Low-frequency phonon dynamics and related thermal properties of axially stressed single-walled carbon nanotubes

Synthesis temperatures of composite materials are usually far less than the ones of their use, thus carbon nanotubes (CNTs) embedded into a polymer matrix undergo significant axial stress. We develop a continuous theory, which describes the dynamics of stressed single-walled (SW-) CNTs and predicts their low-frequency phonon spectra. The changes in dispersion laws of SWCNT low-frequency phonon modes due to the axial stress of different signs are discussed. Then, the results obtained are used to analyze low-temperature (T<70 K) heat capacity and thermal conductivity of individual nanotubes. We demonstrate that compressive stress leads to increase in heat capacity CV of an individual SWCNT, while tensile stress causes CV to decrease. In the latter case at T→0 heat capacity diminishes according to a linear law ~T instead of a power one ~T1/2.Nevertheless, according to our results, axial stress hardly affects low-temperature thermal conductance of SWCNTs.Influence of investigated effects on the corresponding macroscopic properties of CNT-based composite materials are discussed as well

Role of Mechanical van der Waals Coupling in the G-Band Splitting of Individual Multiwall Carbon Nanotubes

Characterization of multiwalled carbon nanotubes (MWCNT) by Raman spectroscopy is challenging due to their structural complexity, inhomogeneity, and complicated interlayer van der Waals (vdW) interactions. These latter effects can be however well investigated in individual MWCNTs, prepared by the on-chip purification of arc-discharge (AD) MWCNT powder, combining atomic force microscopy, polarized Raman imaging, and spectroscopy. In this work, we reveal the inhomogeneity of the Raman signal from individual AD-MWCNTs and attribute it to the extraction of inner layers during the sonication stage of the dispersion procedure. We report the splitting of the Raman-active G-band, describing it in terms of the variation of interlayer mechanical vdW coupling as a function of diameter and interlayer distance in the probed AD-MWCNTs. Finally, we present a practical method for investigating the polarization behavior of MWCNTs with a nonuniform Raman response based on Raman mapping and advanced data fitting. Our work gives additional insights into the characterization of structurally nonuniform MWCNTs and allows distinguishing between these MWCNTs and 1D moiré crystals based on collapsed SWCNTs or studying telescopic 1D vdW heterostructures with Raman spectroscopy.peerReviewe

Rare predicted loss-of-function variants of type I IFN immunity genes are associated with life-threatening COVID-19

BackgroundWe previously reported that impaired type I IFN activity, due to inborn errors of TLR3- and TLR7-dependent type I interferon (IFN) immunity or to autoantibodies against type I IFN, account for 15-20% of cases of life-threatening COVID-19 in unvaccinated patients. Therefore, the determinants of life-threatening COVID-19 remain to be identified in similar to 80% of cases.MethodsWe report here a genome-wide rare variant burden association analysis in 3269 unvaccinated patients with life-threatening COVID-19, and 1373 unvaccinated SARS-CoV-2-infected individuals without pneumonia. Among the 928 patients tested for autoantibodies against type I IFN, a quarter (234) were positive and were excluded.ResultsNo gene reached genome-wide significance. Under a recessive model, the most significant gene with at-risk variants was TLR7, with an OR of 27.68 (95%CI 1.5-528.7, P=1.1x10(-4)) for biochemically loss-of-function (bLOF) variants. We replicated the enrichment in rare predicted LOF (pLOF) variants at 13 influenza susceptibility loci involved in TLR3-dependent type I IFN immunity (OR=3.70[95%CI 1.3-8.2], P=2.1x10(-4)). This enrichment was further strengthened by (1) adding the recently reported TYK2 and TLR7 COVID-19 loci, particularly under a recessive model (OR=19.65[95%CI 2.1-2635.4], P=3.4x10(-3)), and (2) considering as pLOF branchpoint variants with potentially strong impacts on splicing among the 15 loci (OR=4.40[9%CI 2.3-8.4], P=7.7x10(-8)). Finally, the patients with pLOF/bLOF variants at these 15 loci were significantly younger (mean age [SD]=43.3 [20.3] years) than the other patients (56.0 [17.3] years; P=1.68x10(-5)).ConclusionsRare variants of TLR3- and TLR7-dependent type I IFN immunity genes can underlie life-threatening COVID-19, particularly with recessive inheritance, in patients under 60 years old