This paper uses various mean-field approaches and the Monte
Carlo simulation to calculate asymmetric simple exclusion processes
with particles of arbitrary size in the successive defects system.
In this system, the hopping probability p (p<1) and the size d
of particles are not constant. Through theoretical calculation
and computer simulation, it obtains the exact theoretical results
and finds that the theoretical results are in agreement with
the computer simulation. These results are helpful in analysing the
effect of traffic with different hopping probabilities p and sizes
d of particle.

In this paper, we study the dynamics of the synchronous
totally asymmetric simple exclusion process (TASEP) on lattices with
two consecutive junctions in a multiple-input-multiple-output (MIMO)
traffic system, which consists of m sub-chains for the input and the
output, respectively. In the middle of the system, there are N
(nN
synchronously increasing, the vertical phase boundary moves toward
the right and the horizontal phase boundary moves toward the upside in
the phase diagram. The boundary conditions of the system as well as
the numbers of input and output determine the no-equilibrium
stationary states, stationary-states phases, and phase boundaries.
We use the results to compare with computer simulations and find
that they are in very good agreement with each other.

In this paper, a stochastic SIS epidemic model on
homogeneous networks is considered. The largest Lyapunov exponent is
calculated by Oseledec multiplicative ergodic theory, and the
stability condition is determined by the largest Lyapunov exponent.
The probability density function for the proportion of infected
individuals is found explicitly, and the stochastic bifurcation is
analysed by a probability density function. In particular, the new
basic reproductive number R*, that governs whether an epidemic
with few initial infections can become an endemic or not, is
determined by noise intensity. In the homogeneous networks, despite
of the basic productive number R_{0}>1, the epidemic will die out
as long as noise intensity satisfies a certain condition.

In this paper, we consider spatial-temporal correlation
functions of the turbulent velocities. With numerical simulations on
the Gledzer--Ohkitani--Yamada (GOY) shell model, we show that the
correlation function decays exponentially. The advecting velocity
field is regarded as a colored noise field, which is spatially and
temporally correlative. For comparison, we are also given the scaling
exponents of passive scalars obtained by the Gaussian random
velocity field, the multi-dimensional normal velocity field and
the She--Leveque velocity field, introduced by She, et al. We
observe that extended self-similarity scaling exponents H(p)/
H(2) of passive scalar obtained by the colored noise field are more
anomalous than those obtained by the other three velocity fields.

By introducing a more general auxiliary ordinary differential equation (ODE), a modified
variable separated ODE method is
developed for solving the mKdV--sinh-Gordon equation. As a result,
many explicit and exact solutions including some new formal
solutions are successfully picked up for the mKdV--sinh-Gordon
equation by this approach.

This paper proposes two simple and robust schemes to
generate an atomic-ensemble Greenberger--Horne--Zeilinger-type
(GHZ-type) entangled state via linear optics and single photon
detection. These schemes are based on two-photon
Hong--Ou--Mandel-type interference, therefore they are insensitive
to the phase fluctuation. This advantage will make the realizations
of these two schemes easier. One scheme can scale efficiently
with the number of ensembles because of the used quantum memory.
Both schemes are also robust to the noise and within the reach of
current technology.

It is known that exp≤[iλ≤(Q_{1}P_{1}-i/2)] is a unitary single-mode
squeezing operator, where Q_{1}, P_{1} are the coordinate and
momentum operators, respectively. In this paper we employ Dirac's
coordinate representation to prove that the exponential operator
S_{n}≡ exp≤[iλ\sum\limits_{i}=1^{n}(Q_{i}P_{i}+1
+Q_{i}+1P_{i}))], (Q_{n}+1=Q_{1}, P_{n}+1=P_{1}), is an
N-mode squeezing operator which enhances the standard squeezing.
By virtue of the technique of integration within an ordered product
of operators we derive S_{n}'s normally ordered expansion and
obtain new N-mode squeezed vacuum states, its Wigner function is
calculated by using the Weyl ordering invariance under similar
transformations.

In this paper, we study the entanglement dynamics of atoms
locally coupled to a cavity field. By studying two different models
within the framework of cavity QED, we show that the so-called
atomic entanglement sudden death always occurs if initially the
cavity field is in the thermal state, in clear contrast with that in
the vacuum state where the same entanglement decay is in infinite
time.

Based on the construction of supersymmetric generators, we
use the Lewis--Riesenfeld invariant method to deduce the exact and
explicit eigen-energy spectrum with the time-dependent thermo
Jaynes--Cummings model. One of the advantages of this approach is
that it can transform the hidden form, related to the chronological
product, of the time evolution operator into an explicit expression.
Moreover, the dynamical and statistics properties of physical
quantities are obtained for the given initial states in the thermo
Jaynes--Cummings system.

This paper proposes a fermionic linear optical scheme
for the teleportation and entanglement concentration via
entanglement swapping based on charge detection. It also proves that
this method is useful in generating entangled states such as GHZ
states, W states, and cluster states by using fermionic polarizing
beam splitters and single spin rotations assisted by a parity check on
the fermionic qubits. This scheme is nearly deterministic (i.e.,
with 100\% successful probability) and does not need the joint
Bell state measurement required in the previous schemes.

We present a scheme for implementing a three-qubit phase
gate via manipulating rf superconducting quantum interference device
(SQUID) qubits in the decoherence-free subspace with respect to
cavity decay. Through appropriate changes of the coupling constants
between rf SQUIDs and cavity, the scheme can be realized only in one
step. A high fidelity is obtained even in the presence of
decoherence.

This paper proposes a scheme to generate arbitrary
four-atom entangled decoherence-free states by using simple linear
optical elements, four one-sided cavities in which four atoms are
confined respectively. By conveniently tuning the titled angle of
one half-wave plate, it can obtain arbitrary four-atom entangled
decoherence-free states with a successful probability of 1 as long as
there is no photon loss.

DNA computation (DNAC) has been proposed to solve the
satisfiability (SAT) problem due to operations in parallel on
extremely large numbers of strands. This paper attempts to treat the
DNA-based bio-molecular solution for the SAT problem from the
quantum mechanical perspective with a purpose to explore the
relationship between DNAC and quantum computation (QC). To achieve
this goal, it first builds up the correspondence of operations
between QC and DNAC. Then it gives an example for the case of two
variables and three clauses for details of this theory. It also
demonstrates a three-qubit experiment for solving the simplest SAT
problem with a single variable on a liquid-state nuclear magnetic
resonance ensemble to verify this theory. Some discussions are made
for the potential application and for further exploration of the
present work.

Considering intrinsic decoherence, the two-atom two-mode
Raman coupled model is investigated in this paper. Utilizing the
constants of motion in this model, we obtain the analytic expressions
of the density operator of the system for investigating the entanglement
of two atoms. The speed of entanglement decay increases with the
increasing of the coupling coefficient of one atom. The difference
between the oscillation periods when the initial state parameter of
atomic subsystem belongs to two intervals becomes smaller with the
increasing of the coupling coefficient of one atom. The increasing
of the initial photon number of the second field can hasten the
vanishing of entanglement of atomic subsystem. The robustness of
atomic entanglement against decoherence depends on the interval of
the initial state parameter of atomic subsystem.

By using the Euler--MacLaurin formula, this paper studies
the thermodynamic properties of an ideal Fermi gas confined in a
d-dimensional rectangular container. The general expressions of
the thermodynamic quantities with the finite-size corrections are
given explicitly and the effects of the size and shape of the
container on the properties of the system are discussed. It is shown
that the corrections of the thermodynamic quantities due to the
finite-size effects are significant to be considered for the case of
strong degeneracy but negligible for the case of weak degeneracy or
non-degeneracy. It is important to find that some familiar
conclusions under the thermodynamic limit are no longer valid for
the finite-size systems and there are some novel characteristics
resulting from the finite-size effects, such as the nonextensivity
of the system, the anisotropy of the pressure, and so on.

This paper presents a novel approach of M-ary
baseband pulse amplitude modulated signal processing via a
parameter-optimized nonlinear dynamic system. This nonlinear system
usually shows the phenomenon of stochastic resonance by adding
noise. To thoroughly discuss the signal processing performance of
the nonlinear system, we tune the system parameters to obtain a
nonlinear detector with optimal performance. For characterizing the
output of the nonlinear system, the derivation of the probability of
detection error is given by the system response speed and the
probability density function of the nonlinear system output. By
varying the noise intensity with fixed system parameters, the
phenomenon of stochastic resonance is shown and by tuning the system
parameters with fixed noise, the probability of detection error is
minimized and the nonlinear system is optimized. The detection
performance of the two cases is compared with the theoretical
probability of detection error, which is validated by numerical
simulation.

This paper studies delay-dependent asymptotical stability
problems for the neural system with time-varying delay. By dividing the
whole interval into multiple segments such that each segment has a
different Lyapunov matrix, some improved delay-dependent stability
conditions are derived by employing an integral equality technique. A
numerical example is given to demonstrate the effectiveness and
less conservativeness of the proposed methods.

We present a scheme for the anti-control of chaos in the p--Ge
photoconductor system by using a chaotic laser to irradiate and
disturb this system. The numerical simulations show that this scheme
can be effectively used to control periodic states in this p--Ge
system into chaotic states. Moreover, the different chaos states
with different chaotic orbits can be obtained by appropriately
adjusting the disturbance intensity and disturbance frequency, and
by increasing this intensity or reducing this frequency, this p--Ge
system gradually evolves to fully developed chaotic states.

Chaotic systems perform well as a new rich source of
cryptography and pseudo-random coding. Unfortunately their digital
dynamical properties would degrade due to the finite computing
precision. Proposed in this paper is a modified digital chaotic
sequence generator based on chaotic logistic systems with a coupling
structure where one chaotic subsystem generates perturbation signals
to disturb the control parameter of the other one. The numerical
simulations show that the length of chaotic orbits, the output
distribution of chaotic system, and the security of chaotic
sequences have been greatly improved. Moreover the chaotic sequence
period can be extended at least by one order of magnitude longer
than that of the uncoupled logistic system and the difficulty in
decrypting increases 2^{128}*2^{128} times indicating that the
dynamical degradation of digital chaos is effectively improved. A
field programmable gate array (FPGA) implementation of an algorithm
is given and the corresponding experiment shows that the output
speed of the generated chaotic sequences can reach 571.4~Mbps
indicating that the designed generator can be applied to the
real-time video image encryption.

This paper concerns the disturbance rejection problem of a
linear complex dynamical network subject to external disturbances. A
dynamical network is said to be robust to disturbance, if the
H_{∞} norm of its transfer function matrix from the disturbance
to the performance variable is satisfactorily small. It is shown
that the disturbance rejection problem of a dynamical network can be
solved by analysing the H_{∞} control problem of a set of
independent systems whose dimensions are equal to that of a single
node. A counter-intuitive result is that the disturbance rejection
level of the whole network with a diffusive coupling will never be
better than that of an isolated node. To improve this, local
feedback injections are applied to a small fraction of the nodes in
the network. Some criteria for possible performance improvement are
derived in terms of linear matrix inequalities. It is further
demonstrated via a simulation example that one can indeed improve
the disturbance rejection level of the network by pinning the nodes
with higher degrees than pinning those with lower degrees.

Bifurcation control and the existence of chaos in a class of
linear impulsive systems are discussed by means of both theoretical
and numerical ways. Chaotic behaviour in the sense of Marotto's
definition is rigorously proven. A linear impulsive controller,
which does not result in any change in one period-1 solution of the
original system, is proposed to control and anti-control chaos. The
numerical results for chaotic attractor, route leading to chaos,
chaos control, and chaos anti-control, which are illustrated with
two examples, are in good agreement with the theoretical analysis.

The combined bottleneck effect is investigated by modeling
traffic systems with an on-ramp and a nearby bus stop in a two-lane
cellular automaton model. Two cases, i.e. the bus stop locates in
the downstream section of the on-ramp and the bus stop locates in
the upstream section of the on-ramp, are considered separately. The
upstream flux and downstream flux of the main road, as well as the
on-ramp flux are analysed in detail, with respect to the entering
probabilities and the distance between the on-ramp and the bus stop.
It is found that the combination of the two bottlenecks causes the
capacity to drop off, because the vehicles entering the main road
from the on-ramp would interweave with the stopping (pulling-out)
buses in the downstream (upstream) case. The traffic conflict in the
former case is much heavier than that in the latter, causing the
downstream main road to be utilized inefficiently. This suggests
that the bus stop should be set in the upstream section of the
on-ramp to enhance the capacity. The fluxes both on the main road
and on the on-ramp vary with the distance between the two
bottlenecks in both cases. However, the effects of distance
disappear gradually at large distances. These findings might give
some guidance to traffic optimization and management.

Complex networks have established themselves in recent
years as being particularly suitable and flexible for representing
and modelling many complex natural and artificial systems.
Oil--water two-phase flow is one of the most complex systems. In
this paper, we use complex networks to study the inclined oil--water
two-phase flow. Two different complex network construction methods
are proposed to build two types of networks, i.e. the flow pattern
complex network (FPCN) and fluid dynamic complex network (FDCN).
Through detecting the community structure of FPCN by the
community-detection algorithm based on K-means clustering, useful
and interesting results are found which can be used for identifying
three inclined oil--water flow patterns. To investigate the dynamic
characteristics of the inclined oil--water two-phase flow, we construct
48 FDCNs under different flow conditions, and find that the
power-law exponent and the network information entropy, which are
sensitive to the flow pattern transition, can both characterize the
nonlinear dynamics of the inclined oil--water two-phase flow. In this
paper, from a new perspective, we not only introduce a complex
network theory into the study of the oil--water two-phase flow but also
indicate that the complex network may be a powerful tool for exploring
nonlinear time series in practice.

This paper presents an inverse Monte Carlo method to
reconstruct pair interaction potential from pair correlation
function. This approach adopts an iterative algorithm on interaction
potential to fit known pair correlation function by compelling
deviations of canonical average to meet with Hamiltonian parameters
on a basis of statistical mechanism. The effective interaction
potential between particles in liquid Ag--Rh alloys has been
calculated with the inverse Monte Carlo method. It demonstrates an
effective and simple way to obtain the effective potential of
complex melt systems.

This paper makes some qualitative and quantitative
analyses about halo formation rules of some mirror nuclei with the
relativistic mean-field (RMF) theory and the Woods--Saxon mean-field
model. By analysing two opposite effects of Coulomb interaction on
the proton halo formation, it finds that the energy level shift has
a larger contribution than that of the Coulomb barrier when the mass
number A is small, the hindrance of the Coulomb barrier becomes more
obvious with the increase of the mass number A, and the overall
effect of the Coulomb interaction almost disappears when A≈39 as
its two effects counteract with each other.

Using a time-dependent multilevel approach, we demonstrate
that lithium atoms can be transferred to states of lower principle
quantum number by exposing them to a frequency chirped microwave
pulse. The population transfer from n = 79 to n = 70 states of
lithium atoms with more than 80% efficiency is achieved by means
of the sequential two-photon Δ n = - 1 transitions. It is
shown that the coherent control of the population transfer can be
accomplished by the optimization of the chirping parameters and
microwave field strength. The calculation results agree well with
the experimental ones and novel explanations have been given to
understand the experimental results.

The tunneling between double wells of atom in crossed
electromagnetic fields is investigated by a one-dimensional
Hamiltonian model. The crossed fields induced outer well is apart
from the nuclear origin and it is very difficult to access by means
of spectroscopy but it will be possible if there exists the tunneling of
the electron between the outer well and the Coulomb potential
predominated well at the nuclear origin. A one-dimensional quantum
calculation with B-spline basis has been performed for hydrogen atom
in crossed fields accessible in our laboratory, at B=0.8~T and
F=-220~V.cm^{-1}. The calculation shows that the
wavefunctions of some excited states close to the Stark saddle point
in the outer well extend over to the Coulomb potential well, making
it possible to penetrate the quantum information of the outer well.
However, the tunneling rate is very small and the spectral
measurement of the transitions from the ground state should be of
a high resolution and high sensitivity.

Interference effects on the photoionization cross sections
between two neighbouring atoms are considered based on the coherent
scattering of the ionized electrons by the two nuclei when their
separation is less than or comparable to the de Broglie wave length
of the ionized electrons. As an example, the single atomic nitrogen
ionization cross section and the total cross sections of two
nitrogen atoms with coherently added photoionization amplitudes are
calculated from the threshold to about 60~\AA (1~\AA=0.1~nm) of the
photon energy. The photoionization cross sections of atomic nitrogen
are obtained by using the close-coupling R-matrix method. In the
calculation 19 states are included. The ionization energy of the
atomic nitrogen and the photoionization cross sections agree well
with the experimental results. Based on the R-matrix results of
atomic nitrogen, the interference effects between two neighbouring
nitrogen atoms are obtained. It is shown that the interference
effects are considerable when electrons are ionized just above the
threshold, even for the separations between the two atoms are larger
than two times of the bond length of N_{2} molecules. Therefore, in
hot and dense samples, effects caused by the coherent interference
between the neighbours are expected to be observable for the total
photoionization cross sections.

This paper studies the multiphoton ionization of the
hydrogen atom exposed to the linearly or circularly polarized laser
pulses by solving the time-dependent Schr?dinger equation. It
finds that the ratio of the ionization probabilities by linearly and
circularly polarized laser pulses varies with the numbers of
absorbing photons. With the same laser intensity, the circularly
polarized laser pulse favors to ionize the atom with more ease than the
linearly polarized laser pulse if only two or three photons are
necessary to be absorbed. For the higher order multiphoton
ionization, the linearly polarized laser pulse has the advantage
over circularly polarized laser pulse to ionize the atom.

This paper proposes an accurate valuable interpretation
scheme to study the evolvement of the photoionization processes from
the isolated to the condensed atoms by a unique ab initio
method. The variations of the photoionization cross sections of the
atomic sodium with the photoelectron energy and the boundary radius
of the atomic configuration space are studied in this new scheme by
the R-matrix method. The discrepancy in the photoionization spectra of
the isolated and the condensed sodium has been explained
quantitatively and understood successfully by this alternative view
in detail for the first time.

This paper studies the superfluidity of ultracold spin-2
Bose atoms with weak interactions in optical lattices by calculating
the excitation energy spectrum using the Bogoliubov approach. The energy
spectra exhibit the characteristics of the superfluid-phase
explicitly and it finds the nonvanishing critical speeds of
superfluid. The obtained results display that the critical speeds of
superfluid are different for five spin components and can be
controlled by adjusting the lattice parameters in experiments.
Finally it discusses the feasibilities of implementing and measuring
superfluid.

This paper studies the influence of the reagent vibration
on the reaction O(^{1}D)+HF → HO+F by using a quasi-classical
trajectory method on the new \textitab initio ^{1}A' ground
singlet potential energy surface (Gómez-Carrasco et al
2007 Chem. Phys. Lett.435 188--193). The product
angular distributions which reflect the vector correlation are
calculated. Four polarization-dependent differential cross sections
(PDDCSs) which are sensitive to many photoinitiated bimolecular
reaction experiments are presented in the center of the mass frame,
respectively. The differential cross section indicates that the OH
product mainly tends to the forward scattering, and other PDDCSs are
also influenced by the vibration levels of HF.

By means of the theory of electromagnetic wave propagation
and transfer matrix method, this paper investigates the band rules
for the frequency spectra of three kinds of one-dimensional (1D)
aperiodic photonic crystals (PCs), generalized Fibonacci GF(p,1),
GF(1,2), and Thue--Morse (TM) PCs, with negative refractive index
(NRI) materials. It is found that all of these PCs can open a broad
zero-? gap, TM PC possesses the largest zero-? gap,
and with the increase of p, the width of the zero-? gap for
GF(p,1) PC becomes smaller. This characteristic is caused by the
symmetry of the system and the open position of the zero-?
gap. It is found that for GF(p,1) PCs, the possible limit
zero-? gaps open at lower frequencies with the increase of
p, but for GF(1,2) and TM PCs, their limit zero-? gaps
open at the same frequency. Additionally, for the three
bottom-bands, we find the interesting perfect self-similarities of
the evolution structures with the increase of generation, and obtain
the corresponding subband-number formulae. Based on 11 types of
evolving manners Q_{i}(i=1,2,....,11) one can plot out the
detailed evolution structures of the three kinds of aperiodic PCs
for any generation.

A novel optimal design of sub-wavelength metal rectangular
gratings for the polarizing beam splitter (PBS) is proposed. The
method is based on effective medium theory and the method of
designing single layer antireflection coating. The polarization
performance of PBS is discussed by rigorous couple-wave analysis
(RCWA) method at a wavelength of 1550~nm. The result shows that
sub-wavelength metal rectangular grating is characterized by a high
reflectivity, like metal films for TE polarization, and high
transmissivity, like dielectric films for TM polarization. The
optimal design accords well with the results simulated by RCWA
method.

The controllable periodic M-shape gratings are fabricated
on the surface of silica glass by three coplanar interfering beams
from a single femtosecond pulse. The configuration of the M-shape
periodic structure is characterized by optical microscopy and atomic
force microscopy. The experimental results and the theoretical
simulation show that the period and the modulation depth ratio
between the neighboring grooves of the fabricated gratings can be
controlled by adjusting the collision angles and pulse energy of
the three beams, respectively.

Extending the double Jaynes--Cummings model to a more
complicated case where the mode--mode competition is considered, we
investigate the entanglement character of two isolated atoms by
means of concurrence, and discuss the dependence of atom--atom
entanglement on the different initial state and the relative
coupling strength between the atom and the corresponding cavity
field. The results show that the amplitude and the period of the
atom--atom entanglement evolution can be controlled by the choice of
initial state and relative coupling strength, respectively. We find
that the phenomenon of entanglement sudden death (ESD) is sensitive
to the initial conditions. The length of the time interval for
zero entanglement depends not only on the initial degree of
entanglement between two atoms but also on the relative coupling
strength of atom--field interaction. The ESD effect can be weakened
by enhancing the mode--mode competition between the three- and
single-photon processes.

A study is made of the effects of Doppler broadening on
pure gain without inversion, which means that neither one-photon
nor two-photon inversions are allowed, and non-pure gain without
inversion, which means that one-photon inversion does not occur
but two-photon inversion is present, in a closed Λ-type
three-level system with incoherent pumping. It is shown that when
the driving field is resonant but the probe field is not, in a
certain range of Doppler width, for the case of the lower degree of
frequency up-conversion, generally, pure gain without inversion
increases monotonically and non-pure gain without inversion does
not monotonically increase or decrease with increasing Doppler width;
for the case of the higher degree of frequency
up-conversion, pure gain without inversion decreases
monotonically but non-pure gain without inversion cannot be
produced. In the case of two-photon resonance, in some range of
Doppler width, pure gain without inversion does not
monotonically increase or decrease while non-pure gain without
inversion decreases monotonically with Doppler width increasing.
Finally, an experimental scheme for examining our theoretical result
is given.

A violet laser diode (LD) structure is grown on a
free-standing c-plane GaN substrate and 4~μ m× 800~μ
m ridge waveguide LDs are fabricated. The electrical and the
optical characteristics of LDs under different facet-coating and
chip-mounting conditions are investigated under pulse mode
operation. The active region temperatures of p-side up and p-side
down mounted LDs are calculated with different injection currents.
The calculated thermal resistances of p-side up and p-side down
mounted LDs are 4.6~K/W and 3~K/W, respectively. The threshold
current of the p-side down mounted LD is much lower than that of the p-side
up mounted LD. The blue shift of the emission wavelength with increasing
injection current is observed only for the LD with p-side down mounting
configuration, due to the more efficient heat dissipation.

We have investigated coexisting four-wave mixing and
six-wave mixing (SWM) in ultra-thin, micrometre and long vapour
cells. There exists competition between Dicke-narrowing features
and polarization interference in the micrometre cell. The
oscillation behaviour of SWM signal intensities and linewidths
results from destructive interference. With a larger destructive
interference, the SWM signal in ultra-thin cells shows a narrow
spectrum, in contrast to the long cell case. Due to the
Dicke-narrowing features, a narrow spectrum can be obtained, and
such spectra can be used for high precision measurements and
metrological standards.

This paper proposes a method for measuring the stimulated
Brillouin scattering (SBS) threshold based on waveform variation of
SBS optical limiting. The output waveforms for different pump power
densities are numerically simulated, and validated in the Nd:YAG
seed-injected laser system. The results indicate that SBS does not
take place in the case of a low pump power density and thus the
output power scales up linearly with pump power. Once the pump power
density exceeds the SBS threshold, SBS takes place and thereby the
energies are transferred from pump to Stokes. As a result, a small
shoulder appears in the trailing edge of the output waveform, which
provides another method to determine the SBS threshold.

This paper calculates the wavelengths of the interband
transitions as a function of the Al mole fraction of Al_{x}Ga_{1-x}N bulk material. It is finds that when the Al mole fraction is
between 0.456 and 0.639, the wavelengths correspond to the solar-blind
(250~nm to 280~nm). The influence of the structure parameters of
Al_{y}Ga_{1-y}N/GaN quantum wells on the wavelength and absorption
coefficient of intersubband transitions has been investigated by
solving the Schr?dinger and Poisson equations self-consistently. The
Al mole fraction of the Al_{y}Ga_{1-y}N barrier changes from
0.30 to 0.46, meanwhile the width of the well changes from 2.9~nm to
2.2~nm, for maximal intersubband absorption in the window of the air
(3~μm <λ <5~μm). The absorption coefficient of the
intersubband transition between the ground state and the first
excited state decreases with the increase of the wavelength. The
results are finally used to discuss the prospects of GaN-based bulk
material and quantum wells for a solar-blind and middle infrared
two-colour photodetector.

We report on new experimental results for
below-diffraction-limited hybrid recording. In our experiments, by
means of focused laser assisted magnetic recording, the magnetic
domains within TbFeCo thin films are obtained under an external
perpendicular direct magnetic field. For a single magnetic medium,
the domain size is mainly determined by the focused spot, which is
about 620~nm for the laser wavelength λ =406~nm, and
a numerical aperture of the lens of 0.80. However, when a silicon thin
film structure is inserted between the substrate and the magnetic medium,
the recording domains can be reduced obviously. By optimizing the
experimental condition, even the size can be reduced to about
100~nm, which is below the diffraction limit, i.e. about 1/6 of the spot
size. This is very useful for improving the hybrid recording density
in practical applications.

We design three kinds of photonic crystal fibres (PCF)
with two zero-dispersion wavelengths (ZDWs) using the improved full
vector index method (FVIM) and finite-difference frequency domain
(FDFD) techniques. Based on these designed fibres, the effect of
fibre structure, pump power and wavelength on the modulation
instability (MI) gain in the anomalous dispersion region close to
the second ZDW of the PCFs is comprehensively analysed in this paper.
The analytical results show that an optimal MI gain can be obtained
when the optimal pump wavelength (1530~nm) is slightly shorter than
the second ZDW (1538~nm) and the optimal pump power is 250~W.
Importantly, the total MI gain bandwidth has been increased to 260~nm
for the first time, so far as we know, for an optimally-designed fibre
with Λ = 1.4~nm and d/Λ = 0.676, and
the gain profile became much smoother. The optimal pump wavelength
relies on the second ZDW of the PCF whereas the optimal pump power
depends on the corporate operation of the optimal fibre structure and
optimal pump wavelength, which is important in designing the most
appropriate PCF to attain higher broadband and gain
amplification.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Zhang Yi-Po, Yang Jin-Wei, Liu Yi, Song Xian-Ying, Yuan Guo-Liang, Li Xu, Zhou Yan, Zhou Jun, Yang Qing-Wei, Chen Liao-Yuan, Rao Jun, Duan Xu-Ru, Pan Chuan-Hong, HL-2A Team

Chin. Phys. B 2009, 18 (12): 5385 ; doi: 10.1088/1674-1056/18/12/044
Full Text: PDF (2103KB) (
649
)

During the current flat-top phase of electron cyclotron
resonance heating discharges in the HL-2A Tokamak, the behaviour of
runaway electrons has been studied by means of hard x-ray detectors
and neutron diagnostics. During electron cyclotron resonance
heating, it can be found that both hard x-ray radiation intensity
and neutron emission flux fall rapidly to a very low level, which
suggests that runaway electrons have been suppressed by electron
cyclotron resonance heating. From the set of discharges studied in
the present experiments, it has also been observed that the
efficiency of runaway suppression by electron cyclotron resonance
heating was apparently affected by two factors: electron cyclotron
resonance heating power and duration. These results have been
analysed by using a test particle model. The decrease of the
toroidal electric field due to electron cyclotron resonance heating
results in a rapid fall in the runaway electron energy that may lead
to a suppression of runaway electrons. During electron cyclotron
resonance heating with different powers and durations, the runaway
electrons will experience different slowing down processes. These
different decay processes are the major cause for influencing the
efficiency of runaway suppression. This result is related to the
safe operation of the Tokamak and may bring an effective control of
runaway electrons.

A scheme of generating energetic ions by the interaction
of an ultrahigh-intensity laser pulse and a thin solid foil is
studied. The combination of the effects of radiation pressure and
Coulomb explosion makes the ion acceleration more effective. The
maximum ion velocity variation with time is predicted theoretically
while the temporal evolution of the electrostatic field due to the
Coulomb explosion is taken into consideration. Two-dimensional
particle-in-cell simulations are done to verify the theory.

To reduce the oxygen transmission rate through a
polyethylene terephthalate (PET) bottle (an organic plastic)
diamond-like carbon (DLC) coatings on the inner surface of the PET
bottle were deposited by radio frequency plasma-enhanced chemical
vapour deposition (RF-PECVD) technology with C_{2}H_{2} as the
source of carbon and Ar as the diluted gas. As the barrier layer to
humidity and gas permeation, this paper analyses the DLC film
structure, composition, morphology and barrier properties by Fourier
transform infrared, atomic force microscopy, scanning electron
microscopy and oxygen transmission rate in detail. From the
spectrum, it is found that the DLC film mainly consists of
sp^{3} bonds. The barrier property of the films is significantly
relevant to the sp^{3} bond concentration in the coating, the film
thickness and morphology. Additionally, it is found that DLC film
deposited in an inductively coupled plasma enhanced capacitively
coupled plasma source shows a compact, homogeneous and crack-free
surface, which is beneficial for a good gas barrier property in PET
bottles.

Injection of high-Z impurities into plasma has been proved
to be able to reduce the localized thermal load and mechanical forces on
the in-vessel components and the vacuum vessel, caused by
disruptions in Tokamaks. An advanced prediction and mitigation
system of disruption is implemented in HL-2A to safely shut down
plasmas by using the laser ablation of high-Z impurities with a
perturbation real-time measuring and processing system. The
injection is usually triggered by the amplitude and frequency of
the MHD perturbation field which is detected with a Mirnov coil and leads
to the onset of a mitigated disruption within a few milliseconds. It
could be a simple and potential approach to significantly reducing the
plasma thermal energy and magnetic energy before a disruption,
thereby achieving safe plasma termination. The plasma
response to impurity injection, a mechanism for improving plasma
thermal and current quench in major disruptions, the design of
the disruption prediction warner, and an evaluation of the mitigation success rate
are discussed in the present paper.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

The influence of electron--phonon (EP) scattering on spin
polarization of current output from a mesoscopic ring with Rashba
spin--orbit (SO) interaction is numerically investigated. There are
three leads connecting to the ring at different positions;
unpolarized current is injected to one of them, and the other two
are output channels with different bias voltages. The spin
polarization of current in the outgoing leads shows oscillations as a
function of EP coupling strength owing to the quantum interference
of EP states in the ring region. As temperature increases, the
oscillations are evidently suppressed, implying decoherence of
the EP states. The simulation shows that the magnitude of polarized
current is sensitive to the location of the lead. The polarized
current depends on the connecting position of the lead in a
complicated way due to the spin-sensitive quantum interference
effects caused by different phases accumulated by transmitting
electrons with opposite spin states along different paths.

On the basis of the full velocity difference (FVD) model,
an improved multiple car-following (MCF) model is proposed by taking
into account multiple information inputs from preceding vehicles.
The linear stability condition of the model is obtained by using the
linear stability theory. Through nonlinear analysis, a modified
Korteweg-de Vries equation is constructed and solved. The traffic
jam can thus be described by the kink--antikink soliton solution for
the mKdV equation. The improvement of this new model over the
previous ones lies in the fact that it not only theoretically retains many
strong points of the previous ones, but also performs more
realistically than others in the dynamical evolution of congestion.
Furthermore, numerical simulation of traffic dynamics shows that the
proposed model can avoid the disadvantage of negative velocity that
occurs at small sensitivity coefficients λ in the FVD model by
adjusting the information on the multiple leading vehicles. No
collision occurs and no unrealistic deceleration appears in the
improved model.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

This paper theoretically investigates the orbital
magnetization of electron-doped (n-type) semiconductor
heterostructures and of hole-doped (p-type) bulk semiconductors,
which are respectively described by a two-dimensional electron/hole
Hamiltonian with both the included Rashba spin--orbit coupling and
Zeeman splitting terms. It is the Zeeman splitting, rather than the
Rashba spin--orbit coupling, that destroys the time-reversal
symmetry of the semiconductor systems and results in nontrivial
orbital magnetization. The results show that the magnitude of the
orbital magnetization per hole and the Hall conductance in the
p-type bulk semiconductors are about 10^{-2}--10^{-1} effective
Bohr magneton and 10^{-1}--1 e^{2}/h, respectively. However,
the orbital magnetization per electron and the Hall conductance in
the n-type semiconductor heterostructures are too small to be easily
observed in experiment.

The screening effect of the random-phase-approximation on
the states of shallow donor impurities in free strained wurtzite
GaN/Al_{x}Ga_{1-x}N heterojunctions under hydrostatic pressure
and an external electric field is investigated by using a
variational method and a simplified coherent potential
approximation. The variations of Stark energy shift with electric
field, impurity position, Al component and areal electron density
are discussed. Our results show that the screening dramatically
reduces both the blue and red shifts as well as the binding
energies of impurity states. For a given impurity position, the
change in binding energy is more sensitive to the increase in
hydrostatic pressure in the presence of the screening effect than
that in the absence of the screening effect. The weakening of the blue
and red shifts, induced by the screening effect, strengthens gradually
with the increase of electric field. Furthermore, the screening
effect weakens the mixture crystal effect, thereby influencing the
Stark effect. The screening effect strengthens the influence of
energy band bending on binding energy due to the areal electron
density.

The nonequilibrium Kondo effect is studied in a molecule
quantum dot coupled asymmetrically to two ferromagnetic electrodes
by employing the nonequilibrium Green function technique. The
current-induced deformation of the molecule is taken into account,
modeled as interactions with a phonon system, and
phonon-assisted Kondo satellites arise on both sides of the usual main
Kondo peak. In the antiparallel electrode configuration, the
Kondo satellites can be split only for the asymmetric dot-lead
couplings, distinguished from the parallel configuration where
splitting also exists, even though it is for symmetric case. We also
analyze how to compensate the splitting and restore the suppressed
zero-bias Kondo resonance. It is shown that one can change the TMR
ratio significantly from a negative dip to a positive peak only by
slightly modulating a local external magnetic field, whose value is
greatly dependent on the electron--phonon coupling strength.

Based on an improved energy dispersion relation, the
terahertz field induced nonlinear transport of miniband electrons in
a short period AlGaN/GaN superlattice is theoretically studied in
this paper with a semiclassical theory. To a short period
superlattice, it is not precise enough to calculate the energy
dispersion relation by just using the nearest wells in tight binding
method: the next to nearest wells should be considered. The results
show that the electron drift velocity is 30% lower under a dc
field but 10% higher under an ac field than the traditional
simple cosine model obtained from the tight binding method. The
influence of the terahertz field strength and frequency on the
harmonic amplitude, phase and power efficiency is calculated. The
relative power efficiency of the third harmonic reaches the peak
value when the dc field strength equals about three times the
critical field strength and the ac field strength equals about four
times the critical field strength. These results show that the
AlGaN/GaN superlattice is a promising candidate to convert radiation
of frequency ω to radiation of frequency 3ω or even
higher.

AlGaN/GaN heterostructures on vicinal sapphire
substrates and just-oriented sapphire substrates (0001) are grown by
the metalorganic chemical vapor deposition method. Samples are studied
by high-resolution x-ray diffraction, atomic force microscopy,
capacitance--voltage measurement and the Van der Pauw Hall-effect
technique. The investigation reveals that better crystal quality and
surface morphology of the sample are obtained on the vicinal substrate.
Furthermore, the electrical properties are also improved when the sample
is grown on the vicinal substrate. This is due to the fact that the
use of vicinal substrate can promote the step-flow mode of
crystal growth, so many macro-steps are formed during crystal
growth, which causes a reduction of threading dislocations in the
crystal and an improvement in the electrical properties of the
AlGaN/GaN heterostructure.

We investigate theoretically the spin-dependent electron
transport in a straight waveguide with Rashba spin--orbit coupling
(SOC) under the irradiation of a transversely polarized
electromagnetic (EM) field. Spin-dependent electron conductance and
spin polarization are calculated as functions of the emitting
energy of electrons or the strength of the EM field by adopting the mode
matching approach. It is shown that the spin polarization can be
manipulated by external parameters when the strength of Rashba
SOC is strong. Furthermore, a sharp step structure is found to exist
in the total electron conductance. These results can be understood
by the nontrivial Rashba subbands intermixing and the electron
intersubband transition when a finite-range transversely polarized
EM field irradiates a straight waveguide.

In the generalized gradient approximation, the energy and
electronic structure are investigated for a single copper atomic
chain wrapped in (4, 4), (5, 5) and (6, 6) armchair carbon nanotubes
by using the first-principles projector-augmented wave potential
within the framework of density functional theory. The results show
that the (4, 4) and (5, 5) tubes are too narrow to wrap a Cu chain,
but the (6, 6) tube is nearly ideal to wrap a Cu chain on its centre
axis. Wider tubes are anticipated to wrap more than one Cu
chain spontaneously with forces amounting to a fraction of a
nanonewton. Although the tube--chain interaction decreases with the
increase of the tube diameter of (4, 4), (5, 5) and (6, 6)
successively, the charge density of the Cu@(6, 6) combined system
still does not show complete superposition of that of the pristine (6, 6) tube and
Cu chain. Successively reducing the restrictions of (4, 4), (5,
5) and (6, 6) tubes on the Cu chain leads to a reduction in shift of the
highest peak of the Cu chain towards lower energies, that is from
-0.5177~eV of the isolated Cu chain to -1.36785~eV, -0.668~eV and
-0.588~eV for the Cu@(4, 4), Cu@(5, 5) and Cu@(6, 6) systems,
respectively. In reverse, the strong metallic character of the Cu chain
also enhances the metallic character of the combined systems so that
the broader pseudogaps of the pristine carbon nanotubes around the Fermi
level change into the narrow pseudogaps of the combined systems.

A new analytical model for reverse characteristics of
4H--SiC merged PN--Schottky diodes (MPS or JBS) is developed. To
accurately calculate the reverse characteristics of the 4H--SiC MPS
diode, the relationship between the electric field at the Schottky
contact and the reverse bias is analytically established by solving
the cylindrical Poisson equation after the channel has pinched off.
The reverse current density calculated from the
Wentzel--Kramers--Brillouin (WKB) theory is verified by comparing it
with the experimental result, showing that they are in good
agreement with each other. Moreover, the effects of P-region spacing
(S) and P-junction depth (X_{j}) on the characteristics of 4H--SiC MPS
are analysed, and are particularly useful for optimizing the
design of the high voltage MPS diodes.

This paper studies the degradation of device parameters
and that of stress induced leakage current (SILC) of thin tunnel
gate oxide under channel hot electron (CHE) stress at high
temperature by using n-channel metal oxide semiconductor field
effect transistors (NMOSFETs) with 1.4-nm gate oxides. The
degradation of device parameters under CHE stress exhibits
saturating time dependence at high temperature. The emphasis of this
paper is on SILC of an ultra-thin-gate-oxide under CHE stress at high
temperature. Based on the experimental results, it is found that
there is a linear correlation between SILC degradation and V_{h}
degradation in NMOSFETs during CHE stress. A model of
the combined effect of oxide trapped negative charges and interface
traps is developed to explain the origin of SILC during CHE stress.

This paper theoretically reports the nonlocal Andreev
reflection and spin current in a normal metal-ferromagnetic
metal-superconducting Aharonov--Bohm interferometer. It is found that the
electronic current and spin current are sensitive to systematic
parameters, such as the gate voltage of quantum dots and the
external magnetic flux. The electronic current in the normal metal
lead results from two competing processes: quasiparticle
transmission and nonlocal Andreev reflection. The appearance of zero
spin-up electronic current (or spin-down electronic current) signals
the existence of nonlocal Andreev reflection, and the presence
of zero electronic current results in the appearance of pure spin
current.

This paper applies the Bogoliubov--de Gennes equation and
the Blonder--Tinkham--Klapwijk approach to study the oscillatory
behaviour of differential conductance in a normal metal/insulator/metal/d-wave
superconductor junction carrying a
supercurrent I_{s}. We find that (i) a three-humped structure
appears at a nearly critical supercurrent I_{s} and z ≈
0.5 for the normal metal/insulator/metal/d_x^{2} + y^{2}-wave
superconductor junction; (ii) the zero-bias conductance peak splits
into two peaks with sufficiently large applied current for the normal
metal/insulator/metal/d_{xy}-wave superconductor junction; (iii)
the conductance spectrum exhibits oscillating behaviour with the
bias voltage and the peaks of the resonances are suppressed by
increasing supercurrent I_{s}.

The eigenproblems of spin waves in a symmetrical
ferromagnetic bilayered system with periodic boundary conditions are
solved using the interface-rescaling approach (IRA). The results
show that interface coupling between two sublayers would not
change the excitation energy of odd bulk modes, but change
excitation energy of even bulk modes. We call this peculiar
phenomenon the phenomenon of even bulk mode variance (PEBMV).
There are two kinds of mechanisms which cause PEBMV:
phase reversal and phase translation of the magnon at the
interface, corresponding, respectively, to the antiferromagnetic and
ferromagnetic interface coupling cases. PEBMV embodies the selective
effect of the interface on different bulk magnons.

Zn_0.95Co_0.05O precipitate-free single crystal
thin films were synthesized by a dual beam pulsed laser deposition
method. The films form a wurtzite structure whose hexagonal axis is
perpendicular or parallel to the plane of the surface depending on
the C-plane (0001) or R-plane (11\bar 20) sapphire substrate. Based
on the results of high-resolution transmission electron microscopy
and x-ray diffraction, C-plane films show larger lattice mismatch.
The films exhibit magnetic and semiconductor properties at room
temperature. The coercivity of the film is about 8000 A/m at room
temperature. They are soft magnetic materials with small remanent
squareness S for both crystal orientations. There is no evidence to
show that the anisotropy is fixed to the hexagonal axis (C-axis) for
the wurtzite structure.

This paper analyses a three-cavity frequency-quadrupling
terahertz gyroklystron with successive frequency-doubling in each
cavity with self-consistent nonlinear theory. The beam--wave
interaction efficiency and the electron bunching process are
studied. The variation of output efficiency with the length of drift
tubes and output power and the variation of Ohmic loss with the length of
output cavity are considered. Numerical simulations predict an
optimal output efficiency of 1.8%, a power output of more than
2~kW and a gain of 33~dB after taking into account Ohmic losses when
the frequency-quadrupling gyroklystron, driven by a 40-kV, 3-A
electron beam and 1 Watt input power, operates at 225~GHz.

The spatiotemporal and spectral characteristics of
ultrawide-band terahertz pulses after passing through a Fresnel lens
are studied by using the scalar diffraction theory. The simulation
shows that the transmitted terahertz waveforms compress with
increasing propagation distance, and the multi-frequency focusing
phenomenon at different focal points is observed. Additionally, the
distribution of terahertz fields in a plane perpendicular to the
axis is also discussed, and it is found that the diffraction not
only induces focusing on-axis but also inhibits focusing at off-axis
positions. Therefore, the Fresnel lens may be a useful alternative
approach to being a terahertz filter. Moreover, the terahertz pulses
travelling as a basic mode of a Gaussian beam are discussed in
detail.

Femtosecond pump-terahertz probe studies of carrier
dynamics in semi-insulating GaAs have been investigated in detail
for various pump powers. It is observed that, at high pump powers,
the reflection peaks flip to the opposite polarity and dramatically
enhance as the pump arrival time approaches the reflected wave of
the terahertz pulse. The abnormal polarity-flip and enhancement can
be interpreted by the pump-induced enhancement in the photoconductivity
of GaAs and half-wave loss. Moreover, the carrier relaxation
processes and surface states filling in GaAs are also studied in
these measurements.

The widely used energy transfer theory is a foundation of
luminescence, in which the rates of Stokes and anti-Stokes processes
have the same calculation formula. An improvement on the anti-Stokes
energy transfer to explain the fluorescence intensity reversal
between the red and green fluorescence of Er(0.5)Yb(9.5):FOV is reported
in the present article. The range of the intensity reversal
\varSigma was measured to be 877. Dynamic processes for 16
levels were simulated. A coefficient, the improvement factor of the
intensity ratio of Stokes to anti-Stokes processes in quantum
Raman theory compared to classical Raman theory, is introduced
to successfully describe the anti-Stokes energy transfer. A new
method to calculate the distance between the rare earth ions, which
is critical for the energy transfer calculation, is proposed. The
validity of these important improvements is also proved by
experiment.

This paper studies both the intraband polarization and
terahertz emission of a semiconductor superlattice in combined dc and
ac electric fields by using the superposition of two identical time
delayed and phase shifted optical pulses. By adjusting the delay
between these two optical pulses, our results show that the
intraband polarization is sensitive to the time delay. The peak
values appear again for the terahertz emission intensity due to the
superposition of two optical pulses. The emission lines of terahertz
blueshift and redshift in different ac electric fields and dynamic
localization appears. The emission lines of THz only appear to
blueshift when the biased superlattice is driven by a single optical
pulse. Due to excitonic dynamic localization, the terahertz emission
intensity decays with time in different dc and ac electric fields.
These are features of this superlattice which distinguish it from a
superlattice generated by a single optical pulse to drive it.

Nano metal-particle dispersed glasses are the attractive
candidates for nonlinear optical material applications. Au/SiO_{2}
nano-composite thin films with 3~vol\% to 65~vol% Au are prepared
by inductively coupled plasma sputtering. Au particles as perfect
spheres with diameters between 10~nm and 30~nm are uniformly
dispersed in the SiO_{2} matrix. Optical absorption peaks due
to the surface plasmon resonance of Au particles are observed. The
absorption property is enhanced with the increase of Au content,
showing a maximum value in the films with 37~vol% Au. The
absorption curves of the Au/SiO_{2} thin films with 3~vol\% to
37~vol% Au accord well with the theoretical optical absorption
spectra obtained from Mie resonance theory. Increasing Au content
over 37~vol% results in the partial connection of Au particles,
whereby the intensity of the absorption peak is weakened and
ultimately replaced by the optical absorption of the bulk. The band
gap decreases with Au content increasing from 3~vol\% to 37~vol %
but increases as Au content further increases.

8000 CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

The mass neutrino interference phases along the null
trajectory and the geodesic line in Kerr space--time are studied on
the plane θ=π/2. Because of the rotation object in Kerr
space--time, a particle travelling along the radial geodesic must
have a dragging effect produced by the angular momentum of the
central object. We give the correction of the phase due to the
rotation of the space--time. We find that the type-I interference
phase along the geodesic remains the double of that along the null on
the condition that the rotating quantity parameter a^{2} is
preserved and the higher order terms are negligible (e.g. a^{4}).
In addition, we calculate the proper oscillation length in Kerr
space--time. All of our results can return to those in Schwarzschild
space--time as the rotating parameter a approaches zero.

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