Cosmological distance indicators

We review three distance measurement techniques beyond the local universe: (1) gravitational lens time delays, (2) baryon acoustic oscillation (BAO), and (3) HI intensity mapping. We describe the principles and theory behind each method, the ingredients needed for measuring such distances, the current observational results, and future prospects. Time delays from strongly lensed quasars currently provide constraints on $H_0$ with < 4% uncertainty, and with 1% within reach from ongoing surveys and efforts. Recent exciting discoveries of strongly lensed supernovae hold great promise for time-delay cosmography. BAO features have been detected in redshift surveys up to z <~ 0.8 with galaxies and z ~ 2 with Ly-$\alpha$ forest, providing precise distance measurements and $H_0$ with < 2% uncertainty in flat $\Lambda$CDM. Future BAO surveys will probe the distance scale with percent-level precision. HI intensity mapping has great potential to map BAO distances at z ~ 0.8 and beyond with precisions of a few percent. The next years ahead will be exciting as various cosmological probes reach 1% uncertainty in determining $H_0$, to assess the current tension in $H_0$ measurements that could indicate new physics.Comment: Review article accepted for publication in Space Science Reviews (Springer), 45 pages, 10 figures. Chapter of a special collection resulting from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space Ag

Constraining IGM enrichment and metallicity with the C IV forest correlation function

The production and distribution of metals in the diffuse intergalactic medium (IGM) have implications for galaxy formation models and the baryon (re)cycling process. The relative abundance of metals in high versus low-ionization states has also been argued to be sensitive to the Universe's reionization history. However, measurements of the background metallicity of the IGM at z~4 are sparse and in poor agreement with one another, and reduced sensitivity in the near-IR renders detecting individual metal absorbers nearly impossible. We present a new clustering-based technique that enables the detection of these weak IGM absorbers by statistically averaging over all spectral pixels, here applied to the C IV forest. We simulate the z=4.5 IGM with different models of inhomogeneous metal distributions and investigate its two-point correlation function (2PCF) using mock skewers of the C IV forest. The 2PCF demonstrates a clear peak at the doublet separation of the C IV line. The peak amplitude scales quadratically with metallicity, while enrichment morphology affects both the shape and amplitude of the 2PCF. The effect of enrichment topology can also be framed in terms of the metal mass- and volume-filling factors, and we show their trends as a function of the enrichment topology. For models consistent with the distribution of metals at z~3, we find that we can constrain [C/H] to within 0.2 dex, log$\,M_{\rm{min}}$ to within 0.4 dex, and $R$ to within 15%. We show that strong absorbers arising from the circumgalactic medium of galaxies can be easily identified and masked, allowing one to recover the underlying IGM signal. The auto-correlation of the metal-line forest presents a new and compelling avenue to simultaneously constrain IGM metallicity and enrichment topology with high precision at z>4, thereby pushing such measurements into the Epoch of Reionization.Comment: 19 pages, 17 figures, 1 appendix. Submitted to MNRA

Constraining IGM enrichment and metallicity with the C IV forest correlation function

Interstellar matter and star formatio

Dynamic electro-optic response of graphene/graphitic flakes in nematic liquid crystals

Electric field induced dynamic reorientation phenomenon of graphene/graphitic flakes in homogeneously aligned nematic liquid crystal (NLC) medium has been demonstrated by optical microscopy. The flakes reorient from parallel to perpendicular configuration with respect to boundary plates of confining cells for an applied field strength of as low as tens of millivolt per micrometer. After field removal the reoriented flakes recover to their initial state with the help of relaxation of NLC. Considering flake reorientation phenomenon both in positive and negative dielectric anisotropy NLCs, the reorientation process depends on interfacial Maxwell-Wagner polarization and NLC director reorientation. We propose a phenomenological model based on electric field induced potential energy of graphitic flakes and coupling contribution of positive NLC to generate the rotational kinetic energy for flake reorientation. The model successfully explains the dependence of flake reorientation time over flake shape anisotropy, electric-field strength, and flake area. Using present operating scheme it is possible to generate dark field-off state and bright field-on state, having application potential for electro-optic light modulation devices. ©2013 Optical Society of America.114151sciescopu

Field-induced stretching and dynamic reorientation of functionalized multiwalled carbon nanotube aggregates in nematic liquid crystals

Multiwalled carbon nanotubes (MWCNTs) exhibited distinct electrical stretching behavior in nematic liquid crystals (NLC) depending on nanotube surface state. We found that two different samples prepared by chemical functionalization (f-CNT) and physical grinding (g-CNT) revealed distinct field dependence from each other. The threshold stretching field was lower in the f-CNT aggregates than in g-CNT aggregates. This was attributed to polar functionality induced weakened van der Waals interaction in f-CNTs, which was confirmed in infrared (IR) and Raman spectroscopy. Dynamic reorientation of f-CNTs was observed under polarized optical microscopy where f-CNTs were found to follow orientation of NLC director. Uniformly aligned f-CNTs also exhibited selective light absorption in sufficiently long transient field off-state which could find potential applications in memory and modulator devices as well as the versatile functional composites. © 2015 Elsevier Ltd1441sciescopu

Immunocompromised patients with acute respiratory distress syndrome : Secondary analysis of the LUNG SAFE database

The aim of this study was to describe data on epidemiology, ventilatory management, and outcome of acute respiratory distress syndrome (ARDS) in immunocompromised patients. Methods: We performed a post hoc analysis on the cohort of immunocompromised patients enrolled in the Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure (LUNG SAFE) study. The LUNG SAFE study was an international, prospective study including hypoxemic patients in 459 ICUs from 50 countries across 5 continents. Results: Of 2813 patients with ARDS, 584 (20.8%) were immunocompromised, 38.9% of whom had an unspecified cause. Pneumonia, nonpulmonary sepsis, and noncardiogenic shock were their most common risk factors for ARDS. Hospital mortality was higher in immunocompromised than in immunocompetent patients (52.4% vs 36.2%; p < 0.0001), despite similar severity of ARDS. Decisions regarding limiting life-sustaining measures were significantly more frequent in immunocompromised patients (27.1% vs 18.6%; p < 0.0001). Use of noninvasive ventilation (NIV) as first-line treatment was higher in immunocompromised patients (20.9% vs 15.9%; p = 0.0048), and immunodeficiency remained independently associated with the use of NIV after adjustment for confounders. Forty-eight percent of the patients treated with NIV were intubated, and their mortality was not different from that of the patients invasively ventilated ab initio. Conclusions: Immunosuppression is frequent in patients with ARDS, and infections are the main risk factors for ARDS in these immunocompromised patients. Their management differs from that of immunocompetent patients, particularly the greater use of NIV as first-line ventilation strategy. Compared with immunocompetent subjects, they have higher mortality regardless of ARDS severity as well as a higher frequency of limitation of life-sustaining measures. Nonetheless, nearly half of these patients survive to hospital discharge. Trial registration: ClinicalTrials.gov, NCT02010073. Registered on 12 December 2013