Haze factors

Fig. 6.29. Variation of (a) the total and diffuse transmittance curves (TT and DT), (b) the haze factor measured at A = 600nm (DT/TT at 600nm), as a function of the H2O/DEZ ratio, for 2.5 j,rn-fhick LP-CVD ZnO B films deposited at 155°C, 0.5mbar and with B2H6/DEZ = 0.6...

Total and diffuse transmittance spectra (TT and DT, resp.) and haze factor (i.e., DT/TT measured at 600 nm) are presented in Fig. 6.29 as a function of the H2O/DEZ ratio. As the thickness d of the ZnO samples does not vary significantly within this series, we may assume that the trends observed hereafter are not due to a variation of d. TT does not vary within this series, with the single exception of the TT curve for the ZnO sample deposited with a H2O/DEZ ratio of 0.8, i.e., the only sample deposited with an excess of DEZ. The TT of this sample is systematically lower than the TT curves of the ZnO samples deposited with an excess of water. The reduction of TT in the NIR area is similar for all the curves. This indicates that free carrier... 

The reduction in <5 corresponds to the reduction in p and in the haze factor as observed in Figs. 6.28b and 6.29b, respectively. As the carrier density N does not vary with H2O/DEZ, we can safely assume that the density of ionized impurities within the ZnO films also remains constant when the H2O/DEZ ratio is increased. The observed decrease in p would therefore be induced here solely by an increase in grain boundary scattering, i.e., by an increase in the density of grain boundaries. This increase of grain boundary density evidently occurs when the grains become smaller (i.e., when <5 is reduced). 

Finally, as it is not possible to experimentally test all the various kinds of surface textures within actual solar cell configurations, it can be useful to use numerical simulations, in order to evaluate the best combination of surface textures and roughness for both front and back TOO layers. The method usually applied for such simulations is to take the main optical properties of each layer of the solar cell (absorption, thickness, haze factor, ADF, surface roughness,. ..), and then to put them all together in order to compute the quantum efficiency curve of the resulting solar cell. Such a task of optically simulating solar cells is very complex and beyond the scope of the present chapter. However, it is important to note here that a numerical simulation is always only an imperfect tool and can in no way fully replace experimental work and measurements on actual solar cells. 

Critical properties of TCO coatings are electrical resistance and transparency [3], but for solar cell applications very often texture and large haze factors, i.e., ratio of diffuse to total transmission, have similar importance. Large haze factors have been shown to influence positively the efficiency of silicon solar cells, because the reflection at the TCO-silicon interface is reduced and the scattering increases the pathway of light inside the active material. The preparation and characteristics of several TCO materials have been reviewed by Chopra et al. [92] and Dawar and Joshi [93]. The optical and electrical properties of ITO and aluminum doped zinc oxide have been studied in detail by Granqvist and coworkers [94, 95], but these films were prepared by sputtering and not by CVD. Very recently they also published an overview of transparent conductive electrodes for electrochromic devices [7]. 

Major and Chopra [224] report a noteworthy haze factor of 16% for ZnO In. This value is very reasonable for applications of these coatings to silicon solar cells. Milky films, i.e.. films with large haze factors, or films with enormous surface roughness, leading to scattering, have also been grown by Minami et al. [219] and Cossement and Sreydio [237]. 

Laser communication systems based on free-space propagation through the atmosphere suffer drawbacks because of factors like atmospheric turbulence and attenuation by rain, snow, haze, or fog. Nevertheless, free-space laser communication systems were developed for many appHcations (89—91). They employ separate components, such as lasers, modulators, collimators, and detectors. Some of the most promising appHcations are for space communications, because the problems of turbulence and opacity in the atmosphere are absent. 

In the context of crystallinity as a crucial factor with respect to haze, it has to be pointed out that PET and PBT as the most industrially used polyesters are both crystallizable depending on the conditions of subsequent processing. The amorphous state can be obtained by a rapid quenching of the melt below the Tg. Heating above the 7 g induces fast crystallization. PBT exhibits a significantly increased crystallization rate when compared with PET. 

Many deleterious effects have been associated with photochemically polluted air ozone is deflnitely associated with respiratory problems, plant damage, and material damage PAN has deflnitely been associated with plant damage, and some other members of this class of chemical compounds have been associated with eye irritation the hydroxyl radical is considered to be an important factor in the conversion of gas-phase intermediates to end products, such as sulfur dioxide to particulate sulfate the particulate complex is responsible for haze formation and has also been associated with eye irritation and respiratory effects. The aldehydes have been associated with eye irritation. Ozone and PAN themselves do not cause eye irritation. For purposes of control, much more research is needed, in order to relate the laboratory data about the concentrations of these various materials that have significant effects to their formation in the atmosphere from emission and their atmospheric distribution. The lack of convenient measurement methods has hindered progress in gaining this understanding. 

The effect of pH on haze intensity was striking (Siebert et ah, 1996a) (see Fig. 2.16). When the pH rose from near 3 to slightly above 4, the haze intensity increased by a factor of 7 with the same amounts of protein and polyphenol. At higher pH, the haze intensity declined. While proteins... 

In addition clouds and haze level (Bais et al., 1993, Estupinan, et al., 1996, Seckmeyer et al. 1996), as well as other tropospheric minor constituents such as S02 (Zerefos et al. 1995a) and surface albedo (WMO, 1994) are also very important in determining UV-B levels at ground, and are among the controlling factors of UV-B transfer through the atmosphere (Zerefos, 1997). 

The sun, an important factor to take into account in remote sensing using spectroscopic imaging instruments. The passive optical system and the atmosphere through which the energy passes, both from the sun to the earth s surface and back to the instrument, interferes with the data collected. Atmospheric distortions include the effect of scattered dry air molecules (haze) and absorption by air molecules. 

Despite the diverse chemical types represented by forest pesticides, the variety of their formulations, and the many rates and routes of application, two factors remain consistently present in their environment—sunlight and powerful reagents. Quite apparently, these forces are active and acting. The well-known "blue haze" observed over forests in many parts of the world remote from man s chemical wastes is a result of photooxidation reactions of volatile natural chemicals similar to those which generate manmade smog. 

Protein clouding in white wines seems to be a greater problem when the wine pH is close to the isoelectric point of the various protein fractions. This is due to the fact that bentonite will remove, preferentially, the most positively charged proteins. The electrostatic charge of various protein fractions explains the observable phenomena of not being able to stabilize certain wines with the use of bentonite alone, or only with excessive amounts that can strip the wine character. But the pi of proteins only partially explains wine haze formation. It is also important to note that other factors, as yet not clearly identified, can intervene. 

Calderon, R, Van Buren, J.R, Robinson, W.B. (1968). Factors influencing the formation of precipitates and hazes by gelatin and condensed hydrolysable tannins. J. Agric. Food Chem., 16, 479-482. 

The mechanism of protein haze formation in wines is not fully understood. Slow denaturation of wine proteins is thought to lead to protein aggregation, flocculation into a hazy suspension and, finally, formation of visual precipitates. The importance of non-proteinaceous factors in white wine protein haze formation such as proan-thocyanidins (Koch and Sajak 1959 Waters et al. 1995a Yokotsuka et al. 1991) have been suspected for some time. Other factors such as polysaccharides, alcohol levels and pH have also been implicated (Mesquita et al. 2001 Siebert et al. 1996a). It has been observed that grape protein added to model wine does not precipitate or produce haze when heated, whereas visually obvious hazes occur when the same protein is added to a commercial wine (Pocock 2006). 

The size and amount of protein haze formed in a wine is strongly influenced by other wine components. Pocock (2006) has demonstrated that one wine component, the sulfate anion, previously referred to as factor X, is essential for haze formation. If the sulfate anion is not present, heating does not result in sufficient denaturation of the proteins to lead to their aggregation, thus a haze will not form. 

Pocock, K.F., H0j, P.B., Adams, K.S., Kwiatkowski, M.J., Waters, E.J. (2003). Combined heat and proteolytic enzyme treatment of white wines reduces haze forming protein content without detrimental effect. Aust. J. Grape Wine Res., 9, 56-63 Pocock, K.F., Alexander, G.M., Hayasaka, Y, Jones, P.R., Waters, E.J. (2006). Sulfate - a candidate for the missing essential factor that is required for the formation of protein haze in white wine. J. Agric. Food Chem., 55, 1799-1807... 

Haze, K., Yoshida, H., Yanagi, H., Yura, T. and Mori, K. (1999) Mammalian transcription factor ATF6 is synthesized as a transmembrane protein and activated by proteolysis in response to endoplasmic reticulum stress. Mol. Biol. Cell 10, 3787-3799. 

Haze formation is mostly attributed to proteins, polyphenols, and their interactions. It is also possible that there are also other factors that inbuence haze formation in beer, but their effect has not been yet clearly debned [ 15]. The amount of haze formed depends both on the concentration of proteins and polyphenols, and on their ratio. Polyphenols can combine with proteins to form colloidal suspensions that scatter light, which creates the cloudy appearance of beer. Beer polyphenols originate partly from barley and partly from hops. The beer polyphenols most closely associated with haze formation are the proanthocyanidins, which are dimers and trimers of catechin, epicatechin, and gaUocatechin. These have been shown to interact strongly with haze-active proteins [13,15-17] and their concentration in beer was directly related to the rate of haze formation [18]. Ahrenst-Larsen and Erdal [19] have demonstrated that anthocyanogen-free barley produces beer that is extremely resistant to haze formation, without any stabilizing treatment, provided that hops do not contribute polyphenols either. Not all proteins are equally involved in haze formation. It has been shown that haze-active proteins contain signibcant amounts of proline and that proteins that lack proline form little or no haze in the presence of polyphenols [13,15-17]. In beer, the source of the haze-active protein has been shown to be the barley hordein, an alcohol-soluble protein rich in proUne [16]. 

Waters, E.J., Wallace, W., Tate, M.E. and Williams, P.J. (1993) Isolation and partial characterization of a natural haze protective factor from wine, J. Agric. Food Chem., 41, 724-730. 

Solution stability of the aqueous resin system is also a key factor with regard to co-solvents for electrodeposition paints. It was determined at both room temperature and 40°C. The criteria used were pH, conductivity, and haze. Haze is a function of light transmission at 5560 A and was measured using a Cary model 14 spectrometer. All tests were run in sealed containers. 

The formol index (total free amino acids) was the best predictor of browning rate of concentrates during storage for a given commodity. While haze and sediment formation were quality factors of major interest in this study, none of the juices or concentrates produced were particularly troublesome in this regard. The phenolic and protein profiles should still provide a reference with which unstable experimental or commercial samples can be compared in the future, however. In addition to color and appearance, quality factors of flavor, astringency, bitterness, viscosity and mouthfeel warrant investigation. 

An emulsion after having been cleared by carbon will not spontaneously form anew, but this cannot be said of a haze. This may be due to any one of the many factors that can cause a haze to form (Table 4 10). 

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