Thresholdless dressed-atom laser in a photonic band-gap material

We demonstrate the capability of complete thresholdless lasing operation between dressed states of a two-level atom located inside a microscopic cavity engineered in a photonic band-gap material. We distinguish between threshold and thresholdless behaves by analyzing the Mandel's Q parameter for the cavity field. We find that the threshold behave depends on whether the spontaneous emission is or is not present on the lasing transition. In the presence of the spontaneous emission, the mean photon number of the cavity field exhibits threshold behavior indicating that the system may operate as an ordinary laser. When the spontaneous emission is eliminated on the lasing transition, no threshold is observed for all values of the pumping rate indicating the system becomes a thresholdless laser. Moreover, we find that under a thresholdless operation, the mean photon number can increase nonlinearly with the pumping rate, and this process is accompanied by a sub-Poisson statistics of the field. This suggests that the nonclassical statistics can be used to distinguish a nonlinear operation of the dressed-atom laser.Comment: 6 pages 4 figure

The suction effect during freak wave slamming on a fixed platform deck: Smoothed particle hydrodynamics simulation and experimental study

During the process of wave slamming on a structure with sharp corners, the wave receding after wave impingement can induce strong negative pressure (relative to the atmospheric pressure) at the bottom of the structure, which is called the suction effect. From the practical point of view, the suction force induced by the negative pressure, coinciding with the gravity force, pulls the structure down and hence increases the risk of structural damage. In this work, the smoothed particle hydrodynamics (SPH) method, more specifically the δ+SPH model, is adopted to simulate the freak wave slamming on a fixed platform with the consideration of the suction effect, i.e., negative pressure, which is a challenging issue because it can cause the so-called tensile instability in SPH simulations. The key to overcome the numerical issue is to use a numerical technique named tensile instability control (TIC). Comparative studies using SPH models with and without TIC will show the importance of this technique in capturing the negative pressure. It is also found that using a two-phase simulation that takes the air phase into account is essential for an SPH model to accurately predict the impact pressure during the initial slamming stage. The freak wave impacts with different water depths are studied. All the multiphase SPH results are validated by our experimental data. The wave kinematics/dynamics and wave impact features in the wave-structure interacting process are discussed, and the mechanism of the suction effect characterized by the negative pressure is carefully analyzed

MobiFuzzyTrust: An efficient fuzzy trust inference mechanism in mobile social networks

PublishedJournal Article© 2014 IEEE. Mobile social networks (MSNs) facilitate connections between mobile users and allow them to find other potential users who have similar interests through mobile devices, communicate with them, and benefit from their information. As MSNs are distributed public virtual social spaces, the available information may not be trustworthy to all. Therefore, mobile users are often at risk since they may not have any prior knowledge about others who are socially connected. To address this problem, trust inference plays a critical role for establishing social links between mobile users in MSNs. Taking into account the nonsemantical representation of trust between users of the existing trust models in social networks, this paper proposes a new fuzzy inference mechanism, namely MobiFuzzyTrust, for inferring trust semantically from one mobile user to another that may not be directly connected in the trust graph of MSNs. First, a mobile context including an intersection of prestige of users, location, time, and social context is constructed. Second, a mobile context aware trust model is devised to evaluate the trust value between two mobile users efficiently. Finally, the fuzzy linguistic technique is used to express the trust between two mobile users and enhance the human's understanding of trust. Real-world mobile dataset is adopted to evaluate the performance of the MobiFuzzyTrust inference mechanism. The experimental results demonstrate that MobiFuzzyTrust can efficiently infer trust with a high precision.This work was partly supported by the National Nature Science Foundation of China under grant 61201219 and the EU FP7 CLIMBER project under Grant Agreement No. PIRSES-GA-2012-318939

Improved lattice QCD with quarks: the 2 dimensional case

QCD in two dimensions is investigated using the improved fermionic lattice Hamiltonian proposed by Luo, Chen, Xu, and Jiang. We show that the improved theory leads to a significant reduction of the finite lattice spacing errors. The quark condensate and the mass of lightest quark and anti-quark bound state in the strong coupling phase (different from t'Hooft phase) are computed. We find agreement between our results and the analytical ones in the continuum.Comment: LaTeX file (including text + 10 figures

Evolutionary Consequences of Dusty Tori in Active Galactic Nuclei

Deep surveys of {\em Chandra} and {\em HST} (Hubble Space Telescope) show that active galactic nucleus (AGN) populations are changing with hard X-ray luminosities. This arises an interesting question whether the dusty torus is evolving with the central engines. We assemble a sample of 50 radio-quiet PG quasars to tackle this problem. The covering factors of the dusty tori can be estimated from the multiwavelength continuum. We find they are strongly correlated with the hard X-ray luminosity. Interestingly this correlation agrees with the fraction of type II AGNs discovered by {\em Chandra} and {\em HST}, implying strong evidence for that the AGN population changing results from the evolution of the tori. We also find that the frequencies of the dips around 1$\mu$m in the continuum correlate with the covering factors in the present sample, indicating the dip frequencies are adjusted by the covering factors. In the scenario of fueling black hole from the torus, the covering factor is a good and the dip frequency is a potential indicator of the torus evolution.Comment: 4 pages in emulateapj5.sty. Accepted by ApJ Letter

High quality electron beam acceleration by ionization injection in laser wakefields with mid-infrared dual-color lasers

For the laser wakefield acceleration, suppression of beam energy spread while keeping sufficient charge is one of the key challenges. In order to achieve this, we propose bichromatic laser ionization injection with combined laser wavelengths of 2.4 μ m and 0.8 μ m for wakefield excitation and triggering electron injection via field ionization, respectively. A laser pulse at 2.4 μ m wavelength enables one to drive an intense acceleration structure with a relatively low laser power. To further reduce the requirement of laser power, we also propose to use carbon dioxide as the working gas medium, where carbon acts as the injection element. Our three dimensional particle-in-cell simulations show that electron beams at the GeV energy level with both low energy spreads (around 1%) and high charges (several tens of picocoulomb) can be obtained by the use of this scheme with laser peak power totaling sub-100 TW

Bi-ferroic memristive properties of multiferroic tunnel junctions

The giant tunnelling electroresistance (TER) and memristive behaviours of ferroelectric tunnel junctions make them promising candidates for future information storage technology. Using conducting ferromagnetic layers as electrodes results in multiferroic tunnel junctions (MFTJs) which show spin dependent transport. The tunnelling magnetoresistance (TMR) of such structures can be reversibly controlled by electric pulsing owing to ferroelectric polarisation-dependent spin polarisation at the ferroelectric/ferromagnetic interface. Here, we show multilevel electric control of both TMR and TER of MFTJs, which indicates the bi-ferroic or magneto-electric memristive properties. This effect is realised by manipulating the ferroelectric domain configuration via non-volatile partial ferroelectric switching obtained by applying low voltage pulses to the junction. Through electrically modulating the ratio between up- and down-polarised ferroelectric domains, a broad range of TMR (between ∼3% and ∼30%) and TER (∼1000%) values can be achieved. The multilevel control of TMR and TER using the electric pulse tunable ferroelectric domain configuration suggests a viable way to obtain multiple state memory

Federated Learning for Distributed IIoT Intrusion Detection Using Transfer Approaches

This is the author accepted manuscript. the final version is available from IEEE via the DOI in this recordConsidering that low-cost and resource-cons- trained sensors coupled inherently could be vulnerable to growing numbers of intrusion threats, industrial Internet-of-Things (IIoT) systems are faced with severe security concerns. Data sharing for building high-performance intrusion detection models is also prohibited due to the sensitivity, privacy, and high value of IIoT data. This article presents an anomaly-based intrusion detection system with federated learning for privacy-preserving machine learning in future IIoT networks. To tackle the urgent issue of training local models with non-independent and identically distributed (non-IID) data, we adopt instance-based transfer learning at local. Furthermore, to boost the performance of this system for IIoT intrusion detection, we propose a rank aggregation algorithm with a weighted voting approach. The proposed system achieves superior detection performance with 95.97% and 73.70% accuracy for AdaBoost and Random Forest, respectively, outperforming the baseline models by 12.72% and 14.8%.China Scholarship CouncilEngineering and Physical Sciences Research Council (EPSRC)European Union Horizon 202

An interpretation of fluctuations in enzyme catalysis rate, spectral diffusion, and radiative component of lifetimes in terms of electric field fluctuations

Time-dependent fluctuations in the catalysis rate ({delta}k(t)) observed in single-enzyme experiments were found in a particular study to have an autocorrelation function decaying on the same time scale as that of spectral diffusion {delta}{omega}0(t). To interpret this similarity, the present analysis focuses on a factor in enzyme catalysis, the local electrostatic interaction energy (E) at the active site and its effect on the activation free energy barrier. We consider the slow fluctuations of the electrostatic interaction energy ({delta}E(t)) as a contributor to {delta}k(t) and relate the latter to {delta}{omega}0(t). The resulting relation between {delta}k(t) and {delta}{omega}0(t) is a dynamic analog of the solvatochromism used in interpreting solvent effects on organic reaction rates. The effect of the postulated {delta}E(t) on fluctuations in the radiative component ({delta}{gamma}Formula(t)) of the fluorescence decay of chromophores in proteins also is examined, and a relation between {delta}{gamma}Formula(t) and {delta}{omega}0(t) is obtained. Experimental tests will determine whether the correlation functions for {delta}k(t), {delta}{omega}0(t), and {delta}{gamma}Formula are indeed similar for any enzyme. Measurements of dielectric dispersion, {varepsilon}({omega}), for the enzyme discussed elsewhere will provide further insight into the correlation function for {delta}E(t). They also will determine whether fluctuations in the nonradiative component {gamma}Formula of the lifetime decay has a different origin, fluctuations in distance for example

The Calculation of the Perturbative Expansion of Wilson Loops on Lattice

We introduce an approach to expand gauge-invariant Wilson operators on lattice. This approach is based on non-abelian Stokes theorem and overcomes some shortage of some former methods. It is also suitable for expanding any Wilson operators on lattice.Comment: 9 pages and 4 figure