A
bstract
We have computed the self-energies and a set of three-particle vertex functions for massless QCD at the four-loop level in the
M
S
¯
renormalization scheme. The vertex functions are ...evaluated at points where one of the momenta vanishes. Analytical results are obtained for a generic gauge group and with the full gauge dependence, which was made possible by extensive use of the Forcer program for massless four-loop propagator integrals. The bare results in dimensional regularization are provided in terms of master integrals and rational coefficients; the latter are exact in any space-time dimension. Our results can be used for further precision investigations of the perturbative behaviour of the theory in schemes other than
M
S
¯
. As an example, we derive the five-loop beta function in a relatively common alternative, the minimal momentum subtraction (MiniMOM) scheme.
Using integral field data we extract the optical spectra of shocked interstellar clouds in Kepler's supernova remnant located in the inner regions of our Galaxy, as well as in the Large Magellanic ...Cloud, the Small Magellanic Cloud, NGC 6822, and IC 1613. Using self-consistent shock modeling, we make a new determination of the chemical composition of the interstellar medium in N, O, Ne, S, Cl, and Ar in these galaxies and obtain accurate estimates of the fraction of refractory grains destroyed in the shock. By comparing our derived abundances with those obtained in recent works using observations of B-stars, F supergiant stars, and H ii regions, we provide a new calibration for abundance scaling in the range of .
We have extended our previous computations of the even-N moments of the flavour-singlet four-loop splitting functions to N=12 for the pure-singlet quark case and N=10 for all other cases. These ...results, obtained using physical quantities in inclusive deep-inelastic scattering, have been and will be used to validate conceptionally much more challenging determinations of these splitting functions from off-shell operator matrix elements (OMEs). For the quark-gluon and gluon-gluon splitting functions, which have yet to be computed to higher N using OMEs, we construct approximations based on our moments and endpoint constraints, where we present new large-x results for the gluon-gluon case. These approximations facilitate an approximate N3LO evolution of parton distributions which are sufficiently accurate outside the region of small momentum fractions x.
RNA structures present throughout RNA virus genomes serve as scaffolds to organize multiple factors involved in the initiation of RNA synthesis. Several of these RNA elements play multiple roles in ...the RNA replication pathway. An RNA structure formed around the 5'- end of the poliovirus genomic RNA has been implicated in the initiation of both negative- and positive-strand RNA synthesis. Dissecting the roles of these multifunctional elements is usually hindered by the interdependent nature of the viral replication processes and often pleiotropic effects of mutations. Here, we describe a novel approach to examine RNA elements with multiple roles. Our approach relies on the duplication of the RNA structure so that one copy is dedicated to the initiation of negative-strand RNA synthesis, while the other mediates positive-strand synthesis. This allows us to study the function of the element in promoting positive-strand RNA synthesis, independently of its function in negative-strand initiation. Using this approach, we demonstrate that the entire 5'-end RNA structure that forms on the positive-strand is required for initiation of new positive-strand RNAs. Also required to initiate positive-strand RNA synthesis are the binding sites for the viral polymerase precursor, 3CD, and the host factor, PCBP. Furthermore, we identify specific nucleotide sequences within "stem a" that are essential for the initiation of positive-strand RNA synthesis. These findings provide direct evidence for a trans-initiation model, in which binding of proteins to internal sequences of a pre-existing positive-strand RNA affects the synthesis of subsequent copies of that RNA, most likely by organizing replication factors around the initiation site.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We compute the next-to-next-to-leading order (NNLO) contributions to the splitting functions governing the evolution of the unpolarized flavour-singlet parton densities in perturbative QCD. The exact ...expressions are presented in both Mellin-
N and Bjorken-
x space. We also provide accurate parametrizations for practical applications. Our results agree with all partial results available in the literature. As in the non-singlet case, the correct leading logarithmic predictions for small momentum fractions
x do not provide good estimates of the respective complete splitting functions. We investigate the size of the corrections and the stability of the NNLO evolution under variation of the renormalization scale. The perturbative expansion appears to converge rapidly at
x≳10
−3. Relatively large third-order corrections are found at smaller values of
x.
Virtually all liquids can be maintained for some time in a supercooled state, that is, at temperatures below their equilibrium melting temperatures, before eventually crystallizing. If cooled ...sufficiently quickly, some of these liquids will solidify into an amorphous solid, upon passing their glass transition temperature. Studies of these supercooled liquids reveal a considerable diversity in behaviour in their dynamical properties, particularly the viscosity. Angell characterized this in terms of their kinetic fragility. Previous synchrotron X-ray scattering studies have shown an increasing degree of short- and medium-range order that develops with increased supercooling. Here we demonstrate from a study of several metallic glass-forming liquids that the rate of this structural ordering as a function of temperature correlates with the kinetic fragility of the liquid, demonstrating a structural basis for fragility.
We compute the full three-loop coefficient functions for the structure functions
F
2
and
F
L
in massless perturbative QCD. The results for
F
L
complete the next-to-next-to-leading order description ...of unpolarized electromagnetic deep-inelastic scattering. The third-order coefficient functions for
F
2
form, at not too small values of the Bjorken variable
x, the dominant part of the next-to-next-to-next-to-leading order corrections, thus facilitating improved determinations of the strong coupling
α
s
from scaling violations. The three-loop corrections to
F
L
are larger than those for
F
2
. Especially for the latter quantity the expansion in powers of
α
s
is very stable, for photon virtualities
Q
2
≫
1
GeV
2
, over the full
x-range accessible to fixed-target and collider measurements.
Summary
Penetration of topically applied compounds may occur via the stratum corneum, skin appendages and hair follicles. The follicular infundibulum increases the surface area, disrupts the ...epidermal barrier towards the lower parts of the follicle, and serves as a reservoir. Topical delivery of active compounds to specific targets within the skin, especially to distinct hair follicle compartments or cell populations, may help to treat local inflammatory reactions selectively, with reduced systemic side‐effects. Various in vitro and in vivo methods exist for studying the hair follicle structure and follicular penetration pathways. These include cyanoacrylate skin surface stripping, confocal microscopy and cyanoacrylate scalp follicle biopsy. The complex anatomical structure as well as the cyclical activity of the hair follicle must be taken into consideration when designing delivery systems. In addition, delivery into and retention inside the infundibular reservoir are controlled by, for example, molecule or particle size, their polarity and the type of preparation. Preferred penetration depth and storage time must also be considered. Particles with release mechanisms should be preferred; however, the release of drugs from nanoparticles still requires further investigations.
We discuss the prescription for the Dirac matrix γ5 in dimensional regularization used in most second- and third-order QCD calculations of collider cross sections. We provide an alternative ...implementation of this approach that avoids the use of an explicit form of γ5 and of its (anti-)commutation relations in the most important case of no more than one γ5 in each fermion trace. This treatment is checked by computing the third-order corrections to the structure functions F2 and g1 in charged-current deep-inelastic scattering with axial-vector couplings to the W-bosons. We derive the so far unknown third-order helicity-difference splitting function ΔPns(2)s that contributes to the next-to-next-to-leading order (NNLO) evolution of the polarized valence quark distribution of the nucleon. This function is negligible at momentum fractions x≳0.3 but relevant at x≪1.
We present the first calculations of next-to-next-to-next-to-next-to-leading order (N4LO) contributions to anomalous dimensions of spin-N twist-2 operators in perturbative QCD. Specifically, we have ...obtained the respective non-singlet quark–quark anomalous dimensions at N=2 and N=3 to the fifth order in the strong coupling αs. These results set the scale for the N4LO contributions to the evolution of the non-singlet quark distributions of hadrons outside the small-x region, and facilitate a first approximate determination of the five-loop cusp anomalous dimension. While the N4LO coefficients are larger than expected from the lower-order results, their inclusion stabilizes the perturbative expansions for three or more light flavours at a sub-percent accuracy for αs<0.3.
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