Universality of Long-Range Correlations in Expansion-Randomization Systems

We study the stochastic dynamics of sequences evolving by single site mutations, segmental duplications, deletions, and random insertions. These processes are relevant for the evolution of genomic DNA. They define a universality class of non-equilibrium 1D expansion-randomization systems with generic stationary long-range correlations in a regime of growing sequence length. We obtain explicitly the two-point correlation function of the sequence composition and the distribution function of the composition bias in sequences of finite length. The characteristic exponent $\chi$ of these quantities is determined by the ratio of two effective rates, which are explicitly calculated for several specific sequence evolution dynamics of the universality class. Depending on the value of $\chi$, we find two different scaling regimes, which are distinguished by the detectability of the initial composition bias. All analytic results are accurately verified by numerical simulations. We also discuss the non-stationary build-up and decay of correlations, as well as more complex evolutionary scenarios, where the rates of the processes vary in time. Our findings provide a possible example for the emergence of universality in molecular biology.Comment: 23 pages, 15 figure

Model dependence of single-energy fits to pion photoproduction data

Model dependence of multipole analysis has been explored through energy-dependent and single-energy fits to pion photoproduction data. The MAID energy-dependent solution has been used as input for an event generator producing realistic pseudo data. These were fitted using the SAID parametrization approach to determine single-energy and energy-dependent solutions over a range of lab photon energies from 200 to 1200 MeV. The resulting solutions were found to be consistent with the input amplitudes from MAID. Fits with a $\chi$-squared per datum of unity or less were generally achieved. We discuss energy regions where consistent results are expected, and explore the sensitivity of fits to the number of included single- and double-polarization observables. The influence of Watson's theorem is examined in detail.Comment: 12 pages, 8 figure

A Solvable Sequence Evolution Model and Genomic Correlations

We study a minimal model for genome evolution whose elementary processes are single site mutation, duplication and deletion of sequence regions and insertion of random segments. These processes are found to generate long-range correlations in the composition of letters as long as the sequence length is growing, i.e., the combined rates of duplications and insertions are higher than the deletion rate. For constant sequence length, on the other hand, all initial correlations decay exponentially. These results are obtained analytically and by simulations. They are compared with the long-range correlations observed in genomic DNA, and the implications for genome evolution are discussed.Comment: 4 pages, 4 figure

Satellite power system: Concept development and evaluation program. Volume 3: Power transmission and reception. Technical summary and assessment

Efforts in the DOE/NASA concept development and evaluation program are discussed for the solar power satellite power transmission and reception system. A technical summary is provided together with a summary of system assessment activities. System options and system definition drivers are described. Major system assessment activities were in support of the reference system definition, solid state system studies, critical technology supporting investigations, and various system and subsystem tradeoffs. These activities are described together with reference system updates and alternative concepts for each of the subsystem areas. Conclusions reached as a result of the numerous analytical and experimental evaluations are presented. Remaining issues for a possible follow-on program are identified

Two-Nucleon Scattering without partial waves using a momentum space Argonne V18 interaction

We test the operator form of the Fourier transform of the Argonne V18 potential by computing selected scattering observables and all Wolfenstein parameters for a variety of energies. These are compared to the GW-DAC database and to partial wave calculations. We represent the interaction and transition operators as expansions in a spin-momentum basis. In this representation the Lippmann-Schwinger equation becomes a six channel integral equation in two variables. Our calculations use different numbers of spin-momentum basis elements to represent the on- and off-shell transition operators. This is because different numbers of independent spin-momentum basis elements are required to expand the on- and off-shell transition operators. The choice of on and off-shell spin-momentum basis elements is made so that the coefficients of the on-shell spin-momentum basis vectors are simply related to the corresponding off-shell coefficients.Comment: 14 pages, 8 Figures, typos correcte

Probing Delta structure with pion electromagnetic production

The Dubna-Mainz-Taipei dynamical model for pion electromagnetic production, which can describe well the existing data from threshold up to 1 GeV photon lab energy, is presented and used to analyze the recent precision data in the $\Delta$ region. We find that, within our model, the bare Delta is almost spherical while the physical Delta is oblate. The deformation is almost saturated by the pion cloud effects. We further find that up to Q^2 = 4.0 (GeV/c)^2, the extracted helicity amplitude A_{3/2} and A_{1/2} remain comparable with each other, implying that hadronic helicity is not conserved at this range of Q^2. The ratio E_{1+}/M_{1+} obtained show, starting from a small and negative value at the real photon point, a clear tendency to cross zero, and to become positive with increasing Q^2. This is a possible indication of a very slow approach toward the pQCD region. Finally, we find that the bare helicity amplitude A_{1/2} and S_{1/2}, but not A_{3/2}, starts exhibiting the scaling behavior at about Q^2 \ge 2.5 (GeV/c)^2.Comment: Invited talk presented at the 2nd Asia-Pacific Conference on Few-Body Problems in Physics, Shanghai, P.R. China, 2002 (10 pages LATEX including 1 table and 5 figures

Helicity-dependent photoabsorption cross sections on the nucleon

We examine the energy dependence of single-meson photoproduction as it contributes to the Gerasimov-Drell-Hearn (GDH) sum rule. For photon energies above approximately 1 GeV, through the full resonance region, this contribution dominates the proton sum rule integral. Over the same energy region, our single-pion contribution to the neutron sum rule also qualitatively follows a recent set of GDH data. The predicted neutral-pion contribution to the neutron sum rule is nearly zero above 1 GeV in this result. The SAID and Mainz (MAID) results are very different for a number of observables over this energy region.Comment: 7 pages, 5 figur

Electroexcitation of the Roper resonance from CLAS data

The helicity amplitudes of the electroexcitation of the Roper resonance on proton are extracted at 1.7 < Q2 < 4.2 GeV2 from recent high precision JLab-CLAS cross sections data and longitudinally polarized beam asymmetry for pi+ electroproduction on protons. The analysis is made using two approaches, dispersion relations and unitary isobar model, which give consistent results. It is found that the transverse helicity amplitude for the gamma* p --> P11(1440) transition, which is large and negative at Q2=0, becomes large and positive at Q2 ~ 2 GeV2, and then drops slowly with Q2. Longitudinal helicity amplitude, that was previously found from CLAS data as large and positive at Q2=0.4,0.65 GeV2, drops with Q2. These results rule out the presentation of P11(1440) as a 3qG hybrid state, and provide strong evidence in favor of this resonance as a first radial excitation of the 3q ground state.Comment: 3 pages, 2 figures, Talk on the Workshop on "The Physics of Excited Nucleons", Bonn, Germany, October 200