2,295 research outputs found
Tracing baryons in the warm-hot intergalactic medium with broad Ly alpha absorption
We discuss physical properties and baryonic content of broad Ly alpha
absorbers (BLAs) at low redshift. These absorption systems, recently discovered
in high-resolution, high-signal to noise quasar absorption line spectra,
possibly trace the warm-hot intergalactic medium (WHIM) in the temperature
range between 10^5 and 10^6 K. To extend previous BLA measurements we have
analyzed STIS data of the two quasars H 1821+643 and PG 0953+415 and have
identified 13 BLA candidates along a total (unblocked) redshift path of
dz=0.440. Combining our measurements with previous results for the lines of
sight toward PG 1259+593 and PG 1116+215, the resulting new BLA sample consists
of 20 reliably detected systems as well as 29 additional tentative cases,
implying a BLA number density of dN/dz=22-53. We estimate that the contribution
of BLAs to the baryon density at z=0 is Omega_b(BLA)>0.0027 h_70^-1 for
absorbers with log (N/b)>11.3. This number indicates that WHIM broad Ly alpha
absorbers contain a substantial fraction of the baryons in the local Universe.
(Abridged abstract)Comment: 17 pages, 7 figures; Accepted for publication in A&
Probing the IGM/Galaxy Connection IV: The LCO/WFCCD Galaxy Survey of 20 Fields Surrounding UV Bright Quasars
We publish the survey for galaxies in 20 fields containing ultraviolet bright
quasars (with z_em 0.1 to 0.5) that can be used to study the association
between galaxies and absorption systems from the low-z intergalactic medium
(IGM). The survey is magnitude limited (R~19.5 mag) and highly complete out to
10' from the quasar in each field. It was designed to detect dwarf galaxies (L
~ 0.1 L*) at an impact parameter rho 1Mpc (z=0.1) from a quasar. The complete
sample (all 20 fields) includes R-band photometry for 84718 sources and
confirmed redshifts for 2800 sources. This includes 1198 galaxies with 0.005 <
z < (z_em - 0.01) at a median redshift of 0.18, which may associated with IGM
absorption lines. All of the imaging was acquired with cameras on the Swope 40"
telescope and the spectra were obtained via slitmask observations using the
WFCCD spectrograph on the Dupont 100" telescope at Las Campanas Observatory
(LCO). This paper describes the data reduction, imaging analysis, photometry,
and spectral analysis of the survey. We tabulate the principal measurements for
all sources in each field and provide the spectroscopic dataset online.Comment: Accepted to the Astrophysical Journal Supplements; 20 pages, only 6
figures shown in this version. See
http://www.ucolick.org/~xavier/WFCCDOVI/index.html for a full-length
manuscript and other supportive materia
The Large, Oxygen-Rich Halos of Star-Forming Galaxies Are A Major Reservoir of Galactic Metals
The circumgalactic medium (CGM) is fed by galaxy outflows and accretion of
intergalactic gas, but its mass, heavy element enrichment, and relation to
galaxy properties are poorly constrained by observations. In a survey of the
outskirts of 42 galaxies with the Cosmic Origins Spectrograph onboard the
Hubble Space Telescope, we detected ubiquitous, large (150 kiloparsec) halos of
ionized oxygen surrounding star-forming galaxies, but we find much less ionized
oxygen around galaxies with little or no star formation. This ionized CGM
contains a substantial mass of heavy elements and gas, perhaps far exceeding
the reservoirs of gas in the galaxies themselves. It is a basic component of
nearly all star-forming galaxies that is removed or transformed during the
quenching of star formation and the transition to passive evolution.Comment: This paper is part of a set of three papers on circumgalactic gas
observed with the Cosmic Origins Spectrograph on HST, to be published in
Science, together with related papers by Tripp et al. and Lehner & Howk, in
the November 18, 2011 edition. This version has not undergone final
copyediting. Please see Science online for the final printed versio
The effects of multiple aerospace environmental stressors on human performance
An extended Fitt's law paradigm reaction time (RT) task was used to evaluate the effects of acceleration on human performance in the Dynamic Environment Simulator (DES) at Armstrong Laboratory, Wright-Patterson AFB, Ohio. This effort was combined with an evaluation of the standard CSU-13 P anti-gravity suit versus three configurations of a 'retrograde inflation anti-G suit'. Results indicated that RT and error rates increased 17 percent and 14 percent respectively from baseline to the end of the simulated aerial combat maneuver and that the most common error was pressing too few buttons
Probing the IGM/Galaxy Connection V: On the Origin of Lya and OVI Absorption at z<0.2
We analyze the association of galaxies to Lya and OVI absorption, the most
commonly detected transitions in the low-z intergalactic medium (IGM), in the
fields of 14 quasars with z_em = 0.06-0.57. Confirming previous studies, we
observe a high covering fraction for Lya absorption to impact parameter rho =
300kpc: 33/37 of our L>0.01L* galaxies show Lya equivalent width W_Lya>50mA.
Galaxies of all luminosity L>0.01L* and spectral type are surrounded by a
diffuse and ionized circumgalactic medium (CGM), whose baryonic mass is
estimated at ~10^(10.5 +/- 0.3) Msun for a constant N_H. The virialized halos
and extended CGM of present-day galaxies are responsible for most strong Lya
absorbers (W_Lya > 300mA) but cannot reproduce the majority of observed lines
in the Lya forest. We conclude that the majority of Lya absorption with
W_Lya=30-300mA occurs in the cosmic web predicted by cosmological simulations
and estimate a characteristic width for these filaments of ~400kpc. Regarding
OVI, we observe a near unity covering fraction to rho=200kpc for L>0.1L*
galaxies and to rho = 300kpc for sub-L* (0.1 L*<L<L*) galaxies. Similar to our
Lya results, stronger OVI systems (W_OVI > 70mA) arise in the virialized halos
of L>0.1L* galaxies. Unlike Lya, the weaker OVI systems (W_OVI~30mA) arise in
the extended CGM of sub-L* galaxies. The majority of OVI gas observed in the
low-z IGM is associated with a diffuse medium surrounding individual galaxies
with L~0.3L*, and rarely originates in the so-called warm-hot IGM (WHIM)
predicted by cosmological simulations.Comment: Submitted to the Astrophysical Journal; 26 pages, 9 figures. See
http://www.ucolick.org/~xavier/WFCCDOVI/index.html for mor
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Intracranial pressure monitoring in normal dogs using subdural and intraparenchymal miniature strain-gauge transducers.
BackgroundMonitoring of intracranial pressure (ICP) is a critical component in the management of intracranial hypertension. Safety, efficacy, and optimal location of microsensor devices have not been defined in dogs.Hypothesis/objectiveAssessment of ICP using a microsensor transducer is feasible in anesthetized and conscious animals and is independent of transducer location. Intraparenchymal transducer placement is associated with more adverse effects.AnimalsSeven adult, bred-for-research dogs.MethodsIn a prospective investigational study, microsensor ICP transducers were inserted into subdural and intraparenchymal locations at defined rostral or caudal locations within the rostrotentorial compartment under general anesthesia. Mean arterial pressure and ICP were measured continuously during physiological maneuvers, and for 20 hours after anesthesia.ResultsBaseline mean ± SD values for ICP and cerebral perfusion pressure were 7.2 ± 2.3 and 78.9 ± 7.6 mm Hg, respectively. Catheter position did not have a significant effect on ICP measurements. There was significant variation from baseline ICP accompanying physiological maneuvers (P < .001) and with normal activities, especially with changes in head position (P < .001). Pathological sequelae were more evident after intraparenchymal versus subdural placement.Conclusions and clinical importanceUse of a microsensor ICP transducer was technically straightforward and provided ICP measurements within previously reported reference ranges. Results support the use of an accessible dorsal location and subdural positioning. Transient fluctuations in ICP are normal events in conscious dogs and large variations associated with head position should be accounted for when evaluating animals with intracranial hypertension
A Quantitative and Qualitative Study of Facebook Privacy using the Antecedent-Privacy Concern-Outcome Macro Model
Information privacy is a complex and important phenomenon to understand. Because of this, several recent review articles have integrated findings across various studies and contexts. In this study we investigate information privacy in the online social networking context using the Antecedent-Privacy Concern-Outcome (APCO) Macro Model as the theoretical lens. We use both quantitative and qualitative data collected in a survey of Facebook users. Online social networking provides a rich window into privacy concerns and the resulting behavioral reactions. By analyzing both types of data, we are able to show additional support and insights for our hypotheses tests. These results provide future research opportunities that include modifying the APCO model and refining its constructs to be more context and risk-specific
Infinite families of crank functions, Stanton-type conjectures, and unimodality
Dyson's rank function and the Andrews--Garvan crank function famously give combinatorial witnesses for Ramanujan's partition function congruences modulo 5, 7, and 11. While these functions can be used to show that the corresponding sets of partitions split into 5, 7, or 11 equally sized sets, one may ask how to make the resulting bijections between partitions organized by rank or crank combinatorially explicit. Stanton recently made conjectures which aim to uncover a deeper combinatorial structure along these lines, where it turns out that minor modifications of the rank and crank are required. Here, we prove two of these conjectures. We also provide abstract criteria for quotients of polynomials by certain cyclotomic polynomials to have non-negative coefficients based on unimodality and symmetry. Furthermore, we extend Stanton's conjecture to an infinite family of cranks. This suggests further applications to other combinatorial objects. We also discuss numerical evidence for our conjectures, connections with other analytic conjectures such as the distribution of partition ranks
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