On counting triangulations in d dimensions

Given a set of n labeled points on S^d, how many combinatorially different geometric triangulations for this point set are there? We show that the logarithm of this number is at most some positive constant times n^d/2+1. Evidence is provided that for even dimensions d the bound can be improved to some constant times n^d/2.     

Protonated,hydroxo, and mixed protonated - hydroxo species in metal - ligand equilibria: Complexes of thorium(IV) with xylenol orange in aqueous solution solution

Summary The equilibrium constants of chelate formation of thorium(IV) with 3,3-bis[N,N-di(carboxymethyl)-amino-methyll-o-cresolsulphonphthalein (xylenol orange, dcac) at 25° in aqueous solution have been evaluated. The values have been obtained both while considering and ignoring the presence of metal hydroxo species, using the method described earlier. The change in equilibrium constant values obtained in both these situations has been explained by introducing some possible equations, and it has been concluded that the consideration of metal hydroxo species, does not lead to any marked changes in the valules of the formation constants of complex formed, even at higherpH.Presented at the National Symposium on Coordination Chemistry, I.A.C.S., Calcutta, January 1977.     

Ag nanoparticle mediated growth of CdS nanobelts

Catalytic growth of CdS have been carried out on large scale by evaporation of bulk CdS on Ag deposited Si (1 1 1) at atmospheric pressure. The as prepared CdS had wurtzite structure as evidenced by X-ray diffraction. The nanostructures were beltlike with several tens of micrometers length, several micrometers width and few nanometers to tens of nanometers thick as seen by scanning electron microscope and confirmed by TEM studies. The nanobelts were single crystalline in nature and showed reflection corresponding to (1 1 2) and (0 0 2) planes in SAED. The PL studies revealed the green band due to band gap emission and red band due to emission from the surface states. The higher intensity of the defect emission indicated the presence of considerable concentration of surface defects in the as prepared sample. The deposition of CdS could be explained on the basis of catalyst assisted vapor-liquid-solid and vapor-solid mechanism.     

Thermoelectric power of potassium doped lanthanum manganites at low temperatures

The temperature-dependent resistivity and thermoelectric power of monovalent (K) doped La_1−xK_xMnO₃ polycrystalline pellets (x=0.05, 0.10 and 0.15) between 50 and 300 K are reported. K substitution enhances the conductivity of this system. Curie temperature (T_C) also increases from 260 to 309 K with increasing K content. In the paramagnetic region (T>T_C), the electrical resistivity is well represented by adiabatic polaron hopping, while in the ferromagnetic region (T<T_C), the resistivity data show a nearly perfect fit for all the samples to an expression containing, the residual resistivity, spin-wave and two-magnon scattering and the term associated with small-polaron metallic conduction, which involves a relaxation time due to a soft optical phonon mode. Small polaron hopping mechanism is found to fit well to the thermoelectric power (S) data for T>T_C whereas at low temperatures (T<T_C) in ferromagnetic region (S_FM), S_FM is well explained with the spin-wave fluctuation and electron–magnon scattering. Both, resistivity and thermopower data over the entire temperature range (50–300 K) are also examined in light of a two-phase model based on an effective medium approximation.     

Structure of a Cu(II)-containing peptide,diaquo-gly-l-tyr Cu(II) dihydrate, [Cu(C11N2O4H13)(H2O)2·2H2O

The structure of the Cu(II) complex of gly-l-tyr [Cu(C₁₁N₂O₄H₁₃) (H₂O)₂]·2H₂O has been solved by X-ray diffraction methods. The compound crystallizes in the orthorhombic space groupP2₁2₁2₁ witha=11.970(2) Å,b=12.485(2) Å andc=10.418(3) Å, respectively, (MoK)=0.710 Å,D _c =1.59 Mgm^–3,D _m =1.59 Mgm^–3, finalR=0.04. The structure was solved by heavy atom (Cu) phased Fourier and refined by full-matrix least squares methods. The coordination geometry of the ligand around the Cu(II) ion has been established as a distorted tetragonal pyramid. The peptide molecule behaves as a tridentate ligand via its amino (N2), amido (N1) nitrogens and carboxyl (O2) oxygens. The peptide nitrogen is found to be deprotonated.     

Synthesis of modular building blocks using glycosyl phosphate donors for the construction of asymmetric N-glycans

Glycosyl phosphates are known as versatile donors for the synthesis of complex oligosaccharides both chemically and enzymatically. Herein, we report the stereoselective construction of modular building blocks for the synthesis of N-glycan using glycosyl phosphates as donors. We have synthesized four trisaccharide building blocks with orthogonal protecting groups, namely, Manβ2GlcNAc(OAc)₃β6GlcNAc (9), Manβ2GlcNAc-β6GlcNAc(OAc)₃ (15), Manβ2GlcNAc(OAc)₃β4GlcNAc (18) and Manβ2GlcNAcβ4GlcNAc(OAc) (22) for further selective elongation using glycosyltransferases. The glycosylation reaction using glycosyl phosphate was found to be high yielding with shorter reaction time. Initially, The phthalimide protected glucosamine donor was exploited to ensure the formation of β-glycosidic linkage and later converted to the N-acetyl group before the enzymatic synthesis. The selective deprotection of O-benzyl group was performed prior to enzymatic synthesis to avoid its negative interference.     

Evaluation of air permeability characteristics on the hybridization of carbon black with graphene nanoplatelets in bromobutyl rubber/epoxidized natural rubber composites for inner‐liner applications

Nanotechnology has been explored recently as a means of enhancing the properties of conventional elastomers for engineering applications. In the current study, the effect of nanofillers on air impermeability properties of Brominated isobutylene‐isoprene rubber (BIIR)/Epoxidized natural rubber (ENR) blend has analyzed for automotive applications. The ENR chosen is ENR 25 and ENR 50 (25 and 50% epoxidation) and prepared the blends in a ratio of 75:25 (BIIR:ENR), and from both blend based composites, a part of carbon black replaced with graphene nanoplatelets (GNP). The physical and thermal properties were compared for both binary blend nanocomposites to study the level of exfoliation and reinforcement behavior of GNP. Morphology studies were employed to reveal the level of interaction between GNP and carbon black in both blends. The influence of epoxidation in the formation of nanostructures in both blends have been evaluated, and the effect of nanostructures on air permeability properties was studied. The air impermeability of BIIR‐ENR 50 nanocomposites were improved with increasing platelet concentration, a 30% improvement in air permeability is obtained for BIIR‐ENR 50 composites over BIIR ‐ENR 25.