34,737 research outputs found
Towards a Systematic Framework for the Modelling of the Allocation of Carbon Dioxide Emission Quotas in China
The needs for effectively controlling carbon dioxide emissions and properly allocating carbon dioxide emission permits or allowances in China have never been so great. In this paper, a systematic multi-agent-based framework for the modelling and analysis of the allocation of carbon dioxide emission quotas in China is proposed. A carbon trading market model as the core of the activities of allocation management is constructed and discussed. In addition, examples of the modelling and simulation work are presented
Economical quantum cloning in any dimension
The possibility of cloning a d-dimensional quantum system without an ancilla
is explored, extending on the economical phase-covariant cloning machine found
in [Phys. Rev. A {\bf 60}, 2764 (1999)] for qubits. We prove the impossibility
of constructing an economical version of the optimal universal cloning machine
in any dimension. We also show, using an ansatz on the generic form of cloning
machines, that the d-dimensional phase-covariant cloner, which optimally clones
all uniform superpositions, can be realized economically only in dimension d=2.
The used ansatz is supported by numerical evidence up to d=7. An economical
phase-covariant cloner can nevertheless be constructed for d>2, albeit with a
lower fidelity than that of the optimal cloner requiring an ancilla. Finally,
using again an ansatz on cloning machines, we show that an economical version
of the Fourier-covariant cloner, which optimally clones the computational basis
and its Fourier transform, is also possible only in dimension d=2.Comment: 8 pages RevTe
Effect of intensive melt shearing on the formation of Fe-containing intermetallics in LM24 Al-alloy
Fe is one of the inevitable and detrimental impurities in aluminium alloys that degrade the mechanical performance of castings. In the present work, intensive melt shearing has been demonstrated to modify the morphology of Fe-containing intermetallic compounds by promoting the formation of compact α-Al(Fe,Mn)Si at the expense of needle-shaped ÎČ-AlFeSi, leading to an improved mechanical properties of LM24 alloy processed by MC-HPDC process. The promotion of the formation of α -Al(Fe, Mn)Si phase is resulted from the enhanced nucleation on the well dispersed MgAl 2O 4 particles in the melt. The Fe tolerance of LM24 alloy can be effectively improved by combining Mn alloying and intensive melt shearing
Counting statistics of tunneling through a single molecule: effect of distortion and displacement of vibrational potential surface
We analyze the effects of a distortion of the nuclear potential of a
molecular quantum dot (QD), as well as a shift of its equilibrium position, on
nonequilibrium-vibration-assisted tunneling through the QD with a single level
() coupled to the vibrational mode. For this purpose, we derive an
explicit analytical expression for the Franck-Condon (FC) factor for a
displaced-distorted oscillator surface of the molecule and establish rate
equations in the joint electron-phonon representation to examine the
current-voltage characteristics and zero-frequency shot noise, and skewness as
well. Our numerical analyses shows that the distortion has two important
effects. The first one is that it breaks the symmetry between the excitation
spectra of the charge states, leading to asymmetric tunneling properties with
respect to and . Secondly, distortion (frequency
change of the oscillator) significantly changes the voltage-activated cascaded
transition mechanism, and consequently gives rise to a different nonequilibrium
vibrational distribution from that of the case without distortion. Taken in
conjunction with strongly modified FC factors due to distortion, this results
in some new transport features: the appearance of strong NDC even for a
single-level QD with symmetric tunnel couplings; a giant Fano factor even for a
molecule with an extremely weak electron-phonon interaction; and enhanced
skewness that can have a large negative value under certain conditions.Comment: 29 pages, 11 figures, published versio
Formation of Long Single Quantum Dots in High Quality InSb Nanowires Grown by Molecular Beam Epitaxy
We report on realization and transport spectroscopy study of single quantum
dots (QDs) made from InSb nanowires grown by molecular beam epitaxy (MBE). The
nanowires employed are 50-80 nm in diameter and the QDs are defined in the
nanowires between the source and drain contacts on a Si/SiO substrate. We
show that highly tunable QD devices can be realized with the MBE-grown InSb
nanowires and the gate-to-dot capacitance extracted in the many-electron
regimes is scaled linearly with the longitudinal dot size, demonstrating that
the devices are of single InSb nanowire QDs even with a longitudinal size of
~700 nm. In the few-electron regime, the quantum levels in the QDs are resolved
and the Land\'e g-factors extracted for the quantum levels from the
magnetotransport measurements are found to be strongly level-dependent and
fluctuated in a range of 18-48. A spin-orbit coupling strength is extracted
from the magnetic field evolutions of a ground state and its neighboring
excited state in an InSb nanowire QD and is on the order of ~300 eV. Our
results establish that the MBE-grown InSb nanowires are of high crystal quality
and are promising for the use in constructing novel quantum devices, such as
entangled spin qubits, one-dimensional Wigner crystals and topological quantum
computing devices.Comment: 19 pages, 5 figure
Modeling GRB 050904: Autopsy of a Massive Stellar Explosion at z=6.29
GRB 050904 at redshift z=6.29, discovered and observed by Swift and with
spectroscopic redshift from the Subaru telescope, is the first gamma-ray burst
to be identified from beyond the epoch of reionization. Since the progenitors
of long gamma-ray bursts have been identified as massive stars, this event
offers a unique opportunity to investigate star formation environments at this
epoch. Apart from its record redshift, the burst is remarkable in two respects:
first, it exhibits fast-evolving X-ray and optical flares that peak
simultaneously at t~470 s in the observer frame, and may thus originate in the
same emission region; and second, its afterglow exhibits an accelerated decay
in the near-infrared (NIR) from t~10^4 s to t~3 10^4 s after the burst,
coincident with repeated and energetic X-ray flaring activity. We make a
complete analysis of available X-ray, NIR, and radio observations, utilizing
afterglow models that incorporate a range of physical effects not previously
considered for this or any other GRB afterglow, and quantifying our model
uncertainties in detail via Markov Chain Monte Carlo analysis. In the process,
we explore the possibility that the early optical and X-ray flare is due to
synchrotron and inverse Compton emission from the reverse shock regions of the
outflow. We suggest that the period of accelerated decay in the NIR may be due
to suppression of synchrotron radiation by inverse Compton interaction of X-ray
flare photons with electrons in the forward shock; a subsequent interval of
slow decay would then be due to a progressive decline in this suppression. The
range of acceptable models demonstrates that the kinetic energy and circumburst
density of GRB 050904 are well above the typical values found for low-redshift
GRBs.Comment: 45 pages, 7 figures, and ApJ accepted. Revised version, minor
modifications and 1 extra figur
Overcoming the Circular Problem for \gamma-ray Bursts in Cosmological Global Fitting Analysis
Due to the lack of low redshift long Gamma-Ray Bursts (GRBs), the circular
problem has been a severe obstacle for using GRBs as cosmological candles. In
this paper, we present a new method to deal with such a problem in MCMC global
fitting analysis. Assuming that a certain type of correlations between
different observables exists in a subsample of GRBs, for the parameters
involved in the correlation relation, we treat them as free parameters and
determine them simultaneously with cosmological parameters through MCMC
analysis on GRB data together with other observational data. Then the circular
problem is naturally eliminated in this procedure. We take the Ghirlanda
relation as an example while keeping in mind the debate about its physical
validity. Together with SNe Ia, WMAP and SDSS data, we include 27 GRBs with the
reported Ghirlanda relation in our study, and perform MCMC global fitting. We
consider the CDM model and dynamical dark energy models. In each case,
in addition to the constraints on the relevant cosmological parameters, we
obtain the best fit values as well as the distributions of the correlation
parameters and . We find that the observational data sets other than
GRBs can affect and considerably through their degeneracies with the
cosmological parameters. The results on and for different cosmological
models are in well agreement within range. The best fit value of
in all models being analyzed is with . For ,
we have the best value in the range of with . It is
also noted that the distributions of and are generally broader than the
priors used in many studies in literature. (Abriged)Comment: 9 pages, 2 figures, 2 tables, Accepted for publication in Ap
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