319 research outputs found
Cosmic Microwave Background Polarization and reionization: constraining models with a double reionization
Neutral hydrogen around high-z QSO and an optical depth tau ~ 0.17 can be
reconciled if reionization is more complex than a single transition at z ~ 6-8.
Tracing its details could shed a new light on the first sources of radiation.
Here we discuss how far such details can be inspected through planned
experiments on CMB large-scale anisotropy and polarization, by simulating an
actual data analysis. By considering a set of double reionization histories of
Cen (2003) type, a relevant class of models not yet considered by previous
works, we confirm that large angle experiments rival high resolution ones in
reconstructing the reionization history. We also confirm that reionization
histories, studied with the prior of a single and sharp reionization, yield a
biased tau, showing that this bias is generic. We further find a monotonic
trend in the bias for the models that we consider, and propose an explanation
of the trend, as well as the overall bias. We also show that in long-lived
experiments such a trend can be used to discriminate between single and double
reionization patterns.Comment: 8 pages, 11 figures. Substantial rewriting, replaced with accepted
version. To be published in A&
Modification of the 21-cm power spectrum by X-rays during the epoch of reionisation
We incorporate a contribution to reionization from X-rays within analytic and
semi-numerical simulations of the 21-cm signal arising from neutral hydrogen
during the epoch of reionization. We explore the impact that X-ray ionizations
have on the power spectrum (PS) of 21-cm fluctuations by varying both the
average X-ray MFP and the fractional contribution of X-rays to reionization. In
general, prior to the epoch when the intergalactic medium is dominated by
ionized regions (H {\sevensize II} regions), X-ray-induced ionization enhances
fluctuations on spatial scales smaller than the X-ray MFP, provided that X-ray
heating does not strongly supress galaxy formation. Conversely, at later times
when \H2 regions dominate, small-scale fluctuations in the 21-cm signal are
suppressed by X-ray ionization. Our modelling also shows that the modification
of the 21-cm signal due to the presence of X-rays is sensitive to the relative
scales of the X-ray MFP, and the characteristic size of \H2 regions. We
therefore find that X-rays imprint an epoch and scale-dependent signature on
the 21-cm PS, whose prominence depends on fractional X-ray contribution. The
degree of X-ray heating of the IGM also determines the extent to which these
features can be discerned. We show that the MWA will have sufficient
sensitivity to detect this modification of the PS, so long as the X-ray photon
MFP falls within the range of scales over which the array is most sensitive
( Mpc). In cases in which this MFP takes a much smaller value,
an array with larger collecting area would be required.Comment: 15 pages, 6 figures, Accepted for publication in MNRAS X-ray heating
contribution now adde
The Abundance of New Kind of Dark Matter Structures
A new kind of dark matter structures, ultracompact minihalos (UCMHs) was
proposed recently. They would be formed during the radiation dominated epoch if
the large density perturbations are existent. Moreover, if the dark matter is
made up of weakly interacting massive particles, the UCMHs can have effect on
cosmological evolution because of the high density and dark matter annihilation
within them. In this paper, one new parameter is introduced to consider the
contributions of UCMHs due to the dark matter annihilation to the evolution of
cosmology, and we use the current and future CMB observations to obtain the
constraint on the new parameter and then the abundance of UCMHs. The final
results are applicable for a wider range of dark matter parametersComment: 4 pages, 1 tabl
Adhesion and proliferation of skeletal muscle cells on single layer poly(lactic acid) ultra-thin films
An increasing interest in bio-hybrid systems and cell-material interactions is evident in the last years. This leads towards the development of new nano-structured devices and the assessment of their biocompatibility. In the present study, the development of free-standing single layer poly(lactic acid) (PLA) ultra-thin films is described, together with the analysis of topography and roughness properties. The biocompatibility of the PLA films has been tested in vitro, by seeding C2C12 skeletal muscle cells, and thus assessing cells shape, density and viability after 24, 48 and 72 h. The results show that free-standing flexible PLA nanofilms represent a good matrix for C2C12 cells adhesion, spreading and proliferation. Early differentiation into myotubes is also allowed. The biocompatibility of the novel ultra-thin films as substrates for cell growth promotes their application in the fields of regenerative medicine, muscle tissue engineering, drug delivery, and-in general-in the field of bio-hybrid devices
Determinants of quality of life after lung transplant: an Italian collaborative study
Background. With the improvement in survival rates after lung transplantation, concern has arisen about evaluating quality of life (QoL). This multicenter cross-sectional study aimed at describing QoL and identifying factors associated with it. Methods. We assessed QoL in 129 lung transplant recipients from 5 centres in Italy, during scheduled followup visits, using the SF-36, GHQ and St George’s respiratory questionnaires (SGRQ). Results. The SF-36 elicited impaired QoL in the physical, but not in the mental domains (PCS=44; MCS=53). The GHQ identified 29 patients (23%) with psychological discomfort and the SGRQ scores were significantly better than those of patients with chronic respiratory disease. On multivariate analysis, exertional dyspnea was an independent predictor of the PCS (adjusted Δ -6.3 (p5. Conclusions. The study identified exertional dyspnea as the main determinant of QoL as measured both by SF36 (PCS) and GHQ. Other objective measures contributed only to the PCS. Thus, the SF-36 (PCS) and GHQ were useful in identifying patients who needed treatment not only for complications but also psychological support and continued physical rehabilitation
Radiation Hydrodynamical Instabilities in Cosmological and Galactic Ionization Fronts
Ionization fronts, the sharp radiation fronts behind which H/He ionizing
photons from massive stars and galaxies propagate through space, were
ubiquitous in the universe from its earliest times. The cosmic dark ages ended
with the formation of the first primeval stars and galaxies a few hundred Myr
after the Big Bang. Numerical simulations suggest that stars in this era were
very massive, 25 - 500 solar masses, with H II regions of up to 30,000
light-years in diameter. We present three-dimensional radiation hydrodynamical
calculations that reveal that the I-fronts of the first stars and galaxies were
prone to violent instabilities, enhancing the escape of UV photons into the
early intergalactic medium (IGM) and forming clumpy media in which supernovae
later exploded. The enrichment of such clumps with metals by the first
supernovae may have led to the prompt formation of a second generation of
low-mass stars, profoundly transforming the nature of the first protogalaxies.
Cosmological radiation hydrodynamics is unique because ionizing photons coupled
strongly to both gas flows and primordial chemistry at early epochs,
introducing a hierarchy of disparate characteristic timescales whose relative
magnitudes can vary greatly throughout a given calculation. We describe the
adaptive multistep integration scheme we have developed for the self-consistent
transport of both cosmological and galactic ionization fronts.Comment: 6 pages, 4 figures, accepted for proceedings of HEDLA2010, Caltech,
March 15 - 18, 201
Development and validation of low-intensity pulsed ultrasound systems for highly controlled in vitro cell stimulation
This work aims to describe the development and validation of two low-intensity pulsed ultrasound stimulation
systems able to control the dose delivered to the biological target. Transducer characterization was performed in
terms of pressure field shape and intensity, for a high-frequency range (500 kHz to 5 MHz) and for a low-
frequency value (38 kHz). This allowed defining the distance, on the beam axis, at which biological samples
should be placed during stimulation and to exactly know the intensity at the target. Carefully designed retaining
systems were developed, for hosting biological samples. Sealing tests proved their impermeability to external
contaminants. The assembly/de-assembly time of the systems resulted ~3 min. Time-domain acoustic simula-
tions allowed to precisely estimate the ultrasound beam within the biological sample chamber, thus enabling the
possibility to precisely control the pressure to be transmitted to the biological target, by modulating the trans-
ducer’s input voltage. Biological in vitro tests were also carried out, demonstrating the sterility of the system and
the absence of toxic and inflammatory effects on growing cells after multiple immersions in water, over seven
day
VLT Observations of NGC 1097's "dog-leg" tidal stream
CONTEXT: Dwarf Spheroidal Galaxies and tidal streams. AIMS: We investigate
the structure and stellar population of two large stellar condensations (knots
A & B) along one of the faint optical "jet-like" tidal streams associated with
the spiral NGC 1097, with the goal of establishing their physical association
with the galaxy and their origin. METHODS: We use the VLT/FORS2 to get deep
V-band imaging and low-resolution optical spectra of two knots along NGC 1097's
northeast "dog-leg" tidal stream. With this data, we explore their morphology
and stellar populations. RESULTS: The FORS2 spectra show that the redshift of
knot A (and perhaps of knot B) is consistent with that of NGC 1097. The FORS2
photometry shows that the two knots match very well the photometric scaling
relations of canonical dwarf spheroidal galaxies (dSph). From the spectral
analysis we find that knot A is mainly composed of stars near G-type, with no
signs of ongoing star formation. Comparing its spectrum to a library of
Galactic GC spectra, we find that the stellar population of this dSph-like
object is most similar to intermediate to metal rich GCs. We find moreover,
that the tidal stream shows an "S" shaped inflection as well as a pronounced
stellar overdensity at knot A's position. This suggests that knot A is being
tidally stripped, and populates the stellar stream with its stars. CONCLUSIONS:
We have discovered that two knots along NGC 1097's northeast tidal stream share
most of their spectral and photometric properties with ordinary dwarf
spheroidal galaxies (dSph). Moreover, we find strong indications that the
"dog-leg" tidal stream arise from the tidal disruption of knot A. Since it has
been demonstrated that tidally stripping dSph galaxies need to loose most of
their dark matter before starting to loose stars, we suggest that knot A is at
present a CDM-poor object.Comment: 13 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
Reionization after Planck: the derived growth of the cosmic ionizing emissivity now matches the growth of the galaxy UV luminosity density
Thomson optical depth tau measurements from Planck provide new insights into
the reionization of the universe. In pursuit of model-independent constraints
on the properties of the ionising sources, we determine the empirical evolution
of the cosmic ionizing emissivity. We use a simple two-parameter model to map
out the evolution in the emissivity at z>~6 from the new Planck optical depth
tau measurements, from the constraints provided by quasar absorption spectra
and from the prevalence of Ly-alpha emission in z~7-8 galaxies. We find the
redshift evolution in the emissivity dot{N}_{ion}(z) required by the
observations to be d(log Nion)/dz=-0.15(-0.11)(+0.08), largely independent of
the assumed clumping factor C_{HII} and entirely independent of the nature of
the ionising sources. The trend in dot{N}_{ion}(z) is well-matched by the
evolution of the galaxy UV-luminosity density (dlog_{10}
rho_UV/dz=-0.11+/-0.04) to a magnitude limit >~-13 mag, suggesting that
galaxies are the sources that drive the reionization of the universe. The role
of galaxies is further strengthened by the conversion from the UV luminosity
density rho_UV to dot(N)_{ion}(z) being possible for physically-plausible
values of the escape fraction f_{esc}, the Lyman-continuum photon production
efficiency xi_{ion}, and faint-end cut-off to the luminosity
function. Quasars/AGN appear to match neither the redshift evolution nor
normalization of the ionizing emissivity. Based on the inferred evolution in
the ionizing emissivity, we estimate that the z~10 UV-luminosity density is
8(-4)(+15)x lower than at $z~6, consistent with the observations. The present
approach of contrasting the inferred evolution of the ionizing emissivity with
that of the galaxy UV luminosity density adds to the growing observational
evidence that faint, star-forming galaxies drive the reionization of the
universe.Comment: 20 pages, 12 figures, 5 tables, Astrophysical Journal, updated to
match version in press, Figure 6 shows the main result of the pape
- …