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Dr. Kartik Sheth, ALMA, and SKA March 19, 2013

Posted by admin in : Astronomy and Astrophysics (ASTRO), Cosmology, Gravitation, and Relativity (CGR) , add a comment

by JC Holbrook

National Society of Black Physicists members Eric Wilcots and Kartik Sheth were part of a new initiative to foster radio astronomy collaborations with South African astronomers and students. Last week marked the official inauguration of ALMA, the Atacama Large Millimeter/Submillimeter Array, in the high altitude Atacama desert of Chile, South America. I was able to sit down with Dr. Sheth to discuss the broader issue of radio astronomy and South Africa.

“I think this celebration was the culmination of thirty years worth of work from a lot of different people. The inauguration of the array was a chance for us to celebrate how much hard work has gone into it.” Dr. Sheth said of the inauguration ceremony in Chile. “We started science operations September 30th of 2011. We have been collecting data for over two and a half years, because even with a small ALMA it is still the most powerful [millimeter/submillimeter] telescope in the world.”

Since ALMA is an array of dishes similar to the radio dishes of the Very Large Array in New Mexico, even during construction as each dish was put into place and connected, the astronomers were already using what was available to collect data. Thus, the months of science data collection with ALMA before the official inauguration.

I pointed out, “You were not even there!”

Dr. Sheth laughed, “Only the dignitaries were invited, so a lot of people from the political arena in the twenty-five plus countries that are part of ALMA. President Piñera inaugurated ALMA…For me it doesn’t mean much… but I’m kinda sad that I’m not there because I really wanted to be there. But I knew that I wasn’t going to be invited, so coming here [to South Africa] really was driven by the NASSP deadline for Master’s proposals.” NASSP is the National Astrophysics and Space Sciences Programme in South Africa. In 2010, I began writing a book about NASSP. The program is a dramatic success story about educating underrepresented groups in astrophysics and space sciences. NASSP include one honor year and a two year masters of science degree. Nearly all NASSP students are funded by the program.

Dr. Sheth explained, “The idea is to foster bridges between the faculty here that are taking on students who eventually want to work with MeerKat and SKA. But MeerKAT and SKA are not built, yet. So, what we would really like the faculty to do is to think about including radio data from existing telescopes and NRAO operates four of them.”

The SKA is currently under construction, yet the South African astronomy students need to learn everything about radio astronomy and the analysis of radio data. Dr. Sheth along with other American radio astronomers is here to encourage South African astronomers and their students the opportunity to learn by working with the existing facilities and their archival data. The four facilities are ALMA, the Robert C. Byrd Greenbank telescope a single dish in West Virginia, the Jansky Very Large Array (JVLA or EVLA) which is the enhanced VLA in New Mexico, and the Very Large Baseline Array (VLBA) which is spread across the Northern Hemisphere. Thus, the visit before the NASSP deadline for submitting Masters of Science thesis proposals. Dr. Sheth hopes that a few NASSP students will propose radio astronomy projects including using NRAO facilities for their Masters work.

According to Dr. Sheth the JVLA is the Northern Hemisphere equivalent of what MeerKat will be. MeerKat is the precursor to the SKA, the Square Kilometer Array.  It is a new state of the art radio observatory currently being built in South Africa. The SKA array itself will consist of 3000 dishes spread across nine African countries: South Africa, Namibia, Botswana, Mozambique, Madagascar, Mauritius, Zambia, Ghana, and Kenya. The SKA Africa headquarters are in Cape Town, South Africa, and they will be coordinating all of the African construction. A question I thought would be uppermost in the minds of South Africans was: Will ALMA be competition for SKA?

His response, “No, not at all. ALMA operates at higher frequencies than what the SKA will operate at. They are not looking at the same part of the electromagnetic spectrum but they will be looking at the same type of objects. EVLA is a mini version of SKA. With the SKA, it will be observing thermal emission and synchrotron emission from sources…” In an email he added, “We are looking at electrons energy as they cool around star forming regions or zip around magnetic fields. So you can get a real idea of the magnetic field that pervades the Milky Way and with the SKA across cosmic time. ALMA cannot really look at atomic gas unless its at very high red shift (i.e. the lines are red shifted into the regime that ALMA can observe) and only using atomic gas tracers like ionized carbon, nitrogen, or oxygen. ALMA cannot look at the atomic hydrogen gas which is emitting in the wavelengths that MeerKat and SKA will work at. So SKA & Meerkat are looking at the atomic gas from which molecular gas forms. And the molecular gas is what ALMA looks at which from stars form. And the stars are what HST and JWST look at. So it is a nice transition.  Together these are giving you the full picture of what the universe looks like. Additionally there is a lot about magnetic fields and transient phenomena — these are also MeerKat and SKA’s core strengths. For instance, these will be excellent instruments for looking at the timing of pulsars.”

Trying to put it altogether I asked, “So, anything that is hot and has electrons moving around will be able to be studied by SKA?”

Kartik Sheth clarified, “No, I wouldn’t call it ‘hot’. The atomic gas is quite cold as well. It is hotter than the molecular gas but not hot compared to stars.”

As a student of astronomy, I had always had a fascination with the connection between wavelengths of light or color, physical properties, chemistry, and celestial bodies. Planetary nebulae, which are mentioned in my last Vector blog, in visible light appear greenish in color. The color is the result of a specific atomic transition in the oxygen atom that occurs under very low density conditions. First the oxygen has to be ionized twice, i.e. it has to have lost two electrons, then it is through collisions that the transitions producing the characteristic green lines emit. A rule-of-thumb temperature for planetary nebulae is 10,000 degrees Kelvin. Thus, if there is a celestial body that appears ‘green’ in visible light you can conclude that it might include oxygen especially if it is a nebula which tends to have low density and it should be around 10,000 degrees Kelvin. Hydrogen is also found in planetary nebulae and the strongest transition line, known as H-alpha, occurs when its electron goes from an excited state to a less excited state releasing energy in the form of red light.

In the case of ALMA and SKA, they are probing two different sections of the electromagnetic spectrum similar to studying green light or red light. In the fullness of time, SKA will cover the same wavelengths and types of celestial bodies as the EVLA but focused on the Southern sky rather than the Northern, but also be more sensitive revealing more physical details. ALMA will add to our understanding of the same region of the sky but is studying different physical properties of celestial bodies. Both will add to our understanding of the Milky Way and the Universe.

The US remains supportive of the Square Kilometer Array project April 7, 2011

Posted by admin in : Astronomy and Astrophysics (ASTRO), History, Policy and Education (HPE), Technology Transfer, Business Development and Entrepreneurism (TBE) , 1 comment so far

Though the United States did not officially join the Founding Board of the Square Kilometer Array (SKA), the US does remain supportive of the project. In large part, the decision not to join the Founding Board is based on the recommendations of the most recent astronomy decadal survey performed by the National Research Council, “New Worlds, New Horizons in Astronomy and Astrophysics,” released in August 2010. This report concluded that the combination of technical readiness and high cost risk made it unfeasible for the National Science Foundation (NSF) to invest in SKA construction during the 2010-2020 decade. NSF has accepted that conclusion and is setting a priority for SKA construction that is consistent with this conclusion and the other recommendations of the decadal survey.

NSF has invested in SKA technology development and in several radio telescopes that serve as scientific and technical pathfinders for the SKA, as well as pursuing some of the science goals envisioned for the international SKA, and will continue to make such investments as funds and independent reviews permit.

The SKA is an exciting project for astronomy. It was originally conceived as a focused project to study the end of the “Dark Ages” – the time when the first stars, black holes, quasars, and other high energy objects formed, ionizing the almost 100% neutral hydrogen gas left around from the Big Bang. You can imagine the universe at say z=20 being dark and transparent. But as the ultraviolet light begins to come from the first sources, the light ionizes larger and larger regions of the Universe – sort of like Swiss Cheese until redshift around z=6 where most of the hydrogen is ionized as it is today.

The SKA will slice through this redshift range giving us an accurate tomographic image of the Universe as it begins to form the elements of the periodic table, and begins to form the seeds of what we now see are galaxies and massive black holes. Its science case has expanded since then, but the main focus of the science is the tomography of the early Universe.

But the final SKA design is far from certain. Technology is still in development, and the final cost of the SKA is quite unknown. It may turn out actually that the SKA evolves to be three very large telescope arrays that are not co-located. A major factor of the SKA to site in a region free from FM carrier frequencies, and there are remarkably few in the world. Among them are sites selected in Africa and in Australia.

No definitive scientific rationale has emerged to favor the African site over the Australian or vice versa. Each project is pursuing pathfinder telescopes as pre-cursors to the SKA, and each is molded better to different capabilities.

But there may be international policy issues that would motivate the US to help fund the project now. The US presently supports, and will build, new major telescopes in Chile, including the LSST, CCAT, and ALMA the latter being an international collaboration. Chile has benefited greatly by hosting these telescopes, not only in building astronomy programs, but through other spill-over effects, e.g., broadband connectivity, service sector jobs and growth in the knowledge-based innovation economy. During President Obama’s recent trip to Chile, he and President Pinera issued a joint communique that they recognized the close historical collaboration in astronomy between the two countries and looked forward to future projects.

There are scientists and policy makers that would like to see an astronomy-catalyzed economic transformation in Africa. South Africa already has a long and distinguished history in astronomy research. Astronomers are developing academic programs and research telescopes in Botswana, Burkina Faso, Ethiopia, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia, Nigeria, Zambia, and others. Last December African astronomers organized the African Astronomical Society to be the voice of the astronomy profession on the continent and to be the continental interlocutor with other astronomy professional societies around the world. The SKA is a tremendous opportunity to help develop astronomy in Africa. If the Chilean example is a guide, the SKA would help develop high-tech industry and build a larger community of African astronomers, physicists, and engineers.

But the results of the decadal survey stunts the rationale for large-scale US investment (and for the US that means NSF funding) in the SKA, at least for this decade. This is probably the right choice. There are other projects, e.g., WFIRST, LSST, where the technology is more mature and thus closer to fruition. As the US faces limited fiscal options the decadal survey is the accepted process for the field to make hard decisions. Without a determined technology for SKA there is no way to make any firm cost determinations. So the question of whether to support the SKA long-term remains open.

But all is not lost for this decade. The South African MeerKAT and Australian ASKAP, both of which will be completed in this decade, will be extremely powerful telescopes. The MeerKAT in particular will be well-suited for pulsar timing studies that can reveal much about relativity, gravitational lensing, and nuclear physics.

Maybe this decade will see investments from other functions of the federal budget, e.g., foreign assistance through the State Department. Maybe the foreign assistance budgets of other donor countries can be brought to bear on the SKA project. After all, the total budget for the SKA construction is actually quite small compared to the total amount pledged by the G20 nations for development in Africa. Maybe the US Commerce Department, other nations’ ministries of industry, and private corporations will view the SKA as a technology incubator and thus find funds to help with technology development. And maybe philanthropists will find the SKA worthy of their donor dollars.

What remains true is that in Africa the SKA project has a full head of steam. South African science minister, Naledi Pandor, has said, “I am intent on ensuring that South Africa wins the bid to host the Square Kilometer Array radio telescope” and “…[I am] …not going to entertain any matter that might distract me from achieving that goal.” The Heads of State of the African Union have endorsed the African bid for the SKA telescope, signaling multilateral cooperation at the highest levels for this project.

The African SKA project team has already achieved impressive results with their KAT-7 precursor telescope, as well as in electronic design, manufacturing and logistics. And the SKA Project Office has conceived and developed the extremely clever idea of an African VLBI network that would use decommissioned communications dishes across the continent. Five years before South Africa’s MeerKAT telescope becomes operational, more than 43,000 hours of observing time (adding up to about five years) have already been allocated to radio astronomers from Africa and around the world.

The SKA human capacity development program is already an unqualified success. The challenge is to keep the steam chest full and to build on all these successes. The National Society of Black Physicists will of course maintain its collaborations with the African astronomy community. In addition to producing outstanding astronomy research results, we believe the African SKA will lead to the creation of an African scientific technological base that will in turn act as the engine of African economic development and will transform the African economy to one that is more based on knowledge, connectivity, technology and innovation. As an international research center located in Africa, the SKA will help unbridle the imaginations of young Africans and inspire them to pursue math and science at school, and to follow careers in science and engineering. This would create a critical mass of problem solving thinkers, able to find solutions to the water, food, health, energy and environmental challenges of the continent.

Simply Harmonic Jello – Fun Physics for Thanksgiving November 23, 2010

Posted by admin in : Acoustics (ACOU), Condensed Matter and Materials Physics (CMMP), History, Policy and Education (HPE), Physics Education Research (PER) , add a comment

Jello is fun and delicious any time of year, and everyone has seen it “wiggling” and “jiggling”.  With a simple stopwatch and counting the frequency of the wiggles, serving jello brings up a special opportunity to work a physics experiment into your snack and dinner menu.

Those wiggles and jiggles can be described as simple harmonic motion, i.e., the force causing the displacement (motion) is proportional to the displacement itself,  F = -kx .

Consider a square block of wiggling jello on a flat plate.  If the jello is set into vibrating motion by a shear force that acts on the top of the jello, static friction will keep the bottom of the jello fixed in place on the plate.   The displacement (or deformation) of the top of the jello due to the shear force is some distance,  x . This displacement divided by the original dimension is called the shear strain.

From Giancoli, Physics for Scientists and Engineers

If you measure the wiggling rate, i.e., count the number of back and forth excursions per unit time, this frequency can be related to the a physical property of the jello called the shear modulus.

The shear modulus,  G relates the shear force,  F , and shear strain,  \frac{x}{h}   by  

 G = \frac{Fh}{Ax}    or F = \frac{GAx}{h}

where   A is the area of the top of the block.

Because the center of mass oscillates with half the displacement of the top,

 F=\frac{1}{2} k_e x ,

and the effective force constant is given by

 k_{e} = 2\frac{ F}{x} = \frac{2GA}{h} .

The frequency of the vibrations for any simple harmonic oscillator is

 f =\frac{1}{2 \pi} \sqrt{\frac{k_e}{m}}

where  m is the  mass oscillating object, in this case the piece of jello.  The piece of jello can be weighed directly (converting from weight to mass) or given by the density of the jello multiplied by its volume  m= \rho Ah .

So the wiggling frequency of jello is        \frac{1}{2 \pi}  \sqrt{\frac{\frac{2GA}{h}}{\rho Ah}} or  \frac{1}{2 \pi h}{\sqrt{ \frac{2G}{\rho}} .

Thus the shear modulus of jello can be determined from the measured vibrational frequency by  G= 2 \rho ( \pi  f h)^2  .

You can try this experiment at home and even study how the shear modulus changes with how you make the jello, i.e., with water, vinegar, juice, soda, or alcohol. And you can investigate how temperature changes the shear modulus.

Post your results here as a comment.   Check back for updates and useful data.

Updates

Units? When doing any calculation in science it is important to keep in mind the units of the factors in used in the equations.  The units have to be consistent throughout, and the final derived units of your calculation should be consistent with quantity that you are trying to calculate.  It is easy to mix up units if you make length measurements using English units, and mass measurements in the metric system for example.   Even when using the metric system throughout, one could easily make the mistake of mixing CGS units with MKS units.  Always check your units.

The density of jello? Understanding what jello is and how it is made is an interesting lesson in biochemistry, particularly protein structure and function.

The more general name for jello is gelatin.  (Jell-0 is a brand name for the foodstuff – edible gelatin – that has become synonymous with the food itself.) Gelatin is made from the connective tissue proteins of cows or pigs. It is made first by breaking down the cellular structure of the connective tissues.  Then collagen proteins from these tissues are isolated, denatured and subsequently rendered to a powdered form.  Sweeteners, flavoring agents, dyes and other additives are added to this powder to make the familiar gelatin dessert.  To make jello you have to add boiling water to the powder which dis-aggregates the proteins.   Cooling the mixture re-aggregates the proteins.   The final jello mold will be a complex solid mixture of proteins, water, air, and chemical additives.

This leads us to consider the density of jello, which like the biological tissue from which it comes, is mostly water.

Water’s density is  1 \frac{g}{cm^3} = 1000 \frac{kg}{m^3} .  So the density has to be close to water.  But the various additives result in partial molar volumes that contract or expand the total volume.   The final volume depends on the thermodynamic nature of the additives and their relative concentrations.  So while it is easy to think that in any given volume of jello there are constituents that are heavier than water, and that the density should be greater than  1 g/cm^3 , the complex mixture of additives could result in the overall density being less than  1 g/cm^3 .  The most prudent thing to do is to take a well measured cube of jello, calculate its volume (or use volume displacement), weigh it, then calculate its density.

Reported densities for  jello have ranged from  0.98 - 1.3 g/cm^3 (with sugar-free variants being on the low end), while for scientific gelatin (without all the food additives) the density has been reported to be  1.3 g/cm^3 .