Browsing by Author "Li, L"

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    A D2O detector for flux normalization of a pion decay-at-rest neutrino source
    (Journal of Instrumentation, 2021-08-01) Akimov, D; An, P; Awe, C; Barbeau, PS; Becker, B; Belov, V; Bernardi, I; Blackston, MA; Bolozdynya, A; Cabrera-Palmer, B; Chernyak, D; Conley, E; Daughhetee, J; Day, E; Detwiler, J; Ding, K; Durand, MR; Efremenko, Y; Elliott, SR; Fabris, L; Febbraro, M; Gallo Rosso, A; Galindo-Uribarri, A; Green, MP; Heath, MR; Hedges, S; Hoang, D; Hughes, M; Johnson, T; Khromov, A; Konovalov, A; Koros, J; Kozlova, E; Kumpan, A; Li, L; Link, JM; Liu, J; Mann, K; Markoff, DM; Mastroberti, J; Mueller, PE; Newby, J; Parno, DS; Penttila, SI; Pershey, D; Rapp, R; Ray, H; Raybern, J; Razuvaeva, O; Reyna, D; Rich, GC; Ross, J; Rudik, D; Runge, J; Salvat, DJ; Salyapongse, AM; Scholberg, K; Shakirov, A; Simakov, G; Sinev, G; Snow, WM; Sosnovstsev, V; Suh, B; Tayloe, R; Tellez-Giron-Flores, K; Tolstukhin, I; Ujah, E; Vanderwerp, J; Varner, RL; Virtue, CJ; Visser, G; Ward, EM; Wiseman, C; Wongjirad, T; Yen, YR; Yoo, J; Yu, CH; Zettlemoyer, J
    We report on the technical design and expected performance of a 592 kg heavy-water-Cherenkov detector to measure the absolute neutrino flux from the pion-decay-at-rest neutrino source at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). The detector will be located roughly 20 m from the SNS target and will measure the neutrino flux with better than 5% statistical uncertainty in 2 years. This heavy-water detector will serve as the first module of a two-module detector system to ultimately measure the neutrino flux to 2-3% at both the First Target Station and the planned Second Target Station of the SNS. This detector will significantly reduce a dominant systematic uncertainty for neutrino cross-section measurements at the SNS, increasing the sensitivity of searches for new physics.
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    A stochastic version of Stein Variational Gradient Descent for efficient sampling
    Li, L; Li, Y; Liu, JG; Liu, Z; Lu, J
    We propose in this work RBM-SVGD, a stochastic version of Stein Variational Gradient Descent (SVGD) method for efficiently sampling from a given probability measure and thus useful for Bayesian inference. The method is to apply the Random Batch Method (RBM) for interacting particle systems proposed by Jin et al to the interacting particle systems in SVGD. While keeping the behaviors of SVGD, it reduces the computational cost, especially when the interacting kernel has long range. Numerical examples verify the efficiency of this new version of SVGD.
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    Changes to the North Atlantic subtropical high and its role in the intensification of summer rainfall variability in the southeastern United States
    (Journal of Climate, 2011-03-01) Li, W; Li, L; Fu, R; Deng, Y; Wang, H
    This study investigates the changes of the North Atlantic subtropical high (NASH) and its impact on summer precipitation over the southeastern (SE) United States using the 850-hPa geopotential height field in the National Centers forEnvironmental Prediction (NCEP) reanalysis, the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), long-term rainfall data, and Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) model simulations during the past six decades (1948-2007). The results show that the NASH in the last 30 yr has become more intense, and its western ridge has displaced westward with an enhanced meridional movement compared to the previous 30 yr. When the NASH moved closer to the continental United States in the three most recent decades, the effect of the NASH on the interannual variation of SE U.S. precipitation is enhanced through the ridge's north-south movement. The study's attribution analysis suggested that the changes of the NASH are mainly due to anthropogenic warming. In the twenty-first century with an increase of the atmospheric CO2 concentration, the center of the NASH would be intensified and the western ridge of the NASH would shift farther westward. These changes would increase the likelihood of both strong anomalously wet and dry summers over the SEUnited States in the future, as suggested by the IPCC AR4 models. © 2011 American Meteorological Society.
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    Contribution of the North Atlantic subtropical high to regional climate model (RCM) skill in simulating southeastern United States summer precipitation
    (Climate Dynamics, 2015-07-26) Li, L; Li, W; Jin, J
    © 2014, Springer-Verlag Berlin Heidelberg.This study assesses the skill of advanced regional climate models (RCMs) in simulating southeastern United States (SE US) summer precipitation and explores the physical mechanisms responsible for the simulation skill at a process level. Analysis of the RCM output for the North American Regional Climate Change Assessment Program indicates that the RCM simulations of summer precipitation show the largest biases and a remarkable spread over the SE US compared to other regions in the contiguous US. The causes of such a spread are investigated by performing simulations using the Weather Research and Forecasting (WRF) model, a next-generation RCM developed by the US National Center for Atmospheric Research. The results show that the simulated biases in SE US summer precipitation are due mainly to the misrepresentation of the modeled North Atlantic subtropical high (NASH) western ridge. In the WRF simulations, the NASH western ridge shifts 7° northwestward when compared to that in the reanalysis ensemble, leading to a dry bias in the simulated summer precipitation according to the relationship between the NASH western ridge and summer precipitation over the southeast. Experiments utilizing the four dimensional data assimilation technique further suggest that the improved representation of the circulation patterns (i.e., wind fields) associated with the NASH western ridge substantially reduces the bias in the simulated SE US summer precipitation. Our analysis of circulation dynamics indicates that the NASH western ridge in the WRF simulations is significantly influenced by the simulated planetary boundary layer (PBL) processes over the Gulf of Mexico. Specifically, a decrease (increase) in the simulated PBL height tends to stabilize (destabilize) the lower troposphere over the Gulf of Mexico, and thus inhibits (favors) the onset and/or development of convection. Such changes in tropical convection induce a tropical–extratropical teleconnection pattern, which modulates the circulation along the NASH western ridge in the WRF simulations and contributes to the modeled precipitation biases over the SE US. In conclusion, our study demonstrates that the NASH western ridge is an important factor responsible for the RCM skill in simulating SE US summer precipitation. Furthermore, the improvements in the PBL parameterizations for the Gulf of Mexico might help advance RCM skill in representing the NASH western ridge circulation and summer precipitation over the SE US.
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    Development of a $^{83\mathrm{m}}$Kr source for the calibration of the CENNS-10 Liquid Argon Detector
    (Journal of Instrumentation, 2020-10-21) Collaboration, COHERENT; Akimov, D; An, P; Awe, C; Barbeau, PS; Becker, B; Belov, V; Bernardi, I; Blackston, MA; Blokland, L; Bolozdynya, A; Cabrera-Palmer, B; Chen, N; Chernyak, D; Conley, E; Daughhetee, J; Coello, M del Valle; Detwiler, JA; Durand, MR; Efremenko, Y; Elliott, SR; Fabris, L; Febbraro, M; Fox, W; Galindo-Uribarri, A; Rosso, A Gallo; Green, MP; Hansen, KS; Heath, MR; Hedges, S; Hughes, M; Johnson, T; Khromov, A; Konovalov, A; Kozlova, E; Kumpan, A; Li, L; Librande, JT; Link, JM; Liu, J; Mann, K; Markoff, DM; McGoldrick, O; Mueller, PE; Newby, J; Parno, DS; Pentilla, S; Pershey, D; Radford, D; Rapp, R; Ray, H; Raybern, J; Razuvaeva, O; Reyna, D; Rich, GC; Rudik, D; Runge, J; Salvat, DJ; Scholberg, K; Shakirov, A; Simakov, G; Snow, WM; Sosnovtsev, V; Suh, B; Tayloe, R; Tellez-Giron-Flores, K; Thornton, RT; Tolstukhin, I; Vanderwerp, J; Varner, RL; Venkataraman, R; Virtue, CJ; Visser, G; Wiseman, C; Wongjirad, T; Yang, J; Yen, Y-R; Yoo, J; Yu, C-H; Zettlemoyer, J
    We report on the preparation of and calibration measurements with a $^{83\mathrm{m}}$Kr source for the CENNS-10 liquid argon detector. $^{83\mathrm{m}}$Kr atoms generated in the decay of a $^{83}$Rb source were introduced into the detector via injection into the Ar circulation loop. Scintillation light arising from the 9.4 keV and 32.1 keV conversion electrons in the decay of $^{83\mathrm{m}}$Kr in the detector volume were then observed. This calibration source allows the characterization of the low-energy response of the CENNS-10 detector and is applicable to other low-energy-threshold detectors. The energy resolution of the detector was measured to be 9$\%$ at the total $^{83\mathrm{m}}$Kr decay energy of 41.5 keV. We performed an analysis to separately calibrate the detector using the two conversion electrons at 9.4 keV and 32.1 keV
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    Dynamic prediction of renal failure using longitudinal biomarkers in a cohort study of chronic kidney disease
    (Statistics in Biosciences, 2016) Li, L; Luo, S; Hu, B; Greene, T
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    First Probe of Sub-GeV Dark Matter Beyond the Cosmological Expectation with the COHERENT CsI Detector at the SNS
    Akimov, D; An, P; Awe, C; Barbeau, PS; Becker, B; Belov, V; Bernardi, I; Blackston, MA; Bock, C; Bolozdynya, A; Browning, J; Cabrera-Palmer, B; Chernyak, D; Conley, E; Daughhetee, J; Detwiler, J; Ding, K; Durand, MR; Efremenko, Y; Elliott, SR; Fabris, L; Febbraro, M; Rosso, A Gallo; Galindo-Uribarri, A; Green, MP; Heath, MR; Hedges, S; Hoang, D; Hughes, M; Johnson, T; Khromov, A; Konovalov, A; Kozlova, E; Kumpan, A; Li, L; Link, JM; Liu, J; Mann, K; Markoff, DM; Mastroberti, J; Mueller, PE; Newby, J; Parno, DS; Penttila, SI; Pershey, D; Rapp, R; Raybern, J; Razuvaeva, O; Reyna, D; Rich, GC; Ross, J; Rudik, D; Runge, J; Salvat, DJ; Salyapongse, AM; Sander, J; Scholberg, K; Shakirov, A; Simakov, G; Sinev, G; Snow, WM; Sosnovstsev, V; Suh, B; Tayloe, R; Tellez-Giron-Flores, K; Tolstukhin, I; Ujah, E; Vanderwerp, J; Varner, RL; Virtue, CJ; Visser, G; Wongjirad, T; Yen, Y-R; Yoo, J; Yu, C-H; Zettlemoyer, J
    The COHERENT collaboration searched for scalar dark matter particles produced at the Spallation Neutron Source with masses between 1 and 220~MeV/c$^2$ using a CsI[Na] scintillation detector sensitive to nuclear recoils above 9~keV$_\text{nr}$. No evidence for dark matter is found and we thus place limits on allowed parameter space. With this low-threshold detector, we are sensitive to coherent elastic scattering between dark matter and nuclei. The cross section for this process is orders of magnitude higher than for other processes historically used for accelerator-based direct-detection searches so that our small, 14.6~kg detector significantly improves on past constraints. At peak sensitivity, we reject the flux consistent with the cosmologically observed dark-matter concentration for all coupling constants $\alpha_D<0.64$, assuming a scalar dark-matter particle. We also calculate the sensitivity of future COHERENT detectors to dark-matter signals which will ambitiously test multiple dark-matter spin scenarios.
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    Fractional stochastic differential equations satisfying fluctuation-dissipation theorem
    (2017-04-23) Li, L; Liu, J-G; Lu, Jianfeng
    We consider in this work stochastic differential equation (SDE) model for particles in contact with a heat bath when the memory effects are non-negligible. As a result of the fluctuation-dissipation theorem, the differential equations driven by fractional Brownian noise to model memory effects should be paired with Caputo derivatives and based on this we consider fractional stochastic differential equations (FSDEs), which should be understood in an integral form. We establish the existence of strong solutions for such equations. In the linear forcing regime, we compute the solutions explicitly and analyze the asymptotic behavior, through which we verify that satisfying fluctuation-dissipation indeed leads to the correct physical behavior. We further discuss possible extensions to nonlinear forcing regime, while leave the rigorous analysis for future works.
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    Fractional Stochastic Differential Equations Satisfying Fluctuation-Dissipation Theorem
    (Journal of Statistical Physics, 2017-10-01) Li, L; Liu, JG; Lu, J
    © 2017, Springer Science+Business Media, LLC. We propose in this work a fractional stochastic differential equation (FSDE) model consistent with the over-damped limit of the generalized Langevin equation model. As a result of the ‘fluctuation-dissipation theorem’, the differential equations driven by fractional Brownian noise to model memory effects should be paired with Caputo derivatives, and this FSDE model should be understood in an integral form. We establish the existence of strong solutions for such equations and discuss the ergodicity and convergence to Gibbs measure. In the linear forcing regime, we show rigorously the algebraic convergence to Gibbs measure when the ‘fluctuation-dissipation theorem’ is satisfied, and this verifies that satisfying ‘fluctuation-dissipation theorem’ indeed leads to the correct physical behavior. We further discuss possible approaches to analyze the ergodicity and convergence to Gibbs measure in the nonlinear forcing regime, while leave the rigorous analysis for future works. The FSDE model proposed is suitable for systems in contact with heat bath with power-law kernel and subdiffusion behaviors.
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    Impact of the Interdecadal Pacific Oscillation on Tropical Cyclone Activity in the North Atlantic and Eastern North Pacific.
    (Sci Rep, 2015-07-24) Li, W; Li, L; Deng, Y
    Tropical cyclones (TCs) are among the most devastating weather systems affecting the United States and Central America (USCA). Here we show that the Interdecadal Pacific Oscillation (IPO) strongly modulates TC activity over the North Atlantic (NA) and eastern North Pacific (eNP). During positive IPO phases, less (more) TCs were observed over NA (eNP), likely due to the presence of stronger (weaker) vertical wind shear and the resulting changes in genesis potential. Furthermore, TCs over NA tend to keep their tracks more eastward and recurve at lower latitudes during positive IPO phases. Such variations are largely determined by changes in steering flow instead of changes in genesis locations. Over the eNP, smaller track variations are observed at different IPO phases with stable, westward movements of TCs prevailing. These findings have substantial implications for understanding decadal to inter-decadal fluctuations in the risk of TC landfalls along USCA coasts.
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    Lognormal and gamma mixed negative binomial regression
    (Proceedings of the 29th International Conference on Machine Learning, ICML 2012, 2012-10-10) Zhou, M; Li, L; Dunson, D; Carin, L
    In regression analysis of counts, a lack of simple and efficient algorithms for posterior computation has made Bayesian approaches appear unattractive and thus underdeveloped. We propose a lognormal and gamma mixed negative binomial (NB) regression model for counts, and present efficient closed-form Bayesian inference; unlike conventional Poisson models, the proposed approach has two free parameters to include two different kinds of random effects, and allows the incorporation of prior information, such as sparsity in the regression coefficients. By placing a gamma distribution prior on the NB dispersion parameter r, and connecting a log-normal distribution prior with the logit of the NB probability parameter p, efficient Gibbs sampling and variational Bayes inference are both developed. The closed-form updates are obtained by exploiting conditional conjugacy via both a compound Poisson representation and a Polya-Gamma distribution based data augmentation approach. The proposed Bayesian inference can be implemented routinely, while being easily generalizable to more complex settings involving multivariate dependence structures. The algorithms are illustrated using real examples. Copyright 2012 by the author(s)/owner(s).
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    Measurement of scintillation response of CsI[Na] to low-energy nuclear recoils by COHERENT
    Akimov, D; An, P; Awe, C; Barbeau, PS; Becker, B; Belov, V; Bernardi, I; Blackston, MA; Bock, C; Bolozdynya, A; Browning, J; Cabrera-Palmer, B; Chernyak, D; Conley, E; Daughhetee, J; Detwiler, J; Ding, K; Durand, MR; Efremenko, Y; Elliott, SR; Fabris, L; Febbraro, M; Rosso, A Gallo; Galindo-Uribarri, A; Green, MP; Heath, MR; Hedges, S; Hoang, D; Hughes, M; Johnson, T; Khromov, A; Konovalov, A; Kozlova, E; Kumpan, A; Li, L; Link, JM; Liu, J; Mann, K; Markoff, DM; Mastroberti, J; Melikyan, YA; Mueller, PE; Newby, J; Parno, DS; Penttila, SI; Pershey, D; Rapp, R; Ray, H; Raybern, J; Razuvaeva, O; Reyna, D; Rich, GC; Ross, J; Rudik, D; Runge, J; Salvat, DJ; Salyapongse, AM; Scholberg, K; Shakirov, A; Simakov, G; Sinev, G; Snow, WM; Sosnovstsev, V; Suh, B; Tayloe, R; Tellez-Giron-Flores, K; Tolstukhin, I; Ujah, E; Vanderwerp, J; Varner, RL; Virtue, CJ; Visser, G; Wongjirad, T; Yen, Y-R; Yoo, J; Yu, C-H; Zettlemoyer, J
    We present results of several measurements of CsI[Na] scintillation response to 3-60 keV energy nuclear recoils performed by the COHERENT collaboration using tagged neutron elastic scattering experiments and an endpoint technique. Earlier results, used to estimate the coherent elastic neutrino-nucleus scattering (CEvNS) event rate for the first observation of this process achieved by COHERENT at the Spallation Neutron Source (SNS), have been reassessed. We discuss corrections for the identified systematic effects and update the respective uncertainty values. The impact of updated results on future precision tests of CEvNS is estimated. We scrutinize potential systematic effects that could affect each measurement. In particular we confirm the response of the H11934-200 Hamamatsu photomultiplier tube (PMT) used for the measurements presented in this study to be linear in the relevant signal scale region.
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    Measurement of the Coherent Elastic Neutrino-Nucleus Scattering Cross Section on CsI by COHERENT
    Akimov, D; An, P; Awe, C; Barbeau, PS; Becker, B; Belov, V; Bernardi, I; Blackston, MA; Bock, C; Bolozdynya, A; Browning, J; Cabrera-Palmer, B; Chernyak, D; Conley, E; Daughhetee, J; Detwiler, J; Ding, K; Durand, MR; Efremenko, Y; Elliott, SR; Fabris, L; Febbraro, M; Rosso, A Gallo; Galindo-Uribarri, A; Green, MP; Heath, MR; Hedges, S; Hoang, D; Hughes, M; Johnson, T; Khromov, A; Konovalov, A; Kozlova, E; Kumpan, A; Li, L; Link, JM; Liu, J; Mann, K; Markoff, DM; Mastroberti, J; Mueller, PE; Newby, J; Parno, DS; Penttila, SI; Pershey, D; Rapp, R; Ray, H; Raybern, J; Razuvaeva, O; Reyna, D; Rich, GC; Ross, J; Rudik, D; Runge, J; Salvat, DJ; Salyapongse, AM; Scholberg, K; Shakirov, A; Simakov, G; Sinev, G; Snow, WM; Sosnovstsev, V; Suh, B; Tayloe, R; Tellez-Giron-Flores, K; Tolstukhin, I; Ujah, E; Vanderwerp, J; Varner, RL; Virtue, CJ; Visser, G; Wongjirad, T; Yen, Y-R; Yoo, J; Yu, C-H; Zettlemoyer, J
    We measured the cross section of coherent elastic neutrino-nucleus scattering (\cevns{}) using a CsI[Na] scintillating crystal in a high flux of neutrinos produced at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. New data collected before detector decommissioning has more than doubled the dataset since the first observation of \cevns{}, achieved with this detector. Systematic uncertainties have also been reduced with an updated quenching model, allowing for improved precision. With these analysis improvements, the COHERENT collaboration determined the cross section to be $(165^{+30}_{-25})\times10^{-40}$~cm$^2$, consistent with the standard model, giving the most precise measurement of \cevns{} yet. The timing structure of the neutrino beam has been exploited to compare the \cevns{} cross section from scattering of different neutrino flavors. This result places leading constraints on neutrino non-standard interactions while testing lepton flavor universality and measures the weak mixing angle as $\sin^2\theta_{W}=0.220^{+0.028}_{-0.026}$ at $Q^2\approx(50\text{ MeV})^2$
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    Monitoring the SNS basement neutron background with the MARS detector
    (JINST, 2021-12-05) Collaboration, COHERENT; Akimov, D; An, P; Awe, C; Barbeau, PS; Becker, B; Belov, V; Bernardi, I; Blackston, MA; Bock, C; Bolozdynya, A; Browning, J; Cabrera-Palmer, B; Chernyak, D; Conley, E; Daughhetee, J; Detwiler, J; Ding, K; Durand, MR; Efremenko, Y; Elliott, SR; Fabris, L; Febbraro, M; Rosso, A Gallo; Galindo-Uribarri, A; Green, MP; Heath, MR; Hedges, S; Hoang, D; Hughes, M; Johnson, BA; Johnson, T; Khromov, A; Konovalov, A; Kozlova, E; Kumpan, A; Li, L; Link, JM; Liu, J; Mann, K; Markoff, DM; Mastroberti, J; Mueller, PE; Newby, J; Parno, DS; Penttila, SI; Pershey, D; Rapp, R; Ray, H; Raybern, J; Razuvaeva, O; Reyna, D; Rich, GC; Ross, J; Rudik, D; Runge, J; Salvat, DJ; Salyapongse, AM; Scholberg, K; Shakirov, A; Simakov, G; Sinev, G; Snow, WM; Sosnovstsev, V; Suh, B; Tayloe, R; Tellez-Giron-Flores, K; Tolstukhin, I; Ujah, E; Vanderwerp, J; Varner, RL; Virtue, CJ; Visser, G; Wongjirad, T; Yen, Y-R; Yoo, J; Yu, C-H; Zettlemoyer, J
    We present the analysis and results of the first dataset collected with the MARS neutron detector deployed at the Oak Ridge National Laboratory Spallation Neutron Source (SNS) for the purpose of monitoring and characterizing the beam-related neutron (BRN) background for the COHERENT collaboration. MARS was positioned next to the COH-CsI coherent elastic neutrino-nucleus scattering detector in the SNS basement corridor. This is the basement location of closest proximity to the SNS target and thus, of highest neutrino flux, but it is also well shielded from the BRN flux by infill concrete and gravel. These data show the detector registered roughly one BRN per day. Using MARS' measured detection efficiency, the incoming BRN flux is estimated to be $1.20~\pm~0.56~\text{neutrons}/\text{m}^2/\text{MWh}$ for neutron energies above $\sim3.5$ MeV and up to a few tens of MeV. We compare our results with previous BRN measurements in the SNS basement corridor reported by other neutron detectors.
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    Nested dictionary learning for hierarchical organization of imagery and text
    (Uncertainty in Artificial Intelligence - Proceedings of the 28th Conference, UAI 2012, 2012-12-01) Li, L; Zhang, XX; Zhou, M; Carin, L
    A tree-based dictionary learning model is developed for joint analysis of imagery and associated text. The dictionary learning may be applied directly to the imagery from patches, or to general feature vectors extracted from patches or superpixels (using any existing method for image feature extraction). Each image is associated with a path through the tree (from root to a leaf), and each of the multiple patches in a given image is associated with one node in that path. Nodes near the tree root are shared between multiple paths, representing image characteristics that are common among different types of images. Moving toward the leaves, nodes become specialized, representing details in image classes. If available, words (text) are also jointly modeled, with a path-dependent probability over words. The tree structure is inferred via a nested Dirichlet process, and a retrospective stick-breaking sampler is used to infer the tree depth and width.
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    Numerical methods for stochastic differential equations based on Gaussian mixture
    Li, L; Lu, J; Mattingly, JC; Wang, L
    We develop in this work a numerical method for stochastic differential equations (SDEs) with weak second order accuracy based on Gaussian mixture. Unlike the conventional higher order schemes for SDEs based on It\^o-Taylor expansion and iterated It\^o integrals, the proposed scheme approximates the probability measure $\mu(X^{n+1}|X^n=x_n)$ by a mixture of Gaussians. The solution at next time step $X^{n+1}$ is then drawn from the Gaussian mixture with complexity linear in the dimension $d$. This provides a new general strategy to construct efficient high weak order numerical schemes for SDEs.
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    Quenching factor measurements of neon nuclei in neon gas
    Balogh, L; Beaufort, C; Brossard, A; Caron, J-F; Chapellier, M; Coquillat, J-M; Corcoran, EC; Crawford, S; Fard, A Dastgheibi; Deng, Y; Dering, K; Durnford, D; Garrah, C; Gerbier, G; Giomataris, I; Giroux, G; Gorel, P; Gros, M; Gros, P; Guillaudin, O; Hoppe, EW; Katsioulas, I; Kelly, F; Knights, P; Kwon, L; Langrock, S; Lautridou, P; Martin, RD; Manthos, I; Matthews, J; Mols, J-P; Muraz, J-F; Neep, T; Nikolopoulos, K; O'Brien, P; Piro, M-C; Samuleev, P; Santos, D; Savvidis, G; Savvidis, I; Fernandez, F Vazquez de Sola; Vidal, M; Ward, R; Zampaolo, M; An, P; Awe, C; Barbeau, P; Hedges, S; Li, L; Runge, J
    The NEWS-G collaboration uses Spherical Proportional Counters (SPCs) to search for weakly interacting massive particles (WIMPs). In this paper, we report the first measurements of the nuclear quenching factor in neon gas at \SI{2}{bar} using an SPC deployed in a neutron beam at the TUNL facility. The energy-dependence of the nuclear quenching factor is modelled using a simple power law: $\alpha$E$_{nr}^{\beta}$; we determine its parameters by simultaneously fitting the data collected with the detector over a range of energies. We measured the following parameters in Ne:CH$_{4}$ at \SI{2}{bar}: $\alpha$ = 0.2801 $\pm$ 0.0050 (fit) $\pm$ 0.0045 (sys) and $\beta$ = 0.0867 $\pm$ 0.020 (fit) $\pm$ 0.006(sys). Our measurements do not agree with expected values from SRIM or Lindhard theory. We demonstrated the feasibility of performing quenching factor measurements at sub-keV energies in gases using SPCs and a neutron beam.
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    Simulating the neutrino flux from the Spallation Neutron Source for the COHERENT experiment
    Collaboration, COHERENT; Akimov, D; An, P; Awe, C; Barbeau, PS; Becker, B; Belov, V; Bernardi, I; Blackston, MA; Bock, C; Bolozdynya, A; Browning, J; Cabrera-Palmer, B; Chernyak, D; Conley, E; Daughhetee, J; Detwiler, J; Ding, K; Durand, MR; Efremenko, Y; Elliott, SR; Fabris, L; Febbraro, M; Galambos, J; Rosso, A Gallo; Galindo-Uribarri, A; Green, MP; Heath, MR; Hedges, S; Hoang, D; Hughes, M; Iverson, E; Johnson, T; Khromov, A; Konovalov, A; Kozlova, E; Kumpan, A; Li, L; Link, JM; Liu, J; Mann, K; Markoff, DM; Mastroberti, J; McIntyre, M; Mueller, PE; Newby, J; Parno, DS; Penttila, SI; Pershey, D; Rapp, R; Ray, H; Raybern, J; Razuvaeva, O; Reyna, D; Rich, GC; Rimal, D; Ross, J; Rudik, D; Runge, J; Salvat, DJ; Salyapongse, AM; Scholberg, K; Shakirov, A; Simakov, G; Sinev, G; Snow, WM; Sosnovstsev, V; Suh, B; Tayloe, R; Tellez-Giron-Flores, K; Tolstukhin, I; Trotter, S; Ujah, E; Vanderwerp, J; Varner, RL; Virtue, CJ; Visser, G; Wongjirad, T; Yen, Y-R; Yoo, J; Yu, C-H; Zettlemoyer, J; Zhang, S
    The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is a pulsed source of neutrons and, as a byproduct of this operation, an intense source of pulsed neutrinos via stopped-pion decay. The COHERENT collaboration uses this source to investigate coherent elastic neutrino-nucleus scattering and other physics with a suite of detectors. This work includes a description of our Geant4 simulation of neutrino production at the SNS and the flux calculation which informs the COHERENT studies. We estimate the uncertainty of this calculation at about 10% based on validation against available low-energy pion production data.
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    Thermodynamic and dynamic contributions to future changes in regional precipitation variance: focus on the Southeastern United States
    (Climate Dynamics, 2014-07-02) Li, L; Li, W
    © 2014, Springer-Verlag Berlin Heidelberg.The frequency and severity of extreme events are tightly associated with the variance of precipitation. As climate warms, the acceleration in hydrological cycle is likely to enhance the variance of precipitation across the globe. However, due to the lack of an effective analysis method, the mechanisms responsible for the changes of precipitation variance are poorly understood, especially on regional scales. Our study fills this gap by formulating a variance partition algorithm, which explicitly quantifies the contributions of atmospheric thermodynamics (specific humidity) and dynamics (wind) to the changes in regional-scale precipitation variance. Taking Southeastern (SE) United States (US) summer precipitation as an example, the algorithm is applied to the simulations of current and future climate by phase 5 of Coupled Model Intercomparison Project (CMIP5) models. The analysis suggests that compared to observations, most CMIP5 models (~60 %) tend to underestimate the summer precipitation variance over the SE US during the 1950–1999, primarily due to the errors in the modeled dynamic processes (i.e. large-scale circulation). Among the 18 CMIP5 models analyzed in this study, six of them reasonably simulate SE US summer precipitation variance in the twentieth century and the underlying physical processes; these models are thus applied for mechanistic study of future changes in SE US summer precipitation variance. In the future, the six models collectively project an intensification of SE US summer precipitation variance, resulting from the combined effects of atmospheric thermodynamics and dynamics. Between them, the latter plays a more important role. Specifically, thermodynamics results in more frequent and intensified wet summers, but does not contribute to the projected increase in the frequency and intensity of dry summers. In contrast, atmospheric dynamics explains the projected enhancement in both wet and dry summers, indicating its importance in understanding future climate change over the SE US. The results suggest that the intensified SE US summer precipitation variance is not a purely thermodynamic response to greenhouse gases forcing, and cannot be explained without the contribution of atmospheric dynamics. Our analysis provides important insights to understand the mechanisms of SE US summer precipitation variance change. The algorithm formulated in this study can be easily applied to other regions and seasons to systematically explore the mechanisms responsible for the changes in precipitation extremes in a warming climate.