325 research outputs found
Conférences sur les émotions et l'homéostasie, Paris, 1930
Walter B. Cannon (1871-1945) est l’une des figures majeures de la physiologie moderne. Ces deux séries de conférences inédites qu’il délivre en français lors d’un séjour à Paris au début de l’année 1930, représentent un moment charnière dans son parcours intellectuel. Elles lui serviront de base à la rédaction de son ouvrage phare La sagesse du corps. Capitales pour l’histoire de la physiologie et de la médecine du 20 e siècle, ces sources éclairent l’émergence du concept de stress, qui, avec les problématiques médicales et sociales qu’il soulève, trouve un écho particulier dans les sciences biomédicales contemporaines
Weight Loss Programs May Have Beneficial or Adverse Effects on Fat Mass and Insulin Sensitivity in Overweight and Obese Black Women
OBJECTIVE: Weight loss interventions have produced little change in insulin sensitivity in black women, but mean data may obscure metabolic benefit to some and adverse effects for others. Accordingly, we analyzed insulin sensitivity relative to fat mass change following a weight loss program. DESIGN AND METHODS: Fifty-four black women (BMI range 25.9 to 54.7 kg/m(2)) completed the 6-month program that included nutrition information and worksite exercise facilities. Fat mass was measured by dual-energy X-ray absorptiometry, and insulin sensitivity index (S(I)) was calculated from an insulin-modified intravenous glucose tolerance test using the minimal model. RESULTS: Baseline S(I) (range 0.74 to 7.58 l/mU(−1)•min(−1)) was inversely associated with fat mass (r = −0.516, p < 0.001), independent of age. On average, subjects lost fat mass (baseline 40.8 ± 12.4 to 39.4 ± 12.6 kg [mean ± SD], P < 0.01), but 17 women (32 %) actually gained fat mass. S(I) for the group was unchanged (baseline 3.3 ± 1.7 to 3.2 ± 1.6, P = 0.67). However, the tertile with greatest fat mass loss (−3.6 kg, range −10.7 to −1.7 kg) improved insulin sensitivity (S(I) +0.3 ± 1.2), whereas the tertile with net fat mass gain (+0.9 kg, range −0.1 to +3.8 kg) had reduced insulin sensitivity (S(I) −0.7 ± 1.3) from baseline values (P < 0.05 by ANOVA). CONCLUSIONS: Black women in a weight loss program who lose fat mass may have improved insulin sensitivity, but fat mass gain with diminished sensitivity is common. Additional support for participants who fail to achieve fat mass loss early in an intervention may be required for success
The Nature of Starbursts: I. The Star Formation Histories of Eighteen Nearby Starburst Dwarf Galaxies
We use archival HST observations of resolved stellar populations to derive
the star formation histories (SFHs) of 18 nearby starburst dwarf galaxies. In
this first paper we present the observations, color-magnitude diagrams, and the
SFHs of the 18 starburst galaxies, based on a homogeneous approach to the data
reduction, differential extinction, and treatment of photometric completeness.
We adopt a star formation rate (SFR) threshold normalized to the average SFR of
the individual system as a metric for classifying starbursts in SFHs derived
from resolved stellar populations. This choice facilitates finding not only
currently bursting galaxies but also "fossil" bursts increasing the sample size
of starburst galaxies in the nearby (D<8 Mpc) universe. Thirteen of the
eighteen galaxies are experiencing ongoing bursts and five galaxies show fossil
bursts. From our reconstructed SFHs, it is evident that the elevated SFRs of a
burst are sustained for hundreds of Myr with variations on small timescales. A
long >100 Myr temporal baseline is thus fundamental to any starburst definition
or identification method. The longer lived bursts rule out rapid
"self-quenching" of starbursts on global scales. The bursting galaxies' gas
consumption timescales are shorter than the Hubble time for all but one galaxy
confirming the short-lived nature of starbursts based on fuel limitations.
Additionally, we find the strength of the H{\alpha} emission usually correlates
with the CMD based SFR during the last 4-10 Myr. However, in four cases, the
H{\alpha} emission is significantly less than what is expected for models of
starbursts; the discrepancy is due to the SFR changing on timescales of a few
Myr. The inherently short timescale of the H{\alpha} emission limits
identifying galaxies as starbursts based on the current characteristics which
may or may not be representative of the recent SFH of a galaxy.Comment: 53 pages, 11 figure
The Calibration of Monochromatic Far-Infrared Star Formation Rate Indicators
(Abridged) Spitzer data at 24, 70, and 160 micron and ground-based H-alpha
images are analyzed for a sample of 189 nearby star-forming and starburst
galaxies to investigate whether reliable star formation rate (SFR) indicators
can be defined using the monochromatic infrared dust emission centered at 70
and 160 micron. We compare recently published recipes for SFR measures using
combinations of the 24 micron and observed H-alpha luminosities with those
using 24 micron luminosity alone. From these comparisons, we derive a reference
SFR indicator for use in our analysis. Linear correlations between SFR and the
70 and 160 micron luminosity are found for L(70)>=1.4x10^{42} erg/s and
L(160)>=2x10^{42} erg/s, corresponding to SFR>=0.1-0.3 M_sun/yr. Below those
two luminosity limits, the relation between SFR and 70 micron (160 micron)
luminosity is non-linear and SFR calibrations become problematic. The
dispersion of the data around the mean trend increases for increasing
wavelength, becoming about 25% (factor ~2) larger at 70 (160) micron than at 24
micron. The increasing dispersion is likely an effect of the increasing
contribution to the infrared emission of dust heated by stellar populations not
associated with the current star formation. The non-linear relation between SFR
and the 70 and 160 micron emission at faint galaxy luminosities suggests that
the increasing transparency of the interstellar medium, decreasing effective
dust temperature, and decreasing filling factor of star forming regions across
the galaxy become important factors for decreasing luminosity. The SFR
calibrations are provided for galaxies with oxygen abundance 12+Log(O/H)>8.1.
At lower metallicity the infrared luminosity no longer reliably traces the SFR
because galaxies are less dusty and more transparent.Comment: 69 pages, 19 figures, 2 tables; accepted for publication on Ap
An Ultraviolet-to-Radio Broadband Spectral Atlas of Nearby Galaxies
The ultraviolet-to-radio continuum spectral energy distributions are
presented for all 75 galaxies in the Spitzer Infrared Nearby Galaxies Survey
(SINGS). A principal component analysis of the sample shows that most of the
sample's spectral variations stem from two underlying components, one
representative of a galaxy with a low infrared-to-ultraviolet ratio and one
representative of a galaxy with a high infrared-to-ultraviolet ratio. The
influence of several parameters on the infrared-to-ultraviolet ratio is studied
(e.g., optical morphology, disk inclination, far-infrared color, ultraviolet
spectral slope, and star formation history). Consistent with our understanding
of normal star-forming galaxies, the SINGS sample of galaxies in comparison to
more actively star-forming galaxies exhibits a larger dispersion in the
infrared-to-ultraviolet versus ultraviolet spectral slope correlation. Early
type galaxies, exhibiting low star formation rates and high optical surface
brightnesses, have the most discrepant infrared-to-ultraviolet correlation.
These results suggest that the star formation history may be the dominant
regulator of the broadband spectral variations between galaxies. Finally, a new
discovery shows that the 24 micron morphology can be a useful tool for
parametrizing the global dust temperature and ultraviolet extinction in nearby
galaxies. The dust emission in dwarf/irregular galaxies is clumpy and warm
accompanied by low ultraviolet extinction, while in spiral galaxies there is
typically a much larger diffuse component of cooler dust and average
ultraviolet extinction. For galaxies with nuclear 24 micron emission, the dust
temperature and ultraviolet extinction are relatively high compared to disk
galaxies.Comment: Accepted for publication in the Astrophysical Journal; Fixed radio
flux density units (mJy
Infrared Spectral Energy Distributions of Nearby Galaxies
The Spitzer Infrared Nearby Galaxies Survey (SINGS) is carrying out a
comprehensive multi-wavelength survey on a sample of 75 nearby galaxies. The
1-850um spectral energy distributions are presented using broadband imaging
data from Spitzer, 2MASS, ISO, IRAS, and SCUBA. The infrared colors derived
from the globally-integrated Spitzer data are generally consistent with the
previous generation of models that were developed based on global data for
normal star-forming galaxies, though significant deviations are observed.
Spitzer's excellent sensitivity and resolution also allow a detailed
investigation of the infrared spectral energy distributions for various
locations within the three large, nearby galaxies NGC3031 (M81), NGC5194 (M51),
and NGC7331. Strong correlations exist between the local star formation rate
and the infrared colors f_nu(70um)/f_nu(160um) and f_nu(24um)/f_nu(160um),
suggesting that the 24 and 70um emission are useful tracers of the local star
formation activity level. Preliminary evidence indicates that variations in the
24um emission, and not variations in the emission from polycyclic aromatic
hydrocarbons at 8um, drive the variations in the f_nu(8.0um)/f_nu(24um) colors
within NGC3031, NGC5194, and NGC7331. If the galaxy-to-galaxy variations in
spectral energy distributions seen in our sample are representative of the
range present at high redshift then extrapolations of total infrared
luminosities and star formation rates from the observed 24um flux will be
uncertain at the factor-of-five level (total range). The corresponding
uncertainties using the redshifted 8.0um flux (e.g. observed 24um flux for a
z=2 source) are factors of 10-20. Considerable caution should be used when
interpreting such extrapolated infrared luminosities.Comment: 32 pages including 16 figures; accepted for publication in the
Astrophysical Journa
High-resolution mass models of dwarf galaxies from LITTLE THINGS
We present high-resolution rotation curves and mass models of 26 dwarf galaxies from LITTLE THINGS. LITTLE THINGS is a high-resolution Very Large Array HI survey for nearby dwarf galaxies in the local volume within 11 Mpc. The rotation curves of the sample galaxies derived in a homogeneous and consistent manner are combined with Spitzer archival 3.6 micron and ancillary optical U, B, and V images to construct mass models of the galaxies. We decompose the rotation curves in terms of the dynamical contributions by baryons and dark matter halos, and compare the latter with those of dwarf galaxies from THINGS as well as Lambda CDM SPH simulations in which the effect of baryonic feedback processes is included. Being generally consistent with THINGS and simulated dwarf galaxies, most of the LITTLE THINGS sample galaxies show a linear increase of the rotation curve in their inner regions, which gives shallower logarithmic inner slopes alpha of their dark matter density profiles. The mean value of the slopes of the 26 LITTLE THINGS dwarf galaxies is alpha =-0.32 +/- 0.24 which is in accordance with the previous results found for low surface brightness galaxies (alpha = -0.2 +/- 0.2) as well as the seven THINGS dwarf galaxies (alpha =-0.29 +/- 0.07). However, this significantly deviates from the cusp-like dark matter distribution predicted by dark-matter-only Lambda CDM simulations. Instead our results are more in line with the shallower slopes found in the Lambda CDM SPH simulations of dwarf galaxies in which the effect of baryonic feedback processes is included. In addition, we discuss the central dark matter distribution of DDO 210 whose stellar mass is relatively low in our sample to examine the scenario of inefficient supernova feedback in low mass dwarf galaxies predicted from recent Lambda SPH simulations of dwarf galaxies where central cusps still remain.Peer reviewe
The intriguing HI gas in NGC 5253: an infall of a diffuse, low-metallicity HI cloud?
(Abridged) We present new, deep HI line and 20-cm radio continuum data of the
very puzzling blue compact dwarf galaxy NGC 5253, obtained with the ATCA as
part of the `Local Volume HI Survey' (LVHIS). Our low-resolution HI maps show
the disturbed HI morphology that NGC 5253 possesses, including tails, plumes
and detached HI clouds. The high-resolution map reveals an HI plume at the SE
and an HI structure at the NW that surrounds an Ha shell. We confirm that the
kinematics of the neutral gas are highly perturbed and do not follow a rotation
pattern. We discuss the outflow and infall scenarios to explain such disturbed
kinematics, analyze the environment in which it resides, and compare it
properties with those observed in similar star-forming dwarf galaxies. The
radio-continuum emission of NGC 5253 is resolved and associated with the
intense star-forming region at the center of the galaxy. We complete the
analysis using multiwavelength data extracted from the literature. We estimate
the SFR using this multiwavelength approach. NGC 5253 does not satisfy the
Schmidt-Kennicutt law of star-formation, has a very low HI mass-to-light ratio
when comparing with its stellar mass, and seems to be slightly metal-deficient
in comparison with starbursts of similar baryonic mass. Taking into account all
available multiwavelength data, we conclude that NGC 5253 is probably
experiencing the infall of a diffuse, low-metallicity HI cloud along the minor
axis of the galaxy, which is comprising the ISM and triggering the powerful
starburst. The tidally disturbed material observed at the east and north of the
galaxy is a consequence of this interaction, which probably started more than
100 Myr ago. The origin of this HI cloud may be related with a strong
interaction between NGC 5253 and the late-type spiral galaxy M 83 in the past.Comment: 19 pages, 12 figures, accepted for publication in MNRA
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