583 research outputs found
Theory of magnetoelectric photocurrent generated by direct interband transitions in semiconductor quantum well
A linearly polarized light normally incident on a semiconductor quantum well
with spin-orbit coupling may generate pure spin current via direct interband
optical transition. An electric photocurrent can be extracted from the pure
spin current when an in-plane magnetic field is applied, which has been
recently observed in the InGaAs/InAlAs quantum well [Dai et al., Phys. Rev.
Lett. 104, 246601 (2010)]. Here we present a theoretical study of this
magnetoelectric photocurrent effect associated with the interband transition.
By employing the density matrix formalism, we show that the photoexcited
carrier density has an anisotropic distribution in k space, strongly dependent
on the orientation of the electron wavevector and the polarization of the
light. This anisotropy provides an intuitive picture of the observed dependence
of the photocurrent on the magnetic field and the polarization of the light. We
also show that the ratio of the pure spin photocurrent to the magnetoelectric
photocurrent is approximately equal to the ratio of the kinetic energy to the
Zeeman energy, which enables us to estimate the magnitude of the pure spin
photocurrent. The photocurrent density calculated with the help of an
anisotropic Rashba model and the Kohn-Luttinger model can produce all three
terms in the fitting formula for measured current, with comparable order of
magnitude, but discrepancies are still present and further investigation is
needed.Comment: 13 pages, 9 figures, 2 table
Density-driven higher-order topological phase transitions in amorphous solids
Amorphous topological states, which are independent of the specific spatial
distribution of microscopic constructions, have gained much attention.
Recently, higher-order topological insulators, which are a new class of
topological phases of matter, have been proposed in amorphous systems. Here, we
propose a density-driven higher-order topological phase transition in a
two-dimensional amorphous system. We demonstrate that the amorphous system
hosts a topological trivial phase at low density. With an increase in the
density of lattice sites, the topological trivial phase converts to a
higher-order topological phase characterized by a quantized quadrupole moment
and the existence of topological corner states. Furthermore, we confirm that
the density-driven higher-order topological phase transition is size dependent.
In addition, our results should be general and equally applicable to
three-dimensional amorphous systems. Our findings may greatly enrich the study
of higher-order topological states in amorphous systems
Voltammetric Behavior of o-Nitrophenol and Damage to DNA
The electrochemical behavior of o-nitrophenol was studied in detail with a glassy carbon electrode (GCE). The dependence of peak potential on pH indicated that equivalent electrons and protons were involved in the process of o-nitrophenol reduction. The interaction of o-nitrophenol with calf thymus DNA was investigated by adding DNA to the o-nitrophenol solution and by immobilizing DNA on GCE, respectively. The peak current decrement and peak potential shift in presence of DNA indicated that o-nitrophenol could interact with DNA. The result was demonstrated that the in situ DNA damage was detected by differential pulse voltammetry after the o-nitrophenol was electrochemically reduced
The Study of Owl's Silent Flight and Noise Reduction on Fan Vane with Bionic Structure
In light of the bionics engineering point of view, we use the biological non-smooth surface in the surface design of the fan blade in order to reduce the fan noise and improve air flow and efficiency .We design several kinds of Sawtooth-shaped distribution, and apply the non-smooth form on the fan model. We analyzed the acoustic performance of various non-smooth fan blades that was reflected when the fan was rotating. Through the wind tunnel test, we obtained the spectrum map, wind comparison chart, efficiency curve and other important parameters that came from the comparison between smooth and non-smooth models and the noise of the fan. This paper will reveal that the non-smooth shape practically is good for preventing formation of off-body vortex, which is caused by turbulent boundary layer on the vane surface, and it will have reference significance for exploring the mechanism of noise reduction on fan vane. Key words: Owl; Bionic; Noise Reduction; Optimization Tes
Observation of Majorana fermions with spin selective Andreev reflection in the vortex of topological superconductor
Majorana fermion (MF) whose antiparticle is itself has been predicted in
condensed matter systems. Signatures of the MFs have been reported as zero
energy modes in various systems. More definitive evidences are highly desired
to verify the existence of the MF. Very recently, theory has predicted MFs to
induce spin selective Andreev reflection (SSAR), a novel magnetic property
which can be used to detect the MFs. Here we report the first observation of
the SSAR from MFs inside vortices in Bi2Te3/NbSe2 hetero-structure, in which
topological superconductivity was previously established. By using
spin-polarized scanning tunneling microscopy/spectroscopy (STM/STS), we show
that the zero-bias peak of the tunneling differential conductance at the vortex
center is substantially higher when the tip polarization and the external
magnetic field are parallel than anti-parallel to each other. Such strong spin
dependence of the tunneling is absent away from the vortex center, or in a
conventional superconductor. The observed spin dependent tunneling effect is a
direct evidence for the SSAR from MFs, fully consistent with theoretical
analyses. Our work provides definitive evidences of MFs and will stimulate the
MFs research on their novel physical properties, hence a step towards their
statistics and application in quantum computing.Comment: 4 figures 15 page
Current epidemiological profile and features of visceral leishmaniasis in people's republic of China
<p>Abstract</p> <p>Background</p> <p>Visceral leishmaniasis (VL) is still an important public health problem in China. In recent years endemic regions spread, prevalence increased, and even an outbreak of the disease occurred in China due to global warming and population movement. It is essential to elucidate the current epidemic situation and epidemiological characteristics of VL for designing control policy. In the present study we describe the current epidemiological profile and characteristics of VL in China based on retrospectively reviewing of VL cases reported between 2005 and 2010 by a passive surveillance system.</p> <p>Methods</p> <p>The present study was a retrospective review of VL cases notified between 2005 and 2010 based on the passive surveillance data. The data were tabulated, diagrammatized and analyzed through descriptive statistics in a Microsoft Excel spreadsheet.</p> <p>Results</p> <p>A total of 2450 VL cases were notified, with a mean of 408 cases per year. 61 counties were identified as endemic area with 2224 autochthonous cases, and the other 118 counties as non-endemic areas with 226 imported cases. 97.71% of cases were concentrated in Xinjiang, Gansu and Sichuan Provinces. 9 major counties reported a mean of > 10 cases per year, with a total of 1759 cases reported. Different types of VL revealed distinct epidemiological characteristics.</p> <p>Conclusions</p> <p>The number of VL cases and endemic counties both increased in the period 2005-2010 in China. Different type or sub-type of VL revealed distinct epidemiological characteristics. Therefore, differential control measures must be taken in different endemic areas against incidence increase and endemic area spread.</p
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