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SURROGATE DATA TEST

Group: dynamic analysis

Old definition:

The method of surragate data has become a central tool for validating the results of nonlinear dynamic analysis. The surrogate data method tests for a statistical difference between a test statistics (e.g. complexity/fractal metrics) computed for the original time series and for an ensemble of test statistics computed on linearised version of the data, the so-called "surrogate data". The major aspects of the surrogate data that need to be considered are:

1.the definition of the null hypothesis about the nonlinear dynamics underlying a given time series

2.the realization of the null hypothesis, i. e., the generation method for the surrogate data

3.the test statistic.

(Ali-Nait, A., Advanced Biosignal Processing, p. 322)

New definition:

Surrogate data methods are now almost invariably applied to potentially nonlinear time series data with the aim of discounting more hum-drum linear noise processes as the source of the observed phenomenon [23]. For the uninitiated, the entire procedure can be briefly de-scribed as follows. One starts with an observed time series which is to be tested against the null hypothesis of the surrogate data test. The standard surrogate data repertoire provides algorithms to test against the hypotheses of (i) independent and identically distributed noise; (ii) linearly filtered noise; or (iii) a monotonic nonlinear transformation of linearly filtered noise. Algorithms for each of these three hypotheses generate an ensemble of fake (artificial) time series data: the surrogate data. These surrogate data sets are guaranteed to have both the properties associated with the underlying null hypothesis and also are otherwise similar to the original observed data. In other words, these surrogate data are what independent repeated observations of the process that generated the original data would yield if that process were consistent with the null hypothesis. Now, one simply evokes whatever statistic is of interest (correlation dimension is a fairly orthodox choice) and compares the value of this statistic computed from the data to the distribution of values elicited from the surrogates. If the statistic value of the data deviates from that of the surrogates, then the null hypothesis may be rejected. Otherwise, it may not. Figure I summarises this process.

Surrogate data methods are often applied in conjunction with either linear or nonlinear modelling regimes. In some sense, surrogate data methods are equivalent to applying specific classes of (usually) parameter free models. In this context surrogate data methods can even be applied to test the residuals of specific models [I7]. However, the purposes of hypotheses testing and modelling are different. A model' will give a wealth of information about features that may or may not be in the data: the features one deduces from the model are attributable to that particular description of the data. On the other hand, surrogate methods provide a rigourous test of whether or not the data belongs to a particular class of systems. One can then be assured (or at least persuaded) that the data are amenable to that particular class of models, or not.

However, one may still think that it is possible to investigate features of data by modelling, for example, discrimination between linearity and nonlinearity. One simple example is as follows. To build time series models, a particularly convenient class is the pseudo-linear models, which are formed by linear combination of any type of functions such as linear and nonlinear functions They have been applied widely for building models of actual time series. When models we build contain nonlinear functions, one may think that as the data include nonlincarity, nonlinear functions are selected. On the other hand, when models contain only linear functions, one may think that as the data are linear, nonlinear functions are not selected.

(Charles W. Wang, Nonlinear Phenomena Research Perspectives, 55-57)

v Older definition is more useful for general understanding about the word. But mine is more detailed for mathematical understanding.

OPTICAL-FIBER PYROMETERS

Group: measurement and process control

Old definition:

Optical-fıber pyrometers are one of the most successful optical-Eber sensors in the field of process control in manufacturing. Typical applications are:

-Casting and rolling lines in steeland other metal plans

-Electric welding and annealing

-Furnaces in chemical and metal plants

-Fusion, epitaxial growth, and sputtering processs in the semiconductor industry

-Food processing, paper manufacturing, and plastic processing

(Soloman S., Sensors and Control Systems in Manufacturing, p.336)

New definition:

A section of these devices merely use an optical fibre to direct the emitted radiation to the detector. Strictly speaking, this section of fibre-optic devices is not a class by itself. The first such sensors used a sapphire rod of 3 mm diameter to pick up the energy from the target and transmit it to a detector. Contemporary fibre-optic pyrometers use a flexible bundle of glass fibres with or without a lens. The spectral response of these fibres extends to about 2 µm, though sonic materials such as fluorides have a wider band-pass. Some are useful at target temperatures FIS low as 100 °C. Beyond collection of radiant energy, fibre-optic glasses can be doped to serve directly as radiation emitters at hot spots so that the fiber optics serve as both the sensor and the media. A sapphire probe is commercially available that has the easing end coated by a refractory metal forming a blackbody cavity. The thin, sapphire rod thermally insulates and connects to an optical fibre as is shown in Fig. 10.48. A ratio method may be utilised to determine the temperature.

Fibre-optic thermometers are especially useful where it is difficult, dangerous or impossible to obtain or maintain a clear sighting path to the target, as in pressure or vacuum chambers. Fibre-optic thermometers have also been used to measure temperatures of turbine blades in gas turbines, and the temperature of small objects in induction heating coils. Next we pass on to an important aspect of temperature measurement which is considered necessary for all kinds of thermal probes. Of course, remote measurements by pyrometers, having no probes, do not come under its purview.

(Ghosh, Introduction to Measurements and Instrumentation, pg.348)

v My definition is more sufficient for explaining how the pyrometer works

MURA

Group: production | manufacturing wastes

There is no old definition

New definition:

Mura refers to unevenness or fluctuation in work, usually caused by fluctuating production plans. A simple example might be a production line that is producing difficult models for half the shift and simple models for the second half, so that workers strain for half the day and coast the other half. The lean system seeks to reduce mura through heijunka, or production levelling, by mixing models, for example.

Mura is traditional general Japanese term for unevenness, inconsistency in physical matter or human spiritual condition. It is also a key concept in the Toyota Production System and is one of the three types of waste (Muda, Mura. Muri; it identifies. Waste reduction is an effective way to increase profitability. Toyota merely picked up these three words with prefix mu-, which every Japanese know, as product improvement program or campaign.

Mura is avoided through Just In Time systems which are based on little or no inventory, by supplying the production process with the right part, at the right time, in the right amount, and first-in, first out component flow. Just in Time systems create a "pull system" in which each sub-process withdraws its needs from the preceding sub-processes, and ultimately from an outside supplier. When a preceding process does not receive a request or withdrawal it does not make more parts. This type of system is designed to maximize productivity by minimizing storage overhead. For example:

1. The assembly line “makes a request to,” or “pulls from” the Paint Shop, which pulls from Body Weld.

2. The Body Weld shop pulls from Stamping.

3. At the same time, requests are going out to supplliers for specific perts, for the vehicles that have been ordered by customers.

4. Small buffers accommodate minor fluctuations, yet allow continuous flow.

If parts or material defects are found in one process, Just-in-Time approach requires that the problem be quickly identified and corrected.

(Pascal Dennis, Lean Production Simplified: A Plain Language Guide to the World's Most Powerful production System, pg. 25)

(David A. Hounshell, From the American System to Mass Production, pg.486)

v My definition is satisfactory for understanding this approach.

PRESENT WORTH METHOD

Group: evaluation of engineering alternatives

Old definition:

The present worth method uses the equivalent present value of all current and future cash flows to evaluate the investment proporsal.The future cash are converted into their present worth by using the appropriate interest factors.Accordingly,some interest rate must be used in the factors.This interest rate is decided in advance and represents the rate-of-return criterion that the company is using to evaulate its investment opportunities.If the aggregate present worth of the project is positive,the return from the project exceeds the rate-of-return criterion.If the present worth of the project is negative,the project does not meet the rate-of-return criterion.

(Groover M.,Automotion,Production Systems and CIM Practice Hall 1st edition,p. 49)

New definition:

Many economists prefer the present worth method because it reveals the sum in today's rupee that is equivalent to a future cash flow stream. For example, Rs. 110 expected one year hence is worth only Rs. 100 today, if the rate of interest is 10 per cent, compounded annually. This means that Rs. 100 is the present value of Rs. 110 to be earned one year hence.

In the present worth method, the present worth of all cash inflows (revenues) is compared against the present worth of all cash outflows (costs) associated with an investment project. In this method of comparison, the cash flow of each alternative will be reduced to time zero by assuming an interest rate i. Then, depending on the type of decision, the best alternative will be selected by comparing the present worth amounts of the alternatives. The difference between the present worth of the cash flows (inflows — outflows) is referred to as the Net Present Worth (NPW) which determines whether or not the project is a feasible investment.

Steps Needed for Present Worth Comparison

The following are the steps involved in present worth comparison:

1. Estimate the interest rate that the firm wishes to earn on its investment.

2. Determine the service life of the project.

3. Ascertain the cash inflows over each service life

4. Find out the cash overflows over each service period

5. Calculate the net cash flows (inflows-outflows)

If there is a single investment proposal, then the decision whether a project will be selected or rejected can be made accordingly.

· If PW > 0, then the proposal will be selected. A positive NPW means that the equivalent worth of the inflows is greater than the equivalent worth of the outflows. So, the project will make profit.

· If PW < 0, then the investment project should he rejected. A negative NPW means the equivalent worth of the inflows is less than the equivalent worth of the outflows.

· If PW= 0, then one should remain indifferent to the investment.

In case there are mutually exclusive alternatives, then the present worth cash flows can be calculated by two prominent methods:

· Revenue-based present worth

· Cost-based present worth

In a revenue/profit-based cash flow diagram, the profit, revenue, salvage value (all inflows to an organization) will be assigned with a positive sign. The costs (outflows) will be assigned with a negative sign. In a cost-based cash flow diagram, on the other hand, the costs (outflows) will be assigned a positive sign and the profit, revenue, salvage value (all inflows), etc. will be assigned a negative sign. In revenue-based cases, the decision is to select the alternative with the maximum profit. Thus, the alternative with the maximum present worth will be selected. In cost bases cases, if the decision is to select the alternative with the minimum cost, then the alternative with the least present worth amount will he selected.

(Sasmita Mishra, Engineering Economics and Costing, pg.96)

v My definition includes more information so makes it easy to understand the meaning of the method.

FACING CYCLE (IN G-CODING)

Group: automation |numerical control and programming

There is no old definition

New definition:

The facing cycle is used when the major direction of cut is along the x axis. The cycle causes the profile to be roughed out by facing control passes on to after the last block of the profile. Two G72 blocks are needed to specify all the values.