4,775 research outputs found
Lyapunov functions for a non-linear model of the X-ray bursting of the microquasar GRS 1915+105
This paper introduces a biparametric family of Lyapunov functions for a
non-linear mathematical model based on the FitzHugh-Nagumo equations able to
reproduce some main features of the X-ray bursting behaviour exhibited by the
microquasar GRS 1915+105. These functions are useful to investigate the
properties of equilibrium points and allow us to demonstrate a theorem on the
global stability. The transition between bursting and stable behaviour is also
analyzed.Comment: Published on International Journal of Non-Linear Mechanics, vol. 88,
pp. 142-14
The complex time behaviour of the microquasar GRS 1915+105 in the \rho-class observed with BeppoSAX. III: The hard X-ray delay and limit cycle mapping
The microquasar GRS1915+105 was observed by BeppoSAX in October 2000 for
about ten days while the source was in \rho-mode, which is characterized by a
quasi-regular type I bursting activity. This paper presents a systematic
analysis of the delay of the hard and soft X-ray emission at the burst peaks.
The lag, also apparent from the comparison of the [1.7-3.4] keV light curves
with those in the [6.8-10.2] keV range, is evaluated and studied as a function
of time, spectral parameters, and flux. We apply the limit cycle mapping
technique, using as independent variables the count rate and the mean photon
rate. The results using this technique were also cross-checked using a more
standard approach with the cross-correlation methods. Data are organized in
runs, each relative to a continuous observation interval. The detected
hard-soft delay changes in the course of the pointing from about 3 s to about
10 s and presents a clear correlation with the baseline count rate.Comment: accepted for publication in A&
Gli uccelli delle isole circumsiciliane
Gli autori sintetizzano tutte le informazioni bibliografiche e inedite sulle specie che sino al 30 agosto
2015 sono state contattate almeno una volta nelle 14 isole circumsiciliane (Eolie, Ustica, Egadi, Pantelleria
e Pelagie), confrontando alla fine la lista complessiva con quella delle isole Maltesi. In totale
sono ad oggi note 434 specie (isole Maltesi incluse); molte di esse hanno mostrato nel corso dei secoli
una notevole capacità di colonizzazione, fluttuando nel tempo o addirittura estinguendosi e ricolonizzando
alcune isole. Questi piccoli territori in mezzo al mare rappresentano ottimi siti di controllo dell’andamento
delle migrazioni nel corso dei decenni; alcune specie hanno chiaramente cambiato il loro
status rispetto al passato, aumentando o diminuendo. Nel corso di circa 15 anni in alcune di queste
isole (Ustica, Marettimo, Lampedusa e Linosa) sono stati condotti dei campi di inanellamento sia primaverili
sia autunnali che hanno permesso di inanellare 102.208 uccelli, in gran parte Passeriformes;
ciò ha consentito di raccogliere una notevole mole di dati sulle strategie migratorie, che vengono qui
brevemente presentati. Le piccole isole sono davvero importanti per gli uccelli migratori transahariani,
che devono sostare durante i loro lunghi viaggi per recuperare energie; la disponibilità di risorse
sotto forma di frutti selvatici o di insetti (a seconda delle specie) consente a queste masse di migratori
di continuare il loro viaggio. La conservazione degli uccelli è dettata dalla Direttiva Uccelli e l’istituzione
delle Zone di Protezione Speciale ha proprio lo scopo di salvaguardare alcune specie in determinati
territori. Questo è un impegno preso da parte di tutti i Paesi dell’Unione Europea, proprio perché
le popolazioni di uccelli non conoscono confini amministrativi e la loro tutela va al di là delle
competenze e degli interessi di un singolo Paese.
Per quanto riguarda le specie nidificanti, è risultata un’elevata correlazione negativa (r=-0,746), altamente
significativa (P=0,002) tra la capacità dispersiva media delle specie e la superficie in km2 delle
isole. Le specie con minore capacità dispersiva hanno colonizzato le isole di maggiori dimensioni, ma
non quelle più piccole; questo con molta probabilità dipende dalla eterogeneità ambientale, a sua volta
legata alla dimensione delle isole ed alla loro posizione geografica. Nel caso delle isole circumsiciliane,
sembra che non sia tanto la distanza dalla costa a determinare il numero di specie, quanto le condizioni
ambientali e la posizione geografica; indubbiamente la posizione tirrenica delle isole settentrionali rappresenta un vantaggio per la presenza di habitat differenziati e la conseguente colonizzazione di specie
ad essi legate, mentre la posizione meridionale, influenzata dall’aridità africana, riduce alcune possibilità
colonizzatrici da parte di alcune specie di uccelli e rende altresì problematica la stessa esistenza di habitat
diversificati. Il numero delle specie nidificanti in un’isola è variabile nel tempo, essendovi specie che
vi nidificano in modo irregolare. La correlazione area/N° specie nelle isole circumsiciliane è pari a 0,58,
ma se si esclude l’isola di Pantelleria, sale a 0,86; essa è pari a 0,92 per le sole isole settentrionali (Eolie,
Ustica ed Egadi), mentre risulta 0,99 per le sole tre isole meridionali del Canale di Sicilia.Authors summarize all bibliographic and unpublished
information on bird species that have been detected at least one time up to 30th August 2015 in the
14 circum-sicilian islands (Eolian, Ustica, Egadi, Pantelleria and Pelagian Is.). The Appendix 1 compares
overall lists with that of the Maltese Is., also lying in the Sicilian waters. On the whole, 434
species are known till now (Maltese Is. included); many of them showed a high colonizing capacity
along the centuries, fluctuating or even becoming extinct and re-colonising some islands. These small
territories in the middle of the Mediterranean sea are very good check-control sites of long-term
migration trend; compared to the past, some species changed their status, increasing or declining.
Additionally, during the last 15 years in some of these islands (Ustica, Marettimo, Lampedusa and
Linosa) bird ringing activity has been carried out, both in spring and in autumn; it allowed to ring
102,208 birds, mainly Passeriformes; this opportunity allowed to collect a remarkable amount of data
on migration strategy, here presented. The small islands are very important stop-over sites for transsaharan
migratory birds, that must rest during their long journey to recover fuel in the form of fat; the
availability of natural resources, such as wild fruits or insects, allows these masses of migrant birds to
continue their trip. The conservation of birds has been established by the Bird Directive and the institution
of Zones of Special Protection has the aim to safeguard some species in some territories. This
agreement was signed by all countries of the EU, because bird populations do not know administrative
borders and their conservation lies beyond the interests and authorities of a single country.
Concerning breeding birds, a high negative correlation (r=-0.746, P=0.002) has been found
between the average dispersal power of species and the area in km2 of islands. Species with minor
dispersal power colonized the biggest but not the smallest islands; this, very probably depended on
habitat heterogeneity of islands, in turn linked to the size of them and to the geographical position,
more than to the distance from the continental land. Tyrrhenian position of northern islands is certainly
an advantage for the presence of diversified habitats and birds inhabiting them, whereas
southern position of Pantelleria and Pelagian Is., as well as Maltese Is., affected by African dryness,
decreases colonizing probabilities of some bird species and the same existence of diversified habitats.
The number of breeding species in each island varied along the time and some species bred
irregularly. The correlation area/No. species in the islands surrounding Sicily resulted to be 0.58,
but if we exclude Pantelleria Is., it grows to 0.86; besides, it grows to 0.92 if we consider only northern
islands (Eolian, Ustica and Egadi Is.), and to 0.99 if we consider only southern islands
Timing analysis of 10-day long BeppoSAX observation of GRS 1915+105 in its ρ class
Published online at http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=6
Rainbow trout (Oncorhynchus mykiss, Walbaum 1792) develop a more robust body shape under organic rearing
Prolonged exposure to captive conditions has led to the development of a rainbow trout ‘farmed’ pheno- type, which is different from that of wild trout. Selec- tion for desirable productive traits in hatcheries has resulted in the development of some morphological traits that are maladaptive in nature. The recent development of organic aquaculture, guided by the well-being of the fish, could potentially produce a new farmed phenotype that would be more adaptive in nature. In this study, rainbow trout reared in intensive and organic farms were compared by means of shape analysis, to detect patterns of shape variation associated with rearing environment. The results of this study highlight a significant effect of the rearing method on rainbow trout shape: organi- cally reared trout showed a higher body profile, in particular in the head and trunk regions, shorter median fins and a deeper caudal peduncle. A combined effect of density and habitat complexity could have contributed to the observed shape differences: in organic rearing systems, lower densi- ties and steady water could increase territoriality and aggressive interactions, promoting body designs more functional in rapid attacks and escapes
Modulating the WNT pathway in Drosophila models of Cornelia de Lange Syndrome
Cornelia de Lange syndrome (CdLS) is a rare genetic disorder affecting neurodevelopment and the gastrointestinal and musculoskeletal systems. CdLS is caused by mutations within NIPBL, SMC1A, SMC3, RAD21, HDAC8 and BRD4 genes. These genes codify for the cohesin complex (or associated proteins), a multiprotein structure playing a role in chromatid adhesion, DNA repair and gene expression regulation. Our laboratory has shown that a strong correlation exists between cohesin complex function and WNT signalling, an intracellular pathway involved in regulation of expression of several genes controlling cell division and embryonic development. Recently, it has been observed that in nipblb- and smc1a-loss-of-function zebrafish embryos, in NIPBL- and SMC1A- mutated patient fibroblasts and in CdLS murine neural stem cells (NSCs) similar patterns of canonical WNT pathway alterations and cyclinD1 downregulation are present. Indeed, zebrafish embryos adverse phenotype was rescued by chemical activation of the WNT pathway. Drosophila melanogaster is an inexpensive model to study CdLS and to screen in vivo for therapeutic compounds. Therefore, we have used flies\u2019 strains mutated in nipped-B and hdac3 genes (respectively NIPBL and HDAC8 in humans) for assessing the existing correlation between cohesin complex and WNT pathway. Moreover, we have selected D. melanogaster mutants to screen for chemicals that revert the CdLS associated-phenotypes efficiently. In particular, we have tested WNT activators in order to investigate which effects they have on the mutated flies, assessing body weight and changes in brain structures (i.e. mushroom bodies) and possibly select compounds to test on vertebrate models. Funding: This work has been supported by Fondazione Cariplo, grant 2015-0783 to Valentina Massa
A new FSA approach for in situ -ray spectroscopy
An increasing demand of environmental radioactivity monitoring comes both
from the scientific community and from the society. This requires accurate,
reliable and fast response preferably from portable radiation detectors. Thanks
to recent improvements in the technology, -spectroscopy with sodium
iodide scintillators has been proved to be an excellent tool for in-situ
measurements for the identification and quantitative determination of
-ray emitting radioisotopes, reducing time and costs. Both for
geological and civil purposes not only K, U, and Th have
to be measured, but there is also a growing interest to determine the
abundances of anthropic elements, like Cs and I, which are used
to monitor the effect of nuclear accidents or other human activities.
The Full Spectrum Analysis (FSA) approach has been chosen to analyze the
-spectra. The Non Negative Least Square (NNLS) and the energy
calibration adjustment have been implemented in this method for the first time
in order to correct the intrinsic problem related with the
minimization which could lead to artifacts and non physical results in the
analysis.
A new calibration procedure has been developed for the FSA method by using in
situ -spectra instead of calibration pad spectra. Finally, the new
method has been validated by acquiring -spectra with a 10.16 cm x 10.16
cm sodium iodide detector in 80 different sites in the Ombrone basin, in
Tuscany. The results from the FSA method have been compared with the laboratory
measurements by using HPGe detectors on soil samples collected in the different
sites, showing a satisfactory agreement between them. In particular, the
Cs isotopes has been implemented in the analysis since it has been
found not negligible during the in-situ measurements.Comment: accepted by Science of Total Environment: 8 pages, 10 figures, 3
table
The Discordance of Mass-Loss Estimates for Galactic O-Type Stars
We have determined accurate values of the product of the mass-loss rate and
the ion fraction of P^{4+}, Mdot q(P^{4+}), for a sample of 40 Galactic O-type
stars by fitting stellar-wind profiles to observations of the P V resonance
doublet obtained with FUSE, ORFEUS/BEFS, and Copernicus. When P^{4+} is the
dominant ion in the wind, Mdot q(P^{4+}) approximates the mass-loss rate to
within a factor of 2. Theory predicts that P^{4+} is the dominant ion in the
winds of O7-O9.7 stars, though an empirical estimator suggests that the range
from O4-O7 may be more appropriate. However, we find that the mass-loss rates
obtained from P V wind profiles are systematically smaller than those obtained
from fits to Halpha emission profiles or radio free-free emission by median
factors of about 130 (if P^{4+} is dominant between O7 and O9.7) or about 20
(if P^{4+} is dominant between O4 and O7). These discordant measurements can be
reconciled if the winds of O stars in the relevant temperature range are
strongly clumped on small spatial scales. We use a simplified two-component
model to investigate the volume filling factors of the denser regions. This
clumping implies that mass-loss rates determined from "density squared"
diagnostics have been systematically over-estimated by factors of 10 or more,
at least for a subset of O stars. Reductions in the mass-loss rates of this
size have important implications for the evolution of massive stars and
quantitative estimates of the feedback that hot-star winds provide to their
interstellar environments.Comment: 26 pages, 4 figures; accepted for publication in Ap
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