The manipulation and direct mechanical measurement of single DNA molecule could give much information about its elastic properties. Single stranded DNA (ssDNA) of 100 bases was adsorbed onto flat gold surface fabricated by depositing gold onto mica surface. Atomic force microscope (AFM) was used to observe the surface topography with different ssDNA concentration. Then the ssDNAs were stretched by AFM tip and in 50% cases ssDNAs could be stretched.Various kinds of force curves have been observed due to the different interaction between AFM tip and ssDNAs.

Objective To evaluate the correlation of the CT features of the collateral circulation and the degree of esophageal-gastric varices in patients with portal hypertension caused by hepatic cirrhosis.Methods 30 cases with portal hypertension were in group A and 30 healthy people were in group B.The diameter of portal vein(PV),gastriccoronary vein(GCV),the total cross-sectional surface area(CSA) of varices in gastro-splenic region were measured in both group A and B,the results and endoscopic signs were analysed with multiple linear regression.Results The diameters of PV were(16.17?2.44) mm in group A and(12.42?1.53) mm in group B,Beta =0.39. The diameters of GCV were(6.22?2.41)mm in group A and (3.39?1.03) mm in group B,Beta =0.85. The total CSA of varicosis in gastro-splenic region were(5.14?5.96) cm2 in group A and (1.32?0.98) cm2 in group B, Beta =1.90. Multiple linear regression equation : y=0.39X1+0.85X2+1.90X3 Conclusion The total CSA of varicosis in gastro-splenic region is a useful CT feature in evaluating portal hypertension.