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The pore structure of the hardened concrete and the microscopic changes of a few selected pores throughout the freeze-thaw test were investigated by a method combining RapidAir and digital metalloscope. Traditional tests were also performed to evaluate the macroscopic change caused by freeze-thaw cycles (FTCs). The investigation shows that the concrete material, of which the spacing factor is 0.405 mm and the air content is 2.38%, can still withstand more than 300 FTCs. Severe microscopic damages occurred after approximately 200 FTCs and the freeze-thaw damage were gradually aggravated afterwards. Prestress forces have a remarkable impact on the failure pattern under FTCs. It was further found that the compressive strength as an indicator is more reliable than the relative dynamic modulus of elasticity in evaluating the freeze-thaw damage on concrete material. In addition, the test and analysis show that the measured prestress losses of bonded specimen are larger than that of unbounded specimen under the attack of FTCs due to the duct grouting effect. The ultimate freeze-thaw prestress loss is about 5% of σ con for both the bonded and unbonded specimens because the grouting cement paste will eventually be completely destroyed.

Prestressed concrete structures are considered to be reliable and durable. However, their long-term performance when subjected to frost attack is still unclear. In this work, experiments were carried out to evaluate the prestress losses in post-tensioned prestressed concrete specimens subjected to freeze–thaw cycles (FTCs). Two cases were considered: in one case, a series of specimens were prepared and tested in a freeze–thaw chamber; in the second case, the same series of specimens were tested in an indoor environment (outside the chamber). The difference between the prestress losses of the specimens inside the freeze–thaw chamber and those outside the chamber equalled the prestress losses due to FTCs. When using mathematical models to predict the prestress losses due to the FTCs, it was found that they were relatively small when the concrete was slightly damaged. However, they increased rapidly when the FTCs were repeated. The eccentricity of the prestress wires led to larger prestress losses when subje...

We have produced the first macroscopic objects comprised of highly aligned single-wall carbon nanotubes (SWNTs). These objects are thin membranes prepared by producing a suspension of SWNT segments, introducing the suspension to a strong magnetic field to align the segments, and filtering the suspension in the magnetic field to produce an aligned membrane of SWNT. These membranes exhibited natural cleavage planes parallel to the magnetic field. This preparation of macroscopic samples of aligned single-wall nanotubes permits exploitation of their highly anisotropic properties, and will enable measurement of the electronic, thermal, magnetic, mechanical, and optical properties of bulk nanotube materials.

Separating the unit cell of YBa2Cu3O7-δ into perovskite and rock salt blocks and considering the interaction between the two blocks, a computer program has been developed to calculate the interaction called combinative energy, between the blocks. The combinative energy in YBa2Cu3O7-δ with different δ value from 0.07 to 0.62 has been calculated. A close relationship between the superconducting transition temperature and the combinative energy in YBa2Cu3O7-δ has been established, and the change of the combinative energy found to be closely related to the transformation from orthorhombic I to II. It is believed that the interaction between the two blocks in the unit cell is of great importance to the superconductivity in YBa2Cu3O7-δ.

Calculation of cohesive energy on Hg-system superconductors HgBa2CuOy(1201), HgBa2CaCu2Oy(1212), HgBa2 Ca2Cu3Oy(1223), HgBa2Ca3Cu4Oy(1234), and HgBa2Ca4Cu5Oy(1245) has been made. A program was developed to calculate the combinative energy between Cu-O planes and remaining parts, and between blocks in the superconductors. The result indicates that if the cell is considered as the two blocks combined together, a close relationship among the combinative energy of the two blocks, the value of Tc, and the number of the Cu-O planes in the Hg-system superconductors is established. The result gives a new way to understand the change of the value of Tc as the number of the Cu-O planes. In contrast, the combinative energy between the Cu-O planes and the remains got from the method separating all the Cu-O planes from the cell and leaving some discrete remaining parts does not show any relationship with the value of Tc. This means that considering the cell as the two blocks in more reasonable, and the interaction between the two blocks plays an important role in superconductivity.