2,444 research outputs found
dGEMRIC as a function of BMI
SummaryObjectiveDelayed gadolinium-enhanced MRI of cartilage (dGEMRIC) reflects cartilage glycosaminoglycan (GAG) distribution. The technique assumes that the plasma levels of the contrast agent Gd-DTPA2â are the same across individuals after intravenous (IV) injection, when dosing by weight. However, adipose tissue has lower extracellular water (ECW) than lean tissue. The aims of this study were to measure (1) plasma Gd-DTPA2â levels vs body mass index (BMI), and (2) dGEMRIC vs BMI after correcting for the doseâBMI effect.Method(1) Plasma Gd-DTPA2â levels were analyzed at 3â90min after IV injection per body weight in 24 individuals with BMI between 21.5 and 46.5. (2) dGEMRIC was compared with BMI in 19 asymptomatic volunteers and 23 with osteoarthritis (OA).Results(1) Plasma Gd-DTPA2â kinetics were similar in obese and non-obese groups, however, overall concentration was higher in the obese group. A very obese subject (BMI 45) would have 1.4 times higher Gd-DTPA2â concentration than a lean subject (BMI 20), which translates into a bias in dGEMRIC of up to 20%. (2) With dose bias taken into account, dGEMRIC showed no correlation with BMI in asymptomatic knees. In OA knees, unnarrowed femoral compartments demonstrated a negative correlation between dGEMRIC and BMI (R=0.57, P=0.004). No correlation was seen in radiographically narrowed compartments.ConclusionBMI can be a source of dosing bias in dGEMRIC and a correction factor should be considered in cross-sectional studies with a large range of BMI. There is no correlation between dGEMRIC and BMI in asymptomatic knees, but a negative correlation in OA knees
The Role of a Hot Gas Environment on the Evolution of Galaxies
Most spiral galaxies are found in galaxy groups with low velocity
dispersions; most E/S0 galaxies are found in galaxy groups with relatively high
velocity dispersions. The mass of the hot gas we can observe in the E/S0 groups
via their thermal X-ray emission is, on average, as much as the baryonic mass
of the galaxies in these groups. By comparison, galaxy clusters have as much or
more hot gas than stellar mass. Hot gas in S-rich groups, however, is of low
enough temperature for its X-ray emission to suffer heavy absorption due to
Galactic HI and related observational effects, and hence is hard to detect. We
postulate that such lower temperature hot gas does exist in low velocity
dispersion, S-rich groups, and explore the consequences of this assumption. For
a wide range of metallicity and density, hot gas in S-rich groups can cool in
far less than a Hubble time. If such gas exists and can cool, especially when
interacting with HI in existing galaxies, then it can help link together a
number of disparate observations, both Galactic and extragalactic, that are
otherwise difficult to understand.Comment: 16 pages with one figure. ApJ Letters, in pres
A non-Markovian quantum trajectory approach to radiation into structured continuum
We present a non-Markovian quantum trajectory method for treating atoms
radiating into a reservoir with a non-flat density of states. The results of an
example numerical simulation of the case where the free space modes of the
reservoir are altered by the presence of a cavity are presented and compared
with those of an extended system approach
A ROSAT HRI survey of bright nearby galaxies
We use the extensive public archive of ROSAT High Resolution Imager (HRI)
observations to carry out a statistical investigation of the X-ray properties
of nearby galaxies. Specifically we focus on the sample of 486 bright (B_T <
12.5) northern galaxies studied by Ho, Filippenko and Sargent (HFS) in the
context of their exploration of the optical spectroscopic properties of nearby
galactic nuclei. Over 20% of HFS galaxies are encompassed in ROSAT HRI fields
of reasonable (> 10ks) exposure. The X-ray sources detected within the optical
extent of each galaxy are categorised as either nuclear or non-nuclear
depending on whether the source is positioned within or outside of a 25
arcsecond radius circle centred on the optical nucleus. A nuclear X-ray source
is detected in over 70% of the galaxies harbouring either a Seyfert or LINER
nucleus compared to a detection rate of only ~40% in less active systems. The
correlation of the H alpha luminosity with nuclear X-ray luminosity previously
observed in QSOs and bright Seyfert 1 galaxies appears to extend down into the
regime of ultra-low luminosity (L(x)~10^38 - 10^40 erg/s) active galactic
nuclei (AGN). The inferred accretion rates for this sample of low-luminosity
AGN are significantly sub-Eddington. In total 142 non-nuclear sources were
detected. In combination with published data for M31 this leads to a luminosity
distribution (normalised to an optical blue luminosity of L(B) = 10^10
L(solar)) for the discrete X-ray source population in spiral galaxies of the
form dN/dL38 = 1.0 +/- 0.2 L38^-1.8, where L38 is the X-ray luminosity in units
of 10^38 erg/s. The implied L(x)/L(B) ratio is ~1.1 x 10^39 erg/s/(10^10
L(solar)). The nature of the substantial number of ``super-luminous''
non-nuclear objects detected in the survey is discussed.Comment: 20 pages, 7 figures, accepted for publication in MNRAS. Also
available from http://www.star.le.ac.uk/~tro/papers/xhfs.p
Dissipationless Collapse of Spherical Protogalaxies and the Fundamental Plane
Following on from the numerical work of Capelato, de Carvalho & Carlberg
(1995, 1997), where dissipationless merger simulations were shown to reproduce
the "Fundamental Plane" (FP) of elliptical galaxies, we investigate whether the
end products of pure, spherically symmetric, one-component dissipationless {\it
collapses} could also reproduce the FP. Past numerical work on collisionless
collapses have addressed important issues on the dynamical/structural
characteristics of collapsed equilibrium systems. However, the study of
collisionless collapse in the context of the nature of the FP has not been
satisfactorily addressed yet. Our aim in this paper is to focus our attention
on the resulting collapse of simple one-component spherical models with a range
of different initial virial coefficients. We find that the characteristic
correlations of the models are compatible with virialized, centrally homologous
systems. Our results strengthen the idea that merging may be a fundamental
ingredient in forming non-homologous objects.Comment: 9 pages, 4 Postscript figures, Astronomy & Astrophysics in press
(2002). Abstract placement correcte
Large-scale variations of the dust optical properties in the Galaxy
We present an analysis of the dust optical properties at large scale, for the
whole galactic anticenter hemisphere. We used the 2MASS Extended Source Catalog
to obtain the total reddening on each galaxy line of sight and we compared this
value to the IRAS 100 microns surface brightness converted to extinction by
Schlegel et al (1998). We performed a careful examination and correction of the
possible systematic effects resulting from foreground star contamination,
redshift contribution and galaxy selection bias. We also evaluated the
contribution of dust temperature variations and interstellar clumpiness to our
method. The correlation of the near-infrared extinction to the far-infrared
optical depth shows a discrepancy for visual extinction greater than 1 mag with
a ratio A_V(FIR) / A_V(gal) = 1.31 +- 0.06. We attribute this result to the
presence of fluffy/composite grains characterized by an enhanced far--infrared
emissivity. Our analysis, applied to half of the sky, provides new insights on
the dust grains nature suggesting fluffy grains are found not only in some very
specific regions but in all directions for which the visual extinction reaches
about 1 mag.Comment: 10 pages, 11 figures, accepted for publication in A&
The Distance to SN 1999em from the Expanding Photosphere Method
We present optical and IR spectroscopy of the first two months of evolution
of the Type II SN 1999em. We combine these data with high-quality optical/IR
photometry beginning only three days after shock breakout, in order to study
the performance of the ``Expanding Photosphere Method'' (EPM) in the
determination of distances. With this purpose we develop a technique to measure
accurate photospheric velocities by cross-correlating observed and model
spectra. The application of this technique to SN 1999em shows that we can reach
an average uncertainty of 11% in velocity from an individual spectrum. Our
analysis shows that EPM is quite robust to the effects of dust. In particular,
the distances derived from the VI filters change by only 7% when the adopted
visual extinction in the host galaxy is varied by 0.45 mag. The superb time
sampling of the BVIZJHK light-curves of SN 1999em permits us to study the
internal consistency of EPM and test the dilution factors computed from
atmosphere models for Type II plateau supernovae. We find that, in the first
week since explosion, the EPM distances are up to 50% lower than the average,
possibly due the presence of circumstellar material. Over the following 65
days, on the other hand, our tests lend strong credence to the atmosphere
models, and confirm previous claims that EPM can produce consistent distances
without having to craft specific models to each supernova. This is particularly
true for the VI filters which yield distances with an internal consistency of
4%. From the whole set of BVIZJHK photometry, we obtain an average distance of
7.5+/-0.5 Mpc, where the quoted uncertainty (7%) is a conservative estimate of
the internal precision of the method obtained from the analysis of the first 70
days of the supernova evolution.Comment: 68 pages, 15 tables, 22 figures, to appear in Ap
Observation of Collective Excitations of the Dilute 2D Electron System
We report inelastic light scattering measurements of dispersive spin and
charge density excitations in dilute 2D electron systems reaching densities
less than 10^{10} cm^{-2}. In the quantum Hall state at nu=2, roton critical
points in the spin inter--Landau level mode show a pronounced softening as r_s
is increased. Instead of a soft mode instability predicted by Hartree--Fock
calculations for r_s ~ 3.3, we find evidence of multiple rotons in the
dispersion of the softening spin excitations. Extrapolation of the data
indicates the possibility of an instability for r_s >~ 11.Comment: Submitted to Physical Review Letter
The gene product Murr1 restricts HIV-1 replication in resting CD4(+) lymphocytes
Although human immunodeficiency virus-1 (HIV-1) infects quiescent and proliferating CD4(+) lymphocytes, the virus replicates poorly in resting T cells(1-6). Factors that block viral replication in these cells might help to prolong the asymptomatic phase of HIV infection(7); however, the molecular mechanisms that control this process are not fully understood. Here we show that Murr1, a gene product known previously for its involvement in copper regulation(8,9), inhibits HIV-1 growth in unstimulated CD4(+) T cells. This inhibition was mediated in part through its ability to inhibit basal and cytokine-stimulated nuclear factor (NF)-kappaB activity. Knockdown of Murr1 increased NF-kappaB activity and decreased IkappaB-alpha concentrations by facilitating phospho-IkappaB-alpha degradation by the proteasome. Murr1 was detected in CD4(+) T cells, and RNA-mediated interference of Murr1 in primary resting CD4(+) lymphocytes increased HIV-1 replication. Through its effects on the proteasome, Murr1 acts as a genetic restriction factor that inhibits HIV-1 replication in lymphocytes, which could contribute to the regulation of asymptomatic HIV infection and the progression of AIDS.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62709/1/nature02171.pd
The rotation curve and mass-distribution in highly flattened galaxies
A new method is developed which permits the reconstruction of the
surface-density distribution in the galactic disk of finite radius from an
arbitrary smooth distribution of the angular velocity via two simple
quadratures. The existence of upper limits for disk's mass and radius during
the analytic continuation of rotation curves into the hidden (non-radiating)
part of the disk is demonstrated.Comment: 13 pages, 2 figure
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