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AMS-02 has been measured with unprecedented precision data for the positron flux. These data show that there is an excess of cosmic positrons detected for energies above 10 GeV with respect to the well known secondary production which is due to the collision of cosmic rays with the atoms of the interstellar medium. In this paper we have investigated the possibility that the positron excess is due to the acceleration of positrons and electrons from pulsar wind nebulae. We have first made the assumption that only one pulsar, Geminga, dominates the production of positrons detected at Earth. We find that a spectral index for the injection spectrum of e + is needed to fit the data but an efficiency for the conversion of pulsar energy into positron of about 100% is required. This is unphysical since also electrons should be accelerated with the same amount. We have done the more realistic case where all the pulsars reported in the ATNF catalogue produce positrons. We have demonstrated that this case fits well the data with efficiency values of the order of 10-20%. These results imply that pulsar wind nebulae in the Galaxy are likely the main contributors to the positron excess.

Photoluminescence intensity of the perovskite QDs coupled with TiO2 was decreased significantly owing to the electron transfer between them. Hererin, the composite of CsPb(Cl0.4Br0.6)3 with TiO2 inverse opal was fabricated and we have proved that the effect of scattering of TiO2 inverse opal layer by layer under the incident excitation light for the enhancement of perovskite QDs photoluminescence intensity is far greater than the decrease of photoluminescence intensity caused by the electron transfer between QDs and TiO2. Particularly, photoelectrochemical characterizations exhibit high charge separation effciency and fast response speed in water. This study opens new possibilities for optoelectronic and photo display applications of perovskites-based NCs.

Here a simple and effective method was explored to fabricate M/TiO2 (M = Ag, Au) composites, which required neither pre-treatment of TiO2 nor any additives as reducing agent. Using amorphous TiO2 spheres functionalized with SH groups as starting materials, the noble metallic ions (Ag, Au) can be adsorbed by TiO2 due to their special affinity with SH groups, which is beneficial to the uniform dispersion of metallic ions on the surface of TiO2. Then the adsorbed ions were reduced to form noble metal nanoparticles by heating process (95 °C) directly without additive as reduction agent. Meanwhile, the amorphous TiO2 was transformed into anatase phase during the heating process. Thus, the transformation of TiO2 along with the reduction of noble metallic ions (Ag, Au) was simultaneously carried out by heating. The XRD patterns proved the formation of anatase TiO2 after heating. The characterizations of XPS and TEM proved the formation of Ag and Au nanoparticles on the surface of TiO2. The element mapping indicated that Ag nanoparticles are dispersed uniformly on the surface of TiO2. The photocatalytic activity of the composites has been investigated by the degradation of methyl orange under visible light irradiation. The results showed that when Ag/TiO2 (2.8 wt%) was used as photocatalyst, about 98% of the MO molecules were degraded in 70 min.