2,006 research outputs found
Structure controllability of complex network based on preferential matching
Minimum driver node sets (MDSs) play an important role in studying the
structural controllability of complex networks. Recent research has shown that
MDSs tend to avoid high-degree nodes. However, this observation is based on the
analysis of a small number of MDSs, because enumerating all of the MDSs of a
network is a #P problem. Therefore, past research has not been sufficient to
arrive at a convincing conclusion. In this paper, first, we propose a
preferential matching algorithm to find MDSs that have a specific degree
property. Then, we show that the MDSs obtained by preferential matching can be
composed of high- and medium-degree nodes. Moreover, the experimental results
also show that the average degree of the MDSs of some networks tends to be
greater than that of the overall network, even when the MDSs are obtained using
previous research method. Further analysis shows that whether the driver nodes
tend to be high-degree nodes or not is closely related to the edge direction of
the network
Ordering-Flexible Multi-Robot Coordination for MovingTarget Convoying Using Long-TermTask Execution
In this paper, we propose a cooperative long-term task execution (LTTE)
algorithm for protecting a moving target into the interior of an
ordering-flexible convex hull by a team of robots resiliently in the changing
environments. Particularly, by designing target-approaching and
sensing-neighbor collision-free subtasks, and incorporating these subtasks into
the constraints rather than the traditional cost function in an online
constraint-based optimization framework, the proposed LTTE can systematically
guarantee long-term target convoying under changing environments in the
n-dimensional Euclidean space. Then, the introduction of slack variables allow
for the constraint violation of different subtasks; i.e., the attraction from
target-approaching constraints and the repulsion from time-varying
collision-avoidance constraints, which results in the desired formation with
arbitrary spatial ordering sequences. Rigorous analysis is provided to
guarantee asymptotical convergence with challenging nonlinear couplings induced
by time-varying collision-free constraints. Finally, 2D experiments using three
autonomous mobile robots (AMRs) are conducted to validate the effectiveness of
the proposed algorithm, and 3D simulations tackling changing environmental
elements, such as different initial positions, some robots suddenly breakdown
and static obstacles are presented to demonstrate the multi-dimensional
adaptability, robustness and the ability of obstacle avoidance of the proposed
method
A comprehensive analysis of Fermi Gamma-Ray Burst Data: IV. Spectral lag and Its Relation to Ep Evolution
The spectral evolution and spectral lag behavior of 92 bright pulses from 84
gamma-ray bursts (GRBs) observed by the Fermi GBM telescope are studied. These
pulses can be classified into hard-to-soft pulses (H2S, 64/92),
H2S-dominated-tracking pulses (21/92), and other tracking pulses (7/92). We
focus on the relationship between spectral evolution and spectral lags of H2S
and H2S-dominated-tracking pulses. %in hard-to-soft pulses (H2S, 64/92) and
H2S-dominating-tracking (21/92) pulses. The main trend of spectral evolution
(lag behavior) is estimated with
(), where is the peak photon
energy in the radiation spectrum, is the observer time relative to the
beginning of pulse , and is the spectral lag of photons
with energy with respect to the energy band - keV. For H2S and
H2S-dominated-tracking pulses, a weak correlation between
and is found, where is the pulse width. We also study the spectral
lag behavior with peak time of pulses for 30 well-shaped pulses
and estimate the main trend of the spectral lag behavior with . It is found that is correlated with
. We perform simulations under a phenomenological model of spectral
evolution, and find that these correlations are reproduced. We then conclude
that spectral lags are closely related to spectral evolution within the pulse.
The most natural explanation of these observations is that the emission is from
the electrons in the same fluid unit at an emission site moving away from the
central engine, as expected in the models invoking magnetic dissipation in a
moderately-high- outflow.Comment: 58 pages, 11 figures, 3 tables. ApJ in pres
Inertia & viscosity dictate drop impact forces
A liquid drop impacting a rigid substrate undergoes deformation and spreading due to normal reaction forces, which are counteracted by surface tension. On a non-wetting substrate, the drop subsequently retracts and takes off. Our recent work (Zhang et al., \textit{Phys. Rev. Lett.}, vol. 129, 2022, 104501) revealed two peaks in the temporal evolution of the normal force --one at impact and another at jump-off. The second peak coincides with a Worthington jet formation, which vanishes at high viscosities due to increased viscous dissipation affecting flow focusing. In this article, using experiments, direct numerical simulations, and scaling arguments, we characterize both the peak amplitude at impact and the one at take off () and elucidate their dependency on the control parameters: the Weber number (dimensionless impact velocity) and the Ohnesorge number (dimensionless viscosity). For low-viscosity liquids like water, the amplitude and the time to reach it are governed by inertial timescales, insensitive to viscosity variations up to 100-fold. For large viscosities, beyond this viscosity-independent regime, we balance the rate of change in kinetic energy and the rate of viscous dissipation to obtain the scaling laws: and , where and are the inertial force and time scales, respectively, which are consistent with our data. The time at which the amplitude appears is set by the inertio-capillary timescale , independent of both the viscosity and the impact velocity of the drop. However, these properties dictate the magnitude of this amplitude
2-(4-Fluorophenyl)-4-(4-methoxyphenyl)-5-(piperidin-1-ylmethyl)thiazole
In the title compound, C22H23FN2OS, the piperidine ring shows chair confirmation and the two benzene rings make a dihedral angle of 17.0 (6)°. The thiazole fragment is essentially planar with an r.m.s. deviation of 0.004 (2) Å and a maximum deviation of 0.006 (2) Å.. In the crystal, intermolecular C—H⋯π interactions lead to the formation of a layer structure
Temperature-controlled electrospinning of EVOH nanofibre mats encapsulated with Ag, CuO, and ZnO particles for skin wound dressing
To treat skin burns, a new wound dressing, nanofibre mats with metal or metal oxide nanoparticles (Ag, CuO, and ZnO), was fabricated using the electrospinning technique. During a therapeutic process, the antibacterial ability and bio-compatibility of a new dressing material are of major concern. To expound the characteristics of ethylene vinyl alcohol (EVOH) nanofibre mats encapsulated with metal or metal oxide nanoparticles, denoted as Ag-EVOH, CuO-EVOH, and ZnO-EVOH, for use as new wound dressing materials, we investigated the suitable processing parameters to fabricate these materials, such as the voltage, tip-to-collector distance, concentration of the solution, and effect of environmental temperature. The antibacterial ability and bio-compatibility of Ag-EVOH, CuO-EVOH, and ZnO-EVOH were then tested and quantified. The outcomes show that the most suitable temperature for the fabrication of the materials is 40 °C (±3 °C). The antibacterial experiment results indicate that 0.08 g/ml of metal/metallic oxide shows the highest antibacterial ability toward Staphylococcus aureus. Furthermore, the largest diameters of the bacteriostatic loops of the three types of nanofibre mats, i.e. Ag-EVOH, CuO-EVOH, and ZnO-EVOH, are 5.89, 5.21, and 4.12 mm, respectively. Finally, the cell proliferations on the three nanofibre mats show a similar growth trend
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