The organic surfactants like CTAB have long been used in numerous methods of chemical synthesis of nanoparticles effectively, in order to avoid agglomeration and provide stability. However, these are ...not really stable at higher temperatures. Hence, in this work, gold nanoparticles have been encapsulated with SiO2 shells along with CTAB surfactant molecules. The thermal behaviour and the associated physicochemical changes in the Au@SiO2 core-shell structures, during the Thermo Gravimetric Analysis (TGA), have been studied using several standard characterization techniques like Fourier Transform Infrared Spectroscopy, Transmission Electron Microscopy, X-ray Diffractometry and UV–Vis Absorption spectroscopy. About 40% weight loss has been observed during the TGA treatment. The TEM results show different stages of agglomeration after TGA, which includes expansion of SiO2 shells, out-diffusion of gold particles and their eventual agglomeration. Detailed FTIR analysis confirms the proposed mechanism, and is well complemented by TEM, XRD and UV–Vis Absorption results.
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•Effect of thermal treatment and associated physicochemical changes of Au@SiO2 is studied.•The multi-step weight loss observed during thermal treatment.•Decomposition of CTAB molecules seems to have played major role in overall weight loss observed.•Softening of SiO2 shell, out-diffusion of gold particle has been presented.
Boolean functions play an important role in symmetric cryptosystems. In this paper, we have constructed near-bent Boolean functions algebraically with the help of Niho power function exponent in the ...trace form over a finite field. Specific cryptographic properties which may gain attention with suitable modifications are observed using these functions. If exponents are either Mersenne numbers or Fermat numbers, then the resulting functions are found to be APN (almost perfect nonlinear).
The mountainous Western Ghats are part of a biodiversity hotspot and extend for about 1600 km, lying close and subparallel to the west coast of peninsular India. The region is a centre of diversity ...for amphibians, and recent preliminary work on some components of both caecilian (Gymnophiona) and frog (Anura) fauna is indicative of a high degree of local endemism. We investigated diversity in mitochondrial rRNA 12S and 16S sequences for long-tailed, unstriped Ichthyophis (Amphibia: Gymnophiona: Ichthyophiidae) that potentially represent four taxonomically confused and poorly known endemic caecilian species. Data were analysed for18 individuals from along c. 1500 km of the Western Ghats region. Genetic diversity is remarkably low, with a maximum uncorrected p-distance of 0.5%. These DNA sequences and new morphological data do not allow us to reject the null hypothesis that the sample comprises only a single, widely distributed, highly interconnected species. The phylogenetic signal among the data is extremely low. However, population genetic analyses reveal that the Palghat Gap, a c. 30 km discontinuity in the Western Ghats considered to be significant in the biogeography of other organisms occurring in this region, corresponds to a significant subdivision of long-tailed, unstriped Ichthyophis into two groups.
The tribological behavior of the sliding surfaces is dependent on the frictional heating. Surface and near surface temperatures may become high enough to cause changes in structure and properties of ...the sliding surfaces. It can also cause oxidation and even melting. Wear and frictional behavior of materials above ambient (25°C) conditions would become critical for polymers as the operating temperature bands of polymers are always limited. In the present study, tribological studies on two-phase and three-phase polystyrene composites at temperatures of 45 and 60°C have been reported. It is found that with increase in temperature the wear rate increases, whereas the friction coefficient decreases. Polymer–ceramic composite exhibited higher friction coefficient than other composites. At temperature of 45°C, the wear rate of the neat polymer increases exponentially whereas at 60°C it decreased. However, addition of fillers into polystyrene brought in drastic reduction in the wear rate of polymer composites. Scanning electron microscopic pictures revealed melting, flowing, and glazing after wear test. Higher pressure velocity resulted in higher wear coefficient.
Abstract
A promising energy range to look for angular correlations between cosmic rays of extragalactic origin and their sources is at the highest energies, above a few tens of EeV (1 EeV ≡ 10
18
...eV). Despite the flux of these particles being extremely low, the area of ∼3000 km
2
covered at the Pierre Auger Observatory, and the 17 yr data-taking period of the
Phase
1
of its operations, have enabled us to measure the arrival directions of more than 2600 ultra-high-energy cosmic rays above 32 EeV. We publish this data set, the largest available at such energies from an integrated exposure of 122,000 km
2
sr yr, and search it for anisotropies over the 3.4
π
steradians covered with the Observatory. Evidence for a deviation in excess of isotropy at intermediate angular scales, with ∼15° Gaussian spread or ∼25° top-hat radius, is obtained at the 4
σ
significance level for cosmic-ray energies above ∼40 EeV.
A three dimensional study of heat transfer from three heated blocks in a
square channel at a Reynolds number of 108 with height of the chip assembly
as the characteristic length is presented. Heated ...blocks affixed to the
bottom plate represent electronic chips mounted on horizontal circuit board.
A hexahedron block is affixed on to the top shrouding wall over the heated
section. Thickness of this block is varied to study the effect on heat
transfer from the chip assembly. A block of thickness equal to the passage
between substrates produces maximum heat transfer enhancement. A block over
the first passage enhances heat transfer from both immediate upstream and
downstream chips considerably. A block over each recirculation zone produces
moderate heat transfer from all the chips for a moderate pressure-drop. It is
also observed that addition of blocks in the top plate does not add much to
the pressure-drop in the duct.
nema
Instantons, which are nonperturbative solutions to Yang-Mills equations, provide a signal for the occurrence of quantum tunneling between distinct classes of vacua. They can give rise to decays of ...particles otherwise forbidden. Using data collected at the Pierre Auger Observatory, we search for signatures of such instanton-induced processes that would be suggestive of super-heavy particles decaying in the Galactic halo. These particles could have been produced during the post-inflationary epoch and match the relic abundance of dark matter inferred today. The nonobservation of the signatures searched for allows us to derive a bound on the reduced coupling constant of gauge interactions in the dark sector: α_{X}≲0.09, for 10^{9}≲M_{X}/GeV<10^{19}. Conversely, we obtain that, for instance, a reduced coupling constant α_{X}=0.09 excludes masses M_{X}≳3×10^{13} GeV. In the context of dark matter production from gravitational interactions alone, we illustrate how these bounds are complementary to those obtained on the Hubble rate at the end of inflation from the nonobservation of tensor modes in the cosmological microwave background.
Abstract
In this work we present the interpretation of the energy spectrum and mass composition data as measured by the Pierre Auger Collaboration above 6 × 10
17
eV. We use an astrophysical model ...with two extragalactic source populations to model the hardening of the cosmic-ray flux at around 5 × 10
18
eV (the so-called “ankle” feature) as a transition between these two components. We find our data to be well reproduced if sources above the ankle emit a mixed composition with a hard spectrum and a low rigidity cutoff. The component below the ankle is required to have a very soft spectrum and a mix of protons and intermediate-mass nuclei. The origin of this intermediate-mass component is not well constrained and it could originate from either Galactic or extragalactic sources.
To the aim of evaluating our capability to constrain astrophysical models, we discuss the impact on the fit results of the main experimental systematic uncertainties and of the assumptions about quantities affecting the air shower development as well as the propagation and redshift distribution of injected ultra-high-energy cosmic rays (UHECRs).
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