An Approach to NMR Assignment of Intrinsically Disordered Proteins

An efficient approach to NMR assignments in intrinsically disordered proteins is presented, making use of the good dispersion of cross peaks observed in [¹⁵N,¹³C′]‐ and [¹³C′,¹H^N]‐correlation spectra. The method involves the simultaneous collection of {3D (H)NCO(CAN)H and 3D (HACA)CON(CA)HA} spectra for backbone assignments via sequential H^N and H^α correlations and {3D (H)NCO(CACS)HS and 3D (HS)CS(CA)CO(N)H} spectra for side‐chain ¹H and ¹³C assignments, employing sequential ¹H data acquisitions with direct detection of both the amide and aliphatic protons. The efficacy of the approach for obtaining resonance assignments with complete backbone and side‐chain chemical shifts is demonstrated experimentally for the 61‐residue [¹³C,¹⁵N]‐labelled peptide of a voltage‐gated potassium channel protein of the Kv1.4 channel subunit. The general applicability of the approach for the characterisation of moderately sized globular proteins is also demonstrated.     

3He-rich solar flares

A new subgroup of³He rich solar flares is found on reanalysing the global data.³He/H ratio as a function of maximum proton flux at an energy of about 10 MeV shows a break-up of the data into two groups. The first group follows the anticorrelation of³He/H ratio with the proton flux, as expected in the plasma process acceleration models. But the second group has a constant³He/H ratio as a function of maximum proton flux. This is not in conformity with the plasma process models. But this is expected in models where the nuclear spallation reactions are responsible for the production of³He. It is also found that the same break-up into two distinct groups follows if one plots the location of the flares in the solar disc. The first group is more or less confined to the west limb of the Sun, whereas the second group is more widely spread out across the solar disk. Visiting Professor, Tata Institute of Fundamental Research, Bombay, August–September, 1983.     

Cosmic ray nuclei of chargeZ⩾3 during the period of low solar activity

A detailed study of the composition and energy spectra of heavy nuclei of charge Z?3 in the primary cosmic rays has been made during the period of low solar activity, using two stacks of nuclear emulsions exposed in balloon flights from Fort Churchill, Canada, in June 1963. Each of the stacks was composed of 120 nuclear emulsions of three different sensitivities and was exposed at about 3·5 g. cm.^?2 of residual air for about 11.1 hr. Reliable resolution of charges of nuclei from lithium to oxygen was obtained; for heavier nuclei, charge groups were determined. From the analysis of 793 tracks of nuclei with Z?3, results on the following aspects were obtained:

1. The differential energy spectra of L (Z=3–5), M (Z=6–9) and H (Z=10–28) nuclei were measured in the energy intervel 150–600 MeV/nucleon; integral fluxes were obtained for energy >600 MeV/nucleon;
2. The energy dependence of the L/M ratio at the top of the atmosphere was determined; the ratios were obtained as 0·45 ± 0·06 and 0·29 ± 0·03 in the energy intervals of 200–575, and >575 MeV/nucleon respectively;
3. Relative abundances of individual nuclei of Li, Be, B, C, N and O at the top of the atmosphere were determined as 36, 29, 55, 100, 60 and 106 respectively in the energy interval 150–600 MeV/nucleon; corresponding values were also obtained for energy >600 MeV/nucleon.
4. The differential fluxes of multiply charged nuclei measured by us and by other investigators were used to determine the solar modulation between solar maximum to solar minimum. It was found that solar modulation of the fluxes of M and He nuclei were consistent with Rβ dependence and that the modulation parameter Δη between 1965 and 1957 was about 1·1.

The implications of these results are discussed.     

Some remarks on vertex Folkman numbers for hypergraphs

Let $F(r,G)$ be the least order of $H$ such that the clique numbers of $H$ and $G$ are equal and any $r$-coloring of the vertices of $H$ yields a monochromatic and induced copy of $G$. The problem of bounding of $F(r,G)$ was studied by several authors and it is well understood. In this note, we extend those results to uniform hypergraphs.     

He3 nuclei in the low energy primary cosmic radiation

The flux of He³ nuclei and the ratio He³/(He³+He⁴) in the low energy primary cosmic radiation have been determined using a stack of nuclear emulsions exposed at 3·1 g. cm.^?2 of atmospheric depth from Fort Churchill, Canada, in June 1963. The grain-densityversus residual range method was used to determine the masses of the helium nuclei. Using a sample of 146 helium nuclei whose masses could be identified, the ratio He³/(He³+He⁴) is obtained as 0·14±0·04 for the kinetic energy interval 115–210 MeV per nucleon and 0·43±0·11 for the rigidity interval 0·85–1·05 BV. The differential fluxes of He³ nuclei are determined as 0·017±0·006, 0·045±0·015, and 0·054±0·017 particles/M². Sr. Sec. MeV/nucleon, in the kinetic energy intervals of 117–183, 183–217, and 217–250 MeV/nucleon respectively. These results are compared with those of other investigators. From the results of the present work the amount of matter traversed in space by the primary cosmic ray helium nuclei of energy 115–210 MeV/nucleon is obtained as 4·7±1·8 gm. cm.^?2 of hydrogen.     

Vertex colorings of graphs without short odd cycles

Motivated by the work of Ne?et?il and Rödl on “Partitions of vertices” we are interested in obtaining some quantitative extensions of their result. In particular, given a natural number r and a graph G of order m with odd girth g, we show the existence of a graph H with odd girth at least g and order that is polynomial in m such that every r‐coloring of the vertices of H yields a monochromatic and induced copy of G. © 2010 Wiley Periodicals, Inc. J Graph Theory 68: 255‐264, 2011     

The effect of ionisation loss on the energy spectra of cosmic ray nuclei undergoing fermi acceleration

The effect of ionisation loss, on the energy spectra of cosmic ray nuclei undergoing Fermi acceleration, has been studied using an analytic expression derived for the energy spectra of the nuclei undergoing acceleration. The spectra thus obtained have negative slopes which become steeper with increasing charge of the nucleus. In cases where the rate of acceleration is slow, solar modulation effects have been superimposed on the above spectra and it is found that the resulting spectral shapes can be fitted with recent satellite measurements for the energy spectra of various groups of cosmic ray nuclei at low energies.