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2009

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Articles 1 - 30 of 4379

Full-Text Articles in Physical Sciences and Mathematics

Electrical Impedance Imaging Of Corrosion On A Partially Accessible 2-Dimensional Region, Court Hoang, Katherine Osenbach Dec 2009

Electrical Impedance Imaging Of Corrosion On A Partially Accessible 2-Dimensional Region, Court Hoang, Katherine Osenbach

Mathematical Sciences Technical Reports (MSTR)

In this paper we examine the inverse problem of determining the amount of corrosion on an inaccessible surface of a two-dimensional region. Using numerical methods, we develop an algorithm for approximating corrosion profile using measurements of electrical potential along the accessible portion of the region. We also evaluate the effect of error on the problem, address the issue of ill-posedness, and develop a method of regularization to correct for this error. An examination of solution uniqueness is also presented.


Anti-Cloaking: The Mathematics Of Disguise, Theresa C. Anderson, Brooke E. Phillips Dec 2009

Anti-Cloaking: The Mathematics Of Disguise, Theresa C. Anderson, Brooke E. Phillips

Mathematical Sciences Technical Reports (MSTR)

Recent developments in cloaking, the ability to selectively bend electromagnetic waves so as to render an object invisible, have been abundant. Based on cloaking principles, we will describe several ways to mathematically disguise objects in the context of electrical impedance imaging. Through the use of a change-of-variables scheme we show how one can make an object appear enlarged, translated, or rotated by surrounding it with a suitable "metamaterial," a man-made material that selectively redirects current. Analysis of eigenvectors and eigenvalues, which describe how current flows, follow. We prove that in order to disguise an object, a metamaterial must encompass both …


Nevada Interagency Volunteer Program: Helping Hands Across Public Lands – Phase Ii: Quarterly Progress Report, Period Covering October 1, 2009 To December 31, 2009, Margaret N. Rees Dec 2009

Nevada Interagency Volunteer Program: Helping Hands Across Public Lands – Phase Ii: Quarterly Progress Report, Period Covering October 1, 2009 To December 31, 2009, Margaret N. Rees

Get Outdoors Nevada

  • The number of records in the volunteer database decreased by 14% over last quarter. The database now contains 5,996 records.
  • Website activity increased, recording an average of 121,918 hits per month, an increase of 8% from last quarter, with an average of 9,686 pages viewed per month.
  • Volunteer fall training has been completed.
  • One hundred and twenty-seven people attended the Volunteer Recognition Event.


Lake Mead National Recreation Area Monitoring And Evaluation Of Sensitive Wildlife: Quarterly Progress Report, Period Ending December 31, 2009, Margaret N. Rees Dec 2009

Lake Mead National Recreation Area Monitoring And Evaluation Of Sensitive Wildlife: Quarterly Progress Report, Period Ending December 31, 2009, Margaret N. Rees

Wildlife Monitoring

Project 1. Relict Leopard Frog Monitoring, Management, and Research

  • All milestones and deliverables are on schedule
  • Fall surveys at all sites have been completed
  • Mark-recapture surveys scheduled for fall were completed
  • Short-term habitat improvements at two sites were conducted
  • RLFCT meeting was hosted
  • Draft annual report was written and presented at the RLFCT meeting

Project 2. Bald Eagle Winter Monitoring and Evaluation

  • All milestones and deliverables are on schedule
  • An annual project review presentation was given to Clark County
  • A draft final report was written and submitted to Clark County
  • All data for this project was transferred to the County …


Joint Fire Science Program – Lake Mead National Recreation Area Revegetating Burned Arid Lands: Identifying Successful Native Species Using Trait And Competition Analysis: Quarterly Progress Report, Time Period: October 1 — December 31, 2009, Margaret N. Rees Dec 2009

Joint Fire Science Program – Lake Mead National Recreation Area Revegetating Burned Arid Lands: Identifying Successful Native Species Using Trait And Competition Analysis: Quarterly Progress Report, Time Period: October 1 — December 31, 2009, Margaret N. Rees

Fire Science

• Article accepted for publication in Journal of Arid Environments.

• Recharged irrigation gel packs for outplanting and watered seed plots at Goodsprings site.

• Completed full year of seed granivory trials at Goodsprings site.

• Presented information on this Task Agreement to 4th International Fire Ecology and Management Congress.

• Maintained nursery plots and added installment of nitrogen treatment.


Retired A Stars And Their Companions. Iii. Comparing The Mass–Period Distributions Of Planets Around A-Type Stars And Sun-Like Stars, Brendan P. Bowler, John Asher Johnson, Geoffrey W. Marcy, Gregory W. Henry, Kathryn M. G. Peek, Debra A. Fischer, Kelsey I. Clubb, Michael C. Liu, Sabine Reffert, Christian Schwab, Thomas B. Lowe Dec 2009

Retired A Stars And Their Companions. Iii. Comparing The Mass–Period Distributions Of Planets Around A-Type Stars And Sun-Like Stars, Brendan P. Bowler, John Asher Johnson, Geoffrey W. Marcy, Gregory W. Henry, Kathryn M. G. Peek, Debra A. Fischer, Kelsey I. Clubb, Michael C. Liu, Sabine Reffert, Christian Schwab, Thomas B. Lowe

Information Systems and Engineering Management Research Publications

We present an analysis of ∼5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass (IM) subgiants (1.5 ≲ M*/M☉≲ 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type stars and comparing the distributions of their orbital and physical characteristics to those of planets around Sun-like stars. We provide updated orbital solutions incorporating new radial velocity measurements for five known planet-hosting stars in our sample; uncertainties in the fitted parameters are assessed using a Markov-Chain Monte Carlo method. The frequency of Jovian planets interior to 3 AU is 26+9−8%, …


Solutions Of A System Of Integral Equations In Orlicz Spaces, Ravi P. Agarwal, Donal O'Regan, Patricia J.Y. Wong Dec 2009

Solutions Of A System Of Integral Equations In Orlicz Spaces, Ravi P. Agarwal, Donal O'Regan, Patricia J.Y. Wong

Mathematics and System Engineering Faculty Publications

We consider the following system of integral equations Ui(t) = ∫1gi(t,s)fi(s,u1(s),u2(s),...,un(s))ds, a.e. t [0,1], 1 ≤ i ≤ n. Our aim is to establish criteria such that the above system has a solution (u±,U2,... ,un) where uiLφ (Orlicz space), 1 < i < n. We further investigate the system Ui(t) = ∫1gi(t,s)fi(s,u1(s),u2(s),...,un(s))ds, a.e. t [0,1], 1 ≤ i ≤ n. and establish the existence of constant-sign solutions in Orlicz spaces, i.e., for each 1 ≤ i ≤ n, Oui > 0 and ui G L


Detection Of Psilocybin Mushroom Analogs In Chocolate: Incorporating Current Events Into The Undergraduate Teaching Laboratory, Brandon Huskins, Christopher Dockery Dec 2009

Detection Of Psilocybin Mushroom Analogs In Chocolate: Incorporating Current Events Into The Undergraduate Teaching Laboratory, Brandon Huskins, Christopher Dockery

Faculty and Research Publications

In this experiment, tryptamine is used as a psilocin analog and is dispersed onto a Fisher brand cellulose laboratory sponge to simulate dehydrated mushrooms. The resulting “mushroom” material is ground, molded into chocolate, and presented to student groups for real-world and applied analyses. Students isolate the tryptamine from the chocolate using their knowledge of drug chemistry, solubility, pH, extractions, etc. Qualitative analysis is conducted by comparison to standards (Thin Layer Chromatography or Gas Chromatography) and quantitative analysis is conducted by Gas Chromatography using the method of internal standards.


Partial Wave Analysis Of The Reaction Γp And The Search For Nucleon Resonances, M. Williams, Gerard P. Gilfoyle, Et. Al. Dec 2009

Partial Wave Analysis Of The Reaction Γp→Pω And The Search For Nucleon Resonances, M. Williams, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

An event-based partial wave analysis (PWA) of the reaction γp has been performed on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world’s first high-precision spin-density matrix element measurements, available to the event-based PWA through the decay distribution of ωπ +π π0. The data confirm the dominance of the t-channel π0 exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F15(1680) and …


Differential Cross Sections And Spin Density Matrix Elements For The Reaction Γp, M. Williams, Gerard P. Gilfoyle, Et. Al. Dec 2009

Differential Cross Sections And Spin Density Matrix Elements For The Reaction Γp→Pω, M. Williams, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

High-statistics differential cross sections and spin-density matrix elements for the reaction γp have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass (c.m.) energies from threshold up to 2.84 GeV. Results are reported in 112 10-MeV wide c.m. energy bins, each subdivided into cos θωc.m. bins of width 0.1. These are the most precise and extensive ω photoproduction measurements to date. A number of prominent structures are clearly present in the data. Many of these have not previously been observed due to limited statistics in earlier measurements.


Highly Nitrated Cyclopropanes As New High Energy Materials: Dft Calculations On The Properties Of C3H6−N(No2)N (N=3–6), Aloysus K. Lawong, David W. Ball Dec 2009

Highly Nitrated Cyclopropanes As New High Energy Materials: Dft Calculations On The Properties Of C3H6−N(No2)N (N=3–6), Aloysus K. Lawong, David W. Ball

Chemistry Faculty Publications

As part of a continuing study of new potential high energy materials, here we present results of calculations on cyclopropane molecules with three or more nitro groups. DFT calculations suggest that all molecules can exist as minimum-energy stationary states. Energy calculations indicate that some nitrocyclopropanes have a specific enthalpy of decomposition in excess of 8kJg−1, suggesting that they be explored as new potential high energy materials.


A High-Yield Synthesis Of Chalcopyrite Cuins2 Nanoparticles With Exceptional Size Control, Aaron Thurber, Alex Punnoose Dec 2009

A High-Yield Synthesis Of Chalcopyrite Cuins2 Nanoparticles With Exceptional Size Control, Aaron Thurber, Alex Punnoose

Physics Faculty Publications and Presentations

We report high-yield and efficient size-controlled syntheses of Chalcopyrite CuInS2 nanoparticles by decomposing molecular single source precursors (SSPs) via microwave irradiation in the presence of 1,2-ethanedithiol at reaction temperatures as low as 100◦C and times as short as 30 minutes. The nanoparticles sizes were 1.8nm to 10.8 nm as reaction temperatures were varied from 100◦C to 200◦C with the bandgaps from 2.71 eV to 1.28 eV with good size control and high yields (64%–95%). The resulting nanoparticles were analyzed by XRD, UV-Vis, ICP-OES, XPS, SEM, EDS, and HRTEM. Titration studies by 1H NMR using SSP 1 with 1,2-ethanedithiol …


Indirect Gravimetric Determination Of Waters Of Hydration, Marina C. Koether Dec 2009

Indirect Gravimetric Determination Of Waters Of Hydration, Marina C. Koether

Faculty and Research Publications

An alternate gravimetric experiment is described that can be employed in the general chemistry or the quantitative analysis laboratory course. The procedure takes less time than conventional methods and introduces students to waters of hydration and indirect determinations.


Double Superhelix Model Of High Density Lipoprotein, Zhiping Wu, Valentin Gogonea, Xavier Lee, Mathew A. Wagner Dec 2009

Double Superhelix Model Of High Density Lipoprotein, Zhiping Wu, Valentin Gogonea, Xavier Lee, Mathew A. Wagner

Chemistry Faculty Publications

High density lipoprotein (HDL), the carrier of so-called “good” cholesterol, serves as the major athero-protective lipoprotein and has emerged as a key therapeutic target for cardiovascular disease. We applied small angle neutron scattering (SANS) with contrast variation and selective isotopic deuteration to the study of nascent HDL to obtain the low resolution structure in solution of the overall time-averaged conformation of apolipoprotein AI (apoA-I) versus the lipid (acyl chain) core of the particle. Remarkably, apoA-I is observed to possess an open helical shape that wraps around a central ellipsoidal lipid phase. Using the low resolution SANS shapes of the protein …


Classical Modeling Of Non-Sequential Double Ionization: Recollision, Time-Delayed Ionization, Drift, And Possible Reattachment, Stanley L. Haan, Z. S. Smith, K. N. Shomsky, P. W. Plantinga Dec 2009

Classical Modeling Of Non-Sequential Double Ionization: Recollision, Time-Delayed Ionization, Drift, And Possible Reattachment, Stanley L. Haan, Z. S. Smith, K. N. Shomsky, P. W. Plantinga

University Faculty Publications and Creative Works

We employ 3d classical ensembles to study Non-Sequential Double Ionization (NSDI) of atoms by strong laser fields at visible and infrared wavelengths. We consider in particular the wavelength dependence of final electron drift directions and the net momentum spectra parallel to the laser polarization. We find that as the wavelength is increased the spectrum transitions from a singlet to a doublet, then to a triplet, and finally back to a doublet. We also show that electrons that escape the central potential-energy well during the pulse may nonetheless be bound to the nucleus after laser turnoff.


Photoassociation Spectroscopy Of Purely Long-Range Krypton Molecules, Z. Smith, J. Banister, R. Norman, K. Hoogeboom Dec 2009

Photoassociation Spectroscopy Of Purely Long-Range Krypton Molecules, Z. Smith, J. Banister, R. Norman, K. Hoogeboom

University Faculty Publications and Creative Works

Photoassociation spectra for purely long-range (PLR) krypton molecules are both computed and measured. The photoassociation laser is tuned just red of the 5s[3/2]2-5p[5/2]2 transition at 810.6 nm, over a frequency range in which fourteen different PLR potential wells support hundreds of vibrational bound states. In the experiment, laser light is directed into a cloud of magneto-optically trapped 84Kr atoms, and the emission of both ultraviolet photons and ions is monitored. Peaks in these signals are observed for laser frequencies within 200 MHz of the atomic resonance. Ongoing work is aimed at improving the experimental signal and understanding the degree of …


Photoassociation Spectroscopy Of Purely Long-Range Krypton Molecules, Z. Smith, J. Banister, R. Norman, K. Hoogeboom Dec 2009

Photoassociation Spectroscopy Of Purely Long-Range Krypton Molecules, Z. Smith, J. Banister, R. Norman, K. Hoogeboom

University Faculty Publications and Creative Works

Photoassociation spectra for purely long-range (PLR) krypton molecules are both computed and measured. The photoassociation laser is tuned just red of the 5s[3/2]2-5p[5/2]2 transition at 810.6 nm, over a frequency range in which fourteen different PLR potential wells support hundreds of vibrational bound states. In the experiment, laser light is directed into a cloud of magneto-optically trapped 84Kr atoms, and the emission of both ultraviolet photons and ions is monitored. Peaks in these signals are observed for laser frequencies within 200 MHz of the atomic resonance. Ongoing work is aimed at improving the experimental signal and understanding the degree of …


A Super-Earth And Two Neptunes Orbiting The Nearby Sun-Like Star 61 Virginis, Steve Vogt, Robert A. Wittenmyer, R. Paul Butler, Simon O'Toole, Gregory W. Henry, Eugenio J. Rivera, Stefano Meschiari, Gregory Laughlin, Chris G. Tinney, Hugh R. A. Jones, Jeremy Bailey, Brad D. Carter, Konstantin Batygin Dec 2009

A Super-Earth And Two Neptunes Orbiting The Nearby Sun-Like Star 61 Virginis, Steve Vogt, Robert A. Wittenmyer, R. Paul Butler, Simon O'Toole, Gregory W. Henry, Eugenio J. Rivera, Stefano Meschiari, Gregory Laughlin, Chris G. Tinney, Hugh R. A. Jones, Jeremy Bailey, Brad D. Carter, Konstantin Batygin

Information Systems and Engineering Management Research Publications

We present precision radial velocity data that reveal a multiple exoplanet system orbiting the bright nearby G5V star 61 Virginis. Our 4.6 years of combined Keck/HIRES and Anglo-Australian Telescope precision radial velocities indicate the hitherto unknown presence of at least three planets orbiting this well-studied star. These planets are all on low-eccentricity orbits with periods of 4.2, 38.0, and 124.0 days, and projected masses (Msin i) of 5.1, 18.2, and 24.0 M⊕, respectively. Test integrations of systems consistent with the radial velocity data suggest that the configuration is dynamically stable. Depending on the effectiveness of tidal dissipation within the inner …


A Super-Earth Orbiting The Nearby Sun-Like Star Hd 1461, Eugenio J. Rivera, R. Paul Butler, Steve Vogt, Gregory Laughlin, Gregory W. Henry, Stefano Meschiari Dec 2009

A Super-Earth Orbiting The Nearby Sun-Like Star Hd 1461, Eugenio J. Rivera, R. Paul Butler, Steve Vogt, Gregory Laughlin, Gregory W. Henry, Stefano Meschiari

Information Systems and Engineering Management Research Publications

We present precision radial velocity (RV) data that reveal a Super-Earth mass planet and two probable additional planets orbiting the bright nearby G0V star HD 1461. Our 12.8 years of Keck High Resolution Echelle Spectrometer precision RVs indicate the presence of a 7.4 M⊕ planet on a 5.77 day orbit. The data also suggest, but cannot yet confirm, the presence of outer planets on low-eccentricity orbits with periods of 446.1 and 5017 days, and projected masses (Msin i) of 27.9 and 87.1 M⊕, respectively. Test integrations of systems consistent with the RV data suggest that the configuration is dynamically stable. …


Modeling Residential Foreclosures In Kent County, Kaitlyn Ratkowiak Dec 2009

Modeling Residential Foreclosures In Kent County, Kaitlyn Ratkowiak

Student Summer Scholars Manuscripts

Residential Foreclosures in Kent County have become commonplace in the past few years. In this project, we hope to analyze data on foreclosures since 2004 to learn more about the mounting crisis, with the hope that we can identify neighborhoods at risk of foreclosures and its associated consequences.


Selective Complexation And Reactivity Of Metallic Nitride And Oxometallic Fullerenes With Lewis Acids And Use As An Effective Purification Method, Steven Stevenson, Mary A. Mackey, Jane E. Pickens, Melissa A. Stuart, Bridget S. Confait, J. Paige Phillips Dec 2009

Selective Complexation And Reactivity Of Metallic Nitride And Oxometallic Fullerenes With Lewis Acids And Use As An Effective Purification Method, Steven Stevenson, Mary A. Mackey, Jane E. Pickens, Melissa A. Stuart, Bridget S. Confait, J. Paige Phillips

Faculty Publications

Metallic nitride fullerenes (MNFs) and oxometallic fullerenes (OMFs) react quickly with an array of Lewis acids. Empty-cage fullerenes are largely unreactive under conditions used in this study. The reactivity order is Sc4O2@Ih-C80 > Sc3N@C78 > Sc3N@C68 > Sc3N@D5h-C80 > Sc3N@Ih-C80. Manipulations of Lewis acids, molar ratios, and kinetic differences within the family of OMF and MNF metallofullerenes are demonstrated in a selective precipitation scheme, which can be used either alone for purifying Sc3N@Ih …


Solid State And Solution Dynamics Of Pyridine Based Tetraaza- Macrocyclic Lanthanide Chelates Possessing Phosphonate Ligating Functionality (Ln-Pctmb): Effect On Relaxometry And Optical Properties, Garry Kiefer, Mark Woods Dec 2009

Solid State And Solution Dynamics Of Pyridine Based Tetraaza- Macrocyclic Lanthanide Chelates Possessing Phosphonate Ligating Functionality (Ln-Pctmb): Effect On Relaxometry And Optical Properties, Garry Kiefer, Mark Woods

Chemistry Faculty Publications and Presentations

The macrocyclic ligand 3,6,9-tris(methylenebutyl phosphonic acid)-3,6,9−15-tetraazabicyclo [9.3.1]pentadeca-1(15),11,13-triene (PCTMB) was synthesized and complexes of Eu3+, Tb3+, and Gd3+ studied by X-ray crystallography, luminescence, and relaxometry. In the crystal these complexes are dimeric and possess 8-coordinate Ln3+ centers that are linked by bridging phosphonates. The rigidity introduced by the pyridyl nucleus forces the EuPCTMB and TbPCTMB to adopt a twisted snub disphenoid (TSD) coordination geometry. Examination of the 5D07F0 luminescent transition of EuPCTMB in the solid state confirmed the existence of a single distinct Eu3+ coordination environment, whereas two …


Resolution For Education For Sustainability At Wku, Office Of Sustainability, Christian Ryan-Downing Dec 2009

Resolution For Education For Sustainability At Wku, Office Of Sustainability, Christian Ryan-Downing

Sustainability Publications and Resources

No abstract provided.


Discovery Of Very High Energy Gamma Rays From Pks 1424+240 And Multiwavelength Constraints On Its Redshift, P. T. Reynolds, Et Al Dec 2009

Discovery Of Very High Energy Gamma Rays From Pks 1424+240 And Multiwavelength Constraints On Its Redshift, P. T. Reynolds, Et Al

Physical Sciences Publications

We report the first detection of very high energy83Gamma-ray emission above 100 GeV. (VHE) gamma-ray emission above 140 GeV from PKS 1424+240, a BL Lac object with an unknown redshift. The photon spectrum above 140 GeV measured by VERITAS is well described by a power law with a photon index of 3.8 ± 0.5stat ± 0.3syst and a flux normalization at 200 GeV of (5.1 ± 0.9stat ± 0.5syst) × 10–11 TeV–1 cm–2 s–1, where stat and syst denote the statistical and systematical uncertainties, respectively. The VHE flux is steady over the observation period between MJD 54881 and 55003 (from …


Voting, The Symmetric Group, And Representation Theory, Zajj Daugherty '05, Alexander K. Eustis '06, Gregory Minton '08, Michael E. Orrison Dec 2009

Voting, The Symmetric Group, And Representation Theory, Zajj Daugherty '05, Alexander K. Eustis '06, Gregory Minton '08, Michael E. Orrison

All HMC Faculty Publications and Research

We show how voting may be viewed naturally from an algebraic perspective by viewing voting profiles as elements of certain well-studied QSn-modules. By using only a handful of simple combinatorial objects (e.g., tabloids) and some basic ideas from representation theory (e.g., Schur's Lemma), this allows us to recast and extend some well-known results in the field of voting theory.


Boron In Antarctic Granulite-Facies Rocks: Under What Conditions Is Boron Retained In The Middle Crust?, Edward S. Grew Dec 2009

Boron In Antarctic Granulite-Facies Rocks: Under What Conditions Is Boron Retained In The Middle Crust?, Edward S. Grew

University of Maine Office of Research Administration: Grant Reports

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a project to investigate the role and fate of Boron in high-grade metamorphic rocks of the Larsemann Hills region of Antarctica. Trace elements provide valuable information on the changes sedimentary rocks undergo as temperature and pressure increase during burial. One such element, boron, is particularly sensitive to increasing temperature because of its affinity for aqueous fluids, which are lost as rocks are buried. Boron contents of unmetamorphosed pelitic sediments range from 20 to over 200 parts per million, but rarely exceed 5 parts …


Graduate Education In Research Ethics For Scientists And Engineers: Final Report, Jorge Ferrer-Negron, William Frey, Efrain O'Neill-Carrillo, Didier Valdes, Carlos Rios-Valazquez Dec 2009

Graduate Education In Research Ethics For Scientists And Engineers: Final Report, Jorge Ferrer-Negron, William Frey, Efrain O'Neill-Carrillo, Didier Valdes, Carlos Rios-Valazquez

Ethics in Science and Engineering National Clearinghouse

No abstract provided.


Reevaluating The Cosmological Origin Of Dark Matter, Scott Watson Dec 2009

Reevaluating The Cosmological Origin Of Dark Matter, Scott Watson

Physics - All Scholarship

The origin of dark matter as a thermal relic offers a compelling way in which the early universe was initially populated by dark matter. Alternative explanations typically appear exotic compared to the simplicity of thermal production. However, recent observations and progress from theory suggest that it may be necessary to be more critical. This is important because ongoing searches probing the microscopic properties of dark matter typically rely on the assumption of dark matter as a single, unique, thermal relic. On general grounds I will argue that non-thermal production of dark matter seems to be a robust prediction of physics …


Mean Survival Time From Right Censored Data, Ming Zhong, Kenneth R. Hess Dec 2009

Mean Survival Time From Right Censored Data, Ming Zhong, Kenneth R. Hess

COBRA Preprint Series

A nonparametric estimate of the mean survival time can be obtained as the area under the Kaplan-Meier estimate of the survival curve. A common modification is to change the largest observation to a death time if it is censored. We conducted a simulation study to assess the behavior of this estimator of the mean survival time in the presence of right censoring.

We simulated data from seven distributions: exponential, normal, uniform, lognormal, gamma, log-logistic, and Weibull. This allowed us to compare the results of the estimates to the known true values and to quantify the bias and the variance. Our …


The Acs Survey Of Galactic Globular Clusters. Ix. Horizontal Branch Morphology And The Second Parameter Phenomenon, Aaron Dotter, Ata Sarajedini, Jay Anderson, Antonio Aparicio, Luigi R. Bedin, Brian Chaboyer Dec 2009

The Acs Survey Of Galactic Globular Clusters. Ix. Horizontal Branch Morphology And The Second Parameter Phenomenon, Aaron Dotter, Ata Sarajedini, Jay Anderson, Antonio Aparicio, Luigi R. Bedin, Brian Chaboyer

Dartmouth Scholarship

The horizontal branch (HB) morphology of globular clusters (GCs) is most strongly influenced by metallicity. The second parameter phenomenon, first described in the 1960s, acknowledges that metallicity alone is not enough to describe the HB morphology of all GCs. In particular, astronomers noticed that the outer Galactic halo contains GCs with redder HBs at a given metallicity than are found inside the solar circle. Thus, at least a second parameter was required to characterize HB morphology. While the term "second parameter" has since come to be used in a broader context, its identity with respect to the original problem has …