773 research outputs found
Identification of sites phosphorylated by the vaccinia virus B1R kinase in viral protein H5R
Background: Vaccinia virus gene B1R encodes a erine/threonine protein kinase. In vitro this protein kinase phosphorylates ribosomal proteins Sa and S2 and vaccinia virus protein H5R, proteins that become phosphorylated during infection. Nothing is known about the sites phosphorylated on these proteins or the general substrate specificity of the kinase. The work described is the first to address these questions.
Results: Vaccinia virus protein H5R was phosphorylated by the B1R protein kinase in vitro, digested with V8 protease, and phosphopeptides separated by HPLC. The N-terminal sequence of one radioactively labelled phosphopeptide was determined and found to correspond to residues 81-87 of the protein, with Thr-84 and Thr-85 being phosphorylated. A synthetic peptide based on this region of the protein was shown to be a substrate for the B1R protein kinase, and the extent of phosphorylation was substantially decreased if either Thr residue was replaced by an Ala.
Conclusions: We have identified the first phosphorylation site for the vaccinia virus B1R protein kinase. This gives important information about the substrate-specificity of the enzyme, which differs from that of other known protein kinases. It remains to be seen whether the same site is phosphorylated in vivo
Langevin Simulation of Thermally Activated Magnetization Reversal in Nanoscale Pillars
Numerical solutions of the Landau-Lifshitz-Gilbert micromagnetic model
incorporating thermal fluctuations and dipole-dipole interactions (calculated
by the Fast Multipole Method) are presented for systems composed of nanoscale
iron pillars of dimension 9 nm x 9 nm x 150 nm. Hysteresis loops generated
under sinusoidally varying fields are obtained, while the coercive field is
estimated to be 1979 14 Oe using linear field sweeps at T=0 K. Thermal
effects are essential to the relaxation of magnetization trapped in a
metastable orientation, such as happens after a rapid reversal of an external
magnetic field less than the coercive value. The distribution of switching
times is compared to a simple analytic theory that describes reversal with
nucleation at the ends of the nanomagnets. Results are also presented for
arrays of nanomagnets oriented perpendicular to a flat substrate. Even at a
separation of 300 nm, where the field from neighboring pillars is only 1
Oe, the interactions have a significant effect on the switching of the magnets.Comment: 19 pages RevTeX, including 12 figures, clarified discussion of
numerical technique
Pion form factor analysis using NLO analytic perturbation theory
I present results for the pion's electromagnetic form factor in the spacelike
region, which implement the most advanced perturbative information currently
available for this observable in conjunction with a pion distribution amplitude
that agrees with the CLEO data on the pion-photon transition form factor at the
level. I show that using for the running strong coupling and its
powers their analytic versions in the sense of Shirkov and Solovtsov, the
obtained predictions become insensitive to the renormalization scheme and scale
setting adopted. Joining the hard contribution with the soft part on account of
local duality and respecting the Ward identity at , the agreement with
the available experimental data, including expectations from planned
experiments at JLab, is remarkable both in trend and magnitude. I also comment
on Sudakov resummation within the analytic approach.Comment: 5 pages, 3 figures embedded; uses espcrc2.tex. Invited talk presented
at QCD04, 5-9 July 2004, Montpellier, Franc
Can extra dimensions accessible to the SM explain the recent measurement of anomalous magnetic moment of the muon?
We investigate whether models with flat extra dimensions in which SM fields
propagate can give a significant contribution to the anomalous magnetic moment
of the muon (MMM). In models with only SM gauge and Higgs fields in the bulk,
the contribution to the MMM from Kaluza-Klein (KK) excitations of gauge bosons
is very small. This is due to the constraint on the size of the extra
dimensions from tree-level effects of KK excitations of gauge bosons on
precision electroweak observables such as Fermi constant. If the quarks and
leptons are also allowed to propagate in the (same) bulk (``universal'' extra
dimensions), then there are no contributions to precision electroweak
observables at tree-level. However, in this case, the constraint from one-loop
contribution of KK excitations of (mainly) the top quark to T parameter again
implies that the contribution to the MMM is small. We show that in models with
leptons, electroweak gauge and Higgs fields propagating in the (same) bulk, but
with quarks and gluon propagating in a sub-space of this bulk, both the above
constraints can be relaxed. However, with only one Higgs doublet, the
constraint from the process b -> s gamma requires the contribution to the MMM
to be smaller than the SM electroweak correction. This constraint can be
relaxed in models with more than one Higgs doublet.Comment: Latex, 11 pages, 1 ps fig. included. In the revised version, a
reference has been added. Version to be published in Phys. Lett.
The 3s Proton Occupancy in 206-Pb
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Test of the DWBA Description of Transfer Reactions at Intermediate Energies by Measuring a Complete Set of Single Nucleon Transfer and Elastic Scattering Data
This research was sponsored by the National Science Foundation Grant NSF PHy 87-1440
Test of the DWBA Description of Transfer Reactions at Intermediate Energies by Measuring a Complete Set of Single Nucleon and Elastic Scattering Data
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
New vistas of the meson structure in QCD from low to high energies
This talk presents issues pertaining to the quark structure of the pion
within QCD, both from the theoretical and from the experimental point of view.
We review and discuss the pion-photon transition form factor and the pion's
electromagnetic form factor vs. corresponding experimental data from the CLEO
Collaboration and the JLab. We also examine the extent to which recent
high-precision lattice computations of the second moment of the pion's
distribution amplitude conform with theoretical models. Finally, we include
predictions for the azimuthal asymmetry of the distribution in the
polarized -pair-induced DY production employing various pion distribution
amplitudes.Comment: 6 pages, 7 figures, 2 tables. Talk presented at International
Workshop on e^+e^- collisions from Phi to Psi, Frascati, Italy, 7-10 April
2008. V2 is an exclusive HEP version which includes predictions from AdS/QCD.
V3: typo in title correcte
A jump-growth model for predator-prey dynamics: derivation and application to marine ecosystems
This paper investigates the dynamics of biomass in a marine ecosystem. A
stochastic process is defined in which organisms undergo jumps in body size as
they catch and eat smaller organisms. Using a systematic expansion of the
master equation, we derive a deterministic equation for the macroscopic
dynamics, which we call the deterministic jump-growth equation, and a linear
Fokker-Planck equation for the stochastic fluctuations. The McKendrick--von
Foerster equation, used in previous studies, is shown to be a first-order
approximation, appropriate in equilibrium systems where predators are much
larger than their prey. The model has a power-law steady state consistent with
the approximate constancy of mass density in logarithmic intervals of body mass
often observed in marine ecosystems. The behaviours of the stochastic process,
the deterministic jump-growth equation and the McKendrick--von Foerster
equation are compared using numerical methods. The numerical analysis shows two
classes of attractors: steady states and travelling waves.Comment: 27 pages, 4 figures. Final version as published. Only minor change
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