Sustainability temporal characteristics

There is a characteristic temporal pattern in the occurrence of radiation-induced tumors following irra ation, a pattern that may be segmented into a latency period during which no excess is expressed, a period marked by a rise to a peak or a plateau that may be sustained, and a period of subsidence that may be absent. Only for leukemia and for bone cancer following uptake of radium-224 is this pattern well delineated a latency period of 2 to 4 years, a peaking at perhaps 6 to 8 years, and subsidence to near zero about 30 years after exposure. For other radiogenic cancers, the minimal latent period is less well defined and is generally taken to be 10 to 15 years. 

For normotensive rats, the typical operation point around a = 10—12 and T = 16 s falls near the Hopf bifurcation point. This agrees with the experimental finding that about 70% of the nephrons perform self-sustained oscillations while the remaining show stable equilibrium behavior [22]. We can also imagine how the system is shifted back and forth across the Hopf bifurcation by variations in the arterial pressure. This explains the characteristic temporal behavior of the nephrons with periods of self-sustained oscillations interrupted by periods of stable equilibrium dynamics. 

Figure 12.6a shows the temporal variation of the proximal tubular pressure Pt as obtained from the single-nephron model for a = 12 and T = 16 s. All other parameters attain their standard values as listed in Table 12.1. Under these conditions the system operates slightly beyond the Hopf bifurcation point, and the depicted pressure variations represent the steady-state limit cycle oscillations reached after the initial transient has died out For physiologically realistic parameter values the model reproduces the observed self-sustained oscillations with characteristic periods of 30-40 s. The amplitudes in the pressure variation also correspond to experimentally observed values. Figure 12.6b shows the phase plot Here, we have displayed the normalized arteriolar radius r against the proximal intratubular pressure. Again, the amplitude in the variations of r appears reasonable. The motion... 

Sustainable chemicals should be short-range chemicals, that is, in which their (i) spatial range is low (mobility), (ii) temporal range is low (persistence) and (iii) effects are not irreversible. Clearly, not all chemicals that should be used can have the above characteristics because, for example, fuels must be inflammable, pesticides must be toxic (even with controlled properties) and reactive reagents must be aggressive/corrosive. The challenge is thus a careful control of the properties ( just needed ) and hazardous properties should be not linked to not-necessary functionalities. 

If a semiconductor element with negative differential conductance is operated in a reactive circuit, oscillatory instabilities may be induced by these reactive components, even if the relaxation time of the semiconductor is much smaller than that of the external circuit so that the semiconductor can be described by its stationary I U) characteristic and simply acts as a nonlinear resistor. Self-sustained semiconductor oscillations, where the semiconductor itself introduces an internal unstable temporal degree of freedom, must be distinguished from those circuit-induced oscillations. The self-sustained oscillations under time-independent external bias will be discussed in the following. Examples for internal degrees of freedom are the charge carrier density, or the electron temperature, or a junction capacitance within the device. Eq.(5.3) is then supplemented by a dynamic equation for this internal variable. It should be noted that the same class of models is also applicable to describe neural dynamics in the framework of the Hodgkin-Huxley equations [16]. 

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