Dimensional Crossover of Dilute Neon inside Infinitely Long Single-Walled Carbon Nanotubes Viewed from Specific Heats

A simple formula for coordinates of carbon atoms in a unit cell of a single-walled nanotube (SWNT) is presented and the potential of neon (Ne) inside an infinitely long SWNT is analytically derived under the assumption of pair-wise Lennard-Jones potential between Ne and carbon atoms. Specific heats of dilute Ne inside infinitely long (5, 5), (10, 10), (15, 15) and (20, 20) SWNT's are calculated at different temperatures. It is found that Ne inside four kinds of nanotubes exhibits 3-dimensional (3D) gas behavior at high temperature but different behaviors at low temperature: Ne inside (5, 5) nanotube behaves as 1D gas but inside (10, 10), (15, 15), and (20, 20) nanotubes behaves as 2D gas. Furthermore, at ultra low temperature, Ne inside (5, 5) nanotube still displays 1D behavior but inside (10, 10), (15, 15), and (20, 20) nanotubes behaves as lattice gas.Comment: 10 pages, 5 figure

Single- and multi-walled carbon nanotubes viewed as elastic tubes with Young's moduli dependent on layer number

The complete energy expression of a deformed single-walled carbon nanotube (SWNT) is derived in the continuum limit from the local density approximation model proposed by Lenosky {\it et al.} \lbrack Nature (London) {\bf 355}, 333 (1992)\rbrack and shows to be content with the classic shell theory by which the Young's modulus, the Poisson ratio and the effective wall thickness of SWNTs are obtained as $Y=4.70$TPa, $\nu=0.34$, $h=0.75{\rm \AA}$, respectively. The elasticity of a multi-walled carbon nanotube (MWNT) is investigated as the combination of the above SWNTs of layer distance $d=3.4 {\rm \AA}$ and the Young's modulus of the MWNT is found to be an apparent function of the number of layers, $N$, varying from 4.70TPa to 1.04TPa for N=1 to $\infty$.Comment: 4 pages, 1 figur

Measurements of All-Particle Energy Spectrum and Mean Logarithmic Mass of Cosmic Rays from 0.3 to 30 PeV with LHAASO-KM2A

International audienceWe present the measurements of all-particle energy spectrum and mean logarithmic mass of cosmic rays in the energy range of 0.3–30 PeV using data collected from LHAASO-KM2A between September 2021 and December 2022, which is based on a nearly composition-independent energy reconstruction method, achieving unprecedented accuracy. Our analysis reveals the position of the knee at 3.67±0.05±0.15  PeV. Below the knee, the spectral index is found to be -2.7413±0.0004±0.0050, while above the knee, it is -3.128±0.005±0.027, with the sharpness of the transition measured with a statistical error of 2%. The mean logarithmic mass of cosmic rays is almost heavier than helium in the whole measured energy range. It decreases from 1.7 at 0.3 PeV to 1.3 at 3 PeV, representing a 24% decline following a power law with an index of -0.1200±0.0003±0.0341. This is equivalent to an increase in abundance of light components. Above the knee, the mean logarithmic mass exhibits a power law trend towards heavier components, which is reversal to the behavior observed in the all-particle energy spectrum. Additionally, the knee position and the change in power-law index are approximately the same. These findings suggest that the knee observed in the all-particle spectrum corresponds to the knee of the light component, rather than the medium-heavy components

An Ultrahigh-energy γ\gamma-ray Bubble Powered by a Super PeVatron

International audienceWe report the detection of a $\gamma$-ray bubble spanning at least 100$\rm deg^2$ in ultra high energy (UHE) up to a few PeV in the direction of the star-forming region Cygnus X, implying the presence Super PeVatron(s) accelerating protons to at least 10 PeV. A log-parabola form with the photon index $\Gamma (E) = (2.71 \pm 0.02) + (0.11 \pm 0.02) \times \log_{10} (E/10 \ {\rm TeV})$ is found fitting the gamma-ray energy spectrum of the bubble well. UHE sources, `hot spots' correlated with very massive molecular clouds, and a quasi-spherical amorphous $\gamma$-ray emitter with a sharp central brightening are observed in the bubble. In the core of $\sim 0.5^{\circ}$, spatially associating with a region containing massive OB association (Cygnus OB2) and a microquasar (Cygnus X-3), as well as previously reported multi-TeV sources, an enhanced concentration of UHE $\gamma$-rays are observed with 2 photons at energies above 1 PeV. The general feature of the bubble, the morphology and the energy spectrum, are reasonably reproduced by the assumption of a particle accelerator in the core, continuously injecting protons into the ambient medium

Pointing calibration of LHAASO-WFCTA telescopes using bright stars

International audienceOne of the main scientific objectives of the Large High Altitude Air Shower Observatory (LHAASO) is to perform accurate measurements of the energy spectra for different cosmic ray masses, from a few TeV to 100 PeV. As one of the main sub-arrays of LHAASO, the Wide Field-of-View Cherenkov Telescope Array (WFCTA), which consists of 18 telescopes, can help in achieving this goal. The pointing accuracy of each telescope is crucial for reconstructing energy and determining mass-sensitive parameters. In this study, a method for absolute pointing calibration using ultraviolet bright stars was established. The proposed method can achieve a pointing accuracy of approximately 0.02° by using more than five stars. When more stars are used in the telescope’s field of view, the accuracy of the pointing calibration can be improved, e.g, a pointing accuracy of 0.01° can be achieved when using more than 15 stars. A high-precision inclinometer with a monitor resolution of 0.003° was installed on the camera to monitor the zenith direction of the telescope at every second. After calibration using bright stars, the absolute pointing accuracy of the inclinometer was 0.02°. •Method for absolute pointing calibration using ultraviolet bright stars established.•A pointing accuracy of ∼0.02°can be achieved using more than five stars.•A pointing accuracy of 0.01°can be achieved when using more than 15 stars•Accuracy of the pointing calibration increases with number of bright stars

LHAASO-KM2A detector simulation using Geant4

International audienceKM2A is one of the main sub-arrays of LHAASO, working on gamma ray astronomy and cosmic ray physics at energies above 10 TeV. Detector simulation is the important foundation for estimating detector performance and data analysis. It is a big challenge to simulate the KM2A detector in the framework of Geant4 due to the need to track numerous photons from a large number of detector units (>6000) with large altitude difference (30 m) and huge coverage (1.3 km^2). In this paper, the design of the KM2A simulation code G4KM2A based on Geant4 is introduced. The process of G4KM2A is optimized mainly in memory consumption to avoid memory overffow. Some simpliffcations are used to signiffcantly speed up the execution of G4KM2A. The running time is reduced by at least 30 times compared to full detector simulation. The particle distributions and the core/angle resolution comparison between simulation and experimental data of the full KM2A array are also presented, which show good agreement