| RACT (reasonably available control technology.)
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| Applied to the goals of the Clean Air Act, EPA-approved forms of technology that will reduce the output of industrial air pollutants. (See MACT)
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| Rad (radiation absorbed dose)
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| Measure of the amount of energy deposited in a tissue or some other medium struck by radiation. One rad = 100 ergs of energy deposited in one gram of tissue.
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| Radioactive
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| An unstable isotope that decays spontaneously and releases subatomic particles or units of energy.
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| Radioactive decay
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| A change in the nuclei of radioactive isotopes that spontaneously emit high-energy electromagnetic radiation and/or subatomic particles while gradually changing into another isotope or different element.
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| Radioactive emissions
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| Any of various forms of radiation and/or particles that may be given off by unstable isotopes. Many such emissions have very high energy and can destroy biological tissues or cause mutations leading to cancer or birth defects.
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| Radioactive isotope
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| An unstable form of an element that spontaneously emits either high-energy electromagnetic radiation or subatomic particles (or both). The decay rate describes the time necessary for a radioactive isotope to change to a stable element.
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| Radioactive materials
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| Substances that are or that contain unstable isotopes and that consequently give off radioactive emissions. (See isotope and radioactive emissions.)
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| Radioactive wastes
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| Waste materials that contain, are contaminated with, or are radioactive substances. Many materials used in the nuclear industry become wastes because of their contamination with radioactive substances.
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| Radioactivity
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| Radiation released from unstable nuclei. See alpha and beta particles and gamma rays.
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| Radioisotope
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| An isotope of an element that is unstable and may tend to gain stability by giving off radioactive emissions. (See isotope and radioactive decay).
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| Radionucleides
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| Isotopes that exhibit radioactive decay.
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| Radionuclides
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| Radioactive forms (isotopes) of elements.
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| Radon
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| An odorless, colorless, radioactive gas produced by the radioactive decay of natural radium.
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| Rain shadow
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| Dry area on the downwind side of a mountain.
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| Rainforest
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| A forest with high humidity, constant temperature, and abundant rainfall (generally over 380 cm [150 in] per year); can be tropical or temperate.
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| Range of tolerance
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| The range of conditions within which an organism or population can survive and reproduce, for example, the range from the highest to lowest temperature that can be tolerated. Within the range of tolerance is the optimum, or best, condition.
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| Rangeland
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| Grasslands and open woodlands suitable for livestock grazing.
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| Rangeland
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| Grazing land for cattle, sheep, and other domestic livestock.
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| Raprenox
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| A process to reduce nitrogen oxide emissions by mixing combustion gases with isocyanic acid, which converts nitrogen oxides to dimolecular nitrogen gas.
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| Raw sludge
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| The untreated organic matter that is removed from sewage water by letting it settle. It consists of organic particles from fees, garbage, paper, and bacteria.
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| Raw wastewater
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| (See raw sludge)
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| Reactive government
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| A government that lives and acts for today, addressing present-day problems as they arise. Shows little or no concern for long-term issues and solutions. Contrast with proactive government.
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| Reactor core
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| Assemblage of fuel rods and control rods inside a reactor vessel. Bathed by water to help control the rate of fission and absorb the heat.
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| Reactor vessel
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| Steel-walled vessel that contains the nuclear reactor.
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| Real price (or cost)
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| The price of a commodity or service in fixed dollars, that is, the value of a dollar at an earlier time. Helpful way to determine whether a resource has experienced a real increase in cost or whether higher costs are simply due to inflation.
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| Recharge area
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| With reference to groundwater, the are over which infiltration and resupply of a given aquifer occurs.
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| Recharge zone
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| Area where water infiltrates into an aquifer.
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| Reclamation
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| Chemical, biological, or physical clean-up and reconstruction of severely contaminated or degraded sites to return them to something like their original topography and vegetation.
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| Recoverable resources
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| Those accessible with current technology but not economical under current conditions.
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| Re-creation
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| Construction of an entirely new biological community to replace one that has been destroyed on that or another site.
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| Recruitment
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| With reference to populations, the maturation and entry of young into the adult breeding population.
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| Recycling
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| Reprocessing of discarded materials into new, useful products; not the same as reuse of materials for their original purpose, but the terms are often used interchangeably.
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| Red tide
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| A population explosion or bloom of minute, single-celled marine organisms called dinoflagellates. Billions of these cells can accumulate in protected bays where the toxins they contain can poison other marine life.
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| Reduced tillage systems
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| Systems, such as minimum till, conserve-till, and no-till, that preserve soil, save energy and water, and increase crop yields.
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| Reduction factors
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| Abiotic and biotic factors that tend to decrease popullation growth and help balance populations and ecosystems, offsetting growth factors.
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| Refuse-derived fuel
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| Processing of solid waste to remove metal, glass, and other unburnable materials; organic residue is shredded, formed into pellets, and dried to make fuel for power plants.
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| Regenerative farming
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| Farming techniques and land stewardship that restore the health and productivity of the soil by rotating crops, planting ground cover, protecting the surface with crop residue, and reducing synthetic chemical inputs and mechanical compaction.
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| Regulations
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| Rules established by administrative agencies; regulations can be more important than statutory law in the day-to-day management of resources.
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| Rehabilitate land
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| A utilitarian program to make an area useful to humans.
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| Rehabilitation
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| To rebuild elements of structure or function in an ecological system without necessarily achieving complete restoration to its original condition.
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| Relative humidity
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| At any given temperature, a comparison of the actual water content of the air with the amount of water that could be held at saturation.
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| Relativists
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| Those who believe moral principles are always dependent on the particular situation.
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| Rem (roentgen equivalent man)
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| Measure that accounts for the damage done by a given type of radiation. One rad = one rem for X rays, gamma rays, and beta particles, but one rad = 10 to 20 rems for alpha particles, because they do more damge.
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| Remediation
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| Cleaning up chemical contaminants from a polluted area.
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| Renewable energy
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| Energy sources, namely solar, wind, and geothermal, that will not be depleted by use.
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| Renewable resources
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| Resources normally replaced or replenished by natural processes; resources not depleted by moderate use; examples include solar energy, biological resources such as forests and fisheries, biological organisms, and some biogeochemical cycles.
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| Replacement fertility/level
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| The fertility rate that will just sustain a stable population.
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| Reproductive age
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| Age during which most women bear their offspring.
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| Reproductive isolation
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| One of the processes of speciation, involving anything that keeps individuals or subpopulations from interbreeding.
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| Reproductive strategy.
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| The particular methodologies seen in nature to enhance the change of subsequent generations-for example, producing massive numbers of young but offering no care or protection vs. producing few young and caring for them.
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| Reserves
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| The amount of a mineral resource (including oil, coal, and natural gas) remaining in Earth that can be exploited using current technologies and at current prices. Usually given as proven reserves, those that have not yet been discovered but that are presumed to exist.
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| Residence time
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| The length of time a component, such as an individual water molecule, spends in a particular compartment or location before it moves on through a particular process or cycle.
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| Resilience
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| The ability of a community or ecosystem to recover from disturbances.
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| Resistance (inertia)
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| The ability of a community to resist being changed by potentially disruptive events.
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| Resource
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| In economic terms, anything with potential use in creating wealth or giving satisfaction.
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| Resource (as a measurement of a mineral or fuel)
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| Total amount of mineral or fuel on earth. Generally only a small fraction can be recovered. Compare with reserve.
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| Resource (in general)
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| Anything used by organisms to meet their needs, including air, water, mineral, plants, fuels, and animals.
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| Resource partitioning
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| In a biological community, various populations sharing environmental resources through specialization, thereby reducing direct competition. See also ecological niche.
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| Resource partitioning
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| The outcome of competition by a group of species, where natural selection factors division of a resource in time or space by specialization of the different species.
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| Resource scarcity
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| A shortage or deficit in some resource.
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| Resources Conservation and Recovery Act of 1979 (RCRA)
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| The cornerstone legislation to control indiscriminate land disposal of hazardous wastes.
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| Respiration
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| See cell respiration.
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| Respiratory fibrotic agents
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| Special class of irritants, including chemical reagents and particulate materials, that damages the lungs, causing scar tissue formation that lowers respiratory capacity.
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| Restoration
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| To bring something back to a former condition. Ecological restoration involves active manipulation of nature to re-create conditions that existed before human disturbance.
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| Restoration ecology
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| Seeks to repair or reconstruct ecosystems damaged by human actions.
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| Restore ecosystems
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| To reinstate an entire community of organisms to naturally occurring association.
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| Resurgence
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| The rapid comeback of a population especially of pests after a severe dieoff, usually caused by pesticides, and return to even higher levels than before the treatment.
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| Retorting
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| Process of removing kerogen from oil shale, usually by burning or heating the shale. Can be carried out in surface vessels (surface retorting) or underground in fractured shale (in site retorting).
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| Retrospective law
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| One that attempts to solve a problem without giving much attention to potential future problems. Contrast with prospective law.
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| Reuse
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| The practice of reusing items as opposed to throwing them away and producing new items, as, for example, bottles collected and refilled (recycling).
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| Reverse osmosis
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| Means of purifying water for pollution control and desalination. Water is forced through porous membranes; pores allow passage of water molecules but not impurities.
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| Rill erosion
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| The removing of thin layers of soil as little rivulets of running water gather and cut small channels in the soil.
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| Riparian woodlands
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| The strip of woods that grow along natural watercourses.
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| Risk
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| Probability that something undesirable will happen as a consequence of exposure to a hazard.
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| Risk acceptability
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| A measure of how acceptable a hazard is to a population.
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| Risk analysis
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| The process of evaluating the risks associated with a particular hazard before taking some action. Often called risk assessment.
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| Risk assessment
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| Evaluation of the short-term and long-term risks associated with a particular activity or hazard; usually compared to benefits in a cost-benefit analysis.
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| Risk characterization
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| The process of determining a risk and its accompanying uncertainties after hazard assessment, dose-response assessment, and exposure assessment have been accomplished.
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| Risk management
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| The task of regulators whose job is to review risk data and make regulatory decisions based on the evidence. The process often is influenced by considerations of costs and benefits as well as by public perception.
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| Risk perception
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| Nonexperts¡¦ intuitive judgements about risks, which often are not in agreement with the level of risk as judged by experts.
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| Risk probability
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| The likelihood a hazardous event will occur.
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| Risk severity
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| A measure of the total damage a hazardous event would cause.
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| RNA
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| Ribonucleic acid; nucleic acid used for transcription and translation of the genetic code found on DNA molecules.
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| Rock cycle
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| The process whereby rocks are broken down by chemical and physical forces; sediments are moved by wind, water, and gravity, sedimented and reformed into rock, and then crushed, folded, melted, and recrystallized into new forms.
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| Rooftop garden
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| A form of above-ground gardening on the top of a flat residential roof, using shallow soil beds and containers like old automobile tired or plastic wading pools.
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| Rubber tapper
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| In tropical forests of South America, people who harvest the latex rubber and Brazil nuts from rain forest trees and are opposed to clearing the forests. Also called serengueros.
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| Ruminant animals
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| Cud-chewing animals, such as cattle, sheep, goats, and buffalo, with multichambered stomachs in which cellulose is digested with the aid of bacteria.
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| Runoff
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| The excess of precipitation over evaporation; the main source of surface water and, in broad terms, the water available for human use.
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| Run-of-the-river flow
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| Ordinary river flow not accelerated by darns, flumes, etc. Some small, modern, high-efficiency turbines can generate useful power with run-of-the-river flow or with a current of only a few kilometers per hour.
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| Rural area
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| An area in which most residents depend on agriculture or the harvesting of natural resources for their livelihood.
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