In-orbit operation of an atomic clock based on laser-cooled 87Rb atoms.

Atomic clocks based on laser-cooled atoms are widely used as primary frequency standards. Deploying such cold atom clocks (CACs) in space is foreseen to have many applications. Here we present tests of a CAC operating in space. In orbital microgravity, the atoms are cooled, trapped, launched, and finally detected after being interrogated by a microwave field using the Ramsey method. Perturbing influences from the orbital environment on the atoms such as varying magnetic fields and the passage of the spacecraft through Earth's radiation belt are also controlled and mitigated. With appropriate parameters settings, closed-loop locking of the CAC is realized in orbit and an estimated short-term frequency stability close to 3.0 × 10-13τ-1/2 has been attained. The demonstration of the long-term operation of cold atom clock in orbit opens possibility on the applications of space-based cold atom sensors.

Highly reliable optical system for a rubidium space cold atom clock.

We describe a highly reliable optical system designed for a rubidium space cold atom clock (SCAC), presenting its design, key technologies, and optical components. All of the optical and electronic components are integrated onto an optimized two-sided 300 mm×290 mm×30 mm optical bench. The compact optical structure and special thermal design ensure that the optical system can pass all of the space environmental qualification tests including both thermal vacuum and mechanical tests. To verify its performance, the optical system is carefully checked before and after each test. The results indicate that this optical system is suitably robust for the space applications for which the rubidium SCAC was built.

Direct current stimulation of Thiobacillus ferrooxidans bacterial metabolism in a bioelectrical reactor without cation-specific membrane.

A bioelectrical reactor without cation-specific membrane was designed to test effects of direct electrical current on growth of Thiobacillus ferrooxidans bacterium. The results indicated that the cell significantly enhanced the growth of T. ferrooxidans. At a current of 30 mA, the maximum cells density reached 1.39 x 10(9)cells/mL within 84 h, which was 10 times faster than under a conventional cultivation method, in which electrical current is not used. A lag phase during the growth of T. ferrooxidans was observed when direct electrical current was applied, and the lag phase became longer under higher current intensity.