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Related Concept Videos

Internal Energy02:00

Internal Energy

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The total of all possible kinds of energy present in a substance is called the internal energy (U), sometimes symbolized as E. Suppose a system with initial internal energy, Uinitial, undergoes a change in energy (transfer of work or heat), and the final internal energy of the system is Ufinal. Change in internal energy equals the difference between Ufinal and Uinitial.
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The internal energy of a thermodynamic system is the sum of the kinetic and potential energies of all the molecules or entities in the system. The kinetic energy of an individual molecule includes contributions due to its rotation and vibration, as well as its translational energy. The potential energy is associated only with the interactions between one molecule and the other molecules of the system. Neither the system's location nor its motion is of any consequence as far as the internal...
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Many cellular signals are hydrophilic and therefore cannot pass through the plasma membrane. However, small or hydrophobic signaling molecules can cross the hydrophobic core of the plasma membrane and bind to internal, or intracellular, receptors that reside within the cell. Many mammalian steroid hormones use this mechanism of cell signaling, as does nitric oxide (NO) gas.
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The International System of Units, known as the SI system, is a universally accepted measurement system recognized and used worldwide. The SI system is based on a set of three base units considered absolute, and their values do not change with location. These base units are meters, kilograms, and seconds.
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External respiration occurs in the lungs, and it is the first step in the journey of oxygen inside the body. When we inhale, oxygen enters our lungs and diffuses across the thin alveolar membrane. The alveoli are tiny, air-filled sacs that provide a vast surface area for gas exchange. Oxygen in the alveoli has a higher partial pressure (105 mmHg) than in the adjacent pulmonary capillaries (40 mmHg), establishing a pressure gradient. As a result, oxygen molecules move from the alveoli into the...
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The internal combustion engine is a heat engine that uses the byproducts of combustion as the working fluid instead of using a heat transfer medium to transfer heat. The combustion is done in a way that produces high-pressure combustion products that can be expanded through a turbine or piston to create work. Internal combustion engines can again be categorized into three kinds: (1) spark ignition gasoline engines, most commonly used in automobiles, (2) compression ignition diesel engines that...
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Related Experiment Video

Updated: Jan 23, 2026

Reliable Method for Assessing Seed Germination, Dormancy, and Mortality under Field Conditions
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Mortality Among International Astronauts.

Robert J Reynolds, Steven M Day

    Aerospace Medicine and Human Performance
    |June 23, 2019
    PubMed
    Summary

    Astronaut mortality studies now include European, Canadian, Chinese, and Japanese space explorers. While no deaths occurred, European astronauts showed significantly lower mortality risk compared to the general population and U.S. astronauts.

    Area of Science:

    • Space exploration
    • Astronaut health
    • Comparative mortality studies

    Background:

    • Previous astronaut mortality research focused solely on U.S. and Soviet/Russian space explorers.
    • International space agencies like ESA, CSA, CNSA, and JAXA present opportunities for broader mortality research.
    • Understanding astronaut health risks is crucial for long-duration space missions.

    Purpose of the Study:

    • To analyze the mortality patterns of astronauts from European, Canadian, Chinese, and Japanese space programs.
    • To compare the mortality risks of these astronaut cohorts against their respective general populations and U.S. astronauts.
    • To investigate the 'healthy worker effect' in international astronaut populations.

    Main Methods:

    • Biographical and vital data were collected from public sources for astronauts from ESA, CSA, CNSA, and JAXA.

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  • Standardized mortality ratios (SMRs) were calculated using general population data from the Human Mortality Database.
  • SMRs were also computed by comparing astronaut cohorts to the mortality rates of U.S. astronauts.

    • Main Results:

    • No deaths were recorded in any of the four international astronaut cohorts studied.
    • The European astronaut cohort exhibited a statistically significant reduction in all-cause mortality risk.
    • This reduction was observed when compared to both the European general population and the U.S. astronaut cohort.

    Conclusions:

    • The 'healthy worker effect' suggests lower mortality in astronaut cohorts than in general populations.
    • The low baseline mortality in Japan's general population may obscure detectable risk reductions in its astronaut cohort.
    • Continued long-term monitoring of these international astronaut populations will enhance the evidence base for space explorer health and safety.