6,604 research outputs found
Two-point correlation function with pion in QCD sum rules
Within the framework of the conventional QCD sum rules, we study the pion
two-point correlation function, , beyond the soft-pion limit. We construct sum rules from the
three distinct Dirac structures, i \gamma_5 \notp, i \gamma_5, \gamma_5
\sigma_{\mu \nu} {q^\mu p^\nu} and study the reliability of each sum rule. The
sum rule from the third structure is found to be insensitive to the continuum
threshold, , and contains relatively small contribution from the
undetermined single pole which we denote as . The sum rule from the structure is very different even though it contains similar
contributions from and as the ones coming from the structure. On the other hand, the sum rule from
the i \gamma_5 \notp structure has strong dependence on both and ,
which is clearly in constrast with the sum rule for . We identify the source of the sensitivity for each of the sum
rules by making specific models for higher resonance contributions and discuss
the implication.Comment: slightly revised. version accepted for publication in Physical Review
Non-collinear magnetic structure and anisotropic magnetoelastic coupling in cobalt pyrovanadate Co2V2O7
The Co2V2O7 is recently reported to exhibit amazing magnetic field-induced
magnetization plateaus and ferroelectricity, but its magnetic ground state
remains ambiguous due to its structural complexity. Magnetometry measurements,
and time-of-flight neutron powder diffraction (NPD) have been employed to study
the structural and magnetic properties of Co2V2O7, which consists of two
non-equivalent Co sites. Upon cooling below the Ne\'el temperature TN = 6.3 K,
we observe magnetic Bragg peaks at 2K in NPD which indicated the formation of
long range magnetic order of Co2+ moments. After symmetry analysis and magnetic
structure refinement, we demonstrate that Co2V2O7 possesses a complicated
non-collinear magnetic ground state with Co moments mainly located in b-c plane
and forming a non-collinear spin-chain-like structure along the c-axis. The ab
initio calculations demonstrate that the non-collinear magnetic structure is
more stable than various ferromagnetic states at low temperature. The
non-collinear magnetic structure with canted up-up-down-down spin configuration
is considered as the origin of magnetoelectric coupling in Co2V2O7 because the
inequivalent exchange striction induced by the spin-exchange interaction
between the neighboring spins is the driving force of ferroelectricity.
Besides, it is found that the deviation of lattice parameters a and b is
opposite below TN, while the lattice parameter c and stay almost constant below
TN, evidencing the anisotropic magnetoelastic coupling in Co2V2O7.Comment: 9 pages, 8 figure
Maternal fucosyltransferase 2 status affects the gut bifidobacterial communities of breastfed infants.
BackgroundIndividuals with inactive alleles of the fucosyltransferase 2 gene (FUT2; termed the 'secretor' gene) are common in many populations. Some members of the genus Bifidobacterium, common infant gut commensals, are known to consume 2'-fucosylated glycans found in the breast milk of secretor mothers. We investigated the effects of maternal secretor status on the developing infant microbiota with a special emphasis on bifidobacterial species abundance.ResultsOn average, bifidobacteria were established earlier and more often in infants fed by secretor mothers than in infants fed by non-secretor mothers. In secretor-fed infants, the relative abundance of the Bifidobacterium longum group was most strongly correlated with high percentages of the order Bifidobacteriales. Conversely, in non-secretor-fed infants, Bifidobacterium breve was positively correlated with Bifidobacteriales, while the B. longum group was negatively correlated. A higher percentage of bifidobacteria isolated from secretor-fed infants consumed 2'-fucosyllactose. Infant feces with high levels of bifidobacteria had lower milk oligosaccharide levels in the feces and higher amounts of lactate. Furthermore, feces containing different bifidobacterial species possessed differing amounts of oligosaccharides, suggesting differential consumption in situ.ConclusionsInfants fed by non-secretor mothers are delayed in the establishment of a bifidobacteria-laden microbiota. This delay may be due to difficulties in the infant acquiring a species of bifidobacteria able to consume the specific milk oligosaccharides delivered by the mother. This work provides mechanistic insight into how milk glycans enrich specific beneficial bacterial populations in infants and reveals clues for enhancing enrichment of bifidobacterial populations in at risk populations - such as premature infants
A general model for collaboration networks
In this paper, we propose a general model for collaboration networks.
Depending on a single free parameter "{\bf preferential exponent}", this model
interpolates between networks with a scale-free and an exponential degree
distribution. The degree distribution in the present networks can be roughly
classified into four patterns, all of which are observed in empirical data. And
this model exhibits small-world effect, which means the corresponding networks
are of very short average distance and highly large clustering coefficient.
More interesting, we find a peak distribution of act-size from empirical data
which has not been emphasized before of some collaboration networks. Our model
can produce the peak act-size distribution naturally that agrees with the
empirical data well.Comment: 10 pages, 10 figure
Manganese dioxide nanosheet functionalized sulfur@PEDOT core-shell nanospheres for advanced lithium-sulfur batteries
MnO2 nanosheet functionalized S@PEDOT core–shell nanospheres demonstrate highly enhanced electrochemical performance for Li–S batteries, benefitting from effectively trapping polysulfides, minimizing polysulfide dissolution, and improving cathode conductivity and wettability.This is the accepted manuscript. The final version is available at http://pubs.rsc.org/en/content/articlelanding/2016/ta/c6ta03211g#!divAbstract
Observation of an unusual field dependent slow magnetic relaxation and two distinct transitions in a family of new complexes
An unusual field dependent slow magnetic relaxation and two distinct
transitions were observed in a family of new rare earth-transition metal
complexes, [Ln (bipy) (HO) M(CN)] 1.5 (bipy) 4HO (bipy = 2,2'-bipyridine; Ln = Gd,Y; M = Fe,
Co). The novel magnetic relaxation, which is quite different from those
in normal spin glasses and superparamagnets but very resembles qualitatively
those in single-molecule magnet Mn-Ac even if they possess different
structures, might be attributed to the presence of frustration that is
incrementally unveiled by the external magnetic field. The two distinct
transitions in [GdFe] were presumed from DC and AC susceptibility as well as
heat capacity measurements.Comment: Revtex, 6 figure
Observation of the e/3 Fractionally Charged Laughlin Quasiparticles
The existence of fractional charges carrying the current is experimentally
demonstrated. Using a 2-D electron system in high magnetic field, we measure
the shot noise associated with tunneling in the fractional quantum Hall regime
at Landau level filling factor 1/3. The noise gives a direct determination of
the quasiparticle charge, which is found to be e*=e/3 as predicted by Laughlin.
The existence of e/3 Laughlin quasiparticles is unambiguously confirmed by the
shot noise to Johnson-Nyquist noise cross-over found for temperature e*V/2k.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Lett. (accepted August
22
Transcription-coupled structural dynamics of topologically associating domains regulate replication origin efficiency
Background
Metazoan cells only utilize a small subset of the potential DNA replication origins to duplicate the whole genome in each cell cycle. Origin choice is linked to cell growth, differentiation, and replication stress. Although various genetic and epigenetic signatures have been linked to the replication efficiency of origins, there is no consensus on how the selection of origins is determined.
Results
We apply dual-color stochastic optical reconstruction microscopy (STORM) super-resolution imaging to map the spatial distribution of origins within individual topologically associating domains (TADs). We find that multiple replication origins initiate separately at the spatial boundary of a TAD at the beginning of the S phase. Intriguingly, while both high-efficiency and low-efficiency origins are distributed homogeneously in the TAD during the G1 phase, high-efficiency origins relocate to the TAD periphery before the S phase. Origin relocalization is dependent on both transcription and CTCF-mediated chromatin structure. Further, we observe that the replication machinery protein PCNA forms immobile clusters around TADs at the G1/S transition, explaining why origins at the TAD periphery are preferentially fired.
Conclusion
Our work reveals a new origin selection mechanism that the replication efficiency of origins is determined by their physical distribution in the chromatin domain, which undergoes a transcription-dependent structural re-organization process. Our model explains the complex links between replication origin efficiency and many genetic and epigenetic signatures that mark active transcription. The coordination between DNA replication, transcription, and chromatin organization inside individual TADs also provides new insights into the biological functions of sub-domain chromatin structural dynamics
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