526. Q U I Z NO. 25

Q U I Z    NO. 25

OCEANS

1. In the following illustration what do you call the land that borders the oceans?

The shore is the land bordering the oceans

2. In the following illustration what is the name of the line separating the shore from the ocean?

Shoreline

3. As shown in the following illustration, what do you call the strip of land lying between low and high tide?

All of the landmass to the left of this line lies adjacent to the ocean and forms it border

This line separates the shore from the ocean, i.e., it represents the contact between water and land

A = high tide

B = low tide

The beach or shore face.

4. What do call the flat-topped ridge illustrated in the following image? Note that sand or

gravel is only deposited there during high tide.

Berm

5. What is the name of the feature that is defined as the area along the shore extending from the seaward position where sand particles are moved by waves to the landward edge of the permanent coast?

This is the technical definition of a beach.

6. What is the name of the feature illustrated below?

6. crest or crest line

7. What is the name of the feature illustrated below?

trough or trough line

8. What is the name of the feature illustrated by the length of the red arrow below?

Wavelength

9. What is the period of an ocean wave?

This is a flat-topped ridge

This red line represents the locus of the highest points on a wave

This red line represents the locus of the lowest points on a wave

Seabed

The period is the time it takes successive crests or troughs to pass a stationary point

10. What do you call the vertical distance from trough to crest?

wave height

11. If a typical wave had a wavelength of say 40 meters, and a period of 8 seconds, then what is its speed?

The magnitude of the velocity or speed is wavelength divided by time; hence, the velocity is 40 meters/8 seconds or 5 meters/sec.

12. In the following illustration what do you call the region over which wind blows

continuously?

Fetch is the maximum distance over which a given wind blows.

13. Please review the wave profile shown in the illustration for question 12. As waves

generated within a storm move outward away from the storm center and begin their travels

to distant shorelines what happens to their crest lines?

They become lower, more rounded, symmetrical, and sinusoidal in form.

14. The range of the period of common swell is __6__ to __16__ seconds.

15. The range of the wavelengths of common swell varies from__56__ to ___400___ meters

16. There is a mathematical relationship between wavelength and wave base for deep water ocean waves. What is that relationship?

Wave base is the limiting depth of particle motion as swell passes through a volume of seawater. It is equal to ½ the wavelength, i.e., wave base = (1/2) * where  is wavelength.

17. Particles lying above wave base follow what kinds of paths as swell pass through a given volume of seawater?

They follow a circular path.

18. Does the diameter of the circular path followed by particles above wave base increase or decrease with depth?

18. The diameter decreases with depth.

19. If you were in a submarine approaching a swell with a wavelength of 800 meters, then at what depth would you have to dive to in order to escape the effects of the oncoming swell?

The wind blows continuously over this region and

in the direction of the purple arrow

19. The answer is 800 meters/2 = 400 meters

20. Please review the following illustration, and then describe the condition under which a deep-water wave becomes a shallow-water wave?

20. When the seabed rises above wave base, then a deep water wave becomes a shallow water wave.

21. What happens to wavelength as deep water waves become shallow water waves?

21. Wavelength decreases

22. What happens to wave height as deep water waves become shallow water waves?

22. Wave height increases

23. What happens to wave period as deep water waves become shallow water waves?

23. Wave period remains unchanged

24. When the water depth is one-half the wavelength of a deep-water wave, water particles just above the bottom follow what kind of a path?

24. They begin to follow an elliptical rather than circular path.

25. Because water particles in a shallow-water wave follow a back-and-forth elliptical path it takes longer for water particles to complete their circuits than do water particles higher in the water column. As a result the seabed is said to exert what on the advancing wave?

25. traction or resistance to forward movement

26. When does an advancing shallow-water wave become unstable and start to break?

26. When the water depth reaches about 1.3 times its height it will break.

27. What is the name of the feature shown in the following illustration?

27. swash zone

28. What is the name given to surf rushing up the shore face?

28. swash

29. What is the name given to surf running back down the shoreface?

Within this zone surf runs up and then down this surface

29. backwash

30. Grains of sand caught in the swash zone will be dragged, pushed, and carried up the shore face in the direction of the swash, and then will be dragged, pushed, and carried down the shore face by the backwash acting under the influence of gravity. This process results in grains of sand being slowly translated down the beach. What is this overall process called?

30. long shore drift

31. Please review the following illustration. Note that as the swell approaches the shore the crests are even and parallel but at an angle to the shoreline. When this geometry occurs, the end of the approaching wave that is closest to the shoreline will feel the drag created by the seabed before the deeper water end does. Hence, it slows down and eventually breaks while the end furthest from the shoreline maintains its deep-water form and speed. As shown in the illustration what is the ultimate result of this overall process?

31. wave refraction – the bending of crestlines into parallelism with the shore line

32. The velocity of a wave is a vector as it has both magnitude and direction. In the following illustration the general vector showing the direction and magnitude of the approaching swell is broken down into components that are perpendicular and parallel to the shoreline. Which of these two components is responsible for long shore currents?

32. The component of wave motion that is parallel to the shoreline.

33. Along a coast line long shore currents traveling in opposite directions commonly meet. When this happens they turn and flow back out to sea. What are these seaward flowing currents called?

33. rip currents

34. How many tides occur in every 24 hour day?

34. 4 – 2 high and 2 low

35. What is the common center of mass of the Earth-Moon pair called?

Deep water swell – crests are parallel and

at angle to shoreline

End closest to shoreline

End furthest from shoreline

35. barycenter

36. Where is the common center of mass of the Earth-Moon pair located?

36. The barycenter lies along a line connecting the centers of the Earth and Moon, at a point about 1707 km (~1068 miles) below the surface of the Earth that faces the moon.

37. Inertial forces acting within the Earth-Moon pair are sometimes referred to as "outward" or "center" fleeing or “centrifugal” forces. After reviewing the above illustration are they everywhere the same on and within the Earth?

Yes

38. According to Sir Issac Newton, the gravitational pull of the Moon on any point on the Earth will vary inversely as the second power of the distance of that point from the Moon. After reviewing the above illustration is the gravitational attraction of the Moon everywhere the same on the Earth?

No

39. After reviewing the above illustration is the gravitational force of the Moon on the surface of the Earth facing the Moon greater or less than the inertial force?

The gravitation force is greater than the inertial or centrifugal force.

40. After reviewing the above illustration is the gravitational force of the Moon on the surface of the Earth facing away from the Moon greater or less than the inertial force?

The gravitation force is less than the inertial or centrifugal force.

41. What effect do your answers to the two previous questions imply about the world’s oceans or hydrosphere?

The hydrosphere (e.g., oceans) bulges toward the moon on the side of the Earth facing the moon, and away from the moon on the side of the Earth facing away from the moon. The Earth spins beneath these bulges resulting in two low and two high tides every 24 hours.

42. Please review the above illustration. As shown in (A) twice a month the centers of the Sun, Moon, and Earth are aligned in a straight line? During these events the gravitational field of the Sun works in concert with the gravity field of the Moon resulting in a tidal range higher than normal. What are these tides called?

Spring

43. As shown in (B) twice a month the centers of the Moon and Earth are aligned in a straight line at a right angle to the center of the Sun. During these events the gravity field of the Sun counteracts that of the Moon resulting in tidal ranges that are less than normal. What are these tides called?

Neap

525. Quotes - Learning

Quotes - Learning  

Anyone who stops learning is old, whether at twenty or eighty.     Anyone who keeps learning stays young. The greatest thing in life is to keep your mind young.
Henry Ford

If history repeats itself, and the unexpected always happens, how incapable must Man be of learning from experience?
George Bernard Shaw

Learning to trust is one of life's most difficult tasks.
Isaac Watts

The secret of success is learning how to use pain and pleasure instead of having pain and pleasure use you. If you do that, you're in control of your life. If you don't, life controls you.
Tony Robbins

Learning is the beginning of wealth. Learning is the beginning of health. Learning is the beginning of spirituality. Searching and learning is where the miracle process all begins.
Jim Rohn

There is no end to education. It is not that you read a book, pass an examination, and finish with education. The whole of life, from the moment you are born to the moment you die, is a process of learning.
Jiddu Krishnamurti

Develop a passion for learning. If you do, you will never cease to grow.
Anthony J. D'Angelo

An organization's ability to learn, and translate that learning into action rapidly, is the ultimate competitive advantage.
Jack Welch

The only thing that interferes with my learning is my education.
Albert Einstein

Leadership and learning are indispensable to each other.
John F. Kennedy

As long as you live, keep learning how to live.
Lucius Annaeus Seneca

A little learning is a dangerous thing; Drink deep, or taste not the Pierian spring.
Alexander Pope

Leave all the afternoon for exercise and recreation, which are as necessary as reading. I will rather say more necessary because health is worth more than learning.
Thomas Jefferson

I am still learning.
Michelangelo

I am not afraid of storms for I am learning how to sail my ship.
Louisa May Alcott

The learning and knowledge that we have, is, at the most, but little compared with that of which we are ignorant.
Plato

Don't limit a child to your own learning, for he was born in another time.
Rabindranath Tagore

Entire ignorance is not so terrible or extreme an evil, and is far from being the greatest of all; too much cleverness and too much learning, accompanied with ill bringing-up, are far more fatal.
Plato

While I thought that I was learning how to live, I have been learning how to die.
Leonardo da Vinci

Flying is learning how to throw yourself at the ground and miss.
Douglas Adams

You cannot open a book without learning something.
Confucius

Everybody who is incapable of learning has taken to teaching.
Oscar Wilde

A little learning is a dangerous thing, but we must take that risk because a little is as much as our biggest heads can hold.
George Bernard Shaw

God lets everything happen for a reason. It's all a learning process, and you have to go from one level to another.
Mike Tyson

I'm not afraid of storms, for I'm learning to sail my ship.
Aeschylus

A weed is a plant that has mastered every survival skill except for learning how to grow in rows.
Doug Larson

There are no secrets to success. It is the result of preparation, hard work, and learning from failure.
Colin Powell

It is only when we forget all our learning that we begin to know.
Henry David Thoreau

Instead of giving money to found colleges to promote learning, why don't they pass a constitutional amendment prohibiting anybody from learning anything? If it works as good as the Prohibition one did, why, in five years we would have the smartest race of people on earth.
Will Rogers

Like success, failure is many things to many people. With Positive Mental Attitude, failure is a learning experience, a rung on the ladder, a plateau at which to get your thoughts in order and prepare to try again.
W. Clement Stone

524. Terahertz radiation: Applications

Terahertz radiation: Applications

Terahertz radiation: applications and sources
Until recently, researchers did not extensively explore the material interactions occurring in the terahertz spectral region—the wavelengths that lie between 30 µm and 1 mm—in part because they lacked reliable sources of terahertz radiation. However, pressure to develop new terahertz sources arose from two dramatically different groups—ultrafast timedomain spectroscopists who wanted to work with longer wavelengths, and longwavelength radio astronomers who wanted to work with shorter wavelengths. Today, with continuous-wave (CW) and pulsed sources readily available, investigators are pursuing potential terahertz-wavelength applications in many fields.

Bio and astro
Much of the recent interest in terahertz radiation stems from its ability to penetrate deep into many organic materials without the damage associated with ionizing radiation such as X-rays (albeit without the spatial resolution). Also, because terahertz radiation is readily absorbed by water, it can be used to distinguish between materials with varying water content—for example, fat versus lean meat. These properties lend themselves to applications in process and quality control as well as biomedical imaging. Tests are currently under way to determine whether terahertz tomographic imaging can augment or replace mammography, and some people have proposed terahertz imaging as a method of screening passengers for explosives at airports. All of these applications are still in the research phase, although TeraView (Cambridge, England), which is partially owned by Toshiba, has developed a technique for detecting the presence of cancerous cells that is currently in human trials.

Terahertz radiation can also help scientists understand the complex dynamics involved in condensed-matter physics and processes such as molecular recognition and protein folding.
CW terahertz technology has long interested astronomers because “approximately one-half of the total luminosity and 98% of the photons emitted since the Big Bang fall into the submillimeter and far-infrared,” says Peter Siegel of the Jet Propulsion Laboratory (Pasadena, CA), and CW THz sources can be used to help study these photons.
One type of CW terahertz source is the optically pumped terahertz laser (OPTL). OPTL lasers are in use around the world, primarily for astronomy, environmental monitoring, and plasma diagnostics. A system installed at the Antarctic Submillimeter Telescope and Remote Observatory at the South Pole is the local oscillator for a THz receiver, which will be used to measure interstellar singly ionized nitrogen, H2D+, and carbon monoxide during the polar winter. Another system is slated for sub-Doppler terahertz astronomy use on the National Aeronautics and Space Administration’s SOFIA airborne astronomical platform.
In 2004, a 2.5-THz laser will ride a Delta rocket into space aboard NASA’s AURA satellite to measure the concentration and distribution of the hydroxyl radical (OH–) in the stratosphere, a critical component in the ozone cycle. (Currently there are no global data for OH– concentrations; only two spot measurements have been made using OPTL systems carried aboard high-altitude balloons.) The AURA system is less than 0.2 m3, weighs less than 22 kg, and consumes 120 W of prime power. It works autonomously and is designed to operate in orbit for more than five years.
The emerging field of time domain spectroscopy (TDS) typically relies on a broadband short-pulse terahertz source (Figure 1). A split antenna is fabricated on a semiconductor substrate to create a switch. A dc bias is placed across the antenna, and an ultrashort pump-laser pulse (<100 fs) is focused in the gap in the antenna. The bias–laser pulse combination allows electrons to rapidly jump the gap, and the resulting current in the antenna produces a terahertz electromagnetic wave. This radiation is collected and collimated with an appropriate optical system to produce a beam.
This TDS switch puts out a train of pulses, whose repetition frequency is the same as that of the femtosecond pump laser. Pulse widths are on the order of 100 fs, with average powers of a few microwatts and a frequency spread of >500 GHz. The pulse bandwidth is typically centered at about 1 to 2 THz. The details of the spectrum can vary significantly, however, depending on the design of the switch and pump-laser power, pulse width, and configuration.
Figure 2a shows a typical TDS setup. The terahertz pulse is distorted by selective absorption as it passes through a sample, causing delays in its arrival time at the detector. The transmitted beam is then focused onto a detector, which is essentially identical to the emitter except that it is unbiased. By varying the time at which the sample pump pulse arrives at the detector, successive portions of the terahertz pulses can be detected and built into a complete image of the pulse in terms of its delay time, or time domain. The data are then processed by fast Fourier transform analysis in order to convert the delay time into the frequency of the terahertz signal that arrives at the detector.
The absorption characteristics of terahertz radiation vary greatly from material to material, and this property can be used to create images. In 1995, Binbin Hu and Martin Nuss at Lucent Technologies’ Bell Laboratories created a terahertz imaging system using TDS and coined the term T-ray for these short, broadband terahertz pulses. The T-ray pulse is measured as it reflects from a sample. Because the pulse is so short, distance can be resolved by looking at the time of flight and then used to create a three-dimensional transparent reconstruction of various objects by measuring the time lapse between pulses reflected from different areas within the object (Figure 2b).
Optically pumped lasers
In its simplest embodiment, an OPTL system consists of a grating-tuned carbon dioxide pump laser and a far-infrared (FIR) gas cell mounted in a laser resonator. The pump beam enters the cell through an aperture in the high-reflecting resonator mirror. The pump laser is tuned to the appropriate absorption band, and lasing occurs. For several reasons, this is not as easy as it sounds. Both the absorption bandwidth of the vibrational energy state and the lasing bandwidth of its excited rotational states are quite narrow. Moreover, slight changes in the OPTL’s pumping wavelength or changes in the cavity length itself can inhibit lasing, and feedback interaction between the pump laser and the terahertz laser can affect stability. Therefore, designers must pay careful attention to all of these things to achieve reliable performance.
In the past, research groups often built their own OPTLs, which were typically large and extremely difficult to use and maintain. Today, OPTL laser systems are smaller and more reliable turnkey systems. These improved systems stem from several developments, including permanently sealed, single- mode, frequency-stabilized, folded-cavity, radio-frequency-excited waveguide CO2 lasers; sealed FIR gas cells that eliminate gas transport issues; and exquisitely stable passive resonator structures. The integration of these various improved laser technologies into a truly operator-friendly system has ensured ease of use.
Indeed, OPTLs can operate at many discrete frequencies, ranging from less than 300 GHz (1,000 µm) to more than 10 THz (30 µm). Different molecular gases each have their own spectrum of available lines. Sideband generation technology can add instantaneous tunability to any of the available OPTL laser lines.
Other terahertz sources
Many other terahertz source technologies have been investigated in the past four decades. Numerous groups worldwide are producing tunable CW terahertz radiation using photomixing of near-IR lasers. For example, Gerald Fraser’s group at the National Institute of Standards and Technology is frequency mixing the output of a near-IR, fixed-frequency diode laser with that of a tunable Ti:sapphire laser in a lowtemperature- grown gallium arsenide photomixer fabricated with the appropriate antenna pattern. This approach yields tens of nanowatts of tunable output with a spectral content governed by the spectral content of the near-IR laser.
Backward-wave oscillators (BWOs) are electron tubes that can be used to generate tunable output at the long-wavelength end of the terahertz spectrum. To operate, however, they require a highly homogeneous magnetic field of approximately 10 kG.
Direct multiplied (DM) sources, such as those marketed by Virginia Diodes, Inc. (Charlottesville, VA), take millimeter-wave sources and directly multiply their output up to terahertz frequencies. DM sources with frequencies up to a little more than 1 THz and approximately 1 µW of output have been used as local oscillators for heterodyne receivers in select applications, most of which are in radio astronomy. However, they can produce substantially more output power at lower frequencies, and they are often well suited to applications requiring frequencies of less than 500 GHz.
In addition, physicists in Italy, Switzerland, the United States, and the United Kingdom have recently demonstrated quantum-cascade semiconductor lasers operating at wavelengths in the 4.4-THz regime. These lasers are made from 1,500 alternating layers (or stages) of gallium arsenide and aluminum gallium arsenide and have produced 2 mW of peak power (20 nW average power), and advances in output power and operating wavelength continue at a rapid pace. Applying a potential across the device causes electrons to cascade through each stage, emitting photons along the way. The photon wavelength is determined by the thickness of the stages. These lasers currently work best at only a few kelvins, but in the future they could become an important source of commercial terahertz systems.
Table 1 compares some of the techniques for generating terahertz radiation. At present, only the OPTL, TDS, and DM systems are commercially available as turnkey systems. However, many researchers assemble TDS systems in the laboratory using readily available laser sources, and DM sources are often procured from a number of research organizations and at least one commercial source. The availability and operation of BWOs at terahertz frequencies are somewhat problematic, but several groups use lower-frequency (<500-GHz) BWOs for device characterization.
The choice of a terahertz source will determine the type of detection scheme required. Sources with submilliwatt output power complicate detection and often necessitate the use of liquid-helium-cooled bolometers or similar devices. Short-pulse terahertz devices often need gated detection using a TDS switch.
For time-domain spectroscopy, or where an overall snapshot of the spectral characteristics of a sample in the terahertz region is important, TDS technology may be the optimal choice. For a more precise, higher-resolution look, consider the OPTL system, using either discrete frequencies or tunable sideband generation technology. Many applications do not need the complete terahertz spectrum of a sample but merely need to identify one or two characteristic features. In these cases, the OPTL system may be preferable to the TDS system because of its operational simplicity, high signal-to-noise ratio, and ability to use conventional, roomtemperature detectors.
Although the practical application of terahertz radiation is in its infancy, the recent availability of reliable sources in the 0.3- to 5-THz range may have a wide-ranging impact on science, industry, and medicine. Short-pulse terahertz systems are used in time-domain spectroscopy to understand biological processes and to create two- and three-dimensional images. CW OPTL systems have been used extensively in aerospace and astronomical applications, primarily for remote sensing, and may find new uses as terahertz applications mature.