446 research outputs found
Kinematic and Thermal Structure at the onset of high-mass star formation
We want to understand the kinematic and thermal properties of young massive
gas clumps prior to and at the earliest evolutionary stages of high-mass star
formation. Do we find signatures of gravitational collapse? Do we find
temperature gradients in the vicinity or absence of infrared emission sources?
Do we find coherent velocity structures toward the center of the dense and cold
gas clumps? To determine kinematics and gas temperatures, we used ammonia,
because it is known to be a good tracer and thermometer of dense gas. We
observed the NH(1,1) and (2,2) lines within seven very young high-mass
star-forming regions with the VLA and the Effelsberg 100m telescope. This
allows us to study velocity structures, linewidths, and gas temperatures at
high spatial resolution of 3-5, corresponding to 0.05 pc. We find on
average cold gas clumps with temperatures in the range between 10 K and 30 K.
The observations do not reveal a clear correlation between infrared emission
peaks and ammonia temperature peaks. We report an upper limit for the linewidth
of 1.3 km s, at the spectral resolution limit of our VLA
observation. This indicates a relatively low level of turbulence on the scale
of the observations. Velocity gradients are present in almost all regions with
typical velocity differences of 1 to 2 km s and gradients of 5 to 10 km
s pc. These velocity gradients are smooth in most cases, but
there is one exceptional source (ISOSS23053), for which we find several
velocity components with a steep velocity gradient toward the clump centers
that is larger than 30 km s pc. This steep velocity gradient is
consistent with recent models of cloud collapse. Furthermore, we report a
spatial correlation of ammonia and cold dust, but we also find decreasing
ammonia emission close to infrared emission sources.Comment: 20 pages, 10 figure
Kinematic structure of massive star-forming regions - I. Accretion along filaments
The mid- and far-infrared view on high-mass star formation, in particular
with the results from the Herschel space observatory, has shed light on many
aspects of massive star formation. However, these continuum studies lack
kinematic information.
We study the kinematics of the molecular gas in high-mass star-forming
regions.
We complemented the PACS and SPIRE far-infrared data of 16 high-mass
star-forming regions from the Herschel key project EPoS with N2H+ molecular
line data from the MOPRA and Nobeyama 45m telescope. Using the full N2H+
hyperfine structure, we produced column density, velocity, and linewidth maps.
These were correlated with PACS 70micron images and PACS point sources. In
addition, we searched for velocity gradients.
For several regions, the data suggest that the linewidth on the scale of
clumps is dominated by outflows or unresolved velocity gradients. IRDC18454 and
G11.11 show two velocity components along several lines of sight. We find that
all regions with a diameter larger than 1pc show either velocity gradients or
fragment into independent structures with distinct velocities. The velocity
profiles of three regions with a smooth gradient are consistent with gas flows
along the filament, suggesting accretion flows onto the densest regions.
We show that the kinematics of several regions have a significant and complex
velocity structure. For three filaments, we suggest that gas flows toward the
more massive clumps are present.Comment: accepted by A&
Thyroid hormone uptake in cultured rat anterior pituitary cells: effects of energy status and bilirubin
Transport of thyroxine (T(4)) into the liver is inhibited in fasting and
by bilirubin, a compound often accumulating in the serum of critically ill
patients. We tested the effects of chronic and acute energy deprivation,
bilirubin and its precursor biliverdin on the 15-min uptake of
[(125)I]tri-iodothyronine ([(125)I]T(3)) and [(125)I]T(4) and on TSH
release in rat anterior pituitary cells maintained in primary culture for
3 days. When cells were cultured and incubated in medium without glucose
and glutamine to induce chronic energy deprivation, the ATP content was
reduced by 45% (P<0. 05) and [(125)I]T(3) uptake by 13% (NS), but TSH
release was unaltered. Preincubation (30 min) and incubation (15 min) with
10 microM oligomycin reduced ATP content by 51% (P<0.05) and 53% (P<0. 05)
under energy-rich and energy-poor culture conditions respectively;
[(125)I]T(3) uptake was reduced by 66% (P<0.05) and 64% (P<0.05). Neither
bilirubin nor biliverdin (both 1-200 microM) affected uptake of
[(125)I]T(3) or [(125)I]T(4). Bilirubin (1-50 microM) did not alter basal
or TRH-induced TSH release. In conclusion, the absence of inhibitory
effects of chronic energy deprivation and bilirubin on thyroid hormone
uptake by pituitary cells supports the view that the transport is
regulated differently than that in the liver
Adaptive changes in transmembrane transport and metabolism of triiodothyronine in perfused livers of fed and fasted hypothyroid and hyperthyroid rats
The transport and subsequent metabolism of triiodothyronine (T3) were studied in isolated perfused livers of euthyroid, hypothyroid, and hyperthyroid rats, both fed and 48-hour-fasted. T3 kinetics (transport and metabolism) during perfusion were evaluated by a two-pool model, whereas the metabolism of T3 was also investigated by determination of T3 breakdown products by chromatography of medium and bile. For comparison of groups, metabolism was corrected for differences in transport. Transport parameters in fed hypothyroid livers were not significantly changed as compared with euthyroid livers, whereas metabolism was decreased. In fed hyperthyroid livers, fractional transfer rate constants for influx (k21) and efflux (k12) were decreased and metabolism, corrected for differences in intracellular mass transfer, was increased. Furthermore, for transport in hyperthyroid livers it was shown that only total mass transfer (TMT) into the metabolizing liver compartment (not into the nonmetabolizing liver compartment) was decreased. Transport and metabolic parameters in fasted hypothyroid livers were decreased as compared with euthyroid fed livers. In fasted hyperthyroid livers, transport and metabolism were not significantly different as compared with that in euthyroid fed livers, so transport was increased versus hyperthyroid fed livers. It appeared therefore that fasting normalized the effects of hyperthyroidism on both the transport and metabolic processes of T3 in the liver. The present study demonstrates normal transport and decreased metabolism in livers of hypothyroid fed rats and decreased transport and increased metabolism in livers of hyperthyroid fed rats. In livers of hypothyroid fasted rats transport and metabolism were decreased, whereas in livers of hyperthyroid fasted rats transport and metabolism were not significantly different from that in euthyroid fed livers. These changes might favor tissue euthyroidism despite the altered thyroid and nutritional state, and can therefore be seen as adaptation mechanisms to these altered states at the tissue level
Changes in renal tri-iodothyronine and thyroxine handling during fasting
OBJECTIVE: Liver handling of thyroid hormones (TH) has been known to alter
significantly during fasting. This study investigates whether renal
handling of TH is also changed during fasting. METHODS: We measured
urinary excretion rates and clearances of free tri-iodothyronine (T(3))
and free thyroxine (T(4)) in healthy subjects prior to and on the third
day of fasting. RESULTS: During fasting, both mean T(3) and T(4) urinary
excretion decreased significantly to a mean value of 42% of control. Also,
total and free (F) serum T(3) concentrations declined significantly, but
serum T(4) did not change. Both FT(3) and FT(4) clearance decreased
significantly during fasting (62% and 42% of control). The fasting-induced
decrease in uric acid clearance correlated well with the decrease in FT(3)
clearance (r=0.94; P<0.001). Serum concentrations of non-esterified fatty
acids (NEFA) were significantly elevated during fasting. CONCLUSIONS: The
findings cannot be fully explained by the fasting-induced decrease in
serum T(3), a
Effects of interleukin-1 beta on thyrotropin secretion and thyroid hormone uptake in cultured rat anterior pituitary cells
The effects of interleukin-1 beta (IL-1 beta) and tumor necrosis
factor-alpha (TNF alpha) on basal and TRH-induced TSH release, and the
effects of IL-1 beta on the uptake of [125I]T3 and [125I]T4 and on nuclear
binding of [125I]T3 were examined. Furthermore, the release of other
anterior pituitary hormones in the presence of IL-1 beta was measured.
Anterior pituitary cells from male Wistar rats were cultured for 3 days in
medium containing 10% FCS. Incubation were performed at 37 C in medium
with 0.5% BSA for measurement of [125I]T3 uptake and with 0.1% BSA for
measurement of [125I]T4 uptake. Exposure to IL-1 beta (1 pM-1 nM) or TNF
alpha (100 pM) for 2-4 h resulted in a significant decline in TSH release,
which was almost 50% (P < 0.05) for 1 nM IL-1 beta and 24% (P < 0.05) for
100 pM TNF alpha. Measurement of other anterior pituitary hormones (FSH,
LH, PRL, and ACTH) in the same incubation medium showed that IL-1 beta did
not alter their release. When the effects of IL-1 beta (1 pM-1 nM) and TNF
alpha (100 pM) on TRH-induced TSH release were measured in short term
experiments, the inhibitory effects had disappeared. The addition of 1-100
nM octreotide, a somatostatin analog, resulted in a decrease in
TRH-induced TSH release up to 33% of the control value (P < 0.05).
Exposure to dexamethasone (1 nM to 1 microM) affected basal and
TRH-induced TSH release similar to the effect of IL-1 beta. The 15-min
uptake of [125I]T3 and [125I]T4, expressed as femtomoles per pM free
hormone, was not affected by the presence of IL-1 beta (1-100 pM). When
IL-1 beta (100 pM) was present during 3 days of culture, TSH release was
reduced to 88 +/- 2% of the control value (P < 0.05). This effect was not
associated with an altered [125I]T3 uptake (15 min to 4 h) or with any
change in nuclear T3 binding. We conclude that 1) IL-1 beta decreases TSH
release by a direct action on the pituitary; 2) this effect is not due to
elevated thyroid hormone uptake or increase T3 nuclear occupancy; 3) IL-1
beta does not affect TRH-induced TSH release or the release of other
anterior pituitary hormones; and 4) TNF alpha affects basal and
TRH-induced TSH release in the same way as IL-1 beta
Kinematic structure of massive star-forming regions - I. Accretion along filaments
The mid- and far-infrared view on high-mass star formation, in particular
with the results from the Herschel space observatory, has shed light on many
aspects of massive star formation. However, these continuum studies lack
kinematic information.
We study the kinematics of the molecular gas in high-mass star-forming
regions.
We complemented the PACS and SPIRE far-infrared data of 16 high-mass
star-forming regions from the Herschel key project EPoS with N2H+ molecular
line data from the MOPRA and Nobeyama 45m telescope. Using the full N2H+
hyperfine structure, we produced column density, velocity, and linewidth maps.
These were correlated with PACS 70micron images and PACS point sources. In
addition, we searched for velocity gradients.
For several regions, the data suggest that the linewidth on the scale of
clumps is dominated by outflows or unresolved velocity gradients. IRDC18454 and
G11.11 show two velocity components along several lines of sight. We find that
all regions with a diameter larger than 1pc show either velocity gradients or
fragment into independent structures with distinct velocities. The velocity
profiles of three regions with a smooth gradient are consistent with gas flows
along the filament, suggesting accretion flows onto the densest regions.
We show that the kinematics of several regions have a significant and complex
velocity structure. For three filaments, we suggest that gas flows toward the
more massive clumps are present.Comment: accepted by A&
Submillimeter Observations of Dense Clumps in the Infrared Dark Cloud G049.40-00.01
We obtained 350 and 850 micron continuum maps of the infrared dark cloud
G049.40-00.01. Twenty-one dense clumps were identified within G049.40-00.01
based on the 350 micron continuum map with an angular resolution of about 9.6".
We present submillimeter continuum maps and report physical properties of the
clumps. The masses of clumps range from 50 to 600 M_sun. About 70% of the
clumps are associated with bright 24 micron emission sources, and they may
contain protostars. The most massive two clumps show extended, enhanced 4.5
micron emission indicating vigorous star-forming activity. The clump size-mass
distribution suggests that many of them are forming high mass stars.
G049.40-00.01 contains numerous objects in various evolutionary stages of star
formation, from pre-protostellar clumps to HII regions.Comment: 6 pages, 3 figures; accepted for publication in Ap
Studies on neotropical Phasmatodea XV: A remarkable new stick insect from highly montane habitats of Hispaniola (Pseudophasmatidae: Xerosomatinae: Hesperophasmatini)
The new genus and new species Tainophasma monticola gen. nov., sp. nov., a highly montane taxon which is remarkable for its very small size, compact body, short legs and proportionally very large head, is described and illustrated from both sexes and the egg
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