3,029 research outputs found
Reactivity of a Cl-boratabenzene Pt(II) complex with Lewis bases : generation of the kinetically favoured Cl-boratabenzene anion
Complex [(IMes)2Pt(H)(ClBC5H4SiMe3)] (IMes = 1,3-di(2,4,6-trimethylphenyl)imidazolin-2-ylidene) reacts with Lewis bases (L = pyridine, trimethylphosphine, acetonitrile, tert-butylisocyanide) to generate the kinetically favoured ion pairs [(IMes)2Pt(H)(L)][ClBC5H4SiMe3]. Over time, the formation of the thermodynamically favoured borabenzene-L adducts is observed with L = pyridine and trimethylphosphine
[(IMes)2Pt(H)(ClBC5H4SiMe3)] : a Borabenzene–Platinum Adduct with an Unusual Pt‐Cl‐B Interaction
A Pt‐Cl‐B interaction is observed when a borabenzene derivative reacts with a platinum(0) precursor with bulky N‐heterocyclic carbene ligands. The resulting platinum(II) complex (see picture; Pt red, N blue, Cl green, B pink, Si yellow) involves a new bonding mode for borabenzene, which usually binds in an η6 fashion to transition metals
Bleomycin-induced lung injury in the rat: effects of the platelet-activating factor (PAF) receptor antagonist BN 52021 and platelet depletion.
Bleomycin is a highly effective antitumor agent, but pulmonary toxicity, characterized by an acute inflammatory reaction and associated pulmonary edema, limits clinical use of the drug. Platelets and platelet-activating factor (PAF), a membrane-derived phospholipid, have been implicated in the mechanisms that can mediate pulmonary microvascular injury. We sought to investigate the role of PAF in bleomycin-induced lung injury in the rat, using the PAF receptor antagonist BN 52021; and the role of platelets though the use of an anti-platelet antibody. Lung injury was induced by intratracheal bleomycin (1.5 mg) and assessed by measurements of lung wet weight and total pulmonary extravascular albumin space (TPEAS). Bleomycin caused a significant increase in both indices after 48 hr, compared with control animals (p less than 0.05). A single dose of BN 52021 (20 mg/kg orally) significantly reduced the bleomycin-induced increase in lung weight, but not the rise in TPEAS (p greater than 0.05). Increasing the dose of BN 52021 (20 mg/kg/12 hr, orally) had no additional effect. Reducing circulating platelet numbers by approximately 75% had no effect on either the increase in lung weight or TPEAS, observed 48 hr after bleomycin (p greater than 0.05). PAF may partially contribute to the acute inflammatory reaction seen after intratracheal bleomycin in rats
Explorations into the Viability of Coupled Radius-Orbit Evolutionary Models for Inflated Planets
The radii of some transiting extrasolar giant planets are larger than would
be expected by the standard theory. We address this puzzle with the model of
coupled radius-orbit tidal evolution developed by
\citet{Ibgui_and_Burrows_2009}. The planetary radius is evolved
self-consistently with orbital parameters, under the influence of tidal torques
and tidal dissipation in the interior of the planet. A general feature of this
model, which we have previously demonstrated in the generic case, is that a
possible transient inflation of the planetary radius can temporarily interrupt
its standard monotonic shrinking and can lead to the inflated radii that we
observe. In particular, a bloated planet with even a circular orbit may still
be inflated due to an earlier episode of tidal heating. We have modified our
model to include an orbital period dependence of the tidal dissipation factor
in the star, , .
With this model, we search, for a tidally heated planet, orbital and radius
evolutionary tracks that fall within the observational limits of the radius,
the semimajor axis, and the eccentricity of the planet in its current estimated
age range. We find that, for some inflated planets (WASP-6b and WASP-15b),
there are such tracks; for another (TrES-4), there are none; and for still
others (WASP-4b and WASP-12b), there are such tracks, but our model might imply
that we are observing the planets at a special time. Finally, we stress that
there is a two to three order-of-magnitude timescale uncertainty of the
inspiraling phase of the planet into its host star, arising from uncertainties
in the tidal dissipation factor in the star .Comment: Submitted to ApJ; 13 pages, 3 figures, 2 tables; (emulateapj format
Epigenetic regulation of cyclooxygenase-2 by methylation of c8orf4 in pulmonary fibrosis
Fibroblasts derived from the lungs of patients with idiopathic pulmonary fibrosis (IPF) and systemic sclerosis (SSc) produce low levels of prostaglandin (PG) E(2), due to a limited capacity to up-regulate cyclooxygenase-2 (COX-2). This deficiency contributes functionally to the fibroproliferative state, however the mechanisms responsible are incompletely understood. In the present study, we examined whether the reduced level of COX-2 mRNA expression observed in fibrotic lung fibroblasts is regulated epigenetically. The DNA methylation inhibitor, 5-aza-2′-deoxycytidine (5AZA) restored COX-2 mRNA expression by fibrotic lung fibroblasts dose dependently. Functionally, this resulted in normalization of fibroblast phenotype in terms of PGE(2) production, collagen mRNA expression and sensitivity to apoptosis. COX-2 methylation assessed by bisulfite sequencing and methylation microarrays was not different in fibrotic fibroblasts compared with controls. However, further analysis of the methylation array data identified a transcriptional regulator, chromosome 8 open reading frame 4 (thyroid cancer protein 1, TC-1) (c8orf4), which is hypermethylated and down-regulated in fibrotic fibroblasts compared with controls. siRNA knockdown of c8orf4 in control fibroblasts down-regulated COX-2 and PGE(2) production generating a phenotype similar to that observed in fibrotic lung fibroblasts. Chromatin immunoprecipitation demonstrated that c8orf4 regulates COX-2 expression in lung fibroblasts through binding of the proximal promoter. We conclude that the decreased capacity of fibrotic lung fibroblasts to up-regulate COX-2 expression and COX-2-derived PGE(2) synthesis is due to an indirect epigenetic mechanism involving hypermethylation of the transcriptional regulator, c8orf4
Deep, ultra-high-resolution radio imaging of submillimetre galaxies using Very Long Baseline Interferometry
We present continent-scale VLBI - obtained with the European VLBI Network
(EVN) at a wavelength of 18cm - of six distant, luminous submm-selected
galaxies (SMGs). Our images have a synthesized beam width of ~30 milliarcsec
FWHM - three orders of magnitude smaller in area than the highest resolution
VLA imaging at this wavelength - and are capable of separating radio emission
from ultra-compact radio cores (associated with active super-massive black
holes - SMBHs) from that due to starburst activity. Despite targeting compact
sources - as judged by earlier observations with the VLA and MERLIN - we
identify ultra-compact cores in only two of our targets. This suggests that the
radio emission from SMGs is produced primarily on larger scales than those
probed by the EVN, and therefore is generated by star formation rather than an
AGN - a result consistent with other methods used to identify the presence of
SMBHs in these systems.Comment: MNRAS, in pres
Spitzer Quasar and ULIRG Evolution Study (QUEST). IV. Comparison of 1-Jy Ultraluminous Infrared Galaxies with Palomar-Green Quasars
We report the results from a comprehensive study of 74 ultraluminous infrared
galaxies (ULIRGs) and 34 Palomar-Green (PG) quasars within z ~ 0.3$ observed
with the Spitzer Infrared Spectrograph (IRS). The contribution of nuclear
activity to the bolometric luminosity in these systems is quantified using six
independent methods that span a range in wavelength and give consistent results
within ~ +/-10-15% on average. The average derived AGN contribution in ULIRGs
is ~35-40%, ranging from ~15-35% among "cool" (f_25/f_60 =< 0.2) optically
classified HII-like and LINER ULIRGs to ~50 and ~75% among warm Seyfert 2 and
Seyfert 1 ULIRGs, respectively. This number exceeds ~80% in PG QSOs. ULIRGs
fall in one of three distinct AGN classes: (1) objects with small extinctions
and large PAH equivalent widths are highly starburst-dominated; (2) systems
with large extinctions and modest PAH equivalent widths have larger AGN
contributions, but still tend to be starburst-dominated; and (3) ULIRGs with
both small extinctions and small PAH equivalent widths host AGN that are at
least as powerful as the starbursts. The AGN contributions in class 2 ULIRGs
are more uncertain than in the other objects, and we cannot formally rule out
the possibility that these objects represent a physically distinct type of
ULIRGs. A morphological trend is seen along the sequence (1)-(2)-(3), in
general agreement with the standard ULIRG - QSO evolution scenario and
suggestive of a broad peak in extinction during the intermediate stages of
merger evolution. However, the scatter in this sequence, implies that black
hole accretion, in addition to depending on the merger phase, also has a strong
chaotic/random component, as in local AGN. (abridged)Comment: 61 pages, 39 figures, 16 tables, accepted for publication in ApJS,
June 2009 issue. Unabbreviated version can be found at
http://www.astro.umd.edu/~veilleux/pubs/quest4.pd
Cadmium accumulation and interactions with zinc, copper, and manganese, analysed by ICP-MS in a long-term Caco-2 TC7 cell model
The influence of long-term exposure to cadmium (Cd) on essential minerals was investigated using a Caco-2
TC7 cells and a multi-analytical tool: microwave digestion and inductively coupled plasma mass spectrometry.
Intracellular levels, effects on cadmium accumulation, distribution, and reference concentration
ranges of the following elements were determined: Na, Mg, Ca, Cr, Fe, Mn, Co, Ni, Cu, Zn, Mo, and Cd.
Results showed that Caco-2 TC7 cells incubated long-term with cadmium concentrations ranging from 0 to
10 lmol Cd/l for 5 weeks exhibited a significant increase in cadmium accumulation. Furthermore, this
accumulation was more marked in cells exposed long-term to cadmium compared with controls, and that
this exposure resulted in a significant accumulation of copper and zinc but not of the other elements
measured. Interactions of Cd with three elements: zinc, copper, and manganese were particularly studied.
Exposed to 30 lmol/l of the element, manganese showed the highest inhibition and copper the lowest on
cadmium intracellular accumulation but Zn, Cu, and Mn behave differently in terms of their mutual
competition with Cd. Indeed, increasing cadmium in the culture medium resulted in a gradual and significant
increase in the accumulation of zinc. There was a significant decrease in manganese from 5 lmol
Cd/l exposure, and no variation was observed with copper.
Abbreviation: AAS – Atomic absorption spectrometry; CRM– Certified reference material; PBS – Phosphate
buffered saline without calcium and magnesium; DMEM – Dubelcco’s modified Eagle’s medium
Improved Modeling of the Mass Distribution of Disk Galaxies by the Einasto Halo Model
(Abridged) The analysis of the rotation curves (RCs) of spiral galaxies
provides an efficient diagnostic for studying the properties of dark matter
halos and their relations with the baryonic material. We have modeled the RCs
of galaxies from The HI Nearby Galaxy Survey (THINGS) with the Einasto halo
model, which has emerged as the best-fitting model of the halos arising in
dissipationless cosmological N-body simulations. We find that the RCs are
significantly better fit with the Einasto halo than with either a
pseudo-isothermal sphere (Iso) or Navarro-Frenk-White (NFW) halo models. In our
best-fit models, the radius of density slope -2 and the density at this radius
are highly correlated. The Einasto index, which controls the overall shape of
the density profile, is near unity on average for intermediate and low mass
halos. This is not in agreement with the predictions from LCDM simulations. The
indices of the most massive halos are in rough agreement with those of
cosmological simulations and appear correlated with the halo virial mass. We
find that a typical Einasto density profile declines more strongly in its
outermost parts than any of the Iso or NFW models whereas it is relatively
shallow in its innermost regions. The core nature of those regions of halos
thus extends the cusp-core controversy found for the NFW model with low surface
density galaxies to the Einasto halo with more massive galaxies like those of
THINGS. We thus find that the Einasto halo model provides, so far, the best
match to the observed RCs, and can therefore be considered as a new standard
model for dark matter halos.Comment: 15 pages, 14 figures, The Astronomical Journal, in press, Volume 4,
2011 Octobe
- …