Variables uncontrolled

Known Variables - Uncontrollable or Controllable Within Limits A long series of experiments sometimes involves situations where variation due to changes in one or more factors is known to exist, but where these factors cannot be completely controlled. An example is raw-material quality. Different lots of raw material or catalyst used in an experimental programme may sometimes vary in chemical composition, impurities, activity, etc. Since these items may not be within the control of the user and may not easily be worked into a balanced experimental design, the differences should at least be recorded and their effect taken into consideration during the analysis... 

As a byproduct of the juice concentrate industry, an estimated 500,000 to 1,000,000 tons of wet pulp are produced each crop year. Unlike suggested more exotic sources of dietary fiber, orange pulp is already an established, commonly consumed food component in the American diet. The functional and nutrient properties of washed orange pulp are intimately related to a series of factors. The foremost of these is the orange species but also significant are climatic and crop year variants, harvest maturity, expression and extraction processing variables, uncontrolled enzymatic and microbial activity as well as method of drying. Because of variations in the material, application and development as a fiber has been limited. 

The growth processes of melt agglomerates are highly sensitive to formulation, processing, and equipment variables. Uncontrollable melt agglomeration is... 

The second class, indeterminate or random errors, is brought about by the effects of uncontrolled variables. Truly random errors are as likely to cause high as low results, and a small random error is much more probable than a large one. By making the observation coarse enough, random errors would cease to exist. Every observation would give the same result, but the result would be less precise than the average of a number of finer observations with random scatter. 

Despite the variety of methods that had been developed, by 1960 kinetic methods were no longer in common use. The principal limitation to a broader acceptance of chemical kinetic methods was their greater susceptibility to errors from uncontrolled or poorly controlled variables, such as temperature and pH, and the presence of interferents that activate or inhibit catalytic reactions. Many of these limitations, however, were overcome during the 1960s, 1970s, and 1980s with the development of improved instrumentation and data analysis methods compensating for these errors. ... 

In order to operate a process facility in a safe and efficient manner, it is essential to be able to control the process at a desired state or sequence of states. This goal is usually achieved by implementing control strategies on a broad array of hardware and software. The state of a process is characterized by specific values for a relevant set of variables, eg, temperatures, flows, pressures, compositions, etc. Both external and internal conditions, classified as uncontrollable or controllable, affect the state. Controllable conditions may be further classified as controlled, manipulated, or not controlled. Excellent overviews of the basic concepts of process control are available (1 6). 

Uncontrolled Variables and Randomization. A number of further variables, such as ambient conditions (temperature, pressure, etc), can be identified but not controlled, or are only ha2ily identified or not identified at all but affect the results of the experiment. To ensure that such uncontrolled variables do not bias the results, randomisation is introduced in various ways into the experiment to the extent that this is practical. 

Randomization means that the sequence of preparing experimental units, assigning treatments, miming tests, taking measurements, and so forth, is randomly deterrnined, based, for example, on numbers selected from a random number table. The total effect of the uncontrolled variables is thus lumped together into experimental error as unaccounted variabiUty. The more influential the effect of such uncontrolled variables, the larger the resulting experimental error, and the more imprecise the evaluations of the effects of the primary variables. Sometimes, when the uncontrolled variables can be measured, their effect can be removed from experimental error statistically. 

Uncontrolled line side diode bridge rectifier. When a variable d.c. is required, it can be replaced by thyristors. Mechanical braking or non-regenerative braking-. 

Improperly set tolerances and uncontrolled variation are one of the greatest causes of defects, scrap, rework, warranty returns, increased product development cycle time, work flow disruption and the need for inspection (Gerth and Hancock, 1995). If manufacturing processes did not exhibit variation, quality problems would not arise, therefore reducing the effects of variability at the design stage, in a cost-effective way, improves product quality (Bergman, 1992 Kehoe, 1996). 

Cycling A periodic change in the controlled variable from one value to another. If uncontrolled this is known as hunting. 

Even though equipment operations have understandable but controllable variables that influence processing, the usual most uncontrollable variable in the process can be the plastic material. The degree of properly compounding or blending by the plastic manufacturer, converter, or in-house by the fabricator is important. Most additives, fillers, and/or reinforcements when not properly compounded will significantly influence processability and fabricated product performances. 

During polymerization, when Initiator Is Introduced continuously following a predetermined feed schedule, or when heat removal Is completely controllable so that temperature can be programmed with a predetermined temperature policy, we may regard functions [mo(t ], or T(t), as reaction parameters. A common special case of T(t) Is the Isothernral mode, T = constant. In the present analysis, however, we treat only uncontrolled, batch polymerizations In which [mo(t)] and T(t) are reaction variables, subject to variation In accordance with the conservation laws (balances). Thus, only their Initial (feed) values, Imo] andTo, are true parameters. 

Randomized, controlled clinical trials reduce bias and variability by a process of selection, randomization and standardization of treatment, and often take place under artificial conditions isolated from those of routine clinical practice (Freemande et al, 1993 Simon et al, 1995b). Yet it is the uncontrolled interactions of a dmg technology with patients, health-care workers and the system of health care that ultimately lead to much of the variability in outcomes and expenditures in clinical practice. Thus the value of RCTs in evaluating cost-effectiveness in clinical practice maybe limited (Reeder, 1995 Simon et al, 1995b Hotopf et al, 1996). 

We will see that CLS and ILS calibration modelling have limited applicability, especially when dealing with complex situations, such as highly correlated predictors (spectra), presence of chemical or physical interferents (uncontrolled and undesired covariates that affect the measurements), less samples than variables, etc. More recently, methods such as principal components regression (PCR, Section 17.8) and partial least squares regression (PLS, Section 35.7) have been... 

Cohen and Coon observed that the response of most uncontrolled (controller disconnected) processes to a step change in the manipulated variable is a sigmoidally shaped curve. This can be modelled approximately by a first-order system with time lag Tl, as given by the intersection of the tangent through the inflection point with the time axis (Fig. 2.34). The theoretical values of the controller settings obtained by the analysis of this system are summarised in Table 2.2. The model parameters for a step change A to be used with this table are calculated as follows... 

Many of the coagulation factors measured by global coagulation tests have limited stability, and the time and temperature of storage of sample will affect their measurements. Concepts of analyte stability and half-life in plasma extend to markers measured by immunoassay. Markers of platelet activation are affected by artifactual activation in vitro upon collection of the blood specimen. This section will highlight some of the nonanalytical variables that, if uncontrolled, can lead to spurious results and thus affect the interpretation of laboratory data. 

Unconsolidated ocean deposits, 17 686-691 Uncontrolled variables, 3 388-389 Uncouplers, 14 349 Uncoupling proteins... 

---