Electrical transport and magnetic ordering in R 2Ti3Ge4 (R=Dy, Ho and Er) compounds

New R ₂Ti₃Ge₄ (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize in the parent, Sm₅Ge₄-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series. The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects.     

Elastic properties of the Ta–V system: bcc Ta0.33V0.67 and C15 TaV2

Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta_0.33V_0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV₂. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase.     

Shoot organogenesis from root-derived callus of Rhinacanthus nasutus (L.) Kurz. and assessment of clonal fidelity of micropropagted plants using RAPD analysis

An efficient regeneration system was established for an ethnomedicinal shrub Rhinacanthus nasutus from root-derived callus organogenesis. The root segments were cultured on MS medium supplemented with various concentrations of Kn (1.0–4.0 μM) alone or in combination with IBA (0.2–0.6 μM) or 2, 4-D (0.5–1.5 μM). The optimum frequency (94 %) of callus induction was recorded on MS medium supplemented with 3.0 μM Kn and 0.4 μM IBA. For shoot regeneration from callus, MS medium supplemented with different concentrations (1.0–7.0 μM) of BA or TDZ alone or in combination with NAA (0.2–1.0 μm) was employed. The highest frequency of shoot regeneration (91 %) and mean number of shoots (28.3) were observed on MS medium supplemented with 5.0 μM BA and 0.7 μM NAA. The shoots were excised and cultured on MS medium with 4.0 μM IBA produced 3.4 roots per shoot in 88 % cultures. Of the 65 plants transferred to soil 54 survived (83 %). The plants were transferred to field after successful hardening. RAPD analysis of the regenerated plants showed high similarity with the mother plant.     

In situ ATR-FTIR studies on MgCl2-diisobutyl phthalate interactions in thin film Ziegler-Natta catalysts

To study the surface structure of MgCl(2) support and its interaction with other active components in Ziegler-Natta catalyst, such as electron donors, we prepared a thin film analogue for Ziegler-Natta ethylene polymerization catalyst support by spin-coating a solution of MgCl(2) in ethanol, optionally containing a diester internal donor (diisobutyl-ortho-phthalate, DIBP) on a flat Si crystal surface. The donor content of these films was quantified by applying attenuated total internal reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). Changes in the interaction of DIBP with MgCl(2) at various temperatures were monitored by in situ ATR-FTIR. Upon increasing the temperature, a shift in the (C═O) band toward lower wavenumbers was observed together with the depletion of (O-H) stretching band due to the desorption of residual ethanol. We assign this shift to gradual redistribution of adsorbed DIBP from adsorption sites on the MgCl(2) (104) surface toward the more acidic MgCl(2) (110) surface. The morphologies of MgCl(2) and MgCl(2)/DIBP films were studied by transmission electron microscopy (TEM) revealing a preferential orientation of ClMgCl layers (001) parallel to the lateral film dimensions. This orientation becomes more pronounced upon annealing. In the absence of donor, the MgCl(2) grow in to large crystals aligned in large domains upon annealing. Both crystal growth and alignment is impeded by the presence of donor.     

Plant Regeneration Through Callus Organogenesis and True-to-Type Conformity of Plants by RAPD Analysis in Desmodium gangeticum (Linn.) DC.

An efficient plant regeneration protocol was established for an endangered ethnomedicinal plant Desmodium gangeticum (Linn.) DC. Morphogenic calli were produced from 96 % of the cultures comprising the immature leaf explants on Murashige and Skoog (MS) medium supplemented with 2,4-dichlorophenoxyacetic acid (4.0 mg?l^?1) in combination with 6-benzylaminopurine (BA; 0.8 mg?l^?1). For callus regeneration, various concentrations of BA (1.0–5.0 mg?l^?1) or thidiazuron (TDZ; 1.0–5.0 mg?l^?1) alone or in combination with indole-3-acetic acid (IAA; 0.2–1.0 mg?l^?1) were used. Highest response of shoot regeneration was observed on MS medium fortified with TDZ (4.0 mg?l^?1) and IAA (0.5 mg?l^?1) combination. Here, 100 % cultures responded with an average number of 22.3 shoots per gram calli. Inclusion of indole-3-butyric acid in half MS medium favored rooting of recovered shoots. Out of 45 rooted plants transferred to soil, 40 survived. Total DNA was extracted from the leaves of the acclimatized plants of D. gangeticum. Analysis of random amplified polymorphic DNA using 13 arbitrary decanucleotide primers showed the genetic homogeneity in all the ten plants regenerated from callus with parental plant, suggesting that shoot regeneration from callus could be used for the true-to-type multiplication of this plant.