Abstract: A low-cost and quick-response type gas-density sensing element is free from positioning error of sensing ambient temperature and gas density and can accurately sense the gas flow even if the environmental conditions sharply change. An output voltage V.sub.1 proportional to an ambient temperature is obtained by heating a sensing element at low temperature and an output voltage V.sub.2 proportional to the ambient temperature and humidity is obtained by heating the sensing element at a high temperature. An output voltage which is proportional to the humidity is obtained by subtracting the voltage value V.sub.1 from the voltage value V.sub.2.

Abstract: A process for efficiently preparing an unsaturated dicarboxylic acid diester, which comprises reacting a conjugated diene, carbon monoxide, an alcohol and oxygen in the presence of a catalyst comprising (a) a platinum metal, a salt thereof or a complex compound of a platinum metal, (b) at least one metal salt selected from the group consisting of a copper salt, an iron salt and a manganese salt and (C) at least one compound selected from the group consisting of (1) an alkali metal compound or an alkaline earth metal compound, (2) a rare earth metal compound, (3) a metal compound of the groups IIIA, IVA, IVB, VA, VB or VIA, and (4) a metal carbonyl complex. The unsaturated dicarboxylic acid diester is useful as an intermediate material in industrial chemical processes and can be efficiently prepared without the use of a dehydrating agent.