68,626 research outputs found
Probing the neutron star spin evolution in the young Small Magellanic Cloud Be/X-ray binary SXP 1062
No full textThe newly discovered Be/X-ray binary in the Small Magellanic Cloud, SXP 1062, provides the first example of a robust association with a supernova remnant (SNR). The short age estimated for the SNR qualifies SXP 1062 as the youngest known source in its class, t ~ 10^4 yr. As such, it allows us to test current models of magnetorotational evolution of neutron stars in a still unexplored regime. Here we discuss possible evolutionary scenarios for SXP 1062 in an attempt to reconcile its long spin period, P ~ 1062 s, and short age. Although several options can be considered, like an anomalously long initial period or the presence of a fossil disc, our results indicate that SXP 1062 may host a neutron star born with a large initial magnetic field, typically in excess of ~ 10^14 G, which then decayed to ~ 10^13 G
Supernova explosions of runaway stars and young neutron stars above the Galactic plane
No full textContext. Several supernova remnants and young neutron stars were recently discovered relatively high above the Galactic plane. Understanding their origin will provide key insights into the properties of the Galactic halo. One possibility is that they originated from runaway OB stars born in the Galactic disk.Aims. We aim to determine the spatial distribution of supernova explosions from runaway OB stars and to assess whether this model can explain certain observed neutron stars.Methods. We mapped the distribution of supernova events produced by runaway OB stars by incorporating their birth rate, initial spatial distribution, lifetime, ejection mechanisms, and velocity distributions. By tracking their motion in the Galactic potential, we determined their final distribution right before the explosion.Results. We show that the neutron star Calvera, which is found at z approximate to 2.2 kpc, could have originated from a runaway OB star. In addition, we compared the probabilities of finding a supernova remnant originating from Type Ia and core-collapse supernovae high above the Galactic plane, finding that supernova remnants related to core-collapse supernovae outnumber those related to Type Ia supernovae
Observations of Bºs→ψ(2S)η and Bº(s)→ψ(2S)π+π- decays
No full textFirst observations of the B0s
→ψ(2S)η, B0 →ψ(2S)π
+
π
− and B0s
→ψ(2S)π
+
π
− decays are made
using a dataset corresponding to an integrated luminosity of 1.0 fb−1 collected by the LHCb experiment in
proton–proton collisions at a centre-of-mass energy of
√
s = 7 TeV. The ratios of the branching fractions
of each of the ψ(2S) modes with respect to the corresponding J/ψ decays are
B(B0s
→ψ(2S)η)
÷
B(B0s
→J/ψη)
= 0.83± 0.14 (stat)±0.12 (syst) ±0.02 (B),
;
B(B0→ψ(2S)π
+
π
−
)
÷
B(B0→J/ψπ
+
π
−
)
= 0.56± 0.07 (stat)±0.05 (syst)± 0.01 (B),
;
B(B0s
→ψ(2S)π
+
π
−
)
÷
B(B0s
→J/ψπ
+
π
−
)
= 0.34± 0.04 (stat)±0.03 (syst)± 0.01 (B),
where the third uncertainty corresponds to the uncertainties of the dilepton branching fractions of the J/ψ
and ψ(2S) meson decays
Branching fraction and CP asymmetry of the decays B+→K0Sπ+ and B+→K0SK+
No full textAn analysis of B+ → K0
Sπ+ and B+ → K0
S K+ decays is performed with the LHCb experiment. The pp
collision data used correspond to integrated luminosities of 1 fb−1 and 2 fb−1 collected at centre-ofmass
energies of
√
s = 7 TeV and
√
s = 8 TeV, respectively. The ratio of branching fractions and the
direct CP asymmetries are measured to be B(B+ → K0
S K+
)/B(B+ → K0
Sπ+
) = 0.064 ± 0.009 (stat.) ±
0.004 (syst.), ACP(B+ → K0
Sπ+
) = −0.022 ± 0.025 (stat.) ± 0.010 (syst.) and ACP(B+ → K0
S K+
) =
−0.21 ± 0.14 (stat.) ± 0.01 (syst.). The data sample taken at
√
s = 7 TeV is used to search for
B+
c
→ K0
S K+ decays and results in the upper limit ( fc · B(B+
c
→ K0
S K+
))/( fu · B(B+ → K0
Sπ+
)) <
5.8 × 10−2 at 90% confidence level, where fc and fu denote the hadronisation fractions of a ¯b
quark
into a B+
c or a B+ meson, respectively
Measurement of the ratio of branching fractions B(B0→K∗0γ )/B(B0s→φγ ) and the directCP asymmetry inB 0→K∗0γ
No full textThe ratio of branching fractions of the radiative B decays B0→K⁎0γ and B0s→ϕγ has been measured using an integrated luminosity of 1.0 fb−1 of pp collision data collected by the LHCb experiment at a centre-of-mass energy of s√=7TeV. The value obtained is
B(B0→K⁎0γ)B(B0s→ϕγ)=1.23±0.06(stat.)±0.04(syst.)±0.10(fs/fd),
where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is associated with the ratio of fragmentation fractions fs/fd. Using the world average value for B(B0→K⁎0γ), the branching fraction B(B0s→ϕγ) is measured to be (3.5±0.4)×10−5.
The direct CP asymmetry in B0→K⁎0γ decays has also been measured with the same data and found to be
ACP(B0→K⁎0γ)=(0.8±1.7(stat.)±0.9(syst.))%.
Both measurements are the most precise to date and are in agreement with the previous experimental results and theoretical expectations
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Evidence for the decay B0→J/ψω and measurement of the relative branching fractions of meson decays to J/ψη and J/ψη′
No full textFirst evidence of the B 0 → J / ψ ω decay is found and the B s 0 → J / ψ η and B s 0 → J / ψ η ′ decays are studied using a dataset corresponding to an integrated luminosity of 1.0 fb -1 collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV. The branching fractions of these decays are measured relative to that of the B 0 → J / ψ ρ 0 decay:frac(B (B 0 → J / ψ ω), B (B 0 → J / ψ ρ 0)) = 0.89 ± 0.19 (stat) - 0.13 + 0.07 (syst),frac(B (B s 0 → J / ψ η), B (B 0 → J / ψ ρ 0)) = 14.0 ± 1.2 (stat) - 1.5 + 1.1 (syst) - 1.0 + 1.1 (frac(f d, f s)),frac(B (B s 0 → J / ψ η ′), B (B 0 → J / ψ ρ 0)) = 12.7 ± 1.1 (stat) - 1.3 + 0.5 (syst) - 0.9 + 1.0 (frac(f d, f s)), where the last uncertainty is due to the knowledge of f d / f s, the ratio of b-quark hadronization factors that accounts for the different production rate of B 0 and B s 0 mesons. The ratio of the branching fractions of B s 0 → J / ψ η ′ and B s 0 → J / ψ η decays is measured to befrac(B (B s 0 → J / ψ η ′), B (B s 0 → J / ψ η)) = 0.90 ± 0.09 (stat) - 0.02 + 0.06 (syst)
P. S. Popov and his Russian-Chinese dictionaries
No full textThe pioneers of Chinese studies in Russia were the Orthodox missionaries in Beijing from 1715 (Kangxi 54). From 1807 (Jiaqing 12) Russian missionaries in Beijing devoted themselves to studying Chinese as a linguistic subject.
There are two interesting Russian-Chinese dictionaries §²§å§ã§ã§Ü§à-
§¬§Ú§ä§Ñ§Û§ã§Üi§Û §³§Ý§à§Ó§Ñ§â§î¡¶¶íºººÏèµ×ֻ㡷(É H¨¤n H¨¦b¨¬ Z¨¬hu¨¬, Russian-Chinese Dictionaries) and §²§å§ã§ã§Ü§à-§¬§Ú§ä§Ñ§Û§ã§Üi§Û §³§Ý§à§Ó§Ñ§â§î¡¶¶íºººÏèµÔö²¹×ֻ㡷(É H¨¤n H¨¦b¨¬ Z¨¥ngb¨³ Z¨¬hu¨¬, Russian-Chinese Dictionaries), edited by the authoritative Russian sinologist P. S. Popov, published first in 1879 with a second edition in 1900. These Dictionaries are new materials for studying Chinese language from 1879 to 1900. I will therefore narrow my research to these two Popov¡¯s Dictionaries.
The hypothesis of this research is that the phonetic record of Popov¡¯s two Dictionaries (1879, 1900) are correct and can be used as reliable and valuable historical documents suitable for further research in the field of phonetics study of Pekingese of the late 19th century.
In order to determine if the hypothesis of the research is correct, I need to explain and answer the issues and questions as list below:
•Determine the accuracy of the phonetic records of these two editions. This is the main thrust of my research, and the point upon which the entire thesis rests.
•Determine the relative stability or instability of Pekingese phonetics from 1879 to 1900. If the phonetics of Pekingese of that period based on the phonetic recordings of the two Dictionaries did not change, we can say that Pekingese was ¡°stable¡± at that time; if it is an opposite case, this phenomenon must be explained.
The purposes of this research are:
•To introduce Popov, P. S., and his two Russian-Chinese Dictionaries edited in 1879 and 1900
•To determine the accuracy of the phonetic records in the Russian-Chinese Dictionaries edited by Popov, P. S. in 1879 and 1900, in order to test that they are reliable historical documents suitable for further research in the field of phonetics study of Pekingese of the last century
•To determine why the number of pronunciations of some characters during the end of the 19th and the beginning of the 20th centuries has decreased in present Pekingese, in order to illustrate the historical development of the phonetics of Pekinges
Population Synthesis As a Probe of Neutron Star Thermal Evolution
No full textThe study of thermal emission from isolated, cooling neutron stars plays a key role in probing the physical conditions of both the star crust and the core. The comparison of theoretical models for the star thermal evolution with the surface temperature derived from X-ray observations of sources of different age is one of the main tools to investigate the properties of the interior and constrain the equation of state. Here we propose to use population synthesis studies as an independent approach to test the physics governing the star cooling. Theoretical Log N-Log S distributions depend on the assumed neutron star thermal evolution. We have computed distributions for several different cooling scenarios and found that comparison with the observed Log N-Log S of isolated neutron stars is effective in discriminating among cooling models. Among the eleven cooling models considered in this paper, all of which may reproduce the observed temperature vs. age diagram, only at most three can explain the Log N-Log S distribution of close-by cooling neutron stars. The Log N-Log S test, being a "global" one and despite some limitations, appears indeed capable to ideally complement the standard temperature vs. age test used up to now
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