44 research outputs found
Valence-Bond Crystal, and Lattice Distortions in a Pyrochlore Antiferromagnet with Orbital Degeneracy
We discuss the ground state properties of a spin 1/2 magnetic ion with
threefold orbital degeneracy on a highly frustrated pyrochlore
lattice, like Ti ion in B-spinel MgTiO. We formulate an
effective spin-orbital Hamiltonian and study its low energy sector by
constructing several exact-eigenstates in the limit of vanishing Hund's
coupling. We find that orbital degrees of freedom modulate the spin-exchange
energies, release the infinite spin-degeneracy of pyrochlore structure, and
drive the system to a non-magnetic spin-singlet manifold. The latter is a
collection of spin-singlet dimers and is, however, highly degenerate with
respect of dimer orientations. This ``orientational'' degeneracy is then lifted
by a magneto-elastic interaction that optimizes the previous energy gain by
distorting the bonds in suitable directions and leading to a tetragonal phase.
In this way a valence bond crystal state is formed, through the condensation of
dimers along helical chains running around the tetragonal c-axis, as actually
observed in MgTiO. The orbitally ordered pattern in the dimerized phase
is predicted to be of ferro-type along the helices and of antiferro-type
between them. Finally, through analytical considerations as well as numerical
ab-initio simulations, we predict a possible experimental tool for the
observation of such an orbital ordering, through resonant x-ray scattering.Comment: 15 pages, 8 figure
Multi-almost periodicity and invariant basins of general neural networks under almost periodic stimuli
In this paper, we investigate convergence dynamics of almost periodic
encoded patterns of general neural networks (GNNs) subjected to external almost
periodic stimuli, including almost periodic delays. Invariant regions are
established for the existence of almost periodic encoded patterns under
two classes of activation functions. By employing the property of
-cone and inequality technique, attracting basins are estimated
and some criteria are derived for the networks to converge exponentially toward
almost periodic encoded patterns. The obtained results are new, they
extend and generalize the corresponding results existing in previous
literature.Comment: 28 pages, 4 figure
The and - transition magnetic moments in QCD sum rules
The method of QCD sum rules in the presence of external elctromagnetic fields
is used to calculate the magnetic moment and
- transition magnetic moment , with
the susceptibilities obtained previously from the study of octet baryon
magnetic moments. The results and
are in good agreement with the recent
experimental data
Brain energy rescue:an emerging therapeutic concept for neurodegenerative disorders of ageing
The brain requires a continuous supply of energy in the form of ATP, most of which is produced from glucose by oxidative phosphorylation in mitochondria, complemented by aerobic glycolysis in the cytoplasm. When glucose levels are limited, ketone bodies generated in the liver and lactate derived from exercising skeletal muscle can also become important energy substrates for the brain. In neurodegenerative disorders of ageing, brain glucose metabolism deteriorates in a progressive, region-specific and disease-specific manner — a problem that is best characterized in Alzheimer disease, where it begins presymptomatically. This Review discusses the status and prospects of therapeutic strategies for countering neurodegenerative disorders of ageing by improving, preserving or rescuing brain energetics. The approaches described include restoring oxidative phosphorylation and glycolysis, increasing insulin sensitivity, correcting mitochondrial dysfunction, ketone-based interventions, acting via hormones that modulate cerebral energetics, RNA therapeutics and complementary multimodal lifestyle changes
Small Demonstration Satellite-4 (SDS-4): Development, Flight Results, and Lessons Learned in JAXA’s Microsatellite Project
The Small Demonstration Satellite 4 (SDS-4) is the first zero momentum three-axis controlled 50kg class satellite from JAXA. It was launched on May 17, 2012 on H-IIA Launch Vehicle, and is now operating successfully. SDS-4 has four main demonstration missions: (1) Space-based automatic identification system experiment for tracking ships, (2) Flat-plate heat pipe on-orbit experiment, (3) Quartz crystal Microbalance for contamination environment monitoring, and (4) In-flight experiment of space materials using THERME, which is developed in the JAXA-CNES joint research program. The satellite has two deployable solar panels to the left and to the right, and two deployable AIS antennas in the front and in the back. In addition to the technology demonstration missions, SDS-4 has another important goal, namely to establish a 50 kg-class highly functional and precise three-axis controlled standard bus for future advanced missions. After a year of on-orbit experiments and evaluations, all missions are now deemed successful and excellent flight data has been obtained. We encountered several serious problems during operations. We investigated the reasons for those misbehaviors in a multi-step process using a methodical FTA approach, and managed finally to resolve all of the problems. This paper concludes with the lessons learned all of which contributed to the overall success of the SDS-4 project