172 research outputs found
The statistics of Wigner delay time in Anderson disordered systems
We numerically investigate the statistical properties of Wigner delay time in
Anderson disordered 1D, 2D and quantum dot (QD) systems. The distribution of
proper delay time for each conducting channel is found to be universal in 2D
and QD systems for all Dyson's symmetry classes and shows a piece-wise power
law behavior in the strong localized regime. Two power law behaviors were
identified with asymptotical scaling and ,
respectively that are independent of the number of conducting channels and
Dyson's symmetry class. Two power-law regimes are separated by the relevant
time scale where is the average level spacing.
It is found that the existence of necklace states is responsible for the second
power-law behavior , which has an extremely small distribution
probability.Comment: 7 page
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
Consequences of scarcity: the impact of perceived scarcity on executive functioning and its neural basis
IntroductionPrevious studies have found a causal relationship between scarcity and the adverse impact it has on executive functioning. However, few studies have directly examined perceived scarcity, and cognitive flexibility (the third component of executive functions) has rarely been included.MethodsUsing a 2 (group: scarcity group vs. control group) × 2 (trial type: repeat trial vs. switch trial) mixed design, this study directly explored perceived scarcity’s impact on cognitive flexibility and revealed its neural basis in the switching tasks. Seventy college students participated in this study through open recruitment in China. A priming task was used to induce perceived scarcity, thus exploring the impact of perceived scarcity on participants’ performance in switching tasks and enabling the analysis of the neural activity of the brain, combined with electroencephalograph (EEG) technology.ResultsIn terms of behavioral outcomes, perceived scarcity led to poorer performance and a greater switching cost of reaction time in the switching tasks. Regarding neural activity, perceived scarcity led to an increase in the amplitude of P3 differential wave (repeat trials minus switch trials) in the parietal cortex during the target-locked epochs in the switching tasks.DiscussionPerceived scarcity can lead to changes in the neural activity of the brain regions related to executive functioning, resulting in a temporary decrease in cognitive flexibility. It may lead to individuals unable to adapt well to the changing environment, unable to quickly devote themselves to new tasks, and reduce work and learning efficiency in daily life
Classification of spin Hall effect in two-dimensional systems
Physical properties such as the conductivity are usually classified according
to the symmetry of the underlying system using Neumann's principle, which gives
an upper bound for the number of independent components of the corresponding
property tensor. However, for a given Hamiltonian, this global approach usually
can not give a definite answer on whether a physical effect such as spin Hall
effect (SHE) exists or not. It is found that the parity and types of spin-orbit
interactions (SOIs) are good indicators that can further reduce the number of
independent components of the spin Hall conductivity for a specific system. In
terms of the parity as well as various Rashba-like and Dresselhaus-like SOIs,
we propose a local approach to classify SHE in two-dimensional (2D) two-band
models, where sufficient conditions for identifying the existence or absence of
SHE in all 2D magnetic point groups are presented
Improving fatty acids production by engineering dynamic pathway regulation and metabolic control
Global energy demand and environmental concerns have stimulated increasing efforts to produce carbon-neutral fuels directly from renewable resources. Microbially derived aliphatic hydrocarbons, the petroleum-replica fuels, have emerged as promising alternatives to meet this goal. However, engineering metabolic pathways with high productivity and yield requires dynamic redistribution of cellular resources and optimal control of pathway expression. Here we report a genetically encoded metabolic switch that enables dynamic regulation of fatty acids (FA) biosynthesis in Escherichia coli. The engineered strains were able to dynamically compensate the critical enzymes involved in the supply and consumption of malonyl-CoA and efficiently redirect carbon flux toward FA biosynthesis. Implementation of this metabolic control resulted in an oscillatory malonyl-CoA pattern and a balanced metabolism between cell growth and product formation, yielding 15.7- and 2.1-fold improvement in FA titer compared with the wild-type strain and the strain carrying the uncontrolled metabolic pathway. This study provides a new paradigm in metabolic engineering to control and optimize metabolic pathways facilitating the high-yield production of other malonyl-CoA–derived compounds.National Science Foundation (U.S.) (Award CBET1144226)National Science Foundation (U.S.) (Award CBET0836513)Rensselaer Polytechnic Institute. Biocatalysis and Metabolic Engineering Constellatio
Dissipationless gyrotropic magnetic Hall effect
A dissipationless longitudinal current can be generated by a pure magnetic
field through the chiral magnetic effect. Herein, we propose that a pure
oscillating magnetic field through Zeeman coupling can further drive an AC
magnetic Hall current in two-dimensional systems without inversion symmetry. We
dub this effect the "gyrotropic magnetic Hall effect" (GMHE), in analogy with
the gyrotropic current achieved by rectifying the optical fields. Importantly,
we find that the GMHE conductivity is a reactive or dissipationless transport
coefficient, which is even under time-reversal symmetry. We reveal the "Zeeman
Berry curvature" as the quantum origin of the GMHE, whose integral over all
states below the Fermi energy gives the GMHE conductivity. Furthermore, by
symmetry analysis, we show that the GMHE can appear in a wide range of
two-dimensional materials. To demonstrate our proposal, we evaluate the GMHE
current in two-dimensional Rashba system and in the surface of topological
insulator, where a low-frequency magnetic field with a small amplitude can be
converted into a detectable Hall voltage
High-efficiency photoelectric detector based on a p-n homojunction of monolayer black phosphorus
We numerically investigate the high-efficiency photovoltaic effect in lateral
p-n homojunction based on monolayer black phosphorus (MBP) by using the
non-equilibrium Green's function combined with the density functional theory.
Due to the built-in electric field of the p-n junction and the wrinkle
structure of MBP, the photocurrent excited by either linearly or elliptically
polarized light is significantly enhanced in a wide photon energy range.
Moreover, because of the electron-photon interaction, the photocurrent is
related to atomic orbitals through the polarizing angle of polarized light.
Therefore, we can read the orbital information of the band structure from the
polarizing angular distribution of photocurrent. These findings suggest the
promising application of MBP-based p-n homojunction in high-efficiency
photoelectric devices and orbital-resolved photovoltaic detection
Enhancement of shot noise due to the fluctuation of Coulomb interaction
We have developed a theoretical formalism to investigate the contribution of
fluctuation of Coulomb interaction to the shot noise based on Keldysh
non-equilibrium Green's function method. We have applied our theory to study
the behavior of dc shot noise of atomic junctions using the method of
nonequilibrium Green's function combined with the density functional theory
(NEGF-DFT). In particular, for atomic carbon wire consisting 4 carbon atoms in
contact with two Al(100) electrodes, first principles calculation within
NEGF-DFT formalism shows a negative differential resistance (NDR) region in I-V
curve at finite bias due to the effective band bottom of the Al lead. We have
calculated the shot noise spectrum using the conventional gauge invariant
transport theory with Coulomb interaction considered explicitly on the Hartree
level along with exchange and correlation effect. Although the Fano factor is
enhanced from 0.6 to 0.8 in the NDR region, the expected super-Poissonian
behavior in the NDR regionis not observed. When the fluctuation of Coulomb
interaction is included in the shot noise, our numerical results show that the
Fano factor is greater than one in the NDR region indicating a super-Poissonian
behavior
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