In epidemiology, Mendelian randomization (commonly abbreviated to MR) is a method using measured variation in genes to interrogate the causal effect of an exposure on an outcome. Under key assumptions (see below), the design reduces both reverse causation and confounding, which often substantially impede or mislead the interpretation of results from epidemiological studies.

In mathematics, any vector space V has a corresponding dual vector space (or just dual space for short) consisting of all linear forms on V, together with the vector space structure of pointwise addition and scalar multiplication by constants.

In mathematics and group theory, a block system for the action of a group G on a set X is a partition of X that is G-invariant. In terms of the associated equivalence relation on X, G-invariance means that

In a dual-thrust solid propellant rocket engine, the propellant mass is composed of two different types (densities) of fuel. In the case of a tandem dual-thrust motor, the fuel closest to the rocket nozzle burns fast and the fuel further into the motor's body burns slower.

In a dual-thrust solid propellant rocket engine, the propellant mass is composed of two different types (densities) of fuel. In the case of a tandem dual-thrust motor, the fuel nearest to the rocket nozzle burns fast, and the fuel further into the motor's body burns slower.

A system of signalling on railroads. The essence of the system consists in having signal posts or stations all along the road at distances depending on the traffic. The space between each two signal posts is termed a block. From the signal posts the trains in day time are signalled by wooden arms termed semaphores, and at night by lanterns. The arms may be moved by hand or by automatic mechanism depending in part on electricity for carrying out its functions. Thus in the Westinghouse system the semaphores are moved by pneumatic cylinders and pistons, whose air valves are opened and shut by the action of solenoid magnets, q. v. The current of these magnets is short circuited by passing trains, so as to let the valves close as the train passes the signal post. The block system causes the semaphore to be set at "danger" or "caution," as the train enters the next block. Then the following train is not allowed to enter the block until the safety signal is shown. The Westinghouse system provides for two semaphores on a post, one indicating "danger" as long as the train is on the next block; the other indicating "caution" as long as the train is on the next two blocks. The rails form part of the circuit, their joints being bridged by copper wire throughout the block, and being insulated where the blocks meet.

Dual wielding is the technique of using two weapons, one in each hand for training or combat. It is not a common combat practice.

Atrioventricular block (AV block) is a type of heart block that occurs when the electrical signal traveling from the atria, or the upper chambers of the heart, to ventricles, or the lower chambers of the heart, is impaired. Normally, the sinoatrial node (SA node) produces an electrical signal to control the heart rate.