7,438 research outputs found
Fixing Conditions in the Freeze Substitution Technique for Light Microscopy Observation of Frozen Beef Tissue
The freeze substitution histological technique allows the indirect light microscopicobservation and the quantitative evaluation of ice crystal size in frozen tissues. Theuseofchemical fixatives in substitu ting fluids improves morphological and histochemical preservation of the tissue. Fixation conditions become important since this step can introduce modifications in crystal sizes . Effects of temperature on: a) diffusion rate of fixing solution in tissue, b) recrystallization rate of ice in frozen beef and c) variations of the froze~ water fraction were ana lyzed, establishing that 1sothermal freeze fixation constitutes an appropriate method for histological observation. Fixing at temperatures lower than that of the sample, in an attempt to reduce recrystallization effects , involves an increase of the frozen water fraction i.n the tissue leading to modifications in size of ice crystals and to changes in the histological structure
On the strategy frequency problem in batch Minority Games
Ergodic stationary states of Minority Games with S strategies per agent can
be characterised in terms of the asymptotic probabilities with which
an agent uses of his strategies. We propose here a simple and general
method to calculate these quantities in batch canonical and grand-canonical
models. Known analytic theories are easily recovered as limiting cases and, as
a further application, the strategy frequency problem for the batch
grand-canonical Minority Game with S=2 is solved. The generalization of these
ideas to multi-asset models is also presented. Though similarly based on
response function techniques, our approach is alternative to the one recently
employed by Shayeghi and Coolen for canonical batch Minority Games with
arbitrary number of strategies.Comment: 17 page
IGR J00234+6141 : a new INTEGRAL source identified as an Intermediate polar
Following an extensive survey of the galactic plane by the INTEGRAL
satellite, new hard X-ray sources are discovered with a significant fraction of
Cataclysmic Variables (CVs) among them. We report here the identification of
one of these hard X-ray sources, IGR J00234+6141, as an accreting magnetic
white dwarf of intermediate polar type. We analyse the high energy emission of
the INTEGRAL source using all available data and provide complementary optical
photometric and spectroscopic data obtained respectively in August and October
2006. Based on a refined INTEGRAL position, we confirm the proposed optical
identification. We clearly detect the presence of a 564 s periodic optical
modulation that we identify as the rotation of the white dwarf. The analysis of
the optical spectrum also demonstrates that the emission lines show a
modulation in radial velocity with an orbital period of Porb = (4.033 +/-
0.005) hr. The two periodicities indicate that IGR00234+6141 is a magnetic CV
of the intermediate polar type. This is one of the faintest and hardest sources
of this type detected by INTEGRAL. This confirms earlier conclusions that IPs
contribute significantly to the population of galactic X-ray sources and
represent a significant fraction of the high energy background.Comment: 6 pages, 7 figures, accepted for publication in A&
Magnetic field and unstable accretion during AM Herculis low states
A study of AM Her low states in September 1990 and 1991 and June-July 1997 is
reported from a coordinated campaign with observations obtained at the
Haute-Provence observatory, at the 6-m telescope of the Special Astrophysical
Observatory and at the 2.6m and 1.25m telescopes of the Crimean observatory.
Spectra obtained at different dates when the source was in low states at a
comparable V magnitude, show the presence of strong Zeeman absorption features
and marked changes in emission lines with a day-to-day reappearance of the HeII
(4686\AA) emission lines in 1991. Despite this variability, the magnetic field
inferred from the fitting of the absorption spectrum with Zeeman hydrogen
splitting, is remarkably constant with a best value of (12.50.5)MG.
Detailed analysis of the UBVRI light curves shows the presence of repetitive
moderate amplitude ( 0.3-0.5 mag) flares predominantly red in colour.
These flares are attributed to small accretion events and are compared to the
large ( 2 mag.) blue flare reported by Shakhovskoy et al. (1993). We
suggest that the general flaring activity observed during the low states is
generated by accretion events. The different characteristics of the flares
(colour and polarization) are the results of different shock geometries
depending on the net mass accretion flux.Comment: accepted in Astronomy & Astrophysics (Main Journal), 10 pages, 6
Figures, Late
Light Microscopy Measurements of Ice Recrystallization in Frozen Corn Starch Pastes Using Isothermal Freeze Fixation
Isothermal freeze fixation was used to analyze ice recrystallization by light microscopy in a 10 % (W/W) frozen corn starch paste during storage at temperatures in the range of -5 to -20 °C.
Different formulations were tested in order to obtain a suitable fixative for this method of indirect observation of the ice crystals. A solution of formaldehyde, ethanol and water (10:45:45 V:V) was selected because it minimized substitution-induced distortion and contraction of the matrix. The diffusion coefficients of the selected fixative in the frozen system were measured at different temperatures in conditions of unidirectional mass transfer in a semi - infinite medium. The activation energy for diffusion was determined (Ea = 95.11 ± I. 15 KJ/mol).
Fixation times for the frozen starch paste at different temperatures were predicted from a mathematical model for unidirectional mass transfer with a discontinuous diffusion coefficient. Matrix contraction during the different stages of the freeze fixation method was evaluated.
Recrystallization of ice in frozen corn starch pastes during storage was analyzed by the measurement of the changes in ice crystal equivalent diameters on the micrographs. A kinetic equation for recrystallization was fitted to the experimental data to obtain the corresponding parameters. Contraction of the matrix affects the kinetic constants but has no effect on activation energy. The effect of recrystallization during fixation on ice crystal measurements was not significant
Swift J0525.6+2416 and IGR J04571+4527: two new hard X-ray selected magnetic cataclysmic variables identified with XMM-Newton
IGR J04571+4527 and Swift J0525.6+2416 are two hard X-ray sources detected in
the Swift/BAT and INTEGRAL/IBIS surveys. They were proposed to be magnetic
cataclysmic variables of the Intermediate Polar (IP) type, based on optical
spectroscopy. IGR J04571+4527 also showed a 1218 s optical periodicity,
suggestive of the rotational period of a white dwarf, further pointing towards
an IP classification. We here present detailed X-ray (0.3-10 keV) timing and
spectral analysis performed with XMM-Newton, complemented with hard X-ray
coverage (15-70 keV) from Swift/BAT. These are the first high signal to noise
observations in the soft X-ray domain for both sources, allowing us to identify
the white dwarf X-ray spin period of Swift J0525.6+2416 (226.28 s), and IGR
J04571+4527 (1222.6 s). A model consisting of multi-temperature optically thin
emission with complex absorption adequately fits the broad-band spectrum of
both sources. We estimate a white dwarf mass of about 1.1 and 1.0 solar masses
for IGR J04571+4527 and Swift J0525.6+2416, respectively. The above
characteristics allow us to unambiguously classify both sources as IPs,
confirming the high incidence of this subclass among hard X-ray emitting
Cataclysmic Variables.Comment: 8 pages, 4 figures, 3 tables. Accepted for publication in MNRA
Extending local features with contextual information in graph kernels
Graph kernels are usually defined in terms of simpler kernels over local
substructures of the original graphs. Different kernels consider different
types of substructures. However, in some cases they have similar predictive
performances, probably because the substructures can be interpreted as
approximations of the subgraphs they induce. In this paper, we propose to
associate to each feature a piece of information about the context in which the
feature appears in the graph. A substructure appearing in two different graphs
will match only if it appears with the same context in both graphs. We propose
a kernel based on this idea that considers trees as substructures, and where
the contexts are features too. The kernel is inspired from the framework in
[6], even if it is not part of it. We give an efficient algorithm for computing
the kernel and show promising results on real-world graph classification
datasets.Comment: To appear in ICONIP 201
The peculiar source XSS J12270-4859: a LMXB detected by FERMI ?
The X-ray source XSS J12270-4859 has been first suggested to be a magnetic
cataclysmic variable of Intermediate Polar type on the basis of its optical
spectrum and a possible 860 s X-ray periodicity. However further X-ray
observations by the Suzaku and XMM-Newton satellites did not confirm this
periodicity but show a very peculiar variability, including moderate repetitive
flares and numerous absorption dips. These characteristics together with a
suspected 4.3 h orbital period would suggest a possible link with the so-
called "dipping sources", a sub-class of Low-Mass X-ray Binaries (LMXB). Based
on the released FERMI catalogues, the source was also found coincident with a
very high energy (0.1-300 GeV) VHE source 2FGL J1227.7-4853. The good
positional coincidence, together with the lack of any other bright X-ray
sources in the field, makes this identification highly probable. However, none
of the other standard LMXBs have been so far detected by FERMI. Most galactic
VHE sources are associated with rotation-powered pulsars. We present here new
results obtained from a 30 ksec high-time resolution XMM observations in
January 2011 that confirm the flaring-dipping behaviour and provide upper
limits on fast X-ray pulsations. We discuss the possible association of the
source with either a microquasar or an accreting rotation powered pulsar.Comment: To appear in the Proceedings of "The Golden Age of Cataclysmic
Variables (Palermo 2011)", in Mem. Soc. Astron. It. (4 pages, 2 figures
Broad-band characteristics of seven new hard X-ray selected cataclysmic variables
Indexación: Web of Science; Scopus.We present timing and spectral analysis of a sample of seven hard X-ray selected cataclysmic
variable candidates based on simultaneous X-ray and optical observations collected
with XMM–Newton, complemented with Swift/BAT and INTEGRAL /IBIS hard X-ray data
and ground-based optical photometry. For six sources, X-ray pulsations are detected for the
first time in the range of ∼296–6098 s, identifying them as members of the magnetic class.
Swift J0927.7−6945, Swift J0958.0−4208, Swift J1701.3−4304, Swift J2113.5+5422 and
possibly PBC J0801.2−4625 are intermediate polars (IPs), while Swift J0706.8+0325 is a
short (1.7 h) orbital period polar, the 11th hard X-ray-selected identified so far. X-ray orbital
modulation is also observed in Swift J0927.7−6945 (5.2 h) and Swift J2113.5+5422
(4.1 h). Swift J1701.3−4304 is discovered as the longest orbital period (12.8 h) deep eclipsing
IP. The spectra of the magnetic systems reveal optically thin multitemperature emission
between 0.2 and 60 keV. Energy-dependent spin pulses and the orbital modulation in
Swift J0927.7−6945 and Swift J2113.5+5422 are due to intervening local high-density absorbing
material (NH ∼ 1022 − 23 cm−2). In Swift J0958.0−4208 and Swift J1701.3−4304, a
soft X-ray blackbody (kT ∼ 50 and ∼80 eV) is detected, adding them to the growing group
of ‘soft’ IPs. White dwarf masses are determined in the range of ∼0.58–1.18 M, indicating
massive accreting primaries in five of them. Most sources accrete at rates lower than the
expected secular value for their orbital period. Formerly proposed as a long-period (9.4 h)
nova-like CV, Swift J0746.3−1608 shows peculiar spectrum and light curves suggesting either
an atypical low-luminosity CV or a low-mass X-ray binary.https://academic.oup.com/mnras/article/470/4/4815/390658
Virtual Reality bridge between Chemistry and Cultural Heritage: the "Sala degli Stemmi" Case Study
In this contribution, we present a multiscale and multidisciplinary VR architecture that aims at creating a common environment where cultural heritage and chemistry meet in order to strengthen the role already played by chemistry in the process of restoration of cultural goods. Our aim is to create a user friendly platform where experts of both fields can share data and ideas in a direct way, in order to achieve deeper insights into cultural goods combining the scientific and historical points of view. As a case study we present the 3D reconstruction of the "Sala degli Stemmi", which is one of the two historical rooms at Palazzo della Carovana in Pisa, presenting a number of artworks that underwent a process of chemical analysis and restoration in 2012. The whole architecture has been developed using the Unity game engine, and it is usable with HTC Vive headsets. The implementation of the VR environment and the potential applications, from both the scientific and educational points of view, are discussed in some detail
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