Single-crystalline transition metal films are ideal playing fields for the epitaxial growth of graphene and graphene-base materials. Graphene-silicon layered structures were successfully constructed on Ir(111) thin film on Si substrate with an yttria-stabilized zirconia buffer layer via intercalation approach. Such hetero-layered structures are compatible with current Si-based microelectronic technique, showing high promise for applications in future micro- and nano-electronic devices.
We report a multi-wavelength study of four new planetary nebula (PN) candidates selected from the INT/WFC Photometric Ha Survey of the Northern Galactic Plane (IPHAS) and Deep Sky Hunter (DSH) catalogues. We present mid-resolution optical spectra of these PNs. The PN status of our sample was confirmed by optical narrow-band images and mid-resolution spectra. Based on the locations of these objects in the log (Ha/[N II]) versus log (Ha/[S II]) diagnostic diagram, we conclude that these sources are evolved lowexcitation PNs. The optical and infrared appearances of these newly discovered PNs are discussed. Three of the new nebulae studied here are detected in infrared and have low infrared-to-radio flux ratios, probably suggesting that they are evolved. Furthermore, we derive the dynamical ages and distances of these nebulae and study the spectral energy distribution for one of them with extensive infrared archival data.
Numerical transport models based on the advection-dispersion equation (ADE) are built on the assumption that sub-grid cell transport is Fickian such that dispersive spreading around the average velocity is symmetric and without significant tailing on the front edge of a solute plume. However, anomalous diffusion in the form of super-diffusion due to preferential pathways in an aquifer has been observed in field data, challenging the assumption of Fickian dispersion at the local scale. This study develops a fully Lagrangian method to simulate sub-grid super-diffusion in a multi-dimensional regional-scale transport. The underlying concept is based on previous observations that solutions to space-fractional ADEs, which can describe super-diffusive dispersion, can be obtained by transforming solutions of classical ADEs. The transformations are equivalent to randomizing particle travel time or relative velocity for each model time step. Here, the time randomizing procedure known as subordination is applied to flow field output from MODFLOW simulations. Numerical tests check the applicability of the novel method in mapping regional-scale super-diffusive transport conditioned on local properties of multi-dimensional heterogeneous media.
Nuclear reactions in stars occur between nuclei in the high-energy tail of the energy distribution and are sensitive to possible deviations from the standard equilibrium thermal-energy distribution, the well-known Maxwell-Boltzmann Distribution (textsf{MBD}). In a previous paper published in Physics Letters 441B(1998)291, DeglInnocenti {it et al}. made strong constrains on such deviations with the detailed helioseismic information of the solar structure. With a small deviation parameterized with a factor exp$[{-delta (E/kT)^2}]$, it was shown $delta$ restricted between -0.005 and +0.002. These constrains have been carefully reexamined in the present work. We find that a normalization factor was missed in the previous modified textsf{MBD}. In this work, the normalization factor $c$ is calculated as a function of $delta$. It shows the factor $c$ is almost unity within the range 0$< delta leq$0.002, which supports the previous conclusion. However, it demonstrates that $delta$ cannot take a negative value from the normalization point of view. As a result, a stronger constraint on $delta$ is defined as 0$leq delta leq$0.002. The astrophysical implication on the solar neutrino fluxes is simply discussed based on a positive $delta$ value of 0.003. The reduction of the $^7$Be and $^8$B neutrino fluxes expected from the modified textsf{MBD} can possibly shed alternative light on the solar neutrino problem. In addition, the resonant reaction rates for the $^{14}$N($p$,$gamma$)$^{15}$O reaction are calculated with a standard textsf{MBD} and a modified textsf{MBD}, respectively. It shows that the rates are quite sensitive even to a very small $delta$. This work demonstrates the importance and necessity of experimental verification or test of the well-known textsf{MBD} at high temperatures.
We present a spectral line survey of the proto-planetary nebula AFGL 2688 in the frequency ranges of 71-111 GHz, 157-160 GHz, and 218-267 GHz using the Arizona Radio Observatory 12m telescope and the Heinrich Hertz Submillimeter Telescope. A total of 143 individual spectral features associated with 32 different molecular species and isotopologues were identified. The molecules C3H, CH3CN, H2CO, H2CS, and HCO+ were detected for the first time in this object. By comparing the integrated line strengths of different transitions, we are able to determine the rotation temperatures, column densities, and fractional abundances of the detected molecules. The C, O, and N isotopic ratios in AFGL 2688 are compared with those in IRC+10216 and the Sun, and were found to be consistent with stellar nucleosynthesis theory. Through comparisons of molecular line strengths in asymptotic giant branch stars, proto-planetary nebulae, and planetary nebulae, we discuss the evolution in circumstellar chemistry in the late stages of evolution.
We report a simple, novel sub-diffraction method, i.e. diffraction interference induced super-focusing in second-harmonic (SH) Talbot effect, to achieve focusing size of less than {lambda}_pump/8 without involving evanescent waves or sub-wavelength apertures. By tailoring point spread functions with Fresnel diffraction interference, we observe periodic SH sub-diffracted spots over a hundred of micrometers away from the sample. Our demonstration is the first experimental realization of the proposal by Toraldo Di Francia pioneered 60 years ago for super-resolution imaging.
We show that the problem k-Dominating Set and its several variants including k-Connected Dominating Set, k-Independent Dominating Set, and k-Dominating Clique, when parameterized by the solution size k, are W[1]-hard in either multiple-interval graphs or their complements or both. On the other hand, we show that these problems belong to W[1] when restricted to multiple-interval graphs and their complements. This answers an open question of Fellows et al. In sharp contrast, we show that d-Distance k-Dominating Set for d >= 2 is W[2]-complete in multiple-interval graphs and their complements. We also show that k-Perfect Code and d-Distance k-Perfect Code for d >= 2 are W[1]-complete even in unit 2-track interval graphs. In addition, we present various new results on the parameterized complexities of k-Vertex Clique Partition and k-Separating Vertices in multiple-interval graphs and their complements, and present a very simple alternative proof of the W[1]-hardness of k-Irredundant Set in general graphs.
High-resolution HST imaging of the compact planetary nebula NGC 6644 has revealed two pairs of bipolar lobes and a central ring lying close to the plane of the sky. From mid-infrared imaging obtained with the Gemini Telescope, we have found a dust torus which is oriented nearly perpendicular to one pair of the lobes. We suggest that NGC 6644 is a multipolar nebula and have constructed a 3-D model which allows the visualization of the object from different lines of sight. These results suggest that NGC 6644 may have similar intrinsic structures as other multipolar nebulae and the phenomenon of multipolar nebulosity may be more common than previously believed.
We report on the results of a radio interferometric observation of NGC7027 in the CO J=2-1 and 13CO J=2-1 lines. The results are analyzed with morpho-kinematic models developed from the software tool Shape. Our goal is to reveal the morpho-kinematic properties of the central region of the nebula, and to explore the nature of unseen high-velocity jets that may have created the characteristic structure of the central region consisting of molecular and ionized components. A simple ellipsoidal shell model explains the intensity distribution around the systemic velocity, but the high velocity features deviate from the ellipsoidal model. Through the Shape automatic reconstruction model, we found a possible trail of a jet only in one direction, but no other possible holes were created by the passage of a jet.
