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Mitigating ground effect on mini quadcopters with model reference adaptive control
Mitigating ground effect becomes a big challenge for autonomous aerial vehicles when they are flying in close proximity to the ground. This paper aims to develop a precise model of ground effect on mini quadcopters, provide an advanced control algorithm to counter the model uncertainty and, as a result, improves the command tracking performance when the vehicle is in the ground effect region. The mathematical model of ground effect has been established through a series of experiments and validated by a flight test. The experiments show that the total thrust generated by rotors increases linearly as the vehicle gets closer to the ground, which is different from the commonly-used ground effect model for a single rotor vehicle. In addition, the model switches from a piecewise linear to a quadratic function when the rotor to rotor distance is increased. A control architecture that utilizes the model reference adaptive controller (MRAC) has also been designed, where MRAC is added to the altitude loop. The performance of the proposed control algorithm has been evaluated through a set of flight tests on a mini quadcopter platform and compared with a traditional proportional–integral–derivative (PID) controller. The results demonstrate that MRAC dramatically improves the tracking performance of altitude command and can reduce the rise time by 80 % under the ground effect
Theoretical understanding of the quasiparticle dispersion in bilayer high- superconductors
The renormalization of quasiparticle (QP) dispersion in bilayer high-
cuprates is investigated theoretically by examining respectively the
interactions of the QP with spin fluctuations (SF) and phonons. It is
illustrated that both interactions are able to give rise to a kink in the
dispersion around the antinodes (near ). However, remarkable
differences between the two cases are found for the peak/dip/hump structure in
the lineshape, the QP weight, and the interlayer coupling effect on the kink,
which are suggested to serve as a discriminance to single out the dominant
interaction in the superconducting state. A comparison to recent photoemission
experiments shows clearly that the coupling to the spin resonance is dominant
for the QP around antinodes in bilayer systems.Comment: 4 pages, 4 figure
Superconducting energy gap in MgCNi3 single crystals: Point-contact spectroscopy and specific-heat measurements
Specific heat has been measured down to 600 mK and up to 8 Tesla by the
highly sensitive AC microcalorimetry on the MgCNi3 single crystals with Tc ~ 7
K. Exponential decay of the electronic specific heat at low temperatures proved
that a superconducting energy gap is fully open on the whole Fermi surface, in
agreement with our previous magnetic penetration depth measurements on the same
crystals. The specific-heat data analysis shows consistently the strong
coupling strength 2D/kTc ~ 4. This scenario is supported by the direct gap
measurements via the point-contact spectroscopy. Moreover, the spectroscopy
measurements show a decrease in the critical temperature at the sample surface
accounting for the observed differences of the superfluid density deduced from
the measurements by different techniques
Integrable model of interacting XX and Fateev-Zamolodchikov chains
We consider the exact solution of a model of correlated particles, which is
presented as a system of interacting XX and Fateev-Zamolodchikov chains. This
model can also be considered as a generalization of the multiband anisotropic
model in the case we restrict the site occupations to at most two
electrons. The exact solution is obtained for the eigenvalues and eigenvectors
using the Bethe-ansatz method.Comment: 10 pages, no figure
ARPES studies of cuprate Fermiology: superconductivity, pseudogap, and quasiparticle dynamics
We present angle-resolved photoemission spectroscopy (ARPES) studies of the
cuprate high-temperature superconductors which elucidate the relation between
superconductivity and the pseudogap and highlight low-energy quasiparticle
dynamics in the superconducting state. Our experiments suggest that the
pseudogap and superconducting gap represent distinct states, which coexist
below T. Studies on Bi-2212 demonstrate that the near-nodal and
near-antinodal regions behave differently as a function of temperature and
doping, implying that different orders dominate in different momentum-space
regions. However, the ubiquity of sharp quasiparticles all around the Fermi
surface in Bi-2212 indicates that superconductivity extends into the
momentum-space region dominated by the pseudogap, revealing subtlety in this
dichotomy. In Bi-2201, the temperature dependence of antinodal spectra reveals
particle-hole asymmetry and anomalous spectral broadening, which may constrain
the explanation for the pseudogap. Recognizing that electron-boson coupling is
an important aspect of cuprate physics, we close with a discussion of the
multiple 'kinks' in the nodal dispersion. Understanding these may be important
to establishing which excitations are important to superconductivity.Comment: To appear in a focus issue on 'Fermiology of Cuprates' in New Journal
of Physic
Thermal Decomposition of the Murchison CM2 Carbonaceous Chondrite: Implications of Space Weathering Processes for Sample Return Missions
Primitive carbonaceous asteroids are the target bodies for the JAXA Hayabusa2 mission to Ryugu and the NASA OSIRIS-REx mission to Bennu. Both asteroids share spectral characteristics of CI/CM type carbonaceous chondrites. Ryugu, in particular, appears to have undergone thermal processing that has modified its spectral properties. The nature and extent of space weathering processes on the surfaces of Bennu and Ryugu are under active investigation using remote sensing data from the missions [4] and through laboratory studies on analog materials. The analog studies are needed in order to understand the mineralogical and chemical changes that occur in space weathered samples that give rise to the observed optical effects measured by remote-sensing and to prepare for the analysis of returned samples. The space weathering effects of micrometeorite impact and solar wind irradiation on primitive carbonaceous chondrites have been simulated by analog studies on the Murchison CM2 chondrite. We performed a coordinated mineralogical, chemical and spectroscopic study to examine in detail the effects of thermal metamorphism on Murchison samples as an analog to processes that may have occurred on Ryugu. The bulk measurements including X-ray diffraction (XRD), Mssbauer spectroscopy, UV-VIS-NIR spectroscopy, thermogravimetric analysis, and evolved gas analysis are reported in a companion paper. Here we report on our preliminary nanoscale mineralogical and chemical analyses of pre- and post-heated Murchison samples using multiple electron beam techniques to understand how the mineralogical, chemical, and physical characteristics of carbonaceous chondrites change with increasing thermal effects
Thermal design and analysis of a hydrogen-burning wind tunnel model of an airframe-integrated scramjet
An aerodynamic model of a hydrogen burning, airframe integrated scramjet engine has been designed, fabricated, and instrumented. This model is to be tested in an electric arc heated wind tunnel at an altitude of 35.39 km (116,094 ft.) but with an inlet Mach number of 6 simulating precompression on an aircraft undersurface. The scramjet model is constructed from oxygen free, high conductivity copper and is a heat sink design except for water cooling in some critical locations. The model is instrumented for pressure, surface temperature, heat transfer rate, and thrust measurements. Calculated flow properties, heat transfer rates, and surface temperature distributions along the various engine components are included for the conditions stated above. For some components, estimates of thermal strain are presented which indicate significant reductions in plastic strain by selective cooling of the model. These results show that the 100 thermal cycle life of the engine was met with minimum distortion while staying within the 2669 N (600 lbf) engine weight limitation and while cooling the engine only in critical locations
Influence of Al doping on the critical fields and gap values in magnesium diboride single crystals
The lower () and upper () critical fields of
MgAlB single crystals (for , 0.1 and )
have been deduced from specific heat and local magnetization measurements,
respectively. We show that and are both decreasing with
increasing doping content. The corresponding anisotropy parameter
value also decreases from
in pure MgB samples down to for whereas
remains on the order of 1 in
all samples. The small and large gap values have been obtained by fitting the
temperature dependence of the zero field electronic contribution to the
specific heat to the two gap model for the three Al concentrations. Very
similar values have also been obtained by point contact spectroscopy
measurements. The evolution of those gaps with Al concentration suggests that
both band filling and interband scattering effects are present
The Dimensional Recurrence and Analyticity Method for Multicomponent Master Integrals: Using Unitarity Cuts to Construct Homogeneous Solutions
We consider the application of the DRA method to the case of several master
integrals in a given sector. We establish a connection between the homogeneous
part of dimensional recurrence and maximal unitarity cuts of the corresponding
integrals: a maximally cut master integral appears to be a solution of the
homogeneous part of the dimensional recurrence relation. This observation
allows us to make a necessary step of the DRA method, the construction of the
general solution of the homogeneous equation, which, in this case, is a coupled
system of difference equations.Comment: 17 pages, 2 figure
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