The rare case of changing-look (CL) AGNs, with the appearance or disappearance of broad Balmer emission lines within a few years, challenges our understanding of the AGN unified model. We present a sample of 21 new CL AGNs at 0.08 < z < 0.58, which doubles the number of such objects known to date. These new CL AGNs were discovered by several ways, from (1) repeat spectra in the SDSS, (2) repeat spectra in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and SDSS, and (3) photometric variability and new spectroscopic observations. We use the photometric data from surveys, including the SDSS imaging survey, the Pan-STARRS1, the DESI Legacy imaging survey, the Wide-field Infrared Survey Explorer (WISE), the Catalina Real-time Transient Survey, and the Palomar Transient Factory. The estimated upper limits of transition timescale of the CL AGNs in this sample spans from 0.9 to 13 years in the rest frame. The continuum flux in the optical and mid-infrared becomes brighter when the CL AGNs turn on, or vice versa. Variations of more than 0.2 mag in W 1 band were detected in 15 CL AGNs during the transition. The optical and mid-infrared variability is not consistent with the scenario of variable obscuration in 10 CL AGNs at more than 3σ confidence level. We confirm a bluer-when-brighter trend in the optical. However, the mid-infrared WISE colors W 1 − W 2 become redder when the objects become brighter in the W 1 band, possibly due to a stronger hot dust contribution in the W 2 band when the AGN activity becomes stronger. The physical mechanism of type transition is important for understanding the evolution of AGNs.

We present optical light curves of 19 radio quiet (RQ) broad absorption line (BAL) QSOs and study their rapid variability characteristics. Systematic CCD observations, aided by a careful data analysis procedure, have allowed us to clearly detect any such microvariability exceeding 0.01--0.02 mag. Our observations cover a total of 13 nights (~72 hours) with each quasar monitored for about 4 hours on a given night. Our sample size is a factor of three larger than the number of radio-quiet BALQSOs previously searched for microvariability. We introduce a scaled F-test statistic for evaluating the presence of optical microvariability and demonstrate why it is generally preferable to the statistics usually employed for this purpose. Considering only unambiguous detections of microvariability we find that ~11 per cent of radio-quiet BALQSOs (two out of 19 sources) show microvariability for an individual observation length of about 4 hr. This new duty cycle of 11 per cent is similar to the usual low microvariability fraction of normal RQQSOs with observation lengths similar to those of ours. This result provides support for models where radio-quiet BALQSO do not appear to be a special case of the RQQSOs in terms of their microvariability properties.Comment: 13 pages, 3 figures, 3 tables, accepted for publication in MNRAS main journa

A combined MD simulator and time dependent Laplace solver are used to analyze the electrically driven phosphatidylserine externalization process in cells. Time dependent details of nanopore formation at cell membranes in response to a high-intensity (100 kV/cm), ultrashort (10 ns) electric pulse are also probed. Our results show that nanosized pores could typically be formed within about 5 ns. These predictions are in very good agreement with recent experimental data. It is also demonstrated that defect formation and PS externalization in membranes should begin on the anode side. Finally, the simulations confirm that PS externalization is a nanopore facilitated event, rather than the result of molecular translocation across the trans-membrane energy barrier.

We present the results of extensive multi-band intra-night optical monitoring of BL Lacertae during 2010-2012. BL Lacertae was very active in this period and showed intense variability in almost all wavelengths. We extensively observed it for a total for 38 nights; on 26 of them observations were done quasi-simultaneously in B, V, R and I bands (totaling 113 light curves), with an average sampling interval of around 8 minutes. BL Lacertae showed significant variations on hour-like timescales in a total of 19 nights in different optical bands. We did not find any evidence for periodicities or characteristic variability time-scales in the light curves. The intranight variability amplitude is generally greater at higher frequencies and decreases as the source flux increases. We found spectral variations in BL Lacertae in the sense that the optical spectrum becomes flatter as the flux increases but in several flaring states deviates from the linear trend suggesting different jet components contributing to the emission at different times.

Radio emission from the high- and super-Eddington accreting active galactic nuclei (AGNs) has various origins: a persistent jet, the magnetized corona, and the wind-like outflows. It is still unclear which is the leading mechanism responsible for the observed radio emission and how the radio emission is related to other characteristic parameters such as the Eddington ratio and black hole mass. In this paper, we present the 5 GHz Very Large Array (VLA) observational results of a sample of 25 extremely high Eddington accreting supermassive black holes (EESBHs, the Eddington ratio λ Edd close to or above 1) in narrow-line Seyfert 1 galaxies, among which 22 sources are detected. Most of the EESBHs show a compact radio structure from a few hundred parsecs to 1 kpc scale. We estimated the lowest star formation rate surface density required for producing the observed radio emission and found that it is higher than the largest value previously detected in circumnuclear starburst galaxies, implying that the radio emission is from the AGN activity. Along with a comparison sample, we find an overall inverse –λ Edd correlation ranging from sub- to super-Eddington ratios. The high-Eddington and mildly super-Eddington AGNs (−0.5 < log ) have a radio-to-X-ray luminosity ratio L R/L X ∼ 10−5–10−4 and a steep radio spectrum, supporting that the radio emission is from transient ejecta (outflows) of corona; however, the jet contribution cannot be entirely ruled out. Our highly super-Eddington sources (log ) have a flatter radio spectrum, along with its low radio luminosity: ; their radio emission is likely dominated by a magnetized corona, and a radiation-pressure-caused jet is also proposed in this paper.

An electrical breakdown model for liquids in response to a submicrosecond (∼100ns) voltage pulse is presented, and quantitative evaluations carried out. It is proposed that breakdown is initiated by field emission at the interface of pre-existing microbubbles. Impact ionization within the microbubble gas then contributes to plasma development, with cathode injection having a delayed and secondary role. Continuous field emission at the streamer tip contributes to filament growth and propagation. This model can adequately explain almost all of the experimentally observed features, including dendritic structures and fluctuations in the prebreakdown current. Two-dimensional, time-dependent simulations have been carried out based on a continuum model for water, though the results are quite general. Monte Carlo simulations provide the relevant transport parameters for our model. Our quantitative predictions match the available data quite well, including the breakdown delay times and observed optical emission.

We present the results from our search for H I 21-cm absorption in a sample of 16 strong Fe II systems (W r (Mg II λ2796) 1.0Å and W r (Fe II λ2600) or W Fe II 1Å) at 0.5 < z < 1.5 using the Giant Metrewave Radio Telescope and the Green Bank Telescope. We report six new H I 21-cm absorption detections from our sample, which have increased the known number of detections in strong Mg II systems at this redshift range by ∼50%. Combining our measurements with those in the literature, we find that the detection rate of H I 21-cm absorption increases with W Fe II , being four times higher in systems with W Fe II 1Å compared to systems with W Fe II < 1Å. The N (H I) associated with the H I 21-cm absorbers would be 2 × 10 20 cm −2 , assuming a spin temperature of ∼500 K (based on H I 21-cm absorption measurements of damped Lyman-α systems at this redshift range) and unit covering factor. We find that H I 21-cm absorption arises on an average in systems with stronger metal absorption. We also find that quasars with H I 21-cm absorption detected towards them have systematically higher E(B − V ) values than those which do not. Further, by comparing the velocity widths of H I 21-cm absorption lines detected in absorption-and galaxy-selected samples, we find that they show an increasing trend (significant at 3.8σ) with redshift at z < 3.5, which could imply that the absorption originates from more massive galaxy haloes at high-z. Increasing the number of H I 21-cm absorption detections at these redshifts is important to confirm various trends noted here with higher statistical significance.

How would negative energy density affect a classic Friedmann cosmology? Although never measured and possibly unphysical, certain realizations of quantum field theories leaves the door open for such a possibility. In this paper we analyze the evolution of a universe comprising varying amounts of negative energy forms. Negative energy components have negative normalized energy densities, Ω < 0. They include negative phantom energy with an equation of state parameter w < −1, negative cosmological constant: w = −1, negative domain walls: w = −2/3, negative cosmic strings: w = −1/3, negative mass: w = 0, negative radiation: w = 1/3 and negative ultralight: w > 1/3. Assuming that such energy forms generate pressure like perfect fluids, the attractive or repulsive nature of negative energy components are reviewed. The Friedmann equation is satisfied only when negative energy forms are coupled to a greater magnitude of positive energy forms or positive curvature. We show that the solutions exhibit cyclic evolution with bounces and turnovers.The future and fate of such universes in terms of curvature, temperature, acceleration, and energy density are reviewed. The end states are dubbed "big crunch," " big void," or "big rip" and further qualified as "warped","curved", or "flat","hot" versus "cold", "accelerating" versus "decelerating" versus "coasting". A universe that ends by contracting to zero energy density is termed "big poof." Which contracting universes "bounce" in expansion and which expanding universes "turnover" into contraction are also reviewed. I. THE FRIEDMANN EQUATION OF ENERGY, EXPANDED TO NEGATIVE ENERGIESThe classic Friedmann equation of energy is typically written in the form [1-4]where H is the Hubble parameter, G is the gravitational constant, ρ is the energy density, R is a scale factor of the universe, and k is a dimensionless constant related to the curvature of the universe. The speed of light c is set to unity. The Hubble parameter H =Ṙ/R =ȧ/a, where a is the dimensionless scale factor of the universe such that a = R/R 0 and R 0 is the scale factor of the universe at some canonical time t 0 . In [5] (hereafter Paper I), the average energy density ρ was explicitly expanded into all possible stable positive energy forms, including phantom energy, cosmological constant, domain walls, cosmic strings, compact matter, radiation, and hypothetical energy forms collectively dubbed ultralight. These "stable" energy forms are considered different than energy fields such as scalar fields in that each has a well defined local form and evolves in the universe as an constant power of a. All energy forms evolve as an integer power of the scale factor a. * bijunath.patla@nist.govIn this paper, we consider stable energy forms with negative energy density, ρ < 0. To the best of our knowledge, some of these energy forms have never been discussed explicitly. It is not being suggested that any of these energy forms are presently important in the universe, but their theoretical inclusion presents cosmologically intere...