[Food water sources analysis of adults in four cities of China in summer].

Objective: To investigate the food water sources of adults in the four cities of China in summer.

Methods: A total of 64 adults aged 18 - 60 yrs from four cities (Beijing, Shanghai, Chengdu and Guangzhou)were selected using convenient sampling method. The food samples were collected by using duplicate portion method and the water content of food samples were determined by using the national standard.

Superconductivity modulated by quantum size effects.

We have fabricated ultrathin lead films on silicon substrates with atomic-scale control of the thickness over a macroscopic area. We observed oscillatory behavior of the superconducting transition temperature when the film thickness was increased by one atomic layer at a time. This oscillating behavior was shown to be a manifestation of the Fabry-Perot interference modes of electron de Broglie waves (quantum well states) in the films, which modulate the electron density of states near the Fermi level and the electron-phonon coupling, which are the two factors that control superconductivity transitions.