202 research outputs found
Unconventional magnetism in the 4d based () honeycomb system AgLiRuO
We have investigated the thermodynamic and local magnetic properties of the
Mott insulating system AgLiRuO containing Ru
(4) for novel magnetism. The material crystallizes in a monoclinic
structure with RuO octahedra forming an edge-shared
two-dimensional honeycomb lattice with limited stacking order along the
-direction. The large negative Curie-Weiss temperature ( = -57
K) suggests antiferromagnetic interactions among Ru ions though magnetic
susceptibility and heat capacity show no indication of magnetic long-range
order down to 1.8 K and 0.4 K, respectively. Li nuclear magnetic
resonance (NMR) shift follows the bulk susceptibility between 120-300 K and
levels off below 120 K. Together with a power-law behavior in the temperature
dependent spin-lattice relaxation rate between 0.2 and 2 K, it suggest dynamic
spin correlations with gapless excitations. Electronic structure calculations
suggest an description of the Ru-moments and the possible importance of
further neighbour interactions as also bi-quadratic and ring-exchange terms in
determining the magnetic properties. Analysis of our SR data indicates
spin freezing below 5 K but the spins remain on the borderline between static
and dynamic magnetism even at 20 mK.Comment: 10 pages, 11 figures. accepted in Phys. Rev.
Structural, thermodynamic, and local probe investigations of a honeycomb material AgLiMnO
The system Ag[LiMn]O belongs to a quaternary
3R-delafossite family and crystallizes in a monoclinic symmetry with space
group and the magnetic Mn() ions form a honeycomb
network in the -plane. An anomaly around 50 K and the presence of
antiferromagnetic (AFM) coupling (Curie-Weiss temperature
K) were inferred from our magnetic susceptibility data. The magnetic specific
heat clearly manifests the onset of magnetic ordering in the vicinity of 48\,K
and the recovered magnetic entropy, above the ordering temperature, falls short
of the expected value, implying the presence of short-range magnetic
correlations. The (ESR) line broadening on approaching the ordering temperature
could be described in terms of a Berezinski-Kosterlitz-Thouless
(BKT) scenario with K. Li NMR line-shift probed as a
function of temperature tracks the static susceptibility (K) of
magnetically coupled Mn ions. The Li spin-lattice relaxation rate
(1/) exhibits a sharp decrease below about 50 K. Combining our bulk
and local probe measurements, we establish the presence of an ordered ground
state for the honeycomb system AgLiMnO.Our ab-initio
electronic structure calculations suggest that in the -plane, the nearest
neighbor (NN) exchange interaction is strong and AFM, while the next NN and the
third NN exchange interactions are FM and AFM respectively. In the absence of
any frustration the system is expected to exhibit long-range, AFM order, in
agreement with experiment.Comment: 11 pages, 13 figures, accepted in Phys Rev
Weeds and Weed Management of Rice in Karnataka State, India
Rice is one of the staple food crops of India, and Karnataka is one of the major rice-producing states. The primary method of rice establishment in Karnataka is transplanting, but farmers are opting to shift to direct-seeding of rice. Weed management is critical for realizing optimal yield of direct-seeded rice (DSR). The objective of this review was to synthesize the published literature on weeds and weed management in rice in Karnataka, identify improved weed-management technologies for delivery to farmers, and suggest research needs. Some 98 weed species are reported to be associated with rice in Karnataka. Weed control to date in Karnataka has mostly been based on herbicides. Hand-weeding was found to be effective in all methods of rice establishment. However, it is time-consuming, tedious, and costly because labor is becoming scarce and unavailable, and labor wages are higher. Several PRE and POST herbicides that were effective in other Asian countries were also found to be effective in managing weeds in rice established by different methods in Karnataka. Bensulfuron plus pretilachlor and pyrazosulfuron in aerobic rice and pendimethalin, thiobencarb, bispyribac-sodium, cyhalofop, fenoxaprop plus chlorimuron plus metsulfuron, and fenoxaprop plus ethoxysulfuron in dry-DSR were found effective in managing weeds. In wet-DSR, butachlor plus safener and pretilachlor plus safener were effective. Thiobencarb, pendimethalin, pretilachlor, azimsulfuron plus metsulfuron, bispyribac-sodium, butachlor, cinosulfuron, oxadiazon, and quinclorac were found promising for weed management in transplanted rice. Integration of herbicides with hand-weeding or intercultivation was found to be effective in rice established by different methods. Options that were found economical in managing weeds varied across the different rice-establishment methods. The need for developing location-specific, sustainable, integrated weed management and extension of available technologies for the farming community in Karnataka is emphasized
Magnetic and electron transport properties of the rare-earth cobaltates, La0.7-xLnxCa0.3CoO3 (Ln = Pr, Nd, Gd and Dy) : A case of phase separation
Magnetic and electrical properties of four series of rare earth cobaltates of
the formula La0.7-xLnxCa0.3CoO3 with Ln = Pr, Nd, Gd and Dy have been
investigated. Compositions close to x = 0.0 contain large ferromagnetic
clusters or domains, and show Brillouin-like behaviour of the field-cooled DC
magnetization data with fairly high ferromagnetic Tc values, besides low
electrical resistivities with near-zero temperature coefficients. The
zero-field-cooled data generally show a non-monotonic behaviour with a peak at
a temperatures slightly lower than Tc. The near x = 0.0 compositions show a
prominent peak corresponding to the Tc in the AC-susceptibility data. The
ferromagnetic Tc varies linearly with x or the average radius of the A-site
cations, (rA). With increase in x or decrease in (rA), the magnetization value
at any given temperature decreases markedly and the AC-susceptibility
measurements show a prominent transition arising from small magnetic clusters
with some characteristics of a spin-glass. Electrical resistivity increases
with increase in x, showed a significant increase around a critical value of x
or (rA), at which composition the small clusters also begin to dominate. These
properties can be understood in terms of a phase separation scenario wherein
large magnetic clusters give way to smaller ones with increase in x, with both
types of clusters being present in certain compositions. The changes in
magnetic and electrical properties occur parallely since the large
ferromagnetic clusters are hole-rich and the small clusters are hole-poor.
Variable-range hopping seems to occur at low temperatures in these cobaltates.Comment: 23 pages including figure
Properties of the ferrimagnetic double-perovskite A_{2}FeReO_{6} (A=Ba and Ca)
Ceramics of A_{2}FeReO_{6} double-perovskite have been prepared and studied
for A=Ba and Ca. Ba_{2}FeReO_{6} has a cubic structure (Fm3m) with 8.0854(1) \AA whereas Ca_{2}FeReO_{6} has a distorted monoclinic symmetry with
and
. The barium compound is metallic from 5 K to 385
K, i.e. no metal-insulator transition has been seen up to 385 K, and the
calcium compound is semiconducting from 5 K to 385 K. Magnetization
measurements show a ferrimagnetic behavior for both materials, with T_{c}=315 K
for Ba_{2}FeReO_{6} and above 385 K for Ca_{2}FeReO_{6}. A specific heat
measurement on the barium compound gave an electron density of states at the
Fermi level, N(E_{F}) equal to 6.1. At 5 K, we
observed a negative magnetoresistance of 10 % in a magnetic field of 5 T, but
only for Ba_{2}FeReO_{6}. Electrical, thermal and magnetic properties are
discussed and compared to the analogous compounds Sr_{2}Fe(Mo,Re)O_{6}.Comment: 5 pages REVTeX, 7 figures included, submitted to PR
Crystal structures and magnetic order of La{0.5+delta}A{0.5-delta}Mn{0.5+epsilon}Ru{0.5-epsilon}O{3} (A= Ca, Sr, Ba): Possible orbital glass ferromagnetic state
The crystallographic and magnetic properties of
La{0.5+delta}A{0.5-delta}Mn{0.5+epsilon}Ru{0.5-epsilon}O{3} (A= Ca, Sr, Ba)
were investigated by means of neutron powder diffraction. All studied samples
show the orthorhombic perovskite crystal structure, space group Pnma, with
regular (Mn,Ru)O{6} octahedra and no chemical ordering of the Mn3+ and Ru4+
ions. Ferromagnetic spin structures were observed below Tc ~ 200-250 K, with an
average ordered moment of ~ 1.8-2.0 Bohr magnetons per (Mn,Ru). The observation
of long-range ferromagnetism and the absence of orbital ordering are
rationalized in terms a strong Mn-Ru hybridization, which may freeze the
orbital degree of freedom and broaden the eg valence band, leading to an
orbital-glass state with carrier-mediated ferromagnetism
Antifungal potential of Azotobacter species and its metabolites against Fusarium verticillioides and biodegradation of fumonisin
Abstract Aims In the study, seven Plant Growth Promoting Rhizobacteria (PGPR) Azotobacter species were screened against three strains of Fusarium verticillioides to test its antifungal activity. Azotobacter strains were tested for the degradation of fumonisin produced by F. verticillioides. Secondary metabolites were isolated and characterized from the Azotobacter strains for the first time. Methods and Results Potential seven Azotobacter species antifungal activity was tested following the dual culture assay against three strains of Fusarium verticillioides namely FVM-42, FVM-86 and MTCC156 estimating the substantial zone of inhibition. Azotobacter species AZT-31 and AZT-50 strains significantly inhibited the growth of F. verticillioides recording drastic growth enhancement of maize under in-vitro conditions by calculating the infection incidence, vigour index and germination percentage. As confirmation, dereplication studies were conducted for the reconfirmation of Azotobacter strains by isolating from rhizoplane. Azotobacter strains played a key role in the degradation of fumonisin produced by F. verticillioides reporting 98% degradation at 2Â h of incubation with the pathogen. Furthermore, in the study first time, we have tried to isolate and characterize the secondary metabolites from the Azotobacter strains exhibiting six compounds from the species AZT-31 (2) and AZT-50 (4). Preliminary in-vitro experiments were carried out using the compounds extracted to check the reduction of infection incidence (90%) and increase in germination percentage upto 50 to 70% when compared to the test pathogen. Conclusion Azotobacter strains referred as PGPR on influencing the growth of plant by producing certain substances that act as stimulators on inhibiting the growth of the pathogen. Significance and Impact of the study The future perspective would be the production of an active combination of carboxamide compound and Azotobacter species for preventively controlling the phytopathogenic fungi of plants and crops and also towards the treatment of seeds
Rice Production Systems
Rice is grown in more than 100 countries spread across six continents and in varying agroecological and socioeconomic conditions. Rice production systems were classified over years differently depending on the context. In this chapter, the method of rice establishment is considered as criteria for classifying rice production systems across the globe. An attempt is made here to summarize the information on rice production systems, resources used, crop productivity attained, the challenges encountered, and possible research needs for improving productivity in rice production systems, to meet the future food demands. Based on the major methods of rice establishment of the world, the rice production systems are categorized as (a) transplanted rice (TPR) production systems and (b) direct-seeded rice (DSR) production systems. DSR production systems are further categorized as (i) dry-seeded rice (dry-DSR) production system, (ii) wet-seeded rice (wet-DSR) production system, and (iii) water-seeded rice (water-DSR) production system. The productivity of TPR and DSR was reported to be similar when the best management practices are adopted. As already occurred in the developed world, a shift in adoption toward DSR production systems is occurring in developing world, due to advantages of DSR production systems such as lesser cost of production, increased resource (water, labor, and energy) use efficiency, and income compared to TPR. Lower environmental footprint was found to be another advantage of DSR production systems when they were combined with other conservation agricultural practices. The need for continuous research efforts was stressed for understanding the evolving rice production systems across the globe and to develop practical integrated crop management strategies that improve rice productivity and production effectively, sustainably, and economically with minimal environment footprint
Metallic and nonmetallic double perovskites: A case study of AFeReO (A= Ca, Sr, Ba)
We have investigated the structure and electronic properties of ferrimagnetic
double perovskites, A2FeReO6 (A= Ca, Sr, Ba). The A=Ba phase is cubic (Fm3m)
and metallic, while the A=Ca phase is monoclinic (P21/n) and nonmetallic.
57Fe Mossbauer spectroscopy shows that iron is present mainly in the
high-spin (S=5/2) Fe3+ state in the Ca compound, while it occurs in an
intermediate state between high-spin Fe2+ and Fe3+ in the Ba compound. It is
argued that a direct Re t2g - Re t2g interaction is the main cause for the
metallic character of the Ba compound; the high covalency of Ca-O bonds and the
monoclinic distortion (which lifts the degeneracy of t2g states) seem to
disrupt the Re-Re interaction in the case of the Ca compound, making it
non-metallic for the same electron count.Comment: 1 eps fil
Assessment of genetic diversity among Malnad Gidda, Punganur and Vechur-dwarf cattle breeds of India using microsatellite markers
The genetic diversity among 3 dwarf breeds of cattle in India, viz. Malnad Gidda, Punganur and Vechur were analysed using 12 sets of microsatellite markers. All 11 amplified microsatellite loci were polymorphic with a mean number of alleles of 7.818±1.66 across breeds and in different breeds it ranged from 7.273 in Malnad Gidda to 3.546 in Vechur. The mean polymorphic information content (PIC) value observed and expected heterozygosity values across the population were 0.642, 0.610 and 0.683, respectively. A moderate level of inbreeding was observed with the inbreeding estimates ranging from -0.027 (ILSTS6) to 0.271 (HAUT24). Among the 3 breeds the highest mean number of alleles (7.273), mean PIC value (0.639), observed heterozygosity (0.630) and lower inbreeding estimates at majority of loci were observed in Malnad Gidda cattle indicating high degree of heterozygosity compared to Punganur and Vechur breeds. Even though departure from Hardy Weinberg Equilibrium (HWE) was found in Vechur and Punganur cattle population at majority of the loci, the population combining the 3 breeds was maintained at HWE with respect to most of loci under study. The genetic distance analysis revealed highest genetic distance between Vechur and Punganur (0.331) and lowest between Malnad Gidda and Punganur (0.125)
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