1,223 research outputs found
Magnetoresistance behavior of a ferromagnetic shape memory alloy: Ni_1.75Mn_1.25Ga
A negative-positive-negative switching behavior of magnetoresistance (MR)
with temperature is observed in a ferromagnetic shape memory alloy
Ni_1.75Mn_1.25Ga. In the austenitic phase between 300 and 120 K, MR is negative
due to s-d scattering. Curiously, below 120K MR is positive, while at still
lower temperatures in the martensitic phase, MR is negative again. The positive
MR cannot be explained by Lorentz contribution and is related to a magnetic
transition. Evidence for this is obtained from ab initio density functional
theory, a decrease in magnetization and resistivity upturn at 120 K. Theory
shows that a ferrimagnetic state with anti-ferromagnetic alignment between the
local magnetic moments of the Mn atoms is the energetically favoured ground
state. In the martensitic phase, there are two competing factors that govern
the MR behavior: a dominant negative trend up to the saturation field due to
the decrease of electron scattering at twin and domain boundaries; and a weaker
positive trend due to the ferrimagnetic nature of the magnetic state. MR
exhibits a hysteresis between heating and cooling that is related to the first
order nature of the martensitic phase transition.Comment: 17 pages, 5 figures. Accepted in Phys. Rev.
Constructing a database of alien plants in the Himalaya to test patterns structuring diversity
Differences in the number of alien plant species in different locations may reflect climatic and other controls that similarly affect native species and/or propagule pressure accompanied with delayed spread from the point of introduction. We set out to examine these alternatives for Himalayan plants, in a phylogenetic framework. We build a database of alien plant distributions for the Himalaya. Focusing on the well-documented regions of Jammu & Kashmir (west) and Bhutan (east) we compare alien and native species for (1) richness patterns, (2) degree of phylogenetic clustering, (3) the extent to which species-poor regions are subsets of species-rich regions and (4) continental and climatic affinities/source. We document 1470 alien species (at least 600 naturalised), which comprise ~14% of the vascular plants known from the Himalaya. Alien plant species with tropical affinities decline in richness with elevation and species at high elevations form a subset of those at lower elevations, supporting location of introduction as an important driver of alien plant richness patterns. Separately, elevations which are especially rich in native plant species are also rich in alien plant species, suggesting an important role for climate (high productivity) in determining both native and alien richness. We find no support for the proposition that variance in human disturbance or numbers of native species correlate with alien distributions. Results imply an ongoing expansion of alien species from low elevation sources, some of which are highly invasive
Realistic Design Studies on a 300-GHz, 1-MW, DEMO-Class Conventional-Cavity Gyrotron
This article presents the realistic initial design studies of a 300-GHz, 1-MW, conventional-cavity gyrotron for its probable application in the next-generation thermonuclear fusion reactors. Keeping the design goals, parameters, and constraints in view, the very high-order TE 49,18 mode is chosen as the operating mode after a careful mode-selection calculation considering realistic ohmic cavity losses. After mode selection and mode competition studies, the cold-cavity design and initial design of a triode-type magnetron injection gun (T-MIG) and a gyrotron magnet are carried out and an electron beam radius of 8.11 mm is obtained with 2.4% velocity spread. Furthermore, investigation on RF behavior of the cavity is performed with the T-MIG beam parameters. By varying the nominal beam parameters, single-mode self-consistent calculations are conducted and achieved the desired output power. Then, multimode time-dependent self-consistent calculations are carried out before and after space-charge neutralization (SCN) with realistic velocity spread (up to 6%) and different beam radii for the assessment of the start-up scenario. Before SCN without velocity spread, the beam voltage is depressed to 70.08 kV and 0.72-MW output power is obtained, whereas with velocity spread (6%), 0.69-MW output power is obtained with 8.11 mm of beam radius. After 60% of SCN in the start-up scenario with velocity spread (6%), the beam voltage increases to 74.83 kV, and thereby, an output power of 0.91 MW is obtained
Quaternion Octonion Reformulation of Quantum Chromodynamics
We have made an attempt to develop the quaternionic formulation of Yang -
Mill's field equations and octonion reformulation of quantum chromo dynamics
(QCD). Starting with the Lagrangian density, we have discussed the field
equations of SU(2) and SU(3) gauge fields for both cases of global and local
gauge symmetries. It has been shown that the three quaternion units explain the
structure of Yang- Mill's field while the seven octonion units provide the
consistent structure of SU(3)_{C} gauge symmetry of quantum chromo dynamics
Synthesis of stacked compounds based on pyrazolo[3,4-d]pyrimidines as new flexible models for studying intramolecular aromatic π-π interactions (APPI)
754-75
Synthesis and high resolution proton NMR studies on isomeric N-1-IN-2-,5,7-trisubstituted-4,6-dioxo-4,5,6,7-tetrahydropyrazolo[3,4-d]pyrimidinest
1228-123
Electromagnetically induced transparency in cold 85Rb atoms trapped in the ground hyperfine F = 2 state
We report electromagnetically induced transparency (EIT) in cold 85Rb atoms,
trapped in the lower hyperfine level F = 2, of the ground state 5
(Tiwari V B \textit{et al} 2008 {\it Phys. Rev.} A {\bf 78} 063421). Two steady
state -type systems of hyperfine energy levels are investigated using
probe transitions into the levels F = 2 and F = 3 of the
excited state 5 in the presence of coupling transitions F = 3
F = 2 and F = 3 F = 3, respectively. The
effects of uncoupled magnetic sublevel transitions and coupling field's Rabi
frequency on the EIT signal from these systems are studied using a simple
theoretical model.Comment: 12 pages, 7 figure
Adapting the HHL algorithm to (non-unitary) quantum many-body theory
Rapid progress in developing near- and long-term quantum algorithms for
quantum chemistry has provided us with an impetus to move beyond traditional
approaches and explore new ways to apply quantum computing to electronic
structure calculations. In this work, we identify the connection between
quantum many-body theory and a quantum linear solver, and implement the
Harrow-Hassidim-Lloyd (HHL) algorithm to make precise predictions of
correlation energies for light molecular systems via the (non-unitary)
linearised coupled cluster theory. We alter the HHL algorithm to integrate two
novel aspects- (a) we prescribe a novel scaling approach that allows one to
scale any arbitrary symmetric positive definite matrix A, to solve for Ax = b
and achieve x with reasonable precision, all the while without having to
compute the eigenvalues of A, and (b) we devise techniques that reduce the
depth of the overall circuit. In this context, we introduce the following
variants of HHL for different eras of quantum computing- AdaptHHLite in its
appropriate forms for noisy intermediate scale quantum (NISQ), late-NISQ, and
the early fault-tolerant eras, as well as AdaptHHL for the fault-tolerant
quantum computing era. We demonstrate the ability of the NISQ variant of
AdaptHHLite to capture correlation energy precisely, while simultaneously being
resource-lean, using simulation as well as the 11-qubit IonQ quantum hardware
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