Archive for June, 2012

Space Elevator Cable

[From the Wikipedia article about the “Space Elevator.”]

Historically, the main technical problem has been considered the ability of the cable to hold up, with tension, the weight of itself below any particular point. The vertical point with the greatest tension on a space elevator cable is at the level of geostationary orbit, 35,786 km (22,236 mi) above the Earth’s equator. This means that the cable material combined with its design must be strong enough to hold up the weight of its own mass from the surface up to 35,786 km. By making any cable larger in cross section at this level compared to at the surface, it can better hold up a longer length of itself. For a space elevator cable, an important design factor in addition to the material is how the cross section area tapers down from the maximum at 35,786 km to the minimum at the surface. To maximize the usable excess strength for a given amount of cable material, the cable’s cross section area will need to be designed in such a way that at any given point, it is proportional to the force it has to withstand.

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A space elevator cable must carry its own weight as well as the (smaller) weight of climbers. The required strength of the cable will vary along its length, since at various points it has to carry the weight of the cable below, or provide a centripetal force to retain the cable and counterweight above. In a 1998 report, NASA researchers noted that “maximum stress [on a space elevator cable] is at geosynchronous altitude so the cable must be thickest there and taper exponentially as it approaches Earth. Any potential material may be characterized by the taper factor – the ratio between the cable’s radius at geosynchronous altitude and at the Earth’s surface.”

The cable must be made of a material with a large tensile strength/density ratio. For example, the Edwards space elevator design assumes a cable material with a specific strength of at least 100,000 kN/(kg/m). This value takes into consideration the entire weight of the space elevator. An untapered space elevator cable would need a material capable of sustaining a length of 4,960 kilometers (3,080 mi) of its own weight at sea level  to reach a geostationary altitude of 35,786 km (22,236 mi) without yielding. Therefore, a material with very high strength and lightness is needed.

For comparison, metals like titanium, steel or aluminium alloys have breaking lengths of only 20–30 km. Modern fibre materials such as kevlar, fibreglass and carbon/graphite fibre have breaking lengths of 100–400 km. Quartz fibers have an advantage that they can be drawn to a length of hundreds of kilometers even with the present-day technology. Nanoengineered materials such as carbon nanotubes and, more recently discovered, graphene ribbons (perfect two-dimensional sheets of carbon) are expected to have breaking lengths of 5000–6000 km at sea level, and also are able to conduct electrical power.

For high specific strength, carbon has advantages because it is only the 6th element in the periodic table. Carbon has comparatively few of the protons and neutrons which contribute most of the dead weight of any material. Most of the interatomic bonding forces of any element are contributed by only the outer few electrons. For carbon, the strength and stability of those bonds is high compared to the mass of the atom. The challenge in using carbon remains to extend to macroscopic sizes the production of such material that are still perfect on the microscopic scale (as microscopic defects are most responsible for material weakness). [But] the current (2009) carbon nanotube technology allows growing tubes up to a few tens of centimeters.

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Ok, so here’s my solution:

That’s right. Genetically modify or “trick” spiders (or silk worms) to weave the carbon nano-tube fibers into long strands.

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So, you think you remember the music of the 50s, 60s and 70s? See how many of the songs below you can guess right off, without doing a Google Search. If you get all ten of them, then you obviously have a very high Music IQ, so give yourself a large pat on the back.

1. Look at that bum over there, man he’s down on his knees.

2. In the middle of the color cartoon, I started to cry.

3. Every form of refuge has its price.

4. When the rooster crows at the break of dawn, look out your window and I’ll be gone.

5. When you know as well as me, you’d rather see me paralyzed.

6. His clothes are dirty, but his hands are clean.

7. Now we can thank the companies, a-scourin’ the deep blue seas, looking for ivory and perfume, and oil to light their livingroom.

8. And some other woman’s crying to her mother, ’cause she turned and I was gone.

9. I should be sleeping like a log.

10. I’ve lived a life that’s full, I’ve traveled each and every highway.

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Mayan Calendar

Speaking of the Mayan calendar, have  you seen the girl of the month?

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Is the world going to end, when the Mayan calendar runs out?

For me it already ended, when the Yokohama Tire Corporation calendar ran out…


Disclaimer:  I’m sure I used to see them in many auto repair shops, hanging right beside the Pirelli Calendars. But I could have just dreamed it.

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Framework Connections

Any unit on early California history must conform to the current California Social Studies Standards and Framework guidelines, to constitute a workable curriculum for 4th grade students. Not all standards need to be covered to the same degree, indeed no single unit can address them all sufficiently, and some may receive rather short shrift, so long as the lessons taken together do comprise a complete thematic unit.

In truth, the standards need only be used to inform instruction, not define it. Nor should the teacher allow them to hang over their desk like a sword of Damocles, or interfere with their teaching style or their ability and their desire to design an educational experience best suited to their students’ interests, learning styles and abilities.

On the other hand, the California Social Studies standards do provide a general sense of the content to be covered in any grade level and I generally will use them and refer to them as guides before planning any curriculum.

More importantly, in my opinion, the unit should conform to the NCHS (National Center for History in Schools) Standards for Historical Thinking. Teaching History and Social Studies is one thing, but teaching a student how to think chronologically; comprehend historical data in the form of documents, maps and art; analyze and interpret fact and fiction; formulate historical questions and  research the answer; and recognize dilemmas and problems in the past and the decisions that were made to address them, that is, historical thinking, is a far more important thing than learning a lot of facts.

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What exactly is social studies? I always thought of it as a watered-down version of history for kids, with a few songs and speeches thrown in to make it interesting and create a spirit of patriotism. As children we sang The Star-Spangled Banner, America the Beautiful, and The Battle Hymn of the Republic, pretty much until we were red, white and blue in the face, and every morning we had to recite the Pledge of Allegiance. I vividly remember my older brother and sister struggling for days with cumbersome words like “consecrate” and “hallowed” when they had to memorize The Gettysburg Address, but for some reason I was spared that torture.

The National Council for the Social Studies (NCSS; 1994) defines “social studies” as an integration of many subjects “to promote civic competence” in a democratic society. Practically any field of endeavor that might help young people develop the ability to make informed and reasoned decisions for the public good should not be excluded from the social studies curriculum, though traditionally history, geography, economics and political science have been the primary subjects.

Prior to fourth grade I don’t remember much of what I was taught under the umbrella of the social studies, but I very vividly remember reading about early California, and especially about the Spanish explorers and conquistadors like Columbus, Magellan, Cortez and Pizarro. I was particularly enthralled by the stories of Cabeza de Vaca and Coronado in their search for the Seven Cities of Gold and the Isla de California, and Balboa’s trek across the isthmus of Panama to discover the great Pacific Ocean, and the journeys of Father Junipero Serra and his founding of many of the California missions. One of the most popular tv shows at the time was Zorro, which, as it turned out, became a wonderful companion to what I was learning in school about the Spanish colonies.

California history is one of my favorite subjects, and my greatest fear in teaching social studies to fourth graders today is that it won’t be “their” favorite. California is, and always has been a land for dreamers. From the very beginning people have come here in search of a better life. As their descendents we are the rightful heirs to their great legacy, and entitled to know the truth about them. Whether our ancestors were pioneers who crossed the plains for gold in covered wagons or Okies in old trucks, escaping the poverty of the Dust Bowl, Chinese immigrants “shanghai-ed” in their own country and sent to work on the transcontinental railroad, or migrant workers from Mexico, we all have a legitimate claim to stake in California.

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