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Search Results: 1 - 10 of 325225 matches for " S. Westerdale "
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A Radon Progeny Deposition Model
V. E. Guiseppe,S. R. Elliott,A. Hime,K. Rielage,S. Westerdale
Physics , 2010, DOI: 10.1063/1.3579565
Abstract: The next generation low-background detectors operating underground aim for unprecedented low levels of radioactive backgrounds. Although the radioactive decays of airborne radon (particularly Rn-222) and its subsequent progeny present in an experiment are potential backgrounds, also problematic is the deposition of radon progeny on detector materials. Exposure to radon at any stage of assembly of an experiment can result in surface contamination by progeny supported by the long half life (22 y) of Pb-210 on sensitive locations of a detector. An understanding of the potential surface contamination from deposition will enable requirements of radon-reduced air and clean room environments for the assembly of low background experiments. It is known that there are a number of environmental factors that govern the deposition of progeny onto surfaces. However, existing models have not explored the impact of some environmental factors important for low background experiments. A test stand has been constructed to deposit radon progeny on various surfaces under a controlled environment in order to develop a deposition model. Results from this test stand and the resulting deposition model are presented.
Impact of pericardial adhesions on diastolic function as assessed by vortex formation time, a parameter of transmitral flow efficiency
Panupong Jiamsripong, Mohsen S Alharthi, Anna M Calleja, Eileen M McMahon, Minako Katayama, John Westerdale, Michele Milano, Jeffrey J Heys, Farouk Mookadam, Marek Belohlavek
Cardiovascular Ultrasound , 2010, DOI: 10.1186/1476-7120-8-42
Abstract: In 8 open-chest pigs, the heart was exposed while preserving the pericardium. We experimentally simulated early pericardial constriction and patchy adhesions by instilling instant glue into the pericardial space and using pericardial-epicardial stitches. We studied left ventricular (LV) function and characterized intraventricular blood flow with conventional and Doppler echocardiography at baseline and following the experimental intervention.Significant decreases in end-diastolic volume, ejection fraction, stroke volume, and late diastolic filling velocity reflected the effects of the pericardial adhesions. The mean VFT value decreased from 3.61 ± 0.47 to 2.26 ± 0.45 (P = 0.0002). Hemodynamic variables indicated the inhibiting effect of pericardial adhesion on both contraction (decrease in systolic blood pressure and +dP/dt decreased) and relaxation (decrease in the magnitude of -dP/dt and prolongation of Tau) function.Patchy pericardial adhesions not only negatively impact LV mechanical functioning but the decrease of VFT from normal to suboptimal value suggests impairment of transmitral flow efficiency.Left ventricular (LV) diastolic filling and its alterations are important indicators of overall cardiac health status [1-4] and contribute to early diagnosis of cardiovascular disease [1,5]. We have shown by echocardiographic particle imaging velocimetry [6], and other investigators have demonstrated by magnetic resonance imaging [7], that transmitral flow can produce an intraventricular rotational body of fluid referred to as a vortex ring [8-10]. This vortex supports more efficient fluid transport as compared to a straight jet alone [11,12]. Gharib et al. [13] derived a dimensionless index that quantitatively characterizes optimal fluid dynamic conditions for vortex formation from the duration of flow through an orifice with known diameter and, thus, referred to the index as vortex formation time (VFT). VFT measurement, when applied to diastolic filling, suggests
A Prototype Neutron Veto for Dark Matter Detectors
Shawn Westerdale,Emily Shields,Frank Calaprice
Physics , 2015,
Abstract: Neutrons are a particularly dangerous background for direct WIMP dark matter searches; their nuclear recoils with the target nucleus are often indistinguishable from nuclear recoils produced by WIMP-nuclear collisions. In this study, we explore the concept of a liquid scintillator neutron veto detector that would allow direct dark matter detectors to potentially reject neutrons with greater than 99% efficiency. Here we outline the construction and testing of a small prototype detector and the potential implications of this technology for future dark matter detectors.
Measurement of Scintillation and Ionization Yield and Scintillation Pulse Shape from Nuclear Recoils in Liquid Argon
H. Cao,T. Alexander,A. Aprahamian,R. Avetisyan,H. O. Back,A. G. Cocco,F. DeJongh,G. Fiorillo,C. Galbiati,L. Grandi,Y. Guardincerri,C. Kendziora,W. H. Lippincott,C. Love,S. Lyons,L. Manenti,C. J. Martoff,Y. Meng,D. Montanari,P. Mosteiro,D. Olvitt,S. Pordes,H. Qian,B. Rossi,R. Saldanha,S. Sangiorgio,K. Siegl,S. Y. Strauss,W. Tan,J. Tatarowicz,S. Walker,H. Wang,A. W. Watson,S. Westerdale,J. Yoo
Physics , 2014, DOI: 10.1103/PhysRevD.91.092007
Abstract: We have measured the scintillation and ionization yield of recoiling nuclei in liquid argon as a function of applied electric field by exposing a dual-phase liquid argon time projection chamber (LAr-TPC) to a low energy pulsed narrow band neutron beam produced at the Notre Dame Institute for Structure and Nuclear Astrophysics. Liquid scintillation counters were arranged to detect and identify neutrons scattered in the TPC and to select the energy of the recoiling nuclei. We report measurements of the scintillation yields for nuclear recoils with energies from 10.3 to 57.3 keV and for median applied electric fields from 0 to 970 V/cm. For the ionization yields, we report measurements from 16.9 to 57.3 keV and for electric fields from 96.4 to 486 V/cm. We also report the observation of an anticorrelation between scintillation and ionization from nuclear recoils, which is similar to the anticorrelation between scintillation and ionization from electron recoils. Assuming that the energy loss partitions into excitons and ion pairs from $^{83m}$Kr internal conversion electrons is comparable to that from $^{207}$Bi conversion electrons, we obtained the numbers of excitons ($N_{ex}$) and ion pairs ($N_i$) and their ratio ($N_{ex}/N_i$) produced by nuclear recoils from 16.9 to 57.3 keV. Motivated by arguments suggesting direction sensitivity in LAr-TPC signals due to columnar recombination, a comparison of the light and charge yield of recoils parallel and perpendicular to the applied electric field is presented for the first time.
Weighted Least-Squares Finite Element Method for Cardiac Blood Flow Simulation with Echocardiographic Data
Fei Wei,John Westerdale,Eileen M. McMahon,Marek Belohlavek,Jeffrey J. Heys
Computational and Mathematical Methods in Medicine , 2012, DOI: 10.1155/2012/371315
Abstract: As both fluid flow measurement techniques and computer simulation methods continue to improve, there is a growing need for numerical simulation approaches that can assimilate experimental data into the simulation in a flexible and mathematically consistent manner. The problem of interest here is the simulation of blood flow in the left ventricle with the assimilation of experimental data provided by ultrasound imaging of microbubbles in the blood. The weighted least-squares finite element method is used because it allows data to be assimilated in a very flexible manner so that accurate measurements are more closely matched with the numerical solution than less accurate data. This approach is applied to two different test problems: a flexible flap that is displaced by a jet of fluid and blood flow in the porcine left ventricle. By adjusting how closely the simulation matches the experimental data, one can observe potential inaccuracies in the model because the simulation without experimental data differs significantly from the simulation with the data. Additionally, the assimilation of experimental data can help the simulation capture certain small effects that are present in the experiment, but not modeled directly in the simulation.
Observation of the Dependence of Scintillation from Nuclear Recoils in Liquid Argon on Drift Field
T. Alexander,H. O. Back,H. Cao,A. G. Cocco,F. DeJongh,G. Fiorillo,C. Galbiati,C. Ghag,L. Grandi,C. Kendziora,W. H. Lippincott,B. Loer,C. Love,L. Manenti,C. J. Martoff,Y. Meng,D. Montanari,P. Mosteiro,D. Olvitt,S. Pordes,H. Qian,B. Rossi,R. Saldanha,W. Tan,J. Tatarowicz,S. Walker,H. Wang,A. W. Watson,S. Westerdale,J. Yoo
Physics , 2013, DOI: 10.1103/PhysRevD.88.092006
Abstract: We have exposed a dual-phase Liquid Argon Time Projection Chamber (LAr-TPC) to a low energy pulsed narrowband neutron beam, produced at the Notre Dame Institute for Structure and Nuclear Astrophysics to study the scintillation light yield of recoiling nuclei in a LAr-TPC. A liquid scintillation counter was arranged to detect and identify neutrons scattered in the LAr-TPC target and to select the energy of the recoiling nuclei. We report the observation of a significant dependence on drift field of liquid argon scintillation from nuclear recoils of 11 keV. This observation is important because, to date, estimates of the sensitivity of noble liquid TPC dark matter searches are based on the assumption that electric field has only a small effect on the light yield from nuclear recoils.
Light Yield in DarkSide-10: a Prototype Two-phase Liquid Argon TPC for Dark Matter Searches
T. Alexander,D. Alton,K. Arisaka,H. O. Back,P. Beltrame,J. Benziger,G. Bonfini,A. Brigatti,J. Brodsky,L. Cadonati,F. Calaprice,A. Candela,H. Cao,P. Cavalcante,A. Chavarria,A. Chepurnov,D. Cline,A. G. Cocco,C. Condon,D. D'Angelo,S. Davini,E. De Haas,A. Derbin,G. Di Pietro,I. Dratchnev,D. Durben,A. Empl,A. Etenko,A. Fan,G. Fiorillo,K. Fomenko,F. Gabriele,C. Galbiati,S. Gazzana,C. Ghag,C. Ghiano,A. Goretti,L. Grandi,M. Gromov,M. Guan,C. Guo,G. Guray,E. V. Hungerford,Al. Ianni,An. Ianni,A. Kayunov,K. Keeter,C. Kendziora,S. Kidner,V. Kobychev,G. Koh,D. Korablev,G. Korga,E. Shields,P. Li,B. Loer,P. Lombardi,C. Love,L. Ludhova,L. Lukyanchenko,A. Lund,K. Lung,Y. Ma,I. Machulin,J. Maricic,C. J. Martoff,Y. Meng,E. Meroni,P. D. Meyers,T. Mohayai,D. Montanari,M. Montuschi,P. Mosteiro,B. Mount,V. Muratova,A. Nelson,A. Nemtzow,N. Nurakhov,M. Orsini,F. Ortica,M. Pallavicini,E. Pantic,S. Parmeggiano,R. Parsells,N. Pelliccia,L. Perasso,F. Perfetto,L. Pinsky,A. Pocar,S. Pordes,G. Ranucci,A. Razeto,A. Romani,N. Rossi,P. Saggese,R. Saldanha,C. Salvo,W. Sands,M. Seigar,D. Semenov,M. Skorokhvatov,O. Smirnov,A. Sotnikov,S. Sukhotin,Y. Suvorov,R. Tartaglia,J. Tatarowicz,G. Testera,A. Teymourian,J. Thompson,E. Unzhakov,R. B. Vogelaar,H. Wang,S. Westerdale,M. Wojcik,A. Wright,J. Xu,C. Yang,S. Zavatarelli,M. Zehfus,W. Zhong,G. Zuzel
Physics , 2012, DOI: 10.1016/j.astropartphys.2013.08.004
Abstract: As part of the DarkSide program of direct dark matter searches using liquid argon TPCs, a prototype detector with an active volume containing 10 kg of liquid argon, DarkSide-10, was built and operated underground in the Gran Sasso National Laboratory in Italy. A critically important parameter for such devices is the scintillation light yield, as photon statistics limits the rejection of electron-recoil backgrounds by pulse shape discrimination. We have measured the light yield of DarkSide-10 using the readily-identifiable full-absorption peaks from gamma ray sources combined with single-photoelectron calibrations using low-occupancy laser pulses. For gamma lines of energies in the range 122-1275 keV, we get consistent light yields averaging 8.887+-0.003(stat)+-0.444(sys) p.e./keVee. With additional purification, the light yield measured at 511 keV increased to 9.142+-0.006(stat) p.e./keVee.
Scintillation efficiency measurement of Na recoils in NaI(Tl) below the DAMA/LIBRA energy threshold
Jingke Xu,Emily Shields,Frank Calaprice,Shawn Westerdale,Francis Froborg,Burkhant Suerfu,Thomas Alexander,Ani Aprahamian,Henning O. Back,Clark Casarella,Xiao Fang,Yogesh K. Gupta,Aldo Ianni,Edward Lamere,W. Hugh Lippincott,Qian Liu,Stephanie Lyons,Kevin Siegl,Mallory Smith,Wanpeng Tan,Bryant Vande Kolk
Physics , 2015, DOI: 10.1103/PhysRevC.92.015807
Abstract: The dark matter interpretation of the DAMA modulation signal depends on the NaI(Tl) scintillation efficiency of nuclear recoils. Previous measurements for Na recoils have large discrepancies, especially in the DAMA/LIBRA modulation energy region. We report a quenching effect measurement of Na recoils in NaI(Tl) from 3keV$_{\text{nr}}$ to 52keV$_{\text{nr}}$, covering the whole DAMA/LIBRA energy region for light WIMP interpretations. By using a low-energy, pulsed neutron beam, a double time-of-flight technique, and pulse-shape discrimination methods, we obtained the most accurate measurement of this kind for NaI(Tl) to date. The results differ significantly from the DAMA reported values at low energies, but fall between the other previous measurements. We present the implications of the new quenching results for the dark matter interpretation of the DAMA modulation signal.
Study of the Structural and Electrical Properties of Cr-Doped BiFeO3 Ceramic  [PDF]
S. S. Arafat, S. Ibrahim
Materials Sciences and Applications (MSA) , 2017, DOI: 10.4236/msa.2017.810051
Abstract: Multiferroic BiFe1-xCrxO3 (x = 0.2 and 0.4) ceramics were synthesized in a single phase. The effects of Cr3+ substitution on the crystal structure, dielectric permittivity and leakage current were investigated. Preliminary X-ray structural studies revealed that the samples had a rhombohedral perovskite crystal structure. The dielectric constant ε' significantly increased while the dielectric loss tanδ was substantially decreased with the increase in Cr3+ substitution. The temperature effect on the dielectric properties exhibited an anomaly corresponding to magneto-electric coupling in the samples and was shifted to lower temperatures with the increase in Cr3+ substitution. The leakage current density also reduced in magnitude with the increase in the Cr3+ substitution.
Degree Splitting of Root Square Mean Graphs  [PDF]
S. S. Sandhya, S. Somasundaram, S. Anusa
Applied Mathematics (AM) , 2015, DOI: 10.4236/am.2015.66086
Abstract: Let \"\" be an injective function. For a vertex labeling f, the induced edge labeling \"\" is defined by, \"\" or \"\"; then, the edge labels are distinct and are from \"\". Then f is called a root square mean labeling of G. In this paper, we prove root square mean labeling of some degree splitting graphs.
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