12,737 research outputs found
Near-Optimal Distributed Approximation of Minimum-Weight Connected Dominating Set
This paper presents a near-optimal distributed approximation algorithm for
the minimum-weight connected dominating set (MCDS) problem. The presented
algorithm finds an approximation in rounds,
where is the network diameter and is the number of nodes.
MCDS is a classical NP-hard problem and the achieved approximation factor
is known to be optimal up to a constant factor, unless P=NP.
Furthermore, the round complexity is known to be
optimal modulo logarithmic factors (for any approximation), following [Das
Sarma et al.---STOC'11].Comment: An extended abstract version of this result appears in the
proceedings of 41st International Colloquium on Automata, Languages, and
Programming (ICALP 2014
Relative entropy of entanglement of a kind of two qubit entangled states
We in this paper strictly prove that some block diagonalizable two qubit
entangled state with six none zero elements reaches its quantum relative
entropy entanglement by the a separable state having the same matrix structure.
The entangled state comprises local filtering result state as a special case.Comment: 5 page
Magnetic properties of a novel Pr Fe Ti phase
In a systematic study of the (Pr1−xTix)Fe5 alloy series, the (Pr0.65Ti0.35)Fe5 alloy has been
found to have a dominant phase with either the rhombohedral Th2Zn17 structure or the
newly discovered Nd2(Fe,Ti)19 (S. J. Collocott, R. K. Day, J. B. Dunlop, and R. L. Davis,
in Proceedings of the Seventh International Symposium on Magnetic Anisotropy and
Coercivity in R‐T Alloys, Canberra, July 1992, p. 437) structure, depending on the
annealing procedure. Powder‐x‐ray‐diffraction patterns and scanning electron
microscopy show that the sample annealed at a temperature of 850 °C followed by
1000 °C has the 2:17 structure whereas annealing at 1000 °C directly leads to the new
2:19 structure. Energy‐dispersive x‐ray analysis yields Pr:Fe:Ti ratios of 10.7:86.2:3.1
for the Pr2(Fe,Ti)17 phase and 9.2:85.9:4.9 for the Pr2(Fe,Ti)19 phase.
57
Fe Mössbauer
spectroscopy (at 295 K) gives values for the average
57
Fe hyperfine field of 15.7 T for the
2:17 phase and 17.5 T for the 2:19 phase, respectively
Accurate range-free localization for anisotropic wireless sensor networks
Journal ArticlePosition information plays a pivotal role in wireless sensor network (WSN) applications and protocol/ algorithm design. In recent years, range-free localization algorithms have drawn much research attention due to their low cost and applicability to large-scale WSNs. However, the application of range-free localization algorithms is restricted because of their dramatic accuracy degradation in practical anisotropic WSNs, which is mainly caused by large error of distance estimation. Distance estimation in the existing range-free algorithms usually relies on a unified per hop length (PHL) metric between nodes. But the PHL between different nodes might be greatly different in anisotropic WSNs, resulting in large error in distance estimation. We find that, although the PHL between different nodes might be greatly different, it exhibits significant locality; that is, nearby nodes share a similar PHL to anchors that know their positions in advance. Based on the locality of the PHL, a novel distance estimation approach is proposed in this article. Theoretical analyses show that the error of distance estimation in the proposed approach is only one-fourth of that in the state-of-the-art pattern-driven scheme (PDS). An anchor selection algorithm is also devised to further improve localization accuracy by mitigating the negative effects from the anchors that are poorly distributed in geometry. By combining the locality-based distance estimation and the anchor selection, a range-free localization algorithm named Selective Multilateration (SM) is proposed. Simulation results demonstrate that SM achieves localization accuracy higher than 0.3r, where r is the communication radius of nodes. Compared to the state-of-the-art solution, SM improves the distance estimation accuracy by up to 57% and improves localization accuracy by up to 52% consequently.This work is partially supported by the National Science Foundation of China (61103203, 61173169,
61332004, and 61420106009), the Hong Kong RGC General Research Fund (PolyU 5106/11E), the International Science & Technology Cooperation Program of China (2013DFB10070), and the EU FP7 QUICK project (PIRSES-GA-2013-612652)
Spin and orbital angular momentum in gauge theories (II): QCD and nucleon spin structure
Parallel to the construction of gauge invariant spin and orbital angular
momentum for QED in paper (I) of this series, we present here an analogous but
non-trivial solution for QCD. Explicitly gauge invariant spin and orbital
angular momentum operators of quarks and gluons are obtained. This was
previously thought to be an impossible task, and opens a more promising avenue
towards the understanding of the nucleon spin structure.Comment: 3 pages, no figure; presented by F. Wang at NSTAR200
Integrating Human Behavioral Model for Intimate-distance Human Robot Collaboration
In this paper, we present a method for integrating a human behavior model into robot motion control to enable safer intimate distance Human Robot Collaboration (HRC). This approach establishes safety parameters based on personality and experience, and optimizes the system through observing human reactions. It integrates a behavior pattern-based emergency shutdown. In our experiment, we tried to validate our claim that incorporating a human behavior model into the robot control will increase the safety of the system in intimate distance conditions. Validation through a mixed-reality approach demonstrates the feasibility of the framework in a simulated environment, ensuring ethical considerations and safety. Notably, it outperforms traditional benchmarks, and other forecasting based approaches, achieving zero collisions in 100 trials and exhibiting a forecasting error rate below 10mm. Despite notable improvements, challenges persist, including residual time delays in safety compensations and potential slowdowns for introverted, inexperienced workers. While these limitations need further refinement, the proposed approach signifies a substantial stride towards safer HRC, successfully preventing collisions in intimate distance conditions
Field-free ultrafast magnetization reversal of a nanodevice by a chirped current pulse via spin-orbit torque
We investigated the magnetization reversal of a perpendicularly magnetized
nanodevice using a chirped current pulse (CCP) via spin-orbit torques (SOT).
Our findings demonstrate that both the field-like (FL) and damping-like (DL)
components of SOT in CCP can efficiently induce ultrafast magnetization
reversal without any symmetry-breaking means. For a wide frequency range of the
CCP, the minimal current density obtained is significantly smaller compared to
the current density of conventional SOT-reversal. This ultrafast reversal is
due to the CCP triggering enhanced energy absorption (emission) of the
magnetization from (to) the FL- and DL-components of SOT before (after)
crossing over the energy barrier. We also verified the robustness of the
CCP-driven magnetization reversal at room temperature. Moreover, this strategy
can be extended to switch the magnetic states of perpendicular synthetic
antiferromagnetic (SAF) and ferrimagnetic (SFi) nanodevices. Therefore, these
studies enrich the basic understanding of field-free SOT-reversal and provide a
novel way to realize ultrafast SOT-MRAM devices with various free layer
designs: ferromagnetic, SAF, and SFi.Comment: 9 pages, 7 figure
Magnetization and Magnetotransport of LnBaCo2O5.5 (Ln=Gd, Eu) Single Crystals
The magnetization, resistivity and magnetoresistance (MR) of single crystals
of GdBaCo2O5.5 and EuBaCo2O5.5 are measured over a wide range of dc magnetic
fields (up to 30 T) and temperature. In LnBaCo2O5.5 (Ln=Gd, Eu), the Co-ions
are trivalent and can exist in three spin states, namely, the S=0 low spin
state (LS), the S= 1 intermediate spin state (IS) and the S=2 high spin state
(HS). We confirm that GdBaCo2O5.5 and EuBaCo2O5.5 have a metal-insulator
transition accompanied by a spin-state transition at TMI >> 365 and 335 K,
respectively. The data suggest an equal ratio of LS (S=0) and IS (S=1) Co3+
ions below TMI, with no indication of additional spin state transitions. The
low field magnetization shows a transition to a highly anisotropic
ferromagnetic phase at 270 K, followed by another magnetic transition to an
antiferromagnetic phase at a slightly lower temperature. The magnetization data
are suggestive of weak correlations between the Gd-spins but no clear signature
of ordering is seen for T > 2 K. Significant anisotropy between the a-b plane
and c axis was observed in magnetic and magnetotransport properties for both
compounds. For GdBaCo2O5.5, the resistivity and MR data imply a strong
correlation between the spin-order and charge carriers. For EuBaCo2O5.5, the
magnetic phase diagram is very similar to its Gd counterpart, but the low-T MR
with current flow in the ab plane is positive rather than negative as for Gd.
The magnitude and the hysteresis of the MR for EuBaCo2O5.5 decrease with
increasing temperature, and at higher T the MR changes sign and becomes
negative. The difference in the behavior of both compounds may arise from a
small valence admixture in the nonmagnetic Eu ions, i.e. a valence slightly
less than 3+.Comment: Accepted for publication in PR
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