Glassy Dielectric Response in Tb_2NiMnO_6 Double Perovskite with Similarities to a Griffiths Phase

Frequency-dependent and temperature-dependent dielectric measurements are performed on double perovskite Tb$_2$NiMnO$_6$. The real ($\epsilon_1$) and imaginary ($\epsilon_2$) parts of dielectric permittivity show three plateaus suggesting dielectric relaxation originating from bulk, grain boundaries and the sample-electrode interfaces respectively. The temperature and frequency variation of $\epsilon_1$ and $\epsilon_2$ are successfully simulated by a $RC$ circuit model. The complex plane of impedance, $Z'$-$Z"$, is simulated using a series network with a resistor $R$ and a constant phase element. Through the analysis of frequency-dependent dielectric constant using modified-Debye model, different relaxation regimes are identified. Temperature dependence of dc conductivity also presents a clear change in slope at, $T^*$. Interestingly, $T^*$ compares with the temperature at which an anomaly occurs in the phonon modes and the Griffiths temperature for this compound. The components $R$ and $C$ corresponding to the bulk and the parameter $\alpha$ from modified-Debye fit tend support to this hypothesis. Though these results cannot be interpreted as magnetoelectric coupling, the relationship between lattice and magnetism is marked.Comment: Accepted in Europhysics Letter

BIOMIMETIC SYNTHESIS, CHARACTERIZATION AND EVALUATION OF ANTIOXIDANT, ANTIMICROBIAL EFFICACY OF SILVER NANOPARTICLES USING ANDREDERA CORDIFOLIA LEAF EXTRACT

Objective: The present study is focussed on the biosynthesis of silver nanoparticles using aqueous extract of Andredera cordifolia and to investigate the free radical scavenging potential, antimicrobial activity of the nanoparticles against different human pathogens.Methods: The formation of silver nanoparticles was indicated by the colour change from colourless to reddish brown. Biosynthesized nanoparticles was characterised using several techniques, viz- UV-Vis spectroscopy, FT-IR, XRD, TEM, SEM and EDAX analysis. The free radical scavenging potential was measured by DPPH, FRAP assay, antimicrobial activity against six microorganisms was tested using disc diffusion method.  Results: UV-Vis spectral analysis showed silver Surface Plasmon Resonance band at 426 nm.  The crystalline morphology and size of the nanoparticles were determined by TEM, SEM, and X-ray diffraction studies which showed the average size of the nanoparticles in the range 40 –60nm.  The biologically synthesized nanoparticles efficiently inhibited pathogenic organisms such as E. coli, Staphylococcus aureus, Klebsiella Pneumonia, Pseudomonas aeruginosa and Proteus vulgaris.  The biosynthesized nanoparticles might serve as a potent antioxidant as revealed by DPPH assay and FRAP assay. Conclusion: The biosynthesis of silver nanoparticles had several advantages in pharmaceutical applications as well as large scale commercial production.Key Words: Silver nanoparticle, Andredera cordifolia leaf, SEM,TEM,XRD,antioxidant, antimicrobial,etc

ANTIOXIDANT AND FREE RADICAL SCAVENGING ACTIVITY OF THE MIXTURE OF ETHANOLIC EXTRACTS OF ALPINIA SPECIOSA AND ALPINIA CALCARATA RHIZOME

Objective: The present study was aimed to investigate the antioxidant and free radipotentials of the mixture ethanolic extract of rhizomes of Alpinia speciosa and Alpinia calcarata.Methods: The ethanolic mixture extract of rhizomes was prepared in the ratio of 50:50 of Alpinia speciosa and Alpinia calcarata was subjected to the analysis of phytochemicals, total phenolics and flavonoid contents and free radical scavenging activities such as DPPH, Nitric oxide radical, Superoxide radical, Hydroxyl radical, Ferric reducing antioxidant power, reducing power and Metal ion-chelating activities were determined.Results: The rhizome mixture extract showed total antioxidant content, good flavonoid and moderate amounts of phenolics content. In DPPH, Nitric oxide and Superoxide radical scavenging activity, IC50 was found 136.22±3.44 µg/ml, 53.67±0.47µg/ml, 74.20±1.48µg/ml respectively with the standard ascorbic acid [3.61±0.20 µg/ml, 49.06±0.18 µg/ml and 39.81±0.22 µg/ml]. For the Hydroxyl radical scavenging activities, the IC50 values were 42.02±2.51 µg/ml with the standard Rutin [17.15±0.02 µg/ml]. The Ferric reducing antioxidant power was found 497.32±7.49 mmol/Fe (II)g with the standard Ascorbic acid 1956.20±74.08 mmol/Fe (II)g. The Metal chelating activity was found 96.23±0.39 mg EDTA/g sample with the standard ascorbic acid 205.86±0.53 mg EDTA/g sample. The reducing power was determined, the concentrations 20 µg/ml absorbance of the rhizome mixture was 0.05 and 100 µg/ml absorbance 0.14 with the standard ascorbic acid was absorbance 0.54 and 2.0.Conclusion: The results of present study showed that mixture ethanolic extract of rhizomes of Alpinia speciosa and Alpinia calcarata possesses high potential antioxidant activity and could be a potential source a natural antioxidant that could have great importance as therapeutic agents in preventing oxidative stress-related degenerative diseases

Marine pearl production: CMFRI develops tissue culture technology

Marine pearl production: CMFRI develops tissue culture technolog

The black clam, Villorita cyprinoides, fishery in the State of Kerala, India

The State of Kerala leads India in the production of clams with estimated annual landings of about 66,000 tons (t) in 2008-09. The black clam, Villorita cyprinoides (Family, Corbiculidae) contributes 45,000 t, or about two-thirds of this total (Narasimham et al., 1993; CMFRI Annual Report, 2009). Most of the annual production of black clams, about 25,000 t, comes from Vembanad Lake where almost 4,000 fishermen harvest them. The other clams harvested in the lake are the grey clam, Meretrix casta, and to a much lesser extent, the yellow clam, Paphia malabarica, and another, the Sunetta scripta. Vembanad Lake also has large sub-fossil deposits of black clam shells that are mined for commercial use (Kripa et al., 2004). The lake also has commercially-important finfish. The fisheries for the clams and the finfish provide the major livelihood for coastal communities around the lake (Sathiadhas et al., 2004). This paper provides an overview of the black clam fishery in Kerala including descriptions of the habitats, biology and ecology, demography of the fishing families, and the harvesting, processing, and marketing of the live clams and also the shell deposits. The information provided in earlier papers on these subjects by Laxmilatha and Appukuttan (2002), Sathiadhas et al. (2004), Arun (2005), Ravindran et al. (2006), and others are summarized. We conducted a survey to collect more detailed descriptions of these subjects and supplement them with photographs

A model for responsible black clam fisheries at R-Block in Vembanad Lake, Kerala

Kuttanad is a stretch of low-lying land of about 110,000 ha along the banks of Vembanad Lake and Pamba River tributaries. It encompasses vast stretch of backwaters, bordering human settlements, mangrove forests and rice fields. Four major rivers such as, Pamba, Meenachil, Achankovil and Manimala discharge into this region. It has the distinction of being one of the few areas in the world, where paddy farming is carried out below the sea level. The area is quite famous for its fishery for clams, pearlspot (Etroplus suratensis), snakehead (Channa spp.) and freshwater prawns (Macrobrachium spp.)

Tissue culture in pearl oyster

The first work on cell culture in marine molluscs started since 1960s. Many researchers attempted to improve the culture media composition by adding vertebrate sera as growth factor. In primary cultures, the tissue dissociation methods and medium composition were frequently complemented with homologous and heterologous substanc

Role of co-operative societies in black clam fishery and trade in Vembanad Lake

Lime shells and live clams are distributed in large quantities in the backwaters and estuaries of Kerala. Vembanad, the largest lake of Kerala, also holds a vast resource of lime shells and live clam, comprising several species. The major species that account for the clam fishery of Vembanad Lake is the black clam Villorita cyprinoides. The lime shells that contribute to the fishery are broadly classified as the ‘white shells’ and the ‘black shells’. The so-called ‘white shells’ are sub-soil deposits of fossilized shells and are known to extend upto 7 feet below the lake bottom. The black shells are obtained from the living population of V. cyprinoides, which contribute more than 90% of the clams from this lake