We present a study of the extinction and depletion-derived dust properties of gamma-ray burst (GRB) absorbers at 1 < z < 3 showing the presence of neutral atomic-carbon (C I). By modelling their ...parametric extinction laws, we discover a broad range of dust models characterizing the GRB C I absorption systems. In addition to the already well-established correlation between the amount of C I and visual extinction, AV, we also observe a correlation with the total-to-selective reddening, RV. All three quantities are also found to be connected to the presence and strength of the 2175 Å dust extinction feature. While the amount of C I is found to be correlated with the SED-derived dust properties, we do not find any evidence for a connection with the depletion-derived dust content as measured from Zn/Fe and N(Fe)dust. To reconcile this, we discuss a scenario where the observed extinction is dominated by the composition of dust particles confined in the molecular gas-phase of the interstellar medium (ISM). We argue that since the depletion level trace non-carbonaceous dust in the ISM, the observed extinction in GRB C I absorbers is primarily produced by carbon-rich dust in the molecular cloud and is therefore only observable in the extinction curves and not in the depletion patterns. This also indicates that the 2175 Å dust extinction feature is produced by dust and molecules in the cold and molecular gas-phase. This scenario provides a possible resolution to the discrepancy between the depletion- and SED-derived amounts of dust in high- z absorbers.
ABSTRACT
This is the second paper of a series reporting on the results from a survey conducted with the ESO VLT/X‐shooter spectrograph. We target high‐metallicity damped Lyman α absorbers (DLAs) with ...the aim of investigating the relation between galaxies detected in emission and those detected in absorption. Here, we report on the discovery of the galaxy counterpart of the zabs= 2.58 DLA on the line‐of‐sight to the z= 3.07 quasar SDSS J 091826.16+163609.0 (hereafter Q 0918+1636). The galaxy counterpart of the DLA is detected in the O iiiλ5007 and O iiλλ3726, 3729 emission lines redshifted into the NIR at an impact parameter of 2.0 arcsec (16 kpc at z= 2.58). Lyα emission is not detected down to a 3σ detection limit of 5 × 10−18 erg s−1 cm−2, which, compared to the strength of the oxygen lines, implies that Lyα emission from this galaxy is suppressed by more than an order of magnitude. The DLA has one of the highest metallicities measured so far at comparable redshifts. We find evidence for substantial depletion of refractory elements on to dust grains. Fitting the main metal line component of the DLA, which is located at zabs= 2.5832, we measure the metal abundances from Zn ii, S ii, Si ii, Cr ii, Mn ii, Fe ii and Ni ii to be −0.12 ± 0.05, −0.26 ± 0.05, −0.46 ± 0.05, −0.88 ± 0.05, −0.92 ± 0.05, −1.03 ± 0.05 and −0.78 ± 0.05, respectively. In addition, we detect absorption in the Lyman and Werner bands of molecular hydrogen (H2), which represents the first detection of H2 molecules with X‐shooter. The background quasar Q 0918+1636 is amongst the reddest QSOs at redshifts 3.02 < z < 3.12 from the SDSS catalogue. Its UV to NIR spectrum is well fitted by a composite QSO spectrum reddened by SMC‐/LMC‐like extinction curves at zabs= 2.58 with a significant amount of extinction given by AV≈ 0.2 mag. This supports previous claims that there may be more metal‐rich DLAs missing from current samples due to dust reddening of the background QSOs. The fact that there is evidence for dust both in the central emitting regions of the galaxy (as evidenced by the lack of Lyα emission) and at an impact parameter of 16 kpc (as probed by the DLA) suggests that dust is widespread in this system.
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•The MMEs are more mafic and finer-grained than their host monzogranites.•Major and trace elements and Sr-Nd isotopic systematics support mixing/mingling model.•The crust-like ...geochemical signatures and zircon and apatite U-Pb age data indicate the possible involvement of juvenile LCC of the ANS in the genesis of the MMEs and their host.•The final episode of the ANS evolution was associated with a complex post-collisional interplay between asthenosphere, lithospheric mantle, and LCC.
The Neoproterozoic Gharib Granitoid Complex (GGC), in the North Eastern Desert (NED) of Egypt, is characterized by the occurrence of varieties of granitoids. Monzogranite, the most abundant granite variety, contains abundant magmatic microgranular enclaves (MMEs) of mafic to intermediate composition. The MMEs are more mafic than their host and marked by a greater amount of amphibole and biotite. They are finer grained and have porphyritic/poikilitic textures.
The sharp, crenulated, and fine-grained quenched contacts of the elongated, rounded, and ellipsoid form of the MMEs with their felsic host indicate rapid cooling during a magma mixing/mingling event. Micro-textural evidence supports the mechanical transfer of minerals that crystallized in felsic magma to the mafic melt (e.g., feldspar phenocrysts cross-cutting the MME-host boundaries, stubby apatite, quartz ocelli, and poikilitic outermost rims of K-feldspar phenocrysts), supercooling/quenching process (e.g., acicular apatite and elongated hornblende and biotite crystals), and disequilibrium growth (e.g., hornblende-biotite clots replaced early crystallized clinopyroxene), which also favour a magma mingling/mixing origin. Linear to curvilinear chemical variations of the MMEs and the host monzogranites on Harker diagrams, highly similar trace element contents, and Sr-Nd isotopic systematics together with mineral-chemical features also support mixing/mingling as the main process in magma genesis and strongly suggest that the MMEs were supercooled hybrid globules within cooler, partially crystallized host felsic magma. The crust-like geochemical signatures (i.e., SiO2 content, metaluminous nature, and lack of upper crustal xenoliths and typical peraluminous minerals), along with low MMEs: (87Sr/86Sr)initial = 0.70136–0.70373; monzogranites: (87Sr/86Sr)initial = 0.70202–0.70320) along with zircon and apatite U-Pb age data indicate the possible involvement of juvenile lower continental crust (LCC) of the Arabian-Nubian Shield (ANS) in their genesis. The medium- to high-K calc-alkaline affinity, the LILE enrichment, and the HFSE depletion along with low Nb/La ratios and positive εNd(t) (MMEs = +4.01 - +5.62, monzogranites = +2.29 - +6.03) indicate the contribution of depleted lithospheric mantle in the magma genesis, whereas the low δEu and fairly high δCe values, stable La/Sm, and variable Sr/Th ratios in apatites from the monzogranites and MMEs indicate the contribution of volatile/fluids from the remnants of the oceanic slab in facilitating melting in the source region. The genesis of the monzogranites and MMEs started with asthenosphere upwelling, followed by melting of the remnants of lithospheric mantle, and underplating of mantle magma, which led to partial melting of the LCC. Multi-element modelling postulates that the low degree mixing between partially crystallized mantle magma and LCC-derived felsic melt (Fmix ∼ 0.1) could produce the parent magma for the monzogranites. Further mixing/mingling of the crystal-charged monzogranite parent magma with new pulses of mafic melts (Fmix ∼ 0.25) developed a hybrid zone and formed the hybrid MMEs. Thus, the final episode of the ANS evolution was associated with a complex post-collisional interplay between asthenosphere, lithospheric mantle, and the LCC caused by the removal of delaminated lithospheric root and dense lower crust following the collision between East and West Gondwana in the Neoproterozoic time.
► A power quality analysis approach based on complex format of wavelet coefficients is presented. ► A decimation-free wavelet transform is used in conjunction with discrete Hilbert Transform to ...develop complex power quantities in time–frequency domain. ► The presented time–frequency phasor approach overcomes the limitations of existing power quality analysis approaches. ► The algorithm is tested in the presence of three phase time-varying power quality disturbances. ► Possible applications of the presented approach are highlighted.
This paper introduces the un-decimated wavelet transform to compute power quantities using complex wavelet coefficients. The advantages and disadvantages of real and complex wavelets are first highlighted, then time–frequency formula for active, reactive and apparent power based on complex wavelet coefficients and with no decimation, are presented in light of Mallat's multi-resolution analysis (MRA). The performance of the proposed approach is evaluated using test cases incorporating time-variant and time-invariant power quality (PQ) disturbances. The results indicate that the use of the decimation-free complex wavelet coefficients in power quantities computation not only overcomes the limitations of other real wavelets but also assigns a direction for the flow of these power quantities by retaining the phase angle information at the approximation and detail levels which is not accessible in case of real wavelets or complex wavelets when used as stand-alone tools. The proposed approach can be useful in many applications involving challenging power quality event detection (high impedance faults, multi-stage PQ dips/swells, non-intentional islanding of distributed generation, etc.), non-intrusive load disaggregation in advanced metering infrastructure and wide area monitoring (WAM).
Abundances of galaxies at redshifts z > 4 are difficult to obtain from damped Lyα (DLA) systems in the sightlines of quasars (QSOs) due to the Lyα forest blanketing and the low number of ...high-redshift QSOs known to date. Gamma-ray bursts (GRBs) with their higher luminosity are well suited to study galaxies out to the formation of the first stars at z > 10. The large wavelength coverage of the X-shooter spectrograph makes it an excellent tool to study the interstellar medium of high-redshift galaxies, in particular if the redshift is not known beforehand. In this paper, we determine the properties of a GRB host at z = 4.667 23 from absorption lines combined with X-ray and optical imaging data. This is one of the highest redshifts where a detailed analysis with medium-resolution data is possible. We measure a relatively high metallicity of S/H = −1.1 ± 0.2 for a galaxy at this redshift. Assuming ultraviolet pumping as origin for the fine-structure lines, the material observed is between 0.3 and 1.0 kpc from the GRB. The extinction determined by the spectral slope from X-rays to the infrared shows a moderate value of A
V
= 0.13 ± 0.05 mag and relative abundances point to a warm disc extinction pattern. Low- and high-ionization as well as fine-structure lines show a complicated kinematic structure probably pointing to a merger in progress. We also detect one intervening system at z = 2.18. GRB-DLAs have a shallower evolution of metallicity with redshift than QSO absorbers and no evolution in their H i column density or ionization fraction. GRB hosts at high redshifts seem to continue the trend of the metallicity-luminosity relation towards lower metallicities but the sample is still too small to draw a definite conclusion. While the detection of GRBs at z > 4 with current satellites is still difficult, they are very important for our understanding of the early epochs of star and galaxy formation.
We report the detections of molecular hydrogen (H2), vibrationally-excited H2 (H 2∗ 2 ∗ $ _{2}^{*} $ ), and neutral atomic carbon (C I), an efficient tracer of molecular gas, in two new afterglow ...spectra of GRBs 181020A (z = 2.938) and 190114A (z = 3.376), observed with X-shooter at the Very Large Telescope (VLT). Both host-galaxy absorption systems are characterized by strong damped Lyman-α absorbers (DLAs) and substantial amounts of molecular hydrogen with logN(H I, H2) = 22.20 ± 0.05, 20.40 ± 0.04 (GRB 181020A) and logN(H I, H2) = 22.15 ± 0.05, 19.44 ± 0.04 (GRB 190114A). The DLA metallicites, depletion levels, and dust extinctions are within the typical regimes probed by GRBs with Zn/H = −1.57 ± 0.06, Zn/Fe = 0.67 ± 0.03, and AV = 0.27 ± 0.02 mag (GRB 181020A) and Zn/H = −1.23 ± 0.07, Zn/Fe = 1.06 ± 0.08, and AV = 0.36 ± 0.02 mag (GRB 190114A). In addition, we examine the molecular gas content of all known H2-bearing GRB-DLAs and explore the physical conditions and characteristics required to simultaneously probe C I and H 2∗ 2 ∗ $ _{2}^{*} $ . We confirm that H2 is detected in all C I- and H 2∗ 2 ∗ $ _{2}^{*} $ -bearing GRB absorption systems, but that these rarer features are not necessarily detected in all GRB H2 absorbers. We find that a large molecular fraction of fH2 ≳ 10−3 is required for C I to be detected. The defining characteristic for H 2∗ 2 ∗ $ _{2}^{*} $ to be present is less clear, though a large H2 column density is an essential factor. We also find that the observed line profiles of the molecular-gas tracers are kinematically “cold”, with small velocity offsets of δv < 20 km s−1 from the bulk of the neutral absorbing gas. We then derive the H2 excitation temperatures of the molecular gas and find that they are relatively low with Tex ≈ 100−300 K, however, there could be evidence of warmer components populating the high-J H2 levels in GRBs 181020A and 190114A. Finally, we demonstrate that even though the X-shooter GRB afterglow campaign has been successful in recovering several H2-bearing GRB-host absorbers, this sample is still hampered by a significant dust bias excluding the most dust-obscured H2 absorbers from identification. C I and H 2∗ 2 ∗ $ _{2}^{*} $ could open a potential route to identify molecular gas even in low-metallicity or highly dust-obscured bursts, though they are only efficient tracers for the most H2-rich GRB-host absorption systems.
Tool wear prediction has become an indispensable technique to prevent downtime in manufacturing and production processes. Airborne emission from a machining process using a low-cost microphone may ...provide a vital signal of tool health. However, the effect of background noise results in anomaly in data that may lead to wrong prediction of tool health. The paper presents an adaptive approach using neural networks for background noise filtration in acoustic signal for a turning process. Acoustic signal of a turning process is mixed with background noise from four different machines and introduced at different RPMs and feed-rate at a constant depth of cut. A comparison of Backpropagation neural network (BPNN), Self-organizing map and k-means clustering algorithm for noise filtration is investigated in this paper. In this regard, back-propagation neural network showed better performance with an average accuracy for all the four sources. It shows 100 % accuracy for grinding machine signal, 94.78 % accuracy for background signal from 3-axis milling machine, 45.57 % and 12.69 % for motor and 4-axis milling machine, respectively. Signal reconstruction is then done using Discrete cosine transform (DCT). The proposed technique shows a promising future for noise filtration in airborne acoustic data of a machining process.
Abstract
The ultraviolet (UV) extinction feature at 2175 Å is ubiquitously observed in the Galaxy but is rarely detected at high redshifts. Here we report the spectroscopic detection of the 2175 Å ...bump on the sightline to the
γ
-ray burst (GRB) afterglow GRB 180325A at
z
= 2.2486, the only unambiguous detection over the past 10 years of GRB follow-up, at four different epochs with the Nordic Optical Telescope (NOT) and the Very Large Telescope (VLT)/X-shooter. Additional photometric observations of the afterglow are obtained with the Gamma-Ray burst Optical and Near-Infrared Detector (GROND). We construct the near-infrared to X-ray spectral energy distributions (SEDs) at four spectroscopic epochs. The SEDs are well described by a single power law and an extinction law with
R
V
≈ 4.4,
A
V
≈ 1.5, and the 2175 Å extinction feature. The bump strength and extinction curve are shallower than the average Galactic extinction curve. We determine a metallicity of Zn/H > −0.98 from the VLT/X-shooter spectrum. We detect strong neutral carbon associated with the GRB with equivalent width of
W
r
(
λ
1656) = 0.85 ± 0.05. We also detect optical emission lines from the host galaxy. Based on the H
α
emission-line flux, the derived dust-corrected star formation rate is ∼46 ± 4
M
⊙
yr
−1
and the predicted stellar mass is log
M
*
/
M
⊙
∼ 9.3 ± 0.4, suggesting that the host galaxy is among the main-sequence star-forming galaxies.
Context. The star-forming nature of long γ-ray burst (GRB) host galaxies provides invaluable constraints on the progenitors of GRBs and might open a short-cut to the characteristics of typical ...star-forming galaxies throughout the history of the Universe. Due to the absence of near-infrared (NIR) spectroscopy, however, detailed investigations, specifically a determination of the gas-phase metallicity of gamma-ray burst hosts, was largely limited to redshifts z < 1 to date. Aims. We observed the galaxy hosting GRB 080605 at z = 1.64 using optical/NIR spectroscopy and high-resolution HST/WFC3 imaging in the rest-frame wavelength range between 1150 and 8700 Å. These data allow us to study a z > 1 GRB host in unprecedented detail and investigate the relation between GRB hosts and field galaxies. Methods. We availed of VLT/X-shooter optical/NIR spectroscopy to measure the metallicity, electron density, star-formation rate (SFR), and reddening of the host of GRB 080605. Specifically, we used different strong-line diagnostics to robustly measure the gas-phase metallicity within the interstellar medium (ISM) for the first time based on N ii at this redshift. Results. The host of the energetic (Eγ,iso ~ 2 × 1053 erg) GRB 080605 at z ~ 1.64 is a morphologically complex, vigorously star-forming galaxy with an Hα-derived SFR of 31-6+12 M⊙ yr-1. Its ISM is significantly enriched with metals. Specifically, N ii/Hα = 0.14 ± 0.02, which yields an oxygen abundance 12 + log (O/H) between 8.3 and 8.6 depending on the adopted strong-line calibrator. This corresponds to values in the range of 0.4 − 0.8 Z⊙. For its measured stellar mass M* = 8.0-1.6+1.3 × 109 M⊙ and SFR, this value is consistent with the fundamental metallicity relation defined by star-forming field galaxies. The absence of strong Lyα emission constrains the escape fraction of resonantly-scattered Lyα photons to fesc ≲ 0.08. Conclusions. Our observations provide a detailed picture of the conditions in the ISM of a highly star-forming galaxy with irregular morphology at z ~ 1.6. They include the first robust metallicity measurement based on N ii for a GRB host at z > 1 and directly illustrate that GRB hosts are not necessarily metal-poor, both on absolute scales as well as relative to their stellar mass and SFR. GRB hosts could thus be fair tracers of the population of ordinary star-forming galaxies at high redshift.
Natural fiber reinforced biocomposites have recently attracted many researchers because of their biodegradability, cost effectiveness and ecofriendliness. The present study investigates the ...properties of willow-fiber reinforced poly(lactic acid) based composites and their foam processability. Microcellular foams of the composites were prepared by foam injection moulding using nitrogen gas as the blowing agent. The effects of willow-fiber addition on the morphology, mechanical properties, thermal stability, crystallization, and heat deflection temperature (HDT) were studied. At 30 weight percent wt% willow-fiber content, unfoamed composites showed good improvement in specific tensile and flexural moduli. Addition of willow-fiber increased crystallinity and the rate of crystallization and yielded narrow crystallite size distribution as observed by differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) results of the foamed composites revealed that increase in willow-fiber content caused smaller average cell size and higher cell density. Specific notch impact strength of foamed composites at both 20 and 30 wt% willow-fiber content showed increasing trend compared to that of their unfoamed counterparts.
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