HNBR and its MWCNT reinforced nanocomposites : Crystalline morphology and electrical response

Morphology and electrical response of hydrogenated acrylonitrile butadiene rubber (HNBR) and its multiwall carbon nanotube (MWCNT) reinforced nanocomposites were studied by means of x-ray diffraction and broadband dielectric spectroscopy. HNBR systems were found to be semi-crystalline, with their crystallinity to increase with the addition of MWCNTs. In their dielectric spectra, four relaxation processes were detected. Ascending in relaxation time, these were attributed to: (i) interfacial polarization at the interface of crystalline and amorphous regions of HNBR and at the interface between HNBR and MWCNTs, (ii) glass to rubber transition of the amorphous part of HNBR, (iii) rearrangement of polar side groups, such as –CN, and (iv) local motions of small segments of the main elastomer chain. Electrical conductivity increases with MWCNT content and frequency increasing. The effect of temperature, on the electrical response, is more pronounced at low frequencies. The temperature dependence of the electrical conductivity strongly deviates from a pure Arrhenius behavior, signifying that the occurring conductance mechanisms do not correspond to a single thermally activated process. Relaxation dynamics imply that crystalline regions exert motion restrictions to large segments of the macromolecules in the amorphous phase and to polar parts of the systems

Search for Dark Matter Axions with CAST-CAPP

The CAST-CAPP axion haloscope, operating at CERN inside the CAST dipole magnet, has searched for axions in the 19.74 $\mu$eV to 22.47 $\mu$eV mass range. The detection concept follows the Sikivie haloscope principle, where Dark Matter axions convert into photons within a resonator immersed in a magnetic field. The CAST-CAPP resonator is an array of four individual rectangular cavities inserted in a strong dipole magnet, phase-matched to maximize the detection sensitivity. Here we report on the data acquired for 4124 h from 2019 to 2021. Each cavity is equipped with a fast frequency tuning mechanism of 10 MHz/min between 4.774 GHz and 5.434 GHz. In the present work, we exclude axion-photon couplings for virialized galactic axions down to $g_{a{\gamma}{\gamma}} = 8 \times {10^{-14}}$ $GeV^{-1}$ at the 90% confidence level. The here implemented phase-matching technique also allows for future large-scale upgrades.Comment: 24 pages, 5 figures, Published version available with Open Access at https://www.nature.com/articles/s41467-022-33913-

New CAST limit on the axion-photon interaction

Hypothetical low-mass particles, such as axions, provide a compelling explanation for the dark matter in the universe. Such particles are expected to emerge abundantly from the hot interior of stars. To test this prediction, the CERN Axion Solar Telescope (CAST) uses a 9 T refurbished Large Hadron Collider test magnet directed towards the Sun. In the strong magnetic field, solar axions can be converted to X-ray photons which can be recorded by X-ray detectors. In the 2013-2015 run, thanks to low-background detectors and a new X-ray telescope, the signal-to-noise ratio was increased by about a factor of three. Here, we report the best limit on the axion-photon coupling strength (0.66 × 10 -10 GeV -1 at 95% confidence level) set by CAST, which now reaches similar levels to the most restrictive astrophysical bounds

Towards a medium-scale axion helioscope and haloscope

We discuss the physics case for and the concept of a medium-scale axion helioscope with sensitivities in the axion-photon coupling a few times better than CERN Axion Solar Telescope (CAST). Search for an axion-like particle with these couplings is motivated by several persistent astrophysical anomalies. We present early conceptual design, existing infrastructure, projected sensitivity and timeline of such a helioscope (Troitsk Axion Solar Telescope Experiment, TASTE) to be constructed in the Institute for Nuclear Research, Troitsk, Russia. The proposed instrument may be also used for the search of dark-matter halo axions

Tests of chameleon gravity

Theories of modified gravity, where light scalars with non-trivial self-interactions and non-minimal couplings to matter—chameleon and symmetron theories—dynamically suppress deviations from general relativity in the solar system. On other scales, the environmental nature of the screening means that such scalars may be relevant. The highly-nonlinear nature of screening mechanisms means that they evade classical fifth-force searches, and there has been an intense effort towards designing new and novel tests to probe them, both in the laboratory and using astrophysical objects, and by reinterpreting existing datasets. The results of these searches are often presented using different parametrizations, which can make it difficult to compare constraints coming from different probes. The purpose of this review is to summarize the present state-of-the-art searches for screened scalars coupled to matter, and to translate the current bounds into a single parametrization to survey the state of the models. Presently, commonly studied chameleon models are well-constrained but less commonly studied models have large regions of parameter space that are still viable. Symmetron models are constrained well by astrophysical and laboratory tests, but there is a desert separating the two scales where the model is unconstrained. The coupling of chameleons to photons is tightly constrained but the symmetron coupling has yet to be explored. We also summarize the current bounds on f(R) models that exhibit the chameleon mechanism (Hu and Sawicki models). The simplest of these are well constrained by astrophysical probes, but there are currently few reported bounds for theories with higher powers of R. The review ends by discussing the future prospects for constraining screened modified gravity models further using upcoming and planned experiments

Calculation of the Electron Momentum Density and Compton-Scattering Measurements for Nickel

Journal URL: http://www.iop.org/EJ/journal/JPhysC

Tandem synthesis of amides and secondary amines from esters with primary amines under solvent-free conditions

An iridium(III)-catalyzed tandem synthesis of amides and amines from esters under solvent-free conditions is described. A commercially available iridium(III) complex, [Cp*IrCl2]2, with sodium acetate showed the best activity for the synthesis of amides and secondary amines. The amide was formed by ester-amide exchange which generates an alcohol in situ which is subsequently transformed to a secondary amine via hydrogen autotransfer. This synthetic protocol with high atom economy generates water as the sole by-product and can afford amides and amines from various esters in a one-pot reaction, expanding the synthetic versatility of ester transformations. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.115161sciescopu