urban decay

Examples of urban decay in the following topics:

• Models of Urban Growth

  • Harlem, New York is an example of a neighborhood with a long history of urban growth and decay.
  • Since that period, the neighborhood experienced urban decay and became a hotbed of crime and poverty.
  • Such preferences echo a common strain of criticism of urban life, which tends to focus on urban decay.
  • According to these critics, urban decay is caused by the excessive density and crowding of cities, and it drives out residents, creating the conditions for urban sprawl.
  • Cities have responded to urban decay and urban sprawl by launching urban renewal programs.

• The Rural Rebound

  • During the 1970s and again in the 1990s, the rural population rebounded in what appeared to be a reversal of urbanization.
  • Since the 1950s, many middle and upper class individuals have moved to nearby suburbs to escape crime and urban decay.
  • White flight during this period contributed to urban decay, a process whereby a city, or part of a city, falls into disrepair and decrepitude.
  • Symptoms of urban decay include depopulation, abandoned buildings, high unemployment, crime, and a desolate, inhospitable landscape.
  • White flight contributed to the draining of cities' tax bases when middle-class people left, exacerbating urban decay caused in part by the loss of industrial and manufacturing jobs as they moved into rural areas or overseas where labor was cheaper.

• Urban Decline

  • Another characteristic of urban decay is blight, the visual, psychological, and physical effects of living daily life among empty lots, abandoned buildings, and condemned houses.
  • But what causes urban decay?
  • In some ways, urban decline is an inevitable result of urbanity itself.
  • Economic decline tends to lead to urban decline.
  • The current response to urban decay has been positive public policy and urban design using the principles of New Urbanism.

• Shrinking Cities and Counter-Urbanization

  • White flight during the post-war period contributed to urban decay, a process whereby a city, or part of a city, falls into disrepair and decrepitude.
  • Symptoms of urban decay include depopulation, abandoned buildings, high unemployment, crime, and a desolate, inhospitable landscape.
  • Urban decay was caused in part by the loss of industrial and manufacturing jobs as they moved into rural areas or overseas, where labor was cheaper.
  • This exurbanization may be a new urban form.
  • Often these approaches aim to increase urban density.

• The Potential of Urban Revitalization

  • Urban revitalization is hailed by many as a solution to the problems of urban decline by, as the term suggests, revitalizing decaying urban areas.
  • Urban revitalization is closely related to processes of urban renewal, or programs of land redevelopment in areas of moderate- to high-density urban land use.
  • Urban revitalization has been around since European city planners in the nineteenth century began to consider how to reorganize overpopulated urban areas.
  • Urban revitalization certainly provides potential for future urban growth, though the story of successes and failures remains mixed so far.
  • Urban renewal can have many positive effects.

• Radioactive Decay Series: Introduction

  • Radioactive decay series describe the decay of different discrete radioactive decay products as a chained series of transformations.
  • Radioactive decay series, or decay chains, describe the radioactive decay of different discrete radioactive decay products as a chained series of transformations.
  • Most radioactive elements do not decay directly to a stable state; rather, they undergo a series of decays until eventually a stable isotope is reached.
  • A parent isotope is one that undergoes decay to form a daughter isotope.
  • While the decay of a single atom occurs spontaneously, the decay of an initial population of identical atoms over time, $t$, follows a decaying exponential distribution, $e^{-t}$, where $\lambda$ is called the decay constant.

• Beta Decay

  • Beta decay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted from an atomic nucleus.
  • There are two types of beta decay.
  • Beta decay is mediated by the weak force.
  • A beta-stable nucleus may undergo other kinds of radioactive decay (for example, alpha decay).
  • The inset shows beta decay of a free neutron

• Gamma Decay

  • Gamma decay is a process of emission of gamma rays that accompanies other forms of radioactive decay, such as alpha and beta decay.
  • Gamma decay accompanies other forms of decay, such as alpha and beta decay; gamma rays are produced after the other types of decay occur.
  • For example, cobalt-60 decays to excited nickel-60 by beta decay through emission of an electron of 0.31 MeV.
  • Path of decay of Co-60 to Ni-60.
  • Explain relationship between gamma decay and other forms of nuclear decay.

• Half-Life of Radioactive Decay

  • The half-life is a parameter for the rate of decay that is related to the decay constant by: ${t}_{\frac{1}{2}}=\frac{ln2}{\lambda}$ .
  • Radioactive decay is a random process at the single-atom level; is impossible to predict exactly when a particular atom will decay.
  • However, the chance that a given atom will decay is constant over time.
  • The equation indicates that the decay constant λ has units of t-1.
  • The half-life is related to the decay constant.

• Rate of Radioactive Decay

  • Radioactivity is one very frequent example of exponential decay.
  • Particular radionuclides decay at different rates, so each has its own decay constant, λ.
  • A quantity undergoing exponential decay.
  • This plot shows decay for decay constants of 25, 5, 1, 1/5, and 1/25 for x from 0 to 5.
  • Apply the equation Nt=N0e−λt in the calculation of decay rates and decay constants