Thursday, February 28, 2008

Gravitational Lensing



In general relativity, the presence of matter (energy density) can curve space-time, and the path of a light ray will be deflected as a result. This process is called gravitational lensing and in many cases can be described in analogy to the deflection of light by (e.g. glass) lenses in optics. Many useful results for cosmology have come out of using this property of matter and light.

There are different regimes: strong lensing, weak lensing and microlensing. The distinction between these regimes depends on the positions of the source, lens and observer, and the mass and shape of the lens.

1.Strong Lensing
The most extreme bending of light is when the lens is very massive and the source is close enough to it : in this case light can take different paths to the observer and more than one image of the source will appear.

If the source varies with time, the multiple images will vary with time as well. However, the light doesn't travel the same distance to each image, due to the bending of space. So there will be time delays for the changes in the images. These time delays can be used to calculate the hubble constant H0. A few systems with these time delays have been found and are under study. Much of the subtlety in this work lies with constructing the model of the mass distribution forming the lens.In some special cases the alignment of the source and the lens will be such that light will be deflected to the observer in an "Einstein ring." One of these was observed in 1998.More often than a ring, the source may get stretched out and curved, and form a tangential or radial arc. A lot of mass is needed to cause an arc to appear, so that properties of arcs (numbers, size, geometry) can often be used to study massive objects like clusters .

2.Weak Lensing
In many cases the lens is not strong enough to form multiple images or arcs. However, the source can still be distorted: both stretched (shear) and magnified (convergence). If all sources were well known in size and shape, one could just use the shear and convergence to deduce the properties of the lens. However, usually one does not know the intrinsic properties of the sources, but has information about the average properties. The statistics of the sources can then be used to get information about the lens. For instance, galaxies in general aren't perfectly spherical, but if one has a collection of galaxies one doesn't expect them all to be lined up. Thus, if this set of galaxies is lensed, on average, or statistically, there will be some overall shear and/or convergence imposed on the distribution, which will give information about the intervening lens(es).
There is a distribution of galaxies far enough away that can be treated as sources, and thus clusters nearby can be "weighed" (i.e. have their mass measured) using their lensing. Superclusters have been considered as well. In addition, theories of cosmology predict the distribution of large scale structure, the distribution of matter in the universe. The statistical properties of the large scale structure (e.g. the probability of finding a galaxy at one place when there is another a certain distance away) can also be measured by weak lensing, because the matter will produce shear and convergence in distant sources (which can be galaxies, or the cosmic microwave background, for example). Weak lensing is a useful complement to measures of the distribution of luminous mass such as galaxy surveys. Lensing measures all the mass, in particular the dark matter as well as the luminous matter.

3.Microlensing
In some cases the lensing is of an image that is so small or faint that one doesn't see the multiple images-- the additional light bent towards the observer just means that the source appears brighter. (The surface brightness remains unchanged but as more images of the object appear the object appears bigger and hence brighter.) This lensing can have effects in many measurements, as sources which would have otherwise been too dim become visible. This can be helpful, as when one wants to view objects that would otherwise be too far away. It can also be a problem, for example when one is trying to measure all objects brighter than a certain amount in a certain region and lensing introduces objects by magnifying objects enough to bring them into the sample.

There are ongoing searches to use lensing to find a type of dark matter called MACHOs (massive compact halo objects). Although MACHOs, as dark matter, cannot be seen themselves, if they pass in front of a source (e.g. a star nearby), they can cause the star to become brighter for a while, e.g. days or weeks. This effect has been observed but determinations of the "dark matter" are not yet conclusive.



Monday, February 25, 2008

TEAM INDIA UP AGAINST LEANDER

The leading Indian Mixed-doubles Champion Mahesh Bhupathi along with a few leading Indian Singles players like Rohan Bopanna, Prakash Amritraj and Karan Rastogi have put forward a formal complaint to the All Indian Tennis Association (AITA) regarding the unprofessional behaviour of Leander Paes, the Team Captain for the Davis Cup.
Certain aspects of Paes' Captaincy has been bothering the players,namely:

1. Lack of confidence in Paes' decision making skills as in not playing Amritraj on Day 1 for the Uzbekistan tie. According to Paes, Amritraj had a stomach problem, however the latter refused to have any such problem and claims he was fit to play.

2. Lack of support or communication through the year even when Paes and his teammates were playing the same tourneys.

3. Captaincy woes exist as the players are not in sync with the captain's thinking and strategy plans.

4. Lack on punctuality on Paes's behalf during Davis Cup ties.

5. According to the above metioned players, Paes runs them down during press conferences which grealtly demoralises them and thwarts team chemistry.

The above players believe that this kind of team-spirit would mar the progress of Indian tennis and would be detrimental to their individual confidence. Confirming the above statements Amritraj stated that though they would love to play for their country, they are unwilling to play the Davis Cup if Paes retains his captaincy. He even stated that "He(Paes) has basically killed the joy for us."

AITA secretary Mr. Khanna confirmed to have received the formal complaint and states that this is an internal matter and assures that it will be sorted out amicably in the best interests of Indian Tennis. Repeated attempts to communicate with Paes for his comments on the issue remained unanswered.

Saturday, February 9, 2008

Reduce Temporary Internet File Space

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The temporary internet files clutter your hard drive with copies of each page visited. These can build up over time and take up disk space. Even more bothersome is that instead of getting new pages each time IE often takes the page out the temp internet files. This can be a problem if you are viewing a website that is updated all the time. If you are on a slow connection such as a 56K or lower then this can be good but if you are on a fast broadband connection then you can get away with decreasing the size of your temp internet files to just one MB without any performance decrease.


-Launch 'Internet Explorer'.
-Select the 'Tools' from the menu bar.
-Then select 'Internet Options'... from the drop down menu.
-Once the internet options has loaded click on the 'general' tab.
-Under the 'temporary internet files section' click the 'settings' button.
-A settings window will load. 'Slide the slider all the way to the left so the size indicated in the text box on the right is one'.
Click OK
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Windows XP-Tips and Tricks

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Disable error reporting 

Open 'Control Panel' 
Click on 'Performance and Maintenance'. 
Click on 'System'. 
Then click on the 'Advanced' tab 
Click on the 'error-reporting' button on the bottom of the windows. 
Select 'Disable error reporting'. 
Click OK.
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Yet there remains a great deal of confusion about just what nanotechnology is, both among the ordinary people whose lives will be changed by the new science, and among the policymakers who wittingly or unwittingly will help steer its course. Unsurprisingly, some of the confusion is actually caused by the increased attention—sensationalistic reporting and creative license have done little to prepare society for the hard decisions that the development of nanotechnology will make necessary.

Much of the confusion, however, comes from the scientists and engineers themselves, because they apply the name “nanotechnology” to two different things—that is, to two distinct but related fields of research, one with the potential to improve today’s world, the other with the potential to utterly remake or even destroy it. The meaning that nanotechnology holds for our future depends on which definition of the word “nanotechnology” pans out. Thus any understanding of the implications of nanotechnology must begin by sorting out its history and its strange dual meaning.

Nanotechnology

Nanotechnology is the creation and utilization of materials, devices, and systems through the control of matter on the nanometer length scale—at the level of atoms, molecules, and supra-molecular structures. The essence of nanotechnology is the ability to work at these levels to generate larger structures with fundamentally new properties and molecular organization. These “nanostructures,” made with building blocks understood from first principles, are the smallest human-made objects and exhibit novel physical, chemical, and biological properties and phe-nomena. Nanotechnology’s goal is to exploit these properties and efficiently manufacture and employ the structures.
Nanotechnology has the potential to significantly impact environmental protection through understanding and control of emissions from a wide range of sources, development of new “green” technologies that minimize the production of undesirable byproducts, and remediation of existing waste sites and polluted water sources. Nanotechnology has the potential to remove the finest contaminants from water supplies and air as well as continuously measure and mitigate pollutants in the environment.
Nanotechnology will be a strategic branch of science and engineering for the next century and will fundamentally restructure many current technologies. Control of matter on the nanoscale already plays an important role in scientific disciplines as diverse as physics, chemistry, materials science, biology, medicine, engineering, and computer simulation. A number of environmental and energy technologies already have benefited substantially from nanotechnology in the areas of reduced waste and improved energy efficiency, environmentally benign composite structures, waste remediation, and energy conversion.
Complex physical processes involving nanoscale structures are essential to phenomena that govern the sequestration, release, mobility, and bioavailability of nutrients and contaminants in the natural environment. Processes at the interfaces between physical and biological systems have relevance to health and biocomplexity issues. Increased knowledge of the dynamics of processes specific to nanoscale structures in natural systems not only will improve understanding of transport and bioavailability, but also lead to the development of nanotechnologies useful in preventing or mitigating environmental harm.