7,800 research outputs found
Strain induced stabilization of stepped Si and Ge surfaces near (001)
We report on calculations of the formation energies of several [100] and
[110] oriented step structures on biaxially stressed Si and Ge (001) surfaces.
It is shown that a novel rebonded [100] oriented single-height step is strongly
stabilized by compressive strain compared to most well-known step structures.
We propose that the side walls of ``hut''-shaped quantum dots observed in
recent experiments on SiGe/Si films are made up of these steps. Our
calculations provide an explanation for the nucleationless growth of shallow
mounds, with steps along the [100] and [110] directions in low- and high-misfit
films, respectively, and for the stability of the (105) facets under
compressive strain.Comment: to appear in Appl. Phys. Lett.; v2=minor corrections,figs resize
Dual parameterization of generalized parton distributions and description of DVCS data
We discuss a new leading-order parameterization of generalized parton
distributions of the proton, which is based on the idea of duality. In its
minimal version, the parameterization is defined by the usual quark singlet
parton distributions and the form factors of the energy-momentum tensor. We
demonstrate that our parameterization describes very well the absolute value,
the Q^2-dependence and the W-dependence of the HERA data on the total DVCS
cross section and contains no free parameters in that kinematics. The
parameterization suits especially well the low-x_{Bj} region, which allows us
to advocate it as a better alternative to the frequently used double
distribution parameterization of the GPDs.Comment: 13 pages, 2 figures, LaTeX. Revised version: equation for the DVCS
cross section corrected; one reference added; numerical results did not
chang
QCD evolution and skewedness effects in color dipole description of DVCS
We show the role played by QCD evolution and skewedness effects in the DVCS
cross section at large within the color dipole description of the process
at photon level. The dipole cross section is given by the saturation model,
which can be improved by DGLAP evolution at high photon virtualities. We
investigate both possibilities as well as the off-forward effect through a
simple phenomenological parametrisation. The results are compared to the recent
ZEUS DVCS data.Comment: LaTeX, 6 pages, 5 Figs. Vers 2: Minor modifications. Accepted by EPJ
Drip and Mate Operations Acting in Test Tube Systems and Tissue-like P systems
The operations drip and mate considered in (mem)brane computing resemble the
operations cut and recombination well known from DNA computing. We here
consider sets of vesicles with multisets of objects on their outside membrane
interacting by drip and mate in two different setups: in test tube systems, the
vesicles may pass from one tube to another one provided they fulfill specific
constraints; in tissue-like P systems, the vesicles are immediately passed to
specified cells after having undergone a drip or mate operation. In both
variants, computational completeness can be obtained, yet with different
constraints for the drip and mate operations
The DVCS Measurement at HERA
The recent results of the studies of Deeply Virtual Compton Scattering (DVCS)
events at HERA are presented. The possibility offered by this process to gain
information about skewed parton distributions (SPD) is emphasized.Comment: Talk given at New Trends in HERA Physics 2001, Ringberg Castle,
Tegernsee, Germany, 17-22 Jun 2001, 13 pages, 10 figures, recent ZEUS data
discussed, references update
Exclusive annihilation p pbar -> gamma gamma in a generalized parton picture
Exclusive proton-antiproton annihilation into two photons at large s (~10
GeV^2) and |t|,|u| ~ s can be described by a generalized parton picture
analogous to the 'soft mechanism' in wide-angle real Compton scattering. The
two photons are emitted in the annihilation of a single fast quark and
antiquark. The matrix element describing the transition of the p-pbar system to
a q-qbar pair can be related to the timelike proton elastic form factors as
well as to the quark/antiquark distributions measured in inclusive
deep-inelastic scattering. The reaction could be studied with the proposed
1.5-15 GeV high-luminosity antiproton storage ring (HESR) at GSI.Comment: 4 pages, revtex4, 3 eps figure
Matter Enhanced Neutrino Oscillations with a Realistic Earth Density Profile
We have investigated matter enhanced neutrino oscillations with a
mantle-core-mantle step function and a realistic Earth matter density profile
in both a two and a three neutrino scenario. We found that the realistic Earth
matter density profile can be well approximated with the mantle-core-mantle
step function and that there could be an influence on the oscillation channel
due to resonant enhancement of one of the mixing angles.Comment: 8 pages, 5 figures (PostScript), MPLA LaTe
Molecular basis for modulation of the p53 target selectivity by KLF4
The tumour suppressor p53 controls transcription of various genes involved in apoptosis, cell-cycle arrest, DNA repair and metabolism. However, its DNA-recognition specificity is not nearly sufficient to explain binding to specific locations in vivo. Here, we present evidence that KLF4 increases the DNA-binding affinity of p53 through the formation of a loosely arranged ternary complex on DNA. This effect depends on the distance between the response elements of KLF4 and p53. Using nuclear magnetic resonance and fluorescence techniques, we found that the amino-terminal domain of p53 interacts with the KLF4 zinc fingers and mapped the interaction site. The strength of this interaction was increased by phosphorylation of the p53 N-terminus, particularly on residues associated with regulation of cell-cycle arrest genes. Taken together, the cooperative binding of KLF4 and p53 to DNA exemplifies a regulatory mechanism that contributes to p53 target selectivity
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