2,104 research outputs found
A Survey of O VI, C III, and H I in Highly Ionized High-Velocity Clouds
(ABRIDGED) We present a Far-Ultraviolet Spectroscopic Explorer survey of
highly ionized high-velocity clouds (HVCs) in 66 extragalactic sight lines. We
find a total of 63 high-velocity O VI absorbers, 16 with 21 cm-emitting H I
counterparts and 47 ``highly ionized'' absorbers without 21 cm emission. 11 of
these high-velocity O VI absorbers are positive-velocity wings (broad O VI
features extending asymmetrically to velocities of up to 300 km/s). The highly
ionized HVC population is characterized by =38+/-10 km/s and <log
N_a(O VI)>=13.83+/-0.36. We find that 81% (30/37) of high-velocity O VI
absorbers have clear accompanying C III absorption, and 76% (29/38) have
accompanying H I absorption in the Lyman series. The lower average width of the
high-velocity H I absorbers implies the H I lines arise in a separate, lower
temperature phase than the O VI. We find that the shape of the wing profiles is
well reproduced by a radiatively cooling, vertical outflow. However, the
outflow has to be patchy and out of ionization equilibrium. An alternative
model, consistent with the observations, is one where the highly ionized HVCs
represent the low N(H I) tail of the HVC population, with the O VI formed at
the interfaces around the embedded H I cores. Though we cannot rule out a Local
Group explanation, we favor a Galactic origin. This is based on the recent
evidence that both H I HVCs and the million-degree gas detected in X-ray
absorption are Galactic phenomena. Since the highly ionized HVCs appear to
trace the interface between these two Galactic phases, it follows that highly
ionized HVCs are Galactic themselves. However, the non-detection of
high-velocity O VI in halo star spectra implies that any Galactic high-velocity
O VI exists at z-distances beyond a few kpc.Comment: 36 pages, 14 figures (3 in color), accepted to ApJS. Some figures
downgraded to limit file siz
Predicting extreme events in a data-driven model of turbulent shear flow using an atlas of charts
Dynamical systems with extreme events are difficult to capture with
data-driven modeling, due to the relative scarcity of data within extreme
events compared to the typical dynamics of the system, and the strong
dependence of the long-time occurrence of extreme events on short-time
conditions.A recently developed technique [Floryan, D. & Graham, M. D.
Data-driven discovery of intrinsic dynamics. Nat Mach Intell ,
1113-1120 (2022)], here denoted as , or CANDyMan, overcomes these difficulties
by decomposing the time series into separate charts based on data similarity,
learning dynamical models on each chart via individual time-mapping neural
networks, then stitching the charts together to create a single atlas to yield
a global dynamical model. We apply CANDyMan to a nine-dimensional model of
turbulent shear flow between infinite parallel free-slip walls under a
sinusoidal body force [Moehlis, J., Faisst, H. & Eckhardt, B. A low-dimensional
model for turbulent shear flows. New J Phys , 56 (2004)], which
undergoes extreme events in the form of intermittent quasi-laminarization and
long-time full laminarization. We demonstrate that the CANDyMan method allows
the trained dynamical models to more accurately forecast the evolution of the
model coefficients, reducing the error in the predictions as the model evolves
forward in time. The technique exhibits more accurate predictions of extreme
events, capturing the frequency of quasi-laminarization events and predicting
the time until full laminarization more accurately than a single neural
network.Comment: 9 pages, 7 figure
Quality of Life, Depression, and Healthcare Resource Utilization among Adults with Type 2 Diabetes Mellitus and Concomitant Hypertension and Obesity: A Prospective Survey
Background. This study compared quality of life, depression, and healthcare resource utilization among adults with type 2 diabetes mellitus (T2DM) and comorbid hypertension (HTN) and obesity with those of adults reporting T2DM alone. Methods. Respondents to the US SHIELD survey self-reported their height, weight, comorbid conditions, hospitalizations, and outpatient visits and completed the Short Form-12 (SF-12) and Patient Health Questionnaire (PHQ-9). Respondents reporting T2DM and HTN and obesity (body mass index, BMI, ≥30 kg/m2) were compared with a T2DM-alone group. Results. Respondents with T2DM, HTN, and obesity (n = 1292) had significantly lower SF-12 Physical and Mental Component Summary scores (37.3 and 50.9, resp.) than T2DM-alone respondents (n = 349) (45.8 and 53.5, resp., P < 0.0001). Mean PHQ-9 scores were significantly higher among T2DM respondents with comorbid HTN and obesity (5.0 versus 2.5, P < 0.0001), indicating greater depression burden. Respondents with T2DM, HTN, and obesity had significantly more resource utilization with respect to physician visits and emergency room visits but not hospitalizations than respondents with T2DM alone (P = 0.03). Conclusions. SHIELD respondents with comorbid conditions of T2DM, HTN, and obesity reported greater healthcare resource utilization, more depression symptoms, and lower quality of life than the T2DM-alone group
Narrow-line magneto-optical cooling and trapping of strongly magnetic atoms
Laser cooling on weak transitions is a useful technique for reaching
ultracold temperatures in atoms with multiple valence electrons. However, for
strongly magnetic atoms a conventional narrow-line magneto-optical trap (MOT)
is destabilized by competition between optical and magnetic forces. We overcome
this difficulty in Er by developing an unusual narrow-line MOT that balances
optical and magnetic forces using laser light tuned to the blue side of a
narrow (8 kHz) transition. The trap population is spin-polarized with
temperatures reaching below 2 microkelvin. Our results constitute an
alternative method for laser cooling on weak transitions, applicable to
rare-earth-metal and metastable alkaline earth elements.Comment: To appear in Phys. Rev. Lett. 4 pages, 5 figure
Characterizing Transition Temperature Gas in the Galactic Corona
We present a study of the properties of the transition temperature (T~10^5 K)
gas in the Milky Way corona, based on measurements of OVI, NV, CIV, SiIV and
FeIII absorption lines seen in the far ultraviolet spectra of 58 sightlines to
extragalactic targets, obtained with Far-Ultraviolet Spectroscopic Explorer
(FUSE) and Space Telescope Imaging Spectrograph. In many sightlines the
Galactic absorption profiles show multiple components, which are analyzed
separately. We find that the highly-ionized atoms are distributed irregularly
in a layer with a scaleheight of about 3 kpc, which rotates along with the gas
in the disk, without an obvious gradient in the rotation velocity away from the
Galactic plane. Within this layer the gas has randomly oriented velocities with
a dispersion of 40-60 km/s. On average the integrated column densities are log
N(OVI)=14.3, log N(NV)=13.5, log N(CIV)=14.2, log N(SiIV)=13.6 and log
N(FeIII)=14.2, with a dispersion of just 0.2 dex in each case. In sightlines
around the Galactic Center and Galactic North Pole all column densities are
enhanced by a factor ~2, while at intermediate latitudes in the southern sky
there is a deficit in N(OVI) of about a factor 2, but no deficit for the other
ions. We compare the column densities and ionic ratios to a series of
theoretical predictions: collisional ionization equilibrium, shock ionization,
conductive interfaces, turbulent mixing, thick disk supernovae, static
non-equilibrium ionization (NIE) radiative cooling and an NIE radiative cooling
model in which the gas flows through the cooling zone. None of these models can
fully reproduce the data, but it is clear that non-equilibrium ionization
radiative cooling is important in generating the transition temperature gas.Comment: 99 pages, 11 figures, with appendix on Cooling Flow model; only a
sample of 5 subfigures of figure 2 included - full set of 69 available
through Ap
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