Departament de Físicahttp://hdl.handle.net/2117/796772024-05-19T21:50:11Z2024-05-19T21:50:11ZColossal reversible barocaloric effects in a plastic crystal mediated by lattice vibrations and ion diffusionZeng, MingEscorihuela Sayalero, CarlosIkeshoji, TamioTakagi, ShigeyukiKim, SangryunOrimo, Shin-ichiBarrio Casado, María delTamarit Mur, José LuisLloveras Muntané, Pol MarcelCazorla Silva, ClaudioSau, Kartikhttp://hdl.handle.net/2117/4081902024-05-19T21:30:12Z2024-05-17T17:03:25ZColossal reversible barocaloric effects in a plastic crystal mediated by lattice vibrations and ion diffusion
Zeng, Ming; Escorihuela Sayalero, Carlos; Ikeshoji, Tamio; Takagi, Shigeyuki; Kim, Sangryun; Orimo, Shin-ichi; Barrio Casado, María del; Tamarit Mur, José Luis; Lloveras Muntané, Pol Marcel; Cazorla Silva, Claudio; Sau, Kartik
Solid-state methods for cooling and heating promise a sustainable alternative to current compression cycles of greenhouse gases and inefficient fuel-burning heaters. Barocaloric effects (BCE) driven by hydrostatic pressure (p) are especially encouraging in terms of large adiabatic temperature changes (|¿T| ˜¿10 K) and isothermal entropy changes (|¿S| ˜¿100 J K-1 kg-1). However, BCE typically require large pressure shifts due to irreversibility issues, and sizeable |¿T| and |¿S| seldom are realized in a same material. Here, the existence of colossal and reversible BCE in LiCB11H12 is demonstrated near its order-disorder phase transition at ˜380 K. Specifically, for ¿p ˜ 0.23 (0.10) GPa, |¿Srev| = 280 (200) J K-1 kg-1 and |¿Trev| = 32 (10) K are measured, which individually rival with state-of-the-art BCE figures. Furthermore, pressure shifts of the order of 0.1 GPa yield huge reversible barocaloric strengths of ˜2 J K-1 kg-1 MPa-1. Molecular dynamics simulations are performed to quantify the role of lattice vibrations, molecular reorientations, and ion diffusion on the disclosed BCE. Interestingly, lattice vibrations are found to contribute the most to |¿S| while the diffusion of lithium ions, despite adding up only slightly to the entropy change, is crucial in enabling the molecular order–disorder phase transition.
2024-05-17T17:03:25ZZeng, MingEscorihuela Sayalero, CarlosIkeshoji, TamioTakagi, ShigeyukiKim, SangryunOrimo, Shin-ichiBarrio Casado, María delTamarit Mur, José LuisLloveras Muntané, Pol MarcelCazorla Silva, ClaudioSau, KartikSolid-state methods for cooling and heating promise a sustainable alternative to current compression cycles of greenhouse gases and inefficient fuel-burning heaters. Barocaloric effects (BCE) driven by hydrostatic pressure (p) are especially encouraging in terms of large adiabatic temperature changes (|¿T| ˜¿10 K) and isothermal entropy changes (|¿S| ˜¿100 J K-1 kg-1). However, BCE typically require large pressure shifts due to irreversibility issues, and sizeable |¿T| and |¿S| seldom are realized in a same material. Here, the existence of colossal and reversible BCE in LiCB11H12 is demonstrated near its order-disorder phase transition at ˜380 K. Specifically, for ¿p ˜ 0.23 (0.10) GPa, |¿Srev| = 280 (200) J K-1 kg-1 and |¿Trev| = 32 (10) K are measured, which individually rival with state-of-the-art BCE figures. Furthermore, pressure shifts of the order of 0.1 GPa yield huge reversible barocaloric strengths of ˜2 J K-1 kg-1 MPa-1. Molecular dynamics simulations are performed to quantify the role of lattice vibrations, molecular reorientations, and ion diffusion on the disclosed BCE. Interestingly, lattice vibrations are found to contribute the most to |¿S| while the diffusion of lithium ions, despite adding up only slightly to the entropy change, is crucial in enabling the molecular order–disorder phase transition.Synthetic dimensions for topological and quantum phasesArgüello Luengo, JavierBhattacharya, UtsoCeli, AlessioChhajlany, Ravindra W.Grass, Tobias DanielPlodzien, MarcinRakshit, DebrajSalamon, Tymoteusz PiotrStornati, PaoloTarruell, LeticiaLewenstein, Maciejhttp://hdl.handle.net/2117/4081742024-05-19T21:30:11Z2024-05-17T10:48:45ZSynthetic dimensions for topological and quantum phases
Argüello Luengo, Javier; Bhattacharya, Utso; Celi, Alessio; Chhajlany, Ravindra W.; Grass, Tobias Daniel; Plodzien, Marcin; Rakshit, Debraj; Salamon, Tymoteusz Piotr; Stornati, Paolo; Tarruell, Leticia; Lewenstein, Maciej
The concept of synthetic dimensions works particularly well in atomic physics, quantum optics, and photonics, where the internal degrees of freedom (Zeeman sublevels of the ground state, metastable excited states, or motional states for atoms, and angular momentum states or transverse modes for photons) provide the synthetic space. In this Perspective article we report on recent progress on studies of synthetic dimensions, mostly, but not only, based on the research realized around the Barcelona groups (ICFO, UAB), Donostia (DIPC), Poznan (UAM), Kraków (UJ), and Allahabad (HRI). We describe our attempts to design quantum simulators with synthetic dimensions, to mimic curved spaces, artificial gauge fields, lattice gauge theories, twistronics, quantum random walks, and more.
2024-05-17T10:48:45ZArgüello Luengo, JavierBhattacharya, UtsoCeli, AlessioChhajlany, Ravindra W.Grass, Tobias DanielPlodzien, MarcinRakshit, DebrajSalamon, Tymoteusz PiotrStornati, PaoloTarruell, LeticiaLewenstein, MaciejThe concept of synthetic dimensions works particularly well in atomic physics, quantum optics, and photonics, where the internal degrees of freedom (Zeeman sublevels of the ground state, metastable excited states, or motional states for atoms, and angular momentum states or transverse modes for photons) provide the synthetic space. In this Perspective article we report on recent progress on studies of synthetic dimensions, mostly, but not only, based on the research realized around the Barcelona groups (ICFO, UAB), Donostia (DIPC), Poznan (UAM), Kraków (UJ), and Allahabad (HRI). We describe our attempts to design quantum simulators with synthetic dimensions, to mimic curved spaces, artificial gauge fields, lattice gauge theories, twistronics, quantum random walks, and more.Parametric analysis of the flow past a square cylinder in the interface of two different-velocity streamsElmansy, Reda Mohamed Yousyf AbdallahBergadà Granyó, Josep MariaSarwar, WasimMellibovsky Elstein, Fernandohttp://hdl.handle.net/2117/4081692024-05-17T07:40:13Z2024-05-17T07:34:47ZParametric analysis of the flow past a square cylinder in the interface of two different-velocity streams
Elmansy, Reda Mohamed Yousyf Abdallah; Bergadà Granyó, Josep Maria; Sarwar, Wasim; Mellibovsky Elstein, Fernando
We address the linear stability of the two-dimensional incompressible flow past a square cylinder immersed in the wake of an upstream splitter plate, which separates two streams of different velocities, UT (top) and UB (bottom), to three-dimensional perturbations. The analysis is done in the so-called wake transition regime, across which two-dimensional vortex shedding incorporates spanwise modulation. In addition to the top and bottom stream Reynolds numbers (ReT,B=DUT,B/¿, with D the square cylinder side and ¿ the kinematic viscosity of the fluid), a parametric analysis is conducted to gauge the effects of splitter plate length (S) and the gap between the trailing edge of the splitter plate and the front face of the cylinder (G) on the leading three-dimensionalizing instabilities. Modes akin to the A- and B-type instabilities that characterize the wake transition regime past circular and square cylinders in homogeneous incoming flow are observed only at very small values of the top-to-bottom Reynolds number ratio R=ReT/ReB, while a third mode, mode C, is ubiquitous beyond more than very mild values of R. Increasing S at constant small G has a stabilizing effect on mode C, whose onset is pushed to higher values of R. Only for long S is mode A observed. Fixing a short S and increasing G results instead in a destabilization of mode C, and mode B is favored over mode A.
2024-05-17T07:34:47ZElmansy, Reda Mohamed Yousyf AbdallahBergadà Granyó, Josep MariaSarwar, WasimMellibovsky Elstein, FernandoWe address the linear stability of the two-dimensional incompressible flow past a square cylinder immersed in the wake of an upstream splitter plate, which separates two streams of different velocities, UT (top) and UB (bottom), to three-dimensional perturbations. The analysis is done in the so-called wake transition regime, across which two-dimensional vortex shedding incorporates spanwise modulation. In addition to the top and bottom stream Reynolds numbers (ReT,B=DUT,B/¿, with D the square cylinder side and ¿ the kinematic viscosity of the fluid), a parametric analysis is conducted to gauge the effects of splitter plate length (S) and the gap between the trailing edge of the splitter plate and the front face of the cylinder (G) on the leading three-dimensionalizing instabilities. Modes akin to the A- and B-type instabilities that characterize the wake transition regime past circular and square cylinders in homogeneous incoming flow are observed only at very small values of the top-to-bottom Reynolds number ratio R=ReT/ReB, while a third mode, mode C, is ubiquitous beyond more than very mild values of R. Increasing S at constant small G has a stabilizing effect on mode C, whose onset is pushed to higher values of R. Only for long S is mode A observed. Fixing a short S and increasing G results instead in a destabilization of mode C, and mode B is favored over mode A.Prediction and understanding of barocaloric effects in orientationally disordered materials from molecular dynamics simulationsEscorihuela Sayalero, CarlosPardo Soto, Luis CarlosRomanini, MichelaObrecht, NicolasLoehlé, SophieLloveras Muntané, Pol MarcelTamarit Mur, José LuisCazorla Silva, Claudiohttp://hdl.handle.net/2117/4081282024-05-19T21:34:15Z2024-05-16T12:26:54ZPrediction and understanding of barocaloric effects in orientationally disordered materials from molecular dynamics simulations
Escorihuela Sayalero, Carlos; Pardo Soto, Luis Carlos; Romanini, Michela; Obrecht, Nicolas; Loehlé, Sophie; Lloveras Muntané, Pol Marcel; Tamarit Mur, José Luis; Cazorla Silva, Claudio
Due to its high energy efficiency and environmental friendliness, solid-state cooling based on the barocaloric (BC) effect represents a promising alternative to traditional refrigeration technologies relying on greenhouse gases. Plastic crystals displaying orientational order-disorder solid-solid phase transitions have emerged among the most gifted materials on which to realize the full potential of BC solid-state cooling. However, a comprehensive understanding of the atomistic mechanisms on which order-disorder BC effects are sustained is still missing, and rigorous and systematic methods for quantitatively evaluating and anticipating them have not been yet established. Here, we present a computational approach for the assessment and prediction of BC effects in orientationally disordered materials that relies on atomistic molecular dynamics simulations and emulates quasi-direct calorimetric BC measurements. Remarkably, the proposed computational approach allows for a precise determination of the partial contributions to the total entropy stemming from the vibrational and molecular orientational degrees of freedom. Our BC simulation method is applied on the technologically relevant material CH3NH3PbI3 (MAPI), finding giant BC isothermal entropy changes (|¿SBC|¿~¿10 J K-1 kg-1) under moderate pressure shifts of ~0.1 GPa. Intriguingly, our computational analysis of MAPI reveals that changes in the vibrational degrees of freedom of the molecular cations, not their reorientational motion, have a major influence on the entropy change that accompanies the order-disorder solid-solid phase transition.
2024-05-16T12:26:54ZEscorihuela Sayalero, CarlosPardo Soto, Luis CarlosRomanini, MichelaObrecht, NicolasLoehlé, SophieLloveras Muntané, Pol MarcelTamarit Mur, José LuisCazorla Silva, ClaudioDue to its high energy efficiency and environmental friendliness, solid-state cooling based on the barocaloric (BC) effect represents a promising alternative to traditional refrigeration technologies relying on greenhouse gases. Plastic crystals displaying orientational order-disorder solid-solid phase transitions have emerged among the most gifted materials on which to realize the full potential of BC solid-state cooling. However, a comprehensive understanding of the atomistic mechanisms on which order-disorder BC effects are sustained is still missing, and rigorous and systematic methods for quantitatively evaluating and anticipating them have not been yet established. Here, we present a computational approach for the assessment and prediction of BC effects in orientationally disordered materials that relies on atomistic molecular dynamics simulations and emulates quasi-direct calorimetric BC measurements. Remarkably, the proposed computational approach allows for a precise determination of the partial contributions to the total entropy stemming from the vibrational and molecular orientational degrees of freedom. Our BC simulation method is applied on the technologically relevant material CH3NH3PbI3 (MAPI), finding giant BC isothermal entropy changes (|¿SBC|¿~¿10 J K-1 kg-1) under moderate pressure shifts of ~0.1 GPa. Intriguingly, our computational analysis of MAPI reveals that changes in the vibrational degrees of freedom of the molecular cations, not their reorientational motion, have a major influence on the entropy change that accompanies the order-disorder solid-solid phase transition.Spanish research related to SMRs projectsQueral Salazar, José CésarRedondo Valero, ElenaSanchez Torrijos, JorgeJimenez Varas, GonzaloLarriba del Apio, SamanthaCuervo Gomez, DianaCabellos de Francisco, Oscar LuisDurán Vinuesa, Luis FelipeHerranz Puebla, Luis EnriqueGarcía Bravo, MaríaMartínez Quiroga, Víctor ManuelFreixa Terradas, Jordihttp://hdl.handle.net/2117/4081252024-05-19T21:29:19Z2024-05-16T11:48:38ZSpanish research related to SMRs projects
Queral Salazar, José César; Redondo Valero, Elena; Sanchez Torrijos, Jorge; Jimenez Varas, Gonzalo; Larriba del Apio, Samantha; Cuervo Gomez, Diana; Cabellos de Francisco, Oscar Luis; Durán Vinuesa, Luis Felipe; Herranz Puebla, Luis Enrique; García Bravo, María; Martínez Quiroga, Víctor Manuel; Freixa Terradas, Jordi
Small modular reactors (SMRs) are advanced nuclear reactors with a power capacity of up to 300 MW(e) per unit. SMRs encompass a variety of reactor technologies including light water reactors, high temperature gas reactors, molten salt reactors, liquid metal cooled fast reactors, and heat pipe technology-based reactors. The research and design of these diverse SMR types require a broad set of technological capabilities related to nuclear engineering and safety. Within this context, this article attempts to assess the current state of research and technological progress achieved by the Spanish research groups and companies. The results reveal a significant level of maturity among these groups and companies in various domains such as neutronic analysis, thermal hydraulic analysis, the improvement of models related to severe accident scenarios and an active involvement in the design of novel SMR.
2024-05-16T11:48:38ZQueral Salazar, José CésarRedondo Valero, ElenaSanchez Torrijos, JorgeJimenez Varas, GonzaloLarriba del Apio, SamanthaCuervo Gomez, DianaCabellos de Francisco, Oscar LuisDurán Vinuesa, Luis FelipeHerranz Puebla, Luis EnriqueGarcía Bravo, MaríaMartínez Quiroga, Víctor ManuelFreixa Terradas, JordiSmall modular reactors (SMRs) are advanced nuclear reactors with a power capacity of up to 300 MW(e) per unit. SMRs encompass a variety of reactor technologies including light water reactors, high temperature gas reactors, molten salt reactors, liquid metal cooled fast reactors, and heat pipe technology-based reactors. The research and design of these diverse SMR types require a broad set of technological capabilities related to nuclear engineering and safety. Within this context, this article attempts to assess the current state of research and technological progress achieved by the Spanish research groups and companies. The results reveal a significant level of maturity among these groups and companies in various domains such as neutronic analysis, thermal hydraulic analysis, the improvement of models related to severe accident scenarios and an active involvement in the design of novel SMR.Country-report pattern corrections of new cases allow accurate 2-week predictions of COVID-19 evolution with the Gompertz modelVillanueva Baxarias, Maria InmaculadaConesa Ortega, DavidCatalà Sabaté, MartíPerramon Malavez, AidaLópez de Rioja, VíctorLópez Codina, DanielAlonso Muñoz, SergioCardona Iglesias, Pere JoanPrats Soler, ClaraÁlvarez Lacalle, EnriqueLópez Cano, M. CayetanaMolinuevo Gómez, DanielMontañola Sales, Cristinahttp://hdl.handle.net/2117/4081192024-05-19T00:01:07Z2024-05-16T11:04:59ZCountry-report pattern corrections of new cases allow accurate 2-week predictions of COVID-19 evolution with the Gompertz model
Villanueva Baxarias, Maria Inmaculada; Conesa Ortega, David; Català Sabaté, Martí; Perramon Malavez, Aida; López de Rioja, Víctor; López Codina, Daniel; Alonso Muñoz, Sergio; Cardona Iglesias, Pere Joan; Prats Soler, Clara; Álvarez Lacalle, Enrique; López Cano, M. Cayetana; Molinuevo Gómez, Daniel; Montañola Sales, Cristina
Accurate short-term predictions of COVID-19 cases with empirical models allow Health Officials to prepare for hospital contingencies in a two–three week window given the delay between case reporting and the admission of patients in a hospital. We investigate the ability of Gompertz-type empiric models to provide accurate prediction up to two and three weeks to give a large window of preparation in case of a surge in virus transmission. We investigate the stability of the prediction and its accuracy using bi-weekly predictions during the last trimester of 2020 and 2021. Using data from 2020, we show that understanding and correcting for the daily reporting structure of cases in the different countries is key to accomplish accurate predictions. Furthermore, we found that filtering out predictions that are highly unstable to changes in the parameters of the model, which are roughly 20%, reduces strongly the number of predictions that are way-off. The method is then tested for robustness with data from 2021. We found that, for this data, only 1–2% of the one-week predictions were off by more than 50%. This increased to 3% for two-week predictions, and only for three-week predictions it reached 10%.
2024-05-16T11:04:59ZVillanueva Baxarias, Maria InmaculadaConesa Ortega, DavidCatalà Sabaté, MartíPerramon Malavez, AidaLópez de Rioja, VíctorLópez Codina, DanielAlonso Muñoz, SergioCardona Iglesias, Pere JoanPrats Soler, ClaraÁlvarez Lacalle, EnriqueLópez Cano, M. CayetanaMolinuevo Gómez, DanielMontañola Sales, CristinaAccurate short-term predictions of COVID-19 cases with empirical models allow Health Officials to prepare for hospital contingencies in a two–three week window given the delay between case reporting and the admission of patients in a hospital. We investigate the ability of Gompertz-type empiric models to provide accurate prediction up to two and three weeks to give a large window of preparation in case of a surge in virus transmission. We investigate the stability of the prediction and its accuracy using bi-weekly predictions during the last trimester of 2020 and 2021. Using data from 2020, we show that understanding and correcting for the daily reporting structure of cases in the different countries is key to accomplish accurate predictions. Furthermore, we found that filtering out predictions that are highly unstable to changes in the parameters of the model, which are roughly 20%, reduces strongly the number of predictions that are way-off. The method is then tested for robustness with data from 2021. We found that, for this data, only 1–2% of the one-week predictions were off by more than 50%. This increased to 3% for two-week predictions, and only for three-week predictions it reached 10%.Pushing the high count rate limits of scintillation detectors for challenging neutron-capture experimentsBalibrea Correa, JavierLerendegui Marco, JorgeBabiano Suárez, VíctorDomingo Pardo, CésarLadarescu, IonTarifeño Saldivia, ArielFuente Rosales, Gabriel de laAlcayne Aicua, VíctorCano Ott, DanielGonzález Romero, Enrique MiguelCasanovas Hoste, AdriàCalviño Tavares, FranciscoCortés Rossell, Guillem Perehttp://hdl.handle.net/2117/4080022024-05-19T21:36:39Z2024-05-15T09:28:01ZPushing the high count rate limits of scintillation detectors for challenging neutron-capture experiments
Balibrea Correa, Javier; Lerendegui Marco, Jorge; Babiano Suárez, Víctor; Domingo Pardo, César; Ladarescu, Ion; Tarifeño Saldivia, Ariel; Fuente Rosales, Gabriel de la; Alcayne Aicua, Víctor; Cano Ott, Daniel; González Romero, Enrique Miguel; Casanovas Hoste, Adrià; Calviño Tavares, Francisco; Cortés Rossell, Guillem Pere
One of the critical aspects for the accurate determination of neutron capture cross sections when combining time-of-flight and total energy detector techniques is the characterization and control of systematic uncertainties associated to the measuring devices. In this work we explore the most conspicuous effects associated to harsh count rate conditions: dead-time and pile-up effects. Both effects, when not properly treated, can lead to large systematic uncertainties and bias in the determination of neutron cross sections. In the majority of neutron capture measurements carried out at the CERN n_TOF facility, the detectors of choice are the C6D6 liquid-based either in form of large-volume cells or recently commissioned sTED detector array, consisting of much smaller-volume modules. To account for the aforementioned effects, we introduce a Monte Carlo model for these detectors mimicking harsh count rate conditions similar to those happening at the CERN n_TOF 20 m flight path vertical measuring station. The model parameters are extracted by comparison with the experimental data taken at the same facility during 2022 experimental campaign. We propose a novel methodology to consider both, dead-time and pile-up effects simultaneously for these fast detectors and check the applicability to experimental data from 197Au(n, gamma), including the saturated 4.9 eV resonance which is an important component of normalization for neutron cross section measurements.
2024-05-15T09:28:01ZBalibrea Correa, JavierLerendegui Marco, JorgeBabiano Suárez, VíctorDomingo Pardo, CésarLadarescu, IonTarifeño Saldivia, ArielFuente Rosales, Gabriel de laAlcayne Aicua, VíctorCano Ott, DanielGonzález Romero, Enrique MiguelCasanovas Hoste, AdriàCalviño Tavares, FranciscoCortés Rossell, Guillem PereOne of the critical aspects for the accurate determination of neutron capture cross sections when combining time-of-flight and total energy detector techniques is the characterization and control of systematic uncertainties associated to the measuring devices. In this work we explore the most conspicuous effects associated to harsh count rate conditions: dead-time and pile-up effects. Both effects, when not properly treated, can lead to large systematic uncertainties and bias in the determination of neutron cross sections. In the majority of neutron capture measurements carried out at the CERN n_TOF facility, the detectors of choice are the C6D6 liquid-based either in form of large-volume cells or recently commissioned sTED detector array, consisting of much smaller-volume modules. To account for the aforementioned effects, we introduce a Monte Carlo model for these detectors mimicking harsh count rate conditions similar to those happening at the CERN n_TOF 20 m flight path vertical measuring station. The model parameters are extracted by comparison with the experimental data taken at the same facility during 2022 experimental campaign. We propose a novel methodology to consider both, dead-time and pile-up effects simultaneously for these fast detectors and check the applicability to experimental data from 197Au(n, gamma), including the saturated 4.9 eV resonance which is an important component of normalization for neutron cross section measurements.Inferring the connectivity of coupled oscillators from event timing analysisAristides, Raul de PalmaCerdeira, HildaMasoller Alonso, CristinaTirabassi, Giuliohttp://hdl.handle.net/2117/4078442024-05-14T05:19:45Z2024-05-10T12:29:33ZInferring the connectivity of coupled oscillators from event timing analysis
Aristides, Raul de Palma; Cerdeira, Hilda; Masoller Alonso, Cristina; Tirabassi, Giulio
Understanding the coupling structure of interacting systems is an important open problem, and many methods have been proposed to reconstruct a network from observed data. Most require continuous observation of the nodes’ dynamics; however, in many situations, we can only monitor the times when some events occur (e.g., in neural systems, spike times). Here, we propose a method for network reconstruction based on the analysis of event times at the network’s nodes. First, from the event times, we generate phase time series. Then, we assimilate the phase time series to the Kuramoto model by using the unscented Kalman filter (UKF) that returns the inferred coupling coefficients. Finally, we use a clustering algorithm to discriminate the coupling coefficients into two groups that we associate with existing and non-existing links. We demonstrate the method with synthetic data from small networks of Izhikevich neurons, where we analyze the spike times, and with experimental data from a larger network of chaotic electronic circuits, where the events are voltage threshold-crossings. We also compare the UKF with the performance of the cross-correlation (CC), and the mutual information (MI). We show that, for neural network reconstruction, UKF often outperforms CC and MI, while for electronic network reconstruction, UKF shows similar performance to MI, and both methods outperform CC. Altogether, our results suggest that when event times are the only information available, the UKF can give a good reconstruction of small networks. However, as the network size increases, the method becomes computationally demanding.
2024-05-10T12:29:33ZAristides, Raul de PalmaCerdeira, HildaMasoller Alonso, CristinaTirabassi, GiulioUnderstanding the coupling structure of interacting systems is an important open problem, and many methods have been proposed to reconstruct a network from observed data. Most require continuous observation of the nodes’ dynamics; however, in many situations, we can only monitor the times when some events occur (e.g., in neural systems, spike times). Here, we propose a method for network reconstruction based on the analysis of event times at the network’s nodes. First, from the event times, we generate phase time series. Then, we assimilate the phase time series to the Kuramoto model by using the unscented Kalman filter (UKF) that returns the inferred coupling coefficients. Finally, we use a clustering algorithm to discriminate the coupling coefficients into two groups that we associate with existing and non-existing links. We demonstrate the method with synthetic data from small networks of Izhikevich neurons, where we analyze the spike times, and with experimental data from a larger network of chaotic electronic circuits, where the events are voltage threshold-crossings. We also compare the UKF with the performance of the cross-correlation (CC), and the mutual information (MI). We show that, for neural network reconstruction, UKF often outperforms CC and MI, while for electronic network reconstruction, UKF shows similar performance to MI, and both methods outperform CC. Altogether, our results suggest that when event times are the only information available, the UKF can give a good reconstruction of small networks. However, as the network size increases, the method becomes computationally demanding.The impact and mitigation of broad-absorption-line quasars in Lyman a forest correlationsPérez Ràfols, Ignasihttp://hdl.handle.net/2117/4078002024-05-13T00:47:54Z2024-05-10T08:40:22ZThe impact and mitigation of broad-absorption-line quasars in Lyman a forest correlations
Pérez Ràfols, Ignasi
Correlations in and with the flux transmission of the Lyman¿a (Ly¿a) forest in the spectra of high-redshift quasars are powerful cosmological tools, yet these measurements can be compromised if the intrinsic quasar continuum is significantly uncertain. One particularly problematic case is broad-absorption-line (BAL) quasars, which exhibit blueshifted absorption associated with many spectral features that are consistent with outflows of up to ~0.1c. As these absorption features can both fall in the forest region and be difficult to distinguish from Ly¿a absorption, cosmological analyses eliminate the ~12–16 per¿cent of quasars that exhibit BALs. In this paper, we explore an alternate approach that includes BALs in the Ly¿a autocorrelation function, with the exception of the expected locations of the BAL absorption troughs. This procedure returns over 95 per¿cent of the path-length that is lost by the exclusion of BALs, as well as increasing the density of sightlines. We show that including BAL quasars reduces the fractional uncertainty in the covariance matrix and correlation function by 12 per¿cent and does not significantly change the shape of the correlation function relative to analyses that exclude BAL quasars. We also evaluate different definitions of BALs, masking strategies, and potential differences in the quasar continuum in the forest region for BALs with different amounts of absorption.
2024-05-10T08:40:22ZPérez Ràfols, IgnasiCorrelations in and with the flux transmission of the Lyman¿a (Ly¿a) forest in the spectra of high-redshift quasars are powerful cosmological tools, yet these measurements can be compromised if the intrinsic quasar continuum is significantly uncertain. One particularly problematic case is broad-absorption-line (BAL) quasars, which exhibit blueshifted absorption associated with many spectral features that are consistent with outflows of up to ~0.1c. As these absorption features can both fall in the forest region and be difficult to distinguish from Ly¿a absorption, cosmological analyses eliminate the ~12–16 per¿cent of quasars that exhibit BALs. In this paper, we explore an alternate approach that includes BALs in the Ly¿a autocorrelation function, with the exception of the expected locations of the BAL absorption troughs. This procedure returns over 95 per¿cent of the path-length that is lost by the exclusion of BALs, as well as increasing the density of sightlines. We show that including BAL quasars reduces the fractional uncertainty in the covariance matrix and correlation function by 12 per¿cent and does not significantly change the shape of the correlation function relative to analyses that exclude BAL quasars. We also evaluate different definitions of BALs, masking strategies, and potential differences in the quasar continuum in the forest region for BALs with different amounts of absorption.Forecasts for WEAVE-QSO: 3D clustering of critical points with Lyman-alpha tomographyCodis, SebastienPérez Ràfols, Ignasihttp://hdl.handle.net/2117/4077992024-05-14T08:57:33Z2024-05-10T08:38:46ZForecasts for WEAVE-QSO: 3D clustering of critical points with Lyman-alpha tomography
Codis, Sebastien; Pérez Ràfols, Ignasi
The upcoming WEAVE-QSO survey will target a high density of quasars over a large area, enabling the reconstruction of the 3D density field through Lyman-a (Ly-a) tomography over unprecedented volumes smoothed on intermediate cosmological scales (˜ 16 Mpc¿h-1). We produce mocks of the Ly-a forest using Ly-a Mass Association Scheme, and reconstruct the 3D density field between sightlines through Wiener filtering in a configuration compatible with the future WEAVE-QSO observations. The fidelity of the reconstruction is assessed by measuring one- and two-point statistics from the distribution of critical points in the cosmic web. In addition, initial Lagrangian statistics are predicted from the first principles, and measurements of the connectivity of the cosmic web are performed. The reconstruction captures well the expected features in the auto- and cross-correlations of the critical points. This remains true after a realistic noise is added to the synthetic spectra, even though sparsity of sightlines introduces systematics, especially in the cross-correlations of points with mixed signature. Specifically, the most striking clustering features involving filaments and walls could be measured with up to 4s of significance with a WEAVE-QSO-like survey. Moreover, the connectivity of each peak identified in the reconstructed field is globally consistent with its counterpart in the original field, indicating that the reconstruction preserves the geometry of the density field not only statistically, but also locally. Hence, the critical points’ relative positions within the tomographic reconstruction could be used as standard rulers for dark energy by WEAVE-QSO and similar surveys.
2024-05-10T08:38:46ZCodis, SebastienPérez Ràfols, IgnasiThe upcoming WEAVE-QSO survey will target a high density of quasars over a large area, enabling the reconstruction of the 3D density field through Lyman-a (Ly-a) tomography over unprecedented volumes smoothed on intermediate cosmological scales (˜ 16 Mpc¿h-1). We produce mocks of the Ly-a forest using Ly-a Mass Association Scheme, and reconstruct the 3D density field between sightlines through Wiener filtering in a configuration compatible with the future WEAVE-QSO observations. The fidelity of the reconstruction is assessed by measuring one- and two-point statistics from the distribution of critical points in the cosmic web. In addition, initial Lagrangian statistics are predicted from the first principles, and measurements of the connectivity of the cosmic web are performed. The reconstruction captures well the expected features in the auto- and cross-correlations of the critical points. This remains true after a realistic noise is added to the synthetic spectra, even though sparsity of sightlines introduces systematics, especially in the cross-correlations of points with mixed signature. Specifically, the most striking clustering features involving filaments and walls could be measured with up to 4s of significance with a WEAVE-QSO-like survey. Moreover, the connectivity of each peak identified in the reconstructed field is globally consistent with its counterpart in the original field, indicating that the reconstruction preserves the geometry of the density field not only statistically, but also locally. Hence, the critical points’ relative positions within the tomographic reconstruction could be used as standard rulers for dark energy by WEAVE-QSO and similar surveys.