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The Big Splat: collision may have created lopsided Moon
Identifying a radiation injury Prof Yash
Pal
Trends
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The Big Splat: collision may have created lopsided Moon
The Earth may once have had two moons which collided several billions of years ago - not so much with a bang but with a “splat” - to form the lopsided lunar landscape that exists today, scientists said.
Astronomers have long wondered why the mountainous far side of the Moon with its thick crust is so different from the relatively flat, crater-filled near side that always faces the Earth. Two planetary scientists have provided a possible answer to the conundrum with a computer model showing that the early Moon collided with a smaller companion which ended up being stuck on to the lunar far side. The unequal nature of the collision produced a lopsided Moon and it could only have occurred in this way because it happened relatively slowly at less than the speed of sound, according to Erik Asphaug and Martin Jutzi at the University of California. If the collision had happened any faster then a giant crater would have been created by the much smaller secondary moon, spreading the debris far and wide rather than concentrating it on just one of the lunar hemispheres, the researchers suggest in their study published in the journal Nature. “It requires an odd collision. Being slow, it does not form a crater but splats material on to one side,” Professor Asphaug said. — The Independent |
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Identifying a radiation injury
A radiation equipment disposed of carelessly in Delhi caused the first radiation death in India last year and exposed six other persons to high radiation doses. One of the challenges in such instances is that physicians may not be able to identify a radiation injury. Radiation injuries occur only if there is gross violation of safety procedures and mishandling of radiation equipment.
During the late 90s, a radiation oncologist from the Tata Memorial Hospital (TMH) Mumbai informed the Atomic Energy Regulatory Board (AERB) that a radiation worker from a Mumbai-based industrial radiography company suffered severe radiation burns. His fingers were in bad shape. He needed urgent treatment. He lost time as the owner of the company took him to several other physicians till a skin specialist referred him to TMH. General Practitioners may think that the injury is due to other reasons such as insect bite. Radiation injury has no special signs or symptoms. Few physicians know how to identify them. Recognising this fact, AERB published “A Handbook for the Medical Management of Persons Exposed in Radiation Accidents” in 1989. A detailed guide published by AERB in 1990, received critical reviews from H.Jammet and Jeane Claude Nenot, Institute of Protection and Nuclear Safety, Paris, France and other internationally acclaimed specialists. AERB also published a poster on the topic. An IAEA/WHO leaflet titled “How to recognize and initially respond to an accidental injury” summarised the radiation effects. The IAEA/WHO leaflet recommends several other documents on the topic. Radiation injuries evolve over time. When the dose is high, the victims may suffer nausea, vomiting, fatigue and possibly fever and diarrhoea. Illness follows, characterized by infection, bleeding and loss of cells lining the gastro-intestinal tract. High local doses can cause reddening of the skin, oedema, dry and wet desquamation, blisters, pain, necrosis, gangrene and hair loss. Mostly, the victim may not know that he is exposed to radiation. Physicians may miss the symptoms. Diagnosis may not be obvious till a radiation specialist reviews the case. Simultaneous appearance of a few of these symptoms must alert the physician. When the whole body of a person is exposed to radiation, blood count changes occur at about 500mSv; threshold dose for vomiting: 1,000 mSv; threshold dose for death: 1,500 mSv. Every one exposed to about 8,000 mSv will die. (Sv is a of unit biologically significant dose. The physical energy absorbed then is one joule per kg. One mSv in one thousandth of a Sv). According to Dr Dr.Jeane Claude Nenot, over the past 60 years, at least 600 events caused significant radiation exposures of about 6,000 individuals, about 70 serious accidents resulted in one or more death each, and a total of 200 deaths were due to Acute Radiation Syndrome (Journal of Radiological Protection, 2009).Thus radiation death is an extremely rare event as thousands of radiation sources have been in use for the past several decades in industry, medicine and research. The writer is Raja Ramanna Fellow, Department of Atomic Energy, Mumbai.
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THIS UNIVERSE
Will the conversation between a man standing steady and another one travelling at the speed of light be normal conversation, if they are talking to each other on a phone? Considering the effect of speed on time.
The first question that occurs to me is “how the phone signal is being transmitted”? I suppose it will be by an electromagnetic signal, microwave or light. Since light travels with a fixed velocity there will be time interval between the time of transmission and reception. This will depend on the instantaneous distance between the two men. Therefore there will be a time gap between your stopping a sentence and your receiving an answer. For example if the other man is at the distance of the sun then there will be a gap of eight minutes between the time the man near the sun starts speaking and your hearing him. It will take another eight minutes foe that man to begin to get a reply from you. The conversation would be pretty messy. But that is not quite the answer to the question you are asking. Let us now look at the problem when one man is travelling at the speed of light with respect to the other. We will forget for a moment that it is impossible for a man to travel at the speed of light because then his dynamic mass will become infinite. But we can consider the case when the speed is slightly less but approaching the speed of light. What would happen is that the signal from each man would suffer a drastic red shift. A roar will become a whisper. This would disappear into the background noise. We will approach this condition gradually as their relative speed is increasing towards the ultimate — ie, the light speed. In other words the two men will not be able to communicate with others, certainly not on some thing like a telephone. They will have to deal with the complicated task of deciphering their red shifted spectra. |
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Trends
CAPE CANAVERAL, Florida: A pair of spacewalking cosmonauts floated outside the International Space Station Wednesday to prepare the orbital outpost for upcoming Russian renovations. The work follows NASA’s completion of the United States’ part of the $100 billion complex, a project that also includes Europe, Japan and Canada.
Female moose manipulate males to fight
ANCHORAGE, Alaska: Moose-mating season, just around the corner in Alaska, means crisp fall days, ripe berries on the bushes and, according to a new study, animal behaviour that might seem more at home in a rowdy singles bar. Female moose, or cows, are able to manipulate amorous males into fighting each other, allowing the more desirable bulls to emerge as mates, according to the study.
Russia says high ice melt opens Arctic trade routes
MOSCOW: Arctic ice cover receded to near record lows this summer, opening elusive northern trade routes from Asia to the West, Russia’s climate research agency said on Wednesday. After the third hottest year on record since 1936 in the Arctic last year, ice cover has melted as much as 56 percent more than average across northern shipping routes, making navigation in the perilous waters “very easy,” it said.
— Reuters |
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