Generation (particle physics)

In particle physics, a generation (or family) is a division of the elementary particles. Between generations, particles differ by their (flavour) quantum number and mass, but their interactions are identical.

There are three generations according to the Standard Model of particle physics. Each generation is divided into two types of leptons and two types of quarks. The two leptons may be classified into one with electric charge −1 (electron-like) and one neutral (neutrino); the two quarks may be classified into one with charge −¹⁄₃ (down-type) and one with charge +²⁄₃ (up-type).

Overview

Each member of a higher generation has greater mass than the corresponding particle of the previous generation, with the possible exception of the neutrinos (whose small but non-zero masses have not been accurately determined). For example, the first-generation electron has a mass of only 6999511000000000000♠0.511 MeV/c², the second-generation muon has a mass of 7002106000000000000♠106 MeV/c², and the third-generation tau has a mass of 7003177700000000000♠1777 MeV/c² (almost twice as heavy as a proton). This mass hierarchy causes particles of higher generations to decay to the first generation, which explains why everyday matter (atoms) is made of particles from the first generation. Electrons surround a nucleus made of protons and neutrons, which contain up and down quarks. The second and third generations of charged particles do not occur in normal matter and are only seen in extremely high-energy environments such as cosmic rays or particle accelerators. The term generation was first introduced by Haim Harari in Les Houches Summer School, 1976.

Particle physics

Particle physics (also high energy physics) is the branch of physics that studies the nature of the particles that constitute matter (particles with mass) and radiation (massless particles). Although the word "particle" can refer to various types of very small objects (e.g. protons, gas particles, or even household dust), "particle physics" usually investigates the irreducibly smallest detectable particles and the irreducibly fundamental force fields necessary to explain them. By our current understanding, these elementary particles are excitations of the quantum fields that also govern their interactions. The currently dominant theory explaining these fundamental particles and fields, along with their dynamics, is called the Standard Model. Thus, modern particle physics generally investigates the Standard Model and its various possible extensions, e.g. to the newest "known" particle, the Higgs boson, or even to the oldest known force field, gravity.

Subatomic particles

Modern particle physics research is focused on subatomic particles, including atomic constituents such as electrons, protons, and neutrons (protons and neutrons are composite particles called baryons, made of quarks), produced by radioactive and scattering processes, such as photons, neutrinos, and muons, as well as a wide range of exotic particles. Dynamics of particles is also governed by quantum mechanics; they exhibit wave–particle duality, displaying particle-like behaviour under certain experimental conditions and wave-like behaviour in others. In more technical terms, they are described by quantum state vectors in a Hilbert space, which is also treated in quantum field theory. Following the convention of particle physicists, the term elementary particles is applied to those particles that are, according to current understanding, presumed to be indivisible and not composed of other particles.

Particle

A particle is a minute fragment or quantity of matter. In the physical sciences, the word is used to describe a small localized object to which can be ascribed several physical or chemical properties such as volume or mass; subatomic particles such as protons or neutrons; and other elementary particles. The word is rather general in meaning, and is refined as needed by various scientific fields. Something that is composed of particles may be referred to as being particulate. However, the term particulate is most frequently used to refer to pollutants in the Earth's atmosphere, which are a suspension of unconnected particles, rather than a connected particle aggregation.

Conceptual properties

The concept of particles is particularly useful when modelling nature, as the full treatment of many phenomena is complex. It can be used to make simplifying assumptions concerning the processes involved. Francis Sears and Mark Zemansky, in University Physics, give the example of calculating the landing location and speed of a baseball thrown in the air. They gradually strip the baseball of most of its properties, by first idealizing it as a rigid smooth sphere, then by neglecting rotation, buoyancy and friction, ultimately reducing the problem to the ballistics of a classical point particle. The treatment of large numbers of particles is the realm of statistical physics.

Generation (1960s TV series)

Generation was a Canadian current affairs television series which aired on CBC Television in 1965.

Premise

The series examined contemporary topics and concerns in the context of the generation gap. Issues such as careers, marriage, Quebec's Quiet Revolution, religion or tobacco were the subject of various episodes.

For most of its run, Generation was a local Toronto programme hosted by Lloyd Robertson. In mid-1965, it was broadcast nationally with selected local episodes supplemented by episodes produced from various regions. June Callwood, Katie Johnson and Bill McVean were additional hosts during the national broadcasts.

Scheduling

The half-hour series aired locally on CBLT from late 1963 until mid-1966. It was broadcast on the national CBC network Wednesdays at 10:30 p.m. (Eastern) from 4 August to 15 September 1965.

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1837 generation

The 1837 generation (Spanish: Generación del '37) was an Argentine literary group. Influenced by the new romantic ideas, they rejected the cultural Spanish heritage of the country. They considered themselves the "sons of the May Revolution", as they were born shortly after it, and wrote some of the earliest Argentine literary works. They did not acknowledge any national roots in the indigenous peoples or the period of European colonization, focusing instead on the Revolution as the birth of the country.

The group established a literary hall in 1837, hence the name. Initially, they claimed to be neutral in the Argentine Civil Wars, but in time they wrote works biased against the federal governor Juan Manuel de Rosas (such as El Matadero by Esteban Echeverría or Facundo by Domingo Faustino Sarmiento) and became fully Unitarians.

Some notable members of this generation were Esteban Echeverría, Juan Bautista Alberdi, Miguel Cané, Bartolomé Mitre, Andrés Lamas, Antonio Somellera, Vicente Fidel López, Carlos Tejedor, Juan Bautista Peña, Florencio Varela, Juan Cruz Varela, José Mármol, José Rivera Indarte (Buenos Aires), Domingo Faustino Sarmiento, Quiroga Rosas, Antonino Aberastain, Santiago Cortínez (San Juan), Benjamín Villafañe, Félix Frías (Tucumán), Francisco Álvarez, Paulino Paz, Enrique Rodríguez, Avelino Ferreyra, Ramón Ferreyra (Córdoba), Juan Thompson (Corrientes).

Immigrant generations

The term first-generation can refer to either people who were born in one country and relocated to another at a young age, or to their children born in the country they have relocated to. The term second-generation refers to children of first-generation immigrants, and thus exhibits the same ambiguity. The term 1.5 generation is a term coined for people who identify as "first generation" who do not meet the definition.

First generation

The term first-generation, as it pertains to a person's nationality or residency in a country, can imply two possible meanings, depending on context:

This ambiguity is captured and corroborated in The Oxford English Dictionary's definition of "generation":

In the United States, among demographers and other social scientists, the term "first generation" is used to refer to foreign-born residents (excluding those born abroad of American parents).

Particle (ecology)

In marine and freshwater ecology, a particle is a small object. Particles can remain in suspension in the ocean or freshwater. However, they eventually settle (rate determined by Stokes' law) and accumulate as sediment. Some can enter the atmosphere through wave action where they can act as cloud condensation nuclei (CCN). Many organisms filter particles out of the water with unique filtration mechanisms (filter feeders). Particles are often associated with high loads of toxins which attach to the surface. As these toxins are passed up the food chain they accumulate in fatty tissue and become increasingly concentrated in predators (see bioaccumulation). Very little is known about the dynamics of particles, especially when they are re-suspended by dredging. They can remain floating in the water and drift over long distances. The decomposition of some particles by bacteria consumes a lot of oxygen and can cause the water to become hypoxic.

Particle analysis

Particle levels in water (or air) can be measured with a turbidity meter and analyzed with a particle counter. They can also be scanned with an underwater microscope, such as ecoSCOPE. Collected particles of size 20 - 200 micrometers hovering in the free water in the vicinity of a harbor had the following contaminant levels (table). Many of those contaminants are carcinogenic.