Vampire off revenants—are common in vampire folklore. Garlic is a common example, a branch of wild rose and hawthorn plant are said to harm vampires, and in Europe, sprinkling mustard seeds on the roof of a house was said to keep them away. Other apotropaics include sacred items, for example a crucifix, rosary, or holy water. Vampires are said to be unable to walk on consecrated ground, such as that of churches or temples, or cross running water. Although not traditionally regarded as an apotropaic, mirrors have been used to ward off vampires when placed, facing outwards, on a door (in
Cross-correlation referred to as cross-autocorrelation. In time series analysis, as applied in statistics, the cross-correlation between two time series is the normalized cross-covariance function. Let formula_37 represent a pair of stochastic processes that are jointly wide-sense stationary. Then the cross-covariance and the cross-correlation are given by Cross-covariance: Cross correlation coefficient: where formula_38 and formula_39 are the mean and standard deviation of the process formula_40, which are constant over time due to stationarity; and similarly for formula_41, respectively. formula_42 indicates the expected value. That the cross-covariance and cross-correlation are independent of "t" is precisely the additional information (beyond being individually wide-sense stationary)