A generalization of paracompactness in terms of grills

In this paper we initiate a generalized form of paracompactness via grills. We shall also define a grill-dependent regularity axiom on a topological space. From our results in such a generalized perspective, E. Michael\u27s famous theorem on regular paracompactness and certain other results like ``a $T_2$ paracompact space is regular" will follow as special cases

Evolution of orbital phases with particle size in nanoscale stoichiometric LaMnO3

The thermodynamically stable long-range orbital order in bulk LaMnO3 becomes metastable at nanoscale around a critical particle size d_C~20 nm. The orbital order-disorder transition switches from reversible to irreversible at d_C while the resistance in the orbital ordered state decays by 2-4% over a time scale of ~3000s. At well below d_C, of course, a stable orbital disordered phase emerges. The orthorhombic distortion of the underlying crystallographic structure (space group Pbnm) decreases systematically with the decrease in particle size and at far below d_C (e.g., at ~10 nm), the structure becomes cubic (space group Pm-3m). Using the crystallographic and electrical resistance data, a phase diagram has been constructed showing the evolution of different orbital phases as a function of particle size across ~10 nm to bulk for stoichiometric LaMnO3.Comment: revised following referees' comments, accepted for publicaton in J. Appl. Phy

Electrical conductivity of cellular Si/SiC ceramic composites prepared from plant precursors

Electrical conductivity (sigma_dc) of the cellular Si/SiC ceramic composites has been measured over a temperature range 25-1073 K while the thermoelectric power (S) has been measured over 25-300 K. Remarkably, these cellular compounds developed through biomimetic route - where the ceramic system grows within a plant bio-template retaining the structural intricacies of the native templates - are found to exhibit excellent mechanical, thermal, and electrical properties quite comparable to or even better than those of the systems prepared through conventional ceramic route. The electrical conductivity measured parallel (sigma||) and perpendicular (sigma+) to the growth axes of the native plants, depicts nearly temperature-independent anisotropy (sigma+/sigma||) of the order \~2 while the thermoelectric power is nearly isotropic. The charge conduction across the entire temperature range is found to follow closely the variable range hopping (VRH) mechanism. The conductivity anisotropy appears to be driven primarily by the unique microcellular morphology of the bio-templates which can be exploited in many electrical applications.Comment: 22 pages including 6 figures; pdf only; submitted to J. Appl. Phy

A generalization of paracompactness in terms of grills

In this paper we initiate a generalized form of paracompactness via grills. We shall also define a grill-dependent regularity axiom on a topological space. From our results in such a generalized perspective, E. Michael\u27s famous theorem on regular paracompactness and certain other results like ``a $T_2$ paracompact space is regular" will follow as special cases

Generalized quasi-uniformity in terms of covers

Recently g-quasi uniformity has been introduced, and in the literature there al- ready is the notion of strong quasi-uniform cover for quasi-uniform spaces. Here in this paper we generalize the notion of strong quasi-uniform cover to study g-quasi uniformity in terms of it. As applications, we also formulate some g-topological concepts via this new type of cover

Magneto-structural studies of monohydroxo-ridged dicopper(II) complexes M[Cu<SUB>2</SUB>L<SUB>2</SUB>(OH)]&#183;2H<SUB>2</SUB>O (M=Na<SUP>+</SUP> (1) and K<SUP>+</SUP> (2); H<SUB>2</SUB>L=2,6-bis[N-(phenyl)carbamoyl]pyridine). Effect of Cu---OH---Cu bridge angle on antiferromagnetic coupling

Using a tridentate bis-amide ligand 2,6-bis[N-(phenyl)carbamoyl]pyridine (H2L), in its deprotonated form, two new monohydroxo-bridged dicopper(II) complexes M[Cu2L2(OH)]&#183;2H2O (M=Na+ (1) and K+ (2)) have been prepared and characterised by a number of methods, including X-ray crystallography. Each copper(II) ion is terminally coordinated by one pyridyl and two amide nitrogen donors. The two copper(II) centres are bridged by a hydroxo group, with each copper(II) centre assuming a distorted square planar geometry. The observation of short Cu---Npy and long Cu---Namide bonds is caused by the steric requirement of the ligand. Interestingly, each cation Na+/K+ is coordinated to four different [Cu2L2(OH)]- units through the amide O-donors, in an uncommon distorted tetrahedral coordination environment. Temperature-dependent magnetic susceptibility measurements revealed that the compounds have S=0 ground state with singlet-triplet energy separation, 2J=-334 and -296 cm-1 for 1 and 2, respectively. The larger Cu---OH---Cu bridge angle in 1 (131.1(6)&#176;) causes better antiferromagnetic exchange coupling than that in 2 (125.7(6)&#176;)

Manganese(III) complexes of 1,2-bis(2-pyridinecarboxamido)benzene: synthesis, spectra, and electrochemistry

The synthesis and solution properties of the high-spin (&#956;eff.= 4.78-4.86 at 298 K) manganese(III) complexes [Mn(bpb)X][X = Cl-, N3-, or SCN-; H2bpb = 1,2-bis(2-pyridinecarboxamido)benzene], are described. The brown crystalline complexes display ligand-to-metal charge-transfer transitions at ca. 430 nm, while in the near-infrared region crystal-field transitions are observed. In N,N-dimethylformamide solution the complexes exhibit a quasi-reversible MnIII-MnII couple [E298&#176;-0.03 to + 0.03 V vs. saturated calomel electrode (s.c.e.)]. The complexes [Mn(bpb)Cl] and [Mn(bpb)(N3)] display an additional quasi-reversible MnIV-MnIII couple [E298&#176;+0.87 (Cl-); + 0.49 V (N3-)vs. s.c.e.]

Magnetodielectric effect in composites of nanodimensional glass and CuO nanoparticles

Nanocomposites comprising CuO particles of average diameter 21 nm coated with 5 nm silica glass containing iron ions were synthesized by a chemical route. An ion exchange reaction at the nanoglass/CuO interface produced iron-doped CuO with copper ion vacancies within the nanoparticles. Room temperature ferromagnetic-like behavior was observed in the nanocomposites. This was ascribed to uncompensated spins contributed by Fe ions with associated copper ion vacancies. A rather high value of magnetodielectric parameter in the range 16–26% depending on the measuring frequency was exhibited by these nanocomposites at a magnetic field of 10 KOe. This was caused by a magnetoresistance of 33% in the iron doped CuO nanoparticles. The experimental results were fitted to the Maxwell–Wagner Capacitor model developed by Catalan. These materials will be suited for magnetic sensor applications

Synthesis, crystal structure and properties of trigonal bipyramidal [M(L<SUP>5</SUP>)<SUB>2</SUB>(H<SUB>2</SUB>O)]&#183;H<SUB>2</SUB>O complexes [M = cobalt(II) (S = 3/2) or copper(II) (S =&#189;); HL<SUP>5</SUP> = N-(2-chloro-6-methylphenyl)pyridine-2-carboxamide]

Using a bidentate ligand N-(2-chloro-6-methylphenyl)pyridine-2-carboxamide (HL5), in its deprotonated form, two new five-co-ordinate complexes of composition [M(L5)2(H2O)]&#183;H2O (M = CoII 1 or CuII 2) have been prepared and characterized including X-ray crystallography. The co-ordination geometry at CoII and CuII is approximately trigonal bipyramidal (two deprotonated amide nitrogens and a water molecule in the equatorial plane and two pyridines in the axial positions), being more distorted in the case of CuII. The observed distortion is caused by (i) a small bite angle of the chelating ligand and (ii) the presence of two ortho substituents, a chloro and a methyl group, on the phenyl ring (steric effect). To the best of our knowledge, 1 represents the first structurally characterized mononuclear high-spin cobalt(II) complex with a pyridine amide ligand. The magnetic moments of 1 and 2 at 300 K reveal that the compounds are paramagnetic (1 has S = 3/2 and 2 has S =&#189;), both as solids and in dmf solution. Temperature dependent magnetic susceptibility measurements confirmed their spin state. The stereochemistry of the cobalt(II) centre in 1 does not change to any measureable extent on dissolution in dmf (cf. solid and solution state absorption spectra). The geometry of the copper(II) centre in 2 observed in the solid state is not retained in dmf solution (absorption spectra), changing to a tetragonal stereochemistry. Cyclic voltammetric measurements (dmf solution; glassy carbon electrode) on 1 reveal an oxidative response at 0.48 V vs. saturated calomel electrode (SCE) and a reductive response at -1.66 V corresponding to CoIII-CoII and CoII-CoI redox couples, respectively. For 2 the CuII-CuI process was observed at -0.53 V vs. SCE