A-band

Examples of A-band in the following topics:

• Sliding Filament Model of Contraction

  • The I-band is spanned by the titin molecule connecting the Z-line with a myosin filament.
  • The region between two neighboring, parallel I-bands is known as the A-band and contains the entire length of single myosin myofilaments.
  • Within the A-band is a region known as the H-band, which is the region not superimposed by actin myofilaments.
  • The myofilaments themselves do not contract or expand and so the A-band remains constant.
  • The A-band remains constant throughout as the length of the myosin myofilaments does not change.

• Conductors

  • According to band theory, a conductor is simply a material that has its valence band and conduction band overlapping, allowing electrons to flow through the material with minimal applied voltage.
  • In solid-state physics, the band structure of a solid describes those ranges of energy, called energy bands, that an electron within the solid may have ("allowed bands") and ranges of energy called band gaps ("forbidden bands"), which it may not have.
  • Within an energy band, energy levels can be regarded as a near continuum for two reasons:
  • On the left, a conductor (described as a metal here) has its empty bands and filled bands overlapping, allowing excited electrons to flow through the empty band with little push (voltage).
  • Semiconductors and insulators have a greater and greater energetic difference between the valence band and the conduction bands, requiring a larger applied voltage in order for electrons to flow.

• Exchange Rate Systems

  • Crawling bands: The market value of a national currency is permitted to fluctuate within a range specified by a band of fluctuation.
  • This band is determined by international agreements or by unilateral decision by a central bank.
  • The bands are adjusted periodically by the country's central bank.
  • Generally the bands are adjusted in response to economic circumstances and indicators.
  • Pegged with horizontal bands:This system is similar to crawling bands, but the currency is allowed to fluctuate within a larger band of greater than one percent of the currency's value.

• Fixed Exchange Rates

  • A central bank does not specify an exact price, but it allows its currency to fluctuate within a band, depicted in Figure 8.
  • Consequently, a central bank allows the market to change the exchange rate within the band.
  • Thus, the exchange rate returns within the band.
  • If a central bank allows its currency to appreciate permanently outside the band, then we call it a revaluation.
  • On the other hand, if the central bank allows the currency to depreciate permanently outside the band, subsequently, we call it a devaluation.

• Semiconductors

  • The energy bands correspond to a large number of discrete quantum states of the electrons.
  • Most of the states with low energy (closer to the nucleus) are occupied, up to a particular band called the valence band.
  • In semiconductors, only a few electrons exist in the conduction band just above the valence band, and an insulator has almost no free electrons.
  • In semiconductors, the band gap is small, allowing electrons to populate the conduction band.
  • As the energy in the system increases, electrons leave the valence band and enter the conduction band.

• Doping: Connectivity of Semiconductors

  • In contrast, the energy states available to the free electrons in a metal sample form a continuum of "energy bands."
  • In the atomic lattice of a substance, there is a set of filled atomic energy "bands" with a full complement of electrons, and a set of higher energy unfilled "bands" which have no electrons.
  • The conduction band is the band above the valence band.
  • In order for a substance to conduct electricity, its valence electrons must cross the band gap, which is the energy gap between the valence band and conduction band.
  • The gap between the valence and conduction bands determines whether a substance will conduct electricity.

• Basics of DNA Replication

  • At the point, the molecules stopped sedimenting and formed a stable band.
  • DNA from cells grown exclusively in 15N produced a lower band than DNA from cells grown exclusively in 14N.
  • The DNA harvested from cells grown for two generations in 14N formed two bands: one DNA band was at the intermediate position between 15N and 14N and the other corresponded to the band of exclusively 14N DNA.
  • Dispersive replication would have resulted in exclusively a single band in each new generation, with the band slowly moving up closer to the height of the 14N DNA band.
  • DNA grown in 15N (red band) is heavier than DNA grown in 14N (orange band) and sediments to a lower level in the cesium chloride density gradient in an ultracentrifuge.

• Force

  • Hang one rubber band vertically on a hook.
  • Find a small household item that could be attached to the rubber band using a paper clip, and use this item as a weight to investigate the stretch of the rubber band.
  • Measure the amount of stretch produced in the rubber band with one, two, and four of these (identical) items suspended from the rubber band.
  • How large a stretch would you expect for the same number of items suspended from two rubber bands?
  • What happens to the amount of stretch of the rubber band (with the weights attached) if the weights are also pushed to the side with a pencil?

• Vibrational Spectroscopy

  • A molecule composed of n-atoms has 3n degrees of freedom, six of which are translations and rotations of the molecule itself.
  • One selection rule that influences the intensity of infrared absorptions, is that a change in dipole moment should occur for a vibration to absorb infrared energy.
  • Absorption bands associated with C=O bond stretching are usually very strong because a large change in the dipole takes place in that mode.
  • (It is easier to bend a bond than to stretch or compress it. )
  • The general regions of the infrared spectrum in which various kinds of vibrational bands are observed are outlined in the following chart.

• Regulation of Broadcast Media

  • frequency allocation: The division of the spectrum into unlicensed frequency bands, such as ISM band and U-NII band, and licensed frequency bands, along with television channel frequencies, FM broadcast band, and amateur radio frequency.
  • Among its provisions was the equal opportunity provision, which provided a foundation for the equal time rule.
  • This provision was a result of legislators' growing concerns that, without mandated equal opportunity for candidates, some broadcasters might try to manipulate elections.
  • The FCC's intent was to "regulat[e] interstate and foreign commerce in communication by wire and radio so as to make available, so far as possible, to all the people of the United States, without discrimination on the basis of race, color, religion, national origin, or sex, a rapid, efficient, Nation wide, and world wide wire and radio communications service . . . ".
  • In 1949, the FCC enacted the Fairness Doctrine for the purpose of ensuring balanced and fair coverage of all controversial issues by a broadcast station.