86 research outputs found
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 TbNiMnO. The real () and
imaginary () 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 and are successfully simulated by a
circuit model. The complex plane of impedance, -, is simulated using a
series network with a resistor 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, . Interestingly,
compares with the temperature at which an anomaly occurs in the phonon
modes and the Griffiths temperature for this compound. The components and
corresponding to the bulk and the parameter 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
Ferromagnetism and the Effect of Free Charge Carriers on Electric Polarization in Y_2NiMnO_6 Double Perovskite
The double perovskite Y_2NiMnO_6 displays ferromagnetic transition at Tc = 81
K. The ferromagnetic order at low temperature is confirmed by the saturation
value of magnetization (M_s) and also, validated by the refined ordered
magnetic moment values extracted from neutron powder diffraction data at 10 K.
This way, the dominant Mn4+ and Ni2+ cationic ordering is confirmed. The
cation-ordered P 21/n nuclear structure is revealed by neutron powder
diffraction studies at 300 and 10 K. Analysis of frequency dependent dielectric
constant and equivalent circuit analysis of impedance data takes into account
the bulk contribution to total dielectric constant. This reveals an anomaly
which coincides with the ferromagnetic transition temperature (T_c).
Pyrocurrent measurements register a current flow with onset near Tc and a peak
at 57 K that shifts with temperature ramp rate. The extrinsic nature of the
observed pyrocurrent is established by employing a special protocol
measurement. It is realized that the origin is due to re-orientation of
electric dipoles created by the free charge carriers and not by spontaneous
electric polarization at variance with recently reported magnetism-driven
ferroelectricity in this materialComment: Published in Physical Review
Griffiths phase-like behaviour and spin-phonon coupling in double perovskite TbNiMnO
The Griffiths phase-like features and the spin-phonon coupling effects
observed in TbNiMnO are reported. The double perovskite compound
crystallizes in monoclinic space group and exhibits a magnetic phase
transition at 111 K as an abrupt change in magnetization. A negative
deviation from ideal Curie-Weiss law exhibited by 1/ curves and
less-than-unity susceptibility exponents from the power-law analysis of inverse
susceptibility are reminiscent of Griffiths phase-like features. Arrott plots
derived from magnetization isotherms support the inhomogeneous nature of
magnetism in this material. The observed effects originate from
antiferromagnetic interactions which arise from inherent disorder in the
system. Raman scattering experiments display no magnetic-order-induced phonon
renormalization below in TbNiMnO which is different from the
results observed in other double perovskites and is correlated to the smaller
size of the rare earth. The temperature evolution of full-width-at-half-maximum
for the {\it stretching} mode at 645 cm presents an anomaly which
coincides with the magnetic transition temperature and signals a close
connection between magnetism and lattice in this material.Comment: 17 pages, 8 figures; accepted in J. Appl. Phy
Magnetic Order of the Hexagonal Rare Earth Manganite Dy(0.5)Y(0.5)MnO3
Hexagonal Dy(0.5)Y(0.5)MnO3, a multiferroic rare-earth manganite with
geometrically frustrated antiferromagnetism, has been investigated with
single-crystal neutron diffraction measurements. Below 3.4 K magnetic order is
observed on both the Mn (antiferromagnetic) and Dy (ferrimagnetic) sublattices
that is identical to that of undiluted hexagonal DyMnO3 at low temperature. The
Mn moments undergo a spin reorientation transition between 3.4 K and 10 K, with
antiferromagnetic order of the Mn sublattice persisting up to 70 K; the
antiferromagnetic order in this phase is distinct from that observed in
undiluted (h)DyMnO3, yielding a qualitatively new phase diagram not seen in
other hexagonal rare-earth manganites. A magnetic field applied parallel to the
crystallographic c axis will drive a transition from the antiferromagnetic
phase into the low-temperature ferrimagnetic phase with little hysteresis.Comment: Six pages, four figures v2: Table I added, Figures 2 and 3 edited,
text edited. August 24, 201
Ameliorative effect of ethanolic extract of roots of Tetracera akara (Burm. f.) Merr. on D-galactosamine induced hepatotoxicity in Wistar rats by downregulation of inflammatory mediators like TNFα, COX-2 and iNOS
161-171Tetracera akara, a climbing shrub locally called Nennalvalli or Pattuvalli, is an ethnomedicinal plant used by Kani tribe of Kerala to treat chronic liver disorders and inflammatory conditions. The present study was aimed to evaluate the hepatoprotective activity of ethanolic extract of roots of Tetracera akara root on D-Galactosamine induced hepatotoxicity in Wistar rats. Hepatotoxicity was induced in Wistar rats by intraperitoneal injection of D-GalN (400 mg/kg in saline) in Wistar rats. Ethanolic extract of T. akara root (TA ETH) was administered to the experimental rats in varying doses of (50, 150 and 300 mg/kg/day), p. o. for 7 days. The hepatoprotective effect was evaluated by the estimation of biochemical markers of hepatic injury, anti-oxidant status of the liver by estimating hepatic catalase, superoxide dismutase, glutathione and malondialdehyde, gene and protein expression level of inflammatory marker genes and histopathological evaluation of experimental animals. Administration of TA ETH (150 and 300 mg/kg) significantly (P ≤0.05) restored the levels of serum bilirubin, protein and other hepatic enzymes almost comparable to the standard drug Silymarin-treated groups. The levels of antioxidant enzymes like SOD and CAT were elevated and lipid peroxidation was inhibited as evident from the reduced levels of MDA. The gene expression studies by quantitative PCR method showed that TA ETH significantly (P ≤0.05) downregulated pro inflammatory cytokines, inflammatory COX-2 genes and upregulated IL 10 gene levels in D-GalN induced liver tissue, which was further confirmed in protein estimation by ELISA method. The histopathological observations were in correlation with the biochemical findings showing the presence of normal hepatic architecture, which further evidenced the hepatoprotective effect of TA ETH. Ethanolic extract of the root of T. akara possesses significant hepatoprotective activity mainly by scavenging reactive free radicals, boosting the endogenous antioxidant system in liver and inhibiting pro-inflammatory mediator like TNF α, COX-2, iNOS and promoting the anti-inflammatory IL 10, thus substantiating the tribal claim
Ameliorative Potential of Tamarindus indica
Nonalcoholic fatty liver disease (NAFLD), the prevalence of which is rising globally with current upsurge in obesity, is one of the most frequent causes of chronic liver diseases. The present study evaluated the ameliorative effect of extract of Tamarindus indica seed coat (ETS) on high fat diet (HFD) induced NAFLD, after daily administration at 45, 90, and 180 mg/kg body weight dose levels for a period of 6 weeks, in albino Wistar rats. Treatment with ETS at all tested dose levels significantly attenuated the pathological alterations associated with HFD induced NAFLD viz. hepatomegaly, elevated hepatic lipid and lipid peroxides, serum alanine aminotransferase, and free fatty acid levels as well as micro-/macrohepatic steatosis. Moreover, extract treatment markedly reduced body weight and adiposity along with an improvement in insulin resistance index. The study findings, therefore suggested the therapeutic potential of ETS against NAFLD, acting in part through antiobesity, insulin sensitizing, and antioxidant mechanisms
Pathological investigations of Vibrio vulnificus infection in Genetically Improved Farmed Tilapia (Oreochromis niloticus L.) cultured at a floating cage farm of India
An outbreak of skin ulcers with morbidity and mortality rate of 80% and 20% respectively, among Genetically Improved Farmed Tilapia (GIFT) sub-adults reared in a brackish water floating cage farm of Kochi, Kerala, India was reported. Bacterial isolation attempts from various internal organs (blood, kidney, liver, spleen and brain) of different diseased fish indicated a common bacterial etiology. Organisms were identified as Vibrio vulnificus based on conventional microbiological methods followed by molecular confirmation. Additionally, V. vulnificus marker specific for fish virulence was present in the isolates. Fish pathogenicity was confirmed by challenge tests. LD50 was calculated as 2.1 × 105.13 CFU/fish and 2.1 × 106.12 CFU/mL in injection and immersion route respectively. pilF polymorphism-based PCR and vvhA gene sequence indicated potential danger for humans. The strain was positive for siderophore, hemolysin, capsule, polar and lateral flagella. The strain could multiply rapidly in healthy fish serum. All these results indicated that the isolate could act as a primary pathogen for tilapia fish. Interestingly, serum survival ratio of the pathogen was significantly larger at higher temperatures (p ≤ .05); which may explain the increase in infective capacity of V. vulnificus at higher temperature. Multiple antibiotic resistance index of the strain was ≤0.2. In conclusion, the paper provides detailed descriptions of clinical signs, microscopic and macroscopic lesions of a natural disease outbreak among tilapia raised in brackish water cage farms of India. The concurrent attempts to identify and characterize the etiology fetches the basis for future development of effective control and preventive measures against V. vulnificus, the most infectious and lethal of all zoonotic vibrios
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