Nuclear power generation:
Nuclear energy → internal energy of water and steam → mechanical energy of generator rotor → electric energy.
nuclear energy power generation
A way to generate electricity by using the thermal energy released by nuclear fission in nuclear reactors. It is very similar to thermal power generation. Only nuclear reactors and steam generators are used to replace boilers for thermal power generation, and nuclear fission energy is used to replace chemical energy of fossil fuels. Except for the boiling water reactor (see light water reactor), other types of power reactors are heated by the coolant in the primary loop through the core, and the heat is transferred to the water in the secondary loop or the tertiary loop in the steam generator, and then steam is formed to drive the turbine generator. Boiling water reactor (BWR) is that the coolant in the primary loop is heated by the reactor core, turned into saturated steam at about 70 atmospheres, separated from the steam, and dried to directly drive the turbine generator.
A brief history The history of nuclear power generation is closely related to the development history of power reactors. The development of power reactors was originally for military needs. 1954, the Soviet Union built the world's first nuclear power plant with an installed capacity of 5 MW. Britain, the United States and other countries have also built various types of nuclear power plants. By 1960, 20 nuclear power plants will be built in five countries, with an installed capacity of 1279 MW. Due to the development of nuclear enrichment technology, the cost of nuclear power generation has been lower than that of thermal power generation 1966. Nuclear power generation has really entered the practical stage. 1978, there were more than 200 nuclear power plant reactors with a total installed capacity of 107776 MW in 22 countries and regions around the world. In 1980s, the shortage of fossil energy became increasingly prominent, and nuclear power generation made rapid progress. By 199 1 year, nearly 30 countries and regions around the world have built 423 nuclear power units with a total capacity of 327.5 million kilowatts, accounting for about 16% of the world's total power generation. The first nuclear power plant in the world-Obninsk nuclear power plant in the Soviet Union.
Chinese mainland's nuclear power started late, and construction of nuclear power plants began in 1980s. The 300,000 kW Qinshan Nuclear Power Station designed and built by China was put into operation at the end of 199 1. Daya Bay Nuclear Power Station is stepping up its construction.
The principle of nuclear power generation The energy of nuclear power generation comes from the fission energy released by the fission reaction of fissile materials (nuclear fuel) in nuclear reactors. Fission reaction refers to the process that heavy elements such as uranium -235, plutonium -239 and uranium -233 are split into two fragments under the action of neutrons, and neutrons and a lot of energy are released at the same time. In the reaction, the nucleus of fissionable matter absorbs one neutron, then splits and releases two or three neutrons. If these neutrons are removed and consumed, at least one neutron can cause nuclear fission of another atom, so that fission can proceed on its own, then this reaction is called a chain reaction of nuclear fission. Realizing chain reaction is the premise of nuclear power generation.
In order to produce nuclear energy with reactors, the following four problems need to be solved: ① To provide the necessary conditions for the nuclear fission chain reaction to be carried out. ② The chain reaction must be controlled by people through certain devices. Uncontrolled fission energy can not only be used to generate electricity, but also lead to disaster. ③ The energy generated by fission reaction should be taken out of the reactor safely. (4) Neutrons and radioactive substances produced by fission reaction are very harmful to human body, and their harm to nuclear power plant staff and nearby residents must be avoided as far as possible.
Using nuclear energy to power micro devices.
At present, researchers all over the world are developing micro-devices smaller than human hair for various purposes, from biochemical sensors to medical implants. But there is an obstacle: at present, no one can come up with an energy source that can match such a small micro-mechanical device.
Now, a group of engineers at the University of Wisconsin think they may have found the right method. They have started a project to use nuclear energy to provide energy, but these generators will be completely different from dome nuclear power plants that provide electricity for homes and factories.
The energy of these micro-devices is not generated by rotating turbines, but by using trace radioactive substances to generate electricity through their decay. This practice has been done before, but on a much larger scale. People have used this method to power various devices, from pacemakers to spacecraft exploring the dark outer space of the solar system.
James blanchard, a professor of nuclear energy engineering at the University of Wisconsin, said, "This is unprecedented on the scale we are discussing now." The research team led by blanchard is trying to develop this technology, and the research has been funded by the US Department of Energy for 450,000 dollars.
Although the mere mention of nuclear energy will make some people's backs cold, researchers say that their generators only use very little radioactive material, so safety should not be a problem. Blanchard said that the most suitable element for this technology is polonium discovered by the Curie couple in 1898.
Radioactive substances have been widely used in many devices, including smoke detectors. Other copiers also use strip radioactive substances to eliminate static electricity between papers. However, if nuclear power is to become the energy source of future micro-machines, this technology must be reduced to the microscopic level. Blanchard said that there are two ways to generate electricity with radioactive materials. The heat released when radioactive substances decay can make some substances release electrons, thus forming electric energy. But the research team prefers a more direct approach.
Blanchard said: "When the radioactive isotope decays, it will release charged particles, so you can directly capture these charged particles and use them to generate electricity." He said that the voltage generated by these particles is very high relative to the scale of these devices. Blanchard said that his research team did not directly consider the use of these micro devices. He believes that once you have the right energy, others will come up with many uses. In fact, dozens of laboratories around the world have been developing micro-electromechanical devices called MEMS, which is one of the key topics in today's high-tech field.
(1) Different forms of energy in nature correspond to different forms of motion: the motion of objects has mechanical energy, the motion of molecules has internal energy, the motion of charges has electrical energy, and the motion inside the nucleus has atomic energy.
(2) Different forms of energy can be transformed into each other: "Friction does work by overcoming friction and converts mechanical energy into internal energy to generate heat; When the water in the kettle boils, steam acts on the lid and lifts the lid, indicating that internal energy can be converted into mechanical energy. Electricity can be converted into internal energy through the work of electric heating wires, and so on. " These examples show that different forms of energy can be transformed into each other, and this transformation process is completed by doing work.
(3) Some form of energy reduction will inevitably lead to other forms of energy increase, and the reduction and increase must be equal. When the energy of one object decreases, the energy of other objects must increase, and the decrease and increase must be equal.
The concrete manifestation of energy conservation
Conservative mechanical system: under the condition that only conservative force does work, the energy of the system is mechanical energy (kinetic energy and potential energy), and the conservation of energy is embodied in the law of conservation of mechanical energy.
Thermodynamic system: energy is expressed as internal energy, heat and work, and the expression of energy conservation is the first law of thermodynamics.
Relativistic mechanics: in relativity, mass and energy can be transformed into each other. Considering the energy change caused by mass change, the law of conservation of energy still holds. Historically, the law of conservation of energy in this case is also called the law of conservation of mass and energy.
The total energy flowing into the system must be equal to the total energy flowing out of the system plus the change of energy inside the system, and energy can be converted from one form to another.
The increase of stored energy in the system is equal to the energy entering the system minus the energy leaving the system.
[Edit this paragraph] The significance of the law of conservation of energy
The law of conservation of energy is one of the most universal and important basic laws in nature. From physical chemistry to geo-biology, to cosmic objects. As small as the nucleus, as long as there is energy transformation, we must abide by the law of conservation of energy. This law plays an important role in daily life, scientific research and engineering technology. The utilization of fuels such as coal and oil, and various energy sources such as hydropower, wind energy and nuclear energy are all realized through energy conversion. The law of conservation of energy is a powerful weapon for people to know and use nature.
Young doctors and winemakers discovered new scientific principles.
[Edit this paragraph]-Discovery of the Law of Conservation and Transformation of Energy
The laws of conservation and transformation of energy, cell theory and evolution are collectively called1the three great discoveries of natural science in the 9th century. The discovery of the law of conservation and transformation of energy is related to a "crazy" doctor.
The doctor called "crazy" is named Mayer (18 14~ 1878), a native of Hamburg, Germany. 1840 started practicing medicine independently in Hamburg. He always asks why, and must observe, study and experiment in person. 1840 came to Indonesia with the fleet on February 22, with doctors on board. One day, the fleet landed in Calcutta, and the crew got sick because of acclimatization, so Mayer bled the crew according to the old method. In Germany, you only need to insert a needle into the patient's vein to treat this disease, and you can release a stream of dark red blood, but here, it is still bright red blood flowing out of the vein. Therefore, Meyer began to think: human blood is red because it contains oxygen, which burns in the human body to generate heat and maintain the body temperature. It's very hot here, and people don't need to burn so much oxygen to maintain their body temperature, so the blood in the blood vessels is still bright red. So, where does the heat come from? A heart with a maximum of 500 grams can't generate so much heat by its movement, and it can't maintain a person's body temperature alone. That body temperature is maintained by the whole body's flesh and blood, which comes from the food people eat. Whether they eat meat or vegetables, they must come from plants, and plants grow by the light and heat of the sun. What about the heat of the sun? If the sun is a piece of coal, it can burn for 4600 years, which is of course impossible. It must be something else, energy we don't know. He boldly introduced that the center of the sun is about 27.5 million degrees (now we know it is150,000 degrees). The more Meyer thinks about it, the more it boils down to one point: how is energy transformed (transferred)?
On his return to Hamburg, he wrote an article "On the Force of Inorganic Boundary" and measured the thermal mechanical equivalent of 365 kg m/kcal by his own method. He submitted a paper to the Yearbook of Physics, but it was not published, so he had to publish it in a little-known medical journal. He gave speeches everywhere: "Look, the sun gives off light and heat, and plants on the earth absorb them and produce chemicals ..." But even physicists couldn't believe his words and called him "crazy" disrespectfully. Meyer's family also suspected that he was crazy and asked a doctor to treat him. Not being understood, he finally committed suicide by jumping off a building.
Meyer was accompanied by an Englishman, Joule (18 18~ 1889), who studied chemistry, mathematics and physics under Dalton's door since childhood. He manages the brewery left by his father while doing scientific research. In 1840, he found that when live wires were put into water, the water would heat up. Through precise experiments, he found that the heat generated by electrified conductor is directly proportional to the square of current intensity, and the resistance of conductor is directly proportional to the electrified time. This is Joule's law. 184 1 year1October, and his paper was published in the Journal of Philosophy. Later, he found that regardless of chemical energy, the heat generated by electric energy is equivalent to a certain work, that is, 460 kg m/kcal. From 65438 to 0845, he took his experimental instruments and reports to attend the academic conference held in Cambridge. He finished the experiment on the spot and declared that the force (energy) of nature is indestructible. Where mechanical power (energy) is consumed, considerable heat will always be obtained. But the famous scientists in the audience shook their heads at this new theory, and even Faraday said, "This is impossible." There is also a math professor named William Thomson (1824~ 1907). He went to college with his father at the age of 8 and was admitted to college at the age of 10. He is a wizard. Today, when he heard a brewer shouting some strange theories here, he left the meeting on the spot very rudely.
Joule paid no attention to people's incomprehension. He went home to continue his experiment. He has been doing it for 40 years. He refined the mechanical equivalent of heat to 423.9 kg m/kcal. 1847, he came to the meeting place of British Science Association with his newly designed experiment. Under his strong pleading, the chairman of the meeting gave him little time to do experiments without giving a report. When demonstrating his new experiment in public, Joule explained: "You see, mechanical energy can be converted into heat quantitatively, and conversely, the heat of 1000 kcal can also be converted into work of 423.9 kg m …" Suddenly, someone in the audience shouted: "Nonsense, heat is a substance, a pyrogen, and has nothing to do with work." It's Tang Musun. Joule calmly replied, "heat can't do work, so why does the piston of a steam engine move?" If energy is not conserved, why can a perpetual motion machine never be built? "Joule insipid words suddenly let the audience was silent. The professors in the audience couldn't help thinking seriously. Some people looked around in front of Joule's instrument, and some people began to argue.
After Tang Musun touched the nail, he began to think. He began to do his own experiments and find his own information. Unexpectedly, he found an article published by Meyer a few years ago, with the same idea as Joule! He took his experimental results and Meyer's paper to find Joule. He decided to humbly apologize and asked Joule to discuss the discovery with him.
Tang Musun met Joule in the brewery and looked at all kinds of homemade instruments in Joule's laboratory. He was deeply moved by Joule's perseverance. Tang Musun took out Meyer's paper and said, "Mr. Joule, it seems that you are right. I came to apologize today. You see, I didn't think you were right until I read this paper. " Joule's face lit up when he saw the newspaper. "Professor Tang Musun, it's a pity that you can't discuss this problem with him anymore. Such a genius committed suicide by jumping off a building because he was not understood. Although he didn't fall to death, he was already insane. "
Tang Musun bowed his head and remained silent for a long time. After a while, he looked up and said, "I'm sorry, I didn't know my sin until now." In the past, how much pressure did we people give you? Please forgive me, a scientist sometimes behaves very ignorant in front of new ideas. "Everything became bright, and they sat side by side and began to study experiments.
1853, they finally completed the accurate expression of the law of energy conservation and transformation.
There are three expressions of the law of conservation of energy transformation: perpetual motion machine cannot cause, the law of conservation of energy transformation and the first law of thermodynamics. These three expressions are described in the literature as follows: "The first law of thermodynamics is the law of conservation of energy." According to the law of conservation of energy, ... the so-called perpetual motion machine must be built. Conversely, the law of conservation of energy can also be deduced from the failure of perpetual motion machine. "It is not difficult to see here that the three expressions are completely equivalent. But the author believes that this kind of equivalence is the modern value given to them by modern people. From the perspective of historical development, we will find that the three expressions have their own continuity, but there are also differences. This difference reflects the different stages of human cognition.
Empirical expression of 1 law-perpetual motion machine can't cause it (1475 ~ 1824)
A long time ago, human beings began to use natural forces to serve themselves. In the thirteenth century, the desire to make perpetual motion machines began to sprout. /kloc-in the 5th century, the great artist, scientist and engineer Leonardo da Vinci (1452 ~ 1519) also devoted himself to the study of perpetual motion machines. He once designed a very clever hydrodynamic machine, but it didn't last forever after it was built. 1475, Leonardo da Vinci summed up the lessons of his own failure in history and came to an important conclusion: "perpetual motion machine is impossible." At work, he also realized that the reason why the machine can never move should be related to friction. Therefore, he made an in-depth and effective study of friction. However, Leonardo da Vinci never gave a scientific explanation for why friction hindered the movement of machines, that is, he could not recognize the essential relationship between friction (mechanical movement) and thermal phenomena.
Since then, although people are still committed to the development of perpetual motion machines, some scientific workers have come to the conclusion that perpetual motion machines cannot be caused, and regard it as an important principle in scientific research. Stevin (1548 ~ 1620), a Dutch mathematical mechanic, applied this principle in 1586 and deduced the parallelogram rule of output for the first time through the analysis of "Stevin chain". Galileo also applied this principle in proving the law of inertia.
Although the application of this principle has made such remarkable achievements, people's enthusiasm for developing perpetual motion machines has not diminished. Huygens (c Huygens 1629 ~ 1695)
This view is reflected in the book Pendulum Clock published by him 1673. In the book, he applied Galileo's research results on inclined plane motion to curved motion, and concluded that when an object rotates around the horizontal axis under the action of gravity, its center of mass will not rise above the height when it falls. So he came to the conclusion that it is impossible to make a perpetual motion machine by mechanical means; But he thinks perpetual motion machines can still be made of magnets. In view of this situation, 1775, the Paris Academy of Sciences had to announce that it would no longer accept the invention of perpetual motion machines.
In history, the young French scientist sadi carnot (1796 ~ 1832) made the most brilliant scientific achievements by applying the principle that perpetual motion machines cannot be made. 1824, he combined this principle with heat theory and deduced the famous Carnot theorem. This theorem points out the direction for improving the efficiency of heat engine and lays the foundation for the second law of thermodynamics. But what needs to be emphasized here is that although Cano applied the principle that a perpetual motion machine cannot lead to a heat engine to a heat engine, his thinking method is still "mechanical". In his argument, he compared the flow of heat from a high-temperature heat source to a low-temperature heat source with the flow of water from a high place to a low place, and thought that heat pushes a heat engine to do work just like water pushes a turbine to do work, and there is no loss of water and heat in the flow.
It can be seen that from 1475, Leonardo da Vinci put forward that "perpetual motion can't be caused" to 1824, and Carnot's theorem can only be applied to mechanical motion and "heat and mass" flow. It is far from the law of energy transformation and conservation in the modern sense. It can only be an experience summary of energy conservation in mechanical motion and is the original form of the law.
189 1 year, Helmholtz (H. Helmholtz1821~1894) 400)
Looking back on his research on the causes of the conservation law of force, he said, "If perpetual motion machine is impossible, what kind of relationship should exist between different forces under natural conditions?" Moreover, do these relationships actually exist? "It can be seen that' perpetual motion machine can't cause' is still superficial, and people still have to work hard to understand its profound connotation.
The Original Expression of Law 2-Conservation of Force (1824 ~ 1850)
The law of energy conversion and conservation must be put forward on the basis of 134: correctly understand the essence of heat; Discover the transformation between various forms of material movement; Corresponding scientific ideas. In the19th century, all three conditions were met.
1798, Rumford (cromford1753 ~1814) submitted an experimental report on the thermal motion theory obtained from the gun barrel experiment to the Royal Society. 1800, David (D·H· David 1778 ~ 1829)
The experiment of melting ice cubes by rubbing them in vacuum supports Renford's report. 180 1 year, Thomas Young (1773 ~ 1829) said that light and heat have the same properties, and emphasized that heat is a kind of movement. From then on, the theory of thermal motion gradually replaced the theory of heat.
At the turn of 18 and 19 centuries, the mutual transformation between various natural phenomena was discovered one after another: after the chemical effect of heat transforming into work and light was discovered, the thermal effect of infrared rays was discovered in 1800. As soon as the battery was invented, the thermal effect and electrolysis of current were discovered. 1820 discovered the magnetic effect of current, and183/kloc-0 discovered the electromagnetic induction phenomenon. Thermoelectric phenomenon was discovered in 182 1 year, and its inverse phenomenon was discovered in 1834. Wait a minute.
At the turn of the century, the idea of taking nature as "vitality" developed into "natural philosophy" in Germany. This philosophy regards the whole universe as the product of historical development caused by the discovery of some fundamental force. From this perspective, all natural forces can be regarded as one thing. At that time, this philosophy was dominant in Germany and some western European countries.
At this time, it is imperative to put forward the principle of conservation of force.
In history, Kano was the first person to put forward the idea of converting thermal energy into work. He thinks: "heat is just a kind of strength, or just a kind of movement in different forms." Heat is a kind of exercise. For a small part of an object, if the force is destroyed, at the same time, it will inevitably produce heat that is strictly proportional to the destructive force. On the contrary, where heat disappears, there must be electricity. Therefore, it can be established that the size of power is essentially unchanged. More precisely, the size of power can neither be produced nor destroyed. "At the same time, he gave a rough numerical value of the mechanical equivalent of heat.
Unfortunately, Kano's idea was discovered in 1878, 46 years after his death. Prior to this, 1842, Mayer, Germany (J R Mayer1814 ~1878) 400).
He was the first person to publish a comprehensive paper on the conservation of force and inorganic boundary force. In this paper, starting from "natural philosophy", he released 25 forms of force transformation from the causal chain of "cause equals effect" in a speculative way. In 1845, he also used the difference between constant pressure specific heat capacity and constant volume specific heat capacity: Cp-Cv=R, and calculated the equivalent value of thermal work as 1 card, which is equal to 365 g m.
1843, British experimental physicist Joule (J P Joule1818 ~1889) 400) style. width = 400; " & gt
In the Journal of Philosophy, he published an experimental report on measuring the mechanical equivalent of heat. Since then, he has done more and more detailed work and determined more accurate equivalent values. In 1850, he published the result: "To produce one pound of water (weighed in vacuum at a temperature of 55-60℃) and increase the heat of 1 Fahrenheit, it takes 772 pounds of mechanical work represented by falling one foot." Joule's work laid a solid experimental foundation for the principle of "conservation of force".
Helmholtz, a German scientist, published his book The Conservation of Force in 1847. In this paper, he proposed that all natural phenomena should be explained by the motion of particles interacting with the central force.
This proves that the sum of vitality and tension is conservative to the central force. In the introduction, he also discussed the relationship between thermal phenomenon, electrical phenomenon, chemical phenomenon and mechanical force, and pointed out the possibility of applying the principle of "conservation of force" to living things. Because Helmholtz's way of discussion is very physical, his influence is greater than that of Meyer and Joule.
Although, so far, the discoverer of this law still calls energy "force"; Moreover, the expression of the law is not accurate enough, but in essence they discovered the law of energy transformation and conservation. Comparing the two expressions, we can see that "conservation of force" is much more profound than "perpetual motion machine cannot cause". "Conservation of force" refers to all forms of material motion when it is recognized; At the same time, it is a theory established by axiomatic structure (Helmholtz) under the guidance of certain philosophical thought (Meyer) and on the basis of experiment (Joule). If we still use "perpetual motion machine can not be caused" to express this law, it has given it a new connotation, that is, the present machine can be mechanical, thermal, electromagnetic, chemical and even biological; At the same time, it also reveals the reason why perpetual motion machine can't move forever.
In addition, we should also see that although the principle of "conservation of force" has the relationship between Joule's thermal mechanical equivalent and electrothermal equivalent, as well as various relationships deduced by Helmholtz, they are independent and cannot be expressed by a unified analytical formula. So "conservation of force" is not mature enough.
Law 3- Analytical expression of the first law of thermodynamics (1850 ~ 1875)
To express the law analytically, only the concepts of heat, work, energy and internal energy can be accurately defined.
After the establishment of thermodynamic theory, many people still find it difficult to understand, especially the second law. Therefore, since 1854, Clausius has done a lot of work, trying to find an acceptable proof method to explain these two principles (then called principles), and preached them in popular language many times. In this way, it was not until about 1860 that the energy principle was generally recognized.
Accurate expression of the law-the law of energy transformation and conservation (1875 ~ 1909)
1860 years later, the law of energy "soon became the cornerstone of all natural sciences. Especially in physics, every new theory must first test whether it conforms to the principle of conservation of energy. " However, before this, the discoverer of this principle only focused on summarizing the name of the law from the conservation of quantity, without emphasizing the transformation ratio of motion. When was the principle summed up as "the law of energy conversion and conservation"? The answer to the question can be obtained from Engels' exposition in Anti-Turin.
Engels said: "If the great basic law of motion newly discovered ten years ago is only summarized as the law of conservation of energy, only as the expression that motion is immortal, that is, only from the quantitative aspect, then this narrow and negative expression is increasingly replaced by the positive expression about energy transformation, in which the qualitative content of the process has gained its own rights for the first time. ..... "Engels published this passage in 1885. He said that negative expressions ten years ago were increasingly replaced by positive expressions. Judging from this, the accurate and perfect expression of the Law of Energy Transformation and Conservation should be formed at 1875 or later.
So far, it seems that all the legal problems have been solved. Actually, it is not.
We know that heat, an important basic concept in thermodynamics, was still defined in18th century until the beginning of 20th century, and this definition was based on the theory of heat. In other words, one of the cornerstones of the building of thermodynamics is still unstable. Therefore, in 1909, C. Carathieodory redefined internal energy: "Any object or system of objects has a state function U in equilibrium, which is called its internal energy. When this object undergoes an adiabatic process from the first state to the second state, its internal energy increase is equal to the work W done by the outside world in this process. "
U2-U 1=W (8)
The internal energy defined in this way has nothing to do with heat, but only with mechanical energy and electromagnetic energy. On this basis, heat can be defined in reverse:
Q=U2-U 1-W (9)
Until this time, the first law of thermodynamics (the law of energy transformation and conservation), the second law and the whole thermodynamic theory completely broke away from the theory of heat.
Throughout the whole paper, we can see that the three expressions of the law of energy transformation and conservation reflect the course of human understanding of this natural law. Each of these three expressions is more profound and closer to the objective truth than the other. This is how human beings understand the material world step by step.
Reprinted from the author: Wang Xiaoyong
[Edit this paragraph] Test of the Law of Conservation of Energy
Any physical law needs to be strictly and repeatedly tested, especially when the law found in the characteristic field is transplanted to other related fields, it often happens that the law is broken, such as the law of parity conservation is broken by experiments in weak interaction and electromagnetic interaction. This is independent of human will. Even laws widely recognized by human society cannot be considered correct in areas that have not been strictly tested.
Joule put forward the law of conservation of energy on the basis of studying mechanical energy and thermal energy. At that time, the scientific community did not understand electromagnetic interaction, so the law of conservation of energy was not tested under electromagnetic interaction. We know that electromagnetic energy generally conforms to the law of conservation of energy, but we can't rule out exceptions in special circumstances. For example, the law of conservation of parity was proved to be correct in general electromagnetic interaction, but it was later found to be incorrect in Amber's special structure. Due to the diversity and complexity of electromagnetic structures, it is very difficult to test the physical laws, which leads to a long and endless test.
We can say that the law of conservation of energy is correct in the existing knowledge field, but if it is always correct in any field and under any circumstances, it is not the attitude of scientific researchers.