Van der Waals forceIn molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and therefore more susceptible to disturbance. The van der Waals force quickly vanishes at longer distances between interacting molecules. Named after Dutch physicist Johannes Diderik van der Waals, the van der Waals force plays a fundamental role in fields as diverse as supramolecular chemistry, structural biology, polymer science, nanotechnology, surface science, and condensed matter physics.
Bounded variationIn mathematical analysis, a function of bounded variation, also known as BV function, is a real-valued function whose total variation is bounded (finite): the graph of a function having this property is well behaved in a precise sense. For a continuous function of a single variable, being of bounded variation means that the distance along the direction of the y-axis, neglecting the contribution of motion along x-axis, traveled by a point moving along the graph has a finite value.
Retractor (medical)A retractor is a surgical instrument used to separate the edges of a surgical incision/wound or to hold away certain organs and tissues (i.e. to provide tissue retraction) so that body parts underneath may be accessed during surgical operations. The broad term retractor typically describes a simple steel tool possessing a curved, hooked, or angled blade, which is manually manipulated to help maintain a desired position of tissue during surgery. More sophisticated retractors may be clamped in place (usually to a tableside frame) or suspended at the end of a robotic arm.
