1,721,938 research outputs found
The influence of the polymer matrix on the PTC properties polyethylene/carbon black composite
No full textCarbon black/polymer composites can be used in a variety of industrial applications, ranging from temperature sensors to fault current limiters. This is mainly due to their positive temperature coefficient of resistivity (PTC). As carbon black particles are loaded in a polymer matrix over a critical volume fraction, the composite becomes an electrical conductor at room temperature and exhibits a strong PTC effect on approaching its melting point. A model based on phase changes in the polymer matrix has been proposed by authors [1]. In this model, carbon black particles mainly reside in the amorphous phase in the composite, thus forming a conductive channel below the melting point. When temperature rises near to the melting point of the polyethylene, the crystalline phase starts to melt leading to formation of new amorphous regions. The volume of the new amorphous regions is larger than that of the previous crystalline region. Some portion of the new amorphous phase will extend into the previous amorphous regions. As the newly formed amorphous phase contains no carbon black, this extension can reduce and finally break up the conducting channel in the previous amorphous phase, resulting in rapid increase in resistivity of the composite. Thus this model can be used to explain the PTC effect in semicrystalline polymeric composite. Obviously the PTC properties can be affected by polymer matrix. In this paper the influence of the polymer matrix (LDPE, LLDPE and HDPE) on the PTC properties has been investigated, with a particular emphasis on the thermal stability of the PTC properties
The mechanism of electrical conduction in polyethylene/carbon black composite
No full textThe mechanism of electrical conduction in the polyethylene (PE)/carbon black (CB) composite is investigated in this paper. It has been found experimentally that there are three distinct regions in the J-E curve of the PE/CB composite. On the basis of energy band of the conductance grain--insulation dielectric--conductance grain system, the electrical conduction equation can be derived correspondingly according to the change in barrier potential under different electric fields. It shows that JµE in the low field strength, Log J/EµE in middle-field strength and Log J/Eµ-1/E in the high field strength. The equations fit well with the results obtained from experiments. The evidence suggests that the mechanism of conduction processes in the PE/CB composite can be attributed to the electrons tunnelling through the intergranular gaps among the CB particles
The mechanism of PTC effect in polyethylene/carbon black composite
No full textThe positive temperature coefficient (PTC) effect in polymeric composite has a variety of applications in industry, as a result many researches have been carried out to understand the mechanisms of the PTC effect. It has been stated in the literature that the PTC effect resulting from a distribution in the continuity of conducting network is principally due to the volumetric expansion of the polymeric matrix. However, the details of mechanism are not yet known. This paper reports an investigation on the PTC effect in polyethylene/carbon black composite. A model based on phase change in the polyethylene matrix is proposed. In this model, carbon black particles mainly reside in the amorphous phase in the composite, thus forming a conductive channel below the melting point. When temperature rises near to the melting point of the polyethylene, the crystalline phase starts to melt leading to formation of new amorphous regions. The volume of the new amorphous regions is larger than that of the previous crystalline region. Some portion of the new amorphous phase will extend into the previous amorphous regions. As the newly formed amorphous phase contains no carbon black, this extension can reduce and finally break up the conducting channel in the previous amorphous phase, resulting in rapid increase in resistivity of the composite. Thus this model can be used to explain the PTC effect in semicrystalline polymeric composite
Observation of a New Xi(b) Baryon
No full textThe observation of a new b baryon via its strong decay into Xi(-)(b)pi(+) (plus charge conjugates) is reported. The measurement uses a data sample of pp collisions at root s = 7 TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 5.3 fb(-1). The known Xi(-)(b) baryon is reconstructed via the decay chain Xi(-)(b) -> J/psi Xi(-) -> mu(+)mu(-)Lambda(0)pi(-), with Lambda(0) -> p pi(-). A peak is observed in the distribution of the difference between the mass of the Xi(-)(b)pi(+) system and the sum of the masses of the Xi(-)(b) and pi(+), with a significance exceeding 5 standard deviations. The mass difference of the peak is 14.84 +/- 0.74(stat) +/- 0.28(syst) MeV. The new state most likely corresponds to the J(P) = 3/2(+) companion of the Xi(b)
Observation of a New Xi(b) Baryon
No full textThe observation of a new b baryon via its strong decay into Xi(-)(b)pi(+) (plus charge conjugates) is reported. The measurement uses a data sample of pp collisions at root s = 7 TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 5.3 fb(-1). The known Xi(-)(b) baryon is reconstructed via the decay chain Xi(-)(b) -> J/psi Xi(-) -> mu(+)mu(-)Lambda(0)pi(-), with Lambda(0) -> p pi(-). A peak is observed in the distribution of the difference between the mass of the Xi(-)(b)pi(+) system and the sum of the masses of the Xi(-)(b) and pi(+), with a significance exceeding 5 standard deviations. The mass difference of the peak is 14.84 +/- 0.74(stat) +/- 0.28(syst) MeV. The new state most likely corresponds to the J(P) = 3/2(+) companion of the Xi(b)
Observation of a New Xi(b) Baryon
No full textThe observation of a new b baryon via its strong decay into Xi(-)(b)pi(+) (plus charge conjugates) is reported. The measurement uses a data sample of pp collisions at root s = 7 TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 5.3 fb(-1). The known Xi(-)(b) baryon is reconstructed via the decay chain Xi(-)(b) -> J/psi Xi(-) -> mu(+)mu(-)Lambda(0)pi(-), with Lambda(0) -> p pi(-). A peak is observed in the distribution of the difference between the mass of the Xi(-)(b)pi(+) system and the sum of the masses of the Xi(-)(b) and pi(+), with a significance exceeding 5 standard deviations. The mass difference of the peak is 14.84 +/- 0.74(stat) +/- 0.28(syst) MeV. The new state most likely corresponds to the J(P) = 3/2(+) companion of the Xi(b)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Search for the radiative Xi(-)(b) -> Xi(-)gamma decay
No full textThe first search for the rare radiative decay Xi(-)(b) -> Xi(-)gamma is performed using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13TeV, corresponding to an integrated luminosity of 5.4 fb(-1). The Xi(-)(b) -> Xi(-)-J/ psi channel is used as normalization. No Xi(-)(b) -> Xi(-)gamma signal is found and an upper limit of B(Xi(-)(b) -> Xi(-)gamma) < 1.3 x 10(-4) at 95% confidence level is obtained.LPH
Search for CP violation in Xi(-)(b) -> pK(-)K(-) decays
No full textA search for CP violation in charmless three-body Xi(-)(b) -> pK(-)K(-) decays is performed using pp collision data recorded with the LHCb detector, corresponding to integrated luminosities of 1 fb(-1) at a center-of-mass energy root S = 7 TeV, 2 fb(-1) at root S = 8 TeV and 2 fb(-1) at = 13 TeV. A good description of the phase-space distribution is obtained with an amplitude model containing contributions from Sigma(1385), Lambda(1405), Lambda(1520), Lambda(1670), Sigma(1775) and Sigma(1915) resonances. The model allows for CP violation effects, which are found to be consistent with zero. The branching fractions of Xi(-)(b) -> Sigma(1385)K-, Xi(-)(b) -> Lambda(1405)K-, Xi(-)(b) -> Lambda(1520)K-, Xi(-)(b) -> Lambda(1670)K-, Xi(-)(b) -> Sigma(1775)K- and Xi(-)(b) -> Sigma(1915)K- decays arc also reported. In addition, an upper limit is placed on the product of ratios of Omega(-)(b) and Xi(-)(b) fragmentation fractions and the Omega(-)(b) -> pK(-)K(-) and Xi(-)(b) -> pK(-)K(-) branching fractions
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