Validation of results

Because mesoscale methods are so new, it is very important to validate the results as much as possible. One of the best forms of validation is to compare the computational results to experimental results. Often, experimental results are not available for the system of interest, so an initial validation calculation is done for a similar system for which experimental results are available. Results may also be compared to any other applicable theoretical results. The researcher can verify that a sulficiently long simulation was run by seeing that the same end results are obtained after starting from several different initial configurations. 

Of all the topics discussed in this text, mesoscale simulations are probably at the most infantile stage of development. The idea of the mesoscale calculations is very attractive and physically reasonable. However, it is not as simple as one might expect. The choice of bead sizes and parameters is crucial to obtaining physically relevant results. More complex bead shapes are expected to be incorporated in future versions of these techniques. When using one simulation technique to derive parameters for another simulation, very small errors in a low-level calculation could result in large errors in the final stages. 

The current generation of mesoscale calculations has proven useful for pre- 

In principle, mesoscale methods can provide a means for connecting one type of simulation to another. For example, a molecular simulation can be used to describe a lipid. One can then derive the parameters for a lipid-lipid potential. These parameters can then be used in a simulation that combines lipids to form a membrane, which, in turn, can be used to compute parameters describing a membrane as a flexible sheet. Such parameters could be used for a simulation with many cells in order to obtain parameters that describe an organ, which could be used for a whole-body biological simulation. Each step, in theory, could be modeled in a different way using parameters derived not from experiment but from a more low-level form of simulation. This situation has not yet been realized, but it is representative of one trend in computational technique development. 

The applicability of mesoscale techniques to systems difficult to describe in any other manner makes it likely that these simulations will continue to be used. At the present time, there is very little performance data available for these simulations. Researchers are advised to carefully consider the fundamental assumptions of these techniques and validate the results as much as possible. 

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There have been some questions raised about the validity of results of extensive and sequential extraction methods. There is the possibility that species of an analyte may change during the extraction process. It is also possible that a species may be liberated and then reabsorbed during extraction or subsequent isolation. The same or similar question could be raised about various initial sampling and subsequent storage methodologies as described next. In spite of these questions, the BCR methodology has been widely accepted [39-41],... 

The analyst needs access to validation data to support validity of results... 

Uncertainty is an unfortunate wording since for non-experts it implies doubts on the validity of results. Certainty would be a better choice, but it certainly will not be possible to change this term. 

It is very important to evaluate the accuracy and the regions of applicability of the methods developed for the effective study of the structure and properties of many-body systems, to demonstrate their utility on selected problems of genuine physical and chemical interest, to improve understanding of the fundamentals on which these methods are based, and to perform mutual checking and validation of results obtained by various... 

Multivariate calibration models are often built on an underdetermined data set, that is, more wavelengths than samples. The use of powerful data reduction techniques, such as PCR and PLS, makes assessing the model validity an extremely important aspect of the analysis procedure. Here, we present four important criteria on which to judge the validity of results from multivariate calibration. 

The question of direct observation and its meaning for the validity of results or their interpretation seems to be misunderstood by some authors. Direct observation is used occasionally to support claims of significance and authenticity. Therefore, a clarification seems to be in order. Strictly, the term direct observation means nothing more than that some property of an intermediate is measured... 

The technique may be subject to a number of positive and/or negative systematic errors, depending on the element to be determined, the instrumental technique used, the matrix composition, and still other factors. However, as shown in Table 2.2, there is a tendency towards the use of the standard additions method and CRMs to minimize some possible matrix effects and to ensure validity of results. Nevertheless, it appears from the survey of the literature that the solubilization sampling introduction technique compares favorably with other atomic spectrometric methods for the determination of trace elements in a variety of matrices. 

The literature frequently reports very high concentrations of elements, for example, Cd and Pb, in supposedly uncontaminated foodstuffs that would normally contain extremely low levels of these elements. It is rather unusual to see that those high and unusual results are checked in any way, which, of course, renders such surveys highly unreliable. Validation of results, both normal and abnormal, should always be performed, also in the interests of the analyst. 

SEC and anionic HPLC-Q-ICP-MS can be used to determine the approximate molecular weight of Se-containing proteins and identify fractions for seleno-amino acid analysis. The coupling of anion and cation HPLC and Q-ICP-MS also allows selenoamino acids in hydrolyzed protein extracts to be measured. However, the lack of knowledge about species, low Se concentrations, and lack of detection power make quantification of Se species difficult. The concurrent use of HPLC-MS-MS is needed to confirm the identity of Se species, but at present the low concentrations of Se in extracts preclude its use. It is essential that CRMs are used to confirm the validity of results regarding total Se and Se species. 

We have shown that, with the exception of DMPO, all spin traps studied exerted a limited negative inotropic and chronotropic effect. This effect was only present at the highest concentrations studied [116]. Bolli et al. [104-108] have previously reported that intracoronary infusions of PBN at concentrations greater than 20 mmol/1 blood caused profound toxicity, as manifest by the rapid, complete and persistent loss of cardiac contractile function, in the absence of ischemia and reperfusion, in open-chest dogs. These authors subsequently used PBN at much lower concentrations ( 1.6 mmol/1) in all of their experiments, and questioned the validity of results obtained in previous studies where the... 

Use of a standardized methodology for ascertaining data on exposure, outcome, or other relevant covariates is an essential feature of an epidemiological study that enhances the validity of results. All study participants should be subjected to the same method for collecting data. In-person interviews are reported to provide the most reliable self-reported exposure data, followed by telephone or mail survey techniques. Standardized forms for collecting existing data also should be used. 

The analytical plan of epidemiological studies should use descrip tive and analytical techniques in describing the sample and results. Descriptive statistics, such as frequency distributions, cross-tabulations, measures of central tendency, and variation, can help explain underlying distributions of variables and direct the assessment of appropriateness of more advanced statistical techniques. Careful weighing of study findings with respect to the design and methods helps to ensure the validity of results. 

Nauchitel and Pertsin have studied the melting properties of 13-, 19-, and 55-particle Lennard-Jones clusters.Questioning the validity of results obtained from free-volume simulations of such systems, they have used hard-sphere boundaries to constrain their clusters to finite volumes. The results of Nauchitel and Pertsin are most interesting for the 55-particle cluster. For certain ranges of temperature and mean density, structural evidence for surface melting was obtained projections of the cluster s coordinates, and radial density distribution functions, like those given in Fig. 17, characterize the cluster as a 13-particle icosahedral core surrounded by a fluidlike shell. However, dynamic calculations like those described for other clusters in the previous section have yet to be obtained to determine how fluidlike these outer atoms really are. 

Any information used to support a medical or promotional claim must include sufficient detail and be of adequate quality to allow evaluation of the validity of results and hence the claim. Such substantiating information must not rely solely on data on file. 

Results verification is totally different from results validation. Results validation (point 4.7.5. and 5.9. of NBN-EN-ISO-CEI 17025 standard) shows, each year, or when it is judged necessary, that a given laboratory has the capacity to apply a particular method, repetitively, in respect of obtained data during initial validation. Trueness and statistical dispersion of results are the basis of the definition of the uncertainty of the standard of measurement [16] and, in some cases, the basis for the definition of the limit of detection and quantification. Management of data from validation results, as control card, could permit the detection and control of eventual deviation. Validation of results is the internal quality control procedure which verifies the stability of performance of the methods for which accreditation is sought, in the limited-scope procedural context. 

Prediction of the consequences of degradation release conventionally involves data and models for three steps of analysis geosphere transport, biosphere transport, and biosphere consequences. I will discuss these and add two others analysis, rather than assumption, of repository degradation, and consideration of the geosphere/biosphere interface and its effect on biosphere consequences. These refinements to safety assessment procedures, when developed and implemented, can be expected to aid validation of results. 

Our studies also show that special care should be paid with respect to the extrapolation of data to the in vivo situation and validation of results in studies with animals will currently remain necessary. However, further experience with these and other complementary in vitro models might eventually result in a significant reduction in the number of animals needed for these experiments. 

All the tests are designed for screening, and as such should be used only for preliminary screening for the presence of the nut residue. The validity of results obtained with the tests should preferably be viewed in conjunction with data from a validated laboratory assay (Table 20.8). Irrespective of the shade of a line observed in any of the lateral flow tests, a response is recorded (i.e., a positive for a test line appearing in two-line tests to indicate the presence of nut proteins). Additionally, a negative test result cannot exclude the possibility that the food contains the nut proteins because they are either distributed unevenly or may be below the detection limit of the test. 

Interpretation is the final phase of LCA. In this phase, results from the previous phases are combined so that conclusions and recommendations can be made. To ensure the validity of results used for interpretation, statistical analysis is often performed to quantify uncertainty. Despite a standardized method for LCA, many challenges remain for LCA in environmental evaluafion of nanotechnology. 

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