Browsing by Subject "physics, multidisciplinary"

Now showing 1 - 8 of 8

Open Access
Active-Space N-Representability Constraints for Variational Two-Particle Reduced Density Matrix Calculations
(2010) Shenvi, Neil; Izmaylov, Artur F
The ground-state energy of a system of fermions can be calculated by minimizing a linear functional of the two-particle reduced density matrix (2-RDM) if an accurate set of N-representability conditions is applied. In this Letter we introduce a class of linear N-representability conditions based on exact calculations on a reduced active space. Unlike wave-function-based approaches, the 2-RDM methodology allows us to combine information from calculations on different active spaces. By adding active-space constraints, we can iteratively improve our estimate for the ground-state energy. Applying our methodology to a 1D Hubbard model yields a significant improvement over traditional 2-positivity constraints with the same computational scaling.
Open Access
Beyond the Death of Linear Response: 1/f Optimal Information Transport
(2010) Aquino, Gerardo; Bologna, Mauro; Grigolini, Paolo; West, Bruce J
Nonergodic renewal processes have recently been shown by several authors to be insensitive to periodic perturbations, thereby apparently sanctioning the death of linear response, a building block of nonequilibrium statistical physics. We show that it is possible to go beyond the "death of linear response'' and establish a permanent correlation between an external stimulus and the response of a complex network generating nonergodic renewal processes, by taking as stimulus a similar nonergodic process. The ideal condition of 1/f noise corresponds to a singularity that is expected to be relevant in several experimental conditions.
Open Access
Comment on "Testing Hypotheses about Sun-Climate Complexity Linking"
(2010) Scafetta, Nicola; West, Bruce J
Open Access
Determination of the Axial-Vector Weak Coupling Constant with Ultracold Neutrons
(2010) Liu, J; Mendenhall, MP; Holley, AT; Back, HO; Bowles, TJ; Broussard, LJ; Carr, R; Clayton, S; Currie, S; Filippone, BW; García, A; Geltenbort, P; Hickerson, KP; Hoagland, J; Hogan, GE; Hona, B; Ito, TM; Liu, C-Y; Makela, M; Mammei, RR; Martin, JW; Melconian, D; Morris, CL; Pattie, RW; Pérez Galván, A; Pitt, ML; Plaster, B; Ramsey, JC; Rios, R; Russell, R; Saunders, A; Seestrom, SJ; Sondheim, WE; Tatar, E; Vogelaar, RB; VornDick, B; Wrede, C; Yan, H; Young, AR; UCNA Collaboration
A precise measurement of the neutron decay beta asymmetry A(0) has been carried out using polarized ultracold neutrons from the pulsed spallation ultracold neutron source at the Los Alamos Neutron Science Center. Combining data obtained in 2008 and 2009, we report A(0) = -0.119 66 +/- 0.000 89(-0.001 40)(+0.001 23), from which we determine the ratio of the axial- vector to vector weak coupling of the nucleon gA/gV = -1.275 90(-0.004 45)(+0.004 09).
Open Access
Detrended fluctuation analysis of scaling crossover effects
(2010) Ignaccolo, M; Latka, M; West, BJ
Detrended fluctuation analysis (DFA) is one of the most frequently used fractal time series algorithms. DFA has also become the tool of choice for analysis of the short-time fluctuations despite the fact that its validity in this domain has never been demonstrated. We adopt an Ornstein-Uhlenbeck Langevin equation to generate a time series which exhibits short-time power-law scaling and incorporates the fundamental property of physiological control systems-negative feedback. To determine the scaling exponent, we derive the analytical expressions for the standard deviation of the solution X(t) of this equation using both the ensemble of statistically independent trajectories and the ensemble obtained by partitioning a single trajectory. The latter approach is used in DFA and many other physiological applications. Surprisingly, the formulas for the standard deviations are different for these two ensembles. We demonstrate that the partitioning amounts to building up deterministic trends that satisfy the "trend + signal" decomposition assumption which is characteristic of DFA. Consequently, the dependence of the rms of DFA residuals F(tau) on the length tau of data window is the same for both ensembles. The growth of F(tau) is significantly different from that of the standard deviation of X(t). While the DFA estimate of the short-time scaling exponent is correct, the polynomial detrending delays the approach of F(tau) to the asymptotic value by as much as an order of magnitude. This delay may underlie the gradual change of the DFA scaling index typically observed in time series that exhibit crossover between the short- and long-time scaling. Copyright (C) EPLA, 2010
Open Access
Polarization Transfer in the He-4((e)over-right-arrow, e '(p)over-right-arrow)H-3 Reaction at Q(2)=0.8 and 1.3 (GeV/c)(2)
(2010) Paolone, M; Malace, SP; Strauch, S; Albayrak, I; Arrington, J; Berman, BL; Brash, EJ; Briscoe, B; Camsonne, A; Chen, J-P; Christy, ME; Chudakov, E; Cisbani, E; Craver, B; Cusanno, F; Ent, R; Garibaldi, F; Gilman, R; Glamazdin, O; Glister, J; Higinbotham, DW; Hyde-Wright, CE; Ilieva, Y; de Jager, CW; Jiang, X; Jones, MK; Keppel, CE; Khrosinkova, E; Kuchina, E; Kumbartzki, G; Lee, B; Lindgren, R; Margaziotis, DJ; Meekins, D; Michaels, R; Park, K; Pentchev, L; Perdrisat, CF; Piasetzky, E; Punjabi, VA; Puckett, AJR; Qian, X; Qiang, Y; Ransome, RD; Saha, A; Sarty, AJ; Schulte, E; Solvignon, P; Subedi, RR; Tang, L; Tedeschi, D; Tvaskis, V; Udias, JM; Ulmer, PE; Vignote, JR; Wesselmann, FR; Wojtsekhowski, B; Zhan, X; E03-104 Collaboration
Proton recoil polarization was measured in the quasielastic He-4((e) over right arrow, e '(p) over right arrow)H-3 reaction at Q(2) = 0.8 and 1.3 (GeV/c)(2) with unprecedented precision. The polarization-transfer coefficients are found to differ from those of the H-1((e) over right arrow, e '(p) over right arrow) reaction, contradicting a relativistic distorted-wave approximation and favoring either the inclusion of medium-modified proton form factors predicted by the quark-meson coupling model or a spin-dependent charge-exchange final-state interaction. For the first time, the polarization-transfer ratio is studied as a function of the virtuality of the proton.
Open Access
Scaling of the F-2 Structure Function in Nuclei and Quark Distributions at x > 1
(2010) Fomin, N; Arrington, J; Day, DB; Gaskell, D; Daniel, A; Seely, J; Asaturyan, R; Benmokhtar, F; Boeglin, W; Boillat, B; Bosted, P; Bruell, A; Bukhari, MHS; Christy, ME; Chudakov, E; Clasie, B; Connell, SH; Dalton, MM; Dutta, D; Ent, R; El Fassi, L; Fenker, H; Filippone, BW; Garrow, K; Hill, C; Holt, RJ; Horn, T; Jones, MK; Jourdan, J; Kalantarians, N; Keppel, CE; Kiselev, D; Kotulla, M; Lindgren, R; Lung, AF; Malace, S; Markowitz, P; McKee, P; Meekins, DG; Miyoshi, T; Mkrtchyan, H; Navasardyan, T; Niculescu, G; Okayasu, Y; Opper, AK; Perdrisat, C; Potterveld, DH; Punjabi, V; Qian, X; Reimer, PE; Roche, J; Rodriguez, VM; Rondon, O; Schulte, E; Segbefia, E; Slifer, K; Smith, GR; Solvignon, P; Tadevosyan, V; Tajima, S; Tang, L; Testa, G; Trojer, R; Tvaskis, V; Vulcan, WF; Wasko, C; Wesselmann, FR; Wood, SA; Wright, J; Zheng, X
We present new data on electron scattering from a range of nuclei taken in Hall C at Jefferson Lab. For heavy nuclei, we observe a rapid falloff in the cross section for x > 1, which is sensitive to short-range contributions to the nuclear wave function, and in deep inelastic scattering corresponds to probing extremely high momentum quarks. This result agrees with higher energy muon scattering measurements, but is in sharp contrast to neutrino scattering measurements which suggested a dramatic enhancement in the distribution of the "superfast" quarks probed at x > 1. The falloff at x > 1 is noticeably stronger in H-2 and He-3, but nearly identical for all heavier nuclei.
Open Access
William Delany Walker obituary
(2010) Goshaw, Alfred T; Erwin, Albert