Quasar 2175 \AA dust absorbers II: Correlation analysis and relationship with other absorption line systems

We present the cold neutral content (H I and C I gas) of 13 quasar 2175 \AA$$ dust absorbers (2DAs) at $z$ = 1.6 - 2.5 to investigate the correlation between the presence of the UV extinction bump with other physical characteristics. These 2DAs were initially selected from the Sloan Digital Sky Surveys I - III and followed up with the Keck-II telescope and the Multiple Mirror Telescope as detailed in our Paper I. We perform a correlation analysis between metallicity, redshift, depletion level, velocity width, and explore relationships between 2DAs and other absorption line systems. The 2DAs on average have higher metallicity, higher depletion levels, and larger velocity widths than Damped Lyman-$\alpha$ absorbers (DLAs) or subDLAs. The correlation between [Zn/H] and [Fe/Zn] or [Zn/H] and log$\Delta$V$_{90}$ can be used as alternative stellar mass estimators based on the well-established mass-metallicity relation. The estimated stellar masses of the 2DAs in this sample are in the range of $\sim$ 10$^9$ to $\sim$2 $\times$ 10$^{11}$ $M_{\odot}$ with a median value of $\sim$2 $\times$ 10$^{10}$ $M_{\odot}$. The relationship with other quasar absorption line systems can be described as (1) 2DAs are a subset of Mg II and Fe II absorbers, (2) 2DAs are preferentially metal-strong DLAs/subDLAs, (3) More importantly, all of the 2DAs show C I detections with logN(C I) $>$ 14.0 cm$^{-2}$, (4) 2DAs can be used as molecular gas tracers. Their host galaxies are likely to be chemically enriched, evolved, massive (more massive than typical DLA/subDLA galaxies), and presumably star-forming galaxies.Comment: 12 pages, 11 figures; accepted for publication in MNRA

Quasar 2175 {\AA} dust absorbers I: metallicity, depletion pattern, and kinematics

We present 13 new 2175 {\AA} dust absorbers at z_abs = 1.0 - 2.2 towards background quasars from the Sloan Digital Sky Survey. These absorbers are examined in detail using data from the Echelle Spectrograph and Imager (ESI) on the Keck II telescope. Many low-ionization lines including Fe II, Zn II, Mg II, Si II, Al II, Ni II, Mn II, Cr II, Ti II, and Ca II are present in the same absorber which gives rise to the 2175 {\AA} bump. The relative metal abundances (with respect to Zn) demonstrate that the depletion patterns of our 2175 {\AA} dust absorbers resemble that of the Milky Way clouds although some are disk-like and some are halo-like. The 2175 {\AA} dust absorbers have significantly higher depletion levels compared to literature Damped Lyman-{\alpha} absorbers (DLAs) and subDLAs. The dust depletion level indicator [Fe/Zn] tends to anti-correlate with bump strengths. The velocity profiles from the Keck/ESI spectra also provide kinematical information on the dust absorbers. The dust absorbers are found to have multiple velocity components with velocity widths extending from ~100 to ~ 600 km/s, which are larger than those of most DLAs and subDLAs. Assuming the velocity width is a reliable tracer of stellar mass, the host galaxies of 2175 {\AA} dust absorbers are expected to be more massive than DLA/subDLA hosts. Not all of the 2175 {\AA} dust absorbers are intervening systems towards background quasars. The absorbers towards quasars J1006+1538 and J1047+3423 are proximate systems that could be associated with the quasar itself or the host galaxy.Comment: 27 pages, 32 figures, 31 tables; Accepted for publication in MNRA

Cold gas and a Milky Way-type 2175 {\AA} bump in a metal-rich and highly depleted absorption system

We report the detection of a strong Milky Way-type 2175 \AA$$ extinction bump at $z$ = 2.1166 in the quasar spectrum towards SDSS J121143.42+083349.7 from the Sloan Digital Sky Survey (SDSS) Data Release 10. We conduct follow up observations with the Echelle Spectrograph and Imager (ESI) onboard the Keck-II telescope and the Ultraviolet and Visual Echelle Spectrograph (UVES) on the VLT. This 2175 \AA$$ absorber is remarkable in that we simultaneously detect neutral carbon (C I), neutral chlorine (Cl I), and carbon monoxide (CO). It also qualifies as a damped Lyman alpha system. The J1211+0833 absorber is found to be metal-rich and has a dust depletion pattern resembling that of the Milky Way disk clouds. We use the column densities of the C I fine structure states and the C II/C I ratio (under the assumption of ionization equilibrium) to derive the temperature and volume density in the absorbing gas. A Cloudy photoionization model is constructed, which utilizes additional atoms/ions to constrain the physical conditions. The inferred physical conditions are consistent with a canonical cold (T $\sim$ 100 K) neutral medium with a high density ($n$(H I) $\sim$ 100 cm$^{-3}$) and a slightly higher pressure than the local interstellar medium. Given the simultaneous presence of C I, CO, and the 2175 \AA$$ bump, combined with the high metallicity, high dust depletion level and overall low ionization state of the gas, the absorber towards J1211+0833 supports the scenario that the presence of the bump requires an evolved stellar population.Comment: 18 pages, 17 figures, to be published in MNRA

Surface Roughness Effect on Multiaxial Fatigue Behavior of Additive Manufactured Metals and Its Modeling

Additive manufacturing (AM) has become a very popular topic recently due to its many advantages including short build cycles, convenience of customozation, and most importantly the ability to build components with complex geometry. However, the surface condition of additive manufactured components is not always satisfactory, particularly with respect to fatigue performance. This is because the as-built surface tends to be rough and post surface treatments or processes such as machining and polishing may not be applicable to all AM parts. On the other hand, since many components are under cyclic loading consisting of normal and shear stress, multiaxial fatigue behavior is one of the most important aspects to evaluate. This paper evaluates the surface roughness effect on fatigue behaviors of Ti-6Al-4V allloy samples additively manufactured by laser based powder bed fusion method (L-PBF). Fully reversed axial, torsional, and combined axial-torsion fatigue tests were conducted on specimens with different surface conditions and with different post heat treatments (annealed and HIP). Fatigue life predictions were made using linear elastic fracture mechanic with satisfactory results, as compared to experimental results

First-principles calculation on the transport properties of molecular wires between Au clusters under equilibrium

Based on the matrix Green's function method combined with hybrid tight-binding / density functional theory, we calculate the conductances of a series of gold-dithiol molecule-gold junctions including benzenedithiol (BDT), benzenedimethanethiol (BDMT), hexanedithiol (HDT), octanedithiol (ODT) and decanedithiol (DDT). An atomically-contacted extended molecule model is used in our calculation. As an important procedure, we determine the position of the Fermi level by the energy reference according to the results from ultraviolet photoelectron spectroscopy (UPS) experiments. After considering the experimental uncertainty in UPS measurement, the calculated results of molecular conductances near the Fermi level qualitatively agree with the experimental values measured by Tao et. al. [{\it Science} 301, 1221 (2003); {\it J. Am. Chem. Soc.} 125, 16164 (2003); {\it Nano. Lett.} 4, 267 (2004).]Comment: 12 pages,8 figure

Sequence Stratigraphy of Fluvial Facies: A New Type Representative from Wenliu Area, Bohai Bay Basin, China

The application of sequence stratigraphy to the fluvial portion of sedimentary basin fills is most challenging, especially where the fluvial deposits under analysis are isolated or far away from coeval shorelines and marine influences. Taking the Wenliu Area as an example, this chapter aims at addressing researches about another type of river. High-resolution stratigraphic analysis of the lower second member of the Shahejie Formation of the W79 Block of Bohai Bay Basin (China) has revealed that the study area, previously interpreted as a shallow water delta system, actually originated in a subaerial setting with a distributional pattern. The base level fluctuations are mainly controlled by the regional tectonic setting. Active subsidence stages tend to make base level rising semi-cycles, while relative stable stages tend to make base level falling semi-cycles

The Plastic Scintillator Detector at DAMPE

he DArk Matter Particle Explorer (DAMPE) is a general purposed satellite-borne high energy $\gamma-$ray and cosmic ray detector, and among the scientific objectives of DAMPE are the searches for the origin of cosmic rays and an understanding of Dark Matter particles. As one of the four detectors in DAMPE, the Plastic Scintillator Detector (PSD) plays an important role in the particle charge measurement and the photons/electrons separation. The PSD has 82 modules, each consists of a long organic plastic scintillator bar and two PMTs at both ends for readout, in two layers and covers an overall active area larger than 82 cm $\times$ 82 cm. It can identify the charge states for relativistic ions from H to Fe, and the detector efficiency for Z=1 particles can reach 0.9999. The PSD has been successfully launched with DAMPE on Dec. 17, 2015. In this paper, the design, the assembly, the qualification tests of the PSD and some of the performance measured on the ground have been described in detail