5,064 research outputs found
Efficient spin-current injection in single-molecule magnet junctions
We study theoretically spin transport through a single-molecule magnet (SMM)
in the sequential and cotunneling regimes, where the SMM is weakly coupled to
one ferromagnetic and one normalmetallic leads. By a master-equation approach,
it is found that the spin polarization injected from the ferromagnetic lead is
amplified and highly polarized spin-current can be generated, due to the
exchange coupling between the transport electron and the anisotropic spin of
the SMM. Moreover, the spin-current polarization can be tuned by the gate or
bias voltage, and thus an efficient spin injection device based on the SMM is
proposed in molecular spintronics.Comment: 4 figure
The upper critical field and its anisotropy in LiFeAs
The upper critical field of LiFeAs single crystals has
been determined by measuring the electrical resistivity using the facilities of
pulsed magnetic field at Los Alamos. We found that of LiFeAs
shows a moderate anisotropy among the layered iron-based superconductors; its
anisotropic parameter monotonically decreases with decreasing
temperature and approaches as . The upper
critical field reaches 15T () and 24.2T () at
1.4K, which value is much smaller than other iron-based high
superconductors. The temperature dependence of can be
described by the Werthamer-Helfand-Hohenberg (WHH) method, showing orbitally
and (likely) spin-paramagnetically limited upper critical field for and , respectively.Comment: 5 pages,5 figure
Progress and challenges in photocatalytic ammonia synthesis
Photocatalytic ammonia (NH_{3}) synthesis from N_{2} and water driven by solar energy is a sustainable and environmentally friendly technology, which has gained considerable attention in recent years. In this review, the recent development in the fundamental understanding of photocatalytic NH_{3} synthesis and the methods of precise NH_{3} detection are summarized. More importantly the strategy for surface engineering and interface engineering of photocatalysts toward photocatalytic NH_{3} production has been thoroughly analyzed with the aim to stimulate critical thinking about the effective methodology for catalyst modification instead of exploring new materials. At the end the challenges and a few concerns are raised from the current reports and future perspectives in this research field are discussed targeting to clarify the reliability and reproducibility of the photochemical process and to direct the future research direction, such as flow reactor design and in-depth understanding of the underlying reaction pathway
Predicting Urban Medical Services Demand in China: An Improved Grey Markov Chain Model by Taylor Approximation
The sharp increase of the aging population has raised the pressure on the current limited medical resources in China. To better allocate resources, a more accurate prediction on medical service demand is very urgently needed. This study aims to improve the prediction on medical services demand in China. To achieve this aim, the study combines Taylor Approximation into the Grey Markov Chain model, and develops a new model named Taylor-Markov Chain GM (1,1) (T-MCGM (1,1)). The new model has been tested by adopting the historical data, which includes the medical service on treatment of diabetes, heart disease, and cerebrovascular disease from 1997 to 2015 in China. The model provides a predication on medical service demand of these three types of disease up to 2022. The results reveal an enormous growth of urban medical service demand in the future. The findings provide practical implications for the Health Administrative Department to allocate medical resources, and help hospitals to manage investments on medical facilities
The magnetoresistance and Hall effect in CeFeAsO: a high magnetic field study
The longitudinal electrical resistivity and the transverse Hall resistivity
of CeFeAsO are simultaneously measured up to a magnetic field of 45T using the
facilities of pulsed magnetic field at Los Alamos. Distinct behaviour is
observed in both the magnetoresistance Rxx({\mu}0H) and the Hall resistance
Rxy({\mu}0H) while crossing the structural phase transition at Ts \approx 150K.
At temperatures above Ts, little magnetoresistance is observed and the Hall
resistivity follows linear field dependence. Upon cooling down the system below
Ts, large magnetoresistance develops and the Hall resistivity deviates from the
linear field dependence. Furthermore, we found that the transition at Ts is
extremely robust against the external magnetic field. We argue that the
magnetic state in CeFeAsO is unlikely a conventional type of spin-density-wave
(SDW).Comment: 4 pages, 3 figures SCES2010, To appear in J. Phys.: Conf. Ser. for
SCES201
Rational Design of High‐Concentration Ti³⁺ in Porous Carbon‐Doped TiO₂ Nanosheets for Efficient Photocatalytic Ammonia Synthesis
Photocatalytic ammonia synthesis is exciting but quite challenging with a very moderate yield at present. One of the greatest challenges is to develop highly active centers in a photocatalyst for N_{2} reduction under ambient conditions. Herein, porous carbon‐doped anatase TiO_{x} (C‐TiO_{x}) nanosheets with high‐concentration active sites of Ti^{3+} are presented, which are produced by layered Ti_{3}SiC_{2} through a reproducible bottom‐up approach. It is shown that the high‐concentration Ti^{3+} sites are the major species for the significant increase in N2 photoreduction activity by the C‐TiO_{x}. Such bottom‐up substitutional doping of C into TiO_{2} is responsible for both visible absorption and generation of Ti^{3+} concentration. Together with the porous nanosheets morphology and the loading of a Ru/RuO_{2} nanosized cocatalyst for enhanced charge separation and transfer, the optimal C‐TiO_{x} with a Ti^{3+}/Ti^{4+} ratio of 72.1% shows a high NH3 production rate of 109.3 µmol g^{−1} h^{−1} under visible‐light irradiation and a remarkable apparent quantum efficiency of 1.1% at 400 nm, which is the highest compared to all TiO_{2}‐based photocatalysts at present
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