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We present a scheme to realize a special quantum cloning machine via input-output cavities. The cloning machine can copy information from one atom to another distant atom. Choosing different parameters, the method can perform optimal symmetric (asymmetric) universal quantum cloning and optimal symmetric (asymmetric) phasecovariant cloning. Compared to previous schemes, our scheme is more insensitive to actual environmental noise and can get higher fidelity in a current cavity quantum electrodynamics system with an entangled state acting as a quantum channel than a single-photon pulse. [ABSTRACT FROM AUTHOR]

The great difference in dynamical range between small-scale accretion disk simulations and large-scale or cosmological simulations creates difficulties in tracking the disk wind kinematics. In the first paper of this series, we studied the dynamics of hydrodynamic winds from the outer edge of the accretion disk toward galactic scales. In this paper, we further incorporate magnetic fields by employing a one-dimensional magnetohydrodynamic model, with fiducial boundary conditions set for hot accretion flows. The wind solution is achieved through requiring gas to pass smoothly through the slow, Alfvén, and fast magnetosonic points. Beyond the fast magnetosonic point, physical quantities are found to show power-law dependences with cylindrical radius R, i.e., and . The magnetization of wind is dominant in determining the wind properties. The wind is accelerated to greater terminal velocities with stronger magnetizations. The fiducial parameters result in a terminal velocity of about 0.016c. The dependence of the wind physical quantities on temperature, field line angular velocity, and adiabatic index is also discussed. [ABSTRACT FROM AUTHOR]

In a hot accretion flow, the radiation from the innermost region of the flow propagates outward and heats the electrons at large radii via Compton scattering. It has been shown in previous works that if the radiation is strong enough, L ≳ 2%LEdd, the electrons at the Bondi radius (rB ~ 105rs) will be heated to above the virial temperature; thus, the accretion will be stopped. The accretion will recover after the gas cools down. This results in the oscillation of the black hole activity. In this paper, we show that this mechanism is the origin of the intermittent activity of some compact young radio sources. Such intermittency is required to explain the population of these sources. We calculate the timescales of the black hole oscillation and find that the durations of active and inactive phases are 3 x 104 (0.1/α)(M/108 M⊙)(L/2%LEdd)-1/2 yr and 105 (α/0.1)(M/108 M⊙)yr, respectively, consistent with those required to explain observations. Such feedback occurring at the parsec scale should be common in low-luminosity active galactic nuclei and should be considered when we consider their matter and energy output. [ABSTRACT FROM AUTHOR]

The influence of fluoride on the anodic dissolution kinetics of titanium was studied by several electrochemical techniques at steady-state open-circuit potentials in 1.0 M HCIO4 containing fluoride with various concentrations ranging from 0 to 0.1 M. The promoting effect of fluoride (especially when [F-] >1 X 10-3 M) on the anodic dissolution behavior of titanium was characterized and discussed by taking into account the changes in the estimated electrochemical and kinetic parameters. The faradaic impedance for the anodic dissolution of titanium was analyzed both by fitting based on an equivalent electrical circuit model and by theoretical derivation based on a two-step mechanism involving one adsorbed intermediate species. By correlating the faradaic impedance expression derived from the dissolution mechanism with that deduced from the equivalent electrical circuit model, some important kinetic parameters (such as the apparent rate constants K1 and K2 and the surface coverage θss) could be estimated from the equivalent circuit elemental parameters (such as Rct, and Ca). The charge-transfer reaction was the rate-determining step at lower fluoride concentrations of [F-] ⩽ 1 X 10-3 M, leading to a high surface coverage of θss ≈ 1, while the chemical dissolution reaction is the rate-determining step at higher fluoride concentrations of [F-] > 1 X 10-3 M, leading to a decreased surface coverage of θss < 0.5. [ABSTRACT FROM AUTHOR]

We study the formation mechanism and microstructure of nickel (Ni) atomic aggregates on the silicone oil surfaces by atomic force microscopy (AFM). Initially, the deposited atoms nucleate and form the compact clusters on the liquid surfaces. Then they perform Brownian motion and adhere upon impact. Finally the branched aggregates are formed. The Ni aggregates exhibit granular structure. The mean size of the granularities in the aggregates is of the order of 10 nm and it decreases with the nominal film thickness. The experiment shows that the Ni aggregates perform a directional diffusion towards the sample edge. The interpretation for this phenomenon is presented. [ABSTRACT FROM AUTHOR]

The catalyst layer (CL) in the polymer electrolyte membrane fuel cell (PEMFC) has not been explored in detail due to its complexities and difficulties associated with accessing it. It is important to understand water ingress and egress at the CL as it offers potential for water management by manipulating the evaporation rate. A technique for in situ visual characterization of the CL is presented. This is accomplished by designing and fabricating a catalyst-visible operational fuel cell and developing a microvisualization system. The dynamics of microdroplets on the CL surface (including formation, growth, coalescence, and removal) were visualized in an operating PEMFC. The liquid water behavior at the interface of the CL and the gas diffusion layer (GDL) were shown to promote the periodic droplet reemergence on the GDL surface in the flow channels. Mechanisms of water condensation and transport within the CL pores are discussed with respect to pore architecture and wetting properties. It has been shown that reduction of pore size and CL thickness alleviates flooding therein and promotes better catalyst utilization. Evaporation was identified as one of the distinguishing mechanisms of the CL, and one of the future challenges will be to control this mechanism. The experimental results should prove useful in clarifying the role of the CL in water management, and in refining models used to optimize PEMFC performance. [ABSTRACT FROM AUTHOR]

Depending on the value of the accretion rate, black hole accretion is divided into cold and hot modes. The two modes have distinctly different physics and correspond to two feedback modes. Most previous feedback works focus only on one mode, or the accretion physics is not always properly adopted. Here, by performing hydrodynamical numerical simulations of active galactic nucleus (AGN) feedback in an elliptical galaxy, we show that including both is important, and gives different results from including just one or the other. We specifically focus on the wind and radiation (but neglecting the jet) feedback in the hot mode, to explore whether this particular mode of feedback can play any important feedback role. For this aim, we have run two test models. In one model, we always adopt the cold mode no matter what value the accretion rate is; in another model, we turn off the AGN once it enters into the hot mode. We have calculated the AGN light curves, black hole growth, star formation, and AGN energy duty cycle; and compared the results with the model in which the two modes are correctly included. Important differences are found. For example, if we were to adopt only the cold mode, the total mass of newly formed stars would become two orders of magnitude smaller, and the fraction of energy ejected within the high accretion regime (i.e., LBH > 2%LEdd) would be too small to be consistent with observations. We have also investigated the respective roles of wind and radiation in the hot mode. [ABSTRACT FROM AUTHOR]

The growth of solids from submicron to millimeter and centimeter sizes is the early step toward the formation of planets inside protoplanetary disks (PPDs). However, such processes and their potential impact on the later stages of solid growth are still poorly understood. In this work, we test the hypothesis that most disks contain at least one ringed structure with a relatively small radius. We have carried out a large family of 1D two-fluid (gas+dust) hydrodynamical simulations by evolving the gas and dust motion self-consistently while allowing dust size to evolve via coagulation and fragmentation. We investigate the joint effects of ringed structures and dust size growth on the overall submillimeter and millimeter flux and spectral index of PPDs. Ringed structures slow down the dust radial drift and speed up the dust growth. In particular, we find that those unresolved disks with a high fragmentation velocity (∼10 m s−1) and a high dust surface density (∼10 g cm−2 in the ring) can have millimeter spectral indices as low as ∼2.0, consistent with millimeter observations of faint disks in nearby star-forming regions. Furthermore, disks with more than one ringed structure can potentially reproduce brighter disks with spectral indices lower than ∼2.5. Future multiwavelength high-resolution observations of these low-spectral-index sources can be used to test the existence of the ringed structures in the unresolved disks and differentiate the effects of dust size growth from optical depth. [ABSTRACT FROM AUTHOR]

Based on our previous modeling of active galactic nucleus (AGN) feedback in isolated elliptical galaxies using the MACER (Massive AGN Controlled Ellipticals Resolved) code, we extend and improve the model to include rotation, to facilitate angular momentum transfer via the Toomre instability in gaseous disks, to limit the star formation to regions of high density and low temperature, and to improve the treatment of hot-mode (low accretion rate) AGN feedback. The model galaxy now has an extended dark matter profile that matches with standard observations, but it has a resolution of parsecs in the inner region and resolves the Bondi radius. We find that the results agree reasonably well with a panoply of observations: (1) Both AGN activity and star formation are primarily in central cold gaseous disks, are bursty, and are mainly driven by the Toomre instability. (2) The AGN duty cycle agrees well with the Soltan argument, i.e., the AGN spends most of its lifetime when it is in low luminosity (half of the time with ), while emitting most of its energy when it is in high luminosity (half of radiant energy emitted with L/LEdd > 0.06). (3) The total star formation is roughly a few percent of the initial stellar mass, occurring in the bursts that would be associated with the observed E+A phenomenon. Most of the star formation occurs in a circumnuclear disk of size ≤1 kpc, which is in agreement with recent observations. (4) The interstellar medium X-ray luminosity varies within a reasonable range (median erg s−1), in agreement with observations. [ABSTRACT FROM AUTHOR]

We report the analysis of simultaneous XMM-Newton+Nuclear Spectroscopic Telescope Array (NuSTAR) observations of two low-luminosity active galactic nuclei (LLAGNs), NGC 3998 and NGC 4579. We do not detect any significant variability in either source over the ∼3 day length of the NuSTAR observations. The broadband 0.5–60 keV spectrum of NGC 3998 is best fit with a cutoff power law, while the one for NGC 4579 is best fit with a combination of a hot thermal plasma model, a power law, and a blend of Gaussians to fit an Fe complex observed between 6 and 7 keV. Our main spectral results are the following: (1) neither source shows any reflection hump with 3σ reflection fraction upper limits of and for NGC 3998 and NGC 4579, respectively; (2) the 6–7 keV line complex in NGC 4579 could be fit with either a narrow Fe K line at 6.4 keV and a moderately broad Fe xxv line or with three relatively narrow lines, which include contribution from Fe xxvi; (3) the NGC 4579 flux is 60% brighter than previously detected with XMM-Newton, accompanied by a hardening in the spectrum; (4) we measure a cutoff energy keV in NGC 3998, which represents the lowest and best constrained high-energy cutoff ever measured for an LLAGN; (5) the NGC 3998 spectrum is consistent with a Comptonization model with either a sphere (τ ≈ 3 ± 1) or slab (τ ≈ 1.2 ± 0.6) geometry, corresponding to plasma temperatures between 20 and 150 keV. We discuss these results in the context of hard X-ray emission from bright AGNs, other LLAGNs, and hot accretion flow models. [ABSTRACT FROM AUTHOR]

Winds from black hole accretion flows are ubiquitous. Previous works mainly focus on the launching of wind on the accretion flow scale. It still remains unclear how far the winds can propagate outward and what their large-scale dynamics is. As the first paper of this series, we study the large-scale dynamics of thermal wind beyond accretion scales via analytical and numerical methods. Boundary conditions, which are crucial to our problem, are analyzed and presented based on small-scale simulations combined with observations of winds. Both black hole and galaxy potential are taken into account. For winds originating from hot accretion flows, we find that the wind can reach large scales. The radial profiles of velocity, density, and temperature can be approximated by and , where vr0, ρ0, and T0 are the velocity, density, and temperature of winds at the boundary , and γ is the polytropic index. During the outward propagation, the enthalpy and rotational energy compensate for the increase of gravitational potential. For thin disks, we find that because the Bernoulli parameter is smaller, winds cannot propagate as far as the hot winds, but stop at a certain radius where the Bernoulli parameter is equal to the potential energy. Before the winds stop, the profiles of dynamical quantities can also be approximated by the above relations. In this case, the rotational energy alone compensates for the increase in potential energy. [ABSTRACT FROM AUTHOR]

Observations have shown that the UV/optical variation amplitude of quasars depends on several physical parameters including luminosity, Eddington ratio, and possibly black hole mass. Identifying new factors which correlate with the variation is essential to probing the underlying physical processes. Combining around 10 years of quasar light curves from SDSS stripe 82 and X-ray data from Stripe 82X, we build a sample of X-ray-detected quasars to investigate the relation between UV/optical variation amplitude () and X-ray loudness. We find that quasars with more intense X-ray radiation (compared to bolometric luminosity) are more variable in the UV/optical. This correlation remains highly significant after excluding the effect of other parameters including luminosity, black hole mass, Eddington ratio, redshift, and rest frame wavelength (i.e., through partial correlation analyses). We further find that the intrinsic link between X-ray loudness and UV/optical variation is gradually more prominent on longer timescales (up to 10 yr in the observed frame), but tends to disappear at timescales <100 days. This suggests a slow and long-term underlying physical process. The X-ray reprocessing paradigm, in which the UV/optical variation is produced by variable central X-ray emission illuminating the accretion disk, is thus disfavored. This discovery points to an interesting scenario in which both the X-ray coronal heating and UV/optical variation in quasars are closely associated with magnetic disc turbulence, and the innermost disc turbulence (where coronal heating occurs) correlates with slow turbulence at larger radii (where UV/optical emission is produced). [ABSTRACT FROM AUTHOR]