 |
|
| SCIENCE & TECHNOLOGY |
|
|
|
Electricity from the sea Global warming will stifle oceans
A whale’s secrets Prof Yash
Pal THIS UNIVERSE
|
|
|
Electricity from the sea Tidal Barrages work rather like a hydroelectric scheme, except that the dam is much bigger. A huge dam (called a “barrage”) is built across a river estuary. When the tide goes in and out, the water flows through tunnels in the dam. The ebb and flow of the tides can be used to turn a turbine, or it can be used to push air through a pipe, which then turns a turbine. A major drawback of tidal power stations is that they can only generate when the tide is flowing in or out — in other words, only for 10 hours each day. There may be a number of benefits, including protecting a large stretch of coastline against damage from high storm tides, and providing a ready-made road bridge. However, the drastic changes to the currents in the estuary could have huge effects on the ecosystem. Barrages in many countries have been operating for quite long time but the concept has been restricted by concerns over cost and local environmental impact. Planners are looking at wave and tidal stream generation, leaving out other approaches to tidal power such as barrages, which has matured. According to new concept, wave-based devices will generate electricity from movements of the sea surface, whereas tidal stream installations sit on the sea floor and use the regular ebb and flow of tides. The option is to use offshore turbines, rather like an underwater wind farm. This has the advantage of being much cheaper to build, and does not have the environmental problems that a tidal barrage would bring. The University of Wales and partners are also researching techniques to extract electrical energy from flowing water using swan turbines. The “swanturbines” design is different to other devices in a number of ways. The most significant is that it is direct drive, where the blades are connected directly to the electrical generator without a gearbox between. This is more efficient and there is no gearbox to go wrong. Another difference is that it uses a “gravity base”, a large concrete block to hold it to the seabed, rather than drilling into the seabed. Countries with long shoreline can make use of this vast natural power resource contained in its breakers and tides. This economical mode of electricity generation from the sea energy is expected to contribute towards country’s growing electricity demand in an environmental friendly way. Wave farms could generate 50 terawatt-hours (TWh - one thousand million kilowatt-hours) per year, and tidal stream installations a further 18TWh. There is only a need of a good site and access to the site for wave or tidal energy to be developed and used. Currently, only a handful of wave and tidal stream devices are installed around the world. Scotland hosts two prototype wave machines, the Pelamis deep-water system and the Limpet shoreline device, while Marine Current Turbines has been testing a prototype tidal stream concept in Devon and is about to install a commercial device at Strangford Narrows in Northern Ireland. Wave and tidal stream technologies are at an earlier stage of development than solar and wind which are more mature. Utilising wave and tidal concepts to generate electricity though are currently costly ways but they offer a great potential towards environment friendly renewable energy resources with a possibility that their prices will come down with development. More important is the assumption about energy production from conventional and polluting resources and there is a need for a sea-change in thinking of society in general and planners in particular. The world is entering in an era where energy is short. We’re now entering a stage where tidal and wave energy which can though supply only a fraction of demand but it is important to be self reliant than depending on imports. The writer is from Dept. of Physics,
S.L.I.E.T., Longowal |
|
Global warming will stifle oceans Global warming will stifle life-giving microscopic plants that live in the surface layer of the oceans, cutting marine food production and accelerating climate change, according to a study. Phytoplankton are not only the foundation of the marine food chain, but every day they take more than 100 million tonnes of carbon dioxide out of the atmosphere, scientists from Oregon State University, NASA and four other institutions said. But as global warming heats the surface layer of the ocean it becomes lighter and therefore separated from the cooler depths from which the phytoplankton get many of their nutrients. This cuts their numbers, not only reducing the food in the oceans but slashing the amount of carbon dioxide they take from the air and therefore accelerating the climate warming process. “Rising levels of carbon dioxide in the atmosphere are a key part of global warming,” said lead researcher Michael Behrenfeld. “This study shows that as the climate warms, phytoplankton production goes down, but this also means that carbon dioxide uptake by ocean plants will decrease ... making the problem worse,” he added. Despite their tiny size, phytoplankton account for about half of the photosynthesis on Earth — converting vast quantities of atmospheric carbon dioxide into organic carbon as food for the planet’s marine ecosystem. The study, published in the science journal Nature, comes from a decade-long analysis of the oceans by NASA’s SeaWiFS satellite which measured the changing colours of the waters caused by changing levels of phytoplankton. The higher the concentrations of these tiny plants, the greener the water. The scientists — who also came from the University of California/Santa Barbara, Princeton University, Rutgers University and the University of Maine — found local variations but a global drop in numbers with higher temperatures. “This clearly showed that overall ocean productivity decreases when the climate warms,” Behrenfeld said. Scientists predict that global temperatures will rise by between two and six degrees Celsius by the end of the century, due mainly to carbon dioxide from burning fossil fuels for power and transport. But they also fear that beyond two degrees of warming the planet’s climate could trip the so-called feedback mechanism with the rising heat releasing even more greenhouse gases than being produced by human activities. A comprehensive study last month by former World Bank chief economist Nicholas Stern found that acting now to tackle climate change could cost one percent of global economic output — a figure that rises 20-fold if action is delayed. — Reuters |
|
An 85-year-old vial of oil from a whaling ship has revealed that a mysterious group of organic chemicals resembling human-made compounds are naturally produced in the sea. A decade ago, scientists monitoring marine mammals’ flesh for pollutants began finding unknown organic compounds containing the halogen atoms bromine and chlorine. More than 20 such compounds were eventually revealed. That raised alarms because the compounds structurally resemble the pesticide DDT and polychlorinated biphenyls (PCBs), which were once used in flame retardants. Researchers wondered whether the recently discovered organic chemicals were manufactured or produced naturally. Symbiotic bacteria in ocean sponges, for example, produce chemicals similar to DDT and PCBs that deter fungal growth.
|
|
|
THIS UNIVERSE When we pour water over quick lime it emits heat. How does it happen? All chemical reactions involve an exchange of energy some of which often manifests itself in terms of heat. Quick lime is calcium oxide, which is prepared by heating limestone to a temperature of the order of 900 degrees Celsius. The reaction produces, in addition, carbon dioxide. When calcium oxide, or quick lime, is mixed with water a chemical reaction occurs producing calcium hydroxide and a lot of heat. The chemists say that the reaction is highly exothermic. Therefore the answer to your question is that here you are talking of a highly exothermic chemical reaction. Incidentally calcium hydroxide is the chemical name of slaked lime, that is used for whitewashing our walls and some people eat in their “PAAN”. Why are the radar antennas fabricated with net structures? The requirement of a dish is to be a good reflector at the wavelength for which it is used. When the separation of the net wires or other metallic elements is significantly smaller than the wavelength concerned the wave is almost completely reflected. Therefore, it is profitable to make the antenna lightweight by using wires instead of a continuous metallic surface. The net structure also reduces the wind load on the antenna. Due to this and the overall reduction on structural weight mesh antennas are more easily maneuverable. Most of the radars operate at microwave frequencies. The wavelengths are of the order of several centimetres to tens of metres. It would be stupid to have solid dishes for them. |
Seawater and energy stored in it, whether in terms of waves and tides or temperature difference in the surface layers of water, has always attracted the attention of engineers due to its vast, renewable and reliable nature. Tides and waves are regular phenomena in the sea due to a balance in the gravitational forces of attraction between earth, moon and sun and may be other planets of our solar system.