233 research outputs found
Towards Efficient Full Pose Omnidirectionality with Overactuated MAVs
Omnidirectional MAVs are a growing field, with demonstrated advantages for
aerial interaction and uninhibited observation. While systems with complete
pose omnidirectionality and high hover efficiency have been developed
independently, a robust system that combines the two has not been demonstrated
to date. This paper presents VoliroX: a novel omnidirectional vehicle that can
exert a wrench in any orientation while maintaining efficient flight
configurations. The system design is presented, and a 6 DOF geometric control
that is robust to singularities. Flight experiments further demonstrate and
verify its capabilities.Comment: 10 pages, 6 figures, ISER 2018 conference submissio
4D STEM: high efficiency phase contrast imaging using a fast pixelated detector
Phase contrast imaging is widely used for imaging beam sensitive and weak phase objects in electron microscopy. In this work we demonstrate the achievement of high efficient phase contrast imaging in STEM using the pnCCD, a fast direct electron pixelated detector, which records the diffraction patterns at every probe position with a speed of 1000 to 4000 frames per second, forming a 4D STEM dataset simultaneously with the incoherent Z-contrast imaging. Ptychographic phase reconstruction has been applied and the obtained complex transmission function reveals the phase of the specimen. The results using GaN and Ti, Nd- doped BiFeO3 show that this imaging mode is especially powerful for imaging light elements in the presence of much heavier elements
Modeling and control of UAV bearing formations with bilateral high-level steering
In this paper we address the problem of controlling the motion of a group of unmanned aerial vehicles (UAVs) bound to keep a formation defined in terms of only relative angles (i.e. a bearing formation). This problem can naturally arise within the context of several multi-robot applications such as, e.g. exploration, coverage, and surveillance. First, we introduce and thoroughly analyze the concept and properties of bearing formations, and provide a class of minimally linear sets of bearings sufficient to uniquely define such formations. We then propose a bearing-only formation controller requiring only bearing measurements, converging almost globally, and maintaining bounded inter-agent distances despite the lack of direct metric information.The controller still leaves the possibility of imposing group motions tangent to the current bearing formation. These can be either autonomously chosen by the robots because of any additional task (e.g. exploration), or exploited by an assisting human co-operator. For this latter 'human-in-the-loop' case, we propose a multi-master/multi-slave bilateral shared control system providing the co-operator with some suitable force cues informative of the UAV performance. The proposed theoretical framework is extensively validated by means of simulations and experiments with quadrotor UAVs equipped with onboard cameras. Practical limitations, e.g. limited field-of-view, are also considered. © The Author(s) 2012
Mutual induction of magnetic 3d and 4f order in multiferroic hexagonal ErMnO3
The complex interplay between the 3d and 4f moments in hexagonal ErMnO3 is
investigated by magnetization, optical second harmonic generation, and
neutron-diffraction measurements. We revise the phase diagram and provide a
microscopic model for the emergent spin structures with a special focus on the
intermediary phase transitions. Our measurements reveal that the 3d exchange
between Mn^{3+} ions dominates the magnetic symmetry at 10 K < T < T_N with
Mn^3+ order according to the Gamma_4 representation triggering 4f ordering
according to the same representation on the Er^{3+}(4b) site. Below 10 K the
magnetic order is governed by 4f exchange interactions of Er^{3+} ions on the
2a site. The magnetic Er^{3+}(2a) order according to the representation Gamma_2
induces a magnetic reorientation (Gamma_4 --> Gamma_2) at the Er^{3+}(4b) and
the Mn^{3+} sites. Our findings highlight the fundamentally different roles the
Mn^{3+}, R^{3+}(2a), and R^{3+}(4b) magnetism play in establishing the magnetic
phase diagram of the hexagonal RMnO3 system
Validity of mortality risk prediction scores in critically ill patients with secondary pulmonary embolism
Herein, we assess the use of the Acute Physiology and Chronic Health Evaluation-IV (APACHE-IV) and pulmonary embolism (PE)–specific risk scores to predict mortality among intensive care unit (ICU) patients who developed secondary PE. This retrospective cohort study used information from 208 United States critical care units recorded in the eICU Collaborative Research Database during 2014 and 2015. We calculated APACHE-IV, Pulmonary Embolism Severity Index (PESI), simplified PESI (sPESI), and ICU-sPESI scores and compared their predicting performance using the area under the receiver operating characteristic (AUROC) curve. Of 812 patients included in our study, 150 died (mortality, 18.5% [95% CI, 15.8%-21.1%]). Compared to survivors, non-survivors had higher APACHE-IV (86 vs 52, P<0.001), PESI (170 vs 129, P<0.001), sPESI (2 vs 2, P<0.001), and ICU-sPESI (4 vs 2, P<0.001) scores. AUROCs were 0.790 (APACHE-IV); 0.737 (PESI); 0.726 (ICU-sPESI); and 0.620 (sPESI). APACHE-IV performed significantly better than all 3 PE-specific mortality scores (APACHE-IV vs PESI, P=0.041; APACHE-IV vs sPESI, P=0.001; and APACHE-IV vs ICU-sPESI, P=0.021). Both the PESI and ICU-sPESI outperformed the sPESI (PESI vs sPESI, P=0.001; ICU-sPESI vs sPESI, P<0.001). APACHE-IV score was found to be the best instrument for predicting mortality risk, but PESI and ICU-sPESI scores may be used when APACHE-IV is unavailable. sPESI AUROC suggests absence of sufficient discriminative value to be used as a predictor of mortality in patients with secondary PE.
Phonons in mesoporous silicon The influence of nanostructuring on the dispersion in the Debye regime
We present a comprehensive scattering study of nanostructured silicon. Neutron and x ray scattering experiments elucidate structural and dynamical properties of electrochemically etched, porous silicon membranes with pores roughly 8 nm across. In particular, inelastic cold neutron scattering techniques reveal the phonon dispersion of the nanostructured, single crystalline samples in the linear Debye regime for energy transfers up to 4 meV. A modified dispersion relation characterized by systematically reduced sound velocities manifests itself in altered elastic properties of porous silicon when compared to bulk silicon. Its relevance for nanostructured silicon as thermoelectric material of interest is discusse
Weighted ergodic theorems for Banach-Kantorovich lattice
In the present paper we prove weighted ergodic theorems and multiparameter
weighted ergodic theorems for positive contractions acting on
. Our main tool is the use of methods of
measurable bundles of Banach-Kantorovich lattices.Comment: 11 page
Thermodynamic Properties of the Anisotropic Frustrated Spin-chain Compound Linarite PbCuSO(OH)
We present a comprehensive macroscopic thermodynamic study of the
quasi-one-dimensional (1D) frustrated spin-chain system
linarite. Susceptibility, magnetization, specific heat, magnetocaloric effect,
magnetostriction, and thermal-expansion measurements were performed to
characterize the magnetic phase diagram. In particular, for magnetic fields
along the b axis five different magnetic regions have been detected, some of
them exhibiting short-range-order effects. The experimental magnetic entropy
and magnetization are compared to a theoretical modelling of these quantities
using DMRG and TMRG approaches. Within the framework of a purely 1D isotropic
model Hamiltonian, only a qualitative agreement between theory and the
experimental data can be achieved. Instead, it is demonstrated that a
significant symmetric anisotropic exchange of about 10% is necessary to account
for the basic experimental observations, including the 3D saturation field, and
which in turn might stabilize a triatic (three-magnon) multipolar phase.Comment: 20 pages, 17 figure
Search for Gravitational Waves from Low Mass Compact Binary Coalescence in LIGO's Sixth Science Run and Virgo's Science Runs 2 and 3
We report on a search for gravitational waves from coalescing compact
binaries using LIGO and Virgo observations between July 7, 2009 and October 20,
2010. We searched for signals from binaries with total mass between 2 and 25
solar masses; this includes binary neutron stars, binary black holes, and
binaries consisting of a black hole and neutron star. The detectors were
sensitive to systems up to 40 Mpc distant for binary neutron stars, and further
for higher mass systems. No gravitational-wave signals were detected. We report
upper limits on the rate of compact binary coalescence as a function of total
mass, including the results from previous LIGO and Virgo observations. The
cumulative 90%-confidence rate upper limits of the binary coalescence of binary
neutron star, neutron star- black hole and binary black hole systems are 1.3 x
10^{-4}, 3.1 x 10^{-5} and 6.4 x 10^{-6} Mpc^{-3}yr^{-1}, respectively. These
upper limits are up to a factor 1.4 lower than previously derived limits. We
also report on results from a blind injection challenge.Comment: 11 pages, 5 figures. For a repository of data used in the
publication, go to:
. Also see the
announcement for this paper on ligo.org at:
<http://www.ligo.org/science/Publication-S6CBCLowMass/index.php
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