On the use of Kolmogorov-Landau approach in deriving various correlation functions in 2-D incompressible turbulence

We look at various correlation functions, which include those that involve both the velocity and the vorticity fields, in 2-D isotropic homogeneous decaying turbulence.We adopt the more intuitive approach due to Kolmogorov (and subsequently, Landau in his text on fluid dynamics) and show that how the 2-D turbulence results, obtainable using other methods, may be established in a simpler way.Also, some experimentally verifiable correlation functions in the dissipation range have been derived for the same system.The paper also showcases the inability of the Kolmogorov-Landau approach to get the ``one-eighth law'' in the enstrophy cascade region.As discussed in the paper, this may raise the spectre of logarithmic corrections once again in 2-D turbulence.Comment: A typos-corrected version of the earlier submissio

Senior International Associate Report (Ambuj Sagar): Meeting Multiple Energy Challenges: Lessons from India

The Rising Powers in International Development (RPID) programme includes a provision for drawing on the experience of senior policymakers and policy advisers. This ‘Senior International Associates’ scheme is an effective way of injecting policy experience from the Rising Powers directly into the work of the RPID. One of the key lines of work of the RPID is concerned with climate change policies in China, India, Brazil and South Africa. The BRICS (Brazil, Russia, India, China and South Africa) Summit and the BRICS Academic Forum held this year in Brazil are particularly concerned with such sustainability issues. This report shows how the RPID contributed to these debates and tapped the rich experience of Professor Ambuj Sagar, a senior international associate from India. Professor Sagar was invited to serve as a senior international associate because of his long and detailed involvement in policy processes both at national (Indian) and global levels.UK Department for International Developmen

Development of Eddy-Current Probes for the Evaluation of Magnetite in the Support-Plate Crevices of Nuclear Steam Generators

Eddy current technique has played an important role in the understanding of the corrosion behavior of steam generator components. Until recently, its role has been primarily in the evaluation of the condition of the heat exchanger tubes. Recent developments have led to the use of this technique for detecting corrosion of the carbon steel plates supporting the tubes. The detection and quantification of possible accumulation of corrosion products such as magnetite in the crevices between tubes and supports may often be a desired objective of such inspections since the presence of such deposits is of interest with respect to tube denting and other corrosion phenomena. This paper discusses the difficulty of an unambiguous determination of the presence of magnetite in the tube support crevices and points to the difficulty of obtaining a quantitative estimate for the amount of magnetite which may be present. This paper further discusses the development of new probes which provide improved discrimination between magnetite and a steel support thqs providing for a better estimate of the amount of magnetite in tube support crevices

Physical Parameters for the Afterglows of GRB 980703, 990123, 990510, and 991216 Determined from Modeling of Multi-Frequency Data

We model the radio, optical, and X-ray emission for the afterglows of GRB 980703, 990123, 990510, and 991216, within the framework of relativistic jets, to determine their physical parameters. The models that yield acceptable fits to the data have jet energies mostly between 10^{50} to 10^{51} erg and initial opening angles between 1 deg and 4 deg. The external medium density is uncertain by at least one order of magnitude in each case, being around 10^{-3}/cm^3 for GRB 980703 and 990123, ~0.1/cm^3 for GRB 990510, and ~3/cm^3 for GRB 991216. If the jets are uniform (i.e. there are no angular gradients of the energy per solid angle) then the 20 keV -- 1 MeV radiative efficiency during the GRB phase must have been at least 2-3% for GRB 990510, 20% for GRB 990123, and 30% for GRB 991216.Comment: accepted for publication by the ApJ, vol. 554. 11 pages, color figures. Last figures replaced with probability distributions of model parameter

On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions

Based on the CCD observations of remote young open clusters NGC 2383, NGC 2384, NGC 4103, NGC 4755, NGC 7510 and Hogg 15, we constructed their observed luminosity functions (LFs). The observed LFs are corrected for field star contamination determined with the help of galactic star count model. In the case of Hogg 15 and NGC 2383 we also considered the additional contamination from neighbouring clusters NGC 4609 and NGC 2384 respectively. These corrections provided the realistic pattern of cluster LF in the vicinity of the MS turn on point and at fainter magnitudes, revealed the so called H-feature arising due to transition of the Pre-MS phase to MS, which is dependent on the cluster age. The theoretical LFs were constructed representing a cluster population model with continuous star formation for a short time scale and a power law Initial Mass Function (IMF) and these were fitted to the observed LF. As a result we are able to determine for each cluster a set of parameters, describing cluster population (the age, duration of star formation, IMF slope and percentage of field star contamination). It was found that in spite of the non-monotonic behaviour of observed LFs, cluster IMFs can be described as the power law functions with slopes similar to Salpeter's value. The present MS turn on cluster ages are several times lower than those derived from the fitting of theoretical isochrones to the turn off region of the upper Main Sequences.Comment: 17 pages, 5 figures, To appear in MNRA