High-energy cosmic-ray electrons and positrons (CREs), which lose energy quickly during their propagation, provide a probe of Galactic high-energy processes and may enable the observation of phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been measured directly up to approximately 2 teraelectronvolts in previous balloon- or space-borne experiments, and indirectly up to approximately 5 teraelectronvolts using ground-based Cherenkov γ-ray telescope arrays. Evidence for a spectral break in the teraelectronvolt energy range has been provided by indirect measurements, although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range 25 gigaelectronvolts to 4.6 teraelectronvolts by the Dark Matter Particle Explorer (DAMPE) with unprecedentedly high energy resolution and low background. The largest part of the spectrum can be well fitted by a 'smoothly broken power-law' model rather than a single power-law model. The direct detection of a spectral break at about 0.9 teraelectronvolts confirms the evidence found by previous indirect measurements, clarifies the behaviour of the CRE spectrum at energies above 1 teraelectronvolt and sheds light on the physical origin of the sub-teraelectronvolt CREs.
The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with 2 1 / 2 years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time that an experiment directly measures the cosmic ray protons up to~100 TeV with high statistics. The measured spectrum confirms the spectral hardening at~300 GeV found by previous experiments and reveals a softening at~13.6 TeV, with the spectral index changing from~2.60 to~2.85. Our result suggests the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee and sheds new light on the origin of Galactic cosmic rays.
A novel semiconductor–rubber–semiconductor triblock copolymer has been designed and prepared according to the principle of thermoplastic elastomers (TPEs). It behaves as a TPE and exhibits good electrical properties.
The electronic and structural properties of the layered ternary compound Ti 3 AlC 2 have been determined using the ab initio pseudopotential method based on density functional theory. We have obtained the equilibrium lattice parameters, the equilibrium atomic positions in the unit cell, and interatomic distances. The calculated bulk modulus is 190 GPa and is comparable to that of TiC. The band structure, density of states (DOS) and effective charges are presented and compared with those of TiC. The band structure indicates that Ti 3 AlC 2 is an electronic conductor. The electronic structure discloses that the bonding in Ti 3 AlC 2 is anisotropic and metallic-covalent-ionic in nature. Compare to the structure of TiC, the presence of Al changes the Ti-C-Ti-C covalent bond chain into a Ti-C-Ti-C-Ti-Al bond chain through its reaction with Ti, forming the layered structure. Effective charge calculations suggest the ionic formula of Ti 3 AlC 2 to be (Ti 1.18z )(Ti 0.59z ) 2 (Al 0.522 )(C 0.922 ) 2 .
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