We extend our previous model, avalanche-burst invasion percolation (AIP) by introducing longrange... more We extend our previous model, avalanche-burst invasion percolation (AIP) by introducing longrange correlations between sites described by fractional Brownian statistics. In our previous models with independent, random site strengths, we reproduced a unique set of power-laws consistent with some of the b-values observed during induced seismicity. We expand upon this model to produce a family of critical exponents which could be characterized by the local long-range correlations inherent to host sediment. Further, in previous correlated invasion percolation studies, fractal behavior was found in only a subset of the range of Hurst exponent, H. We find fractal behavior persists for the entire range of Hurst exponent. Additionally, we show how multiple cluster scaling power laws results from changing the generalized Hurst parameter controlling long-range site correlations, and gives rise to a multifractal system. This emergent multifractal behavior plays a central role in allowing us to extend our model to better account for variations in the observed Gutenber-Richter b-values of induced seismicity.
Given the large variety and number of systems displaying scale invariant characteristics, it is b... more Given the large variety and number of systems displaying scale invariant characteristics, it is becoming increasingly important to understand their fundamental and universal elements. Much work has attempted to apply second order phase transition mechanics due to the emergent scale invariance at the critical point. However for many systems, notions of phases and critical points are both artificial and cumbersome. We characterize the critical features of the avalanche-burst invasion percolation(AIP) model since it exists as a hybrid critical system (of which many selforganized critical systems may fall under). We find behavior strongly representative of critical systems, namely, the presence of a critical Fisher type distribution, ns(τ, σ), but other essential features absent such as an order parameter and to a lesser degree hyperscaling. This suggests that we do not need a full phase transition description in order to observe scale invariant behavior, and provides a pathway for more suitable descriptions.
Proceedings of XIII Nuclei in the Cosmos — PoS(NIC XIII), 2015
Observation across the Milky Way of a 1809-keV γ-ray characteristic of 26 Al decay provides direc... more Observation across the Milky Way of a 1809-keV γ-ray characteristic of 26 Al decay provides direct evidence for ongoing nucleosynthetic production of 26 Al. Although massive stars and supernovae are likely to be the primary sites for 26 Al production, classical novae may also contribute a significant portion of the total amount of Galactic 26 Al. At peak nova temperatures of approximately 0.4 GK, the rate of the 25 Al(p,γ) 26 Si reaction, which bypasses 26 Al production and therefore places an upper limit on the amount of 26 Al contributed by novae to Galactic abundances, is likely dominated by a single 3 + resonance. Constraining the energy and strength of this resonance is therefore critical to determining the 25 Al(p,γ) 26 Si reaction rate. We have used a radioactive 26 P beam produced at the National Superconducting Cyclotron Laboratory to populate the 3 + state via beta decay, and have observed first evidence for its γ decay branch, the last piece of information needed to calculate the resonance strength. We find the 3 + state to have a resonance energy of E r = 414.9 ± 0.6 (stat) ± 0.3 (syst) ± 0.6 (lit.) keV and a resonance strength of ωγ = 23 ± 6 (stat) +11-10 (lit.) meV. We have also used hydrodynamic nova simulations to model 26 Al production and we find that novae may contribute up to 0.6 solar masses of the Galactic 26 Al-38% of the total Galactic 26 Al abundance.
Classical novae are expected to contribute to the 1809-keV Galactic γ-ray emission by producing i... more Classical novae are expected to contribute to the 1809-keV Galactic γ-ray emission by producing its precursor 26 Al, but the yield depends on the thermonuclear rate of the unmeasured 25 Al(p, γ) 26 Si reaction. Using the β decay of 26 P to populate the key J π = 3 + resonance in this reaction, we report the first evidence for the observation of its exit channel via a 1741.6 ± 0.6(stat) ± 0.3(syst) keV primary γ ray, where the uncertainties are statistical and systematic, respectively. By combining the measured γ-ray energy and intensity with other experimental data on 26 Si, we find the centerof-mass energy and strength of the resonance to be Er = 414.9 ± 0.6(stat) ± 0.3(syst) ± 0.6(lit.) keV and ωγ = 23 ± 6(stat) +11 −10 (lit.) meV, respectively, where the last uncertainties are from adopted literature data. We use hydrodynamic nova simulations to model 26 Al production showing that these measurements effectively eliminate the dominant experimental nuclear-physics uncertainty and we estimate that novae may contribute up to 30 % of the Galactic 26 Al.
Classical novae are common thermonuclear explosions in the Milky Way galaxy, occurring on the sur... more Classical novae are common thermonuclear explosions in the Milky Way galaxy, occurring on the surfaces of white-dwarf stars that are accreting hydrogen-rich material from companion stars. Nucleosynthesis in classical novae depends on radiative protoncapture reaction rates on radioactive nuclides. Many of these reactions cannot be measured directly at current accelerator
Proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC2016), 2017
Sulfur isotopic ratios have the potential to distinguish presolar grains of classical novae and t... more Sulfur isotopic ratios have the potential to distinguish presolar grains of classical novae and type II supernovae origin. The current lack of experimentally determined 34g,m Cl(p, γ) 35 Ar reaction rates leads to large uncertainties in the production of 34 S in oxygen-neon classical nova models. As a first step toward determining these reaction rates, we have measured 35 Ar resonances up to 800 keV above the 35 Ar proton emission threshold. These resonances were populated using the 36 Ar(d, t) 35 Ar reaction, and the tritons were momentum analyzed by a high resolution quadrupole-dipole-dipole-dipole (Q3D) magnetic spectrograph. Seventeen new 35 Ar levels have been discovered, and uncertainties associated with the energies of the five previously known levels have been substantially reduced. Experimental level densities were then compared to calculated level densities, using the WBMB Hamiltonian within the sd − p f model space. This comparison indicates that most of the expected resonances in this region have been observed.
Invasion percolation is a model that was originally proposed to describe growing networks of frac... more Invasion percolation is a model that was originally proposed to describe growing networks of fractures. Here we describe a loopless algorithm on random lattices, coupled with an avalanche-based model for bursts. The model reproduces the characteristic b-value seismicity and spatial distribution of bursts consistent with earthquakes resulting from hydraulic fracturing ("fracking"). We test models for both site invasion percolation and bond invasion percolation. These have differences on the scale of site and bond lengths l. But since the networks are characterized by their large-scale behavior, l≪L, we find small differences between scaling exponents. Though data may not differentiate between models, our results suggest that both models belong to different universality classes.
We analyze a new model for growing networks, the constrained Leath invasion percolation (CLIP) mo... more We analyze a new model for growing networks, the constrained Leath invasion percolation (CLIP) model. Cluster dynamics are characterized by bursts in space and time. The model quantitatively reproduces the observed frequency-magnitude scaling of earthquakes in the limit that the occupation probability approaches the critical bond percolation probability in d=2. The model may have application to other systems characterized by burst dynamics.
Background: The thermonuclear 34g,m Cl(p, γ) 35 Ar reaction rates are unknown due to a lack of ex... more Background: The thermonuclear 34g,m Cl(p, γ) 35 Ar reaction rates are unknown due to a lack of experimental nuclear physics data. Uncertainties in these rates translate to uncertainties in 34 S production in models of classical novae on oxygen-neon white dwarfs. 34 S abundances have the potential to aid in the classification of presolar grains. Purpose: Determine resonance energies for the 34g,m Cl(p, γ) 35 Ar reactions within the region of astrophysical interest for classical novae to a precision of a few keV as an essential first step toward constraining their thermonuclear reaction rates. Method: 35 Ar excited states were populated by the 36 Ar(d, t) 35 Ar reaction at E(d)=22 MeV and reaction products were momentum analyzed by a high resolution quadrupole-dipole-dipole-dipole (Q3D) magnetic spectrograph. Results: Seventeen new 35 Ar levels have been detected at a statistically significant level in the region Ex ≈ 5.9-6.7 MeV (Er < 800 keV) and their excitation energies have been determined to typical uncertainties of 3 keV. The uncertainties for five previously known levels have also been reduced substantially. The measured level density was compared to those calculated using the WBMB Hamiltonian within the sd − pf model space. Conclusions: Most of the resonances in the region of astrophysical interest have likely been discovered and their energies have been determined, but the resonance strengths are still unknown, and experimentally constraining the 34g,m Cl(p, γ) 35 Ar reaction rates will require further experiments.
We extend our previous model, avalanche-burst invasion percolation (AIP) by introducing longrange... more We extend our previous model, avalanche-burst invasion percolation (AIP) by introducing longrange correlations between sites described by fractional Brownian statistics. In our previous models with independent, random site strengths, we reproduced a unique set of power-laws consistent with some of the b-values observed during induced seismicity. We expand upon this model to produce a family of critical exponents which could be characterized by the local long-range correlations inherent to host sediment. Further, in previous correlated invasion percolation studies, fractal behavior was found in only a subset of the range of Hurst exponent, H. We find fractal behavior persists for the entire range of Hurst exponent. Additionally, we show how multiple cluster scaling power laws results from changing the generalized Hurst parameter controlling long-range site correlations, and gives rise to a multifractal system. This emergent multifractal behavior plays a central role in allowing us to extend our model to better account for variations in the observed Gutenber-Richter b-values of induced seismicity.
Given the large variety and number of systems displaying scale invariant characteristics, it is b... more Given the large variety and number of systems displaying scale invariant characteristics, it is becoming increasingly important to understand their fundamental and universal elements. Much work has attempted to apply second order phase transition mechanics due to the emergent scale invariance at the critical point. However for many systems, notions of phases and critical points are both artificial and cumbersome. We characterize the critical features of the avalanche-burst invasion percolation(AIP) model since it exists as a hybrid critical system (of which many selforganized critical systems may fall under). We find behavior strongly representative of critical systems, namely, the presence of a critical Fisher type distribution, ns(τ, σ), but other essential features absent such as an order parameter and to a lesser degree hyperscaling. This suggests that we do not need a full phase transition description in order to observe scale invariant behavior, and provides a pathway for more suitable descriptions.
Proceedings of XIII Nuclei in the Cosmos — PoS(NIC XIII), 2015
Observation across the Milky Way of a 1809-keV γ-ray characteristic of 26 Al decay provides direc... more Observation across the Milky Way of a 1809-keV γ-ray characteristic of 26 Al decay provides direct evidence for ongoing nucleosynthetic production of 26 Al. Although massive stars and supernovae are likely to be the primary sites for 26 Al production, classical novae may also contribute a significant portion of the total amount of Galactic 26 Al. At peak nova temperatures of approximately 0.4 GK, the rate of the 25 Al(p,γ) 26 Si reaction, which bypasses 26 Al production and therefore places an upper limit on the amount of 26 Al contributed by novae to Galactic abundances, is likely dominated by a single 3 + resonance. Constraining the energy and strength of this resonance is therefore critical to determining the 25 Al(p,γ) 26 Si reaction rate. We have used a radioactive 26 P beam produced at the National Superconducting Cyclotron Laboratory to populate the 3 + state via beta decay, and have observed first evidence for its γ decay branch, the last piece of information needed to calculate the resonance strength. We find the 3 + state to have a resonance energy of E r = 414.9 ± 0.6 (stat) ± 0.3 (syst) ± 0.6 (lit.) keV and a resonance strength of ωγ = 23 ± 6 (stat) +11-10 (lit.) meV. We have also used hydrodynamic nova simulations to model 26 Al production and we find that novae may contribute up to 0.6 solar masses of the Galactic 26 Al-38% of the total Galactic 26 Al abundance.
Classical novae are expected to contribute to the 1809-keV Galactic γ-ray emission by producing i... more Classical novae are expected to contribute to the 1809-keV Galactic γ-ray emission by producing its precursor 26 Al, but the yield depends on the thermonuclear rate of the unmeasured 25 Al(p, γ) 26 Si reaction. Using the β decay of 26 P to populate the key J π = 3 + resonance in this reaction, we report the first evidence for the observation of its exit channel via a 1741.6 ± 0.6(stat) ± 0.3(syst) keV primary γ ray, where the uncertainties are statistical and systematic, respectively. By combining the measured γ-ray energy and intensity with other experimental data on 26 Si, we find the centerof-mass energy and strength of the resonance to be Er = 414.9 ± 0.6(stat) ± 0.3(syst) ± 0.6(lit.) keV and ωγ = 23 ± 6(stat) +11 −10 (lit.) meV, respectively, where the last uncertainties are from adopted literature data. We use hydrodynamic nova simulations to model 26 Al production showing that these measurements effectively eliminate the dominant experimental nuclear-physics uncertainty and we estimate that novae may contribute up to 30 % of the Galactic 26 Al.
Classical novae are common thermonuclear explosions in the Milky Way galaxy, occurring on the sur... more Classical novae are common thermonuclear explosions in the Milky Way galaxy, occurring on the surfaces of white-dwarf stars that are accreting hydrogen-rich material from companion stars. Nucleosynthesis in classical novae depends on radiative protoncapture reaction rates on radioactive nuclides. Many of these reactions cannot be measured directly at current accelerator
Proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC2016), 2017
Sulfur isotopic ratios have the potential to distinguish presolar grains of classical novae and t... more Sulfur isotopic ratios have the potential to distinguish presolar grains of classical novae and type II supernovae origin. The current lack of experimentally determined 34g,m Cl(p, γ) 35 Ar reaction rates leads to large uncertainties in the production of 34 S in oxygen-neon classical nova models. As a first step toward determining these reaction rates, we have measured 35 Ar resonances up to 800 keV above the 35 Ar proton emission threshold. These resonances were populated using the 36 Ar(d, t) 35 Ar reaction, and the tritons were momentum analyzed by a high resolution quadrupole-dipole-dipole-dipole (Q3D) magnetic spectrograph. Seventeen new 35 Ar levels have been discovered, and uncertainties associated with the energies of the five previously known levels have been substantially reduced. Experimental level densities were then compared to calculated level densities, using the WBMB Hamiltonian within the sd − p f model space. This comparison indicates that most of the expected resonances in this region have been observed.
Invasion percolation is a model that was originally proposed to describe growing networks of frac... more Invasion percolation is a model that was originally proposed to describe growing networks of fractures. Here we describe a loopless algorithm on random lattices, coupled with an avalanche-based model for bursts. The model reproduces the characteristic b-value seismicity and spatial distribution of bursts consistent with earthquakes resulting from hydraulic fracturing ("fracking"). We test models for both site invasion percolation and bond invasion percolation. These have differences on the scale of site and bond lengths l. But since the networks are characterized by their large-scale behavior, l≪L, we find small differences between scaling exponents. Though data may not differentiate between models, our results suggest that both models belong to different universality classes.
We analyze a new model for growing networks, the constrained Leath invasion percolation (CLIP) mo... more We analyze a new model for growing networks, the constrained Leath invasion percolation (CLIP) model. Cluster dynamics are characterized by bursts in space and time. The model quantitatively reproduces the observed frequency-magnitude scaling of earthquakes in the limit that the occupation probability approaches the critical bond percolation probability in d=2. The model may have application to other systems characterized by burst dynamics.
Background: The thermonuclear 34g,m Cl(p, γ) 35 Ar reaction rates are unknown due to a lack of ex... more Background: The thermonuclear 34g,m Cl(p, γ) 35 Ar reaction rates are unknown due to a lack of experimental nuclear physics data. Uncertainties in these rates translate to uncertainties in 34 S production in models of classical novae on oxygen-neon white dwarfs. 34 S abundances have the potential to aid in the classification of presolar grains. Purpose: Determine resonance energies for the 34g,m Cl(p, γ) 35 Ar reactions within the region of astrophysical interest for classical novae to a precision of a few keV as an essential first step toward constraining their thermonuclear reaction rates. Method: 35 Ar excited states were populated by the 36 Ar(d, t) 35 Ar reaction at E(d)=22 MeV and reaction products were momentum analyzed by a high resolution quadrupole-dipole-dipole-dipole (Q3D) magnetic spectrograph. Results: Seventeen new 35 Ar levels have been detected at a statistically significant level in the region Ex ≈ 5.9-6.7 MeV (Er < 800 keV) and their excitation energies have been determined to typical uncertainties of 3 keV. The uncertainties for five previously known levels have also been reduced substantially. The measured level density was compared to those calculated using the WBMB Hamiltonian within the sd − pf model space. Conclusions: Most of the resonances in the region of astrophysical interest have likely been discovered and their energies have been determined, but the resonance strengths are still unknown, and experimentally constraining the 34g,m Cl(p, γ) 35 Ar reaction rates will require further experiments.
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Papers by Ronaldo Ortez