In this work, we investigate an exactly solvable two-leg spin ladder with three-spin interactions. We obtain analytically the finite-size corrections of the low-lying energies and determine the ...central charge as well as the scaling dimensions. The model considered in this work is in the same universality class of critical behavior of the XX chain with central charge c = 1. By using the correlation matrix method, we also study the finite-size corrections of the Renyi entropy of the ground state and of the excited states. Our results are in agreement with the predictions of the conformal field theory.
Using over a million and a half extragalactic spectra from the Sloan Digital Sky Survey we study the correlations of the diffuse interstellar bands (DIBs) in the Milky Way. We measure the correlation ...between DIB strength and dust extinction for 142 DIBs using 24 stacked spectra in the reddening range E(B − V) < 0.2, many more lines than ever studied before. Most of the DIBs do not correlate with dust extinction. However, we find 10 weak and barely studied DIBs with correlations that are higher than 0.7 with dust extinction and confirm the high correlation of additional five strong DIBs. Furthermore, we find a pair of DIBs, 5925.9 and 5927.5 Å, which exhibits significant negative correlation with dust extinction, indicating that their carrier may be depleted on dust. We use Machine Learning algorithms to divide the DIBs to spectroscopic families based on 250 stacked spectra. By removing the dust dependence, we study how DIBs follow their local environment. We thus obtain six groups of weak DIBs, four of which are tightly associated with C2 or CN absorption lines.
The strain rate dependent mechanical behaviour was studied for the common out-of-autoclave aerospace textile composite 5-harness-satin carbon–epoxy. End-loaded 15°,30° and 45° off-axis and 90° ...compression tests were carried out at three different strain rate levels (4×10-4s-1,200s-1 and 1000s-1) to determine the effect of strain rate for transverse compression and combined transverse compression/in-plane shear loading. The dynamic tests were carried out on a split-Hopkinson pressure bar, where high speed photography and digital image correlation allowed a detailed study of the specimen deformation and failure process. Quasi-static reference tests were carried out on an electro-mechanical test machine using the same specimen type and a static DIC system. Pronounced strain rate effects on the axial stress–strain response were observed for all specimen types. Failure envelopes for the combined σ22c-τ12 stress state were derived from the experimental data and compared with the maximum stress criterion, which appears well suited to approximate the experimental failure envelope at all strain rate levels. It was observed that the failure envelope was simply scaled up with increasing strain rate, while the overall shape was found to be strain rate independent.
Abstract
The correlation between neutral hydrogen (H
i
) in the intergalactic medium (IGM) and galaxies attracts great interest. We select four fields that include several coherently strong Ly
α
... absorption systems at
z
∼ 2.2 detected using background quasars from the whole SDSS/(e) Baryon Oscillation Spectroscopic Survey (BOSS) database. Deep narrowband and
g
-band imaging are performed using the Hyper Suprime-Cam on the Subaru Telescope. We select 2642 Ly
α
emitter (LAE) candidates at
z
= 2.177 ± 0.023 down to the Ly
α
luminosity of
L
Ly
α
≈ 2 × 10
42
erg s
−1
to construct the galaxy overdensity maps, covering an effective area of 5.39 deg
2
. Combining the sample with the Ly
α
absorption estimated from 64 (e) BOSS quasar spectra, we find a moderate to strong correlation between the LAE overdensity
δ
LAE
and the effective optical depth
τ
LoS
in lines of sight, with
P
value = 0.09% or <0.01% when the field containing a significant quasar overdensity is included or excluded. Cross-correlation analysis also clearly suggests that up to 4 ± 1 pMpc, LAEs tend to cluster in regions rich in H
i
gas, as indicated by the high
τ
LoS
, and avoid the low
τ
LoS
regions where the H
i
gas is deficient. By averaging the
τ
LoS
as a function of the projected distance (
d
) to LAEs, we find a 30% excess signal at 2
σ
level at
d
< 200 pkpc, indicating the dense H
i
in the circumgalactic medium, and a tentative excess at 400 <
d
< 600 pkpc in the IGM regime, corroborating the cross-correlation signal detected at about 0.5 pMpc. These statistical analyses suggest that galaxy−IGM H
i
correlations exist on scales ranging from several hundred pkpc to several pMpc at
z
∼ 2.2.
We present a deep search for 21 cm emission from the gaseous halo of Messier 31 as part of Project AMIGA, a large Hubble Space Telescope program to study the circumgalactic medium of the Andromeda ...galaxy. Our observations with the Robert C. Byrd Green Bank Telescope target sight lines to 48 background AGNs, more than half of which have been observed in the ultraviolet with the Cosmic Origins Spectrograph, with impact parameters ( ). We do not detect any 21 cm emission toward these AGNs to limits of cm−2 ( per 2 kpc-diameter beam). This column density corresponds to an optical depth of ∼2.5 at the Lyman limit; thus, our observations overlap with absorption line studies of Lyman limit systems at higher redshift. Our non-detections place a limit on the covering factor of such optically thick gas around M31 to (at 90% confidence) for . Although individual clouds have previously been found in the region between M31 and M33, the covering factor of strongly optically thick gas is quite small. Our upper limits on the covering factor are consistent with expectations from recent cosmological "zoom" simulations. Recent COS-Halos ultraviolet measurements of absorption about an ensemble of galaxies at show significantly higher covering factors within at the same , although the metal ion-to- ratios appear to be consistent with those seen in M31.
We perform a Very Large Telescope FOcal Reducer and low-dispersion Spectrograph 2 narrowband imaging search around five star-forming galaxies at redshift z = 0.67-0.69 in the Great Observatories ...Origins Deep Survey South field to constrain the radial extent of large-scale outflows traced by resonantly scattered Mg ii emission. The sample galaxies span star formation rates in the range and have stellar masses , and exhibit outflows traced by Mg ii absorption with velocities . These observations are uniquely sensitive, reaching surface brightness limits of 5.81 × 10−19 erg s−1 cm−2 arcsec2 per 1 arcsec2 aperture (at 5 significance). We do not detect any extended emission around any of the sample galaxies, thus placing 5 upper limits on the brightness of extended Mg ii emission of <6.51 × 10−19 erg s−1 cm−2 arcsec2 at projected distances R > 8-21 kpc. The imaging also resolves the Mg ii absorption observed toward each galaxy spatially, revealing approximately constant absorption strengths across the galaxy disks. In concert with radiative transfer models predicting the surface brightness of Mg ii emission for a variety of simple wind morphologies, our detection limits suggest that either (1) the extent of the Mg ii-emitting material in the outflows from these galaxies is limited to 20 kpc; or (2) the outflows are anisotropic and/or dusty.
We present the discovery of an absorption-line redshift of z= 2.609 for GRB 090426, establishing the first firm lower limit to a redshift for a gamma-ray burst (GRB) with an observed duration of <2 ...s. With a rest-frame burst duration of T90z= 0.35 s and a detailed examination of the peak energy of the event, we suggest that this is likely (at >90 per cent confidence) a member of the short/hard phenomenological class of GRBs. From analysis of the optical-afterglow spectrum we find that the burst originated along a very low H i column density sightline, with NH i < 3.2 × 1019 cm−2. Our GRB 090426 afterglow spectrum also appears to have weaker low-ionization absorption (Si ii, C ii) than ∼95 per cent of previous afterglow spectra. Finally, we also report the discovery of a blue, very luminous, star-forming putative host galaxy (∼2L*) at a small angular offset from the location of the optical afterglow. We consider the implications of this unique GRB in the context of burst duration classification and our understanding of GRB progenitor scenarios.
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