Use of carbon dioxide laser in improving knot security in polyester sutures.

Knot slippage continues to be a serious concern in surgery. This study explored the possibility of improving knot performance by exposing it to radiation from a CO 2 laser. The specimens were mounted in a special device and exposed in a predetermined position for precisely controlled lengths of time. In the first set of experiments, the welding of ends was examined in nylon and polyester sutures. Although the welding was easily achieved, the joint was found brittle and its strength lower than that of a surgical knot. In the next set of experiments, the work was performed at a more fundamental level using oriented, high density, polyester films. The results showed that up to a certain level of exposure the tensile properties did not change, but beyond it a rapid decay took place. Shear tests on polyester sutures twisted together and then exposed to various levels of energy indicated that a bond of maximum strength developed at this exposure. Mersilene sutures of size 3/0 containing a two throw square knot when exposed to energy of this level produced optimal results. The knot strength increased by about 16% (from 13.4 N unexposed to 15.6 N exposed) and the slippage often known to occur in a two-throw knot was completely absent. This work performed under standard atmospheric conditions provided a direction for greatly enhancing the performance of a two-throw knot in terms of both the security and the strength.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermal wave interferometry: a potential application of the photoacoustic effect.

The Rosencwaig-Gersho equation for the photoacoustic signal is recast in a manner that emphasizes the crucial role thermal wave interference plays in the production of the photoacoustic signal. This formalism is then used to suggest a technique for extracting thermal information from the structure in the photoacoustic signal resulting from thermal wave interference. Experimental measurements illustrating this technique are presented.

Monitoring particulate carbon collected on Teflon filters: an evaluation of photoacoustic and transmission techniques.

The Colorado State University Aerosol Workshop provided an excellent opportunity to obtain various particulate samples collected on filters. Our results indicate that the photoacoustic technique is preferable to the transmission technique (integrating plate method) for ambient samples with low-filter loadings since the presence of a nonabsorbing scattering aerosol (ammonium sulfate) only slightly perturbs the photoacoustic signal and significantly affects the transmitted signal. Measurements indicate that the photoacoustic signal depends not only on the energy absorbed from the incident beam but also on the existence of thermal wave interference effects and, especially for heavily loaded filters, on the presence of a nonabsorbing scattering aerosol.

CO(2) Laser Absorption Coefficients for Determining Ambient Levels of O(3), NH(3), and C(2)H(4).

A carbon dioxide laser source was used to determine absorption coefficients for dilute absorber-air mixtures at wavelengths corresponding to several vibration-rotation lines in each branch of the 00 degrees 1-02 degrees 0 band at 9.4 microm and the 00 degrees 1-10 degrees 0 band at 10.4 microm. For all samples the total pressure was 1 atm and the temperature was 300 K; the concentrations ranged from 10 ppm (parts per million by volume) to 357 ppm for NH(3) and C(2)H(4), and from 10 ppm to 80 ppm for O(3). The absorption coefficients are tabulated, and the use of selected laser lines in monitoring ambient concentrations is discussed.

Photometer for detection of sodium day airglow.

Daytime, ground based measurements of sodium airglow emission are particularly difficult to perform. The ratio of airglow signal to Rayleigh and Mie scattering by the atmosphere as well as the very pronounced Fraunhofer structure lead to extraneous signals that are difficult to evaluate and require specialized techniques to eliminate. The photometer described can be characterized by the following principal features: (1) a narrow (4.5-A) interference filter for initial discrimination; (2) cooled photomultiplier detector to reduce noise from dark current fluctuations and chopping to eliminate the average dark current; (3) a sodium vapor resonance cell to provide an effective bandpass comparable to the Doppler line width; (4) separate detection of all light transmitted by the interference filter to evaluate the Rayleigh and Mie components within the Doppler width of the resonance cell; (5) temperature quenching of the resonance cell to evaluate and account for instrumental imperfections.

Determination of Self-Broadening Coefficients of CO, Using CO(2) Laser Radiation at 10.6 micro.

Essentially monochromatic radiation with a frequency corresponding to the frequency of the line center of the P(20) line of the 961-cm(-1) CO(2) band was obtained from a CO(2)laser. Using this radiant energy, transmittances of CO(2) samples were measured as various broadening gases were added. Self-broadening coefficients of CO(2) relative to nitrogen, hydrogen, helium, and argon were determined from the measurements characterizing the transmittance only at the line center; from these measurements ratios of optical collision diameters are calculated.