1,758 research outputs found
Risk of cancer after assisted reproduction: a review of the available evidences and guidance to fertility counselors
Infertile women requiring ovarian stimulation and assisted reproduction techniques (ART) are faced with difficult issues. The fear that using hormones could increase their risk of cancer is the most significant. One of the main challenges for assessing cancer risk after ART is the difficulty to separate it from the underlying condition of infertility per se. The delay or the inability to achieve a pregnancy is an important risk factor for breast, endometrial and ovarian cancer. We analyzed the current literature on the topic
The 2-10 keV luminosity as a Star Formation Rate indicator
Radio and far infrared luminosities of star-forming galaxies follow a tight linear relation. Making use of ASCA and BeppoSAX observations of a well-defined sample of nearby star-forming galaxies, we argue that tight linear relations hold between the X-ray, radio and far infrared luminosities. The effect of intrinsic absorption is investigated taking NGC3256 as a test case. It is suggested that the hard X-ray emission is directly related to the Star Formation Rate. Star formation processes may also account for most of the 2-10 keV emission from LLAGNs of lower X-ray luminosities (for the same FIR and radio luminosity). Deep Chandra observations of a sample of radio-selected star-forming galaxies in the Hubble Deep Field North show that the same relation holds also at high (0.2< z< 1.3) redshift. The X-ray/radio relations also allow a derivation of X-ray number counts up to very faint fluxes from the radio Log N-Log S, which is consistent with current limits and models. Thus the contribution of star-forming galaxies to the X-ray background can be estimated
Analysis of a bakery production system using discrete simulation
The main objective of this study is to analyse different production scenarios of a company, and propose improvements with the use of discrete event simulation. We use a simulation tool, SIMIO software, to reproduce the existing production layout of the company. Our purpose is to gather relevant information about the actual production system behaviour, and to find strategies to increase the production level to meet the market demand.
Based on initial simulation model, some production scenarios were developed involving the production of different
products. The analysis of the developed models highlighted the need for improvements. Among the obtained
results, the creation of different mixed production scenarios allowed to increase the production level while maintaining
the current existing resources. The results of this work can be easily implemented in the company in
order to increase the production level without increasing costs since they do not involve the purchase of new
equipment. In conclusion, this study highlighted the ability of the simulation technique to analyse manufacturing
processes throughout the creation of different scenarios providing insights on the production process improving
the companies’ productive performanceinfo:eu-repo/semantics/publishedVersio
The contribution of Quasars to the Far Infrared Background
Recent observational results obtained with SCUBA, COBE and ISO have greatly
improved our knowledge of the infrared and sub-mm background radiation. These
limits become constraining given the realization that most AGNs are heavily
obscured and must reradiate strongly in the IR/sub-mm. Here we predict the
contribution of AGNs to the IR/sub-mm background, starting from measurements of
the hard X-ray background. We show that an application of what we know of AGN
Spectral Energy Distributions (SEDs) and the IR background requires that a
significant fraction of the 10-150 micron background comes from AGNs. This
conclusion can only be avoided if obscured AGNs are intrinsically brighter in
the X-rays (with respect to the optical-UV) than unobscured AGNs, contrary to
``unified schemes'' for AGNs, or have a dust to gas ratio much lower (< 0.1)
than Galactic. We show that these results are rather robust and not strongly
dependent on the details of the modeling.Comment: 13 pages, 1 figure, Astrophysical Journal, in pres
The resolved fraction of the Cosmic X-ray Background
We present the X-ray source number counts in two energy bands (0.5-2 and 2-10
keV) from a very large source sample: we combine data of six different surveys,
both shallow wide field and deep pencil beam, performed with three different
satellites (ROSAT, Chandra and XMM-Newton). The sample covers with good
statistics the largest possible flux range so far: [2.4*10^-17 - 10^-11] cgs in
the soft band and [2.1*10^-16 - 8*10^{-12}]cgs in the hard band. Integrating
the flux distributions over this range and taking into account the (small)
contribution of the brightest sources we derive the flux density generated by
discrete sources in both bands. After a critical review of the literature
values of the total Cosmic X--Ray Background (CXB) we conclude that, with the
present data, the 94.3%, and 88.8% of the soft and hard CXB can be ascribed to
discrete source emission. If we extrapolate the analytical form of the Log
N--Log S distribution beyond the flux limit of our catalog in the soft band we
find that the flux from discrete sources at ~3*10^-18 cgs is consistent with
the entire CXB, whereas in the hard band it accounts for only 93% of the total
CXB at most, hinting for a faint and obscured population to arise at even
fainter fluxes.Comment: Accepted for publication in Ap
Freeze/thaw stress induces organelle remodeling and membrane recycling in cryopreserved human mature oocytes
Purpose: Our aim was to evaluate the ultrastructure of human metaphase II oocytes subjected to slow freezing and fixed after thawing at different intervals during post-thaw rehydration. Methods: Samples were studied by light and transmission electron microscopy. Results: We found that vacuolization was present in all cryopreserved oocytes, reaching a maximum in the intermediate stage of rehydration. Mitochondria-smooth endoplasmic reticulum (M-SER) aggregates decreased following thawing, particularly in the first and intermediate stages of rehydration, whereas mitochondria-vesicle (MV) complexes augmented in the same stages. At the end of rehydration, vacuoles and MV complexes both diminished and M-SER aggregates increased again. Cortical granules (CGs) were scarce in all cryopreserved oocytes, gradually diminishing as rehydration progressed. Conclusions: This study also shows that such a membrane remodeling is mainly represented by a dynamic process of transition between M-SER aggregates and MV complexes, both able of transforming into each other. Vacuoles and CG membranes may take part in the membrane recycling mechanism
Connecting Galaxy Evolution, Star Formation and the X-ray Background
As a result of deep hard X-ray observations by Chandra and XMM-Newton a
significant fraction of the cosmic X-ray background (CXRB) has been resolved
into individual sources. These objects are almost all active galactic nuclei
(AGN) and optical followup observations find that they are mostly obscured Type
2 AGN, have Seyfert-like X-ray luminosities (i.e., L_X ~ 10^{43-44} ergs
s^{-1}), and peak in redshift at z~0.7. Since this redshift is similar to the
peak in the cosmic star-formation rate, this paper proposes that the obscuring
material required for AGN unification is regulated by star-formation within the
host galaxy. We test this idea by computing CXRB synthesis models with a ratio
of Type 2/Type 1 AGN that is a function of both z and 2-10 keV X-ray
luminosity, L_X. The evolutionary models are constrained by parameterizing the
observed Type 1 AGN fractions from the recent work by Barger et al. The
parameterization which simultaneously best accounts for Barger's data, the CXRB
spectrum and the X-ray number counts has a local, low-L_X Type 2/Type 1 ratio
of 4, and predicts a Type 2 AGN fraction which evolves as (1+z)^{0.3}. Models
with no redshift evolution yielded much poorer fits to the Barger Type 1 AGN
fractions. This particular evolution predicts a Type 2/Type 1 ratio of 1-2 for
log L_X > 44, and thus the deep X-ray surveys are missing about half the
obscured AGN with these luminosities. These objects are likely to be Compton
thick. Overall, these calculations show that the current data strongly supports
a change to the AGN unification scenario where the obscuration is connected
with star formation in the host galaxy rather than a molecular torus alone. The
evolution of the obscuration implies a close relationship between star
formation and AGN fueling, most likely due to minor mergers or interactions.Comment: 36 pages, 8 figures, ApJ in press. Minor changes to match published
versio
Morphological, physiological and pathogenic variability of small-spore Alternaria sp. causing leaf blight of Solanaceous plants in Algeria
Due to premature defoliation, early blight epidemics can cause major yield losses. Large-spore Alternaria species such as A. solani and A. tomatophila have long been recognized as important pathogens responsible for such blight disease in the family Solanaceae and thus represent a serious risk for crop production. Small-spore Alternaria species have also been frequently isolated from plant samples with typical blight symptoms but their incidence as primary pathogens is often controversial. In order to study the diversity of small-spore Alternaria species, 32 isolates were selected from a larger collection of 130 isolates from infected leaves, fruits and stems of tomato from various growing regions of North-West Algeria. Morphological characterization under standard conditions and polymerase chain reaction (PCR) analyses using specific primers to amplify a part of the ITS regions and the 5.8S gene were conducted to confirm their identification as members of the alternata section. They were then examined according to morphological characteristics of conidia and sporulation patterns on potato carrot agar (PCA) and were segregated into three morphological species: A. alternata, A. tenuissima and A. arborescens. Colony type, substrate colour, margin, zonation, pigmentation, colony diameter and conidia production were studied on potato sucrose agar (PSA). Physiological parameters and nutritional requirements of the isolates were also assessed and a data matrix based on cluster analysis and Euclidean distance was constructed. Results of pathogenicity test on tomato showed obvious diversity among the isolates and they could be separated into two groups based on their virulence. The dendrogram based on the influence of cultural, nutritional and physiological characters suggests moderate heterogeneity within the populations of A. alternata and A. tenuissima. The small-spore species formed five clusters that fundamentally paralleled the morphological groupings. However, the results provided no evidence for geographical and pathogenicity clustering of isolates
Analysis and optimisation of a production line using discrete simulation
This study presents a simulation-based procedure to analyse a production line of a metalworking company. We use a simulation tool, ProModel R software, to reproduce the existing production line layout of the company best-selling product which represents about 70% of the total sales. Our purpose is to get information about the existing system behaviour, and to find strategies to increase actual production level to meet the market’s demand. Based on an initial simulation model, different production scenarios were proposed and results have shown that it is possible to increase the production level allowing to meet the increasing demand for
the product. The following changes in the production system were considered: (i) the use of intermediate stock of work-in-process items, (ii) the introduction of new equipment, and (iii) a mixed strategy where the introduction of new equipment is combined with the use of intermediate stock of work-in-process items. In summary, this research exhibits the flexibility of the simulation technique to address manufacturing problems throughout the creation of different scenarios providing some of the behaviour of the systems allowing the anticipation of final outputs.info:eu-repo/semantics/publishedVersio
The deepest X-ray look at the Universe
The origin of the X-ray background, in particular at hard (2-10 keV)
energies, has been a debated issue for more than 30 years. The Chandra deep
fields provide the deepest look at the X-ray sky and are the best dataset to
study the X-ray background. We searched the Chandra Deep Field South for X-ray
sources with the aid of a dedicated wavelet-based algorithm. We are able to
reconstruct the Log N-Log S source distribution in the soft (0.5-2 keV) and
hard (2-10 keV) bands down to limiting fluxes of 2x10^{-17} erg s^{-1} cm^{-2}
and 2x10^{-16} erg s^{-1} cm^{-2}, respectively. These are a factor ~5 deeper
than previous investigations. We find that the soft relation continues along
the extrapolation from higher fluxes, almost completely accounting for the soft
X-ray background. On the contrary, the hard distribution shows a flattening
below ~2x10^{-14} erg s^{-1} cm^{-2}. Nevertheless, we can account for >68% of
the hard X-ray background, with the main uncertainty being the sky flux itself.Comment: Accepted for publication on ApJL. Two figures, requires emulateapj5
(included
- …