25,045 research outputs found
Eigenstructure Assignment Based Controllers Applied to Flexible Spacecraft
The objective of this paper is to evaluate the behaviour of a controller designed using a parametric Eigenstructure Assignment method and to evaluate its suitability for use in flexible spacecraft. The challenge of this objective lies in obtaining a suitable controller that is specifically designated to alleviate the deflections and vibrations suffered by external appendages in flexible spacecraft while performing attitude manoeuvres. One of the main problems in these vehicles is the mechanical cross-coupling that exists between the rigid and flexible parts of the spacecraft. Spacecraft with fine attitude pointing requirements need precise control of the mechanical coupling to avoid undesired attitude misalignment. In designing an attitude controller, it is necessary to consider the possible vibration of the solar panels and how it may influence the performance of the rest of the vehicle. The nonlinear mathematical model of a flexible spacecraft is considered a close approximation to the real system. During the process of controller evaluation, the design process has also been taken into account as a factor in assessing the robustness of the system
Exotic Superconducting Phases of Ultracold Atom Mixtures on Triangular Lattices
We study the phase diagram of two-dimensional Bose-Fermi mixtures of
ultracold atoms on a triangular optical lattice, in the limit when the velocity
of bosonic condensate fluctuations is much larger than the Fermi velocity.
We contrast this work with our previous results for a square lattice system
in Phys. Rev. Lett. {\bf 97}, 030601 (2006).
Using functional renormalization group techniques we show that the phase
diagrams for a triangular lattice contain exotic superconducting phases. For
spin-1/2 fermions on an isotropic lattice we find a competition of -, -,
extended -, and -wave symmetry, as well as antiferromagnetic order. For
an anisotropic lattice, we further find an extended p-wave phase. A Bose-Fermi
mixture with spinless fermions on an isotropic lattice shows a competition
between - and -wave symmetry.
These phases can be traced back to the geometric shapes of the Fermi surfaces
in various regimes, as well as the intrinsic frustration of a triangular
lattice.Comment: 6 pages, 4 figures, extended version, slight modification
Fluxon Dynamics of a Long Josephson Junction with Two-gap Superconductors
We investigate the phase dynamics of a long Josephson junction (LJJ) with
two-gap superconductors. In this junction, two channels for tunneling between
the adjacent superconductor (S) layers as well as one interband channel within
each S layer are available for a Cooper pair. Due to the interplay between the
conventional and interband Josephson effects, the LJJ can exhibit unusual phase
dynamics. Accounting for excitation of a stable 2-phase texture arising
from the interband Josephson effect, we find that the critical current between
the S layers may become both spatially and temporally modulated. The spatial
critical current modulation behaves as either a potential well or barrier,
depending on the symmetry of superconducting order parameter, and modifies the
Josephson vortex trajectories. We find that these changes in phase dynamics
result in emission of electromagnetic waves as the Josephson vortex passes
through the region of the 2-phase texture. We discuss the effects of this
radiation emission on the current-voltage characteristics of the junction.Comment: 14 pages, 6 figure
Unconventional Spin Density Waves in Dipolar Fermi Gases
The conventional spin density wave (SDW) phase (Overhauser, 1962), as found
in antiferromagnetic metal for example (Fawcett 1988), can be described as a
condensate of particle-hole pairs with zero angular momentum, ,
analogous to a condensate of particle-particle pairs in conventional
superconductors. While many unconventional superconductors with Cooper pairs of
finite have been discovered, their counterparts, density waves with
non-zero angular momenta, have only been hypothesized in two-dimensional
electron systems (Nayak, 2000). Using an unbiased functional renormalization
group analysis, we here show that spin-triplet particle-hole condensates with
emerge generically in dipolar Fermi gases of atoms (Lu, Burdick, and
Lev, 2012) or molecules (Ospelkaus et al., 2008; Wu et al.) on optical lattice.
The order parameter of these exotic SDWs is a vector quantity in spin space,
and, moreover, is defined on lattice bonds rather than on lattice sites. We
determine the rich quantum phase diagram of dipolar fermions at half-filling as
a function of the dipolar orientation, and discuss how these SDWs arise amidst
competition with superfluid and charge density wave phases.Comment: 5 pages, 3 figure
Spin Relaxation Times of Single-Wall Carbon Nanotubes
We have measured temperature ()- and power-dependent electron spin
resonance in bulk single-wall carbon nanotubes to determine both the
spin-lattice and spin-spin relaxation times, and . We observe that
increases linearly with from 4 to 100 K, whereas {\em
decreases} by over a factor of two when is increased from 3 to 300 K. We
interpret the trend as spin-lattice relaxation via
interaction with conduction electrons (Korringa law) and the decreasing
dependence of as motional narrowing. By analyzing the latter, we
find the spin hopping frequency to be 285 GHz. Last, we show that the Dysonian
lineshape asymmetry follows a three-dimensional variable-range hopping behavior
from 3 to 20 K; from this scaling relation, we extract a localization length of
the hopping spins to be 100 nm.Comment: 6 pages, 3 figure
Blending Hippo and WNT: Sharing Messengers and Regulation
Two new studies reveal ways in which the Wnt pathway commandeers Hippo components for signaling. Azzolin et al. show how the Hippo transcription factor TAZ mediates Wnt signals, and Rosenbluh et al. show how β-catenin and YAP1 form a kinase-regulated complex with transcription factor TBX5
Orbital symmetry fingerprints for magnetic adatoms in graphene
In this paper, we describe the formation of local resonances in graphene in
the presence of magnetic adatoms containing localized orbitals of arbitrary
symmetry, corresponding to any given angular momentum state. We show that
quantum interference effects which are naturally inbuilt in the honeycomb
lattice in combination with the specific orbital symmetry of the localized
state lead to the formation of fingerprints in differential conductance curves.
In the presence of Jahn-Teller distortion effects, which lift the orbital
degeneracy of the adatoms, the orbital symmetries can lead to distinctive
signatures in the local density of states. We show that those effects allow
scanning tunneling probes to characterize adatoms and defects in graphene.Comment: 15 pages, 11 figures. Added discussion about the multi-orbital case
and the validity of the single orbital picture. Published versio
Recovery-Oriented Training and Staff Attitudes Over Time in Two State Hospitals
Recovery attitudes and concepts are often promoted to community mental health staff through educational and in-service trainings, but no study found has examined this in state hospitals. The current observational study aimed to examine the types of recovery-oriented trainings that occurred at two state hospitals over 1 year and subsequent changes in staff recovery attitudes. A total of 184 state hospital staff completed questionnaires assessing their personal optimism, consumer optimism, and agency recovery orientation at baseline and 1 year later. The types of recovery-oriented trainings staff received were categorized as general/inspirational or specific/practical training. Results found that the majority of staff at the two state hospitals received some recovery-oriented training, mostly general/inspirational training. Staff who received specific/practical training had a greater increase in agency recovery attitudes than staff who received only general/inspirational training or no training. However, the more trainings staff had, the higher their consumer optimism. These results suggest state hospitals are incorporating recovery-oriented staff trainings, but more specific trainings may be needed and all staff involved in different levels of care need to be included
- …