Doping effects on charge density instability in non-centrosymmetric PbxTaSe2

We report on the investigation of vibrational and electronic properties of the Pb doped dichalcogenide PbxTaSe2 using Raman scattering experiments. We observe a marked variation of the main vibrational modes with Pb concentration x. The concentration dependence of the vibrational modes resembles the dependence of the vibrational modes in TaSe2 on the number of crystallographic layers along the c axis direction [1]. The temperature and polarization dependence of Raman spectra of PbxTaSe2 revealed additional broad modes in the low frequency regime which are discussed in context of remnant charge density wave, induced disorder, or PbSe phase formed in the interface of Pb and TaSe2 layers.Comment: 14 page

Apophis planetary defense campaign

We describe results of a planetary defense exercise conducted during the close approach to Earth by the near-Earth asteroid (99942) Apophis during 2020 December–2021 March. The planetary defense community has been conducting observational campaigns since 2017 to test the operational readiness of the global planetary defense capabilities. These community-led global exercises were carried out with the support of NASA's Planetary Defense Coordination Office and the International Asteroid Warning Network. The Apophis campaign is the third in our series of planetary defense exercises. The goal of this campaign was to recover, track, and characterize Apophis as a potential impactor to exercise the planetary defense system including observations, hypothetical risk assessment and risk prediction, and hazard communication. Based on the campaign results, we present lessons learned about our ability to observe and model a potential impactor. Data products derived from astrometric observations were available for inclusion in our risk assessment model almost immediately, allowing real-time updates to the impact probability calculation and possible impact locations. An early NEOWISE diameter measurement provided a significant improvement in the uncertainty on the range of hypothetical impact outcomes. The availability of different characterization methods such as photometry, spectroscopy, and radar provided robustness to our ability to assess the potential impact risk

The Effect of Divalent Metal Ions on the Temperature Stability of Poly(I:C) Duplex

The effect of divalent ions on the thermal stability of the double-stranded polynucleotide polyinosinic:polycytidylic acid (poly(I:C)) in a buffer solution (pH 7) was studied by UV absorption spectroscopy and thermal denaturation by measuring the absorbance at 260 nm. The concentration dependence of the polynucleotide melting temperature (Tm) in the presence of metal ions (2.5 × 10−6–10−2 M) was obtained. It was found that the duplex thermal stability grew gradually upon an increase of Ca2+ and Mn2+ concentration. The thermal stability of the duplex in the presence of Cd2+, Ni2+, and Zn2+ rises up to an ion concentration of about 10−4 M and further falls. In contrast to these ions, the addition of Cu2+ to the solution leads to a sharp decline in Тm of the duplex at a concentration above 10−5 M. The observed difference in the influence of metal ions on the poly(I:C) thermal stability is explained by the different affinity of these ions to both the phosphate groups and the nitrogenous bases of the polynucleotides. Based on the analysis of the Tm concentration dependence, the dominant binding of each ion to the specific polynucleotide components was proposed

Achieving high mid-IR bolometric responsivity for anisotropic composite materials from carbon nanotubes and polymers

An anisotropic carbon nanotube (CNT)-polymer composite for bolometric applications in the mid-IR spectral range (2.5-20 μm) is studied. Composite alignment in conjunction with non-uniform distribution of CNTs in the polymer matrix allows for a significant enhancement of the temperature coefficient of resistance (0.82% K -1) with respect to uniform composite (0.24% K -1). As a result a responsivity of ≈ 500 V W -1 is reached, which is the highest for CNT-based bolometers reported to date. Such remarkable optical and thermal characteristics are explained in terms of fluctuation tunneling theory taking into account the composite anisotropy and the gradient of the CNT concentration. Flatness of the photoresponse in the broad spectral mid-IR range and enhanced responsivity provide a great potential for the use of such novel composite for applications in IR spectroscopy and thermal imaging. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Noncovalent Interaction of Single-Walled Carbon Nanotubes with 1-Pyrenebutanoic Acid Succinimide Ester and Glucoseoxidase

Peculiarities of the interface interactions of 1-pyrenebutanoic acid <i>N</i>-hydroxysuccinimide ester (PSE) with single-walled carbon nanotubes (SWCNTs) and enzyme glucoseoxidase (GOX) have been studied with the resonance Raman spectroscopy and theoretical calculations employing the DFT method and the molecular dynamics (MD) simulation. The interaction of a nanotube with PSE leads to a downshift of the band assigned in the Raman spectrum to the tangential mode of the hybrid with respect to the position of this mode in the spectrum of the pristine SWCNT. The MD simulation demonstrates that the direct interaction between SWCNT and GOX is very strong. This interaction can be expected to change the structure of the enzyme and to significantly affect its activity. The MD simulation also shows that only one PSE molecule used as a linker between SWCNT and GOX is enough to keep GOX near the nanotube surface in the water surrounding and to prevent strong interaction between SWCNT and GOX. However, to stabilize this nanobiohybrid in water at least two PSE linkers are needed. The molecular structure of PSE is determined using the density functional theory approach (DFT/B3LYP/6-31++G(d,p). The geometries and the relative stabilities of all possible PSE conformers are characterized in the calculations. High structural flexibility of the PSE molecule is demonstrated. Calculations (at the M05-2X level of theory) have also been performed on the structures and the interaction energies of complexes formed by various SWCNTs with PSE and pyrene. Pyrene interacts strongly with the surface of carbon nanotubes with different chiralities, but the interaction with zigzag nanotubes is stronger than with armchair ones of the same diameter. Increasing the diameter of the SWCNTs leads to a higher adsorption energy, reaching the maximum value for graphene (−20.8 kcal/mol)