4,772 research outputs found
Feasibility evaluation and critical factor analysis for subway scheduling
In strategic subway scheduling stage, the conflict sometimes comes from different requirements of the subway operator. This study aims to investigate the significant factors concerning strategic subway scheduling problem and to develop an automatic procedure of feasibility analysis in subway scheduling. To this end, accurate simulation of train movement (via a simulator, named HAMLET) is applied first by considering the line geography, train performances, actual speed restrictions, etc. The critical elements of subway scheduling and their correlations are then studied and a bound structure of the critical factors is established. The feasibility of primary plan requirements is analysed with the restrictions of the bound structure. Infeasible aspects and possible adjustments are shortly discussed. Finally, the subsequent applications including schedule generation and optimization according to various objectives are indicated as well
Dark Matter Constraints on Gaugino/Higgsino Masses in Split Supersymmetry and Their Implications at Colliders
In split supersymmetry, gauginos and Higgsinos are the only supersymmetric
particles which are possibly accessible at foreseeable colliders. While the
direct experimental searches, such as LEP and Tevatron experiments, gave robust
lower bounds on the masses of these particles, the cosmic dark matter can give
some upper bounds and thus have important implications for the searches at
future colliders. In this work we scrutinize such dark matter constraints and
show the allowed mass range for charginos and neutralinos (the mass eigenstates
of gauginos and Higgsinos). We find that the lightest chargino must be lighter
than about 1 TeV under the popular assumption M_1=M_2/2 and about 2 or 3 TeV in
other cases. The corresponding production rates of the lightest chargino at the
CERN Large Hadron Collider (LHC) and the International Linear Colldier (ILC)
are also shown. While in some parts of the allowed region the chargino pair
production rate can be larger than 1 pb at LHC and 100 fb at the ILC, other
parts of the region correspond to very small production rates and thus there is
no guarantee to find the charginos of split supersymmetry at future colliders.Comment: version in EPJC (refs added
Electric-field dependent spin diffusion and spin injection into semiconductors
We derive a drift-diffusion equation for spin polarization in semiconductors
by consistently taking into account electric-field effects and nondegenerate
electron statistics. We identify a high-field diffusive regime which has no
analogue in metals. In this regime there are two distinct spin diffusion
lengths. Furthermore, spin injection from a ferromagnetic metal into a
semiconductor is enhanced by several orders of magnitude and spins can be
transported over distances much greater than the low-field spin diffusion
length.Comment: 5 pages, 3 eps figure
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Polarization and dispersion properties of elliptical hole golden spiral photonic crystal fiber
An elliptical air-hole golden spiral photonic crystal fiber (EGS-PCF) is analyzed with the full-vectorial finite element method. The air-holes in the EGS-PCF are arranged in a spiral pattern governed by the Golden Ratio, where the design has been inspired by the optimal arrangement of seeds found in nature. The EGS-PCF exhibits extremely high birefringence (∼0.022 at operating wavelength 1550 nm) which is particularly useful for generating a polarization stable supercontinuum (SC). The fiber can also be designed to have a Zero Dispersion Wavelength (ZDW) at a suitable wavelength for only one polarization and large negative dispersion for the other, leading to a single-polarization SC. In addition, the fiber dispersion can be designed to obtain ZDWs at 800 nm and 1064 nm simultaneously, which can facilitate broadband supercontinuum generation (SCG) through multi-wavelength pumping
Optoelectric spin injection in semiconductor heterostructures without ferromagnet
We have shown that electron spin density can be generated by a dc current
flowing across a junction with an embedded asymmetric quantum well. Spin
polarization is created in the quantum well by radiative electron-hole
recombination when the conduction electron momentum distribution is shifted
with respect to the momentum distribution of holes in the spin split valence
subbands. Spin current appears when the spin polarization is injected from the
quantum well into the -doped region of the junction. The accompanied
emission of circularly polarized light from the quantum well can serve as a
spin polarization detector.Comment: 2 figure
Unitarity constraints on charged pion photoproduction at large p_perp
Around , the coupling to the channel
leads to a good accounting of the charged pion exclusive photoproduction cross
section in the energy range 3 10 GeV, where experimental data
exist. Starting from a Regge Pole approach that successfully describes vector
meson production, the singular part of the corresponding box diagrams (where
the intermediate vector meson-baryon pair propagates on-shell) is evaluated
without any further assumptions (unitarity). Such a treatment provides an
explanation of the scaling of the cross section. Elastic rescattering
of the charged pion improves the basic Regge pole model at forward and backward
angles.Comment: 5 pages; 6 figure
A single-phase gadolinium-doped ceria cathode for highly efficient CO<sub>2</sub> electrolysis
High-temperature solid-oxide CO2 electrolysers enable high-efficiency conversion of electrical energy to valuable fuels and chemicals and as such facilitate a sustainable-energy technology. Conventional cermet-based fuel electrodes used in such solid-oxide cells (SOCs) like nickel-yttria-stabilized zirconia (Ni-YSZ) suffer from morphological degradation and destructive carbon deposition. In recent years, there has been an increasing interest in employing single-phase ceria-based fuel electrodes, which are known to exhibit excellent carbon deposition resistance. Under sufficiently reducing conditions, doped ceria (substituted with trivalent cations such as samarium or gadolinium to generate mobile oxygen vacancies) becomes a mixed ionic-electronic conductor, showing appreciable electronic conductivity. Here, we show for the first time stable high performance in CO2 electrolysis using a ceria-based SOC. The single full cell incorporating a 10 mol% gadolinium-doped ceria (GCO) fuel electrode delivers a current density as high as 1.51 A cm−2 at 800 °C during pure CO2 electrolysis, which is the best electrode performance reported to date among all-ceramic cathode materials. We demonstrate that the electrode performance in CO2 electrolysis is linked with the electronic conductivity, and hence, with the electronic charge carrier concentration in GCO. The results of the present work pave the way for development of robust, nickel-free SOCs for direct CO2 electrolysis.</p
Sixth-harmonic back-EMF based sensorless control for switched-flux permanent magnet machine
In switched-flux permanent magnet (SFPM) machines, the 6th-harmonic back electromotive force (EMF) is dominant, whilst the 3rd-harmonic back-EMF is much smaller. This paper proposes several new position estimation methods for sensorless control based on the 6th-harmonic back-EMF. Firstly, by detecting the zero-crossings of the 6th-harmonic back-EMF with/without eliminating the influence of the 3rd-harmonic back EMF, the related rotor positions can be determined precisely at these zero-crossings. However, since the intermediate rotor positions need to be determined by linear interpretation between two zero-crossings, it only exhibits excellent performance under steady state. Furthermore, the continuous rotor position can be
estimated from the proposed new observer by utilizing the
combined signals of 6th-harmonic back-EMF and flux-linkage,
together with a synchronous reference frame filter (SRFF) and harmonic elimination. Experimental validation show that (a) by eliminating the 3rd-harmonic back-EMF effect, the accuracy of the proposed 6th-harmonic back-EMF zero-crossings detection method can be improved, (b) SRFF is effective to minimize the influence of non-constant amplitudes of the 6th-harmonic backEMF and flux-linkage, (c) the comparison between the fundamental, the 3rd-harmonic back-EMF and the proposed method are presented in order to highlight the effectiveness of proposed control strategy under different operating conditions
Superconductivity and single crystal growth of Ni0:05TaS2
Superconductivity was discovered in a Ni0:05TaS2 single crystal. A Ni0:05TaS2
single crystal was successfully grown via the NaCl/KCl flux method. The
obtained lattice constant c of Ni0:05TaS2 is 1.1999 nm, which is significantly
smaller than that of 2H-TaS2 (1.208 nm). Electrical resistivity and
magnetization measurements reveal that the superconductivity transition
temperature of Ni0:05TaS2 is enhanced from 0.8 K (2H-TaS2) to 3.9 K. The
charge-density-wave transition of the matrix compound 2H-TaS2 is suppressed in
Ni0:05TaS2. The success of Ni0:05TaS2 single crystal growth via a NaCl/KCl flux
demonstrates that NaCl/KCl flux method will be a feasible method for single
crystal growth of the layered transition metal dichalcogenides.Comment: 13pages, 6 figures, Published in SS
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