Stability in time

Efficiency is still low and a-Si lacks stability, as it degrades and loses efficiency when first exposed to sunlight (Staebler-Wronski effect). However, the efficiency stabilizes in time. 

The V-modified Raney nickel catalyst showed noticeable stability in time-on-stream experiment for 55 h, and tolerated several heating-cooling cycles. It is... 

In a limited number of experiments, in which six different hydrogen peroxide concentrations were examined with four different pH values, the validity of the procedure used was checked by comparing the results obtained with the sensor electrode to those obtained by means of titration. The results obtained with the sensor electrode have a maximum divergence of 3% compared with the concentrations obtained by titration. The final aspect of the amperometrical detection method that was examined at laboratory scale is the stability in time of a calibrated sensor electrode. 

Maltodextrins (dextrose equivalent (DE) 4.0-7.0, 13.0-17.0 and 16.5-19.5) are proposed as novel chiral selectors for the construction of EPMEs for S-captopril assay [36]. The EPMEs can be used reliably for the assay of S-captopril as raw material and from pharmaceutical formulations as Novocaptopril tablets, using direct potentiometry. The best response was obtained when maltodextrin with higher DE was used for the electrode s construction. The best enantioselectivity and stability in time was achieved for the lower DE maltodextrin. L-Proline was found to be the main interferent for all proposed electrodes. The surface of the electrodes can be regenerated by simply polishing, obtaining a fresh surface ready to be used in a new assay. 

In human toxicology, more than in ecotoxicology, attention is given to the stability of the mixture. Because composition of mixtures may not be stable in time, it is important to get insight into the variability in components and their relative proportions. Refer to Chapter 1 for a discussion on mixture composition and its stability in time in relation to, for example, fate processes in the environment. Also, biotransformation may change the composition of a mixture inside the human body, and as a consequence affect its toxicity. See Chapter 2 for a discussion on this issue. 

The instability arises and evolves owing to thermodynamic fluctua tion (3.29). Such a fluctuation may cause complete system state decay (see, e.g., region V of unstable saddles in Figure 3.4). Flowever, it may also happen that the arising instability creates a new state of the system to be stabilized in time and space. An example is the formation of the limit (restricted) cycle in a system that involves the exceptional point of the unstable focus type. The orbital stability of such a system means exactly the existence of certain time stabilized variations in the thermody namic parameters (for example, the concentrations of reactants) that are... 

The composition of the material and the parameters investigated should remain unchanged over the entire period of use of the material. The study of the material s stability in time will mainly depend on its role. If the material is foreseen to be used in a short term interlaboratory study the stability has to be monitored only over the real duration of the exercise and additionally mimic situations which may be encountered during its short lifetime e.g. transport under severe climatic conditions. Stability studies may vary from some days to several years. The sources and risk of (in)stability should be studied or known before the RM is produced. They should be monitored on the batch of (C)RMs. This study can only be performed by scientists aware of the type of material and its potential sources of instability. Consequently, collaboration with the end-users is mandatory. 

Membran systems are known to play an important role in functioning biological objects (in mass transfer processes, passive and active transport of substance, regulation of an endocellular metabolism, in bio-energetics, etc.). Unique properties of biomembranes are caused by their structure, in particular, presence of bimolecular focused layers of lipids. At the same time, one of the main disadvantages of modelling lipid membran systems (monolayers, flat bilayers, liposomes), is their low stability in time and to action of external factors. 

The source in this instrumental set-up is the reference electrode, the most popular examples of which are the silver/silver chloride electrode or the mercury/mercury chloride (saturated calomel) electrode. The important requirements of a reference electrode are reversibility, reproducibility and stability in time. Often these are incorporated into the ISE housing so that it contains the working and reference electrodes together and this combination electrode is attached to the voltmeter. 

In general, micro-scale methods - for example, the formation of mineral precipitates in the pore space of a sediment waste body -will be employed rather than using large-scale enclosure systems such as clay covers or wall constructions. A common feature of geochemically designed deposits, therefore, is their tendency to increase overall stability in time, due to the formation of more stable minerals and closure of pores, thereby reducing water permeation. 

Fig. 2. Examples of substitution of a porphyrin complex for the enhancement of the selectivity and stability in time (adapted from refs. 17 and 18).

RuPcY and Co and Mn-tetraphenylporphyrin Y (tePPorY) have been examined as mimics for methane oxygenase (27). Table 5 gives relevant data. Traces of methanol seem to be obtained from methane but at reaction temperatures (above 573 K) where the stability in time of the catalysts was very limited as evidenced by the large CO2 yield. Personally, we have not yet been able to reproduce these data. 

For the purpose of hydrogen uptake or oxidation, two main strategies have been developed to ensure higher current collection and better stability in time (i) entrapment in a conductive matrix, and (ii) stable binding to a conductive network. 

Results about functionalization and cross-linking of polyolefins in different gases (inert gases, oxygen, nitrogen, air, etc.) will be presented. Some considerations about the stability in time of these modifications are also given. Experiments in model situations in plasma treatment of polyolefins are presented at the end of this section. 

Consequently, it allows a quick and simple determination of the optimal exposure time to ultrasound. Obtaining the optimum debundling of the CNTs, while minimizing as much as possible damage caused by sonication, by reducing the exposure time, are crucial issues — the sine qua non conditions to produce technically interesting C NT/polymer nanocomposites, among others. I n the same order of ideas, UV-Vis spectroscopy can also be used to quantitatively characterize the colloidal stability in time of CNT dispersions. ... 

When repeated transport experiments are performed, in which both the aqueous feed and receiving solutions are renewed every day while the membrane remains the same as in the first run, daily partitioning of the carrier from the SLM to the renewed aqueous solutions causes a decrease of the carrier concentration in the membrane and thus a decrease of Dm and proportionally of Pm- The evolution of the permeability measurements versus the number of runs is a way to describe SLM leaching by the aqueous solutions and characterizes SLM stability in time. 

Compared with other enzyme-based heterogeneous catalysts [43,120-122], this one has high esterification catalytic performances, associated with higher stability in time. Whatever the supports used in literature [40-43], the conversions are... 

The standard buffer solutions have been developed in a way so that each of them should have (1) inexpensive chemicals, (2) simple recipe, and (3) reproducibility and stability in time. 

We will briefly describe the modeling technology developed by Surdam et al. (1989a,b,c,d) and Surdam and MacGowan (1992) to predict the spatial distribution of carbonate stability in time-temperature space. 

We can distinguish two types of applications depending on whether the temperature of the thermistor is the tempeiatuie of the environment, or a result of its heating by the Joule effect [HIL 91], In the first case, thermistors are used as temperature sensors they provide excellent stability in time. In the second case, let The the temperature of the thermistor in service conditions. In a stationary regime, the electrical power is dissipated in the form of heat in the environment where temperature is... 

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