16,283 research outputs found
Parsec-scale jet properties of the gamma-ray quasar 3C 286
The quasar 3C~286 is one of two compact steep spectrum sources detected by
the {\it Fermi}/LAT. Here, we investigate the radio properties of the
parsec(pc)-scale jet and its (possible) association with the -ray
emission in 3C~286. The Very Long Baseline Interferometry (VLBI) images at
various frequencies reveal a one-sided core--jet structure extending to the
southwest at a projected distance of 1 kpc. The component at the jet base
showing an inverted spectrum is identified as the core, with a mean brightness
temperature of ~K. The jet bends at about 600 pc (in
projection) away from the core, from a position angle of to
. Based on the available VLBI data, we inferred the proper motion
speed of the inner jet as mas yr (), corresponding to a jet speed of about at an inclination
angle of between the jet and the line of sight of the observer. The
brightness temperature, jet speed and Lorentz factor are much lower than those
of -ray-emitting blazars, implying that the pc-scale jet in 3C~286 is
mildly relativistic. Unlike blazars in which -ray emission is in
general thought to originate from the beamed innermost jet, the location and
mechanism of -ray emission in 3C~286 may be different as indicated by
the current radio data. Multi-band spectrum fitting may offer a complementary
diagnostic clue of the -ray production mechanism in this source.Comment: 9 pages, 4 figures, accept for publication in MNRA
An all fiber source of frequency entangled photon pairs
We present an all fiber source of frequency entangled photon pairs by using
four wave mixing in a Sagnac fiber loop. Special care is taken to suppress the
impurity of the frequency entanglement by cooling the fiber and by matching the
polarization modes of the photon pairs counter-propagating in the fiber loop.
Coincidence detection of signal and idler photons, which are created in pair
and in different spatial modes of the fiber loop, shows the quantum
interference in the form of spatial beating, while the single counts of the
individual signal (idler) photons keep constant. When the production rate of
photon pairs is about 0.013 pairs/pulse, the envelope of the quantum
interference reveals a visibility of , which is close to the
calculated theoretical limit 97.4%Comment: 11 pages, 6 figures, to appear in Phys. Rev.
Spin relaxation in submonolayer and monolayer InAs structures grown in a GaAs matrix
Electron-spin dynamics in InAs/GaAs heterostructures consisting of a single layer of InAs (1/3-1 monolayer) embedded in (001) and (311)A GaAs matrix was studied by means of time-resolved Kerr rotation spectroscopy. The spin-relaxation time of the submonolayer InAs samples is significantly enhanced, compared with that of the monolayer InAs sample. The electron-spin-relaxation time and the effective g factor in submonolayer samples were found to be strongly dependent on the photogenerated carrier density. The contribution from both the D'yakonov-Perel' mechanism and Bir-Aronov-Pikus mechanism are discussed to interpret the temperature dependence of spin decoherence at various carrier densities. © 2009 The American Physical Society.published_or_final_versio
Scalar control of a new phase-decoupling permanent magnet synchronous motor for servo application
This paper presents a new scalar-controlled phase-decoupling permanent magnet synchronous motor (PD-PMSM) which takes the advantages of smooth torque, fast response and good controllability for servo applications. Because of the PD nature, the proposed scalar control strategy can simply adjust the phase current amplitude and its angle with respect to the back EMF to achieve direct torque control. Experimental results are given to verify the advantages of the proposed scalar-controlled PD-PMSM. © 2005 IEEE.published_or_final_versio
Magnetic field processing to enhance critical current densities of MgB2 superconductors
Magnetic field of up to 12 T was applied during the sintering process of pure
MgB2 and carbon nanotube (CNT) doped MgB2 wires. We have demonstrated that
magnetic field processing results in grain refinement, homogeneity and
significant enhancement in Jc(H) and Hirr. The Jc of pure MgB2 wire increased
by up to a factor of 3 to 4 and CNT doped MgB2 by up to an order of magnitude
in high field region respectively, compared to that of the non-field processed
samples. Hirr for CNT doped sample reached 7.7 T at 20 K. Magnetic field
processing reduces the resistivity in CNT doped MgB2, straightens the entangled
CNT and improves the adherence between CNTs and MgB2 matrix. No crystalline
alignment of MgB2 was observed. This method can be easily scalable for a
continuous production and represents a new milestone in the development of MgB2
superconductors and related systems
Optimal leach protocol with improved bat algorithm in wireless sensor networks
© 2019, Korean Society for Internet Information. All rights reserved. A low-energy adaptive clustering hierarchy (LEACH) protocol is a low-power adaptive cluster routing protocol which was proposed by MIT’s Chandrakasan for sensor networks. In the LEACH protocol, the selection mode of cluster-head nodes is a random selection of cycles, which may result in uneven distribution of nodal energy and reduce the lifetime of the entire network. Hence, we propose a new selection method to enhance the lifetime of network, in this selection function, the energy consumed between nodes in the clusters and the power consumed by the transfer between the cluster head and the base station are considered at the same time. Meanwhile, the improved FTBA algorithm integrating the curve strategy is proposed to enhance local and global search capabilities. Then we combine the improved BA with LEACH, and use the intelligent algorithm to select the cluster head. Experiment results show that the improved BA has stronger optimization ability than other optimization algorithms, which the method we proposed (FTBA-TC-LEACH) is superior than the LEACH and LEACH with standard BA (SBA-LEACH). The FTBA-TC-LEACH can obviously reduce network energy consumption and enhance the lifetime of wireless sensor networks (WSNs)
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