33 research outputs found
Online Whole-body Motion Planning for Quadrotor using Multi-resolution Search
In this paper, we address the problem of online quadrotor whole-body motion
planning (SE(3) planning) in unknown and unstructured environments. We propose
a novel multi-resolution search method, which discovers narrow areas requiring
full pose planning and normal areas requiring only position planning. As a
consequence, a quadrotor planning problem is decomposed into several SE(3) (if
necessary) and R^3 sub-problems. To fly through the discovered narrow areas, a
carefully designed corridor generation strategy for narrow areas is proposed,
which significantly increases the planning success rate. The overall problem
decomposition and hierarchical planning framework substantially accelerate the
planning process, making it possible to work online with fully onboard sensing
and computation in unknown environments. Extensive simulation benchmark
comparisons show that the proposed method is one to several orders of magnitude
faster than the state-of-the-art methods in computation time while maintaining
high planning success rate. The proposed method is finally integrated into a
LiDAR-based autonomous quadrotor, and various real-world experiments in unknown
and unstructured environments are conducted to demonstrate the outstanding
performance of the proposed method
Swashplateless-elevon Actuation for a Dual-rotor Tail-sitter VTOL UAV
In this paper, we propose a novel swashplateless-elevon actuation (SEA) for
dual-rotor tail-sitter vertical takeoff and landing (VTOL) unmanned aerial
vehicles (UAVs). In contrast to the conventional elevon actuation (CEA) which
controls both pitch and yaw using elevons, the SEA adopts swashplateless
mechanisms to generate an extra moment through motor speed modulation to
control pitch and uses elevons solely for controlling yaw, without requiring
additional actuators. This decoupled control strategy mitigates the saturation
of elevons' deflection needed for large pitch and yaw control actions, thus
improving the UAV's control performance on trajectory tracking and disturbance
rejection performance in the presence of large external disturbances.
Furthermore, the SEA overcomes the actuation degradation issues experienced by
the CEA when the UAV is in close proximity to the ground, leading to a smoother
and more stable take-off process. We validate and compare the performances of
the SEA and the CEA in various real-world flight conditions, including
take-off, trajectory tracking, and hover flight and position steps under
external disturbance. Experimental results demonstrate that the SEA has better
performances than the CEA. Moreover, we verify the SEA's feasibility in the
attitude transition process and fixed-wing-mode flight of the VTOL UAV. The
results indicate that the SEA can accurately control pitch in the presence of
high-speed incoming airflow and maintain a stable attitude during fixed-wing
mode flight. Video of all experiments can be found in
youtube.com/watch?v=Sx9Rk4Zf7sQComment: 8 pages, 13 figure
Ferromagnetic Moment and Spin Rotation Transitions in Tetragonal Antiferromagnetic Sr\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3eCl\u3csub\u3e2\u3c/sub\u3e
Sr2Cu3O4Cl2 is a variant of the lamellar copper oxides, containing an extra Cu2+ ion in the center of every second plaquette of the square CuO2 lattice. The two types of Cu form interpenetrating Heisenberg antiferromagnets, which order at 380 and 40 K. Magnetization measurements yield a small spontaneous ferromagnetic moment below 380 K and two spin rotation transitions. The results are explained in detail by a pseudodipolar coupling between the two Cu lattices. A quantitative analysis of the data yields several previously unknown microscopic coupling constants, relevant to other lamellar, chain, and ladder copper oxides
Field-Dependent Antiferromagnetism and Ferromagnetism of the Two Copper Sublattices in Sr\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3eCl\u3csub\u3e2\u3c/sub\u3e
The Cu3O4 layer in Sr2Cu3O4Cl2 is a variant of the square CuO2 lattice of the high-temperature superconductors, in which the center of every second plaquette contains an extra Cu2+ ion. The ions that make up the conventional CuO2 network, called CuI, have CuI-CuI exchange energy ≈130meV, and order antiferromagnetically at about 380 K; the CuII-CuII exchange is only ≈10meV, and the CuII’s order at ≈40K. A study is reported here of the dependence of the magnetization on field, temperature, and crystallographic orientation for this interesting system. We show that the small permanent ferromagnetic moment, that appears when the CuI spins order, and the unusual spin rotation transitions seen most clearly for one particular direction of the magnetic field, are the result of several small bond-dependent anisotropic terms in the spin Hamiltonian that are revealed because of the frustration of the isotropic Heisenberg interaction between CuI and CuII spins. These include a term which favors collinearity of the CuI and CuII spins, which originates from quantum fluctuations, and also the pseudodipolar interaction. Some of these small interactions also come into play in other lamellar cuprates, connected with the high-Tc superconductivity materials, and in many spin-chain and spin-ladder compounds
Enhanced hydrogen production by insertional inactivation of adhE gene in Klebsiella oxytoca HP1
Ethanol is the main byproduct of anaerobic H-2-producing fermentation in Klebsiella oxytoca HP1. Two moles of NAD(P)H are consumed to yield one mole of ethanol that may decrease bacterial hydrogen production. In this article the adhE gene that codes for acetaldehyde dehydrogenase was disrupted for the first time. A homologous recombination vector pTA-Str was constructed in which the adhE gene was disrupted by inserting an aminoglycoside-3'-adenyltransferase (aadA) gene. As expected, the vector includes the insertion 5'-adhE-aadA-adhE-3'. The amplified DNA fragment 5'-adhE-aadA-adhE-31 from pTA-Str was transformed into K. oxytoca, HP1 and one recombinant was obtained. PCR analysis of the resulting genomic DNA indicated the appropriate deletion and insertion. Compared with the H-2-production of wild type K. oxytoca HP1, the hydrogen yield of the mutant increased by 16.07% and ethanol concentration decreased by 77.47%, suggesting that inactivation of the adhE gene in K. oxytoca HP1 is a potential method for enhancing bacterial H-2-production
Observation of the spin-polarized surface state in a noncentrosymmetric superconductor BiPd
Recently, noncentrosymmetric superconductor BiPd has attracted considerable
research interest due to the possibility of hosting topological
superconductivity. Here we report a systematic high-resolution angle-resolved
photoemission spectroscopy (ARPES) and spin-resolved ARPES study of the normal
state electronic and spin properties of BiPd. Our experimental results show the
presence of a surface state at higher-binding energy with the location of Dirac
point at around 700 meV below the Fermi level. The detailed photon energy,
temperature-dependent and spin-resolved ARPES measurements complemented by our
first principles calculations demonstrate the existence of the spin polarized
surface states at high-binding energy. The absence of such spin-polarized
surface states near the Fermi level negates the possibility of a topological
superconducting behavior on the surface. Our direct experimental observation of
spin-polarized surface states in BiPd provides critical information that will
guide the future search for topological superconductivity in noncentrosymmetric
materials.Comment: 30 pages, 12 figures, Expanded version of arXiv:1505.03466, To appear
in Nature Communication
Mean velocity and suspended sediment concentration profile model of turbulent shear flow with probability density function
This work purposes a general mean velocity and a suspended sediment concentration (SSC) model to express distribution at every point of the cross section of turbulent shear flow by using a probability density function method. The probability density function method was used to describe the velocity and concentration profiles interacted on directly by fluid particles in the turbulent shear flow to solve turbulent flow and avoid different dynamical mechanics. The velocity profile model was obtained by solving for the profile integral with the product of the laminar velocity and probability density, through adopting an exponential probability density function to express probability distribution of velocity alteration of a fluid particle in turbulent shear flow. An SSC profile model was also created following a method similar to the above and based on the Schmidt diffusion equation. Different velocity and SSC profiles were created while changing the parameters of the models. The models were verified by comparing the calculated results with traditional models. It was shown that the probability density function model was superior to log-law in predicting stream-wise velocity profiles in coastal currents, and the probability density function SSC profile model was superior to the Rouse equation for predicting average SSC profiles in rivers and estuaries. Outlooks for precision investigation are stated at the end of this article
Antifungal Activities of Crude Extractum from Camellia semiserrata Chi (Nanshancha) Seed Cake Against Colletotrichum musae, Colletotrichum gloeosporioides and Penicillium italicum in vitro and in vivo Fruit Test
Antifungal activities of crude extractum of Nanshancha Seed Cake (NSC), to inactivate postharvest pathogens were investigated. Highest inhibitory rate was found against C. musae, C. gloeosporioides and C. papaya P.Henn, which was much stronger than that by tea saponin. Compared to tea saponin, effects of NSC extractum was relatively weak and similar on C. gloeosporioides Penzig and P. italicum. In an in vivo study, best controlling effects by NSC extractum was found with banana anthracnose disease development, which showed no inhibitory effects by tea saponin. NSC extractum controlled in vitro C. musae growth through directly inhibiting germination rate and germ tube elongation, and causing distortation, rupture and indentation of C. musae mycelium. In banana fruit subject to C. musae inoculation, higher PAL, POD, GLU and CHT activity was observed in banana fruit treated with crude NSC extractum than that of water control fruits. Current study proved the best controlling effects of crude NSC extractum in C. musae in vitro and in vivo development, which through direct inhibition of C. musae growth and increasing defense system of the banana fruit