In the restframe ultra-violet (UV), two of the parameters that best characterize the range of emission-line properties in quasar broad emission-line regions are the equivalent width and the blueshift of the C IV λ 1549 line relative to the quasar rest frame. We explore the connection between these emission-line properties and the UV through X-ray spectral energy distribution (SED) for radio-quiet (RQ) quasars. Our sample consists of a heterogeneous compilation of 406 quasars from the Sloan Digital Sky Survey (at z > 1.54) and Palomar-Green survey (at z < 0.4) that have well-measured C IV emission-line and X-ray properties (including 164 objects with measured Γ). We find that RQ quasars with both strong C IV emission and small C IV blueshifts can be classified as "hard-spectrum" sources that are (relatively) strong in the X-ray as compared to the UV. On the other hand, RQ quasars with both weak C IV emission and large C IV blueshifts are instead "soft-spectrum" sources that are (relatively) weak in the X-ray as compared to the UV. This work helps to further bridge optical/soft X-ray "Eigenvector 1" relationships to the UV and hard X-ray. Based on these
Recent advances in the physical vapor deposition (PVD) of protective fluoride films have raised the far ultraviolet (FUV: 912 -1600 Å) reflectivity of aluminum-based mirrors closer to the theoretical limit. The greatest gains, at more than 20%, have come for lithium fluoride protected aluminum (LiF+Al), which has the shortest wavelength cutoff of any conventional overcoat. Despite the success of the NASA FUSE mission, the use of LiF-based optics is rare as LiF is hygroscopic and requires handling procedures that can drive risk. With NASA now studying two large mission concepts for astronomy (LUVOIR and HabEx) that mandate throughput down to 1000 Å, the development of LiF-based coatings becomes crucial. This paper discusses steps that are being taken to qualify these new enhanced LiF protected aluminum (eLiF) mirror coatings for flight. In addition to quantifying the hygroscopic degradation, we have developed a new method of protecting eLiF with an ultrathin (10 -20 Å) capping layer of a non-hygroscopic material to increase durability. We report on the performance of eLiF-based optics and assess the steps that need to be taken to qualify such coatings for LUVOIR, HabEx, and other FUV-sensitive space missions.
Amyloid β-protein (Aβ) assembles into oligomers that play a seminal role in Alzheimer's disease (AD), a leading cause of dementia among the elderly. Despite undisputed importance of Aβ oligomers, their structure and the basis of their toxicity remain elusive. Previous experimental studies revealed that the [K16A] substitution strongly inhibits toxicity of the two predominant Aβ alloforms in the brain, Aβ 40 [K16A] substitution induces formation of more compact oligomers than the [K28A] substitution. If the structure-function paradigm applies to Aβ oligomers, then the observed substitution-specific structural changes in Aβ 40 and Aβ 42 oligomers are critical for understanding the structural basis of Aβ oligomer toxicity and correct identification of therapeutic targets against AD.
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