Time scale of response

The time scale of responsiveness clearly affects the ability of a microbial community to respond to dynamic fluxes of DOM and a major unanswered question is how common is the necessity for a taxonomic shift before detectable changes in degradative ability are evident Also, the time scale of observation will dictate which of these responses are documented, with short-term bioassays probably reflecting the extant community, whereas seasonal changes may include taxonomic replacement. Any particular question will have a logical time scale and this should govern the time span under consideration. 

The important feature of the MEL model is the acclimation of vegetation to maintain a nutritional balance when faced with changes in resource availability, Vc, Vn. By acclimation authors (Bastetter etal, 1997) mean any process that results in a compensatory redistribution of uptake effort in response to a deviation from optimal element ratios in biomass. These processes include not only physiological and morphological responses of individual plants, such as changes in enzyme concentrations in tissue and root shoot ratios, but also genetic adaptation of populations and competitive replacement of species by other species with more favorable distribution of uptake efforts. This aspect is essentially important for the time scale of response. 

Time-scale of Response. A list of some of the events which occur during the development of infection structures, and the estimated times when the response occurs after contact with the inductive... 

However, if the creep compliance curves are compared at their respective TgS,we see in Figure 5.16 that the softening dispersions are, within experimental uncertainty, at the same place in the time scale of response. Specifically the positions of the four Jpit/ar) curves at a compliance level of 1.0 x 10 Pa appear to be spread on a time scale by not much more than one decade of time. Relative uncertainties of Tg values of 1.5°C can account for this spread in positions. Until more precise relative TgS can be measured we can tentatively surmise that at Tg all polymers at the same rate are deep in the softening zone. This conclusion appears reasonable when we consider that short-range chain dynamics should determine both creep rates just above the glassy level as well as changes in the local liquid structure, the kinetics of which determine Tg. 

The scan rate, u = EIAt, plays a very important role in sweep voltannnetry as it defines the time scale of the experiment and is typically in the range 5 mV s to 100 V s for nonnal macroelectrodes, although sweep rates of 10 V s are possible with microelectrodes (see later). The short time scales in which the experiments are carried out are the cause for the prevalence of non-steady-state diflfiision and the peak-shaped response. Wlien the scan rate is slow enough to maintain steady-state diflfiision, the concentration profiles with time are linear within the Nemst diflfiision layer which is fixed by natural convection, and the current-potential response reaches a plateau steady-state current. On reducing the time scale, the diflfiision layer caimot relax to its equilibrium state, the diffusion layer is thiimer and hence the currents in the non-steady-state will be higher. 

The relaxation and creep experiments that were described in the preceding sections are known as transient experiments. They begin, run their course, and end. A different experimental approach, called a dynamic experiment, involves stresses and strains that vary periodically. Our concern will be with sinusoidal oscillations of frequency v in cycles per second (Hz) or co in radians per second. Remember that there are 2ir radians in a full cycle, so co = 2nv. The reciprocal of CO gives the period of the oscillation and defines the time scale of the experiment. In connection with the relaxation and creep experiments, we observed that the maximum viscoelastic effect was observed when the time scale of the experiment is close to r. At a fixed temperature and for a specific sample, r or the spectrum of r values is fixed. If it does not correspond to the time scale of a transient experiment, we will lose a considerable amount of information about the viscoelastic response of the system. In a dynamic experiment it may... 

Whether a viscoelastic material behaves as a viscous Hquid or an elastic soHd depends on the relation between the time scale of the experiment and the time required for the system to respond to stress or deformation. Although the concept of a single relaxation time is generally inappHcable to real materials, a mean characteristic time can be defined as the time required for a stress to decay to 1/ of its elastic response to a step change in strain. The... 

The response is extremely fast on the time scale of a shock-wave experiment. The dislocation loop adjusts very quickly to the applied stress t. 

The choice of the method is governed by what is suitable for the given species (reactants or products), by the availability of instrumentation, and by the experience and familiarity of the investigator with the different methods. As mentioned, the time scale of the reaction must be compatible with the analytical method, and its response, precision, and sensitivity must be appropriate for the concentrations chosen. Generally speaking, it is best to select a method that can provide concentrations to a precision of at least 1-2%. 

For large K (K = 1000 in Fig. 17) an upper limit is reached, where the interfacial kinetics are sufficiently fast - on the time scale of the SECM measurement - such that the concentrations of Red in the two phases, adjacent to the interface, are always in equilibrium even though Red is generally depleted. The tip current response is then dependent... 

In the presence of added Lewis bases, sonochemical ligand substitution also occurs for Fe(C0)5, ancl act or roost metal carbonyls. Sonication of Fe(C0)5 in the presence of phosphines or phosphites produces Fe(C0)5 nLn, n=1, 2, and 3. The ratio of these products is independent of length of sonication the multiply substituted products increase with increasing initial [L] Fe(C0)i L is not sonochemically converted to Fe(C0)3L2 on the time scale of its production from Fe(C0)5. These observations are consistent with the same primary sonochemical event responsible for clusterification ... 

There are two superposition principles that are important in the theory of Viscoelasticity. The first of these is the Boltzmann superposition principle, which describes the response of a material to different loading histories (22). The second is the time-temperature superposition principle or WLF (Williams, Landel, and Ferry) equation, which describes the effect of temperature on the time scale of the response. 

Structure and function need to be jointly considered in the assessment of effects of stressors on river systems. It has been shown that the two sets of parameters offer complementary information since they cover different time scales and responses. This being shown in the case of biofilms is not a unique characteristic of them, but it might be applied to all other biological communities (e.g. macroinvertebrates, fish). These differ from the biofilm in its higher size and life span, and therefore in their integrative capacity to reflect effects in one part of the ecosystem. Higher traffic levels in addition to biofilms should be considered to study the whole ecosystem. In all of these biological compartments, the combined use of descriptors may amplify our ability to predict the effect of stressors on river basins. 

In spectroscopy we may distinguish two types of process, adiabatic and vertical. Adiabatic excitation energies are by definition thermodynamic ones, and they are usually further defined to refer to at 0° K. In practice, at least for electronic spectroscopy, one is more likely to observe vertical processes, because of the Franck-Condon principle. The simplest principle for understandings solvation effects on vertical electronic transitions is the two-response-time model in which the solvent is assumed to have a fast response time associated with electronic polarization and a slow response time associated with translational, librational, and vibrational motions of the nuclei.92 One assumes that electronic excitation is slow compared with electronic response but fast compared with nuclear response. The latter assumption is quite reasonable, but the former is questionable since the time scale of electronic excitation is quite comparable to solvent electronic polarization (consider, e.g., the excitation of a 4.5 eV n — n carbonyl transition in a solvent whose frequency response is centered at 10 eV the corresponding time scales are 10 15 s and 2 x 10 15 s respectively). A theory that takes account of the similarity of these time scales would be very difficult, involving explicit electron correlation between the solute and the macroscopic solvent. One can, however, treat the limit where the solvent electronic response is fast compared to solute electronic transitions this is called the direct reaction field (DRF). 49,93 The accurate answer must lie somewhere between the SCRF and DRF limits 94 nevertheless one can obtain very useful results with a two-time-scale version of the more manageable SCRF limit, as illustrated by a very successful recent treatment... 

Under conditions of short laser pulses and where ra is less than the transducer response time, r0, three transducer voltage responses can be described depending on the time scale of the heat deposition, zh. 

The accuracy of the thermochemical data obtained by this technique has been examined in numerous systems. In general, the data compares well, 1 kcal/mol, with that obtained by other spectroscopic and calorimetric methods. The accuracy and reproducibility of the data is dependent on the magnitude and time scale of the heat deposition detected by PAC that is associated with a given chemical process. Highly exothermic reactions are easy to detect, whereas ones that are not are difficult to detect. A thermoneutral reaction is invisible to PAC. Reactions that occur significantly slower than the response time of the transducer are not detected. Reactions that occur either slightly slower or faster than the response time are difficult to resolve accurately. Clearly, the proper choice of the transducer is extremely important in order to resolve accurately a given chemical event. 

At least two classes of regulated secretion can be defined [54]. The standard regulated secretion pathway is common to all secretory cells (i.e. adrenal chromaffin cells, pancreatic beta cells, etc.) and works on a time scale of minutes or even longer in terms of both secretory response to a stimulus and reuptake of membranes after secretion. The second, much faster, neuron-specific form of regulated secretion is release of neurotransmitters at the synapse. Release of neurotransmitters may occur within fractions of a second after a stimulus and reuptake is on the order of seconds. Indeed, synaptic vesicles may be recycled and ready for another round of neurotransmitter release within 1-2 minutes [64]. These two classes of regulated secretion will be discussed separately after a consideration of secretory vesicle biogenesis. 

From the slope of the straight line, the effective mixing cell volume was calculated to be 30.1 cm, with a 50% relaxation time of about 0.08 s. Similar mixing characteristics were observed following a step decrease (i.e., CO + N ), giving an effective mixing cell volume of 31.8 cm and a 50% relaxation time of 0.09 s. Since these response times of the reactor are not much faster than the time scale of the adsorption process (a halfscale relaxation time of about 0.2 s), the transients of the reactor cell were included in our analysis. For our simulations, the mixing cell volume was taken to be 31 cm. ... 

Parametric sensitivity analysis showed that for nonreactive systems, the adsorption equilibrium assumption can be safely invoked for transient CO adsorption and desorption, and that intrapellet diffusion resistances have a strong influence on the time scale of the transients (they tend to slow down the responses). The latter observation has important implications in the analysis of transient adsorption and desorption over supported catalysts that is, the results of transient chemisorption studies should be viewed with caution, if the effects of intrapellet diffusion resistances are not properly accounted for. 

In this expression p is a mass parameter associated to the electronic fields, i.e. it is a parameter that fixes the time scale of the response of the classical electronic fields to a perturbation. The factor 2 in front of the classical kinetic energy term is for spin degeneracy. The functional f [ i , ] plays the role of potential energy in the extended parameter space of nuclear and electronic degrees of freedom. It is given by. 

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