We present a systematic analysis of the spectral and temporal properties of 17 gamma-ray bursts (GRBs) co-detected by Gamma-Ray Monitor (GBM) and Large Area Telescope (LAT) on board the Fermi satellite by May 2010. We performed a timeresolved spectral analysis of all the bursts with the finest temporal resolution allowed by statistics, in order to reduce temporal smearing of different spectral components. We found that the time-resolved spectra of 14 out of 17 GRBs are best modeled with the classical "Band" function over the entire Fermi spectral range, which may suggest a common origin for emissions detected by LAT and GBM. GRB 090902B and GRB 090510 require the superposition of a MeV component and an extra power law component, with the former having a sharp cutoff above E p . For GRB 090902B, this MeV component becomes progressively narrower as the time bin gets smaller, and can be fit with a Planck function as the time bin becomes small enough. In general, we speculate that phenomenologically there may be three elemental spectral components that shape the time-resolved GRB spectra: a Band-function component (e.g. in GRB 080916C) that extends in a wide energy range and does not narrow with decreasing time bins, which may be of non-thermal origin; a quasi-thermal component (e.g. in GRB 090902B) with the spectra progressively narrowing with reducing time bins; and another non-thermal power law component extending to high energies. The spectra of different bursts may be decomposed into one or more of these elemental components. We compare this sample with the BATSE sample and investigate some correlations among spectral parameters. We discuss the physical implications of the data analysis results for GRB prompt emission, including jet composition (matter-dominated vs. Poyntingflux-dominated outflow), emission sites (internal shock, external shock or photosphere), -2as well as radiation mechanisms (synchrotron, synchrotron self-Compton, or thermal Compton upscattering).

The fabrication of intrinsic carbon defects is usually tangled with doping effects, and the identification of their unique roles in catalysis remains a tough task. Herein, a K+‐assisted synthetic strategy is developed to afford porous carbon (K‐defect‐C) with abundant intrinsic defects and complete elimination of heteroatom via direct pyrolysis of K+‐confined metal–organic frameworks (MOFs). Positron‐annihilation lifetime spectroscopy, X‐ray absorption fine structure measurement, and scanning transmission electron microscopy jointly illustrate the existence of abundant 12‐vacancy‐type carbon defects (V12) in K‐defect‐C. Remarkably, the K‐defect‐C achieves ultrahigh CO Faradaic efficiency (99%) at −0.45 V in CO2 electroreduction, far surpassing MOF‐derived carbon without K+ etching. Theoretical calculations reveal that the V12 defects in K‐defect‐C favor CO2 adsorption and significantly accelerate the formation of the rate‐determining COOH* intermediate, thereby promoting CO2 reduction. This work develops a novel strategy to generate intrinsic carbon defects and provides new insights into their critical role in catalysis.

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We study in details how the pulse width of gamma-ray bursts is related with energy under the assumption that the sources concerned are in the stage of fireballs. Due to the Doppler effect of fireballs, there exists a power law relationship between the two quantities within a limited range of frequency. The power law range and the power law index depend strongly on the observed peak energy E p as well as the rest frame radiation form, and the upper and lower limits of the power law range can be determined by E p . It is found that, within the same power law range, the ratio of the F W HM of the rising portion to that of the decaying phase of the pulses is also related with energy in the form of power laws. A platform-power-law-platform feature could be observed in the two relationships. In the case of an obvious softening of the rest frame spectrum, the two power law relationships also exist, but the feature would evolve to a peaked one. Predictions on the relationships in the energy range covering both the BATSE and Swift bands for a typical hard burst and a typical soft one are made. A sample of FRED (fast rise and exponential decay) pulse bursts shows that 27 out of the 28 sources belong to either the platform-power-law-platform feature class or the peaked feature group, suggesting that the effect concerned is indeed important for most of the sources of the sample. Among these bursts, many might undergo an obvious softening evolution of the rest frame spectrum.

To examine phonon transport during the friction process of commensurate–incommensurate transition, the vibrational density of states of contact surfaces is calculated based on molecular dynamics simulations. The results indicate that, compared with the static state, the relative sliding of the contact surfaces causes a blue shift in the interfacial phonon spectrum in or close to commensurate contact, whereas the contrast of the phonon spectrum in incommensurate contact is almost indiscernible. Further findings suggest that the cause of friction can be attributed to the excitation of new in-plane acoustic modes, which provide the most efficient energy dissipation channels in the friction process. In addition, when the tip and the substrate are subjected to a same biaxial compressive/tensile strain, fewer new acoustic modes are excited than in the no strain case. Thus, the friction can be controlled by applying in-plane strain even in commensurate contact. The contribution of the excited acoustic modes to friction at various frequency bands is also calculated, which provides theoretical guidance for controlling friction by adjusting excitation phonon modes.

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Friction represents a major energy dissipation mode, yet the atomistic mechanism of how friction converts mechanical motion into heat remains elusive. It has been suggested that excess phonons are mainly excited at the washboard frequency, the fundamental frequency at which relative motion excites the interface atoms, and the subsequent thermalization of these nonequilibrium phonons completes the energy dissipation process. Through combined atomic force microscopy measurements and atomistic modeling, here we show that the nonlinear interactions between a sliding tip and the substrate can generate excess phonons at not only the washboard frequency but also its harmonics. These nonequilibrium phonons can induce resonant vibration of the tip and lead to multiple peaks in the friction force as the tip sliding velocity ramps up. These observations disclose previously unrecognized energy dissipation channels associated with tip vibration and provide insights into engineering friction force through adjusting the resonant frequency of the tip–substrate system.

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