No abstract

With the growing threat of energy crises, new technologies for harvesting wasted ambient mechanical energy are becoming one of the most important fi elds of research. [ 1 ] Currently, there are three physical effects used for harvesting small scale mechanical energy: electromagnetic, [ 2,3 ] piezoelectric, [ 4,5 ] and triboelectric effects. [ 6,7 ] In parallel to the development of micro-/nanopower sources, it is necessary to explore the possibility of harvesting large-scale ambient mechanical energy, such as ocean waves and natural wind. [ 8 ] Such energy is abundant and has much less dependence on season, day or night, and the weather than solar energy does. Moreover, the mechanical energy generated by human motion, such as walking or shaking, is usually wasted. [ 9 ] Harvesting this kind of energy has potential for powering portable electronic devices.Triboelectric nanogenerators (TENGs) fabricated using the polymer-polymer or polymer-metal fi lm materials have been extensively developed to power some small electronic devices (such as liquid crystal displays (LCDs) and light-emitting diodes (LEDs)). [ 10,11 ] The mechanism is based on the triboelectric effect, [ 12 ] in which cycled contact-separation between two different triboelectric materials can induce a voltage drop for driving electrons to fl ow in the external circuit. Although many kinds of TENGs have been fabricated, [ 13,14 ] they are based on a working process with the acting surfaces being exposed to ambient atmosphere, which can limit their applications in some cases. It has been reported that the ambient environment such as humidity can largely weaken the triboelectric effect, [ 15 ] so that the fabricated TENGs cannot work under harsh conditions with the presence of water. To solve this problem, it is necessary to develop fully enclosed or packaged TENGs that can tolerate the environment in which they will be employed.Here, we have demonstrated the fi rst fully enclosed TENGs, which can be used to harvest the wave and biomechanical energies. A TENG was fabricated by using the polytetrafl uoroethylene (PTFE)-polyamide (PA) fi lm materials in an enclosed sphere, which can be used to harvest the wave energy from water for driving electronic devices. Two TENGs in an enclosed cylinder can be used to directly light up 60 green LEDs by moving the mass rod at the center of the cylinder; this has potential applications for harvesting the wave and biomechanical energies. The energies produced by the TENGs can be stored in a Li-ion battery for driving an ascorbic acid (AA) biosensor. Figure 1 a shows a schematic diagram of a conventional TENG, which consists of a Cu fi lm as the top electrode, a PTFE fi lm, a PA fi lm, and a Cu fi lm as the bottom electrode. The TENG was driven by a homemade force loading system with the working frequency of 1 Hz. Figure 1 b shows the output performance of the fabricated TENG in air, where the open-circuit voltage ( V oc ) and the short-circuit current ( I sc ) were about 50 V and 14 μ A under the forward connection to th...

Cosmic rays (CRs) in starburst galaxies produce high-energy gamma-rays by colliding with the dense interstellar medium. Arp 220 is the nearest ultraluminous infrared galaxy that has star formation at extreme levels, so it has long been predicted to emit high-energy gamma-rays. However, no evidence of gamma-ray emission was found despite intense search efforts. Here we report the discovery of high-energy gamma-ray emission above 200 MeV from Arp 220 at a confidence level of ∼6.3σ using 7.5 years of Fermi Large Area Telescope observations. The gamma-ray emission shows no significant variability over the observation period and it is consistent with the quasi-linear scaling relation between the gamma-ray luminosity and total infrared luminosity for star-forming galaxies, suggesting that these gamma-rays arise from CR interactions. As the high-density medium of Arp 220 makes it an ideal CR calorimeter, the gamma-ray luminosity can be used to measure the efficiency of powering CRs by supernova (SN) remnants given a known supernova rate in Arp 220. We find that this efficiency is about 4.2 ± 2.6% for CRs above 1 GeV.

We demonstrate that the excess of sub-PeV/PeV neutrinos recently discovered by IceCube could originate through hadronuclear processes from the same sources responsible for cosmic rays (CRs) with energy above the second knee at $\sim 5\times 10^{17}\,$eV. We furthermore propose that hypernova remnants with semi-relativistic ejecta in star-forming galaxies are these sources. By virtue of their fast ejecta, such objects can accelerate protons to $\gtrsim \,$EeV energies, and the resulting {CRs} can interact with the dense surrounding medium during propagation in their host galaxies to produce high-energy neutrinos and gamma rays via proton--proton collisions. A scenario in which hypernova remnants account for the observed CR flux above the second knee can also account for the neutrino flux detected by IceCube. The accompanying gamma ray flux remains below the diffuse isotropic gamma ray background observed by the {\it Fermi} Large Area Telescope (LAT)