852 research outputs found
Reexamining charmless B\to PV decays in QCD factorization approach
Using the QCD factorization approach, we reexamine the two-body hadronic
charmless -meson decays to final states involving a pseudoscalar~() and a
vector~() meson, with inclusion of the penguin contractions of
spectator-scattering amplitudes induced by the ~(where
or , and denotes an off-shell gluon) transitions, which are
of order . Their impacts on the CP-averaged branching ratios and
CP-violating asymmetries are examined. We find that these higher order penguin
contraction contributions have significant impacts on some specific decay
modes. Since , decays involve the same electro-weak
physics as puzzles, we present a detailed analysis of these decays
and find that the five R-ratios for , system are in
agreement with experimental data except for . Generally, these new
contributions are found to be important for penguin-dominated decays.Comment: 45 pages, 12 figures. Theoretical uncertainties considered. Gauge
invariance proved. Version to appear in PR
Electron transport through Al-ZnO-Al: an {\it ab initio} calculation
The electron transport properties of ZnO nano-wires coupled by two aluminium
electrodes were studied by {\it ab initio} method based on non-equilibrium
Green's function approach and density functional theory. A clearly rectifying
current-voltage characteristics was observed. It was found that the contact
interfaces between Al-O and Al-Zn play important roles in the charge transport
at low bias voltage and give very asymmetric I-V characteristics. When the bias
voltage increases, the negative differential resistance occurs at negative bias
voltage. The charge accumulation was calculated and its behavior was found to
be well correlated with the I-V characteristics. We have also calculated the
electrochemical capacitance which exhibits three plateaus at different bias
voltages which may have potential device application.Comment: 10 pages, 6 figure
Dissipative dynamics in a tunable Rabi dimer with periodic harmonic driving
Recent progress on qubit manipulation allows application of periodic driving
signals on qubits. In this study, a harmonic driving field is added to a Rabi
dimer to engineer photon and qubit dynamics in a circuit quantum
electrodynamics device. To model environmental effects, qubits in the Rabi
dimer are coupled to a phonon bath with a sub-Ohmic spectral density. A
non-perturbative treatment, the Dirac-Frenkel time-dependent variational
principle together with the multiple Davydov D {\it Ansatz} is employed to
explore the dynamical behavior of the tunable Rabi dimer. In the absence of the
phonon bath, the amplitude damping of the photon number oscillation is greatly
suppressed by the driving field, and photons can be created thanks to
resonances between the periodic driving field and the photon frequency. In the
presence of the phonon bath, one still can change the photon numbers in two
resonators, and indirectly alter the photon imbalance in the Rabi dimer by
directly varying the driving signal in one qubit. It is shown that qubit states
can be manipulated directly by the harmonic driving. The environment is found
to strengthen the interqubit asymmetry induced by the external driving, opening
up a new venue to engineer the qubit states
Engineering Photon Delocalization in a Rabi Dimer with a Dissipative Bath
A Rabi dimer is used to model a recently reported circuit quantum
electrodynamics system composed of two coupled transmission-line resonators
with each coupled to one qubit. In this study, a phonon bath is adopted to
mimic the multimode micromechanical resonators and is coupled to the qubits in
the Rabi dimer. The dynamical behavior of the composite system is studied by
the Dirac-Frenkel time-dependent variational principle combined with the
multiple Davydov D ans\"{a}tze. Initially all the photons are pumped into
the left resonator, and the two qubits are in the down state coupled with the
phonon vacuum. In the strong qubit-photon coupling regime, the photon dynamics
can be engineered by tuning the qubit-bath coupling strength and
photon delocalization is achieved by increasing . In the absence of
dissipation, photons are localized in the initial resonator. Nevertheless, with
moderate qubit-bath coupling, photons are delocalized with quasiequilibration
of the photon population in two resonators at long times. In this case, high
frequency bath modes are activated by interacting with depolarized qubits. For
strong dissipation, photon delocalization is achieved via frequent
photon-hopping within two resonators and the qubits are suppressed in their
initial down state.Comment: 11 pages, 11 figure
A Monitoring System Design in Transmission Lines based on Wireless Sensor Networks
AbstractA smart grid application in monitoring the condition of transmission line with wireless sensor networks was described in this paper. ZigBee and GPRS (General Packet Radio Service) technology were adopted in this system to ensure normal transmission of signals, even in remote areas where there is no telecommunication service, and data could be transmitted over a long distance. In addition, the system provided warnings before the damage caused by meteorological disasters to ensure the line security
Reexamination of the resonance contributions in B->X_s e^+ e^-
With help of the recent developments in the heavy quarkonium physics, we
reexamine the long distance(LD) effects in \Bsee dominantly from the charmonium
resonances and through the decay chains B\ra X_s
J/\Psi (\Psi^{\prime}) \ra X_s e^+ e^-. We find that the resonance to
nonresonance interference are reduced substantially.Comment: Revtex file,11 pages,1 figures,Phys.Lett.B in pres
Design Space Exploration of Neural Network Activation Function Circuits
The widespread application of artificial neural networks has prompted
researchers to experiment with FPGA and customized ASIC designs to speed up
their computation. These implementation efforts have generally focused on
weight multiplication and signal summation operations, and less on activation
functions used in these applications. Yet, efficient hardware implementations
of nonlinear activation functions like Exponential Linear Units (ELU), Scaled
Exponential Linear Units (SELU), and Hyperbolic Tangent (tanh), are central to
designing effective neural network accelerators, since these functions require
lots of resources. In this paper, we explore efficient hardware implementations
of activation functions using purely combinational circuits, with a focus on
two widely used nonlinear activation functions, i.e., SELU and tanh. Our
experiments demonstrate that neural networks are generally insensitive to the
precision of the activation function. The results also prove that the proposed
combinational circuit-based approach is very efficient in terms of speed and
area, with negligible accuracy loss on the MNIST, CIFAR-10 and IMAGENET
benchmarks. Synopsys Design Compiler synthesis results show that circuit
designs for tanh and SELU can save between 3.13-7.69 and 4.45-8:45 area
compared to the LUT/memory-based implementations, and can operate at 5.14GHz
and 4.52GHz using the 28nm SVT library, respectively. The implementation is
available at: https://github.com/ThomasMrY/ActivationFunctionDemo.Comment: 5 pages, 5 figures, 16 conferenc
Analysing Railway Safety with Systems Thinking
Railway system is a socio-technical system because the operation of such system also
heavily relies on the management of human activities and operating procedures in the organisation, as well as the execution of technical subsystems. Safety of these systems therefore is more than just about engineering their technical subsystems. The latest approach from systems engineering considers that an accident is due to inadequate controlled interactions in the system and is usually a dynamic event chain started from the activation of a hazard and culminated in a complex process of sequential and concurrent events until the system is eventually out of control. Meanwhile the analysis of these systems’s safety becomes much harder when simply applying the traditional techniques of safety assessment. It is because, first of all, a social-technical system consists of a lot of complex and
non-linear interactions, traditional techniques show their limits when analysing complex systems. And secondly, the safety of a social-technical system requires a system perspective, which should take all the behaviours (desired and undesired but predicted) of a system as a whole in the context of its environment. To capture the information needed, the models for these analyses (i.e., fault tree and FMEA table) will become too complex to have a systemic view of each individual causal factor. In this paper, we proposed an approach based on system thinking and system dynamics to analyse the safety of a social-technical system. The case study of a tram accident is simple enough for the purpose of demonstrating its feasibility and benefits. The comparison with fault tree analysis was conducted, but it was not for the evaluation of our approach. The real evaluation comes from the extensive
applications in real world
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