Question

what are the advantage of charge transfer device, ccd and cid? over PMT

Preason (6) 10. What is gained by analyzing a larger number of replicates of a sample? What are the practical limitations on minimizing the standard deviation? more pollakin si accuracyf More bius more, higher beller. samples - Pacuracy b 8

Answer 1

limitations on minimizing the standard deviation The population mean of the distribution of sample means is the same as the population mean of the distribution being sampled from..... Thus as the sample size increases, the standard deviation of the means decreases, and as the sample size decreases, the standard deviation of the sample means increases. A low standard deviation indicates that the data points tend to be very close to the mean. A high standard deviation indicates that the data points are spread out over a large range Standard deviation is a popular measure of variability because it returns to the of values. onginal units of measure of the data set Minimizing the standard deviation is the same as minimizing the variance. However, the mean of the sums is fixed, so minimizing the variance is the same as minimizing the sum of squares of the group-values. This is getting a bit closer to a 'standard' optimization problem.

BENEFITS A Measure Variation Replicates improve the measurement of variation. Normally, if only one array exists per condition, then fold change is used to determine differential expression However, the variation of the expression level for each gene is different and unknown Multiple studies have shown that fold change multiple measurement of variation can be estimated. If the data follow an on its own is an unreliable indicator1,2. If measurements (1e., replicates) exist for each gene within each condition, the approximately normal distribution, the t-test or its variants reveal significant differential expression. If the data distribution is unclear, non-parametric tests such as the Mann-Whitney test can be applied Several publications make specific recommendations on the number of replicates required to detect various fold changes B.Increase Precision Averaging across replicates enhances the precision of measurements If the standard deviation of an expression measurement is s, then the standard deviation of the replicates is. As the number of replicates increases, both the detectable average across n difference from background and the detectable fold change decrease. C. Detect Outliers The presence of outlier samples interpretation of data. Most array platforms have internal controls that detect various problems in an experiment. However, internal controls may not identify all issues. A more powerful approach is also to consider the correlation between replicates. Subtle problems with the array, the sample, or the experimental procedure often become obvious in a pair- wise plot of replicate measurements. Data To illustrate the points above, a data set can have a severe impact on the 15

Q) what are the advantage of charge tranfer device, ccd and cid Ans= This structure has the advantages of higher transfer efficiency and lower dark current, from reduced surface recombination. The penalty is smaller charge capacity, by a factor of 2-3 compared to the surface-channel CCD A charge-coupled device (CCD) is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value This is achieved by "shifting the signals between stages within the device one at a time. CCDS move charge between capacitive bins in the device, with the shift allowing for the transfer of charge between bins. Carefully designing and controlling experiments is as important as the execution of the experiment itself. One approach that ensures greater experimental success in gene expression studies using microarrays is the incorporation of replicates. Replication of conditions lends statistical power that increases the confidence of the conclusions drawn from these experiments. Using replicates offers three major advantages: . Replicates can be used to measure variation in the experiment so that statistical tests can be applied to evaluate differences. Averaging allows smaller changes to be detected replicates increases the precision of gene expression measurements and across - Replicates the arr can be compared to locate outlier results that may occur due to aberrations within