913 research outputs found
Entanglement dynamics and quantum state transport in spin chains
We study the dynamics of a Heisenberg-XY spin chain with an unknown state
coded into one qubit or a pair of entangled qubits, with the rest of the spins
being in a polarized state. The time evolution involves magnon excitations, and
through them the entanglement is transported across the channel. For a large
number of qubits, explicit formulae for the concurrences, measures for
two-qubit entanglements, and the fidelity for recovering the state some
distance away are calculated as functions of time. Initial states with an
entangled pair of qubits show better fidelity, which takes its first maximum
value at earlier times, compared to initial states with no entangled pair. In
particular initial states with a pair of qubits in an unknown state (alpha
up-up + beta down-down) are best suited for quantum state transport.Comment: 4 pages, 3 figure
Size-dependent magnetization fluctuations in NiO nanoparticles
The finite size and surface roughness effects on the magnetization of NiO
nanoparticles is investigated. A large magnetic moment arises for an
antiferromagnetic nanoparticle due to these effects. The magnetic moment
without the surface roughness has a non-monotonic and oscillatory dependence on
, the size of the particles, with the amplitude of the fluctuations varying
linearly with . The geometry of the particle also matters a lot in the
calculation of the net magnetic moment. An oblate spheroid shape particle shows
an increase in net magnetic moment by increasing oblateness of the particle.
However, the magnetic moment values thus calculated are very small compared to
the experimental values for various sizes, indicating that the bulk
antiferromagnetic structure may not hold near the surface. We incorporate the
surface roughness in two different ways; an ordered surface with surface spins
inside a surface roughness shell aligned due to an internal field, and a
disordered surface with randomly oriented spins inside surface roughness shell.
Taking a variational approach we find that the core interaction strength is
modified for nontrivial values of which is a signature of
multi-sublattice ordering for nanoparticles. The surface roughness scale
is also showing size dependent fluctuations, with an envelope decay
. The net magnetic moment values calculated using
spheroidal shape and ordered surface are close to the experimental values for
different sizes.Comment: 19 pages, 8 figures, Accepted for publication in Int. J. Mod. Phys.
Formation of quasi-free and bubble positronium states in water and aqueous solutions
It is shown that in aqueous solutions a positronium atom is first formed in
the quasi-free state, and, after 50-100 ps, becomes localized in a nanobubble.
Analysis of the annihilation spectra of NaNO3 aqueous solutions shows that the
hydrated electron is not involved in the positronium (Ps) formation
Ultrastructure of the epithelial cells and oleo-gumresin secretion in Boswellia serrata (Burseraceae)
The ultrastructure of epithelial cells of oleo-gumresin ducts in Boswellia serrata, the source of Indian olibanum, is described. Oleo-gumresin ducts are present in primary and secondary phloem. The duct lumen forms an enlarged apoplastic space surrounded by epithelial cells. The epithelial cells are rich in dictyosomes, lipid bodies, mitochondria with dilated cristae, multivesicular bodies, osmiophilic materials, plastids and vesicIes. Plastids have poorly developed internal membranes. Dictyosomes and plastids are possible sites of resin synthesis. The gum component of the exudate is formed in dictyosomes and from the outer layers of the inner tangential wall (wall facing the duct lumen). This wall is replenished from inside by the activity of dictyosomes. The secretory materials are transported to the apoplast by granulocrine and eccrine secretion. They migrate through the loose microfibrils of the inner tangential wall into the duct lumen. Rarely, epithelial cells of young ducts have rudimentary plasmodesmata on the inner tangential wall which may be channels for passage of secretory materials into the duct lumen
Spin Decoherence from Hamiltonian dynamics in Quantum Dots
The dynamics of a spin-1/2 particle coupled to a nuclear spin bath through an
isotropic Heisenberg interaction is studied, as a model for the spin
decoherence in quantum dots. The time-dependent polarization of the central
spin is calculated as a function of the bath-spin distribution and the
polarizations of the initial bath state. For short times, the polarization of
the central spin shows a gaussian decay, and at later times it revives
displaying nonmonotonic time dependence. The decoherence time scale dep ends on
moments of the bath-spin distribuition, and also on the polarization strengths
in various bath-spin channels. The bath polarizations have a tendency to
increase the decoherence time scale. The effective dynamics of the central spin
polarization is shown to be describ ed by a master equation with non-markovian
features.Comment: 11 pages, 6 figures Accepted for publication in Phys.Rev
Albedo variations in relation with solar altitude and transmission factor over Arabian Sea at different weather conditions
1341-1349Albedo variations with respect to different weather conditions with the observed shortwave radiation data over Arabian Sea using Pyranometer, during June to August 2002, and March -June 2003. The hourly albedo variations are analysed and presented in relation with solar altitude (SinH) and transmission factor (TF). TF classified into three groups: under clear sky (TF > 0.65), partly cloudy (0.4 12 m/s), there is no significant changes observed in albedo. Variations in TF and albedo during the overcast conditions are significant, however wind also dominating
IEEE 802.15.4-PHY Packet Detection and Transmission System With Differential Encoding For Low Power IoT Networks
Synchronization is the first operation in a digital base band receiver. The accuracy of the synchronizer shapes up the performance of the base band receiver. Synchronization is broadly divided into Carrier Frequency and Phase Synchronization, Symbol Timing and Frame Synchronization. If number of false detections in frame synchronization are high then large amount of power is wasted for processing unwanted packets. In this paper, we are proposing a packet detection and transmission system with differential encoding for low power IoT networks which reduces the number of false packet detections compared to existing preamble detection techniques. The proposed frame synchronization method decides packet is valid or not by cross correlating received packet with fixed preamble sequence and determine its boundaries. The proposed system is analyzed with smart metering power data and corresponding probabilities of packet missing and false detection, power consumption and bit error rate are analyzed. At 3 dB SNR the number of false detections are reduced by 170 compared to conventional correlation method thereby saving 15.8 % of processing power at receiver
Relation between outgoing longwave radiation and findlater jet over Arabian Sea during summer monsoon and influence on Indian monsoon rainfall
428-435This work analyses the relationship between outgoing Longwave radiation (OLR) and Findlater jet (FLJ) intensities
at 850 hPa pressure level and also their relation with Indian summer monsoon rainfall (ISMR; June-September) for a period of 1997-2010 over Arabian Sea and India. FLJ is a low-level jet (LLJ) which can be observed during southwest monsoon months. This LLJ generally supports the large-scale moisture and momentum transport from ocean to atmosphere, which results in rainfall over India. FLJ and OLR are associated during the monsoon months. However FLJ (positively) and OLR (negatively) are related with ISMR. Monthly and seasonal correlation coefficients among FLJ, OLR and ISMR presented and the deviations during El Nino/La Nina are discussed. Based on this analysis we recommend that the variations in FLJ should include interannual variability in atmospheric dynamics
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