Multi-walled carbon nanotube (MWCNT)/portland cement(PC) composites have been fabricated to evaluate their electromagnetic interference (EMI) shielding effectiveness (SE). The results show that they ...can be used for the shielding of EMI in the microwave range. The incorporation of 15wt.% MWCNTs in the PC matrix produces a SE more than 27dB in X-band (8.2–12.4GHz), and this SE is found to be dominated by absorption. Furthermore, the structural analysis, surface morphology and surface interaction of MWCNTs with PC matrix have been explored using XRD, SEM and X-ray photoelectron spectroscopy technique.
Display omitted
•An attempt to find out application of Barium Ferrite & Graphite integrated with Polyaniline composite for electromagnetic Radiation Shielding.•Using and testing of composite ...materials shielding effectiveness instead of the other widely used materials.•Synthesis and Characterization of materials for its application as a shielding material.•Dielectric and Electromagnetic shielding behavior study of PANI/EG/BaFe12O19 composite.
Barium ferrite was incorporated into polyaniline matrix along with expanded graphite (EG) in order that the resultant conductive composite can be used for electromagnetic shielding. The different properties like complex permittivity (ε′′), permeability (μ′′), and effectiveness of shielding have been studied by vector network analyzer using theoretical enumeration given in Weir and Nicholson–Ross algorithms. The microwave absorption characteristic of the composites have been calculated in the X-band (8.2–12.4GHz) frequency range which shows a shielding effectiveness up-to 37.1dB, which strongly depends on dielectric loss.
Composite sheets consisting of phenolic resin filled with a mixture of reduced graphene oxide (RGO), γ-Fe2O3 and carbon fibers have been produced by compression molding. Its electrical conductivity ...lies in the range 0.48–171.21S/cm. Transmission and scanning electron microscopy observations confirm the presence of nano particles of γ-Fe2O3 (∼9.8nm) and carbon fiber (∼1mm) which gives flexural strength to composite sheets. Thermogravimetric analysis show that the thermal stability of the sheets depend upon the amount of RGO and phenol resin in the composite. Complex parameters, i.e., permittivity (ε*=ε′−iε″) and permeability (μ*=μ′−iμ″) of RGO/γ-Fe2O3/carbon fiber have been calculated from experimental scattering parameters (S11 and S21) using theoretical calculations given in Nicholson−Ross and Weir algorithms. The microwave absorption properties of the sheets have been studied in the 8.2–12.4GHz (X-Band) frequency range. The maximum shielding effectiveness observed is 45.26dB, which strongly depends on dielectric loss and volume fraction of γ-Fe2O3 in RGO matrix.
Abstract
A non-local-thermodynamic-equilibrium (NLTE) level population model of the first and second ionisation stages of iron, nickel and cobalt is used to fit a sample of XShooter optical + ...near-infrared (NIR) spectra of Type Ia supernovae (SNe Ia). From the ratio of the NIR lines to the optical lines limits can be placed on the temperature and density of the emission region. We find a similar evolution of these parameters across our sample. Using the evolution of the Fe ii 12 570 Å to 7 155 Å line as a prior in fits of spectra covering only the optical wavelengths we show that the 7200 Å feature is fully explained by Fe ii and Ni ii alone. This approach allows us to determine the abundance of Ni ii/Fe ii for a large sample of 130 optical spectra of 58 SNe Ia with uncertainties small enough to distinguish between Chandrasekhar mass (MCh) and sub-Chandrasekhar mass (sub-MCh) explosion models. We conclude that the majority (85%) of normal SNe Ia have a Ni/Fe abundance that is in agreement with predictions of sub-MCh explosion simulations of ∼Z⊙ progenitors. Only a small fraction (11%) of objects in the sample have a Ni/Fe abundance in agreement with MCh explosion models.
Expanded graphite (EG) was incorporated into fly ash matrix along with nanoferrite γ-Fe2O3 particles so that the resultant conductive fly ash composite can be used for electromagnetic shielding in ...microwave range (X-band). Transmission electron microscopy (TEM) images of EG/γ-Fe2O3/fly ash hybrid structure show that fly ash particle (0.87μm) is wrapped by sheets of expanded graphite containing the γ-Fe2O3 particles (15–25nm). Display omitted
► By changing the wt% of expanded graphite (EG), γ-Fe2O3 and fly ash the composites have been formed. ► Fly ash particle (0.87μm) is covered by sheets of EG containing the γ-Fe2O3 particles (15–25nm). ► EG/γ-Fe2O3 /fly ash composites shows a shielding effectiveness ∼ 90 dB in the X-band frequency range.
Expanded graphite (EG) was incorporated into fly ash matrix along with nanoferrite γ-Fe2O3 particles so that the resultant conductive fly ash composite can be used for electromagnetic shielding in microwave range. Conductivity of composites lies in the range 0.34–32.86S/cm. TEM images show that fly ash particle (0.87μm) is covered by sheets of EG containing the magnetic nanoparticles. Complex parameters have been calculated from experimental scattering parameters (S11 and S21) using theoretical calculations given in Nicholson–Ross and Weir algorithms. The microwave absorption properties of the composites have been studied in the 8.2–12.4GHz (X-band) frequency range which shows a shielding effectiveness up-to 90dB, which strongly depends on dielectric loss and weight fraction of fly ash and γ-Fe2O3 in EG matrix.
The observed tension (∼9% difference) between the local distance ladder measurement of the Hubble constant, H0, and its value inferred from the cosmic microwave background could hint at new, exotic, ...cosmological physics. We test the impact of the assumption about the expansion history of the universe ( ) on the local distance ladder estimate of H0. In the fiducial analysis, the Hubble flow Type Ia supernova (SN Ia) sample is truncated to z < 0.15, and the deceleration parameter (q0) is fixed to −0.55. We create realistic simulations of the calibrator and Pantheon samples, and account for a full systematics covariance between these two sets. We fit several physically motivated dark-energy models, and derive combined constraints from calibrator and Pantheon SNe Ia and simultaneously infer H0 and dark-energy properties. We find that the assumption on the dark-energy model does not significantly change the local distance ladder value of H0, with a maximum difference (ΔH0) between the inferred value for different models of 0.47 km , i.e., a 0.6% shift in H0, significantly smaller than the observed tension. Additional freedom in the dark-energy models does not increase the error in the inferred value of H0. Including systematics covariance between the calibrators, low-redshift SNe, and high-redshift SNe can induce small shifts in the inferred value for H0. The SN Ia systematics in this study contribute 0.8% to the total uncertainty of H0.
Highly conducting polyaniline (PANI)–multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by in situ polymerization. The FTIR and XRD show systematic shifting of the characteristic bands ...and peaks of PANI, with the increase in MWCNT phase, suggesting significant interaction between the phases. The SEM and TEM pictures show thick and uniform coating of PANI over surface of individual MWCNT. Based on observed morphological features in SEM, the probable formation mechanism of these composites has been proposed. The electrical conductivity of PANI–MWCNT composite (19.7
S
cm
−1) was even better than MWCNT (19.1
S
cm
−1) or PANI (2.0
S
cm
−1). This can be ascribed to the synergistic effect of two complementing phases (i.e. PANI and MWCNT). The absorption dominated total shielding effectiveness (SE) of −27.5 to −39.2
dB of these composites indicates the usefulness of these materials for microwave shielding in the Ku-band (12.4–18.0
GHz). These PANI coated MWCNTs with large aspect ratio are also proposed as hybrid conductive fillers in various thermoplastic matrices, for making structurally strong microwave shields.
Blends of polystyrene with polyaniline (PANI) coated multiwalled carbon nanotubes (MWCNTs) were designed which inherit dielectric and magnetic attributes from PANI and MWCNT respectively. The high ...resolution transmission electron microscopy image shows the PANI coating over MWCNT containing entrapped Fe catalyst. These blends show absorption dominated total shielding effectiveness (
SE
T
) of −45.7
dB (>99.99% attenuation) in the 12.4–18.0
GHz range, suggesting their utility for making efficient microwave absorbers. The enhanced
SE
T
was ascribed to optimization of conductivity, skin-depth, complex permittivity and permeability. A good agreement between theoretical and experimental shielding measurements was also observed.
ABSTRACT
The nature of dark matter (DM) is a central question in cosmology today. While elementary particles could explain DM, compact astrophysical objects such as black holes formed in the early ...Universe offer a theoretically appealing alternate route. Here, we constrain the fraction of DM that can be made up of primordial black holes (PBHs) with masses $M \gtrsim 0.01\, {\rm M}_\odot$, with Type Ia supernovae. Utilizing the Dyer–Roeder distance relation, we find a maximum fractional amount of DM in compact objects (fp) of 0.50 at 95 per cent confidence level (C.L.), in the flat Lambda cold dark matter model and 0.49 when marginalizing over a constant dark energy equation of state or spatial curvature, demonstrating robustness to the cosmological model. With a prior on the homogeneity parameter, η, including values >1, we derive η = 1.08 ± 0.17, hence, fp < 0.32 at 95 per cent C.L., showing that the prior assumption of η ≤ 1 gives a conservative upper limit on fp. The Hubble constant we infer is consistent with the homogeneous case, showing that inhomogeneities like compact DM cannot account for the observed Hubble tension. In conclusion, we can exclude stellar masses PBHs as comprising all of the observed DM.
PDF
