366 research outputs found
Multi-Robot Trajectory Planning with Feasibility Guarantee and Deadlock Resolution: An Obstacle-Dense Environment
This article presents a multi-robot trajectory planning method which
guarantees optimization feasibility and resolves deadlocks in an obstacle-dense
environment. The method is proposed via formulating an optimization problem,
where the modified buffered Voronoi cell with warning band is utilized to avoid
the inter-robot collision and the deadlock is resolved by an adaptive
right-hand rule. Meanwhile, a novel safe corridor derived from historical
planned trajectory is proposed to provide a proper space for obstacle avoidance
in trajectory planning. Comparisons with state-of-the-art works are conducted
to illustrate the safety and deadlock resolution in cluttered scenarios.
Additionally, hardware experiments are carried out to verify the performance of
the proposed method where eight nano-quadrotors fly through a 0.6m cubic
framework
ROME: Robustifying Memory-Efficient NAS via Topology Disentanglement and Gradients Accumulation
Single-path based differentiable neural architecture search has great
strengths for its low computational cost and memory-friendly nature. However,
we surprisingly discover that it suffers from severe searching instability
which has been primarily ignored, posing a potential weakness for a wider
application. In this paper, we delve into its performance collapse issue and
propose a new algorithm called RObustifying Memory-Efficient NAS (ROME).
Specifically, 1) for consistent topology in the search and evaluation stage, we
involve separate parameters to disentangle the topology from the operations of
the architecture. In such a way, we can independently sample connections and
operations without interference; 2) to discount sampling unfairness and
variance, we enforce fair sampling for weight update and apply a gradient
accumulation mechanism for architecture parameters. Extensive experiments
demonstrate that our proposed method has strong performance and robustness,
where it mostly achieves state-of-the-art results on a large number of standard
benchmarks.Comment: Observe new collapse in memory efficient NAS and address it using
ROM
Zn3As2 Nanowires and nanoplatelets: highly efficient infrared emission and photodetection by an earth abundant material
The development of earth abundant materials for optoelectronics and photovoltaics promises improvements in sustainability and scalability. Recent studies have further demonstrated enhanced material efficiency through the superior light management of novel nanoscale geometries such as the nanowire. Here we show that an industry standard epitaxy technique can be used to fabricate high quality II-V nanowires (1D) and nanoplatelets (2D) of the earth abundant semiconductor Zn3As2. We go on to establish the optoelectronic potential of this material by demonstrating efficient photoemission and detection at 1.0 eV, an energy which is significant to the fields of both photovoltaics and optical telecommunications. Through dynamical spectroscopy this superior performance is found to arise from a low rate of surface recombination combined with a high rate of radiative recombination. These results introduce nanostructured Zn3As2 as a high quality optoelectronic material ready for device exploration.T.B., P.C., Y.G., H.H.T., and C.J. acknowledge the Australian
Research Council. T.B., P.C., Y.G., H.H.T., and C.J. thank the
Australian National Fabrication Facility for access to the growth
and microscopy facilities and Centre for Advanced Microscopy
and Australian Microscopy and Microanalysis Research Facility
for access to microscopy facilities used in this work. Y.W., B.B.,
H.E.J., and L.M.S. acknowledge the financial support of the
National Science Foundation through grants DMR-1105362,
1105121, and ECCS-1100489
Search for the solar neutrons using the Yangbajing neutron monitor and the neutron telescope during the 23rd solar cycle
The geographical location of Yangbajing (latitude 30, 4300m above sea level) has advantages for the direct
detection of the solar are neutron events. The Yangbajing neutron monitor and neutron telescope were established
in 1998 October at Yangbajing under the China-Japan cooperation and be used for the observation
of solar neutron events during the 23th solar cycle. On 28 November 1998 the Yangbajing neutron monitor
recorded a 3.8 sigma excess that has time coincidence with the reported neutron event of the Yangbajing neutron
telescope. The response of Yangbajing neutron monitor and neutron telescope on the solar particle event
associated with theX17.2 class are at October 28, 2003 was researched too
Doping-enhanced radiative efficiency enables lasing in unpassivated GaAs nanowires
Nanolasers hold promise for applications including integrated photonics, on-chip optical interconnects and optical sensing. Key to the realization of current cavity designs is the use of nanomaterials combining high gain with high radiative efficiency. Until now, efforts to enhance the performance of semiconductor nanomaterials have focused on reducing the rate of non-radiative recombination through improvements to material quality and complex passivation schemes. Here we employ controlled impurity doping to increase the rate of radiative recombination. This unique approach enables us to improve the radiative efficiency of unpassivated GaAs nanowires by a factor of several hundred times while also increasing differential gain and reducing the transparency carrier density. In this way, we demonstrate lasing from a nanomaterial that combines high radiative efficiency with a picosecond carrier lifetime ready for high speed applications
Charge Crowding in Graphene-Silicon Diodes
The performance of nanoscale electronic devices based on a two-three
dimensional (2D-3D) interface is significantly affected by the electrical
contacts that interconnect these materials with external circuitry. This work
investigates charge transport effects at the 2D-3D ohmic contact coupled with
the thermionic injection model for graphene/Si Schottky junction. Here, w e
focus on the intrinsic properties of graphene-metal contacts, paying particular
attention to the nature of the contact failure mechanism under high electrical
stress. According to our findings, severe current crowding (CC) effects in
highly conductive electrical contact significantly affect device failure that
can be reduced by spatially varying the contact properties and geometry. The
impact of electrical breakdown on material degradation is systematically
analyzed by atomic force, Raman, scanning electron, and energy dispersive X-ray
spectroscopies. Our devices withstand high electrostatic discharge spikes over
a longer period, manifesting high robustness and operational stability. This
research paves the way towards a highly robust and reliable graphene/Si
heterostructure in futuristic on-chip integration in dynamic switching. The
methods we employed here can be extended for other nanoscale electronic devices
based on 2D-3D interface
Left ventricular dysfunction measured by tissue Doppler imaging and strain rate imaging in hypertensive adolescents
Purpose : Left ventricular (LV) hypertrophy and impaired diastolic function may occur early in systemic hypertension. Diastolic dysfunction is associated with increased cardiovascular risk. Tissue Doppler imaging (TDI)-derived tissue velocity and strain rate are new parameters for assessing diastolic dysfunction. The aim of this study is to determine whether TDI and strain rate imaging (SRI) would improve the ability to recognize early impaired diastolic and systolic functions compared with conventional echocardiography in hypertensive adolescents. Methods : We included 38 hypertensive patients with systolic blood pressure above 140 mmHg or diastolic blood pressure above 90 mmHg. Ejection fraction and myocardial performance index (MPI) were estimated by conventional echocardiography. Peak systolic myocardial velocity, early diastolic myocardial velocity (Em), and peak late diastolic myocardial velocity (Am) were obtained by using TDI and SRI. Results : In the hypertensive group, interventricular septal thickness was significantly increased on M-mode echocardiography. Em/Am was significantly decreased at the mitral valve annulus. Among hypertensive subjects, the E strain rate at basal, mid, and apex was significantly decreased. Systolic strain was significantly decreased at the septum in the hypertensive group. Conclusion : Strain rate might be a useful new parameter for the quantification of both regional and global LV functions and could be used in long-term follow up in hypertensive patients. Early identification by SRI of subjects at risk for hypertensive and ventricular dysfunction may help to stratify risk and guide therapy. Further studies, including serial assessment of LV structure and function in a larger number of adolescents with hypertension, is necessary
The energy spectrum of all-particle cosmic rays around the knee region observed with the Tibet-III air-shower array
We have already reported the first result on the all-particle spectrum around
the knee region based on data from 2000 November to 2001 October observed by
the Tibet-III air-shower array. In this paper, we present an updated result
using data set collected in the period from 2000 November through 2004 October
in a wide range over 3 decades between eV and eV, in which
the position of the knee is clearly seen at around 4 PeV. The spectral index is
-2.68 0.02(stat.) below 1PeV, while it is -3.12 0.01(stat.) above 4
PeV in the case of QGSJET+HD model, and various systematic errors are under
study now.Comment: 12 pages, 7 figures, accepted by Advances in space researc
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