An experiment is carried out on the surface oscillation of buoyant-thermocapillary convection in an open cylindrical annulus. When the radial temperature difference AT reaches a critical value △Tc, a regular oscillation appears and soon disappears on the open surface, which varies when the liquid layer＇s thickness h and temperature difference △T are varied. With growth of △T, dominant frequency of the visible oscillation will grow too but is found within certain frequencies. Driving forces, buoyance and thermocapillarity, are responsible for this phenomanon and the ＂balance＂ point is considered to exist when h is between 4.5-5.0 mm. Surface oscillation region is also found restricted within a narrow gap when Bo is smaller than 3.7.
Since Mr.Tsien brought up his idea of physical mechanics,as a new field in engineering science,to public attention in the early 50's of the 20th century,innumerable application examples of physical mechanics approach in diverse fields have manifested its strong vitality increasingly.One of important aspects in applications of physical mechanics is to appropriately choose the microscopic quantity for the system in consideration and build a bridge to connect its relevant microscopic information to its desired macroscopic properties.We present two unique cases of using the physical mechanics approach to study colloidal stability.In the first case we measured the outcomes from artificially induced collisions at individual particle levels,by means of directly observing artificially induced collisions with the aid of optical tweezers.In the second case,by using T-matrix method,the microscopic quantity extinction cross section of the doublet can be accurately evaluated and therefore the measurement range and accuracy of the turbidity methodology for determining the CRC are greatly improved.
