TLFeBOOK in .NET

Integrated QRCode in .NET TLFeBOOK

levels with socioeconomic status and cognition/learning abilities. Coscia, Ris, Succop, & Dietrich (2003) used growth curve analyses to examine cognitive effects for 196 children, ages 6 to 15 years, with lead exposure. At age 15, higher lead levels were associated with lower verbal comprehension scores over time and greater decline in vocabulary development. Similar negative trajectories were not evidenced for perceptual areas (Coscia et al., 2003). Notably, effects of blood lead levels on cognition appear to be moderated by high blood folate levels (Solon et al., 2008). Language, cognition, and educational functioning are not the only domains affected by lead exposure. Notably, research indicates that lead exposure also is associated with greater absenteeism, lower graduation rates, and delinquency (Dietrich, Ris, Succop, Berger, & Bornschein, 2001). In a follow-up study of 780 children with high blood lead levels at 12 to 33 months of age, blood lead levels at age 5 were not signi cantly correlated with behavior problems; however, at age 7, blood lead levels were related directly to externalizing and school problems (Chen, Cai, Dietrich, Radcliffe, & Rogan, 2007). Children with elevated lead levels are more inattentive, hyperactive, aggressive, disorganized, and less able to follow directions; elevated bone lead levels are associated with elevated risk for delinquency and aggression as well (M. Marlowe, Bliss, & Schneider, 1994; Needleman, 2002; J. H. G. Williams & Ross, 2007). Among children with emotional disturbance, hair lead levels were associated with aggression, withdrawal, distractibility, and social problems (M. Marlowe, Errera, Ballowe, & Jacobs, 1983). Some of the domains affected by lead exposure include poor attention, executive function, working memory, and language delays as well as delays in motor development (Bellinger, Leviton, Waternaux, Needleman, & Rabinowitz, 1987; Bellinger, Leviton, Waternaux, Needleman, & Rabinowitz, 1988; Bellinger et al., 1992; Wigg, Vimpani, McMichael, & Baghurst, 1988). Given that some focal de cits may emerge at differing ages, it is imperative that longitudinal data be examined across functional domains. For example, in one study, cognitive ability at age 10 best correlated with blood lead levels at 2 years of age (Bellinger et al., 1992) and tooth lead levels (Hansen, Trillingsgaard, Beese, Lyngbye, & Grandjean, 1989). In another study, executive function set shifting was best correlated with concurrent blood lead levels (Stiles & Bellinger, 1993), as was processing speed (Hansen et al., 1989). Long term, low levels of lead have been associated with ne motor de cits that become evident only at school age (Dietrich, Berger, & Succop, 1993). Speci c to PCB (and mercury) exposure and 7-year-old children, identi ed de cits included verbal naming, reaction time, and long-term memory (Grandjean et al., 2001).

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Using equation [9.1], N (t) is de ned almost everywhere. As can be seen in Figure 9.1, N (t) presents jumps of amplitude greater than 1. The state Y (t) of the system at time t, is XN (t) . Observe that Y (t) is not equivalent to the stochastic process, but that it allows us, in most cases, to proceed to standard analyses. The scheme in Figure 9.1 presents a possible execution of the process and illustrates the interpretation of the random variables previously introduced. In this example, the process is initially in state s4 and remains in it until t0 , when it moves to state s6 . At time t0 + t1 , the system successively visits, in a zero time, states s3 and s12 before reaching state s7 where it sojourns for some time. The observation Y (t) in continuous time conceals the vanishing states s3 and s12 of the process.

Note that for simplicity of presentation we here use a single index instead of two indexes to represent a Floquet mode (and a waveguide mode as well).