Vreman Research Paper

1. Introduction

Section:

The rotating turbulent flow in hydraulic machinery contains quite complicated multiscale helicity turbulence structures due to the driven rotating and interacting between viscous fluid and impeller structure. One of the things that make rotating turbulent flow in hydro-turbine different than channel flow is the complexity of flow passage, which results in multiscale helicity turbulence structures and multiscale effect. All these above aggravate the complexity of rotation turbulent. Hydraulic factor caused by rotating turbulent flow is one of the most important parameters which can induce unit vibration, Due to diversity and complexity of rotating turbulent flow inside a hydraulic machinery, the development physics of the overscale structures in the rotating turbulent flow is not fully clear even now. The vibration amplitude induced by rotating turbulent flow is large, and usually all of the unit is difficult to avoid. Especially, in some case that deviation from the optimal working conditions, such as small open flow condition and transient process condition. The swirl, flow separation, and backflow in flow passage would become more obvious and complicated, which easily induce the abnormal vibration or fatigue damaged occurred in structure with vibration frequency more multifarious, for instance, in Francis turbine of Gong-Zui project, Shi-Quan project, Liu-Jia-Xia project, Li-Jia-Xia project, and so forth. The pressure pulsation amplitude in the draft tube under small open flow condition is larger. Its frequency is also larger than unit rotation frequency, even multitimes of the unit rotation frequency [1].

As for Gong-Zui project after 20-year operation, turbine loses efficiency severely, crack occurred on the connection between runner crown and blade exit, front face of blade was damaged severely by sediment, and the cavitation is found on the back face of blade. Due to the damage of turbine, Canada company GE Hydro is committed to improve two turbines for more capacity. After improvement, obvious vibration and large noise were found in some condition. In this situation, many theoretical analyses, model tests, and field tests were done. The results show that high vibration and large noise are induced by interblade vortices under the no-load or low load condition, which can be avoided by means of air admission [1]. From June 2003 to August 2003, several overspeed 140% tests were done for No. 5 and No. 6 unit of Three Gorges left bank hydropower station; all the tests have abnormal vibration when guide vane is closed to 4% and vibration frequency is the same as low frequency pressure pulsation in guide vane, spiral case, and vanes surface. So the vibration is due to resonance between fluid and structure [2–4

The aim of the study was to determine what wavelength range (color) of light is most effective toward decreasing TSB in the blood: turquoise light with peak emission at 497 nm or blue light with peak emission at 459 nm. Besides wavelength, the irradiance of the light delivered to the infants’ skin is a crucial factor, which must be controlled for when comparing the efficacy of the light. Thus, we needed to keep the irradiance of the two light sources equal. The irradiance level was normalized through adjustment of the distance between the lamp and the infants’ skin level. Usually, the irradiance is measured as µW/cm2 or µW/cm2/nm using handheld radiometers such as neoBLUE or BiliBlanket Meter II. However, because photons of different wavelength (497 vs. 459 nm) have different energy levels, we decided that normalizing the irradiance on the basis of photons would provide a most appropriate basis for comparison of the efficacy of phototherapy of the two wavelengths. The level of irradiance was chosen to reflect the irradiance of blue light delivered to neonates during phototherapy as recommended by the American Academy of Pediatrics guidelines (2). This irradiance level of 30 µW/cm2/nm was measured with a neoBLUE radiometer at a distance of 29 cm between lamp and skin. This radiometer is being routinely used in our neonatal intensive care unit. For this reason, we treated the neonates with an irradiance of 5.2 ± 0.1 × 1015 photons/cm2/s of each of the two colors of light. Given that photons at 497 nm have a slightly lower energy than photons at 459 nm (8%, calculated from Planck’s equation), it is worth noting that normalizing irradiance on the basis of photons resulted in a relative small difference in irradiance measured on the basis of µW/cm2 (Table 4).

There were no significant differences between the rates of decrease of TSB through use of turquoise LEDs with peak emission at 497 nm and blue LEDs with peak emission at 459 nm with an equal light irradiance delivered to the infants. Thus, with respect to effectiveness, the turquoise light had no advantage over the blue light. However, potential side effects may be less serious in phototherapy with longer wavelengths: in cell cultures containing bilirubin, turquoise light caused less DNA damage (12) and was less cytotoxic (13), compared with blue light. Furthermore, during phototherapy with blue light, the serum level of riboflavin decreased due to photodecomposition (14).

Even though phototherapy has been used for more than 50 y (3), the most efficient light emission spectrum is still not known for certain. Presumably, the main reasons are that (i) the results from photoexposure of bilirubin–albumin solutions/plasma in vitro have been extrapolated to the clinical use on neonates, (ii) the routine blue light treatment is effective, and until recently, no substantial side effects were observed (11), and (iii) clinical studies comparing different light sources are difficult to perform as the irradiance, exposed body surface area, and exposure time all must be equal in the groups, and the irradiance must be measured by a radiometer with constant sensitivity across the entire emission range of the light sources used, which none of the handheld clinical radiometers can accomplish. The first clinical studies fulfilling these criteria are to our knowledge our previous (7) and the present studies.

Seidman et al. (15) compared the efficacy of blue LED light with peak emission at 459 nm with turquoise light with peak emission at 505 nm both with an irradiance on the infants in the range 5–8 µW/cm2/nm and found the same efficacy of the two light sources. But the irradiance of both light sources was measured by a radiometer with peak sensitivity at 450 nm, whereby the irradiance of the turquoise light was highly underestimated.

By using a skin optical model and taking into account the present knowledge of bilirubin photochemistry, Lamola et al. (9), after initiation of our study, have published a paper suggesting that light with an emission spectrum with peak at 475–480 nm would be expected to have the greatest bilirubin-reducing rate in neonates. Therefore, by combining the theoretical calculations by Agati et al (6) and Lamola et al (9), and our previous (7) and present clinical data, we suggest that the most efficient bilirubin-reducing light emission spectrum might be a spectrum with peak emission in the range 475–490 nm.

The different results obtained in this study in relation to our previous one may be explained by (i) use of different light sources (LED tubes vs. broader spectrum fluorescent light tubes), (ii) the fact that the peak emission wavelength of the blue LED device was shifted toward longer wavelengths (452–459 nm), whereby it might be more efficient in the present study (6,16) and (iii) in our previous study, we compared turquoise and blue lights with equal irradiance expressed as µW/cm2/nm, measured by a broadband photodiode power meter (model 460; EG&G, Salem, MA).

The rate of decline of TSB was of the same magnitude as observed in other phototherapy studies using blue LEDs (17). The decrease of serum bilirubin is dependent on biologic diversity among the individuals and on the treatment. A few infants had only a modest [▵TSB0–24 (%)] (Figure 1), and the reason might be multifactorial, which was not explored further in this study.

Of the other parameters determined, [▵TSB0–24 (%)] was negatively correlated to birth weight. As the weight increases, the exposed body surface area in relation to weight decreases, and the skin becomes thicker and more mature, which might reduce the effect of the light.

[▵TSB0–24 (%)] was positively associated to the postnatal age. With increasing age, the normal bilirubin excretion pathway matures and spontaneous accumulation of bilirubin decreases.

Contrary to phototherapy with fluorescent light, LED light therapy does not cause significant transepidermal water loss, because LEDs emit significantly less infrared radiation (18). During routine care of the infants, the average weight gain was 0.7%, independent of light source.

Half of the breastfed infants were supplemented with formula due to suspicion that they did not receive enough breast milk, but the volumes were most often small. This supplementation did not enhance [▵TSB0–24 (%)], perhaps because of the small volumes. That formula supplementation can enhance the decline of TSB during phototherapy as has previously been reported (19).

The strengths of the study were the use of LEDs (the phototherapy light source of the future), that the light irradiance was measured by a radiometer with a constant spectral sensitivity, and that the patient population was homogeneous.

Conclusion

Using LEDs with equal light irradiance on the infants, turquoise light with peak emission at 497 nm and blue light with peak emission at 459 nm had equal bilirubin-reducing effect in treatment of jaundiced neonates.

Perspectives

More clinical studies are needed to determine which LED lamp emission spectrum has the greatest bilirubin-reducing effect. Very likely, the peak of such a spectrum should be in the spectral range 475–490 nm. It is needed toward optimization of future phototherapy devices to be used in the management of newborn hyperbilirubinemia. So there may still be room for improvement of the phototherapy in neonates.

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