Exercise Meaningful in Having Good Mental Health

In this cross-sectional study, we analysed data from 1 237 194 people aged 18 years or older in the USA from the 2011, 2013, and 2015 Centers for Disease Control and Prevention Behavioral Risk Factors Surveillance System survey. We compared the number of days of bad self-reported mental health between individuals who exercised and those who did not, using an exact non-parametric matching procedure to balance the two groups in terms of age, race, gender, marital status, income, education l...

 We Must Think Outside the Rocket Equation

The rocket equation contains three variables. Given any two of these, the third becomes cast in stone. Hope, wishing, or tantrums cannot alter this result. Although a momentum balance, these variables can be cast as energies. They are the energy expenditure against gravity (often called delta V or the change in rocket velocity), the energy available in your rocket propellant (often called exhaust velocity or specific impulse), and the propellant mass fraction (how much propellant you need com...

 Latinos Less Likely to Be Online Than Whites

While about two-thirds of Latino (65%) and black (66%) adults went online in 2010, more than three-fourths (77%) of white adults did so. In terms of broadband use at home, there is a large gap between Latinos (45%) and whites (65%), and the rate among blacks (52%) is somewhat higher than that of Latinos. Fully 85% of whites owned a cell phone in 2010, compared with 76% of Latinos and 79% of blacks. Hispanics, on average, have lower levels of education and earn less than whites. Controlling f...