A. K. Rajarajan

HP-sequence design for lattice proteins—An exact enumeration study on diamond as well as square lattice

We present an exact enumeration algorithm for identifying the native configuration--a maximally compact self-avoiding walk configuration that is also the minimum energy configuration for a given set of contact-energy schemes; the process is implicitly sequence-dependent. In particular, we show that the 25-step native configuration on a diamond lattice consists of two sheet-like structures and is the same for all the contact-energy schemes, {(-1, 0, 0); (-7, -3, 0); (-7, -3, -1); (-7, -3, 1)}; on a square lattice also, the 24-step native configuration is independent of the energy schemes considered. However, the designing sequence for the diamond lattice walk depends on the energy schemes used whereas that for the square lattice walk does not. We have calculated the temperature-dependent specific heat for these designed sequences and the four energy schemes using the exact density of states. These data show that the energy scheme (-7, -3, -1) is preferable to the other three for both diamond and square lattice because the associated sequences give rise to a sharp low-temperature peak. We have also presented data for shorter (23-, 21-, and 17-step) walks on a diamond lattice to show that this algorithm helps identify a unique minimum energy configuration by suitably taking care of the ground-state degeneracy. Interestingly, all these shorter target configurations also show sheet-like secondary structures.

Inelastic neutron scattering measurements and lattice dynamics of ZnS1-xSex

Inelastic neutron scattering measurements to determine the phonon density of states along with lattice dynamical studies based on a supercell and a simple transferable potential model have been done to confirm the two mode behavior exhibited by ZnS1-xSex. In addition, the contribution of bond-length distribution to the existence of anomalous modes found in the frequency range of the ZnS-like TO and LO modes has been emphasized.

Effect of fast neutron irradiation induced defects on the metamagnetic transition In Ce(Fe0.96Ru0.04)2

Effect of fast neutron irradiation induced defects on the anti-ferromagnetic (AFM) to ferromagnetic (FM) transition in Ce(Fe0.96Ru0.04)2 is studied by magnetic measurements. We observe that at a given temperature, AFM–FM transition occurs at a lower field in irradiated specimens compared to that in pristine samples. While irradiation does not seem to affect the hysteresis of the transition, zero field susceptibility is enhanced by more than an order of magnitude. Analysis of reversible magnetization vs field data at low fields indicates superparamagnetic behavior of nano-sized FM domains, which are conjectured to nucleate on the crystal defects produced by the fast neutron irradiation. The number density and size of the nano-sized domains in the irradiated and pristine samples are estimated from the magnetization data.

Noble metal ions incorporated in lattice points of perovskites - water gas shift activity of BaCe1-xPtxO3-d

Recently precious metals supported on oxides were reported to be very promising catalysts for the lower-temperature WGS reaction. Here we report the synthesis of platinum doped barium cerate and its use as catalysts for WGS reaction. It has been found that maximum CO conversion was obtained at 3500C which enhanced after the first cycle. XPS analysis shows that after the first cycle more ionic Platinum species are present on the surface of the catalyst. Neutron diffraction at room temperature shows that the oxygen vacancies are in the O2 position and increases with increasing Pt substitution.

Magnetic resonance on correlated semimetals: the case of U2Ru2Sn, CeRu4Sn6 and FeSb2

A comparative magnetic resonance study on correlated semiconductors is presented. Nuclear spin-lattice relaxation measurements provide an excellent method to gain local information about the gap formation in this new class of materials. In contrast to U2Ru2Sn (Δ/kB ≈ 230 K) in CeRu4Sn6 the gap is slightly reduced (Δ/kB ≈ 200 K) and correlations form out of a residual density of states in the gap. For FeSb2 there is revived interest after classifying this system as the second Fe containing Kondo insulator beside FeSi. Surprisingly, FeSb2 shows a colossal Seebeck coefficient at low temperatures. Using 121,123Sb nuclei as a local probe, our NMR/NQR investigations strongly support the gap scenario. The spin-lattice relaxation rate 123(1/T1) in the entire investigated temperature range 2–200 K is perfectly fitted with rectangle DOS model with narrow impurity in-gap band. These in-gap states might originate the high thermopower observed. The obtained gap value is (Δ/kB ≈ 473 K).