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Physical quantity

A physical quantity is defined as a physical property of a body or entity with which it is possible to describe phenomena that can be measured (quantified by measurement). A physical quantity can be expressed as the combination of a magnitude expressed by a number – usually a real number – and a unit of measurement. They

Electrical conductance

The electrical conductance of a component in an electric circuit is a property of a component that describes how the electric current in the component is related to the electrical potential difference (voltage) across it. The greater the electrical conductance, the larger the current for a given potential difference, and the smaller the potential difference,


Vaporization. Evaporation. Water vapor. Saturated vapor. Wet saturated vapor. Dry saturated vapor. Superheated vapor.


Anatomy (from the Greek ἀνατομή, anatomē, “dissection”, from ἀνατέμνω anatémnō “I cut up, cut open” from ἀνά aná “up”, and τέμνω témnō “I cut”) is the branch of Biology concerned with the study of the structure of organisms and their parts (the study of form in animals, plants, and other organisms, or specifically in humans). Simply, the study of the internal structure of


Attention is a cognitive process that allows to select some environmental stimuli, ignoring others. From an evolutionary point of view, it is an extremely useful mechanism for human survival because it allows us to organize the information coming from the external environment, which is constantly changing, and to regulate mental processes accordingly. Attention refers to


Ferrofluids (sometimes referred as magnetic liquids) are colloidal suspensions of magnetic nanoparticles, represent a special class of magnetic fluids and are manufactured fluids consisting of dispersions of magnetized nanoparticles in a variety of non-magnetic liquid carriers. They were originally invented independently around the same time in the early 1960s at NASA Lewis Laboratories, and aslo by

Astronomical coordinate systems

Astronomical coordinate systems (also called celestial coordinates) are organized arrangements for specifying positions of satellites, planets, stars, galaxies, and other celestial objects relative to physical reference points available to a situated observer (e.g. the true horizon and north cardinal direction to an observer situated on the Earth’s surface). Astronomers use astronomical coordinates on the sky


Astrometry is a branch of Astronomy that studies stellar motions (i.e., studies the geometric relationships between celestial objects, their motion, and their position). Astrometry is now one of many fields of research within astronomy. Historically, astrometry was all that astronomy was about until about the 19th century. Toward the end of the 19th century not


Neurons are the cells considered to be the basis of nervous tissue. They are responsible for the electrical signals that communicate information about sensations, and that produce movements in response to those stimuli, along with inducing thought processes within the brain. An important part of the function of neurons is in their structure, or shape.

Mass number

An element’s mass number (A) is the sum of the number of protons and the number of neutrons. The small contribution of mass from electrons is disregarded in calculating the mass number. This approximation of mass can be used to easily calculate how many neutrons an element has by simply subtracting the number of protons

Atomic number

Neutral atoms of an element contain an equal number of protons and electrons. The number of protons determines an element’s atomic number (Z) and distinguishes one element from another. For example, carbon’s atomic number (Z) is 6 because it has 6 protons. The number of neutrons can vary to produce isotopes, which are atoms of


Carbon [symbol C] (from Latin: carbo “coal”) is a nonmetallic and tetravalent (rarely bivalent) chemical element—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Individual carbon atoms have an incomplete outermost electron shell. With an atomic number of 6 (six electrons and six protons), the first

Muscle tissue

Muscle tissue is excitable, responding to stimulation and contracting to provide movement, and occurs as three major types: skeletal (voluntary) muscle, smooth muscle, and cardiac muscle in the heart. Muscle tissue is composed of cells that have the special ability to shorten or contract in order to produce movement of the body parts. The tissue is

Biological tissue

A biological tissue is an ensemble of similar cells and their extracellular matrix, characterized by similar structure and functions. Tissues represent the next level of organization after cellular organization; in practice, they are formed by cells of the same type that associate together to perform a common function. Each tissue therefore possesses one or more

Nervous system

The nervous system is the major controlling, regulatory, and communicating system in the body. It is the center of all mental activity including thought, learning, and memory. Together with the endocrine system, the nervous system is responsible for regulating and maintaining homeostasis. Through its receptors, the nervous system keeps us in touch with our environment,

Muscular system

The muscular system is composed of specialized cells called muscle fibers. Their predominant function is contractibility. Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction. Exceptions to this are the action of cilia, the flagellum on sperm cells,


The cytoplasm is the gel-like fluid inside the cell, which represents the portion (about half of the total volume of the cell) contained within the cell membrane present in both eukaryotic and prokaryotic cells. It consists of cellular organelles dispersed in a fluid matrix called the cytosol. It is the medium for chemical reaction. It