Define and explain Variance and Standard Deviation. Walk me through their calculation formulas and discuss how quantitative analysts (Quants) apply them in finance. Provide a simple example of a daily return series and calculate its standard deviation.

请定义并解释方差（Variance）和标准差（Standard Deviation）的概念，包括它们的计算公式和在金融领域中如何被量化分析师（Quant）应用。请提供一个简单的日收益率序列示例，并计算其标准差。