25 research outputs found
Centrosymmetric-noncentrosymmetric Structural Phase Transition in Quasi one-dimensional compound, (TaSe)I
(TaSe)I, a compound belonging to the family of quasi-one-dimensional
transition-metal tetrachalcogenides, has drawn significant attention due to a
recent report on possible coexistence of two antagonistic phenomena,
superconductivity and magnetism below 2.5~K (Bera et. al, arXiv:2111.14525).
Here, we report a structural phase transition of the trimerized phase at
temperature, ~145~K using Raman scattering, specific heat, and
electrical transport measurements. The temperature-dependent single-crystal
X-ray diffraction experiments establish the phase transition from a
high-temperature centrosymmetric to a low-temperature non-centrosymmetric
structure, belonging to the same tetragonal crystal family. The first-principle
calculation finds the aforementioned inversion symmetry-breaking structural
transition to be driven by the hybridization energy gain due to the off-centric
movement of the Ta atoms, which wins over the elastic energy loss.Comment: 11 pages, 5 figures, Under review as a regular articl
High transport spin polarization in the van der Waals ferromagnet FeGeTe
The challenging task of scaling-down the size of the power saving electronic
devices can be accomplished by exploiting the spin degree of freedom of the
conduction electrons in van der Waals (vdW) spintronic architectures built with
2D materials. One of the key components of such a device is a near-room
temperature 2D ferromagnet with good metallicity that can generate a highly
spin-polarized electronic transport current. However, most of the known 2D
ferromagnets have either a very low temperature ordering, poor conductivity, or
low spin polarization. In this context, the FeGeTe (with )
family of ferromagnets stand out due to their near-room temperature
ferromagnetism and good metallicity. We have performed spin-resolved Andreev
reflection spectroscopy on FeGeTe ( 273 K) and
demonstrated that the ferromagnet is capable of generating a very high
transport spin polarization, exceeding 50. This makes FeGeTe a
strong candidate for application in all-vdW power-saving spintronic devices.Comment: Accepted for publication in Physical Review
Enhanced coercivity and emergence of spin cluster glass state in 2D ferromagnetic material Fe3GeTe2
Two-dimensional (2D) van der Waals (vdW) magnetic materials with high
coercivity and high are desired for spintronics and memory storage
applications. FeGeTe (F3GT) is one such 2D vdW ferromagnet with a
reasonably high , but with a very low coercive field,
(100~Oe). Some of the common techniques of enhancing are
by introducing pinning centers, defects, stress, doping, etc. They involve the
risk of undesirable alteration of other important magnetic properties. Here we
propose a very easy, robust, and highly effective method of phase engineering
by altering the sample growth conditions to greatly enhance the intrinsic
coercivity (7-10 times) of the sample, without compromising its fundamental
magnetic properties (210K). The phase-engineered sample
(F3GT-2) comprises of parent F3GT phase with a small percentage of randomly
embedded clusters of a coplanar FeTe (FT) phase. The FT phase serves as both
mosaic pinning centers between grains of F3GT above its antiferromagnetic
transition temperature (70~K) and also as anti-phase domains
below . As a result, the grain boundary disorder and metastable
nature are greatly augmented, leading to highly enhanced coercivity, cluster
spin glass, and meta-magnetic behavior. The enhanced coercivity (1~kOe)
makes F3GT-2 much more useful for memory storage applications and is likely to
elucidate a new route to tune useful magnetic properties. Moreover, this method
is much more convenient than hetero-structure and other cumbersome techniques.Comment: 12 pages, 11 figure
Raman signatures of lattice dynamics across inversion symmetry breaking phase transition in quasi-1D compound, (TaSe)I
Structural phase transition can occur due to complex mechanisms other than
simple dynamical instability, especially when the parent and daughter structure
is of low dimension. This article reports such an inversion symmetry-breaking
structural phase transition in a quasi-1D compound (TaSe)I at T
141~K studied by Raman spectroscopy. Our investigation of collective lattice
dynamics reveals three additional Raman active modes in the low-temperature
non-centrosymmetric structure. Two vibrational modes become Raman active due to
the absence of an inversion center, while the third mode is a soft phonon mode
resulting from the vibration of Ta atoms along the \{-Ta-Ta-\} chains.
Furthermore, the most intense Raman mode display Fano-shaped asymmetry,
inferred as the signature of strong electron-phonon coupling. The group theory
and symmetry analysis of Raman spectra confirm the displacive-first-order
nature of the structural transition. Therefore, our results establish
(TaSeI as a model system with broken inversion symmetry and strong
electron-phonon coupling in the quasi-1D regime.Comment: Main text - 6 figures, 11 pages, supplementary - 10 figures, 13 page
Physiochemical response of papaya genotypes exposed to low temperature regimes
Susceptibility to low temperature stress is the major threat to papaya cultivation. Here, we studied a low temperature stress tolerance in papaya plant. We have investigated the effect of different low temperature regimes, 28°/18°C (day/night) to 16°/06°C (day/night) with a gradual decrease of 2°C on every two days and one set with direct exposure to the low temperature of 18°/08°C (day/night), called the acclimatized plant, in five diverse papaya genotypes (Pusa Nanha, Red Lady P-7-2, P-7-9, and P-7-14) and cold tolerant wild relative of cultivated papaya genotype (Vasconcellea cundinamarcensis V.M. Badillo) under controlled regulated conditions. It was observed that there were significant variations in the physiological and biochemical parameters like photosynthetic gas exchange parameters, chlorophyll content, fluorescence parameters, relative water content (RWC), membrane stability index (MSI), total sugars content, total soluble proteins content, lipid peroxidation, and proline accumulation in leaf tissues. Maximum stomatal conductance, chlorophyll fluorescence, RWC, MSI, total sugars, total soluble proteins, proline and lowest MDA contents were observed in Vasconcellea cundinamarcensis followed by inbred P-7-9 as compared to other genotypes under low temperature stress. Among all the papaya genotypes, P-7-9 showed more adaptability to low temperature stress and it further give new insights for developing low temperature tolerant papaya genotypes, especially under changing climate situations
Planar dynamics and control of tethered satellite systems
A mathematical model is developed for studying the inplane dynamics and
control of tethered two-body systems in a Keplerian orbit. The formulation accounts
for:
• elastic deformation of the tether in both the longitudinal and inplane trans-
verse directions;
• inplane libration of the flexible tether as well as the rigid platform;
• time dependent variation of the tether attachment point at the platform end;
• deployment and retrieval of the point mass subsatellite;
• generalized force contributions due to various control actuators (e.g. momentum gyros, thrusters and passive dampers);
• structural damping of the tether;
• shift in the center of mass of the system due to the tether deployment and
retrieval.
The governing nonlinear, nonautonomous and coupled equations of motion are obtained using the Lagrange procedure. They are integrated numerically to assess the
system response as affected by the design parameters and operational disturbances.
Attitude dynamics of the system is regulated by two different types of actuators, thruster and tether attachment point offset, which have advantages at longer
and shorter tether lengths, respectively. The attitude controller is designed using
the Feedback Linearization Technique (FLT). It has advantages over other control
methods, such as gain scheduling and adaptive control, for the class of time varying
systems under consideration. It is shown that an FLT controller based on the rigid
system model, can successfully regulate attitude dynamics of the original flexible
system. A hybrid scheme, using the thruster control at longer tether lengths and
the offset control for a shorter tether, is quite attractive, particularly during retrieval, as its practical implementation for attitude control is significantly improved.
Introduction of passive dampers makes the hybrid scheme effective even for vibration
control during the retrieval.
For the stationkeeping phase, the offset control strategy is also used to regulate both the longitudinal as well as inplane transverse vibrations of the tether. The
LQG/LTR based vibration controller using the offset strategy is implemented in
conjunction with the FLT type attitude regulator utilizing thrusters as before. This
hybrid controller for simultaneous regulation of attitude and vibration dynamics is
found to be quite promising. The performance of the vibration controller is further
improved by introduction of passive dampers. The LQG based vibration controller
is found to be robust against the unmodelled dynamics of the flexible system.
Finally, effectiveness of the FLT and LQG based offset controllers is assessed
through a simple ground based experiment. The controllers successfully regulated
attitude dynamics of the tethered system during stationkeeping, deployment and
retrieval phases.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat
Not Available
Not AvailableDuring green revolution intensive use of chemical in agriculture might have helped to achieve a dramatic increase in crop yield ensuring food security in India, but meanwhile, the intensive application of chemical fertilizers and pesticides led to gradual decline in soil health and environment, and food safety became a major concern. This has raised question regarding the sustainability of agriculture/horticulture in the long term, urging attention
towards sustainable production practices. Accepting the harmful effect of the excessive use of chemical fertilizers on soil health and pesticides on human health, there is a need for an integrated management system. Organic farming can provide quality food without adversely affecting the soil‘s health and the environment, thus may be one of the options for sustainability. Organic food is not only attractive but also associated to quality, healthy and natural products in opposition to the more processed and conventional food. The paper has been reviewed for organic fruit production with sustainable approach in horticulture in India.Not Availabl
Antioxidant and antimicrobial activities and GC/MS-based phytochemical analysis of two traditional Lichen species Trypethellium virens and Phaeographis dendritica
Abstract Background Lichens are complex plants living in symbiotic relationship between fungi and algae. They are used for human and animal nutrition and are used in folk medicine in many countries over a considerable period of time. In the present study, various solvent extracts of Trypethelslium virens and Phaeographis dendritica were tested for their antioxidant and antimicrobial activity. Results The phytochemical analysis by GC/MS revealed phenolics (1.273%), terpene (0.963%), hydrocarbons (2.081%), benzofurans (2.081%), quinone (1.273%), alkanes (0.963%), and aliphatic aldehydes (0.963%) as the predominant compounds in Trypethellium virens SPTV02, whereas secondary alcohol (1.184%), alkaloids (1.184%), and fatty acids (4.466) were the major constituents in Phaeographis dendritica. The antioxidant property of methanolic extract of T. virens and P. dendritica revealed the presence of total phenolic and terpenoids. The methanolic extracts of both the lichens exhibited encouraging DPPH antiradical activity, with the IC50 of 62.4 ± 0.76 µg/ml for T. virens and 68.48 ± 0.45 µg/ml for P. dendritica. Similarly, ferric reducing power assay result exhibited higher reducing activity. Further, the lichen extracts (methanolic) indicated promising antimicrobial activities against pathogens showing MIC from 62.5 to 500 µg/ml. Conclusion The study results concludes that both the lichens could be used as new natural source of antioxidants and antimicrobial agents which can be exploited for pharmaceutical applications