Bimodal species

Luminescence of Pyrosoma. All species of the genus Pyrosoma (about 10 species) are bioluminescent. Pyrosoma is one of the few organisms reported to luminesce in response to light (Bowlby et al., 1990). The luminescence emission spectrum of Pyrosoma atlantica is bimodal according to Kampa and Boden (1957), with the primary peak near 482 nm, and the secondary near 525 nm. Swift et al. (1977) reported the emission maxima of two Pyrosoma species at 485 and 493 nm, respectively, and Bowlby et al. (1990) found an emission peak at 475 nm with P. atlantica. A corrected bioluminescence spectrum of P. atlantica (A.max 485 nm) reported by Herring (1983) is shown in Fig. 10.5.2. 

Improved control was observed, however, upon addition of benzyl alcohol to the dinuclear complexes.887 X-ray crystallography revealed that whereas (296) simply binds the alcohol, (297) reacts to form a trinuclear species bearing four terminal alkoxides. The resultant cluster, (298), polymerizes rac-LA in a relatively controlled manner (Mw/Mn=1.15) up to 70% conversion thereafter GPC traces become bimodal as transesterification becomes increasingly prevalent. NMR spectroscopy demonstrates that the PLA bears BnO end-groups and the number of active sites was determined to be 2.5 0.2. When CL is initiated by (298) only 1.5 alkoxides are active and kinetic analysis suggests that the propagation mechanisms for the two monomers are different, the rate law being first order in LA, but zero order in CL. 

As it seems unlikely that any explanation of a bimodal DPD can be devised on the basis of a monoeidic polymerisation mechanism, we reject the alternative (i) and will investigate the usefulness of (ii). An important, though not absolute, constraint on the choice of the second species participating in the formation of the polymers, is that it must be ionic, since the ionic conductivity of the reaction mixture corresponds closely to that calculated from c0 as shown in Reference [1]. 

The mean rate of energy release S and the rate of consumption/production of species j, Vj, are calculated on the basis of the detailed or reduced reaction mechanism of fuel oxidation in air and a single-point bimodal normalized PDF of temperature P T, T) in the turbulent flame brush ... 

It is not an absolute necessity for LCP to have no free ions. If free ions are present, LCP is possible only if there are fast equilibria between free ions, ion pairs, and covalent species. If the equilibrium between free ions and ion pairs is slow, the result is a bimodal distribution. Further, to have any possibility of LCP with free ions present, the concentration and reactivity of the free ions should not be such that the reaction is too fast. 

In essentially all species of animals, including humans, serotonin is important in aggression (Kravitz, 2000). Relationships between CSF concentrations of a serotonin metabolite, 5-hydroxyindoleacetic acid (5-HIAA), and human aggression were described in As-berg et al. s landmark study (1976), which showed a bimodal distribution among depressed patients. A meta-analysis of 27 studies, involving 1202 psychiatric patients, showed an association between attempted suicide and low levels of CSF 5-HIAA (Lester, 1995). 

PL emission spectra exhibit characteristic bimodal curves, as shown in Figure 13.2.3, with two peaks at 2.13 eV (580 nm) and 2.88 eV (430 nm). The former is attributed to Mn(II) and the latter to the polymeric species of AA. The latter emission is not attributable to the additives of AA like the polymerization inhibitor. It is particularly noteworthy that the fonner peak, at 2.13 eV, increases with increasing the amount of Mn(II) concentration, at the cost of the latter peak at 2.88 eV, as shown in Figure 13.2.4. This suggests the possibility of energy transfer from the polymeric species to the active center, Mn(II), of the phosphor ZnS Mn. 

Figure 1. Example of compositionally resolved bimodal and monomodal distributions of aerosols. The ordinate gives the percent of the species found in the given size fraction of the impactor. The mode near 0.3 xm is the accumulation mode , and that above 8 xm is the coarse mode The minimum of mass between 1 and 2 xm is typical the chlorine distribution is anomalous. Chlorine is in fact a coarse-mode marine aerosol that has lost its larger particles during transport from the ocean to Davis, California, a distance of roughly 100 km. (Reproduced with permission from reference 15. Copyright 1988.)...

The PEO-rich PSt-h-PEO block copolymers form spherical micelles in aqueous solutions [63]. The DLS measurements indicate the presence of a bimodal size distribution - two very narrowly distributed species. The smaller more mobile species had Rh corresponding to the star model of block copolymer micelles. However, 99% or more of the block copolymer is present as simple micelles. 

Fig. 4.27 represents the velocity profiles v(r) and degrees of conversion P(r) at the exit of a reactor for different values of Da/Da and constant [A] = 0.7 mol%. At Da = 0.5 (a rather low degree of conversion at the axis of the reactor), a low-viscosity stream flows out (breaks through) into the central zone (Fig. 4.27 b, curves 1 and 2). This means that the end-product leaving the reactor is a mixture consisting of two species (fractions) with very different molecular weights, leading to the appearance of a pronounced bimodal MWD-H, which is not due to the chemical process but is a direct consequence of the hydrodynamic situation in the reactor. 

The relative stability of the delocalized, non-vertical radical cation relative to a localized, vertical isomer was demonstrated also in gas phase experiments [404]. The molecular ions of m/e 132 obtained by gas phase ionization of the [4 + 2] dimer exhibited a bimodal decay, a result which was interpreted as evidence for the presence of two isomeric ions with different structures. The possibility that the reactive ion is a species with excess internal energy was discounted, when equivalent decay curves were observed in experiments using 10 eV and 70 eV electron impact ionization energy. In dramatic contrast, the molecular ions derived from the [2 + 2] dimer fail to react apparently the ion population resulting in this experiment is homogeneous [404],... 

The slower 4.15 S species was favoured by low concentration and at 1 mg/ml the relative amounts of the two components were about equal (Table II). In 1 M sodium thiocyanate at 20°C, Con A (5 mg/ml) sedimented as a single broad peak as seen in Figure 7 (A), with an S2g w value of 4.14 S. After dialysis, Figure 7 (B), the familar bimodal pattern returned with most of the Con A present as the faster component. This peak gave an s2g value of 5.86 S., W... 

In summary, the studies on the impact of nx/ Ndv-ratios on polymerization rate, molar mass, MMD and PDI support the view on the existence of several active species. The relative concentrations of the active species are governed by the molar ratios x/ Nd- Particularly the occurrence of bimodal distributions provides strong evidence for the existence of two distinct active catalyst species. 

As can be seen from Table 14 the addition order affects reaction rate, molar mass and PDI. The authors suggested that in-situ activation results in the formation of two types of active species the relative concentrations of which were governed by the addition sequence. Addition order (1) EASC + NdV + DIBAH promotes the formation of insoluble species which produced polymer with a broad, bimodal MMD (PDI = 7.5) at low catalyst activity. Addition order (3) DIBAH + NdV + EASC leads to the formation of more soluble catalyst species which exhibit increased catalyst activity and produce BR with a monomodal MMD (PDI = 3.4). The influence of the addition order on cis-1,4-content is negligible. 

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