656 research outputs found
Intracellular distribution of DNA methyltransferase during the cell cycle
AbstractThe intracellular distribution of DNA methyltransferase has been analyzed in synchronously proliferating human cells. The localization of DNA methyltransferase was determined immunocytochemically using monoclonal antibodies directed against this enzyme. DNA methyltransferase was found to accumulate predominantly in nuclei with weak cytoplasmic staining. The DNA methyltransferase antigen was absent in early G1 phase, appeared in late G1 prior to the onset of DNA synthesis and persisted throughout S and G2 phases of the cell cycle. Mitotic cells showed a particularly strong staining intensity. These results show that DNA methyltransferase levels fluctuate during the cell cycle. This has possible implications on the stability of the DNA methylation pattern
ESTIMATION OF CENTER OF MASS VELOCITY BY RIGHT POSTERIOR SPINE ILIAC LANDMARK DURING COUNTERMOVEMENT JUMP
When the impulse phase is proceeded by approach movement (e.g. volleyball spike jump), the vertical velocity of CoM at the beginning of the impulse phase must be known. To reduce the number of landmarks, the aim of this study was to verify the concordance between the velocity of CoM and the Right Posterior Spine Iliac at touchdown after flight phase. Ten female volleyball players of the first national volleyball league of Austria performed ten maximal CMJ without arm movement. Paired t-test was used to compare velocities between the two methods. No significant differences between the methods with maximal individual differences lower than 0.1m/s at touchdown could be found. If only the landing velocity at touchdown must be known, it seems to be sufficient to determine the velocity of Right Posterior Spine Iliac landmark
Superconformal operators in Yang-Mills theories on the light-cone
We employ the light-cone superspace formalism to develop an efficient
approach to constructing superconformal operators of twist two in Yang-Mills
theories with N=1,2,4 supercharges. These operators have an autonomous scale
dependence to one-loop order and determine the eigenfunctions of the dilatation
operator in the underlying gauge theory. We demonstrate that for arbitrary N
the superconformal operators are given by remarkably simple, universal
expressions involving the light-cone superfields. When written in components
field, they coincide with the known results obtained by conventional
techniques.Comment: 29 pages, Late
On planar gluon amplitudes/Wilson loops duality
There is growing evidence that on-shell gluon scattering amplitudes in planar
N=4 SYM theory are equivalent to Wilson loops evaluated over contours
consisting of straight, light-like segments defined by the momenta of the
external gluons. This equivalence was first suggested at strong coupling using
the AdS/CFT correspondence and has since been verified at weak coupling to one
loop in perturbation theory. Here we perform an explicit two-loop calculation
of the Wilson loop dual to the four-gluon scattering amplitude and demonstrate
that the relation holds beyond one loop. We also propose an anomalous conformal
Ward identity which uniquely fixes the form of the finite part (up to an
additive constant) of the Wilson loop dual to four- and five-gluon amplitudes,
in complete agreement with the BDS conjecture for the multi-gluon MHV
amplitudes.Comment: 16 pages, 1 figure. v2: minor correction
Integrability of two-loop dilatation operator in gauge theories
We study the two-loop dilatation operator in the noncompact SL(2) sector of
QCD and supersymmetric Yang-Mills theories with N=1,2,4 supercharges. The
analysis is performed for Wilson operators built from three quark/gaugino
fields of the same helicity belonging to the fundamental/adjoint representation
of the SU(3)/SU(N_c) gauge group and involving an arbitrary number of covariant
derivatives projected onto the light-cone. To one-loop order, the dilatation
operator inherits the conformal symmetry of the classical theory and is given
in the multi-color limit by a local Hamiltonian of the Heisenberg magnet with
the spin operators being generators of the collinear subgroup of full
(super)conformal group. Starting from two loops, the dilatation operator
depends on the representation of the gauge group and, in addition, receives
corrections stemming from the violation of the conformal symmetry. We compute
its eigenspectrum and demonstrate that to two-loop order integrability survives
the conformal symmetry breaking in the aforementioned gauge theories, but it is
violated in QCD by the contribution of nonplanar diagrams. In SYM theories with
extended supersymmetry, the N-dependence of the two-loop dilatation operator
can be factorized (modulo an additive normalization constant) into a
multiplicative c-number. This property makes the eigenspectrum of the two-loop
dilatation operator alike in all gauge theories including the maximally
supersymmetric theory. Our analysis suggests that integrability is only tied to
the planar limit and it is sensitive neither to conformal symmetry nor
supersymmetry.Comment: 70 pages, 10 figure
Twist-three analysis of photon electroproduction with pion
We study twist-three effects in spin, charge, and azimuthal asymmetries in
deeply virtual Compton scattering on a spin-zero target. Contributions which
are power suppressed in 1/Q generate a new azimuthal angle dependence of the
cross section which is not present in the leading twist results. On the other
hand the leading twist terms are not modified by the twist three contributions.
They may get corrected at twist four level. In the Wandzura-Wilczek
approximation these new terms in the Fourier expansion with respect to the
azimuthal angle are entirely determined by the twist-two skewed parton
distributions. We also discuss more general issues like the general form of the
angular dependence of the differential cross section, validity of factorization
at twist-three level, and a relation of skewed parton distributions to spectral
functions.Comment: 21 pages, LaTeX, 2 figures, text clarifications, an equation, a note
and references adde
Baryon Distribution Amplitudes in QCD
We develop a new theoretical framework for the description of leading twist
light-cone baryon distribution amplitudes which is based on integrability of
the helicity evolution equation to leading logarithmic accuracy.
A physical interpretation is that one can identify a new `hidden' quantum
number which distinguishes components in the distribution
amplitudes with different scale dependence. The solution of the corresponding
evolution equation is reduced to a simple three-term recurrence relation. The
exact analytic solution is found for the component with the lowest anomalous
dimension for all moments , and the WKB-type expansion is constructed for
other levels, which becomes asymptotically exact at large . Evolution
equations for the distribution amplitudes (e.g. for the nucleon)
are studied as well. We find that the two lowest anomalous dimensions for the
operators (one for each parity) are separated from the rest of
the spectrum by a finite `mass gap'. These special states can be interpreted as
scalar diquarks.Comment: 75 pages, LaTeX style, 18 figures embedded with epsf.st
Extraction of the pion distribution amplitude from polarized muon pair production
We consider the production of muon pairs from the scattering of pions on
longitudinally polarized protons. We calculate the cross section and the single
spin asymmetry for this process, taking into account pion bound state effects.
We work in the kinematic region where the photon has a large longitudinal
momentum fraction, which allows us to treat the bound state problem
perturbatively. Our predictions are directly proportional to the pion
distribution amplitude. A measurement of the polarized Drell-Yan cross section
thus allows the determination of the shape of the pion distribution amplitude.Comment: 13 pages, using revtex, two figures added separately as one uuencoded
Z-compressed fil
Nonforward anomalous dimensions of Wilson operators in N=4 super-Yang-Mills theory
We present the next-to-leading order results for universal non-forward
anomalous dimensions of Wilson twist-2 operators in N=4 supersymmetric
Yang-Mills theory. The whole calculation was performed using supersymmetric
Ward identities derived in this paper together with already known QCD results
and does not involve any additional calculation of diagrams. We also considered
one particular limit of our result, which could potentially be interesting in
the context of AdS/CFT correspondence.Comment: 15 pages, references added, typos corrected, version accepted in JHE
Time-variability in the Interstellar Boundary Conditions of the Heliosphere: Effect of the Solar Journey on the Galactic Cosmic Ray Flux at Earth
During the solar journey through galactic space, variations in the physical
properties of the surrounding interstellar medium (ISM) modify the heliosphere
and modulate the flux of galactic cosmic rays (GCR) at the surface of the
Earth, with consequences for the terrestrial record of cosmogenic
radionuclides. One phenomenon that needs studying is the effect on cosmogenic
isotope production of changing anomalous cosmic ray fluxes at Earth due to
variable interstellar ionizations. The possible range of interstellar ram
pressures and ionization levels in the low density solar environment generate
dramatically different possible heliosphere configurations, with a wide range
of particle fluxes of interstellar neutrals, their secondary products, and GCRs
arriving at Earth. Simple models of the distribution and densities of ISM in
the downwind direction give cloud transition timescales that can be directly
compared with cosmogenic radionuclide geologic records. Both the interstellar
data and cosmogenic radionuclide data are consistent with cloud transitions
during the Holocene, with large and assumption-dependent uncertainties. The
geomagnetic timeline derived from cosmic ray fluxes at Earth may require
adjustment to account for the disappearance of anomalous cosmic rays when the
Sun is immersed in ionized gas.Comment: Submitted to Space Sciences Review
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