Pa'l Bailador

El transbordador espacial se queda en tierra

Tomado de: http://www.motor.com.co/revista-motor/el-ultimo-vuelo-del-transbordador-espacial_9740524-4
Autor: José Clopatofsky

El aparato más complejo, sofisticado y peligroso hecho por el hombre hace su última misión espacial, después de 136 vuelos y pasa a la historia de los intentos del hombre por conquistar el espacio.

Antieconómico y muy difícil de sostener técnicamente, después de 136 vuelos en 34 años, si es exitosa su última salida, la Nasa jubila su flota de transbordadores.

En este final de junio o en los días próximos, dependiendo del clima, se cerrará el ciclo de la máquina más compleja -y peligrosa- desarrollada por el hombre en materia espacial y probablemente de todos los tipos. El transbordador espacial Atlantis de la NASA (STS, Space Transport System y luego genéricamente Space Shuttle) hará el último viaje al espacio antes de ser dado de baja junto con los otros cinco ejemplares de este subliminal aparato cuyas misiones nunca lograron el rendimiento que les planificó ni la invulnerabilidad de la aeronave más compleja construida hasta la fecha.

En efecto, de los seis aparatos fabricados desde cuando el presidente de Estados Unidos, Richard Nixon, autorizó la construcción de este proyectil tripulado, en febrero de 1972, cinco fueron operativos ya que el primero que se hizo, llamado Enterprise, no estaba previsto para salir al espacio sino para ensayos de vuelos en la atmósfera, tres sobrevivieron y apenas lograron realizar 135 misiones, cuando el proyecto contemplaba 50 vuelos al año.

La necesidad del transbordador venía de la ineficiencia de los cohetes que se estaban usando para colocar satélites y otros elementos en el espacio pues no eran recuperables ni tripulados.
Hacer un avión capaz de salir de la órbita terrestre, realizar misiones de todo tipo y regresar a la tierra, fue la solución que se adoptó mezclando los proyectos de la NASA y la Fuerza Aérea de Estados Unidos. Las cuentas de los promotores del proyecto resultaron completamente irreales pues calcularon cada vuelo en 10.5 millones de dólares y terminaron costando entre 300 y 400 millones en promedio y hay operaciones cuya factura pasó de los 1.000 millones de billetes verdes.

A pesar de que su planificación económica fue un desatino, el Transbordador siguió adelante tan solo para encontrar más dificultades pues operativamente la nave presentó costos astronómicos de recuperación después de los vuelos, derivados especialmente del reemplazo de miles de las "tejas" de silicio (lleva cerca de 30 mil) que protegen la nariz del avión del altísimo calor que produce la fricción con el aire al regresar a la atmósfera cuando alcanza cerca de 27.000 kilómetros por hora. En esos momentos, el frente del transbordador puede estar a más de 2.000 grados centígrados.

Las "tejas" se desprendían o deterioraban aunque nunca fueron la causa de los accidentes tal como se temía siempre que despegaba una misión. El Challenger se incendió porque se presentaron fugas de combustible luego de 73 segundos de vuelo y el Columbia se desintegró al regresar a la atmósfera porque un pedazo de espuma aislante se desprendió y rompió el ala izquierda del aparato, a pesar de lo cual la NASA autorizó su regreso a la tierra, aunque no es claro si habría alguna forma de reparar el plano en el espacio.

El transbordador es un avión pequeño, pero muy ancho y espacioso pues se trata de un carguero. Mide 17.25 metros de altura en la cola, 37.24 metros de largo y se apoya en una envergadura de 23.8 metros de ancho. Para dar una referencia, metros más o menos, es muy cercano al tamaño de un Airbus 320.

Cualquiera de los transbordadores depende de propulsión externa para ascender y salir de la órbita terrestre. Para ello lo acoplan en la plataforma de lanzamiento a dos cohetes. Para surtir el combustible, hay un gran tanque desechable que mide 46.14 metros de largo y 8.28 metros de diámetro. Va lleno de oxígeno e hidrógeno líquidos y alimenta los tres motores del transbordador que funcionan durante 8 minutos y medio después del lanzamiento, hasta una altura de 109 kilómetros.

Otros dos cohetes laterales, recuperables, que pesan cada uno 6 toneladas, van cargados con perclorato de amonio (oxidante) y aluminio (combustible). Todo el conjunto pesa 2.041 toneladas pero apenas regresan 104 toneladas después del viaje, representadas en el peso de la nave vacía.

Para maniobrar en el espacio y para regresar a la tierra quebrando la resistencia de la atmósfera, los transbordadores llevan tres motores que pueden generar un empuje de 1.8 meganewtons y son las plantas motrices más poderosas jamás construidas. Estos motores son reutilizables y se encienden en varias fases de cada
misión. Se fabricaron 46 unidades.

En el diseño de la fantástica máquina que resume la tecnología espacial pues se actualizó constantemente aunque nunca perdió su esencia técnica, tal como pasó con el avión supersónico Concorde, jugó más el aparato que el hombre pues no tiene ningún sistema de protección para los 5 a 7 tripulantes que suelen conducirlo. También es cierto que en cualquiera de las condiciones de funcionamiento, salvo tal vez en su aproximación final a la pista, no hay condiciones exteriores en caso de una eyección para que sobrevivieran sus pilotos, que volaron siempre amarrados a un potencial ataúd.

Los dos accidentes y los fantásticos costos de volar los transbordadores acabaron por enterrar el ambicioso y espectacular programa espacial de los Estados Unidos, que llegó a ser compartido con los orbitadores rusos y la estación espacial soviética, generando una paz en el espacio en donde se temía una guerra de alcances insospechados. En 2004, el presidente Bush le dictó la sentencia de defunción al programa a partir de 2010 una vez se terminara el montaje de la estación espacial, que ahora será atendida por las naves rusas Soyouz.

Bush, sin embargo, dejó el sueño espacial abierto pues lanzó un nuevo programa "Constellation" que supuestamente llevaría de nuevo al hombre a la luna en 2020. En realidad era una reestructuración del programa Apolo, que funcionaría con cohetes y módulos como el ya visto. Poco se demoró el presidente Obama en descartar también este proyecto con una frase contundente:
"A la luna ya fuimos, el espacio es enorme".

Para acometer la conquista del espacio en términos más ambiciosos se hará una nueva generación del transbordador, más eficiente y capaz en el cual el hombre visite asteroides en 2025 y vaya a Marte (2030), según Obama, pero hasta la fecha, cuando el transbordador hace su vuelo de despedida, todo está en puras palabras y fantasía.

Entre tanto, hay sociedades privadas que trabajan en crear un sistema de vuelos comerciales de carga, no tripulados en órbitas bajas. Se trata de las firmas Space X y Orbital Science que han recibido apoyo económico de la Nasa, mientras se inventa una manera rentable de conciliar los sueños espaciales del hombre con la verdadera utilidad de estos aparatos.

José Clopatofsky

Con información de Nasa y múltiples sitios de Internet relacionados.

Los seis aparatos

ENTERPRISE: Salió en junio de 1977. Fue una maqueta operativa que nunca estuvo en el espacio pues se utilizó para todos los ensayos preliminares de vuelo. Está en el Museo del Aire y del Espacio, en Washington.
COLUMBIA: Debutó en abril del 81 y fue el primer transbordador que estuvo en el espacio. Después de 28 vuelos y 300 días en órbita, estalló al regresar a la atmósfera terrestre el 1 de febrero de 2003. Hizo la misión más larga, de 17 días y 15 horas.
CHALLENGER: Aparece en abril del 83. Hizo 9 misiones y en una de ellas se hizo la primera salida al espacio por parte de un astronauta. Se incendió al despegar el 28 de enero de 1986.
DISCOVERY: Entró en servicio en agosto de 1984 y realizó 39 misiones, el récord en la materia. Lo jubilaron el 9 de marzo de este año. Puso en órbita el telescopio Hubble y por primera vez tuvo una mujer en sus mandos, Eileen Collins.
ATLANTIS: Lo activaron en octubre de 1985. Hizo 33 misiones que
sumaron 303 días en órbita. Envió la sonda Galileo hacia Júpiter y atendió fundamentalmente labores militares en la estación rusa MIR y en la ISS (International Space Station). A última hora, le autorizaron una misión adicional que será la final del proyecto.
ENDEAVOUR: El más nuevo pues se estrenó el 7 de mayo de 1992 y realizó el, hasta ahora, vuelo final que cerraría la era de los transbordadores el 1 de junio de este año. En 25 misiones hizo el mantenimiento del telescopio espacial Hubble y recuperó el satélite japonés Space Flyer. Lo usaron básicamente en el montaje de la ISS.

Aló... aquí houston
El corazón de las misiones estaba en Houston, donde opera el centro de dirección de vuelo, cuya complejidad se aprecia claramente. El puesto de mandos del transbordador y en general todo su interior son un mar de indicadores y computadores desde los cuales se maneja no solo la nave sino también toda la carga, brazos para manipularla, cámaras, instrumentos de medición y el ambiente interno de la cabina.

Dependencia
Una vez en tierra, el transbordador no tenía posibilidad de movimientos autónomos por falta de motores. Para ir de una base a otra, por ejemplo, cuando aterrizaba en California y debía ir al sitio de lanzamiento en el Kennedy Space Center de Florida, lo volaban sobre un Boeing 747 "Jumbo" acondicionado para este efecto. También estaba previsto remolcarlo en carreteras normales, rodando sobre sus propias ruedas. Un enorme aparato se encargaba de moverlo desde su hangar de preparación y colocarlo en el sitio de lanzamientos.

Llegaba con el impulso
Una de las características desconocidas de los transbordadores es que una vez quebrada la resistencia para reingresar a la atmósfera terrestre, no disponía de motores para llegar a la pista. Funciona como un planeador de ahí que la maniobra de llegada es sumamente compleja y se debía preparar con suma atención desde el punto de vista meteorológico. En Estados Unidos había tres bases preparadas para recibirlo de manera permanente (Kennedy en Florida y Edwards y Vanderberg en California, pero en el resto del mundo había muchos sitios adecuados para un aterrizaje en caso de que el mal tiempo lo obligara y se acabara el impulso.
Después de entrar a la atmósfera a unos 40.000 kilómetros por hora y a 120 kilómetros de altura, se hace el descenso hacia la pista sin motores. A 3.000 metros de altura y a 12 kilómetros de la
pista, se aplican los frenos aerodinámicos para bajar la velocidad de 680 a 346 kph, que es su velocidad de toque (260 kph en un avión normal). El tren de ruedas se saca a 430 kph. Al tocar tierra se activan los frenos aerodinámicos (Speed brakes) y los mecánicos y cuando va a 110 kph. sale un paracaídas, que se despliega asistido por un pequeño cohete, que completa la detención.
Aunque tiene obviamente toda suerte de automatismos de pilotaje en la mayoría de las misiones el aterrizaje se hizo manualmente.
La pista de Florida tiene casi 5 kilómetros de largo y 91 metros de ancho y todas las alternas son similares o más grandes.

FRASES

La aventura tecnológica más costosa y osada de la historia aterriza definitivamente. Estados Unidos da por terminado el proyecto de los transbordadores espaciales y ahora piensa en otra fantasía: ir a Marte en el 2030.

En cualquier de sus manifestaciones, el Transbordador era espectacular. Por ejemplo cuando era trasladado entre las bases sobre un Boeing 747 especialmente acondicionado para esta tarea tan singular.

Cada vez que se encendían los megamotores había un riesgo enorme de incendios y explosiones.

COPYRIGHT © 2011 EL TIEMPO Casa Editorial

A man’s wisdom gives him patience; it is to his glory to overlook an offense. – Proverbs 19:11 (NIV)

It is one thing to be patient when things are going our way; it is another thing to be patient when we feel wronged. As C.S. Lewis stated, “Everyone feels benevolent if nothing happens to be annoying us at the moment.” We show our true wisdom when we are faced with offense. Can we overlook the faults of others – even when it hurts?

© 2011 theDailyBibleVerse.org

Anticuña de la Semana: 'Un mundo de diversión, los nuevos juguetes: El Play Nule'

Tomado de: http://www.radioactiva.com/oir.aspx?id=1473083

http://www.radioactiva.com/

Mike Matas: A next-generation digital book

Tomado de: http://www.ted.com/talks/mike_matas.html
Autor: Mike Matas

© TED Conferences, LLC

Half a Miracle: Medellín's rebirth is nothing short of astonishing. But have the drug lords really been vanquished?

Tomado de: http://www.foreignpolicy.com/articles/2011/04/25/half_a_miracle?page=full
Autor: FRANCIS FUKUYAMA, SETH COLBY

Francis Fukuyama is Nomellini senior fellow at Stanford University's Freeman Spogli Institute for International Studies.
Seth Colby is executive director of the Schwartz Forum on Constructive Capitalism at the Johns Hopkins School of Advanced International Studies.

Fifteen years ago, a single mother named Libia Gomez converted part of her modest cinder-block house into a shop selling sundries ranging from pencils to toothpaste. The location was hardly ideal. Gomez lived in Santo Domingo Savio, a onetime squatter community on a steep, forested slope overlooking the Colombian city of Medellín that had evolved into a permanent slum.

Santo Domingo had grown so violent that even the police would not dare to enter. Gomez could see Medellín's city center, a mere two miles to the south, from Santo Domingo, but getting there safely was nearly impossible because traveling down the hill into town would have required crossing multiple zones controlled by rival armed groups. The rest of the city was not much better: Several years after Pablo Escobar, kingpin of the Medellín cocaine cartel, had been gunned down by police while fleeing across the rooftops of the middle-class barrio Los Olivos, Medellín remained the world's most violent city.

Today, Gomez is able to look down on the once impassable route from aboard the Metrocable, a ski-resort-style gondola system that carries residents of Santo Domingo high over the cityscape of red-brick buildings to the metro linking them to the rest of Medellín. Her shop sits in the shadow of the Parque Biblioteca España, an ultramodern library complex that presides over the city like the Spanish citadels of 500 years ago. The surrounding community has become one of the city's most popular tourist draws. "In the old days, my son would be afraid to walk to school. Now he walks freely," Gomez told us.

This is the sort of story people offer when they talk about the "Miracle of Medellín." In 1991, the city had an astronomical 381 homicides per 100,000 residents (by contrast, the murder rate in Ciudad Juárez, the bloody epicenter of Mexico's drug war, was only half that last year). But today Medellín has, incredibly, become as safe as Washington.

Medellín's reinvention holds potentially important lessons not only for the drug war in Mexico, but also for everyone else. Over the past generation, Americans have grown cynical about grand experiments in urban planning and other sweeping social-policy programs. But for most of the world's population, consumed with the necessities of day-to-day existence, getting social services right matters a lot more than ideology, as populist autocrats like Hugo Chávez and Islamist groups like Hamas and Hezbollah have figured out. Think government can't deliver smart, intelligent urban design that changes lives? Travel to Medellín, and it's hard to remember why it is that Americans have given up trying.

From the outset, Medellín had one big thing going against it: It was in Colombia. Over a 10-year period in the middle of the 20th century known as La Violencia, the country's two main political parties engaged in a brutal civil war that claimed 200,000 lives. The warring factions brokered a power-sharing deal in 1958, but peace was only temporary; the pact excluded other political movements -- most notably the leftist Fuerzas Armadas Revolucionarias de Colombia (FARC) -- which took to the jungles and began a still-ongoing guerrilla war against the Colombian state.

The war was enabled, and prolonged, by the traditional weakness of Colombia's national government, which operated only a small army and national police. Members of the country's traditional elite liked things this way, preferring to protect themselves by arming local paramilitaries. Over time, the paramilitaries grew in size, power, and independence and, like the leftist groups, began trafficking in drugs to support themselves. As peasants fleeing the violence in the countryside sought refuge in Medellín, the city's population exploded, growing from 350,000 in 1951 to 1.5 million in 1985 -- an influx the city was in no condition to absorb. The new inhabitants colonized the hillsides and created insular communities, like Santo Domingo, in which the state had no presence at all.

These conditions were exacerbated by the rise of the drug trade in the late 1970s, driven by demand for cocaine in the United States. But Medellín's problems didn't end with the fall of Escobar and the dismantling of the Medellín cartel in 1993; other drug cartels, guerrilla groups, and paramilitaries stepped in. By the early 2000s, so many people were being kidnapped and held for ransom by the FARC that a weekly radio show, Las Voces del Secuestro, was established to allow their relatives to broadcast messages to them.

Things began to change with the election of Álvaro Uribe as president of Colombia in 2002. Pledging "Democratic Security," Uribe dramatically expanded Colombia's military and national police and launched an all-out offensive against the FARC. Doing so rewrote the basic Colombian social contract: Henceforth, it would be the state and not private militias that provided security to Colombian citizens. The president negotiated an agreement with the largest paramilitary organization, the Autodefensas Unidas de Colombia; the group's fighters were required to lay down their weapons and abide by Colombia's anti-drug laws in exchange for pardons. But the demobilization has been severely criticized by observers both inside and outside Colombia. Human Rights Watch's Maria McFarland, a longtime Colombia observer, argues that the policy was too lenient on the paramilitaries and unenthusiastically enforced; many within the Colombian elite, she and other critics have charged, could not afford to push the judicial process too far for fear of exposing their own ties to the militias. Nevertheless, between 2002 and 2003 Medellín's homicide rate fell 46 percent, and it kept falling until 2007.

At the same time, Medellín was undergoing a crucial social and political transformation. In the early 1990s, fed-up members of the city's community organizations and religious, academic, and business institutions began convening regularly to discuss ideas to fix their embattled city. Alonso Salazar, the current mayor of Medellín and a participant in the meetings, recalls, "At that moment, a social movement came to life within the city that was dedicated to the resistance of the drug trade and violence."

It would take a political revolution, however, to turn the ideas into a real-world policy agenda. This revolution was led by a newcomer to politics: Sergio Fajardo, a professor with a Ph.D. in mathematics from the University of Wisconsin who became mayor in 2004, boosted by an unorthodox coalition of business people, grassroots community organizers, and the middle class.

Telegenic with his trademark blue jeans, open shirt, and curly locks, Fajardo began writing a regular column in the 1990s for the Medellín newspaper El Mundo about local politics. "We realized," Fajardo told us, "that politicians are the ones who make important decisions in society whether we like it or not, so we said to ourselves that we have to get into politics. Instead of saying how things should be, we said this is the way it is done." In Fajardo's view, Medellín had two fundamental, and related, problems: extreme inequality and a culture of violence. Fajardo believed that policies aimed at repairing the city's damaged social fabric could alleviate both.

The most striking feature of Fajardo's approach was his plan to erect high-quality public architecture in Medellín's poorest neighborhoods. "Architecture sends an important political message," he says. "When you go to the poorest neighborhood and build the city's most beautiful building, that gives a sense of dignity." Fajardo and his colleagues believed in social urbanism: the idea that modernist buildings and transportation systems of the sort Libia Gomez now enjoys would help bridge the enormous gulf of distrust separating the poor from mainstream society. In barrios like Santo Domingo and Comuna 13, the city created digitized maps of every street and building, noting where drug gangs operated and money flowed, and devised architectural features to disrupt them.

Fajardo also needed to deal with the thousands of demobilized fighters who had never interacted with normal society without a gun in their hands. This was no small task; many had lived in a world of violence and criminality for most of their adult lives. More than 70 percent of them were functionally illiterate, and few had employable skills. Unsurprisingly, the success of the reintegration programs Fajardo's administration launched has not been unequivocal. Human Rights Watch claims that many of the more than 30,000 officially "demobilized" in the country were not even active combatants, but, rather, poor individuals seeking generous social programs. In Medellín, 16 percent of the more than 5,000 participants have been expelled, arrested, or killed, and the temptation to relapse is unlikely to go away as long as jobs are few and wages are low. Still, Medellín's failure rate is lower than most other demobilization efforts in Africa and Asia -- and the cartels have not returned, at least not in force.

Of course, these new social programs cost a tremendous amount of money. The renovation of Comuna 13 alone, a barrio of 135,000 inhabitants, cost $155 million over a three-year period. Total spending by Medellín's city government doubled between 2004 and 2008. But two sources of funding in particular have made the gargantuan expense of rebuilding Medellín affordable: Medellín's city-owned utility company, Empresas Públicas de Medellín, which is well run and profitable, and a high municipal tax rate that is tolerated by a uniquely civic-minded business elite. Many in this group refused to flee to Miami even at the height of the violence and have come to believe that a safer city is worth the extra cost. "We had a responsibility to our own family, the business, and the city," says Juan Luis Restrepo, the American-educated owner of a Medellín-based textile company.

Can Medellín's example help save Mexico? Yes and no. Because of Colombia's centralized system of government, Uribe was able to professionalize and expand law enforcement from Bogotá; federally organized Mexico's huge problem with police corruption, a major barrier to winning the drug war, lies primarily at the local level, beyond the constitutional reach of authorities in Mexico City.

That said, there are useful lessons Mexico can draw from the Medellín miracle. Like Colombia in the 1990s, Mexico is vastly underpoliced and has a weak judiciary, problems that can be solved in time with sufficient resources and will. But Colombia's drug war shows that the battle will not be won by military force alone. The government needs to bolster its legitimacy by offering people alternatives to crime and violence, as well as a renewed commitment to public services -- something Medellín's metro, its starkly beautiful new buildings, and civilized public spaces now do.

The harder lesson here, however, is that there are no quick fixes in a drug war, and two steps forward are often followed by one step back. After bottoming out in 2007, Medellín's homicide rate has since doubled (though it is still one-fifth of what it was at the city's early-1990s nadir). Nearly everyone in the city agrees that the uptick in violence was the result of the Colombian government's 2008 decision to extradite to the United States former paramilitary leader turned crime boss Diego Murillo Bejarano, locally known as Don Berna. What that meant, in effect, was that the critics had been correct: The Colombian government hadn't actually successfully demobilized the drug-trafficking paramilitaries. Instead, by seriously crippling the competing guerrillas, the government had given a monopoly to Don Berna. It was peace achieved through market dominance, not demilitarization -- and when Don Berna's extradition decapitated his organization and prompted a violent scramble for power among lower-ranking lieutenants, the peace fell apart.

But still, the chances that Colombia will return to the lawlessness of the 1990s are slim. This is the long and arduous path that Mexico has embarked on under President Felipe Calderón. It will not win the drug war anytime soon, but with sufficient political will, it can at least start moving in that direction.

All contents ©2011 The Slate Group, LLC. All rights reserved.

Valor Ganado utilizando Microsoft Office Project 2007

Tomado de: http://www.scribd.com/doc/27367986/Valor-Ganado-utilizando-microsoft-office-project-2007
Autor: Jeysson Poquioma

Copyright © 2011 Scribd Inc.

Trabajo, responsabilidad y principios son la base de una vida exitosa: Luis Carlos Sarmiento Angulo

Tomado de: http://www.caracol.com.co/nota.aspx?id=1454390

El presidente del Grupo Aval reveló en Caracol Radio los detalles de su vida. Dijo que no llora desde hace muchos años, pero recordó que la última vez que lo hizo fue cuando falleció su padre.

Reconoció que la prioridad en su vida ha sido su familia y que de hay el éxito de todas sus labores.

El hombre que maneja millones de pesos a nivel nacional e internacional manifestó que en su billetera tan solo carga un millón de pesos y manifestó que “me alcanza para bastante rato”.

“Ese millón me lo gasto pagando la peluquería o mando a comprar un remedio o dar una propina en plata en efectivo y todo los demás lo paga la oficina”, dijo Sarmiento Angulo en diálogo con Caracol Radio.

Un día de Sarmiento comienza a las 6:30 de la mañana cuando se despierta, para proceder a leer los periódicos, hace media hora de deporte y luego sale para la oficina. Regresa a su casa a “como a las nueve de la noche”.

Cuando está en la oficina se ocupa de los problemas del día a día y “me ocupo de lo que se ha hecho mal y apagar incendios”. También a leer y a pensar mucho en los negocios del grupo.

Manifestó que es una persona muy tranquila y que en su oficina tiene un computador y reconoció que no es ducho en sistemas porque la “generación electrónica me llegó un poco tarde”.

Luis Carlos Sarmiento manifestó que tiene problemas para conciliar el sueño y que se despierta varias veces en la noche debido a un problema químico en su organismo.

“Me gusta ir mucho a Europa porque esta la primavara y también voy a Bahamas o Miami porque en esta ciudad están mis hijos y mis nietos”, subrayó.

Comentó que a su hijo Luis Carlos Sarmiento lo regañaba mucho cuando era pequeño.

También aceptó que tiene un reloj muy sencillo y que compra la ropa hecha porque “ir al sastre es muy desesperante”.

Aceptó que le han regalado muchas cosas entre ropa, libros y lo más reciente un ipad.

“Siento una gran satisfacción y orgullo por lo poco o mucho que logrado sin atropellar a nadie”, subrayó el presidente del Grupo Aval.

Según Sarmiento un gran amigo fue Enrique Santamaría, quien ya murió y con quien compartió muchas andanzas por la vida.

Comentó que hasta el momento nadie lo consultado de la revista FORBES y que la información que toman provienen de datos públicos de los bancos para calcular cuanto tiene.

© CARACOL S.A.

Japan Nuclear Crisis: What Is a Full Meltdown?

Tomado de: http://news.yahoo.com/s/dailybeast/12930_japannuclearcrisiswhatisafullmeltdown
Autor: Josh Dzieza

NEW YORK – As Japan races to prevent a nuclear catastrophe, Josh Dzieza asks MIT's Ron Ballinger and Columbia’s David Brenner about partial and full meltdowns, hydrogen blasts, and windblown radiation. Plus, full coverage of Japan’s crisis.

Japan is on the brink of a nuclear disaster in the wake of its devastating earthquake and tsunami, with a third explosion at the Fukushima Daiichi nuclear power station damaging the steel containment structure of one reactor, and a fire at another spewing radioactive material into the air. Before the latest explosion and fire, as workers raced to stay ahead of a full meltdown, The Daily Beast spoke with Ron Ballinger, professor of nuclear science and engineering at MIT, and David Brenner, director of the Columbia University Center for Radiological Research, about the difference between partial and full meltdowns, hydrogen blasts, and windblown radiation.

What’s the difference between a “partial” and “full” meltdown?
Brenner: Both phrases are not technical phrases. What they're to do with is the radioactive core of the nuclear reactor, which needs to be covered with water to keep it cool. What one means by meltdown is that at some point the core isn't covered by water. It could mean that a few inches are uncovered for a few seconds, or that the entire core is uncovered. The phrase covers a multitude of sins.

Ballinger: In that context they're talking about fuel that's been damaged and partially melted. Some of the fuel has probably been oxidized and breached and melted at the top of the core where the heat rises. The core height is about 4 meters, so the top meter of the core has probably been damaged.

And a full meltdown?
Ballinger: If they don't cool the plant, if they're not successful... then eventually the entire core would melt. Then it would melt into the bottom of the vessel. Then you get to this theoretical point where if they can’t cool it, then eventually the vessel itself, the steel, would melt, and you’d end up with a bunch of melted fuel and steel on the bottom of the concrete faceplate of the plant, in the containment vessel. And then it would have to get out of there. That’s what I would call a full meltdown....

Are meltdowns necessarily dangerous?
Brenner: They’re certainly not good. You can contrast the two major nuclear incidents of the past: Both Chernobyl and Three Mile Island were meltdowns, but the difference in scale is enormous. Chernobyl was the equivalent of 1 million Three Mile Islands. A “meltdown” certainly is not a good thing, but the ultimate consequence is how much radioactivity is released into the environment. You can have a situation like Three Mile Island, where it’s extremely small amount, or a situation like Chernobyl.

Which does Fukushima look like?
Certainly looks much more like a Three Mile Island. There are a lot of similarities between this and Three Mile Island. In both cases they were able to shut the reactor down almost immediately. That was not the case in Chernobyl. The whole point was that they couldn't shut the reactor down. In Three Mile Island and in the Japanese reactors, they shut it down.
Once you shut it down, there's still a low-level reaction going, so you have to keep water covering the fuel. What happened in Three Mile Island and Japan is that they couldn't do that. The secondary cooling system that pumps water over the core failed.

Cooling
All of the Daiichi reactors shut down automatically when the earthquake struck. The problem is that it fission reactions don’t just stop; they fade slowly, continuing to produce energy and tremendous heat for days. Normally a cooling system would run water over the core after it shut down, but that system lost power, first when the power station was cut off from the grid, then again when the tsunami swamped the backup diesel generators.

Now that the cooling system has failed, what happens?
The core is going to get hotter and hotter. The nuclear material is enclosed in a metal cylinder, zirconium, which can react with water at high temperatures and produce hydrogen, which is explosive in the right situation. So when you start to get buildups of hydrogen, you have to vent it. But when you vent it, you also vent the radioactive material in the air inside the container. That’s probably where the radioactivity detected comes from.

Ballinger: There are two vectors going on. There’s the decay heat generated by the fission products in the fuel, and that heat has to be removed. If they can’t remove the heat, then the thing heats up. But the decay heat rate is decreasing with time, because the radioactive fission products are decaying away, at the same time you’re having to remove the heat. So the amount of heat you have to remove is decreasing with time, so the amount of cooling they need is going to decrease with time.

The other source of vector is the reaction between the zirconium and water. The zirconium alloy will react with water to produce hydrogen and oxide, but it also produces heat that has to be removed. So one source of heat—the decay of the fission products—is decreasing with time, and the other is a function of temperature, so you decrease the temperature, you decrease the oxygenation rate. It’s like baking a cake. If you set the oven at 300 degrees it’ll cook in a hour. If you set it for 350 degrees it will cook in 20 minutes. So as they cool the plant down, the rate of oxygenation will also go down. And it’s not a linear function. For every 50 degrees Centigrade, you change the chemical reaction rate by a factor of two.

Are there any signs that indicate how successful they’re being in cooling the reactor?
You can get an idea of how successful that is by looking at how often they have to vent the gas—the non-condensable gasses, the hydrogen and stuff. That’s going down and down and down. So they’re having success at cooling. It doesn’t mean there’s not a lot of fuel damage, it just means the oxygenation rates are going down, so they’re having success at cooling it.

There were explosions at the No. 2 and 3 reactors when they vented them. Why do they keep exploding? And what can they do to prevent an explosion?
The trick when you’re venting is to make sure you have a lot of dilution, to make sure you don’t have a hydrogen concentration above 5 or 6 percent. So I’m sure what they’re doing is they’re venting it slower and using a lot of blowers to make sure the concentration doesn’t get that high. Hydrogen is a funny gas. It tends to pool. It’s lighter than air, so it rises, and in a building—think of where the fans are, they’re in the ceiling, well that’s where the sparks from the motors are. Hydrogen will tend to rise and pool in the ceiling area, so the hydrogen concentration could be less than flammable on average, but in certain areas if you’re not careful it can get above the flammable point. They either vented too fast or didn’t realize it was concentrating.

I’ve read that there’s spent fuel stored near the reactor. Is it common practice to store fuel on site?
Yes, there are two places where they put spent fuel. When they take it out of the reactor it’s still generating heat. The decay heat is still there. So they put it in pools full of water. After a long enough period of time they can take the fuel and put it in these monstrous cement casks that you could fire a missile at and nothing happens, and they put them out on a pad and it’s cooled by natural convection.

Radiation
Officials have expanded the evacuation radius around the stricken reactors. First it was 3 kilometers, then when they vented the reactor it was expanded to 10 kilometers. When the reactor exploded, it went up to 20. Then the Nuclear Regulatory Commission in the United States said radiation was unlikely to reach the West Coast in harmful amounts.

Is the amount of radiation emitted when they vent the reactor dangerous?
Brenner: Depends on how much comes out. From the point of view of the surrounding population, probably not. But the situation is still ongoing, so we don’t know. There’s one good thing in this terrible situation: Winds are offshore at the moment, blowing what radioactivity is in the air out into the ocean.

Could the wind blow the radiation to North America?
Brenner: Yes, but the question is how much. The Chernobyl accident was far larger than we can imagine this one to be. You could detect the radioactivity worldwide. But it’s a matter of how much radioactivity would arrive at the West Coast. Right now it’s absolutely negligible. And even in a worst-case scenario, it’s hard to imagine it would be significant. It’s hard to imagine a significant exposure to anyone on the West Coast simply because of the distance involved: As the wind blows the plume further, it gets more and more dispersed. The worst case still wouldn’t be Chernobyl.

Would it be dangerous to people nearer the reactor? They’ve evacuated people within a 20-kilometer radius.
Brenner: It’s not an unreasonable precaution. In any scenario, the dose will be less and less as you get further from the source. But it will certainly be closer to Three Mile Island than Chernobyl.

How long will the radiation last?
Brenner: It depends on the isotope. Iodine has a half-life of a week. Cesium will be around for years. But the consequences depend on how much is released. Even if cesium is around for a long time, if there’s not much of it, it won’t be an issue. And it depends on which direction the wind is blowing, and again, that’s favorable right now.

Josh Dzieza is an editorial assistant at The Daily Beast.

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To this end I labor, struggling with all his energy

We proclaim him, admonishing and teaching everyone with all wisdom, so that we may present everyone perfect in Christ. To this end I labor, struggling with all his energy, which so powerfully works in me. – Colossians 1:28-29