172,552 research outputs found
The role of IgG avidity in diagnosis of cytomegalovirus infection in newborns and infants [Uloga IgG aviditeta u dijagnostici infekcije citomegalovirusom u novorođenčadi i dojenčadi]
To evaluate the value of IgG avidity in diagnosis of congenital cytomegalovirus (CMV) infection in newborns and infants we collected serum samples from 40 infants under 12 months of age with suspected congenital CMV infection. Sera were tested for IgM, IgG and IgG avidity. For 25 of them, virus isolation and/or polymerase chain reaction (PCR) on urine specimens were performed. Thirteen (32.5%) patients showed the presence of CMV IgM antibodies, 3 (7.5%) had equivocal IgM result, and 24 (60.0%) patients had IgG antibodies only. Using IgG avidity, CMV infection (low avidity index-AI) was documented in 61.5% IgM positive and 54.2% IgM negative patients. Eight of nine (88.8%) IgM positive patients were positive either on virus isolation or PCR. In IgM negative patients, 46.6% urine cultures were positive for CMV and 66.6% were PCR positive. According to age, IgG avidity demonstrated acute/recent primary CMV infection in 58.8% patients younger than three months compared with 91.7% and 81.8% in 3-6 and 6-12 months old babies, respectively. In conclusion, IgG avidity is useful in diagnosis of CMV infection either in IgM positive or IgM negative children older than 3 months of age. In infants less than 3 months, transplacentally derived maternal IgG antibodies of high avidity influence on the IgG avidity result. In these children, CMV infection should be confirmed by direct virologic methods such as virus isolation or PCR
Cosmology-independent Estimate of the Fraction of Baryon Mass in the IGM from Fast Radio Burst Observations
The excessive dispersion measure (DM) of fast radio bursts (FRBs) has been proposed to be a powerful tool to study intergalactic medium (IGM) and to perform cosmography. One issue is that the fraction of baryons in the IGM, f IGM, is not properly constrained. Here, we propose a method of estimating f IGM using a putative sample of FRBs with the measurements of both DM and luminosity distance d L. The latter can be obtained if the FRB is associated with a distance indicator (e.g., a gamma-ray burst or a gravitational-wave event), or the redshift z of the FRB is measured and d L at the corresponding z is available from other distance indicators (e.g., SNe Ia) at the same redshift. As d L/DM essentially does not depend on cosmological parameters, our method can determine f IGM independent of cosmological parameters. We parameterize f IGM as a function of redshift and model the DM contribution from a host galaxy as a function of star formation rate. Assuming f IGM has a mild evolution with redshift with a functional form and by means of Monte Carlo simulations, we show that an unbiased and cosmology-independent estimate of the present value of f IGM with a ~12% uncertainty can be obtained with 50 joint measurements of d L and DM. In addition, such a method can also lead to a measurement of the mean value of DM contributed from the local host galaxy
Probing reionization with Lyman-alpha emission lines
Lyman-alpha emission from high-redshift galaxies may be a powerful probe of
the ionization history of the IGM at z>6: the observed Lyman-alpha emission
line is sensitive to the neutral fraction of IGM hydrogen in the range 0.1-1.
We present calculations of observed Lyman-alpha emission lines from z>6
galaxies, illustrating the effect of varying the many free parameters
associated with the emitting galaxy, its halo, and the IGM around the galaxy.
In particular, we use a dynamic model of the IGM that includes the effect of
IGM infall toward the emitting galaxy. Galactic winds may play a crucial role
in determining observed Lyman-alpha line fluxes. We compare our model
predictions with observations of two z=6.5 galaxies and conclude that, if
galactic winds are allowed for, existing observations place no constraint on
the neutral fraction of the IGM at z=6.5. Future space-based observations will
constrain the importance of galactic winds; if winds are unimportant for the
observed z=6.5 galaxies, our models suggest that the IGM neutral fraction at
z=6.5 is <~0.1.Comment: 17 pages, 25 figures, submitted to MNRA
The velocity field of baryonic gas in the universe
The dynamic evolution of the baryonic intergalactic medium (IGM) caused by
the underlying dark matter gravity is governed by the Navier-Stokes equations
in which many cooling and heating processes are involved. However, it has long
been recognized that the growth mode dynamics of cosmic matter clustering can
be sketched by a random force driven Burgers' equation if cooling and heating
are ignored. Just how well the dynamics of the IGM can be described as a
Burgers fluid has not been fully investigated probably because cooling and
heating are essential for a detailed understanding of the IGM. Using IGM
samples produced by a cosmological hydrodynamic simulation in which heating and
cooling processes are properly accounted for, we show that the IGM velocity
field in the nonlinear regime shows the features of a Burgers fluid, that is,
when the Reynolds number is high, the velocity field consists of an ensemble of
shocks. Consequently, (1) the IGM velocity is generally smaller than that
of dark matter; (2) for the smoothed field, the IGM velocity shows tight
correlation with dark matter given by , with , such
that the lower the redshift, the smaller ; (3) the velocity PDFs are
asymmetric between acceleration and deceleration events; (4) the PDF of
velocity difference satisfies the scaling relation for a
Burgers fluid, i.e., . We find the scaling
function and parameters for the IGM which are applicable to the entire scale
range of the samples (0.26 - 8 h Mpc). These properties show that the
similarity mapping between the IGM and dark matter is violated on scales much
larger than the Jeans length of the IGM.Comment: 14 pages, 10 jpg-figures, accepted for publication in the
Astrophysical Journal. References adde
Constraint on intergalactic dust from thermal history of intergalactic medium
This Letter investigates the amount of dust in the intergalactic medium
(IGM). The dust photoelectric heating can be the most efficient heating
mechanism in the IGM where the density is very small and there are a lot of
hard ultraviolet photons. Comparing the observational thermal history of IGM
with a theoretical one taking into account the dust photoelectric heating, we
can put an upper limit on the dust-to-gas ratio, , in the IGM. Since
the rate of the dust photoelectric heating depends on the size of dust, we find
the following results: If the grain size is \ga 100 \AA, at is \la 1/100 Galactic value corresponding to \Omega_{\rm dust}^{\rm
IGM}\la 10^{-5}. On the other hand, if the grain size is as small as
\AA, is \la 1/1000 Galactic value corresponding to \Omega_{\rm
dust}^{\rm IGM}\la 10^{-6}.Comment: 5 pages, 2 figures; accepted for publication in MNRAS pink page
The intergalactic medium thermal history at redshift z=1.7--3.2 from the Lyman alpha forest: a comparison of measurements using wavelets and the flux distribution
We investigate the thermal history of the intergalactic medium (IGM) in the
redshift interval z=1.7--3.2 by studying the small-scale fluctuations in the
Lyman alpha forest transmitted flux. We apply a wavelet filtering technique to
eighteen high resolution quasar spectra obtained with the Ultraviolet and
Visual Echelle Spectrograph (UVES), and compare these data to synthetic spectra
drawn from a suite of hydrodynamical simulations in which the IGM thermal state
and cosmological parameters are varied. From the wavelet analysis we obtain
estimates of the IGM thermal state that are in good agreement with other
recent, independent wavelet-based measurements. We also perform a reanalysis of
the same data set using the Lyman alpha forest flux probability distribution
function (PDF), which has previously been used to measure the IGM
temperature-density relation. This provides an important consistency test for
measurements of the IGM thermal state, as it enables a direct comparison of the
constraints obtained using these two different methodologies. We find the
constraints obtained from wavelets and the flux PDF are formally consistent
with each other, although in agreement with previous studies, the flux PDF
constraints favour an isothermal or inverted IGM temperature-density relation.
We also perform a joint analysis by combining our wavelet and flux PDF
measurements, constraining the IGM thermal state at z=2.1 to have a temperature
at mean density of T0/[10^3 K]=17.3 +/- 1.9 and a power-law temperature-density
relation exponent gamma=1.1 +/- 0.1 (1 sigma). Our results are consistent with
previous observations that indicate there may be additional sources of heating
in the IGM at z<4.Comment: 15 pages, 14 figures, matches version accepted for publication on
MNRA
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Evidence for somatic selection of natural autoantibodies.
Natural autoantibodies are primarily immunoglobulin M (IgM) antibodies that bind to a variety of self-antigens, including self-IgG. Accounting for a large proportion of the early B cell repertoire, such polyspecific autoantibodies are speculated to contribute to the homeostasis and/or competence of the primary humoral immune system. Recent studies indicate that the leukemia cells from most patients with chronic lymphocytic leukemia (CLL) also express such IgM autoantibodies. Similarly, the leukemia cells from many CLL patients react with murine monoclonal antibodies (mAbs) specific for crossreactive idiotypes (CRIs) associated with human IgM autoantibodies. In particular, leukemic cells frequently react with G6, a mAb specific for an Ig heavy chain (H chain)-associated CRI, and/or with 17.109, a mAb that defines a kappa light chain (L chain)-associated CRI. Generated against IgM rheumatoid factor (RF) paraproteins, G6 and 17.109 each recognize a major CRI that is present in many IgM RF paraproteins. Furthermore, over 90% of the IgM paraproteins found to bear both H and L chain-associated CRIs also are found to have RF activity. Molecular characterization of these CRIs demonstrates that each is a serologic marker for expression of a highly conserved Ig V gene. As such, the frequent production of IgM polyspecific autoantibodies in CLL simply may reflect the frequent use of such highly conserved autoantibody-encoding Ig V genes with little or no somatic mutation. To test this hypothesis, we generated murine transfectomas to pair the 17.109-reactive kappa L chain of SMI, a 17.109/G6-reactive CLL population, with the Ig H chain of SMI or other G6-reactive leukemia cells or tonsillar lymphocytes. Cotransfection of vectors encoding the Ig H and L chains of SMI generated transfectomas that produce IgM kappa RF autoantibodies reactive with human IgG1 and IgG4. In contrast to G6/17.109-reactive IgM kappa RF Waldenstrom's paraproteins, the SMI IgM kappa also reacts with several other self-antigens, including myoglobin, actin, and ssDNA. However, cotransfection of the SMI L chain with a vector encoding any one of 10 different G6-reactive Ig H chains generated transfectomas that produce IgM kappa antibodies without detectable polyspecific autoantibody activity. These results indicate that polyspecific antiself-reactivity of G6/17.019-reactive Ig is dependent on the somatically generated Ig third complementarity determining region. Collectively, these studies imply that selection may be responsible for the frequent expression of polyspecific autoantibodies in CLL and early B cell ontogeny
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