7,494 research outputs found
The puzzling symbiotic X-ray system 4U1700+24
Symbiotic X-ray binaries form a subclass of low-mass X-ray binary systems
consisting of a neutron star accreting material from a red giant donor star via
stellar wind or Roche lobe overflow. Only a few confirmed members are currently
known; 4U 1700+24 is a good candidate as it is a relatively bright X-ray
object, possibly associated with the late-type star V934 Her. We analysed the
archive {\it XMM}-Newton and Swift/XRT observations of 4U 1700+24 in order to
have a uniform high-energy ( keV) view of the source. We confirmed the
existence of a red-shifted O VIII Ly- transition (already observed in
the 2002 {\it XMM}-Newton data) in the high-resolution spectra collected via
the RGS instruments. The red-shift of the line is found in all the analysed
observations and, on average, it was estimated to be . We also
observed a modulation of the centroid energy of the line on short time scales
(a few days) and discuss the observations in the framework of different
scenarios. If the modulation is due to the gravitational red-shift of the
neutron star, it might arise from a sudden re-organization of the emitting
-ray matter on the scale of a few hundreds of km. Alternatively, we are
witnessing a uni-polar jet of matter (with typical velocity of km
s) possibly emitted by the neutron star in an almost face-on system. The
second possibility seems to be required by the apparent lack of any modulation
in the observed -ray light curve. We also note also that the low-resolution
spectra (both {\it XMM}-Newton and Swift/XRT in the keV band) show the
existence of a black body radiation emitted by a region (possibly associated
with the neutron star polar cap) with typical size from a few tens to hundreds
of meters. The size of this spot-like region reduces as the overall luminosity
of 4U 1700+24 decreases.Comment: In press on A&
Percolation Effects in Very High Energy Cosmic Rays
Most QCD models of high energy collisions predict that the inelasticity
is an increasing function of the energy. We argue that, due to percolation of
strings, this behaviour will change and, at GeV, the
inelasticity will start to decrease with the energy. This has straightforward
consequences in high energy cosmic ray physics: 1) the relative depth of the
shower maximum grows faster with energy above the knee; 2) the energy
measurements of ground array experiments at GZK energies could be
overestimated.Comment: Correction of equation (19) and figures 3 and 4. 4 pages, 4 figure
Model Subject Specific Pedagogy Tematik Integratif Untuk Pengembangan Karakter Hormat Dan Tanggung Jawab Siswa
: This research aimed at producing a learning package in the form of thematic-integrativeSubject Specific Pedagogy (SSP) that could improve the character of the fourth grade of elementary school, especially the character of respect and responsibility. This research also aimed to find theeffectiveness of the thematic-integrative SSP in developing the character values of respect and responsibility of the fourth grade students of SD Karanganyar. This research and development consistedof a number of steps: (1) preleminary study; (2) planning; (3) early product development; (4) limitedtry-out; (5) revision of the main product; (6) field try-out; (7) revision on operational product; (8) fieldtry-out of the operational product; (9) final revision of product; (10) dissemination and implementation. The try-out subjects were Grade IV students of SD Karanganyar. The subjects of one-one tryout consisted of 3 students. The subjects of small group try-out consisted of 10 students who had nobeen involved in the one-one try-out, while the subjects of field try-out consisted of 30 students 30students of Grades IV A and IV B. The results of the research were SSP components consisting of: syllabus, learning implementation plans, students\u27 worksheets, and evaluation instrument. The results othe evaluation showed that the developed syllabus obtained an actual score of 42, which belonged tothe âvery goodâ category. The learning implementation plans (RPP) developed gained an actual scoreof 53, which belonged to the âgoodâ category, the students\u27 worksheet (LKS) got an actual score of 43which belonged to the âgoodâ category, while the evaluation instrument developed was consideredvalis and belonged to the âgoodâ category
Unveiling the hard X-ray spectrum from the "burst-only" source SAX J1753.5-2349 in outburst
Discovered in 1996 by BeppoSAX during a single type-I burst event, SAX
J1753.5-2349 was classified as "burst-only" source. Its persistent emission,
either in outburst or in quiescence, had never been observed before October
2008, when SAX J1753.5-2349 was observed for the first time in outburst. Based
on INTEGRAL observations,we present here the first high-energy emission study
(above 10 keV) of a so-called "burst-only". During the outburst the SAX
J1753.5-2349 flux decreased from 10 to 4 mCrab in 18-40 keV, while it was found
being in a constant low/hard spectral state. The broad-band (0.3-100 keV)
averaged spectrum obtained by combining INTEGRAL/IBIS and Swift/XRT data has
been fitted with a thermal Comptonisation model and an electron temperature >24
keV inferred. However, the observed high column density does not allow the
detection of the emission from the neutron star surface. Based on the whole set
of observations of SAX J1753.5-2349, we are able to provide a rough estimate of
the duty cycle of the system and the time-averaged mass-accretion rate. We
conclude that the low to very low luminosity of SAX J1753.5-2349 during
outburst may make it a good candidate to harbor a very compact binary system.Comment: 5 pages, 3 figures, 2 tables; accepted for publication in MNRAS
Letter
L'area delle risorgive nel sistema insediativo mesolitico: alcuni esempi dal pordenonese
The authors present the work undertaken on the lithic material collected in the spring area between Orcenico Superiore and Savorgnano (Pordenone-Italy). The sites are located on an NE-SW elongated Lateglacial gravel ridge, which to the present day is to be considered a stable area (i.e. preserved from alluvial and erosive action of Tagliamento and Meduna rivers). Different periods are represented in the lithic industries, spanning from the Mesolithic to the Bronze Age. This paper presents the results of the study carried out on the Mesolithic industries, mainly to be ascribed to the Castelnovian tradition. The typological composition of the assemblages shows different activities which could be associated with residential camps, without any particular specialization although this kind of interpretation could be biased by the non systematic nature of the findings. Different operational chains were in place, aiming to produce either bladelets or flakes. Raw materials are mostly of local origin, although few pieces were brought in from the Prealps, showing a North-South mobility along river routes. At the same time, there are scarce lithic materials imported from the upper part of the Udine plain, which is rich in good quality flint pebbles. Further technological and typological differences show a rather neat separation between sites on either sides of Tagliamento river. When we consider the distribution of Mesolithic sites in Friuli, a logistical settlement system seems to emerge: bigger sites are located at the edge of ecologically differentiated areas in connection with stable water sources such as the spring area between Orcenico and S. Vito al Tagliamento and the piedmont; complementary to those, task-related short-term sites characterised by less materials and fewer lithic types are found in the Prealps at middle altitude
Number of spanning clusters at the high-dimensional percolation thresholds
A scaling theory is used to derive the dependence of the average number
of spanning clusters at threshold on the lattice size L. This number should
become independent of L for dimensions d<6, and vary as log L at d=6. The
predictions for d>6 depend on the boundary conditions, and the results there
may vary between L^{d-6} and L^0. While simulations in six dimensions are
consistent with this prediction (after including corrections of order loglog
L), in five dimensions the average number of spanning clusters still increases
as log L even up to L = 201. However, the histogram P(k) of the spanning
cluster multiplicity does scale as a function of kX(L), with X(L)=1+const/L,
indicating that for sufficiently large L the average will approach a finite
value: a fit of the 5D multiplicity data with a constant plus a simple linear
correction to scaling reproduces the data very well. Numerical simulations for
d>6 and for d=4 are also presented.Comment: 8 pages, 11 figures. Final version to appear on Physical Review
A Method to Find Community Structures Based on Information Centrality
Community structures are an important feature of many social, biological and
technological networks. Here we study a variation on the method for detecting
such communities proposed by Girvan and Newman and based on the idea of using
centrality measures to define the community boundaries (M. Girvan and M. E. J.
Newman, Community structure in social and biological networks Proc. Natl. Acad.
Sci. USA 99, 7821-7826 (2002)). We develop an algorithm of hierarchical
clustering that consists in finding and removing iteratively the edge with the
highest information centrality. We test the algorithm on computer generated and
real-world networks whose community structure is already known or has been
studied by means of other methods. We show that our algorithm, although it runs
to completion in a time O(n^4), is very effective especially when the
communities are very mixed and hardly detectable by the other methods.Comment: 13 pages, 13 figures. Final version accepted for publication in
Physical Review
Protease and hemicellulase assisted extraction of dietary fiber from wastes of Cynara cardunculus
6057-6075The action of protease and hemicellulase for the extraction of fractions enriched in soluble fiber from bracts and stems of Cynara cardunculus was evaluated. Using a two-factor simplex design comprising protease amounts of 0-200 ?L and hemicellulase amounts of 0-200 mg for 5 g of material, we explored the effect of a 5 h enzymatic treatment at 40 °C on the chemical composition and yield of the fractions isolated. The fractions contained inulin and pectin. In general, the protein, inulin, and polyphenol contents and also the yields were higher for fractions obtained from stems. The most marked effects were observed when enzymes were used at higher concentrations, especially for hemicellulase. The inclusion of a pre-heating step increased the yield and the inulin content for fractions isolated from bracts and stems and decreased the protein and polyphenol contents, and the galacturonic acid for bracts. These fractions, in general, contained the polyphenolic compounds monocaffeoylquinic acid, apigenin, and pinoresinol
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