A technical Question Concerning the Venera Landers

Hello One and All, I am currently teaching an IB Physics honors class. An interesting question came up regarding how the Venera landers were kept operational on the surface of Venus. Can anyone on this list direct me to any non-technical web sites for my students that discuss how the Soviet Venera landers werekept cool while operating on the surface of Venus? Did they use passive cooling or active refrigeration? Also what materials and metals were used to construct the pressure vessels that housed the scientific instrumentation of the landers? Were they constructed from titanium or an alloy of titanium? Were the pressure vessels constructed in an analogous way to a thermos vessel or like a Dewars flask? Many thanks for your kind help beforehand, Yours truly, Alex Michael Bonnici