Duration time, concept

The majority of experimental mixture studies have analyzed the effects that arise from simultaneous exposure to chemicals. Very few studies exist where sequential exposure to several chemicals was analyzed. Only a concept founded on an understanding of the relationship between dose or concentration and exposure duration, time to effect, and recovery can hope to deal with the effect of sequential exposures. Conceptual frameworks for descriptions of time-dependent toxicity from a mechanistic perspective are available (e.g., Rozman and Doull 2000 Ashauer et al. 2006). However, the link between existing dose-time response models and a framework for mixture effect analysis from sequential exposure has yet to be made. A recent example of an interesting study that looked at sequential exposures is from Ashauer et al. (2007b), who base their analysis on a 1-compartment model for substance uptake, plus additional parameters for effect propagation and recovery. Generalizations are not yet in sight. 

Hence, the concept of a ratio of the characteristic time of the polymeric fluid, 0f, to the duration time of a process, 9 (e.g. the residence time of a material flowing through a pore), has become a significant parameter when investigating viscoelastic flow in porous media. This ratio is called the... 

Time is a fundamental property of the physical world. Because time encompasses the antinomic qualities of transience and duration, the definition of time poses a dilemma for the formulation of a comprehensive physical theory. The partial elimination of time is a common solution to this dilemma. In his mechanical philosophy, Newton appears to resort to the elimination of the transient quality of time by identifying time with duration. It is suggested, however, that the transient quality of time may be identified as the active component of the Newtonian concept of inertia, a quasi occult quality of matter that is correlated with change, and that is essential to defining duration. The assignment of the transient quality of time to matter is a necessary consequence of Newton s attempt to render a world system of divine mathematical order. Newton s interest in alchemy reflects this view that matter is active and mutable in nature... 

The presented concept leads to a mixed-integer nonlinear programming (MINLP) model. The binary variables representing assignment decisions and sequencing decisions are complemented by continuous variables representing timings, durations, hold-ups, feed streams, supplied product, under- and overproduction. The... 

The previous general continuous-time formulations are mostly oriented towards arbitrary network processes. On the other hand, different continuous-time formulations focused their attention on particular features of a wide variety of sequential processes. One of the first contributions following this direction is based on the concept of time slots, which stand for a set of predefined time intervals with unknown durations. The main idea is to postulate an appropriate number of time slots for each processing unit in order to allocate them to the batches to be processed. The definition of the number of time slots required is not a trivial decision and represents an important trade-offbetween optimality and computational performance. Other alternative approaches for sequential processes were developed based on the concept of batch precedence. Model variables defining the processing sequence of batch tasks are explicitly embedded into these formulations and, consequently,... 

Chapter 16 - It is shown, that there is principal difference between the description of generally reagents diffusion and the diffusion defining chemical reaction course. The last process is described within the framework of strange (anomalous) diffusion concept and is controled by active (fractal) reaction duration. The exponent a, defining the value of active duration in comparison with real time, is dependent on reagents structure. 

Fig. 27. Thermally balanced PP and NP sequences. (PP) In the balanced PP sequence, the sample is first kept at the relaxation field By for a time — t and, then pre-polarized at the polarization field Bp for a time Tp, and finally allowed to relax for time T before the start of the detection period. The time Tp should be set to about 4Ti(Bp). As T varies during a multi-block sequence, the polarization interval position moves horizontally but the total block duration and the mean power dissipation remain constant. (NP) The balanced non-polarized sequence is conceptually similar, except for the fact that the polarization interval is replaced by a magnetization annihilation interval in which the field is zero and whose duration should be about 47 (0). In both cases, the time should be about or more than 4Ti(Br). The concept can be combined with any detection mode, not just the simple FID detection shown here.

Unpredictability also is a central feature in the concept of learned helplessness. This concept, using uncontrollable shock, was introduced by Overmier and Seligman (1967) and is based on the observation that animals exposed to an invariable stressor such as electric foot shock, which, due to the experimental set-up, is uncontrollable in nature, developed behavioral deficits. As first shown by Weiss (1968), rats exposed to uncontrollable shock showed significant weight loss due to decreased food and water intake. Moreover, these animals spent more time immobile in the forced swim test, and they revealed altered sleep patterns as well as a weakened response to previously rewarding brain stimulation, i.e., anhedonia (Henn et al. 1985 Weiss 1991). Importantly, these changes are not seen in animals that receive the same shocks but can exert control over their duration. 

In this variant of CT-REDOR (cf. Figure 3C), the duration of the f-channel dephasing pulses tpo is stepped from 0 to 2it while keeping the evolution time constant. This concept is quite similar to the 0-REDOR approach developed by Gullion and Pennington " but serves a different purpose. While the latter experiment aims at the determination of individual coupling constants in multiple-spin systems, the CT-VPD-REDOR enables... 

This third edition essentially retains the structure of the second edition but its contents have been revised, with considerable changes in some parts. Thus, account is taken of the fact that a new generation of antidepressants has been available for some years, that concepts of the mechanisms of neuroleptic action have altered several times and have led to products with new mechanisms of action, and that therapeutic advances have even been recorded in a field that was only recently considered to be hopeless, namely Alzheimer s disease. New methodological developments, especially in the use of imaging techniques in psychiatry, and changes in opinions on the best possible use of psychopharmaceuticals and their duration of use in schizophrenia and depression have been suitably taken into account. 

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