thomas, S. J.; Rodgers, B.; van der Bliek, N. S. ...
The Astronomical journal,
03/2023, Letnik:
165, Številka:
3
Journal Article
Recenzirano
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Abstract
Although the majority of Herbig Ae/Be (HAEBE) stars are likely multiple systems, relatively few multiples have been identified. We aim to create a statistically significant survey of HAEBE ...multiplicity as a function of stellar mass, to shed light on mixed-mass star formation. Two independent adaptive optics IR imaging surveys were conducted, between 1993 and 2007. A total of 143 stars were observed, including 126 HAEBE stars. These surveys are significantly more sensitive than previous imaging work and, combined with accurate distance and proper-motion data from GAIA Data Release 3, provide a broad survey of intermediate-mass multiplicity. We perform a statistical probability analysis to identify the likely physical companions, and analyze multiepoch observations for common proper motions. We find 250 stellar detections around 88 sample stars. Of these, 70 systems are likely multiple systems, and 42 companions around 29 systems are reported here for the first time. Correcting for completeness, we find a multiplicity fraction of 54%. Multiples are found randomly across all spectral types, but high-order multiples are more common among the hottest stars. Statistically likely companions are found at distances of up to several thousand astronomical units and Δ
K
magnitudes ranging from <0.1 to ∼9, although companions with Δ
K
< 1.5 are rare. Companions around Herbig Ae stars tend to be closer than those around Herbig Be stars. We confirm 24 proper-motion companions in 21 systems, including roughly half of the statistically very likely companions; however, many proper-motion results are inconclusive.
Titanium-based alloys are widely used in biomedical applications because of their good properties such as fatigue resistance, workability, corrosion resistance and biocompatibility. The effect of ...milling time on the deformation-driven alloying mechanisms in the system Ti-30Nb-13Ta-2Mn (wt.%) during mechanical alloying (MA) has been studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). High-energy milling was performed in controlled atmosphere of argon at different times (1, 5, 10, 20, 30, 50, 70, 90 and 110 h), using agate as grinding media. The XRD-patterns showed the formation of Ti-β solid solution occurred above 20 h of milling. Due to the high energy of this process, the formation of Ti-β and Nb-fcc crystalline phases embedded in an amorphous phase was promoted. The longer alloying time above 50 h resulted in spherical morphology and texturing of the synthetized alloy which were evidenced from the SEM and XRD analyses, respectively. Lattice parameters, mean crystallite size and microstrain (root mean square, rms) were obtained from Rietveld analysis using MAUD software. The nanocrystalline domains were also quantified by TEM, which showed the coexistence of amorphous and nanocrystalline particles of Mn2Ti, MnTi, NbTi4, Nb-fcc and Ti-β embedded in an amorphous phase.
•Ti-30Nb-13Ta-2Mn alloy was prepared by mechanical alloying.•Ta and Nb formed a solid solution with Ti and stabilizing the β-phase.•Mn as alloying element promoted the formation of an amorphous phase.•Formation of micro-texture was detected in the powders milled above 50 h.•Nanocrystalline domains of Mn2Ti, MnTi and NbTi4 were detected by HRTEM.
•An improved impedimetric e-tongue dedicated to wines has been developed.•New sensors are layered nanocomposites alternating PEDOT:PSS and AuNPs or LuPc2.•A new feature extraction method based on an ...equivalent circuit has been developed.•PCA shows that the system can discriminate extremely similar red wines.•The improved e-tongue also enhances the capability to predict chemical variables using PLS-1.
An impedimetric electronic tongue to discriminate red wines with similar characteristics (same region, vintage and ageing method) is developed. The excellent performance achieved is due to the remarkable sensing properties of the nanocomposites forming the array and to the methodology developed to extract the input variables used in the statistical analysis. The multisensor system is formed by one PEDOT:PSS sensor and two nanocomposites formed by layers of PEDOT:PSS and gold nanoparticles (PEDOT:PSS/AuNP) or layers of PEDOT:PSS and lutetium bisphthalocyanine (PEDOT:PSS/LuPc2). The well-known electrocatalytic activity of the sensing materials is promoted in the layered composites and enhances the cross-selectivity of the sensors. Besides, a feature extraction method that uses an equivalent electric circuit model to obtain the input variables used in the statistical analysis has been developed. By using the statistical procedure of Principal Component Analysis, the improved electronic tongue is able to discriminate three wines from the variety Tempranillo, one wine of the variety Tinta de Toro (a clon of Tempranillo) and one wine elaborated with a coupage of 90% Tempranillo and 10% Garnacha variety. The combination of layered nanomaterials and the new feature extraction method also enhances the capability of the impedimetric electronic tongue to predict chemical variables using Partial Least Squares regression.
Dual screen-printed carbon electrodes modified with 4-carboxyphenyl-functionalized double-walled carbon nanotubes (HOOC-Phe-DWCNTs/SPCEs) have been used as scaffolds for the preparation of ...electrochemical immunosensors for the simultaneous determination of the cytokines Interleukin-1β (IL-1β) and factor necrosis tumor α (TNF-α). IL-1β. Capture antibodies were immobilized onto HOOC-Phe-DWCNTs/SPCEs in an oriented form making using the commercial polymeric coating Mix&Go™. Sandwich type immunoassays with amperometric signal amplification through the use of poly-HRP-streptavidin conjugates and H2O2 as HRP substrate and hydroquinone as redox mediator were implemented. Upon optimization of the experimental variables affecting the immunosensor performance, the dual immunosensor allows ranges of linearity extending between 0.5 and 100 pg/mL and from 1 to 200 pg/mL for IL-1β and TNF-α, respectively, these ranges being adequate for the determination of the cytokines in clinical samples. The achieved limits of detection were 0.38 pg/mL (IL-1β) and 0.85 pg/mL (TNF-α). In addition, the dual immunosensor exhibits excellent reproducibility of the measurements, storage stability of the anti-IL-Phe-DWCNTs/SPCE and anti-TNF-Phe-DWCNTs/SPCE conjugates, and selectivity as well as negligible cross-talking. The dual immunosensor was applied to the simultaneous determination of IL-1β and TNF-α in human serum spiked at clinically relevant concentration levels and in real saliva samples.
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•Electrochemical immunosensor for simultaneous determination of IL-β1 and TNF-α cytokines.•Oriented immobilization of capture antibodies and signal amplification.•Improved analytical performance with respect to previous approaches and ELISA methods.•Application to human serum and saliva.
A novel form of alkali low-energy ion scattering is used to probe the deposition of nanoclusters onto a solid surface via buffer layer assisted growth (BLAG) in ultrahigh vacuum. A thin amorphous ...solid water (ASW) buffer layer is grown on a TiO2(110) single crystal cooled to 100 K. Au atoms deposited onto this layer arrange themselves into nanoclusters. The sample is then annealed to 320 K to desorb the ASW and enable the clusters to soft-land onto the substrate. Time-of-flight low-energy ion scattering, using Li+, Na+, and K+ projectiles, probes the materials during each step of the BLAG process to measure the surface composition and reveal the details of how the clusters form. The neutralization probability of Na+ ions singly scattered from the Au nanoclusters indicates that they increase in size after annealing and that the magnitude of the increase is a function of the buffer layer thickness. The adsorption of a thin, incomplete water layer prior to Au deposition forms nanoclusters that are possibly even smaller than those produced by direct deposition onto the clean substrate.
Au nanoclusters grown on SiO2 by physical vapor deposition are exposed to Br2 and then measured with 1.5 keV Na+ low energy ion scattering. It is found that the clusters are able to dissociate the ...molecules, which then adsorb as individual Br atoms, but Br2 does not stick to the bare substrate nor to bulk Au. Adsorption is the first step in any surface chemical reaction, and this result shows how nanoclusters can induce adsorption of species that otherwise do not stick. Results from the literature indicate that catalysis involving nanoclusters occurs at the edges and that the edge atoms are positively charged. This information in conjunction with the ion scattering results lead to the conclusion that the Br adatoms are negatively charged and ionically bonded at the edges of the clusters. Br2 is also a known catalytic poison and this work shows how its adsorption blocks sites that would otherwise be involved in nanocatalysis.
Ti-based alloys are being widely used as bio-implant materials because of their excellent properties. This work reports the synthesis of Ti–30Nb–13Ta–2Mn (wt. %) foams with and without bimodal ...microstructure using NaCl (0, 20 and 30 vol %) as space-holder particles (SHP). Samples with bimodal microstructure were obtained by mixing milled and un-milled powders in a proportion of 1:4. Samples without bimodal microstructure were synthesized using only un-milled powders. Hot pressing was used to consolidate the green samples using argon gas as protective atmosphere under 30 MPa at 780 °C for 30 min. The consolidated metallic foams were characterized by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) to study their microstructure and phase analyses. The Young's modulus values were between 39 and 19 GPa, and the yield strength values were obtained between 180 and 400 MPa. From the mechanical properties point of view, samples with bimodal microstructure and with 20 and 30 vol % of NaCl have a great potential to be explored for biomedical applications due to their mechanical properties of Young's modulus smaller than 30 GPa and yield strength higher than 180 MPa. Further, the foams were modelled using finite element analysis (FEA) with random distribution of the pores in order to estimate the compressive behavior, and the Young's modulus measured using FEA was in an excellent agreement with the experimental data.
Bowel inflammation, impaired intestinal epithelial barrier (IEB), and gut dysbiosis could represent early events in Parkinson's disease (PD). This study examined, in a descriptive manner, the ...correlation among enteric α-synuclein, bowel inflammation, impairments of IEB and alterations of enteric bacteria in a transgenic (Tg) model of PD before brain pathology. Human A53T α-synuclein Tg mice were sacrificed at 3, 6, and 9 months of age to evaluate concomitance of enteric inflammation, IEB impairments, and enteric bacterial metabolite alterations during the early phases of α-synucleinopathy. The molecular mechanisms underlying the interplay between α-synuclein, activation of immune/inflammatory responses and IEB alterations were investigated with in vitro experiments in cell cultures. Tg mice displayed an increase in colonic levels of IL-1β, TNF, caspase-1 activity and enteric glia activation since 3 months of age. Colonic TLR-2 and zonulin-1 expression were altered in Tg mice as compared with controls. Lipopolysaccharide levels were increased in Tg animals at 3 months, while fecal butyrate and propionate levels were decreased. Co-treatment with lipopolysaccharide and α-synuclein promoted IL-1β release in the supernatant of THP-1 cells. When applied to Caco-2 cells, the THP-1-derived supernatant decreased zonulin-1 and occludin expression. Such an effect was abrogated when THP-1 cells were incubated with YVAD (caspase-1 inhibitor) or when Caco-2 were incubated with anakinra, while butyrate incubation did not prevent such decrease. Taken together, early enteric α-synuclein accumulation contributes to compromise IEB through the direct activation of canonical caspase-1-dependent inflammasome signaling. These changes could contribute both to bowel symptoms as well as central pathology.
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