Bose-Einstein Condensation in the presence of an artificial spin-orbit interaction

Bose-Einstein condensation in the presence of a synthetic spin-momentum interaction is considered, focusing on the case where a Dirac or Rashba potential is generated via a tripod scheme. We found that the ground states can be either plane wave states or superpositions of them, each characterized by their unique density distributions.Comment: 5 pages, no figure

Impacts of Ageing Population on Monetary and Exchange Rate Managements in Singapore

This paper finds that the ageing of the population in Singapore will cause a reversal of the current net Central Provident Fund (CPF) contribution into a substantial net CPF withdrawal from 2025, with a peak occurring at 2035. The result is qualitatively robust to changes in the underlying assumptions of the projection. The paper then highlights the implications of this change on the exchange rate and monetary managements in Singapore. First, the Monetary Authority of Singapore (MAS)’s ability to influence Singapore’s exchange rate will be greatly hampered. Second, the net CPF withdrawal will mean sustained liquidity injection into (instead of the usual liquidity drain from) the economy. To avoid unnecessary inflation, the MAS has to find a sustainable way to mob up the excess liquidity due to the sustained liquidity injection. As a simple reversal of MAS’s current foreign exchange market operation will result in substantial shrinkage of foreign reserves, the paper proposes the issuance of government bonds to achieve the dual objectives of mobbing up the excess liquidity and avoiding the shrinkage of foreign reserves. This measure will also help the bond market development in Singapore. Finally, the paper proposes two other measures that can help maintain MAS’s influence on Singapore’s exchange rate to a reasonable level in the longer future.Ageing Population, Central Provident Fund, Exchange Rate System, Monetary Policy, Singapore.

Natural laminar flow experiments on modern airplane surfaces

Flight and wind-tunnel natural laminar flow experiments have been conducted on various lifting and nonlifting surfaces of several airplanes at unit Reynolds numbers between 0.63 x 10 to the 6th power/ft and 3.08 x 10 to the 6th power/ft, at Mach numbers from 0.1 to 0.7, and at lifting surface leading-edge sweep angles from 0 deg to 63 deg. The airplanes tested were selected to provide relatively stiff skin conditions, free from significant roughness and waviness, on smooth modern production-type airframes. The observed transition locations typically occurred downstream of the measured or calculated pressure peak locations for the test conditions involved. No discernible effects on transition due to surface waviness were observed on any of the surfaces tested. None of the measured heights of surface waviness exceeded the empirically predicted allowable surface waviness. Experimental results consistent with spanwise contamination criteria were observed. Large changes in flight-measured performance and stability and control resulted from loss of laminar flow by forced transition. Rain effects on the laminar boundary layer caused stick-fixed nose-down pitch-trim changes in two of the airplanes tested. No effect on transition was observed for flight through low-altitude liquid-phase clouds. These observations indicate the importance of fixed-transition tests as a standard flight testing procedure for modern smooth airframes