Thus, polygyny may also be due to a lower male: female ratio in these areas but this may ultimately be due to male infants having increased mortality from infectious diseases. Another example is that poor socioeconomic factors may ultimately in part be due to high pathogen load preventing economic development. Fossil record
Evidence of infection in fossil remains is a subject of interest for paleopathologists, scientists who study occurrences of injuries and illness in extinct life forms. Signs of infection have been discovered in the bones of carnivorous dinosaurs. When present, however, these infections seem to tend to be confined to only small regions of the body. A skull attributed to the early carnivorous dinosaur Herrerasaurus ischigualastensis exhibits pit-like wounds surrounded by swollen and porous bone. The unusual texture of the bone around the wounds suggests they were affected by a short-lived, non-lethal infection. Scientists who studied the skull speculated that the bite marks were received in a fight with another Herrerasaurus. Other carnivorous dinosaurs with documented evidence of infection include Acrocanthosaurus, Allosaurus, Tyrannosaurus and a tyrannosaur from the Kirtland Formation. The infections from both tyrannosaurs were received by being bitten during a fight, like the Herrerasaurus specimen. Outer space
A 2006 Space Shuttle experiment found that Salmonella typhimurium, a bacterium that can cause food poisoning, became more virulent when cultivated in space.
A perforation is a small hole in a thin material or web. There is usually more than one perforation in an organized fashion, where all of the holes collectively are called a perforation. The process of creating perforations is called perforating, which involves puncturing the workpiece with a tool. Perforations are usually used to allow easy separation of two sections of the material, such as allowing paper to be torn easily along the line. Packaging with perforations in paperboard or plastic film is easy for consumers to open. Other purposes include filtrating fluids, sound deadening, allowing light or fluids to pass through, and to create an aesthetic design.Various applications include plastic films to allow the packages to breathe, medical films, micro perforated plate and sound and vapor barriers. Processes
Pins and needles
Rotary pinned perforation rollers are precision tools that can be used to perforate a wide variety of materials. The pins or needles can be used cold or heated. Cold perforation tools include needle punches. There are a handful of manufacturers that specialize in hot and cold needle perforation tooling and equipment. In materials that have elasticity this can result in a "volcano" hole that is preferred in many applications. Pinned rollers can be made from a variety of materials, including plastic, steel, and aluminum. In more brittle films, cold perforation can cause slitting rather than creating a round hole, which can jeopardize the materials integrity under pressure. The solution to this is often heating the pin; i.e. hot pin perforation.