.
The spatial asymptotic approach is used to derive expressions for the diffusion coefficient from the neutron transport equation to improve the standard P
1
-based formula. A general explicit ...analytical expression is obtained in the frame of the P
N
model, which also allows an easy evaluation of the coefficient in the limit for
N
→
∞
. The analytical formulae are presented at any order of the scattering anisotropy. An alternative formula is derived through the interpretation of the diffusive contribution of the exact transport solution obtained by means of Case’s method applied to a plane configuration in the presence of isotropic scattering. Some numerical results are presented to illustrate the performances of the different formulations once they are used in the diffusion model for the solution of source-injected and critical problems.
Acquired aplastic anemia (AA) is a rare heterogeneous disorder characterized by pancytopenia and hypoplastic bone marrow. The incidence is 2–3 per million population per year in the Western world, ...but 3 times higher in East Asia. Survival in severe aplastic anemia (SAA) has improved significantly due to advances in hematopoietic stem cell transplantation (HSCT), immunosuppressive therapy, biologic agents, and supportive care. In SAA, HSCT from a matched sibling donor (MSD) is the first-line treatment. If a MSD is not available, options include immunosuppressive therapy (IST), matched unrelated donor, or haploidentical HSCT. The purpose of this guideline is to provide health care professionals with clear guidance on the diagnosis and management of pediatric patients with AA. A preliminary evidence-based document prepared by a group of pediatric hematologists of the Bone Marrow Failure Study Group of the Italian Association of Pediatric Hemato-Oncology (AIEOP) was discussed, modified and approved during a series of consensus conferences that started online during COVID 19 and continued in the following years, according to procedures previously validated by the AIEOP Board of Directors.
The solution of the linear transport equation used for the study of neutral particle fields requires the imposition of appropriate boundary conditions. The choice of the conditions to impose for an ...infinite medium is not straightforward. The question has been given different formulations in the literature with various justifications based on some physical reasoning. Some aspects of the question are here analysed, from both the mathematical and the physical point of view. It is concluded that the inspiring golden rule should be the establishment of conditions that do not require any reference to the properties of the specific medium being considered for their justification.
ABSTRACT
We present F850LP − F160W colour gradients for 11 early‐type galaxies (ETGs) at 1.0 < zspec < 1.9 selected from the GOODS‐South field. Significant negative F850LP − F160W colour gradients ...(core redder than the outskirts) have been detected in ∼70 per cent of our sample within the effective radius Re, the remaining 30 per cent having a flat colour profile consistent with a null gradient. Extending the analysis to R > Re, enclosing the whole galaxy, we have found that the fraction of high‐z ETGs with negative F850LP − F160W colour gradients rises up to 100 per cent. For each galaxy, we investigate the origin of the radial colour variation with an innovative technique based on the matching of both the spatially resolved colour and the global spectral energy distribution (SED) to predictions of composite stellar population models. In fact, we find that the age of the stellar populations is the only parameter whose radial variation alone can fully account for the observed colour gradients and global SEDs for six ETGs in our sample, without the need of radial variation of any other stellar population property. For four out of these six ETGs, a pure metallicity variation can also reproduce the detected colour gradients. None the less, a minor contribution to the observed colour gradients from the radial variation of star formation time‐scale, abundance of low‐ to high‐mass stars and dust cannot be completely ruled out. For the rest of the sample, our analysis suggests a more complex scenario whereby more properties of the stellar populations need to simultaneously vary, likely with comparable weights, to generate the observed colour gradients and global SEDs. Our results show that, despite the young mean age of our galaxies (<3– 4 Gyr), they already exhibit significant differences among their stellar content. We have discussed our results within the framework of the widest accepted scenarios of galaxy formation and conclude that none of them can satisfactorily account for the observed distribution of colour gradients and for the spatially resolved content of high‐z ETGs. Our results suggest that the distribution of colour gradients may be due to different initial conditions in the formation mechanisms of ETGs.
We present the morphological analysis based on HST-NIC2 (0.075 arcsec pixel−1) images in the F160W filter of a sample of nine massive field (>1011 M⊙) galaxies spectroscopically classified as ...early-types at 1.2 < z < 1.7. Our analysis shows that all of them are bulge-dominated systems. In particular, six of them are well fitted by a de Vaucouleurs profile (n= 4) suggesting that they can be considered pure elliptical galaxies. The remaining three galaxies are better fitted by a Sérsic profile with index 1.9 < n
fit < 2.3 suggesting that a disc-like component could contribute up to 30 per cent to the total light of these galaxies. We derived the effective radius R
e and the mean surface brightness (SB) 〈μ〉e within R
e of our galaxies and we compared them with those of early-types at lower redshifts. We find that the SB 〈μ〉e of our galaxies should get fainter by 2.5 mag from z∼ 1.5 to ∼0 to match the SB of the local ellipticals with comparable R
e, that is, the local Kormendy relation. Luminosity evolution without morphological changes can only explain half of this effect, as the maximum dimming expected for an elliptical galaxy is ∼1.6 mag in this redshift range. Thus, other parameters, possibly structural, may undergo evolution and play an important role in reconciling models and observations. Hypothesizing an evolution of the effective radius of galaxies we find that R
e should increase by a factor of 1.5 from z∼ 1.5 to ∼0.
.
We develop a fully analytical study of the spectrum of the neutron diffusion operator both for spatially homogeneous and reflected reactors in a multi-group energy model. We illustrate and discuss ...the results of the analysis of the time spectrum of the diffusion operator, to highlight some general properties of the neutronic evolution in a multiplying system. Various new results are presented, particularly regarding the possible existence of complex time eigenvalues, the appearance of a continuum part of the spectrum and the orthogonality properties of the eigenfunctions in the case of an infinite reflector.
We have derived colour gradients for a sample of 20 early-type galaxies (ETGs) at 1 < z
spec < 2 selected from the GOODS-South field. The sample includes both normal ETGs (13) having effective radii ...comparable to the mean radius of local ones and compact ETGs (seven) having effective radii from two to six times smaller. Colour gradients have been derived in the F606W−F850LP bands (UV−U
restframe) taking advantage of the ultradeep HST/ACS observations covering this field and providing a spatial resolution of about 0.8 kpc at the redshift of the galaxies. Despite the narrow wavelength baseline covered (1000 Å), sampling approximatively the emission dominated by the same stellar population, we detect significant radial colour variations in 50 per cent of our sample. In particular, we find five ETGs with positive colour gradients (cores bluer than the external regions) and five galaxies with negative colour gradients (cores redder than the external regions), as commonly observed in the local Universe. These results show that at 1 < z < 2, when the Universe was only 3-4 Gyr old, ETGs constituted a composite population of galaxies whose different assembly histories have generated different stellar distributions with the bluest stellar population either in the centre or in the outskirts as well as throughout the whole galaxy. Moreover, we find that compact galaxies seem to preferentially show a blue core while moving towards normal galaxies; central stellar populations become progressively redder. None the less, the narrow baseline covered together with the low statistics still prevents us to be conclusive about a possible physical connection between colour gradients and the degree of compactness of high-z ETGs.
We present an analysis of the evolution of galaxy clustering in the redshift interval in the Hubble Deep Field South (HDF South). The HST optical data are combined with infrared ISAAC/VLT ...observations, and photometric redshifts are used for all the galaxies brighter than . The clustering signal is obtained in different redshift bins using two different approaches: a standard one, which uses the best redshift estimate of each object, and a second one, which takes into account the redshift probability function of each object. This second method makes it possible to improve the information in the redshift intervals where contamination from objects with insecure redshifts is important. With both methods, we find that the clustering strength up to in the HDF South is consistent with the previous results in the HDF North. Whereas at redshift lower than the HDF galaxy population is un/anti biased with respect to the underlying dark matter, at high redshift the bias increases up to , depending on the cosmological model. These results support previous claims that, at high redshift, galaxies are preferentially located in massive haloes, as predicted by the biased galaxy formation scenario. In order to quantify the impact of cosmic errors on our analyses, we have used analytical expressions from Bernstein. Once the behaviour of higher order moments is assumed, our results show that errors in the clustering measurements in the HDF surveys are indeed dominated by pure shot noise in most regimes, as assumed in our analysis. We also show that future observations with instruments like the Advanced Camera on HST will improve the signal to noise ratio by at least a factor of 2, as a consequence, more detailed analyses of the errors will be required. In fact, pure shot noise will give a smaller contribution with respect to other sources of errors, such as finite volume effects or non Poissonian discreteness effects.
ABSTRACTWe present the morphological analysis based on HST-NIC2 (0.075 arcsec pixel-1) images in the F160W filter of a sample of nine massive field (>1011Modot) galaxies spectroscopically classified ...as early-types at 1.2 < z < 1.7. Our analysis shows that all of them are bulge-dominated systems. In particular, six of them are well fitted by a de Vaucouleurs profile (n = 4) suggesting that they can be considered pure elliptical galaxies. The remaining three galaxies are better fitted by a Sersic profile with index 1.9 < nfit < 2.3 suggesting that a disc-like component could contribute up to 30 per cent to the total light of these galaxies. We derived the effective radius Re and the mean surface brightness (SB) < mu >e within Re of our galaxies and we compared them with those of early-types at lower redshifts. We find that the SB < mu >e of our galaxies should get fainter by 2.5 mag from z similar to 1.5 to similar to 0 to match the SB of the local ellipticals with comparable Re, that is, the local Kormendy relation. Luminosity evolution without morphological changes can only explain half of this effect, as the maximum dimming expected for an elliptical galaxy is similar to 1.6 mag in this redshift range. Thus, other parameters, possibly structural, may undergo evolution and play an important role in reconciling models and observations. Hypothesizing an evolution of the effective radius of galaxies we find that Re should increase by a factor of 1.5 from z similar to 1.5 to similar to 0.
The K20 survey Mignoli, M; Cimatti, A; Zamorani, G ...
Astronomy and astrophysics (Berlin),
07/2005, Letnik:
437, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The K20 survey is a near infrared-selected, deep (Ks < 20) redshift survey targeting galaxies in two independent regions of the sky, the Chandra Deep Field South and the field around the quasar ...0055-2659, for a total area of 52 arcmin2. The total Ks-selected sample includes 545 objects. Low-resolution (R - 300-600) optical spectra for 525 of them have been obtained with the FORS1/FORS2 spectrographs at the ESO/VLT, providing 501 spectroscopic identifications (including 12 type-1 AGN and 45 stars); consequently, we were able to measure redshifts and identify stars in 96% of the observed objects, whereas the spectroscopic completeness with respect to the total photometrically selected sample is 92% (501/545). The K20 survey is therefore the most complete spectroscopic survey of a near infrared-selected sample to date. The K20 survey contains 444 spectroscopically identified galaxies, covering a redshift range of 0.05 < z < 2.73, with a mean redshift z = 0.75; excluding the 32 "low-quality" redshifts does not significantly change these values. This paper describes the final K20 spectroscopic catalogue, along with the technique used to determine redshifts, measure the spectral features and characterize the spectra. The classification of the galaxy spectra has been performed according to a simple parametric recipe that uses the equivalent widths of the two main emission lines (OIIl3727 and Ha+NII) and two continuum indices (the 4000 AA break index, D4000, and a near-UV color index, C(28-39)). We defined three main spectroscopic classes: red early-type galaxies, blue emission-line galaxies and the intermediate galaxies, which show emission lines but a red continuum. More than 95% of the examined galaxies is included in one of these spectral types and a composite spectrum is built for each of the three galaxy classes. The full spectroscopic catalogue, the reduced individual spectra and the composite spectra are released to the community through the K20 web page (http://www.arcetri.astro.it/6k20/). The blue emission-line and the early-type galaxies have been divided in redshift bins, and the corresponding composite spectra have been built, in order to investigate the evolution of the spectral properties of the K20 galaxies with redshift. The early-type average spectra are remarkable in their similarity, showing only subtle but systematic differences in the D4000 index, which are consistent with the ageing of the stellar population. Conversely, the star-forming galaxies present a significant "blueing" of the optical/near-UV continuum with redshift, although the OII equivalent width remains constant (633 AA) in the same redshift intervals. We reproduce the observed properties with simple, dust-free population synthesis models, suggesting that the high-redshift galaxies are younger and more active than those detected at lower redshift, whilst the equivalent width of the emission lines apparently require a lower metallicity for the low-redshift objects. This may be consistent with the metallicity-luminosity relationship locally observed for star-forming galaxies.
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