I-beam
(noun)
A beam shaped like a capital letter I (with serifs top and bottom), used in construction.
Examples of I-beam in the following topics:
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Steel-Frame Construction
- Steel frame construction is a building technique in which vertical steel columns and horizontal I-beams form a 'skeleton frame'.
- Steel frame usually refers to a building technique with a 'skeleton frame' of vertical steel columns and horizontal I-beams, constructed in a rectangular grid to support the floors, roof, and walls of a building which are all attached to the frame.
- The horizontal elements of the "I" are flanges, while the vertical element is termed the 'web'.
- In steel frame construction, steel beams are connected to the columns with bolts and threaded fasteners, like screws, or permanent mechanical fasteners, called rivets.
- This I-beam is used to support the first floor of a house.
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Momentum Transfer and Radiation Pressure Atom
- Now consider a beam of light perpendicularly incident on a surface, and let us assume the beam of light is totally absorbed.
- The momentum the photons carry is a conserved quantity (i.e., it cannot be destroyed) so it must be transferred to the surface; thus the absorption of the light beam causes the surface to gain momentum.
- This gives us: pressure = momentum transferred per second per unit area = energy deposited per second per unit area / c = I/c, (where I is the intensity of the beam of light).
- Because light is detuned to the "red" (i.e., at lower frequency) of the transition, the atoms will absorb more photons if they move towards the light source, due to the Doppler effect.
- Thus if one applies light from two opposite directions, the atoms will always scatter more photons from the laser beam pointing opposite to their direction of motion (typical setups applies three opposing pairs of laser beams as in ).
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Center of Mass of the Human Body
- First, let's take two scales and a wooden beam (H meter long), long enough to contain the entire body of the subject.
- Put the scales H meters apart, and place the beam across the scales, as illustrated in .
- Now, let the subject lie on the beam.
- Make sure that his/her heels are aligned with one end of the beam.
- However, the equation of motion for torque $( \tau = I\alpha)$ helps.
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Absorption
- Phenomenologically you can imagine that there are many independent absorbers in the beam, each with a cross section $\sigma_\nu$ and a number density $n$.
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Emission
- The rate of the former is proportion to the intensity of the beam so it is convenient to lump it with the absorbing properties of the material.
- As a beam travels through the material, its intensity increases such that
- We know what $I_\nu$ is and we will spend much effort figuring out what $j_\nu$is for different physical systems.
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Energy, Intensity, Frequency, and Amplitude
- All these pertinent factors are included in the definition of intensity I as power (P) per unit area:
- Although you can increase the number of photons by increasing the intensity of a beam, the energy of individual photons in the beam is determined by the frequency of the beam.
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Cathode Ray Tube, TV and Computer Monitors, and the Oscilloscope
- It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images.
- The CRT uses an evacuated glass envelope which is large, deep (i.e., long from front screen face to rear end), fairly heavy, and relatively fragile.
- An image is produced by controlling the intensity of each of the three electron beams, one for each additive primary color (red, green, and blue) with a video signal as a reference.
- The beam is deflected horizontally by applying an electric field between a pair of plates to its left and right, and vertically by applying an electric field to plates above and below.
- Cutaway rendering of a color CRT: 1) Three Electron guns (for red, green, and blue phosphor dots) 2) Electron beams 3) Focusing coils 4) Deflection coils 5) Anode connection 6) Mask for separating beams for red, green, and blue part of displayed image 7) Phosphor layer with red, green, and blue zones 8) Close-up of the phosphor-coated inner side of the screen
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Interference Microscopy
- It is thus based on measuring the differences in refractive index upon recombining the two beams.
- Interference occurs when a light beam is retarded or advanced relative to the other.
- The microscope is a bright field light microscope with the addition of the following elements: a polarizer between the light source and the condenser, a DIC beam-splitting prism, a DIC beam-combining prism, and an analyzer .
- Manipulating the prism changes the beam separation, which alters the contrast of the image.
- Two parallel light beams pass through the specimen and combine to produce an image.
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Beams and Borrowed Divisions
- Beams are used to group any notes at the beat division level or shorter that fall within the same beat.
- In this example, the eighth notes are not grouped with beams, making it difficult to interpret the triple meter.
- If we re-notate the above example so that the notes that fall within the same beat are grouped together with a beam, it makes the music much easier to read.
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Diffraction Revisited
- George Paget Thomson passed a beam of electrons through a thin metal film and observed the predicted interference patterns.
- Clinton Joseph Davisson and Lester Halbert Germerguided their beam through a crystalline grid to observe diffraction patterns.
- For example, the scattering of X-rays is highly dependent on the atomic number of the atoms (i.e., the number of electrons), whereas neutron scattering depends on the properties of the nuclei.
- Typical electron diffraction pattern obtained in a transmission electron microscope with a parallel electron beam.