Browsing by Author "Li, J"

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Open Access
A segmented, enriched N-type germanium detector for neutrinoless double beta-decay experiments
(Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2014-01-01) Leviner, LE; Aalseth, CE; Ahmed, MW; Avignone, FT; Back, HO; Barabash, AS; Boswell, M; De Braeckeleer, L; Brudanin, VB; Chan, YD; Egorov, VG; Elliott, SR; Gehman, VM; Hossbach, TW; Kephart, JD; Kidd, MF; Konovalov, SI; Lesko, KT; Li, J; Mei, DM; Mikhailov, S; Miley, H; Radford, DC; Reeves, J; Sandukovsky, VG; Umatov, VI; Underwood, TA; Tornow, W; Wu, YK; Young, AR
We present data characterizing the performance of the first segmented, N-type Ge detector, isotopically enriched to 85% 76Ge. This detector, based on the Ortec PT6×2 design and referred to as SEGA (Segmented, Enriched Germanium Assembly), was developed as a possible prototype for neutrinoless double beta-decay measurements by the Majorana collaboration. We present some of the general characteristics (including bias potential, efficiency, leakage current, and integral cross-talk) for this detector in its temporary cryostat. We also present an analysis of the resolution of the detector, and demonstrate that for all but two segments there is at least one channel that reaches the Majorana resolution goal below 4 keV FWHM at 2039 keV, and all channels are below 4.5 keV FWHM. © 2013 Elsevier B.V.
Open Access
Asymptotic Inference about Predictive Accuracy Using High Frequency Data
(Economic Research Initiatives at Duke (ERID) Working Paper, 2013-07-06) Li, J; Patton, AJ
This paper provides a general framework that enables many existing inference methods for predictive accuracy to be used in applications that involve forecasts of latent target variables. Such applications include the forecasting of volatility, correlation, beta, quadratic variation, jump variation, and other functionals of an underlying continuous-time process. We provide primitive conditions under which a "negligibility" result holds, and thus the asymptotic size of standard predictive accuracy tests, implemented using a high-frequency proxy for the latent variable, is controlled. An extensive simulation study verifies that the asymptotic results apply in a range of empirically relevant applications, and an empirical application to correlation forecasting is presented.
Open Access
Electron beam energy spread measurements using optical klystron radiation
(Physical Review Special Topics - Accelerators and Beams, 2010-08-04) Jia, B; Li, J; Huang Scott, S; Schmidler, C; Wu, YK
In accelerators, the electron beam longitudinal dynamics critically depend on the energy distribution of the beam. Noninvasive, highly accurate measurement of the energy spread of the electron beam in the storage ring remains a challenge. Conventional techniques are limited to measuring a relatively large energy spread using the energy spread induced broadening effect of radiation source size or radiation spectrum. In this work, we report a versatile method to accurately measure the electron beam relative energy spread from 10 -4 to 10-2 using the optical klystron radiation. A novel numerical method based on the Gauss-Hermite expansion has been developed to treat both spectral broadening and modulation on an equal footing. A large dynamic range of the measurement is realized by properly configuring the optical klystron. In addition, a model-based scheme has been developed for the first time to compensate the beam-emittance-induced inhomogeneous spectral broadening effect to improve the accuracy of the energy spread measurement. Using this technique, we have successfully measured the relative energy spread of the electron beam in the Duke storage ring from 6×10-4 to 6×10-3 with an overall uncertainty of less than 5%. The optical klystron is a powerful diagnostic for highly accurate energy spread measurement for storage rings and other advanced electron accelerators. © 2010 The American Physical Society.
Open Access
Gigantic jets with negative and positive polarity streamers
(JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, 2010-07-15) Chou, JK; Kuo, CL; Tsai, LY; Chen, AB; Su, HT; Hsu, RR; Cummer, SA; Li, J; Frey, HU; Mende, SB; Takahashi, Y; Lee, LC
Open Access
Impacts of habitat loss on migratory shorebird populations and communities at stopover sites in the Yellow Sea
(Biological Conservation, 2022-05) Wang, X; Chen, Y; Melville, DS; Choi, CY; Tan, K; Liu, J; Li, J; Zhang, S; Cao, L; Ma, Z
Open Access
Interaction Between the FOXO1A-209 Genotype and Tea Drinking Is Significantly Associated with Reduced Mortality at Advanced Ages.
(Rejuvenation Res, 2016-06) Zeng, Y; Chen, H; Ni, T; Ruan, R; Nie, C; Liu, X; Feng, L; Zhang, F; Lu, J; Li, J; Li, Y; Tao, W; Gregory, SG; Gottschalk, W; Lutz, MW; Land, KC; Yashin, A; Tan, Q; Yang, Z; Bolund, L; Ming, Q; Yang, H; Min, J; Willcox, DC; Willcox, BJ; Gu, J; Hauser, E; Tian, X; Vaupel, JW
On the basis of the genotypic/phenotypic data from Chinese Longitudinal Healthy Longevity Survey (CLHLS) and Cox proportional hazard model, the present study demonstrates that interactions between carrying FOXO1A-209 genotypes and tea drinking are significantly associated with lower risk of mortality at advanced ages. Such a significant association is replicated in two independent Han Chinese CLHLS cohorts (p = 0.028-0.048 in the discovery and replication cohorts, and p = 0.003-0.016 in the combined dataset). We found the associations between tea drinking and reduced mortality are much stronger among carriers of the FOXO1A-209 genotype compared to non-carriers, and drinking tea is associated with a reversal of the negative effects of carrying FOXO1A-209 minor alleles, that is, from a substantially increased mortality risk to substantially reduced mortality risk at advanced ages. The impacts are considerably stronger among those who carry two copies of the FOXO1A minor allele than those who carry one copy. On the basis of previously reported experiments on human cell models concerning FOXO1A-by-tea-compounds interactions, we speculate that results in the present study indicate that tea drinking may inhibit FOXO1A-209 gene expression and its biological functions, which reduces the negative impacts of FOXO1A-209 gene on longevity (as reported in the literature) and offers protection against mortality risk at oldest-old ages. Our empirical findings imply that the health outcomes of particular nutritional interventions, including tea drinking, may, in part, depend upon individual genetic profiles, and the research on the effects of nutrigenomics interactions could potentially be useful for rejuvenation therapies in the clinic or associated healthy aging intervention programs.
Open Access
Jump Regressions
(Econometrica, 2017-01-01) Tauchen, GE; Li, J; Todorov, V
© 2017 The Econometric SocietyWe develop econometric tools for studying jump dependence of two processes from high-frequency observations on a fixed time interval. In this context, only segments of data around a few outlying observations are informative for the inference. We derive an asymptotically valid test for stability of a linear jump relation over regions of the jump size domain. The test has power against general forms of nonlinearity in the jump dependence as well as temporal instabilities. We further propose an efficient estimator for the linear jump regression model that is formed by optimally weighting the detected jumps with weights based on the diffusive volatility around the jump times. We derive the asymptotic limit of the estimator, a semiparametric lower efficiency bound for the linear jump regression, and show that our estimator attains the latter. The analysis covers both deterministic and random jump arrivals. In an empirical application, we use the developed inference techniques to test the temporal stability of market jump betas.
Open Access
Lightning mapping observation of a terrestrial gamma-ray flash
(Geophysical Research Letters, 2010-06-01) Lu, G; Blakeslee, RJ; Li, J; Smith, DM; Shao, XM; McCaul, EW; Buechler, DE; Christian, HJ; Hall, JM; Cummer, SA
We report the observation with the North Alabama Lightning Mapping Array (LMA) related to a terrestrial gamma-ray flash (TGF) detected by RHESSI on 26 July 2008. The LMA data explicitly show the TGF was produced during the initial development of a compact intracloud (IC) lightning flash between a negative charge region centered at about 8.5 km above sea level (-22C temperature level) a higher positive region centered at 13 km, both confined to the convective core of an isolated storm in close proximity to the RHESSI footprint. After the occurrence of an LMA source with a high peak power (26 kW), the initial lightning evolution caused an unusually large IC current moment that became detectable 2 ms after the first LMA source and increased for another 2 ms, during which the burst of gamma-rays was produced. This slowly building current moment was most likely associated with the upward leader progression, which produced an uncommonly large IC charge moment change (+90 Ckm) in 3 ms while being punctuated by a sequence of fast discharge. These observations suggest that the leader development may be involved in the TGF production. Copyright © 2010 by the American Geophysical Union.
Open Access
Loss of PRDM1/BLIMP-1 function contributes to poor prognosis of activated B-cell-like diffuse large B-cell lymphoma.
(Leukemia, 2017-03) Xia, Y; Xu-Monette, ZY; Tzankov, A; Li, X; Manyam, GC; Murty, V; Bhagat, G; Zhang, S; Pasqualucci, L; Visco, C; Dybkaer, K; Chiu, A; Orazi, A; Zu, Y; Richards, KL; Hsi, ED; Choi, WWL; van Krieken, JH; Huh, J; Ponzoni, M; Ferreri, AJM; Møller, MB; Parsons, BM; Winter, JN; Piris, MA; Westin, J; Fowler, N; Miranda, RN; Ok, CY; Li, Y; Li, J; Medeiros, LJ; Young, KH
PRDM1/BLIMP-1, a master regulator of plasma-cell differentiation, is frequently inactivated in activated B-cell-like (ABC) diffuse large B-cell lymphoma (DLBCL) patients. Little is known about its genetic aberrations and relevant clinical implications. A large series of patients with de novo DLBCL was effectively evaluated for PRDM1/BLIMP-1 deletion, mutation, and protein expression. BLIMP-1 expression was frequently associated with the ABC phenotype and plasmablastic morphologic subtype of DLBCL, yet 63% of the ABC-DLBCL patients were negative for BLIMP-1 protein expression. In these patients, loss of BLIMP-1 was associated with Myc overexpression and decreased expression of p53 pathway molecules. In addition, homozygous PRDM1 deletions and PRDM1 mutations within exons 1 and 2, which encode for domains crucial for transcriptional repression, were found to show a poor prognostic impact in patients with ABC-DLBCL but not in those with germinal center B-cell-like DLBCL (GCB-DLBCL). Gene expression profiling revealed that loss of PRDM1/BLIMP-1 expression correlated with a decreased plasma-cell differentiation signature and upregulation of genes involved in B-cell receptor signaling and tumor-cell proliferation. In conclusion, these results provide novel clinical and biological insight into the tumor-suppressive role of PRDM1/BLIMP-1 in ABC-DLBCL patients and suggest that loss of PRDM1/BLIMP-1 function contributes to the overall poor prognosis of ABC-DLBCL patients.
Open Access
Multi-instrumental observations of a positive gigantic jet produced by a winter thunderstorm in Europe
(Journal of Geophysical Research Atmospheres, 2010-01-01) Van Der Velde, OA; Bór, J; Li, J; Cummer, SA; Arnone, E; Zanotti, F; Füllekrug, M; Haldoupis, C; Naitamor, S; Farges, T
At 2336:56 UTC on 12 December 2009, a bright gigantic jet (GJ) was recorded by an observer in Italy. Forty-nine additional sprites, elves, halos and two cases of upward lightning were observed that night. The location of the GJ corresponded to a distinct cloud top (-34°C) west of Ajaccio, Corsica. The GJ reached approximately 91 km altitude, with a "trailing jet" reaching 49-59 km, matching with earlier reported GJs. The duration was short at 120-160 ms. This is the first documented GJ which emerged from a maritime winter thunderstorm only 6.5 km tall, showing high cloud tops are not required for initiation of GJs. In the presence of strong vertical wind shear, the meteorological situation was different from typical outbreaks of fall and winter thunderstorms in the Mediterranean. During the trailing jet phase of the GJ, a sprite with halo triggered by a nearby cloud-to-ground lightning flash occurred at a relatively low altitude (<72 km). At the same time, the trailing jet and beads were reilluminated. Electromagnetic waveforms from Hungary, Poland, and the USA revealed this GJ is the first reported to transfer negative charge (approximately 136 C) from the ionosphere to the positively charged origins in the cloud (i.e., a positive cloud-to-ionosphere discharge, +CI), with a large total charge moment change of 11600 C km and a maximum current of 3.3 kA. Early VLF transmitter amplitude perturbations detected concurrently with the GJ confirm the production of large conductivity changes due to electron density enhancements in the D-region of the ionosphere. Copyright 2010 by the American Geophysical Union.
Open Access
Parity assignments in 172,174Yb using polarized photons and the K quantum number in rare earth nuclei
(Physical Review C - Nuclear Physics, 2005-03-01) Savran, D; Muller, S; Zilges, A; Babilon, M; Ahmed, MW; Kelley, JH; Tonchev, A; Tornow, kW; Weller, HR; Pietralla, N; Li, J; Pinayev, IV; Wu, YK
The 100% polarized photon beam at the high intensity γ ray source (HIγS) at Duke University has been used to determine the parity of six dipole excitations between 2.9 and 3.6 MeV in the deformed nuclei 172,174Yb in photon scattering (γ →, γ′) experiments. The measured parities are compared with previous assignments based on the K quantum number that had been assigned in nuclear resonance fluorescence (NRF) experiments by using the Alaga rules. A systematic survey of the relation between γ-decay branching ratios and parity quantum numbers is given for the rare earth nuclei. © 2005 The American Physical Society.
Open Access
Realized Semicovariances: Looking for Signs of Direction Inside the Covariance Matrix
(Economic Research Initiatives at Duke (ERID) Working Paper, 2017-09-05) Bollerslev, T; Li, J; Patton, AJ; Quaedvlieg, R
Open Access
Variable and threshold selection to control predictive accuracy in logistic regression
(Journal of the Royal Statistical Society. Series C: Applied Statistics, 2014-01-01) Kuk, AYC; Li, J; John Rush, A
Summary: Using data collected from the 'Sequenced treatment alternatives to relieve depression' study, we use logistic regression to predict whether a patient will respond to treatment on the basis of early symptom change and patient characteristics. Model selection criteria such as the Akaike information criterion AIC and mean-squared-error of prediction MSEP may not be appropriate if the aim is to predict with a high degree of certainty who will respond or not respond to treatment. Towards this aim, we generalize the definition of the positive and negative predictive value curves to the case of multiple predictors. We point out that it is the ordering rather than the precise values of the response probabilities which is important, and we arrive at a unified approach to model selection via two-sample rank tests. To avoid overfitting, we define a cross-validated version of the positive and negative predictive value curves and compare these curves after smoothing for various models. When applied to the study data, we obtain a ranking of models that differs from those based on AIC and MSEP, as well as a tree-based method and regularized logistic regression using a lasso penalty. Our selected model performs consistently well for both 4-week-ahead and 7-week-ahead predictions. © 2014 Royal Statistical Society.