小球藻光生物反应器脱除空气中二氧化碳的研究

采用自制的光生物反应器,研究了不同条件对小球藻脱除空气中CO2效果的影响.光生物反应器为圆柱形有机玻璃容器,底面积0.0154m2,高0.2m,容积为3L,反应器内小球藻藻体干重约为7.2g.实验结果表明,用小球藻来固定CO2不仅能脱除通入气体中的CO2,而且可以促进小球藻生长.通入气体的流量和CO2浓度对CO2的脱除率有很大影响.在适宜的实验条件下(通入气体流速为0.6L/min、CO2浓度约1%、温度25~30℃、光强3500lux、pH9.5~8.5),入口气体中CO2约有50%被脱除,该光生物反应器脱除CO2的能力约为0.118g/(L.h).可见利用小球藻光生物反应器固定CO2具有较好的脱除效果,值得进一步研究.     

Improvement of resolution for phase retrieval by use of a scanning slit

An improved method for resolution of object reconstruction using phase retrieval by use of a scanning slit aperture is proposed. The reconstruction is based on measurements of the Fraunhofer diffraction intensities of wave fields transmitted through a scanning slit in the Fresnel-zone plane of an object. In the improved method, the measurement coordinates of the intensities depend not only on the slit's position used in a previous method but also on the slit's position scaled by the ratio between two distances among the object, Fresnel-zone, and detector planes. The spatial-frequency band for the object reconstruction, which is limited in a previous method by the extent of the Fourier transform of the slit function, can be extended to the bandwidth dependent on the scanning area with the slit. In addition, even in the measurement of the Fresnel diffraction intensities of wave fields transmitted through the slit, the improved resolution can be retained by compensation for a transverse shift of the intensities.     

Phase retrieval from diffraction intensities by use of a scanning slit aperture

A noniterative method of retrieving the phase of a wave field from intensities measured during scanning of a slit aperture is proposed. In the measurements, one records the diffraction intensities of wave fields transmitted through a slit that is scanned along two directions in the Fresnel-zone plane of an object's field. From these intensities, the phase in the Fresnel-zone plane can be retrieved by a method in which a novel phase calculation technique that uses Fourier transforms is included. Because the method does not require lens systems, it provides a potentially useful means for coherent imaging by use of x rays, electrons, or nuclear particles.     

Frequency Tuning and Chirping of a Pulsed CO2 Laser by an Intracavity Prism

Abstract

Based on results of TEA-CO₂ laser-frequency tuning by an intracavity dispersive prism, the feasibility of CO₂ laser-frequency chirping by a nonlinear intracavity prism or due to self-bending effects is discussed. The proposed scheme is shown to be superior to other nonlinear optics methods for CO₂ laser-frequency chirping.     

Aluminium foaming using a CO2 laser

Abstract

This paper explores the possibility of laser assisted aluminium foaming from a foamable precursor material. A preliminary study of the experimental results shows a unidirectional and localised expansion of the foam. A pore size gradient and a density gradient exist in the structure as the processing conditions change. The foam has large pores and lower density for slow processing speeds, in contrast to the case of fast processing speed where there is a small pore size but higher density. On the top surface as the melt collapses, there is a closure of pores.     

Patterning of fine particles by means of supercritical CO2

A new method for positioning fine particles on surfaces has been developed. Supercritical CO₂-assisted printing (SCAP) was utilized to spray and deposit the prepared particles on solid substrates. By means of masks, regular arrays of the particles were successfully created in designed patterns. Typical size of the particles employed was in the range of submicrometers to micrometers. Supercritical CO₂ (sc-CO₂) acted as an effective dispersion and transportation medium in this process. Good dispersion state of the particles was achieved by stirring in sc-CO₂. Fabrications of fine patterns of solder particles and other ceramic powders on smooth plates were demonstrated. Under optimum operation conditions, fine structures of 30 μm in width can be formed in a minimal pitch of 60 μm. Ultra high yield of the patterning was obtained since the deposition rate could be as high as 100 μm per second. Main factors affecting the process were discussed. The research results indicate that the SCAP is a potential approach to the organization of fine particles into microstructures. Hopefully, it may find wide industrial applications where lithography is needed, such as solder printing in surface mounting technology for higher density electronics and thick film fabrication for miniature systems.     

Energy recovery by means of a radial piston expander in a CO2 refrigeration system

Natural refrigeration fluids as CO₂ represent a very promising alternative to hydrofluorocarbons (HFCs) but they generally entail lower COP values. The possibility of recovering the large throttling losses by using an expander could give a substantial contribution to the performance improvement. In this work, a reciprocating expander developed from a hydraulic motor was experimentally analyzed. Despite of the mechanical losses due to the different original application of the machine, the thermodynamic cycles showed very promising results with the adoption of this solution. The machine isentropic efficiency was 19%, while the indicated efficiency was 66%, showing a very interesting potential of the expander. Thus, by considering a reasonable value of mechanical efficiency about 65%, the isentropic efficiency would be around 40%. Consequently, the entailed COP potential improvement, compared to a refrigeration system with simple throttling valve is currently at 7.4%, while it might overcome 20%.     

Absorption of 9.6-micron CO2 laser radiation by CO2 at elevated temperatures

Absorption of 9.6-micron CO2 laser radiation by CO2 at temperatures between 296 and 625 K has been measured at a pressure of 200 Torr. Experimental results for the R1O-R26 and P1O-P28 transitions have been obtained and compared with computed values of absorption. The relative optical broadening coefficients due to He and N2 have been measured on the R16-R22 and P16-P22 transitions over the same temperature range.     

Recording of long-period gratings in special single-mode fibers by a CO2 laser

The paper deals with the fabrication of long-period gratings (LPG) in special optical fibers with an inverted parabolic-index profile of the cladding by periodically exposing the fibers to radiation of a high-power CO₂ laser. Details on the fiber fabrication and preparation of LPGs with a period of about 1 mm in the fibers are presented. The fabricated LPGs were evaluated on the basis of their transmission spectra determined by measuring the output spectral density of the fiber with the LPGs. It is shown that the position of the band and its strength depend on the laser beam velocity, beam power and the interaction time of radiation with the fiber.     

Thermal-feedback-controlled coagulation of egg white by the CO2 laser

Temperature feedback control during laser-assisted tissue coagulation was investigated and demonstrated with the egg-white model. We observed the dynamics of photothermal denaturation during CO2 laser irradiation by simultaneously controlling surface temperature and monitoring He-Ne laser transmission of egg-white samples. Once a quasi-constant surface temperature was established, transmission of egg white tended to decrease linearly with time. Analysis of experimental data strongly suggested a first-order rate process. Since transmission was primarily affected by heat-induced increase in the scattering coefficient and depth of coagulation, we speculated that changes in transmission were reliable indicators of accumulating photothermal damage. Our experiments demonstrated that thermal feedback can effectively control or limit photothermal damage.