Tensile stress in wedge-shaped oil films

The precise pressure distribution in the range of negative pressure on lubricated sliding surfaces is measured and the behavior of the oil film in the vicinity of vacuum-pressure investigated using a special apparatus in which a specially shaped axial slider generated negative pressure when moved in a precision cylinder. Tensile stress was detected in the wedge-shaped oil film. Another test rig which was capable of generation of a predetermined tensile stress by dead weight loading confirmed that tensile stress is developed even in bulk lubricating oil. The mechanism of tensile stress generation in lubricating oil is discussed in the light of experimental results.     

Control of the thermal lensing effect with different pump light distributions

We built a 32-laser-diode-formed virtual point source pumping system and achieved different pump light distributions from central intense to central uniform and central depressed. Continuous wave TEM(00) operations of a Nd:YAG laser were performed under these pump light distributions and their thermal lensing effects were estimated. Results show that the operation under central depressed pump light distribution has the lowest thermal lensing effect and can provide the highest output power, which agrees with the results derived from the theoretical calculation with the heat conduction equation.     

Novel biodegradable superabsorbent hydrogels derived from cotton cellulose and succinic anhydride: Synthesis and characterization

The synthesis of novel superabsorbent hydrogels was investigated with the reaction of cotton cellulose and succinic anhydride (SA) in the presence of 4‐dimethylaminopyridine as an esterification catalyst in a mixture of lithium chloride (LiCl) and N‐methyl‐2‐pyrrolidinone (NMP) or in a mixture of tetrabutylammonium fluoride (TBAF) and dimethyl sulfoxide (DMSO), followed by NaOH neutralization. Interestingly, a hydrogel was obtained without any crosslinking agent, and this indicated the partial formation of a diester between the cellulosic hydroxyl group and SA. The products obtained in LiCl/NMP exhibited superior absorbency to these obtained in TBAF/DMSO. The former absorbed an amount of water about 400 times its dry weight, and this was comparable to a conventional sodium polyacrylate superabsorbent hydrogel. Furthermore, in an aqueous NaCl solution, the absorbency of the product hydrogels was higher than that of the sodium polyacrylate superabsorbent hydrogel. The formed hydrogels biologically degraded almost completely after 25 days, and this showed their excellent biodegradability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3251–3256, 2006     

Water vapor permeability of poly(lactide)s: Effects of molecular characteristics and crystallinity

Amorphous‐made poly(L ‐lactide) [i.e., poly(L ‐lactic acid) (PLLA)], poly(L ‐lactide‐co‐D ‐lactide)[P(LLA‐DLA)](77/23), and P(LLA‐DLA)(50/50) films and PLLA films with different crystallinity (X_c) values were prepared, and the effects of molecular weight, D ‐lactide unit content (tacticity and optical purity), and crystallinity of poly(lactide) [i.e., poly(lactic acid) (PLA)] on the water vapor permeability was investigated. The changes in number‐average molecular weight (M_n) of PLLA films in the range of 9 × 10⁴–5 × 10⁵ g mol^?1 and D ‐lactide unit content of PLA films in the range of 0–50% have insignificant effects on their water vapor transmission rate (WVTR). In contrast, the WVTR of PLLA films decreased monotonically with increasing X_c from 0 to 20%, while leveled off for X_c exceeding 30%. This is probably due to the higher resistance of “restricted” amorphous regions to water vapor permeation compared with that of the “free” amorphous regions. The free and restricted amorphous regions are major amorphous components of PLLA films for X_c ranges of 0–20% and exceeding 30%, respectively, resulting in the aforementioned dependence of WVTR on X_c. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Vacuum sieve tray for tritium extraction from liquid Pb–17Li

Formation of droplet of liquid Li–17Pb released from a nozzle into vacuum was studied for the evaluation of the feasibility as a tritium extraction process. Size of droplets formed from the nozzles was estimated by theoretical and experimental methods. For the theoretical estimation, the non-dimensional comparison of the physical bulk property of liquid Pb–17Li with water (H₂O) at ambient temperature was applied. It was found to be reasonable to apply the Plateau-Rayleigh-Instability theory for the droplet size formula of the fluid Pb–17Li for the nozzle diameter 0.4 mm–1.0 mm, temperature 400 °C–500 °C, at initial velocity of 3 m/s. The experimental results of the droplet size showed good agreement with the theory. This device was used for the parametric study of extraction of deuterium during their free fall in vacuum. The scaling of the device suggests the engineering feasibility of the process.     

Single-walled carbon nanotubes grown on natural minerals

Single-walled carbon nanotubes (SWNTs) are successfully grown on magnesite crystal by pyrolysis of methane gas under moderate conditions, demonstrating the possibility of naturally occurring SWNTs.The obtained SWNTs were analyzed by Raman scattering, transmission electron microscope (TEM), and thermogravimetric (TG) measurements. These measurements revealed that high purity SWNTs having diameters of about 1-1.8 nm occur on the surface of natural magnesite sample by the pyrolysis of methane gas at 1073-1173 K. Structural properties and formation mechanism of the obtained SWNTs were discussed.     

Positive photosensitive polyimides using polyamic acid esters with phenol moieties

Polyimide resists developable with basic aqueous solutions were realized by polyamic acid esters with phenol moieties (PPh's) and naphthoquinone diazides. The polyimide precursors (PPh's) were synthesized from diamines and dicarboxylic acids that have phenol moieties through ester linkage. A selective reaction of alcohol groups with acid dianhydride groups made the synthesis of the PPh's possible, even if the phenol groups were in the reaction mixtures. The PPh's were soluble in basic aqueous developer, but their dissolution rates were too low for use as resists. To increase the resist dissolution rate, polyamic acids were added to the PPh's. By adjusting the dissolution rates in basic aqueous developers, fine patterns could be realized. The polyimide resists had high thermal stability and reliable adhesive property to silicon substrate. © 1994 John Wiley & Sons, Inc.