The ErCo _{2} compound is prepared by arc-melting and its entropy changes
are calculated using Maxwell relation. Its entropy change reaches
38~J/(kg \cdot K)
and its refrigerant capacity achieves 291 J/kg at 0--5 T. The mean field
approximation is used to calculate the magnetic entropy of ErCo _{2}
compound. Results estimated by using the Maxwell relation deviate from mean
field approximation calculations in ferrimagnetic state; however, the data
obtained by the two ways are consistent in the vicinity of phase transition
or at higher temperatures. This indicates that entropy changes are mainly
derived from magnetic degree of freedom, and the lattice has almost no
contribution to the entropy change in the vicinity of phase transition but
its influence is obvious in the ferrimagnetic state below T_{C}.

A pseudospectral method with symplectic algorithm for the solution of
time-dependent Schr\"{o}dinger equations (TDSE) is introduced. The
spatial part of the wavefunction is discretized into sparse grid by
pseudospectral method and the time evolution is given in symplectic
scheme. This method allows us to obtain a highly accurate and stable
solution of TDSE. The effectiveness and efficiency of this method is
demonstrated by the high-order harmonic spectra of one-dimensional
atom in strong laser field as compared with previously published
work. The influence of the additional static electric field is also
investigated.

This paper studies Mei symmetry which leads to a generalized Hojman
conserved quantity for variable mass systems with unilateral
holonomic constraints. The differential equations of motion for the
systems are established, the definition and criterion of the Mei
symmetry for the systems are given. The necessary and sufficient
condition under which the Mei symmetry is a Lie symmetry for the
systems is obtained and a generalized Hojman conserved quantity
deduced from the Mei symmetry is got. An example is given to
illustrate the application of the results.

Under the travelling wave transformation, the Camassa--Holm equation
with dispersion is reduced to an integrable ordinary differential
equation
(ODE), whose general solution
can be obtained using the trick of one-parameter group. Furthermore,
by using a complete discrimination system for polynomial, the
classification of all single travelling wave solutions to the
Camassa--Holm equation with dispersion is obtained.
In particular, an affine subspace structure in the set of the
solutions of the reduced ODE is
obtained. More generally, an implicit linear structure in the Camassa--Holm equation with
dispersion is found. According to the linear structure, we obtain
the superposition of multi-solutions to Camassa--Holm equation with
dispersion.

In this paper an efficient quantum secure direct communication (QSDC) scheme with
authentication is presented, which is based on quantum entanglement and
polarized single photons. The present protocol uses Einstein--Podolsky--Rosen
(EPR) pairs and polarized
single photons in batches. A particle of the EPR pairs is retained
in the sender's station, and the other is transmitted forth and back
between the sender and the receiver, similar to the `ping--pong'
QSDC protocol. According to the shared information beforehand, these
two kinds of quantum states are mixed and then transmitted via a
quantum channel. The EPR pairs are used to transmit secret messages
and the polarized single photons used for authentication and
eavesdropping check. Consequently, because of the dual contributions
of the polarized single photons, no classical information is needed.
The intrinsic efficiency and total efficiency are both 1 in this
scheme as almost all of the instances are useful and each EPR pair
can be used to carry two bits of information.

The Holevo capacity of a generalized amplitude-damping channel
is investigated by using a numerical method.
It is shown that the Holevo capacity depends
on the channel parameters representing the ambient temperature and fidelity.
In particular, under a special condition,
the Holevo capacity of the generalized amplitude-damping channel
can be written as an analytical expression.

Using the projective Riccati equation expansion (PREE) method, new
families of variable separation solutions (including solitary wave
solutions, periodic wave solutions and rational function solutions)
with arbitrary functions for two nonlinear physical models are
obtained. Based on one of the variable separation solutions and by
choosing appropriate functions, new types of interactions between
the multi-valued and single-valued solitons, such as a peakon-like
semi-foldon and a peakon, a compacton-like semi-foldon and a
compacton, are investigated.

In this paper the so-called sudden death effect of entanglement is
investigated in a quantum model. The results show that one can
expect the resurrection of the original entanglement to occur in a
periodic way following each sudden death event. The length of the
time interval for the zero entanglement depends not only on the
degree of entanglement of the initial state but also on the initial
state.

Based on the calculation of all the pairwise entanglements in the n
( n \leq 6 )-qubit Heisenberg XX open chain with system impurity, we
find an important result: pairwise entanglement can only be
transferred by an entangled pair. The non-nearest pairwise
entanglements will have the possibility to exist as long as there has
been even number of qubits in their middle. This point indicates that
we can obtain longer distance entanglement in a solid system.

In this paper, the Klein--Gordon equation with equal scalar and vector Makarov potentials is studied by the factorization method. The energy equation and the normalized bound state solutions are obtained, a recurrence relation between the different principal quantum number n corresponding
to a certain angular quantum number \ell is established and some special cases of Makarov potential are discussed.

Broadcast encryption allows the sender to securely distribute his/her
secret to a dynamically changing group of users over a broadcast
channel. In this paper, we just take account of a simple broadcast
communication task in quantum scenario, in which the central party
broadcasts his secret to multi-receiver via quantum channel. We
present three quantum broadcast communication schemes. The first
scheme utilizes entanglement swapping and
Greenberger--Horne--Zeilinger state to fulfil a task that the central
party broadcasts the secret to a group of receivers who share a group
key with him. In the second scheme, based on dense coding, the
central party broadcasts the secret to multi-receiver, each of which
shares an authentication key with him. The third scheme is a quantum
broadcast communication scheme with quantum encryption, in which the
central party can broadcast the secret to any subset of the legal
receivers.

In the measurement-based model of quantum computing, a one-way
quantum computer consisting of many qubits can be immersed in a
common environment as a simple decoherence mechanism. This paper
studies the dynamics of entanglement witness for 3-qubit cluster
states in the common environment. The result shows that environment
can induce an interesting feature in the time evolution of the
entanglement witness: i.e., the periodical collapse and revival of
the entanglement dynamics.

We propose a simple scheme to generate an arbitrary photon-added coherent state of a travelling optical field by combining an array of degenerate parametric amplifiers and corresponding
single-photon detectors. Particularly, when the single-photon-added coherent state is observed by
developing the novel technique of Zavatta et al (2004 Science 306 660), we can simultaneously obtain the generalized N -qubit W state.

In this paper, a synchronization scheme for a class of chaotic
neural networks with time-varying delays is presented. This class of
chaotic neural networks covers several well-known neural networks,
such as Hopfield neural networks, cellular neural networks, and
bidirectional associative memory networks. The obtained criteria are
expressed in terms of linear matrix inequalities, thus they can be
efficiently verified. A comparison between our results and the
previous results shows that our results are less restrictive.

This paper reports a new reverse butterfly-shaped chaotic attractor and its
experimental confirmation. Some basic dynamical properties, and chaotic
behaviours of this new reverse butterfly attractor are studied. Simulation
results support brief theoretical derivations. Furthermore, the system is
experimentally confirmed by a simple electronic circuit.

In this paper, the synchronization in a unified fractional-order
chaotic system is investigated by two methods. One is the
frequency-domain method that is analysed by using the Laplace
transform theory. The other is the time-domain method that is
analysed by using the Lyapunov stability theory. Finally, the
numerical simulations are used to illustrate the effectiveness
of the proposed synchronization methods.

In this paper a time delay equation for sea--air oscillator model is
studied. The aim is to create an approximate solving method of
nonlinear equation for sea--air oscillator model. Employing the
method of variational iteration, it obtains the approximate solution
of corresponding equation. This method is an approximate analytic
method, which can be often used for analysing other behaviour of the
sea surface temperature anomaly of the atmosphere--ocean oscillator
model.

In this paper, with a given manifold y= H(x) , we have constructed
a response system for a continuous-time chaotic system as a drive
system, and used impulsive control theory to demonstrate
theoretically that this response system can achieve impulsive
generalized synchronization (GS) with the drive system. Our
theoretical result is supported by numerical examples.

Based on the open-plus-closed-loop (OPCL) control method a systematic
and comprehensive controller is presented in this paper for a chaotic
system, that is, the Newton--Leipnik equation with two strange
attractors: the upper attractor (UA) and the lower attractor (LA).
Results show that the final structure of the suggested controller for
stabilization has a simple linear feedback form. To keep the
integrity of the suggested approach, the globality proof of the
basins of entrainment is also provided. In virtue of the OPCL
technique, three different kinds of chaotic controls of the system
are investigated, separately: the original control forcing the
chaotic motion to settle down to the origin from an arbitrary
position of the phase space; the chaotic intra-attractor control for
stabilizing the equilibrium points only belonging to the upper
chaotic attractor or the lower chaotic one; and the inter-attractor
control for compelling the chaotic oscillation from one basin to
another one. Both theoretical analysis and simulation results verify
the validity of the proposed means.

In this paper, the Chebyshev polynomial approximation is applied to
the problem of stochastic period-doubling bifurcation of a stochastic
Bonhoeffer--van der Pol (BVP for short) system with a bounded random
parameter. In the analysis, the stochastic BVP system is transformed
by the Chebyshev polynomial approximation into an equivalent
deterministic system, whose response can be readily obtained by
conventional numerical methods. In this way we have explored plenty
of stochastic period-doubling bifurcation phenomena of the stochastic
BVP system. The numerical simulations show that the behaviour of the
stochastic period-doubling bifurcation in the stochastic BVP system
is by and large similar to that in the deterministic mean-parameter
BVP system, but there are still some featured differences between
them. For example, in the stochastic dynamic system the
period-doubling bifurcation point diffuses into a critical interval
and the location of the critical interval shifts with the variation
of intensity of the random parameter. The obtained results show that
Chebyshev polynomial approximation is an effective approach to
dynamical problems in some typical nonlinear systems with a bounded
random parameter of an arch-like probability density function.

By using the new experimental data of \Lambda\Lambda potential,
this paper has performed a full calculation for strange hadronic
matter with different strangeness contents as well as its
consequences on the global properties of neutron star matter in
relativistic mean field model. It finds that the new weak
hyperon--hyperon interaction makes the equations of state much
stiffer than the result of the previous strong hyperon--hyperon
interaction, and even stiffer than the result without consideration
of hyperon--hyperon interaction. This new hyperon--hyperon
interaction results in a maximum mass of 1.75M_{\odot} (where
M_{\odot} stands for the mass of the Sun), about
0.2--0.5M_{\odot} larger than the previous prediction with
the presence of hyperons. After examining carefully the onset
densities of kaon condensation it finds that this new weak version of
hyperon--hyperon interaction favours the occurrence of kaons in
comparison with the strong one.

To compare with the predictions of the transitional
dynamical symmetry X(5)
proposed by Iachello (2001 Phys. Rev. Lett. 87 052502), the critical
behaviours of U(5)--SU(3) are studied in the space of two control
parameters in the interacting boson model (IBM). A simple-shaped phased diagram
has been presented. It is found that X(5) predictions cannot be exactly
reproduced by our calculations and that the best agreement is close to the
calculations with boson numbers N = 11 and 12. By comparing with experimental
data on X(5)-like nuclei, we find that X(5) predictions and IBM
calculations can reproduce the energy ratios and E2 transition ones.

The technique of stimulated Raman adiabatic passage (STIRAP) is used to
transfer potassium atoms from the 22p state to the
21p
Rydberg state through the intermediate state
22s. The results show that complete population transfer is related to pulse
duration and overlap, and occurs when the pulse duration and overlap have
adequate values. At the same time, population trapping is also formed.
Complete population transfer can also occurs when the two-photon resonance
condition ({\it\Delta}_{s}= {\it\Delta}_{p}) is met.

B3LYP level density functional theory (DFT) and multiconfiguration
self-consistent-field (MCSCF) level \textit{ab initio} method
calculations have been performed on the basis of relativistic
effective core potentials to investigate the nature of EuC and
EuC_{2} molecules. The computed results indicate that the ground
states of EuC and EuC_{2} are ^{12}\sum^{+} and ^{8}A_{2}
respectively. Dissociation potential energy curves of the low-lying
electronic states of EuC have been calculated using the MCSCF method,
and the same level calculation on EuC_{2} indicates that the
dissociation energy of EuC_{2} of ground state compares well with
the available experimental data. The bond characteristic is also
discussed using Mulliken populations.

Electron impact excitation of tetrasulfur S_{4} molecule is
investigated in this work using R-matrix method. The twelve
low-lying electronic states are used in close-coupling expansion to
represent the target states, and the integral cross sections for
elastic scattering and excitation into the six lowest electronic
states are calculated.

We report the coexistence of TE and TM surface modes in certain same
frequency domain at the interface between one isotropic regular medium and
another biaxially anistotropic left-handed medium. The conditions for the
existence of TE and TM polarized surface waves in biaxially anisotropic
left-handed materials are identified, respectively. The Poynting vector and
the energy density associated with surface modes are calculated.
Depending on the system parameters, either TE or TM surface modes can
have the
time averaged Poynting vector directed to or opposite to the mode phase
velocity. It is seen that the characteristics of surface waves in biaxially
anisotropic left-handed media are significantly different from that in
isotropic left-handed media.

We propose a scheme for preparing four-particle
Greenberger--Horne--Zeilinger states using two identical bimodal
cavities, each supports two modes with different frequencies. This
scheme is an alternative to another published work [Christopher C
Gerry 1996 {\it Phys. Rev.} A {\bf 53} 4591]. Comparisons between
them are discussed. The fidelity and the probability of success
influenced by cavity decay for the generated states are also
considered.

We have investigated the evolution of the atomic quantum entropy and
the entanglement of atom--photon in the system with competing
k-photon and l-photon transitions by means of fully quantum
theory, and examined the effects of competing photon numbers (k
and l), the relative coupling strength between the atom and the
two-mode field (\lambda/g), and the initial photon number of the
field on the atomic quantum entropy and the entanglement of
atom--photon. The results show that the multiphoton competing
transitions or the large relative coupling strength can lead to the
strong entanglement between atoms and photons. The maximal
atom--photon entanglement can be prepared via the appropriate
selection of system parameters and interaction time.

A new quantum optical mechanism to realize simultaneously negative
electric permittivity and magnetic permeability is suggested. In
order to obtain a negative permeability, we choose a proper atomic
configuration that can dramatically enhance the contribution of the
magnetic-dipole allowed transition via the atomic phase coherence. It
is shown that the atomic system chosen with proper optical parameters
can give rise to striking electromagnetic responses (leading to a
negative refractive index) and that the atomic vapour becomes a
left-handed medium in an optical frequency band. Differing from the
previous schemes of artificial composite metamaterials (based on
classical electromagnetic theory) to achieve the left-handed
materials, which consist of anisotropic millimetre-scale composite
structure units, the left-handed atomic vapour presented here is
isotropic and homogeneous at the atomic-scale level. Such an
advantage may be valuable in realizing the superlens (and hence
perfect image) with left-handed atomic vapour.

We report on the experimental observation of soliton pulses in an
erbium doped fibre ring laser. The passive mode-locking is achieved
using the nonlinear polarization rotation technique. By adjusting the
pump power and the intracavity polarization controllers, a normal
soliton, a stable 8th harmonic mode-locked pulse and a noise-like
pulse have been observed in our laser. The experimental results
revealed that the noise-like pulse is not suitable for the optical
telecommunication, and in order to obtain the stable harmonic
mode-locked soliton, a strong unstable CW laser field is necessary to
mediate global soliton interaction. The formation mechanism of the
harmonic mode-locked pulse has also been analysed.

This paper describes a tunable dual-wavelength Ti:sapphire laser system with
quasi-continuous-wave and high-power outputs. In the design of the laser, it
adopts a frequency-doubled Nd:YAG laser as the pumping source, and the
birefringence filter as the tuning element. Tunable dual-wavelength outputs
with one wavelength range from 700~nm to 756.5~nm, another from 830~nm to 900mn
have been demonstrated. With a pump power of 23~W at 532~nm, a repetition rate
of 7~kHz and a pulse width of 47.6~ns, an output power of 5.1~W at 744.8~nm and
860.9~nm with a pulse width of 13.2~ns and a line width of 3~nm has been
obtained, it indicates an optical-to-optical conversion efficiency of
22.2{\%}.

Polarization switching (PS) dynamics and synchronization
performances of two mutually coupled vertical-cavity
surface-emitting lasers (VCSELs) are studied theoretically in
this paper. A group of dimensionless rate equations is derived
to describe our model. While analysing the PS characteristics,
we focus on the effects of coupling rate and frequency detuning
regarding different mutual injection types. The results indicate
that the x-mode injection defers the occurrence of PS, while
the y-mode injection leads the PS to occur at a lower current.
Strong enough polarization-selective injection can suppress the
PS. Moreover, if frequency detuning is considered, the effects
of polarization-selective mutual injection will be weakened. To
evaluate the synchronization performance, the correlation
coefficients and output dynamics of VCSELs with both pure mode
and mixed mode polarizations are given. It is found that
performance of complete synchronization is sensitive to the
frequency mismatch but it is little affected by mixed mode
polarizations, which is opposite to the case of
injection-locking synchronization.

Temperature dependence of the electron diffusion in metallic targets,
where the electron--electron collision is the dominant process, is
investigated with the help of an extended two-temperature model. In
sharp contrast to the low electron temperature case, where only the
electron---phonon collisions are commonly considered, the electron
diffusion process underlying the high electron temperatures evolves
dramatically different in both temporal and spatial domains.
Calculated results of the ablation yield at different pulse durations
are presented for a copper plate impinged by ultrashort laser pulses
with energy fluences ranging from 0.1 J/cm^{2} to 10 J/cm^{2}.
The excellent agreement between the simulation results and the
experimental data indicates the significant role of
electron--electron collisions in material ablations using intense
ultrashort laser pulses.

A two-dimensional (2D) photonic crystal waveguide in the
\Gamma--K direction with triangular lattice on a
silicon-on-insulator (SOI) substrate in the near-infrared band is
fabricated by the combination of electron beam lithography and
inductively coupled plasma etching. Its transmission characteristics
are analysed from the stimulated band diagram by the effective index
and the 2D plane wave expansion (PWE) methods. In the experiment, the
transmission band edge in a longer wavelength of the photonic crystal
waveguide is about 1590\,nm, which is in good qualitative agreement
with the simulated value. However, there is a disagreement between
the experimental and the simulated results when the wavelength ranges
from 1607 to 1630\,nm, which can be considered as due to the
unpolarized source used in the transmission measurement.

Based on a parabolically tapered multimode interference (MMI) coupler
with a deep-etched SiO_{2}/SiON rib waveguide, a compact wavelength
demultiplexer operating at 1.30 and 1.55\mum wavelengths is
proposed and analysed by using three-dimensional semi-vectorial
finite-difference beam propagation method (3D-SV-FD-BPM). The results
show that a MMI section of 330.0\mum in length, which is only
76% length of a straight MMI coupler, is achieved with the
contrasts of 42.3 and 39.2dB in quasi-TE mode, and 38.4 and 37.8dB in
quasi-TM mode at wavelengths 1.30 and 1.55\mum, respectively, and
the insertion losses below 0.2dB at both wavelengths and in both
polarization states. The alternating direction implicit algorithm
with the Crank--Nicholson scheme is applied to the discretization of
the 3D-SV-FD-BPM formulation along the longitudinal direction.
Moreover, a modified FD scheme is constructed to approximate the
resulting equations along the transverse directions, in which the
discontinuities of the derivatives of magnetic field components
H_{y} and H_{x} along the vertical and horizontal interfaces,
respectively, are involved.

The collision characteristics of the orthogonally
polarized solitons with initial linear frequency chirp
in the linear birefringent fibre for \beta _{2}<0 are numerically
studied. It is found that initial chirp changes the threshold value
of solitons to form the bound-state in the birefringent fibre. The
effect of initial positive chirp on the threshold value is more
obvious than that of negative chirp. In the case of \delta = 0.7
and initial interval 2\tau_{0} = 1.25, the two solitons are mutually
bound for 0.2 \le C \le 1, and they do not form the bound-state for
-1 \le C<0.2. Frequency shifts increase with the increase of chirp
parameter C for -1 \le C<0.2, and have the oscillatory structure
for C \ge 0.2. The effect of positive chirp on temporal FWHM is
greater than that of negative chirp. The peak of temporal waveform
oscillates with the propagation distance. The period and amplitude of
the oscillation for the chirped case are greater than those for the
unchirped case, and they vary with the increase of | C| . The peak
of output temporal waveform can be controlled by changing the initial
chirp.

Nanofluids or liquids with suspended nanoparticles are likely to be
the future heat transfer media, as they exhibit higher thermal
conductivity than those of liquids. It has been proposed that
nanoparticles are apt to congregate and form clusters, and hence the
interaction between nanoparticles becomes important. In this paper,
by taking into account the interaction between nearest-neighbour
inclusions, we adopt the multiple image method to investigate the
effective thermal conductivity of nanofluids. Numerical results show
that then the thermal conductivity ratio between the nanoparticles
and fluids is large, and the two nanoparticles are close up and even
touch, and the point-dipole theory such as Maxwell--Garnett theory
becomes rough as many-body interactions are neglected. Our theoretical
results on the effective thermal conductivity of CuO/water and
Al$_{2}$O$_{3}$/water nanofluids are in good agreement with experimental
data.

An alternative model for the prediction of surface roughness length
is developed. In the model a new factor is introduced to compensate
for the effects of wake diffusion and interactions between the wake
and roughness obstacles. The experiments are carried out by the use
of the hot wire anemometry in the simulated atmospheric boundary
layer in a wind tunnel. Based on the experimental data, a new
expression for the zero-plane displacement height is proposed for
the square arrays of roughness elements, which highlights the
influence of free-stream speed on the roughness length. It appears
that the displacement height increases with the wind speed while the
surface roughness length decreases with Reynolds number increasing.
It is shown that the calculation results based on the new
expressions are in reasonable agreement with the experimental data.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Chen Xi-Meng, Gao Zhi-Min, Liu Zhao-Yuan, Ding Bao-Wei, Lu Yan-Xia, Fu Hong-Bin, Shao Jian-Xiong, Cui Ying, Zhang Hong-Qiang, Liu Yu-Wen, Du Juan, Sun Guang-Zhi

Chin. Phys. B 2007, 16 (7): 02040; doi: 10.1088/1009-1963/16/7/039
Full Text: PDF (330KB) (
447
)

The ratios of transfer ionization (TI) to single-electron
capture (SC) cross sections have been measured for the
collisions of partially stripped C^{q+} ions (q=1--4) with
He. The collision velocity ranges from 0.7 to 4.4v_{0}
(v_{0} is the Bohr velocity). The projectile-ion and
recoil-ion coincidence technique is used to separate the
processes of TI and SC. The ratios reach the maximum when the
velocity is about 3.7v_{0} This can be explained
qualitatively based on the two-step mechanism. The experimental
results are also compared with the results calculated using the
classical trajectory Monte Carlo (CTMC) method. The CTMC results
are in agreement with the experimental data basically. The
discrepancies in higher velocity region are interpreted by the
effective charge effect.

The RF electric field penetration and the power deposition into
planar-type inductively coupled plasmas in low-pressure discharges
have been studied by means of a self-consistent model which consists
of Maxwell equations combined with the kinetic equation of electrons.
The Maxwell equations are solved based on the expansion of the
Fourier--Bessel series for determining the RF electric field.
Numerical results show the influence of a non-Maxwellian electron
energy distribution on the RF electric field penetration and the
power deposition for different coil currents. Moreover, the
two-dimensional spatial profiles of RF electric field and power
density are also shown for different numbers of RF coil turns.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Using transmission electron microscopy and electron diffraction, we
have investigated the microstructure of a
Zr_{55}Al_{10}Ni_{5}Cu_{30} bulk metallic glass under a
uniaxial compression until a failure occurs at room temperature. It
is shown that the amorphous structure has changed locally in the
vicinity of the failure plane after the plastic deformation. An
increase in free volume is observed within the localized areas due to
the concentration of plastic flow, suggesting that the increasing of
local free volume dominates the deformation mechanism of the metallic
glass. The effect of free volume on the `serrated flow' behaviour in
the stress--strain curves during the uniaxial compression is
discussed.

In this paper the crystal structure, electronic structure and
hydrogen site occupation of LaNi_{4.5}Al_{0.5}H_{y} hydride
phase (y=5.0, 6.0) have been investigated by using full-potential
linearized augmented plane wave method. The hydrogen atoms were
found to prefer the 6m, 12o and 12n sites, while no 4h sites were
occupied. A narrowed Ni-d band is found due to the lattice expansion,
the total density of states at E_{F} increases with y, which
indicates that the compounds become less stable. The interaction
between Al and Ni, H plays a dominant role in the stability of
LaNi_{4.5}Al_{0.5}H_{y} hydride phase. The smaller the shift of
E_{F} towards the higher energy region, the more stable the
compounds will be.
The obtained results are compared with experimental data and discussed in the light of
previous works.

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

This paper reports a double helix model of charge transfer in DNA
molecule. The calculated results show that the transmission
characteristics of DNA are not only related to the longitudinal
transfer but also to the helicity of molecule. It finds that there
are four transmission bands centred at 0.92, 3.07, 7.75 and 8.87eV,
also the width and intensity of bands corresponding to the helix
direction are less than that of the longitudinal direction. With the
increase of hopping energy, transmission bands become wide so that
the transmission ability is enhanced.

With the help of nonequilibrium Green's function technique, the
electronic transport through series Aharonov--Bohm (AB)
interferometers is investigated. We obtain the AB interference
pattern of the transition probability characterized by the algebraic
sum \phi and the difference \theta of two magnetic fluxes, and
particularly a general rule of AB oscillation period depending on the
ratio of integer quantum numbers of the fluxes. A parity effect is
observed, showing the asymmetric AB oscillations with respect to the
even and odd quantum numbers of the total flux in antiparallel AB
interferometers. It is also shown that the AB flux can shift the Fano
resonance peaks of the transmission spectrum.

In this paper the quantum transport through an Aharonov--Bohm (AB)
quantum-dot-ring with two dot-array arms described by a single-band
tight-binding Hamiltonian is investigated in the presence of
additional magnetic fields applied to the dot-array arms to produce
spin flip of electrons. A far richer interference pattern than
that in the charge transport alone is found. Besides the usual AB
oscillation the tunable spin polarization of the current by the
magnetic flux is a new observation and is seen to be particularly
useful in technical applications. The spectrum of transmission
probability is modulated by the quantum dot numbers on the up-arc and down-arc
of the ring, which, however, does not affect the period of the AB
oscillation.

This paper reports on N-, mixed-, and Ga-polarity buffer layers are
grown by molecular beam epitaxy (MBE) on sapphire (0001) substrates,
with the GaN thicker films grown on the buffer layer with different
polarity by hydride vapour epitaxy technique (HVPE). The surface
morphology, structural and optical properties of these HVPE-GaN
epilayers are characterized by wet chemical etching, scanning
electron microscope, x-ray diffraction, and photoluminescence
spectrum respectively. It finds that the N-polarity film is unstable
against the higher growth temperature and wet chemical etching, while
that of GaN polarity one is stable. The results indicate that the
crystalline quality of HVPE-GaN epilayers depends on the polarity of
buffer layers.

Using a microcircuit fabricated on a diamond anvil cell, we have measured
in-situ conductivity of HgSe under high pressures, and investigated the
temperature dependence of conductivity under several different pressures. The result
shows that HgSe has a pressure-induced transition sequence from a semimetal
to a semiconductor to a metal, similar to that in HgTe. Several
discontinuous changes in conductivity are observed at around 1.5, 17, 29
and 49GPa, corresponding to the phase transitions from zinc-blende to
cinnabar to rocksalt to orthorhombic to an unknown structure, respectively.
In comparison with HgTe, it is speculated that the unknown structure may be
a distorted CsCl structure. For the cinnabar-HgSe, the energy gap as a
function of pressure is obtained according to the temperature dependence of
conductivity. The plot of the temperature dependence of conductivity
indicates that the unknown structure of HgSe has an electrical property of a
conductor.

We have studied the electric-field-driven motion of a polaron by solving the
time-dependent Schr\"{o}dinger equation nonadiabatically and the lattice
equation of motion simultaneously. It is found that the polaron may
experience two sequent transitions under high fields; one is the
transition from the subsonic to the supersonic state, and the other from the
supersonic to dissociated state. The acoustic mode is decoupled from the
charge when the polaron moves at a speed faster than the sound speed, and
then the optical mode is decoupled at the second transition to make the
polaron dissociate completely.

We investigate the electronic transport properties of the
single-impurity Anderson model. By employing the cluster expansions,
the equations of motion of Green's functions are transformed into
the corresponding equation of motion of connected Green's functions,
which contains the correlation of two conduction electrons beyond
the Lacroix approximation. With the method we show that the
asymmetric line shape of zero bias conductance manifests itself as
the Fano effect, and the Kondo effect is observed in the narrow peak
of differential conductance curve of the system. The Fano and the
Kondo effects can coexist in the single-impurity Anderson model when
the impurity level is adjusted to an appropriate position.

This paper investigates the electronic transport properties in an
Aharonov--Bohm interferometer with a quantum dot coupling to left and
right electrodes. By employing cluster expansions, it transforms the equations of
motion of Green's functions into the corresponding
equation of motion of connected Green's functions, which provides a
natural and uniform truncation scheme. With this method under the
Lacroix's truncation approximation, it shows that the asymmetric line
shape of zero bias conductance manifests itself as the Fano effect,
and the Kondo effect has been observed in the narrow peak of
differential conductance curve of the system. Our numerical results
also show that the building of Fano state suppresses the amplitude
of Kondo resonance.

This paper investigates theoretically the electronic structure and
transport of a two-level quantum dot irradiated under a strong laser
field at low temperatures. Using the method of Keldysh equation of
motion for nonequilibrium Green functions, it examines the
time-averaged density of states and conductance for the system with
photon polarization parallel with and perpendicular to the tunnelling
current direction respectively. It is demonstrated that, by analysing
some numerical examples, more photon sidebands resonance states and
multi- and single-photon transitions are found when diagonal matrix
elements dominate the interaction, while the electronic transitions
due to multiphoton absorption are more or less suppressed when
off-diagonal interaction dominates.

Hot carrier injection (HCI) at high temperatures and different
values of gate bias V_{g} has been performed in order to study
the actions of negative bias temperature instability (NBTI) and hot
carriers. Hot-carrier-stress-induced damage at V_{g}=V_{d}, where V_{d} is the voltage of the transistor drain,
increases as temperature rises, contrary to conventional hot carrier
behaviour, which is identified as being related to the NBTI. A
comparison between the actions of NBTI and hot carriers at low and
high gate voltages shows that the damage behaviours are quite
different: the low gate voltage stress results in an increase in
transconductance, while the NBTI-dominated high gate voltage and
high temperature stress causes a decrease in transconductance. It is
concluded that this can be a major source of hot carrier damage at
elevated temperatures and high gate voltage stressing of p-channel
metal--oxide--semiconductor field-effect transistors (PMOSFETs). We
demonstrate a novel mode of NBTI-enhanced hot carrier degradation in
PMOSFETs. A novel method to decouple the actions of NBTI from that
of hot carriers is also presented.

Silicon-based microelectrodes have been confirmed to be helpful in
neural prostheses. The fabricated 7-channel silicon-based
microelectrode was feasible to be implanted into the brain cortex.
The manufacturing process by micro-electromechanical system (MEMS)
technology was detailed with four photolithographic masks. The
microscopic photographs and SEM images indicated that the probe
shank was 3mm long, 100\mum wide and 20\mu m thick with
the recording sites spaced 120\mu m apart for good signal
isolation. To facilitate the insertion and minimize the trauma, the
microelectrode is narrowed down gradually near the tip with the tip
taper angle of 6 degrees. Curve of the single recording site
impedance versus frequency was shown by test in vitro and the
impedance declined from 150.5k\Omega to 6.0k\Omega with
frequency changing from 10\,k to 10MHz.

In_{0.3} Ga_{0.7}N metal--insulator--semiconductor (MIS) and
metal--semiconductor (MS) surface barrier photodetectors have been
fabricated. The
In_{0.3} Ga_{0.7}N epilayers were grown on sapphire by metalorganic
chemical vapour deposition (MOCVD). The photoresponse and reverse
current--voltage characteristics of the In_{0.3} Ga_{0.7}N MIS and MS
photodetectors were measured. A best zero bias responsivity of 0.18 A/W at
450~nm is obtained for the In_{0.3} Ga_{0.7}N MIS photodetector with
10~nm Si_{3}N_{4} insulator layer, which is more than ten times
higher than the
In_{0.3} Ga_{0.7}N MS photodetector. The reason is attributed to the
decrease of the interface states and increase of surface barrier height
by the inserted insulator. The influence of the thickness of the
Si_{3}N_{4} insulator layer on the photoresponsivity of the MIS
photodetector is also discussed.

The exchange bias of bilayer magnetic films consisting of
ferromagnetic (FM) and antiferromagnetic (AFM) layers in an
uncompensated case is studied by use of the many-body Green's
function method of quantum statistical theory. The effects of
the layer thickness and temperature and the interfacial coupling
strength on the exchange bias H_{E} are investigated. The
dependence of the exchange bias H_{E} on the FM layer
thickness and temperature is qualitatively in agreement with
experimental results. When temperature varies, both the
coercivity H_{C} and H_{E} decrease with the
temperature increasing. For each FM thickness, there exists a
least AFM thickness in which the exchange bias occurs, which is
called pinning thickness.

This paper reports that the intergrowth ceramics
Bi_{5}TiNbWO_{15} (BW-BTN) have been prepared with the
conventional solid-state reaction method. The dielectric and
conductivity properties of samples were studied by using the
dielectric relaxation and AC impedance spectroscopy in detail. Two
distinct relaxation mechanisms were detected both in the plots of
dielectric loss (tan\delta) and the imaginary part ({Z}'') versus
frequency in the frequency range of 10 Hz--13MHz. We attribute the
higher frequency relaxation process to the hopping process of the
oxygen vacancies inside the grains, while the other seems to be
associated with the space charges bound at the grain boundary layers.
The AC impedance spectroscopy indicates that the conductivities at
625K for bulk and grain boundary are about 1.12\times10^{-3}S/m and 1.43\times10^{-3}S/m respectively. The
accumulation of the space charges in the grain boundary layers
induces a space charge potential of 0.52eV.

This paper reports that the blend films of poly
(2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV)
and N,N'-bis(1-ethylpropyl)-3,4: 9,10-perylene bis
(tetracarboxyl diimide) (EP-PDI) with the weight ratio of 1:2.5
have been prepared by spin-coating from chloroform (CF) and
chlorobenzene (CB) solutions respectively. The absorption
spectra and the morphology of the blend films show that large
crystal-like EP-PDI aggregates are formed in film prepared from
CB solution, which corresponds to a new absorption shoulder near
590nm, while there is no shoulder around 590\,nm in the
UV--Vis absorption spectra of the blend film from CF solution.
The electric-field dependence spectra of the photocurrent
generation quantum yield of the film from CB solution shows that
at weak electric field the EP-PDI aggregates act as more
efficient sensitizers, but at strong electric field the quantum
yields become almost invariable over the entire spectral range
no matter what the state of EP-PDI, monomer or aggregate. At
strong electric field, the photocurrent generation yields of
both films from CF and CB solution saturate and their yield
spectra become spectrally similar, mentioning that at strong
electric field the photoexcitons dissociate efficiently and the
free charges are collected by the electrodes almost completely.

8000 CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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