Cyclic variations

There is a cyclic variation in the amount of sulphate found in rust formed on steel exposed at different times of the year (Fig. 3.3), and the amount depends on the month of the year rather than on the period of exposure, at least for periods of up to two years. Consequently, the month of exposure will have an important influence on the corrosion rate up to a year or so (see Table 3.2). In one test, specimens exposed for two months from September corroded at 0-035 mm/y compared with 0.0136 mm/y for specimens exposed from May, and the amount of rust formed on steel follows this cyclic pattern over periods of up to two years and possibly for... 

Much of the variation in these time series for the past 700 kyr can be described by a combination of a 100 kyr cycle plus additional cycles with periods of 20 and 40 kyr. This result immediately suggests that the ice-age cycles are caused by variations in the amount and seasonality of solar radiation reaching the Earth (insolation), because the 20, 40, and 100 kyr periods of climate history match the periods of cyclic variations in Earth s orbit and axial tilt, line hypothesis that these factors control climate was proposed by Milutin Milankovitch in the early part of the 20th century and is widely known as "Milankovitch Theory." It is now generally accepted that the Milankovitch variations are the root cause of the important 20 and 40 kyr climate cycles. The 100 kyr cycle, however, proves to be a puzzle. The magnitude of the insolation variation at this periodicity is relatively trivial, but the 100 kyr cycle dominates the climate history of the last 700 kyr. Further,... 

Dement, W. Kleitman, N. (1957). Cyclic variations in EEG during sleep and their relation to eye movements, body motility, and dreaming. Electroencephalogr. Clin. Neurophysiol. Suppl. 9, 673-90. 

As early as 1972, Kuhn described a model in which he assumed that RNA replication with a certain error rate could have occurred without the participation of enzymes. Natural phenomena with cyclic behaviour are an important factor in Kuhn s thinking these drive duplication processes. Examples are summer and winter, day and night, or high and low tide (whereby the latter were probably subject to greater variations on the primeval Earth than they are today). These rhythms were often linked with considerable temperature variations, which, for example, made possible the transition from double to single strand RNA (and vice versa). It can be assumed that the cyclic variations involved reactions in which monomers were linked to form polymers. 

We attribute the long-term and short-term 14C variations to cyclic variations in the 14C production rate Pi4 (t) which are... 

In ultrasonic relaxation measurements perturbation of an equilibrium is achieved by passing a sound wave through a solution, resulting in periodic variations in pressure and temperature.40,41 If a system in chemical equilibrium has a non-zero value of AH° or AV° then it can be cyclically perturbed by the sound wave. The system cannot react to a sound wave with a frequency that is faster than the rates of equilibration of the system, and in this case only classical sound absorption due to frictional effects occurs. When the rate for the host-guest equilibration is faster than the frequency of the sound wave the system re-equilibrates during the cyclic variation of the sound wave with the net result of an absorption of energy from the sound wave to supply heat to the reaction (Fig. 4). 

The objective of control is quite different. The purpose of control is to keep a process property, e.g. the composition, as close to a preset value as is technically possible and economically desirable. The deviation from the set point is caused by intentional or random fluctuations of the process condition. In order to control the fluctuating process, samples must be taken with such frequency and analyzed with such reproducibility and speed that the process condition can be reconstructed. From this reconstruction predictions can be made for the near future and control action can be optimal. Another goal can be the detection of nonrandom deviations, like drift or cyclic variations. This also sets the conditions for sampling frequency and sample size. 

A special type of heterogeneous objects exhibits cyclic changes of its properties. Frequencies of cyclic variations can be a sign of daily influences as temperature of the environment or shift-to-shift variations. Seasonal frequencies are common in environmental objects like air or surfacewater. 

Geologists in the nineteenth century deduced that the Earth has experienced several ice ages, during which the ice sheets that cover the poles today reached much farther afield. In 1930 the Serbian mathematician Milutin Milankovitch showed how changes in the shape of the Earth s orbit around the Sun could trigger an ice age by altering the seasonal distribution of sunlight at the planet s surface. There are three cyclic variations in the orbit, with periods of 23,000, 41,000, and 100,000 years. The interplay of these Milankovitch cycles produces a complex but predictable and slow variation in climate over hundreds of thousands of years. 

Warren JC, Cheatum SG, Greenwald GS, Barker KL (1967) Cyclic variation of uterine metabolic activity in the golden hamster. Endocrinology, 80 714-718. 

In Figure 5 the long-term component of the monthly O3 series at Arosa, Vigna di Valle and Lerwick is plotted. All cyclical variations are filtered and the decline is singled out. It is worth noting the inversion between Arosa (latitude 46.78°N) and Vigna di Valle (latitude 42.08°N) curves, due to the sites different altitudes. 

So far we have analyzed the environment-induced correction to the level splitting (the Lamb shift). Using the results above one can evaluate also the environment-induced correction to the Berry phase for a slow cyclic variation of the magnetic field B [17, 18, 20, 19]. 

Lapan, B., and M.M. Friedman. 1950. Glycogen and reducing substances in vaginal mucus Gestational and cyclical variations. Am J Obstet Gynecol 59 361. 

The Australian domestic nitric acid market was found to suffer from cyclical variations, with seasonal highs and lows each year. This fluctuation is attributed to the major acid consumers (fertilizer and explosives manufacturers) being susceptible to seasonal variations in demand, and to the level of world commodity prices. However, the overall trend has been for 3% annual growth. Current Australian production is 200 000 tonnes each year (100% acid basis). Exports from and imports into Australia are virtually non-existent. A protective barrier in the form of high shipping costs, has in the past effectively closed the domestic market. 

In experiments with cultured cells it has been shown that osteocytes, but not periosteal fibroblasts, are extremely sensitive to fluid flow, resulting in increased prostaglandin as well as nitric oxide production [104, 105], Three different cell populations, namely osteocytes, osteoblasts, and periosteal fibroblasts, were subjected to two stress regimes, pulsatile fluid flow and intermittent hydrostatic compression [104], Intermittent hydrostatic compression was applied at 0.3 Hz with a 13-kPa peak pressure. The pulsatile fluid flow was a fluid flow with a mean shear stress of 0.5 Pa with cyclic variations of 0.02 Pa at 5 Hz. The maximal hydrostatic pressure rate was 130 kPa/sec and the maximal fluid shear stress rate was 12 Pa/sec. Under both stress regimes, osteocytes appeared more sensitive than osteoblasts, and osteoblasts more sensitive than periosteal fibroblasts. However, despite the large difference in peak stress and peak stress rate, pulsatile fluid flow was more effective than intermittent hydrostatic compression. Osteocytes, but not the other cell types, responded to 1 hour pulsatile fluid flow treatment with a sustained prostaglandin E2 upregula-... 

Clearly these large fluctuations are due to cyclic variations not turbulent fluctuations. The dashed curve is an attempt to remove this cyclic variation effect by using the most probable density value as the mean value of a normal distribution. The standard deviation of the distribution is determined from fitting the data to the side of the new mean that has not been distorted by flame arrival. The reduction of the apparent fluctuations near the flame arrival crank angle is dramatic. Both curves of Figure 5 have had the Poisson statistical fluctuations subtracted. 

Many hormonal secretion processes also exhibit strong circadian components. This is true, for instance, for cortisol, antidiuretic hormone, and growth hormone. The secretion of growth hormone is markedly increased during the early periods of sleep, and the secretion of antidiuretic hormone also reflects the sleep-wake cycle. The mechanisms underlying these oscillations can often be traced back to cyclical variations in the activity of the central nervous system. At the same time, the circadian rhythm modulates the above-mentioned ultradian oscillations. 

Continuous emulsion copolymerization processes for vinyl acetate and vinyl acetate—ethylene copolymer have been reported (59—64). Cyclic variations in the number of particles, conversion, and particle-size distribution have been studied. Control of these variations based on on-line measurements and the use of preformed latex seed particles has been discussed (61,62). 

Szot RJ, Murphy SD. 1971. Relations between cyclic variations in adrenocortical secretory activity in rats and the adrenocortical response to toxic chemical stress. Environ Res 4 530-538. 

Badger, T. M., Hoog, J.-O, Ronis, M. J. J., and Ingelman-Sundberg, M. Cyclic variation of class I alcohol dehydrogenase in male rats treated with ethanol. Biochem. Biophys. Res. Commun. 274, 684-688, 2000. 

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